TWI855198B - Optical film manufacturing method - Google Patents

Abstract

The subject of the present invention is to provide an optical film with a coating having fewer defects and excellent uniformity. A laminate (8) formed by releasably attaching a protective film (2) to the first main surface of a long film substrate (1) is conveyed to a stripping section (10) along the length direction by rollers. In the stripping section, after the protective film is stripped from the first main surface of the film substrate, a coating liquid is applied to the first main surface of the film substrate. The surface resistance of the back side of the protective film is preferably less than 1×10 ¹¹ Ω/sq.

Description

Optical film manufacturing method

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

As an optical film with functions such as optical compensation for liquid crystal display devices and anti-external light reflection for organic EL (Electroluminescence) elements, a thin coating is used. Thin films have low self-sustaining properties and are difficult to handle alone, so a solution is applied to a support such as a plastic film to form a coating, and the coating is dried and processed in a state where it is in close contact with the support.

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

[Patent document 1] Japanese Patent Publication No. 2004-46068 [Patent document 2] WO2016/121856

[The problem the invention is trying to solve]

In a method of forming a coating by conveying a film substrate as a support in the longitudinal direction using a roll-to-roll method and coating a solution thereon, if there are scratches on the film substrate, the scratches may be transferred to the coating or the liquid crystal molecules may have poor alignment. In addition, since the surface condition of the film substrate may cause poor coating, the film thickness or optical properties of the coating may become uneven. [Technical means to solve the problem]

One embodiment of the present invention is a method for manufacturing a long optical film, wherein a coating is formed on the first main surface of a long film substrate having a first main surface and a second main surface. First, a laminate is prepared in which a protective film is releasably attached to the first main surface of the long film substrate. The laminate is conveyed to a peeling section by a roller along the length direction of the film substrate (a first conveying step), and in the peeling section, the protective film is peeled off from the first main surface of the film substrate (a protective film peeling step). The film substrate after the protective film is peeled off is transported from the peeling section to the coating section along the length direction of the film substrate (second transporting step), and in the coating section, the coating is applied on the first main surface of the film substrate (coating step), thereby obtaining a laminate having a coating on the first main surface of the film substrate.

The coating liquid may also be a liquid crystal composition containing a liquid crystal compound. The liquid crystal composition may also contain a photocurable liquid crystal compound. The liquid crystal composition containing a photocurable liquid crystal compound may also be coated on a film substrate and then the liquid crystal compound may be photocured.

The film substrate may have an alignment restraining force that allows the liquid crystal molecules to align in a specific direction. For example, the film substrate may be a stretched film in which the molecules are aligned non-parallel to the longitudinal direction, or may be an oblique stretched film.

The surface resistance R of the back side of the protective film (the side opposite to the film substrate bonding side) is preferably 1×10 ¹¹ Ω/sq or less. Under the conditions of a peeling angle of 180° and a peeling speed of 10 m/min, the peeling force F when peeling the protective film from the film substrate is preferably 1.5 N/50 mm or less. The surface resistance R and the peeling force F preferably satisfy the relationship of log ₁₀ R+2.3F≦11.5.

The optical film may be a film having other optical layers laminated on the coating in a roll-to-roll manner. The optical layer laminated on the coating may also include a polarizing element. The optical film may be a circular polarizing plate formed by laminating coatings and polarizing elements. [Effect of the invention]

Since the protective film is temporarily attached to the film substrate just before the coating liquid is applied, the scratches on the film substrate caused by roller conveyance are suppressed. In addition, since the surface resistance of the back side of the protective film temporarily attached to the film substrate and the adhesion force (peeling force) between the film substrate and the protective film are small, the coating defects caused by the electrification of the film substrate after the protective film is peeled off are suppressed. Therefore, a coating with fewer defects such as scratches or stripes caused by the film substrate can be obtained.

[Overview of the steps] In the present invention, a solution is applied to one main surface of a long film substrate to form a coating. FIG1 is a cross-sectional view of an optical film 9 formed by providing a coating 3 on the first main surface 1A of a film substrate 1. FIG2 is a cross-sectional view of a laminate 8 formed by releasably attaching a protective film 2 to the first main surface 1A of a film substrate 1.

FIG3 is a conceptual diagram showing an outline of a film forming apparatus and film forming steps for forming a coating layer 3 on a film substrate 1. In FIG3, a roll 80 obtained by winding a long film of a laminate 8 into a roll shape is wound around a roll-out roll 81. The laminate 8 rolled out from the roll 80 continuously moves to the downstream side along the conveying path formed by conveying rolls 83, 85, and 87, and is conveyed to the stripping section 10 (first conveying step).

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. The film substrate 1 after the protective film is peeled off is transported from the peeling section 10 to the coating section 30 (second transporting step). In the coating section 30, the coating liquid is coated on the first main surface 1A of the film substrate 1 (coating step).

The laminate 9 (optical film) formed by forming the coating layer 3 on the first main surface 1A of the film substrate 1 is rolled up by a roll 91, thereby obtaining a long optical film roll 90. The coating liquid 30 and the roll 91 may be heated by a heating unit 50. When the coating liquid contains a photopolymerizable component such as a photopolymerizable liquid crystal compound, light curing may be performed in a curing unit 60.

When the film substrate is conveyed by roll-to-roll while the solution is applied, scratches along the length direction are easily generated on the film substrate due to contact and friction with the conveying roller. If there are scratches on the film substrate, when a coating is formed thereon, the scratches on the film substrate will be transferred to the coating, which may cause optical defects. In addition, when a liquid crystal composition is applied on the film substrate, the liquid crystal molecules are easily aligned along the extension direction of the scratches, which may cause poor alignment defects.

In the embodiment of the present invention, the protective film 2 is releasably attached to the first main surface 1A of the film substrate 1. Since the protective film 2 is attached to the first main surface 1A of the film substrate 1 during the period from the unwinding roller 81 to the stripping section 10 (the first conveying step), the first main surface 1A of the film substrate 1 does not directly contact the conveying roller 87 in the first conveying step. Since the coating liquid is applied to the first main surface 1A of the film substrate 1 immediately after the protective film 2 is stripped from the film substrate 1, the generation of scratches on the first main surface of the film substrate caused by contact with the conveying roller 87 can be prevented, and the transfer of the scratches to the coating layer 3 or the poor alignment of the liquid crystal molecules can be suppressed.

In this embodiment, since coating is performed immediately after the protective film 2 is peeled off from the film substrate 1, the peeling section 10 and the coating section 30 are arranged close to each other, and the conveying path of the film substrate in the second conveying step is short. Therefore, there is a situation where the bonding state of the film substrate and the protective film, or the physical effect such as static electricity when the peeling section 10 peels off the protective film from the film substrate, affects the coating of the coating liquid in the coating section 30. Specifically, when the area with a smaller coating thickness is formed into a stripe shape extending in the width direction, there is a situation where the stripe shape is seen as uneven when the optical film is applied to an image display device.

In one embodiment of the present invention, the surface resistance of the back surface 2A of the protective film 2 is less than 1×10 ¹¹ Ω/sq. Since the surface resistance of the protective film 2 is small, the generation of the stripe-like unevenness extending in the width direction is suppressed.

When the coating liquid was applied on the film substrate immediately after the protective film was peeled off, the sample with stripe-like unevenness on the coating layer was analyzed. The results showed that no thickness unevenness or physical deformation was found on the film substrate after the coating layer was peeled off. Therefore, it is believed that the stripe-like uneven thickness of the coating layer formed on the film substrate is caused by the shrinkage of the coating liquid when it is applied on the surface of the film substrate.

Since the surface resistance of the back surface 2A of the protective film 2 is small, the internal charge of the film substrate 1 and the protective film 2 is reduced when they are attached. Therefore, after the protective film 2 is peeled off, the charge of the film substrate 1 is also reduced, and the shrinkage when the coating liquid is applied on the first main surface 1A of the film substrate 1 is suppressed, which is considered to prevent the occurrence of stripe-like thickness unevenness caused by poor coating.

