JP4665939B2 - Manufacturing method of optical film - Google Patents

Description

  The present invention relates to a cellulose ester film, and more particularly to an optical film having improved optical properties and tear strength of a cellulose ester film itself used in a polarizing plate of a liquid crystal display device or a circularly polarizing plate used in an organic EL display. is there. Further, the present invention relates to a polarizing plate using the cellulose ester film or a display device having a cellulose ester film.

  Cellulose triacetate film is transparent, has excellent physical and mechanical properties, and has little dimensional change due to changes in temperature and humidity, and has been used in a wide range of fields such as photographic film bases, drafting tracing films, and electrical insulation materials. Recently, it is used as a polarizing plate used in a liquid crystal display, a protective film for an optical polarizing plate used in an organic EL display, an optical compensation film support, or a retardation plate.

  Cellulose triacetate films used for polarizing plates of liquid crystal display elements are required to have high light transmittance, optical non-orientation, good adhesion to polarizing films, excellent flatness, and easy absorption of ultraviolet rays. The

  Furthermore, when used for a liquid crystal display for mounting on automobiles, good durability such as no deterioration under high humidity heat and excellent dimensional stability is also required.

  The cellulose triacetate film has excellent properties in light transmission and optical non-orientation, etc., but has no property of absorbing ultraviolet rays, for example, so as to prevent deterioration of liquid crystal in liquid crystal displays due to ultraviolet rays. In general, an ultraviolet absorber is added to a cellulose triacetate film which is a protective film for a polarizing plate provided on the outermost side of a liquid crystal display.

  Specifically, the cellulose ester film used for the protective film for liquid crystal contains fine particles in order to improve ultraviolet resistance and transportability.

  For example, Patent Document 1 discloses a technique containing metal oxide particles of 0.2 μm or less, Patent Document 2 discloses a technique containing methyl group-containing silica fine particles in cellulose acetate, and Patent Document 3 discloses a cellulose ester film. Patent Document 4 describes a technique for applying particles to a resin and containing particles and does not deteriorate the transparency of cellulose ester.

All of these films are produced by casting a dissolved cellulose ester.
JP-A-6-130226 JP-A-7-11055 JP-A-10-44327 Japanese Patent Laid-Open No. 10-95862

  By the way, in casting film formation, film shrinkage occurs when the solvent is dried, and the film surface quality is inevitably deteriorated. Therefore, measures are taken to improve the surface quality during or after drying. Yes.

  For example, Japanese Patent Application Laid-Open No. 4-152125 describes a technique of holding and drying in the width direction, and Japanese Patent Application Laid-Open No. 6-278149 describes a technique of processing with a heating roll and a cooling roll. In particular, the holding and drying technique is an important technique because it has a large improvement effect.

  However, when the film containing the particles is simply held and dried, a gap is formed between the particles and the film, and the tear strength of the film also deteriorates simultaneously with the deterioration of the optical properties of the film such as an increase in haze and a decrease in transmittance. There were drawbacks.

  The present invention has been made in view of the above circumstances, and its purpose is to prevent deterioration of the optical properties of the cellulose ester film formed by casting film formation, and at the same time, to improve the tear strength of the film and to provide sufficient machinery. The object is to provide a cellulose ester film having a sufficient strength. Moreover, it is providing the manufacturing method.

  The above object of the present invention has been achieved by the following constitution.

  1. A cellulose ester film comprising flat particles.

  2. 2. The cellulose ester film according to 1, wherein the flat particles have an aspect ratio of 2 to 7.

  3. The cellulose ester film according to 1 or 2, wherein the flat particles have an average particle size of 0.2 to 10 µm.

  4). The cellulose ester film according to any one of claims 1 to 3, wherein the flat particles are contained in an amount of 5% by mass or more of all particles having an average particle diameter of 0.2 to 10 µm.

  5. The cellulose ester film according to any one of 1 to 4, wherein the flat particles are secondary particles having particles having a primary average particle diameter of 0.2 μm or less.

  6). A cellulose ester film produced through a process of holding and drying in the width direction, containing particles having an average particle diameter of 0.2 to 10 μm, and having a haze converted to a thickness of 80 μm of 0.6% or less And the dynamic friction coefficient of the front and back of a film is 0.3-1.5, The cellulose-ester film characterized by the above-mentioned.

  7. The cellulose ester film according to any one of 1 to 6, wherein the cellulose film has a tear strength in terms of a thickness of 80 μm of 18 g or more.

  8). The cellulose ester film according to any one of 1 to 7, wherein the cellulose ester film contains a lower fatty acid ester of cellulose as a main component.

  9. The cellulose ester film is a lower fatty acid cellulose ester, and is dissolved in an organic solvent in the course of heating to 0 to 120 ° C. after cooling to −100 to −10 ° C., and the resulting cellulose ester-containing organic solvent solution The cellulose ester film according to any one of 1 to 8, wherein the cellulose ester film is a film produced by coating the composition on an endless belt or a drum support.

  10. The cellulose ester film according to any one of 1 to 9, wherein the cellulose ester film is a protective film for a polarizing plate.

  11. 11. The cellulose ester film according to any one of 1 to 10, wherein the cellulose ester film has an in-plane retardation value R0 of 200 nm or less.

