Optical Film

Abstract

To provide an optical film having in-plane phase difference being excellent relative to distortion.SOLUTION: An optical film includes a cured product of a curable resin composition including a polymer component (A) and a curable monomer with two or more curable functional groups (B). The polymer component (A) includes polyvinyl butyral. The optical film has an in-plane phase difference of 0-10 nm at 1% distortion at the wavelength of 589 nm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an optical film. [Background technology]

[0002] In recent years, in order to realize thinner, lighter, more flexible electronic devices relating to various display elements such as liquid crystal displays and organic electroluminescence (EL) displays, the use of thin transparent plastic films as substrates for components constituting the devices, instead of conventional rigid substrates such as glass, has been considered. In such a situation, it may be required to maintain optical isotropy even when the thin transparent plastic film or the like is provided, for example, on the surface (screen) side of the display element and the display element is used in a bent state. In such a case, distortion occurs in the thin transparent plastic film due to bending, which increases the in-plane retardation and makes it impossible to maintain optical isotropy, which leads to a decrease in visibility in the display element. Patent Document 1 discloses an optical film having excellent flexibility and breaking strength and a low photoelastic coefficient, which is obtained by curing an active energy ray-curable composition containing a plasticizer made of an acrylic polymer (A) having no aromatic groups and having a weight average molecular weight of 500 to 5,000 obtained by high-temperature continuous polymerization of a monomer containing a (meth)acrylate at a temperature of 180 to 350°C without using a thiol-based chain transfer agent, and a urethane (meth)acrylate (C) having no aromatic groups. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-091752 Summary of the Invention [Problem to be solved by the invention]

[0004] However, Patent Document 1 is an invention relating to the reduction of contrast nonuniformity due to birefringence change caused by biased external forces due to the increase in size of optical films accompanying the increase in size of liquid crystal displays, and is studied from the perspective of reducing the photoelastic coefficient, and does not mention the reduction of in-plane retardation due to distortion.

[0005] In view of the above, an object of the present invention is to provide an optical film having an in-plane retardation that is excellent in resistance to distortion. [Means for solving the problem]

[0006] As a result of extensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by forming an optical film into a layer made of a cured product of a curable resin composition in which a specific polymer component (A) contains a curable monomer (B) having a specific number of curable functional groups, and have thus completed the present invention. That is, the present invention provides the following [1] to [8]. [1] An optical film comprising a cured product of a curable resin composition containing a polymer component (A) and a curable monomer (B) having two or more curable functional groups, The polymer component (A) contains polyvinyl butyral, and the optical film has an in-plane retardation of 0 to 10 nm at a wavelength of 589 nm and a strain of 1%. [2] The optical film according to [1] above, wherein the thickness of the optical film is 25 μm or less. [3] The optical film according to the above [1] or [2], wherein the haze value of the optical film is 1.0% or less. [4] The optical film according to any one of the above [1] to [3], wherein the optical film has a total light transmittance of 85% or more. [5] The optical film according to any one of the above [1] to [4], wherein the optical film has a breaking elongation of 5.0% or more. [6] The optical film according to any one of the above [1] to [5], wherein the polymer component (A) has a weight average molecular weight of 10,000 or more. [7] A laminate comprising the optical film according to any one of the above [1] to [6] and a functional layer. [8] The laminate according to the above [7], wherein the functional layer includes at least one layer of an adhesive layer, a pressure-sensitive adhesive layer, a pressure-sensitive adhesive layer, a gas barrier layer, a conductive layer, and a hard coat layer. [Effects of the Invention]

[0007] According to the present invention, an optical film having an in-plane retardation excellent in resistance to distortion can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0008] In this specification, preferred definitions can be selected arbitrarily, and combinations of preferred definitions can be considered more preferred. In this specification, the expression "XX to YY" means "XX or more and YY or less." In this specification, for preferred numerical ranges (e.g., ranges of content, etc.), the lower and upper limits described in stages can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60." In this specification, for example, "(meth)acrylic acid" refers to both "acrylic acid" and "methacrylic acid," and the same applies to other similar terms.

[0009] <Optical film> The optical film of the present invention is an optical film comprising a cured product of a curable resin composition containing a polymer component (A) and a curable monomer (B) having two or more curable functional groups, The polymer component (A) contains polyvinyl butyral, and the optical film has an in-plane retardation of 0 to 10 nm at a wavelength of 589 nm and a strain of 1%. In the present invention, the optical film is a layer made of a cured product of a curable resin composition containing a polymer component (A) containing polyvinyl butyral and a curable monomer (B) having two or more curable functional groups, thereby making it possible to reduce the in-plane retardation at a strain of 1% to 0 to 10 nm. Because the obtained optical film has an excellent in-plane retardation at a strain of 1%, it exhibits excellent visibility even when applied to the surface (screen) side of a display element as a substrate for electronic device components such as flexible display devices.

[0010] The optical film of the present invention may be a single layer or a multi-layer film. The method for forming the optical film will be described in detail in the method for producing the laminate described below.

[0011] (Curable resin composition) The curable resin composition used in the present invention contains a polymer component (A) and a curable monomer (B) having two or more curable functional groups.

