Acrylic resin film, polarizing plate, liquid crystal display panel and resin composition

Abstract

Provided is an acrylic resin film that is excellent in heat resistance and transparency and can suppress blocking during film roll storage. The acrylic resin film is composed primarily of an acrylic resin and contains an aromatic vinyl unit. The acrylic resin film has a glass transition temperature of 120°C or higher, a sum of the kurtosis Rku values ​​on both sides of the film of 10 to 50, and an internal haze of 1.0% or lower.

Description

[Technical Field]

[0001] The present invention relates to an acrylic resin film, a polarizing plate, a liquid crystal display panel, and a resin composition. [Background technology]

[0002] In a liquid crystal display device, two polarizing plates are usually placed on both sides of a liquid crystal cell. A polarizing plate generally has a polarizer protective film attached to both sides of the polarizer with an adhesive to protect the polarizer. High transparency is required for the polarizer protective film, and optical films made of cellulose-based materials are often used.

[0003] It has been proposed to use optical films made of acrylic resins or norbornene resins as polarizer protective films for the purpose of improving durability, etc. However, these optical films are prone to wrinkles and creases due to contact between films when wound into a roll, and as a method for solving this problem, a method has been proposed in which fine particles such as silica particles are added to a norbornene resin film to ensure roll winding properties (slipperiness) (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 074513 Summary of the Invention [Problem to be solved by the invention]

[0005] Although the method described in Patent Document 1 can solve the problem of wrinkles and wrinkle marks occurring during winding, the inventors' investigations have revealed that, as film quality levels improve due to the increasing resolution and area of ​​liquid crystal display panels, defects occur due to tight winding of the film during storage in the form of a film roll. Furthermore, the inventors attempted to solve the above-mentioned phenomenon by adding silica to an acrylic resin film using the method described in Patent Document 1, but found that the conventional method resulted in high haze and other problems that made it difficult to meet the requirements for an optical film.

[0006] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an acrylic resin film that has excellent heat resistance and transparency and is capable of suppressing blocking during film roll storage. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems and have completed the present invention.

[0008] That is, one aspect of the present invention relates to the following.

[0009] [1] An acrylic resin film whose main component is an acrylic resin and contains aromatic vinyl units, wherein the glass transition temperature is 120°C or higher, the sum of the kurtosis Rku on both sides is 10 or more and 50 or less, and the internal haze is 1.0% or less.

[0010] [2] The acrylic resin film according to [1], wherein the sum of the ten-point average roughness Rzjis of both surfaces is 0.05 μm or more and 1.0 μm or less.

[0011] [3] The acrylic resin film according to [1] or [2], wherein the coefficient of static friction between one surface and the other surface is 0.8 or less.

[0012] [4] An acrylic resin film whose main component is acrylic resin and contains aromatic vinyl units, having a glass transition temperature of 120°C or higher, a sum of the 10-point average roughness Rzjis of both surfaces of 0.05 μm or more and 1.0 μm or less, a static friction coefficient between one surface and the other surface of 0.8 or less, and an internal haze of 1.0% or less.

[0013] [5] The acrylic resin film according to any one of [1] to [4], wherein the acrylic resin has a ring structure in the main chain.

[0014] [6] The acrylic resin film according to any one of [1] to [5], wherein the content of the aromatic vinyl unit is more than 0% by weight and 25% by weight or less.

[0015] [7] The acrylic resin film according to any one of [1] to [6], further comprising an antiblocking agent, wherein the antiblocking agent comprises acrylic crosslinked particles having an average particle size of 0.5 μm or more and 2.5 μm or less.

[0016] [8] The acrylic resin film according to [5] or [6], wherein the content of the acrylic crosslinked particles is 0.05% by weight or more and 0.9% by weight or less.

[0017] [9] The acrylic resin film according to any one of [1] to [8], which has a dimensional change rate of −2.0% or more and −0.1% or less when left standing in an atmosphere of 85° C. and 85% RH for 120 hours.

[0018]

[10] The acrylic resin film according to any one of [1] to [9], which is a polarizer protective film.

[0019]

[11] A polarizing plate comprising the acrylic resin film according to

[10] .

[0020]

[12] A liquid crystal display panel comprising the polarizing plate according to

[11] .

[0021]

[13] An acrylic resin composition containing an acrylic resin as a main component and containing aromatic vinyl units, further containing an antiblocking agent, wherein the antiblocking agent is acrylic crosslinked particles having an average particle size of 0.5 μm or more and 2.5 μm or less, the content of the acrylic crosslinked particles being 0.05 wt % or more and 0.9 wt % or less, and the content of the aromatic vinyl units being more than 0 wt % and 25 wt % or less.

[0022]

[14] The acrylic resin composition according to

[13] , which contains a methyl methacrylate-styrene copolymer.

[0023]

[15] The acrylic resin composition according to

[13] or

[14] , which is in the form of pellets. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide an acrylic resin film that is excellent in transparency and heat resistance and is capable of suppressing blocking during storage of a film roll. DETAILED DESCRIPTION OF THE INVENTION

[0025] Although the following describes embodiments for carrying out the present invention, the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments and examples obtained by appropriately combining the technical means disclosed in different embodiments and examples. All academic literature and patent documents described in this specification are incorporated herein by reference. Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and greater than A)" or "B or less (including B and less than B)."

[0026] (acrylic resin film) One aspect of the acrylic resin film of this embodiment is an acrylic resin film primarily composed of an acrylic resin and containing aromatic vinyl units, characterized by a glass transition temperature of 120°C or higher, a sum of the kurtosis Rku values ​​on both sides of the film of 10 to 50, and an internal haze of 1.0% or less. Thus, by controlling the sum of the kurtosis values ​​on both sides of the film to a predetermined value and further controlling the internal haze to a predetermined value while containing an acrylic resin as the primary component and containing aromatic vinyl units, an acrylic resin film can be obtained that exhibits excellent heat resistance and transparency, as well as excellent anti-blocking properties during film roll storage. The sum of the 10-point average roughness Rzjis values ​​on both sides of the acrylic resin film may be 0.14 μm to 1.0 μm, and the static friction coefficient between one side and the other side may be 0.8 or less.

[0027] Another aspect of the acrylic resin film of this embodiment is an acrylic resin film that contains an acrylic resin as a main component and an aromatic vinyl unit, and is characterized by having a glass transition temperature of 120°C or higher, a sum of the ten-point average roughness Rzjis of each of the two surfaces of 0.05 μm to 1.0 μm, a static friction coefficient between one surface and the other of 0.8 or lower, and an internal haze of 1.0% or lower. Thus, by controlling the sum of the Rzjis of each surface of the film and the static friction coefficient to predetermined values ​​and further controlling the internal haze to a predetermined value while containing an acrylic resin as a main component and containing an aromatic vinyl unit, an acrylic resin film that is excellent in heat resistance and transparency and also in anti-blocking properties during film roll storage can be obtained.

[0028] The glass transition temperature of the acrylic resin film of this embodiment is 120°C or higher. It is preferably higher than 120°C, more preferably 121°C or higher, even more preferably 122°C or higher, and particularly preferably 123°C or higher. When the acrylic resin film has a glass transition temperature of 120°C or higher, the dimensional change rate of the stretched film when the film is placed in a high-temperature environment is reduced. In practical use, the acrylic resin film of this embodiment is often laminated with other films, and a small dimensional change rate can suppress the occurrence of distortion and warping caused by the difference in dimensional change rate between the film and the laminated film.

[0029] The glass transition temperature of the acrylic resin constituting the acrylic resin film is preferably 120°C or higher, more preferably over 120°C, even more preferably 121°C or higher, even more preferably 122°C or higher, and particularly preferably 123°C or higher.

[0030] 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 suitably used. For example, the ring structure can be at least one selected from the group consisting of a glutarimide ring, a lactone ring, maleic anhydride, maleimide, and glutaric anhydride. These ring structures can impart heat resistance. Among these, a glutarimide ring is particularly preferred in terms of ease of production, cost, and quality stability against moisture.

