JP5682749B2 - Manufacturing method of optical film - Google Patents

Description

  The present invention is a resin that can be used for optical films such as protective films for polarizing plates used for liquid crystal display devices (LCDs), retardation films, viewing angle widening films, and antireflection films used for plasma displays. The present invention relates to a film manufacturing method, a resin film obtained by the manufacturing method, a polarizing plate using the resin film as a transparent protective film, and a liquid crystal display device including the polarizing plate.

  Various optical films such as a transparent protective film for protecting the polarizing element of the polarizing plate are disposed in the image display region of the liquid crystal display device. As such an optical film, for example, a resin film excellent in transparency such as a cellulose ester film is used.

  Moreover, such an optical film is often manufactured as a long resin film by, for example, a solution casting film forming method. Specifically, the solution casting film forming method is a method in which a resin solution (dope) in which a transparent resin as a raw material resin is dissolved in a solvent is cast on a traveling support and dried to a peelable extent. In this method, a long resin film is produced by peeling the film obtained from the support from the support, and performing drying, stretching and the like while carrying the peeled film with a carrying roller.

  In such a solution casting film forming method, it is required to increase the film forming speed, but with the increase in the film forming speed, entrainment of air entrained on the metal support that occurs during the casting occurs and the production efficiency is increased. There is a problem of going down. On the other hand, the current situation is to increase the decompression in the decompression chamber, but the blower ability (mechanical ability) cannot keep up with the high speed of film formation and is approaching the limit. On the other hand, if the pressure is reduced too much, air vibrations occur in the reduced pressure chamber, and the film thickness unevenness (cast horizontal stage) increases.

  Therefore, in order to improve the adhesion between the casting film and the support, as a technique applied to the decompression chamber, electrostatic application is applied to the support surface (see Patent Document 1), and an insulating film is provided on the support surface. Electrostatic application (see Patent Document 2 or 3) and provision of an intervening film between a support and a casting film (see Patent Document 4) have been reported.

Japanese Patent No. 4268286 JP 2008-87473 A JP 2008-87474 A Japanese Patent Laid-Open No. 2007-230078

  However, the current situation is that it is no longer possible to cope with the high-speed film formation only by the electrostatic application process. Even if an insulating film or intervening film is provided on the surface of the support, there is a limit to the accuracy, so the film surface deteriorates and problems such as film thickness deviation occur during long-term production. It is necessary to stop and clean and rework.

  On the other hand, when entraining entrained air, there is a tendency to entrain bubbles from both ends of the outermost cast film, and the response is becoming a major problem.

  Furthermore, the film thickness unevenness is also severe with respect to the recent trend toward higher quality. In addition, by increasing the degree of decompression of the decompression device as the film is formed, the outside atmosphere of the decompression device is sucked together with the accompanying air, and fluttering occurs at the end when casting from the support. This fluttering causes non-uniformity of the support landing point in the width direction at the time of casting, leading to a large orientation angle deviation of the width, leading to a decrease in optical performance.

  The present invention has been made in view of such circumstances, and does not cause entrained air entrainment or film thickness unevenness, width orientation angle deviation, etc. even when film formation is performed at a high speed for a long period of time. It aims at providing the method of manufacturing a film with high productivity.

  As a result of intensive studies, the present inventors have found that the above problems can be solved by a method for producing a resin film having the following configuration, and have further completed the present invention based on such findings.

  The method for producing a resin film according to one aspect of the present invention includes a casting step in which a resin solution in which a transparent resin is dissolved in a solvent is cast from a casting die on a traveling support to form a casting film. And a peeling step for peeling the cast film from the support, and a drying step for drying the peeled cast film. In the casting step, either the roller surface in contact with the back of the support or the back of the support A crab insulating film is formed, and an electrostatic voltage is applied from the surface of the support to charge the surface of the support.

  According to such a configuration, entrained air entrainment due to an increase in the film forming speed can be suppressed, and a high-quality resin film can be formed at a high speed for a long period of time without causing lateral orientation angle deviation and film thickness unevenness. be able to. Furthermore, an insulating film is formed on either the roller surface in contact with the back surface of the support or the back surface of the support, and a hardness difference is provided between the back surface of the support and the roller surface in contact with the back surface of the support. Shave can be reduced. If the wear on the back surface of the support can be reduced in this way, mechanical vibration of the support can be reduced, and film thickness unevenness (horizontal unevenness) can be improved.

  Moreover, in the said manufacturing method, it is preferable that an insulating film is comprised by at least 1 selected from the group which consists of silicon rubber, ceramics, and a silicon oxide film, and the film thickness is 5-1000 micrometers. According to such a configuration, it is considered that the lateral orientation angle deviation and the film thickness unevenness can be further suppressed, and the speed of the film formation can be more reliably ensured.

Furthermore, in the said manufacturing method, it is more preferable to make a metal compound contain in the both ends of a cast film. According to such a configuration, it is possible to stabilize the casting end portion, which is the least robust, and it is only necessary to apply static electricity only to the end portion, thereby simplifying the equipment and facilitating maintenance. Can do.

  Moreover, in the said manufacturing method, it is preferable to apply an electrostatic voltage after a peeling process and before casting from a casting die on a support body, and to charge the support body surface. Furthermore, it is preferable to neutralize the support after the peeling step and before charging the support surface. According to such a configuration, the charge remaining on the support after the peeling step is removed, and charging is performed before the casting is newly cast on the support. The occurrence of air entrainment can be suppressed more efficiently.

  In the manufacturing method, it is preferable that the casting step is performed under an oxygen concentration of 5% or less. According to such a configuration, it is possible to prevent an explosion of the organic solvent gas in the casting process when an electrostatic voltage is applied.

  Moreover, in the said manufacturing method, an electrostatic voltage can be applied with any one selected from the group which consists of an electrostatic application apparatus, a charging bar, and an electrostatic sprayer.

