KR20140121473A

KR20140121473A - Thermoplastic pom material

Info

Publication number: KR20140121473A
Application number: KR1020147024605A
Authority: KR
Inventors: 베른슈토르프 베른트 슈테펜 폰; 로랑스 뽀띠에
Original assignee: 바스프 에스이
Priority date: 2012-02-02
Filing date: 2013-02-01
Publication date: 2014-10-15
Also published as: CN104204083B; JP2015505575A; WO2013113880A1; EP2809722A1; SG11201404549WA; RU2014135489A; CN104204083A; BR112014018988A2

Abstract

The present invention relates to a thermoplastic composition comprising a mixture of polyoxymethylene homopolymers or copolymers, their preparation, their use for the production of metal or ceramic molded articles, and the resulting molded articles.

Description

[0001] THERMOPLASTIC POM MATERIAL [0002]

The present invention relates to thermoplastic compositions comprising a mixture of polyoxymethylene homopolymers or copolymers, their preparation, their use for the production of metal or ceramic molded articles and the resulting molded articles.

Polyoxymethylene homopolymers or copolymers, also referred to as polyacetyl or polyformaldehyde or POM, are high molecular weight thermoplastics that generally exhibit high stiffness, low coefficient of friction, excellent dimensional stability and thermal stability. Thus, they are used in particular for the manufacture of precisely machined parts.

The properties making them useful in applications involving molded articles are high strength, hardness and stiffness, especially over a wide temperature range. Further processing is carried out by injection molding at a temperature in the range of, for example, 180 to 230 DEG C or by extrusion. Polyoxymethylene is prepared, for example, by direct polymerization of formaldehyde or by cationic polymerization of trioxane or by transition metal-center cationic polymerization. For stabilization, the terminal groups are often protected by etherification or esterification to inhibit depolymerization upon exposure to acid or thermal stress.

Other stabilization methods to cope with acid and thermal stress action are the production of copolymers, for example, by copolymerizing trioxane with 1,4-dioxane. Here, for stabilization, unstable terminal groups are hydrolyzed to form formaldehyde. Typical copolymers are available, for example, under the tradename Hostaform (R) from Ticona / Celanese and Ultraform (R) from BASF SE.

The melting point of the homopolymer is generally about 178 ° C and the melting point of the copolymer is generally about 166 ° C.

Processes for preparing polyoxymethylene homopolymers or copolymers are disclosed, for example, in WO 2007/023187 and WO 2009/077415.

US 6,388,049 relates to low molecular weight polyoxymethylene polymers and compositions comprising them.

Production Examples 14 to 16 refer to trioxane-based and butanediol-formaldehyde-based copolymers using methally as a modifier. The amount of comonomer added in each case is 1.46 mol%, corresponding to about 4.4 wt% butanediol formal. The number average molar masses obtained are 1100, 5500 and 35,000 g / mol.

Polyoxymethylene is also used as a binder for powder injection molding. Here, the POM molding composition filled with an inorganic powder, particularly a metal powder or a ceramic powder is processed by injection molding to obtain a molded article, and then the binder is removed and the product is sintered. A high fluidity POM composition should be used to maintain the pressure required in the injection molding process within an acceptable range, since high loading of the inorganic powder in the POM hinders fluidity.

Polymer particles marketed under the trade name Catamold® include inorganic particles, especially metal particles or ceramic particles. In general, these particles are first coated with a thin layer of polyethylene and then compounded with a polyoxymethylene binder. These Catamold granules are processed by injection molding to obtain a green product, which is then converted into a brown product by removal of the binder, . The process is known as Metal Injection Molding (MIM) and can produce metal or ceramic molded articles having complex shapes.

The proportion of inorganic filler in the catamold granules is about 90% by weight.

The green products prepared using polyoxymethylene homopolymers or copolymers have very good mechanical properties, in particular dimensional stability.

Due to the decomposition of POM binder acidic atmosphere at 110~140 ℃, for example, the binder removed by the exposure to the atmosphere HN0 ₃ is often achieved. The thin polyethylene coating of the inorganic particles bonds them together in the resulting brown product. Acid depolymerization of the POM can completely remove the binder.

The brown product is preferably sintered in a sintering oven at a temperature in the range of about 1300-1500 DEG C to provide the desired metal molded article or ceramic molded article.

Thermoplastic compositions suitable for the Catamold process for the production of metal moldings are disclosed, for example, in EP-A-0 446 708.

Thermoplastic compositions for the production of ceramic moldings are disclosed, for example, in EP-A-0 444 475.

Molding compositions comprising metal oxides are disclosed, for example, in EP-A-0 853 995.

The better the flowability of the filled polyoxymethylene homopolymer or copolymer composition, the finer the structure can be formed in the molded article. On the other hand, the metal particles or ceramic particles must be able to be transported uniformly with the molding composition. A suitable characteristic profile including flowability and creep compliance is achieved by using a POM having a weight average molar mass of at least about 85,000 g / mol.

By reducing the molecular weight, the flowability of the POM can be improved or the flow improver can be added. Here, the flow improver should have very good compatibility with the POM to prevent defects in the desired molded part and exhibit fast decomposition in an acid gas atmosphere.

EP-A-0 446 708 discloses a polyoxymethylene homopolymer or a mixture of polyoxymethylene homopolymers or copolymers by adding an aliphatic polyurethane, an aliphatic, non-crosslinked polyepoxide, an aliphatic polyamide or polyacrylate or poly (C _2-6 -alkylene oxide) To obtain a copolymer.

It is an object of the present invention to provide a polyoxymethylene homopolymer or copolymer based on a polyoxymethylene homopolymer or copolymer having improved flowability and exhibiting better flow behavior than known molding compositions when an inorganic powder is introduced into an extrusion process or an injection molding process, To provide thermoplastic molding compositions having good mechanical properties of known molding compositions based on polymers or copolymers.

The present invention

As component B1, from 10 to 90% by weight of a polyoxymethylene homopolymer or copolymer having a weight average molar mass (Mw) in the range from 50,000 to 400,000 g / mol, and

As component B 2, from butanediol formaldehyde in the range of from 0.5 to 4% by weight, preferably from 2 to 3.5% by weight, in particular from 2.5 to 3% by weight, based on the polymer, from trioxane and butanediol as monomers, By weight of a polyoxymethylene copolymer having a weight average molecular weight (Mw) in the range of 5,000 to 15,000 g / mol, derived from about 90%

The above objects are achieved through a thermoplastic composition comprising

The object is also achieved by separately polymerizing the trioxane and optionally comonomers in the presence of at least one di (C _1-6 -alkyl) acetal and at least one cationic initiator as modifiers, respectively, to form components B1 and B2, B2. &Lt; / RTI >

The object is also achieved by polymerizing trioxane and (optionally in the case of component B1) comonomer in the presence of one or more di (C _1-6 -alkyl) acetals and at least one cationic initiator, respectively, And B2 and then mixing the components B1 and B2 at a temperature in the range of 150 to 220 DEG C under a pressure in the range of 0.5 to 5 bar to obtain a flowable polyoxymethylene homopolymer or copolymer .

