Optical film, polarizing film, image display device, and liquid crystal display device

Abstract

To provide an optical film with high transmittance and low haze, which includes a layer containing solid silica microparticles, a polarizing film including the optical film, an image display device, and a liquid crystal display device.SOLUTION: An optical film has an antireflection layer formed on one or both sides of a (meth)acrylic resin film which contains a (meth)acrylic resin. The antireflection layer includes: a binder resin with a refractive index of 1.50 or less relative to light with a wavelength of 594 nm; and solid silica microparticles with an average primary particle diameter of 15 to 90 nm. A content rate of the solid silica microparticles is 30 to 80 weight % in solid content of the antireflection layer. The total light transmittance of the optical film is 93% or more, and its haze is 2% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an optical film, a polarizing film, an image display device, and a liquid crystal display device.

Background Art

[0002] In a liquid crystal display device, usually, two polarizing films are arranged on both sides of a liquid crystal cell. As the polarizing film, a polarizer protection film for protecting the polarizer on both sides of the polarizer is generally used, which is bonded with an adhesive.

[0003] In recent years, there has been an increasing demand for higher brightness and lower power consumption of liquid crystal panels, and an improvement in the transmittance as a polarizing film is desired. Against this background, it has been proposed to provide an antireflection layer (low refractive index layer) on the polarizing film. For example, in Patent Document 1, it has been proposed to arrange a polarizing plate (polarizing film) provided with a primer layer containing hollow fine particles and a water-dispersible low refractive polymer resin on the backlight unit side of the liquid crystal cell.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, hollow fine particles such as hollow silica fine particles are produced by forming a shell on the outer shell of a core serving as a template and then selectively removing only the core. Since the process is complicated, the cost is high, and there is also a problem of a large environmental load during manufacturing. In particular, hollow fine particles with a particle diameter of 100 nm or less used in fields where transparency is required are difficult to manufacture and are limited in use from the viewpoint of economy.

[0006] Therefore, an object of the present invention is to provide an optical film having a high transmittance and a low haze, which has an antireflection layer containing solid silica fine particles, and a polarizing film, an image display device, and a liquid crystal display device including the optical film.

Means for Solving the Problems

[0007] Specific means for solving the above problems include the following embodiments. <1> An optical film in which an antireflection layer is formed on one or both surfaces of a (meth)acrylic resin film containing a (meth)acrylic resin, wherein the antireflection layer contains a binder resin having a refractive index of 1.50 or less with respect to light having a wavelength of 594 nm and solid silica fine particles having an average primary particle diameter of 15 to 90 nm, and the content of the solid silica fine particles in the solid content of the antireflection layer is 30 to 80% by weight, and the total light transmittance of the optical film is 93% or more and the haze is 2% or less.

[0008] <2> The optical film according to <1>, wherein the Young's modulus of the binder resin is 200 MPa or less.

[0009] <3> The optical film according to <1> or <2>, wherein the thickness of the antireflection layer is 50 to 300 nm.

[0010] <4> The optical film according to any one of <1> to <3>, wherein the (meth)acrylic resin film contains a (meth)acrylic resin having a ring structure in the main chain.

[0011] <5> The optical film according to <4>, wherein the ring structure is at least one selected from a glutarimide structure, a lactone ring structure, a maleic anhydride structure, an N-substituted maleimide structure, and a glutaric anhydride structure.

[0012] <6> A polarizing film in which the optical film according to any one of <1> to <5> is laminated to a polarizer via an adhesive layer.

[0013] An image display device including the polarizing film described in <7> <6>.

[0014] <8> A liquid crystal cell, A front-side polarizing film laminated via an adhesive layer on the viewing side of the liquid crystal cell, A back-side polarizing film laminated via an adhesive layer on the side opposite to the viewing side of the liquid crystal cell, And a backlight unit disposed outside the back-side polarizing film, The front-side polarizing film and the back-side polarizing film each have a polarizer and polarizer protection films disposed on both surfaces of the polarizer, The polarizer protection film disposed on the backlight unit side of the back-side polarizing film is the optical film according to any one of <1> to <5>, and the antireflection layer of the optical film is located on the backlight unit side. A liquid crystal display device.

Effect of the Invention

[0015] According to the present invention, it is possible to provide an optical film having a high transmittance and a low haze with an antireflection layer containing solid silica fine particles, and a polarizing film, an image display device, and a liquid crystal display device including the optical film.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0017] Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited to this embodiment. In this specification, the notation "A to B" using numerical values A and B means "A or more and B or less" unless otherwise specified. When a unit is attached only to numerical value B in such notation, the unit shall also be applied to numerical value A. Further, in this specification, the term "(meth)acrylic" means both "acrylic" and "methacrylic", and the term "(meth)acrylic acid" means both "acrylic acid" and "methacrylic acid". Further, in this specification, the term "solid silica fine particles" means "silica fine particles that are not hollow (that is, those obtained by excluding hollow silica fine particles from silica fine particles)".

[0018] <Optical film> The optical film according to this embodiment is one in which 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, and the total light transmittance is 93% or more and the haze is 2% or less. By using such an optical film as a polarizer protection film, the reflectance of the polarizing film can be reduced and the transmittance can be improved.

[0019] [(Meth)acrylic resin film] The (meth)acrylic resin film contains a (meth)acrylic resin as a main component. The content 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.

[0020] The glass transition temperature (Tg) of the (meth)acrylic resin is preferably 120°C or higher, more preferably higher than 120°C, still more preferably 121°C or higher, even 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 be small. Since the (meth)acrylic resin film is often laminated and used with other films in actual use, when the dimensional change rate is small, distortion and warping caused by the difference in the dimensional change rate with the other laminated films can be suppressed.

[0021] The glass transition temperature can be measured using a differential scanning calorimeter (DSC7000X, manufactured by Hitachi High-Tech Science Corporation) under a nitrogen atmosphere at a heating rate of 20°C / min and determined by the midpoint method.

[0022] 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 preferably used. According to the (meth)acrylic resin having a ring structure in the main chain, heat resistance can be imparted to the (meth)acrylic resin film. 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, from the viewpoints of production simplicity, cost, quality stability against moisture, etc., a (meth)acrylic resin having a glutarimide structure or a lactone ring structure in the main chain is preferable.

