JP5304286B2 - Manufacturing method of optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an optical film which enough catches a solidification prevention liquid scattering into a decompression chamber, is free from adhesion to a casting film, and has a surface of good smoothness, the optical film produced by using the method, a polarizing plate using the optical film, and an indication device. <P>SOLUTION: In the method for producing the optical film, the decompression chamber is divided in the width direction of the casting film into at least three rooms. While the air pressure of a room at the end in the width direction of the casting film is reduced to be lower than the air pressure of a room on the side of an adjacent middle part, the casting film is cast from a dope outflow opening on a support. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an optical film manufacturing method, an optical film obtained by the manufacturing method, a polarizing plate and a display device using the optical film.

  In recent years, the demand for liquid crystal display devices has increased due to the widespread use of liquid crystal displays mounted on automobiles, large liquid crystal television displays, mobile phones, notebook computers, and the like. A liquid crystal display device is widely used as a monitor because it saves space and energy compared to a conventional CRT display device. Furthermore, it is also spreading for TV. In such a liquid crystal display device, an optical film is used, and its demand is rapidly increasing.

  By the way, as an optical film used for a liquid crystal display device, for example, a polarizing film of a polarizing plate has a cellulose ester film laminated as a protective film on one or both sides of a polarizer made of a stretched polyvinyl alcohol film.

  Such an optical film is required to have a smooth surface without optical defects. In particular, as the size of monitors and TVs increases and the definition becomes higher, these required qualities are becoming stricter.

  There is a solution casting film forming method as an optical film manufacturing method. In this method, a resin is dissolved in a solvent, the solution (dope) is cast on a support from a dope outlet of a casting die, a predetermined amount of solvent is evaporated on the support, In this method, the film is peeled and stretched as necessary.

  If the moving speed of the support is increased in order to increase productivity, the adhesion between the dope film (also referred to as a casting film) cast on the support from the dope outflow port and the support deteriorates, and the support There was a problem that the dope film until reaching the body fluttered, and a film with poor flatness was formed. As a countermeasure, a method is used in which a decompression chamber is provided upstream of the dope outlet in the support moving direction, and the dope film is in close contact with the support.

  In addition, the resin solution is dried as a casting film on the support to a predetermined concentration, but the end of the casting film is dried to a predetermined concentration or more compared to the center part of the casting film. It may remain as a film. This film hinders peeling, and the shape of the film end part may be deformed, resulting in poor flatness. In addition, the film that could not be peeled off was scattered in the central part of the next cast film, causing a foreign matter failure.

  In order to solve such a problem, a liquid (also referred to as anti-caking liquid) that dissolves the raw material resin flows down from both ends of the dope outlet to the end of the casting film, so that the end of the casting film There is known a method for preventing the formation of a film due to the drying of the film.

  However, a decompression chamber is provided on the upstream side of the dope outlet in the direction of movement of the support so that the casting film flowing out from the dope outlet is in close contact with the support surface. The liquid is sucked in, and the sucked anti-solidification liquid is scattered in the decompression chamber, and the scattered anti-solidification liquid falls on the support at a position other than both ends of the decompression chamber and is mixed into the casting film. Due to this mixing, the surface of the cast film was deformed, and there was a problem that a round or elliptical deformed pattern was generated on the surface of the produced film.

  With respect to such a problem, in Patent Document 1, a scattering prevention member for preventing the anti-caking liquid from splashing is provided in the decompression chamber, the anti-caking liquid adhering to the anti-scattering member is stored in a basket, and the accumulated liquid is piped. The method of collecting by is proposed.

JP 2007-276458 A

1. When a dope containing a resin and a solvent is cast from a dope outlet of a casting die onto a moving support, a casting film cast from the dope outlet onto the support is supported by the support. A liquid that decompresses and casts a decompression chamber that holds the pressure at the upstream side in the moving direction of the support at the dope outlet in a state lower than atmospheric pressure so as to be in close contact with the body, and dissolves the resin In the manufacturing method of the optical film that flows down to both ends of the dope outlet,
The decompression chamber is divided into three or more chambers in the width direction of the casting membrane;
In a state where the pressure of the room at the end in the width direction of the casting film is reduced so as to be lower than the pressure of the room on the adjacent central part side,
The method for producing an optical film, wherein the casting film is cast on the support from the dope outlet.

  2. 2. The method for producing an optical film as described in 1 above, wherein the pressure in the chamber at the end in the width direction of the cast film is 10 to 500 Pa lower than the pressure in the room on the adjacent central portion side.

3. The surface of the inner wall of the room is surface-treated by at least one treatment selected from plasma discharge treatment, ultraviolet irradiation treatment and corona discharge treatment,
3. The method for producing an optical film as described in 1 or 2 above, wherein a contact angle between the surface-treated surface and pure water is 5 ° to 30 °.

  4). 4. The method for producing an optical film as described in any one of 1 to 3, wherein the 10-point average roughness Rz of the surface of the inner wall of the room is 1 to 50 [mu] m.

  5. 5. The method for producing an optical film as described in any one of 1 to 4, wherein the inner wall surface of the room has a mesh shape.

  6). 6. The method for producing an optical film as described in 5 above, wherein the surface of the inner wall of the room is a mesh having an opening of 0.02 to 0.5 mm.

  7). 7. An optical film produced by the method for producing an optical film according to any one of 1 to 6 above.

  8). A polarizing plate having the optical film according to 7 on at least one surface.

  9. 9. A display device using the polarizing plate described in 8 above.

