Optical film

Abstract

To provide an optical film having antiblocking properties without impairing functions as an optical film.SOLUTION: An optical film according to the present invention includes a (meth)acrylic resin film containing a (meth)acrylic resin as a main component and including crosslinked particles, and an easy-adhesion layer formed on the (meth)acrylic resin film. The glass-transition temperature of the (meth)acrylic resin film is 120°C. or higher, the average particle size of the crosslinked particles is 1.0 μm or more and 2.5 μm or less, the content of the lubricating particles in the easy-adhesive layer is 0.1 wt% or less, and the total value of the ten-point average roughness Rzjis on the surface of the easy-adhesive layer and the ten-point average roughness Rzjis on the surface of the (meth)acrylic resin film opposite to the easy-adhesive layer is from 23 nm or more to 200 nm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Optical films, such as polarizer protective films, are required to have optical transparency, optical homogeneity, and smoothness. Conventionally, cellulose-based films have been widely used as polarizer protective films, but in recent years, (meth)acrylic resin films have sometimes been used to improve durability. Furthermore, in order to improve adhesion to the polarizer, an easy-adhesion layer is sometimes formed by applying a composition for forming an easy-adhesion layer to the surface of a (meth)acrylic resin film.

[0003] These optical films may come into contact with each other when wound into a roll, resulting in scratches, irregular defects, etc. Therefore, in order to prevent such scratches and irregular defects, it has been proposed to add lubricating particles having antiblocking properties, such as silica particles having a specific particle size, to the adhesion layer to improve the slip properties of the optical film (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-52944 Summary of the Invention [Problem to be solved by the invention]

[0005] However, since lubricating particles such as silica particles tend to aggregate in the composition for forming an easy-adhesion layer, it becomes difficult to uniformly distribute the lubricating particles on the surface of the (meth)acrylic resin film, and the anti-blocking property may not be fully exhibited. Furthermore, the aggregation of the lubricating particles may affect the transparency and other functions of the optical film.

[0006] Therefore, an object of the present invention is to provide an optical film that has anti-blocking properties without impairing the functions of the optical film. [Means for solving the problem]

[0007] Specific means for solving the above problems include the following embodiments. <1> An optical film comprising a (meth)acrylic resin film containing crosslinked particles as a main component and an easy-adhesion layer formed on the (meth)acrylic resin film, wherein the optical film satisfies the following: (i) the (meth)acrylic resin film has a glass transition temperature of 120°C or higher; (ii) the average particle size of the crosslinked particles is 1.0 μm or more and 2.5 μm or less; (iii) the content of the lubricating particles in the adhesive layer is 0.1% by weight or less; (iv) The sum of the 10-point average roughness Rzjis on the surface of the easy-adhesion layer and the 10-point average roughness Rzjis on the surface of the (meth)acrylic resin film opposite to the easy-adhesion layer is 23 nm or more and 200 nm or less.

[0008] <2> An optical film comprising a (meth)acrylic resin film containing crosslinked particles as a main component and an easy-adhesion layer formed on the (meth)acrylic resin film, wherein the optical film satisfies the following: (i) The (meth)acrylic resin film contains a (meth)acrylic resin having a ratio of methyl methacrylate units of 98% by weight or more and a syndiotacticity of 54% or more in triad expression, (ii) the average particle size of the crosslinked particles is 1.0 μm or more and 2.5 μm or less; (iii) the content of the lubricating particles in the adhesive layer is 0.1% by weight or less; (iv) The sum of the 10-point average roughness Rzjis on the surface of the easy-adhesion layer and the 10-point average roughness Rzjis on the surface of the (meth)acrylic resin film opposite to the easy-adhesion layer is 23 nm or more and 200 nm or less.

[0009] <3> The thickness of the easy-adhesion layer is 50 nm or more and 600 nm or less. <1> or <2> The optical film according to claim 1.

[0010] <4> when the two optical films are superimposed such that the (meth)acrylic resin film and the easy-adhesion layer are in contact with each other, the static friction coefficient measured in accordance with JIS K 7125:1999 is 0.3 or more and 2.0 or less; <1> or <2> The optical film according to claim 1.

[0011] <5> The (meth)acrylic resin film contains a (meth)acrylic resin having a ring structure in the main chain. <1> The optical film according to claim 1.

[0012] <6> the ring structure is at least one selected from the group consisting of a glutarimide structure, a lactone ring structure, a maleic anhydride structure, an N-substituted maleimide structure, and a glutaric anhydride structure; <5> The optical film according to claim 1.

[0013] <7> The (meth)acrylic resin having a ring structure in the main chain contains a structural unit represented by the following general formula (1): <5> The optical film according to claim 1. [ka] (In the formula, R 1 and R 2 each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R 3 represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

[0014] <8> The proportion of the structural unit represented by the general formula (1) in the (meth)acrylic resin having a ring structure in the main chain is 2% by weight or more and 30% by weight or less. <7> The optical film according to claim 1.

[0015] <9> The (meth)acrylic resin film contains a (meth)acrylic resin having a proportion of methyl methacrylate units of 98% by weight or more and a syndiotacticity of 54% or more in triad expression. <1> The optical film according to claim 1.

[0016] <10> The (meth)acrylic resin film contains an aromatic vinyl unit. <1> ~ <9> 10. The optical film according to any one of claims 1 to 9.

[0017] <11> The (meth)acrylic resin film further contains a copolymer containing an aromatic vinyl unit. <5> or <9> The optical film according to claim 1.

[0018] <12> The copolymer further contains a (meth)acrylic acid ester unit or a (meth)acrylonitrile unit. <11> The optical film according to claim 1.

[0019] <13> A composition for forming an easy-adhesion layer on a (meth)acrylic resin film, The (meth)acrylic resin film contains a (meth)acrylic resin as a main component, contains crosslinked particles having an average particle diameter of 1.0 μm or more and 2.5 μm or less, and has a glass transition temperature of 120° C. or more; The composition for forming an easy-adhesion layer has a content of lubricating particles of 0.1% by weight or less.

[0020] <14> A composition for forming an easy-adhesion layer on a (meth)acrylic resin film, the (meth)acrylic resin film contains a (meth)acrylic resin as a main component and crosslinked particles having an average particle diameter of 1.0 μm or more and 2.5 μm or less; The (meth)acrylic resin film contains a (meth)acrylic resin having a proportion of methyl methacrylate units of 98% by weight or more and a triad syndiotacticity of 54% or more, The composition for forming an easy-adhesion layer has a content of lubricating particles of 0.1% by weight or less. [Effects of the Invention]

[0021] According to the present invention, an optical film having anti-blocking properties can be provided without impairing the functions of the optical film. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic cross-sectional view of an optical film according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, one embodiment of the present invention will be described, but the present invention is not limited to this embodiment. In this specification, the term "(meth)acrylic" means both "acrylic" and "methacrylic". The same applies to terms such as "(meth)acryloyl", "(meth)acrylic acid", and "(meth)acrylonitrile".

[0024] <Optical film> The optical film according to this embodiment includes a (meth)acrylic resin film containing crosslinked particles as a main component, and an easy-adhesion layer formed on the (meth)acrylic resin film.

[0025] Here, the (meth)acrylic resin refers to a resin in which the proportion of structural units derived from a polymerizable monomer having a (meth)acryloyl group is 50% by weight or more, and the fact that the (meth)acrylic resin is the main component means that the content of the (meth)acrylic resin in the (meth)acrylic resin film is 50% by weight or more.

[0026] A schematic cross-sectional view of an optical film according to this embodiment is shown in FIG. 1. The optical film 1 shown in FIG. 1 has a (meth)acrylic resin film 3 containing crosslinked particles 4, and an easy-adhesion layer 2 formed on the (meth)acrylic resin film 3. Since the (meth)acrylic resin film 3 contains the crosslinked particles 4, unevenness is formed on the surface of the (meth)acrylic resin film 3. Since the easy-adhesion layer 2 is formed on the surface of the (meth)acrylic resin film 3 on which unevenness is formed, unevenness also appears on the surface of the easy-adhesion layer 2. As a result, the optical film 1 has anti-blocking properties.

[0027] In the optical film according to this embodiment, when two optical films are superimposed such that the (meth)acrylic resin film and the easy-adhesion layer are in contact with each other, the static friction coefficient measured in accordance with JIS K 7125: 1999 is preferably 0.3 to 2.0, more preferably 0.4 to 1.8. When the static friction coefficient between the (meth)acrylic resin film and the easy-adhesion layer is within the above range, good anti-blocking properties tend to be exhibited.

[0028] [(Meth)acrylic resin film] The (meth)acrylic resin film constitutes the substrate of the optical film and contains a (meth)acrylic resin as a main component. The content of the (meth)acrylic resin in the (meth)acrylic resin film is preferably 50% by weight or more, more preferably 60% by weight or more, even more preferably 70% by weight or more, and particularly preferably 75% by weight or more.

