KR102353400B1 - Method for manufacturing optical film - Google Patents

Abstract

(Project) An optical film with few defects in which the film thickness changed locally is manufactured.
(Solution) In the manufacturing method of the optical film of this invention, the elongate base material 1 provided with the film forming surface 11 and the back surface 12 is unwound from the wound body 2 of a flexible base material, and it continues to the downstream side. After it is conveyed and the back surface 12 of the base material 1 is wash|cleaned, the liquid crystal material is apply|coated on the film forming surface 11 of the base material 1 . The rear surface of the substrate is cleaned by supplying a cleaning liquid between the rear surface of the substrate and the cleaning roll 41, and spreading the cleaning liquid onto the substrate by the cleaning roll.

Description

The manufacturing method of an optical film {METHOD FOR MANUFACTURING OPTICAL FILM}

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

Since a liquid crystal material has large optical anisotropy compared with general resin material, when used for optical films, such as retardation film and a polarizer, a film thickness can be made small, and it is advantageous for thickness reduction and weight reduction of a device. A liquid crystal optical film is a liquid crystal optical film by applying a liquid crystal material (a liquid crystal monomer and/or a liquid crystal polymer) on a film substrate, and performing polymerization of a liquid crystal monomer, alignment treatment of the liquid crystal material, solvent removal (drying), etc. as necessary. It is prepared by forming a layer.

In the manufacture of an optical film, there is a problem that foreign substances or the like adhering to a base material flow into the interface between the coating layer and the base material or into the coating layer, thereby becoming an optical defect. Moreover, in manufacture of the optical film using liquid crystal material use, when a foreign material exists on a base material, it also becomes a problem that an orientation defect and a processus|protrusion defect generate|occur|produce in the liquid crystal apply|coated thereon.

Therefore, the method of apply|coating a liquid crystal material after washing|cleaning the application surface of a base material and removing a foreign material is proposed. As a method of removing foreign substances adhering to the substrate, a method using ultrasonic air (eg, Patent Document 1), a method of spraying a cleaning gas (eg, Patent Document 2), a method of washing the substrate with water (eg, Patent Document 1) Document 3), a method of contacting an adhesive roll (for example, Patent Document 4), and the like are known.

When a substrate subjected to rubbing treatment is used to align liquid crystal molecules in a predetermined direction, since many foreign substances are adhered to the surface of the substrate, a cleaning treatment is performed before application of the liquid crystal material for the purpose of removing the adhered foreign substances. . Since the surface of the base material which has been subjected to an orientation treatment such as rubbing cannot be cleaned by rubbing, a non-contact cleaning method is generally employed. For example, in patent document 5, the method of removing an adhering foreign material by irradiating an ultraviolet-ray to the surface of the base material to which orientation processing was performed is disclosed.

Japanese Patent Laid-Open No. 10-309553 Japanese Patent Laid-Open No. 2009-66982 Japanese Patent Laid-Open No. 2007-105662 Japanese Patent Laid-Open No. 9-304621 Japanese Laid-Open Patent Publication No. 2003-4948

In an optical film having a small film thickness of an application layer formed on a substrate, such as a liquid crystal optical film, defects such as dotted interference unevenness (hereinafter, sometimes referred to as "spot unevenness") may occur. According to the studies of the present inventors, various defects resulting 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 surface on which the liquid crystal layer is formed). No change was seen.

As a result of further examination, it was found that in the area where the spot unevenness occurred, the film thickness was locally reduced, and it appeared periodically in the conveyance direction (MD) of the substrate, and it was found that it was influenced by foreign substances adhering to the application roll. It was estimated. Then, the present inventors made the blade (scraper) for foreign material removal contact the application roll at the time of apply|coating a liquid crystal material on a base material, cleaned the roll surface, and tried reduction of spot unevenness. However, in the method of cleaning the roll surface, the effect of reducing spot unevenness could not be clearly confirmed.

In view of the above, in the method for manufacturing an optical film for forming a liquid crystal layer on a substrate, the present invention is to reduce the occurrence of "spot unevenness" defects in which the film thickness is locally reduced, thereby obtaining a high-quality optical film. The purpose.

As a result of examination in view of the above, it was found that spot unevenness was reduced by in-line cleaning of the surface (rear surface) opposite to the film forming surface of the substrate from feeding the substrate until application of the liquid crystal material. As a result of further examination, it was found that spot unevenness was significantly reduced by wet cleaning while contacting the back surface of the substrate with the roll through the cleaning solution, leading to the present invention.

The present invention relates to a method for producing an optical film using a liquid crystal material. In the manufacturing method of the optical film of this invention, the elongate base material is unwound from the winding body of a flexible base material, and it is conveyed continuously downstream (feeding process). The substrate has a first main surface that is a film forming surface, and a second main surface that is a rear surface of the film forming surface. In the manufacturing method of this invention, the 2nd main surface of a base material is wash|cleaned (cleaning process), and thereafter, a liquid crystal material is apply|coated on the 1st main surface of a base material (film forming process).