The above object is also achieved through a flowable polyoxymethylene copolymer obtainable by the process.

This object is also achieved by a process for the preparation of

- 20 to 70% by volume of a sinterable powder inorganic material selected from the group consisting of metals, metal alloys, metal carbonyls, metal oxides, metal carbides, metal nitrides and mixtures thereof as component A,

- as component B, 30 to 80% by volume of a thermoplastic composition as defined above or obtainable by said process, and

As component C, from 0 to 5% by volume of a lubricant and / or dispersant

, And a total volume of components A to C of 100% by volume.

This object is also achieved through a process for the production of this type of molding composition by melting component B at a temperature in the range of from 150 to 220 캜 to obtain a melt stream and weigh component A and optionally C into the melt stream of component B. do.

This object is also achieved through the use of the molding composition for the production of metal or ceramic molded articles.

The object is also achieved by a method of producing a metal or ceramic molded article by obtaining a green product by injection molding or extrusion of the molding composition, removing the binder from the green product to obtain a brown product, and then sintering the brown product .

This object is also achieved through a molded article made from the molding composition as defined above or obtainable by the method described above.

The expression "polyoxymethylene" or "polyoxymethylene homopolymer or copolymer" means a polyoxymethylene homopolymer and / or a polyoxymethylene copolymer.

In the present invention, with butanediol formal ratios ranging from 0.5 to 4% by weight, preferably from 1 to 4% by weight, preferably from 2 to 3.5% by weight and especially from 2.5 to 3% by weight, based on the polymer, Preferably from 5000 to 10,000 g / mol, or from 6000 to 13,000 g / mol, preferably from 6000 to 9000 g, based on the polymer, based on the polymer, / mol, or a weight average molecular weight (Mw) in the range of 6500 to 11000 g / mol, particularly preferably in the range of 6500 to 8000 g / mol, especially 7000 to 7500 g / mol, Can be used as a viscosity modifying additive for high molecular weight polyoxymethylene homopolymers or copolymers without compromising the mechanical properties of the blend or reaction product as compared to the oxymethylene homopolymer or copolymer.

Where the molecular weight can be measured as described in the Examples. The molecular weight is generally measured by gel permeation chromatography (GPC) or SEC (size exclusion chromatography). The number average molecular weight is generally measured by GPC-SEC.

Component B2 is now described in detail below.

The ratio between the weight average molecular weight (Mw) and the number average molecular weight (Mn), also referred to as polydispersity or Mw / Mn, is preferably in the range of 1.5 to 3.0, preferably 1.5 to 2.45.

As a preferred alternative, the number average molar mass (Mn) is preferably from 3000 to 6000 g / mol, particularly preferably from 3200 to 5000 g / mol, especially from 3500 to 4100 g / mol. Within this molecular weight range, a particularly advantageous flow improvement is achieved for high molecular weight polyoxymethylene homopolymers or copolymers.

The use of the polyoxymethylene copolymer of the present invention having a proportion of butanediol formal in the range of from 1 to 4% by weight, based on the polymer, results in a lower comonomer content in comparison with US 6,388,049, High crystallinity and higher hardness. Where the results for high molecular weight polyoxymethylene homopolymers or copolymers are favorable for their hardness and mechanical properties for the application, despite their good viscosity reduction properties.

Very generally, the polyoxymethylene copolymer (POM) of the present invention has at least 50 mol% -CH ₂ O- repeating units in the main polymer chain. In addition to the -CH ₂ O- repeating unit, 50 mol% or less, preferably 0.01 to 20 mol%, particularly 0.1 to 10 mol%, and very particularly preferably 0.5 to 6 mol% Methylene copolymers are preferred:

Wherein R ¹ to R ⁴ are independently of each other a hydrogen atom, a C ₁ -C ₄ -alkyl group, or a halogen-substituted alkyl group having 1 to 4 carbon atoms, R ⁵ is -CH ₂ -, -CH ₂ O-, or C ₁ -C ₄ -alkyl or C ₁ -C ₄ -haloalkyl-substituted methylene group, or the corresponding oxymethylene group, and n is a value within the range of 0 to 3. The group can advantageously be introduced into the copolymer through ring opening of the cyclic ether. Preferred cyclic ethers are those of the formula:

Wherein R ¹ to R ⁵ and n are as defined above. By way of example only, ethylene oxide, propylene 1,2-oxide, butylene 1,2-oxide, butylene 1,3-oxide, 1,3-dioxane, 1,3- , 3-dioxepane (= butanediol formal, BUFO) can be mentioned as cyclic ether, and linear oligoformal or polyformal such as polydioxolane or polydioxepane can be mentioned as comonomer.

For example, an oxymethylene terpolymer prepared by reacting one of the disclosed cyclic ethers or trioxane with a third monomer, preferably a bifunctional compound, of the formula:

And / or

In the above formula, Z is a chemical bond -O-, -ORO- (R = C ₁ -C ₈ -alkylene or C ₃ -C ₈ -cycloalkylene).

Preferred monomers of this type include, but are not limited to, ethylene diglycidate, diglycidyl ether, and a 2: 1 molar ratio of glycidyl compound and a diether derived from formaldehyde, dioxane or trioxane, and also Diols prepared from 2 moles of glycidyl compounds and 1 mole of aliphatic diols having 2 to 8 carbon atoms, such as ethylene glycol, 1,4-butanediol, 1,3-butanediol, cyclobutane- Diol, 1,2-propanediol and diglycidyl ether of cyclohexane-1,4-diol.

End-group-stabilized polyoxymethylene polymers having mainly CC or -O-CH ₃ bonds at the chain ends are particularly preferred.

More than 90% by weight of the polymer, based on the polymer, is derived from trioxane and butanediol formal as monomers.

The polyoxymethylene copolymer has a proportion of butanediol formal ranging from 0.5 to 4% by weight, preferably from 1 to 4% by weight, preferably from 2 to 3.5% by weight, especially from 2.5 to 3% by weight, based on the polymer or monomer Preferably derived exclusively from trioxane and butanediol formamide as monomers.

