JP7708319B2 - Release Film - Google Patents

Description

The present invention relates to a release film, an adhesive sheet, and a method for using the adhesive sheet.

Conventionally, release films based on polyester film have been used in a variety of applications due to their excellent mechanical strength, dimensional stability, chemical resistance, optical properties, and cost performance. For example, they are used in the manufacture of polarizing plates and retardation plates for liquid crystal displays (hereinafter abbreviated as LCD), for the manufacture of components for plasma display panels (hereinafter abbreviated as PDP), for the manufacture of components for organic electroluminescence (hereinafter abbreviated as organic EL), for the manufacture of components for various displays, and for various optical applications.

In recent years, in applications using adhesive layers, durability may be required more than ever before. For example, when an adhesive layer is used for bonding components of a touch panel mounted inside an automobile, the application requires that the components are firmly bonded together even when exposed to a high temperature atmosphere in summer or a low temperature environment in winter, since the adhesive layer is used outdoors. Therefore, with the improvement in durability of the adhesive layer itself, the adhesive strength of the adhesive layer itself has tended to be stronger than before. Therefore, the release film of a light release type that has been used widely in the past may be difficult to peel off from the adhesive layer, and there is a demand for even lighter release.
In addition, the recent trend of adhesives is that adhesive layers with low elastic modulus are preferred because they have better step absorption. When using adhesive layers with low elastic modulus, the surface of the adhesive layer is easily deformed when the release film is peeled off, and stringing may occur. Therefore, the release film is required to have even lighter release properties, so-called ultra-lighter release properties.

One way to make release films extremely easy to release is to increase the thickness of the release layer to make them easy to release. However, with this method, depending on the type of release agent used, migration components from the release layer may migrate to the surface of the adhesive layer, making it difficult to obtain the desired adhesive strength.

On the other hand, if a release agent with low migration properties is used to suppress migration from the release layer, the transfer of migrating components to the surface of the adhesive layer is reduced, but if the release layer is applied thickly, the slipperiness of the release layer surface is poor, and when the film is wound into a roll, the films block each other, and the peeling force of the release layer increases and the appearance of the release layer surface deteriorates at the bottom winding part of the roll where pressure is applied by the film. To solve this problem, a method of preventing blocking of the release film by incorporating fine particles in the release layer has been investigated. (Patent Documents 1 and 2)

In addition, as another study, it has been proposed to provide a resin layer containing particles on the surface of the film opposite to the surface on which the release layer is provided (Patent Document 3).

JP 2004-255704 A JP 2017-61081 A JP 2016-165825 A

However, while containing fine particles in the release layer can prevent blocking, it can be difficult to maintain the fine particles stable on the surface of the release layer, the release layer itself can become brittle, and the release characteristics of the release layer can change as particles fall off, making it difficult to obtain a stable release force.

Furthermore, when a resin layer containing particles is provided on the surface opposite to the surface on which the release layer is provided, blocking can be prevented; however, depending on the degree of unevenness formation, the unevenness of the particles contained in the resin layer may be transferred to the release layer during film roll formation, changing the release characteristics of the release layer and making it difficult to obtain a stable release force.
The present invention has been made in consideration of the above-mentioned circumstances, and the problem to be solved is to provide a release film and a film laminate which realizes ultra-easy peelability for various adhesives, while the peel properties of the release layer are not easily changed by blocking.

In view of the above circumstances, the present inventors conducted intensive research and found that the above problems can be solved by using a release film having a specific configuration, and thus completed the present invention. That is, the present invention provides the following items [1] to [28].
[1] A release film comprising a resin layer (A) on one surface of a base film and a resin layer (B) on the other surface of the base film, wherein the resin layer (A) contains a silicone resin-based release agent and has a thickness of 0.2 to 2.0 μm, and the resin layer (B) contains a non-silicone resin-based release agent.
[2] A release film comprising a resin layer (A) on at least one side of a base film, the resin layer (A) being a cured product of a resin layer composition containing a curable silicone resin and a light release agent, the light release agent having a dimethylsiloxane skeleton (DM) represented by the following formula (I) and a methylphenylsiloxane skeleton (MP) represented by the following formula (II), and having a thickness of 0.2 to 1.5 μm.


[3] The release film according to the above [2], wherein the maximum cross-sectional height (Rt) of the film surface opposite to the surface on which the resin layer (A) is provided is 2.0 μm or less.
[4] The release film according to the above [2] or [3], wherein the surface of the base film opposite to the surface on which the resin layer (A) is provided is provided with a polyester layer containing 0.4 to 1.0 mass% of particles having an average particle size of 1 to 6 μm.
[5] The release film according to any one of the above [2] to [4], wherein the weight average molecular weight of the light release agent is 10,000 or more and 100,000 or less.
[6] The release film according to any one of the above [1] to [5], wherein the elastic modulus of the resin layer (A) at 25° C., measured using a nanoindenter apparatus, is 500 MPa or less.
[7] The release film according to the above [1] or [6], wherein the non-silicone resin-based release agent is at least one selected from the group consisting of wax, a compound containing a long-chain alkyl group, and a fluorine compound.
[8] The release film according to the above [1], [6] or [7], wherein the content of the release agent in the non-volatile components of the resin layer (B) is 10 to 70 mass%.
[9] The release film according to any one of the above [1] and [6] to [8], wherein the resin layer (B) is substantially free of particles.
[10] The release film according to any one of the above [1] to [9], wherein the normal peel strength of the resin layer (A) is 5 g/25 mm or less, as measured by the following evaluation method.
<Evaluation method>
An acrylic adhesive tape ("No. 7475" manufactured by Tesa) is attached to the resin layer (A) surface of the release film, cut to a size of 25 mm x 150 mm, and left at room temperature for 1 hour. The peeling force is 180° at a pulling speed of 0.3 m/min.
[11] The release film according to any one of the above [1] and [6] to [10], further comprising an undercoat layer between at least one of the resin layer (A) or the resin layer (B) and the base film.
[12] The release film according to the above [11], wherein the undercoat layer is an antistatic layer.
[13] The release film according to the above [11] or [12], wherein the undercoat layer contains the following compounds (A) to (C):
(A) a polymer in which a compound consisting of thiophene or a thiophene derivative is doped with another anionic compound, or a self-doped polymer having an anionic group in a compound consisting of thiophene or a thiophene derivative; (B) a polyhydroxy compound; (C) one or more compounds selected from the group consisting of polyurethane resins, polyester resins, and acrylic resins.
[14] The release film according to any one of the above [1] and [6] to [13], wherein the surface resistivity of at least one surface of the resin layer (A) or the resin layer (B) is 1×10 ¹² Ω/□ or less.
[15] The release film according to any one of the above [1] to [14], wherein the base film is a polyester film.
[16] The release film according to the above [15], wherein the polyester film has a three-layer structure.
[17] The release film according to any one of the above [1] to [16], wherein the resin layer (A) has a post-press heavy peel rate of 100% or less, as evaluated by the following method.
<Evaluation method>
An acrylic adhesive tape ("No. 7475" manufactured by Tesa) was attached to the surface of the resin layer (A), cut to a size of 25 mm x 150 mm, and left at room temperature for 1 hour. The peel strength at 180° under the condition of a tensile speed of 0.3 m/min was defined as (F1).
Next, the resin layer (A) is laminated so as to contact the surface, and pressed for 20 hours at a temperature of 40° C., a humidity of 90% RH, and a load of 1 MPa. An acrylic adhesive tape (Tesa's "No. 7475") is attached to the resin layer (A) surface after the treatment, and then cut to a size of 25 mm x 150 mm and left at room temperature for 1 hour. The peel force at 180° peeled under the condition of a pulling speed of 0.3 m/min is defined as (F2).
The heavy peeling rate after pressing is calculated using the following formula.
Heavy peeling rate after pressing (%) = (F2 - F1) / F1 x 100
[18] The release film according to any one of the above [1] to [17], wherein the center line average roughness (Ra(A)) of the resin layer (A) surface is 30 nm or less.
[19] The release film according to any one of the above [1] or [6] to [18], wherein the center line average roughness (Ra(B)) of the resin layer (B) surface is 60 nm or less.
[20] A pressure-sensitive adhesive sheet comprising the release film according to any one of [1] to [19] above and another release film via an adhesive layer.
[21] The pressure-sensitive adhesive sheet according to the above-mentioned [20], wherein the pressure-sensitive adhesive layer is formed from an acrylic pressure-sensitive adhesive composition.
[22] The pressure-sensitive adhesive sheet according to the above [20] or [21], wherein the pressure-sensitive adhesive layer has an elastic modulus (25°C) of 6.0 MPa or less.
[23] The pressure-sensitive adhesive sheet according to any one of [20] to [22] above, wherein the pressure-sensitive adhesive layer contains 2-ethylhexyl acrylate and/or butyl acrylate.
[24] The pressure-sensitive adhesive sheet according to any one of [20] to [23] above, which is for use as an optically transparent pressure-sensitive adhesive sheet.
[25] The release film according to any one of the above [1] to [19], which is for a display.
[26] The release film according to any one of [1] to [19] above, which is for a foldable display.
[27] A method for using the pressure-sensitive adhesive sheet according to any one of the above-mentioned [20] to [23], comprising peeling off the other release film and then attaching the exposed surface of the pressure-sensitive adhesive layer to an optical member.
[28] A method for using the pressure-sensitive adhesive sheet described in [27] above, wherein the optical component is a polarizing plate or a touch sensor.

The release film of the present invention can provide a release film and film laminate that achieves extremely easy peeling properties for various adhesives while being less susceptible to changes in the peeling properties of the release layer due to blocking.

An example of an embodiment of the present invention will be described in detail below. However, the present invention is not limited to the embodiment described below, and can be modified as desired without departing from the gist of the present invention.

<<<<Release film>>>
A release film according to an embodiment of the present invention (hereinafter, sometimes referred to as "the present release film") is a release film having a resin layer (A) on one side of a base film and a resin layer (B) on the other side. The release film is preferably a rolled-up release film (release film roll) and is preferably stored in the form of a release film roll. In this case, the release layer (A) may be disposed on either the inside or outside of the roll.

In this release film, the resin layer (A) on one side is characterized by containing a silicone resin-based release agent. The thickness of the resin layer (A) is 0.2 to 2.0 μm, and the elastic modulus of the resin layer (A) at 25° C., measured using a nanoindenter device, is preferably 500 MPa or less. The resin layer (B) on the other film surface is characterized by containing a non-silicone resin-based release agent.
When the release film having the above-mentioned structure is rolled, the surface of the resin layer (A) is superimposed on the surface of the resin layer (B), and at that time, the resin layer (B) reduces damage caused by adhesion to the surface of the resin layer (A), suppresses blocking, and prevents the resin layer (A) from peeling heavily and the deterioration of the surface appearance at the lower winding part of the roll where more pressure is applied to the film. In addition, the resin layer (A) realizes ultra-light peelability, but also has good adhesion to the base film because it does not substantially contain particles, and further, there is no particle shedding, so migration to adhesive tape, etc. can be reduced.

<<Base film>>
The base film in the present release film is not particularly limited in material as long as it has a film shape. For example, it may be made of paper, resin, metal, etc. Among these, it is preferable to use a resin from the viewpoint of mechanical strength and flexibility.
Examples of the resin substrate film include films formed from polymers such as polyethylene, polypropylene, polyester, polystyrene, polycarbonate, polyethersulfone, polyamide, polyimide, etc. Furthermore, as long as it is possible to form a film, it may be a mixture of these materials (polymer blend) or a composite of the structural units (copolymer).
Among the above-listed films, polyester films are particularly preferred because of their excellent physical properties such as heat resistance, flatness, optical properties, and strength.

<Polyester film>
The polyester film constituting the laminated film of the present invention may be a single layer or a multilayer, and may be a multilayer of four or more layers other than a two-layer or three-layer structure, as long as it does not exceed the gist of the present invention, and is not particularly limited. In the present invention, a polyester film having at least a three-layer structure is preferable. As the polyester film, a biaxially oriented polyester film is preferable from the viewpoints of thinning and dimensional stability.

The polyester used in the present invention may be a homopolyester or a copolymer polyester. In the case of a homopolyester, it is preferable to use one obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of aromatic dicarboxylic acids include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of aliphatic glycols include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. A representative polyester is polyethylene terephthalate. On the other hand, examples of the dicarboxylic acid component of the copolymer polyester include one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (e.g., p-oxybenzoic acid), and examples of the glycol component include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 4-cyclohexanedimethanol, and neopentyl glycol.

In the case of copolymer polyester, examples include those obtained by polycondensation of a dicarboxylic acid component and a glycol component. Examples of the dicarboxylic acid component include one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, oxycarboxylic acid (e.g., p-oxybenzoic acid, etc.), and examples of the glycol component include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 4-cyclohexanedimethanol, neopentyl glycol, and the like. The copolymer polyester is preferably a copolymer containing 30 mol % or less of a third component based on the total of the dicarboxylic acid component and the glycol component.
In addition, the main component resin means the resin that has the largest mass proportion among the resins constituting the present polyester film, and means a resin that accounts for 50 mass% or more, 75 mass% or more, 90 mass% or more, or 100 mass% of the resins constituting the present polyester film.

There are no particular limitations on the polymerization catalyst for the polyester film, and conventionally known compounds can be used, such as antimony compounds, titanium compounds, germanium compounds, manganese compounds, aluminum compounds, magnesium compounds, and calcium compounds. Among these, titanium compounds and germanium compounds are preferred because they have high catalytic activity, can be polymerized in small amounts, and have a low amount of metal remaining in the film, resulting in high film brightness. Furthermore, titanium compounds are even more preferred because germanium compounds are expensive.

In the case of polyesters using a titanium compound, the titanium element content is preferably 50 ppm or less, more preferably 1 to 20 ppm, and even more preferably in the range of 2 to 10 ppm. If the titanium compound content is too high, the polyester may be deteriorated in the melt extrusion process, resulting in a film with a strong yellowish tinge. If the content is too low, the polymerization efficiency may be poor, leading to increased costs and inability to obtain a film with sufficient strength.
In addition, when using a polyester containing a titanium compound, it is preferable to use a phosphorus compound to reduce the activity of the titanium compound in order to suppress deterioration during the melt extrusion process. As the phosphorus compound, orthophosphoric acid is preferable in consideration of the productivity and thermal stability of the polyester. The phosphorus element content is preferably in the range of 1 to 300 mass ppm, more preferably 3 to 200 mass ppm, and even more preferably 5 to 100 mass ppm relative to the amount of polyester to be melt extruded. If the content of the phosphorus compound is equal to or less than the upper limit, gelation or foreign matter will not occur, and if it is equal to or more than the lower limit, the activity of the titanium compound can be sufficiently reduced, coloration can be suppressed, and a yellowish film will not be formed.

In order to suppress the amount of precipitation of oligomer components, the film may be produced using polyester with a low content of oligomer components as the raw material. Various known methods can be used to produce polyester with a low content of oligomer components, such as a method of solid-phase polymerization after polyester production.

In addition, the amount of oligomer components precipitated may be suppressed by forming the polyester film into a three or more layer structure and forming the outermost layer of the polyester film from a polyester raw material having a low content of oligomer components. The polyester may also be obtained by melt polycondensation under reduced pressure at a higher reaction temperature after esterification or transesterification.

It is also possible to incorporate an ultraviolet absorbing agent into the polyester film in order to improve the weather resistance of the film and prevent deterioration of the adherend (e.g. liquid crystal). There are no particular limitations on the ultraviolet absorbing agent, so long as it is a compound that absorbs ultraviolet light and can withstand the heat applied during the polyester film manufacturing process.

There are organic and inorganic UV absorbers as UV absorbents, with organic UV absorbers being preferred from the viewpoint of transparency. There are no particular limitations on organic UV absorbers, and examples include cyclic imino esters, benzotriazoles, and benzophenones. From the viewpoint of durability, cyclic imino esters and benzotriazoles are more preferred. It is also possible to use two or more types of UV absorbers in combination.

Particles can be blended into the polyester layer of the polyester film for the main purpose of imparting slipperiness and preventing scratches during each process. When blending particles, the type of particles to be blended is not particularly limited as long as they are particles that can impart slipperiness. Specific examples include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, zirconium oxide, and titanium oxide, and organic particles such as acrylic resin, styrene resin, urea resin, phenolic resin, epoxy resin, and benzoguanamine resin. In addition, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester manufacturing process can also be used. Among these, silica particles and calcium carbonate particles are particularly preferred because they are effective even in small amounts.

The average particle size of the particles is preferably in the range of 0.01 to 5 μm, more preferably 0.03 to 4 μm, and even more preferably 0.05 to 3.0 μm. If the average particle size is equal to or less than the upper limit, the haze of the film is kept low and the film has good slip properties.

Furthermore, the particle content in the polyester layer of the polyester film is preferably 5% by mass or less, more preferably in the range of 0.001 to 3% by mass, even more preferably 0.01 to 1% by mass, and particularly preferably 0.05 to 0.5% by mass. When there are no particles or only a small amount of particles, the film becomes highly transparent and a good film is obtained, but in order to prevent a decrease in slipperiness, it may be necessary to take measures such as adding particles to the coating layer to improve slipperiness. Furthermore, when the particle content is equal to or less than the above upper limit, the haze does not become high and sufficient film transparency can be ensured.

