Optical film manufacturing method

Abstract

To provide an optical film having a coating layer with few defects and high uniformity.SOLUTION: A long film substrate (1) and a protective film (2) are sandwiched between a pair of nip rolls (41,42) and bonded together, forming a laminate (8). The laminate is conveyed on the roll to a peeling part (10) along the longitudinal direction. At the peeling part, the protective film is peeled from the first principal face of the film substrate, before the first principal face of the film substrate is treated with a coating liquid. Preferably, two rolls forming the pair of nip rolls each have conductivity.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for producing an optical film. [Background technology]

[0002] Thin coating films are used as optical films that provide functions such as optical compensation in liquid crystal displays and antireflection of external light in organic EL devices. Thin films have poor self-supporting properties and are difficult to handle as a single film. Therefore, a coating layer is formed by applying a solution onto a support such as a plastic film, and the coating layer is dried or processed while still in close contact with the support.

[0003] For example, Patent Document 1 discloses a method for producing a laminated phase difference film by applying a resin solution onto a support to form a resin coating layer and stretching a laminate of the support and the coating layer. Patent Document 2 discloses a method for producing an aligned liquid crystal layer by applying a liquid crystal composition onto a stretched film as a support and aligning the liquid crystal compound homogeneously along the stretching direction (alignment direction) of the film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-46068 [Patent Document 2] WO2016 / 121856 Summary of the Invention [Problem to be solved by the invention]

[0005] In the method of forming a coating layer by coating a solution onto a film substrate as a support while transporting it longitudinally using the roll-to-roll method, scratches on the film substrate can cause defects such as transfer of scratches to the coating layer and poor alignment of liquid crystal molecules. Furthermore, coating defects caused by the surface condition of the film substrate can result in uneven film thickness and optical properties of the coating layer. [Means for solving the problem]

[0006] One embodiment of the present invention is a method for producing a long optical film, in which a coating layer is formed on the first main surface of a long film substrate having a first main surface and a second main surface.

[0007] First, a long film substrate and a protective film are sandwiched and bonded between a pair of nip rolls to obtain a laminate in which the protective film is releasably bonded to the first main surface of the film substrate (bonding step). Both the first roll and the second roll constituting the pair of nip rolls are electrically conductive.

[0008] A laminate of a film substrate and a protective film is transported by rolls along the longitudinal direction to a peeling section (first transport step), where the protective film is peeled off from the first main surface of the film substrate (protective film peeling step). The film substrate from which the protective film has been peeled is transported along the longitudinal direction of the film substrate from the peeling section to a coating section (second transport step), where a coating is applied to the first main surface of the film substrate (coating step), to obtain a laminate having a coating layer on the first main surface of the film substrate.

[0009] The coating liquid may be a liquid crystal composition containing a liquid crystal compound. The liquid crystal composition may contain a photocurable liquid crystal compound. After the liquid crystal composition containing the photocurable liquid crystal compound is applied to a film substrate, the liquid crystal compound may be photocured.

[0010] The film substrate may have an alignment control force that aligns the liquid crystal molecules in a predetermined direction. The film substrate may be, for example, a stretched film in which the molecules are oriented non-parallel to the longitudinal direction, or an obliquely stretched film.

[0011] The optical film may be formed by laminating another optical layer on the coating layer by roll-to-roll production. The optical layer laminated on the coating layer may include a polarizer. The optical film may be a circular polarizer in which the coating layer and a polarizer are laminated. [Effects of the Invention]

[0012] Because the protective film remains temporarily attached to the film substrate until immediately before the coating liquid is applied, scratches on the film substrate due to roll transport are suppressed. Furthermore, by sandwiching and laminating the film substrate and protective film between two conductive rolls, internal charging of the laminate is less likely to occur, suppressing coating defects due to charging of the film substrate. Therefore, a coating layer with fewer defects, such as scratches and streaks, caused by the film substrate can be obtained. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view of an optical film having a coating layer on a film substrate. [Figure 2] FIG. 2 is a cross-sectional view of a laminate in which a protective film is temporarily attached onto a film substrate. [Figure 3] FIG. 2 is a diagram showing an outline of a process for bonding a film substrate and a protective film together. [Figure 4] 1 is a diagram showing an outline of a film-forming apparatus and a film-forming process for forming a coating layer on a film substrate. FIG. [Figure 5] FIG. 2 is a perspective view showing an example of the shape of a pressure roll. [Figure 6] FIG. 1 is a cross-sectional view of an optical film according to an embodiment. [Figure 7] FIG. 1 is a cross-sectional view of an optical film according to an embodiment. [Figure 8] FIG. 1 is a cross-sectional view of an optical film according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Process overview] In the present invention, a coating layer is formed by applying a solution to one main surface of a long film substrate. Fig. 1 is a cross-sectional view of an optical film 9 in which a coating layer 3 is provided on a first main surface 1A of a film substrate 1. Fig. 2 is a cross-sectional view of a laminate 8 in which a protective film 2 is peelably attached to the first main surface 1A of the film substrate 1.

[0015] 3 is a conceptual diagram showing an outline of a laminating device and laminating process for laminating a film substrate 1 and a protective film 2 to obtain a laminate 8. In FIG. 3, a roll 28, in which a long protective film 2 is wound in a roll shape, is wound around an unwinding roll 29. The protective film unwound from the roll 28 is continuously transported downstream of a transport path formed along transport rolls 44 and 45, and is transported to a laminating unit 40.

[0016] The laminating unit 40 includes a pair of nip rolls 41 and 42. The film substrate 1 and the protective film 2 transported from the upstream side (the left side of the figure) are sandwiched between the top and bottom of the pair of nip rolls consisting of the first roll 41 and the second roll 42, and are thereby laminated together, thereby obtaining a laminate 8 in which the protective film 2 is releasably attached to the film substrate 1 (laminating step). As will be described in detail later, the first roll 41 in contact with the film substrate 1 and the second roll 42 in contact with the protective film 2 are both conductive rolls.

[0017] The laminate of the film substrate 1 and the protective film 2 is continuously transported downstream of a transport path formed along transport rolls 46, 47, and is wound up by a winding roll 49 to obtain a rolled body 80 in which the long film of the laminate 8 is wound into a roll.

[0018] 4 is a conceptual diagram showing an overview of a film-forming apparatus and film-forming process for forming a coating layer 3 on a film substrate 1. In FIG. 4, a roll 80 of a laminate 8 is wound around an unwinding roll 81. The laminate 8 unwound from the roll 80 moves continuously downstream of a transport path formed along transport rolls 83, 85, and 87, and is transported to a peeling section 10 (first transport step).

[0019] In the peeling section 10, the protective film 2 is peeled off from the film substrate 1 (peeling step). By peeling off the protective film 2, the first main surface 1A of the film substrate 1 is exposed. After the protective film is peeled off, the film substrate 1 is transported from the peeling section 10 to the coating section 30 (second transport step). In the coating section 30, a coating liquid is applied onto the first main surface 1A of the film substrate 1 (coating step).

[0020] A laminate 9 (optical film) in which a coating layer 3 is formed on the first main surface 1A of a film substrate 1 is wound around a winding roll 91 to obtain a long rolled optical film 90. Heating may be performed in a heating unit 50 between the coating unit 30 and the winding roll 91. When the coating liquid contains a photopolymerizable component such as a photopolymerizable liquid crystal compound, photocuring may be performed in a curing unit 60.

[0021] When a solution is applied to a film substrate while it is being transported roll-to-roll, scratches are likely to occur along the film substrate's length due to contact and friction with the transport rolls. If scratches exist on the film substrate, when a coating layer is formed on top of it, the scratches on the film substrate can be transferred to the coating layer, causing optical defects. Furthermore, when a liquid crystal composition is applied to the film substrate, the liquid crystal molecules tend to align along the extension direction of the scratches, which can cause alignment defects.