  According to the method for producing an optical film of the present invention, the decompression chamber is divided into three or more chambers in the width direction of the casting film, and the pressure in the chamber at the end in the width direction of the casting film is the adjacent central portion. Since the pressure is reduced so as to be lower than the air pressure in the room on the side, an air flow from the center side toward the end is generated. By this air flow, the solidification preventing liquid that is sucked into the decompression chamber and scattered in the decompression chamber when flowing into the both ends of the dope outlet is prevented from moving toward the central portion of the decompression chamber. It is considered that they are collected and sucked in the room, and are prevented from falling onto the support from the decompression chamber in the vicinity of the center and mixing into the casting film. Therefore, by using the method for producing an optical film of the present invention, an optical film having a smooth surface without mixing into the cast film of the anti-caking liquid can be obtained, and produced by the production method. A polarizing plate and a display device using an optical film can be provided.

It is the schematic which shows the manufacturing method of the optical film of this invention. It is the schematic which shows the dope casting process in the manufacturing method of the optical film of this invention. The arrangement | positioning condition of the casting die seen from the support body side in the manufacturing method of the optical film of this invention, the pressure reduction chamber, and the dripping nozzle of a solidification prevention liquid is shown. It is the schematic which shows the surface shape of the shielding board which concerns on this invention. The schematic diagram of the plasma processing apparatus of the surface of the decompression indoor wall which concerns on this invention is shown.

  Next, embodiments of the present invention will be described, but the present invention is not limited thereto.

  FIG. 1 is a schematic diagram illustrating an example of a flow from a casting process to a winding process in the method for producing an optical film of the present invention. A dope (resin solution) obtained by dissolving a resin raw material in a solvent is cast from a casting die 1 onto a support 2 (casting process), and a casting film 3 formed on the support 2 is formed on the support 2. After being dried to a predetermined concentration, it is peeled from the support 2 by the peeling roll 4 (peeling step). Then, after drying by the initial drying device 13 (initial drying step), the film is stretched by the stretching device 14, further dried by the post-drying device 15 (post-drying step), and wound by the winding device 18 (winding step). .

  FIG. 2 is an enlarged view of a casting process in which the dope is cast on the support 2 by the casting die 1.

  In the casting method of the optical film of the present invention, in the casting step, a dope containing a resin and a solvent is cast from the dope outlet 1a of the casting die 1 onto the moving support 2 and cast. In the step of forming the membrane 3, in order to prevent both ends of the casting membrane 3 from solidifying on the support 2 to form a film, the resin used for the dope stored in the liquid storage tank 32 is used. A dissolving liquid (anti-solidification liquid) 33 is flowed down from both ends of the dope outlet 1a to the casting film 3 by using the pump 31 and the dropping nozzle 30, and the upstream side of the dope outlet 1a in the moving direction of the support 2 is moved. The decompression chamber 10 is maintained in a decompressed state, and the decompression chamber 10 is divided into three or more rooms in the width direction of the casting film 3 by a shielding plate. The pressure in the room at the end in the width direction of the membrane is lower than the pressure in the room on the adjacent central side. And it is characterized in and.

  FIG. 3 is a schematic view showing the arrangement of the casting die 1, the decompression chamber 10 divided into five chambers, and the anti-caking liquid dripping nozzle 30 as viewed from the support 2 side. The anti-caking liquid 33 dropped from the dropping nozzle 30 is supplied to both ends in the width direction of the dope outlet 1 a of the casting die 1. The decompression chamber 10 is divided into five rooms 10a, 10b, 10c, 10d, and 10e by the shielding plate 70 in the width direction of the dope outlet 1a. The shielding plate 70 and the support 2 are separated by a predetermined distance. Among the five rooms divided by the shielding plate 70, each of the chambers 10a and 10e at the end in the width direction of the casting film 3 has an air pressure lower than the air pressure in the adjacent central rooms 10b and 10d. The pressure is reduced by the suction port 101.

  In this way, by reducing the pressure in the chambers 10a and 10e at the end portions in the width direction of the casting film 3, the gas flow between the chambers 10a and 10e at the end portions of the decompression chamber and the support 2 is adjacent. The anti-caking liquid splashed in the end rooms 10a and 10e can be collected effectively without going to the matching central chambers 10b and 10d, thus preventing the anti-caking liquid from adhering to the casting film. It is considered that the smoothness of the product film can be improved.

  Further, it is more preferable that the pressure in the chambers 10a and 10e at the end in the width direction of the casting film 3 is 10 to 500 Pa lower than the pressure in the adjacent chambers 10b and 10d. When the difference in atmospheric pressure is in the range of 10 to 500 Pa, a more stable airflow can be created, which is preferable.

  Further, the method of providing the pressure difference between the rooms of the decompression chamber may be gradually lowered from the center room toward the rooms at both ends. Further, the distribution of the pressure difference may be biased without being symmetric in the width direction.

  Further, the surface of the inner wall of each room is subjected to surface treatment by at least one treatment selected from plasma discharge treatment, ultraviolet irradiation treatment and corona discharge treatment, and the contact angle between the surface-treated surface and pure water is 5 ° to It is preferable that it is 30 degrees or less. By such treatment, the scattered solidification preventing liquid is easily adapted to the wall surface, and the wet surface area is increased by spreading the wet. As a result, it is preferable that the drying speed of the anti-caking liquid is increased and the anti-caking liquid does not fall on the support as droplets even without a recovery member. As for the treatment method, an appropriate method can be used as long as the object of the present invention is not violated. For example, a method of inserting a member constituting the inner wall of each room into a corona or plasma discharge, a method of bringing a corona or plasma discharge electrode close to the surface of a member to be processed, and the like can be mentioned. In the ultraviolet irradiation treatment, it is more preferable to irradiate a member constituting the inner wall of the room with ultraviolet rays having a short wavelength (for example, a wavelength of about 200 to 300 nm) using a low-pressure mercury lamp or the like.

