JPH0447921A - Manufacture of polyester sheet and cooling device used therefor - Google Patents

Abstract

PURPOSE:To make it possible to stably and efficiently manufacture polyester sheet having the small difference between the physical properties of sheet surface, which comes into contact with the surface of a drum, and that, which comes into contact with air, by a method wherein the liquid in a cooling bath, the width of which is slightly narrower than that of sheet, is directly and continuously brought into contact with the sheet surface, which does not come into contact with the drum, at the position, in which the temperature of the above-mentioned sheet is brought into the specified one. CONSTITUTION:At the position, in which the temperature of the surface of the side not contacting with a rotary cooling drum of sheet-like melt under the cooling process on said drum is brought to 200+ or -25 deg.C, the liquid in a cooling bath, the width of which is slightly narrower than that of said surface, is directly and continuously brought into contact with said surface of the sheet so as to quench said surface below about 100 deg.C. The cooling bath 2 has an upward open structure and a width slightly narrower than the total width of a sheet 1' and further side walls, the upper ends of which are equidistant from the sheet 1'. If the width of the cooling bath is wider than the total width of the sheet 1', cooling liquid cones into contact with the surface of the rotary cooling drum, resulting in unfavorably staining said surface.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a polyester sheet manufacturing method and a cooling device used therein. More specifically, a sheet-like melt of thermoplastic polyester is brought into close contact with a rotating cooling drum, and during the cooling process, the cooling of the sheet surface on the side not in contact with the drum is promoted, and the difference in the cooling process on both sides of the sheet is compensated for. The present invention relates to a method of manufacturing a polyester sheet that reduces sheet deformation caused by differences in surface properties and physical properties, and a cooling device effective for promoting cooling of the surface of the sheet.

<Prior Art> As a method for producing a substantially amorphous sheet from thermoplastic polyester, a sheet-like melt of the polyester is usually extruded onto a rotating cooling drum, and then the sheet-like melt is brought into close contact with the drum. A method of rapidly cooling is used. The rotating cooling drum is forcibly cooled by passing cooling water through its interior, and the surface of the sheet-like melt that is in contact with the surface of the drum (hereinafter referred to as the drum surface) is rapidly cooled by the drum. The surface of the sheet-like melt that does not touch the surface (the surface opposite to the drum surface, hereinafter referred to as the air surface) is cooled by heat transfer to the drum surface and atmospheric gas (usually air), so It is cooled at a slower rate than the cooling rate.

This difference in cooling speed between the drum surface and the air surface is an inevitable problem in methods that use a rotating cooling drum, and it becomes especially noticeable when the thickness of the sheet on the rotating cooling drum becomes approximately 2 m or more. Differences in physical properties due to differences in processes cannot be ignored.

In order to deal with this problem, various countermeasures have been proposed. An outline of this will be described below. One method is to install two rotating cooling drums and alternately cool both sides of the sheet. This method can uniformly cool both sides of the sheet by appropriately selecting the contact time with the first drum, but the structure is complex, equipment costs are high, and the start-up work is extremely complicated. There is a drawback.

Simpler methods include a method in which high-speed airflow is blown onto the air surface to promote cooling, and a method in which water or the like is applied to the air surface and cooling is performed using the latent heat of vaporization. The former is
It is not possible to obtain sufficient cooling capacity with airflow alone, and furthermore, the turbulence of the airflow causes uneven thickness of the sheet extruded onto the drum, and there is also the problem of surface defects caused by dust etc. blown up by the airflow. . In addition, it is difficult to apply the liquid uniformly with the latter, and if it is applied to a high temperature area, it boils almost instantly, resulting in cooling spots that correspond to the coating spots.
Moreover, no great effect can be obtained in a temperature range where this problem does not occur.

<Object of the Invention> The object of the present invention is to rapidly cool the air surface using a simple cooling means that does not cause such problems and is easy to operate.
It is an object of the present invention to provide a method for producing a polyester sheet with small differences in air surface properties and physical properties.

Another object of the present invention is to provide a cooling device that rapidly cools the sheet air surface on a rotating cooling drum efficiently, uniformly, and stably.

<Structure of the Invention> The first feature of the present invention is to extrude a sheet-like melt of thermoplastic polyester onto a rotating cooling drum, then bring the sheet-like melt into close contact with the drum, and cool it to produce a polyester sheet. In the method of cooling the sheet-like melt on the rotating cooling drum, when the temperature of the sheet surface on the side not in contact with the drum reaches 200±25°C, the sheet surface is narrowed slightly more than this. A method for manufacturing a polyester sheet, which comprises cooling the sheet to approximately 100° C. or lower by directly and continuously contacting the liquid in a wide cooling bath.

