CN114791645A - Method for manufacturing optical film - Google Patents
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- CN114791645A CN114791645A CN202210561136.4A CN202210561136A CN114791645A CN 114791645 A CN114791645 A CN 114791645A CN 202210561136 A CN202210561136 A CN 202210561136A CN 114791645 A CN114791645 A CN 114791645A
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
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- G02B5/3016—Polarising elements involving passive liquid crystal elements
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Abstract
The invention aims to manufacture an optical film with less defects caused by local film thickness change. In the method for manufacturing the optical film, a long substrate (1) having a film-forming surface (11) and a back surface (12) is unwound from a roll (2) of a flexible substrate, continuously transported to the downstream side, the back surface (12) of the substrate (1) is cleaned, and then a liquid crystal material is applied to the film-forming surface (11) of the substrate (1). A cleaning liquid is supplied between the back surface of the substrate and a 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
The present application is a divisional application filed by the applicant under the name of "method for manufacturing optical film" with application number 201610076537.5. The application date of the parent application is 2016, 2 and 3, and the priority date is 2015, 2 and 16.
Technical Field
The present invention relates to a method for manufacturing an optical film using a liquid crystal material.
Background
Since the liquid crystal material has a larger optical anisotropy than a general resin material, when it is used for an optical film such as a retardation film or a polarizing plate, the thickness of the film can be reduced, and it is advantageous for reduction in thickness and weight of a device. A liquid crystal optical film is manufactured by applying a liquid crystal material (liquid crystal monomer and/or liquid crystal polymer) on a film substrate, and performing polymerization of the liquid crystal monomer, alignment treatment of the liquid crystal material, solvent removal (drying), and the like as necessary to form a liquid crystal layer.
The following problems are found in the manufacture of optical films: foreign matters and the like adhering to the substrate are mixed into the interface between the coating layer and the substrate and the coating layer, and become optical defects. In addition, there is a problem in the production of an optical film using a liquid crystal material that: if foreign matter is present on the substrate, alignment defects and protrusion defects occur in the liquid crystal applied thereon.
Therefore, a method of cleaning the coated surface of the substrate to remove foreign matter and then coating the liquid crystal material has been proposed. As a method for removing foreign matter adhering to a substrate, there are known: a method using ultrasonic air (for example, patent document 1), a method of blowing a cleaning gas (for example, patent document 2), a method of washing a substrate with water (for example, patent document 3), a method of contacting a bonding roll (for example, patent document 4), and the like.
In the case of using a base material subjected to a rubbing treatment for aligning liquid crystal molecules in a predetermined direction, since a large amount of foreign matter adheres to the surface of the base material, a cleaning treatment is performed before the liquid crystal material is coated to remove the adhering foreign matter. Since the surface of the substrate subjected to the alignment treatment such as rubbing cannot be scrubbed, a non-contact cleaning method is generally used. For example, patent document 5 discloses a method of removing adhering foreign matter by irradiating the surface of a substrate subjected to an alignment treatment with ultraviolet rays.
Documents of the prior art
Patent document
Patent document 1: japanese laid-open patent publication No. 10-309553
Patent document 2: japanese patent laid-open publication No. 2009-66982
Patent document 3: japanese laid-open patent publication No. 2007-105662
Patent document 4: japanese laid-open patent publication No. 9-304621
Patent document 5: japanese patent laid-open publication No. 2003-4948
Disclosure of Invention
Problems to be solved by the invention
In an optical film such as a liquid crystal optical film in which the thickness of a coating layer formed on a substrate is small, a defect such as point-like interference unevenness (hereinafter, referred to as "point-like unevenness") may occur. According to the study of the present inventors, various defects derived from 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 liquid crystal layer formation surface), but the number of point-like unevenness hardly changes.
Further studies were carried out, with the results: in a portion where the spot unevenness occurs, the film thickness of the film is locally reduced, and may be periodically reflected in the conveyance direction (MD) of the substrate, and is estimated to be influenced by the foreign matter adhering to the coating roller. Therefore, the present inventors have attempted to reduce the spot unevenness by cleaning the roller surface by bringing a blade (doctor blade) for removing foreign matter into contact with the coating roller when the liquid crystal material is coated on the substrate. However, in the method of cleaning the roller surface, the effect of reducing the point unevenness cannot be clearly confirmed.
In view of the above, the present invention aims to: in the production of an optical film having a liquid crystal layer formed on a substrate, the occurrence of "point-like unevenness" defects in which the local film thickness is reduced, and a high-quality optical film is obtained.
Means for solving the problems
As a result of research in view of the above circumstances, it was found that: during the period from the time when the substrate is pulled out until the liquid crystal material is applied, the film formation surface and the opposite surface (back surface) of the substrate are cleaned in-line, thereby reducing the dot unevenness. As a result of further studies, it was found that the back surface of the substrate was brought into contact with the roller by a cleaning liquid and wet cleaning was performed, thereby significantly reducing the point unevenness, and the present invention was completed.
The present invention relates to a method for manufacturing an optical film using a liquid crystal material. In the method for producing an optical film of the present invention, a long substrate is unwound from a roll of a flexible substrate and continuously transported to the downstream side (a drawing-out step). 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 then the liquid crystal material is applied to 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 preferably has a concave-convex pattern on the surface, and among these, a cleaning roller in which the convex portions of the concave-convex pattern extend in a non-parallel manner in the circumferential direction of the roller is preferably used. Consider that: as described above, in the present invention, the cleaning roller is brought into contact with the back surface of the substrate through the cleaning liquid to perform wet cleaning, whereby foreign matter adhering to the back surface of the substrate is removed, and the point unevenness is reduced.