In the cleaning step, cleaning is performed by supplying a cleaning liquid between the back surface of the substrate and the cleaning roll, and spreading the cleaning liquid on the substrate by the cleaning roll. It is preferable that the cleaning roll has an uneven pattern on the surface, and among these, those in which the convex portions of the uneven pattern extend non-parallel to the circumferential direction of the roll are preferably used. As described above, in the present invention, it is considered that the wet cleaning is performed while the cleaning roll and the rear surface of the substrate are brought into contact with the cleaning liquid, thereby removing foreign substances adhering to the rear surface of the substrate, thereby reducing spot unevenness.

Examples of the cleaning roll used in the present invention include a gravure roll, a Meyer bar roll, and the like. Further, as the cleaning liquid, a highly volatile liquid having a lower boiling point than water is preferably used.

ADVANTAGE OF THE INVENTION According to the manufacturing method of this invention, the high-quality optical film in which generation|occurrence|production of the "spot unevenness|variety" defect which a film thickness becomes small locally is suppressed is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows one Embodiment of an optical film film forming apparatus.
It is a schematic plan view for demonstrating the surface shape of a gravure roll.
It is a schematic plan view for demonstrating the surface shape of a Meyer bar roll.
Fig. 3B is a cross-sectional view taken along line B1-B2 of the Meyer bar roll of Fig. 3A;

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows one Embodiment of the film forming apparatus used for manufacture of the optical film of this invention. In the film forming apparatus 100 shown in FIG. 1, the winding object 2 of the elongate base material is set in the drawing|feeding-out part 10. As shown in FIG. The base material 1 unwound from the winding body 2 is continuously conveyed from the feeding unit 10 to the downstream side of the film forming apparatus, and is formed on the downstream side of the guide roller 52 via guide rollers 51 and 52. It is returned to the government 40 (feeding process). The back surface of the base material 1 is cleaned by the washing|cleaning part 40 (washing process). The base material 1 after washing|cleaning is conveyed downstream again, it is conveyed to the film forming part 60 via the guide roller 54, and application|coating of the liquid crystal material on a base material is performed (film forming process).

[write]

The base material 1 should just have flexibility, and the thing excellent in mechanical strength, thermal stability, moisture shielding property, etc. is used preferably. 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, the 1st main surface is called "film forming surface", and the 2nd main surface which is the surface on the opposite side is called "back surface".

As a base material, a resin film, metal foil, paper, cloth, these laminated bodies, etc. are used, for example. Especially, since it is excellent in surface smoothness and there is little generation|occurrence|production of a foreign material from the base material itself, a resin film is used preferably.

As a resin material which comprises a base film, Polyester, such as a polyethylene terephthalate and a polyethylene naphthalate; Cellulose polymers, such as a diacetyl cellulose and a triacetyl cellulose; acrylic polymers such as polymethyl methacrylate; Styrenic polymers, such as polystyrene and an acrylonitrile-styrene copolymer; polyolefins such as polyethylene, polypropylene, and ethylene/propylene copolymer; Cyclic polyolefins, such as polynorbornene; amide-based polymers such as nylon and aromatic polyamide; polycarbonate; vinyl chloride; imide-based polymers; sulfone-based polymers; polyether sulfone; polyether ether ketone; polyphenylene sulfide; vinyl alcohol-based polymer; vinylidene chloride; Epoxy polymer etc. are mentioned. Among these, those that do not dissolve in the solvent at the time of application of the liquid crystal material are preferably used.

The base material may be colorless and transparent, and a colored or opaque thing may be sufficient as it. When the laminate of the substrate and the liquid crystal layer is put to practical use as an optical film after forming the liquid crystal layer on the substrate, the substrate is preferably used which is transparent and has uniform optical properties.

The thickness of the base material is not particularly limited as long as it has both self-support and flexibility. Generally, the thickness of a base material is about 20 micrometers - 200 micrometers, 30 micrometers - 150 micrometers are preferable, and 35 micrometers - 100 micrometers are more preferable. When the liquid crystal layer is formed on a flexible substrate such as a film, the length of the substrate is finite, so the length that can be continuously formed is limited. Generally, as for the drawing|feeding-out part 10 and the winding-up part (not shown) after film forming, the upper limit of the weight and diameter of the winding object set to the mount is determined. Therefore, when the thickness of a base material is small, the continuous film forming length can be enlarged and the improvement of productivity will be achieved. Therefore, it is preferable that the thickness of a base material is as small as possible in the range which does not impair film forming property or handling property.

On the other hand, according to the examination of the present inventors, when the thickness of the base material is small, in the optical film in which the liquid crystal layer is formed on the base material, the tendency for the number of occurrence of spot spots to increase was seen. On the other hand, as described in detail later, in the present invention, by cleaning the back surface of the substrate by a predetermined method before application of the liquid crystal material, the occurrence of spot spots is suppressed even when the thickness of the substrate is small.

