JP3994244B2 - Method for producing protective film for polarizing plate - Google Patents

Description

この表−１から判る通り、本発明になるフィルムはヘイズが低く、光学特性に優れており、かつ、輝点異物が少ない。従って、偏光板保護フィルムとして極めて好ましいことが判る。
【００４１】
【発明の効果】
本発明のフィルムは、ヘイズが低く、光学特性に優れており、かつ、輝点異物が少ない。
本発明の偏光板保護フィルムは、ヘイズが低く、光学特性に優れており、かつ、輝点異物が少ないことから、極めて優れたものである。
【図面の簡単な説明】
【図１】本発明になる偏光板の概略図
【符号の説明】
１ 偏光板保護フィルム
２ 偏光子
３ 偏光板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a protective film for a polarizing plate.
[0002]
[Prior art and problems to be solved by the invention]
Liquid crystal display devices (LCDs) can be directly connected to IC circuits with low voltage and low power consumption, and in particular, because they can be made thin, they are widely used as display devices for word processors and personal computers. Has been.
This LCD has a basic configuration in which, for example, polarizing plates are provided on both sides of a liquid crystal cell.
[0003]
By the way, the polarizing plate passes only light having a polarization plane in a certain direction. Therefore, the LCD plays an important role in visualizing the change in the alignment of the liquid crystal due to the electric field. That is, the performance of the LCD greatly depends on the performance of the polarizing plate.
A general structure of a polarizing plate is shown in FIG. In FIG. 1, reference numeral 1 denotes a polarizer, and a polarizing plate protective film 2 is laminated on both sides of the polarizer 1. The LCD is configured by laminating the polarizing plate having such a configuration on the liquid crystal cell.
[0004]
The polarizer is obtained by adsorbing and stretching iodine or the like on a polymer film. That is, a solution called H ink containing a dichroic substance (iodine) is wet-adsorbed on a polyvinyl alcohol film, and then the film is uniaxially stretched to orient the dichroic substance in one direction. It is.
The polarizing plate protective film is provided for the purpose of improving durability.
[0005]
Conventionally, as a polarizing plate protective film, cellulose resin, polycarbonate resin, polyarylate resin, polysulfone resin, polyethersulfone resin, norbornene resin, polystyrene resin, polyacrylate resin, polyester resin, and the like have been proposed.
In particular, cellulose triacetate is used.
[0006]
By the way, it has been found that the conventional cellulose triacetate film contains bright spot foreign matter.
With this bright spot foreign matter, a cellulose triacetate film is placed between two polarizers arranged in an orthogonal state (crossed Nicols), light is applied from the outside of one polarizer, and a microscope is used from the outside of the other polarizer. When observed, it is a foreign substance that appears to shine like a star shines with light leaking at the foreign part.
[0007]
Therefore, such a cellulose triacetate film in which many bright spot foreign substances are present is not preferable as a polarizing plate protective film.
Therefore, the first problem to be solved by the present invention is to provide a film with less bright spot foreign matter.
The second problem to be solved by the present invention is to provide a film suitable as a polarizing plate protective film having few bright spot foreign matters and excellent optical characteristics.
[0008]
[Means for Solving the Problems]
Cellulose triacetate film obtained by the solution casting method using a crushed product obtained by crushing the cellulose triacetate film (film formation) produced by the solution casting method as part of the raw material while intensively pursuing research on bright spot foreign matter It was found that the number of bright spot foreign matters was significantly reduced.
[0009]
In other words, although the investigation of the cause of the bright spot foreign matter is still in the state, a crushed product obtained by crushing a cellulose triacetate film formed by the solution casting method and a new cellulose triacetate are mixed and used as a raw material. In the cellulose triacetate film obtained by the solution casting method, it was found that the bright spot foreign matter was remarkably reduced.
[0010]
The present invention has been made based on this finding.
That is, the above-mentioned problem is: (A crushed product obtained by crushing a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method) / {(A lower fatty acid ester of cellulose produced by a solution casting method) A crushed product obtained by crushing a material as a main component) + (lower fatty acid ester of cellulose)} = 10 to 70 wt%,
A crushing step of crushing a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method;
A film production step of producing a film by a solution casting method using a crushed product obtained by the crushing step and a lower fatty acid ester of cellulose as a raw material,
The lower fatty acid ester of cellulose is cellulose triacetate
It is solved by the manufacturing method of the protective film for polarizing plates characterized by this.
