JP2003103693A - Cellulose ester laminated film and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cellulose ester laminated film which is suitable as a protective film for a polarizing plate of a liquid crystal image display and of which the application properties for an antistatic layer-applying composition, a hard coat layer-applying composition, a nonglare applying composition, an applying composition for a nonglare layer and the like are improved without deteriorating physical properties and optical properties and to provide its manufacturing method. SOLUTION: For the cellulose ester laminated film 10 of 20 to 80 μm in film thickness prepared by a co-cast filming method, a relation between an average substitution degree A of a cellulose ester constituting a surface layer 1a existing within 10 μm from at least one side film surface in up and down both surfaces of the film and an average substitution degree B of the cellulose ester constituting an inner layer 1b existing over 10 μm from the same film surface, is represented by the following formulas 2.35 <= substitution degree A<=2.85 and 2.75 <= substitution degree B<=2.95 and satisfies the substitution degree A < the substitution degree B.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cellulose ester laminated film suitable as a protective film for a polarizing plate in a liquid crystal image display device, and a method for producing the same.

[0002]

2. Description of the Related Art Generally, a liquid crystal image display device (LCD)
Since it can be directly connected to an IC circuit with low voltage and low power consumption and can be thinned, it is widely used as a display device for a word processor, a personal computer, or the like. By the way, the basic configuration of this LCD is one in which polarizing plates are provided on both sides of a liquid crystal cell. Since the polarizing plate allows only light having a polarization plane in a certain direction to pass through, it plays an important role in visualizing the change in the orientation of the liquid crystal due to the electric field in the LCD.
Performance is greatly affected. The polarizing plate comprises a polarizer and protective films laminated on both sides of the polarizer. And
A cellulose ester film is widely used as a protective film for such a polarizing plate.

By adding a function to a cellulose ester film used as a protective film for such a polarizing plate, particularly a cellulose triacetate (TAC) film, it is possible to impart a wide viewing angle and an antireflection property at a low cost, and thus a high added value. There is an increasing demand for polarizing plate protective films, and among them, control of coating processability (coating liquid wettability) on the surface of TAC has become an important issue.

On the other hand, the co-casting film forming technique for producing a cellulose ester laminated film has been filed various applications so far as a method for giving a characteristic performance to the surface or inside of the cellulose ester film to be formed. There is. For example, in JP-A-2001-71418, a cellulose ester film in which a small amount of a matting agent is added to ensure sufficient flatness and tacking prevention property, and also transparency can be sufficiently ensured, and its production A method is disclosed. In addition, JP-A-8-207210
In the publication, core portions having different acetylation degrees (substitution degrees), that is, an inner layer (substitution degree 2.7 or less) and a surface layer (substitution degree 2.8).
By having the above) and
A cellulose acetate laminated film having improved dimensional stability and resistance to moist heat has been proposed.
In 07210, in order to protect the cellulose ester having a low degree of substitution, a layer of cellulose ester having a high degree of substitution was provided on the surface.

[0005]

However, the applicability of the conventional cellulose ester film largely depends on the preparation and know-how of the coating solution side, and the environment at the time of application such as humidity and the drying after film formation. Regardless, it is difficult to avoid the influence of the solvent remaining in the film, and there is a problem that it is very difficult to ensure coating stability.

As a result of intensive studies in view of the above points, the present inventors have found that a cellulose ester film having a low degree of substitution improves the coatability, but the cellulose ester film having a low degree of substitution is found. Then, there are some parts that are inferior in physical properties and optical characteristics.
It was found that the coating processability (coating liquid wettability) of the film surface can be improved by setting the average substitution degree of the cellulose ester of the film surface layer (skin layer) and the inner layer and changing the substituent. Came to.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a cellulose ester laminated film with improved coatability and a method for producing the same, without deteriorating the physical properties and optical properties. It is in.

[0008]

The above objects of the present invention are as follows.
This has been achieved by a cellulose ester laminated film in which a low-substituted cellulose ester is placed on the surface of a cellulose ester film and a high-substituted cellulose ester is placed inside.

First, the cellulose ester laminated film according to the first aspect of the present invention is a cellulose ester laminated film having a film thickness of 20 to 80 μm produced by a solution casting film forming method. The average degree of substitution A of the cellulose ester constituting the surface layer existing within 10 μm from at least one of the film surfaces (hereinafter referred to as the degree of substitution A) and the inner layer existing over 10 μm from the film surface are constituted. The average degree of substitution B of the cellulose ester (hereinafter, referred to as degree of substitution B) has the following expressions: 2.35 ≦ substitution degree A ≦ 2.85, and 2.75 ≦ substitution degree B ≦ 2.95. , And substitution degree A
<The degree of substitution B is satisfied.

The invention of claim 2 is characterized in that, in the above-mentioned claim 1, the cellulose ester laminated film is produced by a co-casting film forming method.

The method for producing a cellulose ester laminated film according to the third aspect of the present invention is a co-casting film forming method in which the film thickness is 2
A method for producing a cellulose ester laminated film of 0 to 80 μm, wherein the temperature of the cellulose ester dope for forming the surface layer is 3 ° C. or more higher than the temperature of the cellulose ester dope for forming the inner layer. It is characterized by being done.