The second feature of the present invention is that a cooling liquid bath is provided at the bottom of the rotating cooling drum, and the width of the bath is slightly narrower than the width of the sheet cooled by the drum, and the upper ends of the side walls of the bath are all equidistant from the sheet surface. This polyester sheet cooling device is characterized by having the following structure and further having a mechanism that allows the entire bus to be raised and lowered.

The details will be explained below.

The thermoplastic polyester in the present invention is a substantially linear saturated polyester containing an aromatic dicarboxylic acid as a main acid component and an alkylene glycol as a main diol component. The thermoplastic polyester is preferably crystalline, particularly one having a maximum crystallization rate within a temperature range of 120 to 200°C. Typical polymers include:
Polyethylene terephthalate, polyethylene-2,6-
Mention may be made of naphthalene dicarboxylate.

The thermoplastic polyester melt is extruded from a die into a sheet, and the sheet melt is brought into close contact with a rotating cooling drum.
As mentioned above, the method of rapidly cooling to form a sheet is well known. As a result of researching the influence of the cooling rate of the sheet-like melt on the sheet properties in this method, the inventor found that the sheet air surface on the rotating cooling drum was
When rapidly cooled from around ℃ (200±25℃) to around 100℃, the difference in surface characteristics between the air surface of the sheet and the drum surface becomes small to a non-problematic level, 2ffl! For sheets with a thickness of 1 or more, the cooling rate of the air surface is extremely slow, and the temperature at the bottom (lower part) of the drum is around 200°C. Discover that surfaces can be cooled to a certain temperature in a short time.

An example of these temperature changes is shown in Figure 19 and Figure 2. Figure 1 shows the case of conventional cooling, and Figure 2 shows the case where the air surface at the bottom of the drum is forcibly cooled with cooling water.

In the method of the present invention, a thermoplastic polyester is melted and the resulting melt is placed in a die (for example, a T-die).

- The sheet-shaped melt is extruded into a sheet through a die, etc.), and the sheet-shaped melt is brought into close contact with a rotating cooling drum, and then rapidly cooled to form a sheet. A method that can be preferably used is particularly a method in which an electrostatic charge is applied to the air surface of the sheet-like melt to bring the sheet-like melt into close contact with the drum surface. The thickness of the sheet is preferably at least 2nwn. Further, it is preferable that the sheet thickness is 4 mm or less.

In the method of the present invention, during the cooling process on the rotating cooling drum, when the temperature of the air surface of the sheet reaches 200±25°C, the air surface is directly exposed to the cooling liquid of the cooling bath, especially at the bottom of the drum. and rapidly cooled by continuous contact.

Figure 3 is the cooling bag used for this rapid cooling! It is a schematic diagram showing an example. Figure 4 is a partially enlarged schematic diagram of this device (
(This is a view from a direction 90 degrees different from Figure 3).

In Figure 32 and Figure 4, 1 is a rotating cooling drum (only the bottom is shown), 1' is a thermoplastic polyester sheet, 2 is a cooling bath, and 3 is an elevating platform. The cooling bath 2 is installed on an elevating pedestal 3 that can be approached close to the rotary cooling drum 1 and the sheet 1' thereon. The cooling bath 2 has an upper opening structure, has a width slightly narrower than the entire width of the sheet 1', and has a structure in which all the upper ends of the side walls are equidistant from the sheet 1'. In other words, the upper ends of the two side walls of the cooling bath 2 parallel to the side walls of the drum 1 (this interval is the bath width) have an arc-shaped structure that matches the curvature of the drum 1, and the cooling bath 2 is connected to the sheet 1. ', the gap between the seat surface and the upper end of the cooling bath is the same in all four directions. The cooling liquid (usually water) is supplied from the liquid supply port provided at the bottom of the bath 2, overflows from the side wall of the bath 2, is received in a gutter provided on the outside of the side wall, and is then discharged to the outside of the system. .

When the liquid is passed through the cooling bath 2 and gradually brought closer to the sheet 1' while overflowing from the side, the initial liquid level and the sheet 1' begin to come into full contact at a certain position due to surface tension. As they are brought closer together, the contact area gradually increases, and when the gap between the cooling bath 2 and the sheet 1' becomes less than a certain value determined by the amount of liquid flowing, the resistance head of the liquid flowing out of the gap will meet the end of the arc of the cooling bath 2. It becomes larger than the step in the center and begins to flow from the entire circumference, at which time the maximum cooling effect is achieved. This gap is several meters or less. Usually it is 2-3rs.

