JP7746689B2 - Release film, release film with adhesive layer, and film laminate - Google Patents

Description

The present invention relates to a release film, a release film with an adhesive layer, and a film laminate.

One example of a method for manufacturing liquid crystal display devices used in image display devices such as liquid crystal televisions, computer displays, mobile phones, and digital cameras is to use a release film with an adhesive layer, i.e., a base film laminated to one side of an adhesive layer with a release layer interposed therebetween, and then attach the adhesive layer to a polarizing plate to produce an adhesive-layered polarizing plate. Then, when attaching the polarizing plate to a liquid crystal cell, the base film (release film) with the release layer is peeled off, and the adhesive layer is attached to the glass substrate of the liquid crystal cell.

In recent years, as displays have become larger, the dimensions of optical components such as polarizing plates and release films have also increased, and the release films used in the manufacture of the above-mentioned liquid crystal display devices are now required to have the property of being easily peelable even when the peeling area is large.
Silicone is a material with excellent properties, such as the flexibility of the siloxane skeleton and the low surface energy due to methyl group substitution, which allows it to be peeled off with little force (also referred to as "easy peelability"). For this reason, as a release film for protecting adhesives used to bond optical components, such as components constituting liquid crystal displays, attention has been focused on release films provided with a release layer formed by curing a heat/ultraviolet curable silicone-based release agent whose main component is silicone resin.

Regarding release films with a release layer containing silicone as the primary resin component, for example, Patent Document 1 discloses a release film that peels easily, has excellent retention during storage, and is resistant to atmospheric exposure and non-migration. The release film is made by applying a coating material whose primary resin component is curable silicone to at least one side of a polyester film, and the coating material contains solvent-curable silicone, solventless-curable silicone, and a reactive release modifier as primary components, and the ratio of SiH groups to vinyl groups in the coating material is within a specific range.

Patent Document 2 discloses a release film characterized by having a silicone-based release layer formed on one side of a polyester film from a coating liquid containing a reactive silicone resin having hexenyl, vinyl, phenyl, and hydrosilyl groups as functional groups, a non-reactive silicone resin with a mass-average molecular weight of 50,000 to 100,000, and a platinum-based catalyst.

Patent Document 3 discloses a release film comprising a release layer on at least one side of a polyester film, wherein the composition forming the release layer contains a curable silicone (A) having a number average molecular weight of 50,000 or more and a curable silicone (B) having a number average molecular weight of 30,000 or less, wherein the curable silicone (B) has a T unit structure, and the content of T unit structures in the polysiloxane chain of the curable silicone (B) is 3 mol % or more in siloxane units.

Optical components such as polarizing plates and touch sensors are sometimes distributed in a state in which an adhesive layer and a release film are laminated together. For example, an optical component may be distributed in a state in which a protective film is releasably laminated on one side of the optical component via a light adhesive layer, and a release film with an adhesive layer is laminated on the other side, i.e., in a state of release film/adhesive layer/optical film/light adhesive layer/protective film.
In this case, if the peeling force when peeling the release film from the adhesive layer is greater than the adhesion force between the optical component and the light adhesive layer, the protective film may peel off first, which is known as the "sad separation phenomenon." Therefore, release films with adhesive layers used for optical applications are required to have excellent light peeling properties, so that they can be peeled off with even less force.

Furthermore, in the past, even if the adhesive layer surface (also simply referred to as the "adhesive layer surface") of a release film with an adhesive layer had some unevenness on the side not in contact with the release film, i.e., the side opposite the release film, this was not a problem because the adhesive layer surface was bonded to the optical component. However, in recent years, as components have become thinner and quality requirements regarding optical properties have increased, the unevenness of the adhesive layer surface of a release film with an adhesive layer has become an issue. That is, if the adhesive layer surface has unevenness, distortion occurs at the interface between the adhesive layer and the optical component when the film is bonded to the optical component, and this distortion can cause light scattering, which can interfere with accurate optical inspection.
Therefore, with respect to a release film with an adhesive layer, the surface of the adhesive layer on the side not in contact with the release film is required to be smooth with few irregularities.

JP 2009-214359 A JP 2016-188265 A Japanese Patent Application Laid-Open No. 2020-108937

The inventors of the present invention investigated the causes of unevenness on the surface of the adhesive layer on the side of a release film with an adhesive layer that is not in contact with the release film, i.e., the side opposite the release film, and found that the unevenness is formed on the surface of the adhesive layer mainly for two reasons due to the interaction between the release layer and the adhesive layer. Specifically, the inventors found that unevenness on the surface of the adhesive layer can result in unevenness on the surface of the adhesive layer due to the unevenness on the surface of the release layer, and that elution of incompatible components from the release layer to the adhesive layer can cause repelling when the adhesive layer composition is applied, or that the incompatible components can penetrate into the adhesive layer and form a phase-separated structure, resulting in unevenness on the surface of the adhesive layer.

The present invention relates to a release film and a release film with an adhesive layer, and aims to provide a new release film that can suppress unevenness on the adhesive layer surface to make it smooth, while also providing excellent easy peelability, as well as a new release film with an adhesive layer and a film laminate that uses this film.

The present invention provides a release film having a release layer on one side of a base film,
The release film proposed has an elastic modulus of 1.4 MPa or less, and after the release film is pressed under a pressure of 1 MPa for 1 hour, an acrylic adhesive tape is attached to the release layer, the tape is cut to a size of 50 mm x 300 mm, and the tape is heated and held at 100°C (set temperature) for 1 hour in a hot air oven, and then allowed to stand at 23°C and 50% RH for 1 hour. The 180° peel strength of the release film is 15 mN/cm or less under conditions of a tensile speed of 300 mm/min.

The present invention also proposes a release film having a release layer formed on one side of a substrate film by curing a release layer composition.
In this case, the release layer composition proposed is a release layer composition whose main component is a curable silicone resin having a number average molecular weight (Mn) of 20,000 or more and 350,000 or less, or a release layer composition containing 0.01 to 5.0 mol % of phenyl groups relative to the total siloxane components.

The present invention also proposes a release film with an adhesive layer, which has a configuration in which an adhesive layer is laminated on the release layer of the release film.

The present invention also proposes a film laminate having an optical component bonded to the surface of the adhesive layer of the adhesive-coated release film.

The release film, adhesive-attached release film, and film laminate proposed by the present invention not only have excellent easy releasability, but also suppress unevenness on the adhesive layer surface, achieving excellent smoothness. Therefore, the release film, adhesive-attached release film, and film laminate proposed by the present invention are particularly suitable for use in optical applications.

1 is a graph obtained by plotting the relationship between the elastic modulus of the release surface of the release films (sample films) obtained in Reference Examples 1 to 3 and the coating thickness (after drying) and fitting the relationship using logarithmic transformation and power approximation of linear regression.

Next, an example of an embodiment of the present invention will be described. However, the present invention is not limited to the embodiment described below.

<<<<Release Film>>>
A release film according to one embodiment of the present invention (referred to as "the present release film") is a release film having a release layer (referred to as "the present release layer") on at least one side of a base film (referred to as "the present base film").

The present release film only needs to have the present release layer on one side of the present base film, and as described below, may have other layers between the present base film and the present release layer.

<<This base film>>
The material of the present substrate film is not particularly limited as long as it is in the form of a film. For example, it may be made of paper, resin, metal, etc. Among these, resin is preferred from the viewpoint of mechanical strength and flexibility.

Examples of resin substrate films include films made from polymers such as polyethylene, polypropylene, polyester, polystyrene, polycarbonate, polyethersulfone, polyamide, and polyimide. Furthermore, as long as they can be formed into a film, they may also be mixtures of these materials (polymer blends) or composites of their constituent units (copolymers).