[0012] <Polymer component (A)> The polymer component (A) contains polyvinyl butyral. Examples of the polyvinyl butyral that can be used include those having structural units represented by the following formulas (i-1), (i-2), and (i-3). [ka]

[0013] The weight-average molecular weight (Mw) of the polyvinyl butyral is preferably 10,000 or more, more preferably 12,000 to 200,000, more preferably 15,000 to 100,000, and particularly preferably 18,000 to 80,000. When the weight-average molecular weight of the polyvinyl butyral is in this range, the film-forming properties of the optical film are improved. The molecular weight distribution (Mw / Mn) (Mn: number average molecular weight) is preferably in the range of 1.0 to 5.0, more preferably 2.0 to 4.5. The weight average molecular weight (Mw) and the molecular weight distribution (Mw / Mn) are values ​​measured by gel permeation chromatography (GPC) in terms of polystyrene.

[0014] Taking all structural units of polymer component (A) as 100 mol%, the proportion of units having a butyral group represented by formula (i-1) above is preferably 80 mol% or more, more preferably 85 mol% or more, and particularly preferably 90 mol% or more, with the upper limit being 100 mol%. The remainder of polymer component (A) is made up of units having functional groups represented by formula (i-2) or (i-3).

[0015] The glass transition temperature (Tg) of the polyvinyl butyral is preferably 40 to 150° C., more preferably 50 to 120° C. When the Tg of the polyvinyl butyral is in this range, the toughness of the optical film is increased. Here, Tg refers to the temperature at the maximum point of tan δ (loss modulus / storage modulus) obtained by a differential scanning calorimeter (measured in the range of 0 to 150° C. at a temperature rise rate of 5° C. / min).

[0016] The content ratio of the above three types of structural units constituting the polyvinyl butyral may be adjusted as desired depending on the desired physical properties. Furthermore, the polyvinyl butyral may contain structural units other than the above three structural units, but the content of the above three structural units is preferably 80 to 100 mol %, more preferably 90 to 100 mol %, and even more preferably 100 mol %, based on the total amount of the polyvinyl butyral.

[0017] The polymer component (A) may be used alone or in combination of two or more. The polymer component (A) may also be used in combination with another polymer component (A'). Examples of the other polymer component (A') include polymer components such as polyvinyl acetal resins other than polyvinyl butyral, such as polyvinyl formal, acrylic resins, polyester resins, polyamide resins, and polyethylene resins, with polyvinyl formal, acrylic resins, polyester resins, polyamide resins, and polyethylene resins being preferred. In order not to reduce the optical isotropy, it is preferable that the other polymer component (A') does not have an aromatic structure in the molecule.

[0018] When other polymer component (A') is added, the amount of resin added is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 50 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of polyvinyl butyral, and is preferably 1 part by mass or more, more preferably 3 parts by mass or more.

[0019] <Curable monomer (B)> The curable monomer (B) is a monomer having two or more curable functional groups (polymerizable unsaturated bonds) and capable of participating in a polymerization reaction, or a polymerization reaction and a crosslinking reaction. In this specification, the term "curing" refers to a broad concept including the "polymerization reaction of a monomer" or the "polymerization reaction of a monomer and the subsequent crosslinking reaction of the polymer."

[0020] The molecular weight of the curable monomer (B) is usually 3,000 or less, preferably 100 to 2,000, and more preferably 100 to 1,500. The number of curable functional groups (polymerizable unsaturated bonds) in the curable monomer (B) is two or more. If the number of curable functional groups in the curable monomer (B) is less than two, the strength of the curable resin composition and the optical film cured therefrom may be insufficient, contamination due to residual unreacted materials may occur, and changes in physical properties over time may occur. The number of curable functional groups in the curable monomer (B) (however, when the curable monomer (B) is a mixture of multiple types, the average number thereof) is preferably 2 to 10, more preferably 2 to 3. When the number of curable functional groups in the curable monomer (B) is within this range, an optical film with excellent optical isotropy and small in-plane retardation with respect to strain can be obtained by using the curable monomer (B) in combination with the polymer component (A).

[0021] The monomer having two or more curable functional groups includes a polyfunctional (meth)acrylic acid derivative. The polyfunctional (meth)acrylic acid derivative is not particularly limited, and known compounds can be used, for example, di- to hexa-functional (meth)acrylic acid derivatives.

[0022] [ka]

[0023] In the formula, R 1 represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R 1 Examples of the alkyl group having 1 to 6 carbon atoms represented by R include a methyl group, an ethyl group, and a propyl group, and a methyl group is preferred. 7 represents a divalent organic group. 7 Examples of the divalent organic group represented by the formula include groups represented by the following formula:

[0024] [ka]

[0025] (In the formula, s represents an integer of 1 to 20, t represents an integer of 1 to 30, u and v each independently represent an integer of 1 to 30, and "-" at both ends represents a bond.)