  12 In the method of producing a cellulose ester film through a step of casting and drying the cellulose ester film obtained by casting a cellulose ester solution containing particles on a support, and then peeling the cellulose ester film from the support. The manufacturing method of the cellulose-ester film characterized by the amount of residual solvents at the time of peeling from 10 mass% or more.

  13. 13. The method for producing a cellulose ester film according to 12, which comprises a step of stretching 1.01 times or more in the width direction in a region where the residual solvent amount is less than 50% by mass in the drying zone after peeling.

  14 13. The method for producing a cellulose ester film according to 12, comprising a step of stretching 1.01 to 1.50 times in the width direction in a region where the residual solvent amount is 10 to 35% by mass.

  15. 12 to 14 characterized in that the particles are flat particles and secondary particles having an average particle diameter of 0.2 to 10 μm, having particles having a primary average particle diameter of 0.2 μm or less. The manufacturing method of the cellulose-ester film of any one.

  A cellulose ester film produced by the method according to any one of 16.12 to 15.

  17. A polarizing plate comprising the cellulose ester film according to any one of 17.1 to 11 and 16 on at least one surface.

  18. A display device using the cellulose ester film according to any one of 1 to 11 and 16.

  19. A display device using the polarizing plate according to item 19.17.

  That is, in the present invention, when forming a film by casting film formation, a gap is formed between the particles and the film due to holding and drying the film containing the particles, and the optical properties of the film are deteriorated. It was made to improve the defect that the tear strength deteriorates. Focusing on the particle shape of the particles, if the primary particles were small particles of 0.2 μm or less, they were formed at the time of holding and drying the film. The present inventors have found that the secondary particles are likely to be deformed into a flat shape and that the generation of gaps between the particles and the film can be suppressed, and the present invention has been achieved.

  On the other hand, even when the particles contain particles having a size of 0.2 μm or more, if the residual amount of the solvent in the film is 10% by mass or more, if the particles are retained and dried, the particles are likely to be deformed to have a flat shape. At the same time, it was found that the generation of gaps between the films was suppressed, and the present invention was achieved.

  Hereinafter, the present invention will be described in detail.

  The invention of claim 1 of the present invention is characterized in that the cellulose ester film contains flat particles.

  The cellulose ester according to the present invention is particularly preferably a cellulose ester substituted with an acyl group having 2 to 4 carbon atoms. Cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate, cellulose acetate propio Examples thereof include nate butyrate.

  These can also be mixed and used as appropriate. The total acyl group substitution degree of the cellulose ester is preferably 2.3 to 3.0.

  In the case of cellulose acetate, cellulose acetate having a polymerization degree of 250 to 400 and a bound acetic acid amount of 54 to 62.5% is particularly preferable, and a cellulose acetate having a bound acetic acid amount of 58 to 62.5% is more preferable because of its strong base strength.

  As the cellulose ester, either a cellulose ester synthesized from cotton linter and a cellulose ester synthesized from wood pulp (derived from coniferous or hardwood) can be used alone or in combination.

  It is preferable to use a large amount of cellulose ester synthesized from a cotton linter that has good releasability from a belt support (for example, an endless belt) or a drum support because of high productivity.

  When the ratio of cellulose ester synthesized from cotton linter is 60% by mass or more, the effect of releasability becomes remarkable. Therefore, the content is preferably 60% by mass or more, more preferably 85% by mass or more, and further, it is used alone. Is most preferred.

  In general, a plasticizer is added to the cellulose ester film. Although it does not specifically limit as a plasticizer which can be used by this invention, In a phosphate ester type | system | group, a triphenyl phosphate, a tricresyl phosphate, a cresyl diphenyl phosphate, an octyl diphenyl phosphate, a diphenyl biphenyl phosphate, a trioctyl phosphate, a tributyl phosphate In the phthalate ester system, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, etc., in the glycolate system, triacetin, tributyrin, butyl phthalyl butyl glycolate, ethyl Phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, etc. alone or in combination Preferred.

  If necessary, two or more plasticizers may be used in combination. In this case, the use ratio of the phosphate ester type plasticizer is 50% or less, which is unlikely to cause hydrolysis of the cellulose ester film, and is durable. It is preferable because it is excellent.

  It is more preferable that the ratio of the phosphate ester plasticizer is small, and it is particularly preferable to use only the phthalate ester or glycolate ester plasticizer. Alternatively, an oligomer or polymer having a molecular weight of 1000 to 100,000 such as an aliphatic linear polyester, a polyvinyl acetate copolymer, or a methyl methacrylate copolymer can be added as a polymer plasticizer.

  In the present invention, the amount of the plasticizer to be added is preferably 3 to 30% by mass, more preferably 10 to 25% by mass, based on the cellulose ester. More preferably, it is 15 to 25% by mass. If it exceeds 30% by mass, mechanical strength and dimensional stability tend to deteriorate.

  In the cellulose ester film of the present invention, it is preferable to use an ultraviolet absorber. From the viewpoint of preventing deterioration of the liquid crystal, the ultraviolet absorber is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less, and has good liquid crystal display properties. Those having as little absorption of visible light as possible with a wavelength of 400 nm or more are preferably used.

  In the present invention, the transmittance particularly at a wavelength of 370 nm needs to be 10% or less, preferably 5% or less, more preferably 2% or less.

  Examples of commonly used compounds include, but are not limited to, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like.

