JP2003020345A - Cellulose ester film and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cellulose ester film which is excellent in durability, hardly undergoing dimensional change or deformation at high temperature and humidity, is used especially as a protective film for a polarizing plate, exhibits an excellent processibility when converted from the protective film into a polarizing plate, gives a polarizing plate excellent in aging stability, and imparts an excellent display enjoyability to a liquid crystal display. SOLUTION: This cellulose ester film, as a protective film for a polarizing plate, has a thickness of 100 μm or lower. The refractive index of one side A of the film is 1.470-1.490 and that of the other side B, 1.480-1.500 μm, the difference between these refractive indexes being 0.010 or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cellulose ester film, and more particularly, to a cellulose ester film having excellent durability with little dimensional change and deformation under high temperature and high humidity.

The cellulose ester film according to the present invention is particularly used as a protective film for a polarizing plate, and is excellent in processability when the protective film for a polarizing plate is processed into a polarizing plate, and also has a long-term stability of the polarizing plate. It has excellent display appreciability in a liquid crystal display using a polarizing plate.

[0003]

2. Description of the Related Art Generally, a liquid crystal image display device (LCD) has low power consumption and low power consumption and can be directly connected to an IC circuit.
Since it can be made particularly thin, it is widely used as a display device for personal computers, mobile phones, liquid crystal televisions and the like. The LCD has a structure in which polarizing plates are provided on both sides of a liquid crystal cell, for example, and the polarizing plate allows only light on a deflecting surface in a certain direction to pass. Therefore, in the LCD, it plays an important role of visualizing the change of the liquid crystal orientation due to the electric field. That is, the performance of the LCD largely depends on the performance of the deflecting surface. The polarizing plate generally has a protective film for polarizing plate laminated so as to sandwich both sides of the deflector. The LCD is constructed by stacking the deflector plate on the liquid crystal cell. Among these constituent elements, the deflector is one in which iodine or the like is adsorbed and stretched on a polymer film. That is, a solution called H ink containing a dichroic substance (iodine) is wet-adsorbed onto polyvinyl alcohol film, and then the film is uniaxially stretched to orient the dichroic substance in one direction. is there.

On the other hand, cellulose resin, especially cellulose triacetate, is used for the protective film for polarizing plate. This protective film for a polarizing plate is manufactured using a belt casting system device. That is, in the belt casting apparatus, a casting die is provided near the belt, and a drying unit and a take-up roll are provided via a peeling roll. After the dope is cast on the belt from the casting die, the film is peeled off by a peeling roll and further completely dried by a roll drying section, and then the film is wound up by a winding roll.

Specifically, a dope prepared by dissolving cellulose triacetate and a plasticizer in a mixed solvent containing a good solvent for cellulose triacetate, for example, methylene chloride and a poor solvent for cellulose triacetate, for example, methanol, ethanol, butanol or cyclohexane is used. With a precision gear pump that sends out a certain amount of dope, it is cast from a casting die onto an endless belt that continuously rotates, the solvent is evaporated on the belt, and the dope solidifies, and then the web is separated from the belt by a roll. The cellulose triacetate film is obtained by peeling it through a roll group, drying it while winding it around a roll group, or drying it through a tenter and winding it in a winding section.

With the rapid development of information-related equipment in recent years,
The demand for LCDs is growing, and there is a strong demand to supply polarizing plates and protective films for polarizing plates, which are the constituent materials of LCDs. In order to meet such a demand, increasing the production amount of protective films for polarizing plates is an important issue in the industry.

In order to improve the productivity of such a protective film for a polarizing plate, various techniques for improving the film forming speed have been studied. For example, as a method for accelerating the solidification of the dope on the belt, a method of solidifying after casting by containing a poor solvent in the dope, a multilayer casting method in which casting is performed by dividing from a plurality of casting dies, the surface of the belt For example, the dope may be solidified at a temperature of 10 ° C. or lower.

In the method using a poor solvent, a poor solvent having a boiling point higher than that of the good solvent is mixed and used in addition to a good solvent of cellulose triacetate, so that the ratio of the poor solvent increases as the solvent evaporates and the dope is added. Solidify.

There is also a method of increasing the film-forming speed by carrying out multilayer casting from two dies. The multi-layer casting method is a method in which, for example, half of the film thickness of the final film (film thickness ratio is arbitrary) is cast from each die to reduce the thickness of the initial web to enhance peeling ( Japanese Patent Sho 60
No. 27562).