Among the films exemplified above, polyester films are particularly preferred because they have excellent physical properties such as heat resistance, flatness, optical properties, and strength.
The polyester film may be a single layer film or a multilayer film (laminated film) having two or more layers with different properties.
The polyester film may be a non-stretched film (sheet) or a stretched film. Among them, a uniaxially or biaxially stretched film is preferred. Among them, a biaxially stretched film is more preferred from the viewpoint of balance of mechanical properties and flatness.

The polyester that is the main component resin of the polyester film may be either a homopolyester or a copolymer polyester.
The term "main component resin" refers to the resin with the largest mass proportion among the resins constituting the polyester film, and is expected to account for 50 mass% or more, 75 mass% or more, 90 mass% or more, or 100 mass% of the resins constituting the polyester film.

The homopolyester is preferably one obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol, such as terephthalic acid or 2,6-naphthalenedicarboxylic acid, and such as ethylene glycol, diethylene glycol, 1,4-butanediol, or 1,4-cyclohexanedimethanol, as the aromatic dicarboxylic acid and such as ethylene glycol, diethylene glycol, 1,4-butanediol, or 1,4-cyclohexanedimethanol.
Typical examples of homopolyester include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

On the other hand, when the polyester is a copolymer polyester, it is preferable that the copolymer contains 30 mol % or less of a third component.
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, etc. On the other hand, examples of the glycol component of the copolymer polyester include one or more of ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, etc.

Among these, polyethylene terephthalate, which contains 60 mol% or more, preferably 80 mol% or more, of ethylene terephthalate units, is preferred for the substrate film.

The present substrate film may contain particles, mainly for the purposes of imparting easy slipperiness and preventing scratches during each process.
When particles are blended, the type of particles to be blended is not particularly limited as long as they are particles that can impart lubricity, and examples thereof include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide, and organic particles such as acrylic resin, styrene resin, urea resin, phenolic resin, epoxy resin, and benzoguanamine resin. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

The shape of the particles is not particularly limited. For example, they may be spherical, lumpy, rod-like, flat, etc. Furthermore, there are no particular limitations on the hardness, specific gravity, color, etc. of the particles. Furthermore, two or more types of particles with different physical properties may be used in combination, if necessary.

The average particle size of the particles is preferably 0.1 μm or more and 5 μm or less, and more preferably 0.5 μm or more or 4 μm or less, and even more preferably 1 μm or more or 4 μm or less. Using particles with such an average particle size gives the film an appropriate surface roughness, ensuring good slipperiness and smoothness.

Regarding the particle content in the present base film, if there are no particles or if there are only a few particles, the film will have high transparency but may have insufficient slipperiness. On the other hand, if the particle content is too high, the film may have insufficient transparency. From this perspective, the particle content in the present base film is preferably 5% by mass or less, and more preferably 0.1% by mass or more or 3% by mass or less.
In applications requiring a high level of inspection, the transfer of convex shapes resulting from particles present on the surface of the substrate film to the adhesive layer can be a problem. Therefore, to prevent the particles from interfering with the inspection, it may be preferable to configure at least one or both surfaces of the substrate film to be particle-free. Alternatively, the amount or size of particles on the surface in contact with the adhesive layer can be reduced to smooth that surface, while the surface roughness of the opposite surface can be increased, thereby creating a configuration in which the amount or size of particles on the front and back surfaces are different from each other.

<<Main release layer>>
This release layer is a layer formed by curing a release layer composition (referred to as "this release layer composition") whose main component resin is a curable silicone resin ("this curable silicone resin"), and is arranged on at least one side of this substrate film.
The present release layer can also be said to be a release layer containing a cured product obtained by curing the present release layer composition.

<This release layer composition>
The release layer composition may be any composition containing a curable silicone resin as a main component resin.
The release layer composition may contain components other than the curable silicone resin, and may contain, as necessary, for example, catalysts, reaction control agents, crosslinking agents, polymerization initiators, particles, diluents, and other additives.

The term "main component resin" refers to the resin that has the largest mass proportion among the resins that make up the release layer composition, and is expected to account for 50 mass% or more, 75 mass% or more, 90 mass% or more, or 100 mass% of the resins that make up the release layer composition.

The release layer composition or the release layer preferably contains 0.01 to 5.0 mol % of phenyl groups relative to the total amount of siloxane components, that is, the total amount of siloxane components contained in the release layer composition or the release layer.
By containing a predetermined amount of phenyl groups, the release layer composition or the release layer can cover alkenyl groups (e.g., vinyl groups, hexenyl groups) or Si-H groups that may remain on the surface of the release layer, thereby reducing the interaction between the release layer and the adhesive layer and expected to provide an even easier peeling effect.
From this viewpoint, it is preferable that the present release layer composition or the present release layer contains 0.01 to 5.0 mol% of phenyl groups relative to the total amount of siloxane components, and it is particularly preferable that the phenyl group content be 0.05 mol% or more or 4.0 mol% or less, of which 0.1 mol% or more or 3.0 mol% or less, and of which 0.2 mol% or more or 2.0 mol% or less.

To ensure that the release layer composition or the release layer contains phenyl groups in the above proportion, a curable silicone resin containing a specified proportion of phenyl groups may be used. However, this method is not limited to this. For example, a compound containing phenyl groups, such as a non-curable silicone resin or silane compound having phenyl groups, may be added.

Furthermore, if the amount of alkenyl groups, i.e., residual functional groups having double bonds such as hexenyl groups and vinyl groups, is small relative to the total amount of siloxane components in the present release layer composition or present release layer, the release layer may not be sufficiently cured, while if the amount of alkenyl groups is greatly excessive, the release force after exposure to air tends to be strong. For this reason, the present release layer composition or present release layer preferably contains 0.4 to 1.0 mol% of alkenyl groups relative to the total amount of siloxane components, and particularly preferably contains 0.5 mol% or more or 0.9 mol% or less, and particularly preferably contains 0.6 mol% or more or 0.8 mol% or less of alkenyl groups.
Furthermore, if the amount of Si-H groups in the release layer composition or the release layer is small relative to the total amount of siloxane components, the release layer will not cure sufficiently, while if the amount of Si-H groups is excessive, the remaining Si-H groups may react with the adhesive layer, affecting the release strength of the release film. For this reason, the release layer composition or the release layer preferably contains 0.8 to 2.2 mol% of Si-H groups relative to the total amount of siloxane components, and particularly preferably contains 1.2 mol% or more or 2.1 mol% or less, and particularly preferably contains 1.4 mol% or more or 2.0 mol% or less of Si-H groups.

The total siloxane component content in the release layer composition or release layer can be measured, for example, by 1H-NMR from the integral ratio of the main chain dimethylsiloxane unit to other units, and the phenyl group content, alkenyl group content, and Si-H group content can also be evaluated, for example, by measuring 1H-NMR. However, these methods are not limited to these.

<Fully cured silicone resin>
In the present invention, the term "curable silicone resin" refers to a silicone resin that has the property of being able to be cured. This also includes silicone resins that can be cured by mixing a crosslinking agent in advance.
The curing method of the curable silicone resin is optional, and may be, for example, a resin that cures by a condensation reaction in response to moisture in the air, a resin that cures by an addition reaction caused by heating, or a resin that cures by addition polymerization or radical polymerization caused by light.
Among these, thermosetting silicone resins that cure by an addition reaction caused by heating are preferred, since they do not produce by-products in the curing reaction and the physical properties of the cured film are stable.
When the present curable silicone resin is a thermosetting type, it is preferable that an alkenyl group such as a vinyl group (Vi group) or a hexenyl group be introduced into a side chain and/or terminal of the main chain consisting of a siloxane bond in the structure.

The present curable silicone resin may be any polymer having a main chain of siloxane bonds consisting of silicon and oxygen.
Examples of the present curable silicone resin include those in which various substituents have been introduced into the side chains or terminals of the main chain consisting of siloxane bonds, such as methyl groups, phenyl groups, polyethers, epoxy groups, amines, carboxyl groups, aralkyl groups, and the like, or combinations of two or more of these groups.

