JP2008015396A - Manufacturing method of optical film - Google Patents

Abstract

An optical film manufacturing method capable of manufacturing an optical film having uniform optical characteristics at low cost is provided.
A rubbing treatment step of rubbing an alignment film surface of a long plastic film F having an alignment film formed on the surface with a rubbing roll 4, a coating step of applying liquid crystal molecules to the alignment film surface, and a liquid crystal molecule And a fixing step for fixing the film, wherein in the rubbing process, the film is supported and conveyed by the conveying belt 3 having a metal surface, and the lower surface of the conveying belt that supports the film is supported. A plurality of backup rolls 5 are arranged so as to face the rubbing roll, and the rubbing strength RS defined by the following formula (1) is set to 2300 mm or more.
RS = N · M {1 + 2πr · nr / (v / 60)} (1)
[Selection] Figure 2

Description

  The present invention relates to a method of manufacturing an optical film used for optical compensation and antireflection of a liquid crystal display device and the like, and particularly to a manufacturing method capable of manufacturing an optical film having uniform optical characteristics at low cost.

  Conventionally, various optical elements manufactured by applying and aligning a liquid crystal material on the surface of a substrate are known. In the manufacturing process of such an optical element, in order to align the liquid crystal material on the surface of the substrate, for example, a rubbing process is generally performed in which the substrate surface is rubbed in one direction with a raised cloth. For example, when the optical element is a liquid crystal cell, the rubbing process is performed on a glass substrate unit basis. However, in the case of an optical element (optical film) using a plastic film as a base material, it is continuous in a so-called roll-to-roll method using a long plastic film, rather than performing a rubbing process in units of cut films. The rubbing process is overwhelmingly advantageous in terms of manufacturing efficiency and cost.

  Therefore, when manufacturing an optical film, various methods have been conventionally proposed as a method of continuously rubbing a long film by the roll-to-roll method as described above.

  For example, Patent Document 1 is characterized in that a rubbing process is performed on the film surface with a rubbing roll disposed on the conveying belt while conveying a long film with a conveying belt having a mirror-finished metal surface. A rubbing method is proposed.

  Further, in Patent Document 2, a rubbing process is performed on the film surface with the rubbing roll while a long film is continuously conveyed between the rubbing roll and a backup roll disposed to face the rubbing roll. A rubbing method characterized by this has been proposed.

On the other hand, when manufacturing an optical film, as a base material to be rubbed, a material having a linear structure, for example, a triacetyl cellulose (TAC) film or a polyethylene terephthalate (PET) film is generally used. It has been. In addition, liquid crystal molecules having one or more functional groups are used as the liquid crystal material applied to the surface of the base material (film) that has been subjected to the rubbing treatment. Then, the liquid crystal molecules are made into a solution using an appropriate organic solvent, applied to the surface of the film that has been subjected to rubbing treatment, dried, oriented, exposed to appropriate ultraviolet rays, etc., crosslinked, and fixed. Manufactures optical films.
JP 2004-170454 A JP-A-6-110059

  However, for example, when a long TAC film or PET film is used as a base material and a continuous rubbing treatment is performed by a roll-to-roll method, the base material is wound around a roll before the rubbing treatment is performed. Blocking (a phenomenon in which the substrates are in close contact with each other without having an optical interface) may occur.

  In the base material as described above, since the surface state of the part where blocking occurs changes, even if the base material is subjected to rubbing treatment, the orientation characteristics change between the part where blocking occurs and the other part. There is a problem that a uniform alignment state may not be obtained due to the occurrence of domains in liquid crystalline molecules. For example, when the optical film to be manufactured is a retardation film for use in a liquid crystal display, uniformity within the screen is important. Therefore, a retardation film having a non-uniform orientation as described above has almost no commercial value. It will not be possible.

  In order to obtain uniform alignment characteristics even for a base material on which blocking has occurred, for example, in the method described in Patent Document 1, it is conceivable to increase the pushing amount of the rubbing roll. However, there is no disclosure or suggestion on how much the push-in amount should be increased, and if the push-in amount is too large, the rubbing process can be performed in a stable state due to the slackness of the conveyor belt. There is no problem.

  In addition, it is considered that even if the amount of rubbing roll pushed in is increased in the method described in Patent Document 2, uniform orientation characteristics may be obtained for the substrate on which blocking has occurred. However, there is no disclosure or suggestion on how much the push amount should be increased, and in order to increase the push amount and perform the rubbing process in a stable state, a rubbing roll and a backup roll are provided. Since high installation accuracy is required during this period, there is a problem that it is not realistic.

