DE1052679B - Process for the production of polyamide moldings with a uniformly fine crystalline structure and a large surface hardness - Google Patents

Description

Process for the production of polyamide moldings with uniformly fine crystalline structure and great surface hardness The properties of molded bodies from polyamides including polyurethanes depend on which crystalline Have formed during solidification. Certain types of their structure can be easily examined by microscopic examination using polarized light recognize. In the injection molding process, in which z. B. from the outside usually a relatively If the melt is quenched quickly, the result is normally a very inhomogeneous one Structure which in polarized light shows large and small spherulites next to a shows amorphous zone formed predominantly at the edge. By using higher mold temperatures it is possible to reduce the width of the amorphous edge zones, but it remains inhomogeneous structure with large and small spheroiths and with cluster-shaped arrangements this structure is preserved.

The use of mold temperatures above 800 C is with polyamides in practice only feasible with great difficulty, and the difficulties increase extremely with increasing temperature because the injection molded parts then z. B. need much longer cooling times and much more difficult to demold are. This is particularly unpleasant with polycaprolactam. With this one Polyamide is also the surface hardness by increasing the mold temperature to 1200 C, measured as micro Vickers hardness at 0.1 kg load, not yet increased.

It has now been found that known polyamide melts can be obtained by cooling with a content of 0.1 to 100 / o of substances at least one aromatic nucleus carry a phenolic hydroxyl group and at least one aliphatic radical Forms whose temperature is above 800 C, but below the melting temperature of the relevant Polyamide is held, moldings can be produced in an economical manner that have a uniform, fine-crystalline structure that extends over the entire cross-section The edge zones are also recorded uniformly. As a result, the surfaces show a noticeable greater hardness than moldings made from the same mass under comparable conditions were made in cold molds. Due to the content of substances with a phenolic character is also caused that the solidification is accelerated and the molded body remove very easily from the hot mold. This means that working hours are noticeable shortened. The so economically achievable surface beards are z. B. in polycaprolactam as high as those of polycaprolactam molded bodies that machined from slowly solidified block material are.

The required temperature of the molds, e.g. B. in injection molding or bottle blowing process, depends of course in detail on the type of polyamide, the temperature of the melted mass, the injection molding conditions, wall thicknesses etc., in any case it is above 80 ° C. Substances active in the manner indicated are particularly polysubstituted, e.g. B. di-tert-butyl-p-cresol or methylenebis-tert-butyl-p-cresol.

It is known that moldings made of polyamide powders by sintering be obtained, have a fine-grain structure, which makes particularly favorable storage and sliding properties are effected. Using the methods described here, gets a similarly uniform, fine-grained structure in processes in which the Mass solidified in molds by cooling, e.g. B. in the injection molding process. With higher ones Additions make the structure more and more fine-grained.

The molded bodies obtained have a more crystalline structure due to their more strongly crystalline structure a greater hardness, but its toughness is practically not reduced because the used Additives are characterized by good compatibility with polyamides. It is true the addition of phenols and alkylated phenols to polyamides was known, however it has always been used to make polyamides soft and flexible. A freeze in molds above 800 C, however, this is not intended.

Example 1.

If 0.5% of di-tert-butyl-pcresol is added to polycaprolactam, this gives one when using different mold temperatures in injection molding under otherwise the same Conditions different microstructures. Also serve as a comparison under the Parts made of polycaprolactam manufactured under the same conditions without the mentioned addition.

It can be seen that the crystal structure is at the temperature of the mold of 80 ° C for the phenol-containing polyamide becomes finely crystalline and uniform and is much stronger towards the edge.

At 1200 C the edge zone is already clearly crystallized up to the surface. The cut surface of the phenol-free polyamide also has advantages of the heated one Recognize shape, but the structure is much larger. Show particularly clearly differences in surface hardness (see table below).

Micro Vickers hardness, 0.1 kg load (MVH) Measured Material shape- at 65 5 / o temperature air humidity 30 ° C 4.6 Polycaprolactam # 80 ° C 4.4 120 ° C 4.5 30 ° C 4.5 Polycaprolactam at 0.5% 80 ° C 4.6 Di-tert-butyl-p-cresol # 800 C 5.2 Example 2 If 2% di-tert-butyl-p-cresol is added to polyadipic acid hexamethylenediamide, bodies with a uniform structure are obtained on injection molding in a mold at a temperature of 900 / o C. With the same product without this additive, all other conditions being the same, the amorphous edge zone is considerably wider and the structure shows spherulites of very different sizes.

Claims (1)

PATENT CLAIM Process for the production of polyamide moldings with a uniform, fine-crystalline structure and great surface hardness, which are in forms solidify by cooling, characterized in that known polyamide melts with a content of 0.1 to 100 / o of substances at least one aromatic nucleus carry a phenolic hydroxyl group and at least one aliphatic radical, solidifies in molds whose temperature is above 800 C, but below the melting temperature of the polyamide in question is held.