JP2005111669A - Manufacturing method for polymer film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a polymer film of high quality useful for an optical film used in various display devices such as a liquid crystal image display device or an organic electroluminescence display, especially a protective film for a polarizing plate used in the display devices and a phase difference film, having high smoothness and extremely reduced in the variation of a retardation value. <P>SOLUTION: In the manufacturing method of the polymer film having a thickness of 20-200 μm by a solution casting film forming method, the viscosity of a dope at casting in a casting process is 1-200 poise and the warpage quantity of the end part of a support part, on which a dope film (web) is formed by casting the dope, is 0.01-2 mm as compared with the central part in the width direction of the surface of the support part. Further, drying air is applied to the dope film (web) on the support at an angle of 60-120° after 3 sec is elapsed from the time when the dope is cast on the support to set that the wind velocity V1 of a wind flowing in the lateral direction of the surface of the web is set to 10 m/sec or above and the wind velocity V2 of the wind flowing in the longitudinal direction of the surface of the web to go toward a casting die is set to 4 m/sec or below. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polymer film used in various display devices such as a liquid crystal image display device (LCD) or an organic EL (electroluminescence) display, in particular, a protective film for a polarizing plate and a retardation film used in these display devices. It is related with the manufacturing method of a polymer film (henceforth only a film) useful.

  Conventionally, a liquid crystal image display device (LCD) can be directly connected to an IC circuit with low voltage and low power consumption, and can be thinned, so that it is widely used as a display device for a word processor, a personal computer or the like. Yes. By the way, the basic configuration of the liquid crystal image display device is one in which polarizing plates are provided on both sides of the liquid crystal cell. Since the polarizing plate allows only light of a polarization plane in a certain direction to pass, it plays an important role in visualizing the change in the orientation of the liquid crystal due to the electric field in the liquid crystal image display device. The performance is greatly affected.

  As a protective film for a polarizing plate, a cellulose ester film is often used at present because of its low birefringence, but in recent years, other polymer films have also come out.

  Taking a cellulose triacetate as an example of a protective film for a polarizing plate, the surface of the film is alkali saponified and uniaxially stretched and iodine-stained on one or both sides of a polarizing film made of polyvinyl alcohol film, such as polyvinyl alcohol. It is used by sticking together via an adhesive.

  The cellulose triacetate film is produced, for example, by the following solution casting film forming method. This cellulose triacetate film is produced by first dissolving cellulose triacetate in a mixed solvent obtained by adding a good solvent for cellulose triacetate such as methylene chloride and a poor solvent for cellulose triacetate such as methanol, ethanol, butanol or cyclohexane. A cellulose triacetate solution (hereinafter referred to as a dope) is prepared by adding a plasticizer, an ultraviolet absorber, and fine particles for improving the slipperiness of the film, and the dope has an infinite transition having a mirror-finished surface. A dope film (hereinafter referred to as a web) is obtained by uniformly casting from a casting die onto an endless rotationally driven metal support (for example, a stainless steel endless belt or drum), which is dried on the support. Then peel it off with a peeling roll. , And dried for an additional hot air or the like in the transport drying step, after dried sufficiently, by winding in the winding machine, thereby obtaining a cellulose triacetate film.

  However, in such a method for producing a cellulose ester film by the conventional solution casting method, streaky unevenness is observed on the surface of the obtained film, and the retardation value varies greatly depending on the location of the film. There was a trend.

  Conventionally, image display devices using these polymer films have been subjected to anti-glare treatment to increase the visibility by reducing the reflection of external light, so that streaky unevenness cannot be visually confirmed. It was inconspicuous.

  However, in recent years, clear finishes with high contrast and the appearance of the displayed image have been rapidly spreading, and in this clear finish, the unevenness that was completely unclear with anti-glare processing products seems to be emphasized so as to be raised. Therefore, it is a big problem in appearance.

  Some image display devices that employ such a clear finish take measures such as attaching an acrylic plate to the outermost surface of the display screen in order to make this unevenness less noticeable, both in terms of cost and compactness. It was a problem.

  Such streaky unevenness and variations in retardation values can be achieved by reducing the viscosity of the dope used during solution casting and forming a smooth surface by surface leveling. It has been found that the variation of is also reduced. However, if the dope viscosity is lowered, the fluidity increases, so when the web is dried on the support surface, blown unevenness is caused by the drying air, or if the support is slightly warped, the dope flows. The film thickness is uneven and the retardation value varies greatly. For this reason, in the conventional solution casting film forming method, a high-quality optical film is formed with a thick polymer film of about 100 μm currently on the market manufactured using a low-viscosity dope, It was extremely difficult.

Therefore, conventionally, prior art documents relating to a technique for improving the flatness of a film in a method for producing a cellulose ester film by such a solution casting film forming method include the following.
JP-A-2000-319412 discloses a method for producing a cellulose ester film by a solution casting film forming method, in which a cellulose ester dope is transferred from a casting die. A web is formed by casting on the surface, the absolute value of the static pressure of the drying air applied to the surface of the web is 20 to 100 mmAq, and the width of the outlet of the drying air and the static pressure deviation in the longitudinal direction are ± 20%. A technique for forming a film is disclosed as follows.

  However, the method for producing a cellulose ester film described in Patent Document 1 is not sufficient for obtaining a high-quality cellulose ester film with high smoothness like a mirror surface and little variation in retardation values. It was.

  As a result of intensive studies in view of the above points, the inventors of the present invention have found that in the method for producing a polymer film by the solution casting film forming method, even if a low-viscosity dope is used, blowing with dry air on the support is performed. The inventors have found a method capable of producing a high-quality polymer film without causing unevenness and having high smoothness like a mirror surface and very little variation in retardation value, and have completed the present invention.

  The object of the present invention is to solve the above-mentioned problems of the prior art and to use a polymer film for various display devices such as a liquid crystal image display device or an organic electroluminescence display, particularly a polarizing plate protective film used for these display devices. It is an object of the present invention to provide a method capable of producing a high-quality polymer film that is useful for retardation films, has high smoothness, and has very little variation in retardation values.

  In order to achieve the above object, according to the first aspect of the present invention, a polymer film raw material solution (dope) is cast from a casting die onto a rotary drive metal support by a solution casting film forming method. Then, a casting process for forming a dope film (web), a peeling process for peeling the web formed on the support from the support, and a web peeled from the support via a plurality of transport rolls A method for producing a polymer film having a thickness of 20 to 200 μm, comprising: a drying step of drying while transporting; and a winding step of winding a polymer film formed by drying a web in a drying step around a winding core, In the casting step, the dope viscosity during casting is 1 to 200 poise, and the amount of warping at the end of the support where the dope is cast to form a dope film (web) is the width of the support surface. Direction Compared to the central portion, it is characterized in that it is 0.01 to 2 mm.

  The invention according to claim 2 of the present invention is the method for producing a polymer film according to claim 1, wherein the casting die is cast after 3 seconds or more have passed since the dope was cast on the support in the casting step. A drying air blow is applied to the dope film (web) on the support at an angle in the range of 60 ° to 120 ° from the drying air blowing device disposed above the front support, and the web surface flows in the width direction. Wind speed: V1 is 10 m / sec or less, and wind speed V2 is 4 m / sec or less flowing in the longitudinal direction on the web surface toward the casting die.

  As described above, the invention according to claim 1 of the present invention is a method for producing a polymer film having a thickness of 20 to 200 μm by a solution casting film forming method, wherein the dope viscosity during casting in the casting step is The warp amount at the end of the support portion where the dope is cast and the dope film (web) is formed is 0.01 to 200 poise, compared to the widthwise center of the support surface, 0.01 According to the method for producing a polymer film of the present invention, even if a low-viscosity dope is used, a mirror surface is produced without causing unevenness of blowing on the support due to dry air. The polymer used in various display devices such as a liquid crystal image display device or an organic electroluminescence display has high smoothness, extremely little variation in retardation value, and high quality. It achieved Irumu, especially protective film for a polarizing plate used in these display devices, and very useful for the retardation film, the effect that it is possible to produce a polymer film.