According to a fourth aspect of the present invention, in the above-mentioned third aspect, the temperature of the cellulose ester dope for forming the surface layer is 15 to 30 ° C., and the temperature of the cellulose ester dope for forming the inner layer is 30. It is characterized by being ~ 35 ° C.

According to a fifth aspect of the present invention, in the above-mentioned third or fourth aspect, the solid content concentration of the cellulose ester dope for forming the surface layer is 20% by weight or less, and the cellulose for forming the inner layer is formed. The ester dope has a solid content concentration of more than 20% by weight and 33% by weight or less.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In the cellulose ester laminated film of the present invention, the target cellulose ester film comprises a lower fatty acid ester of cellulose. Here, the lower fatty acid in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms, for example, cellulose acetate such as cellulose diacetate (DAC) or cellulose triacetate (TAC), cellulose propionate, cellulose butyrate. And mixed fatty acid esters such as cellulose acetate propionate (CAP) and cellulose acetate butyrate. The most preferred lower fatty acid ester of cellulose is cellulose triacetate.

Here, TAC with a low degree of substitution is used for the surface layer.
It is preferable to use (cellulose triacetate), CAP (cellulose acetate propionate), DAC (cellulose diacetate) or the like, and use TAC with a high degree of substitution for the inner layer.

The surface layer has a low degree of substitution so that the orientation of the molecules is easily aligned, so that the coating property is improved. on the other hand,
Mechanical strength and optical characteristics (retardation) are secured by making the inside a normal TAC.

Due to the uniform molecular orientation of the surface layer, the hygroscopicity is lowered or the moisture is evenly absorbed.
Originally, the lower the degree of cellulose ester substitution is, the worse the hygroscopicity is, but the higher the hygroscopicity is. However, according to the production method of the present invention, the hygroscopicity is good, that is, the hygroscopicity is low, and thus the coating property is improved.

Incidentally, retardation is one of the important optical characteristics of the cellulose ester film. Retardation is represented by the product of the birefringence and the film thickness, retardation is significantly related to the performance of a liquid crystal display device incorporating a cellulose ester film, the deviation of the retardation of the cellulose ester film occurs, If this deviation exceeds a certain range, the liquid crystal display element cannot exhibit sufficient performance. Especially when the deviation from the target retardation value in the width direction becomes large, even in one cellulose ester film cut out according to the size of the liquid crystal display element, a uniform screen display cannot be performed due to partially different optical characteristics, The cut-out cellulose ester films have different optical properties.

According to the method of the present invention, a stable film can be formed, the surface properties and optical properties of the cellulose ester laminated film can be improved, and the dispersion of retardation value is small, and the cellulose ester of excellent quality can be obtained. The laminated film can be efficiently manufactured with high quality.

The film thickness of the cellulose ester laminated film of the present invention will be described. The thinner the surface layer of the cellulose ester laminated film is, the more excellent the transparency is. Elution can be suppressed and productivity is excellent. The thickness of the surface layer satisfying these requirements is preferably 5 to 20 μm, more preferably 7
˜15 μm, most preferred is 10 μm.

If the overall film thickness of the cellulose ester film is too thin, the strength of the polarizing plate as a protective film is insufficient, and the dimensional stability of the polarizing plate and the storage stability under heat and humidity deteriorate. If the film thickness is thick, the polarizing plate becomes thick, and it becomes difficult to make the liquid crystal display thin. The film thickness of the cellulose ester laminated film satisfying both of these requirements is 20 to 80 μm, preferably 30 to 50 μm, and more preferably 35 to 45 μm.
And most preferably 40 μm.

Improving the performance of a liquid crystal image display device due to the cellulose ester film by incorporating an ultraviolet absorber, a plasticizer, an antioxidant, a processing stabilizer, a matting agent and the like into the cellulose ester film. You can

In the cellulose ester laminated film according to the present invention, the ultraviolet absorber preferably used has high transparency and is excellent in the effect of preventing deterioration of the polarizing plate and the liquid crystal element, and is a benzotriazole type ultraviolet absorber or a benzophenone type. UV absorbers are preferred, and benzotriazole UV absorbers with less unwanted coloration are particularly preferred.

The cellulose ester film of the present invention preferably contains a plasticizer. The plasticizer that can be used is not particularly limited, but in the phosphoric acid ester system, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc., In the phthalate ester system, diethyl phthalate,
Dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, etc., glycolate ester type, triacetin, tributyrin, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate,
It is preferable to use methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate or the like alone or in combination. It is particularly preferable to use a phosphoric acid ester-based plasticizer in combination with a plasticizer having a freezing point of 20 ° C. or less because of excellent dimensional stability and water resistance. The plasticizer having a freezing point of 20 ° C. or lower is not particularly limited as long as the freezing point is 20 ° C. or lower, and can be selected from the above plasticizers. Examples thereof include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, tributyl phosphate, diethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, triacetin, ethyl phthalyl ethyl glycolate and the like. You can These plasticizers are preferably used alone or in combination. The amount of these plasticizers used is preferably 1 to 15% by weight based on the cellulose ester in view of film performance, processability and the like. For liquid crystal display members, 5 to 15% by weight from the viewpoint of dimensional stability.
Is more preferable, and particularly preferably 7 to 12% by weight. In addition, the freezing point is 20 relative to cellulose ester.
The content of the plasticizer at a temperature of 0 ° C or lower is preferably 1 to 10% by weight, more preferably 3 to 7% by weight.

