JP7733976B2 - Reinforcing films, optical and electronic components - Google Patents

Description

The present invention relates to a reinforcing film and optical and electronic components to which the reinforcing film is attached.

Adhesives in the form of adhesive sheets are widely used in a variety of applications, including mobile electronic devices such as mobile phones, smartphones, and tablet computers, as well as other electronic devices, for purposes such as bonding adherends together and securing items to adherends. For example, adhesive sheets are used as reinforcing materials (reinforcing films) that impart rigidity and impact resistance to the optical and electronic components that make up the above-mentioned devices. Patent Documents 1 and 2 disclose this type of prior art.

Furthermore, portable electronic devices that can be bent or rolled have been attracting attention in recent years, and progress is being made in the development of adhesive sheets that can be used to secure flexible devices (typically image display devices such as organic electroluminescence (EL) and liquid crystal display devices) built into such electronic devices (Patent Documents 3 to 6).

Meanwhile, looking at the performance of adhesives, recently, an adhesive sheet has been proposed that exhibits low adhesive strength when initially attached to an adherend, but can subsequently increase significantly (Patent Document 7). Before the increase in adhesive strength, an adhesive sheet with such properties exhibits reworkability, which is useful for preventing yield losses due to incorrect or failed application of the adhesive sheet, and after the increase in adhesive strength, it can exhibit strong adhesive strength suitable for the adhesive sheet's intended purpose.

Patent No. 6366199 Patent No. 6366200 Patent No. 6376271 JP 2016-108555 A Japanese Patent Application Laid-Open No. 2017-095657 Japanese Patent Application Laid-Open No. 2017-095659 Patent No. 6373458

Reinforcing films can also be used in the flexible devices described above. For example, in the manufacture of the flexible devices described above, the components that make up the device are often thin, so it is desirable to reinforce the device by applying an adhesive sheet as a reinforcing film to prevent defects caused by deformation and improve handleability. Flexible devices can be repeatedly folded or bent, so reinforcing films used in flexible devices are required to have the property of recovering their shape normally even after repeated bending (flexion recovery), and the property of preventing defects such as peeling (flexion retention). Reinforcing films with such flex recovery and flexion retention can be used in a variety of applications, including flexible devices, and are therefore useful with few limitations on their range of application.

For example, even for adhesives that exhibit low adhesive strength initially after application but subsequently increase significantly, such as those proposed in Patent Document 7, it is desirable for the adhesive to have flex recovery and flex retention when used as a reinforcing film. One method for improving flex retention is to appropriately set the storage modulus of the adhesive. However, for adhesives designed to increase in adhesive strength as described above, changing the storage modulus affects both the initial low adhesive strength and the adhesive strength after increase. Furthermore, when considering flex recovery in addition to flex retention, it is not easy to satisfy all of these properties. It would be practically beneficial to be able to improve flex recovery and flex retention for adhesives that exhibit low adhesive strength initially after application but subsequently increase significantly in adhesive strength.

The present invention was created in light of the above circumstances, and aims to provide a reinforcing film that exhibits easy peelability initially after being attached to an adherend, is capable of significantly increasing adhesive strength thereafter, and has flex recovery and flex retention. Another object of the present invention is to provide optical and electronic components to which the reinforcing film is attached.

This specification provides a reinforcing film having a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer includes a polymer (A) and a polymer (B). The polymer (B) includes a monomer unit having a polyorganosiloxane skeleton and a (meth)acrylic monomer unit. The monomer unit having a polyorganosiloxane skeleton contained in the polymer (B) is derived from a polyorganosiloxane skeleton-containing monomer S1. The polyorganosiloxane skeleton-containing monomer S1 has a functional group equivalent of 2000 to 7000 g/mol. The pressure-sensitive adhesive layer has a surface elastic modulus of 1 to 20 kPa at 23°C.

According to the above configuration, the adhesive layer contains polymer (A) and polymer (B) containing a monomer unit having a polyorganosiloxane skeleton. Therefore, the adhesive layer exhibits easy peelability initially after application to an adherend, and subsequently exhibits significantly increased adhesive strength. Furthermore, when the functional group equivalent of the polyorganosiloxane skeleton-containing monomer S1 is 2000 g/mol or more, the adhesive layer tends to exhibit excellent easy peelability initially after application. When the functional group equivalent is 7000 g/mol or less, the adhesive layer tends to exhibit excellent increased adhesive strength. Furthermore, the reinforcing film exhibits flex recovery and flex retention. Specifically, a reinforcing film in which the surface modulus of the adhesive layer at 23°C (23°C surface modulus) is 1 kPa or more exhibits the above-mentioned adhesive properties while exhibiting good flex recovery. Furthermore, when the surface modulus of the adhesive layer at 23°C is 20 kPa or less, the adhesive layer exhibits the above-mentioned adhesive properties while exhibiting good flex retention. Therefore, problems such as peeling are unlikely to occur even when the film is used in a manner that requires repeated folding.

In some preferred embodiments of the technology disclosed herein (including reinforcing films, optical components, and electronic components; the same applies hereinafter), the pressure-sensitive adhesive layer has a bulk modulus _G'23 at 23°C of 10 to 200 kPa. Pressure-sensitive adhesives having a bulk modulus _G'23 in this range tend to have an initial adhesive strength within a suitable range that provides excellent easy peelability. They also tend to have excellent processability and generally tend to achieve both strain relaxation and flex recovery at room temperature.

In some preferred embodiments, the pressure-sensitive adhesive layer has a bulk modulus _G'80 at 80°C of 5 to 100 kPa. A pressure-sensitive adhesive having a bulk modulus _G'80 in this range generally tends to achieve both flex recovery and flex retention. For example, even when used under high-temperature conditions of around 80°C, the pressure-sensitive adhesive may have elasticity suitable for flex recovery and adhesive retention that achieves flex retention.

In some preferred embodiments, the pressure-sensitive adhesive layer has a tan δ ₈₀ at 80°C of 0.10 to 0.60. A pressure-sensitive adhesive having the above tan δ ₈₀ (loss modulus at 80°C G" ₈₀ /storage modulus at 80°C G' ₈₀ ) of 0.10 or more is likely to exhibit adhesive strength suitable for bending retention. Furthermore, by having the above tan δ ₈₀ of 0.60 or less, plastic deformation of the pressure-sensitive adhesive is suppressed and good bending recovery is likely to be obtained. Furthermore, even when the reinforcing film is held in a bent state for a long period of time, it is likely to exhibit holding strength (flexion holding strength) that does not cause peeling from the adherend.

The polymer (A) is preferably an acrylic polymer. The effects of the technology disclosed herein are preferably achieved by a pressure-sensitive adhesive layer containing polymer (A), which is an acrylic polymer, and polymer (B), which contains monomer units having a polyorganosiloxane skeleton.

In some preferred embodiments, the content of the polymer (B) in the pressure-sensitive adhesive layer is 0.5 to 5 parts by weight per 100 parts by weight of the polymer (A). By setting the amount of polymer (B) to 0.5 parts by weight or more per 100 parts by weight of polymer (A), easy peelability at the initial stage of application is likely to be achieved. By setting the amount of polymer (B) to 5 parts by weight or less, the desired increase in adhesive strength is likely to be achieved. Furthermore, by setting the amount of polymer (B) used within the above range, good flex recovery and flex retention are likely to be achieved.

In some preferred embodiments, the molar ratio ([NCO]/[OH]) of isocyanate groups to hydroxyl groups contained in the pressure-sensitive adhesive layer is 0.002 to 0.03. Pressure-sensitive adhesive layers having a molar ratio ([NCO]/[OH]) of 0.002 or greater tend to have excellent flex recovery and processability. Furthermore, by setting the molar ratio ([NCO]/[OH]) to 0.03 or less, it tends to be easier to achieve a favorable increase in adhesive strength. In the pressure-sensitive adhesive layer, at least a portion of the isocyanate groups and hydroxyl groups may be present in a chemically bonded (crosslinked) state. The pressure-sensitive adhesive layer may contain, for example, a crosslinking agent. In such a configuration, the isocyanate groups may be, for example, part of the crosslinking agent, and the hydroxyl groups may be, for example, part of the polymer (A).

The reinforcing film disclosed herein is suitable as a reinforcing film that imparts rigidity and impact resistance to optical components such as polarizing plates and wavelength plates during processing and transport of the optical components. Therefore, this specification provides an optical component to which any of the reinforcing films disclosed herein is attached.

The reinforcing film disclosed herein is also suitable as a reinforcing film for electronic components in devices such as portable electronic devices. Therefore, this specification provides an electronic component to which any of the reinforcing films disclosed herein is attached.

1 is a cross-sectional view schematically illustrating a configuration of a reinforcing film according to an embodiment. FIG. 10 is a cross-sectional view schematically showing the configuration of a reinforcing film according to another embodiment. FIG. 10 is a cross-sectional view schematically showing the configuration of a reinforcing film according to another embodiment.

Preferred embodiments of the present invention will be described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings on carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field.
In the following drawings, components and parts that perform the same function may be denoted by the same reference numerals, and duplicated explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the actual product.

In this specification, the term "acrylic polymer" refers to a polymer containing monomer units derived from (meth)acrylic monomers in the polymer structure, and typically refers to a polymer containing more than 50% by weight of monomer units derived from (meth)acrylic monomers. A (meth)acrylic monomer refers to a monomer having at least one (meth)acryloyl group per molecule. Here, "(meth)acryloyl group" refers collectively to acryloyl groups and methacryloyl groups. Therefore, the concept of a (meth)acrylic monomer here encompasses both a monomer having an acryloyl group (acrylic monomer) and a monomer having a methacryloyl group (methacrylic monomer). Similarly, in this specification, "(meth)acrylic acid" refers collectively to acrylic acid and methacrylic acid, and "(meth)acrylate" refers collectively to acrylate and methacrylate.

<Structural example of reinforcing film>
The reinforcing film disclosed herein has the form of a pressure-sensitive adhesive sheet having an adhesive surface formed by a pressure-sensitive adhesive. The pressure-sensitive adhesive sheet used as the reinforcing film is configured to include a pressure-sensitive adhesive layer. The reinforcing film disclosed herein may be in the form of a substrate-attached pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer is laminated on one or both sides of a supporting substrate, or may be in the form of a substrate-less pressure-sensitive adhesive sheet that does not have a supporting substrate. Hereinafter, the supporting substrate may also be simply referred to as the "substrate."
In this specification, the term "reinforcing film" refers to a pressure-sensitive adhesive sheet (reinforcing pressure-sensitive adhesive film) used to reinforce an adherend, as described below. The reinforcing film can be in the form of, for example, a substrate-less pressure-sensitive adhesive sheet, with a support material or the like attached to one adhesive surface, and then the other adhesive surface can be attached to the adherend to be reinforced, so it is not limited to the form of a substrate-attached pressure-sensitive adhesive sheet. In this respect, it can be understood as a broader concept than the "reinforcing film" described below, which has the form of a substrate-attached pressure-sensitive adhesive sheet.

The structure of a reinforcing film according to one embodiment is shown schematically in Figure 1. This reinforcing film 1 is configured as a substrate-attached single-sided adhesive sheet comprising a sheet-like support substrate 10 having a first surface 10A and a second surface 10B, and an adhesive layer 21 provided on the first surface 10A. The adhesive layer 21 is affixed to the first surface 10A of the support substrate 10. The reinforcing film 1 is used by attaching the adhesive layer 21 to an adherend. Before use (i.e., before attachment to an adherend), the reinforcing film 1 can be a component of a release-liner-attached reinforcing film 100, as shown in Figure 1, in which the surface (adhesive surface) 21A of the adhesive layer 21 is in contact with a release liner 31, at least the side facing the adhesive layer 21 being a releasable surface (release surface). A preferred release liner 31 is, for example, a sheet-like substrate (liner substrate) configured so that one side serves as a release surface by providing a release layer made of a release treatment agent on that surface. Alternatively, the release liner 31 may be omitted, and a support substrate 10 having the second surface 10B as the release surface may be used, with the reinforcing film 1 rolled up so that the adhesive surface 21A abuts against the second surface 10B of the support substrate 10 (roll form). When attaching the reinforcing film 1 to an adherend, the release liner 31 or the second surface 10B of the support substrate 10 is peeled off from the adhesive surface 21A, and the exposed adhesive surface 21A is pressed against the adherend.

The structure of a reinforcing film according to another embodiment is shown schematically in Figure 2. This reinforcing film 2 is configured as a substrate-attached double-sided adhesive sheet comprising a sheet-like support substrate 10 having a first surface 10A and a second surface 10B, an adhesive layer 21 provided on the first surface 10A side, and an adhesive layer 22 provided on the second surface 10B side. The adhesive layer (first adhesive layer) 21 is adhered to the first surface 10A of the support substrate 10, and the adhesive layer (second adhesive layer) 22 is adhered to the second surface 10B of the support substrate 10. The reinforcing film 2 is used by adhering the adhesive layers 21 and 22 to different locations on an adherend. The adhesive layers 21 and 22 may be adhered to different components or to different locations within a single component. Before use, the reinforcing film 2 may be a component of a release-liner-attached reinforcing film 200, as shown in FIG. 2 , in which the surface (first adhesive surface) 21A of the pressure-sensitive adhesive layer 21 and the surface (second adhesive surface) 22A of the pressure-sensitive adhesive layer 22 are in contact with release liners 31, 32, each of which has a release surface on at least the side facing the pressure-sensitive adhesive layers 21, 22. The release liners 31, 32 may preferably be, for example, sheet-like substrates (liner substrates) each having a release layer made of a release treatment agent on one side thereof, so that the release surface is the release liner. Alternatively, the release liner 32 may be omitted, and a release liner 31 having release surfaces on both sides may be used. This may be superimposed on the reinforcing film 2 and wound spirally to form a reinforcing film with a release liner in a roll form, in which the second adhesive surface 22A is in contact with the back surface of the release liner 31.

The structure of a reinforcing film according to yet another embodiment is shown schematically in Figure 3. This reinforcing film 3 is configured as a substrate-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer 21. The reinforcing film 3 is used by attaching a first adhesive surface 21A, which is one surface (first surface) of the pressure-sensitive adhesive layer 21, and a second adhesive surface 21B, which is the other surface (second surface) of the pressure-sensitive adhesive layer 21, to different locations on an adherend. Before use, the reinforcing film 3 may be a component of a release-liner-attached reinforcing film 300, as shown in Figure 3, in which the first adhesive surface 21A and the second adhesive surface 21B are in contact with release liners 31, 32, each of which has a release surface on at least the side facing the pressure-sensitive adhesive layer 21. Alternatively, the release liner 32 may be omitted, and a release liner 31, which has release surfaces on both sides, may be used. This may be superimposed on the reinforcing film 3 and wound into a spiral shape to form a reinforcing film with a release liner in a roll form in which the second adhesive surface 21B is in contact with the back surface of the release liner 31.

The reinforcing film may be in roll form or sheet form, and may be cut, punched, or otherwise processed into an appropriate shape depending on the application and mode of use. The pressure-sensitive adhesive layer in the technology disclosed herein is typically formed continuously, but is not limited to this and may be formed in a regular or random pattern, such as dots or stripes.

<Adhesive Layer>
The reinforcing film disclosed herein includes a pressure-sensitive adhesive layer containing a polymer (A) and a polymer (B). Such a pressure-sensitive adhesive layer may be formed from a pressure-sensitive adhesive composition containing a polymer (A) that is a complete or partial polymer of a monomer raw material A, and a polymer (B). The form of the pressure-sensitive adhesive composition is not particularly limited, and may be in various forms, such as a solvent-based, water-dispersible, hot-melt, or active energy ray-curable (e.g., photocurable) form.

(Surface elastic modulus at 23°C)
The pressure-sensitive adhesive layer disclosed herein is characterized in that the surface elastic modulus of its surface (adhesive surface) at 23°C (23°C surface elastic modulus) is within the range of 1 to 20 kPa. When the 23°C surface elastic modulus is 1 kPa or more, the pressure-sensitive adhesive layer can have good flex recovery while realizing the adhesive properties based on the inclusion of polymer (A) and polymer (B). Furthermore, when the surface elastic modulus is 20 kPa or less, the pressure-sensitive adhesive layer can exhibit good flex retention while realizing the adhesive properties.

From the viewpoint of improving flex recovery, the 23°C surface modulus is preferably 2 kPa or more, more preferably 3 kPa or more, even more preferably 4 kPa or more (e.g., 5 kPa or more), and may be 8 kPa or more, 10 kPa or more, or 12 kPa or more (e.g., 14 kPa or more). The higher the surface modulus, the better the initial easy peelability tends to be. Furthermore, from the viewpoint of achieving both good flex recovery and flex retention while preferably exhibiting increased adhesive strength, the 23°C surface modulus is suitably 15 kPa or less, preferably 12 kPa or less, more preferably 9 kPa or less, even more preferably 7 kPa or less (e.g., 6 kPa or less), and may be 4 kPa or less.

The surface elastic modulus at 23°C of the adhesive layer can be adjusted by the type and characteristics (molecular weight, glass transition temperature, molecular structure, etc.) of polymer (A), the type (chemical structure, etc.) and characteristics (molecular weight, glass transition temperature, etc.) and amount used of polymer (B), and the type and amount used of the crosslinking agent. The surface elastic modulus at 23°C of the adhesive layer is measured by the method described in the Examples below.

