Method for manufacturing optical films

Abstract

The present invention provides a method for manufacturing optical films in which the occurrence of optical irregularities is suppressed. [Solution] A method for manufacturing an optical film containing a cycloolefin resin, comprising: a casting step of simultaneously or sequentially casting a dope 1 containing a cycloolefin resin and a dope 2 containing a resin different from dope 1 onto a casting support to form a laminated web having at least two layers; a laminated web peeling step of peeling the laminated web from the casting support; a web layer 2 peeling step of peeling a web layer 2 formed from dope 2 from the peeled laminated web to make the laminated web a web layer 1 formed from dope 1; and a web layer 1 winding step of winding the web layer 1 as an optical film.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing an optical film. More specifically, it relates to a method for manufacturing an optical film that can suppress the occurrence of optical irregularities. [Background technology]

[0002] Display devices are equipped with appropriate optical films tailored to their specific characteristics. Recently, development of optical films has been progressing to meet the demands for higher transparency, thinner films, and lower costs in display devices.

[0003] Typical methods for manufacturing optical films include solution deposition and melt deposition. In solution deposition, a dope is first created by dissolving the resin to be filmed and additives in a solvent. Then, the dope is cast onto a support such as an endless belt or drum to form a web. The web is then peeled from the support, stretched, dried, etc., and wound to obtain an optical film. Here, a technique has been disclosed in which multiple different dopes are cast simultaneously during casting to form a laminate, and the laminate is then maintained in width (shrinkage suppression) using a pin tenter and further dried before being wound as a laminate (see, for example, Patent Document 1). The laminate is said to be such that each layer can be peeled off and each layer can be used as an optical film. The invention described in Patent Document 1 aims to produce a number of films equal to the number of laminates in a single production run. Furthermore, the film in question is a cellulose ester-based optical film, and is an optical film containing cellulose resin. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2013-46992 [Overview of the project] [Problems that the invention aims to solve]

[0005] As described above, conventionally, films containing cellulose resin have been used as optical films. On the other hand, films containing cycloolefin resin have superior water resistance and transparency compared to films containing cellulose resin. For this reason, the development of optical films containing cycloolefin resin is being actively pursued. Hereafter, cycloolefin resin may be referred to as COP. COP is an abbreviation for "cyclo-olefin polymer".

[0006] In recent years, when optical films containing cycloolefin resin have been applied to highly transparent display devices, optical irregularities have sometimes occurred. In particular, optical irregularities have occurred when optical films are manufactured by winding them as a laminate, as described in Patent Document 1. These optical irregularities were different from the optical irregularities caused by periodic transverse film formation or fluffing during conventional solution film formation. These optical irregularities were weak and occurred across the entire surface. Improvement was needed regarding such optical irregularities. "Fluffing" refers to the phenomenon in which the surface of the dope, which has spread out in a film-like manner during casting, is affected by wind generated by drying or transport.

[0007] This disclosure has been made in view of the above-mentioned problems and circumstances. The problem to be solved by this disclosure is to provide a method for manufacturing an optical film that can suppress the occurrence of optical irregularities. [Means for solving the problem]

[0008] The inventors, after conducting thorough investigations to solve the above problems, discovered that by peeling each web from the laminated web and winding each layer separately, it is possible to suppress the occurrence of optical unevenness in the resulting optical film, leading to this disclosure. In other words, the above problems related to this disclosure are solved by the following means.

[0009] 1. A method for producing an optical film containing a cycloolefin resin, A casting step of casting dope 1 containing a cycloolefin resin and dope 2 containing a resin different from dope 1 simultaneously or sequentially onto a casting support to form a laminated web having at least two laminated layers, a laminated web peeling step of peeling the laminated web from the casting support, a web layer 2 peeling step of peeling the web layer 2 formed from dope 2 from the peeled laminated web, so that the laminated web becomes the web layer 1 formed from dope 1, and a web layer 1 winding step of winding the web layer 1 as an optical film; the method for producing an optical film is characterized by comprising the above steps.

[0010] 2. The method for producing an optical film according to item 1, further comprising a stretching step of stretching the web layer 1 after the web layer 2 peeling step and before the web layer 1 winding step.

[0011] 3. The method for producing an optical film according to item 1, wherein when the weight average molecular weight of the cycloolefin resin contained in dope 1 is defined as Mw1, and the weight average molecular weight of the resin different from that in dope 1 contained in dope 2 is defined as Mw2, the absolute value of the difference between Mw1 and Mw2 is more than 100,000 and less than 300,000.

[0012] 4. The method for producing an optical film according to item 1, wherein the resin contained in dope 2 is a cellulose resin.

[0013] 5. The method for producing an optical film according to item 1, wherein when peeling the laminated web from the casting support, when the residual solvent amount (mass%) of the web layer 1 is defined as residual 1, and the residual solvent amount (mass%) of the web layer 2 is defined as residual 2, residual 1 is larger than residual 2, and a value obtained by dividing residual 1 by residual 2 is 1.1 or more and 1.6 or less. Effects of the Invention

[0014] In the method for producing an optical film of the present disclosure, first, a laminated web is produced in which at least one web layer 1 and at least one web layer 2 are laminated. Then, the web layer 2 is peeled from the laminated web to obtain the web layer 1. Then, the web layer 1 is wound up to obtain an optical film, whereby an optical film with suppressed occurrence of optical unevenness can be obtained.

[0015] The expression mechanism or action mechanism of the effect of the present disclosure is not clarified, but is inferred as follows.

[0016] The inventors have found that when an optical film containing a cycloolefin resin is produced, optical unevenness that weakly occurs over the entire surface of the obtained optical film is likely to occur. It is estimated that this optical unevenness is mainly caused by minute film thickness unevenness resulting from minute irregularities on the surface of the optical film containing the cycloolefin resin. In the method for producing an optical film of the present disclosure, during casting, another dope 2 is laminated on the surface of the dope 1 that becomes the optical film, on the opposite side to the support, to form a laminated web. It is inferred that this can suppress the occurrence of irregularities on the surface of the dope 1 and the web layer 1 formed from the dope 1. Furthermore, in a laminate of optical films obtained by winding a laminated web as it is, when the temperature and humidity environment changes, differences in stress and shrinkage caused by the difference in resin between the respective optical films occur, and it is inferred that this influence causes optical unevenness due to shrinkage variation in the optical film. Such environmental changes in temperature and humidity often occur when rolls of optical film are transported across countries over a long period of time. In the method for producing an optical film of the present disclosure, after peeling the web layer 2 from the laminated web to obtain the web layer 1 consisting of a single layer, the web layer 1 is wound up as an optical film. It is inferred that this prevents the occurrence of differences in stress and shrinkage caused by resin differences between respective web layers, and can suppress the occurrence of optical unevenness due to shrinkage variation.

[0017] Furthermore, if the optical film has a stretching step in which the web is stretched before winding, by peeling the web layer 2 from the laminated web before the stretching step to obtain a single-layer web layer 1, an optical film can be obtained in which optical unevenness due to shrinkage variations is suppressed. In the stretching step, stretching is performed with a certain amount of residual solvent remaining, so it is presumed that by making the web layer a single layer, the surface is smoothed and the occurrence of optical unevenness is suppressed. When stretching a web layer with multiple layers, each layer containing a different resin, multiple layers with different hardnesses are stretched, so it is presumed that a relative difference in residual stress (shrinkage difference) occurs, resulting in optical unevenness. [Brief explanation of the drawing]

[0018] [Figure 1] This is a flowchart showing one embodiment of a method for manufacturing an optical film according to the present disclosure. [Figure 2] This is a schematic diagram illustrating the manufacturing flow in one embodiment of the method for manufacturing an optical film according to the present disclosure. [Modes for carrying out the invention]

[0019] One embodiment of the “Method for Manufacturing an Optical Film” of this Disclosure is a method for manufacturing an optical film containing a cycloolefin resin. The method for manufacturing an optical film of this embodiment, as shown in Figure 1, comprises a casting step S01, a laminated web peeling step S02, a web layer 2 peeling step S03, and a web layer 1 winding step S05. The casting step S01 is a step of simultaneously or sequentially casting a dope 1 containing a cycloolefin resin and a dope 2 containing a different resin than dope 1 onto a casting support to form a laminated web in which at least two layers are laminated. The laminated web peeling step S02 is a step of peeling the laminated web from the casting support. The web layer 2 peeling step S03 is a step of peeling the web layer 2 formed from dope 2 from the peeled laminated web to make the laminated web a web layer 1 formed from dope 1. The web layer 1 winding step S05 is a step of winding the web layer 1 as an optical film. Because the optical film manufacturing method of this embodiment includes a web layer 2 peeling step, the web layer 1 without the web layer 2 can be wound up as an optical film, and an optical film with suppressed optical unevenness can be obtained.

[0020] In this embodiment, the method for manufacturing the optical film preferably includes a stretching step S04 in which the web layer 1 is stretched after the web layer 2 peeling step S03 and before the web layer 1 winding step S05. When a laminated web, in which web layer 1 and web layer 2 are laminated, is stretched, optical unevenness is likely to occur. In contrast, stretching the single-layer web layer 1 after peeling web layer 2 from the laminated web can suppress the occurrence of optical unevenness. In this specification, optical unevenness refers to a state in which, when a black image is displayed on a liquid crystal display device and visually observed, a white haze-like light leakage occurs in the black image area. This is a phenomenon that occurs in a liquid crystal display device due to a partial change in the phase difference of the optical film.

[0021] In the optical film manufacturing method of this embodiment, it is preferable that the absolute value of the difference between Mw1 and Mw2 below is greater than 100,000 and less than 300,000. Mw1 is the weight-average molecular weight of the cycloolefin resin contained in Dope 1. Mw2 is the weight-average molecular weight of the resin different from Dope 1 contained in Dope 2. In the optical film manufacturing method of this embodiment, since the absolute value of the difference between Mw1 and Mw2 above is greater than 100,000 and less than 300,000, mixing of Dope 1 and Dope 2 in the casting process is suppressed.

[0022] In the optical film manufacturing method of this embodiment, it is preferable that the resin contained in the dope 2 is a cellulose resin. In the optical film manufacturing method of this embodiment, because the resin contained in the dope 2 is a cellulose resin, the elastic modulus is higher than that of cycloolefin resin, and optical irregularities caused by fluffing are less likely to occur. In addition, because the resin contained in the dope 2 is a cellulose resin, it has good release properties from films containing cycloolefin resin.