[0022] In the embodiment of the present invention, a protective film 2 is removably attached to the first main surface 1A of the film substrate 1. Because the protective film 2 is attached to the first main surface 1A of the film substrate 1 from the unwind roll 81 until it reaches the peeling section 10 (first conveying step), the first main surface 1A of the film substrate 1 does not come into direct contact with the conveying roll 87 in the first conveying step. Because the coating liquid is applied to the first main surface 1A of the film substrate 1 immediately after the protective film 2 is peeled from the film substrate 1, it is possible to prevent scratches on the first main surface of the film substrate due to contact with the conveying roll 87 and suppress the transfer of scratches to the coating layer 3 and poor alignment of the liquid crystal molecules.

[0023] In this embodiment, since coating is performed immediately after peeling the protective film 2 from the film substrate 1, the peeling unit 10 and the coating unit 30 are arranged close to each other, and the transport path of the film substrate in the second transport step is short. Therefore, the state of attachment between the film substrate and the protective film, and physical effects such as static electricity when peeling the protective film from the film substrate in the peeling unit 10, may affect the application of the coating liquid in the coating unit 30. Specifically, regions with thin coating layer thickness may be formed in the form of streaks extending in the width direction, and these may be visually recognized as streaky unevenness when the optical film is applied to an image display device.

[0024] In one embodiment of the present invention, the pair of nip rolls 41, 42 that bond the film substrate 1 and the protective film 2 together are conductive, thereby suppressing the occurrence of streaky unevenness extending in the width direction as described above.

[0025] When a coating liquid was applied to a film substrate immediately after peeling off the protective film, a sample in which streaky unevenness occurred in the coating layer was analyzed. No thickness unevenness or physical deformation was observed in the film substrate after peeling off the coating layer. Therefore, it is thought that the streaky unevenness in the thickness of the coating layer formed on the film substrate is due to repelling caused by charging of the film substrate when the coating liquid is applied to the surface of the film substrate.

[0026] One cause of electrostatic charging of the film substrate is the charge generated when the protective film is peeled off. However, even when the film substrate was neutralized with a static elimination bar after the protective film was peeled off, the above-mentioned streaky unevenness was not sufficiently eliminated. To further investigate the electrostatic charging of the film substrate, a toner test was conducted in which toner was attached to the film surface. It was confirmed that the toner adhered in lines extending in the width direction to both the laminate in which the protective film was bonded to the film substrate and the film substrate alone. From these results, it is presumed that if the laminate of the film substrate and the protective film is electrostatically charged, the electrostatic state (internal charge) of the film substrate is maintained even after the protective film is peeled off, which causes the coating liquid to repel, resulting in the formation of streaky unevenness in the coating layer.

[0027] In the embodiment of the present invention, first roll 41 and second roll 42 constituting the pair of nip rolls are electrically conductive, and therefore, when film substrate 1 and protective film 2 are laminated in lamination section 40, it is possible to prevent charging of laminate 8 due to charging of nip rolls. Therefore, even after protective film 2 is peeled off, internal charging of film substrate 1 is low, which is thought to suppress repelling when coating liquid is applied to first main surface 1A of film substrate 1 and prevent the occurrence of streaky thickness unevenness due to poor coating.

[0028] [material] Each material used in this embodiment will be described below.

[0029] <Coating liquid> The coating liquid applied onto the film substrate 1 is a solution containing solid components (solutes) that constitute the coating layer 3 and a solvent that dissolves and disperses the solid components. Various resin materials and liquid crystal materials are used as the solid components.

[0030] Examples of resin materials for the coating layer include cellulose-based resins such as acetyl cellulose, polyester-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, maleimide-based resins, polyolefin-based resins, (meth)acrylic-based resins, cyclic polyolefin resins (norbornene-based resins), polyarylate-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, and polysulfone-based resins.

[0031] A liquid crystal composition containing a liquid crystal compound is applied onto the film substrate 1, the liquid crystal compound is aligned in a predetermined direction, and then the alignment state is fixed to form a coating layer (liquid crystal layer) in which the liquid crystal molecules are aligned in a predetermined direction.

[0032] Examples of liquid crystal compounds include rod-shaped liquid crystal compounds and discotic liquid crystal compounds. Rod-shaped liquid crystal compounds are preferred because they are easily homogeneously oriented due to the alignment control force of the film substrate. Rod-shaped liquid crystal compounds may be main-chain or side-chain liquid crystals. Rod-shaped liquid crystal compounds may be liquid crystal polymers or polymers of polymerizable liquid crystal compounds. As long as the liquid crystal compound (monomer) before polymerization exhibits liquid crystallinity, it may not exhibit liquid crystallinity after polymerization.

[0033] The liquid crystal compound is preferably a thermotropic liquid crystal that exhibits liquid crystallinity upon heating. Thermotropic liquid crystals undergo phase transitions between a crystalline phase, a liquid crystal phase, and an isotropic phase as the temperature changes. The liquid crystal compound contained in the liquid crystal composition may be any of nematic liquid crystals, smectic liquid crystals, and cholesteric liquid crystals. A chiral agent may be added to the nematic liquid crystal to impart cholesteric alignment.

[0034] Examples of rod-shaped liquid crystal compounds exhibiting thermotropic properties include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles.

[0035] Examples of the polymerizable liquid crystal compound include a polymerizable liquid crystal compound in which the alignment state of a rod-shaped liquid crystal compound can be fixed using a polymer binder, a polymerizable liquid crystal compound having a polymerizable functional group in which the alignment state of a liquid crystal compound can be fixed by polymerization, etc. Among these, a photocurable liquid crystal compound having a photocurable functional group is preferred.

[0036] The photocurable liquid crystal compound (liquid crystal monomer) has a mesogen group and at least one photocurable functional group in one molecule. The temperature at which the liquid crystal monomer exhibits liquid crystallinity (liquid crystal phase transition temperature) is preferably 40 to 200°C, more preferably 50 to 150°C, and even more preferably 55 to 100°C.

[0037] Examples of the mesogenic group of the liquid crystal monomer include cyclic structures such as a biphenyl group, a phenylbenzoate group, a phenylcyclohexane group, an azoxybenzene group, an azomethine group, an azobenzene group, a phenylpyrimidine group, a diphenylacetylene group, a diphenylbenzoate group, a bicyclohexane group, a cyclohexylbenzene group, and a terphenyl group. The terminal of these cyclic units may have a substituent such as a cyano group, an alkyl group, an alkoxy group, or a halogen group.

[0038] Examples of the photocurable functional group include a (meth)acryloyl group, an epoxy group, and a vinyl ether group. Of these, a (meth)acryloyl group is preferred. The photocurable liquid crystal monomer preferably has two or more photocurable functional groups in one molecule. By using a liquid crystal monomer containing two or more photocurable functional groups, a crosslinked structure is introduced into the liquid crystal layer after photocuring, which tends to improve the durability of the optical film.

[0039] Any suitable liquid crystal monomer can be used as the photocurable liquid crystal monomer. For example, the liquid crystal monomers disclosed in International Publication No. 00 / 37585, U.S. Pat. No. 5,211,877, U.S. Pat. No. 4,388,453, International Publication No. 93 / 22397, European Patent No. 0,261,712, German Patent No. 19,504,224, German Patent No. 4,408,171, British Patent No. 2,280,445, Japanese Patent Application Laid-Open No. 2017-206460, International Publication No. 2014 / 126113, International Publication No. 2016 / 114348, International Publication No. 2014 / 010325, Japanese Patent Application Laid-Open No. 2015 Examples of the compounds include those described in JP-A-200877, JP-A-2010-31223, WO 2011 / 050896, JP-A-2011-207765, JP-A-2010-31223, JP-A-2010-270108, WO 2008 / 119427, JP-A-2008-107767, JP-A-2008-273925, WO 2016 / 125839, and JP-A-2008-273925. By selecting the liquid crystal monomer, it is also possible to adjust the expression of birefringence and the wavelength dispersion of retardation.