The molecular weight of the polymer can be adjusted to a predetermined value using a regulator conventionally used for trioxane polymerization or by using a reaction temperature and a reaction residence time. The modifiers that can be used are acetal and / or formaldehydes of monohydric alcohols, alcohols themselves, and also small amounts of water that are generally inevitably present and function as chain transfer agents.

The chain ends of the polymers of the present invention comprise from 3 to 6% by weight, based on the polymer, of a moiety having the general formula -OR, wherein R is C _1-6 -alkyl, preferably C _1-4 -alkyl .

In the preparation of the polyoxymethylene copolymers of the present invention, from 3.75 to 4.25% by weight, preferably from 3.8 to 4.2% by weight, especially from 3.9 to 4.1% by weight, based on the sum of the polymer or monomers and modifiers, It is preferred to use an additional di (C _1-6 -alkyl) radical as an adjunct.

It is particularly preferred, for example, to employ an adjunctive use of methal as a modulating agent on a laboratory scale, or it is particularly preferred to employ an adjunctive use of butyral (n-butyral) as a modifier, for example.

It is particularly preferred to use butyral (n-butyral), which has the advantage of non-toxicity, as a modulator, which is classified as toxic. The use of butyral as modifier presents additional advantages over polyoxymethylene copolymers known from US 6,388,049.

Thus, it is preferred to use butyral as the controlling agent in the preparation of the polymer. It is preferred to use a butyral amount of from 0.5 to 4% by weight, especially from 1 to 3.5% by weight, in particular from 1.5 to 2.5% by weight, based on the polymer.

With particular amounts of comonomers and specified molecular weights, polyoxymethylene with particularly suitable mechanical properties which makes it suitable as a viscosity modifying additive for high molecular weight polyoxymethylene homopolymers or copolymers without any major damage of mechanical properties, Copolymer is obtained.

Thus, polyoxymethylene copolymers having a butanediol formaldehyde content in the range of from 0.5 to 4% by weight, preferably from 1 to 4% by weight, preferably from 2 to 3.5% by weight and especially from 2.5 to 3% by weight, based on the polymer, By weight, of which butyral in an amount of from 0.5 to 4% by weight, particularly preferably from 1 to 3.5% by weight, in particular from 1.5 to 2.5% by weight, based on the polymer, is used as an adjunct to the preparation. The number average of the polyoxymethylene copolymer is particularly preferably from 3000 to 6000 g / mol, more preferably from 3200 to 5000 g / mol, particularly from 3500 to 4100 g / mol.

Particularly suitable mechanical properties are derived with a particular combination of molecular weight, comonomer ratio, comonomer selection, ratio of modifier and choice of modifier, thereby making it possible to advantageously be used as a viscosity modifying additive for high molecular weight polyoxymethylene homopolymers or copolymers .

The initiator (also referred to as catalyst) used is a cationic initiator commonly used in trioxane polymerization. Protonic acids such as fluorinated or alkylated alkyl- and arylsulfonic acids such as perchloric acid and trifluoromethanesulfonic acid or Lewis acids such as tin tetrachloride, arsenous pentafluoride, phosphorus pentafluoride and boron trifluoride, and also their complex salts, Such as boron trifluoride etherate and triphenylmethyl hexafluorophosphate. The amount of the initiator (catalyst) to be used is about 0.01 to 1000 ppm, preferably 0.01 to 500 ppm, particularly 0.01 to 200 ppm. It is generally recommended to dilute the initiator, preferably at a concentration of 0.005 to 5% by weight. The solvent used for this purpose may be an inert compound such as aliphatic or cycloaliphatic hydrocarbons such as cyclohexane, halogenated aliphatic hydrocarbons, glycol ethers, and the like. Triglyme (triethylene glycol dimethyl ether) and 1,4-dioxane are particularly preferable as a solvent.

The present invention particularly preferably uses a Bronsted acid 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 modifiers as cationic initiators . In particular, HClO ₄ is used as the cationic initiator.

In addition to the initiator, a cocatalyst may be used incidentally. These are any type of alcohol, examples being aliphatic alcohols having 2 to 20 carbon atoms, such as tert-amyl alcohol, methanol, ethanol, propanol, butanol, pentanol, hexanol; Aromatic alcohols having from 2 to 30 carbon atoms, such as hydroquinone; Halogenated alcohols having from 2 to 20 carbon atoms, such as hexafluoroisopropanol, of any type of glycol, especially diethylene glycol and triethylene glycol; And aliphatic dihydroxy compounds, especially diols having 2 to 6 carbon atoms such as 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,4- Very particular preference is given to hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and neopentyl glycol.

Monomers, initiators, cocatalysts and optionally modifiers can be premixed in any desired manner or added separately to the polymerization reactor.

In addition, the components for stabilization may comprise sterically hindered phenols as disclosed in EP-A 129369 or EP-A 128739.

The polyoxymethylene copolymer of component B2 of the present invention is prepared by polymerization of trioxane, incidentally and optionally further comonomers, in the presence of one or more cationic initiators and one or more di (C _1-6 -alkyl) acetals as modifiers do.

It is preferable that the polymerization mixture is deactivated immediately after the polymerization reaction and preferably without any phase change. Initiator residues (catalyst residues) are generally deactivated by adding a deactivator (termination) to the polymer melt. Examples of suitable deactivators are ammonia, and also primary, secondary or tertiary aliphatic and aromatic amines such as trialkylamines such as triethylamine or triacetone diamine. Other suitable compounds are salts that react with bases, such as, for example, soda or borax, and also carbonates and hydroxides of alkali metals and alkaline earth metals, and also alcoholates, such as ethanolate. The amount of the deactivator usually added to the polymer is preferably 0.01 ppmw (parts per million by weight) to 2% by weight. Also preferred are alkyl compounds of alkali metals and alkaline earth metals as deactivators, which have from 2 to 30 carbon atoms in the alkyl moiety. Li, Mg, and Na can be mentioned as particularly preferred metals, and n-butyllithium is particularly preferred here.

In one embodiment of the invention, chain termination of from 3 to 30 ppm, preferably from 5 to 20 ppm, especially from 8 to 15 ppm, based on the sum of monomers and modifiers can be used incidentally. Here, sodium methoxide is particularly used as a chain terminator.

POMs prepared from trioxane and butanediol formals are generally obtained by bulk polymerization, and any reactor having a high level of mixing action may be used for this purpose. The reaction can be carried out uniformly in the melt, for example, or heterogeneously, for example, by polymerization, to form solid or solid granules. Examples of suitable equipment are a tray reactor, a plow kneader, a tubular reactor, a list reactor, a kneader (e.g. a Buss kneader), an extruder such as an extruder with one or two screws and a stirring reactor, Can have a dynamic mixer.

