Composition for forming antireflection layer

Abstract

Provided is a composition for forming an anti-reflection layer for forming an anti-reflection layer on one surface or both surfaces of a (meth) acrylic resin film containing a (meth) acrylic resin, the composition for forming the anti-reflection layer contains a water-dispersible polyurethane resin having a refractive index of 1.50 or less with respect to light having a wavelength of 594 nm, solid silica fine particles having an average primary particle diameter of 15-90 nm, and water, and the content of the solid silica fine particles in the solid content of the composition for forming the anti-reflection layer is 30-80 wt%.

Description

Technical Field

[0001] The present invention relates to a composition for forming an antireflection layer. Background Art

[0002] A liquid crystal display device generally has two polarizing films (polarizers) disposed on both sides of a liquid crystal cell. As the polarizing film, a polarizing film in which a polarizer protection film for protecting a polarizer is adhered to both sides of the polarizer with an adhesive is generally used.

[0003] In recent years, demands for higher brightness and lower power consumption of liquid crystal displays have been gradually increasing, and an improvement in the transmittance of the polarizing film has been desired. Based on such a background, an antireflection layer (low refractive index layer) has been proposed to be provided on the polarizing film. For example, Patent Document 1 proposes a polarizer (polarizing film) provided with a primer layer on the backlight unit side of the liquid crystal cell, the primer layer containing hollow fine particles and a water-dispersible low refractive polymer resin.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-531314 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] However, hollow fine particles such as hollow silica fine particles are produced by forming a shell on the outer shell of a core as a template and then selectively removing only the core, and the process is complicated. Therefore, there are problems of high cost and a large environmental burden during manufacturing. In particular, it is difficult to manufacture hollow fine particles having a particle size of 100 nm or less used in fields requiring transparency, and their use is limited from an economic point of view.

[0009] Therefore, an object of the present invention is to provide a composition for forming an antireflection layer, which contains solid silica fine particles and is used for forming an antireflection layer on a (meth)acrylic resin film.

[0010] Solutions to the Problems

[0011] Specific means for solving the above problems include the following embodiments.

[0012] <1> A composition for forming an antireflection layer, which is used for forming an antireflection layer on one side or both sides of a (meth)acrylic resin film containing a (meth)acrylic resin,

[0013] The composition for forming an antireflection layer contains: a water-dispersible polyurethane resin having a refractive index of 1.50 or less for light with a wavelength of 594 nm, solid silica fine particles having an average primary particle diameter of 15 to 90 nm, and water.

[0014] The content of the solid silica fine particles in the solid content of the composition for forming an antireflection layer is 30 to 80% by weight.

[0015] <2>The composition for forming an antireflection layer according to <1>, wherein the Young's modulus of the polyurethane resin is 200 MPa or less.

[0016] <3>The composition for forming an antireflection layer according to <1> or <2>, wherein the (meth)acrylic resin film contains a (meth)acrylic resin having a ring structure in the main chain.

[0017] <4>The composition for forming an antireflection layer according to <3>, wherein the ring structure is at least one selected from a succinimide structure, a lactone ring structure, a maleic anhydride structure, an N-substituted maleimide structure, and a glutaric anhydride structure.

[0018] Effects of the Invention

[0019] According to the present invention, it is possible to provide a composition for forming an antireflection layer that contains solid silica fine particles and is used for forming an antireflection layer on a (meth)acrylic resin film. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a cross-sectional schematic view showing an example of the layer structure of the polarizing film of the present embodiment.

[0021] Figure 2 It is a cross-sectional schematic view showing an example of the layer structure of the liquid crystal display device of the present embodiment.

[0022] DESCRIPTION OF REFERENCE NUMERALS

[0023] 10 Polarizing film, 20 Polarizing element, 30 Polarizing element protective film, 31 Easy-bonding layer, 32 (Meth)acrylic resin film, 33 Anti-reflection layer, 40 Polarizing element protective film, 41 Easy-bonding layer, 42 (Meth)acrylic resin film, 51, 52 Adhesive layer, 100 Liquid crystal display device, 110 Liquid crystal cell, 120a, 120b Polarizing element, 130a, 130b Polarizing element protective film, 131a, 131b Easy-bonding layer, 132a, 132b (Meth)acrylic resin film, 133a, 133b Anti-reflection layer, 140a, 140b Polarizing element protective film, 141a, 141b Easy-bonding layer, 142a, 142b (Meth)acrylic resin film, 151a, 152a Adhesive layer, 160a Front-side polarizing film, 160b Back-side polarizing film, 170a, 170b Adhesive layer, 180 Backlight unit Detailed implementation mode

[0024] Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited to this embodiment. In this specification, the expression "A to B" using numerical values A and B means "A or more and B or less" unless otherwise specified. When a unit is given only to the numerical value B in the above expression, the unit also applies to the numerical value A. In addition, in this specification, a term such as "(meth)acrylic" means both "acrylic" and "methacrylic", and a term such as "(meth)acrylic acid" means both "acrylic acid" and "methacrylic acid". In addition, in this specification, a term such as "solid silica fine particles" means "non-hollow silica fine particles (that is, those obtained by removing hollow silica fine particles from silica fine particles)".

[0025] <Anti-reflection layer forming composition>

[0026] The anti-reflection layer forming composition of the present embodiment is an anti-reflection layer forming composition for forming an anti-reflection layer on one or both sides of a (meth)acrylic resin film containing a (meth)acrylic resin, and contains: a water-dispersible polyurethane resin having a refractive index of 1.50 or less for light with a wavelength of 594 nm, solid silica fine particles having an average primary particle size of 15 to 90 nm, and water. The content rate of the solid silica fine particles in the solid components of the anti-reflection layer forming composition is 30 to 80% by weight. By using the anti-reflection layer forming composition of the present embodiment to form an anti-reflection layer on a (meth)acrylic resin film, the reflectance of the film can be reduced and the transmittance can be increased. It should be noted that an optical film having an anti-reflection layer formed on a (meth)acrylic resin film can be appropriately used as a polarizing element protective film, for example.

[0027] Hereinafter, each component contained in the anti-reflection layer forming composition will be described.

[0028] (Water-dispersible polyurethane resin)

[0029] A water-dispersible polyurethane resin can be obtained by reacting a polyol and a polyisocyanate.

[0030] As the polyol, as long as it has two or more hydroxyl groups in the molecule, there is no particular limitation, and any suitable polyol can be used. Examples of the polyol include polyester polyol, polycarbonate diol, polyether polyol, etc.

[0031] Typically, polyester polyol can be obtained by reacting a polybasic acid component with a polyol component. Examples of the polybasic acid component include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, biphenyldicarboxylic acid, and tetrahydrophthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, linolenic acid, maleic acid, fumaric acid, mesaconic acid, and itaconic acid; alicyclic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid; reactive derivatives thereof such as acid anhydrides, alkyl esters, and acyl halides; etc. In addition, examples of the polyol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 4,4'-dihydroxyphenylpropane, 4,4'-dihydroxymethylmethane, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, glycerol, 1,1,1-trimethylolpropane, 1,2,5-hexanetriol, pentaerythritol, glucose, sucrose, sorbitol, etc.

