WO2013113880A1 - Thermoplastic pom material - Google Patents

Description

 Thermoplastic POM mass

The invention relates to thermoplastic compositions containing mixtures of polyoxymethylene homo- or copolymers, their preparation, their use for the production of metallic or ceramic moldings and the moldings obtainable in this way. Polyoxymethylene homopolymers or copolymers, also referred to as polyacetal or polyformaldehyde or POM, are generally high molecular weight thermoplastics which exhibit high stiffness, low coefficients of friction and excellent dimensional stability and thermal stability. Therefore, they are used in particular for the production of precision parts.

In particular, the high strength, hardness and stiffness in a wider temperature range make them advantageous for molding applications. The further processing takes place, for example, by injection molding at temperatures in the range of 180 to 230 ° C, as well as by extrusion. The preparation of polyoxymethylene is carried out, for example, by direct polymerization of formaldehyde or by cationic or transition metal-centered cationic polymerization of trioxane. For stabilization, in order to prevent depolymerization under acid influence or thermal stress, the end groups are often protected by etherification or esterification.

Another possibility for stabilization against acid influence and thermal stress is the preparation of copolymers, for example by copolymerization of trioxane with 1, 4-dioxane. Here, the unstable end groups are degraded by hydrolysis to formaldehyde for stabilization. Typical copolymers ^® for example, under the brand names Hostaform ^® from Ticona / Celanese and Ultra form available from BASF SE.

The homopolymer typically has a melting point of about 178 ° C, the copolymer of about 166 ° C.

Processes for the preparation of polyoxymethylene homopolymers or copolymers are described, for example, in WO 2007/023187 and WO 2009/077415.

US 6,388,049 relates to low molecular weight polyoxymethylene polymers and compositions containing them. Preparation Examples 14 to 16 give trioxane-based and butanediol-formal copolymers in which methylal was used as regulator. The amount of comonomer added is 1.46 mol%, corresponding to about 4.4% by weight of butanediol formal. Number average molecular weights of 1100, 5500 and 35000 g / mol are obtained.

Polyoxymethylene is also used as a binder for powder injection molding. In this case, filled with inorganic powders, in particular metal powders or ceramic powders, POM molding compounds are processed by injection molding into moldings and subsequently debinded and sintered. Since the high loading of the POM with the inorganic powders impairs the flowability, it is necessary to use well-flowing POM materials in order to keep the pressures required during the injection molding to a reasonable level.

Under the brand Catamold ^® polymer particles are distributed, the inorganic material powder, particularly metal powders or ceramic powders contain. These powders are typically first coated with a thin layer of polyethylene and then compounded in a polyoxymethylene binder. This Catamold granulate is then processed by injection molding into a green body, transferred by debinding in a brown body and then sintered to a sintered shaped body. The process is known as Metal Injection Molding (MIM) and allows the production of metal or ceramic moldings with complex shapes.

The Catamold granules have a content of inorganic fillers of about 90 wt .-%.

The green bodies produced using polyoxymethylene homo- or copolymers have very good mechanical properties, in particular dimensional stability.

The debinding is often carried out by the action of an acidic atmosphere, for example HN0 ₃ atmosphere at 1 10 to 140 ° C with degradation of the POM binder. In the brown body obtained, the inorganic particles are connected to one another via their thin polyethylene coating. Due to the acidic depolymerization of the POM, the binder can be removed without residue.

The sintering of the brown body preferably follows in a sintering furnace at temperatures in the range of about 1300 to 1500 ° C to obtain the desired metal or ceramic shaped body. For the Catamold process suitable thermoplastic compositions for the production of metallic moldings are described for example in EP-A-0 446 708. Thermoplastic materials for the production of ceramic molded articles are described, for example, in EP-A-0 444 475.

Metal-oxide-containing molding compositions are described, for example, in EP-A-0 853 995.

The better the flowability of the filled Polyoxymethylenhomo- or -copolymermassen, the finer structures can be formed in the molding. On the other hand, the metal or ceramic particles should be transported homogeneously with the molding compound. A suitable property spectrum of flowability and creep compliance is frequently achieved by POM with a weight-average molecular weight above about 85,000 g / mol.

To improve the flowability of the POM, the molecular weight could be lowered or flow improvers added. A flow improver should have a very good miscibility with POM and show a rapid degradation under an acid-gas atmosphere in order to avoid defects in the desired moldings.

The addition of aliphatic polyurethanes, aliphatic uncrosslinked polyepoxide, aliphatic polyamides or polyacrylates or poly (C _2- 6-alkylene oxides) to polyoxymethylene homo- or copolymers described in the EP-A-0446708.

The object of the present invention is to provide thermoplastic compositions based on polyoxymethylene homopolymers or copolymers having improved flowability, which exhibit a better flow behavior when filled with inorganic material powders in extrusion or injection molding than known molding compositions, and which at the same time are the good ones retained mechanical properties of the known molding compositions based on Polyoxymethylenhomo- or copolymers. The object is achieved by a thermoplastic composition containing

10 to 90% by weight of a polyoxymethylene homo- or copolymer having a weight average molecular weight (M _w ) in the range of 50,000 to 400,000 g / mol as component B1 and 10 to 90 wt .-% of a polyoxymethylene copolymer having a weight average molecular weight (M _w ) in the range of 5,000 to 15,000 g / mol, based on the polymer derived at least 90 wt .-% of trioxane and butanediol as monomers , with a proportion of butanediol formal, based on the polymer, in the range of 0.5 to 4 wt .-%, preferably 2 to 3.5 wt .-%, in particular 2.5 to 3 wt .-% as component B2.

The object is further achieved by a process for the preparation of these thermoplastic compositions by separate preparation of the components B1 and B2 by each polymerization of trioxane and optionally comonomers in the presence of at least one cationic initiator and at least one di (Ci _-6- alkyl) acetal as Controller and subsequent mixing of components B1 and B2.

The object is further achieved by a process for the preparation of flowable polyoxymethylene homopolymers or copolymers by separately preparing the components B1 and B2, as defined above, by respectively polymerizing trioxane and (in component B1 optionally) comonomers in the presence of at least one cationic Starters and at least one di (Ci _-6- alkyl) acetal as a regulator and subsequent mixing of components B1 and B2 at a temperature in the range of 150 to 220 ° C under a pressure in the range of 0.5 to 5 bar.

The object is also achieved by flowable polyoxymethylene copolymers obtainable by the above process. The object is further achieved by a molding composition for the production of inorganic shaped bodies, containing, based on the total volume of the molding composition,

From 20 to 70% by volume of a sinterable pulverulent inorganic material selected from metals, metal alloys, metal carbonyls, metal oxides, metal carbides, metal nitrides or mixtures thereof, as component A,

- 30 to 80 vol .-% of a thermoplastic composition as defined above or obtainable by the above method, as component B, - 0 to 5 vol .-% of a lubricating and / or dispersing aid as component C, wherein the total volume of the components A to C 100% by volume.