There is no particular limitation on the shape of the particles used, and any of spherical, lumpy, rod-like, flat, etc. can be used, and there are no particular limitations on the hardness, specific gravity, color, etc. Two or more types of these particles may be used in combination as necessary.

The method of adding particles to the polyester layer is not particularly limited, and any conventionally known method can be used. For example, the particles can be added at any stage in the production of the polyester that constitutes each layer, but it is preferable to add the particles after the esterification or transesterification reaction is completed.

The polyester film may have a multi-layer structure of two or more layers, but a three-layer structure is preferable. In a three-layer structure, as described below, particles may be contained in the polyester layers (surface layers) on both surfaces, and particles may not be contained in the middle layer. Therefore, the transparency of the polyester film can be increased while improving the slipperiness and blocking resistance. The polyesters constituting each layer are as described above.

In addition, when the polyester film has a multi-layer structure of two or more layers, the average particle size of the particles used in the polyester layer (typically, the polyester layer on the side on which the release layer is not provided) on the side (opposite release surface) opposite to the surface on which the release layer is provided is preferably 1 to 6 μm, more preferably 2 to 5 μm, and particularly preferably 3 to 5 μm. The content of the particles in the polyester layer is, for example, 0.03 to 1.0 mass%, preferably 0.3 to 1.0 mass%, more preferably 0.4 to 1.0 mass%, and particularly preferably 0.4 to 0.8 mass%. By simultaneously satisfying the above average particle size and addition amount, the maximum cross-sectional height (Rt) of the opposite release surface becomes large and has a moderate uneven shape, and the release film can achieve both blocking prevention and releasability.
Even when the polyester film is composed of a single layer, the single polyester layer may contain particles from the viewpoints of anti-blocking resistance and releasability, and the average particle size and the amount of added particles may be within the ranges described above.

In a two-layer or more polyester film, the polyester layer (surface layer) on the side on which the release layer is provided may or may not contain particles, but it is preferable for it to contain particles from the viewpoint of slipperiness, etc. The particle content (mass %) in the polyester layer (surface layer) on the side on which the release layer is provided is preferably less than the particle content (mass %) in the polyester layer on the side opposite to the side on which the release layer is provided (anti-release side). Specifically, the particle content (mass %) in the polyester layer on the side on which the release layer is provided is preferably in the range of 0.001 to 0.8 mass %, more preferably 0.01 to 0.5 mass %, and even more preferably 0.02 to 0.2 mass %.

In addition to the particles described above, conventionally known ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc. may be added to the polyester film of the present invention as necessary.

The thickness of the polyester film in the present invention is not particularly limited as long as it is within the range that can be formed into a film, but is preferably 10 to 300 μm, more preferably 15 to 200 μm, even more preferably 25 to 125 μm, and most preferably 38 to 75 μm.

<Method of producing polyester film>
Next, a specific example of the production of a polyester film will be described, but the production method is not limited to the following production example. For example, when producing a biaxially oriented polyester film, the above-mentioned polyester raw material is first melt-extruded from a die using an extruder, and the molten sheet is cooled and solidified by a cooling roll to obtain an unstretched sheet. In this case, it is preferable to increase the adhesion between the sheet and the rotating cooling drum in order to improve the flatness of the sheet, and an electrostatic application adhesion method or a liquid application adhesion method is preferably adopted. Next, the obtained unstretched sheet is stretched in one direction by a roll or tenter type stretching machine. The stretching temperature is usually 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Next, in the direction perpendicular to the first-stage stretching direction, the sheet is stretched at usually 70 to 170°C, and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Subsequently, a method of performing heat treatment under tension or relaxation of 30% or less at a temperature of 180 to 270°C to obtain a biaxially oriented film can be mentioned. In the above stretching, a method of stretching in one direction in two or more stages can be adopted. In that case, it is preferable to perform the stretching so that the final stretch ratios in both directions are each within the above range.

In addition, simultaneous biaxial stretching can also be used to produce polyester films. In the simultaneous biaxial stretching method, the unstretched sheet is simultaneously stretched and oriented in the machine direction and width direction under temperature control, usually at 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is usually 4 to 50 times, preferably 7 to 35 times, more preferably 10 to 25 times in area. Then, the sheet is heat-treated under tension or relaxation of 30% or less at a temperature of 170 to 270°C to obtain a stretched and oriented film. As for the simultaneous biaxial stretching device employing the above-mentioned stretching method, a conventionally known stretching method such as a screw method, a pantograph method, or a linear drive method can be used.

<<Resin layer (A)>>
Next, the formation of the resin layer (A) constituting the release film in the present invention will be described.

The resin layer (A) is a layer formed by curing a resin layer (A) composition whose main component is a curable silicone resin, and is disposed on at least one side of the above-mentioned base film. The resin layer (A) can also be said to be a release layer containing a cured product formed by curing the resin layer (A) composition.

The above-mentioned "main component resin" means the resin that has the largest mass proportion among the resins constituting this resin layer (A) composition, and is assumed to account for 50 mass % or more, or 75 mass % or more, or 90 mass % or more, or 100 mass % of the resins constituting this resin layer (A) composition.

It is preferable that the resin layer (A) in the present invention contains a curable silicone resin.

The curable silicone resin may be a resin whose main component is a curable silicone resin, or a modified silicone obtained by graft polymerization with an organic resin such as an acrylic resin, a urethane resin, an epoxy resin, or an alkyd resin. In addition, when the adhesive layer is a silicone adhesive, it is preferable that the adhesive layer contains a fluorosilicone resin.

As the type of curable silicone resin, any of the existing curing reaction types, such as heat curable types such as addition type and condensation type, and electron beam curable types such as ultraviolet curable types, can be used, and multiple types of curable silicone resins may be used in combination. Furthermore, there is no particular restriction on the form of application of the curable silicone resin when forming the resin layer (A), and it may be in any of the form of a solution in an organic solvent, a solvent-free form, or an aqueous emulsion form.

Solventless curable silicone is a silicone with a viscosity that allows it to be applied without diluting it with a solvent, and is a silicone resin with a relatively low molecular weight that is made up of short polysiloxane chains.
On the other hand, solvent-based curable silicones are silicone resins that are so viscous that they cannot be applied unless they are diluted with a solvent, and have a relatively high molecular weight compared to solventless curable silicones.
From the viewpoints of providing good adhesion to the substrate film, providing a uniform coat appearance without coating unevenness, and facilitating adjustment of the thickness of the resin layer (A), solvent-curable silicones are preferred.

Although there is no limitation on the type of silicone resin used in the present invention, it is preferable to use a curable silicone resin containing an alkenyl group in the present invention from the viewpoint of excellent release properties such as light peelability. As the curable silicone resin containing an alkenyl group, a diorganopolysiloxane represented by the following general formula (1) can be exemplified.
R _(3-a) X _a SiO-(RXSiO) _m -(R ₂ SiO) _n -SiX _a R _(3-a) ...(1)

In general formula (1), R is a monovalent hydrocarbon group having 1 to 10 carbon atoms, and X is an organic group containing an alkenyl group. a is an integer from 0 to 3, preferably 1, and m is 0 or more, but when a=0, m is 2 or more, and m and n are numbers that satisfy 100≦m+n≦20000, and the above formula does not mean a block copolymer. R is a monovalent hydrocarbon group having 1 to 10 carbon atoms, and specific examples include alkyl groups such as methyl, ethyl, propyl, and butyl groups, cycloalkyl groups such as cyclohexyl groups, and aryl groups such as phenyl and tolyl groups, with methyl and phenyl groups being particularly preferred. X is an alkenyl-containing organic group having 2 to 10 carbon atoms, and specific examples thereof include a vinyl group, an allyl group, a hexenyl group, an octenyl group, an acryloylpropyl group, an acryloylmethyl group, a methacryloylpropyl group, a cyclohexenylethyl group, and a vinyloxypropyl group. Of these, a vinyl group, a hexenyl group, and the like are particularly preferred. Specific examples include a dimethylsiloxane-methylhexenylsiloxane copolymer capped at both molecular chain terminals with trimethylsiloxy groups (96 mol % dimethylsiloxane units, 4 mol % methylhexenylsiloxane units), a dimethylsiloxane-methylhexenylsiloxane copolymer capped at both molecular chain terminals with dimethylvinylsiloxy groups (97 mol % dimethylsiloxane units, 3 mol % methylhexenylsiloxane units), and a dimethylsiloxane-methylhexenylsiloxane copolymer capped at both molecular chain terminals with dimethylhexenylsiloxy groups (95 mol % dimethylsiloxane units, 5 mol % methylhexenylsiloxane units).

Next, the polyorganosiloxane containing SiH groups, which is necessary to react with the curable silicone resin containing alkenyl groups to form a stronger silicone release layer, is an organohydrogenpolysiloxane having at least two, and preferably three or more, hydrogen atoms bonded to silicon atoms in one molecule, and linear, branched, cyclic, etc. can be used, and examples of the compound represented by the following general formula (2) include, but are not limited to, these.
HbR ¹ _(3-b) SiO-(HR ¹ SiO) _x -(R ¹ ₂ SiO) _y -SiR ¹ _(3-b) H _b ...(2)

In general formula (2), ^R1 is a monovalent hydrocarbon group having 1 to 6 carbon atoms that does not contain an aliphatic unsaturated bond. b is an integer from 0 to 3, and x and y are each an integer. Specific examples include methylhydrogenpolysiloxane capped at both molecular chain terminals with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer capped at both molecular chain terminals with trimethylsiloxy groups, methylhydrogenpolysiloxane capped at both molecular chain terminals with dimethylhydrogensiloxy groups, and dimethylsiloxane-methylhydrogensiloxane copolymer capped at both molecular chain terminals with dimethylhydrogensiloxy groups.

Specific examples of commercially available silicone resins that can be used in the present invention include KS-774, KS-775, KS-778, KS-779H, KS-847H, KS-856, X-62-2422, X-62-2461, X-62-1387, X-62-5039, and X-6 2-5040, KNS-3051, X-62-1496, KNS320A, KNS316, X-62-1574A/B, X-62-7052, X-62-7028A/B, X-62-7619, X-62-7213, X-41-3035, Momentive Performance Materials' YSR-3022, TPR-67 00, TPR-6720, TPR-6721, TPR6500, TPR6501, UV9300, UV9425, XS56-A2775, XS56-A2982, UV9430, TPR6600, TPR6604, TPR6605, and Dow Corning Toray Co., Ltd.'s SRX357, SRX211, SD7220, and SD72 Examples of the DEHESIVE series manufactured by Wacker Asahi Kasei Silicone Co., Ltd. include, but are not limited to, DEHESIVE 636, 919, 920, 921, 924, and 929.

It is preferable to use a platinum-based catalyst for the resin layer (A) that promotes an addition reaction. Examples of this component include platinum-based compounds such as chloroplatinic acid, an alcohol solution of chloroplatinic acid, a complex of chloroplatinic acid and an olefin, and a complex of chloroplatinic acid and an alkenylsiloxane, platinum black, platinum-supported silica, and platinum-supported activated carbon.

The content of the curing catalyst in the resin layer (A) is preferably 0.5 to 500 ppm by mass, more preferably 5 ppm by mass or more, even more preferably 10 ppm by mass or more, more preferably 300 ppm by mass or less, and even more preferably 200 ppm by mass or less, relative to the curable silicone resin. When the platinum-based catalyst content in the release layer is equal to or greater than the lower limit, sufficient peeling force is obtained, the curing reaction proceeds sufficiently, and no problems such as deterioration of the coated surface condition occur. On the other hand, when the platinum-based catalyst content in the resin layer (A) is equal to or less than the upper limit, in addition to being advantageous in terms of cost, no problems occur in the process, such as increased reactivity and generation of gel foreign matter.

In addition, because addition reactions are very reactive, acetylene alcohol may be added as a reaction inhibitor in some cases. The component is an organic compound having a carbon-carbon triple bond and a hydroxyl group, preferably a compound selected from the group consisting of 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, and phenylbutynol.

The content of the reaction inhibitor is preferably 0.001 to 5.0 parts by mass, more preferably 0.01 to 2.0 parts by mass, even more preferably 0.05 to 1.5 parts by mass, and most preferably 0.1 to 0.5 parts by mass per 100 parts by mass of the total amount of the resin layer (A) composition (based on non-volatile components). By keeping it within the above range, the curable silicone resin is not inhibited from curing without reducing the reaction activity, and the easy peelability of the release film can be ensured.

A catalyst can be used in the resin layer (A) constituting the release film in order to promote hydrolysis and condensation reaction.Specific examples of the catalyst include organic acids such as acetic acid, butyric acid, maleic acid, and citric acid, inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid, and sulfuric acid, basic compounds such as triethylamine, organic metal salts such as tetrabutyl titanate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctate, dibutyltin diolate, diphenyltin diacetate, dibutyltin oxide, dibutyltin dimethoxide, dibutylbis(triethoxysiloxy)tin, and dibutyltin benzyl maleate, and fluorine-containing compounds such as KF and NH ₄ F.The above catalysts may be used alone or in combination of two or more.Among them, organic metal salts are particularly preferred in that they improve the coating film durability.

In order to adjust the release properties of the resin layer (A), various release control agents may be used in combination. When increasing the release strength, the content of organopolysiloxane resin, silica particles, silicone species with high release strength, etc. is generally adjusted appropriately in the resin layer (A) to obtain the desired release strength.

Specific examples of commercially available heavy release agents include KS-3800 and X-92-183 manufactured by Shin-Etsu Chemical Co., Ltd., and SD7292, BY24-843, and BY24-4980 manufactured by Dow Corning Toray Co., Ltd.

When the peeling force is to be lightened, various low molecular weight siloxanes are selected and the content in the resin layer (A) is appropriately adjusted so that the siloxane migration component exerts its releasing properties. Examples of low molecular weight siloxane compounds include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, etc. In addition, other compounds of these low molecular weight cyclic siloxanes include dimethylsiloxane oligomers blocked with trimethylsiloxy groups at both ends of the molecular chain; dimethylsiloxane oligomers blocked with dimethylhydroxysiloxy groups at both ends of the molecular chain; and the like. These compounds may be used in combination as necessary.

As described above, the resin layer (A) composition may contain a light release agent as necessary, and a silicone oil having a dimethylsiloxane skeleton (DM) represented by the following formula (3) and a methylphenylsiloxane skeleton (MP) represented by the following formula (4) is preferred. By having the light release agent have a dimethylsiloxane skeleton (DM) and a methylphenylsiloxane skeleton (MP), even if it migrates to the adhesive layer to be bonded, it is possible to penetrate into the adhesive layer, and the decrease in adhesive strength can be reduced. The ratio (DM:MP) of the dimethylsiloxane skeleton (DM) represented by the following formula (3) and the methylphenylsiloxane skeleton (MP) represented by the following formula (4) is preferably in the range of 98:2 to 70:30 in molar ratio, more preferably in the range of 95:5 to 80:20, and particularly preferably in the range of 92:8 to 85:15. By setting DM:PM within the above range, the releasability of this release film can be ensured.
The light release agent preferably has a mass average molecular weight of less than 10,000. When the mass average molecular weight of the light release agent is less than 10,000, this is advantageous in terms of migration and light release properties.

These low molecular weight siloxane compounds are typically contained in the silicone resin as migratory components at 0.1 to 15.0% by mass, preferably 0.5 to 10.0% by mass, and more preferably 0.5 to 5.0% by mass, to achieve the desired light release. If the content is 0.1% by mass or more, the migratory components are sufficient to provide sufficient releasability, and if the content of low molecular weight siloxane is 15.0% by mass or less, the migratory components do not precipitate excessively, eliminating concerns about process contamination.

The resin layer (A) composition may contain a dilution solvent as necessary. Examples of dilution solvents include aromatic hydrocarbons such as toluene, aliphatic hydrocarbons such as hexane, heptane, and isooctane, esters such as ethyl acetate and butyl acetate, ketones such as methyl ethyl ketone (MEK) and isobutyl methyl ketone, alcohols such as ethanol and 2-propanol, and ethers such as diisopropyl ether and dibutyl ether. These are preferably used alone or in combination, taking into account solubility, coatability, boiling point, and the like.

In order to improve the coating adhesion to the film, it is preferable to use an organosilicon compound represented by the following general formula (5) in the resin layer (A).
Si(X) _d (Y) _e (R ¹ ) _f ...(5)
[In the above formula, X is an organic group having at least one selected from an epoxy group, a mercapto group, a (meth)acryloyl group, an alkenyl group, a haloalkyl group, and an amino group; ^R1 is a monovalent hydrocarbon group having 1 to 10 carbon atoms; Y is a hydrolyzable group; d is an integer of 1 or 2; e is an integer of 2 or 3; f is an integer of 0 or 1; and d+e+f=4.]

