JP5585161B2 - Method for producing cellulose acylate film, laminated cellulose acylate film, polarizing plate and liquid crystal display device - Google Patents

Description

  The present invention relates to a method for producing a cellulose acylate film used for a protective film constituting a polarizing plate used in a liquid crystal display device, a cellulose acylate film, a polarizing plate, and a liquid crystal display device.

  A liquid crystal display device is widely used as an image display device because of its advantages such as low power consumption and space saving.

  In recent years, with improvement in image quality, enlargement, generalization, and expansion of places where it is used, improvements in durability, display function, and visual recognition function are required.

  The improvement of such functions is also required for the protective film for polarizing plates constituting the polarizing plate used in the display device, and in particular, it is made of a long length to cope with the contrast, durability, and large screen in visibility. Membrane properties are required.

  On the other hand, cellulose ester films are widely used in optical applications such as polarizing plate protective films and optical compensation films because they are excellent in transparency and can produce films having controlled refractive index anisotropy.

  And as a cellulose-ester film used for an optical use, what contained the specific plasticizer of Unexamined-Japanese-Patent No. 2007-56102 as an additive in a film, for example, and improved water resistance is known.

  Furthermore, a cellulose acylate layer having a specific degree of acyl group substitution was laminated to prevent deterioration in quality due to the additive, to provide adhesion with a hydrophilic material such as a polarizer, and to have excellent optical properties. A film is known (see Patent Documents 1 and 2).

  However, these cellulose acylate films are also insufficient to simultaneously satisfy the above-described contrast properties, durability, and long film-forming properties for accommodating a large screen.

JP 2004-268281 A JP 2004-284335 A

An object of the present invention is to provide a cellulose acylate film that provides a polarizing plate that is excellent in long film-forming properties and is excellent in durability and contrast, a manufacturing method for manufacturing the same, a polarizing plate, and a liquid crystal display device using the same. lies in further excellent productivity, good long film formability and durability, producing a cellulose acylate film to give a polarizing plate having excellent contrast properties, is to provide a method for producing a cellulose acylate film .

  The above object of the present invention is achieved by the following means.

1. Cellulose acylate layer A having an average acyl group substitution degree of 2.7 or less, and an average acyl group adjacent to both sides of the cellulose acylate layer A and larger than the average acyl group substitution degree of the cellulose acylate layer A A method for producing a cellulose acylate film, comprising producing a laminated cellulose acylate film having a laminate having a three-layer structure comprising a cellulose acylate layer B having a substitution degree,
A step (1) of preparing a solution 1 containing a cellulose acetate resin a having an acyl group substitution degree of 2.7 or less;
The degree of acyl group substitution is 2. so that the average degree of acyl group substitution of cellulose acetate resin b having a degree of acyl group substitution greater than 2.8 and cellulose acylate layer B is greater than 2.7. A step (2) of preparing a solution 2 containing cellulose acetate resin b and cellulose acetate resin d by mixing cellulose acetate resin d that is 7 or less,
The solution 1 and the solution 2 are co-cast , the cellulose acylate layer A has a dry film thickness in the range of 51 to 90 μm, and the cellulose acylate layer B has a dry film thickness of 0.5 to A step (3) of producing the laminated cellulose acylate film so as to be within a range of 10 μm ;
A method for producing a cellulose acylate film, comprising:

2. A ratio P (cellulose acetate resin d / cellulose acetate resin b (mass ratio)) of the content of the cellulose acetate resin d and the content of the cellulose acetate resin b in the solution 2 is 0.01 to 0.4. 2. The method for producing a cellulose acylate film as described in 1 above, wherein

3. Wherein step (2) has a step of the acyl substitution degree of mixing a cellulose acetate resin b is greater than 2.8, and a cellulose acetate resin c containing cellulose acetate resins b and cellulose acetate resin d, 3. The method for producing a cellulose acylate film as described in 1 or 2 above.