[0011]
In particular, a crushed product obtained by crushing a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method and a lower fatty acid ester of cellulose (lower fatty acid ester of cellulose produced by a solution casting method) Crushed product obtained by pulverizing a material containing as a main component) / {(crushed product obtained by pulverizing a material mainly comprising a lower fatty acid ester of cellulose prepared by a solution casting method) + (lower fatty acid ester of cellulose)} = 10 to 70 wt% (preferably 20 wt% or more, more preferably 30 wt% or more, particularly preferably 40 wt% or more, preferably 60 wt% or less, more preferably 50 wt% or less), and this mixture is used as a raw material. This is solved by a film characterized by being produced by a solution casting method.
[0012]
In addition, the above-mentioned problem is that a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method is crushed, and the crushed product and a lower fatty acid ester of cellulose are used as raw materials to produce the solution by the solution casting method. This is solved by the method for producing a film.
In particular, a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method is crushed, and this crushed product and a lower fatty acid ester of cellulose are obtained (lower fatty acid of cellulose produced by a solution casting method). Crushed product obtained by crushing a material containing ester as a main component) / {(Crushed product obtained by crushing a material containing cellulose lower fatty acid ester as a main component produced by a solution casting method) + (lower fatty acid ester of cellulose)} = 10 to 70 wt% (preferably 20 wt% or more, more preferably 30 wt% or more, particularly preferably 40 wt% or more, preferably 60 wt% or less, more preferably 50 wt% or less), and this mixture is used as a raw material. And a film manufacturing method characterized by being produced by a solution casting method.
[0013]
The crushing of the material mainly composed of the lower fatty acid ester of cellulose produced by the solution casting method is preferably crushing using a fixed blade and a rotary blade. Moreover, it is preferable to crush using a fixed blade and a rotary blade after the vertical cutting with the vertical cutting blade.
The lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms, and cellulose acetate, cellulose propionate, cellulose butyrate and the like are preferable examples of the lower fatty acid ester of cellulose. In addition, mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate may be used. The most preferred lower fatty acid ester of cellulose is cellulose triacetate. In particular, cellulose triacetate having an acetylation degree of 59 to 62%.
[0014]
The film preferably has a haze value of 0.5% or less.
In addition, when only a crushed product obtained by crushing a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method is used as a raw material, and produced by the solution casting method using this as a raw material, that is, a new lower fatty acid of cellulose When no ester was used, the number of bright spot foreign matter was small, but the haze was high and the optical characteristics were further lowered, so that it could not be used as a film for optical applications.
[0015]
And the film of the said invention has few bright spot foreign materials, is excellent in an optical characteristic, and is very suitable as a polarizing plate protective film.
Therefore, the polarizing plate protective film composed of the film of the present invention and the polarizing plate using this film exhibit excellent characteristics in optical properties.
In the present invention, the polarizing plate protective film is a term in the sense that it is used by being laminated on a polarizer. If the film exists between two polarizers, other functions such as an antistatic function are provided. It also includes what is called an antistatic film.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The film of the present invention is produced by a solution casting method using a crushed product obtained by crushing a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method and a lower fatty acid ester of cellulose as a raw material. It is a film. In particular, a crushed product obtained by crushing a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method and a lower fatty acid ester of cellulose (lower fatty acid ester of cellulose produced by a solution casting method) Crushed product obtained by pulverizing a material containing as a main component) / {(crushed product obtained by pulverizing a material mainly comprising a lower fatty acid ester of cellulose prepared by a solution casting method) + (lower fatty acid ester of cellulose)} = 10 to 70 wt% (preferably 20 wt% or more, more preferably 30 wt% or more, particularly preferably 40 wt% or more, preferably 60 wt% or less, more preferably 50 wt% or less), and this mixture is used as a raw material. A film produced by a solution casting method.
[0017]
The method for producing a film of the present invention comprises crushing a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method, and using a solution casting method using the crushed product and a lower fatty acid ester of cellulose as raw materials. It is a manufacturing method. In particular, a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method is crushed, and this crushed product and a lower fatty acid ester of cellulose are obtained (lower fatty acid of cellulose produced by a solution casting method). Crushed product obtained by crushing a material containing ester as a main component) / {(Crushed product obtained by crushing a material containing cellulose lower fatty acid ester as a main component produced by a solution casting method) + (lower fatty acid ester of cellulose)} = 10 to 70 wt% (preferably 20 wt% or more, more preferably 30 wt% or more, particularly preferably 40 wt% or more, preferably 60 wt% or less, more preferably 50 wt% or less), and this mixture is used as a raw material. And a method of producing by a solution casting method. Crushing of a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method is crushing using a fixed blade and a rotary blade. Or it is crushing using a fixed blade and a rotary blade after vertical cutting with a vertical cutting blade.
