Optical film, polarizing plate, and liquid crystal display panel

Abstract

The present invention provides an optical film having an acrylic resin film mainly composed of an acrylic resin, and a highly adhesive layer formed on the acrylic resin film, the acrylic resin film having a glass transition temperature of 120 DEG C or more, the sum of the kurtosis Rku of both surfaces of the optical film being 10-50, and the thickness of the optical film being 10-50. And an internal haze of 1.0% or less.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical film, a polarizing plate, and a liquid crystal display panel. BACKGROUND

[0002] In a liquid crystal display device, two polarizing plates are generally arranged on both sides of a liquid crystal cell. As the polarizing plate, a polarizing plate in which a polarizing member protection film for protecting a polarizing member is attached to both sides of the polarizing member with an adhesive is generally used. As the polarizing member protection film, high transparency is required, and an optical film formed of a cellulose-based material is often used.

[0003] For the purpose of improving durability and the like, an optical film formed of an acrylic resin or a norbornene resin has been proposed as a polarizing member protection film. However, these optical films are likely to generate wrinkles or wrinkle marks when the films are wound into a roll, and as a method for solving this problem, a method of adding fine particles such as silica particles to a norbornene resin film to ensure the winding property of the roll has been proposed (Patent Document 1). In addition, a method of forming an easy-adhesion layer containing particles such as silica on one side of the film to ensure the winding property of the roll and the like has been proposed (Patent Documents 2 and 3).

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: International Publication No. 2018 / 074513

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2007-127893

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 2010-55062 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] Although the generation of wrinkles or wrinkle marks at the time of winding can be solved by the methods of Patent Documents 1 to 3, according to the research by the present inventors and the like, it has been clarified that with the improvement in the film quality level due to the high definition and large area of liquid crystal display panels, defects caused by the tight winding of the film in storage and the like are generated when the film is made into a roll. In addition, the present inventors and the like have attempted to solve the above phenomenon by adding silica to an acrylic resin film by the method described in Patent Document 1, but it is known that in the conventional method, the haze increases and the like, and it is difficult to satisfy the requirements as an optical film.

[0011] The present application has been achieved in order to solve the above problem. An object of the present application is to suppress blocking at the time of storage of a film roll while maintaining the heat resistance and transparency of an optical film.

[0012] Solution to problem

[0013] The present inventors made intensive studies in order to solve the above problems, and as a result, completed the present invention.

[0014] That is, one embodiment of the present invention relates to the following.

[0015] [1] An optical film having an acrylic resin film in which an acrylic resin is a main component, and an easy-adhesion layer formed on the acrylic resin film, the glass transition temperature of the acrylic resin film being 120°C or higher, the sum of the kurtosis Rku of both faces of the optical film being 10 or higher and 50 or lower, and the internal haze being 1.0% or lower.

[0016] [2] The optical film according to [1], wherein the static friction coefficient between one face and the other face of the optical film is 0.8 or lower.

[0017] [3] The optical film according to [1] or [2], wherein the sum of the 10-point average roughness Rzj of each of both faces of the optical film is 0.05 μm or higher and 1.0 μm or lower.

[0018] [4] The optical film according to any one of [1] to [3], wherein the acrylic resin contains at least one or more ring structures selected from a lactone ring structure, a glutarimide structure, a glutaric anhydride structure, an N-substituted maleimide structure, and a maleic anhydride structure.

[0019] [5] The optical film according to any one of [1] to [3], wherein the meso-tacticity represented by a triad is 54% or higher.

[0020] [6] The optical film according to any one of [1] to [5], wherein the acrylic resin film contains an anti-blocking agent, and the anti-blocking agent contains acrylic crosslinking particles having an average particle diameter of 0.1 μm or higher and 2.5 μm or lower.

[0021] [7] The optical film according to [6], wherein the anti-blocking agent contains acrylic crosslinking particles having an average particle diameter of 0.1 μm or higher and 2.0 μm or lower.

[0022] [8] The optical film according to [6] or [7], wherein the acrylic resin film contains the acrylic crosslinking particles at 0.05% by weight or higher and 0.9% by weight or lower.

[0023] [9] The optical film according to any one of [1] to [8], which has a dimensional change rate of -2.0% or higher and -0.1% or lower when left in an atmosphere of 85°C, 85% RH for 120 hours.

[0024]

[10] A polarizing plate provided with the optical film described in any one of [1] to [9].

[0025]

[11] A liquid crystal display panel provided with the polarizing plate described in

[10] .

[0026] Effects of the Invention

[0027] According to the present application, an optical film having excellent transparency and heat resistance, and capable of preventing blocking during storage of a film roll can be provided. DETAILED DESCRIPTION

[0028] An embodiment of the present application will be described, but the present application is not limited thereto. The present application is not limited to each structure described below, and various modifications can be made within the scope shown in the claims, and an embodiment obtained by appropriately combining technical means respectively disclosed in different embodiments and examples is also included in the technical scope of the present application. In addition, all academic and patent documents described in this specification are incorporated by reference in this specification. Note that, in this specification, "A to B" indicating a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)" respectively, unless otherwise specifically described.

[0029] (Optical film)

[0030] The optical film of the present embodiment is characterized by having an acrylic resin film having an acrylic resin as a main component, and an easy-adhesion layer formed on the acrylic resin film, the glass transition temperature of the acrylic resin film being 120°C or higher, the sum of the kurtosis Rku of both surfaces of the optical film being 10 or more and 50 or less, and the internal haze being 1.0% or less. Thus, by having an acrylic resin as a main component, and controlling the sum of the kurtosis of both surfaces of the film to a prescribed value, and further controlling the internal haze to a prescribed value, an optical film having excellent heat resistance and transparency, and further excellent blocking resistance during storage of a film roll can be obtained.

[0031] (Acrylic resin film)

[0032] The glass transition temperature of the acrylic resin film of the present embodiment is 120°C or higher. It is preferable that the glass transition temperature exceed 120°C, more preferable that it be 121°C or higher, further preferable that it be 122°C or higher, and particularly preferable that it be 123°C or higher. By making the glass transition temperature of the acrylic resin film 120°C or higher, the dimensional change rate of the stretched film in a high-temperature environment is reduced. In actual use, the acrylic resin film of the present embodiment is often used in combination with an easy-adhesion layer or other film, and if the dimensional change rate is small, the generation of strain or warping due to differences in dimensional change rate between the acrylic resin film and the other film stacked thereon can be suppressed.

[0033] The glass transition temperature of the acrylic resin constituting the acrylic resin film is preferably 120°C or higher, more preferably exceeds 120°C, further preferably is 121°C or higher, further more preferably is 122°C or higher, and particularly preferably is 123°C or higher.

[0034] Here, as the acrylic resin having a glass transition temperature of 120°C or higher, an acrylic resin having a ring structure in the main chain can be preferably used. For example, as the ring structure, at least one or more selected from the group consisting of a glutarimide ring, a lactone ring, maleic anhydride, maleimide, and glutaric anhydride can be mentioned. By this, heat resistance can be imparted. In addition, among them, from the viewpoints of ease of production, cost, and quality stability against moisture, a glutarimide ring is particularly preferable.

[0035] The content of the ring structure in the acrylic resin having a glass transition temperature of 120°C or higher is preferably in the range of 2 to 80% by weight. If the content of the ring structure is in this range, both the glass transition temperature and the thickness-direction phase difference Rth become good, and thus it is preferable. The content of the ring structure in the acrylic resin can be calculated by measuring the molar ratio of the ring structure portion to the portion other than the ring structure portion by H-NMR, and converting the weight. 1 H-NMR, the molar ratio of the ring structure portion to the portion other than the ring structure portion is measured, and the weight is converted to calculate. In addition, the acrylic resin having a glass transition temperature of 120°C or higher is a main component of the acrylic resin film, and is contained in an amount exceeding 50% by weight in 100% by weight of the acrylic resin film. Among them, in 100% by weight of the acrylic resin film, it is preferable that it be 70% by weight or more, more preferable that it be 80% by weight or more, further preferable that it be 85% by weight or more, and particularly preferable that it be 90% by weight or more.

[0036] Note that, as the acrylic resin having a glass transition temperature of 120°C or higher, an acrylic resin having no ring structure in the main chain can be used.

[0037] The internal haze of the optical film of the present embodiment is 1.0% or less. The internal haze is preferably 0.7% or less, more preferably 0.5% or less, and particularly preferably 0.3% or less. By making the internal haze 1.0% or less, the quality when mounted to a liquid crystal panel becomes good.

[0038] In the present specification, the internal haze is defined as the haze value measured using a haze meter (turbidimeter) with a glass cell in which the obtained film is placed and pure water is filled in the periphery of the glass cell as the object.

[0039] The haze of the optical film of the present embodiment is not particularly limited as long as the internal haze is in the above range, and from the viewpoint of transparency, the haze is preferably 3.0% or less, more preferably 2.0% or less, and further preferably 1.0% or less.