[0023] In the optical film manufacturing method of this embodiment, when peeling the laminated web from the casting support, it is preferable that the residue 1 below is greater than the residue 2 below, and the value obtained by dividing the residue 1 below by the residue 2 below is 1.1 or more and 1.6 or less. Residue 1 is the content (mass%) of residual solvent in the web layer 1. Residue 2 is the content (mass%) of residual solvent in the web layer 2. In the optical film manufacturing method of this embodiment, since the value obtained by dividing the residue 1 by the residue 2 is 1.1 or more, when doping is laminated to form a laminated web, the interface between web layers becomes smooth, and uneven film thickness is less likely to occur. Also, since the value obtained by dividing the residue 1 by the residue 2 is 1.6 or less, shrinkage during drying can be suppressed, and uneven film thickness is less likely to occur.

[0024] The following provides a detailed description of this disclosure, its components, and the forms and manners for implementing this disclosure. In this specification, the "~" symbol, which indicates a numerical range, is used to mean that the numbers before and after it are included as the lower and upper limits.

[0025] (1) Dope preparation process The optical film manufacturing method of this embodiment preferably includes a dope preparation step before the casting step. The dope preparation step is a step of preparing dope 1 and dope 2. In the dope preparation step, at least the resin and solvent are stirred in a stirring tank to prepare the dope to be cast onto the casting support. The "casting support" is sometimes referred to as the "support". As the solvent, it is preferable to use a mixed solvent of a good solvent and a poor solvent. The dope is a solution obtained by dissolving the resin in a solvent, and a film is obtained by spreading this in a thin film form and drying it. The obtained film is the web.

[0026] (1-1) Preparation of Dope 1 Dope 1 contains a cycloolefin resin. Hereinafter, the cycloolefin resin may be referred to as COP. Dope 1 is a solution in which at least COP is dissolved in a solvent mainly composed of a solvent suitable for COP. Dope 1 can be obtained by dissolving COP and other compounds in the solvent by placing the solvent, COP, and other compounds as needed into a dissolution vessel and stirring. Alternatively, dope 1 may be prepared by mixing a solution of COP with solutions of other compounds as needed.

[0027] A higher resin content in dope 1 is preferable because it reduces the drying load after casting onto the support. However, if the resin content is too high, the load during filtration increases, which may reduce accuracy. A suitable resin content that balances these factors is preferably in the range of 10 to 35% by mass, and more preferably in the range of 15 to 30% by mass. The resin with the highest content in dope 1 is COP.

[0028] The solvent used in the preparation of Dope 1 may be used alone or in combination of two or more, but it is preferable in terms of production efficiency to use a mixture of a good solvent and a poor solvent for COP, and it is even more preferable in terms of COP solubility if there is a higher proportion of good solvent.

[0029] The preferred mixing ratio of a good solvent to a poor solvent is within the range of 0 to 98:2, expressed as a mass ratio of good solvent:poor solvent = 70:3. A good solvent is defined as one that dissolves the COP used on its own, while a poor solvent is one that causes swelling or does not dissolve the COP on its own. Therefore, the good and poor solvents can vary depending on the average degree of substitution of the COP.

[0030] The good solvent is not particularly limited, but examples include organic halogen compounds such as methylene chloride, dioxolanes, acetone, methyl acetate, and methyl acetoacetate. Among these, methylene chloride or methyl acetate are preferred as good solvents. The poor solvent is not particularly limited, but examples include methanol, ethanol, n-butanol, cyclohexane, and cyclohexanone. Furthermore, it is preferable that dope 1 contains 0.01 to 2% by mass of water.

[0031] The solvent used to dissolve COP may be the solvent recovered from the film by drying during the casting process and reused. The recovered solvent may contain trace amounts of additives added to COP, such as plasticizers, UV absorbers, polymers, and monomer components. Even if these are present, the solvent can be reused, and if necessary, it can be purified before reuse.

[0032] When preparing Dope 1, general methods can be used to dissolve COP. Specifically, methods performed at atmospheric pressure, below the boiling point of the main solvent, and above the boiling point of the main solvent under pressure are preferred. Furthermore, combining heating and pressurization is preferable because it allows heating above the boiling point at atmospheric pressure. Another preferred method is to dissolve by stirring while heating at a temperature above the boiling point of the solvent at atmospheric pressure and within a range where the solvent does not boil under pressure. This prevents the formation of gels or lumpy undissolved matter called "mamako." In addition, a preferred method is to mix COP with a poor solvent to wet or swell it, and then add a good solvent to dissolve it.

[0033] Pressurization may be carried out by injecting an inert gas such as nitrogen gas or by increasing the vapor pressure of the solvent through heating. Heating is preferably done from an external source, and a jacket-type dissolution vessel, for example, is preferable because it allows for easy temperature control.

[0034] When dissolving COP in a solvent, a higher heating temperature is preferable from the viewpoint of COP solubility. However, if the heating temperature is too high, the required pressure will increase, resulting in poor productivity. The heating temperature is preferably in the range of 30 to 120°C, more preferably in the range of 60 to 110°C, and particularly preferably in the range of 70 to 105°C. The pressure is adjusted so that the solvent does not boil at the set temperature.

[0035] For dissolving COP, a cooling dissolution method is also preferably used, which allows COP to be dissolved in a solvent such as methyl acetate.

[0036] The obtained COP-containing solution is preferably filtered using a suitable filter material such as filter paper to obtain dope 1. A filter material with a low absolute filtration accuracy is preferable in order to remove insoluble matter. However, if the absolute filtration accuracy is too low, clogging of the filter material tends to occur. Therefore, a filter material with an absolute filtration accuracy of 0.008 mm or less is preferred, a filter material with an absolute filtration accuracy in the range of 0.001 to 0.008 mm is even more preferred, and a filter material with an absolute filtration accuracy in the range of 0.003 to 0.006 mm is particularly preferred.

[0037] There are no particular restrictions on the material of the filter media, and ordinary filter media can be used. Specifically, plastic filter media and metal filter media are preferred because they do not shed fibers. Examples of plastic filter media include polypropylene and fluororesins such as Teflon (a registered trademark of Chemours). Examples of metal filter media include stainless steel.

[0038] It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material COP by filtration. Bright spot foreign matter refers to points (foreign matter) that appear when light leaks from the opposite side when two polarizing plates are placed in a crossed nicol state, a film or the like is placed between them, and light is shone from one side of the polarizing plate and observed from the other side. Dope 1 has 200 bright spots / cm² with a diameter of 0.01 mm or more. 2 The following is preferable: The number of bright spots with a diameter of 0.01 mm or more is more preferably 100 per cm. 2 The following is preferred: 50 pieces / m 2 The following is the case, most preferably 0 to 10 pieces / cm 2 The following conditions apply. Furthermore, it is preferable to have fewer bright spots with a diameter of less than 0.01 mm.

[0039] The above COP-containing solution can be filtered using conventional methods. It is preferable to filter the COP-containing solution while heating it at a temperature above the solvent's boiling point at atmospheric pressure, but within a range where the solvent does not boil under pressure, because this minimizes the increase in the "filter pressure difference (differential pressure)" before and after filtration.

[0040] The preferred temperature for filtration is in the range of 30 to 120°C, more preferably in the range of 45 to 70°C, and particularly preferably in the range of 45 to 55°C. Furthermore, a low filtration pressure is preferable. Specifically, the filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and particularly preferably 1.0 MPa or less.

[0041] The following is a specific example of a COP.

[0042] The COP contained in Dope 1 is preferably a polymer of cycloolefin monomers, or a copolymer of a cycloolefin monomer and another copolymerizable monomer.

[0043] The cycloolefin monomer is preferably a cycloolefin monomer having a norbornene skeleton, and more preferably a cycloolefin monomer having a structure represented by the following general formula (A-1) or (A-2).

[0044]

Chemical Formula

[0045] In general formula (A-1), R 1 ~R 4 each independently represent a hydrogen atom, a hydrocarbon group having 1 to 30 carbon atoms, or a polar group. p represents an integer of 0 to 2. Provided that not all of R 1 ~R 4 simultaneously represent hydrogen atoms, R 1 and R 2 do not simultaneously represent hydrogen atoms, and R 3 and R 4 do not simultaneously represent hydrogen atoms.

[0046] In general formula (A-1), the hydrocarbon group having 1 to 30 carbon atoms represented by R 1 ~R 4 is, for example, preferably a hydrocarbon group having 1 to 10 carbon atoms, and more preferably a hydrocarbon group having 1 to 5 carbon atoms. The hydrocarbon group having 1 to 30 carbon atoms may further have a linking group containing, for example, a halogen atom, an oxygen atom, a nitrogen atom, a sulfur atom, or a silicon atom. Examples of such linking groups include divalent polar groups such as carbonyl groups, imino groups, ether bonds, silyl ether bonds, and thioether bonds. Examples of the hydrocarbon group having 1 to 30 carbon atoms include a methyl group, an ethyl group, a propyl group, and a butyl group.

[0047] In general formula (A-1), R 1 ~R 4Examples of polar groups represented by include carboxyl groups, hydroxyl groups, alkoxy groups, alkoxycarbonyl groups, aryloxycarbonyl groups, amino groups, amide groups, and cyano groups. Among these, carboxyl groups, hydroxyl groups, alkoxycarbonyl groups, and aryloxycarbonyl groups are preferred. Furthermore, from the viewpoint of ensuring solubility during solution film formation, alkoxycarbonyl groups and aryloxycarbonyl groups are preferred.

[0048] In general formula (A-1), p is preferably 1 or 2 from the viewpoint of improving the heat resistance of the optical film. This is because when p is 1 or 2, the resulting polymer becomes bulkier, which tends to improve the glass transition temperature.

[0049] [ka]

[0050] In general formula (A-2), R 5 R represents a hydrogen atom, a hydrocarbon group having 1 to 5 carbon atoms, or an alkylsilyl group having 1 to 5 carbon atoms. 6 p represents a carboxyl group, hydroxyl group, alkoxycarbonyl group, aryloxycarbonyl group, amino group, amide group, cyano group, or halogen atom. Examples of halogen atoms include fluorine, chlorine, bromine, or iodine. p represents an integer from 0 to 2.

[0051] R in general formula (A-1) 5 It is preferable that this represents a hydrocarbon group having 1 to 5 carbon atoms, and more preferably a hydrocarbon group having 1 to 3 carbon atoms.

[0052] R in general formula (A-2) 6 Preferably, represents a carboxyl group, a hydroxyl group, an alkoxycarbonyl group, or an aryloxycarbonyl group. Furthermore, from the viewpoint of ensuring solubility during solution film formation, alkoxycarbonyl groups and aryloxycarbonyl groups are preferred.

[0053] In general formula (A-2), p is preferably 1 or 2 from the viewpoint of improving the heat resistance of the optical film. This is because when p is 1 or 2, the resulting polymer becomes bulkier, which tends to improve the glass transition temperature.