In order to orientate a liquid crystal molecule in a predetermined direction, you may use an orientation base material. Examples of the orientation substrate include a stretched polymer film, a film having a surface subjected to a rubbing treatment, a film having a rubbing orientation film on the surface, and the like. As the alignment layer, a polyvinyl alcohol-based thin film, a polyimide-based thin film, a polysiloxane-based thin film, a glassy polymer thin film, or the like can be used. The rubbing treatment is performed, for example, by rubbing the base material with a rubbing roll wound with a rubbing cloth made of fine fibers such as rayon or cotton. By adjusting the arrangement angle of the rubbing roll, an optical film having various optical axes (orientation direction of liquid crystal molecules) can be produced by giving a predetermined angle to the conveyance direction and the rubbing direction of the substrate.

When a rubbing treatment base material is used, the wound body of the base material after the rubbing treatment may be set in the feeding unit 10 of the film forming apparatus 100, and after feeding an untreated substrate from the feeding unit 10, the rubbing treatment of the substrate may be carried out. From the viewpoint of preventing the mixing of foreign substances into the liquid crystal layer and preventing process contamination, it is preferable to set and use the wound body of the base material after the rubbing treatment in the feeding unit of the film forming apparatus. When the rubbing process of a base material is performed after feeding an unprocessed base material from a feeding part, a rubbing process is performed after feeding|feeding of a base material, but before a washing|cleaning process.

The surface of the base film may be subjected to a treatment such as an easy adhesion treatment, a mold release treatment, an antistatic treatment, an antiblocking treatment, or the like. Moreover, embossing (knurling) etc. may be given to the edge part of the width direction of a base material for the purpose of blocking prevention etc.

[Liquid crystal material]

The liquid crystal material contains a liquid crystal monomer, a liquid crystal polymer, or a mixture thereof. Liquid crystal monomers and liquid crystal polymers (these are collectively referred to as "liquid crystal compounds" in some cases) may exhibit thermotropic liquid crystallinity or lyotropic liquid crystallinity.

As the liquid crystal monomer, a liquid crystal compound having at least one polymerizable functional group such as an unsaturated double bond such as an acryloyl group, a methacryloyl group, or a vinyl group, or an epoxy group, which exhibits alignment properties such as nematic property and smectic property, at the terminal. used The liquid crystal material containing a liquid crystal monomer may contain a polymerization initiator in addition to a liquid crystal monomer. As a polymerization method of a polymerizable liquid crystal monomer, thermal polymerization, ultraviolet polymerization, etc. are mentioned, for example, A suitable polymerization initiator is used according to the polymerization method.

As the liquid crystal polymer, a main chain liquid crystal polymer or a side chain liquid crystal polymer exhibiting a liquid crystal orientation such as nematic property or smectic property, or a composite liquid crystal compound thereof is used. Although the molecular weight in particular of a liquid crystal polymer is not restrict|limited, It is preferable that a weight average molecular weight is about 2000-100000.

The cholesteric alignment property of the liquid crystal material can also be made by making the nematic liquid crystal material contain a chiral agent or by introducing a chiral component into the structure of the liquid crystal polymer. The type and amount of the chiral agent can be appropriately determined depending on the selective reflection wavelength of the cholesteric liquid crystal and set values such as the helical pitch.

When the liquid crystal material is applied on the substrate, a solution of the liquid crystal compound is usually used. The solvent for dissolving the liquid crystal material is 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 parachlorophenol, benzene, toluene, and xylene , methoxybenzene, aromatic hydrocarbons such as 1,2-dimethoxybenzene, acetone, ethyl acetate, tert-butyl alcohol, glycerin, 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, dimethyl sulfoxide, acetonitrile, Butyronitrile, carbon disulfide, etc. are mentioned. You may use a solvent in mixture of 2 or more types.

The liquid crystal material solution may contain additives, such as a pigment|dye, a leveling agent, a plasticizer, a ultraviolet absorber, and a deterioration inhibitor, as needed other than a polymerization initiator, a chiral agent, etc. Solid content, viscosity, etc. of a liquid-crystal material solution are suitably set according to the kind, molecular weight, thickness of a liquid-crystal layer, a film forming method, etc. of a liquid-crystal material.

[Tax Department]

In the conveyance path|route of the base material 1 WHEREIN: The washing|cleaning part 40 is provided between the feeding|feeding-out part 10 and the film forming part 60. As shown in FIG. In the washing|cleaning part 40, wet washing is performed while the back surface 12 of the base material 1 and the washing|cleaning roll 41 are brought into contact via a washing|cleaning liquid. In the present invention, when the cleaning liquid supplied between the cleaning roll and the back surface of the substrate is spread on the substrate by the cleaning roll, a shear force is applied to the interface between the cleaning liquid and the substrate, whereby foreign substances adhering to the substrate, etc. are efficiently cleaned and removed Therefore, it is estimated that spot unevenness is suppressed.

In the form shown in FIG. 1 , the cleaning unit 40 includes a backup roll 42 formed to contact the film forming surface 11 of the substrate 1 and a cleaning roll formed to contact the back surface 12 of the substrate 1 ( 41) is provided. The cleaning liquid 47 is stored in the cleaning pan 48, and the cleaning liquid adhering to the surface of the cleaning roll 41 is scraped off by the doctor blade 44, and the surplus is removed from the back surface ( 12) is induced.