A film thickness of 20 to 80 according to the invention of claim 1
In the cellulose ester laminated film of μm, the substitution degree A of the cellulose ester constituting the upper and lower surface layers present within 10 μm from the film surface is within the range of 2.35 ≦ substitution degree A ≦ 2.85. Is limited. The reason is that when the substitution degree A of the cellulose ester constituting the surface layer is less than 2.35, the solubility is deteriorated and foreign matter that is difficult to remove by filtration is generated, which is not preferable. If the substitution degree A of the cellulose ester constituting the surface layer exceeds 2.85, the desired coating performance will be insufficient, which is not preferable.

Further, the substitution degree B of the cellulose ester constituting the inner layer existing beyond 10 μm from the surface of the film is within the range of 2.75 ≦ substitution degree B ≦ 2.95. ing. The reason is that if the degree of substitution B of the cellulose ester constituting the inner layer is less than 2.75, the mechanical strength of the film may decrease, which is not preferable, whereas the cellulose ester constituting the inner layer is not preferable. If the substitution degree B of 2. exceeds 2.95, foreign matter different from that found in the low substitution cellulose ester is generated, which is not preferable.

Further, the relationship between the substitution degree A and the substitution degree B is limited to the substitution degree A <the substitution degree B. The reason is that the degree of substitution A of the cellulose ester constituting the surface layer is low, so that the molecular orientation is easily aligned, and thus the coating property is improved. On the other hand, the mechanical strength and optical characteristics (retardation) are secured by supplementing the cellulose ester constituting the inner layer with a high substitution degree B.

According to the invention of claim 2, in the above claim 1, it is limited that the cellulose ester laminated film is produced by a co-casting film forming method. I mean,
Originally, the lower the degree of cellulose ester substitution, the worse the hygroscopicity (that is, the higher), but according to the co-casting film forming method of the present invention, the hygroscopicity of the surface of the cellulose ester laminated film becomes good (that is, low). This is because the coating property is improved.

The co-casting method according to the manufacturing method of the present invention will be described.

Co-casting is a sequential multi-layer casting method in which two or three layers are formed through different dies. Simultaneous multi-layering in which two or three layers are combined in a die having two or three slits. Any of a casting method and a multilayer casting method in which sequential multilayer casting and simultaneous multilayer casting are combined may be used.

In the method for producing a cellulose ester laminated film according to the invention of claim 3, in the method for producing a cellulose ester laminated film having a film thickness of 20 to 80 μm by a co-casting film forming method, a cellulose ester for forming a surface layer is formed. It is limited that the temperature of the dope is 3 ° C. or more higher than the temperature of the cellulose ester dope for forming the inner layer. The reason is that if the temperature difference between the dope for forming the surface layer and the dope for forming the inner layer is less than 3 ° C., the orientation of the molecules on the film surface may be disturbed, or the desired coating property may not be achieved. Because there is no.

According to the invention of claim 4, in claim 3, the temperature of the cellulose ester dope for forming the surface layer is limited to 15 to 30 ° C. The reason is that if the temperature of the surface layer-forming dope is lower than 15 ° C., the dope viscosity becomes too high and the surface smoothness deteriorates. On the other hand, if the temperature is higher than 0 ° C., on the contrary, the viscosity becomes too low and it is likely to be affected by the dry air, which also causes a problem in flatness, which is not preferable.

On the other hand, the temperature of the cellulose ester dope for forming the inner layer is limited to 30 to 35 ° C. The reason is that if the temperature of the dope for forming the internal layer is less than 30 ° C., the smoothness of the film surface is affected as a result, which is not preferable, and if the temperature of the dope for forming the internal layer exceeds 35 ° C. This is because bubbles may occur inside the film, which is not preferable.

The invention of claim 5 is, in the above-mentioned claim 3 or claim 4, limited in that the solid content concentration of the cellulose ester dope for forming the surface layer is 20% by weight or less. The reason is that if the solid concentration of the dope for forming the surface layer exceeds 20% by weight, the dissolution becomes difficult, which is not preferable.

Further, it is limited that the solid content concentration of the cellulose ester dope for forming the inner layer is more than 20% by weight and 33% by weight or less. The reason is that the solid content of the dope for forming the inner layer is 20% by weight.
If the solid content is less than 33% by weight, the drying load is large and therefore the orientation of the surface layer may be disturbed. Therefore, if the solid concentration of the inner layer-forming dope exceeds 33% by weight, the viscosity becomes high and This is because it is difficult to spread and it is not preferable.

In the present invention, the dope solution in which the cellulose ester is dissolved is a state in which the cellulose ester is dissolved in a solvent (solvent), and the dope solution contains an additive such as a plasticizer. Of course, other additives may be added if necessary. The concentration of the cellulose ester in the dope solution is preferably 10 to 30% by weight, more preferably 18 to 20% by weight.

