JP2001018281A - Method for molding polymer sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make vaporization heat within a specified range in gas acting on a press pressure improve thickness spots even in high speed casting by incorporating a misty cooling medium within a specified range. SOLUTION: A sheet 12 extruded from a nozzle 11 is introduced onto a cooling roll 13 rotating at a high speed, and the ear-corresponding part of the sheet is made to adhere electrostatically by a needle-shaped electrode 14 to which high voltage is applied. Next, it is led to a chamber 15, which is filled with a gas in which a misty cooling medium, air, etc., are mixed. In this state, the sheet 10 is cooled by the cooling medium, which is contained in the gas in a ratio of 1-200 g/m3, the vaporization heat of which is 30-50 kJ/mole, simultaneously adhered to the cooling roll 13 by the press pressure of the gas, and solidified. In this way, the amount and speed of the gas discharged from the chamber 15 can be controlled to be low, preventing the thickness uniformity of the sheet from being deteriorated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a sheet by extruding a molten polymer into a sheet and cooling and solidifying the sheet. More specifically, the present invention relates to a method for forming a thin polymer sheet having excellent thickness uniformity by a gas pressing method at a high speed. The present invention relates to a method of casting and molding.

[0002]

2. Description of the Related Art A gas static pressing method, particularly a casting method using an air chamber (Japanese Patent Publication No. 47-39930) is effectively used for forming a sheet of a polymer having a high viscosity in a molten state, for example, polypropylene. However, in the case of a polymer having low viscosity, for example, polyethylene terephthalate, a problem occurs in the uniformity of thickness (thickness unevenness).

The cause of the thickness unevenness is that an airflow blown toward the upstream of the cooling roll from a gap between the outer wall on the base side of the chamber and the cooling roll collides with a sheet coming out of the base and vibrates the sheet. It is in.

[0004] As a measure for improving unevenness of thickness in a casting method using an air chamber, for example, Japanese Patent Application Laid-Open No. 61-1357 discloses a method.
No. 25, an air knife is provided on the upstream side of the air chamber, and a high-speed airflow from the air knife is blown into the air chamber to suppress the airflow blowing from the air chamber toward the upstream of the cooling roll. A device has been proposed in which the inside is pressed to bring the sheet into close contact with a cooling roll.

In Japanese Utility Model Application Laid-Open No. 6-728, the gap between the outer wall of the mouth of the chamber and the sheet is automatically adjusted to the minimum with high precision according to the conditions, thereby minimizing the amount of air blown from the chamber. There has been proposed a device for improving thickness unevenness.

According to the improvement described in Japanese Patent Application Laid-Open No. 61-135725, the function of preventing air flow from the air chamber to the upstream side of the cooling roll and the function of pressurizing the air chamber are not independent. Is difficult.

According to the improvement described in Japanese Utility Model Application Laid-Open No. 6-728, a polymer having a small viscosity such as polyester is easily affected by vibration, so that the gap between the outer wall on the base side of the chamber and the sheet is made very narrow. Then, there is a problem that a trouble such as the sheet being cut into contact with the chamber is apt to occur, and a sufficient effect cannot be obtained and the equipment becomes large.

[0008]

The main cause of the thickness unevenness in the air chamber method depends on the casting conditions such as the relative position of the die and the cooling roll, but the sheet flows on the surface of the sheet and is in a free space. The most reliable and effective method is to reduce the pressure on the chamber to reduce uneven thickness.However, if the pressure is reduced, the sheet-like material and the cooling roll adhere to each other. Since the force is reduced and the heat transfer amount is reduced, uneven cooling or insufficient cooling occurs.

The inventor of the present invention has solved the above-mentioned problems, studied a measure for improving thickness unevenness which is easy to operate, is easy to operate, and is effective even for a polymer having low viscosity such as polyester. The inventors have found that if the pressurized gas itself is a gas having a high cooling action, the required cooling action can be obtained even with a low pressurization, and the uneven thickness can be improved even in the case of high-speed casting, and the present invention has been reached.

[0010]

That is, according to the present invention, a molten polymer is extruded from an orifice-shaped die into a sheet.
In a method of forming a sheet in which a gas is pressed and adhered to a cooling roll surface and solidified, a mist-like refrigerant having a latent heat of vaporization of 30 to 50 kJ / mol is added to the pressing gas.
A method for forming a polymer sheet, characterized in that the content of the polymer sheet is from 200 to 200 g / m ³ .

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, when a sheet-like material of a molten polymer extruded from a die is brought into close contact with a cooling roll surface by gas pressure in an air chamber and solidified, the gas has a latent heat of vaporization of 30 to 50%. A mist-like refrigerant of 50 kJ / mol is contained in an amount of 1 to 200 g / m ³ . When the mist-like refrigerant is vaporized, the sheet-like material is cooled, so that the sheet can be cast at a high speed.

Further, by the cooling action of the mist-like refrigerant, it is possible to suppress the pressure of the gas for bringing the sheet into close contact with the cooling roll surface. As a result of suppressing the pressure of the gas to a low level, the air volume and pressure of the leaked airflow blown out of the chamber can be suppressed to a low level, and factors such as vibration of the sheet-like material that deteriorate the uniformity of the thickness can be suppressed, and the uniformity of the thickness is excellent. Sheets can be formed.

The mist refrigerant of the present invention has a latent heat of vaporization of 3
It is a mist-like substance composed of an inorganic compound and / or an organic compound of 0 to 50 kJ / mol. The mist-like refrigerant may be composed of a single compound as described above, or may be composed of a mixture of two or more compounds.

Examples of the above compounds include water, lower alcohols such as methyl alcohol and ethyl alcohol, and some alicyclic compounds such as methylcyclohexane. Among these compounds, a mixture with water or an alcohol containing water as a main component is particularly preferable from the viewpoint of ease of handling, safety, cost, and the like.

In the present invention, the content of the mist-like refrigerant in the pressurized gas is in the range of 1 to 200 g / m ³ . Although the lower limit of the content of the mist-like refrigerant is 1 g / m ³ ,
/ M ³ , particularly preferably 10 g / m ³ , since the cooling effect of the sheet-like material becomes excellent. The upper limit of the content of the mist-like refrigerant is 200 g / m ³ ,
0 g / m ³ , particularly 50 g / m ³ , is preferable because part of the mist is formed into droplets and surface defects caused by dropping on the sheet can be prevented.

The pressure of the gas is preferably 5 to 500 Pa, particularly preferably 10 to 200 Pa. The length of the air chamber in the sheet traveling direction depends on the casting speed, but is preferably 5 to 50 cm.

In the present invention, examples of the method for converting the refrigerant into a mist include a method of bringing the refrigerant into contact with ultrasonic vibration and a method of bringing dry water into contact with hot water.

As a method of filling the generated mist into the air chamber, there are a method of introducing mist into a suction port of a blower to the air chamber, and a method of introducing mist into a transfer pipe in a process of transferring gas from the blower to the air chamber. And the like. Furthermore, a method of generating mist by the above method in an air chamber may be used.

In the present invention, the sheet-like material extruded from the die is guided into the chamber through a narrow gap between the outer wall on the upstream side of the chamber and the cooling roll, and is mixed with the mist of the gas and the refrigerant in the chamber. It is cooled by gas, and at the same time, it adheres to the cooling roll due to the pressure of the mixed gas and is cooled and solidified, guided to the outside of the chamber through the gap between the downstream outer wall of the chamber and the cooling roll, further cooled and wound up It is transferred to the next step such as a step or a stretching step.

In the present invention, the gas pressure is a pressure of a gas mainly composed of air and containing a mist of a refrigerant, which acts on a sheet or a sheet by static pressure, and can be generated by an air chamber. it can.

In the present invention, the thickness of the sheet is 5 to 100.
μm is preferable, and if it is less than 5 μm, it is difficult to obtain a uniform thickness,
On the other hand, if it exceeds 100 μm, a defect of poor adhesion to a cooling roll may occur or a sheet may be poorly cooled. A more preferred sheet thickness range is 5 to 85 μm.

The casting speed in the present invention is preferably 30 m / min or more at the peripheral speed of the cooling roll. The upper limit is not particularly limited, but is preferably 200 m / min.

The polymer in the present invention includes, for example, aromatic polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, polyvinyls such as polystyrene, polyamides such as nylon, polycarbonate and the like. And aromatic polyesters are particularly preferred.

In the case of a polymer having a low melt viscosity such as an aromatic polyester, the sheet extruded from the die has a large neck-in, and the sheet becomes narrower and the thickness uniformity in the width direction is liable to deteriorate. It is preferable to use in combination with the present invention a method of forcibly bringing both ears of the article into close contact with the surface of the cooling roll by means of an electrostatic adhesion method, a liquid film adhesion method and / or a roll pressing method.

In the present invention, the orifice-shaped base is
For example, a die having a flat rectangular opening, such as a T-die, a fishtail die, an I-die, or the like.

The sheet molded in the present invention can be subsequently stretched in a stretching step to form a biaxially stretched film. A polyester film having the same or higher physical properties can be obtained.