The object is also achieved by a method for producing such molding compositions by melting the component B at a temperature in the range of 150 to 220 ° C to obtain a melt stream and metered addition of the components A and optionally C to the melt stream of the component B.

The object is further achieved by the use of the above molding compositions for the production of metallic or ceramic moldings.

The object is further achieved by a process for the production of metallic or ceramic moldings by injection molding or extrusion of the molding composition into a green body, subsequent debindering of the green body to obtain a brown body and subsequent sintering of the brown body.

The object is further achieved by a shaped body produced from the above-described molding compositions or obtainable by the processes described above.

The term "polyoxymethylene" or "polyoxymethylene homo- or copolymers" refers to both a polyoxymethylene homopolymer and a polyoxymethylene copolymer. It has been found according to the invention that polyoxymethylene copolymers having a weight average molecular weight (M _w ) in the range of 5000 to 15,000, preferably 5000 to 10,000 g / mol or 6000 to 13,000, preferably 6000 to 9000 g / mol or 6500 to 1 1000, particularly preferred 6500 to 8000 g / mol, in particular 7000 to 7500 g / mol, based on the polymer derived from at least 90 wt .-% of trioxane and butanediol as monomers, with a proportion of butanediol, based on the polymer, im Range of 0.5 to 4 wt .-%, preferably 1 to 4 wt .-%, preferably 2 to 3.5 wt .-%, in particular 2.5 to 3 wt .-%, as viscosity modifying additives for Polyoxymethylenhomo Higher molecular weight copolymers or copolymers can be used without compromising the mechanical properties of the resulting blend or reaction product as compared to higher molecular weight polyoxymethylene homopolymers or copolymers.

The molecular weight determination can be carried out as described in the examples. The determination of the molecular weights is usually carried out by gel permeation chromatography (GPC) or SEC (Size Exclusion Chromatography). The number average molecular weight is generally determined by GPC-SEC.

Hereinafter, the component B2 will be described in detail first. Preferably, the ratio between weight average molecular weight (M _w ) and number average molecular weight (M _n ), also referred to as polydispersity or M _w / M _n , is in the range of 1.5 to 3.0, preferably 1.5 to 2, 45th Alternatively and preferably, the number average molecular weight (M _n ) is preferably 3000 to 6000 g / mol, particularly preferably 3200 to 5000 g / mol, in particular 3500 to 4100 g / mol. In this molecular weight range, a particularly advantageous flow improvement is achieved for polyoxymethylene homopolymers or copolymers having a higher molecular weight.

The use of a polyoxymethylene copolymer according to the present invention, which has a proportion of butanediol formal, based on the polymer, in the range of 1 to 4 wt .-%, due to the comonomer reduced compared to US 6,388,049 comonomer shows a higher crystallinity and a higher hardness despite the low molecular weight. In spite of good viscosity-reducing properties for polyoxymethylene homopolymers or copolymers having a higher molecular weight, this results in an advantageous hardness of these polymer blends and thus advantageous mechanical properties for use. Polyoxymethylene copolymers (POM) according to the invention generally have at least 50 mol% of repeating units - CH ₂ O - in the main polymer chain. Polvoxymethylene copolymers are preferred which in addition to the repeating units -CH ₂ 0- even up to 50, preferably 0.01 to 20, in particular 0.1 to 10 mol% and very particularly preferably 0.5 to 6 mol% of recurring units

aufweisen, wobei R¹ bis R⁴ unabhängig voneinander ein Wasserstoffatom, eine Crbis C₄-Alkylgruppe oder eine halogensubstituierte Alkylgruppe mit 1 bis 4 C-Atomen und R⁵ eine -CH₂-, -CH₂0 -, eine C bis C₄-Alkyl- oder d- bis C₄-Haloalkyl substituierte Methylengruppe oder eine entsprechende Oxymethylengruppe darstellen und n einen Wert im Bereich von 0 bis 3 hat. Vorteilhafterweise können diese Gruppen durch Ringöffnung von cyclischen Ethern in die Copolymere eingeführt werden. Bevorzugte cyc- lische Ether sind solche der Formel

wobei R¹ bis R⁵ und n die oben genannte Bedeutung haben. Nur beispielsweise seien Ethylenoxid, 1 ,2-Propylenoxid, 1 ,2-Butylenoxid, 1 ,3-Butylenoxid, 1 ,3-Dioxan, 1 ,3-Di- oxolan und 1 ,3-Dioxepan (= Butandiolformal, BUFO) als cyclische Ether sowie lineare Oligo- oder Polyformale wie Polydioxolan oder Polydioxepan als Comonomere genannt.

, said R ¹ to R ⁴ independently represent a hydrogen atom, a Crbis C ₄ alkyl group or a halogen-substituted alkyl group having 1 to 4 carbon atoms and R ⁵ is a -CH ₂ -, -CH ₂ 0 -, a C to C ₄ Alkyl or C 1 to C ₄ haloalkyl-substituted methylene group or a corresponding oxymethylene group and n has a value in the range of 0 to 3. Advantageously, these groups can be introduced into the copolymers by ring opening of cyclic ethers. Preferred cyclic ethers are those of the formula

wherein R ¹ to R ⁵ and n have the abovementioned meaning. For example, ethylene oxide, 1, 2-propylene oxide, 1, 2-butylene oxide, 1, 3-butylene oxide, 1, 3-dioxane, 1, 3-dioxolane and 1, 3-dioxepane (= butanediol, BUFO) as cyclic Ethers and linear oligo- or polyformals such as polydioxolane or polydioxepan called comonomers.

Likewise suitable are oxymethylene terpolymers which are obtained, for example, by reacting trioxane, one of the cyclic ethers described above, with a third monomer, preferably bifunctional compounds, of the formula

and or

CL CL _^ 0 wherein Z is a chemical bond, -O-, -ORO- (R = Cr to C ₈ -alkylene or C ₃ - to C ₈ - cycloalkylene) can be prepared. Preferred monomers of this type are ethylene diglycide, diglycidyl ether and diether from glycidylene and formaldehyde, dioxane or trioxane in the molar ratio 2: 1 and diether from 2 mol glycidyl compound and 1 mol of an aliphatic diol having 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 name just a few examples.

End-group-stabilized polyoxymethylene polymers which have predominantly C-C or -O-CH ₃ bonds at the chain ends are particularly preferred.

The polymers according to the invention are derived, based on the polymer, from at least 90% by weight of trioxane and butanediol formal as monomers.

