Method for producing colored polyoxymethylene copolymers

Abstract

The present invention relates to a method for producing colored polyoxymethylene copolymers by mixing, in a degasser, untreated polyoxymethylene copolymer in particulate form containing 2 to 30% by weight of unreacted residual monomers with a colorant in particulate form. The present invention also relates to the colored polyoxymethylene copolymers obtainable by the method and to the use of the colored polyoxymethylene copolymers for producing molded parts.

Description

[Technical field]

[0001] The present invention relates to a method for producing a colored polyoxymethylene copolymer in a degasser by mixing an untreated polyoxymethylene copolymer in particulate form containing 2-30% by weight of unreacted residual monomer with a colorant in particulate form.

[0002] Furthermore, the present invention relates to the coloured polyoxymethylene copolymers obtainable by said process and to the use of the coloured polyoxymethylene copolymers for producing moulded parts. [Background technology]

[0003] Polyoxymethylene copolymers have been known for a long time. They have many excellent properties that make them suitable for a wide variety of industrial applications. They can be obtained by cationic polymerization of cyclic oligomers and comonomers with formaldehyde in the presence of a catalyst and optional activators.

[0004] The polymerization reaction is usually carried out by melt kneading. After the polymerization reaction, an untreated polyoxymethylene copolymer is obtained, which contains a large amount of unreacted residual monomer. Furthermore, the untreated polyoxymethylene copolymer generally contains unstable end groups at the chain ends of the polyoxymethylene copolymer.

[0005] Thus, in the production methods described in the state of the art, raw polyoxymethylene copolymers are heat treated in order to remove unreacted residual monomers and further depolymerize unstable end groups. The heat treated polyoxymethylene copolymer is then dried and deodorized, and the finished polyoxymethylene copolymer is stored in silos in pelletized form.

[0006] The finished polyoxymethylene copolymers (hereinafter also referred to as "polyoxymethylene copolymers" or "POM") are used, for example, for the production of moldings in the automotive and sanitary ware industries. The polyoxymethylene copolymers obtained by the production methods described in the state of the art are not pigmented, and the copolymers are suitable for the production of unpigmented moldings.

[0007] To produce colored molded articles of the state of the art, the finished polyoxymethylene copolymer in granular form and the colorant are mixed in a processing machine of conventional design (e.g., an extruder). In the state of the art, colored polyoxymethylene copolymers can be obtained in granular form and then used to produce colored molded articles. Another method described in the state of the art for producing colored polyoxymethylene copolymer molded articles is the use of a processing machine of conventional design with additional equipment for metering the colorant. The processed polyoxymethylene copolymer is mixed with the colorant in the processing machine and fed into an injection mold to obtain the colored molded article. Summary of the Invention [Problem to be solved by the invention]

[0008] The properties of the colored polyoxymethylene copolymers of the prior art as well as the molded articles obtained from the colored polyoxymethylene copolymers of the prior art do not in all cases satisfy demanding applications. The molded articles often do not show a satisfactory uniform distribution in the obtained molded articles. Moreover, in some cases, the colored molded articles show inadequate formaldehyde emissions. Therefore, the object of the present invention is to provide a method for producing colored polyoxymethylene copolymers that does not have the disadvantages of the prior art or has only minor disadvantages. The molded articles obtained from the colored polyoxymethylene copolymers should show a uniform distribution of the colorant and a bright color. Moreover, the molded articles should show low formaldehyde emissions. Moreover, the method for producing the colored polyoxymethylene copolymers should be cost-effective and simple. [Means for solving the problem]

[0009] This object is achieved by a process for the preparation of a colored polyoxymethylene copolymer, comprising the steps of: a) providing component (A1) and component (A2), component (A1) comprising an untreated polyoxymethylene copolymer in particulate form, the untreated polyoxymethylene copolymer comprising a polyoxymethylene copolymer and 2 to 30 weight percent unreacted residual monomer (based on the total weight of the untreated polyoxymethylene copolymer), and component (A2) comprising a colorant in particulate form; b) simultaneously feeding components (A1) and (A2) to a degasser, in which the untreated polyoxymethylene copolymer is melted and mixed with component (A2), thereby at least partially removing unreacted residual monomers from the untreated polyoxymethylene copolymer and obtaining a colored polyoxymethylene copolymer; c) removing the colored polyoxymethylene copolymer from the degasser. Effect of the Invention