[0032] The polycarbonate diol is preferably an aliphatic polycarbonate diol. The polyurethane resin synthesized from such an aliphatic polycarbonate diol not only has excellent mechanical properties, but also has excellent water resistance, oil resistance, and long-term weather resistance. In particular, it has a lower refractive index than aromatic polycarbonate diol, so it is advantageous for achieving an antireflection effect. Examples of the aliphatic polycarbonate diol include poly(hexamethylene carbonate) diol, poly(cyclohexane carbonate) diol, etc.

[0033] Typically, polyether polyol can be obtained by ring-opening polymerization and addition of an alkylene oxide in a polyol. Examples of the polyol include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerol, trimethylolpropane, etc.

[0034] The polyisocyanate is not particularly limited as long as it is a compound having two or more isocyanate groups in the molecule. Examples of the polyisocyanate include toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), 1,5-naphthalene diisocyanate (NDI), dimethylbiphenyl diisocyanate (TODI), hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), p-phenylene diisocyanate, 1,4-diisocyanate, xylylene diisocyanate (XDI), and the like.

[0035] It should be noted that the antireflection layer-forming composition of the present embodiment contains solid silica fine particles at a high concentration. Therefore, in order to achieve dispersion stabilization based on the zeta potential, it is necessary to maintain the pH of the composition from neutral to alkaline. Therefore, the polyurethane resin is preferably nonionic or anionic.

[0036] The refractive index of the polyurethane resin for light with a wavelength of 594 nm is 1.50 or less, preferably 1.49 or less. When the refractive index of the polyurethane resin for light with a wavelength of 594 nm is 1.50 or less, the refractive index difference from the solid silica fine particles is small. Therefore, scattering at the interface with the solid silica fine particles is suppressed, and the transparency of the antireflection layer tends to be improved. The lower limit value of the refractive index of the polyurethane resin for light with a wavelength of 594 nm is not particularly limited and is usually 1.47 or more.

[0037] The Young's modulus of the polyurethane resin is preferably 200 MPa or less, more preferably 100 MPa or less. When the Young's modulus of the polyurethane resin is 200 MPa or less, even in the case of containing a large amount of solid silica fine particles, the flexibility of the antireflection layer can be maintained, and it has a tendency to follow stretching. The lower limit value of the Young's modulus of the polyurethane resin is not particularly limited and is usually 1 MPa or more.

[0038] The number average molecular weight of the polyurethane resin is preferably 5,000 to 600,000, more preferably 10,000 to 400,000. The number average molecular weight of the polyurethane resin can be determined by polystyrene conversion using gel permeation chromatography.

[0039] (Solid silica fine particles)

[0040] In order to sufficiently reduce the refractive index of the antireflection layer and to impart anti-blocking properties to the optical film, the antireflection layer-forming composition of the present embodiment contains solid silica fine particles.

[0041] The average primary particle diameter of the solid silica particles is 15 to 90 nm, preferably 20 to 80 nm. When the average primary particle diameter of the solid silica particles is 15 nm or more, the dispersion stability in the antireflection layer-forming composition is good, and the tendency for whitening to occur due to a decrease in the interparticle distance in the antireflection layer and the inability to follow stretching is suppressed. In addition, when the average primary particle diameter of the solid silica particles is 90 nm or less, the tendency for deterioration of transparency due to scattering at the interface with the polyurethane resin and the occurrence of halos due to external haze caused by irregularities is suppressed.

[0042] It should be noted that the average primary particle diameter of the solid silica particles can be measured by the dynamic light scattering method.

[0043] As the solid silica particles, commercially available colloidal silica can be used. Examples of commercially available colloidal silica include the Quartron PL series manufactured by Fuso Chemical Industry Co., Ltd., the SNOWTEX series manufactured by Nissan Chemical Industries, Ltd., the AERODISP series and the AEROSIL series manufactured by NIPPON AEROSIL CO., LTD., etc.

[0044] The content of the solid silica particles in the solid component of the antireflection layer-forming composition is 30 to 80% by weight, preferably 40 to 70% by weight, and more preferably 50 to 60% by weight. When the content of the solid silica particles is 30% by weight or more based on the solid component, the refractive index of the formed antireflection layer is sufficiently reduced, and the desired antireflection performance can be exhibited. In addition, when the content of the solid silica particles is 80% by weight or less based on the solid component, the tendency for the formed antireflection layer to harden and not follow stretching, resulting in whitening due to cracks, is suppressed.

[0045] It should be noted that in order to achieve the desired antireflection performance, in addition to the solid silica particles, hollow silica particles, hollow polymer particles, etc. can also be used in combination.

[0046] (Crosslinking agent)

[0047] The antireflection layer-forming composition of the present embodiment may contain a crosslinking agent. For example, when the polyurethane resin has a carboxyl group, as the crosslinking agent, a polymer having a group capable of reacting with the carboxyl group is preferred. Examples of the group capable of reacting with the carboxyl group include an organic amino group, an oxazoline group, an epoxy group, a carbodiimide group, etc. Among these, the crosslinking agent having an oxazoline group has a long pot life at room temperature when mixed with the polyurethane resin and undergoes a crosslinking reaction by heating, so the operability is good.

[0048] (Additive)

[0049] The antireflection layer-forming composition of the present embodiment may further contain optional additives. Examples of the additives include a dispersion stabilizer, a thixotropic agent, an antioxidant, an ultraviolet absorber, an antifoaming agent, a thickening agent, a dispersant, a surfactant, a catalyst, a filler, a lubricant, an antistatic agent, and the like.

[0050] (Solvent)

[0051] The antireflection layer-forming composition of the present embodiment is an aqueous composition that must contain water. Among them, a small amount of an organic solvent may be contained in order to improve dispersibility or solubility, or as an antifoaming agent or a leveling agent. As the organic solvent, from the viewpoints of compatibility with water and ease of handling, an alcohol-based solvent, a ketone-based solvent, an ester-based solvent, and an ether-based solvent are preferable. Examples of the alcohol-based solvent include methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, and propylene glycol. Examples of the ketone-based solvent include acetone, methyl ethyl ketone, and isobutyl ketone. Examples of the ester-based solvent include ethyl acetate and butyl acetate. Examples of the ether-based solvent include dimethoxyethane and tetrahydrofuran.

[0052] The solid content concentration in the antireflection layer-forming composition is preferably 1.5 to 15% by weight, more preferably 2 to 10% by weight. When the solid content concentration is 1.5% by weight or more, there is a tendency that the drying time becomes short and the productivity is improved. In addition, when the solid content concentration is 15% by weight or less, there is a tendency that bubbles are easily discharged and the pot life becomes long.

[0053] <Optical thin film>

[0054] In the optical thin film of the present embodiment, an antireflection layer containing solid silica fine particles is formed on one or both surfaces of a (meth)acrylic resin film containing a (meth)acrylic resin. By using such an optical thin film as a polarizing element protective film, the reflectance of the polarizing film can be reduced and the transmittance can be increased.