[0026] Specific examples of the bifunctional (meth)acrylic acid derivative represented by the above formula include tricyclodecane dimethanol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propoxylated ethoxylated bisphenol A di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene, etc. Among these, from the viewpoint of heat resistance and toughness, tricyclodecane dimethanol di(meth)acrylate and the like, which have R 7 and propoxylated ethoxylated bisphenol A di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, etc., in which R 7 and 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene, etc., in which R 7 Preferably, the divalent organic group represented by the following formula has a 9,9-bisphenylfluorene skeleton.

[0027] Other examples of bifunctional (meth)acrylic acid derivatives include neopentyl glycol adipate di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, caprolactone-modified dicyclopentenyl di(meth)acrylate, ethylene oxide-modified phosphate di(meth)acrylate, di(acryloxyethyl) isocyanurate, and allylated cyclohexyl di(meth)acrylate.

[0028] Examples of trifunctional (meth)acrylic acid derivatives include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propionic acid-modified dipentaerythritol tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, and tris(acryloxyethyl)isocyanurate.

[0029] Examples of tetrafunctional (meth)acrylic acid derivatives include pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, propoxylated pentaerythritol tetra(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate.

[0030] Examples of the pentafunctional (meth)acrylic acid derivatives include propionic acid-modified dipentaerythritol penta(meth)acrylate.

[0031] Examples of the hexafunctional (meth)acrylic acid derivative include dipentaerythritol hexa(meth)acrylate and caprolactone-modified dipentaerythritol hexa(meth)acrylate.

[0032] A cyclopolymerizable monomer may be used as the curable monomer (B). The cyclopolymerizable monomer is a monomer that has the property of undergoing radical polymerization while undergoing cyclization. Examples of the cyclopolymerizable monomer include non-conjugated dienes, and for example, an α-allyloxymethylacrylic acid-based monomer can be used. C1-4 alkyl esters of 2-allyloxymethylacrylic acid and cyclohexyl 2-(allyloxymethyl)acrylate are preferred, C1-4 alkyl esters of 2-allyloxymethylacrylic acid are more preferred, and methyl 2-(allyloxymethyl)acrylate is even more preferred. Cyclopolymerizable monomers such as dimethyl-2,2'-[oxybis(methylene)]bis-2-propenoate, diethyl-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-propyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(i-propyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-butyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-hexyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, and dicyclohexyl-2,2'-[oxybis(methylene)]bis-2-propenoate can also be used.

[0033] The curable monomer (B) can be used alone or in combination of two or more. The content of the curable monomer (B) having two or more curable functional groups is preferably 40 mass% or more, more preferably 50 to 100 mass%, even more preferably 80 to 100 mass%, and particularly preferably 90 to 100 mass%, of the total amount of the curable monomer (B).

[0034] The curable resin composition used in the present invention can be prepared by mixing the polymer component (A), the curable monomer (B) having two or more curable functional groups, and, if desired, a polymerization initiator described below and other components, and dissolving or dispersing the mixture in a suitable solvent.

[0035] The total content of the polymer component (A) and the curable monomer (B) having two or more curable functional groups in the curable resin composition is preferably 40 to 99.5 mass%, more preferably 60 to 99 mass%, and even more preferably 80 to 98 mass%, based on the total mass of the curable resin composition excluding the solvent.

[0036] The content of the polymer component (A) and the curable monomer (B) having two or more curable functional groups in the curable resin composition, expressed as a mass ratio of the polymer component (A) to the curable monomer (B) having two or more curable functional groups, is preferably polymer component (A):curable monomer (B) having two or more curable functional groups=20:80 to 90:10, more preferably 30:70 to 50:50, and even more preferably 40:60 to 50:50. In the curable resin composition, when the mass ratio of the polymer component (A) to the curable monomer (B) having two or more curable functional groups is within this range, it becomes easier to control the in-plane retardation of the resulting optical film to be small relative to distortion.

[0037] The curable resin composition used in the present invention may be a thermosetting curable resin composition or an ultraviolet-curable curable resin composition. Such a curable resin composition may contain a polymerization initiator as desired. The polymerization initiator may be any initiator that initiates a curing reaction, and examples thereof include a thermal polymerization initiator and a photopolymerization initiator. Here, the thermal polymerization initiator is a compound that causes a polymerization reaction by absorbing thermal energy, and examples thereof include a compound that generates radicals upon heating (thermal radical generator), a compound that generates an acid upon heating (thermal acid generator), and a compound that generates a base upon heating (thermal base generator). On the other hand, the photopolymerization initiator is a compound that causes a polymerization reaction by absorbing light energy, and examples thereof include a compound that generates radicals by absorbing light energy (photoradical generator), a compound that generates an acid by absorbing light energy (photoacid generator), and a compound that generates a base by absorbing light energy (photobase generator). Any of these may be used, and from the viewpoint of the reactivity of the polymerization reaction (ease of control by illuminance or light amount), a photopolymerization initiator is preferred. Here, the light is preferably active energy rays such as visible light, ultraviolet light, or X-rays.