[0054] Cycloolefin monomers having the structure represented by general formula (A-2) are preferred because they improve solubility in organic solvents. Generally, organic compounds lose their crystallinity by disrupting their symmetry, thus improving their solubility in organic solvents. In general formula (A-2), R 5 and R 6 In this case, the carbon atoms are substituted only on one side of the ring-forming carbon atom relative to the molecular axis of symmetry. Therefore, the molecular symmetry is low. That is, cycloolefin monomers having the structure represented by general formula (A-2) have high solubility and are suitable for the production of optical films by solution casting.

[0055] In a polymer of cycloolefin monomers, the content of cycloolefin monomers having the structure represented by general formula (A-2) is preferably 70 mol% or more relative to the total amount of all cycloolefin monomers constituting the cycloolefin resin. When a certain amount or more of cycloolefin monomers having the structure represented by general formula (A-2) is included, the orientation of the resin increases, and the phase difference (retardation) value tends to rise.

[0056] Specific examples of cycloolefin monomers having the structure represented by general formula (A-1) are shown below in example compounds 1 to 14. Furthermore, specific examples of cycloolefin monomers having the structure represented by general formula (A-2) are shown in example compounds 15 to 34.

[0057] [ka]

[0058] Examples of copolymerizable monomers that can copolymerize with cycloolefin monomers include copolymerizable monomers that can undergo ring-opening copolymerization with cycloolefin monomers, and copolymerizable monomers that can undergo addition copolymerization with cycloolefin monomers.

[0059] Examples of ring-opening copolymerizable monomers include cycloolefins such as cyclobutene, cyclopentene, cycloheptene, cyclooctene, and dicyclopentadiene.

[0060] Examples of copolymerizable monomers that can be added copolymerized include unsaturated double bond-containing compounds, vinyl cyclic hydrocarbon monomers, and (meth)acrylates. As unsaturated double bond-containing compounds, olefin compounds having 2 to 12 carbon atoms are preferred, and olefin compounds having 2 to 8 carbon atoms are more preferred. Examples of olefin compounds having 2 to 8 carbon atoms include ethylene, propylene, and butene. Examples of vinyl cyclic hydrocarbon monomers include vinylcyclopentene monomers such as 4-vinylcyclopentene and 2-methyl-4-isopropenylcyclopentene. Examples of (meth)acrylates include alkyl (meth)acrylates having 1 to 20 carbon atoms, such as methyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate.

[0061] The content of the cycloolefin monomer in a copolymer of a cycloolefin monomer and a copolymerizable monomer can be, for example, 20 to 80 mol%, preferably 30 to 70 mol%, relative to the total amount of all monomers constituting the copolymer.

[0062] As mentioned above, cycloolefin resins are polymers obtained by polymerizing or copolymerizing cycloolefin monomers having a norbornene skeleton, and examples include the following. Preferably, the cycloolefin monomer is a cycloolefin monomer having a structure represented by general formula (A-1) or (A-2).

[0063] (1) Cycloolefin monomer ring-opening polymer (2) A ring-opening copolymer of a cycloolefin monomer and a copolymerizable monomer that can be ring-opened therewith. (3) Hydrogenated ring-opening (co) polymers of (1) or (2) above (4) The ring-opened (co)polymer of (1) or (2) above is cyclized by a Friedel-Crafts reaction, and then the (co)polymer is hydrogenated. (5) Saturated copolymer of a cycloolefin monomer and an unsaturated double bond-containing compound (6) Addition copolymers of cycloolefin monomers with vinyl cyclic hydrocarbon monomers and hydrogenated versions thereof (7) Alternating copolymer of cycloolefin monomer and (meth)acrylate

[0064] The polymers described in (1) to (7) above can all be obtained by known methods, for example, by the methods described in Japanese Patent Publication No. 2008-107534 and Japanese Patent Publication No. 2005-227606. For example, the catalyst and solvent used in the ring-opening copolymerization described in (2) above can be those described in paragraphs 0019 to 0024 of Japanese Patent Publication No. 2008-107534. The catalysts used in the hydrogenation described in (3) and (6) above can be those described in paragraphs 0025 to 0028 of Japanese Patent Publication No. 2008-107534. The acidic compound used in the Friedel-Crafts reaction described in (4) above can be those described in paragraph 0029 of Japanese Patent Publication No. 2008-107534. The catalyst used in the addition polymerization described in (5) to (7) above can be, for example, one described in paragraphs 0058 to 0063 of Japanese Patent Application Publication No. 2005-227606. The alternating copolymerization reaction described in (7) above can be carried out, for example, by the method described in paragraphs 0071 and 0072 of Japanese Patent Application Publication No. 2005-227606.

[0065] Among the polymers described in (1) to (7) above, polymers (1) to (3) and (5) are preferred, and polymers (3) and (5) are more preferred. That is, it is preferable that the cycloolefin resin contains at least one of the structural units represented by the following general formula (B-1) and the following general formula (B-2). This makes it possible to increase the glass transition temperature and light transmittance of the resulting cycloolefin resin. Furthermore, it is even more preferable to contain only the structural unit represented by general formula (B-2), or to contain both the structural unit represented by general formula (B-1) and the structural unit represented by general formula (B-2). The structural unit represented by general formula (B-1) is a structural unit derived from the cycloolefin monomer represented by the aforementioned general formula (A-1), and the structural unit represented by general formula (B-2) is a structural unit derived from the cycloolefin monomer represented by the aforementioned general formula (A-2).

[0066] [ka]

[0067] In the general formula (B-1), X represents either "-CH=CH-" or "-CH2CH2-". 1 ~R 4 and p are R in general formula (A-1), respectively. 1 ~R 4 It is synonymous with p.

[0068] [ka]

[0069] In general formula (B-2), X represents either "-CH=CH-" or "-CH2CH2-". 5 ~R 6 and p are R in general formula (A-2), respectively. 5 ~R 6 It is synonymous with p.

[0070] The cycloolefin resin may be a commercially available product. Examples of commercially available cycloolefin resins include Arton® G (e.g., G7810), Arton F, Arton R (e.g., R4500, R4900, and R5000), and Arton RX, all manufactured by JSR Corporation.

[0071] The intrinsic viscosity [η]inh of cycloolefin resins is 0.2 to 5 cm³ when measured at 30°C. 3 It is preferable that the amount be / g, and 0.3-3cm 3 It is more preferable that the amount be / g, and the amount be 0.4~1.5cm 3 It is particularly preferable that the value be / g.

[0072] The number-average molecular weight (Mn) of the cycloolefin resin is preferably 8,000 to 100,000, more preferably 10,000 to 80,000, and particularly preferably 12,000 to 50,000. The weight-average molecular weight (Mw) of the cycloolefin resin is preferably 20,000 to 300,000, more preferably 30,000 to 250,000, and particularly preferably 40,000 to 200,000. The number-average molecular weight and weight-average molecular weight of the cycloolefin resin can be measured in polystyrene equivalent by gel permeation chromatography (GPC).

[0073] <Gel Permeation Chromatography> Solvent: Methylene chloride Columns: Shodex K806, K805, K803G (three columns manufactured by Showa Denko were connected together and used) Column temperature: 25℃ Sample concentration: 0.1% by mass Detector: RI Model 504 (manufactured by GL Sciences) Pump: L6000 (manufactured by Hitachi, Ltd.) Flow rate: 1.0ml / min Calibration curve: A calibration curve was used for 13 samples of standard polystyrene (STK standard polystyrene, manufactured by Tosoh Corporation) with a Mw value in the range of 500 to 2,800,000. It is preferable to use the 13 samples at approximately equal intervals.

[0074] When the intrinsic viscosity [η]inh, number-average molecular weight, and weight-average molecular weight are within the above range, the cycloolefin resin exhibits good heat resistance, water resistance, chemical resistance, mechanical properties, and moldability as a film.

[0075] The glass transition temperature (Tg) of cycloolefin resins is typically 110°C or higher, preferably between 110°C and 350°C, more preferably between 120°C and 250°C, and even more preferably between 120°C and 220°C. A Tg of 110°C or higher makes it easier to suppress deformation under high-temperature conditions. On the other hand, a Tg of 350°C or lower facilitates molding and also helps to suppress resin degradation due to heat during molding.

[0076] The cycloolefin resin content in the resulting optical film is preferably 70% by mass or more, and more preferably 80% by mass or more.

[0077] (1-2) Preparation of Dope 2 Dope 2 contains a different resin than dope 1. The "different resin than dope 1" is preferably a resin that is present in dope 1 at a concentration of less than 10% by mass, and is not present in dope 1. For example, if dope 1 contains only cycloolefin resin, the different resin is a resin other than cycloolefin resin. This different resin is preferably cellulose resin. The cellulose resin content in dope 2 is preferably 10-35% by mass, and more preferably 15-25% by mass. The "different resin than dope 1" is the resin with the highest content in dope 2. When dissolving the cellulose resin in the solvent, a higher heating temperature is preferable from the viewpoint of cellulose resin solubility. However, if the heating temperature is too high, the required pressure increases, resulting in poor productivity. The heating temperature is preferably in the range of 45-120°C, more preferably in the range of 60-110°C, and particularly preferably in the range of 70-105°C. The pressure is adjusted so that the solvent does not boil at the set temperature.

[0078] The preparation of dope 2 can be carried out in the same manner as the preparation of dope 1, except that some changes in conditions are made due to the inclusion of a different resin than that of dope 1, as described above.

[0079] The following describes specific examples of cellulose resins. Cellulose acylates are preferred as cellulose resins. Particularly preferred cellulose acylates include those with an acyl group substitution degree in the range of 2.10 to 2.98, where the acyl group is at least one selected from acetyl, propionyl, and butyryl groups. Specific examples of cellulose acylates include cellulose triacetate, cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose propionate, cellulose butyrate, and cellulose acetate propionate butyrate. In this disclosure, cellulose triacetate, cellulose acetate propionate, and cellulose diacetate are preferred as cellulose acylates. The cellulose used as the raw material for cellulose acylates is not particularly limited, and cotton linters, wood pulp, kenaf, etc., can be used. These may also be used in mixtures. There are no particular limitations on the method for synthesizing cellulose acylate, but for example, it can be synthesized by the method described in Japanese Patent Publication No. 10-45804. The degree of substitution of the acyl group can be measured by ASTM-D817-96. The number-average molecular weight of cellulose acylate is preferably in the range of 70,000 to 300,000, and more preferably in the range of 80,000 to 200,000, in order to obtain a suitable mechanical strength for use as a protective film for polarizing plates.

[0080] The "resin different from dope 1" in dope 2 may be an acrylic resin or polyarylate. The preparation of acrylic resins and polyarylates can be carried out in the same manner as the preparation of dope 1, except that the conditions are appropriately changed for acrylic resins and polyarylates.