[0031] The content of the structural unit containing a ring structure in the acrylic resin having a glass transition temperature of 120°C or higher is preferably in the range of 2% by weight to 80% by weight, more preferably in the range of 3% by weight to 60% by weight. When the content of the structural unit containing a ring structure is within this range, both the glass transition temperature and the thickness direction retardation Rth are favorable, which is preferable. The content of the structural unit containing a ring structure in the acrylic resin is 1The molar ratio of the structural unit containing the target ring structure to the other structural units can be measured using H-NMR, and the molar ratio can be calculated by converting the molar ratio into weight. Furthermore, an acrylic resin having a glass transition temperature of 120°C or higher is the main component of the acrylic resin film, and is contained in an amount of more than 50% by weight of 100% by weight of the acrylic resin film. Of these, 70% by weight or more is preferred, 80% by weight or more is more preferred, 85% by weight or more is even more preferred, and 90% by weight or more is particularly preferred.

[0032] The acrylic resin having a glass transition temperature of 120° C. or higher may be an acrylic resin that does not have a ring structure in the main chain.

[0033] The internal haze of the acrylic resin film of this embodiment is 1.0% or less. In particular, the internal haze is preferably 0.7% or less, more preferably 0.5% or less, and particularly preferably 0.3% or less. By having an internal haze of 1.0% or less, the quality when mounted on a liquid crystal panel is good.

[0034] In this specification, the internal haze is defined as the haze value measured using a haze meter (turbidity meter) on a glass cell for measuring liquid, with the obtained film placed in the cell and the surrounding area filled with pure water.

[0035] The haze of the acrylic resin film of the present embodiment is not particularly limited as long as the internal haze is within the above-mentioned range. However, from the viewpoint of transparency, the haze is preferably 3.0% or less, more preferably 2.0% or less, and even more preferably 1.0% or less.

[0036] In one aspect of the acrylic resin film of this embodiment, by setting the sum of the kurtosis Rku values ​​on both sides to 10 or more and 50 or less, blocking during film roll storage can be effectively suppressed. This can suppress defects that may occur in the film. Here, in an acrylic resin film, setting the sum of the kurtosis Rku values ​​on both sides to 10 or more can suppress blocking due to tight winding during film roll storage, thereby suppressing film defects. This tendency is more pronounced when storing long film rolls (e.g., 8000 m). This allows acrylic resin films of lengths other than standard lengths (e.g., 4000 m) to be wound, improving yield. Furthermore, even in the case of standard-length acrylic resin films, the inner acrylic resin film is less likely to undergo plastic deformation during film roll storage, making the acrylic resin film easier to use. On the other hand, setting the sum of the kurtosis Rku values ​​on both sides of an acrylic resin film to 50 or less can suppress a decrease in the transparency of the acrylic resin film. It is more preferable that the sum of the kurtosis Rku values ​​on both sides of an acrylic resin film be 15 or more and 30 or less. When the sum of the kurtosis on both sides is 10 or more, friction between the films is easily reduced. Furthermore, when the films are stacked in a roll, air trapped between the films is easily released, suppressing blocking caused by tight winding and presumably reducing film defects. Furthermore, when the sum of the kurtosis on both sides is 50 or less, diffuse reflection of light on the film surface can be suppressed, preventing a decrease in the clarity of the panel display.

[0037] Here, "blocking" refers to a state in which films are stuck together, including a state in which they are partially melted at high temperatures and a state in which they are completely overlapped. When tight winding occurs, pressure is applied to the film, causing blocking (sticking) between the films. As a result, when the films are peeled off, a strong force is required, causing damage to the film. Therefore, by setting the kurtosis on both sides of the film within a predetermined range as in this embodiment, even if tight winding occurs, it is possible to prevent the films from sticking together in the film roll, and the films can be peeled off with a weak force, thereby preventing damage to the film (film defects).

[0038] Here, kurtosis Rku can be calculated from a roughness curve in accordance with JIS B 0601. Kurtosis Rku represents the sharpness in the height direction, where Rku=3 means that the height distribution is normal, Rku>3 means that the surface has many sharp peaks and valleys, and Rku<3 means that the surface is flat.

[0039] In another aspect of the acrylic resin film of this embodiment, the sum of the ten-point average roughnesses Rzjis on both sides is 0.05 μm or more and 1.0 μm or less. When the sum of the ten-point average roughnesses Rzjis on both sides is 0.05 μm or more, friction between the films is easily reduced. Furthermore, when the films are stacked in a roll, air trapped between the films is easily released, suppressing blocking due to tight winding and presumably reducing film defects. Here, when the sum of the ten-point average roughnesses Rzjis on both sides of the acrylic resin film is 0.05 μm or more, blocking due to tight winding during film roll storage can be suppressed, thereby suppressing film defects. This tendency becomes more pronounced when long film rolls (e.g., 8000 m) are stored. As a result, only a fixed length (e.g., 4000 m) of acrylic resin film can be wound, resulting in reduced yield. Furthermore, even with standard-length acrylic resin films, the inner acrylic resin film undergoes plastic deformation during film roll storage, making the plastically deformed acrylic resin film unusable. On the other hand, if the sum of the 10-point average roughness Rzjis of both surfaces of the acrylic resin film is 1.0 μm or less, the deterioration of the transparency of the acrylic resin film can be suppressed. Furthermore, if the sum of the 10-point average roughness Rzjis of both surfaces is 1.0 μm or less, diffuse reflection of light on the film surface can be suppressed, thereby suppressing the deterioration of the clarity of the panel display.

[0040] In particular, the sum of the ten-point average roughnesses Rzjis of both surfaces of the acrylic resin film is preferably 0.05 μm or more and 1.0 μm or less, more preferably 0.05 μm or more and 0.6 μm or less, even more preferably 0.06 μm or more and less than 0.50 μm, even more preferably 0.06 μm or more and 0.40 μm or less, and particularly preferably 0.07 μm or more and 0.30 μm or less. Furthermore, the ten-point average roughness Rzjis of one surface and / or the other surface of the acrylic resin film is preferably more than 0.020 μm and 0.20 μm or less.

[0041] The kurtosis Rku and Rzjis of a film can be measured using an optical surface roughness tester such as a laser microscope. The acrylic resin film of this embodiment has a surface roughness value that is smaller than the resolution of the laser microscope, so sufficient measurement accuracy cannot be achieved with a lens with a small numerical aperture. Therefore, in this specification, values ​​measured using a lens with a numerical aperture of 0.95 or more are used.

[0042] From the viewpoints of economy and environmental load, it is preferable to add an antiblocking agent to the acrylic resin to improve the surface roughness of the film. Among these, organic fine particles are preferred from the viewpoints of affinity with the acrylic resin and dispersibility, and crosslinked acrylic particles are most preferred because they allow for easy control of haze.

[0043] The coefficient of static friction between one side and the other side of the acrylic resin film 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. If the coefficient of static friction is 0.8 or less, blocking between films during film roll storage can be effectively suppressed. There is no particular lower limit for the coefficient of static friction, but from the viewpoint of winding slippage and meandering during production, a value of 0.2 or more is preferred.

[0044] The content of aromatic vinyl units in the acrylic resin film of this embodiment is preferably more than 0 wt% and not more than 25 wt%, more preferably from 0.5 wt% to 20 wt%. When the content of aromatic vinyl units in the acrylic resin film of this embodiment is more than 0 wt% and not more than 25 wt%, the transparency of the acrylic resin film of this embodiment is high.

[0045] The acrylic resin film preferably has a dimensional change rate, when left standing for 120 hours in an atmosphere of 85°C and 85% RH, of -2.0% or more, more preferably -1.7% or more, and even more preferably -1.5% or more, as an average value in the film's longitudinal direction (MD direction) and transverse direction (TD direction). A dimensional change rate of -2.0% or more suppresses shrinkage over time during film roll storage, improving the stability of the wound appearance over time. Furthermore, warping and dimensional change upon attachment to a polarizer are alleviated, thereby suppressing contrast reduction and peripheral unevenness in liquid crystal display devices. The dimensional change rate may be, for example, -0.1% or less. A dimensional change rate of -0.1% or less allows the acrylic resin film to easily follow the shrinkage of the polarizer itself when attached to the polarizer. The dimensional change rate when left standing in an atmosphere of 85°C and 85% RH for 120 hours can be measured using a three-dimensional measuring device by leaving the acrylic resin film standing in an environmental tester set to 85°C and 85% RH for 120 hours and measuring the dimensional change before and after.