<Washing Roll>

As the cleaning roll 41, various rolls used for solution coating, such as a knife roll (comma roll), a kiss roll, a gravure roll, and a Meyer bar roll, are used. The cleaning roll may be a rotating roll or a non-rotating roll. When the cleaning roll is a rotating roll, the rotation direction may be either forward rotation or reverse rotation.

From the viewpoint of increasing the cleaning efficiency of the substrate, it is preferable that irregularities are formed on the surface of the cleaning roll. As for the uneven pattern on the surface of the cleaning roll, it is preferable that the convex portions extend non-parallel to the circumferential direction of the roll. When the convex portions extending non-parallel to the circumferential direction of the cleaning roll 41 come into contact with the back surface of the substrate, foreign substances or the like adhering to the substrate are more efficiently cleaned and removed, and spots tend to be suppressed.

As a roll which has a convex part extending in the direction nonparallel to the circumferential direction, a gravure roll, a Meyer bar roll, an embossing roll etc. are mentioned, for example. As the cleaning roll, a gravure roll and a Meyer bar roll are particularly preferably used from the viewpoint that the cleaning liquid can be spread on the back surface of the substrate without damaging the substrate.

It is a top view which shows an example of the uneven|corrugated pattern shape of the surface of a gravure roll. Concave portions (gravure grooves) 141 and convex portions 142 are formed in a pattern on the surface of the gravure roll 140 . When a gravure roll is used as a cleaning roll, it is thought that the liquid collected in this recessed part comes into contact with the base material surface, and the foreign material adhering to the base material surface is scraped off by contact with the convex part, and a foreign material is removed. In addition, although a rectangular (square type) thing is shown as a gravure pattern shape in FIG. 2, if the convex part extends in an oblique direction, the shape of a gravure pattern is not specifically limited, For example, triangular, honeycomb type, etc. may be a polygonal shape, a diagonal shape, or a linear shape such as a broken line shape.

Fig. 3A is a plan view showing an example of the concave-convex pattern shape of the surface of the Meyer bar roll 240, and Fig. 3B is a cross-sectional view taken along the line B1-B2. In the Meyer bar roll, a thin wire 242 such as a wire is spirally wound on the surface of a roll body (cylinder) 241, and a convex portion extending in a circumferential direction and non-parallel to the circumferential direction is formed by the thin wire 242. . When a Meyer bar roll is used as the cleaning roll, the liquid collected in the gap between the adjacent thin wires 242 comes into contact with the surface of the substrate, and foreign substances adhering to the surface of the substrate come into contact with the thin wire 242 wound spirally. It is thought that the foreign material is removed by scraping off. In addition, although the form in which one set of thin wires 242 was wound around a cylinder is shown in FIG. 3A and FIG. 3B, as for a Meyer bar, the thing by which many thin wires were wound may be sufficient. The thin wire 242 may be wound without a gap, or may be wound at regular intervals. The interval between adjacent thin wires is preferably equal to or less than the width of the thin wires.

Although the height of the convex part on the surface of the cleaning roll is not particularly limited, it is preferably in the range of about 0.1 µm to 10 µm, similar to the height of the convex part on a general gravure roll or Meyer bar roll. When the height of a convex part is too small, a washing|cleaning effect may become inadequate. On the other hand, when the height of the convex portion is too large, the expansion thickness of the cleaning liquid becomes large, so that the cleaning efficiency is lowered or it takes a long time to dry the cleaning liquid, thereby reducing the production efficiency.

<Cleaning liquid>

In the cleaning step, a cleaning liquid is supplied between the cleaning roll 41 and the back surface 12 of the substrate 1 . When the cleaning roll 41 and the back surface 12 of the base material 1 come into contact with each other, the cleaning liquid is spread on the back surface of the base material, and cleaning is performed. The washing liquid is not particularly limited as long as it does not dissolve the base material 1 as a liquid, and water, an organic solvent, a mixture of water and an organic solvent, and the like are used.

From the viewpoint of efficiently performing in-line cleaning on the conveyance path from the feeding unit 10 to the film forming unit 60 , as the cleaning liquid, a liquid having a low boiling point and high volatility is preferably used. As a highly volatile liquid, Alcohol, such as methanol, ethanol, and isopropyl alcohol; Ketones, such as acetone and methyl ethyl ketone; halogenated alkyls such as chloroform, dichloromethane and dichloroethane; Ethers, such as diethyl ether, ethyl propyl ether, and ethyl isopropyl ether, etc. are mentioned. Moreover, a mixture of these organic solvents, a mixture of these organic solvents and water, etc. can also be used. In addition, for the purpose of improving the cleaning power or the like, a surfactant, a hydrophilic organic compound, or the like may be added to the cleaning liquid. Examples of the hydrophilic organic compound include an organic compound having a hydroxyl group, an amino group, an amide group, an imino group, an imide 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, etc. can

