JP7484158B2 - Adhesive sheet - Google Patents

Description

The present invention relates to an adhesive sheet that has excellent heat resistance and removability.

Adhesive sheets (sometimes called "adhesive tapes") are a joining means with excellent workability and high adhesive reliability, and are therefore widely used in situations such as fixing components that make up electronic devices. Specifically, the adhesive tapes are used for fixing components in various industrial fields, such as fixing metal plates that make up relatively large electronic devices such as flat-screen televisions, home appliances, and office equipment, fixing exterior components to housings, fixing rigid components such as exterior components and batteries to relatively small electronic devices such as mobile electronic terminals, cameras, and personal computers, temporarily fixing the components, and also for labeling purposes that display product information.

In recent years, in each of the above-mentioned industrial fields, for the purpose of saving resources from the viewpoint of protecting the global environment, it has become common to disassemble reusable or reusable parts used in products after use and reuse them. In this case, when adhesive tape is used, it is necessary to peel off the adhesive tape attached to the parts, but since the adhesive tape usually has a high adhesive strength and is attached to many places in the product, the work of peeling it off involves considerable labor. Therefore, there is a demand for an adhesive tape that can be relatively easily peeled off and removed when reused or re-used.
Furthermore, adhesive tapes used for fixing components inside electronic devices are required to have excellent adhesion and removability even in high-temperature environments of about 100° C., which are expected to exist inside electronic devices.

As such an adhesive tape, for example, a transparent pressure-sensitive adhesive sheet comprising at least three layers has been proposed, in which the two outer layers are each composed of a transparent adhesive based on a hydrogenated vinyl aromatic block copolymer and a tackifier resin, and at least one layer is composed of a transparent adhesive based on a vinyl aromatic block copolymer and is present between the two layers, and has a higher elongation at break than the two outer layers (see, for example, Patent Document 1).

JP 2004-162064 A

However, the pressure-sensitive adhesive sheet described in Patent Document 1 uses a styrene-based resin as the base resin, which has excellent extensibility but poor heat resistance, and therefore has the problem that it cannot be used to fix components inside electronic devices that become exposed to high temperatures.
An object of the present invention is to provide a pressure-sensitive adhesive sheet which has both excellent extensibility and heat resistance and can be easily peeled off from an adherend by stretching.

The means for solving the above problems are as follows.
<1> A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer including a pressure-sensitive adhesive component and a curable component obtained by curing a polyfunctional polymerizable monomer,
The pressure-sensitive adhesive sheet is characterized by having a breaking elongation of 300% or more, a breaking strength of 8 N/mm2 ^or more, and a temperature rise retention force of 160°C or more.
<2> The pressure-sensitive adhesive sheet according to <1>, wherein the pressure-sensitive adhesive layer has a gel fraction of 30 mass % or more.
<3> The pressure-sensitive adhesive sheet according to any one of <1> and <2>, wherein the pressure-sensitive adhesive component has no reactivity with the polyfunctional polymerizable monomer.
<4> The pressure-sensitive adhesive sheet according to any one of <1> to <3>, wherein the pressure-sensitive adhesive component contains an acrylic triblock copolymer.
<5> The pressure-sensitive adhesive sheet according to any one of <1> to <4>, wherein the polyfunctional polymerizable monomer contains a tri- or higher functional polymerizable monomer.
<6> The pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive containing the pressure-sensitive adhesive component and the polyfunctional polymerizable monomer,
The pressure-sensitive adhesive sheet according to any one of <1> to <5>, wherein the content of the polyfunctional polymerizable monomer is 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of a solid content of the pressure-sensitive adhesive component.
<7> A laminated pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive sheet according to any one of <1> to <6>, further comprising the pressure-sensitive adhesive layer on one or both sides of the pressure-sensitive adhesive sheet.
<8> The pressure-sensitive adhesive sheet according to any one of <1> to <7>, which has removability such that it can be peeled off from an adherend by stretching.

The present invention provides an adhesive sheet that combines excellent extensibility and heat resistance and can be easily peeled off from an adherend by stretching.

FIG. 1 is a schematic cross-sectional view showing an example of the pressure-sensitive adhesive sheet of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the pressure-sensitive adhesive sheet of the present invention. FIG. 3 is a schematic cross-sectional view showing another example of the pressure-sensitive adhesive sheet of the present invention.

(Adhesive sheet)
The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer containing a pressure-sensitive adhesive component and a curable component obtained by curing a polyfunctional polymerizable monomer.
The pressure-sensitive adhesive sheet preferably has a release liner in addition to the pressure-sensitive adhesive layer, and may have other layers such as an intermediate layer and an undercoat layer, provided that the object of the present invention is not impaired.

In the present invention, the adhesive layer in the adhesive sheet contains an adhesive component and a curing component obtained by curing a polyfunctional polymerizable monomer, thereby improving heat resistance while maintaining flexibility (stretchability), and obtaining an adhesive sheet that can be easily peeled off from an adherend by stretching it horizontally.

In the present invention, the pressure-sensitive adhesive sheet has a breaking elongation of 300% or more, preferably 400% or more, more preferably 600% or more, and even more preferably 800% or more, and preferably 3,000% or less, more preferably 2,000% or less, and even more preferably 1,500% or less.
When the adhesive sheet has a breaking elongation of 300% or more, even if the adhesive sheet is firmly adhered to an adherend, when the adhesive sheet is re-peeled, the stress for stretching the adhesive surface of the adherend is not too large, and the adhesive sheet can be easily peeled off without being excessively stretched when peeled off.

The pressure-sensitive adhesive sheet has a breaking strength of 8 N/mm ² or more, preferably 9 N/mm ² or more, and more preferably 10 N/mm ² or more. The breaking strength is preferably 15 N/mm ² or less, and more preferably 13 N/mm ² or less.
When the breaking strength of the adhesive sheet is 8 N/mm2 or ^more and 15 N/ ^mm2 or less, the adhesive tape can be prevented from tearing even when it is stretched and peeled off, and the load for stretching the adhesive tape does not become excessive, making it easy to re-peel the tape by peeling it off.

The breaking strength and breaking elongation of the adhesive sheet refer to the strength and elongation measured when the adhesive sheet is punched out into a dumbbell shape with a gauge length of 20 mm and a width of 10 mm, and pulled in the length direction at a tensile speed of 300 mm/min using a Tensilon tensile tester (model: RTF-1210, manufactured by A&D Co., Ltd.) under conditions of a measurement atmosphere of 23°C and 50% RH, until it breaks.