[0010] Surprisingly, it has been found that colored polyoxymethylene copolymers (cPOM) can be produced by mixing raw polyoxymethylene copolymers (rPOM) in particulate form, containing unreacted residual monomers, with a colorant in a degasser. The process for producing colored polyoxymethylene copolymers allows colored polyoxymethylene copolymers to be obtained in a simple and cost-effective manner. Furthermore, moldings made from the colored polyoxymethylene copolymers obtained by the process of the present invention show a uniform distribution of the colorant, thereby showing a bright color. Furthermore, the obtained moldings surprisingly show low formaldehyde emissions. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 shows a preferred arrangement of a degasser. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described in detail below.

[0013] Untreated polyoxymethylene copolymer (rPOM); component (A1) In step a), a component (A1) is provided which comprises untreated polyoxymethylene copolymer (rPOM).

[0014] Raw polyoxymethylene copolymers (rPOM) are known per se. The copolymers are preferably prepared by polymerization of trioxane (as monomer) with one or more comonomers.

[0015] Very generally, the polyoxymethylene copolymer (POM) contained in the untreated polyoxymethylene copolymer (rPOM) in component (A1) has in the main polymer chain at least 50 mol % -CHO- repeat units and at most 50 mol %, preferably 0.01 to 20 mol %, in particular 0.1 to 10 mol %, and very particularly preferably 0.5 to 6 mol % of repeat units of the following formula (I): [ka] (In the formula, R 1 ~R 4 are each independently a hydrogen atom, a C1-C4 alkyl group, or an alkyl group having 1 to 4 carbon atoms substituted with alkoxy; R 5 is a methylene group substituted with -CH2-, -OCH2-, C1 to C4 alkyl, or C1 to C4 alkoxy, or the corresponding oxymethylene group, and n is 0 to 3.

[0016] In a further embodiment, the polyoxymethylene copolymer (POM) contained in the untreated polyoxymethylene copolymer (rPOM) in component (A1) has at least 50 mol % -CHO- repeat units in the main polymer chain and up to 50 mol %, preferably 0.01 to 20 mol %, in particular 0.1 to 10 mol %, and very particularly preferably 0.5 to 6 mol % of the compound of formula (I): [ka] (In the formula, R 1 ~R 4 are each independently a hydrogen atom, a C1-C4 alkyl group, or an alkyl group having 1 to 4 carbon atoms substituted with alkoxy; R 5 is a chemical bond, -CH2-, -OCH2-, a methylene group substituted with C1-C4 alkyl, or C1-C4 alkoxy, or the corresponding oxymethylene group, and n is 0 to 3. The repeating unit has the following structure:

[0017] Advantageously, these groups can be introduced into the copolymer by ring-opening of a cyclic ether as a comonomer. Preferred cyclic ethers (comonomers) are those of formula (II): [ka] (In the formula, R 1 ~R 5and n are as defined above). Merely by way of example, mention may be made of ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide, 1,3-dioxane, 1,3-dioxolane, 1,3-dioxepane (=butanediol formal, BUFO) as cyclic ethers; and linear oligoformals or polyformals (for example polydioxolanes or polydioxepanes) as comonomers.

[0018] For example, trioxane, one of the above cyclic ethers of formula (II), and a third monomer, preferably of formula (III) and / or formula (IV): [ka] Likewise suitable are oxymethylene terpolymers prepared by reaction of difunctional compounds of the formula: where Z is a chemical bond, -O-, -ORO- (R is C1-C8 alkylene or C3-C8 cycloalkylene).

[0019] Preferred comonomers of this type are ethylene diglycidyl, diglycidyl ethers, and diethers derived from glycidyl and formaldehyde, dioxane, or trioxane in a 2:1 molar ratio, or diethers derived from 2 moles of a glycidyl compound and 1 mole of an aliphatic diol having 2 to 8 carbon atoms (e.g., 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.

[0020] The melting point of the polyoxymethylene copolymer (POM) contained in the untreated polyoxymethylene copolymer (rPOM) in component (A1) may be at least preferably in the range of 150-200° C., more preferably the melting point is in the range of 160-180° C. These melting points are determined according to DIN EN ISO 11357-3 (April 2013) at a heating and cooling rate of 20 K / min and a sample mass of about 8.5 mg.

