TWI666304B - Manufacturing method of optical film - Google Patents

Abstract

The object of the present invention is to produce an optical film with fewer defects with local film thickness variations. In the manufacturing method of the optical film of the present invention, the long substrate 1 having the film-forming surface 11 and the back surface 12 is unwound from the wound body 2 of the flexible substrate, and is continuously conveyed to the downstream side. After the back surface 12 of the substrate 1 is cleaned, a liquid crystal material is coated on the film-forming surface 11 of the substrate 1. A cleaning liquid is supplied between the back surface of the substrate and the cleaning roller 41, and the cleaning liquid is spread on the substrate by the cleaning roller, thereby cleaning the back surface of the substrate.

Description

Manufacturing method of optical film

The present invention relates to a method for manufacturing an optical film using a liquid crystal material.

The liquid crystal material has larger optical anisotropy than a general resin material. Therefore, when used in an optical film such as a retardation film or a polarizing element, the film thickness can be reduced, which is conducive to thinning or lightening the device. The liquid crystal optical film is formed by coating a liquid crystal material (liquid crystal monomer and / or liquid crystal polymer) on the film substrate, and polymerizing the liquid crystal monomer, aligning the liquid crystal material, and removing (drying) the solvent as needed to form a liquid crystal. Layers.

In the manufacture of optical films, the problem is that foreign matter or the like adhered to the substrate enters the interface between the coating layer and the substrate, or into the coating layer, and becomes an optical disadvantage. In addition, in the production of an optical film using a liquid crystal material, if there is a foreign substance on the substrate, it is also a problem that alignment defects or protrusion defects occur on the liquid crystal applied thereon.

Therefore, a method of applying a liquid crystal material after cleaning the coated surface of the substrate to remove foreign matter has been proposed. As a method for removing foreign matter adhering to a substrate, a method using ultrasonic air (for example, Patent Document 1), a method for blowing a cleaning gas (for example, Patent Document 2), a method for washing a substrate with water (for example, Patent Document 3), And a method of contacting the adhesive roller (for example, Patent Document 4).

When using a substrate that is subjected to a rubbing treatment in order to align the liquid crystal molecules in a specific direction, a large amount of foreign matter adheres to the surface of the substrate. Therefore, the purpose of removing the adhered foreign matter is to perform a cleaning treatment before coating the liquid crystal material. The surface of the substrate subjected to the alignment treatment such as rubbing cannot be scrubbed, so in general, a non-contact cleaning method is used. For example, in the patent In Proposal 5, a method of irradiating ultraviolet rays on the surface of a substrate subjected to an alignment treatment to remove a foreign substance is disclosed.

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 10-309553

[Patent Document 2] Japanese Patent Laid-Open No. 2009-66982

[Patent Document 3] Japanese Patent Laid-Open No. 2007-105662

[Patent Document 4] Japanese Patent Laid-Open No. 9-304621

[Patent Document 5] Japanese Patent Laid-Open No. 2003-4948

An optical film having a small film thickness of a coating layer formed on a substrate, such as a liquid crystal optical film, may have a defect such as a dot-like interference spot (hereinafter sometimes referred to as "dot-like unevenness"). According to the research by the present inventors, various defects caused by the liquid crystal layer or the interface between the liquid crystal layer and the substrate can be reduced by cleaning the surface of the substrate (the formation surface of the liquid crystal layer). There was almost no change in the number of generations.

Further research was performed, and it was estimated that the spot-shaped unevenness was generated, and the film thickness of the film was locally reduced. It may be periodically displayed in the conveyance direction (MD) of the substrate, and was affected by the foreign matter adhering to the coating roller. Therefore, the present inventors have tried to contact a coating roller when a liquid crystal material is coated on a substrate with a blade (squeegee) for removing foreign matter, and clean the surface of the roller to reduce spot unevenness. However, in the method of cleaning the surface of a roller, the effect of reducing the spot unevenness cannot be clearly confirmed.

In view of the above circumstances, an object of the present invention is to reduce the occurrence of "spot-like unevenness" defects in a localized film thickness in an optical film in which a liquid crystal layer is formed on a substrate, and obtain a high-quality optical film.

In consideration of the above circumstances, it was found that, after the substrate is withdrawn until the liquid crystal material is applied, the surface (back surface) of the substrate opposite to the film-forming surface is cleaned online, thereby reducing spot unevenness. As a result of further research, it was found that by performing wet cleaning while bringing the back surface of the substrate into contact with the roller through the cleaning liquid, the spot unevenness was greatly reduced, thereby completing the present invention.

The present invention relates to a method for manufacturing an optical film using a liquid crystal material. In the manufacturing method of the optical film of this invention, a long-shaped base material is unwound from the winding body of a flexible base material, and it is conveyed continuously to a downstream side (extraction process). The substrate has a first main surface as a film-forming surface and a second main surface as a back surface of the film-forming surface. In the manufacturing method of the present invention, the second main surface of the substrate is cleaned (cleaning step), and thereafter, the liquid crystal material is coated on the first main surface of the substrate (film forming step).

