JP7745340B2 - Optical film manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing an optical film.

Thin coating films are used as optical films that provide functions such as optical compensation in liquid crystal display devices and anti-reflection of external light in organic EL devices. Thin films have poor self-supporting properties and are difficult to handle on their own, so a coating layer is formed by applying a solution to a support such as a plastic film, and then drying and processing are carried out while the coating layer remains in close contact with the support.

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

Japanese Patent Application Laid-Open No. 2004-46068 WO2016/121856

In a method in which a coating layer is formed by coating a solution onto a film substrate as it is transported longitudinally using the roll-to-roll method, scratches on the film substrate can cause defects such as the scratches being transferred to the coating layer or poor alignment of the 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.

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.

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 attached to the first main surface of the film substrate (lamination process). Both the first roll and the second roll that make up the pair of nip rolls are electrically conductive.

The laminate of the film substrate and protective film is roll-conveyed along the longitudinal direction to a peeling section (first conveying step), where the protective film is peeled off from the first main surface of the film substrate (protective film peeling step). After the protective film is peeled off, the film substrate is conveyed along the longitudinal direction of the film substrate from the peeling section to a coating section (second conveying step), where a coating is applied to the first main surface of the film substrate (coating step), yielding a laminate with a coating layer on the first main surface of the film substrate.

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 applying a liquid crystal composition containing a photocurable liquid crystal compound onto a film substrate, the liquid crystal compound may be photocured.

The film substrate may have an alignment control force that aligns the liquid crystal molecules in a specific 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.

The optical film may be one in which another optical layer is laminated on a coating layer using a roll-to-roll process. The optical layer laminated on the coating layer may include a polarizer. The optical film may be a circular polarizing plate in which a coating layer and a polarizer are laminated.

Because the protective film remains temporarily attached to the film substrate until immediately before the coating liquid is applied, scratches on the film substrate caused by 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 caused by charging of the film substrate. This results in a coating layer with fewer defects, such as scratches and streaks, caused by the film substrate.

FIG. 1 is a cross-sectional view of an optical film having a coating layer on a film substrate. FIG. 2 is a cross-sectional view of a laminate in which a protective film is temporarily attached onto a film substrate. FIG. 2 is a diagram showing an outline of a process for bonding a film substrate and a protective film together. 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. FIG. 2 is a perspective view showing an example of the shape of a pressure roll. FIG. 1 is a cross-sectional view of an optical film according to an embodiment. FIG. 1 is a cross-sectional view of an optical film according to an embodiment. FIG. 1 is a cross-sectional view of an optical film according to an embodiment.

[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.

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

The laminating unit 40 is equipped with a pair of nip rolls 41, 42. The film substrate 1 and protective film 2 transported from the upstream side (left side of the figure) are sandwiched between the pair of nip rolls consisting of the first roll 41 and the second roll 42, and are laminated together, resulting in a laminate 8 in which the protective film 2 is releasably adhered to the film substrate 1 (laminating process). As will be described in detail later, the first roll 41, which contacts the film substrate 1, and the second roll 42, which contacts the protective film 2, are both conductive rolls.

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

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

In the peeling section 10, the protective film 2 is peeled off from the film substrate 1 (peeling process). 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 process). In the coating section 30, a coating liquid is applied to the first main surface 1A of the film substrate 1 (coating process).

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

When a solution is applied to a film substrate while it is being transported roll-to-roll, scratches are likely to occur along the length of the film substrate 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.

In an 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 process), the first main surface 1A of the film substrate 1 does not come into direct contact with the conveying roll 87 during the first conveying process. Immediately after the protective film 2 is peeled from the film substrate 1, a coating liquid is applied to the first main surface 1A of the film substrate 1, preventing scratches on the first main surface of the film substrate due to contact with the conveying roll 87 and suppressing the transfer of scratches to the coating layer 3 and poor alignment of liquid crystal molecules.

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

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.

When a coating liquid was applied to a film substrate immediately after peeling off the protective film, a sample was analyzed that showed streaky unevenness in the coating layer. No thickness unevenness or physical deformation was observed in the film substrate after peeling off the coating layer. Therefore, it is believed that the streaky unevenness in the coating layer formed on the film substrate is caused by repelling, which is caused by the film substrate becoming charged when the coating liquid is applied to its surface.