In this case, the polyoxymethylene copolymers are derived, preferably exclusively, from trioxane and butanediol as monomers, with a content of butanediol formal, based on the polymer or on the monomers, in the range of 0.5 to 4 wt .-%, preferably 1 to 4 wt .-%, preferably 2 to 3.5 wt .-%, in particular 2.5 to 3 wt. -%. The molecular weights of the polymer can be adjusted to the desired values by the regulators customary in the trioxane polymerization and by the reaction temperature and residence time. Suitable regulators are acetals or formals of monohydric alcohols, the alcohols themselves and the small amounts of water which act as chain transfer agents and whose presence can generally never be completely avoided.

Preferably, the inventive polymer at the chain ends, based on the polymer, 3 to 6 wt .-% of radicals of the general formula -OR, wherein R is Ci-6-alkyl, preferably Ci _-4 alkyl.

Preferably, in the preparation of the polyoxymethylene copolymer of the invention, based on the polymer or the sum of monomers and regulators, 3.75 to 4.25 wt .-%, preferably 3.8 to 4.2 wt .-%, in particular 3 , 9 to 4.1 wt .-% methylal or an equimolar amount of another di (Ci _-6- alkyl) acetal concomitantly used as a regulator.

Particularly preferred are methylal, z. B. on a laboratory scale, or ButylaI (n-butyl), z. B large-scale, also used as regulator. More preferably, butylal (n-butylal) is used as a regulator which has the advantage of being non-toxic, while Methylal is classified as toxic. The use of butylal as a regulator is a further advantage over the polyoxymethylene copolymers known from US Pat. No. 6,388,049. Preference is given to using butylalI as regulator in the preparation of the polymer. Butylal, based on the polymer, in an amount of 0.5 to 4 wt .-%, particularly preferably 1 to 3.5 wt .-%, in particular 1, 5 to 2.5 wt .-%, is preferably used. Together with the specific amount of comonomer and the specific molecular weight, polyoxymethylene copolymers with particularly suitable mechanical properties are obtained which render them suitable as viscosity-modifying additives for polyoxymethylene homo- or copolymers of higher molecular weight, without the mechanical properties, in particular the hardness, being impaired to a greater extent become. Polyoxymethylene copolymers with a proportion of butanediol formal, based on the polymer, in the range from 0.5 to 4 wt.%, Preferably 1 to 4 wt.%, Preferably 2 to 3.5 wt. , in particular 2.5 to 3 wt .-%, in their preparation Butylal as a regulator in an amount, based on the polymer, from 0.5 to 4 wt .-%, particularly preferably 1 to 3.5 wt .-%, in particular 1, 5 to 2.5% by weight, is used. The number average of the polyoxymethylene copolymer is more preferably 3000 to 6000 g / mol, more preferably 3200 to 5000 g / mol, especially 3500 to 4100 g / mol. This special combination of molecular weight, comonomer content, comonomer selection, regulator fraction and regulator selection leads to particularly suitable mechanical properties which allow the advantageous use as a viscosity-modifying additive for relatively high molecular weight polyoxymethylene homopolymers or copolymers. Initiators (also referred to as catalysts) are the cationic initiators customary in the trioxane polymerization. Proton acids are suitable, such as fluorinated or chlorinated alkyl- and arylsulfonic acids, for example perchloric acid, trifluoromethanesulfonic acid or Lewis acids, for example tin tetrachloride, arsenic pentafluoride, phosphoric pentafluoride and boron trifluoride and their complex compounds and salt-like compounds, for example boron trifluoride etherates and triphenylmethylhexafluorophosphate. The initiators (catalysts) are used in amounts of about 0.01 to 1000 ppm, preferably 0.01 to 500 ppm and in particular from 0.01 to 200 ppm. In general, it is advisable to add the initiator in dilute form, preferably in concentrations of 0.005 to 5 wt .-%. Suitable solvents for this purpose are inert compounds such as aliphatic, cycloaliphatic hydrocarbons such as cyclohexane, halogenated aliphatic hydrocarbons, glycol ethers, etc. can be used. Particular preference is given to triglyme (triethylene glycol dimethyl ether) as solvent and 1,4-dioxane. Particularly preferred according to the invention as cationic initiators Bronsted acids in an amount in the range of 0.01 to 1 ppm (preferably 0.02 to 0.2 ppm, in particular 0.04 to 0.1 ppm), based on the sum of monomers and regulators, used. In particular, HCI0 _{4 is used} as a cationic initiator or initiator. In addition to the initiators cocatalysts can be included. These are alcohols of any type, for example aliphatic alcohols having 2 to 20 C atoms, such as t-amyl alcohol, methanol, ethanol, propanol, butanol, pentanol, hexanol; aromatic alcohols having 2 to 30 C atoms, such as hydroquinone; halogenated alcohols having 2 to 20 C atoms, such as hexafluoroisopropanol; Very particular preference is given to glycols of any type, in particular diethylene glycol and triethylene glycol; and aliphatic dihydroxy compounds, in particular diols having 2 to 6 carbon atoms, such as 1, 2-ethanediol, 1, 3 Propanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and neopentylglycol.

Monomers, initiators, cocatalyst and, if appropriate, regulators may be premixed in any way or may also be added to the polymerization reactor separately from one another.

Further, the stabilizing components may contain sterically hindered phenols as described in EP-A 129369 or EP-A 128739.

The preparation of the polyoxymethylene copolymers of the invention B2 is carried out by polymerization of trioxane, butanediol and optionally further comonomers, in the presence of at least one cationic initiator and at least one di (Ci _-6- alkyl) acetal as a regulator.

The polymerization mixture is preferably deactivated directly after the polymerization, preferably without a phase change taking place. The deactivation of the initiator residues (catalyst residues) is generally carried out by adding deactivators (terminating agents) to the polymerization melt. Suitable deactivators are, for example, ammonia and primary, secondary or tertiary, aliphatic and aromatic amines, for example trialkylamines such as triethylamine, or triacetonediamine. Also suitable are basic-reacting salts, such as soda and borax, furthermore the carbonates and hydroxides of the alkali metals and alkaline earth metals, and also alkoxides, such as sodium ethanolate. The deactivators are usually added to the polymers in amounts of preferably 0.01 ppmw (parts per million by weight) up to 2 wt .-%. Furthermore, alkali metal or alkaline earth metal alkyls are preferred as deactivators which have 2 to 30 C atoms in the alkyl radical. Particularly preferred metals are Li, Mg and Na, with n-butyllithium being particularly preferred. According to one embodiment of the invention, from 3 to 30 ppm, preferably from 5 to 20 ppm, in particular from 8 to 15 ppm, based on the sum of monomers and regulator, of a chain terminating agent can be used. In particular, sodium methylate is used as a chain terminator. POMs from trioxane and butanediol formal are generally obtained by bulk polymerization, using any reactors with high mixing efficiency. The reaction can be carried out homogeneously, for example in a melt, or heterogeneously, for example as polymerization to a solid or solid granules. Suitable examples are shell reactors, plowshare mixers, tubular reactors, list reactors, kneaders (eg Busskneter), extruder with, for example, one or two Screws, and stirred reactors, wherein the reactors may have static or dynamic mixer.