The pressure-sensitive adhesive sheet has a temperature-rise retention strength of 160° C. or more, preferably 180° C. or more, and more preferably 200° C. or more. When the temperature-rise retention strength is 160° C. or more, the pressure-sensitive adhesive sheet has good heat resistance while retaining extensibility.
The elevated temperature retention of the pressure-sensitive adhesive sheet can be measured as follows.
One side of the adhesive sheet is lined with aluminum foil having an average thickness of 50 μm, and the sheet is cut to a size of 25 mm width x 100 mm length. This is then placed on the surface of a clean, smooth stainless steel plate (hairline polished with No. 360 waterproof abrasive paper) in an atmosphere of 23°C and 50% RH so that the adhesion area is 25 mm x 25 mm. A 2 kg roller is rolled back and forth over the upper surface to press them together, and the sheet is left to stand in an environment of 23°C for 1 hour to prepare a test specimen.
With the stainless steel plate constituting the test piece fixed so that the test piece is held vertically, a load of 0.5 kg is applied to the sheet in an environment of 40°C. From that time, the temperature is increased at a rate of 1°C/min in the range of 40°C to 200°C, and the temperature is measured until the sheet falls from the stainless steel plate.

In the present invention, the gel fraction value obtained by measuring the insoluble content after immersing the pressure-sensitive adhesive layer in toluene for 24 hours is used as an index for clarifying the proportion of the cured component obtained by curing the polyfunctional polymerizable monomer. The gel fraction of the pressure-sensitive adhesive layer is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more and 80% by mass or less. When the gel fraction is 30% by mass or more, the cured component is present in an appropriate amount in the pressure-sensitive adhesive layer, so that excellent stretchability and heat resistance can be achieved at the same time.
The gel fraction can be measured as follows.
The adhesive was applied to a release liner so that the average thickness after drying was 50 μm, dried at 100° C. for 3 minutes, irradiated with ultraviolet (UV) light (accumulated light amount 1,000 mJ/cm ² ), and cut into a 50 mm square to serve as a sample. Next, the mass (G1) of the sample before immersion in toluene was measured in advance, and after immersion in a toluene solution at 23° C. for 24 hours, the toluene-insoluble portion of the sample was separated by filtering through a 300 mesh wire net, and the mass (G2) of the residue after drying at 110° C. for 1 hour was measured, and the gel fraction was calculated according to the following formula.
Gel fraction (mass%)=G2/G1×100

The term "sheet" in the pressure-sensitive adhesive sheet of the present invention means a form consisting of only a pressure-sensitive adhesive layer, or a form having at least one pressure-sensitive adhesive layer on a release liner, and includes all product forms such as individual leaves, rolls, thin plates, or strips (tapes).
Although the "adhesive sheet" may also be referred to as an "adhesive tape" or an "adhesive film," the following description will refer to it as an "adhesive sheet." The surface of the adhesive layer in the adhesive sheet may also be referred to as the "adhesive surface."

The pressure-sensitive adhesive sheet of the present invention is a pressure-sensitive adhesive sheet that combines stretch-release property, heat resistance, and adhesiveness due to the pressure-sensitive adhesive layer itself. That is, since the pressure-sensitive adhesive layer is a resin layer that combines a resin substrate and adhesiveness, a resin substrate is not particularly required.
An example of the pressure-sensitive adhesive sheet of the present invention is a pressure-sensitive adhesive sheet 10 consisting of only a pressure-sensitive adhesive layer 1, as shown in FIG.
As shown in Fig. 2, there is also included a double-sided laminated pressure-sensitive adhesive sheet 10 in which a pressure-sensitive adhesive layer 1a is further formed on both sides of the pressure-sensitive adhesive layer 1. As shown in Fig. 3, there is also included a single-area layered pressure-sensitive adhesive sheet 10 in which a pressure-sensitive adhesive layer 1a is further formed on one side of the pressure-sensitive adhesive layer 1. In Figs. 2 and 3, the pressure-sensitive adhesive layer 1 also functions as a resin substrate.
Although not shown, in FIGS. 1 to 3, the surface of the pressure-sensitive adhesive layer 1 preferably has a release liner.

<Adhesive Layer>
The pressure-sensitive adhesive layer contains an adhesive component and a curable component obtained by curing a polyfunctional polymerizable monomer, and preferably contains a tackifier resin and a crosslinking agent, and further contains other components as necessary.
The pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive containing a pressure-sensitive adhesive component and a polyfunctional polymerizable monomer.

<<Adhesive components>>
The adhesive component is not reactive with the polyfunctional polymerizable monomer. Here, the adhesive component is not reactive with the polyfunctional polymerizable monomer means that the polyfunctional polymerizable monomer does not react with the adhesive component to form a covalent bond. As a result, the adhesive component exists in the adhesive layer independently of the cured component obtained by curing the polyfunctional polymerizable monomer, and therefore, the adhesive layer can be provided with excellent heat resistance and removability while maintaining its flexibility (stretchability).
The adhesive component constituting the pressure-sensitive adhesive contains an acrylic triblock copolymer and further contains other components as necessary. By using the acrylic triblock copolymer as the adhesive component, the heat resistance can be improved.

- Acrylic triblock copolymer -
The acrylic triblock copolymer has two polymer blocks (A1) and (A2) composed of methacrylic acid ester units and one polymer block (B) composed of acrylic acid ester units, and has an (A1)-(B)-(A2) block structure.

--Polymer blocks (A1) and (A2)--
The acrylic triblock copolymer has two polymer blocks (A1) and (A2) composed of methacrylic acid ester units. The polymer blocks (A1) and (A2) may be the same or different, but are preferably the same from the viewpoints of improving cohesive strength and heat resistance. When they are the same, they are simply referred to as (A).

Examples of methacrylic acid esters that serve as structural units of the polymer blocks (A1) and (A2) include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, lauryl methacrylate, Examples of methacrylic acid esters include methacrylic acid esters without functional groups such as tridecyl methacrylate, stearyl methacrylate, isobornyl methacrylate, phenyl methacrylate, and benzyl methacrylate; and methacrylic acid esters with functional groups such as methoxyethyl methacrylate, ethoxyethyl methacrylate, diethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, 2-aminoethyl methacrylate, glycidyl methacrylate, and tetrahydrofurfuryl methacrylate. These may be used alone or in combination of two or more.

