KR101122972B1 - Manufacturing Method of Optical Film - Google Patents

Abstract

The present invention is a method for producing an optical film having a phase difference function and a viewing angle enlargement function used for a liquid crystal display (LCD), and the like, and a film alignment angle distribution having a desired precision without causing wrinkles or the like over approximately the entire area of the film. It can achieve, and it provides the manufacturing method of the optical film which has an excellent retardation compensation performance and a viewing angle magnification function with a uniform orientation angle in the width direction (TD direction). According to the orientation angle of the completed optical film at the time of film forming of an optical film, the roll axis orientation direction of one or several conveyance rolls in a film forming line is set to the angle range which is larger than 0 degree and 5 degrees or less with respect to the direction perpendicular | vertical to a film conveyance direction. It is a manufacturing method of the optical film characterized by adjusting.

Optical film, conveyance roll, phase difference, orientation angle, film forming

Description

Manufacturing Method of Optical Film

1 defines an orientation angle.

2 defines an orientation angle.

3 shows a method of controlling an orientation angle.

4 shows a method of controlling an orientation angle.

5 shows a method of controlling an orientation angle.

6 shows a method of controlling an orientation angle.

<Explanation of symbols for the main parts of the drawings>

F: film

θ: orientation angle

Φ: angle of roll axis

[Document 1] Japanese Unexamined Patent Publication No. 2002-71957

[Document 2] Japanese Unexamined Patent Publication No. 2-191904

[Document 3] Japanese Unexamined Patent Publication No. 5-127019

[Document 4] Japanese Unexamined Patent Publication No. 6-160623

[Patent 5] Japanese Unexamined Patent Publication No. 6-160624

[Patent 6] Japanese Unexamined Patent Publication No. 6-300917

TECHNICAL FIELD This invention relates to the manufacturing method of the optical film provided with the retardation function and viewing angle enlargement function used for a liquid crystal display device (LCD).

Generally, the basic structure of a liquid crystal display device is provided with polarizing plates on both sides of a liquid crystal cell. Since the polarizing plate passes only light of a polarization plane in a predetermined direction, the liquid crystal display device plays an important role in visualizing a change in liquid crystal alignment due to an electric field, and the performance of the liquid crystal display device is greatly influenced by the performance of the polarizing plate.

As a manufacturing method of an optical film, the solution casting film forming method and the melt casting film forming method are largely classified. The former is a method in which a polymer is dissolved in a solvent, the solution is cast on a support to evaporate the solvent, and further stretched as necessary to form a film. This method has been widely adopted in terms of excellent uniformity of film thickness, but has a problem such as an increase in size of equipment for drying a solvent. The latter is a method in which a polymer is heated and melted, cast on a support, cooled and solidified, and stretched as necessary to form a film. The latter does not need to be dried, so that the installation can be made relatively compact. There is a problem that the uniformity of the thickness is poor.

Conventionally, the cellulose ester film excellent in transparency and adhesiveness has been widely used as a polarizing plate protective film in recent years because of its small birefringence property, and it is possible to shorten the manufacturing process of the liquid crystal display device by giving the cellulose ester film an optical compensation function. Can also be suppressed. Here, when a cellulose ester film is used as an optical compensation sheet, it can also serve as a polarizing plate protective film.

The manufacture of such a film is performed as follows by the solution casting film forming method, taking a cellulose triacetate (TAC) film as an example.

That is, first, the cellulose triacetate is added to a mixed solvent in which a good solvent for cellulose triacetate such as methylene chloride and the poor solvent for cellulose triacetate such as methanol, ethanol, butanol or cyclohexane are added. It melt | dissolves, and also adds a plasticizer, a ultraviolet absorber, and the microparticles | fine-particles for the slip property improvement of a film to produce the cellulose triacetate solution (henceforth "dope"), and dope has a mirror-treated surface It is uniformly flexible from a casting die to obtain a dope film (hereinafter referred to as a 'web') on an endlessly rotating endless rotating drive metal support (for example, a stainless steel endless belt or drum), which is dried on the support and then peeled off. Peeling with a roll, conveying a web by the conveyance roll which provided the regulating force to the film edge part, and roll conveyance By stretching the web by a tenter before or after the transverse direction, to prepare a cellulose ester film it was wound by winding group after drying.

As a method of giving an optical compensation function to such a cellulose ester film, what was described in the following prior patent document is known.

Document 1 discloses an optical film using a cellulose ester containing an acetyl group and a propionyl group or a butyl group. In the method described in this document 1, the film formed in order to express the desired high retardation is formed in the same direction as the film conveying direction, that is, in the machine direction (MD direction) or in a direction orthogonal to the conveying direction, that is, in the width direction (TD direction). It is done to expand in).

As a method of extending | stretching the film after peeling from a support body, what was described in the following prior literature is known.

In the said document 2, the manufacturing technique of the retardation film which carries out longitudinal uniaxial (free-width) extending | stretching of a machine direction is disclosed.

In the said document 3, the manufacturing technique of the retardation board which performs uniaxial stretching and sequential biaxial stretching is disclosed.

However, in the stretching method by longitudinal uniaxial stretching described in Document 2, it is difficult to maintain the heating temperature uniformly between the stretching rolls, and there is a problem in controllability of the retardation, and when stretching in the MD direction, the TD direction Since the force regulating the contraction of the film is hardly exerted, and it contracts substantially freely, it is easy to generate a nonuniformity of the film thickness on the stripe connected in the MD direction or a nonuniformity of the retardation on the stripe in the MD direction (a shade in cross nicol). There was a problem. Moreover, shrinkage | contraction rate of the film width direction differs in roll vicinity and center of a roll, the axial shift | offset | difference which the optical slow axis becomes nonuniform in the width direction of a film (base) tends to occur, and it has the fault that it is very difficult to control this axial shift | offset. .

Further, in the uniaxial stretching described in Document 3, which is widely used in general, the temperature controllability is excellent, but there is a problem that stress is generated in a direction orthogonal to the stretching direction, and it is difficult to avoid an axial shift called Boeing.

Moreover, in the method of shrinking to MD direction by the heat processing of document 3, there existed a problem that a desired shrinkage amount was not obtained according to the kind of resin.

Therefore, various methods are disclosed in the documents 4 to 6 to obtain an appropriate retardation by shrinking in the MD direction after performing uniaxial stretching of the film.

In these documents 4 to 6, a technique for producing a retardation plate is provided in which the tenter clip portion is provided with a wave-shaped relaxation portion to maintain the width and shrink in the MD direction.

However, in the methods described in these documents 4 to 6, there is a problem that wrinkles tend to gather during clipping, and there is a high risk of fracture during conveyance in and after the tenter, and there is a problem that control of the shrinkage ratio in the MD direction of the film is difficult.

In recent years, it is common to use the film for phase difference correction for the liquid crystal display device which extended the viewing angle. Due to the large screen and high precision, the quality required for the retardation film becomes strict, especially in the retardation film having a large in-plane retardation, the demand for the slow axis (orientation axis) direction (orientation angle) of the retardation is severe, and the whole area of the film Accuracy of ± 1 ° or less, preferably about ± 0.3 to 0.5 ° over.

By the way, although the film forming line of an optical film is manufactured symmetrically as much as possible, the request of the orientation angle of the said film approaches the limit of mechanical precision, and it is difficult to satisfy the said request | requirement.

In the manufacture of the optical film, care should be taken to make the film line unevenness in the conveying line, heating / drying equipment, and casting as uniform as possible in the width direction.However, due to repeated thermal deformation or wear of the sliding parts applied to the manufacturing equipment, Since mechanical left and right nonuniformity deteriorates with time, the orientation angle of a film also changes with time.

Moreover, when the film manufactured by the solution casting film forming method is drawn inline, and an optical film is manufactured, since the conveyed film is soft including a solvent, it is more influenced by the left-right unevenness of a conveyance line, and the orientation angle of a film The widthwise distribution of is likely to occur.

On the other hand, when the film produced by the melt casting film forming method is stretched in-line to produce an optical film, the film to be conveyed is cast into a cooling drum because it is at a high temperature, for example, at 250 ° C. in the casting die portion, and then is peeled off. Since it is soft at high temperature compared with the film manufactured by the solution casting film formation method later, the influence of the left and right nonuniformity of a conveyance line is more strongly received, and the width direction distribution of the orientation angle of a film is easy to produce.

