JP2008151961A - Method for manufacturing optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical film preventing light leakage in black display of a liquid crystal display device inexpensively with uniform optical characteristics. <P>SOLUTION: The method includes steps of: rubbing a long plastic film F; applying and fixing liquid crystalline molecules on the surface of the rubbed film to form a first optical compensation layer 13 satisfying nx>ny=nz; and laminating a second optical compensation layer 14 satisfying nx>ny>nz and 1.2≤Nz≤2 thereon. In the rubbing step, the film is conveyed by a conveyer belt 3 having a metal surface, and a backup roll mechanism 5 supporting the undersurface of the conveyer belt is arranged. The mechanism includes a plurality of backup rolls 51 individually rotating along the conveyance direction of the conveyer belt, and each backup roll is arranged along a straight line directly under the rubbing roll and almost parallel to the rotation axis of the rubbing roll. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical film manufacturing method, and in particular, an optical film that contributes to good prevention of light leakage in black display of a liquid crystal display device and can be manufactured to have uniform optical characteristics at low cost. Regarding the method.

  Conventionally, as a liquid crystal display device having a vertical alignment (VA) mode liquid crystal cell, a transflective liquid crystal display device has been proposed in addition to a transmissive liquid crystal display device and a reflective liquid crystal display device (for example, (See Patent Documents 1 and 2).

  As a specific example of such a transflective liquid crystal display device, for example, a reflective film in which a light transmitting window is formed on a metal film such as aluminum is provided on the inner side of the lower substrate of the liquid crystal cell. A liquid crystal display device that functions as a transmission / reflection plate can be given. In such a liquid crystal display device, in the reflective mode, external light incident from the upper substrate side of the liquid crystal cell is reflected by the reflective film inside the lower substrate after passing through the liquid crystal layer, and is again transmitted through the liquid crystal layer. The light is emitted from the upper substrate side and contributes to display. On the other hand, in the transmissive mode, light from the backlight incident from the lower substrate side passes through the liquid crystal layer through the window portion of the reflective film, and then is emitted from the upper substrate side to contribute to display. Therefore, in the reflective film formation region, the region where the window is formed becomes the transmissive display region, and the other region becomes the reflective display region.

  However, in a reflective or transflective liquid crystal display device having a conventional VA mode liquid crystal cell, there is a problem that light leakage occurs in black display and the contrast is lowered (first problem).

  On the other hand, 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 base material, it is common to perform a rubbing process that rubs the base material surface in one direction with, for example, 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, conventionally, when manufacturing an optical film, various methods for continuously rubbing a long film by the roll-to-roll method as described above have been proposed.

  For example, Patent Document 3 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 4, a rubbing treatment 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 arranged to face the rubbing roll. A rubbing method characterized by this has been proposed.

  In manufacturing an optical film, a material having a linear structure, such as a triacetyl cellulose (TAC) film, is generally used as a base material to be rubbed. 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.

  However, for example, when a long TAC film or the like is used as a base material and the rubbing treatment is continuously performed by a roll-to-roll method, blocking is performed on the base material wound around the roll before the rubbing treatment ( There is a case in which the base materials adhere to each other without having an optical interface).

  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 used in a liquid crystal display device, 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 obtained (second problem).

  In order to obtain uniform orientation characteristics even for a substrate on which blocking has occurred, for example, in the method described in Patent Document 3, it is conceivable to increase the pushing amount of the rubbing roll. However, in the method described in Patent Document 3, since there is no backup roll for supporting the lower surface of the conveyor belt, if the pushing amount is excessively increased, the rubbing is performed in a stable state due to the slackness of the conveyor belt and the film. There is a problem that processing cannot be performed.

  In addition, it is considered that even if the amount of rubbing roll pushed in is increased in the method described in Patent Document 4, uniform orientation characteristics may be obtained for the substrate on which blocking has occurred. However, in the method described in Patent Document 4, since only one backup roll that rotates along the film conveyance direction is disposed, the rotation axis of the rubbing roll is particularly inclined from the direction perpendicular to the film conveyance direction. When this is done, there is a problem that the rubbing treatment cannot be performed in a stable state due to the influence of the slackness of the film.

In order to solve the above problems, the lower surface of the conveyance belt that supports the film may be supported by a plurality of bar-shaped backup rolls that are arranged substantially parallel to each other and rotate along the conveyance direction of the conveyance belt. Conceivable. However, particularly when the rotation axis of the rubbing roll is tilted from the direction perpendicular to the film transport direction, there remains a problem that the effect of the slack of the transport belt and the film cannot be sufficiently avoided.
Japanese Patent Laid-Open No. 11-242226 Japanese Patent Laid-Open No. 2001-209065 JP 2004-170454 A JP-A-6-110059

  The present invention has been made to solve the first and second problems in the prior art, and an optical film that contributes to preventing light leakage in black display of a liquid crystal display device at low cost. Another object of the present invention is to provide a manufacturing method that can be manufactured so as to have uniform optical characteristics.

As a result of intensive studies by the inventors of the present invention to solve the above problems, the first problem is as follows.
(1) As an optical film disposed on at least one side of the liquid crystal cell, a first optical compensation layer having a refractive index characteristic of nx> ny = nz, a refractive index characteristic of nx>ny> nz, and an Nz coefficient A film in which a second optical compensation layer satisfying 1.2 ≦ Nz ≦ 2 is used is used. A polarizer is disposed on the first optical compensation layer side of the optical film, and an absorption axis of the polarizer and each slow axis of the first optical compensation layer and the second optical compensation layer are formed. It has been found that by setting the angle within a predetermined range, light leakage in black display can be remarkably improved, particularly in a reflective or transflective liquid crystal display device having a VA mode liquid crystal cell.

Regarding the second issue,
(2) A plurality of backup rolls along a straight line that is directly under the rubbing roll and substantially parallel to the rotation axis of the rubbing roll, on the lower surface of the conveying belt that supports and conveys the long plastic film during the rubbing treatment. Even if the rotation axis of the rubbing roll is inclined from the direction perpendicular to the film conveyance direction and the pushing amount of the rubbing roll is increased, the flatness of the conveyance belt is improved and the slack is hardly generated. thing,
(3) By configuring each backup roll to rotate along the conveyance direction of the conveyance belt, the rotation of each backup roll does not hinder the movement of the conveyance belt in the conveyance direction and thus the conveyance of the plastic film,
(4) By the above (2) and (3), it becomes possible to perform a rubbing treatment in a stable state, and it is possible to impart a uniform orientation characteristic to the plastic film, and thus an optical film having a uniform optical characteristic. Being manufacturable,
I found.
The inventors of the present invention have completed the present invention based on the above new findings (1) to (4).

  That is, the present invention provides a rubbing treatment step of rubbing the surface of a long plastic film with a rubbing roll having a rotation axis inclined from a direction perpendicular to the conveyance direction of the plastic film, and the surface of the plastic film subjected to the rubbing treatment step. A first optical compensation layer having a refractive index characteristic of nx> ny = nz is formed on the plastic film by applying liquid crystal molecules to the substrate and fixing the applied liquid crystal molecules. A compensation layer forming step and a first layer formed by coating on the first optical compensation layer, having a refractive index characteristic of nx> ny> nz and satisfying an Nz coefficient of 1.2 ≦ Nz ≦ 2. A second optical compensation layer forming step of laminating two optical compensation layers, and in the rubbing treatment step, the long plastic is conveyed by a conveyor belt having a metal surface. A backup roll mechanism that supports and conveys the film and supports a lower surface of a conveyance belt that supports the plastic film is disposed, and the backup roll mechanism includes a plurality of rotations that respectively rotate along the conveyance direction of the conveyance belt. A production of an optical film comprising a backup roll, wherein each of the plurality of backup rolls is disposed along a straight line that is directly below the rubbing roll and substantially parallel to the rotation axis of the rubbing roll. A method is provided.

  According to the present invention, the first optical compensation layer having the refractive index characteristic of nx> ny = nz, the refractive index characteristic of nx> ny> nz, and the Nz coefficient satisfying 1.2 ≦ Nz ≦ 2. Since an optical film in which the second optical compensation layer is laminated is obtained, it is possible to satisfactorily prevent light leakage during black display of the liquid crystal display device by disposing it in the liquid crystal cell. In addition, since the first optical compensation layer is formed of liquid crystal molecules and the second optical compensation layer is formed by coating, the thickness of the optical film can be remarkably reduced, and a liquid crystal display to which this is applied This can greatly contribute to thinning of an image display device such as a device.

  In the present invention, “nx” is the refractive index in the direction in which the in-plane refractive index of each layer is maximized (ie, the slow axis direction), and “ny” is the slow axis in the plane of each layer. The refractive index in the vertical direction (that is, the fast axis direction), and “nz” means the refractive index in the thickness direction of each layer. Further, “ny = nz” means not only the case where ny and nz are exactly equal, but also the case where ny and nz are substantially equal. The term “substantially equal” is intended to include the case where ny and nz are different within a range that does not have a practical effect on the overall optical characteristics of the optical film. Further, the “Nz coefficient” is obtained by Nz = (nx−nz) / (nx−ny) using refractive indexes nx, ny, and nz measured with light having a wavelength of 590 nm at 23 ° C.

