JP2000336179A - Cellulose ester film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject cellulose ester film that has high transparency, excellent workability, high productivity, and is useful as a polarizing plate for a liquid-crystal display device by using a cellulose ester and a specific amount of a plasticizer and producing a film through casting, as the plasticizer is prevented from reducing its amount. SOLUTION: This film comprises (A) a cellulose ester, preferably cellulose acetate, (B) a plasticizer in an amount of 2-40 wt.% based on the component A, for example, triphenyl phosphine and the film is formed by the casting technique. In this case, the component B distributes on one surface of the film so that its amount may reach 87-96 wt.% based on the total amount in the film. This film is prepared by casting a dope including the components A and B. In a preferred embodiment, the film drying is carried out at about 40-80 deg.C within 10 minutes.

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 particularly suitable for optical applications and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, thin transparent plastic films have recently been used as protective films for polarizing plates, optical compensation films such as retardation plates, and the like.
There is an increasing demand for optical materials such as plastic substrates, photographic supports or moving image cells and optical filters, and OHP films. In particular, liquid crystal displays have recently been improved in image display quality and are now offered as lightweight and portable.
It is widely used as an image display device such as a personal computer, a word processor, a portable terminal device, a television, and a digital still camera or a movie camera. In order to display an image on such a liquid crystal display, it is essential to provide a polarizing plate. Since the quality of the polarizing plate is required to be improved in accordance with the improvement of the image display quality of the liquid crystal display, the transparent plastic film used as the protective film of the polarizing plate is also required to have higher quality. I have.

For optical films such as protective films for polarizing plates, high transparency, low optical anisotropy, high flatness, and easy surface treatment are required to maintain high resolution and display quality of contrast. , High durability (dimensional stability, moisture and heat resistance,
(Water resistance), with no foreign matter in the film and on the surface, no scratches or scratches on the surface (scratch resistance), moderate film rigidity (handling), moderate water permeability It is said that it is necessary to have various excellent characteristics.

[0004] As the plastic film having the above-mentioned preferable characteristics, a film made of cellulose ester, norbornene resin, acrylic resin, polyarylate resin, polycarbonate resin, etc. is known. From the viewpoint, cellulose esters are mainly used. In particular, cellulose esters such as cellulose triacetate are most commonly used for optical applications because when used as a film-forming material, a film showing extremely high transparency and low optical anisotropy can be easily obtained. .

[0005] As a method for producing a film from these plastic materials (film-forming method), various film-forming techniques such as a solution film-forming method, a melt film-forming method and a rolling method are known.
In order to obtain a film exhibiting good flatness and low optical anisotropy, a solution casting method (also called a casting casting method) is particularly suitable. The solution casting method involves dissolving a raw material plastic material such as cellulose acetate in a solvent, and adding various additives such as a plasticizer, an ultraviolet absorber, a deterioration inhibitor, a slipping agent, and a peeling accelerator, as necessary. Solution (dope)
On a surface of a temporary support such as a metal endless belt (endless band) or a rotating drum, it is cast by a dope supply means (die) and dried to an appropriate level on the support to form a coagulated film. In this method, the coagulated film is peeled off from the temporary support, and the coagulated film is then passed through a drying device by various transport means to completely remove the solvent from the coagulated film.

[0006]

SUMMARY OF THE INVENTION In order to increase the productivity of a film by the solution casting method, the drying speed must be increased.
That is, the dope cast on the temporary support is dried quickly,
A method of peeling off the temporary support as soon as possible is conceivable. However, for example, when a cellulose ester film is used as a protective film for a polarizing plate, it is necessary to apply a processing such as punching or cutting after attaching the cellulose ester film to both surfaces of a long polarizing plate sheet. However, in the case of cellulose ester film simply dried and produced at a high speed, cutting debris is liable to be generated, which causes foreign matter to adhere, or the shape of the processed cross section deviates from the shear direction perpendicular to the film, and tilts toward the film surface side. It has been found that the shape tends to be irregular or rough at random, and so-called delamination or delamination occurs in a multilayer structure. Such a problem in processing characteristics is a serious limitation in increasing the productivity by increasing the drying speed of the film. When a photosensitive layer is formed by coating a photosensitive layer on a cellulose ester film,
If cutting chips are generated during operations such as slit cutting and perforation perforation, it may cause a foreign matter adhesion failure and significantly impair image quality.