[0040] By making the sum of the kurtosis Rku of both surfaces of the optical film 10 or more and 50 or less, the sticking of the films during the storage of the film roll can be effectively prevented. Thus, the defects that can occur in the films can be prevented. Here, if the sum of the kurtosis Rku of both surfaces of the optical film is less than 10, the sticking accompanied by the winding occurs during the storage of the film roll, and as a result, the film defects occur. This tendency becomes significant during the storage of a long (for example, 8000 m) film roll. Therefore, only the optical film of a prescribed size (for example, 4000 m) can be wound, and the yield is reduced. In addition, even the optical film of the prescribed size cannot be used because the optical film on the inside is plastically deformed during the storage of the film roll. On the other hand, if the sum of the kurtosis Rku of both surfaces of the optical film exceeds 50, the transparency of the optical film is reduced. The sum of the kurtosis Rku of both surfaces of the optical film is more preferably 15 or more and 30 or less. If the sum of the kurtosis is 10 or more, the friction between the films is easily reduced. In addition, it is presumed that the air between the films is easily discharged when the films are overlapped in a roll shape, the sticking accompanied by the winding can be suppressed, and the film defects can be suppressed. In addition, if the sum of the kurtosis is 50 or less, the light can be suppressed from being diffusely reflected on the surface, and the case where the clarity of the panel display is impaired can be suppressed.

[0041] Here, the "sticking" refers to the state where the films are fixed to each other, and includes the state where a part is fused at a high temperature, and the state where the films are closely (pittari) overlapped. If the winding occurs, the pressure is applied to the films, and the sticking (fixing) of the films to each other occurs, as a result, the case where the films are peeled from each other with a strong force occurs, and the damage to the films occurs. Therefore, by making the kurtosis of both surfaces of the films in the prescribed range as in the present embodiment, the fixing of the films to each other in the film roll can be suppressed even if the winding occurs, the films can be peeled from each other with a weak force, and thus the damage (film defects) to the films can be suppressed.

[0042] Here, the kurtosis Rku can be calculated from the roughness curve in accordance with JIS B 0601. The sharpness in the height direction means that Rku = 3: the height distribution is a normal distribution, Rku > 3: the surface is sharp with many peaks and valleys, and Rku < 3: the surface is flat.

[0043] The sum of the 10-point average roughness Rzjis of each of the two faces of the optical film is preferably 0.05 μm or more and 1.0 μm or less. If the sum of the 10-point average roughness Rzjis of each of the two faces is 0.05 μm or more, the films are easily reduced in friction against each other. In addition, it is presumed that when the films are overlapped in a roll shape, air between the films is easily expelled, and the occurrence of blocking accompanying the rolling up can be suppressed, and the occurrence of film defects can be suppressed. In addition, if the sum of the 10-point average roughness Rzjis of each of the two faces is 1.0 μm or less, the surface can be suppressed from diffusely reflecting light, and the occurrence of a case in which the clarity of a display of a panel is impaired can be suppressed. Of these, the sum of the 10-point average roughness Rzjis of each of the two faces of the optical film is more preferably 0.05 μm or more and 0.6 μm or less, and further preferably 0.05 μm or more and 0.5 μm or less.

[0044] In the case where the acrylic resin has a ring structure in the main chain, the sum of the 10-point average roughness Rzjis of each of the two faces of the optical film is preferably 0.15 μm or more and 1.0 μm or less, more preferably 0.16 μm or more and less than 1.0 μm, and further preferably 0.17 μm or more and 0.6 μm or less, and more preferably 0.2 μm or more and 0.5 μm or less. In addition, the 10-point average roughness Rzjis of one face and / or the other face of the optical film is preferably more than 0.080 μm and 0.25 μm or less.

[0045] On the other hand, in the case where the acrylic resin does not have a ring structure in the main chain, particularly in the case where the meso-tacticity represented by the triad is 54% or more as described later, the sum of the 10-point average roughness Rzjis of each of the two faces of the optical film is preferably 0.05 μm or more and 1.0 μm or less, more preferably 0.06 μm or more and less than 0.60 μm, further preferably 0.06 μm or more and less than 0.50 μm, further more preferably 0.06 μm or more and 0.40 μm or less, and further more preferably 0.07 μm or more and 0.30 μm or less. In addition, the 10-point average roughness Rzjis of one face and / or the other face of the optical film is preferably more than 0.020 μm and 0.20 μm or less.

[0046] The film's kurtosis Rku and Rzjis (surface roughness) can be measured using an optical surface roughness meter, such as a laser microscope. The surface roughness values ​​of the optical film of this embodiment are smaller than the resolution of a laser microscope, so sufficient measurement accuracy cannot be achieved using a lens with a small numerical aperture. Therefore, in this specification, values ​​measured using a lens with a numerical aperture of 0.95 or greater are used.

[0047] Regarding the surface roughness of the film, from the perspectives of economic efficiency and environmental impact, it is preferred to add an anti-blocking agent, described below, to the acrylic resin. Among these, organic fine particles are preferred from the perspectives of affinity and dispersibility with the acrylic resin, and acrylic cross-linked particles are most preferred from the perspective of ease of haze control.

[0048] The static friction coefficient of an optical film, measured with one side of the film bonded to the other, is preferably 0.8 or less, more preferably 0.7 or less, even more preferably 0.6 or less, and particularly preferably 0.5 or less. A static friction coefficient of 0.8 or less effectively prevents adhesion between films within a film roll. While the lower limit of the static friction coefficient is not particularly limited, it is preferably 0.2 or greater to prevent winding deviation and meandering during production.

[0049] The dimensional change rate of the optical film when it is left to stand for 120 hours in an atmosphere of 85°C and 85% RH is preferably an average value of -2.0% or more in the longitudinal direction (MD direction) and the width direction (TD direction) of the film, more preferably -1.7% or more, and further preferably -1.5% or more. If the above-mentioned dimensional change rate is -2.0% or more, the shrinkage over time can be suppressed during the storage of the film roll, and the stability of the winding appearance over time is improved. In addition, the warping and dimensional changes when attached to the polarizer are alleviated, which can suppress the contrast reduction and peripheral unevenness of the liquid crystal display device. The above-mentioned dimensional change rate can be, for example, -0.1% or less. If the above-mentioned dimensional change rate is -0.1% or less, when attached to the polarizer, even if the polarizer itself shrinks, the optical film can easily follow the shrinkage. The dimensional change rate when left to stand for 120 hours in an atmosphere of 85°C and 85% RH here can be measured using a three-dimensional measuring instrument to measure the dimensional change of the optical film before and after it is left to stand for 120 hours in an environmental testing machine set to 85°C and 85% RH.

[0050] In this specification and claims, the dimensional change rate refers to the change in the pore spacing between 1 mm diameter holes formed 20 mm inward from the diagonal line of a 90 mm x 90 mm film before and after the film is left standing for 120 hours in an atmosphere of 85°C and 85% RH. The pore spacing change rate refers to the change in the pore spacing after standing, based on the pore spacing before standing, and is calculated using the following formula.

[0051] [(hole spacing after standing) - (hole spacing before standing)] × 100 / (hole spacing before standing) ... (A)

[0052] The linear expansion coefficient of the optical film at 40°C to 60°C is preferably 80 ppm or less, more preferably 72 ppm or less. If it is 80 ppm or less, the shrinkage and expansion of the film due to temperature changes during storage and transportation of the roll can be suppressed, and it is less likely to cause the roll to tighten. On the other hand, as a lower limit, it is preferably 40 ppm or more. If the linear expansion coefficient of the film is 40 ppm or more, when stacked with a polarizer, the linear expansion difference with other components is small, so it is less likely to cause warping, etc.

[0053] The linear expansion coefficient can be measured, for example, using a thermomechanical analyzer TMA-4000SA manufactured by Bruker AXS. Specifically, under a nitrogen atmosphere, a film cut into 4 mm x 20 mm is subjected to a tensile load of 3.1 g. The film is heated at a rate of 2°C / min within a temperature range not exceeding the glass transition temperature. The temperature is plotted on the X-axis and the change in film length is plotted on the Y-axis to create a graph. During the heating and cooling processes, the slope within the temperature range of 40°C to 60°C is calculated using the least squares method to determine the linear expansion coefficient.

[0054] (Anti-blocking agent)

[0055] The acrylic resin film is preferably formed from an acrylic resin composition comprising an acrylic resin and an anti-blocking agent. The anti-blocking agent is preferably acrylic crosslinked particles from the viewpoints of compatibility with the acrylic resin, dispersibility, and transparency. The particles may be of any shape, but a true spherical shape is preferred from the perspective of easily exhibiting anti-blocking properties.

[0056] When the refractive index of the acrylic resin is set to 100%, the refractive index of the anti-blocking agent is preferably 98% to 102%, more preferably 99% to 101%. The refractive index of the anti-blocking agent is preferably 1.47 to 1.55, more preferably 1.47 to 1.53, and even more preferably 1.48 to 1.52. Using an anti-blocking agent with a refractive index within this range can produce a highly transparent acrylic resin film. Acrylic crosslinked particles are preferred because they meet the above refractive index requirements.