[0055] [(Meth)acrylic resin film]

[0056] (The (meth)acrylic resin film contains a (meth)acrylic resin as a main component. The content rate of the (meth)acrylic resin in the (meth)acrylic resin film is preferably more than 50% by weight, more preferably 70% by weight or more, still more preferably 80% by weight or more, still more preferably 85% by weight or more, and particularly preferably 90% by weight or more.

[0057] The glass transition temperature (Tg) of the (meth)acrylic resin is preferably 120 °C or higher, more preferably exceeding 120 °C, further preferably 121 °C or higher, further more preferably 122 °C or higher, and particularly preferably 123 °C or higher. When the glass transition temperature of the (meth)acrylic resin is 120 °C or higher, the dimensional change rate of the (meth)acrylic resin film in a high-temperature environment tends to become smaller. In actual use, the (meth)acrylic resin film is mostly laminated with other films. As a result, if the dimensional change rate is small, the strain and warpage caused by the difference in the dimensional change rate between the (meth)acrylic resin film and the other laminated films can be suppressed.

[0058] For the glass transition temperature, a differential scanning calorimeter (DSC7000X manufactured by Hitachi High-Tech Science Corporation) can be used to measure it at a heating rate of 20 °C / minute in a nitrogen atmosphere and obtain it by the midpoint method.

[0059] Here, as the (meth)acrylic resin having a glass transition temperature of 120 °C or higher, a (meth)acrylic resin having a ring structure in the main chain can be appropriately used. By using the (meth)acrylic resin having a ring structure in the main chain, heat resistance can be imparted to the (meth)acrylic resin film. As the ring structure, for example, at least one ring structure selected from a succinimide structure, a lactone ring structure, a maleic anhydride structure, an N-substituted maleimide structure, and a glutaric anhydride structure can be mentioned. Among these, from the viewpoints of production simplicity, cost, and quality stability against moisture, a (meth)acrylic resin having a succinimide structure or a lactone ring structure in the main chain is preferred.

[0060] The proportion of the ring structure in the (meth)acrylic resin is preferably 2 to 30% by weight. When the proportion of the ring structure is within the above range, the glass transition temperature and the retardation Rth in the thickness direction tend to be good. The proportion of the ring structure in the (meth)acrylic resin can be calculated by performing weight conversion after measuring the molar ratio of the ring structure part and the part other than it as the object of 1H-NMR measurement. 1 After measuring the molar ratio of the ring structure part and the part other than it as the object of 1H-NMR measurement, weight conversion is performed to calculate it.

[0061] Hereinafter, each ring structure will be described.

[0062] The (meth)acrylic resin having a succinimide structure in the main chain is, for example, a resin containing a succinimide 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.

[0063]

[0064] (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.)

[0065] (The proportion of the glutarimide structure in the (meth)acrylic resin is preferably 2 to 30% by weight. When the proportion of the glutarimide structure is 2% by weight or more, there is a tendency to easily impart desired heat resistance. In addition, when the proportion of the glutarimide structure is 30% by weight or less, there is a tendency to be able to suppress the addition amount of the imidizing agent, and to be able to suppress the odor caused by the residual volatile components, and furthermore to be able to suppress the retardation Rth in the thickness direction.)

[0066] When R in the above general formula (1) 3 is methyl, the proportion of the glutarimide structure in the (meth)acrylic resin can be measured by, for example, the following method. First, use 1 H-NMR BRUKER AvanceIII (400 MHz) to perform 1 1H-NMR measurement of the resin. Then, calculate the molar ratio based on the area A of the peak of the proton derived from O-CH3 constituting methyl methacrylate and the area B of the peak of the proton derived from N-CH3 constituting the glutarimide ring in the vicinity of 3.5 to 3.8 ppm. Perform weight conversion on the molar ratio, whereby the proportion of the glutarimide structure can be calculated.)

[0067] When producing polymethyl methacrylate resin, in addition to methyl methacrylate, other monomers such as methyl acrylate, (meth)ethyl acrylate, (meth)butyl acrylate, (meth)isobutyl acrylate, (meth)tert-butyl acrylate, (meth)benzyl acrylate, and (meth)cyclohexyl acrylate can be used in combination. In addition, in addition to the above, nitrile monomers such as acrylonitrile and methacrylonitrile; maleimide monomers such as maleimide, N-methyl maleimide, N-phenyl maleimide, and N-cyclohexyl maleimide; etc. can be used in combination. Among them, the content rate of the acrylate unit in the polymethyl methacrylate resin is preferably less than 1% by weight, more preferably less than 0.5% by weight, and further preferably less than 0.3% by weight.)

[0068] The structure of the polymethyl methacrylate resin is not particularly limited, and it can be any of a linear (linear) polymer, a block polymer, a core-shell polymer, a branched polymer, a ladder polymer, a crosslinked polymer, etc. In the case of a block polymer, it can be any of the A-B type, A-B-C type, A-B-A type, and other types. In the case of a core-shell polymer, it can include one layer of core and one layer of shell, or the core and the shell can each include multiple layers.)

[0069] The method for producing polymethyl methacrylate resin is not particularly limited, and known emulsion polymerization methods, emulsion-suspension polymerization methods, suspension polymerization methods, bulk polymerization methods, solution polymerization methods, etc. can be used. In the case of being used in the optical field, from the aspect of less impurities, bulk polymerization method and solution polymerization method are preferred. The polymethyl methacrylate resin can be produced, for example, according to the methods described in Japanese Patent Laid-Open No. 56-8404, Japanese Patent Publication No. 6-86492, Japanese Patent Publication No. 7-37482, Japanese Patent Publication No. 52-32665, etc.

[0070] The method for producing a (meth)acrylic resin having a succinimide structure in the main chain includes a step (imide-forming step) of heating and melting the above-mentioned polymethyl methacrylate resin and then treating it with an imidizing agent.

[0071] The imidizing agent is not particularly limited as long as it can generate the succinimide unit represented by the above general formula (1), and substances described in International Publication No. 2005 / 054311, etc. can be used. Specifically, as the imidizing agent, ammonia can be mentioned; amines containing aliphatic hydrocarbon groups such as methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, tert-butylamine, n-hexylamine, etc.; amines containing aromatic hydrocarbon groups such as aniline, benzylamine, toluidine, trichloroaniline, etc.; amines containing alicyclic hydrocarbon groups such as cyclohexylamine, etc. In addition, urea-based compounds that generate the above-exemplified amines by heating, such as urea, 1,3-dimethylurea, 1,3-diethylurea, 1,3-dipropylurea, etc., can also be used. Among these, from the viewpoints of cost and physical properties, methylamine, ammonia, and cyclohexylamine are preferred, and methylamine is more preferred. It should be noted that methylamine and the like in a gaseous state at normal temperature can be used in a state dissolved in alcohols such as methanol.

