JPS5833420A - Heat-forming for polyester-sheet - Google Patents

Abstract

PURPOSE:To increase the yield of formed products in a deep drawing process by following method in which polyester sheet must be hot-formed as an abnormal endothermic peak does not exist, or before said abnormal peak is lapped over the glass-transition temperature of the sheet proper, when the transition temperature of the glass is measured. CONSTITUTION:At the hot-forming for polyester-sheet, said sheet must be formed as an abnormal endothermic peak appearing at the lower temperature than the glass-transition temperature of the sheet proper does not quite exist, or before said abnormal peak is lapped over the glass-transition temperature of the sheet proper. Consequently, the increase for stability in production process and the yield of the formed product are achieved especially in the deep drawing process.

Description

[Detailed Description of the Invention] The present invention relates to a thermoforming method for polyester sheets that has high stability in the production process (improved yield rate of molded products) when performing deep drawing, etc.; is thermoforming of polyester sheets, especially when the drawing ratio is 1.
It is an object of the present invention to provide a method for thermoforming polyester sheets, which improves the stability of the production process in deep drawing of 0 or more and improves the yield of housing-shaped products.

Until now, polyethylene terephthalate films and sheets have been widely used in the fields of electrical components, printing, agricultural materials, packaging, etc. as biaxially stretched films.

Recently, it has begun to be used in the food packaging field for tray or cup products by taking advantage of its excellent properties, and there has been an increase in demand for bo-1 ethylene tele-7 tallate sheet that can be easily ripened.

Although polyethylene terephthalate is a crystalline polymer, its crystallization rate is slower than that of ethylene, polytetrapyrene, polyamide, etc., so it can be turned into an amorphous state by cooling from a molten state to a rapid rate. It is possible to express Amorphous sheets have a lower elastic modulus and greater elongation than crystalline sheets with developed spherulites, so they can be acid-formed (elongated) at relatively low temperatures and with small force. For these reasons, in the production of biaxial polyethylene terephthalate film, the sheet-shaped melt discharged from the extruder nozzle is
The usual method is to cool and solidify the sheet on the surface of a rotating quenching body maintained at 0 to 80°C to form an amorphous sheet that can be easily stretched, and then biaxially stretched.

For this reason, the surface of the conventional rotary quenching body was
When the amorphous polyethylene terephthalate sheet obtained by holding the sheet at ℃ is thermoformed and deep drawn, for example, it is placed in a high-speed continuous vacuum forming machine equipped with a multi-piece die, and the drawing ratio is set to 1. It was thought that the desired product could be obtained efficiently by forming a deep-drawn product with a diameter of 0 or more using the plug-assist method, which also used a combination of compressed air and vacuum to faithfully reflect the shape of the mold. However, surprisingly, a molded product could not be obtained stably, and the yield was approximately 5,096, and it was found that the polyethylene terephthalate sheet obtained by the conventional method had extremely poor moldability.

The inventors of the present invention have found a method to eliminate such drawbacks, measure the stability of the thermoforming process, and improve the molding yield. The present inventors have discovered that the yield during deep drawing can be significantly improved by using a sheet for ripening, and have thus arrived at the present invention.

The gist of the present invention is that when thermoforming a polynisdel sheet, when the glass transition temperature of the sheet is measured by D8C, there is no abnormal endothermic peak that appears at a lower temperature than the original glass transition temperature of the sheet, or A method for thermoforming a polyester sheet, characterized in that thermoforming is performed before an abnormal endothermic peak overlaps with the original glass transition temperature.

In the present invention, the amorphous structure of polyethylene terephthalate changes depending on the cooling rate f when cooling and solidifying a sheet-like melt. We discovered that an abnormal endothermic peak occurs overlapping the original glass transition temperature, resulting in a thicker peak, and that once this sheet-like melt is rapidly cooled at a sufficiently high rate, it can be stretched without any abnormal endothermic peak. Even if a superior sheet is manufactured, an abnormal endothermic peak will occur at a temperature lower than the glass transition temperature when it is left for a long time in the range of 0°C to glass transition temperature. We found that the peak becomes larger and shifts toward higher temperatures, and that sheets with such abnormal endothermic peaks have a higher elastic modulus, lower elongation, and are less likely to stretch (
This is based on the finding that a material in which the abnormal endothermic peak at 41 overlaps with the original glass transition temperature undergoes brittle fracture.