Examples of the cleaning roller used in the present invention include a gravure roll, a wire bar roll, and the like. In addition, as the cleaning liquid, a highly volatile liquid having a boiling point lower than that of water is preferably used.
Effects of the invention
According to the manufacturing method of the present invention, a high-quality optical film in which the occurrence of "point-like unevenness" defects that locally decrease in film thickness is suppressed can be obtained.
Drawings
Fig. 1 is a schematic view showing an embodiment of an optical film forming apparatus.
Fig. 2 is a schematic plan view for explaining the surface shape of the gravure roll.
Fig. 3A is a schematic plan view for explaining the surface shape of the bar roller.
Figure 3B is a cross-sectional view of the bar roll of figure 3A taken along line B1-B2.
Detailed Description
Fig. 1 is a schematic view showing one embodiment of a film forming apparatus used for manufacturing an optical film of the present invention. In the film forming apparatus 100 shown in fig. 1, a long roll 2 of a substrate is provided in a take-out section 10. The substrate 1 unwound from the roll 2 is continuously conveyed from the unwinding section 10 to the downstream side of the film deposition apparatus, passes through the guide rollers 51 and 52, and is conveyed to the cleaning section 40 provided on the downstream side of the guide roller 52 (unwinding step). The cleaning unit 40 cleans the back surface of the substrate 1 (cleaning step). The cleaned substrate 1 is further conveyed downstream, passed through a guide roller 54, and conveyed to a film forming section 60, where the liquid crystal material is applied to the substrate (film forming step).
[ base Material ]
The substrate 1 may be flexible, and a substrate 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 the present specification, the first main surface is referred to as a "film-forming surface", and the second main surface, which is the surface opposite thereto, is referred to as a "back surface".
As the substrate, for example, a resin film, a metal foil, paper, cloth, a laminate thereof, or the like is used. Among them, a resin film is preferably used because of excellent surface smoothness and less generation of foreign substances from the substrate itself.
Examples of the resin material constituting the base film include polyesters such as polyethylene terephthalate and polyethylene naphthalate; cellulose polymers such as diacetylcellulose and triacetylcellulose; acrylic polymers such as polymethyl methacrylate; styrene polymers such as polystyrene and acrylonitrile-styrene copolymer; polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymers; cyclic polyolefins such as polynorbornene; amide polymers such as nylon and aromatic polyamide; a polycarbonate; vinyl chloride; an imide polymer; a sulfone-based polymer; polyether sulfone; polyether ether ketone; polyphenylene sulfide; a vinyl alcohol polymer; vinyl chloride; epoxy polymers, and the like. Among them, 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 may be colored or opaque. When a laminate of a substrate and a liquid crystal layer is practically used as an optical film after the liquid crystal layer is formed on the substrate, the substrate is preferably transparent and has uniform optical properties.
The thickness of the base material is not particularly limited as long as it has both self-supporting and flexibility. The thickness of the substrate is generally about 20 μm to 200. mu.m, preferably 30 μm to 150. mu.m, more preferably 35 μm to 100. mu.m. When a liquid crystal layer is formed on a flexible substrate such as a film, the length of the substrate is limited, and therefore the length of the substrate that can be continuously formed is limited. In general, the upper limits of the weight and diameter of the roll to be set on the stand are determined for the extraction section 10 and the winding section (not shown) after film formation. Therefore, when the thickness of the substrate is small, the continuous film formation length can be increased, and productivity can be improved. Therefore, the thickness of the base material is preferably as small as possible within a range that does not impair film forming properties and handling properties.
On the other hand, according to the study of the present inventors, when the thickness of the substrate is small, the number of occurrences of the point-like unevenness tends to increase in the optical film in which the liquid crystal layer is formed on the substrate. In contrast, as will be described in detail later, in the present invention, the occurrence of dot-like unevenness can be suppressed even when the thickness of the base material is small by cleaning the back surface of the base material by a predetermined method before the application of the liquid crystal material.
In order to align the liquid crystal molecules in a predetermined direction, an alignment substrate may be used. Examples of the alignment base material include a stretched polymer film, a film having a surface subjected to a rubbing treatment, and a film having a surface provided with a rubbing alignment film. As the alignment film, a polyvinyl alcohol film, a polyimide film, a polysiloxane film, a glass polymer film, or the like can be used. The rubbing treatment is performed by rubbing the base material with a rubbing roll wound with a rubbing cloth made of fine fibers such as rayon and cotton. By adjusting the arrangement angle of the rubbing rollers, the conveyance direction of the base material and the rubbing direction are maintained at a predetermined angle, and thus optical films having various optical axes (alignment directions of liquid crystal molecules) can be produced.
When the rubbing treatment substrate is used, the roll of the substrate after the rubbing treatment may be set in the extracting section 10 of the film forming apparatus 100, or the substrate may be rubbed after the unprocessed substrate is extracted from the extracting section 10. From the viewpoint of preventing contamination of the liquid crystal layer with foreign substances and preventing contamination of the process, it is preferable that the roll of the base material after the rubbing treatment is disposed in the take-out section of the film forming apparatus and then reused. When the rubbing treatment of the base material is performed after the unprocessed base material is extracted from the extraction portion, the rubbing treatment is performed after the extraction of the base material and before the cleaning treatment.