[0038] Examples of the thermal polymerization initiator include organic peroxides and azo compounds. Examples of organic peroxides include dialkyl peroxides such as di-t-butyl peroxide, t-butylcumyl peroxide, and dicumyl peroxide; diacyl peroxides such as acetyl peroxide, lauroyl peroxide, and benzoyl peroxide; ketone peroxides such as methyl ethyl ketone peroxide, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; and peroxides such as 1,1-bis(t-butylperoxy)cyclohexane. Examples of the peroxyester include ketals; hydroperoxides such as t-butyl hydroperoxide, cumene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, p-menthane hydroperoxide, diisopropylbenzene hydroperoxide, and 2,5-dimethylhexane-2,5-dihydroperoxide; and peroxyesters such as t-butyl peroxyacetate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxybenzoate, and t-butyl peroxyisopropyl carbonate. Examples of azo compounds include 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2-(carbamoylazo)isobutyronitrile, and 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile.

[0039] Photopolymerization initiators include 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-[4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl]-2-methyl-propan-1-one, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamine, and the like. Alkylphenone-based photopolymerization initiators such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, ethyl (2,4,6-trimethylbenzoyl)-phenylphosphine phosphate, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide; bis(η 5Titanocene photopolymerization initiators such as (2,4-cyclopentadien-1-yl)-bis[2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl]titanium; oxime ester photopolymerization initiators such as 1,2-octanedione-1-[4-(phenylthio)-2-(O-benzoyloxime)] and ethanone-1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime); benzophenone, p-chlorobenzophenone, benzoylbenzoic acid, methyl o-benzoylbenzoate, 4-methylbenzophenone, 4-phenylbenzophenone, hydroxybenzophenone, acrylated benzophenone, 4-benzoyl benzophenone-based photopolymerization initiators such as 13-acryloyl-4'-methyl-diphenyl sulfide, 3,3'-dimethyl-4-methoxybenzophenone, 2,4,6-trimethylbenzophenone, and 4-(13-acryloyl-1,4,7,10,13-pentaoxatridecyl)-benzophenone; and thioxanthone-based photopolymerization initiators such as thioxanthone, 2-chlorothioxanthone, 3-methylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diisopropylthioxanthone, 2,4-dichlorothioxanthone, 1-chloro-4-propoxythioxanthone, 2-methylthioxanthone, 2-isopropylthioxanthone, and 4-isopropylthioxanthone.

[0040] Among the above photopolymerization initiators, phosphorus-based photopolymerization initiators such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, ethyl(2,4,6-trimethylbenzoyl)-phenylphosphineate, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide are preferred. The polymerization initiators can be used alone or in combination of two or more.

[0041] The content of the polymerization initiator is preferably from 0.05 to 15 mass %, more preferably from 0.05 to 10 mass %, and even more preferably from 0.05 to 5 mass %, based on the total amount of the curable resin composition.

[0042] Furthermore, when the curable resin composition is ultraviolet-curable, it may contain a photopolymerization initiation aid such as triisopropanolamine or 4,4'-diethylaminobenzophenone in addition to the polymer component (A), the curable monomer (B) having three or more curable functional groups, and the photopolymerization initiator.

[0043] The solvent used in preparing the curable resin composition is not particularly limited, and examples thereof include aliphatic hydrocarbon solvents such as n-hexane and n-heptane; aromatic hydrocarbon solvents such as toluene and xylene; halogenated hydrocarbon solvents such as dichloromethane, ethylene chloride, chloroform, carbon tetrachloride, 1,2-dichloroethane, and monochlorobenzene; alcohol solvents such as methanol, ethanol, propanol, butanol, and propylene glycol monomethyl ether; ketone solvents such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; ester solvents such as ethyl acetate and butyl acetate; cellosolve solvents such as ethyl cellosolve; and ether solvents such as 1,3-dioxolane.

[0044] The content of the solvent in the curable resin composition is not particularly limited, but is usually 0.1 to 1,000 g, preferably 1 to 50 g, per 1 g of the polymer component (A). By appropriately adjusting the amount of the solvent, the viscosity of the curable resin composition can be adjusted appropriately.

[0045] The curable resin composition may further contain known additives such as plasticizers, antioxidants, and ultraviolet absorbers, within the scope of not impairing the objects and effects of the present invention.

[0046] The in-plane retardation of the optical film can be calculated by the following formula (1). Re(λ)=(nx-ny)×d (1) Here, Re(λ) is the in-plane retardation of the optical film measured with light of wavelength λ nm at 23° C. For example, “Re(450)” is the in-plane retardation of the optical film measured with light of wavelength 450 nm at 23° C. Furthermore, “nx” is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), “ny” is the refractive index in the in-plane direction perpendicular to the slow axis (i.e., the fast axis direction), and d is the thickness (nm) of the optical film. On the other hand, the absolute value of the retardation in the thickness direction is usually 500 nm or less, preferably 450 nm or less. The value obtained by dividing the in-plane retardation by the thickness of the optical film (birefringence) is usually 100×10 -5 or less, preferably 20 × 10 -5 The following is the result. When the in-plane retardation, thickness direction retardation and birefringence of the optical film are within the above ranges, the optical film has excellent optical isotropy and can be preferably used as a member for optical applications. The in-plane retardation at 0% strain was measured by the method described in the examples below.