[0072] In the imide-forming step, by adjusting the addition amount of the imidizing agent, the ratio of the succinimide unit and the methyl methacrylate unit in the obtained (meth)acrylic resin can be adjusted. In addition, by adjusting the degree of imidization, the physical properties of the obtained (meth)acrylic resin, the optical properties of the (meth)acrylic resin film formed from the (meth)acrylic resin, etc. can be adjusted.

[0073] The addition amount of the imidizing agent is preferably 0.5 to 20 parts by weight relative to 100 parts by weight of the polymethyl methacrylate resin. When the addition amount of the imidizing agent is 0.5 part by weight or more, the proportion of the succinimide structure becomes higher, and as a result, there is a tendency for the heat resistance of the (meth)acrylic resin to increase and the generation of appearance defects after molding to be prevented. In addition, when the addition amount of the imidizing agent is 20 parts by weight or less, there is a tendency for the imidizing agent not to remain easily in the (meth)acrylic resin, the generation of appearance defects after molding to be prevented, and foaming to be prevented.

[0074] It should be noted that in the imidization process, according to needs, in addition to adding an imidizing agent, a ring-closing accelerator (catalyst) can also be added.

[0075] The method of heating and melting the polymethyl methacrylate resin and treating it with an imidizing agent is not particularly limited, and all methods known in the past can be adopted. For example, by using methods such as an extruder, a batch reactor (pressure vessel), etc., the polymethyl methacrylate resin can be imidized.

[0076] When using an extruder to heat and melt the polymethyl methacrylate resin and treat it with an imidizing agent, as the extruder, 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. By using a twin-screw extruder, the mixing of the imidizing agent (when using a ring-closing accelerator, it is the imidizing agent and the ring-closing accelerator) with the polymethyl methacrylate resin can be promoted.

[0077] Examples of the twin-screw extruder include a non-intermeshing co-rotating type, an intermeshing co-rotating type, a non-intermeshing counter-rotating type, an intermeshing counter-rotating type, etc., and an intermeshing co-rotating type is preferably used. The intermeshing co-rotating twin-screw extruder can rotate at a high speed, so the mixing of the imidizing agent (when using a ring-closing accelerator, it is the imidizing agent and the ring-closing accelerator) with the polymethyl methacrylate resin can be further promoted.

[0078] The above-exemplified extruders can be used alone or in series. For example, a series-type reactive extruder described in Japanese Patent Laid-Open No. 2008-273140 can be used.

[0079] In the case of carrying out the imidization reaction in an extruder, for example, the polymethyl methacrylate resin can be introduced from the raw material inlet of the extruder, melted, and after filling the barrel, the imidizing agent can be injected into the extruder using a dosing pump.

[0080] In this case, the temperature of the reaction zone (resin temperature) in the extruder is preferably set to 180 - 270 °C, more preferably 200 - 250 °C. When the temperature of the reaction zone (resin temperature) is 180 °C or higher, the imidization reaction tends to proceed sufficiently and the heat resistance is improved. In addition, when the temperature of the reaction zone is 270 °C or lower, the decomposition of the resin is suppressed, and as a result, the reduction in the bending resistance of the film formed from the obtained (meth)acrylic resin is suppressed. Here, the reaction zone in the extruder refers to the zone in the barrel of the extruder from the injection position of the imidizing agent to the resin discharge port (die section).

[0081] By extending the reaction time in the reaction zone of the extruder, further imidization can be achieved. The reaction time in the reaction zone of the extruder is preferably more than 10 seconds, and more preferably more than 30 seconds. When the reaction time is 10 seconds or less, imidization may hardly proceed.

[0082] The resin pressure in the extruder is preferably set to atmospheric pressure to 50 MPa, and more preferably 1 to 30 MPa. When the resin pressure is 1 MPa or more, the solubility of the imidizing agent is high and the reaction tends to proceed further. In addition, when the resin pressure is 50 MPa or less, no special device is required, which is preferable in terms of cost.

[0083] When using an extruder, in order to remove by-products such as unreacted imidizing agent, methanol, and monomers, it is preferable to install an exhaust port capable of reducing the pressure below atmospheric pressure.

[0084] When using a batch reactor (pressure vessel) to heat and melt polymethyl methacrylate resin and treat it with an imidizing agent, the structure of the batch reactor is not particularly limited. As the batch reactor, as long as it has a structure capable of melting polymethyl methacrylate resin by heating and stirring, and capable of adding an imidizing agent (when using a ring-closing promoter, it is an imidizing agent and a ring-closing promoter), a structure with good stirring efficiency is preferable. Using such a batch reactor can prevent the polymer viscosity from increasing due to the progress of the reaction and insufficient stirring. As a batch reactor having such a structure, for example, a stirring tank MAXBLEND manufactured by Sumitomo Heavy Industries, Ltd. can be cited.

[0085] It should be noted that reaction devices corresponding to high viscosities such as a horizontal twin-screw reactor such as BIVOLAK manufactured by Sumitomo Heavy Industries, Ltd. and a vertical twin-screw stirring tank such as SUPERBLEND can also be appropriately used.

[0086] As a specific example of the imidization method, for example, publicly known methods described in Japanese Patent Application Laid-Open No. 2008-273140, Japanese Patent Application Laid-Open No. 2008-274187, etc. can be cited.

[0087] The method for producing a (meth)acrylic resin having a glutarimide structure in the main chain may further include a step of treating with an esterifying agent (esterification step) on the basis of the imidization step. Through this esterification step, the acid value of the imidized resin obtained in the imidization step can be adjusted to a desired range.

[0088] As the esterifying agent, for example, dimethyl carbonate, 2,2-dimethoxypropane, dimethyl sulfoxide, triethyl orthoformate, trimethyl orthoacetate, trimethyl orthoformate, diphenyl carbonate, dimethyl sulfate, methyl tosylate, methyl trifluoromethanesulfonate, methyl acetate, methanol, ethanol, methyl isocyanate, p-chlorophenyl isocyanate, dimethylcarbodiimide, dimethyl-tert-butylchlorosilane, isopropenyl acetate, dimethylurea, tetramethylammonium hydroxide, dimethyldiethoxysilane, tetra-N-butoxysilane, dimethyl(trimethylsilyl) phosphite, trimethyl phosphite, trimethyl phosphate, tricresyl phosphate, diazomethane, ethylene oxide, propylene oxide, cyclohexene oxide, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, benzyl glycidyl ether, etc. can be cited. Among these, from the viewpoints of cost, reactivity, etc., dimethyl carbonate and trimethyl orthoacetate are preferred, and dimethyl carbonate is more preferred from the viewpoint of cost.

[0089] The addition amount of the esterifying agent 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 esterifying agent is within the above range, there is a tendency that the acid value can be adjusted to an appropriate range and the unreacted esterifying agent hardly remains in the resin.

[0090] In the esterification step, in addition to the esterifying agent, a catalyst can also be used in combination. As the catalyst, for example, aliphatic tertiary amines such as trimethylamine, triethylamine, and tributylamine can be cited. Among these, triethylamine is preferred from the viewpoints of cost, reactivity, etc.