The polynisdel constituting the polyester sheet used in the present invention is polyethylene pre-7talate or ethylene terephthalate copolymer in which 80 or more of the repeating units are ethylene terephthalate units, furthermore, polyethylene terephthalate is 80 or more by weight, and other thermoplastic resins are used. This indicates a resin mixture composed of 20% by weight or less. A must for the polyester mentioned above! Depending on the situation, other additives 1 such as antiblocking agents, nucleating agents, etc. may be included.

In order to produce the polyester sheet used in carrying out the present invention, first, the polyester defined in the present invention is melt-extruded into a sheet from the mouth of an extruder to obtain a sheet-like melt, and then the sheet-like melt is applied to the surface of the sheet-like melt. It can be obtained by cooling and solidifying on the surface of a rotating quenching body kept at a temperature of 60°C or less, preferably 40 to 60°C. When producing the above polyester sheet, if the temperature of the surface of the rotating quenching body is too low, horizontal wrinkles will occur on the sheet surface, causing uneven thickness, and when the resulting sheet is deep drawn, its formability will deteriorate. Therefore, the temperature of the surface of the rotary quenching body is preferably 40°C or more and 60°C or less.

On the other hand, when the temperature of the surface of the rotary quenching body exceeds 60°C, the quenching effect on the sheet is weak (stretchability of the obtained sheet becomes poor).

In order to preserve the polynisdel sheet obtained by the method described above in a state where it can be used in the present invention, the storage temperature should be 25°C or lower, preferably 20°C or lower, and the storage period should not be long. is preferred, and preferably within 3 months.

According to the thermoforming method of the present invention, excellent effects such as the ability to significantly improve the molding yield in the deep drawing process using a multi-cavity high-speed continuous pressure/vacuum molding machine are produced.

The present invention will be explained in more detail with reference to Examples below.

In addition, the intrinsic viscosity [η] and the abnormal endothermic peak in the examples were determined by the following measuring method.

Intrinsic viscosity [da]: Phenol/tetrachloroethane (50150 weight ratio)
It was measured at 25°C using a mixed solvent of

Abnormal endothermic peak: Cut the sheet to about 10 to 20 cm and measure the D8C curve at a heating rate of 10° C./min to observe the endothermic peak that appears at a temperature lower than the glass transition temperature or at the glass transition.

Examples 1-2. Comparative Examples 1 and 2 Pellets of polyethylene terephthalate having an intrinsic viscosity [η] = 0.73 were discharged from a melt extruder of f 90 w@φ at a resin temperature of 290°C, and the pellets were prepared as Example 1 and Comparative Example 1 in Table 1. It is cooled and solidified on the surface of the rotary quenching body maintained at the temperature shown in , to a thickness of 0.45 cm.

A sheet with a width of 7005 m was obtained. Further, the sheet obtained in Example 1 was stored under the conditions of Example 2 and Comparative Example 2. The D8C curves of these sheets are shown in the figure. Picture song 1! A,
B, C and D are Example 1 and Comparative Example 1. Example 2.
Each corresponds to Comparative Example 2.

In Example 10 song IIA, abnormal endothermic peak force 1 is not observed. In curve C of Example 2, a small abnormal endothermic peak force is observed at a temperature lower than the original glass transition temperature. Also, in Comparative Examples 1 and 2, song 1 [For B and curves, a large 'abnormal endothermic peak force appears superimposed on the original glass transition temperature.' Each of these sheets was put into a high-speed I/Ly/continuous molding machine with a force of 70 mm per caliber and a drawing ratio of 1. A .35 deep drawn product was molded using 36 pieces.The time required for one cycle was 8.
As shown in Table 1, the molding yield was 9 seconds in Examples 1 and 2.
A score of 81 or higher was a good score.

Table 1 Temperature (0C) Procedural Amendment (Method) February 8, 1980 Haruki Shimada, Commissioner of the Patent Office 1, Indication of Case Patent Application No. 1983-131096 2, Title of Invention Method for Thermoforming Polyester Sheet 3, Relationship with the case of the person making the amendment Patent applicant: 2-3-19 Kyobashi, Chuo-ku, Tokyo (603) Osamu Kanazawa, President and Director of Mitsuru Rayon Co., Ltd. 34, Agent: 2-3 Kyobashi, Chuo-ku, Tokyo No. 19 Mitsubishi Rayon Co., Ltd. (6949) Patent Attorney Toshio Yoshizawa The specification is corrected as shown in the attached ``Corrected Specification.''

