WO2007108189A1

WO2007108189A1 - Process for producing optical film, optical film and polarizing plate

Info

Publication number: WO2007108189A1
Application number: PCT/JP2006/325498
Authority: WO
Inventors: Masahiro Shibuya
Original assignee: Konica Minolta Opto, Inc.
Priority date: 2006-03-20
Filing date: 2006-12-21
Publication date: 2007-09-27

Abstract

A process for producing an optical film, in which even when inorganic microparticles are contained, mixing of cellulose ester insoluble matter into the film can be satisfactorily prevented to thereby enable effective prolongation of filter paper exchange cycle; an optical film produced by the process; and a polarizing plate making use of the optical film. There is provided a process for producing an optical film, comprising preparing a dope containing a cellulose ester and inorganic microparticles, filtering the same and forming the dope into an optical film according to a solution casting technique, wherein the filtration is carried out with the use of filter paper (X) of 10 sec/300 cc to 15 sec/300 cc air permeability and filter paper (Y) of 5 sec/300 cc to below 10 sec/300 cc air permeability.

Description

Specification

Optical film manufacturing method, optical film and polarizing plate

Technical field

The present invention relates to a method for producing an optical film, an optical film obtained by the method, and a polarizing plate using the optical film.

Background art

Conventionally, liquid crystal display devices (LCDs) can be directly connected to IC circuits with low voltage and low power consumption, and can also be reduced in thickness, so display in word processors, personal computers, etc. Widely used as a device. The basic structure of this LCD is to provide polarizing plates on both sides of the liquid crystal cell, and the performance of the LCD depends greatly on the performance of the polarizing plate. A polarizing plate consists of a polarizer and a protective film laminated on both sides of the polarizer. For example, cellulose ester films are widely used as protective films for such polarizing plates.

[0003] Such a cellulose ester film is generally produced by a solution casting method. This cellulose ester film is produced by mixing cellulose ester with a good solvent for cellulose ester such as methylene chloride and a poor solvent for cellulose ester such as methanol, ethanol, butanol or cyclohexane. A cellulose ester solution (hereinafter also referred to as a dope) is prepared by dissolving in a solvent and adding a plasticizer or an ultraviolet absorber to the endless metal having a mirror-finished surface. After the casting die force is uniformly cast on a support (for example, a belt or drum, hereinafter also referred to as a support), the solvent is evaporated on the support, and the dope film (hereinafter also referred to as a web) is solidified. Then, this is peeled off by a peeling roll, transferred by a transfer roll, and further dried by a drying device or a tenter. By drying, a cellulose ester film is obtained.

[0004] In recent years, liquid crystal display devices have been increasingly improved in image quality and definition. Along with this, there is an increasing demand for the reduction of foreign substances contained in the protective film for polarizing plates used in liquid crystal display devices. Cell used for protective film for polarizing plate Since rosester is a semi-synthetic polymer, it is strongly influenced by the quality of the starting material, not just the generation of unnecessary components due to the heterogeneous reaction in the esterification process. Therefore, it is more necessary to remove unnecessary components than general synthetic polymers.

[0005] Foreign substances detected from the cellulose ester film include those caused by the additive used, those caused by dust mixed in the manufacturing process, and unacetylated or low-vinegar contained in the cellulose ester. And the like due to the degree of cellulose ester fiber.

[0006] In order to reduce foreign matters in a film, it is known to perform filtration prior to subjecting the dope to a solution casting method, and various types of filters related to filtration of such dopes and filters used for the filtration are known. Proposals have been made.

[0007] For example, a technique is disclosed in which a dope is filtered and formed into a film using a filter paper having a drainage time of 20 seconds or more and a filtration pressure of 16 kgZcm ² or less (Patent Document 1).

Patent Document 1: JP 2000-204173 A

Disclosure of the invention

Problems to be solved by the invention

[0008] The filtration of the dope is generally performed at a constant speed from the viewpoint of continuous supply to the film production process by the solution casting method, but a filter paper having a relatively coarse mesh as in Patent Document 1 is used. Filter

The technology used has not been able to sufficiently prevent the entry of foreign matter into the film from the beginning when the foreign matter is not sufficiently captured. Also, the force that increases the filtration pressure as foreign matter is captured and accumulated on the filter paper. The force that trapped foreign matter passes through the filter paper due to the increased filtration pressure, and it is not sufficient to prevent foreign matter from entering the film. I got it. Therefore, it is necessary to replace the filter paper at a stage where the filtration pressure is relatively low. Therefore, it is necessary to replace the filter paper in a relatively short cycle. In the conventional filter paper, when the filtration pressure is higher, for example, 1500 kPa or more, the foreign matter trapped on the filter paper passes through the filter paper, and the foreign matter cannot be sufficiently prevented from entering the film.

[0009] Thus, the inventors of the present invention examined the use of a filter paper having relatively fine eyes, and found that the remaining low without remaining completely dissolved, especially in the dope among foreign substances. A new problem has arisen that insoluble matter such as cellulose ester having a low degree of vinegar begins to mix into the film relatively early. Therefore, the filter paper exchange cycle could not be extended sufficiently.

[0010] The problem that such cellulose ester insoluble matter is mixed in the film is particularly remarkable when inorganic fine particles such as sili- tide are contained and dispersed in the dope. That is, the organic fine particles are often used for the purpose of preventing blocking of the obtained film. However, when the inorganic fine particles were contained in the dope, the cellulose ester insoluble matter was significantly mixed into the film.