[0091] It should be noted that in the esterification step, only heat treatment or the like can be performed without using an esterifying agent for treatment. In the case of only performing heat treatment (mixing and dispersing of the molten resin in the extruder), at least a part of the carboxyl group can be made into an acid anhydride group by dehydration reaction between carboxyl groups by-produced in the imidization step, dealcoholization reaction between the carboxyl group and the alkyl ester group, etc. At this time, a ring-closing promoter (catalyst) can also be used. Even in the case of treatment with an esterifying agent, acid anhydridation based on heat treatment can be performed.

[0092] 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 there is no limitation on its production method. Among them, it is preferably obtained as follows: After obtaining a polymer having a hydroxyl group and an ester group in the molecular chain by polymerization (polymerization step), the obtained polymer is heat-treated to introduce a lactone ring structure into the polymer (lactonization condensation step).

[0093] In the polymerization step, a polymer having a hydroxyl 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).

[0094]

[0095] (In the formula, R 4 and R 5 each independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.)

[0096] Examples of the unsaturated monomer represented by the above general formula (2) include methyl 2-(hydroxymethyl)acrylate, ethyl 2-(hydroxymethyl)acrylate, isopropyl 2-(hydroxymethyl)acrylate, n-butyl 2-(hydroxymethyl)acrylate, tert-butyl 2-(hydroxymethyl)acrylate, and the like. 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 high heat resistance improvement effect. These unsaturated monomers can be used alone or in combination of two or more.

[0097] The content of the unsaturated monomer represented by the above general formula (2) in the monomer component is preferably 5 to 50% by weight, more preferably 10 to 40% by weight, and further preferably 10 to 30% by weight. When the content of the unsaturated monomer represented by the above general formula (2) is 5% by weight or more, the heat resistance, solvent resistance, surface hardness, etc. of the obtained resin tend to be improved. In addition, when the content of the unsaturated monomer represented by the above general formula (2) is 50% by weight or less, the occurrence of crosslinking reaction and gelation during the formation of the lactone ring structure is suppressed, and the decrease in fluidity is also suppressed. In addition, the occurrence of a situation where a volatile substance is generated and silver streaks are generated due to the residual unreacted hydroxyl group and further condensation reaction during molding is suppressed, and the increase in the retardation in the thickness direction Rth is also suppressed.

[0098] In addition to the unsaturated monomer represented by the above general formula (2), the monomer component may contain other monomers. Examples of other monomers include (meth)acrylate, hydroxyl group-containing monomers, unsaturated carboxylic acids, unsaturated monomers represented by the following general formula (3), and the like. These other monomers can be used alone or in combination of two or more.

[0099]

[0100] (In the formula, R 6 represents a hydrogen atom or a methyl group, 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 group, Ac represents an acetyl group, R 7represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.)

[0101] As the above-mentioned (meth)acrylate, as long as it is a (meth)acrylate other than the unsaturated monomer represented by the above general formula (2), there is no particular limitation. For example, acrylate esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, cyclohexyl acrylate, benzyl acrylate, etc.; methacrylate esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, etc.; and the like. Among these, from the viewpoints of heat resistance and transparency, methyl methacrylate is preferred.

[0102] When using (meth)acrylate, the content of (meth)acrylate in the monomer component is preferably 10 to 95% by weight, more preferably 10 to 90% by weight, still more preferably 40 to 90% by weight, and particularly preferably 50 to 90% by weight.

[0103] (The (meth)acrylic resin film) In addition to the above-mentioned (meth)acrylic resin, the (meth)acrylic resin film may further contain other thermoplastic resins. As other thermoplastic resins, olefin-based polymers, vinyl halide-based polymers, styrene-based polymers, ester-based polymers, amide-based polymers, etc. can be cited. The content of other thermoplastic resins in the (meth)acrylic resin film is preferably less than 50% by weight, more preferably less than 30% by weight.

[0104] In order to improve the mechanical strength, the (meth)acrylic resin film may contain a crosslinked elastomer. The crosslinked elastomer can be produced by known polymerization methods such as suspension polymerization, dispersion polymerization, emulsion polymerization, solution polymerization, bulk polymerization, etc.

[0105] In addition, the (meth)acrylic resin film may contain other additives as needed. As additives, for example, antioxidants; stabilizers such as light stabilizers, weather stabilizers, heat stabilizers, etc.; ultraviolet absorbers, flame retardants, antistatic agents, fillers, plasticizers, lubricants; and the like.

[0106] (Manufacturing method of the film)

[0107] (The manufacturing method of the (meth)acrylic resin film is not particularly limited, and methods such as injection molding, melt extrusion molding, blown film molding, blow molding, compression molding, etc. can be adopted. In addition, a solution casting method or a spin coating method in which the (meth)acrylic resin is dissolved in a solvent and then formed can also be adopted. Among these, the melt extrusion method without using a solvent is preferably adopted. According to the melt extrusion method, the manufacturing cost can be reduced, and the load on the global environment and the working environment caused by the solvent can be reduced.

[0108] Hereinafter, an example of manufacturing a (meth)acrylic resin film by the melt extrusion method will be described. It should be noted that in the following description, the film obtained by the melt extrusion method is distinguished from the film obtained by other methods such as the solution casting method, and is referred to as a "melt extrusion film".

[0109] In the case of manufacturing a (meth)acrylic resin film by the melt extrusion method, first, the (meth)acrylic resin is supplied to an extruder and heated to melt.

[0110] The (meth)acrylic resin is preferably pre-dried before being supplied to the extruder. By performing such pre-drying, foaming of the resin extruded from the extruder can be prevented.

[0111] Next, the (meth)acrylic resin that has been heated and melted in the extruder is supplied to a T-die through a gear pump, a filter, etc. At this time, if a gear pump is used, the extrusion amount of the (meth)acrylic resin is uniform, and there is a tendency to reduce the thickness unevenness in the long side direction of the film. On the other hand, if a filter is used, foreign substances in the (meth)acrylic resin can be removed, and there is a tendency to obtain a (meth)acrylic resin film with excellent appearance without defects.

[0112] Next, the (meth)acrylic resin supplied to the T-die is extruded from the T-die in the form of a sheet-like molten resin. Then, the sheet-like molten resin is sandwiched between two cooling rolls and cooled to form a film.

[0113] As the two cooling rolls for sandwiching the sheet-like molten resin, one is preferably a rigid metal roll with a smooth surface, and the other is a flexible roll having a metal elastic outer cylinder with a smooth surface that can elastically deform. By sandwiching the sheet-like molten resin between the rigid metal roll and the flexible roll with the metal elastic outer cylinder and cooling to form a film, minute irregularities, die marks, etc. on the surface can be corrected, and a film with a smooth surface and a thickness unevenness of 5 μm or less can be obtained. It should be noted that in this specification, "cooling roll" is used in the sense of including "contact roll".