  The invention according to claim 2 of the present invention is the casting die in the method for producing a polymer film according to claim 1, wherein the casting die is cast after 3 seconds or more after casting the dope on the support. A drying air blow is applied to the dope film (web) on the support at an angle in the range of 60 ° to 120 ° from the drying air blowing device disposed above the front support, and the web surface flows in the width direction. Wind speed of wind: V1 is 10 m / sec or less, and wind speed of wind flowing in the longitudinal direction on the web surface toward the casting die: V2 is 4 m / sec or less. According to the production method, it is possible to more reliably prevent the occurrence of blown unevenness due to the drying air on the support, the smoothness is high like a mirror surface, and the variation of the retardation value is extremely small. High quality, Polymer films used in various display devices such as crystal image display devices or organic electroluminescence displays, in particular, polymer films that are extremely useful for protective films for polarizing plates and retardation films used in these display devices There is an effect that can be.

  Next, an embodiment of the present invention will be described.

  First, the first aspect of the present invention is a method for producing a polymer film having a thickness of 20 to 200 μm by a solution casting film forming method.

  The method according to the present invention comprises a casting process in which a polymer film raw material solution (dope) is cast from a casting die onto a rotationally driven metal support to form a dope film (web), and the film is formed on the support. A peeling process for peeling the web from the support, a drying process for drying the web peeled from the support through a plurality of transport rolls, and a polymer film formed by drying the web in the drying process. A winding step of winding around a core.

  The feature of the invention of claim 1 of the present invention is that the dope viscosity at the casting step is 1 to 200 poises in the casting step, and the dope is cast to form a dope film (web). The amount of warping at the end is 0.01 to 2 mm as compared with the center in the width direction of the support surface.

  Further, the invention according to claim 2 of the present invention is characterized in that, in the method for producing a polymer film according to claim 1, the dope is cast on the support in the casting step, and after 3 seconds or more have passed, From the drying air blowing device arranged above the support in front of the rolling die, the drying surface is applied to the dope film (web) on the support at an angle in the range of 60 ° to 120 °, so that the web surface is in the width direction. The speed of the wind flowing through the web: V1 is 10 m / sec or less, and the wind speed of the wind flowing in the longitudinal direction on the web surface toward the casting die: V2 is 4 m / sec or less.

  Hereinafter, these will be described in order.

  Preferred requirements for the polymer film to be subjected to the method of the present invention are that it is easy to produce, has good adhesion to the actinic radiation curable resin layer, and is optically transparent.

  Here, being optically transparent means that the transmittance of visible light is 60% or more, preferably 80% or more, and particularly preferably 90% or more.

  The polymer film to be subjected to the method of the present invention is not particularly limited as long as it has the above-mentioned properties. For example, a cellulose ester film, a polycarbonate film, a polysulfone film (including a polyethersulfone film) is used. ), Polyarylate film, polyethylene terephthalate, polyester film such as polyethylene naphthalate, polyethylene film, polypropylene film, cellophane, cellulose diacetate film, cellulose triacetate film, cellulose acetate butyrate film, polyvinylidene chloride film, polyvinyl alcohol film, Ethylene vinyl alcohol film, syndiotactic polystyrene film, polycarbonate film, cycloolefin polymer Mer film (trade name Arton, manufactured by JSR), Zeonex, Zeonea (manufactured by Nippon Zeon), polymethylpentene film, polyetherketone film, polyetherketoneimide film, polyamide film, fluororesin film, nylon film, A polymethyl methacrylate film, an acrylic film, a glass plate, etc. can be mentioned. Among these, a cellulose triacetate film, a polycarbonate film, and a polysulfone film (including a polyethersulfone film) are preferable. In addition, two or more compatible polymers may be blended to perform dope dissolution described later, but the present invention is not limited to these.

  In the present invention, the polymer film preferably contains an ultraviolet absorber from the viewpoint of preventing deterioration when the polymer film is placed outdoors as an image display device. As the ultraviolet absorber, one that is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less and has little absorption of visible light having a wavelength of 400 nm or more can be preferably used. For example, the transmittance at a wavelength of 380 nm is preferably 20%, more preferably less than 10%, and particularly preferably less than 5%.

  Examples of ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and doriadine compounds. However, it is not limited to these.

  Hereinafter, although the specific example of a ultraviolet absorber is given, this invention is not limited to these.

Etc. As a benzotriazole ultraviolet absorber, UV-1: 2 (2'-hydroxy-5'-methylphenyl) benzotriazole UV-2: 2 (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) )
Benzotriazole UV-3: 2 (2'-hydroxy-3'tert-butyl-5'-methylphenyl)
Benzotriazole UV-4: 2 (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) -5-chlorobenzotriazole UV-5: 2 (2′-hydroxy-3 ′ (3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′methylphenyl) benzotriazole UV-6: 2,2 methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H— Benzotriazol-2-yl) phenol UV-7: 2 (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -chlorobenzotriazole UV-8: 2- (2H-benzotriazole-2- Yl) -6- (linear and side chain dodecyl) -4-methylphenol (TINUVIN: Ciba Specialty Chemicals)
UV-9: Octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl -4-hydroxy-5-
(Chloro-2H-benzotriazol-2-yl) phenyl] propionate and mixture (TINUVIN109: manufactured by Ciba Specialty Chemicals)
UV-10: 2,4-dihydroxybenzophenone UV-11: 2,2'-di-hydroxy-4-methoxybenzophenone UV-12: 2-hydroxy-4-methoxy-5-sulfobenzophenone UV-13: bis (2 -Methoxy-4-hydroxy-5-benzoylphenylmethane)
In the present invention, benzotriazole-based UV absorbers and benzophenone-based UV absorbers that are highly transparent as UV absorbers and excellent in preventing the deterioration of polarizing plates and liquid crystals can be preferably used for the polymer film. Particularly preferred are benzotriazole-based UV absorbers with less unnecessary coloration. The ultraviolet absorber is preferably one that does not bleed out or volatilize in the film forming process.

  As the UV absorber, a polymer UV absorber can be preferably used, and in particular, a polymer type UV absorber described in JP-A-6-148430 is preferably used.

  In the present invention, the ultraviolet absorber is preferably added in an amount of 0.1 to 10% by weight, particularly preferably 0.5 to 5% by weight, based on the polymer component.

  Moreover, in this invention, these ultraviolet absorbers may be used independently and may be used by mixing 2 or more types from which it differs.

  As a method for adding the ultraviolet absorber, the ultraviolet absorber is dissolved in an organic solvent such as alcohol, methylene chloride, dioxosilane and the like, and then added to the dope, or may be added directly into 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 the polymer to be dispersed and then added to the dope.

  In the present invention, if necessary, fine particles such as silicon dioxide can be added to the polymer film as a matting agent. Fine particles such as silicon dioxide are preferably surface-treated with an organic substance because the haze of the film can be reduced. Preferred organic materials for the surface treatment include halosilanes, alkoxysilanes, silazanes, and siloxanes. The larger the average particle size of the fine particles, the greater the mat effect, and the smaller the average particle size, the better the transparency. Therefore, the preferable average particle size of the primary particles is 5 to 50 nm, more preferably 7 to 14 nm. is there.

  Examples of the fine particles of silicon dioxide used in the present invention include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, OX50, TT600, etc. manufactured by Aerosil Co., preferably AEROSIL200, 200V, R972, R972V, R974, R202, R812 etc. are mentioned.

  In the present invention, the fine particles are used in an amount of 0.04 to 0.4% by weight based on the polymer. Preferably, it is 0.05 to 0.3% by weight, more preferably 0.05 to 0.2% by weight.

