HK1038033B - Stabilized polyoxymethylene moulding materials - Google Patents

Description

Stabilized polyoxymethylene molding materials

Technical Field

The invention relates to thermoplastic polyoxymethylene molding materials containing the following essential constituents:

A)10 to 99.98 wt.% of a polyoxymethylene homopolymer or copolymer

B)0.005 to 2% by weight of a sterically hindered phenol

C)0.001 to 2% by weight of polyamide

D) 0.002-2 wt% of alkaline earth metal silicate or alkaline earth metal glycerophosphate

E)0.01 to 5 wt% of at least one ester or amide of a saturated or unsaturated aliphatic carboxylic acid having 10 to 40 carbon atoms with a polyhydric alcohol having 2 to 40 carbon atoms, or an aliphatic saturated alcohol or amine, or an ether derived from an alcohol with ethylene oxide

F)0 to 5% by weight of a melamine/formaldehyde condensate

G) From 0 to 74% by weight of further additives, the% by weight of components A) to G) summing to 100% in each case.

The invention also relates to the use of such molding materials for producing moldings of any type, and to the moldings produced therefrom.

Background

Polyoxymethylene homopolymers and/or copolymers have long been known. Polymers having many excellent properties are suitable for a wide variety of industrial uses. However, there is a constant search for compositions which improve the processability, such as flowability, curing time, etc., and/or the mechanical properties and dimensional stability of the moldings produced from such polymers.

According to DE-A-2319359, molding materials composed of 98 to 25% by weight, based on the total material, of polyoxymethylene copolymers and 2 to 75% by weight of acicular calcium silicates have improved processability, dimensional stability and heat-aging behavior.

The prior art also describes processes for stabilizing polyoxymethylene molding materials with suitable additives. To this end, antioxidants, for example sterically hindered phenol derivatives, are added to the polyoxymethylene molding materials. Such phenol derivatives are listed, for example, in DE-A-2702661. EP-A-19761 relates to glass-fiber-reinforced polyoxymethylene molding materials containing alkoxymethylmelamines for improving the impact strength. Polyoxymethylene molding materials which are stable to heat over ｃA relatively long period of time at temperatures in the range from 100 to 150 ℃ are known from EP-A-52740, which describes the addition of partially etherified special melamine/formaldehyde condensates. DE-A-3011280 describes stabilized polyoxymethylene copolymer materials which comprise as stabilizers a mixture of at least one amino-substituted triazine, at least one sterically hindered phenol and at least one metal-containing compound. The metal-containing compound preferably comprises potassium hydroxide, calcium hydroxide, magnesium hydroxide or magnesium carbonate.

Despite these measures, the known polyoxymethylene molding materials still have unsatisfactory thermal stability problems for certain applications, which adversely affect processing, lead to the finished moldings, for example, being deposited on the mold or to the mold release properties being impaired and/or lead to discoloration and poor mechanical properties during the subsequent use of the moldings. A further disadvantage is that the mixture may also contain formaldehyde adducts which, during high-temperature processing, lead to an annoying odor as a result of the evolution of formaldehyde.

DE A3628560, DE A-3628561 and DE A3628562 disclose mixtures containing sterically hindered phenols and alkaline earth metal silicates and alkaline earth metal glycerophosphates as stabilizers. According to the specification, polyamides may also be used as further costabilizers. Despite the rather good thermal stability of such materials, there is still a need for improved color quality.

Disclosure of Invention

It is an object of the present invention to provide polyoxymethylene molding materials which have better thermal stability during processing and at higher use temperatures. At the same time, it is also expected to achieve better color constancy and permanent lightening of the color. Deposition of material on the mold and formaldehyde emission during processing are substantially minimized.

We have found that this object is achieved by the molding materials defined at the outset. Preferred embodiments are described in the dependent claims.

Preferably, the invention provides thermoplastic polyoxymethylene molding materials containing the following essential components:

A)99.21 to 99.98 wt.% of polyoxymethylene homopolymer or copolymer

B)0.005 to 0.35% by weight of a sterically hindered phenol

C)0.001 to 0.04 wt.% of polyamide

D) 0.002-0.05 wt% of alkaline earth metal silicate or alkaline earth metal glycerophosphate

E)0.01 to 0.15 wt.% of at least one ester or amide of a saturated or unsaturated aliphatic carboxylic acid having 10 to 40 carbon atoms with a polyhydric alcohol having 2 to 40 carbon atoms, or an aliphatic saturated alcohol or amine, or an ether derived from an alcohol with ethylene oxide

F)0 to 5% by weight of a melamine/formaldehyde condensate

G) From 0 to 74% by weight of further additives, the% by weight of components A) to G) summing to 100% in each case.