[0114] Even when using rigid metal rollers and flexible rollers, since the surface of any cooling roller is metal, if the film to be formed is thin, there is a concern that the surfaces of the cooling rollers come into contact with each other, resulting in damage to the outer surface of the cooling roller and breakage of the cooling roller itself. Therefore, when forming a film by sandwiching a sheet-like molten resin between two cooling rollers, it is preferable that: first, sandwich the sheet-like molten resin between two cooling rollers for cooling, temporarily obtain a thick blank film, and then perform uniaxial stretching or biaxial stretching on the blank film to manufacture a film with a specified thickness. For example, when manufacturing a film with a thickness of 40 μm, it is preferable that: first, sandwich the sheet-like molten resin between two cooling rollers for cooling, temporarily obtain a blank film with a thickness of 150 μm, and then stretch the blank film by biaxial stretching in the longitudinal and transverse directions to manufacture a film with a thickness of 40 μm.

[0115] In this way, when the (meth)acrylic resin film is a stretched film, the (meth)acrylic resin is formed into a blank film in an unstretched state and then subjected to uniaxial stretching or biaxial stretching, whereby a stretched film can be manufactured.

[0116] In order to improve the bending resistance in both the longitudinal direction (MD direction) and the width direction (TD direction) of the (meth)acrylic resin film, biaxial stretching is preferably performed.

[0117] In this specification, for the sake of convenience of description, the film obtained after forming the (meth)acrylic resin into a film shape and before performing stretching, that is, the film in an unstretched state, is referred to as a "blank film".

[0118] When stretching the blank film, the stretching of the blank film can be carried out immediately after forming the blank film, or the blank film can be temporarily stored or moved after forming the blank film, and then the stretching of the blank film can be carried out.

[0119] (Method for stretching the film)

[0120] The method for stretching the blank film is not particularly limited, and any stretching method known in the past can be adopted. For example, transverse stretching based on a tenter, longitudinal stretching based on rollers, and sequential biaxial stretching obtained by sequentially combining them can be adopted. In addition, a simultaneous biaxial stretching method for simultaneously stretching in the longitudinal and transverse directions, or a method of performing longitudinal stretching based on rollers and then transverse stretching based on a tenter can also be adopted.

[0121] There is no particular limitation on the stretching temperature when stretching the blank film, and it can be appropriately determined according to the mechanical strength, surface properties, thickness accuracy, etc. required for the stretched film. Generally, when the glass transition temperature of the blank film ((meth)acrylic resin) determined by the DSC method is set as Tg, it is preferably set in the temperature range of (Tg - 30°C) to (Tg + 30°C), more preferably in the temperature range of (Tg - 20°C) to (Tg + 30°C), further preferably in the temperature range of (Tg) to (Tg + 30°C), and particularly preferably in the temperature range of (Tg + 10°C) to (Tg + 30°C). When the stretching temperature is within the above temperature range, there is a tendency to reduce the thickness unevenness of the obtained stretched film and to make the mechanical properties such as elongation at break, tear propagation strength, and MIT bending resistance good. In addition, there is a tendency to prevent the occurrence of failures such as the film sticking to the roller, etc.

[0122] There is no particular limitation on the stretching ratio when stretching the blank film, and it can be appropriately determined according to the mechanical strength, surface properties, thickness accuracy, etc. of the stretched film. It also depends on the stretching temperature. The stretching ratio is usually preferably selected in the range of 1.1 to 3 times, more preferably in the range of 1.3 to 2.5 times, and further preferably in the range of 1.5 to 2.3 times. When the stretching ratio is within the above range, there is a tendency to significantly improve the mechanical properties such as elongation at break, tear propagation strength, and rub resistance fatigue of the film. Therefore, a stretched film with a thickness unevenness of 5 μm or less and further an internal haze of 1.0% or less can be manufactured.

[0123] When the (meth)acrylic resin film contains a crosslinked elastomer, the mechanical strength of the film is excellent, and therefore any of the unstretched film, uniaxially stretched film, and biaxially stretched film can be appropriately used.

[0124] The smaller the retardation of the (meth)acrylic resin film, the better. Preferably, the in-plane retardation Δnd is 5.0 nm or less, and the retardation in the thickness direction Rth is 20.0 nm or less. More preferably, Δnd is 2.0 nm or less and Rth is 5.0 nm or less. Further preferably, Δnd is 1.0 nm or less and Rth is 3.0 nm or less.

[0125] The thickness of the (meth)acrylic resin film is preferably 5 to 200 μm, more preferably 10 to 100 μm. When the thickness is 5 μm or more, there is a tendency to obtain sufficient strength. In addition, when the thickness is 200 μm or less, there is a tendency to suppress the reduction of transparency and the reduction of the drying property of the solvent (such as water) of the adhesive, and in addition, the optical film can be thinned.

[0126] The wetting tension of the surface of the (meth)acrylic resin film is preferably 40 mN / m or more, more preferably 50 mN / m or more. In order to increase the wetting tension of the surface, corona discharge treatment, plasma treatment, ozone treatment, ultraviolet irradiation, flame treatment, chemical treatment, etc. can be carried out. Among these, corona discharge treatment and plasma treatment are preferred.

[0127] In this embodiment, it is preferable to provide a coating step such as an antireflection layer and an easy-bonding layer before stretching in the tenter. By coating before stretching in the tenter, a drying furnace does not need to be provided separately. In addition, by stretching the coating film and the substrate simultaneously, the strength and the adhesion to the substrate tend to be improved.

[0128] [Antireflection layer]

[0129] The optical film of this embodiment has an antireflection layer (low refractive index layer) on one side or both sides of the (meth)acrylic resin film. By providing the antireflection layer in this way, the reflectance of the optical film can be reduced, and the transmittance of the polarizing film when used as a polarizing element protection film can be increased.

[0130] The antireflection layer can be formed by coating the antireflection layer-forming composition of the present embodiment on the (meth)acrylic resin film and then drying it.

[0131] The thickness of the antireflection layer is preferably 50 to 300 nm. When the thickness of the antireflection layer is 50 nm or more, there is a tendency to obtain a sufficient antireflection effect. In addition, when the thickness of the antireflection layer is 300 nm or less, there is a tendency to suppress the occurrence of iridescence due to interference light in the visible light region.

[0132] Based on the theory of thin film interference of a single-layer film, when the thickness d of the antireflection layer satisfies the following formula, the reflectance is minimized due to the interference between the surface reflected light and the substrate reflected light. In the formula, λ represents the wavelength of the incident light, and n2 represents the refractive index of the antireflection layer.

[0133] d = (1 / 4) × (λ / n2)

[0134] If λ is set to 550 nm and n2 is set to 1.46, then d = 94 nm is the optimum value. In practice, the thickness can be set within the above range while considering the above formula and also considering thickness unevenness, the strength of the coating film, etc.

[0135] It is preferable to hydrophilize the surface of the (meth)acrylic resin film in advance by corona discharge treatment, plasma treatment, etc. before coating the antireflection layer-forming composition.

[0136] The coating method of the composition for forming an antireflection layer is not particularly limited, and methods such as bar coating, roll coating, gravure coating, rod coating, slot die coating, curtain coating, and spray column coating can be used.