[0023] 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, both the glass transition temperature and the retardation in the thickness direction Rth tend to be good. The proportion of the ring structure in the (meth)acrylic resin 1 can be calculated by measuring the molar ratio of the target ring structure part to the other part using 1H-NMR and then converting it to weight.

[0024] The following describes each ring structure.

[0025] The (meth)acrylic resin having a glutarimide structure in the main chain is, for example, a resin containing 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.

[0026]

Chemical formula

[0027] 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, it tends to be easy to impart desired heat resistance. Also, when the proportion of the glutarimide structure is 30% by weight or less, the addition amount of the imidizing agent can be suppressed, the odor due to residual volatile components can be suppressed, and the retardation Rth in the thickness direction can be reduced.

[0028] When R 3 in the above general formula (1) is a methyl group, the proportion of the glutarimide structure in the (meth)acrylic resin can be measured, for example, by the following method. First, 1 using H-NMR BRUKER AvanceIII (400 MHz), the 11H-NMR measurement is performed. Then, the molar ratio is calculated from the area A of the peak derived from the proton constituting O-CH3 of methyl methacrylate in the vicinity of 3.5 to 3.8 ppm and the area B of the peak derived from the proton constituting N-CH3 of the glutarimide ring in the vicinity of 3.0 to 3.3 ppm. By converting the molar ratio to weight, the proportion of the glutarimide structure can be calculated.

[0029] When producing a polymethyl methacrylate resin, in addition to methyl methacrylate, other monomers such as methyl acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate, etc. may be used in combination. Also, in addition to the above, nitrile monomers such as acrylonitrile and methacrylonitrile; maleimide monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide, N-cyclohexylmaleimide, etc. can be used in combination. However, the content rate of acrylate ester units in the polymethyl methacrylate resin is preferably less than 1% by weight, more preferably less than 0.5% by weight, and even more preferably less than 0.3% by weight.

[0030] The structure of the polymethyl methacrylate resin is not particularly limited, and it may be any of a linear polymer, block polymer, core-shell polymer, branched polymer, ladder polymer, crosslinked polymer, etc. In the case of a block polymer, it may be of any type such as A-B type, A-B-C type, A-B-A type, and other types. In the case of a core-shell polymer, it may consist of one layer of core and one layer of shell, or each of the core and shell may consist of multiple layers.

[0031] The method for producing a methyl polymethacrylate 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 employed. When used in the optical field, the bulk polymerization method and the solution polymerization method are preferred in terms of reducing impurities. The methyl polymethacrylate resin can be produced, for example, according to the methods described in JP-A-56-8404, JP-B-6-86492, JP-B-7-37482, JP-B-52-32665, etc.

[0032] The method for producing a (meth)acrylic resin having a glutarimide structure in the main chain includes a step (imidation step) of heating and melting the above methyl polymethacrylate resin and then treating it with an imidizing agent.

[0033] The imidizing agent is not particularly limited as long as it can generate the glutarimide unit represented by the above general formula (1), and those described in WO 2005 / 054311 etc. can be used. Specifically, examples of the imidizing agent include ammonia; aliphatic hydrocarbon group-containing amines such as methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, t-butylamine, n-hexylamine, etc.; aromatic hydrocarbon group-containing amines such as aniline, benzylamine, toluidine, trichloroaniline, etc.; alicyclic hydrocarbon group-containing amines such as cyclohexylamine, etc. Also, 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 be used. Among these, from the viewpoints of cost and physical properties, methylamine, ammonia, and cyclohexylamine are preferred, and methylamine is more preferred. Note that gaseous methylamine etc. at room temperature may be used in a state dissolved in alcohols such as methanol.

[0034] In the imidization step, by adjusting the addition amount of the imidizing agent, the ratios of the glutarimide units and methyl methacrylate units in the resulting (meth)acrylic resin can be adjusted. Further, by adjusting the degree of imidization, the physical properties of the resulting (meth)acrylic resin and the optical properties of the (meth)acrylic resin film formed by molding the (meth)acrylic resin can be adjusted.

[0035] The addition amount of the imidizing agent is preferably 0.5 to 20 parts by weight with respect to 100 parts by weight of the polymethyl methacrylate resin. When the addition amount of the imidizing agent is 0.5 parts by weight or more, as a result of the increase in the ratio of the glutarimide structure, the heat resistance of the (meth)acrylic resin is improved, and the occurrence of appearance defects after molding is likely to be prevented. Further, when the addition amount of the imidizing agent is 20 parts by weight or less, it becomes difficult for the imidizing agent to remain in the (meth)acrylic resin, and the occurrence of appearance defects and foaming after molding are likely to be prevented.

[0036] In the imidization step, a ring-closing accelerator (catalyst) may be added in addition to the imidizing agent, if necessary.

[0037] The method of 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 adopted. For example, the polymethyl methacrylate resin can be imidized by a method using an extruder, a batch-type reaction tank (pressure vessel), or the like.

[0038] When the polymethyl methacrylate resin is heated and melted using an extruder and treated with the 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, it is preferable to use a twin-screw extruder. According to the twin-screw extruder, the mixing of the imidizing agent (when using a ring-closing accelerator, the imidizing agent and the ring-closing accelerator) with respect to the polymethyl methacrylate resin can be promoted.

[0039] Examples of the twin-screw extruder include a non-intermeshing co-rotating type, an intermeshing co-rotating type, a non-intermeshing counter-rotating type, and an intermeshing counter-rotating type. It is preferable to use an intermeshing co-rotating type twin-screw extruder. Since the intermeshing co-rotating type twin-screw extruder can rotate at high speed, it can further promote the mixing of the imidizing agent (when using a ring-closing accelerator, the imidizing agent and the ring-closing accelerator) for the polymethyl methacrylate resin.

[0040] The above-exemplified extruders may be used alone or a plurality of them may be connected in series. For example, a tandem type reactive extruder described in JP-A-2008-273140 may be used.

[0041] When allowing the imidization reaction to proceed in the extruder, for example, the polymethyl methacrylate resin is charged from the raw material charging section of the extruder, the resin is melted, and after filling the cylinder, the imidizing agent may be injected into the extruder using an addition pump.

[0042] In this case, the temperature of the reaction zone (resin temperature) in the extruder is preferably 180 to 270°C, more preferably 200 to 250°C. When the temperature of the reaction zone (resin temperature) is 180°C or higher, the imidization reaction proceeds sufficiently and the heat resistance tends to improve. Also, when the temperature of the reaction zone is 270°C or lower, the decomposition of the resin is suppressed, and as a result, the decrease in the flexural fatigue resistance of the film formed from the obtained (meth)acrylic resin tends to be suppressed. Here, the reaction zone in the extruder refers to the region in the cylinder of the extruder from the injection position of the imidizing agent to the resin discharge port (die section).

[0043] By increasing the reaction time in the reaction zone of the extruder, the imidization can be further advanced. 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 10 seconds or less, the imidization may hardly proceed.

[0044] The resin pressure in the extruder is preferably from atmospheric pressure to 50 MPa, more preferably from 1 to 30 MPa. When the resin pressure is 1 MPa or more, the solubility of the imidizing agent increases, and the reaction tends to proceed further. Also, when the resin pressure is 50 MPa or less, a special device is not required, which is preferable in terms of cost.

[0045] When using an extruder, it is preferable to install a vent hole that can be depressurized to below atmospheric pressure in order to remove unreacted imidizing agent, by-products such as methanol, and monomers.

[0046] When heating and melting polymethyl methacrylate resin using a batch reactor (pressure vessel) and treating it with an imidizing agent, the structure of the batch reactor is not particularly limited. As the batch reactor, it suffices to have a structure capable of melting polymethyl methacrylate resin by heating, stirring it, and adding an imidizing agent (when using a ring-closing accelerator, the imidizing agent and the ring-closing accelerator), and a structure with good stirring efficiency is preferable. According to such a batch reactor, it is possible to prevent the polymer viscosity from increasing due to the progress of the reaction and the stirring from becoming insufficient. Examples of such a batch reactor having such a structure include, for example, the stirring tank Max Blend manufactured by Sumitomo Heavy Industries, Ltd.

[0047] In addition, reaction devices suitable for high viscosities such as horizontal twin-screw reaction devices such as the Bi-Volac manufactured by Sumitomo Heavy Industries, Ltd., and vertical twin-screw stirring tanks such as Super Blend can also be suitably used.

[0048] Specific examples of the imidization method include, for example, known methods described in JP-A-2008-273140, JP-A-2008-274187, and the like.

[0049] The method for producing a (meth)acrylic resin having a glutarimide structure in the main chain may include a step of treating with an esterifying agent (esterification step) in addition to the imidization step. By this esterification step, the acid value of the imidized resin obtained in the imidization step can be adjusted within a desired range.

[0050] Examples of the esterifying agent include dimethyl carbonate, 2,2-dimethoxypropane, dimethyl sulfoxide, triethyl orthoformate, trimethyl orthoacetate, trimethyl orthoformate, diphenyl carbonate, dimethyl sulfate, methyl toluenesulfonate, methyl trifluoromethylsulfonate, methyl acetate, methanol, ethanol, methyl isocyanate, p-chlorophenyl isocyanate, dimethylcarbodiimide, dimethyl-t-butylsilyl chloride, 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, and the like. Among these, from the viewpoints of cost, reactivity, etc., dimethyl carbonate and trimethyl orthoacetate are preferable, and from the viewpoint of cost, dimethyl carbonate is more preferable.

[0051] The addition amount of the esterifying agent is preferably 0 to 12 parts by weight, more preferably 0 to 8 parts by weight, based on 100 parts by weight of the polymethyl methacrylate resin. When the esterifying agent is within the above range, the acid value can be adjusted to an appropriate range, and the unreacted esterifying agent tends to be less likely to remain in the resin.

[0052] In the esterification step, in addition to the esterifying agent, a catalyst can also be used in combination. 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.

[0053] In addition, in the esterification step, it is also possible to perform only heat treatment or the like without treating with an esterifying agent. When only heat treatment (kneading and dispersion of molten resin in an extruder) is performed, at least a part of the carboxy groups can be converted into acid anhydride groups by dehydration reaction between carboxy groups by-produced in the imidization step, dealcoholization reaction between a carboxy group and an alkyl ester group, etc. At this time, it is also possible to use a ring-closing accelerator (catalyst). Even when treating with an esterifying agent, it is also possible to promote the formation of acid anhydride groups by heat treatment.

[0054] 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, those obtained by obtaining a polymer having a hydroxy group and an ester group in the molecular chain by polymerization (polymerization step) and then introducing a lactone ring structure into the polymer by heat treatment (lactonization condensation step) are preferred.

[0055] In the polymerization step, a polymer having a hydroxy group and an ester group in the molecular chain is obtained by performing a polymerization reaction of a monomer component containing an unsaturated monomer represented by the following general formula (2).

[0056]

Chemical formula

[0057] 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, t-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 may be used alone or in combination of two or more.

[0058] The content of the unsaturated monomer represented by the general formula (2) in the monomer component is preferably 5 to 50% by weight, more preferably 10 to 40% by weight, and even more preferably 10 to 30% by weight. 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. Further, when the content of the unsaturated monomer represented by the general formula (2) is 50% by weight or less, the crosslinking reaction during the formation of the lactone ring structure is suppressed from causing gelation, and the decrease in fluidity tends to be suppressed. In addition, the remaining unreacted hydroxy groups suppress the further progress of the condensation reaction during molding, the generation of volatile substances, the occurrence of silver streaks, and the increase in the thickness direction retardation Rth.

[0059] The monomer component may contain other monomers in addition to the unsaturated monomer represented by the general formula (2). Examples of other monomers include (meth)acrylate esters, hydroxy group-containing monomers, unsaturated carboxylic acids, unsaturated monomers represented by the following general formula (3), and the like. These other monomers may be used alone or in combination of two or more.

[0060] [Chemical formula] (In the formula, R 6represents a hydrogen atom or a methyl group, X represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group, -OAc group, -CN group, or -CO-R 7 group, Ac represents an acetyl group, and R 7 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.)

[0061] The above (meth)acrylate ester is not particularly limited as long as it is a (meth)acrylate ester other than the unsaturated monomer represented by the above general formula (2). For example, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, cyclohexyl acrylate, benzyl acrylate and other acrylate esters; methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate and other methacrylate esters; and the like. Among these, from the viewpoints of heat resistance and transparency, methyl methacrylate is preferred.

[0062] When using a (meth)acrylate ester, the content of the (meth)acrylate ester 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.

[0063] The (meth)acrylic resin film may contain other thermoplastic resins in addition to the above-mentioned (meth)acrylic resin. Examples of other thermoplastic resins include olefin-based polymers, vinyl halide-based polymers, styrene-based polymers, ester-based polymers, amide-based polymers, and the like. The content of other thermoplastic resins in the (meth)acrylic resin film is preferably less than 50% by weight, and more preferably less than 30% by weight.

[0064] (Meta)acrylic resin films may contain a crosslinked elastomer to improve mechanical strength. The crosslinked elastomer can be produced by known polymerization methods such as suspension polymerization, dispersion polymerization, emulsion polymerization, solution polymerization, bulk polymerization, etc.

[0065] In addition, (meta)acrylic resin films may contain other additives as required. Examples of additives include antioxidants; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; ultraviolet absorbers, flame retardants, antistatic agents, fillers, plasticizers, lubricants; and the like.

[0066] (Method for manufacturing the film) The method for manufacturing (meta)acrylic resin films is not particularly limited, and methods such as injection molding, melt extrusion molding, inflation molding, blow molding, compression molding, etc. can be adopted. Also, a solution casting method or a spin coating method in which the (meta)acrylic resin is dissolved in a solvent and then molded can be adopted. Among these, it is preferable to adopt a melt extrusion method that does not use a solvent. According to the melt extrusion method, the manufacturing cost can be reduced, and the load on the global environment and the working environment due to the solvent can be reduced.

[0067] Hereinafter, an example of manufacturing a (meta)acrylic resin film by the melt extrusion method will be described. 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".

[0068] When manufacturing a (meta)acrylic resin film by the melt extrusion method, first, the (meta)acrylic resin is supplied to an extruder and heated and melted.

[0069] The (meta)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.

[0070] Next, the (meth)acrylic resin heated and melted in the extruder is supplied to the 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 tends to be uniform, and the thickness unevenness in the longitudinal direction of the film can be reduced. On the other hand, if a filter is used, foreign matters in the (meth)acrylic resin can be removed, and a (meth)acrylic resin film excellent in appearance without defects can be obtained.

[0071] Next, the (meth)acrylic resin supplied to the T-die is extruded from the T-die as a sheet-like molten resin. Then, the sheet-like molten resin is sandwiched between two cooling rolls and cooled to form a film.

[0072] As the two cooling rolls for sandwiching the sheet-like molten resin, one is a rigid metal roll with a smooth surface, and the other is preferably a flexible roll provided with a metal elastic outer cylinder capable of elastic deformation with a smooth surface. By sandwiching the sheet-like molten resin between the rigid metal roll and the flexible roll provided with the metal elastic outer cylinder and cooling to form a film, minute irregularities and die lines 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. In this specification, the "cooling roll" is used in the meaning including the "touch roll".

[0073] Even when using a rigid metal roll and a flexible roll, since the surface of any cooling roll is made of metal, if the film to be formed is thin, there is a risk that the surfaces of the cooling rolls will come into contact with each other, causing damage to the outer surface of the cooling roll or even breaking the cooling roll itself. Therefore, when forming a film by sandwiching a sheet-like molten resin between two cooling rolls, first, sandwich the sheet-like molten resin between the two cooling rolls and cool it to once obtain a relatively thick master roll film, and then it is preferable to uniaxially or biaxially stretch the master roll film to produce a film with a predetermined thickness. For example, when producing a film with a thickness of 40 μm, first, sandwich the sheet-like molten resin between two cooling rolls and cool it to once obtain a master roll film with a thickness of 150 μm, and then it is preferable to stretch the master roll film by biaxial stretching in the longitudinal and transverse directions to produce a film with a thickness of 40 μm.

[0074] Thus, when the (meth)acrylic resin film is a stretched film, after molding the (meth)acrylic resin into an unstretched master roll film, a stretched film can be produced by performing uniaxial stretching or biaxial stretching.

[0075] In order to improve the flex resistance in both the longitudinal direction (MD direction) and the width direction (TD direction) of the (meth)acrylic resin film, it is preferable to perform biaxial stretching.

[0076] In this specification, for convenience of explanation, the film before stretching, that is, the film in the unstretched state, after molding the (meth)acrylic resin into a film shape is referred to as the "master roll film".

[0077] When stretching the master roll film, after molding the master roll film, the stretching of the master roll film may be immediately performed, or after molding the master roll film, it may be once stored or moved and then the stretching of the master roll film may be performed.

[0078] (Film stretching method) The method of stretching the raw film is not particularly limited, and any conventionally known stretching method can be adopted. For example, transverse stretching by a tenter, longitudinal stretching by a roll, and sequential biaxial stretching obtained by sequentially combining these can be adopted. Also, a simultaneous biaxial stretching method that stretches the film in the longitudinal and transverse directions simultaneously, or a method that performs transverse stretching by a tenter after performing longitudinal stretching by a roll can also be adopted.

[0079] The stretching temperature when stretching the raw film is not particularly limited, and it may 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 raw film ((meth)acrylic resin) obtained by the DSC method is defined as Tg, it is preferably 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), still more 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). If the stretching temperature is within the above temperature range, the thickness unevenness of the obtained stretched film can be reduced, and the mechanical properties such as elongation rate, tear propagation strength, and MIT bending resistance can be made good. Also, there is a tendency to prevent problems such as the film sticking to the roll.

[0080] The stretching ratio when stretching the raw film is not particularly limited, and it may be appropriately determined according to 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 in the range of 1.1 to 3 times, more preferably in the range of 1.3 to 2.5 times, and still more preferably in the range of 1.5 to 2.3 times. If the stretching ratio is within the above range, the mechanical properties such as the elongation rate, tear propagation strength, and fatigue resistance to rubbing of the film can be significantly improved. Therefore, a stretched film with a thickness unevenness of 5 μm or less and an internal haze of 1.0% or less can be manufactured.

[0081] When the (meth)acrylic resin film contains a crosslinked elastomer, since it has excellent mechanical strength of the film, any of an unstretched film, a uniaxially stretched film, and a biaxially stretched film can be preferably used.

[0082] The smaller the retardation of the (meth)acrylic resin film, the better. It is preferably that 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. Even more preferably, Δnd is 1.0 nm or less and Rth is 3.0 nm or less.

[0083] The thickness of the (meth)acrylic resin film is preferably 5 to 200 μm, and more preferably 10 to 100 μm. When the thickness is 5 μm or more, sufficient strength tends to be obtained. Further, when the thickness is 200 μm or less, a decrease in transparency and a decrease in the drying property of the solvent (such as water) of the adhesive tend to be suppressed, and the optical film can be made thinner.

[0084] The wetting tension of the surface of the (meth)acrylic resin film is preferably 40 mN / m or more, and 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. may be performed. Among these, corona discharge treatment and plasma treatment are preferred.

[0085] In the present embodiment, it is preferable to provide a coating step such as an antireflection layer and an easy-adhesion layer before tenter stretching. By coating before tenter stretching, it is not necessary to provide a separate drying furnace. Further, by stretching the coating film simultaneously with the base material, the strength and the adhesion to the base material tend to be improved.

[0086] [Antireflection layer] The optical film according to this embodiment has an antireflection layer on one or both sides of a (meth)acrylic resin film. By providing such an antireflection layer, the reflectance of the optical film can be reduced, and the transmittance of the polarizing film when used as a polarizer protection film can be improved.

[0087] The antireflection layer is mainly composed of a binder resin having a refractive index of 1.50 or less with respect to light having a wavelength of 594 nm and solid silica fine particles having an average primary particle diameter of 15 to 90 nm. This antireflection layer can be formed by applying a composition for forming an antireflection layer containing a binder resin and solid silica fine particles to a (meth)acrylic resin film and then drying it.

[0088] Hereinafter, the composition for forming an antireflection layer and the method for forming an antireflection layer using the composition for forming an antireflection layer will be described.

[0089] The composition for forming an antireflection layer may be aqueous or organic, but from the viewpoints of the environment and workability, it is preferably aqueous. However, a small amount of an organic solvent may be contained to improve dispersibility or solubility, or as an antifoaming agent or a leveling agent. As the organic solvent, an alcohol-based solvent, a ketone-based solvent, an ester-based solvent, and an ether-based solvent are preferable because of their compatibility with water and ease of handling. 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.

[0090] As the binder resin, known water-dispersible or water-soluble polymers can be used. Examples thereof include aqueous (water-dispersible) polyurethane resins, aqueous polyester resins, aqueous (meth)acrylic resins, polyvinyl alcohol, polyvinyl pyrrolidone, polycarboxylic acids, and the like. Among these, from the viewpoint of adhesion to the (meth)acrylic resin film, aqueous polyurethane resins, aqueous polyester resins, and aqueous (meth)acrylic resins are preferred. These binder resins may be used alone or in combination of two or more.

[0091] Since the composition for forming an antireflection layer contains hollow silica fine particles at a high concentration, it is necessary to maintain the pH of the composition from neutral to alkaline in order to achieve dispersion stabilization by the zeta potential. For this reason, the binder resin is preferably nonionic or anionic.

[0092] The aqueous polyurethane resin as the binder resin can be obtained by reacting a polyol and a polyisocyanate.

[0093] The polyol is not particularly limited as long as it has two or more hydroxy groups in the molecule, and any suitable polyol can be employed. Examples of the polyol include polyester polyols, polycarbonate diols, polyether polyols, and the like.

[0094] A polyester polyol can typically be obtained by reacting a polybasic acid component with a polyol component. Examples of the polybasic acid component include aromatic dicarboxylic acids such as ortho-phthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, biphenyldicarboxylic acid, 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, itaconic acid; alicyclic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid; reactive derivatives such as acid anhydrides, alkyl esters, acid halides of these acids; and the like. 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, glycerin, 1,1,1-trimethylolpropane, 1,2,5-hexanetriol, pentaerythritol, glucose, sucrose, sorbitol, etc.

[0095] The polycarbonate diol is preferably an aliphatic polycarbonate diol. The polyurethane resin synthesized from such an aliphatic polycarbonate diol has not only excellent mechanical properties but also excellent water resistance, oil resistance, and long-term weather resistance. In particular, it has a lower refractive index compared to aromatic polycarbonate diols, which is advantageous for achieving an antireflection effect. Examples of the aliphatic polycarbonate diol include poly(hexamethylene carbonate) glycol, poly(cyclohexane carbonate) glycol, and the like.

[0096] The polyether polyol can typically be obtained by subjecting a polyhydric alcohol to ring-opening polymerization and addition of an alkylene oxide. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerin, trimethylolpropane, and the like.

[0097] 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), tolidine diisocyanate (TODI), hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), p-phenylene diisocyanate, 1,4-diisocyanate, xylene diisocyanate (XDI), and the like.

[0098] The aqueous polyester resin as the binder resin can be obtained by polymerizing a polyol and a dicarboxylic acid by an esterification method. Alternatively, it can be obtained by polymerizing a polyol and a dicarboxylic acid diester by a transesterification method. When producing the aqueous polyester resin, any suitable condensation reaction catalyst may be used.

[0099] An aqueous (meth)acrylic resin as a binder resin can be obtained by polymerizing a (meth)acrylic monomer. At this time, it is preferable to use a (meth)acrylic monomer having a glass transition temperature higher than room temperature. Examples of the (meth)acrylic monomer having a glass transition temperature higher than room temperature include methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, and the like. Further, for the purpose of improving the adhesive strength and the coating film physical properties, one or more (meth)acrylic monomers having a glass transition temperature lower than room temperature can be mixed and used. Examples of the (meth)acrylic monomer having a glass transition temperature lower than room temperature include methoxyethyl aminoacrylate, butyl acrylate, hexyl acrylate, ethylhexyl acrylate, and the like.

[0100] The binder resin has a refractive index of 1.50 or less with respect to light having a wavelength of 594 nm, and preferably 1.49 or less. When the refractive index of the binder resin with respect to light having a wavelength of 594 nm is 1.50 or less, the refractive index difference from the solid silica fine particles is small, so scattering at the interface with the solid silica fine particles is suppressed, and the transparency of the antireflection layer tends to increase. The lower limit value of the refractive index of the binder resin with respect to light having a wavelength of 594 nm is not particularly limited, but is usually 1.47 or more.

[0101] The Young's modulus of the binder resin is preferably 200 MPa or less, and more preferably 100 MPa or less. When the Young's modulus of the binder resin is 200 MPa or less, even when a large amount of solid silica fine particles are contained, the flexibility of the antireflection layer is maintained, and it tends to be able to follow stretching. The lower limit value of the Young's modulus of the binder resin is not particularly limited, but is usually 1 MPa or more.

[0102] The number average molecular weight of the binder resin is preferably 5000 to 600000, and more preferably 10000 to 400000. The number average molecular weight of the binder resin can be determined by polystyrene conversion using gel permeation chromatography.

[0103] The composition for forming an antireflection layer contains solid silica fine particles in order to sufficiently lower the refractive index of the antireflection layer and to impart antiblocking properties to the optical film.

[0104] The average primary particle diameter of the solid silica fine particles is 15 to 90 nm, preferably 20 to 80 nm. When the average primary particle diameter of the solid silica fine particles is 15 nm or more, the dispersion stability in the composition for forming an antireflection layer becomes good, and the interparticle distance in the antireflection layer becomes small, and it is possible to suppress the occurrence of whitening due to the inability to follow stretching. Also, when the average primary particle diameter of the solid silica fine particles is 90 nm or less, it is possible to suppress the occurrence of scattering at the interface with the binder resin and the deterioration of transparency, and it is also possible to suppress the occurrence of white blur due to external haze caused by unevenness.

[0105] The average primary particle diameter of the solid silica fine particles can be measured by the dynamic light scattering method.

[0106] As the solid silica fine particles, commercially available colloidal silica can be used. Examples of commercially available colloidal silica include the Quotron 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.

[0107] 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, preferably 40 to 70% by weight, and more preferably 50 to 60% by weight. When the content of the solid silica fine particles is 30% by weight or more based on the solid content, the refractive index of the formed antireflection layer sufficiently decreases, and it is possible to exhibit the desired antireflection performance. Also, when the content of the solid silica fine particles is 80% by weight or less based on the solid content, it is possible to suppress the hardening of the formed antireflection layer and the whitening due to cracks due to the inability to follow stretching.

[0108] In addition, in order to achieve the desired antireflection performance, in addition to solid silica fine particles, hollow silica fine particles, hollow polymer fine particles, etc. may be used in combination.

[0109] The composition for forming an antireflection layer may contain a crosslinking agent. For example, when the binder resin has a carboxyl group, as the crosslinking agent, a polymer having a group capable of reacting with the carboxyl group is preferable. 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, a crosslinking agent having an oxazoline group has a long pot life at room temperature when mixed with the binder resin, and the crosslinking reaction proceeds by heating, so the workability is good.

[0110] Also, the composition for forming an antireflection layer may further contain an arbitrary additive. Examples of the additive 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, etc.

[0111] The solid content concentration in the composition for forming an antireflection layer is preferably 1.5 to 15% by weight, and more preferably 2 to 10% by weight. When the solid content concentration is 1.5% by weight or more, the drying time tends to be shortened and the productivity tends to be improved. Also, when the solid content concentration is 15% by weight or less, the bubbles tend to escape easily and the pot life tends to be long.

[0112] The thickness of the antireflection layer is preferably 50 to 300 nm. When the thickness of the antireflection layer is 50 nm or more, a sufficient antireflection effect tends to be obtained. Also, when the thickness of the antireflection layer is 300 nm or less, the occurrence of rainbow unevenness due to interference light in the visible light region tends to be suppressed.

[0113] 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 becomes minimum due to the interference between the surface reflected light and the reflected light in the substrate. In the formula, λ represents the wavelength of the irradiated light, and n2 represents the refractive index of the antireflection layer. d = (1 / 4) × (λ / n2) When λ is 550 nm and n2 is 1.46, d = 94 nm becomes the optimal value. In practice, considering the above formula, the thickness may be set within the above range while taking into account thickness unevenness, film strength, etc.

[0114] Before applying the composition for forming the antireflection layer, it is preferable to hydrophilize the surface of the (meth)acrylic resin film in advance by corona discharge treatment, plasma treatment, etc.

[0115] The coating method of the composition for forming the antireflection layer is not particularly limited, and methods such as bar coating method, roll coating method, gravure coating method, rod coating method, slot orifice coating method, curtain coating method, fountain coating method, etc. can be adopted.

[0116] The drying temperature after applying the composition for forming the antireflection layer is preferably 50°C or higher, and more preferably 80°C or higher.

[0117] [Easy - adhesion layer] The optical film according to this embodiment may have an easy - adhesion layer on the surface opposite to the antireflection layer to improve the adhesiveness with a polarizer. Examples of the easy - adhesion layer include a layer formed by applying a composition mainly composed of a polyurethane resin having a carboxy group as described in Japanese Patent No. 5354733.

[0118] In addition, when antireflection layers are formed on both surfaces of the optical film according to this embodiment, one of the antireflection layers can also be used as the easy - adhesion layer.

[0119] [Polarizing film] The polarizing film according to this embodiment is a laminate in which the optical film according to the above - described embodiment is laminated to a polarizer via an adhesive layer.

[0120] As the polarizer, an appropriate polarizer according to the purpose can be adopted. Examples of the polarizer include those obtained by adsorbing dichroic substances such as iodine and dichroic dyes on hydrophilic polymer films such as polyvinyl alcohol-based films, partially formalized polyvinyl alcohol-based films, and ethylene-vinyl acetate copolymer-based partially saponified films, and then uniaxially stretching them; polyene-based oriented films such as dehydrated products of polyvinyl alcohol and dehydrochlorinated products of polyvinyl chloride; and the like. Among these, from the viewpoint of a high polarization dichroism ratio, a polarizer obtained by adsorbing a dichroic substance such as iodine on a polyvinyl alcohol-based film and then uniaxially stretching it is preferable. The thickness of the polarizer is not particularly limited and is generally about 1 to 80 μm.

[0121] The adhesive for forming the adhesive layer is not particularly limited, 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 adopted.

[0122] FIG. 1 shows a schematic cross-sectional view showing an example of the layer structure of the polarizing film according to the present embodiment. The polarizing film 10 shown in FIG. 1 has a laminated structure in which polarizer protection films 30 and 40 are respectively bonded to both sides of the polarizer 20 via adhesive layers 51 and 52.

[0123] The polarizer protection film 30 has, in order from the polarizer 20 side, an easy-adhesion layer 31, a (meth)acrylic resin film 32, and an antireflection layer 33. The polarizer protection film 40 has, in order from the polarizer 20 side, an easy-adhesion layer 41 and a (meth)acrylic resin film 42. The polarizer protection film 40 may have an adhesive layer (not shown) for bonding to a liquid crystal cell or the like on the surface opposite to the polarizer 20.

[0124] In the polarizing film 10 shown in FIG. 1, the optical film according to the present embodiment described above is used as the polarizer protection film 30.

[0125] <Image display device> The image display device according to this embodiment includes the polarizing film according to the above-described embodiment. Examples of the image display device include a liquid crystal display device (LCD) and the like.

[0126] The liquid crystal display device includes a liquid crystal cell and a backlight unit as a light source, and also includes polarizing films disposed on both sides of the liquid crystal cell (the backlight unit side and the viewing side). The polarizing film according to this embodiment can be used on either the backlight unit side or the viewing side. When used as the polarizing film on the backlight unit side, by installing the antireflection layer to face the backlight unit side, the reflectance can be reduced and the luminance of the liquid crystal panel can be improved. On the other hand, when used as the polarizing film on the viewing side, by making the antireflection layer the outermost layer, the surface reflected light can be reduced and the visibility of the liquid crystal panel can be improved.

[0127] A schematic cross-sectional view showing an example of the layer configuration of the liquid crystal display device according to this embodiment is shown in FIG. 2. The liquid crystal display device 100 shown in FIG. 2 includes a liquid crystal cell 110, a front-side polarizing film 160a laminated via an adhesive layer 170a on the viewing side of the liquid crystal cell 110, a back-side polarizing film 160b laminated via an adhesive layer 170b on the side opposite to the viewing side of the liquid crystal cell 110, and a backlight unit 180 disposed outside the back-side polarizing film 160b.

[0128] The front-side polarizing film 160a has a laminated structure in which polarizer protection films 130a and 140a are respectively laminated on both sides of a polarizer 120a via adhesive layers 151a and 152a. The polarizer protection film 130a located on the side far from the liquid crystal cell 110 has, in order from the polarizer 120a side, an easy-adhesion layer 131a, a (meth)acrylic resin film 132a, and an antireflection layer 133a. The polarizer protection film 140a located on the liquid crystal cell 110 side has, in order from the polarizer 120a side, an easy-adhesion layer 141a and a (meth)acrylic resin film 142a.

[0129] The backside polarizing film 160b has a laminated structure in which polarizer protection films 130b and 140b are respectively laminated on both sides of the polarizer 120b via adhesive layers 151b and 152b. The polarizer protection film 130b located on the side farther from the liquid crystal cell 110 has, in order from the polarizer 120b side, an easy-adhesion layer 131b, a (meth)acrylic resin film 132b, and an antireflection layer 133b. Also, the polarizer protection film 140b located on the liquid crystal cell 110 side has, in order from the polarizer 120b side, an easy-adhesion layer 141b and a (meth)acrylic resin film 142b.

[0130] In the liquid crystal display device 100 shown in FIG. 2, the optical films according to the above-described embodiment are used as the polarizer protection films 130a and 130b.

Example

[0131] 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.

[0132] The measurement methods for various physical properties described in the examples and comparative examples are as follows. (Haze) The haze of the optical film was measured in accordance with JIS K7136 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH2000).

[0133] (Total light transmittance) The total light transmittance of the optical film was measured in accordance with JIS K7361-1 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH2000).

[0134] (Young's modulus of the binder resin) An aqueous dispersion of a polyurethane resin as a binder resin was poured into a glass container so that the film thickness after drying would be 100 μm, and left 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 test pieces. Regarding these test pieces, a tensile test was conducted at a tensile speed of 5 mm / min using a tensile tester (manufactured by Instron Japan Co., Ltd., tensile testing machine 5564), and the Young's modulus was measured from the slope of the obtained SS curve.

[0135] (Refractive index of the binder resin) Regarding the test pieces obtained in the measurement of the above Young's modulus, the refractive index with respect to light with a wavelength of 594 nm was measured using a prism coupler (manufactured by Metricon, model 2010).

[0136] (Calculation of the ratio of the glutarimide structure in the (meth)acrylic resin) (The ratio of the glutarimide structure in the (meth)acrylic resin was calculated as follows. First, 1 1H-NMR BRUKER AvanceIII (400 MHz) was used to perform 1H-NMR measurement of the (meth)acrylic resin. 1 Then, the molar ratio was calculated from the area A of the peak derived from the proton constituting O-CH3 of methyl methacrylate in the vicinity of 3.5 to 3.8 ppm and the area B of the peak derived from the proton constituting N-CH3 of the glutarimide ring in the vicinity of 3.0 to 3.3 ppm. The ratio of the glutarimide structure was calculated by converting the molar ratio to weight.

[0137] (Glass transition temperature) 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 / min in a nitrogen atmosphere, and the glass transition temperature was determined by the midpoint method.

[0138] <Production Example 1: Production of (meth)acrylic resin> As the extruder, an intermeshing co-rotating twin-screw extruder with a diameter of 40 mm (L / D = 90) was used, and the set temperature of each temperature control zone of the extruder was 250 to 280°C, and the screw rotation speed was 85 rpm. The polymethyl methacrylate resin was melted and filled by a kneading block, and then 1.8 parts by weight of monomethylamine (manufactured by Mitsubishi Gas Chemical Company, Inc.) was injected from the nozzle with respect to 100 parts by weight of the polymethyl methacrylate resin. The resin coming out as a strand from the die provided at the outlet of the extruder was cooled in a water tank and then pelletized by a pelletizer to obtain resin (I). Next, the set temperature of each temperature control zone of the intermeshing co-rotating twin-screw extruder with a diameter of 40 mm was set to 240 to 260°C. 0.56 part by weight of dimethyl carbonate was injected from the nozzle with respect to 100 parts by weight of the polymethyl methacrylate resin to reduce the carboxyl groups in resin (I). Further, the by-products after the reaction and the excess dimethyl carbonate were removed. The resin coming out as a strand from the die provided at the outlet of the extruder was cooled in a water tank and then pelletized by a pelletizer to obtain 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.

[0139] <Production Example 2: Production of (meth)acrylic resin film> After drying the (meth)acrylic resin 1 obtained in Production Example 1 at 100°C for 5 hours, it was formed into a film using an intermeshing co-rotating twin-screw extruder with a diameter of 15 mm (L / D = 45) equipped with a T-die at the outlet of the extruder. The sheet-like molten resin extruded from the T-die was cooled by a cooling roll to obtain a raw film with a width of 160 mm and a thickness of 160 μm. At that time, the surface in contact with the casting roll was defined as surface B, and the other surface was defined as surface A.

[0140] <Example 1> 7.6 g of colloidal silica (manufactured by Fuso Chemical Industry Co., Ltd., Quartron PL-03, average primary particle diameter: 35 nm, solid content: 20%) was charged into a glass container, 25.5 g of pure water and 0.5 g of 1% aqueous ammonia were added, and the mixture was stirred with a magnetic stirrer for 10 minutes. Next, 4 g of an aqueous polyurethane resin (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Superflex 460, solid content: 38%) was added as a binder resin, and the mixture was stirred for 10 minutes to prepare a composition for forming an antireflection layer. This composition for forming an antireflection layer had an overall solid content concentration of 8% by weight and a content rate of solid silica fine particles in the solid content of 50% by weight.

[0141] The A surface of the (meth)acrylic film obtained in Production Example 2 was subjected to corona discharge treatment, and the composition for forming an antireflection layer was applied using a bar coater (#5) to form a coating film. Then, the film was put into a hot air dryer (100 °C) and dried for 3 minutes to prepare a coated raw film with an antireflection layer thickness of 800 nm. Next, the obtained coated raw film was simultaneously biaxially stretched under the conditions of a stretching ratio of 2 times (longitudinal and transverse) and 145 °C using a biaxial stretching device (manufactured by Imoto Seisakusho Co., Ltd., IMC-1905) to prepare an optical film with an antireflection layer thickness of 200 nm. And, the haze and total light transmittance of the obtained optical film were measured. The results are shown in Table 1.

[0142] <Examples 2 to 5, Comparative Examples 2 to 6> An optical film was produced in the same manner as in Example 1 except that the composition of the composition for forming an antireflection layer was changed as shown in Table 1. And, the haze and total light transmittance of the obtained optical film were measured. The results are shown in Table 1.

[0143] An optical film was produced in the same manner as in Example 1 except that the composition for forming an antireflection layer was not applied. And, the haze and total light transmittance of the obtained optical film were measured. The results are shown in Table 1.

[0144] In addition, the abbreviations in Table 1 indicate the following meanings respectively. · SF460 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Superflex 460) · SF420NS (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Superflex 420NS) · PL-3 (manufactured by Fuso Chemical Industry Co., Ltd., Quotron PL-3) · PL-7 (manufactured by Fuso Chemical Industry Co., Ltd., Quotron PL-7) · ST-30 (manufactured by Nissan Chemical Industries, Ltd., Snowtex ST-30) · ST-1040 (manufactured by Nissan Chemical Industries, Ltd., Snowtex ST-1040)

[0145]

Table 1

[0146] From the results in Table 1, it can be seen that by setting the refractive index and Young's modulus of the binder resin within a predetermined range and the content of the solid silica fine particles within a predetermined range, an optical film with high total light transmittance and low haze can be obtained.

Explanation of Symbols

[0147] 10 Polarizing film, 20 Polarizer, 30 Polarizer protection film, 31 Easy adhesion layer, 32 (Meth)acrylic resin film, 33 Anti-reflection layer, 40 Polarizer protection film, 41 Easy adhesion layer, 42 (Meth)acrylic resin film, 51, 52 Adhesive layer, 100 Liquid crystal display device, 110 Liquid crystal cell, 120a, 120b Polarizer, 130a, 130b Polarizer protection film, 131a, 131b Easy adhesion layer, 132a, 132b (Meth)acrylic resin film, 133a, 133b Anti-reflection layer, 140a, 140b Polarizer protection film, 141a, 141b Easy adhesion 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

Claims

1. An optical film having an antireflection layer formed on one or both sides of a (meth)acrylic resin film containing a (meth)acrylic resin, wherein the antireflection layer contains a binder resin having a refractive index of 1.50 or less with respect to light having a wavelength of 594 nm and solid silica fine particles having an average primary particle diameter of 15 to 90 nm, and the content of the solid silica fine particles in the solid content of the antireflection layer is 30 to 80% by weight, and the total light transmittance of the optical film is 93% or more and the haze is 2% or less.

2. The optical film according to claim 1, wherein the Young's modulus of the binder resin is 200 MPa or less.

3. The optical film according to claim 1, wherein the thickness of the antireflection layer is 50 to 300 nm.

4. 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.

5. The optical film according to claim 4, wherein the ring structure is at least one selected from a glutarimide structure, a lactone ring structure, a maleic anhydride structure, an N-substituted maleimide structure, and a glutaric anhydride structure.

6. A polarizing film in which the optical film according to any one of claims 1 to 5 is laminated to a polarizer via an adhesive layer.

7. An image display device including the polarizing film according to claim 6.

8. A liquid crystal cell, a front-side polarizing film laminated to the viewing side of the liquid crystal cell via an adhesive layer, a back-side polarizing film laminated to the side opposite to the viewing side of the liquid crystal cell via an adhesive layer, and a backlight unit disposed outside the back-side polarizing film, wherein each of the front-side polarizing film and the back-side polarizing film has a polarizer and polarizer protection films disposed on both sides of the polarizer, and the polarizer protection film disposed on the backlight unit side of the back-side polarizing film is the optical film according to any one of claims 1 to 5, and the antireflection layer of the optical film is located on the backlight unit side.

Images