[0029] Any appropriate (meth)acrylic resin can be used as the (meth)acrylic resin. Specific examples include poly(meth)acrylic acid esters (e.g., polymethyl methacrylate, etc.), methyl methacrylate-(meth)acrylic acid copolymers, methyl methacrylate-(meth)acrylic acid ester copolymers, methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymers, methyl (meth)acrylate-styrene copolymers, and polymers having alicyclic hydrocarbon groups (e.g., methyl methacrylate-cyclohexyl methacrylate copolymers, methyl methacrylate-norbornyl (meth)acrylate copolymers, etc.). Among these, poly(methyl (meth)acrylate and other C1-C6 alkyl (meth)acrylates (poly(meth)acrylic acid ester-based resins having alkyl groups with 1 to 6 carbon atoms) are preferred, and polymethyl methacrylate-based resins containing methyl methacrylate as the main component (50% by weight or more, preferably 70% by weight or more) are more preferred.

[0030] The (meth)acrylic resin film may contain an aromatic vinyl unit. This aromatic vinyl unit may be one that constitutes the (meth)acrylic resin that is the main component, or may be one that constitutes a resin separate from the (meth)acrylic resin that is the main component. The content of the aromatic vinyl unit in the (meth)acrylic resin film is preferably 0% by weight or more and 25% by weight or less, and more preferably 0.5% by weight or more and 20% by weight or less.

[0031] The (meth)acrylic resin film preferably has a glass transition temperature of 120°C or higher, more preferably above 120°C, even more preferably 121°C or higher, and particularly preferably 122°C or higher. When the (meth)acrylic resin film has a glass transition temperature of 120°C or higher, the dimensional change rate of the film in a high-temperature environment tends to be small. In practical use, (meth)acrylic resin films are often laminated with other films, and a small dimensional change rate can suppress distortion and warping caused by differences in dimensional change rate with other laminated films.

[0032] The glass transition temperature can be determined by the midpoint method using a differential scanning calorimeter (DSC7000X, manufactured by Hitachi High-Tech Science Corporation) in a nitrogen atmosphere at a temperature rise rate of 20°C / min.

[0033] ((Meth)acrylic resin having a ring structure in the main chain) The (meth)acrylic resin film preferably contains, as a (meth)acrylic resin having a glass transition temperature of 120°C or higher, a (meth)acrylic resin having a ring structure in its main chain (hereinafter also referred to as a "first (meth)acrylic resin"). Examples of the ring structure include at least one ring structure selected from a glutarimide structure, a lactone ring structure, a maleic anhydride structure, an N-substituted maleimide structure, and a glutaric anhydride structure. Among these, a (meth)acrylic resin having a glutarimide structure or a lactone ring structure in its main chain is preferred, and from the viewpoints of ease of production, cost, quality stability against moisture, etc., a (meth)acrylic resin having a glutarimide structure in its main chain is more preferred.

[0034] The proportion of the ring structure in the first (meth)acrylic resin is not particularly limited, but is, for example, 1% by weight to 80% by weight, preferably 2% by weight to 30% by weight. A high proportion of the ring structure within this range is preferred in terms of increasing the glass transition temperature, while a low proportion of the ring structure within this range is preferred in terms of decreasing the retardation.

[0035] Each ring structure will be explained below.

[0036] The (meth)acrylic resin having a glutarimide structure in the main chain is, for example, a resin having a glutarimide unit represented by the following general formula (1) and a methyl methacrylate unit, and can be produced by heating and melting a polymethyl methacrylate resin and then treating it with an imidizing agent.

[0037] [ka] (In the formula, R 1and R 2 each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and R 3 represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

[0038] The proportion of glutarimide units in the (meth)acrylic resin having a glutarimide structure in the main chain is preferably 2% by weight or more and 30% by weight or less. When the proportion of glutarimide units is 2% by weight or more, the desired heat resistance tends to be easily imparted. Furthermore, when the proportion of glutarimide units is 30% by weight or less, the amount of imidizing agent added can be reduced, odor due to remaining volatile components can be suppressed, and thickness direction retardation Rth tends to be reduced.

[0039] R in the above general formula (1) 3 When is a methyl group, the proportion of glutarimide units can be measured, for example, by the following method. 1 H-NMR BRUKER AvanceIII (400MHz) was used to measure the 1 H-NMR measurement is performed. The molar ratio is calculated from the area A of the peak at around 3.5 ppm to 3.8 ppm, which is derived from the protons constituting the O-CH3 of methyl methacrylate, and the area B of the peak at around 3.0 ppm to 3.3 ppm, which is derived from the protons constituting the N-CH3 of the glutarimide ring. The proportion of glutarimide units can be calculated by converting the molar ratio into weight.

[0040] When producing polymethyl methacrylate resin, other monomers such as methyl acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, benzyl (meth)acrylate, and cyclohexyl (meth)acrylate may be used in combination with methyl methacrylate. In addition to the above, other monomers may also be used in combination: nitrile-based monomers such as acrylonitrile and methacrylonitrile; maleimide-based monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide, and N-cyclohexylmaleimide; and aromatic vinyl-based monomers such as styrene and α-methylstyrene. However, the proportion of acrylic ester units in the polymethyl methacrylate resin is preferably less than 1% by weight. In particular, the proportion of methyl acrylate units is preferably less than 0.5% by weight, and more preferably less than 0.3% by weight.

[0041] The structure of the polymethyl methacrylate resin is not particularly limited, and may be any of a linear polymer, a block polymer, a core-shell polymer, a branched polymer, a ladder polymer, a crosslinked polymer, and the like.

[0042] The method for producing polymethyl methacrylate resin is not particularly limited, and known methods such as emulsion polymerization, emulsion-suspension polymerization, suspension polymerization, bulk polymerization, and solution polymerization can be used. When used in the optical field, bulk polymerization and solution polymerization are preferred because they reduce impurities. Polymethyl methacrylate resin can be produced, for example, according to the methods described in JP-A-56-8404, JP-B-6-86492, JP-B-7-37482, and JP-B-52-32665.

[0043] The method for producing a (meth)acrylic resin having a glutarimide structure in the main chain includes a step of heating and melting the above-mentioned polymethyl methacrylate resin, and then treating it with an imidizing agent (imidization step).

[0044] The imidizing agent is not particularly limited as long as it can generate the glutarimide unit represented by the general formula (1), and those described in International Publication No. 2005 / 054311 can be used. Specific examples of the imidizing agent include aliphatic hydrocarbon group-containing amines such as ammonia, methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, t-butylamine, and n-hexylamine; aromatic hydrocarbon group-containing amines such as aniline, benzylamine, toluidine, and trichloroaniline; and alicyclic hydrocarbon group-containing amines such as cyclohexylamine. Among these, from the viewpoints of cost and physical properties, methylamine, ammonia, and cyclohexylamine are preferred, and methylamine is more preferred. Methylamine and the like, which are gaseous at room temperature, may be used in a dissolved state in an alcohol such as methanol.

[0045] In the imidization step, the ratio of glutarimide units and (meth)acrylic acid ester units in the resulting (meth)acrylic resin can be adjusted by adjusting the amount of imidization agent added. Furthermore, by adjusting the degree of imidization, the physical properties of the resulting (meth)acrylic resin and the optical properties of a (meth)acrylic resin film obtained by molding the (meth)acrylic resin can be adjusted.

[0046] The amount of imidizing agent added is preferably 0.5 to 20 parts by weight per 100 parts by weight of polymethyl methacrylate resin. When the amount of imidizing agent added is 0.5 parts by weight or more, the proportion of glutarimide units increases, which tends to improve the heat resistance of the (meth)acrylic resin and prevent appearance defects after molding. When the amount of imidizing agent added is 20 parts by weight or less, the imidizing agent is less likely to remain in the (meth)acrylic resin, which tends to prevent appearance defects and foaming after molding.

[0047] In the imidization step, a ring closure promoter (catalyst) may be added in addition to the imidization agent.

[0048] The method for heating and melting the polymethyl methacrylate resin and treating it with the imidizing agent is not particularly limited, and any conventionally known method can be used. For example, the polymethyl methacrylate resin can be imidized by a method using an extruder, a batch-type reaction tank (pressure vessel), etc.

[0049] When the polymethyl methacrylate resin is heated and melted using an extruder and treated with the imidizing agent, various extruders such as a single-screw extruder, a twin-screw extruder, and a multi-screw extruder can be used. Among these, a twin-screw extruder is preferably used. The twin-screw extruder can promote mixing of the imidizing agent (if a ring-closure accelerator is used, the imidizing agent and the ring-closure accelerator) with the polymethyl methacrylate resin.

