CN101610892A - Cellulose ester membrane, its manufacture method, the polarizer that has used cellulose ester membrane and display unit - Google Patents

Abstract

Even the invention provides in the stretching process of sheet stock sheet stock in the manufacture method that is stretched to the cellulose ester membrane that mist degree also can not uprise more than 1.2 times on the width, the cellulose ester membrane that adopts this method manufacturing, the polarizer that has used this film and display unit.In process for producing cellulose ester film based on solution casting system embrane method, the extensibility of sheet stock is 20～60% in the stretching process, and the temperature of the hot blast that blows out from the hot blasting device in the stretching process is Tg+35 ℃～Tg+80 ℃ with respect to the glass transition temperature (Tg) of the film after reeling.The residual solvent amount that preferably is about to enter the film before the stretching process is 10～35 quality %.

Description

Cellulose ester film, method for producing same, polarizing plate using cellulose ester film, and display device

Technical Field

The present invention relates to a cellulose ester film that can be used for various functional films such as a protective film for a polarizing plate, a retardation film, a viewing angle expanding film, and an antireflection film for a plasma display, which are used in a Liquid Crystal Display (LCD), a method for producing the cellulose ester film, a polarizing plate using the cellulose ester film, and a display device.

Background

In recent years, liquid crystal display devices have been applied to televisions and large monitors due to improvement in image quality and improvement in high-definition technology, and particularly, these liquid crystal display devices are expected to be large in size and to be produced efficiently to reduce costs.

In addition, in recent years, with the rapid growth of liquid crystal TVs, the demand for optical films has also rapidly increased, and improvement in productivity thereof has been strongly demanded. In the case of cellulose ester films formed by solution casting, a small amount of dry solvent is required for the film, and therefore, the production rate can be increased.

By expanding the casting width on a casting support made of a rotation-driven stainless steel endless belt or a rotation-driven stainless steel drum or the like, a wide film can be obtained by a solution casting film-forming method.

On the other hand, the width of the casting support and the casting die has an upper limit due to the limitation in the production of the apparatus. In the case where the casting support is an endless belt, the upper limit of the width is currently 2000 mm. In this case, it is safe that the upper limit of the casting width is at most about 1900mm in consideration of meandering (meandering) or the like during the conveyance of the endless belt. In addition, when the casting support is a drum made of metal, the maximum width is about 2500mm due to the manufacturing restriction. In the case of drum film formation, gelation caused by cooling causes a casting film to have self-supporting properties, and therefore, film formation is required in a cooled portion, but the end portion is not usable because of temperature change due to heat release, and the casting width is limited to about 2000 mm.

In any of the methods, the width of casting is limited due to the limitation of the equipment manufacturing, and it is currently considered to obtain a wide film by stretching the cast film to obtain a wide film width as much as possible. As a method for obtaining a wide film by stretching a film after casting, it is known that a wide film is obtained by stretching the film about 2 to 4 times as much as the casting width, which is used for PET, polyvinyl alcohol, or the like.

However, in the case of the cellulose ester film, since the molecular structure is rigid, it has been considered that the elongation cannot be increased so far. Patent documents 1 and 2 below propose stretching a cellulose ester film by a factor of 1.2.

Patent document 1 describes: stretching to 1.2-4.0 times when the residual solvent content is less than 120 mass% and the temperature is 115-160 ℃. Patent document 2 describes: the temperature difference of the membrane passing part is 0-4 ℃, and the membrane passing part is stretched to 1.2-1.8 times when the temperature is between room temperature and 160 ℃.

Patent document 1: japanese laid-open patent publication No. 2002-71957

Patent document 2: japanese laid-open patent publication No. 2002-131540

Disclosure of Invention

Problems to be solved by the invention

However, the production methods described in patent documents 1 and 2 have problems that: since the haze of cellulose ester is high and the transmittance of light is low, when the cellulose ester is incorporated in a display device, the contrast is low. It is considered that this problem is caused by unnecessary force applied to the film during stretching.

An object of the present invention is to solve the above-described problems of the prior art and to provide a method for producing a cellulose ester film, a cellulose ester film produced by the method, a polarizing plate and a display device using the cellulose ester film, in which the haze does not increase even when a sheet is stretched in the width direction by 1.2 times or more in the sheet stretching step.

Means for solving the problems

In order to achieve the above object, the invention of claim 1 relates to a method for producing a cellulose ester film, comprising the steps of casting a resin solution containing a cellulose ester resin on a casting support to form a casting film, drying a solvent in the casting film until the casting film is in a peelable state, peeling the casting film from the casting support, holding both ends of the peeled web, stretching the web in a width direction, drying the solvent, and winding the film to obtain the cellulose ester film, wherein a stretching ratio of the web in the stretching step is 20 to 60%, and a temperature of hot air blown out from a hot air blowing device in the stretching step is Tg +35 to Tg +80 ℃ with respect to a glass transition temperature (Tg) of the wound film.

The invention according to claim 2 is the method for producing the cellulose ester film according to claim 1, wherein the amount of the residual solvent in the film immediately before the stretching step is 10 to 35% by mass.

The invention according to claim 3 is the method for producing a cellulose ester film according to claim 1 or 2, comprising a removing device for removing organic components other than the solvent contained in the exhaust air sent from the stretching step.

The invention according to claim 4 is the method for producing the cellulose ester film according to claim 3, wherein the exhaust air from which the organic component has been removed is reused as a part of the drying air upstream of the stretching step.

The invention according to claim 5 is the method for producing the cellulose ester film according to claim 4, wherein a plurality of the removing means are connected together.

The invention according to claim 6 is a cellulose ester film produced by the method according to any one of claims 1 to 3, wherein the width of the film after winding is 1650 to 2500 mm.

The invention according to claim 7 is the cellulose ester film according to claim 6, wherein the film thickness of the wound film is 40 to 80 μm.

The invention of claim 8 is a polarizing plate using the cellulose ester film of claim 6 or 7 on one side.

The invention of claim 9 is a display device using the cellulose ester film of claim 6 or 7.

Effects of the invention

The invention of claim 1 is a method for producing a cellulose ester film, wherein the sheet is stretched at a rate of 20 to 60% in the stretching step, and the temperature of hot air blown out from a hot air blowing device in the stretching step is Tg +35 ℃ to Tg +80 ℃ relative to the glass transition temperature (Tg) of the film after winding; the method for producing a cellulose ester film comprises the steps of casting a resin solution containing a cellulose ester resin on a casting support to form a casting film, drying a solvent in the casting film until the casting film is in a peelable state, peeling the casting film from the casting support, holding both ends of the peeled web, and stretching the web in the width direction, drying the solvent, and winding the film to obtain the cellulose ester film. Therefore, according to the invention of claim 1, it is possible to achieve an effect of producing a cellulose ester film having optical characteristics such as good transparency and flatness without increasing the haze of the film even when high stretching is performed.

The invention according to claim 2 is the method for producing the cellulose ester film according to claim 1, wherein the amount of the residual solvent in the film immediately before the stretching step is 10 to 35% by mass. Therefore, according to the invention of claim 2, it is possible to ensure a moderate self-supporting property while further reducing the stress applied to the film.

When the temperature in the stretching step is increased as in the present invention, the amount of organic components such as a plasticizer volatilized tends to increase. However, according to the invention of claim 3, since the device for removing the organic component contained in the exhaust air from the stretching step is provided, the contamination of the film by the organic component and the contamination of the film manufacturing apparatus can be prevented. Further, according to claim 4, since the cellulose ester film is reused as a part of the drying air upstream of the stretching step, the production cost of the cellulose ester film can be reduced.

The invention according to claim 5 is the method for producing the cellulose ester film according to claim 4, wherein a plurality of the removing means are connected. Therefore, according to the invention of claim 5, the concentration of the organic component in the exhaust air can be reliably reduced, and therefore the exhaust air can be effectively reused again as a part of the drying air upstream of the stretching step.

The invention according to claim 6 is a cellulose ester film produced by the method according to any one of claims 1 to 3, wherein the width of the film after winding is 1650 to 2500 mm. Therefore, according to the invention of claim 6, an effect of manufacturing a wide cellulose ester film for a liquid crystal display device can be achieved.

The cellulose ester film of claim 7, wherein the film thickness after winding is 40 to 80 μm. Therefore, according to the invention of claim 7, an effect is achieved that a contribution can be made to thinning of the display device.

According to the invention of the polarizing plate of claim 8, when it is incorporated in a liquid crystal display device, the effect is achieved that the visibility is good without causing a decrease in contrast.

According to the invention of the display device of claim 9, the effect is achieved that the visibility is good without causing a decrease in contrast.

Drawings

FIG. 1 is a flowchart showing a specific example of an apparatus for carrying out the method for producing a cellulose ester film of the present invention.

FIG. 2 is an enlarged sectional view showing a specific example of a liquid crystal display panel using a cellulose ester film produced by the method of the present invention.