  The contact angle is generally represented by the angle between the solid line and the angle formed by the broken line drawn by the liquid at the contact point of the three layers and the solid surface when the solid, liquid and its saturated vapor are brought into contact with each other. It is widely used as a measure of wetness of liquid on the surface. The contact angle can be measured by dropping 5 μl of pure water on the surface of the member and measuring the contact angle at a temperature of 23 ° C. with a measuring device (using a goniometer Elmer G1 manufactured by Elma Kogyo Co., Ltd.).

  Moreover, it is preferable that 10-point average roughness Rz of the surface of the inner wall of a room is 1-50 micrometers. By setting the 10-point average roughness Rz of the surface to be in the range of 1 to 50 μm, the scattered anti-caking liquid is easily adapted to the wall surface, and spreads wet to increase the wet surface area. As a result, it is preferable that the drying speed of the anti-caking liquid is increased and the anti-caking liquid does not fall on the support as droplets even without a recovery member. Rz can be measured using a stylus type surface roughness meter as described in JIS B 0601-1994. As measurement conditions for the surface 10-point average roughness Rz, the cut-off was 0.25 mm and the measurement length was 4 mm.

  Moreover, it is preferable that the surface of the inner wall of a room is mesh shape. By making the surface of the inner wall mesh-like, the scattered solidification preventing liquid is easily adapted to the wall surface, and spreads by wetting, thereby increasing the wet surface area. As a result, it is preferable that the drying speed of the anti-caking liquid is increased and the anti-caking liquid does not fall on the support as droplets even without a recovery member. An example in which a mesh pattern is formed on the surface of the shielding plate is shown in FIG. For example, grooves having a width of 100 μm and a depth of 50 μm can be formed in a mesh shape by forming a lattice in the form of a grid in the vertical and horizontal directions at a pitch of 254 μm. Moreover, the surface can be formed into a mesh shape by attaching a net to the surface of the inner wall. In this case, the mesh shape of the inner wall is more preferably 0.02 to 0.5 mm. When the mesh is an opening of 0.02 to 0.5 mm, it is possible to prevent adhesion of the anti-caking liquid to the support. The method of making the inner wall of the room mesh-like is not particularly limited as long as it does not contradict the purpose of the present invention.For example, a method of attaching a net having a predetermined thickness to the inner wall or a mesh-like unevenness on the inner wall. The forming method is preferred.

  The material for the inner wall of the room is not particularly limited, but a material having a low contact angle between the surface and pure water is preferable, and a metal material, a resin material, a material having a resin layer formed on the surface of the metal material, or the like is used. be able to.

  Next, the optical film manufacturing method of the present invention will be described in more detail with reference to FIG.

  The embodiment of the optical film manufacturing method using the solution casting method of the present invention includes a dope preparation step (not shown), a casting step, a peeling step, a drying step, and a winding step. is there.

  That is, in the method for producing an optical film by the solution casting film forming method of this embodiment, a dope (resin solution) obtained by dissolving a resin film raw material in a solvent is supplied from a casting die, for example, a rotationally driven metal having a width of 1.8 m or more In this method, the cast film (film) cast on an endless belt (belt support) and then peeled off from the belt support is dried, and then wound up to produce an optical film. Each step will be described.

[Dope preparation process]
In the present invention, cellulose ester is preferably used as the resin film raw material. When cellulose ester is used as the resin film raw material, a mixed solvent of methylene chloride and alcohol is preferably used as the solvent.

  Other additives added to the dope include a plasticizer, an ultraviolet absorber, an antioxidant, a dye, and a matting agent. In the present invention, these additives may be added when preparing a cellulose ester solution, or may be added when preparing a dispersion such as a matting agent.

  Although the example in case resin of an optical film is a cellulose ester below is shown, this invention is not necessarily limited to this.

  First, cellulose ester is usually dissolved by a stirring dissolution method in a dissolution vessel, a heating dissolution method, an ultrasonic dissolution method, or the like. Under pressure, the solvent is boiling above the boiling point at normal pressure of the solvent. A method of heating at a temperature within a range not to dissolve and dissolving while stirring is more preferable in order to prevent generation of massive undissolved material called gel or mamako. Further, a cooling dissolution method described in JP-A-9-95538 or a method of dissolving under high pressure described in JP-A-11-21379 may be used.

  A method in which the cellulose ester is mixed with a poor solvent and wetted or swollen, and then mixed with a good solvent and dissolved is also preferably used. At this time, an apparatus for mixing or dissolving cellulose ester with a poor solvent and an apparatus for mixing and dissolving with a good solvent may be separately provided.

  The type of the pressure vessel used for dissolving the cellulose ester is not particularly limited as long as it can withstand a predetermined pressure and can be heated and stirred under pressure. In addition, instruments such as a pressure gauge and a thermometer are appropriately disposed in the pressurized container. The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or by increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  The heating temperature after adding the solvent is higher than the boiling point of the solvent to be used. In the case of two or more mixed solvents, the heating temperature is higher than the boiling point of the lower boiling solvent and the solvent does not boil. Is preferred. If the heating temperature is too high, the required pressure increases and productivity decreases. The range of preferable heating temperature is 20-120 degreeC, 30-100 degreeC is more preferable, The range of 40-80 degreeC is further more preferable. The pressure is adjusted so that the solvent does not boil at the set temperature.

  After dissolving the cellulose ester, take it out from the container while cooling, or take it out from the container with a pump and cool it with a heat exchanger, etc., and use the resulting resin dope for film formation. May be cooled to room temperature.

  The mixture of the raw material cellulose ester and the solvent is dissolved by a dissolving device having a stirrer, and at this time, the peripheral speed of the stirring blade is preferably at least 0.5 m / second and is dissolved by stirring for 30 minutes or more.

  In the present invention, the cellulose ester dope is filtered to remove foreign matter, particularly foreign matter that is mistakenly recognized as an image in a liquid crystal image display device.