As mentioned above, the width of the cooling bath 2 needs to be slightly narrower than the total width of the seat 1'. This width is sheet 1
If it is wider than the full width of the rotary cooling drum, the cooling liquid comes into contact with the surface of the rotating cooling drum and stains the surface, which is not preferable. Since both ends of the sheet are usually separated from the central part, which becomes the product, as edges in a later process and collected, product quality is not affected even if the ends of the sheet are not rapidly cooled by direct contact with the cooling liquid.

The cooling liquid (usually water) that comes into contact with the seat air surface quickly separates from the air surface due to its surface tension. For example, if the sheet speed (surface peripheral speed of the rotating cooling drum) is 9 m/min or less, the sheet will not be carried into the subsequent process along with the sheet. Furthermore, even at higher speeds and when using a liquid with a low surface tension, entrainment of the liquid can be easily prevented by using an appropriate liquid draining device such as an air knife or a suction roll.

Although the sheet produced by the method of the present invention can be edge-trimmed at both ends and the center portion made into a product (unstretched sheet), it is usually further subjected to stretching treatment to produce a product as a stretched film. This stretching process can be performed by a conventionally known method.

<Example> The present invention will be further explained below with reference to Examples.

Comparative Example A melt of polyethylene terephthalate (containing pigment) was extruded from a die onto a rotating cooling drum, and the sheet-like melt was brought into close contact with the drum and cooled to produce a sheet with a thickness of 2.5 ffm. adjusted to 4m/min,
The temperature of the seat air surface at the bottom of the rotating cooling drum is approximately 19
It was 0°C.

The resulting sheet was then multiplied by 3.1 times in the longitudinal direction and 3 times in the transverse direction.
．． Stretch each film by a factor of 2 to produce an opaque biaxially oriented film. The surface properties of this film on the drum side and air side were evaluated based on glossiness. The results are shown in Table-1.

Example A cooling device shown in Figure 3 was installed at the bottom of the rotating cooling drum,
The same procedure as in the comparative example was carried out, except that cooling water was flowed through the cooling bath at a liquid rate of 20 liters/min, and the seat air surface at the bottom was directly cooled with the cooling water. The temperature of the seat air surface on the exit side of the cooling bath was approximately 90° C. or lower.

Table 1 shows the surface properties of the obtained biaxially stretched film.

*; Glossiness is a value (unit: %) measured by a luminous flux reflected in the regular reflection direction with respect to the incident light on the measurement surface using a glossmeter manufactured by Nippon Denshoku Kogyo ■.

<Effects of the Invention> According to the method of the present invention, a polyester sheet with a small difference in physical properties between the sheet drum surface and the air surface can be stably and efficiently produced. This polyester sheet is suitable as a raw material for stretched films, especially biaxially stretched films.

Furthermore, according to the present invention, it is possible to provide a sheet air surface cooling device that is effective for manufacturing such polyester sheets. Using this device, the sheet air surface can be rapidly cooled efficiently, uniformly, and stably.

[Brief explanation of the drawing]

FIG. 11 and FIG. 2 are diagrams showing changes in sheet temperature. FIG. 3 is a schematic diagram showing an example of the cooling device of the present invention. FIG. 4 is a partially enlarged schematic diagram of this device. Figure-31-
4, 1 is a rotating cooling drum, 1' is a polyester sheet, 2 is a cooling bath, and 3 is an elevating platform for the cooling bath. Figure-1 Figure-2 Location of cooling drum (bottom) Figure-4 Overflow drainage

Claims (1)

[Scope of Claims] 1. A method for manufacturing a polyester sheet by extruding a sheet-like melt of thermoplastic polyester onto a rotating cooling drum, then bringing the sheet-like melt into close contact with the drum, and cooling the sheet. During the cooling process of the molten material on the rotating cooling drum, when the temperature of the sheet surface on the side not in contact with the drum reaches 200±25°C, the sheet surface is heated with liquid in a cooling bath with a width slightly narrower than this temperature. A method for producing a polyester sheet, which comprises rapidly cooling the polyester sheet to approximately 100°C or less by bringing it into direct and continuous contact with a polyester sheet. 2. The method for producing a polyester sheet according to claim 1, wherein the thickness of the sheet is at least 2 mm. 3. The method for producing a polyester sheet according to claim 1, wherein the cooling liquid is water. 4. The method for producing a polyester sheet according to claim 1, wherein the contact between the sheet surface and the liquid in the cooling bath is due to the surface tension of the liquid. 5. A cooling liquid bath is provided at the bottom of the rotating cooling drum, and the width of the bath is slightly narrower than the width of the sheet cooled by the drum.
A polyester sheet cooling device characterized by having a structure in which the upper ends of the bus side walls are all equidistant from the seat surface, and further having a mechanism that allows the entire bus to be raised and lowered up and down.