Another method is to increase the surface temperature to 10 ° C.
It utilizes the property of solidifying by lowering the temperature by casting the dope on the support kept below (JP-A-62-37113, 62-64514).
No. 62-115035).

According to these conventional methods, the web can be peeled from the support with a relatively high solvent content.
Since both sides can be dried in a state containing a large amount of solvent, there are advantages that the drying efficiency is further improved and the time required for film formation can be greatly shortened. However, in these conventional methods, after peeling, the web is rapidly dried, resulting in surface properties and mechanical properties,
There is a problem in that it is difficult to obtain a preferable cellulose triacetate film due to a decrease in the stability of physical properties.

[0012]

Therefore, in the past, cellulose triacetate films have been conventionally manufactured in order to suppress brittleness, impart flexibility, and improve physical properties, so that triphenyl phosphate, diethyl phthalate or ethyl phthalate is manufactured. It has been practiced to include a plasticizer such as ruethyl glycolate. In order to impart appropriate plasticity to the film, it is necessary to add an appropriate amount of a plasticizer to the cellulose triacetate composition, and the addition amount is usually 5 to cellulose triacetate.
It was 30%. On the other hand, a cellulose triacetate film containing no plasticizer has also been proposed (Japanese Patent Laid-Open No. 1-214802).

When the cellulose triacetate film is used for optics, for example, for polarizing plates, the environment in which they are used is quite different. For example, it has come to be used in an environment where it can be in a high temperature and high humidity state such as a liquid crystal display mounted on an automobile, and is also used for a display of a large-sized liquid crystal television, and more durability is required. There is.

Although dimensional stability is important among the durability, the cellulose triacetate film generally has a larger deformation at high temperature and high humidity than other transparent supports such as polyethylene terephthalate film, and thus dimensional stability. I had a problem that it was not good. Therefore, the applications of the conventional cellulose triacetate film have been limited to specifications in which dimensional stability is not strictly required.

Further, conventionally, a method for improving the distortion of the film when the temperature changes and a method for improving the deformation resistance under high temperature and high humidity have been proposed (JP-A-9-90333).
Japanese Unexamined Patent Application Publication No. 10-152568 and Japanese Unexamined Patent Application Publication No. 10-152568) are not sufficient, and further improvement is required.

Therefore, in order to make the protective film for a polarizing plate usable in a wider range of applications, the dimensional stability, the deformation resistance under high temperature and high humidity are further improved, and the demand for an expanding LCD is met. In order to meet the demand for supplying a protective film for a polarizing plate, it is required to obtain a cellulose ester film having stable physical properties even in high-speed film formation for improving the production amount of the protective film for a polarizing plate.

The present invention meets the above-mentioned demands in this technical field, and the present inventors have found that the drying rate of the solvent at the time of forming the cellulose ester film is within a specific range and the cellulose ester film is By having the refractive index of is within a specific range, it was found that the dimensional stability of the cellulose ester film, the stability of the physical properties under high temperature and high humidity environment is greatly improved, and the present invention has been completed. Is.

The present invention further improves the dimensional stability of the protective film for a polarizing plate, the deformation resistance under high temperature and high humidity, and the stable physical properties even in high-speed film formation for improving the production amount of the protective film for a polarizing plate. It is an object of the present invention to provide a cellulose ester film having specific properties and a method for producing the same.

[0019]

In order to achieve the above object, the invention according to claim 1 is a cellulose ester film having a thickness of 100 μm or less, in which one of the front and back surfaces is refracted. Rate 1.470-1.49
0, the other surface has a refractive index of 1.480 to 1.500, and the difference between the refractive indexes of the respective surfaces is 0.010 or less.

In Claim 2, the cellulose ester film according to Claim 1 has the following Condition 1 and Condition 2.
It is characterized in that the difference in refractive index measured by each of the above is 0.005 or less.

Condition 1: Film sample at 23 ° C. and 55%
The humidity is adjusted for 24 hours in the environment of RH, and then the refractive index is measured.

Condition 2: The film sample was left for 5 hours in a dry environment where the humidity was maintained at 105 ° C., then at 23 ° C. and 55% R
Humidity is controlled for 24 hours in the environment of H, and the refractive index is measured.

According to a third aspect of the invention, in the cellulose ester film according to the first aspect, the difference between the refractive index of one surface of the film measured under the condition 2 of the second aspect and the refractive index of the other surface is the difference. It is characterized by being 0.008 or less.

[0024] In claim 4, the cellulose ester film according to claim 1 has the following condition 1 and condition 3
The difference between the respective measured refractive indexes is 0.015 or less.