[0137] The drying temperature after coating the composition for forming an antireflection layer is preferably 50°C or higher, more preferably 80°C or higher.

[0138] [Easy adhesion layer]

[0139] The optical film of the present embodiment may have an easy adhesion layer for improving the adhesion to a polarizing member on the surface on the side opposite to the antireflection layer. As the easy adhesion layer, for example, a layer formed by coating a composition mainly composed of a polyurethane resin having a carboxyl group as described in Japanese Patent No. 5354733 can be cited.

[0140] It should be noted that when antireflection layers are formed on both sides of the optical film of the present embodiment, one of the antireflection layers can also be used as the easy adhesion layer.

[0141] [Polarizing film]

[0142] The polarizing film of the present embodiment is formed by laminating the optical film of the present embodiment to a polarizing member via an adhesive layer.

[0143] As the polarizing member, an appropriate polarizing member that meets the purpose can be used. As the polarizing member, for example, those obtained by adsorbing dichroic substances such as iodine and dichroic dyes on hydrophilic polymer films such as polyvinyl alcohol-based films, partially formaldehydeated polyvinyl alcohol-based films, and ethylene-vinyl acetate copolymer-based partially saponified films and performing uniaxial stretching; polyolefin-based oriented films such as dehydrated products of polyvinyl alcohol and dehydrochlorinated products of polyvinyl chloride; etc. Among these, from the aspect of a high polarization dichroism ratio, a polarizing member obtained by adsorbing a dichroic substance such as iodine on a polyvinyl alcohol-based film and performing uniaxial stretching is preferred. The thickness of the polarizing member is not particularly limited, and is usually about 1 to 80 μm.

[0144] As the adhesive for forming the adhesive layer, there is no particular limitation, and any adhesive such as a polyvinyl alcohol-based adhesive, an acrylic-based adhesive, a polyurethane-based adhesive, an isocyanate-based adhesive, an epoxy-based adhesive, and a melamine-based adhesive can be used.

[0145] Figure 1 Fig. shows a schematic cross-sectional view showing an example of the layer structure of the polarizing film of the present embodiment. Figure 1 The polarizing film 10 shown has a laminated structure in which polarizing member protection films 30 and 40 are respectively adhered to both sides of the polarizing member 20 via adhesive layers 51 and 52.

[0146] The polarizing element protection film 30 has, in order from the polarizing element 20 side, an easily adhesive layer 31, a (meth)acrylic resin film 32, and an antireflection layer 33. Further, the polarizing element protection film 40 has, in order from the polarizing element 20 side, an easily adhesive layer 41 and a (meth)acrylic resin film 42. The polarizing element protection film 40 may have an adhesive layer (not shown) for bonding to a liquid crystal cell or the like on the surface on the side opposite to the polarizing element 20.

[0147] Figure 1 In the polarizing film 10 shown, as the polarizing element protection film 30, the optical film of the present embodiment described above is used.

[0148] <Image display device>

[0149] The image display device of the present embodiment includes the polarizing film of the present embodiment described above. As the image display device, for example, a liquid crystal display device (LCD) or the like can be cited.

[0150] The liquid crystal display device includes a liquid crystal cell and a backlight unit as a light source, and includes polarizing films disposed on both sides (the backlight unit side and the visual recognition side) of the liquid crystal cell. The polarizing film of the present embodiment can be used for either the backlight unit side or the visual recognition side. When used as the polarizing film on the backlight unit side, by disposing it with the antireflection layer facing the backlight unit side, the reflectance can be reduced and the brightness of the liquid crystal display can be increased. On the other hand, when used as the polarizing film on the visual recognition side, by making the antireflection layer the outermost layer, the surface reflected light can be reduced and the visual recognition property of the liquid crystal display can be improved.

[0151] Figure 2 A schematic cross-sectional view showing an example of the layer structure of the liquid crystal display device of the present embodiment is shown. Figure 2 The liquid crystal display device 100 shown includes: a liquid crystal cell 110, a front-side polarizing film 160a laminated on the front side of the visual recognition side of the liquid crystal cell 110 via an adhesive layer 170a, a back-side polarizing film 160b laminated on the side opposite to the visual recognition side of the liquid crystal cell 110 via an adhesive layer 170b, and a backlight unit 180 disposed outside the back-side polarizing film 160b.

[0152] The front-side polarizing film 160a has a laminated structure in which polarizing film protective films 130a and 140a are respectively adhered to both sides of the polarizing member 120a by adhesive layers 151a and 152a. The polarizing film protective film 130a on the side away from the liquid crystal cell 110 sequentially has an easy-adhesion layer 131a, a (meth)acrylic resin film 132a, and an antireflection layer 133a from the side of the polarizing member 120a. In addition, the polarizing film protective film 140a on the side of the liquid crystal cell 110 sequentially has an easy-adhesion layer 141a and a (meth)acrylic resin film 142a from the side of the polarizing member 120a.

[0153] The back-side polarizing film 160b has a laminated structure in which polarizing film protective films 130b and 140b are respectively adhered to both sides of the polarizing member 120b by adhesive layers 151b and 152b. The polarizing film protective film 130b on the side away from the liquid crystal cell 110 sequentially has an easy-adhesion layer 131b, a (meth)acrylic resin film 132b, and an antireflection layer 133b from the side of the polarizing member 120b. In addition, the polarizing film protective film 140b on the side of the liquid crystal cell 110 sequentially has an easy-adhesion layer 141b and a (meth)acrylic resin film 142b from the side of the polarizing member 120b.

[0154] In Figure 2 the liquid crystal display device 100 shown, the above-described optical films of the present embodiment are used as the polarizing film protective films 130a and 130b.

[0155] [Examples]

[0156] Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

[0157] The measurement methods of various physical properties described in the examples and comparative examples are as follows.

[0158] (Haze)

[0159] The haze of the optical film was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH2000) in accordance with JIS K7136.

[0160] (Total light transmittance)

[0161] The total light transmittance of the optical film was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH2000) in accordance with JIS K7361-1.

[0162] (Young's modulus of the binder resin)

[0163] The aqueous dispersion of the polyurethane resin as the binder resin was poured into a glass container so that the film thickness after drying became 100 μm, and allowed to stand at room temperature for 24 hours. Then, it was dried at 50 °C for 3 hours and at 120 °C for 20 minutes to obtain a sheet of the polyurethane resin. The obtained sheet of the polyurethane resin was punched into a dumbbell shape according to JIS K7162 to obtain a test piece. For this test piece, a tensile tester (manufactured by Instron Japan Co., Ltd., tensile testing machine 5564) was used to conduct a tensile test at a tensile speed of 5 mm / minute, and the Young's modulus was measured based on the slope of the obtained SS curve.

[0164] (Refractive index of the binder resin)

[0165] For the test piece obtained by the above measurement of the Young's modulus, a prism coupler (manufactured by Metricon Corporation, Model 2010) was used to measure the refractive index of light with a wavelength of 594 nm.

[0166] (Calculation of the proportion of the glutarimide structure in the (meth)acrylic resin)

[0167] The proportion of the glutarimide structure in the (meth)acrylic resin was calculated as follows. First, 1 H-NMRBRUKER AvanceIII (400 MHz) was used to conduct 1 H-NMR measurement of the (meth)acrylic resin. Then, the molar ratio was calculated from the area A of the peak of the proton derived from O-CH3 constituting methyl methacrylate around 3.5 to 3.8 ppm and the area B of the peak of the proton derived from N-CH3 constituting the glutarimide ring around 3.0 to 3.3 ppm. The molar ratio was converted by weight, and thus the proportion of the glutarimide structure was calculated.

[0168] (Glass transition temperature)

[0169] Using a differential scanning calorimeter DSC7020 (manufactured by SII), 10 mg of the (meth)acrylic resin was heated at a heating rate of 20 °C / minute in a nitrogen atmosphere, and the glass transition temperature was determined by the midpoint method.

[0170] <Production Example 1: Production of (meth)acrylic resin>

[0171] As an extruder, a meshing co-rotating twin-screw extruder with a diameter of 40 mm (L / D = 90) was used. The set temperatures of the respective temperature control zones of the extruder were set to 250 to 280°C, and the screw rotation speed was set to 85 rpm. The polymethyl methacrylate resin was melted by a kneading block. After being filled, 1.8 parts by weight of monomethylamine (manufactured by Mitsubishi Gas Chemical Company, Inc.) relative to 100 parts by weight of the polymethyl methacrylate resin was injected from a nozzle. The resin coming out in the form of a wire from the die provided at the exit of the extruder was cooled in a water bath and then granulated by a granulator, thereby obtaining resin (I). Next, the set temperatures of the respective temperature control zones of the meshing co-rotating twin-screw extruder with a diameter of 40 mm were set to 240 to 260°C. 0.56 parts by weight of dimethyl carbonate relative to 100 parts by weight of the polymethyl methacrylate resin was injected from a nozzle to reduce the carboxyl groups in resin (I). Furthermore, the by-products after the reaction and the excess dimethyl carbonate were removed. The resin coming out in the form of a wire from the die provided at the exit of the extruder was cooled in a water bath and then granulated by a granulator, obtaining a (meth)acrylic resin 1 having a glutarimide structure in the main chain. The glass transition temperature of the (meth)acrylic resin 1 was 123°C, and the proportion of the glutarimide structure was 6% by weight.

[0172] <Production Example 2: Production of (meth)acrylic resin film>

[0173] After drying the (meth)acrylic resin 1 obtained in Production Example 1 at 100°C for 5 hours, a film was produced using a meshing co-rotating twin-screw extruder with a diameter of 15 mm (L / D = 45) equipped with a T-die at the exit of the extruder. The sheet-like molten resin extruded from the T-die was cooled by a cooling roll to obtain a blank film having a width of 160 mm and a thickness of 160 μm. At this time, the surface in contact with the casting roll was defined as surface B, and the other surface was defined as surface A.

[0174] <Example 1>

[0175] 7.6 g of colloidal silica (manufactured by Fuso Chemical Industry Co., Ltd., Quartron PL-03, average primary particle size: 35 nm, solid content: 20%) was put into a glass container, 25.5 g of pure water and 0.5 g of 1% ammonia water were added, and the mixture was stirred with a magnetic stirrer for 10 minutes. Next, as a binder resin, 4 g of an aqueous polyurethane resin (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., SUPERFLEX 460, solid content: 38%) was added and stirred for 10 minutes, thereby preparing a composition for forming an antireflection layer. The overall solid content concentration of the composition for forming an antireflection layer was 8% by weight, and the content ratio of silica fine particles in the solid content was 50% by weight.

[0176] The A side of the (meth)acrylic acid-based thin film obtained in Production Example 2 was subjected to corona discharge treatment, and the antireflection layer-forming composition was applied using a rod coater (#5) to form a coating film. Thereafter, the thin film was put into a hot air dryer (100 °C) and dried for 3 minutes to produce a coated blank with an antireflection layer thickness of 800 nm. Next, the obtained coated blank was simultaneously biaxially stretched using a biaxial stretching device (manufactured by Iwamoto Seisakusho Co., Ltd., IMC-1905) under the conditions of a stretching ratio of 2 times (longitudinal / transverse) and 145 °C to produce an optical thin film with an antireflection layer thickness of 200 nm. Then, the haze and total light transmittance of the obtained optical thin film were measured. The results are shown in Table 1.

[0177] <Examples 2 to 5, Comparative Examples 2 to 6>

[0178] The composition of the antireflection layer-forming composition was changed as shown in Table 1, and an optical thin film was produced in the same manner as in Example 1 except for this. Then, the haze and total light transmittance of the obtained optical thin film were measured. The results are shown in Table 1.

[0179] The antireflection layer-forming composition was not applied, and an optical thin film was produced in the same manner as in Example 1 except for this. Then, the haze and total light transmittance of the obtained optical thin film were measured. The results are shown in Table 1.

[0180] It should be noted that the abbreviations in Table 1 have the following meanings, respectively.

[0181] · SF460 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., SUPERFLEX460)

[0182] · SF420NS (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., SUPERFLEX420NS)

[0183] · PL-3 (manufactured by Fuso Chemical Industry Co., Ltd., Quartron PL-3)

[0184] · PL-7 (manufactured by Fuso Chemical Industry Co., Ltd., Quartron PL-7)

[0185] · ST-30 (manufactured by Nissan Chemical Industries, Ltd., SNOWTEX ST-30)

[0186] · ST-1040 (manufactured by Nissan Chemical Industries, Ltd., SNOWTEX ST-1040) [Table 1]

[0187]

[0188] From the results in Table 1, it can be seen that by using an antireflection layer-forming composition in which the refractive index and Young's modulus of the binder resin are within a specified range and the content rate of solid silica fine particles is within a specified range, an optical film with high total light transmittance and low haze can be obtained.

Claims

1. A composition for forming an antireflection layer, which is used to form an antireflection layer on one or both sides of a (meth)acrylic resin film containing a (meth)acrylic resin, The composition for forming an antireflection layer contains: a water-dispersible polyurethane resin having a refractive index of 1.50 or less for light with a wavelength of 594 nm, solid silica fine particles having an average primary particle diameter of 15 to 90 nm, and water, The content rate of the solid silica fine particles in the solid components of the composition for forming an antireflection layer is 30 to 80% by weight.

2. The composition for forming an antireflection layer according to claim 1, wherein, The Young's modulus of the polyurethane resin is 200 MPa or less.

3. The composition for forming an antireflection layer according to claim 1 or 2, wherein, The (meth)acrylic resin film contains a (meth)acrylic resin having a ring structure in the main chain.

4. The composition for forming an antireflection layer according to claim 3, wherein, The ring structure is at least one selected from a succinimide structure, a lactone ring structure, a maleic anhydride structure, an N-substituted maleimide structure, and a glutaric anhydride structure.

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