  Filter media used for filtration preferably have a low absolute filtration accuracy, but if the absolute filtration accuracy is too low, the filter media is likely to be clogged, and the filter media must be frequently replaced. There is a problem of lowering.

  For this reason, the filter medium used for the cellulose ester dope preferably has an absolute filtration accuracy of 0.008 mm or less, more preferably in the range of 0.001 to 0.008 mm, and more preferably in the range of 0.003 to 0.006 mm. Further preferred.

  There are no particular restrictions on the material of the filter medium, and normal filter media can be used. However, plastic fiber filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel fibers are used to remove fibers. This is preferable.

  Filtration of cellulose ester dope can be performed by a normal method, but the method of filtering while heating under pressure at a temperature that is above the boiling point of the solvent at a normal pressure and does not boil is the differential pressure before and after the filter medium. (Hereinafter, it may be referred to as filtration pressure) The rise of a small is preferable.

  A preferred temperature range is 45 to 120 ° C, more preferably 45 to 70 ° C, and even more preferably 45 to 55 ° C.

  The filtration pressure is preferably 3500 kPa or less, more preferably 3000 kPa or less, and even more preferably 2500 kPa or less. The filtration pressure can be controlled by appropriately selecting the filtration flow rate and the filtration area.

[Casting process]
First, in the casting process, the dope adjusted in the melting pot is fed to the casting die 1 by a conduit and is transported infinitely, for example, at a casting position on the support 2 made of a rotationally driven stainless steel endless belt. In this step, the dope is cast from the casting die 1.

  The casting die 1 is preferably a pressure die that can adjust the slit shape of the dope outlet 1a and easily make the film thickness uniform.

  The gap between the dope outlet 1a of the casting die 1 and the surface of the support 2 is preferably set with a gap of 0.2 to 10 mm, more preferably 0.5 to 5 mm.

  The slit gap of the casting die 1 is preferably 0.05 to 1.5 mm, more preferably 0.15 to 1.0 mm.

  Next, the support 2 will be described.

  The surface roughness Ra of the support 2 is 0.0001 to 1 μm, more preferably 0.0003 to 0.1 μm, and still more preferably 0.0005 to 0.05 μm.

  In the illustrated film forming apparatus having a rotationally driven endless belt as the support body 2, the belt support body 2 is disposed between a pair of drums 19 and an intermediate portion thereof, and an upper transition portion and a lower transition portion of the endless belt support body 2 are respectively provided. It consists of a plurality of rolls (not shown) supported from the back side. The plurality of rolls are called support rolls, and the distance between adjacent support rolls is greater than 0 m and within a range of 5 m or less, preferably 1 to 5 m, and desirably 2 to 5 m.

  In addition, one or both of the drums 19 at both ends of the rotary drive endless belt support 2 are provided with a drive device that applies tension to the belt support 2, whereby the belt support 2 is tensioned. Used in a stretched state.

  When an endless belt is used as the support 2, the belt temperature during film formation can be cast at a temperature in the general temperature range of 0 ° C. to less than the boiling point of the solvent, and further from 5 ° C. to the boiling point of the solvent− A range of 5 ° C. is more preferred. At this time, it is necessary to control the ambient atmospheric humidity above the dew point.

  In the present invention, in order to prevent both end portions of the casting film 3 from solidifying on the support 2 to form a film, a liquid (solidification preventing liquid) for dissolving the resin used for the dope is used as the dope flow. A decompression chamber 10 is provided that flows down from both ends of the outlet 1a to the casting membrane and holds the upstream side in the moving direction of the support 2 of the dope outlet 1a in a decompressed state, and the decompression chamber is in the width direction of the casting membrane. The chambers 10a to 10e are divided into five rooms 10a to 10e by a shielding plate, and among the rooms 10a to 10e, the pressures of the chambers 10a and 10e at the end portions in the width direction of the cast film are adjacent to the central part 10b, The pressure is lower than 10d. Since the configuration of the decompression chamber and the setting conditions have already been described, description thereof is omitted here. When the conveying speed of the support 2 is 10 m / min or more, the decompression chamber 10 applies a reduced pressure to the casting film 3 coming out from the lip of the casting die 1 to mix air, or form a horizontal streak in the width direction of the film. However, since the decompression chamber 10 is provided, a liquid (solidification preventing liquid) for dissolving the resin used for the dope is wound into the decompression chamber 10. The entrained anti-caking liquid adheres to the inner wall of each chamber of the decompression chamber, and part of it adheres to the surface of the support, and the pattern is transferred to the film, resulting in quality failure. Depending on the conditions, the solidification preventing liquid scattered in the decompression chamber 10 can be removed by suction in the chamber at the end and does not adhere to the surface of the support 2 again.

  The anti-caking liquid is not particularly limited as long as it dissolves the resin used for the dope, but it is preferable to use the solvent used for the dope, and more preferably, the same solvent composition as the dope. It is good to use. By using a solvent having the same composition as that of the dope, the solvent evaporation rate on the film surface becomes uniform even when it flows down to the casting film 3, and a more uniform casting film can be formed.

  Examples of organic solvents having good solubility for cellulose derivatives include ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, tetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolane, 1 , Ethers such as 2-dimethoxyethane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, γ-butyrolactone, and other esters, methyl cellosolve, dimethylimidazolinone, dimethylformamide, dimethylacetamide, acetonitrile, Examples include dimethyl sulfoxide, sulfolane, nitroethane, methylene chloride, and methyl acetoacetate, and 1,3-dioxolane, THF, methyl ethyl ketone, acetone, methyl acetate, and methylene chloride are preferable. In addition to the organic solvent, it is preferable to contain 1 to 40% by mass of an alcohol having 1 to 4 carbon atoms. After the above-mentioned alcohol is cast on the casting membrane, the solvent starts to evaporate and the ratio of the alcohol increases, thereby causing the web to gel, making the web strong, and casting from the metal support. It can be used as a gelling solvent that facilitates peeling. Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, and propylene glycol monomethyl ether. Of these, ethanol is preferred because it has excellent dope stability, has a relatively low boiling point, good drying properties, and no toxicity. These organic solvents alone are not soluble in cellulose derivatives and are called poor solvents.