Condition 1: Film sample at 23 ° C. and 55%
The humidity is adjusted for 24 hours in the environment of RH, and then the refractive index is measured.

Condition 3: Film sample at 80 ° C. and 90%
After left for 50 hours in RH environment, 23 ℃ and 55% RH
Humidity is controlled for 24 hours under the environment, and the refractive index is measured.

According to a fifth aspect of the invention, in the cellulose ester film according to the first aspect, the difference between the refractive index of one surface of the film and the refractive index of the other surface of the film measured under the condition 3 of the fourth embodiment is 0. It is characterized by being 0.005 or less.

The invention according to claim 6 produces a cellulose ester film by a solution casting method using a cellulose ester solution (hereinafter referred to as a dope) having a solvent content of 300% by weight or more with respect to a dry web. A dope contains a hydrophobic compound having a molecular weight of 300 or more and a specific gravity of 1.10 to 1.35 with respect to cellulose ester in a weight ratio of 2 to 8%, and the support, that is, mirror-finished. The change in the solvent content of the web from the casting portion to the peeling portion on the support composed of the driving rotating metal endless belt or the driving rotating metal drum having a curved surface is 3.7 to 12 weight per second. It is characterized by being set as%.

The invention according to claim 7 is a cellulose ester film produced by the method according to claim 6.

In the eighth aspect, in the cellulose ester film according to the seventh aspect, the difference in refractive index measured under the conditions 1 and 2 according to the second aspect is 0.
It is characterized by being 005 or less.

In claim 9, the cellulose ester film according to claim 7 is the difference between the refractive index of one surface of the film measured under the condition 2 of claim 3 and the refractive index of the other surface. Is 0.008 or less.

In the tenth aspect, the cellulose ester film according to the seventh aspect is the condition 1 according to the fourth aspect.
And the difference in refractive index measured under the condition 3 respectively,
It is characterized by being 0.015 or less.

In the eleventh aspect, the cellulose ester film according to the seventh aspect is the condition 3 according to the fifth aspect.
The difference between the refractive index of one surface of the film and the refractive index of the other surface of the film is 0.005 or less.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described.

In the method for producing a cellulose ester film according to the present invention, the solvent content of the dry web is 300.
Cellulose ester solution (dope) containing more than wt%
A method for producing a cellulose ester film by a solution casting film-forming method, wherein the dope has a molecular weight of 300.
A drive-rotating stainless steel containing a hydrophobic compound having a specific gravity of 1.10 to 1.35 with respect to a cellulose ester in a weight ratio of 2 to 8% and having a mirror-finished surface which is generally a support. The change in the solvent content of the web from the casting portion on the endless belt or the driving rotary drum to the peeling portion is set to 3.7 to 12% by weight per second.

Here, first, the hydrophobic compound means a compound which is substantially insoluble in water. For example, the hydrophobic compound is represented by the solubility in water at 20 ° C. and has a solubility of 1.5% by weight or less. Examples of such a hydrophobic compound include a phosphoric acid ester-based compound, a phthalic acid ester-based compound, or a plasticizer made of a polymerized compound having these as a monomer.

Next, the change (drying rate) of the solvent content per second of the web between the casting portion and the peeling portion on the support will be described.

The dope used in the present invention refers to a cellulose triacetate solution in which cellulose triacetate is dissolved in a mixed solvent of a good solvent and a poor solvent, and the dope film is formed by casting the dope, solidifying it on a support and drying it. Will be called the web. The film may be called a film when the web is dried to form a film and the content of the solvent in the web is considerably reduced. However, it should be noted that the clear boundary between the web and the film is not clear, and the description in the specification of the present invention does not make a clear distinction.

The drying rate used in the present invention is calculated based on the solvent content. That is, solvent content (wt%)
Is the web weight M obtained by putting the web sampled at the measuring points in the casting part and the peeling part into a weighing bottle.
(G) was weighed, after which the web sample was heated at 115 ° C. for 1 hour, cooled to room temperature so as not to adsorb water, and the weighing bottle was weighed to obtain the weight N (g) of the dry web as the following formula. Calculated according to.

Solvent content (% by weight) = {(M−N) / N} × 100 Then, the solvent content is calculated for each of the casting part and the peeling part, and the difference between them is calculated from the casting part to the peeling part. Of solvent content per second divided by the time required (seconds) (%)
/ Sec) is the drying rate.