In the cleaning step, a cleaning liquid is supplied between the back surface of the substrate and the cleaning roller, and the cleaning liquid is spread on the substrate by the cleaning roller, thereby performing cleaning. The cleaning roller is preferably one having a concave-convex pattern on the surface, and among them, it is preferable to use a cleaning roller whose convex portion of the concave-convex pattern extends non-parallel to the circumferential direction of the roller. It is generally considered that in the present invention, wet cleaning is performed by bringing the cleaning roller into contact with the back surface of the substrate through the cleaning liquid, and foreign matter adhering to the back surface of the substrate is removed, thereby reducing spot unevenness.

Examples of the cleaning roller used in the present invention include a gravure roller and a wire rod roller. In addition, as the cleaning liquid, a highly volatile liquid having a boiling point lower than that of water is preferably used.

According to the manufacturing method of the present invention, it is possible to obtain a high-quality optical film in which the occurrence of "spot-like unevenness" defects in which the film thickness becomes locally small can be obtained.

1‧‧‧ substrate

2‧‧‧ coiled body

10‧‧‧Extraction Department

11‧‧‧ film-making surface (first main surface)

12‧‧‧ back (second main face)

20‧‧‧ drying furnace

40‧‧‧Cleaning Department

41‧‧‧cleaning roller

42‧‧‧Support roller

44‧‧‧Scraper

47‧‧‧washing plate

48‧‧‧ cleaning fluid

51, 52, 54‧‧‧Guide roller

60‧‧‧Film Making Department

61‧‧‧mould

62‧‧‧Support roller

140‧‧‧gravure roller

141‧‧‧concave

142‧‧‧ convex

240‧‧‧ wire rod roller

241‧‧‧cylinder

242‧‧‧Thin line (convex)

FIG. 1 is a schematic view showing an embodiment of an optical film forming apparatus.

Fig. 2 is a schematic plan view for explaining a surface shape of a gravure roll.

FIG. 3A is a schematic plan view for explaining the surface shape of the wire rod roller.

Fig. 3B is a sectional view taken along line B1-B2 of the rod roll of Fig. 3A.

FIG. 1 is a schematic diagram showing an embodiment of a film forming apparatus used in the production of an optical film of the present invention. In the film forming apparatus 100 shown in FIG. 1, a rolled body 2 of a long substrate is provided in the extraction portion 10. The substrate 1 unwound from the winding body 2 is continuously conveyed from the extraction unit 10 to the downstream side of the film forming apparatus, and passes through the guide rollers 51 and 52 to the cleaning unit 40 provided on the downstream side of the guide roller 52 (extraction step). ). In the cleaning section 40, the back surface of the substrate 1 is cleaned (cleaning step). The cleaned substrate 1 is further conveyed to the downstream side, passes through the guide roller 54, and is conveyed to the film forming unit 60 to apply the liquid crystal material to the substrate (film forming step).

[Substrate]

The substrate 1 only needs to have flexibility, and a support having excellent mechanical strength, thermal stability, water resistance, and the like is preferably used. The substrate has a first main surface and a second main surface, and a liquid crystal layer is formed on the first main surface. Hereinafter, in this specification, a first main surface is referred to as a "film-forming surface", and a second main surface that is a surface on the opposite side thereof is referred to as a "back surface".

As the base material, for example, a resin film, a metal foil, paper, cloth, a laminated body thereof, or the like is used. Among them, a resin film is preferably used because it has excellent surface smoothness and less generation of foreign matter from the substrate itself.

Examples of the resin material constituting the base film include polyesters such as polyethylene terephthalate and polyethylene naphthalate; and cellulose-based polymers such as diethyl cellulose and triethyl cellulose ; Acrylic polymers such as polymethyl methacrylate; styrene polymers such as polystyrene or acrylonitrile styrene copolymer; polyolefins such as polyethylene, polypropylene, ethylene propylene copolymer; polynorbornene Isocyclic polyolefins; fluorene polymers such as nylon or aromatic polyamines; polycarbonates; vinyl chloride; fluorene imine polymers; fluorene polymers; polyether fluorene; polyetheretherketone; polybenzene Sulfide; vinyl alcohol polymer; vinylidene chloride; epoxy polymer. Among these, a resin material which is insoluble in a solvent when the liquid crystal material is applied is preferably used.

The substrate may be colorless and transparent, or colored or opaque. After the liquid crystal layer is formed on the substrate, and when the laminated body of the substrate and the liquid crystal layer is used as an optical film for practical use, it is preferable to use a support having a transparent and uniform optical characteristics as the substrate.

The thickness of the substrate is not particularly limited as long as it has both self-supporting properties and flexibility. The thickness of the substrate is generally about 20 μm to 200 μm, preferably 30 μm to 150 μm, and more preferably 35 μm to 100 μm. When a liquid crystal layer is formed on a flexible substrate such as a film, the length of the substrate can be limited because the length of the substrate is limited. Generally, the upper limit of the weight or diameter of the winding body provided on the stand for the extraction part 10 or the winding part (not shown) after film formation is determined. Therefore, if the thickness of the substrate is small, the length of continuous film formation can be increased, and productivity can be improved. Therefore, it is preferable that the thickness of the substrate is as small as possible within a range that does not impair the film-forming property or the handleability.