  The present invention has been made to solve such problems of the prior art, and manufactures an optical film having uniform optical characteristics at low cost even when a base material that causes blocking is used. It is an object of the present invention to provide a manufacturing method that can be used.

In order to solve the above-mentioned problems, the inventors of the present invention have intensively studied,
(1) When the rubbing treatment is performed, even if the amount of pushing of the rubbing roll is increased by arranging a plurality of backup rolls that support the lower surface of the conveying belt that supports and conveys the long plastic film, It is possible to perform a rubbing process in a stable state,
(2) Even when blocking occurs in the plastic film, it is possible to obtain uniform orientation characteristics by setting a parameter value called “rubbing strength” to a predetermined value or more. thing,
(3) However, unless an alignment film is formed on the surface of the plastic film before the rubbing treatment, scratches are likely to occur during film conveyance (particularly, when the roughness of the film surface is small, scratches are likely to occur remarkably). ) In addition, the surface of the film is scraped during the rubbing treatment, and it tends to adhere to the film surface as a foreign substance, resulting in poor appearance of the optical film (appearance of bright spots and decrease in contrast)
I found.
The inventors of the present invention have completed the present invention based on the above new findings.

That is, the present invention provides a rubbing treatment step of rubbing the alignment film surface of a long plastic film having an alignment film formed on the surface with a rubbing roll, and a liquid crystal property on the alignment film surface of the plastic film after the rubbing treatment step. A method for producing an optical film comprising a coating step of coating molecules, and a fixing step of fixing the coated liquid crystalline molecules,
In the rubbing treatment step, the long plastic film is supported and transported by a transport belt having a metal surface, and the lower surface of the transport belt that supports the plastic film is supported and is opposed to the rubbing roll. Provided is a method for producing an optical film, in which a backup roll is provided and the rubbing strength RS defined by the following formula (1) is set to 2300 mm or more.
RS = N · M {1 + 2πr · nr / (v / 60)} (1)
Here, N is the number of rubbing times (number of rubbing rolls) (dimensionless amount), M is the pushing amount (mm) of the rubbing roll, π is the circumferential ratio, and r is the rubbing roll (including raised cloth). The radius (mm), nr represents the number of rotations (rpm) of the rubbing roll, and v represents the conveyance speed (mm / min) of the plastic film.

  According to such an invention, since it is possible to continuously rub the long plastic film by a roll-to-roll method, the cost is low, and the rubbing strength is set to 2300 mm or more, Uniform orientation characteristics can be imparted to the plastic film, and thus an optical film having uniform optical characteristics can be produced.

  In addition, since an alignment film is formed on the surface of the plastic film before the rubbing treatment, scratches are less likely to occur during film transportation, and foreign materials are less likely to adhere to the surface when the rubbing treatment is performed. It is possible to maintain the appearance.

  The “rubbing roll push-in amount” in the present invention refers to the rubbing roll (when a brushed cloth is wound around the rubbing roll) when the position of the rubbing roll is changed with respect to the alignment film surface of the plastic film. The origin (0 point) is the position at which the bristles of the raised cloth first contacted the alignment film surface, and it means the amount of the rubbing roll pushed from the origin toward the plastic film (position variation).

  Preferably, the alignment film is made of polyvinyl alcohol.

  The thickness of the alignment film can be appropriately set according to the surface roughness of the plastic film before the alignment film is formed, but is preferably 0.1 μm to 5 μm (more preferably 0.2 μm to 2 μm). The thickness is more preferably 0.3 μm or more and 1 μm or less.

  Further, if the surface roughness Rz of the plastic film before the alignment film is formed is too small, scratches are likely to occur during film conveyance, whereas if it is too large, it becomes difficult to perform a rubbing treatment on the roughness protrusions. , Foreign matter tends to adhere. Accordingly, the thickness is preferably 120 nm to 600 nm (more preferably 200 nm to 500 nm, still more preferably 300 nm to 450 nm). In addition, the surface roughness Rz in this invention means the maximum height prescribed | regulated by JIS B0601 of 2001 fiscal year.

Further, as a result of intensive studies, the inventors of the present invention have found the following events (A) and (B).
(A) When a rubbing process is performed, a plurality of rod-shaped backup rolls that support the lower surface of a conveyor belt that supports and conveys a long plastic film are arranged substantially parallel to each other, thereby being supported by the backup roll. The flatness of the conveyor belt tends to increase. (B) In the above (A), when the distance between the axes of the adjacent backup rolls is set to be smaller than 50 mm, the outer diameter of the backup rolls is necessarily reduced. In this case, if the conveyance speed of the plastic film is constant, the backup roll rotates at a high speed during the rubbing process compared to the case where the outer diameter of the backup roll is large, and the conveyance belt is caused by the heat generated at this time. There is a possibility that problems such as deformation of the plastic film supported on the substrate may occur. On the other hand, when the distance between the axes of adjacent backup rolls is set to be larger than 90 mm, there is a problem in that the flatness of the conveyor belt is lowered, thereby causing alignment unevenness and appearance defects. Therefore, in order to avoid the above problems, the distance between the axes of adjacent backup rolls is preferably set to 50 mm or more and 90 mm or less, and more preferably set to 60 mm or more and 80 mm or less.

  That is, preferably, the plurality of backup rolls are a plurality of rod-shaped backup rolls arranged substantially parallel to each other, and the distance between the axes of adjacent backup rolls is 50 mm or more and 90 mm or less (more preferably, 60 mm or more). 80 mm or less).

  According to such a preferable configuration, it is possible to impart more uniform orientation characteristics to the plastic film, and thus it is possible to produce an optical film having even more uniform optical characteristics.

  In the case where the outer diameter (diameter) of the backup roll is set to be smaller than 30 mm, if the transport speed of the plastic film is constant, the backup roll at the time of the rubbing process is compared with the case where the outer diameter of the backup roll is large. Rotates at a high speed, and the heat generated at this time may cause problems such as deformation of the plastic film supported by the conveyor belt. On the other hand, when the outer diameter of the backup roll is set to be larger than 80 mm, there is a problem that orientation unevenness is likely to occur and appearance defects are likely to occur due to a decrease in the flatness of the conveyor belt.

  Therefore, the outer diameter of the backup roll is preferably set to 30 mm or more and 80 mm or less (more preferably 40 mm or more and 70 mm or less).

  The production method according to the present invention is particularly effective when the plastic film is a triacetyl cellulose film or a polyethylene terephthalate film.

  Moreover, it is preferable that the raising cloth is wound around the rubbing roll.

  As the raised fabric, for example, any one of rayon, cotton, nylon, polyacetate and a mixture thereof is preferably used.

  Furthermore, the thickness of the conveyor belt is preferably 0.5 mm to 2.0 mm (more preferably 0.7 to 1.5 mm) in order to impart flexibility while preventing it from being easily slackened. The

  According to the method for producing an optical film of the present invention, it is possible to produce an optical film having uniform optical characteristics at low cost. In addition, it is difficult for flaws and foreign matters to adhere to the surface, and a good appearance of the optical film can be maintained.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a perspective view showing a schematic configuration of a rubbing treatment apparatus for performing a rubbing treatment step in the method for producing an optical film according to one embodiment of the present invention. As shown in FIG. 1, the rubbing treatment apparatus 100 according to the present embodiment includes a driving roll 1 and 2 and a long plastic film F that is installed between the driving rolls 1 and 2 and has an alignment film formed on the surface. An endless track conveyor belt 3 that supports and conveys, a rubbing roll 4 that is disposed above and below the conveyor belt 3 so as to be vertically movable, and a lower surface of the conveyor belt 3 that supports the plastic film F. And a plurality of (in this embodiment, five) rod-like backup rolls 5 disposed so as to oppose the four. In addition, before and after the rubbing apparatus 100, an appropriate static eliminator or dust remover may be installed as necessary.

The conveyor belt 3 is a metal surface (the entire conveyor belt 3 may be made of metal) having a mirror-finished surface that supports the plastic film F. As such a metal, various metal materials such as copper and steel can be used, but stainless steel is preferably used in terms of strength, hardness and durability. In order to ensure adhesion with the plastic film F, the surface finish (Ra) is preferably 0.02 μm or less, more preferably 0.01 μm or less as the degree of mirror finish. In order to prevent the plastic film F from slackening, it is necessary to prevent the conveyance belt 3 that supports the plastic film F from slackening. In view of the fact that it is necessary to provide a certain degree of flexibility in order to prevent the conveyor belt 3 from slacking and to be installed between the drive rolls 1 and 2, the thickness of the conveyor belt 3 is 0.5 mm to 2 mm. The thickness is preferably 0 mm, more preferably 0.7 mm to 1.5 mm. Further, considering the tension of the conveyor belt 3 while preventing the slack of the conveyor belt 3, the tension applied to the conveyor belt 3 is preferably 0.5 to 20 kgf / mm ² , more preferably. ² to 15 kg weight / mm ² .

  The rubbing roll 4 has a brushed cloth wound around its outer peripheral surface. What is necessary is just to select suitably the material, shape, etc. of a raising cloth according to the material of the plastic film F to which the rubbing process is performed. In general, rayon, cotton, nylon, polyacetate, or a mixture thereof can be applied as the raised cloth. The rotation axis of the rubbing roll 4 according to the present embodiment is inclined (for example, an inclination angle of 0 ° to 45 °) from a direction perpendicular to the conveyance direction of the plastic film F (the direction indicated by the arrow in FIG. 1). That is, it can be set to an arbitrary axial angle with respect to the long side of the plastic film F. Moreover, the rotation direction of the rubbing roll 4 can be appropriately selected according to the conditions of the rubbing treatment.

  As described above, the plurality of backup rolls 5 are disposed so as to support the lower surface of the conveyance belt 3 that supports the plastic film F and to face the rubbing roll 4. By providing such a plurality of backup rolls 5, even if the rubbing roll 4 is pushed in a tilted state, or even if the pushing amount of the rubbing roll 4 is increased, a stable state is achieved. It is possible to perform a rubbing process.

  When the rubbing process is performed on the plastic film F using the rubbing apparatus 100 having the above-described configuration, the end of the long plastic film F wound around a predetermined roll (not shown) has a plurality of transports. It is supplied onto the conveyor belt 3 via a roll (not shown). Then, by rotating the drive rolls 1 and 2, the upper part of the transport belt 3 moves in the direction indicated by the arrow in FIG. 1, and the plastic film F is also transported with the transport belt 3 along with this, A rubbing process is performed.

Here, the rubbing treatment step according to the present embodiment is characterized in that the rubbing strength RS defined by the following formula (1) is set to 2300 mm or more (more preferably 2600 mm or more).
RS = N · M {1 + 2πr · nr / (v / 60)} (1)

  2 is a front view partially showing the rubbing treatment apparatus 100 shown in FIG. 1, FIG. 2 (a) is a front view of the vicinity of the rubbing roll 4, and FIG. 2 (b) is a rubbing roll 4 and a plastic film F. It is a front view which expands and shows the contact location vicinity with the surface. As shown in FIG. 2, in the above formula (1), N is the number of rubbing times (corresponding to the number of rubbing rolls 4, 1 in this embodiment) (dimensionless amount), and M is the pushing amount of the rubbing roll 4 ( mm), π is the circumference, r is the radius (mm) of the rubbing roll 4 (including the raised cloth 4a in this embodiment), nr is the number of rotations (rpm) of the rubbing roll, and v is a plastic film. F means the conveyance speed (mm / min). The pushing amount M of the rubbing roll is wound around the rubbing roll 4 when the position of the rubbing roll 4 is changed with respect to the alignment film surface of the plastic film F as shown in FIG. The position (the position indicated by the broken line in FIG. 2B) where the bristles of the raised cloth 4a first contact the surface of the alignment film of the plastic film F is defined as the origin (0 point), and the rubbing from the origin toward the plastic film F is performed. It means the amount of pressing the roll 4 (the amount of pressing to the position shown by the solid line in FIG. 2B).

  As described above, by setting the rubbing strength RS to 2300 mm or more, even if the plastic film F is blocked, it is possible to impart uniform orientation characteristics, and thus an optical film having uniform optical characteristics. It is possible to manufacture.

  As a plastic film F to which the manufacturing method according to the present embodiment is applied, a function capable of aligning liquid crystal molecules applied to the surface as will be described later by rubbing the alignment film formed on the surface. As long as is provided, the material is not particularly limited.

  For example, as the plastic film F, polyolefins such as triacetyl cellulose (TAC), polyethylene, polypropylene, poly (4-methylpentene-1), polyimide, polyimide amide, polyether imide, polyamide, polyether ether ketone, polyether Ketone, polyketone sulfide, polyethersulfone, polysulfone, polyphenylene sulfide, polyphenylene oxide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyacetal, polycarbonate, polyarylate, acrylic resin, polyvinyl alcohol, polypropylene, cellulose plastics, epoxy resin And a film made of a phenol resin or the like. However, the manufacturing method according to the present embodiment is particularly effective for a film that is prone to blocking, such as a triacetyl cellulose film or a polyethylene terephthalate film.

  Examples of the alignment film formed on the surface of the plastic film F include polyvinyl alcohol, polyimide, and polyamide. Examples of the method for forming the alignment film include spin coating, bar coating, slot die coating, and dip coating.

  In addition, as long as the rubbing strength RS is set to 2300 mm or more, each parameter can be arbitrarily selected. However, in general, the conveyance speed v of the plastic film F is 1 to 50 m / min because of the apparatus specifications and the like. The rubbing roll 4 has a rotation speed nr of 1 to 3000 rpm, preferably 500 to 2000 rpm, and the pushing amount M of the rubbing roll 4 is 100 to 2000 μm, preferably 100 to 1000 μm. And a combination in which the rubbing strength RS is 2300 mm or more is selected.

  Liquid crystal molecules are applied to the surface of the alignment film of the plastic film F that has been rubbed as described above, and an optical film is produced by curing or solidifying the applied liquid crystal molecules.

  When applying liquid crystal molecules, a solution in which a liquid crystal compound is dissolved is generally used. As the liquid crystal molecules contained in the solution, a liquid crystal polymer, a liquid crystal prepolymer, a liquid crystal monomer and the like are appropriately used.

  In the case of using a liquid crystal polymer, after the liquid crystal polymer solution is applied to the surface of the plastic film F, it is heated until it reaches a temperature range showing the liquid crystal phase, dried, and then rapidly cooled to room temperature while showing the liquid crystal phase. Thus, it is possible to fix a liquid crystal state exhibiting optical anisotropy.

  In the case of using a liquid crystal prepolymer or a liquid crystal monomer, these solutions are applied to the surface of the plastic film F, then heated to a temperature range showing a liquid crystal phase, dried, and then brought to a temperature showing a liquid crystal phase. It is possible to fix the liquid crystal state exhibiting optical anisotropy by cooling and crosslinking by exposure to ultraviolet rays or the like.

As the liquid crystal monomer, for example, a monomer represented by any of the following chemical formulas (2) to (17) can be selected.

  The liquid crystal monomer solution preferably contains a polymerization agent and a crosslinking agent. These polymerizing agent and crosslinking agent are not particularly limited, and for example, the following can be used. Examples of the polymerization agent include benzoyl peroxide (BPO) and azobisisobutyronitrile (AIBN). Examples of the crosslinking agent include isocyanate crosslinking agents, epoxy crosslinking agents, and metal chelate crosslinking. An agent can be used. Any one of these may be used, or two or more may be used in combination.

  The liquid crystal monomer solution coating liquid can be prepared, for example, by dissolving and dispersing the liquid crystal monomer in an appropriate solvent. Examples of the solvent include, but are not limited to, for example, halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, methylene chloride, trichloroethylene, tetrachloroethylene, chlorobenzene, and orthodichlorobenzene, phenol, p- Phenols such as chlorophenol, o-chlorophenol, m-cresol, o-cresol, p-cresol, aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, 1,2-dimethoxybenzene, acetone, methyl ethyl ketone (MEK), ketone solvents such as methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone and N-methyl-2-pyrrolidone, and esters such as ethyl acetate and butyl acetate Solvent, alcohol solvent such as t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, 2-methyl-2,4-pentanediol, dimethylformamide Amide solvents such as dimethylacetamide, nitrile solvents such as acetonitrile and butyronitrile, ether solvents such as diethyl ether, dibutyl ether, tetrahydrofuran and dioxane, or carbon disulfide, ethyl cellosolve, butyl cellosolve, etc. Can be used. Among these, toluene, xylene, mesitylene, MEK, methyl isobutyl ketone, cyclohexanone, ethyl cellosolve, butyl cellosolve, ethyl acetate, butyl acetate, propyl acetate, and ethyl acetate cellosolve are preferable. These solvents may be, for example, one kind or a mixture of two or more kinds.

  The coating liquid may be flow-deployed by a conventionally known method such as a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, an extrusion method, a curtain coating method, a spray coating method, Of these, spin coating and extrusion coating are preferred from the viewpoint of coating efficiency.

  The temperature condition of the heat treatment after applying the liquid crystal monomer solution coating liquid on the alignment film surface of the plastic film F depends on, for example, the type of liquid crystal monomer used, specifically the temperature at which the liquid crystal monomer exhibits liquid crystallinity. Although it can determine suitably, it is the range of 40-120 degreeC normally, Preferably it is the range of 50-100 degreeC, More preferably, it is the range of 60-90 degreeC. If the temperature is 40 ° C. or higher, the liquid crystal monomer can usually be sufficiently aligned, and if the temperature is 120 ° C. or lower, for example, the choice of the plastic film F is widened in terms of heat resistance. .

  The liquid crystal compound to be dissolved is not particularly limited as long as it can be applied. For example, a rod-like liquid crystal compound, a plate-like liquid crystal compound, or a polymer thereof is used. More specifically, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, Liquid crystal compounds such as phenyldioxanes, tolanes, alkenylcyclohexylbenzonitriles, and polymers thereof are preferably used.

  The optical film manufactured by the manufacturing method according to the present embodiment described above can be provided with functions such as phase difference, color compensation, viewing angle expansion, and antireflection by appropriately applying known methods. It can be used as an optical film for various display devices such as a liquid crystal display, a plasma display, and an EL display.

  In the present embodiment, as a preferred configuration, for a plurality of rod-shaped backup rolls 5 arranged substantially parallel to each other, the distance between the axes of adjacent backup rolls 5 (L1 to L4 in FIG. 2) is 50 mm or more and 90 mm. Or less (more preferably, 60 mm or more and 80 mm or less).

  With such a configuration, the flatness of the conveyor belt 3 supported by the backup roll 5 is likely to increase. Further, since the inter-axis distances L1 to L4 are set to 50 mm or more (thus, the outer diameter of the backup roll inevitably increases to some extent), the backup roll 5 does not rotate at high speed during the rubbing process. Problems such as deformation of the plastic film F supported by the conveyor belt 3 are unlikely to occur due to heat generated in the belt. Furthermore, since the inter-axis distances L1 to L4 are set to 90 mm or less, the flatness of the transport belt 3 is not lowered, and uniform orientation characteristics can be imparted to the plastic film F.

  The outer diameter of each backup roll 5 is preferably set to 30 mm or more and 80 mm or less (more preferably 40 mm or more and 70 mm or less). By setting the outer diameter of the backup roll 5 to 30 mm or more, the backup roll 5 does not rotate at high speed during the rubbing process, and the plastic film F supported by the conveyor belt 3 is deformed by the heat generated at this time. Such problems are unlikely to occur. Further, by setting the outer diameter of the backup roll to 80 mm or less, the flatness of the transport belt 3 is not lowered, and uniform orientation characteristics can be imparted to the plastic film F.

  In the present embodiment, the case where the backup roll 5 is a rod-shaped roll has been described as an example. However, the present invention is not limited to this, and as shown in FIG. It is also possible to apply a plate (bearing plate) comprising

  Hereinafter, the features of the present invention will be further clarified by showing examples and comparative examples.

<Example 1>
(1) Rubbing treatment Using a polyethylene terephthalate film (Toray ultra-high smooth PET: U35) with a surface roughness Rz = 120 nm as a base material, forming a polyvinyl alcohol (PVA) with a thickness of 0.3 μm on the base material surface as an alignment film The rubbed film was rubbed using the rubbing apparatus 100 shown in FIGS. 1 and 2. The mirror finish on the surface of the transport belt 3 is Ra = 0.01 μm, the outer diameters of the drive rolls 1 and 2 are 550 mm, the transport speed of the film is 5 m / min, the outer diameter of the backup roll 5 is 50 mm, and each adjacent backup roll The inter-axis distances L1 to L4 of 5 were all 80 mm. The radius of the rubbing roll 4 (including the raised cloth 4a) was 76.89 mm, and a roll of a rayon raised cloth was used. The rotation axis of the rubbing roll 4 was inclined by 24.3 ° from the direction perpendicular to the film conveyance direction, the rotation speed was 1500 rpm, and the pushing amount was 0.4 mm. The rubbing strength under such conditions was 3479 mm. For measurement of the surface roughness Rz, a three-dimensional surface shape roughness meter: Wyko-NT3000 manufactured by Beiko Japan was used. The measurement area was 92 μm × 121 μm. The same applies to Examples 2 to 6 and Comparative Examples 1 to 3 described later. Further, a spectrophotometer: MCPD2000 manufactured by Otsuka Electronics Co., Ltd. was used for measuring the thickness of the alignment film. The same applies to Examples 2 to 6 described later.