  Further, according to the present invention, it is possible to continuously rub a long plastic film by a roll-to-roll method, and thus it is possible to produce an optical film at a low cost. Further, according to the present invention, the backup roll mechanism that supports the lower surface of the conveyance belt that supports the plastic film is disposed directly below the rubbing roll and along a straight line that is substantially parallel to the rotation axis of the rubbing roll. Since the rotation axis of the rubbing roll is inclined from the direction perpendicular to the conveying direction of the conveyor belt, each backup roll is connected to the inclined rubbing roll via the plastic film and the conveyor belt. It will be arranged directly below. Furthermore, according to the present invention, each backup roll rotates along the conveyance direction of the conveyance belt (the conveyance direction of the plastic film), so that the rotation of each backup roll moves in the conveyance direction of the conveyance belt and thus the plastic film. There is no hindrance to the transport. Therefore, even if the pushing amount of the rubbing roll is increased while the rotation axis of the rubbing roll is inclined from the direction perpendicular to the conveying direction of the conveying belt, the flatness of the conveying belt is improved and it is difficult to cause looseness and the conveying. The rubbing process can be performed in a stable state without hindering the movement of the belt. As a result, uniform orientation characteristics can be imparted to the plastic film, and as a result, an optical film having uniform optical characteristics can be manufactured.

  Preferably, the first optical compensation layer functions as a half-wave plate, and the second optical compensation layer functions as a quarter-wave plate.

  In the present invention, the “half-wave plate” means an in-plane retardation value (= (nx−ny) × d (d: layer thickness) with respect to the wavelength of light (usually the visible light region). Thickness (nm))) is approximately ½, and linearly polarized light having a specific vibration direction is converted into linearly polarized light having a vibration direction orthogonal to the vibration direction of the linearly polarized light, It has a function of converting polarized light into left circularly polarized light (or left circularly polarized light into right circularly polarized light). In the present invention, the “¼ wavelength plate” means that the in-plane retardation value is about 1/4 with respect to the wavelength of light (usually in the visible light region). A function of converting linearly polarized light having a wavelength of 1 to circularly polarized light (or circularly polarized light to linearly polarized light).

  The optical film is suitably used for a liquid crystal display device having a vertical alignment (VA) mode liquid crystal cell.

  Preferably, the second optical compensation layer is formed of at least one polymer selected from the group consisting of polyimide, polyamide, polyetherketone, polyamideimide, and polyesterimide.

  Preferably, the backup roll mechanism includes a pedestal portion disposed along a straight line substantially parallel to the rotation axis of the rubbing roll, and a shaft support on the pedestal portion so as to be rotatable around a normal line of the surface of the conveyor belt. The plurality of backup rolls are pivotally supported by the plurality of support portions so as to be rotatable along the conveyance direction of the conveyance belt.

  According to such a preferable configuration, even if the rotating shaft of the rubbing roll is inclined from the direction perpendicular to the conveying direction of the conveying belt, the pedestal part constituting the backup roll mechanism is similarly inclined (that is, the inclined The pedestal is tilted so as to be along a straight line substantially parallel to the rotation axis of the rubbing roll, and is supported by the support portion (by the friction force applied from the lower surface of the conveyor belt) as the conveyor belt moves. The support portion pivotally supported by the pedestal portion naturally rotates so that the backup roll is rotated along the conveyance direction of the conveyance belt. In other words, even if the inclination angle of the rubbing roll is not fixed, even if the setting value of the inclination angle is changed, it is only necessary to change the pedestal portion to the same inclination angle as the rubbing roll, so that each backup roll is directly under the rubbing roll. It is possible to arrange and rotate along the conveying direction of the conveying belt.

  More preferably, the backup roll mechanism has the rubbing roll so that when the rotation shaft of the rubbing roll is inclined from a direction perpendicular to the conveying direction of the conveying belt, the pedestal portion is also inclined accordingly. And a connecting mechanism for connecting the pedestal part.

  According to such a preferable configuration, when the rotating shaft of the rubbing roll is inclined from the direction perpendicular to the conveying direction of the conveying belt, the rubbing roll and the pedestal portion are coupled so that the pedestal portion is also inclined accordingly. Since the connecting mechanism is provided, there is an advantage that the setting is extremely easy as compared with the configuration in which the rubbing roll and the backup roll mechanism (pedestal part) are individually inclined.

  In addition, it is preferable that the rotating shaft of the rubbing roll is inclined from more than 0 ° to 45 ° or less from the direction perpendicular to the plastic film conveying direction.

  Here, for the plurality of backup rolls, when the distance between the centers of adjacent backup rolls in the rotation axis direction is set to be greater than 200 mm, the flatness of the transport belt is lowered, resulting in uneven orientation. There is a risk of defects. On the other hand, when the center-to-center distance is set to be smaller than 60 mm, the width of the member that supports the backup roll is reduced, and the strength for stably holding the backup roll is reduced. To do. Therefore, in order to avoid the above problems reliably, the distance between the centers of the adjacent backup rolls in the rotation axis direction is preferably set to 60 mm or more and 200 mm or less, and preferably set to 70 mm or more and 150 mm or less. More preferred.

  Further, when the width of the plurality of backup rolls in the rotation axis direction is set to be smaller than 20 mm, there is a possibility that the conveyor belt is damaged by frictional heat. On the other hand, when the width is set to be larger than 150 mm, the backup roll may be disposed immediately below the rubbing roll when the rotation axis of the rubbing roll is inclined from the direction perpendicular to the conveying direction of the plastic film. As a result, the flatness of the conveying belt is lowered, and as a result, alignment unevenness may occur and appearance defects may occur. Therefore, in order to surely avoid the above problems, the width in the rotation axis direction of each of the plurality of backup rolls is preferably set to 20 mm or more and 150 mm or less, and more preferably set to 25 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.

  It is preferable that a raised cloth is wound around the rubbing roll. As the raised cloth, for example, any one of rayon, cotton, nylon, triacetate 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, a first optical compensation layer having a refractive index characteristic of nx> ny = nz, a refractive index characteristic of nx> ny> nz, and an Nz coefficient of 1. An optical film obtained by laminating a second optical compensation layer satisfying 2 ≦ Nz ≦ 2 can be obtained, and by arranging this in a liquid crystal cell, light leakage in black display of a liquid crystal display device can be satisfactorily prevented. Is possible. Further, even when the rotation axis of the rubbing roll is inclined from the direction perpendicular to the film conveyance direction, it is possible to produce an optical film having uniform optical characteristics at low cost. Specifically, it is difficult for foreign matters to adhere to the surface, and a good appearance of the optical film can be maintained. This is because the flatness of the conveyor belt is improved by arranging a plurality of backup rolls directly below the rubbing roll with the center-to-center distance in the rotation axis direction being a predetermined value.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

I. Configuration First optical element, a configuration example of an optical element comprising an optical film manufactured by the manufacturing method according to the present invention.

<Overall configuration of optical element>
FIG. 1 is a cross-sectional view illustrating a schematic configuration of an optical element including an optical film manufactured by the manufacturing method according to the present invention. FIG. 2 is an exploded perspective view for explaining the relationship between the absorption axis and the slow axis of each layer constituting the optical element shown in FIG. As shown in FIG. 1, the optical element 10 according to this embodiment includes a polarizer 11 and an optical film 200. The optical film 200 includes a substrate 12, a first optical compensation layer 13 formed on the substrate 12, and a second optical compensation layer 14 formed on the first optical compensation layer 13. The polarizer 11 is disposed on the substrate 12 side of the optical film 200.

  Except between the 1st optical compensation layer 13 and the base material 12, each layer which comprises the optical element 10 is laminated | stacked via arbitrary appropriate adhesive layers or adhesive bond layers (not shown). Practically, any appropriate protective layer (transparent protective film) 15 is laminated on the surface of the polarizer 11 on the side where the optical compensation layers 13 and 14 are not laminated.

  The first optical compensation layer 13 has a refractive index characteristic of nx> ny = nz. The second optical compensation layer 14 has a refractive index characteristic of nx> ny> nz, and the Nz coefficient satisfies 1.2 ≦ Nz ≦ 2.

  In the present embodiment, as shown in FIG. 2, the first optical compensation layer 13 is laminated so that the slow axis B forms a predetermined angle α with respect to the absorption axis A of the polarizer 11. . The angle α is set to + 17 ° ≦ α ≦ + 27 ° or −27 ° ≦ α ≦ −17 °, preferably + 19 ° ≦ α ≦ + 25 ° or −25 ° ≦ α ≦ −19 °, more preferably + 21 ° ≦ α ≦ + 24 ° or −24 ° ≦ α ≦ −21 °, most preferably + 22 ° ≦ α ≦ + 23 ° or −23 ° ≦ α ≦ −22 °. The second optical compensation layer 14 is laminated so that the slow axis C forms a predetermined angle β with respect to the absorption axis A of the polarizer 11. The angle β is + 85 ° ≦ β ≦ + 95 °, preferably + 87 ° ≦ β ≦ + 93 °, more preferably + 88 ° ≦ β ≦ + 92 °, and most preferably + 89 ° ≦ β ≦ + 91 °. Note that the positive and negative of α and β are positive in the counterclockwise direction with respect to the absorption axis A and negative in the clockwise direction. By laminating two specific optical compensation layers in a specific positional relationship as described above, a black color of a liquid crystal display device (particularly a reflective or transflective liquid crystal display device) having a VA mode liquid crystal cell is obtained. Light leakage during display can be remarkably prevented.