Among these, from the viewpoint of improving the heat resistance and durability of the resulting polymer, methacrylic acid esters having no functional group are preferred, and methyl methacrylate, ethyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, and phenyl methacrylate are more preferred, with methyl methacrylate being even more preferred since it results in clearer phase separation between the polymer blocks (A1) and (A2) and the polymer block (B) and increases the cohesive force (leaving less adhesive residue).
The polymer blocks (A1) and (A2) may be composed of one type of methacrylic acid ester or two or more types of methacrylic acid esters. The acrylic triblock copolymer has two polymer blocks (A1) and (A2) as polymer blocks composed of methacrylic acid ester units, and the methacrylic acid esters constituting the polymer blocks (A1) and (A2) may be the same or different.
The proportion of the methacrylic acid ester units contained in the polymer blocks (A1) and (A2) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more in each of the polymer blocks (A1) and (A2). The proportion of the methacrylic acid ester units contained in the polymer blocks (A1) and (A2) may be 100% by mass.

The stereoregularity of the methacrylic acid ester units contained in each of the polymer blocks (A1) and (A2) composed of methacrylic acid ester units may be the same or different.

In the acrylic triblock copolymer, the total content of the polymer blocks (A1) and (A2) is preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, and particularly preferably 20% by mass or less. The total content of the polymer blocks (A1) and (A2) is preferably 4% by mass or more, more preferably 8% by mass or more, even more preferably 10% by mass or more, and even more preferably 15% by mass or more. When the total content of the polymer blocks (A1) and (A2) is within the above range, when the acrylic triblock copolymer is contained in an adhesive, it tends to exhibit excellent cohesive strength and to be less likely to leave adhesive residue, while the viscosity of the adhesive does not increase too much, ensuring processability. In addition, the adhesive tends to be more excellent in heat-resistant adhesion and constant load retention. The contents of the polymer blocks (A1) and (A2) contained in the acrylic triblock copolymer may be the same or different.

The glass transition temperature (Tg) of each of the polymer blocks (A1) and (A2) is preferably 60°C or higher and 140°C or lower, more preferably 70°C or higher and 130°C or lower, and even more preferably 80°C or higher and 130°C or lower. When the glass transition temperature (Tg) is within this range, the polymer blocks (A1) and (A2) act as physical pseudo-crosslinking points at the normal use temperature of the adhesive, and cohesive force is exerted, and when the acrylic triblock copolymer (I) is contained in the adhesive, the adhesive has excellent adhesive properties, durability, heat resistance, etc. Note that the glass transition temperature (Tg) in this specification is the extrapolation start temperature of the curve obtained by DSC measurement.

The glass transition temperatures (Tg) of the polymer blocks (A1) and (A2) may be the same or different. Even if the glass transition temperatures (Tg) of the polymer blocks (A1) and (A2) are different, it is a preferred embodiment that the glass transition temperatures (Tg) of both polymer blocks are within the above range.

--Polymer block (B)--
The acrylic triblock copolymer has one polymer block (B) consisting of an acrylic ester unit.

Examples of the acrylic acid esters that are constituent units of the polymer block (B) include acrylic acid esters that do not have a functional group, such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, isooctyl acrylate, decyl acrylate, isobornyl acrylate, lauryl acrylate, octadecyl acrylate, cyclohexyl acrylate, phenyl acrylate, and benzyl acrylate; and acrylic acid esters that have a functional group, such as methoxyethyl acrylate, ethoxyethyl acrylate, 2-hydroxyethyl acrylate, 2-aminoethyl acrylate, glycidyl acrylate, tetrahydrofurfuryl acrylate, diethylaminoethyl acrylate, and phenoxyethyl acrylate.

Among these, from the viewpoint of transparency and flexibility when made into an adhesive, acrylic acid esters represented by the general formula CH ₂ ═CH-COOR ¹ (wherein R ¹ represents an organic group having 1 to 10 carbon atoms) are preferred, and from the viewpoint of clear phase separation between polymer blocks (A1) and (A2) and polymer block (B) and the adhesive exhibiting high cohesive strength, acrylic acid esters not having functional groups, such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, isooctyl acrylate, decyl acrylate, isobornyl acrylate, cyclohexyl acrylate, phenyl acrylate, and benzyl acrylate, are more preferred. Furthermore, in terms of the adhesive having appropriate adhesiveness at room temperature and exhibiting stable adhesive strength over a wide temperature range and wide peel speed conditions, at least one selected from methyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, and isooctyl acrylate is even more preferable, and n-butyl acrylate is particularly preferable.

The polymer block (B) may be composed of one type of these acrylic acid esters, or may be composed of two or more types. The proportion of the acrylic acid ester units contained in the polymer block (B) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The proportion of the acrylic acid ester units contained in the polymer block (B) may be 100% by mass.

In the acrylic triblock copolymer, the content of polymer block (B) is preferably 65% by mass or more, more preferably 70% by mass or more, even more preferably 75% by mass or more, and even more preferably 80% by mass or more. The content of polymer block (B) is preferably 96% by mass or less, more preferably 92% by mass or less, even more preferably 90% by mass or less, and even more preferably 85% by mass or less. When the content of polymer block (B) is within the above range, when the acrylic triblock copolymer is used as a pressure-sensitive adhesive, excellent cohesive strength is exhibited and creep properties are further improved.

The glass transition temperature (Tg) of the polymer block (B) is preferably from -100°C to 30°C, more preferably from -80°C to 10°C, and even more preferably from -70°C to 0°C. If the glass transition temperature (Tg) is within this range, it can have excellent tack and adhesive strength when used in an adhesive.

The polymer blocks (A1) and (A2) and the polymer block (B) may contain each other's monomer components to the extent that the effect of the present invention is not impaired. For example, the boundary between the polymer block (A1) or (A2) and the polymer block (B) may have a tapered structure. In addition, the polymer block (A1) or (A2) and the polymer block (B) may not contain each other's monomer components.

The polymer blocks (A1) and (A2) and the polymer block (B) may contain other monomer units as necessary. Examples of such other monomers include vinyl monomers having a carboxyl group such as (meth)acrylic acid, crotonic acid, maleic acid, maleic anhydride, and fumaric acid; vinyl monomers having a functional group such as (meth)acrylamide, (meth)acrylonitrile, vinyl acetate, vinyl chloride, and vinylidene chloride; aromatic vinyl monomers such as styrene, α-methylstyrene, p-methylstyrene, and m-methylstyrene; conjugated diene monomers such as butadiene and isoprene; olefin monomers such as ethylene, propylene, isobutene, and octene; and lactone monomers such as ε-caprolactone and valerolactone.
When each polymer block contains these other monomers, the content thereof is preferably 20 mass% or less, more preferably 10 mass% or less, and even more preferably 5 mass% or less, based on the total mass of the monomers constituting each polymer block.

