Process for the preparation of impact-resistnat polyalkylene terephthalate moulding masses.

The invention relates to a process for the preparation of impact-resistant molding compositions obtained by thermal treatment of plastic mixtures which predominantly contain poly (alkylene terephthalate) in solid form - and the molding compositions thus obtained as such.

Poly (alkylene terephthalates) are valuable construction materials with a number of excellent properties such as high rigidity, surface hardness, abrasion resistance, good heat resistance, dimensional stability and quick processing to complex and large moldings.

For some applications, however, the notched impact strength of the poly (alycene terephthalates) is insufficient, in particular at temperatures below 20 ° C., so that there is a need to develop poly (alkylene terephthalate) molding compositions with an improved level of notched impact strength.

There are already numerous proposals to improve the low-temperature impact strength of poly (alkylene terephthalate) molding compositions by condensing aliphatic dicarboxylic acids or diol mixtures or by blending with other polymers such as modified elastomers and polyolefins.

However, all of the measures described have the defect that either the increase in the cold impact strength is only slight or that a significant improvement in the cold impact strength is associated with an undesirable deterioration in other properties, in particular the rigidity and heat resistance.

For example, DE-OS 29 30 343 describes molding compositions based on poly (alkylene terephthalate) which contain mixed polyether ester amides in order to improve the impact resistance. However, it has proven to be disadvantageous that relatively high proportions of the polyether ester amide have to be incorporated into the poly (alkylene terephthalate) in order to achieve an increase in the level of the impact strength at all. As a result of such high proportions of the second component, the stiffness and heat resistance of the polyester deteriorate significantly.

The object of the invention was to remedy the disadvantages of the prior art described.

A method has now been found for the production of improved molding compositions in which a plastic mixture is made<ul id="ul0001" list-style="none"><li>A. 70 to 95 wt .-% poly (alkylene terephthalate) and</li><li>B. 5 to 30 wt .-% of a known polyether amide</li></ul>is treated at temperatures 15 to 60 ° C below the melting point of the pure component A. in an inert gas atmosphere.

The invention further relates to the molding compositions which are obtained by the process described above.

Suitable poly (alkylene terephthalates) for component A. are poly (ethylene terephthalate), poly (propylene terephthalate) and preferably poly (butylene terephthalate).

Up to 20 mol%, preferably 5 to 15 mol%, of the terephthalic acid in the poly (alkylene terephthalate) can be replaced by aromatic, cycloalphatic or alphatic dicarboxylic acids. Examples of regulated dicarboxylic acids are isophthalic acid, phthalic acid, cyclohexane-1,4-dicarboxylic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid or the like

Up to 20 mol%, preferably 5 to 15 mol%, of the respective alkane diol in the poly (alkylene terephthalate) can be obtained using other diols such as, for example, ethylene glycol, prepanediol (1.3), hexanediol (1.6), neopentyl glycol, 1,4-dimethylolcyelohexane, dodecam diol. (1.12) or similar.

The poly (alkylene terephthalate) used according to the invention is produced in the usual way by transesterification or esterification and subsequent polycondensation of terephthalic acid or its polyester-forming derivatives and the corresponding alkanediol in the presence of catalysts (Sorensen and Campbell, Preparative Methods of Polymer Chemistry, Interscience Publishers Inc., NY, 1961, pages 111 to 127; Kunststoff-Handbuch, volume VIII, C. Hanser Verlag Munich, 1973, or Journal of Polymer Science, Part A 1, 4, pages 1851 to 1859, 1966).

The poly (alkylene terephthalate) which is used according to the invention has a viscosity number (J) of approximately 55 to 100 cm3 / g, preferably 65 to 95 cm3 / g.

The polyetheramides of component B. are obtained by condensing<ul id="ul0002" list-style="none"><li>1. one or more polyamide-forming compounds from the group of ω-aminocarboxylic acids or lactams with at least 10 C atoms,</li><li>2nd a diamine with a polyether block which preferably contains 6 to 30 ether oxygen atoms which are separated from one another by a linear aliphatic chain of preferably 3 to 4 carbon atoms,</li><li>3rd one or more other aliphatic, cycloaliphatic or aromatic dicarboxylic acids</li></ul>receive.

As the polyamide-forming compound (B.1), ω-aminocaubonic acids or lactams with at least 10 C atoms, preferably laurolactam, ω-aminododecanoic acid or ω-aminoundecanoic acid, are used. A further preferred possibility is to use, instead of the monomolecular aminocarboxylic acids or lactams, their polymers or copolymers with an average molecular weight of 500 Lis 20,000, preferably 4,000 to 15,000.

The stated values ​​for the average molecular weights are obtained by determining the end group concentration (amine and acid number).

Component B.2 diamines are derived from ethylene oxide, propylene oxide and tetrahydrofuran. The polyethers can be homopolymers and / or copolymers. Mixtures of homopolymers and / or copolymers can also be used. Their number average molecular weights are between 160 and 3,000, preferably between 300 and 2,200, in particular between 500 and 1,200. Polytetrahydrofuran with amino end groups (eg bis (3-aminopropyl) polytetrahydrofuran) is preferably used.