  In this invention, it is preferable to use 1 or more types of these ultraviolet absorbers, and you may contain 2 or more types of different ultraviolet absorbers.

  The ultraviolet absorber preferably used in the present invention is a benzotriazole ultraviolet absorber, a benzophenone ultraviolet absorber, or the like. An embodiment in which a benzotriazole-based ultraviolet absorber with less unnecessary coloring is added to the cellulose ester film is particularly preferable.

  Among them, an ultraviolet absorber having a distribution coefficient described in Japanese Patent Application No. 11-295209 of 9.2 or more, preferably 10.1 or more is preferably used.

  In addition, triazine-based ultraviolet absorbers or polymer ultraviolet absorbers described in Japanese Patent Application No. 11-332725 and JP-A-6-130226 are also preferably used.

  The ultraviolet absorber is added by dissolving the ultraviolet absorber in an alcohol, such as methanol or ethanol, or an organic solvent such as methylene chloride, dioxolane, acetone, or methyl acetate, and then into an organic solvent solution of cellulose ester (also simply referred to as a dope). It may be added or added directly during the dope composition.

  For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and cellulose ester to disperse and then added to the dope.

  The amount of the UV absorber used in the present invention is 0.1 to 2.5% by mass, preferably 0.5 to 2.0% by mass, more preferably 0.8 to 2.0% by mass, based on the cellulose ester. It is. When the amount of the ultraviolet absorber used is more than 2.5% by mass, the transparency tends to deteriorate, which is not preferable.

  Examples of the solvent for the cellulose ester according to the present invention include lower alcohols such as methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, and n-butanol, cyclohexanedioxanes, and lower aliphatic hydrocarbon chlorides such as methylene chloride. Things can be used.

  As a solvent ratio, for example, methylene chloride is preferably 70 to 95% by mass, and other solvents are preferably 5 to 30% by mass. The concentration of the cellulose ester is preferably 10 to 50% by mass.

  The method for producing the cellulose ester film in the present invention is not particularly limited, and may be a method generally used in the art. For example, U.S. Pat. Nos. 2,492,978, 2,739,070, 2,739, No. 069, No. 2,492,977, No. 2,336,310, No. 2,367,603, No. 2,607,704, British Patent Nos. 64,071, No. 735,892, 45-9074, 49-4554, 49-5614, 60-27562, 61-39890, 62-4208 and the like can be referred to.

  In addition to cellulose ester and solvent, additives such as necessary plasticizers and UV absorbers are mixed with the solvent in advance, dissolved or dispersed, and then added to the solvent before dissolving the cellulose ester. You may throw into dope.

  The heating temperature after the addition of the solvent is not less than the boiling point at 1 atm of the solvent used, and is preferably in a range where the solvent does not boil, for example, 60 ° C. or more, particularly 80 to 110 ° C. It is. The pressure is determined so that the solvent does not boil at the set temperature.

  After dissolving the cellulose ester, take it out of the container while cooling, or take it out from the container with a pump and cool it with a heat exchanger, etc., and use it for film formation. Although it is good, it is more preferable to cool to a temperature 5 to 10 ° C. lower than the boiling point and perform casting at that temperature because the dope viscosity can be reduced.

  In the present invention, the dope obtained by dissolving the cellulose ester is cast on a support (casting process), heated to remove a part of the solvent (drying process on the support), and then peeled off from the support. Then, it is the best means to obtain a cellulose ester film by passing the peeled film through a holding and drying step (film holding and drying step) and further drying and heating (film drying step).

  As the support in the casting step, a support in which a belt-like or drum-like stainless steel is mirror-finished is used. The temperature of the support in the casting process can be cast in a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, but the dope is gelled by casting on a support at 5 to 30 ° C. In order to increase the peeling limit time, it is preferable to cast it on a support at 5 to 15 ° C.

  Here, the peeling limit time means the time during which the dope cast on the support is at the limit of the casting speed at which a transparent and flat film can be continuously obtained. A shorter peeling limit time is preferable because of excellent productivity.

  The drying process on the support will be described. In the drying step, the dope is cast and once gelled, and when the time required from the casting to peeling is 100%, the dope temperature is set to 40% within a time corresponding to 30% from the casting start. By setting the temperature to ˜70 ° C., the evaporation of the solvent is promoted, and it can be peeled off from the support as soon as possible.

  In order to further increase the peel strength, the dope temperature is preferably set to 55 to 70 ° C. within a time corresponding to 30% from the start of casting. It is preferable to maintain at this temperature for a time longer than the time corresponding to 20% of the time for drying on the support, and more preferably 40% or more.

  In order to maintain the support at this temperature, it is preferable to adjust the support temperature by a method such as hot water, electric heating, or hot air. Regarding drying on the support, it is preferable to peel the dope from the support in a state where the residual solvent amount is 60 to 150% because the peel strength from the support is small, and the residual solvent amount is more preferably 80 to 120%. .

  The temperature of the dope when peeling the dope is preferably 0 to 30 ° C., because the base strength at the time of peeling can be increased and the base breakage at the time of peeling can be prevented, and 5 to 20 ° C. is more preferable.

  In the present invention, the amount of residual solvent in the film formed on the support is represented by the following formula.