The novel molding materials of the invention comprise, as component A), from 10 to 99.98%, preferably from 30 to 99%, in particular from 40 to 98%, by weight of a polyoxymethylene homopolymer or copolymer.

Such polymers are known per se to the person skilled in the art and are disclosed in the literature.

Typically, such polymers contain at least 50% of-CH in the polymer backbone₂An O-repeat unit.

Homopolymers are generally prepared by polymerization of formaldehyde or trioxane, preferably in the presence of suitable catalysts.

For the purposes of the present invention, polyoxymethylene copolymers are preferred as component A, in particular in addition to containing the repeating unit-CH₂O-and also those which contain up to 50%, preferably from 0.1 to 20%, in particular from 0.3 to 10%, particularly preferably from 2 to 6%, by mol of recurring units of the formula:

wherein R is¹～R⁴Each independently is hydrogen, C₁～C₄Alkyl or haloalkyl of 1 to 4 carbon atoms, R⁵is-CH₂-、-CH₂O-or C₁～C₄Alkyl-or C₁～C₄Haloalkyl-substituted methylene or corresponding oxymethylene, n being 0 to 3. Advantageously, such groups can be introduced into the copolymer by ring opening of the cyclic ether. Preferred cyclic ethers are those of the formula:

wherein R is¹～R⁵And n has the above-mentioned meaning. As cyclic ethers, mention may be made, for example, of ethylene oxide, 1, 2-propylene oxide, 1, 2-butylene oxide, 1, 3-dioxane, 1, 3-dioxolane and 1, 3-dioxepan, while as comonomers there may be mentioned linear oligo-or paraformaldehyde, for example polydioxolane or polydioxepane.

Further suitable components A) are formaldehyde terpolymers, for example, by reacting trioxane and one of the abovementioned cyclic ethers with a third monomer, preferably a bifunctional compound of the formula

And/or

Wherein Z is 1 bond, -O-, -ORO- (R ═ C)₁～C₈Alkylene or C₂～C₈Cycloalkylene).

Preferred monomers of this type are ethylene diglycidyl ether, diglycidyl ether and diethers of a glycidyl compound with formaldehyde, dioxane or trioxane in a molar ratio of 2: 1, and diethers of 2 moles of a glycidyl compound with 1 mole of an aliphatic diol having from 2 to 8 carbon atoms, such as the diglycidyl ethers of ethylene glycol, 1, 4-butanediol, 1, 3-butanediol, cyclobutane-1, 3-diol, 1, 2-propanediol and cyclohexane-1, 4-diol, to mention just a few examples.

The preparation of the above-mentioned homopolymers and copolymers is known to the person skilled in the art and is disclosed in the literature and, therefore, need not be described in detail here.

Preferred polyoxymethylene copolymers have a melting point of at least 150 ℃ and a weight average molecular weight M_w5000 to 200,000, preferably 7000E150,000。

Polyoxymethylene polymers whose end groups are stabilized and whose ends have C-C bonds are particularly preferred.

Suitable sterically hindered phenols B) are in principle all compounds which have a phenolic structure and have at least 1 bulky group on the phenol ring.

For example, compounds of the formula:

in the formula R¹And R²Which may be identical or different, are each alkyl, substituted alkyl or substituted triazolyl, R³Is alkyl, substituted alkyl, alkoxy or substituted amino.

Antioxidants of this type are disclosed, for example, in DE-A-2702661 (US-A4360617).

Another preferred class of sterically hindered phenols is derived from substituted benzenecarboxylic acids, especially substituted benzenepropanoic acids.

Particularly preferred compounds of this class are those of the formula

In the formula R⁴、R⁵、R⁷And R⁸Independently of one another, are each C₁-C₈Alkyl, which in turn may be substituted (at least 1 of which is a bulky group), R⁶Is a divalent aliphatic group having 1 to 10 carbon atoms, and may have a C-O bond in its main chain.

Preferred compounds corresponding to these formulae are:

(Irganox  245 from Ciba-Geigy)

(Irganox  259 from Ciba-Geigy)

In general, the following compounds may be mentioned as examples of sterically hindered phenols:

2, 2 ' -methylenebis (4-methyl-6-tert-butylphenol), 1, 6-hexanediol bis [ 3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ], pentaerythritol tetrakis [ 3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ], distearyl 3, 5-di-tert-butyl-4-hydroxybenzylphosphonate, 2, 6, 7-trioxa-1-phosphabicyclo [2.2.2] oct-4-ylmethyl-3, 5-di-tert-butyl-4-hydroxyhydrocinnamate, 3, 5-di-tert-butyl-4-hydroxy-3, 5-distearylthiotriamino amine, 2- (2 ' -hydroxy-3 ', 5 ' -di-tert-butylphenyl) -5-chlorobenzotriazole, 2, 6-di-tert-butyl-4-hydroxymethylphenol, 1, 3, 5-trimethyl-2, 4, 6-tris (3, 5-di-tert-butyl-4-hydroxybenzyl) benzene, 4 ' -methylenebis (2, 6-di-tert-butylphenol), 3, 5-di-tert-butyl-4-hydroxybenzyldimethylamine and N, N ' -hexamethylenebis-3, 5-di-tert-butyl-4-hydroxyhydrocinnamide.

Those hindered phenols which have proven particularly effective and which can be used preferably are:

2, 2' -methylenebis (4-methyl-6-tert-butylphenol), 1, 6-hexanediol bis 3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate, (Irganox)^259) Pentaerythritol tetrakis [ 3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate ] and Irganox from Ciba Geigy^245 which have been described above and are particularly suitable.

The antioxidants (B) can be used individually or in mixtures in amounts of from 0.005 to 2%, preferably from 0.05 to 2%, in particular from 0.1 to 1% by weight, based on the total weight of the molding materials A) to G).

In some cases, sterically hindered phenols having no more than 1 sterically hindered group in the ortho position relative to the phenolic hydroxyl group have proven particularly advantageous, especially in the evaluation of color stability in diffuse light over long periods of storage.

Polyamides which can be used as component C) are known per se. For example, semi-crystalline or amorphous resins as described in encyclopedia of Polymer science and engineering, Vol.11, pp.315 to 489, published by John Wiley & Sons, 1988, may be used, the melting point of the polyamide being preferably less than 225 ℃ and especially less than 215 ℃.

Examples of such polyamides are polyhexamethylenenonanediamide, polyhexamethylenesebacamide, polyhexamethylenedodecanediamide, poly-11-aminoundecanamide and bis (p-aminocyclohexyl) methyldodecanediamide or the ring-opening polymerization products of lactams, such as polycaprolactam or polylaurolactam. Also suitable are polyamides based on terephthalic acid or isophthalic acid as acid component and/or trimethylhexamethylenediamine or bis (p-aminocyclohexyl) propane as diamine component and polyamide-based resins obtained by copolymerization of 2 or more of the above-mentioned polymers or their components.

Mention may be made, as polyamides particularly suitable, of copolyamides based on caprolactam, 1, 6-hexamethylenediamine, p' -diaminodicyclohexylmethane and adipic acid. 1 example of this is Ultramid by BASF corporation^1C is a product sold under the trade name of Vietnam.

Another suitable polyamide is Elvamide from DuPont^Products sold under the trade name.

The preparation of these polyamides is similar to that described in the above-mentioned publications. The ratio of terminal amino groups to terminal acid groups can be controlled by varying the molar ratio of the starting compounds.

The polyamide content in the novel molding materials is from 0.001 to 2%, preferably from 0.005 to 1.99%, in particular from 0.01 to 0.08%, by weight.

In many cases, the dispersibility of the polyamides used can be improved by the presence of a polycondensate of 2, 2-bis (4-hydroxyphenyl) propane (bisphenol A) and epichlorohydrin.

The condensate of epichlorohydrin and bisphenol A is commercially available. The preparation thereof is also known to the person skilled in the art. These polycondensates are known under the trade name Phenoxy^(from Union carbide) and Epikote^(from Shell). The molecular weight of such polycondensates may vary within wide limits; in principle, various commercially available products are suitable.