[0081] Acrylic resins are polymers of acrylic acid esters or methacrylic acid esters, and also include copolymers with other monomers.

[0082] Therefore, acrylic resins also include methacrylic resins. While there are no particular limitations on the acrylic resin, it is preferable that it consists of methyl methacrylate units in the range of 50 to 99% by mass and other monomer units copolymerizable thereto in the range of 1 to 50% by mass.

[0083] Other constituent units of acrylic resins formed by copolymerization include alkyl methacrylates with 2 to 18 C1 of the alkyl group, alkyl acrylates with 1 to 18 C1 of the alkyl group, hydroxyalkyl acrylates such as isobornyl methacrylate and 2-hydroxyethyl acrylate, α,β-unsaturated acids such as acrylic acid and methacrylic acid, acrylamides such as acryloylmorpholine and N-hydroxyphenylmethacrylamide, divalent carboxylic acids containing unsaturated groups such as N-vinylpyrrolidone, maleic acid, fumaric acid, and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, N-substituted maleimide, glutarimide, and glutaric anhydride.

[0084] Examples of copolymerizable monomers that form the constituent units obtained by removing glutarimide and glutaric anhydride from the above constituent units include monomers corresponding to the above constituent units. Specifically, these monomers include alkyl methacrylates with 2 to 18 C1 of the alkyl group, alkyl acrylates with 1 to 18 C1 of the alkyl group, hydroxyalkyl acrylates such as isobornyl methacrylate and 2-hydroxyethyl acrylate, α,β-unsaturated acids such as acrylic acid and methacrylic acid, acrylamides such as acryloylmorpholine and N-hydroxyphenylmethacrylamide, divalent carboxylic acids containing unsaturated groups such as N-vinylpyrrolidone, maleic acid, fumaric acid, and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, and N-substituted maleimide.

[0085] Furthermore, glutarimide units can be formed, for example, by reacting an intermediate polymer having (meth)acrylic acid ester units with a primary amine to imidize it (see Japanese Patent Publication No. 2011-26563). The primary amine is an imidizing agent.

[0086] Glutaric anhydride units can be formed, for example, by heating an intermediate polymer having (meth)acrylic acid ester units (see Japanese Patent Publication No. 4961164).

[0087] Among the above-mentioned constituent units, the acrylic resin is particularly preferably composed of isobornyl methacrylate, acryloylmorpholine, N-hydroxyphenylmethacrylamide, N-vinylpyrrolidone, styrene, hydroxyethyl methacrylate, maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride, or glutarimide. These constituent units are particularly preferred from the viewpoint of mechanical strength.

[0088] The acrylic resin preferably has a weight-average molecular weight (Mw) in the range of 50,000 to 1,000,000, more preferably in the range of 100,000 to 1,000,000, and particularly preferably in the range of 200,000 to 800,000. Having a weight-average molecular weight within this range allows for control of dimensional changes in response to changes in ambient temperature and humidity. Furthermore, having a weight-average molecular weight within this range improves the release properties from metal supports during film production, drying properties with organic solvents, heat resistance, and mechanical strength. A weight-average molecular weight of 50,000 or more results in excellent heat resistance and mechanical strength. A weight-average molecular weight of 1,000,000 or less results in excellent release properties from metal supports and drying properties with organic solvents.

[0089] There are no particular restrictions on the method for producing acrylic resins, and known methods can be used. These known methods include suspension polymerization, emulsion polymerization, bulk polymerization, and solution polymerization. As polymerization initiators, ordinary peroxide-based and azo-based ones can be used, and redox-based ones can also be used. The polymerization temperature can be within the range of 30 to 100°C for suspension or emulsion polymerization, and within the range of 80 to 160°C for bulk or solution polymerization. To control the reduced viscosity of the obtained copolymer, alkyl mercaptans or the like can be used as chain transfer agents during polymerization.

[0090] From the viewpoint of maintaining the mechanical strength of the film, it is preferable that the glass transition temperature (Tg) of the acrylic resin be in the range of 80 to 120°C.

[0091] Commercially available acrylic resins can also be used. Examples include Delpet 60N, 80N, 980N, SR8200 (all manufactured by Asahi Kasei Chemicals); Dianaal BR52, BR80, BR83, BR85, BR88, EMB-143, EMB-159, EMB-160, EMB-161, EMB-218, EMB-229, EMB-270, EMB-273 (all manufactured by Mitsubishi Rayon); KT75, TX400S, IPX012 (all manufactured by Denki Kagaku Kogyo Co., Ltd.). Two or more types of acrylic resins can also be used in combination.

[0092] The acrylic resin preferably contains additives, and as an example of additives, it is preferable to include acrylic particles (rubber elastic particles) described in International Publication No. 2010 / 001668 to improve the mechanical strength of the film and adjust the rate of dimensional change. Examples of commercially available multilayer acrylic granular composites include, for example, "Metablen W-341" from Mitsubishi Rayon, "Kaneace" from Kaneka Corporation, "Paraloid" from Kureha Corporation, "Acryloid" from Rohm & Haas Corporation, "Stafloid" from Aica Corporation, Chemisnow MR-2G, MS-300X (all from Soken Chemical Co., Ltd.), and "Parapet SA" from Kuraray Co., Ltd. These can be used individually or in combination of two or more.

[0093] The volume-average particle size of the acrylic particles is 0.35 μm or less, preferably 0.01 to 0.35 μm, and more preferably 0.05 to 0.30 μm. If the particle size is above a certain level, the film can be easily stretched under heat, and if the particle size is below a certain level, the transparency of the resulting film is less likely to be impaired.

[0094] The polyarylate preferably contains aromatic dialcohol component units and aromatic dicarboxylic acid component units. The aromatic dialcohol component units and aromatic dicarboxylic acid component units are monomer units.

[0095] The polyarylate used can be the polyarylate described as a <constituent material of polyarylate film> in Japanese Patent Publication No. 2018-158965. Specific examples of aromatic dialcohol and aromatic dicarboxylic acid components contained in the polyarylate are given below.

[0096] Aromatic dialcohols that form aromatic dialcohol component units contained in polyarylates include, for example, 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (hereinafter also referred to as BisTMC), 1,1-bis-(4-hydroxyphenyl)-3,3,5,5-tetramethylcyclohexane, 1,1-bis-(4-hydroxyphenyl)-3,3,4-trimethylcyclohexane, 1,1-bis-(4-hydroxyphenyl)-3,3-dimethyl-5-ethyl-cyclohexane, 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclopentane, 1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, 1,1-bis-(3,5-diphenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, and 1,1-bis-(3-methyl-4-hydroxyphenyl) Examples include -3,3,5-trimethylcyclohexane, 1,1-bis-(3-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, 1,1-bis-(3,5-dichloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, 1,1-bis-(3,5-dibromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, 1,1-bis(3,5-diphenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, 1,1-bis(3,5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, and 1,1-bis(4-hydroxyphenyl)cyclohexane. Among these, BisTMC is preferred due to its high versatility.

[0097] Furthermore, aromatic dialcohol components contained in polyarylates include, for example, 1,1-bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 1,1-bis(4-methyl-2-hydroxyphenyl)methane, 1,1-bis(3,5-dimethyl-4-hydroxyphenyl)methane, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 2,2-bis(4-hydroxyphenyl)propane (BPA), 2,2-bis(3-methyl-4-hydroxyphenyl)propane (BPC), and 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane (TMBPA). Among these, isopropylidene-containing bisphenols such as 2,2-bis(4-hydroxyphenyl)propane (BPA), 2,2-bis(3-methyl-4-hydroxyphenyl)propane (BPC), and 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane (TMBPA) can be mentioned. Furthermore, examples of aromatic dialcohol components contained in polyarylates include bis(4-hydroxyphenyl)sulfone, bis(2-hydroxyphenyl)sulfone, bis(3,5-dimethyl-4-hydroxyphenyl)sulfone (TMBPS), bis(3,5-diethyl-4-hydroxyphenyl)sulfone, bis(3-methyl-4-hydroxyphenyl)sulfone, bis(3-ethyl-4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfide, bis(3,5-dimethyl-4-hydroxyphenyl)sulfide, bis(3,5-diethyl-4-hydroxyphenyl)sulfide, bis(3-methyl-4-hydroxyphenyl)sulfide, bis(3-ethyl-4-hydroxyphenyl)sulfide, 2,4-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenyl ether, and 4,4'-dihydroxydiphenyl ketone.

[0098] The aromatic dicarboxylic acids that form the aromatic dicarboxylic acid component units contained in the polyarylate are preferably terephthalic acid, isophthalic acid, or mixtures thereof. Furthermore, the above aromatic dicarboxylic acids may further include aromatic dicarboxylic acids other than terephthalic acid and isophthalic acid. Examples of such aromatic dicarboxylic acids include orthophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenic acid, 4,4'-dicarboxydiphenyl ether, bis(p-carboxyphenyl)alkane, and 4,4'-dicarboxyphenyl sulfone.

[0099] As the polyarylate, Unitika's Unifiner M-2040 can be suitably used.

[0100] Dope 1 and Dope 2 may contain the following components in addition to the components mentioned above. The following components may be contained in both Dope 1 and Dope 2, or in either one.

[0101] (Plasticizer) Dope 1 and Dope 2 preferably contain at least one plasticizer, for example, to impart processability to polarizing plate protective films. The plasticizer is preferably used alone or in a mixture of two or more types.

[0102] It is preferable to include at least one plasticizer selected from the group consisting of sugar esters, polyesters, and styrene compounds. This allows for a high degree of both effective control of moisture permeability and compatibility with base resins such as cellulose esters.

[0103] The plasticizer preferably has a molecular weight of 15,000 or less, and more preferably 10,000 or less. This allows for both improved heat and humidity resistance and compatibility with base resins such as cellulose esters. If the compound with a molecular weight of 10,000 or less is a polymer, it is preferable that its weight-average molecular weight (Mw) is 10,000 or less. The preferred range for the weight-average molecular weight (Mw) is 100 to 10,000, and more preferably 400 to 8,000.

[0104] In particular, to obtain the effects of this disclosure, it is preferable to include a compound with a molecular weight of 1500 or less in an amount of 6 to 40 parts by mass per 100 parts by mass of the base resin. Furthermore, it is more preferable to include the compound in an amount of 10 to 20 parts by mass. The base compound is a cycloolefin resin for dope 1 and a cellulose resin for dope 2. Including the compound within the above range is preferable because it allows for effective control of moisture permeability and compatibility with the base resin. For dope 2, instead of the cellulose resin, it may be an acrylic resin or polyarylate, which is a "resin different from dope 1".

[0105] Dope 1 and Dope 2 may contain sugar ester compounds for the purpose of preventing hydrolysis. Specifically, as sugar ester compounds, sugar esters can be used that have at least one pyranose structure or furanose structure with 1 to 12 such structures, and in which all or part of the OH groups of the structure are esterified.

[0106] Dope 1 and Dope 2 preferably contain polyester.

[0107] The polyester is not particularly limited, but for example, polyester polyols or end-capped polyesters can be used. Polyester polyols are polymers with hydroxyl groups at their ends, which can be obtained by a condensation reaction between a dicarboxylic acid or an esterifying derivative thereof and a glycol. End-capped polyesters are polymers in which the hydroxyl groups at the ends of the polyester polyol are capped with monocarboxylic acid. Esterifying derivatives include esterified dicarboxylic acids, dicarboxylic acid chlorides, and anhydrides of dicarboxylic acids.

[0108] Dope 1 and Dope 2 may contain, in addition to or instead of, the above-mentioned sugar ester and polyester, a styrene-based compound for the purpose of improving the water resistance of the film.

[0109] The styrene-based compound may be a homopolymer of styrene monomers, or a copolymer of a styrene monomer and other copolymer monomers. The content of constituent units derived from styrene monomers in the styrene-based compound is preferably 30 to 100 mol%, more preferably 50 to 100 mol%, in order for the molecular structure to have a certain level of bulk.

[0110] Examples of styrene monomers include styrene; alkyl-substituted styrenes such as α-methylstyrene, β-methylstyrene, and p-methylstyrene; halogen-substituted styrenes such as 4-chlorostyrene and 4-bromostyrene; hydroxystyrenes such as p-hydroxystyrene, α-methyl-p-hydroxystyrene, 2-methyl-4-hydroxystyrene, and 3,4-dihydroxystyrene; vinylbenzyl alcohols; alkoxy-substituted styrenes such as p-methoxystyrene, p-tert-butoxystyrene, and m-tert-butoxystyrene; and 3-vinylbenzoic acid and 4-vinylbenzoic acid. This includes vinyl benzoates such as fragrant acid; 4-vinylbenzyl acetate; 4-acetoxystyrene; amide styrenes such as 2-butylamidostyrene, 4-methylamidostyrene, and p-sulfonamidostyrene; aminostyrenes such as 3-aminostyrene, 4-aminostyrene, 2-isopropenylaniline, and vinylbenzyldimethylamine; nitrostyrenes such as 3-nitrostyrene and 4-nitrostyrene; cyanostyrenes such as 3-cyanostyrene and 4-cyanostyrene; vinylphenylacetonitrile; aryl styrenes such as phenylstyrene; and indenes. The styrene monomer may be a single type or a combination of two or more types.

[0111] Dope 1 and Dope 2 may contain optional components such as antioxidants, colorants, UV absorbers, matting agents, acrylic particles, hydrogen-bonding solvents, and ionic surfactants. These components can be added in an amount ranging from 0.01 to 20 parts by mass per 100 parts by mass of the base resin. Here, the base resin is a cycloolefin resin in Dope 1, and a "resin different from Dope 1" in Dope 2.

[0112] (Antioxidant) Commonly known antioxidants can be used. In particular, lactone-based, sulfur-based, phenol-based, double-bond-based, hindered amine-based, and phosphorus-based compounds are preferred.

[0113] These antioxidants are added to the resin, which is the main raw material of the optical film, in an amount of 0.05 to 20% by mass, preferably 0.1 to 1% by mass. The resin, which is the main raw material, refers to the entire resin component contained in the dope. A synergistic effect can be obtained by using several different types of compounds in combination rather than using only one type of antioxidant. For example, the combination of lactone-based, phosphorus-based, phenol-based, and double-bond-based compounds is preferred.

[0114] (Coloring agent) Dope 1 and Dope 2 preferably contain colorants for color adjustment, to the extent that they do not impair the effects of the present disclosure. Colorants refer to dyes and pigments, and in this disclosure refer to those that have the effect of making the color tone of the liquid crystal screen bluer, or adjusting the yellow index or reducing haze.

[0115] Various dyes and pigments can be used as colorants, but anthraquinone dyes, azo dyes, and phthalocyanine pigments are particularly effective.

[0116] <UV absorber> Since dope 1 and dope 2 can be used on the viewing side or backlight side of the polarizing plate, they may contain an ultraviolet absorber for the purpose of imparting ultraviolet absorption functionality.

[0117] While not particularly limited, examples of UV absorbers include benzotriazole-based, 2-hydroxybenzophenone-based, and phenyl salicylate-based UV absorbers. Furthermore, examples include triazoles such as 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole, and benzophenones such as 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, and 2,2'-dihydroxy-4-methoxybenzophenone.

[0118] The above-mentioned ultraviolet absorbers can be used individually or in combination of two or more types.

[0119] The amount of UV absorber used varies depending on the type of UV absorber, usage conditions, etc., but generally, it is added in the range of 0.05 to 10% by mass, preferably 0.1 to 5% by mass, relative to the base resin.

[0120] (Mat agent) Dope 1 and Dope 2 preferably contain fine particles (matting agents) that improve the slipperiness of the film roll in which the optical film is wound. In particular, adding these particles is effective from the viewpoint of improving slipperiness during winding and preventing the occurrence of scratches and blocking.

[0121] The matting agent can be either an inorganic or organic compound, as long as it does not impair the transparency of the resulting film roll and has heat resistance during melting. These matting agents may be used individually or in combination of two or more types.

[0122] By using particles with different particle sizes and shapes (for example, needle-shaped and spherical), it is possible to achieve both high transparency and slipperiness.

[0123] Among these, silicon dioxide is particularly preferred because its refractive index is close to that of cycloolefin resins, acrylic resins, and cellulose ester resins, resulting in excellent transparency (haze).

[0124] Specific examples of silicon dioxide include commercially available products with product names such as Aerosil® 200V, Aerosil® R972V, Aerosil® R972, R974, R812, 200, 300, R202, OX50, TT600, NAX50 (all manufactured by Nippon Aerosil Co., Ltd.); Seahostar® KEP-10, Seahostar® KEP-30, Seahostar® KEP-50 (all manufactured by Nippon Shokubai Co., Ltd.); Silohobic® 100 (manufactured by Fuji Silicia Co., Ltd.); Nipseal® E220A (manufactured by Nippon Silica Industry Co., Ltd.); and Admafine® SO (manufactured by Admatex Co., Ltd.), which can be preferably used.

[0125] The particle shape can be irregular, needle-shaped, flattened, spherical, etc., and there are no particular restrictions on the shape that can be used, but spherical particles are particularly preferable because they can produce a film roll with good transparency.

[0126] The particle size is preferably smaller than the wavelength of visible light, and even more preferably less than or equal to half the wavelength of visible light, because if the particle size is close to the wavelength of visible light, light will scatter and transparency will be poor. If the particle size is too small, the slipperiness may not be improved. Therefore, the particle size is particularly preferably in the range of 80 nm to 180 nm. Note that if the particle is an aggregate of primary particles, the particle size refers to the size of the aggregate. If the particle is not spherical, it refers to the diameter of the circle corresponding to its projected area.

[0127] The matting agent is preferably added to the base resin in an amount of 0.05 to 10% by mass, more preferably 0.1 to 5% by mass.

[0128] (2) Casting process The casting process involves simultaneously or sequentially casting the dope 1 and dope 2 prepared in the dope preparation process onto a casting support to form a laminated web with at least two layers. The layer formed from dope 1 is web layer 1, and the layer formed from dope 2 is web layer 2. The laminated web is preferably three layers, and preferably the three layers are stacked in the order of web layer 2, web layer 1, and web layer 2 from the side in contact with the casting support. In this way, because the laminated web is formed with web layer 1 sandwiched between two web layers 2, web layer 2 comes into contact with the casting support, resulting in good peelability from the casting support. This allows for an improvement in production speed. Furthermore, since the layer exposed on the surface is web layer 2, when web layer 1 is formed from dope 1, dope 2 covers the surface of dope 1, protecting the surface of dope 1. This suppresses deformation of the surface of dope 1 due to wind. This suppresses the occurrence of uneven film thickness in the resulting optical film, thereby reducing optical inconsistencies.

[0129] As shown in Figure 1, the casting support 1 for casting dope 1 and dope 2 is preferably belt-shaped. Furthermore, the casting support 1 is preferably a stainless steel belt with a mirror-finished surface. Alternatively, the casting support 1 may be a drum-shaped casting with a plated surface. In Figure 1, the arrows indicate the direction of transport of the web layer 1. The arrows on the casting support 1 indicate the movement of dope 1 or web layer 1 on the casting support 1.

[0130] In the casting process, it is preferable to deliver the dope to a pressurized die through a liquid delivery pump and then cast the dope from the pressurized die slit. Examples of liquid delivery pumps include pressurized metering gear pumps.

[0131] A pressure die is preferred that allows for adjustment of the slit shape in the die's mouthpiece portion and facilitates uniform film thickness. Pressure dies include coat hanger dies and T-dies, and all are preferably used. The surface of the casting support 1 is preferably mirror-finished. In the optical film manufacturing method of this embodiment, a laminated web is obtained by a co-casting method in which multiple dopes are cast simultaneously.

[0132] From a productivity standpoint, the casting width is preferably 1.3 m or more. More preferably 1.3 to 4.0 m. If it exceeds 4.0 m, there is a risk of stripes appearing during the manufacturing process or reduced stability during the subsequent transport process. Even more preferably, it is 1.3 to 3.0 m from the standpoint of transportability and productivity.

[0133] The surface temperature of the casting support 1 in the casting process should be -50°C or higher and below the boiling point of the solvent. Higher temperatures are preferable because they allow for faster drying of the web layer. However, if the temperature is too high, the web layer may foam or its flatness may deteriorate.

[0134] The preferred temperature for the casting support 1 is 0 to 55°C, and more preferably 22 to 50°C.

[0135] There are no particular limitations on the method for controlling the temperature of the casting support 1, but methods include blowing hot or cold air onto it, or bringing hot water into contact with the back side of the metal support. Using hot water is preferable because heat transfer is more efficient, resulting in a shorter time until the temperature of the casting support 1 becomes constant. When using hot air, it is sometimes necessary to use air at a temperature higher than the target temperature.

[0136] When casting the dope onto the casting support 1 to form a web film, it is preferable to heat the dope on the casting support 1 to evaporate the solvent.

[0137] Methods for evaporating the solvent include blowing air from the surface side of the dope, transferring heat from the back side of the casting support 1 using a liquid, and transferring heat from both sides using radiant heat. A method combining blowing air from the surface side of the dope and transferring heat from the back side of the casting support 1 using a liquid is also preferred. Among these, the back side liquid heat transfer method is preferred because it has good drying efficiency. Methods combining these methods are also preferred. It is preferable to form a web layer by drying the dope on the casting support 1 after casting in an atmosphere of 35 to 100°C. To maintain an atmosphere of 35 to 100°C, it is preferable to apply hot air at this temperature to the dope surface or heat it by means of infrared radiation or other means.

[0138] From the viewpoint of surface quality, moisture permeability, and peelability, it is preferable that the cast dope peels off from the casting support 1 as a web layer within 30 to 120 seconds.

[0139] As described above, the method of co-casting multiple dopes is not particularly limited, and known methods can be used. For example, when casting multiple dopes, a method can be used in which multiple casting nozzles are arranged at intervals in the direction of travel on the casting support 1, and multiple dopes are cast from these casting nozzles to form a laminate. For example, the methods described in Japanese Patent Publication No. 1-122419, Japanese Patent Publication No. 61-158414, Japanese Patent Publication No. 11-198285 may be used. Alternatively, dopes may be cast from two casting nozzles. For example, the methods described in Japanese Patent Publication No. 60-27562, Japanese Patent Publication No. 61-94724, Japanese Patent Publication No. 61-947245, Japanese Patent Publication No. 61-104813, Japanese Patent Publication No. 61-158413, and Japanese Patent Publication No. 6-134933 may be used. Furthermore, the solvent of the surface-side dope may contain a larger amount of alcohol components, which are poor solvents, than the solvent of the dope on the side in contact with the casting support 1. For example, the methods described in Japanese Patent Publication No. 61-94724 and Japanese Patent Publication No. 61-94725 may be used.

[0140] Multiple casting nozzles may be used to form a web layer by casting dope from one nozzle, peel off the web layer, and then cast dope from a second nozzle beneath it to form a laminated web. For example, the method described in Japanese Patent Publication No. 44-20235 may be used.

[0141] (3) Laminated web delamination process The laminated web peeling process is a process of peeling the laminated web from the casting support 1. This process involves peeling the laminated web 7, which was formed on the casting support 1 by the evaporation of the solvent from the dope, at the peeling position. The peeled laminated web 7 is sent to the next process via one or more rollers 11.

[0142] The temperature at the peeling position on the casting support 1 is preferably in the range of -50 to 40°C, more preferably in the range of 10 to 40°C, and most preferably in the range of 15 to 30°C.

[0143] The amount of residual solvent at the time of peeling the laminated web 7 from the casting support 1 is adjusted as appropriate depending on the strength of the drying conditions, the length of the casting support 1, etc. In order for the resulting optical film to exhibit good flatness, the amount of residual solvent in the laminated web 7 when peeling it from the casting support 1 is preferably 10 to 150% by mass. If peeling is performed when the amount of residual solvent is higher, the web may be too soft, impairing its flatness at the time of peeling, and twisting and vertical streaks due to peeling tension are likely to occur. Therefore, the amount of residual solvent at the time of peeling is determined by balancing economic speed and quality. More preferably, it is 20 to 40% by mass or 60 to 130% by mass, and particularly preferably 20 to 30% by mass or 70 to 120% by mass.

[0144] In the optical film manufacturing method of this embodiment, when peeling the laminated web from the casting support, it is preferable that residue 1 is greater than residue 2, and the value obtained by dividing residue 1 by residue 2 is 1.1 or more and 1.6 or less. Residue 1 is the amount of residual solvent (mass%) in web layer 1, and residue 2 is the amount of residual solvent (mass%) in web layer 2. When peeling the laminated web from the casting support, the amounts of residue 1 and residue 2 can be measured by taking samples of web layer 1 and web layer 2 from the laminated web and measuring the amount of residual solvent by gas chromatography or mass spectrometry.

[0145] In the optical film manufacturing method of this embodiment, the amount of residual solvent is defined by the following formula.

[0146] Residual solvent amount (mass%) = {(MN) / N} × 100 M is the mass of a sample taken from the laminated web, web layer, or optical film at any point during or after the manufacturing of the optical film. In other words, it is the mass of the object being measured, such as the laminated web 7, for which residual solvent is being measured. N is the mass of the sample taken above after heating at 115°C for 1 hour. When measuring the amount of residual solvent when peeling the laminated web 7, M is the mass of the laminated web 7 at the time of peeling.

[0147] The peeling tension when separating the casting support 1 from the laminated web 7 is preferably 300 N / m or less. More preferably, it is in the range of 196 to 245 N / m, but if wrinkles are likely to form during peeling, it is preferable to peel with a tension of 190 N / m or less.

[0148] (4) Web layer 2 peeling process The web layer 2 peeling step is a process in which the "web layer 2 formed from dope 2" is peeled off from the peeled laminated web 7, leaving the laminated web 7 as "web layer 1 formed from dope 1". Through this step, a single web layer 1 is obtained from the laminated web 7. As shown in Figure 1, if the laminated web 7 has a three-layer structure of web layer 2 / web layer 1 / web layer 2, the two "web layer 2 indicated by reference numeral 9" and "web layer 2 indicated by reference numeral 10" that sandwich web layer 1 are peeled off from the laminated web 7. When web layer 2 is peeled off from the laminated web 7, only "web layer 1 indicated by reference numeral 8" remains, and this web layer 1 becomes an optical film.

[0149] As shown in Figure 1, the two web layers 2 peeled off from the laminated web 7 are wound one onto the web layer 2 winding section 2a of the web layer 2 winding device 2b, and the other onto the web layer 2 winding section 3a of the web layer 2 winding device 3b. When each web layer 2 is wound, it is wound into a roll in a direction perpendicular to its width direction, forming a roll body. The winding method is not particularly limited and can be a constant torque method, a constant tension method, a tapered tension method, etc. The web layers 1 are then sent to the first stretching section 4 via the rollers 11.

[0150] (5) Stretching process The optical film manufacturing method of this embodiment preferably includes a stretching step of stretching the web layer 1 after the web layer 2 peeling step and before the web layer 1 winding step. The stretching step is preferably a two-stage stretching step, divided into stretching in the transport direction and stretching in the width direction. The following describes a method of stretching in two stages, but the stretching method is not limited to this.

[0151] (5-1) First stage extension As shown in Figure 1, the first stretching stage preferably involves stretching the web layer 1 in the transport direction using the first stretching unit 4. Hereinafter, the transport direction will also be referred to as the "MD direction." MD is an abbreviation for Machine Direction. In this case, the web layer 1 shrinks in the width direction perpendicular to the MD direction within the web surface. Hereinafter, the width direction will also be referred to as the "width direction" or "TD direction." "TD direction" is an abbreviation for Traverse Direction. Stretching may be performed according to the required optical properties, and it is preferable to stretch in at least one direction, or in two mutually orthogonal directions. For example, biaxial stretching may be performed in the width direction of the web layer 1 and in the transport direction perpendicular to it. The stretching ratio is defined as "(stretched size of the film after stretching) / (stretched size of the film before stretching)." When performing biaxial stretching, it is preferable to set the stretching ratio for both the TD direction and the MD direction within the range of 1.1 to 2.0 times.

[0152] The stretching method in the first stretching section 4 is not particularly limited. For example, a stretching method for stretching the web layer 1 in the transport direction is to create a difference in peripheral speed between multiple rollers and use that difference to stretch the web layer 1 in the transport direction. Furthermore, a stretching method for stretching in the transport direction is to fix both side edges of the web layer 1 with clips or pins and widen the spacing between the clips or pins in the transport direction to stretch the web layer 1 in the longitudinal direction. Also, a stretching method for stretching the web layer 1 in the width direction is to widen the spacing between the clips or pins in the width direction to stretch the web layer 1 in the width direction. Another method is to widen the spacing between the clips or pins simultaneously in the transport direction and the width direction to stretch the web layer 1 in both the longitudinal and transverse directions. These stretching methods can improve the performance, productivity, flatness, and dimensional stability of the film.

[0153] These stretching methods may be used in combination. In the case of a tenter method in which both side edges of the web layer 1 are gripped with clips or the like, driving the clip portion with a linear drive method allows for smooth stretching and reduces the risk of tearing of the web layer 1. These width retention or widthwise stretching methods are preferably performed by a tenter method, which may be a pin tenter or a clip tenter.

[0154] (Amount of residual solvent) It is preferable that the amount of residual solvent immediately before the first stretching stage is in the range of 1 to 15% by mass, and that the stretching ratio is in the range of 1.1 to 2.0 times, from the viewpoint of improving the adhesion of the film and suppressing the deterioration of the film strength.

[0155] The first stage of stretching promotes entanglement between polymer molecules in the thickness direction of web layer 1. These polymer molecules are the matrix molecules in web layer 1. As a result, even when the polarizer protective film is bonded to the polarizer layer via an adhesive during polarizer fabrication, the adhesive can easily penetrate into the polarizer protective film through the entangled parts (crosslinked parts) between the matrix molecules. Consequently, the resulting optical film (polarizer protective film) can be firmly fixed to the polarizer layer via the adhesive, improving the peel strength of the optical film (polarizer protective film) from the polarizer layer. In other words, the adhesion between the resulting optical film (polarizer protective film) and the polarizer layer is improved, ensuring a function to suppress deterioration of film strength. The polarizer layer is also called a "polarizing film," "polarizer film," or "polarizer film."

[0156] In the first stage of stretching, the web layer 1 is contracted in the width direction. For example, the following methods can be used to contract the web layer 1: One method is to (1) increase the density of the web by treating the web layer 1 at a high temperature without maintaining its width. Another method is to (2) apply tension to the web layer 1 in the transport direction (MD direction) to contract the web in the width direction (TD direction). Yet another method is to (3) drastically reduce the amount of residual solvent in the web.

[0157] (5-2) Second stage extension As shown in Figure 1, the second stretching stage preferably involves stretching the web layer 1 in the width direction using the second stretching section 5. The second stretching stage may stretch the web layer 1 only in the MD direction or only in the TD direction within the plane of the web layer 1. Furthermore, the second stretching stage may stretch in both the MD and TD directions, or in an oblique direction. There are no limitations on the stretching direction, but from the viewpoint of obtaining a wide film, it is preferable to include stretching in at least the width direction. The stretching method using the second stretching section 5 can be the same as the stretching method described above for the stretching method using the first stretching section 4. The stretching method using the first stretching section 4 and the stretching method using the second stretching section 5 may be the same or different.

[0158] To ensure a high phase difference, a wide width, and to promote adhesive penetration when bonding to the polarizing film, it is preferable to stretch the web layer 1 at a high magnification in the second stretching stage. However, if the stretching magnification is too high, the stretching stress may cause crazing to occur within the resulting optical film, or the entanglement between matrix molecules that maintain the strength of the optical film to dissociate, potentially weakening the optical film. Therefore, the stretching magnification in the second stretching stage is preferably within the range of 1.1 to 2.0 times.

[0159] Furthermore, when stretching is performed multiple times, such as in the first and second stretching stages, it is preferable that the stretching at the highest magnification, which carries the highest risk of matrix molecule dissociation, be performed in the final stage. Therefore, it is preferable that the stretching at the highest magnification is performed in the second stretching stage. This allows the entanglement of the matrix molecules to be strengthened by the time of the stretching at the highest magnification, thus suppressing the dissociation of the matrix molecules and preventing aggregate breakdown even when stretching at the highest magnification is performed.

[0160] (6) Drying of the laminated film and web layer 1 The laminated film and web layer 1 are preferably dried during the process of being conveyed by rollers. This drying is preferably carried out as appropriate between the time the laminated film is peeled off the casting support and the time the web layer 1 is wound up as an optical film. The amount of residual solvent in the resulting optical film is preferably 1% by mass or less, more preferably 0.1% by mass or less, and particularly preferably 0.01% by mass or less.

[0161] The drying method is not particularly limited. For example, a roller drying method can be used, in which the film is passed alternately through a number of rollers arranged vertically to dry it. Alternatively, the film may be stretched using the tenter method described above while simultaneously drying the film. Drying may also be performed in the first stretching section, the second stretching section, and so on.

[0162] The means for drying the film are not particularly limited and include, for example, hot air, infrared rays, heated rollers, microwaves, etc. From the viewpoint of simplicity, hot air is preferred as the drying method. The drying temperature is preferably increased in stages within the range of 40 to 200°C. From the viewpoint of dimensional stability, the drying temperature is more preferably within the range of 50 to 140°C.

[0163] (7) Web layer 1 winding process The web layer 1 winding process is the process of winding web layer 1 as an optical film. As shown in Figure 1, the web layer 1 winding process involves winding the web layer 1 onto the web layer 1 winding section 6a of the web layer 1 winding device 6b. The web layer 1 winding device can be the same as the web layer 2 winding device described above.

[0164] (8) Optical film The optical film obtained by the optical film manufacturing method of this embodiment is an optical film with less film thickness unevenness and suppressed optical unevenness. The obtained optical film can be used as an optical film for display devices such as liquid crystal displays and organic EL displays. Examples of optical films include polarizing plate protective films, transparent substrate films, and light diffusion films. Polarizing plate protective films include phase difference films and brightness enhancement films. [Examples]

[0165] The effects of this disclosure will be explained using the following examples. However, the technical scope of this disclosure is not limited to the following examples. In the following examples, when the notations "%" and "parts" are used, they refer to "mass%" and "parts by mass" unless otherwise specified.

[0166] (Example 1) (Doping process) (Preparation of Dope 1) As the cycloolefin resin, we used Arton® G7810 manufactured by JSR Corporation. Hereafter, this cycloolefin resin may be referred to as "G7810".

[0167] The weight-average molecular weight (Mw1) of G7810 was measured by gel permeation chromatography (GPC) under the following conditions. The weight-average molecular weight (Mw1) of G7810 was 95,000.

[0168] The measurement conditions for gel permeation chromatography are as follows: Solvent: Methylene chloride Columns: Shodex® K806, K805, K803G (Used by connecting three columns manufactured by Showa Denko Corporation) Column temperature: 25℃ Sample concentration: 0.1% by mass Detector: RI Model 504 (manufactured by GL Sciences Co., Ltd.) Pump: L6000 (manufactured by Hitachi, Ltd.) Flow rate: 1.0ml / min Calibration curve: A calibration curve was used based on 13 samples of standard polystyrene (STK standard polystyrene, manufactured by Tosoh Corporation). The samples used were the above-mentioned polystyrene with Mw values ​​ranging from 500 to 2,800,000.

[0169] (Preparation of particulate dispersion (M-1)) A fine particle dispersion (M-1) with the following composition was prepared. Fine particles (Aerosil® R812: manufactured by Nippon Aerosil Co., Ltd., average primary particle diameter 7 nm, average secondary particle diameter 100 nm, apparent specific gravity 50 g / L) 4 parts by mass 76 parts by mass of dichloromethane 20 parts by mass of ethanol

[0170] 25 parts by mass of the above-mentioned cycloolefin resin (G7810), 65 parts by mass of dichloromethane, 10 parts by mass of ethanol, and 0.75 parts by mass of fine particle dispersion (M-1) were added to a mixing tank. The contents of the mixing tank were then stirred to dissolve each component. Subsequently, the mixture was filtered through filter paper with an average pore size of 34 μm and a sintered metal filter with an average pore size of 10 μm to obtain a cycloolefin resin-containing solution (dope 1).

[0171] (Preparation of Dope 2) Triacetylcellulose (TAC) was used as a different resin from Dope 1. Specifically, ECC Corporation's ECTA TAC was used.

[0172] For TAC, the weight-average molecular weight (Mw2) was measured by GPC under the same conditions as for the cycloolefin resin described above. The weight-average molecular weight (Mw2) of TAC was 300,000.

[0173] Sixteen parts by mass of TAC, seventy-nine parts by mass of dichloromethane, five parts by mass of ethanol, and 0.75 parts by mass of fine particle dispersion (M-1) were added to a mixing tank. The contents of the mixing tank were then stirred to dissolve each component. Subsequently, the solution was filtered through filter paper with an average pore size of 34 μm and a sintered metal filter with an average pore size of 10 μm to obtain a TAC-containing solution (doped 2).

[0174] (Casting process (S01)) Dope 1 and Dope 2, prepared in the dope preparation process, were delivered to their respective pressurized dies via conduits through a pressurized metering gear pump. Dope 1 and Dope 2 were co-cast in a width of 1800 mm from the pressurized die slits onto the casting position on the casting support, which consisted of an endlessly rotating stainless steel belt that continuously transferred material. Dope 1 was cast onto the surface of the casting support, and Dope 2 was cast onto the surface of Dope 1 opposite to the support. Here, by adjusting the amount of each dope cast, the web layer 1 formed from Dope 1 was made thicker, and the web layer 2 formed from Dope 2 was made thinner. Then, simultaneous multilayer co-casting was performed so that the thickness of web layer 1 was 100 μm and the thickness of web layer 2 was 30 μm, forming a laminated web 7. The laminated web was heated on the casting support until it became self-supporting, and then dried by evaporating the solvent until it could be peeled off the casting support with a peeling roll.

[0175] Furthermore, the length of the conduit from the pump to the casting die was set to 30m, and the gear ratio of the gear pump used for dope transfer was adjusted to set the pump's rotational speed to 70rpm.

[0176] The initial extruded film thickness of the cast film was controlled by adjusting the widthwise gap of the pressurized die slit that discharges the dope using the heat bolts of the casting die, so that the film thickness deviation immediately after discharge was 5.5% of the total film thickness.

[0177] (Laminated web delamination process (S02)) In the casting process (S1), after forming the laminated web, the laminated web was peeled from the casting support using a peeling roll while maintaining its self-supporting properties. The amount of residual solvent in web layer 1 and web layer 2 of the peeled laminated web was measured. To measure the amount of residual solvent, a portion (approximately 5 cm x 5 cm) was cut from the laminated web, peeled off, and web layer 1 and web layer 2 were extracted. Then, the amount of residual solvent (residual 1, residual 2) in web layer 1 and web layer 2 was measured using the following method.

[0178] The amount of residual solvent is defined by the following formula: Residual solvent amount (mass%) = {(MN) / N} × 100 M is the mass of a sample taken from the laminated web, web layer, or optical film at any point during or after the manufacturing of the optical film. In other words, it is the mass of the object to be measured, such as the web layer 1, for which residual solvent is being measured. N is the mass of the sample taken above after heating at 115°C for 1 hour.

[0179] (Web layer 2 peeling process S03) The web layer 2 was peeled off from the laminated web to obtain web layer 1. This can also be described as peeling off web layer 2, which was attached to web layer 1, from web layer 1 to obtain web layer 1. The obtained web layer 1 was transferred to the stretching process via rollers. In the web layer 2 peeling process, it is preferable to peel off web layer 2 from the laminated web by methods such as bending, peeling from the cut portion, peeling by heat, or peeling by moist heat treatment.

[0180] (Shrinkage process) The web layer 1 was subjected to high-temperature treatment without maintaining its width, thereby increasing the density of the film and causing the web layer 1 to shrink in the width direction by 7%. The high-temperature treatment was performed using hot air while the web layer 1 was conveyed by rollers.

[0181] When the amount of residual solvent in the web layer 1 before stretching in the stretching process was measured using the method described above, it was found to be 5% by mass or less.

[0182] (Stretching process) (Extension of the first stage) Subsequently, the film was transported within a first stretching section heated with 140°C hot air, and the web layer 1 was stretched in the width direction while applying localized heating to the web layer 1.

[0183] (1st cutting process) The ends of the stretched film in the width direction were cut.

[0184] (Second stage extension) Except for stretching the web layer 1 in the transport direction with hot air at a temperature of 180°C, the web layer 1 was stretched by the second stretching section in the same manner as in the "first stage stretching" described above. The amount of residual solvent in the web layer 1 was measured using the same method as described above and was found to be 1 to 5% by mass.

[0185] (2nd cutting process) Similar to the first cutting step, both ends of the stretched web layer 1 in the width direction were cut.

[0186] (Web layer 1 winding process (S05)) The web layer 1 described above was used as an optical film and wound onto the web layer 1 winding section. The winding tension was set to 40 N / m, with a 70% taper and a 25% corner taper. The pressure of the touch roll (TR) was kept fixed at 16 N / m from the start to the end of winding. The optical film roll width was 2,000 mm and the winding length was 7,800 m, and the line speed for transporting the optical film was set to 60 m / min.

[0187] Optical film 1 was fabricated through the above process.

[0188] (Examples 2-8, Comparative Examples 2-3) As shown in Tables 1 and 2, optical films were prepared in the same manner as in Example 1, except that the molecular weight, residual 1, and film thickness of the cycloolefin resin in Dope 1; and the resin used for Dope 2, which was different from Dope 1, and whose molecular weight, residual 2, and film thickness were varied. The above film thickness is the film thickness of each film after it has been wound up.