On the other hand, according to research by the present inventors, when the thickness of the substrate is small, the optical film in which a liquid crystal layer is formed on the substrate can be observed to increase the number of dot-like unevenness. . On the other hand, as described in detail later, in the present invention, because the back surface of the substrate is cleaned by a specific method before coating the liquid crystal material, even if the thickness of the substrate is small, spot-like unevenness can be suppressed. It happened.

In order to align the liquid crystal molecules in a specific direction, an alignment substrate may be used. Examples of the alignment substrate include a stretched polymer film, a film subjected to a rubbing treatment on the surface, and a film having a rubbed alignment film on the surface. As the alignment film, a polyvinyl alcohol film, a polyimide film, a polysiloxane film, a glassy polymer film, or the like can be used. The rubbing treatment is performed by rubbing on a substrate with a rubbing roller that rolls a rubbing cloth containing fine fibers such as 纤维 or cotton. It is also possible to produce an optical film having various optical axes (alignment directions of liquid crystal molecules) by adjusting the arrangement angle of the friction roller to have a specific angle between the transport direction of the substrate and the friction direction.

In the case of using a friction-treated substrate, the wound body of the friction-treated substrate may be set in the extraction portion 10 of the film forming apparatus 100, or the untreated substrate may be self-extracted from the extraction portion 10. After extraction, the substrate is rubbed. From the viewpoint of preventing foreign matter from being mixed into the liquid crystal layer or preventing step contamination, it is preferred to use the wound body of the base material after the rubbing treatment in the extraction portion of the film forming apparatus. In the case where the untreated base material is pulled out from the extraction portion and the base material is subjected to the rubbing treatment, the rubbing treatment is performed after the base material is pulled out and before the cleaning treatment.

The surface of the base film can be easily treated, demoulded, antistatic, and anti-blocking. In addition, embossing (knurling) and the like can be performed on the ends in the width direction of the base material for the purpose of anti-blocking and the like.

[Liquid crystal material]

The liquid crystal material contains a liquid crystal monomer or a liquid crystal polymer, or a mixture thereof. The liquid crystal monomer and the liquid crystal polymer (which may be collectively referred to as a "liquid crystal compound") may be those exhibiting thermotropic liquid crystallinity or those exhibiting liquid crystallinity.

As the liquid crystal monomer, one having an orientation such as nematicity or smecticity and having at least one polymerizable functional group such as an unsaturated double bond such as an acrylfluorenyl group, a methacrylfluorenyl group, a vinyl group, or an epoxy group at the terminal is used. Liquid crystalline compound. The liquid crystal material containing a liquid crystal monomer may contain a polymerization initiator in addition to the liquid crystal monomer. Examples of the polymerization method of the polymerizable liquid crystal monomer include thermal polymerization and ultraviolet polymerization, and an appropriate polymerization initiator is used depending on the polymerization method.

As the liquid crystal polymer, a main chain type liquid crystal polymer or a side chain type liquid crystal polymer that exhibits liquid crystal alignment such as nematicity or smecticity, or a composite liquid crystal compound of these types is used. The molecular weight of the liquid crystal polymer is not particularly limited, and a weight average molecular weight is preferably about 2,000 to 100,000.

The liquid crystal material can also be made cholesterol-aligning because the nematic liquid crystal material contains a chiral agent or a palmar component is introduced into the structure of the liquid crystal polymer. The type or amount of the chiral agent can be appropriately determined according to the selected reflection wavelength of the cholesteric liquid crystal, or the set value of the spiral pitch.

When a liquid crystal material is coated on a substrate, a solution of a liquid crystal compound is usually used. The solvent for dissolving the liquid crystal material can be appropriately determined according to the type of the liquid crystal material or the type of the substrate. Specific examples of the solvent include halogenated hydrocarbons such as chloroform, dichloromethane, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, and chlorobenzene; phenols such as phenol and p-chlorophenol; Aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, 1,2-dimethoxybenzene, acetone, ethyl acetate, tert-butanol, glycerol, ethylene glycol, triethylene glycol, ethyl acetate Glycol monomethyl ether, diethylene glycol dimethyl ether, ethyl cyrus, butyl cyrus, 2-pyrrolidone, N-methyl-2-pyrrolidone, pyridine, triethylamine, Tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethylmethylene, acetonitrile, butyronitrile, carbon disulfide, and the like. The solvent may be used in combination of two or more kinds.

The liquid crystal material solution may contain additives such as a coloring agent, a leveling agent, a plasticizer, an ultraviolet absorber, and a deterioration preventing agent in addition to a polymerization initiator, a chiral agent, and the like. The solid content, viscosity, etc. of the liquid crystal material solution are appropriately set according to the type or molecular weight of the liquid crystal material, the thickness of the liquid crystal layer, and the method of forming a film.