The trioxane polymerization can be thought of as three reaction steps, the initiation, the propagation and the transfer reactions. In the transfer reactions, chain transfer to the polymer, to a protic species such as water, or to a transfer agent such as butylal can occur. The transfer reactions to other polymer chains allow the random distribution of the comonomer units along the polymer chains. These reactions occur between the carbonium of one active chain and the oxygen of another polymer chain as long as active carbonium ions are present in the reaction mixture.

Transfer reactions to protic species such as water reduce both the molecular weight and the thermal stability of the polymer as unstable hydroxyl end groups are formed. Therefore, the polymerization is carried out under dry conditions.

Transfer reactions to aprotic species such as low molecular weight acetals reduce the molecular weight and produce stable ether end groups, thus increasing the thermal stability of the polymer. Therefore, chain transfer agents or regulators such as methylal or butylal are preferably used, which are added in the desired amount to the monomer mixture. In the POM used in conventional catamold compositions, the butylal content is usually about 0.35 wt% and the weight average molecular weight of the POM is about 97,000 g / mol, with a ratio M _w / M _n of about 4 ; 2.

The POM polymerization has no termination step. The living polymer is in equilibrium with formaldehyde monomer until a comonomer end group is achieved which is a stable end group. A process for stabilizing the polymer ends is therefore the depolymerization of the unstable chain ends until only stable comonomer end groups remain. This process is used in the shell-and-roll process in which the polymers obtained have a majority of methylal or butylal derived end groups (eg, -O- (CH ₂ ) 4 -OH). The chain ends can also be deactivated by adding an alkaline compound. This approach is particularly used in continuous processes in which live end groups are typically inactivated with sodium methoxide. The resulting polymer has a plurality of -CH ₂ -O-CH _{3 end} groups.

In the case of bulk polymerization, for example in an extruder, the melted-on polymer produces a so-called melt seal, as a result of which volatile constituents remain in the extruder. The above monomers are metered into the extruder in the extruder. polymer melt present, together or separately from the initiators (catalysts), at a preferred temperature of the reaction mixture of 62 to 1 14 ° C. The monomers (trioxane) are preferably also metered in a molten state, for example at 60 to 120.degree. Due to the exothermic nature of the process, the polymer usually only has to be melted in the extruder at the start of the process; Subsequently, the amount of heat released is sufficient to melt the molten POM polymer or to keep it molten.

The melt polymerization is generally carried out at 1, 5 to 500 bar and 130 to 300 ° C, and the residence time of the polymerization mixture in the reactor is usually 0.1 to 20, preferably 0.4 to 5 min. Preferably, the polymerization is carried out to a conversion above 30%, e.g. 60 to 90%.

A crude POM is frequently obtained which, as mentioned, contains considerable proportions, for example up to 40%, of unreacted residual monomers, in particular trioxane and formaldeyde. Formaldehyde can also be present in the crude POM if only trioxane was used as the monomer since it can be formed as a degradation product of the trioxane. In addition, other oligomers of formaldehyde may also be present, e.g. the tetrameric tetroxane.

This crude POM is preferably degassed in one or more stages in known degassing devices, for example in degassing pots (flash pots), vented extruders with one or more screws, thin film evaporators, spray dryers or other conventional degassing devices. Particularly preferred are degassing pots (flash pots).

Preferably, the degassing of the raw POM is operated in such a way that is degassed in a first flash to below 6 bar absolute, to obtain a gaseous stream and a liquid stream, which is fed to a second flash, which is operated at below 2 bar absolute , obtaining a vapor stream, which is recycled into the monomer plant.

For example, in a two-stage degassing, the pressure in the first stage is preferably 2 to 18, in particular 2 to 15 and particularly preferably 2 to 10 bar, and in the second stage preferably 1, 05 to 4, in particular 1, 05 to 3.05 and especially preferably 1.05 to 3 bar amount.

The teilentgaste Polyoxymethylenhomo- or copolymers can then be fed to an extruder or kneader and therein customary additives and processing aids (additives), provided in the usual amounts for these substances. Such additives are, for example, lubricants or mold release agents, colorants, such as Pigments or dyes, flame retardants, antioxidants, light stabilizers, formaldehyde scavengers, polyamides, nucleating agents, fiber and pulverulent fillers or reinforcing agents or antistatic agents and other additives or mixtures thereof.

From the extruder or kneader, the desired product POM is obtained as a melt.

The preferred batch synthesis by the shell circle method involves the following steps:

In the first step, a non-closed reaction vessel ("shell") is filled with the liquid monomer / comonomer mixture Initiator is particularly preferred by a pump, for example an HPLC pump, at a temperature in the range of preferably 60 to 100 ° C 70 to 90 ° C., in particular 75 to 85 ° C. A solvent may also be used, the boiling point of which is more than 100 ° C., and which is miscible with the monomers.

In the second step, the initiator, preferably aqueous HCI0 ₄ in a solvent, is mixed with the monomers.

After an induction time, the polymerization and crystallization take place simultaneously in the third step, at the end of which, after the homogeneous reaction, there is a solid polymer block. The induction time is often less than 120 seconds, for example 20 to 60 seconds.

In the fourth step, the solid crude POM is removed from the shell, mechanically comminuted, and further processed in an extruder, for example by depolymerization to reach stable end groups (degassing). In addition, stabilizers and other ingredients can be added. As a standard mixture of stabilizers, a mixture of antioxidant, acid scavenger and nucleating agent can be considered.

After emptying the reaction container this can be filled again with liquid monomer to start a new cycle.

In contrast to the process according to the invention, the preparation of the POM copolymers according to US Pat. No. 6,388,049 in completely molten state takes place in tubular reactors. The blend production takes place in two series-connected reactors. For example, the resulting polymer may be ground into a coarse powder, sprayed with a buffer solution, and then fed to the extruder. The buffer serves to neutralize acids remaining in the melt. To successfully complete the shell circle process, the synthesis should be fast, ie, have a short induction period. In addition, the resulting oligomers should be rapidly and completely solidified in the polymerization and form a polymer block which does not adhere too strongly to the container wall. The preparation of the low molecular weight POM of component B2 is particularly advantageously possible by using a small amount of initiator, a high amount of regulator and capping the chain ends. The low molecular weight POM thus obtained is both thermally stable and chemical resistant and has a viscosity which may be lower by a factor of 1000 compared to a conventional high molecular weight POM as heretofore used in catamold compositions ,

When using the low molecular weight POM of component B2 as a viscosity modifying additive for POM having a weight average molecular weight of at least 50,000 g / mol, preferably at least 80,000 g / mol of component B1, the addition results in a thermally and chemically stable POM system , whose viscosity can be reduced by a factor of at least 10, without appreciably affecting the mechanical strength of the high molecular weight POM. For the construction of component B1 and its preparation, reference may be made to the above statements on component B2, with the exception of the molecular weight, the ratio M _w / M _n and the amounts of regulator and cationic initiator. In addition, not necessarily (but preferably) the comonomer butanediol formal must be used in component B1.