[0040] In addition to the liquid crystal monomer, the liquid crystal composition may contain a compound that controls the alignment of the liquid crystal monomer in a predetermined direction. For example, by adding a side-chain liquid crystal polymer to the liquid crystal composition, the liquid crystal compound (monomer) can be aligned in a homeotropic manner. Furthermore, by adding a chiral agent to the liquid crystal composition, the liquid crystal compound can be aligned in a cholesteric manner.

[0041] The liquid crystal composition may contain a photopolymerization initiator. When the liquid crystal monomer is cured by ultraviolet irradiation, the liquid crystal composition preferably contains a photopolymerization initiator (photoradical generator) that generates radicals upon light irradiation in order to promote photocuring. Types of liquid crystal monomers Depending on the type of photocurable functional group, a photocation generator or a photoanion generator may be used. The amount of the photopolymerization initiator used is about 0.01 to 10 parts by weight per 100 parts by weight of the liquid crystal monomer. In addition to the photopolymerization initiator, a sensitizer or the like may also be used.

[0042] A liquid crystal composition can be prepared by mixing a liquid crystal monomer and, if necessary, various alignment control agents, polymerization initiators, etc. with a solvent.

[0043] (solvent) The solvent of the coating liquid is not particularly limited as long as it can dissolve the solute and does not corrode the substrate (or has low corrosive properties), and examples thereof include halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, and orthodichlorobenzene; phenols such as phenol and parachlorophenol; aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, and 1,2-dimethoxybenzene; acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone, and N-methyl- Examples of suitable solvents include ketone solvents such as 2-pyrrolidone; ester solvents such as ethyl acetate and butyl acetate; alcohol solvents such as t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, and 2-methyl-2,4-pentanediol; amide solvents such as dimethylformamide and dimethylacetamide; nitrile solvents such as acetonitrile and butyronitrile; ethyl solvents such as diethyl ether, dibutyl ether, and tetrahydrofuran; ethyl cellosolve, butyl cellosolve, etc. A mixed solvent of two or more solvents may also be used.

[0044] The solid content of the coating liquid is usually about 5 to 60% by weight. The coating liquid may contain additives such as a surfactant and a leveling agent.

[0045] <Film substrate> By using a long film substrate 1 as the substrate, a series of processes from applying the coating liquid to drying can be carried out by roll-to-roll. If the coating liquid is a liquid crystal composition, operations such as alignment treatment of the liquid crystal molecules after coating and photocuring can also be carried out as a series of processes on the film substrate 1. In addition, the process of laminating the coating layer 3 formed on the film substrate 1 to another substrate can also be carried out by roll-to-roll, improving the productivity of optical films.

[0046] The width of the film substrate 1 is preferably 30 cm or more, and may be 50 cm or more, 80 cm or more, 100 cm or more, or 120 cm or more. From the viewpoint of productivity of the optical film, a larger width of the film substrate 1 is preferable, but it is generally 500 cm or less, and may be 400 cm or less, or 300 cm or less. The length of the film substrate is preferably 100 m or more, and may be 300 m or more, 500 m or more, 800 m or more, 1000 m or more, or 1200 m or more. There is no particular upper limit to the length of the film substrate 1, but it is generally 10,000 m or less, and may be 7,000 m or less, or 5,000 m or less. The thickness of the film substrate 1 is preferably about 10 to 200 μm.

[0047] The resin material constituting the film substrate 1 is not particularly limited as long as it is insoluble in the solvent of the coating liquid and can withstand processes such as drying, orientation, and curing. Examples of the resin material include polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; cyclic polyolefins such as norbornene-based polymers; cellulose-based polymers such as diacetyl cellulose and triacetyl cellulose; acrylic polymers; styrene-based polymers; polycarbonate, polyamide, polyimide, etc.

[0048] Films made of hydrophobic resin materials such as polyolefin, cyclic polyolefin, and acrylic polymers are prone to internal charging when bonded to the protective film 2, which can cause coating defects when a coating liquid is applied after the protective film is peeled off. As described above, the pair of nip rolls 41, 42 that bond the film substrate 1 and the protective film 2 together are conductive, which suppresses charging of the laminate 8, and therefore coating defects can be prevented even when a hydrophobic resin film is used as the film substrate 1.

[0049] The film substrate 1 may have an alignment regulating force for aligning the liquid crystal molecules in a predetermined direction. For example, the film substrate 1 may have an alignment film on the first main surface. An appropriate alignment film may be selected depending on the type of liquid crystal compound, the material of the substrate, and the like. Examples of alignment films for homogeneously aligning the liquid crystal molecules in a predetermined direction include polyimide-based or polyvinyl alcohol-based alignment films that have been subjected to a rubbing treatment. Alternatively, a photo-alignment film may be used. A resin film may be subjected to a rubbing treatment without providing an alignment film.

[0050] The film substrate 1 may have an alignment film for homeotropically aligning liquid crystal molecules. Examples of alignment agents for forming an alignment film (vertical alignment film) with homeotropic alignment properties include lecithin, stearic acid, hexadecyltrimethylammonium bromide, octadecylamine hydrochloride, monobasic carboxylic acid chromium complexes, organic silanes such as silane coupling agents and siloxane compounds, perfluorodimethylcyclohexane, tetrafluoroethylene, and polytetrafluoroethylene.

[0051] A stretched film may be used as the film substrate 1. In a stretched film, the resin material (polymer) that makes up the film is oriented in the stretching direction, and has the effect of aligning liquid crystal molecules along the stretching direction. By using a stretched film, it is possible to provide an alignment control force for aligning liquid crystal molecules in a predetermined direction even when no alignment film is formed on the film substrate. Since no alignment film is required, the manufacturing costs of the optical film can be reduced. Furthermore, not providing an alignment film prevents contamination due to rubbing residue and poor alignment.

[0052] The stretching direction of the stretched film (the orientation direction of the polymer) is not particularly limited and may be parallel or non-parallel to the longitudinal direction of the film substrate. By using a stretched film in which the molecules are oriented non-parallel to the longitudinal direction, a liquid crystal layer in which the liquid crystal molecules are oriented non-parallel to the longitudinal direction can be formed as the coating layer 3.

[0053] The stretching ratio of the stretched film may be such that it can exert an alignment control force, for example, about 1.1 to 5 times. The stretched film may be a biaxially stretched film. Even in the case of a biaxially stretched film, if different stretching ratios are used in the longitudinal and transverse directions, the liquid crystal molecules can be aligned in the direction with the larger stretching ratio.

[0054] The stretched film may be an obliquely stretched film, which has an orientation axis in a direction that is neither parallel nor perpendicular to the longitudinal direction (for example, a direction at an angle of 10 to 80° relative to the longitudinal direction). Therefore, by using an obliquely stretched film as the film substrate 1, a liquid crystal layer can be formed in which liquid crystal molecules are oriented in a direction that is neither parallel nor perpendicular to the longitudinal direction.

[0055] <Protective film> 2, the protective film 2 temporarily attached to the first main surface 1A of the film substrate 1 preferably has an adhesive layer 292 on one surface of a core material 291. The protective film 2 may have an antistatic layer (not shown) on the back surface of the core material 291 (the surface opposite to the surface on which the adhesive layer is formed).

[0056] (core material) The material of the core material 291 of the protective film 2 is not particularly limited as long as it is flexible, and metal foil, resin film, etc. are used. Resin film is preferred because it is an inexpensive material and has excellent processability. Specific examples of resin materials constituting the core material 291 include those mentioned above as the resin materials of the film substrate 1. The core material 291 may be a stretched film. The thickness of the core material 291 is not particularly limited. From the viewpoint of achieving both self-supporting properties and flexibility, the thickness of the core material 291 is preferably about 10 to 100 μm.

[0057] (Adhesive layer) The adhesive layer 292 may be made of an adhesive used in general adhesive tapes, etc., as long as it can be attached to the film substrate 1 and can be peeled off from the film substrate 1. The protective film 2 may be a self-adhesive film obtained by integrally molding the resin material constituting the core material 291 and the resin material of the adhesive layer 292 by multilayer extrusion.