[0011] The present invention provides a method for producing an optical film, which can sufficiently prevent the cellulose ester insoluble matter from being mixed into the film even if inorganic fine particles are contained, and can effectively extend the filter paper replacement cycle. It is an object to provide an optical film obtained by the method and a polarizing plate using the optical film.

Means for solving the problem

[0012] The present invention is a method for producing an optical film by a solution casting method using the dope after filtering the dope containing cellulose ester and inorganic fine particles.

A method for producing an optical film, characterized by using a filter paper X having an air permeability of 10 seconds Z300cc or more and 15 seconds Z300cc or less and a filter paper Y having an air permeability of 5 seconds Z3 OOcc or more and less than 10 seconds Z300cc, and the method And an polarizing film using the optical film.

[0013] The present invention is also a method for producing an optical film by a solution casting method using a dope containing a cellulose ester and inorganic fine particles and then using the dope, wherein the filtration pressure is any of 1500 to 2000 kPa. The ratio of the number of insolubles in the dope immediately after filtration a to the number of insolubles in the dope immediately after filtration j8 (β, α) is 0.5 or less, and the number of insolubles The present invention relates to a method for producing an optical film, wherein j8 is 50 Z80 mm ² or less, an optical film obtained by the method, and a polarizing plate using the optical film.

[0014] The present invention is also a method for producing an optical film by a solution casting method using a dope containing a cellulose ester and inorganic fine particles and then filtering the dope. When the pressure is between 1500 and 2000 kPa, the ratio of the inorganic fine particle content P in the dope immediately after filtration to the inorganic fine particle content P in the dope immediately before filtration (P /

1 2 2

The present invention relates to a method for producing an optical film, wherein P) is 0.999 or more, an optical film obtained by the method, and a polarizing plate using the optical film.

The invention's effect

[0015] In the method for producing an optical film of the present invention, even if inorganic fine particles are contained in the dope, the cellulose ester insoluble matter can be sufficiently prevented from being mixed into the film for a long period of time. Therefore, the filter paper replacement cycle can be effectively extended. In the present invention, usually, even if filtration is continued for 9 days or more, the cellulose ester insoluble matter can be sufficiently prevented from being mixed into the film, and as a result, foreign matters can be effectively prevented from being mixed into the film.

BEST MODE FOR CARRYING OUT THE INVENTION

[0016] In the present invention, first, a dope containing a cellulose ester and inorganic fine particles is prepared. Specifically, a dope is prepared in which organic fine particles are dispersed in a cellulose ester solution in which cellulose ester is dissolved.

[0017] The cellulose ester is not particularly limited as long as it is a cellulose ester conventionally used in the field of optical films. For example, cellulose triacetate, cellulose diacetate, cenorelose acetate propionate, cenorelose acetate butyrate, or the like. Cellulose acetate propionate butyrate can be used, and cellulose triacetate, cenorelose diacetate, and cenorelose acetate propionate are preferred. You can use two or more cellulose esters in combination!

[0018] The cellulose used as a raw material for the cellulose ester is not particularly limited, and examples thereof include cotton linter, wood pulp (coniferous pulp, hardwood pulp), and kenaf. Further, the cellulose esters obtained from these can be mixed and used at an arbitrary ratio.

[0019] In the cellulose ester, when the acylating agent of the cellulose raw material is an acid anhydride (acetic anhydride, propionic anhydride, butyric anhydride), an organic solvent such as an organic acid such as acetic acid such as methylene chloride is used. Synthesize using a protic catalyst such as sulfuric acid. When the acylating agent is acid chloride (CH COCl, CH COCl, CH COCI), The reaction is carried out using such a basic compound. Specifically, it can be synthesized by the method described in JP-A-10-45804. The acyl group reacts with the hydroxyl group of the cellulose molecule. Cellulose molecules have the power of many glucose units connected, and the glucose unit has three hydroxyl groups. The number of substituted acyl groups at these three hydroxyl groups is called the degree of substitution. For example, cellulose triacetate has a acetyl group bonded to all three hydroxyl groups of a glucose unit.

[0020] The degree of substitution of the acyl group can be measured according to ASTM-D817-96.

[0021] Cellulose esters having a polymerization degree of 100 to 1000, particularly 250 to 400 are preferably used.

[0022] The cellulose ester is dissolved in a solvent or the like to form a dope. The solvent that can be used in the present invention is preferably a mixture of a good solvent and a poor solvent in view of production efficiency. The mixing ratio of good solvent to poor solvent is preferably 70 to 95% by mass for good solvent and 30 to 5% by mass for poor solvent. The concentration of the cellulose ester is 10 to 30 mass ^_0/0 preferably fixture 15 to 25 weight ^_0/0 and more preferred. The cellulose ester concentration is a ratio with respect to the whole dope.

[0023] The good solvent and the poor solvent as used in the present invention are defined as a good solvent if it dissolves the cellulose ester used alone, and a poor solvent if it does not dissolve or dissolve alone. Therefore, the good solvent and the poor solvent vary depending on the amount of bound acetic acid of the cellulose ester. For example, acetone becomes a good solvent when the amount of bound acetic acid is 55% and becomes a poor solvent when the amount of bound acetic acid is 60%. Good solvents used in the present invention include organic halogen compounds such as methylene chloride and dioxolans. The poor solvent used in the present invention is preferably, for example, methanol, ethanol, n-butanol, or cyclohexane. Of the solvents used, the solvent with the highest usage rate is called the main solvent.