As component D), the novel polyoxymethylene molding materials contain from 0.002 to 2.0% by weight, preferably from 0.005 to 0.5% by weight, in particular from 0.01 to 0.3% by weight, of 1 or more alkaline earth metal silicates and/or alkaline earth metal glycerophosphates, based on the total weight of the molding material. Calcium, and especially magnesium, has proven to be very useful as the alkaline earth metal forming silicates and glycerophosphates. Calcium glycerophosphate, especially magnesium glycerophosphate and/or calcium silicate, especially magnesium silicate, is very suitable, and particularly preferred alkaline earth metal silicates are those of the formula:

Me·xSiO₂·nH₂O

in the formula:

me is an alkaline earth metal, preferably calcium or, in particular, magnesium,

x is 1.4 to 10, preferably 1.4 to 6,

n is greater than or equal to 0, preferably 0 to 8.

Component D) is advantageously used in finely ground form. Products having an average particle size of less than 100 μm, preferably less than 50 μm, are particularly suitable.

For example, the preferred calcium and magnesium silicates and/or calcium and magnesium glycerophosphates may be specified using the following characteristic data:

calcium silicate and magnesium silicate:

the contents of CaO and MgO are respectively as follows: 4 to 32%, preferably 8 to 30%, in particular 12 to 25% by weight;

SiO₂CaO and SiO₂The molar ratio of MgO is as follows: 1.4 to 10, preferably 1.4 to 6, in particular 1.5 to 4,

bulk density: 10 to 80g/100ml, preferably 10 to 40g/100ml,

average particle size: less than 100 μm, preferably less than 50 μm;

glycerophosphate of calcium and magnesium:

the contents of CaO and MgO are respectively as follows: more than 70%, preferably more than 80% by weight,

residue after burning: 45 to 65% by weight of a surfactant,

melting point: above 300 c and at least one,

average particle size: less than 100 μm, preferably less than 50 μm.

As component E), the novel molding materials comprise from 0.01 to 5, preferably from 0.09 to 2, in particular from 0.1 to 0.7, of at least one ester or amide of saturated or unsaturated aliphatic carboxylic acids having from 10 to 40, preferably from 16 to 22, carbon atoms with from 20 to 40, preferably from 2 to 6, carbon atoms of polyhydric alcohols or aliphatic saturated alcohols or amines or ethers derived from alcohols and ethylene oxide.

The carboxylic acid may be a mono-or di-acid. Examples thereof are pelargonic acid, palmitic acid, lauric acid, margaric acid, dodecanedioic acid, behenic acid, and particularly preferably stearic acid, capric acid and montanic acid (a mixture of fatty acids of 30 to 40 carbon atoms).

The aliphatic alcohols may be mono-to tetrahydric alcohols. Examples of alcohols are n-butanol, n-octanol, stearyl alcohol, ethylene glycol, propylene glycol, neopentyl glycol and pentaerythritol, glycerol and pentaerythritol being preferred.

The aliphatic amines can be monofunctional to trifunctional amines. Examples of such amines are stearylamine, ethylenediamine, propylenediamine, hexamethylenediamine and di (6-aminohexyl) amine, ethylenediamine and hexamethylenediamine being particularly preferred. Preferred esters and amides are glyceryl distearate, glyceryl tristearate, ethylenediamine distearate, glyceryl monopalmitate, glyceryl trilaurate, glyceryl monobehenate and pentaerythritol tetrastearate.

Mixtures of different esters or amides or combinations of esters and amides can also be used, any desired mixing ratio being possible.

Polyether polyols or polyester polyols esterified or etherified with mono-or polycarboxylic acids, preferably fatty acids, are also suitable. Suitable products are the commercial products, e.g. Loxiol^EP 728, from Henkel.

Preferred ethers are derived from alcohols and ethylene oxide and have the formula:

RO(CH₂CH₂O)_nH

wherein R is an alkyl group having 6 to 40 carbon atoms, and n is an integer of 1 or more. Particular preference is given to saturated C where R is n ≈ 50₁₆～C₁₈The fatty alcohol of (a), which is a Pasteur product sold under the trade name Lutensol^AT 50。

As component F), the novel molding materials may comprise from 0 to 5%, preferably from 0.001 to 5%, more preferably from 0.01 to 3%, in particular from 0.05 to 1%, by weight of a melamine/formaldehyde condensate. This is preferably a precipitated condensate in finely divided form which is crosslinked and water-insoluble. The preferred molar ratio of formaldehyde to melamine is 1.2: 1-10: 1, especially 1.2: 1-2: 1. The preparation of the compositions and of the condensates is described in DE-A2540207.

As component G), the novel molding materials may comprise from 0 to 74%, preferably from 0 to 50%, in particular from 0 to 40%, by weight of additives.

As component G), the novel molding materials may comprise from 0.0001 to 1%, preferably from 0.001 to 0.8%, in particular from 0.01 to 0.3%, by weight of a nucleating agent other than D) and E).

Suitable nucleating agents are all known compounds, for example melamine cyanurate, boron compounds such as boron nitride, silica, pigments such as Heliogenblau^(copper phthalocyanine pigment, registered trademark of BASF corporation) or branched polyoxymethylene, and the nucleating effect is obtained with a small amount.

In particular, talc is used as a nucleating agent, the talc being a hydrous magnesium silicate with a composition of Mg₃[(OH)₂/Si₄O₁₀]Or MgO.4SiO₂·H₂And O. Such tri-layer phyllosilicates have a triclinic, monoclinic or orthorhombic crystal structure and have a lamellar form. Mn, Ti, Cr, Ni, Na and K may be present as further trace elements, some of the OH groups of which may be substituted by fluorine.

Particular preference is given to using talc having a particle size of < 20 μm at 100%. The particle size distribution is generally determined by sedimentation analysis, preferably as follows:

less than 20 μm in 100% by weight

99% by weight of < 10 μm

85% by weight of < 5 μm

60% by weight of < 3 μm

43% by weight of < 2 μm

Such products are commercially available under the trade name Micro-Talc I.T. extra (from Norwegian Talc Minerals).

The fillers (other than D)) in amounts of up to 50%, preferably 5 to 40%, by weight are, for example, acicular potassium titanate single crystals, carbon fibers, preferably glass fibers, it being possible to use, for example, woven glass cloths, glass mats, glass surfacing mats and/or glass yarns or short glass fibers of low-alkali E glass having a diameter of 5 to 200 μm, preferably 8 to 50 μm, the fibrous fillers preferably having an average length after addition of 0.05 to 1 μm, in particular 0.1 to 0.5. mu.m.

Other suitable fillers are, for example, calcium carbonate or glass beads, preferably in ground form, or mixtures of these fillers.

Examples of other fillers in amounts of not more than 50%, preferably 0 to 40% by weight, are polymeric impact modifiers (also referred to below as elastomeric polymers or elastomers).

Preferred types of such elastomers are ethylene/propylene (EPM) and ethylene/propylene/diene (EPDM) rubbers.

EPM rubbers generally contain virtually no double bonds, whereas EPDM rubbers may contain 1 to 20 double bonds per 100 carbon atoms.

Examples of diene monomers of EPDM rubbers are conjugated dienes such as isoprene and butadiene; non-conjugated dienes of 5 to 25 carbon atoms, such as 1, 4-pentadiene, 1, 4-hexadiene, 1, 5-hexadiene, 2, 5-dimethyl-1, 5-hexadiene and 1, 4-octadiene; cyclic dienes such as cyclopentadiene, cyclohexadiene, cyclooctadiene and dicyclopentadiene; and alkenyl norbornenes such as 5-ethylidene-2-norbornene, 5-butylidene-2-norbornene, 2-methallyl-5-norbornene and 2-isopropenyl-5-norbornene; and tricyclodienes, such as 3-methyltricyclo [5.2.1.0.2.6] -3, 8-decadiene, or mixtures of these. 1, 5-hexadiene, 5-ethylidene norbornene and dicyclopentadiene are preferred. The diene content of the EPDM rubber is preferably 0.5 to 50 wt%, especially 1 to 8 wt%, based on the total weight of the rubber.

The EPDM rubbers may also be grafted with other monomers, for example with glycidyl (meth) acrylate, (meth) acrylate and (meth) acrylamide monomers.

Other types of preferred rubbers include copolymers of ethylene with esters of (meth) acrylic acid. In addition, the rubber may also contain an epoxy-containing monomer. These epoxy-containing monomers are preferably incorporated in the rubber by adding epoxy-containing monomers of the general formula (I) or (II) to the monomer mixture:

in the formula R⁶～R¹⁰Each is hydrogen or an alkyl group having 1 to 6 carbon atoms, m is an integer of 0 to 20, g is an integer of 0 to 10, and p is an integer of 0 to 5.

Preferably, R⁶～R⁸Each is hydrogen, m is 0 or 1, and g is 1. Corresponding compounds are allyl glycidyl ether and vinyl condensed glycidyl ether.

Preferred compounds of the formula II are epoxy-containing esters of acrylic acid and/or methacrylic acid, such as glycidyl acrylate and glycidyl methacrylate.

Advantageously, the copolymer comprises from 50 to 98% by weight of ethylene and from 0 to 20% by weight of an epoxy group-containing monomer, the remainder being constituted by (meth) acrylic esters.

Copolymers containing the following components are particularly preferred: 50 to 98%, in particular 55 to 95%, by weight of ethylene, in particular 0.3 to 20% by weight of acrylic acid

Glycidyl esters and/or 0 to 40%, in particular 0.1 to 20%, by weight of glycidyl methacrylate and 1 to 50%, in particular 10 to 40%, by weight of n-butyl acrylate and/or 2-ethylhexyl acrylate

And (3) an ester.

Further preferred esters of acrylic and/or methacrylic acid are methyl, ethyl, propyl, isobutyl and tert-butyl esters.

Vinyl esters and vinyl ethers may also be used as monomers.

The above-mentioned ethylene copolymers can be prepared by methods known per se, preferably by random copolymerization at superatmospheric pressure and elevated temperature, suitable methods generally being known.

Other preferred elastomers are emulsion polymers, the preparation of which is described, for example, in Blackley's monograph on emulsion polymerization'. Emulsifiers and catalysts which can be used are known per se.

In principle, elastomers of uniform composition or of shell structure can be used. The shell-like structure is determined by the order of addition of the monomers; the morphology of the polymer is also affected by this order of addition.

As typical monomers for the production of rubber parts, mention may be made here of acrylates, such as n-butyl acrylate and 2-ethylhexyl acrylate, the corresponding methacrylates, butadiene and isoprene and mixtures thereof. These monomers may be combined with other monomers such as styrene, acrylonitrile, vinyl ethers, and other acrylates or methacrylates such as methyl methacrylate, methyl acrylate, ethyl acrylate, and propyl acrylate.

The soft or rubbery phase of the elastomer (glass transition temperature below 0 ℃) may comprise a core, shell or intermediate shell (in the case of elastomers comprising more than 2 shell structures); in the case of multi-shell elastomers, many of the shells may also be composed of a rubber phase.

If the elastomer consists not only of a rubber phase but also of one or more hard components (glass transition temperature higher than 20 ℃), such elastomers are generally prepared by polymerizing styrene, acrylonitrile, methacrylonitrile, alpha-methylstyrene, p-methylstyrene, acrylates and methacrylates such as methyl acrylate, ethyl acrylate and methyl methacrylate as the main monomers. Here, it is also possible to use smaller amounts of other comonomers.

In some cases, it has proven advantageous to use emulsion polymers having reactive groups on the surface. Such groups are, for example, epoxy, amino or amido groups and functional groups, which can be introduced using monomers of the general formula:

in the formula:

R¹⁵is hydrogen or C₁-C₄An alkyl group, a carboxyl group,

R¹⁶is hydrogen, C₁-C₈Alkyl or aryl, especially phenyl,

R¹⁷is hydrogen, C₁-C₁₀Alkyl radical, C₆-C₁₂Aryl OR-OR₁₈，

R¹⁸Is C₁-C₈Alkyl or C₆-C₁₂Aryl, each of which may be substituted with an O or N containing group, and

x is 1 bond, C₁-C₁₀Alkylene or C₆-C₁₂Arylene radicals or

The graft monomers described in EP-A208187 are also suitable for introducing reactive groups on the surface.

Mention may be made, as further examples, of acrylamide, methacrylamide and substituted esters of acrylic or methacrylic acid, such as (N-tert-butylamino) ethyl methacrylate, (N, N-dimethylamino) ethyl acrylate, (N, N-dimethylamino) methyl acrylate and (N, N-diethylamino) ethyl acrylate.

Furthermore, the particles of the rubber phase may also be crosslinked. Crosslinking-active monomers are, for example, 1, 3-butadiene, divinylbenzene, diallyl phthalate and dihydrodicyclopentadienyl acrylate and also the compounds described in EP-A50265.

Graft-linking monomers, i.e., monomers having 2 or more polymerizable double bonds that react at different rates in the polymerization reaction, can also be used. Preferably used compounds of this type are those in which at least 1 reactive group polymerizes at about the same rate as the other monomers, while the other reactive groups polymerize substantially more slowly. The different polymerization rates result in a certain proportion of unsaturated double bonds in the rubber. The other phase is then grafted onto such a rubber, some or all of the double bonds present in the rubber subsequently reacting with the grafting monomers to form chemical bonds, i.e.the grafted phase is at least partially attached to the graft base by means of chemical bonds.

Examples of such graft-linking monomers are allyl-containing monomers, in particular allyl esters of ethylenically unsaturated carboxylic acids, such as allyl acrylate, allyl methacrylate, diallyl maleate, diallyl fumarate, diallyl itaconate and the corresponding monoallyl compounds of these dicarboxylic acids. There are also a large number of other suitable graft-linking monomers; reference may be made in detail to, for example, U.S. patent 4,148,846.

In general, the proportion of these crosslinking monomers in component G) is not more than 5% by weight, preferably not more than 3% by weight, based on G).

Some preferred emulsion polymers are listed below. Mention may first be made here of graft polymers having a core and at least 1 shell and having the following composition:

core layer monomer	Shell monomer
		1, 3-butadiene, isoprene, butyl acrylate, ethylhexyl acrylate or mixtures thereof, if desired together with crosslinking monomers	Styrene, acrylonitrile, (meth) acrylates, if desired together with the reactive groups described here

It is also possible to replace the graft polymer having a multishell structure with a homogeneous, i.e.monomeric, elastomer of 1, 3-butadiene, isoprene and n-butyl acrylate or a copolymer thereof. Such products may also be prepared using crosslinking monomers or monomers having reactive groups.

The elastomers D) can also be prepared by other conventional processes, for example suspension polymerization.

Examples of other suitable elastomers are thermoplastic polyurethanes, such as those described in EP-A115846, EP-A115847 and EP-A117664.

Mixtures of the various types of rubbers mentioned above can of course also be used.

The novel molding materials may comprise further conventional additives and processing aids. Formaldehyde scavengers, plasticizers, adhesion promoters and pigments may be mentioned here by way of example only. Such additives are generally used in amounts of 0.001 to 5% by weight.

The novel thermoplastic molding materials can be prepared by mixing the components in a manner known per se, so that further details need not be described here. The mixing of the components is preferably carried out in an extruder.

The novel thermoplastic molding materials have a balanced property spectrum and exhibit very good thermal stability, resulting in virtually no coating on the mold during processing and virtually no discoloration. The shaped articles are therefore particularly suitable for use as molded articles, such as chains, rollers, sliding rails or gears.

Detailed Description

Examples

The following components were used:

component A)

A polyoxymethylene copolymer comprising 97% by weight trioxane and 3% by weight butanediol formal. The product also contained about 3% by weight of unconverted trioxane and 5% by weight of thermally unstable fractions. The MVR of the copolymer after degradation of the thermally labile fraction was 6ml/10 min (190 ℃, 2.16kg, determined according to ISO 1133/B).

Component B)

Irganox from Ciba Geigy^：

Component C)

Polyamide oligomers having a molecular weight of about 3000, prepared from caprolactam, hexamethylenediamine, adipic acid and propionic acid (as molecular weight regulator), analogously to examples 5-4 (PA-double end group) of U.S. Pat. No. 3,3960984.

Component D)

Synthetic magnesium silicate (Ambosol from Sociele Nobel, Puteaux)^) Having the following properties:

MgO content of 14.8 wt% or more

SiO₂The content is more than or equal to 59 percent by weight

SiO₂MgO molar ratio: 2.7mol/mol

Apparent density of 20 to 30g/100m (as in original text)

Loss on ignition of < 25% by weight

Component E)

E1: loxiol  VP 1206 from Henkel corporation (glyceryl distearate)

E2: loxiol  EP 728 from Henkel (polyol fatty acid)

E3: lutensol  AT 50 from Basff (RO (CH)₂CH₂)_xH; r is saturated straight chain C₁₆-C₁₈Fatty alcohol) x ═ 50

E4: synthetic wax, available from Henkel corporation (Ethylenediamine distearate)

Component F):

melamine/formaldehyde condensates obtained as described in example 1 of DE-A2540207.

Molding materials were prepared by mixing component A with components B to F in the amounts specified in the tables at 23 ℃ in a dry mixer. The mixture thus obtained is introduced into a twin-screw extruder (ZSK 25, from Werner & Pfleiderer) with devolatilization, homogenized at 230 ℃ to devolatilize it, the homogenized mixture is then extruded through a die and the extrudate is finally granulated.

To test the thermal stability, the following measurements were performed:

WL N₂: the percent weight loss after heating 1.2g of the granular sample at 220 ℃ for 2 hours under nitrogen.

WL air: the percent weight loss of 1.2g of the granulated sample after heating in air at 220 ℃ for 2 hours.

MVR was determined according to ISO 1133/B.

The compositions of the molding materials and the test results are given in the table below.

Components		Examples	1	1V	2	2V
							A		By weight%	99.21	99.26	99.41	99.25
B		By weight%	0.35	0.35	0.35	0.35
							C		By weight%	0.04	0.04	0.04	--
D		By weight%	0.05	--	0.05	0.05
							F		By weight%	0.20	0.20	--	0.20
E1		By weight%	0.15	0.15	0.15	0.15
							E2		By weight%	--	--	--	--
E3		By weight%	--	--	--	--
							E4		By weight%	--	--	--	--
And (3) analysis:
							weight loss 2 hours:
	N2	〔％〕	0.15	0.42	0.19	0.07
								air (a)	〔％〕	1.35	6.41	1.72	3.28
	MVR	[ml/10min]	6.35	5.56	5.83	5.69

Components		Examples	3V	3	4	5
							A		By weight%	99.36	99.21	99.21	99.21
B		By weight%	0.35	0.35	0.35	0.35
							C		By weight%	0.04	0.04	0.04	0.04
D		By weight%	0.05	0.05	0.05	0.05
							F		By weight%	0.20	0.20	0.20	0.20
E1		By weight%	--	--	--	--
							E2		By weight%	--	0.15	--	--
E3		By weight%	--	--	0.15	--
							E4		By weight%	--	--	--	0.15
Weight loss:
								N2	〔％〕	0.24	0.15	0.08	0.07
	air (a)	〔％〕	1.65	1.20	1.42	1.26
								MVR	[ml/10min]	6.10	5.72	6.04	5.96

Claims (8)

1. A thermoplastic polyoxymethylene molding material comprising the following essential constituents:

A)99.21 to 99.98 wt.% of polyoxymethylene homopolymer or copolymer

B)0.005 to 0.35% by weight of a sterically hindered phenol

C)0.001 to 0.04 wt.% of polyamide

D) 0.002-0.05 wt% of alkaline earth metal silicate or alkaline earth metal glycerophosphate

E)0.01 to 0.15 wt.% of at least one ester or amide of a saturated or unsaturated aliphatic carboxylic acid having 10 to 40 carbon atoms with a polyhydric alcohol having 2 to 40 carbon atoms, or an aliphatic saturated alcohol or amine, or an ether derived from an alcohol with ethylene oxide

F)0 to 5% by weight of a melamine/formaldehyde condensate

G) From 0 to 74% by weight of further additives, the% by weight of components A) to G) summing to 100% in each case.

2. A thermoplastic molding material as claimed in claim 1, wherein a sterically hindered phenol having not more than 1 sterically hindered group in the ortho position relative to the phenolic hydroxyl group is used.

3. A thermoplastic molding material as claimed in claim 1 or 2, in which component F) is composed of a finely divided, crosslinked, water-insoluble precipitated polycondensate of formaldehyde and melamine in a molar ratio of from 1.2: 1 to 10: 1.

4. A thermoplastic molding material as claimed in claim 1, in which component E) is ethylenediamine distearate, glycerol distearate, a polyether polyol fatty acid ester, a polyester polyol fatty acid ester or an ether of the formula:

RO(CH₂CH₂O)_nH

wherein R is an alkyl group having 6 to 40 carbon atoms, and n is 1 or more.

5. A thermoplastic molding material as claimed in claim 1, wherein alkaline earth metal silicates of the formula are used as component D):

Me·xSiO₂·nH₂O

in the formula:

me is an alkaline earth metal

x is 1.4 to 10

n is greater than or equal to 0.

6. A thermoplastic molding material as claimed in claim 1, which comprises from 0.001 to 5% by weight of component F).

7. The use of the thermoplastic molding materials as claimed in claim 1 for producing fibers, films and moldings.

8. A molding produced from the thermoplastic molding materials as claimed in claim 1.