The acrylic triblock copolymer has an (A1)-(B)-(A2) block structure in which polymer block (A1), polymer block (B), and polymer block (A2) are bonded in that order. By using the acrylic triblock copolymer in this structure, a pressure sensitive adhesive with excellent adhesive strength, constant load retention, and cohesive strength can be obtained.

The weight average molecular weight (Mw) of the acrylic triblock copolymer is preferably 50,000 or more and 300,000 or less, and more preferably 50,000 or more and 150,000 or less. If the weight average molecular weight (Mw) of the acrylic triblock copolymer is less than 50,000, the extensibility may decrease.

The molecular weight distribution (Mw/Mn) of the acrylic triblock copolymer is preferably 1.0 to 1.5, more preferably 1.0 to 1.4. In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are the weight average molecular weight and number average molecular weight calculated using standard polystyrene as determined by gel permeation chromatography (GPC).

Here, the weight average molecular weight and number average molecular weight measured by the GPC method are values calculated as standard polystyrene, measured under the following measurement conditions using a GPC apparatus (HLC-8329GPC) manufactured by Tosoh Corporation.
[Measurement condition]
Sample concentration: 0.5% by mass (tetrahydrofuran solution)
Sample injection volume: 100 μL
Eluent: THF (tetrahydrofuran)
Flow rate: 1.0 mL/min Measurement temperature: 40° C.
Main column: 2 "TSKgel GMHHR-H (20)" manufactured by Tosoh Corporation Guard column: "TSKgel HXL-H" manufactured by Tosoh Corporation
Detector: Differential refractometer Standard polystyrene molecular weight: 10,000 to 20,000,000 (manufactured by Tosoh Corporation)

Other components in the adhesive component include, for example, acrylic diblock copolymers and other polymers.

<<Curing component>>
The curable component constituting the pressure-sensitive adhesive contains a polyfunctional polymerizable monomer, and further contains other components as required.
The polyfunctional polymerizable monomer preferably has two or more ethylenically unsaturated double bonds in the molecular structure, more preferably has three or more ethylenically unsaturated double bonds, and further preferably has 3 to 10 ethylenically unsaturated double bonds in the molecular structure.
Examples of the ethylenically unsaturated double bond include a vinyl group, a (meth)acrylic group, and a (meth)acryloyl group.

Examples of the polyfunctional monomer include hexadiol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol tri(meth)acrylate, neopentyl glycol di(meth)acrylate, bispentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, ethoxylated 1,6-hexanediol di(meth)acrylate, and polypropylene glycol di(meth)acrylate. acrylate, 1,4-butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 2-n-butyl-2-ethyl 1,3-propanediol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, hydroxypivalic acid trimethylolpropane tri(meth)acrylate, ethoxylated phosphoric acid tri(meth)acrylate, ethoxylated tripropylene glycol di(meth)acrylate, neopentyl glycol modified trimethylolpropane di(meth)acrylate, stearic acid modified pentane Pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, tetramethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, caprolactone modified trimethylolpropane tri(meth)acrylate, propoxylated glyceryl tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, caprolactone modified dipentaerythritol Examples of the acrylates include ethylene glycol hexa(meth)acrylate, dipentaerythritol hydroxypenta(meth)acrylate, neopentyl glycol oligo(meth)acrylate, 1,4-butanediol oligo(meth)acrylate, 1,6-hexanediol oligo(meth)acrylate, trimethylolpropane oligo(meth)acrylate, pentaerythritol oligo(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, propoxylated neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, and propoxylated trimethylolpropane tri(meth)acrylate. These may be used alone or in combination of two or more.

The content of the polyfunctional polymerizable monomer is preferably 1 part by mass or more and 20 parts by mass or less, and more preferably 2 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the solid content of the adhesive component.
When the content of the polyfunctional polymerizable monomer is from 1 part by mass to 20 parts by mass, both excellent extensibility and heat resistance can be achieved.

Examples of other components in the curable component include a polyfunctional polymerizable oligomer and a photopolymerization initiator.
Examples of polyfunctional polymerizable oligomers include urethane acrylic oligomers (e.g., aromatic urethane acrylic oligomers, aliphatic urethane acrylic oligomers, etc.), epoxy acrylate oligomers, polyester acrylate oligomers, and other special oligomers. These may be used alone or in combination of two or more. Among these, oligomers having 2 to 5 unsaturated carbon-carbon bonds are preferred.

As a photopolymerization initiator, any substance that generates radicals when irradiated with light, particularly ultraviolet light with a wavelength of 220 nm to 500 nm, can be used. Examples of such photopolymerization initiators include acetophenone, 2,2-diethoxyacetophenone, p-dimethylaminoacetophenone, benzophenone, 2-chlorobenzophenone, p,p'-dichlorobenzophenone, p,p-bisdiethylaminobenzophenone, Michler's ketone, benzil, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-propyl ether, benzoin isobutyl ether, benzoin-n-butyl ether, benzyl methyl ketal, thioxanthone, 2-chlorothioxanthone, 2-hydroxy-2-methyl-1-phenyl-1-one, 1-(4-isopropylphenyl)2-hydroxy-2-methylpropan-1-one, methylbenzoyl formate, 1-hydroxycyclohexyl phenyl ketone, azobisisobutyronitrile, benzoyl peroxide, and di-tert-butyl peroxide. These may be used alone or in combination of two or more.

<Other ingredients>
Other components in the adhesive layer include, for example, additives such as tackifying resins, antioxidants, ultraviolet absorbers, fillers, polymerization inhibitors, surface conditioners, antistatic agents, defoamers, viscosity modifiers, light stabilizers, weather stabilizers, heat stabilizers, antioxidants, leveling agents, organic pigments, inorganic pigments, pigment dispersants, plasticizers, softeners, flame retardants, metal deactivators, silica beads, organic beads, etc.; inorganic fillers such as silicon oxide, aluminum oxide, titanium oxide, zirconia, antimony pentoxide, etc.

- Tackifying resin -
Examples of the tackifier resin that can be used include rosin-based tackifier resins, polymerizable rosin-based tackifier resins, polymerizable rosin ester-based tackifier resins, rosin phenol-based tackifier resins, stabilized rosin ester-based tackifier resins, disproportionated rosin ester-based tackifier resins, hydrogenated rosin ester-based tackifier resins, terpene-based tackifier resins, terpene phenol-based tackifier resins, petroleum resin-based tackifier resins, and (meth)acrylate-based tackifier resins.
Among these, as the tackifier resin, it is preferable to use one type alone or two or more types in combination of disproportionated rosin ester tackifier resins, polymerizable rosin ester tackifier resins, rosin phenol tackifier resins, hydrogenated rosin ester tackifier resins, (meth)acrylate resins, and terpene phenol resins.

The pressure-sensitive adhesive sheet of the present invention may be a so-called substrate-less pressure-sensitive adhesive sheet consisting of a single or multiple pressure-sensitive adhesive layers.
Such a pressure-sensitive adhesive sheet can be produced, for example, by applying the pressure-sensitive adhesive onto a release liner using a roll coater, a die coater or the like, drying the adhesive, and then curing the adhesive by irradiating it with ultraviolet light.

-Release liner-
The release liner is not particularly limited and can be appropriately selected depending on the purpose. Examples of the release liner include papers such as kraft paper, glassine paper, and wood-free paper; resin films such as polyethylene, polypropylene (OPP, CPP), and polyethylene terephthalate; laminated paper in which the above-mentioned papers and resin films are laminated together; and papers that have been sealed with clay, polyvinyl alcohol, or the like and then treated with a release agent such as a silicone-based resin on one or both sides.
Examples of the ultraviolet ray irradiation means include ultraviolet ray (UV) irradiation lamps, etc. Examples of the types of ultraviolet ray (UV) irradiation lamps include high pressure mercury lamps, ultra-high pressure mercury lamps, metal halide lamps, LEDs, etc.

The pressure-sensitive adhesive sheet of the present invention comprises a pressure-sensitive adhesive layer, and the average thickness of the pressure-sensitive adhesive layer corresponds to the total thickness of the pressure-sensitive adhesive sheet. The substrate-less pressure-sensitive adhesive sheet is formed on a release liner, and is covered with the release liner until use.
The average thickness of the pressure-sensitive adhesive sheet (average thickness of the pressure-sensitive adhesive layer) is preferably 500 μm or less, more preferably 200 μm or less, even more preferably 150 μm or less, and particularly preferably 100 μm or less. When the average thickness is within the above numerical range, excellent adhesiveness and heat resistance can be achieved while being thin.
In this specification, the "average thickness of the adhesive layer" refers to the average thickness of the adhesive layer (only the adhesive layer) after removing the release liner, measured at five locations at 100 mm intervals in the longitudinal direction using a dial thickness gauge Type G manufactured by Ozaki Seisakusho Co., Ltd.

The adhesive sheet of the present invention may be a laminated adhesive sheet in which an additional adhesive layer is formed on one or both sides of the adhesive layer. The average thickness of the additional adhesive layer is preferably 50 μm or less, more preferably 30 μm or less.

<Applications>
The pressure-sensitive adhesive sheet of the present invention has both excellent extensibility and heat resistance, and can be easily peeled off from an adherend by stretching it horizontally. Therefore, the pressure-sensitive adhesive sheet can be suitably used for applications such as fixing metal plates or exterior parts to housings that make up relatively large electronic devices such as flat-screen televisions, home appliances, and office equipment, fixing exterior parts and rigid parts such as batteries to relatively small electronic devices such as portable electronic terminals, cameras, and personal computers, and temporary fixing of parts in various industrial fields, temporary fixing of chips in the semiconductor manufacturing process, and labels that display product information.

The following describes examples of the present invention, but the present invention is not limited to these examples.

<Weight average molecular weight Mw, molecular weight distribution (Mw/Mn)>
The weight average molecular weight Mw and the molecular weight distribution (Mw/Mn) are weight average molecular weights measured by gel permeation chromatography (GPC) in terms of standard polystyrene, and were measured by the following method.
The molecular weight was measured by GPC using a GPC apparatus (HLC-8329GPC) manufactured by Tosoh Corporation, and was measured in terms of polystyrene under the following GPC measurement conditions.
[Measurement condition]
Sample concentration: 0.5% by mass (tetrahydrofuran solution)
Sample injection volume: 100 μL
Eluent: tetrahydrofuran (THF)
Flow rate: 1.0 mL/min Column temperature (measurement temperature): 40° C.
Main column: 2 "TSKgel GMHHR-H (20)" manufactured by Tosoh Corporation Guard column: "TSKgel HXL-H" manufactured by Tosoh Corporation
Detector: Differential refractometer Standard polystyrene molecular weight: 10,000 to 20,000,000 (manufactured by Tosoh Corporation)

(Synthesis Example 1 of Acrylic Triblock Copolymer)
<Acrylic triblock copolymer (1)>
A three-way cock was attached to a 3 L three-neck flask and the inside of the flask was replaced with nitrogen, and then 1,861 g of toluene and 14.3 g of 1,2-dimethoxyethane were added with stirring at room temperature, followed by 44.3 g of a toluene solution containing 22.3 mmol of isobutylbis(2,6-di-t-butyl-4-methylphenoxy)aluminum, and further by adding 1.04 g of a cyclohexane solution of sec-butyllithium containing 1.78 mmol of sec-butyllithium.
Subsequently, 21.9 g of methyl methacrylate was added thereto. The reaction solution was initially colored yellow, but became colorless after stirring at room temperature for 60 minutes.
Subsequently, the internal temperature of the polymer solution was cooled to -30°C, and 249 g of n-butyl acrylate was added dropwise over 2 hours, and after completion of the dropwise addition, the mixture was stirred at -30°C for 5 minutes.
Further, 21.9 g of methyl methacrylate was added thereto, and the mixture was stirred overnight at room temperature.
After 24 g of methanol was added to terminate the polymerization reaction, the resulting reaction solution was poured into 15 kg of methanol to precipitate a precipitate, which was then collected and dried to obtain 296 g of an acrylic triblock copolymer (1).
The weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the obtained acrylic triblock copolymer (1) were determined by the GPC measurement by the above-mentioned method, and the weight average molecular weight (Mw) was 100,000 and the molecular weight distribution (Mw/Mn) was 1.2.

(Synthesis Example 2 of Acrylic Triblock Copolymer)
<Acrylic triblock copolymer (2)>
A 3 L three-neck flask was fitted with a three-way cock and the inside of the flask was purged with nitrogen, and then 1861 g of toluene and 14.3 g of 1,2-dimethoxyethane were added with stirring at room temperature, followed by 44.3 g of a toluene solution containing 22.3 mmol of isobutylbis(2,6-di-t-butyl-4-methylphenoxy)aluminum, and further by adding 1.04 g of a cyclohexane solution of sec-butyllithium containing 1.78 mmol of sec-butyllithium.
Subsequently, 36.4 g of methyl methacrylate was added thereto. The reaction solution was initially colored yellow, but became colorless after stirring at room temperature for 60 minutes.
Subsequently, the internal temperature of the polymer solution was cooled to -30°C, and 220 g of n-butyl acrylate was added dropwise over 2 hours, and after completion of the dropwise addition, the mixture was stirred at -30°C for 5 minutes.
Further, 220 g of methyl methacrylate was added thereto, and the mixture was stirred overnight at room temperature.
After 24 g of methanol was added to terminate the polymerization reaction, the resulting reaction solution was poured into 15 kg of methanol to precipitate a precipitate, which was then collected and dried to obtain 296 g of an acrylic triblock copolymer (2).
The weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the obtained acrylic triblock copolymer (2) were determined by the GPC measurement by the above-mentioned method, and the weight average molecular weight (Mw) was 75,000 and the molecular weight distribution (Mw/Mn) was 1.2.

(Synthesis Example 3 of Acrylic Triblock Copolymer)
<Acrylic triblock copolymer (3)>
A 3 L three-neck flask was fitted with a three-way cock and the inside of the flask was purged with nitrogen, and then 1861 g of toluene and 14.3 g of 1,2-dimethoxyethane were added with stirring at room temperature, followed by 44.3 g of a toluene solution containing 22.3 mmol of isobutylbis(2,6-di-t-butyl-4-methylphenoxy)aluminum, and further by adding 1.04 g of a cyclohexane solution of sec-butyllithium containing 1.78 mmol of sec-butyllithium.
Subsequently, 36.4 g of methyl methacrylate was added thereto. The reaction solution was initially colored yellow, but became colorless after stirring at room temperature for 60 minutes.
Subsequently, the internal temperature of the polymer solution was cooled to -30°C, and 220 g of 2-ethylhexyl acrylate was added dropwise over 2 hours, and after completion of the dropwise addition, the mixture was stirred at -30°C for 5 minutes.
Further, 36.4 g of methyl methacrylate was added thereto, and the mixture was stirred overnight at room temperature.
After 24 g of methanol was added to terminate the polymerization reaction, the resulting reaction solution was poured into 15 kg of methanol to precipitate a precipitate, which was then collected and dried to obtain 296 g of an acrylic triblock copolymer (3).
The weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the obtained acrylic triblock copolymer (3) were determined by the GPC measurement by the above-mentioned method, and the weight average molecular weight (Mw) was 75,000 and the molecular weight distribution (Mw/Mn) was 1.2.

Example 1
<Preparation of Pressure Sensitive Adhesive A>
To 100 parts by mass of the acrylic triblock copolymer (1), 2.5 parts by mass of a polyfunctional polymerizable monomer (pentaerythritol triacrylate, manufactured by Toa Gosei Co., Ltd., Aronix M305, molecular weight 298, trifunctional) and 0.4 parts by mass of a photopolymerization initiator (Irgacure 184, manufactured by IGM Resins B.V.) were added, and ethyl acetate was further added and stirred to obtain a pressure-sensitive adhesive A having a solid content of 40% by mass.

<Preparation of adhesive sheet>
The obtained adhesive A was coated on a release liner (PET38x1, A3, manufactured by Nippa) using a comma coater so that the average thickness after drying would be 100 μm, and then dried for 2 minutes in a dryer at 80° C. Next, after bonding to a release liner (PET38x1, A3, manufactured by Nippa), it was irradiated with ultraviolet light using an electrodeless UV lamp system manufactured by Heraeus so that the accumulated light amount was 1,000 mJ/ ^cm2 , thereby producing the adhesive sheet of Example 1.

Example 2
<Preparation of Pressure Sensitive Adhesive B>
To 100 parts by mass of the acrylic triblock copolymer (1), 10 parts by mass of a polyfunctional polymerizable monomer (pentaerythritol triacrylate, manufactured by Toa Gosei Co., Ltd., Aronix M305, molecular weight 298, trifunctional) and 0.4 parts by mass of a photopolymerization initiator (Irgacure 184, manufactured by IGM Resins B.V.) were added, and ethyl acetate was further added and stirred to obtain a pressure-sensitive adhesive B having a solid content of 40% by mass.

<Preparation of adhesive sheet>
The obtained adhesive B was coated on a release liner (PET38x1, A3, manufactured by Nippa) using a comma coater so that the average thickness after drying would be 100 μm, and then dried for 2 minutes in a dryer at 80° C. Next, after bonding to a release liner (PET38x1, A3, manufactured by Nippa), it was irradiated with ultraviolet light using an electrodeless UV lamp system manufactured by Heraeus so that the accumulated light amount was 1,000 mJ/ ^cm2 , thereby producing an adhesive sheet of Example 2.

Example 3
<Preparation of Pressure Sensitive Adhesive C>
To 100 parts by mass of the acrylic triblock copolymer (1), 2.5 parts by mass of a multifunctional polymerizable monomer (dipentaerythritol hexaacrylate, manufactured by Toa Gosei Co., Ltd., Aronix M404, molecular weight 524, hexafunctional) and 0.4 parts by mass of a photopolymerization initiator (Irgacure 184, manufactured by IGM Resins B.V.) were added, and ethyl acetate was further added and stirred to obtain a pressure-sensitive adhesive C having a solid content of 40% by mass.

<Preparation of adhesive sheet>
The obtained adhesive C was coated on a release liner (PET38x1, A3, manufactured by Nippa) using a comma coater so that the average thickness after drying would be 100 μm, and then dried for 2 minutes in a dryer at 80° C. Next, after bonding to a release liner (PET38x1, A3, manufactured by Nippa), it was irradiated with ultraviolet light using an electrodeless UV lamp system manufactured by Heraeus so that the accumulated light amount was 1,000 mJ/ ^cm2 , thereby producing an adhesive sheet of Example 3.

Example 4
<Preparation of Pressure Sensitive Adhesive D>
To 100 parts by mass of the acrylic triblock copolymer (2), 2.5 parts by mass of a multifunctional polymerizable monomer (pentaerythritol triacrylate, manufactured by Toa Gosei Co., Ltd., Aronix M305, molecular weight 298, trifunctional) and 0.4 parts by mass of a photopolymerization initiator (Irgacure 184, manufactured by IGM Resins B.V.) were added, and ethyl acetate was further added and stirred to obtain a pressure-sensitive adhesive D having a solid content of 40% by mass.