4). 4. The cellulose acylate film according to any one of 1 to 3, wherein the cellulose acetate resin c has the same acyl group substitution degree as the average acyl group substitution degree of the laminated cellulose acylate film. Production method.

5. 5. The method for producing a cellulose acylate film according to any one of 3 and 4, wherein the cellulose acetate resin c is the laminated cellulose acylate film.

6). 6. The method for producing a cellulose acylate film as described in 5 above, wherein the cellulose acetate resin c is a crushed product obtained by crushing the laminated cellulose acylate film.

7). The cellulose according to any one of 1 to 6, wherein a difference between an average acyl group substitution degree of the cellulose acylate layer A and an acyl group substitution degree of the cellulose acetate resin b is 0.25 or more. A method for producing an acylate film.

  8). 8. The method for producing a cellulose acylate film according to any one of 1 to 7, wherein the cellulose acylate layer A has an average acyl group substitution degree of 2.5 or less.

9 . 9. A laminated cellulose acylate film produced by the method for producing a cellulose acylate film according to any one of 1 to 8 above.

10 . 10. A polarizing plate comprising the laminated cellulose acylate film as described in 9 above and a polarizing film.

11 . A liquid crystal display device comprising the polarizing plate described in 10 above.

12 . Cellulose acylate layer A containing cellulose acetate having an average acyl group substitution degree of 2.7 or less, and adjacent to both sides of cellulose acylate layer A and larger than the average acyl group substitution degree of cellulose acylate layer A A cellulose acylate film having a laminate composed of a three-layer structure with a cellulose acylate layer B having an average acyl group substitution degree, wherein the cellulose acylate layer B has an acyl group substitution degree of 2.8. cellulose acetate resin b is larger, acyl group substitution degree contains a cellulose acetate resin d is 2.7 or less, the cellulose acylate layer dry film thickness range and the cellulose of 51~90μm of a A laminated cellulose acylate film, wherein the dry film thickness of the acylate layer B is in the range of 0.5 to 10 μm .

13 . The cellulose acylate layer B is laminated according to the 12, characterized in that it contains a mixture of said cellulose acetate resin b, the cellulose acetate resin c containing the cellulose acetate resin b and the cellulose acetate resin d Cellulose acylate film.

  By the above means of the present invention, a laminated cellulose acylate film that provides a polarizing plate having excellent slipperiness and excellent long film-forming properties, and having good adhesion and excellent durability and contrast. , A production method for producing the same, a polarizing plate, a liquid crystal display device using the same, and a laminate that provides a polarizing plate having excellent productivity, excellent long film-forming properties, and excellent durability and contrast. The manufacturing method of a cellulose acylate film which manufactures a cellulose acylate film can be provided.

It is a schematic cross section which shows a part of example of the co-casting die used for co-casting.

The present invention comprises a cellulose acylate layers A Average acyl substitution degree is 2.7 or less, adjacent to both sides of the cellulose acylate layers A large than the average acyl substitution degree of the cellulose acylate layers A A cellulose acylate film production method for producing a laminated cellulose acylate film having a three-layer laminate comprising a cellulose acylate layer B having an average acyl group substitution degree, wherein the acyl group substitution degree is 2 preparing a solution 1 containing .7 or less cellulose acetate resin a (1), and cellulose acetate resin b is greater than the acyl substitution degree of 2.8, average acyl group of the cellulose acylate layer B degree of substitution, so that larger than 2.7, a mixture of a cellulose acetate resin d acyl substitution degree is 2.7 or less, the cell Over scan acetate resin b and preparing a solution 2 containing cellulose acetate resin d (2), and cast co-cast using the solution 1 and solution 2, dry thickness of the cellulose acylate layers A The step (3) of producing the laminated cellulose acylate film so that the dry film thickness of the cellulose acylate layer B is in the range of 0.5 to 10 μm. And

In the present invention, the specific cellulose acylate layer A (hereinafter also simply referred to as layer A) and the cellulose acylate layer B (hereinafter also simply referred to as layer B) are co-cast on both sides of the cellulose acylate layer A. It is possible to obtain a laminated cellulose acylate film that gives a polarizing plate that has excellent lubricity and long film-forming properties, and has good adhesion and excellent durability and contrast. It is done.