As an example of a method for ensuring that the release layer composition or the release layer contains phenyl groups in a predetermined proportion, there can be mentioned the use of a curable silicone resin containing 0.01 to 5.0 mol% of phenyl groups, particularly 0.05 mol% or more or 4.0 mol% or less, of which 0.1 mol% or more or 3.0 mol% or less, and of which 0.2 mol% or more or 2.0 mol% or less of phenyl groups.
In this case, the molar ratio of phenyl groups to methyl groups (phenyl/methyl) in the present curable silicone resin is more preferably 0.0001 to 0.05, and even more preferably 0.0005 or more or 0.04 or less, even more preferably 0.001 or more or 0.03 or less, and even more preferably 0.02 or more or 0.02 or less.

An example of the present curable silicone resin is a silicone resin in which one or more of a phenyl group, a Si—H group (also simply referred to as an “H group”), and an alkenyl group have been introduced into a side chain or terminal of a linear main chain consisting of siloxane bonds.
In this case, the phenyl group content in the present curable silicone resin is preferably 0.01 to 5.0 mol%, and more preferably 0.05 mol% or more or 4.0 mol% or less, and even more preferably 0.1 mol% or more or 3.0 mol% or less, and even more preferably 0.2 mol% or more or 2.0 mol% or less.
In this case, the content of Si—H groups in the present curable silicone resin is preferably 0.8 to 2.2 mol %, more preferably 1.2 mol % or more or 2.1 mol % or less, and even more preferably 1.4 mol % or more or 2.0 mol % or less.
In this case, the vinyl group content in the present curable silicone resin is preferably 0.4 to 1.0 mol %, more preferably 0.4 mol % or more or 1.0 mol % or less, and even more preferably 0.6 mol % or more or 0.9 mol % or less.

The present curable silicone resin may be a combination of two or more curable silicone resins. In that case, it is preferable that the content ratio of each of the above-mentioned functional groups be within the above-mentioned range, on average, for the two or more curable silicone resins.

The number average molecular weight (Mn) of the present curable silicone resin is preferably 20,000 or more and 350,000 or less.
If the number average molecular weight (Mn) of the curable silicone resin is too low, when an adhesive layer is laminated on the release film, a large amount of the low molecular weight silicone resin will leach out or migrate into the adhesive layer, which is not preferable. Even if the release layer is applied thickly, the light release effect tends to be poor. On the other hand, if the number average molecular weight (Mn) of the curable silicone resin is too high, the viscosity increases, the fluidity of the release layer composition decreases, and when the release layer composition is applied, streaky coating unevenness occurs, making it difficult to smooth the surface of the release layer, which is not preferable.
From this viewpoint, the number average molecular weight (Mn) of the present curable silicone resin is preferably 20,000 or more, more preferably 50,000 or more, even more preferably 100,000 or more, and even more preferably 150,000 or more. On the other hand, it is preferably 350,000 or less, even more preferably 300,000 or less, and even more preferably 250,000 or less.

From the same viewpoint, the mass average molecular weight (Mw) of the present curable silicone resin is preferably 35,000 to 600,000, more preferably 50,000 or more or 500,000 or less, even more preferably 100,000 or more or 450,000 or less, and even more preferably 120,000 or more.

The curable silicone resin preferably has a ratio (Mw/Mn) of mass average molecular weight (Mw) to number average molecular weight (Mn) of 1.7 to 2.7, and more preferably 1.9 or more or 2.5 or less. By satisfying this range, it is expected that the crosslinking reaction will proceed efficiently.

The present curable silicone resin may be a combination of two or more types of curable silicone resins, in which case it is preferable that the average molecular weight of the two or more types of curable silicone resins be within the above range.

The present curable silicone resin preferably has a viscosity of 10 to 400 mcps at 25° C. when diluted with n-heptane solvent to adjust the content to 15% by mass.
If the viscosity of the curable silicone resin is 10 mcps or more, the appropriate viscosity of the coating solution can suppress repelling and provide a good coating appearance, which is preferable. On the other hand, if the viscosity is 400 mcps or less, the fluidity of the release layer composition can be maintained, the occurrence of streaky coating unevenness can be suppressed when the release layer composition is applied, and the surface of the release layer can be made smooth, which is preferable.
From this viewpoint, the viscosity of the present curable silicone resin is more preferably 40 mcps or more, more preferably 80 mcps or more, and more preferably 300 mcps or less, more preferably 200 mcps or less.

The present curable silicone resin may be either a solventless curable silicone or a solvent curable silicone, or a combination of both.
Here, "solventless curable silicone" refers to a silicone with a viscosity that allows it to be applied without diluting it with a solvent, and is made up of short polysiloxane chains and has a relatively low molecular weight.
On the other hand, "solvent-curable silicone" is a silicone that is so viscous that it cannot be applied without being diluted with a solvent, and has a relatively high molecular weight compared to solventless-curable silicone.
In particular, it is preferable that the present curable silicone resin has a medium number average molecular weight (Mn) and a medium viscosity, as described above, and furthermore, it is preferable that it is a solvent-type curable silicone, from the viewpoints of providing good adhesion to the present substrate film, good coating appearance (evenness), and ease of adjusting the film thickness of the present release layer.

<Other ingredients>
As described above, in addition to the present curable silicone resin, the present release layer composition may contain, as necessary, for example, a curing catalyst, particles, a diluting solvent, a reaction control agent, a crosslinking agent, a polymerization initiator, an adhesion promoter, and other additives.
For example, one example of the release layer composition of the present invention is a composition containing the present curable silicone resin, a crosslinking agent having a hydrosilyl group (SiH group) on the side chain and/or end of a main chain consisting of a siloxane bond, a catalyst containing platinum (Pt), and a solvent.

(catalyst)
The release layer composition may optionally contain a curing catalyst, i.e., a catalyst for promoting the hydrosilylation addition reaction between the alkenyl group bonded to the silicon atom of the curable silicone and the hydrogensilane (SiH) group of the silicone crosslinker.
Examples of the curing catalyst include, but are not limited to, platinum black, platinic chloride, chloroplatinic acid, reaction products of chloroplatinic acid with monohydric alcohols, complexes of chloroplatinic acid with olefins, platinum-based catalysts such as platinum bisacetoacetate, palladium-based catalysts, and rhodium-based catalysts.

The content of the curing catalyst in the release layer composition is preferably 0.5 to 500 ppm by mass, calculated as a metal equivalent, relative to the curable silicone, and more preferably 5 ppm by mass or more or 300 ppm by mass or less, and even more preferably 10 ppm by mass or more or 200 ppm by mass or less.

(Crosslinking agent)
The crosslinking agent is preferably a crosslinking agent having a siloxane bond (also referred to as a "silicone crosslinking agent"), and particularly preferably one having silicon-bonded hydrogen atoms (SiH groups) on the side chains and/or ends of the main chain consisting of siloxane bonds.

For example, examples include those represented by the following general formula (1) that contain at least two, preferably three or more (usually about 3 to 200), more preferably 3 to 100, and especially 3 to 50 silicon-bonded hydrogen atoms (SiH groups) per molecule.

R _b H _c SiO _(4-b-c)/2 (1)

In formula (1), R is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms. Furthermore, b is a positive number that satisfies the range of 0.7 to 2.1, particularly 0.8 to 2.0, c is a positive number that satisfies the range of 0.001 to 1.0, and b+c is a positive number that satisfies the range of 0.8 to 3.0, particularly 1.0 to 2.5.

Here, R can be the same group as R in the alkenyl group-containing organopolysiloxane, but preferably does not contain an aliphatic unsaturated bond such as an alkenyl group.

These silicon-bonded hydrogen atoms may be bonded to silicon atoms at the ends of the molecular chain, to silicon atoms in the middle of the molecular chain (non-terminal), or to both.