Description of the symbols

1: endless belt (tape casting support)

2: casting die head

3: stripping roller

5: spoke machine (drawing process)

5 a: hot air blowing slit (Hot air blowing device)

5 b: exhaust air outlet

6: roller conveying and drying device

7: conveying roller

8: winding machine

10: sheet stock

11: hot-air (drying air)

12: exhaust air

13 a: organic component removing device (organic component removing apparatus)

13 b: organic component removing device (organic component removing apparatus)

14: exhaust air

15: drying air

16: exhaust air

20: cellulose ester film

Detailed description of the invention

The following describes embodiments of the present invention, but the present invention is not limited thereto.

The method for producing a cellulose ester film of the present invention is carried out by a solution casting film-forming method comprising casting a resin solution (dope) containing a cellulose ester resin on a casting support made of a rotary driven stainless steel endless belt or a drum or the like to form a casting film, drying the solvent in the casting film until the casting film reaches a peelable state, peeling the casting film from the casting support, then, the solvent is dried and the film is wound to obtain a cellulose ester film through a drawing step of holding both ends of the peeled sheet and drawing the sheet in the width direction, the method is characterized in that the sheet stretch ratio in the stretching step is 20-60%, and the temperature of hot air blown out from a hot air blowing device in the stretching step is Tg + 35-Tg +80 ℃ relative to the glass transition temperature (Tg) of the film after winding.

The stretching step in this embodiment is a tenter system in which both side edge portions of a sheet (or film) are held by clips or the like and stretched, and a hot air blowing device is a hot air blowing slit opening of a tenter.

In the present embodiment, the resin solution (dope) containing the cellulose ester resin contains at least 1 or more of a plasticizer, a retardation adjuster, an ultraviolet absorber, fine particles, and a small molecular weight substance, as well as the cellulose ester resin and a solvent.

This will be described in detail below.

The cellulose ester is derived from cellulose and has a hydroxyl group substituted with an acyl group or the like. Examples thereof include cellulose acylate such as cellulose acetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate, and cellulose acetate having an aliphatic polyester graft side chain. Among them, cellulose acetate propionate, and cellulose acetate having an aliphatic polyester graft side chain are preferable. Other substituents may be contained within a range not affecting the effect of the present invention.

As an example of the cellulose triacetate, the substitution degree of an acetyl group is preferably 2.0 to 3.0. When the substitution degree is within this range, good moldability can be obtained, and desired in-plane retardation (Ro) and thickness retardation (Rt) can also be obtained. If the substitution degree of acetyl groups is less than this range, the moist heat resistance of the retardation film, particularly the dimensional stability under moist heat conditions, may be poor, and if the substitution degree is too large, the retardation characteristics required may not be exhibited.

The cellulose used as a raw material of the cellulose ester in the present invention is not particularly limited, and examples thereof include cotton linter, wood pulp, kenaf, and the like. The cellulose esters obtained from these raw material celluloses may be used by mixing them at an arbitrary ratio.

In the present invention, the cellulose ester preferably has a number average molecular weight of 60000 to 300000, and thus the resulting film has high mechanical strength. More preferably 70000 to 200000.

In the present specification, an organic solvent having good solubility in a cellulose ester film is referred to as a good solvent, and a solvent which plays a major role in dissolution and is used in a large amount therein is referred to as a main solvent or a main solvent.

Examples of the good solvent include ketones such as acetone, methyl ethyl ketone, cyclopentanone, and cyclohexanone, ethers such as Tetrahydrofuran (THF), 1, 4-dioxane, 1, 3-dioxolane, and 1, 2-dimethoxyethane, esters such as methyl formate, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, and γ -butyrolactone, and methyl cellosolve, dimethyl imidazolidinone, dimethylformamide, dimethylacetamide, acetonitrile, dimethyl sulfoxide, sulfolane, nitroethane, dichloromethane, and methyl acetoacetate, and preferably 1, 3-dioxolane, THF, methyl ethyl ketone, acetone, methyl acetate, and dichloromethane.

The dope preferably contains 1 to 40 mass% of an alcohol having 1 to 4 carbon atoms in addition to the organic solvent. These alcohols can be used as gelling solvents: when the dope is cast on the casting support, the solvent starts to evaporate, the alcohol ratio increases, and the web (the dope film obtained by casting the cellulose derivative dope on the casting support is referred to as a web) is gelled, the web is firm, and the cellulose ester resin is easily peeled from the casting support.

Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, and propylene glycol monomethyl ether. Among them, ethanol is preferable in terms of good stability of the cement, low boiling point, good drying property, and no toxicity. These organic solvents are used alone and are not soluble in the cellulose derivative, and are called poor solvents.

As a solvent which satisfies this condition and can dissolve the cellulose ester resin, which is a preferable high molecular compound, at a high concentration, a mixed solvent of dichloromethane and ethanol in a ratio of 95: 5 to 80: 20 is most preferable. Alternatively, a mixed solvent of methyl acetate and ethanol in a ratio of 60: 40 to 95: 5 may be preferably used.

The film of the present invention may contain the following various additives: plasticizers for imparting processability, flexibility and moisture-proofness to the film, fine particles (matting agents) for imparting smoothness to the film, ultraviolet absorbers for imparting ultraviolet absorbing function, antioxidants for preventing deterioration of the film, and the like.

As the plasticizer used in the present invention, in order to avoid haze generation, bleeding out from the film, or volatilization of the film, it is preferable to have the following functional groups: the functional group can interact with a cellulose ester resin or a polycondensate of a hydrolyzable polycondensed reactive metal compound through a hydrogen bond or the like.

Examples of such a functional group include a hydroxyl group, an ether group, a carbonyl group, an ester group, a carboxylic acid residue, an amino group, an imino group, an amide group, an imide group, a cyano group, a nitro group, a sulfonyl group, a sulfonic acid residue, a phosphono group, and a phosphonic acid residue, and a carbonyl group, an ester group, and a phosphono group are preferable.

Examples of these plasticizers include phosphate plasticizers, phthalate plasticizers, trimellitate plasticizers, pyromellitic plasticizers, polyol ester plasticizers, glycolate plasticizers, citrate plasticizers, fatty acid ester plasticizers, carboxylic ester plasticizers, and polyester plasticizers, and non-phosphate plasticizers such as polyol ester plasticizers, glycolate plasticizers, and polycarboxylic ester plasticizers are particularly preferable.

The polyol ester is formed from an ester of an aliphatic polyhydric alcohol having 2 or more members and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule. The polyol is represented by the following general formula (1).

General formula (1) R1- (OH)_n

(wherein R1 represents an n-valent organic group, and n represents a positive integer of 2 or more.)

Examples of preferable polyols include the following compounds, but the present invention is not limited to these compounds.

Examples of the preferable polyhydric alcohol include ribitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1, 2-propanediol, 1, 3-propanediol, dipropylene glycol, tripropylene glycol, 1, 2-butanediol, 1, 3-butanediol, 1, 4-butanediol, dibutylene glycol, 1, 2, 4-butanetriol, 1, 5-pentanediol, 1, 6-hexanediol, hexanetriol, galactitol, mannitol, 3-methylpentane-1, 3, 5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol, and the like. Particularly preferred are triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane and xylitol.

The monocarboxylic acid usable for the polyol ester is not particularly limited, and known aliphatic monocarboxylic acids, alicyclic monocarboxylic acids, aromatic monocarboxylic acids, and the like can be used. When an alicyclic monocarboxylic acid or an aromatic monocarboxylic acid is used, moisture permeability and retention can be improved, and therefore, it is preferable.

Examples of preferable monocarboxylic acids include the following compounds, but the present invention is not limited to these compounds.

As the aliphatic monocarboxylic acid, a linear or branched fatty acid having 1 to 32 carbon atoms can be preferably used. More preferably 1 to 20 carbon atoms, and particularly preferably 1 to 10 carbon atoms. When acetic acid is contained, compatibility with the cellulose ester resin can be increased, and therefore, it is preferable to use acetic acid in combination with other monocarboxylic acid.

Examples of preferred aliphatic monocarboxylic acids include saturated fatty acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-caproic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, hexacosanoic acid, heptacosanoic acid, nonacosanoic acid, triacontanoic acid, and behenic acid, and unsaturated fatty acids such as undecylenic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, and eicosatetraenoic acid.

Examples of preferred alicyclic monocarboxylic acids include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, and derivatives thereof.

Examples of the preferred aromatic monocarboxylic acid include benzoic acid derivatives in which an alkyl group is introduced into the benzene ring of benzoic acid, such as benzoic acid and toluic acid, and aromatic monocarboxylic acids having 2 or more benzene rings, such as biphenylcarboxylic acid, naphthalenecarboxylic acid and tetralincarboxylic acid, or derivatives thereof, and benzoic acid is particularly preferred.

The molecular weight of the polyol ester is not particularly limited, but is preferably 300 to 1500, more preferably 350 to 750. The polyol ester having a large molecular weight is preferred because it is less volatile as the molecular weight is larger, and the polyol ester having a small molecular weight is preferred in view of moisture permeability and compatibility with the cellulose ester resin.