  The total thickness of the optical element 10 is preferably 40 to 150 μm, more preferably 40 to 130 μm, and most preferably 40 to 120 μm. According to the optical element 10 according to the present embodiment, light leakage in the liquid crystal display device can be satisfactorily prevented with only the two optical compensation layers 13 and 14. Furthermore, since the first optical compensation layer 13 is formed of liquid crystalline molecules as will be described later, the thickness for causing the first optical compensation layer 13 to function as a half-wave plate is markedly greater than in the past. Can be thinned. In addition, since the second optical compensation layer 14 is formed by applying a polymer material, the thickness for causing the second optical compensation layer 14 to function as a quarter-wave plate is markedly greater than in the past. Can be thinned. As a result, the optical element 10 according to the present embodiment can be remarkably reduced in overall thickness as compared with the conventional equivalent optical element, and the image display apparatus such as a liquid crystal display apparatus to which the optical element 10 is applied can be thinned. It can contribute greatly.

<Configuration of first optical compensation layer>
As described above, the first optical compensation layer 13 has a refractive index characteristic of nx> ny = nz. Preferably, the first optical compensation layer 13 functions as a half-wave plate. When the first optical compensation layer 13 functions as a half-wave plate, the wavelength dispersion characteristic of the second optical compensation layer 14 that functions as a quarter-wave plate (in particular, the in-plane retardation value is λ / 4 (λ: a wavelength range outside of the wavelength of light) is corrected appropriately. The in-plane retardation value Re [590] of the first optical compensation layer 13 is preferably 200 to 300 nm, more preferably 220 to 280 nm, and most preferably 230 to 270 nm. Re [590] is an in-plane retardation value of the optical compensation layer measured with light having a wavelength of 590 nm at 23 ° C. (= (nx−ny) × d (d: thickness of the optical compensation layer (nm))) Means.

  The thickness of the first optical compensation layer 13 can be set so that it can function most appropriately as a half-wave plate. In other words, the thickness of the first optical compensation layer 13 may be set so as to obtain a desired in-plane retardation value. Specifically, the thickness of the first optical compensation layer 13 is preferably 0.5 to 5 μm, more preferably 1 to 4 μm, and most preferably 1.5 to 3 μm.

  As a material for forming the first optical compensation layer 13, liquid crystal molecules are used. The liquid crystal phase is preferably a liquid crystal molecule having a nematic phase. By using liquid crystal molecules, the difference between nx and ny of the first optical compensation layer 13 can be significantly increased as compared with the non-liquid crystal material. As a result, the thickness of the first optical compensation layer 13 for obtaining a desired in-plane retardation value can be significantly reduced. As such a liquid crystalline molecule, a liquid crystal polymer, a liquid crystal prepolymer, a liquid crystal monomer, or the like is appropriately used. You may use combining these. The lyotropic or thermotropic mechanism of liquid crystal molecules may be used. The alignment state of the liquid crystal is preferably homogeneous alignment.

  When the liquid crystalline molecule forming the first optical compensation layer 13 is a liquid crystal monomer, for example, a polymerizable monomer or a crosslinkable monomer is preferable. This is because the alignment state of the liquid crystalline molecules can be fixed by polymerizing or crosslinking the polymerizable monomer or the crosslinkable monomer. If the liquid crystal monomers (polymerizable monomer or crosslinkable monomer) are polymerized or crosslinked after the liquid crystal monomer is aligned, the alignment state can be fixed. Here, a polymer is formed by polymerization and a three-dimensional network structure is formed by crosslinking, but these are non-liquid crystalline. Therefore, the formed first optical compensation layer 13 does not cause a transition to a liquid crystal phase, a glass phase, or a crystal phase due to a temperature change, which is characteristic of a liquid crystal compound. As a result, the first optical compensation layer 13 becomes an optical compensation layer having excellent stability that is not affected by temperature changes. The polymerizable monomer and the crosslinkable monomer may be used in combination.

As the liquid crystal monomer, for example, a monomer represented by any of the following chemical formulas (1) to (16) can be selected.

<Configuration of Second Optical Compensation Layer>
As described above, the second optical compensation layer 14 has a refractive index characteristic of nx>ny> nz. That is, the second optical compensation layer 14 is a biaxial optical compensation layer. Preferably, the second optical compensation layer 14 functions as a quarter wavelength plate. In order to achieve sufficient visual compensation at all wavelengths, it is preferable that the wavelength dispersion of the second optical compensation layer 14 exhibits the same wavelength dispersion as that of the liquid crystal in the liquid crystal cell to be applied. By correcting the chromatic dispersion characteristics of the second optical compensation layer 14 functioning as a quarter-wave plate by the optical characteristics of the first optical compensation layer 13 functioning as a half-wave plate, a wide wavelength range is obtained. The circularly polarized light function can be exhibited. The in-plane retardation value Re [590] of the second optical compensation layer 14 is preferably 90 to 160 nm, more preferably 100 to 150 nm, and most preferably 110 to 140 nm. Further, the thickness direction retardation value Rth [590] of the second optical compensation layer is preferably 80 to 150 nm, more preferably 90 to 140 nm, and most preferably 100 to 130 nm. Rth [590] is a retardation value in the thickness direction of the optical compensation layer measured with light having a wavelength of 590 nm at 23 ° C. (= (nx−nz) × d (d: thickness of the optical compensation layer (nm))) Means.

  The Nz coefficient of the second optical compensation layer 14 satisfies 1.2 ≦ Nz ≦ 2. Preferably 1.3 ≦ Nz ≦ 1.8, more preferably 1.4 ≦ Nz ≦ 1.7. By adjusting the Nz coefficient of the second optical compensation layer 14 to the above range, the optical compensation and the axis for the VA mode liquid crystal cell can be performed while the second optical compensation layer 14 functions as a quarter wavelength plate. The compensation function can also be exhibited, and the contrast of the liquid crystal display device can be improved.

  The thickness of the second optical compensation layer 14 can be set so that it can function most appropriately as a quarter-wave plate. In other words, the thickness of the second optical compensation layer 14 may be set so as to obtain a desired in-plane retardation value. Specifically, the thickness of the second optical compensation layer 14 is preferably 1 to 10 μm, more preferably 1.2 to 6 μm, and most preferably 1.4 to 3 μm. This thickness is much thinner than that which can be realized with a conventional biaxial quarter-wave plate. As will be described later, this can be achieved by forming the second optical compensation layer 14 by subjecting the polymer material applied to the base material to specific heating and stretching treatments.

  As a material for forming the second optical compensation layer 14, any appropriate material can be used as long as the above optical characteristics can be obtained. For example, as such a material, a non-liquid crystalline material can be mentioned, and a non-liquid crystalline polymer is preferable. Unlike a liquid crystalline material, a non-liquid crystalline material can form a film exhibiting optical uniaxiality of nx = ny> nz depending on its own property regardless of the orientation of a substrate. As a result, it is possible to use not only an oriented substrate but also an unoriented substrate. Moreover, when using an unoriented base material, the process of coating an orientation film on the surface, the process of laminating an orientation film, etc. can be omitted.

  Examples of the non-liquid crystalline polymer include polyamide and polyimide as described in paragraphs 0018 to 0072 of JP-A No. 2004-46065 because they are excellent in heat resistance, chemical resistance, transparency, and rigidity. Polymers such as polyester, polyetherketone, polyamideimide and polyesterimide are preferred. Any one kind of these polymers may be used alone, or a mixture of two or more kinds having different functional groups such as a mixture of polyaryl ether ketone and polyamide may be used. . Among such polymers, it is particularly preferable to use polyimide because of its high transparency, high orientation, and high stretchability. Since polyimide has high heat resistance and small thermal expansion, the second optical compensation layer 14 formed from polyimide has the advantage that the generated thermal unevenness is small. In addition, since polyimide has a so-called positive dispersion characteristic in which the retardation value increases as the wavelength becomes shorter, and is close to the wavelength dispersion of the VA mode liquid crystal cell, it is excellent in optical compensation of the VA mode liquid crystal cell.

  The molecular weight of the polymer is not particularly limited, but for example, the weight average molecular weight (Mw) is preferably in the range of 1,000 to 1,000,000, more preferably in the range of 2000 to 500,000.

<Configuration of polarizer>
Any appropriate polarizer may be used as the polarizer 11 depending on the purpose. For example, dichroic substances such as iodine and dichroic dyes are adsorbed on hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films. And a polyene-based oriented film such as a uniaxially stretched product, a polyvinyl alcohol dehydrated product or a polyvinyl chloride dehydrochlorinated product. Among these, a polarizer obtained by adsorbing a dichroic substance such as iodine on a polyvinyl alcohol film and uniaxially stretching is particularly preferable because of its high polarization dichroic ratio. The thickness of these polarizers is not particularly limited, but is generally about 1 to 80 μm.

  A polarizer obtained by uniaxially stretching iodine by adsorbing iodine to a polyvinyl alcohol film is prepared by, for example, dyeing polyvinyl alcohol by immersing it in an aqueous solution of iodine and stretching it 3 to 7 times the original length. Can do. If necessary, it may contain boric acid, zinc sulfate, zinc chloride or the like, or may be immersed in an aqueous solution such as potassium iodide. Further, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing.

  By washing the polyvinyl alcohol film with water, not only can the surface of the polyvinyl alcohol film be cleaned and the anti-blocking agent can be washed, but the polyvinyl alcohol film can also be swollen to prevent unevenness such as uneven coloring. can get. Stretching may be performed after dyeing with iodine, may be stretched while dyeing, or may be dyed with iodine after stretching. It can be stretched in an aqueous solution such as boric acid or potassium iodide or in an aqueous solution.