  The pressure in each chamber of the decompression chamber is preferably reduced by 10 to 800 Pa than the atmospheric pressure.

  The gap between the lower end face of the decompression chamber and the surface of the support 2 is in the range of 0.5 to 5 mm so that the suction air volume does not become too large, thereby suppressing the generation of the dope dry film at the end of the lip 1 of the casting die. This is desirable.

  In order to increase the film forming speed, two or more pressure casting dies 1 may be provided on the casting support 2 and the dope amount may be divided to form a multilayer film.

  When casting the dope on the support 2, it is preferable to control the temperature below the boiling point of the solvent used for dissolving the raw material resin, and below the boiling point of the solvent having the lowest boiling point in the mixed solvent.

  In the system using an endless belt as the support 2, since the cast film 3 is dried and solidified on the support 2 until the film strength becomes detachable from the support 2, the residual solvent amount in the cast film 3 is reduced. It is preferable to dry to 150 mass% or less, and 80-120 mass% is more preferable. Moreover, as for the casting membrane temperature when peeling the casting membrane 3 from the support body 2, 0-30 degreeC is preferable. Further, immediately after peeling from the support 2, the temperature of the cast film 3 rapidly decreases due to solvent evaporation from the support 2 contact surface side, and volatile components such as water vapor and solvent vapor in the atmosphere tend to condense. Therefore, the casting film temperature during peeling is more preferably 5 to 30 ° C.

  The dope film (casting film) formed by the dope cast on the endless belt support 2 is heated on the support 2 to evaporate the solvent until the cast film can be peeled from the support 2. It is a process. In order to evaporate the solvent, there are a method of blowing air from the casting film side, a method of transferring heat from the back surface of the support 2 by liquid, a method of transferring heat from the front and back by radiant heat, and the like.

[Peeling process]
In the system using an endless belt for the support 2, the peeling tension when peeling the support 2 and the casting film 3 is the tension per 1 m of the casting film width, and the casting film 3 is wrinkled during peeling. Since it is easy to enter, it is preferable to peel with a minimum tension that can be peeled to 170 N, and more preferably, peel with a minimum tension of 140 N.

[Drying process]
In the system using an endless belt for the support 2, the cast film 3 after peeling is introduced into the initial drying device 13. In the initial drying device 13, the casting film 3 is meandered by a plurality of transport rolls 17 arranged in a staggered manner as viewed from the side, and the casting film 3 is blown from the front portion of the bottom of the initial drying device 13. Rarely, it is dried by the warm air 26 discharged from the rear portion of the ceiling of the initial drying device 13.

  The diameter of the roll used is preferably 85 to 300 mm, more preferably 100 to 200 mm.

  Thereafter, post-drying is performed by the post-drying device 15. In the post-drying device 15, the casting film 3 is meandered by a plurality of transport rolls 17 arranged in a staggered manner as viewed from the side, and the casting film 3 is dried in the meantime. Moreover, although the film conveyance tension | tensile_strength in the post-drying apparatus 15 is influenced by the physical property of dope, the amount of residual solvents at the time of peeling and a film conveyance process, the temperature in the post-drying apparatus 15, etc., per 1 m of casting film width | variety The tension is preferably 30 to 250N, and more preferably 60 to 150N. 80 to 120N is most preferable.

  The means for drying the cast film 3 (or film) is not particularly limited and is generally performed by hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to dry with hot air from the viewpoint of simplicity. For example, the air is blown from the front portion of the bottom of the post-drying device 15 and dried by the warm air 25 discharged from the rear portion of the ceiling of the post-drying device 15. The drying temperature is preferably 40 to 160 ° C, and more preferably 50 to 160 ° C in order to improve the flatness and dimensional stability.

  These steps from casting to post-drying may be performed in an air atmosphere or in an inert gas atmosphere such as nitrogen gas. In this case, it goes without saying that the dry atmosphere is carried out in consideration of the explosion limit concentration of the solvent.

  Next, an embossing process and a static elimination process can be provided.

  The embossing provided in the both-sides edge part of the cast film 3 after a post-drying process is demonstrated. For the resin film that has finished the post-drying process, embossing is performed on the film by the embossing apparatus 60 in the previous stage of introduction into the winding process.

  Here, the height of the emboss is set in a range of 0.05 to 0.3 times the film thickness T, and the width is set in a range of 0.005 to 0.02 times the film width L. For example, when the film thickness is 40 μm and the film width is 100 cm, the height of the emboss 31 is set to 2 to 12 μm and the width is set to 5 to 30 mm. Embossing may be formed on both sides of the film.

  It is preferable that a static eliminator is installed before winding and immediately after the winding unit to neutralize the film.

  The static eliminator can be configured to apply a reverse potential by a static eliminator or a forced charging device at the time of winding so that the charging potential when the original winding is re-drawn is ± 2 kV or less. It can also be set as the structure which static-eliminates with the static elimination device converted into positive / negative alternately at 1-150Hz.

  Moreover, it can replace with said static elimination device and can utilize the ionizer and static elimination bar which generate | occur | produce ion wind. Here, the ionizer static elimination is performed by blowing an ion wind toward the film wound up from the embossing device via the transport roll. The ion wind is generated by a static eliminator. Any known static eliminator can be used without limitation.

  The static elimination at the time of film forming winding is to induce coating unevenness when the charged potential is ± 2kV or more when the original film is redrawn and the functional film is applied, especially when pursuing thin film and high speed. Since film peeling electrification at the time of re-feeding becomes high, static elimination during film formation is essential.