[Cleaning Department]

A cleaning section 40 is provided between the extraction section 10 and the film forming section 60 in the transport path of the substrate 1. The cleaning unit 40 performs wet cleaning while bringing the back surface 12 of the substrate 1 into contact with the cleaning roller 41 via a cleaning liquid. It is presumed that in the present invention, when the cleaning liquid supplied between the cleaning roller and the back surface of the substrate is spread on the substrate by the cleaning roller, it can be effectively cleaned by applying a shearing force to the interface between the cleaning liquid and the substrate. Removal of foreign matter adhering to the substrate can suppress spot-like unevenness.

In the form shown in FIG. 1, the cleaning unit 40 includes a support roller 42 provided so as to be in contact with the film-forming surface 11 of the substrate 1, and a cleaning roller 41 provided so as to be in contact with the back surface 12 of the substrate 1. The cleaning liquid 47 is stored in the cleaning tray 48. The remaining part of the cleaning liquid attached to the surface of the cleaning roller 41 is scraped off with a scraper 44, and the substrate 1 is led to the back surface 12.

<Cleaning roller>

As the cleaning roller 41, a knife roller (a doctor blade roller), a contact roller, a gravure roller, a wire rod roller, or the like, and various rollers used for solution coating are used. The cleaning roller can be a rotating roller or a non-rotating roller. Roll. When the cleaning roller is a rotary roller, the rotation direction may be any one of forward rotation and reverse rotation.

From the viewpoint of improving the cleaning efficiency of the substrate, it is preferable that unevenness is formed on the surface of the cleaning roller. The uneven pattern on the surface of the cleaning roller is preferably such that the convex portion extends non-parallel to the circumferential direction of the roller. The convex portion extending non-parallel to the circumferential direction of the cleaning roller 41 is in contact with the back surface of the base material, so that foreign matter adhering to the base material and the like can be more effectively cleaned and removed, and spot unevenness tends to be suppressed.

Examples of the roll having a convex portion extending in a direction not parallel to the circumferential direction include a gravure roll, a wire rod roll, an embossing roll, and the like. Since the cleaning solution is spread on the back surface of the substrate without damaging the substrate, it is particularly preferable to use a gravure roller and a wire rod roller as the cleaning roller.

FIG. 2 is a plan view showing an example of an uneven pattern shape on the surface of a gravure roll. A concave portion (gravure groove) 141 and a convex portion 142 are formed in a pattern on the surface of the gravure roll 140. It is generally considered that when a gravure roll is used as a cleaning roll, the liquid stored in the concave portion is in contact with the surface of the substrate, and the foreign matter adhering to the surface of the substrate is scraped off by contact with the convex portion, and the foreign matter is removed. In addition, in FIG. 2, the shape of the intaglio pattern is illustrated as a shape of a quadrangle (square type), but the shape of the intaglio pattern is not particularly limited if the convex portion extends in an oblique direction. Polygonal, oblique, or curved.

FIG. 3A is a plan view showing an example of an uneven pattern shape on the surface of the wire rod roller 240, and FIG. 3B is a cross-sectional view taken along line B1-B2. The wire rod roller is a roller in which thin wires 242 such as a wire are spirally wound on the surface of the roller body (cylinder) 241. The thin wires 242 are formed with convex portions extending in a direction not parallel to the circumferential direction. It is generally considered that when a wire rod roller is used as a cleaning roller, the liquid stored in the gap between adjacent thin wires 242 comes into contact with the surface of the substrate, and foreign matter adhered to the surface of the substrate comes into contact with the thin wire 242 wound in a spiral shape While being scraped off, foreign matter is removed. Moreover, in FIG. 3A and B, the form where one thin wire 242 is wound around a cylinder is shown, but a wire rod may also be wound by a plurality of thin wires. Thin line 242 can be rolled without gap Winding can also be wound at certain intervals. The interval between adjacent thin lines is preferably the same as or less than the width of the thin lines.

The height of the convex portion on the surface of the cleaning roller is not particularly limited, but it is preferably in the range of about 0.1 μm to 10 μm, as is the height of the convex portion of a general gravure roll or wire rod roll. If the height of the convex portion is too small, the cleaning effect may be insufficient. On the other hand, if the height of the convex portion is too large, the unfolding thickness of the cleaning liquid becomes large, so that the cleaning efficiency may be reduced, or the drying of the cleaning liquid may take a long time, thereby reducing the production efficiency.

<Cleaning solution>

In the cleaning step, a cleaning liquid is supplied between the cleaning roller 41 and the back surface 12 of the substrate 1. The cleaning roller 41 is brought into contact with the back surface 12 of the substrate 1, and a developing cleaning solution is applied to the back surface of the substrate to perform cleaning. The cleaning liquid is a liquid and is not particularly limited as long as it does not dissolve the substrate 1. Water, an organic solvent, a mixture of water and an organic solvent, and the like can be used.