  Moreover, the resin film which concerns on the other one aspect | mode of this invention is obtained by the manufacturing method of the said resin film, It is characterized by the above-mentioned. According to such a configuration, it is possible to obtain a high-quality resin film in which the occurrence of lateral orientation angle deviation and lateral unevenness is suppressed.

  The polarizing plate according to another embodiment of the present invention is a polarizing plate including a polarizing element and a transparent protective film disposed on a surface of the polarizing element, wherein the transparent protective film is the resin film. It is characterized by being. According to such a configuration, as a transparent protective film of the polarizing element, since a high-quality resin film without a width orientation angle deviation or film thickness unevenness is applied, for example, when applied to a liquid crystal display device, A polarizing plate capable of realizing high image quality of a liquid crystal display device is obtained.

  The liquid crystal display device according to another embodiment of the present invention is a liquid crystal display device including a liquid crystal cell and two polarizing plates arranged so as to sandwich the liquid crystal cell, the two polarizing plates. At least one of the plates is the polarizing plate. According to such a configuration, a polarizing plate provided with a high-quality resin film having no width alignment angle deviation or film thickness unevenness is used, so that high image quality of the liquid crystal display device can be realized.

  ADVANTAGE OF THE INVENTION According to this invention, the high quality resin film by which generation | occurrence | production of the width orientation angle deviation and film thickness nonuniformity was suppressed can be manufactured at a high speed for a long period, without entrainment of entrained air. Moreover, the polarizing plate provided with such a resin film and a liquid crystal display device are provided.

FIG. 1 is a schematic view showing a basic configuration of an apparatus 1 for producing a resin film by a solution casting method using an endless belt support 11. FIG. 2 is a schematic view showing the periphery of the casting die 20 according to the embodiment of the present invention. FIG. 3 is a schematic view showing the periphery of the casting die 20 when a metal compound is contained at both ends of the casting film.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

  The method for producing a resin film according to the present embodiment is a casting process in which a resin solution (dope) in which a transparent resin is dissolved is cast on a continuously running support to form a casting film (web). And a peeling step for peeling the cast film from the support, and a drying step for drying the peeled cast film, which is a manufacturing method based on a so-called solution casting film forming method. For example, it is performed by a resin film manufacturing apparatus using a solution casting film forming method as shown in FIG. In addition, as a manufacturing apparatus of a resin film, it is not limited to what is shown in FIG. 1, The thing of another structure may be sufficient.

  FIG. 1 is a schematic diagram showing a basic configuration of an apparatus 1 for producing a resin film by a solution casting method using an endless belt support 11. The resin film manufacturing apparatus 1 includes an endless belt support 11, a casting die 20, a peeling roller 13, a drying device 14, a winding device 15, and the like. The casting die 20 casts a resin solution (dope) 16 in which a transparent resin is dissolved on the surface of the endless belt support 11. The endless belt support 11 is supported to be drivable by a pair of driving rollers and driven rollers, forms a casting film made of the resin solution 16 cast from the casting die 20, and is dried while being conveyed. The peeling roller 13 peels the dried cast film from the endless belt support 11. The peeled cast film is further dried by the drying device 14, and the dried cast film is wound around the winding device 15 as a resin film.

  As shown in FIG. 1, the endless belt support 11 is an endless metal belt having a mirror surface and an infinite transition. As the belt, for example, a belt made of stainless steel or the like is preferably used from the viewpoint of peelability of the cast film. From the viewpoint of effectively utilizing the width of the endless belt support 11, the width of the cast film cast by the casting die 20 is preferably 80 to 99% with respect to the width of the endless belt support 11. . And in order to finally obtain a resin film with a width of 1500 to 4000 mm, the width of the endless belt support 11 is preferably 1800 to 4500 mm. Further, instead of the endless belt support, a rotating metal drum (endless drum support) having a mirror surface may be used.

  First, the casting process of the resin film manufacturing method according to the present embodiment will be described. As shown in detail in FIG. 2, in the casting process, an insulating film is formed on either the back surface of the support 11 or the surface of the roller (for example, the conveyance roller 17) in contact with the back surface of the support 11. Is applied to charge the surface of the support (FIG. 2, A).

  According to the method for producing a resin film of the present invention, it is possible to suppress the occurrence of entrained air entrainment due to an increase in the film formation speed, and it is possible to lengthen a high-quality resin film without causing a lateral orientation angle deviation or film thickness unevenness. A film can be formed at a high speed for a period. Furthermore, an insulating film is formed on either the roller surface in contact with the back surface of the support or the back surface of the support, and a hardness difference is provided between the back surface of the support and the roller surface in contact with the back surface of the support. Shave can be reduced. If the wear on the back surface of the support can be reduced in this way, mechanical vibration of the support can be reduced, and film thickness unevenness (horizontal unevenness) can be improved.

  The casting solution of the resin solution 16 by the casting die 20 includes a melt casting method in which the resin is heated and the molten resin pressurized by a screw is extruded from a die, or the resin is dissolved in a solvent to be fluid. There is a solution casting method in which a dope having a thickness is cast on a metal drum or a belt and the solvent is evaporated through a drying process, but in this embodiment, as an optical film such as optical characteristics, strength, and smoothness of the film From the viewpoint of performance, it is preferable to cast using a solution casting method.

  Moreover, in the manufacturing method of the resin film of this invention, since it can respond to the increase in film forming speed, the casting speed of the casting film in this embodiment shall be about 50-150 m / min, for example. it can.

  The material for forming the insulating film 22 is not particularly limited, and examples thereof include silicon rubber, ceramics, and silicon oxide film. You may use these in mixture of 2 or more types.