The organosilicon compound represented by the general formula (5) can be one having two hydrolyzable groups Y (D unit source) or three hydrolyzable groups Y (T unit source) that can form a siloxane bond by hydrolysis and condensation reaction.

In formula (5), the monovalent hydrocarbon group R ¹ has 1 to 10 carbon atoms, and is preferably a methyl group, an ethyl group, or a propyl group.

In the general formula (5), examples of the hydrolyzable group Y include the following: methoxy, ethoxy, butoxy, isopropenoxy, acetoxy, butanoxime, and amino groups. These hydrolyzable groups may be used alone or in combination. The use of methoxy or ethoxy groups is particularly preferred because they provide good storage stability to the coating material and have suitable hydrolyzability.

Specific examples of organosilicon compounds contained in the resin layer (A) include vinyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, 5-hexenyltrimethoxysilane, p-styryltrimethoxysilane, trifluoropropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiisopropenoxysilane, etc.

It is preferable that the resin layer (A) does not substantially contain particles. By substantially not containing particles in the resin layer (A), it is possible to stabilize the peeling characteristics while reducing migration. Incidentally, "substantially not containing" means that the resin layer (A) may contain particles in a small amount so long as it does not impair the effects of the present invention, and may contain, for example, particles that are inevitably mixed in. The specific particle content in the present resin layer (A) (A layer) is, for example, less than 0.05% by mass, preferably less than 0.01% by mass, and more preferably less than 0.0001% by mass, based on the non-volatile components. The range of the particle content in the present resin layer (A) composition based on the non-volatile components is also the same as the above-mentioned particle content.

Furthermore, within the scope of the present invention, the resin layer (A) composition may contain, as necessary, antifoaming agents, coatability improvers, thickeners, organic lubricants, antistatic agents, conductive agents, ultraviolet absorbers, antioxidants, foaming agents, dyes, pigments, etc.

The number average molecular weight (Mn) of the curable silicone resin is preferably 9000 or more and 350000 or less. When the number average molecular weight (Mn) of the curable silicone resin is set to the above lower limit value or more, when the adhesive layer is laminated on the release film, the amount of low molecular weight silicone resin that dissolves or migrates to the adhesive layer can be reduced, and the resin layer (A) can be applied thickly to easily obtain a light peeling effect. On the other hand, when the number average molecular weight (Mn) of the curable silicone resin is set to the above upper limit value or less, the viscosity increases and the fluidity of the resin layer (A) composition is prevented from decreasing. Therefore, when the resin layer (A) composition is applied, it is possible to prevent streaky coating unevenness from occurring, and to easily smooth the resin layer (A) surface.
From this viewpoint, the number average molecular weight (Mn) of the curable silicone resin is preferably 9000 or more, more preferably 10000 or more, even more preferably 20000 or more, and even more preferably 30000 or more. On the other hand, it is preferably 350000 or less, more preferably 50000 or less, and even more preferably 40000 or less.

From the same viewpoint as the number average molecular weight, the mass average molecular weight (Mw) of the curable silicone resin is preferably 10,000 to 500,000, more preferably 20,000 or more, even more preferably 50,000 or more, and especially preferably 80,000 or more, and more preferably 250,000 or less, and even more preferably 100,000 or less.

The ratio (Mw/Mn) of the mass average molecular weight (Mw) to the number average molecular weight (Mn) of the curable silicone resin is preferably 1.7 to 3.5, more preferably 1.9 to 3.0, and even more preferably 2.0 to 3.0. By satisfying this range, it is expected that the crosslinking reaction will proceed efficiently.
The number average molecular weight (Mn) and the mass average molecular weight (Mw) are values obtained by gel permeation chromatography (GPC) measurement based on polystyrene standard. A specific measurement method is to measure a chromatogram using a GPC measurement device, and to obtain the number average molecular weight (Mn) and the mass average molecular weight (Mw) based on a calibration curve using standard polystyrene. Specifically, 4 mg of the sample for measurement is dissolved in 4 mL of THF to prepare a measurement solution, and 100 μL of the measurement solution is injected into the GPC measurement device for measurement. Tetrahydrofuran (THF) was used as the eluent. For the analysis, "Ecosec8320" manufactured by Tosoh Corporation was used, and "TSKgel guardcolumn HXL-L" manufactured by Tosoh Corporation was used as a guard column, and four "TSKgel GMHXL" manufactured by Tosoh Corporation were used in conjunction as a column. The analysis was performed under conditions of an oven temperature of 40° C. and a THF flow rate of 1.0 mL/min, and RI was used for detection.

The curable silicone resin may be a combination of two or more types of curable silicone resins. In that case, it is preferable that the average of the number average molecular weight (Mn) and mass average molecular weight (Mw) of the two or more types of curable silicone resins is within the above range. The average here refers to a weighted average weighted by the mass of each resin. In addition, when a base agent and a silicone crosslinking agent are used as the curable silicone resin, it is preferable that the mass average molecular weight (Mn), number average molecular weight (Mw), and Mw/Mn of the base agent are within the above range.

The viscosity of the curable silicone resin at 25° C. when adjusted to 15% by mass by dilution with n-heptane solvent is preferably 1 to 400 mcps, more preferably 5 to 300 mcps, and even more preferably 10 to 200 mcps.
If the viscosity of the curable silicone resin is 1 mcps or more, then the appropriate viscosity of the coating liquid suppresses repelling, and a uniform coat appearance with high visibility is obtained, which is preferable. If the viscosity is 400 mcps or less, then the fluidity of the resin layer (A) composition can be maintained, and the occurrence of streaky coating unevenness when the resin layer (A) composition is applied can be suppressed, and the resin layer (A) surface can be made smooth.
The viscosity was measured by diluting the curable silicone resin with n-heptane to 15% by mass, and measuring the viscosity of the solution at 25° C. using an E-type viscometer (TVE-22L, manufactured by Toki Sangyo Co., Ltd.).

When the curable silicone resin has alkenyl groups in the silicone resin, the content of alkenyl groups is preferably 0.4 to 2.5 mol%, more preferably 0.5 to 2.0 mol%, and even more preferably 0.5 to 1.5 mol% relative to the total amount of siloxane components. By satisfying this range, a certain amount or more of alkenyl groups is contained, so that the release layer is sufficiently cured, while the amount of alkenyl groups is not excessive, so that the peel force after exposure to air does not become heavy.

When the curable silicone resin has Si-H groups in the silicone resin, the content of Si-H groups is preferably 0.8 to 2.5 mol%, more preferably 0.8 to 2.0 mol%, and even more preferably 1.0 to 2.0 mol% of the total amount of siloxane components. By satisfying this range, a certain amount or more of Si-H groups is contained, so that the release layer is sufficiently cured, while the amount of Si-H groups is not excessive, so that reaction with the adhesive layer is prevented, and heavy peeling of the release film can be suppressed.

The curable silicone resin may contain alkenyl groups and Si-H groups (also simply referred to as "H groups") in the side chains and/or terminals of the main chain consisting of siloxane bonds in the same structure. In that case, it is preferable that the content of alkenyl groups and Si-H groups is within the above range.

The total content of siloxane components in the release layer composition can be measured, for example, by ¹ H-NMR from the integral ratio of the dimethylsiloxane unit in the main chain to the other units. The vinyl group and Si-H group contents indicate the ratio to the total amount of functional groups bonded to the siloxane chain, and can be evaluated by measuring ¹ H-NMR. However, the method is not limited to this.

From the viewpoints of achieving ultra-light release, preventing blocking, and suppressing increased migration, the thickness of the resin layer (A) is preferably in the range of 0.2 to 2.0 μm, more preferably 0.4 to 1.5 μm, even more preferably 0.4 to 1.2 μm, and most preferably 0.4 to 1.0 μm. If the thickness of the resin layer (A) is less than 0.2 μm, it is difficult to achieve light release of the resin layer (A) even if the elastic modulus of the resin layer (A) is within a specified range, as described below. Furthermore, if the thickness is greater than 2.0 μm, the migration of the resin layer (A) components to the adhesive tape or the like may increase, or blocking may not be sufficiently prevented.

The elastic modulus of the resin layer (A) at 25°C is preferably 500 MPa or less, more preferably 65 to 400 MPa, and even more preferably 80 to 300 MPa. By satisfying these ranges, good peelability from the adhesive layer can be exhibited. The elastic modulus of the resin layer (A) can be adjusted by the type of silicone resin used and the thickness of the resin layer (A), and for example, the thinner the resin layer (A), the higher the elastic modulus tends to be. The elastic modulus referred to here is a value measured by a nanoindenter.

The normal peel strength of the resin layer (A) is preferably 5 g/25 mm or less, more preferably 0.1 to 4 g/25 mm, and even more preferably in the range of 0.5 to 3 g/25 mm. When the normal peel strength is 5 g/25 mm or less, good peelability can be exhibited even for adhesive layers whose elastic modulus is reduced due to the increase in size and thickness of optical components. On the other hand, when the normal peel strength exceeds 5 g/25 mm, peeling from the adhesive layer may be difficult, and the adhesive layer may be transferred to the release film side due to deformation or breakage of the adhesive layer.

The residual adhesion rate of the resin layer (A) is an index of the migration of migration components derived from the resin layer (A) to the adhesive tape or the like to be laminated. In the case of a resin layer (A) with high migration, many migration components adhere to the laminated evaluation film, so the peeling force of the adhesive tape to be laminated to the evaluation film becomes small, and the residual adhesion rate (%) also decreases. Therefore, it is good that the residual adhesion rate (%) is high, preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. If the residual adhesion rate is 80% or more, it can be considered that there is no problem in practical use.

The heavy peeling rate of the resin layer (A) after pressing is preferably 100% or less, more preferably 50% or less, and even more preferably 20% or less. If the heavy peeling rate after pressing is 100% or less, when this release film is wound into a roll, the heavy peeling of the resin layer (A) at the lower winding part of the roll where pressure is applied by the film is kept small, and no defects due to heavy peeling occur. The method for calculating the heavy peeling rate after pressing is as described in the examples.

The resin layer (A) may be formed by in-line coating, in which the film surface is treated during the film production process, or by offline coating, in which a coating is applied outside the system onto a film that has already been produced, but it is more preferable that the resin layer be formed by offline coating.

As a method for providing a resin layer (A) on a film, conventional coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating, etc. can be used.

The film constituting the release film in the present invention may be subjected to a surface treatment such as corona treatment or plasma treatment in advance.

There are no particular limitations on the curing conditions when forming the resin layer (A). When forming the resin layer (A) by offline coating, the heat treatment is usually performed at 80°C or higher for 10 seconds or more, preferably at 100 to 200°C for 3 to 40 seconds, more preferably at 120 to 190°C for 3 to 40 seconds, and even more preferably at 150 to 180°C for 3 to 40 seconds.

If necessary, heat treatment may be combined with irradiation of active energy rays such as ultraviolet light. As the energy source for curing by irradiation of active energy rays, known devices and energy sources can be used. For example, light sources include fusion (H) lamps, metal halide lamps, high-pressure mercury lamps (ozone generating type, ozone-less type), UV-LEDs, etc.

The active energy ray irradiation is not particularly limited, but in the case of ultraviolet irradiation, the cumulative light amount is in the range of 10 to 3000 mJ/cm ² , preferably 50 to 2000 mJ/cm ² , and more preferably 100 to 1000 mJ/cm ^2. By setting the cumulative light amount of ultraviolet irradiation within the above range, curing of the resin layer (A) is promoted, while by not irradiating excessively, the resin layer (A) is not destroyed and the peeling force after irradiation can be prevented from becoming heavy.

In the release film of the present invention, it is preferable that the surface resistivity of at least one of the surfaces of the resin layer (A) or the resin layer (B) is 1× ¹⁰ Ω/□ or less. The lower the surface resistivity of the resin layer (A) or the resin layer (B), the better the antistatic property is, and the charging of the film in the process can be suppressed, thereby preventing the adhesion of foreign matter and the like.

The center line average roughness (Ra(A)) of the resin layer (A) surface is preferably 30 nm or less. A center line average roughness (Ra(A)) of 30 nm or less is preferable because it enables ultra-light peeling. With regard to (Ra(A)), 25 nm or less is more preferable, and 20 nm or less is particularly preferable. On the other hand, with regard to the lower limit, a value of 5 nm or more is preferable from the viewpoint of film handling.

<<Resin layer (B)>>
The resin layer (B) in the present invention will be described below.

The resin layer (B) constituting the release film in the present invention is provided on the surface of the base film opposite to the surface on which the resin layer (A) is provided, and may be a resin layer (B) containing a non-silicone-based release agent, and more preferably is a resin layer (B) containing a non-silicone-based release agent and having antistatic properties.

The non-silicone release agent used in the resin layer (B) is not particularly limited as long as it is a release agent other than a silicone compound, and any conventionally known release agent can be used. Examples of such release agents include long-chain alkyl group-containing compounds, fluorine compounds, and waxes.
Among these, long-chain alkyl compounds and waxes are preferred from the viewpoint of less staining and excellent blocking reduction, and long-chain alkyl compounds are particularly preferred from the viewpoint of blocking reduction. These release agents may be used alone or in combination.

Silicone compounds are compounds that have siloxane bonds in the molecule, and also include those that have various functional groups on the side chains and/or ends of the main chain consisting of siloxane bonds. Examples include ether groups, hydroxyl groups, amino groups, epoxy groups, carboxylic acid groups, halogen groups such as fluorine, perfluoroalkyl groups, and hydrocarbon groups (alkyl groups, alkenyl groups, aryl groups, various aromatic groups, etc.). If the resin layer (B) contains a silicone compound, it will be strongly blocked with the resin layer (A), causing deformation of the surface of the resin layer (A), etc., and the release properties of the resin layer (A) will deteriorate, making it difficult to use it in this release film.

A long-chain alkyl group-containing compound is a compound having a straight-chain or branched alkyl group with a carbon number of usually 6 or more, preferably 8 or more, and more preferably 12 or more. Examples of the alkyl group include hexyl, octyl, decyl, lauryl, octadecyl, and behenyl. Examples of compounds having an alkyl group include various long-chain alkyl group-containing polymer compounds, long-chain alkyl group-containing amine compounds, long-chain alkyl group-containing ether compounds, and long-chain alkyl group-containing quaternary ammonium salts. Considering heat resistance and staining resistance, a polymer compound is preferable. In addition, from the viewpoint of obtaining effective releasability, a polymer compound having a long-chain alkyl group in the side chain is more preferable.

A polymer compound having a long-chain alkyl group on the side chain can be obtained by reacting a polymer having a reactive group with a compound having an alkyl group capable of reacting with the reactive group. Examples of the reactive group include hydroxyl groups, amino groups, carboxyl groups, and acid anhydrides. Examples of compounds having these reactive groups include polyvinyl alcohol, polyethyleneimine, polyethyleneamine, reactive group-containing polyester resins, and reactive group-containing poly(meth)acrylic resins. Among these, polyvinyl alcohol is preferable in terms of releasability and ease of handling.

Examples of compounds having an alkyl group capable of reacting with the reactive group include long-chain alkyl group-containing isocyanates such as hexyl isocyanate, octyl isocyanate, decyl isocyanate, lauryl isocyanate, octadecyl isocyanate, and behenyl isocyanate, long-chain alkyl group-containing acid chlorides such as hexyl chloride, octyl chloride, decyl chloride, lauryl chloride, octadecyl chloride, and behenyl chloride, long-chain alkyl group-containing amines, and long-chain alkyl group-containing alcohols. Among these, taking into consideration releasability and ease of handling, long-chain alkyl group-containing isocyanates are preferred, and octadecyl isocyanate is particularly preferred.

Polymers having long-chain alkyl groups on their side chains can also be obtained by polymerization of long-chain alkyl (meth)acrylates or copolymerization of long-chain alkyl (meth)acrylates with other vinyl group-containing monomers. Examples of long-chain alkyl (meth)acrylates include hexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, octadecyl (meth)acrylate, and behenyl (meth)acrylate.

Waxes are waxes selected from natural waxes, synthetic waxes, and waxes blended with these. Natural waxes include vegetable waxes, animal waxes, mineral waxes, and petroleum waxes. Examples of vegetable waxes include candelilla wax, carnauba wax, rice wax, wood wax, and jojoba oil. Examples of animal waxes include beeswax, lanolin, and whale wax. Examples of mineral waxes include montan wax, ozokerite, and ceresin. Examples of petroleum waxes include paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include synthetic hydrocarbons, modified waxes, hydrogenated waxes, fatty acids, acid amides, amines, imides, esters, and ketones. Examples of synthetic hydrocarbons include Fischer-Tropsch wax (also known as Sazowar wax) and polyethylene wax, as well as the following low molecular weight polymers (specifically, polymers having a viscosity number average molecular weight of 500 to 20,000): polypropylene, ethylene-acrylic acid copolymer, polyethylene glycol, polypropylene glycol, and block or grafted polyethylene glycol and polypropylene glycol. Examples of modified waxes include montan wax derivatives, paraffin wax derivatives, and microcrystalline wax derivatives. The derivatives referred to here are compounds obtained by any of the following processes, or a combination of these: refining, oxidation, esterification, and saponification. Examples of hydrogenated waxes include hydrogenated castor oil and hydrogenated castor oil derivatives.