(2) Preparation of coating liquid containing liquid crystal compound 0.03 g of a photopolymerization initiator (Irgacure 907 manufactured by Ciba Specialty Chemicals) was added to 1 g of an ultraviolet polymerizable nematic liquid crystal compound represented by the following chemical formula, and the solid content was 20 The solution was diluted with toluene so as to be in weight percent and stirred for 10 minutes to obtain a coating solution.

(3) Application / fixation of liquid crystalline molecules The coating liquid is applied to the surface of the alignment film subjected to the rubbing treatment of the triacetyl cellulose film using a cap coater, dried at 90 ° C. for 2 minutes, and then brought to room temperature. The liquid crystalline molecules were cured by cooling and irradiating ultraviolet rays with an integrated light quantity of 100 mJ / cm ² to prepare a retardation film (¼ wavelength plate).

<Example 2>
A retardation film (¼ wavelength plate) was produced according to Example 1 except that a polyethylene terephthalate film (PET: RC06 manufactured by Toray) having a surface roughness Rz = 330 nm was used as the substrate.

<Example 3>
A retardation film (¼ wavelength plate) was produced in the same manner as in Example 1 except that a polyethylene terephthalate film (Toray optical PET: R41) having a surface roughness Rz = 750 nm was used as the substrate.

<Example 4>
A retardation film (¼ wavelength plate) was produced in the same manner as in Example 1 except that polyvinyl alcohol (PVA) having a thickness of 1.0 μm was formed as an alignment film on the substrate surface.

<Example 5>
A retardation film (¼ wavelength plate) was produced according to Example 2 except that polyvinyl alcohol (PVA) having a thickness of 1.0 μm was formed as an alignment film on the substrate surface.

<Example 6>
A retardation film (¼ wavelength plate) was produced in the same manner as in Example 3 except that polyvinyl alcohol (PVA) having a thickness of 1.0 μm was formed as an alignment film on the substrate surface.

<Comparative Example 1>
A retardation film (¼ wavelength plate) was produced in the same manner as in Example 1 except that no alignment film was formed on the substrate surface.

<Comparative example 2>
A retardation film (¼ wavelength plate) was produced in the same manner as in Example 2 except that no alignment film was formed on the substrate surface.

<Comparative Example 3>
A retardation film (¼ wavelength plate) was produced in the same manner as in Example 3 except that no alignment film was formed on the substrate surface.

<Evaluation results>
(1) Evaluation of the number of flaws The retardation films produced in Examples 1 to 6 and Comparative Examples 1 to 3 are sandwiched between two polarizing plates arranged so that their absorption axes are orthogonal to each other, and the viewing side polarizing plate The number of flaws was evaluated by visually recognizing the laminated film so that the absorption axis of the film and the slow axis of the retardation film were parallel to each other. The number of flaws was counted in a 10 cm × 10 cm region on the surface of the retardation film, and this number was evaluated in proportion to the number per 1 m ² .

(2) Evaluation of the number of bright spots Similar to the evaluation of the number of flaws, the retardation produced in Examples 1 to 6 and Comparative Examples 1 to 3 between two polarizing plates arranged so that their absorption axes are orthogonal to each other The number of bright spots was evaluated by sandwiching the film and visually recognizing the laminated film so that the absorption axis of the polarizing plate on the viewing side and the slow axis of the retardation film were parallel to each other. The number of bright spots was counted in an area of 10 cm × 10 cm on the surface of the retardation film, and this number was evaluated in proportion to the number per 1 m ² .

(3) Evaluation of contrast Retardation films and polarizing plates produced in Examples 1 to 6 and Comparative Examples 1 to 3 on the upper and lower surfaces of a liquid crystal panel (VA mode panel) due to the relationship of optical axes as shown in FIG. The luminance in black display and white display was measured with a Topcon luminance meter: BM-5. The ratio between the luminance of white display and the luminance of black display was evaluated as contrast.

The evaluation results are shown in Table 1.