Further, the surface of the base film may be subjected to treatment such as easy adhesion treatment, release treatment, antistatic treatment, and anti-blocking treatment. For the purpose of preventing blocking or the like, the widthwise ends of the base material may be subjected to knurling (knurling) or 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 "liquid crystal compound") may be those exhibiting thermotropic liquid crystallinity or those exhibiting lyotropic liquid crystallinity.
As the liquid crystal monomer, a liquid crystal compound exhibiting alignment properties such as nematic properties and smectic properties and having at least 1 unsaturated double bond such as an acryloyl group, a methacryloyl group and a vinyl group at the end, and a polymerizable functional group such as an epoxy group can be used. The liquid crystal material containing a liquid crystal monomer may contain a polymerization initiator in addition to the liquid crystal monomer. Examples of the method of polymerizing the polymerizable liquid crystal monomer include thermal polymerization and ultraviolet polymerization, and an appropriate polymerization initiator can be used according to the polymerization method.
As the liquid crystal polymer, a main chain type liquid crystal polymer or a side chain type liquid crystal polymer, or a composite type liquid crystal compound thereof, which exhibits liquid crystal alignment such as nematic or smectic, can be used. The molecular weight of the liquid crystal polymer is not particularly limited, and a liquid crystal polymer having a weight average molecular weight of about 2000 to 100000 is preferable.
The liquid crystal material may be aligned with cholesterol by including a chiral agent in the nematic liquid crystal material or introducing a chiral component into the structure of the liquid crystal polymer. The kind and amount of the chiral agent to be added can be appropriately determined according to the set values of the selective reflection wavelength, the helical pitch, and the like of the cholesteric liquid crystal.
When coating a liquid crystal material on a substrate, a solution of a liquid crystal compound is generally used. The solvent for dissolving the liquid crystal material may be appropriately determined depending on the type of the liquid crystal material and the type of the base material. Specific examples of the solvent include: halogenated hydrocarbons such as chloroform, dichloromethane, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, and the like; phenols such as phenol and p-chlorophenol; aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene and 1, 2-dimethoxybenzene; acetone, ethyl acetate, t-butanol, glycerol, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, ethyl cellosolve, butyl cellosolve, 2-pyrrolidone, N-methyl-2-pyrrolidone, pyridine, triethylamine, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetonitrile, butyronitrile, carbon disulfide, and the like. Two or more solvents may be used in combination.
The liquid crystal material solution may contain additives such as a coloring matter, a leveling agent, a plasticizer, an ultraviolet absorber, and a deterioration preventing agent, in addition to the polymerization initiator, the chiral agent, and the like, as necessary. The solid content, viscosity, and the like of the liquid crystal material solution can be appropriately set according to the type, molecular weight, thickness of the liquid crystal layer, film forming method, and the like of the liquid crystal material.
[ cleaning part ]
In the transport path of the substrate 1, a cleaning unit 40 is provided between the delivery unit 10 and the film forming unit 60. In the cleaning section 40, wet cleaning is performed while the back surface 12 of the substrate 1 is brought into contact with the cleaning roller 41 through the cleaning liquid. In the present invention, it is assumed that: 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, a shearing force is applied to the interface between the cleaning liquid and the substrate, whereby foreign matter and the like adhering to the substrate can be effectively cleaned and removed, and unevenness in a point shape can be suppressed.
In the embodiment shown in fig. 1, the cleaning unit 40 includes a support roller 42 provided to be in contact with the film formation surface 11 of the substrate 1, and a cleaning roller 41 provided to be in contact with the back surface 12 of the substrate 1. A cleaning liquid 47 is stored in the cleaning tray 48, and the remaining portion of the cleaning liquid adhering to the surface of the cleaning roller 41 is scraped off by the blade 44, and the cleaning liquid is guided to the back surface 12 of the substrate 1.
< cleaning roller >
As the cleaning roller 41, various rollers used for solution application, such as a knife roller (comma roller), a lick roller (キスロ - ル), a gravure roller, and a wire bar roller, are used. The cleaning roller may be a rotating roller or a non-rotating roller. When the cleaning roller is a rotating roller, the rotation direction may be either normal rotation or reverse rotation.
In view of improving the cleaning efficiency of the substrate, it is preferable that the surface of the cleaning roller has irregularities. The uneven pattern on the surface of the cleaning roller preferably has projections extending in a direction not parallel to the circumferential direction of the roller. The convex portions extending in nonparallel relation to the circumferential direction of the cleaning roller 41 contact the back surface of the base material, whereby foreign matter and the like adhering to the base material can be more effectively cleaned and removed, and the unevenness of dots tends to be suppressed.
Examples of the roller having the convex portion extending in a direction nonparallel to the circumferential direction include a gravure roller, a wire bar roller, and an embossing roller. Since the cleaning liquid is spread on the back surface of the substrate without damaging the substrate, a gravure roll and a wire bar roll are particularly preferably used as the cleaning roll.
Fig. 2 is a plan view showing an example of the shape of the uneven pattern on the surface of the gravure roll. The surface of the gravure roll 140 is formed with concave portions (gravure grooves) 141 and convex portions 142 in a pattern. Consider that: when a gravure roll is used as a cleaning roll, the liquid stored in the concave portions is brought into contact with the surface of the substrate, and foreign matter adhering to the surface of the substrate is scraped off by the contact with the convex portions, thereby removing the foreign matter. In fig. 2, a pattern shape of a quadrangle (Square type) is illustrated as the shape of the depressed pattern, but the shape of the depressed pattern is not particularly limited if the convex portions extend in the oblique direction, and may be, for example, a polygonal shape such as a triangle or a honeycomb, an oblique line shape, a linear shape such as a curved line shape, or the like.