(23°C bulk elastic modulus _G'23 )
The bulk modulus _G'23 at 23°C (23°C bulk modulus _G'23 ) of the pressure-sensitive adhesive layer is appropriately set within a range that satisfies the above-mentioned range of the surface modulus at 23°C, and is not limited to a specific range. In some embodiments, the 23°C bulk modulus G'23 of the pressure-sensitive adhesive layer is suitably 10 kPa or more. By setting the bulk modulus _G'23 to a predetermined value or more, the initial adhesive strength after application tends to fall within a suitable range that provides excellent easy peelability. In addition, the _pressure -sensitive adhesive layer tends to have excellent processability and, generally, excellent flex recovery properties at room temperature. The bulk modulus _G'23 is preferably 15 kPa or more, more preferably 20 kPa or more, even more preferably 25 kPa or more, and particularly preferably 30 kPa or more. In other embodiments, the bulk modulus _G'23 may be 50 kPa or more, 80 kPa or more, or 100 kPa or more.

In some embodiments, the 23°C bulk modulus _G'23 of the PSA layer is suitably 200 kPa or less. PSA having a bulk modulus _G'23 of a predetermined value or less generally tends to have excellent strain relaxation properties in the room temperature range and is also likely to exhibit increased adhesive strength. The bulk modulus _G'23 is preferably 150 kPa or less, more preferably 90 kPa or less. In some preferred embodiments, the bulk modulus _G'23 may be 60 kPa or less, or may be 40 kPa or less (e.g., 35 kPa or less).

(80°C bulk elastic modulus _G'80 )
The bulk modulus _G'80 at 80°C (80°C bulk modulus _G'80 ) of the PSA layer is appropriately set within a range that satisfies the above-mentioned range of the surface modulus at 23°C, and is not limited to a specific range. In some embodiments, the bulk modulus _G'80 at 80°C of the PSA layer is preferably 5 kPa or more. By setting the bulk modulus _G'80 to a predetermined value or more, flex recovery is generally likely to be improved, and even when used under high temperature conditions, the PSA layer can have elasticity suitable for flex recovery. In some preferred embodiments, the bulk modulus _G'80 may be 7 kPa or more, 9 kPa or more, or 10 kPa or more. In other embodiments, the bulk modulus _G'80 may be 15 kPa or more, 30 kPa or more, or 50 kPa or more.

In some embodiments, the 80°C bulk elastic modulus _G'80 of the PSA layer is suitably 100 kPa or less. By limiting the bulk elastic modulus _G'80 to a predetermined value or less, it is generally easy to obtain good flex retention, and it is easy to achieve both flex recovery and flex retention. For example, in various environments, including high-temperature conditions, it is possible to obtain an adhesive retention that has elasticity suitable for flex recovery and realizes flex retention. The bulk elastic modulus _G'80 is preferably 90 kPa or less, more preferably 60 kPa or less. In some embodiments, the bulk elastic modulus _G'80 may be 20 kPa or less, 16 kPa or less, or 14 kPa or less (e.g., 12 kPa or less).

(80℃ _tanδ80 )
The tan δ ₈₀ at 80°C (80°C tan δ ₈₀ ) of the PSA layer is appropriately set within a range that satisfies the above-mentioned range of the surface elastic modulus at 23°C, and is not limited to a specific range. In some embodiments, the 80°C tan δ ₈₀ of the PSA layer is suitably 0.10 or more. The higher the tan δ ₈₀ , the more likely the PSA will exhibit adhesive strength suitable for bending retention. The tan δ ₈₀ is preferably 0.20 or more. In some preferred embodiments, the tan δ ₈₀ may be 0.30 or more, 0.40 or more, or 0.45 or more.

In some embodiments, the 80°C tan δ ₈₀ of the pressure-sensitive adhesive layer is preferably 0.60 or less. When the tan δ ₈₀ is 0.60 or less, plastic deformation of the pressure-sensitive adhesive is suppressed, and good flex recovery is likely to be obtained. Furthermore, even when the reinforcing film is held in a bent state for a long period of time, it is likely to exhibit holding power that prevents peeling from the adherend. Furthermore, the increase in adhesive strength is likely to be within a suitable range. The 80°C tan δ ₈₀ may be 0.55 or less. In other embodiments, the 80°C tan δ ₈₀ may be 0.50 or less, or may be 0.35 or less.

The 23°C bulk modulus _G'23 , 80°C bulk modulus _G'80 and 80°C tan _δ80 of the pressure-sensitive adhesive layer can be adjusted by the type and properties (molecular weight, glass transition temperature, molecular structure, etc.) of polymer (A), the type (chemical structure, etc.) and properties (molecular weight, glass transition temperature, etc.) and amount used of polymer (B), the type and amount used of crosslinking agent, etc. The 23°C bulk modulus _G'23 , 80°C bulk modulus _G'80 and 80°C tan _δ80 of the pressure-sensitive adhesive layer are measured by the method described in the Examples below.

(Polymer (A))
As the polymer (A), one or more of various polymers that exhibit rubber elasticity at room temperature, such as acrylic polymers, rubber polymers, polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine-based polymers, which are known in the field of pressure-sensitive adhesives, can be used. In the reinforcing film disclosed herein, the polymer (A) is typically the main component of the polymer components contained in the pressure-sensitive adhesive layer, i.e., a component that accounts for more than 50% by weight, and may, for example, be a component that accounts for 75% by weight or more of the above polymer components. In some embodiments, the polymer (A) is a component that accounts for more than 50% by weight of the entire pressure-sensitive adhesive layer, and may be a component that accounts for 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more (e.g., 97% by weight or more).

The glass transition temperature _TA of the polymer (A) is not particularly limited and can be selected so as to obtain desirable properties in the reinforcing film disclosed herein. In some embodiments, a polymer (A) having a _TA of less than 0°C can be preferably used. A pressure-sensitive adhesive containing such a polymer (A) exhibits moderate fluidity (e.g., mobility of the polymer chains contained in the pressure-sensitive adhesive), and is therefore suitable for realizing a reinforcing film whose adhesive strength increases to a predetermined value or more upon heating. The reinforcing film disclosed herein can be preferably produced using a polymer (A) having a _TA of less than -10°C, less than -20°C, less than -30°C, or less than -35°C. In some embodiments, the _TA may be less than -40°C or less than -50°C. In some preferred embodiments, the _TA is -55°C or less, more preferably -58°C or less, even more preferably -62°C or less, and may even be -65°C or less (e.g., -66°C or less). The lower limit of _{the TA} is not particularly limited. From the viewpoint of easy availability of materials and improving the cohesive strength of the pressure-sensitive adhesive layer, it is usually preferable to use a polymer (A) having a T _A of −80° C. or higher, −70° C. or higher. In some embodiments, the T _A may be, for example, −63° C. or higher, −55° C. or higher, −50° C. or higher, or −45° C. or higher.

In this specification, the glass transition temperature (Tg) of polymers including polymer (A) and polymer (B) described below refers to a nominal value described in literature, catalogs, etc., or a Tg calculated by Fox's equation based on the composition of the monomer raw materials used to prepare the polymer. The Fox equation, as shown below, is a relational expression between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer.
1/Tg=Σ(Wi/Tgi)
In the Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi represents the glass transition temperature (unit: K) of a homopolymer of monomer i. When the target polymer for specifying Tg is a homopolymer, the Tg of the homopolymer and the Tg of the target polymer coincide.

The glass transition temperature of the homopolymer used to calculate Tg should be a value listed in publicly available sources. Specifically, the values are listed in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989). For monomers for which the Polymer Handbook lists multiple values, the highest value should be used.

As the glass transition temperature of a homopolymer of a monomer not described in the Polymer Handbook, a value obtained by the following measurement method is used.
Specifically, 100 parts by weight of monomer, 0.2 parts by weight of 2,2'-azobisisobutyronitrile, and 200 parts by weight of ethyl acetate as a polymerization solvent were charged into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the mixture was stirred for 1 hour while passing nitrogen gas through. After removing oxygen from the polymerization system in this manner, the temperature was raised to 63°C and the reaction was carried out for 10 hours. The mixture was then cooled to room temperature to obtain a homopolymer solution with a solids concentration of 33% by weight. This homopolymer solution was then cast onto a release liner and dried to prepare a test sample (sheet-like homopolymer) with a thickness of approximately 2 mm. This test sample was punched out into a disk shape with a diameter of 7.9 mm, sandwiched between parallel plates, and the viscoelasticity was measured in shear mode using a viscoelasticity tester (manufactured by TA Instruments Japan, model name "ARES") at a temperature range of -70°C to 150°C and a heating rate of 5°C/min while applying a shear strain at a frequency of 1 Hz. The temperature corresponding to the peak top temperature of tan δ was taken as the Tg of the homopolymer.

Although not particularly limited, the weight-average molecular weight (Mw) of the polymer (A) is typically approximately 20 x 10 ⁴ or more. A polymer (A) with such an Mw is likely to produce a pressure-sensitive adhesive exhibiting good cohesive properties. From the viewpoint of achieving higher cohesive strength, in some preferred embodiments, the Mw of the polymer (A) may be, for example, 30 x 10 ⁴ or more, 40 x 10 ⁴ or more, 50 x 10 ⁴ or more, 60 x 10 ⁴ or more, or 80 x 10 ⁴ or more. Furthermore, the Mw of the polymer (A) is typically approximately 500 x 10 ⁴ or less. A polymer (A) with such an Mw is likely to form a pressure-sensitive adhesive exhibiting appropriate fluidity (polymer chain mobility), making it suitable for realizing a reinforcing film with low initial adhesive strength and a large increase in adhesive strength. It is also preferable that the Mw of the polymer (A) is not too high from the viewpoint of improving compatibility with the polymer (B). In some preferred embodiments, the Mw of polymer (A) may be, for example, 250×10 ⁴ or less, 200×10 ⁴ or less, 150×10 ⁴ or less, 100×10 ⁴ or less, or 70×10 ⁴ or less.

In this specification, the Mw of polymer (A) and polymer (B) described below can be determined in polystyrene equivalent terms by gel permeation chromatography (GPC). More specifically, Mw can be measured according to the method and conditions described in the examples described below.

Acrylic polymers can preferably be used as the polymer (A) in the reinforcing film disclosed herein. Using an acrylic polymer as the polymer (A) tends to make it easier to achieve good compatibility with the polymer (B). Good compatibility between the polymer (A) and the polymer (B) is preferable because it can contribute to reducing the initial adhesive strength and improving the adhesive strength after heating by improving the mobility of the polymer (B) within the adhesive layer. In addition, acrylic polymers, which offer a high degree of freedom in molecular design, are suitable as adhesive materials that can improve adhesive properties, flex recovery, and flex retention in a balanced manner.

The acrylic polymer may be, for example, a polymer containing 50% by weight or more of monomer units derived from a (meth)acrylic acid alkyl ester, i.e., a polymer in which 50% by weight or more of the total amount of the monomer components (monomer starting material A) used to prepare the acrylic polymer are (meth)acrylic acid alkyl esters. As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having a linear or branched alkyl group having 1 to 20 carbon atoms (i.e., _C1-20 ) can be preferably used. Since it is easy to balance the properties, the proportion of the (meth)acrylic acid _C1-20 alkyl ester in the monomer starting material A may be, for example, 50% by weight or more, or even 60% by weight or more. In some preferred embodiments, the proportion of the (meth)acrylic acid _C1-20 alkyl ester in the monomer starting material A is 70% by weight or more, more preferably 80% by weight or more, even more preferably 85% by weight or more, and particularly preferably 90% by weight or more. Using an acrylic polymer with such a monomer composition makes it easier to obtain a pressure-sensitive adhesive that achieves a good balance between increased adhesive strength and flex recovery and flex retention. Furthermore, the proportion of the (meth)acrylic acid C _1-20 alkyl ester in the monomer raw material A may be, for example, 99.9% by weight or less, 98% by weight or less, or 95% by weight or less. In some embodiments, the proportion of the (meth)acrylic acid C _1-20 alkyl ester in the monomer raw material A may be, for example, 90% by weight or less, 85% by weight or less, or 80% by weight or less.

Non-limiting specific examples of (meth)acrylic acid C _1-20 alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and (meth)acrylic acid. Examples of the acrylate include isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

Among these, it is preferable to use at least a C _1-18 alkyl (meth)acrylate, and it is more preferable to use at least a C _1-14 alkyl (meth)acrylate. In some embodiments, the acrylic polymer may contain at least one monomer unit selected from a C _4-12 alkyl (meth)acrylate (preferably a C _4-10 alkyl acrylate, for example a C _6-10 alkyl acrylate). For example, an acrylic polymer containing one or both of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) is preferred, and an acrylic polymer containing at least 2EHA is particularly preferred.

In some preferred embodiments, the proportion of the _C6-10 alkyl acrylate (preferably a _C8-9 alkyl acrylate, typically 2EHA) in the monomer raw material A for preparing the acrylic polymer is 70% by weight or more, more preferably 80% by weight or more, even more preferably 85% by weight or more, and particularly preferably 90% by weight or more. Acrylic polymers with such a monomer composition are particularly suitable for achieving the effects of the technology disclosed herein. Furthermore, the proportion of the _C6-10 alkyl acrylate (preferably a _C8-9 alkyl acrylate, typically 2EHA) in the monomer raw material A may be, for example, 99.9% by weight or less. From the viewpoints of low initial adhesion, flex recovery, and the like, it may also be 98% by weight or less, or even 95% by weight or less.

In some preferred embodiments, it is preferable that the proportion of a (meth)acrylic acid _C1-3 alkyl ester (e.g., a (meth)acrylic acid _C1 alkyl ester, typically methyl methacrylate (MMA)) in the monomer raw material A for preparing the acrylic polymer is limited. A (meth)acrylic acid _C1-3 alkyl ester (e.g., a (meth)acrylic acid _C1 alkyl ester, typically MMA) tends to have a relatively high Tg, and a PSA containing an acrylic polymer using the above monomer component tends to have high cohesiveness. By limiting the amount of the (meth)acrylic acid _C1-3 alkyl ester used, the cohesive strength of the PSA can be appropriately reduced, and a modulus of elasticity (typically, surface modulus) suitable for achieving both bending retention and increased adhesive strength can be preferably achieved. From such a viewpoint, the proportion of the (meth)acrylic acid _C1-3 alkyl ester (for example, (meth)acrylic acid _C1 alkyl ester, typically MMA) in the monomer raw material A is suitably 8% by weight or less, preferably 6% by weight or less, more preferably 3% by weight or less, and even more preferably 1% by weight or less (for example, 0 to 0.3% by weight).

Monomer raw material A may contain, in addition to the (meth)acrylic acid alkyl ester as the main component, other monomers (copolymerizable monomers) that are copolymerizable with the (meth)acrylic acid alkyl ester, as necessary. Monomers having polar groups (e.g., carboxy groups, hydroxyl groups, nitrogen atom-containing rings, etc.) are preferably used as copolymerizable monomers. Monomers having polar groups can be useful for introducing crosslinking points into the acrylic polymer or for increasing the cohesive strength of the acrylic polymer. Copolymerizable monomers can be used alone or in combination of two or more.

Non-limiting examples of copolymerizable monomers include the following:
Hydroxyl group-containing monomers: for example, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate.
Monomers having a nitrogen atom-containing ring: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylmorpholine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, N-vinylpyridazine, etc.;
For example, monomers having a succinimide skeleton, such as N-(meth)acryloyloxymethylene succinimide, N-(meth)acryloyl-6-oxyhexamethylene succinimide, and N-(meth)acryloyl-8-oxyhexamethylene succinimide;
Maleimides, such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, and N-phenylmaleimide; and
For example, itaconimides such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, and N-laurylitaconimide.
Carboxy group-containing monomers: for example, acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc.
Acid anhydride group-containing monomers: for example, maleic anhydride, itaconic anhydride.
Epoxy group-containing monomers: for example, epoxy group-containing acrylates such as glycidyl (meth)acrylate and 2-ethyl (meth)acrylate glycidyl ether, allyl glycidyl ether, glycidyl ether (meth)acrylate, and the like.
Cyano group-containing monomers: for example, acrylonitrile, methacrylonitrile, etc.
Isocyanate group-containing monomers: for example, 2-isocyanatoethyl (meth)acrylate.
Amide group-containing monomers: for example, (meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, and N,N-di(t-butyl)(meth)acrylamide; N-alkyl(meth)acrylamides such as N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, and N-n-butyl(meth)acrylamide; N-vinylcarboxylic acid amides such as N-vinylacetamide; monomers having a hydroxyl group and an amide group, for example, N-(2-hydroxyethyl)(meth)acrylamide; N-hydroxyalkyl(meth)acrylamides such as N-(meth)acrylamide, N-(2-hydroxypropyl)(meth)acrylamide, N-(1-hydroxypropyl)(meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3-hydroxybutyl)(meth)acrylamide, and N-(4-hydroxybutyl)(meth)acrylamide; monomers having an alkoxy group and an amide group, for example, N-alkoxyalkyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide, N-methoxyethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide; and others such as N,N-dimethylaminopropyl(meth)acrylamide.
Aminoalkyl (meth)acrylates: for example, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate.
Alkoxy group-containing monomers: for example, alkoxyalkyl (meth)acrylates such as 2-methoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, and ethoxypropyl (meth)acrylate; and alkoxyalkylene (meth)acrylates such as methoxyethylene glycol (meth)acrylate and methoxypolypropylene glycol (meth)acrylate.
Monomers containing a sulfonic acid group or a phosphoric acid group: for example, styrenesulfonic acid, allylsulfonic acid, sodium vinylsulfonate, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, sulfopropyl (meth)acrylate, (meth)acryloyloxynaphthalenesulfonic acid, 2-hydroxyethyl acryloylphosphate, etc.
(Meth)acrylic acid esters having an alicyclic hydrocarbon group: for example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and the like.
(Meth)acrylic acid esters having an aromatic hydrocarbon group: for example, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, etc.
Vinyl ethers: for example, vinyl alkyl ethers such as methyl vinyl ether and ethyl vinyl ether.
Vinyl esters: for example, vinyl acetate, vinyl propionate, etc.
Aromatic vinyl compounds: for example, styrene, α-methylstyrene, vinyltoluene, etc.
Olefins: for example, ethylene, butadiene, isoprene, isobutylene, etc.
Other examples include heterocycle-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, halogen atom-containing (meth)acrylates such as vinyl chloride and fluorine atom-containing (meth)acrylates, silicon atom-containing (meth)acrylates such as silicone (meth)acrylate, and (meth)acrylic acid esters obtained from terpene compound derivative alcohols.