Correction statement l1 Name of invention Thermoforming method of polyester sheet 2. Scope of claims When thermoforming polyester sheets.

When the glass transition temperature of the sheet is measured using a differential scanning calorimeter, there is no abnormal endothermic peak that appears at a lower temperature than the original glass transition temperature of the sheet, or thermoforming occurs before the abnormal endothermic peak overlaps with the original glass transition temperature. A method for thermoforming polyester sheets, which is characterized by:

3. Detailed Description of the Invention The present invention relates to a thermoforming method for polyester sheets that has high stability in the production process (improved yield rate of molded products) when performing deep drawing, etc., and its purpose is to However, thermoforming of polyester sheet, drawing ratio is 1,
It is an object of the present invention to provide a method for thermoforming a polyester sheet, which improves the stability of the production process in deep drawing of 0 or more and improves the yield of molded products.

Until now, polyethylene terephthalate films and sheet-like products have been widely used as biaxially oriented films in the fields of electrical parts, printing, agricultural materials, packaging, etc.

Recently, there has been a movement to utilize the excellent properties of polyethylene terephthalate sheets for use in food packaging fields such as trays and cup products, and demand for polyethylene terephthalate sheets that can be easily thermoformed has increased.

By the way, although polyethylene terephthalate is an MA bulky polymer, its crystallization rate is slower than that of polyethylene, polypropylene, polyamide, etc., and therefore it is possible to develop an amorphous state by rapidly cooling it from a molten state. Since the amorphous sheet has a lower elastic modulus and a higher elongation than the crystalline sheet in which the spheres 1 are developed, it has the characteristic that it can be formed or stretched at a relatively low temperature and with a small force. For this reason, in the production of polyethylene tele-7 tallate biaxial stretched film, the sheet-like melt discharged from the extruder nozzle is kept at a temperature of 70 to 80°C.
In the usual method, the sheet is cooled and solidified on the surface of a rotating quenching body held in a rotating quenching body to form an amorphous sheet that is easily stretched, and then biaxially stretched.

For this reason, the surface of the conventional rotary quenching body was
When thermoforming, especially deep drawing, an amorphous polyethylene terephthalate sheet obtained by holding the sheet at It was thought that the desired product could be obtained efficiently by forming deep-drawn products using the plug-assist method, which also used a combination of compressed air and vacuum to faithfully reflect the shape of the mold. Surprisingly, a molded product could not be stably obtained, the yield was about 50%, and it was found that the polyethylene terephthalate sheet obtained by the conventional method had extremely poor moldability.

The inventors of the present invention have conducted intensive studies to find a method for measuring the stability of the thermoforming process and improving the molding yield. The present invention was achieved by discovering that thermoforming using a sheet significantly improves the yield during deep drawing.

The gist of the present invention is that when thermoforming a polyester sheet, when the glass transition temperature of the sheet is measured by DSC, there is no abnormal endothermic peak that appears at a lower temperature than the original glass transition temperature of the sheet, or there is no abnormal endothermic peak. A method for thermoforming a polyester sheet, characterized in that thermoforming is performed before the peak overlaps with the original glass transition temperature.

In the present invention, the amorphous structure of polyethylene terephthalate is
- It changes depending on the cooling rate when cooling and solidifying a tortoise melt, and as the cooling rate becomes slower, it becomes amorphous with a higher specific gravity and an abnormal endothermic peak appears on the DSC curve, overlapping the original glass transition temperature. Furthermore, even if this sheet-like melt is rapidly cooled at an optically fast speed to produce a sheet with excellent stretchability and no abnormal endothermic peaks, the temperature will be approximately 0°C. ~ When left in the range of glass transition temperature for a long time, an abnormal endothermic peak occurs on the lower side than the glass transition temperature, and as the temperature increases, the abnormal endothermic peak becomes larger and shifts to the higher temperature side. In addition, sheets with such abnormal endothermic peaks have a high elastic modulus, a decrease in elongation, and a tendency to become difficult to stretch (
This is based on the finding that brittle fracture occurs when the abnormal endothermic peak overlaps with the original glass transition temperature at 1%.