  The means for forming the insulating film on the support is particularly limited as long as it is a method of forming a uniform film thickness on the back surface of the support 11 or the surface of the roller (for example, the transport roller 17) in contact with the back surface of the support. The insulating film material can be formed, for example, by subjecting the surface of the roller in contact with the back surface of the support or the back surface of the support to thermal spraying or vacuum deposition.

  The thickness of the insulating film 22 is usually 5 to 1000 μm, preferably 10 to 500 μm. If the thickness of the insulating film is less than 5 μm, it is not preferable because the insulating film is likely to be scraped by friction and hinders long-term production, and if it exceeds 1000 μm, it is difficult to form a thin film with a uniform surface property.

  In the present embodiment, the means used for charging the surface of the support by applying an electrostatic voltage is not particularly limited, and examples thereof include an electrostatic application device, a charging bar, and an electrostatic sprayer.

  Such an electrostatic voltage is preferably applied after the peeling step and then before casting from the casting die on the support, as shown in FIG. Further, as shown in FIG. 2, it is preferable that the support is neutralized after the peeling step and before the next electrostatic application. Thereby, the charge remaining after the cast film is peeled can be removed, and uneven charging that may be caused by the residual charge can be suppressed. And after static elimination, by applying an electrostatic voltage before newly casting and charging a support surface, generation | occurrence | production of air can be suppressed more reliably, suppressing charging nonuniformity. In FIG. 2, A indicates that the support 11 is in a charged state.

  In addition, the means used for performing the static elimination is not particularly limited, and examples thereof include a static elimination bar and a static elimination blower.

  Furthermore, in the method for producing a resin film according to this embodiment, it is preferable that the casting step is performed under an oxygen concentration of 5% or less. That is, it is sufficient that the oxygen concentration in the casting process is 5% or less. For example, a mixed gas having an oxygen concentration of 5% or less mixed with nitrogen gas or carbon dioxide gas is supplied into the casting process. Can be adjusted. When processes other than the casting process are arranged on the same premises, it is necessary to adjust the entire premises to an oxygen concentration of 5% or less.

  Furthermore, as shown in FIG. 3, in the method for producing a resin film according to this embodiment, a metal compound is contained at both ends of the casting film, and an electrostatic voltage is applied only to both ends of the casting film. More preferred. Thus, by including a metal compound at both ends of the casting film, which is the least robust, the adhesion between the casting film end and the support can be improved, and the casting film end can be stabilized. As a result, it leads to suppression of air entrainment and wide optical unevenness. Further, by applying an electrostatic voltage only to both ends of the casting film, it is possible to simplify the equipment (cost reduction) and facilitate maintenance.

  As a metal compound to be contained at both ends of the cast film, an alkaline earth metal such as magnesium or beryllium or an oxide such as zinc or manganese can be used.

  Further, as a method for containing the metal compound at both ends of the casting film, for example, as shown in FIG. 3, the metal compound inlet 26 is provided on both sides of the casting die 20, and the metal compound is poured from there. The method etc. are mentioned. More specifically, for example, a metal compound-containing dope in which a metal compound is contained in the dope in an amount of about 0.001 to 5% by weight, preferably about 0.01 to 1% by weight, is poured from the inflow port 26. A metal compound is contained at both ends of the cast film.

  Moreover, when making a metal compound contain in a casting film both ends, the width | variety of the casting film both ends which contain the metal compound is 0.01W-0 for each edge part when the casting film full width is set to W. Adjust so that it is in the range of 1 W (that is, 0.02 to 0.2 W of the total width of both ends). This adjustment can be performed, for example, by adjusting the inflow amount of the metal compound at the inlet 26.

  In addition, since both ends of the cast film containing the metal compound can be cut off and removed after the drying step, the metal compound as described above does not remain in the final product. The metal compound does not affect the properties of the resin film produced by the production method according to the present embodiment. Further, the cut film can be re-prepared and reused for the dope for the casting film end. The cutting (slit) step may be performed either before or after stretching the film.

  The casting film (web) formed on the endless belt support 11 in the casting process as described above is removed from the resin film by a peeling process or a drying process using the peeling roller 13, the drying device 14, the winding device 15, and the like. Can be manufactured. The process described below is not particularly limited and can be adopted as long as it is a general process. Specifically, for example, the following steps can be used, but the present invention is not limited to the following steps.

  First, while the formed cast film (web) is conveyed by the endless belt support 11, the solvent in the dope is dried. The drying is performed, for example, by heating the endless belt support 11 or blowing heated air on the web. At that time, although the temperature of the web varies depending on the dope solution, it is preferably in the range of −5 ° C. to 70 ° C. in consideration of the conveyance speed accompanying the evaporation time of the solvent, the degree of dispersion of the fine particles, productivity, etc. A range of from 60 ° C to 60 ° C is more preferable. The higher the temperature of the web, the faster the solvent can be dried. However, when the temperature is too high, the web tends to foam or the flatness tends to deteriorate.

  When the endless belt support 11 is heated, for example, a method of heating the web on the endless belt support 11 with an infrared heater, a method of heating the front and back surfaces of the endless belt support 11 with an infrared heater, the endless belt Examples include a method of heating by heating air on the back surface of the belt support 11, and the method can be appropriately selected as necessary.

  When the heated air is blown, the wind pressure of the heated air is preferably 50 to 5000 Pa in consideration of the uniformity of solvent evaporation, the degree of dispersion of fine particles, and the like. The temperature of the heating air may be dried at a constant temperature, or may be supplied in several steps in the running direction of the endless belt support 11.

  The time from casting the dope onto the endless belt support 11 to peeling the web from the endless belt support 11 varies depending on the film thickness of the resin film to be produced and the solvent used. In consideration of the peelability from the endless belt support 11, it is preferably in the range of 0.5 to 5 minutes.

  The traveling speed of the endless belt support 11 is preferably about 50 to 150 m / min, for example.

