JPS6172509A - Forming process of resin sheet - Google Patents

Abstract

PURPOSE:To obtain a resin sheet less in haze and high in market value by a method in which while cooling and solidifying by a cooling roller, the crystalline thermoplastic resin extruded in molten state, obtained resin sheet is air cooled under a specified condition. CONSTITUTION:The crystalline thermoplastic resin extruded from an extruding die 1 in molten state is cast on the surface of a cooling roller 2, and is solidified by cooling, whereby it is formed into a resin sheet. Further simultaneously, at the time when the temperature of the surface of said resin sheet not being in contact with the surface 21 of the cooling roller is in the temperature range giving 0.7-70% of relatively crystallizing speed to the highest crystallizing speed of the resin, the air cooling of said resin sheet is begun by the cooling device 3 provided opposite to the surface 21 of the cooling roller, and thus, a product is obtained. Polyethylene phthalate is preferably used for crystalline thermoplastic resin.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for forming a melt-extruded crystalline thermoplastic resin sheet, and particularly to a method for cooling the resin sheet with little haze.

(Prior art) Molten crystalline thermoplastic resin
No. 7-6142), etc.), it is closely attached to two surfaces of the cooling row and cast, cooled to an appropriate temperature [K, solidified, and biaxially stretched at a predetermined stretching ratio to become a resin sheet of a predetermined thickness. put to use.

The cooling conditions for the crystalline thermoplastic resin (hereinafter referred to as characteristic resin) sheet that has entered gearing are the haze (degree of haze) of the resin sheet, the corrugations, and unevenness (flatness) of the surface that are finally seen due to the characteristic resin. Alternatively, it has a large effect on physical properties such as strength, and if the cooling rate in the crystallization temperature range of the characteristic resin is slow, the resin will become highly crystallized, and when stretched, it will cause cutting, uneven thickness, etc. Problems such as insufficient strength or haze may occur.

In order to increase the cooling efficiency of the resin sheet, various proposals have been made including the above-mentioned electrostatic charge application method.

For example, methods such as blowing cooling air or cooling water spray onto the surface of the characteristic resin sheet during casting, or flowing cooling water (
Japanese Patent Publication No. 44-30388) is known, but these methods have the drawback of impairing the flatness of the resin sheet surface. To avoid this difficulty, JP-A-49-108163 discloses a technique of slow cooling to an amorphous temperature range and then rapid cooling.

In addition, when forming thick sheets that are prone to problems, parallel airflow outlets are provided at several locations opposite the cooling roller on the non-contact surface with the cooling σ-roller. A method has been proposed (Japanese Unexamined Patent Publication No. 52-93477) in which the resin is quickly cooled while removing the dust generated by solidification of the substance, thereby passing through and escaping the temperature range where crystallization is likely to occur.
Furthermore, a method has been proposed in which a cooling air flow is passed through a countercurrent to increase the cooling effect (Japanese Unexamined Patent Publication No. 59669/1983).

The methods proposed so far have focused on quickly cooling the resin sheet as a whole, and while taking care not to damage the flatness of the resin sheet surface, cooling air etc. However, there is little consideration given to the relationship between cooling conditions and haze, and there is a lack of concrete descriptions.

However, the haze of a resin sheet affects its commercial value, and is enough to control its life and death, especially when it is used as a photographic material.

(Objective of the Invention) An object of the present invention is to provide a method for forming a melt-extruded biaxially oriented resin sheet of the above-mentioned characteristic resin, which has less haze.

(Group composition of the invention) The present inventors have conducted extensive studies on reducing the haze of biaxially oriented resin 7-t. It is necessary to suppress the degree of crystallinity of this surface, and I learned that to do this, it is sufficient to delay the start of air cooling.

That is, an object of the present invention is to cast a crystalline thermoplastic resin extruded in a molten state onto the surface of a cooling roller, cool it, and solidify it to form a resin sheet. The resin sheet is air-cooled in a temperature range in which the temperature of the surface of the resin sheet not in contact with the cooling roller surface provides a relative crystallization rate of 0.1 to 70% with respect to the maximum crystallization rate of the resin. Start at the point when it is completed.
This is achieved by a characteristic resin sheet forming method.

The crystallization rate of the characteristic resin according to the present invention has the relationship shown in FIG. 1 with the temperature of the characteristic resin.

In FIG. 1, the horizontal axis is the temperature [T] of the characteristic resin, and the vertical axis is the crystallization speed G'.

The crystallization rate is defined by the growth rate dr/dt (microns (-) 7 seconds (S)) of spherulites generated in the characteristic resin in the radius r direction.

r 03 product [μ/S) The crystallization rate G increases as the 01 temperature T decreases at the melting points M and P of the characteristic resin, and reaches the maximum crystallization rate Ga at the temperature TM, It decreases again and the straight line T=T
Regarding M, it is symmetric. However, the range used in the present invention is from M, P, to TM.

Further, the above-mentioned relative crystallization rate [f is defined as 6 fractions of the crystallization rate G at each temperature based on GM.

? = (G/GM)

(Example) The present invention will be specifically explained using an example (FIG. 2).

In Fig. 2, 1 is an extrusion die, 11 is a slit for discharging the molten characteristic resin from the extrusion die 1, and 2 is a casting cooling roller, which has a diameter of 5001 and supplies cooling water with a water temperature of 30°C to the cooling roller 2. 2m/- while circulating inside
It is rotating at a circumferential speed of .

Reference numeral 3 denotes an arc-shaped air cooling device provided concentrically on the cooling roller and facing the casting surface 21 thereof.
1 is a characteristic resin cooling roller. Check the heating T on the non-contact surface with a non-contact infrared thermometer, and slide the air cooling device concentrically to cool the cooling roller at an arbitrary relative crystallization speed ffi. It can be installed at point Pi.

The cooled resin sheet (original sheet) is taken out from the row 24.
It is peeled off at the point, and then longitudinally stretched and transversely stretched to continuously form a product sheet.

In this example, polyethylene terephthalate was extruded from an extrusion die 1 at 290°C as a raw sheet with a thickness of 2 yrm,
Points P5 listed in Table-1
'2,...,29) Start air cooling from point 241
] Stretching was carried out to continuously produce polyethylene terephthalate sheets with a thickness of 175 μm, and the haze of each sample was measured using a haze meter (Tokyo table 1, Shishi 1).

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between temperature T and crystallization rate G of a characteristic resin. FIG. 2 is a side view for explaining the casting portion of the extrusion biaxial stretching film forming machine. 1...-extrusion die, 1... cooling roller, 3... air cooling device. Agent Patent Attorney No 1) Yoshi acid Figure 1 Figure 2

Claims (1)

[Claims] When a crystalline thermoplastic resin extruded in a molten state is cast onto a cooling roller surface and cooled and solidified to form a resin sheet, the resin sheet is air-cooled by an air cooling device provided opposite to the cooling roller surface. The process starts when the temperature of the surface of the resin sheet that is not in contact with the cooling roller surface falls within a temperature range that provides a relative crystallization rate of 0.1 to 70% with respect to the maximum crystallization rate of the resin. A method for forming a resin sheet.