  In the method of the present invention, the solvent used for dissolving the polymer may be used singly or in combination, but it is preferable to use a mixture of a good solvent and a poor solvent in terms of increasing production efficiency. In view of the solubility of the film and the amount of film foreign matter due to minute insoluble matter is reduced. The preferable range of the mixing ratio of the good solvent and the poor solvent is 70 to 98% by weight for the good solvent and 30 to 2% by weight for the poor solvent.

  Here, the good solvent and the poor solvent used in the present invention define a good solvent that dissolves the polymer used alone, and a poor solvent that swells or does not dissolve alone.

  The good solvent used in the present invention is not particularly limited. For example, when the polymer is cellulose triacetate, an organic halogen compound such as methylene chloride or dioxolane, and when the polymer is cellulose acetate propionate, methylene chloride, acetone, acetic acid are used. And methyl. Moreover, it is although it does not specifically limit as a poor solvent, For example, methanol, ethanol, i-propyl alcohol, n-butanol, cyclohexane, acetone, cyclohexanone etc. are used preferably.

  Hereinafter, the method of the present invention will be described in detail by taking a cellulose ester film as an example of the polymer film.

  For example, US Pat. No. 2,492,978, US Pat. No. 2,739,070, US Pat. No. 2,739,069, US Pat. No. 2,492,977, and US Pat. No. 2,336,310, No. 2,367,603, No. 2,607,704, British Patent No. 64,071, No. 735,892, No. 45-9074, No. 49-4554 49-5614, 60-27562, 61-39890, 62-4208 and the like can be referred to.

  In the method of the present invention, cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate, cellulose acetate propionate butyrate and the like are preferably used as the cellulose ester film. In the case of cellulose triacetate, cellulose triacetate having a polymerization degree of 250 to 400 and a bound acetic acid amount of 54 to 62.5% is particularly preferable.

  As the cellulose ester, either cellulose ester synthesized from cotton linter or cellulose ester synthesized from wood pulp can be used alone or in combination.

  About the specific manufacturing method of the cellulose ester of this invention, it is compoundable by the method described in Unexamined-Japanese-Patent No. 10-45804, for example.

  If the number average molecular weight of the cellulose ester is too low, the strength will be low, and if it is too high, the viscosity of the solution may be too high, so it is preferably 70000-300000, more preferably 80000-200000.

  It is preferable to use a large amount of cellulose ester synthesized from a cotton linter that has good releasability from a rotationally driven metal support made of an endless belt or a drum because of high productivity efficiency. Moreover, in order for the effect of peeling to become remarkable, it is preferable that the ratio of the cellulose ester synthesize | combined from the cotton linter is 60 weight% or more, More preferably, it is 85 weight% or more, Furthermore, it uses independently. Most preferred.

  In particular, a cellulose ester film having a total acyl group substitution degree of less than 2.85 is preferred because the dimensional change can be reduced, and a cellulose ester film having a total acyl group substitution degree of less than 2.75 is preferred. A remarkable effect is observed with a cellulose ester film of less than 70.

  In the method for producing a polymer film of the present invention, it is preferable to add a plasticizer to the polymer film in view of mechanical strength, dimensional stability, and the like. The addition amount is preferably 3 to 30% by weight based on, for example, cellulose ester film or cellulose ester film obtained by acylating cellulose with an acetyl group and an acyl group having 3 to 4 carbon atoms. 30 weight% is more preferable and 15-25 weight% is especially preferable. In general, when the amount of plasticizer added increases, the dimensional change is likely to occur. However, according to the method of the present invention, the dimensional change rate can be remarkably reduced.

  Although it does not specifically limit as a plasticizer which can be used by this invention, Phosphate ester plasticizer, phthalate ester plasticizer, trimellitic ester plasticizer, pyromellitic acid plasticizer, glycolate plasticizer Citric acid ester plasticizers, polyester plasticizers, and the like can be preferably used.

  Here, in the phosphoric acid ester system, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate and the like can be preferably used. In the phthalic acid ester system, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, butyl benzyl phthalate and the like can be preferably used. As the trimellitic acid plasticizer, tributyl trimellitate, triphenyl trimellitate, triethyl trimellitate and the like can be preferably used. In the pyromellitic acid ester plasticizer, tetrabutyl pyromellitate, tetraphenyl pyromellitate, tetraethyl pyromellitate and the like can be preferably used. In the glycolic acid ester system, triacetin, tributyrin, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate and the like can be preferably used. As the citrate plasticizer, triethyl citrate, tri-n-butyl citrate, acetyl triethyl citrate, acetyl tri-n-butyl citrate, acetyl tri-n- (2-ethylhexyl) citrate, etc. are preferably used. Can do. In the polyester plasticizer, a copolymer of a dibasic acid such as an aliphatic dibasic acid, an alicyclic dibasic acid, or an aromatic dibasic acid and a glycol can be used. The aliphatic dibasic acid is not particularly limited, and adipic acid, sebacic acid, phthalic acid, terephthalic acid, 1,4-cyclohexyl dicarboxylic acid and the like can be used. As the glycol, ethylene glycol, diethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, or the like may be used. it can. These dibasic acids and glycols may be used alone or in combination of two or more. The molecular weight of the polyester is preferably in the range of 500 to 2000 in terms of weight average molecular weight from the viewpoint of compatibility with the cellulose resin.

  In the method of the present invention, it is particularly preferable to use a plasticizer having a vapor pressure of less than 1333 Pa at 200 ° C., more preferably a plasticizer having a vapor pressure of 666 Pa or less, and more preferably 1 to 133 Pa. Although the plasticizer which has non-volatility is not specifically limited, For example, arylene bis (diaryl phosphate) ester, tricresyl phosphate, trimellitic acid tri (2-ethylhexyl) etc. are mentioned. These plasticizers can be used alone or in combination of two or more.

  In the method for producing a polymer film according to the present invention, the dope viscosity during casting in the casting step is 1 to 200 poise, and the warp of the end of the support portion where the dope is cast to form a dope film (web) The amount is 0.01 to 2 mm as compared with the center in the width direction of the support surface.

  Here, taking the case where the polymer film is a cellulose ester film as an example, first, dissolution of the cellulose ester is usually performed by means such as a stirring dissolution method, a heating dissolution method, and an ultrasonic dissolution method in a dissolution vessel. Heating at a temperature above the boiling point of the solvent at normal pressure and in a range where the solvent does not boil, under pressure, and dissolving with stirring prevents the formation of massive undissolved materials called gels and mamaco Therefore, it is more preferable. Further, a cooling dissolution method described in JP-A-9-95538 or a method of dissolving under high pressure described in JP-A-11-21379 may be used.

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

  In the method of the present invention, the solid content concentration of the dope which is a polymer solution is usually about 10 to 40% by weight, and the dope viscosity is prepared in the range of 1 to 200 poise.

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

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

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

  After dissolving the cellulose ester, it is taken out from the container while cooling, or it is taken out from the container with a pump or the like and cooled with a heat exchanger or the like, and the resulting polymer dope is used for film formation. May be cooled to room temperature.

  The particle size d of the cellulose ester as a raw material is such that particles having a size of 0.1 mm ≦ d ≦ 20 mm are constituted at a ratio of 60% by weight or more, so that good solubility can be obtained without generating an aggregate of cellulose ester. Desirable to get.

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

  In the method of the present invention, the cellulose ester dope is filtered to remove foreign matters, particularly foreign matters that are mistakenly recognized as images in a liquid crystal image display device. It may be said that the quality of the protective film for polarizing plates is determined by this filtration.

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

  For this reason, in the method of the present invention, the filter medium used for the cellulose ester dope preferably has an absolute filtration accuracy of 0.008 mm or less, more preferably in the range of 0.001 to 0.008 mm, and 0.003 to 0.00. A filter medium in the range of 006 mm is more preferable.