Both components B1 and B2 are particularly preferably copolymers, in particular with the same comonomers in the same comonomer proportions.

The polyoxymethylene homo- or copolymer of component B1 has a weight average molecular weight (M _w ) in the range of 50,000 to 400,000 g / mol, preferably 80,000 to 300,000 g / mol, in particular 95,000 to 210000 g / mol.

For its preparation, based on the polymer, preferably 0.05 to 0.7 wt .-%, particularly preferably 0.07 to 0.5 wt .-%, in particular 0.1 to 0.35 wt .-% butanediol formal used. When using another di (Ci _-6- alkyl) acetal as a regulator, a corresponding equivalent amount of the regulator is used. The amount of cationic initiator in the preparation is preferably 0.05 to 2 ppm, more preferably 0.1 to 1 ppm. The resulting polyoxymethylene homopolymers or copolymers of component B1 preferably have a ratio M _w / M _n in the range from 3.5 to 9, more preferably 4 to 8, in particular 4.2 to 7.7.

In the thermoplastic compositions according to the invention, according to a first embodiment of the invention, 10 to 90% by weight, preferably 10 to 70% by weight, in particular 10 to 50% by weight of component B1 and correspondingly 10 to 90% by weight, preferably 30 to 90 wt .-%, in particular 50 to 90 wt .-% of the component B2 used. In the thermoplastic compositions according to the invention 70 to 99.5 wt .-%, preferably 80 to 99 wt .-%, in particular 90 to 98 wt .-% of component B1 and 0.5 to 30 wt. According to a second embodiment of the invention .-%, preferably 1 to 20 wt .-%, in particular 2 to 10 wt .-% of the component B2 used.

The preparation of the thermoplastic compositions is carried out by separate preparation of components B1 and B2 and subsequent mixing of the two components. The mixing can be carried out in any suitable apparatus, such as kneaders or extruders. Initially, particulate components B1 and B2 can be premixed mechanically as a solid and subsequently melted together. It is also possible to melt component B1 in an extruder and to add component B2 to this melt. The mixing is preferably carried out at a temperature in the range of 150 to 220 ° C, in particular 180 to 200 ° C under a pressure in the range of 0.5 to 5 bar, in particular 0.8 to 2 bar.

When mixing the components B1 and B2 under the conditions indicated above, in addition to the mechanical mixing, a chemical reaction of both components may also occur, in particular a transacetalization. Therefore, after mixing, the components B1 and B2 no longer need to be present in their original form in the mixture, but may have been partially or wholly converted into a uniform or modified product. If a homopolymer is used as component B1, a uniform or modified copolymer can be obtained after addition of component B2 and its reaction. The invention therefore also relates to a process for the preparation of flowable polyoxymethylene copolymers by separate preparation of the components B1 and B2, as defined above, each by polymerization of trioxane and (at B1, where appropriate) comonomers in the presence of at least one cationic initiator and at least one di (Ci _-6 alkyl) acetal as regulators and subsequent mixing of the components B1 and B2 at a temperature in Range from 150 to 220 ° C under a pressure in the range of 0.5 to 5 bar and the polyoxymethylene homo- or copolymers obtainable in this way.

The thermoplastic compositions according to the invention are preferably used for the preparation of molding compositions which serve for the production of inorganic moldings. For this purpose, the thermoplastic materials are filled with sinterable powdered inorganic material. Corresponding filled thermoplastic materials are known per se from the prior art, using different polyoxymethylene homopolymers or copolymers, or only using component B2 in the thermoplastic composition. For a description of the corresponding molding compositions, reference may be made, for example, to EP-A-0 444 475, EP-A-0 446 708 or EP-A-0 853 995.

A corresponding molding composition according to the invention for the production of inorganic shaped bodies contains, based on the total volume of the molding composition,

From 20 to 70% by volume of a sinterable pulverulent inorganic material selected from metals, metal alloys, metal carbonyls, metal oxides, metal carbides, metal nitrides or mixtures thereof, as component A, from 30 to 80% by volume of a thermoplastic composition, such as as described above, or obtainable by the above process, as component B,

- 0 to 5 vol .-% of a lubricating and / or dispersing aid as component C, wherein the total volume of the components A to C is 100 vol .-%.

When using a powdered metal or a powdered metal alloy or mixtures thereof are in the molding compositions preferably before 40 to 65 vol .-%, more preferably 45 to 60 vol .-% of component A.

Examples of metals which may be present in powder form are iron, cobalt, nickel and silicon. Alloys are, for example, light alloys based on aluminum and titanium and alloys with copper or bronze. There are also hard metals such as tungsten carbide, boron carbide or titanium nitride in combination with metals such as cobalt and nickel into consideration. The latter may special in the production of metal-bonded hard cutting tools (so-called cermets) are used.

When using metal carbonyls appropriate amounts are used.

When using metal oxides, metal carbides, metal nitrides or mixtures thereof, preference is given to using 20 to 50% by volume, particularly preferably 25 to 45% by volume, in particular 30 to 40% by volume, of the respective pulverulent inorganic material.

Suitable metal oxides are those which are reducible with hydrogen and sinterable, so that metal moldings can be produced from the inside by heating under a hydrogen atmosphere or in the presence of hydrogen. Examples of metals whose oxides can be used can be found in Groups VIB, VIII, IB, IIB, IVA of the Periodic Table. Examples geeigner metal oxides are Fe ₂ 0 _3, FeO, Fe ₃ 0 _4, NiO, CoO, Co ₃ 0 _4, CuO, Cu ₂ 0, Ag ₂ 0, W0 _3, Mo0 _3, SnO, Sn0 _2, CdO, PbO, Pb ₃ 0 ₄ , Pb0 ₂ , Cr ₂ 0 ₃ . Preferably, the lower oxides are used, such as Cu ₂ 0 instead of CuO and PbO instead of Pb0 ₂ , since the higher oxides are oxidizing agents that can react under certain conditions, for example with organic binders. The oxides can be used individually or as mixtures. For example, pure iron moldings or pure copper moldings can be obtained. When using mixtures of oxides, for example, alloys and doped metals are accessible. For example, iron oxide / nickel oxide / molybdenum oxide mixtures produce steel parts and copper oxide / tin oxide mixtures which may still contain zinc, nickel or lead oxide bronzes. Particularly preferred metal oxides are iron oxide, nickel oxide and / or molybdenum oxide.

The metal oxides used according to the invention having a particle size of at most 50 μm, preferably not more than 30 μm, particularly preferably not more than 10 μm, in particular not more than 5 μm, can be prepared by different processes, preferably by chemical reactions. For example, the hydroxides, oxide hydrates, carbonates or oxalates can be precipitated from solutions of metal salts, the particles optionally being obtained in very finely divided form in the presence of dispersants. The precipitates are separated and brought to maximum purity by washing. By heating, the precipitated particles are dried and reacted at elevated temperatures to the metal oxides.