[0057] The polymerizable monomer forming the above-described acrylic crosslinking particles can be selected from any (meth)acrylate and other copolymerizable monomers, and it is preferable to contain methyl methacrylate from the viewpoint of compatibility with the acrylic resin and refractive index. The content of structural units derived from methyl methacrylate in the acrylic crosslinking particles is preferably 80% by weight or more and 99% by weight or less, and more preferably 83% by weight or more and 96% by weight or less. Note that, in the case where the content of structural units derived from methyl methacrylate in the acrylic resin is high, it is preferable that the content of structural units derived from methyl methacrylate in the acrylic crosslinking particles be high.

[0058] The above-described acrylic crosslinking particles also contain structural units derived from a multifunctional monomer that contains two or more polymerizable groups in the molecule as a polymerizable monomer. The content of the multifunctional monomer in the polymerizable monomer can be arbitrarily set, and it is preferable to be 0.5% by weight or more and 30% by weight or less. If it is less than 0.5% by weight, the heat resistance and dispersibility of the acrylic crosslinking particles are poor. If it is more than 30% by weight, coalescence of the particles and formation of abnormal particles can occur when the acrylic crosslinking particles are manufactured.

[0059] The average particle diameter of the above-described acrylic crosslinking particles is preferably 0.1 μm or more and 2.5 μm or less, and more preferably 0.1 μm or more and 2.0 μm or less. If it is less than 0.1 μm, the amount of addition for imparting anti-blocking properties needs to be increased, and thus the mechanical properties and economics can be poor at times. If it is more than 2.5 μm, clogging of the polymer filter can occur. In addition, from the viewpoint of long-term operability of the polymer filter, it is preferable to use one having a narrow distribution of particle diameters and a small content of coarse particles.

[0060] The amount of addition of the acrylic crosslinking particles of the present embodiment is preferably 0.05% by weight or more and 0.9% by weight or less, more preferably 0.07% by weight or more and 0.5% by weight or less, and further preferably 0.1% by weight or more and 0.2% by weight or less. If the amount of addition is less than 0.05% by weight, sufficient anti-blocking effects cannot be obtained, and by setting the amount of addition to be 0.9% by weight or less, it is possible to prevent deterioration of economics and increase in haze. In addition, in order to control the sliding properties and surface properties, a plurality of particles having different particle diameter distributions can be mixed. In this case, the amount of addition of the acrylic crosslinking particles is the total of the amounts of addition of the plurality of particles.

[0061] (easy-adhesion layer)

[0062] The optical film of the present embodiment has an easy-adhesion layer on the acrylic resin film. The easy-adhesion layer is formed on one side or both sides of the acrylic resin film. By providing the easy-adhesion layer, for example, in the case of use as a polarizing element protective film, when adhered to a polarizing element with an adhesive, the adhesion of the polarizing element protective film to the polarizing element by the adhesive can be enhanced. In addition, by providing the easy-adhesion layer on an unstretched film and then stretching, a stretched film having an easy-adhesion layer can also be obtained.

[0063] As the easy-adhesion layer used in the present embodiment, a publicly known technique described in Japanese Patent Application Publication No. 2009-193061, Japanese Patent Application Publication No. 2010-55062, and the like can be used. That is, for example, it can be formed from an easy-adhesion agent composition containing a polyurethane resin having a carboxyl group and a cross-linking agent. By using a polyurethane resin, an easy-adhesion layer in which the adhesion of the polarizing element protective film to the polarizing element is excellent can be obtained. From the viewpoint of operability and the viewpoint of environmental protection, the easy-adhesion agent composition is preferably water-based.

[0064] (acrylic resin)

[0065] As described above, the glass transition temperature of the acrylic resin film is 120°C or higher, and as the acrylic resin used as the acrylic resin film, an acrylic resin having a glass transition temperature of 120°C or higher can be appropriately used. As the acrylic resin having a glass transition temperature of 120°C or higher, as described above, an acrylic resin having a ring structure in the main chain and an acrylic resin not having a ring structure in the main chain can be used. Hereinafter, each ring structure will be described.

[0066] (acrylic resin having a glutarimide ring in the main chain)

[0067] The acrylic resin having a glutarimide ring as a ring structure in the main chain is a resin containing a glutarimide unit and a methyl methacrylate unit represented by the following general formula (1), and is obtained by heating and melting an acrylic resin having a content of acrylic ester units of less than 1% by weight and treating with an imidization agent.

[0068]

[0069] (here, R 1 and R 2 each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R 3 represents 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).

[0070] The content of the glutarimide ring of the present embodiment is, for example, a value that can be measured by the following method. Using a differential scanning calorimeter (DSC) Q2000 manufactured by TA Instruments, a sample is heated at a rate of 10°C / min from 30°C to 200°C, and the content of the glutarimide ring is calculated from the area of the endothermic peak of the glutarimide ring. 1H-NMR was performed. According to the peak area of the O-CH3 proton derived from the methyl methacrylate around 3.5 ppm to 3.8 ppm and the peak area of the N-R proton derived from the glutarimide group around 3.0 ppm to 3.3 ppm, the molar ratio was calculated. 3 The peak area of the proton was weight-converted using the molar ratio calculated.

[0071] In the process of treating with the imidization agent, in addition to the methyl methacrylate, for example, methyl acrylate, (meth)acrylic acid ethyl ester, (meth)acrylic acid butyl ester, (meth)acrylic acid isobutyl ester, (meth)acrylic acid tert-butyl ester, (meth)acrylic acid benzyl ester, (meth)acrylic acid cyclohexyl ester, or the like can be used in combination. In the case where they are used in combination, the acrylate unit is preferably less than 1% by weight. Further, the acrylate unit is more preferably less than 0.5% by weight, and further preferably less than 0.3% by weight.

[0072] In addition, in addition to the above-described monomer, an acrylonitrile, a nitrile-based monomer such as methacrylonitrile, a maleimide, a maleimide-based monomer such as N-methyl maleimide, N-phenyl maleimide, N-cyclohexyl maleimide, and an aromatic vinyl-based monomer such as styrene can be copolymerized.

[0073] The structure of the above-described methyl methacrylate resin is not particularly limited, and can be any of a linear (chain) polymer, a block polymer, a core-shell polymer, a branched polymer, a ladder polymer, a crosslinked polymer, and the like.

[0074] In the case of a block polymer, it can be any of an A-B type, an A-B-C type, an A-B-A type, and a block polymer of a type other than these. In the case of a core-shell polymer, it can be composed of only one core and one shell, or can be composed of a plurality of layers, respectively.

[0075] As a method for producing a polymethyl methacrylate, there is no particular limitation, and a publicly known emulsion polymerization method, emulsion-suspension polymerization method, suspension polymerization method, bulk polymerization method, solution polymerization method, or the like can be applied. When used in the optical field, from the viewpoint of less impurities, a bulk polymerization method or a solution polymerization method is particularly preferable. For example, it can be produced according to the method described in Japanese Patent Application Laid-Open No. 56-8404, Japanese Patent No. 6-86492, Japanese Patent No. 7-37482, Japanese Patent No. 52-32665, or the like.

[0076] The method for producing an acrylic resin of the present embodiment includes a process of heating and melting a methyl methacrylate resin or an acrylic resin in which a monomer other than the above-described methyl methacrylate monomer is copolymerized, and treating with an imidization agent (imidization process). Thereby, an acrylic resin having a glutarimide group can be produced.

[0077] The imidization agent is not particularly limited as long as it generates a glutarimide ring represented by the general formula (1), and examples include the imidization agents described in WO 2005 / 054311. Specifically, examples include amines containing aliphatic hydrocarbon groups such as ammonia, methylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, t-butylamine, and n-hexylamine; amines containing aromatic hydrocarbon groups such as aniline, benzylamine, toluidine, and trichloroaniline; and amines containing alicyclic hydrocarbons such as cyclohexylamine. In addition, urea compounds that generate the exemplified amines by heating, such as urea, 1,3-dimethylurea, 1,3-diethylurea, and 1,3-dipropylurea, can also be used. Of these imidization agents, methylamine, ammonia, and cyclohexylamine are preferred from the viewpoints of cost and physical properties, and methylamine is particularly preferred.

[0078] Methylamine and the like that are gaseous at room temperature can be used in a state of being dissolved in an alcohol such as methanol.

[0079] In this imidization step, the proportion of the glutarimide unit and the (meth)acrylate unit in the obtained acrylic resin can be adjusted by adjusting the addition proportion of the imidization agent.

[0080] In addition, by adjusting the degree of imidization, the physical properties of the obtained acrylic resin, the transparency of a stretched film formed by molding the acrylic resin of the present embodiment, and the like can be adjusted.

[0081] The imidization agent is preferably 0.5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the acrylic resin containing a methyl methacrylate unit. When the amount of the imidization agent added is within this range, the imidization agent is less likely to remain in the resin, and the possibility of inducing appearance defects after molding and foaming is extremely low. In addition, the content of the glutarimide ring in the finally obtained resin composition is also appropriate, and thus the heat resistance is less likely to decrease, appearance defects after molding are less likely to be induced, and it is preferred.

[0082] In this imidization step, a ring closure accelerator (catalyst) can be added as needed in addition to the imidization agent.

[0083] The method of heating and melting and treating with the imidization agent is not particularly limited, and all methods known in the art can be used. For example, the acrylic resin containing a methyl methacrylate unit described above can be imidized by a method using an extruder, a batch-type reaction tank (pressure vessel), or the like.

[0084] The extruder is not particularly limited. For example, a single-screw extruder, a twin-screw extruder, or a multi-screw extruder, or the like can be used. The extruder can be used alone or a plurality of extruders can be connected in series. In the case of using a twin-screw extruder, a non-intermeshing type co-rotating type, an intermeshing type co-rotating type, a non-intermeshing type counter-rotating type, and an intermeshing type counter-rotating type, or the like can be mentioned. Among them, the intermeshing type co-rotating type twin-screw extruder can rotate at a high speed, and thus can further promote the mixing of the imidization agent (and the ring closure promoter in the case of using the ring closure promoter) with respect to the raw material polymer, and thus is preferred.

[0085] In the case where imidization is performed in the extruder, for example, methyl methacrylate resin is fed from a raw material feeding portion of the extruder, the resin is melted, and after filling the inside of the cylinder, an imidization agent is injected into the extruder using an addition pump, whereby the imidization reaction can be performed in the extruder.

[0086] In this case, the temperature (resin temperature), the time (reaction time), and the resin pressure in the extruder are also not particularly limited as long as the pentandiamide imidization can be performed.

[0087] In the case of using an extruder, in order to remove unreacted imidization agent, by-products, and the like, it is also preferred to install a vent hole capable of reducing the pressure to below atmospheric pressure. According to such a configuration, unreacted imidization agent, or by-products such as methanol, and monomers can be removed.

[0088] In the case of using a batch-type reaction tank (pressure vessel) to produce an acrylic resin containing a pentandiamide ring in the main chain, the structure of the batch-type reaction tank (pressure vessel) is not particularly limited. As long as it has a structure capable of melting and stirring an acrylic resin containing a methyl methacrylate unit by heating, and capable of adding an imidization agent (and a ring closure promoter in the case of using the ring closure promoter), it is preferred to have a structure with good stirring efficiency.

[0089] As a specific example of the imidization method, for example, the methods described in Japanese Patent Application Publication No. 2008-273140, Japanese Patent Application Publication No. 2008-274187, and the like, or publicly known methods can be mentioned.

[0090] In the production method of the acrylic resin of the present embodiment, in addition to the above imidization step, a step of treating with an esterification agent can be included. By this esterification step, the acid value of the imidized resin obtained in the imidization step can be adjusted to a desired range.

[0091] As the esterifying agent, there is no particular limitation as long as it can esterify the residual carboxyl group in the molecular chain. For example, dimethyl carbonate, 2,2-dimethoxypropane, dimethyl sulfoxide, triethyl orthoformate, trimethyl orthoacetate, trimethyl orthoformate, diphenyl carbonate, dimethyl sulfate, methyl tosylate, methyl triflate, methyl acetate, methanol, ethanol, methyl isocyanate, p-chlorophenyl isocyanate, dimethyl carbodiimide, and the like can be exemplified. Among them, from the viewpoints of cost, reactivity, and the like, dimethyl carbonate and trimethyl orthoacetate are preferred, and from the viewpoint of cost, dimethyl carbonate is preferred.

[0092] In the imidization step, the esterifying agent is preferably 0 to 30 parts by weight, and more preferably 0 to 15 parts by weight, relative to 100 parts by weight of the acrylic resin containing a methyl methacrylate unit. If the esterifying agent is within these ranges, the acid value can be adjusted to an appropriate range. On the other hand, if it is more than the range, there is a possibility that unreacted esterifying agent remains in the resin, and when the obtained resin is used for molding, it sometimes becomes a cause of foaming or odor generation.

[0093] In addition to the esterifying agent, a catalyst can also be used in combination. The catalyst is not particularly limited as long as it can promote esterification. For example, aliphatic tertiary amines such as trimethylamine, triethylamine, and tributylamine can be exemplified. Among them, from the viewpoints of cost, reactivity, and the like, triethylamine is preferred.

[0094] In the esterification step, it can also be processed without using an esterifying agent and only heating treatment or the like is performed. In the case where only heating treatment (kneading, dispersing, or the like of the molten resin in the extruder) is performed, a part or all of the carboxyl groups can be converted to anhydride groups by dehydration of the carboxyl groups to each other, dealkylation of the carboxyl groups and the alkoxycarbonyl groups, or the like in the acrylic resin having a glutarimide ring as a byproduct in the imidization step. At this time, a ring closure accelerator (catalyst) can also be used. Even in the case where processing is performed using an esterifying agent, anhydride groups can be formed by heating treatment.

[0095] In the imide resin that has passed through the imidization step and the esterification step, since unreacted imidization agent, unreacted esterifying agent, volatile components and resin decomposition products as byproducts of the reaction, and the like are contained, an exhaust hole that can be depressurized to below atmospheric pressure can be installed.

[0096] (acrylic resin having a lactone ring in the main chain)

[0097] The acrylic resin having a lactone ring as a ring structure in the main chain is not limited as long as it is a thermoplastic polymer having a lactone ring structure in the molecule (a thermoplastic polymer into which a lactone ring structure is introduced in the molecular chain), and the production method thereof is not limited either. It is preferable to obtain a polymer having a hydroxyl group and an ester group in the molecular chain after polymerization (polymerization step), and then to introduce a lactone ring structure into the polymer by heat treatment of the obtained polymer (a) (lactone ring formation condensation step).

[0098] In the polymerization step, a polymer having a hydroxyl group and an ester group in the molecular chain is obtained by performing polymerization of a monomer component including an unsaturated monomer represented by the following general formula (2).

[0099]

[0100] (where, R 4 and R 5 each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

[0101] As the unsaturated monomer represented by the general formula (2), for example, 2- (hydroxymethyl) methyl acrylate, 2- (hydroxymethyl) ethyl acrylate, 2- (hydroxymethyl) isopropyl acrylate, 2- (hydroxymethyl) n-butyl acrylate, 2- (hydroxymethyl) t-butyl acrylate, and the like can be exemplified. Among them, 2- (hydroxymethyl) methyl acrylate and 2- (hydroxymethyl) ethyl acrylate are preferable from the viewpoint of high heat resistance improving effect, and 2- (hydroxymethyl) methyl acrylate is particularly preferable. These unsaturated monomers can be used alone or in combination of two or more.

[0102] The content ratio 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 further preferably 10 to 30% by weight. If the content ratio is less than 5% by weight, the heat resistance, solvent resistance, and surface hardness of the obtained lactone ring-containing polymer can be decreased, and if it is more than 50% by weight, crosslinking reaction can occur during formation of the lactone ring structure, and gelation can easily occur, flowability can be decreased, and thus melt molding can be difficult, or unreacted hydroxyl groups can easily remain, and thus condensation reaction can further proceed during molding, and volatile substances can be generated, and silver streaks can easily occur, or the thickness direction phase difference Rth can be increased, and the like.

[0103] The monomer component preferably includes other monomers in addition to the unsaturated monomer represented by the general formula (2). As the other monomers, there is no limitation as long as they are selected within a range not impairing the effects of the present application, and for example, (meth) acrylate, a hydroxyl group-containing monomer, an unsaturated carboxylic acid, and an unsaturated monomer represented by the following general formula (3) can be preferably selected. The above other monomers can be used alone or in combination of two or more.

[0104]

[0105] (Among them, R 6 represents a hydrogen atom or a methyl group, and X represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group, an -OAc group, a -CN group, or a -CO-R 7 Ac represents acetyl, R 7 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. ).

[0106] The (meth)acrylate is not limited as long as it is a (meth)acrylate other than the unsaturated monomer represented by general formula (2). Examples thereof include acrylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, cyclohexyl acrylate, and benzyl acrylate; and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, and benzyl methacrylate. These may be used alone or in combination of two or more. Among these, methyl methacrylate is particularly preferred from the viewpoints of heat resistance and transparency.

[0107] When the above-mentioned (meth)acrylate is used, in order to fully exert the effect of the present invention, the content ratio thereof in the monomer component is preferably 10% by weight to 95% by weight, more preferably 10% by weight to 90% by weight, further preferably 40% by weight to 90% by weight, and particularly preferably 50% by weight to 90% by weight.