In the present invention, the surface of the web means
It refers to the side of the web that is exposed to air or other dry gas as a doped film on the support or after peeling on both sides. The dry gas of the dry air is not limited to the above, as long as it is a gas that can evaporate the solvent, such as nitrogen gas and carbon dioxide gas in addition to air.

In the method for producing a cellulose ester film according to the present invention, when a cellulose ester solution (dope) having a solvent content of 300% by weight or more with respect to a dry web is used, a cellulose ester film is produced by a solution casting method. The change in the solvent content of the web from the casting portion to the peeling portion on the support is limited to 3.7 to 12% by weight per second. The reason is that the change in the solvent content of the web is 3.
When the amount is less than 7% by weight, it is not realistic because the film drying ability cannot be secured at the film forming speed for the purpose of improving the production amount. On the contrary, when the amount exceeds 12% by weight, the drying is not performed. Suddenly, the physical properties of the film,
This is because mechanical properties are deteriorated and the stability of the properties cannot be obtained.

In order to enhance the effect of the present invention, the change in the solvent content of the web between the casting portion and the peeling portion on the support is 3.8% by weight or more per second. Is preferred, and less than 10.0% by weight is preferred.

In order to enhance the effect of the present invention, the protective film for polarizing plate is preferably a thin film. Specifically, the cellulose ester film is
The thickness is preferably 100 μm or less, more preferably 60 μm or less. Particularly preferably, it is an ultrathin film having a thickness of about 40 μm or less and about 30 μm. Here, if the thickness of the cellulose ester film exceeds 100 μm, it is not practical as a polarizing plate film due to optical properties, and if it is less than 20 μm,
It is not practical due to the physical strength of the film, and is extremely difficult to manufacture.

Next, the refractive index of the film will be described.

In the present invention, the refractive index of one surface A of the front and back surfaces of the produced film is from 1.470 to
1.490, and the refractive index of the other surface B is 1.48.
It is 0 to 1.500.

Here, the refractive index n of a substance is expressed by the following equation, where c is the light velocity in a vacuum and v is the propagation velocity of light in the substance.

Refractive index n = light velocity in vacuum / propagation velocity of light in substance = c / v That is, the magnitude of the refraction factor is determined according to the delay of the propagation velocity of light in the substance with respect to the velocity of light in vacuum. To do. At this time, since the propagation velocity of light in a substance is an eigenvalue determined by the state of the substance, the refractive index is represented by an absolute value.

Here, the refractive index of the cellulose ester film can be easily measured by a measuring instrument which is commercially available from each instrument manufacturer, but in the present invention, Abbe refractometer type 1T manufactured by Atago Co., Ltd. is used. Shall be used to handle the refractive index of the film measured by the method specified by the manufacturer.

In the above, one of the front and back surfaces of the cellulose ester film has a refractive index of 1.470.
It was found that when the refractive index of the other surface B is less than 1.480 and the refractive index of the other surface B is less than 1.480, the mechanical strength and physical properties of the film are weakened, which is not practical. In addition, the refractive index of one side A of the cellulose ester film is 1.490.
And the refractive index of the other surface B exceeds 1.500, the dimensional stability becomes insufficient, and the dimensional shrinkage of the film in a high temperature and high humidity environment becomes large, and it becomes unpractical as a protective film for a polarizing plate. There was found.

The solvent drying rate during film formation is within a specific range and the refractive index of the film is within a specific range. The present inventors have found that the stability of (1) is significantly improved and have completed the present invention.

Further, according to the present invention, it has been found that the operation and effect which cannot be foreseen from the prior art are produced, and the effect of the present invention is further enhanced.

As described above, the cellulose ester film according to the present invention is a cellulose ester film having a thickness of 100 μm or less, and one of the front and back surfaces A has a refractive index of 1.470 to 1. 490, the refractive index of the other surface B is 1.480 to 1.500, and the difference in the refractive index of each of these surfaces is 0.010 or less. It is preferable to have the following requirements.

That is, in the cellulose ester film according to the present invention, the difference in refractive index measured under the following conditions 1 and 2 is 0.005 or less.

Condition 1: Film sample at 23 ° C. and 55%
The humidity is adjusted for 24 hours in the environment of RH, and then the refractive index is measured.

Condition 2: The film sample was left for 5 hours in a dry environment where the humidity was maintained at 105 ° C., then at 23 ° C. and 55% R
Humidity is controlled for 24 hours in the environment of H, and the refractive index is measured.