Fig. 3A is a plan view showing an example of the shape of the uneven pattern on the surface of the bar roller 240, and fig. 3B is a cross-sectional view taken along line B1-B2. The wire bar roll is a roll in which a thin wire 242 such as a wire is spirally wound on the surface of a roll main body (cylinder) 241, and a convex portion extending in a direction nonparallel to the circumferential direction is formed by the thin wire 242. Consider that: when a wire bar roller is used as the cleaning roller, the liquid stored in the gap between the adjacent thin wires 242 comes into contact with the surface of the substrate, and the foreign matter adhering to the surface of the substrate is scraped off by the contact with the spirally wound thin wires 242, thereby removing the foreign matter. In fig. 3A and B, a form in which one thin wire 242 is wound around a cylinder is illustrated, but a wire rod may be wound around a plurality of thin wires. The thin wire 242 may be wound without a gap or may be wound at a constant interval. The interval between adjacent filaments is preferably about the same as or less than the width of the filament.
The height of the convex portion on the surface of the cleaning roller is not particularly limited, but is preferably in the range of about 0.1 to 10 μm as in the height of the convex portion of a typical gravure roll, wire bar roll or the like. If the height of the projection is too small, the cleaning effect may be insufficient. On the other hand, if the height of the projection is too large, the developing thickness of the cleaning liquid becomes large, and therefore, the cleaning efficiency may be lowered, or a long time may be required for drying the cleaning liquid, thereby lowering 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 cleaning solution is spread on the back surface of the substrate to clean the substrate. The cleaning liquid is liquid, and is not particularly limited as long as it does not dissolve the substrate 1, and water, an organic solvent, a mixture of water and an organic solvent, or the like can be used.
From the viewpoint of efficiently performing the on-line cleaning on the transport path from the extraction unit 10 to the film forming unit 60, it is preferable to use a liquid having a low boiling point and high volatility as the cleaning liquid. Examples of the highly volatile liquid include: alcohols such as methanol, ethanol, and isopropanol; ketones such as acetone and methyl ethyl ketone; halogenated alkanes such as chloroform, dichloromethane, dichloroethane and the like; ethers such as diethyl ether, ethyl propyl ether, and ethyl isopropyl ether. Further, a mixture of these organic solvents with water, or the like may also be used. In addition, a surfactant, a hydrophilic organic compound, or the like may be added to the cleaning liquid for the purpose of improving the cleaning power or the like. Examples of the hydrophilic organic compound include organic compounds having a hydroxyl group, an amino group, an amide group, an amine group, an amide 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, an SO group, and the like.
< cleaning method >
The cleaning method is not particularly limited as long as the cleaning liquid supplied between the cleaning roller 41 and the back surface 12 of the substrate 1 is spread on the substrate. The method of supplying the cleaning liquid between the cleaning roller and the substrate is not particularly limited. In fig. 1, a mode (direct gravure method) in which the cleaning roller 41 is brought into direct contact with the cleaning liquid 47 in the cleaning tray 48 is illustrated, but for example: a method (indirect gravure (offset) method) in which the cleaning liquid in the cleaning tray is brought into contact with another roll (flexographic roll) and the cleaning liquid adhering to the surface of the flexographic roll is moved to the cleaning roll arranged in contact with the flexographic roll, and the like. In addition to the method of adhering the cleaning liquid to the surface of the cleaning roller 41, the cleaning liquid may be supplied between the cleaning roller 41 and the back surface 12 of the substrate 1 by a method of applying the cleaning liquid to the back surface 12 of the substrate 1 by a slot die, spraying or the like, a method of moving the substrate in a cleaning tray, a method of adhering the cleaning liquid to the surface of the cleaning roller 41 by spraying or the like, before the substrate 1 is brought into contact with the cleaning roller 41.
Since the substrate 1 is conveyed to the downstream side (left side in fig. 1) while being in contact with the cleaning roller 41, the cleaning liquid supplied between the cleaning roller 41 and the substrate is inevitably spread on the surface of the substrate. The cleaning roller 41 may be in direct contact with the back surface 12 of the substrate 1, or may have a gap. The gap between the cleaning roller and the back surface of the substrate is preferably, for example, about 0.1 to 10 μm. If the gap is too large, the shearing force at the interface between the roller and the substrate when they are brought into contact with each other through the cleaning liquid becomes small, and the cleaning efficiency tends to decrease. When the cleaning roller has the uneven pattern on the surface, the clearance between the cleaning roller and the substrate can be adjusted to a desired range according to the height of the convex portion on the roller surface, as described above. When the cleaning roller does not have the uneven pattern on the surface, the gap can be adjusted according to the relative positional relationship between the cleaning roller and the substrate.
In fig. 1, the back surface 12 of the substrate 1 is shown in contact with the cleaning roller 41 in the cleaning section 40, and the deposition surface 11 is shown in contact with the backup roller 42, but if the substrate transport path is configured such that the back surface 12 of the substrate 1 is in contact with the cleaning roller 41 via the cleaning liquid, the backup roller in the cleaning section 40 is not necessarily required. In addition, the back surface 12 of the substrate 1 may be cleaned from the film formation surface 11 at the same time by using a roll having an uneven surface instead of the back roll 42.
The substrate 1 having the back surface 12 cleaned in the cleaning section 40 is conveyed to the film forming section 60 via the guide roller 54. When the substrate is conveyed from the cleaning section 40 to the film forming section 60, the cleaning liquid adhering 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, a method of passing the substrate through a heating oven, and the like.