[0108] (Acrylic resin having maleic anhydride, maleimide and glutaric anhydride structures in the main chain)

[0109] In this embodiment, an acrylic resin having a maleimide or glutaric anhydride structure as a ring structure in the main chain is also preferably used. Examples of maleic anhydride structures include styrene-N-phenylmaleimide-maleic anhydride copolymers. Examples of maleimide structures include olefin-maleimide copolymers described in Japanese Patent Application Laid-Open No. 2004-45893. Examples of glutaric anhydride structures include copolymers having glutaric anhydride units described in Japanese Patent Application Laid-Open No. 2003-137937.

[0110] (Acrylic resin having no ring structure in the main chain)

[0111] As the acrylic resin having a glass transition temperature of 120°C or higher, for example, a method of introducing a carboxyl group of methacrylic acid or the like can be exemplified. If the carboxyl group is above a certain amount, there is a risk of forming a crosslinked body, or the risk of foaming at the time of film formation increases, and thus it is preferable to inhibit it to be below a certain amount. Specifically, the amount of the carboxyl group in the acrylic resin is preferably 0.6 mmol / g or less, and preferably 0.4 mmol / g or less.

[0112] As the acrylic resin having a glass transition temperature of 120°C or higher, an acrylic resin having a triad isotacticity of 54% or more represented by a triad can be appropriately used. If the triad isotacticity of the acrylic resin represented by a triad is 54% or more, there is a tendency that the glass transition temperature of the acrylic resin becomes high, and the heat resistance of the acrylic resin improves. The triad isotacticity of the acrylic resin represented by a triad is preferably 55% or more, more preferably 56% or more, and further preferably 57% or more. In addition, from the viewpoints of the molding processing temperature of the acrylic resin, the toughness and the secondary processability of the molded body, the triad isotacticity of the acrylic resin represented by a triad is preferably 67% or less, more preferably 65% or less, and further preferably 63% or less.

[0113] The triad isotacticity of the acrylic resin represented by a triad is the proportion of the chain of 3 structural units (triad) being rr. In addition, in the chain of 2 structural units (diad), the same stereoscopic arrangement is called meso (m), and the opposite is called racemic (r).

[0114] As the method of synthesizing the acrylic resin having a triad isotacticity of 54% or more represented by a triad, there is no particular limitation, and for example, an anionic polymerization method, a radical polymerization method can be exemplified. Among them, the radical polymerization method is preferable (for example, refer to International Publication No. 2023 / 238885, International Publication No. 2023 / 238886). In the radical polymerization method, since an organic metal compound used as a polymerization initiator in the anionic polymerization method, an organic solvent used as a medium are not used, impurities are not easily left, and from the viewpoint of the environment, it is preferable. Here, the glass transition temperature and the triad isotacticity of the acrylic resin represented by a triad of the acrylic resin can be controlled by the polymerization temperature of the acrylic resin. For example, by lowering the polymerization temperature of the acrylic resin, the glass transition temperature of the acrylic resin becomes high, and the isotacticity of the acrylic resin becomes large. In addition, the glass transition temperature of the acrylic resin can also be controlled by the molecular weight of the acrylic resin.

[0115] The content of the structural unit derived from methyl methacrylate in the acrylic resin represented by the triad is preferably 98% by weight or more, more preferably 99% by weight or more, and further preferably 100% by weight.

[0116] The monomer other than methyl methacrylate that constitutes the acrylic resin represented by the triad having a syndiotacticity of 54% or more is not particularly limited, and examples thereof include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and the like; phenyl acrylate and the like; cyclohexyl acrylate, norbornyl acrylate, and the like; ethyl methacrylate, propyl methacrylate, butyl methacrylate, and the like; phenyl methacrylate and the like; cyclohexyl methacrylate, norbornyl methacrylate, and the like; styrene, α-methylstyrene, and the like; acrylamide; methacrylamide; acrylonitrile; and methacrylonitrile.

[0117] (Other properties of the acrylic resin)

[0118] Hereinafter, other properties of the acrylic resin having a ring structure in the main chain and the acrylic resin not having a ring structure in the main chain will be described. Hereinafter, the description of "acrylic resin" refers to at least either one of the acrylic resin having a ring structure in the main chain and the acrylic resin not having a ring structure in the main chain.

[0119] The weight average molecular weight of the acrylic resin is preferably 50,000 or more and 200,000 or less, and more preferably 90,000 or more and 150,000 or less. When the weight average molecular weight of the acrylic resin is 50,000 or more, there is a tendency that the mechanical properties of the molded body of the acrylic resin are improved, and when the weight average molecular weight of the acrylic resin is 200,000 or less, there is a tendency that the moldability of the acrylic resin is improved.

[0120] The weight average molecular weight of the acrylic resin can be 400,000 or more. When the weight average molecular weight of the acrylic resin is 400,000 or more, there is a tendency that the mechanical properties of the molded body of the acrylic resin are further improved, and for example, a resin film having excellent bending resistance can be obtained. In this case, the weight average molecular weight of the acrylic resin is preferably 600,000 or more, more preferably 700,000 or more, and further preferably 800,000 or more. In addition, from the viewpoint of the moldability of the acrylic resin, the weight average molecular weight of the acrylic resin is preferably 2,500,000 or less, more preferably 2,000,000 or less, further preferably 1,500,000 or less, and particularly preferably 1,200,000 or less.

[0121] The ratio of the weight average molecular weight to the number average molecular weight (dispersity) of the acrylic resin is preferably 1.6 or more and 2.5 or less, more preferably 1.7 or more and 2.2 or less. When the dispersity of the acrylic resin is 1.6 or more, there is a tendency that the flowability of the acrylic resin is improved and the acrylic resin is easily molded, and when the dispersity is 2.5 or less, there is a tendency that the mechanical properties such as the impact resistance, the toughness, the bending resistance, and the like of the molded body of the acrylic resin are improved.

[0122] Note that the number average molecular weight and the weight average molecular weight of the acrylic resin are values converted to standard polystyrene measured by gel permeation chromatography (GPC). In addition, the number average molecular weight and the weight average molecular weight of the acrylic resin can be controlled by the kind and the amount of use of the polymerization initiator and the chain transfer agent used when the acrylic resin is synthesized.

[0123] (acrylic resin composition)

[0124] As the acrylic resin film, an acrylic resin composition to which an additive is added in the acrylic resin can be used, and an antiblocking agent and an additive can also be used in combination. As the additive, an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, a specific wavelength absorber or a specific wavelength absorbing pigment for the purpose of preventing blue light, a radical scavenger, or the like, a phase difference adjusting agent, a catalyst, a plasticizer, a lubricant, an antistatic agent, a coloring agent, an anti-shrinkage agent, an antibacterial / antimold agent, an optical brightener, a compatibilizer, or the like, alone or in combination of two or more, can be added within a range not impairing the object of the present application.

[0125] As the ultraviolet absorber, for example, a triazine-based compound, a benzotriazole-based compound, a benzophenone-based compound, a cyanoacrylate-based compound, a benzoxazine-based compound, an oxadiazole-based compound, and the like can be exemplified. Among them, from the viewpoint of the ultraviolet absorbing performance with respect to the amount of addition, the volatility in the case of melt extrusion, a triazine-based compound is preferred.

[0126] As the phase difference adjusting agent, in the case of imparting a negative phase difference, for example, a compound having a styrene skeleton, such as an acrylonitrile-styrene copolymer, can be exemplified.

[0127] As the mixing method of the acrylic resin and the antiblocking agent, there is no particular limitation, and all the methods conventionally known can be used. For example, a method of supplying to an extruder for melt kneading using a gravimetric feeder, a method of mixing in a solution state using a solvent in which the acrylic resin and the antiblocking agent are highly compatible, and the like can be exemplified.

[0128] In the case of using an extruder for the mixing, the extruder used is not particularly limited, and various extruders can be used. Specifically, a single-screw extruder, a twin-screw extruder, or a multi-screw extruder, or the like can be used. Among them, a twin-screw extruder is preferably used. With a twin-screw extruder, the degree of freedom of the conditions for uniformly mixing the acrylic resin and the anti-blocking agent is large. In addition, the acrylic resin and the anti-blocking agent can be fed from the upstream side of the extruder and mixed using a raw material feeding hopper or the like, or only the anti-blocking agent can be fed and mixed at the middle of the extruder using a side feeder, a gravimetric feeder, or the like. Alternatively, a substance in which the anti-blocking agent has been made into a master batch using another extruder can also be used.

[0129] In order to reduce foreign matter in the resin, a filter can also be provided at the end of the extruder. In order to increase the pressure of the (A) acrylic resin / acrylic resin composition before the filter, a gear pump is preferably provided. As the type of filter, a disc filter made of stainless steel that is capable of removing foreign matter from a molten polymer is preferably used, and as the filter element, a fiber type, a powder type, or a composite type thereof is preferably used.

[0130] (Method for manufacturing optical film)

[0131] One embodiment of the method for manufacturing an optical film of the present application will be described, but the present application is not limited thereto. That is, all methods known in the art can be used as long as the acrylic resin composition of the present embodiment can be molded to manufacture a film.