It is also possible to come to very finely divided metal oxides in one step. For example, by burning iron pentacarbonyl with oxygen, extremely fine, spherical iron oxide particles having specific surface areas of up to 200 m ² / g are obtained. The metal oxides used according to the invention or at least 65% by volume of the powder preferably have a BET surface area of at least 5, preferably at least 7 m ² / g.

In addition to the metal oxides reducible with hydrogen, other metal compounds which are not reducible on sintering, such as non-hydrogen reducible metal oxides, metal carbides or metal nitrides, may also be present. Examples of oxides are Zr0 ₂ , Al ₂ 0 ₃ and Ti0 ₂ . Examples of carbides are SiC, WC or TiC. An example of a nitride is TiN.

When sinterable inorganic non-metallic powders are used as component A, the proportion is preferably 40 to 65% by volume, particularly preferably 40 to 60% by volume. Preferred powders of this type are oxidic ceramic powders, such as Al ₂ O ₃ , ZrO ₂ and Y ₂ O ₃ , and also non-oxide ceramic powders, such as SiC, Si ₃ N ₄ , TiB and AlN, which can be used individually or in the form of mixtures. For these powders, the average particle size is preferably 0.1 to 50 μηη, more preferably 0.1 to 30 μηη, in particular 0.2 to 10 μηι.

The corresponding sinterable powdery inorganic materials can also be prepared as described in EP-A-1 717 539 and DE-T1-10084853.

Spherical metal particles can be produced by chemical processes or by atomization with inert gases.

According to one embodiment of the invention, at least 65% by volume of component A has a particle size of at most 5 μm, preferably not more than 1.5 μm, in particular not more than 0.5 μm, and the remainder of component A has a particle size of at most 10 μm. preferably at most 3 μηη, in particular at most 1 μηη.

The novel molding materials may contain from 0 to 5% by volume of a lubricant and / or dispersing agent as component C. When component C is used, its proportion is preferably 0.2 to 5% by volume, more preferably 1 to 5% by volume. Examples of suitable dispersing aids are oligomeric polyethylene oxides having an average molecular weight in the range from 200 to 1000, preferably 200 to 600, stearic acid, hydroxystearic acid, fatty alcohols, fatty alcohol sulfonates and block copolymers of ethylene oxide and propylene oxide. Advantageously, component A contains on the surface the dispersing agent or agents C. For the dispersion of metal oxide particles, particularly alkoxylated fatty alcohols or alkoxylated fatty acid amides are suitable. Suitable lubricants are for example poly-1, 3-dioxepan-0-CH ₂ -0-CH2-CH2-CH ₂ - CH ₂ -, poly-1, 3-dioxolan-0-CH2-0-CH2-CH ₂ - or their mixtures, preferably in an amount of 0.2 to 20 wt .-%, preferably 0.5 to 10 wt .-%, particularly preferably 0.5 to 5 wt .-%, based on the amount of the binder B. Poly-1,3-dioxepane is particularly preferred because of its rapid depolymerization under acidic conditions.

Poly-1, 3-dioxepane, also referred to as Polybutandiolformal or PolyBUFO, and poly-1, 3-dioxolane can be prepared by analogous methods such as the Polyoxymethylenhomo- or - copolymers, so that here further details are unnecessary. The weight average molecular weight is generally in the range of 10,000 to 150,000, preferably (in the case of poly-1,3-dioxepane) in the range of 15,000 to 50,000, more preferably (in the case of poly-1, 3-dioxepane) in the range from 18,000 to 35,000 and preferably (in the case of poly-1,3-dioxolane) from 30,000 to 120,000, more preferably (in the case of poly-1,3-dioxolane) from 40,000 to 1 10,000.

Reference may also be made to WO 2008/006776 for further description, there component B ₃ ).

Under the conditions of compounding or injection molding, virtually no transacetalization takes place between the polyoxymethylene polymers B and C, ie virtually no exchange of comonomer units takes place. In addition, the molding compositions according to the invention may also contain customary additives and processing aids which favorably influence the rheological properties of the mixtures during the shaping. Particularly suitable are processing stabilizers. The molding compositions are prepared by melting the component B at a temperature in the range of 150 to 220 ° C to obtain a melt stream and metering the components A and optionally C to the melt stream of component B. The preparation of the molding compositions in conventional mixing devices, such as Kneading, grinding or extruding done. When blending on extruders, the mixture can be extruded and granulated. A particularly preferred device for metering the component A contains as an essential element located in a heated metal cylinder screw conveyor, which promotes the component A in the melt of component B. The molding compositions are suitable for the production of metallic or ceramic moldings. The production takes place by injection molding or extrusion of the molding mass to a green body, subsequent debinding of the green body to obtain a brown body and then sintering the brown body.

In this case, the debinding can be carried out by treating the green body with a gaseous acidic atmosphere at a temperature in the range of 20 to 180 ° C for 0.1 to 24 hours.

The preparation of the metallic or ceramic moldings takes place according to the methods known from the prior art, as described, for example, in EP-A-0 444 475, EP-A-0 446 708 and EP-A-0 853 995. In addition, reference may also be made to the methods described in EP-A-1 717 539 and DE-T1-100 84 853.

Compared to known molding compositions, the molding compositions according to the invention are characterized by improved flowability while maintaining the advantageous mechanical properties, such as strength, hardness and rigidity after cooling.

The invention is explained in more detail by the following examples.

Examples

Preparation of POM Oligomers (Component B2) Laboratory scale polymerization was performed in a process that reflects the shell circle process. The monomers and the controller were heated to 80 ° C in open iron or aluminum reactors with magnetic stirring. The mixture was a transparent liquid. At an instant t = 0, an initiator solution consisting of HClO ₄ in triglyme was injected, with a proton concentration of typically 5 ppm relative to the monomers, or correspondingly lower for the low molecular weight POM. In a successful polymerization, the mixture became turbid in a short time (induction period typically in the range of a few seconds to one minute) and the polymer precipitated. Aftercare and determination of weight loss

The obtained polymer block was then ground to a powder and refluxed for one hour in an extraction solution of methanol, water and sodium carbonate. After cooling, the polymer was filtered off and washed with a washing solution of aqueous sodium carbonate. The powder was then dried and the weight loss was determined. This procedure gives an indication of the Polymerization yield, since remaining monomers or low molecular weight oligomers are extracted in this step. The living centers of the crude polymer chains as well as residual acid sites are partially extracted or neutralized. All cations should be neutralized to obtain a polymer that is stable enough for further study or further processing. Acid residues would otherwise shift the balance towards formaldehyde and affect thermal stability.