As the carboxylic acid used for the polyol ester, 1 kind may be used alone, or 2 or more kinds may be used in combination. In addition, the OH groups in the polyol may be fully esterified, or a portion of the OH groups may be retained.

[0059]

The glycolic acid ester plasticizer is not particularly limited, and glycolic acid ester plasticizers having an aromatic ring or a cycloalkyl ring in the molecule can be preferably used. As a preferable glycol ester plasticizer, butyl phthalate butyl glycolate, ethyl phthalate ethyl glycolate, methyl phthalate ethyl glycolate, or the like can be used.

As the phosphate-based plasticizer, triphenyl phosphate, tricresyl phosphate, tolyldiphenyl phosphate, octyldiphenyl phosphate, diphenyldiphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. may be used, and as the phthalate-based plasticizer, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di (2-ethylhexyl) phthalate, dicyclohexyl phthalate, etc. may be used.

These plasticizers may be used alone or in combination of 2 or more.

The amount of the plasticizer is preferably 1 to 20 mass%. More preferably 6 to 16% by mass, and particularly preferably 8 to 13% by mass.

Preferably, fine particles such as a delustering agent are added to the cellulose ester resin of the present invention to impart slipperiness thereto. Examples of the fine particles include fine particles of an inorganic compound and fine particles of an organic compound.

Examples of the fine particles of the inorganic compound include fine particles of silica, titania, alumina, zirconia, tin oxide, and the like. Among these, fine particles of a compound containing a silicon atom are preferable, and silica fine particles are particularly preferable. Examples of the silica fine particles include AEROSIL 200, 200V, 300, R972V, R974, R202, R812, R805, OX50, TT600 and the like manufactured by AEROSIL co.

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

The primary particle size of the fine particles is not particularly limited, but the average particle size in the final film is preferably about 0.05 to 5.0. mu.m. More preferably 0.1 to 1.0 μm.

The average particle diameter of the fine particles is an average value of the length of the particles in the major axis direction in the film observation region when the cellulose ester film is observed with an electron microscope or an optical microscope. The particles in the film to be observed may be primary particles or secondary particles in which the primary particles are aggregated, and most of the particles are generally observed as secondary particles.

The dispersion of the fine particles is preferably carried out by treating the composition in which the fine particles and the solvent are mixed with a high-pressure dispersing apparatus. The high-pressure dispersion apparatus is an apparatus that passes a composition in which fine particles and a solvent are mixed through a narrow tube at a high speed to achieve special conditions such as a high shear state and a high pressure state.

Examples of the high-pressure dispersing apparatus include an ultrahigh-pressure Homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation, a Nanomizer manufactured by Nanomizer, and a Manton-Gaulin type high-pressure dispersing apparatus, such as a Homogenizer manufactured by Izumifood Machinery.

In the present invention, the fine particles are dispersed in a solvent containing 25 to 100 mass% of a lower alcohol, and then mixed with a dope prepared by dissolving a cellulose ester resin in the solvent.

The content ratio of the lower alcohol is preferably 50 to 100% by mass, more preferably 75 to 100% by mass.

Examples of the lower alcohols include methanol, ethanol, propanol, isopropanol, and butanol.

The solvent other than the lower alcohol is not particularly limited, and a solvent used for film formation of cellulose ester is preferably used.

From the viewpoint of preventing deterioration, it is preferable that various optical films such as a polarizer protective film, a retardation film, and an optical compensation film contain an ultraviolet absorber.

The ultraviolet absorber is preferably a product having a high ultraviolet absorbability at a wavelength of 370nm or less from the viewpoint of preventing deterioration of a polarizer and a liquid crystal, and having a low absorption of visible light at a wavelength of 400nm or more from the viewpoint of liquid crystal display properties.

In the present embodiment, examples of the ultraviolet absorber that can be used include hydroxybenzophenone compounds, benzotriazole compounds, salicylate compounds, benzophenone compounds, cyanoacrylate compounds, and nickel complex compounds, and benzotriazole compounds that are less colored are preferred. Further, it is preferable to use ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574, and polymer ultraviolet absorbers described in JP-A-6-148430.

Specific examples of useful ultraviolet absorbers include 2- (2 '-hydroxy-5' -methylphenyl) benzotriazole, 2- (2 '-hydroxy-3', 5 '-di-tert-butylphenyl) benzotriazole, 2- (2' -hydroxy-3 '-tert-butyl-5' -methylphenyl) benzotriazole, 2- (2 '-hydroxy-3', 5 '-di-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2' -hydroxy-3 '- (3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5' -methylphenyl) benzotriazole, 2-methylenebis (4- (1, a mixture of 3, 3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, 2- (2 ' -hydroxy-3 ' -tert-butyl-5 ' -methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side-chain dodecyl) -4-methylphenol, 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- (5-chloro-2H-benzotriazol-2-yl) phenyl ] propionate, etc., but are not limited to these compounds.

Further, as commercially available ultraviolet absorbers, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (both manufactured by Ciba specialty Chemicals) can be preferably used.

Specific examples of the ultraviolet absorber benzophenone-based compound usable in the present invention include, but are not limited to, 2, 4-dihydroxybenzophenone, 2' -dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane), and the like.

In the present invention, the amount of the ultraviolet absorber added is preferably in the range of 0.01 to 10% by mass, more preferably 0.1 to 5% by mass, based on the cellulose ester (cellulose derivative). If the amount of the ultraviolet absorber used is too small, the ultraviolet absorbing effect may be insufficient, and if the amount of the ultraviolet absorber is too large, the transparency of the film may be deteriorated, which is not preferable. The ultraviolet absorber is preferably a product having high thermal stability.

Further, examples of the ultraviolet absorber which can be used for the cellulose ester film of the present embodiment include polymeric ultraviolet absorbers (or ultraviolet absorbing polymers) described in JP-A-6-148430 and JP-A-2002-47357. In particular, it is preferable to use a polymer ultraviolet absorber represented by the general formula (1) or the general formula (2) described in JP-A-6-148430, or the general formulae (3), (6) and (7) described in JP-A-2002-47357.

The antioxidant is also generally called a deterioration preventing agent, and is preferably contained in a cellulose ester film as an optical film. That is, when a liquid crystal image display device or the like is in a high-humidity high-temperature state, the cellulose ester film as the optical film may be deteriorated. The antioxidant can retard the decomposition of the film due to, for example, halogen in the residual solvent in the film, phosphoric acid in the phosphoric acid plasticizer, or the like, and plays a preventive role, and therefore, it is preferable that the film contains the antioxidant.

As such an antioxidant, a hindered phenol compound is preferably used, and examples thereof include 2, 6-di-t-butyl-p-cresol, pentaerythritol-tetrakis [ 3- (3, 5-di-t-butyl-4-hydroxyphenyl) propionate ], triethylene glycol-bis [ 3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate ], 1, 6-hexanediol-bis [ 3- (3, 5-di-t-butyl-4-hydroxyphenyl) propionate ], 2, 4-bis (n-octylthio) -6- (4-hydroxy-3, 5-di-t-butylanilino) -1, 3, 5-triazine, 2-thiobis-diethylene-bis [ 3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ], octadecyl-3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate, N' -hexamethylenebis (3, 5-di-tert-butyl-4-hydroxy-hydrocinnamamide), 1, 3, 5-trimethyl-2, 4, 6-tris (3, 5-di-tert-butyl-4-hydroxybenzyl) benzene, tris (3, 5-di-tert-butyl-4-hydroxybenzyl) -isocyanurate, and the like. Particularly preferred are 2, 6-di-t-butyl-p-cresol, pentaerythritol-tetrakis [ 3- (3, 5-di-t-butyl-4-hydroxyphenyl) propionate ], triethylene glycol-bis [ 3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate ].

In addition, for example, a hydrazine metal deactivator such as N, N' -bis [ 3- (3, 5-di-t-butyl-4-hydroxyphenyl) propionyl ] hydrazine, or a phosphorus processing stabilizer such as tris (2, 4-di-t-butylphenyl) phosphite may be used in combination.

Hereinafter, embodiments of the cellulose ester film according to the present invention will be described in detail. The film is prepared by a solution casting film-making process.

Fig. 1 is a flowchart showing a specific example of an apparatus for carrying out the method for producing a cellulose ester film by the solution casting film-forming method. The invention is not limited in its practice by the accompanying drawings as shown below.

First, in a dissolution tank not shown in the figure, a cellulose ester resin is dissolved in a mixed solvent of a good solvent and a poor solvent, and then the plasticizer and the ultraviolet absorber are added to prepare a resin solution (dope).

In FIG. 1, the dope prepared in the dissolution tank is then sent to the casting die (2) through a pipe by, for example, a quantitative gear pump of a pressure type, and the casting of the dope is started from the casting die (2) at the casting position on the casting belt (1). The casting belt (1) is equivalent to the casting support of the present invention, which is an endless belt made of stainless steel, and is rotationally driven and circularly runs.