  As shown in Table 1, the retardation films according to Comparative Examples 1 to 3 had a contrast of less than 600 and had a problem at a practical level. On the other hand, the retardation films according to Examples 1 to 6 had a contrast of 600 or more, and no problem occurred at a practical level. However, it was found that when the surface roughness Rz of the substrate is too large (Examples 3 and 6, Rz = 750 nm), although there is no problem at a practical level, a bright spot is likely to occur. When the surface roughness Rz of the substrate is large, the tendency can be seen by comparing Example 3 and Example 6, and the occurrence of bright spots can be suppressed by increasing the thickness of the alignment film (PVA). It is considered possible. However, in consideration of the demand for thin film and an increase in manufacturing cost, it is preferable to make the thickness of the alignment film as small as possible. Therefore, it can be said that the surface roughness Rz of the substrate is preferably about 600 nm or less. Further, it was found that when the surface roughness Rz of the base material is small and the thickness of the alignment film (PVA) is small (Example 1), there is no problem at a practical level, but scratches are likely to occur during film conveyance. Therefore, the surface roughness Rz of the base material is not preferably as small as possible in order to suppress the occurrence of the bright spots described above, and it can be said that it is preferably about 120 nm or more.

FIG. 1 is a perspective view showing a schematic configuration of a rubbing treatment apparatus for performing a rubbing treatment step in the method for producing an optical film according to one embodiment of the present invention. 2 is a front view partially showing the rubbing treatment apparatus shown in FIG. 1, FIG. 2 (a) is a front view in the vicinity of the rubbing roll, and FIG. 2 (b) is a contact between the rubbing roll and the plastic film surface. It is a front view which expands and shows a location vicinity. FIG. 3 is an appearance photograph showing another example of the backup roll of the rubbing apparatus shown in FIG. FIG. 4 is an explanatory diagram for explaining a contrast evaluation method in an example of the present invention and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Drive roll 3 ... Conveyor belt 4 ... Rubbing roll 4a ... Brushed cloth 5 ... Backup roll 100 ... Rubbing apparatus F ... Plastic film

Claims (10)

A rubbing treatment step of rubbing the alignment film surface of a long plastic film having an alignment film formed on the surface with a rubbing roll, and a coating step of applying liquid crystalline molecules to the alignment film surface of the plastic film after the rubbing treatment step And a method for producing an optical film comprising a fixing step of fixing the applied liquid crystalline molecules,
In the rubbing treatment step, the long plastic film is supported and transported by a transport belt having a metal surface, and the lower surface of the transport belt that supports the plastic film is supported and is opposed to the rubbing roll. A method for producing an optical film, characterized in that a backup roll is provided and a rubbing strength RS defined by the following formula (1) is set to 2300 mm or more.
RS = N · M {1 + 2πr · nr / (v / 60)} (1)
Here, N is the number of rubbing times (number of rubbing rolls) (dimensionless amount), M is the pushing amount (mm) of the rubbing roll, π is the circumferential ratio, and r is the rubbing roll (including raised cloth). The radius (mm), nr represents the number of rotations (rpm) of the rubbing roll, and v represents the conveyance speed (mm / min) of the plastic film.   The method for producing an optical film according to claim 1, wherein the alignment film is made of polyvinyl alcohol.   The method for producing an optical film according to claim 1, wherein the alignment film has a thickness of 0.1 μm to 5 μm.   The method for producing an optical film according to any one of claims 1 to 3, wherein a surface roughness Rz of the plastic film before the alignment film is formed is 120 nm or more and 600 nm or less.   The plurality of backup rolls are a plurality of bar-shaped backup rolls arranged substantially parallel to each other, and the distance between the axes of adjacent backup rolls is set to 50 mm or more and 90 mm or less. 4. The method for producing an optical film according to any one of 4 above.   6. The method for producing an optical film according to claim 5, wherein an outer diameter of the backup roll is set to 30 mm or more and 80 mm or less.   The method for producing an optical film according to claim 1, wherein the plastic film is a triacetyl cellulose film or a polyethylene terephthalate film.   The method for producing an optical film according to any one of claims 1 to 7, wherein a brushed cloth is wound around the rubbing roll.   The method for producing an optical film according to claim 8, wherein the raised cloth is any one of rayon, cotton, nylon, polyacetate, and a mixture thereof.   The method for producing an optical film according to any one of claims 1 to 9, wherein the transport belt has a thickness of 0.5 mm to 2.0 mm.