[0024] A general method can be used as a method for dissolving the cellulose ester. For example, (1) a method in which a cellulose ester is dissolved in an organic solvent mainly composed of a good solvent for the cellulose ester while being stirred and stirred. And (2) A method in which cellulose ester is mixed with a poor solvent, moistened or swollen, further mixed with a good solvent and dissolved with stirring. In these methods, the cellulose ester is not completely dissolved, and some of the insoluble matter remains, and the filtration pressure is increased relatively early by capturing them in the filtration step described later. Therefore, in order to prevent the insoluble matter of cellulose ester from passing through, it is necessary to shorten the exchange cycle of the filter paper. However, in the present invention, it is necessary to use a dope prepared by such a method. Since it is possible to sufficiently prevent the dissolved material from passing through and to have a function of dissolving these insoluble materials during filtration, the filter paper replacement cycle can be effectively extended as a result.

[0025] The insoluble matter of cellulose ester is a cause of "bright spots" which are one of the defects recognized as foreign substances in the film. It is completely dissolved in a dope such as cellulose, undissolved product due to poor dissolution of cellulose ester, and is derived from cellulose ester.

[0026] The dissolution conditions include a method performed at normal pressure, a method performed below the boiling point of the main solvent, a high-temperature dissolution method performed under pressure above the boiling point of the main solvent, a cooling dissolution method performed by cooling, and a considerably high pressure. There are various methods such as a high-pressure dissolution method performed in the above, and any method may be adopted. Specifically, in the high-temperature dissolution method, heating is performed under pressure at a temperature not lower than the boiling point of the main solvent at room temperature and the main solvent does not boil, and dissolved while stirring. In the present invention, from the viewpoint of preparation cost, it is preferable to employ a method carried out at normal pressure or a method carried out below the boiling point of the main solvent. This is because even if such a method is employed, the object of the present invention can be effectively achieved.

[0027] As the inorganic fine particles contained and dispersed in the dope, those conventionally used as a matting agent contained in the film in the field of optical films can be used. As a specific example, for example, diacid salt Silicon (silica), titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum caate And magnesium silicate and calcium phosphate. Preferably, it is diacid key. There are no particular restrictions on the fine particles of nickel silicate, but examples include AEROSIL200, 200V, 300, R972, R972V, R972CF, R974, R202, R805, R812, 0X50, and TT600 manufactured by Aerosil Co., Ltd. Preferably, AEROSIL200, 200V, R972, R972V, R974, R202, R805, R812, etc. are used.

[0028] Inorganic fine particles having an average primary particle size of 10 to 50 nm, particularly 10 to 30 nm are preferably used. In the present specification, the average primary particle size refers to the average value of the lengths of the primary particles in the major axis direction at the observation location when the inorganic fine particles are observed with an electron microscope or an optical microscope. For details, take a photomicrograph and select any 100 primary particles. The major axis length of the selected primary particles is measured, the average value is obtained, and the average primary particle size is obtained.

[0030] The content of the inorganic fine particles as the object of the present invention is particularly limited as long as it is achieved rather than, for normal ί or Se Honoré loin Este Honoré [This 0.01 to 0.50 wt ^_0/0, Specially 0.05% to 0.30% by weight is preferred.

[0031] In the present invention, the dope is usually 10000 to 25000 mPa'sec at 40 ° C, particularly 1

It has a viscosity of 3000-22000 mPa 'sec.

[0032] In the present specification, the viscosity is a commercially available vibratory viscometer which is usually handled in the engineering industry.

(For example, Piscomate Series FVM—80A, FVM—80A—EX, FVM—80A—EXT

H: Measured by CBC Co., Ltd.), and converted to the measured value at 40 ° C.

[0033] In addition to the cellulose ester, the solvent, and the inorganic fine particles, the dope may contain additives such as a plasticizer and an ultraviolet absorber as necessary. The inorganic fine particles and the additive agent may be mixed with a solvent in advance and dissolved or dispersed, and then charged into a solvent before dissolving the cellulose ester or charged into the dope after dissolving the cellulose ester. In addition, the inorganic fine particles and the above-mentioned additives may be used simultaneously with the cell mouth ester, and using them at the same time is preferable from the viewpoint of preparation cost.

[0034] The plasticizer is not particularly limited, but in the phosphate ester type, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphosphate, trioctyl phosphate, tributyl phosphate. In the case of phthalates such as ferrate, jetyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethyl hexyl phthalate, etc. It is preferable to use butyl phthalyl butyl dallicolate, ethyl phthalyl ethyl dallicolate, methyl phthalyl ethyl glycolate, butyl phthalyl butyl dallicolate or the like alone or in combination. The above plasticizers may be used in combination of two or more as required. These are possible By containing a plasticizer, a film excellent in dimensional stability and water resistance can be obtained, which is particularly preferable.

[0035] The amount of additional force of the plasticizer is not particularly limited, and is usually 12% by weight or less based on the cellulose ester. When two or more plasticizers are used in combination, the total amount of these plasticizers may be within the above range.

[0036] As the ultraviolet absorber, one that has an excellent ability to absorb ultraviolet rays having a wavelength of 370 nm or less and absorbs as little visible light as possible has a wavelength of 40 Onm or more is preferably used. Specific examples include, but are not limited to, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like.

[0037] After the dope is prepared, the dope is filtered. Specifically, the dope is fed by a pressurizing pump through a pipe connected to a dope preparation tank (for example, a closed kettle) containing the prepared dope, and then filtered. In general, filtration is generally performed at a constant speed.