Among the above waxes, synthetic waxes are preferred from the viewpoint of stable properties, and among these, polyethylene waxes are more preferred, with oxidized polyethylene wax being even more preferred. From the viewpoints of stability of properties such as blocking and ease of handling, the number average molecular weight (Mn) of the synthetic wax is preferably in the range of 500 to 30,000, more preferably 1,000 to 15,000, and even more preferably 2,000 to 8,000.

A fluorine compound is a compound that contains fluorine atoms. In terms of the coating appearance by in-line coating, organic fluorine compounds are preferably used, such as perfluoroalkyl group-containing compounds, polymers of olefin compounds containing fluorine atoms, and aromatic fluorine compounds such as fluorobenzene. In terms of releasability, compounds having a perfluoroalkyl group are preferable. Furthermore, compounds containing long-chain alkyl compounds as described below can also be used as fluorine compounds.

Examples of compounds having a perfluoroalkyl group include perfluoroalkyl group-containing (meth)acrylates such as perfluoroalkyl (meth)acrylate, perfluoroalkyl methyl (meth)acrylate, 2-perfluoroalkyl ethyl (meth)acrylate, 3-perfluoroalkyl propyl (meth)acrylate, 3-perfluoroalkyl-1-methylpropyl (meth)acrylate, and 3-perfluoroalkyl-2-propenyl (meth)acrylate, and polymers thereof; and perfluoroalkyl group-containing vinyl ethers such as perfluoroalkyl methyl vinyl ether, 2-perfluoroalkyl ethyl vinyl ether, 3-perfluoropropyl vinyl ether, 3-perfluoroalkyl-1-methylpropyl vinyl ether, and 3-perfluoroalkyl-2-propenyl vinyl ether, and polymers thereof. In consideration of heat resistance and contamination, a polymer is preferable. The polymer may be a single compound or a polymer of multiple compounds. In addition, from the viewpoint of releasability, the perfluoroalkyl group preferably has 3 to 11 carbon atoms. It may also be a polymer with a compound containing a long-chain alkyl compound as described below. From the viewpoint of adhesion to the substrate, a polymer with vinyl chloride is also preferred.

In forming the resin layer (B), it is preferable to contain an antistatic agent from the viewpoint of preventing adhesion of foreign matter, etc. For example, a polymer in which a compound made of thiophene or a thiophene derivative is doped with another anionic compound, a self-doped polymer having an anionic group in a compound made of thiophene or a thiophene derivative, or a polymer containing a monomer with an alkylsulfonate ion as a counter ion as a component can be used. Among these, it is more preferable to contain a compound made of thiophene or a thiophene derivative from the viewpoint of obtaining excellent antistatic performance.

Examples of compounds made of thiophene or thiophene derivatives include polymers of compounds made of thiophene or thiophene derivatives doped with other anionic compounds, and examples of self-doped polymers having anionic groups in compounds made of thiophene or thiophene derivatives include those obtained by polymerizing a compound of the following formula (6) or (7) in the presence of a polyanion.

In the above formula (6), R ¹ and R ² each independently represent a hydrogen atom or an aliphatic hydrocarbon group, alicyclic hydrocarbon group, aromatic hydrocarbon group, or the like having 1 to 20 carbon atoms.

In the above formula (7), n represents an integer from 1 to 4.

Examples of polyanions used during polymerization include poly(meth)acrylic acid, polymaleic acid, polystyrene sulfonic acid, polyvinyl sulfonic acid, etc. Methods for producing such polymers include the method described in JP-A-7-90060.

In the present invention, a compound of the above formula (7) in which n is 2 and polystyrene sulfonic acid is used as the polyanion is preferably used.

In addition, when these polyanions are acidic, they may be partially or completely neutralized. The base used for neutralization is preferably ammonia, organic amines, or alkali metal hydroxides.

Specific examples of polymers containing a monomer with an alkylsulfonate ion as a counter ion include polymers having the constituent element shown in the following formula (8) as a repeating unit. These may be homopolymers or copolymers, or may be copolymerized with multiple other components. From the viewpoint of improving antistatic properties, homopolymers are preferred.

Examples of the polymer structure include those in which, in the above formula, the substituent R ¹ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ² is -O- or -NH-, R ³ is an alkylene group having 1 to 6 carbon atoms or other structure capable of forming the structure of formula (8), at least one of R ⁴ , R ⁵ and R ⁶ is a hydrogen atom and the other substituents are an alkyl group having 1 to 3 carbon atoms or a hydroxyalkyl group in the alkyl group having 2 to 3 carbon atoms, and X ^- is an alkylsulfonate ion having an alkyl group having 1 to 4 carbon atoms.

In forming the resin layer (B), it is preferable to include a polyhydroxy compound in order to improve the coating appearance and antistatic performance. As the polyhydroxy compound, it is preferable to use one or more compounds selected from polyglycerin and alkylene oxide adducts of polyglycerin or derivatives thereof. Polyglycerin is a compound represented by the following general formula (9).

In the above formula (9), n is 2 or more, and in the present invention, n in the formula is usually in the range of 2 to 20, preferably 3 to 15, and more preferably 3 to 12.

An alkylene oxide adduct to polyglycerin has a structure in which an alkylene oxide is addition polymerized to the hydroxyl group of polyglycerin represented by the above general formula (9).

Here, the structure of the alkylene oxide added to each hydroxyl group of the polyglycerin skeleton may be different. Also, it is sufficient that the alkylene oxide or its derivative is added to at least one hydroxyl group in the molecule, and it is not necessary that the alkylene oxide or its derivative is added to all hydroxyl groups.

The alkylene oxide to be added to polyglycerin is preferably ethylene oxide or propylene oxide. If the alkylene chain of the alkylene oxide is too long, the hydrophobicity becomes strong, dispersibility in the coating liquid deteriorates, and the antistatic properties and transparency of the resin layer (B) tend to deteriorate. Ethylene oxide is particularly preferred. The number of additions is preferably in the range of 200 to 2000, more preferably 300 to 1000, and even more preferably 400 to 900, in terms of the number average molecular weight (Mn) of the final compound.

The above polyglycerols or alkylene oxide adducts of polyglycerols may be used alone or in combination of two or more types.

In order to form the resin layer (B), various conventionally known polymers can be used as binder components from the viewpoint of improving the coating appearance and transparency. Specific examples of polymers include polyester resins, urethane resins, acrylic resins, polyvinyl alcohol, vinyl chloride-vinyl acetate copolymers, etc. From the viewpoint of making the resin layer (B) stronger and reducing blocking, it is preferable to use polyester resins and urethane resins.

Examples of polyester resins that can be used include those that are made of the following polyvalent carboxylic acids and polyvalent hydroxy compounds as main components. That is, examples of polyvalent carboxylic acids that can be used include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid, 5-sodium sulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, succinic acid, trimellitic acid, trimesic acid, pyromellitic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, trimellitic acid monopotassium salt, and ester-forming derivatives thereof. Examples of polyhydric hydroxy compounds that can be used include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, and potassium dimethylolpropionate.
The polyester resin is a polycondensation product of a polyvalent carboxylic acid and a polyvalent hydroxy compound. One or more polyvalent carboxylic acids and one or more polyvalent hydroxy compounds are appropriately selected from the above-mentioned compounds, and the polyester resin is synthesized by a conventional polycondensation reaction. The polyester resin may be made into a water dispersion, and in this case, a hydrophilic functional group or the like may be appropriately introduced into the polyester resin.

A urethane resin is a polymeric compound that has urethane bonds in its molecules. Usually, urethane resins are produced by the reaction of polyols with isocyanates. Examples of polyols include polycarbonate polyols, polyester polyols, polyether polyols, polyolefin polyols, and acrylic polyols. These compounds may be used alone or in combination. The urethane resin may be a water dispersion, in which case, for example, hydrophilic functional groups may be appropriately introduced into the polyol.

Polycarbonate polyols are obtained by dealcoholization reaction between polyhydric alcohols and carbonate compounds. Examples of polyhydric alcohols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, and 3,3-dimethylolheptane. Examples of the carbonate compound include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, etc., and examples of the polycarbonate-based polyols obtained by the reaction of these compounds include poly(1,6-hexylene) carbonate, poly(3-methyl-1,5-pentylene) carbonate, etc.

Polyester polyols include polycarboxylic acids (malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, maleic acid, terephthalic acid, isophthalic acid, etc.) or their acid anhydrides and polyhydric alcohols (ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pent ... 2-methyl-1,3-propanediol, 1,6-pentanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 2-methyl-1,3-propanediol, 1,6-pentanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 2-methyl-1,3-propanediol, 1,6-pentanediol, 2-methyl-1,3-propanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 2-methyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-methyl-1,3-propane 2-ethyl-2,4-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-hexyl-1,3-propanediol, cyclohexanediol, bishydroxymethylcyclohexane, dimethanolbenzene, bishydroxyethoxybenzene, alkyldialkanolamines, lactonediols, etc.

Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, etc.

Of the above polyols, polycarbonate polyols and polyester polyols are more preferably used to improve adhesion with various functional layers.

Examples of polyisocyanate compounds used to obtain urethane resins include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and tolidine diisocyanate; aliphatic diisocyanates having an aromatic ring such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic diisocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic diisocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and isopropylidenedicyclohexyl diisocyanate. These may be used alone or in combination.

A chain extender may be used when synthesizing the urethane resin. There are no particular restrictions on the chain extender as long as it has two or more active groups that react with isocyanate groups. In general, chain extenders with two hydroxyl groups or two amino groups can be mainly used.

Examples of chain extenders having two hydroxyl groups include glycols such as aliphatic glycols such as ethylene glycol, propylene glycol, and butanediol, aromatic glycols such as xylylene glycol and bishydroxyethoxybenzene, and ester glycols such as neopentyl glycol hydroxypivalate. Examples of chain extenders having two amino groups include aromatic diamines such as tolylenediamine, xylylenediamine, and diphenylmethanediamine; aliphatic diamines such as ethylenediamine, propylenediamine, hexanediamine, 2,2-dimethyl-1,3-propanediamine, 2-methyl-1,5-pentanediamine, trimethylhexanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,8-octanediamine, 1,9-nonanediamine, and 1,10-decanediamine; and alicyclic diamines such as 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, dicyclohexylmethanediamine, isopropylidenecyclohexyl-4,4'-diamine, 1,4-diaminocyclohexane, and 1,3-bisaminomethylcyclohexane.

The urethane resin in the present invention may be one that uses a solvent as a medium, and preferably one that uses water as a medium. To disperse or dissolve the urethane resin in water, there are forced emulsification types that use an emulsifier, self-emulsification types in which hydrophilic groups are introduced into the urethane resin, and water-soluble types. In particular, self-emulsification types in which ionic groups are introduced into the urethane resin structure to form an ionomer are preferred, as they have excellent storage stability of the liquid and excellent water resistance, transparency, and adhesion of the resulting coating layer.

The ionic group to be introduced may be a carboxyl group, sulfonic acid, phosphoric acid, phosphonic acid, or quaternary ammonium salt, but a carboxyl group is preferred. Various methods can be used to introduce a carboxyl group into the urethane resin at each stage of the polymerization reaction. For example, a method of using a resin having a carboxyl group as a copolymerization component during prepolymer synthesis, or a method of using a component having a carboxyl group as one component of a polyol, polyisocyanate, or chain extender, etc. is available. In particular, a method of using a carboxyl group-containing diol and introducing a desired amount of carboxyl groups depending on the amount of this component is preferred. For example, dimethylolpropionic acid, dimethylolbutanoic acid, bis-(2-hydroxyethyl)propionic acid, bis-(2-hydroxyethyl)butanoic acid, etc. can be copolymerized with the diol used in the polymerization of the urethane resin. In addition, it is preferable to neutralize the carboxyl group with ammonia, amine, alkali metals, inorganic alkalis, etc. to make it into a salt form. Particularly preferred are ammonia, trimethylamine, and triethylamine. In such polyurethane resins, the carboxyl groups from which the neutralizing agent is removed during the drying process after coating can be used as crosslinking reaction points with other crosslinking agents, which not only provides excellent stability in the liquid state before coating, but also makes it possible to further improve the durability, solvent resistance, water resistance, blocking resistance, etc. of the resulting coating layer.

The acrylic resin is a polymer made of polymerizable monomers including acrylic and methacrylic monomers. These may be homopolymers or copolymers, or copolymers with polymerizable monomers other than acrylic and methacrylic monomers. The acrylic resin also includes copolymers of these polymers with other polymers (e.g., polyester, polyurethane, etc.). For example, block copolymers and graft copolymers. That is, the acrylic resin may be an acrylic-modified polyester resin or an acrylic-modified polyurethane resin. The acrylic resin also includes a polymer (or a mixture of polymers in some cases) obtained by polymerizing a polymerizable monomer in a polyester solution or polyester dispersion. Similarly, the acrylic resin also includes a polymer (or a mixture of polymers in some cases) obtained by polymerizing a polymerizable monomer in a polyurethane solution or polyurethane dispersion. Similarly, the acrylic resin also includes a polymer (or a mixture of polymers in some cases) obtained by polymerizing a polymerizable monomer in another polymer solution or dispersion, and these are also referred to as acrylic-modified polyester resins and acrylic-modified polyurethane resins in this specification. The polyesters and polyurethanes used in the acrylic resins can be appropriately selected from those exemplified as the polyesters and polyurethanes as the binder components described above.
The acrylic resin may contain a hydroxyl group or an amino group in order to further improve adhesion to the base film.

The above-mentioned polymerizable monomers are not particularly limited, but representative compounds include, for example, various carboxyl group-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, and citraconic acid, and their salts; various hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, monobutyl hydroxyl fumarate, and monobutyl hydroxy itaconate; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, lauryl (meth)acrylate, and the like. various nitrogen-containing compounds such as (meth)acrylamide, diacetone acrylamide, N-methylol acrylamide, or (meth)acrylonitrile; various styrene derivatives such as styrene, α-methylstyrene, divinylbenzene, or vinyl toluene; various vinyl esters such as vinyl propionate; various silicon-containing polymerizable monomers such as γ-methacryloxypropyltrimethoxysilane or vinyltrimethoxysilane; phosphorus-containing vinyl monomers; various vinyl halides such as vinyl chloride or vinylidene chloride; and various conjugated dienes such as butadiene.

In order to improve the strength of the resin layer (B), a crosslinking agent can be used in combination. The crosslinking agent can be a conventionally known material, such as an oxazoline compound, an epoxy compound, a melamine compound, an isocyanate compound, a carbodiimide compound, or an organosilicon compound. From the viewpoint of increasing the strength of the resin layer (B), a melamine compound is more preferable. It is also possible to use two or more types of crosslinking agents in combination.

The resin layer (B) in this release film may contain particles in order to improve the slipperiness of the film, but a more preferred embodiment is one in which the resin layer does not substantially contain particles. By not substantially containing particles in the resin layer (B), the release properties can be stabilized while reducing the migration of the release component.

Note that "substantially free" means that the resin layer (B) may contain particles in such a small amount that the effect of the present invention is not hindered, and may contain, for example, particles that are unavoidably mixed in. The specific particle content in the resin layer (B) is, for example, less than 0.05% by mass, preferably less than 0.01% by mass, and more preferably less than 0.0001% by mass, based on the non-volatile components. The range of the particle content in the resin layer (B) based on the non-volatile components is also the same as the above particle content.

Furthermore, within the scope of the present invention, the resin layer (B) may contain, as necessary, an antifoaming agent, a coatability improver, a thickener, an organic lubricant, an antistatic agent, an ultraviolet absorber, an antioxidant, a foaming agent, a dye, a pigment, etc.

In the resin layer (B), the content of the release agent in the non-volatile components is preferably 10 to 70% by mass. When the content of the release agent is 10% by mass or more, good blocking prevention performance is obtained.
In the case where a long-chain alkyl group-containing compound is used as a non-silicone-based release agent in the resin layer (B), the proportion of the long-chain alkyl group-containing compound in the total non-volatile components in the resin layer (B) composition is preferably in the range of 5 to 90 mass%, more preferably 10 to 70 mass%, even more preferably 20 to 60 mass%, and most preferably 20 to 40 mass%. When the proportion of the long-chain alkyl group-containing compound is in the above range, good blocking prevention performance is obtained, and by reducing the change in the release properties of the release layer due to blocking, it is possible to greatly suppress heavy peeling of the release layer in the lower winding part of the roll where more pressure is applied to the film.

When wax is used as a non-silicone release agent in the resin layer (B), the wax is preferably in the range of 5 to 90% by mass, more preferably 10 to 80% by mass, and even more preferably 25 to 70% by mass, as a proportion of the total non-volatile components in the resin layer (B). When the proportion of wax is in the above range, good blocking prevention performance is obtained, and by reducing the change in the release properties of the release layer due to blocking, the heavy peeling of the release layer at the lower winding part of the roll where more pressure is applied to the film can be greatly suppressed. In addition, when used in combination with a melamine compound, heavy peeling may progress. Therefore, when using wax, it is necessary to pay attention to the combination with a crosslinking agent, etc. On the other hand, a compound containing a long chain alkyl group is more preferable because it does not have the following problems.
Examples of preferred composition combinations include a long-chain alkyl group-containing compound and a melamine compound, a long-chain alkyl group-containing compound and an oxazoline compound, a long-chain alkyl group-containing compound and a melamine compound and an oxazoline compound, and a wax and a melamine compound and an oxazoline compound.