The trioxane polymerization can theoretically be separated into three reaction stages of initiation, rippling and transfer reaction. During the propagation reaction, chain transfer can occur to the polymer, a proton species such as water, or a transfer agent such as butyral. Transfer reactions to other polymer chains enable a random distribution of comonomer units along the polymer chain. These reactions occur between the carbonium of the active chain and the oxygen of another polymer chain as long as the active carbonium ion is present in the reaction mixture.

As unstable hydroxy end groups are formed, the transfer reaction to a proton species such as water reduces the molecular weight of the polymer and its thermal stability. Therefore, the polymerization reaction is carried out under the maximum drying conditions.

Transfer reactions to proton species, such as low molecular weight acetals, increase the thermal stability of the polymer as it reduces molecular weight and produces stable ether end groups. Thus, it is preferred to use a chain transfer agent or modifier such as methally or butyral, and the desired amount is added to the monomer mixture. The butyral content in the POM used in conventional Catamold compositions is generally about 0.35 wt.%, The weight average molar mass of POM is about 97,000 g / mol, and the Mw / Mn ratio is about 4.2.

The POM polymerization reaction does not have a termination step. The living polymer is in equilibrium with the formaldehyde monomer until the system reaches the terminal end of the comonomer with a stable end group. Thus, the method of stabilizing the end of the polymer here is the depolymerization of the unstable chain end until only the stable comonomer end group remains. This method is used in a circulating tray process wherein the majority of the resulting polymer has a terminal group derived from either a metal or butyral (e.g., -O- (CH ₂ ) ₄ -0H). The chain terminal can also be deactivated by addition of an alkaline compound. This procedure is used in a continuous process, in particular when the living end groups are deactivated with sodium methanolate. Most of the resulting polymers have -CH ₂ -O-CH ₃ -terminal groups.

For example, in the case of bulk polymerization in an extruder, the molten polymer exhibits the effect known for melt sealing, with the result that volatile components remain in the extruder. At the desired reaction-mixture temperature of 62-114 캜, the monomer is metered into the polymer melt present in the extruder with or without an initiator (catalyst). The monomer (trioxane) is also preferably metered in, for example, in a molten state at 60 to 120 占 폚. Because the process is exothermic, the polymer in the extruder typically only needs to melt at the start of the process and the amount of heat generated is sufficient to melt the resulting POM polymer or to keep it in a molten state.

The melt polymerization generally takes place at 1.5 to 500 bar and 130 to 300 캜, and the residence time of the polymerization mixture in the reactor is usually 0.1 to 20 minutes, preferably 0.4 to 5 minutes. It is preferable to carry out the polymerization reaction until the conversion exceeds 30%, for example, 60% to 90%.

As noted, crude POMs comprising a substantial proportion, such as not more than 40% unreacted residual monomers, especially trioxane and formaldehyde, are often obtained. Formaldehyde may also be present in the crude POM since the formaldehyde may be produced as the decomposition product of the trioxane even if only trioxane is used as the monomer. Other oligomers of formaldehyde, such as tetrameretroxacin, may also be present.

The crude POM is preferably liquefied at one or more stages of a known liquefier, such as, for example, a flash port, a venting extruder with one or more screws, a thin film evaporator, a spray drier or other conventional liquefier. A flash port is particularly preferred.

In the preferred liquefaction process of the crude POM, the material is liquefied to less than 6 bar (absolute) in the first flash to produce a gas stream and a liquid stream and the liquid stream is moved to a second flash operating at less than 2 bar Steam stream and it is recycled to the monomer plant.

For example, in the case of two-stage liquefaction, the pressure in the first stage may preferably be from 2 to 18 bar, in particular from 2 to 15 bar, particularly preferably from 2 to 10 bar, May be 1.05 to 4 bar, in particular 1.05 to 3.05 bar, particularly preferably 1.05 to 3 bar.

The partially liquefied polyoxymethylene homopolymer or copolymer is then introduced into an extruder or kneader where conventional additional materials and processing aids (additives) are provided in conventional amounts for these materials. Examples of this type of additive are lubricants, release agents, colorants such as pigments or dyes, flame retardants, antioxidants, photostabilizers, formaldehyde scavengers, polyamides, nucleating agents, fibrous and powder fillers or fibrous and powder- And / or other additional substances, or mixtures thereof.

POMs in the form of finished products are obtained as melts from extruders or kneaders.

A preferred batch synthesis using a recycle tray process comprises the following steps:

In the first step, the liquid monomer / comonomer mixture is introduced into an unsealed reaction vessel ("tray"). The initiator is introduced via a pump, for example an HPLC pump, preferably at a temperature in the range from 60 to 100 占 폚, particularly preferably from 70 to 90 占 폚, especially from 75 to 85 占 폚. A solvent miscible with the monomer and having a boiling point exceeding 100 캜 can be used incidentally.

In a second step, an initiator, preferably aqueous HClO ₄ , is added to the solvent along with the monomers.

In the third step, after the introduction time, polymerization and crystallization take place simultaneously, and when this is terminated, the product of the homogeneous reaction is a solid block of the polymer. Wherein the introduction time is often less than 120 seconds, such as 20 to 60 seconds.

In the fourth step, the solid crude POM is removed from the tray and milled by a machine and further processed in an extruder to obtain a stable end group, for example, through depolymerization (liquefaction). Stabilizers and other ingredients may also be metered into the material. Mixtures that can be considered to be standard stabilizer mixtures consist of antioxidants, acid scavengers and nucleating agents.

Once the reaction vessel has been emptied, a new circuit can be started by injecting the liquid monomer again.

Unlike the process of the present invention, the process for preparing the POM copolymer of US 6,388,049 is carried out in a fully molten state in a tubular reactor. The formulation is carried out in two reactors connected in series.

The resulting polymer may be milled, for example, to obtain a coarse powder, to spray the buffer solution, and then to the extruder. The buffer serves to neutralize the residual acid in the melt.

For a successful implementation of the circulating tray process, the synthesis must be rapid. That is, the introduction time should be short. The resulting oligomer must also be rapidly and completely cured during the polymerization reaction and should form a polymer block that does not excessively adhere to the container wall.

The low molecular weight POM of component B2 can be made particularly advantageous by using small amounts of initiator, large amounts of modifier and chain end capping. The low molecular weight POM is heat resistant as well as chemically resistant and its viscosity may be as low as 1000 factors compared to conventional high molecular weight POMs used to date in Catamold compositions.