  In the present invention, in particular, as the layer B, by using a mixture of the laminated cellulose acylate film of the present invention and a cellulose acylate having an acyl group substitution degree of greater than 2.7, the productivity is excellent and the long film formation And a method for producing a laminated cellulose acylate film that provides a polarizing plate having excellent durability and durability and contrast is obtained.

(Laminate)
A cellulose acylate layer A having an average acyl group substitution degree of 2.7 or less, and a cellulose acylate layer having an average acyl group substitution degree adjacent to both sides of the layer A and larger than the average acyl group substitution degree of the layer A The laminate composed of the rate layer B is produced by co-casting in the step (3) using the solutions 1 and 2 produced in the following steps (1) and (2).

The laminated cellulose acylate film of the present invention has the laminate according to the present invention, but may have a structure of three or more layers having a layer A on the side opposite to the layer B.

In this case, as the third layer, the cellulose acylate layers having the same composition as the layer B Ru Yes in (hereinafter sometimes referred to as layer D.).

In the case of three layers, layer B or the outermost layer on the side opposite to layer B can be brought into contact with a polarizer and used as a polarizing plate.

(Process (1))
In the step (1), a solution 1 containing a cellulose acetate resin a having an acyl group substitution degree of 2.7 or less, used for forming the cellulose acylate layer A having an average acyl group substitution degree of 2.7 or less. Prepare.

  The acyl group substitution degree and the average acyl group substitution degree referred to in the present invention refer to values measured according to ASTM-D817-96. The average acyl group substitution degree is a value obtained by measuring the entire object as a measurement object in the above measurement.

The cellulose acetate resin a having an acyl group substitution degree of 2.7 or less can be produced by a known method of saponifying cellulose triacetate to prepare the acyl group substitution degree.

The number average molecular weight of the cellulose acetate resin a having an acyl group substitution degree of 2.7 or less is preferably in the range of 60,000 to 300,000, and more preferably 70000 to 200,000.

  The number average molecular weight Mn of the cellulose ester can be measured using gel permeation chromatography (GPC), and the number average molecular weight is a value measured under the following measurement conditions.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three products manufactured by Showa Denko KK)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) Mw = 100000 to 500 calibration curves with 13 samples are used. Samples are used at approximately equal intervals.

  Although there is no limitation in particular as a cellulose which is a raw material of a cellulose acylate, Cotton linter, wood pulp, kenaf etc. can be mentioned. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

  The ester group forming the cellulose acylate is preferably a linear or branched carboxylic acid ester having about 2 to 22 carbon atoms, and these carboxylic acids may form a ring and are esters of aromatic carboxylic acids. However, lower fatty acid esters having 6 or less carbon atoms are preferably used.

  Examples of the solvent used for the solution 1 include a chlorine-based organic solvent such as methylene chloride (methylene chloride), an ester-based organic solvent such as methyl acetate, ethyl acetate, and ethyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1 , 4-dioxane, cyclohexanone, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3 3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol , Alcohols such as methanol and ethanol, and mixed solvents thereof.

  Among these, a mixed solvent of methylene chloride and alcohol is preferably used.

  As content of the cellulose acylate in the solution 1, 10-50 mass% is preferable, Furthermore, 10-30 mass% is preferable.

  As a film thickness of the layer A formed using the solution 1, 1-100 micrometers is preferable and 5-70 micrometers is especially preferable.

(Process (2))
In the step (2), a solution 2 used for forming a cellulose acylate layer B having an average acyl group substitution degree larger than the average acyl group substitution degree of the layer A is prepared.

Solution 2 is an acyl group substitution degree contains cellulose acetate resin b is greater than 2.8, and a cellulose acetate resin d acyl substitution degree is 2.7 or less.

Cellulose acetate resin b is a single material produced in one production line.