  The peeling roll 13 is disposed in the vicinity of the surface of the endless belt support 11 on the side where the dope 16 is cast, and the distance between the endless belt support 11 and the peeling roller 13 is 1 to 100 mm. It is preferable. The dried cast film (web) is peeled off as a film by pulling the dried cast film (web) with tension using the peeling roller 13 as a fulcrum. When the film is peeled from the endless belt support 11, the film is stretched in the film transport direction (Machine Direction: MD direction) by the peeling tension and the subsequent transport tension. For this reason, it is preferable that the peeling tension and the conveying tension when peeling the film from the endless belt support 11 are 50 to 400 N / m.

  Moreover, the residual solvent rate of the film when peeling the film from the endless belt support 12 is the peelability from the endless belt support 12, the residual solvent rate at the time of peeling, the transportability after peeling, and after transporting and drying. Considering the physical characteristics of the resulting resin film, it is preferably 30 to 200% by mass. The residual solvent ratio of the film is defined by the following formula (I).

Residual solvent ratio (mass%) = {(M ₁ −M ₂ ) / M ₂ } × 100 (I)
Here, M ₁ is shows the mass at any point in the film, M ₂ shows the mass after drying for 1 hour at 115 ° C. The film was measured M _1.

  The drying device 14 includes a plurality of transport rollers, and dries the film while transporting the film between the rollers. In that case, you may dry using heating air, infrared rays, etc. independently, and you may dry using heating air and infrared rays together. It is preferable to use heated air from the viewpoint of simplicity. The drying temperature varies depending on the amount of residual solvent in the film, but it is determined by appropriately selecting the residual solvent ratio in the range of 30 to 180 ° C. in consideration of drying time, unevenness of shrinkage, stability of the amount of expansion and contraction, etc. That's fine. Moreover, it may be dried at a constant temperature, or may be divided into two to four stages of temperature, and may be divided into several stages of temperature. Further, the film can be stretched in the MD direction while being transported in the drying device 14.

  The residual solvent ratio of the film after the drying treatment in the drying apparatus 14 is preferably 0.001 to 5% by mass in consideration of the load of the drying process, the dimensional stability expansion / contraction ratio during storage, and the like. In the present embodiment, a film in which the solvent is gradually removed in the drying step and the total residual solvent amount is 15% by mass or less is referred to as a resin film.

  The winding device 15 winds the resin film having a predetermined residual solvent ratio on the winding core to a required length by the drying device 14. In addition, it is preferable that the temperature at the time of winding is cooled to room temperature in order to prevent abrasion, loosening, and the like due to shrinkage after winding. The winder to be used can be used without particular limitation, and may be a commonly used one. Specifically, it can be wound using, for example, a winder using a constant tension method, a constant torque method, a taper tension method, a program tension control method with a constant internal stress, or the like.

  In addition, the manufacturing apparatus of a resin film is not limited to the thing of said structure, For example, you may provide the extending | stretching apparatus etc. separately. Examples of the stretching device include a stretching device that stretches the film peeled from the endless belt support 11 in a direction (Transverse Direction: TD direction) orthogonal to the film transport direction.

  Hereinafter, the composition of the resin solution (dope) used in the present embodiment will be described.

  The resin solution used in this embodiment is obtained by dissolving a transparent resin in a solvent.

  The transparent resin is not particularly limited as long as it is a resin having transparency when formed into a substrate by a solution casting film forming method or the like, but is easily manufactured by a solution casting film forming method or the like. It is preferable that the adhesive property with other functional layers such as a hard coat layer is excellent and that it is optically isotropic. Here, the transparency means that the visible light transmittance is 60% or more, preferably 80% or more, and more preferably 90% or more.

  Specific examples of the transparent resin include cellulose ester resins such as cellulose diacetate resin, cellulose triacetate resin, cellulose acetate butyrate resin, and cellulose acetate propionate resin; polyethylene terephthalate resin and polyethylene naphthalate resin. Acrylic resins such as polymethyl methacrylate resins; Polysulfone (including polyether sulfone) resins, polyethylene resins, polypropylene resins, cellophane, polyvinylidene chloride resins, polyvinyl alcohol resins, ethylene vinyl alcohol resins, Shinji Vinyl resins such as tactic polystyrene resins, cycloolefin resins and polymethylpentene resins; polycarbonate resins; polyarylate resins Polyetherketone resins; polyether ketone imide resin; can be mentioned fluorine-based resin or the like; a polyamide resin. Among these, cellulose ester resins, cycloolefin resins, polycarbonate resins, and polysulfone (including polyethersulfone) resins are preferable. Furthermore, cellulose ester resins are preferred, and among cellulose ester resins, cellulose acetate resins, cellulose propionate resins, cellulose butyrate resins, cellulose acetate butyrate resins, cellulose acetate propionate resins, and cellulose triacetate resins are preferred, Cellulose triacetate resin is particularly preferred. Moreover, the said transparent resin may use the transparent resin illustrated above independently, and may use it in combination of 2 or more type.

  Next, the cellulose ester resin will be described.

  The number average molecular weight of the cellulose ester-based resin is preferably 30,000 to 200,000 in view of high mechanical strength when formed into a resin film and an appropriate dope viscosity in the solution casting film forming method. Moreover, it is preferable that weight average molecular weight (Mw) / number average molecular weight (Mn) exists in the range of 1-5, and it is more preferable that it exists in the range of 1.4-3.0.

  The average molecular weight and molecular weight distribution of a resin such as a cellulose ester resin can be measured using gel permeation chromatography or high performance liquid chromatography. Therefore, the number average molecular weight (Mn) and the weight average molecular weight (Mw) can be calculated using these, and the ratio can be calculated.