The low molecular weight POM of component B2 is used as a viscosity modifying additive for POM having a weight average molecular weight of component B1 of not less than 50,000 g / mol, preferably not less than 80,000 g / mol, A POM system is created that is thermally and chemically stable and can be reduced in viscosity by a factor of 10 or more without damaging it.

With respect to the structure of component B1 and its preparation, reference may be made to the above mentioned with reference to component B2, with the exception of molecular weight, Mw / Mn ratio and amount of modifier and cationic initiator. In addition, it is not necessary (but preferred) to use the comonomer butanediol formal additionally to component B1.

It is particularly preferred that components B1 and B2 are both copolymers, in particular using the same comonomer in the same proportion.

The weight average molecular weight (Mw) of the polyoxymethylene homopolymer or copolymer of component B1 is in the range of 50,000 to 400,000 g / mol, preferably 80,000 to 300,000 g / mol, in particular 95,000 to 210,000 g / mol.

It is preferred to use butanediol formal from 0.05 to 0.7% by weight, especially from 0.07 to 0.5% by weight, in particular from 0.1 to 0.35% by weight, based on the polymer. Other di (C _1-6 -alkyl) acetals are used as modifiers and corresponding equivalent amounts of modifiers are used.

The amount of the cationic initiator in the production process is preferably 0.05 to 2 ppm, particularly preferably 0.1 to 1 ppm.

The Mw / Mn ratio of the polyoxymethylene homopolymer or copolymer of component B1 to be produced is preferably in the range of from 3.5 to 9, in particular from 4 to 8, in particular from 4.2 to 7.7.

In a first embodiment of the invention, the thermoplastic composition of the invention comprises 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 from 30 to 90% by weight, in particular from 50 to 90% by weight, of component B2.

In a second embodiment, the thermoplastic composition of the present invention comprises 70 to 99.5% by weight, preferably 80 to 99% by weight, especially 90 to 98% by weight of component B1 and correspondingly 0.5 to 30% by weight, preferably 1 To 20% by weight, in particular 2 to 10% by weight, of component B2.

The thermoplastic composition is prepared by separately preparing components B1 and B2 and then mixing the two components. The mixing can be carried out in any suitable suitable apparatus such as a kneader or an extruder. Where it can be initiated by mechanical premixing of the solid particulate components B1 and B2 and then melted together. It is also possible to melt component B1 in an extruder and add component B2 to the melt. The mixing process is preferably carried out at a temperature in the range of 150 to 220 캜, particularly 180 to 200 캜, under a pressure in the range of 0.5 to 5 bar, particularly 0.8 to 2 bar.

When the components B1 and B2 are mixed under the above-mentioned conditions, the chemical reaction of the two components, particularly the acetal conversion reaction, can occur simultaneously with the mechanical mixing process. Thus, components B1 and B2 do not have to be present in their original form in the mixture after the mixing process, but instead they can be somewhat or completely reacted to provide a homogeneous or altered product. When a homopolymer is used as component B 1, the addition of component B 2 and its reaction can produce a homogeneous or modified copolymer.

Thus, the present invention relates to a process for the preparation of a composition, as defined above, which comprises polymerizing trioxane and, optionally in the case of component B1, a comonomer in the presence of at least one di (C _1-6 -alkyl) acetal and at least one cationic initiator, B1 and B2 separately and then mixing the components B1 and B2 at a temperature in the range of 150 to 220 DEG C under a pressure in the range of 0.5 to 5 bar and a process for the production of a flowable polyoxymethylene homopolymer or copolymer Polyoxymethylene homopolymers or copolymers.

The thermoplastic composition is preferably used in the present invention for the production of molding compositions for the production of inorganic molded articles. To this end, the thermoplastic composition is filled with an sinterable powdery inorganic material. Corresponding packed thermoplastic compositions using other polyoxymethylene homopolymers or copolymers in the thermoplastic composition or using only component B2 are known per se from the prior art. For a description of the molding composition, 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 of the present invention for the production of an inorganic molded article may be prepared on the basis of the total volume of the molding composition

As component C, from 0 to 5% by volume of a lubricant and / or dispersant

, And the total volume of components A to C is 100% by volume.

When a powdered metal or a powdered metal alloy or a mixture thereof is used, the amount present in the molding composition is preferably 40 to 65% by volume, particularly preferably 45 to 60% by volume, of the component A.

Examples of metals which may be included in powder form are iron, cobalt, nickel, and silicon. Examples of alloys are light metal alloys based on aluminum and titanium, and also alloys including copper or bronze. A hard metal such as tungsten carbide, boron carbide, or titanium nitride may be used in combination with a metal such as cobalt and nickel. The latter can be used, in particular, in the production of cutting tools (known as cermets) with bonded hard metals.

If metal carbonyl is used, the appropriate amount is used.

When a metal oxide, a metal carbide, a metal nitride, or a mixture thereof is used, the amount of each powdery inorganic material used is preferably 20 to 50% by volume, particularly 25 to 45% by volume, particularly 30 to 40% by volume.

Suitable metal oxides are hydrogen-reducible and sinterable and can be used to make metal moldings by heating in the presence of hydrogen or in a hydrogen atmosphere. Examples of metals that can be used with the oxide are found in the VIB family, the VIII family, the IB family, the IIB family, and the IVA family of the Periodic Table of the Elements. Examples of suitable metal oxides include Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , NiO, CoO, Co ₃ O ₄ , CuO, Cu ₂ O, Ag ₂ O, WO ₃ , MoO ₃ , SnO, SnO ₂ , CdO, PbO, Pb ₃ O ₄ , PbO ₂ , and Cr ₂ O ₃ . It is preferable to use a lower-order oxide, for example, Cu ₂ O in place of CuO, PbO in place of PbO ₂ , and more advanced oxides, for example, oxidants capable of reacting with organic binders under certain conditions. The oxides can be used individually or in the form of a mixture. Thus, for example, pure iron molded articles or pure copper molded articles can be obtained. When a mixture of oxides is used, alloys and doped metals, for example, can be obtained. For example, steel components are made using a mixture of iron oxide / nickel oxide / molybdenum oxide and bronze is made using a copper oxide / tin oxide mixture that may include zinc oxide, nickel oxide or lead oxide. Particularly preferred metal oxides are iron oxide, nickel oxide and / or molybdenum oxide.