When casting the dope through the casting die (2), a roll lick type doctor blade method in which the film thickness of the dope film (web) cast by the doctor blade is adjusted, a reverse roll coating method in which the film thickness is adjusted by a reverse rotation roll, or the like can be used, and a pressure die in which the slit shape of the die portion can be adjusted and the film thickness can be easily made uniform is preferable. The pressure die includes a coat hanger die (coat hanger die), a T die, and the like, and can be used preferably.

The casting belt (1) is suspended between a pair of drums, and an upper conveying portion and a lower conveying portion in the middle thereof are supported from the inside by a plurality of rollers (not shown), respectively.

A driving device for applying tension to the casting belt (1) is provided on one or both of the drums for curling the two ends of the casting belt (1), so that the casting belt (1) is used in a stretched state with tension applied.

In the present embodiment, in order to secure a width of 1650 to 2500mm of the film after winding, a width of the casting tape is 2000 to 2500mm, and a casting width of the cellulose ester solution is 1900 to 2480 mm. Thus, a cellulose ester film for a liquid crystal display device having a wide width can be produced by a casting support method.

Here, as long as the width of the casting support (1), the casting width of the cellulose ester solution, and the width of the film after winding are each equal to or more than the above lower limit, it is possible to cope with the recent increase in size of the liquid crystal display device.

Further, the width of the casting belt (1), the casting width of the cellulose ester solution, and the width of the film after winding are not more than the upper limit, and even in a state where the amount of the residual solvent in the film after peeling is large, the film does not sag or uneven stretching.

In the present embodiment, the circumferential speed of the casting belt (1) is 80 to 200 m/min.

That is, the peripheral speed of the casting belt (1) is set higher than the peripheral speed of the conventional drum, so that the film production speed can be increased and the productivity of the cellulose ester film can be increased.

The temperature of the casting belt (1) during film formation may be in the range of 0 ℃ to less than the boiling point of the solvent, and in the case of a mixed solvent, casting may be performed at a temperature less than the boiling point of the solvent having the lowest boiling point, and more preferably in the range of 5 ℃ to 5 ℃ less than the boiling point of the solvent.

As described above, the dope cast to the surface of the casting belt (1) is gelled by cooling, the strength of the gel film (film strength) is increased, and the strength of the gel film (film strength) can also be increased by facilitating drying in the period until before peeling.

In order to increase the film forming speed, a casting belt (1) for casting is provided with more than 2 pressure casting die heads (12), and the amount of the mucilage is distributed to carry out multilayer film forming.

In the casting belt (1), in order to dry and solidify the web (10) to a film strength that can be peeled from the casting belt (1) by the peeling roller (16), it is preferable to dry the web (10) so that the amount of the residual solvent is 150 mass% or less, more preferably 80 to 120 mass%. Further, it is preferable that the temperature of the web is 0 to 30 ℃ when the web (10) is peeled from the casting belt (1). Further, immediately after the web (10) is peeled from the casting belt (1), the temperature is rapidly lowered in a short time by evaporation of the solvent from the bonding surface side of the casting belt (1), and volatile components such as water vapor and solvent vapor in the atmosphere are easily concentrated, so that the temperature of the web at the time of peeling is more preferably 5 to 30 ℃.

Here, the residual solvent amount is represented by the following formula.

Residual solvent amount (% by mass) { (M-N)/N } × 100

Wherein M is the mass of a sample taken at an arbitrary point in the process of producing a sheet, and N is the mass of M heated at 110 ℃ for 3 hours.

The elongation is represented by the following formula.

Distance between clamps in front of the spoke machine (5) in the stretching process: h; distance between clips at the end of tenter (5) in stretching step: H.

elongation H/h.times.100%

A dope film (web) formed of a dope cast on a casting belt (1) is heated on the casting belt (1), and a solvent is evaporated until the web can be peeled from the casting belt (1) by a peeling roller (3).

When the solvent is evaporated, a method of blowing air from the web side, and/or a method of transferring heat from the back surface of the casting belt (1) by liquid, a method of transferring heat from the front surface and the back surface by radiant heat, and the like can be employed.

The film is easily stretched in the transport direction at the time of peeling and the film shrinks in the width direction, and therefore the peeling is preferably performed under a condition that the peeling tension at the time of peeling the web (10) from the casting tape (1) by the peeling roller (3) is 170N/m which is the lowest possible peeling tension, more preferably 140N/m which is the lowest possible peeling tension.

After drying and curing the web (10) on the casting support (1) to a peelable film strength, the web (10) is peeled off by a peeling roller (3), and subsequently, the web (10) is stretched by a tenter (5) in the stretching step.

The amount of the residual solvent in the sheet (film) (10) before being fed to the tenter (5) in the stretching step is preferably 10 to 35% by mass.

In the stretching step, hot air (11) is blown from a hot air blowing device, i.e., a hot air blowing slit opening (5a) in the front portion of the bottom of the tenter (5), and exhaust air (12) is discharged from a discharge opening (5b) in the rear portion of the top of the tenter (5), whereby the sheet (10) can be dried while being stretched.

The hot air blowing device in the stretching step of the present invention is not particularly limited as long as it can effectively heat the film by blowing hot air, and specifically, it corresponds to the hot air blowing slit opening (5a) of the tenter (5) in the stretching step. Examples thereof include a slit shape as shown in the figure and a perforated plate shape.

In the present invention, the stretch ratio of the web in the tenter (5) in the stretching step is 20 to 60%, and the temperature of the hot air (11) blown out from the hot air blowing slit opening (5a) in the tenter (5) is Tg +35 to Tg +80 ℃ with respect to the glass transition temperature (Tg) of the film after winding. Further, the temperature is more preferably from Tg +40 ℃ to Tg +50 ℃.

Here, if the stretch ratio of the sheet material (10) in the tenter (5) in the stretching step is lower than the lower limit value, a wide film cannot be obtained, which is not preferable. When the stretch ratio of the web (10) in the tenter (5) is higher than the upper limit value, the haze of the film increases and the light transmittance decreases, and therefore, when the film is incorporated into a liquid crystal display device, the contrast decreases, which is not preferable.

Further, if the temperature of the hot air (11) blown from the hot air blowing slit opening (5a) of the tenter (5) in the stretching step is lower than the lower limit value, the film is subjected to excessive stress during stretching, so that the haze is increased, the light transmittance is lowered, and the contrast is lowered when the liquid crystal display device is incorporated, which is not preferable. Further, if the temperature of the hot air (11) blown from the hot air blowing slit opening (5a) of the tenter (5) is higher than the upper limit value, the film is softened and loses self-supporting property, and the sheet is broken in the inside of the tenter or in the nip portion, which is not preferable.

Here, it is preferable that the hot air (11) in the tenter (5) in the stretching step has a temperature of Tg +35 ℃ or higher, since a wide film can be obtained. Further, when the temperature of hot air (11) in the tenter (5) in the stretching step is Tg +80 ℃ or less, the haze of the film is not increased, the transmittance of light is high, and when incorporated in a liquid crystal display device, the contrast is prevented from being lowered, which is preferable.

In the drying step after being peeled from the casting belt (1), the web (or film) (10) shrinks in the width direction due to the evaporation of the solvent. Drying at higher temperatures results in greater shrinkage. It is preferable to perform drying while suppressing shrinkage as much as possible so that the planarity of the film to be produced is good.

The width holding or the transverse stretching in the stretching step is preferably performed by a tenter (5), and a pin tenter or a clip tenter may be used.

The present embodiment has, for example, 2 organic component removing devices (removing means) (13a) (13b) for removing small molecular weight organic components (plasticizers, etc.) contained in the exhaust air (12) from the tenter (5) in the stretching step, and the concentration of the organic components in the exhaust air (14) after passing through these organic component removing devices (13a) (13b) is 1 to 100 [ mu ] g/m³。

In the present embodiment, the exhaust air (14) from which the organic component is removed by the organic component removing devices (13a) and (13b) is reused as part of the hot air upstream of the tenter (5) in the partial stretching step, i.e., the drying air (11). Further, although 2 organic component removing devices (13a) and (13b) are shown, it is possible to have a multistage organic component removing device, and it is preferable to continuously install 2 to 4 organic component removing devices (13a) and (13b), for example.

A post-drying device (6) is provided after the tenter (5) in the stretching step. In the post-drying device (6), the web (10) is meandering by a plurality of conveying rollers (7) arranged in a zigzag shape (thousand ) as viewed from the side, and the web (10) is dried during this. The film transport tension in the post-drying device (6) is influenced by the physical properties of the dope, the amount of the residual solvent at the time of peeling and in the film transport step, the temperature in the post-drying device (6), and the like, and is preferably 30 to 250N/m, more preferably 60 to 150N/m. Most preferably 80 to 120N/m.

The method for drying the sheet (or film) (10) is not particularly limited, and it is usually carried out by hot air, infrared ray, heated roll, microwave, or the like. From the viewpoint of convenience, it is preferable to dry with hot air, for example, by blowing dry air (15) through a hot air inlet in the front part of the bottom of the post-drying device (6), and by discharging exhaust air (16) through an outlet in the rear part of the top of the post-drying device (6). The temperature of the drying air (15) is preferably 40 to 160 ℃, and more preferably 50 to 160 ℃ for improving planarity and dimensional stability.