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

  In the method of the present invention, filtration of the cellulose ester dope can be performed by a normal method, but a method of filtering while heating under pressure at a temperature not lower than the boiling point at normal pressure of the solvent and in a range where the solvent does not boil, The increase in the differential pressure before and after the filter medium (hereinafter sometimes referred to as filtration pressure) is small and preferable.

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

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

  If the cellulose of the raw material contains an unsubstituted or low-substituted cellulose ester of an acyl group, foreign matter failure (hereinafter sometimes referred to as bright spot or bright spot foreign matter) may occur. The bright spot is a normal cellulose ester film when a cellulose ester film is placed between two polarizing plates in an orthogonal state (crossed Nicols), irradiated with light from one side and observed with an optical microscope (50 times) from the opposite side. If this is the case, the light is blocked, black, and nothing can be seen, but if there is a foreign object, the light leaks from it and appears to shine like a spot. The larger the diameter of the bright spot, the greater the actual harm in the case of the liquid crystal image display device. The diameter of the bright spot is preferably 50 μm or less, more preferably 10 μm or less, and further preferably 8 μm or less. The diameter of the bright spot means a diameter measured by approximating the bright spot to a perfect circle.

As long as the bright spot foreign matter has a diameter of 400 / cm ² or less, there is no practical problem, but 300 / cm ² or less is preferable, and 200 / cm ² or less is more preferable. In order to reduce the number and size of such bright spot foreign matters, it is necessary to sufficiently filter fine foreign matters.

  In addition, for example, as described in JP-A-2000-137115, a pulverized product of a cellulose ester film once formed is re-added at a certain ratio in a dope, and used as a raw material for cellulose ester and its additive Can be preferably used because it can reduce bright spot foreign matter.

  A stainless steel endless belt or drum having a mirror-finished surface is generally used as the film-forming support.

  The surface roughness Ra of the support is from 0.0001 to 1 μm, more preferably from 0.0003 to 0.1 μm, still more preferably from 0.0005 to 0.03 μm.

  Further, it is a peeling step that a roughening zone having an average roughness Ra of 0.5 to 2 μm is provided at both ends of the support, and the dope is cast so that a 5 to 30 mm wide dope overlaps the roughening zone. Is preferable from the viewpoint of smoothly peeling.

  Below, the manufacturing method of the polymer film by this invention is demonstrated with reference to drawings.

  FIG. 1 is an enlarged perspective view of a casting process portion of a solution casting film forming apparatus for carrying out the method of the present invention. FIG. 2 is a longitudinal sectional view of the same part. FIG. 3 is a drawing of a solution casting film forming apparatus for carrying out the method of the present invention. First, cellulose ester is dissolved in a mixed solvent of a good solvent and a poor solvent, and the above plasticizer and ultraviolet absorber are added thereto. To prepare a cellulose ester solution (dope) and cast the dope from a casting die (2) onto a stainless steel endless belt support (1) having a mirror-finished surface (1) (10) is obtained, and the web (10) is peeled off by the peeling roll (6) when the web (10) is moved approximately 3/4 rounds by the rotation of the endless belt support (1).

  In the illustrated film forming apparatus having a rotationally driven endless belt as the support (1), the belt support (1) is disposed between a pair of drums and an intermediate portion between the pair of drums and the endless belt support (1) ( 1a) and a lower transition portion (1b) are each composed of a plurality of rolls (not shown) supporting the rear side. The plurality of rolls are called support rolls, and the distance between adjacent support rolls is greater than 0 m and within a range of 5 m or less, preferably 1 to 5 m, and desirably 2 to 5 m. Further, among the support rolls supporting the upper transition part (1a) of the endless belt support (1) from the back side, the distance between the support rolls adjacent to each other is the lower transition of the endless belt support (1). Of the support rolls supporting the part (1b) from the back side, the distance is preferably narrower than the distance between the support rolls adjacent to each other.

  Also, a drive device for applying tension to the belt support (1) is provided on one or both of the drums at both ends of the rotary drive endless belt support (1), whereby the belt support (1) Is used in a tensioned state. Due to this tension, both end portions of the belt support (1) are warped more than the width central portion. In the present invention, the amount of warpage (H) at both ends of the support (1) portion on which the dope is cast and the dope film (web) is formed is equal to the widthwise central portion of the support (1) surface. In comparison, it is 0.01 to 2 mm. The belt warp amount (H) is more preferably 1 mm or less.

  By the way, generally, the viscosity of the dope used in the solution casting film forming method exceeds 200 poise. Since such a high viscosity dope has low fluidity, both sides of the support (1) are used. Even when the amount of warping of the end portion was 2 mm or more, the phenomenon that the dope flowed and the end portions on both sides of the web became thin or the retardation value varied was not observed. However, in the case of using a low-viscosity dope as in the method of the present invention, the amount of warping of the end of the support (1) appears very severely in the quality of the product film, so it is necessary to cope with it.

  Here, the warping of the end of the endless belt support (1) shortens the interval between the plurality of support rolls installed on the back surface of the belt as described above, and the casting installed directly under the casting die (2). Reduction can be achieved by bringing the belt into contact with the support roll other than the back roll with a holding angle in the range of 0.01 to 1.5 °. The belt holding angle in the back roll is preferably 0.2 to 6 °, and more preferably 1 to 5 °.

  The dope is fed to the casting die (2) through a pressurized metering gear pump, and the dope is cast from the extrusion die (2) onto the endless belt at the casting position. The belt temperature during film formation can be cast at a temperature in the general temperature range of 0 ° C. to less than the boiling point of the solvent, and more preferably in the range of 5 ° C. to the boiling point of the solvent −5 ° C. At this time, it is necessary to control the ambient atmospheric humidity above the dew point.

  In addition to the extrusion die (2), there is a doctor blade method that adjusts the film thickness with a blade, or a reverse roll coater method that adjusts with a reverse rotating roll, etc., but the slit shape of the base part can be adjusted, A pressure die that facilitates uniform film thickness is preferred. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used.

  In the casting die (2), the angle formed between the wall surface of the internal slit (2a) and the support surface is preferably 40 to 90 °, particularly preferably 60 to 75 °.

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

  The gap of the slit (2a) of the casting die (2) is preferably 0.05 to 1.5 mm, more preferably 0.15 to 1.0 mm.

  The ratio between the linear flow velocity U1 (m / sec) of the dope discharged from the die slit (2a) and the traveling speed U2 (m / sec) of the support, and the draft ratio β defined by U1 / U2 is 0.4 to 2.0 is preferable.

Casting die (2) Solvent vapor concentration expressed by the following formula near the lower part of the side: α (%),
Solvent vapor concentration: α (%) = (volume of solvent vapor / volume of space containing solvent) × 100
Similarly, the ratio of α / V (second / m) to the wind speed V (m / second) near the lower part of the side surface of the casting die (2) is preferably 10 or more. As a result, the solvent vapor concentration near the lower part of the side of the casting die (2) is always kept at an optimal value, and the edge of the web cast from the casting die (2) to the support tbe has a sawtooth shape (die lip end). It is possible to effectively prevent a film from being formed on the part and causing it to come into contact with the web edge while vibrating and causing a film breakage in a subsequent process after peeling.

  As shown in detail in FIG. 1 and FIG. 2, in drying the web cast on the surface of the support (1), a drying air blowing device (2) disposed above the support (1) in front of the casting die (2) ( From 12), the drying introduced from the drying air inlet (13) through a plurality of slits (14) provided to face the web (10) at an angle (θ) of 60 ° to 120 ° with respect to the surface of the web (10). The wind (20) is blown and the timing at which the wind (20) starts to be applied is more than 3 seconds after casting the dope from the casting die (2). Wind velocity of wind flowing in the direction: V1 is 10 m / sec or less, and wind velocity of wind flowing in the longitudinal direction on the web surface toward the casting die (2): V2 is 4 m / sec or less.