The smaller the surface resistance of the back surface 2A of the protective film 2, the more the occurrence of stripe-like unevenness on the coating layer 3 formed on the film substrate 1 is suppressed. The surface resistance of the back surface 2A of the protective film 2 is preferably 1×10 ¹⁰ Ω/sq or less, more preferably 5×10 ⁹ Ω/sq or less, further preferably 1×10 ⁹ Ω/sq or less, and may be 5×10 ⁸ Ω/sq or less. The surface resistance is usually 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 peeling force when peeling the protective film 2 from the first main surface 1A of the film substrate 1 may affect the surface properties. The peeling force when peeling the protective film 2 from the film substrate 1 is preferably 1.5 N/50 mm or less, more preferably 1.0 N/50 mm or less, and further preferably 0.8 N/50 mm or less. The peeling force is a measured value in a peeling test, and the above peeling test is to peel the protective film from the film substrate under the conditions of a peeling angle of 180° and a tensile speed of 10 m/min.

In order to reduce coating defects, the smaller the peeling force, the better. In addition, in order to suppress the rapid movement when peeling the protective film from the film substrate, the peeling force is also preferably smaller. On the other hand, if the peeling force is too small, when the roll conveys the laminate of the film substrate and the protective film, there is a situation where the protective film is accidentally peeled off from the film substrate, resulting in poor conveying. Therefore, the peeling force when peeling the protective film from the film substrate is preferably 0.05 N/50 mm or more, more preferably 0.1 N/50 mm or more, and further preferably 0.15 N/50 mm or more, and can also be 0.2 N/50 mm or more.

The smaller the surface resistance R of the back side 2A of the protective film 2 and the smaller the peeling force F when peeling the protective film 2 from the film substrate 1, the more the tendency of coating failure caused by the film substrate is suppressed. The surface resistance R (Ω/sq) and the peeling force F (N/50 mm) preferably satisfy the following formula (1). log ₁₀ R＋2.3F≦11.5 (1)

The smaller the surface resistance R and the peeling force F are, the smaller the value of log ₁₀ R+2.3F becomes, thereby suppressing the tendency of coating defects. The value of log ₁₀ R+2.3F is preferably 11.0 or less, more preferably 10.5 or less, and may be 10.3 or less.

[Materials] Below, the materials used in this implementation are described.

<Coating liquid> The coating liquid applied to the film substrate 1 is a solution containing a solid component (solute) constituting the coating layer 3 and a solvent for dissolving and dispersing the solid component. As the solid component, various resin materials or liquid crystal materials can be used.

Examples of the resin material for the coating include cellulose resins such as acetyl cellulose, polyester resins, polycarbonate resins, polyamide resins, polyimide resins, butylene imide resins, polyolefin resins, (meth)acrylic resins, cyclic polyolefin resins (northene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, polysulfone resins, and the like.

A liquid crystal composition containing a liquid crystal compound is coated on a film substrate 1 to align the liquid crystal compound in a specific direction, and then the alignment state is fixed to form a coating layer (liquid crystal layer) in which liquid crystal molecules are aligned in a specific direction.

As the liquid crystal compound, rod-shaped liquid crystal compounds and disc-shaped liquid crystal compounds can be exemplified. From the perspective of easy surface alignment due to the alignment restriction force of the film substrate, the liquid crystal compound is preferably a rod-shaped liquid crystal compound. The rod-shaped liquid crystal compound can be a main chain liquid crystal or a side chain liquid crystal. The rod-shaped liquid crystal compound can be a liquid crystal polymer or a polymer of a polymerizable liquid crystal compound. If the liquid crystal compound (monomer) before polymerization exhibits liquid crystal properties, it may not exhibit liquid crystal properties after polymerization.

The liquid crystal compound is preferably a thermotropic liquid crystal that exhibits liquid crystal properties by heating. Thermotropic liquid crystal undergoes 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 one of a nematic liquid crystal, a lamellar liquid crystal, and a cholesteric liquid crystal. A chiral agent may also be added to the nematic liquid crystal to give it a cholesteric orientation.

Examples of the thermotropic rod-shaped liquid crystal compound include azomethines, oxyazos, cyanobiphenyls, cyanophenyl esters, benzoates, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolans, and alkenylcyclohexylbenzonitriles.

Examples of polymerizable liquid crystal compounds include polymerizable liquid crystal compounds that can fix the alignment of rod-shaped liquid crystal compounds using a polymer binder, polymerizable liquid crystal compounds having polymerizable functional groups that can fix the alignment of liquid crystal compounds by polymerization, etc. Among them, 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 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 further preferably 55 to 100°C.

Examples of the mesogen group of the liquid crystal monomer include cyclic structures such as biphenyl, phenylbenzoate, phenylcyclohexyl, oxyazophenyl, azomethine, azophenyl, phenylpyrimidinyl, diphenylethynyl, diphenylbenzoate, bicyclohexyl, cyclohexylphenyl, and terphenyl. The ends of these cyclic units may have substituents such as cyano, alkyl, alkoxy, and halogen.

As the photocurable functional group, (meth)acryl, epoxy, vinyl ether, etc. can be cited. Among them, (meth)acryl 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 cross-linked structure is introduced into the liquid crystal layer after photocuring, so there is a trend that the durability of the optical film is improved.

As the photocurable liquid crystal monomer, any appropriate liquid crystal monomer may be used. For example, International Publication No. 00/37585, U.S. Patent No. 5211877, U.S. Patent No. 4388453, International Publication No. 93/22397, European Patent No. 0261712, German Patent No. 19504224, German Patent No. 4408171, British Patent No. 2280445, Japanese Patent Publication No. 2017-206460, International Publication No. 2014/126113, International Publication No. 2016/114348, International Publication No. 2014/010325, Japanese Patent Publication No. 2015-20087 7, Japanese Patent Publication No. 2010-31223, International Publication No. 2011/050896, Japanese Patent Publication No. 2011-207765, Japanese Patent Publication No. 2010-31223, Japanese Patent Publication No. 2010-270108, International Publication No. 2008/119427, Japanese Patent Publication No. 2008-107767, Japanese Patent Publication No. 2008-273925, International Publication No. 2016/125839, Japanese Patent Publication No. 2008-273925, etc. By selecting the liquid crystal monomer, the appearance of birefringence or the wavelength dispersion of delay can also be adjusted.

In addition to the liquid crystal monomer, the liquid crystal composition may also contain a compound that controls the liquid crystal monomer to align in a specific direction. For example, by making the liquid crystal composition contain a side-chain liquid crystal polymer, the liquid crystal compound (monomer) can be aligned vertically. In addition, by adding a chiral agent to the liquid crystal composition, the liquid crystal compound can be aligned in a cholesterol-type manner.

The liquid crystal composition may contain a photopolymerization initiator. When the liquid crystal monomer is cured by ultraviolet irradiation, in order to promote photocuring, the liquid crystal composition preferably contains a photopolymerization initiator (photoradical generator) that generates free radicals by light irradiation. 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 about 0.01 to 10 parts by weight relative to 100 parts by weight of the liquid crystal monomer. In addition to the photopolymerization initiator, a sensitizer may also be used.

The liquid crystal composition can be prepared by mixing a liquid crystal monomer, various alignment control agents as needed, and a polymerization initiator 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 corrosiveness). Examples include: chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, o-dichlorobenzene and other halogenated hydrocarbons; phenols such as phenol and p-chlorophenol; aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, 1,2-dimethoxybenzene; acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyridine Ketone solvents such as pyrrolidone and N-methyl-2-pyrrolidone; ester solvents such as ethyl acetate and butyl acetate; alcohol solvents such as tert-butyl alcohol, glycerol, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, 2-methyl-2,4-pentanediol; amine solvents such as dimethylformamide and dimethylacetamide; nitrile solvents such as acetonitrile and butyronitrile; ether solvents such as diethyl ether, dibutyl ether, tetrahydrofuran; ethyl thiocyanate, butyl thiocyanate, etc. A mixed solvent of two or more solvents may also be used.