[0046] In this specification and claims, the dimensional change rate refers to the rate of change in the hole spacing before and after opening 1 mm diameter holes at positions 20 mm inward from the four corners of a 90 mm x 90 mm film and leaving the film standing for 120 hours in an atmosphere of 85°C and 85% RH. Here, the rate of change in the hole spacing refers to the rate of change in the hole spacing after leaving the film standing, based on the hole spacing before leaving the film standing, and is calculated by the formula [(Hole spacing after standing) - (Hole spacing before standing)] × 100 / (Hole spacing before standing) (A) It is calculated as follows.

[0047] The linear expansion coefficient of the acrylic resin film at 40 to 60°C is preferably 80 ppm or less, and more preferably 72 ppm or less. If it is 80 ppm or less, shrinkage and expansion of the film due to temperature changes during storage and transportation of the film roll are suppressed, and tight winding is less likely to occur. On the other hand, the lower limit is preferably 40 ppm or more. If the linear expansion of the film is 40 ppm or more, when laminated with a polarizer, the difference in linear expansion from other components is small, and warping is less likely to occur.

[0048] The linear expansion coefficient can be measured using, for example, a thermomechanical analyzer, TMA-4000SA, manufactured by Bruker AXS. Specifically, in a nitrogen atmosphere, a 4 mm x 20 mm piece of film is cut and heated at a rate of 2°C / min within a temperature range not exceeding the glass transition temperature under a tensile load of 3.1 g. A chart is then created with temperature plotted on the X axis and the change in film length plotted on the Y axis. The slope of the temperature increase / decrease process over the temperature range from 40°C to 60°C is calculated using the least squares method to determine the linear expansion coefficient.

[0049] (Anti-blocking agent) The acrylic resin film is preferably formed from an acrylic resin composition in which an antiblocking agent is added to an acrylic resin. The antiblocking agent is preferably an acrylic crosslinked particle from the viewpoints of compatibility with the acrylic resin, dispersibility, and transparency. Any particle shape can be selected, but spherical particles are preferred because they are more likely to exhibit antiblocking properties.

[0050] The refractive index of the antiblocking agent is preferably 98% to 102% and more preferably 99% to 101% when the refractive index of the acrylic resin is taken as 100%. The refractive index of the antiblocking agent is preferably 1.47 to 1.55, more preferably 1.47 to 1.53, and even more preferably 1.48 to 1.52. By using an antiblocking agent with a refractive index within this range, a highly transparent acrylic resin film can be obtained. Among these, acrylic crosslinked particles are preferred because they satisfy the above refractive index.

[0051] The polymerizable monomer forming the acrylic crosslinked particles can be selected from any (meth)acrylic acid ester and other monomers copolymerizable with (meth)acrylic acid ester, but preferably contains methyl methacrylate in terms of compatibility with the acrylic resin and refractive index. The content of structural units derived from methyl methacrylate in the acrylic crosslinked particles is preferably 80% by weight or more and 99% by weight or less, more preferably 83% by weight or more and 96% by weight or less. Note that when the content of structural units derived from methyl methacrylate in the acrylic resin is high, the content of structural units derived from methyl methacrylate in the acrylic crosslinked particles is preferably high.

[0052] The acrylic crosslinked particles further contain structural units derived from a polyfunctional monomer containing two or more polymerizable groups in the molecule as a polymerizable monomer. The content of the polyfunctional monomer in the polymerizable monomer can be set arbitrarily, but is preferably 0.5% by weight or more and 30% by weight or less. If the content is less than 0.5% by weight, the heat resistance and dispersibility of the acrylic crosslinked particles are poor. If the content is greater than 30% by weight, particle coalescence and the formation of irregularly shaped particles may occur during the production of the acrylic crosslinked particles.

[0053] The average particle size of the acrylic crosslinked particles is preferably 0.5 μm or more and 2.5 μm or less, and more preferably 0.5 μm or more and 2.0 μm or less. When the average particle size of the acrylic crosslinked particles is 0.5 μm or more, a large amount is not required to exhibit antiblocking properties, resulting in excellent mechanical properties and economical efficiency. On the other hand, when the average particle size of the acrylic crosslinked particles is 2.5 μm or less, the possibility of clogging the polymer filter is reduced. Furthermore, from the viewpoint of the long-term running properties of the polymer filter, it is preferable to use acrylic crosslinked particles with a narrow particle size distribution and a low content of coarse particles.

[0054] The amount of acrylic crosslinked particles added in this 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 even more preferably 0.1% by weight or more and 0.2% by weight or less. When the amount of acrylic crosslinked particles added is 0.05% by weight or more, the blocking suppression effect is enhanced, and when the amount is 0.9% by weight or less, deterioration in economic efficiency can be suppressed and an increase in haze can be suppressed. Furthermore, multiple types of acrylic crosslinked particles with different particle size distributions may be mixed to control slip properties and surface properties. In this case, the amount of acrylic crosslinked particles added is the sum of the amounts of the multiple types of particles added.

[0055] (Easy adhesion layer) The acrylic resin film of the present embodiment may have an easy-adhesion layer on one or both sides thereof. For example, when the film is used as a polarizer protective film, the easy-adhesion layer can reinforce the adhesive between the polarizer protective film and the polarizer when the film is attached to the polarizer via an adhesive. Furthermore, a stretched film having an easy-adhesion layer can be obtained by providing an easy-adhesion layer on an unstretched film and then stretching the film.

[0056] The easy-adhesion layer used in this embodiment can be formed using known techniques described in, for example, JP 2009-193061 A and JP 2010-55062 A. That is, for example, the easy-adhesion layer can be formed from an easy-adhesion composition containing a urethane resin having a carboxyl group and a crosslinking agent. By using a urethane resin, an easy-adhesion layer having excellent adhesion between the polarizer protective film and the polarizer can be obtained. The easy-adhesion composition is preferably aqueous from the viewpoints of workability and environmental protection.

[0057] (acrylic resin) As described above, the acrylic resin film has a glass transition temperature of 120°C or higher, and an acrylic resin having a glass transition temperature of 120°C or higher can be suitably used as the acrylic resin film. 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. Each ring structure will be described below.

[0058] (acrylic resin with glutarimide ring in the main chain) The acrylic resin having a glutarimide ring as a ring structure in the main chain is a resin containing glutarimide units represented by the following general formula (1) and methyl methacrylate units, and can be obtained by heating and melting an acrylic resin having an acrylate unit content of less than 1% by weight, and treating it with an imidizing agent.

[0059] [ka]

[0060] (where R 1 and R 2 each independently represents hydrogen or an alkyl group having 1 to 8 carbon atoms; 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.

[0061] The content of glutarimide rings according to this embodiment is a value that can be measured, for example, by the following method. 1 This is done using H-NMR. The area of ​​the peaks derived from the O-CH3 protons of methyl methacrylate at around 3.5 ppm to 3.8 ppm and the area of ​​the NR of the glutarimide group at around 3.0 ppm to 3.3 ppm are measured. 3 The molar ratio determined from the peak area derived from protons is used to convert the weight.

[0062] In the step of treating with an imidizing agent, other than methyl methacrylate, such as methyl acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, benzyl (meth)acrylate, and cyclohexyl (meth)acrylate may also be used in combination, but when these are used in combination, the acrylic acid ester unit content is preferably less than 1 wt%, more preferably less than 0.5 wt%, and even more preferably less than 0.3 wt%.

[0063] In addition to the above-mentioned monomers, it is also possible to copolymerize nitrile monomers such as acrylonitrile and methacrylonitrile, maleimide monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide, and N-cyclohexylmaleimide, and aromatic vinyl monomers such as styrene.

[0064] The structure of the methyl methacrylate resin is not particularly limited, and may 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.

[0065] The block polymer may be any of AB, ABC, ABA, and other types of block polymers. The core-shell polymer may be composed of only one core layer and one shell layer, or each may be composed of multiple layers.