One cause of static buildup on 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 streaky irregularities described above were not fully eliminated. To further investigate static buildup on the film substrate, a toner test was conducted in which toner was adhered to the film surface. This confirmed that toner adhered in lines extending across the width of 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 when the laminate of the film substrate and protective film is charged, the film substrate's charged state (internal charge) is maintained even after the protective film is peeled off, causing the coating liquid to repel and resulting in the formation of streaky irregularities in the coating layer.

In an embodiment of the present invention, the first roll 41 and second roll 42 that make up the pair of nip rolls are electrically conductive, which prevents charging of the laminate 8 due to charging of the nip rolls when laminating the film substrate 1 and protective film 2 at the lamination unit 40. As a result, even after peeling off the protective film 2, internal charging of the film substrate 1 is low, suppressing repelling when applying the coating liquid to the first main surface 1A of the film substrate 1 and preventing the occurrence of streaky thickness unevenness due to poor coating.

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

<Coating liquid>
The coating liquid applied to 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.

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.

A liquid crystal composition containing liquid crystal compounds is applied to the film substrate 1, the liquid crystal compounds are 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.

Liquid crystal compounds include rod-shaped liquid crystal compounds and discotic liquid crystal compounds. Rod-shaped liquid crystal compounds are preferred because they are more likely to be homogeneously oriented due to the alignment-regulating 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) exhibits liquid crystallinity before polymerization, it may not exhibit liquid crystallinity after polymerization.

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

Examples of rod-shaped liquid crystal compounds that exhibit 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.

Examples of polymerizable liquid crystal compounds include polymerizable liquid crystal compounds in which the alignment state of rod-shaped liquid crystal compounds can be fixed using a polymer binder, and polymerizable liquid crystal compounds having polymerizable functional groups that can fix the alignment state of liquid crystal compounds through polymerization. Among these, photocurable liquid crystal compounds having photocurable functional groups are preferred.

The photocurable liquid crystal compound (liquid crystal monomer) has a mesogen group and at least one photocurable functional group per 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.

Mesogenic groups of liquid crystal monomers include cyclic structures such as biphenyl, phenylbenzoate, phenylcyclohexane, azoxybenzene, azomethine, azobenzene, phenylpyrimidine, diphenylacetylene, diphenylbenzoate, bicyclohexane, cyclohexylbenzene, and terphenyl. The ends of these cyclic units may have substituents such as cyano, alkyl, alkoxy, and halogen groups.

Examples of photocurable functional groups include (meth)acryloyl groups, epoxy groups, and vinyl ether groups. Of these, (meth)acryloyl groups are preferred. Photocurable liquid crystal monomers preferably have two or more photocurable functional groups per molecule. Using a liquid crystal monomer containing two or more photocurable functional groups introduces a crosslinked structure into the liquid crystal layer after photocuring, which tends to improve the durability of the optical film.

Any suitable liquid crystal monomer may be used as the photocurable liquid crystal monomer. For example, see 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, and Japanese Patent Application Laid-Open No. 2015 Examples of suitable liquid crystal monomers include compounds 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 possible to adjust the birefringence and the wavelength dispersion of retardation.

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 specific direction. For example, by including a side-chain liquid crystal polymer in 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.

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. Depending on the type of liquid crystal monomer (type of photocurable functional group), a photocation generator or a photoanion generator may be used. The amount of the photopolymerization initiator used is approximately 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.

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.

(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, 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, and butyl cellosolve. A mixed solvent of two or more solvents may also be used.

The solids concentration of the coating liquid is usually around 5 to 60% by weight. The coating liquid may also contain additives such as surfactants and leveling agents.

<Film substrate>
By using a long film substrate 1 as the substrate, a series of steps from application of the coating liquid to drying can be carried out by roll-to-roll. When 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 steps on the film substrate 1. In addition, the step of laminating the coating layer 3 formed on the film substrate 1 to another substrate can also be carried out by roll-to-roll, thereby improving the productivity of the optical film.