The production of polyalkylene oxides with amino end groups can, for. B. according to DE-OSS 15 70 542, 24 12 056, 24 12 057 and US-PS 2 401 607.

The specified molecular weights can be determined by titration of the amino groups.

Component B.3 is formed by aliphatic, cycloaliphatic or aromatic dicarboxylic acids with 4 to 12 carbon atoms in the carbon skeleton. Examples include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, hexahydroterephthalic acid or phthalic acids. Terephthalic acid and dodecanedioic acid are preferably used for these components.

The polyether amides are constructed in such a way that they have homo- or copolyamide segments and polyether or polyether amide segments in the polymer chain. The weight ratio of components B.1 and (B.2 + B.3) is in the range of 20_: 80 to 50 _: 50. A weight ratio in the range from 25-45: 75-55 is preferred. The amine and carboxyl groups of (B.2 + B.3) are in approximately equivalent proportions, ie in a ratio of 1: 0.95 to 1 _: 1.05.

They are produced, for example, by melting the components together and subsequent polycondensation. If lactams are used, the lactam rings must be cleaved before the polycondensation, preferably in the presence of the dicarboxylic acid.

Preferred polyetheramides are prepared by reacting GJ-aminoundecanoic acid and / or ω-aminododecanoic acid or laurolactam, dodecanedioic acid and / or terephthalic acid and bis (3-aminopropyl) polytetrahydrofuran with a molecular weight of 500 to 1200.

The viscosity number (J) of these products is in the range from 140 to 260, preferably 160 to 210, cm3 / g.

The production of such polyether amides can be found, for example, in DE-PS 29 32 234, DE-OS 29 36 976 and EP-PS 25 828.

Three polyetheramides have a proportion of 5 to 30% by weight, preferably 10 to 25% by weight, of the plastic mixture. The rest is formed by the poly (alkylene terephthalate) of component A.

Components A and B are mixed with one another to carry out the thermal treatment of the plastic mixtures. In order to avoid signs of segregation during further processing, the mixture is preferably melted, homogenized and then brought into the final processing form, such as, for. B. pellet, granules, powder etc. This operation is preferably carried out in an extruder at temperatures of about 260 to 280 ° C. However, any other known method which can be used for the stated purpose can also be used.

The plastic mixture thus produced is about 2 to 12 hours, preferably 4 to 10 hours, at a temperature which is 15 to 60 ° C, preferably 20 to 50 ° C, below the melting point of the respective pure component A. in an inert gas atmosphere and preferably thermally treated while moving the plastic mixture. You can work at normal pressure as well as in a light vacuum. The treatment can e.g. B. be carried out in a tumble dryer or fluidized bed reactor.

Nitrogen is particularly suitable as an inert gas. However, other inert gases can also be used. It has proven to be advantageous to work in a light stream of inert gas.

Customary additives and auxiliaries such as pigments, processing agents, fillers and reinforcing materials, hydrolysis, thermal or UV stabilizers can be incorporated both during production (melt mixture) and into the finished, treated molding compositions.

The method according to the invention is distinguished from the prior art in that<ul id="ul0003" list-style="none"><li>d) poly (alkylene terephthalate) molding compositions can be set to notch impact strength by means of substantially lower polyether amide additives and thus have high rigidity and heat resistance in addition to a good level of toughness, and</li><li>b) Poly (alkylene terephthalate) molding compositions which have been modified with the high proportion of polyether amide which was previously necessary to achieve a moderate notch impact improvement, now have excellent notched impact strength, in particular at a lower temperature.</li></ul>

The solution is surprising for a person skilled in the art because both the solid phase post-condensation of a pure poly (alkylene terephthalate)_-Molding composition and the simple mixing of such molding compositions with a large number of polymers which improve the notched impact strength have not produced the intended results. The result according to the invention is just as unexpected because the blending of a polyester subjected to the solid phase post-condensation with a polyether amide does not give any particular effect - a clear effect only arises when the plastic mixture itself is subjected to the conditions according to the invention.

The parameters listed in the description and in the examples were determined using the measurement methods mentioned below:<ul id="ul0004" list-style="none"><li>The viscosity number (J) of the poly (alkylene terephthalate) was determined on solutions of 0.23 g of polyester in 100 ml of phenol / sym-tetrachloroethane (60/40 parts by weight) at 2₅ ° C measured. </li></ul>

The viscosity number (J) of the pure polyether amides was determined on solutions of 0.5 g of product at 25 ° C. in 100 ml of m-cresol (DIN 53 727).

Impact strength according to DIN 53 453 limit bending stress according to DIN 53 452 Z -E-Moudul according to DIN 53 457 / 2.1 heat resistance according to ISO / R 75 (method A and B)

The examples marked with letters are not according to the invention.

Examples

Try 1 to 3 and A.

In a 0.5 m^3-Tumble dryers are thermally treated 120 kg of the plastic mixture in the form of granules (composition see Table 1) under the conditions given in Table 1.

The characteristic properties of the molding compositions are shown in Tables 2 and 3.

Trial B

A dry mixture of poly (butylene terephthalate) and polyetheramide granules of the composition given in Table 1 is melted and homogenized at 265 ° C. in a twin-screw extruder.

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