[ film-forming part ]
In the film forming section 60, a liquid crystal material solution is applied to the film forming surface 11 of the substrate 1, and film formation is performed according to a conventional method. In fig. 1, a die coater using an extrusion die 61 is illustrated. In this coater, the liquid crystal material discharged from the lip of the die 61 is applied to the film-forming surface of the substrate while the back surface 12 of the substrate 1 is brought into contact with the backup roll 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 die and the conveying speed of the substrate.
The film forming method in the film forming section 60 is not limited to die coating, and various methods such as lick roll coating, gravure coating, reverse coating, spray coating, wire bar coating, air knife coating, and curtain coating can be used.
The characteristics of an optical film using a liquid crystal material are often dependent on the 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 plate are proportional to the thickness of the liquid crystal layer. Therefore, in order to make the properties of the optical film uniform, it is preferable to make the film thickness uniform during film formation. In order to make the film thickness uniform, as shown in fig. 1, it is preferable to perform film formation while supporting the back surface 12 of the substrate 1 with a support roller 62.
On the other hand, if a foreign matter is present between the backup roller 62 and the back surface 12 of the substrate 1, the film formation surface 11 of the substrate 1 is deformed into a convex shape by the pressing. Consider that: when the liquid crystal material is applied to the substrate, the thickness of the coating layer in the deformed portion of the substrate is locally reduced, and point-like unevenness occurs. In contrast, in the present invention, since the adhered foreign matter is removed by cleaning the back surface 12 of the substrate 1 on line, it is estimated that the occurrence of the point-like unevenness can be suppressed even when the film is formed while supporting the substrate with the support roller.
The thickness of the liquid crystal layer is set so that the film thickness after drying is, for example, about 0.1 to 20 μm in accordance with the characteristics of the target optical film. Generally, the smaller the thickness of the liquid crystal layer is, the more pronounced the occurrence of the dot-like unevenness tends to be. In contrast, in the present invention, by performing the above-described cleaning step, the occurrence of dot-like unevenness can be suppressed even when the film thickness of the liquid crystal layer after drying is 20 μm or less. Therefore, the production method of the present invention is suitable for producing a liquid crystal optical film having a coating layer with a small thickness.
[ order after coating ]
The coating film of the liquid crystal material applied to the film-forming surface 11 of the substrate 1 is conveyed into the drying furnace 20 together with the substrate 1, and the solvent is removed to form a film. In addition to drying, alignment treatment of liquid crystal molecules, polymerization of liquid crystal monomers, and the like may be performed. For example, in the case of using a liquid crystal monomer exhibiting thermotropic liquid crystallinity, the alignment state of the liquid crystal can be fixed by heating the monomer to a temperature range in which the monomer exhibits a liquid crystal phase or higher, drying the monomer, cooling the monomer to a temperature at which the monomer exhibits a liquid crystal phase, and polymerizing the monomer by irradiation with ultraviolet rays. In addition, the lyotropic liquid crystal may be aligned by applying a shearing force to align liquid crystal molecules in a predetermined orientation.
The substrate on which the liquid crystal layer is formed may be directly wound in a state where the substrate is in close contact with the liquid crystal layer. The liquid crystal layer formed over the substrate may be transferred to another film, or the substrate and the liquid crystal layer may be separated and then wound up. 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 wound in a state of being closely attached to the substrate can be used as an optical film in a practical manner integrally with the substrate. Further, the liquid crystal layer may be subjected to other steps such as stretching in a state of being closely attached to the substrate. Thereafter, the substrate and the liquid crystal layer may be used as an optical film integrally, or the liquid crystal layer peeled from the substrate may be used as an optical film, or the liquid crystal layer may be transferred to another film and then used as an optical film. Other coating layers and the like may be further coated on the liquid crystal layer.
The optical film of the present invention thus obtained has reduced point unevenness and fewer optical defects, and therefore can be used as an optical film for an image display device. Specific examples of the optical film for an image display device include an optical compensation film such as a retardation plate, a polarizing plate, and a polarizing plate protective film.
Examples
The present invention will be described in more detail below with reference to examples relating to the production of liquid crystal optical films, but the present invention is not limited to the following examples.
Production example 1: production of negative C plate Using cholesteric liquid Crystal Material
In production examples 1A to 1M, a polyester film (not subjected to rubbing treatment) having a thickness of 75 μ M was used as a base film, and the following coating liquids were applied to the base film to produce optical films each having a negative C plate (selective reflection wavelength: 200 to 220nm) formed of a cholesteric liquid crystal layer.
< preparation of coating liquid for liquid Crystal Material >
The following nematic liquid crystal monomers: 90 parts by weight,
[ CHEM 1 ]
A polymeric chiral agent of the formula: 10 parts by weight of,
[ CHEM 2 ]
And a UV polymerization initiator (trade name "Irgacure 907" manufactured by BASF Co.): 5 parts by weight of a solvent dissolved in methyl ethyl ketone: 300 parts by weight of the solution was prepared as a polymerizable liquid crystal material solution containing a chiral agent.
Production example 1A (example)
Winding of the substrate filmThe body is placed in a drawing section of a film forming apparatus, and while drawing and moving the substrate film, the back surface of the substrate is cleaned by bringing a gravure roll, which rotates in the direction opposite to the conveying direction of the substrate, into contact with the back surface side of the substrate film using isopropyl alcohol as a cleaning liquid. The above-mentioned polymerizable liquid crystal material solution was applied onto the film-forming surface of the cleaned substrate so that the film thickness after drying became 2 μm, dried at 70 ℃ for 3 minutes, cooled to room temperature, and made to 300mJ/cm 2 The accumulated light amount of (2) is irradiated with ultraviolet rays, whereby the liquid crystal monomer is assimilated to determine the orientation of the liquid crystal molecules. The obtained liquid crystal layer was wound up to form a laminate with a substrate film.