Therefore, according to the present invention, the generation of cutting chips during processing is small, and the delamination within a layer or between layers is reduced.
That is, an object is to provide a cellulose ester film having excellent processability. The present invention is particularly applicable to optical films (eg, polarizing plates of liquid crystal display devices, optical compensation sheets,
Another object of the present invention is to provide a cellulose ester film which is advantageous as a film material utilizing the excellent transparency and processability of a cellulose ester film, such as various types of substrate films and protective films of photographic materials.

[0008]

Means for Solving the Problems As a result of repeated studies on the above-mentioned problems, the present inventor has found that on the surface of the temporary support, in order to accelerate drying of the cellulose ester dope film cast on the temporary support. When heated and dried at a high temperature, the solvent in the dope film foamed, and as a result, it was noticed that optical properties such as transparency of the obtained cellulose ester film were deteriorated. On the other hand, when the cellulose ester dope cast on the temporary support is dried by heating at a low temperature for a long time, not only does the productivity decrease, but also the plasticizer rapidly evaporates together with the solvent from the surface of the dope. However, since the amount of the plasticizer present on the surface side is considerably reduced as compared with the amount of the plasticizer on the inner side, the surface side of the finally obtained cellulose ester film tends to become brittle, and therefore, the cellulose ester film It has been noticed that the workability of the steel is greatly reduced.

As a result of further studies based on the above findings, the present inventor has found that the drying of the cellulose ester dope film cast on the temporary support is performed by heating at a relatively low temperature on the surface of the dope film. While suppressing the evaporation of the plasticizer, the method is carried out by evaporating and removing only the solvent as much as possible to form a coagulated film in a short time, and at an early stage, the coagulated film is peeled off from the temporary support, and then The present inventors have found that a cellulose ester film having excellent optical properties and excellent mechanical strength can be obtained by carrying out a method of performing sufficient drying, and arrived at the present invention.

The present invention relates to a cellulose ester film produced by a casting film-forming method, comprising a cellulose ester and a plasticizer in an amount of 2 to 40% by weight based on the cellulose ester. The abundance of the plasticizer on the film surface on at least one side is 87 to 87 of the abundance of the plasticizer inside the cellulose ester film.
A cellulose ester film characterized by being in the range of 96% by weight (preferably in the range of 90 to 95% by weight).

[0011] The cellulose ester film of the present invention comprises:
It is desirable that the film be composed mainly of cellulose triacetate. Further, in the cellulose ester film of the present invention, the sound wave propagation velocity measured along the casting direction (MD direction) at the time of film production is desirably in the range of 2.0 to 2.5 km / sec.

The present invention is also directed to a method of casting a dope solution containing a cellulose ester and a plasticizer in an amount of 2 to 40% by weight based on the cellulose ester to form a film on at least one side of the film surface. If the amount of plasticizer is
There is also a method for producing a cellulose ester film in the range of 87 to 96% by weight of the amount of the plasticizer present in the obtained cellulose ester film.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The cellulose ester film of the present invention comprises a cellulose ester and an amount of 2 to 40% by weight (preferably 5 to 20% by weight) based on the cellulose ester. It is a cellulose ester film containing a plasticizer as a main component and produced by a casting film forming method. As the cellulose ester used as a raw material resin in the production of the cellulose ester film of the present invention, for example, lower fatty acid esters of cellulose such as cellulose triacetate, cellulose acetate propionate, and cellulose acetate butyrate can be used. For the production of the cellulose ester film of the present invention, it is particularly preferable to use cellulose triacetate (triacetyl cellulose). When cellulose triacetate is used in the present invention, the degree of acetylation is preferably in the range of 58.5% to 62.5%.

