DE1804119A1 - Process for the production of high molecular weight polyesters - Google Patents

Description

Process for the production of high molecular weight

Polyester.

The structure of linear polyesters from dicarboxylic acids (or their esters with lower, monohydric alcohols) and diols, of which polyethylene terephthalate in particular has achieved great practical importance, is known to take place by condensation in the melt,

The properties of such polyesters associated with the molecular weights that can be achieved thereby meet the requirements ₍ for a very wide range of applications.

However, areas of use for polyesters have become known for which higher molecular weights are desired than they are as a result the increase in the degradation reaction with the increasing degree of condensation can be achieved by the process of melting condensation. For the production of such high molecular weight polyester one must therefore take another route, which consists in that one Melt condensation breaks off before degradation reactions occur to a significant extent, the polyester can solidify and the condensation then continues in the solid phase. This happens in the V / that the polyester in the form of granules, powder or Film at temperatures between 10 ° C and 60 ° C below its softening range lie, brought and then kept in this temperature range in the gas stream or under vacuum as long as until the desired high molecular weight is reached. The speed and uniformity of heating to condensation temperature is for the duration of the entire process

009824/1958

BAD OFÜÖiNAL

Ge.

the earlier treatment and the quality of the treatment Polyesters essential

Now polyesters are polar substances and it would therefore - as it is known that polar itself or very hot water-containing substances in the alternating electric field in a very short time and i let it dry appropriate, ^e, - given a chance, the thermal post-treatment low-molecular polyester to be carried out by means of high frequency. In the case of polyethylene terephthalate, however, rapid heating according to this method is opposed to its amorphous state, which is due to the way in which it is produced, as well as its water content. This is because the moisture would lead to considerable hydrolytic degradation at higher temperatures, while the amorphous state would result in deliquescence well below the crystalline crystal temperature. In addition, despite the very short heating-up time, the presence of oxygen causes oxidative damage. For these reasons, the polyesters intended for post-condensation have hitherto been dried and crystallized in the conventional manner and only brought into a hole frequency field for the actual post-condensation stage. However, certain difficulties of exact temperature control in the high-frequency fold over a longer period of time stand in the way of this mode of operation. ♦

The present invention now relates to a process for the production of high molecular weight polyesters, in particular high molecular weight Polyethylene terephthalate, by condensation of the corresponding lower molecular weight polyester in the solid phase, which thereby is characterized by the fact that the low molecular weight poly / ester in the presence of a flowing dry gas according to a certain temperature program by means of high frequency to condensation temperature heats up, the heating process so performed is that until the desired condensate temperature is reached Crystallization and extensive drying of the used

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009824/1958

Polyester has taken place, and then in a field-free Space the actual Naclikondensatinn makes in a known manner in the Xnertgasstrom or under vacuum.

For the method according to the invention it is essential to depend depending on the type of starting material by carefully regulating the heating process either with Ililfts a suitable arrangement of several electrode pairs or by occasionally switching off the field when using wearing only one pair of electrodes so that the temperature range, in which the crystallization. with optimal gas speed occurs, is not exceeded before the ™

Polyester is transformed into a crystal in a form characterized by a higher softening temperature, and that the water released during the heating process is immediately removed from the polyester bed, because only then can hydrolytic degradation be kept within permissible limits. When the material has reached the temperature desired for condensation, which is generally 10 C to 60 C below the crystal! If tschmolzpunkte.s is located in an apparatus which is independent of the high-frequency heater and which is at the condensation temperature, then subsequent condensation in a known manner in a vacuum or in a flowing, hot inert gas, no more problems arise with regard to the temperature control in this stage g .

The implementation of the procedure according to the invention is designed In general, in practice, one starts with that amorphous material either slowly, i.e. over a period of 5 to 15 minutes by selecting the field strength in the inert gas flow heated up to the level of condensation or heating in a high-frequency field in a stream of air or inert gas as quickly as possible to 100 to 180 C (preferably 120 - 160 C) and then in the field-free space when it is reached ^ Wait for the temperature until the polyester is sufficiently

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SAD ORIGINAL

is crystallized and only then to the desired in the inert gas stream Brings condensation temperature of about 200 to 25O ° C. At this temperature then in the field-free space wio above mentioned post-condensed in a known manner. The course of the transformation from the amorphous to the crystalline state can be traced with the help of the changes in the transparency of the polyester that occur in the process.