The steps from the casting to the post-drying may be performed in an air atmosphere, or may be performed in an inert gas atmosphere such as nitrogen. Of course, consideration is given to the explosive critical concentration of the solvent in the dry atmosphere.

The sheet conveying tension during drying is 30 to 300N/width m, and more preferably 40 to 270N/width m.

Preferably, a web (10) surface cleaning device is provided after the steps from casting to post-drying.

The cleaning device not only applies ultrasonic vibration to the sheet (10) during conveyance, but also blows off the adhered matter by applying high-pressure air to the surface to remove the sucked and adhered dust. Further, a known apparatus or method such as a method of performing flame treatment (corona treatment or plasma treatment) or a method of providing a sticking roller may be used, but the present invention is not limited thereto. The cleaning devices disposed may be used alone, or 2 or more of them may be used in combination.

Since adhesion of dust or the like to the sheet material (10) is caused by electrostatic action in many cases, it is preferable to provide a static removing device such as a static removing bar in front of the cleaning device to remove static electricity from the sheet material (10). The static eliminating bar may be made of any known material without any particular limitation.

In the drying step, the plasticizer contained in the sheet material (10) is evaporated, and as a measure for suppressing the condensation phenomenon of the plasticizer on the roller and the wall surface, it is preferable to introduce a fresh gas of a specific amount or more to the air volume supplied per unit time. Preferably, the amount of fresh gas supplied is set to 5 to 50% of the total supply air volume.

The fresh gas supply amount is set to 5 to 50% because: if the supply amount is less than 5%, the fresh gas is too small to completely suppress the plasticizer condensation, and if it exceeds 50%, the fresh gas is too large, which results in a serious waste in view of running costs.

In order to prevent the film from being stretched in the transport direction in the post-drying device (6), a tension cut roll is preferably provided. After the completion of drying and before winding, a cutter (slit) is preferably provided to cut off the end portion, so that a good winding state can be obtained.

The cellulose ester film having completed the post-drying step (6) is subjected to a process of forming an embossment on the film by providing an embossing device before being introduced into the winding step.

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

The width of the emboss is desirably small because the embossed portion eventually becomes a lost portion, and for example, when a film of 50 μm or less is used and high-speed film formation is performed at 50 m/min or more, the width of the emboss is the minimum necessary width for suppressing the slip of the film. However, it is necessary to determine the embossing height × embossing width in association with the aforementioned embossing height to eliminate all of the pyramid, horse back, polygonal shape, winding deviation failures. Further, the embossings may be disposed not only at both end portions of the film but also at a central portion thereof.

In the present invention, it is preferable to provide a static eliminator before and immediately after winding to eliminate static electricity from the film.

The static eliminator can eliminate static by adopting the following structure, so that the charged potential when the film roll is repeatedly drawn is less than +/-2 KV: the electrostatic separator is configured to apply a reverse potential to the wound-up member by an electrostatic eliminator or a forced charging device, or configured to perform electrostatic elimination by an electrostatic eliminator in which the forced charging potential is alternately changed between positive and negative of 1 to 150 Hz.

Further, an ionizer or a static eliminating bar that generates ion wind may be used instead of the above static eliminator. Here, the static electricity removal by the ionizer is performed by blowing ion wind to the film taken up from the embossing apparatus through the transport roller. The ion wind is generated by the static eliminator. As the static eliminator, a known static eliminator can be used without limitation.

In the step of winding the dried film by a winding device (8) to obtain a film roll of the optical film, the amount of the residual solvent of the dried film (20) is set to 0.5 mass% or less, preferably 0.1 mass% or less, whereby a film having good dimensional stability can be obtained.

As a method for winding the film, a commonly used film winding machine can be used, and tension control methods such as a fixed torque method, a fixed tension method, a taper tension method, and a programmed tension control method in which an internal stress is constant can be used.

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

The cellulose ester film of the present invention preferably has a width of 1650 to 2500mm after being wound.

In the present invention, the thickness of the dried cellulose ester film is preferably in the range of 40 to 80 μm based on the finished film from the viewpoint of thinning of the liquid crystal display device. Here, the film thickness of the film after drying is a film in a state where the residual solvent amount in the film is 0.5 mass% or less.

Here, if the film thickness of the cellulose ester film after winding is too thin, the necessary strength as a protective film for a polarizing plate, for example, may not be obtained. If the film thickness is too large, the advantage of making the film thinner is lost compared to the conventional cellulose ester film. The film thickness can be adjusted by controlling the dope concentration, the liquid feeding amount of the pump, the slit gap of the joint of the casting die, the extrusion pressure of the casting die, the speed of the casting support, and the like so as to achieve a desired thickness. In addition, as a method for making the film thickness uniform, it is preferable to use a film thickness detection apparatus and to feed programmed feedback information back to each apparatus to perform adjustment.

In the steps from immediately after casting to drying by the solution casting film forming method, the atmosphere in the drying apparatus may be air or an inert atmosphere such as nitrogen or carbon dioxide. However, of course, the risk of explosion limits in dry atmospheres of evaporated solvents must generally be taken into account.

In the present invention, the water content of the cellulose ester film is preferably 0.1 to 5%, more preferably 0.3 to 4%, and still more preferably 0.5 to 2%.

In the present invention, the transmittance of the cellulose ester film is desirably 90% or more, more preferably 92% or more, and further preferably 93% or more.

In addition, the haze of the cellulose ester film produced by the method of the present invention is 0.3 to 2.0 when 3 sheets of the cellulose ester film are stacked, and therefore, the cellulose ester film of the present invention has optical characteristics of very low film haze, good transparency, and good planarity.

In the present embodiment, the in-plane retardation (Ro) defined by the following formula is 30 to 300nm at a temperature of 23 ℃ and a humidity of 55% RH, and the thickness-direction retardation (Rt) is 70 to 400nm at a temperature of 23 ℃ and a humidity of 55% RH.

Ro＝(nx-ny)×d

Rt＝{(nx+ny)/2-nz}×d

(wherein Ro represents a film in-plane retardation value, Rt represents a film thickness direction retardation value, nx represents a refractive index in a film in-plane slow axis direction, ny represents a refractive index in a film in-plane fast axis direction, nz represents a refractive index in a film thickness direction (refractive index measured at a wavelength of 590 nm), and d represents a film thickness (nm).)

Further, the retardation values Ro, Rt may be measured by an automatic birefringence meter (imprint yield ). For example, the measurement is carried out at a wavelength of 590nm under an environment of 23 ℃ and 55% RH using KOBRA-21 ADH (manufactured by Oji instruments Co., Ltd.).

The cellulose ester film produced by the method of the present invention can be used for a liquid crystal display member, and more specifically, is preferably used for a polarizing plate protective film. In particular, in the protective film for a polarizing plate, which is strictly required to have both moisture permeability and dimensional stability, the cellulose ester film produced by the method of the present invention is preferably used.

By using the protective film for a polarizing plate made of the cellulose ester film of the present embodiment, a polarizing plate which is thin and has excellent durability, dimensional stability, and optical isotropy can be provided.

Incidentally, the polarizing film is a conventionally used film, and for example, a film obtained by treating a stretch-oriented film such as a polyvinyl alcohol film with a dichroic dye such as iodine and stretching the film in the longitudinal direction. Since the polarizing film itself does not have sufficient strength and durability, a cellulose ester film having no anisotropy as a protective film is generally bonded to both surfaces thereof to form a polarizing plate.

The polarizing plate may be produced by laminating the cellulose ester film produced by the method of the present invention as a retardation film, or by laminating the cellulose ester film produced by the method of the present invention as a retardation film and a protective film directly on a polarizing film. The method of bonding is not particularly limited, and may be performed by using an adhesive made of an aqueous solution of a water-soluble polymer.

The water-soluble polymer binder is preferably a completely saponified polyvinyl alcohol aqueous solution. Further, a long polarizing plate can be obtained by laminating a long polarizing film treated with a dichroic dye and a long retardation film produced by the method of the present invention, which are stretched in the longitudinal direction. The polarizing plate may be a laminated polarizing plate in which a release sheet is laminated on one or both surfaces of a pressure-sensitive adhesive layer (for example, an acrylic pressure-sensitive adhesive layer) by a pressure-sensitive adhesive layer (the laminated polarizing plate can be easily laminated on a liquid crystal cell or the like by releasing the release sheet).

The polarizing plate thus obtained can be used for various display devices. In particular, a liquid crystal display device using a liquid crystal cell including a VA mode in which liquid crystal molecules are aligned substantially vertically when no voltage is applied and a TN mode in which liquid crystal molecules are aligned substantially horizontally and twisted (ね side れ) when no voltage is applied is preferable.

The polarizing plate can be manufactured by a conventional method. For example, the following methods are included: the optical film or cellulose ester film is subjected to alkali saponification treatment, and the optical film or cellulose ester film is bonded to both sides of a polarizing film obtained by immersing and stretching a polyvinyl alcohol film in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. The alkali saponification treatment is a treatment of immersing the cellulose ester film in a high-temperature strong alkali solution in order to improve the wetting with the aqueous adhesive and improve the bondability.

The cellulose ester film produced by the method of the present embodiment may be provided with various functional layers such as a hard coat layer, an antiglare layer, an antireflection layer, an antifouling layer, an antistatic layer, a conductive layer, an optically anisotropic layer, a liquid crystal layer, an alignment layer, an adhesive layer, a bonding layer, and an undercoat layer. These functional layers can be provided by coating, vapor deposition, sputtering, plasma CVD, atmospheric pressure plasma treatment, or the like.

The polarizing plate thus obtained may be provided on one side or both sides of the liquid crystal cell, and a liquid crystal display device may be obtained using the polarizing plate.

In the present invention, a liquid crystal display device includes: the liquid crystal display device includes a liquid crystal cell in which rod-shaped liquid crystal molecules are sandwiched between a pair of glass substrates, and 2 polarizing plates each including a polarizing film disposed so as to sandwich the liquid crystal cell and transparent protective layers disposed on both sides of the polarizing film.

By using the protective film for a polarizing plate comprising the cellulose ester film produced by the method of the present invention, a polarizing plate having excellent durability, dimensional stability and optical isotropy can be provided while being made into a thin film. Further, a liquid crystal display device using the polarizing plate or the retardation film can maintain stable display performance for a long period of time.

The cellulose ester film produced by the method of the present embodiment can be used as a substrate for an antireflection film or an optical compensation film.

Examples

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples.

Example 1

(mucilage composition 1)

Cellulose triacetate 100 parts by mass

(Mn＝148000、Mw＝310000、Mw/Mn＝2.1)

8 parts by mass of triphenyl phosphate

Phthalic ethyl ester-glycolic acid ethyl ester (ethly phenyl-ethly glycollate)

2 parts by mass

440 parts by mass of methylene chloride

40 parts by mass of ethanol

Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 0.5 parts by mass

Tinuvin 171(Ciba Specialty Chemicals) 0.5 parts by mass

0.2 part by mass of AEROSIL972V (manufactured by AEROSIL CORPORATION, Japan)

The materials are sequentially added into a closed container, the temperature in the container is raised from 20 ℃ to 80 ℃, and then the temperature is kept at 80 ℃ and stirred for 3 hours, so that the cellulose triacetate is completely dissolved. Then, the stirring was stopped, and the liquid temperature was lowered to 43 ℃. The resulting slurry was filtered using a filter paper (an' er filter paper No.244, manufactured by And Filter paper Co., Ltd.) to obtain a slurry.

The above-mentioned prepared dope is uniformly cast on a support (1) using a casting support type solution casting film forming apparatus shown in fig. 1, a dope film (web) formed by casting is dried on the support (1), and when the web reaches the lower surface of the support made of an endless belt and substantially surrounds one circumference, the web (film) (10) is peeled from the support (1) by a peeling roller (3), the support (1) being made of a driven-rotating stainless steel endless belt having a mirror-finished surface.

Then, the peeled sheet (10) is introduced into a tenter (5), both ends of the sheet are nipped by clips, and the sheet (10) is stretched in the width direction while drying by blowing hot air (11) at 160 ℃.

Here, the amount of the residual solvent in the sheet (film) (10) immediately before the tenter (5) which is to be subjected to the stretching step is 12% by mass.

Then, the sheet was stretched at a rate of 20% in a tenter (5) in the stretching step, and the temperature of hot air (11) blown from a hot air blowing slit opening (5a) in the tenter (5) was set to 160 ℃. Here, the temperature of the hot air (11) in the tenter (5) is set so that the glass transition temperature of the cellulose triacetate film after winding is: tg 125 ℃, i.e. Tg +35 ℃.

In addition, in this embodiment, two continuous organic component removing devices (13a) (13b) are provided for removing organic components other than the solvent contained in the exhaust air (12) of the tenter (5), and the concentration of the low molecular weight organic component in the exhaust air (14) after passing through these organic component removing devices (13a) (13b) is 20 μ g/m³。

The organic components contained in the exhaust air (12) of the tenter (5) are measured by: taking a certain volume of exhaust air, and analyzing by adopting GC/MS (gas chromatography/mass spectrometry) in a closed state.

The exhaust air (14) from which the organic component is removed by the organic component removal devices (13a) and (13b) is reused again as a part of the hot air (11) upstream of the tenter (5).

Then, the sheet (film) (10) is dried by a drying air (15) of 100 ℃ using a roller conveying and drying device (6) having a plurality of mirror conveying rollers (7) arranged in a zigzag shape in side view. The dried film (20) was wound up by a winding apparatus (8), and the film thickness was 80 μm and the film width was obtained: 1860mm cellulose triacetate film (20).

Embossing both ends in the width direction of the cellulose acetate film wound around the take-up roll is performed so that the height of the protrusions formed by the embossing is in the range of 4 to 12 μm and the height difference of the protrusions formed by the embossing is 2 μm or less.

As a means for removing or reducing the surface potential of the cellulose acetate film during winding, a static discharge blower (ブロア) was used.

The following table 1 shows the kind of the dope composition used for producing the cellulose triacetate film, the stretching ratio (%) of the web (10), the temperature (c) of the hot air (11) blown from the hot air blowing slit opening (5a) in the tenter (5) used in the stretching step, the glass transition temperature (Tg) of the cellulose triacetate film after winding (c), the amount of the residual solvent at the time of entry of the web (10) immediately before entering the tenter (5), and the film thickness (μm).

Next, the haze value of the cellulose triacetate film obtained in example 1 was measured, and the results are shown in table 1 below.

Here, the haze of the cellulose triacetate film was measured as follows. That is, the film obtained by casting was sampled, 10 positions were randomly selected from the sampled films, and the cellulose triacetate films 3 were stacked together in a manner prescribed in JIS K6714, and the haze was measured using a haze meter (1001DP type, manufactured by japan electrochromism industries).

Examples 2 to 15

As in example 1, a cellulose triacetate film was produced using the dope composition 1, but in each example, the film forming conditions were partially changed as follows.

First, in example 2, the stretching was carried out under substantially the same conditions as in example 1 except that the stretching ratio of the sheet material (10) in the tenter (5) in the stretching step was changed to 30 (%).

In examples 3 and 4, substantially the same conditions as in examples 1 and 2 were applied, except that the temperature of the hot air (11) blown out from the hot air blowing slit opening (5a) in the tenter (5) was changed to 170 ℃.

In examples 5 and 6, substantially the same conditions as in examples 1 and 2 were applied, except that the temperature of the hot air (11) was changed to 180 ℃.

In example 7, substantially the same conditions as in example 5 were applied, except that the elongation of the sheet (10) was changed to 40 (%).

In example 8, substantially the same conditions as in example 7 were applied except that the stretching ratio of the sheet (10) was changed to 55 (%), and the amount of the residual solvent at the time of entry of the sheet (10) immediately before entry into the tenter (5) was changed to 35 (%).

In example 9, substantially the same conditions as in example 7 were applied, except that the temperature of the hot air (11) was changed to 200 ℃.

In example 10, substantially the same conditions as in example 9 were applied, except that the amount of the residual solvent at the time of entry of the sheet (10) immediately before entering the tenter (5) was changed to 35 (%).

In example 11, substantially the same conditions as in example 10 were applied, except that the elongation of the sheet (10) was changed to 60 (%).

In examples 12 and 13, substantially the same conditions as in example 6 were applied, except that the residual solvent content of the sheet (10) immediately before entering the tenter (5) was changed to 20 mass% and 35 mass%, respectively.

In examples 14 and 15, substantially the same conditions as in example 6 were applied, except that the film thicknesses were changed to 40 μm and 60 μm, respectively.

Comparative examples 1 to 6

For comparison, a cellulose triacetate film was produced using the dope composition 1 of example 1, which was different from example 1 in that: in comparative examples 1 and 6, the sheet material (10) in the tenter (5) was made to have elongation (%) of 18% and 65% out of the range of the present invention; in comparative examples 2 to 5, the temperature of the hot air (11) blown out from the hot air blowing slit opening (5a) in the tenter (5) was outside the range of the present invention.

In comparative example 6, in order to produce a cellulose triacetate film having a film thickness of 80 μm using the dope composition 1 of example 1, the same procedure as in example 1 was followed, but when the web material (10) was stretched to a stretching ratio of 65% by the tenter (5), the web material (10) broke, and a film could not be produced.

The kind of the dope composition used for producing the cellulose triacetate film, the stretching ratio (%) of the web (10), the temperature (DEG C) of the hot air (11) blown out from the hot air blowing slit opening (5a) in the tenter (5) in the stretching step, the glass transition temperature (Tg) (. DEG C) of the cellulose triacetate film, the amount of the residual solvent (%) at the entrance of the web (10) immediately before entering the tenter (5), and the film thickness (. mu.m) in examples 2 to 15 and comparative examples 1 to 6 are shown in Table 1 below.

Then, the haze values of the cellulose triacetate films obtained in examples 2 to 15 and comparative examples 1 to 5 were measured as in example 1, and the results are shown in table 1 below.

Example 16

A cellulose acetate propionate film was produced in substantially the same manner as in example 1 using the following dope composition 2.

(mucilage composition 2)

Cellulose acetate propionate 100 parts by mass

(degree of substitution of acetyl + degree of substitution of propionyl ═ 2.45, Mn ═ 60000, Mw ═ 180000, Mw/Mn ═ 3.00)

8 parts by mass of triphenyl phosphate

2 parts by mass of phthalic ethyl ester and ethyl glycolate

360 parts by mass of methylene chloride

60 parts by mass of ethanol

Tinuvin 109 (manufactured by Ciba Specialty Chemicals) 0.5 parts by mass

Tinuvin 171(Ciba Specialty Chemicals) 0.5 parts by mass

0.2 part by mass of AEROSIL972V (manufactured by AEROSIL CORPORATION, Japan)

In example 16, the amount of the residual solvent in the web (10) immediately before the tenter (5) which was subjected to the stretching step was 12% by mass, and the stretching ratio of the web (10) in the tenter (5) was set to 25%. The temperature of hot air (11) blown out from the hot air blowing slit opening (5a) of the tenter (5) was 185 ℃.

Here, the temperature of the hot air (11) in the tenter (5) is Tg +40 ℃ with respect to the glass transition temperature Tg of the cellulose acetate propionate film after winding of 145 ℃. The thickness of the cellulose acetate propionate film after winding was 40 μm.

Examples 17 to 26

As in example 16, cellulose acetate propionate was produced using dope composition 2, but in each example, film forming conditions were partially changed as described below.

First, in examples 17 and 18, substantially the same conditions as in example 16 were applied, except that the stretching ratio of the sheet material (10) in the tenter (5) in the stretching step was changed to 35 (%), 40 (%).

In example 19, substantially the same conditions as in example 16 were applied, except that the stretching ratio of the sheet (10) in the tenter (5) in the stretching step was changed to 60 (%), and the temperature of the hot air (11) blown out from the hot air blowing slit port (5a) of the tenter (5) was changed to 180 ℃.

In example 20, the procedure was carried out under substantially the same conditions as in example 18 except that the temperature of the hot air (11) blown out from the hot air blowing slit opening (5a) of the tenter (5) was changed to 200 ℃.

In examples 21 to 23, the process was carried out under substantially the same conditions as in example 17 except that the amounts of the residual solvent upon entry of the sheet (10) immediately before entry into the tenter (5) were changed to 10 (%), 20 (%), and 35 (%), respectively.

In examples 24 to 26, the same conditions as in example 17 were used, except that the film thicknesses were changed to 50 μm, 60 μm and 80 μm, respectively.

Comparative examples 7 to 9

For comparison, a cellulose acetate propionate film was produced using the dope composition 2 of example 16, which was different from example 16 in that: the temperature of hot air (11) blown out from a hot air blowing slit opening (5a) of a tenter (5) is out of the range of the present invention.

The following table 1 describes the kind of dope composition for producing cellulose acetate propionate films, the elongation (%) of the web (10), the temperature (c) of the hot air (11) blown from the hot air blowing slit (5a) in the tenter (5), the glass transition temperature (Tg) of the cellulose acetate propionate film after winding (c), the amount of residual solvent at the time of entry of the film in the tenter (5), and the film thickness (μm) in examples 16 to 26 and comparative examples 7 to 9.

Then, the haze values of the cellulose acetate propionate films obtained in examples 16 to 26 and comparative examples 7 to 9 were measured in the same manner as in example 1, and the results are shown in table 1 below.

Comparative example 10

For comparison, a cellulose acetate propionate film was produced in substantially the same manner as in example 1 using the following dope composition 3.

(mucilage composition 3)

Cellulose triacetate 100 parts by mass

(Mn＝148000、Mw＝310000、Mw/Mn＝2.1)

440 parts by mass of methylene chloride

40 parts by mass of ethanol

0.2 part by mass of AEROSIL972V (manufactured by AEROSIL CORPORATION, Japan)

Here, the residual solvent content of the sheet (film) (10) immediately before the tenter (5) in the stretching step was set to 12% by mass.

The web is stretched at a rate of 30% in the tenter (5), and the temperature of hot air (11) blown from a hot air blowing slit opening (5a) of the tenter (5) is set at 180 ℃. Here, the temperature of the hot air (11) in the tenter (5) is Tg +70 ℃ with respect to the glass transition temperature Tg of the cellulose triacetate film after winding, which is 110 ℃.

Since the dope composition 3 of comparative example 10 does not contain a plasticizer, when the sheet material (10) is stretched to a stretch ratio of 10% or more by the tenter (5), a film cannot be produced because of breakage.

TABLE 1

	Mucilage composition	Elongation (%)	Hot air temperature (. degree. C.) in stretching step	Film Tg (. degree.C.)	Amount of solvent remaining at the time of entry (% by mass)	Film thickness (mum)	Haze degree
								Example 1	1	20	160	125	12	80	0.5
Example 2	1	30	160	125	12	80	0.8
								Example 3	1	20	170	125	12	80	0.5
Example 4	1	30	170	125	12	80	0.7
								Example 5	1	20	180	125	12	80	0.5
Example 6	1	30	180	125	12	80	0.6
								Example 7	1	40	180	125	12	80	0.9
Example 8	1	55	180	125	35	80	1.7
								Example 9	1	40	200	125	12	80	0.7
Example 10	1	40	200	125	35	80	0.5
								Example 11	1	60	200	125	35	80	1.5
Example 12	1	30	180	125	20	80	0.5
								Example 13	1	30	180	125	35	80	0.4
Example 14	1	30	180	125	12	40	0.3
								Example 15	1	30	180	125	12	60	0.4
Example 16	2	25	185	145	12	40	0.3
								Example 17	2	35	185	145	12	40	0.4
Example 18	2	40	185	145	12	40	0.5
								Example 19	2	60	180	145	12	40	1.4
Example 20	2	40	200	145	12	40	0.2
								Example 21	2	35	185	145	10	40	0.5
Example 22	2	35	185	145	20	40	0.3
								Example 23	2	35	185	145	35	40	0.2
Example 24	2	35	185	145	12	50	0.4
								Example 25	2	35	185	145	12	60	0.4
Example 26	2	35	185	145	12	80	0.6
								Comparative example 1	1	18	205	125	8	80	2.5
Comparative example 2	1	30	135	125	8	80	5.1
								Comparative example 3	1	42	206	125	8	80	7.2
Comparative example 4	1	30	206	125	8	80	6.1
								Comparative example 5	1	42	206	125	40	80	6.5
Comparative example 6	1	65	170	125	12	80	-
								Comparative example 7	2	45	145	145	8	80	5.8
Comparative example 8	2	42	155	145	8	80	3.2
								Comparative example 9	2	42	155	145	40	80	3.5

From the results of table 1 above, it can be seen that: according to the cellulose ester films of examples 1 to 26 of the present invention, in the method for producing a cellulose ester film by a solution casting film formation method, it is possible to produce a cellulose ester film which is excellent in optical properties such as transparency and planarity without increasing the haze of the film even after high stretching, and to improve the production speed and productivity of the film, and further to meet the recent demands for a thinner film, a wider film width and a higher quality of a protective film for a polarizing plate and the like.

On the contrary, when the cellulose ester films obtained in comparative examples 1 to 5 and comparative examples 7 to 9 are subjected to high stretching, the haze of the film increases, and the transparency and the flatness decrease. Therefore, the production rate of cellulose ester films cannot be increased, the productivity of films cannot be improved, and the requirements for making films thinner, wider, and higher in quality, such as polarizing plate protective films, cannot be satisfied.

Example 27

(production of polarizing film)

To produce the liquid crystal display panel shown in fig. 2, a polarizing film is first produced. That is, a polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched at a temperature of 110 ℃ at a stretch ratio of 5. This was immersed in an aqueous solution composed of 0.075g of iodine, 5g of potassium iodide and 100g of water for 60 seconds, and then immersed in an aqueous solution composed of 6g of potassium iodide, 7.5g of boric acid and 100g of water at 68 ℃. This was washed with water and dried to obtain a polarizing film.

(preparation of polarizing plate)

Next, the polarizing film prepared in example 6 was laminated with the film thickness 80 according to the following steps 1 to 5: a polarizing plate 1 was fabricated from a cellulose triacetate film (T-1) having a thickness of m and a cellulose acetate propionate film (T-2) having a thickness of 40 μm fabricated in example 21. Step 1: the film was immersed in a 2 mol/l sodium hydroxide solution at 50 ℃ for 60 seconds, then washed with water and dried to obtain a saponified T-1, T-2 film on the side to which the polarizing film was bonded.

And a step 2: the polarizing film is immersed in a polyvinyl alcohol adhesive tank having a solid content of 2 mass% for 1 to 2 seconds.

Step 3: the extra adhesive attached to the polarizing film in step 2 was lightly wiped off, and the T-1, T-2 films obtained by the treatment in step 1 were stacked on both sides of the polarizing film.

And step 4: the polarizing film and the T-1, T-2 film prepared in the step 3 are formed at a rate of 20-30N/cm²And a conveying speed of about 2 m/min.

Step 5: the polarizing film produced in step 4 and the T-1, T-2 film were dried in a dryer at 80 ℃ for 2 minutes to produce a polarizing plate 1.

Next, as the polarizing plate 2 bonded to the other surface of the liquid crystal display panel, the polarizing plate 1 was prepared as described above, and was disposed so that the bonding direction thereof was symmetrical to the polarizing plate 1 about the liquid crystal.

Thus, as shown in Table 2, the film T-3 of the polarizing plate 2 was a cellulose acetate propionate film having a thickness of 40 μm prepared in example 21, and the film T-4 of the polarizing plate 2 was a cellulose triacetate film having a thickness of 80 μm prepared in example 6.

(production of liquid Crystal display Panel)

Then, the polarizing plates on both sides of a commercially available liquid crystal display panel (NEC color liquid crystal display, MultiSync, LCD 1525J: model LA-1529HM) were carefully separated from each other, and the polarizing plate 1 and the polarizing plate 2 thus produced were bonded to the liquid crystal to produce a liquid crystal display panel.

At this time, as shown in FIG. 2, the lamination was performed so that the cellulose triacetate films (T-1) and (T-4) having a thickness of 80 μm produced in example 6 as the polarizing plate 1 and the polarizing plate 2 were positioned outside the liquid crystal at the center, and the cellulose acetate propionate films (T-2) and (T-3) having a thickness of 40 μm produced in example 21 were positioned on the liquid crystal at the center.

In this case, the outer film (T-1) side of the polarizing plate 1 is the display side of the liquid crystal display panel, and the outer film (T-4) side of the polarizing plate 2 is the backlight (backlight) side.

The contrast of the thus obtained liquid crystal display panel of example 27 was measured, and the results are shown in table 2 below.

(measurement of contrast at the time of mounting of display Panel)

The contrast ratio at the time of mounting the display panel was measured by evaluating the viewing angle of the display panel. Here, the viewing angle evaluation is performed by measuring the viewing angle of the liquid crystal display panel using EZ-contrast manufactured by ELDIM corporation. The measurement method is as follows: the contrast of the liquid crystal display panel in the white display and the black display is classified in all directions within the following range of values according to the contrast in the direction inclined at an angle of 80 ° from the normal direction of the panel surface.

Very excellent-: the contrast ratio is more than 40 in all directions

Very excellent: the contrast ratio is more than 30 in all directions

Very good: the contrast ratio is more than 20 in all directions

O: the contrast ratio is more than 15 in all directions

And (delta): there is a region having a contrast of 5 or more but less than 15 in all directions

X: there is a region with a contrast ratio of less than 5 in all directions

Examples 28 to 31

A liquid crystal display panel was produced as in example 27, but it was different from example 27 in the following point.

In example 28, a cellulose triacetate film (T-1) having a thickness of 80 μm prepared in example 6 and a cellulose acetate propionate film (T-2) having a thickness of 60 μm prepared in example 25 were laminated on a polarizing film to prepare a polarizing plate 1, and as the polarizing plate 2 laminated on the other surface of the liquid crystal display panel, the polarizing plate 1 was prepared as described above, and the lamination direction was arranged so as to be centered on the liquid crystal.

Thus, as shown in Table 3, the film T-3 of the polarizing plate 2 was a cellulose acetate propionate film having a film thickness of 60 μm prepared in example 25, and the film T-4 of the polarizing plate 2 was a cellulose triacetate film having a film thickness of 80 μm prepared in example 6.

In example 29, a cellulose triacetate film (T-1) having a thickness of 80 μm prepared in example 6 and a cellulose acetate propionate film (T-2) having a thickness of 80 μm prepared in example 26 were laminated on a polarizing film to prepare a polarizing plate 1, and as a polarizing plate 2 laminated on the other surface of a liquid crystal display panel, the polarizing plate 1 was prepared as described above, and the lamination direction was arranged so as to be centered on the liquid crystal.

Thus, as shown in Table 2, the film T-3 of the polarizing plate 2 was the cellulose acetate propionate film having a thickness of 80 μm prepared in example 26, and the film T-4 of the polarizing plate 2 was the cellulose triacetate film having a thickness of 80 μm prepared in example 6.

In example 30, a cellulose triacetate film (T-1) having a film thickness of 80 μm prepared in example 13 and a cellulose acetate propionate film (T-2) having a film thickness of 60 μm prepared in example 25 were laminated on a polarizing film to prepare a polarizing plate 1, and as a polarizing plate 2 laminated on the other surface of a liquid crystal display panel, the polarizing plate 1 was prepared as described above, and the lamination direction was arranged so as to be centered on the liquid crystal.

Thus, as shown in Table 2, the film T-3 of the polarizing plate 2 was a cellulose acetate propionate film having a film thickness of 60 μm prepared in example 25, and the film T-4 of the polarizing plate 2 was a cellulose triacetate film having a film thickness of 80 μm prepared in example 13.

In example 31, a cellulose triacetate film (T-1) having a thickness of 80 μm prepared in example 13 and a cellulose acetate propionate film (T-2) having a thickness of 40 μm prepared in example 17 were laminated on a polarizing film to prepare a polarizing plate 1, and as a polarizing plate 2 laminated on the other surface of a liquid crystal display panel, the polarizing plate 1 was prepared as described above, and the lamination direction was arranged so as to be centered on the liquid crystal.

Thus, as shown in Table 2, the film T-3 of the polarizing plate 2 was a cellulose acetate propionate film having a thickness of 40 μm prepared in example 17, and the film T-4 of the polarizing plate 2 was a cellulose triacetate film having a thickness of 80 μm prepared in example 13.

The contrast of the liquid crystal display panels of examples 28 to 31 thus obtained was measured in the same manner as in example 27, and the results are shown in Table 2 below.

Comparative example 11

For comparison, a liquid crystal display panel was produced as in example 27, and it was different from example 27 in that: the polarizing plate 1 was prepared by laminating the cellulose triacetate film (T-1) having a thickness of 80 μm prepared in comparative example 2 and the cellulose acetate propionate film (T-2) having a thickness of 80 μm prepared in comparative example 8 on a polarizing film, and the polarizing plate 2 laminated on the other surface of the liquid crystal display panel was arranged so that the laminating direction thereof was symmetrical about the liquid crystal as described above in the preparation of the polarizing plate 1.

Thus, as shown in Table 2, the film T-3 of the polarizing plate 2 was the cellulose acetate propionate film having a thickness of 80 μm produced in comparative example 8, and the film T-4 of the polarizing plate 2 was the cellulose triacetate film having a thickness of 80 μm produced in comparative example 2.

The contrast of the liquid crystal display panel of comparative example 11 thus obtained was measured in the same manner as in example 27, and the results thereof are shown in table 2 below.

[ Table 2]

From the results of table 2 above, it can be seen that: the liquid crystal display panels of examples 27 to 31 of the present invention had a contrast ratio superior to that of the liquid crystal display panel of comparative example 11.

Claims (9)

1. A method for producing a cellulose ester film, comprising casting a resin solution containing a cellulose ester resin on a casting support to form a casting film, drying a solvent in the casting film until the casting film is in a peelable state, peeling the casting film from the casting support, holding both ends of the peeled web, stretching the web in a width direction, and after the stretching step, drying the solvent and winding the web to obtain a cellulose ester film; wherein,

the sheet material has a stretching ratio of 20 to 60% in the stretching step, and the temperature of hot air blown out from a hot air blowing device in the stretching step is Tg +35 to Tg +80 ℃ with respect to the glass transition temperature Tg of the film after winding.

2. The method for producing a cellulose ester film according to claim 1, wherein the amount of the residual solvent in the film immediately before the stretching step is 10 to 35% by mass.

3. The method for producing a cellulose ester film according to claim 1 or 2, wherein a removing device for removing organic components other than the solvent contained in the exhaust air sent from the stretching step is provided.

4. The method for producing a cellulose ester film according to claim 3, wherein the exhaust air from which the organic component has been removed is reused as a part of the drying air upstream of the stretching step.

5. The method for producing a cellulose ester film according to claim 4, wherein the removing means is a plurality of continuous means.

6. A cellulose ester film produced by the method according to any one of claims 1 to 3, wherein the width of the film after winding is 1650 to 2500 mm.

7. The cellulose ester film according to claim 6, wherein the film thickness after winding is 40 to 80 μm.

8. A polarizing plate comprising the cellulose ester film according to claim 6 or 7 on one side thereof.

9. A display device using the cellulose ester film according to claim 6 or 7.

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