[0018]
The lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms, and examples thereof include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, and cellulose acetate butyrate. The most preferred lower fatty acid ester of cellulose is cellulose triacetate. In particular, cellulose triacetate having an acetylation degree of 59 to 62%.
[0019]
In addition, the film has a haze value (a value obtained by laminating five sheets) of 0.5% or less. The lower limit of the haze value is not particularly limited. However, at present, the lower limit of the haze value (the value for a laminate of five sheets) is about 0.1 in reality.
This will be described in more detail below.
[0020]
In the present invention, a crushed product obtained by crushing a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method is used.
As a material mainly composed of a lower fatty acid ester of cellulose (cellulose triacetate) produced by a solution casting method, there is, for example, a defective product in which the ears at both ends of the film product of the material or turbulence is disturbed. That is, when a cellulose triacetate film product is produced by the solution casting method, an end portion that does not become a product, or a defective product due to winding disturbance or the like occurs. These are not defective products due to poor material quality (characteristics). It is only said that it is not a pass product in form. Therefore, it can be used again as a raw material. In addition, use as a raw material prevents waste of resources.
[0021]
The material as described above is first finely crushed.
For example, the “BO Series Open Flat Cutter” (a device that aligns the shape of crushed material through a sieve installed under the blade after making the film fine with a rotating blade and a fixed blade) manufactured by Horai Co., Ltd. Crushing was performed using an opening having a diameter of 3 mm. Since this crushed film piece was cut many times during the convection between the fixed blade, the rotary blade and the sieve for a while, the film surface was rubbed, and many polygonal shapes other than the square were also seen.
[0022]
Alternatively, the sheet was crushed with a “sheet pelletizer (a device that vertically cuts a sheet with a vertical cutting blade of a roll cutter and then crosses it with a rotary blade and a fixed blade)” manufactured by Horai Co., Ltd. This crushed film piece was a 4 mm square in both length and width.
Or, it was crushed with “granulator (apparatus for bundling a film in a strip shape, compressing with a compression roll and then cutting it into a fixed length with a rotary blade)” manufactured by Italy EXACT. The crushed film piece was in the form of a pellet having a length of 5 mm.
[0023]
Cellulose triacetate using this crushed product and new cellulose triacetate as raw materials by the usual solution casting method (the solution casting method similar to the solution casting method used to produce the crushed cellulose triacetate film product) Get a film product.
That is, a mixture of the crushed product, new cellulose triacetate, necessary additives, and a solvent (for example, an organic solvent such as methylene chloride, ethanol, acetone, methanol) is heated, stirred, and dissolved. In addition, the density | concentration of the acetylcellulose in dope is about 10-35 wt%, for example. Next, the dope obtained as described above is filtered. After filtration, the dope is cast on a support using a casting apparatus. Then, the solvent is evaporated until it can be peeled off on the support, and then peeled off. The film of the present invention is obtained by drying the peeled cellulose triacetate film.
[0024]
In addition, it peels in the state in which the organic solvent in a film is contained to some extent, and dries by setting drying time moderately. In the case where the vertical tension is more strongly applied, it is preferable to dry in a state where the horizontal dimension is fixed. In a state where the lateral dimension is fixed, it is preferable to dry the organic solvent to a residual amount of less than 20 wt%. When it does in this way, the film whose retardation value is 20 nm or less (especially 10 nm or less. Furthermore, 5 nm or less) is obtained.
[0025]
The polarizing plate protective film of this invention consists of a film obtained as described above or as described above.
The polarizing plate of the present invention is formed by laminating the above film and a polarizer. In addition, a conventionally well-known thing can be used for the polarizer in which a film (polarizing plate protective film) is provided in the surface. For example, a film made of a hydrophilic polymer such as polyvinyl alcohol is treated with a dichroic dye such as iodine and stretched, or a plastic film such as vinyl chloride is treated and a polyene is oriented. . A polarizing plate is comprised as what laminated | stacked the said polarizing plate protective film on the at least one surface side of the polarizer.
[0026]
Hereinafter, an example is given and demonstrated.