From the viewpoint of efficiently performing on-line cleaning on the transport path from the extraction section 10 to the film forming section 60, it is preferable to use a liquid having a low boiling point and a high volatility as the cleaning liquid. Examples of highly volatile liquids include alcohols such as methanol, ethanol, and isopropanol; ketones such as acetone and methyl ethyl ketone; haloalkanes such as chloroform, dichloromethane, and dichloroethane; diethyl ether and ethyl Ethers such as propyl propyl ether and ethyl isopropyl ether. In addition, a mixture of these organic solvents or a mixture of these organic solvents and water may be used. In addition, for the purpose of improving the cleaning power, a surfactant, a hydrophilic organic compound, or the like may be added to the cleaning solution. Examples of the hydrophilic organic compound include a hydroxyl group, an amine group, a fluorenylamino group, an imine group, a fluorenimine group, a nitro group, a cyano group, an isocyanate group, a carboxyl group, an ester group, an ether group, a carbonyl group, a sulfonic acid group, Organic compounds such as SO group.

<Cleaning method>

The cleaning method is not particularly limited as long as it is a method in which a cleaning liquid supplied between the cleaning roller 41 and the back surface 12 of the substrate 1 is applied and spread on the substrate. The method for supplying the cleaning liquid between the cleaning roller and the substrate is not particularly limited. In FIG. 1, the cleaning roller 41 and the cleaning tray are illustrated. The form in which the cleaning liquid 47 in 48 is in direct contact (direct gravure method), but for example, other rollers (rubber plate rollers) can be brought into contact with the cleaning liquid in the cleaning plate, so that the cleaning liquid adhered to the surface of the rubber plate roller can be used to A method of moving a cleaning roller disposed in contact with a rubber plate roller (a rubber plate gravure) and the like. In addition to the method of attaching the cleaning liquid to the surface of the cleaning roller 41, the method of applying the cleaning liquid by using a slit mold or spraying the back surface 12 of the substrate 1 before the substrate 1 contacts the cleaning roller 41 may be used. A method of moving the substrate in the cleaning pan, a method of attaching the cleaning liquid to the surface of the cleaning roller 41 by spraying or the like, and supplying the cleaning liquid between the cleaning roller 41 and the back surface 12 of the substrate 1.

The substrate 1 is conveyed to the downstream side (left side in FIG. 1) while being in contact with the cleaning roller 41, so the cleaning liquid supplied between the cleaning roller 41 and the substrate must be spread on the surface of the substrate. The cleaning roller 41 may be in direct contact with the back surface 12 of the base material 1 or may have a gap. The gap between the cleaning roller and the back surface of the substrate is preferably about 0.1 μm to 10 μm, for example. When the gap is too large, the shear force at the interface between the roller and the substrate via the cleaning liquid becomes small, and the cleaning efficiency tends to decrease. When the cleaning roller has a concave-convex pattern on the surface, as described above, the gap between the cleaning roller and the substrate can be adjusted to a desired range according to the height of the convex portion on the surface of the roller. When the cleaning roller does not have an uneven pattern on its surface, the gap can be adjusted according to the relative positional relationship between the cleaning roller and the substrate.

In FIG. 1, in the cleaning unit 40, the back surface 12 of the substrate 1 is in contact with the cleaning roller 41 and the film-forming surface 11 is in contact with the support roller 42. However, if the back surface 12 of the substrate 1 is in contact with the cleaning roller 41 If the conveying path of the substrate is formed by the contact of the cleaning liquid, the support roller in the cleaning section 40 is not necessarily required. In addition, instead of the support roller 42, a roller or the like having a concavo-convex surface can be used to clean the film-forming surface 11 simultaneously with the back surface 12 of the substrate 1.

The substrate 1 washed on the back surface 12 of the cleaning section 40 is conveyed to the film forming section 60 through the guide roller 54. Furthermore, during the period when the substrate is being transported from the cleaning section 40 to the film forming section 60, the cleaning liquid adhered to the surface of the substrate can be dried. The drying method is not particularly limited, and examples thereof include a method of blowing a clean gas, and a method of passing a substrate in a heating oven.

[Film production department]

A liquid crystal material solution is coated on the film-forming surface 11 of the substrate 1 in the film-forming portion 60, and a film is formed according to a conventional method. In FIG. 1, a die coater using an extrusion die 61 is shown. In this coating machine, the liquid crystal material sprayed from the opening of the mold 61 is coated on the film-forming surface of the substrate while the back surface 12 of the substrate 1 is in contact with the support roller 62. The thickness of the coating film of the liquid crystal material is adjusted by adjusting the coating amount of the liquid crystal material from the mold and the transport speed of the substrate.

The film forming method in the film forming section 60 is not limited to die coating, and it can use contact roll coating, gravure coating, reverse coating, spray coating, wire rod coating, knife roller coating, and air knife coating. , Curtain coating and other methods.

In many cases, the characteristics of an optical film using a liquid crystal material depend on the film thickness of the liquid crystal layer. For example, the retardation value of the retardation film, the rotation angle of the optical axis of the optical rotation element, and the absorbance of the polarizing element are proportional to the thickness of the liquid crystal layer. Therefore, in order to make the characteristics of the optical film uniform, it is preferable that the film thickness be uniform at the time of film formation. In order to make the film thickness uniform, as shown in FIG. 1, it is preferable to form a film while supporting the back surface 12 of the substrate 1 with a support roller 62.