[0058] The composition of the adhesive constituting the adhesive layer 292 is not particularly limited, and an adhesive having a base polymer such as an acrylic polymer, a silicone polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate / vinyl chloride copolymer, modified polyolefin, epoxy-based, fluorine-based, or rubber-based polymer such as natural rubber or synthetic rubber can be appropriately selected and used. In particular, an acrylic adhesive having an acrylic polymer as a base polymer is preferably used because the adhesive strength (peel strength) is easily adjusted and there is little adhesive residue on the film substrate 1 as an adherend.

[0059] The acrylic base polymer preferably has a main skeleton of a (meth)acrylic acid alkyl ester monomer unit. As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 20 carbon atoms is preferably used. The content of the (meth)acrylic acid alkyl ester is preferably 40% by weight or more, more preferably 50% by weight or more, and even more preferably 60% by weight or more, based on the total amount of monomer components constituting the base polymer. The acrylic polymer may be a copolymer of a plurality of (meth)acrylic acid alkyl esters. The arrangement of the constituent monomer units may be random or block.

[0060] The acrylic base polymer preferably contains, as a copolymerization component, a monomer component having a crosslinkable functional group. Examples of the monomer having a crosslinkable functional group include a hydroxyl group-containing monomer and a carboxyl group-containing monomer. In particular, it is preferable that the base polymer contains, as a copolymerization component, a hydroxyl group-containing monomer such as 2-hydroxyethyl (meth)acrylate or 4-hydroxybutyl (meth)acrylate. The hydroxyl group or carboxyl group of the base polymer serves as a reaction site with the crosslinking agent. By introducing a crosslinked structure into the base polymer, the cohesive strength of the pressure-sensitive adhesive is improved, and the pressure-sensitive adhesive exhibits appropriate adhesive strength to the film substrate as an adherend, while also tending to reduce the peel force when peeling the protective film 2 from the film substrate 1.

[0061] The molecular weight of the base polymer is adjusted appropriately so that the pressure-sensitive adhesive layer 292 has the desired adhesive strength, and is, for example, a weight-average molecular weight in polystyrene equivalent of about 50,000 to 2,000,000, preferably about 70,000 to 1,800,000, more preferably about 100,000 to 1,500,000, and even more preferably about 200,000 to 1,000,000. When a crosslinked structure is introduced into the base polymer, it is preferable that the molecular weight of the base polymer before the introduction of the crosslinked structure is within the above range.

[0062] A crosslinked structure may be introduced into the base polymer for the purpose of adjusting the adhesive strength of the pressure-sensitive adhesive layer 292. For example, a crosslinked structure is introduced by adding a crosslinking agent to a solution obtained after polymerizing the base polymer, and heating the solution as necessary.

[0063] Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and metal chelate-based crosslinking agents. Among these, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred due to their high reactivity with the hydroxyl and carboxyl groups of the base polymer and the ease of introducing a crosslinked structure. The amount of crosslinking agent used can be adjusted appropriately depending on the composition and molecular weight of the base polymer, the desired adhesive properties, and the like. To provide the pressure-sensitive adhesive with appropriate cohesive strength and adjust the peel strength when peeling the protective film from the adherend within an appropriate range, the amount of crosslinking agent used is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, and even more preferably 1.5 parts by weight or more, per 100 parts by weight of the base polymer. To provide appropriate adhesion to the adherend, the amount of crosslinking agent used is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and even more preferably 10 parts by weight or less, per 100 parts by weight of the base polymer.

[0064] The introduction of a crosslinked structure into the base polymer increases the gel fraction of the adhesive, and as the viscous behavior decreases, the peel force required to peel the protective film from the adherend tends to decrease. The gel fraction of the adhesive layer 292 is preferably 70.0% or more, more preferably 80.0% or more, and even more preferably 90.0% or more. If the gel fraction of the adhesive layer 292 is excessively high, the wettability to the adherend may decrease, resulting in insufficient adhesive strength. Therefore, the gel fraction of the adhesive layer 292 is preferably 99% or less, more preferably 98% or less. The gel fraction can be determined as the content insoluble in a solvent such as ethyl acetate. Specifically, it is determined as the weight fraction (unit: wt%) of the insoluble content after immersing the adhesive layer in ethyl acetate at 23°C for 7 days relative to the sample before immersion. Generally, the gel fraction of a polymer is equal to the degree of crosslinking; the more crosslinked portions in the polymer, the higher the gel fraction.

[0065] The adhesive layer 292 may contain additives such as a silane coupling agent, a tackifier, a plasticizer, a softener, an anti-degradant, a filler, a colorant, an ultraviolet absorber, an antioxidant, a surfactant, and an antistatic agent.

[0066] The thickness of the adhesive layer 292 is not particularly limited, but from the viewpoint of achieving both adhesive strength to the adherend and ease of releasability from the adherend, the thickness of the adhesive layer 292 is preferably 1 to 50 μm, more preferably 2 to 40 μm, and even more preferably 3 to 35 μm. The thinner the thickness of the adhesive layer 292, the better the ease of releasability from the adherend tends to be.

[0067] The peel force when peeling the protective film 2 from the film substrate 1 is preferably 1.5 N / 50 mm or less, and may be 1.0 N / 50 mm or less or 0.8 N / 50 mm or less. The peel force is measured in a peel test in which the protective film is peeled from the film substrate at a peel angle of 180° and a pulling speed of 10 m / min. By reducing the peel force, zipping when peeling the protective film from the film substrate can be suppressed. Furthermore, since vibration of the film substrate 1 caused by the peel force of the protective film 2 is reduced, the running state of the film substrate 1 in the coating section 30 (on the backup roll 31) is stabilized, and uneven application of the coating liquid can be suppressed.

[0068] From the viewpoint of suppressing zipping and uneven coating, it is preferable that the peel strength of the protective film 2 is small. On the other hand, if the peel strength is too small, the protective film may unintentionally peel off from the film substrate when the laminate of the film substrate and the protective film is transported by rolls, causing transport problems. Therefore, the peel strength when peeling the protective film from the film substrate is preferably 0.05 N / 50 mm or more, and may be 0.1 N / 50 mm or more, 0.15 N / 50 mm or more, or 0.2 N / 50 mm or more.

[0069] (antistatic layer) The protective film 2 may have an antistatic layer on the back surface of the core material 291. By providing an antistatic layer, the surface resistance of the back surface 2A of the protective film 2 is reduced, and charging can be more effectively suppressed when the film substrate 1 and the protective film 2 are bonded together. Furthermore, by providing the protective film 2 with an antistatic layer, charging of the film substrate 1 when the protective film 2 is peeled from the film substrate 1 is prevented, and adhesion of dust to the film substrate 1 and coating defects caused by static electricity can be suppressed.

[0070] Examples of the antistatic layer include a layer formed by incorporating an antistatic component into a binder resin. Various types of resins can be used as the binder resin, such as thermosetting resins, ultraviolet-curable resins, electron beam-curable resins, and two-component resins. Examples of the antistatic component include organic or inorganic conductive substances and various antistatic agents. Examples of organic conductive substances include conductive polymers such as polyaniline, polypyrrole, polythiophene, polyethyleneimine, and allylamine-based polymers. Examples of inorganic conductive substances include various metals, alloys, and conductive metal oxides. The inorganic conductive substance is preferably contained in the antistatic layer as fine particles with a particle diameter of 0.1 μm or less (typically 0.01 μm to 0.1 μm). The antistatic component may be a cationic antistatic agent, an anionic antistatic agent, an amphoteric antistatic agent, a nonionic antistatic agent, or the like.

[0071] The surface resistance of the back surface 2A of the protective film 2 is 1×10 10 Ω / sq or less, 5×10 9 Ω / sq or less, 1×10 9 Ω / sq or less, or 5×10 8 The surface resistance may be Ω / sq or less. Generally, the surface resistance is 1×10 3 Ω / sq or more, 1×10 4 Ω / sq or more, or 1×10 5 The smaller the surface resistance of the back surface 2A of the protective film 2, the more likely it is that charging will be suppressed when the film substrate 1 and the protective film 2 are attached to each other and when the protective film 2 is peeled off from the film substrate 1.

[0072] [Optical film fabrication] A laminate 8 is formed by laminating the pressure-sensitive adhesive layer 292 of the protective film 2 to one surface of the film substrate 1, and then the protective film 2 is peeled off from the film substrate 1 of the laminate 8. A coating layer 3 is formed on the first main surface 1A of the film substrate 1, thereby obtaining a laminate (optical film) 9 having the coating layer 3 on the film substrate 1. Below, each step will be described, focusing on the case where a liquid crystal composition containing a liquid crystal compound is used as the coating liquid and an aligned liquid crystal layer is formed as the coating layer 3.

[0073] <Lamination process> As shown in FIG. 3 , while the film substrate 1 and the protective film 2 are each transported by rolls, the film substrate 1 and the protective film 2 are sandwiched and bonded by a pair of nip rolls 41, 42 in a bonding section 40, thereby forming a laminate 8. The bonding step may be carried out continuously with the manufacturing step of the film substrate 1. For example, if the film substrate 1 is a stretched film, the protective film 2 may be bonded onto the film substrate 1 in a roll-to-roll manner before the stretched film is wound into a roll. By carrying out the bonding of the protective film 2 continuously with the manufacturing step of the film substrate 1, the number of times the rolls come into contact with the first main surface 1A of the film substrate 1 can be reduced, thereby suppressing the occurrence of scratches.

[0074] As described above, the first roll 41 and the second roll 42 constituting the pair of nip rolls are both conductive. Examples of conductive rolls include metal rolls and conductive rubber rolls. The conductive roll may be a coated roll in which the outer peripheral surface of an insulating material is coated with a conductive material, as long as the contact surface with the film substrate 1 and the protective film 2 is conductive. The surface resistance of the conductive roll is, for example, 1×10 10 Ω / sq or less, 1×10 9 Ω / sq or less, 1×10 8 Ω / sq or less or 1×10 7 It may be Ω / sq or less.

[0075] The metal roll may be one in which a metal coating is applied to the outer circumferential surface of an insulating material (e.g., a resin material). The conductive rubber roll may be one in which the outer circumferential surface of a metal roll or a resin roll is covered with conductive rubber. Examples of conductive rubber materials that make up the conductive rubber roll include rubber materials such as natural rubber, butadiene rubber, acrylic rubber, silicone rubber, urethane rubber, and fluororubber mixed with a conductive material such as carbon black.

[0076] The first roll 41 in contact with the film substrate 1 and the second roll 42 in contact with the protective film 2 may be the same type of roll or different types of rolls. For example, both nip rolls 41, 42 may be metal rolls, both may be conductive rubber rolls, or one may be a metal roll and the other a conductive rubber roll. From the viewpoint of suppressing bonding defects such as air bubbles at the bonding interface, it is preferable that at least one of rolls 41, 42 is a conductive rubber roll. Both rolls 41, 42 may be conductive rubber rolls. Silicone rubber is particularly preferable as the rubber material for the conductive rubber roll because its hardness can be easily adjusted and the distribution of nip pressure in the width direction can be easily made uniform.

[0077] <First conveying process> The laminate 8, in which the protective film 2 is bonded to the first main surface 1A of the film substrate 1, is first wound up as a roll-shaped wound body 80 and set on an unwinding roll 81. The laminate 8 unwound from the wound body 80 set on the unwinding roll 81 moves continuously downstream of a conveyance path formed along conveyance rolls 83, 85, and 87, and is conveyed to a peeling section 10.

[0078] 3 and 4, the laminate 8 of the film substrate 1 and the protective film 2 is temporarily wound into a roll, but the step of bonding the film substrate 1 and the protective film 2 to form the laminate 8 (the above-mentioned bonding step) and the first conveying step may be carried out consecutively. For example, after bonding the film substrate 1 and the protective film 2, the laminate 8 may be conveyed directly to the peeling section 10 without being wound up.

[0079] <Peeling process> In the peeling step, the protective film 2 is peeled from the laminate 8 transported to the peeling section 10, exposing the first main surface 1A of the film substrate 1. There are no particular limitations on the method for peeling the protective film, but peeling is generally performed on a peeling roll 11. If transport rolls 13 and 23 downstream of the peeling roll 11 are arranged so that the wrap angle of the protective film 2 with respect to the peeling roll 11 is larger than the wrap angle of the film substrate 1 with respect to the peeling roll 11, the protective film 2 can be peeled from the film substrate 1 on the peeling roll 11. The peeling roll may be a pair of nip rolls that sandwich the laminate 8 from above and below. The protective film 2 peeled from the first main surface of the film substrate 1 is transported along a transport path defined by transport rolls 23 and 25 and taken up as a roll 20 by a take-up roll 21.

[0080] <Second conveying process> In the second conveying step, the film substrate 1 after the protective film 2 has been peeled off is conveyed to the coating unit 30. After the protective film 2 has been peeled off in the peeling unit 10, the first main surface 1A of the film substrate 1 is exposed while the film substrate 1 is conveyed from the peeling unit 10 to the coating unit 30. In this embodiment, the conveying path of the film substrate 1 in the second conveying step is short and there is little opportunity for the first main surface 1A of the film substrate 1 to come into contact with the conveying roll, so the frequency of scratches on the film substrate in the second conveying step is low.

[0081] By ensuring that the transport roll does not come into contact with the first main surface 1A of the film substrate 1 while transporting the film substrate 1 from the peeling section 10 (peeling roll 11) to the coating section 30 (backup roll 31), it is possible to prevent scratches from occurring on the first main surface 1A of the film substrate 1 during the second transport step.

[0082] As shown by the dashed line in Fig. 4, in the second conveying step, a roll 15 may come into contact with the first main surface 1A of the film substrate 1. When the roll 15 comes into contact with the first main surface 1A of the film substrate 1, a force acts on the film substrate 1, pressing it from the first main surface side (the lower side in the figure) toward the upper side in the figure. This reduces vibration of the film substrate 1 caused by the peeling force of the protective film 2, and can suppress uneven application of the coating liquid.

[0083] In the transport path (second transport step) of the film substrate 1 from when the protective film 2 is peeled off in the peeling section 10 until when the coating liquid is applied in the application section 30, the roll 15 in contact with the first main surface 1A of the film substrate 1 can act as a "pressure roll" for the film substrate 1.

[0084] The pressure roll does not need to be in contact with the entire width of the film substrate 1 as long as it can suppress vibration of the film substrate 1 caused by peeling of the protective film 2 at the peeling section 10. The pressure roll may be in contact with only both ends of the film substrate 1 in the width direction, and not with the center portion in the width direction. For example, a barbell-shaped roll 151 as shown schematically in FIG. 5 can be used as the pressure roll 15 that contacts the first main surface 1A of the film substrate 1.

[0085] Roll 151 has cylindrical rolls 15R and 15L at both ends, and rolls 15R and 15L at both ends are connected via connecting shaft 15C having a smaller diameter than these rolls. When this roll 151 is used, roll 151 comes into contact with only both ends of the film substrate in the width direction, and does not come into contact with the center of the film substrate in the width direction.

[0086] In the second conveying step, scratches may be formed on the first main surface of the film substrate at both widthwise ends (areas where the rolls 15R and 15L contact) due to contact with the rolls 15. However, by designating these areas as non-product areas and designating only the center in the widthwise direction, which does not contact the rolls 15, as the product area, an optical film (coating layer 3) with fewer defects due to scratches on the film substrate 1 can be obtained. For example, if the coating liquid is applied only to the center in the widthwise direction of the film substrate 1 and no coating layer is formed on both widthwise ends of the film substrate, only the center in the widthwise direction becomes the product area. Alternatively, at an appropriate stage after the formation of the coating layer, the both end areas may be cut and removed from the product by methods such as punching the film or slitting the edges, leaving only the center in the widthwise direction of the film substrate as the product area.

[0087] Thus, in the second conveying step, when a roll contacts the first main surface 1A of the film substrate 1, it is preferable that the press roll contacts the first main surface 1A at both widthwise ends and not at the center in the widthwise direction. In this configuration, vibration of the film substrate 1 caused by peeling of the protective film 2 is suppressed, coating unevenness of the coating layer 3 is reduced, and a coating layer 3 with few defects caused by scratches on the film substrate 1 is obtained.

[0088] At each end of the film substrate 1, the width of the contact area between the film substrate and the pressure roll is, for example, 1 to 50 cm. If the width of the contact area between the film substrate and the pressure roll is excessively small, the vibration suppression effect of the film substrate may be insufficient, and the running performance of the film substrate may be reduced. If the width of the contact area between the film substrate and the pressure roll is excessively large, the width of the non-product area of ​​the optical film may be large, resulting in reduced production efficiency and yield. The width of the contact area between the film substrate and the pressure roll may be 2 cm or more, 3 cm or more, or 5 cm or more, or may be 30 cm or less, 25 cm or less, 20 cm or less, 15 cm or less, or 10 cm or less.

[0089] The pressure rolls may be arranged so as to extend outward from both widthwise ends of the film substrate 1, or may be arranged more inward than both widthwise ends. When the pressure rolls are arranged more inward than both widthwise ends of the film substrate 1, the distance from the widthwise ends of the film substrate to the pressure rolls may be within 30 cm, 20 cm, 15 cm, 10 cm, 5 cm, 3 cm, or 1 cm.

[0090] After the protective film 2 is peeled off in the peeling unit 10, and before the coating liquid is applied in the coating unit 30, the pressure rolls in contact with the first main surface 1A of the film substrate 1 may be any roll capable of suppressing vibration of the film substrate by pressing down both ends of the film substrate, and the shape of the pressure roll is not limited to the barbell shape shown in FIG. 5 . For example, two separate rolls may be disposed at both ends in the width direction. The pressure roll in contact with the first main surface 1A of the film substrate 1 may be a nip roll paired with a roll in contact with the second main surface 1B of the film substrate 1 to sandwich the film substrate 1. Two or more pressure rolls in contact with the first main surface 1A of the film substrate 1 may be provided between the peeling unit 10 and the coating unit 30.

[0091] In the second conveying step, the means for suppressing vibration of the film substrate by pressing the film substrate from the first main surface 1A side of the film substrate 1 does not necessarily have to be a rotating body. For example, a pin or the like that presses the film substrate from the first main surface side (the lower side in the figure) toward the second main surface side may be disposed between the peeling unit 10 and the coating unit 30 as a film pressing mechanism.

[0092] In the second conveying step, both ends of the film substrate may be held by tenter clips. In this case, both end regions of the film substrate in the width direction can be pressed from both the first and second main surfaces without contacting the center of the film substrate in the width direction with a roll or the like, thereby suppressing vibration of the film substrate 1 caused by peeling of the protective film 2. In this case, the lower clip in contact with the first main surface of the film substrate acts as a film pressing mechanism.

[0093] As shown in Figure 4, in the second conveying step between the peeling section 10 and the coating section 30, by bringing the roll 13 into contact with the second main surface 1B of the film substrate 1, the film substrate 1 is also pressed from the second main surface 1B side, so that vibration of the film substrate 1 caused by the peeling force of the protective film 2 can be more effectively suppressed.

[0094] The roll 13 in contact with the second main surface 1B of the film substrate 1 may be in contact with only both ends of the film substrate, or may be in contact with the entire width of the film substrate. From the viewpoint of transportability of the film substrate, it is preferable that the roll 13 be in contact with the entire width of the second main surface of the film substrate.

[0095] <Coating process> A coating liquid is applied onto the first main surface 1A of the film substrate 1 transported to the coating unit 30. In the embodiment shown in Fig. 4, the coating liquid discharged from a die 33 is applied onto the first main surface 1A of the film substrate 1 with the second main surface 1B of the film substrate 1 in contact with the backup roll 31.

[0096] There are no particular limitations on the method for applying the coating liquid onto the film substrate 1. In addition to die coating, examples of the application method include kiss roll coating, gravure coating, reverse coating, spray coating, Mayer bar coating, knife roll coating, and air knife coating. The thickness of the coating liquid is preferably adjusted so that the thickness of the coating layer 3 after drying the solvent is approximately 0.1 to 20 μm.

[0097] In this embodiment, the protective film 2 is temporarily attached to and protected by the first main surface 1A of the film substrate 1 until immediately before the coating step, thereby suppressing the occurrence of scratches on the first main surface 1A of the film substrate 1 due to roll conveyance. Furthermore, by sandwiching and laminating the film substrate 1 and the protective film 2 between two conductive rolls 41, 42, internal charging of the laminate 8 is unlikely to occur, and the occurrence of coating defects due to charging of the film substrate 1 after peeling off the protective film 2 is suppressed. Therefore, it is possible to form a coating layer 3 with few defects, such as scratches and streaks, caused by the film substrate 1.

[0098] <Post-application process> After the coating liquid is applied, the film substrate 1 may be heated in a heating section 50. The heating section 50 includes, for example, a heating furnace 55, and the film substrate 1 and the coating liquid applied thereon are heated while the film substrate 1 is transported through the heating furnace 55. For example, the solvent in the coating liquid can be removed by heating.

[0099] When the coating liquid is a liquid crystal composition and the liquid crystal compound contained in the liquid crystal composition is a thermotropic liquid crystal, the liquid crystal compound is oriented in a predetermined direction by heating the liquid crystal composition layer to a liquid crystal phase. Specifically, the liquid crystal composition coated on the film substrate is heated to a temperature equal to or higher than the N (nematic phase)-I (isotropic liquid phase) transition temperature to create an isotropic liquid state. From there, the liquid crystal composition is gradually cooled as necessary to develop a nematic phase. At this time, it is desirable to temporarily maintain the temperature at which the liquid crystal phase is exhibited and grow the liquid crystal phase domain to form a monodomain. Alternatively, after coating the liquid crystal composition, the temperature may be maintained for a certain period within the temperature range at which the nematic phase is developed to align the liquid crystal molecules in a predetermined direction.

[0100] The heating temperature for aligning the liquid crystal compound in a predetermined direction may be appropriately selected depending on the type of liquid crystal composition, and is usually about 40 to 200°C. If the heating temperature is too low, the transition to the liquid crystal phase tends to be insufficient, while if the heating temperature is too high, alignment defects may increase. The heating time may be adjusted so that the liquid crystal phase domains grow sufficiently, and is usually about 30 seconds to 30 minutes.

[0101] After the liquid crystal compound is oriented by heating, it is preferable to cool the film to a temperature below the glass transition temperature. The cooling method is not particularly limited, and for example, the film may be cooled by removing it from the heated atmosphere to room temperature. Forced cooling by air cooling, water cooling, or the like may also be used.

[0102] If the liquid crystal compound is curable, it is preferable to perform curing in the curing unit 60. For example, if the liquid crystal compound is photocurable, photocuring is performed while the photocurable liquid crystal compound (liquid crystal monomer) maintains liquid crystal regularity. The light irradiated from the light source 61 may be any light capable of polymerizing the photocurable liquid crystal compound, and typically, ultraviolet or visible light with a wavelength of 250 to 450 nm is used. If the liquid crystal composition contains a photopolymerization initiator, light of a wavelength to which the photopolymerization initiator is sensitive may be selected. Examples of light sources that can be used for irradiation include low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, LEDs, black lights, and chemical lamps. To promote the photocuring reaction, light irradiation is preferably performed under an inert gas atmosphere such as nitrogen gas.

[0103] During photocuring, the liquid crystal compound can be aligned in a predetermined direction by using polarized light in a predetermined direction. As described above, when the liquid crystal compound is aligned by the alignment regulating force of the film substrate 1, the irradiated light may be unpolarized (natural light).

[0104] The irradiation intensity may be adjusted appropriately depending on the composition of the liquid crystal composition, the amount of photopolymerization initiator added, etc. The irradiation energy (cumulative irradiation light amount) is usually 20 to 10,000 mJ / cm 2 Approximately 50-5000mJ / cm 2 is preferred, and 100 to 800 mJ / cm 2 In order to accelerate the photocuring reaction, the photoirradiation may be carried out under heated conditions.

[0105] The polymerized product obtained by photocuring the liquid crystal monomer is non-liquid crystal, and does not undergo transitions between liquid crystal, glass, and crystalline phases due to temperature changes. Therefore, a liquid crystal layer photocured with the liquid crystal monomer aligned in a predetermined direction is less likely to experience changes in molecular orientation due to temperature changes. Furthermore, because the liquid crystal layer has a significantly higher birefringence than a film made of a non-liquid crystal material, the thickness of an optically anisotropic element having a desired retardation can be significantly reduced.

[0106] The optical properties of the coating layer (liquid crystal layer) 3 are not particularly limited. The in-plane retardation and thickness retardation of the coating layer 3 may be appropriately set depending on the application, etc. When the liquid crystal molecules are homogeneously aligned, the in-plane retardation of the coating layer 3 is, for example, about 20 to 1000 nm. When the coating layer 3 is a quarter-wave plate, the in-plane retardation is preferably 100 to 180 nm, more preferably 120 to 150 nm. When the coating layer 3 is a half-wave plate, the in-plane retardation is preferably 200 to 340 nm, more preferably 240 to 300 nm. When the liquid crystal is homeotropically aligned, the in-plane retardation of the coating layer 3 is approximately 0 (for example, 5 nm or less, preferably 3 nm or less), and the absolute value of the thickness retardation is about 30 to 500 nm.

[0107] The retardation of a coating layer 3 such as a liquid crystal layer is proportional to its thickness. When a coating liquid is applied, if a locally thin portion is formed due to repelling or the like on the surface of the film substrate, the retardation of that portion will be small, resulting in optical unevenness in the display device. As described above, in this embodiment, the film substrate and the protective film are sandwiched and bonded together by a nip roll consisting of two conductive rolls, which makes it difficult for internal charging to occur during bonding and suppresses the occurrence of streaky thickness unevenness due to coating defects. Therefore, retardation unevenness caused by thickness unevenness of the optical film (coating layer) is unlikely to occur, resulting in excellent optical uniformity.

[0108] The orientation direction of the liquid crystal molecules in the coating layer (liquid crystal layer) 3 may be parallel or non-parallel to the longitudinal direction of the film substrate 1 (roll-to-roll transport direction). As mentioned above, by utilizing the orientation restricting force of an obliquely stretched film or the like, a liquid crystal layer can be formed in which the liquid crystal molecules are oriented non-parallel to the longitudinal direction. When the liquid crystal molecules are oriented non-parallel to the longitudinal direction, if there are scratches on the film substrate along the longitudinal direction, the liquid crystal molecules in the liquid crystal layer formed thereon will be oriented in the longitudinal direction along the scratches, causing poor orientation. As mentioned above, by applying the liquid crystal composition on the film substrate 1 immediately after peeling off the protective film 2 temporarily attached to the film substrate 1, it is possible to prevent scratches on the film substrate and reduce poor orientation of the liquid crystal layer.

[0109] <Optical film processing> A laminate 9 (optical film) in which a coating layer 3 is formed on the first main surface 1A of a film substrate 1 is wound around a winding roll 91 to obtain a long rolled optical film 90. This laminate 9 can be used as an optical film as is. Since the regions at both ends in the width direction of the film substrate 1 are non-product regions, they may be cut and removed by slitting after the coating layer 3 is formed and before the film substrate 1 is wound around the winding roll 91, or at an appropriate stage after the film substrate 1 is wound around the winding roll 91. Alternatively, the film may be punched to cut out individual products so as to exclude the regions at both ends in the width direction.

[0110] The laminate 9 in which the coating layer 3 is formed on the first main surface 1A of the film substrate 1 may be used as an optical film as is, or the film substrate 1 may be peeled off and only the coating layer 3 may be used as an optical film. When the coating layer 3 is a resin layer, the laminate of the film substrate 1 and the coating layer 3 may be stretched to impart optical anisotropy to the coating layer 3.

[0111] Other layers may be laminated on the coating layer 3. For example, an optical layer 4 is bonded onto the coating layer 3 via an adhesive layer 5, thereby obtaining a laminate 96 shown in FIG.

[0112] The optical layer 4 laminated on the coating layer 3 is not particularly limited, and any optically isotropic or optically anisotropic film commonly used as an optical film can be used without any particular limitation. Specific examples of the optical layer 4 include transparent films such as retardation films and polarizer protective films, and functional films such as polarizers, viewing angle widening films, viewing angle limiting (peeping prevention) films, and brightness enhancement films. The optical layer 4 may be a single layer or a laminate. The optical layer 4 may be a liquid crystal layer. The optical layer 4 may be a polarizing plate in which a transparent protective film is bonded to one or both sides of a polarizer. When the polarizing plate has a transparent protective film on one side, the polarizer and the coating layer may be bonded together, or the transparent protective film and the coating layer may be bonded together.

[0113] The adhesive constituting adhesive layer 5 is not particularly limited as long as it is optically transparent, and examples thereof include epoxy resin, silicone resin, acrylic resin, polyurethane, polyamide, polyether, polyvinyl alcohol, etc. The thickness of adhesive layer 5 is appropriately set depending on the type of adherend, the adhesive material, etc. When using a curing type adhesive that exhibits adhesion through a crosslinking reaction after application, the thickness of adhesive layer 5 is preferably 0.01 to 5 μm, and more preferably 0.03 to 3 μm.

[0114] The adhesive may be in any of various forms, such as a water-based adhesive, a solvent-based adhesive, a hot-melt adhesive, an active energy ray-curable adhesive, etc. Among these, a water-based adhesive or an active energy ray-curable adhesive is preferred because it allows the thickness of the adhesive layer to be reduced.

[0115] An adhesive is applied to one or both of the surfaces of the coating layer 3 and the optical layer 4, and then cured, thereby laminating the coating layer 3 and the optical layer 4 via the adhesive layer 5. The curing method for the adhesive may be selected appropriately depending on the type of adhesive. For example, a water-based adhesive can be cured by heating. An active energy ray-curable adhesive can be cured by irradiation with active energy rays such as ultraviolet light.

[0116] A laminate 96 in which the optical layer 4 is bonded to the coating layer 3 on the film substrate 1 via the adhesive layer 5 may be used as an optical film as is. In this case, the film substrate 1 constitutes part of the optical film. As shown in FIG. 7, the film substrate may be peeled off from the coating layer 3. An appropriate pressure-sensitive adhesive layer 6 may be laminated on the surface of the coating layer 3 exposed by peeling off the film substrate, as shown in FIG. 8.

[0117] The adhesive constituting the adhesive layer 6 is not particularly limited, and can be appropriately selected from those having a base polymer such as an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyether, a fluorine-containing polymer, or a rubber-based polymer. In particular, adhesives such as acrylic adhesives and rubber-based adhesives that have excellent transparency, moderate wettability, cohesion, and adhesion, and excellent weather resistance and heat resistance are preferred. The thickness of the adhesive layer is appropriately set depending on the type of adherend, and is generally about 5 to 500 μm.

[0118] The adhesive layer 6 is laminated on the coating layer 3, for example, by laminating a pre-formed adhesive sheet onto the surface of the coating layer 3. After applying an adhesive composition to the coating layer 3, the adhesive layer 6 may be formed by drying the solvent, crosslinking, photocuring, or the like. In order to increase the adhesive strength (anchoring strength) between the coating layer 3 and the adhesive layer 6, the surface of the coating layer 3 may be subjected to a surface treatment such as corona treatment or plasma treatment, or an easy-adhesion layer may be formed, before laminating the adhesive layer 6.

[0119] A separator 7 is preferably temporarily attached to the surface of the pressure-sensitive adhesive layer 6. The separator 7 protects the surface of the pressure-sensitive adhesive layer 6 until the optical film is bonded to another member. Plastic films such as acrylic, polyolefin, cyclic polyolefin, and polyester are preferably used as constituent materials of the separator. The thickness of the separator is usually about 5 to 200 μm. The surface of the separator is preferably subjected to a release treatment. Examples of the release agent include silicone-based materials, fluorine-based materials, long-chain alkyl-based materials, and fatty acid amide-based materials.

[0120] Another optical layer may be laminated via an appropriate adhesive or pressure-sensitive adhesive layer on the exposed surface of the coating layer 3 after peeling off the film substrate 1. For example, another optical layer may be laminated on the coating layer 3 via an appropriate adhesive layer, and a pressure-sensitive adhesive layer may further be laminated on top of that.

[0121] The optical film having the coating layer can be used, for example, as an optical film for an image display device. An example of an optical film in which another optical layer 4 is laminated onto the coating layer 3 is a circular polarizer in which an aligned liquid crystal layer as the coating layer 3 and a polarizer are laminated together.

[0122] The polarizing plate may consist of only one layer of polarizer, or as mentioned above, a transparent protective film may be attached to one or both sides of the polarizer. Examples of polarizers include hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and partially saponified ethylene-vinyl acetate copolymer films, which are uniaxially stretched after adsorbing a dichroic substance such as iodine or a dichroic dye, and polyene-based oriented films such as dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride.

[0123] Among these, polyvinyl alcohol (PVA) polarizers are preferred because of their high polarization degree. These polarizers are made by adsorbing a dichroic substance, such as iodine or a dichroic dye, onto a polyvinyl alcohol film, such as polyvinyl alcohol or partially formalized polyvinyl alcohol, and then aligning the film in a predetermined direction. For example, a PVA polarizer can be obtained by dyeing a polyvinyl alcohol film with iodine and stretching it. Alternatively, a PVA resin layer may be formed on a resin substrate, and the resulting laminate may be dyed with iodine and stretched.

[0124] In a circular polarizer having a polarizing plate and a liquid crystal layer laminated together, it is preferable that the liquid crystal molecules in at least one of the liquid crystal layers are homogeneously aligned. In the circular polarizer, the liquid crystal molecules are aligned in a homogeneously aligned liquid crystal layer such that the alignment direction of the liquid crystal molecules is neither parallel nor perpendicular to the absorption axis direction of the polarizer.

[0125] For example, when the circular polarizer has only one liquid crystal layer, the liquid crystal layer as coating layer 3 is a quarter-wave plate, and the angle between the absorption axis direction of the polarizer and the alignment direction of the liquid crystal molecules (generally the slow axis direction) is set to 45°. The angle between the absorption axis direction of the polarizer and the alignment direction of the liquid crystal molecules may be 35 to 55°, 40 to 50°, or 43 to 47°.

[0126] In a configuration in which the polarizing plate 4 and the coating layer 3 serving as a quarter-wave plate are laminated so that the angle between their optical axes is 45°, a liquid crystal layer in which the liquid crystal molecules are aligned perpendicular to the substrate surface (homeotropic alignment) may be further provided. By laminating the coating layer 3 serving as a quarter-wave plate and a homeotropic liquid crystal layer functioning as a positive C plate in this order on the polarizing plate, a circular polarizing plate can be formed that can block reflected light even from external light coming from an oblique direction. A homeotropically aligned liquid crystal layer (positive C plate) and a homogeneously aligned liquid crystal layer (quarter-wave plate serving as a positive A plate) may be laminated in this order on the polarizing plate.

[0127] In a circular polarizer having multiple liquid crystal layers stacked on a polarizer, all of the liquid crystal layers may be homogeneously aligned liquid crystal layers. In this case, it is preferable that the liquid crystal layer disposed closer to the polarizer 4 is a half-wave plate, and the liquid crystal layer disposed farther from the polarizer is a quarter-wave plate. In this stacked structure, the half-wave plate is preferably arranged so that the angle between the slow axis direction of the half-wave plate and the absorption axis direction of the polarizer is 75°±5°, and the angle between the slow axis direction of the quarter-wave plate and the absorption axis direction of the polarizer is 15°±5°. A circular polarizer having such a stacked structure functions as a circular polarizer over a wide wavelength range of visible light, thereby reducing the coloring of reflected light.

[0128] As described above, in the embodiment of the present invention, the protective film is temporarily attached to the surface of the film substrate until immediately before the coating liquid is applied, thereby suppressing scratches on the film substrate and reducing defects in the coating layer caused by scratches on the film substrate. Furthermore, even if the coating layer is an oriented liquid crystal layer in which the liquid crystal molecules are oriented non-parallel to the longitudinal direction of the film substrate, alignment defects are reduced. Furthermore, because coating defects caused by bonding the film substrate and the protective film are suppressed, the in-plane uniformity of the coating layer is high, enabling the realization of good display characteristics. [Explanation of symbols]

[0129] 1. Film substrate 2 Protective Film 291 Core material 292 Adhesive layer 3 Coating layer (liquid crystal layer) 4 Optical layer (polarizing plate) 5 Adhesive layer 6 Adhesive layer 7 Separator 8 Laminate 9,96,97,98 Laminates (Optical Films) 29,81 Unwinding roll 21, 49, 91 Winding roll 40 Laminating section 41,42 Nip roll 10 Peeling section 11 Peeling roll 30 Application section 31 Backup Roll 33 Dice 50 Heating section 55 Heating Furnace 60 Hardened part 61 Light source 44, 45, 46, 47 Transport roll 83, 85, 87 Transport roll 13 Transport roll 15,151 Presser roll 71, 73, 75, 77, 79 Transport rolls

Claims

1. A method for producing a long optical film, comprising: a lamination step in which a long film substrate having a first main surface and a second main surface and a protective film are sandwiched and laminated between a pair of nip rolls consisting of a first roll and a second roll, thereby obtaining a laminate in which the protective film is releasably attached to the first main surface of the film substrate; a first conveying step of conveying the laminate by rolls along the longitudinal direction of the film substrate to a peeling section; a protective film peeling step of peeling the protective film from the first main surface of the film substrate in the peeling section; a second transport step of transporting the film substrate from the peeling section to a coating section along the longitudinal direction of the film substrate after the protective film has been peeled off; and a coating step of applying a coating liquid onto the first main surface of the film substrate in the coating section to obtain a laminate having a coating layer on the first main surface of the film substrate; and the first roll and the second roll are both electrically conductive. A method for manufacturing an optical film.

2. The method for producing an optical film according to claim 1 , wherein at least one of the first roll and the second roll is a conductive rubber roll.

3. The method for producing an optical film according to claim 1 or 2, wherein the coating liquid is a liquid crystal composition containing a liquid crystal compound.

4. the liquid crystal composition contains a photocurable liquid crystal compound, The method for producing an optical film according to claim 3 , further comprising a step of photocuring the liquid crystal compound after the coating step.

5. 5. The method for producing an optical film according to claim 1, wherein the film substrate is a stretched film in which molecules are oriented non-parallel to the longitudinal direction.

6. The method for producing an optical film according to any one of claims 1 to 5, wherein in the second transport step, a roll does not come into contact with a central portion in the width direction of the first main surface of the film substrate.

7. 7. The method for producing an optical film according to claim 6, wherein in the second conveying step, a film holding mechanism contacts both widthwise end portions of the first main surface of the film substrate at least once, and the film holding mechanism does not contact a widthwise central portion of the first main surface of the film substrate.

8. The method for producing an optical film according to claim 7 , wherein the film pressing mechanism is a pressing roll that contacts only both widthwise ends of the first main surface of the film substrate.

9. The method for producing an optical film according to any one of claims 1 to 8, further comprising a step of laminating another optical layer on the coating layer in a roll-to-roll manner.

10. The method for producing an optical film according to claim 9 , wherein the optical layer comprises a polarizer.

Images