<Preparation of adhesive sheet>
The obtained adhesive D was coated on a release liner (PET38x1, A3, manufactured by Nippa) using a comma coater so that the average thickness after drying would be 100 μm, and then dried for 2 minutes in a dryer at 80° C. Next, after bonding to a release liner (PET38x1, A3, manufactured by Nippa), it was irradiated with ultraviolet light using an electrodeless UV lamp system manufactured by Heraeus so that the accumulated light amount was 1,000 mJ/ ^cm2 , thereby producing an adhesive sheet of Example 4.

Example 5
<Preparation of Pressure Sensitive Adhesive E>
To 100 parts by mass of the acrylic triblock copolymer (3), 2.5 parts by mass of a polyfunctional polymerizable monomer (pentaerythritol triacrylate, manufactured by Toa Gosei Co., Ltd., Aronix M305, molecular weight 298, trifunctional) and 0.4 parts by mass of a photopolymerization initiator (Irgacure 184, manufactured by IGM Resins B.V.) were added, and ethyl acetate was further added and stirred to obtain a pressure-sensitive adhesive E having a solid content of 40% by mass.

<Preparation of adhesive sheet>
The obtained adhesive E was coated on a release liner (PET38x1, A3, manufactured by Nippa) using a comma coater so that the average thickness after drying would be 100 μm, and then dried for 2 minutes in a dryer at 80° C. Next, after bonding to a release liner (PET38x1, A3, manufactured by Nippa), it was irradiated with ultraviolet light using an electrodeless UV lamp system manufactured by Heraeus so that the accumulated light amount was 1,000 mJ/ ^cm2 , thereby producing an adhesive sheet of Example 5.

Example 6
<Preparation of Pressure Sensitive Adhesive F>
To 100 parts by mass of the acrylic triblock copolymer (1), 5 parts by mass of a polyfunctional polymerizable monomer (pentaerythritol triacrylate, manufactured by Toa Gosei Co., Ltd., Aronix M305, molecular weight 298, trifunctional), 2.5 parts by mass of a polyfunctional polymerizable monomer (polyethylene glycol #600 diacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd., A600, molecular weight 708, bifunctional), and 0.4 parts by mass of a photopolymerization initiator (Irgacure 184, manufactured by IGM Resins B.V.) were added, and ethyl acetate was further added and stirred to obtain a pressure-sensitive adhesive F having a solid content of 40% by mass.

<Preparation of adhesive sheet>
The obtained adhesive F was coated on a release liner (PET38x1, A3, manufactured by Nippa) using a comma coater so that the average thickness after drying would be 100 μm, and then dried for 2 minutes in a dryer at 80° C. Next, after bonding to a release liner (PET38x1, A3, manufactured by Nippa), it was irradiated with ultraviolet light using an electrodeless UV lamp system manufactured by Heraeus so that the accumulated light amount was 1,000 mJ/ ^cm2 , thereby producing an adhesive sheet of Example 6.

(Comparative Example 1)
<Preparation of Adhesive G>
Ethyl acetate was added to 100 parts by mass of the acrylic triblock copolymer (1) to obtain a pressure-sensitive adhesive G having a solid content of 40% by mass.

<Preparation of adhesive sheet>
The obtained adhesive G was coated on a release liner (PET38×1, A3, manufactured by Nippa Corporation) using a comma coater so that the average thickness after drying was 100 μm, and dried for 2 minutes in a dryer at 80° C. Next, the adhesive sheet of Comparative Example 1 was produced by bonding to a release liner (PET38×1, A3, manufactured by Nippa Corporation).

(Comparative Example 2)
<Preparation of Adhesive H>
To 100 parts by mass of the acrylic triblock copolymer (1), 0.8 parts by mass of a multifunctional polymerizable monomer (pentaerythritol triacrylate, manufactured by Toa Gosei Co., Ltd., Aronix M305, molecular weight 298, trifunctional) and 0.4 parts by mass of a photopolymerization initiator (Irgacure 184, manufactured by IGM Resins B.V.) were added, and ethyl acetate was further added and stirred to obtain a pressure-sensitive adhesive H having a solid content of 40% by mass.

<Preparation of adhesive sheet>
The obtained adhesive H was coated on a release liner (PET38x1, A3, manufactured by Nippa) using a comma coater so that the average thickness after drying would be 100 μm, and then dried for 2 minutes in a dryer at 80° C. Next, after bonding to a release liner (PET38x1, A3, manufactured by Nippa), it was irradiated with ultraviolet light using an electrodeless UV lamp system manufactured by Heraeus so that the accumulated light amount was 1,000 mJ/ ^cm2 , thereby producing an adhesive sheet of Comparative Example 2.

(Comparative Example 3)
<Preparation of Pressure Sensitive Adhesive I>
To 100 parts by mass of the acrylic triblock copolymer (1), 30 parts by mass of a polyfunctional polymerizable monomer (pentaerythritol triacrylate, manufactured by Toa Gosei Co., Ltd., Aronix M305, molecular weight 298, trifunctional) and 0.4 parts by mass of a photopolymerization initiator (Irgacure 184, manufactured by IGM Resins B.V.) were added, and ethyl acetate was further added and stirred to obtain a pressure-sensitive adhesive I having a solid content of 40% by mass.

<Preparation of adhesive sheet>
The obtained adhesive I was coated on a release liner (PET38x1, A3, manufactured by Nippa) using a comma coater so that the average thickness after drying would be 100 μm, and then dried for 2 minutes in a dryer at 80° C. Next, after bonding to a release liner (PET38x1, A3, manufactured by Nippa), it was irradiated with ultraviolet light using an electrodeless UV lamp system manufactured by Heraeus so that the accumulated light amount was 1,000 mJ/ ^cm2 , thereby producing an adhesive sheet of Comparative Example 3.

(Comparative Example 4)
<Preparation of Pressure Sensitive Adhesive J>
To 100 parts by mass of the acrylic triblock copolymer (1), 10 parts by mass of a polyfunctional polymerizable monomer (polyethylene glycol #600 diacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd., A600, molecular weight 708, bifunctional) and 0.4 parts by mass of a photopolymerization initiator (Irgacure 184, manufactured by IGM Resins B.V.) were added, and ethyl acetate was further added and stirred to obtain a pressure-sensitive adhesive J having a solid content of 40% by mass.

