Process for the preparation of high molecular weight polyesters for injection moulding purposes

© @ Logged On: July 9, 1970, 6260/70 © Issue Priority:

©©© Union priority: Germany, 9 July 1969, 19 34 719.4

<td>©</td><td colspan="2">Start of patent term: December 15, 1971 Longest possible duration:</td>

<td>©</td><td>Issued on:</td><td>August 25, 1972</td>

<td>©</td><td>Inventor:</td><td></td>

© dependence:

© Pamphlets considered to delineate the prior art:

OE 301182

No. 301182

For the preparation of high molecular weight polyesters can be such a procedure that transesterifying the ester of a dicarboxylic acid and a lower aliphatic alcohol with an excess amount of a diol and subjecting the thus obtained Bishydroxyalkylester the polycondensation.

It is known to employ salts of lower aliphatic carboxylic acids as esterification and polycondensation catalysts for the preparation of high molecular weight polyesters, such as polyethylene terephthalate. For example, German Patent No. 1007 600 describes a process according to which manganese acetate serves as a transesterification catalyst. In U.S. Patent No. 2,951,060, for the production of polyester, manganese salts of aliphatic mono- and oxycarboxylic acids of up to 6 carbon atoms are claimed. British Patent No. 753,880 describes a process using Cd, Co, Zn or Mn salts of aliphatic monocarboxylic acids having 2 to

10 Carbon atoms.

A process has now been developed for preparing linear saturated polyesters of aromatic dicarboxylic acids, optionally containing up to 10% by weight of aliphatic dicarboxylic acids, and saturated aliphatic or cycloaliphatic diols using manganese salts of the formula (RCOO).₂Mn found as a transesterification catalyst, wherein the anion of the manganese salt contains 3 to 20 carbon atoms, preferably 5 to 18 carbon atoms, and an epoxy group. The epoxy group may be located anywhere on the saturated, unsaturated aliphatic, cycloaliphatic or araliphatic radical R of the carboxylic acid manganese salt. The radical R may optionally contain, in addition to the epoxy group, ether-bonded oxygen atoms.

Such transesterification catalysts are of particular interest if the polyester, for example polyethylene terephthalate, is to be used as starting material for the production of thermoplastic molding compositions for injection molding. It has surprisingly been found that the manganese salts used according to the invention, which contain a reactive anion as a result of the epoxy group, modify the polyester such that a significant improvement in the injection molding properties of thermoplastic molding compositions based on high molecular weight polyesters is achieved. Comparative tests show that the known transesterification and polycondensation catalysts do not contribute to the solution of the problems encountered in the injection molding of

Polyester molding compounds occur. For example, in injection molding demoulding problems have to be solved since molded parts of unmodified polyester material strongly adhere to the walls of the mold. Furthermore, the unmodified polyester molding composition tends to form a flow ridge at the edges of the molding even if the pressure during injection molding is adjusted so that the mold is just filled.

The use of epoxidized carbonsaurer manganese salts causes the injection molded parts have even with Einstel30 ment higher injection pressures no flow ridge. At the same time, a noticeable increase in the crystallinity of the molded parts produced is achieved. It is particularly noteworthy, however, that the manganese salts used according to the invention have a significant influence on the releasability of the injection-molded articles. Comparative experiments show that the addition of mold release agents is unnecessary because the sprayed parts fall out of the mold smoothly after only 5 seconds of mold life.

Suitable transesterification and polycondensation catalysts are, for example, the manganese salts of 9,10-epoxystearic acid, of 2,3-epoxy-3-methyl-2-decylbutyric acid, of 10,11-epoxyundecylenic acid, of glycidic acid, of 2,3-epoxyhexanoic acid, of 4,5-epoxycyclo-octanecarboxylic acid, 3,4-epoxycyclohexanecarboxylic acid, glycidic ether of glycolic acid and glycidyl ether of p-hydroxybenzoic acid.

In general, it is sufficient to use 0.0001 to 0.005 mol% of the Mn compound, based on the molar amount of lower dicarboxylic acid ester used for the transesterification.

To prepare the polyesters, the lower esters, for example methyl esters of aromatic dicarboxylic acids, such as terephthalic acid, are reacted with diols, for example ethylene glycol, and then subjected to the bishydroxyalkyl esters of polycondensation thus distilled off the excess diol. According to this principle, it is also possible to prepare modified polyethylene terephthalate which, in addition to terephthalic acid, also contains other aromatic or aliphatic dicarboxylic acids as basic units, for example isophthalic acid, naphthalenedicarboxylic acid (2, 6) or adipic acid. Further, modified polyethylene terephthalates can be prepared which contain ethylene glycol as well as aliphatic diols such as neopentyl glycol or butanediol (1,4) as an alcoholic component. Also, polyesters of oxycarboxylic acids can be used.

In principle, the production of an injection-moldable polyethylene terephthalate consists of the following operations:

1. Transesterification of dimethyl terephthalate with ethylene glycol using the catalysts provided according to the invention.

Second Polycondensation of the obtained Diglykolterephthalats to poly äthy glycol terephthalate either further using the manganese salt as a catalyst or with the addition of known poly55 condensation catalysts such as Sb₂O_s, GeO_z or GeHPO_s, The melt condensation is best carried out to a RSV value between 0, 6 and 1.1 dl / g.