[0047] The in-plane retardation of the optical film at a wavelength of 589 nm and a strain of 1% is 0 to 10 nm. If the in-plane retardation at a strain of 1% exceeds 10 nm, there is a risk of a decrease in optical isotropy. The in-plane retardation of the optical film at a wavelength of 589 nm and a strain of 1% is preferably 0 to 8 nm, more preferably 0 to 6 nm, and even more preferably 0 to 4 nm. When the in-plane retardation at a strain of 1% is within this range, for example, when the optical film is applied to a flexible display element, the deterioration of optical isotropy that occurs when the display element is bent can be suppressed, the displayed content can be easily maintained or confirmed, and the intended functions that the display element originally has can be fully exhibited. The in-plane retardation at a strain of 1% in the present invention is the value possessed by an optical film produced by the production method described in the Examples, i.e., the value possessed by an optical film having a thickness of 20 μm, which is obtained by applying a curable resin composition to a casting film, heating the resulting coating at 100°C for 2 minutes, and then curing it by irradiating it with ultraviolet light, and then removing the casting film. The in-plane retardation at a strain of 1% was measured by the method described in the examples below.

[0048] The thickness of the optical film of the present invention made of the cured product of the curable resin composition is preferably 25 μm or less, more preferably 0.1 to 20 μm, even more preferably 0.1 to 10 μm, and particularly preferably 0.2 to 10 μm. When the thickness of the optical film is within this range, the thickness of the laminate can be prevented from increasing, and a thin laminate can be obtained. In this case, when applied to a device that requires a thinner device, the laminate does not cause an increase in the overall thickness of the applied device, which is preferable. Furthermore, a thin laminate can ensure flexibility after mounting.

[0049] The total light transmittance of the optical film is preferably 85% or more, more preferably 90% or more, and even more preferably 95% or more. If the total light transmittance is within this range, for example, when a functional layer described below is formed to form a laminate, the optical transparency of the entire laminate can be easily maintained. The total light transmittance was measured by the method described in the examples below.

[0050] The haze value of the optical film is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.1% or less. If the haze value is within this range, for example, when a functional layer described below is formed to form a laminate, the light diffusion of the entire laminate can be easily maintained low. The haze value was measured by the method described in the examples below.

[0051] The breaking elongation of the optical film is preferably 5.0% or more, more preferably 6.0% or more, and even more preferably 7.0% or more. When the breaking elongation of the optical film is within this range, for example, 5.0% or more, it becomes easy to adjust the breaking elongation of the laminate including the functional layer to about 4% or more, and as a result, it becomes easy to obtain a laminate with excellent flexibility. The breaking elongation was measured by the method described in the examples below.

[0052] (Laminate) The laminate of the present invention preferably comprises an optical film and a functional layer, and in one embodiment, may comprise an optical film on which a functional layer is laminated. The optical film can be used as a layer on which the functional layer is provided or as a substrate. In another embodiment of the present invention, the laminate may include a processing film, an optical film, and a functional layer in this order. When the laminate is actually used, the processing film is peeled off from the laminate and attached to, for example, a predetermined electronic device such as a display. The functional layer is not particularly limited, but is preferably at least one layer selected from an adhesive layer, a pressure-sensitive adhesive layer, a pressure-sensitive adhesive layer, a gas barrier layer, a conductive layer, and a hard coat layer. The position of the functional layer is not particularly limited.

[0053] For example, materials constituting a conductive layer (electrode, transparent conductive layer, etc.) used as a functional layer include metals, alloys, metal oxides, electrically conductive compounds, mixtures thereof, etc. Examples of transparent conductive layers include antimony-doped tin oxide (ATO), fluorine-doped tin oxide (FTO), semiconductive metal oxides such as tin oxide, germanium-doped zinc oxide (GZO), zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); metals such as gold, silver, chromium, and nickel; mixtures of these metals with conductive metal oxides; inorganic conductive substances such as copper iodide and copper sulfide; and organic conductive materials such as polyaniline, polythiophene, and polypyrrole. Examples of methods for forming the conductive layer include printing, vapor deposition, sputtering, ion plating, thermal CVD, and plasma CVD. The thickness of the conductive layer may be appropriately selected depending on the application, etc. It is usually 10 nm to 50 μm, preferably 20 nm to 20 μm.

[0054] The adhesive layer is a layer used, for example, when attaching the laminate to an adherend, etc. The material for forming the adhesive layer is not particularly limited, and known adhesives or pressure-sensitive adhesives such as acrylic, silicone, rubber, and epoxy adhesives, heat seal materials, etc. can be used, and an epoxy adhesive is preferred as the material for forming the adhesive layer. Similarly, the pressure-sensitive adhesive layer is a layer used, for example, when attaching the laminate to an adherend or the like. Examples of pressure-sensitive adhesives used in the pressure-sensitive adhesive layer include acrylic pressure-sensitive adhesives, urethane pressure-sensitive adhesives, silicone pressure-sensitive adhesives, rubber pressure-sensitive adhesives, etc. Among these, acrylic pressure-sensitive adhesives and urethane pressure-sensitive adhesives are preferred in terms of adhesive strength, transparency, and handleability. Furthermore, pressure-sensitive adhesives capable of forming a crosslinked structure are preferred. The pressure-sensitive adhesive may be in any form, such as a solvent-type pressure-sensitive adhesive, an emulsion-type pressure-sensitive adhesive, or a hot-melt pressure-sensitive adhesive. The thickness of the adhesive layer may be appropriately selected depending on the application, etc. It is usually 1 to 50 μm, preferably 5 to 25 μm.