[Winding process]
The cast film 3 that has been dried is wound up as a film by the winding device 18. This is a step of obtaining the original roll of the optical film. A film having good dimensional stability can be obtained by setting the residual solvent amount of the film 20 to be dried to 0.5% by mass or less, preferably 0.1% by mass or less.

  The winding method of the film may be a generally used winder, and there are methods for controlling the tension such as a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, etc. Use it properly.

  The film may be bonded to the winding core (winding core) by either a double-sided adhesive tape or a single-sided adhesive tape.

  The film thickness of the optical film produced by the production method of the present invention varies depending on the purpose of use, but from the viewpoint of thinning the liquid crystal display device and film strength, it is preferable to adjust the finished film to a range of 10 to 150 μm, Furthermore, it is more preferable to adjust to the range of 20-100 micrometers, and it is especially preferable to adjust to the range of 25-80 micrometers.

  Next, the cellulose ester film produced by the production method of the present invention can be used for polarizing plates and display devices.

  The polarizing plate in this invention has the protective film for polarizing plates which consists of an optical film manufactured by this invention in at least one surface.

  And in this invention, a liquid crystal display device has said polarizing plate in the at least one surface of a liquid crystal cell.

  Next, these polarizing plates and a liquid crystal display device using the polarizing plates will be described.

  The polarizing plate can be produced by a general method. The cellulose ester film according to the present invention subjected to alkali saponification treatment is preferably bonded to at least one surface of a polarizer produced by immersing and stretching a polyvinyl alcohol film in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. . The cellulose ester film according to the present invention may be used on the other surface, or another protective film for polarizing plate may be used. With respect to the cellulose ester film according to the present invention, a commercially available cellulose ester film can be used as the protective film for polarizing plate used on the other surface. For example, as a commercially available cellulose ester film, KC8UX2M, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC8UY-HA, KC8UX-RHA, KC8UX-RHA-N (manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used. Or you may use films, such as cyclic olefin resin other than a cellulose-ester film, an acrylic resin, polyester, a polycarbonate, as a protective film for polarizing plates of the other surface. In this case, since the saponification suitability is low, it is preferable to perform adhesion processing on the polarizing plate through an appropriate adhesive layer.

  The polarizing plate of the present invention is obtained by using the cellulose ester film according to the present invention as a protective film for a polarizing plate on at least one side of a polarizer. In that case, it is preferable to arrange | position so that the slow axis of this cellulose-ester film may be substantially parallel or orthogonal to the absorption axis of a polarizer.

  It is preferable that the cellulose ester film by this invention is arrange | positioned at the liquid crystal display cell side as one polarizing plate arrange | positioned on both sides of the liquid crystal cell which is a horizontal electric field switching mode type | mold.

  Examples of the polarizer preferably used for the polarizing plate include a polyvinyl alcohol polarizing film, which includes a polyvinyl alcohol film dyed with iodine and a dichroic dye dyed. As the polyvinyl alcohol film, a modified polyvinyl alcohol film modified with ethylene is preferably used. For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound.

  The film thickness of the polarizer is 5 to 40 μm, preferably 5 to 30 μm, and particularly preferably 5 to 20 μm. One side of the cellulose ester film according to the present invention is bonded to the surface of the polarizer to form a polarizing plate. It is preferably bonded with an aqueous adhesive mainly composed of completely saponified polyvinyl alcohol or the like. Moreover, in the case of resin films other than a cellulose ester film, it can be bonded to the polarizing plate via an appropriate adhesive layer.

  Since the polarizer is stretched in a uniaxial direction (usually the longitudinal direction), when the polarizing plate is placed in a high-temperature and high-humidity environment, the stretching direction (usually the longitudinal direction) shrinks, and the direction orthogonal to the stretching ( Usually stretches in the width direction). As the film thickness of the protective film for polarizing plate decreases, the expansion / contraction ratio of the polarizing plate increases, and in particular, the amount of contraction in the stretching direction of the polarizer increases. Usually, the stretching direction of the polarizer is bonded to the casting direction (MD direction) of the protective film for polarizing plate. Therefore, when thinning the protective film for polarizing plate, it is important to suppress the stretch rate in the casting direction. It is. Since the cellulose ester film according to the present invention has no unevenness on the surface and is excellent in smoothness, it is preferably used as such a protective film for a polarizing plate.

The polarizing plate can be constituted by further bonding a protective film on one surface of the polarizing plate and a separate film on the opposite surface. The protective film and the separate film are used for the purpose of protecting the polarizing plate at the time of shipping the polarizing plate and at the time of product inspection.
(Liquid crystal display device)
By incorporating a polarizing plate using an optical film produced according to the present invention into a liquid crystal display device, various liquid crystal display devices with excellent visibility can be produced.

  Here, the liquid crystal display device generally absorbs light by a polarizing plate protective film / dichroic material having polarizing scattering anisotropy adjacent to a light reflection plate, a backlight, a light guide plate, and a light diffusion plate. It is preferable that the structure of the dichroic polarizing film / polarizing plate protective film using the action, and the liquid crystal display panel and the viewing side polarizing plate are stacked in this order.

  The optical film produced by the present invention can be used in various drive systems such as reflective, transmissive, transflective LCD or TN, STN, OCB, HAN, VA (PVA, MVA) and IPS. It is preferably used in LCDs, and has the effect that there is little color unevenness, glare and wavy unevenness, and eyes are not tired even during long-time viewing.

  As described above, a liquid crystal display device having a polarizing plate using an optical film produced according to the present invention on at least one surface of a liquid crystal cell has very excellent display quality.