Production example 1B (example)
In preparation example 1A, cleaning was performed while contacting the gravure roll with isopropyl alcohol as a cleaning liquid on the film formation surface side, in addition to the back surface side of the base film. That is, in production example 1B, the gravure roll was cleaned while being brought into contact with both the back surface and the film formation surface of the base film. Thereafter, a liquid crystal layer was formed on the base film by applying a polymerizable liquid crystal material solution, drying, cooling, and irradiating with ultraviolet rays in the same manner as in production example 1A.
Production examples 1C and 1D (examples)
A wire bar roll was used instead of a gravure roll. Except for this, after cleaning in the same manner as in production examples 1A and 1B, a polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet rays, thereby forming a liquid crystal layer. That is, in production example 1C, cleaning was performed while the wire bar roller was brought into contact with the back surface of the base film, and in production example 1D, cleaning was performed while the wire bar roller was brought into contact with both surfaces of the base film.
Production example 1E (comparative example)
The back surface and the film-forming surface of the substrate film were not cleaned, and a liquid crystal layer was formed on the substrate film by applying a polymerizable liquid crystal material solution, drying, cooling, and irradiating with ultraviolet rays in the same manner as in production example 1A.
Production example 1F (comparative example)
In preparation example 1B, the back surface side of the substrate film was not cleaned, but the gravure roll was cleaned while being brought into contact with the film formation surface of the substrate film. Thereafter, a liquid crystal layer was formed on the base film by applying a polymerizable liquid crystal material solution, drying, cooling, and irradiating with ultraviolet rays in the same manner as in production example 1A.
Production example 1G (comparative example)
In production example 1D, the cleaning of the back surface side of the substrate film was not performed, and the cleaning was performed while the wire bar roller apparatus was in contact with the film formation surface of the substrate film. Thereafter, a polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet rays in the same manner as in production example 1A, thereby forming a liquid crystal layer on the substrate film.
Production example 1H (comparative example)
In the same manner as in production example 1E, the back surface and the film formation surface of the base film were not cleaned, and in the same manner as in production example 1A, the polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet light, thereby forming a liquid crystal layer on the base film. In preparation example 1H, a doctor blade was brought into contact with a backup roll in contact with the back surface of the base material at the time of coating the polymerizable liquid crystal material solution, and film formation was performed while constantly cleaning the backup roll.
Production example 1I (comparative example)
The guide roller that contacts the back surface of the substrate on the front surface of the film forming section in the vicinity of the film forming apparatus is changed to a bonding roller, and the back surface of the substrate is cleaned by the contact with the bonding roller. On the other hand, in production example 1I, cleaning using a cleaning roller was not performed. Except for this, a liquid crystal layer was formed on a substrate film by coating a polymerizable liquid crystal material solution, drying, cooling, and irradiating with ultraviolet light in the same manner as in preparation example 1A.
Production example 1J (comparative example)
The guide roller that contacts the film formation surface of the substrate immediately before the film formation section of the film formation apparatus is changed to a bonding roller, and the substrate film formation surface is cleaned by contact with the bonding roller. On the other hand, in production example 1J, cleaning using a cleaning roller was not performed. Except for this, a liquid crystal layer was formed on a substrate film by coating a polymerizable liquid crystal material solution, drying, cooling, and irradiating with ultraviolet light in the same manner as in preparation example 1A.
Production example 1K (comparative example)
The guide roller in contact with the back surface of the substrate and the guide roller in contact with the film forming surface in the front surface of the film forming section in the vicinity of the film forming apparatus are changed to bonding rollers, and the back surface and the film forming surface of the substrate are cleaned by the contact with the bonding rollers. On the other hand, in production example 1K, cleaning using a cleaning roller was not performed. Except for this, a liquid crystal layer was formed on a substrate film by coating a polymerizable liquid crystal material solution, drying, cooling, and irradiating with ultraviolet light in the same manner as in preparation example 1A.
Production example 1L (comparative example)
In the same manner as in preparation example 1A, the back surface side of the base material film was cleaned while contacting the gravure roll with isopropyl alcohol as a cleaning liquid. Thereafter, the substrate film was wound up (off-line cleaning) once without applying the liquid crystal material solution. The wound substrate film is again placed in the film forming apparatus, and the liquid crystal layer is formed on the substrate film by coating, drying, cooling, and ultraviolet irradiation of the polymerizable liquid crystal material solution, without cleaning the back surface and film forming surface of the substrate film.
Production example 1M (comparative example)
In production example 1L, a wire bar roll was used instead of the gravure roll, and the back surface side of the substrate film was cleaned off-line and then once wound. The wound substrate film is again placed in the film forming apparatus, and the liquid crystal layer is formed on the substrate film by coating, drying, cooling, and ultraviolet irradiation of the polymerizable liquid crystal material solution, without cleaning both the back surface and the film forming surface of the substrate film.
[ evaluation ]
In a dark room, white light was irradiated from the liquid crystal layer side in a state where the liquid crystal layer was laminated on the base film to the optical films obtained in production examples 1A to 1M, and the presence or absence of a portion where an annular interference fringe was generated in the reflected light due to a change in film thickness was visually confirmed. Counted out at 1m 2 The number of portions in the region (2) where the annular interference fringes occur is defined as a point-like unevenness. Table 1 lists the cleaning conditions and the number of uneven spots of the base materials in production examples 1A to 1M.