In the cellulose ester film according to the present invention, the difference between the refractive index of one surface A and the refractive index of the other surface B of the film measured under the above condition 2 is 0.008 or less. .

Furthermore, the cellulose ester film according to the present invention has a difference in refractive index of 0.015 or less measured under the following conditions 1 and 3, respectively.

Condition 1: Film sample at 23 ° C. and 55%
The humidity is adjusted for 24 hours in the environment of RH, and then the refractive index is measured.

Condition 3: Film sample at 80 ° C. and 90%
After left for 50 hours in RH environment, 23 ℃ and 55% RH
Humidity is controlled for 24 hours under the environment, and the refractive index is measured.

In the cellulose ester film according to the present invention, the difference between the refractive index of one surface A and the refractive index of the other surface B of the film measured under the above condition 3 is 0.005.
It is the following.

Here, the difference in refractive index will be described.

The refractive index of the film can be easily measured by a measuring device commercially available from each device manufacturer, as described above. In the present invention, the Abbe refractometer type 1T manufactured by Atago Co., Ltd. is used to handle the refractive index of the film measured by the method specified by the manufacturer.

In the cellulose ester film of the present invention, when the difference in refractive index measured under the above conditions 1 and 2 exceeds 0.005, and when the difference in refractive index measured under the conditions 1 and 3 is 0. It was found that in the case where it exceeds 0.015, the dimensional stability of the film under a high temperature environment or under a high temperature and high humidity environment is deteriorated, and also the physical shape change such as curling and deformation is deteriorated.

Thus, it was found that by suppressing the difference in refractive index within the range of the present invention, stable physical properties can be obtained without causing the above deterioration, and the present invention was completed. It was Although various studies have been made to improve the dimensional stability, the relationship between such a difference in refractive index and dimensional stabilization has not been known, and the dimensional stability can be controlled by controlling the film characteristics according to the present invention. It was possible to improve the sex.

In the present invention, as a means for achieving the above-mentioned difference in refractive index, the drying rate of the solvent at the time of film formation described above and the refractive index of the film are related, and these are set within a specific range. Is effective.

That is, in the method for producing a cellulose ester film according to the present invention, a cellulose ester film is produced by a solution casting method using a cellulose ester solution (dope) having a solvent content of 300% by weight or more with respect to a dry web. The dope contains 2 to 8% by weight of a hydrophobic compound having a molecular weight of 300 or more and a specific gravity of 1.10 to 1.35 with respect to the cellulose ester. The change in the solvent content of the web from the casting portion to the peeling portion on the support composed of the endless belt made of the driven rotating metal or the drum made of the driven rotating metal having the formed surface is 3.7 to 12 per second. The feature is that it is set to% by weight.

The present invention is directed to the cellulose ester film produced by this method.

The cellulose ester film of the present invention produced by the above method has a difference in refractive index of 0.005 or less measured under the conditions 1 and 2, respectively.

In the cellulose ester film of the present invention produced by the above method, the difference between the refractive index of one surface A and the refractive index of the other surface B of the film measured under the above-mentioned condition 2 is 0. It is 0.008 or less.

The cellulose ester film of the present invention produced by the above method has a difference in refractive index of 0.015 or less measured under the above conditions 1 and 3, respectively.

In the cellulose ester film of the present invention produced by the above method, the difference between the refractive index of one surface A of the film and the refractive index of the other surface B of the film measured under the above condition 3 is 0. It is 005 or less.

The cellulose ester according to the present invention is used for a protective film for a polarizing plate and has a molecular weight of 30.
A hydrophobic compound consisting of a phthalate ester compound having a specific gravity of 1.10 to 1.35 of 0 or more is contained in an amount of 2 to 8% by weight with respect to the cellulose ester, and one surface of both front and back surfaces of the film is contained. Refractive index of A is 1.470 to 1.4
90, and the refractive index of the other surface B is 1.480 to
It is 1.500.

First, the cellulose ester will be described.

In the method of the present invention, when a protective film for a polarizing plate is prepared by a solution casting method using a dope having a solvent content of 300% by weight or more with respect to a dry web, a polarizing plate made of cellulose ester is used. A protective film for phthalate, which is a hydrophobic compound, is used in a weight ratio of 2 to cellulose ester.
.About.8%, and the web drying rate from the casting portion to the peeling portion on the support is 3.7 to 12% by weight per second.

In the present invention, various cellulose ester films can be used, but a cellulose acetate film is preferable, and a cellulose triacetate film is particularly preferable.