The content of the cellulose acetate resin d in the layer B is adjusted and contained so that the average acyl group substitution degree of the layer B is 2.7 or more. The adjustment is performed by calculating the average acyl group substitution degree when mixed from the acyl group substitution degree and the content of cellulose acetate resin b and cellulose acetate resin d.

Ratio P of content of cellulose acetate resin d and content of cellulose acetate resin b
(Cellulose acetate resin d / cellulose acetate resin b (mass ratio)) is preferably 0.01 to 0.4.

In step (2), cellulose acetate resin d and cellulose acetate resin b are mixed in a mixing step. As the mixing step, both of them may be mixed as solids, either one of them may be in a solution state, or both may be in a solution state. Thus, solution 2 is prepared.

In the mixing step, a mixture containing only the cellulose acetate resin d and a mixture containing only the cellulose acetate resin b may be mixed. In particular, the mixing step contains cellulose acetate resin b and cellulose. It is a preferable aspect from the aspect of adjusting the content and reusing the laminated cellulose acylate film, being a step of mixing the acetate resin b and the cellulose acetate resin c containing the cellulose acetate resin d. It is.

That is, in the present invention, it is a preferred embodiment to use the laminated cellulose acylate film of the present invention, particularly as the cellulose acetate resin c.

  That is, it is a preferred embodiment that the laminated cellulose acylate film is crushed as the cellulose acylate resin c and the crushed product is used as a so-called return material.

  In this case, by recovering and using the produced laminated cellulose acylate film, a production method that can be most utilized and has high productivity can be obtained.

In this case, the acyl group substitution degree of the cellulose acetate resin c is the same as the average acyl group substitution degree of the laminated cellulose acylate film, and the cellulose acetate resin a and the cellulose acetate resin d are the same.

  The average acyl group substitution degree of the laminated cellulose acylate film is a value measured by the method of measuring the acyl group substitution degree with the laminated cellulose acylate film itself as a measurement target.

  Also in the mixing step in this case, both of them may be mixed as solids, either one of them may be in a solution state, or both may be in a solution state.

The number average molecular weight of the cellulose acetate resin b is preferably in the range of 60000-300000, and more preferably 70000-200000.

In the present invention, by using a mixture of cellulose acetate resin b and cellulose acetate resin d as layer B in particular, a laminated cellulose acylate that provides a polarizing plate having good lubricity, excellent adhesion, and high contrast properties A film is obtained.

The reason why the above effect is obtained is not clear, but when co-casting using the solution 2 containing the mixture of the cellulose acetate resin b and the cellulose acetate resin d and the solution 1, the cellulose acetate resin in the layer B The content of b and cellulose acetate resin d becomes non-uniform, and when dried, the surface becomes uneven due to the non-uniformity of the surface, and the surface is roughened only with cellulose acylate. It is estimated that.

  According to the production method of the present invention, the surface roughness of the laminated acylate film can be obtained with an Ra value (arithmetic average roughness), a value defined in JIS, B601 (1994)) of 2.0 or more. . In the present invention, a laminated acylate film having a Ra value of 3.0 or more is a preferred embodiment.

The effect of the present invention is great when the difference between the average acyl group substitution degree of layer A and the acylation substitution degree of cellulose acetate resin b is 0.25 or more.

  Further, when the average acyl group substitution degree of the layer A is 2.5 or less, the effect becomes significant.

  As the solvent used in the solution 2, the same solvent as that used in the layer A can be used.

The total content of the cellulose acetate resin d and the cellulose acetate resin b in the solution 2 is preferably 10 to 50% by mass, and more preferably 10 to 30% by mass.

  As a film thickness of the layer B formed using the solution 2, 0.5-15 micrometers is preferable and 1-10 micrometers is especially preferable.

  Layer A and Layer B are known plasticizers and UV absorbers, light stabilizers, antioxidants, metal inert agents, radical chain inhibitors, peroxide decomposers, secondary amines, A degradation inhibitor such as a secondary amine may be contained.

(Process (3))
In the step (3), the solution 1 and the solution 2 are co-cast to produce a laminated cellulose acylate film. The laminated cellulose acylate film of the present invention may have a structure of three or more layers as described above, but an example of a three-layer structure (layer A, layer B and third layer D) will be described below. explain.

  FIG. 1 shows a part of an apparatus used for co-casting.

  The laminated cellulose acylate film in the present invention is obtained by laminating dopes (solution 1 and solution 2) by co-casting.

  As shown in the figure, the co-casting has a plurality of (three in FIG. 1) slits 13, 1, 15 in the base part 11 of the co-casting die 10, and is simultaneously formed on the metal support 16. A laminated cellulose acylate film having a configuration of layer A21 / layer B22 / layer D23 by casting solution 2 (17), solution 1 (18), and solution 3 (19) for forming layer D from the slits of A web 20 is formed.

  The laminated cellulose acylate film web 20 is then evaporated to form a film, which is peeled from the metal support 16 to form a laminated cellulose acylate film.

  The surface temperature of the metal support is preferably 10 to 55 ° C., and the temperature of the solution is preferably 25 to 60 ° C. Further, the temperature of each solution is preferably the same as or higher than the temperature of the support.

  Although the more preferable range of the temperature of a metal support body is dependent on the organic solvent to be used, it is 20-55 degreeC, and the more preferable range of solution temperature is 35-45 degreeC.

(Polarizer)
The laminated cellulose acylate film of the present invention can be used as various optical functional films, but is suitably used as a polarizing plate by being laminated with a polarizing film.

  The polarizing plate of the present invention is obtained by laminating the laminated cellulose acylate film of the present invention on at least one surface of a polarizer. The laminated cellulose acylate film of the present invention or another film is preferably laminated on the opposite surface of the polarizing film.

  As the polarizing film, for example, a polarizing film obtained by orienting a stretchable film containing a dichroic dye such as iodine to align the dichroic dye can be used.

  For example, the laminated cellulose acylate film of the present invention is bonded to at least one surface of a polarizing film (polarizer) produced by immersing and stretching a polyvinyl alcohol film in an iodine solution, and then polarized. A plate can be made.

  After laminating the polarizing film and the laminated cellulose acylate film of the present invention, a stretching treatment may be further performed.

<Liquid crystal display device>
Although the polarizing plate of this invention can be utilized for various display apparatuses, it is used with a liquid crystal and is suitably used as a liquid crystal display apparatus.

  The liquid crystal display device is not particularly limited, and a known liquid crystal display device can be used, and includes the polarizing plate and the liquid crystal layer of the present invention. Moreover, it is preferable to have the structure by which the board | substrate containing a liquid crystal is arrange | positioned between two polarizing plates.

  At least the polarizing plate of the present invention is preferably provided on the display side of the liquid crystal display device, and a clear hard coat layer, an antiglare layer, an antireflection layer and the like are preferably provided on the surface thereof.

  Hereinafter, the present embodiment will be described more specifically by way of examples, but the present invention is not limited to these examples. In addition, a part represents a mass part.

(Preparation of laminated cellulose acylate film 1)
(Preparation of solutions 11 and 21)
<Composition of Solution 11>
Cellulose acetate resin a1 (acyl group substitution degree 2.4) 100 parts Methylene chloride 314 parts Ethanol 56 parts <Composition of Solution 21>
Cellulose acetate resin b1 (acyl group substitution degree 2.9) 69 parts Cellulose acetate resin a1 (acyl group substitution degree 2.4) 20 parts Methylene chloride 314 parts Ethanol 56 parts A mixture having the above composition at 30 ° C. Dissolved and filtered to give solutions 11 and 21.

  Using the co-casting die shown in FIG. 1, using the solutions 11 and 21, the layer B1 using the solution 21, the layer A1 using the solution 11 and the layer D1 using the solution 21 are formed by the co-casting method. A three-layer laminated cellulose acylate film 1 was produced.