In the illustrated embodiment, a dry air blowing device (15) is also disposed on the back side of the upper transition portion (1a) of the endless belt support (1), and the upper transition portion ( The drying air (20) introduced from the drying air inlet (16) is blown from a plurality of slits (17) provided so as to face 90 ° with respect to 1a). Also, drying air blowing devices (18) and (19) are arranged on both the upper and lower surfaces of the lower transition portion (1b) of the endless belt support (1), and the drying air (20) is applied to the surface of the web (10). In addition, in the polymer film manufacturing method of the present invention, the side surface of the casting die (2) is provided by providing an enclosure near the lower end of the side surface of the casting die (2) or by spraying solvent vapor. The vicinity of the lower end on the side is preferably set to the desired solvent vapor concentration. Also by this, the quality of the film can be further improved.

For the same purpose, in the dope casting step, the dope-soluble solvent is allowed to flow down from the lower end on the side surface of the casting die (2) onto the support, and the dope-soluble solvent is allowed to flow down. It is desirable that the amount is 0.1 to 1.0 cm ³ / min, and the temperature of the dope-soluble solvent is not more than its boiling point.

  In addition, when the support transport speed is 10 m / min or more, the casting film coming out from the lip of the casting die (2) is depressurized to cause air mixing and horizontal streaks in the width direction of the film. In order to suppress fluttering of the casting ribbon, the decompression chamber is preferably provided upstream of the casting die (2), and the pressure is reduced by 10 to 600 Pa, more preferably 10 to 200 Pa.

  The gap between the lower end face of the decompression chamber and the surface of the support (1) is in the range of 0.5 to 5 mm, and the suction air volume is not too large, so that the dope dry film on the casting die (2) lip end This is desirable because the occurrence of this is suppressed.

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

  When casting the dope onto the support (1), the temperature is controlled below the boiling point of the solvent used for dissolving the raw polymer, and below the boiling point of the solvent having the lowest boiling point in the mixed solvent. The temperature can be cast at a temperature in the general temperature range of 0 ° C. to less than the boiling point of the solvent, but it is more preferable to cast on a support (1) at 5 to 30 ° C.

  Further, a dope adjusted to have a dope viscosity of 1 to 200 poise is cast from the casting die (2) onto the support (1) so as to have a substantially uniform film thickness. When the amount of residual solvent is 200% or more by weight of the solid content, the casting film temperature is below the boiling point of the solvent, and when it is in the range of 100% to 200%, the boiling point of the solvent is below the boiling point of the solvent + 10 ° C. The cast film (web) (10) is dried by the drying air (20) so that it is in the range of + 20 ° C. or lower.

  The gap between the tip of the slit (14) of the dry air blowing device (12) and the web (10) is preferably 5 to 200 mm, more preferably 10 to 150 mm.

  Variation of the wind speed in the width direction of the dry wind (20) blown out from the slit (14), the difference between the maximum wind speed and the minimum wind speed is W1 m / sec, the wind casting die (2) along the width direction The ratio of the average wind speed W2 m / sec: W1 / W2 is preferably 0.3 or less.

  On the support (1), the web (10) is dried and solidified until the strength of the film is peelable from the support (1). Therefore, the residual solvent in the web (10) is dried to 150% by weight or less. Is preferable, and 80 to 120% is more preferable.

  The web temperature when the web (10) is peeled from the support (1) is preferably 0 to 30 ° C. In addition, immediately after the web (10) is peeled off from the support (1), the temperature once decreases rapidly due to solvent evaporation from the support (1) adhesion surface side, and volatile components such as water vapor and solvent vapor in the atmosphere. Is easy to condense, the web temperature during peeling is more preferably 5 to 30 ° C.

  Here, the residual solvent amount can be expressed by the following equation.

Residual solvent amount (% by weight) = {(M−N) / N} × 100
In the formula, M is the weight of the web at an arbitrary time point, and N is the weight when the weight M is dried at 110 ° C. for 3 hours.

  The release tension is usually 20 to 25 kg / m when the support (1) and the web (10) are peeled, but in the cellulose ester film according to the production method of the present invention, which is thinner than the conventional, Since the web (10) is likely to wrinkle at the time of peeling, it is preferably peeled at a minimum tension capable of peeling to 17 kg / m, and more preferably peeled at a minimum tension to 14 kg / m.

  The web (10) after peeling is introduced into the primary drying device (3A). In the primary drying device (3A), the web (10) is meandered by a plurality of conveying rolls (7) arranged in a staggered manner when viewed from the side, while the web (10) is placed at the bottom of the drying device (3A). It is blown from the front part and dried by warm air (5) discharged from the rear part of the ceiling of the drying device (3A).

The web (10) is then introduced into the tenter dryer (4). Therefore, the side edges of the web (10) are gripped with a clip and stretched, and the web (10) is dried. Further, the web (10) is introduced into the secondary drying device (3B). In the secondary drying device (3B), the web (10) is meandered by a plurality of conveying rolls (7) arranged in a staggered manner when viewed from the side, while the web (10) is moved to the secondary drying device (3B). ) And is dried by warm air (5) discharged from the rear part of the ceiling of the secondary drying device (3B) and dried as a cellulose ester film (11) as a winder (8). ). The primary and secondary drying devices (3A) and (3B) are each dried using warm air (5), but may be dried by infrared rays.

  While the amount of the residual solvent in the web (10) is 10 to 150% by weight, it is desirable to carry it with a roll having a surface roughness Ry of 0.6 μm or less and a surface energy at 20 ° C. of 18 to 100 mN / m.

  The surface roughness Ry refers to the “maximum height Ry” defined by JIS standard B0601. Usually, it is considered that the web (10) is brought into contact with a roll having a matte surface and transported, but as a result of investigation, the roll having a mirror surface has a surface roughness Ry of 0.6 μm or less. We have found that a completely smooth mirror roll can prevent dirt. The surface roughness Ry is preferably 0.4 μm or less, and more preferably 0.2 μm or less. In other words, the smoother the surface, the better. In other words, the mirror surface is better. In addition, the measuring method of surface energy is computable using the formula of Fowkes-Owens from the contact angle with water and a methylene iodide.

  Also, while the amount of residual solvent in the web (10) is 10 to 150% by weight, the web (10) is very soft, so the diameter of the transport roll is thin (less than 85 mm) and the web (10) becomes a roll. Although it is easy to be deformed by the pressing force, not only that, but the additive that precipitates, evaporates or volatilizes from the web (10) adheres to the roll, and the web (10) is easily soiled or pressed. Also, if the roll is thick (diameter exceeding 300 mm), if the tension applied to the web (10) is weak, the friction between the web (10) and the roll will not be sufficient, causing slippage, and scratching the web (10). End up. When a strong tension is applied to the web (10) so that it does not slide, the soft web expands and contracts and the desired optical properties are not obtained, and uneven stripes extending in the transport direction are emphasized, and the web (10) Since it is strongly pressed against the roll, it is pushed and deformed. Therefore, the diameter of the roll to be used is preferably 85 to 300 mm, and more preferably 100 to 200 mm.

  In the web (or film) drying step, a method of drying while conveying the web (or film) by a roll suspension method, a pin tenter method or a clip tenter method is generally adopted.

  As an image display member, a tenter method in which both side edges of a web (or film) are fixed with a clip or the like and is stretched is known, which is preferable for improving flatness and dimensional stability.

  As a method using this tenter method, for example, Japanese Patent Laid-Open No. 59-211006 discloses a technique for manufacturing a substrate of a liquid crystal display panel from a film such as a phenoxy resin, and this film includes a cellulose acetate film. It is suggested that it can also be used. Japanese Patent Application Laid-Open Nos. 4-284221 and 62-115535 disclose methods for producing a cellulose triacetate film using a tenter dryer.