[0189] Dope 2 in Example 7 was prepared as follows. Polymethyl methacrylate (PMMA) was used as a different resin from that used for Dope 1. The PMMA used was VB7103, manufactured by Mitsubishi Rayon Co., Ltd. The weight-average molecular weight (Mw2) of the PMMA was measured by GPC under the same conditions as for the cycloolefin resin described above. The weight-average molecular weight (Mw2) of the PMMA was 300,000. 25 parts by mass of the above PMMA, 62 parts by mass of dichloromethane, 12 parts by mass of ethanol, and 1.0 part by mass of fine particle dispersion (M-1) were placed in a mixing tank. The mixture in the mixing tank was then stirred to dissolve each component. Subsequently, the solution was filtered using filter paper with an average pore size of 34 μm and a sintered metal filter with an average pore size of 10 μm to obtain a PMMA-containing solution (Dope 2).

[0190] Dope 2 of Example 8 was prepared as follows. Polyarylate was used as a different resin from that used for Dope 1. Unitika's product name M-2040 was used as the polyarylate. The weight-average molecular weight (Mw2) of the polyarylate was measured by GPC under the same conditions as for the cycloolefin resin described above. The weight-average molecular weight (Mw2) of the polyarylate was 80,000. 26 parts by mass of the above polyarylate, 72 parts by mass of dichloromethane, 1.0 part by mass of ethanol, and 1.0 part by mass of fine particle dispersion (M-1) were placed in a mixing tank. The mixture in the mixing tank was then stirred to dissolve each component. After that, the solution was filtered using filter paper with an average pore size of 34 μm and a sintered metal filter with an average pore size of 10 μm to obtain a polyarylate-containing solution (dope 2).

[0191] For Dope 2 of Comparative Example 3, the following preparation was carried out. A fluorinated polyimide (fluorinated PI) was used as a different resin from that used for Dope 1. The fluorinated polyimide used was MX280f, manufactured by Kawamura Sangyo Co., Ltd. The weight-average molecular weight (Mw2) of the fluorinated polyimide was measured by GPC under the same conditions as for the cycloolefin resin described above. The weight-average molecular weight (Mw2) of the fluorinated polyimide was 150,000. 27 parts by mass of the above fluorinated polyimide, 71 parts by mass of dichloromethane, 0.1 parts by mass of ethanol, and 1.3 parts by mass of fine particle dispersion (M-1) were added to a mixing tank. The mixture in the mixing tank was then stirred to dissolve each component. Subsequently, the solution was filtered using filter paper with an average pore size of 34 μm and a sintered metal filter with an average pore size of 10 μm to obtain a fluorinated polyimide-containing solution (Dope 2).

[0192] [Table 1]

[0193] [Table 2]

[0194] In Tables 1 and 2, TAC means triacetylcellulose. PMMA means polymethyl methacrylate. Fluorine-based PI means fluorine-based polyimide. ECTA means ECTA (trade name), which is triacetylcellulose manufactured by ECC. VB7103 means VB7103 (trade name), which is polymethyl methacrylate (PMMA), manufactured by Mitsubishi Rayon. M-2040 means Unifiner M-2040 (trade name), which is polyarylate manufactured by Unitika. MX280f means KPI-MX280f (trade name), which is fluorine-based polyimide, manufactured by Kawamura Sangyo. COP means cycloolefin resin. G7810 means Arton® G7810 (trade name), which is cycloolefin resin manufactured by JSR. R5000 means Arton R5000 (trade name), which is cycloolefin resin manufactured by JSR.

[0195] Except for Comparative Example 1, in Tables 1 and 2, the first layer is the outermost layer and is the layer exposed to the surface. The second layer is the layer on the casting support side of the first layer and is the second layer from the surface. The third layer is the layer on the casting support side of the second layer and is the third layer from the surface. In the case of a two-layer structure with no third layer and only the first and second layers, the second layer becomes the layer in contact with the casting support. In the case of a three-layer structure with a third layer, the third layer becomes the layer in contact with the casting support. The second layer with dope 1 becomes the web layer 1. The first and third layers with dope 2 become the web layer 2. In Comparative Example 1, since there are no first and third layers with dope 2 and only the second layer with dope 1 is present, the second layer is both the layer exposed to the surface and the layer in contact with the casting support.

[0196] Furthermore, "None" in the "Peeling Position" column means that peeling did not occur. In other words, in Comparative Example 2, a two-layer optical film was formed without peeling the web layer 1 made of dope 1 and the web layer 2 made of dope 2.

[0197] (Example 9) An optical film was obtained in the same manner as in Example 1, except that the casting process S01 and the web layer 2 peeling process S03 were modified. In the casting process S01, dope 2 was cast onto the surface of the casting support, dope 1 was cast onto the surface of dope 2, and dope 2 was cast onto the surface of dope 1. In the web layer 2 peeling process S03, two web layers 2 sandwiching web layer 1 were peeled off from the three-layer laminated web to obtain web layer 1.

[0198] (Comparative Example 1) An optical film was obtained in the same manner as in Example 1, except that the casting process S01 and the web layer 2 peeling process S03 were modified. In the casting process S01, only dope 1 was cast onto the surface of the casting support, and the laminated web was made up of a single web layer consisting only of web layer 1. Since the laminated web is a web layer consisting only of web layer 1, the web layer 2 peeling process S03 was eliminated.

[0199] (evaluation) [Uneven film thickness] For the optical film, the film thickness was measured at multiple locations aligned in the width direction using a Digimatic Thickness Gauge (manufactured by Mitutoyo Corporation). Film thickness measurements were performed on one row in the width direction of the optical film. The film thickness measurements were taken at 100 mm intervals along the width direction of an 1800 mm wide optical film. The deviation in film thickness within each 100 mm range was calculated, and the average value of the "film thickness deviation" at a total of 18 locations was determined as the film thickness unevenness.

[0200] The evaluation criteria for the measured film thickness unevenness were as follows: A to C were considered acceptable, and D was considered unacceptable. A: Less than 0.04 μm B: 0.04 μm or larger, less than 0.06 μm C: 0.06 μm or larger, less than 0.08 μm D:0.08μm or more

[0201] [Optical unevenness] A liquid crystal display device was fabricated by bonding a liquid crystal cell to two polarizing plates, with the liquid crystal cell sandwiched between the two polarizing plates. During bonding, the absorption axis of the polarizer in the polarizing plate positioned on the viewing side and the absorption axis of the polarizer in the polarizing plate positioned on the backlight side were made perpendicular to each other.

[0202] A VA-type liquid crystal cell was used, comprising two glass substrates and a liquid crystal layer placed between them. The total thickness of the two glass substrates was 0.100 mm.

[0203] The polarizing plate was fabricated by sandwiching a polarizer between two optical films and bonding them together using an ultraviolet-curing adhesive. The polarizer was fabricated as follows: First, a long polyvinyl alcohol film with a thickness of 60 μm was continuously conveyed via guide rolls and immersed in a dyeing bath (30°C) containing iodine and potassium iodide to perform a dyeing treatment. After that, the film was stretched to 2.5 times its original size. Subsequently, the film was subjected to a total stretching and crosslinking treatment in an acidic bath (60°C) to which boric acid and potassium iodide were added, resulting in a total stretch of 5 times. After that, the resulting iodine-PVA polarizer with a thickness of 12 μm was dried in a dryer at 50°C for 30 minutes. This yielded a polarizer with a moisture content of 4.9% by mass.

[0204] The fabricated liquid crystal display was stored for 500 hours in an environment of 60°C and 90% RH. Afterward, the liquid crystal display was left at room temperature and pressure (23°C and 55% RH) for 24 hours. Then, the liquid crystal display was placed in a darkroom, and the occurrence of display unevenness due to light leakage from the front during black display was visually observed. This display unevenness was evaluated as optical unevenness.

[0205] The evaluation criteria for observed optical irregularities were as follows: A and B were considered acceptable, and C was considered unacceptable. A: No unevenness was observed in either the bright or dark room. B: It's not noticeable in a brightly lit room, but unevenness can be observed in a dark room. C: Unevenness is observed in both bright and dark rooms, and is at a level that poses practical problems.

[0206] [Production Speed] The production speed was expressed as a ratio to the production speed of the optical film manufacturing method in Comparative Example 1, with the production speed set to 1. Here, the amount of optical film produced per unit time was compared as the production speed.

[0207] A production speed of 0.7 or higher is preferable, 1.0 or higher is even preferable, 1.2 or higher is particularly preferable, and 1.8 or higher is the most preferable.

[0208] Tables 1 and 2 show that the optical film obtained by the optical film manufacturing method of this disclosure has suppressed optical unevenness. Furthermore, it can be seen that the optical film manufacturing method of this disclosure has a sufficiently fast production speed. [Industrial applicability]

[0209] According to this disclosure, it is possible to provide a method for manufacturing an optical film in which the occurrence of optical irregularities is suppressed. [Explanation of Symbols]

[0210] 1 Support for casting 2a Web layer 2 winding section 2b Web layer 2 winding device 3a Web layer 2 winding section 3b Web Layer 2 Winding Device 4 1st extension section 5 Second stretching section 6a Web layer 1 winding section 6b Web layer 1 winding device 7. Laminated Web 8 Web Layer 1 9 Web Tier 2 10 Web Tier 2 11 Rollers S01 Casting process S02 Laminated Web Delamination Process S03 Web layer 2 peeling process S04 Stretching process S05 Web Layer 1 Winding Process

Claims

1. A method for producing an optical film containing a cycloolefin resin, A casting step in which dope 1 containing a cycloolefin resin and dope 2 containing a resin different from dope 1 are simultaneously or sequentially cast onto a casting support to form a laminated web in which at least two layers are stacked, A laminated web peeling step of peeling the laminated web from the casting support, A web layer 2 peeling step is performed to peel off the web layer 2 formed from the dope 2 from the peeled laminated web, thereby making the laminated web a web layer 1 formed from the dope 1. A method for manufacturing an optical film, characterized by comprising a web layer 1 winding step of winding the web layer 1 as an optical film.

2. A method for manufacturing an optical film according to claim 1, comprising a stretching step of stretching the web layer 1 after the web layer 2 peeling step and before the web layer 1 winding step.

3. The method for producing an optical film according to claim 1, characterized in that when Mw1 is the weight-average molecular weight of the cycloolefin resin contained in dope 1, and Mw2 is the weight-average molecular weight of a resin different from dope 1 contained in dope 2, the absolute value of the difference between Mw1 and Mw2 is greater than 100,000 and less than 300,000.

4. The method for producing an optical film according to claim 1, characterized in that the resin contained in the dope 2 is a cellulose resin.

5. The method for manufacturing an optical film according to claim 1, characterized in that when the laminated web is peeled off from the casting support, the amount of residual solvent (mass%) of the web layer 1 is denoted as residual 1, and the amount of residual solvent (mass%) of the web layer 2 is denoted as residual 2, residual 1 is greater than residual 2, and the value obtained by dividing residual 1 by residual 2 is 1.1 or more and 1.6 or less.

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