The solid content concentration of the coating liquid is usually about 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 a substrate, a series of steps from coating to drying of the coating liquid can be implemented by roll-to-roll. When the coating liquid is a liquid crystal composition, the alignment treatment or photocuring of the liquid crystal molecules after coating can also be implemented as a series of steps on the film substrate 1. In addition, the step of bonding the coating layer 3 formed on the film substrate 1 to other substrates can also be implemented 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 the productivity of the optical film, the larger the width of the film substrate 1, the better, and it is usually 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, and it is usually 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.

The resin material constituting the film substrate 1 is not particularly limited as long as it does not dissolve in the solvent of the coating liquid and can withstand drying, orientation treatment, hardening and other treatments. Examples thereof include: polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; cyclic polyolefins such as norolefin polymers; cellulose polymers such as diacetyl cellulose and triacetyl cellulose; acrylic polymers; styrene polymers; polycarbonate, polyamide, polyimide, etc.

Films made of hydrophobic resin materials such as polyolefin, cyclic polyolefin, and acrylic polymer are prone to internal charging when attached to the protective film 2, which may cause poor coating when applying the coating liquid after peeling off the protective film. As described above, by using a protective film 2 with a small surface resistance on the back side 2A (the side opposite to the surface attached to the film substrate 1), internal charging is suppressed, so that even when a hydrophobic resin film is used as the film substrate 1, poor coating can be prevented.

The film substrate 1 may also have an alignment restriction force for aligning the liquid crystal molecules in a specific direction. For example, the film substrate 1 may also be provided with an alignment film on the first main surface. The alignment film may be selected appropriately according to the type of liquid crystal compound or the material of the substrate. As an alignment film for aligning the liquid crystal molecules along the surface in a specific direction, a film obtained by rubbing a polyimide or polyvinyl alcohol alignment film may be cited. In addition, a photoalignment film may also be used. It is also possible to rub the resin film without providing an alignment film.

The film substrate 1 may also have an alignment film for vertically aligning the liquid crystal molecules. Examples of the alignment agent for forming the vertically oriented alignment film (vertical alignment film) include lecithin, stearic acid, cetyltrimethylammonium bromide, octadecylamine hydrochloride, monocarboxylic acid chromium complex, silane coupling agent or organic silane such as siloxane compound, perfluorodimethylcyclohexane, tetrafluoroethylene, polytetrafluoroethylene, etc.

A stretch film can also be used as the film substrate 1. In the stretch film, the resin material (polymer) constituting the film is aligned in the stretching direction, and the stretch film has the function of aligning the liquid crystal molecules along the stretching direction. By using the stretch film, even when the alignment film is not formed on the film substrate, it can have an alignment restriction force for aligning the liquid crystal molecules in a specific direction. Since there is no need to form an alignment film, the manufacturing cost of the optical film can be reduced. In addition, by not providing an alignment film, contamination or poor alignment caused by friction gas can be prevented.

The stretching direction of the stretch film (alignment direction of the polymer) is not particularly limited and may be parallel to the length direction of the film substrate or may be non-parallel to the length direction of the film substrate. By using a stretch film in which molecules are aligned non-parallel to the length direction, a liquid crystal layer in which liquid crystal molecules are aligned non-parallel to the length direction can be formed as the coating layer 3.

The stretching ratio of the stretching film can be any level that can exert the alignment restraining force, for example, about 1.1 to 5 times. The stretching film can also be a biaxial stretching film. Even if it is a biaxial stretching film, as long as the longitudinal and transverse stretching ratios are different, the liquid crystal molecules can be aligned along the direction with the larger stretching ratio.

The stretched film may also be an oblique stretched film. The oblique stretched film has an alignment axis in a direction that is neither parallel nor orthogonal to the longitudinal direction (e.g., a direction that is 10 to 80 degrees relative to the longitudinal direction). Therefore, by using the oblique stretched film as the film substrate 1, a liquid crystal layer having liquid crystal molecules aligned in a direction that is neither parallel nor orthogonal to the longitudinal direction can be formed.

<Protective film> As shown in FIG. 2, the protective film 2 temporarily adhered to the first main surface 1A of the film substrate 1 preferably has an adhesive layer 292 on one side of the core material 291. The protective film 2 may also have an antistatic layer 295 on the back side of the core material 291 (the side opposite to the side where the adhesive layer is formed).

(Core material) The core material 291 of the protective film 2 is not particularly limited as long as it is flexible, and metal foil or resin film can be used. Considering that the material is cheap and has excellent processability, a resin film is preferred. As a specific example of the resin material constituting the core material 291, the resin material described above as the film substrate 1 can be cited. The core material 291 can also be a stretched film. The thickness of the core material 291 is not particularly limited. In order to have both self-sustaining properties and flexibility, the thickness of the core material 291 is preferably about 10 to 100 μm.

(Adhesive layer) The adhesive layer 292 can be formed of an adhesive used in a general adhesive tape, etc., as long as it can be attached to the film substrate 1 and can be peeled off from the film substrate 1. As the protective film 2, a self-adhesive film can also be used, which is obtained by integrally molding the resin material constituting the core material 291 and the resin material of the adhesive layer 292 through multi-layer extrusion.

The composition of the adhesive constituting the adhesive layer 292 is not particularly limited, and an adhesive having an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyvinyl ether, a vinyl acetate/vinyl chloride copolymer, a modified polyolefin, an epoxy, a fluorine, a natural rubber, a synthetic rubber, or other rubber-based polymer as a base polymer can be appropriately selected and used. In particular, from the perspective of easy adjustment of the adhesion (peeling force) and less adhesive residue on the film substrate 1 as the adherend, an acrylic adhesive having an acrylic polymer as a base polymer can be preferably used.

As the acrylic base polymer, a polymer having a monomer unit of alkyl (meth)acrylate as the main skeleton is preferably used. As the alkyl (meth)acrylate, an alkyl (meth)acrylate having an alkyl carbon number of 1 to 20 is preferably used. The content of the alkyl (meth)acrylate is preferably 40% by weight or more, more preferably 50% by weight or more, and further preferably 60% by weight or more relative to the total amount of the monomer components constituting the base polymer. The acrylic polymer may be a copolymer of a plurality of alkyl (meth)acrylates. The arrangement of the constituent monomer units may be random or block.

The acrylic base polymer preferably contains a monomer component having a functional group capable of crosslinking as a copolymer component. As the monomer having a functional group capable of crosslinking, a hydroxyl-containing monomer or a carboxyl-containing monomer can be cited. Among them, as the copolymer component of the base polymer, it is preferably a hydroxyl-containing monomer such as (meth) ethyl acrylate and (meth) butyl acrylate. The hydroxyl group or carboxyl group of the base polymer will become a reaction point for reacting with the crosslinking agent. By introducing a crosslinking structure into the base polymer, the cohesive force of the adhesive is improved, showing a moderate adhesion to the film substrate as the adherend, and there is a tendency for the peeling force to decrease when the protective film 2 is peeled off from the film substrate 1.

The molecular weight of the base polymer is appropriately adjusted so that the adhesive layer 292 has the desired adhesion. For example, the weight average molecular weight converted to polystyrene is about 50,000 to 2 million, preferably about 70,000 to 1.8 million, more preferably about 100,000 to 1.5 million, and further preferably about 200,000 to 1 million. Furthermore, when a cross-linking structure is introduced into the base polymer, it is preferred that the molecular weight of the base polymer before the cross-linking structure is introduced is within the above range.

A cross-linking structure may be introduced into the base polymer for the purpose of adjusting the adhesion of the adhesive layer 292. For example, a cross-linking agent may be added to a solution of the polymerized base polymer and the solution may be heated as necessary to introduce the cross-linking structure.

Examples of the crosslinking agent include isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents. Among them, isocyanate crosslinking agents and epoxy crosslinking agents are preferred because of their high reactivity with the hydroxyl or carboxyl groups of the base polymer and the ease of introducing a crosslinking structure. The amount of the crosslinking agent used can be appropriately adjusted according to the composition or molecular weight of the base polymer, the target bonding properties, and the like. In order to make the adhesive have a moderate cohesive force and adjust the peeling force when peeling the protective film from the adherend to a suitable range, the amount of the crosslinking agent used is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, and further preferably 1.5 parts by weight or more, relative to 100 parts by weight of the base polymer. In order to have a moderate adhesion to the adherend, the amount of the crosslinking agent used is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and further preferably 10 parts by weight or less, relative to 100 parts by weight of the base polymer.

