Process for the preparation of impact-resistant 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 (alkylene 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.

DE-OS-1 694 168 describes the use of 0.05 to 20% by weight, based on the mixture as a whole, of copolymers of α-olefins and vinyl esters of saturated aliphatic monocarboxylic acids for modifying poly (ethylene terephthalate) molding compositions.

DE-OSS 2 756 698 and 3 040 999 and US Pat. No. 4,101,502 claim reinforced poly (alkylene terephthalate) molding compositions which are mixed with ethylene / vinyl acetate copolymers to improve toughness.

Impact-resistant molding compositions made of poly (ethylene terephthalate) or poly (butylene terephthalate) and copolymers of α-olefins and esters of acrylic acid are described, for example, in DE-OSS 1,694,170 and 2,248,242.

However, the low impact strength of these additives in the blends remains unsatisfactory, so that high proportions of the modifying agent are required in order to achieve a relatively slight increase in the impact strength level. As a result, the stiffness and heat resistance of the impact-resistant polyester molding compositions have deteriorated significantly.

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

The subject of the invention is the method presented in claim 1.

The invention further relates to the molding compositions which are obtained by the process according to claim 1.

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, cycloaliphatic or aliphatic dicarboxylic acids. Examples of suitable 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 alkanediol in the poly (alkylene terephthalate) can be replaced by other diols such as, for example, ethylene glycol, propanediol (1.3), hexanediol (1.6), neopentyl glycol, 1,4-dimethylolcyclohexane, dodecanediol - (1.12) or similar.

The poly (alkylene terephthalate) used according to the invention is prepared in a conventional manner 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 about 55 to 100 cm³/ g, preferably from 65 to 95 cm³/G.

As component B., a-olefin copolymers having an elasticizing effect are used with respect to component A. For the purposes of the invention, α-olefins are preferably ethylene, propene or butene-1. Ethylene is particularly preferred.

One of the possible comonomers of the α-olefin is vinyl ester, and the other is methacrylic acid and acrylic acid esters.

Vinyl acetate or vinyl propionate are primarily used as vinyl esters.

Methacrylic acid and acrylic acid esters used according to the invention are esters of methacrylic acid and aliphatic alcohols with 1 to 18 carbon atoms in the carbon chain. The butyl acrylate is preferred.

Particularly preferred copolymers based on α-olefin / vinyl ester are those of ethylene and vinyl acetate with ethylene contents of 30 to 90, preferably 45 to 80% by weight, based on the copolymer, and an average molecular weight (M._w) from 10,000 to 500,000, preferably 50,000 to 300,000. - The molecular weight (M_w) is determined viscosimetrically.

These copolymers are produced by known processes.

Particularly preferred copolymers based on α-olefin / methacrylic acid esters are those of ethylene and butyl methacrylate (butyl acrylate) with ethylene contents between 40 and 98, preferably 55 to 95% by weight, based on the copolymer and an average molecular weight (M._w) from 20,000 to 250,000, preferably from 50,000 to 150,000. - The molecular weight (M_w) is determined viscosimetrically.

These copolymers are produced by known processes.

The copolymers make up 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. B. pellets, 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="ul0001" list-style="none"><li>a) poly (alkylene terephthalate) molding compositions can be adjusted notched impact strength by means of substantially lower a-olefin copolymer 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 a-olefin copolymers which was previously necessary to achieve only a moderate notch impact improvement, now show excellent notched impact strength, in particular at a lower temperature.</li></ul>

The solution is particularly surprising for a person skilled in the art, since 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 given 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 an α-olefin copolymer does not give a particular effect - a significant 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:

The viscosity number (J) of the poly (alkylene terephthalate) was measured on solutions of 0.23 g of polyester in 100 ml of phenol / sym-tetrachloroethane (60/40 parts by weight) at 25 ° C.<ul id="ul0002" list-style="none"><li>Notched impact strength according to DIN 53453</li><li>Limit bending stress according to DIN 53 452</li><li>Tensile modulus according to DIN 53 457 / 2.1</li><li>Heat resistance according to ISO / R 75 (method A and B)</li><li>Melt index (MFI) according to DIN 53 735</li></ul>

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

Examples

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.<tables id="tabl0001" num="0001"><img file="EP0141016B1_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0141016B1_D0002.tif" /></tables>

Explanations to Table 1

<ul id="ul0003" list-style="none"><li>1) PBTP: poly (butylene terephthalate) viscosity number (J) before mixing</li><li>²) Copolymer of 55 parts by weight. Ethylene / 45 parts by weight Vinyl acetate - MFI (190 ° C / 2.16 kp = 2.8 g / 10 min.)</li><li>³) Copolymer of 80 parts by weight. Ethylene / 20 parts by weight Butyl acrylate - MFI (190 ° C / 2.16 kp = 1.7 g / 10 min.)</li><li>⁴) Copolymer of 70 parts by weight. Ethylene / 30 parts by weight Butyl acrylate - MFI (190 ° C / 2.16 kp = 2.5 g / 10 min.)</li></ul><tables id="tabl0003" num="0003"><img file="EP0141016B1_D0003.tif" /></tables><tables id="tabl0004" num="0004"><img file="EP0141016B1_D0004.tif" /></tables>