[0027]
【Example】
[Sample 1]
[Dope Formula A]
Cellulose triacetate (acetylation degree 61.0%) 100 parts by weight ethylphthalyl ethyl glycolate 5 parts by weight 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) benzotriazole 2 parts by weight methylene Chloride 475 parts by weight Ethanol 50 parts by weight The above composition was put into a closed container and completely dissolved while heating and stirring.
[0028]
Next, this dope was filtered.
After filtration, it was uniformly cast on a stainless steel band support at a dope temperature of 33 ° C. and a width of 1500 mm using a belt casting apparatus. After evaporating the solvent until it can be peeled off from the stainless steel band support, it is peeled off from the stainless steel band support, slitted to 1300 mm width, then dried while being transported by many rolls, and slit to 1100 mm width. Thus, a cellulose triacetate film having a thickness of 80 μm was obtained.
[0029]
[Sample 2]
[Dope Formula B]
Cellulose triacetate (acetylation degree 61.0%) 50 parts by weight Cellulose triacetate film crushed product A 53.5 parts by weight Ethylphthalylethyl glycolate 2.5 parts by weight 2- (2′-hydroxy-3 ′, 5′- Di-tert-butylphenyl) benzotriazole 1 part by weight Methylene chloride 475 parts by weight Ethanol 50 parts by weight * Cellulose triacetate film crushed product A was obtained by applying the cellulose triacetate film obtained in [Sample 1] to “BO” It is crushed with a "series open flat cutter (sieving mesh 5 mm)".
[0030]
The above composition was used in the same manner as described above to obtain a cellulose triacetate film having a width of 1100 mm and a thickness of 80 μm.
[Sample 3]
[Dope Formula C]
Cellulose triacetate (acetylation degree 61.0%) 40 parts by weight Cellulose triacetate film crushed product A 64.2 parts by weight Ethylphthalyl ethyl glycolate 2 parts by weight 2- (2′-hydroxy-3 ′, 5′-di-) t-Butylphenyl) benzotriazole 0.8 parts by weight Methylene chloride 475 parts by weight Ethanol 50 parts by weight Using the above composition, a cellulose triacetate film having a width of 1100 mm and a thickness of 80 μm was obtained.
[0031]
[Sample 4]
[Dope Formula D]
Cellulose triacetate (acetylation degree 61.0%) 30 parts by weight Cellulose triacetate film crushed product A 74.9 parts by weight Ethylphthalylethyl glycolate 1.5 parts by weight 2- (2′-hydroxy-3 ′, 5′- Di-t-butylphenyl) benzotriazole 0.6 parts by weight Methylene chloride 475 parts by weight Ethanol 50 parts by weight Using the above composition, a cellulose triacetate film having a width of 1100 mm and a thickness of 80 μm was obtained.
[0032]
[Sample 5]
[Dope Formula E]
Cellulose triacetate (acetylation degree 61.0%) 70 parts by weight Cellulose triacetate film crushed product A 32.1 parts by weight Ethylphthalylethyl glycolate 3.5 parts by weight 2- (2′-hydroxy-3 ′, 5′- Di-t-butylphenyl) benzotriazole 1.4 parts by weight Methylene chloride 475 parts by weight Ethanol 50 parts by weight Using the above composition, a cellulose triacetate film having a width of 1100 mm and a thickness of 80 μm was obtained.
[0033]
[Sample 6]
[Dope Formula F]
Cellulose triacetate (acetylation degree 61.0%) 80 parts by weight Cellulose triacetate film crushed product A 21.4 parts by weight Ethylphthalylethyl glycolate 4 parts by weight 2- (2′-hydroxy-3 ′, 5′-di- t-Butylphenyl) benzotriazole 1.6 parts by weight Methylene chloride 475 parts by weight Ethanol 50 parts by weight Using the above composition, a cellulose triacetate film having a width of 1100 mm and a film thickness of 80 μm was obtained.
[0034]
[Sample 7]
[Dope prescription G]
Cellulose triacetate (acetylation degree 61.0%) 90 parts by weight Cellulose triacetate film crushed product A 10.7 parts by weight Ethylphthalylethyl glycolate 4.5 parts by weight 2- (2′-hydroxy-3 ′, 5′- Di-t-butylphenyl) benzotriazole 1.8 parts by weight Methylene chloride 475 parts by weight Ethanol 50 parts by weight Using the above composition, a cellulose triacetate film having a width of 1100 mm and a film thickness of 80 μm was obtained.