[0038] The filter paper used for filtration has an air permeability of 10 seconds Z300cc or more 15 seconds Z300cc or less, preferably 10.5 seconds Z300cc or more 14 seconds Z300cc or less (referred to as "filter X" in this specification). And air permeability of 5 seconds Z300cc or more and less than 10 seconds and less than Z300cc, preferably 6 seconds Z300cc or more and 9 seconds or less Z300cc or less (referred to as “filtration Y” in this specification). By using such a combination of filter paper X and filter paper cake, even if inorganic fine particles are contained, it is possible to sufficiently prevent the cellulose ester insoluble matter from being mixed into the film. As a result, it is possible to effectively prevent foreign matters from entering the film over a long period of time, and the filter paper replacement cycle can be sufficiently extended. Although the details of the phenomenon that the cellulose ester insoluble matter can be sufficiently prevented from being mixed into the film even if inorganic fine particles are contained by using filter paper X and filter paper 濾 in combination, the following mechanism is not clear. It is thought that it is based on. Cellulose ester insolubles are generally swollen in the solvent in the dope and are easily deformed, so that they easily pass through the filter paper when the filtration pressure increases. Therefore, when inorganic fine particles are contained in the dope, the cellulose ester insoluble matter forms aggregates with the inorganic fine particles and is easily captured by the filter paper. The pressure is higher. On the other hand, the cellulose ester insoluble matter is still easy to deform even if it forms aggregates with inorganic fine particles. As a result, as the filtration pressure increases, cellulose ester insoluble matter and aggregates of the insoluble matter and inorganic fine particles (hereinafter simply referred to as “cellulose ester insoluble matter, etc.”) are easier to filter. It is thought that mixing into the film becomes remarkable. However, when the filter paper X and the filter paper Y are used in combination in the present invention, the initial filtration pressure can be kept relatively low, so that the passage of filter paper insoluble matter trapped on the filter paper can be suppressed. However, the cellulose ester insoluble matter, etc. trapped on the filter paper is effectively exposed to the dope stream to promote the disintegration of the aggregates and the dissolution of the cellulose ester insoluble matter in the dope. Since the rise can be suppressed, the filtration pressure can be kept relatively low as a result. Therefore, since it is possible to prevent the cellulose ester insoluble matter from being mixed into the film for a long period of time, it can be considered that the filter paper replacement cycle can be extended more effectively.

[0039] Foreign substances are derived from impurities mixed in additives that are only insoluble in cellulose ester, dust mixed from outside, and small pieces mixed from materials such as manufacturing equipment such as melting pots and piping. It is meant to include what is to be done. This foreign material can be observed visually and is transparent or opaque in the film and recognized as an impurity.

[0040] When only the filter paper X is used in an overlapping manner and when the air permeability of the filter paper X is too high, the filtration pressure is relatively high from the beginning, so that cellulose ester insoluble matter and the like may be trapped on the filter paper and trapped. It passes relatively easily through the filter paper. When the filtration pressure is increased, the cellulose paper insoluble matter and the like pass through the filter paper. For this reason, mixing of insoluble cellulose ester into the film becomes a problem relatively early, and the filter paper replacement cycle cannot be extended sufficiently. When only filter paper Y is used in layers, and when air permeability force S of filter paper Y is too small, other foreign matters such as cellulose ester insoluble matter pass through the filter paper, so initial force of foreign matter on the film Mixing cannot be prevented sufficiently. In addition, even a slight increase in filtration pressure makes the passage of trapped foreign matter noticeable, and the contamination of foreign matter into the film becomes significant. For this reason, it is necessary to control the filtration pressure to be relatively low. Therefore, when the filtration is performed at a constant speed as well as the filtration efficiency is lowered, the filter paper is relatively short. V, need to be replaced in the cycle.

In the present invention, at least one filter paper X and one filter paper Y are used. Specifically, one or more, preferably 1 to 4 sheets of filter paper X and 1 or more, preferably 1 to 4 sheets of filter paper Y are used in an overlapping manner. When two or more filter papers X are used, the air permeability of the filter papers X may be the same or different as long as they are within the above-described air permeability range of the filter paper X. When two or more filter papers Y are used, the air permeability of the filter papers Y may be the same or different as long as they are within the air permeability range of the filter paper Y described above.

[0042] The total number of filter paper X and filter paper Y to be used is not particularly limited as long as the object of the present invention is achieved. From the standpoint of balance, usually 2 to 8 sheets, particularly 3 to 5 sheets are preferred.

[0043] The use ratio (XZY) of the filter paper X and the filter paper Y is 20Z80 to 80Z20, particularly 30 to 70 to 70, in terms of the number of sheets, from the viewpoint of more effectively preventing the cellulose ester insoluble matter from being mixed. preferable.

[0044] The stacking order of the filter paper X and the filter paper ridge is not particularly limited as long as the object of the present invention is achieved. For example, the filter paper X and the filter paper may be random or regular. From the viewpoints of effects, insoluble matter mixing prevention effect, filtration amount, filtration pressure, and filter life, the order of collection for each filter paper X or filter paper basket is preferable. That is, it is preferable to collect all the filter paper X on one of the upstream side or the downstream side in the dope flow direction and to collect all the filter paper cakes on the other side! /.

[0045] Collecting all the filter papers X on one of the upstream side and the downstream side means that all the filter papers X and the stacks of filter papers used in the stack are stacked upstream or downstream in the dope flow direction. Means that all filter papers X are placed adjacent to each other on one side

[0046] On the other hand, the collection of all the filter paper cocoons means that all the filter paper X used in the stack and the stack of filter paper cocoons are stacked on the upstream side or the downstream side where all the filter paper Xs are gathered. On the other hand, the other means that all the filter papers are placed adjacent to each other. Therefore, for example, when all the filter papers X are gathered upstream in the dope flow direction, all the filter paper bottles are gathered downstream. Also, for example, downstream in the dope flow direction When collecting all the filter papers X, collect all the filter papers Y upstream.