<Configuration of base material and protective layer>
As the base material 12, the surface can be rubbed or the alignment film formed on the surface can be rubbed so that the liquid crystal molecules applied to the surface can be aligned as described later. In addition, the material is not particularly limited as long as it can be used as the protective layer of the polarizer 11. As the protective layer 15, any appropriate film that can be used as a protective layer of the polarizer 11 can be used. Preferably, the base material 12 and the protective layer 15 are transparent protective films.

  Specific examples of the material that is the main component of such a film include cellulose resins such as triacetylcellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, Examples thereof include transparent resins such as polysulfone, polystyrene, polynorbornene, polyolefin, acrylic, and acetate. In addition, thermosetting resins such as acrylic, urethane, acrylic urethane, epoxy, and silicone, or ultraviolet curable resins are also included. In addition to this, for example, a glassy polymer such as a siloxane polymer is also included. Moreover, the polymer film as described in Unexamined-Japanese-Patent No. 2001-343529 (WO01 / 37007) can also be used. As a material of this polymer film, for example, a resin containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in the side chain The composition can be used, and examples thereof include a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer. The polymer film may be obtained by, for example, extruding the resin composition. As a material of the base material 12 and the protective layer 15, TAC, polyimide resin, polyvinyl alcohol resin, and glassy polymer are preferable, and TAC is more preferable.

  The substrate 12 and the protective layer 15 are preferably transparent and have no color. Specifically, the thickness direction retardation value Rth [550] is preferably −90 nm to +90 nm, more preferably −80 nm to +80 nm, and most preferably −70 nm to +70 nm.

  As thickness of the base material 12 and the protective layer 15, as long as said preferable thickness direction retardation value is obtained, it can be set as arbitrary appropriate thicknesses. Specifically, the thickness of the base material 12 and the protective layer 15 is preferably 5 mm or less, more preferably 1 mm or less, particularly preferably 1 to 500 μm, and most preferably 5 to 150 μm.

  The base material 12 and the protective layer 15 may be the same or different. The protective layer 15 is subjected to a hard coat process, an antireflection process, an antisticking process, an antiglare process, and the like as necessary.

<Other components of optical element>
The optical element 10 according to the present embodiment may be configured to further include another optical layer. As such another optical layer, any appropriate optical layer may be employed depending on the purpose and the type of image display device such as a liquid crystal display device to be applied. Specific examples include a liquid crystal film, a light scattering film, a diffraction film, an optical compensation layer (retardation film) other than the first and second optical compensation layers 13 and 14 described above, and the like.

  The optical element 10 according to the present embodiment may be configured to further include a pressure-sensitive adhesive layer or an adhesive layer as an outermost layer on at least one side. Thus, by providing a pressure-sensitive adhesive layer or an adhesive layer as the outermost layer, for example, lamination with another member (for example, a liquid crystal cell) is facilitated, and the optical element 10 is peeled off from the other member. Can be prevented. Any appropriate material can be used as a material for forming the pressure-sensitive adhesive layer and the adhesive layer. Preferably, a material excellent in hygroscopicity and heat resistance is used. This is because foaming and peeling due to moisture absorption, deterioration of optical characteristics due to a difference in thermal expansion, and warpage of the liquid crystal cell can be prevented.

  Practically, the surface of the pressure-sensitive adhesive layer or adhesive layer is covered with any appropriate separator until the optical element 10 is actually used to prevent contamination. The separator is formed by, for example, a method of providing a release coat with a release agent such as silicone-based, long-chain alkyl-based, fluorine-based, molybdenum sulfide, or the like on any appropriate film.

  Each layer constituting the optical element 10 is provided with an ultraviolet absorbing ability by, for example, treatment with an ultraviolet absorber such as a salicylic acid ester compound, a benzophenone compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound. It may be what you did.

II. Method for Manufacturing Optical Element Next, a method for manufacturing the optical element 10 having the above-described configuration will be described.

<Outline of manufacturing method>
The manufacturing method of the optical element 10 according to the present embodiment is a rubbing roll in which the surface of a long plastic film (which will eventually become the base material 12) is inclined from the direction perpendicular to the plastic film conveyance direction. A rubbing treatment step for rubbing, and applying a liquid crystalline molecule on the surface of the plastic film that has undergone the rubbing treatment step, fixing the applied liquid crystalline molecule, and then applying the first optical compensation layer 13 on the plastic film. And a second optical compensation layer forming step of laminating a second optical compensation layer 14 formed by coating on the first optical compensation layer 13. . The optical film 200 is manufactured through the above steps.

  Furthermore, the manufacturing method of the optical element 10 according to the present embodiment includes a step of laminating the polarizer 11 on the surface of the plastic film (base material 12) that is not subjected to the rubbing process, an optical compensation layer 13 of the polarizer 11, And a step of laminating the protective layer 15 on the surface on which the 14 is not laminated.

  In addition, the order of each said process can be changed suitably. Hereinafter, details of each process will be described in detail.

<Plastic film rubbing process>
FIG. 3 is a front view showing a schematic configuration of a rubbing processing apparatus for performing the rubbing processing step. 4 is a diagram showing a schematic configuration of the backup roll mechanism shown in FIG. 3. FIG. 4 (a) is a plan view, FIG. 4 (b) is a perspective view in the vicinity of the backup roll, and FIG. The figure seen from the conveyance direction of a film is shown, respectively. As shown in FIG. 3, the rubbing treatment apparatus 100 according to the present embodiment has an endless track that is installed between the driving rolls 1 and 2 and the driving rolls 1 and 2 and supports and transports a long plastic film F. The conveyor belt 3, the rubbing roll 4 disposed above and below the conveyor belt 3 so as to be movable up and down, and the lower surface of the conveyor belt 3 that supports the plastic film F (which eventually becomes the substrate 12) are supported. And a backup roll mechanism 5. 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. In addition, the tension applied to the conveyor belt 3 is preferably 0.5 to 20 kgf / mm 2, more preferably, considering the tension strength of the conveyor belt 3 while preventing slack of the conveyor belt 3. 2 to 15 kg weight / mm 2.

  The rubbing roll 4 has a brushed cloth 4a 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, triacetate, or a mixture thereof can be applied as the raised cloth 4a. The rotation axis of the rubbing roll 4 according to the present embodiment is inclined from a direction perpendicular to the conveyance direction of the plastic film F (the direction indicated by the arrow A in FIG. 3) (for example, the inclination angle exceeds 0 ° and is 45 ° or less). ), That is, an arbitrary axial angle with respect to the long side of the plastic film F can be set. Moreover, the rotation direction of the rubbing roll 4 can be appropriately selected according to the conditions of the rubbing treatment. The outer diameter of the rubbing roll 4 (including the raised cloth 4a) is preferably set to 130 mm to 170 mm (more preferably 140 mm to 160 mm).

  The rubbing direction (orientation direction) of the plastic film F by the rubbing roll 4 is set to a predetermined angle θ with respect to the absorption axis A (see FIG. 2) of the polarizer 11 when the plastic film F and the polarizer 11 are laminated. It is assumed to be the direction to be formed. The rubbing direction of the plastic film F is substantially the same as the direction of the slow axis B (see FIG. 2) of the first optical compensation layer 13 formed on the surface of the plastic film F. Therefore, the predetermined angle θ formed between the rubbing direction of the plastic film F and the absorption axis A of the polarizer 11 is + 17 ° ≦ θ ≦ + 27 ° or the angle α formed between the slow axis B and the absorption axis A, or −27 ° ≦ θ ≦ −17 °, preferably + 19 ° ≦ θ ≦ + 25 ° or −25 ° ≦ θ ≦ −19 °, more preferably + 21 ° ≦ θ ≦ + 24 ° or −24 ° ≦ θ ≦ −. 21 °, most preferably + 22 ° ≦ θ ≦ + 23 ° or −23 ° ≦ θ ≦ −22 °.

  When the polarizer 11 is obtained by uniaxially stretching a polymer film on which a dichroic substance is adsorbed, the stretching direction coincides with the direction of the absorption axis A. And when mass-producing the polarizer 11, it is common to prepare a long polymer film and to perform a extending | stretching process continuously in the longitudinal direction. For this reason, when laminating (bonding) a long polarizer and a long plastic film F, the longitudinal direction of the two substantially coincides with the direction of the absorption axis A of the polarizer. Therefore, the angle θ formed between the rubbing direction of the plastic film F and the absorption axis A of the polarizer 11 substantially coincides with the angle formed between the rubbing direction of the plastic film F and the longitudinal direction of the plastic film F. What is necessary is just to set the inclination-angle of the rotating shaft of the rubbing roll 4 so that the rubbing direction of F and the longitudinal direction of the plastic film F may form the said predetermined angle (theta).

  As shown in FIG. 4, the backup roll mechanism 5 includes a plurality of backup rolls 51 that respectively rotate along the conveyance direction of the conveyance belt 3 (the direction indicated by the arrow A in FIG. 4A). Each backup roll 51 is disposed directly below the rubbing roll 4 and along a straight line substantially parallel to the rotation axis of the rubbing roll 4.