[0021] The molecular weight (weight average Mw; determined as described below) of the polyoxymethylene copolymer (POM) contained in the untreated polyoxymethylene copolymer (rPOM) can be adjusted in a wide range. The molecular weight Mw is preferably in the range of 1000 to 24000 g / mol ±10%, and the number average molecular weight Mn (determined as described below) may preferably be in the range of 8000 to 85000. Preferably, the polyoxymethylene copolymer (POM) contained in the untreated polyoxymethylene copolymer (rPOM) has a molecular weight (Mw) in the range of 80000 to 220,000 g / mol ±10%, and the molecular weight (Mn) is in the range of 9000 to 38000 g / mol. The Mw / Mn ratio (polydispersity index) of the polyoxymethylene copolymer (POM) contained in the untreated polyoxymethylene copolymer (rPOM) is preferably in the range of 1.4-14, and the Mw / Mn is more preferably in the range of 2.1-14.

[0022] The molecular weight of the polymer was determined via size exclusion chromatography on a size exclusion chromatography (SEC) apparatus. The SEC apparatus included the following combination of separation columns: a preparatory column of 5 cm length and 7.5 mm diameter, a second linear column of 30 cm length and 7.5 mm diameter. The separation material for both columns was PL-HFIP gel obtained from Polymer Laboratories. The detector used included an Agilent G1362A differential refractive index detector. A mixture of hexafluoroisopropanol and 0.05% potassium trifluoroacetate was used as the eluent. The flow rate was 0.5 ml / min and the column temperature was 40° C. 60 microliters of solution was injected with a concentration of 1.5 g sample per liter of eluent. The sample solution was prefiltered through Millipor Millex GF (pore width 0.2 micrometers). For calibration, narrow-distribution PMMA standards with molecular weights M ranging from 505 to 2.740.000 g / mol from PSS (Mainz, DE) were used. The polydispersity index is defined as the weight average molecular weight divided by the number average molecular weight.

[0023] In a further embodiment, the molecular weight of the polymer was determined via size exclusion chromatography in the following SEC (size exclusion chromatography) apparatus: the SEC apparatus included the following combination of separation columns (preparatory column 5 cm long and 8 mm diameter, second linear column 30 cm long and 7.5 mm diameter, third column 30 cm long and 7.5 mm diameter). The separation material of column 1 was HFIP-LGGuard, columns 2 and 3 were PL-HFIP gel. The detector used included an Agilent 1100 differential refractometer. A mixture containing hexafluoroisopropanol and 0.05% potassium trifluoroacetate was used as the eluent. The flow rate was 1 ml / min and the column temperature was 35° C. 50 microliters of solution was injected at a concentration of 1.5 g of sample per liter of eluent. The sample solution was pre-filtered through Millipor Millex GF (pore width 0.2 micrometers). For calibration, narrowly distributed PMMA standards from PSS (Mainz, DE) with molecular weights M ranging from 800 to 2.200.000 g / mol were used. The polydispersity index is defined as the weight average molecular weight divided by the number average molecular weight.

[0024] The molecular weight distribution of the polyoxymethylene copolymer (POM) contained in the untreated polyoxymethylene copolymer (rPOM) may be unimodal or substantially unimodal. It may also have a multimodal molecular weight distribution. It is possible that the rPOM has a bimodal molecular weight distribution.

[0025] For the preparation of raw polyoxymethylene (rPOM), the polymerization is generally carried out in the presence of at least one Lewis acid. The Lewis acid generally acts as an initiator or catalyst for the polymerization. The term "at least one Lewis acid" in this specification is understood to mean exactly one Lewis acid and also a mixture of two or more Lewis acids.

[0026] Thereby, preferably it may be carried out in the presence of two (more preferably one) Lewis acids.

[0027] It may be preferred that the at least one Lewis acid is at least one (e.g., two, more preferably one) halide of boron, tin, titanium, phosphorus, antimony or arsenic. Thereby, preferably, the halide is a chloride or a fluoride, or the halide may include both. Examples thereof are boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentafluoride, phosphorus pentachloride, antimony pentafluoride and arsenic pentafluoride, and in particular also their complex compounds.