[0066] The method for producing polymethyl methacrylate is not particularly limited, and known methods such as emulsion polymerization, emulsion-suspension polymerization, suspension polymerization, bulk polymerization, and solution polymerization can be applied. However, when used in the optical field, bulk polymerization and solution polymerization are particularly preferred from the viewpoint of producing fewer impurities. For example, polymethyl methacrylate can be produced in accordance with the methods described in JP-A-56-8404, JP-B-6-86492, JP-B-7-37482, or JP-B-52-32665.

[0067] The method for producing an acrylic resin according to the present embodiment includes a step of heating and melting a methyl methacrylate resin or an acrylic resin copolymerized with a monomer other than the methyl methacrylate monomer, and treating the resin with an imidizing agent (imidization step), thereby producing an acrylic resin having glutarimide.

[0068] The imidizing agent is not particularly limited as long as it can generate a glutarimide ring represented by general formula (1), and examples thereof include those described in WO2005 / 054311. Specific examples include aliphatic hydrocarbon group-containing amines such as ammonia, methylamine, n-propylamine, i-propylamine, n-butylamine, i-butylamine, tert-butylamine, and n-hexylamine; aromatic hydrocarbon group-containing amines such as aniline, benzylamine, toluidine, and trichloroaniline; and alicyclic hydrocarbon-containing amines such as cyclohexylamine. Urea-based compounds that generate the exemplified amines upon heating, such as urea, 1,3-dimethylurea, 1,3-diethylurea, and 1,3-dipropylurea, can also be used. Among these imidizing agents, methylamine, ammonia, and cyclohexylamine are preferred from the standpoint of both cost and physical properties, with methylamine being particularly preferred.

[0069] Methylamine, which is gaseous at room temperature, may be used in a state of being dissolved in an alcohol such as methanol.

[0070] In this imidization step, the ratio of glutarimide units and (meth)acrylic acid ester units in the resulting acrylic resin can be adjusted by adjusting the ratio of the imidization agent added.

[0071] Furthermore, by adjusting the degree of imidization, it is possible to adjust the physical properties of the resulting acrylic resin and the transparency of the stretched film obtained by molding the acrylic resin according to this embodiment.

[0072] The amount of the imidizing agent is preferably 0.5 to 20 parts by weight per 100 parts by weight of the acrylic resin containing methyl methacrylate units. When the amount of the imidizing agent added is within this range, the imidizing agent is unlikely to remain in the resin, and the possibility of causing appearance defects or foaming after molding is extremely low. Furthermore, the content of glutarimide rings in the final resin composition is appropriate, which is preferable because it is less likely to reduce heat resistance and less likely to cause appearance defects after molding.

[0073] In this imidization step, in addition to the imidizing agent, a ring closure promoter (catalyst) may be added as needed.

[0074] The method of heating and melting the resin and treating it with the imidizing agent is not particularly limited, and any conventionally known method can be used. For example, the acrylic resin containing the methyl methacrylate unit can be imidized by a method using an extruder, a batch-type reaction tank (pressure vessel), etc.

[0075] The extruder is not particularly limited. For example, a single-screw extruder, a twin-screw extruder, or a multi-screw extruder can be used. A single extruder may be used, or a plurality of extruders may be connected in series. When a twin-screw extruder is used, examples include a non-intermeshing co-rotating type, an intermeshing co-rotating type, a non-intermeshing counter-rotating type, and an intermeshing counter-rotating type. Among these, an intermeshing co-rotating twin-screw extruder is preferred because it can rotate at high speed and can further promote mixing of the imidizing agent (if a ring-closure accelerator is used, the imidizing agent and the ring-closure accelerator) with the raw material polymer.

[0076] When imidization is carried out in an extruder, for example, a methyl methacrylate resin is charged into a raw material charging port of the extruder, the resin is melted, and the cylinder is filled with the resin. Then, an imidizing agent is injected into the extruder using an addition pump, whereby the imidization reaction can proceed in the extruder.

[0077] In this case, the temperature (resin temperature), time (reaction time) and resin pressure for treatment in the extruder are not particularly limited as long as glutarimidization is possible.

[0078] When an extruder is used, it is also preferable to equip it with a vent hole that can reduce the pressure to below atmospheric pressure in order to remove unreacted imidizing agent and by-products. With such a configuration, it is possible to remove unreacted imidizing agent, by-products such as methanol, and monomers.

[0079] When an acrylic resin containing a glutarimide ring in the main chain is produced using a batch-type reaction tank (pressure vessel), the structure of the batch-type reaction tank (pressure vessel) is not particularly limited. The structure may be such that the acrylic resin containing methyl methacrylate units can be melted by heating and stirred, and an imidizing agent (when a ring-closure accelerator is used, the imidizing agent and the ring-closure accelerator) can be added, but a structure that allows for good stirring efficiency is preferred.

[0080] Specific examples of the imidization method include known methods such as those described in JP-A Nos. 2008-273140 and 2008-274187.

[0081] The method for producing an acrylic resin according to the present embodiment may include, in addition to the imidization step, a step of treating with an esterifying agent, which allows the acid value of the imidized resin obtained in the imidization step to be adjusted to within a desired range.

[0082] The esterifying agent is not particularly limited as long as it can esterify the carboxyl groups remaining in the molecular chain. Examples include dimethyl carbonate, 2,2-dimethoxypropane, dimethyl sulfoxide, triethyl orthoformate, trimethyl orthoacetate, trimethyl orthoformate, diphenyl carbonate, dimethyl sulfate, methyl toluene sulfonate, methyl trifluoromethyl sulfonate, methyl acetate, methanol, ethanol, methyl isocyanate, p-chlorophenyl isocyanate, and dimethylcarbodiimide. Among these, dimethyl carbonate and trimethyl orthoacetate are preferred from the viewpoints of cost and reactivity, and dimethyl carbonate is preferred from the viewpoint of cost.

[0083] In this imidization step, the amount of the esterifying agent is preferably 0 to 30 parts by weight, more preferably 0 to 15 parts by weight, per 100 parts by weight of the acrylic resin containing methyl methacrylate units. If the amount of the esterifying agent falls within this range, the acid value can be adjusted to an appropriate range. On the other hand, if the amount is greater than this range, unreacted esterifying agent may remain in the resin, which may cause foaming or odor generation when the resulting resin is molded.

[0084] In addition to the esterifying agent, a catalyst can also be used. The catalyst is not particularly limited as long as it can promote esterification. 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.

[0085] In this esterification step, it is also possible to carry out only a heat treatment or the like without treatment with an esterifying agent. When only a heat treatment (such as kneading or dispersing the molten resin in an extruder) is carried out, some or all of the carboxyl groups in the acrylic resin having glutarimide rings by-produced in the imidization step can be converted to acid anhydride groups through a dehydration reaction between carboxyl groups or a dealcoholization reaction between carboxyl groups and alkyloxycarbonyl groups. In this case, a ring closure accelerator (catalyst) can also be used.

[0086] Even when the treatment is carried out with an esterifying agent, it is possible to promote the conversion to an acid anhydride group by heat treatment.

[0087] The imide resin that has undergone the imidization step and the esterification step contains unreacted imidization agent, unreacted esterification agent, volatile components by-produced by the reaction, resin decomposition products, etc., so it is possible to install a vent hole that can reduce the pressure to below atmospheric pressure.

[0088] (acrylic resin with lactone ring in the main chain) 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 having a lactone ring structure introduced into the molecular chain), and the method for producing it is also not limited, but preferably it is obtained by polymerizing a polymer (a) having a hydroxyl group and an ester group in the molecular chain (polymerization step), and then heat-treating the obtained polymer (a) to introduce a lactone ring structure into the polymer (lactone cyclization condensation step).

[0089] In the polymerization step, a polymer having a hydroxyl group and an ester group in the molecular chain is obtained by carrying out a polymerization reaction of a monomer component containing an unsaturated monomer represented by the following general formula (2).

[0090] [ka]

[0091] (However, R 4 and R 5 each independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

[0092] Examples of the unsaturated monomer represented by general formula (2) include methyl 2-(hydroxymethyl)acrylate, ethyl 2-(hydroxymethyl)acrylate, isopropyl 2-(hydroxymethyl)acrylate, normal butyl 2-(hydroxymethyl)acrylate, and tertiary butyl 2-(hydroxymethyl)acrylate. Among these, methyl 2-(hydroxymethyl)acrylate and ethyl 2-(hydroxymethyl)acrylate are preferred, and methyl 2-(hydroxymethyl)acrylate is particularly preferred because of its high effect of improving heat resistance. These unsaturated monomers may be used alone or in combination of two or more.

[0093] The content of the unsaturated monomer represented by 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. If the content is less than 5% by weight, the heat resistance, solvent resistance, and surface hardness of the resulting lactone ring-containing polymer may be reduced. If the content is more than 50% by weight, a crosslinking reaction may occur during the formation of the lactone ring structure, making the polymer more susceptible to gelation, resulting in reduced fluidity and making melt molding difficult. Furthermore, unreacted hydroxyl groups may remain, which may further promote condensation during molding, generating volatile substances that may lead to silver streaks, or may increase the thickness direction retardation Rth.

[0094] The monomer component preferably contains another monomer other than the unsaturated monomer represented by general formula (2). The other monomer is not limited as long as it is selected within a range that does not impair the effects of the present invention, but preferred examples include (meth)acrylic acid esters, hydroxyl group-containing monomers, unsaturated carboxylic acids, and unsaturated monomers represented by the following general formula (3). The other monomers may be used alone or in combination of two or more.

[0095] [ka]

[0096] (However, 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 represents a group, an Ac group represents an acetyl group, and R 7 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

[0097] The (meth)acrylic acid ester is not limited as long as it is a (meth)acrylic acid ester other than the unsaturated monomer represented by general formula (2), but 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, and 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.

[0098] When the above (meth)acrylic acid ester is used, the content thereof in the monomer component is preferably 10% by weight to 95% by weight, more preferably 10% by weight to 90% by weight, even more preferably 40% by weight to 90% by weight, and particularly preferably 50% by weight to 90% by weight, in order to fully exert the effects of the present invention.

[0099] (An acrylic resin with maleic anhydride, maleimide, and glutaric anhydride structures in the main chain) In this embodiment, it is also preferable to use an acrylic resin having a maleimide or glutaric anhydride structure as a ring structure in the main chain. Examples of the maleic anhydride structure include styrene-N-phenylmaleimide-maleic anhydride copolymers. Examples of the maleimide structure include olefin-maleimide copolymers such as those described in JP-A-2004-45893. Examples of the glutaric anhydride structure include copolymers having glutaric anhydride units such as those described in JP-A-2003-137937.

[0100] (acrylic resin with no ring structure in the main chain) For example, an acrylic resin having a glass transition temperature of 120°C or higher can be obtained by introducing carboxyl groups such as methacrylic acid. If the amount of carboxyl groups exceeds a certain level, there is a risk of crosslinking or an increased risk of foaming during film formation, so it is preferable to keep the amount below a certain level. Specifically, the amount of carboxyl groups in the acrylic resin is preferably 0.6 mmol / g or less, and more preferably 0.4 mmol / g or less.

[0101] As an acrylic resin having a glass transition temperature of 120°C or higher, an acrylic resin having a syndiotacticity of 54% or higher, expressed as a triad, can be suitably used. When the syndiotacticity of an acrylic resin is 54% or higher, the glass transition temperature of the acrylic resin increases, and the heat resistance of the acrylic resin tends to improve. The syndiotacticity of the acrylic resin, expressed as a triad, is preferably 55% or higher, more preferably 56% or higher, and even more preferably 57% or higher. Furthermore, from the viewpoints of the molding temperature of the acrylic resin, the toughness of the molded body, and secondary processability, the syndiotacticity of the acrylic resin, expressed as a triad, is preferably 70% or lower, more preferably 67% or lower, even more preferably 65% ​​or lower, and even more preferably 63% or lower.

[0102] The syndiotacticity of acrylic resins, expressed as a triad, is the proportion of three structural unit sequences (triads) that are rr. In addition, in two structural unit sequences (diads), those with the same configuration are called meso (m) and those with the opposite configuration are called racemo (r).

[0103] Methods for synthesizing acrylic resins with a triad syndiotacticity of 55% or more are not particularly limited, but include, for example, anionic polymerization and radical polymerization. Among these, radical polymerization is preferred (see, for example, International Publication Nos. WO 2023 / 238885 and WO 2023 / 238886). Radical polymerization does not use organometallic compounds as polymerization initiators or organic solvents as media, as used in anionic polymerization. This makes it less likely for impurities to remain, making it preferable from an environmental perspective. The glass transition temperature and syndiotacticity of the acrylic resin can be controlled by the polymerization temperature of the acrylic resin. For example, lowering the polymerization temperature of the acrylic resin increases the glass transition temperature of the acrylic resin and increases the syndiotacticity of the acrylic resin. The glass transition temperature of the acrylic resin can also be controlled by the molecular weight of the acrylic resin.

[0104] The content of structural units derived from methyl methacrylate in an acrylic resin having a triad syndiotacticity of 54% or more is preferably 98% by weight or more, more preferably 99% by weight or more, and even more preferably 100% by weight.

[0105] Monomers other than methyl methacrylate that constitute acrylic resins having a syndiotacticity of 54% or more, expressed as triads, are not particularly limited, and examples thereof include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; aryl acrylates such as phenyl acrylate; cycloalkyl acrylates such as cyclohexyl acrylate and norbornenyl acrylate; alkyl methacrylates other than methyl methacrylate, such as ethyl methacrylate, propyl methacrylate, and butyl methacrylate; aryl methacrylates such as phenyl methacrylate; cycloalkyl methacrylates such as cyclohexyl methacrylate and norbornenyl methacrylate; aromatic vinyl compounds such as styrene and α-methylstyrene; acrylamide; methacrylamide; acrylonitrile; and methacrylonitrile.

[0106] (other monomer units) The acrylic resin may further contain other monomer units. Examples of the other monomer units include, but are not limited to, aromatic vinyl units and (meth)acrylonitrile units. Examples of the aromatic vinyl units include, but are not limited to, styrene units, α-methylstyrene units, methoxystyrene units, vinyltoluene units, and halostyrene units. Among these, styrene units are preferred.

[0107] In this specification and claims, the (meth)acrylonitrile unit means an acrylonitrile unit or a methacrylonitrile unit.

[0108] (Other properties of acrylic resins) 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 below. Hereinafter, the term "acrylic resin" refers to at least either the acrylic resin having a ring structure in the main chain or the acrylic resin not having a ring structure in the main chain.

[0109] The weight-average molecular weight of the acrylic resin is preferably from 50,000 to 200,000, and more preferably from 90,000 to 150,000. When the weight-average molecular weight of the acrylic resin is 50,000 or more, the mechanical properties of the molded product of the acrylic resin tend to be improved, and when it is 200,000 or less, the moldability of the acrylic resin tends to be improved.

[0110] The weight-average molecular weight of the acrylic resin may be 400,000 or more. When the weight-average molecular weight of the acrylic resin is 400,000 or more, the mechanical properties of the molded product of the acrylic resin tend to be further improved, and for example, a resin film with excellent flex 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 even more preferably 800,000 or more. Furthermore, from the viewpoint of the moldability of the acrylic resin, the weight-average molecular weight of the acrylic resin is preferably 2.5 million or less, more preferably 2 million or less, even more preferably 1.5 million or less, and particularly preferably 1.2 million or less.

[0111] The ratio of the weight-average molecular weight to the number-average molecular weight of the acrylic resin (polydispersity index) is preferably 1.6 to 2.5, more preferably 1.7 to 2.2. When the polydispersity index of the acrylic resin is 1.6 or more, the flowability of the acrylic resin tends to improve and it tends to be easier to mold, while when it is 2.5 or less, the mechanical properties such as impact resistance, toughness, and flex resistance of the molded acrylic resin tend to improve.