The metal oxide used in the present invention having a particle size of 50 μm or less, preferably 30 μm or less, particularly preferably 10 μm or less, particularly 5 μm or less, can be produced by various processes, preferably by a chemical reaction . For example, a solution of a metal salt can be used to precipitate hydroxides, oxydates, carbonates or oxalates, optionally in the presence of a dispersing agent, to form very fine precipitates. The precipitate is separated to a maximum purity level by washing. The precipitated particles are dried by heating and converted to metal oxides at elevated temperatures.

It is also possible to reach very fine metal oxide directly in a single step. For example, pentacarbonyl iron is ignited in the presence of oxygen to obtain very fine spherical iron oxide particles having a specific surface area of 200 m ² / g or less.

At least 65 vol% of the powder or the BET surface area of the metal oxide used in the present invention is preferably at least 5 m ² / g, preferably at least 7 m ² / g.

Other metal compounds that are not reduced during the sintering process, such as non-hydrogen reducing metal oxides, metal carbides, or metal nitrides, may be present with the hydrogen reducing metal oxide. An example of an oxide here is ZrO ₂ , Al ₂ O ₃ or TiO ₂ . Examples of carbides are SiC, WC or TiC. An example of a nitride is TiN.

When the sinterable inorganic nonmetal powder is used as the component A, the ratio is preferably 40 to 65% by volume, particularly 40 to 60% by volume.

Preferred powders of this type are oxide 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 AIN, Can be used. The average grain size of these powders is preferably 0.1 to 50 mu m, particularly preferably 0.1 to 30 mu m, particularly 0.2 to 10 mu m.

Corresponding sinterable powdery inorganic materials can also be prepared as disclosed in EP-A-1 717 539 and DE-T1-100 84 853.

The spherical metal particles can be produced by a chemical process or by passing an inert gas through the nozzle.

In one embodiment of the invention, the particle size of 65 vol.% Of component A is less than or equal to 5 microns, preferably less than or equal to 1.5 microns, in particular less than or equal to 0.5 microns, and the remaining particle size of component A is preferably less than or equal to 10 microns, 3 mu m or less, particularly 1 mu m or less.

The molding composition of the present invention may comprise from 0 to 5% by volume of a lubricant and / or dispersant as component C. When the component C is used additionally, the ratio thereof is preferably 0.2 to 5% by volume, particularly 1 to 5% by volume. Examples of suitable dispersing agents are oligomer polyethylene oxides having an average molecular weight in the range of 200 to 1000, preferably 200 to 600, stearic acid, hydroxystearic acid, fatty alcohols, fatty alcohol sulfonic acid salts and blocks of ethylene oxide and propylene oxide Lt; / RTI > Component A preferably comprises dispersant (s) C on the surface. Alkoxylated fatty alcohols or alcohol fatty acid amides are particularly suitable for the dispersion of metal oxide particles.

Examples of suitable lubricants are poly-l, 3-dioxane in an amount preferably from 0.2 to 20% by weight, preferably from 0.5 to 10% by weight, particularly preferably from 0.5 to 5% by weight, based on the amount of the binder B O-CH ₂ -O-CH ₂ -CH ₂ -CH ₂ -CH ₂ -, poly-1,3-dioxolane-O-CH ₂ -O-CH ₂ -CH ₂ , or mixtures thereof. Poly-l, 3-dioxepane is particularly preferred in acidic conditions due to its rapid depolymerization.

The poly-1,3-dioxepane and poly-1,3-dioxolane, also known as polybutanediol formal or poly BUFO, can be prepared in a similar manner to the polyoxymethylene homopolymers or copolymers and therefore need to be described in greater detail herein There is no. The molecular weight (weight average) is generally in the range of 10,000 to 150,000, preferably in the range of 15,000 to 50,000 (in the case of poly-1,3-dioxepane), particularly preferably in the range of 18,000 Preferably in the range of 30,000 to 120,000 (in the case of poly-1,3-dioxolane), particularly preferably in the range of 40,000 to 110,000 (in the case of poly-1,3-dioxolane).

Reference can also be made to component B ₃ ) of WO 2008/006776 for further explanation.

Under the conditions of compounding or injection molding, no acetal conversion reaction actually occurs between the polyoxymethylene polymers B and C. That is, the exchange of the comonomer unit does not actually occur.

The molding compositions of the present invention may also comprise conventional additives and processing aids having an advantageous effect on the rheological properties of the mixture during the molding process. Process stabilizers are particularly suitable.

The molding composition is prepared by melting component B at a temperature ranging from 150 to 220 캜 to obtain a melt stream and weighing component A and optionally C into the melt stream of component B. The molding composition can here be produced in a conventional mixing apparatus such as a kneader, a milling machine, or an extruder. When compounded in an extruder, the mixture can be extruded and granulated. A particularly preferred apparatus for feeding component A comprises a transport screw which is located in a cylinder which can carry and heat component A into the melt of component B as an essential element.

The molding composition is suitable for the production of metal or ceramic molded articles. The manufacturing process is to obtain a green product using injection molding or extrusion of a molding composition, then remove the binder from the green product to obtain a brown product, and then sinter the brown product.

Wherein removal of the binder can be accomplished by treating the green product with a gaseous acid-containing atmosphere at a temperature in the range of 20-180 占 폚 for 0.1-24 hours.

Metal or ceramic shaped articles are produced here by means known from the prior art, for example in EP-A-0 444 475, EP-A-0 446 708 and EP-A-0 853 995. For supplementary information, reference can also be made to the methods disclosed in EP-A-1 717 539 and DE-T1-100 84 853.

Compared to known molding compositions, the molding compositions of the present invention are characterized by improved fluidity while retaining favorable mechanical properties such as strength, hardness and stiffness after cooling.

The following examples further illustrate the invention.

Example

POM oligomer (preparation of component B2)

Laboratory scale polymerization was simulated to simulate a circulating tray process. The monomers and modifiers were heated to 80 DEG C in an open iron or aluminum reactor with magnetic stirring. Wherein the mixture was a clear liquid. At t = 0, an initiator solution consisting of HClO ₄ in triglyme was injected, with a proton concentration of generally 5 ppm for monomers or lower for low molecular weight POMs. When the polymerization was successful, the mixture became turbid in a short time (the introduction time was generally in the range of several seconds to one minute) and the polymer precipitated.