Residual solvent amount = (mass of residual volatile matter / film mass after heat treatment) × 100%
The residual volatile matter mass is a value obtained by subtracting the film mass after the heat treatment from the film mass before the heat treatment when the film is heat treated at 115 ° C. for 1 hour.

  In the film holding and drying step, the residual solvent amount when holding and drying the film is preferably 10% by mass or more, more preferably 15% by mass or more, and most preferably 20% by mass or more.

  When the primary particles of 0.2 to 10 μm are not contained, the amount of residual solvent is not particularly specified, but 5% by mass or more is preferable.

  In the film holding and drying step, generally, a method of holding both ends of the film by a roll suspension method, a pin tenter method, or a clip tenter method and drying while transporting is adopted.

  When used as a liquid crystal display member, it is preferable to dry while maintaining the width by a tenter method in order to improve dimensional stability.

  In particular, it is preferable to maintain the width when the residual solvent amount immediately after peeling from the support is at least 10% by mass or more in order to further improve the dimensional stability. In particular, it is preferable to stretch in the width direction within a region where the residual solvent amount is 10% by mass or more and less than 50% by mass, and the stretching ratio is preferably 1.01 or more.

  More preferably, it is preferably stretched so as to be 1.01 to 1.50 times, particularly 1.03 to 1.2 times in the width direction in the region where the residual solvent amount is 10 to 35% by mass.

  In the film holding and drying step after peeling from the support, the film tends to shrink in the width direction by evaporation of the solvent. Shrinkage increases with drying at higher temperatures. Drying while suppressing this shrinkage as much as possible is preferable for improving the flatness of the finished film.

  From this point, for example, there is a method of drying the whole drying process or a part of the process as shown in Japanese Patent Laid-Open No. 62-46625 while holding the both ends of the web with a width in the width direction, that is, a tenter method. preferable. Furthermore, it can also extend | stretch in a film forming direction (elongate direction) using the roll from which peripheral speed differs.

  The film drying step is a step of further drying the film peeled and held and dried from the support, and the residual solvent amount is 3% by mass or less, preferably 1% by mass or less, more preferably 0.5% by mass or less. It is preferable for obtaining a film having good dimensional stability.

  The fine particles used in the present invention change to a flat particle by changing the shape of the secondary particles of the fine particles as the film is deformed in the film holding and drying step. Deterioration is suppressed.

  The drying heating means in the film drying step is not particularly limited, and is generally performed by hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to carry out with hot air in terms of simplicity. The drying temperature is preferably in the range of 40 to 150 ° C. and gradually increased to 3 to 5 steps, and more preferably in the range of 80 to 140 ° C. in order to improve dimensional stability.

  These steps from casting to drying and heating may be performed in an air atmosphere or an inert gas atmosphere such as nitrogen gas. It goes without saying that the dry atmosphere is carried out in consideration of the explosion limit concentration of the solvent.

  The winder used for producing the cellulose ester film of the present invention may be a commonly used winder such as a constant tension method, a constant torque method, a taper tension method, a program tension control method with a constant internal stress. Can be rolled up.

  The thickness of the cellulose ester film according to the present invention is generally 20 to 200 [mu] m, but is 20 to 65 [mu] m in order to reduce the thickness and weight of the polarizing plate used in the display device. Is more preferable, more preferably 30 to 60 μm, still more preferably 35 to 50 μm.

  If it is thinner than this, the stiffness of the film will be reduced, so that troubles due to wrinkles and the like are likely to occur on the polarizing plate manufacturing process, and if it is thicker than this, there is little contribution to the thinning of the display device. .

  The flat particles in the present invention preferably have an aspect ratio of 2 to 7, more preferably 2.5 to 6.5, and most preferably 3 to 6.

  In the present invention, the aspect ratio means average particle diameter / particle thickness diameter. The average particle diameter means the diameter of a circle having an area equal to the projected area of the particles when the particles are observed from the film with an optical microscope or an electron microscope, and the thickness diameter is from the side of the film with an optical microscope or an electron microscope. When a particle is observed, it refers to the diameter of a circle having an area equal to the projected area of the particle.

  The primary particle size of the flat particles in the present invention, preferably particles having an aspect ratio of 2 to 7, is preferably 0.2 μm or less, preferably 5 to 200 nm, more preferably 10 to 150 nm.

  Primary particles produce secondary particles in the cellulose production process, and finally the average particle size in the film should be about 0.2 to 10.0 μm. Preferably it is 1.0-8.0 micrometers, More preferably, it is 2.0-5.0 micrometers.

  In the cellulose ester film according to the present invention, secondary particles having an average particle diameter of 0.2 to 10.0 μm may not be formed, and dissipated primary particles may also be present. When the particles are contained in an amount of 5% by mass or more of all particles having an average particle size of 0.2 to 10 μm, the effect of the present invention is more strongly exhibited. Preferably it is 10 mass% or more.

  When the average particle size of the secondary particles exceeds 10 μm, it is not preferable because deterioration of haze or the like may be observed or a failure may occur in a wound state as a foreign matter.

  Further, when the average particle size of the secondary particles is less than 0.2 μm, a sufficient effect of improving the winding property is not seen, and particularly when the cellulose ester film is 20 to 65 μm, it is remarkable.

  The primary particles forming secondary particles having an average particle diameter of 0.2 to 10.0 μm according to the present invention, or the primary particles of 0.2 to 10 μm (also simply referred to as fine particles) may be inorganic compounds or organic compounds. Well, examples of inorganic compounds include fine particles such as silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide and tin oxide.

  Among these, a compound containing a silicon atom is preferable, and silicon dioxide fine particles are particularly preferable. Examples of the silicon dioxide fine particles include AEROSIL 200, 200V, 300, R972, R972V, R974, manufactured by Aerosil Co., Ltd. R202, R812, R805, OX50, TT600 etc. are mentioned.

  Examples of the organic compound include particles made of acrylic resin, silicone resin, fluorine compound resin, urethane resin, and the like.

  In the present invention, the fine particles are preferably used by adding 0.04 to 0.3% by mass to the cellulose ester, more preferably 0.05 to 0.2% by mass, and most preferably 0.05. It is -0.15 mass%.

  In the present invention, in order to form a cellulose ester film, a method of treating a composition in which fine particles and a solvent are mixed with a high-pressure dispersing apparatus is preferably used.

  The high-pressure dispersion device used in the present invention 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. It is preferable that the maximum pressure condition inside the apparatus is 9.8 MPa or more in a thin tube having a tube diameter of 1 to 2000 μm, for example, by treating with a high-pressure dispersion apparatus.

  More preferably, it is 19.6 MPa or more. At that time, it is preferable that the maximum reaching speed reaches 100 m / sec or more, and the heat transfer speed reaches 418 kJ (kilojoules) / hour or more.

  The high-pressure dispersion apparatus as described above includes an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation or a nanomizer manufactured by Nanomizer, and a Manton Gorin type high-pressure dispersion apparatus such as a homogenizer manufactured by Izumi Food Machinery, Inc. Can be mentioned.

  In order to obtain a cellulose ester film in the present invention, the fine particles are dispersed in a solvent containing 25 to 100% by mass of a lower alcohol, and then mixed with a dope in which cellulose ester is dissolved in the solvent, and then the mixed solution is used as a support. It is effective to use a method in which the film is cast on top and dried to form a film.

  The content ratio of the lower alcohol is preferably 50 to 100% by mass, and more preferably 75 to 100% by mass. Preferred examples of lower alcohols include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and the like.

  Although it does not specifically limit as solvents other than a lower alcohol, It is preferable to use the solvent used at the time of film forming of a cellulose ester.

  In the present invention, the fine particles are preferably dispersed in a solvent at a concentration of 1 to 30% by mass. Dispersing at a concentration exceeding this is not preferable because the viscosity increases rapidly. The concentration of fine particles in the dispersion is preferably 5 to 25% by mass, more preferably 10 to 20% by mass.

  The invention of claim 6 of the present invention is a cellulose ester film produced through a process of holding and drying in the width direction, containing particles having an average particle size of 0.2 to 10 μm or less, and having a thickness of 80 μm. The cellulose ester film is characterized in that the converted haze is 0.6% or less, and the dynamic friction coefficient of the front and back surfaces of the film is 0.3 to 1.5.

  In this invention, the haze converted into the thickness of 80 micrometers of a film can be measured according to ASTM-D1003-52, for example. The haze is 0 to 0.6%, preferably 0 to 0.4%, more preferably 0.1 to 0.2%.

  In the present invention, the dynamic friction coefficient of the front and back surfaces of the film can be measured by a method defined by JIS-K-7125 (1987), for example.

  However, in this case, when a dynamic friction coefficient of the film is measured, when a metal such as a hard sphere is used as the counterpart material, the effect of adding fine particles to the film cannot be confirmed. It is necessary to measure the dynamic friction coefficient between films.

  Then, according to said JIS-K-7125, it can measure by arrange | positioning so that a film may be used for a test piece and a counterpart material, and film front and back may contact. In the present invention, the dynamic friction coefficient of the front and back surfaces of the film is 0.3 to 1.5, more preferably 0.5 to 1.3, and still more preferably 0.6 to 1.0.

  In the present invention, it is preferable that a so-called knurling process is performed in which unevenness is imparted to both ends in the width direction of the cellulose ester film to make the ends bulky.

Ratio X (%) = (a / d) × 100
The above expression is an expression representing the ratio X (%) of the knurling height (a μm) to the film thickness (d μm), and X is set in the range of 0 to 25%. Preferably it is 0 to 15%, more preferably 0 to 10%. If the knurling height ratio is larger than this range, deformation of the winding shape is likely to occur, and if the ratio is small, the winding property is deteriorated, which is not preferable.

  Here, the cellulose ester containing the particles is cast on a support, heated to remove a part of the solvent, and then the cellulose ester film obtained by peeling from the support is retained and dried (width maintained). A method for producing a cellulose ester film by further performing a drying process through the steps is optimal, but holding and drying with a residual solvent amount of 10% by mass or more at the time of peeling from the support improves dimensional stability. It is preferable in order to exhibit the effect more.

  In the present invention, it is preferable that the cellulose ester film has less foreign matter. In particular, it is preferable that there are few foreign substances recognized in the polarization crossed Nicols state. The foreign substance recognized in the polarization crossed Nicol state refers to that measured by placing two polarizing plates in a direct (crossed Nicol) state and placing a cellulose ester film between them. Such a foreign substance is called a bright spot foreign substance, and in the polarization crossed Nicol state, the light from the opposite side, which observes only the part of the foreign substance in the dark field, is shined and observed, so its size is easily And the number can be identified.