<Washing method>

The cleaning method is not particularly limited as long as it is a method of spreading the cleaning liquid supplied between the cleaning roll 41 and the back surface 12 of the substrate 1 on the substrate. The method of supplying the cleaning liquid between the cleaning roll and the substrate is also not particularly limited. In FIG. 1 , a mode in which the cleaning roll 41 is directly brought into contact with the cleaning liquid 47 in the cleaning pan 48 (direct gravure method) is shown, but for example, a different roll (offset roll) to the cleaning liquid in the cleaning pan 48 . A method of moving the cleaning liquid adhering to the offset roll surface to a cleaning roll arranged so as to be in contact with the offset roll (offset gravure) or the like may be employed. In addition to the method of adhering the cleaning liquid to the surface of the cleaning roll 41, a method of applying the cleaning liquid to the back surface 12 of the substrate 1 by a slot die or spray or the like before the substrate 1 comes into contact with the cleaning roll 41; The cleaning liquid may be supplied between the cleaning roll 41 and the back surface 12 of the substrate 1 by a method of running the substrate in the cleaning pan, a method of attaching the cleaning liquid to the surface of the cleaning roll 41 by spraying, etc. .

Since the base material 1 is conveyed downstream (left side in Fig. 1) while in contact with the cleaning roll 41, the cleaning liquid supplied between the cleaning roll 41 and the base material inevitably spreads on the surface of the base material. The cleaning roll 41 and the back surface 12 of the base material 1 may be in direct contact, and may have a gap. The gap between the cleaning roll and the back surface of the substrate is preferably about 0.1 µm to 10 µm, for example. When the gap is excessively large, the shear force at the interface when the roll and the substrate come into contact with each other through the cleaning liquid becomes small, and the cleaning efficiency tends to decrease. When the cleaning roll has an uneven pattern on its surface, as described above, the gap between the cleaning roll and the substrate can be adjusted to a desired range according to the height of the convex portion on the roll surface. When the cleaning roll does not have an uneven pattern on the surface, the gap can be adjusted by the relative positional relationship between the cleaning roll 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 roll 41 , and the film forming surface 11 is in contact with the backup roll 42 . In (1), if the transport path of the base material is configured so that the back surface 12 and the cleaning roll 41 are in contact with the cleaning liquid through the cleaning liquid, the backup roll in the cleaning unit 40 is not necessarily required. Moreover, instead of the backup roll 42, washing|cleaning with respect to the film forming surface 11 may be performed simultaneously with the back surface 12 of the base material 1 using the roll etc. which have an unevenness|corrugation on the surface.

The base material 1 whose back surface 12 was washed by the washing|cleaning part 40 is conveyed to the film forming part 60 via the guide roller 54. As shown in FIG. Further, drying of the cleaning liquid adhering to the surface of the substrate may be performed while the substrate is conveyed from the cleaning unit 40 to the film forming unit 60 . The drying method is not specifically limited, The method of spraying clean air, the method of passing a base material in a heating oven, etc. are mentioned.

[The filmmaking department]

In the film forming part 60, a liquid crystal material solution is apply|coated on the film forming surface 11 of the base material 1, and film forming is performed in accordance with a conventional method. In FIG. 1 , a die coater using an extrusion die 61 is shown. In this coater, the liquid crystal material discharged from the lip of the die 61 is applied onto 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 . By adjusting the application amount of the liquid crystal material from the die and the conveyance speed of the substrate, the thickness of the coating film of the liquid crystal material is adjusted.

The film forming method in the film forming unit 60 is not limited to die coat, and various methods such as kiss roll coat, gravure coat, reverse coat, spray coat, Meyer bar coat, knife roll coat, air knife coat, and curtain coat. this is used

The characteristics of the optical film using a liquid crystal material depend on the film thickness of a liquid crystal layer in many cases. For example, the retardation value of retardation film, the rotation angle of the optical axis by the optical rotation element, and the absorbance of a polarizer are proportional to the thickness of a liquid crystal layer. Therefore, in order to make the characteristic of an optical film uniform, it is preferable that the film thickness at the time of film forming is uniform. In order to make a film thickness uniform, as shown in FIG. 1, it is preferable that film forming is performed, supporting the back surface 12 of the base material 1 with the backup roll 62. As shown in FIG.

On the other hand, when a foreign material exists between the backup roll 62 and the back surface 12 of the base material 1, the film forming surface 11 of the base material 1 will deform|transform convexly by the pressurization. When the liquid crystal material is applied thereon, it is considered that the coating thickness of the portion where the base material is deformed becomes locally small, causing spot unevenness. In contrast, in the present invention, by in-line cleaning of the back surface 12 of the substrate 1, foreign matter is removed, so that even when film forming is performed while supporting the substrate with a backup roll, the occurrence of spot spots is suppressed. It is estimated.

The thickness of a liquid crystal layer is set so that the film thickness after drying may be set to about 0.1 micrometer - about 20 micrometers according to the characteristic etc. of the optical film made into the objective, for example. In general, as the thickness of the liquid crystal layer decreases, the occurrence of spots tends to become more remarkable. On the other hand, in the present invention, by passing through the washing step, the occurrence of spot spots is suppressed even when the film thickness of the liquid crystal layer after drying is 20 µm or less. Therefore, the manufacturing method of this invention is used suitably for manufacture of the liquid crystal optical film with a small thickness of an application layer.

[Process after application]

The coating film of the liquid crystal stock applied on the film forming surface 11 of the base material 1 is conveyed into the drying furnace 20 together with the base material 1, the solvent is removed and a liquid crystal layer is formed. In addition to drying, alignment treatment of liquid crystal molecules, polymerization of a liquid crystal monomer, or the like may be performed. For example, when a liquid crystal monomer exhibiting thermotropic liquid crystallinity is used, it is heated until the monomer becomes above the temperature range in which the liquid crystal phase is exhibited, dried, cooled to a temperature in a state in which the liquid crystal phase is exhibited, and irradiated with ultraviolet rays. By superposing|polymerizing by this, it is possible to fix the orientation state of a liquid crystal. Moreover, a lyotropic liquid crystal can also orientate a liquid crystal molecule in a predetermined orientation by providing a shearing force.

You may wind up the base material after forming a liquid-crystal layer in the state which made the base material and liquid-crystal layer closely_contact|adhered as it is. After the liquid crystal layer formed on the base material is transferred to another film or the base material and the liquid crystal layer are peeled off, the base material and the liquid crystal layer may be wound up separately. Moreover, you may provide the liquid-crystal layer peeled from the base material, or the liquid-crystal layer transcribe|transferred to another film to other processes, such as drying, orientation treatment, and extending|stretching.

The liquid-crystal layer wound up in the state closely_contact|adhered to a base material may be provided for practical use as an optical film integrally with a base material. Moreover, it can also use for other processes, such as extending|stretching, in the state which made the liquid-crystal layer closely_contact|adhered on the base material. Then, the base material and the liquid crystal layer may be integrally used as an optical film, and the liquid crystal layer which peeled from the base material, or what transcribe|transferred the liquid crystal layer on another film may be used as an optical film. Another coating layer or the like may be additionally applied on the liquid crystal layer.

The optical film of this invention obtained in this way can be used as an optical film for image display apparatuses since spot unevenness is reduced and there are few optical defects. Specific examples of the optical film for image display devices include optical compensation films such as retardation plates, polarizers, polarizer protective films, and optical rotation elements.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples related to the preparation of the liquid crystal optical film, but the present invention is not limited to the following Examples.

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

In Production Examples 1A to 1M, a polyester film having a thickness of 75 µm (without rubbing treatment) was used as the base film, and the following coating liquid was applied on the base film, and a negative C plate composed of a cholesteric liquid crystal layer (selection The optical film provided with reflection wavelength: 200-220 nm) was manufactured.

<Preparation of coating liquid of liquid crystal material>

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

[Formula 1]

A polymerizable chiral agent of the following formula: 10 parts by weight,

[Formula 2]

and UV polymerization initiator (trade name "Irgacure 907" manufactured by BASF): 5 parts by weight, methyl ethyl ketone: 300 parts by weight, to prepare a polymerizable liquid crystal material solution containing a chiral agent.

[Preparation Example 1A (Example)]

The wound body of the base film is set in the feeding unit of the film forming apparatus, and while the base film is drawn and driven, isopropyl alcohol as a cleaning solution is used as a cleaning solution and a gravure roll rotating in the opposite direction to the conveying direction of the base film is brought into contact with the back side of the base film. , the back surface of the substrate was washed. After washing, the polymerizable liquid crystal material solution was applied to a film thickness of 2 µm on the film-forming surface of the substrate, dried at 70°C for 3 minutes, cooled to room temperature, and ultraviolet rays were applied at an accumulated light amount of 300 mJ/cm2 By irradiation, the liquid crystal monomer was cured and the orientation of the liquid crystal molecules was fixed. The obtained liquid crystal layer was wound up as a laminated body with a base film.

[Preparation Example 1B (Example)]

In Production Example 1A, in addition to the back side of the base film, the film forming side was also washed while contacting the gravure roll with isopropyl alcohol as a cleaning solution. That is, in manufacture example 1B, it wash|cleaned, contacting a gravure roll with respect to both surfaces of the back surface of a base film, and a film forming surface. Then, similarly to manufacture example 1A, application|coating of a polymeric liquid crystal material solution, drying, cooling, and ultraviolet irradiation were performed, and the liquid crystal layer was formed on the base film.

[Preparation Examples 1C, 1D (Example)]

A Meyer bar roll was used instead of the gravure roll. 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, washing was performed while bringing the Meyer bar roll into contact with the back surface of the base film, and in Production Example 1D, washing was performed while bringing the Meyer bar roll into contact with both sides of the base film.

[Production Example 1E (Comparative Example)]

The liquid crystal layer was formed on the base film by applying, drying, cooling and UV irradiation of the polymerizable liquid crystal material solution in the same manner as in Production Example 1A without washing the back surface or the film forming surface of the base film.

[Production Example 1F (Comparative Example)]

In the said manufacture example 1B, it wash|cleaned, making the gravure roll contact only with respect to the film forming surface of a base film, without performing washing|cleaning of the back side of a base film. Then, similarly to manufacture example 1A, application|coating of a polymeric liquid crystal material solution, drying, cooling, and ultraviolet irradiation were performed, and the liquid crystal layer was formed on the base film.

[Production Example 1G (Comparative Example)]

In Production Example 1D, washing was performed while contacting the Meyer bar roll only to the film forming surface of the base film without washing the back side of the base film. Then, similarly to manufacture example 1A, application|coating of a polymeric liquid crystal material solution, drying, cooling, and ultraviolet irradiation were performed, and the liquid crystal layer was formed on the base film.

[Production Example 1H (Comparative Example)]

In the same manner as in Production Example 1E, neither the backside nor the film forming surface of the base film was washed, and the polymerizable liquid crystal material solution was applied, dried, cooled, and irradiated with ultraviolet rays in the same manner as in Production Example 1A, and the substrate film was A liquid crystal layer was formed on the In Production Example 1H, the scraper was brought into contact with the backup roll in contact with the back surface of the substrate at the time of application of the polymerizable liquid crystal material solution, and the film was formed while always cleaning the backup roll.

[Production Example 1I (Comparative Example)]

The guide roll which contacts the back surface of a base material just before the film forming part of a film forming apparatus was changed into an adhesive roll, and the back surface of the base material by contact with an adhesive roll was wash|cleaned. On the other hand, in Production Example 1I, cleaning using a cleaning roll was not performed. Other than that, application|coating of a polymeric liquid crystal material solution, drying, cooling, and ultraviolet irradiation were performed similarly to manufacture example 1A, and the liquid crystal layer was formed on the base film.

[Production Example 1J (Comparative Example)]

Just before the film forming part of the film forming apparatus, the guide roll in contact with the film forming surface of the base material was changed to an adhesive roll, and the film forming surface of the base material by contact with the adhesion roll was washed. On the other hand, in Production Example 1J, washing using a washing roll was not performed. Other than that, application|coating of a polymeric liquid crystal material solution, drying, cooling, and ultraviolet irradiation were performed similarly to manufacture example 1A, and the liquid crystal layer was formed on the base film.

[Production Example 1K (Comparative Example)]

Immediately before the film forming part of the film forming apparatus, each of the guide roll in contact with the back surface of the substrate and the guide roll in contact with the film forming surface was changed to an adhesive roll, and the back surface and film forming surface of the substrate by contact with the adhesion roll were washed. . On the other hand, in manufacture example 1K, washing|cleaning using a washing|cleaning roll was not performed. Other than that, application|coating of a polymeric liquid crystal material solution, drying, cooling, and ultraviolet irradiation were performed similarly to manufacture example 1A, and the liquid crystal layer was formed on the base film.

[Production Example 1L (Comparative Example)]

In the same manner as in Production Example 1A, the back side of the base film was washed while the gravure roll was brought into contact with isopropyl alcohol as a cleaning solution. After that, the polymerizable liquid crystal material solution was not applied, and the base film was once wound up (offline washing). The base film after winding is set in the film forming apparatus again, and neither the back surface of the base film nor the film forming surface is washed, but the polymerizable liquid crystal material solution is applied, dried, cooled, and irradiated with ultraviolet rays to form the base film on the base film. A liquid crystal layer was formed.

[Production Example 1M (Comparative Example)]

In Production Example 1L, a Meyer bar roll was used instead of the gravure roll and the back side of the base film was off-line washed, and then the base film was wound up once. The base film after winding is set in the film forming apparatus again, and neither the back surface of the base film nor the film forming surface is washed, but the polymerizable liquid crystal material solution is applied, dried, cooled, and irradiated with ultraviolet rays to form the base film on the base film. A liquid crystal layer was formed.

[evaluation]

In a dark room, the optical film obtained in Preparation Examples 1A to 1M is irradiated with white light from the liquid crystal layer side in a state in which the liquid crystal layer is laminated on the base film, and the annular interference fringes are reflected in the reflected light due to the change in the film thickness. The presence or absence of a point in which the occurrence of was observed was visually confirmed. The number of points where an annular interference fringe occurred in an area of 1 m 2 was counted, and this was taken as the number of spots. Table 1 shows a list of the cleaning conditions and the number of spots on the substrate in Production Examples 1A to 1M.

In Production Examples 1F and 1G, although the film forming surface of the substrate was washed, there was no clear change in the number of spots compared to Production Example 1E in which no cleaning was performed. Moreover, also in manufacture example 1H which cleaned the backup roll, and manufacture example 1J which wash|cleaned the film forming surface with the adhesive roll, the clear change of the number of spots was not seen.

On the other hand, in Production Examples 1A to 1D and Production Examples 1I and 1K in which the back surface was cleaned in-line, the number of spots was significantly reduced. On the other hand, in Production Examples 1L and 1M in which the back surface was washed off-line, no clear change in the number of spots was observed. From these results, it can be seen that spot unevenness is significantly reduced by in-line cleaning of the back surface of the substrate.

The number of spots in Production Examples 1I and 1K in which the back surface of the substrate was washed by contact with the pressure-sensitive adhesive roll was 7 and 6 per 1 m 2 , respectively. When the defect due to spot unevenness exists at 6 points per 1 m 2 , when the optical film is used in an image display device having a screen size of 5 inches (about 140 pieces per 1 m 2 ), the defect rate corresponds to about 4%. However, when the screen size is 11 inches, the defective rate is about 20%, and when the screen size is 20 inches or more, the defective rate rises to almost 100%. Therefore, it turns out that when an optical film is used for formation of a large sized image display apparatus, the defect rate by spot unevenness is high in cleaning with an adhesive roll, and it turns out that it is very difficult to obtain the piece of the optical film of good quality.

On the other hand, as in Production Examples 1A to 1D, by wet cleaning the back surface of the substrate by bringing the roll and the substrate into contact with the cleaning solution, there is almost no spot unevenness, and high quality that can be suitably used for the formation of large-sized image display devices. It can be seen that an optical film of

[Production Example 2: Preparation of positive A plate on rubbing substrate]

In Production Examples 2A to 2M, a triacetyl cellulose film having a thickness of 40 µm on which a rubbing treatment was applied to the surface was used as the base film, and the following coating solution was applied on the base film, and the positive A consisting of a nematic liquid crystal layer An optical film with a plate was prepared.

<Preparation of coating liquid of liquid crystal material>

Liquid crystal monomer exhibiting a nematic liquid crystal phase (trade name "Paliocolor LC242" manufactured by BASF): 100 parts by weight, and photopolymerization initiator (trade name: "Irgacure 907" manufactured by BASF): 3 parts by weight, dissolved in 400 parts by weight of toluene , a polymerizable liquid crystal material solution was prepared.

<Rubbing treatment of base material>

The rubbing process was performed to the 40-micrometer-thick triacetyl cellulose film which performed the saponification process by the method of Example 1-1 of Unexamined-Japanese-Patent No. 2006-235611. The rubbing angle was made to incline by 24.3 degrees with respect to the conveyance direction of a base film. The base material after a rubbing process was once wound up in roll shape, after water washing and drying.

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

The base film was washed in the same manner as in Production Examples 1A to 1D, setting the wound body of the rubbing process-finished base film to the feeding unit of the film forming apparatus, and feeding and traveling the base film. On the film-forming surface of the base material after washing, the polymerizable liquid crystal material solution is applied so that the film thickness after drying becomes 1 µm, dried at 90°C for 2 minutes, cooled to room temperature, and ultraviolet rays are applied to 300 mJ in integrated light quantity By irradiating /cm 2 , the liquid crystal monomer was cured and the orientation of the liquid crystal molecules was fixed. The obtained liquid crystal layer was wound up as a laminated body with a base film.

[Production Examples 2E to 2M (Comparative Example)]

The washing method of the base material after the rubbing treatment was changed to the same method as in Production Examples 1E to 1M. Other than that, the liquid crystal layer was formed on the base film by applying, drying, cooling, and UV irradiation of the polymerizable liquid crystal material solution in the same manner as in Preparation Examples 2A to 2D.

[evaluation]

The number of spots of the optical films obtained in Production Examples 2A to 2M was evaluated by the same evaluation method as in Production Example 1. Table 2 shows the evaluation results.

In Production Examples 2E to 2M, as compared with Production Examples 1E to 1M, the tendency for the number of spots to increase was observed. This is presumed to originate from the adhesion of foreign substances (rubbing residues, etc.) generated during the rubbing treatment to the surface of the substrate. On the other hand, in Production Examples 2A to 2D in which the back surface was washed inline, spot unevenness was not observed in the same manner as in Production Examples 1A to 1D.

From these results, it can be seen that, by in-line cleaning of the back surface of the substrate by the method of the present invention, regardless of the presence or absence of the rubbing treatment of the substrate or the type of liquid crystal material, there is almost no spot unevenness and a high-quality optical film is obtained.

1: description
11: film making surface (first main surface)
12: back (2nd main surface)
2: wound body
10: delivery unit
20: drying furnace
40: cleaning unit
41: cleaning roll
42 : Backup Roll
44 : Doctor Blade
47: cleaning fan
48: cleaning solution
51, 52, 54: guide roller
60: film making
61: die
62: backup roll
140: gravure roll
141: concave
142: convex part
240: Meyer Bar Roll
241: cylinder
242: thin wire (convex part)

Claims (4)

A method for manufacturing an optical film, comprising:
A feeding step in which an elongated substrate having a first main surface and a second main surface is unwound from the winding body of the flexible substrate and continuously conveyed downstream;
a cleaning step in which the second main surface of the substrate is washed; and
a film forming process in which a liquid crystal material is applied on the first main surface of the substrate;
In the cleaning step, the cleaning liquid is adhered to the surface of the cleaning roll, the cleaning liquid is supplied between the second main surface of the substrate and the cleaning roll, and the cleaning liquid is spread on the substrate by the cleaning roll, thereby cleaning the substrate The manufacturing method of the optical film which this is implemented. The method of claim 1,
The method for manufacturing an optical film, wherein the cleaning roll has an uneven pattern on its surface, and convex portions of the uneven pattern extend non-parallel to the circumferential direction of the roll. 3. The method of claim 2,
The method for producing an optical film, wherein the cleaning roll is a gravure roll or a Meyer bar roll. 4. The method according to any one of claims 1 to 3,
The method for producing an optical film, wherein the cleaning liquid is a liquid having a lower boiling point than water.

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