  That is, the solution 21 as the solution 2 (17) in FIG. 1, the solution 11 as the solution 1 (18) in FIG. 1, and the solution 3 (19) for forming the layer D in FIG. Using the solution 21, the temperature of each solution was set to 35 ° C., and cast on a stainless steel support so that the dry film thicknesses were layer B1, 3 μm, layer A1, 54 μm, and layer D1, 3 μm.

  After casting, the film was dried at 80 ° C. for 3 minutes, peeled, and further dried at 120 ° C. for 10 minutes to obtain a laminated cellulose acylate film 1.

(Preparation of laminated cellulose acylate film 2)
(Preparation of solutions 12 and 22)
<Composition of Solution 12>
Cellulose acetate resin a2 (acyl group substitution degree 2.4) 100 parts Methylene chloride 314 parts Ethanol 56 parts <Composition of Solution 22>
Cellulose acetate resin b2 (acyl group substitution degree 2.9) 69 parts Cellulose acetate resin a2 (acyl group substitution degree 2.4) 1 part 19.2 parts of the above laminated cellulose acylate film 1 (cellulose acetate resin c) Methylene chloride 314 Part Ethanol 56 parts The mixture having each of the above compositions was stirred and dissolved at 30 ° C and filtered to obtain solutions 12 and 22.

  Using the co-casting die shown in FIG. 1, using the solutions 12 and 22, the layer B2 using the solution 22, the layer A2 using the solution 12, and the layer D2 using the solution 22 are formed by the co-casting method. A laminated cellulose acylate film 2 having a three-layer structure was produced.

  That is, the solution 22 as the solution 2 (17) in FIG. 1, the solution 12 as the solution 1 (18) in FIG. 1, and the solution 3 (19) for forming the layer D in FIG. Using the solution 22, the temperature of each solution was set to 35 ° C., and cast on a stainless steel support so that the dry film thickness was layer B2, 3 μm, layer A2, 54 μm, layer D2, 3 μm.

  After casting, the film was dried at 80 ° C. for 3 minutes, peeled, and further dried at 120 ° C. for 10 minutes to obtain a laminated cellulose acylate film 2.

(Preparation of laminated cellulose acylate films 3-9)
In the production of the laminated cellulose acylate film 2, the ratio P of the content of the cellulose acetate resin a2 and the cellulose acetate resin b2 is shown in Table 1 by changing the amount of the laminated cellulose acylate film 1 in the solution 22. The laminated cellulose acylate films 3 to 9 were produced in the same manner as in the production of the laminated cellulose acylate film 2 except that the values were adjusted.

(Preparation of laminated cellulose acylate films 10 to 21)
In the production of the laminated cellulose acylate film 1, the acyl group substitution degree of the cellulose acetate resin b1 and the cellulose acetate resin a1 of the solution 12 is set to the values shown in Table 1, and the configuration shown in Table 1 is obtained. Otherwise, the laminated cellulose acylate films 10 to 21 were produced in the same manner as in the production of the laminated cellulose acylate film 1 described above.

(Production of laminated cellulose acylate films 22 to 25)
In the production of the laminated cellulose acylate film 2, the layer D is not provided (one slit of the die is not used), and the others are laminated cellulose having a two-layer configuration as shown in Table 1. Acylate films 22 to 25 were produced.

(Preparation of laminated cellulose acylate film 26)
In the production of the laminated cellulose acylate film 2, a laminated cellulose acylate film 26 was produced in the same manner as in the production of the laminated cellulose acylate film 2 except that the composition of the solution 22 was changed as follows.

Cellulose acetate resin b2 (acyl group substitution degree 2.9) 69 parts Cellulose acetate resin a2 (acyl group substitution degree 2.4) 10 parts Laminated cellulose acylate film 1 (cellulose acetate resin c) 10 parts Methylene chloride 314 parts Ethanol 56 parts The following evaluation was performed on the laminated cellulose acylate film.