As for the number of bright spot foreign matter, it is preferable that 200 or less foreign matters having a size of 5 to 50 μm recognized in a polarization crossed Nicol state per 250 mm ² area and substantially no foreign matter exceeding 50 μm are present. More preferably, the number of foreign matters of 5 to 50 μm is 100 or less, more preferably 50 or less.

In order to obtain a cellulose ester film having few foreign substances as described above, any means can be used, but it can be achieved by filtering a dope composition obtained by dissolving cellulose ester in a solvent using the following filter paper. In this case, it is preferable to use a filter paper having a drainage time of 20 seconds or more as a kind of filter paper, and form a film by filtering at a filtration pressure of 1.57 × 10 ⁶ Pa or less.

More preferably, the filter paper is used for 30 seconds or more and the filtration pressure is 1.18 × 10 ⁶ Pa or less, more preferably the filter paper is for 40 seconds or more and the filtration pressure is 9.8 × 10 ⁵ Pa or less. That is. It is more preferable to use two or more of the above filter papers, and the filtration pressure can be controlled by appropriately selecting the filtration flow rate and the filtration area.

  The cellulose ester film of the present invention has an in-plane retardation value R0 represented by the following formula of 200 nm or less, preferably 150 nm or less at 23 ° C. and 55% RH.

  In particular, when the cellulose ester film of the present invention is used as an optical film for a liquid crystal display device, the retardation value R0 in the in-plane direction represented by the following formula is preferably 20 nm or less, more preferably 10 nm or less, and still more preferably. Is 5 nm, most preferably 0-1 nm.

  Here, “at 23 ° C. and 55% RH” means that a measurement sample cut in a 35 mm square is allowed to stand under the conditions of 23 ° C. and 55% RH for 8 hours and then measured under the same conditions.

R0 = (Nx−Ny) × d
In the formula, Nx represents the refractive index in the slow axis direction in the film plane, Ny represents the refractive index in the fast axis direction in the film plane, and d represents the thickness (nm) of the film.

  The retardation value Rt in the film thickness direction defined by the following formula is preferably 0 to 200 nm, preferably 20 to 100 nm or less, and preferably 25 to 50 nm.

Rt = ((Nx + Ny) / 2−Nz) × d
In the formula, Nz represents the refractive index of the film in the thickness direction, and Nx, Ny, and d are synonymous with those in R0.

  The retardation value Rt or R0 is measured using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments) in a three-dimensional refraction at a wavelength of 590 nm in an environment of 23 ° C. and 55% RH. A rate measurement is performed, Nx and Ny are measured, and thereby Rt and R0 can be calculated.

  The production method of the polarizing plate obtained using the cellulose ester film of the present invention is not particularly limited, and can be produced by a general method. For example, there is a method in which a cellulose ester film is treated with an alkali and bonded to both surfaces of a polarizing film prepared by immersing, holding and drying in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. Instead of the alkali treatment, a method for enhancing adhesiveness as described in JP-A-6-94915 and JP-A-6-118232 may be used.

  A liquid crystal display member is a member used in a liquid crystal display device. For example, a polarizing plate, a protective film for a polarizing plate, a retardation plate, a reflective plate, a viewing angle widening film, an antiglare film, a non-reflective film, a reflection Examples thereof include a prevention film, an antistatic film, and a brightness enhancement film. Among them, it is more preferable to apply the present invention to polarizing plates, protective films for polarizing plates, retardation plates, and viewing angle widening films that have strict requirements on dimensional stability.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto. The “parts” shown below indicate “parts by mass” unless otherwise specified.

Example 1
-Preparation of sample 1 Preparation of Dispersion A Ethanol 27 parts Particle 1 (silicon dioxide fine particle) (trade name: Aerosil 200V,
(Primary particle size: 15 nm; manufactured by Nippon Aerosil Co., Ltd.) 3 parts or more of these were mixed, stirred for 30 minutes at 500 rpm, and dispersed at a pressure of 19.6 MPa with a Manton Gorin type high-pressure disperser. Dispersion A was prepared.
2. Preparation of additive liquid A 22 parts of the above dispersion A Cellulose triacetate synthesized from cotton linter (oxidation degree 61%)
12 parts UV absorber 1 (2- (2'-hydroxy-3 ', 5'
-Di-t-butylphenyl) benzotriazole) 26 parts methylene chloride 290 parts The above additive liquid A was measured with a centrifugal particle size distribution analyzer (CAPA500, manufactured by HORIBA, Ltd.). ) Had an average particle size of 1.2 μm.
3. Dope composition A
Cellulose triacetate synthesized from cotton linter (acetylation degree 61.0%)
85 parts cellulose triacetate synthesized from wood pulp (acetylation degree 61.0%)
15 parts ethyl phthalyl ethyl glycolate (plasticizer) 4 parts methylene chloride 475 parts ethanol 50 parts of the dope composition A is put into a sealed container, heated to 70 ° C., and completely stirred for cellulose triacetate (TAC). It melt | dissolved and dope composition A was obtained. The time required for dissolution was 4 hours. After the dope composition A is filtered, the dope composition A and the additive liquid A are mixed with an in-line mixer so that the addition ratio of fine particles to cellulose triacetate is 0.05% by mass, and then a belt casting apparatus is used. Used and cast uniformly on a stainless steel band support at a dope temperature of 35 ° C. and 30 ° C. After drying to a peelable range, the dope was peeled from the stainless steel band support. At this time, the residual solvent amount of the dope was 25%. The time required from casting the dope to peeling was 3 minutes.

