JPH06335932A - Manufacture of cast film - Google Patents

Abstract

PURPOSE:To obtain a cast film with a high leveling condition, excellent flatness, no fine air bubble, excellent appearance, extremely less residual solvent and excellent mechanical properties by performing efficiently solvent evaporation from the inside of the cast film and a polymer soln. CONSTITUTION:In a method for manufacturing a cast film wherein after a soln, of a polymer material is applied on a substrate for the case film, the applied soln. is dried and the solvent in the soln. is removed, the polymer material soln. applied on the substrate is irradiated with IR rays to dry the applied soln. As the IR rays to be irradiated, such IR rays which have wave length being higher absorption factor in the solvent substance than in the polymer material in the soln.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cast film, and more particularly to a method for producing an excellent cast film which is excellent in smoothness, thickness accuracy and transparency and has no appearance defect with high productivity.

[0002]

2. Description of the Related Art As a method for producing a thin film from a polymer material, there is a cast film forming method in which a solution of a polymer material in a solvent is cast on the surface of a support to evaporate the solvent component. The polymer film obtained by this method is called a cast film.

Conventionally, in the method for producing a cast film, a polymer polymer solution (hereinafter abbreviated as polymer solution) is applied onto a support such as a plastic film or a metal endless belt, and then heated with air or the like. Evaporating the solvent by passing through a heated drying zone and by heat drying the support as an auxiliary means,
Then, there was a method of separating the film-formed cast film from the support.

[0004]

The physical properties of the cast film produced by the conventional method are as follows: even if they are the same polymer, the type of solvent used, the evaporation rate of the solvent (drying conditions), and the casting conditions. (Temperature and humidity, concentration of polymer solution, accuracy between die / belt, etc.), heat treatment condition heating method, tension, etc.) and the like.

Particularly, the drying condition and the heat treatment condition have a problem that they govern the evaporation rate of the solvent and the concentration of the residual solvent, and have a great influence on the flatness of the cast film, appearance defects such as microscopic bubbles and mechanical properties.

An object of the present invention is to obtain a method for producing a cast film which solves the above problems. That is,
Efficient solvent evaporation from the polymer solution and the inside of the cast film, excellent leveling and flatness, excellent appearance characteristics without micro bubbles, extremely low residual solvent, and production of cast film with excellent mechanical properties Aim to get a way.

[0007]

The method for producing a cast film according to the present invention comprises a step of applying a solution of a polymer material on a support for a cast film, and then drying the applied solution. In the method for producing a cast film by removing the solvent component, in order to dry the applied solution, the high molecular polymer material solution applied on the support is irradiated with infrared rays, and Is characterized by using infrared light having a wavelength having a higher absorptivity in a solvent substance than in a polymer material in a solution.

For example, in order to obtain a cast film composed of a polymer having polycarbonate as a main component, methylene chloride is usually used as a solvent for the coating solution.

The absorption rate of light in this methylene chloride has a wavelength width of 0.1 μm with a wavelength of about 7.9 μm as the center.
A sharp peak of absorptivity and a wavelength of about 13.5 μm
There is a peak of absorptance in the range of about 1 μm in wavelength width centering on, and the absorptance at other wavelengths is extremely small. On the other hand, polycarbonate has a wavelength of about 13.5μ.
The absorption rate of light is small in a wavelength range of about 1 μm centering on m.

Therefore, by irradiating the coating solution with infrared rays having a wavelength peak of about 13.5 μm and having an intensity peak in the range of about 1 μm, the methylene chloride can be selectively heated. it can.

Due to this effect, evaporation of methylene chloride can be effectively promoted from the inside, and heating and drying with a high leveling effect, which suppresses the formation of a hardened skin layer on the surface, can be carried out. This effect is effective not only in the evaporation region of the solvent but also in the diffusion region, and the final residual solvent of the cast film can be effectively reduced.

Further, when tetrahydrofuran is used as a solvent, absorption wavelengths of 3.5 μm, 9.3 μm and 10.8 μm are used, and when 1,4-dioxane is used as a solvent, absorption wavelengths of 11.5 μm and 16 μm are used. 3.5 μ when either absorption wavelength is 1.3-dioxolane as solvent
The same effect can be expected by utilizing the absorption wavelength of m and 10.8 μm.

As described above, in order to achieve the object of the present invention, a cast film is used to cast infrared rays of a specific wavelength, which has a low absorption in the polymer forming the cast film and has an absorption in the solvent forming the polymer solution. Can be achieved by using it as a drying means or as a drying auxiliary means. This method can be applied to not only the polycarbonate resin exemplified here but also a cellulose teriacetate resin, a polyimide resin, a polyarylate resin, etc. which are usually formed by a casting method.

When this method is applied, it is preferable to select a solvent having a large absorption in the region where the infrared absorption of the high molecular polymer to obtain the cast film is small.

[0015]

Example 1 As a coating solution, 50 parts of methylene chloride, 35 parts of tetrahydrofuran and 15 parts of polycarbonate resin were used.

This polymer solution was continuously cast from a casting die having a discharge width of 1000 mm onto a stainless steel mirror belt so as to have a wet thickness of 500 μm.
It was passed through the drying zone at a belt speed of m / min.

The temperature of the first drying zone is set to a temperature lower than the boiling point of 40 ° C. of methylene chloride, and the air velocity is 0.
The carbon dioxide gas laser having a wavelength of 10.8 μm was irradiated in an atmosphere of 1 m / sec or less. After that, the temperature was raised and heated in a continuously connected drying zone, and peeled from the belt to produce a polycarbonate casting film.

The residual solvent concentration of the film thus obtained was 7%. After peeling, the film thickness after drying at a temperature of 125 ° C. for 30 minutes was 50 μm ± 1 μm or less. Further, the surface flatness seen by the surface roughness meter reflection method was very good.

[0019]

Comparative Example 1 The same polymer solution as in Example 1 was used as the coating solution. Then, a casting film was manufactured under the same conditions as in Example 1 except that the carbon dioxide laser irradiation was not performed.

The residual solvent concentration of the film thus obtained was 15%. Further, the thickness of the film dried on the same strip as in Example 1 was 50 μm ± 2 μm. Further, the surface flatness seen by a surface roughness meter and a reflection method was worse than that in Example 1, and the surface was on a rough wave.

[0021]

As shown in the concrete examples of Example 1 and Comparative Example 1, by applying the present invention, it is possible to efficiently evaporate the solvent in the drying zone under a very low wind speed condition. It is possible to obtain a cast film having good leveling and less residual solvent without being disturbed by wind.

Claims (1)

[Claims] 1. A method for producing a cast film by applying a solution of a high molecular weight polymer material on a support for cast film and then drying the applied solution to remove the solvent component in the solution. To irradiate the high molecular polymer material solution coated on the support with infrared rays in order to dry the solution, and the infrared ray to be irradiated is a solvent substance rather than the high molecular polymer material in the solution. A method for producing a cast film, which comprises using infrared rays having a high absorption rate.