On the other hand, if there is a foreign object between the support roller 62 and the back surface 12 of the base material 1, the film-forming surface 11 of the base material 1 is deformed into a convex shape by being squeezed. It is generally considered that if a liquid crystal material is applied thereon, the coating thickness of the deformed portion of the substrate becomes locally small, and spot-like unevenness occurs. On the other hand, in the present invention, the back surface 12 of the substrate 1 is cleaned online to remove the adhered foreign matter. Therefore, it is estimated that when the substrate is formed while supporting the substrate with a support roller, dot unevenness also occurs. suppressed.

The thickness of the liquid crystal layer is set according to the characteristics of the target optical film, for example, such that the film thickness after drying is about 0.1 μm to 20 μm. Generally, the smaller the thickness of the liquid crystal layer, the more the dot unevenness tends to be noticeable. On the other hand, in the present invention, by passing through the cleaning step described above, even when the film thickness of the liquid crystal layer after drying is 20 μm or less, the occurrence of dot unevenness can be suppressed. Therefore, the manufacturing method of the present invention is preferably used in the manufacture of a liquid crystal optical film with a small coating layer thickness.

[Steps after coating]

The coating film of the liquid crystal material applied on the film-forming surface 11 of the substrate 1 is transported together with the substrate 1 into the drying furnace 20 to remove the solvent and form a liquid crystal layer. In addition to drying, alignment treatment of liquid crystal molecules or polymerization of liquid crystal monomers can be performed. For example, when using a liquid crystal monomer that exhibits thermotropic liquid crystal properties, the monomer is heated to a temperature region above the liquid crystal phase, dried, and then cooled to a temperature showing the state of the liquid crystal phase, and polymerized by ultraviolet irradiation. This can fix the alignment state of the liquid crystal. In addition, liquid crystal liquid crystals can also align liquid crystal molecules in a specific alignment direction by applying a shearing force.

The substrate after the liquid crystal layer is formed can be directly wound up in a state where the substrate and the liquid crystal layer are in close contact. The liquid crystal layer formed on the substrate may be transferred to another film, or the substrate and the liquid crystal layer may be curled after the substrate and the liquid crystal layer are separated, respectively. In addition, the liquid crystal layer peeled from the substrate or the liquid crystal layer transferred to another film may be subjected to other steps such as drying, alignment treatment, and stretching.

The liquid crystal layer rolled up in a state of being in close contact with the substrate can be integrated with the substrate as an optical film for practical use. In addition, the state where the liquid crystal layer is adhered to the substrate can also be used for other steps such as stretching. Thereafter, the substrate and the liquid crystal layer may be used as an optical film integrally, or a liquid crystal layer peeled from the substrate or a liquid crystal layer transferred on another film may be used as the optical film. It is also possible to apply another coating layer on the liquid crystal layer.

The optical film of the present invention obtained in this manner can be used as an optical film for an image display device because it reduces dot unevenness and has fewer optical defects. Specific examples of the optical film used for the image display device include an optical compensation film such as a retardation plate, a polarizing element, a polarizing element protective film, and an optical rotation element.

[Example]

The present invention will be described in more detail with reference to the following examples of production of a liquid crystal optical film, but the present invention is not limited to the following examples.

[Production Example 1: Production of Negative C Plate Using Cholesterol Liquid Crystal Material]

In Production Examples 1A to 1M, a 75 μm-thick polyester film (not rubbed) was used as For the base film, the following coating solution was coated on the base film to produce an optical film of a negative C plate (selective reflection wavelength: 200 to 220 nm) including a cholesteric liquid crystal layer.

<Preparation of Liquid Coating Material Liquid>

The following nematic liquid crystal monomer: 90 parts by weight,

Polymerizable chiral agent of the formula: 10 parts by weight,

And UV polymerization initiator (trade name "Irgacure907" manufactured by BASF): 5 parts by weight of methyl ethyl ketone: 300 parts by weight, to prepare a polymerizable liquid crystal material solution containing a chiral agent.

[Production Example 1A (Example)]

The winding body of the base film is set on the extraction part of the film forming device, and the base film is pulled out and moved. The isopropanol is used as the cleaning liquid, and the conveying direction of the base film on the back side of the base film is in the opposite direction. Rotate the gravure roll in the direction to clean the back of the substrate. Apply the polymerizable liquid crystal material solution on the film-forming surface of the cleaned substrate so that the film thickness after drying is 2 μm. After drying at 70 ° C for 3 minutes, cool to room temperature, and irradiate 300 mJ of ultraviolet light with a cumulative light meter. / cm ² , thereby hardening the liquid crystal monomer and fixing the alignment of the liquid crystal molecules. The obtained liquid crystal layer is wound up as a laminated body with a base film.

[Production Example 1B (Example)]

In the above-mentioned Production Example 1A, in addition to the back surface side of the base film, the film-forming surface side was also cleaned with isopropyl alcohol as the cleaning liquid while contacting the gravure roll. That is, in Production Example 1B, the back surface of the base film and both surfaces of the film-forming surface were cleaned while contacting the gravure roll. its Thereafter, in the same manner as in Production Example 1A, the polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet rays to form a liquid crystal layer on the substrate film.