Post treatment and weight loss measurement

The resulting polymer block was then milled to obtain a powder which was heated under reflux for 1 hour in an extractive solution of methanol, water and sodium carbonate. After cooling, the polymer was separated by filtration and washed with aqueous sodium carbonate washing solution. The powder was then dried and the weight loss measured. Since the residual monomers or very low molecular weight oligomers are extracted at this stage, this method indicates the polymerization yield. The living center of the crude polymer chain, and also the residual acid center are extracted to some extent or neutralized. All cations must be neutralized to obtain a polymer with sufficient stability for further irradiation or further processing. Otherwise, the acid residue is equilibrated in the direction of formaldehyde and the thermal stability is impaired.

Thermal stability investigation

A few grams of the extracted and dried polymer was heated to 220 DEG C under nitrogen. After 4 hours, weight loss from the polymer was measured. The results show how many unstable terminal groups consist of the polymer affected by the distribution and amount of comonomers along the polymer chain, and also by the amount of modifier.

Thermal stability

WL N ₂ : Weight loss (WL) percent from the gut composed of 1.2 g of pellets when heated to 222 ° C in nitrogen for 2 hours

At the start of the WL measurement process, the balances used for this purpose were adjusted. The weight of a sword piece was measured with an accuracy of 0.1 mg in a twin-wall container consisting of two test tubes (nominal test tube, 100 x 10 mm; specially made, rear wall test tube, 100 x 12.5 mm) with one test tube in one test tube .

A thin copper wire about 400 mm long was fixed to the upper lip of the outer tube. This was used to suspend the twin-wall vessel in a particular apparatus (see Figure 9 of WO 2006/074997 and the description of the relevant drawings). For WL measurements in nitrogen, the upper half of the apparatus was used for 15 minutes for adaptation to a specific atmosphere without increasing the temperature. The test tube was then lowered to the bottom and maintained at 222 [deg.] C for 2 hours. The nitrogen flow rate was 15 1 / h, which was controlled in turn in each test tube.

After 2 hours, the twin-wall vessel was removed from the apparatus with the help of a copper wire and allowed to cool for 20-25 minutes in air. Weights were then measured again on the balance and WL was calculated from the following.

WL [%] - (loss x 100 / initial weight).

Molar mass measurement

The molecular weight of the polymer was determined by size exclusion chromatography on SEC apparatus. The SEC apparatus consisted of a combination of the following separation columns: a first column of 5 cm in length and 7.5 mm in diameter, a second linear column of 30 cm in diameter and 7.5 mm in diameter. The separation material in both columns was PL-HFIP gel from Polymer Laboratories. As a detector, Agilent's differential refractometer G1362A was used. A mixture consisting of hexafluoroisopropanol and 0.05% of potassium trifluoroacetate was used as the eluent. The flow rate was 0.5 ml / min and the column temperature was 40 < 0 > C. 60 microliters of the solution was injected at a temperature of 1.5 g of the test piece per liter of the eluent. This test piece solution was preliminarily filtered through a Millipor Millex GF (pore width 0.2 mu m). A narrow distribution PMMA standard from PSS (Germany, Mainz) with a molar mass M of 505-2740,000 g / mol was used for calibration.

Reactions using butyral as modulator

The POMs manufactured by the circulating tray process and corresponding to component B1 and marketed by BASF SE under the trade name Ultraform® are shown in Table 1 below.

The POM used in the Catamold process disclosed in the introduction corresponds to Ultraform® Z2320, which is produced with a butyral content of 0.35% by weight.

The proportion of butyral was then increased to reduce the molecular weight. Butanediol comonomer was constant at 2.7 wt% based on the polymer. The initiator concentration was 0.05 ppm based on monomer.

Table 2 shows the results.

Rheology survey

A rheology investigation was conducted on the POM of the present invention as in the example of Table 2. For this, a plate-plate-flow system was used at 190 ° C and kinematic viscosity was measured as a function of shear rate.

Table 3 below shows the results.

The oligomer of the present invention has a very low melt viscosity.

Extrusion of POM blend

The different proportions of the low molecular weight POM oligomer of Table 2 and the blend made from Ultraform® Z2320, Component B1 were extruded in an intermediate extruder at 190 ° C. for 2 minutes. This formulation was also subjected to the rheological measurement and DSC (differential scanning calorimetry). Table 4 below shows the properties of the resulting blends.

The results show that the change in viscosity after restarting with the use of component B2 is significantly less for the comparative composition. Thus, the POM formulations using the low molecular weight POMs of the present invention are significantly more stable than the comparative formulations.

Thus, the low molecular weight POM of component B2 can be used particularly advantageously as a viscosity modifying additive for a polyoxymethylene homopolymer or copolymer having component B1 having a weight average molar mass of 50,000 g / mol or more.

The low molecular weight POM of the present invention is chemically and mechanically stable and does not reduce overall strength or overall mechanical properties when mixed with the high molecular weight POM of component B1. The viscosity of the high molecular weight POM can be greatly reduced here and this effect is maintained through a plurality of melt processes.

It is also possible to carry out conventional Catamold manufacturing processes with POM formulations, since no formaldehyde vapors are generated and the POM formulations remain solids.

This advantage does not be achieved using the compounds of the POM dimethyl ether as for example with _{Me-O- (CH 2 0)} 4 -Me even a low molecular weight. The advantages mentioned are achieved only with special use of the POM of the present invention.

In another experiment, in Example 11, the low molecular weight POM oligomer of Example 3 and the blend made with Ultraform Z2320 were mixed in a mini-extruder at a weight ratio of 50:50. Here, three kinds of test pieces were mixed for 1 minute, 2 minutes or 5 minutes.

The molecular weight profiles for the formulations were then plotted using size exclusion chromatography, respectively.

The accompanying Figure 1 shows the dependence of the size exclusion chromatography (SEC) detector signal in arbitrary units when plotted against molar mass (g / mol). The solid line represents the molar mass distribution during one minute of mixing, the triangle represents the molar mass distribution after two minutes of mixing, and the circle represents the molar mass distribution during the mixing time of five minutes.

The molar mass distribution appeared to remain the same during the three blends, indicating the stability of the polymer blend. The bimodal molar mass distribution resulting from the blend polymer is also maintained. Therefore, there is no molar mass balance through the acetal conversion reaction.

Thus, the bimodal molar mass distribution of the POM blend is retained even after thermal stress and the shear viscosity is significantly reduced, thereby significantly improving the processing characteristics. In particular, improved fluidity means that long flow paths and small wall thicknesses can be tolerated in the injection molding process without deteriorating the results.

Unlike other flow modifiers, phase separation does not occur under shear when the POM oligomer is added, so there is no exudation of the flow modifier and deposition occurs in the mold.

The combination of a low molecular weight POM and a high molecular weight POM does not weaken the molded article and imparts high strength.