The polyester constituting the polyester sheet used in the present invention is polyethylene terephthalate or ethylene terephthalate copolymer in which 80 or more of the repeating units are ethylene/terephthalate units, and K is polyethylene terephthalate of 80 or more by weight, other thermoplastic resins. This refers to a resin mixture consisting of 20% by weight or less. The polyester may contain other additives such as an antiblocking agent, a nucleating agent, etc., if necessary.

In order to produce the polyester sheet used in carrying out the present invention, first, the polyester is melt-extruded from the die of the extruder specified in the present invention into a sheet-like melt, and then the sheet-like melt is applied to the surface of the polyester sheet. It can be obtained by cooling and solidifying on the surface of a rotating quenching body kept at a temperature of 60°C or less, preferably 40 to 60°C. When manufacturing the above-mentioned polyester sheet, if the temperature of the surface of the rotary quenching body is too low, horizontal wrinkles will occur on the sheet surface, causing uneven thickness, and when the resulting sheet is deep-drawn, its formability will deteriorate. The temperature of the surface of the rotary quenching body is preferably 40°C or more and 60°C or less. On the other hand, if the temperature of the surface of the rotary quenching body exceeds 60°C, the quenching effect on the sheet will be weak (the resulting sheet will have poor stretchability).

In order to store the polyester sheet obtained by the method described above in a state that can be used in the present invention, the storage temperature is 25°C or lower, preferably 20°C or lower, and the storage period is preferably not long. Preferably within 3 months.

According to the thermoforming method of the present invention, it is possible to significantly improve the molding yield in the deep drawing process using a high-speed continuous pressure/vacuum forming machine capable of forming a large number of molds.

The present invention will be specifically explained below using Examples.

Note that the intrinsic viscosity [η] and abnormal endothermic peak in the examples were determined by the following measurement method.

Intrinsic viscosity [η]: 7 k/-/f) Measured at 25°C in a mixed solvent of 5 chloroethane (50,750 weight ratio).

Abnormal endothermic peak: Cut the sheet to about 10 to 209 ml, measure the DSC curve at a heating rate of 10° C./min, and observe the endothermic peak that appears at a temperature lower than the glass transition temperature or overlaps with the glass transition.

Examples 1-2. Comparative Examples 1-2 Polyethylene terephthalate pellets k 90 wxφ with intrinsic viscosity [η] = 0.73 were extruded from melt extrusion 1 [at a resin temperature of 290°C, and the pellets were prepared as Example 1 and Comparative Example 1 in Table 1. It is cooled and solidified on the surface of the rotary quenching body maintained at the indicated temperature to a thickness of 0.45 cm.

A sheet with a width of 700 m was obtained. Further, the sheet obtained in Example 1 was stored under the conditions of Example 2 and Comparative Example 20. The DSC curves of these sheets are shown in the figure. Curves A, B, and C in the diagram
and D are Example 1 and Comparative Example 1. Example 2. Each corresponds to Comparative Example 2.

In curve A of Example 1, no abnormal endothermic peak is observed. In curve C of Example 2, a small abnormal endothermic peak is observed at a temperature lower than the original glass transition temperature. Also, in Comparative Example 1
In Curve B and Curve IID of 2 and 2, a large abnormal endothermic peak appears superimposed on the original glass transition temperature. Each of these sheets was put through a high-speed inline continuous forming machine to form 9mm diameter 7mm.
A deep drawn product with a drawing ratio of 0.01 m and a drawing ratio of 1.35 was formed using 36 pieces. The time required for one cycle was 8 seconds.

As shown in Table 1, the molding yield was 9 in Examples 1 and 2.
A value of 8% or more was good.

Table 1 4: Brief Explanation of Drawings The drawings are DEC curves of each polyester sheet in Examples and Comparative Examples.

Claims (1)

[Claims] When thermoforming a polyester sheet. When the glass transition temperature of the sheet is measured using a differential scanning calorimeter, there is no abnormal endothermic peak that appears at a lower temperature than the original glass transition temperature of the sheet, or there is no abnormal endothermic peak that appears at a temperature lower than the original glass transition temperature of the sheet, or thermoforming occurs before the abnormal endothermic peak overlaps with the original glass transition temperature. A method for thermoforming a polyester sheet, characterized by: