DE1694092C3 - Stabilized polyoxymethylene mass - Google Patents

Description

High molecular weight polyoxymethylenes which are to be processed into moldings must be different Stabilization processes are subjected. The breakdown of unstable hemiacetal chain ends is known to prevent the polymers through esterification or etherification. Can be particularly effective the disintegration occurring at the end of the chain through the incorporation of stable comonomer building blocks into the polymer chain be prevented.

In addition, however, it is necessary to add stabilizers to the polymer. This is how antioxidants protect like phenols or aromatic amines the polymers against the attack of oxygen. One However, adequate stabilization is only achieved if, in addition to antioxidants, certain stabilizers are used are present, which prevent the decomposition of the polymer under high thermal stress.

Such stabilizers are known in large numbers, in particular the following should be mentioned: urea, thiourea and hydrazine compounds, amidines, urethanes, amides of polybasic carboxylic acids, polyamides and Vinyl polymers with nitrogen-containing groups. In combination with phenols, some of these stabilizers show very good effectiveness, especially in the stabilization of copolymers of trioxane.

However, it has not yet been possible to use stabilizer combinations that do not have at least one of the following disadvantages:

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1. Discoloration of the stabilized polymer after processing;

2. discoloration of the polymer after storage at elevated temperatures;

3. Embrittlement of the polymer after storage at elevated temperatures;

4. Discoloration of the polymer after storage in hot water;

5. Diffusion of the stabilizer out of the polymer after storage at room temperature or elevated temperature;

6. Difficulty in homogeneously mixing the stabilizer into the polymer.

It is also already known that free barbituric acids, iiaibesters, Aiiophansäureesier or Cvansäürcü as

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Use 60 stabilizers for polyoxymethylene. However, the stabilizing effect of these compounds is ^{unsatisfactory, especially at temperatures above 220 °} C. in the presence of air.

The invention now relates to a stabilized polyoxymethylene mass, characterized in that it uses a mixture of (A) 0.01 to 3 percent by weight as a stabilizer, based on the polymer, the alkaline earth metal salts of acids, which contain a ureide structure, and (B) contains 0.1 to 4 weight percent of a phenol, the total stabilizer concentration Does not exceed 5 percent by weight.

Suitable stabilizers are, for example, Mg, Ca, Sr and Ba salts of barbituric acid, diethyl barbituric acid, Allophanic acid and cyanuric acid; Ca, Sr and Ba salts are preferably used.

Above all, it was surprising that the salts mentioned had a significantly better stabilizing effect than other salts, e.g. B. barbituric acid and cyanuric acid, and that they also contain other derivatives of these acids, z. B. far surpass their esters in the stabilizer effect and also have a lower tendency to discolour own. The compounds claimed can be particularly advantageous for stabilizing copolymers of the trioxane are used, the oxyalkylene groups with 2 to 6 adjacent carbon atoms contained in the main valence chain and the en: have reduced viscosity from 0.2 to 2.0, gcm: ssen in a 0.5% solution in butyric octone at 140 ° C in Presence of 2% diphenylamine.

An optimal stabilizing effect of the salts mentioned is achieved if you add them; m nen with Brings phenols to use. Suitable phenols are especially those which are in o- and p-positions to Phenol group carry substituents, such as. B. 2,6-dimethyl-4-tert-butylphenol. Bisphenols, e.g. B. 2,2-methylenebis (4-methyl-6-tert.-butylphenol) or polyphenols such as the condensation product of 4-tert-butylphenol and formaldehyde.

The concentration of stabilizers to be used depends essentially on the type of stabilizer to be used Polymers. Homopolymers of formaldehyde or trioxane usually require higher stabilizer concentrations as copolymers. In general, the claimed salts are in concentrations between 0.01 and 3 percent by weight, preferably between 0.03 and 0.5 percent by weight, the Phenols between 0.1 and 4 percent by weight, preferably between 0.2 and 2 percent by weight, are used. However, the total concentration of stabilizers should not exceed 5 percent by weight.

The polymers to be stabilized can be used in any way, e.g. B. by polymerization of formaldehyde or its cyclic oligomers. Copolymers of are particularly suitable Trioxane, the oxyalkylene groups in the main valence chain with 2 to 6 adjacent carbon atoms. The amount of oxyalkylene groups Make up 0.1 to 50 percent by weight of the total polymer. Such copolymers are z. B. by cationic ^ copolymerization of trioxane with cyclic ones Easily accessible ethers, cyclic acetals or linear polyacetals. Especially for manufacturing Comonomers suitable for the polymers are ethylene oxide and its derivatives, oxacyclobutanes and cyclic ones Formal z. B. of glycol, 1,3- and 1,4-butanediol, diethylene glycol or 1,4-butanedic! S- (2) or

linear polyformals from aliphatic and cycloaliphatic Diols and formaldehyde.

The polymers must be of high molecular weight, ie, they have a reduced viscosity of 0.2 to 2.0 have, measured in a 0.5% solution in butyrolactone at 14O ⁰ C in the presence of 2% diphenylamine. It is preferred to use polymers whose reduced viscosity is between 0.5 and 1.5. It is also desirable that the polymers have a certain minimum stability even before stabilization. You should z. B. suffer a weight loss of not more than 80% in 30 minutes at 220 °. It is an advantage of the claimed stabilizers that they can be incorporated sufficiently homogeneously into the powdered polymer by simple mechanical mixing. However, they can also be applied to the polymer in any other desired manner.

To achieve optimum stability, it is necessary that the polymers have stable, ie etherified or esterified, end groups. When using copolymers of trioxane, however, it is possible to carry out the end group stabilization and the admixing of the stabilizers in one reaction stage, e.g. B. by kneading the polymer in the presence of the stabilizers at 170 to 220 ⁰ C, the unstable polymer components escape in the form of formaldehyde.

In some cases it may be desirable to use additional stabilizers, pigments, or glass fibers to incorporate other fillers into the polymer.

The stabilized polymer can be used to manufacture threads, foils, pipes, profiles and injection-molded articles will.

example 1

Butylidene bis (6-tert-butyl-3-methylphenol) and 0.1 percent by weight barium cyanurate mixed. ^{The polymer was processed at 210 °} C. in an injection molding process. In contrast to polymers containing the% instead of SaI-zes 0.1 allophanates, the moldings produced by the inventive process showed only a very slight discoloration after 10 days storage at 12O ⁰ C in air.

B e i s ρ i e 1 3

Pipes made from acetylated polyformaldehyde, which had been stabilized with 0.2 percent by weight calcium allophanate and 0.7 percent by weight 2,2-methyl-bis- (4-methyl-6-tert-butylphenol), produced by the extrusion process showed after storage for 10 days almost no discoloration at 120 ° C. Samples of the tubes lost 2.1% of their weight in air ^{at 230 ° C. in 45 minutes.}

B is ρ ie 1 4
20th

From a granulated copolymer of trioxane and 2 percent by weight of ethylene oxide, which 0.5 percent by weight of 2,2'-methylene-bis (4-methyl-6-tert-butylphenol) and 0.1 percent by weight of each costabilizer, were immediately after the granulating and 3 mm thick pressed sheets prepared by 30minutigem heating the copolymers in a sealed manner to 23O ⁰ C with a diameter of 4.5 cm. At the same C were prepared from the granules press plates and stored for 10 days at 12O ⁰ C in air directly without pretreatment at 230 ^0th The yellow discoloration of the plates caused by these different stresses was identified as

A copolymer of trioxane and 4 percent by weight 1,3-dioxolane with stable end groups was intimately mixed by mechanical stirring with 0.75 percent by weight of a condensation product of p-tert-butylphenol and formaldehyde and the stabilizers given in the table below. The weight loss of the samples after heating at 230 ° C. in air for 45 minutes was then determined. It can be seen from the table that the effect of the claimed stabilizers is determined from the color value components x, X ₀ , γ, y ₀ determined in accordance with DIN 5033 using a trichromatic colorimeter. The following table clearly shows the superiority of the stabilizers according to the invention over known stabilizers marked ^{with +).} The degradation and discoloration of the samples with the cyanurates and barbiturates is the least.

are at least equal. Weight loss, 2 Weight percent 4,4'- Costabilizer 50 Strontium-
cyanurate
Strontium- Weight
loss Color of the press plates
(Yellow value) after after stabilizer 45 min., 230 ° C, air A copolymer of trioxane and 2 per weight 55 barbiturate 45 min.,
210 ° PI uft without 10 days 30 min. cent ethylene oxide was 0.5 barium Tempe 12O ⁰ C 23O ⁰ C 0.82
0.73 cyanurate tion 10 5 0.1% calcium barbiturate
0.1% strontium barbiturate 0.78 Dicyandi- 0.73 2 21 7th 0.1% barium barbiturate 0.90 _6o amid +) 0.72 -1 0.1% dicyandiamide +) 0.78 Stearyl 16 3 0.1% 1,1-ethylene-bis-imidazoli- guanidine +) 0.80 -2 don (2) +) 1.01 2-heptadecyl 25th 25th 0.1% adipic acid dihydrazide ¹ ") 3.50 imidazoline +) 0.90 2 0.1% barbituric acid +) 68 > 70 2.40 3 example > 70 > 70 1.60 11th

Claims (2)

Patent claims: 1. Stabilized polyoxymethylene mass, characterized in that it is used as Stabilizer a mixture of (A) 0.01 to 3 percent by weight, based on the polymer, of the alkaline earth metal salts of acids containing an ureide structure, and (B) 0.1 to 4 percent by weight of one Contains phenol, the total stabilizer concentration not exceeding 5 percent by weight. 2. Composition according to claim 1, characterized in that it is used as a stabilizer component (A) Contains Ca, Sr and / or Ba barbiturates, cyanurates or allophanates.