  As described above, the backup roll mechanism 5 that supports the lower surface of the conveyance belt 3 that supports the plastic film F is disposed directly below the rubbing roll 4 and along a straight line that is substantially parallel to the rotation axis of the rubbing roll 4. When the rotation axis of the rubbing roll 4 is inclined from the direction perpendicular to the conveying direction of the conveying belt (for example, the straight line C1 in FIG. 4A is the rotation of the rubbing roll 4). Even in the case of a shaft), each backup roll 51 is disposed directly under the inclined rubbing roll 4 via the plastic film F and the conveyor belt 3. Furthermore, since each backup roll 51 rotates along the conveyance direction of the conveyance belt 3 (the conveyance direction of the plastic film F), the rotation of each backup roll 51 moves in the conveyance direction of the conveyance belt 3 and consequently the plastic film F. There is no hindrance to the transport. Therefore, even if the pushing amount of the rubbing roll 4 is increased in a state where the rotation axis of the rubbing roll 4 is inclined from the direction perpendicular to the conveying direction of the conveying belt 3, the flatness of the conveying belt 3 is improved and the slack is reduced. The rubbing process can be performed in a stable state without being easily generated and without disturbing the movement of the conveyor belt 3. As a result, uniform orientation characteristics can be imparted to the plastic film F, and as a result, the optical film 200 and the optical element 10 having uniform optical characteristics can be manufactured.

  As a preferable configuration, the backup roll mechanism 5 according to the present embodiment can rotate around a pedestal portion 52 disposed along a straight line substantially parallel to the rotation axis of the rubbing roll 4 and the normal line of the surface of the conveyor belt 3. A plurality of support portions 53 pivotally supported on the pedestal portion 52 are further provided, and each backup roll 51 is pivotally supported by each support portion 53 so as to be rotatable along the transport direction of the transport belt 3. If it demonstrates more concretely, the support part 53 which concerns on this embodiment is pivotally supported by the base part 53 with the shaft member 54, and the periphery of the shaft member 54 is made rotatable. Further, the backup roll 51 according to the present embodiment is pivotally supported on the support portion 53 by the shaft member 55 and is rotatable around the shaft member 55.

  According to such a preferable configuration, even if the rotation axis of the rubbing roll 4 is inclined from the direction perpendicular to the conveyance direction of the conveyance belt 3 (the direction of the straight line C0 in FIG. 4A), the backup roll mechanism 5 is provided. By inclining the pedestal 52 in the same manner (that is, by tilting the pedestal 52 so as to follow a straight line substantially parallel to the rotation axis of the inclined rubbing roll), the movement of the conveyor belt 3 ( Support supported by the pedestal 52 so that the backup roll 51 supported by the support 53 is rotated along the direction of conveyance of the conveyance belt 3 (by a frictional force applied from the lower surface of the conveyance belt 3). The part 53 rotates naturally. In other words, even if the inclination angle of the rubbing roll 4 is not fixed, and the setting value of the inclination angle is changed, the backup roll 51 is rubbed only by changing the pedestal 52 to the same inclination angle as the rubbing roll 4. It is possible to make a state of being arranged immediately below the roll 4 and rotating along the conveying direction of the conveying belt 3.

  Further, as shown in FIG. 4C, the backup roll mechanism 5 according to the present embodiment has a preferable configuration in which the rotation axis of the rubbing roll 4 is inclined from the direction perpendicular to the conveyance direction of the conveyance belt 3. In addition, a coupling mechanism 56 that couples the rubbing roll 4 and the pedestal portion 52 so as to incline the pedestal portion 52 accordingly. More specifically, the coupling mechanism 56 according to the present embodiment supports the rubbing roll 4 so as to be rotatable around the rotation axis and to be vertically movable, and to support the pedestal 52. The frame is shaped like a letter, and can be rotated in the direction of the arrow B in FIG. 4C by a motor M attached to the top of the frame. When the coupling mechanism 56 is rotated in the direction of the arrow B in FIG. 4C by the motor M, the rubbing roll 4 and the pedestal portion 52 supported by the coupling mechanism 56 are rotated (inclined) by the same angle in the same direction. ). Therefore, the setting becomes extremely easy as compared with the configuration in which the rubbing roll 4 and the pedestal portion 52 are individually inclined. In the present embodiment, the configuration in which the coupling mechanism 56 is automatically rotated using the motor M has been described. However, the present invention is not limited to this, and a configuration in which the coupling mechanism 56 is manually rotated is employed. Is also possible.

  In the present embodiment, as a preferable configuration, the distance L1 between the centers of adjacent backup rolls 51 in the rotation axis direction (see FIG. 4A) is 60 mm or more and 200 mm or less (more preferably, 70 mm or more and 150 mm or less). Set to Further, the width L2 (see FIG. 4A) of each backup roll 51 in the rotation axis direction is set to 20 mm to 150 mm (more preferably 25 mm to 70 mm). In addition, the separation distance L3 (see FIG. 4A) between the adjacent backup rolls 51 is 40 mm or more and 60 mm or less (more preferably 45 mm or more and 55 mm or less), and the outer diameter of each backup roll 51 is 70 mm or more and 110 mm or less ( More preferably, the length of the pedestal portion 52 is set to 1500 mm or more and 2500 mm or less (however, a value larger than the width of the conveyor belt 3).

  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 driving the drive rolls 1 and 2 to rotate, the conveyance belt 3 moves in the direction indicated by the arrow C in FIG. 3, and accordingly, the plastic film F is also conveyed together with the conveyance belt 3 and rubbed by the rubbing roll 4. Processing will be performed.

  In addition, as the plastic film F to which the manufacturing method according to the present embodiment is applied, the surface of the plastic film F is rubbed or the alignment film formed on the surface is rubbed as described above as the configuration of the substrate 12. As a result, the material capable of aligning liquid crystal molecules coated on the surface is imparted, and the material is not particularly limited as long as it can be used as a protective layer of the polarizer 11.

  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 allowance coating, and dip coating.

  In general, the conveying speed of the plastic film F is 1 to 50 m / min, preferably 1 to 10 m / min, and the rotation speed of the rubbing roll 4 is 1 to 3000 rpm, Is in the range of 500 to 2000 rpm, and the pushing amount of the rubbing roll 4 is 100 to 2000 μm, preferably 100 to 1000 μm. The “pushing amount of the rubbing roll 4” means that when the position of the rubbing roll 4 is changed with respect to the surface of the plastic film F, the bristles of the raised cloth wound around the rubbing roll 4 are the plastic film first. The position in contact with the F surface is defined as the origin (0 point), which means the amount of pressing of the rubbing roll 4 from the origin toward the plastic film F (position variation).

<First optical compensation layer forming step>
The surface of the plastic film F or the alignment film surface subjected to the rubbing treatment as described above is coated with liquid crystalline molecules, and the coated liquid crystalline molecules are cured or solidified so that the first optical compensation is performed. Layer 13 is formed.

  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, as described above, a liquid crystal polymer, a liquid crystal prepolymer, a liquid crystal monomer, and the like are appropriately used.

  When using the liquid crystal polymer, after applying the liquid crystal polymer solution to the surface of the plastic film F or the alignment film surface, heating until it reaches the temperature range showing the liquid crystal phase and drying it, the liquid crystal phase remains in the state showing By rapidly cooling to room temperature, a liquid crystal state exhibiting optical anisotropy can be fixed.

  When using a liquid crystal prepolymer or a liquid crystal monomer, these solutions are applied to the surface of the plastic film F or the surface of the alignment film, and then heated until the temperature is higher than the temperature range showing the liquid crystal phase, and then dried to show the liquid crystal phase. It is possible to fix the liquid crystal state exhibiting optical anisotropy by cooling to a state temperature and crosslinking by exposing to ultraviolet rays or the like.

  When a liquid crystal polymer is used as the liquid crystal molecule, 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 solution can be prepared, for example, by dissolving and dispersing the liquid crystal monomer represented by any one of the above-described chemical formulas (1) to (16) 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, mesitylene, methoxybenzene, 1,2-dimethoxybenzene, acetone , Ketone solvents such as methyl ethyl ketone (MEK), methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone, N-methyl-2-pyrrolidone, ethyl acetate, butyl acetate, Ester solvents such as propyl acid, 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 Alcohol solvents, amide solvents such as dimethylformamide and 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, ethyl acetate 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 the coating liquid of the liquid crystal monomer solution is applied to the surface of the plastic film F or the alignment film is, for example, the type of the liquid crystal monomer to be used, specifically the temperature at which the liquid crystal monomer exhibits liquid crystallinity. Although it can determine suitably according to it, 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 flat 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.

  As described above, the liquid crystal molecules are applied to the surface of the plastic film F or the alignment film surface, and the applied liquid crystal molecules are cured or solidified, whereby liquid crystals are aligned along the rubbing direction of the plastic film F. Since the sex molecules are oriented, the direction of the slow axis B (see FIG. 2) of the formed first optical compensation layer 13 is substantially the same as the rubbing direction of the plastic film F.

<Lamination process of polarizer and protective layer>
Lamination of the polarizer 11 and the protective layer (transparent protective film) 15 on the surface of the plastic film F (base material 12) that is not subjected to the rubbing treatment is optional in the method for manufacturing the optical element 10 according to this embodiment. Can be implemented at any time. For example, lamination | stacking of the polarizer 11 and the protective layer 15 can be implemented at the time of following (1)-(4).
(1) Before the rubbing treatment step The polarizer 11 and the protective layer 15 are laminated in advance on the plastic film F (plastic film F before the rubbing treatment). And the rubbing process is given to the surface at the side of the plastic film F of the laminated body which consists of the protective layer 15 / polarizer 11 / plastic film F.
(2) Between the rubbing treatment step and the first optical compensation layer forming step After the rubbing treatment step is performed on the plastic film F, the protective layer 15 and the polarizer are formed on the surface of the plastic film F on which the rubbing treatment is not performed. 11 are stacked. Then, the first optical compensation layer 13 is formed on the surface of the laminate made of the protective layer 15 / polarizer 11 / plastic film F on the plastic film F side.
(3) Between the first optical compensation layer forming step and the second optical compensation layer forming step After the rubbing treatment step is performed on the plastic film F, the first surface is applied to the surface of the plastic film F on which the rubbing treatment is performed. The optical compensation layer 13 is formed. And the protective layer 15 and the polarizer 11 are laminated | stacked on the surface at the side of the plastic film F of the laminated body which consists of a plastic film F / 1st optical compensation layer 13. FIG. Further, the second optical compensation layer 14 is formed on the surface of the laminate composed of the protective layer 15 / polarizer 11 / plastic film F / first optical compensation layer 13 on the first optical compensation layer 13 side.
(4) After the second optical compensation layer forming step After forming a laminate composed of the plastic film F / first optical compensation layer 13 / second optical compensation layer 14, the plastic film F side of the laminate is formed. A protective layer 15 and a polarizer 11 are laminated on the surface.

  As a method of laminating the polarizer 11 and the protective layer 15, any appropriate laminating method (for example, adhesion) can be used. Adhesion is performed using any suitable adhesive or adhesive. What is necessary is just to select suitably the kind of adhesive agent or an adhesive according to the kind of to-be-adhered body (plastic film F, polarizer 11, protective layer 15). Specific examples of the adhesive include polymer adhesives such as acrylic, vinyl alcohol, silicone, polyester, polyurethane, and polyether, isocyanate adhesives, rubber adhesives, and the like. Specific examples of the pressure sensitive adhesive include acrylic, vinyl alcohol, silicone, polyester, polyurethane, polyether, isocyanate, and rubber pressure sensitive adhesives.

  According to the manufacturing method according to the present embodiment, as described above, the slow axis B of the first optical compensation layer 13 is adjusted by adjusting the inclination angle of the rubbing roll 4 in the rubbing process of the plastic film F. Since it can set, the polarizer 11 can use the elongate polarizing film extended | stretched to the longitudinal direction (namely, which has the absorption axis A in a longitudinal direction). That is, a long plastic film F that has been rubbed so that a rubbing direction (orientation direction) forms a predetermined angle with respect to the longitudinal direction and a long polarizing film are aligned in the longitudinal direction. , Can be bonded continuously in a roll-to-roll manner. Therefore, the optical element 10 can be obtained with extremely excellent production efficiency. Furthermore, according to the manufacturing method which concerns on this embodiment, it is not necessary to cut out and laminate the plastic film F and the polarizer (polarizing film) 11 in the diagonal direction with respect to the longitudinal direction. For this reason, in each cut-out film, it is hard to produce dispersion | variation in the orientation direction and the direction of an absorption axis, and the optical element 10 with few dispersion | variation in quality between products as a result is obtained. Furthermore, since no waste is generated by cutting, the optical element 10 can be obtained at low cost, and the manufacture of the large optical element 10 is facilitated.

  As another embodiment, the first optical compensation layer is formed on the protective layer 15 ′ of the long laminate composed of the protective layer 15 / polarizer 11 / protective layer 15 ′ via an adhesive or an adhesive. 13 may be transferred from the plastic film F.

<Second optical compensation layer forming step>
In this step, the second optical compensation layer 14 formed by coating is laminated on the first optical compensation layer 13 formed as described above. In this step, first, a material for forming the second optical compensation layer 14 (specifically, a non-liquid crystalline material as described above is used. Hereinafter, the “optical compensation layer forming material” is appropriately referred to). The containing coating liquid is applied to the base sheet. Any appropriate method can be adopted as the coating method. Specific examples of the coating method include spin coating, roll coating, flow coating, printing, dip coating, casting film formation, bar coating, and gravure printing.

  As the concentration of the optical compensation layer forming material in the coating liquid, any appropriate concentration can be adopted as long as the second optical compensation layer 14 having the above-described configuration is obtained and can be applied. . For example, the coating liquid preferably contains 5 to 50 parts by weight, more preferably 10 to 40 parts by weight of the optical compensation layer forming material with respect to 100 parts by weight of the solvent. A coating solution having such a concentration range has a viscosity that allows easy coating. What is necessary is just to select the solvent used for the said coating liquid suitably according to the kind of optical compensation layer forming material. Specific examples of the solvent that can be used include the same solvents as those used in the coating liquid for forming the first optical compensation layer 13 described above. The coating liquid may further contain various additives such as a stabilizer, a plasticizer, and metals as necessary. The coating amount of the coating solution is such that the second optical compensation layer 14 can function properly as a quarter-wave plate (as described above, preferably 1 to 10 μm, more preferably 1.2). To 6 μm, most preferably 1.4 to 3 μm).

  Further, the coating liquid may further contain a resin different from the optical compensation layer forming material as long as the optical characteristics of the obtained second optical compensation layer 14 are appropriate. Examples of such resins include various general-purpose resins, engineering plastics, thermoplastic resins, and thermosetting resins. By using such a resin in combination, it is possible to form the second optical compensation layer 14 having appropriate mechanical strength and durability according to the purpose.

  Any appropriate base material sheet can be used as the base material sheet on which the coating liquid is applied as long as an appropriate second optical compensation layer 14 is obtained. Typically, the base sheet is made of a polyester polymer such as polyethylene terephthalate or polyethylene naphthalate, a cellulose polymer such as diacetyl cellulose or triacetyl cellulose, a polycarbonate polymer, an acrylic polymer such as polymethyl methacrylate, polystyrene, Styrene polymers such as acrylonitrile / styrene copolymers, polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, olefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amides such as nylon and aromatic polyamides Polymer, imide polymer, sulfone polymer, polyethersulfone polymer, polyetheretherketone polymer, polyphenylene sulfide polymer Mer, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene-based polymer, formed from an epoxy-based polymer, or a mixture thereof. In particular, polyethylene terephthalate is preferable.

  The base sheet is subjected to stretching treatment, recrystallization treatment, and the like as necessary. The thickness of the base sheet is preferably 20 to 100 μm, more preferably 30 to 90 μm, and most preferably 30 to 80 μm. By having a thickness in such a range, the strength to favorably support the very thin second optical compensation layer 14 in the transfer step described later is provided, and operability such as slipping property and roll running property is also provided. Maintained properly.

  Next, the coating film of the solution of the optical compensation layer forming material formed on the substrate sheet is dried to form a polymer layer. This polymer layer finally becomes the second optical compensation layer 14. Any appropriate method (for example, natural drying, heat drying, air drying) can be used as the drying method. The appropriate drying temperature varies depending on the type of the optical compensation layer forming material, the type of solvent, the optical characteristics of the target second optical compensation layer 14, and the like. The drying temperature is preferably 20 to 400 ° C, more preferably 60 to 300 ° C, and most preferably 65 to 250 ° C. The drying time is preferably 0.5 to 200 minutes, more preferably 1 to 120 minutes, and most preferably 5 to 100 minutes. Drying may be performed at a constant temperature or may be performed while changing the temperature continuously or stepwise.

  Next, the polymer layer obtained as described above is heated and stretched together with the base sheet (that is, the polymer layer and the base sheet are integrated), and the second optical compensation layer 14 is formed on the base sheet. Form. Any appropriate method (for example, fixed end stretching or free end stretching) can be employed as the stretching method. The draw ratio is preferably 1.2 to 3.0 times, more preferably 1.3 to 2.9 times, most preferably with respect to the length of the integrated polymer layer and the base sheet before stretching. It is set to 1.3 to 2.8 times. When the draw ratio is in such a range, the above-described desired Nz coefficient can be obtained in the second optical compensation layer 14. The stretching temperature is preferably 120 to 200 ° C, more preferably 130 to 190 ° C, and most preferably 135 to 180 ° C. By setting the stretching temperature in such a range, the optical characteristics of the obtained second optical compensation layer 14 can be stably controlled even when a stretching process is performed at an extremely large stretching ratio.

  The stretching direction may be set according to the direction of the slow axis C (see FIG. 2) desired for the second optical compensation layer 14. Here, as described above, the direction of the slow axis B (see FIG. 2) of the first optical compensation layer 13 is set to + 21 ° ≦ α ≦ + 24 with respect to the absorption axis A of the polarizer 11 (see FIG. 2). In order to obtain desired optical characteristics when the angle α is set to ° or −24 ° ≦ α ≦ −21 °, the slow axis C of the second optical compensation layer 14 and the absorption axis of the polarizer 11 are obtained. It has been found that A may be substantially orthogonal. Since the direction of the slow axis C corresponds to the stretching direction of the polymer layer and the substrate sheet, the stretching of the polymer layer and the substrate sheet is performed in the width direction (the direction orthogonal to the longitudinal direction. (Orthogonal direction). That is, a long polarizing film stretched in the longitudinal direction (that is, having an absorption axis A in the longitudinal direction) is used as the polarizer 11, and this long polarizing film, a long polymer layer, and a base sheet are used. Are aligned with each other in the longitudinal direction, the slow axis C of the second optical compensation layer 14 and the absorption axis of the polarizer 11 are obtained by stretching the polymer layer and the base sheet in the width direction. A is substantially orthogonal to A. Thereby, in order to make the slow axis C of the 2nd optical compensation layer 14 orthogonally cross with the absorption axis A of the polarizer 11, it is not necessary to cut out a polymer layer and a base material sheet in the diagonal direction with respect to a longitudinal direction, and roll -Manufacturing efficiency can be increased because the two-roll method allows continuous bonding.