The solvent used in the present invention may be used alone or in combination, but it is preferable to use a mixture of a good solvent and a poor solvent in terms of production efficiency, and more preferably, a mixture of the good solvent and the poor solvent. The ratio is 70 to 95% by weight for the good solvent and 30 to 5% by weight for the poor solvent.

The good solvent and the poor solvent used in the present invention are
The one that dissolves the cellulose ester used alone is defined as a good solvent, and the one that swells or does not dissolve alone is defined as a poor solvent. Therefore, the good solvent and the poor solvent change depending on the amount of bound acetic acid of the cellulose ester. For example, when acetone is used as the solvent, the amount of bound acetic acid of the cellulose ester of 55% results in a good solvent, and the bound acetic acid amount of 6%.
If it is 0%, it becomes a poor solvent.

Examples of the good solvent used in the present invention include organic halogen compounds such as methylene chloride and dioxolanes.

As the poor solvent used in the present invention, for example, methanol, ethanol, n-butanol, cyclohexane and the like are preferably used.

As a method for dissolving the cellulose ester when preparing the dope solution described above, a general method can be used, but as a preferable method, the cellulose ester is mixed with a poor solvent and wet or swelled. Let
Further, a method of mixing with a good solvent is preferably used. At this time, under pressure, a method of heating at a temperature not lower than the boiling point of the solvent at room temperature and the solvent does not boil, a method of dissolving while stirring, in order to prevent the generation of lumpy undissolved material called gel or Mamako, More preferable.

Pressurization may be carried out by a method of injecting an inert gas such as nitrogen gas or by increasing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

The heating temperature after the addition of the solvent is preferably not lower than the boiling point of the solvent used and in the range in which the solvent does not boil, for example, 60 ° C. or higher, preferably 70 to 110 ° C. . Also, the pressure is adjusted at the set temperature so that the solvent does not boil.

After the dissolution, the product is taken out from the container while being cooled, or is taken out from the container by a pump or the like and cooled by a heat exchanger or the like, and is used for film formation. The cooling temperature at this time may be room temperature, but it is more preferable to cool to a temperature 5 to 10 ° C. lower than the boiling point and perform casting at that temperature because the dope viscosity can be reduced.

The support used in the casting process is preferably a belt-shaped or drum-shaped stainless steel mirror-finished support. The temperature of the support in the casting step can be cast in a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, but casting on the support at 0 to 30 ° C. gels the dope. It is preferable because the peeling limit time can be raised, and it is more preferable to cast on a support at 5 to 15 ° C. The peeling limit time refers to the time during which the cast dope remains on the support at the limit of the casting speed at which a transparent film having good flatness can be continuously obtained. The shorter the peeling limit time is, the more excellent the productivity is, which is preferable.

The surface temperature of the support on the casting side is 10 to 55 ° C, the temperature of the solution is 25 to 60 ° C,
Furthermore, the temperature of the solution is preferably higher than the temperature of the support by 0 ° C. or more, more preferably 5 ° C. or more. The solution temperature and the support temperature are preferably higher because the drying speed of the solvent can be increased, but if the temperature is too high, foaming or flatness may be deteriorated.

A more preferable range of the temperature of the support is 2
0-40 degreeC, the more preferable range of solution temperature is 35-
45 ° C.

The temperature of the support at the time of peeling is 10 to 4
When the temperature is 0 ° C, more preferably 15 to 30 ° C, the adhesion between the film and the support can be reduced, which is preferable.

In order for the cellulose ester film at the time of production to exhibit good flatness, the residual solvent amount when peeled from the support is preferably 10 to 80%, more preferably 20 to 40% or 60 to. It is 80%, and particularly preferably 20 to 30%.

In the present invention, the residual solvent amount is defined by the following equation.

Amount of residual solvent = (weight before heat treatment−weight after heat treatment) / (weight after heat treatment) × 100%

The heat treatment for measuring the amount of residual solvent means that the film is heat-treated at 115 ° C. for 1 hour.

The peeling tension at the time of peeling the film from the support is usually 20 to 25 kg / m, but the content of the ultraviolet absorber per unit weight of the cellulose ester is large, and the peeling tension is higher than in the conventional case. Since the thinned cellulose ester film of the present invention is easily wrinkled during peeling, it is preferable to peel at a peelable minimum tension of 17 kg / m, and more preferably at a minimum tension of 1
It is to peel at 4 kg / m.

Further, in the step of drying the cellulose ester film, it is preferable to further dry the film peeled from the support so that the residual solvent amount is 3% by weight or less, and more preferably 0.5% by weight or less. is there.

In the film drying step, generally, a roll suspension method or a pin tenter method is used to dry the film while conveying it. 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 hold the width at a place where the residual solvent amount is large immediately after peeling from the support, because the effect of improving the dimensional stability is further exhibited. The means for drying the film is not particularly limited, and generally, hot air, infrared rays, heating rolls, microwaves or the like is used.
It is preferable to use hot air for the sake of simplicity. Drying temperature is 40
It is preferable to gradually increase the temperature by dividing it into 3 to 5 stages in the range of to 150 ° C, and it is more preferable to perform the temperature in the range of 80 to 140 ° C in order to improve the dimensional stability.

Next, the method for producing the cellulose ester laminated film of the present invention will be described with reference to the drawings.

FIG. 1 is a process diagram showing an example of an apparatus for producing a cellulose ester laminated film of the present invention.
Shows a sectional view of the slit die (6) of FIG.

Referring to the figure, the apparatus used in the method for producing a cellulose ester laminated film having a film thickness of 20 to 80 μm by the solution casting film forming method, especially the co-casting film forming method, is a pair of front and rear drums (7) (7). ), A rotating metal endless belt (support) (8), a die (6) for casting the dope that is the raw material solution of the cellulose ester film on the cast surface of the endless belt (8), and a die ( A peeling roll (9) for peeling the film (web) formed on the endless belt (8) from the endless belt (8) by 6) and a winding means (not shown) for winding the peeled web. ing.

The dope solution tank (1) for preparing the cellulose ester dope solution contains the dope solution (1a), and the additive solution tank (2) contains the additive solution (2a). .

The dope solution (1a) is sent to the in-line mixers (5a) and (5b) by the solution sending pumps (4b) and (4c), and the additive solution (2
A) is sent to the in-line mixer (5a) by the pump (4a). The dope liquid (1a) and the additive liquid (2a) were thoroughly mixed by the in-line mixer (5a), and the slit die (6) slit (1
Sent to 3). Similarly, in the in-line mixer (5b), the dope liquid (1a) and the ultraviolet absorber additive liquid (3a) charged in the additive liquid tank (2) are thoroughly mixed, and the slit (12) of the slit die (6) is mixed. Sent to.

The upper and lower surface layers from the slit die (6) are composed of a mixed solution of the dope solution (1a) and the additive solution (2a), and the inner layer is
A casting belt which is co-cast from the casting port (11) in the state of a mixed solution of the dope liquid (1a) and the ultraviolet absorber additive liquid (3a), and which continuously rotates from the drums (7) and (7) ( 8) Cast on top. The three-layered cast cellulose ester dope layer is dried,
The cellulose ester laminated film (10) is peeled from the casting belt (8) by the peeling roller (9).

As shown in FIG. 3, the cellulose ester laminated film (10) having a film thickness of 20 to 80 μm according to the present invention thus produced has upper and lower surface layers (10a) (10a) existing within 10 μm from the film surface. ), The degree of substitution A of the cellulose ester is 2.35 ≦ the degree of substitution A ≦ 2.
Within the range of 85 and 1 from the surface of the film
The degree of substitution B of the cellulose ester constituting the inner layer (10b) which exceeds 0 μm is 2.75 ≦ the degree of substitution B ≦ 2.
It is within the range of 95, and the relationship between the substitution degree A and the substitution degree B is such that the substitution degree A <the substitution degree B.

The polarizing plate can be manufactured by a general method. For example, there is a method in which the cellulose ester laminated film of the present invention is subjected to an alkali treatment, and the polarizing film produced by dipping and stretching in an iodine solution is attached to both surfaces using a completely saponified polyvinyl alcohol aqueous solution. The alkali saponification treatment refers to a treatment in which the cellulose ester film is immersed in a high temperature strong alkaline liquid in order to improve the wetting of the water-based adhesive and the adhesiveness at this time.

The polarizing film, which is the main component of the polarizing plate, is an element that allows only the light having a polarization plane in a certain direction to pass therethrough. A typical polarizing film known at present is a polyvinyl alcohol type polarizing film. There are a polyvinyl alcohol film dyed with iodine and a dye dyed with a dichroic dye. Those used are those obtained by forming a polyvinyl alcohol aqueous solution into a film and dyeing it by uniaxially stretching it, or dyeing it and then uniaxially stretching it, and then preferably subjecting it to a durability treatment with a boron compound. On the surface of the polarizing film, a transparent plastic film, which is a protective film for polarizing plate by the cellulose ester laminated film of the present invention, is laminated to form a polarizing plate.

[0065]

EXAMPLES Next, examples of the present invention will be described, but the present invention is not limited to these examples.

Examples 1 to 5 (Preparation of dope) Dope a Cellulose ester a having the degree of substitution shown in Table 1 was added to
Dope a was prepared by mixing the following ratios.

Cellulose ester a 100 parts by weight triphenyl phosphate 7 parts by weight Ultraviolet absorber (Tinuvin 326) 3 parts by weight Methylene chloride 475 parts by weight Ethanol 50 parts by weight Dope b Cellulose ester b having the degree of substitution shown in Table 1 ,
Dope b was prepared by mixing in the following ratios.

[0068] Cellulose ester b 100 parts by weight Triphenyl phosphate 7 parts by weight UV absorber (Tinuvin 326) 3 parts by weight Methylene chloride 295 parts by weight 30 parts by weight of ethanol

(Preparation of Cellulose Ester Film) A cellulose triacetate laminated film was prepared from the dope a and dope b of the above cellulose ester composition by the co-casting film forming method using the production apparatus shown in FIGS. 1 and 2. did.

Casting Process First, dope a and dope b adjusted to the temperatures shown in Table 1 were transferred to a co-casting die (6) through a conduit, and the die (6) was placed so that the dope a was on both upper and lower surfaces of the web. ) Inside slit (12) (1
Merge at 3). The dope a and the dope b are co-cast (cast) on the endless belt (8) whose surface temperature is adjusted to 25 ° C., and then heated to partially cast the solvent on the casting belt (8). Removed by drying at room temperature and the residual solvent amount is 1
Dry to 00% by weight. Then peeling roller
The cellulose ester laminated film (10) is peeled off from the casting belt (8) by (9).

Drying Step After that, the web is dried by a dryer (not shown) including a large number of rolls arranged in a staggered manner, and the final residual solvent amount is 0.
It became 3% by weight. Upper and lower surface layers of the cellulose ester laminated film after drying (10) (10a) (10a), and the inner layer (10b)
The film thickness of is as shown in Table 1.

Comparative Examples 1 and 2 The procedure is almost the same as in the above Examples, but for comparison, the substitution degree A of the cellulose ester constituting the surface layer is
The cellulose ester laminated film having a degree of substitution B of the cellulose ester constituting the inner layer (Comparative Example 1) and the temperature of the cellulose ester dope for forming the surface layer are the same as those of the cellulose ester dope for forming the inner layer. A cellulose ester laminated film (Comparative Example 2) that was the same as the temperature was produced.

[0073]

[Table 1]

Examples 6 to 10 (Preparation of dope) Dope c A dope c was prepared so that the cellulose ester having a substitution degree of 2.75 had the solid content concentration shown in Table 2. At that time, triphenyl phosphate was added to the cellulose ester in an amount of 7% by weight, and the ultraviolet absorber (Tinuvin 109) was added to the cellulose ester in an amount of 3% by weight. The weight ratio of methylene chloride and ethanol is 10: 1.

In Examples 7 and 9, not only the acetyl group but also the propionyl group was used as the substituent of the cellulose ester, and in addition to the production by the co-casting film formation method, the film surface layer (skin It was examined that coating processability (coating liquid wettability) of the film surface can be improved by setting the average substitution degree of the cellulose ester of the (layer) and the inner layer and changing the substituent.

Dope d Dope d was prepared in the same manner as dope c except that a cellulose ester having a degree of substitution of 2.88 was used, so that the solid content concentration shown in Table 2 was obtained.

(Production of Cellulose Ester Film) The dope temperatures of the casting step are dope c: 25 ° C. and dope d:
Each dope adjusted to 30 ° C was transferred to the co-casting die (6) through the conduit, and the slits (12) and (13) in the die (6) were placed so that the dope c was on both upper and lower surfaces of the web. Join. Endless belt with surface temperature adjusted to 30 ℃
(8) These dope c and dope d are co-cast (cast) and then heated to cast a part of the solvent on the casting belt.
(8) Remove by drying on the above, and dry until the residual solvent amount becomes 100% by weight. Then, the cellulose ester laminated film (10) is peeled off from the casting belt (8) by the peeling roller (9).

Drying Step After that, the web is dried by a dryer (not shown) including a large number of rolls arranged in a staggered manner, and the final residual solvent amount is 0.
It became 6% by weight. Upper and lower surface layers of the cellulose ester laminated film after drying (10) (10a) (10a), and the inner layer (10b)
Is the upper and lower surface layers (10a) formed by dope c.
(10a) is 10 μm, and the inner layer (10
b) is 20μm, total film thickness of film (10) is 40μ
m.

[0079]

[Table 2]

Comparative Examples 3 to 6 Cellulose ester laminated films of Examples 6 to 10 above
The dope c and the dope d used when producing (10) were cast on the casting belt (8) in single layers. Peeling roller
The residual solvent amount at the time of peeling according to (9) was 100% by weight, and the drying conditions thereafter were 0.3% by weight of the residual solvent amount and 0.
The drying temperature was adjusted to 6% by weight to prepare a cellulose ester film. The film thickness after drying was 40 μm. Table 3 shows the substitution degree of the cellulose ester used in the dope c and the dope, the solid content concentration of the cellulose ester, and the residual solvent amount of the film.

[0081]

[Table 3]

Next, the moisture permeability and the mechanical strength of the films of Examples 1 to 10 and Comparative Examples 1 to 6 were measured.

(Measurement of Moisture Permeability) The moisture permeability of each sample was measured according to the method described in JIS Z 0208.

(Measurement of Mechanical Strength) The tear strength of each sample was measured by using an Elemendorf tear tester (digital tearing tester; manufactured by Toyo Seiki Seisakusho). Table 4 shows the average of the measured values in the MD and TD directions. The obtained results are shown in Table 4.

[0085]

[Table 4]

As described above, the cellulose ester film of the present invention has a low moisture permeability despite the low degree of substitution, probably because the orientation of the cellulose fibers is completely different from the conventional one. . In addition, a film having high tear strength could be produced.