[0055] The thickness of the laminate can be appropriately determined depending on the intended use of the adherend, electronic device, etc. From the viewpoint of handleability, the substantial thickness of the laminate is preferably 0.3 to 50 μm, more preferably 0.5 to 25 μm, and more preferably 0.7 to 12 μm. The term "substantial thickness" refers to the thickness in use. That is, although the laminate may have a processing film or the like as described above, the thickness of the portion (processing film or the like) that is removed during use is not included in the "substantial thickness."

[0056] (Method of manufacturing laminate) The laminate of the present invention can be produced using a casting film in one embodiment. By using a casting film, the laminate can be produced efficiently and easily.

[0057] The method for producing the laminate of the present invention preferably includes the following (Step 1) to (Step 3). (Step 1): A step of forming an optical film (coating film) on a processing film using a curable resin composition containing a polymer component (A) and a curable monomer (B) having two or more curable functional groups. (Step 2): A step of curing the optical film (coating film) obtained in Step 1 to form an optical film. (Step 3): A step of forming a functional layer on the optical film obtained in Step 2.

[0058] The method for applying the curable resin composition to the process film is not particularly limited, and known application methods such as spin coating, spray coating, bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating can be used.

[0059] The method for drying the resulting coating film is not particularly limited, and any conventionally known drying method such as hot air drying, hot roll drying, or infrared irradiation can be used. The temperature for drying the coating is usually 30 to 150°C, and preferably 80 to 130°C.

[0060] The optical film (coating film) obtained in step 1 is cured to form an optical film. The method for curing the optical film (coating film) is not particularly limited, and known methods can be used. For example, when the optical film (coating film) is formed using a curable resin composition containing a thermal polymerization initiator, the optical film (coating film) can be cured by heating the optical film (coating film). The heating temperature is usually 30 to 150°C, preferably 50 to 130°C. In addition, when the optical film (coating film) is formed using a curable resin composition containing a photopolymerization initiator, the optical film (coating film) can be cured by irradiating the optical film (coating film) with active energy rays. The active energy rays can be irradiated using a high-pressure mercury lamp, an electrodeless lamp, a xenon lamp, etc.

[0061] The wavelength of the active energy rays is preferably 200 to 400 nm, more preferably 350 to 400 nm. The irradiation dose is usually an illuminance of 50 to 1,000 mW / cm. 2 , light intensity 50~5,000mJ / cm 2 , preferably 1,000 to 5,000 mJ / cm 2 The irradiation time is usually 0.1 to 1,000 seconds, preferably 1 to 500 seconds, and more preferably 10 to 100 seconds. In consideration of the heat load in the light irradiation step, irradiation may be carried out multiple times to satisfy the above-mentioned light amount.

[0062] In this case, in order to prevent deterioration of the polymer component (A) and coloring of the optical film (coating film) due to irradiation with active energy rays, the curable resin composition may be irradiated with active energy rays through a filter that absorbs light of wavelengths unnecessary for the curing reaction. According to this method, light of wavelengths unnecessary for the curing reaction and that deteriorate the polymer component (A) is absorbed by the filter, so deterioration of the polymer component (A) is suppressed, and a colorless and transparent optical film can be easily obtained. The filter may be a resin film such as a polyethylene terephthalate film. When a resin film is used, it is preferable to provide a step of laminating a resin film such as a polyethylene terephthalate film on the optical film (coating film) between steps 1 and 2. The resin film is usually peeled off after step 2.

[0063] The optical film (coating film) can also be cured by irradiating it with an electron beam. When irradiating with an electron beam, the optical film (coating film) can usually be cured without using a photopolymerization initiator. When irradiating with an electron beam, an electron beam accelerator or the like can be used. The irradiation dose is usually in the range of 10 to 1,000 krad. The irradiation time is usually 0.1 to 1,000 seconds, preferably 1 to 500 seconds, and more preferably 10 to 100 seconds.

[0064] The optical film (coating film) may be cured in an inert gas atmosphere such as nitrogen gas, if necessary. By performing the curing in an inert gas atmosphere, it becomes easier to avoid oxygen, moisture, etc. from interfering with the curing.

[0065] A desired functional layer is formed on the optical film obtained in step 2. As a method for forming the functional layer, the methods described above can be appropriately adopted.

[0066] When the laminate has a processing film, the laminate may have the processing film on one side or on both sides, in which case it is preferable to use two types of processing film so that the processing film that is peeled first is easier to peel. The process film is preferably in the form of a sheet or film, which is not limited to a long film but also includes a short, flat plate. Examples of processing films include paper substrates such as glassine paper, coated paper, and fine paper; laminated paper obtained by laminating these paper substrates with thermoplastic resins such as polyethylene and polypropylene; the above paper substrates that have been sealed with cellulose, starch, polyvinyl alcohol, acrylic-styrene resin, and the like; plastic films such as polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin films such as polyethylene and polypropylene; and glass. For ease of handling, the casting film may be a paper substrate or a plastic film having a release layer formed thereon. The release layer can be formed using a conventionally known release agent, such as a silicone-based release agent, a fluorine-based release agent, an alkyd-based release agent, or an olefin-based release agent. The thickness of the release agent layer is not particularly limited, but is usually 0.02 to 2.0 μm, more preferably 0.05 to 1.5 μm. The thickness of the casting film is preferably 1 to 500 μm, more preferably 5 to 300 μm, from the viewpoint of ease of handling. The processing film is usually peeled off in a predetermined process depending on the application of the laminate.

[0067] As described above, the manufacturing method including the steps (Step 1) to (Step 3) forms an optical film using a processing film, but the laminate obtained by this method may or may not have a processing film. According to the above-described method for producing a laminate, the laminate according to one aspect of the present invention can be produced efficiently, continuously, and easily. [Example]

[0068] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0069] The in-plane retardation, elongation at break, strength at break, Young's modulus, total light transmittance and haze value of the optical films produced in the examples and comparative examples were evaluated by the following methods.

[0070] (1) In-plane phase difference (1-a) In-plane retardation (0% distortion) The optical films (thickness: 10 μm) obtained in the examples and comparative examples were peeled off from the process film to form 40 mm × 40 mm test pieces, and the in-plane phase difference (strain 0%) (retardation value) of the test pieces was measured at a temperature of 23°C using a phase difference measuring device (manufactured by Oji Scientific Instruments, model name "KOBRA-WR", wavelength: 589 nm). (1-b) In-plane retardation (distortion 1.0%) The optical films (thickness: 20 μm) obtained in the examples and comparative examples were peeled from the casting film to prepare 60 mm × 15 mm test pieces. Next, both ends (10 mm from each end) of the test piece in the longitudinal direction, excluding the measurement area for in-plane retardation, were reinforced with PET film (thickness: 100 μm) via double-sided tape. One end reinforced with the PET film was fixed to the measuring jig side in the vertical direction, and the other end was placed on the weight-hanging jig side so that it was located in the vertical direction below. Next, with a weight hanging from the test piece, a phase difference measuring device (manufactured by Oji Scientific Instruments, model name "KOBRA-WR", wavelength: 589 nm) was used to measure the in-plane phase difference (retardation value) of the test piece at a strain of 1.0% under conditions of a temperature of 23° C. Here, the weight at which the strain of the test piece used in Examples 1 and 2 was 1.0% was 227 g, and the weight at which the strain of the test piece used in Comparative Example 1 was 1.0% was 1027 g. (2) Breaking elongation, breaking strength and Young's modulus The optical films (thickness: 10 μm) obtained in the examples and comparative examples were peeled from the process film to form test pieces of 100 mm (length) × 15 mm (width). These were fixed in a jig, and the elongation at break, stress at break, and Young's modulus were measured at a temperature of 23°C, 50% RH, and a speed of 300 mm / min using an autograph (manufactured by Shimadzu Corporation, model name "AUTOGRAPH AG-X Plus"). (3) Total light transmittance and haze value The optical films (thickness: 10 μm) obtained in the examples and comparative examples were peeled from the casting film to form 50 mm × 50 mm test pieces, and the total light transmittance (%) of the test pieces was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "SH-7000") in accordance with JIS K7361-1:1997. Similarly, the haze value (%) was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "SH-7000") in accordance with JIS K7136:2000.

[0071] Example 1 Optical film formation Curable resin composition 1 was prepared as follows. As the polymer component (A), 100 parts by mass of polyvinyl butyral powder (manufactured by Sekisui Chemical Co., Ltd., product name: "KS-10," glass transition temperature Tg = 105°C, weight-average molecular weight 40,000) was dissolved in methyl ethyl ketone to prepare a 20% by mass solution of polyvinyl butyral. Next, 122 parts by mass of bifunctional polyethylene glycol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: A-400, molecular weight 522.6) as the curable monomer (B) and 5 parts by mass of (2,4,6-trimethylbenzoyl)-phenylphosphine oxide (manufactured by BASF, IRGACURE TPO) as the polymerization initiator were added to this solution and mixed to prepare a curable resin composition 1 diluted to a solids concentration of 21% by mass. The curable monomer (B) and polymerization initiator used in this example, other experimental examples, and comparative examples all contained no solvent and were raw materials with a solids content of 100% by mass. Next, a release film (manufactured by Lintec Corporation, product name: PET38 2150, thickness 38 μm) was used as a process film, and the curable resin composition 1 was applied to the low release force side of this release film, and the coating film was dried by heating at 100°C for 2 minutes. Next, the low release force side of the release film was laminated on top of this dried coating film, and using a conveyor-type ultraviolet irradiation device (manufactured by Heraus Corporation, model name "CV-100Q-G"), the ultraviolet lamp height was 85 mm, the ultraviolet lamp output was 100%, the line speed was 3.7 m / min, and the illuminance at a light wavelength of 365 nm was 400 mW / cm. 2 , light intensity 800mJ / cm 2 The curing reaction was carried out by irradiating ultraviolet light through the release film under the conditions of 1000 kJ / cm2 (measured with a UV Power Puck (registered trademark) II manufactured by Heraus), to form an optical film. Two types of optical films with thicknesses of 10 μm and 20 μm were prepared. The optical film was evaluated for in-plane retardation (strain 0%), in-plane retardation (strain 1.0%), breaking elongation, breaking strength, Young's modulus, total light transmittance, and haze value. The results are shown in Table 1.