  After peeling from the stainless steel band support, it is passed through the drying zone of the first zone 50 ° C., the second zone 90 ° C. and the third zone 120 ° C. while being transported by many rolls while maintaining the width, and further the 130 ° C. drying heating zone Then, drying was terminated, and a knurling process having a width of 10 mm and a height of 4 μm was applied to both ends of the film to prepare a sample 1 of a cellulose triacetate film having a thickness of 40 μm.

The film width was 1300 mm and the winding length was 3000 m. The winding tension was an initial tension of 20 kg / 1300 mm and a final winding tension of 10 kg / 1300 mm.
・ Preparation of Samples 2 to 9 In the preparation of Sample 1, the amount of residual solvent was changed by changing the drying zone and the drying time for holding the width, and the conditions of the particles were changed as shown in Table 1. Samples 2 to 4 of cellulose triacetate film were prepared. Moreover, in the same samples 5-9, the same sample was produced using the silicia (Fuji Silysia Chemical Co., Ltd. average particle diameter of 1.8 micrometers) instead of the Aerosil 200V.

The following performance evaluation was performed about the cellulose triacetate film samples 1-9 produced as mentioned above. The results obtained are shown in Table 1 below.
(Evaluation methods)
-Average particle diameter and aspect ratio Particles were observed with a scanning electron microscope (magnification 3000 times), and the diameter of a circle circumscribing the particles was defined as the particle diameter. Also, 100 particles were observed at different locations, and the average value was taken as the average particle size (primary particle size or secondary particle size). The aspect ratio was measured based on the average particle size.
-Haze It measured according to ASTM-D1003-52.
-Dynamic friction coefficient The dynamic friction coefficient between the film surface and the back surface is cut out so that the front and back surfaces of the film are in contact with each other according to JIS-K-7125 (1987), a 200 g weight is placed, the sample moving speed is 100 mm / min, and the contact area is 80 mm. The weight was pulled horizontally under the condition of × 200 mm, the average load (F) while the weight was moving was measured, and the dynamic friction coefficient (μm) was obtained from the following formula.

Coefficient of dynamic friction = F (gf) / weight of weight (gf)
-Surface quality Judgment was made visually by the following criteria.

○ ・ ・ ・ There is almost no unevenness on the surface, and there is no problem as a product △ ・ ・ ・ Slightly unevenness is visible on the surface, but there is no problem as a product × ・ ・ ・ Many unevenness is conspicuous on the surface, and it cannot be used as a product level.

  As is clear from Table 1, it can be seen that the sample 5 containing no flat particles has a high coefficient of dynamic friction, and the surface quality is deteriorated, such as unevenness on the film surface. That is, it is caused by the fact that the shape of the particles does not become flat because there is no residual drying in the width direction and there is no residual solvent amount in the film. Sample 9 has a haze value and a coefficient of dynamic friction outside the range of claim 6, and it can be seen that good results cannot be obtained.

Example 2
Of the dope composition of Example 1, the following composition in which methylene chloride was changed to the same amount of methyl acetate: Ethylphthalyl ethyl glycolate (plasticizer) 4 parts Methyl acetate 475 parts Ethanol 50 parts -100 to -10 After cooling to 0 ° C., the remaining cellulose triacetate was added and completely dissolved in an organic solvent in the process of heating to 0 to 120 ° C., and the obtained dope was added in-line with additive solution A in the same manner as in Example 1. The same samples 21 to 29 were prepared by mixing with a mixer. The same evaluation as in Example 1 was performed using this sample. The results obtained are shown in Table 2 below.

  As is apparent from Table 2, the sample obtained by changing the method for producing the dope composition also has a surface quality such that the sample 25 containing no flat particles has a high coefficient of dynamic friction and conspicuous irregularities on the film surface. It can be seen that is deteriorated. In addition, since the sample 29 has a haze value and a dynamic friction coefficient outside the range of claim 6, it can be seen that good results cannot be obtained.

Example 3
1. Preparation of Dispersion B Ethanol 27 parts Particle 3 (silicon dioxide fine particles) (trade name: Aerosil 200V)
Nippon Aerosil Co., Ltd.) 3 parts or more of the above were mixed, stirred for 30 minutes at 500 rpm, and then dispersed with a Manton Gorin type high-pressure disperser at a pressure of 19.6 MPa to prepare dispersion B.
2. Preparation of additive liquid B Cellulose acetate propionate (acetyl substitution degree 2.0
Propionyl substitution degree 0.8) 12 parts UV absorber 2 (Tinubin 571, manufactured by Ciba Specialty Chemicals)
13 parts UV absorber 3 (Tinubin 109, manufactured by Ciba Specialty Chemicals)
15 parts methylene chloride 290 parts Dispersion B 22 parts 3. Preparation of dope composition B Cellulose acetate propionate (acetyl substitution degree 2.0
Propionyl substitution degree 0.8) 100 parts Ethyl phthalyl ethyl glycolate (plasticizer) 2 parts Triphenyl phosphate (plasticizer) 8 parts Methylene chloride 475 parts Ethanol 50 parts are put into a sealed container and heated to 70 ° C. Then, cellulose acetate propionate (CAP) was completely dissolved with stirring to obtain a dope composition B. The time required for dissolution was about 4 hours.
4). Preparation of Cellulose Ester Film Next, after the dope composition B is filtered, the dope composition B and the additive liquid B are mixed in an in-line mixer so that the addition ratio of fine particles to cellulose acetate propionate is 0.05 mass%. Then, using a belt casting apparatus, the mixture was uniformly cast on a stainless band support having a dope temperature of 35 ° C. and a temperature of 30 ° C. After drying to a peelable range, the dope was peeled from the stainless steel band support. The residual solvent amount of the dope at this time was 40%. The time required from casting the dope to peeling was 3 minutes.

  After peeling from the stainless steel band support, it was conveyed by a number of rolls while maintaining the width. Drying passes through the drying zone of the first zone 50 ° C, the second zone 90 ° C, the third zone 120 ° C, and further finishes the drying in the 130 ° C drying heating zone, and the knurling process with a width of 10 mm and a height of 8 µm at both ends of the film. To give a cellulose ester film having a thickness of 60 μm. Stretching was performed 1.06 times in the width direction when the residual solvent amount in the second zone was 30%.

  The film width was 1300 mm and the winding length was 3000 m. The winding tension was an initial tension of 20 kg / 1300 mm and a final winding tension of 10 kg / 1300 mm. The cellulose ester film thus produced was evaluated in the same manner as in Examples 1 and 2.

  The resulting cellulose ester film had a secondary particle size of 2.8 μm, an aspect ratio of 4.9, a haze of 0.0%, a dynamic friction coefficient of 0.7, and a surface quality of ◯, giving good results. It was.

Example 4
A polarizing plate was prepared and evaluated according to the following method.

  According to the following method, the polarizing plate 1 of the present invention was produced using the cellulose ester film produced in Example 3.

(Preparation of polarizing film)
A 120 μm-thick polyvinyl alcohol film was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). Immerse in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide, and 100 g of water for 60 seconds, then immerse in an aqueous solution of 68 ° C. consisting of 6 g of potassium iodide, 7.5 g of boric acid, and 100 g of water, washed with water, dried and polarized. A membrane was obtained.

(Preparation of polarizing plate)
Subsequently, according to the following processes 1-5, the obtained polarizing film and the cellulose-ester film produced in Example 3 were bonded together, and the polarizing plate 1 of this invention was produced.

  Step 1: The cellulose ester film prepared in Example 3 was cut into two pieces having a size of 30 cm in the longitudinal direction and 18 cm in the width direction, immersed in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried. I let you.

  Step 2: The polarizing film cut to a size of 30 cm in the longitudinal direction and 18 cm in the width direction was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.

  Step 3: Gently remove the excess adhesive adhered to the polarizing film in Step 2, place it on the cellulose ester film prepared in Step 1, and further laminate the same cellulose ester film in contact with the adhesive Arranged.

Step 4: Excess adhesive and bubbles were removed from the end of the laminate of the polarizing film and each film laminated in Step 3 with a hand roller, and bonded together. The pressure of the hand roller was 20 to 30 N / cm ² and the roller speed was about 2 m / min.

  Step 5: The sample prepared in Step 4 was treated for 1 minute in a dryer at 80 ° C. to prepare the polarizing plate 1 of the present invention.

  Similarly, a comparative polarizing plate 2 was produced using the sample 25 produced in Example 2.

  Using the polarizing plate 1 of the present invention and the polarizing plate 2 for comparison, the polarizing plate on the outermost surface of a commercially available liquid crystal display panel (NEC color liquid crystal display MultiSync LCD1525J, model name LA-1529HM) is carefully peeled off and polarized here. The polarizing plate 1 of the present invention or the polarizing plate 2 of the comparative example, which were aligned, was attached. At the time of pasting, each of the pasting was repeated 10 times due to misalignment or adhesion of bubbles or foreign matters. At that time, new polarizing plates were used. As a result, in the polarizing plate 2 for comparison, the cellulose ester film was torn twice in 10 times, and a part of the cellulose ester film was not peeled off and remained on the liquid crystal panel side. The film did not tear. Each liquid crystal display panel was visually evaluated for contrast. As a result, it was found that the liquid crystal display panel using the polarizing plate 1 of the present invention was superior in contrast to the comparative polarizing plate 2.

Claims (3)

A method for producing an optical film comprising a cellulose ester film containing flat particles having an aspect ratio of 2 to 7 and an average particle size of 0.2 to 10 μm, wherein primary particles having an average particle size of 5 to 200 nm are used as a solvent. mixed with the step of producing the dispersed secondary particles in high-pressure dispersing device, the step of the secondary particle is mixed with the cellulose ester solution to prepare a dope solution, a step of then peeling by casting a dope on a support, A method for producing an optical film , comprising a step of drying while holding the width after peeling.   2. The method for producing an optical film according to claim 1, wherein the step of drying while maintaining the width is a step of stretching 1.01 to 1.50 times in the width direction.   The method for producing an optical film according to claim 1, wherein the flat particles are silicon dioxide particles that are not surface-treated.