[Evaluation]
(Dynamic friction coefficient (long film forming property))
As described below, the coefficient of dynamic friction was measured to evaluate the slipperiness, which was used as an indicator of long film-forming properties.

  The dynamic friction coefficient between the film surface and the back surface is cut out so that the front and back surfaces of the film are in contact with each other according to JIS-K-7125 (1987), a 200 g weight is placed, the sample moving speed is 100 mm / min, and the contact area is 80 mm × 200 mm. The weight is pulled horizontally under the conditions described above, the average load (F) while the weight is moving is measured, and the dynamic friction coefficient (μ) is obtained from the following equation. The smaller the dynamic friction coefficient, the less “squeaking” occurs. The dynamic friction coefficient is 0.80 or less in a practically favorable range.

Coefficient of dynamic friction (μ) = F (g) / Weight of weight (g)
(Surface roughness)
Further, the surface roughness Ra of the surface of the laminated cellulose acylate film was measured using a surface roughness measuring device HD3300 manufactured by WYKO.

(Durability of polarizing plate)
The layer D side of the laminated cellulose acylate film was immersed in a 2 mol / L NaOH aqueous solution at 60 ° C. for 90 seconds, then washed with normal temperature water, dried at 80 ° C., and each single-side saponified optical film was obtained. . Separately, 120 μm thick polyvinyl alcohol was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid, and a polarizing film was prepared that was stretched four times at 50 ° C. in the longitudinal direction. The polarizing film was prepared by bonding the saponified surface of the saponified optical film to one surface of the polarizing film with a fully saponified 5% by weight aqueous polyvinyl alcohol adhesive. In the case of the two-layer configuration, the layer A side and the polarizing film were bonded to form a polarizing plate.

  As described below, the degree of polarization change and film adhesion (adhesion between layer A and layer B) were evaluated and used as an index of durability of the polarizing plate.

For the polarizing plate produced by the above method, first, the parallel transmittance and the direct transmittance were measured, and the degree of polarization was calculated according to the following formula. After that, each polarizing plate was subjected to forced degradation for 1000 hours under the condition of 60 ° C. and 90%, and then the parallel transmittance and the direct transmittance were measured again, and the degree of polarization was calculated according to the following formula and evaluated according to the following rank. The amount of change in polarization degree was determined by the following formula.
Polarization degree change rate (%) = ((H ₀ −H ₉₀ ) / (H ₀ + H ₉₀ )) ^1/2 × 100
Polarization degree change = P ₀ −P ₁₀₀₀
H ₀ : Parallel transmittance H ₉₀ : Direct transmittance P ₀ : Polarization degree before forced deterioration P ₁₀₀₀ : Polarization degree after 1000 hours of forced deterioration ◎: Polarization degree change rate of less than 10% ○: Polarization degree change rate of 10% or more Less than 25% X: Polarization degree change rate of 25% or more.

(Film adhesion)
It was measured by sensory evaluation. ○ means that it is not peeled off when it is peeled off, × means that it is easily peeled off.

(Contrast)
The front contrast of the liquid crystal display device was evaluated as follows to evaluate the contrast. 1000 or more is a practically good range.

The measurement was performed after the backlight of each liquid crystal display device was lit continuously for one week in an environment of 23 ° C. and 55% RH. For measurement, EZ-Contrast 160D manufactured by ELDIM was used to measure the luminance from the normal direction of the display screen of white display and black display with a liquid crystal display device, and the ratio was defined as the front contrast.
Front contrast = (brightness of white display measured from normal direction of display device) / (brightness of black display measured from normal direction of display device)
The evaluation results are shown in the following table.

  From Table 2, the laminated cellulose acylate film of the present invention is a polarizing plate having excellent slipperiness, excellent long film forming properties, excellent adhesion, excellent durability, and excellent contrast. I understand that you give.