By introducing a cross-linked structure into the base polymer, the gel fraction of the adhesive increases, and as the viscous behavior decreases, the peeling force when peeling 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 further preferably 90.0% or more. If the gel fraction of the adhesive layer 292 is too large, the wettability to the adherend is reduced, and the adhesion becomes insufficient. Therefore, the gel fraction of the adhesive layer 292 is preferably 99% or less, and more preferably 98% or less. The gel fraction can be obtained as the insoluble content in solvents such as ethyl acetate. Specifically, the weight fraction (unit: weight %) of the insoluble content of the adhesive layer after immersion in ethyl acetate at 23°C for 7 days relative to the sample before immersion can be obtained. Generally, the gel fraction of a polymer is equal to the degree of crosslinking. The more crosslinked parts in the polymer, the greater the gel fraction.

The adhesive layer 292 may also contain additives such as silane coupling agents, adhesive imparting agents, plasticizers, softeners, anti-degradation agents, fillers, colorants, ultraviolet absorbers, antioxidants, surfactants, antistatic agents, etc.

The thickness of the adhesive layer 292 is not particularly limited. In order to take into account both the adhesion to the adherend and the peeling property from the adherend, the thickness of the adhesive layer 292 is preferably 1 to 50 μm, more preferably 2 to 40 μm, and further preferably 3 to 35 μm. There is a trend that the smaller the thickness of the adhesive layer 292, the better the peeling property from the adherend.

(Antistatic layer) The protective film 2 preferably has an antistatic layer 295 on the back side of the core material 291. By having the antistatic layer, the surface resistance of the back side 2A of the protective film 2 becomes smaller, so that the internal charging of the laminate of the film substrate 1 and the protective film 2 can be suppressed. In addition, by providing the protective film 2 with the antistatic layer 295, the film substrate 1 can be prevented from being charged when the protective film 2 is peeled off from the film substrate 1, and dust adhesion to the film substrate 1 due to static electricity or coating defects can be suppressed.

As an antistatic layer, for example, a layer formed by making the adhesive resin contain an antistatic component can be cited. As the adhesive resin, various types of resins such as thermosetting resins, ultraviolet curing resins, electron beam curing resins, and two-liquid mixed resins can be used. As antistatic components, organic or inorganic conductive substances, various antistatic agents, etc. can be cited. As organic conductive substances, conductive polymers such as polyaniline, polypyrrole, polythiophene, polyethyleneimine, and allylamine polymers can be cited. As inorganic conductive substances, various metals, alloys, and conductive metal oxides can be cited. The inorganic conductive material is preferably contained in the antistatic layer in the form of microparticles with a particle size 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 non-ionic antistatic agent, or the like.

<Laminate> The laminate 8 is formed by laminating the adhesive layer 292 of the protective film 2 to one surface of the film substrate 1. The lamination method of laminating the protective film 2 on the film substrate 1 is not particularly limited. For example, in the manufacturing step of the film substrate 1, the protective film 2 can be laminated to the film substrate 1 in a roll-to-roll manner before the film substrate 1 is rolled into a roll. By laminating the protective film 2 after the manufacturing step of the film substrate 1, the number of contacts between the roll and the first main surface 1A of the film substrate 1 can be reduced, thereby suppressing the generation of scratches.

When the film substrate 1 is a stretched film, it is preferred to immediately attach the protective film 2 after stretching. For example, after stretching by a tentering method that holds both ends of the film, the protective film 2 is attached before the first main surface 1A of the film substrate 1 contacts the conveying roller, thereby preventing scratches from being generated on the first main surface 1A of the film substrate 1.

As described above, the peeling force when peeling the protective film 2 from the film substrate 1 is preferably 1.5 N/50 mm or less, more preferably 1.0 N/50 mm or less, and further preferably 0.8 N/50 mm or less. By adjusting the composition and thickness of the adhesive layer 292, the peeling force can be made within the above range. Specifically, there is a trend that the smaller the thickness of the adhesive layer 292, the smaller the peeling force becomes. In addition, by increasing the amount of cross-linked structure introduced into the base polymer constituting the adhesive layer 292, there is a trend that the gel fraction increases and the peeling force becomes smaller.

As described above, the surface resistance of the back surface 2A of the protective film 2 is preferably 1×10 ¹⁰ Ω/sq or less, more preferably 5×10 ⁹ Ω/sq or less, further preferably 1×10 ⁹ Ω/sq or less, and may be 5×10 ⁸ Ω/sq or less. By providing an antistatic layer on the back surface of the core material 291, the surface resistance can be reduced.

[Production of optical film] The protective film 2 is peeled off from the film substrate 1 of the laminate 8, and the coating 3 is formed on the first main surface 1A of the film substrate 1, thereby obtaining a laminate (optical film) 9 having the coating 3 on the film substrate 1. The following is a description of each step, centering on the case where a liquid crystal composition containing a liquid crystal compound is used as a coating liquid to form an aligned liquid crystal layer as the coating 3.

<First conveying step> The laminated body 8 formed by laminating the protective film 2 on the first main surface 1A of the film substrate 1 is temporarily rolled into a roll 80 and placed on a roll-out roller 81. The laminated body 8 rolled out from the roll 80 placed on the roll-out roller 81 is continuously moved to the downstream side along the conveying path formed by the conveying rollers 83, 85, and 87, and is conveyed to the peeling section 10.

The step of bonding the film substrate 1 and the protective film 2 to form the laminate 8 and the first conveying step may be performed continuously. For example, after bonding the film substrate 1 and the protective film 2, the laminate 8 may be directly conveyed to the peeling unit 10 without being rolled up.

<Peeling step> In the peeling step, the protective film 2 is peeled off from the laminate 8 transported to the peeling section 10, so that the first main surface 1A of the film substrate 1 is exposed. The method of peeling the protective film is not particularly limited, and is usually a method of peeling on a peeling roller 11. If the conveying rollers 13 and 23 downstream of the peeling roller 11 are arranged in a manner such that the protective film 2 has a greater embrace angle with respect to the peeling roller 11 than the film substrate 1 has a embrace angle with respect to the peeling roller 11, the protective film 2 can be peeled off from the film substrate 1 on the peeling roller 11. The peeling roller can be a pair of upper and lower clamping rollers for holding the laminate 8. The protective film 2 peeled off from the first main surface of the film substrate 1 is conveyed along the conveying path formed by the conveying rollers 23 and 25, and is wound into a roll 20 by the winding roller 21.

As described above, by adjusting the peeling force when peeling the protective film 2 from the film substrate 1, deformation of the film substrate 1 caused by rapid movement during peeling can be suppressed. In addition, since the surface resistance of the back surface 2A of the protective film 2 is small, the peeling electrification of the film substrate 1 can be suppressed.

<Second conveying step> In the second conveying step, the film substrate 1 after the protective film 2 is peeled off is conveyed to the coating section 30. During the period when the film substrate 1 after the protective film 2 is peeled off in the peeling section 10 is conveyed from the peeling section 10 to the coating section 30, the first main surface 1A of the film substrate 1 is exposed. In this embodiment, the conveying path of the film substrate 1 in the second conveying step is shorter, and the first main surface 1A of the film substrate 1 and the conveying roller have less contact opportunities, so the frequency of scratches on the film substrate in the second conveying step is extremely low.

If the transport roller is prevented from contacting the first main surface 1A of the film substrate 1 while the film substrate 1 is being transported from the stripping section 10 (stripping roller 11) to the coating section 30 (support roller 31), scratches on the first main surface 1A of the film substrate 1 can be prevented from being generated in the second transport step.

As shown by the dotted line in FIG3 , in the second conveying step, the roller 15 may also contact the first main surface 1A of the film substrate 1. By making the roller 15 contact the first main surface 1A of the film substrate 1, a pressing force from the first main surface side (the lower side in the figure) to the upper side in the figure acts on the film substrate 1. Therefore, the vibration of the film substrate 1 caused by the peeling force of the protective film 2 is reduced, and the uneven coating of the coating liquid can be suppressed.

In the conveying path of the film substrate 1 (second conveying step) from the peeling of the protective film 2 in the peeling section 10 to the coating of the coating liquid in the coating section 30, the roller 15 in contact with the first main surface 1A of the film substrate 1 can function as a "pressing roller" for the film substrate 1.

The pressing roller only needs to suppress the vibration of the film substrate 1 caused by the peeling of the protective film 2 in the peeling portion 10, and does not need to be in contact with the entire width direction of the film substrate 1. The pressing roller may only contact the two end portions in the width direction of the film substrate 1 without contacting the central portion in the width direction. For example, as the pressing roller 15 in contact with the first main surface 1A of the film substrate 1, a lever-shaped roller 151 schematically shown in FIG. 4 can be used.

The roller 151 has cylindrical rollers 15R and 15L at both ends, and the rollers 15R and 15L at both ends are connected via a connecting shaft 15C having a diameter smaller than the rollers. If the roller 151 is used, the roller 151 only contacts the both ends of the film substrate in the width direction, and does not contact the center of the film substrate in the width direction.

In the second conveying step, the two ends of the film substrate in the width direction (areas where the rollers 15R and 15L contact) may form scratches on the first main surface of the film substrate due to contact with the roller 15. However, if such areas are regarded as non-product areas and only the center in the width direction that does not contact the roller 15 is regarded as the product area, an optical film (coating 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 in the width direction of the film substrate 1 and the coating is not formed on the two ends in the width direction of the film substrate, only the center in the width direction becomes the product area. Furthermore, the regions at both ends can be cut off from the product by punching the film at an appropriate stage after the coating is formed, or by cutting the ends into strips, so that only the central portion in the width direction of the film substrate is used as the product region.

As described above, in the second conveying step, when the roller contacts the first main surface 1A of the film substrate 1, it is preferred that the first main surface 1A contacts the pressing roller at both ends in the width direction, and the first main surface in the center in the width direction does not contact the roller. In this state, the vibration of the film substrate 1 caused by the peeling of the protective film 2 can be suppressed, and the uneven coating of the coating layer 3 can be reduced, and a coating layer 3 with fewer defects caused by scratches on the film substrate 1 can be obtained.

At both ends of the film substrate 1, the width of the portion where the film substrate and the pressing roller are in contact is, for example, 1 to 50 cm respectively. When the width of the portion where the film substrate and the pressing roller are in contact is too small, the vibration suppression effect of the film substrate is insufficient, or the mobility of the film substrate is reduced. When the width of the portion where the film substrate and the pressing roller are in contact is too large, the width of the non-product area of the optical film is larger, resulting in reduced production efficiency or yield. The width of the portion where the film substrate and the pressing roller are in contact may be greater than 2 cm, greater than 3 cm, or greater than 5 cm, and may also be less than 30 cm, less than 25 cm, less than 20 cm, less than 15 cm, or less than 10 cm.

The pressing roller may be arranged to extend outward from both ends in the width direction of the film substrate 1, or may be arranged inside the both ends in the width direction. When the pressing roller is arranged inside the both ends in the width direction of the film substrate 1, the distance from one end in the width direction of the film substrate to the pressing roller may be within 30 cm, within 20 cm, within 15 cm, within 10 cm, within 5 cm, within 3 cm, or within 1 cm.

In the period from the time when the protective film 2 is peeled off in the peeling section 10 to the time when the coating liquid is applied in the coating section 30, the pressing roller in contact with the first main surface 1A of the film substrate 1 can suppress the vibration of the film substrate by pressing both ends of the film substrate, and its shape is not limited to the lever shape shown in FIG. 4. For example, two rollers may be arranged separately at both ends in the width direction. The pressing roller in contact with the first main surface 1A of the film substrate 1 may also be paired with a roller in contact with the second main surface 1B of the film substrate 1 to serve as a clamping roller for clamping the film substrate 1. Two or more pressing rollers in contact with the first main surface 1A of the film substrate 1 may also be provided between the peeling section 10 and the coating section 30.

In the second conveying step, the member that presses the film substrate from the first main surface 1A side of the film substrate 1 to suppress the vibration of the film substrate does not necessarily have to be a rotating body. For example, between the stripping part 10 and the coating part 30, a push pin that presses the film substrate from the first main surface side (lower side in the figure) toward the second main surface side can also be arranged as a film pressing mechanism.

In the second conveying step, the two ends of the film substrate may be gripped by a tenter clip. In this case, the regions of the two ends of the film substrate in the width direction may be pressed from both the first main surface and the second main surface without the rollers etc. contacting the central portion of the film substrate in the width direction, thereby suppressing the vibration of the film substrate 1 caused by the peeling of the protective film 2. In this case, the lower clamp in contact with the first main surface side of the film substrate functions as a film pressing mechanism.

As shown in FIG. 3 , in the second transport step between the stripping section 10 and the coating section 30 , by bringing the roller 13 into contact with the second main surface 1B of the film substrate 1 , the film substrate 1 can also be pressed from the second main surface 1B side, thereby being able to more effectively suppress the vibration of the film substrate 1 caused by the stripping force of the protective film 2 .

The roller 13 in contact with the second main surface 1B of the film substrate 1 may be in contact with only the two ends of the film substrate or may be in contact with the entire width direction of the film substrate. From the perspective of the transportability of the film substrate, the roller 13 is preferably in contact with the entire width direction of the second main surface of the film substrate.

<Coating step> The coating liquid is coated on the first main surface 1A of the film substrate 1 transported to the coating section 30. In the state shown in FIG. 3 , the coating liquid ejected from the die nozzle 33 is coated on the first main surface 1A of the film substrate 1 while the second main surface 1B of the film substrate 1 is in contact with the support roller 31 .

The method of applying the coating liquid on the film substrate 1 is not particularly limited. As the coating method, in addition to die-mouth coating, contact roller coating, gravure coating, reverse coating, spray coating, Meyer bar coating, knife roll coating, air knife coating, etc. can also be cited. The coating thickness of the coating liquid is preferably adjusted so that the thickness of the coating layer 3 after the solvent is dried becomes about 0.1 to 20 μm.

In this embodiment, since the protective film 2 is temporarily adhered to the first main surface 1A of the film substrate 1 immediately before the coating step, the generation of scratches on the first main surface 1A of the film substrate 1 caused by roller conveyance is suppressed. In addition, since the surface resistance of the back surface 2A of the protective film 2 temporarily adhered to the film substrate 1 and the adhesion force (peeling force) between the film substrate 1 and the protective film 2 are adjusted to a specific range, the generation of coating defects caused by the charging of the first main surface 1A of the film substrate 1 after the protective film 2 is peeled off is suppressed. Therefore, a coating layer 3 with fewer defects such as scratches or stripes caused by the film substrate 1 can be formed.

<Steps after coating> The film substrate 1 after coating with the coating liquid can also be heated by the heating unit 50. The heating unit 50 includes, for example, a heating furnace 55, and the film substrate 1 and the coating liquid coated thereon are heated while the film substrate 1 is being transported in the heating furnace 55. For example, the solvent of 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 composition layer is heated to form a liquid crystal phase, whereby the liquid crystal compound is aligned in a specific direction. 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, so that the liquid crystal composition becomes an isotropic liquid state. Then, if necessary, it is slowly cooled to present a nematic phase. At this time, it is more ideal to temporarily maintain the temperature of the liquid crystal phase so that the liquid crystal phase grows into a single phase. Alternatively, after the liquid crystal composition is coated, the temperature can be maintained within the temperature range of the nematic phase for a certain period of time to align the liquid crystal molecules in a specific direction.

The heating temperature for aligning the liquid crystal compound in a specific direction can be appropriately selected according to 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, and if the heating temperature is too high, there is a tendency for the alignment defects to increase. The heating time can be adjusted in such a way that the liquid crystal phase region grows sufficiently, and is usually about 30 seconds to 30 minutes.

It is preferred to heat the liquid crystal compound to align it and then cool it to a temperature below the glass transition temperature. The cooling method is not particularly limited, for example, it can be taken out from the heated atmosphere to room temperature. Strong cooling such as air cooling or water cooling can also be performed.

When the liquid crystal compound has curability, it is preferred to use the curing part 60 for curing. For example, when the liquid crystal compound has photocurability, photocuring is performed in a state where the photocurable liquid crystal compound (liquid crystal monomer) has liquid crystal regularity. The irradiation light from the light source 61 only needs to be able to polymerize the photocurable liquid crystal compound, and usually ultraviolet light or visible light with a wavelength of 250 to 450 nm is used. When the liquid crystal composition contains a photopolymerization initiator, it is sufficient to select light with a wavelength to which the photopolymerization initiator is sensitive. As the irradiation light source, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a xenon lamp, an LED (Light Emitting Diode), a black light lamp, a chemical lamp, etc. can be used. To promote the photocuring reaction, the light irradiation is preferably carried out in an inert gas atmosphere such as nitrogen.

During 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 by the alignment restraining force of the film substrate 1, the irradiated light can also be non-polarized light (natural light).

The irradiation intensity can be appropriately adjusted according to the composition of the liquid crystal composition, the amount of photopolymerization initiator added, etc. The irradiation energy (accumulated irradiation light quantity) is usually about 20 to 10,000 mJ/cm ² , preferably 50 to 5,000 mJ/cm ² , and more preferably 100 to 800 mJ/cm ^2. To promote the photohardening reaction, light irradiation can also be performed under heating conditions.

The polymer formed after the liquid crystal monomer is photocured is non-liquid crystal and will not undergo transitions between the liquid crystal phase, glass phase, and crystal phase due to temperature changes. Therefore, the liquid crystal layer obtained after photocuring the liquid crystal monomer in a state of being oriented in a specific direction is unlikely to undergo changes in molecular orientation due to temperature changes. In addition, the liquid crystal layer has significantly greater birefringence than a film containing non-liquid crystal materials, so the thickness of an optically anisotropic element with the desired delay can be significantly reduced.

The optical properties of the coating (liquid crystal layer) 3 are not particularly limited. The front retardation and thickness direction retardation of the coating 3 can be appropriately set according to the purpose, etc. When there are liquid crystal molecules aligned along the surface, the front retardation of the coating 3 is, for example, about 20 to 1000 nm. When the coating 3 is a 1/4 wavelength plate, the front retardation is preferably 100 to 180 nm, and more preferably 120 to 150 nm. When the coating 3 is a 1/2 wavelength plate, the front retardation is preferably 200 to 340 nm, and more preferably 240 to 300 nm. When there is liquid crystal in vertical alignment, the in-plane retardation of the coating layer 3 is approximately 0 (eg, less than 5 nm, preferably less than 3 nm), and the absolute value of the retardation in the thickness direction is approximately 30 to 500 nm.

The retardation of the coating 3 such as the liquid crystal layer is proportional to the thickness. When applying the coating, if a portion with a smaller thickness is formed due to the shrinkage of the surface of the film substrate, the retardation of the portion becomes smaller, thereby generating optical unevenness in the display device. As described above, in the present embodiment, the surface resistance of the back surface 2A of the protective film 2 and the adhesion (peeling force) between the film substrate 1 and the protective film 2 are adjusted to a specific range, and the generation of stripe-like thickness unevenness caused by poor coating is suppressed. Therefore, it is difficult to generate retardation unevenness caused by uneven thickness of the optical film (coating), and the optical uniformity is excellent.

The orientation direction of the liquid crystal molecules in the coating (liquid crystal layer) 3 may be parallel to the length direction (roll-to-roll conveying direction) of the film substrate 1, or may be non-parallel to the length direction. As described above, by utilizing the orientation limiting force of an obliquely stretched film or the like, a liquid crystal layer in which the liquid crystal molecules are oriented non-parallel to the length direction can be formed. In the case where the liquid crystal molecules are oriented non-parallel to the length direction, if there is a scratch along the length direction on the film substrate, the liquid crystal molecules in the liquid crystal layer formed thereon are oriented along the scratch in the length direction, thus resulting in poor orientation. As described above, by coating the liquid crystal composition on the film substrate 1 immediately after peeling off the protective film 2 temporarily attached to the film substrate 1, the generation of scratches on the film substrate can be suppressed, thereby reducing poor orientation of the liquid crystal layer.

<Processing of optical film> By rolling up the laminate 9 (optical film) having the coating 3 formed on the first main surface 1A of the film substrate 1 using a winding roll 91, a long optical film roll 90 can be obtained. The laminate 9 can be used directly as an optical film. Since the regions at both ends of the film substrate 1 in the width direction are non-product regions, the regions can be cut off and removed by cutting into long strips during the period from the formation of the coating 3 until the winding is performed using the winding roll 91, or at an appropriate stage after the winding is performed using the winding roll 91. In addition, the film can be punched out in a manner that does not include the regions at both ends in the width direction to cut out a single product.

The laminate 9 formed by forming the coating 3 on the first main surface 1A of the film substrate 1 can be used directly as an optical film, or the film substrate 1 can be peeled off and only the coating 3 can be used as an optical film. When the coating 3 is a resin layer, the laminate of the film substrate 1 and the coating 3 can be extended to give the coating 3 optical anisotropy.

Other layers may also be laminated on the coating layer 3. For example, the optical layer 4 may be laminated on the coating layer 3 via the adhesive layer 5, thereby obtaining the laminate body 96 shown in FIG. 5 .

The optical layer 4 laminated on the coating 3 is not particularly limited, and optically isotropic or optically anisotropic films that can be generally used as optical films can be used without particular restrictions. Specific examples of the optical layer 4 include transparent films such as phase difference films or polarizing element protective films, polarizing elements, viewing angle expansion films, viewing angle limiting (anti-obstruction) films, and brightness enhancement films. The optical layer 4 can be a single layer or a laminate. The optical layer 4 can also be a liquid crystal layer. The optical layer 4 can also be a polarizing plate formed by laminating a transparent protective film to one or both sides of a polarizing element. When a polarizing plate is provided with a transparent protective film on one side, the polarizing element can be laminated to the coating, or the transparent protective film can be laminated to the coating.

The adhesive constituting the adhesive layer 5 is not particularly limited in material 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 the adhesive layer 5 is appropriately set according to the type of the adherend or the material of the adhesive. When a curing adhesive that exhibits adhesion by a crosslinking reaction after coating is used, the thickness of the adhesive layer 5 is preferably 0.01 to 5 μm, and more preferably 0.03 to 3 μm.

As the adhesive, various types of adhesives can be used, such as water-based adhesives, solvent-based adhesives, hot melt adhesives, active energy ray-curing adhesives, etc. Among them, water-based adhesives or active energy ray-curing adhesives are preferred from the perspective of reducing the thickness of the adhesive layer.

By applying an adhesive on one or both of the surfaces of the coating layer 3 and the optical layer 4 and curing them, the coating layer 3 and the optical layer 4 are laminated via the adhesive layer 5. The curing of the adhesive can be appropriately selected according to the type of adhesive. For example, a water-based adhesive can be cured by heating. An active energy ray curing adhesive can be cured by irradiation with active energy rays such as ultraviolet rays.

The laminate 96 formed by bonding the optical layer 4 to the coating 3 on the film substrate 1 via the adhesive layer 5 can be directly used as an optical film. In this case, the film substrate 1 constitutes a part of the optical film. The film substrate can also be removed by peeling off the coating 3 as shown in FIG6. As shown in FIG7, an appropriate adhesive layer 6 can be deposited on the surface of the coating 3 exposed by peeling off the film substrate.

The adhesive constituting the adhesive layer 6 is not particularly limited, and an adhesive having an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyether, a fluorine polymer, a rubber polymer, etc. as a base polymer can be appropriately selected and used. Particularly preferred are adhesives such as acrylic adhesives or rubber adhesives that have excellent transparency, exhibit appropriate wettability, cohesion and adhesion, and have excellent weather resistance or heat resistance. The thickness of the adhesive layer is appropriately set according to the type of the adherend, etc., and is generally about 5 to 500 μm.

When the adhesive layer 6 is deposited on the coating layer 3, for example, the adhesive formed in advance in a sheet form is adhered to the surface of the coating layer 3. Alternatively, the adhesive layer 6 may be formed by applying an adhesive composition on the coating layer 3 and then drying, crosslinking, photocuring, etc. the solvent. In order to improve the adhesion (gripping force) between the coating layer 3 and the adhesive layer 6, the surface of the coating layer 3 may be subjected to surface treatment such as corona treatment or plasma treatment, or an easy-adhesion layer may be formed before depositing the adhesive layer 6.

It is preferred that a spacer 7 is temporarily adhered to the surface of the adhesive layer 6. The spacer 7 protects the surface of the adhesive layer 6 before the optical film is bonded to other components. As the constituent material of the spacer, plastic films such as acrylic resin, polyolefin, cyclic polyolefin, polyester, etc. can be appropriately used. The thickness of the spacer is generally about 5 to 200 μm. It is preferred that a release treatment be performed on the surface of the spacer. Examples of release agents include polysilicone-based materials, fluorine-based materials, long-chain alkyl-based materials, fatty acid amide-based materials, etc.

On the exposed surface of the coating layer 3 after peeling off the film substrate 1, other optical layers can also be deposited via a suitable adhesive layer or a bonding agent layer. For example, other optical layers can also be deposited on the coating layer 3 via a suitable adhesive layer, and a bonding agent layer can also be deposited thereon.

The optical film with a coating can be used as an optical film for an image display device, for example. As an example of an optical film formed by laminating another optical layer 4 on a coating 3, a circular polarizer formed by laminating an oriented liquid crystal layer and a polarizer as the coating 3 can be cited.

The polarizing plate may be composed of only one layer of polarizing element, or a transparent protective film may be laminated to one or both sides of the polarizing element as described above. Examples of the polarizing element include: a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, and a partially saponified film of an ethylene-vinyl acetate copolymer film adsorbed with a dichroic substance such as iodine or a dichroic dye and then uniaxially stretched; a polyene alignment film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride, etc.

Among them, in terms of having a higher degree of polarization, a polyvinyl alcohol (PVA) polarizing element is preferably formed by adsorbing a dichroic substance such as iodine or a dichroic dye to a polyvinyl alcohol film such as polyvinyl alcohol or partially formalized polyvinyl alcohol and aligning it in a specific direction. For example, a PVA polarizing element is obtained by dyeing and stretching a polyvinyl alcohol film with iodine. Alternatively, a PVA resin layer may be formed on a resin substrate and dyed and stretched with iodine in a laminated state.

In a circular polarizer having a polarizer and a liquid crystal layer, it is preferred that at least one liquid crystal layer has liquid crystal molecules aligned along a plane. In a circular polarizer, the alignment direction of the liquid crystal molecules in the liquid crystal layer having liquid crystal molecules aligned along a plane is arranged in a manner that is neither parallel nor orthogonal to the absorption axis direction of the polarizer.

For example, when the circular polarizer has only one liquid crystal layer, the liquid crystal layer as coating layer 3 is a 1/4 wavelength plate, and the angle between the absorption axis direction of the polarizer and the alignment direction of the liquid crystal molecules (generally, the retardation 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 can be 35-55°, 40-50°, or 43-47°.

In the structure formed by laminating the polarizing plate 4 and the coating 3 as a quarter-wave plate in such a way that the angle between the optical axes of the two is 45°, a liquid crystal layer having liquid crystal molecules vertically aligned (homeotropically aligned) relative to the substrate surface can also be provided. By sequentially laminating the coating 3 as a quarter-wave plate and the vertical liquid crystal layer functioning as a positive C plate on the polarizing plate, a circular polarizing plate capable of shielding reflected light from external light coming from an oblique direction can be formed. It is also possible to sequentially laminate a vertically aligned liquid crystal layer (positive C plate) and a surface-aligned liquid crystal layer (quarter-wave plate as a positive A plate) on the polarizing plate.

In the circular polarizer formed by laminating a plurality of liquid crystal layers on a polarizer, the liquid crystal layers may all be plane-aligned liquid crystal layers. In this case, it is preferred that the liquid crystal layer disposed on one side close to the polarizer 4 is a 1/2 wavelength plate, and the liquid crystal layer disposed on one side away from the polarizer is a 1/4 wavelength plate. In the laminated structure, it is preferred that the angle formed by the retardation axis direction of the 1/2 wavelength plate and the absorption axis direction of the polarizer is 75°±5°, and the angle formed by the retardation axis direction of the 1/4 wavelength plate and the absorption axis direction of the polarizer is 15°±5°. This layered circular polarizer functions as a circular polarizer over a wide wavelength range of visible light, thereby reducing the chromatic aberration of reflected light.

As described above, in the embodiment of the present invention, since the protective film is temporarily adhered to the surface of the film substrate until the coating liquid is applied, the generation of scratches on the film substrate is suppressed, and the coating defects caused by the scratches on the film substrate are less. In addition, even when the coating is an oriented liquid crystal layer, and the liquid crystal molecules are aligned non-parallel to the length direction of the film substrate, there are fewer defects due to poor alignment. Furthermore, the poor coating caused by the lamination of the film substrate and the protective film is suppressed, so the in-plane uniformity of the coating becomes higher, and good display characteristics can be achieved. [Example]

Hereinafter, the present invention will be described more specifically by showing examples, but the present invention is not limited to the following examples.

<Preparation of coating solution> A photopolymerizable liquid crystal compound exhibiting a nematic liquid crystal phase ("Paliocolor LC242" manufactured by BASF) was dissolved in cyclopentanone to prepare a solution having a solid content concentration of 30% by weight. A surfactant ("BYK-360" manufactured by BYK-Chemie) and a photopolymerization initiator ("Omnirad907" manufactured by IGM Resins) were added to the solution to prepare a liquid crystal composition solution. The amount of the leveling agent and the polymerization initiator added was set to 0.01 parts by weight and 3 parts by weight, respectively, relative to 100 parts by weight of the photopolymerizable liquid crystal compound.

<Preparation of film substrate with protective film> Using pellets of cyclic polyolefin resin ("ZEONOR 1420R" manufactured by Zeon Japan), it was formed into a film by melt extrusion and then biaxially stretched to obtain a stretched film with a thickness of 33 μm and an in-plane delay of 135 nm. After the protective film was attached to one side of the stretched film substrate, the laminate was rolled into a roll.

As a protective film, an acrylic adhesive layer is prepared on one side of a biaxially oriented polyester film. By changing the composition and thickness of the adhesive layer and the type of antistatic layer provided on the back side, the surface resistance of the back side of the protective film and the peeling force from the film substrate can be adjusted.

<Preparation of Aligned Liquid Crystal Layer> The above-mentioned laminate was placed on the roll-out roll of the coating device shown in FIG3 , and the protective film was peeled off from the film substrate while the laminate was transported roll-to-roll. The above-mentioned liquid crystal composition was coated on the surface of the substrate in a manner such that the thickness after drying was 1 μm, and heated at 100°C for 3 minutes to align the liquid crystal. After cooling to room temperature, the laminate was irradiated with ultraviolet light with a cumulative light amount of 400 mJ/cm ² in a nitrogen atmosphere for photocuring, and a laminate with a surface-aligned liquid crystal layer formed on the film substrate was obtained.

[Evaluation] ＜Peeling force＞ The laminate of the film substrate and the protective film was cut into pieces with a width of 50 mm and a length of 100 mm. The peeling force when the protective film was peeled off from the film substrate was measured at a peeling angle of 180° and a tensile speed of 10 m/min.

<Surface resistance> The surface resistance was measured at a temperature of 23°C and a relative humidity of 50% using a resistivity meter (Model 152-1 manufactured by TREK) with a probe (Hiresta-UX MCP-HT800 manufactured by Nittoseiko Analytech Co., Ltd.) in contact with the back side of the protective film (the side not formed with the adhesive layer) at an applied voltage of 10 V for 30 seconds. The surface resistance of the protective film without an antistatic layer (Comparative Examples 1 and 2) exceeded the upper limit of the measurement (1×10 ¹³ Ω/sq).

<Striation unevenness> A transparent acrylic adhesive sheet is attached to a glass substrate, an aligned liquid crystal layer is attached thereto, and then the film substrate is peeled off from the aligned liquid crystal layer. The sample is placed between two polarizing plates arranged by crossed polarizers and visually observed on a tracking table. Samples in which stripe-like unevenness extending in the width direction is observed are marked as NG, and samples in which no stripe-like unevenness is confirmed are marked as OK.

[Evaluation Results] The evaluation results of the surface resistance R of the back side of the protective film used in the embodiment and the comparative example, the peeling force F from the film substrate, and the stripe unevenness of the alignment liquid crystal layer are shown in Table 1.

[Table 1] Surface resistance Peeling force Uneven stripes R(Ω/sq) log ₁₀ R F(N/50mm) Embodiment 1 1.1×10 ¹⁰ 10.02 0.12 OK Embodiment 2 2.9×10 ⁸ 8.46 0.12 OK Embodiment 3 3.4×10 ⁷ 7.53 0.12 OK Embodiment 4 5.0×10 ⁹ 9.70 0.75 OK Embodiment 5 1.1×10 ¹⁰ 10.02 0.64 OK Embodiment 6 2.9×10 ⁸ 8.46 0.64 OK Embodiment 7 3.4×10 ⁷ 7.53 0.64 OK Embodiment 8 2.9×10 ⁸ 8.46 1.22 OK Embodiment 9 3.4×10 ⁷ 7.53 1.22 OK Comparison Example 1 >10 ¹³ >13 0.64 NG Comparison Example 2 >10 ¹³ >13 1.22 NG Comparison Example 3 1.1×10 ¹⁰ 10.02 1.22 NG

No alignment defects of the liquid crystal were found in all the examples and comparative examples. This is believed to be because a protective film was temporarily attached to the surface of the film substrate before the liquid crystal composition was applied, thereby suppressing the generation of scratches on the film substrate.

In Examples 1 to 9 using a protective film with an antistatic layer on the back, no stripe unevenness was observed. In contrast, in Comparative Examples 1 and 2 using a protective film without an antistatic layer, stripe-like unevenness extending in the width direction occurred on the entire surface of the alignment liquid crystal layer. In Comparative Example 3 using a protective film with a large peeling force F, stripe-like unevenness also occurred in the same manner as in Comparative Examples 1 and 2.

According to the above results, it can be seen that by temporarily adhering a protective film with a smaller surface resistance and a smaller peeling force on the back side to the film substrate, and immediately applying the liquid crystal composition after peeling off the protective film from the film substrate, an aligned liquid crystal layer with no alignment defects and excellent in-plane uniformity can be obtained.

The film thickness and in-plane retardation distribution of the aligned liquid crystal layers obtained in the examples and comparative examples were measured. The results showed that the thickness of the aligned liquid crystal layers of Examples 1 to 3 where the stripe unevenness occurred was 30 to 40 nm smaller than that of other parts, and the in-plane retardation became smaller at the thinner thickness parts. On the other hand, no stripe-like thickness unevenness was confirmed on the film substrate after the aligned liquid crystal layer was peeled off.

Based on the above results, it is speculated that in Comparative Examples 1 to 3, due to the partial charging of the film substrate after the protective film is peeled off, the liquid crystal composition is coated due to shrinkage, resulting in poor coating. In contrast, in the embodiment, it is believed that since the surface resistance and/or peeling force of the protective film are small, the influence of the charging of the film substrate after the protective film is peeled off is small, the poor coating is suppressed, and an aligned liquid crystal layer with high in-plane uniformity is formed.

1: Film substrate 1A: First main surface 1B: Second main surface 2: Protective film 2A: Back surface 3: Coating (liquid crystal layer) 4: Optical layer (polarizer) 5: Adhesive layer 6: Adhesive layer 7: Isolation element 8: Laminated body 9: Laminated body (optical film) 10: Peeling section 11: Peeling roller 13: Transport roller 15: Pressing roller 15C: Connecting shaft 15L: Roller 15R: Roller 20: Winding body 21: Take-up roller 23: Transport roller 25: Transport roller 30: coating section 31: support roller 33: die nozzle 50: heating section 55: heating furnace 60: curing section 61: light source 71, 73, 75, 77, 79: conveying roller 80: winding body 81: unwinding roller 83, 85, 87: conveying roller 90: winding body 91: take-up roller 96: laminate (optical film) 97: laminate (optical film) 98: laminate (optical film) 151: pressing roller 291: core material 292: adhesive layer 295: Anti-static layer

FIG. 1 is a cross-sectional view of an optical film having a coating on a film substrate. FIG. 2 is a cross-sectional view of a laminate having a protective film temporarily adhered to a film substrate. FIG. 3 is a diagram showing an outline of a film-forming device and film-forming steps for forming a coating on a film substrate. FIG. 4 is a three-dimensional view showing an example of the shape of a pressing roller. FIG. 5 is a cross-sectional view of an optical film of an embodiment. FIG. 6 is a cross-sectional view of an optical film of an embodiment. FIG. 7 is a cross-sectional view of an optical film of an embodiment.

1: Membrane substrate

2: Protective film

8: Laminated body

9: Laminated body (optical film)

10: Peeling part

11: Peel off the roller

13: Transport roller

15: Press the roller

20: Coiled body

21: Rolling roller

23: Transport roller

25: Transport roller

30: Painting Department

31: Support roller

33: Mouthpiece

50: Heating section

55: Heating furnace

60: Hardened part

61: Light source

71,73,75,77,79: conveyor rollers

80: coiled body

81: Roll out roller

83,85,87: Transport rollers

90: Coiled body

91: Roller

Claims (10)

A method for manufacturing an optical film, which is a method for manufacturing a long optical film, comprises: a step of preparing a laminate, wherein a protective film is releasably attached to the first main surface of a long film substrate having a first main surface and a second main surface; a first conveying step, wherein the laminate is conveyed to a peeling section by rolling along the length direction of the film substrate; a protective film peeling step, wherein the protective film is peeled off from the film substrate in the peeling section; The first main surface of the film substrate is peeled off; the second conveying step is to convey the film substrate after the protective film is peeled off from the peeling section to the coating section along the length direction of the film substrate; and the coating step is to apply a coating liquid on 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; the surface resistance of the protective film on the side opposite to the bonding surface of the film substrate is 1×10 ¹¹ Ω/sq or less, and under the conditions of a peeling angle of 180° and a peeling speed of 10 m/min, a peeling force F (N/50 mm) when the protective film is peeled off from the film substrate and a surface resistance R (Ω/sq) of the back side of the protective film satisfy log ₁₀ R+2.3F≦11.5. The method for manufacturing an optical film as claimed in claim 1, wherein the peeling force when the protective film is peeled off from the film substrate is 1.5N/50mm or less at a peeling angle of 180° and a peeling speed of 10m/min. A method for manufacturing an optical film as claimed in claim 1 or 2, wherein the coating liquid is a liquid crystal composition containing a liquid crystal compound. The method for manufacturing an optical film as claimed in claim 3, wherein the liquid crystal composition comprises a photocurable liquid crystal compound, and comprises a step of photocuring the liquid crystal compound after the coating step. A method for manufacturing an optical film as claimed in claim 1 or 2, wherein the film substrate is a stretched film with molecules oriented non-parallel to the longitudinal direction. A method for manufacturing an optical film as claimed in claim 1 or 2, wherein in the second conveying step, the roller does not contact the central portion of the first main surface of the film substrate in the width direction. A method for manufacturing an optical film as claimed in claim 6, wherein in the second conveying step, the film pressing mechanism contacts the two end portions of the first main surface of the film substrate in the width direction at least once, and the film pressing mechanism does not contact the central portion of the first main surface of the film substrate in the width direction. A method for manufacturing an optical film as claimed in claim 7, wherein the film pressing mechanism is a pressing roller that contacts only the two end portions of the first main surface of the film substrate in the width direction. A method for manufacturing an optical film as claimed in claim 1 or 2, comprising the step of laminating other optical layers on the above-mentioned coating layer in a roll-to-roll manner. A method for manufacturing an optical film as claimed in claim 9, wherein the optical layer comprises a polarizing element.