Hereinafter, although the example implemented with the manufacturing method of the optical film using this invention is shown, this invention is not limited by this.
(Examples 1 to 5, Comparative Examples 1 and 2)
(Dope preparation for solution casting film formation)
The following materials were put into a closed container, heated, stirred and completely dissolved and filtered to prepare a dope. Silicon dioxide fine particles (Aerosil R972V) were added after being dispersed in ethanol.

(Dope composition)
Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 8 parts by weight Biphenyl diphenyl phosphate (liquid plasticizer) 4 parts by weight 5-chloro-2- (3,5-di-sec-butyl-2- Hydroxyphenyl)
-2H-benzotriazole (liquid UV absorber) 1 part by weight Methylene chloride 418 parts by weight Ethanol 23 parts by weight Aerosil R972V 5 parts by weight (Preparation of optical film)
Using the above dope, an optical film was produced as follows. Film formation was performed with the manufacturing apparatus shown in FIG. First, the filtered dope was cast in the form of a film from a casting die made of a coat hanger die onto a metal support made of an endless belt made of SUS316 and polished to a super mirror surface.

  As the solidification preventing liquid, methylene chloride and ethanol were mixed in the same composition as the dope composition, and were allowed to flow down from the both ends of the dope outlet to the casting film.

  As shown in FIG. 3, the decompression chamber on the upstream side in the moving direction of the support at the dope outlet is divided into five chambers in the casting width direction, and individually adjusted to a value lower than the atmospheric pressure and decompressed. A decompressor was used. Here, the air pressure in the central room 10c and the adjacent rooms 10b and 10d are the same, and the difference (reduced pressure difference) between the air pressure in the rooms 10a and 10e at both ends and the air pressure in the adjacent central rooms 10b and 10d. The values shown in Table 1 were set. In each room, each decompression pump 102 and each pipe 103 were connected to control the degree of decompression.

  The constituent material of each room was an SUS plate (4 mm thick), the surface 10-point average roughness Rz was 0.5 μm, and the surface contact angle was 60 °. The depressurized air pressure P1 of the two rooms at both ends is set to an equal value, and the depressurized air pressure P2 of the central room is an air pressure difference (depressurization difference) of the values shown in Table 1 (ΔP = P1-P2) It was set as the manufacturing conditions of the optical film of Examples 1-5 and Comparative Examples 1 and 2 provided.

  As a support, a metal belt is used, and the cast film cast on the support is peeled off by a peeling roll, and then dried in an initial drying zone of 90 ° C. while being transported by a roll. In the drying zone, drying was terminated to produce a cellulose triacetate film having a film thickness of 40 μm, a film width of 2000 mm, and a winding length of 5200 m.

The optical films of Examples 1 to 5 and Comparative Examples 1 and 2 obtained as described above were evaluated as follows.
(Evaluation of deformation pattern on film surface)
With respect to 1000 m after winding of the optical film thus prepared, the film surface was visually observed to see if there was a circular or elliptical deformation pattern, and the average number of deformation patterns per 100 m ² was compared. Evaluation levels were as follows.

Level 7: Less than 0.01 Level 6: 0.01 or more and less than 0.02 Level 5: 0.02 or more and less than 0.05 Level 4: 0.05 or more and less than 0.1 Level 3: 0.1 or more and less than 0.5 pieces Level 2: 0.5 or more and less than 1 level Level 2 or more can be used as a product Level 1: 1 or more There is a problem as a product Evaluation results are shown in Table 1.

(Examples 6 to 10)
In Examples 6 to 10, the difference (decompression difference) between the atmospheric pressures of the chambers 10a and 10e at both ends and the atmospheric pressures of the adjacent chambers 10b and 10d in Example 4 is −200 Pa, The surface of the SUS plate constituting the inner surface of each room was plasma-treated so that the contact angles shown in Table 2 were obtained. Others were produced and evaluated in the same manner as in Example 4. FIG. 5 shows a schematic diagram of the plasma processing apparatus 200 on the surface of the SUS plate 101. As the plasma processing apparatus 200, a downflow type atmospheric pressure plasma processing apparatus was used, and as the flow gas 201, a gas in which N ₂ / O ₂ was mixed at a ratio of 99/1 volume% was used. A voltage of 30,000 V and 20 kHz was applied to the electrodes 202 and 203. The surface treatment is performed by adjusting the conveyance speed for passing the SUSU plate 101 under the head of the plasma processing apparatus 200 to adjust the contact angle of the surface. An optical film was manufactured.

  The evaluation results are shown in Table 2.

(Examples 11 to 15)
In Examples 11 to 15, the difference (decompression difference) between the atmospheric pressures of the chambers 10a and 10e at both ends and the atmospheric pressures of the adjacent central chambers 10b and 10d in Example 4 is −200 Pa. It was produced and evaluated in the same manner as in Example 4 except that the surface of the SUS plate constituting the inner surface of each room was sandblasted. The surface treatment by sandblasting produced optical films of Examples 11 to 15 using those treated to have Rz shown in Table 3.

  The evaluation results are shown in Table 3.

(Examples 16 to 25)
In Examples 16 to 25, the difference (vacuum difference) between the atmospheric pressures of the chambers 10a and 10e at both ends and the atmospheric pressures of the adjacent central chambers 10b and 10d in Example 4 is −200 Pa. It was produced and evaluated in the same manner as in Example 4 except that a SUS net (wire diameter: 0.5 mm) was attached to the surface of the SUS plate constituting the inner surface of each room.

  As the used SUS plate, in Examples 16 to 20, a flat plate was used as the side plate constituting the decompression chamber and the shielding plate separating the decompression chamber, but in Examples 21 to 25, the shielding plate portion was used. The same flat plate was used in which holes with a diameter of 10 mm were formed vertically and horizontally at a pitch of 20 mm. The optical film of Examples 16-25 was manufactured using the SUS net | network pasted on the inner surface side of each room | chamber of the used SUS board with a mesh opening of Table 4. FIG.