The degree of acetylation of cellulose triacetate is 57.
-62.5% is preferable and 59-62% is more preferable. Here, the degree of acetylation means the weight% of CH ₃ COOH (acetic acid) in the cellulose acetate after hydrolysis. The cellulose acetate is not limited to acetic acid, and may be partially esterified with a fatty acid such as propionic acid or butyric acid as long as the degree of acetylation is satisfied. It may contain cellulose esters such as pionate and cellulose butyrate.

The plasticizer used in the present invention is preferably a phosphoric acid ester compound, a phthalic acid ester compound, or a polymer compound having these as a monomer.

A phthalate compound will be described as an example.

Examples of the phthalate compound include
Dimethyl phthalate, diethyl phthalate, dimethoxyethyl phthalate, ethyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, dibutyl phthalate, diheptyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, diisodecyl phthalate, butyl benzyl Examples thereof include phthalate, diisononyl phthalate and imethyl isophthalate.

The cellulose ester film according to the present invention may contain a plasticizer other than the phthalate compound. For example, phosphoric acid ester compounds such as triphenyl phosphate, tricresyl phosphate, triethyl phosphate, biphenyl diphenyl phosphate, etc., other toluene sulfonamide compounds, triacetin, trimellitic acid ester, pyromellitic acid ester, etc., alone or in combination. Can be used together.

In the present invention, the content of, for example, a phthalic acid ester compound with respect to the cellulose ester is 2 to 8% by weight, preferably 3 to 7%. Here, if the weight ratio of the phthalate compound exceeds 8%, the dimensional stability is not sufficient, and specifically, the dimensional shrinkage of the film is large under a high temperature and high humidity environment. For example, when used as a protective film for a polarizing plate in a high-temperature and high-humidity environment, due to dimensional shrinkage of the film, a failure such as light leakage occurs on the polarizing plate, which makes it unusable. Therefore, it is not preferable. If the content is less than 2%, the mechanical strength of the film itself is not sufficient. It becomes brittle and is not sufficient in terms of workability. Therefore, when the polarizing plate is processed into a protective film, when cutting the film or during the punching process, a smooth cut surface is not formed, and chips may be generated, which may cause defects in the product, which is not preferable.

According to the above constitution of the cellulose ester film of the present invention, the dimensional stability of the cellulose ester film is obtained even when the cellulose ester film is used under various environmental conditions such as high temperature environment and high temperature and high humidity environment. Physical properties such as curl and deformation resistance do not deteriorate.

Furthermore, according to the cellulose ester film of the present invention, when the protective film for a polarizing plate is processed into a polarizing plate, it is generally performed through the steps of coating, bonding and adhering an adhesive layer. However, in this case, it is excellent in processability (applicability of the adhesive layer, laminating property, and adhesive property).

Next, a method for evaluating the dimensional stability of the cellulose ester film will be described.

The dimensional stability of the cellulose ester film according to the present invention refers to the property that the cellulose ester film undergoes little dimensional change in the machine direction, the transverse direction and the oblique direction under severe conditions of temperature and humidity. Specifically, the film is placed under various heating conditions, humidification conditions, and hot humidity conditions, and the longitudinal, lateral, and diagonal dimensional changes as the forced deterioration of the film are measured.

For example, for the sample of the film to be measured,
The film is cut into a size of 150 mm in the width direction × 120 mm in the length direction, and a cross-shaped mark is made on the film surface at two points at intervals of 100 m in each of the width direction and the length direction with a sharp blade such as a razor.

Next, this film was heated at 23 ° C. and 55%.
The humidity is controlled for 24 hours or more under the environment of RH, and the distance L1 between the marks in the width direction and the length direction before treatment is measured with a microscope. Next, this film sample was subjected to high temperature treatment in an electric high temperature tank (condition: left for 120 hours under 90 ° C. environmental conditions) or high temperature and high humidity treatment (conditions: 80 ° C. and 90
After leaving it in the environment of% RH for 120 hours, again,
This film sample was tested at 23 ° C and 55% RH for 2
The humidity is controlled for 4 hours, and the distance L2 between the marks in the width direction and the length direction after the treatment is measured with a microscope. The rate of change before and after this process is calculated by the following equation.

Dimensional change rate (%) = (L2−L1) / L1 × 100 L1: distance between marks before treatment L2: distance between marks after treatment, that is, the position of the mark to be attached to the cellulose ester film to be measured is the film. The desired dimensional stability measurement can be performed by attaching in the longitudinal direction, the width direction, and the oblique direction.