  In particular, in the drying step after peeling from the support, the web (or 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, a method of drying all or part of the drying process as shown in Japanese Patent Application Laid-Open No. 62-46625 while holding the width ends of the web (10) with a clip in the width direction. / Tenter method is preferred.

  When the residual solvent amount is 10 to 100% by weight, and / or when the residual solvent amount is 5 to 10% by weight and the residual solvent amount is 90 to 150 ° C. If the stretching is about 1 to 20%, the effect of improving the flatness of the cellulose ester film is particularly preferable.

Moreover, it is preferable that the difference in tension acting on the web (10) along the conveying direction before and after the tenter is 8 N / mm ² or less.

  A preheating step for preheating the web (10), a stretching step for stretching the web (10) using a tenter after the preheating step, and a stretching amount of the web (10) in the stretching step after the stretching step. And a relaxation step of relaxing by a smaller amount than that, the temperature T1 in the preheating step and the stretching step is set to (glass transition temperature Tg-60 of film) or higher, and the temperature T2 in the relaxation step is It is preferable that the temperature be (T1-10) ° C. or lower. In particular, the stretch ratio of the web (10) in the stretching step is 0 to 30% as a ratio to the web width immediately before entering the stretching step, while the stretch ratio of the web (10) in the relaxation step is − It is desirable to set it as 10 to 10%. In addition, the polymer film manufacturing method by this invention mentioned above is especially suitable for manufacture of the film for polarizing plates. That is, as a film to be manufactured, a polarizing film is particularly mentioned.

  In the method of the present invention, the means for drying the web (or film) is not particularly limited, and is generally performed by hot air, infrared rays, a heating roll, microwaves or the like. It is preferable to dry with hot air in terms of simplicity. The drying temperature is preferably 40 to 150 ° C., and more preferably 50 to 150 ° C. in order to improve flatness and dimensional stability.

  In this way, in the web (or film) drying step, the web peeled from the support (1) is further dried, and finally the residual solvent amount is 3 wt% or less, preferably 1 wt% or less, more preferably Is preferably 0.5% by weight or less in order to obtain a film having good dimensional stability. In the web drying process, as described above, generally, a method of drying while conveying the web by a roll suspension method, a pin tenter method, or a clip tenter method is adopted.

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

  The web conveyance tension at the time of drying is 30 to 300 N / width m, and 40 to 270 N / width m is more preferable.

  Preferably, a web (or film) surface cleaning device is arranged before and / or after the drying step and / or the thermal straightening device.

  The cleaning device applies ultrasonic vibration to the web (or film) in the middle of conveyance, blows high-pressure air onto the surface, blows off the adhering matter and sucks it, and removes adhering dust and the like. . In addition, known means and methods such as a method for performing flame treatment (corona treatment, plasma treatment) and a method for installing an adhesive roll can be used without any particular limitation. In addition, the cleaning means to arrange | position may be single and may be two or more.

  Since the adhesion of dust or the like to the web (10) is often due to the action of static electricity, it is possible to remove static electricity from the web (10) by placing a static elimination means, for example, a static elimination bar, in front of the above-described cleaning device. preferable. As the charge removal bar, a known bar can be used without any particular limitation.

  In the drying process, as a measure to suppress the phenomenon that the plasticizer contained in the web (or film) evaporates and condenses on the rolls and wall surfaces, a fresh gas of a specific amount or more is allowed to flow into the supply air volume per unit time. It is preferable. And it is preferable to set the quantity of the fresh gas supplied to 5 to 50% of the total supply air volume.

  The reason why the supply amount of fresh gas is 5 to 50% is that if the amount is less than 5%, the amount of fresh gas is too small to suppress the plasticizer condensation. If the amount exceeds 50%, the amount of fresh gas is too large. This is because the running cost increases waste.

  In addition to the above measures, for example, the following configuration can be adopted. First, a configuration in which a part of the air in the drying / correction process chamber is circulated and the plasticizer is forcibly removed by passing it through a cooler coil or the like and then raised to a specified temperature with a heater. A configuration in which the temperature of the portion in contact with the metal surface is increased, for example, a configuration in which the temperature of the portion in contact with the metal surface is increased by a steam / surface heater or the like. Third, fresh air is supplied to lower the vapor pressure of the plasticizer on the roll surface. As a means for supplying fresh air, a configuration in which a slit is provided in the width direction in the vicinity of the roll, air air is supplied from the punch plate box, and the air velocity distribution of the supplied air is suppressed is used. Is not to be done.

  It is preferable that the film temperature at the time of taking out the film from the drying process or the heat correction process chamber or the cooling process of the film coming out of them is 60 ° C. or less.

  This is because, when the straightening and the cooling process box are carried out at a temperature exceeding 60 ° C., the plasticizer is likely to be condensed.

  Next, embossing provided on both side edges of the polymer film will be described. The polymer film that has finished the transport drying process is subjected to processing for forming an emboss on the film by an embossing apparatus prior to introduction into the winding process. As an embossing apparatus, an apparatus described in JP-A-63-74850 can be used.

  Here, the height h (μm) of the emboss is set in the range of 0.05 to 0.3 times the film thickness T, and the width W is set in the range of 0.005 to 0.02 times the film width L. . For example, when the film thickness is 40 μm and the film width is 100 cm, the thickness of the emboss 31 is set to 2 to 12 μm and the emboss width is set to 5 to 30 mm.

  Embossing may be formed on both sides of the film. In this case, the height h1 + h2 (μm) of the emboss is set in the range of 0.05 to 0.3 times the film thickness T, and the width W is set in the range of 0.005 to 0.02 times the film width L. . For example, when the film thickness is 40 μm, the emboss height h 1 + h 2 (μm) is set to 2 to 12 μm. The emboss width is set to 5 to 30 mm.

  The lower limit of the embossed height is from the height necessary to prevent partial uneven adhesion between the films. On the other hand, the upper limit is too high, and the embossed shape is too high. This is because it deforms to induce a failure.

  Regarding the width of the emboss, the embossed part will eventually become a loss part, but it is desirable to reduce it. For example, when the film thickness is reduced from 80 μm to 40 μm, the frictional force between the film and the roll becomes 50 μm as a boundary. It was found that the grip force was extremely reduced, and when the film-forming speed was increased to 30 m / min or more, it was found that the friction force between the film and the roll was extremely reduced especially at 50 m / min or more. did. For this reason, the emboss width is the minimum necessary for suppressing slipping of the film, particularly when a high-speed film formation of 50 m / min or more is performed with a thin film of 50 μm or less. However, it is also linked to the height of the above-mentioned embossing, and the embossing height × embossing width for clearing all of the pyramid shape, the horse back, the polygonal shape, and the winding slippage failure is determined. In addition, embossing can be arrange | positioned not only at the both ends of a film but at the center part.

  In the method of the present invention, it is preferable that a static eliminator is installed before the winding and immediately after the winding part to neutralize the film.

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

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

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

  In the method of the present invention, the winder for producing the polymer film may be one generally used, such as a constant tension method, a constant torque method, a taper tension method, a program tension control method with a constant internal stress, and the like. It can be wound up by a winding method.

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

  At the start of the initial winding, it is preferable that the winding tension is 280 N / m width or less and only the embossed portion is wound so that the pressing force of the touch roll winding + the initial winding tension is 60 N / m width or more.

  With respect to the winding condition range of 280 N / m or more, the radial tension applied to the embossed part due to the tension during winding and the pressing force of the touch roll is too large, and the film peeling charge amount during the aforementioned re-feeding is too large. On the other hand, at 60 N / m or less, the take-up tension is too weak, especially during long take-up of 2000 m or more, and when the finished product roll is transported or unwound due to the feed tension at the time of re-feeding It is for waking up.

  The pressing of the touch roll is preferably monitored by installing a pressing pressure detector and set to a width of 3 to 100 N / m.

  As the pressing means of the touch roll, for example, a double-acting low friction cylinder or a servomotor is used to apply tension feedback, and the pressing is performed so that each side can be controlled independently. It is preferable to measure the pressure on both sides with a pressure detector.

  The material of the touch roll is metal or hard synthetic resin. The position to be touched is preferably the position immediately after the tangent line where the film contacts the product roll.

  The direction in which the touch roll moves as it rolls up is more preferably the normal direction from the winding core.

  It is preferable to perform winding by setting the control of the edge point control (EPC) of the winding unit to be fixed automatically from 0 to 5 seconds before winding is completed and from 0 to 5 seconds after winding is started. .

The winding hardness of the wound original product is
[Winding hardness of embossed portion−winding hardness of intermediate position from film end to center] <170
Is preferable.

  If the winding hardness exceeds 170, the adhesive strength of the embossed part is too large, and the problem of the film peeling charge amount at the time of re-feeding is too large at the time of re-feeding the product roll. This is because the winding state in the middle becomes a loose winding state, and the product main winding is distorted into a polygonal shape and causes a failure.

  The winding hardness can be measured according to a JIS standard viscous hardness meter, or PROCEQ S., Switzerland. A. An electronic film hardness tester, an echo chip, or a Paro tester 2 manufactured by the company can be used. The impact device uses the D type.

Hardness value: L is measured by the rebound speed V / the striking speed V ₀ . The repulsion speed V is the rebound speed from the impact body specimen, and the impact speed V ₀ is the impact speed from the impact body specimen, and the average value of 10-point measurement was calculated. In addition, since the hardness of the central portion has a large variation in the hardness measurement point in the original winding, it is set as an intermediate portion between the upper surface of the embossed portion, the embossed portion, and the central portion.

  The process average atmosphere (US Federal Standard 209D) until the web (10) is peeled from the support (1) is set to be class 10 or higher and class 10,000 or lower, and the web (10) is peeled from the support (1). By setting the process average atmosphere (Federal Standard 209D) after class to a class of 100 or more and class 10000 or less, the number of foreign matters that are a major problem with display defects and appearance deterioration when processed into a display device Can be obtained.

  In film transport drying, the web (10) peeled from the belt is further dried, and the residual solvent amount at the time of winding is 3% by weight or less, preferably 1% by weight or less, more preferably 0.5% by weight or less. This is preferable in terms of film dimensional stability and environment.

  In the method of the present invention, the thickness of the polymer film is 20 to 200 μm, preferably 25 to 150 μm. If it is thinner than this, the stiffness of the film will decrease, so it will be easy to cause troubles such as wrinkles and film breakage in the polarizing plate production process. If it is thicker than this, the display will become thicker and heavier. .

In the polymer film according to the present invention, the in-plane retardation value variation ΔR ₀ depending on the film location is preferably 5 nm or less.

The in-plane retardation value R ₀ (nm) referred to in the present invention is represented by the following formula.

R ₀ = (Nx−Ny) × d
Nx: Refractive index in the x direction which is the maximum refractive index direction in the plane of the film Ny: Refractive index in the y direction which is the direction in the film plane perpendicular to the x direction d: Film thickness (nm)
In the present invention, an ordinary refractometer can be used for measuring the refractive index of the polymer film. For example, after measuring the entire refractive index, using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), in an environment of a temperature of 23 ° C. and a humidity of 55% RH, a wavelength of 590 nm is three-dimensional. The refractive index measurement is performed to calculate the refractive indexes Nx and Ny, and the thickness of the film is measured to obtain the R ₀ value.

  The polymer film obtained by the method of the present invention can be used as a member of an optical element or a display device, and this member is a member used for various display devices such as a liquid crystal display device or an organic electroluminescence display. Thus, for example, a polarizing plate, a protective film for polarizing plate, a retardation plate, a reflecting plate, a viewing angle widening film, an optical compensation film, an antiglare film, a non-reflective film, an antistatic film and the like can be mentioned.

  Among them, it is more preferable to apply the present invention to a polarizing plate, a protective film for a polarizing plate, a retardation plate, and a viewing angle widening film in which smoothness of the film surface and uniform optical properties are strictly required.

  In the method of the present invention, the method for producing the polarizing plate is not particularly limited, and the polarizing plate can be produced by a general method. For example, as an example of a cellulose triester film, there is a method in which the film is bonded to both surfaces of a polarizing film prepared by alkali treatment and immersed in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. Instead of the alkali treatment, a method for improving adhesiveness as described in JP-A-6-94915 and JP-A-6-118232 may be used.

  By the above method, it is possible to obtain an optically homogeneous high-quality film with less streak unevenness and excellent smoothness and less variation in retardation value.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

Examples 1-3
(Preparation of dope)
A dope of cellulose triacetate was prepared as follows.

Cellulose triacetate 100 parts by weight (acetyl substitution degree 2.88, number average molecular weight 150,000)
Triphenyl phosphate 10 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight Tinuvin 326 (manufactured by Ciba Specialty Chemicals) 1 part by weight AEROSIL 200V (manufactured by Nippon Aerosil Co., Ltd.) 0.1 part by weight Methylene chloride 660 parts by weight Ethanol 40 parts by weight Part The above materials are sequentially put into a sealed container, the temperature in the kettle is raised from 20 ° C. to 80 ° C., and the mixture is stirred for 3 hours while maintaining the temperature at 80 ° C. to completely dissolve the cellulose triacetate. did. After that, the stirring was stopped, the liquid temperature was lowered to 43 ° C., and then immediately sent through a connected pipe to the filtration process. Using a filter paper with an absolute filtration accuracy of 0.005 mm, a filtration flow rate of 300 L / m ² · hour Filtration was performed at a filtration pressure of 1.0 × 10 ⁶ Pa.

  The dope prepared as described above was cast and dried using the solution casting film forming apparatus shown in FIGS. 1 to 3 to produce a cellulose acetate film.

  The dope prepared as described above was cast on a support (1) made of a stainless steel endless belt through a casting die (2) kept at 30 ° C. by circulating hot water. The dope viscosity at the time of casting was 50 poise.

  In this casting process, after 3 seconds have passed since the dope was cast on the support (1), the dry air blowing device (12) disposed above the support (1) in front of the casting die (2). From the plurality of slits (14) placed at an angle of dry θ = 70 °, 40 ° C. wind (20) was applied to the surface of the dope film (web) (10) on the support (1). At this time, the velocity of the wind flowing in the width direction on the surface of the web (10): V1 is 10 m / second, and the velocity of the wind flowing in the longitudinal direction on the surface of the web (10) toward the casting die (2): V2 is 4 m. Per second.

  In addition, the amount of warping (belt warping) (H) at the end of the support (1) where the dope is cast and the dope film (web) is formed is the width direction of the surface of the support (1). Compared to the central portion, it was 0.2 mm in Example 1, 1 mm in Example 2, and 2 mm in Example 3.

  Finally, after drying on the support (1) until the amount of residual solvent in the web (10) reaches 100% by weight, the web (10) is removed from the support (1) by a peeling roll (6). It peeled.

  Next, the web (10) is dried with 120 ° C. drying air (5) in a roll conveyance drying process (3A) arranged in a staggered manner, and then introduced into the tenter (4), and both ends of the web (10) are introduced. With a clip, dried by applying a drying air of 105 ° C while maintaining the width, and further dried with a drying air of 100 ° C (5) in a roll conveyance drying process (3B) arranged in a staggered manner and wound up The cellulose triacetate film (11) was wound up in a machine (8) to finally produce a cellulose triacetate film (11) having a thickness of 80 μm. Note that throughout the above steps, the web (10) and the film (11) have a conveyance speed of the support (1) made of an endless belt and a winder (8) so that the conveyance tension of the film (11) is 180 N / width m. The winding speed was appropriately adjusted.

(Evaluation of retardation value variation ΔR ₀ )
The cellulose acetate film thus prepared was evaluated for retardation value variation ΔR ₀ by the following method.

The retardation value variation ΔR ₀ is measured using an automatic sub-refractometer KOBRA-21ADH (manufactured by Oji Scientific Instruments) in an environment of a temperature of 23 ° C. and a humidity of 55% RH, and a laser focus manufactured by Keyence Corporation. The film thickness of the film is measured with a displacement meter LT-8010, the average film thickness d is obtained, and 10 points are measured in the width direction of the sample according to the above-described method, and the maximum value of the calculated retardation value _R0. The difference between the minimum values was defined as retardation value variation ΔR ₀ . If ΔR ₀ is 5 nm or less, an easy-to-see display image free from color shift and unevenness can be obtained by the image display device.

(Display screen, image appearance evaluation)
Using the produced cellulose acetate film, a polarizing plate was produced by the following method, and it was attached to a panel for visual appearance evaluation.

(Preparation of polarizing plate)
A 120 μm-thick polyvinyl alcohol film was immersed in 100 g of an aqueous solution containing 1 g of iodine and 4 g of boric acid, and stretched 6 times at 50 ° C. to form a polarizing film. Each polarizing plate was prepared by bonding each cellulose ester film subjected to the following alkali saponification treatment to the front and back surfaces of this polarizing film using a 5% aqueous solution of completely saponified polyvinyl alcohol as an adhesive.

(Alkaline saponification treatment)
Step Treatment liquid Treatment temperature Treatment time Saponification step: 2 mol / L NaOH 50 ° C. 90 seconds Water washing step: Water 30 ° C. 45 seconds Neutralization step: 10 wt% HCl 30 ° C. 45 seconds Water washing step: Water 30 ° C. 45 seconds Under the above conditions Each cellulose ester film was subjected to saponification, water washing, neutralization and water washing in this order, and then dried at 80 ° C.

(Evaluation with polarizing plate attached to liquid crystal display panel)
Carefully peel off the polarizing plates pasted on both the front and back sides of the LCD cell glass of a commercially available liquid crystal display panel (manufactured by NEC, color liquid crystal display MultiSync LCD1525J: model name LA-1529HM), and the polarizing plate in which the polarization direction is adjusted here A liquid crystal display panel was prepared, and the appearance was evaluated by the following method.

  About the liquid crystal display panel, under illumination with white LED, as the optical characteristics, the unevenness of the reflected light and the uniformity of the screen were observed from the angle of 35 ° from the normal direction, and evaluated according to the following criteria. Is shown in Table 1 below.

◎: There is no streak of reflected light, and the image is clear with no unevenness. ○: Slight unevenness of reflected light is recognized, but the image has no unevenness and can be clearly recognized. Light streak unevenness and image unevenness are recognized ×: Comparative examples 1 and 2 in which reflected light streak unevenness and image unevenness are conspicuous and the screen is difficult to see
Next, for comparison, a cellulose triacetate film is produced in the same manner as in Example 1. As shown in Table 1 below, the dope is cast to form a dope film (web). The amount of warp (H) at the end of the support (1) portion is 3 mm, which is outside the scope of the present invention, in Comparative Example 1, compared to the center in the width direction of the surface of the support (1). 2 was 4 mm, which is outside the scope of the present invention.

For the cellulose acetate films of Comparative Examples 1 and 2 produced in this manner, as in the case of Example 1, the retardation value variation ΔR _{0 was} evaluated, and the evaluation was performed with the polarizing plate attached to the liquid crystal display panel. The obtained results are shown in Table 1 below.

Comparative Examples 3-5
Next, for comparison, a cellulose triacetate film is produced in the same manner as in Example 2 described above. As shown in Table 2 below, in Comparative Example 3, the dope is used as a support ( 1) After 2 seconds, which are outside the scope of the present invention after casting on the upper side, the support from the casting die (2) front support (1) and the drying air blowing device (12) located above is supported. Dry air (20) was applied to the surface of the dope film (web) (10) on the body (1). Further, in Comparative Examples 4 and 5, the point of applying the drying air (20) after 3 seconds after casting is the same as in the case of Example 2 described above, but in Comparative Example 4, the web ( 10) Velocity of wind flowing in the width direction on the surface: V1 is set to 12 m / second, which is outside the scope of the present invention. In Comparative Example 5, a casting die (2 ) Velocity of the wind heading to: V2 was set to 5 m / second, which is outside the scope of the present invention.

About the cellulose acetate films of Comparative Examples 3 to 5 thus produced, as in the case of Example 1, the retardation value variation ΔR _{0 was} evaluated, and the evaluation was performed with the polarizing plate attached to the liquid crystal display panel. The obtained results are shown in Table 2 below.

As is clear from the results in Table 1 above, in the cellulose triacetate films of Examples 1 to 3 of the present invention, the retardation value variation ΔR ₀ is 5 nm or less, and the polarizing plate attached to the liquid crystal display panel is used. In the external appearance evaluation, it was confirmed that there was no stripe unevenness of reflected light, the image was not uneven, and the image was clear and excellent in visibility when used in a liquid crystal display device. On the other hand, in the cellulose triacetate films of Comparative Examples 1 to 5, the retardation value variation ΔR ₀ exceeds 5 nm, and the appearance evaluation with the polarizing plate attached to the liquid crystal display panel is evaluation of Δ or ×, Obviously, irregularities in the reflected light and irregularities in the image were recognized, or irregularities in the reflected light and irregularities in the image were conspicuous, making it difficult to see the screen.

  As described above, according to the method of the present invention, it was possible to produce a cellulose triacetate film useful for a liquid crystal display device having a smooth surface, non-striking unevenness, and optically homogeneous and high quality. .

1 is a partial perspective view of an apparatus for carrying out the method of the present invention. It is a partial longitudinal cross-sectional view of the same apparatus. It is a schematic longitudinal cross-sectional view which shows the whole apparatus which implements the method of this invention.

Explanation of symbols

1: Endless belt support V1: Wind speed V2 of the wind flowing in the width direction on the web surface: Wind speed H of wind flowing in the longitudinal direction on the web surface toward the casting die H: Warpage amount of the support end (belt warping up) amount)
2: Casting die 2a: Die slit 3A: Drying device 3B: Drying device 4: Tenter 5: Drying air 6: Peeling roll 7: Conveying roll 8: Winder 10: Web 11: Film 12: Drying air blowing device 14 : Slit θ: Slit angle

Claims (2)

  A flow for forming a dope film (web) by casting a polymer film raw material solution (dope) from a casting die onto a rotating metal support (hereinafter referred to as “support”) by a solution casting film forming method. In the extending step, the peeling step for peeling the web formed on the support from the support, the drying step for drying the web peeled from the support via a plurality of transport rolls, and the drying step A method for producing a polymer film having a thickness of 20 to 200 μm, comprising a winding step of winding a polymer film formed by drying a web around a core, wherein the dope viscosity during casting is 1 The warp amount at the end of the support portion where the dope is cast and the dope film (web) is formed is 0.01 to 10 poises compared to the widthwise center of the support surface. 2m And characterized in that, the production method of the polymer film.   3 seconds or more after casting the dope on the support in the casting process, a dry air blowing device disposed above the support in front of the casting die is applied to the dope film (web) on the support. The wind speed of the wind flowing in the width direction on the web surface by applying the drying wind at an angle in the range of 60 ° to 120 °: V1 of 10 m / sec or less and the wind flowing in the longitudinal direction on the web surface toward the casting die 2. The method for producing a polymer film according to claim 1, wherein the wind speed: V2 is 4 m / second or less.

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