[0112] The number-average molecular weight and weight-average molecular weight of the acrylic resin are values ​​measured by gel permeation chromatography (GPC) in terms of standard polystyrene. The number-average molecular weight and weight-average molecular weight of the acrylic resin can be controlled by the type and amount of polymerization initiator and chain transfer agent used in synthesizing the acrylic resin.

[0113] (aromatic vinyl unit) The acrylic resin film of this embodiment contains an aromatic vinyl unit. The aromatic vinyl unit may be contained in the acrylic resin that is the main component, or may be contained in a resin other than the acrylic resin that is the main component (for example, a copolymer containing an aromatic vinyl unit). The content of the aromatic vinyl unit in the acrylic resin film of this embodiment is preferably more than 0 wt% and not more than 25 wt%, more preferably 0.5 wt% or more and not more than 20 wt%.

[0114] The copolymer containing an aromatic vinyl unit is not particularly limited, but examples thereof include a copolymer containing a (meth)acrylonitrile unit and an aromatic vinyl unit, and a copolymer containing a (meth)acrylic acid ester unit and an aromatic vinyl unit, where the (meth)acrylonitrile unit and the aromatic vinyl unit are the same as the (meth)acrylonitrile unit and the aromatic vinyl unit described above, respectively.

[0115] The content of (meth)acrylonitrile units in the copolymer containing (meth)acrylonitrile units and aromatic vinyl units is preferably 22% by weight or more and 28% by weight or less, and more preferably 23% by weight or more and 27% by weight or less. When the content of (meth)acrylonitrile units in the copolymer containing (meth)acrylonitrile units and aromatic vinyl units is 22% by weight or more and 28% by weight or less, the transparency of the acrylic resin film of this embodiment is maintained.

[0116] The content of aromatic vinyl units in the copolymer containing (meth)acrylic acid ester units and aromatic vinyl units is preferably 10% by weight or more and 30% by weight or less, and more preferably 15% by weight or more and 28% by weight or less. When the content of aromatic vinyl units in the copolymer containing (meth)acrylic acid ester units and aromatic vinyl units is 10% by weight or more and 30% by weight or less, the transparency of the acrylic resin film of this embodiment is maintained.

[0117] The content of the copolymer containing an aromatic vinyl unit in the acrylic resin film of the present embodiment is not particularly limited, but is, for example, 10% by weight or more and 20% by weight or less.

[0118] (Acrylic resin composition) The acrylic resin composition of this embodiment is primarily composed of an acrylic resin and contains aromatic vinyl units, and is used to produce the acrylic resin film of this embodiment. The acrylic resin composition of this embodiment further contains an antiblocking agent, which is a crosslinked acrylic particle having an average particle size of 0.5 μm or more and 2.5 μm or less. The acrylic resin composition of this embodiment has an acrylic crosslinked particle content of 0.05 wt % or more and 0.9 wt % or less, and an aromatic vinyl content of more than 0 wt % and 25 wt % or less.

[0119] The acrylic resin film may be a film obtained by molding an acrylic resin composition in which an additive is added to an acrylic resin, or an antiblocking agent and an additive may be used in combination. Examples of additives include commonly used antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, specific wavelength absorbers or specific wavelength absorbing dyes for cutting blue light, and light resistance stabilizers such as radical scavengers, retardation adjusters, catalysts, plasticizers, lubricants, antistatic agents, colorants, shrinkage inhibitors, antibacterial and deodorizing agents, fluorescent brighteners, compatibilizers, and the like, which may be added alone or in combination of two or more, as long as they do not impair the object of the present invention.

[0120] Examples of ultraviolet absorbers include triazine-based compounds, benzotriazole-based compounds, benzophenone-based compounds, cyanoacrylate-based compounds, benzoxazine-based compounds, and oxadiazole-based compounds. Among these, triazine-based compounds are preferred in terms of ultraviolet absorption performance relative to the amount added and volatility when melt extrusion is performed.

[0121] When the retardation adjuster is to impart a negative retardation, it may be, for example, a compound having a styrene skeleton, such as an acrylonitrile-styrene copolymer.

[0122] The method for mixing the acrylic resin and the antiblocking agent is not particularly limited, and any conventionally known method can be used, such as feeding them into an extruder using a gravimetric feeder and melt-kneading them, or mixing them in the form of a solution in a solvent that has excellent compatibility with both the acrylic resin and the antiblocking agent.

[0123] When mixing is performed using an extruder, the extruder used is not particularly limited, and various extruders can be used. Specifically, a single-screw extruder, twin-screw extruder, or multi-screw extruder can be used. Among these, a twin-screw extruder is preferably used. A twin-screw extruder allows for greater flexibility in the conditions for uniformly mixing the acrylic resin and the antiblocking agent. Alternatively, the acrylic resin and the antiblocking agent may be introduced and mixed from the upstream side of the extruder using a raw material introduction hopper or the like, or the antiblocking agent alone may be introduced and mixed midway through the extruder using a side feeder, gravimetric feeder, or the like. Alternatively, the antiblocking agent may be prepared in advance as a masterbatch in a separate extruder and used.

[0124] A filter can be installed at the end of the extruder to reduce foreign matter in the resin. A gear pump is preferably installed before the filter to increase the pressure of the (A) acrylic resin / acrylic resin composition. The preferred type of filter is a stainless steel leaf disc filter capable of removing foreign matter from the molten polymer, and the preferred filter element is a fiber type, powder type, or a combination of these.

[0125] (Method of manufacturing acrylic resin film) An example of a method for producing the acrylic resin film of the present embodiment will be described below, but the method is not limited to this. In other words, any conventionally known method can be used as long as it can produce a film by molding the acrylic resin composition of the present embodiment.

[0126] Specifically, examples of the method include injection molding, melt extrusion molding, inflation molding, blow molding, and compression molding. The acrylic resin film of this embodiment can also be produced by a solution casting method or spin coating method in which the acrylic resin composition of this embodiment is dissolved in a solvent capable of dissolving it, and then molding the resulting solution.

[0127] Among these, it is preferable to use the melt extrusion method, which does not use a solvent, because the melt extrusion method can reduce production costs and the burden on the global environment and working environment caused by solvents.

[0128] When the acrylic resin composition of this embodiment is formed into a film by melt extrusion, the acrylic resin composition of this embodiment is first pre-dried and then fed into an extruder, where the acrylic resin composition is heated and melted. The acrylic resin composition is then fed into a die such as a T-die through a gear pump or filter. The acrylic resin composition fed into the T-die is then extruded as a sheet-like molten resin and cooled and solidified using a cooling roll or the like to obtain an unstretched film (also referred to as a raw film). To improve the surface properties (smoothness) of the film, the film can be sandwiched between a metal roll and a flexible roll equipped with a metal elastic outer cylinder.

[0129] When the acrylic resin composition of this embodiment is formed into an unstretched film by solution casting, the acrylic resin composition of this embodiment is dissolved in an organic solvent, the solution is cast onto a support, and the unstretched film is produced by heating and drying. Solvents that can be used in the solution casting method can be selected from known solvents. Halogenated hydrocarbon solvents such as methylene chloride and trichloroethane are preferred because they easily dissolve the acrylic resin of this embodiment and have low boiling points. Highly polar non-halogenated solvents such as dimethylformamide and dimethylacetamide can also be used. 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 may be used alone or in combination. The amount of solvent used can be any amount as long as it dissolves the thermoplastic resin sufficiently to allow for sufficient casting. In this specification, "dissolved" refers to the resin being present in the solvent in a homogeneous state sufficient for sufficient casting. It is not necessary for the solute to be completely dissolved in the solvent. The resin concentration in the solution is preferably 1% to 90% by weight, more preferably 5% to 70% by weight, and even more preferably 10% to 50% by weight. A preferred support may be an endless belt made of stainless steel. Alternatively, a film such as a polyimide film or a polyethylene terephthalate film may also be used.

[0130] The acrylic resin film of the present embodiment is obtained by stretching an unstretched film (also referred to as a raw film). By stretching the unstretched film, it is possible to produce a stretched film of a desired thickness, and further, it is possible to improve the mechanical properties of the stretched film.