Third Solid condensation of the granules obtained after discharge of the melt to a higher RSV value. The polyester should have a reduced specific viscosity (RSV, measured on a 1% strength solution in phenol-tetrachloroethane 60:40 at 25 ° C.) of between 0.6 and 2.0 dl / g, preferably 0.9 and 1 , 6 dl / g. Particularly suitable are polyesters with a reduced specific

Viscosity between 1.1 and 1.5 dl / g.

No. 301182

To Kr7.ip.1nng optimum properties of an injection molded article made from this polyester, a crystallization aid is added to the polyester. For this purpose, solid inert inorganic substances such as

Talc, kaolin, titanium dioxide, alumina, calcium carbonate and others with a particle size &lt;5 μ.

They are added in an amount of 0.05 to 2, preferably 0.1 to 0.5,% by weight, based on the polyester.

The crystallization aid can be added alone before, during or after the polycondensation. But you can roll the inorganic crystallization aid but also on the finished polyester granules and then incorporated by melting in an extruder in the polyethylene terephthalate. It is also possible to spray the molding compound directly after rolling up the crystallization aid.

As a general procedure, all operations must be carried out in the absence of air and moisture in order to prevent discoloration and hydrolysis of the polyester. The polyester molding composition should preferably contain less than 0.01% by weight of water. If a rapid crystallization in the injection mold and thus a short injection cycle to be achieved, it is necessary to keep the mold to at least 100 ° C. Mold temperatures between 120 and 150 ° C are the cheapest.

Example 1:

1.1. A mixture of 10 kg of dimethyl terephthalate, 8.8 kg of ethylene glycol and 10 g of manganese-9,10-epoxystearat is heated with stirring to 225 ° C and driven off through a column of methanol until the transesterification is complete. Subsequently, by increasing the temperature, excess glycol is distilled off. After addition of 40 g of talc 3.5 g of germanium phosphite are added as a polycondensation catalyst, the temperature of the melt is increased to 285 ° C and the pressure is lowered to 1 to 0.2 Torr. After a total of 3.5 hours, calculated from the beginning of the vacuum program, the polycondensation proceeding under elimination of ethylene glycol is terminated. An RSV value of 0.88 dl / g was measured.

1.2, The obtained after discharging the melt and granulating the polyester strand granules (particle size 1.5 x 2 x 2 mm) is first dried sharply at 180 ° C under oil pump vacuum and then 8 hours of solid condensation at 235 ° C and 0.05 Torr subjected. It is achieved an RSV value of 1.450 dl / g; the water content of the granules was 0.005 wt .-%. Subsequently, the molding compound was sprayed into 60 x 60 x 2 mm sheets? Cylinder temperature 270/260/260 ° C. Mold temperature 140 ° C, injection time 15 sec, injection pressure 140 atü. The mold life was varied to assess the gluing of the panels (1st series) and the forcing to measure the strength of the flow burr (2nd series). The results are summarized in tabular form.

Example 2:

2.1. A mixture of 10 kg of dimethyl terephthalate, 8.9 kg of ethylene glycol and 6 g of 10,11-epoxyundecyl acidic manganese is prepared analogously to the process of Example 1.1. subjected to transesterification and polycondensation. The same polycondensation time was needed; the RSV value of the resulting colorless polyester composition was 0.90 dl / g.

2.2, The recovered polyester granules are brought in accordance with the conditions listed in Example 1.2, within an hour to an RSV value of 1.450 dl / g. The water content of the granules was 0.005%. Thereafter, the finished injection molding compound - again under the same spray conditions as in Example 1.2. - processed into plates, each with a series of 100 plates is used for evaluation. The quality of the plates is equivalent to that of Example 1, ie they have flat, glossy surfaces, show an excellent demolding already at 10 sec. mold life and only have a flow burr at a pressure of over 130 atm. The table summarizes the results.

Example 3:

3.1. For comparison, analogous to the procedure in Example 1.1. made a polyester composition in which 3.45 g of manganese acetate was used as a transesterification catalyst. The duration of the transesterification was the same as in the previous experiments, the polycondensation took 4 h. There was obtained a colorless granules with the RSV value 0.87 dl / g.

3.2. The solid condensation followed the melt condensation. Under the example 1.2. the time to reach RSV of 1.450 dl / g was 9 h. The water content of the granules was 0.005%. Thereafter, with the same machine setting as in 1.2. produced under variation of the mold life and the reprint series of 100 plates. The plates showed a flow ridge even at a pressure of 80 atü, it was 2 mm at 130 atü. The releasability of the plates was much worse than in Examples 1.2. and

2.2. Up to a mold life of 45 seconds, the plates stuck strongly and did not have glossy, flat surfaces. The results are summarized in the table.

No. 301182

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<td></td><td>1st series: releasability b. wide. Mold life</td><td>Form life of 100 sheets fall density [sec] d 5 54 1,373 10 67 1,373 15 89 1,374</td><td>2nd series: Fließgrat b. wide. Reprint</td><td>Reprint [atü] flow burr [mm] 60 0.05 100 1.5 140 3</td>

<td>RSV d. Granules before d. Spraying, dl / g</td><td colspan="4">1,450</td>

<td>transesterification</td><td colspan="4">Manganese- acetate</td>

<td>Polyester molding compound</td><td colspan="4">Polyethylene terephthalate with 0, 4 Gew. -% talc</td>

<td>example</td><td colspan="4">CO</td>

No. 301182