DESCRIPTION OF SYMBOLS 10 Co-casting die 11 Base part 13, 14, 15 Slit 16 Metal support 17 Solution 2
18 Solution 1
19 Solution 3
20 laminated cellulose acylate film web 21 layer A
22 Layer B
23 Layer D

Claims (13)

Cellulose acylate layer A having an average acyl group substitution degree of 2.7 or less, and an average acyl group adjacent to both sides of the cellulose acylate layer A and larger than the average acyl group substitution degree of the cellulose acylate layer A A method for producing a cellulose acylate film, comprising producing a laminated cellulose acylate film having a laminate having a three-layer structure comprising a cellulose acylate layer B having a substitution degree,
A step (1) of preparing a solution 1 containing a cellulose acetate resin a having an acyl group substitution degree of 2.7 or less;
The degree of acyl group substitution is 2. so that the average degree of acyl group substitution of cellulose acetate resin b having a degree of acyl group substitution greater than 2.8 and cellulose acylate layer B is greater than 2.7. A step (2) of preparing a solution 2 containing cellulose acetate resin b and cellulose acetate resin d by mixing cellulose acetate resin d that is 7 or less,
The solution 1 and the solution 2 are co-cast , the cellulose acylate layer A has a dry film thickness in the range of 51 to 90 μm, and the cellulose acylate layer B has a dry film thickness of 0.5 to A step (3) of producing the laminated cellulose acylate film so as to be within a range of 10 μm ;
A method for producing a cellulose acylate film, comprising: A ratio P (cellulose acetate resin d / cellulose acetate resin b (mass ratio)) of the content of the cellulose acetate resin d and the content of the cellulose acetate resin b in the solution 2 is 0.01 to 0.4. The method for producing a cellulose acylate film according to claim 1, wherein: Wherein step (2) has a step of the acyl substitution degree of mixing a cellulose acetate resin b is greater than 2.8, and a cellulose acetate resin c containing cellulose acetate resins b and cellulose acetate resin d, The method for producing a cellulose acylate film according to claim 1 or 2. The cellulose acylate film according to any one of claims 1 to 3, wherein an acyl group substitution degree of the cellulose acetate resin c is the same as an average acyl group substitution degree of the laminated cellulose acylate film. Manufacturing method. The said cellulose acetate resin c is the said laminated cellulose acylate film, The manufacturing method of the cellulose acylate film of any one of Claim 3 or 4 characterized by the above-mentioned. The method for producing a cellulose acylate film according to claim 5, wherein the cellulose acetate resin c is a crushed product obtained by pulverizing the laminated cellulose acylate film. 7. The difference between the average acyl group substitution degree of the cellulose acylate layer A and the acyl group substitution degree of the cellulose acetate resin b is 0.25 or more, 7. A method for producing a cellulose acylate film.   The method for producing a cellulose acylate film according to any one of claims 1 to 7, wherein an average acyl group substitution degree of the cellulose acylate layer A is 2.5 or less. A laminated cellulose acylate film produced by the method for producing a cellulose acylate film according to any one of claims 1 to 8 . A polarizing plate comprising the laminated cellulose acylate film according to claim 9 and a polarizing film. A liquid crystal display device comprising the polarizing plate according to claim 10 . Cellulose acylate layer A containing cellulose acetate having an average acyl group substitution degree of 2.7 or less, and adjacent to both sides of cellulose acylate layer A and larger than the average acyl group substitution degree of cellulose acylate layer A A cellulose acylate film having a laminate composed of a three-layer structure with a cellulose acylate layer B having an average acyl group substitution degree, wherein the cellulose acylate layer B has an acyl group substitution degree of 2.8. cellulose acetate resin b is larger, acyl group substitution degree contains a cellulose acetate resin d is 2.7 or less, the cellulose acylate layer dry film thickness range and the cellulose of 51~90μm of a A laminated cellulose acylate film, wherein the dry film thickness of the acylate layer B is in the range of 0.5 to 10 μm . The cellulose acylate layer B, and the cellulose acetate resin b, according to claim 12, characterized in that it contains a mixture of cellulose acetate resin c containing cellulose acetate resins b and the cellulose acetate resin d Laminated cellulose acylate film.

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