[Production Examples 1C, 1D (Examples)]

Instead of a gravure roll, a wire rod roll was used. Other than that, after washing in the same manner as in Production Examples 1A and 1B, the polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet rays to form a liquid crystal layer. That is, in Production Example 1C, the back surface of the base film was cleaned while contacting the wire rod roller, and in Production Example 1D, the back surface of the base film was double-sided contact wire rod roller and cleaned.

[Production Example 1E (Comparative Example)]

Neither the back surface of the base film nor the film-forming surface was cleaned. In the same manner as in Production Example 1A, a polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet rays on the base film. A liquid crystal layer is formed.

[Production Example 1F (Comparative Example)]

In the above-mentioned Production Example 1B, the back surface of the base film was not cleaned, and only the film-forming surface of the base film was cleaned while contacting the gravure roll. Thereafter, in the same manner as in Production Example 1A, the polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet rays to form a liquid crystal layer on the substrate film.

[Production Example 1G (Comparative Example)]

In the above-mentioned Production Example 1D, the back surface of the base film was not cleaned, and only the film-forming surface of the base film was cleaned while contacting the wire rod roller. Thereafter, in the same manner as in Production Example 1A, the polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet rays to form a liquid crystal layer on the substrate film.

[Production Example 1H (Comparative Example)]

In the same manner as in Production Example 1E, neither the back surface of the base film nor the film-forming surface was cleaned. In the same manner as in Production Example 1A, the polymerizable liquid crystal material solution was applied, dried, and cooled. And ultraviolet irradiation to form a liquid crystal layer on the substrate film. to In Production Example 1H, when the polymerizable liquid crystal material solution was applied, the support roller contacting the back surface of the substrate was brought into contact with a squeegee, and the film was formed while the support roller was often cleaned.

[Production Example 1I (Comparative Example)]

The guide roller in contact with the back surface of the substrate is changed to an adhesive roller directly in front of the film forming section of the film forming device, and the back surface of the substrate is cleaned by contact with the adhesive roller. On the other hand, in Production Example 1I, cleaning using a cleaning roller was not performed. Except for this, in the same manner as in Production Example 1A, the polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet rays to form a liquid crystal layer on the substrate film.

[Production example 1J (comparative example)]

In front of the film forming part of the film forming device, the guide roller in contact with the film forming surface of the substrate is changed to an adhesive roller, and the film forming surface of the substrate is cleaned by contact with the adhesive roller. On the other hand, in Production Example 1J, cleaning using a cleaning roller was not performed. Except for this, the polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet rays in the same manner as in Production Example 1A to form a liquid crystal layer on the substrate film.

[Production Example 1K (Comparative Example)]

In front of the film-forming part of the film-making device, the guide rollers in contact with the back surface of the substrate and the guide rollers in contact with the film-making surface were changed to adhesive rollers respectively. Cleaning of film making surface. On the other hand, in Production Example 1K, cleaning using a cleaning roller was not performed. Except for this, in the same manner as in Production Example 1A, the polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet rays to form a liquid crystal layer on the substrate film.

[Production example 1L (comparative example)]

In the same manner as in Production Example 1A, the back side of the substrate film was cleaned while using isopropyl alcohol as a cleaning liquid while contacting the gravure roll. After that, the liquid crystal material solution is not applied, and the substrate film is temporarily wound up (offline cleaning). The rolled substrate film is set again in the film-forming device, and neither the back surface of the substrate film nor the film-forming surface is cleaned, and the polymerizable liquid crystal material solution is applied, dried, cooled, and UV Irradiation forms a liquid crystal layer on the substrate film.

[Production Example 1M (Comparative Example)]

In the above-mentioned Production Example 1L, a wire rod roller was used instead of the gravure roller, and the back surface side of the base film was cleaned off-line, and then the base film was temporarily wound. The rolled substrate film is set in the film forming device again, and neither the back surface of the substrate film nor the film-forming surface is cleaned, and the polymerizable liquid crystal material solution is applied, dried, cooled, and irradiated with ultraviolet rays. Forming a liquid crystal layer on the substrate film.

〔Evaluation〕

In a dark room, the optical film obtained in the above Production Examples 1A to 1M was irradiated with white light from the liquid crystal layer side in a state where a liquid crystal layer was laminated on the base film, and it was visually confirmed that the reflected light generated by the film thickness change Presence or absence of circular interference fringes. Count the number of areas where ring-shaped interference fringes occurred in the 1m ² area, and set it as a point-like unevenness. Table 1 shows the cleaning conditions of substrates in Production Examples 1A to 1M and a list of spot-like unevenness.

In Production Examples 1F and 1G, the cleaning of the film-forming surface of the substrate was performed. Compared with Production Example 1E without cleaning, no clear change in the spot-like unevenness was found. In addition, in Production Example 1H of Cleaning the Support Roller and Production Example 1J of Cleaning the Film-Formed Surface with an Adhesive Roller, No Spot Unevenness was Found The number clearly changes.

On the other hand, in Production Examples 1A to 1D and Production Examples 1I and 1K where the back surface was cleaned online, the spot-like unevenness was significantly reduced. On the other hand, in Production Examples 1L and 1M in which the back surface was cleaned off-line, no definite change in dot-like unevenness was found. From these results, it can be seen that by cleaning the back surface of the substrate online, the spot unevenness is greatly reduced.