The molecular structure of the silicone crosslinking agent may be any of a linear, cyclic, branched, and three-dimensional network structure.
Furthermore, the number of silicon atoms (or degree of polymerization) in one molecule is preferably 2 to 1,000, more preferably 3 or more or 500 or less, even more preferably 3 or more or 300 or less, and even more preferably 4 or more or 150 or less.

Examples of silicone crosslinking agents include tris(dimethylhydrogensiloxy)methylsilane, tris(dimethylhydrogensiloxy)phenylsilane, 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane-dimethylsiloxane cyclic copolymer, methylhydrogenpolysiloxane capped at both ends with trimethylsiloxy groups, and dimethylsiloxane-methylhydrogen capped at both ends with trimethylsiloxy groups. Examples of the copolymer include a phenylsiloxane copolymer, a dimethylpolysiloxane capped at both ends with dimethylhydrogensiloxy groups, a methylhydrogenpolysiloxane capped at both ends with dimethylhydrogensiloxy groups, a dimethylsiloxane-methylhydrogensiloxane copolymer capped at both ends with dimethylhydrogensiloxy groups, a methylhydrogensiloxane-diphenylsiloxane copolymer capped at both ends with trimethylsiloxy groups, a methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer capped at both ends with trimethylsiloxy groups, a copolymer consisting of ( _CH3 )2HSiO1 _{/2 units} and SiO4 _{/2 units} , a copolymer consisting of ( _CH3 )2HSiO1 _/2 units, SiO4 _/2 units and ( _C6H5 )SiO3 _{/2 units} , and compounds in which some or all of the methyl groups in these exemplary compounds have been substituted with other alkyl groups such as ethyl groups or propyl groups, or aryl groups such as phenyl groups. However, it is not limited to these.

(particle)
The release layer composition may contain particles as needed to adjust the release force or to prevent blocking.
In this case, the type of particle is not particularly limited as long as it is a particle that can impart the above-mentioned properties, and examples thereof include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide, and organic particles such as silicone resin, acrylic resin, styrene resin, urea resin, phenolic resin, epoxy resin, and benzoguanamine resin.
Among these, it is preferable that the particles are made of silicone resin because of its good compatibility with the silicone resin that is the binder resin component.

The shape of the particles is not particularly limited, and may be, for example, spherical, blocky, rod-like, flat, or the like.
Furthermore, there are no particular limitations on the hardness, specific gravity, color, etc. of the particles.
Two or more types of these particles may be used in combination as needed.

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

(Reaction inhibitor)
The release layer composition may optionally contain a reaction inhibitor.
The reaction inhibitor may be, for example, acetylene alcohol.
The reaction inhibitor may be used alone or in combination of two or more types, if necessary.
The content of the reaction inhibitor is preferably 0.001 to 5.0 parts by mass per 100 parts by mass of the total amount of the release layer composition, and more preferably 0.01 part by mass or more or 1.0 part by mass or less, and even more preferably 0.05 part by mass or more or 0.5 part by mass or less.

<Thickness of this release layer>
The thickness of the release layer is not particularly limited. If the thickness of the release layer is large, the influence of the substrate film, for example, the influence of the hardness of the substrate film, is less likely to be transmitted to the release surface of the release film, which is preferable. From this point of view, the thickness of the release layer (after drying) is preferably 0.25 μm or more, more preferably 0.30 μm or more, and even more preferably 0.35 μm or more. On the other hand, if the thickness of the release layer is too thick, blocking may occur, the coating appearance may deteriorate, etc., so it is preferably 2.0 μm or less, and even more preferably 1.5 μm or less, even more preferably 1.0 μm or less, and even more preferably 0.8 μm or less.

<<Other demographics>>
The present release film may have "another layer" between the present base film and the present release layer.
Examples of the "other layer" include an anchor coat layer for increasing the adhesion between the substrate film and the release layer, as well as cured resin layers having various functions.
The cured resin layer is a layer mainly composed of a cured resin, in other words, a resin having a crosslinked structure, and examples thereof include an oligomer sealing layer that seals out the bleed (bleeding, plate-out) of compounds or oligomers onto the film surface, and an antistatic layer that has antistatic properties, but is not limited to these.

<<Method of manufacturing the release film>>
The present release film can be produced by forming a coating layer such as an antistatic layer or an oligomer sealing layer, as needed, on one or both sides of the present base film, and then applying the present release layer composition to these surfaces, drying, and curing the resulting film.

The release layer composition can be applied by any conventional coating method, such as multi-roll coating, reverse gravure coating, direct gravure coating, bar coating, or die coating. Examples of coating methods are described in "Coating Methods" (published by Maki Shoten, Harasaki Yuji, 1979).

The polyester film may be subjected to a surface treatment such as corona treatment or plasma treatment before applying the release layer composition.

The coating amount of the release layer composition, i.e., the thickness (after drying) of the release layer, is preferably small from the viewpoint of preventing blocking and suppressing an increase in migration (i.e., the property of the release agent component migrating to the adhesive tape, etc.), while it is preferably large from the viewpoint of maintaining easy releasability (low peel force).
In consideration of these points, the coating amount of the release layer composition, i.e., the thickness of the release layer (after drying), is preferably 0.1 to 5.0 g/ ^m2 , more preferably 0.2 g/ ^m2 or more or 3.0 g/m2 or ^less , and even more preferably 0.3 g/ ^m2 or more or 2.0 g/ ^m2 or less.

When the release layer composition is cured by heating, it may be heated using a conventionally known heat treatment device. Examples include a heating oven, a hot plate, a hot air dryer, a near-infrared lamp, and an air dryer. The heat treatment temperature is preferably 35 to 220°C, more preferably 40°C or higher or 200°C or lower, and even more preferably 50°C or higher or 180°C or lower.
Furthermore, the heat treatment time is preferably 3 seconds to 3 minutes, more preferably 5 seconds or more or 2 minutes or less, and even more preferably 5 seconds or more or 1 minute or less.

On the other hand, when the release layer composition is cured by ultraviolet irradiation, ultraviolet irradiation can be performed using a conventionally known ultraviolet irradiation device. In this case, the light source that can be used may be, for example, a fusion (H) lamp, a metal halide lamp, a high-pressure mercury lamp (ozone-generating type, ozone-less type), or a UV-LED.

The amount of ultraviolet light irradiation is not particularly limited, but is preferably 10 to 3000 (mJ/cm ² ) in terms of cumulative light amount, more preferably 50 (mJ/cm ² ) or more or 2000 (mJ/cm ² ) or less, and even more preferably 100 (mJ/cm ² ) or more or 1500 (mJ/cm ² ) or less.

<<Physical properties of this release film>>
The release film may have the following physical properties:

<Elastic modulus>
The elastic modulus of the release layer in the release film is preferably 1.4 MPa or less.
If the modulus of elasticity of the release layer is 1.4 MPa or less, the smoothness of the surface of the adhesive layer formed on the release layer can be improved.
From this viewpoint, the elastic modulus of the release layer is preferably 1.4 MPa or less, more preferably 1.3 MPa or less, and even more preferably 1.1 MPa or less.
On the other hand, with regard to the lower limit, from the viewpoint of the film strength of the release layer, it is preferably 0.1 MPa or more, more preferably 0.2 MPa or more, more preferably 0.3 MPa or more, even more preferably 0.4 MPa or more, and particularly preferably 0.5 MPa or more.

<Adhesion energy>
The adhesion energy of the release layer in the release film is preferably 25 mJ/ ^m2 or more and 39 mJ/ ^m2 or less, more preferably 30 mJ/ ^m2 or more and 39 mJ/ ^m2 or less, even more preferably 35 mJ/ ^m2 or more and 39 mJ/ ^m2 or less, and even more preferably 36 mJ/ ^m2 or more and 38 mJ/ ^m2 or less.
When the adhesion energy of this release layer satisfies the above range, the release layer forms a surface with moderate wettability, and even when an adhesive layer is formed on this release layer, incompatible components are eluted from the release layer to the adhesive layer side, thereby achieving easy peelability while suppressing the occurrence of repelling when applying the adhesive layer composition or the incompatible components penetrating into the adhesive layer to form a phase separation structure.