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 perspective of optical film productivity, 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 approximately 10 to 200 μm.

The resin material that makes up 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 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.

Films made from 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 mentioned above, the pair of nip rolls 41, 42 that bond the film substrate 1 and protective film 2 together are conductive, which suppresses charging of the laminate 8 and prevents coating defects even when a hydrophobic resin film is used as the film substrate 1.

The film substrate 1 may have an alignment control 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 other factors. 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. A photo-alignment film may also be used. A resin film may also be subjected to a rubbing treatment without providing an alignment film.

The film substrate 1 may be provided with an alignment layer for homeotropically aligning the liquid crystal molecules. Examples of alignment agents for forming a homeotropically oriented alignment layer (vertical alignment layer) 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.

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, which has the effect of orienting liquid crystal molecules along the stretching direction. By using a stretched film, it is possible to provide an orientation control force for orienting liquid crystal molecules in a predetermined direction, even if an orientation film is not formed on the film substrate. Since no orientation film is required, the manufacturing costs of the optical film can be reduced. Furthermore, not providing an orientation film prevents contamination and poor orientation caused by rubbing residue.

The stretching direction of the stretched film (polymer orientation direction) 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 coating layer 3.

The stretching ratio of the stretched film may be such that it can exert an alignment control force, for example, approximately 1.1 to 5 times. The stretched film may also 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 greater stretching ratio.

The stretched film may be an obliquely stretched film. An obliquely stretched film has an orientation axis that is neither parallel nor perpendicular to the longitudinal direction (for example, a direction at an angle of 10 to 80 degrees 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 the liquid crystal molecules are oriented in a direction that is neither parallel nor perpendicular to the longitudinal direction.

<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 also 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).

(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 that can form 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.

(Adhesive layer)
The adhesive layer 292 may be made of an adhesive that is 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 in which the resin material that constitutes the core material 291 and the resin material of the adhesive layer 292 are integrally molded by multilayer extrusion.

The composition of the adhesive that makes up the adhesive layer 292 is not particularly limited, and can be appropriately selected and used based on a polymer such as an acrylic polymer, 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. Acrylic adhesives based on an acrylic polymer are particularly preferred, as their adhesive strength (peel strength) is easily adjusted and they leave little adhesive residue on the film substrate 1 as an adherend.

The acrylic base polymer preferably has a main skeleton of (meth)acrylic acid alkyl ester monomer units. The (meth)acrylic acid alkyl ester preferably has an alkyl group with 1 to 20 carbon atoms. The content of (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 multiple (meth)acrylic acid alkyl esters. The arrangement of the constituent monomer units may be random or block.

The acrylic base polymer preferably contains, as a copolymerization component, a monomer component having a crosslinkable functional group. Examples of monomers having a crosslinkable functional group include hydroxyl group-containing monomers and carboxyl group-containing monomers. Of these, it is preferable for the base polymer to contain, 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. Introducing a crosslinked structure into the base polymer improves the cohesive strength of the pressure-sensitive adhesive, providing 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.

The molecular weight of the base polymer is adjusted appropriately so that the adhesive layer 292 has the desired adhesive strength. For example, the weight average molecular weight in polystyrene equivalent is approximately 50,000 to 2,000,000, preferably approximately 70,000 to 1,800,000, more preferably approximately 100,000 to 1,500,000, and even more preferably approximately 200,000 to 1,000,000. Furthermore, if 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 be within the above range.

A crosslinked structure may be introduced into the base polymer for purposes such as adjusting the adhesive strength of the adhesive layer 292. For example, a crosslinked structure can be introduced by adding a crosslinking agent to the solution obtained after polymerizing the base polymer and heating the solution as necessary.

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 with which crosslinking structures can be introduced. 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 other factors. To impart appropriate cohesive strength to the adhesive and adjust the peel force 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 base polymer. To achieve 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 base polymer.

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 substrate tends to decrease. The gel fraction of the adhesive layer 292 is preferably 70.0% or higher, more preferably 80.0% or higher, and even more preferably 90.0% or higher. If the gel fraction of the adhesive layer 292 is excessively high, wettability to the substrate may decrease, resulting in insufficient adhesive strength. Therefore, the gel fraction of the adhesive layer 292 is preferably 99% or lower, more preferably 98% or lower. The gel fraction can be determined as the insoluble content 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.

The adhesive layer 292 may contain additives such as silane coupling agents, tackifiers, plasticizers, softeners, anti-degradation agents, fillers, colorants, UV absorbers, antioxidants, surfactants, and antistatic agents.

The thickness of the adhesive layer 292 is not particularly limited, but from the perspective 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.

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 tensile 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.

From the perspective of suppressing zipping and uneven coating, it is preferable that the peel strength of the protective film 2 be small. On the other hand, if the peel strength is excessively 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 roll, 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.

(Antistatic layer)
The protective film 2 may have an antistatic layer on the back surface of the core material 291. By providing the 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.

An example of an antistatic layer is a layer formed by incorporating an antistatic component into a binder resin. Various types of binder resins can be used, including thermosetting resins, UV-curable resins, electron beam-curable resins, and two-component resins. Antistatic components include organic or inorganic conductive substances and various antistatic agents. Organic conductive substances include conductive polymers such as polyaniline, polypyrrole, polythiophene, polyethyleneimine, and allylamine-based polymers. 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, or a nonionic antistatic agent.

The surface resistance of the back surface 2A of the protective film 2 may be 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 Ω/sq or less. The surface resistance is generally 1×10 ³ Ω/sq or more, and may be 1×10 ⁴ Ω/sq or more, or 1×10 ⁵ Ω/sq or more. 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 bonded together and when the protective film 2 is peeled off from the film substrate 1.

[Preparation of Optical Film]
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 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. Each step will be described below, 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.

<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, when 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.

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, and may be 1×10 ⁹ Ω/sq or less, 1×10 ⁸ Ω/sq or less, or 1×10 ⁷ Ω/sq or less.

Metal rolls may be made of insulating material (e.g., resin material) with a metal coating applied to the outer surface. Conductive rubber rolls may be made of metal rolls or resin rolls with the outer surface coated with conductive rubber. Examples of conductive rubber materials that can be used for conductive rubber rolls 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.

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 perspective of suppressing lamination defects such as air bubbles at the lamination 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 preferred as the rubber material for the conductive rubber roll because its hardness can be easily adjusted and it is easy to uniformly distribute the nip pressure across the width.

<First conveying step>
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 into 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 transport path formed along transport rolls 83, 85, and 87, and is transported to a peeling section 10.

In Figures 3 and 4, the laminate 8 of the film substrate 1 and the protective film 2 is temporarily wound into a roll-shaped wound body, but the step of bonding the film substrate 1 and the protective film 2 to form the laminate 8 (the bonding step described above) 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.

<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. The method for peeling the protective film is not particularly limited, but peeling is generally performed on a peeling roll 11. If the transport rolls 13, 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 the transport rolls 23, 25 and taken up as a roll 20 by the take-up roll 21.

<Second conveying step>
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.

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), damage to the first main surface 1A of the film substrate 1 can be prevented during the second transport step.

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

During the transport path of the film substrate 1 (second transport step) from when the protective film 2 is peeled off in the peeling section 10 until the coating liquid is applied in the coating 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.

The pressure roll does not need to contact 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 contact only both ends of the film substrate 1 in the width direction, and not the center portion in the width direction. For example, a barbell-shaped roll 151 as shown schematically in Figure 5 can be used as the pressure roll 15 that contacts the first main surface 1A of the film substrate 1.

Roll 151 has cylindrical rolls 15R and 15L at both ends, which are connected via connecting shaft 15C, which has a smaller diameter than these rolls. When this roll 151 is used, roll 151 only comes into contact with 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.

During the second conveying process, scratches may form on the first main surface of the film substrate at both widthwise ends (areas where rolls 15R and 15L come into contact) due to contact with rolls 15. However, by designating these areas as non-product areas and designating only the center widthwise area that does not come into contact with rolls 15 as the product area, an optical film (coating layer 3) with fewer defects caused by scratches on the film substrate 1 can be obtained. For example, if the coating liquid is applied only to the center widthwise of the film substrate 1 and no coating layer is formed on both widthwise ends of the film substrate, only the center widthwise area becomes the product area. Furthermore, at an appropriate stage after the coating layer is formed, 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 widthwise area of the film substrate as the product area.