[0132] Specifically, for example, injection molding, melt extrusion molding, inflation molding, blow molding, compression molding, or the like can be given. In addition, a solution casting method, a spin coating method, in which the acrylic resin composition of the present embodiment is dissolved in a solvent in which it can be dissolved and then molded, can be used to manufacture the film of the present embodiment.

[0133] Among them, a melt extrusion method that does not use a solvent is preferably used. According to the melt extrusion method, the manufacturing cost can be reduced, and the load on the earth's environment and the working environment due to the solvent can be reduced.

[0134] When the acrylic resin composition of the present embodiment is molded into a film by the melt extrusion method, first, the acrylic resin composition of the present embodiment is pre-dried and then fed to an extruder, and the acrylic resin composition is heated and melted. Further, the acrylic resin composition is fed to a die such as a T-die through a gear pump and a filter. Next, the acrylic resin composition fed to the T-die is extruded as a sheet-shaped molten resin, and is cooled and solidified using a cooling roll or the like, and an unstretched film (also referred to as a raw material film) is obtained. At this time, in order to make the surface properties (smoothness) of the film good, it can be sandwiched between a metal roll and a flexible roll having a metal-made elastic outer cylinder.

[0135] In the case where the acrylic resin composition of the present embodiment is molded into an unstretched film by a solution casting method, the acrylic resin composition of the present embodiment is made into a solution together with an organic solvent, and the solution is cast on a support, and then heated and dried to produce an unstretched film. The solvent that can be used in the solution casting method can be selected from publicly known solvents. Halogenated hydrocarbon solvents such as dichloromethane and trichloroethane easily dissolve the acrylic resin of the present embodiment, and have low boiling points, and thus are preferred solvents. In addition, non-halogen solvents having high polarity such as dimethylformamide and dimethylacetamide can also be used. Furthermore, aromatic solvents such as toluene, xylene, and anisole, cyclic ether solvents such as dioxane, dioxolane, tetrahydrofuran, and pyran, and ketone solvents such as methyl ethyl ketone can also be used. These solvents can be used alone. Alternatively, a plurality of solvents can be used in combination. The amount of the solvent used can be set to an arbitrary amount as long as the thermoplastic resin is dissolved in a degree that enables casting. Note that, in the present specification, "dissolution" means that the resin exists in a uniform state in the solvent in a degree that enables casting. It is not necessary that the solute be completely dissolved in the solvent. The concentration of the resin in the solution is preferably 1 to 90% by weight, more preferably 5 to 70% by weight, and further preferably 10 to 50% by weight. As a preferred support, a stainless steel endless belt can be used. Alternatively, a film such as a polyimide film or a polyethylene terephthalate film can also be used.

[0136] The optical film of the present embodiment is obtained by stretching an unstretched film (also referred to as a raw material film). By stretching the unstretched film, a stretched film having a desired thickness can be produced, and further, the mechanical properties of the stretched film can be improved. As a stretching method, a publicly known method can be used. For example, an unstretched raw material film molded by melt extrusion can be uniaxially stretched or biaxially stretched to produce a film having a predetermined thickness. In order to impart excellent mechanical properties to both the length direction (MD direction) and the width direction (TD direction) of the stretched film, biaxial stretching is preferred. As a biaxial stretching method, simultaneous biaxial stretching or sequential biaxial stretching can be used.

[0137] The stretching ratio (in the case of biaxial stretching, both the MD direction and the TD direction of the film) is preferably 1.5 to 3.0 times, more preferably 1.8 to 2.8 times. If the stretching ratio is within this range, the mechanical properties of the film accompanying the stretching can be sufficiently improved. In addition, the degree of orientation does not excessively increase, and the dimensional change when left in an atmosphere of 85°C, 85% RH for 120 hours can be reduced, and the possibility of a reduction in the peeling strength when laminated to a polarizing member is also small. The stretching speed is preferably 1.1 times / minute or more, more preferably 5 times / minute or more. In addition, it is preferably 100 times / minute or less, more preferably 50 times / minute or less. In the case of sequential biaxial stretching, the stretching speed in the first stage and the stretching speed in the second stage can be the same or different. In sequential biaxial stretching, generally, the stretching in the first stage is the stretching in the length direction (MD direction), and the stretching in the second stage is the stretching in the width direction (TD direction).

[0138] The stretching temperature is not particularly limited, and is preferably performed at Tg+7°C to Tg+50°C, more preferably at Tg+10°C to Tg+40°C. If the stretching temperature is Tg+7°C or higher, the risk of breakage during the stretching process can be suppressed. On the other hand, if the stretching temperature is Tg+50°C or lower, sufficient molecular orientation can be obtained, and the mechanical strength of the film can be suppressed from decreasing. If the stretching temperature is high within the above range, the molecular orientation is moderated, and thus the mechanical strength decreases, and on the other hand, the dimensional change in an atmosphere of 85°C, 85% RH decreases. In addition, in the case of a film containing an anti-blocking agent, if the stretching is performed at low temperature, the particles easily float to the surface, and surface roughness, slip properties, and external haze can easily be exhibited. The stretching conditions can be arbitrarily set by those skilled in the art in consideration of the above balance.

[0139] The optical film of the present embodiment is wound in a roll shape by a publicly known method. According to the film of the present embodiment, even in the case where the film width is widened or the winding length is lengthened, defects caused by adhesion between films are less likely to occur. In addition, if knurling of the end portion or the like, which has been conventionally used for adhesion countermeasures, is further combined, the effect is more enhanced.

[0140] (Use)

[0141] In the case where the optical film of the present embodiment is used as a polarizing member protective film, the film is laminated to a polarizing member to become a polarizing plate. The polarizing member is not particularly limited, and any publicly known polarizing member can be used. For example, a polarizing member obtained by incorporating iodine into stretched polyvinyl alcohol can be cited.

[0142] The polarizing plate can be further laminated to various films, and is suitably used in the field of displays such as liquid crystal displays, organic EL displays, and the like. However, the use thereof is not limited to these.

[0143] Examples

[0144] The present application will be described more specifically based on examples and comparative examples, but the present application is not limited thereto. Those skilled in the art can make various modifications, corrections, and changes without departing from the scope of the present application.

[0145] (Surface roughness)

[0146] The surface roughness of the optical film was measured in accordance with JIS B0601:2013 using a laser microscope LEXT OLS5100 manufactured by Evident. Specifically, first, a confocal image of a range of 257 pm x 257 pm of the film was acquired using an objective lens with a magnification of 50 times and a numerical aperture of 0.95. Next, three evaluation lines were drawn at equal intervals in the MD direction and the TD direction, respectively, and a roughness curve was extracted. From the obtained roughness curve, the 10-point average roughness Rzjis and the kurtosis Rku were calculated using an analysis software, and the average at the measurement position was calculated. The measurement was performed five times by changing the measurement position, and the average of them was used as the surface roughness. However, in the case where a local abnormality such as a damage was clearly confirmed from the image, the measurement value was not included, and the abnormal portion was avoided to perform measurement again.

[0147] (Coefficient of static friction)

[0148] The coefficient of static friction of the optical film was measured in accordance with JIS K7125:1999 using a digital force gauge ZTS-5N manufactured by IMADA and a coefficient of friction measurement jig COF-2N-V. Specifically, the A face of the film was fixed on a smooth stainless steel plate, the B face of the film was adhered to a slider of 60 x 60 mm and 200 g in weight using a double-sided tape, the slider was moved at a speed of 100 mm / min by a pulley, the load at that time was read by a load cell, and the coefficient of static friction was calculated. The film sheet was replaced and the measurement was performed five times, and the average was calculated.

[0149] (Haze, internal haze)

[0150] The haze of the optical film was measured in accordance with JIS 7136:2000 using a haze meter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. In addition, the optical film was placed in a glass cuvette for liquid measurement, and distilled water was brought into contact with both faces of the optical film, and the internal haze of the optical film was measured.

[0151] (Glass transition temperature)

[0152] The glass transition temperature of the acrylic resin or the acrylic resin film was measured using 10 mg of the acrylic resin or the acrylic resin composition. Specifically, using a differential scanning calorimeter (DSC7000X manufactured by Hitachi High-Tech Science Corporation), the temperature was increased at a rate of 20°C / min under a nitrogen atmosphere, and the glass transition temperature was determined by the midpoint method.

[0153] (Rate of change in size)

[0154] A hole was punched in the film using a punch having a diameter of 1 mm at a position 20 mm from the inside of the diagonal line in the diagonal direction of the film cut out from the optical film using a cutter to have a size of 90 mm x 90 mm, and the hole interval was measured using a three-dimensional measuring device (MF201 manufactured by Mitutoyo Corporation). Subsequently, the film on which the hole interval was measured was left to stand in an environmental test machine (LH-20 manufactured by Nagano Science Corporation) set to 85°C, 85% RH for 120 hours, and the hole interval was measured again. The rate of change in size was calculated from the hole interval before and after the standing under the atmosphere of 85°C, 85% RH by Formula (A).