When such a copolymerizable monomer is used, its amount is not particularly limited, but is typically 0.01 wt% or more of the monomer raw material A. To maximize the effects of the copolymerizable monomer, the amount of copolymerizable monomer used may be 0.1 wt% or more, or even 1 wt% or more, of the monomer raw material A. In some preferred embodiments, the content of the copolymerizable monomer in the monomer raw material A is 3 wt% or more, more preferably 5 wt% or more, and even more preferably 7 wt% or more (e.g., 8 wt% or more). The greater the amount of copolymerizable monomer used, the higher the cohesive strength and the improved flex recovery. Furthermore, the amount of copolymerizable monomer used can be 50 wt% or less, preferably 30 wt% or less, of the monomer raw material A. This prevents the cohesive strength of the PSA from becoming too high and improves the tackiness at room temperature (25°C). In some preferred embodiments, the amount of copolymerizable monomer used is 20 wt% or less, more preferably 15 wt% or less (e.g., 12 wt% or less), and may be 10 wt% or less, of the monomer raw material A. By limiting the amount of copolymerizable monomer used, the cohesive strength of the adhesive is reduced, the modulus of elasticity (typically the surface modulus of elasticity) falls within a suitable range, making it easier to achieve excellent bending retention and increased adhesive strength.

In some embodiments, monomer raw material A may contain a monomer having a nitrogen atom-containing ring. Use of a monomer having a nitrogen atom-containing ring can adjust the cohesive strength and polarity of the adhesive, and favorably improve the adhesive strength after heating. By including a monomer having a nitrogen atom-containing ring in monomer raw material A, the compatibility between polymer (A) formed from monomer raw material A and polymer (B) tends to improve. This makes it easier to obtain a reinforcing film whose adhesive strength can be significantly increased by heating.

Monomers having a nitrogen atom-containing ring can be appropriately selected from, for example, the above examples and used singly or in combination of two or more. In some embodiments, monomer raw material A preferably contains, as the monomer having a nitrogen atom-containing ring, at least one monomer selected from the group consisting of N-vinyl cyclic amides and cyclic amides having a (meth)acryloyl group.

Specific examples of N-vinyl cyclic amides include N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, and N-vinyl-3,5-morpholinedione, with N-vinyl-2-pyrrolidone and N-vinyl-2-caprolactam being particularly preferred.
Specific examples of cyclic amides having a (meth)acryloyl group include N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylmorpholine, etc. A suitable example is N-acryloylmorpholine (ACMO).

The amount of the monomer having a nitrogen atom-containing ring used is not particularly limited, and is typically 40% by weight or less of the monomer starting material A, and may be 30% by weight or less, 20% by weight or less, or 10% by weight or less. In some preferred embodiments, from the viewpoint of reducing cohesive strength and elastic modulus (typically surface elastic modulus), the content of the monomer having a nitrogen atom-containing ring in the monomer starting material A is 7% by weight or less, more preferably 5% by weight or less, and even more preferably 3% by weight or less (e.g., 1.5% by weight or less). Furthermore, the amount of the monomer having a nitrogen atom-containing ring used is typically 0.01% by weight or more of the monomer starting material A (preferably 0.1% by weight or more, e.g., 0.5% by weight or more). In some embodiments, from the viewpoint of achieving appropriate cohesive strength and elastic modulus, the amount of the monomer having a nitrogen atom-containing ring used may be 0.8% by weight or more of the monomer starting material A, or may be 1.0% by weight or more.

In some preferred embodiments, monomer raw material A contains a hydroxyl group-containing monomer. Use of a hydroxyl group-containing monomer adjusts the cohesive strength and polarity of the PSA, and ultimately the elastic modulus (typically the surface elastic modulus), thereby enabling the effects of the technology disclosed herein to be preferably realized. Furthermore, the hydroxyl group-containing monomer provides a reactive site with a crosslinking agent (e.g., an isocyanate-based crosslinking agent) described below, and can increase the cohesive strength of the PSA through a crosslinking reaction.

Hydroxyl group-containing monomers that can be suitably used include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and N-(2-hydroxyethyl)(meth)acrylamide. Among these, preferred examples include 2-hydroxyethyl acrylate (HEA), 4-hydroxybutyl acrylate (4HBA), and N-(2-hydroxyethyl)acrylamide (HEAA). 4HBA is particularly preferred from the viewpoint of obtaining cohesive strength suitable for flex recovery and flex retention.

The amount of hydroxyl-containing monomer used is not particularly limited, and is typically 40% by weight or less of the monomer raw material A, and may be 30% by weight or less, or even 20% by weight or less. In some preferred embodiments, from the perspective of reducing cohesive strength and, therefore, elastic modulus (typically, surface elastic modulus), the content of hydroxyl-containing monomer in monomer raw material A is 15% by weight or less, more preferably 12% by weight or less (e.g., 10% by weight or less). By limiting the amount of hydroxyl-containing monomer used, the mobility of polymer (B) within the adhesive layer is improved, making it easier to achieve increased adhesive strength. In other embodiments, the content of hydroxyl-containing monomer may be 5% by weight or less of the monomer raw material A. Furthermore, the amount of hydroxyl-containing monomer used is preferably 0.01% by weight or more of the monomer raw material A (preferably 0.1% by weight or more, e.g., 0.5% by weight or more). From the viewpoint of obtaining appropriate cohesive strength and elastic modulus, in some preferred embodiments, the amount of hydroxyl group-containing monomer used is 1% by weight or more of monomer raw material A, more preferably 3% by weight or more, even more preferably 5% by weight or more, and particularly preferably 7% by weight or more (for example, 8% by weight or more).

In some embodiments, a monomer having a nitrogen atom-containing ring and a hydroxyl group-containing monomer can be used in combination as copolymerizable monomers. In this case, the total amount of the monomer having a nitrogen atom-containing ring and the hydroxyl group-containing monomer can be, for example, 0.1% by weight or more of monomer raw material A, preferably 1% by weight or more, more preferably 3% by weight or more, even more preferably 5% by weight or more, and particularly preferably 7% by weight or more (e.g., 9% by weight or more), and may be 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more. Furthermore, the total amount of the monomer having a nitrogen atom-containing ring and the hydroxyl group-containing monomer can be, for example, 50% by weight or less of monomer raw material A, and preferably 30% by weight or less. In some preferred embodiments, the total amount of the monomer having a nitrogen atom-containing ring and the hydroxyl group-containing monomer is 20% by weight or less of monomer raw material A, more preferably 15% by weight or less (e.g., 12% by weight or less).

In an embodiment in which monomer raw material A contains a combination of a monomer having a nitrogen atom-containing ring and a hydroxyl group-containing monomer, the relationship (by weight) between the content of the monomer having a nitrogen atom-containing ring ( _WN ) and the content of the hydroxyl group-containing monomer ( _WOH ) in the monomer raw material A is not particularly limited. _WN / _WOH may be, for example, 0.01 or more, and typically 0.05 or more is appropriate, and may be 0.10 or more, or 0.12 or more. Furthermore, _WN / _WOH may be, for example, 10 or less, and typically 1 or less is appropriate, and is preferably 0.50 or less, or may be 0.30 or less, or may be 0.20 or less, or may be 0.15 or less.

In some embodiments, it is preferable that monomer raw material A does not contain a monomer having a polyorganosiloxane skeleton (monomer S1), which is preferably used as a constituent component of monomer raw material B described below, or that the content of this monomer is less than 10% by weight (more preferably less than 5% by weight, e.g., less than 2% by weight) of monomer raw material A. Monomer raw material A with such a composition can suitably realize a reinforcing film that favorably achieves both initial reworkability and strong adhesion after increased adhesive strength. For similar reasons, in other embodiments, it is preferable that monomer raw material A does not contain monomer S1, or if it contains monomer S1, its content (by weight) is lower than the content of monomer S1 in monomer raw material B.

The method for obtaining polymer (A) is not particularly limited, and various polymerization methods can be used as appropriate, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization. In some embodiments, solution polymerization is preferably used. The polymerization temperature during solution polymerization can be selected appropriately depending on the types of monomers and solvents used, the type of polymerization initiator, and other factors, and can be, for example, approximately 20°C to 170°C (typically approximately 40°C to 140°C).

The initiator used for polymerization can be appropriately selected from conventionally known thermal polymerization initiators, photopolymerization initiators, etc., depending on the polymerization method. One polymerization initiator can be used alone, or two or more can be used in combination.

Examples of thermal polymerization initiators include azo-based polymerization initiators (e.g., 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid) dimethyl, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2 Examples of suitable thermal polymerization initiators include 2,2'-azobis(N,N'-imidazolin-2-yl)propane dihydrochloride, 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(N,N'-dimethyleneisobutylamidine) dihydrochloride, etc.; persulfates such as potassium persulfate; peroxide polymerization initiators (e.g., dibenzoyl peroxide, t-butyl permaleate, lauroyl peroxide, etc.); and redox polymerization initiators. The amount of thermal polymerization initiator used is not particularly limited, but can be, for example, 0.01 to 5 parts by weight, preferably 0.05 to 3 parts by weight, per 100 parts by weight of the monomer component (monomer raw material A) used to prepare the acrylic polymer.

The photopolymerization initiator is not particularly limited, but examples include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators. The amount of photopolymerization initiator used is not particularly limited, but can be, for example, 0.01 to 5 parts by weight, preferably 0.05 to 3 parts by weight, per 100 parts by weight of monomer raw material A.

In some embodiments, polymer (A) may be included in the PSA composition for forming the PSA layer in the form of a partially polymerized product (polymer syrup) obtained by irradiating a mixture of the monomer raw material A described above with a polymerization initiator with ultraviolet (UV) light to polymerize a portion of the monomer component. The PSA composition containing such polymer syrup can be applied to a predetermined substrate and then irradiated with ultraviolet light to complete the polymerization. In other words, the polymer syrup can be considered a precursor to polymer (A). The PSA layer disclosed herein can be formed, for example, using a PSA composition containing the polymer syrup and polymer (B).

(Polymer (B))
The polymer (B) in the technology disclosed herein is a polymer of a monomer component (monomer raw material B) containing a monomer having a polyorganosiloxane skeleton (hereinafter also referred to as "monomer S1") and a (meth)acrylic monomer. Polymer (B) can be described as a copolymer of monomer S1 and a (meth)acrylic monomer. Polymer (B) can be used alone or in combination of two or more types. Due to the low polarity and mobility of the polyorganosiloxane structure derived from monomer S1, polymer (B) suppresses the initial adhesive strength upon application to an adherend and can function as an adhesive strength increase retarder that increases the adhesive strength to the adherend upon heating. Monomer S1 is not particularly limited, and any monomer containing a polyorganosiloxane skeleton can be used. Due to the low polarity derived from its structure, monomer S1 promotes uneven distribution of polymer (B) on the surface of the adhesive layer in the reinforcing film before use (before application to an adherend), thereby exhibiting easy peelability (low adhesiveness) during initial application. Monomer S1 preferably has a structure having a polymerizable reactive group at one end. A structure containing such monomer S1 units and (meth)acrylic monomer units results in the formation of a polymer (B) having a polyorganosiloxane skeleton in the side chain. Polymer (B) with such a structure tends to have low initial adhesive strength and high adhesive strength after heating due to the mobility and ease of movement of the side chain. Furthermore, in some embodiments, monomer S1 preferably has a polymerizable reactive group at one end and does not have a functional group at the other end that undergoes a crosslinking reaction with polymer (A). Polymer (B) copolymerized with monomer S1 of such a structure tends to have low initial adhesive strength and high adhesive strength after heating due to the mobility of the polyorganosiloxane structure derived from monomer S1.

As the monomer S1, for example, a compound represented by the following general formula (1) or (2) can be used. More specifically, examples of the single-end reactive silicone oils manufactured by Shin-Etsu Chemical Co., Ltd. include X-22-174ASX, X-22-2426, X-22-2475, and KF-2012. The monomer S1 can be used alone or in combination of two or more.
In the above general formulas (1) and (2), ^R3 is hydrogen or methyl, ^R4 is a methyl group or a monovalent organic group, and m and n are integers of 0 or more.

The functional group equivalent weight of monomer S1 can be any appropriate value within the range in which the desired effect is achieved using monomer S1, and is not limited to a specific range. From the viewpoint of sufficiently suppressing initial adhesive strength, the functional group equivalent weight is, for example, 100 g/mol or more, or 200 g/mol or more, and is suitably 300 g/mol or more (e.g., 500 g/mol or more), preferably 800 g/mol or more, and more preferably 1500 g/mol or more. In a particularly preferred embodiment, from the viewpoint of achieving both low adhesive strength at the initial stage of application and increased adhesive strength after heating, the functional group equivalent weight is 2000 g/mol or more, more preferably 2500 g/mol or more, and may be 3000 g/mol or more, 4000 g/mol or more, or 5000 g/mol or more. In some other embodiments, the functional group equivalent weight may be 9,000 g/mol or more, 12,000 g/mol or more, or 15,000 g/mol or more.

From the viewpoint of sufficiently increasing adhesive strength, the functional group equivalent is suitably, for example, 30,000 g/mol or less, and may be 20,000 g/mol or less, less than 15,000 g/mol, or less than 10,000 g/mol. In some preferred embodiments, the functional group equivalent of monomer S1 is 7,000 g/mol or less, more preferably 5,500 g/mol or less, even more preferably 4,500 g/mol or less, and may be 4,200 g/mol or less, or may be 3,500 g/mol or less. When the functional group equivalent of monomer S1 is within the above range, compatibility within the adhesive layer (e.g., compatibility with the base polymer) is likely to be good, the mobility of the polyorganosiloxane skeleton (chain) of polymer (B) is good, and the mobility of polymer (B) can be easily adjusted within an appropriate range, making it easier to achieve an adhesive layer that combines low initial adhesive strength with increased adhesive strength after heating.

Here, "functional group equivalent" refers to the weight of the main skeleton (e.g., polydimethylsiloxane) bound to one functional group. The unit g/mol is calculated in terms of 1 mol of functional group. The functional group equivalent of monomer S1 can be calculated, for example, from the spectral intensity of ¹ H-NMR (proton NMR) based on nuclear magnetic resonance (NMR). Calculation of the functional group equivalent (g/mol) of monomer S1 based on the spectral intensity of ¹ H-NMR can be performed based on a general structural analysis method related to ¹ H-NMR spectrum analysis, with reference to the description of Japanese Patent No. 5,951,153, if necessary. In the functional group equivalent of monomer S1, the functional group refers to a polymerizable functional group (e.g., an ethylenically unsaturated group such as a (meth)acryloyl group, a vinyl group, or an allyl group).

When two or more monomers having different functional group equivalents are used as the monomer S1, the arithmetic mean value can be used as the functional group equivalent of the monomer S1. That is, the functional group equivalent of the monomer S1 consisting of n types of monomers having different functional group equivalents (monomer S1 ₁ , monomer S1 ₂ , ..., monomer S1 _n ) can be calculated by the following formula:
Functional group equivalent of monomer S1 (g/mol) = (functional group equivalent of monomer _S11 × amount of monomer _S11 + functional group equivalent of monomer _S12 × amount of monomer _{S12 + ... + functional group equivalent of monomer S1n ×} amount of monomer _S1n ) / (amount of monomer S11 + amount of _{monomer S12 +} ... + amount of monomer _S1n )

The content of monomer S1 can be any appropriate value within the range in which the desired effect is achieved using monomer S1, and is not limited to a specific range. From the viewpoint of sufficiently suppressing initial adhesive strength, in some embodiments, the content of monomer S1 relative to the total amount of monomer components (monomer raw material B) used to prepare polymer (B) may be, for example, 5% by weight or more. To better demonstrate its effect as an adhesive strength increase retarder, it is preferably 10% by weight or more, more preferably 12% by weight or more, even more preferably 15% by weight or more, particularly preferably 18% by weight or more, and may even be 20% by weight or more. Furthermore, from the viewpoint of polymerization reactivity and compatibility, the content of monomer S1 in monomer raw material B may be, for example, 80% by weight or less, and suitably 60% by weight or less, preferably 50% by weight or less, more preferably 40% by weight or less, and even more preferably 30% by weight or less. By setting the polymerization ratio of monomer S1 within an appropriate range, an increase in adhesive strength can be favorably achieved.

Monomer raw material B contains, in addition to monomer S1, a (meth)acrylic monomer copolymerizable with monomer S1. Using one or more (meth)acrylic monomers can favorably adjust the mobility of polymer (B) within the adhesive layer. This can also help improve the compatibility between polymer (B) and polymer (A). Because polymer (B) containing (meth)acrylic monomer units has good compatibility with acrylic polymers, improving the mobility of polymer (B) within the adhesive layer makes it easier to reduce initial adhesive strength and improve adhesive strength after heating.