[0131] As the stretching method, a conventionally known method can be used. For example, an unstretched raw film formed by melt extrusion can be stretched uniaxially or biaxially to produce a film of a predetermined thickness. Biaxial stretching is preferred to impart excellent mechanical properties to the stretched film in both the longitudinal direction (MD) and the width direction (TD). The biaxial stretching method may be simultaneous biaxial stretching or sequential biaxial stretching.

[0132] The stretching ratio (in both the MD and TD directions of the film in the case of biaxial stretching) is preferably 1.5 to 3.0 times, and more preferably 1.8 to 2.8 times. A stretching ratio within this range can sufficiently improve the mechanical properties of the film during stretching. Furthermore, the degree of orientation does not increase too much, and dimensional change after standing for 120 hours in an atmosphere of 85°C and 85% RH can be reduced. Furthermore, there is little possibility of a decrease in peel strength when the film is attached to a polarizer. The stretching speed is preferably 1.1 times / min or more, and more preferably 5 times / min or more. It is also preferably 100 times / min or less, and more preferably 50 times / min or less. In the case of sequential biaxial stretching, the stretching speeds in the first stage and the second stage may be the same or different. In sequential biaxial stretching, the first stage stretching is usually in the longitudinal direction (MD), and the second stage stretching is in the width direction (TD).

[0133] The stretching temperature is not particularly limited, but is preferably Tg+7°C to Tg+50°C, and more preferably Tg+10°C to Tg+40°C. A stretching temperature of Tg+7°C or higher can reduce the risk of breakage during the stretching process. On the other hand, a stretching temperature of Tg+50°C or lower can achieve sufficient molecular orientation and prevent a decrease in the mechanical strength of the film. If the stretching temperature is higher within the above range, molecular orientation is relaxed, resulting in a decrease in mechanical strength, while dimensional change in an 85°C, 85% RH atmosphere is reduced. Furthermore, in the case of a film containing an antiblocking agent, stretching at a low temperature tends to cause particles to float to the surface, resulting in surface roughness, slipperiness, and external haze. Those skilled in the art can arbitrarily set the stretching conditions while taking the above balance into consideration.

[0134] The acrylic resin film of this embodiment is wound into a roll by a known method. The film of this embodiment is less likely to have defects due to inter-film blocking, even when the film width is wide or the wound length is long. Furthermore, it is more effective to combine it with knurling of the edges, which has traditionally been used to prevent blocking.

[0135] (Application) The acrylic resin film of the present embodiment is preferably a functional film used in various display devices such as liquid crystal displays, plasma displays, and organic EL displays, as well as touch panels. Specifically, the acrylic resin film of the present embodiment can be an optical film such as a polarizer protective film for a liquid crystal display device, a retardation film, an antireflection film, a brightness enhancement film, a hard coat film, an antiglare film, an antistatic film, or an optical compensation film for widening a viewing angle.

[0136] When the acrylic resin film of the present embodiment is used as a polarizer protective film, it is bonded to a polarizer to form a polarizing plate. The polarizer is not particularly limited, and any conventionally known polarizer can be used. For example, a polarizer obtained by incorporating iodine into stretched polyvinyl alcohol can be used.

[0137] This polarizing plate can be further laminated with various films and suitably used in the field of displays such as liquid crystal displays and organic EL displays, although its applications are not limited to these. [Example]

[0138] The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited thereto. Those skilled in the art can make various changes, modifications, and alterations without departing from the scope of the present invention.

[0139] (Glass transition temperature of acrylic resin or raw film) The glass transition temperature of the acrylic resin or raw film was measured using 10 mg of the acrylic resin or raw film. Specifically, the glass transition temperature was determined by the midpoint method using a differential scanning calorimeter (Hitachi High-Tech Science, DSC7000X) under a nitrogen atmosphere at a temperature increase rate of 20°C / min.

[0140] (Average particle size of acrylic crosslinked particles) Using a laser diffraction particle size analyzer, Mastersizer 3000 (Malvern Instruments), the volumetric particle size distribution of the acrylic crosslinked particles was measured by the laser diffraction / scattering method based on the Mie theory in accordance with ISO13320:2009 and JIS Z8825-1, and the average particle size of the acrylic crosslinked particles was calculated.

[0141] (Surface roughness of acrylic resin film) The surface roughness of acrylic resin films was measured using an Evident LEXT OLS5100 laser microscope in accordance with JIS B0601:2013. Specifically, a 50x magnification, 0.95 numerical aperture objective lens was used to capture a confocal image of a 257 μm x 257 μm area of ​​the film. Three equally spaced evaluation lines were then drawn in both the MD and TD directions to create a roughness curve. Kurtosis (Rku) and 10-point average roughness (Rzjis) were calculated from the resulting roughness curve using analysis software, and the average values ​​at each measurement point were calculated. Measurements were performed five times at different measurement points, and the average value was used as the surface roughness. However, if localized defects such as scratches were clearly visible in the image, they were not included in the measurement and the measurement was repeated, avoiding the abnormal area.

[0142] (Static friction coefficient of acrylic resin film) The static friction coefficient of acrylic resin film was measured in accordance with JIS K7125:1999 using Imada's ZTS-5N digital force gauge and COF-2N-V friction coefficient measurement jig. Specifically, side A of the film was fixed to a smooth stainless steel plate, and side B of the film was attached with double-sided tape to a 60 mm x 60 mm, 200 g sled. The load applied when the sled was moved at a speed of 100 mm / min via a pulley was read with a load cell, and the static friction coefficient between sides A and B was calculated. The measurement was performed five times with different pieces of film, and the average value was calculated.

[0143] (Acrylic resin film haze, internal haze) The haze of the acrylic resin film was measured in accordance with JIS 7136: 2000 using a haze meter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. The internal haze of the acrylic resin film was measured by placing the acrylic resin film in a glass cell for measuring liquids so that distilled water was in contact with both sides of the acrylic resin film.

[0144] (Blocking test of acrylic resin film) Ten 100mm x 100mm sheets of acrylic resin film were stacked and left at 60°C for 2 hours with a 1kg load. After cooling at 23°C for 1 hour, the condition of the optical film was visually inspected and the optical film was peeled off by hand to evaluate the blocking resistance of the optical film. The criteria for judging blocking resistance are as follows: 1: When the films are stuck together and peeling marks appear when peeled off. 2: The films are stuck together, but no marks are left when peeled off. 3: When the films are not stuck together.

[0145] (Production of acrylic resin 1) A 40mm diameter co-rotating intermeshing twin-screw extruder (L / D = 90) equipped with a die at the outlet was used. The temperature of each temperature-controlled zone was set to 250-280°C, and the screw rotation speed was set to 85 rpm. Methyl methacrylate resin was melted and filled using a kneading block. Next, 1.8 parts by weight of monomethylamine (manufactured by Mitsubishi Gas Chemical Company) per 100 parts by weight of methyl methacrylate resin was injected through the nozzle to imidize the methyl methacrylate resin. The strand extruded from the die was then cooled in a water bath and pelletized using a pelletizer to obtain imidized resin 1.

[0146] The temperature of each temperature-controlled zone of a 40 mm diameter co-rotating intermeshing twin-screw extruder (L / D = 90) equipped with a die at the outlet was set to 240-260°C, and the screw rotation speed was set to 85 rpm. The imidized resin 1 was melted and filled using a kneading block. Next, 0.56 parts by weight of dimethyl carbonate was injected per 100 parts by weight of imidized resin 1 to esterify the carboxyl groups in imidized resin 1. The by-products and excess dimethyl carbonate were removed after the reaction. The strand extruded from the die was cooled in a water bath and then pelletized using a pelletizer to obtain acrylic resin 1. Acrylic resin 1 had a glass transition temperature of 123°C and a weight-average molecular weight of 97,800.