The method according to the invention makes it possible, in elegant, faster and more straightforward kind of low molecular weight to high molecular weight polyesters - as they are for example for the Injection molding processing will be needed - to come. However, it is not limited to this body class alone, but rather can take into account the respective product properties are used in all condensable polymers such as polyamides, polyimides, polyureas and others.

The method is explained in more detail below with the aid of a few examples. The course of condensation was determined by measuring ^ spcz. tracked. For the measurement, 500 mg of polyester were dissolved in 50 ml of phenol / tetrachloroethane (3 ^J 2) solvent mixture.

Example 1:

500 g granulated polyethylene terephthalate of the specific viscosity spec. = 0.85 and a moisture content; it of approx. 0.4 <ä was heated to 125 ° C within 3 minutes 45 seconds in a high-frequency field in a nitrogen stream. After a pause of j minutes, the field was switched on again until 240 C was reached in the product. After this heating process was ^ spec. 0.817. The hot material was then dm 240 C-hot Ν ,, - current within 12 hours on- ^ spec. = '1.48 post-condensed.

0Q9824 / 1958

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example 2t

A polyester material of the same origin as in Example 1, pre-dried in a vacuum drying cabinet, was used within 5 minutes Heated to 125 C for 30 sec. In a high frequency field in an N stream. After a 5 minute break, the temperature was raised with the aid of high frequency increased to 240 ° C (η spec. = 0.835) 12-hour post-condensation fülxrte to-iisspec. 1, '♦ 9

The example shows that, despite the additional pre-drying step, the erroiclite degree of condensation differs only insignificantly from that

of the product according to Example 1 differs. M.

Example 3;

Undried granulated Polyäthylenterophthalate from T ^ spec. 0.88 and a moisture content of $ 0.4 was within brought to 2frO ° C by 5 minutes in the high-frequency field. While During the heating process, gas did not flow through the material. The specific viscosity decreased to 0.75. aside from that the material had melted into a lump.

The example shows the poles for rapid heating and des Lack of carrier gas to remove the released water.

Example for: ■

A continuously operating metering device was used Polyester granulate is applied evenly to the conveyor belt of an Ilochfrequency dryer with 2 electrodes. the The speed of the tape was adjusted so that the polyester a temperature when passing through the 1st high-frequency field of 16O C reached. In the 2nd downstream field was then the heating to the 2fr0 ° C amounting to condensation temperature is carried out. The distance between the two pairs of electrodes was just big enough that the polyester was sufficient before re-entering the field of the second pair of klektrodons Had time to crystallize.

00982 A / 1958

8AD ORIGINAL

Ge. fri3

The water released from the polyester bed was constantly removed by preheated inert gas. '

The hot pellets were then continuously in an independent from the 'IIF device reactor in known manner condensed in the solid phase until a viscosity v _(on trapeze. 1.5 was reached.

Example $:

Using a metering device as described in Example 4, an I-hole frequency dryer was charged with polyester granulate. During the heating to 160 ° C., the polyester bed became flowed through by dry air.

In a field-free space, the polyester remained so long until crystallization was over. Then the further heating to the 24o C amount of condensation temperature made, where the bed was now flowed through by dry inert gas. The rest of the procedure corresponded to that described in Example 4.

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009824/1958

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Claims (2)

Go. 413 '. Claims I O U 4 I Ί 1. Process for the production of high molecular weight polyester, ins- " special high molecular weight polyethylene terephthalate Condensation of the corresponding lower molecular weight polyesters in the solid phase, characterized in that the low molecular weight polyester in the presence of a flowing dry gas according to a certain ^ temperature program heated to the condensation temperature by means of high frequency, the heating process being carried out in such a way that until the desired condensation temperature is reached, crystallization and extensive drying of the incorporated ™ put polyester has taken place, and then in one field-free space the actual post-condensation in a manner known per se in an inert gas stream or under vacuum undertakes. 2. The method according to claim 1, characterized in that the temperature during the Aufheiζvorganges in such a way is that the crystallization of the polyester has largely ended before the temperature range is more optimal Crystallization rate is exceeded. 00 982A / 1958 8AO ORiGiNAi