The reason (estimate) why wax, as a non-silicone release agent, has a higher heavy release rate than a compound containing a long-chain alkyl group depending on the combination with a crosslinking agent is thought to be as follows.
In addition to being water-repellent, wax also has oil-repellent properties, which makes it less compatible with the melamine compounds it is combined with, making the melamine compounds more likely to be repelled.
On the other hand, in the evaluation of the heavy peeling rate in the present invention, since the press treatment is performed under high temperature (40° C.) and high humidity (90% RH) in the presence of moisture, it is presumed that aggregates are easily formed on the surface of the resin layer (B) which combines wax and a melamine compound, and this improves the adhesion with the silicone release layer on the opposite side, resulting in a high heavy peeling rate.
As described above, the present invention is characterized in that a release agent is selected with an eye on the oil repellency effect, which has not been given much attention in conventional non-silicone release agents, and a release film is formed having a resin layer (B).

When a compound made of thiophene or a thiophene derivative is used as an antistatic agent in the resin layer (B), the proportion of the compound made of thiophene or a thiophene derivative in the total non-volatile components of the resin layer (B) is preferably in the range of 5 to 50% by mass, more preferably 5 to 40% by mass, and even more preferably 5 to 30% by mass. When it is in the above range, good antistatic properties can be obtained.

In the resin layer (B), the polyhydroxy compound preferably accounts for 10 to 80% by mass, more preferably 20 to 70% by mass, and even more preferably 30 to 65% by mass, of the total non-volatile components of the resin layer (B). When the content is within the above range, good antistatic properties can be obtained.

The proportion of the binder component in the total non-volatile components of the resin layer (B) is preferably in the range of 5 to 50% by mass, more preferably 5 to 40% by mass, and even more preferably 5 to 30% by mass. When the proportion of the binder component is in the above range, the strength of the resin layer (B) is good, and blocking can be reduced.

The crosslinking agent preferably accounts for 5 to 70% by mass, preferably 10 to 60% by mass, and more preferably 15 to 50% by mass of the total non-volatile components of the resin layer (B). When the crosslinking agent ratio is within the above range, the strength of the resin layer (B) is improved and blocking can be reduced.

<Characteristics of Resin Layer (B)>
The resin layer (B) in the present invention may have the following properties.

In this release film, the surface roughness (Ra(B)) of the resin layer (B) is preferably 20 nm or more, more preferably in the range of 25 to 60 nm, more preferably 30 to 55 nm, and even more preferably 38 to 50 nm. If it is 20 nm or more, blocking is less likely to occur in the rolled state after the release layer is provided. On the other hand, if the surface roughness is 60 nm or less, when this release film is wound into a roll, the unevenness of the film is not transferred to the release layer, and the release properties of the release layer are maintained.

The thickness of the resin layer (B) is preferably 0.005 to 0.25 μm, more preferably 0.008 to 0.15 μm, and even more preferably 0.01 to 0.10 μm. By making the thickness of the resin layer (B) 0.25 μm or less, the migration of the non-silicone release agent component in the resin layer (B) to the release layer when the release film is wound into a roll is suppressed, and if the thickness of the resin layer (B) is 0.005 μm or more, good blocking prevention properties can be imparted. It can be assumed that unreacted compounds of various compounds, reacted compounds, or a mixture thereof are present in the resin layer (B).

The surface resistivity of the resin layer (B) surface is preferably 1×10 ¹² Ω/□ or less, more preferably 1×10 ¹⁰ Ω/□ or less, even more preferably 1×10 ⁸ Ω/□ or less, and most preferably 1×10 ⁶ Ω/□ or less. There is no particular lower limit for the surface resistivity, but taking into account the cost of the antistatic agent, it is preferably 1×10 ⁴ Ω/□ or more. The lower the surface resistivity of the resin layer (B), the better the antistatic properties are, and the more effectively the film can be prevented from charging during the process and the adhesion of foreign matter and the like can be prevented.

The normal peel strength of the resin layer (B) is preferably 400 to 2000 g/25 mm, more preferably 400 to 1500 g/25 mm, and even more preferably 400 to 1000 g/25 mm. By making the normal peel strength of the resin layer (B) 2000 g/25 mm or less, good blocking prevention properties can be imparted, and when this release film is wound into a roll, heavy peeling of the resin layer (A) can be suppressed at the lower winding part of the roll where pressure is applied by the film.

The surface free energy of the resin layer (B) is preferably 50 mN/m or less, more preferably 40 mN/m or less, and even more preferably 30 mN/m or less. By making the surface free energy of the resin layer 50 mN/m or less, good blocking prevention properties can be imparted, and when this release film is wound into a roll, heavy peeling of the release layer (A) can be suppressed at the lower winding part of the roll where pressure is applied by the film. Details of the surface free energy are as described in the examples.

The elastic modulus of the resin layer (B) at 25°C is preferably 500 MPa or more. The elastic modulus here is a value measured by a nanoindenter. If the elastic modulus is 500 MPa or more, when this release film is wound into a roll, heavy peeling of the resin layer (A) does not occur even in the lower winding part of the roll where pressure is applied by the film.

<Undercoat layer>
The present release film preferably has an undercoat layer between at least one of the resin layer (A) and the substrate film and the resin layer (B). The undercoat layer may be provided either between the resin layer (A) and the substrate film, or between the resin layer (B) and the substrate film, or may be provided on both sides.

The undercoat layer is used not only to improve the adhesion between the film and the resin layer (A) or resin layer (B), but also to impart various functions to the release film. Examples of the undercoat layer include antistatic performance to suppress peeling static electricity in the process of peeling off a functional layer such as an adhesive layer provided on the resin layer (A) and prevent adhesion of foreign matter, and oligomer sealing performance to seal the precipitation of oligomers from the polyester film when heat treatment is performed at high temperature for a long time. In the present release film, it is preferable that the undercoat layer has antistatic performance. The undercoat layer may be a single layer or a structure of two or more layers.

The undercoat layer having antistatic properties can use, as an antistatic agent, for example, a polymer in which a compound made of thiophene or a thiophene derivative is doped with another anionic compound, a self-doped polymer having an anionic group in a compound made of thiophene or a thiophene derivative, or a polymer containing, as a component, a monomer having an alkylsulfonate ion as a counter ion.
In the present release film, from the viewpoint of providing good antistatic performance, it is more preferable that the undercoat layer contains a compound made of thiophene or a thiophene derivative.

In forming an undercoat layer having antistatic properties, it is preferable to use one or more compounds selected from polyglycerin represented by the above general formula (9) and alkylene oxide adducts of polyglycerin or their derivatives in order to improve the antistatic properties.

The undercoat layer having antistatic properties may contain a binder component. As the binder, various conventionally known polymers such as polyester resin, acrylic resin, urethane resin, polyvinyl alcohol resin, etc. can be used. From the viewpoint of improving the transparency and antistatic properties of the undercoat layer, urethane resin is preferred.

In order to improve the strength of the undercoat layer, a crosslinking agent can be used in combination. The crosslinking agent can be any conventionally known material, such as an oxazoline compound, an epoxy compound, a melamine compound, an isocyanate compound, a carbodiimide compound, or an organosilicon compound. From the viewpoint of increasing the strength of the undercoat layer, a melamine compound is more preferable. Two or more types of crosslinking agents can be used in combination.

When a compound made of thiophene or a thiophene derivative is used as an antistatic agent in the undercoat layer, the compound made of thiophene or a thiophene derivative preferably accounts for 5 to 50% by weight, more preferably 5 to 40% by weight, and even more preferably 5 to 30% by weight of the total non-volatile components of the undercoat layer. When it is within the above range, good antistatic properties can be obtained.

In the undercoat layer, the proportion of one or more compounds selected from polyglycerin and alkylene oxide adducts of polyglycerin or derivatives thereof in the total non-volatile components of the undercoat layer is preferably in the range of 10 to 80% by weight, more preferably 20 to 70% by weight, and even more preferably 30 to 65% by weight. When in the above range, good antistatic properties can be obtained.

The proportion of the binder component in the total non-volatile components of the undercoat layer is preferably in the range of 5 to 50% by weight, more preferably 5 to 40% by weight, and even more preferably 5 to 30% by weight. When the proportion of the binder component is in the above range, the strength of the undercoat layer is good, and good antistatic properties can be achieved.

The crosslinking agent preferably accounts for 5 to 70% by weight, more preferably 10 to 60% by weight, and even more preferably 15 to 50% by weight of the total non-volatile components of the undercoat layer. When the crosslinking agent ratio is within the above range, the strength of the undercoat layer is good and blocking can be reduced.

The undercoat layer having oligomer sealing properties may be provided with an undercoat layer having oligomer sealing properties that contains an organic compound containing one or more metal elements selected from aluminum, titanium, and zirconium.

The undercoat layer having oligomer sealing properties may be provided directly on the substrate film, or may be provided on the undercoat layer having antistatic properties.

It can be assumed that the undercoat layer contains unreacted compounds of the various compounds in the resin composition, reacted compounds, or a mixture of these.

<Characteristics of the undercoat layer>
The thickness of the undercoat layer having antistatic properties is preferably 0.005 μm to 0.25 μm, more preferably 0.008 μm to 0.15 μm, and even more preferably 0.01 μm to 0.10 μm. If the thickness of the undercoat layer is within the above range, good antistatic properties can be imparted.

The surface resistivity of the undercoat layer surface having antistatic properties is preferably 1×10 ¹² Ω/□ or less, more preferably 1×10 ¹⁰ Ω/□ or less, even more preferably 1×10 ⁸ Ω/□ or less, and most preferably 1×10 ⁶ Ω/□ or less. There is no particular lower limit to the surface resistivity, but taking into account the cost of the antistatic agent, it is preferable to set it to 1×10 ⁴ Ω/□ or more. The lower the surface resistivity of the resin layer (B), the better the antistatic properties are, and the more effectively the film can be prevented from charging during the process and the adhesion of foreign matter and the like can be prevented.

<Method of forming resin layer (B) and undercoat layer>
Next, the method for forming the resin layer (B) and the undercoat layer will be described.

The resin layer (B) and the undercoat layer are formed by coating the film with a coating liquid. This may be done by in-line coating during the film production process, or by applying the coating outside the system onto a film that has already been produced, a method known as off-line coating. In-line coating is more preferred.

In-line coating is a method of coating within the polyester film production process, specifically, a method of coating at any stage from melt extrusion of polyester to stretching, heat setting and winding up. Usually, coating is performed on any of the following: an unstretched sheet obtained by melting and quenching, a stretched uniaxially stretched film, a biaxially stretched film before heat setting, or a film after heat setting and before winding up.
Although not limited to the following, for example, in the case of sequential biaxial stretching, a method in which a uniaxially stretched film stretched in the longitudinal direction (machine direction) is coated and then stretched in the transverse direction is particularly excellent. According to such a method, film formation and formation of the resin layer (B) can be performed simultaneously, which is advantageous in terms of production costs, and since stretching is performed after coating, the thickness of the resin layer (B) can be changed by the stretching ratio, making it easier to perform thin film coating than with off-line coating films. In addition, by providing the resin layer (B) on the film before stretching, the resin layer (B) can be stretched together with the polyester film, thereby allowing the resin layer (B) to be firmly attached to the polyester film.
Furthermore, in the production of biaxially stretched polyester film, by stretching while gripping the film ends with clips or the like, the film can be restrained in the longitudinal and lateral directions, and in the heat setting step, high temperatures can be applied while maintaining flatness and without wrinkles, etc. Therefore, since the heat treatment performed after coating can be performed at a high temperature that cannot be achieved by other methods, the resin layer (B) and the undercoat layer are cured more rapidly than in offline coating, and a stronger coating film can be formed.

When the resin layer (B) is formed by in-line coating, it is preferable to produce the base film by coating a resin layer (B) composition, which is prepared by preparing an aqueous solution or aqueous dispersion of the above-mentioned series of compounds so that the solids concentration (total non-volatile components) is adjusted to approximately 0.1 to 50 mass %, onto a polyester film.

Methods for applying the resin layer (B) composition or the undercoat layer composition to the film can include conventional coating methods such as air doctor coating, blade coating, rod coating, bar coating, knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss roll coating, cast coating, spray coating, curtain coating, calendar coating, and extrusion coating.

There are no particular limitations on the drying and curing conditions when forming the resin layer (B) and undercoat layer on the film. When forming the resin layer (B) by in-line coating, it is preferable to carry out heat treatment at 70 to 270°C for 3 to 200 seconds, more preferably at 100 to 260°C, and even more preferably at 110 to 250°C for 10 to 100 seconds.

On the other hand, when the resin layer (B) is provided by offline coating, for example, it is preferable to carry out heat treatment at 80 to 200°C for 3 to 40 seconds, and more preferably at 100 to 180°C for 3 to 40 seconds.

Regardless of whether off-line coating or in-line coating is used, heat treatment and irradiation with active energy rays such as ultraviolet light may be used in combination as necessary. The film constituting the release film of the present invention may be previously subjected to a surface treatment such as a corona treatment or a plasma treatment.

<<Layer structure of release film>>
The release film in the present invention may have a laminated structure, and a preferred embodiment is a form in which an adhesive layer is laminated on the surface of the resin layer (A) side of the release film. A more preferred embodiment is a first release film in which the release film is used as the first release film, an adhesive layer is used on the resin layer (A) side of the release film, and a release film having a different peeling force from the release film is used as the second release film on the other surface of the adhesive layer to which the resin layer (A) of the release film is attached, and the two are attached to each other. A further preferred embodiment is a film in which the adhesive layer is an optical transparent adhesive sheet (OCA), and the release film is used and attached as the release film on the side with a lighter peeling force. The adhesive layer may be a single layer or a structure of two or more layers.
In addition, the above-mentioned "release film having a different peeling force from that of the present release film" means that the peeling force of the release film evaluated by the measurement method as described in the examples is different from the peeling force of the resin layer (A) side of the present release film. In addition, the release film having a different peeling force from that of the present release film is preferably larger than the peeling force of the resin layer (A) of the present release film, and specifically, the peeling force is preferably 1.5 to 10 times, more preferably 1.5 to 8 times, and even more preferably about 1.5 to 6 times. By satisfying the above-mentioned peeling force, it is possible to reduce the problem of peeling of the resin layer (A) of the present release film in a situation where peeling is not originally required.

<Adhesive layer>
The adhesive layer will be described below.
The adhesive layer is a layer made of an adhesive composition, and may be an acrylic adhesive composition mainly made of an acrylic resin, a rubber-based adhesive composition mainly made of rubber, a urethane-based adhesive composition mainly made of a urethane resin, or a silicone-based adhesive composition mainly made of a silicone resin. Among them, an acrylic adhesive composition mainly made of an acrylic resin is preferred because the adhesive composition can adjust the adhesive strength and peel strength in a well-balanced manner and is inexpensive.
The above-mentioned "main component resin" means the resin with the highest mass ratio among the resins constituting the adhesive composition. For example, it means a component that occupies 50 mass% or more, preferably 60 mass% or more, more preferably 70 mass% or more of the total amount of the resins constituting the adhesive composition. The upper limit is 100 mass%, but is usually 99.99 mass%.

(Acrylic resin)
The acrylic resin that is the main component resin of the pressure-sensitive adhesive composition may be a (meth)acrylic polymer.
The (meth)acrylic polymer is a polymer having an alkyl (meth)acrylate ester as a main constituent unit. Examples of the alkyl (meth)acrylate ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, isobornyl (meth)acrylate, 4-t-butylcyclohexyl (meth)acrylate, tricyclodecanyl (meth)acrylate, dicyclopentaenyl (meth)acrylate, and adamantyl (meth)acrylate. These may be used alone or in combination of two or more. Among these, methyl (meth)acrylate is preferred from the viewpoints of compatibility with other (meth)acrylates constituting the (meth)acrylic polymer and heat resistance of the cured resin layer (B)(B). The content of the (meth)acrylic acid alkyl ester in the monomers forming the (meth)acrylic polymer is, for example, 50% by mass or more, preferably 60 to 99.99% by mass, more preferably 75 to 98.9% by mass, and even more preferably 87 to 97.8% by mass. The (meth)acrylic polymer may have a radically polymerizable double bond.

For the purpose of improving the glass transition temperature, mechanical properties, compatibility, etc., the (meth)acrylic polymer can be copolymerized with (meth)acrylic acid esters other than (meth)acrylic acid alkyl esters, (meth)acrylic acid, and other compounds having a vinyl group.
Examples of (meth)acrylic acid esters that can be used as a copolymerization component other than the above-mentioned (meth)acrylic acid alkyl esters include hydroxyalkyl (meth)acrylates, methoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxymethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and other (meth)acrylic acid alkoxyalkyl esters, phenyl (meth)acrylate, benzyl (meth)acrylate, glycidyl (meth)acrylate, and γ-butyrolactone (meth)acrylate, which will be described later.
Examples of the compound having a vinyl group include acrylamide compounds such as dimethylacrylamide, hydroxyethylacrylamide, and dimethylaminopropylacrylamide; styrene compounds such as styrene, α-methylstyrene, and p-methoxystyrene; and maleic anhydride.
In addition, components (a1) and (a2) described below can also be used appropriately.

In the present invention, the monomer constituting the (meth)acrylic polymer may contain, in addition to the (meth)acrylic acid alkyl ester, an acrylic monomer (a1) as a copolymerization component, which serves as a reaction point with the crosslinking agent described below.

The acrylic monomer (a1) is a reactive site of the crosslinking structure when it is copolymerized with other copolymerization components to form an acrylic resin, and a monomer containing a functional group that can react with the functional group contained in the crosslinking agent described below may be used. Examples of such acrylic monomer (a1) include hydroxyl group-containing monomers, amino group-containing monomers, acetoacetyl group-containing monomers, isocyanate group-containing monomers, and glycidyl group-containing monomers. Among these, hydroxyl group-containing monomers are preferably used because they can efficiently crosslink with the crosslinking agent. The acrylic monomer (a1) may be used alone or in combination of two or more types.

Examples of hydroxyl group-containing monomers include hydroxyalkyl esters of acrylic acid such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl 2-hydroxyethyl phthalate and N-methylol (meth)acrylamide; secondary hydroxyl group-containing monomers such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro 2-hydroxypropyl (meth)acrylate; and tertiary hydroxyl group-containing monomers such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate.

Among the above hydroxyl group-containing monomers, primary hydroxyl group-containing monomers are preferred because of their excellent reactivity with crosslinking agents, and furthermore, the use of 2-hydroxyethyl acrylate is particularly preferred because it contains less impurities such as di(meth)acrylate and is easy to manufacture.

In addition, as the hydroxyl group-containing monomer used in the present invention, it is also preferable to use one having a content of di(meth)acrylate, which is an impurity, of 0.5% by mass or less, more preferably 0.2% by mass or less, and especially 0.1% by mass or less. Specifically, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, etc. are particularly preferable as the hydroxyl group-containing monomer, which are preferred because they have a low molecular weight and are therefore easy to purify.

Examples of amino group-containing monomers include t-butylaminoethyl (meth)acrylate, ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, etc.

Examples of acetoacetyl group-containing monomers include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate.

Examples of isocyanate group-containing monomers include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, and their alkylene oxide adducts.

Examples of glycidyl group-containing monomers include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

The content of acrylic monomer (a1) in the monomers constituting the (meth)acrylic polymer is preferably 0.01 to 20% by mass, more preferably 0.1 to 10% by mass, and even more preferably 0.2 to 3% by mass. When the content of acrylic monomer (a1) is equal to or greater than the lower limit, the crosslinking points during crosslinking are appropriate, resulting in good cohesive strength after crosslinking. When the content is equal to or less than the upper limit, a decrease in adhesive strength due to the (a1) component can be prevented.

Furthermore, the monomer constituting the (meth)acrylic polymer may contain, in addition to the (meth)acrylic acid alkyl ester, or the (meth)acrylic acid alkyl ester and the component (a1), a copolymerizable monomer (a2) other than (a1) as a copolymerization component, as necessary.
Examples of the copolymerizable monomer (a2) include aromatic ring-containing monomers such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, ethoxylated o-phenylphenyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and styrene; amide monomers such as (meth)acryloylmorpholine, dimethyl (meth)acrylamide, diethyl (meth)acrylamide, and (meth)acrylamide; acrylonitrile, methacrylonitrile, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, itaconic acid dialkyl esters, fumaric acid dialkyl esters, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone.

The content of the copolymerizable monomer (a2) in the monomers forming the (meth)acrylic polymer is preferably 0 to 20 mass%, more preferably 1 to 15 mass%, and particularly preferably 2 to 10 mass%. When the content of the copolymerizable monomer (a2) is within the above range, it is possible to prevent a decrease in adhesive properties due to the (a2) component.
In the present invention, in consideration of application to foldable displays, it is preferable that the adhesive layer contains 2-ethylhexyl acrylate and/or butyl acrylate from the viewpoint of imparting flexibility to the adhesive layer.

In addition to the main component resin, the adhesive composition may contain, as necessary, a crosslinking agent and other resins (other than the main component resin and the crosslinking agent) that constitute the adhesive components (e.g., acrylic resins, rubber, silicone resins, urethane resins).

(Crosslinking Agent)
The pressure-sensitive adhesive composition may contain a crosslinking agent depending on the curing method.
Examples of the crosslinking agent include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, aldehyde-based crosslinking agents, and amine-based crosslinking agents. Among them, isocyanate-based crosslinking agents are preferably used in terms of improving adhesion to the substrate or reactivity with the acrylic resin. The crosslinking agents may be used alone or in combination of two or more.
The content of the crosslinking agent is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, and even more preferably 0.1 to 3 parts by mass, relative to 100 parts by mass of the main component resin. If the content of the crosslinking agent is within the above range, the cohesive strength is not insufficient, and the desired durability can be obtained, while a decrease in flexibility and adhesive strength can be prevented.

Regarding the curing reaction, when photocuring is performed by irradiating active energy rays, it is preferable to incorporate a polyfunctional (meth)acrylate into the adhesive composition as a crosslinking agent. Examples of such polyfunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, ethylene oxide modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and glycerin polyglycidyl ether poly(meth)acrylate.

(Other resins constituting adhesive components)
The pressure-sensitive adhesive composition may contain, if necessary, a resin (e.g., an acrylic resin, a rubber, a silicone resin, a urethane resin) that constitutes a pressure-sensitive adhesive component other than the main component resin and the crosslinking agent.
For example, additives that may be blended include tackifiers such as rosin, rosin esters, hydrogenated rosin esters, phenolic resins, aromatic modified terpene resins, aliphatic petroleum resins, alicyclic petroleum resins, styrene-based resins, and xylene-based resins; conventional additives such as silane coupling agents, antistatic agents, colorants, fillers, antioxidants, ultraviolet absorbers, and functional dyes; and additives such as compounds that change color or undergo color change when exposed to ultraviolet rays or radiation.
The amount of these additives blended is preferably 10 mass % or less of the entire pressure-sensitive adhesive composition (based on non-volatile components), and more preferably 5 mass % or less. In terms of excellent durability, it is preferable that the additives contain as few low molecular weight components having a molecular weight of less than 10,000 as possible.

<Method of forming adhesive layer>
The method for forming the adhesive layer is not particularly limited, and the adhesive layer may be formed by applying the above-mentioned adhesive composition onto the resin layer (A) of the present release film, followed by appropriate drying, curing, etc. Alternatively, the adhesive composition may be applied onto a base film or a release film having a release strength different from that of the present release film, followed by appropriate drying, curing, etc., and then laminating the release layer (A layer) of the present release film to the surface opposite to the surface provided with the release film having a release strength different from that of the present release film.
The pressure-sensitive adhesive composition may be cured depending on the crosslinking agent and main component resin, and may be cured by heating or by irradiation with light such as ultraviolet light. The pressure-sensitive adhesive composition may be appropriately diluted with an organic solvent or the like and then applied onto a release layer or the like.

<Characteristics of adhesive layer>
(Thickness of adhesive layer)
The thickness of the adhesive layer is not particularly limited. For example, from the viewpoint of providing sufficient adhesive strength and filling unevenness or steps of the substrate to which the adhesive is attached, it is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. On the other hand, from the viewpoint of material use efficiency, permeability, and outgas, it is preferably 10,000 μm or less, more preferably 3,000 μm or less, and even more preferably 1,000 μm or less.

(Elastic modulus of adhesive layer)
In the present invention, the adhesive layer preferably has a modulus of elasticity of 6.0 MPa or less at 25 ° C. The modulus of elasticity here is a value measured by a nanoindenter. When the modulus of elasticity is 6.0 MPa or less, the adhesive layer has good followability to deformation and can be applied to foldable display applications. From these viewpoints, the modulus of elasticity of the adhesive layer is more preferably 5.0 MPa or less, even more preferably 4.0 MPa or less, and particularly 3.0 MPa or less. In addition, the modulus of elasticity of the adhesive layer at 25 ° C. is preferably 0.5 MPa or more, more preferably 1.0 MPa or more, and even more preferably 1.5 MPa or more, from the viewpoint of adhesive layer formability.

(Glass transition temperature (Tg) of adhesive layer)
The glass transition temperature is calculated from the following Fox formula.



Tg: glass transition temperature of the copolymer (K)
Tga: glass transition temperature of the homopolymer of monomer A (K)
Wa: weight fraction of monomer A Tgb: glass transition temperature (K) of homopolymer of monomer B
Wb: weight fraction of monomer B Tgn: glass transition temperature (K) of homopolymer of monomer N
Wn: weight fraction of monomer N (Wa + Wb + ... + Wn = 1)

In the present invention, in consideration of application to foldable displays, the Tg is preferably in the range of -55°C to -70°C, more preferably in the range of -58°C to -68°C.
By satisfying the above range, it is possible to obtain an adhesive layer that has good conformability to deformations such as bending.

<<How to use the film laminate>>
The present film laminate can be used in various lamination configurations. For example, the release film with the adhesive layer may be a film laminate in which an optical member is attached to the surface of the adhesive layer. Such a film laminate can be produced by peeling off the present release film and attaching the optical member to an adherend by the exposed adhesive layer. Examples of the optical member include a polarizing plate and a touch sensor. The optical member may also be an in-vehicle optical member such as a touch panel mounted on an automobile.

(Polarizing plate)
The material and structure of the polarizing plate are arbitrary, and for example, a polarizing plate of this type is widely used in which a TAC (triacetyl cellulose) film is laminated as a protective film on a stretched polyvinyl alcohol film using iodine as an orientation dye. The polarizing plate may have a layer structure on the surface that has a hard coat having substantially no phase difference, antiglare, low reflection, antistatic, or other functions.

(Touch sensor)
A touch sensor is a component that detects the touched point when a user touches an image displayed on a screen with a finger or a touch pen. Depending on the sensor technology, examples include a capacitive type, a resistive film type, and a surface wave type using infrared rays or ultrasound.
Generally, touch sensors are mounted on display devices such as liquid crystal display panels and organic EL displays.
In recent years, there has been a trend to use a base film as an alternative to a glass substrate, focusing on flexibility, and it is preferable to use a touch sensor film. The touch sensor film generally has a patterned transparent conductive layer for performing the function of a sensing electrode.

The film laminate may have a layer structure including the release film with the adhesive layer and another release film, and the release film with the adhesive layer is bonded to the other release film via the adhesive layer. The film laminate having such a layer structure has a structure of the release film/adhesive layer/other release film, and can be used as a double-sided adhesive sheet.
The other release film is a film having a release layer formed on the surface of a substrate such as a resin film, and the surface on which the release layer is formed is preferably attached to the adhesive layer. The release layer of the other release film may be any other layer than the above-mentioned release layer.

In a film laminate having the above structure, the ratio (MB/MA) of the modulus of elasticity (MA) of the release layer of this release film to the modulus of elasticity (MB) of the release layer of the other release film is preferably in the range of 4 to 30, more preferably in the range of 4 to 25. When the modulus of elasticity falls within the above range, it is possible to reduce the problem of the release film peeling off in situations where peeling is not actually necessary in the film laminate.

The film laminate to which the other release film described above has been attached may be used by peeling off the release film and attaching the exposed adhesive layer surface of the remaining release film with adhesive layer to an optical member. Then, the other release film may be peeled off from the adhesive layer of the release film with adhesive layer. After that, the release film may be attached again onto the adhesive layer attached to the optical member. In this way, the release film of the present invention has an extremely light peelability and low migration property, so it is also possible to use the so-called release film by peeling it off again.

The normal peel strength of the other release film, measured at a peel speed of 0.3 m/min and a 180° peel, is greater than that of the present release film, and more specifically, is preferably about 2 to 10 times, and more preferably 2 to 6 times, the normal peel strength of the present release film. By satisfying the above peel strength ratio, it is possible to reduce the problem of the present release film peeling off in situations where peeling is not actually necessary.

The above-mentioned release film and film laminate are preferably used for in-vehicle applications. When used for in-vehicle applications, the adhesive layer needs to have high adhesive strength in order to maintain high adhesive strength even when exposed to high temperatures in summer or low temperatures in winter. This release film can achieve ultra-light peelability, so that the peeling performance is good even when the adhesive layer has high adhesive strength.

<<<<Explanation of terms, etc.>>>
In the present invention, the term "film" includes the term "sheet", and the term "sheet" includes the term "film".
Furthermore, when the term "panel" is used, such as an image display panel, a protective panel, a touch panel, etc., it encompasses a plate, a sheet, and a film.

In the present invention, when it is described as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as the meaning of "preferably larger than X" or "preferably smaller than Y".
In addition, when it is stated that the amount is "X or more" (X is any number), it also means that the amount is "preferably greater than X" unless otherwise specified, and when it is stated that the amount is "Y or less" (Y is any number), it also means that the amount is "preferably smaller than Y" unless otherwise specified.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. The evaluation methods used in the examples and comparative examples are as follows.

(1) Method for Measuring the Intrinsic Viscosity of Polyester 1 g of polyester from which other polymer components incompatible with polyester and pigments had been removed was precisely weighed, and dissolved in 100 ml of a mixed solvent of phenol/tetrachloroethane = 50/50 (mass ratio), and the intrinsic viscosity was measured at 30°C.

(2) Method for measuring average particle size (d50: μm) The cumulative 50% value (mass basis) in the equivalent sphericity distribution measured using a centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) was taken as the average particle size.

(3) Method for measuring the thickness of the resin layer (A) In order to suppress reflection from the back surface, black tape ("Vinyl Tape VT-50" manufactured by Nichiban Co., Ltd.) was attached to the back surface of the sample film to be measured in advance. For the measurement, a spectrophotometer (UV-visible spectrophotometer "V-670" manufactured by JASCO Corporation) was used to measure the absolute reflectance in the wavelength range of 300 to 800 nm under the conditions of synchronous mode, incident angle of 5°, N polarization, response Fast, data acquisition interval of 1.0 nm, bandwidth of 10 nm, and scanning speed of 1000 m/min. The film thickness was obtained by comparing the data obtained by this measurement with the data calculated assuming the refractive index of silicone to be 1.43.

(4) Method for measuring the thickness of the resin layer (B) and the undercoat layer The surface of the cured resin layer (B) was stained with _RuO4 and embedded in epoxy resin. Then, slices prepared by ultrathin sectioning were stained with _RuO4 , and the cross section of the coating layer was measured using a TEM (Hitachi High-Technologies Corporation H-7650, accelerating voltage 100 kV).

(5) Measurement of surface resistivity Using a low resistivity meter (Mitsubishi Chemical Corporation, "Loresta GP MCP-T600"), the surface resistivity was measured after conditioning the sample for 30 minutes in a measurement atmosphere at a temperature of 23°C and a relative humidity of 50%, and the value after 1 minute was recorded as the surface resistivity. If the resistance value exceeded the upper limit of the measurable range, it was deemed unmeasurable.

(6) Measurement of average surface roughness The arithmetic average roughness (Ra) of the resin layer (B) was measured using a surface roughness meter (two-dimensional roughness meter "Surfcorder SE3500" manufactured by Kosaka Laboratory Co., Ltd.) conforming to JIS B 0601-2001. In addition, the maximum cross-sectional height (Rt) of the opposite release surface was measured. Rt can be calculated as the sum of the maximum peak height Rp and the maximum valley depth Rv of the roughness curve in the evaluation length.

(7) Molecular weight measurement of cured silicone resin Using a GPC measuring device, a chromatogram was measured, and the number average molecular weight (Mn) and mass average molecular weight (Mw) were determined based on a calibration curve using standard polystyrene, and are shown in Table 2. Specifically, 4 mg of a sample for measurement was dissolved in 4 mL of THF to prepare a measurement solution, and 100 μL of the measurement solution was injected into a GPC measuring device for measurement. Tetrahydrofuran (THF) was used as the eluent. For the analysis, Tosoh Corporation's "Ecosec8320" was used, Tosoh Corporation's "TSKgel guardcolumn HXL-L" was used as a guard column, and Tosoh Corporation's "TSKgel GMHXL" was used as a column, four of which were connected together. In addition, the analysis was performed under conditions of an oven temperature of 40° C. and a THF flow rate of 1.0 mL/min, and RI was used for detection.

(8) Compositional Analysis of Curable Silicone Resins The compositional analysis of the curable silicone resins used in the examples and comparative examples was carried out using a 400 MHz-NMR (Bruker Avance 400M). ^1H -NMR measurements were carried out at 30°C using _CDCl3 as the solvent and the peak derived from the methyl group of dimethylsiloxane as the chemical shift reference.