Moreover, in the film after peeling from a support body, the width direction distribution of an optical characteristic arises also by the film thickness nonuniformity and the width direction nonuniformity of drying.

These width direction distributions are remarkable especially when a film forming speed is increased for productivity improvement.

In the manufacture of optical films, particularly retardation films, where high precision is required, it is important to maintain such a distribution in the width direction of the alignment angle to the required precision.

In the viewing angle magnification film, axial shift (inclination of the orientation angle) becomes a problem, but control at a very high precision (0.1 to 0.2 °) is required.

The method of controlling the axial shift | offset | difference of a film is conventionally disclosed to give the film the orientation angle of 45 degrees of inclination by extending | stretching, However, when it is a perpendicular | vertical angle (90 degree) with respect to a film conveyance direction, it is accurate There is no way to keep it.

A known technique is a tenter for reducing the punching loss of a polarizing plate for TN (liquid crystal cell twisted nematic mode) by setting the orientation angle (direction of the optical slow axis) to 15 to 45 ° with respect to the film (base) conveying direction. As a technique regarding a stretching machine, it is not a technique which uniformly controls the orientation angle of the width direction (TD direction).

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems of the prior art, and to provide a method for producing an optical film having an excellent retardation compensation performance and a viewing angle enlargement function, in which the orientation angle is uniform in the width direction (TD direction) over approximately the entire area of the film. To provide.

MEANS TO SOLVE THE PROBLEM As a result of earnestly researching in view of said point, this inventor gives what is called a torsional force to the film conveyed in the film forming line of an optical film, controls an orientation angle, and adjusts the appropriate temperature and the axis of a roll at that time. By performing the method, an orientation angle distribution with a desired precision can be achieved without the problem of wrinkles and the like, and the orientation angle is uniform in the width direction (TD direction) over approximately the entire area of the film, and has excellent phase difference compensation performance and viewing angle enlargement function. The discovery that optical films can be made has led to the completion of the present invention.

In order to achieve the said objective, invention of the manufacturing method of the optical film of Claim 1 measures the orientation angle of the width direction of a completed optical film in multiple points, and one or more at the time of film forming of an optical film according to the said measured value The arrangement direction of the roll axis | shaft of several conveyance roll is adjusted to the angle range larger than 0 degree and 5 degrees or less with respect to the direction perpendicular | vertical to a film conveyance direction, It is characterized by the above-mentioned.

Next, invention of the manufacturing method of the optical film of Claim 2 is carried out by the solution casting film forming method of the film formation of the said optical film, the amount of residual solvent in a film is the range of 10-70 mass%, and one or more conveyance rolls is carried out. It is characterized by adjusting the arrangement direction of the roll axis of an angle range larger than 0 degrees and 5 degrees or less with respect to a film conveyance direction and a right angle direction. In this case, it is preferable to carry out in the range of the 30-140 degreeC atmosphere temperature where a film is conveyed and dried.

Invention of the manufacturing method of the optical film of Claim 3 is carried out by the melt casting film forming method of the film formation of the said optical film, and adjusts to the angle range which is larger than 0 degree and 5 degrees or less with respect to an optical film conveyance direction and a right angle direction. It is done.

Moreover, the invention of the manufacturing method of the optical film of Claim 4 is a manufacturing method of the optical film of any one of said Claims 1-3, The orientation angle of the said completed film is measured online in the film forming of an optical film, According to the result, the arrangement direction of the roll shaft of a conveyance roll is adjusted. It is characterized by the above-mentioned.

Next, embodiment of this invention is described.

First, when performing the manufacturing method of the optical film which concerns on this invention by the solution casting film forming method, as a target resin, cellulose ester-type resin is used preferably, As a cellulose ester-type resin, cellulose triacetate and a cellulose acetate propio Nate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate butyrate and the like are preferably used. In the case of cellulose triacetate, cellulose triacetate having a polymerization degree of 250 to 400 and a combined acetic acid amount of 54 to 62.5% is particularly preferable.

A cellulose ester can be used individually or in mixture of either the cellulose ester synthesize | combined from cotton linter and the cellulose ester synthesize | combined from wood pulp.

About the specific manufacturing method of the cellulose ester-type resin used preferably by this invention, it can synthesize | combine 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 is low. If the number average molecular weight of the cellulose ester is too high, the viscosity of the solution may be too high. Therefore, 70000 to 300000 are preferable, and 80000 to 200000 are preferable.

It is preferable to use more cellulose ester synthesize | combined from the cotton linter with the peelability from the rotation drive metal support body which consists of an endless belt and a drum, since high productivity efficiency is preferable. In addition, in order to make a peelable effect remarkable, it is preferable that the ratio of the cellulose ester synthesize | combined from cotton linter is 60 mass% or more, More preferably, it is most preferable to use 85 mass% or more, or individual.

In particular, cellulose ester films having a total acyl group substitution degree of less than 2.85 are preferable because they can reduce dimensional change, and also preferred are cellulose ester films having a total acyl group substitution degree of less than 2.75. The effect is recognized.

In this invention, it is preferable that the optical film which consists of a cellulose ester-type resin film contains a ultraviolet absorber from a viewpoint of prevention of deterioration at the time of being placed outdoors as a liquid crystal display device. As a ultraviolet absorber, the thing excellent in the ultraviolet absorbing power of wavelength 370 nm or less, and having little visible light absorption with a wavelength of 400 nm or more can be used preferably. For example, it is preferable that the transmittance | permeability in wavelength 380nm is 20%, Preferably it is less than 10%, Especially preferably, it is less than 5%.

As an ultraviolet absorber, an oxybenzophenone type compound, a benzotriazole type compound, a salicylic acid ester type compound, a benzophenone type compound, a cyanoacrylate type compound, a nickel complex salt type compound, a triazine type compound, etc. are mentioned, for example, The invention is not limited to these.

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

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" -tetrahydrophthalimidemethyl) -5'methylphenyl) benzotriazole

UV-6: 2,2methylenebis (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-benzotriazol-2-yl) -6- (linear and branched dodecyl) -4-methylphenol (TINUVIN 171: manufactured by Ciba Specialty Chemicals)

UV-9: octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate, 2-ethylhexyl-3- [ 3-tert-butyl-4-hydroxy-5- (chloro-2 H-benzotriazol-2-yl) phenyl] propionate and mixtures (tinuvin 109: 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, the optical film is preferably a benzotriazole-based ultraviolet absorber and a benzophenone-based ultraviolet absorber having high transparency as an ultraviolet absorber and excellent in preventing the deterioration of a polarizing plate or a liquid crystal, and among them, there is less unnecessary coloring. Especially preferred is a benzotriazole ultraviolet absorber. It is preferable that a ultraviolet absorber does not bleed out or volatilizes in a film forming process.

Moreover, although a polymeric ultraviolet absorber can also be used suitably as a ultraviolet absorber, the ultraviolet absorber of the polymer type of Unexamined-Japanese-Patent No. 6-148430 is used preferably.

In this invention, it is preferable to add 0.1-10 mass% of ultraviolet absorbers with respect to a resin component, and it is especially preferable to add 0.5-5 mass%.

In addition, in this invention, these ultraviolet absorbers may be used independently, or may be used by another 2 or more types of mixture.

The addition method of a ultraviolet absorber may add to a dope after melt | dissolving a ultraviolet absorber in organic solvents, such as alcohol, methylene chloride, and dioxosilane, or may be added directly in a dope composition. What does not dissolve in an organic solvent like inorganic powder is dispersed in an organic solvent and a cellulose ester using a dissolver or a sand mill, and then added to the dope.

Moreover, in this invention, you may add microparticles | fine-particles, such as a silicon dioxide, etc. as a mat agent as needed for an optical film. Particles such as silicon dioxide are preferable because surface treatment with an organic substance can lower the haze of the film. Preferred organic substances at the time of surface treatment include halosilanes, alkoxysilanes, silazanes, and siloxanes. The larger the average particle size of the fine particles is, the larger the matte effect is, and the smaller the average particle size is, the more excellent in transparency. The average particle size of the preferred primary particle of the fine particles is 5 to 50 nm, more preferably 7 to 14 nm.

In the present invention, as the fine particles of silicon dioxide to be used, aerosil (AEROSIL) -200, 200V, 300, R972, R972V, R974, R202, R812, OX50, TT600, etc. manufactured by Aerosil Co., Ltd. Although an aceyl-200, 200V, R972, R972V, R974, R202, R812 etc. are mentioned preferably.