Hereinafter, the present invention will be further described with reference to the drawings.
FIG. 1 is an example of an embodiment of the present invention. In FIG.
11 is a base, 12 is a sheet, 13 is a cooling roll, 1
4 is a needle-like electrode, 15 is an air chamber.

The casting method will be described with reference to FIG. 1. A sheet-like material 12 extruded from a die 11 is guided onto a cooling roll 13 rotating at a high speed, and a needle-like electrode 14 to which a high voltage is applied is equivalent to a lug of the sheet-like material. The part is electrostatically contacted and then guided to the chamber 15. The inside of the chamber is filled with a gas in which a mist-like refrigerant and air are mixed, and the sheet-like material is cooled by the mist-like refrigerant contained in the gas. At the same time, it is brought into close contact with the cooling roll by the pressure of the gas and solidifies.

In order to increase the casting speed of the sheet, it is necessary to increase the cooling speed of the sheet. In the conventional method, the pressure of the gas in the chamber is increased, and the adhesive force between the sheet and the cooling roll is increased to increase the cooling rate of the sheet. However, in this conventional method, as a result of increasing the pressure of the gas, the amount and speed of the gas blown out from the gap between the outer wall of the mouthpiece of the chamber and the cooling roll and the like become large, and the gas strongly collides with the molten sheet in the free space. Vibrating the sheet to significantly deteriorate the uniformity of the sheet thickness.

However, according to the present invention, a cooling action of a new sheet is added by the action of the mist-like refrigerant mixed with the gas in the chamber, so that the pressing action of the gas can be reduced by that amount, and as a result, the chamber can be reduced. The air volume and / or the air velocity of the gas blown out of the sheet can be suppressed to be low, and the uniformity of the sheet thickness can be prevented from deteriorating.

[0031]

The present invention will be further described with reference to the following examples.

[Examples 1 to 3] Using the apparatus shown in FIG. 1, polyethylene terephthalate was melt-extruded, and a DC voltage of 7 Kv was applied to both ends of the extruded sheet by needle-shaped strip electrodes. At the same time, the latent heat of vaporization is 4 as a mist-like refrigerant.
Using 0.7 kJ / mol of water, the water was mist-formed by an ultrasonic vibrator, introduced into the middle of the air supply pipe, mixed with the airflow from the blower, and led to the chamber. A sheet was formed under the conditions shown in Table 1, and at that time, the sheet surface temperature at the outlet of the chamber was measured, and thickness unevenness in the length direction of the sheet was evaluated. Table 1 shows the evaluation results.

[Comparative Examples 1 to 3] Using the apparatus shown in FIG. 1, the air filled in the chamber did not contain mist-like refrigerant, and the cooling ability of the sheet-like material in the chamber was as shown in Example 1.
Extruding polyethylene terephthalate in the same manner as in Example 1 except that the internal pressure of the chamber was changed so as to be equal to ~ 3 (so that the film temperature at the chamber outlet becomes equal), and the length direction of the obtained sheet was obtained. Was evaluated for thickness unevenness. Table 1 shows the evaluation results.

[0034]

[Table 1]

As is clear from the results shown in Table 1, the unevenness of the thickness of the sheet according to the present invention was good, but the cooling method equivalent to that of the present invention was obtained by the conventional method in which the pressurized gas did not contain the mist-like refrigerant. Therefore, the pressure of the pressurized gas needs to be greatly increased, and the thickness unevenness is poor. In addition, in Table 1, it shows that the evaluation result of a thickness unevenness column is as follows. ：: Thickness unevenness is less than 4% ········ Very good Δ: Thickness unevenness is 4% or more and less than 6% ··· Good ×: Thickness unevenness is 7% or more ······· Poor

[0036]

According to the present invention, a high-quality polymer sheet, particularly a thin polymer sheet with little unevenness in thickness, can be produced at high speed and stably.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of an embodiment of the present invention.

[Explanation of symbols]

 11: Base 13: Cooling roll 12: Sheet 14: Needle electrode 15: Air chamber

Claims (3)

[Claims] 1. A method for forming a sheet in which a molten polymer is extruded from an orifice-shaped die into a sheet, and is adhered and solidified on a cooling roll surface by pressing a gas. A method for forming a polymer sheet, comprising 1 to 200 g / m ³ of a mist-like refrigerant of 50 kJ / mol. 2. The method for forming a polymer sheet according to claim 1, wherein the pressure of the gas is 5 to 500 Pa. 3. The method for forming a polymer sheet according to claim 1, wherein the sheet has a thickness of 5 to 100 μm.