[0035]
[Sample 8]
[Dope prescription H]
Cellulose triacetate (acetylation degree 61.0%) 50 parts by weight Cellulose triacetate film crushed product B 53.5 parts by weight Ethylphthalylethyl glycolate 2.5 parts by weight 2- (2′-hydroxy-3 ′, 5′- Di-t-butylphenyl) benzotriazole 1 part by weight Methylene chloride 475 parts by weight Ethanol 50 parts by weight * The cellulose triacetate film crushed product B is a film obtained by cutting the cellulose triacetate film obtained in [Sample 1] with a vertical cutter of a roll cutter. It is a crushed product that is cut into 5 mm squares both vertically and horizontally by cutting the film vertically while taking the film and then crossing the film with a rotary blade and a fixed blade.
[0036]
The above composition was used in the same manner as described above to obtain a cellulose triacetate film having a width of 1100 mm and a thickness of 80 μm.
[Sample 9]
[Dope Formula I]
Cellulose triacetate (acetylation degree 61.0%) 50 parts by weight Cellulose triacetate film crushed product C 53.5 parts by weight Ethylphthalylethyl glycolate 2.5 parts by weight 2- (2′-hydroxy-3 ′, 5′- Di-t-butylphenyl) benzotriazole 1 part by weight Methylene chloride 475 parts by weight Ethanol 50 parts by weight * Cellulose triacetate film crushed product C is obtained by removing the cellulose triacetate film obtained in [Sample 1] from the Italian EXACT company "Granulator" Is crushed into a 5 mm long pellet.
[0037]
The above composition was used in the same manner as described above to obtain a cellulose triacetate film having a width of 1100 mm and a thickness of 80 μm.
[Sample 10]
[Dope Formula J]
Cellulose triacetate film crushed product A 107 parts by weight Methylene chloride 475 parts by weight Ethanol 50 parts by weight In the same manner as above, a cellulose triacetate film having a width of 1100 mm and a film thickness of 80 μm was obtained.
[0038]
The cellulose triacetate film obtained as described above was examined for the number of bright spot foreign substances and haze, and the results are shown in Table 1.
The haze was measured using a T-2600DA type manufactured by Tokyo Denshoku Industries Co., Ltd., in accordance with JIS K 7105, by superposing five samples. The smaller the value, the better.
[0039]
For the bright spot foreign matter, the sample (cellulose triacetate film) is placed between two polarizing plates arranged in an orthogonal state (crossed Nicols), light is applied from the outside of one polarizing plate, and the microscope is applied from the outside of the other polarizing plate. The number of foreign matters (bright spot foreign matter) that appeared to be white per 25 mm ² was measured at 100 locations, and the average value was displayed. The microscope conditions at this time were a transmission light source with a magnification of 30 times. The smaller the number of bright spot foreign matter, the better.
[0040]

As can be seen from Table 1, the film according to the present invention has a low haze, excellent optical properties, and few bright spot foreign substances. Therefore, it turns out that it is very preferable as a polarizing plate protective film.
[0041]
【The invention's effect】
The film of the present invention has low haze, excellent optical properties, and few bright spot foreign matter.
The polarizing plate protective film of the present invention is extremely excellent because it has low haze, excellent optical properties, and few bright spot foreign matter.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a polarizing plate according to the present invention.
1 Polarizing plate protective film 2 Polarizer 3 Polarizing plate

Claims (3)

(A crushed product obtained by crushing a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method) / {(A material obtained by crushing a material obtained mainly by a lower fatty acid ester of cellulose produced by a solution casting method) Crushed product) + (lower fatty acid ester of cellulose)} = 10 to 70 wt%,
A crushing step of crushing a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method;
Comprising a film production step of producing a film by a solution casting method using a crushed product obtained by the crushing step and a lower fatty acid ester of cellulose as a raw material,
The method for producing a protective film for a polarizing plate, wherein the lower fatty acid ester of cellulose is cellulose triacetate. The protective film for a polarizing plate according to claim 1 , wherein the crushing of the material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method is crushing using a fixed blade and a rotary blade. Manufacturing method. Crushing of a material mainly composed of a lower fatty acid ester of cellulose produced by a solution casting method is characterized by crushing using a fixed blade and a rotary blade after vertical cutting with a vertical cutting blade. The manufacturing method of the protective film for polarizing plates of Claim 1 or Claim 2.

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