[0147] Example 1 Using a 15mm diameter co-rotating twin-screw extruder (L / D = 45) equipped with a die at the outlet, 89.9 wt% of acrylic resin 1, 0.1 wt% of crosslinked acrylic particles MX80H3wT (manufactured by Soken Chemical Industries, Ltd.) with an average particle size of 0.8 μm and a refractive index of 1.49 (hereinafter referred to as acrylic crosslinked particles 1), and 10 wt% of acrylonitrile-styrene copolymer AS-61NT (manufactured by Shin Chemical Shoji Co., Ltd.) with an acrylonitrile (AN) unit content of 26 wt% and a styrene (ST) unit content of 74 wt% (hereinafter referred to as AS resin 1) were kneaded. Next, the strand extruded from the die was cooled in a water bath, pelletized using a pelletizer, and then dried at 100 °C for 5 hours to obtain a resin composition.

[0148] The resin composition was melted using a 15 mm diameter co-rotating twin-screw extruder (L / D=45) equipped with a T-die at the outlet, and the sheet extruded from the T-die was cooled using a cooling roll to obtain a raw film having a width of 160 mm and a thickness of 160 μm. The glass transition temperature of the raw film was 121°C.

[0149] Using a film biaxial stretching device IMC-1905 (manufactured by Imoto Machinery Co., Ltd.), the raw film was simultaneously biaxially stretched at 145°C so that the stretching ratio in the longitudinal and transverse directions became 2 times, thereby obtaining an acrylic resin film.

[0150] Example 2 An acrylic resin film was obtained in the same manner as in Example 1, except that an acrylonitrile-styrene copolymer AS-61NT7200 (manufactured by Shin Chemical Shoji Co., Ltd.) containing 26% by mass of AN units, 74% by mass of ST units, and a colorant (hereinafter referred to as AS Resin 2) was used instead of AS Resin 1. The glass transition temperature of the raw film was 121°C.

[0151] Example 3 An acrylic resin film was obtained in the same manner as in Example 2, except that the amount of acrylic crosslinked particles 1 was changed to 0.2 wt % and the amount of acrylic resin 1 was changed to 89.8 wt %. The glass transition temperature of the raw film was 121°C.

[0152] Example 4 An acrylic resin film was obtained in the same manner as in Example 2, except that the amount of acrylic crosslinked particles 1 was changed to 0.07 wt % and 0.03 wt % of crosslinked acrylic particles xx-6390Z (manufactured by Sekisui Plastics Co., Ltd.) having an average particle size of 0.15 μm and a refractive index of 1.49 (hereinafter referred to as acrylic crosslinked particles 2) was further added. At this time, the glass transition temperature of the raw film was 121°C.

[0153] Example 5 An acrylic resin film was obtained in the same manner as in Example 1, except that a methyl methacrylate-styrene copolymer MS-750 (manufactured by Toyo Styrene) (hereinafter referred to as MS Resin 1), having a methyl methacrylate (MMA) unit content of 75 wt% and an ST unit content of 25 wt%, was used instead of AS Resin 1. The glass transition temperature of the raw film at this time was 122°C.

[0154] Example 6 An acrylic resin film was obtained in the same manner as in Example 5, except that the amount of acrylic resin 1 added was changed to 79.9 wt % and the amount of MS resin 1 added was changed to 20 wt %. At this time, the glass transition temperature of the raw film was 121°C.

[0155] Example 7 An acrylic resin film was obtained in the same manner as in Example 6, except that the amount of acrylic resin 1 was changed to 79.8% by weight and the amount of acrylic crosslinked particles 1 was changed to 0.2% by weight. At this time, the glass transition temperature of the raw film was 121°C.

[0156] Example 8 An acrylic resin film was obtained in the same manner as in Example 4, except that MS Resin 1 was used instead of AS Resin 2. The glass transition temperature of the raw film was 122°C.

[0157] Example 9 An acrylic resin film was obtained in the same manner as in Example 5, except that acrylic crosslinked particles 3 were used instead of acrylic crosslinked particles 1. The raw film had a glass transition temperature of 122°C.

[0158] Example 10 An acrylic resin film was obtained in the same manner as in Example 6, except that acrylic crosslinked particles 3 were used instead of acrylic crosslinked particles 1. The raw film had a glass transition temperature of 121°C.

[0159] (Production of acrylic crosslinked particles 4) Acrylic crosslinked particles 4 (multilayer structure particles) having an average particle size of 0.29 μm were obtained in the same manner as in Production Example 3 of JP 2017-177596 A.

[0160] (Comparative Example 1) An acrylic resin film was obtained in the same manner as in Example 7, except that acrylic crosslinked particles 4 were used instead of crosslinked acrylic particles 1, MS resin 1 was not used, and the amount of acrylic resin 1 added was changed to 99.8 wt%. The glass transition temperature of the raw film was 123°C.

[0161] (Comparative Example 2) An acrylic resin film was obtained in the same manner as in Example 1, except that acrylic crosslinked particles 2 were used instead of crosslinked acrylic particles 1, AS resin 1 was not used, and the amount of acrylic resin 1 added was changed to 99.9 wt%. The glass transition temperature of the raw film was 123°C.

[0162] Table 1 shows the properties of the AS resin and the MS resin.

[0163] [Table 1]

[0164] Table 2 shows the properties of the crosslinked acrylic particles.

[0165] [Table 2]

[0166] Table 3 shows the properties and evaluation results of the optical film.

[0167] [Table 3]

[0168] Table 3 shows that the acrylic resin films of Examples 1 to 10 are excellent in transparency and heat resistance and can suppress blocking during film roll storage. In contrast, the acrylic resin film of Comparative Example 1 cannot suppress blocking during film roll storage because the sum of Rku on both sides is 5.8 or the sum of Rzjis on both sides is 0.037 μm. Furthermore, the acrylic resin film of Comparative Example 2 cannot suppress blocking during film roll storage because the sum of Rku on both sides is 5.3 or the sum of Rzjis on both sides is 0.040 μm.

Claims

1. An acrylic resin film containing an acrylic resin as a main component and containing an aromatic vinyl unit, The glass transition temperature is 120°C or higher, The sum of the kurtosis Rku on both sides is 10 or more and 50 or less, An acrylic resin film having an internal haze of 1.0% or less.

2. 2. The acrylic resin film according to claim 1, wherein the sum of ten-point average roughnesses Rzjis on both surfaces is 0.05 μm or more and 1.0 μm or less.

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

4. An acrylic resin film containing an acrylic resin as a main component and containing an aromatic vinyl unit, The glass transition temperature is 120°C or higher, The sum of the 10-point average roughness Rzjis of both surfaces is 0.05 μm or more and 1.0 μm or less, The coefficient of static friction between one surface and the other surface is 0.8 or less, An acrylic resin film having an internal haze of 1.0% or less.

5. The acrylic resin film according to claim 1 or 4, wherein the acrylic resin has a ring structure in a main chain.

6. The acrylic resin film according to claim 1 or 4, wherein the content of the aromatic vinyl unit is more than 0% by weight and not more than 25% by weight.

7. further comprising an antiblocking agent; The acrylic resin film according to claim 1 or 2, wherein the antiblocking agent contains acrylic crosslinked particles having an average particle size of 0.5 μm or more and 2.5 μm or less.

8. The acrylic resin film according to claim 7 , wherein the content of the acrylic crosslinked particles is 0.05% by weight or more and 0.9% by weight or less.

9. 5. The acrylic resin film according to claim 1, wherein the dimensional change rate when left standing in an atmosphere of 85° C. and 85% RH for 120 hours is −2.0% or more and −0.1% or less.

10. The acrylic resin film according to claim 1 or 4, which is a polarizer protective film.

11. A polarizing plate comprising the acrylic resin film according to claim 10.

12. A liquid crystal display panel comprising the polarizing plate according to claim 11.

13. An acrylic resin composition containing an acrylic resin as a main component and containing an aromatic vinyl unit, further comprising an antiblocking agent; the antiblocking agent is an acrylic crosslinked particle having an average particle size of 0.5 μm or more and 2.5 μm or less, the content of the acrylic crosslinked particles is 0.05% by weight or more and 0.9% by weight or less, The acrylic resin composition has a content of aromatic vinyl units of more than 0% by weight and not more than 25% by weight.

14. The acrylic resin composition according to claim 13, comprising a methyl methacrylate-styrene copolymer.

15. The acrylic resin composition according to claim 13 or 14, which is in the form of pellets.

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