<Preparation of adhesive sheet>
The obtained adhesive J was coated on a release liner (PET38x1, A3, manufactured by Nippa) using a comma coater so that the average thickness after drying would be 100 μm, and then dried for 2 minutes in a dryer at 80° C. Next, after bonding to a release liner (PET38x1, A3, manufactured by Nippa), it was irradiated with ultraviolet light using an electrodeless UV lamp system manufactured by Heraeus so that the accumulated light amount was 1,000 mJ/ ^cm2 , thereby producing an adhesive sheet of Comparative Example 4.

Next, the properties of the obtained adhesive sheets of Examples 1 to 6 and Comparative Examples 1 to 4 were evaluated as follows. The results are shown in Tables 1 to 3.

<Measurement of the average thickness of the adhesive sheet>
The average thickness of each PSA sheet was determined by measuring the thickness of the sheet (only the adhesive layer) after removing the release liner at five locations along the length at 100 mm intervals using a Dial Thickness Gauge Type G manufactured by Ozaki Seisakusho Co., Ltd., and averaging the thickness.

<Method for evaluating temperature retention>
One side of each adhesive sheet was backed with aluminum foil having an average thickness of 50 μm, and the sheet was cut to a size of 25 mm width x 100 mm length. This was then placed on the surface of a clean, smooth-surfaced stainless steel plate (hairline polished with No. 360 waterproof abrasive paper) in an atmosphere of 23° C. and 50% RH so that the adhesion area was 25 mm x 25 mm. A 2 kg roller was rolled back and forth over the upper surface to press them together, and the sheet was left to stand for 1 hour in an environment of 23° C. to prepare a test specimen.
The stainless steel plate constituting the test specimen was fixed so that the test specimen was held vertically, and a load of 0.5 kg was applied to the sheet in an environment of 40° C. From that time, the temperature was increased at 1° C./min in the range of 40° C. to 200° C., and the temperature was measured until the sheet dropped from the stainless steel plate. If the film did not fall even when the temperature reached 200° C., it was indicated as “≧200”.

<Method of evaluating breaking strength and breaking elongation>
The breaking strength and breaking elongation of each adhesive sheet were measured by punching out the adhesive sheet into a dumbbell shape with a gauge length of 20 mm and a width of 10 mm, and pulling it in the length direction at a tensile speed of 300 mm/min using a Tensilon tensile tester (model: RTF-1210, manufactured by A & D Co., Ltd.) under conditions of a measurement atmosphere of 23°C and 50% RH, and measuring the strength and elongation at the time of break.

<Measurement of Gel Fraction>
Each adhesive was coated on a release liner so that the average thickness after drying was 50 μm, dried at 100° C. for 3 minutes, irradiated with ultraviolet (UV) rays (accumulated light amount 1,000 mJ/cm ² ), and cut into a 50 mm square to serve as a sample. Next, the mass (G1) of the above sample before immersion in toluene was measured in advance, and after immersion in a toluene solution at 23° C. for 24 hours, the toluene-insoluble portion of the sample was separated by filtering through a 300 mesh wire net, and the mass (G2) of the residue after drying at 110° C. for 1 hour was measured, and the gel fraction was calculated according to the following formula.
Gel fraction (mass%)=G2/G1×100

<Method for evaluating removability>
Each adhesive sheet, 10 mm wide x 60 mm long, was attached to a clean, smooth-surfaced stainless steel plate with a 10 mm wide x 10 mm long grip protruding from it, and then the other side was attached to a clean, smooth-surfaced stainless steel plate, and pressed with a roller once while applying a load of 2 kg to prepare a test piece. After attachment, the sheet was left for 1 hour in an environment of 23°C and 50% RH, and the grip part of the adhesive sheet was stretched by hand in the horizontal direction of the adhesive sheet at a speed of approximately 300 mm/min in an environment of 23°C and 50% RH.
The test was repeated three times, and the degree of tearing of each pressure-sensitive adhesive sheet and the degree of residual pressure-sensitive adhesive on the adherend after peeling off the pressure-sensitive adhesive sheet were visually evaluated according to the following criteria.
[Evaluation criteria]
⊚: The film was peeled off cleanly all three times.
◯: The adhesive sheet was peeled off cleanly twice, but was torn once. The area of the adhesive sheet that remained without stretching was ⅕ or less of the initial applied area.
Δ: The adhesive sheet was peeled off cleanly twice, but was torn once. The area of the adhesive sheet that remained without stretching was ⅕ or more of the initial applied area.
×: The adhesive sheet could not be peeled off, or the adhesive sheet was torn two or more times.

1, 1a Adhesive layer 10 Adhesive sheet

Claims (7)

A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer including a pressure-sensitive adhesive component and a curable component obtained by curing a polyfunctional polymerizable monomer,
The adhesive component includes an acrylic triblock copolymer,
A pressure-sensitive adhesive sheet having a breaking elongation of 300% or more, a breaking strength of 8 N/mm2 ^or more, and a temperature-rise retention strength of 160°C or more, as measured by the following method .
<Measurement method>
One side of the pressure-sensitive adhesive sheet is lined with aluminum foil having an average thickness of 50 μm, and the sheet is cut to a size of 25 mm width x 100 mm length. This is then placed on the surface of a clean, smooth-surfaced stainless steel plate (hairline polished with No. 360 waterproof abrasive paper) in an atmosphere of 23° C. and 50% RH so that the adhesion area is 25 mm x 25 mm. A 2 kg roller is rolled back and forth over the upper surface to press them together, and the sheet is left to stand in an environment of 23° C. for 1 hour to prepare a test piece.
With the stainless steel plate constituting the test specimen fixed so that the test specimen is held vertically, a load of 0.5 kg is applied to the adhesive sheet in an environment of 40°C. From that time, the temperature is increased at 1°C/min in the range of 40°C to 200°C, and the temperature is measured until the adhesive sheet falls from the stainless steel plate. The adhesive sheet according to claim 1, wherein the gel fraction of the adhesive layer is 30% by mass or more. The adhesive sheet according to any one of claims 1 to 2, wherein the adhesive component is not reactive with the polyfunctional polymerizable monomer. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the polyfunctional polymerizable monomer includes a trifunctional or higher functional polymerizable monomer. the pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive containing the pressure-sensitive adhesive component and the polyfunctional polymerizable monomer,
5. The pressure-sensitive adhesive sheet according to claim 1, wherein the content of the polyfunctional polymerizable monomer is from 1 part by mass to 20 parts by mass with respect to 100 parts by mass of a solid content of the pressure-sensitive adhesive component. A laminated adhesive sheet further comprising the adhesive layer on one or both sides of the adhesive sheet according to any one of claims 1 to 5. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, which has removability and can be peeled off from an adherend by stretching.

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