In producing the cellulose ester film of the present invention, a cellulose ester as a raw material resin is used.
An amount of the plasticizer in the range of 2 to 40% by weight (preferably, an amount in the range of 5 to 20% by weight) based on the cellulose ester is dissolved in a suitable organic solvent, and a solution of the cellulose ester composition ( Dope) is prepared. The cellulose ester and the plasticizer may be used as a mixture of two or more kinds. In addition, various known additives such as an ultraviolet absorber, a deterioration inhibitor, a slipping agent, and a peeling accelerator can be added to the dope, if desired. As an organic solvent,
For example, halogenated hydrocarbons (eg, dichloromethane), alcohols (eg, methanol, ethanol, propanol, butanol), esters (eg, methyl formate, methyl acetate), ethers (eg, dioxane, dioxolan, diethyl ether) ) Can be used.

Examples of the plasticizer used in combination with the cellulose ester in the production of the dope include phosphate plasticizers such as triphenyl phosphate (TPP) and biphenyl diphenyl phosphate (BDP), and phthalate esters such as diethyl phthalate. Known plasticizers such as a system plasticizer and a polyester polyurethane elastomer can be used. Particularly preferred are phosphate plasticizers such as triphenyl phosphate (TPP) and biphenyl diphenyl phosphate (BDP). If necessary, an ultraviolet absorber, a deterioration inhibitor,
Various known additives such as a slip agent and a release accelerator may be added.

For the preparation of the dope, a method of stirring and mixing the raw material resin or the like in a solvent and dissolving it by a well-known method may be used. Alternatively, a method in which the swelled mixture is cooled to −10 ° C. or lower and then heated to 0 ° C. or higher to dissolve it may be used.

Next, a cellulose ester composition solution (dope) is cast on a temporary support. This casting may be performed by a method of simultaneously casting two or more types of dopes on a temporary support using a co-casting die.

As the temporary support, a continuous metal band (metal belt) whose surface is mirror-finished may be used, or a rotating drum such as a cooling drum may be used. The casting of the dope on the surface of the temporary support is generally performed by running the temporary support in a continuous liquid in the case of a metal band.
In the case of a rotating drum, the process is performed while continuously rotating.

The dope cast on the temporary support is formed into a film. The solvent is evaporated off by heating and drying the dope film to form a self-supporting coagulated film. Is peeled off from the temporary support and then run in a heating and drying oven to obtain a sufficiently dried cellulose ester film.

In the production of the cellulose ester film of the present invention, as described above, during the drying operation on the temporary support, that is, during the operation of evaporating and removing the solvent, the film is present near the surface of the doped film. It is necessary to suppress evaporation or scattering of the plasticizer. Therefore, the heating temperature is about 40 to 8
The temperature is preferably adjusted to a temperature in the range of 0 ° C., and it is desirable to perform the coagulation of the dope film formed by casting the dope and the stripping operation in a short time. The time from the formation (casting) of the dope film to the stripping of the solidified film is desirably 10 minutes or less.

Further, the amount of the surface plasticizer can be increased by co-casting so that the amount of the plasticizer in the surface layer is larger than the amount of the plasticizer in the inner layer. In this case, the amount of the plasticizer in the front layer is preferably in a range of 1.1 to 2.0 times the amount of the plasticizer in the inner layer in order to prevent the precipitation of the plasticizer.

The coagulated film of the doped film peeled off from the temporary support is then heated and dried in a heating furnace. The heating and drying in the heating furnace is desirably performed by heating at 80 to 150 ° C. for 10 to 60 minutes.

Although the thickness of the cellulose ester film of the present invention varies depending on the use of the film, it is generally in the range of 20 to 500 μm, preferably 50 to 2 μm.
It is in the range of 00 μm.