  The cellulose ester resin preferably has an acyl group having 2 to 4 carbon atoms as a substituent. As the substitution degree, for example, when the substitution degree of the acetyl group is X and the substitution degree of the propionyl group or butyryl group is Y, the total value of X and Y is 2.2 or more and 2.95 or less, X is preferably more than 0 and 2.95 or less.

  In addition, the portion not substituted with an acyl group usually exists as a hydroxyl group. These cellulose ester resins can be synthesized by a known method. The measuring method of the substitution degree of an acyl group can be measured according to the provisions of ASTM-D817-96.

  The cellulose that is the raw material of the cellulose ester resin is not particularly limited, and examples thereof include cotton linters, wood pulp (derived from coniferous trees and hardwoods), kenaf and the like. The cellulose ester resins obtained from them can be mixed and used at an arbitrary ratio, but it is preferable to use 50% by mass or more of cotton linter. When the acylating agent is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), these cellulose ester resins use an organic acid such as acetic acid or an organic solvent such as methylene chloride, It can be obtained by reacting with a cellulose raw material using such a protic catalyst.

  As the solvent used in the present embodiment, a solvent containing a good solvent for the transparent resin can be used. The good solvent varies depending on the transparent resin used. For example, in the case of a cellulose ester resin, the good solvent and the poor solvent change depending on the acyl group substitution degree of the cellulose ester. For example, when acetone is used as the solvent, the cellulose ester acetate ester (acetyl group substitution degree 2.4), cellulose Acetate propionate is a good solvent, and cellulose acetate (acetyl group substitution degree 2.8) is a poor solvent. Therefore, since the good solvent and the poor solvent differ depending on the transparent resin used, the case of a cellulose ester resin will be described as an example.

  Examples of good solvents for cellulose ester resins include organic halogen compounds such as methylene chloride, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dioxolane derivatives, cyclohexanone, Ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3- Hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, etc. Can be mentioned. Among these, organic halogen compounds such as methylene chloride, dioxolane derivatives, methyl acetate, ethyl acetate, acetone and the like are preferable. These good solvents may be used alone or in combination of two or more.

  The dope may contain a poor solvent as long as the transparent resin does not precipitate. Examples of poor solvents for cellulose ester resins include alcohols having 1 to 8 carbon atoms such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol, methyl ethyl ketone, and methyl isobutyl. Examples include ketones, propyl acetate, monochlorobenzene, benzene, cyclohexane, tetrahydrofuran, methyl cellosolve, and ethylene glycol monomethyl ether. These poor solvents may be used alone or in combination of two or more.

  In addition, the resin solution used in the present embodiment may contain other components (additives) other than the transparent resin and the solvent as long as the effects of the present invention are not impaired. Examples of the additive include fine particles, plasticizers, antioxidants, ultraviolet absorbers, heat stabilizers, conductive substances, flame retardants, lubricants, and matting agents.

  The fine particles are appropriately selected according to the purpose of use. Specific examples of the purpose of use include, for example, a case where visible light is scattered by being contained in a transparent resin, a case where slipperiness is imparted, and the like. By containing, both the scattering of visible light and the improvement of slipperiness can be improved. Moreover, in any case, it is necessary to adjust the particle size and content of the fine particles to such an extent that the transparency of the film is not impaired. The fine particles may be inorganic fine particles such as silicon oxide or organic fine particles such as acrylic resin.

  Examples of the inorganic fine particles include silicon oxide, titanium oxide, aluminum oxide, zirconium oxide, magnesium oxide, calcium carbonate, strontium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, and aluminum silicate. And fine particles such as magnesium silicate and calcium phosphate. Among these, fine particles such as silicon oxide, titanium oxide, aluminum oxide, zirconium oxide, and magnesium oxide are preferably used.

  Examples of the organic fine particles include acrylic resins such as polymethyl methacrylate resin, acrylic styrene resins, silicone resins, polystyrene resins, polycarbonate resins, benzoguanamine resins, melamine resins, polyolefin resins, polyester resins, Fine particles composed of polyamide-based resin, polyimide-based resin, polyfluorinated ethylene-based resin, and the like can be given. Among these, crosslinked polystyrene particles, acrylic resin fine particles of polymethyl methacrylate particles, and the like are preferable.

  As the fine particles, the fine particles exemplified above may be used alone, or two or more kinds may be used in combination.

  The average particle diameter of the fine particles is preferably 0.1 to 10 μm, and more preferably 0.3 to 5 μm. If the average particle size of the fine particles is too small, the functionality due to the fine particles tends not to be sufficiently exhibited. On the other hand, if it is too large, not only the functionality due to the fine particles cannot be sufficiently exhibited, but also the translucency of the resin film tends to be lowered. In addition, although the average particle diameter of microparticles | fine-particles can be measured also by TEM observation of the cross section of a resin film, it can also be measured using a laser diffraction type particle size distribution measuring apparatus etc.

  The content of the fine particles is preferably 0.01 to 35% by mass and more preferably 0.05 to 30% by mass with respect to the transparent resin. If the content of the fine particles is too small, the functionality due to the fine particles tends to be insufficient. Moreover, when there is too much, there exists a tendency for the translucency of a resin film to fall.

  The shape of the fine particles is not particularly limited, and examples thereof include a spherical shape, a flat plate shape, and a needle shape, and a spherical shape is preferable.

  The plasticizer can be used without particular limitation, for example, phosphate ester plasticizer, phthalate ester plasticizer, trimellitic ester plasticizer, pyromellitic acid plasticizer, glycolate plasticizer, Examples include citrate plasticizers and polyester plasticizers. When the plasticizer is contained, the content is preferably 1 to 40% by mass, and 3 to 20% by mass with respect to the cellulose ester-based resin in consideration of dimensional stability and processability. More preferably, it is more preferably 4 to 15% by mass. If the content of the plasticizer is too small, a smooth cut surface cannot be obtained when slitting or punching, and there is a tendency for generation of chips. That is, the effect of including a plasticizer cannot be sufficiently exhibited.

