DE1779640B2 - PROCESS FOR MANUFACTURING SHAPED BODIES FROM POLYAETHYLENE TEREPHTHALATE BY VACUUM DRAWING OF PLATES OR FILMS - Google Patents

Description

The invention relates to a \ experience for the production of molded articles from polyethylene terephthalate according to the generic term of the patent.

It is already known to heat 0.1 to 6 mm thick polyethylene terephthalate plate 1 or foils quickly to a temperature of 75 to 180 ° C and immediately afterwards pull it into a shaped body m with the application of negative pressure (Dutch patent application 65-15 507).

It is further known that amorphous or partially crystallized polyethylene terephthalate at an elevated temperature, particularly at temperatures above about 120 ⁰ C, crystallized and further crystallized.

Accordingly, in vacuum drawing of amorphous polyethylene terephthalate, depending on the Processing temperature and time usually a more or less strong crystallization of the polymer instead of.

A similar known process involves molding polyethylene terephthalate with relatively high viscosity, wherein the molded article is subjected to an additional heat treatment to increase the degree of crystallinity of the polyester. It is important that the formed Polymers must have a crystallinity of at least 15 to 30% so that the molded body has favorable mechanical properties Properties, especially a satisfactory dimensional stability at higher temperatures, possesses (Dutch patent application 65-15 263).

When vacuum drawing sheets or foils made of thermoplastic material, it takes along, as is known As the deformation increases, the strength of the material is locally proportional to the degree of deformation. Included the strength of the material is often inadmissible, especially at the edges between the wall part and the bottom of the molded body and at the corners. To avoid this, you cool it Material locally in order to make it less deformable in these places.

However, the cooling of sheets or films made of polyethylene terephthalate has the disadvantage that the Crystallization of the polymer is delayed or reduced or completely prevented at the corresponding points will.

The object on which the invention is based is to develop the method according to the preamble of the claim to train that with him

Produce flawless moldings from jpojyäthylenterephthalat, which do not have any thin spots

permit. '"?'

This task * lrd by the in the identifier of the Claim specified features solved

The term polyethylene terephthalate is also intended to include copolymers that are not more than 10% of the other Monomerically derived polymer units contain, for example, monomer units that are different from others Derive acids other than terephthalic acid, such as isophthalic acid, or from diols other than ethylene glycol. That The polyester material used can also contain additives, e.g. fillers, pigments or Stabilizers.

While when vacuum drawing sheets or foils made of conventional thermoplastics such as polyvinyl chloride, polyethylene or polystyrene, localized increased heating leads to greater deformability of the areas heated to a higher degree than the other parts of the sheet, such local overheating surprisingly shows the opposite effect in the case of polyethylene terephthalate sheets. This can be attributed to the fact that at the more heated areas of the plates or foils made of practically amorphous polyethylene terephthalate, the crystallization of the polymer begins or progresses to a sufficiently strong degree compared to the parts of the plates or foils that are not additionally heated, to make it plastic Deformability of these more heated

Decrease spots appropriately before shaping takes place. The degree of crystallinity and accordingly the decrease in plastic deformability are mainly due to the Temperature and the holding time at this temperature

certainly. The temperature profile in the sheet or film to be drawn, i.e. the desired pattern of the plastic deformability depends on the shape and wall thickness of the vacuum drawing from it object to be manufactured. Also the viscosity of the polymer used as the starting material plays a role, since a highly viscous polymer crystallizes more slowly than a polymer with a relatively low viscosity. However, the most favorable conditions in individual cases can also be included a few attempts.

The plates or foils can be heated with the help of infrared heaters, with which the Inside of the material can be quickly brought to the desired temperature. So can a Sufficiently large number of individually regulated, relatively small infrared emitters above the heating plate or film arranged and the thermal radiation of the individual radiation sources so adjusted so that the material receives the desired temperature profile. The vacuum drawing can after any known method can be carried out, for example with the aid of matrices and / or Patrices.

The invention is explained further with the aid of the following example.

example

A 2.45 mm thick plate of amorphous polyethylene terephthalate with a relative viscosity of 1.95 (measured in a 1 (wt.)% solution in m-cresol at 25 ° C) with the dimensions 500 χ 900 mm is in a vacuum press with punch support (Sendler, type 1060 DS) inserted.

An upper part for a sideboard is pulled out of the plate, which is 70 mm away from one of the The narrow sides have a sunk basin with the side dimensions 340 χ 370 ram, the depth 160 mm amounts to

The plate to be drawn is heated for about 1 minute under a group of infrared radiators, after which the vacuum deep drawing is carried out by lowering the auxiliary punch, lifting the die and applying the negative pressure. Then the auxiliary punch ^ is raised again and the shaped object is again about IV ₂ - Heated for 2 minutes with the infrared heaters

Finally, the shaped body produced in this way is allowed to cool in the mold for about 1 minute. The entire molding process, including heating the mat, takes about 5 minutes. A shell made of a polymer with a degree of crystallinity of about 30% is obtained.

Two experiments are carried out:

A) With even heating of the whole plate and

B) with more intensive irradiation of that section of the plate that deforms into the sunken basin will.

The temperature and crystallinity of the plates in the Moment of vacuum drawing (measured in comparative tests with heated in an analogous manner and abruptly cooled plates) are as follows:

A) temperature 110 ^° C. and crystallinity 1-2% over the entire plate;

B) in the normally heated part of the plate the temperature is about 110 ^° C. and the crystallinity 1 -2%, while in the additionally heated section the temperature is 130 ^° C. and the crystallinity is 15%

The moldings produced in the two experiments generally consist of a polymer with uniform crystallinity, but show the following differences in thickness on the walls and on the bottom on:

Wall thickness, mm

Floor thickness, mm

1.00-1.55
O-1.30

1.20-UO
1.30-UO

In addition, the molding obtained in test A), in contrast to that in test B) produced molding at the corners and the edges between the bottom and wall of the pool part very thin and transparent places.

These results clearly show that with the aid of the method of the invention an extreme and non-uniform local strength reduction of the drawn material can be prevented.

Claims (1)

Claim: A process for preparing Eormkörpern of polyethylene terephthalate by vacuum drawing of plates or sheets of virtually amorphous at 90 to 12Q ⁰ C preheated polyethylene terephthalate, characterized in that tiaß in the parts of the sheets or films, which are deformed during the vacuum drawing the most, by their added heating to At least 20 degrees above the temperature, of the remaining plate or film parts, the crystallization of the polymer compared to item not more strongly heated plate or film parts takes place to the extent that the plastic deformability of the more strongly heated
Way is decreased. Share in desired