As such, when a roll contacts the first main surface 1A of the film substrate 1 in the second conveying step, it is preferable that the pressure roll contacts the first main surface 1A at both ends in the width direction and that the roll does not contact the first main surface in the center in the width direction. This configuration suppresses vibration of the film substrate 1 caused by peeling of the protective film 2, reduces uneven application of the coating layer 3, and produces a coating layer 3 with fewer defects caused by scratches on the film substrate 1.

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 will 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 30 cm or less, 25 cm or less, 20 cm or less, 15 cm or less, or 10 cm or less.

The pressure rolls may be positioned so that they extend outward from both widthwise ends of the film substrate 1, or may be positioned more inward than both widthwise ends. When the pressure rolls are positioned 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.

After the protective film 2 is peeled off in the peeling unit 10 and before the coating liquid is applied in the application unit 30, the pressure rolls in contact with the first main surface 1A of the film substrate 1 may be any roll that can press down both ends of the film substrate to suppress vibration of the film substrate, and their shape is not limited to the barbell shape shown in Figure 5. For example, two rolls may be arranged separately 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 that pairs with a roll in contact with the second main surface 1B of the film substrate 1 and clamps 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 application unit 30.

In the second conveying step, the means for pressing the film substrate from the first main surface 1A side of the film substrate 1 to suppress vibration of the film substrate 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.

In the second conveying step, both ends of the film substrate may be gripped with tenter clips. In this case, too, the regions of both widthwise ends of the film substrate can be pressed from both the first and second main surfaces without contacting the widthwise center of the film substrate 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 holding mechanism.

As shown in Figure 4, in the second conveying process 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 pressed from the second main surface 1B side as well, thereby more effectively suppressing vibration of the film substrate 1 caused by the peeling force of the protective film 2.

The roll 13 in contact with the second main surface 1B of the film substrate 1 may contact only both ends of the film substrate, or may contact the entire width of the film substrate. From the perspective 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.

<Coating process>
The 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 the die 33 is applied onto the first main surface 1A of the film substrate 1 in a state where the second main surface 1B of the film substrate 1 is in contact with the backup roll 31.

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

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 process, thereby preventing scratches on the first main surface 1A of the film substrate 1 due to roll transport. Furthermore, by sandwiching and bonding the film substrate 1 and protective film 2 between two conductive rolls 41, 42, internal charging of the laminate 8 is less likely to occur, preventing coating defects due to charging of the film substrate 1 after the protective film 2 is peeled off. This allows for the formation of a coating layer 3 with fewer defects, such as scratches and streaks, caused by the film substrate 1.

<Post-application process>
After the coating liquid is applied, the film substrate 1 may be heated in the 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.

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 above the N (nematic phase)-I (isotropic liquid phase) transition temperature to create an isotropic liquid state. From there, it is slowly cooled as necessary to develop the 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.

The heating temperature used to align the liquid crystal compound in a predetermined direction can be selected appropriately depending on the type of liquid crystal composition, and is typically around 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 can be adjusted so that the liquid crystal phase domains grow sufficiently, and is typically around 30 seconds to 30 minutes.

After aligning the liquid crystal compound by heating, it is preferable to cool it to a temperature below the glass transition temperature. There are no particular limitations on the cooling method; for example, it may be possible to remove it from the heated atmosphere and cool it to room temperature. Forced cooling, such as air cooling or water cooling, may also be used.

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) retains liquid crystal regularity. The light irradiated from the light source 61 is sufficient as long as it is 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 should 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.

When photocuring, the liquid crystal compound can be aligned in a specific direction by using polarized light in a specific direction. As described above, when the liquid crystal compound is aligned using the alignment control force of the film substrate 1, the irradiated light can be unpolarized (natural light).

The irradiation intensity may be adjusted appropriately depending on the formulation of the liquid crystal composition, the amount of photopolymerization initiator added, etc. The irradiation energy (cumulative irradiation light amount) is usually about 20 to 10,000 mJ/ ^cm² , preferably 50 to 5,000 mJ/ ^cm² , and more preferably 100 to 800 mJ/ ^cm² . To promote the photocuring reaction, light irradiation may be performed under heated conditions.

After photocuring the liquid crystal monomer, the polymerized product 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 oriented in a predetermined direction is less likely to experience changes in molecular orientation due to temperature changes. Furthermore, because liquid crystal layers have a significantly greater birefringence than films made from non-liquid crystal materials, the thickness of optically anisotropic elements with the desired retardation can be significantly reduced.

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 set appropriately depending on the application. When the liquid crystal molecules are homogeneously aligned, the in-plane retardation of the coating layer 3 is, for example, approximately 20 to 1,000 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 approximately 30 to 500 nm.

The retardation of a coating layer 3, such as a liquid crystal layer, is proportional to its thickness. If localized areas of thin thickness are formed due to repelling or other reasons on the surface of the film substrate when the coating liquid is applied, the retardation in those areas will be small, resulting in optical unevenness in the display device. As mentioned above, in this embodiment, the film substrate and protective film are sandwiched and bonded together using a nip roll consisting of two conductive rolls, which makes it less likely for internal charging to occur during bonding and suppresses the occurrence of streaky thickness unevenness due to coating defects. As a result, retardation unevenness caused by thickness unevenness in the optical film (coating layer) is less likely to occur, resulting in excellent optical uniformity.

The orientation direction of the liquid crystal molecules in the coating layer (liquid crystal layer) 3 can be parallel or non-parallel to the longitudinal direction of the film substrate 1 (the roll-to-roll transport direction). As mentioned above, by utilizing the orientation control force of an obliquely stretched film or the like, it is possible to form a liquid crystal layer in which the liquid crystal molecules are oriented non-parallel to the longitudinal direction. If 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 on top of the film substrate will be oriented longitudinally along the scratches, causing alignment defects. As mentioned above, by applying the liquid crystal composition to 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 alignment defects in the liquid crystal layer.

<Optical film processing>
A laminate 9 (optical film) having a coating layer 3 formed on the first main surface 1A of the 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.

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.

Other layers may be laminated on the coating layer 3. For example, by laminating the optical layer 4 onto the coating layer 3 via the adhesive layer 5, the laminate 96 shown in Figure 6 can be obtained.

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 particular restriction. 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.

The adhesive that makes up adhesive layer 5 may be made of any material that is optically transparent, including epoxy resin, silicone resin, acrylic resin, polyurethane, polyamide, polyether, and polyvinyl alcohol. The thickness of adhesive layer 5 is set appropriately depending on the type of adherend and the adhesive material. When using a curing 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.

Various types of adhesives can be used, including water-based adhesives, solvent-based adhesives, hot-melt adhesives, and active energy ray-curable adhesives. Of these, water-based adhesives and active energy ray-curable adhesives are preferred, as they allow the thickness of the adhesive layer to be reduced.

An adhesive is applied to either or both of the surface of the coating layer 3 and the surface of the optical layer 4, and then cured, thereby laminating the coating layer 3 and the optical layer 4 via the adhesive layer 5. The method for curing the adhesive can 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 exposure to active energy rays such as ultraviolet light.

The 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 Figure 7, the film substrate may be peeled off from the coating layer 3. As shown in Figure 8, 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.

The adhesive that makes up the adhesive layer 6 is not particularly limited, and can be appropriately selected and used from adhesives based on acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyethers, fluorine-based polymers, rubber-based polymers, etc. In particular, adhesives that have excellent transparency, moderate wettability, cohesion, and adhesion, and excellent weather resistance and heat resistance, such as acrylic adhesives and rubber-based adhesives, are preferred. The thickness of the adhesive layer is set appropriately depending on the type of adherend, etc., and is generally around 5 to 500 μm.

The adhesive layer 6 can be laminated onto 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 can be formed by drying the solvent, crosslinking, photocuring, etc. To increase the adhesive strength (anchoring strength) between the coating layer 3 and the adhesive layer 6, the surface of the coating layer 3 can be subjected to a surface treatment such as corona treatment or plasma treatment, or an easy-adhesion layer can be formed, before laminating the adhesive layer 6.

A separator 7 is preferably temporarily attached to the surface of the adhesive layer 6. The separator 7 protects the surface of the adhesive layer 6 until the optical film is bonded to another member. Suitable materials for the separator include plastic films made of acrylic, polyolefin, cyclic polyolefin, polyester, etc. The thickness of the separator is typically about 5 to 200 μm. The surface of the separator is preferably subjected to a release treatment. Examples of release agents include silicone-based materials, fluorine-based materials, long-chain alkyl-based materials, and fatty acid amide-based materials.

After peeling off the film substrate 1, another optical layer may be laminated on the exposed surface of the coating layer 3 via an appropriate adhesive or pressure-sensitive adhesive layer. 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 be further laminated on top of that.

An optical film with a 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 a coating layer 3 is a circular polarizer in which an oriented liquid crystal layer as the coating layer 3 is laminated with a polarizer.

The polarizing plate may consist of only a single layer of polarizer, or as mentioned above, a transparent protective film may be laminated 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 have been 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.

Among these, polyvinyl alcohol (PVA) polarizers are preferred because of their high polarization degree. They 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 can be formed on a resin substrate, and the resulting laminate can be dyed with iodine and stretched.

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

For example, if the circular polarizer has only one liquid crystal layer, the liquid crystal layer serving 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°.

In a configuration in which the polarizing plate 4 and the coating layer 3 acting as a quarter-wave plate are laminated so that the optical axes of the two form a 45° angle, 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 acting as a quarter-wave plate and a homeotropic liquid crystal layer functioning as a positive C plate, in that 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 that is a positive A plate) may also be laminated, in that order, on the polarizing plate.

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 located closer to the polarizer 4 is a half-wave plate, and the liquid crystal layer located farther from the polarizer is a quarter-wave plate. In this stacked configuration, the half-wave plate is preferably arranged so that the angle between the slow axis direction and the absorption axis direction of the polarizer is 75°±5°, and the angle between the slow axis direction and the absorption axis direction of the polarizer is 15°±5°. A circular polarizer with such a stacked configuration functions as a circular polarizer over a wide wavelength range of visible light, thereby reducing the coloring of reflected light.

As described above, in an 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, there are fewer alignment defects. Furthermore, because coating defects caused by bonding the film substrate and protective film are suppressed, the in-plane uniformity of the coating layer is high, enabling the realization of good display characteristics.

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 pressure-sensitive adhesive layer 7 separator 8 laminate 9, 96, 97, 98 laminate (optical film)
29, 81 Unwinding roll 21, 49, 91 Winding roll 40 Bonding section 41, 42 Nip roll 10 Peeling section 11 Peeling roll 30 Coating section 31 Backup roll 33 Die 50 Heating section 55 Heating furnace 60 Curing section 61 Light source 44, 45, 46, 47 Transport roll 83, 85, 87 Transport roll 13 Transport roll 15, 151 Pressing roll 71, 73, 75, 77, 79 Transport roll

Claims (10)

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 a 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,
the first roll and the second roll are both electrically conductive.
A method for manufacturing an optical film. 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. 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. 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. The method for manufacturing an optical film described in any one of claims 1 to 4, wherein the film substrate is a stretched film in which molecules are oriented non-parallel to the longitudinal direction. The method for manufacturing an optical film according to any one of claims 1 to 5, wherein, in the second conveying step, the roll does not contact the central portion in the width direction of the first main surface of the film substrate. The method for manufacturing an optical film according to claim 6, wherein, in the second conveying step, the film holding mechanism contacts both widthwise ends of the first main surface of the film substrate at least once, and the film holding mechanism does not contact the widthwise center of the first main surface of the film substrate. The method for manufacturing an optical film according to claim 7, wherein the film holding mechanism is a holding roll that contacts only both widthwise ends of the first main surface of the film substrate. The method for producing an optical film described in any one of claims 1 to 8, comprising a step of laminating another optical layer on the coating layer using a roll-to-roll process. The method for producing an optical film according to claim 9 , wherein the optical layer comprises a polarizer.