  The antioxidant can be used without any particular limitation, but for example, a hindered phenol compound is preferably used. Moreover, when it contains the said antioxidant, it is preferable that content of antioxidant is 1 ppm-1.0% by mass ratio with respect to a cellulose-ester resin, and it is more preferable that it is 10-1000 ppm.

  The resin film produced by the production method according to the present embodiment can be used for a polarizing plate or a liquid crystal display member because of its high dimensional stability. In this case, deterioration prevention of the polarizing plate or the liquid crystal is possible. Therefore, an ultraviolet absorber is preferably used.

  As the ultraviolet absorber, those which are excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less and have little absorption of visible light having a wavelength of 400 nm or more are preferably used from the viewpoint of good liquid crystal display properties. Specifically, the transmittance at 380 nm is preferably less than 10%, more preferably less than 5%. Specific examples of the ultraviolet absorber include oxybenzophenone compounds, benzotriazole compounds (benzotriazole ultraviolet absorbers), salicylic acid ester compounds, benzophenone compounds (benzophenone ultraviolet absorbers), and cyanoacrylates. Compounds, nickel complex compounds, triazine compounds, and the like. In these, a benzotriazole type ultraviolet absorber and a benzophenone type ultraviolet absorber are preferable. The content of the ultraviolet absorber is preferably 0.1% by mass to 2.5% by mass, and 0.8% by mass to 2.0% by mass in consideration of the effect as an ultraviolet absorber, transparency, and the like. % Is more preferable.

  Examples of the heat stabilizer include kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide, inorganic fine particles such as alumina, and alkaline earth metal salts such as calcium and magnesium.

  The conductive material is not particularly limited, and examples thereof include ionic conductive materials such as anionic polymer compounds, conductive fine particles such as metal oxide fine particles, and antistatic agents. By containing the conductive substance, a resin film having a preferable impedance can be obtained. Here, the ion conductive substance is a substance that shows electric conductivity and contains ions that are carriers for carrying electricity.

  Next, as an example of a method for preparing a dope, a case where a cellulose ester resin is used as a transparent resin will be described.

  The method for dissolving the cellulose ester resin when preparing the dope is not particularly limited, and a general method can be used. By combining heating and pressurization, it is possible to heat above the boiling point of the solvent at normal pressure, and it is possible to dissolve the cellulose ester resin in the solvent above the boiling point at normal pressure. It is preferable from the viewpoint of preventing the occurrence of. In addition, a method in which a cellulose ester resin is mixed with a poor solvent and wetted or swollen, and then a good solvent is added and dissolved is also preferably used.

  The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas, or a method of heating the solvent in a sealed container and increasing the vapor pressure of the solvent by the heating. The heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  A higher solvent temperature (heating temperature) for dissolving the cellulose ester-based resin is preferable from the viewpoint of solubility of the cellulose ester. However, when the heating temperature is increased, the pressure in the container is increased by the pressurization. Productivity must be reduced. Therefore, the heating temperature is preferably 45 to 120 ° C. The pressure is adjusted to a pressure at which the solvent does not boil at the set temperature. Alternatively, a cooling dissolution method is also preferably used, whereby the cellulose ester resin can be dissolved in a solvent such as methyl acetate.

  Next, the obtained cellulose ester resin solution is filtered using a suitable filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like. However, if the absolute filtration accuracy is too small, there is a problem that the filter medium is likely to be clogged. For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, and a filter medium with 0.001 to 0.008 mm is more preferable.

There is no restriction | limiting in particular in the material of a filter medium, A normal filter medium can be used. For example, a plastic filter material such as polypropylene or Teflon (registered trademark), a filter paper using cellulose fiber or rayon, or a metal filter material such as stainless steel is preferable because the fiber does not fall off. It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material cellulose ester resin solution by filtration. The bright spot foreign matter is a state where two polarizing plates are placed in a crossed Nicols state, a resin film is placed between them, light is applied from one polarizing plate side, and observation is performed from the other polarizing plate side. It is a point (foreign matter) where light from the opposite side appears to leak, and the number of bright spots having a diameter of 0.01 mm or more is preferably 200 / cm ² or less.

  The filtration is not particularly limited and can be carried out by a usual method, but the method of filtration while heating at a temperature not lower than the boiling point of the solvent at normal pressure and at which the solvent does not boil under pressure may be performed before and after the filtration. The increase in the difference in filtration pressure (referred to as differential pressure) is small and preferable. The temperature is preferably 35 to 60 ° C. The filtration pressure is preferably smaller, for example, 1.6 MPa or less.

  When the additives are contained, for example, the additives may be dissolved in an organic solvent such as alcohol, methylene chloride, dioxolane, etc. and then added to the dope, or may be added directly to the dope composition. In addition, for inorganic powders that do not dissolve in organic solvents, the additive and cellulose ester resin are added to the dope using a dissolver or sand mill with the additive dispersed in the cellulose ester resin. It is preferable.

  The fine particles are dispersed in the obtained cellulose ester resin solution. The method for dispersing is not particularly limited, and can be performed, for example, as follows. For example, first, a dispersion solvent and fine particles are stirred and mixed, and then dispersed using a disperser. This is a fine particle dispersion. The fine particle dispersion is added to the cellulose ester resin solution and stirred.

  Examples of the dispersing solvent include lower alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, and butyl alcohol. Moreover, although it does not specifically limit to lower alcohol, It is preferable to use the thing similar to the solvent used when preparing the solution of a cellulose-ester-type resin.