Evaluation of Surface Coatability of Cellulose Ester Laminated Film Also, the following (1) antistatic layer coating composition, (2) hard coat layer coating composition, (3) antiglare coating composition, and (4) reflection A coating solution of the coating composition for the prevention layer was prepared, and the coating solution was applied to the cellulose ester laminated films of Examples 1 to 10 and the cellulose ester films of Comparative Examples 1 to 6 to apply the film surface. The property, that is, the coating processing performance was visually judged.

Preparation and Application of Coating Solution (1) Coating Composition for Antistatic Layer Polymethylmethacrylate (weight average molecular weight 550,000, Tg: 90 ° C.) 0.6 parts by weight Propylene glycol monomethyl ether 60.0 parts by weight Methyl ethyl ketone 19 0.0 parts by weight Ethyl lactate 8.3 parts by weight Methanol 12.0 parts by weight Conductive polymer resin P-1 (0.1 to 0.3 μm particles) 0.5 parts by weight The above antistatic layer coating composition Coating with a wire bar to a wet film thickness of 6 μm in an environment of 60 ° C. and 60% RH, and then drying in a drying section set at 80 ± 5 ° C. to obtain a resin having a dry film thickness of about 0.2 μm. Layers were provided.

(2) Coating composition for hard coat layer Dipentaerythritol hexaacrylate monomer 22.5 parts by weight Dipentaerythritol hexaacrylate dimer 7.5 parts by weight Dipentaerythritol hexaacrylate trimer Ingredient 7 or more 0.5 parts by weight Diethoxybenzophenone photoinitiator 2.2 parts by weight Silicone-based surfactant 0.4 parts by weight Propylene glycol monomethyl ether 30.0 parts by weight Methyl ethyl ketone 30.0 parts by weight The above hard coat layer coating composition 13 wet film thickness
After being coated so as to have a thickness of 5 μm and dried in a drying section set at 80 ± 5 ° C., it is irradiated with ultraviolet rays so as to have a dose of 150 mJ / m ² to form a clear hard coat layer having a dry film thickness of 5 μm. Provided.

(3) Antiglare coating composition Dipentaerythritol hexaacrylate monomer 16.3 parts by weight Dipentaerythritol hexaacrylate dimer 6.5 parts by weight Dipentaerythritol hexaacrylate trimer The above components 6. 5 parts by weight 1,4-butanediol glycidyl ether 3.3 parts by weight Diethoxybenzophenone (UV initiator) 0.7 parts by weight Aromatic sulfonium salt-based UV initiator 0.2 parts by weight Silica (Cycilia 350: Fuji Silysia Ltd. 0.8 parts by weight Hydrophilic silica (Aerosil 200V: manufactured by Nippon Aerosil Co., Ltd.) 0.7 parts by weight Methyl ethyl ketone 22.8 parts by weight Ethyl acetate 22.8 parts by weight Isopropyl alcohol 19.5 parts by weight The above antiglare coating composition High-speed stirrer (TK homomixer, special machinery industry And stirred at Co., Ltd.)), and then,
Collision type disperser (Manton Gorin, manufactured by Gorin Co., Ltd.)
Dispersed.

A wet film thickness of 13 was obtained by applying the above antiglare coating composition.
200mJ / cm ² after applying μm and drying at 80 ± 5 ℃
The resin film was prepared by irradiating and curing with ultraviolet rays.

(4) Coating composition for antireflection layer Titanium polymer (Nippon Soda: B-4) 4.57 parts by weight Butanol 47.53 parts by weight Isopropyl alcohol 47.53 parts by weight Dipentaerythritol hexaacrylate monomer 0 11 parts by weight Dipentaerythritol hexaacrylate dimer 0.037 parts by weight Dipentaerythritol hexaacrylate trimer 0.037 parts by weight Diethoxybenzophenone UV initiator 0.004 parts by weight γ-methacryloxypropyltrimethoxy Silane 0.183 parts by weight The above antireflection coating composition is applied in a wet film thickness of 10 μm.
m, coated and dried, and then irradiated with 300 mJ / cm ² of ultraviolet rays, and then dried at 80 ± 5 ° C. to provide an antireflection layer.

As described above, (1) antistatic layer coating composition, (2) hard coat layer coating composition, (3)
Coating of the film surface of the cellulose ester films of Examples 1 to 10 and the cellulose ester films of Comparative Examples 1 to 6 coated with the coating solutions of the antiglare coating composition and (4) coating composition for antireflection layer. The properties, that is, the coating processing performance and the visual evaluation, were obtained, and the obtained results are shown in Table 5. The applicability evaluation criteria are as follows.

Evaluation criteria for coating property ⊚: There is no cissing of the coating film ○: Repelling of the coating film is seen on the edge of the film Δ: Repelling of the coating film is partially seen in the center of the film X: The cissing of the coating film is intermittently observed in the central part of the film

[0095]

[Table 5]

As is clear from the results shown in Table 5, in Examples 1 to 10 according to the present invention, the cellulose ester laminate was obtained in any case where the solutions of the coating compositions (1) to (4) were applied. It is clear that the coatability on the surface of the film has been dramatically improved. Further, even in the cellulose ester laminated films of Examples 6 to 10 according to the present invention in which the residual solvent amount was intentionally increased, stable coating performance was obtained, and the cellulose ester laminated film of the present invention had excellent properties. You can see that On the other hand, in Comparative Examples 1 to 6, in any of the cases where the solutions of the coating compositions of (1) to (4) were applied, the central part of the film surface was partially or intermittently applied. Repelling of the film was observed and stable coating performance was not obtained.

[0097]

As described above, the present invention according to claim 1 has a film thickness of 20 which is produced by the solution casting film forming method.
A cellulose ester laminated film having a thickness of ˜80 μm, the substitution degree A of the cellulose ester constituting the surface layer existing within 10 μm from at least one of the upper and lower surfaces of the film, and 10 μm from the film surface. The relationship of the substitution degree B of the cellulose ester constituting the inner layer existing beyond is expressed by the following formula: 2.35.
≤ Substitution degree A ≤ 2.85, and 2.75 ≤ Substitution degree B ≤ 2.
95, and the degree of substitution A <the degree of substitution B is satisfied. According to the cellulose ester laminated film of the present invention, the surface layer is formed of a molecule of low substitution degree cellulose ester. Since the orientations are easily aligned, the hygroscopicity is low, or the hygroscopicity is uniform and the coating property is improved. On the other hand, the inner layer secures mechanical strength and optical characteristics (retardation).

The invention according to claim 3 of the present invention is a method for producing a cellulose ester laminated film having a film thickness of 20 to 80 μm by a co-casting film forming method, which comprises a cellulose ester for forming a surface layer. The temperature of the dope is higher than the temperature of the cellulose ester dope for forming the inner layer by 3 ° C. or more, and according to the method of the present invention, the cellulose constituting the surface layer is formed. A cellulose ester laminated film having a substitution degree A of the ester lower than the substitution degree B of the cellulose ester constituting the inner layer is obtained. Originally, the lower the substitution degree of the cellulose ester is, the worse the hygroscopicity is, that is, the hygroscopicity is increased. According to the manufacturing method of the present invention, the hygroscopicity is good, that is, the hygroscopicity is low. Also in the cellulose ester laminate film is increased, resulting stable coating performance, cellulose esters laminated film according to the present invention has an effect that it has superior properties.

[Brief description of drawings]

FIG. 1 is a process drawing showing an example of an apparatus for producing a cellulose ester laminated film of the present invention.

FIG. 2 is an enlarged vertical sectional view of the slit die of FIG.

FIG. 3 is a schematic partial enlarged cross-sectional view of a cellulose ester laminated film of the present invention.

[Explanation of symbols]

1 Dope tank 1a Dope solution 2 Additive liquid tank 2a additive liquid 3 Additive liquid tank 3a additive liquid 5a in-line mixer 5b inline mixer 6 slit die 8 Endless belt (support) 9 Peeling roll 10 Cellulose ester laminated film 10a surface layer 10b inner layer 11 casting mouth 12 slits 13 slits

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B29L 9:00 B29L 9:00 F term (reference) 2H090 HB07X HC19 LA09 4F100 AJ06A AJ06B AJ06C BA02 BA10A BA10C BA14 BA44A BA44C EH462 4F205 AA01 AG03 AH73 GA07 GB02 GB26 GC07 GE24 GF24

Claims (5)

[Claims] 1. A film thickness 2 produced by a solution casting film forming method.
A cellulose ester laminated film having a thickness of 0 to 80 μm, wherein the average degree of substitution A of the cellulose ester constituting the surface layer present within 10 μm from at least one of the upper and lower surfaces of the film (hereinafter, substitution degree A And the average substitution degree B (hereinafter, referred to as substitution degree B) of the cellulose ester constituting the inner layer existing over 10 μm from the film surface is expressed by the following equation:
2. Cellulose, wherein 2.35 ≦ substitution degree A ≦ 2.85 and 2.75 ≦ substitution degree B ≦ 2.95 and substitution degree A <substitution degree B is satisfied. Ester laminated film. 2. The cellulose ester laminated film according to claim 1, wherein the cellulose ester laminated film is produced by a co-casting film forming method. 3. A film thickness of 20 to 80 μm by a co-casting film forming method.
Of the cellulose ester dope for forming the surface layer, the temperature of the cellulose ester dope for forming the surface layer is 3 ° C. or more higher than the temperature of the cellulose ester dope for forming the inner layer. A method for producing a cellulose ester laminated film, comprising: 4. The temperature of the cellulose ester dope for forming the surface layer is 15 to 30 ° C., and the temperature of the cellulose ester dope for forming the inner layer is 30 to 3.
It is 5 degreeC, The manufacturing method of the cellulose-ester laminated film of Claim 3 characterized by the above-mentioned. 5. The solid content concentration of the cellulose ester dope for forming the surface layer is 20% by weight or less, and the solid content concentration of the cellulose ester dope for forming the inner layer is more than 20% by weight and 33% by weight. % Or less, The manufacturing method of the cellulose-ester laminated film of Claim 3 or 4 characterized by the above-mentioned.