  Next, the second optical compensation layer 14 formed on the base sheet is transferred to the surface of the first optical compensation layer 13. The transfer method is not particularly limited. For example, the transfer is performed by bonding the second optical compensation layer 14 supported on the base sheet to the first optical compensation layer 13 via an adhesive. A typical example of the adhesive is a curable adhesive. Typical examples of the curable adhesive include a photocurable adhesive such as an ultraviolet curable adhesive, a moisture curable adhesive, and a thermosetting adhesive. Specific examples of the thermosetting adhesive include thermosetting resin adhesives such as urethane resin, epoxy resin, isocyanate resin, and polyimide resin. Specific examples of the moisture curable adhesive include isocyanate resin-based moisture curable adhesive. Moisture curable adhesives cure by reacting with moisture in the air, adsorbed water on the surface of the adherend, active hydrogen groups such as hydroxyl groups and carboxyl groups, and so on. It can be cured and has excellent operability. Furthermore, since it is not necessary to heat for hardening, the 1st and 2nd optical compensation layers 13 and 14 are not heated at the time of bonding (adhesion). For this reason, there is no risk of heat shrinkage, and even when the first and second optical compensation layers 13 and 14 are extremely thin, it is possible to remarkably prevent cracks and the like from occurring during bonding. is there. The isocyanate resin adhesive is a general term for polyisocyanate adhesives and polyurethane resin adhesives.

  Finally, if the base sheet is peeled from the second optical compensation layer 14, the lamination of the first optical compensation layer 13 and the second optical compensation layer 14 is completed, and the optical element 10 according to this embodiment is completed. can get.

III. Applications of Optical Element Next, applications of the optical element 10 will be described.

<Applications of optical elements>
The optical element 10 is suitably used for various image display devices (for example, a liquid crystal display device and a self-luminous display device). Specific examples of the applicable image display device include a liquid crystal display device, an EL display, a plasma display (PD), and a field emission display (FED). When the optical element 10 is used in a liquid crystal display device, for example, it is useful for preventing light leakage and viewing angle compensation in black display. The optical element 10 is suitably used for a liquid crystal display device having a VA mode liquid crystal cell, and particularly suitably for a reflective or transflective liquid crystal display device. Moreover, when using the optical element 10 for EL display, it is useful for electrode reflection prevention, for example.

<Image display device>
As an image display device to which the optical element 10 according to the present embodiment is applied, a liquid crystal display device will be specifically described as an example. Here, only the configuration of the liquid crystal panel included in the liquid crystal display device will be described, but any other appropriate configuration may be adopted depending on the purpose for other configurations included in the liquid crystal display device.

  As described above, the optical element 10 according to the present embodiment is preferably used for a liquid crystal display device including a VA mode liquid crystal cell, and particularly preferably used for a reflective or transflective liquid crystal display device. It is done. FIG. 5 is a cross-sectional view illustrating a schematic configuration of a liquid crystal panel to which the optical element 10 according to the present embodiment is applied. A liquid crystal panel 300 shown in FIG. 5 is a liquid crystal panel for a reflective liquid crystal display device, and is arranged on the liquid crystal cell 20, the phase difference plate 30 disposed above the liquid crystal cell 20, and the phase difference plate 30. The optical element 10 is provided.

  The liquid crystal cell 20 is provided on a pair of glass substrates 21, 21 ′, a liquid crystal layer 22 as a display medium disposed between the substrates 21, 21 ′, and a surface of the lower substrate 21 ′ on the liquid crystal layer 22 side. The reflective electrode 23, a color filter (not shown) provided on the upper substrate 21, and a spacer 24 that controls the distance (cell gap) between the substrates 21 and 21 ′ are provided.

  As the retardation plate 30, any appropriate retardation plate can be adopted depending on the purpose and the alignment mode of the liquid crystal cell 20. However, the retardation plate 30 may be omitted depending on the purpose and the alignment mode of the liquid crystal cell 20. In addition, the phase difference plate 30 can be omitted from the viewpoint that good optical compensation is performed only by the optical element 10 according to the present embodiment.

  When the liquid crystal cell 20 is in the VA mode, the liquid crystal molecules in the liquid crystal layer 22 are aligned perpendicular to the surfaces of the substrates 21 and 21 'when no voltage is applied. Such vertical alignment is realized by disposing a nematic liquid crystal having negative dielectric anisotropy between the substrates 21 and 21 'on which a vertical alignment film (not shown) is formed. When the linearly polarized light that has passed through the optical element 10 is incident on the liquid crystal layer 22 from the upper substrate 21 in a state where the liquid crystal molecules are vertically aligned, the incident light travels along the major axis direction of the vertically aligned liquid crystal molecules. . Since birefringence does not occur in the major axis direction of the liquid crystal molecules, incident light travels without changing its polarization state, is reflected by the reflective electrode 23, passes through the liquid crystal layer 22 again, and is emitted from the upper substrate 21. At this time, since the polarization state of the emitted light is not different from the polarization state of the incident light, the emitted light is transmitted through the optical element 10 and a bright display is obtained.

  On the other hand, when a voltage is applied between the electrodes provided on the substrates 21 and 21 ', the major axes of the liquid crystal molecules in the liquid crystal layer 22 are aligned parallel to the surfaces of the substrates 21 and 21'. The liquid crystal molecules exhibit birefringence with respect to the linearly polarized light incident on the liquid crystal layer 22 in this state, and the polarization state of the incident light changes according to the inclination of the liquid crystal molecules. When a predetermined maximum voltage is applied between the electrodes, the light reflected from the reflective electrode 23 and emitted from the upper substrate 21 is, for example, linearly polarized light whose polarization orientation is rotated by 90 °, and is thus absorbed by the optical element 10. A dark display is obtained. Then, when the voltage is not applied again, the display can be returned to the bright state by the orientation regulating force. Further, gradation display becomes possible by changing the intensity of transmitted light from the optical element 10 by changing the applied voltage to control the inclination of the liquid crystal molecules.

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

<Example 1>
(1) Preparation of alignment substrate For a film in which a saponified triacetyl cellulose film is used as a substrate and polyvinyl alcohol (PVA) having a thickness of 1.0 μm is formed as an alignment film on the substrate surface. The rubbing process was performed using the rubbing apparatus 100 shown in FIG. 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, and the outer diameters of the backup rolls 51 are all 90 mm. The center-to-center distance L1 in the rotation axis direction of the backup rolls 51 is 80 mm, and the width L2 in the rotation axis direction of each backup roll 51 is 30 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 is inclined 22.5 ° from the direction perpendicular to the film transport direction, and each backup roll 51 is arranged directly below the rubbing roll 4 and along a straight line parallel to the rotation axis. did. The number of rotations of the rubbing roll 4 was 1500 rpm, and the pushing amount was 0.4 mm. For measuring the thickness of the alignment film, a spectrophotometer: MCPD2000 manufactured by Otsuka Electronics was used. The same applies to Example 2 and Comparative Examples 1 and 2 described later.

(2) Production of Laminate Consisting of First Optical Compensation Layer / Alignment Substrate 10 g of Polymerizable Liquid Crystal Compound Showing a Nematic Liquid Crystal Layer (manufactured by BASF: trade name “Pariocolor LC242”) and photopolymerization for this polymerizable liquid crystal compound 0.5 g of an initiator (manufactured by Ciba Specialty Chemicals: trade name “Irgacure 907”) was dissolved in 40 g of toluene to prepare a liquid crystal composition (coating liquid).

And after apply | coating said coating liquid with the bar coater on the orientation film | membrane surface which gave the rubbing process of the orientation base material produced as mentioned above, a liquid crystal is obtained by heat-drying for 2 minutes at 90 degreeC. Oriented. A positive uniaxial film having a refractive index characteristic of nx> ny = nz by irradiating the liquid crystal layer thus formed with 20 mJ / cm ² of light using a metal halide lamp and curing the liquid crystal layer. A first optical compensation layer was formed. The thickness of the first optical compensation layer and the in-plane retardation value are adjusted by changing the coating amount of the coating liquid, the thickness is 2.2 μm, and the in-plane retardation value Re [590] is 250 nm. there were. Note that a spectrophotometer: MCPD2000 manufactured by Otsuka Electronics Co., Ltd. was used for measuring the thickness of the first optical compensation layer. Further, the in-plane retardation value Re [590] of the first optical compensation layer is measured with an automatic birefringence measuring apparatus (manufactured by Oji Scientific Instruments: automatic birefringence meter KOBRA31PR) at a measurement temperature of 23 ° C. and a measurement wavelength of 590 nm. Refractive indexes nx, ny and nz were measured and calculated from the measured values.

(3) Preparation of laminate comprising first optical compensation layer / alignment substrate / polarizer / protective layer After a polyvinyl alcohol film is dyed in an aqueous solution containing iodine, a speed ratio is adjusted in an aqueous solution containing boric acid. A polarizer was produced by uniaxially stretching 6 times between different rolls. This polarizer, a TAC film (thickness 40 μm) as a protective layer, and a laminate composed of an alignment substrate and a first optical compensation layer are laminated using an adhesive (the absorption axis direction of the polarizer is the longitudinal direction). The angle between the absorption axis of the polarizer and the slow axis of the first optical compensation layer is 22.5 ° or -22.5 °), and the first optical compensation layer / alignment substrate / polarized light A laminate composed of a child / protective layer was produced.

(4) Production of Laminate Consisting of Second Optical Compensation Layer / Base Material Sheet Using methyl isobutyl ketone as a solvent, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane) and 2, A solution prepared by mixing 15% by weight of a polyimide synthesized from 2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl) with a thickness of 25 μm manufactured by Nippon Zeon Co., Ltd. as a base sheet: “Zeonor” (the thickness before stretching was 100 μm) was applied and dried at 120 ° C. for 5 minutes. The film thus obtained was stretched 1.4 times by free end uniaxial stretching in the width direction at a stretching temperature of 140 ° C. As described above, a laminate composed of the second optical compensation layer / base sheet was produced.