(9) Measurement of normal peel strength of resin layer (A) The resin layer (A) surface of the sample film was pressed (twice back and forth) with a rubber roller (2 kg), and an adhesive tape ("No. 7475" manufactured by Tesa) was attached, and then cut to a size of 25 mm x 300 mm. The peel strength was measured after leaving it at room temperature (23°C) for 1 hour. The peel strength was measured by peeling the sample film at 180° using "Intesco Model 2001" manufactured by Intesco Co., Ltd. under the condition of a tensile speed of 0.3 m/min.

(10) Measurement of Residual Adhesion Rate of Resin Layer (A) (Evaluation of Migration)
The sample film was cut to A4 size (210 mm x 297 mm), and a 75 μm biaxially stretched PET film (Diafoil T100-75, manufactured by Mitsubishi Chemical Corporation) was placed on the release layer (A layer) surface and pressed for 2 hours under conditions of a temperature of 23° C. and a pressure of 1 MPa. The "75 μm biaxially stretched PET film" alone was used as the evaluation film.
On the other hand, the same "75 μm biaxially stretched PET film" as above was laminated on an untreated base film not provided with a resin layer (A) and pressed under the same conditions as above, and the "75 μm biaxially stretched PET film" alone was used as a reference film.
An adhesive tape ("No. 31B" manufactured by Nitto Denko Corporation) was attached to the contact surface (resin layer (A) (A layer)) of the evaluation film with the sample film and the contact surface of the reference film with the base film by pressing (twice back and forth) with a rubber roller (2 kg), and then cut to a size of 50 mm x 300 mm. After leaving it at room temperature for 1 hour, the peel force was measured.
The peel strength was measured using an Intesco Model 2001 manufactured by Intesco Ltd., by peeling the evaluation film and the reference film at 180° at a pulling speed of 0.3 m/min.
The measured peel strength of the evaluation film and the peel strength of the reference film were then substituted into the following formula to determine the residual adhesion rate (%). Note that no treatment such as heat treatment was performed here.
Residual adhesion rate (%)=(peel strength of evaluation film/peel strength of reference film)×100

In films with high migration, a lot of silicone adheres to the overlapping film, reducing the peeling force of the adhesive tape and decreasing the residual adhesion rate (%). Therefore, the migration of the resin layer (A) of the release film was evaluated as follows based on the residual adhesion rate value.

(11) Heavy peeling rate after pressing of resin layer (A) (alternative evaluation of blocking property)
An acrylic adhesive tape ("No. 7475" manufactured by Tesa) was attached to the resin layer (A) surface of the release film of each of the examples and comparative examples, then cut to a size of 25 mm x 150 mm and left at room temperature for 1 hour. The peel strength at 180° under the condition of a tensile speed of 0.3 m/min was defined as (F1).
Next, the other surface (resin layer (B) surface in the present invention) of the release film of the examples and comparative examples is placed so as to face the resin layer (A) surface, and press treatment is performed for 20 hours at a temperature of 40°C, a humidity of 90% RH, and a load of 1 MPa. An acrylic adhesive tape ("No. 7475" manufactured by Tesa) is attached to the resin layer (A) surface after the treatment, and then cut to a size of 25 mm x 150 mm and left at room temperature for 1 hour. The peel force at 180° peeled under the condition of a tensile speed of 0.3 m/min is defined as (F2).
The heavy peeling rate after pressing was calculated using the following formula, and this heavy peeling rate was used as an index of blocking resistance. Note that the blocking resistance is judged to be better as the heavy peeling rate is smaller.
Heavy peel rate after pressing (%) = (F2 - F1) / F1 x 100

(12) Blocking property evaluation The release layer surface and the non-release surface of the release films of the examples and comparative examples were arranged so as to face each other, and pressed with a press machine at a pressure of 10 kg/ ^cm2 , 40°C, and 80% RH for 20 hours to obtain a measurement sample for evaluating blocking resistance. After that, using a peeling device (Shimadzu Corporation "AGI"), the peeling force was measured under the conditions of a tensile speed of 300 mm/min and 180° peeling, and the peeling force at this time was used as an index of blocking resistance. It is considered that the blocking resistance is better when the peeling force is smaller.
Evaluation Criteria
A (good): The peeling force is 20 g/25 mm or less, and peeling is possible without any problems.
B (poor): The peel force exceeded 20 g/25 mm, and blocking occurred.

(13) Adhesion between the base film and the resin layer (A) A sample film was left in a thermo-hygrostat under an atmosphere of 60° C. and 80% RH for 4 weeks, and then removed. Thereafter, the resin layer (A) surface of the sample film was rubbed with a feeler five times, and the adhesion was evaluated according to the degree of peeling of the release layer according to the following evaluation criteria.
Evaluation Criteria
◯: The coating film did not turn white and no peeling was observed.
×: The coating film turned white or fell off.

(14) Measurement of normal peel strength of resin layer (B) An acrylic adhesive tape ("No. 7475" manufactured by Tesa) was attached to the resin layer (B) of the sample film by pressing (twice back and forth) with a rubber roller (2 kg), and then cut to a size of 25 mm x 150 mm. The peel strength was measured after leaving the tape at room temperature (23°C) for 1 hour. The peel strength was measured using "Intesco Model 2001" manufactured by Intesco Co., Ltd., and the sample film was peeled at 180° under the condition of a tensile speed of 0.3 m/min.

(15) Measurement of Surface Free Energy of Resin Layer Droplets of ion-exchanged water and diiodomethane were prepared on the resin layer of the sample film using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., product name "DMo-501") in a measurement atmosphere of 23°C and 50% RH, and the contact angle was measured 60 seconds after each liquid was dropped onto the laminated polyester film.
For the contact angle data for ion-exchanged water and diiodomethane obtained by this method, the surface free energy of the antireflection layer surface was calculated according to the Owens-Wendt theoretical formula using the surface tension component values of each solvent (Table 1).

(16) Measurement of Elastic Modulus of Resin Layer (A) The elastic modulus of the resin layer (A) was measured at a penetration depth of 50 nm at room temperature (25° C.) using a nanoindenter (TI 950 TriboIndenter) manufactured by Hysitron.

(17) Measurement of Elastic Modulus of Adhesive Layer Using a nanoindenter (TI 950 TriboIndenter) manufactured by Hysitron, the elastic modulus of the adhesive layer was measured at a point with an indenter (conical: spherical, radius of curvature: 10 μm) at room temperature (25° C.) and an indentation depth of 500 nm.

(18) Adhesive Peel Strength The adhesive composition shown in Table 8 was applied to the release layer surface of the sample film so as to have a film thickness of 2 mil in a wet state, and the applied adhesive composition was cured by heat treatment at 150° C. for 3 minutes to form an adhesive layer (thickness (after drying) 20 μm).

After that, another release film was laminated onto the adhesive layer to obtain a film laminate consisting of sample film/adhesive layer/other release film. The release films prepared in Comparative Examples 1 to 4 described below were used as the other release films. The peel force was measured when peeling the sample film from the adhesive layer of the obtained film laminate. The peel force was measured using an "Intesco Model 2001" manufactured by Intesco Co., Ltd., at a tensile speed of 0.3 m/min and 180° peeling.

The polyesters used in the examples and comparative examples were prepared as follows:

<Method for producing polyester (A)>
100 parts by mass of dimethyl terephthalate and 60 parts by mass of ethylene glycol were used as starting materials, and 0.09 parts by mass of magnesium acetate tetrahydrate was added as a catalyst to a reactor. The reaction was started at 150°C, and the reaction temperature was gradually increased with the distillation of methanol, and reached 230°C after 3 hours. After 4 hours, the transesterification reaction was essentially completed. 0.04 parts by mass of ethyl acid phosphate was added to the reaction mixture, and then 0.04 parts by mass of antimony trioxide was added to carry out a polycondensation reaction for 4 hours. That is, the temperature was gradually increased from 230°C to 280°C. Meanwhile, the pressure was gradually reduced from normal pressure, and finally reached 0.3 mmHg. After the start of the reaction, the reaction was stopped at a point corresponding to an intrinsic viscosity of 0.65 due to a change in the stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure to obtain a polyester (A) having an intrinsic viscosity of 0.65.

<Method for producing polyester (B)>
Polyester (B) was obtained in the same manner as in the production method of polyester (A), except that, after adding 0.04 part by mass of ethyl acid phosphate, 0.2 part by mass of silica particles having an average particle size of 2.3 μm dispersed in ethylene glycol and 0.04 part by mass of antimony trioxide were added and the polycondensation reaction was terminated at the point corresponding to an intrinsic viscosity of 0.65. The obtained polyester (B) had an intrinsic viscosity of 0.65.

Example 1-1
A mixed raw material obtained by mixing polyesters (A) and (B) in a ratio of 90% by mass and 10% by mass, respectively, was used as the raw material for the outermost layer (surface layer), and polyester (A) was used as the raw material for the intermediate layer. Each of these was supplied to two extruders and melted at 290°C. After that, the mixture was co-extruded onto a cooling roll set at 25°C in a layer structure of two types and three layers (surface layer/intermediate layer/surface layer = extrusion amount of 1:18:1), and then cooled and solidified to obtain an unstretched sheet. Next, the film was stretched 3.4 times in the longitudinal direction at a film temperature of 85°C by utilizing the difference in roll peripheral speed, and then coating solution 1 for resin layer (B) shown in Table 4 was applied to one side of the longitudinally stretched film, and the following undercoat layer composition was applied to the other side. The film was then introduced into a tenter, stretched 4.5 times in the transverse direction at 120°C, heat-treated at 225°C, and then relaxed by 2% in the transverse direction to obtain a biaxially stretched polyester film having a thickness of 50 μm and a resin layer (B) thickness (after drying) of 0.05 μm and an undercoat layer thickness (after drying) of 0.05 μm.

Next, the resin layer (A) was coated on the undercoat layer surface of the obtained polyester film with the coating solution 1 for the resin layer (A) shown in Table 3 by bar coating using a No. 4 bar so that the coating thickness (after drying) was 1.0 μm, and then dried at 150 ° C for 30 seconds to obtain a release film.

Examples 1-2 to 1-12:
The same production as in Example 1-1 was carried out except that the coating solutions 2 to 12 for the resin layer (B) shown in Table 4 were applied to one side of the longitudinally stretched film, to obtain release films.

As shown in Table 4, the obtained release film had a thin resin layer (A) with an elastic modulus of 500 MPa or less, while the resin layer (B) contained a non-silicone release agent, which achieved an ultra-light peel strength (normal peel strength) of 5 g/25 mm or less, while achieving a heavy peel strength after pressing of 100% or less and blocking resistance. In addition, the film had good adhesion to the substrate and low migration.

Examples 1-13 to 1-28
A mixed raw material obtained by mixing polyesters (A) and (B) in a ratio of 97% by mass and 3% by mass, respectively, was used as the raw material for the outermost layer (surface layer), and polyester (A) was used as the raw material for the intermediate layer. Each of these was supplied to two extruders and melted at 290°C. After that, the materials were co-extruded onto a cooling roll set at 25°C in a layer structure of two types and three layers (surface layer/intermediate layer/surface layer = extrusion amount of 1:18:1), and then cooled and solidified to obtain an unstretched sheet. Next, the film was stretched 3.4 times in the longitudinal direction at a film temperature of 85°C by utilizing the difference in roll peripheral speed, and then a coating solution for the resin layer (B) shown in Table 4 was applied to one side of the longitudinally stretched film, and the following undercoat layer composition was applied to the other side. The film was then introduced into a tenter, stretched 4.5 times in the transverse direction at 120°C, heat-treated at 225°C, and then relaxed by 2% in the transverse direction to obtain a biaxially stretched polyester film having a thickness of 50 μm and a resin layer (B) thickness (after drying) of 0.05 μm and an undercoat layer thickness (after drying) of 0.05 μm.

Next, the resin layer (A) was coated on the undercoat layer surface of the obtained polyester film with the coating solution 1 for the resin layer (A) shown in Table 3 by bar coating using a No. 4 bar so that the coating thickness (after drying) was 1.0 μm, and then dried at 150 ° C for 30 seconds to obtain a release film.

As shown in Table 5, the obtained release film had a thin resin layer (A) with an elastic modulus of 500 MPa or less, while the resin layer (B) contained a non-silicone release agent, which achieved an ultra-light peel strength (normal peel strength) of 5 g/25 mm or less, while also achieving a heavy peel strength after pressing of 100% or less and blocking resistance. In addition, the film had good adhesion to the substrate and low migration.

Comparative Example 1-1
A release film was obtained in the same manner as in Example 1-1, except that the resin layer (B) and the undercoat layer were not provided on the longitudinally stretched film.

Comparative Example 1-2
A release film was obtained in the same manner as in Example 1-1, except that the resin layer (B) was not provided on the longitudinally stretched film.

As shown in Table 5, the release films obtained in Comparative Examples 1-1 and 1-2 did not have a resin layer (B) containing a non-silicone release agent, so the heavy peeling rate after pressing was high, raising concerns about the occurrence of blocking.

Comparative Example 1-3
A release film was obtained in the same manner as in Example 1-1, except that the resin layer (B) composition was changed to Coating Solution 13 not containing a non-silicone-based release agent.
As shown in Table 5, since the obtained release film did not contain a non-silicone release agent in the resin layer (B), the heavy release rate after pressing was high, and there was concern about the occurrence of blocking.

Comparative Examples 1-4
A release film was obtained in the same manner as in Example 1-1, except that the coating solution 2 for the resin layer (A) was used.
As shown in Table 5, the obtained release film had a thin resin layer (A) and a high elastic modulus, so that the peel strength (normal peel strength) was about three times higher than those of Examples 1-1 to 1-12, and it was not possible to realize ultra-light peeling. In addition, the adhesion to the substrate was poor.

Reference example 1
A release film was obtained in the same manner as in Example 1, except that the resin layer (A) was changed to Coating Solution 3 (particle content: 0.19% by mass).
As shown in Table 5, the resin layer (A) of the obtained release film was brittle due to the presence of the particles, and therefore the adhesion to the substrate was poor, and the particles fell off, resulting in relatively high migration. In addition, the heavy peeling rate after pressing was high, raising concerns about the occurrence of blocking.

Examples of the compound constituting the resin layer (A) are as follows.
a1: Curable silicone resin (a silicone resin in which a vinyl group has been introduced into the side chain and/or end of the main chain consisting of a siloxane bond, number average molecular weight: 10600, viscosity at 25°C when adjusted to 15% by mass by dilution with n-heptane solvent: 1.7 mcps)
a2: A mixture containing a curable silicone resin (a silicone resin in which vinyl groups have been introduced to the side chains and/or ends of the main chain consisting of siloxane bonds, number average molecular weight: 364,000) and a silicone crosslinker (a silicone resin in which Si-H groups have been introduced to the side chains and/or ends of the main chain consisting of siloxane bonds) (viscosity at 25°C when adjusted to 15% by mass with n-heptane solvent: 410 mcps)

The content (mol %) of each functional group in the curable silicone resin is as follows:

b1: Silicone crosslinker (CL750: manufactured by Momentive Performance Materials)
c1: Addition type platinum catalyst (CM678: manufactured by Momentive Performance Materials)
c2: Addition type platinum catalyst (PL-50T: manufactured by Shin-Etsu Chemical Co., Ltd.)
d1: Particles (Tospearl 120: manufactured by Momentive Performance Materials)

The coating liquid constituting the resin layer (A) is as follows:

Examples of compounds constituting the resin layer (B) and the undercoat layer are as follows:

(Release Agent)
AI: Compound containing long chain alkyl group 200 parts of xylene and 600 parts of octadecyl isocyanate were added to a four-neck flask and heated under stirring. From the point when xylene started to reflux, 100 parts of polyvinyl alcohol with an average degree of polymerization of 500 and a degree of saponification of 88 mol% were added little by little at 10-minute intervals over about 2 hours. After the addition of polyvinyl alcohol was completed, the mixture was refluxed for another 2 hours to terminate the reaction. The reaction mixture was cooled to about 80°C and then added to methanol, whereupon the reaction product precipitated as a white precipitate. The precipitate was filtered off, 140 parts of xylene was added, heated to completely dissolve, and then methanol was added again to precipitate. This operation was repeated several times, and the precipitate was washed with methanol and dried and pulverized to obtain the product.
AII: Wax 300 g of oxidized polyethylene wax having a melting point of 105°C, acid value of 16 mgKOH/g, density of 0.93 g/mL and average molecular weight of 5000, 650 g of ion-exchanged water, 50 g of decaglycerin monooleate surfactant, and 10 g of 48% aqueous potassium hydroxide solution were added to a 1.5 L emulsification facility equipped with a stirrer, thermometer, and temperature controller, and the mixture was then purged with nitrogen, sealed, and stirred at high speed at 150°C for 1 hour, cooled to 130°C, and passed through a high-pressure homogenizer at 400 atmospheres to produce a wax emulsion cooled to 40°C.