[0050] Examples of twin-screw extruders include non-intermeshing co-rotating types, intermeshing co-rotating types, non-intermeshing counter-rotating types, and intermeshing counter-rotating types, and it is preferable to use an intermeshing co-rotating type. Since an intermeshing co-rotating twin-screw extruder can rotate at high speed, it can further promote mixing of the imidizing agent (if a ring-closure accelerator is used, the imidizing agent and the ring-closure accelerator) with the polymethyl methacrylate resin.

[0051] The extruders exemplified above may be used alone or in combination with a plurality of extruders connected in series. For example, the tandem reactive extruder described in JP-A-2008-273140 may be used.

[0052] When the imidization reaction is carried out in an extruder, for example, polymethyl methacrylate resin is charged into the raw material charging port of the extruder, the resin is melted, and the cylinder is filled with the resin, and then an imidization agent is injected into the extruder using an addition pump.

[0053] In this case, the temperature of the reaction zone (resin temperature) in the extruder is preferably 180°C or higher and 270°C or lower, and more preferably 200°C or higher and 250°C or lower. When the temperature of the reaction zone (resin temperature) is 180°C or higher, the imidization reaction proceeds sufficiently, and heat resistance tends to be improved. Furthermore, when the temperature of the reaction zone is 270°C or lower, decomposition of the resin is suppressed, and as a result, a decrease in the fold resistance of a film formed from the resulting (meth)acrylic resin tends to be suppressed. Here, the reaction zone in the extruder refers to the region in the cylinder of the extruder between the injection position of the imidization agent and the resin discharge port (die portion).

[0054] By increasing the reaction time in the reaction zone of the extruder, imidization can be further promoted. The reaction time in the reaction zone of the extruder is preferably more than 10 seconds, more preferably more than 30 seconds. If the reaction time is less than 10 seconds, imidization may not proceed very much.

[0055] The resin pressure in the extruder is preferably atmospheric pressure or higher and 50 MPa or lower, more preferably 1 MPa or higher and 30 MPa or lower. When the resin pressure is 1 MPa or higher, the solubility of the imidizing agent increases, and the reaction tends to proceed more rapidly. Furthermore, when the resin pressure is 50 MPa or lower, no special equipment is required, which is preferable from a cost perspective.

[0056] When an extruder is used, it is preferable to equip it with a vent hole that can reduce the pressure to below atmospheric pressure in order to remove unreacted imidizing agent, by-products such as methanol, monomers, and the like.

[0057] Instead of an extruder, a horizontal twin-screw reactor such as Vivolac manufactured by Sumitomo Heavy Industries, Ltd., or a vertical twin-screw stirring tank such as Superblend, which is suitable for high viscosity materials, can also be suitably used.

[0058] When a batch-type reactor (pressure vessel) is used to heat and melt a polymethyl methacrylate resin and treat it with an imidizing agent, the structure of the batch-type reactor is not particularly limited. The batch-type reactor may have any structure that can melt and stir the polymethyl methacrylate resin by heating, and can add an imidizing agent (if a ring-closure accelerator is used, the imidizing agent and ring-closure accelerator). A structure with good stirring efficiency is preferred. Such a batch-type reactor can prevent the polymer viscosity from increasing as the reaction progresses, resulting in insufficient stirring. An example of a batch-type reactor with such a structure is the Maxblend stirring tank manufactured by Sumitomo Heavy Industries, Ltd.

[0059] Specific examples of the imidization method include known methods described in, for example, JP-A Nos. 2008-273140 and 2008-274187.

[0060] The method for producing a (meth)acrylic resin having a glutarimide structure in its main chain may include, in addition to the imidization step, a step of treating with an esterifying agent (esterification step). This esterification step allows the acid value of the imidized resin obtained in the imidization step to be adjusted within a desired range.

[0061] Examples of the esterifying agent include dimethyl carbonate, 2,2-dimethoxypropane, dimethyl sulfoxide, triethyl orthoformate, trimethyl orthoacetate, trimethyl orthoformate, diphenyl carbonate, dimethyl sulfate, methyl toluene sulfonate, methyl trifluoromethyl sulfonate, methyl acetate, methanol, ethanol, methyl isocyanate, p-chlorophenyl isocyanate, dimethylcarbodiimide, dimethyl-t-butylsilyl chloride, isopropenyl acetate, dimethyl urea, tetramethylammonium hydroxide, dimethyldiethoxysilane, tetra-N-butoxysilane, dimethyl(trimethylsilane) phosphite, trimethyl phosphite, trimethyl phosphate, tricresyl phosphate, diazomethane, ethylene oxide, propylene oxide, cyclohexene oxide, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and benzyl glycidyl ether. Among these, dimethyl carbonate and trimethyl orthoacetate are preferred from the viewpoints of cost, reactivity, etc., and dimethyl carbonate is more preferred from the viewpoint of cost.

[0062] The amount of the esterifying agent added is preferably 0 to 12 parts by weight, more preferably 0 to 8 parts by weight, relative to 100 parts by weight of the polymethyl methacrylate resin. When the amount of the esterifying agent is within the above range, the acid value can be adjusted to an appropriate range, and unreacted esterifying agent tends to be less likely to remain in the resin.

[0063] In the esterification step, a catalyst can be used in addition to the esterifying agent. Examples of the catalyst include aliphatic tertiary amines such as trimethylamine, triethylamine, and tributylamine. Among these, triethylamine is preferred from the viewpoints of cost, reactivity, etc.

[0064] In the esterification step, only a heat treatment or the like can be performed without treatment with an esterifying agent. When only a heat treatment (kneading and dispersing the molten resin in an extruder) is performed, at least a portion of the carboxy groups can be converted to acid anhydride groups by a dehydration reaction between the carboxy groups by-produced in the imidization step, a dealcoholization reaction between the carboxy groups and the alkyl ester groups, or the like. In this case, a ring closure accelerator (catalyst) can also be used. Even when treating with an esterifying agent, it is also possible to promote the conversion to acid anhydride groups by a heat treatment.

[0065] The (meth)acrylic resin having a lactone ring structure in the main chain is not particularly limited as long as it is a thermoplastic polymer having a lactone ring structure in the molecule (a thermoplastic polymer having a lactone ring structure introduced into the molecular chain), and its production method is also not limited. Among them, a (meth)acrylic resin obtained by polymerizing a polymer having a hydroxy group and an ester group in the molecular chain (polymerization step) and then heat-treating the obtained polymer to introduce a lactone ring structure into the polymer (lactone cyclization condensation step) is preferred.

[0066] In the polymerization step, a polymer having a hydroxy group and an ester group in the molecular chain is obtained by carrying out a polymerization reaction of a monomer component containing an unsaturated monomer represented by the following general formula (2).

[0067] [ka] (In the formula, R 4 and R 5 each independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

[0068] Examples of the unsaturated monomer represented by the general formula (2) include methyl 2-(hydroxymethyl)acrylate, ethyl 2-(hydroxymethyl)acrylate, isopropyl 2-(hydroxymethyl)acrylate, n-butyl 2-(hydroxymethyl)acrylate, and t-butyl 2-(hydroxymethyl)acrylate. Among these, methyl 2-(hydroxymethyl)acrylate and ethyl 2-(hydroxymethyl)acrylate are preferred, and methyl 2-(hydroxymethyl)acrylate is more preferred from the viewpoint of a high effect of improving heat resistance. These unsaturated monomers may be used alone or in combination of two or more.

[0069] The content of the unsaturated monomer represented by the general formula (2) in the monomer component is preferably 5% by weight or more and 50% by weight or less, more preferably 10% by weight or more and 40% by weight or less, and even more preferably 10% by weight or more and 30% by weight or less. When the content of the unsaturated monomer represented by the general formula (2) is 5% by weight or more, the heat resistance, solvent resistance, surface hardness, etc. of the resulting resin tend to be improved. Furthermore, when the content of the unsaturated monomer represented by the general formula (2) is 50% by weight or less, the occurrence of a crosslinking reaction during the formation of a lactone ring structure, which causes gelation, and the decrease in fluidity tend to be suppressed. Furthermore, the remaining unreacted hydroxy groups tend to further promote a condensation reaction during molding, which generates volatile substances, resulting in silver streaks, and the increase in thickness direction retardation Rth tend to be suppressed.

[0070] The monomer component may contain other monomers in addition to the unsaturated monomer represented by the general formula (2) above. Examples of other monomers include (meth)acrylic acid esters, hydroxy group-containing monomers, unsaturated carboxylic acids, and unsaturated monomers represented by the following general formula (3). One type of other monomer may be used alone, or two or more types may be used in combination.

[0071] [ka] (In the formula, R 6represents a hydrogen atom or a methyl group, and X represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group, an -OAc group, a -CN group, or a -CO-R 7 represents an acetyl group; Ac represents an acetyl group; R 7 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

[0072] The (meth)acrylic acid ester is not particularly limited as long as it is a (meth)acrylic acid ester other than the unsaturated monomer represented by the general formula (2), and examples thereof include acrylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, cyclohexyl acrylate, and benzyl acrylate; and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, and benzyl methacrylate; etc. Among these, methyl methacrylate is preferred from the viewpoints of heat resistance and transparency.