[0024]

[Example 1] Cellulose acetate (degree of acetylation 60.8%, degree of polymerization 300) was replaced with methylene chloride 8
It was dissolved in a mixed solvent consisting of 2 parts by weight and 15 parts by weight of methanol with stirring to prepare a cellulose acetate solution having a concentration of 15% by weight. A plasticizer (a mixture of 10 parts by weight of triphenyl phosphate and 5 parts by weight of biphenyl diphenyl phosphate with respect to the cellulose acetate in the solution) was added to the cellulose acetate solution and mixed to produce a dope. The dope is cast on the surface of a running metal belt (temporary support) to form a dope film. The dope film is heated and dried at 50 ° C. for 5 minutes to form a coagulated film, which is immediately pulled from the metal belt. I peeled it off. The coagulated film is further heated in a heating furnace at 100 ° C. for 10 minutes, and
It was dried by heating at 0 ° C. for 5 minutes to obtain a dried cellulose acetate film (thickness: 100 μm).

The appearance, processing characteristics, amount of surface plasticizer, and sound wave propagation velocity (sonic velocity) in the length direction of the cellulose acetate film obtained above were measured. The measurement method and measurement results will be described later.

Example 2 Heat drying from casting of a dope onto a metal belt to stripping of a solidified film was performed at 50 ° C. for 10 times.
Minutes, but according to the method described in Example 1,
Dry cellulose acetate film (thickness: 10
0 μm).

The appearance, processing characteristics, amount of surface plasticizer, and sound wave propagation velocity (sound velocity) in the longitudinal direction of the cellulose acetate film obtained above were measured. The measurement method and measurement results will be described later.

Example 3 A dried cellulose acetate film was dried according to the method described in Example 1 except that the amount of the dope cast on the metal belt was adjusted so that the thickness of the obtained cellulose acetate film after drying was 135 μm. Was produced.

The appearance, processing characteristics, surface plasticizer amount, and sound wave propagation velocity (sonic velocity) in the length direction of the cellulose acetate film obtained above were measured. The measurement method and measurement results will be described later.

Example 4 A dried state was prepared according to the method described in Example 1, except that the amount of the dope cast on the metal belt was adjusted so that the thickness of the obtained cellulose acetate film after drying was 122 μm. Was produced.

The appearance, processing characteristics, amount of surface plasticizer, and sound wave propagation velocity (sound velocity) in the length direction of the cellulose acetate film obtained above were measured. The measurement method and measurement results will be described later.

[Comparative Example 1] Heat drying from casting of a dope onto a metal belt to stripping of a coagulated film was performed at 50 ° C for 20 minutes.
Minutes, but according to the method described in Example 1,
Dry cellulose acetate film (thickness: 10
0 μm).

The appearance, processing characteristics, surface plasticizer amount, and sound wave propagation velocity (sonic velocity) in the length direction of the cellulose acetate film obtained above were measured. The measurement method and measurement results will be described later.

[Comparative Example 2] Heat drying from casting of a dope on a metal belt to stripping of a coagulated film was performed at 100 ° C for 2 hours.
Minutes, but according to the method described in Example 1,
Dry cellulose acetate film (thickness: 10
0 μm).

The appearance, processing characteristics, amount of surface plasticizer, and sound wave propagation velocity (sonic velocity) in the length direction of the cellulose acetate film obtained above were measured. The measurement method and measurement results will be described later.

Comparative Example 3 A dried cellulose acetate film was dried according to the method described in Comparative Example 1 except that the amount of the dope cast on the metal belt was adjusted so that the thickness after drying of the obtained cellulose acetate film was 135 μm. Was produced.

The appearance, processing characteristics, surface plasticizer amount, and sound wave propagation velocity (sonic velocity) in the length direction of the cellulose acetate film obtained above were measured. The measurement method and measurement results will be described later.

[Comparative Example 4] A dried state was prepared according to the method described in Comparative Example 1 except that the amount of the dope cast on the metal belt was adjusted so that the thickness of the obtained cellulose acetate film after drying was 122 µm. Was produced.

The appearance, processing characteristics, amount of surface plasticizer, and sound wave propagation velocity (sonic velocity) in the length direction of the cellulose acetate film obtained above were measured. The measurement method and measurement results will be described later.

[Evaluation of Cellulose Ester Film] (1) Appearance The appearance of the obtained cellulose ester film was visually observed to evaluate the transparency. (2) Processing characteristics The obtained cellulose ester film is vertically cut and cut with a paper cutter, and the cut surface is observed with an optical microscope to determine whether the cut surface is perpendicular to the film surface (good workability). , Or inclined (poor workability).

(3) Amount of Surface Plasticizer The amount of surface plasticizer was measured by a known method of irradiating infrared rays (IR) to the film surface (described in JP-A-8-57879). (4) Sound wave propagation speed Using a sound wave meter (SST-110 manufactured by Nomura Corporation), the MD direction of the cellulose acetate film (the length direction during production)
The propagation velocity of longitudinal wave vibration of ultrasonic pulse along was calculated.

(5) Evaluation Results The results are shown in Table 1 below.

[0043]

[Table 1] Table 1 セ ル ロ ー ス Cellulose ace Appearance Processing properties Surface Plasticizer amount Sound wave propagation speed Tate film (%) (km / sec) ────────────────────────────────── Example 1 Transparent AA 95 2.3 Example 2 Transparent AA 90 2.5 Example 3 Transparent AA 90 2.3 Example 4 Transparent AA 92 2.4 ──────────────────────── Comparative Example 1 Transparent BB 85 2.7 Comparative Example 2 Opaque −−−−−−−− Comparative Example 3 Transparent BB 80 2.9 Comparative Example 4 Transparent BB 82 2.8────────────────────────────────────

Note: The transparency of the cellulose triacetate film of Comparative Example 2 was greatly reduced by foaming.
The measurement of the processing characteristics, the amount of the surface plasticizer, and the sound wave propagation speed were omitted because the film was unsuitable as an optical film.

[0045]

The cellulose ester film of the present invention has high transparency and excellent processing characteristics and can be manufactured with high productivity. It can be advantageously used for a sheet or various substrates such as a photographic light-sensitive material, and a film utilizing the excellent transparency and processability of a cellulose ester film such as a protective film.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H049 BA02 BA06 BB33 BB49 BC09 4F071 AA09 AE04 AF06Y AH12 BB02 BC01 BC17 4F205 AA01 AB07 AC05 AG01 AH73 AR15 GA07 GB02 GC07 GE03 GE24 GF01 GF02 GF24 GN22 EG1 002 024 GP00 GQ00

Claims (5)

[Claims] 1. A cellulose ester film produced by a casting film-forming method, comprising a cellulose ester and a plasticizer in an amount in the range of 2 to 40% by weight based on the cellulose ester. A cellulose ester film, wherein the amount of the plasticizer present on the film surface is in the range of 87 to 96% by weight of the amount of the plasticizer present inside the cellulose ester film. 2. The method according to claim 1, wherein the amount of the plasticizer present on at least one surface is in the range of 90 to 95% by weight of the amount of the plasticizer present inside the cellulose ester film. Cellulose ester film. 3. The cellulose ester film according to claim 1, wherein the cellulose ester is cellulose acetate. 4. The cellulose according to claim 1, wherein a sound wave propagation velocity measured along a casting direction at the time of film production is in a range of 2.0 to 2.5 km / sec. Ester film. 5. A casting film comprising a cellulose ester and a dope solution containing a plasticizer in an amount in the range of 2 to 40% by weight based on the cellulose ester, to form a film of the plasticizer on at least one side of the film surface. The abundance is 87 of the abundance of the plasticizer inside the obtained cellulose ester film.
A method for producing a cellulose ester film in the range of -96% by weight.