  When the retardation value of the second optical compensation layer (polyimide layer) alone was measured using KOBRA21-ADH manufactured by Oji Scientific Instruments, the relationship of nx> ny> nz was satisfied, and the in-plane retardation value Re [590] was 130 nm, the thickness direction retardation value Rth [590] was 182 nm, and the Nz coefficient was 1.4.

(5) Fabrication of optical element Urethane resin-based adhesion of a laminate comprising the first optical compensation layer / alignment substrate / polarizer / protective layer and a laminate comprising the second optical compensation layer / substrate sheet Laminated through the agent (thickness 5 μm) (the absorption axis direction of the polarizer is the longitudinal direction, and the angle between the absorption axis of the polarizer and the slow axis of the second optical compensation layer is 90 °), and finally By peeling the substrate sheet, an optical element composed of the second optical compensation layer / first optical compensation layer / alignment substrate / polarizer / protective layer was produced. The total thickness (measured with a digital micrometer) of the optical element produced as described above was 118 μm, which was much thinner than a conventional equivalent optical element.

<Example 2>
For a film in which a saponified triacetyl cellulose film is used as a substrate used for the preparation of an alignment substrate, and a polyvinyl alcohol (PVA) having a thickness of 2.0 μm is formed as an alignment film on the surface of the substrate. An optical element was produced according to Example 1 except that the rubbing treatment was performed. The total thickness (measured with a digital micrometer) of the manufactured optical element was 119 μm, which was much thinner than a conventional equivalent optical element.

<Comparative Example 1>
In the rubbing process, a rubbing apparatus 100A shown in FIG. 6 (a plurality of (five) rod-shaped backup rolls 5A that are arranged substantially parallel to each other on the lower surface of the conveyor belt 3 and rotate along the conveying direction of the conveyor belt 3) An optical element was produced in accordance with Example 1 except that the structure supported by 1) was used.

<Comparative example 2>
In the rubbing process, an optical element was manufactured according to Example 2 except that the rubbing apparatus 100A shown in FIG. 6 was used.

<Evaluation results>
(1) Flatness evaluation of conveyance belt The flatness of the conveyance belt 3 was evaluated about the rubbing processing apparatus used in the Example and the comparative example. Specifically, the dimension of the gap between the rubbing roll 4 and the conveying belt 3 was sequentially measured at a plurality of locations along the rotation axis direction of the rubbing roll 4 using a gap gauge. Then, the difference between the maximum value and the minimum value of the gap measured along the rotation axis direction of the rubbing roll 4 was evaluated as the flatness of the surface of the conveyor belt 3.

  As a result of the evaluation, the rubbing processing apparatus 100A used in the comparative example had a flatness of 130 μm, whereas the rubbing processing apparatus 100 used in the example had a flatness of 50 μm, and the flatness of the conveyor belt 3 was It turns out that it improves.

(2) Evaluation of the number of bright spots The first optical compensation layer / alignment substrate produced in Examples 1 and 2 and Comparative Examples 1 and 2 between two polarizing plates arranged so that their absorption axes are orthogonal to each other By sandwiching the laminate consisting of the above, and visually observing in a state where the absorption axis of the polarizing plate on the viewing side and the slow axis of the laminate (the slow axis of the first optical compensation layer) are parallel, The number of bright spots that were visible was evaluated. The number of bright spots was counted in a 10 cm × 10 cm region on the surface of the laminate, and this number was evaluated by proportionally converting the number per 1 m 2. In addition, it was confirmed that the bright spots that were visible for the laminate comprising the first optical compensation layer / alignment substrate remained substantially after the optical element was produced.

(3) Evaluation of contrast The optical elements produced in Examples and Comparative Examples were mounted on a commercially available liquid crystal panel having a VA mode liquid crystal cell, and the contrast was evaluated. Specifically, an optical element having an angle of + 22.5 ° formed between the slow axis of the first optical compensation layer and the absorption axis of the polarizer was bonded to the upper side of the liquid crystal panel with an adhesive. Next, an optical element having an angle between the slow axis of the first optical compensation layer and the absorption axis of the polarizer of −22.5 ° was bonded to the lower side of the liquid crystal panel with an adhesive. At this time, the angle formed between the absorption axis of the polarizer in the optical element bonded to the upper side and the absorption axis of the polarizer in the optical element bonded to the lower side was set to 90 °. Then, the luminance in black display and white display of the liquid crystal panel was measured with a Topcon luminance meter: BM-5, and the ratio between the luminance of white display and the luminance of black display was evaluated as contrast.

Table 1 shows the evaluation results of the above (2) and (3).

  As shown in Table 1, using any of the optical elements according to Examples 1 and 2 and Comparative Examples 1 and 2, as a result of suppressing light leakage in black display, a contrast of 550 having no problem at a practical level is obtained. Obtained. Both of the optical elements according to Examples and Comparative Examples have a first optical compensation layer having a refractive index characteristic of nx> ny = nz, a refractive index characteristic of nx> ny> nz, and an Nz coefficient. Is laminated with a second optical compensation layer satisfying 1.2 ≦ Nz ≦ 2, and the absorption axis of the polarizer disposed on the first optical compensation layer side, the first optical compensation layer and the second optical compensation layer This is because the angle formed with each slow axis of the optical compensation layer is set in a specific range. However, in the case of Examples 1 and 2, it was found that generation of bright spots can be suppressed as compared with Comparative Examples 1 and 2. As described above, since the flatness of the conveyance belt of the rubbing treatment apparatus used in the examples is improved as compared with the comparative example, it becomes possible to perform the rubbing treatment on the base material in a stable state. This is considered to be due to the fact that uniform orientation characteristics could be imparted to the substrate.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an optical element including an optical film manufactured by the manufacturing method according to the present invention. FIG. 2 is an exploded perspective view for explaining the relationship between the absorption axis and the slow axis of each layer constituting the optical element shown in FIG. FIG. 3 is a front 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 the present invention. 4 is a diagram showing a schematic configuration of the backup roll mechanism shown in FIG. 3. FIG. 4 (a) is a plan view, FIG. 4 (b) is a perspective view in the vicinity of the backup roll, and FIG. The figure seen from the conveyance direction of a film is shown, respectively. FIG. 5 is a cross-sectional view showing a schematic configuration of a liquid crystal panel to which the optical element shown in FIG. 1 is applied. FIG. 6 is a perspective view showing a schematic configuration of a rubbing apparatus according to a comparative example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Drive roll 3 ... Conveyor belt 4 ... Rubbing roll 4a ... Raised cloth 5 ... Backup roll mechanism 10 ... Optical element 11 ... Polarizer 12 ... Base material 13 ... 1st optical compensation layer 14 ... 2nd optical compensation Layer 15 ... Protective layer 51 ... Backup roll 52 ... Base part 53 ... Support part 56 ... Connection mechanism 100 ... Rubbing device 200 ... Optical film 300 ... Liquid crystal panel F ... Plastic film M ... Motor

Claims (6)

A rubbing treatment step in which the surface of the long plastic film is rubbed by a rubbing roll having a rotation axis inclined from a direction perpendicular to the plastic film conveyance direction;
First, a liquid crystal molecule is applied to the surface of the plastic film that has undergone the rubbing treatment process, the applied liquid crystal molecule is fixed, and the first refractive index characteristic of nx> ny = nz is formed on the plastic film. A first optical compensation layer forming step of forming an optical compensation layer;
A second optical compensation layer formed by coating having a refractive index characteristic of nx>ny> nz and an Nz coefficient of 1.2 ≦ Nz ≦ 2 on the first optical compensation layer. A second optical compensation layer forming step of laminating,
In the rubbing treatment step, the long plastic film is supported and transported by a transport belt having a metal surface, and a backup roll mechanism that supports the lower surface of the transport belt that supports the plastic film is disposed.
The backup roll mechanism includes a plurality of backup rolls that respectively rotate along the conveyance direction of the conveyance belt,
Each of the plurality of backup rolls is disposed immediately below the rubbing roll and along a straight line substantially parallel to the rotation axis of the rubbing roll.   2. The method for producing an optical film according to claim 1, wherein the first optical compensation layer functions as a half-wave plate, and the second optical compensation layer functions as a quarter-wave plate.   The method for producing an optical film according to claim 1, wherein the optical film is used in a liquid crystal display device including a vertical alignment (VA) mode liquid crystal cell.   The second optical compensation layer is formed of at least one polymer selected from the group consisting of polyimide, polyamide, polyetherketone, polyamideimide, and polyesterimide. The manufacturing method of the optical film of description. The backup roll mechanism is
A pedestal portion disposed along a straight line substantially parallel to the rotation axis of the rubbing roll;
A plurality of support portions pivotally supported on the pedestal portion so as to be rotatable around a normal line of the surface of the conveyor belt;
5. The optical film according to claim 1, wherein each of the plurality of backup rolls is pivotally supported by the plurality of support portions so as to be rotatable along a conveyance direction of the conveyance belt. Manufacturing method.   The backup roll mechanism includes the rubbing roll and the pedestal portion so that when the rotation axis of the rubbing roll is inclined from a direction perpendicular to the conveying direction of the conveying belt, the pedestal portion is also inclined accordingly. The method for manufacturing an optical film according to claim 1, further comprising a connecting mechanism that connects the two.

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