[0047] More preferably, all the filter papers X are gathered on the upstream side in the dope flow direction, and all the filter papers Y are gathered on the downstream side.

[0048] The air permeability of the filter paper is a characteristic value of the filter paper expressed by the time required to allow 300 ml of air to pass through the filter paper under a specific pressure and filtration area. Means clogged.

[0049] In this specification, values measured in accordance with air permeability ί and IS-P8117 (1998 edition) are used.

[0050] Filter paper X and filter paper Y are also one type selected from the group consisting of natural fibers such as wood pulp and cotton linter, regenerated fibers such as rayon, and synthetic fiber fibers such as polyester fibers. It is formed using more fibers as a raw material.

[0051] The average fiber diameter of the fibers forming the filter paper X and the filter paper Y and the thickness of the filter paper are not particularly limited as long as the filter paper and the filter paper Y have the above-described air permeability, respectively. Is preferably within the following range:

Filter paper X; average fiber diameter 7-15 / ζ πι; thickness 0.5-2mm;

Filter paper cake; average fiber diameter 10-20 111; thickness 0.5-2 mm.

[0052] The thickness is measured in accordance with JIS-P8118, and is measured when a certain load is applied.

[0053] Filter paper X and filter paper Y are commercially available.

[0054] As a commercial product of filter paper X, for example, high air permeability types such as KD03RE, KD03T, and KD03 made by Azumi filter paper can be used.

[0055] As a commercial product of filter paper Y, for example, low air permeability types such as KD03RE, KD03T, and KD03 made by Azumi filter paper can be used.

[0056] The present invention does not preclude the use of a filter paper other than the filter paper X and the filter paper Y as long as the object of the present invention is achieved.

[0057] In the present invention, since the increase in the filtration pressure is suppressed, the filtration pressure can be maintained at 2000 kPa or less, particularly 1800 kPa or less even if filtration is continued for 9 days or more at the filtration amount described below. Continuing to filter means to continue filtering without replacing the filter paper It is. When replacing the filter paper, when the filtration pressure reaches the above value, the filtration is temporarily stopped, the filter paper is replaced with a new one, and the filtration is resumed. In reality, it is difficult to precisely match the filter paper replacement timing when the filtration pressure reaches the above value. Therefore, in the present invention, the filtration pressure is within the range of 1500 to 2000 kPa. Pause and replace the filter paper. If the filter paper is exchanged when the filtration pressure is within such a range, the effects of the present invention can be fully enjoyed. In the present invention, the filtration pressure within the above range immediately before ending (temporarily stopping) the filtration for replacing the filter paper is referred to as the final pressure. If the end pressure is less than the above range, the replacement cycle is shortened. When the final pressure is larger than the above range, the cellulose ester insoluble matter or the like is significantly mixed into the film.

On the other hand, when filtration is performed using the above filter paper, the filtration pressure immediately after the start of filtration is usually 500 to 710 kPa, particularly 580 to 710 kPa. Such a filtration pressure immediately after the start of filtration is referred to as an initial pressure.

[0059] The filtration pressure is specifically the liquid feeding pressure on the filter press entering side, that is, the dope pressure that the filter paper receives on the surface of the dope preparation tank side, and can be measured by a commercially available pressure gauge that is normally handled in the engineering industry. It is.

[0060] Filtration is usually carried out at a filtration rate of 50-: LOOkgZ (at m ² '), and 60-90 kgZ (at m ² ').

[0061] The filtration amount is the dope treatment amount at the time of filtration, that is, the dope treatment amount per filtration area lm ^{2 on} which the filter paper performs the filtration treatment in one hour.

[0062] Although the filtration area is not particularly limited, it is usually 10 to L00m ² , particularly 20 to 20 from the viewpoint of supplying a continuously and smoothly filtered dope to the optical film production process described later.

It is set to 80m ^2.

[0063] The filtration temperature, that is, the dope temperature during filtration is not particularly limited. From the standpoint of dope solubility, liquid feedability, and film quality to be produced, it is usually set to 35 to 50 ° C, particularly 35 to 45 ° C. Such a dope filtration temperature is usually achieved in the dope preparation tank in the dope preparation process.

[0064] In the present invention, it is possible to sufficiently prevent other foreign matters from being mixed into the film with only the cellulose ester insoluble matter. That is, the filtration pressure is any value within the initial pressure range. A is the number of foreign substances in the film produced by the dope filter filtered at the time, and B is the number of foreign substances in the film produced by the dope force when the filtration pressure is any value within the above-mentioned final pressure range. B / A force when ↑ ^ 1.00 ~: L 50, especially 1.00 ~: L 40.

[0065] It is easy to know the filtration pressure when the dope constituting the film produced through the continuous line process is filtered based on the process speed after filtration, the change in filtration pressure with time, and the like. is there.

[0066] In the present invention, since the filtration is performed using the filter paper X and the filter paper Y, the residual ratio of the cellulose ester insoluble matter by filtration can be maintained for a long time while being relatively low. That is, even if the filtration pressure is any value between 1500 and 2000 kPa, the ratio of the number of insoluble matter β in the dope immediately after filtration to the number of insoluble matter a in the dope immediately before filtration (β / α) is 0. 5 or less, preferably an at 0.47 or less, yet insolubles number j8 50 or Z 80 mm ² or less, preferably 45 Z80mm ² below. At this time, the insoluble matter number α is preferably 100 pieces Z80mm ² or less, particularly 90 pieces Z80mm ² or less.

[0067] The number of insoluble substances in the dope immediately before filtration a and the number of insoluble substances in the dope immediately after filtration β are obtained by taking out the dope immediately before filtration and the dope immediately after filtration at a predetermined filtration pressure. The value measured on the basis of the number of bright spot foreign matter in the 80 μm thick film prepared from the above dope is used. In this way, the number of insoluble matters is measured based on the number of bright spot foreign matter, and aggregates of cellulose ester insoluble matter and inorganic fine particles can also be recognized as bright spot foreign matter. The numbers α and j8 include the number of aggregates of cellulose ester insoluble matter and inorganic fine particles.

[0068] Further, in the present invention, the filter paper X and the filter paper Y are used for the filtration as described above, so that the inorganic fine particles by the filter paper can be sufficiently prevented from being mixed into the film of cellulose ester insoluble matter as described above. Can be effectively avoided for a long time. In other words, even when the filtration pressure is any value between 1500 and 2000 kPa, the inorganic fine particle content P in the dope immediately after filtration relative to the inorganic fine particle content P in the dope immediately before filtration P

1 2 ratio (P

2

/ P) [approx. 0.999 or more, preferably ί or 0.995 or more.

[0069] The content of inorganic fine particles in the dope immediately before filtration and the content of inorganic fine particles in the dope immediately after filtration are the dough immediately before filtration and the dough immediately after filtration at a predetermined filtration pressure. It can be measured by taking out the substrate and measuring the content of inorganic fine particles in these dopes.

[0070] After filtration as described above in the present invention, further filtration may be performed.

That is, secondary filtration is performed after performing the above filtration as primary filtration.

[0071] The secondary filtration is performed for the purpose of further reducing foreign substances, and various general filters that are not particularly limited can be used as the filter material. In particular, polypropylene, Teflon ( A plastic filter such as a registered trademark or a metal filter such as stainless steel is preferable because the filter fiber does not fall off.

[0072] After the dope is filtered, an optical film is produced by a solution casting method. From the viewpoint of film production efficiency, the filtered dope is preferably sent continuously to the optical film production process by the solution casting method, but after standing in a stock tank and degassing. Then, send it to the optical film manufacturing process with a pressure pump through a pipe connected to the stock tank.

In the present invention, the optical film production process is not particularly limited, and may be an optical film production process employing a solution casting method generally employed in the field of optical films. For example, the dope is cast on a support (casting process), heated to remove part of the solvent (drying process on the support), then peeled off from the support, and the peeled film is dried (film drying). Step) to obtain an optical film. In the optical film manufacturing process, for example, U.S. Pat.Nos. 2,492,978, 2,739,070, 2,739,069, 2,492,977, 2,336,310 Nos. 2,367,603, 2,607,704, British Patents 64,071, 735,892, JP-B 45-9074, 49-4554, 49-5614 60-27562, 61-39890 and 62-4208 can be referred to for film formation.

[0074] As the support in the casting step, a support in which a belt-shaped or drum-shaped stainless steel is mirror-finished is preferably used. The temperature of the support in the casting process is in the general temperature range of 0 ° C to a temperature lower than the boiling point of the solvent, and the casting force is more effectively cast on the support at 0 ° C to 35 ° C. It is more preferable to cast it on a support of 5 to 35 ° C. because gelling can increase the peeling limit time. The peel time is transparent and flat This is the time during which the cast dope is on the support, with the limit of the casting speed at which a good film can be obtained continuously. A shorter stripping limit time is preferable because it is excellent in productivity.

[0075] In the drying process on the support, the dope is cast, once gelled, and when the time from casting to peeling is 100%, the dope temperature is 40 to 70 within 30% from casting. By setting the temperature to ° C, the evaporation of the solvent can be promoted, and it can be peeled off from the support as quickly as possible.Furthermore, since the peel strength is increased, the dope temperature should be within 55%, which is preferable. Is more preferable. It is preferable to maintain this temperature at 20% or more, more preferably 40% or more. For drying on the support, it is preferable that 80% to 120% is preferable because the strength of the support is peeled off when the residual solvent amount is 60 to 150% because the peel strength from the support becomes small. The temperature of the dope at the time of peeling is preferably 0 to 30 ° C. The base strength at the time of peeling can be increased, and the base breakage at the time of peeling can be prevented. The amount of residual solvent is indicated by the weight ratio of the residual solvent amount to the solid content.

[0076] In the film drying step, the film peeled off from the support is further dried, so that the residual solvent amount is 3% by mass or less, preferably 0.5% by mass or less. In the film drying process, generally, a roll suspension method or a pin tenter method is used for drying while transporting the film. For a liquid crystal display member, it is preferable to dry while maintaining the width by a pin tenter method in order to improve dimensional stability. In particular, it is particularly preferable to maintain the width where the amount of residual solvent is large immediately after peeling from the support, since the effect of improving the dimensional stability is more exhibited. The means for drying the film is not particularly limited, and is generally performed with hot air, infrared rays, a heating roll, microwaves or the like. It is preferable to carry out with hot air in terms of simplicity. The drying temperature is preferably in the range of 40 to 150 ° C and divided into 3 to 5 stages, and it is preferable to increase the temperature stepwise in order to improve dimensional stability. preferable.

[0077] The thickness of the optical film of the present invention is not particularly limited, but is preferably 10 to LOO / z m, more preferably 20 to 80 m, more preferably for a liquid crystal display member.

The optical film of the present invention is useful as a liquid crystal display member. What is a liquid crystal display member? A member used in a liquid crystal display device, for example, a protective film for a polarizing plate, a retardation plate, a reflector, a viewing angle improving film, an antiglare film, an antireflective film, and an antistatic film. Etc.

[0079] A polarizing plate can be produced by a general method using the optical film of the present invention. For example, there is a method in which an optical film (cellulose ester film) is treated with an alkali and bonded to both surfaces of a polarizing film produced by immersing and stretching in an iodine solution using a complete Ken-type polybulualcohol aqueous solution. Instead of the alkali treatment, a method for improving adhesiveness as described in JP-A-6-94915 and JP-A-6-118232 may be used. Example

[0080] Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples.

[0081] Example Z Comparative Example

A dope having the following component strength was prepared. Cellulose triacetate with a polymerization degree of 350 was used.

[0082] 100 parts by weight of senorelose triacetate

7 parts by weight of triphenolate phosphate

394 parts by weight of methylene chloride

34 parts by weight of ethanol

Silica (manufactured by Nippon Aerosil Co., Ltd., average primary particle size 16 nm) 0.07 parts by weight

Specifically, the above components were sequentially charged into a pressure-resistant sealed kettle, the temperature inside the kettle was raised to 40 ° C, and then stirred at 40 ° C for 4 hours to dissolve each component. Thereafter, the stirring was stopped, the dope temperature was lowered to 35 ° C., and immediately, the solution was continuously fed from a sealed kettle to a filter press as a filtration device through a pipe connected thereto. The viscosity of the dope was 15000 mPa 'sec in terms of 40 ° C.

A filter press having a filtration area force of 0 m ² was used, and this was loaded with filter paper (filter paper) having the configuration shown in Table 1 or Table 2. The filter papers were stacked in the order shown in the table so that the leftmost filter paper was oriented upstream in the dope flow direction and the rightmost filter paper was oriented downstream in the dope flow direction. 75k of dope prepared as above The primary filtration was performed at a constant speed with a filtration amount of gZ (m ² 'hour). The filtration pressure immediately after the start of the filtration was measured and shown in the table as the initial pressure. Thereafter, the dope was further filtered by passing it through a metal filter (NF-06D2; manufactured by Nippon Seisen Co., Ltd.) having a filtration area of 20 m ² .

The filtered dope was continuously subjected to a solution casting method to produce a film. Specifically, the filtered 35 ° C dope was cast on a 32 ° C stainless belt support using a belt casting apparatus. Thereafter, after drying on the support, the force film on the stainless steel band support was peeled off. At this time, the residual solvent amount of the film was 80%. After the support of the stainless steel band was peeled off, the film was dried in a drying zone maintained at 80 ° C for 15 minutes to produce a film with a film thickness of 80 / zm with a residual solvent amount of 0.15%.

•Implementation time

The continuous line process, such as dope preparation, dope filtration and film production ability, is carried out until the primary filtration pressure reaches the final pressure shown in Table 1 or Table 2, and the primary filtration pressure is changed from the initial pressure to the final pressure. The time to be evaluated.

[0083] Yes; 9.0 More than 0 days;

X; 5.0 days or more and less than 9.0 days, there were practical problems;

X X; 5. Less than 5.0 days.

-Number of undissolved dope (s, β)

When the primary filtration pressure was the final pressure, the dope immediately before the primary filtration and the dope immediately after the primary filtration were taken out, and the numbers of cellulose ester insolubles contained in these dopes (OC and β, respectively) were measured. Specifically, a separate film was prepared from each dope according to the following method, and the number of bright spot foreign materials attributed to insoluble matter was determined as a value per 80 mm ² of film.

[0084] (Method for producing film)

The corresponding dope collected from a specific part of the pipe was flowed on a flat plate, and it was formed into a film using a simple film forming apparatus having a blade with an appropriate gap. Remove the film from which the solvent has dried and become peelable from the flat plate, and place it in the drying frame Thereafter, the film was dried at 110 ° C. for 20 minutes to obtain a film having a thickness of 80 m.

[0085] (Measurement method of bright spot foreign matter)

Of the solid materials observed with a commercially available optical microscope, the average of the major axis and minor axis is 10 m or more, and the particles appear to be transparent when observed with transmitted light. The quantity of solid matter was measured as a bright spot foreign material and converted to a quantity per 80 mm ² .

[0086] Further, the film portion obtained from the first filtered dope through the continuous line process when the primary filtration pressure is the final pressure is traced, and the film portion is insoluble in the same manner as described above. The number of bright spot foreign materials caused by the above was determined as the value per 80 mm ² of film, and the number of insoluble materials as the “final” product was obtained.

[0087] Evaluation criteria for the number of insolubles as the "final" product are as follows.

[0088] 〇; 20 or less;

X; 21-50 (there was a problem in practical use);

X X; 51 or more.

• Number of foreign objects

The dope force filtered when the primary filtration pressure is the initial pressure Film part produced through the above continuous line process X

A, and film portion X produced through the above-mentioned continuous line process, which was filtered when the filtration pressure was the final pressure X

B was tracked and the number of foreign objects in these film portions was measured.

[0089] For details of the measurement of the foreign matter, the film portion X and the film portion X are visually observed.

A B

The film properties in the actual film manufacturing method are determined by calculating the average number of transparent or opaque foreign matters with a length of 20 μm or more in the longitudinal direction of the film as an average value per lm ^2. The performance of the filter paper was evaluated.

[0090] O; Average number of foreign bodies was less than 10;

X: The average value of the number of foreign matters is 10 or more and 20 or less, which is problematic in practical use;

X X: The average number of foreign bodies exceeded 20.

[0091] The number of foreign matter at the end of film part X relative to the average value A of the initial number of foreign substances at film part X

A B

The ratio of average value B was calculated and evaluated.

[0092] 〇; 1.00≤B / A≤1.50; X; 1. 50 <B / A ≤ 2.00 (There were practical problems);

X X; 2. 00 <B / A.

• Silica ratio (P / P)

twenty one

When the primary filtration pressure is the final pressure, the dope immediately before the primary filtration and the dope immediately after the primary filtration are taken out, the content of inorganic fine particles contained in these dopes (P and P respectively) is measured, and the silica ratio is obtained. It was. For details, separately from each dope according to the following method.

2

An film was prepared, and the content of inorganic fine particles contained in the film was measured by a silica quantitative analysis test to determine the silica ratio.

[0093] (Method for producing film)

A film was prepared in the same manner as the film preparation method in the measurement of the number of insoluble dope substances.

[0094] (Silica quantitative analysis test)

0.5 g of the sample was melted with alkali, prepared into a 50 ml aqueous solution, and measured by ICP-AES. I

CP—AES is an abbreviation for ICPZAES (Inductively Coupled Plasma Atomic Emission Spectrometer).

Elemental analysis can be carried out by a prescribed method to determine the content of inorganic fine particles contained in the film.

[0095] [Table 1]

§] [96

[0097] Filter paper xl: Rayon (average fiber diameter 10 m) 100% filter paper (thickness 1.6 mm, air permeability 10.

5 seconds Z300cc) is used.

[0098] Filter paper x2: Rayon (average fiber diameter 8 m) 100% filter paper (thickness 1.7 mm, air permeability 14.0 sec Z300cc) was used.

[0099] Filter paper x3: Use rayon (average fiber diameter 6 m) 100% filter paper (thickness 1.7 mm, air permeability 16.0 sec Z300cc).

[0100] Filter paper yl: Rayon (average fiber diameter 40 m) 100% filter paper (thickness 1.6 mm, air permeability 3.0) Second Z300cc).

[0101] Filter paper y2: Use rayon (average fiber diameter 30 m) 100% filter paper (thickness 1.6 mm, air permeability 6.0 sec Z300cc).

[0102] Filter paper y3: Use rayon (average fiber diameter 20 m) 100% filter paper (thickness 1.6 mm, air permeability 8.0 seconds Z300cc).

Industrial applicability

[0103] The method of the present invention is applied to an optical film such as a protective film for a polarizing plate, a retardation plate, a reflective plate, a viewing angle improving film, an antiglare film, an antireflective film, and an antistatic film used in a liquid crystal display device. Useful for manufacturing.

Claims

The scope of the claims

[1] A method of producing an optical film by a solution casting method using a dope containing cellulose ester and inorganic fine particles and then filtering the dope.

10 seconds Z300cc or more 15 seconds Z300cc or less filter paper X and air permeability 5 seconds Z300cc or more 1

0 seconds A method for producing an optical film, comprising using filter paper Y of less than Z300cc.

[2] The filter paper X and the filter paper Y are used at least one each, and the usage ratio (XZY) of the filter paper X and the filter paper Y is 20Z80 to 80Z20 in terms of the number of sheets.

2. A method for producing an optical film according to item 1.

[3] The filter paper X and the filter paper Υ are used in layers, and all the filter paper X is concentrated on one of the upstream side and the downstream side in the dope flow direction, and the other! The method for producing an optical film according to claim 2, wherein all the filter paper sheets are collected.

[4] The method for producing an optical film according to claim 3, wherein all the filter papers X are gathered upstream in the dope flow direction, and all the filter paper bottles are gathered downstream.

[5] A method for producing an optical film by a solution casting method using a dope containing cellulose ester and inorganic fine particles and then filtering the dope, wherein the filtration pressure is any value of 1500 to 2 OOOkPa. In some cases, the ratio of the insoluble matter number j8 in the dope immediately after filtration to the insoluble matter number α in the dope immediately before filtration (ι8 Ζ α) is 0.5 or less, and the insoluble matter number j8 is 50 Z80mm ² or less An optical film manufacturing method,

[6] A method for producing an optical film by a solution casting method using a dope containing cellulose ester and inorganic fine particles and then filtering the dope, wherein the filtration pressure is any value between 1500 and 2 OOOkPa. In some cases, the ratio (P / P) of the inorganic fine particle content P in the dope immediately after filtration to the inorganic fine particle content P in the dope immediately before filtration is 0.999.

1 2 2 1 or more, A method for producing an optical film.

[7] The method for producing an optical film according to any one of [1] to [6], wherein the filtration is started at a filtration pressure of 500 to 710 kPa.

[8] The filtration amount of the filtration is 50 to: LOOkgZ (in m ² ′).

8. The method for producing an optical film according to any one of items 1 to 7.

[9] The method for producing an optical film according to any one of claims 1 to 8, wherein the dope has a viscosity (40 ° C) of 10,000 to 25000 mPa'sec.

[10] The method for producing an optical film according to any one of [1] to [9], wherein a filtration temperature of the filtration is 35 to 50 ° C.

[11] When the filtration pressure of the filtration is any value between 500 and 710 kPa, the number of foreign substances in the film produced from the filtered dope is A, and when the filtration pressure is any value between 1500 and 2000 kPa. BZA is 1.

The method for producing an optical film according to any one of claims 1 to 10, wherein the optical film has a range of 00 to 1.50.

[12] An optical film obtained by the method for producing an optical film according to any one of claims 1 to 11.

[13] A polarizing plate using the optical film according to claim 12.