  The evaluation results are shown in Table 4.

From the results of Table 1, in the method for producing an optical film of the present invention, the decompression chamber is divided into three or more rooms in the width direction of the casting film, and the air pressure in the chamber at the end in the width direction of the casting film. However, by reducing the pressure so that it is lower than the air pressure of the adjacent central portion side room, the anti-caking liquid scattered in the reduced pressure chamber is less likely to adhere on the support, and the smoothness of the optical film surface can be improved. I understand. Moreover, it turns out that it is preferable that the atmospheric | air pressure of the room | chamber of the edge part of the width direction of a cast film is 10-500 Pa lower than the atmospheric | air pressure of the room of the adjacent center part side. From the results shown in Table 2, plasma treatment is performed on the inner wall of each chamber of the decompression chamber, and the contact angle is set to 5 ° to 30 °. It can be understood that the surface area is large, the drying speed of the anti-caking liquid is high, and the anti-caking liquid does not fall as a droplet on the support without using a collecting member. Further, from the results in Table 3, by setting the 10-point average roughness Rz of the inner wall surface of each chamber of the decompression chamber to 1 to 50 μm, the scattered anti-solid solution can be easily adapted to the wall surface, and the anti-solid solution is a droplet. It turns out that it does not fall on a support body and becomes preferable. In addition, from the results of Table 4, the surface of the inner wall of each chamber of the decompression chamber has a mesh shape of 0.02-0.5 mm openings, so that the scattered anti-solid solution can be easily applied to the wall surface, preventing solidification. It can be seen that the liquid is preferable because it does not drop on the support as a droplet.
(Preparation of polarizing plate)
In accordance with the method described below, the optical films of Examples 1 to 25 and Comparative Examples 1 and 2 were subjected to alkali saponification treatment, and then polarizing plates were produced.
<Alkali saponification treatment>
Saponification step: 2 mol / L NaOH 50 ° C. 90 seconds water washing step: Water 30 ° C. 45 seconds neutralization step: 10% by mass HCl 30 ° C. 45 seconds water washing step: water 30 ° C. 45 seconds Each sample was saponified under the above conditions. , Water washing, neutralization and water washing in this order, followed by drying at 80 ° C.

A 120 μm thick polyvinyl alcohol film was immersed in 100 kg of an aqueous solution containing 1 kg of iodine and 4 kg of boric acid, and stretched 6 times at 50 ° C. to prepare a polarizing film. The optical films of Examples 1 to 15 and Comparative Examples 1 and 2 were applied to one side of this polarizing film, and Konica Minolta Tack KC8UCR (manufactured by Konica Minolta Opto Co., Ltd.) was subjected to the alkali saponification treatment on the opposite side. A polarizing plate was prepared by bonding saponified polyvinyl alcohol 5% by mass aqueous solution as an adhesive.
(Characteristic evaluation as a liquid crystal display device)
Strip the polarizing plate on the viewing side of the Sony 40-type display KLV-40V1000, and make each polarizing plate perpendicular to each other so that the polarizing axis of the polarizing plate does not change according to the size of the liquid crystal cell. A 40-inch TFT color liquid crystal display was prepared, and the properties of the optical film as a polarizing plate were evaluated.

  The liquid crystal display device on which the polarizing plate using the optical film of Examples 1 to 25 of the present invention is mounted is different from the liquid crystal display device on which the polarizing plate using the optical film of Comparative Example 1 is mounted. There was no display unevenness such as unevenness, and excellent display properties were shown. Thereby, it was confirmed that the polarizing plate of this invention is excellent as a polarizing plate for image display apparatuses, such as a liquid crystal display.

DESCRIPTION OF SYMBOLS 1 Casting die 1a Dope outflow port 2 Support body 3 Casting film 4 Peeling roll 17 Conveyance roll 10 Decompression chamber 10a-10d chamber 13 Initial drying apparatus 15 Post-drying apparatus 18 Winding apparatus 30 Dripping nozzle 31 Pump 32 Liquid storage tank 33 Anti-caking liquid 70 Shield plate 101 Suction port 20 Film 60 Embossing device

Claims (6)

When a dope containing a resin and a solvent is cast from a dope outlet of a casting die onto a moving support, a casting film cast from the dope outlet onto the support is supported by the support. A liquid that decompresses and casts a decompression chamber that holds the pressure at the upstream side in the moving direction of the support at the dope outlet in a state lower than atmospheric pressure so as to be in close contact with the body, and dissolves the resin In the manufacturing method of the optical film that flows down to both ends of the dope outlet,
The decompression chamber is divided into three or more chambers in the width direction of the casting membrane;
In a state where the pressure of the room at the end in the width direction of the casting film is reduced so as to be lower than the pressure of the room on the adjacent central part side,
The method for producing an optical film, wherein the casting film is cast on the support from the dope outlet. 2. The method for producing an optical film according to claim 1, wherein a pressure in a room at an end portion in the width direction of the cast film is 10 to 500 Pa lower than a pressure in a room on the adjacent central side. The surface of the inner wall of the room is surface-treated by at least one treatment selected from plasma discharge treatment, ultraviolet irradiation treatment and corona discharge treatment,
The method for producing an optical film according to claim 1, wherein a contact angle between the surface treated surface and pure water is 5 ° to 30 °. 4. The method for producing an optical film according to claim 1, wherein the 10-point average roughness Rz of the surface of the inner wall of the room is 1 to 50 μm. 5. The method for producing an optical film according to any one of claims 1 to 4, wherein the inner wall surface of the room has a mesh shape. 6. The method for producing an optical film according to claim 5, wherein the surface of the inner wall of the room has a mesh shape of 0.02-0.5 mm.

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