Due to its stability in the melt, POM formulations are suitable for Catamold® processes for the injection molding of metal powders or ceramic powders. In this process, the POM molding composition undergoes three melting and shearing procedures during mixing of the two polymer components, during the introduction of the metal powder or ceramic powder, and finally during injection molding. Thermal stresses further occur during the reduction and reuse of injection molded articles such as sprue parts. This is the part where the advantages mentioned for the POM system of the present invention become apparent.

Flow performance of metal-powder-filled POM formulations

A stainless steel 17-4PH having 60% by volume of a stainless steel metal powder (general powder particle size distribution D ₁₀ <3 μm, D ₅₀ <8 μm, D ₉₀ <21 μm) POM component B2 and high molecular weight POM component B1 Z2320-003. Flow spirals were produced by injection molding in order to study the flow performance of metal-powder-filled POM blends. 2 shows an image of the generated helix.

The helix of FIG. 2 shows the POM (spiral length> 100 cm) of Example 3 at 100% in the first column from the left hand to the right hand; 90% of POM in Example 3 + 10% of Z2320-003 (spiral length of about 70 cm); 80% of POM in Example 3 + Z2320-003 of 20% (spiral length of about 62 cm).

The middle row is 70% of the POM + 30% Z2320-003 (spiral length of about 48 cm) of Example 3 from the left hand side to the right hand side; 60% POM in Example 3 + 40% Z2320-003 (spiral length about 42 cm); 50% POM in Example 3 + Z2320-003 at 50% (spiral length 34 cm).

The final row is only Z2320-003 (spiral length approx. 19 cm) from the left hand towards the right hand; Z2320-003 + represents a conventional flow improver (spiral length 24 cm).

The obvious increase in flow spiral length is evident as the concentration of low molecular weight POM increases.

The use of a low molecular weight POM makes it possible to produce metal binders with very good flow performance (high flow). In addition, metal powder of higher concentration can be used. Various metal-powder-binder systems were fabricated and studied. Table 5 shows the obtained results. In addition, Z2320-003 was used as a high molecular weight POM component B1 (100, 60, 50 and 40 wt.% Based on POM binder).

PolyBUFO: polybutanediol formal having a weight average molecular weight (Mw) of 18,000 to 35,000; Content based on total POM binder

Since there are fewer organic binders to be burned off before sintering, the ability to increase the metal powder loading of the POM binder in the present invention improves the tolerance range in the finally obtained metal moldings.

Claims

As component B1, from 10 to 90% by weight of a polyoxymethylene homopolymer or copolymer having a weight average molar mass (Mw) in the range from 50,000 to 400,000 g / mol, and
As component B 2, from butanediol formaldehyde in the range of from 0.5 to 4% by weight, preferably from 2 to 3.5% by weight, in particular from 2.5 to 3% by weight, based on the polymer, from trioxane and butanediol as monomers, By weight of a polyoxymethylene copolymer having a weight average molecular weight (Mw) in the range of 5,000 to 15,000 g / mol, derived from about 90%
&Lt; / RTI >

2. The process according to claim 1, wherein the component B2 has a weight-average molar mass Mw of 6000 to 9000 g / mol, preferably 6500 to 8000 g / mol, especially 7000 to 7500 g / mol, (Mw) of from 70,000 to 300,000 g / mol, preferably from 95,000 to 210,000 g / mol.

The composition according to claim 1, wherein the number average molecular weight (Mn) of component B2 is from 3000 to 6000 g / mol, preferably from 3200 to 5000 g / mol, especially from 3500 to 4100 g / mol.

4. The composition according to any one of claims 1 to 3, wherein the component B2 has an Mw / Mn ratio in the range of 1.5 to 3.0, preferably 1.5 to 2.45.

5. Use according to any of the claims 1 to 4, in a butanediol formal ratio in the range of from 1 to 5% by weight, preferably from 2 to 3.5% by weight, especially from 2.5 to 3% by weight, based on the polymer, Wherein at least 90% by weight, based on the polymer, of component B1 is derived from trioxane and butanediol formal, preferably from trioxane and butanediol, as monomers.

6. A process according to any one of claims 1 to 5, wherein the preparation of the polymer of component B2 is carried out in the presence of 3.75 to 4.25% by weight, preferably 3.8 to 4.2% by weight, in particular 3.9 to 4.1% by weight, Di (C _1-6 -alkyl) acetals of the same molar amount are used incidentally as a modifier.

Each of components B1 and B2 is prepared separately by polymerizing trioxane and optionally comonomers in the presence of at least one di ( _C1-6 -alkyl) acetal and at least one cationic initiator as modifiers, followed by mixing components B1 and B2 A method for producing a thermoplastic composition according to any one of claims 1 to 6,

Polymerizing trioxane and optionally comonomers, respectively, in the presence of one or more di (C _1-6 -alkyl) acetals and at least one cationic initiator as modifiers, to obtain a composition as defined in any one of claims 1 to 6 B1 and B2 are separately prepared, and then the components B1 and B2 are mixed at a temperature in the range of 150 to 220 DEG C under a pressure in the range of 0.5 to 5 bar to prepare a flowable polyoxymethylene copolymer.

Based on the total volume of the molding composition,
As the component A, a sinterable powder inorganic material selected from a metal, a metal alloy, a metal carbonyl, a metal oxide, a metal carbide, a metal nitride and a mixture thereof in an amount of 20 to 70%
As component B, from 30 to 80% by volume of a thermoplastic composition obtainable by the process according to any one of claims 1 to 6 or according to claim 8, and
As component C, 0 to 5% by volume of a lubricant and /
, Wherein the total volume of components A to C is 100% by volume.

The molding composition according to claim 9, wherein the component A has a particle size of at least 65 vol% and a particle size of the remainder of the component A is at most 10 탆.

A process for producing a molding composition according to claim 9 or 10, wherein component B is melted at a temperature ranging from 150 to 220 캜 to obtain a melt stream and component A and optionally C are metered into the melt stream of component B.

Use of the molding composition according to claims 9 or 10 for the production of metal or ceramic molded articles.

A process for producing a green product by injection molding or extrusion of the molding composition according to claim 9 or 10, followed by removal of the binder from the green product to obtain a brown product, and thereafter sintering the brown product Gt;

14. The method of claim 13, wherein the binder is removed by treating the green product with a gaseous acid-containing atmosphere at a temperature in the range of from 20 to 180 DEG C for from 0.1 to 24 hours.

A molded article made from the molding composition according to claim 8 or 9 or obtained by the process according to claim 13 or 14.

A flowable polyoxymethylene copolymer obtainable by the process according to claim 8.