[ TABLE 1 ]
In production examples 1F and 1G, the film formation surface of the substrate was cleaned, but no clear change in the number of point-like irregularities was observed as compared with production example 1E in which cleaning was not performed. In addition, even in production example 1H in which the backup roll was cleaned and production example 1J in which the film formation surface was cleaned with a pressure sensitive adhesive roll, no clear change in the number of spot irregularities was observed.
On the other hand, in production examples 1A to 1D and production examples 1I and 1K in which back surface cleaning was performed on line, the number of point-like unevenness was greatly reduced. On the other hand, in production examples 1L and 1M in which the back surface was cleaned off-line, no clear change in the number of point-like irregularities was observed. From these results, it can be seen that: by cleaning the back surface of the substrate on-line, the point unevenness is greatly reduced.
Preparation examples 1I and 1K in which cleaning of the back surface of the base material was performed by contact with the pressure roller 2 The number of point-like irregularities of (a) is 7 and 6, respectively. At each 1m 2 If there is a defect due to dot unevenness at 6 positions, the screen size of the image display device is 5 inches (per 1 m) 2 About 140 sheets), which corresponds to a defect rate of about 4%. However, the defect rate was about 20% when the screen size was 11 inches, and increased to about 100% when the screen size was 20 inches or more. Therefore, it can be seen that: when an optical film is used to form a large-sized image display device, the defect rate due to point-like unevenness is high when the optical film is cleaned with a pressure-sensitive adhesive roller, and it is extremely difficult to obtain a high-quality optical film sheet.
In contrast, it is known that: as in production examples 1A to 1D, the roller was brought into contact with the substrate through the cleaning liquid to perform wet cleaning of the back surface of the substrate, whereby a high-quality optical film which is almost free from spot unevenness and can be suitably used for forming a large-sized image display device was obtained.
Production example 2: production of Positive A sheet on Friction base Material
In production examples 2A to 2M, a triacetyl cellulose film having a thickness of 40 μ M, the surface of which was subjected to rubbing treatment, was used as a base film, and the following coating liquids were applied to the base film to produce an optical film including a positive A plate formed of a nematic liquid crystal layer.
< preparation of coating liquid for liquid Crystal Material >
A liquid crystal monomer exhibiting a nematic liquid crystal phase (trade name "Paliocolor LC 242", manufactured by BASF Co., Ltd.): 100 parts by weight of a photopolymerization initiator (trade name "Irgacure 907", manufactured by BASF Co.): 3 parts by weight of the resulting polymer was dissolved in 400 parts by weight of toluene to prepare a polymerizable liquid crystal material solution.
< rubbing treatment of substrate >
A triacetyl cellulose film having a thickness of 40 μm and subjected to a saponification treatment was subjected to a rubbing treatment by the method described in example 1-1 of Japanese unexamined patent publication No. 2006-235611. The rubbing angle was inclined by 24.3 ° with respect to the conveyance direction of the base material film. The base material after the rubbing treatment was washed with water and dried, and then wound into a roll shape.
Production examples 2A to 2D (examples)
The roll of the base material film subjected to the rubbing treatment was set in a drawing section of the film forming apparatus, and the base material was cleaned in the same manner as in production examples 1A to 1D while drawing the base material film and moving it. The above-mentioned polymerizable liquid crystal material solution was applied to the film forming surface of the cleaned substrate so that the film thickness after drying became 1 μm, dried at 90 ℃ for 2 minutes, cooled to room temperature, and controlled at 300mJ/cm 2 The accumulated light quantity of (2) is irradiated with ultraviolet rays, thereby curing the liquid crystal monomer and fixing the orientation of the liquid crystal molecules. The obtained liquid crystal layer was wound up to form a laminate with a substrate film.
Production examples 2E to 2M (comparative examples)
The method for cleaning the base material subjected to the rubbing treatment was changed to the same method as in production examples 1E to 1M. Except for this, a liquid crystal layer was formed on the base film by applying a polymerizable liquid crystal material solution, drying, cooling, and irradiating with ultraviolet light in the same manner as in production examples 2A to 2D.
[ evaluation ]
The number of point-like unevenness in the optical films obtained in production examples 2A to 2M was evaluated by the same evaluation method as in production example 1. The evaluation results are shown in table 2.
[ TABLE 2 ]
In production examples 2E to 2M, the number of point-like unevenness tends to be larger than in production examples 1E to 1M. The reason for this is assumed to be that foreign matters (friction slag and the like) generated during the rubbing treatment adhere to the surface of the base material. On the other hand, in production examples 2A to 2D in which back surface cleaning was carried out on line, as in production examples 1A to 1D, no dot-like unevenness was observed.
From these results, it can be seen that: by cleaning the back surface of the substrate on-line by the method of the present invention, an optical film having high quality and almost no spot unevenness can be obtained regardless of the presence or absence of rubbing treatment of the substrate and the type of liquid crystal material.
Description of the symbols
1: substrate material
11: film surface (first main surface)
12: back face (second main face)
2: wound body
10: extraction part
20: drying furnace
40: cleaning part
41: cleaning roller
42: back-up roll
44: doctor blade
47: cleaning disc
48: cleaning liquid
51. 52, 54: guide roller
60: film forming part
61: die head
62: support roller
140: gravure roller
141: concave part
142: convex part
240: wire rod roller
241: cylinder
242: thin lines (protrusions).