[0090]

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

[Examples 1 to 3 and Comparative Examples 1 to 4] In producing cellulose ester films by the method of the present invention, dopes were first prepared. That is, the following compounding composition in which triacetyl cellulose was dissolved in a solvent was placed in a closed container and completely dissolved while stirring at 41 ° C. to prepare a dope, and the prepared dope was filtered with a filter paper.

(Dope composition) Cellulose triacetate (Acetification degree 61.0%) 100 parts by weight Triphenyl phosphate 2 parts by weight Ethylphthalylethyl glycolate 11 parts by weight 2- (2'-hydroxy-3 ', 5'- Di-t-butylphenyl) benzotriazole 8 parts by weight Methylene chloride 475 parts by weight Ethanol 50 parts by weight Next, although not shown, a dope temperature of 33 ° C. was measured by an apparatus for producing a cellulose ester film by a solution casting film forming method. Then, the dope was uniformly cast on a support made of a stainless steel endless belt. The solvent was evaporated while controlling the first half of the endless belt to 12 ° C. and the second half to 40 ° C. When the endless belt had made one round, it was peeled by a peeling roll. Then, the drying was completed while being transported by a number of transport rollers in the drying zone, and a cellulose triacetate film having a film thickness of 80 μm was obtained.

Here, in order to prepare the cellulose triacetate film samples of Examples 1 to 3 and Comparative Examples 1 to 4 of the present invention, as shown in Table 1, the drying rate was changed by adjusting the film forming rate. By proportionally adjusting the amounts of triphenyl phosphate and ethylphthalylethyl glycolate to be used, the content rate can be changed to
These samples were made.

For each sample, by the method described above,
The refractive index, the difference in refractive index, and the dimensional change rate were measured and evaluated.

Further, with respect to the cellulose triacetate film sample, the following moisture permeability, processability and appreciability were evaluated.

Moisture permeability: Under the conditions of 23 ° C. and 55% RH, a cup in which 5 g of calcium chloride was weighed and capped and sealed with each film sample was prepared at 23 ° C.
The moisture permeability of the cellulose triacetate film based on the hygroscopicity of calcium chloride was evaluated from the weight change (g / m ² · 24H) before and after standing for 24 hours under the condition of 80% RH.

Workability: Each cellulose triacetate film sample is coated with water-based adhesive property and the same film sample is bonded to prepare a simulated sample, which is easy to apply and easy to bond. That was confirmed by watching.

Appreciability: Using each cellulose triacetate film sample as a protective film for a polarizing plate, a polarizing plate was prepared from a polarizer and a protective film for a polarizing plate by a method known in the art, and this was used for a liquid crystal display. It was used as a display panel to determine whether or not there was a visual hindrance.

The evaluation results are shown in Table 1.

[Examples 4 to 9 and Comparative Examples 5 to 12] Cellulose ester films were produced by the method of the present invention in the same manner as in Examples 1 to 3, but the casting amount of the dope was adjusted. A cellulose triacetate film having a thickness of 40 μm was obtained. With respect to each cellulose triacetate film sample, the refractive index, the difference in refractive index, the dimensional change rate, the moisture permeability, the processability, and the appreciability were similarly evaluated by the methods described in Examples 1 to 3 above. The evaluation results are also shown in Table 1.

Comparative Examples 13 and 14 2 parts by weight of triphenyl phosphate (molecular weight 326) and 11 parts by weight of ethylphthalylethyl glycolate (molecular weight 280) in the cellulose triacetate film sample prepared in Example 1 were added with dibutyl. The sample of Comparative Example 13 was replaced with 13 parts by weight of phthalate (molecular weight 278), and the sample of Comparative Example 14 was replaced with 13 parts by weight of ethylphthalylethyl glycolate (molecular weight 280). The film samples of Comparative Examples 13 and 14 were evaluated in the same manner as in the above example. The obtained results are summarized in Table 1.

[0102]

[Table 1]

As can be seen from the results in Table 1 above, according to the cellulose triacetate film of the present invention, the dimensional stability was determined by defining the change in the refractive index before and after the condition of the dimensional change of the film and the drying rate. Excellent display, stable display even under high temperature and high humidity, and improved workability such as laminating property and coating property when manufacturing a polarizing plate.
And by improving the moisture permeability of the film, the stability of the polarizing plate over time can be achieved, and stable display performance can be achieved even in a harsh environment, and the cellulose triacetate film of the present invention was used as a protective film for a polarizing plate. The appreciation of the liquid crystal display panel was very good, and there was no hindrance in visual recognition.