In the present invention, the fine particles are used by adding 0.04-0.4 mass%, preferably 0.05-0.3 mass%, more preferably 0.05-0.2 mass% with respect to the resin.

In the method of the present invention, the solvent used for dissolving the resin may be used alone or in combination, but it is preferable to use a mixture of a good solvent and a poor solvent in terms of increasing the production efficiency, and the more the good solvent is used for the resin solubility and the fine insoluble matter. It is preferable at the point to reduce the film foreign material by. The preferable ranges of the mixing ratio of a good solvent and a poor solvent are 70-98 mass% of good solvents, and 30-2 mass% of poor solvents.

Here, a good solvent or a poor solvent used for the present invention is defined as a poor solvent in which a solvent to be used alone is dissolved, or a swelling alone or not dissolved in a good solvent.

Although it does not specifically limit as a good solvent used by this invention, For example, when resin is cellulose triacetate, organic halogen compounds, such as methylene chloride, or dioxolanes, and cellulose acetate propionate, methylene chloride and acetone And methyl acetate. Moreover, 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.

The manufacturing method of the optical film which consists of a cellulose-ester type resin film by the solution casting film formation method is for example US patent 2,492,978, US patent 2,739,070, US patent 2,739,069, US patent 2,492,977, US patent 2,336,310, US patent 2,367,603, US Patent 2,607,704, UK Patent 64,071, UK Patent 735,892, Japan Patent Publication (S) 45-9074, Japan Patent Publication (S) 49-4554, Japan Patent Publication (S) 49-5614 And Japanese Patent Publication No. 60-27562, Japanese Patent Publication No. 61-39890, Japanese Patent Publication No. 62-4208, and the like.

In the manufacturing method of the optical film of this invention, it is preferable to add a plasticizer to an optical film from a viewpoint of mechanical strength, dimensional stability, etc. As the addition amount, it is 3-30 mass% as mass% with respect to the cellulose ester film which acylated the cellulose ester film or cellulose with the acetyl group and the acyl group of 3-4 carbon atoms, for example, when an optical film is a cellulose ester film. It is preferable to set it as this, 10-30 mass% is more preferable, and 15-25 mass% is especially preferable. In general, the dimension changes easily with increasing amount of plasticizer added, but according to the method of the present invention, the rate of dimensional change can be significantly reduced.

Although it does not specifically limit as a plasticizer which can be used by this invention, A phosphoric acid ester plasticizer, a phthalic acid ester plasticizer, a trimellitic acid ester plasticizer, a pyromellitic acid plasticizer, a glycolate plasticizer, a citrate ester plasticizer, polyester A system plasticizer etc. can be used preferably.

Here, in the phosphate 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-based plasticizer, tributyl trimellitate, triphenyl trimellitate, triethyl trimellitate and the like can be preferably used. In a pyromellitic acid ester plasticizer, tetrabutyl pyromellitate, tetraphenyl pyromellitate, tetraethyl pyromellitate, etc. can be used preferably. As 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 citric acid ester plasticizer, triethyl citrate, tri-n-butyl citrate, acetyl triethyl citrate, acetyl tri-n-butyl citrate, acetyl tri-n- (2-ethylhexyl) citrate and the like are preferable. It is available. As a polyester plasticizer, the copolymer of dibasic acids and glycols, such as aliphatic dibasic acid, alicyclic dibasic acid, and aromatic dibasic acid, can be used. Although it does not specifically limit as aliphatic dibasic acid, Adipic acid, sebacic acid, phthalic acid, terephthalic acid, 1, 4- cyclohexyl dicarboxylic acid, etc. can be used. Examples of glycols include ethylene glycol, diethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, and the like. It is available. These dibasic acids and glycols may be used alone, or may be used by mixing two or more kinds. It is preferable that the molecular weight of polyester exists in the range of 500-2000 by weight average molecular weight from a viewpoint of compatibility with a cellulose resin.

Moreover, in the method of this invention, it is especially preferable to use the plasticizer whose vapor pressure in 200 degreeC is less than 1333 Pa, More preferably, it is the plasticizer of vapor pressure 666 Pa or less, More preferably, it is 1-133 Pa. Although the plasticizer which has nonvolatility 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 individually or in combination of 2 or more types.

In the manufacturing method of the optical film which concerns on this invention, when the optical film is a cellulose ester film, solid content concentration of the dope which is a cellulose ester solution is about 10-40 mass% normally, and the dope viscosity at the time of casting | flow_spread in a casting | flow_spread process is 1 thru | or. It is produced in the 200 poise range. Here, the dissolution of the cellulose ester is generally used by means such as a stirring dissolving method, a heating dissolving method, an ultrasonic dissolving method, and the like in a dissolving kiln, and the pressure is not lower than the boiling point at normal pressure of the solvent under pressure, and the solvent does not boil. The method of dissolving with heating and stirring at temperature is more preferable in order to prevent generation of lumpy undissolved matter called gel or coagulum. Moreover, the cooling dissolution method of Unexamined-Japanese-Patent No. 9-95538, the method of melt | dissolving under the high pressure of Unexamined-Japanese-Patent No. 11-21379, etc. can also be used.

A method in which the cellulose ester is mixed with the poor solvent to wet or swell and then mixed with the good solvent to dissolve again is preferably used. At this time, the apparatus which mixes and dissolves a cellulose ester with a poor solvent, and the apparatus which melt | dissolves by mixing with a good solvent can also be divided.

In the present invention, the type of pressurized container used for dissolving the cellulose ester is not particularly limited, but can withstand a predetermined pressure, and may be heated and stirred under pressure. In addition, as a pressurized container, instruments such as a pressure gauge and a thermometer are appropriately arranged and installed. Pressurization can also be performed by the method of press-fitting inert gas, such as nitrogen gas, or the vapor pressure rise of a solvent by heating. It is preferable to perform heating from the outside, for example, a jacket type thing is preferable because temperature control is easy.

The heating temperature to which the solvent is added is equal to or higher than the boiling point of the solvent to be used, and in the case of two or more kinds of mixed solvents, a temperature in which the boiling point is heated to a temperature higher than or equal to that of the solvent having a low boiling point is preferable. If the heating temperature is too high, the required pressure increases, which leads to poor productivity. Although the range of preferable heating temperature is 20-120 degreeC, 30-100 degreeC is more preferable, and the range of 40-80 degreeC is still more preferable. In addition, the pressure is adjusted so that the solvent does not boil as a set temperature.

In addition to the cellulose ester and the solvent, additives such as plasticizers and ultraviolet absorbers required may be mixed with the solvent in advance, dissolved or dispersed, and then added to the solvent before dissolving the cellulose ester, or added to the dope after dissolving the cellulose ester.

After dissolving the cellulose ester, the cellulose ester is extracted by cooling from a vessel or extracted from the vessel with a pump or the like and cooled by a heat exchanger or the like, and the dope of the obtained cellulose ester is used for film formation, but the cooling temperature at this time may be cooled to room temperature. have.

The mixture of a cellulose ester raw material and a solvent is melt | dissolved by the dissolution apparatus which has a stirrer, At this time, the circumferential speed of a stirring blade is at least 0.5 m / sec or more, It is preferable to melt | dissolve by stirring for 30 minutes or more.

In the method of the present invention, the cellulose ester dope must remove the foreign material, in particular, the foreign material which is erroneously recognized as an image in the liquid crystal display device. It can be said that the quality as an optical film is determined by such filtration.

The smaller the absolute filtration accuracy of the filter medium used for filtration is preferable, but if the absolute filtration accuracy is too small, clogging of the filter medium is likely to occur, and the filter medium is frequently exchanged, which results in a problem of low productivity.

For this reason, it is preferable that absolute filtration precision is 0.008 mm or less, as for the filter medium used for cellulose ester dope by the method of this invention, the range of 0.001 to 0.008 mm is more preferable, The filter medium of the range of 0.003 to 0.006 mm is more preferable. Do.

There is no restriction | limiting in particular in the material of a filter medium, Although a normal filter medium can be used, The filter medium made from plastic fibers, such as a polypropylene and Teflon (trademark), and the metal filter medium, such as stainless fiber, are preferable because a fiber does not fall off.

Filtration of cellulose ester dope in the method of this invention can be performed by a conventional method, but the method of filtering, heating under pressure to the temperature of the range which is more than the boiling point in the normal pressure of a solvent and a solvent does not boil, and the pressure difference before and behind a filter medium ( Hereinafter, the rise of the 'filtration pressure' is small, which is preferable.