The dispersing machine can be used without any particular limitation, and a general dispersing machine can be used. Dispersers can be broadly divided into media dispersers and medialess dispersers. Medialess dispersers are preferred from the viewpoint of lower haze (higher translucency). Examples of the media disperser include a ball mill, a sand mill, and a dyno mill. Examples of the medialess disperser include an ultrasonic type, a centrifugal type, and a high pressure type, and a high pressure type dispersing device is preferable. The high-pressure dispersion device is a device that creates special conditions such as high shear and high pressure by passing a composition in which fine particles and a solvent are mixed at high speed through a narrow tube. Examples of the high-pressure dispersing device include an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation, a nanomizer manufactured by Nanomizer, and the like, and a Menton Gorin type high-pressure dispersing device. Examples of the Menton Gorin type high-pressure dispersion device include a homogenizer manufactured by Izumi Food Machinery, UHN-01 manufactured by Sanwa Machinery Co., Ltd., and the like.

  Moreover, as a solvent made to flow down from the both ends of the discharge port of a casting die, the same solvent as the resin solution (dope) can be used. Specifically, a good solvent for the transparent resin may be contained, and a poor solvent may be contained as necessary.

  According to the manufacturing method according to the present embodiment as described above, entrained air entrainment due to an increase in the film forming speed can be suppressed, and a high-quality resin film can be produced without causing lateral orientation angle deviation and film thickness unevenness. Is obtained.

  In addition, it is preferable that the width | variety of the resin film obtained here is 1000-2500 mm from the point of the use to a large sized liquid crystal display device, the use efficiency of the film at the time of polarizing plate processing, and production efficiency.

  Moreover, it is preferable that the film thickness of a resin film is 20-70 micrometers from points, such as a viewpoint of thickness reduction of a liquid crystal display device, and the production stabilization of a resin film. Here, the film thickness is an average film thickness, and 20 to 200 locations in the width direction of the resin film are measured with a contact-type film thickness meter manufactured by Mitutoyo Corporation, and the average value of the measured values. Is shown as the film thickness.

(Polarizer)
The polarizing plate which concerns on this embodiment is equipped with a polarizing element and the transparent protective film arrange | positioned on the surface of the said polarizing element, and the said transparent protective film is the said resin film. The polarizing element is an optical element that emits incident light converted to polarized light.

  As the polarizing plate, for example, a resin film or a saponified polyvinyl alcohol aqueous solution is used on at least one surface of a polarizing element produced by immersing and stretching a polyvinyl alcohol film in an iodine solution. What laminated | stacked the said laminated | multilayer film is preferable. Further, the resin film may be laminated on the other surface of the polarizing element, or a transparent protective film for another polarizing plate may be laminated. As the transparent protective film for the polarizing plate, for example, as a commercially available cellulose ester film, KC8UX2M, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC8UY-HA, KC8UX-RHA (above, manufactured by Konica Minolta Opto) Is preferably used. Or you may use resin films, such as cyclic olefin resin other than a cellulose-ester film, an acrylic resin, polyester, a polycarbonate. In this case, since the saponification suitability is low, it is preferable to perform an adhesive process on the polarizing plate through an appropriate adhesive layer.

  As described above, the polarizing plate uses the resin film as a protective film laminated on at least one surface side of the polarizing element. In that case, when the said resin film works as a phase difference film, it is preferable to arrange | position so that the slow axis of a resin film may be substantially parallel or orthogonal to the absorption axis of a polarizing element.

  Moreover, as a specific example of the said polarizing element, a polyvinyl alcohol-type polarizing film is mentioned, for example. Polyvinyl alcohol polarizing films include those obtained by dyeing iodine on polyvinyl alcohol films and those obtained by dyeing dichroic dyes. As the polyvinyl alcohol film, a modified polyvinyl alcohol film modified with ethylene is preferably used.

  The polarizing element is obtained as follows, for example. First, a film is formed using a polyvinyl alcohol aqueous solution. The obtained polyvinyl alcohol film is uniaxially stretched and then dyed or dyed and then uniaxially stretched. And preferably, a durability treatment is performed with a boron compound.

  The thickness of the polarizing element is preferably 5 to 40 μm, more preferably 5 to 30 μm, and more preferably 5 to 20 μm.

  When the cellulose ester resin film is laminated on the surface of the polarizing element, it is preferable to bond the cellulose ester resin film 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-type resin film, it is preferable to carry out the adhesive process to a polarizing plate through a suitable adhesion layer.

  The polarizing plate as described above uses the resin film according to this embodiment as a transparent protective film. Since this resin film is of high quality with no lateral alignment angle deviation and no film thickness unevenness, the image quality of the liquid crystal display device can be improved when the obtained polarizing plate is applied to, for example, a liquid crystal display device.

(Liquid crystal display device)
The liquid crystal display device according to this embodiment includes a liquid crystal cell and two polarizing plates arranged so as to sandwich the liquid crystal cell, and at least one of the two polarizing plates is the polarizing plate. . Note that the liquid crystal cell is a cell in which a liquid crystal substance is filled between a pair of electrodes, and by applying a voltage to the electrodes, the alignment state of the liquid crystal is changed and the amount of transmitted light is controlled. Such a liquid crystal display device uses the polarizing plate as a transparent protective film for the polarizing plate. By doing so, a high-quality liquid crystal display device can be obtained.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples.

[Example 1]
A resin film was produced by the following method.
(Preparation of dope)
The following materials were put into a sealed container, heated at 80 ° C., completely dissolved with stirring, and filtered to prepare a dope.

Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 8 parts by weight Plasticizer (ethylphthalylethyl glycolate) 2 parts by weight Ultraviolet absorber (Tinuvin 326, manufactured by BASF Japan Ltd.) 1 part by weight Inorganic fine particles ( Aerosil 200V, manufactured by Nippon Aerosil Co., Ltd.) 0.1 parts by weight Methylene chloride 418 parts by weight Ethanol 23 parts by weight (Production of cellulose acetate film)
First, a ceramic insulating film (thickness: 50 μm) was provided on the back surface of an endless belt support made of SUS316 by ceramic spraying. Then, the dope obtained as described above was cast at a dope temperature of 35 ° C. and a casting speed of 140 m from the endless belt support at a temperature of 20 ° C. by a casting die comprising a coat hanger die. The film was cast at a rate of 1 minute.

  When casting, the dope containing 0.5% by weight of a metal compound (magnesium oxide) was poured from the end of the casting die. The casting width of the metal compound-containing dope was 0.05 W, where W is the total width of the casting film.

[Example 2]
A cellulose acetate film was produced in the same manner as in Example 1 except that the metal compound was not contained at both ends of the cast film.

[Example 3]
A cellulose acetate film was produced in the same manner as in Example 1 except that the insulating film was formed with a thickness of 50 μm on the transport roller that was in contact with the back surface of the support instead of the back surface of the support.

[Example 4]
Except that the insulating film was formed with a thickness of 500 μm on the transport roller in contact with the back surface of the support instead of the back surface of the support, and the metal film was not contained at both ends of the casting film, the same as in Example 1, A cellulose acetate film was produced.

[Comparative Example 1]
A cellulose acetate film was produced in the same manner as in Example 1 except that the insulating film was formed on the support surface instead of the back surface of the support with a thickness of 800 μm.

[Comparative Example 2]
A cellulose acetate film was produced in the same manner as in Example 1 except that the insulating film was not provided.

(Evaluation)
The following evaluation tests were performed on the resin films (Examples 1 to 4 and Comparative Examples 1 and 2) obtained as described above.

(With or without foam generation)
The resin films produced in Examples 1 to 4 and Comparative Examples 1 and 2, respectively, were cut out to a length of 1 m in the longitudinal direction with the full width, and the presence or absence of generation of bubbles on the film surface of this film sample was visually evaluated. The reduced pressure value when bubbles were generated was recorded as the reduced pressure when bubbles were generated. The results are shown in Table 1.

(Thickness unevenness)
For each of the resin films, the evaluation of the film thickness deviation was carried out by measuring each film with a surface roughness measuring machine (SURFTEST SU-3100) manufactured by Mitutoyo Corporation by measuring 50 mm square, and the evaluation was performed according to the following ranks. went.
◎ Film thickness deviation 0.15 μm or less ○ Film thickness deviation 0.15 μm to 0.20 μm
△ Thickness deviation 0.20μm ~ 0.25μm
X Film thickness deviation 0.25 μm or more The results are shown in Table 1.

(Orientation angle deviation)
Using a phase difference device (KOBRA-WR) manufactured by Oji Scientific Instruments Co., Ltd., 100 mm from both ends of the film and the orientation angle at the center of the film width were measured, and the difference between these maximum and minimum values was taken as the deviation. The evaluation was performed according to the following rank.
◎ Orientation angle deviation ± 0.3 degrees or less ○ Orientation angle deviation ± 0.3 to less than ± 0.7 degrees △ Orientation angle deviation ± 0.7 to less than ± 1.0 degrees × Orientation angle deviation ± 1.0 degrees or more The results are shown in Table 1.

[Discussion]
As can be seen from Table 1, in the resin films prepared in Examples 1 to 4 in which an insulating film is provided on the surface of the transport roller in contact with the back surface of the support or the back surface of the support, the air travel speed is 140 m / min. Bubble generation due to entrainment could be sufficiently suppressed, and the orientation angle deviation was small. Further, no film thickness unevenness was observed even after 2 weeks. Further, in the resin films according to Examples 1 and 3 in which the metal compound is contained at both ends of the cast film, the air entrainment can be further suppressed as compared with the resin films according to Examples 2 and 4 that are not included. It was.

  On the other hand, in the resin film according to Comparative Example 1 in which an insulating film was provided on the support surface, air entrainment was suppressed, but the orientation angle deviation became large and film thickness unevenness occurred. Moreover, in the resin film which concerns on the comparative example 2 which did not provide the insulating film, air entrainment could not be suppressed.

  From the above, it was shown that according to the method for producing a resin film according to the present embodiment, a high-quality resin film can be obtained at a high speed for a long period of time without involving air.

1 Resin film production equipment
11 Endless belt support 13 Peeling roller
14 Drying device 15 Winding device
17 Conveying roller 20 Casting die 24 Static elimination bar 26 Metal compound inlet

Claims (7)

A casting step in which a resin solution in which a transparent resin is dissolved in a solvent is cast from a casting die on a continuously running support to form a casting film, and the casting film is removed from the support. A peeling step for peeling, and a drying step for drying the cast film peeled off,
In the casting step, an insulating film is formed on either the roller surface in contact with the back surface of the support or the back surface of the support, and the support surface is charged by applying an electrostatic voltage from the support surface. A method for producing a resin film.   The method for producing a resin film according to claim 1, wherein the insulating film is composed of at least one selected from the group consisting of silicon rubber, ceramics, and silicon oxide film, and has a film thickness of 5 to 1000 μm. The manufacturing method of the resin film of Claim 1 or 2 which makes a metal compound contain in the both ends of a cast film.   The method for producing a resin film according to any one of claims 1 to 3, wherein after the peeling step, the surface of the support is charged by applying an electrostatic voltage before casting from the casting die onto the support.   The method for producing a resin film according to claim 1, wherein the support is neutralized after the peeling step and before the surface of the support is charged.   The manufacturing method of the resin film in any one of Claims 1-5 which performs a casting process on the conditions whose oxygen concentration is 5% or less.   The method for producing a resin film according to claim 1, wherein the electrostatic voltage is applied by any one selected from the group consisting of an electrostatic application device, a charging bar, and an electrostatic sprayer.

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