[0072] Example 2 Optical films having thicknesses of 10 μm and 20 μm were prepared in the same manner as in Example 1, except that bifunctional polyethylene glycol diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: A-600, molecular weight 742.9) was used instead of the curable monomer (B) in the curable resin composition 1 of Example 1. The optical film was evaluated for in-plane retardation (strain 0%), in-plane retardation (strain 1.0%), breaking elongation, breaking strength, Young's modulus, total light transmittance, and haze value. The results are shown in Table 1.

[0073] (Comparative Example 1) As the polymer component (A), 100 parts by mass of polyimide resin (PI) powder (KPI-MX300F, manufactured by Kawamura Sangyo Co., Ltd., Tg = 354°C, weight-average molecular weight 280,000) was dissolved in methyl ethyl ketone (MEK) and toluene (MEK:toluene = 1:1) to prepare a 15% by mass solution of PI. Next, 122 parts by mass of tricyclodecane dimethanol diacrylate (A-DCP, manufactured by Shin-Nakamura Chemical Co., Ltd., molecular weight 304.4) as the curable monomer (B) and 5 parts by mass of (2,4,6-trimethylbenzoyl)-phenylphosphine oxide (IRGACURE TPO, manufactured by BASF) as a polymerization initiator were added to this solution and mixed to prepare curable resin composition 2. Next, a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., PET100A-4100, thickness 50 μm) having an easy-adhesion layer on one side was used as a process film, and curable resin composition 2 was applied to the side of this PET film opposite the easy-adhesion layer side, and the coating was dried by heating at 100°C for 2 minutes. Furthermore, a PET film (Cosmoshine A4100, manufactured by Toyobo Co., Ltd., thickness 50 μm) was laminated on the dried coating film so that the surface opposite to the easy-adhesion surface faced the adhesive surface, and the coating was then irradiated using a conveyor-type ultraviolet irradiation device (CV-100Q-G, manufactured by Heraus Co., Ltd.) with an ultraviolet lamp height of 85 mm, an ultraviolet lamp output of 100%, a line speed of 3.7 m / min, and an illuminance of 400 mW / cm at a light wavelength of 365 nm. 2 , light intensity 800mJ / cm 2The curing reaction was carried out by irradiating ultraviolet light through the PET film under the conditions (measured with UV Power Puck (registered trademark) II manufactured by Heraus) to prepare optical films with thicknesses of 10 μm and 20 μm. The optical film was evaluated for in-plane retardation (strain 0%), in-plane retardation (strain 1.0%), breaking elongation, breaking strength, Young's modulus, total light transmittance, and haze value. The results are shown in Table 1.

[0074] The chemical structural formulas of the curable monomers (B) used in the examples and comparative examples are shown below.

[0075] [ka]

[0076] [ka]

[0077] [ka]

[0078] [Table 1]

[0079] It can be seen that the optical films of Examples 1 and 2, which used polyvinyl butyral as the polymer component (A) and a curable monomer (B) having two or more curable functional groups in the curable resin composition, have excellent in-plane retardation against distortion compared to the optical film of Comparative Example 1, which used polyimide as the polymer component (A). Furthermore, since it has a low Young's modulus, stress during bending is small, and the device is easy to bend. [Industrial Applicability]

[0080] The optical film of the present invention has a small in-plane retardation against distortion and easily maintains optical isotropy, and is therefore expected to be applied to substrates of components such as flexible display elements, for example, flexible organic EL elements.

Claims

1. An optical film comprising a cured product of a curable resin composition containing a polymer component (A) and a curable monomer (B) having two or more curable functional groups, the polymer component (A) contains polyvinyl butyral, the curable monomer (B) is a polyfunctional (meth)acrylic acid derivative, The optical film has an in-plane retardation of 0 to 10 nm at a wavelength of 589 nm and a strain of 1%.

2. The optical film according to claim 1 , wherein the optical film has a thickness of 25 μm or less.

3. The optical film according to claim 1 or 2, wherein the haze value of the optical film is 1.0% or less.

4. 4. The optical film according to claim 1, wherein the optical film has a total light transmittance of 85% or more.

5. 5. The optical film according to claim 1, wherein the optical film has a breaking elongation of 5.0% or more.

6. 6. The optical film according to claim 1, wherein the polymer component (A) has a weight average molecular weight of 10,000 or more.

7. A laminate comprising the optical film according to any one of claims 1 to 6 and a functional layer.

8. The laminate according to claim 7 , wherein the functional layer comprises at least one layer selected from the group consisting of an adhesive layer, a pressure-sensitive adhesive layer, a pressure-sensitive adhesive layer, a gas barrier layer, a conductive layer, and a hard coat layer.

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