[0104]

As described above, the cellulose ester film according to the present invention is a cellulose ester film having a thickness of 100 μm or less, and one of the front and back surfaces thereof has a refractive index of 1.470 to 1. .490, the refractive index of the other surface is 1.480 to 1.500, and the difference in the refractive index of each of these surfaces is 0.010 or less. The cellulose of the present invention. According to the ester film, there is an effect that the dimensional stability of the protective film for a polarizing plate and the deformation resistance under high temperature and high humidity can be further improved.

Further, the method for producing a cellulose ester film of the present invention is, as described above, carried out by a solution casting film forming method using a cellulose ester solution (dope) having a solvent content of 300% by weight or more based on the dry web. In the method for producing a cellulose ester film, the dope has a hydrophobic compound having a molecular weight of 300 or more and a specific gravity of 1.10 to 1.35 with respect to the cellulose ester in a weight ratio of 2 to 2.
The content of the solvent is 8%, and the change in the solvent content of the web from the casting portion to the peeling portion on the support is 3.
According to the method of the present invention, the production amount of a cellulose ester film useful as a protective film for a polarizing plate having the above-mentioned excellent properties is improved. Even in high-speed film formation, it is possible to obtain stable physical properties.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08L 1:12 C08L 1:12 F term (reference) 2H049 BA02 BB33 BC22 4F071 AA09 AF31 AF31Y AF54 AF57 AG34 AH16 BA02 BB02 BC01 4F205 AA01 AC05 AG01 AR08 GA07 GB02 GC07 GN22 GN24

Claims (11)

[Claims] 1. A cellulose ester film having a thickness of 100 μm or less, one surface of which has a refractive index of 1.470 to 1.490 and the other surface has a refractive index of 1.480. ˜1.500 and the difference in the refractive index between their respective surfaces is 0.010 or less, a cellulose ester film. 2. The cellulose ester film according to claim 1, wherein the difference in refractive index measured under the following conditions 1 and 2 is 0.005 or less. Condition 1: A film sample is conditioned under an environment of 23 ° C. and 55% RH for 24 hours, and then the refractive index is measured. Condition 2: The film sample is left for 5 hours in a dry environment with a humidity of 105 ° C., and then conditioned for 24 hours in an environment of 23 ° C. and 55% RH to measure the refractive index. 3. The difference between the refractive index of one surface of the film and the refractive index of the other surface of the film measured under the condition 2 of claim 2 is 0.008 or less. 1. The cellulose ester film according to 1. 4. The cellulose ester film according to claim 1, wherein the difference in refractive index measured under the following conditions 1 and 3 is 0.015 or less. Condition 1: A film sample is conditioned under an environment of 23 ° C. and 55% RH for 24 hours, and then the refractive index is measured. Condition 3: After leaving the film sample in an environment of 80 ° C. and 90% RH for 50 hours, 2 in an environment of 23 ° C. and 55% RH
Humidify for 4 hours and measure the refractive index. 5. The difference between the refractive index of one surface of the film and the refractive index of the other surface of the film measured under the condition 3 of claim 4,
It is 0.005 or less, The cellulose ester film of Claim 1 characterized by the above-mentioned. 6. The solvent content of the dry web is 300.
In a method for producing a cellulose ester film by a solution casting film forming method using a cellulose ester solution having a weight% or more (hereinafter referred to as a dope), the dope is
2 to 8% by weight of a hydrophobic compound having a molecular weight of 300 or more and a specific gravity of 1.10 to 1.35 with respect to cellulose ester.
The change in the solvent content of the web between the casting portion and the peeling portion on the support is 3.7 to 1 second per second.
A method for producing a cellulose ester film, which comprises 12% by weight. 7. A cellulose ester film produced by the method according to claim 6. 8. The cellulose ester film according to claim 7, wherein the difference in refractive index measured under the condition 1 and the condition 2 according to claim 2 is 0.005 or less. 9. The difference between the refractive index of one surface of the film and the refractive index of the other surface of the film measured under the condition 2 of claim 3 is 0.008 or less. Item 7. A cellulose ester film according to item 7. 10. The cellulose ester film according to claim 7, wherein the difference in refractive index measured under the conditions 1 and 3 according to claim 4 is 0.015 or less. 11. The difference between the refractive index of one surface of the film and the refractive index of the other surface of the film measured under the condition 3 of claim 5 is 0.005 or less. 7. The cellulose ester film according to 7.