[0073] When a (meth)acrylic acid ester is used, the content of the (meth)acrylic acid ester in the monomer component is preferably 10% by weight or more and 95% by weight or less, more preferably 10% by weight or more and 90% by weight or less, even more preferably 40% by weight or more and 90% by weight or less, and particularly preferably 50% by weight or more and 90% by weight or less.

[0074] ((Meth)acrylic resin in which the proportion of methyl methacrylate units is 98% by weight or more and the syndiotacticity (rr) expressed as a triad is 54% or more) It is also preferable that the (meth)acrylic resin film contains a (meth)acrylic resin having a proportion of methyl methacrylate units of 98% by weight or more and a triad syndiotacticity of 54% or more (hereinafter also referred to as "second (meth)acrylic resin").

[0075] The second (meth)acrylic resin preferably has a proportion of methyl methacrylate units of 99% by weight or more and a proportion of other polymerizable monomer units other than methyl methacrylate units of 1% by weight or less, more preferably has a proportion of methyl methacrylate units of 99.5% by weight or more and a proportion of other polymerizable monomer units other than methyl methacrylate units of 0.5% by weight or less, and is even more preferably a homopolymer of methyl methacrylate.

[0076] Examples of polymerizable monomers other than methyl methacrylate include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate; aryl acrylates such as phenyl acrylate; cycloalkyl acrylates such as cyclohexyl acrylate and norbornenyl acrylate; alkyl methacrylates other than methyl methacrylate such as ethyl methacrylate, propyl methacrylate, and n-butyl methacrylate; aryl methacrylates such as phenyl methacrylate; cycloalkyl methacrylates such as cyclohexyl methacrylate and norbornenyl methacrylate; aromatic vinyl monomers such as styrene and α-methylstyrene; vinyl cyanide monomers such as acrylonitrile and methacrylonitrile; acrylamide; methacrylamide; and the like.

[0077] The second (meth)acrylic resin has a syndiotacticity (rr) expressed as a triad of 54% or more, preferably 55% or more, more preferably 56% or more, and even more preferably 57% or more. When the syndiotacticity (rr) expressed as a triad of 54% or more, the glass transition temperature of the (meth)acrylic resin tends to be high and the heat resistance tends to be improved. There is no particular upper limit for the syndiotacticity (rr), but from the viewpoints of the molding temperature and the toughness and secondary processability of the molded body, it is preferably 70% or less, more preferably 67% or less, even more preferably 65% ​​or less, and particularly preferably 63% or less.

[0078] Syndiotacticity (rr) is the proportion of two diads in a triad of three consecutive structural units that are both racemo (rr). Diads in polymer molecules with the same configuration are called meso, and those with the opposite configuration are called racemo, and are abbreviated as m and r, respectively.

[0079] Syndiotacticity (rr) is measured in deuterated chloroform at 22°C and 16 cycles. 1 The H-NMR spectrum is measured, and from the spectrum, the area (X) of the region from 0.60 ppm to 0.95 ppm and the area (Y) of the region from 0.60 ppm to 1.25 ppm are measured when tetramethylsilane (TMS) is set to 0 ppm, and the chromaticity can be calculated using the formula: (X / Y) × 100.

[0080] As a method for producing the second (meth)acrylic resin, a conventionally known polymerization method can be used, for example, a radical polymerization method such as continuous bulk polymerization, solution polymerization, emulsion polymerization, emulsifier-free (soap-free) emulsion polymerization, or suspension polymerization. Among them, from the viewpoint of the degree of freedom in structural design of the (meth)acrylic resin, the simplicity of polymerization, productivity, etc., a production method using aqueous polymerization is preferred, a suspension polymerization method and an emulsion polymerization method are more preferred, and a suspension polymerization method is even more preferred. The second (meth)acrylic resin can be produced, for example, according to the method described in International Publication No. 2023 / 238885.

[0081] (copolymer containing aromatic vinyl units) The (meth)acrylic resin film may further contain a copolymer containing an aromatic vinyl unit in addition to the first (meth)acrylic resin or the second (meth)acrylic resin. Examples of the copolymer containing an aromatic vinyl unit include a (meth)acrylic acid ester-aromatic vinyl copolymer such as a methyl methacrylate-styrene copolymer; and a (meth)acrylonitrile-aromatic vinyl copolymer such as an acrylonitrile-styrene copolymer.

[0082] Examples of aromatic vinyl include styrene, α-methylstyrene, methoxystyrene, vinyltoluene, halostyrene, etc. Among these, styrene is preferred.

[0083] Examples of (meth)acrylic acid esters include acrylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, cyclohexyl acrylate, and benzyl acrylate; and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, and benzyl methacrylate; and among these, methyl methacrylate is preferred.

[0084] The proportion of aromatic vinyl units in the (meth)acrylic acid ester-aromatic vinyl copolymer is preferably 10% by weight or more and 30% by weight or less, and more preferably 15% by weight or more and 28% by weight or less. When the proportion of aromatic vinyl units is within the above range, the transparency of the (meth)acrylic resin film tends to be maintained.

[0085] The proportion of (meth)acrylonitrile units in the (meth)acrylonitrile-aromatic vinyl copolymer is preferably 22% by weight or more and 28% by weight or less, and more preferably 23% by weight or more and 27% by weight or less. When the proportion of (meth)acrylonitrile units is within the above range, the transparency of the (meth)acrylic resin film tends to be maintained.

[0086] The content of the copolymer containing an aromatic vinyl unit in the (meth)acrylic resin film is, for example, preferably from 0 to 30% by weight, and more preferably from 3 to 25% by weight.

[0087] (Other thermoplastic resins) The (meth)acrylic resin film may contain other thermoplastic resins in addition to those mentioned above, such as olefin polymers, vinyl halide polymers, styrene polymers, ester polymers, and amide polymers.

[0088] The content of other thermoplastic resins in the (meth)acrylic resin film is, for example, preferably 0% by weight or more and 50% by weight or less, and more preferably 0% by weight or more and 30% by weight or less.

[0089] The smaller the orientation birefringence of the (meth)acrylic resin film, the better. -4 Over 1.7 x 10 -4 If the orientation birefringence is within the above range, the retardation value of the (meth)acrylic resin film tends to be small.

[0090] In addition, the smaller the photoelastic coefficient of the (meth)acrylic resin film, the better. -12 Pa -1 Over 10x10 -12 Pa -1 It is preferable that it is less than or equal to -4×10 -12 Pa -1 Over 4×10 -12 Pa -1 More preferably, it is:

[0091] (crosslinked particles) Since the (meth)acrylic resin film contains crosslinked particles, unevenness is formed on the surface of the (meth)acrylic resin film. Since the easy-adhesion layer is formed on the surface of the (meth)acrylic resin film on which unevenness has been formed, unevenness also appears on the surface of the easy-adhesion layer, thereby realizing anti-blocking properties.

[0092] Examples of the crosslinked particles include crosslinked acrylic resin particles, crosslinked polystyrene resin particles, melamine resin particles, crosslinked silicone resin particles, etc. Among these, crosslinked acrylic resin particles are preferred from the viewpoints of compatibility with (meth)acrylic resins, dispersibility, transparency, etc.

[0093] The monomer forming the crosslinked acrylic resin particles can be selected from any (meth)acrylic acid ester and other monomers copolymerizable with (meth)acrylic acid ester. Among these, methyl methacrylate is preferred from the viewpoints of compatibility with (meth)acrylic resins and refractive index. In this case, the proportion of methyl methacrylate units in the crosslinked acrylic resin particles is preferably 80% by weight or more and 99% by weight or less.

[0094] The crosslinked acrylic resin particles further contain structural units derived from a polyfunctional monomer having two or more polymerizable groups in the molecule, and the proportion of the polyfunctional monomer units in the crosslinked acrylic resin particles is preferably 0.5% by weight or more and 30% by weight or less.

[0095] The refractive index of the crosslinked particles is preferably 98% or more and 102% or less, and more preferably 99% or more and 101% or less, when the refractive index of the (meth)acrylic resin is taken as 100%. The refractive index of the crosslinked particles is preferably 1.47 or more and 1.55 or less, more preferably 1.47 or more and 1.53 or less, and even more preferably 1.48 or more and 1.52 or less. By using crosslinked particles with a refractive index within this range, a highly transparent (meth)acrylic resin film tends to be obtained. Among these, crosslinked acrylic resin particles are preferred because they satisfy the above refractive index.

[0096] From the viewpoint of imparting anti-blocking properties, the average particle size of the crosslinked particles is preferably 1.0 μm or more and 2.5 μm or less, more preferably 1.5 μm or more and 2.3 μm or less. When the average particle size of the crosslinked particles is 1.0 μm or more, irregularities can be formed on the surface of the (meth)acrylic resin film, and anti-blocking properties tend to be imparted to the easy-adhesion layer formed on the surface of the (meth)acrylic resin film. Furthermore, when the average particle size of the crosslinked particles is 2.5 μm or less, the optical properties required for an optical film tend to be maintained without impairing the surface smoothness of the optical film.

