DE1247645B - Injection molding compounds containing high molecular weight polyacetals - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

C08g

German: 39 b -22/10

Number: 1247 645

File number: F 44793IV c / 39 b

Filing date: December 23, 1964

Opened on: August 17, 1967

High molecular weight polyoxymethylenes are characterized by a number of excellent properties that seemed to secure them a wide range of possible uses in the technical sector. It has been found, however, that in the manufacture of technical articles, especially after the preferred economically favorable injection molding process, the prescribed or permissible tolerances can not be met in many cases, whereby the importance of this plastic is quite considerably limited.

The cause of the widely fluctuating dimensions of the molded parts is the crystalline Look for structure. A microscopic examination of thin sections reveals an inhomogeneous, Recognize coarse spherulitic structure that alternates with finely crystalline, granular areas. These the inhomogeneous structure that forms during the solidification of the melt results in different Shrinkage values, distortions and internal stresses that lead to the dimensional fluctuations of the result in molded structures made of this material.

This invention relates to injection molding compositions which contain high molecular weight polyoxymethylene and talc in amounts of from 0.0001 to 0.5 percent by weight, based on the weight of the polyoxymethylene, evenly distributed.

The polyoxymethylene used should have an intrinsic viscosity of 0.5 to 1.2, measured in a 0.5% solution in butyrene acetone at 150 ° C. The talc must be in finely divided form with particles less than 10 μ in diameter and is used in amounts of 0.0001 to 0.5 percent by weight, preferably 0.001 to 0.2 percent by weight, with particularly favorable results in amounts of 0.01 to 0.1 percent by weight , based on the polyoxymethylene, is used.

These injection molding compounds are distinguished by the fact that molded parts produced from them are dimensionally stable and are reproducible in their dimensions. The deviations in dimensions from standard manufactured parts are significantly reduced.

The effect of adding talc is to improve and standardize the crystal structure the molded parts. Such an effect of the talc added in very small amounts is complete unexpectedly.

The injection molding compositions of the present invention are generally prepared so that the solid high molecular weight polyoxymethylene e.g. in the form of granules or powder with talc in the

Injection molding compounds, the high molecular weight
Contain polyacetals

Applicant:

Paint factories Bayer Aktiengesellschaft,
Leverkusen

Named as inventor:

Dr. Wilhelm Hechelhammer, Krefeld-Bockum

Mixes given quantities, this mixture melts and processed into granules. Preferably grinds or you tumble the plastic granulate with the talc over a longer period of time. In general 24 to 60 hours are sufficient for this process.

The grinding can take place, for example, in a ball mill. Mixing of the Granulate and the solid understood in a tumble drum. This process makes one special intensive mixing and shredding of the material guaranteed.

According to the invention, an injection molding compound or molded body produced therefrom with an extremely fine-crystalline, homogeneous structure and crystallite diameters of 4 to 8 μ is obtained. Untreated high molecular weight polyoxymethylene, on the other hand, results in an injection molding compound or molded body with a non-uniform, coarse spherulitic structure and a crystal diameter of up to 100 μm.
All polyacetals (polyoxymethylenes) can be treated according to the invention. For the purposes of this invention, polyacetals are all thermoplastic high polymers that contain formaldehyde as the main component, such as the polymers of formaldehyde itself and those of trioxane, their derivatives esterified or etherified at the end groups and their copolymers, which contain other molecules to prevent thermal degradation in the polyformaldehyde chain built-in included. Such foreign molecules can, for. B. ether residues, nitrogen-containing residues or sulfur-containing residues.

Preferably, copolymers of trioxane with dithiolane, oxthiolane, dioxolane or five bis Treat seven-membered heterocyclic nitrogen compounds according to the invention. Using of high molecular weight polyoxymethylenes which, after their production, undergo a thermal treatment

709 637/747

Claims (1)

must be subjected to this thermal aftertreatment with the incorporation of the Crystallization seeds are combined according to the present invention. example 1 5 kg of a granulate made of a high molecular weight polyformaldehyde with an intrinsic viscosity of 1.0 were used tumbled with 0.1% talc for 48 hours, then melted in an extruder and mixed, spun off as wire and granulated. In the same way, the same high molecular weight polyformaldehyde was extruded and granulated to make Comparison to obtain a starting material with the same thermal loading. Both granulates were dried and then injection-molded for 3 hours at ⁰ IOO C on a screw injection molding machine per hundred small gears. After spraying, they were stored under exclusion of moisture and measured after 48 hours with the aid of a micrometer screw. Two measuring points, offset by 90 ° C., were selected. Result: scattering
the diameter Diffe
renz
mm Gears made of untreated is made of polyacetal. 41.13 to 40.80 0.33 Polyacetal gears with 0.1 »/ 0 talc 41.06 to 40.83 0.23 This means that the tolerance field becomes significantly smaller and the outliers are prevented. Fine cuts leave the molded part made of polyacetal with 0.1% talc a regularly fine crystalline Recognize the structure with crystallite diameters of 4 to 6 μ, while the untreated polyacetal is large has irregular spherulites with crystallite diameters of up to 80 μ. Example 2 A mixture of 20 kg of polyoxymethylene granules with an intrinsic viscosity of 1.0 and 20 g of talc are used ground in a porcelain ball mill for 60 hours, then melted in an extruder, spun off as wire and chopped up. When injected to form molded bodies, this mass has a uniform fem-crystalline structure with crystal sizes of 4 to 6 μ. Without adding talc, moldings are obtained with an inhomogeneous one Structure with crystal sizes up to 80 μ. Measurement result on thirty injection-molded gears
Without talc:
at the measuring points A 64.31 - 63.74 = 0.57 mm, at the measuring points B 64.25 - 63.45 = 0.80 mm. With 0.1% talc: at measuring points A 64.19 - 63.81 = 0.38 mm, at measuring points B 63.81 - 63.37 = 0.44 mm. But it results from the addition of 0.1% talc at measuring point A a reduction of the tolerance field by 33 ° / n, at measuring point B a reduction of the tolerance field by 46%. Example 3 5 kg of a copolymer of trioxane and dioxolane in granular form were 0.1% talc Spined for 24 hours and on a screw injection molding machine with a high dynamic pressure setting sprayed into fifty gears to achieve a good homogenizing effect. Under under the same conditions, fifty gears were made from the same polyoxymethylene without any talc treatment injected. In the first case, a homogeneous structure with crystallite sizes of 6 to 9 μ is obtained, in the second Case shows a non-uniform structure with crystallite sizes up to 100 μ. The tolerance range for material treated with talc is compared to that without talc 50% reduced. Claim: Injection molding compounds containing high molecular weight polyoxymethylene and talc in amounts of 0.0001 to 0.5 percent by weight, based on the weight of the polyoxymethylene, evenly distributed contain. Considered publications:
Belgian patents nos. 638113, 567 381,
586874. 709 637/747 8.67 © Bundesdruckerei Berlin