In the manufacturing examples 1I and 1K, the back surface of the substrate was cleaned by contact with the adhesive roller, and the number of dot irregularities was 7 and 6 per 1 m ² . When the dot unevenness is 6 cases per 1m ² , if the optical film is used for an image display device with a screen size of 5 inches (approximately 140 pieces per 1m ² ), the defect rate is equivalent to about 4 %. However, when the screen size is 11 inches, the defect rate is about 20%. If the screen size is 20 inches or more, the defect rate rises to approximately 100%. Therefore, when an optical film is used to form a large-scale image display device, it can be seen that the defect rate caused by dot unevenness is high during cleaning of the adhesive roller, and it is extremely difficult to obtain a good optical film.

In contrast, as shown in Production Examples 1A to 1D, it can be seen that by contacting the roller with the substrate through the cleaning liquid and performing wet cleaning on the back surface of the substrate, almost no spot unevenness can be obtained, which can also be preferably used for High-quality optical film formed by large image display devices.

[Preparation Example 2: Fabrication of Positive A Plate on Friction Substrate]

In Production Examples 2A to 2M, as the base film, a triethyl cellulose film having a thickness of 40 μm subjected to a rubbing treatment on the surface was used, and the following coating solution was applied to the base film to prepare a layer including a nematic liquid crystal The optical film of the positive A plate.

<Preparation of Liquid Coating Material Liquid>

Liquid crystal monomer (trade name "Paliocolor LC242" manufactured by BASF) which shows a nematic liquid crystal phase: 100 parts by weight and a photopolymerization initiator (trade name "Irgacure 907" manufactured by BASF): 3 parts by weight dissolved in toluene 400 parts by weight to prepare a polymerizable liquid crystal material solution.

<Friction treatment of base material>

The triethylammonium cellulose film having a thickness of 40 μm subjected to saponification treatment was subjected to a rubbing treatment by the method described in Example 1-1 of Japanese Patent Laid-Open No. 2006-235611. The rubbing angle is 24.3 ° with respect to the transport direction of the base film. The substrate after the rubbing treatment is washed with water and dried, and then temporarily wound into a roll shape.

[Production Examples 2A to 2D (Examples)]

The wound body of the substrate film subjected to the rubbing treatment was set in the extraction portion of the film forming apparatus, and the substrate film was moved while being extracted, and the substrate was cleaned in the same manner as in Production Examples 1A to 1D. On the film-forming surface of the cleaned substrate, the polymerizable liquid crystal material solution was coated to a dry film thickness of 1 μm, dried at 90 ° C for 2 minutes, and cooled to room temperature, and then irradiated with ultraviolet rays as a cumulative light meter. 300mJ / cm ² to harden the liquid crystal monomer and fix the alignment of liquid crystal molecules. The obtained liquid crystal layer is wound up as a laminated body with a base film.

[Production example 2E ~ 2M (comparative example)]

The method for cleaning the substrate subjected to the rubbing treatment was changed to the same method as in Production Examples 1E to 1M. Otherwise, in the same manner as in Production Examples 2A to 2D, the polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet rays to form a liquid crystal layer on the base film.

〔Evaluation〕

By the same evaluation method as in Production Example 1, the number of dot unevenness of the optical films obtained in Production Examples 2A to 2M was evaluated. The evaluation results are shown in Table 2.

In Production Examples 2E to 2M, as compared with Production Examples 1E to 1M, it was found that the number of spot-like unevenness tended to increase. It is presumed that the foreign matter (such as friction dross) generated during the rubbing treatment adhered to the surface of the substrate. On the other hand, in Production Examples 2A to 2D in which the back surface was cleaned online, spot-like unevenness was not observed in the same manner as in Production Examples 1A to 1D.

From these results, it can be seen that, regardless of the presence or absence of friction treatment of the substrate or the type of liquid crystal material, according to the method of the present invention, by cleaning the back surface of the substrate online, high-quality optics with almost no spot unevenness can be obtained. membrane.

Claims (4)

An optical film manufacturing method, which is a method for manufacturing an optical film, and includes: winding a body from a flexible substrate, unwinding a long substrate having a first main surface and a second main surface, and downstream Extraction step of continuous side transport; cleaning step of cleaning the second main surface of the substrate; and film forming step of coating a liquid crystal material on the first main surface of the substrate; in the cleaning step, the substrate is A cleaning liquid is supplied between the second main surface and the cleaning roller, and the cleaning liquid is coated and spread on the substrate by the cleaning roller, thereby cleaning the substrate. The method for manufacturing an optical film according to claim 1, wherein the cleaning roller has a concave-convex pattern on a surface, and convex portions of the concave-convex pattern extend non-parallel to a circumferential direction of the roller. The method for manufacturing an optical film according to claim 2, wherein the cleaning roller is a gravure roller or a wire rod roller. The method for manufacturing an optical film according to any one of claims 1 to 3, wherein the cleaning liquid is a liquid having a boiling point lower than that of water.