(Antistatic Agent)
BI: Conductive agent consisting of polyethylenedioxythiophene and polystyrenesulfonic acid (Orgacon ICP1010 manufactured by Agfa-Gevaert) neutralized with concentrated aqueous ammonia to pH=9; non-volatile component: 1.2% by mass; solvent: water

(Polyhydroxy Compounds)
CI: polyglycerin having an average of n=4 in the above formula (9). CII: a compound having an average of 4 molecules of polyethylene oxide added to a polyglycerin skeleton having an average of n=2 in the above formula (9).

(binder)
DI: A water dispersion of a polyester resin copolymerized with the following composition. Monomer composition: (acid component) 2,6-naphthalenedicarboxylic acid/5-sodium sulfoisophthalic acid/(diol component) ethylene glycol/diethylene glycol=92/8//80/20 (mol%)
DII: Water dispersion of urethane resin polymerized with the following composition. When polyester polyol (C1a) is composed of 282 parts by mass of terephthalic acid, 282 parts by mass of isophthalic acid, 62 parts by mass of ethylene glycol, and 250 parts by mass of neopentyl glycol, a polyester polyurethane composed of 876 parts by mass of (C1a), 244 parts by mass of tolylene diisocyanate, 81 parts by mass of ethylene glycol, and 67 parts by mass of dimethylolpropionic acid was neutralized with ammonia and dispersed in water (concentration 20%, viscosity at 25° C. 50 mPa·s).

(Crosslinking Agent)
EI: Hexamethoxymethylolmelamine EII: Acrylic polymer EPOCROSS having an oxazoline group and a polyalkylene oxide chain (amount of oxazoline group = 4.5 mmol/g, manufactured by Nippon Shokubai Co., Ltd.)

(Surfactant)
FI: A nonionic surfactant having a structure having polyethylene oxide in the side chain, as shown in the following formula.

In the above formula, m and n are integers indicating the number of moles of ethylene oxide added, and in this example, the average of m+n was 10.

The coating liquid constituting the resin layer (B) is as follows. Note that the amounts in Table 3 are based on the non-volatile components.

<Undercoat Layer Composition>
The coating liquid constituting the undercoat layer is as follows.
(BI)/(CII)/(DII)/(FI)=10% by mass/35% by mass/50% by mass/5% by mass

<Method for producing polyester (1)>
100 parts by mass of dimethyl terephthalate and 55 parts by mass of ethylene glycol were used as starting materials, and 0.04 parts by mass of magnesium acetate tetrahydrate was added to the reactor as a catalyst. The reaction was started at 150°C, and the reaction temperature was gradually increased with the distillation of methanol, and reached 230°C after 3 hours. After 4 hours, the transesterification reaction was essentially completed. 0.02 parts by mass of ethyl acid phosphate was added to the reaction mixture, and then 0.04 parts by mass of antimony trioxide was added to carry out a polycondensation reaction for 4 hours. That is, the temperature was gradually increased from 230°C to 280°C. Meanwhile, the pressure was gradually reduced from normal pressure, and finally reached 0.3 mmHg. After the start of the reaction, the reaction was stopped at a point corresponding to an intrinsic viscosity of 0.59 dl/g due to a change in the stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure to obtain a polyester (1) with an intrinsic viscosity of 0.59 dl/g.

<Production method of polyester (2)>
100 parts by mass of dimethyl terephthalate and 45 parts by mass of ethylene glycol were used as starting materials, and 0.06 parts by mass of magnesium acetate tetrahydrate was added to the reactor as a catalyst. The reaction was started at 150°C, and the reaction temperature was gradually increased with the distillation of methanol, and reached 230°C after 3 hours. After 4 hours, the transesterification reaction was essentially completed. After adding 0.03 parts by mass of ethyl acid phosphate to this reaction mixture, 0.3 parts by mass of silica particles having an average particle size of 2.7 μm dispersed in ethylene glycol and 0.03 parts by mass of antimony trioxide were added, and the polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually increased from 230°C to 280°C. Meanwhile, the pressure was gradually reduced from normal pressure, and finally reached 0.3 mmHg. After the start of the reaction, the reaction was stopped at a point corresponding to an intrinsic viscosity of 0.59 dl/g due to a change in the stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure to obtain a polyester (2) having an intrinsic viscosity of 0.59 dl/g.

<Production method of polyester (3)>
Polyester (3) having an intrinsic viscosity of 0.60 dl/g was obtained in the same manner as polyester (2), except that 10 parts by mass of organic particles (styrene-divinylbenzene: styrene-based resin) having an average particle size of 4.5 μm were added instead of the silica particles in polyester (2).

<Method of producing polyester film>
[PET-A]
A blend of polyester (1) and polyester (2) in a mass ratio of 80/20 was used as the A layer, and a blend of polyester (1) and polyester (3) in a mass ratio of 95.5/4.5, using only polyester (1) as the raw material for B layer, was supplied to the C layer extruder, heated and melted at 285°C, and co-extruded to a layer structure of three kinds of three layers (A (A layer)/B (B layer)/C (C layer)) with A layer and C layer as the outermost layer (surface layer) and B layer as the middle layer, with a thickness composition ratio of A/B/C = 5/90/5 under extrusion conditions, and cooled and solidified while being in close contact with a mirror-finished cooling drum with a surface temperature of 40 to 50°C, to prepare an unstretched polyethylene terephthalate film. This film was stretched 3.0 times in the longitudinal direction while passing through a group of heating rolls at 85°C, to obtain a uniaxially oriented film. The cured resin layer composition shown below was applied to both sides of this uniaxially stretched film, and then this film was introduced into a tenter stretching machine and stretched 4.1 times in the width direction at 100°C. Further, it was subjected to a heat treatment at 235°C, and then a relaxation treatment of 2% in the width direction was performed to obtain a biaxially oriented polyester film having a thickness of 50 μm and having a cured resin layer with a thickness (after drying) of 0.05 μm on both sides.

(Cured resin layer composition)
(A): Thiophene-based antistatic agent: A conductive agent consisting of polyethylenedioxythiophene and polystyrene sulfonic acid, "Orgacon ICP1010" manufactured by Agfa-Gevaert, neutralized with concentrated aqueous ammonia to a pH of 9.
(B) Polyhydroxy compound: Polyglycerol having an average degree of polymerization of 4 (C) Water dispersion of polyester resin having a condensed polycyclic structure copolymerized in the following composition Monomer composition: (acid component) 2,6-naphthalenedicarboxylic acid/5-sodium sulfoisophthalic acid // (diol component) ethylene glycol/diethylene glycol = 92/8 // 80/20 (mol%)
A/B/C=7/10/83 (mass%)

<Release Layer Composition>
a1: Curable silicone resin (a silicone resin in which a vinyl group has been introduced into the side chain and/or end of the main chain consisting of a siloxane bond, number average molecular weight: 10600, viscosity at 25°C when adjusted to 15% by mass by dilution with n-heptane solvent: 1.7 mcps)

(Composition analysis of curable silicone resin)
The composition of the curable silicone resins used in the examples and comparative examples was analyzed using a 400 MHz-NMR (Bruker Avance 400M), and the results are shown in Table 1. ¹ H-NMR measurements were performed at 30° C. using CDCl ₃ as the solvent and using the peak derived from the methyl group of dimethylsiloxane as the chemical shift standard. Table 1 below shows the content (mol %) of each functional group in the curable silicone resin.

b1: Crosslinking agent (CL750: manufactured by Momentive Performance Materials)
c1: Addition type platinum catalyst (CM678: manufactured by Momentive Performance Materials)
e1: Light release agent (methylphenyl silicone oil, Mw: less than 10,000, phenyl group content ratio; DM:MP=91:9 (mol%))
e2: Light release agent (methylphenyl silicone oil, Mw: 21000, phenyl group content ratio; DM:MP = 91:9 (mol%))
e3: Light release agent (methylphenyl silicone oil, Mw: 71000, phenyl group content ratio; DM:MP = 90:10 (mol%))
e4: Light release agent BY24-850 (manufactured by Toray Dow) (polydimethylsiloxane, Mw: 100,000 or more, phenyl group content ratio; DM:MP=100:0 (mol%))

[Example 2-1]
The following release layer composition was applied to the flat surface of the A layer side of PET-A so that the coating thickness (after drying) was 1 g/ ^m2 , and then dried at 150°C for 30 seconds to obtain a release film (sample film).

Release Layer Composition
Base agent: a1; 100 parts by weight Crosslinking agent: b1; 3 parts by weight Catalyst: c1; 3 parts by weight Light release agent: e1; 1 part by weight Solvent: Toluene; 1000 parts by weight MEK; 9000 parts by weight

[Examples 2-2 to 2-5]
Regarding the release layer composition, a film laminate was obtained by producing in the same manner as in Example 2-1, except that the type and amount of the light release agent were changed as shown in Table 7 below.

[Comparative Example 2-1]
A film laminate was obtained in the same manner as in Example 1, except that no light release agent was added to the release layer composition.

[Comparative Example 2-2]
A release film (sample film) was obtained in the same manner as in Example 1, except that the composition of the release layer in Example 1 was changed to the release layer composition shown below.

Release Layer Composition
Base agent: a1; 100 parts by weight Crosslinking agent: b1; 3 parts by weight Catalyst: c1; 3 parts by weight Light release agent: e4; 1 part by weight Solvent: Toluene; 1000 parts by weight MEK; 9000 parts by weight

*1 means no heat treatment.

From the results of this example, it was confirmed that by making the release layer containing a cured silicone resin relatively thick, using a light release agent of a specific composition in combination, and setting the elastic modulus to 500 MPa or less while keeping the maximum cross-sectional height (Rt) of the opposite release surface within a specified range, it is possible to obtain a release film that not only has a light release force, but also has low migration and is less prone to blocking, and yet has good adhesion to the substrate.
When comparing Comparative Example 1 with each Example in terms of the peel strength (normal peel strength) of the adhesive tape, the lightest type achieved approximately 60% of the peel strength of Comparative Example 1, thereby achieving an ultra-light peel strength.
In contrast, Comparative Example 1 was at the same level as the conventional product (light release type), and it was found that the peel strength against the adhesive layer was large. Comparative Example 2 contained a light release agent with a large molecular weight in the release layer, and therefore the light release effect was poor.

Example 3-1
The release layer used in Example 1-1 was evaluated for peelability using the adhesive described below. The results are shown in Table 8.
Adhesive A: 2EHA/BA/HEA=36/59/5% by mass (elastic modulus: 2.9 MPa, Tg: -59.0°C)
Adhesive B: 2EHA/HEA/AAc=92.8/7/0.2% by mass (elastic modulus: 2.7 MPa, Tg: -66.7°C)
2EHA; 2-ethylhexyl acrylate BA; butyl acrylate HEA; hydroxyethyl acrylate AAc; acrylic acid

Example 3-2
In Example 3-1, evaluation was performed in the same manner as in Example 3-1, except that the release layer used in Example 2-1 was used as the release layer. The results are shown in Table 8.

It was found that all of the resin layers used in the examples peeled off more easily than the reference examples (conventional technology).

According to the release film of the present invention, a release film can be provided that realizes ultra-light peelability while being resistant to changes in the peeling properties of the release layer due to blocking, and has high industrial value. In addition, the release film of the present invention and the film laminate including the release film have the characteristics of both ultra-light peelability and blocking resistance, and are therefore suitable for applications in which changes in the peeling properties of the release layer and deterioration of the appearance of the resin layer (A) surface are undesirable. For example, the film is suitable for use in various applications in which the film is bonded via an adhesive layer, such as for the manufacture of capacitive touch panels, optical members (polarizing plates, retardation plates, prism sheets, conductive films, resin films, glass substrates, etc.) used in liquid crystal displays, for the manufacture of organic electroluminescence components, and for the manufacture of various display components, as well as for the protection of various adhesive layers. In particular, the film can be applied to foldable displays that have a soft adhesive layer that easily follows deformation due to bending.

Claims (28)

A release film having a resin layer (A) on one side of a base film and a resin layer (B) on the other side, the resin layer (A) containing a silicone resin-based release agent and having a thickness of 0.2 to 2.0 μm, and the resin layer (B) containing a non-silicone resin-based release agent. A resin layer (A) is provided on at least one side of a base film,
The release film has a thickness of 0.2 to 1.5 μm, and the resin layer (A) is a cured product of a resin layer composition containing a curable silicone resin and a light release agent, and the light release agent has a dimethylsiloxane skeleton (DM) represented by the following formula (I) and a methylphenylsiloxane skeleton (MP) represented by the following formula (II):

The release film according to claim 2, wherein the maximum cross-sectional height (Rt) of the film surface opposite the surface on which the resin layer (A) is provided is 2.0 μm or less. The release film according to claim 2 or 3, wherein the surface of the base film opposite to the surface on which the resin layer (A) is provided is provided with a polyester layer containing 0.4 to 1.0 mass % of particles having an average particle size of 1 to 6 μm. A release film according to any one of claims 2 to 4, wherein the weight average molecular weight of the light release agent is 10,000 or more and 100,000 or less. A release film described in any one of claims 1 to 5, wherein the elastic modulus of the resin layer (A) at 25°C measured using a nanoindenter device is 500 MPa or less. The release film according to claim 1 or 6, wherein the non-silicone resin-based release agent is at least one selected from the group consisting of wax, a compound containing a long-chain alkyl group, and a fluorine compound. A release film as described in claim 1, 6 or 7, wherein the content of the release agent in the non-volatile components of the resin layer (B) is 10 to 70 mass %. A release film according to any one of claims 1 and 6 to 8, wherein the resin layer (B) is substantially free of particles. 10. The release film according to claim 1, wherein the normal peel strength of the resin layer (A) is 5 g/25 mm or less, as measured by the following evaluation method.
<Evaluation method>
An acrylic adhesive tape ("No. 7475" manufactured by Tesa) is attached to the resin layer (A) surface of the release film, cut to a size of 25 mm x 150 mm, and left at room temperature for 1 hour. The peeling force is 180° at a pulling speed of 0.3 m/min. A release film according to any one of claims 1 and 6 to 10, comprising an undercoat layer between at least one of the resin layer (A) or the resin layer (B) and the base film. The release film according to claim 11, wherein the undercoat layer is an antistatic layer. The release film according to claim 11 or 12, wherein the undercoat layer contains the following compounds (A) to (C):
(A) a polymer in which a compound consisting of thiophene or a thiophene derivative is doped with another anionic compound, or a self-doped polymer having an anionic group in a compound consisting of thiophene or a thiophene derivative; (B) a polyhydroxy compound; (C) one or more compounds selected from the group consisting of polyurethane resins, polyester resins, and acrylic resins. 14. The release film according to claim 1, wherein the surface resistivity of at least one of the surfaces of the resin layer (A) or the resin layer (B) is 1×10 ¹² Ω/□ or less. A release film according to any one of claims 1 to 14, wherein the base film is a polyester film. The release film according to claim 15, wherein the polyester film has a three-layer structure. The release film according to any one of claims 1 to 16, wherein the resin layer (A) has a heavy peeling rate after pressing of 100% or less, as evaluated by the following method.
<Evaluation method>
An acrylic adhesive tape ("No. 7475" manufactured by Tesa) was attached to the surface of the resin layer (A), cut to a size of 25 mm x 150 mm, and left at room temperature for 1 hour. The peel strength at 180° under the condition of a tensile speed of 0.3 m/min was defined as (F1).
Next, the resin layer (A) is laminated so as to contact the surface, and pressed for 20 hours at a temperature of 40° C., a humidity of 90% RH, and a load of 1 MPa. An acrylic adhesive tape (Tesa's "No. 7475") is attached to the resin layer (A) surface after the treatment, and then cut to a size of 25 mm x 150 mm and left at room temperature for 1 hour. The peel force at 180° peeled under the condition of a pulling speed of 0.3 m/min is defined as (F2).
The heavy peeling rate after pressing is calculated using the following formula.
Heavy peeling rate after pressing (%) = (F2 - F1) / F1 x 100 The release film according to any one of claims 1 to 17, wherein the center line average roughness (Ra(A)) of the surface of the resin layer (A) is 30 nm or less. The release film according to claim 1 or any one of claims 6 to 18, wherein the center line average roughness (Ra(B)) of the surface of the resin layer (B) is 60 nm or less. An adhesive sheet comprising a release film according to any one of claims 1 to 19 and another release film via an adhesive layer. The adhesive sheet according to claim 20, wherein the adhesive layer is formed from an acrylic adhesive composition. An adhesive sheet as described in claim 20 or 21, wherein the elastic modulus (25°C) of the adhesive layer is 6.0 MPa or less. An adhesive sheet according to any one of claims 20 to 22, wherein the adhesive layer contains 2-ethylhexyl acrylate and/or butyl acrylate. An adhesive sheet according to any one of claims 20 to 23, which is for use as an optically transparent adhesive sheet. A release film according to any one of claims 1 to 19, which is for use in a display. A release film according to any one of claims 1 to 19, which is for a foldable display. A method for using an adhesive sheet according to any one of claims 20 to 23, comprising peeling off the other release film and then bonding the exposed surface of the adhesive layer to an optical member. A method for using the adhesive sheet described in claim 27, wherein the optical component is a polarizing plate or a touch sensor.