Claims (5)
1. A method for manufacturing an optical film, comprising:
a drawing-out step of unwinding a long substrate having a first main surface and a second main surface from a roll of the flexible substrate and continuously conveying the substrate to a downstream side;
a cleaning step of cleaning only the second main surface of the substrate; and
a film forming step of applying a liquid crystal material to the first main surface of the substrate,
in the cleaning step, a cleaning liquid is applied to the surface of the cleaning roller, the cleaning liquid is supplied between the second main surface of the substrate and the cleaning roller, and the cleaning liquid is spread on the second main surface of the substrate by the cleaning roller to clean the second main surface of the substrate,
the cleaning roller is a gravure roller or a wire bar roller having a concavo-convex pattern on the surface, and the convex portions of the concavo-convex pattern extend in a non-parallel manner in the circumferential direction of the roller,
the optical film comprises a liquid crystal layer, and the thickness of the liquid crystal layer is 0.1-20 μm.
2. The method for manufacturing an optical film according to claim 1,
in the film forming step, the liquid crystal material is applied to the first main surface of the substrate while supporting the second main surface of the substrate by the first support roller.
3. The method for manufacturing an optical film according to claim 1 or 2,
in the cleaning step, the cleaning liquid in the cleaning disk is made to adhere to the surface of the cleaning roller, and the cleaning liquid is supplied between the second main surface of the substrate and the cleaning roller.
4. The method for manufacturing an optical film according to claim 1 or 2,
in the cleaning step, the cleaning liquid is applied and spread on the second main surface of the substrate while supporting the first main surface of the substrate by a second support roller.
5. The method for manufacturing an optical film according to claim 1 or 2,
the cleaning liquid is a liquid having a boiling point lower than that of water.
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| JP2015028071A JP6482891B2 (en) | 2015-02-16 | 2015-02-16 | Manufacturing method of optical film |
| JP2015-028071 | 2015-02-16 | ||
| CN201610076537.5A CN105891929A (en) | 2015-02-16 | 2016-02-03 | Method for manufacturing optical film |
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| CN201610076537.5A Division CN105891929A (en) | 2015-02-16 | 2016-02-03 | Method for manufacturing optical film |
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| JP6875964B2 (en) * | 2016-09-07 | 2021-05-26 | 東山フイルム株式会社 | Manufacturing method of long hard coat film for transparent conductive film |
| CN106291785A (en) * | 2016-10-27 | 2017-01-04 | 宁波视睿迪光电有限公司 | Lens arra manufacture method and birefringent lens array |
| JP6859109B2 (en) * | 2017-01-18 | 2021-04-14 | 日東電工株式会社 | Polarizing plate with optical compensation layer and organic EL panel using it |
| CN110691998B (en) * | 2017-06-13 | 2021-11-16 | 富士胶片株式会社 | Method for producing liquid crystal film and method for producing functional film |
| JP6962210B2 (en) * | 2018-01-19 | 2021-11-05 | 株式会社リコー | Device that discharges liquid |
| JP2020166059A (en) * | 2019-03-28 | 2020-10-08 | 日本ゼオン株式会社 | Manufacturing method for liquid crystal hardening film |
| JP7292130B2 (en) | 2019-06-28 | 2023-06-16 | 日東電工株式会社 | Polarizer manufacturing method and polarizer manufacturing apparatus |
| JPWO2021033639A1 (en) | 2019-08-16 | 2021-02-25 |
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| JPH09304621A (en) * | 1996-05-17 | 1997-11-28 | Kanegafuchi Chem Ind Co Ltd | Production of phase difference film |
| JP3158074B2 (en) | 1997-05-09 | 2001-04-23 | 株式会社伸興 | Dust removal device |
| JP3436655B2 (en) * | 1997-05-15 | 2003-08-11 | 出光興産株式会社 | Substrate cleaning method |
| US6812982B2 (en) * | 2000-05-12 | 2004-11-02 | Fuji Photo Film Co., Ltd. | Optical compensatory sheet producing method and apparatus, thermal treating method and apparatus, and dust removing method and apparatus |
| JP2003004948A (en) | 2001-06-25 | 2003-01-08 | Dainippon Printing Co Ltd | Method for manufacturing optical element |
| JP2005279577A (en) * | 2004-03-30 | 2005-10-13 | Shin Nisseki Ekisho Film Kk | Film purification method |
| CN1872546A (en) * | 2005-05-26 | 2006-12-06 | 日东电工株式会社 | Cleaning sheet and cleaning method for a screen printing plate |
| JP2007039524A (en) * | 2005-08-02 | 2007-02-15 | Fujifilm Corp | Alkali saponification method, cellulose acylate film, optical film, polarizing plate, and liquid crystal display device |
| JP2007105662A (en) | 2005-10-14 | 2007-04-26 | Nippon Paper Chemicals Co Ltd | Method and apparatus for washing optical plastic film, method for manufacturing optical plastic film and coating apparatus |
| JP2009066982A (en) | 2007-09-14 | 2009-04-02 | Fujifilm Corp | Solution film forming method and cleaning apparatus |
| CN102224287B (en) * | 2008-11-25 | 2013-03-27 | 3M创新有限公司 | Apparatus and method for cleaning flexible webs |
| SG183419A1 (en) * | 2010-02-22 | 2012-09-27 | Entegris Inc | Post-cmp cleaning brush |
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| JP2016150286A (en) | 2016-08-22 |
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| KR20160100834A (en) | 2016-08-24 |
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