[0097] The content of crosslinked particles in the (meth)acrylic resin film is preferably 0.01 wt% to 1.0 wt%, more preferably 0.03 wt% to 0.7 wt%, even more preferably 0.05 wt% to 0.5 wt%, and particularly preferably 0.08 wt% to 0.4 wt%, based on the weight of the (meth)acrylic resin film. When the content of crosslinked particles is 0.01 wt% or more, sufficient winding properties tend to be obtained. When the content of crosslinked particles is 1.0 wt% or less, the transparency of the (meth)acrylic resin film tends to be maintained.

[0098] The 10-point average roughness Rzjis of the surface of the (meth)acrylic resin film is preferably 5 nm or more and 100 nm or less, and more preferably 10 nm or more and 90 nm or less. If the 10-point average roughness Rzjis of the surface of the (meth)acrylic resin film is 5 nm or more, when an optical film having an easy-adhesion layer formed on the (meth)acrylic resin film is wound into a roll, anti-blocking properties tend to be exhibited even if the surface on the easy-adhesion layer side and the surface opposite the easy-adhesion layer overlap. Furthermore, if the 10-point average roughness Rzjis of the surface of the (meth)acrylic resin film is 100 nm or less, the unevenness formed on the surface does not become too large, preventing an impact on the transparency and other functions of the optical film. Furthermore, when the optical film is wound into a roll, scratches and unevenness defects tend to be prevented from occurring on the surface of the film.

[0099] The 10-point average roughness Rzjis of the surface of the (meth)acrylic resin film can be measured using a laser microscope LEXT OLS5100 manufactured by Evident Co., Ltd. in accordance with JIS B 0601:2013.

[0100] (additives) The (meth)acrylic resin film may contain any additives as needed, such as antioxidants, stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers, ultraviolet absorbers, flame retardants, antistatic agents, fillers, plasticizers, and lubricants.

[0101] (Film manufacturing method) The method for producing the (meth)acrylic resin film is not particularly limited, and methods such as injection molding, melt extrusion molding, inflation molding, blow molding, and compression molding can be used. Also, a solution casting method in which the (meth)acrylic resin is dissolved in a solvent and then molded, or a spin coating method can be used. Among these, it is preferable to use a melt extrusion method that does not use a solvent. The melt extrusion method can reduce production costs and also reduce the burden on the global environment and working environment caused by solvents.

[0102] Hereinafter, an example of producing a (meth)acrylic resin film by melt extrusion will be described. In the following description, a film obtained by melt extrusion will be referred to as a "melt-extruded film" to distinguish it from films obtained by other methods such as solution casting.

[0103] When a (meth)acrylic resin film is produced by melt extrusion, first, a (meth)acrylic resin is fed into an extruder and heated to melt it.

[0104] The (meth)acrylic resin is preferably pre-dried before being fed to the extruder. Such pre-drying can prevent foaming of the resin extruded from the extruder. The pre-drying method is not particularly limited, and can be carried out, for example, by forming the raw material (e.g., the (meth)acrylic resin) into pellets or the like and using a hot air dryer, a vacuum dryer, or the like.

[0105] Next, the (meth)acrylic resin heated and melted in the extruder is fed to a T-die via a gear pump, a filter, etc. Using a gear pump tends to make the extrusion amount of the (meth)acrylic resin uniform, thereby reducing thickness unevenness in the longitudinal direction of the film. On the other hand, using a filter tends to remove foreign matter from the (meth)acrylic resin, resulting in a (meth)acrylic resin film with excellent appearance and no defects.

[0106] Next, the (meth)acrylic resin supplied to the T-die is extruded from the T-die as a sheet-like molten resin. The sheet-like molten resin is then sandwiched between two cooling rolls and cooled to form a film.

[0107] Of the two cooling rolls that sandwich the sheet-like molten resin, one is preferably a rigid metal roll with a smooth surface, and the other is a flexible roll with a smooth, elastically deformable metal outer cylinder. By sandwiching the sheet-like molten resin between a rigid metal roll and a flexible roll with a metal outer cylinder, cooling it, and forming a film, minute surface irregularities and die lines are corrected, and a film with a smooth surface and thickness variation of 5 μm or less can be obtained. In this specification, the term "cooling roll" is used to encompass the term "touch roll."

[0108] Even when using a rigid metal roll and a flexible roll, since both cooling rolls have metal surfaces, if the film to be produced is thin, the surfaces of the cooling rolls may come into contact with each other, causing scratches on the outer surface of the cooling roll or damage to the cooling roll itself. Therefore, when producing a film by sandwiching a sheet-like molten resin between two cooling rolls, it is preferable to first sandwich and cool the sheet-like molten resin between the two cooling rolls, obtain a relatively thick raw film, and then uniaxially or biaxially stretch the raw film to produce a film of a predetermined thickness. For example, when producing a film with a thickness of 40 μm, it is preferable to first sandwich and cool the sheet-like molten resin between the two cooling rolls, obtain a raw film with a thickness of 150 μm, and then stretch the raw film by longitudinal and transverse biaxial stretching to produce a film with a thickness of 40 μm.

[0109] In this way, when the (meth)acrylic resin film is a stretched film, the (meth)acrylic resin is formed into an unstretched raw film, and then the unstretched raw film is subjected to uniaxial stretching or biaxial stretching, thereby producing a stretched film.

[0110] In order to improve the flex resistance of the (meth)acrylic resin film in both the machine direction (MD) and the width direction (TD), it is preferable to carry out biaxial stretching.

[0111] In this specification, for the sake of convenience, a film obtained by forming a (meth)acrylic resin into a film shape and before stretching it, that is, a film in an unstretched state, is referred to as a "raw film."

[0112] When stretching a raw film, the raw film may be continuously stretched immediately after being formed, or the raw film may be temporarily stored or moved after being formed, and then stretched.

[0113] In addition, when the raw film is stretched immediately after being formed, it is sufficient that the raw film maintains a film state sufficient for stretching even in a very short time in the film production process, and it is not necessary for the raw film to be in a perfect film state. Furthermore, the raw film does not need to have the properties of a finished film.

[0114] (Film stretching method) The method for stretching the raw film is not particularly limited, and any conventionally known stretching method can be used. For example, transverse stretching using a tenter, longitudinal stretching using rolls, and sequential biaxial stretching, which is a sequential combination of these, can be used. Also usable are simultaneous biaxial stretching methods in which longitudinal and transverse stretching are performed simultaneously, and methods in which longitudinal stretching using rolls is performed followed by transverse stretching using a tenter.

[0115] When stretching a raw film, it is preferable to first preheat the raw film to a temperature 0.5°C to 5°C, preferably 1°C to 3°C, higher than the stretching temperature, and then cool it to the stretching temperature and stretch it. Preheating within the above range allows the raw film to maintain a precise thickness in the width direction, and tends to prevent a decrease in thickness precision or thickness unevenness in the stretched film. Also, it tends to prevent the raw film from sticking to the roll or sagging under its own weight.

[0116] The stretching temperature when stretching the raw film is not particularly limited and may be appropriately determined depending on the mechanical strength, surface properties, thickness accuracy, etc. required of the stretched film. Generally, when the glass transition temperature of the raw film ((meth)acrylic resin composition) determined by DSC is Tg, the temperature is preferably in the range of (Tg-30°C) to (Tg+30°C), more preferably (Tg-20°C) to (Tg+30°C), even more preferably (Tg) to (Tg+30°C), and particularly preferably (Tg+10°C) to (Tg+30°C). A stretching temperature within the above temperature range tends to reduce thickness unevenness in the resulting stretched film and improve mechanical properties such as elongation, tear propagation strength, and MIT flex resistance. Furthermore, it tends to prevent problems such as the film sticking to the roll.

[0117] The stretching ratio when stretching the raw film is not particularly limited and may be appropriately determined depending on the mechanical strength, surface properties, thickness accuracy, etc. of the stretched film. Although it also depends on the stretching temperature, the stretching ratio is generally preferably selected from the range of 1.1 to 3, more preferably from 1.3 to 2.5, and even more preferably from 1.5 to 2.3. When the stretching ratio is within the above range, the mechanical properties of the film, such as elongation, tear propagation strength, and fatigue resistance, tend to be significantly improved. Therefore, it is possible to produce a stretched film with a thickness variation of 5 μm or less and an internal haze of 1.0% or less.

[0118] When the (meth)acrylic resin film contains a crosslinked elastic material, the film has excellent mechanical strength, and therefore any of an unstretched film, a uniaxially stretched film, and a biaxially stretched film can be suitably used.

[0119] The smaller the retardation value of the (meth)acrylic resin film, the better. Preferably, the in-plane retardation Δnd is 5.0 nm or less and the thickness direction retardation Rth is 20.0 nm or less, more preferably Δnd is 2.0 nm or less and Rth is 5.0 nm or less, and even more preferably Δnd is 1.0 nm or less and Rth is 3.0 nm or less.

[0120] The thickness of the (meth)acrylic resin film is preferably 5 μm or more and 200 μm or less, and more preferably 10 μm or more and 100 μm or less. When the thickness of the (meth)acrylic resin film is 5 μm or more, sufficient strength tends to be obtained. Furthermore, when the thickness of the (meth)acrylic resin film is 200 μm or less, a decrease in transparency and a decrease in the drying speed of the adhesive solvent (water, etc.) tend to be suppressed, and the optical film can be made thinner.

[0121] The surface wetting tension of the (meth)acrylic resin film is preferably 40 mN / m or more, more preferably 50 mN / m or more. To increase the surface wetting tension, the film may be subjected to corona discharge treatment, plasma treatment, ozone treatment, ultraviolet irradiation, flame treatment, chemical treatment, etc. Among these, corona discharge treatment and plasma treatment are preferred.

[0122] [Easy adhesive layer] Forming an easy-adhesion layer on the surface of a (meth)acrylic resin film significantly improves adhesion to a polarizer. The easy-adhesion layer can be formed by applying an easy-adhesion layer-forming composition to the surface of a (meth)acrylic resin film that has been formed with unevenness by blending crosslinked particles, and then drying the composition. This results in unevenness appearing on the surface of the easy-adhesion layer formed on the surface of the (meth)acrylic resin film, achieving anti-blocking properties (see Figure 1).

[0123] The content of lubricating particles in the adhesion layer is 0.1% by weight or less. Because lubricating particles such as silica particles tend to aggregate in the adhesion layer-forming composition, it is difficult to uniformly distribute the lubricating particles on the surface of the (meth)acrylic resin film, and anti-blocking properties may not be fully exhibited. Furthermore, aggregation of lubricating particles may affect the transparency and other functions of the optical film. Therefore, the content of lubricating particles such as silica particles in the adhesion layer-forming composition is preferably 0.1% by weight or less, and more preferably, no lubricating particles are contained. The lubricating particles refer to particles that impart anti-blocking properties.

[0124] The content of lubricating particles in the easy-adhesion layer can be determined, for example, by observing the number concentration using a transmission electron microscope (TEM), creating several easy-adhesion layers with a number concentration close to that concentration, and drawing a calibration curve to calculate the content.

[0125] The composition for forming an easy-adhesion layer to be applied to the surface of the (meth)acrylic resin film can be either aqueous or organic. From the viewpoints of environmental friendliness and workability, aqueous compositions for forming an easy-adhesion layer are preferred. However, from the viewpoints of dispersibility and solubility, a small amount of organic solvent may be contained. As the organic solvent, alcohol-based solvents, ketone-based solvents, ester-based solvents, and ether-based solvents are preferred from the viewpoints of compatibility with water and ease of handling.

[0126] The adhesive layer can be formed using known techniques such as those described in JP-A-2009-193061 and JP-A-2010-55062. For example, the adhesive layer can be formed using a composition for forming an adhesive layer containing a urethane resin having a carboxyl group and a crosslinking agent. By using a urethane resin, an adhesive layer having excellent adhesion to a polarizer can be obtained.

[0127] Before applying the composition for forming an easy-adhesion layer, it is preferable to subject the surface of the (meth)acrylic resin film to corona discharge treatment, plasma treatment, or the like.

[0128] The composition for forming an easy-adhesion layer can be applied by any appropriate method, such as bar coating, roll coating, gravure coating, rod coating, slot orifice coating, curtain coating, or fountain coating.

[0129] The drying temperature of the composition for forming an easy-adhesion layer is preferably 50°C or higher, and more preferably 80°C or higher.

[0130] The Young's modulus of the adhesive layer is not particularly limited and is, for example, 0.005 GPa or more and 2.5 GPa or less. The Young's modulus of the adhesive layer is preferably 1.0 GPa or more and 2.5 GPa or less. Usually, when the Young's modulus of the adhesive layer is less than 1.0 GPa, the static friction coefficient between the (meth)acrylic resin film and the adhesive layer increases, and anti-blocking properties tend to be poor. In this regard, in the optical film according to this embodiment, the (meth)acrylic resin film contains crosslinked particles having an average particle diameter of 1.0 μm or more and 2.5 μm or less, and therefore, even when an adhesive layer having such a small Young's modulus is formed, it is possible to exhibit good anti-blocking properties.

[0131] The Young's modulus of the easy-adhesion layer can be measured by forming a sheet of the composition for forming an easy-adhesion layer alone so that the thickness of the sheet after drying is 100 μm, and performing a tensile test in accordance with JIS K 7161-2:2014.

[0132] The 10-point average roughness Rzjis of the surface of the adhesive layer is preferably 18 nm or more and 100 nm or less, and more preferably 30 nm or more and 90 nm or less. When the 10-point average roughness Rzjis of the surface of the adhesive layer is 18 nm or more, the surface unevenness of the adhesive layer tends to be sufficient and anti-blocking properties can be exhibited. Furthermore, when the 10-point average roughness Rzjis of the surface of the adhesive layer is 100 nm or less, the unevenness formed on the surface does not become too large, which can prevent the unevenness from affecting functions such as transparency of the optical film, and also tends to prevent scratches and unevenness defects from occurring on the surface of the film when the optical film is wound into a roll.

[0133] The 10-point average roughness Rzjis of the surface of the adhesive layer can be measured using a laser microscope LEXT OLS5100 manufactured by Evident Co., Ltd. in accordance with JIS B 0601:2013.

[0134] The sum of the 10-point average roughness Rzjis on the surface of the adhesive layer and the 10-point average roughness Rzjis on the surface of the (meth)acrylic resin film opposite the adhesive layer is 23 nm or more and 200 nm or less, preferably 30 nm or more and 90 nm or less. When the total Rzjis value is 23 nm or more, slipperiness tends to be ensured. Furthermore, when the total Rzjis value is 200 nm or less, deterioration of transparency due to external haze caused by surface irregularities tends to be prevented.

[0135] The thickness of the adhesive layer is preferably 50 nm or more and 600 nm or less. When the thickness of the adhesive layer is 50 nm or more, the strength of the adhesive layer is improved, and adhesion tends to be improved. Furthermore, when the thickness of the adhesive layer is 600 nm or less, the adhesive layer tends to prevent unevenness caused by crosslinked particles contained in the (meth)acrylic resin film from being smoothed, and anti-blocking properties tend to be ensured.

[0136] [Application] The optical film according to this embodiment is preferably a functional film used in various display devices such as liquid crystal displays, plasma displays, and organic EL displays, as well as in touch panels. Specifically, the optical film according to this embodiment may be a polarizer protective film for a liquid crystal display device, a retardation film, an antireflection film, a brightness enhancement film, a hard coat film, an antiglare film, an antistatic film, an optical compensation film for widening a viewing angle, or the like. [Example]

[0137] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0138] The methods for measuring various physical properties described in the examples are as follows.

[0139] (Calculation of the percentage of glutarimide units) The proportion of glutarimide units in the (meth)acrylic resin (Resin 1) was calculated as follows. First, a nuclear magnetic resonance spectrometer (AVANCEIII 400 MHz, manufactured by Bruker) was used to measure the proportion of glutarimide units in the (meth)acrylic resin. 1 H-NMR measurement was performed. The molar ratio was calculated from the area A of the peak derived from the protons constituting the O-CH3 of methyl methacrylate around 3.5 ppm to 3.8 ppm and the area B of the peak derived from the protons constituting the N-CH3 of the glutarimide ring around 3.0 ppm to 3.3 ppm. The molar ratio was converted into weight to calculate the proportion of glutarimide units.

[0140] (conversion rate) The conversion rate was calculated from the ratio of the weight of the solid content of the (meth)acrylic resin after drying for 30 minutes in an oven heated to 150°C to the weight of the charged monomer, i.e., the formula: (weight of the solid content of the (meth)acrylic resin) × 100 / (weight of the charged monomer).

[0141] (Syndiotacticity in triplicate display) The syndiotacticity (rr) of the (meth)acrylic resin (resin 2) in triad notation was calculated as follows. First, the syndiotacticity (rr) of the (meth)acrylic resin was measured in a deuterated chloroform solution at 22°C with 16 cumulative cycles using a nuclear magnetic resonance spectrometer (AVANCEIII 400MHz, manufactured by Bruker). 1 H-NMR measurement was performed. From the spectrum, the area (X) of the region from 0.60 ppm to 0.95 ppm and the area (Y) of the region from 0.60 ppm to 1.25 ppm were measured when tetramethylsilane (TMS) was set to 0 ppm, and then the syndiotacticity (rr) expressed in triad form was calculated using the formula: (X / Y) × 100.

[0142] (Weight average molecular weight, number average molecular weight, and dispersity) The weight-average molecular weight (Mw), number-average molecular weight (Mn), and dispersity (Mw / Mn) of the (meth)acrylic resin (resin 2) were calculated by a standard polystyrene conversion method using gel permeation chromatography (GPC). Specifically, analysis was performed using a sample solution prepared by dissolving 20 mg of the (meth)acrylic resin in 10 mL of tetrahydrofuran, using the following equipment and conditions. Measuring equipment: HLC-8220GPC (manufactured by Tosoh Corporation) Detector: RI detector Eluent: tetrahydrofuran Guard column: TSKgel guard column SuperHL (manufactured by Tosoh Corporation) Analytical column: TSKgel SuperH5000, SuperH4000, SuperH3000, and SuperH2000 (all manufactured by Tosoh Corporation) connected in series Eluent flow rate: 0.60 mL / min Measurement temperature: 40℃ Standard material: Standard polystyrene (manufactured by Tosoh Corporation)

[0143] (glass transition temperature) Using a differential scanning calorimeter (DSC7000X, manufactured by Hitachi High-Tech Science Corporation), the temperature was increased at a rate of 20°C / min under a nitrogen atmosphere, and the glass transition temperature was determined by the midpoint method.

[0144] (Young's modulus) The Young's modulus was measured by forming a sheet from the composition for forming an easy-adhesion layer alone and performing a tensile test in accordance with JIS K 7161-2: 2014. The composition for forming an easy-adhesion layer was formed into a film by pouring an aqueous dispersion of polyurethane into a glass container so that the film thickness after drying would be 100 μm, leaving it at room temperature for 24 hours, and then drying it at 50°C for 3 hours and at 120°C for 20 minutes.

[0145] (surface roughness) Surface roughness was measured in accordance with JIS B 0601:2013 using a laser microscope (LEXT OLS5100) manufactured by Evident Co., Ltd. A 50x magnification, 0.95 numerical aperture objective lens was used to capture confocal images of the film within a 257 μm × 257 μm area. Three equally spaced evaluation lines were then drawn in each of the MD and TD directions to extract a roughness curve. From the resulting roughness curve, the 10-point average roughness (Rzjis) was calculated using analysis software, and the average value at each measurement point was calculated. Measurements were performed five times at different measurement points, and the average value was used as the surface roughness. However, if localized defects such as scratches were clearly visible in the image, they were not included in the measurement, and measurements were repeated, avoiding the abnormal areas.

[0146] (static friction coefficient) The static friction coefficient was measured in accordance with JIS K 7125:1999. One piece of film was fixed onto a smooth stainless steel plate, and the other piece of film was attached with double-sided tape to a 60 mm x 60 mm sled weighing 200 g. The load when the sled was moved at a speed of 20 mm / min via a pulley was then read with a load cell, and the static friction coefficient was calculated. The measurement was performed five times with different film pieces, and the average value was calculated.

[0147] (Blocking test) Ten 100 mm x 100 mm film pieces were placed so that the surface of the substrate ((meth)acrylic resin film) and the surface of the easy-adhesion layer were in contact, and a pressure of 1 kg was applied from above and left for 2 hours at 60°C. After that, the film was allowed to cool for 1 hour at 23°C, and the condition of the film was visually inspected and peeled off by hand, and evaluated according to the following criteria. -Evaluation criteria- A: No adhesion between films is observed. B: The films are stuck together. C: The films are strongly adhered to each other, and peeling marks appear on the film.

[0148] <Production Example 1: Production of (meth)acrylic resin> The extruder used was a 40 mm diameter co-rotating intermeshing twin-screw extruder (L / D = 90). The temperature setting for each temperature-controlled zone of the extruder was 250°C to 280°C, and the screw rotation speed was 85 rpm. After melting and filling the extruder with a kneading block, 1.8 parts by weight of monomethylamine (manufactured by Mitsubishi Gas Chemical Company, Inc.) was injected per 100 parts by weight of polymethyl methacrylate resin. The resin exiting the die at the extruder outlet as strands was cooled in a water bath and pelletized in a pelletizer to obtain resin (I). Next, the temperature setting for each temperature-controlled zone of the 40 mm diameter co-rotating intermeshing twin-screw extruder was set to 240°C to 260°C, and resin (I) was fed from the hopper. 0.56 parts by weight of dimethyl carbonate per 100 parts by weight of polymethyl methacrylate resin was injected from the nozzle to reduce the carboxyl groups in resin (I). Furthermore, by-products and excess dimethyl carbonate were removed after the reaction. The resin that came out as strands from the die provided at the outlet of the extruder was cooled in a water tank and then pelletized in a pelletizer to obtain a (meth)acrylic resin having a glutarimide structure in the main chain. The glass transition temperature of the obtained (meth)acrylic resin was 123°C, and the proportion of glutarimide units in the (meth)acrylic resin was 6% by weight. Hereinafter, the (meth)acrylic resin obtained in Production Example 1 will be referred to as "Resin 1."

[0149] <Production Example 2: Production of (meth)acrylic resin> A 4-liter glass reactor equipped with an H-shaped impeller was charged with 150 parts by weight of deionized water, 0.20 parts by weight of tribasic calcium phosphate as a dispersant, 0.0075 parts by weight of sodium α-olefin sulfonate, and 0.30 parts by weight of sodium chloride. Next, under a nitrogen atmosphere, 100 parts by weight of methyl methacrylate (MMA), 0.289 parts by weight of n-octyl mercaptan as a chain transfer agent, and 0.065 parts by weight of 2,2'-azobis(isobutyrate)dimethyl (V-601, Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were added to the reactor while stirring at 250 rpm. The liquid temperature in the reactor was then raised to 70°C to initiate polymerization. Two hours after the start of polymerization, 0.10 parts by weight of tribasic calcium phosphate was added to the reactor. An exothermic peak associated with the gel effect was observed 4 hours and 20 minutes after the start of polymerization. Next, heating was started 7 hours after the start of polymerization, and the liquid temperature in the reactor was raised to 95°C. The conversion rate 7 hours after the start of polymerization was 93%. Next, 2 hours after the liquid temperature in the reactor reached 95°C, the liquid temperature in the reactor was cooled to room temperature to terminate the polymerization, and a (meth)acrylic resin dispersion was obtained. The conversion rate at the end of polymerization was 99%.

[0150] The (meth)acrylic resin dispersion was acid-washed using 0.1 times the weight of the charged monomer with 1N hydrochloric acid, followed by washing with water to remove the dispersant. The washed (meth)acrylic resin dispersion was then dehydrated and dried to obtain beads of (meth)acrylic resin. The obtained (meth)acrylic resin had a glass transition temperature of 120°C, a triad syndiotacticity of 57%, a weight-average molecular weight (Mw) of 83,000, a polydispersity (Mw / Mn) of 1.63, and a proportion of methyl methacrylate units of 100% by weight. Hereinafter, the (meth)acrylic resin obtained in Production Example 2 will be referred to as "Resin 2."

[0151] Example 1 A mixture containing 79.9 parts by weight of Resin 1 produced in Production Example 1, 20 parts by weight of a methyl methacrylate-styrene copolymer containing 25% by weight of styrene units (MS-750, manufactured by Toyo Styrene Co., Ltd.; hereinafter referred to as "Resin 3"), and 0.1 parts by weight of crosslinked acrylic resin particles having an average particle size of 2.2 μm (J-4PY, manufactured by Negami Chemical Industrial Co., Ltd.; refractive index: 1.50; hereinafter referred to as "Particle 1") was kneaded in a 15 mm diameter, co-rotating, intermeshing twin-screw extruder (L / D = 45). The resin that emerged as strands from a die at the extruder outlet was cooled in a water bath and then pelletized in a pelletizer to obtain a (meth)acrylic resin composition (refractive index: 1.49).

[0152] The resulting (meth)acrylic resin composition was dried at 100°C for 5 hours and then formed into a film using a 15mm diameter, co-rotating, intermeshing twin-screw extruder (L / D = 45) equipped with a T-die at the extruder outlet. The sheet-like molten resin extruded from the T-die at the extruder outlet was cooled with a cooling roll to obtain a raw film having a width of 160mm and a thickness of 160µm. The surface in contact with the casting roll was defined as Side B, and the other side as Side A. The glass transition temperature of the raw film was 123°C.

[0153] Surface B of the original film is corona discharge treated (corona discharge electron irradiation dose: 100 W / m 2 / min). 5g of an aqueous urethane resin having a carboxy group (Superflex 210, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., solid content: 35%) and 1g of a crosslinking agent (Epocross WS700, manufactured by Nippon Shokubai Co., Ltd., solid content: 25%) were added to 26g of pure water, and the mixture was stirred for 3 minutes to prepare a composition for forming an easy-adhesion layer. The obtained composition for forming an easy-adhesion layer was applied to the corona-discharge-treated surface of the raw film that had been subjected to a corona discharge treatment using a bar coater (number 10). The raw film was then placed in a hot air dryer (100°C) and dried for 3 minutes to obtain an easy-adhesion-treated film.

[0154] The obtained easy-adhesion treated film was subjected to simultaneous biaxial stretching at a stretch ratio of 2 times (longitudinal and transverse directions) at 145°C using a biaxial stretching device (IMC-1905, manufactured by Imoto Manufacturing Co., Ltd.) to produce an optical film.

[0155] <Example 2> An optical film was produced in the same manner as in Example 1, except that the type of water-based urethane resin forming the easy-adhesion layer was changed.

[0156] Example 3 An optical film was produced in the same manner as in Example 1, except that the type of water-based urethane resin forming the easy-adhesion layer was changed.

[0157] Example 4 An optical film was produced in the same manner as in Example 3, except that the raw film was produced using a (meth)acrylic resin composition containing 99.9 parts by weight of resin 1 and 0.1 parts by weight of particles 1.

[0158] <Example 5> An optical film was produced in the same manner as in Example 3, except that Resin 3 was changed to an acrylonitrile-styrene copolymer (manufactured by Shin Chemical Shoji Co., Ltd., AS-61NT7200; hereinafter referred to as "Resin 4") having a styrene unit ratio of 74% by weight and containing a colorant.

[0159] Example 6 An optical film was produced in the same manner as in Example 3, except that Resin 1 was changed to Resin 2.

[0160] Example 7 An optical film was produced in the same manner as in Example 3, except that particle 1 was changed to crosslinked acrylic resin particles having an average particle diameter of 1.2 μm (manufactured by Negami Chemical Industrial Co., Ltd., J-3PY, refractive index: 1.50; hereinafter referred to as "particle 2").

[0161] Example 8 An optical film was produced in the same manner as in Example 4, except that particles 1 were changed to particles 2.

[0162] Example 9 An optical film was produced in the same manner as in Example 5, except that particles 1 were changed to particles 2.

[0163] Example 10 An optical film was produced in the same manner as in Example 6, except that particles 1 were changed to particles 2.

[0164] <Comparative Example 1> An optical film was produced in the same manner as in Example 3, except that particle 1 was changed to crosslinked acrylic resin particles having an average particle diameter of 0.8 μm (MX80H3wT, manufactured by Soken Chemical & Engineering Co., Ltd., refractive index: 1.49; hereinafter referred to as "particle 3").

[0165] <Comparative Example 2> An optical film was produced in the same manner as in Example 3, except that particle 1 was changed to crosslinked acrylic resin particles having an average particle diameter of 0.15 μm (manufactured by Sekisui Chemical Co., Ltd., xx-6390Z, refractive index: 1.49; hereinafter referred to as "particle 4").

[0166] <Comparative Example 3> An optical film was produced in the same manner as in Example 4, except that particles 1 were changed to particles 4.

[0167] <Comparative Example 4> An optical film was produced in the same manner as in Example 5, except that particles 1 were changed to particles 4.

[0168] <Comparative Example 5> An optical film was produced in the same manner as in Example 1, except that particles 1 were changed to particles 4.

[0169] <Comparative Example 6> An optical film was produced in the same manner as in Comparative Example 3, except that the type of aqueous urethane resin forming the easy-adhesion layer was changed.

[0170] <Comparative Example 7> An optical film was produced in the same manner as in Comparative Example 4, except that the type of aqueous urethane resin forming the easy-adhesion layer was changed.

[0171] Tables 1 and 2 show the evaluation results of the blocking test together with the values ​​of the glass transition temperature, Young's modulus, surface roughness, and static friction coefficient measured according to the above methods.

[0172] In Tables 1 and 2, the resins forming the easy-adhesion layer are as follows. Resin A: urethane resin (Superflex 210, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and crosslinker (Epocross WS700, manufactured by Nippon Shokubai Co., Ltd.) Resin B: Urethane resin (Superflex 870, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) Resin C: Urethane resin (Superflex 460S, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)

[0173] [Table 1]

[0174] [Table 2]

[0175] As shown in Tables 1 and 2, in Examples 1 to 10, the surface of the easy-adhesion side is formed with appropriate irregularities, and an appropriate surface roughness is provided, so that when the optical film is wound into a roll, the coefficient of friction between the surface of the substrate and the surface of the easy-adhesion layer can be reduced. As a result, it was confirmed from the evaluation results in Tables 1 and 2 that the optical film has antiblocking properties. [Explanation of symbols]

[0176] 1 Optical film 2 Easy adhesive layer 3. (Meth)acrylic resin film 4 Crosslinked particles

Claims

1. An optical film comprising a (meth)acrylic resin film containing crosslinked particles as a main component and an easy-adhesion layer formed on the (meth)acrylic resin film, the optical film satisfying the following: (i) the (meth)acrylic resin film has a glass transition temperature of 120°C or higher; (ii) the average particle size of the crosslinked particles is 1.0 μm or more and 2.5 μm or less; (iii) the content of the lubricating particles in the adhesive layer is 0.1% by weight or less; (iv) The sum of the 10-point average roughness Rzjis on the surface of the easy-adhesion layer and the 10-point average roughness Rzjis on the surface of the (meth)acrylic resin film opposite to the easy-adhesion layer is 23 nm or more and 200 nm or less.

2. An optical film comprising a (meth)acrylic resin film containing crosslinked particles as a main component and an easy-adhesion layer formed on the (meth)acrylic resin film, the optical film satisfying the following: (i) The (meth)acrylic resin film contains a (meth)acrylic resin having a ratio of methyl methacrylate units of 98% by weight or more and a triad syndiotacticity of 54% or more, (ii) the average particle size of the crosslinked particles is 1.0 μm or more and 2.5 μm or less; (iii) the content of the lubricating particles in the adhesive layer is 0.1% by weight or less; (iv) The sum of the 10-point average roughness Rzjis on the surface of the easy-adhesion layer and the 10-point average roughness Rzjis on the surface of the (meth)acrylic resin film opposite to the easy-adhesion layer is 23 nm or more and 200 nm or less.

3. The optical film according to claim 1 or 2, wherein the easy-adhesion layer has a thickness of 50 nm or more and 600 nm or less.

4. 3. The optical film according to claim 1, wherein when two of the optical films are superimposed such that the (meth)acrylic resin film and the easy-adhesion layer are in contact with each other, the static friction coefficient measured in accordance with JIS K 7125:1999 is 0.3 or more and 2.0 or less.

5. The optical film according to claim 1 , wherein the (meth)acrylic resin film contains a (meth)acrylic resin having a ring structure in the main chain.

6. 6. The optical film according to claim 5, wherein the ring structure is at least one selected from the group consisting of a glutarimide structure, a lactone ring structure, a maleic anhydride structure, an N-substituted maleimide structure, and a glutaric anhydride structure.

7. The optical film according to claim 5 , wherein the (meth)acrylic resin having a ring structure in its main chain contains a structural unit represented by the following general formula (1): 【Chemistry 1】 (In the formula, R １ and R ２ each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms; R ３ represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

8. 8. The optical film according to claim 7, wherein the ratio of the structural unit represented by the general formula (1) in the (meth)acrylic resin having a ring structure in the main chain is 2% by weight or more and 30% by weight or less.

9. 2. The optical film according to claim 1, wherein the (meth)acrylic resin film contains a (meth)acrylic resin having a proportion of methyl methacrylate units of 98% by weight or more and a triad syndiotacticity of 54% or more.

10. The optical film according to claim 1 or 2, wherein the (meth)acrylic resin film contains an aromatic vinyl unit.

11. The optical film according to claim 5 or 9, wherein the (meth)acrylic resin film further contains a copolymer containing an aromatic vinyl unit.

12. The optical film according to claim 11 , wherein the copolymer further comprises a (meth)acrylic acid ester unit or a (meth)acrylonitrile unit.

13. A composition for forming an easy-adhesion layer on a (meth)acrylic resin film, comprising: the (meth)acrylic resin film contains a (meth)acrylic resin as a main component, contains crosslinked particles having an average particle diameter of 1.0 μm or more and 2.5 μm or less, and has a glass transition temperature of 120° C. or more; The composition for forming an easy-adhesion layer has a content of lubricating particles of 0.1 wt % or less.

14. A composition for forming an easy-adhesion layer on a (meth)acrylic resin film, comprising: the (meth)acrylic resin film contains a (meth)acrylic resin as a main component and crosslinked particles having an average particle diameter of 1.0 μm or more and 2.5 μm or less; The (meth)acrylic resin film contains a (meth)acrylic resin having a ratio of methyl methacrylate units of 98% by weight or more and a syndiotacticity of 54% or more in triad expression, The composition for forming an easy-adhesion layer has a content of lubricating particles of 0.1 wt % or less.

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