Although the preferable range of filtration temperature is 45-120 degreeC, 45-70 degreeC is more preferable and it is more preferable that it is the range of 45-55 degreeC.

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

When cellulose which is a raw material contains unsubstituted or low-substituted cellulose esters of acyl groups, foreign matter failure (hereinafter, also referred to as "viscosity" or "viscosity foreign matter") may occur. The bright spot is a cellulose ester film placed between two polarizing plates in an orthogonal state (cross nicol), and when light is irradiated from one side and observed with an optical microscope (50 times) from the opposite side, the light is blocked if it is a normal cellulose ester film. Nothing is seen, but if there is a foreign object, light leaks from it and looks like a spot. The larger the diameter of the bright point is, the larger the defect is in the case of the liquid crystal display device, and the diameter of the bright point is preferably 50 m or less, more preferably 10 m or less, and even more preferably 8 m or less. In addition, the diameter of a bright spot means the diameter measured by approximating a bright spot to a round shape.

If the point foreign matter is 400 pieces / cm 2 or less, there is no problem in practical use, but 300 pieces / cm 2 or less is preferable, and 200 pieces / cm 2 or less is more preferable. In order to reduce the number and size of the bright spot foreign matter, it is necessary to sufficiently filter the fine foreign matter.

For example, the method of re-adding the pulverized cellulose ester film formed into a film at a fixed ratio to make it the raw material of a cellulose ester and its additives as described in Unexamined-Japanese-Patent No. 2000-137115 is a bright point foreign material. Since it can reduce, it can use preferably.

Next, in order to manufacture an optical film by the method of this invention, when an optical film is a cellulose ester-type resin film, first, a cellulose ester is melt | dissolved in the mixed solvent of a good solvent and a poor solvent, and the plasticizer and ultraviolet absorber mentioned above are added to this. Add to prepare cellulose ester solution (dope).

The belt temperature at the time of film formation may be flexible at a temperature in the general temperature range of 0 ° C. to less than the boiling point of the solvent, and may be flexible in a range of 5 ° C. to the solvent boiling point 15 ° C. More preferred. At this time, it is necessary to control the ambient humidity at or above the dew point.

Moreover, the dope adjusted so that a dope viscosity might be 1-200 poise is cast so that it may become a substantially uniform film thickness from a casting die on a support body, and a casting film temperature will be a solvent when the amount of residual solvent in a casting film is 200% or more of solid content mass. The casting film (web) is dried by the drying wind below the boiling point and further within the range of 200% or less to the peeling so that the solvent boiling point is 120 ° C or less.

On the support, in order to dry-solidify until a web becomes the film strength which can peel from a support, it is preferable to dry the amount of residual solvent in a web to 150 mass% or less, and 50-120% is more preferable.

As for the web temperature at the time of peeling a web from a support body, 0-30 degreeC is preferable. In addition, the web temperature is 5 to 30 ° C. at the time of peeling, since the temperature of the web immediately decreases by evaporation of the solvent on the contact surface of the support immediately after peeling from the support, and volatile components such as water vapor and solvent vapor in the atmosphere are easily condensed. desirable.

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

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

In the above formula, M is the mass at any point in the web, and N is the mass when the mass M is dried at 110 ° C. for 3 hours.

Generally in the drying process of a web (or film), the method of drying while conveying a web by a roll suspension system or a pin tenter system or a clip tenter system is employ | adopted.

The web after peeling is introduce | transduced into a primary drying apparatus, for example. In the primary drying apparatus, the web is meandered by a plurality of conveying rolls arranged in a zigzag view from the side, during which the web is dried by warm air introduced from the upper portion of the drying apparatus and discharged from the bottom portion of the drying apparatus.

Next, the web is introduced into a tenter drying apparatus. Therefore, the web is dried while gripping both edges of the web with a clip.

As a liquid crystal display member, the tenter system which fixes and extends the both edges of a web with a clip etc. is known, but it is preferable in order to improve planarity and dimensional stability.

In particular, in the drying process after peeling from a support body, a web will shrink | contract in the width direction by evaporation of a solvent. Drying at higher temperatures results in greater shrinkage. Drying while suppressing this shrinkage as much as possible is preferable in order to improve the planarity of the finished film. In this regard, for example, a method / tenter for drying a pre-drying process or a part of the process as described in JP-A-62-46625 while keeping the widths of both ends of the web wide with clips in the width direction. The manner is preferred.

Gripping and stretching in the tenter can be performed in any of the ranges of 50 to 150 mass% of the residual solvent amount of the film immediately after peeling to 0 mass% of the actual residual solvent immediately before winding, but is performed in a range of 5 to 30% of the residual solvent amount. It is preferable as in the present invention.

It is also often done to divide the tenter into several temperature zones in the running direction of the base. Although the temperature at the time of extending | stretching is selected so that a desired physical property or planar property may be obtained, the temperature of the drying zone before and behind a tenter may also select the temperature different from the temperature at the time of extending | stretching for various reasons. For example, when the ambient temperature of the drying zone before the tenter is different from the temperature in the tenter, it is generally performed to set the temperature of the zone close to the inlet of the tenter to an intermediate temperature between the temperature of the drying zone before the tenter and the tenter central temperature. Similarly, in the case where the temperature in the tenter and the temperature in the tenter are different, the temperature in the region close to the tenter outlet is set to the temperature intermediate between the temperature in the tenter and the tenter. The temperature of the drying zone before and after the tenter is generally 30 to 120 ° C., preferably 50 to 100 ° C., and the temperature of the stretching portion in the tenter is 50 to 180 ° C., preferably 80 to 140 ° C., and the tenter inlet or The temperature of the outlet portion is appropriately selected from their intermediate temperatures.

In addition, the magnification of the film is selected so that the desired physical properties and planarity can be obtained. For example, in the case of cellulose ester-type resin, it is 0 to 150%, Preferably it is 0 to 50%.

The pattern of film stretching, i.e., the trajectory of the gripping clip, is selected from the optical properties and the planarity of the film as well as the temperature, and varies, but the pattern remains constant for a while after the initiation of the gripping, and is stretched thereafter to maintain the constant width again after the completion of the stretching. This is often used. In the vicinity of the end of clip gripping near the tenter exit, it is generally performed to relax the width to suppress the base vibration by opening the gripping.

The stretching pattern is also related to the stretching speed, but the stretching speed is generally 10 to 1000 (% / min), preferably 100 to 500 (% / min). This stretching speed is not constant when the trajectory of the clip is curved, and gradually changes in the traveling direction of the base.

In addition, the web (film) after drying by the said tenter system is introduce | transduced into a secondary drying apparatus next. In the secondary drying apparatus, the web is meandered by a plurality of conveying rolls arranged in a zigzag view from the side, during which the web is introduced from the upper portion of the secondary drying apparatus, and is subjected to the warm air discharged from the bottom portion of the secondary drying apparatus. It is dried and wound up by a winder as a cellulose ester film.

In the manufacturing method of the optical film which consists of a cellulose ester-type resin film of this invention, although the means for drying a web does not have a restriction | limiting in particular, Usually, it performs by hot air, infrared rays, a heating roll, a microwave, etc. In view of simplicity, drying with hot air is preferable. 40-150 degreeC of drying temperature is preferable, but since 80-130 degreeC improves planarity and dimensional stability, it is more preferable.

Thus, in the drying process of a web, the web peeled from a support body is further dried, and finally, it is 3 mass% or less, Preferably it is 1 mass% or less, More preferably, it is 0.5 mass% or less that dimensional stability is good It is preferable in obtaining a film.

It is preferable that these processes from casting | flow_spread to post-drying are in air atmosphere or inert gas atmosphere, such as nitrogen gas. In this case, it goes without saying that the drying atmosphere is carried out in consideration of the explosion limit concentration of the solvent.

Moreover, it is preferable to perform the process of forming embossing in the both edges of an optical film by the embossing apparatus in the step before introducing into a winding process about the optical film which completed the conveyance drying process. In the embossing apparatus, the apparatus described in Unexamined-Japanese-Patent No. 63-74850 can be used, for example.

In the method of the present invention, the winding machine according to the manufacture of the optical film is generally used, or can be wound by a winding method such as a constant tension method, a constant torque method, a tapered tension method, or a program tension control method having a constant internal stress. .

Although the film thickness of the optical film after winding in the method of this invention differs according to a use purpose, the film thickness range used by this invention as a completed film is 30-200 micrometers, considering the recent tendency of thinning, 40-120 micrometers The range of is preferable, especially 80 micrometers or less, More preferably, it is 20-60 micrometers, More preferably, it is 30-50 micrometers.

The manufacturing method of the optical film which concerns on this invention is a method of giving a so-called torsional force to the film conveyed in the film forming line of an optical film, and controlling an orientation angle, and performing axial adjustment of the appropriate temperature and the roll of a conveyance roll, That is, in the film formation of the optical film which consists of cellulose ester-type resin by the solution casting film forming method, the amount of residual solvent in a film is 10-70 mass%, and one according to the plus and minus of the width average value of the orientation angle of a completed film. Or the arrangement direction of the roll axis | shaft of several conveyance roll is adjusted to the angle range larger than 0 degree and 5 degrees or less with respect to the direction perpendicular | vertical to a film conveyance direction. In this case, it is preferable to carry out in the range whose atmosphere temperature at which a film is conveyed-dried is 30-140 degreeC.

According to the present invention, it is possible to achieve the orientation angle distribution of the high-precision film without the problem of wrinkles or the like by appropriately selecting the range of the amount of residual solvent in the film and the film temperature in the solution casting film forming method and adjusting the roll axis. It is possible to produce an optical film having an excellent retardation compensating performance and a viewing angle enlargement function in which the orientation angle is uniform in the width direction (TD direction) over approximately the entire area of the film.

Here, the orientation angle in the present invention indicates the slow axis direction (angle with respect to the width direction during flexible film formation) in the plane of the thermoplastic resin film, and the measurement of the orientation angle uses an automatic birefringence cobra (KOBRA) -21ADH. Do it. The measurement method of the orientation angle is performed at intervals of 3 to 10 cm in the film width direction, for example, at five points, preferably all orientation angles are ± 1.7 °, more preferably ± 1.5 °, More preferably within ± 1.0 °.

A detailed control method will be described with reference to the drawings. The orientation angle is defined as the slow axis direction of the in-plane retardation of the film. As shown in FIG. 1, when the slow axis direction is substantially orthogonal to the conveyance direction of a film, the direction perpendicular | vertical to a conveyance direction is made into 0 degree, and a still-system rotation direction is defined as a positive value. In addition, when the slow-axis direction is substantially parallel to the conveyance direction of a film, as shown in FIG. 2, a conveyance direction shall be 0 degree and a still-system rotation direction is defined as plus.

It is possible to make the orientation angle close to 0 degree which is a preferable value by measuring the orientation angle of the width | variety of the completed film based on the said definition, and changing the angle of a roll according to the plus and minus of these average values. In the roll arrangement as shown in FIG. 3, when the average value of the orientation angles measured from the film upper surface (upper surface side) is positive, the roll axis is arranged so that the passage length of the film on the right side in the advancing direction becomes longer as seen in FIG. 4. By changing the direction, the average value of the orientation angles can be brought close to zero. As the arrangement direction of the roll axis to change, if it is the structure which the passage length of the same side of a film becomes long, in addition to the horizontal direction like FIG. 4, it may be the vertical direction like FIG. The arrangement direction (not shown) may be changed at the same time. When changing the arrangement direction of several roll axis | shaft, you may change the arrangement direction of the some roll axis | shaft in a continuous roll or a distant position.

When the adjustment of the arrangement direction of the roll axis is too small, there is no effect of correcting the orientation angle, and when too large, pulling and wrinkles of the film to be conveyed occur, so that there is a range of appropriate values. It is preferable to adjust the arrangement direction of a roll axis to the angle of the range larger than 0 degree and 5 degrees or less with respect to the direction perpendicular | vertical to the conveyance direction of a film.

Moreover, in order to exhibit the correction effect of an orientation angle to the maximum, when it is solution casting as mentioned above, it is preferable that the amount of residual solvent of a film is 10-70 mass%. When the amount of residual solvent is too small, the effect of the correction of the orientation angle is small, and when the amount of residual solvent is too large, wrinkles are formed in the film when the arrangement direction of the roll axis is changed.

In manufacture of an optical film, although the extending | stretching installation which extended | stretched in the film forming line in the direction orthogonal to the conveyance direction or the conveyance direction of a film may be provided, this invention is effective regardless of the presence or absence of an extending | stretching installation. When there exists an extending installation, you may change the arrangement direction of the roll axis before an extension installation, or the arrangement direction of the roll axis after an extension installation. Moreover, the arrangement direction of the roll axis before and after an extending | stretching installation can also be changed simultaneously.

Next, the manufacturing method of the optical film of this invention is mentioned by the melt casting film forming method. Here, as the melt casting film forming method, a method using a T die capable of reducing film thickness nonuniformity and nonuniformity of litation is preferable. In the extrusion method using a T die, the polymer is melted at a meltable temperature, and the film-like (sheet-like) molten resin is pushed from the T die onto the cooling drum (support). Subsequently, the molten resin in film form (sheet form) is solidified by cooling drum, and the resin film is peeled from a cooling drum.

Next, when performing the manufacturing method of the optical film which concerns on this invention by the melt casting film forming method, if the target thermoplastic resin can be formed into a film by the melt casting film forming method, it will not specifically limit.

For example, polycarbonate (glass transition temperature Tg: about 150 degreeC), an alicyclic structure containing polymer, a polyvinyl alcohol, polyamide, polyimide, a cellulose ester-type resin, etc. are mentioned. Especially, since a photoelastic coefficient is small, a cellulose ester and an alicyclic structure containing polymer are preferable.

As cellulose ester-type resin, cellulose acetate propionate (glass transition temperature Tg: about 170 degreeC), cellulose acetate butyrate, and cellulose acetate propionate butyrate are preferable. Since the substitution degree of the acetyl group of the said cellulose ester is at least 1.5 or more, since the dimensional stability of the film obtained is excellent, it is preferable. As a measuring method of substitution degree of the acyl group of a cellulose ester, it can carry out based on ASTMD-817-91. Since the molecular weight of a cellulose ester is 50000-300000, especially 60000-20000 as a number average molecular weight, since the mechanical strength of the film obtained can be strengthened, it is preferable.

The alicyclic structure-containing polymer is a polymer having an alicyclic structure in the repeating unit, and the alicyclic structure may be any of main chain and side chain. Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure, but the cycloalkane structure is preferable because of its excellent thermal stability.

The alicyclic structure-containing polymer is a known polymerization method such as metathesis-opening ring-opening polymerization or addition polymerization of a monomer containing a monomer having a norbornene ring structure, a monocyclic olefin, a cyclic conjugated diene, a vinyl aromatic compound and a vinyl alicyclic hydrocarbon compound. It can superpose | polymerize and can obtain by hydrogenating a carbon-carbon unsaturated bond as needed.

The alicyclic structure-containing polymer used in the present invention preferably has a polyisoprene or polystyrene weight average molecular weight (Mw) measured by gel permeation chromatography of a cyclohexane solution (toluene solution when the polymer does not dissolve). And it is more preferable that they are 30000-45000. It is preferable that it is 1.2-3.5, and, as for molecular weight distribution (Mw / Mn), it is preferable that it is 1.5-3.0. Moreover, it is preferable that glass transition temperature (Tg) is 80-200 degreeC. By setting the properties of the alicyclic structure-containing polymer in the above range, good heat resistance and molding processability can be obtained.

The thermoplastic resin of the present invention may contain additives such as plasticizers, ultraviolet absorbers, antioxidants, matting agents, antistatic agents, flame retardants, dyes and emulsions for various purposes.

As a plasticizer, the thing similar to what is used by the manufacturing method of the optical film by the said solution casting film forming method can be used.

Suitable antioxidants are hindered phenolic compounds, and specific examples thereof include 2,6-di-t-butyl-p-cresol and pentaerythryl-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, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate ], Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 1,3,5-trimethyl-2,4,6-tris (3,5-di- t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxybenzyl) -isocyanurate, and the like. Especially 2,6-di-t-butyl-p-cresol, pentaerythryl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] and triethylene glycol -Bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N'-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di You may use together phosphorus process stabilizers, such as -t- butylphenyl) phosphite. In order to acquire the effect, 1 ppm-1.0% are preferable as a mass ratio with respect to a thermoplastic resin, and 10-1000 ppm is especially preferable for the addition amount of these compounds.

As a ultraviolet absorber which can be used for the manufacturing method of the optical film of this invention by the melt casting film forming method, the thing similar to what is used by the manufacturing method of the optical film by the said solution casting film forming method can be used.

The range of 0.01-10 mass% is preferable with respect to a thermoplastic resin, and, as for the compounding quantity of these ultraviolet absorbers, 0.1-5 mass% is more preferable. When the amount is too small, the ultraviolet absorbing effect may be insufficient. On the contrary, when the amount is too large, the transparency of the film may deteriorate. It is preferable that a ultraviolet absorber has high thermal stability.

In this invention, in order to provide slip property of a film, it is preferable to add microparticles | fine-particles. As the fine particles used in the present invention, any of inorganic compounds or organic compounds may be used as long as they have heat resistance at the time of melting. For example, the inorganic compounds include silicon-containing compounds, silicon dioxide, aluminum oxide, zirconium oxide, calcium carbonate, Talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate, and the like are preferred, and more preferably, an inorganic compound containing zirconium oxide or zirconium oxide. Especially, since haze can be suppressed small, silicon dioxide is especially used suitably, Even when carrying out the manufacturing method of the optical film of this invention by the melt casting film forming method, manufacture of the optical film by the said solution casting film forming method Almost the same mat agent used in the method can be used.

When performing the manufacturing method of the optical film of this invention by the melt casting film forming method, the melt casting film forming method includes the melt extrusion method, such as the method using T die, the inflation method, the calender method, the hot press method, the injection molding method, etc. . Among them, a method using a T-die that is small in thickness nonuniformity, easy to process into a thickness of about 50 to 500 µm, and which can reduce nonuniformity in film thickness or nonuniformity of retardation is preferable. The extrusion method using a T die is a method of melting the polymer described above at a meltable temperature, extruding it from the T die onto a cooling drum in a film form (sheet form), cooling and solidifying it, and peeling it from the cooling drum. It is excellent in thickness precision and can be used suitably also in this invention.

The conditions of melt extrusion can be performed similarly to the conditions used for thermoplastic resins, such as another polyester. For example, the cellulose ester dried under hot air, vacuum or reduced pressure is melted at an extrusion temperature of about 200 to 300 ° C. using a single screw or twin screw extruder, filtered through a leaf disk type filter, etc. to remove foreign substances, It is flexible to a film form (sheet form) from a T die, and it solidifies on a cooling drum. When introducing into the extruder from the feed hopper, it is preferable to prevent oxidative decomposition and the like under reduced pressure or in an inert gas atmosphere.

The extrusion flow rate is preferably performed stably by introducing a gear pump. Moreover, as a filter used for removal of a foreign material, the stainless fiber sintering filter is used preferably. The stainless fiber sintered filter is made by integrating a stainless fiber body into a entangled state and then compacted to sinter the contact points. The filtration precision can be adjusted by changing the density depending on the thickness and the amount of compression of the fiber. It is preferable to set it as the multilayer body which repeated filtration precision several times continuously with a tank and a mill. In addition, the filtration life of the filter can be extended by taking a configuration in which the filtration accuracy is sequentially increased or a method of repeating the chuck and the mill of the filtration accuracy, which is preferable because the capturing accuracy of foreign substances, gels, and the like can be improved.

Strips or defects can occur when a die or a wound is attached to the die. Although such a defect is called a die line, in order to reduce the defect of the surface of a die line etc., it is preferable to make it the structure which made the retention part of resin as few as possible in the piping from an extruder to a die. It is preferable to use the thing which does not have a scar etc. in the die | dye or a lip as much as possible. Since the volatile component may precipitate from the resin around the die and cause the die line, the atmosphere containing the volatile component is preferably aspirated. In addition, since precipitation may also occur in devices such as electrostatic application, it is preferable to apply alternating current or to prevent precipitation by other heating means.

Additives, such as a plasticizer, may be previously mixed with resin or kneaded in the middle of an extruder. In order to add uniformly, it is preferable to use mixing apparatuses, such as a stationary mixer.

The temperature of the cooling drum is preferably below the glass transition temperature of the thermoplastic resin. In order to bring the resin into close contact with the cooling drum, it is preferable to use a method of contacting by electrostatic application, a method of contacting by wind pressure, a method of nipping the entire width or end portion, and a method of contacting at reduced pressure.

The thermoplastic resin sheet molded by the melt casting film forming method has a characteristic that the thickness direction retardation (Rt) is small, unlike the resin sheet molded by the solution casting film forming method, and thus requires a drawing condition different from that of the solution casting film forming method. There is also. In order to acquire desired optical property, depending on a case, both of extending | stretching of the advancing direction of a film, and extending | stretching of a film width direction may be performed simultaneously or sequentially. Moreover, depending on a case, there may be only the case of extending | stretching of the film width direction. By this stretching operation, the molecules are oriented and the film is adjusted to the required retardation value.

Although the method of extending | stretching does not have a restriction | limiting in particular, A well-known pin tenter, a clip-type tenter, etc. can be used preferably. Although the extending | stretching direction may be an arbitrary direction (tilting direction) also in a width direction also in a longitudinal direction, since lamination | stacking with a polarizing film can be made into a roll form by making a extending direction into a width direction, it is preferable. By extending | stretching in the width direction, the slow axis of the optical film which consists of thermoplastic resin films becomes a width direction. In addition, the transmission axis of a polarizing film is also the width direction normally. A favorable viewing angle is obtained by assembling a polarizing plate laminated so that the transmission axis of the polarizing film and the slow axis of the optical film are parallel to the liquid crystal display device.

The stretching conditions may be selected in temperature and magnification so that desired retardation characteristics are obtained. Usually, the draw ratio is 1.1 to 2.0 times, preferably 1.2 to 1.5 times, and the draw temperature is usually the glass transition temperature (Tg) -50 ° C. to Tg + 50 ° C., preferably Tg−, of the resin constituting the sheet. It is performed in the temperature range of 40 degreeC-Tg + 40 degreeC. If the draw ratio is too small, the desired retardation may not be obtained. On the contrary, if the draw ratio is too large, it may break. When extending | stretching temperature is too low, it breaks and when too high, desired retardation may not be obtained.

When the retardation of the thermoplastic resin film produced by the above method is corrected to a value for a purpose, the film may be stretched or shrunk in the longitudinal direction or the width direction. In order to shrink | contract in the longitudinal direction, there exists a method of shrinking a film, for example, by making width | variety stretch out temporarily and relaxing in the longitudinal direction, or gradually narrowing the space | interval of the clip which a transverse stretching machine adjoins. The latter method can be performed by using a general simultaneous biaxial stretching machine to smoothly narrow the gap between clips adjacent in the longitudinal direction, for example, by driving the clip portion in a pantograph method or a linear drive method.

In some cases, a heat treatment zone is provided for the purpose of correcting planarity and improving dimensional stability from stretching to winding. For example, the area | region which keeps it to the temperature of glass transition temperature (Tg) -30 degreeC-Tg of resin which comprises a sheet for several tens of seconds-several tens of minutes may be provided, and the area which conveys between rolls arrange | positioned by zigzag may be provided.

Although the film thickness of an optical film differs according to a use purpose, as a completed film, the film thickness range used by this invention is 30-200 micrometers, Considering the recent tendency of thinning, the range of 40-120 micrometers is preferable, Especially the range of 40-100 micrometers is preferable. The film thickness can be adjusted by adjusting the extrusion flow rate, the die slit gap, the speed of the cooling drum, and the like so as to have a desired thickness. Further, as means for making the film thickness uniform, it is preferable to feed back the feedback information programmed using the film thickness detection means to the respective devices so as to adjust it.

In the thermoplastic resin film stretched in the width direction obtained as described above, molecules are oriented by stretching to have a constant retardation.

The manufacturing method of the optical film by this invention is a method of giving a so-called torsional force to the film conveyed in the film forming line of an optical film, and controlling an orientation angle, and performing axial adjustment of the appropriate temperature and the roll of a conveyance roll, That is, in the film formation of the optical film which consists of cellulose ester-type resin by a melt casting film forming method, after casting of molten resin and peeling of a film, the film temperature is in the range of the glass transition temperature (Tg) +/- 30 degreeC of this film. According to the plus and minus of the width average value of the orientation angle of the finished film, the arrangement direction of the roll axis of one or the plurality of conveying rolls is in the range of angles greater than 0 ° and 5 ° or less with respect to the direction perpendicular to the film conveying direction. To adjust.

In the case of a melt casting film forming method, it is preferable that film temperature is the range of the glass transition point +/- 30 degreeC of a film. If the film temperature is too low, the effect of the correction of the orientation angle is small, and if the film temperature is too high, wrinkles are formed in the film when the arrangement direction of the roll axis is changed.

In addition, the glass transition temperature (Tg) of a film means here the glass transition temperature (Tg) of the film composition containing resin, an additive, and a solvent which are main materials of a film.

The measurement of the glass transition temperature (Tg) can be measured using a commonly known thermomechanical analyzer (TMA), differential scanning calorimeter (DSC), differential thermal analyzer (DTA), dynamic viscoelasticity measuring device (DMA) and the like.

According to this invention, in the melt casting film forming method, the range of the film temperature during conveyance after peeling is appropriately selected and the roll axis of the conveying roll is adjusted to adjust the orientation angle distribution of the film with high accuracy without the problem of wrinkles or the like. It can achieve, and it can manufacture the optical film which has an excellent retardation compensation performance and a viewing angle enlargement function by which an orientation angle is uniform in the width direction (TD direction) over the substantially whole area | region of a film.

Moreover, in this invention, in the film formation of the optical film by the manufacturing method of any one of the above, the orientation angle of a film is measured online, and the installation direction of the roll axis of a conveyance roll is adjusted according to the result. .

According to the present invention, the orientation angle can be immediately adjusted based on the information while measuring the orientation angle in the film formation of the film online, and the productivity is excellent.

The optical film manufactured by the method of this invention can be made into an elliptical polarizing plate by bonding to at least one surface of a polarizing film.

The polarizing film is what is conventionally used, for example, the film which can be extended | stretched orientation like a polyvinyl alcohol film is processed by the dichroic dye like iodine, and is longitudinally stretched. Since the polarizing film itself does not have sufficient strength and durability, it is generally called a polarizing plate by adhering the cellulose triacetate film without anisotropy as a protective film on both surfaces.

A polarizing plate can also be manufactured by bonding the optical film which concerns on this invention to the said polarizing film, or bonding the optical film of this invention together with a polarizing film directly with a protective film.

Moreover, an elongate polarizing plate can be obtained by bonding the elongate polarizing film which extended | stretched in the longitudinal direction and processed the dichroic dye, and the long optical film of this invention. The polarizing plate easily adheres to a liquid crystal cell by peeling off a peelable sheet on one or both surfaces thereof through a pressure-sensitive adhesive layer (for example, an acrylic pressure-sensitive adhesive layer, etc.). Can be done).

Thus, the polarizing plate of this invention obtained can be used for various display apparatuses. In particular, a liquid crystal display device using a VA mode in which the liquid crystal molecules are substantially vertically aligned when no voltage is applied or a TN mode liquid crystal cell in which the liquid crystal molecules are substantially horizontally twisted and aligned is not applied.

Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these.

<Examples 1-9, Comparative Examples 1-8>

By the method of this invention, the optical film which consists of cellulose acetate propionate resin by the solution casting film forming method was manufactured.

(Production of dope)

First, the dope of cellulose acetate propionate was manufactured as follows.

 100 parts by mass of cellulose acetate propionate

(Acetyl group substitution degree 1.95, propionyl group substitution degree 0.7)

10 parts by mass of triphenylphosphate

2 parts by mass of ethyl phthalyl ethyl glycolate

Tinuvin 326 (Ciba Specialty Chemical Co., Ltd.) 1 part by mass

0.1 part of aerosil 200V (made by Nippon Aerosil company)

300 parts by mass of methylene chloride

40 parts by mass of ethanol

The above materials were sequentially placed in a sealed container, the temperature in the container was raised from 20 ° C to 80 ° C, and then stirred for 3 hours while the temperature was kept at 80 ° C to completely dissolve the cellulose acetate propionate. . Then, stirring was stopped and liquid temperature was lowered to 43 degreeC. This dope was filtered using filter paper (Azumiro-shi No. 244 from Azumiro Shigashi Co., Ltd.), and dope was obtained.

The dope prepared as mentioned above was cast | flow_spreaded on the 30 degreeC support body which consists of stainless steel endless belts through the casting | dye insulated at 30 degreeC, and finally, the amount of residual solvent in a web is 80 mass After drying on the support until it became%, the web was peeled from the support with a peeling roll.

Next, the web is dried in a roll conveying drying step in which the web is zigzag-shaped, then introduced into a stretching machine made of a tenter, the both ends of the web are inserted into a clip, and the film is stretched substantially in the width direction under conditions in which residual solvent is present. It was made to dry with moderate drying air.

Further, the web (film) was dried in a roll conveying drying step arranged in a zigzag shape, wound by a winder, and finally a cellulose acetate propionate film having a thickness of 60 µm was prepared.

In this embodiment, a heating chamber having a temperature of 60 ° C. is provided before the stretching machine, and two conveying rolls capable of adjusting the arranging angle of the roll shaft are provided therein, and the arranging angle of the roll shaft of each conveying roll is appropriately adjusted to provide cellulose acetate. The propionate film was stretched. Here, the arrangement | positioning angle of a roll axis is an angle shown by (phi) of FIG. 4, It is an angle measured in the direction which increases the conveyance direction of a film to 0 degree, and also in a system direction. The placement angle of the roll shaft of each conveyance roll was adjusted to 90 degrees -2 degrees, ie, 88 degrees, and the cellulose acetate propionate film was extended | stretched.

In Examples 1 to 9, the roll axis arrangement angle in the range of the present invention was set to 85 ° or more and less than 90 °, and the amount of residual solvent in the film was changed to 10 to 70%. In Comparative Examples 1 to 11, the roll axis arrangement angle and the amount of residual solvent were outside the scope of the present invention.

In this way, the orientation angle | corner of the produced | generated cellulose acetate propionate film was measured 5 points in the width direction with the measuring device Cobra-21ADH manufactured by Oji Corporation. The obtained results are shown in Table 1 below.

In addition, in Table 1, the uniformity of the orientation angle of the film was evaluated based on the following criteria.

A: The absolute value of an average orientation angle was 1.0 degrees or less, the difference of the maximum orientation angle and the minimum orientation angle was 1.5 degrees or less, the orientation angle characteristic was very excellent, and was very suitable as a retardation film and a viewing angle expansion film.

B: Although the absolute value of an average orientation angle is 1.0 degrees or less, the difference of a maximum orientation angle and a minimum orientation angle is 1.5 degrees or more, and although an orientation angle distribution is large, an average orientation angle is suppressed and is used sufficiently as a retardation film and a viewing angle expansion film. It was possible.

C: Although the absolute value of an average orientation angle is 1.0 degrees or more, although the difference of a maximum orientation angle and a minimum orientation angle is 1.5 degrees or less, and an average orientation angle is large, distribution of orientation angle is suppressed and it is practically as a retardation film or a viewing angle expansion film. It was available.

D: The absolute value of the average orientation angle was 1.0 degrees or more, the difference between the maximum orientation angle and the minimum orientation angle was 1.5 degrees or more, and the average orientation angle and orientation angle distribution were large, and it was difficult to use it as a retardation film or a viewing angle expansion film. .

E: Wrinkles generate | occur | produced at the time of manufacture, the orientation angle measurement is impossible, and the film obtained as a result was not usable as a retardation film or a viewing angle expansion film.

Table 1 shows the measurement results of the orientation angles of the resulting films and the evaluation results.

From the results of Table 1, in Examples 1 to 9 of the present invention, in the film formation of the optical film made of cellulose acetate propionate resin by the solution casting film forming method, the amount of residual solvent in the film is within the specific range of the present invention, By adjusting and extending the installation angle of the roll axis | shaft of the conveyance roll in the heating room of temperature, it was able to achieve the film which has the outstanding orientation angle characteristic by extending | stretching in the specificity of this invention. The optical film which consists of cellulose acetate propionate resin obtained in this way was especially usable as a retardation film or a viewing angle expansion film.

On the other hand, the cellulose acetate propione by Comparative Examples 1-4 which set the residual solvent amount at the time of extending | stretching a cellulose acetate propionate film, and the installation angle of the roll axis of the conveyance roll in the heating chamber of a specific temperature, respectively, out of the scope of the present invention. The uniform film was not able to obtain a uniform distribution of the film orientation angle, and could not be used as a retardation film or a viewing angle expanding film.

Examples 1-9 and Comparative Examples 1-8, as can be seen in Comparative Example 1, when the arrangement angle φ of the roll axis is set to the right angle (90 °) in the film conveyance direction similar to the prior art, the orientation angle When an average value is positive (+1.8 degree) and the arrangement direction (phi) of a roll axis is made smaller than 90 degree, the result of a favorable orientation angle is an example obtained. On the other hand, when the arrangement angle phi of a roll axis is 90 degrees, and the average value of an orientation angle is negative, the favorable result is similarly obtained even if the arrangement angle phi of a roll axis is changed more than 90 degreeC. Similar results were obtained also when other resins, polycarbonates, cycloolefins, polyimides, and the like were used.

<Examples 10-18, Comparative Examples 9-16>

By the method of this invention, the optical film which consists of cellulose acetate propionate resin by the melt casting film forming method was manufactured.

100 parts by mass of cellulose acetate propionate

(Acetyl group substitution degree 1.95, propionyl group substitution degree 0.7, glass transition temperature: about 170 degreeC)

Plasticizer: 10 parts by mass of dibutyl phthalate

Antioxidant: 0.07 parts by mass of 2,6-di-t-butyl-p-cresol

Tinuvin 326 (Ciba Specialty Chemical Co., Ltd.) 1 part by mass

0.1 part of aerosil 200V (made by Nippon Aerosil company)

The mixture of materials containing the cellulose acetate propionate resin described above is melt mixed at 240 ° C using a twin screw extruder, filtered through a metal filter, and then extruded into a film (sheet form) from the T die with a gear pump, The film-like resin was solidified while being brought into close contact with the cooling drum at 130 ° C., and the film was peeled off with a peeling roll. The film was stretched with an overheated stretching machine at 140 ° C. to produce a film. The heating chamber was provided in front of the drawing machine, and the conveyance rolls which can adjust the arrangement | positioning angle of a roll shaft were provided there. The atmosphere temperature of this heating chamber is set to 105 degreeC-175 degreeC with respect to the glass transition temperature (Tg: about 140 degreeC) of a cellulose acetate propionate resin film, and the arrangement | positioning angle of the roll axis of each conveyance roll is 90 degrees-96 degrees It changed in the range of, and measured and evaluated similarly to Examples 1-9 and Comparative Examples 1-8.

Thus, the orientation angle of the obtained cellulose acetate propionate resin film was measured similarly to the case of the said Example 1, and the obtained result is shown in following Table 2.

In Examples 10-18 of this invention from the result of Table 2, in film forming of the optical film which consists of cellulose acetate propionate resin by the melt casting film forming method, after casting of molten resin and peeling of a film, the film temperature was seen. It was able to achieve the film which has the outstanding orientation angle characteristic by adjusting in the specific range of this invention and extending | stretching the installation angle of the roll axis of the conveyance roll in the heating chamber of a specific temperature in the specific range of invention. The optical film which consists of cellulose acetate propionate resin obtained in this way was especially usable as a retardation film or a viewing angle expansion film.

In Examples 10 to 18, the film formation by melt casting method of cellulose acetate propionate resin was exemplified. Any of resins having a melting point can be used, and similarly good results were obtained by selecting the temperature range of the present invention for the glass transition temperature of each raw material.

<Example 19, Comparative Example 17>

Means for measuring the retardation of the film in the line after winding of the tenter stretching machine, but an optical film made of a cellulose acetate propionate resin by a solution casting film forming method in the same manner as in Comparative Example 1 KOBLY-WI) manufactured by KK Corporation was installed, and the phase difference of the film during conveyance was measured online.

In Example 19, 100 film rolls were produced over three days while changing the arrangement direction of the roll axis based on the orientation angle of the film measured online. In the comparative example 17, 100 film rolls were similarly manufactured in the state in which the arrangement direction of the roll shaft was fixed at 90 degrees similarly to the comparative example 1. The uniformity of the said orientation angle was evaluated using the film manufactured in this way.

As a result, in evaluation of 100 film rolls, Example 19 was A = 98%, B = 2%, and C = D = E = 0%. In contrast, Comparative Example 17 was A = B = 0%, C = 3%, D = 97%, and E = 0%. In the examples of the present invention, very good yield was obtained.

In the manufacturing method of the optical film of Claim 1 of this invention, according to the orientation angle of the completed film, the arrangement direction of the roll axis of one or some conveyance rolls in a film forming line is 0 with respect to the direction perpendicular | vertical to a film conveyance direction. By the manufacturing method of the optical film characterized by adjusting to the angle range larger than ° and 5 degrees or less, the above-mentioned problem of the prior art is solved, and the orientation angle is over the whole area | region of a film in the width direction (TD direction). It is possible to provide a method for producing an optical film having a uniform and excellent retardation compensation performance and a viewing angle enlargement function.

Invention of the manufacturing method of the optical film of Claim 2 of this invention is a method of providing a so-called torsional force to the film conveyed in the film forming line of an optical film, and controlling an orientation angle. In the film forming of the optical film which consists of a cellulose-ester type resin film by the solution casting film forming method, ie, adjusting the roll axis of a conveyance roll by selecting the range of solvent amount and atmospheric drying temperature suitably, the amount of residual solvent in a film is 10 It is the range of -70 mass%, and the placement direction of the roll axis of one or several conveyance rolls is larger than 0 degree with respect to the direction perpendicular | vertical to a film conveyance direction according to the plus minus of the width average value of the orientation angle of a completed film. By adjusting to an angle range of 5 ° or less, the orientation angle distribution of the film with the desired precision can be achieved without the problem of wrinkles or the like. Well, there is the effect that the alignment over the substantially entire region of each of the film width direction (TD direction) to be uniform, producing an optical film having excellent performance, and wide viewing angle compensation retardation function.

Next, the invention of the manufacturing method of the optical film of Claim 3 is a method of applying a so-called torsional force to the film conveyed in the film forming line of an optical film similarly, and controlling an orientation angle. In film formation of film, the film temperature after casting of molten resin and peeling of film is in the range of glass transition temperature (Tg) ± 30 ° C. of this film, and according to plus minus of width average value of orientation angle of finished film Or it exhibits the effect that a highly accurate orientation angle distribution can be achieved by adjusting the arrangement direction of the roll axis of several conveyance roll to the angle range larger than 0 degree and 5 degrees or less with respect to the direction perpendicular | vertical to a film conveyance direction.

Moreover, invention of Claim 4 is a manufacturing method of the optical film as described in any one of said Claims 1-3, In film forming of an optical film, the orientation angle of a film is measured online and according to the result of a conveyance roll By adjusting the installation direction of the roll axis, the orientation angle can be immediately adjusted based on the information while measuring the orientation angle during film formation of the film online, thereby exhibiting an effect of excellent productivity.

Claims (4)

At the time of film formation of an optical film, the arrangement direction of the roll axis of one or some conveyance rolls of a film forming line is larger than 0 degree with respect to the direction perpendicular to a film conveyance direction, and is 5 degrees or less according to the orientation angle of the completed optical film. It adjusts to an angle range, The manufacturing method of the optical film characterized by the above-mentioned. The film forming of the optical film is carried out by a solution casting film forming method, the amount of residual solvent in the film is in the range of 10 to 70% by mass, and according to the plus and minus of the width average value of the alignment angle of the completed optical film. The manufacturing direction of the optical film characterized by adjusting the arrangement direction of the roll axis of one or several conveyance rolls to the angle range larger than 0 degree and 5 degrees or less with respect to the direction perpendicular | vertical to a film conveyance direction. The film forming of the optical film is carried out by a melt casting film forming method, the film temperature after casting of the molten resin and peeling of the film is in the range of the glass transition temperature (Tg) ± 30 ° C. of the film. According to the plus and minus of the width average value of the orientation angle of the optical film which were made, the arrangement direction of the roll axis of one or several conveyance rolls is adjusted to the angle range which is larger than 0 degree and 5 degrees or less with respect to the direction perpendicular | vertical to a film conveyance direction. The manufacturing method of the optical film characterized by the above-mentioned. The manufacturing method of the said optical film WHEREIN: The orientation angle of the optical film completed online is measured and the installation direction of the roll axis of a conveyance roll is adjusted according to the plus and minus of the average value in any one of Claims 1-3. The manufacturing method of the optical film characterized by the above-mentioned.

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