Investigation of thermal stability

A few grams of the extracted and dried polymer were heated to 220 ° C under a nitrogen atmosphere. After four hours, the weight loss of the polymer was determined. The result indicates how many unstable end groups are contained in the polymer, influenced by the amount and distribution of the comonomers along the polymer chain, as well as by the amount of regulators.

thermal stability

GV N ₂ : The weight loss (GV) in percent of a sample of 1, 2 g of granules with heating to 222 ° C for 2 hours under nitrogen.

At the beginning of the determination of GV the used balance was adjusted. The sample was weighed out to an accuracy of 0.1 mg in a jacketed vessel consisting of two test tubes (normal test tube, 100 × 10 mm, custom-made, thick-walled test tube 100 × 12.5 mm).

An approximately 400 mm long thin copper wire was attached to the upper bead of the outer glass. With this, the double-walled vessels were suspended in a special apparatus (see FIG. 9 and the related description of the figures in WO 2006/074997). In the determination of GV under nitrogen, this was done to adjust the special atmosphere for 15 min in the upper half of the apparatus, ie without increasing the temperature. Subsequently, the test tubes were lowered to the bottom and left there for 2 h at 222 ° C. The nitrogen flow was 15 l / h and was controlled on each test tube by means of a Rotas.

After 2 h, the double-walled vessels were removed from the apparatus by means of the copper wire and cooled in air for 20 to 25 minutes. Then the balance was weighed back and GM according to GV [%] = (loss x100 / initial weight) calculated. Molar Mass

The molecular weight determination of the polymers was carried out by size exclusion chromatography in a SEC apparatus. This SEC apparatus consisted of the following separation column combination: a guard column of length 5 cm and diameter 7.5 mm, a second linear column of length 30 cm and diameter 7.5 mm. Release material in both columns was PL-HFIP gel from Polymer Laboratories. The detector used was a differential refractometer from Agilent G1362 A. A mixture of hexafluoroisopropanol with 0.05% trifluoroacetic acid potassium salt served as eluent. The flow rate was 0.5 ml / min at a column temperature of 40 ° C. 60 microliters of a solution of the concentration 1, 5 g of sample per 1 liter of eluent were injected. This sample solution was previously filtered through Millipor Millex GF (pore size 0.2 microns). Calibration was carried out using narrowly distributed PMMA standards from PSS (Mainz, DE) with molecular weights of M = 505 to 2,740,000 g / mol.

Reactions with Butylal as regulator

The commercially available POMs produced by the Shell ^Circle process and marketed by BASF SE under the brand Ultraform® and which correspond to component B1 are listed in Table 1 below.

Table 1

The POM used for the initially described Catamold method corresponds to the Ultraform ^® Z2320, which is prepared with a butyral content of 0.35 wt .-%. To reduce the molecular weight was subsequently increased, the proportion of ButylaI. The proportion of butanediol comonomer was in each case unchanged 2.7% by weight, based on the polymer. The initiator concentration was 0.05 ppm based on the monomers.

The results are summarized in Table 2 below.

Table 2

Rheology investigations Rheology investigations were carried out on the POM according to the invention in accordance with the example in Table 2. For this, a plate-plate rheometer at 190 ° C was used and the dynamic viscosity as a function of Seher rate was determined. The results are summarized in Table 3 below.

Table 3

Die erfindungsgemäßen Oligomere haben eine sehr niedrige Schmelzviskosität. Extrusion von POM-Blends Blends aus Ultraform^® Z2320 Komponente B1 mit unterschiedlichen Anteilen niedri- germolekularer POM-Oligomere aus Tabelle 2 wurden für zwei Minuten bei 190°C in einem Midi-Extruder extrudiert. Die Blends wurden ebenfalls den vorstehenden Rheo- logie-Messungen unterzogen sowie einer DSC-Messung (Differential Scanning Calori- metry). Die erhaltenen Blend-Eigenschaften, sind in der nachstehenden Tabelle 4 zu- sammengefasst.

The oligomers of the invention have a very low melt viscosity. Extrusion of POM blends Blends of Ultraform ^® Z2320 component B1 with different proportions niedri- germolekularer POM oligomers in Table 2 were extruded for two minutes at 190 ° C in a midi-extruder. The blends were also subjected to the above rheology measurements and a DSC measurement (differential scanning calorimetry). The resulting blend properties are summarized in Table 4 below.

Table 4

It becomes clear from the results that, with the use of component B2, the viscosity change after the restart is significantly lower than for the comparative measure. Thus, the POM blend according to the invention using the low molecular weight POM is significantly more stable than the comparative blends.

Thus, the low molecular weight POM of component B2 can be used particularly advantageously as a viscosity-modifying additive for polyoxymethylene homopolymers or copolymers having a weight-average molecular weight of at least 50,000 g / mol of component B1.

The low molecular weight POM of component B2 are chemically and mechanically stable and reduce neither the overall strength nor the overall mechanics when mixed with high molecular weight POM component B1. In this case, the viscosity of the high molecular weight POM can be greatly reduced, the effect being retained in several melt passes. No formaldehyde evaporates, the POM blend remains a solid, and therefore the classic Catamold manufacturing process can also be performed with the POM blends.

These advantages are not achieved when using even lower molecular weight compounds, for example POM dimethyl ethers such as Me-0- (CH ₂ O) ₄ -Me. Only the specific use of the POM according to the invention leads to the advantages mentioned.

In another experiment, 1 1 Biends from Ultraform ^® Z2320 were with low-POM-oligomer of Example 3 in the weight ratio 50 in Example 50 were mixed in a mini-extruder. Three samples were mixed for one minute, two minutes and five minutes respectively.

Subsequently, a molecular weight profile for the mixed blend was recorded by size exclusion chromatography.

The attached FIG. 1 shows the dependence of the size exclusion chromatography (SEC) detector signal in arbitrary units, plotted against the molecular weight in g / mol. The solid line shows the molecular weight distribution for mixing for one minute, the triangles show the molecular weight distribution after mixing for 2 minutes, and the circles show the molecular weight distribution for a mixing time of 5 minutes.

It was found that the molecular weight distribution remains the same at the three mixing times, which indicates a stability of the polymer blend. Furthermore, the bimodal molecular weight distribution resulting from the blend polymers is retained. It does not come to a molecular weight balance by transacetalization. As a result, it can be stated that in the case of the POM blends, the bimodal molecular weight distribution is retained even after thermal stress, and the shear viscosity decreases greatly, so that the processing properties improve markedly. Due to the improved flowability, especially in injection molding, long flow paths and thin wall thicknesses can be tolerated without the result deteriorating.

In contrast to other flow improvers, the addition of the POM oligomers does not lead to a phase separation under shear and thus also to no exudation of the flow improver, which in turn would result in tool deposits.

Due to the combination of low molecular weight POM with high molecular weight POM, the molding compositions are not brittle, but still have a high strength.