[0155] (Refractive index of acrylic resin composition and acrylic crosslinked particles)

[0156] First, the refractive index of the acrylic resin composition was calculated as follows according to JIS K7142:2014. Specifically, the acrylic resin composition was melt-pressed at 240°C to produce a film having a thickness of 100 μm, and the refractive index (wavelength 589 nm) of the obtained film was measured at 23°C using a refractometer (DR-M2 manufactured by Atago Corporation). The obtained refractive index was taken as the refractive index of the acrylic resin composition.

[0157] Subsequently, using a high-refractive liquid of halogen series and a low-refractive liquid such as methanol, the refractive index of the acrylic crosslinked particles was calculated using a mixed liquid having a changed ratio by the following method. Here, when the acrylic crosslinked particles are dispersed in the mixed liquid, the dispersion liquid becomes turbid when the refractive index of the mixed liquid and the acrylic crosslinked particles is different, and the liquid becomes transparent when the refractive index of the mixed liquid and the acrylic crosslinked particles is the same. Therefore, the refractive index of the mixed liquid when it becomes a transparent liquid was taken as the refractive index of the acrylic crosslinked particles.

[0158] <Manufacture of acrylic resin>

[0159] (Manufacture Example of Acrylic Resin 1)

[0160] An extruder used was a 40 mm diameter intermeshing co-rotating twin screw extruder (L / D = 90). The set temperature of each temperature control zone of the extruder was set to 250 to 280°C, and the screw rotation speed was set to 85 rpm. After the methyl methacrylate resin was melted and filled with a kneading block, 1.8 parts by weight of monomethylamine (manufactured by Mitsubishi Gas Chemical Company, Inc.) per 100 parts by weight of the above methyl methacrylate resin was injected from a nozzle. The resin coming out from a die provided at the outlet of the extruder in the form of a strand was cooled in a water tank and then pelletized with a pelletizer, thereby obtaining the resin (I). Subsequently, using a 40 mm diameter intermeshing co-rotating twin screw extruder, the set temperature of each temperature control zone of the extruder was set to 240 to 260°C. Reduction of carboxyl groups in the resin was performed by injecting 0.56 parts by weight of dimethyl carbonate per 100 parts by weight of the above methyl methacrylate resin from a nozzle. The byproduct and excess dimethyl carbonate after the reaction were removed. The resin coming out from a die provided at the outlet of the extruder in the form of a strand was cooled in a water tank and then pelletized with a pelletizer, thereby obtaining an acrylic resin 1 having a glutarimide ring. The glass transition temperature of this acrylic resin 1 was 123°C, Mw was 8.1 x 104, and Mw / Mn was 1.59.

[0161] (Calculation of the content of the ring structure)

[0162] Use 1 H-NMR BRUKER Avance III (400 MHz) was used to measure the obtained acrylic resin. The content of the ring structure was calculated by weight conversion from the molar ratio of the ring structure part to the part other than the ring structure part. Specifically, in the case of glutarimide, the content of the ring structure was calculated by weight conversion from the molar ratio using the area A of the peak of the O-CH3 proton derived from methyl methacrylate near 3.5 to 3.8 ppm and the area B of the peak of the N-CH3 proton derived from glutarimide near 3.0 to 3.3 ppm. As a result, the content of the ring structure was 6% by weight.

[0163] (Example 1)

[0164] A mixture containing the acrylic resin 1 manufactured in the above acrylic resin manufacturing example and 0.1% by weight of acrylic crosslinking particles (manufactured by Soken Chemical Co., Ltd., MX80H3wT, refractive index 1.49) having an average particle diameter of 0.8 μm as an antiblocking agent (AB agent) was kneaded with a 15 mm diameter intermeshing co-rotating twin screw extruder (L / D = 45). The resin coming out from a die provided at the outlet of the extruder in the form of a strand was cooled in a water tank and then pelletized with a pelletizer, thereby obtaining an acrylic resin composition (refractive index 1.49).

[0165] After drying the obtained acrylic resin composition at 100°C for 5 hours, a film was produced using a 15 mm diameter intermeshing co-rotating twin-screw extruder (L / D = 45) having a T-die at the outlet of the extruder, with a contact roll nip. The sheet-like molten resin extruded from the T-die provided at the outlet of the extruder was cooled with a cooling roll to obtain a raw material film having a width of 160 mm and a thickness of 160 μm. The glass transition temperature of the raw material film was measured according to the above method, and the result was 123°C. At this time, the surface in contact with the casting roll was defined as the B surface, and the other surface was defined as the A surface.

[0166] Next, an optical film was obtained by performing the easy-adhesion coating shown below on the B surface of the raw material film (acrylic resin film).

[0167] (Formation of easy-adhesion layer)

[0168] One surface of the raw material film was subjected to a corona discharge treatment (corona discharge electron irradiation amount: 100 W / m 2 / min). With respect to 100 g of a water-based polyurethane resin having a carboxyl group (Daiichi Kogyo Seiyaku Co., Ltd., trade name: SUPERFLEX 210, solid content: 33%), 20 g of a crosslinking agent (Nippon Shokubai Co., Ltd., trade name: EPOCROS WS700, solid content: 25%), and 15 g of colloidal silica (Fuso Chemical Co., Ltd., trade name: PL-3, solid content: 20%) were added, and the mixture was stirred for 3 minutes to obtain an easy-adhesion agent composition. The obtained easy-adhesion agent composition was applied to the corona discharge treated surface of the raw material film subjected to the corona discharge treatment using a bar coater (No. #6). The raw material film on which the easy-adhesion agent was applied was placed in a hot air drier (80°C) to dry the urethane composition for about 1 minute to obtain an easy-adhesion treated film on which an easy-adhesion layer was formed.

[0169] A biaxial stretching device (IMC-1905) manufactured by Inoue Mfg. Co., Ltd. was used to simultaneously biaxially stretch the obtained easy-adhesion treated film at a stretching ratio of 2 times (vertical and horizontal) at 145°C to produce a stretched film (optical film).

[0170] (Blocking test)

[0171] Ten test pieces (optical films) each having a size of 100 mm x 100 mm were overlapped, and a pressure of 1 kg was applied from above, and the overlapped test pieces were left to stand at 60°C for 2 hours. Then, the overlapped test pieces were naturally cooled at 23°C for 1 hour, and the state of the optical films was visually confirmed, and the optical films were peeled by hand, and the results were evaluated according to the following criteria.

[0172] 1: The films were firmly fixed to each other, and a peeling trace was produced on the films when peeled.

[0173] 2: The films are fixed to each other, and no peeling marks are generated on the films at the time of peeling.

[0174] 3: The fixing of the films to each other is not visible.

[0175] The evaluation results of Rku, Rzjis, the static friction coefficient, the haze, the internal haze, the glass transition temperature, the dimensional change rate, and the blocking test are shown in Table 1.

[0176] (Example 2)

[0177] An optical film was obtained in the same manner as in Example 1, except that an acrylic resin composition (refractive index 1.49) to which 0.2% by weight of the AB agent was added was used.

[0178] (Example 3)

[0179] An optical film was obtained in the same manner as in Example 1, except that an acrylic resin composition (refractive index 1.49) to which 0.5% by weight of the AB agent was added was used.

[0180] (Comparative Example 1)

[0181] An optical film was obtained in the same manner as in Example 1, except that no AB agent was added.

[0182] (Comparative Example 2)

[0183] An optical film was obtained in the same manner as in Example 1, except that an acrylic resin composition (refractive index 1.49) to which 1% by weight of the AB agent was added was used.

[0184] (Comparative Example 3)

[0185] An optical film was obtained in the same manner as in Example 1, except that PARAPET HM (Kuraray Co., Ltd., refractive index 1.49, Tg 118°C, Mw = 7.8 million, Mw / Mn = 1.72) which is a PMMA resin not containing a ring structure was used as the acrylic resin 3 instead of the acrylic resin 1.

[0186] [Table 1]

[0187]

[0188] As is apparent from Table 1, the optical films of Examples 1 to 3 are excellent in transparency and heat resistance, and can prevent blocking at the time of roll storage of the films. In contrast, the sum of the kurtosis Rku of both surfaces of the optical film of Comparative Example 1 is 6.4, and thus blocking at the time of roll storage of the films cannot be prevented. In addition, the sum of the kurtosis Rku of both surfaces of the optical film of Comparative Example 2 is 53.2, and thus the transparency is reduced. Furthermore, the glass transition temperature of the optical film of Comparative Example 3 is 118°C, and thus the heat resistance is reduced.

[0189] <Manufacture of acrylic resin>

[0190] (Production Example of Acrylic Resin 2)

[0191] A 4L glass reactor equipped with a stirrer having H-type stirring wings was charged with 150 parts by weight of deionized water, 0.20 parts by weight of tricalcium phosphate as a dispersant, 0.0075 parts by weight of sodium α-olefin sulfonate, and 0.30 parts by weight of sodium chloride. Subsequently, under a nitrogen atmosphere, while stirring at 250 rpm, 100 parts by weight of methyl methacrylate (MMA), 0.289 parts by weight of n-octyl mercaptan as a chain transfer agent, and 0.065 parts by weight of 2,2'-azobis(isobutyric acid) dimethyl ester (manufactured by FUJIFILM Wako Pure Chemical Corporation, V-601) as a polymerization initiator were added to the reactor. Subsequently, the liquid temperature in the reactor was raised to 70°C to initiate polymerization, and after 2 hours of initiation of polymerization, 0.10 parts by weight of tricalcium phosphate was added to the reactor. At this time, 4 hours and 20 minutes after the initiation of polymerization, an exothermic peak accompanied by a gel effect was observed. Subsequently, 7 hours after the initiation of polymerization, heating was started, and the liquid temperature in the reactor was raised to 95°C. Note that the conversion rate after 7 hours of initiation of polymerization was 93%. Subsequently, 2 hours after the liquid temperature in the reactor reached 95°C, the liquid temperature in the reactor was cooled to room temperature, the polymerization was ended, and an acrylic resin dispersion liquid was obtained. Note that the conversion rate at the end of polymerization was 99%.

[0192] The acrylic resin dispersion liquid was subjected to acid washing using 0.1 times the amount of 1N hydrochloric acid by weight ratio with respect to the weight of the monomers charged, and then was subjected to water washing, whereby the dispersant was removed. Subsequently, the washed acrylic resin dispersion liquid was dehydrated and then was dried, whereby a beaded acrylic resin 2 was obtained. The glass transition temperature of the acrylic resin 2 was 120°C, the triad representation syndiotacticity was 57%, the Mw was 83,000, the Mw / Mn was 1.63, and the content of the structural unit derived from methyl methacrylate was 100% by weight.

[0193] (Conversion rate)

[0194] The conversion rate was calculated by the weight method using the proportion of the solid content weight of the acrylic resin dried in an oven heated to 150°C for 30 min with respect to the weight of the monomers charged, i.e., the formula

[0195] (Solid content weight of acrylic resin) x 100 / (weight of monomers charged)

[0196] The conversion rate was calculated.

[0197] (Triad representation syndiotacticity)

[0198] The H-NMR spectrum of the acrylic resin was measured using a nuclear magnetic resonance device (manufactured by Bruker, AVANCE III 400MHz) in a deuterated chloroform solution at 22°C for a cumulative number of 16 times. 1 H-NMR spectrum. Next, the area (X) of the region of 0.60 to 0.95 ppm and the area (Y) of the region of 0.60 to 1.25 ppm were measured when tetramethylsilane (TMS) was set to 0 ppm, and then the syndiotacticity represented by the formula

[0199] (X / Y) x 100

[0200] The meso-tacticity represented by the triad was calculated.

[0201] (weight average molecular weight, number average molecular weight, and dispersity)

[0202] The weight average molecular weight (Mw), the number average molecular weight (Mn), and the dispersity (Mw / Mn) of the acrylic resin were calculated using gel permeation chromatography (GPC). At this time, a sample solution prepared by dissolving 20 mg of the acrylic resin in 10 mL of tetrahydrofuran was subjected to analysis under the following conditions.

[0203] Measurement machine: HLC-8420GPC (manufactured by Tosoh Corporation)

[0204] Detector: RI detector

[0205] Eluent: Tetrahydrofuran

[0206] Guard column: TSKgel guard column Super H-L (manufactured by Tosoh Corporation)

[0207] Analysis column: TSKgel Super H5000, Super H4000, Super H3000, Super H2000 (manufactured by Tosoh Corporation) (in series)

[0208] Eluent flow rate: 0.60 mL / min

[0209] Measurement temperature: 40°C

[0210] Standard substance: Standard polystyrene (manufactured by Tosoh Corporation)

[0211] (Example 4)

[0212] An original material film was obtained in the same manner as in Example 1, except that the acrylic resin 2 was used instead of the acrylic resin 1. The glass transition temperature of the original material film was measured, and the result was 121°C.

[0213] Next, the following easy-adhesion coating was performed on the B surface of the base film (acrylic resin film) to obtain an optical film.

[0214] (Formation of Easy Adhesion Layer)

[0215] One side of the original film was subjected to corona discharge treatment (corona discharge electron irradiation dose 100 W / m 2 / min). 0.6 g of a crosslinking agent (manufactured by Nippon Shokubai Co., Ltd., trade name: EPOCROS WS700, solid content: 25%) and 18.9 g of deionized water were added to 3 g of a water-based polyurethane resin having a carboxyl group (Daiichi Kogyo Seiyaku Co., Ltd., trade name: SUPERFLEX 210, solid content: 33%), and the mixture was stirred for 3 minutes to obtain an easy-adhesion agent composition. The obtained easy-adhesion agent composition was applied to the corona discharge treated surface of the original film subjected to corona discharge treatment using a rod coater (No. #6). The original film coated with the easy-adhesion agent was placed in a hot air dryer (80°C) to dry the urethane composition for about 1 minute to obtain an easy-adhesion treated film having an easy-adhesion layer formed thereon.

[0216] The obtained adhesion-improving treated film was simultaneously biaxially stretched at 135° C. using a biaxial stretching apparatus (IMC-1905) manufactured by Imoto Seisakusho Co., Ltd. at a stretching ratio of 2 (vertical and transverse) to produce a stretched film (optical film).

[0217] Table 2 shows Rku, Rzjis, static friction coefficient, haze, internal haze, glass transition temperature, dimensional change rate, and blocking test evaluation results.

[0218] (Example 5)

[0219] An optical film was obtained in the same manner as in Example 4, except that 0.12 wt% of acrylic crosslinked particles having an average particle size of 1.2 μm (J-3PY manufactured by Negami Industry Co., Ltd., refractive index 1.50) were used instead of 0.1 wt% of acrylic crosslinked particles having an average particle size of 0.8 μm. The glass transition temperature of the original film was measured and found to be 120°C.

[0220] (Example 6)

[0221] An optical film was obtained in the same manner as in Example 4, except that 0.12 wt% of acrylic crosslinked particles having an average particle size of 2.2 μm (J-4PY manufactured by Negami Industry Co., Ltd., refractive index 1.50) were used instead of 0.1 wt% of acrylic crosslinked particles having an average particle size of 0.8 μm. The glass transition temperature of the original film was measured and found to be 120°C.

[0222] (Comparative Example 4)

[0223] An optical film was obtained in the same manner as in Example 4 except that the AB agent was not added. The glass transition temperature of the raw material film was measured, and the result was 120°C.

[0224] [Table 2]

[0225]

[0226] As is apparent from Table 2, the optical films of Examples 4 to 6 are excellent in transparency and heat resistance, and can prevent blocking during storage of the film roll. In contrast, the sum of the kurtosis Rku of both sides of the optical film of Comparative Example 4 is 7.1, and thus blocking during storage of the film roll cannot be prevented.

Claims

1. An optical film comprising an acrylic resin film containing an acrylic resin as a main component, and an easy-adhesion layer formed on the acrylic resin film, The glass transition temperature of the acrylic resin film is 120° C. or higher. The sum of kurtosis Rku of both surfaces of the optical film is 10 or more and 50 or less, and the internal haze is 1.0% or less.

2. The optical film according to claim 1, wherein The static friction coefficient between one surface and the other surface of the optical film is 0.8 or less.

3. The optical film according to claim 1 or 2, wherein: The sum of 10-point average roughness Rzjis of both surfaces of the optical film is 0.05 μm or more and 1.0 μm or less.

4. The optical film according to claim 1 or 2, wherein The acrylic resin contains at least one ring structure selected from the group consisting of a lactone ring structure, a glutarimide structure, a glutaric anhydride structure, an N-substituted maleimide structure, and a maleic anhydride structure.

5. The acrylic resin film according to claim 1 or 2, wherein The syndiotacticity expressed by triads of the acrylic resin is 54% or more.

6. The optical film according to claim 1 or 2, wherein: The acrylic resin film contains an anti-blocking agent, The anti-blocking agent includes acrylic cross-linked particles having an average particle size of 0.1 μm or more and 2.5 μm or less.

7. The optical film according to claim 6, wherein The anti-blocking agent includes acrylic cross-linked particles having an average particle size of 0.1 μm or more and 2.0 μm or less.

8. The optical film according to claim 6, wherein The acrylic resin film contains 0.05 wt % or more and 0.9 wt % or less of the acrylic crosslinked particles. 9 . The optical film according to claim 1 , wherein the dimensional change rate thereof when left to stand in an atmosphere of 85° C. and 85% RH for 120 hours is −2.0% or more and −0.1% or less. 10 . A polarizing plate comprising the optical film according to claim 1 . A liquid crystal display panel comprising the polarizing plate according to claim 10 .

Images