In the polymer (B) used in the technology disclosed herein, the composition of the (meth)acrylic monomer contained in the monomer raw material B is preferably set so that the glass transition temperature T _B1 based on the composition of the (meth)acrylic monomer is higher than the glass transition temperature _TA of the polymer (A). T _B1 can be set, for example, to be higher than 0°C. Here, the glass transition temperature T _B1 based on the composition of the (meth)acrylic monomer refers to the Tg calculated by the Fox formula based on the composition of only the (meth)acrylic monomer among the monomer components used to prepare the polymer (B). T _B1 can be calculated from the glass transition temperature of a homopolymer of each (meth)acrylic monomer and the weight fraction of each (meth)acrylic monomer in the total amount of the (meth)acrylic monomers by applying the above-mentioned Fox formula to only the (meth)acrylic monomers among the monomer components used to prepare the polymer (B). Polymer (B) having a relatively high glass transition temperature T _B1 (typically higher than 0°C) tends to suppress the initial adhesive strength. Also, polymer (B) having a relatively high glass transition temperature T _B1 (typically higher than 0°C) tends to provide a reinforcing film having a large adhesive strength increase ratio.

In some preferred embodiments, T _B1 is 10°C or higher, more preferably 30°C or higher, even more preferably 40°C or higher, and may be 45°C or higher. As T _B1 increases, the adhesive strength at the initial stage of application generally tends to be better suppressed. This is thought to be because, with a polymer (B) having a T _B1 at or above a predetermined temperature, the increase in mobility and mobility of the polyorganosiloxane structural moiety that accompanies temperature increases to room temperature or a temperature range somewhat higher than room temperature is effectively suppressed by the monomer units derived from the (meth)acrylic monomer contained in the polymer (B), thereby better maintaining the low adhesive strength due to the presence of the polyorganosiloxane structural moiety. From the viewpoint of more stably maintaining the low adhesive strength at the initial stage of application, in some embodiments, T _B1 may be, for example, 50°C or higher, 55°C or higher, or 60°C or higher. Furthermore, T _B1 may be, for example, 120°C or lower, or 100°C or lower. As T _B1 decreases, the adhesive strength tends to increase more easily due to heating. In some preferred embodiments, T _B1 is, for example, 90° C. or less, more preferably 70° C. or less, even more preferably 60° C. or less, and particularly preferably 55° C. or less (for example, 50° C. or less).

From the viewpoint of making it easier to exert the effect of appropriately setting T _B1 , the total amount of the monomer S1 and the (meth)acrylic monomer in all the monomer components for preparing the polymer (B) may be, for example, 50% by weight or more, 70% by weight or more, 85% by weight or more, 90% by weight or more, 95% by weight or more, or even substantially 100% by weight.

The glass transition temperature _TB of the polymer (B) is not particularly limited and can be selected so as to obtain preferred properties in the reinforcing film disclosed herein. The _TB of the polymer (B) may be, for example, less than 50°C, 30°C or less, 20°C or less, 15°C or less, or 10°C or less. When the _TB of the polymer (B) is low, the mobility (typically, temperature-sensitive mobility) of the polymer (B) is improved, and the adhesive strength can be significantly increased. In some preferred embodiments, the _TB of the polymer (B) is 5°C or less, or may be less than 0°C, -5°C or less, or -10°C or less. In some embodiments, the _TB of the polymer (B) may be, for example, -40°C or more, or -30°C or more. The higher _{the TB} , the more the polymer (B) unevenly distributed on the surface side of the pressure-sensitive adhesive layer when attached to an adherend contributes to a decrease in initial adhesive strength, and the film tends to have excellent easy peel properties at the initial stage of attachment. In some preferred embodiments, the T _B of the polymer (B) is −20° C. or higher, and may be −15° C. or higher. By setting the T _B within an appropriate range, it is possible to control the easy peelability at the initial stage of application and the increase in adhesive strength after heating within preferred ranges.

In some embodiments, the composition of the monomer components for preparing polymer (B) can be set so that T _B1 is higher than T _B , i.e., T _B1 - _{T B} is greater than 0°C. With such a composition, the effect of adjusting the mobility of polymer (B) by the composition of the (meth)acrylic monomer contained in the monomer components is likely to be favorably exhibited. T _B1 - T _B may be, for example, about 40°C to 100°C, or about 50°C to 90°C. In some preferred embodiments, T _B1 - T _B is 45°C or higher, more preferably 50°C or higher, and even more preferably 55°C or higher (e.g., 58°C or higher). Furthermore, from the viewpoint of favorably exhibiting the effect of containing polymer (B), T _B1 - _{T B} is preferably 80°C or lower, more preferably 70°C or lower, and even more preferably 65°C or lower (e.g., 62°C or lower).

From the viewpoint of facilitating control of the mobility of polymer (B) within the pressure-sensitive adhesive layer, in some embodiments, the composition of the monomer components for preparing polymer (B) can be set in relation to the glass transition temperature TA of polymer ( _A ) so that _TB is 20°C or more higher than _TA , i.e., _TB - _TA is 20°C or more. In some preferred embodiments, _TB - _TA is, for example, 30°C or more, more preferably 40°C or more, even more preferably 50°C or more, and may be 60°C or more or may be 70°C or more. Furthermore, from the viewpoint of increasing adhesive strength, _TB - _TA may be, for example, 130°C or less, or may be 120°C or less, preferably 100°C or less, more preferably 80°C or less, even more preferably 65°C or less, may be 55°C or less, or may be 45°C or less.

Examples of (meth)acrylic monomers that can be used for monomer starting material B include (meth)acrylic acid alkyl esters. Here, "alkyl" refers to a chain (including linear and branched) alkyl (group) and does not include the alicyclic hydrocarbon groups described below. For example, one or more of the monomers exemplified above as (meth)acrylic acid alkyl esters that can be used for polymer (A) can be used as constituents of monomer starting material B. In some embodiments, monomer starting material B can contain at least one _C4-12 (meth)acrylic acid alkyl ester (preferably a _{C4-10 (meth)acrylic acid alkyl ester, for example a C6-10 (} meth)acrylic acid alkyl ester). In other embodiments, monomer starting material B can contain at least one _C1-18 methacrylic acid alkyl ester (preferably a _C1-14 methacrylic acid alkyl ester, for example a _C1-10 methacrylic acid alkyl ester). Monomer raw material B may contain, as a (meth)acrylic monomer, one or more selected from the group consisting of MMA, n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (2EHMA).

Other examples of the (meth)acrylic monomer include (meth)acrylic acid esters having an alicyclic hydrocarbon group. For example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, etc. can be used. In some embodiments, monomer raw material B may contain at least one (meth)acrylic monomer selected from dicyclopentanyl methacrylate, isobornyl methacrylate, and cyclohexyl methacrylate.

The content of the (meth)acrylic acid alkyl ester and the (meth)acrylic acid ester having an alicyclic hydrocarbon group in monomer raw material B may be, for example, 10% by weight or more and 95% by weight or less, 20% by weight or more and 95% by weight or less, 30% by weight or more and 90% by weight or less, 40% by weight or more and 90% by weight or less, or 50% by weight or more and 85% by weight or less. From the viewpoint of ease of increasing adhesive strength by heating, the use of a (meth)acrylic acid alkyl ester may be advantageous. In some embodiments, the content of the (meth)acrylic acid ester having an alicyclic hydrocarbon group may be less than 50% by weight, less than 30% by weight, less than 15% by weight, less than 10% by weight, or less than 5% by weight of monomer raw material B. It is not necessary to use a (meth)acrylic acid ester having an alicyclic hydrocarbon group.

In some preferred embodiments, the (meth)acrylic monomer constituting the monomer raw material B may include a monomer M2 having a homopolymer Tg of 50°C or higher. By copolymerizing the monomer S1 and the monomer M2 in the polymer (B), the mobility and movability of the polyorganosiloxane structural moiety with increasing temperature are appropriately controlled, making it easier to achieve both easy initial releasability (reworkability) and increased adhesive strength after heating. In some embodiments, the Tg of the homopolymer of the monomer M2 may be 60°C or higher, 70°C or higher, 80°C or higher, or 90°C or higher. Furthermore, there is no particular upper limit to the Tg of the homopolymer of the monomer M2, but from the perspective of ease of synthesis of the polymer (B), it is typically appropriate for it to be 200°C or lower. In some embodiments, the Tg of the homopolymer of the monomer M2 may be, for example, 180°C or lower, 150°C or lower, or 120°C or lower.

Monomer M2 can be, for example, one of the (meth)acrylic monomers listed above whose homopolymer Tg satisfies the conditions. For example, one or more monomers selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid esters having an alicyclic hydrocarbon group can be used. As the (meth)acrylic acid alkyl ester, a methacrylic acid alkyl ester in which the alkyl group has 1 to 4 carbon atoms can be preferably used.

In embodiments in which monomer feedstock B contains monomer M2, the content of monomer M2 may be, for example, 5% by weight or more, 10% by weight or more, 15% by weight or more, 20% by weight or more, 25% by weight or more, or 30% by weight or more of monomer feedstock B. In some embodiments, the content of monomer M2 may be 35% by weight or more, 40% by weight or more, 45% by weight or more, 50% by weight or more, or 55% by weight or more of monomer feedstock B. The content of monomer M2 may be, for example, 90% by weight or less, typically 80% by weight or less, preferably 75% by weight or less, or may be 70% by weight or less, or may be 65% by weight or less. In some preferred embodiments, the content of monomer M2 is 60% by weight or less (e.g., 50% by weight or less, typically 42% by weight or less). By limiting the copolymerization ratio of monomer M2 with a Tg of 50°C or higher in polymer (B) to a specified value or less, it is possible to preferably achieve an increase in adhesive strength after heating based on the mobility of polymer (B) at around 50°C. From a similar perspective, the content of monomer M2 in monomer raw material B may be 35% by weight or less, 25% by weight or less, or 15% by weight or less (e.g., 5% by weight or less).

The content of the monomer M2 can be preferably applied, for example, to an embodiment in which the monomer M2 is composed of one or more monomers selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid esters having an alicyclic hydrocarbon group, or an embodiment in which the monomer M2 is composed of one or more monomers selected from (meth)acrylic acid alkyl esters (e.g., methacrylic acid alkyl esters). One preferred example of such an embodiment is an embodiment in which the monomer M2 is composed of MMA.

In some embodiments, the (meth)acrylic monomer may contain monomer M3, the homopolymer of which has a Tg of less than 50°C (typically -20°C or higher and less than 50°C). Use of monomer M3 makes it easier to obtain a reinforcing film that exhibits a good balance between adhesive strength and cohesive strength after the adhesive strength has increased. From the perspective of making it easier to achieve this effect, it is preferable to use monomer M3 in combination with monomer M2.

Monomer M3 can be, for example, one of the (meth)acrylic monomers listed above whose homopolymer Tg satisfies the conditions. For example, one or more monomers selected from the group consisting of (meth)acrylic acid alkyl esters can be used.

In an embodiment in which monomer raw material B contains monomer M3, the content of monomer M3 may be, for example, 5% by weight or more, 10% by weight or more, 15% by weight or more, 20% by weight or more, 25% by weight or more, 30% by weight or more, or 35% by weight or more of monomer raw material B. Furthermore, the content of monomer M3 is typically suitably 70% by weight or less of monomer raw material B, and may be 60% by weight or less, or 50% by weight or less. The above content of monomer M3 is preferably applicable, for example, to an embodiment in which monomer M3 consists of one or more monomers selected from (meth)acrylic acid alkyl esters (e.g., methacrylic acid alkyl esters).

In some embodiments of the reinforcing film disclosed herein, it is preferable that the content of monomers in the monomer raw material B, whose homopolymer Tg is higher than 170°C, is 30% by weight or less. Herein, unless otherwise specified, the term "a monomer content of X% by weight or less" refers to an embodiment in which the content of the monomer is 0% by weight, i.e., an embodiment in which the monomer is substantially not contained. Furthermore, "substantially not contained" means that the monomer is not used, at least intentionally. If the copolymerization ratio of monomers whose homopolymer Tg is higher than 170°C is high, the mobility of polymer (B) tends to be insufficient, and it may be difficult to increase the adhesive strength by heating to a temperature range higher than 50°C.

In some embodiments, it is preferable that monomer raw material B contains at least MMA as a (meth)acrylic monomer. Polymer (B) copolymerized with MMA makes it easier to obtain a reinforcing film with high adhesive strength after heating. The proportion of MMA in the total amount of (meth)acrylic monomers contained in monomer raw material B may be, for example, 5% by weight or more, 10% by weight or more, 20% by weight or more, 30% by weight or more, or 40% by weight or more. Furthermore, the proportion of MMA in the total amount of monomer raw material B is typically 95% by weight or less. In some preferred embodiments, the proportion of MMA in the total amount of monomer raw material B may be 75% by weight or less, 65% by weight or less, 60% by weight or less, or 55% by weight or less (e.g., 50% by weight or less) from the perspective of increasing adhesive strength after heating.

Other examples of monomers that may be included together with monomer S1 as a monomer unit constituting polymer (B) include the carboxyl group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, isocyanate group-containing monomers, amide group-containing monomers, monomers having a nitrogen atom-containing ring (such as N-vinyl cyclic amides, cyclic amides having a (meth)acryloyl group, monomers having a succinimide skeleton, maleimides, and itaconimides), aminoalkyl (meth)acrylates, vinyl esters, vinyl ethers, olefins, (meth)acrylic acid esters having an aromatic hydrocarbon group, heterocyclic ring-containing (meth)acrylates, halogen atom-containing (meth)acrylates, and (meth)acrylic acid esters obtained from terpene compound-derived alcohols, among others.

Further examples of monomers that can be included together with monomer S1 as monomer units constituting polymer (B) include oxyalkylene di(meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, and tripropylene glycol di(meth)acrylate; monomers having a polyoxyalkylene skeleton, such as polyethylene glycol; Polymerizable polyoxyalkylene ethers having a polymerizable functional group such as a (meth)acryloyl group, a vinyl group, or an allyl group at one end of a polyoxyalkylene chain such as polypropylene glycol, and an ether structure (alkyl ether, aryl ether, aryl alkyl ether, or the like) at the other end; alkoxyalkyl (meth)acrylates such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, and ethoxypropyl (meth)acrylate; salts such as alkali metal (meth)acrylates; trimethylol Polyhydric (meth)acrylates such as propane tri(meth)acrylate; halogenated vinyl compounds such as vinylidene chloride and 2-chloroethyl (meth)acrylate; oxazoline group-containing monomers such as 2-vinyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, and 2-isopropenyl-2-oxazoline; aziridine group-containing monomers such as (meth)acryloylaziridine and 2-aziridinylethyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, lactones and 2-hydroxyethyl (meth)acrylate Examples of suitable vinyl monomers include hydroxyl group-containing vinyl monomers such as adducts of the above; fluorine-containing vinyl monomers such as fluorine-substituted (meth)acrylic acid alkyl esters; reactive halogen-containing vinyl monomers such as 2-chloroethyl vinyl ether and monochlorovinyl acetate; organosilicon-containing vinyl monomers such as vinyltrimethoxysilane, γ-(meth)acryloxypropyltrimethoxysilane, allyltrimethoxysilane, trimethoxysilylpropylallylamine, and 2-methoxyethoxytrimethoxysilane; and macromonomers having a radically polymerizable vinyl group at the terminal of a monomer obtained by polymerizing a vinyl group. These can be copolymerized with monomer S1 either alone or in combination of two or more.

In some embodiments, polymer (B) that does not have a functional group that undergoes a crosslinking reaction with polymer (A) can be preferably used. In other words, polymer (B) is preferably included in the pressure-sensitive adhesive layer in a form that is not chemically bonded to polymer (A). A pressure-sensitive adhesive layer containing polymer (B) in this form exhibits good mobility of polymer (B) when heated, making it suitable for improving the adhesive strength increase ratio. The functional group that undergoes a crosslinking reaction with polymer (A) can vary depending on the type of functional group possessed by polymer (A), but can be, for example, an epoxy group, an isocyanate group, a carboxy group, an alkoxysilyl group, an amino group, etc.

The Mw of polymer (B) is not particularly limited. The Mw of polymer (B) may be, for example, 1,000 or more, or 5,000 or more. In some preferred embodiments, from the viewpoint of favorably exhibiting an increase in adhesive strength after heating, the Mw of polymer (B) is 10,000 or more, more preferably 12,000 or more, or may be 15,000 or more, 20,000 or more, 22,000 or more, or 25,000 or more. In other embodiments, the Mw of polymer (B) may be 30,000 or more, 50,000 or more, or 70,000 or more. The upper limit of the Mw of polymer (B) is, for example, 500,000 or less, 350,000 or less, 200,000 or less, or 150,000 or less. From the viewpoint of adjusting the compatibility and mobility within the adhesive layer within an appropriate range and suitably exhibiting low adhesiveness in the initial stage of application, in some preferred embodiments, the Mw of polymer (B) is 100,000 or less, more preferably 80,000 or less, even more preferably 60,000 or less, and particularly preferably 40,000 or less (e.g., 30,000 or less), and may be 25,000 or less, or even 20,000 or less. By setting the Mw of polymer (B) within an appropriate range, it is easy to obtain an adhesive that excels in both easy peelability and increased adhesive strength in the initial stage of application.

In some preferred embodiments, the Mw of polymer (B) is preferably lower than the Mw of polymer (A). This makes it easier to realize a reinforcing film that combines good reworkability at the initial stage of application with increased adhesive strength after heating. In some embodiments, the Mw of polymer (B) may be, for example, 0.8 times or less, 0.75 times or less, 0.5 times or less, or 0.3 times or less of the Mw of polymer (A). In some preferred embodiments, the ratio of Mw _{B of polymer (B) to Mw A of} polymer (A) (Mw _B / Mw _A ) is 0.3 or less, more preferably 0.2 or less, even more preferably 0.1 or less, and particularly preferably 0.06 or less (e.g., 0.05 or less). The ratio (Mw _B / Mw _A ) is, for example, suitably 0.010 or more, preferably 0.020 or more, more preferably 0.03 or more, and even more preferably 0.04 or more. By setting the Mw of polymer (A) and the Mw of polymer (B) within an appropriate range, the effects of the technology disclosed herein can be more effectively achieved. In some other embodiments, the Mw of polymer (B) may be 0.03 times or less (e.g., 0.02 times or less) the Mw of polymer (A).

Polymer (B) can be produced, for example, by polymerizing the above-mentioned monomers using known methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization.

A chain transfer agent can be used, if necessary, to adjust the molecular weight of polymer (B). Examples of chain transfer agents that can be used include compounds having a mercapto group, such as octyl mercaptan, lauryl mercaptan, t-nonyl mercaptan, t-dodecyl mercaptan, mercaptoethanol, and α-thioglycerol; thioglycolic acid esters, such as thioglycolic acid, methyl thioglycolate, ethyl thioglycolate, propyl thioglycolate, butyl thioglycolate, t-butyl thioglycolate, 2-ethylhexyl thioglycolate, octyl thioglycolate, isooctyl thioglycolate, decyl thioglycolate, dodecyl thioglycolate, ethylene glycol thioglycolate, neopentyl glycol thioglycolate, and pentaerythritol thioglycolate; and α-methylstyrene dimer.

The amount of chain transfer agent used is not particularly limited, but typically, 0.05 to 20 parts by weight, preferably 0.1 to 15 parts by weight, and more preferably 0.2 to 10 parts by weight, of chain transfer agent is contained per 100 parts by weight of monomer. By adjusting the amount of chain transfer agent added in this way, it is possible to obtain polymer (B) with an appropriate molecular weight. Chain transfer agents can be used alone or in combination of two or more.

Methods for adjusting the molecular weight of polymer (B) include the use of the chain transfer agent, and various conventionally known methods can be used alone or in appropriate combination. The same applies to the molecular weight of polymer (A). Non-limiting examples of such methods include selection of the polymerization method, selection of the type and amount of polymerization initiator used, selection of the polymerization temperature, selection of the type and amount of polymerization solvent used in solution polymerization methods, and selection of the light irradiation intensity in photopolymerization methods. Those skilled in the art will understand how to obtain a polymer with a desired molecular weight based on the description of the present application, including the specific examples described below, and the common general technical knowledge at the time of filing this application.

In the reinforcing film disclosed herein, the amount of polymer (B) used per 100 parts by weight of polymer (A) can be, for example, 0.1 parts by weight or more. From the viewpoint of achieving a higher effect (preferably, easy peelability at the initial stage of application), it is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, even more preferably 1.5 parts by weight or more, and may be 2 parts by weight or more. In some embodiments, from the viewpoint of improving reworkability, the amount of polymer (B) used can be, for example, 3 parts by weight or more, or may be 4 parts by weight or more, or may be 5 parts by weight or more. Furthermore, the amount of polymer (B) used per 100 parts by weight of polymer (A) can be, for example, 75 parts by weight or less, 30 parts by weight or less, 10 parts by weight or less, or 8 parts by weight or less. From the viewpoint of optimally achieving the desired increase in adhesive strength, in some preferred embodiments, the amount of polymer (B) used per 100 parts by weight of polymer (A) is 5 parts by weight or less, more preferably 4 parts by weight or less, even more preferably 3 parts by weight or less, and particularly preferably 2.5 parts by weight or less. In some other preferred embodiments, the amount of polymer (B) used per 100 parts by weight of polymer (A) is 1.5 parts by weight or less (e.g., 1.2 parts by weight or less). By using polymer (B) in this range, it is easy to achieve good flex recovery and flex retention. Furthermore, it is possible to better achieve both easy peeling properties and increased adhesive strength at the initial stage of application.

The pressure-sensitive adhesive layer may optionally contain a polymer (optional polymer) other than polymer (A) and polymer (B), provided that the performance of the reinforcing film disclosed herein is not significantly impaired. The amount of such optional polymer used is typically 20% by weight or less of the total polymer components contained in the pressure-sensitive adhesive layer, and may be 15% by weight or less, or 10% by weight or less. In some embodiments, the amount of the optional polymer used may be 5% by weight or less, 3% by weight or less, or 1% by weight or less of the total polymer components. The pressure-sensitive adhesive layer may be substantially free of polymers other than polymer (A) and polymer (B).

(Crosslinking agent)
A crosslinking agent may be used in the pressure-sensitive adhesive layer as needed for purposes such as adjusting cohesive strength. Examples of crosslinking agents that can be used include crosslinking agents known in the field of pressure-sensitive adhesives, such as epoxy-based crosslinking agents, isocyanate-based crosslinking agents, silicone-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, silane-based crosslinking agents, alkyl etherified melamine-based crosslinking agents, and metal chelate-based crosslinking agents. Isocyanate-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-based crosslinking agents are preferably used. An isocyanate-based crosslinking agent is preferably used as a crosslinking agent that satisfies both flex recovery and flex retention. The crosslinking agents can be used alone or in combination of two or more.

As an isocyanate-based crosslinking agent, a polyfunctional isocyanate (a compound having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used. Isocyanate-based crosslinking agents can be used alone or in combination of two or more.

Examples of polyfunctional isocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates.
Specific examples of aliphatic polyisocyanates include 1,2-ethylene diisocyanate; tetramethylene diisocyanates such as 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, and 1,4-tetramethylene diisocyanate; hexamethylene diisocyanates such as 1,2-hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 2,5-hexamethylene diisocyanate; 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and lysine diisocyanate.

Specific examples of alicyclic polyisocyanates include isophorone diisocyanate; cyclohexyl diisocyanates such as 1,2-cyclohexyl diisocyanate, 1,3-cyclohexyl diisocyanate, and 1,4-cyclohexyl diisocyanate; cyclopentyl diisocyanates such as 1,2-cyclopentyl diisocyanate and 1,3-cyclopentyl diisocyanate; hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

Specific examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, Examples include 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, xylylene-1,4-diisocyanate, and xylylene-1,3-diisocyanate.

Preferred polyfunctional isocyanates include those having an average of three or more isocyanate groups per molecule. Such trifunctional or higher isocyanates may be multimers (e.g., dimers or trimers) of difunctional or trifunctional or higher isocyanates, derivatives (e.g., addition reaction products of polyhydric alcohols with two or more molecules of polyfunctional isocyanates), polymers, etc. Examples include dimers and trimers of diphenylmethane diisocyanate, isocyanurates of hexamethylene diisocyanate (trimer adducts with an isocyanurate structure), reaction products of trimethylolpropane and tolylene diisocyanate, reaction products of trimethylolpropane and hexamethylene diisocyanate, trimethylolpropane adducts of xylylene diisocyanate, trimethylolpropane adducts of isophorone diisocyanate, trimethylolpropane adducts of hexamethylene diisocyanate, polymethylene polyphenyl isocyanate, polyether polyisocyanate, polyester polyisocyanate, and adducts of these with various polyols, and polyfunctional isocyanates such as polyisocyanates multifunctionalized with isocyanurate bonds, biuret bonds, allophanate bonds, etc.

Commercially available products of the above-mentioned polyfunctional isocyanates include Asahi Kasei Chemicals Corporation's product name "Duranate TPA-100," Tosoh Corporation's product names "Coronate L," "Coronate HL," "Coronate HK," "Coronate HX," and "Coronate 2096," and Mitsui Chemicals, Inc.'s product names "Takenate D110N," "Takenate D120N," "Takenate D140N," and "Takenate D160N."

Examples of epoxy crosslinking agents include bisphenol A, epichlorohydrin-type epoxy resins, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane. These may be used alone or in combination of two or more.

Metal chelate compounds include metal components such as aluminum, iron, tin, titanium, and nickel, and chelate components such as acetylene, methyl acetoacetate, and ethyl lactate. These can be used alone or in combination of two or more.

When a crosslinking agent is used, the amount used is not particularly limited and can be, for example, an amount greater than 0 parts by weight per 100 parts by weight of polymer (A). The amount of crosslinking agent used can be, for example, 0.01 parts by weight or more, preferably 0.05 parts by weight or more, per 100 parts by weight of polymer (A). Increasing the amount of crosslinking agent used tends to suppress initial adhesive strength and improve reworkability. It also tends to provide excellent flex recovery and processability. In some embodiments, the amount of crosslinking agent used per 100 parts by weight of polymer (A) may be 0.1 parts by weight or more, 0.5 parts by weight or more, or even 0.8 parts by weight or more. On the other hand, from the viewpoint of allowing a moderate degree of mobility of polymer (B) and achieving increased adhesive strength after heating, the amount of crosslinking agent used per 100 parts by weight of polymer (A) is typically 15 parts by weight or less, and may be 10 parts by weight or less, or 5 parts by weight or less.

The technology disclosed herein can be preferably implemented in an embodiment using at least an isocyanate-based crosslinking agent as a crosslinking agent. From the viewpoint of achieving both good reworkability at the initial stage of application and increased adhesive strength after heating, in some embodiments, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of polymer (A) can be, for example, 0.01 parts by weight or more, preferably 0.05 parts by weight or more, more preferably 0.07 parts by weight or more, and may be 0.10 parts by weight or more, or even 0.15 parts by weight or more (e.g., 0.20 parts by weight or more). Increasing the amount of isocyanate-based crosslinking agent used tends to provide appropriate cohesive strength and elastic modulus, and also provides excellent flex recovery and processability. Furthermore, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of polymer (A) can be, for example, 5 parts by weight or less, preferably less than 1.0 part by weight, more preferably less than 0.5 parts by weight, even more preferably less than 0.3 parts by weight, and particularly preferably less than 0.2 parts by weight (e.g., 0.15 parts by weight or less). This appropriately reduces the adhesive's cohesive strength and, in turn, its modulus of elasticity (typically, its surface modulus of elasticity), resulting in good bending retention and also making it easier for adhesive strength to increase after heating.

While not particularly limited, when an isocyanate-based crosslinking agent is used in a configuration in which the pressure-sensitive adhesive layer contains a hydroxyl-containing monomer as a monomer unit, the molar ratio of isocyanate groups to hydroxyl groups ([NCO]/[OH]) in the pressure-sensitive adhesive layer can be, for example, 0.001 or greater. Increasing the amount of isocyanate-based crosslinking agent relative to the hydroxyl-containing monomer in this manner tends to bring the pressure-sensitive adhesive's modulus of elasticity (typically, surface modulus of elasticity) into a suitable range, improving flex recovery. It also tends to provide excellent processability. In some preferred embodiments, the molar ratio ([NCO]/[OH]) is 0.002 or greater, more preferably 0.004 or greater, and even more preferably 0.006 or greater (e.g., 0.007 or greater). It may also be 0.010 or greater, 0.020 or greater, or 0.030 or greater. The molar ratio ([NCO]/[OH]) can be, for example, 1.0 or less, or 0.10 or less. By limiting the molar ratio to a predetermined value or less, a crosslinked structure suitable for significantly increasing the adhesive strength after heating relative to the initial adhesive strength after application can be preferably formed. In some preferred embodiments, the molar ratio ([NCO]/[OH]) is 0.030 or less, more preferably 0.015 or less, even more preferably 0.012 or less (e.g., 0.009 or less), and may be 0.005 or less. In the adhesive layer, at least a portion of the isocyanate groups and hydroxyl groups may exist in a chemically bonded (crosslinked) state. More specifically, the isocyanate groups may exist in a chemically bonded (crosslinked) state with the hydroxyl groups. Meanwhile, some of the hydroxyl groups may exist chemically bonded to the isocyanate groups, while the other portion may exist in a state not chemically bonded (crosslinked) to the isocyanate groups.

In some preferred embodiments, the pressure-sensitive adhesive layer contains a catalyst. The catalyst can be added to promote curing of the pressure-sensitive adhesive layer during formation, typically to more effectively promote one of the crosslinking reactions described above. Therefore, the catalyst is also referred to as a curing catalyst or a crosslinking catalyst. Adding a catalyst promotes initial curing and suppresses side reactions that can cause bubbles on the surface of the pressure-sensitive adhesive layer. Examples of catalysts include organometallic compounds such as iron-based catalysts, tin-based catalysts, titanium-based catalysts, zirconium-based catalysts, lead-based catalysts, cobalt-based catalysts, and zinc-based catalysts, as well as tertiary amine compounds. These can be used alone or in combination of two or more. Among these, iron-based catalysts and tin-based catalysts are preferred from the perspective of balancing reaction rate and pot life, with iron-based catalysts being particularly preferred.

Examples of iron-based catalysts include iron acetylacetonate and iron 2-ethylhexanoate. Iron-based catalysts can be used alone or in combination of two or more.

Examples of tin-based catalysts include dibutyltin dichloride, dibutyltin oxide, dibutyltin dibromide, dibutyltin maleate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin sulfide, tributyltin methoxide, tributyltin acetate, triethyltin ethoxide, tributyltin ethoxide, dioctyltin oxide, dioctyltin dilaurate, tributyltin chloride, tributyltin trichloroacetate, and tin 2-ethylhexanoate. Tin-based catalysts can be used alone or in combination of two or more.

The amount of catalyst used is not particularly limited and can be, for example, 0.0001 parts by weight or more, preferably 0.001 parts by weight or more, more preferably 0.003 parts by weight or more, even more preferably 0.006 parts by weight or more, and particularly preferably 0.008 parts by weight or more, per 100 parts by weight of polymer (A). Using an appropriate amount of catalyst suppresses the generation of bubbles from the adhesive layer, making it easier to obtain a smooth adhesive surface. Furthermore, the amount of catalyst used per 100 parts by weight of polymer (A) can be, for example, 1 part by weight or less, and may even be 0.1 parts by weight or less. In some preferred embodiments, the amount of catalyst used per 100 parts by weight of polymer (A) is 0.03 parts by weight or less, more preferably 0.02 parts by weight or less, even more preferably 0.01 parts by weight or less, and may even be 0.005 parts by weight or less. By appropriately limiting the amount of catalyst used per 100 parts by weight of polymer (A), it is easy to achieve a suitable increase in adhesive strength.

Although not particularly limited, when a catalyst is used in a configuration in which the pressure-sensitive adhesive layer contains a hydroxyl group-containing monomer as a monomer unit, the amount of catalyst used can be an amount such that the molar ratio of catalyst to hydroxyl groups contained in the pressure-sensitive adhesive layer ([catalyst]/[OH]) is, for example, 1.0×10 ⁻⁶ or more, preferably 1.0×10 ⁻⁵ or more, more preferably 1.0×10 ⁻⁴ or more, even more preferably 2.0×10 ⁻⁴ or more, and particularly preferably 3.0×10 ⁻⁴ or more. By using an appropriate amount of catalyst, bubble generation from the pressure-sensitive adhesive layer is suppressed, making it easier to obtain a smooth adhesive surface. Furthermore, the molar ratio ([catalyst]/[OH]) can be, for example, 5.0×10 ⁻² or less, and may be 5.0×10 ⁻³ or less. In some preferred embodiments, the molar ratio ([catalyst]/[OH]) is 3.0× ¹⁰ or less, more preferably 1.0×10 ^or less, even more preferably 5.0×10 ^or less, and may be 3.0×10 ^or less. By appropriately limiting the catalyst content, it is easy to achieve a suitable increase in adhesive strength.

(Tackifying resin)
The pressure-sensitive adhesive layer may contain a tackifying resin as needed. The tackifying resin is not particularly limited, but examples thereof include rosin-based tackifying resins, terpene-based tackifying resins, phenol-based tackifying resins, hydrocarbon-based tackifying resins, ketone-based tackifying resins, polyamide-based tackifying resins, epoxy-based tackifying resins, and elastomer-based tackifying resins. The tackifying resins may be used alone or in combination of two or more.

The amount of tackifier resin is not particularly limited and can be set so as to achieve appropriate adhesive performance depending on the purpose and application. The amount of tackifier resin per 100 parts by weight of polymer (A) (when two or more types of tackifier resins are included, the total amount of these resins) can be, for example, approximately 5 to 500 parts by weight. The technology disclosed herein can also be preferably implemented in an embodiment in which the amount of tackifier resin used is limited. For example, the amount of tackifier resin per 100 parts by weight of polymer (A) can be less than 20 parts by weight, or even less than 10 parts by weight, or even less than 3 parts by weight, or even less than 1 part by weight (0 parts by weight to less than 1 part by weight). In some embodiments, the PSA layer contains substantially no tackifier resin.

In addition, the adhesive layer in the technology disclosed herein may optionally contain known additives that can be used in adhesives, such as leveling agents, plasticizers, softeners, colorants (dyes, pigments, etc.), fillers, antistatic agents, antioxidants, UV absorbers, antioxidants, light stabilizers, and preservatives, as long as the effects of the present invention are not significantly impaired.

The pressure-sensitive adhesive layer constituting the reinforcing film disclosed herein may be a cured layer of a pressure-sensitive adhesive composition. That is, the pressure-sensitive adhesive layer can be formed by applying (e.g., coating) a water-dispersible, solvent-based, photocurable, hot-melt, or other pressure-sensitive adhesive composition to an appropriate surface, followed by an appropriate curing treatment. When two or more curing treatments (drying, crosslinking, polymerization, cooling, etc.) are performed, these can be performed simultaneously or in multiple stages. For pressure-sensitive adhesive compositions using a partially polymerized product (polymer syrup) of a monomer raw material, the curing treatment typically involves a final copolymerization reaction. That is, the partially polymerized product is subjected to a further copolymerization reaction to form a fully polymerized product. For example, a photocurable pressure-sensitive adhesive composition is subjected to light irradiation. Curing treatments such as crosslinking and drying may be performed as needed. For example, if a photocurable pressure-sensitive adhesive composition requires drying, it is recommended that photocuring be performed after drying. For pressure-sensitive adhesive compositions using a fully polymerized product, the curing treatment typically involves drying (heat drying), crosslinking, or other treatments as needed.

The adhesive composition can be applied using a conventional coater such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, or spray coater.

The thickness of the adhesive layer is not particularly limited and can be, for example, 6 μm or more. In some embodiments, the thickness of the adhesive layer may be 8 μm or more, 10 μm or more, 15 μm or more, or 20 μm or more or more than 20 μm. Increasing the thickness of the adhesive layer tends to increase the adhesive strength after heating. In addition, in some embodiments, the thickness of the adhesive layer may be, for example, 300 μm or less, 200 μm or less, 150 μm or less, 100 μm or less, 70 μm or less, 50 μm or less, or 40 μm or less. Not having an adhesive layer that is too thick can be advantageous from the perspective of reducing the thickness of the reinforcing film and preventing cohesive failure of the adhesive layer. A reinforcing film having an adhesive layer with a thickness within the above range can have a well-balanced adhesive properties such as adhesive strength, flex recovery, and flex retention. In the case of a reinforcing film having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on the first and second surfaces of the substrate, the thickness of the pressure-sensitive adhesive layer described above can be applied to at least the thickness of the first pressure-sensitive adhesive layer. The thickness of the second pressure-sensitive adhesive layer can also be selected from a similar range. In the case of a reinforcing film without a substrate, the thickness of the reinforcing film is the same as the thickness of the pressure-sensitive adhesive layer.

<Support base material>
The reinforcing film according to some embodiments may be in the form of a substrate-attached pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on one or both sides of the support substrate. The material of the support substrate is not particularly limited and can be appropriately selected depending on the purpose and mode of use of the reinforcing film. Non-limiting examples of usable substrates include resin films such as plastic films; foam sheets made of foams such as polyurethane foam, polyethylene foam, and polychloroprene foam; woven and nonwoven fabrics made by single or mixed spinning of various fibrous materials (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, etc.); papers such as Japanese paper, fine paper, kraft paper, and crepe paper; metal foils such as aluminum foil and copper foil; and the like. Substrates having a composite structure of these may also be used. Examples of such composite substrates include substrates having a structure in which metal foil and the above-mentioned plastic film are laminated, and plastic substrates reinforced with inorganic fibers such as glass cloth.

Various film substrates can be preferably used as the substrate for the reinforcing film disclosed herein. The film substrate may be a porous substrate such as a foam film or a nonwoven fabric sheet, a nonporous substrate, or a substrate with a structure in which a porous layer and a nonporous layer are laminated. In some embodiments, the film substrate preferably includes a base film that is capable of independently maintaining its shape (freestanding or independent). Here, "resin film" refers to a resin film with a nonporous structure that is typically substantially bubble-free (void-free). Therefore, the resin film is a concept that is distinct from foam films and nonwoven fabrics. The resin film preferably is capable of independently maintaining its shape (freestanding or independent). The resin film may have a single-layer structure or a multi-layer structure of two or more layers (e.g., a three-layer structure).

Resin materials that can be used to form the resin film include, for example, polyester, polyolefin, polyamide (PA) such as nylon 6, nylon 66, and partially aromatic polyamide, polyimide (PI), polyamideimide (PAI), polyetheretherketone (PEEK), polyethersulfone (PES), polyphenylene sulfide (PPS), polycarbonate (PC), polyurethane (PU), ethylene-vinyl acetate copolymer (EVA), fluororesins such as polytetrafluoroethylene (PTFE), acrylic resin, polyacrylate, polystyrene, polyvinyl chloride, and polyvinylidene chloride. The resin film may be formed using a resin material containing only one of these resins, or a resin material containing a blend of two or more of them. The resin film may be unstretched or stretched (e.g., uniaxially or biaxially stretched).

Suitable examples of resin materials that can be used to make up the resin film include polyimide resin, polyester resin, PPS resin, and polyolefin resin. Here, polyimide resin refers to a resin that contains more than 50% by weight of polyimide. Similarly, polyester resin refers to a resin that contains more than 50% by weight of polyester, PPS resin refers to a resin that contains more than 50% by weight of PPS, and polyolefin resin refers to a resin that contains more than 50% by weight of polyolefin.

Specific examples of polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate, etc.

As a polyolefin resin, one type of polyolefin can be used alone, or two or more types of polyolefins can be used in combination. The polyolefin can be, for example, an α-olefin homopolymer, a copolymer of two or more α-olefins, or a copolymer of one or more α-olefins with other vinyl monomers. Specific examples include polyethylene (PE), polypropylene (PP), poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymers such as ethylene-propylene rubber (EPR), ethylene-propylene-butene copolymers, ethylene-butene copolymers, ethylene-vinyl alcohol copolymers, and ethylene-ethyl acrylate copolymers. Both low-density (LD) and high-density (HD) polyolefins can be used. Examples of polyolefin resin films include unstretched polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, medium-density polyethylene (MDPE) film, high-density polyethylene (HDPE) film, polyethylene (PE) film made by blending two or more types of polyethylene (PE), and PP/PE blend film made by blending polypropylene (PP) and polyethylene (PE).

Specific examples of resin films that can be preferably used as the base film for the reinforcing film disclosed herein include PI film, PET film, PEN film, PPS film, PEEK film, CPP film, and OPP film.

The resin film can be blended with known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, and antiblocking agents, as needed, provided that the effects of the present invention are not significantly impaired. There are no particular restrictions on the amount of additives blended, and they can be set appropriately depending on the purpose, etc.

The method for producing the resin film is not particularly limited. For example, conventional resin film molding methods such as extrusion molding, inflation molding, T-die casting, and calendar roll molding can be used as appropriate.

The substrate may be substantially composed of such a base film. Alternatively, the substrate may include an auxiliary layer in addition to the base film. Examples of such auxiliary layers include optical property adjusting layers (e.g., colored layers, anti-reflection layers), printed layers or laminate layers for imparting a desired appearance to the substrate, antistatic layers, undercoat layers, release layers, and other surface treatment layers.

The thickness of the substrate is not particularly limited and can be selected depending on the purpose and mode of use of the reinforcing film. The thickness of the substrate can be, for example, 1000 μm or less. In some embodiments, from the perspective of the handleability and processability of the reinforcing film, the thickness of the substrate can be, for example, 500 μm or less, 300 μm or less, 250 μm or less, or 200 μm or less. In some embodiments, from the perspective of reducing the size and weight of products to which the reinforcing film is applied, the thickness of the substrate can be, for example, 160 μm or less, 130 μm or less, 100 μm or less, 90 μm or less, 80 μm or less, 60 μm or less, 50 μm or less, 25 μm or less, 10 μm or less, or 5 μm or less. As the thickness of the substrate decreases, the flexibility of the reinforcing film and its ability to conform to the surface shape of the adherend tend to improve. Furthermore, from the viewpoint of handleability and processability, the thickness of the substrate may be, for example, 2 μm or more, 5 μm or more, 10 μm or more, 20 μm or more, 25 μm or more, or even more than 25 μm. In some embodiments, the thickness of the substrate may be, for example, 30 μm or more, 35 μm or more, 55 μm or more, 70 μm or more, 75 μm or more, 90 μm or more, or 120 μm or more. For example, in a reinforcing film that can be used for purposes such as reinforcing, supporting, or shock absorption of an adherend, a substrate having a thickness of 30 μm or more may be preferably used.

The first surface of the substrate may be subjected to conventional surface treatments, such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or the formation of an undercoat layer by applying a primer. Such surface treatments may be intended to improve the anchoring ability of the pressure-sensitive adhesive layer to the substrate. For example, a substrate that has been treated to improve anchoring ability may be preferably used in a reinforcing film having a substrate that includes a resin film as the base film. The above surface treatments may be applied alone or in combination. The composition of the primer used to form the undercoat layer is not particularly limited and can be appropriately selected from known primers. The thickness of the undercoat layer is not particularly limited, but is typically approximately 0.01 μm to 1 μm, and preferably approximately 0.1 μm to 1 μm. Other treatments that may be applied to the first surface of the substrate as needed include antistatic layer formation, colored layer formation, printing, etc.

When the reinforcing film disclosed herein is in the form of a single-sided PSA sheet having a PSA layer only on the first surface of the substrate, the second surface of the substrate may, if necessary, be subjected to a conventional surface treatment such as a release treatment or an antistatic treatment. For example, by treating the back surface of the substrate with a release agent (typically by providing a release layer made of a release agent), the unwinding force of the reinforcing film wound into a roll can be reduced. Examples of release agents that can be used include silicone-based release agents, long-chain alkyl-based release agents, olefin-based release agents, fluorine-based release agents, fatty acid amide-based release agents, molybdenum sulfide, and silica powder. Furthermore, for purposes such as improving printability, reducing light reflectivity, and improving overlapping properties, the second surface of the substrate may be subjected to a corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or the like. Furthermore, in the case of a double-sided PSA sheet, the second surface of the substrate may, if necessary, be subjected to a surface treatment similar to the examples given above for the surface treatment that can be applied to the first surface of the substrate. The surface treatments applied to the first and second surfaces of the substrate may be the same or different.

<Characteristics of the reinforcing film>
The reinforcing film disclosed herein preferably has an initial adhesive strength _N23 measured after being attached to a stainless steel plate and maintained at 23°C for 30 minutes, which is limited to a predetermined value or less. In some embodiments, the adhesive strength _N23 is preferably, for example, less than 500 gf/25 mm, more preferably less than 400 gf/25 mm, even more preferably less than 300 gf/25 mm, and particularly preferably 250 gf/25 mm or less (e.g., 200 gf/25 mm or less), and may even be 150 gf/25 mm or less. A low adhesive strength _N23 is preferable from the viewpoint of reworkability. The lower limit of the adhesive strength _N23 is not particularly limited and may be, for example, 1 gf/25 mm or more. From the viewpoints of ease of application to an adherend and prevention of misalignment before the adhesive strength increases, the adhesive strength _N23 is usually appropriate to be 10 gf/25 mm or more. From the viewpoint of improving adhesive strength after heating, in some embodiments, the adhesive strength N ₂₃ may be, for example, 20 gf/25 mm or more, 50 gf/25 mm or more, 80 gf/25 mm or more, or 100 gf/25 mm or more (e.g., 150 gf/25 mm or more).

The adhesive strength _N23 [gf/25mm] is determined by pressing the film onto a stainless steel (SUS) plate as an adherend, leaving it in an environment of 23°C and 50% RH for 30 minutes, and then measuring the 180° peel adhesive strength in the same environment (i.e., at 23°C) under conditions of a peel angle of 180° and a tensile speed of 300 mm/min. SUS304BA plate is used as the adherend. For measurement, if necessary, the reinforcing film to be measured can be reinforced by attaching an appropriate backing material (e.g., a PET film with a thickness of approximately 25 μm). More specifically, the adhesive strength _N23 can be measured in accordance with the method for measuring initial adhesive strength described in the Examples below.

The reinforcing film disclosed herein exhibits an adhesive strength that increases upon heating. For example, the adhesive strength N ₆₀ , i.e., the adhesive strength measured at 23°C after being attached to a stainless steel plate and held at 60°C for 60 minutes, may be 300 gf/25 mm or more. In some embodiments, the adhesive strength N ₆₀ is 400 gf/25 mm or more, and preferably 500 gf/25 mm or more. A reinforcing film satisfying these characteristics exhibits an adhesive strength that increases to a predetermined value or more upon heating after being attached to an adherend. The technology disclosed herein makes it possible to obtain strong adhesive strength upon heating. In some preferred embodiments, the adhesive strength N ₆₀ is 600 gf/25 mm or more, more preferably 700 gf/25 mm or more, and may even be 800 gf/25 mm or more, or 900 gf/25 mm or more. There is no particular upper limit to the adhesive strength N ₆₀ . From the viewpoint of ease of production and economic efficiency of the reinforcing film, in some embodiments, the adhesive strength N ₆₀ may be, for example, 3000 gf/25 mm or less, 1500 gf/25 mm or less, or 1000 gf/25 mm or less.

The adhesive strength N ₆₀ [gf/25 mm] is determined by pressing the film onto a SUS plate as the adherend, holding it in a 60°C environment for 60 minutes, then leaving it in a 23°C, 50% RH environment for 30 minutes, and then measuring the 180° peel adhesive strength in the same environment under conditions of a peel angle of 180° and a tensile speed of 300 mm/min. As with the adhesive strength N ₂₃ , a SUS304BA plate is used as the adherend. For measurement, if necessary, the reinforcing film to be measured can be reinforced by attaching an appropriate backing material (e.g., a PET film approximately 25 μm thick). More specifically, the adhesive strength N ₆₀ can be measured according to the method for measuring adhesive strength after heating described in the Examples below.

The ratio of the adhesive strength N ₆₀ [gf/25 mm] to the adhesive strength N ₂₃ [gf/25 mm], i.e., the adhesive strength increase ratio N ₆₀ /N ₂₃ , is not particularly limited. In some embodiments, N ₆₀ /N ₂₃ is suitably 1.5 or more, preferably 2.0 or more, more preferably 2.5 or more, and even more preferably 3.0 or more. A reinforcing film with a high N ₆₀ /N ₂₃ exhibits good reworkability at the initial stage of application and can significantly increase the adhesive strength by subsequent heating or the like. In some embodiments, N ₆₀ /N ₂₃ may be 3.5 or more, 4.0 or more, 5.0 or more, 5.5 or more, greater than 6.0, or greater than 7.0. The upper limit of N ₆₀ /N ₂₃ is not particularly limited and is usually 100 or less, and from the viewpoint of ease of production of the reinforcing film and economic efficiency, it may be 30 or less, 15 or less, or 10 or less. In some embodiments, N ₆₀ /N ₂₃ may be, for example, 5 or less, 3 or less, or 2 or less.

The adhesive strength of the reinforcing film disclosed herein after heating represents one characteristic of the reinforcing film and does not limit the manner in which the reinforcing film may be used. In other words, the reinforcing film disclosed herein is not limited to being heated at 60°C for 60 minutes. It can also be used in a manner in which, for example, heating to temperatures above room temperature (usually 20°C to 30°C, typically 23°C to 25°C) is not specifically performed. Even in such a manner, the adhesive strength increases over the long term, achieving a strong bond. Furthermore, the reinforcing film disclosed herein can be heat-treated at a temperature above 30°C (e.g., approximately 50-70°C) or above 60°C at any time after application to promote an increase in adhesive strength. The heating temperature for such heat treatment is not particularly limited and can be set taking into consideration workability, economy, the heat resistance of the reinforcing film substrate and the adherend, and other factors. The heating temperature may be, for example, less than 150°C, 120°C or less, 100°C or less, 80°C or less, or 70°C or less. The heating temperature can be, for example, 40°C or higher, 45°C or higher, 50°C or higher, 55°C or higher, 60°C or higher, or 70°C or higher, or it can be 80°C or higher, or 100°C or higher. The heating time is not particularly limited and can be, for example, 3 hours or less, 1 hour or less, 30 minutes or less, or 10 minutes or less. The heating time can be, for example, 1 minute or more, 15 minutes or more, 30 minutes or more, or 1 hour or more. Alternatively, the heating treatment can be performed for a longer period of time as long as significant thermal degradation of the reinforcing film or the adherend does not occur. The heating treatment can be performed all at once or in multiple stages.

<Reinforcing film with substrate>
When the reinforcing film disclosed herein is in the form of a substrate-attached pressure-sensitive adhesive sheet, the thickness of the reinforcing film may be, for example, 1000 μm or less, 600 μm or less, 350 μm or less, or 250 μm or less. From the viewpoint of miniaturization, weight reduction, thinning, etc. of products to which the reinforcing film is applied, in some embodiments, the thickness of the reinforcing film may be, for example, 200 μm or less, 175 μm or less, 140 μm or less, 120 μm or less, or 100 μm or less (e.g., less than 100 μm). Furthermore, from the viewpoint of handleability, etc., the thickness of the reinforcing film may be, for example, 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, or 30 μm or more. In some embodiments, the thickness of the reinforcing film may be, for example, 50 μm or more, 60 μm or more, 80 μm or more, 100 μm or more, or 120 μm or more. There is no particular upper limit to the thickness of the reinforcing film.
The thickness of the reinforcing film refers to the thickness of the portion that is attached to the adherend. For example, in the case of the reinforcing film 1 having the configuration shown in Figure 1, the thickness refers to the thickness from the adhesive surface 21A of the reinforcing film 1 to the second surface 10B of the substrate 10, and does not include the thickness of the release liner 31.

The reinforcing film disclosed herein can be suitably implemented, for example, in an embodiment in which the thickness Ts of the support substrate is greater than the thickness Ta of the adhesive layer, i.e., in an embodiment in which Ts/Ta is greater than 1. While not particularly limited, Ts/Ta may be, for example, 1.1 or greater, 1.2 or greater, 1.5 or greater, or 1.7 or greater. For example, an increase in Ts/Ta tends to make it easier to achieve good effects even when the reinforcing film is made thinner. In some embodiments, Ts/Ta may be 2 or greater (e.g., greater than 2), 2.5 or greater, or 2.8 or greater. Furthermore, Ts/Ta may be, for example, 50 or less, or 20 or less. From the viewpoint of making it easier for the reinforcing film to exhibit high post-heat adhesive strength even when made thinner, Ts/Ta may be, for example, 10 or less, 8 or less, or 5 or less.

The pressure-sensitive adhesive layer is preferably adhered to the supporting substrate. Here, "adhered" means that, in a reinforcing film whose adhesive strength has increased after application to an adherend, the adhesive layer exhibits sufficient anchoring properties to the supporting substrate to the extent that peeling does not occur at the interface between the adhesive layer and the supporting substrate when the reinforcing film is peeled from the adherend. A substrate-attached reinforcing film in which the adhesive layer is adhered to the supporting substrate can firmly integrate the adherend and the supporting substrate. A suitable example of a reinforcing film in which the adhesive layer is adhered to the substrate is a reinforcing film in which peeling (anchor failure) does not occur between the adhesive layer and the supporting substrate when the adhesive strength after heating is measured as described above. A reinforcing film in which anchor failure does not occur when the adhesive strength after heating is measured is a suitable example of a reinforcing film in which the adhesive layer is adhered to the substrate.

The reinforcing film disclosed herein can be preferably produced, for example, by a method comprising, in this order, contacting a liquid pressure-sensitive adhesive composition with a first surface of a substrate and curing the pressure-sensitive adhesive composition on the first surface to form a pressure-sensitive adhesive layer. Curing the pressure-sensitive adhesive composition can involve one or more of the following: drying, crosslinking, polymerization, and cooling of the pressure-sensitive adhesive composition. This method of curing a liquid pressure-sensitive adhesive composition on the first surface of a substrate to form a pressure-sensitive adhesive layer can improve the anchoring ability of the pressure-sensitive adhesive layer to the substrate compared to a method in which the cured pressure-sensitive adhesive layer is attached to the first surface of the substrate, thereby disposing the pressure-sensitive adhesive layer on the first surface. Utilizing this, a reinforcing film in which the pressure-sensitive adhesive layer is adhered to the substrate can be preferably produced.

In some embodiments, a method for contacting a liquid PSA composition with the first surface of a substrate can involve directly applying the PSA composition to the first surface of the substrate. By contacting the first surface (adhesive surface) of the PSA layer cured on the first surface of the substrate with the release surface, a reinforcing film can be obtained in which the second surface of the PSA layer is adhered to the first surface of the substrate and the first surface of the PSA layer is in contact with the release surface. The release surface can be the surface of a release liner, the back surface of a release-treated substrate, or the like.

In the case of a photocurable pressure-sensitive adhesive composition using a partial polymer (polymer syrup) of a monomer raw material, for example, the pressure-sensitive adhesive composition may be applied to a release surface, and then the first surface of a substrate may be placed over the applied pressure-sensitive adhesive composition to bring the uncured pressure-sensitive adhesive composition into contact with the first surface of the substrate. In this state, the pressure-sensitive adhesive composition sandwiched between the first surface of the substrate and the release surface may be irradiated with light to cure, thereby forming a pressure-sensitive adhesive layer.

The methods exemplified above do not limit the manufacturing method of the reinforcing film disclosed herein. In manufacturing the reinforcing film disclosed herein, any suitable method capable of adhering a pressure-sensitive adhesive layer to the first surface of a substrate can be used, either alone or in combination. Examples of such methods include the method of forming a pressure-sensitive adhesive layer by curing a liquid pressure-sensitive adhesive composition on the first surface of a substrate, as described above, or a method of applying a surface treatment to the first surface of a substrate to enhance the anchoring ability of the pressure-sensitive adhesive layer. For example, if the anchoring ability of the pressure-sensitive adhesive layer to the substrate can be sufficiently improved by providing a primer layer on the first surface of the substrate, the reinforcing film may be manufactured by laminating the cured pressure-sensitive adhesive layer to the first surface of the substrate. The anchoring ability of the pressure-sensitive adhesive layer to the substrate can also be improved by selecting the material of the substrate and the composition of the pressure-sensitive adhesive. Furthermore, the anchoring ability of the pressure-sensitive adhesive layer to the substrate can be enhanced by applying a temperature higher than room temperature to a reinforcing film having a pressure-sensitive adhesive layer on the first surface of the substrate. The temperature applied to enhance anchoring properties may be, for example, approximately 35°C to 80°C, approximately 40°C to 70°C or higher, or approximately 45°C to 60°C.

When the reinforcing film disclosed herein is in the form of a PSA sheet having a first PSA layer provided on a first surface of a substrate and a second PSA layer provided on a second surface of the substrate (i.e., a double-sided PSA sheet with a substrate), the first PSA layer and the second PSA layer may have the same configuration or different configurations. When the first PSA layer and the second PSA layer have different configurations, the difference may be, for example, a difference in composition or structure (thickness, surface roughness, formation area, formation pattern, etc.). For example, the second PSA layer may be a PSA layer that does not contain polymer (B). Furthermore, the surface elasticity modulus of the surface of the second PSA layer (second adhesive surface) at 23°C may be outside the range of 1 to 20 kPa (e.g., greater than 20 kPa), and may be 30 kPa or greater.

<Reinforcing film with release liner>
The reinforcing film disclosed herein can be in the form of a pressure-sensitive adhesive product in which the surface (adhesive surface) of the pressure-sensitive adhesive layer is in contact with the release surface of a release liner. Thus, this specification can provide a reinforcing film with a release liner (adhesive product) that includes any of the reinforcing films disclosed herein and a release liner having a release surface that is in contact with the adhesive surface of the pressure-sensitive adhesive sheet.

The thickness of the release liner is not particularly limited, but a thickness of approximately 5 μm to 200 μm is usually appropriate. A release liner thickness within this range is preferred because it provides excellent workability in bonding to the adhesive layer and in peeling from the adhesive layer. In some embodiments, the thickness of the release liner may be, for example, 10 μm or more, 20 μm or more, 30 μm or more, or 40 μm or more. Furthermore, from the perspective of facilitating peeling from the adhesive layer, the thickness of the release liner may be, for example, 100 μm or less or 80 μm or less. If necessary, the release liner may be subjected to a known antistatic treatment, such as a coating type, kneading type, or vapor deposition type.

The release liner is not particularly limited, and examples include release liners having a release layer on the surface of a liner substrate such as a resin film or paper (which may be paper laminated with a resin such as polyethylene), and release liners made of a resin film formed from a low-adhesion material such as a fluorine-based polymer (e.g., polytetrafluoroethylene) or a polyolefin resin (e.g., polyethylene, polypropylene). Due to their excellent surface smoothness, release liners having a release layer on the surface of a resin film as a liner substrate and release liners made of a resin film formed from a low-adhesion material are preferred. The resin film is not particularly limited as long as it is capable of protecting the adhesive layer, and examples include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyester film (e.g., PET film, PBT film), polyurethane film, and ethylene-vinyl acetate copolymer film. The release layer can be formed using known release agents, such as silicone-based release agents, long-chain alkyl-based release agents, olefin-based release agents, fluorine-based release agents, fatty acid amide-based release agents, molybdenum sulfide, and silica powder. Silicone-based release agents are particularly preferred.

There are no particular restrictions on the thickness of the release layer, but a thickness of approximately 0.01 μm to 1 μm is usually appropriate, with 0.1 μm to 1 μm being preferable. There are no particular restrictions on the method for forming the release layer, and any known method can be used as appropriate depending on the type of release treatment agent used, etc.

<Application>
The reinforcing film provided by this specification can exhibit good reworkability, for example, initially after being attached to an adherend, thereby contributing to suppressing yield declines and improving the quality of products containing the reinforcing film. Furthermore, after being attached to an adherend, the adhesive strength of the reinforcing film can be significantly increased by aging or heating. For example, by heating at an appropriate time after attachment to the adherend, the reinforcing film can be firmly adhered to the adherend. Taking advantage of these characteristics, the reinforcing film disclosed herein can be preferably used in various fields to reinforce components included in various products.

The reinforcing film disclosed herein can be preferably used as a reinforcing film that is attached to an adherend to reinforce the adherend, for example, in the form of a substrate-attached pressure-sensitive adhesive sheet having a film-like substrate having a first side and a second side and a pressure-sensitive adhesive layer provided on at least the first side of the substrate. In such a reinforcing film, the film substrate can preferably be one that includes a resin film as a base film. Furthermore, from the viewpoint of improving reinforcing performance, it is preferable that the pressure-sensitive adhesive layer be fixed to the first side of the film-like substrate.
For example, optical components used in optical products and electronic components used in electronic products are becoming increasingly integrated, smaller, lighter, and thinner, and multiple thin optical/electronic components with different linear expansion coefficients and thicknesses may be stacked. By attaching the above-described reinforcing film to such components, appropriate rigidity can be imparted to the optical/electronic components. This can suppress curling and bending due to stress that may occur between the multiple components with different linear expansion coefficients and thicknesses during the manufacturing process and/or in the manufactured product.
Furthermore, in the manufacturing process of optical products/electronic products, when thin optical/electronic components are subjected to shaping processes such as cutting as described above, by attaching a reinforcing film to the components, it is possible to alleviate local stress concentrations on the optical/electronic components that accompany the processing, thereby reducing the risk of cracks, breakage, peeling of laminated components, etc. Attaching a reinforcing film to an optical/electronic component before handling can also be useful for alleviating local stress concentrations during transportation, stacking, rotation, etc. of the components, and for preventing bending or bending of the components due to their own weight.
Furthermore, when devices such as optical products and electronic products including the above-mentioned reinforced film are used by consumers in the market, even if the device is subjected to unintentional stress such as when it is dropped, placed under a heavy object, hit by a flying object, etc., the inclusion of the reinforced film in the device can alleviate stress on the device. Therefore, the inclusion of the reinforced film in the device can improve the durability of the device.

The reinforcing film disclosed herein can be preferably used, for example, by being attached to components constituting various portable devices. Here, "portable" does not simply mean being portable; it means having a level of portability that allows an individual (average adult) to carry it with relative ease. Examples of portable devices include mobile phones, smartphones, tablet computers, laptop computers, various wearable devices, digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game consoles, electronic dictionaries, electronic organizers, e-books, in-car information devices, portable radios, portable televisions, portable printers, portable scanners, and portable modems, as well as mechanical wristwatches, pocket watches, flashlights, and hand mirrors. Examples of components constituting the above portable electronic devices include optical films and display panels used in image display devices such as thin-film displays (e.g., liquid crystal displays) and film-type displays. The reinforcing film disclosed herein can also be preferably used by being attached to various components in automobiles, home appliances, and the like.

The reinforcing film disclosed herein also has flex recovery and flex retention properties, and can be preferably used to its advantage by being attached to components constituting devices equipped with bendable elements (e.g., flexible devices such as flexible displays, which may also be referred to as rollable devices or foldable devices). Examples of such devices include the various mobile devices (portable devices) mentioned above. Examples of components constituting the above-mentioned mobile electronic devices include optical films and display panels used in image display devices such as liquid crystal displays and organic EL (electroluminescence) displays. The reinforcing film disclosed herein can be preferably used in such mobile electronic devices to reinforce components constituting the device (typically, image display devices referred to as flexible devices or foldable devices).

The reinforcing film disclosed herein is also suitable for applications such as reinforcing optical components used as components of liquid crystal display panels, plasma display panels (PDPs), organic EL displays, etc., during their manufacture, transportation, etc. It is useful as a reinforcing film applied to optical components such as polarizing plates (polarizing films), wave plates, retardation plates, optical compensation films, brightness enhancement films, light diffusion sheets, and reflective sheets for liquid crystal display panels.

The uses of the reinforcing film disclosed herein are not particularly limited, and it can be used in a variety of applications for purposes such as imparting rigidity and impact resistance. The reinforcing film disclosed herein is not only suitable for flexible device applications as described above, but can also be used for applications other than flexible devices. The fact that the reinforcing film has flex recovery and flex retention means that there are fewer restrictions on the range of applications of the reinforcing film, which has great practical advantages.

The following describes several examples of the present invention, but it is not intended that the present invention be limited to these specific examples. Note that "parts" and "%" in the following descriptions are by weight unless otherwise specified.

[Synthesis of Polymer (A)]
(Synthesis Example A1)
A four-neck flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser was charged with 90.2 parts of 2-ethylhexyl acrylate (2EHA), 8.6 parts of 4-hydroxybutyl acrylate (4HBA), 1.2 parts of N-acryloylmorpholine (ACMO), 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator, and ethyl acetate as a polymerization solvent. Nitrogen gas was introduced while gently stirring, and the liquid temperature in the flask was maintained at around 65°C, allowing the polymerization reaction to proceed for 6 hours to prepare an acrylic polymer A1 solution with a polymer concentration of 35%. The weight average molecular weight (Mw) of the acrylic polymer A1 was 540,000.

(Synthesis example A2)
A solution of acrylic polymer A2 was obtained by carrying out solution polymerization in the same manner as in Synthesis Example A1, except that the monomer composition was changed to 2EHA/4HBA/ACMO/n-butyl acrylate (BA) = 86.1 parts/9.7 parts/1.8 parts/2.4 parts.

(Synthesis example A3)
Solution polymerization was carried out in the same manner as in Synthesis Example A1, except that the monomer composition was changed to BA/4HBA=96 parts/4 parts, to obtain a solution of acrylic polymer A3.

(Synthesis example A4)
A solution of acrylic polymer A4 was obtained by carrying out solution polymerization in the same manner as in Synthesis Example A1, except that the monomer composition was changed to 2EHA/2-hydroxyethyl acrylate (HEA)/methyl methacrylate (MMA)/N-vinyl-2-pyrrolidone (NVP) = 65 parts/15 parts/7 parts/13 parts.

[Synthesis of Polymer (B)]
(Synthesis Example B1)
101.15 parts of ethyl acetate, 40 parts of MMA, 20 parts of n-butyl methacrylate (BMA), 20 parts of 2-ethylhexyl methacrylate (2EHMA), 8.7 parts of a polyorganosiloxane skeleton-containing methacrylate monomer having a functional group equivalent of 900 g / mol (trade name: X-22-174ASX, manufactured by Shin-Etsu Chemical Co., Ltd.), 11.3 parts of a polyorganosiloxane skeleton-containing methacrylate monomer having a functional group equivalent of 4600 g / mol (trade name: KF-2012, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.8 parts of thioglycerol as a chain transfer agent were charged into a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, a condenser, and a dropping funnel. Then, after stirring for 30 minutes under a nitrogen atmosphere at 70 ° C., 0.2 parts of AIBN was added as a thermal polymerization initiator, and the mixture was allowed to react at 70 ° C. for 3 hours. Subsequently, after stirring at 80°C for 30 minutes, 0.1 parts of AIBN was further added and the mixture was reacted at 80°C for 2 hours. Thereafter, 0.05 parts of AIBN was further added and the mixture was reacted at 80°C for 2 hours to obtain polymer B1. The Mw of the obtained polymer B1 was 20,000. The functional group equivalent of monomer S1 used in the synthesis of polymer B1 was 2,991 g/mol.

(Synthesis examples B2 to B7)
Polymers B2 to B7 were prepared in the same manner as for polymer B1, except that the composition of the monomer components was changed as shown in Table 1. In Table 1, X-22-174ASX represents a polyorganosiloxane skeleton-containing methacrylate monomer (trade name: X-22-174ASX, manufactured by Shin-Etsu Chemical Co., Ltd., functional group equivalent: 900 g/mol), KF-2012 represents a polyorganosiloxane skeleton-containing methacrylate monomer (trade name: KF-2012, manufactured by Shin-Etsu Chemical Co., Ltd., functional group equivalent: 4600 g/mol), and X-22-2426 represents a polyorganosiloxane skeleton-containing methacrylate monomer (trade name: X-22-2426, manufactured by Shin-Etsu Chemical Co., Ltd., functional group equivalent: 12000 g/mol).

The compositions of the monomer components used in the preparation of polymers B1 to B7 and the functional group equivalent weight of monomer S1 used in the synthesis of each polymer (B) are summarized in Table 1.

The Mw of each of the above polymers was measured using a GPC device (HLC-8220GPC, manufactured by Tosoh Corporation) under the following conditions, and calculated in terms of polystyrene.
[GPC conditions]
Sample concentration: 0.2 wt% (tetrahydrofuran (THF) solution)
Sample injection volume: 10 μL
・Eluent: THF ・Flow rate: 0.6mL/min
・Measurement temperature: 40℃
·column:
Sample column: TSKguardcolumn SuperHZ-H (1 column) + TSKgel SuperHZM-H (2 columns)
Reference column: TSKgel SuperH-RC (1 column)
Detector: differential refractometer (RI)

[Preparation of reinforcing film]
Example 1
100 parts of acrylic polymer A1, 2.0 parts of polymer B1, and 0.10 parts in terms of solid content of isocyanate compound C1 (trade name "Coronate HX", manufactured by Tosoh Corporation) as a crosslinking agent were added, and the mixture was diluted with ethyl acetate so that the total solid content was 30%, thereby obtaining an acrylic pressure-sensitive adhesive solution according to this example.
A release liner (trade name "Diafoil MRF75", manufactured by Mitsubishi Chemical Corporation) made of polyester resin and having a thickness of 75 μm and having one side treated with silicone was prepared, and the acrylic adhesive solution obtained above was applied to the silicone-treated surface, followed by drying at 130°C for 1 minute to form an adhesive layer having a thickness of 25 μm.
Next, a 50 μm thick polyimide substrate (trade name "Upilex 50S", manufactured by Ube Industries, Ltd.) was bonded to the surface of the obtained pressure-sensitive adhesive layer to obtain a reinforcing film according to this example. This reinforcing film has a pressure-sensitive adhesive layer on one side of the substrate, and is in the form of a pressure-sensitive adhesive sheet with a release liner, in which the release surface of a release liner abuts against the pressure-sensitive adhesive layer on the other side.
For the reinforcing film of this example, the molar ratio ([NCO]/[OH]) was calculated from the OH amount (the number of moles of hydroxyl groups in the acrylic polymer A1) and the NCO amount (the number of moles of isocyanate groups in the isocyanate compound) in the pressure-sensitive adhesive layer, and was found to be 0.008.

<Examples 2 to 5>
Except for using polymer B2 (Example 2), polymer B3 (Example 3), polymer B4 (Example 4), or polymer B5 (Example 5) instead of polymer B1, an acrylic pressure-sensitive adhesive solution according to each example was obtained in the same manner as in Example 1. Except for using each of these acrylic pressure-sensitive adhesive solutions, a reinforcing film according to each example was produced in the same manner as in the production of the reinforcing film according to Example 1.

<Examples 6 to 9>
Acrylic pressure-sensitive adhesive solutions of each example were obtained in the same manner as in Example 1, except that the amount of isocyanate compound C1 used was changed to 0.015 parts (Example 6), 0.05 parts (Example 7), 0.20 parts (Example 8), or 0.60 parts (Example 9) relative to 100 parts of acrylic polymer A1, as shown in Table 2. Reinforcing films of each example were prepared in the same manner as in the preparation of the reinforcing film of Example 1, except that these acrylic pressure-sensitive adhesive solutions were used, respectively.

<Examples 10 to 12>
Acrylic pressure-sensitive adhesive solutions of each example were obtained in the same manner as in Example 1, except that the amount of polymer B1 used was changed to 1.0 part (Example 10), 3.0 parts (Example 11), or 6.0 parts (Example 12) per 100 parts of acrylic polymer A1, as shown in Table 2. Reinforcing films of each example were prepared in the same manner as in the preparation of the reinforcing film of Example 1, except that these acrylic pressure-sensitive adhesive solutions were used, respectively.

Example 13
Except for using acrylic polymer A2 instead of acrylic polymer A1, an acrylic pressure-sensitive adhesive solution according to this example was obtained in the same manner as in Example 1. Except for using the obtained acrylic pressure-sensitive adhesive solution, a reinforcing film according to this example was produced in the same manner as in the production of the reinforcing film according to Example 1.

Example 14
An acrylic pressure-sensitive adhesive solution according to this example was obtained in the same manner as in Example 1, except that acrylic polymer A3 was used instead of acrylic polymer A1 and 0.07 parts, in terms of solid content, of isocyanate compound C2 (trade name "Takenate D110N", manufactured by Mitsui Chemicals, Inc.) was used as the crosslinking agent per 100 parts of acrylic polymer A3. A reinforcing film according to this example was produced in the same manner as in the production of the reinforcing film according to Example 1, except that the obtained acrylic pressure-sensitive adhesive solution was used.

<Examples 15 and 16>
Acrylic pressure-sensitive adhesive solutions of each example were obtained in the same manner as in Example 14, except that the amount of isocyanate compound C2 used was changed to 0.09 parts (Example 15) or 0.395 parts (Example 16) in terms of solid content relative to 100 parts of acrylic polymer A3, as shown in Table 2. Reinforcing films of each example were prepared in the same manner as in the preparation of the reinforcing film of Example 1, except that these acrylic pressure-sensitive adhesive solutions were used, respectively.

<Comparative Examples 1 and 2>
Except for using polymer B6 (Comparative Example 1) or polymer B7 (Comparative Example 2) instead of polymer B1, an acrylic pressure-sensitive adhesive solution according to each example was obtained in the same manner as in Example 1. Except for using these acrylic pressure-sensitive adhesive solutions, a reinforcing film according to each example was produced in the same manner as in the production of the reinforcing film according to Example 1.

<Comparative Example 3>
An acrylic pressure-sensitive adhesive solution according to this example was obtained in the same manner as in Example 1, except that acrylic polymer A4 was used instead of acrylic polymer A1 and 0.50 parts, in terms of solid content, of isocyanate compound C2 (trade name "Takenate D110N", manufactured by Mitsui Chemicals, Inc.) was used as the crosslinking agent per 100 parts of acrylic polymer A4. A reinforcing film according to this example was produced in the same manner as in the production of the reinforcing film according to Example 1, except that the obtained acrylic pressure-sensitive adhesive solution was used.

<Comparative Examples 4 and 5>
Acrylic pressure-sensitive adhesive solutions of each example were obtained in the same manner as in Comparative Example 3, except that the amount of isocyanate compound C2 used was changed to 1.10 parts (Comparative Example 4) or 2.50 parts (Comparative Example 5), calculated as solid content, per 100 parts of acrylic polymer A4, as shown in Table 2. Reinforcing films of each example were prepared in the same manner as in the preparation of the reinforcing film of Example 1, except that these acrylic pressure-sensitive adhesive solutions were used, respectively.

<Evaluation>
[Surface elastic modulus]
The reinforcing film of each example was aged at 50°C for 1 day, and the surface elastic modulus was measured. The release liner protecting the adhesive surface was peeled off, and a nanoindenter (Triboindenter manufactured by Hysitron Inc.) was used to press an indenter into the surface of the adhesive layer to a depth of 6 µm, and the maximum load (Pmax) [GPa/mm ² ] was obtained by measurement using the nanoindenter. This was calculated using the formula:
Surface hardness [GPa] = Pmax/A
The surface hardness was calculated by substituting the above formula into the unit of kPa, and the surface elastic modulus at 23°C (23°C surface elastic modulus) was recorded. The measurement conditions are as follows: In the above formula, A is the contact projected area of the indenter [mm ² ].
(Measurement conditions)
Indenter approach speed: 5 μm/s
Maximum displacement: 6 μm
Pushing speed: 5μm/s
Pulling speed: 5μm/s
Indenter used: Conical (spherical indenter: radius of curvature 10 μm)
Measurement method: Single indentation measurement Measurement temperature: Room temperature (23°C)

[Bulk Elastic Modulus G' and tan δ]
A release liner R1 (trade name "Diafoil MRF75", manufactured by Mitsubishi Chemical Corporation) made of a 75 μm thick polyester resin and silicone-treated on one side was prepared, and the acrylic adhesive solution according to each example was applied to the silicone-treated surface, followed by drying at 130° C. for 1 minute to form an adhesive layer of 25 μm thickness. Next, the surface of the resulting adhesive layer was covered with a release liner R2 (trade name "Diafoil MRE75", manufactured by Mitsubishi Chemical Corporation) made of a 75 μm thick polyester resin and silicone-treated on one side, with the silicone-treated surface facing the adhesive layer, and aging was carried out at 50° C. for 1 day.
Only the resulting pressure-sensitive adhesive layer was taken out, laminated to a thickness of about 1 mm, and punched out to a diameter of 8 mm to prepare a cylindrical pellet, which was used as a measurement sample.
The measurement sample was fixed to a φ8 mm parallel plate jig, and the storage modulus G', loss modulus G" and loss tangent tanδ were measured under the following conditions using a dynamic viscoelasticity measuring device ("ARES" manufactured by T.A. Instruments), and the storage modulus G' ₂₃ [kPa] at 23°C, the storage modulus G' ₈₀ [kPa] at 80°C and tanδ at 80°C (loss modulus G" ₈₀ at 80°C /storage modulus G' ₈₀ at 80°C) were determined.
Measurement mode: Shear mode Temperature range: -70°C to 200°C
Temperature rise rate: 5°C/min
・Frequency: 1 Hz
The storage modulus G' corresponds to the portion stored as elastic energy when the material is deformed, and is an index representing the degree of hardness. The loss modulus G'' corresponds to the portion of energy lost that is dissipated due to internal friction, etc. when the material is deformed, and represents the degree of viscosity.

[Initial adhesive strength]
The reinforcing film according to each example was aged at 50°C for one day and cut together with the release liner to a width of 25 mm and a length of 140 mm to serve as a measurement sample. The release liner was peeled off from the measurement sample to expose the adhesive surface, and the sample was pressed against a stainless steel plate (SUS304BA plate) as an adherend by rolling it back and forth with a 2 kg hand roller. The measurement sample thus pressed against the adherend was then left at an ambient temperature of 23°C for 30 minutes, and then the load when the reinforcing film was peeled from the adherend was measured using a tensile tester (Shimadzu Corporation, trade name "Autograph AG-Xplus HS 6000 mm/min high-speed model (AG-50NX plus)") at a peel angle of 180° and a peel rate (tensile speed) of 300 mm/min. The average load during the measurement was recorded as the initial adhesive strength [gf/25 mm].

[Adhesive strength after heating]
For each reinforcing film according to the present invention, a measurement sample was prepared and pressure-bonded to an adherend in the same manner as in the initial adhesive strength measurement. The pressure-bonded measurement sample was then heated at an ambient temperature of 60°C for 60 minutes. After that, the sample was left at an ambient temperature of 23°C for 30 minutes. Using a tensile tester (Shimadzu Corporation, trade name "Autograph AG-Xplus HS 6000mm/min high-speed model (AG-50NX plus)"), the load when the reinforcing film was peeled from the adherend was measured under the conditions of a peel angle of 180° and a peel speed (tensile speed) of 300mm/min. The average load during measurement was recorded as the adhesive strength after heating [gf/25mm].

[Bending retention test]
Each reinforcing film was aged at 50°C for one day, after which the release liner was peeled off. A 25 μm-thick polyimide substrate (trade name "Upilex 25S" manufactured by Ube Industries, Ltd.) was bonded to the exposed adhesive surface and heated at 60°C for 60 minutes for adhesion. The resulting measurement sample (laminate) was then folded with the 25 μm substrate side facing inward to a diameter of 6 mm and heated at 80°C for 15 hours. The sample was then left at room temperature (23°C) and allowed to cool sufficiently. The folded sample was then released from the folded state. The bending angle [°] of the folded sample was measured within 10 minutes using a protractor to evaluate its flex recovery. The bending angle was the opening angle of the measurement sample (the angle at which the measurement sample opens from the folded state). The bending angle closer to 180° indicates better flex recovery, while the bending angle closer to 0° indicates poorer flex recovery.
Next, to evaluate the bending retention, the presence or absence of "peeling" at the bent portion of the measurement sample was visually confirmed, and when no "peeling" was observed, it was evaluated as "G (Good)", and when "peeling" was observed, it was evaluated as "P (Poor)".

The evaluation results for the reinforcing film for each example are shown in Table 2. Table 2 also shows an outline of the composition of the pressure-sensitive adhesive layer for each example.

As shown in Table 2, the reinforcing films of Examples 1 to 16 comprised a pressure-sensitive adhesive layer containing polymer (A) and polymer (B) whose monomer S1 functional group equivalent was 2000 to 7000 g/mol, and the 23°C surface elasticity modulus of the pressure-sensitive adhesive layer was within the range of 1 to 20 kPa. These reinforcing films initially exhibited low adhesive strength, but after the adhesive strength increased, they exhibited sufficient adhesive strength suitable for flexion retention, and both flex recovery and flexion retention were good. On the other hand, the reinforcing films of Comparative Examples 1 to 5, in which either the functional group equivalent of monomer S1 or the 23°C surface elasticity modulus of the adhesive layer was outside the above range, were unable to achieve both initial easy peelability, increased adhesive strength upon heating, and flexion retention. The reinforcing film of Comparative Example 1 had high initial adhesive strength, the reinforcing film of Comparative Example 2 had low adhesive strength after heating, and the reinforcing films of Comparative Examples 3 to 5 exhibited peeling during the flexion retention test.

More specifically, by comparing Examples 1 to 5 and Comparative Examples 1 and 2, in which the functional group equivalent of the monomer S1 used in the synthesis of polymer (B) is different, it can be seen that Examples 1 to 5, which used polymer (B) with a functional group equivalent of 2000 to 7000 g/mol, had low initial adhesive strength and adhesive strength increase ratios (N ₆₀ /N ₂₃ ) of 3.2 to 6.3, and were excellent in initial easy peelability and adhesive strength increase upon heating, that when the functional group equivalent was below the above range (Comparative Example 1), the initial easy peelability decreased, and when it was above the above range (Comparative Example 2), the adhesive strength after heating decreased, and that Comparative Examples 1 and 2 all had smaller adhesive strength increase ratios than Examples 1 to 5. The reinforcing films of Examples 1 to 5 and Comparative Examples 1 and 2 all had pressure-sensitive adhesive layer surface moduli at 23°C within the range of 1 to 20 kPa, and had good flex recovery and flex retention. Furthermore, a comparison of Examples 1 to 5 reveals that the initial adhesive strength tends to be suppressed as the functional group equivalent weight increases within the range of 2000 to 7000 g/mol, while the adhesive strength after heating tends to increase as the functional group equivalent weight decreases. Among these, Examples 1 to 3, which have a functional group equivalent weight in the range of 2000 to 4500 g/mol, exhibited high adhesive strength after heating, and exhibited suitable properties as a reinforcing film.

Furthermore, a comparison of Examples 6 to 9 revealed that the higher the 23°C surface modulus of the pressure-sensitive adhesive layer in the range of 1 to 20 kPa, the more improved the flex recovery, while the initial adhesive strength and post-heat adhesive strength tended to be lower. Examples 7 to 9 were superior to Example 6 in flex recovery, with a 23°C surface modulus of 2 kPa or more and a tanδ ₈₀ at 80°C in the range of 0.10 to 0.60. Furthermore, Example 9 had high values for both the surface modulus and bulk modulus, resulting in relatively lower post-heat adhesive strength compared to Examples 6 to 8. Furthermore, no difference was observed in the 23°C bulk modulus _G'23 of the pressure-sensitive adhesive layer between Examples 6 to 8. It can be said that, for Examples 6 to 8, the 23°C surface modulus had a higher correlation with flex recovery than the 23°C bulk modulus. In Examples 6 to 9, the molar ratio of isocyanate groups to hydroxyl groups ([NCO]/[OH]) in the pressure-sensitive adhesive layers of Examples 7 and 8, which showed a better balance of improved initial adhesive strength, post-heat adhesive strength, flex recovery, and flex retention, was within the range of 0.002 to 0.03.

Furthermore, a comparison of Examples 10 to 12 confirmed that the initial adhesive strength tended to decrease as the amount of polymer (B) used increased. In Examples 10 and 11, in which the amount of polymer (B) used was within the range of 0.5 to 5 parts per 100 parts of polymer (A), the initial adhesive strength was less than 400 gf/25 mm and the adhesive strength after heating was 500 gf/25 mm or greater, achieving a good balance between easy peelability at the initial stage of application and subsequent increase in adhesive strength. Furthermore, as the amount of polymer (B) used increased, the surface modulus at 23°C tended to increase and flex recovery tended to decrease. Furthermore, the results of Examples 13 to 16 confirmed that the desired effects could be achieved even if the type of polymer (A) or crosslinker in the adhesive was changed.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples given above.

1, 2, 3 Reinforcing film 10 Supporting substrate 10A First surface 10B Second surface 21 Pressure-sensitive adhesive layer (first pressure-sensitive adhesive layer)
21A Adhesive surface (first adhesive surface)
21B Adhesive surface (second adhesive surface)
22 Adhesive layer (second adhesive layer)
22A Adhesive surface (second adhesive surface)
31, 32 Release liner 100, 200, 300 Reinforcement film with release liner

Claims (5)

A reinforcing film having a pressure-sensitive adhesive layer,
the pressure-sensitive adhesive layer contains a polymer (A) and a polymer (B),
the polymer (A) is an acrylic polymer, and the acrylic polymer contains a monomer unit derived from a hydroxyl group-containing monomer,
The glass transition temperature _TA of the polymer (A) is −80° C. or higher and lower than −35° C.,
The polymer (B) contains a monomer unit having a polyorganosiloxane skeleton and a (meth)acrylic monomer unit,
the monomer unit having a polyorganosiloxane skeleton is derived from a polyorganosiloxane skeleton-containing monomer S1, and the functional group equivalent of the polyorganosiloxane skeleton-containing monomer S1 is 2000 to 7000 g/mol;
the content of the polymer (B) in the pressure-sensitive adhesive layer is 0.1 to 30 parts by weight based on 100 parts by weight of the polymer (A);
The pressure-sensitive adhesive layer contains an isocyanate-based crosslinking agent,
the molar ratio ([NCO]/[OH]) of the isocyanate group to the hydroxyl group contained in the pressure-sensitive adhesive layer is 0.002 to 0.03;
the pressure-sensitive adhesive layer has a surface elastic modulus of 1 to 20 kPa at 23°C;
The reinforcing film has an initial adhesive strength _N23 of 10 gf/25 mm or more, measured after being attached to a stainless steel plate and kept at 23°C for 30 minutes. The pressure-sensitive adhesive layer has a bulk modulus _G'23 at 23°C of 10 to 200 kPa, a bulk modulus _G'80 at 80°C of 5 to 100 kPa, and a _tanδ80 at 80°C of 0.10 to 0.60. The reinforcing film according to claim 1. The reinforcing film according to claim 1 or 2, wherein the content of the polymer (B) in the pressure-sensitive adhesive layer is 0.5 to 5 parts by weight per 100 parts by weight of the polymer (A). An optical component to which the reinforcing film according to any one of claims 1 to 3 is attached. An electronic component to which the reinforcing film according to any one of claims 1 to 3 is attached.