By the stability in the melt, the POM blends are suitable in an advantageous manner for the metal or ceramic powder-injection molding after the Catamold ^® process. In this process, the POM molding materials are subjected to a threefold melting and shearing: when mixing the two polymer components, when the metal or ceramic powder is introduced, and finally during injection molding. In a recycling and reuse of parts of the injection-molded body, such as the sprues, there is a further thermal stress. This shows the advantages of the POM systems according to the invention.

Flow behavior of filled with metal powder POM blends

60% by volume of stainless steel metal powder (stainless steel 17-4PH with typical powder particle size distribution D ₁₀ <3 μm, D ₅₀ <8 μm, D ₉₀ <21 μm) were mixed in a blend of low molecular weight POM component B2 according to Example 3 and high molecular weight POM component B1 Z2320-003 incorporated using a kneader. Injection molding produced flow spirals to study the flow behavior of the metal powder filled POM blends. Illustrations of the spirals obtained are shown in FIG.

In this case, the spirals in Figure 2 from left to right in the first row 100% POM from Example 3 (spiral length> 100 cm); 90% POM from example 3 + 10% Z2320-003 (spiral length about 70 cm); 80% POM from example 3 + 20% Z2320-003 (spiral length about 62 cm). The middle row shows from left to right 70% POM from example 3 + 30% Z2320- 003 (spiral length about 48 cm); 60% POM from example 3 + 40% Z2320-003 (spiral length about 42 cm); 50% POM from example 3 + 50% Z2320-003 (spiral length 34 cm). The last row shows from left to right exclusively Z2320-003 (spiral length about 19 cm); Z2320-003 + usual flow improver (spiral length 24 cm).

As the concentration of low molecular weight POM increases, there is a clear increase in the flow spiral length.

The use of the low molecular weight POM allows the production of metal binders with very good flow behavior (high flow). In addition, it also allows the use of higher concentrations of metal powder. Different metal powder binder systems have been prepared and investigated. Table 5 shows the results obtained. The high molecular weight POM component B1 was again Z 2320-003 (100 or 60, 50, 40 wt .-%, based on the POM binder).

Table 5

PolyBUFO: polybutanediol formal with a weight average molecular weight (M _w ) of 18,000 to 35,000; Content based on the total POM binder.

The possibility of increasing the metal powder loading of the POM binders according to the invention leads to improved tolerance ranges in the finally obtained metal moldings, since less organic binder has to be burnt off before sintering.

Claims

 claims 1 . Thermoplastic composition containing 10 to 90% by weight of a polyoxymethylene homo- or copolymer having a weight average molecular weight (M _w ) in the range of 50,000 to 400,000 g / mol as component B1 and 10 to 90 wt .-% of a polyoxymethylene copolymer having a weight average molecular weight (M _w ) in the range of 5,000 to 15,000 g / mol, based on the polymer derived at least 90 wt .-% of trioxane and butanediol as monomers , with a proportion of butanediol formal, based on the polymer, in the range of 0.5 to 4 wt .-%, preferably 2 to 3.5 wt .-%, in particular 2.5 to 3 wt .-% as component B2. A composition according to claim 1, characterized in that the weight-average molecular weight (M _w ) of the component B2 6,000 to 9,000 g / mol, preferably 6,500 to 8,000 g / mol, in particular 7,000 to 7,500 g / mol and the component B1 from 70,000 to 300,000 g / mol, preferably 95,000 to 210,000 g / mol. A composition according to claim 1, characterized in that the number average molecular weight (M _n ) of the component B2 is 3,000 to 6,000 g / mol, preferably 3,200 to 5,000 g / mol, in particular 3,500 to 4,100 g / mol. Composition according to one of claims 1 to 3, characterized in that the ratio M _w / M _{n of} the component B2 in the range of 1, 5 to 3.0, preferably 1, 5 to 2.45. Composition according to one of claims 1 to 4, characterized in that the component B1, based on the polymer, at least 90 wt .-% of trioxane and optionally derived butanediol as monomers, preferably from trioxane and butanediol as monomers, with a proportion butanediol formal, based on the polymer, in the range of 1 to 5 wt .-%, preferably 2 to 3.5 wt .-%, in particular 2.5 to 3 wt .-%. 6. A composition according to any one of claims 1 to 5, characterized in that in the preparation of the polymer of the component B2, based on the polymer, from 3.75 to 4.25 wt .-%, preferably 3.8 to 4.2 wt .-%, in particular 3.9 to 4.1 wt .-% methylal or an equimolar amount of another di (Ci _-6 - alkyl) acetal also be used as a controller. A process for the preparation of thermoplastic compositions according to one of claims 1 to 6 by separate preparation of the components B1 and B2 in each case by polymerization of trioxane and optionally comonomers in the presence of at least one cationic initiator and at least one di (Ci _-6 - alkyl) acetal as a regulator and subsequent mixing of components B1 and B2. Process for the preparation of flowable polyoxymethylene copolymers by separately preparing the components B1 and B2 as defined in any one of claims 1 to 6 by respectively polymerizing trioxane and optionally comonomers in the presence of at least one cationic initiator and at least one di (Ci _-6- Alkyl) acetals as a regulator and subsequent mixing of the components B1 and B2 at a temperature in the range of 150 to 220 ° C under a pressure in the range of 0.5 to 5 bar. 9. molding composition for the production of inorganic shaped bodies, containing, based on the total volume of the molding composition, From 20 to 70% by volume of a sinterable powdery inorganic material selected from metals, metal alloys, metal carbonyls, metal oxides, metal carbides, metal nitrides or mixtures thereof, as component A, 30 to 80% by volume of a thermoplastic composition according to one of claims 1 to 6 or obtainable by the process of claim 8 as component B, 0 to 5 vol .-% of a lubricating and / or dispersing aid as component C, wherein the total volume of components A to C is 100 vol .-%. Molding composition according to claim 9, characterized in that at least 65 vol .-% of the component A have a particle size of at most 5 μηη and the rest of the component A have a particle size of at most 10 μηη. 1 1. A process for the preparation of a molding composition according to claim 9 or 10 by melting the component B at a temperature in the range of 150 to 220 ° C to obtain a melt stream and metering the components A and optionally C to the melt stream of the component B. 12. Use of the molding composition according to claim 9 or 10 for the production of metallic or ceramic moldings. 13. A process for the production of metallic or ceramic moldings by injection molding or extruding a molding composition according to claim 9 or 10 to a green body, subsequent debindering of the green body to obtain a brown body and subsequent sintering of the brown body. 14. The method according to claim 13, characterized in that the binder removal by treating the green body with a gaseous acidic atmosphere at a temperature in the range of 20 to 180 ° C for 0.1 to 24 hours. 15. Shaped body produced from molding compositions according to claim 8 or 9 or obtainable by the process according to claim 13 or 14. 16. Flowable polyoxymethylene copolymers obtainable by the process according to claim 8.