The adhesion energy and elastic modulus of this release layer can be calculated in accordance with the JKR two-point method based on the force curve obtained by attaching a silicon probe (LRCH, manufactured by team nanotec, radius of curvature: 250 nm, spring constant: 0.2 N/m) to an atomic force microscope (product name: SPM-9700HT, manufactured by Shimadzu Corporation) and tapping at 600 m/s.

<Heating peel strength (after pressing)>
The present release film is subjected to a press treatment under a pressure of 1 MPa for 1 hour, and then one side of an acrylic adhesive tape, such as No. 502 manufactured by Nitto Denko, is attached to the surface of the release layer of the release film. The tape is then cut to a size of 50 mm x 300 mm, heated and held at 100°C (set temperature) in a hot air oven for 1 hour, and then allowed to stand at 23°C and 50% RH for 1 hour. The 180° peel strength (referred to as "heat peel strength (after pressing)") measured at a tensile speed of 300 mm/min using a tensile tester, such as an "EZgraph" manufactured by Shimadzu Corporation, is preferably 15 mN/cm or less. Of these, 14 mN/cm or less is more preferable, and 11 mN/cm or less is even more preferable.
The peel strength can be measured using, for example, a tensile tester ("EZgraph" manufactured by Shimadzu Corporation), but is not limited to such a tester.

<Heat peeling force (no press)>
The release film is prepared by adhering one side of an acrylic double-sided adhesive tape, such as "No. 502" manufactured by Nitto Denko Corporation, to the release layer surface of the release film, cutting the tape to a size of 50 mm x 300 mm, heating and holding the tape in this state at 100°C (set temperature) for 1 hour, and then leaving the tape to stand at 23°C and 50% RH for 1 hour. The peel strength (referred to as "heat peel strength (without pressing)") estimated using a tensile tester, such as "EZgraph" manufactured by Shimadzu Corporation, at 180° peeling under conditions of a tensile speed of 300 mm/min is preferably 15 mN/cm or less, more preferably 14 mN/cm or less, and even more preferably 11 mN/cm or less.

<TESA7475 tape heat peel strength>
The present release film is prepared by attaching an acrylic adhesive tape, for example, "TESA7475" manufactured by Tesa, to the release layer surface of the present release film, cutting it to a size of 25 mm x 300 mm, heating and holding it in this state at 100°C (set temperature) in a hot air oven for 1 hour, and then leaving it to stand at 23°C and 50% RH for 1 hour, and then fixing the side opposite the release layer of the sample to a SUS plate with double-sided tape. The peel force (referred to as "TESA7475 tape heat peel force") when peeled at 180° under conditions of a tensile speed of 300 mm/min, as estimated using a tensile tester, for example, "EZgraph" manufactured by Shimadzu Corporation, is preferably 30 mN/cm or less, more preferably 25 mN/cm or less, and even more preferably 20 mN/cm or less.

This release film not only satisfies the above-mentioned range for heat peel strength (after pressing), but also satisfies the heat peel strength (without pressing), the TESA 7475 tape heat peel strength, or both, thereby achieving even easier peeling.

<Arithmetic mean height of surface (Sa)>
In the present release film, there are no particular restrictions on the calculated average roughness (Sa, ISO 25178 surface quality) of the surface of the present release layer, the surface of the film not provided with the present release layer, or both of these surfaces, but from the viewpoint of the blocking resistance of the silicone layer in the present invention, the effects of the present invention are significantly obtained when the arithmetic average roughness Sa is 30 nm or less. It is known that as the calculated average roughness of the surface of the present release layer, the surface of the film not provided with the present release layer, or both of these surfaces decreases, blocking becomes more likely to occur, resulting in heavy peeling of the release layer and the generation of peel electrification when the film wound into a roll is unwound.
On the other hand, from the viewpoint of transferring the uneven shape to the adhesive layer formed on the surface of this release layer and inspectability for optical applications, it is preferable that the calculated average roughness (Sa) of the surface of this release layer or the surface of a film on which this release layer is not formed is 30 nm or less, since the surface of the release layer is smooth.
From this viewpoint, it is preferable that the calculated average roughness (Sa) of the surface of the release layer, or the surface of the film on which the release layer is not provided, or both of these surfaces, is 30 nm or less, more preferably 25 nm or less, and even more preferably 20 nm or less.
The calculated average roughness (Sa) of the surface of the release layer or the surface of a film not provided with the release layer can be adjusted to the above range by adjusting the average particle size of the polyester film surface layer, the amount of particles added, the coating thickness of the release layer, etc. However, the present invention is not limited to such a method.

<<<<Release film with adhesive layer>>>
Using this release film, a release film with an adhesive layer (referred to as "the release film with the adhesive layer") can be produced, which has an adhesive layer (the "adhesive layer") on the release layer of the release film.

<<Main adhesive layer>>
The present adhesive layer can be formed by applying an adhesive composition (hereinafter referred to as "the present adhesive composition") onto the present release film and curing it.

<Present Pressure-Sensitive Adhesive Composition>
The present pressure-sensitive adhesive composition may be an acrylic pressure-sensitive adhesive composition containing an acrylic resin as the main component resin, a rubber-based pressure-sensitive adhesive composition containing rubber as the main component, a urethane-based pressure-sensitive adhesive composition containing a urethane resin as the main component, or a silicone-based pressure-sensitive adhesive composition containing a silicone resin as the main component.
Among these, acrylic pressure-sensitive adhesive compositions containing an acrylic resin as the main component are preferred, as they allow the adhesive strength and peel strength to be adjusted in a well-balanced manner and are inexpensive.

The term "main component resin" refers to the resin with the highest mass percentage among the resins constituting the pressure-sensitive adhesive composition. For example, it refers to a component that accounts for 50 mass% or more, preferably 60 mass% or more, and more preferably 70 mass% or more of the total amount of resins constituting the pressure-sensitive adhesive composition. The upper limit is typically 99.99 mass%.

In addition to the above-mentioned main components, the present pressure-sensitive adhesive composition may contain, as necessary, a crosslinking agent as described below, as well as conventionally known additives such as a silane coupling agent, an antistatic agent, other acrylic pressure-sensitive adhesives, other pressure-sensitive adhesives, tackifiers such as urethane resins, 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, colorants, fillers, antioxidants, ultraviolet absorbers, and functional dyes, as well as additives such as compounds that change color or undergo color development when exposed to ultraviolet light or radiation.
The amount of these additives to be blended is preferably 10% by mass or less of the total pressure-sensitive adhesive composition, more preferably 5% by mass or less, and even more preferably 5% by mass or less, and it is preferable that the additives contain as few low-molecular-weight components with a molecular weight of less than 10,000 as possible, in terms of excellent durability.

(acrylic resin)
The acrylic resin that is the main component resin of the present pressure-sensitive adhesive composition may be a (meth)acrylic polymer.

The (meth)acrylic polymer is a polymer having a (meth)acrylic acid alkyl ester as a main constituent unit.
Examples of the (meth)acrylic acid alkyl 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 the compatibility of the (meth)acrylic polymer with the (meth)acrylate and heat resistance. The (meth)acrylic polymer may have a radically polymerizable double bond.

The (meth)acrylic polymer can be copolymerized with (meth)acrylic acid esters other than alkyl (meth)acrylate esters, (meth)acrylic acid, or other compounds having a vinyl group, for the purpose of improving the glass transition temperature, mechanical properties, compatibility, etc. Examples of the (meth)acrylic acid esters other than alkyl (meth)acrylate esters include hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate, alkoxyalkyl (meth)acrylates such as methoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxymethyl (meth)acrylate, and ethoxyethyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, glycidyl (meth)acrylate, and γ-butyrolactone (meth)acrylate.
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.

The glass transition temperature (Tg) can be calculated from the type and mass fraction of the monomers forming the (meth)acrylic polymer using the following Fox formula.
1/Tg=Σ(Wi/Tgi) In this formula, Tg is the glass transition temperature (unit: K) of the (meth)acrylic polymer, Wi is the mass fraction of the monomer units derived from monomer i constituting the (meth)acrylic polymer, and Tgi is the glass transition temperature (unit: K) of the homopolymer of monomer i. The value of Tgi can be the value described in POLYMER HANDBOOK Volume 1 (WILEY-INTERSCIENCE).

In the present invention, the copolymerization component may contain an acrylic monomer (a1) which serves as a reaction site with the crosslinking agent described below.

Acrylic monomer (a1) serves as a reactive site for the crosslinking structure when copolymerized with other copolymerization components to form an acrylic resin. A monomer containing a functional group capable of reacting with the functional group contained in crosslinking agent (B), 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 preferred because they can efficiently undergo crosslinking reactions with the crosslinking agent. Acrylic monomer (a1) may be used alone or in combination of two or more types.

Examples of hydroxyl group-containing monomers include hydroxyalkyl acrylates 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.

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

The hydroxyl group-containing monomer used in the present invention preferably contains 0.5% or less of the impurity di(meth)acrylate, and more preferably 0.2% or less, and even more preferably 0.1% or less. Specific examples of hydroxyl group-containing monomers that are particularly preferred include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 4-hydroxybutyl acrylate, which are preferred because they have low molecular weights and are therefore easy to purify.

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

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 alkylene oxide adducts thereof.

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

The content of the acrylic monomer (a1) in the copolymerization components 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.
If the amount of acrylic monomer (a1) is too small, the number of crosslinking points will be too small during crosslinking, and the cohesive strength after crosslinking will tend to be insufficient, whereas if the amount is too large, the adhesive strength will tend to be too low.

If necessary, a copolymerizable monomer (a2) other than (a1) may be contained as a copolymerization component.
Examples of the copolymerizable monomer (a2) include (meth)acrylic acid alkyl ester monomers such as methyl methacrylate, ethyl (meth)acrylate, n-butyl methacrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-propyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate; phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, ethoxylated o-phenylphenyl (meth)acrylate, and phenoxyethyl (meth)acrylate. Examples of suitable monomers include aromatic ring-containing monomers such as diethylene 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, dialkyl itaconate esters, dialkyl fumarate esters, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone.

The content of copolymerizable monomer (a2) in the copolymerization components is preferably 0 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 2 to 10% by mass. If the amount of copolymerizable monomer (a2) is too high, the adhesive properties tend to decrease.

(Crosslinking agent)
The present pressure-sensitive adhesive composition may contain a crosslinking agent as needed depending on the curing method.
Examples of the crosslinking agent include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an aziridine-based crosslinking agent, a melamine-based crosslinking agent, an aldehyde-based crosslinking agent, an amine-based crosslinking agent, etc. Among these, an isocyanate-based crosslinking agent is 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 will not be insufficient and the desired durability can be obtained, while a decrease in flexibility and adhesive strength can be prevented.

When the curing reaction is carried out by photocuring through irradiation with active energy rays, it is preferable to add a polyfunctional (meth)acrylate to the pressure-sensitive 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.

<Thickness of the 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 outgassing, it is preferably 10,000 μm or less, more preferably 3,000 μm or less, and even more preferably 1,000 μm or less.

<<<Present film laminate>>>
A film laminate (referred to as "the present film laminate") having a configuration in which an optical member is bonded to the surface of the present adhesive layer of the present release film with an adhesive layer can be produced.

Examples of the optical component include polarizing plates and touch sensors. It may also be an optical component for use in automobiles, such as a touch panel.

(Polarizing plate)
The polarizing plate may be made of any material and have any configuration. For example, a polarizing plate of this type that is formed by laminating a TAC (triacetyl cellulose) film as a protective film on a stretched polyvinyl alcohol film that uses iodine as an alignment dye is widely used.
The polarizing plate may have a layer structure on the surface thereof that has a hard coat having substantially no retardation, anti-glare, low reflection, anti-static, or other functions.

(touch sensor)
The touch sensor is a component that detects the touch point when a user touches an image displayed on a screen with a finger or a touch pen, and examples of sensor technologies include a capacitance type, a resistive film type, and a surface wave type using infrared rays or ultrasonic waves.
Generally, touch sensors are mounted on display devices such as liquid crystal display panels and organic EL displays.
Furthermore, in recent years, there has been a trend toward using substrate films as an alternative to glass substrates, focusing on their flexibility.
Touch sensor films typically include a patterned transparent conductive layer to perform the function of the sensing electrodes.

<<<<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 or a protective panel, 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 means "X or more and Y or less", and also means "preferably larger than X" or "preferably smaller than Y".
Furthermore, 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.

Next, the present invention will be explained in more detail using examples. However, the present invention is not limited to the examples described below.

<Evaluation method>
In the following, measurements and evaluations of various physical properties were carried out as follows.

(1) Viscosity of Curable Silicone Resin The curable silicone resin was diluted with n-heptane to a solvent concentration of 15% by mass, and the viscosity of this solution at 25°C was measured using an E-type viscometer ("TVE-22L" manufactured by Toki Sangyo Co., Ltd.).

(2) Molecular Weight Measurement of Curable Silicone Resin A chromatogram was measured using a GPC measurement device, and the number average molecular weight (Mn) and weight average molecular weight (Mw) were determined based on a calibration curve using standard polystyrene, as shown in Table 2. Specifically, 4 mg of the sample to be measured was dissolved in 4 mL of THF to prepare a measurement solution, and 100 μL of the measurement solution was injected into the GPC measurement device for measurement. Tetrahydrofuran (THF) was used as the eluent. For the analysis, an "Ecosec 8320" manufactured by Tosoh Corporation was used, and a "TSKgel guard column HXL-L" manufactured by Tosoh Corporation was used as the guard column, and four "TSKgel GMHXL" columns manufactured by Tosoh Corporation were used in conjunction. The analysis was performed at an oven temperature of 40°C and a THF flow rate of 1.0 mL/min, and RI was used for detection.

(3) Measurement of Release Layer Thickness 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 beforehand. 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 following conditions: synchronous mode, incident angle 5°, N polarization, response Fast, data acquisition interval 1.0 nm, bandwidth 10 nm, and scanning speed 1000 m/min. The film thickness of the release layer was determined by comparing the data obtained from this measurement with data calculated assuming a refractive index of silicone of 1.43.

(4) Heat peeling force (without pressing)
One side of an acrylic double-sided adhesive tape ("No. 502" manufactured by Nitto Denko Corporation) was attached to the surface of the release layer of the sample film, and the sample was cut to a size of 50 mm x 300 mm. In this state, the sample was heated and held at 100°C (set temperature) in a hot air oven for 1 hour, and then allowed to stand at 23°C and 50% RH for 1 hour. After that, the 180° peel force was measured using a tensile tester ("EZgraph" manufactured by Shimadzu Corporation) at a tensile speed of 300 mm/min.

(5) Post-press heat peeling force (after pressing)
The sample having a size of 210 mm x 297 mm (A4 size) was placed on top of the other so that the release layer surface and the surface opposite the release layer surface faced each other.
Five sheets of 38 μm thick PET film "T100-38" manufactured by Mitsubishi Chemical Corporation were placed on top and bottom of the stacked sample, and pressed under a pressure of 1 MPa for 1 hour. One side of an acrylic double-sided adhesive tape ("No. 502" manufactured by Nitto Denko Corporation) was then attached to the surface of the release layer of the sample film, and the peel force was then measured in the same manner as in "heat peel force (without pressing)".
Pressing was started within 15 minutes after sample preparation.
In Table 2, "-" means that the evaluation has not been carried out.

(6) TESA7475 tape heat peel strength One side of an acrylic adhesive tape (TESA7475 manufactured by TESA) was attached to the release layer surface of the sample film, and the tape was cut to a size of 25 mm x 300 mm. In this state, the tape was heated and held at 100°C (set temperature) in a hot air oven for 1 hour, and then left to stand at 23°C and 50% RH for 1 hour. Thereafter, the side of the sample opposite the release layer was fixed to a SUS plate with double-sided tape, and the 180° peel strength was measured using a tensile tester (EZgraph manufactured by Shimadzu Corporation) at a tensile speed of 300 mm/min.
In Table 2, "-" means that the evaluation has not been carried out.

(7) Measurement of Elastic Modulus of Release Layer The surface of the release layer of the sample film was observed with an atomic force microscope, and the obtained image was analyzed to calculate the elastic modulus.
At this time, a silicon probe (manufactured by team nanotec, LRCH, radius of curvature: 250 nm, spring constant: 0.2 N/m) was attached to an atomic force microscope (trade name: SPM-9700HT, manufactured by Shimadzu Corporation), and tapping was performed at 600 m/s. Based on the obtained force curve, calculation was performed in accordance with the JKR two-point method.
The elastic modulus in Examples 1 to 4 is a calculated value based on the data of Reference Examples 1 to 3, whose coating thickness and elastic modulus are known.

(8) Evaluation of unevenness on the adhesive layer surface The adhesive composition described below was applied to the surface of the release layer (release surface) of the sample film so that the film thickness in a wet state was 2 mil, and the adhesive layer was formed by curing it by heat treatment at 150°C for 3 minutes. The unevenness on the adhesive layer surface on the side not in contact with the release surface was evaluated by visual inspection as described below.

<<Adhesive Composition>>
Base agent (acrylic resin): 100 parts by mass of AT352 (manufactured by Saiden Chemical Industry Co., Ltd.) Curing agent: 0.25 parts by mass of AL (manufactured by Saiden Chemical Industry Co., Ltd.) Additive: 0.25 parts by mass of X-301-375SK (manufactured by Saiden Chemical Industry Co., Ltd.) Additive: 0.25 parts by mass of X-301-352S (manufactured by Saiden Chemical Industry Co., Ltd.) Toluene: 40 parts by mass

(Visual inspection)
An adhesive layer was formed on the release surface of the sample film as described above, and the coating appearance of the adhesive layer surface on the side not in contact with the release surface, i.e., the unevenness of the adhesive layer surface, was visually observed and judged according to the following criteria, and the results are shown in Table 2.
(Judgment criteria)
◯ (good): The surface is so good that the surface irregularities are not recognizable, or the surface irregularities are very slight.
△ (poor): Surface irregularities can be recognized.
× (very poor): Surface irregularities are clearly recognizable.

[Raw materials]
The following raw materials were used in the examples and comparative examples.

<Release Layer Composition>
a1: Curable silicone resin composition (a mixture (viscosity: 95 mcps) containing a curable silicone resin (number average molecular weight: 176,000) in which vinyl groups have been introduced into the side chains and/or ends of the main chain consisting of siloxane bonds, and a crosslinker in which Si—H groups have been introduced into the side chains and/or ends of the main chain consisting of siloxane bonds)
a2: Curable silicone resin composition (a curable silicone resin in which vinyl groups have been introduced into the side chains and/or terminals of a main chain consisting of siloxane bonds, number average molecular weight: 10,600, viscosity: 1.7 mcps)
a3: Curable silicone resin composition (a mixture (viscosity: 410 mcps) containing a curable silicone resin (number average molecular weight: 364,000) in which vinyl groups have been introduced into the side chains and/or ends of the main chain consisting of siloxane bonds, and a crosslinker in which Si—H groups have been introduced into the side chains and/or ends of the main chain consisting of siloxane bonds)
a4: Curable silicone resin composition (a mixture (viscosity: 430 mcps) containing a curable silicone resin (number average molecular weight: 399,000) in which hexenyl groups have been introduced into the side chains and/or ends of a main chain consisting of siloxane bonds, and a crosslinker in which Si—H groups have been introduced into the side chains and/or ends of a main chain consisting of siloxane bonds)

(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). The results are shown in Table 1.
The 1H-NMR measurement was carried out at a temperature of 30°C using CDCl ₃ as a solvent and the peak derived from the methyl group of dimethylsiloxane as the chemical shift reference.
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 (PL-50T: manufactured by Shin-Etsu Chemical Co., Ltd.)
c2: Addition type platinum catalyst (CM678: manufactured by Momentive Performance Materials)
c3: Addition type platinum catalyst (SRX212: manufactured by Dow Toray Co., Ltd.)

[Example 1]
A release layer composition comprising the release agent composition A described below was applied by bar coating to one side of a 38 μm thick PET film "T100-38" manufactured by Mitsubishi Chemical Corporation, and the applied composition was cured by heat treatment at 150° C. for 15 seconds to form a release layer having a thickness (after drying) of 0.30 μm, thereby obtaining a release film (sample film).

<Release Agent Composition-A>
Curable silicone resin composition a1: 98% by mass
Addition type platinum catalyst c1: 2 mass%
The release layer composition was diluted with n-heptane to adjust the solid content concentration to 5.4% by mass.

[Example 2]
In Example 1, the solid content concentration of the release layer composition was changed to 3.7 mass % so that the thickness of the release layer (after drying) was 0.38 μm. The same procedure as in Example 1 was repeated to obtain a release film (sample film).

[Example 3]
In Example 1, the solid content concentration of the release layer composition was changed to 1.9 mass % so that the thickness of the release layer (after drying) was 0.48 μm. The same procedure as in Example 1 was repeated to obtain a release film (sample film).

[Example 4]
In Example 1, the solid content concentration of the release layer composition was changed to 1.9 mass % so that the thickness of the release layer (after drying) was 0.59 μm. The same procedure as in Example 1 was repeated to obtain a release film (sample film).

[Comparative Example 1]
In Example 1, except that the release layer composition was changed to the following release agent composition-B, production was carried out in the same manner as in Example 1, and a release film (sample film) having a release layer with a thickness (after drying) of 0.23 μm was obtained.

<Release Agent Composition-B>
Curable silicone resin composition a2: 91% by mass
Crosslinking agent b1: 3% by mass
Addition type platinum catalyst c2: 6% by mass
The release layer composition was diluted with n-heptane to adjust the solid content concentration to 5.4% by mass.

[Comparative Example 2]
In Example 1, except that the release layer composition was changed to the following release agent composition-C, production was carried out in the same manner as in Example 1, and a release film (sample film) having a release layer with a thickness (after drying) of 0.24 μm was obtained.

<Release Agent Composition-C>
Curable silicone resin composition a3: 99% by mass
Addition type platinum catalyst c1: 1 mass%
The release layer composition was diluted with n-heptane to adjust the solid content concentration to 5.4% by mass.

[Comparative Example 3]
In Example 1, except that the release layer composition was changed to the following release agent composition-D, the same procedure as in Example 1 was repeated to obtain a release film (sample film) having a release layer with a thickness (after drying) of 0.28 μm.

<Release Agent Composition-D>
Curable silicone resin composition a4: 99% by mass
Addition type platinum catalyst c3: 1 mass%
The release layer composition was diluted with n-heptane to adjust the solid content concentration to 5.4% by mass.

[Reference example 1]
In Example 1, the solid content concentration of the release layer composition was changed to 5.4 mass % so that the thickness of the release layer (after drying) was 0.23 μm. The same procedure as in Example 1 was repeated to obtain a release film (sample film).

[Reference example 2]
In Example 1, the solid content concentration of the release layer composition was changed to 3.7 mass % so that the thickness of the release layer (after drying) was 0.18 μm. The same procedure as in Example 1 was repeated to obtain a release film (sample film).

[Reference example 3]
In Example 1, the solid content concentration of the release layer composition was changed to 1.9 mass % so that the thickness of the release layer (after drying) was 0.09 μm. The same procedure as in Example 1 was repeated to obtain a release film (sample film).

The properties of each release film (sample film) obtained in the above examples and comparative examples are summarized in Table 2, and the properties of each release film (sample film) obtained in the reference examples are summarized in Table 3.

The "heat peel strength (after pressing)" was evaluated from the perspective of how stable and smooth the peeling could be under more severe conditions by first recreating a condition in which the release surface and the adhesive layer surface were intentionally tightly adhered together through a pressing process.
It was found that in Examples 1 to 4, the peel strength did not change significantly before and after the press treatment and was stable.
On the other hand, when Comparative Examples 1 to 3 were evaluated for "heat peel force (without press)" in the absence of press, it was confirmed that the peel force values were already about 60 to 70% higher than those of Examples 1 to 4, indicating that it would be difficult to achieve ultra-light peel strength.
Furthermore, it was found that the "TESA7475 heat peeling force" exhibited a large change in peeling force depending on the thickness of the release layer, and responded sensitively to the thickness of the release layer, making it easy to see the effect of reducing peeling force.

It was found that in the region where the coating thickness (after drying) of the release layer is less than 0.25 μm, the modulus of elasticity of the release layer is 1.5 MPa or more, and therefore the releasability to the acrylic adhesive tape does not become dramatically easier.
On the other hand, when the elastic modulus of the release layer is 1.4 MPa or less, it is not surprising that the peel force value increases due to the press treatment, even though the press treatment has been performed in advance. However, it was found that the release force value was about 30% lighter at the lightest. Therefore, it can be seen that the release film of the present invention (including the examples) achieves an ultra-light release property that is difficult to achieve at the level of the reference example (conventional).

It is believed that the sample films obtained in Examples 1 to 4 had a release layer thickness of 0.25 μm or more and an elastic modulus of 1.4 MPa or less. It is known that when the elastic modulus of the release layer is 1.4 MPa or less, the possibility of blocking and heavy release due to blocking occurring increases.
Therefore, in the present invention, it has been found that the above-mentioned problems can be solved by using a curable silicone resin with a medium viscosity, specifically, a viscosity of 10 to 400 mcps at 25°C when diluted with n-heptane solvent to 15% by mass.
More preferably, the curable silicone resin has a phenyl structure, which is also thought to contribute to solving the above problems.
On the other hand, the sample films obtained in Examples 1 to 4 did not show a heavy peeling force after pressing, and it was found that the peeling force after heating was lighter.

From the above examples and the results of tests conducted by the inventors to date, it has been found that if the release layer has an elastic modulus of 1.4 MPa or less and a 180° peel strength at 23°C of 15 mN/cm or less, not only will the release layer have excellent light releasability, but it will also be able to suppress unevenness on the adhesive layer surface and achieve excellent smoothness.

Furthermore, from the above examples and the results of tests conducted by the inventors to date, it has been found that by using a curable silicone having a moderate number average molecular weight (Mn) of 20,000 or more and 350,000 or less as the main component resin of the release layer composition, a release film with very light release properties can be obtained, without heavy release due to blocking, even if the dry thickness of the release layer is 0.30 μm or more and the elastic modulus of the release layer is 1.4 MPa or less.
Therefore, it has been found that by setting the dry thickness of the release layer to 0.25 μm or more and 2.0 μm or less, more preferably 0.30 μm or more and 1.5 μm or less, and even more preferably 0.35 μm or more and 1.0 μm or less, and by setting the elastic modulus of the release layer to 1.4 MPa or less, 0.10 MPa or more, more preferably 1.3 MPa or less, 0.20 MPa or more, and even more preferably 1.0 MPa or less and 0.30 MPa or more, an excellent release film can be obtained, particularly in applications where ultra-light releasability is required.

It has also been found that by using a curable silicone with a moderate number-average molecular weight (Mn) of 20,000 or more and 350,000 or less as the main component resin of the release layer composition and adjusting the release layer composition to contain a predetermined amount of phenyl groups, it is possible to further improve the easy releasability and further suppress unevenness on the adhesive layer surface. In this case, the suppression of unevenness on the adhesive layer surface can be attributed to the fact that the release layer surface has appropriate wettability and that it is possible to suppress the elution or migration of low-molecular-weight silicone resin, i.e., incompatible components, into the adhesive layer.

In particular, it has been found that a release film having a release layer formed by applying and curing a release layer composition containing, as the main component resin, a curable silicone having a moderate number average molecular weight (Mn) of 20,000 or more and 350,000 or less can obtain good easy peelability and a highly smooth adhesive layer surface even when the release layer is applied thickly (thickness after drying) to a thickness of 0.30 μm or more.
Furthermore, it was found that a release layer composition having a curable silicone resin with a moderate molecular weight as the main component resin as described above can maintain the viscosity of the coating liquid within an appropriate range even when the coating liquid is prepared at a high concentration to increase the thickness of the release layer in order to achieve light release, and can produce a release film with a good coating appearance (no coating unevenness such as streaks) and stable release properties with reduced variation in peel force values within the surface of the release film.

Furthermore, from the above examples and the results of tests conducted by the inventors to date, it has been found that when an adhesive layer is formed on a release layer, the presence of phenyl groups in the release layer enables easier peeling while suppressing the unevenness of the adhesive layer surface.
At present, the detailed mechanism is unknown, but it is speculated that in release layer compositions (such as release layer compositions a3 and a4) whose main component is a typical high-molecular-weight curable silicone resin, the unreacted reactive groups (alkenyl groups, Si-H groups) that increase as the molecular weight increases to medium levels are hidden from the adhesive by the phenyl groups (interaction between the phenyl groups and the alkenyl groups and Si-H groups).
Furthermore, from the above examples and the results of tests conducted by the inventors, it has been found that it is preferable for the release layer to contain 0.01 to 5.0 mol % of phenyl groups relative to the total amount of siloxane components.

Claims (9)

A release film having a release layer on one side of a base film,
The release layer has an elastic modulus of 1.4 MPa or less and a thickness (after drying) of 0.25 μm to 2.0 μm;
The release layer is a release film obtained by curing a release layer composition in which any one or two or more of a phenyl group, an Si—H group, and an alkenyl group are introduced into a side chain or an end of a linear main chain composed of siloxane bonds, the release layer having as its main component a curable silicone resin (excluding a curable silicone resin having a number average molecular weight (Mn) of 200,000 which has a methyl group, a hexenyl group, and a phenyl group) having a number average molecular weight (Mn) of 20,000 or more and 176,000 or less and having a viscosity of 10 to 400 mcps at 25° C. when diluted to 15% by mass with n-heptane solvent, the release layer containing a crosslinker having a siloxane bond, and the release layer composition containing 0.01 to 5.0 mol % of phenyl groups, 0.4 to 1.0 mol % of alkenyl groups, and 0.8 to 2.2 mol % of Si—H groups, based on the total siloxane components. The release film according to claim 1 , further comprising a cured resin layer between the release layer and the substrate film. The release film of claim 2 , wherein the cured resin layer is an antistatic layer or an oligomer sealing layer. 4. The release film according to claim 1 , wherein the calculated average roughness (Sa) of the release layer surface or the film surface on which no release layer is provided is 30 nm or less. The release film according to any one of claims 1 to 4 , wherein the base film is a polyester film. A release film with an adhesive layer, comprising the release film according to any one of claims 1 to 5 , and an adhesive layer laminated on the release layer. 7. The release film with an adhesive layer according to claim 6 , wherein the adhesive layer is a layer made of an acrylic adhesive composition containing an acrylic resin as a main component. A film laminate comprising an optical member bonded to a surface of the adhesive layer of the release film with an adhesive layer according to claim 6 or 7 . The film laminate according to claim 8 , wherein the optical component is a polarizing plate or a touch sensor.