[0028] The at least one Lewis acid may preferably be at least one halide of boron, in particular boron trifluoride (e.g. boron trifluoride hydrate), or at least one (more preferably, one) coordination compound of a boron halide, and at least one (more preferably, one) organic compound containing oxygen or sulfur atoms or both. Thereby, it may preferably be an organic compound containing at least one (particularly, one) oxygen atom only. The organic compound for forming the coordination compound of a boron halide may be, for example, an alcohol, an ether, or a sulfide. Among the at least one coordination compound of a boron halide, coordination compounds with ethers, in particular alkyl ethers (e.g., C1-C4 alkyl ethers), may be most preferred. Coordination compounds of boron trifluoride with ethers, especially dialkyl ethers (e.g., C1-C4 dialkyl ethers), may be most preferred, especially boron trifluoride dibutyl ether, boron trifluoride diethyl ether, or boron trifluoride dimethyl ether, or mixtures thereof. Boron trifluoride diethyl etherate may be most preferably used.

[0029] The amount of at least one Lewis acid that can be used in the method disclosed herein is not particularly limited. Usually, the amount of at least one Lewis acid may be 10 to 150 ppm, for example, 20 to 140 ppm (in each case based on the total mass of monomer and comonomer). Preferably, an amount of at least one Lewis acid of 30 to 130 ppm (based on the mass of at least one monomer) may be used. In particular, it may be advantageous to use an amount of at least one Lewis acid of 40 to 100 ppm (based on the total mass of monomer and comonomer). A small amount may slow down the reaction initiation, and a large amount may not speed up the reaction and may ultimately require a lot of effort to separate the Lewis acid from the polymer.

[0030] In general, polymerization can be carried out using various methods. Such methods are either known to the skilled artisan or available to the skilled artisan by using their general knowledge. Preferably, rPOM can be produced via cationic polymerization. During cationic polymerization, rPOM can be formed in bulk (i.e., without or substantially without the use of solvent).

[0031] The polymerization can be carried out at temperatures, pressures and equipment generally known to the skilled artisan or available to the skilled artisan by using his general knowledge. For example, it may be carried out in an extruder (e.g. self-cleaning) or two or more extruders in series (e.g. twin screw type). It may also be possible to carry out the process disclosed herein in a kneader (e.g. self-cleaning) or two or more kneaders in series. In general, it may be advantageous to carry out the polymerization at a temperature as low as possible to avoid wasting energy and at a high enough temperature to maintain the polymerization and ensure good mixing, in particular by maintaining at least one monomer and, if present, at least one comonomer in liquid state. Thus, preferably, the polymerization may be carried out at a temperature between 50 and 150°C, whereby more preferably at a temperature between 60 and 120°C. Temperature thereby means the temperature in the bulk.

[0032] Generally, it may be advantageous to inactivate the Lewis acid once the polymerization reaction is completed.

[0033] Thereby, preferably, at least one deactivating agent may be added. More preferably, two deactivating agents may be added, or most preferably, one deactivating agent may be added. The at least one deactivating agent may be, for example, ammonia, an aliphatic amine (e.g., triethylamine, tri-n-butylamine, triethanolamine), a quaternary ammonium salt (e.g., tetrabutylammonium hydroxide), a hydroxide, an inorganic weak acid salt, or an organic acid salt of an alkali metal or an alkaline earth metal.

[0034] At least one deactivating agent can be added neat or as a solution in an organic solvent. The latter can be more effective in terminating the polymerization reaction and is therefore preferred. The organic solvent used in this case can be an aliphatic hydrocarbon (e.g., n-hexane, cyclohexane, or n-heptane), an alcohol (e.g., methanol or ethanol), a ketone (e.g., acetone or methyl ethyl ketone), or an ester.

[0035] The amount of the at least one deactivating agent generally depends on the equivalents of the active sites of the deactivating agent and the equivalents of the at least one Lewis acid to be deactivated (thus, for example, the equivalents of nitrogen atoms and boron atoms). The at least one deactivating agent may advantageously be used in molar excess (for example, from 50:1 to at least 2:1) relative to the at least one Lewis acid.

[0036] The untreated polyoxymethylene copolymer (rPOM) may optionally include at least one additive selected from the group consisting of antioxidants, formaldehyde scavengers, UV absorbers, mold release agents, acid scavengers, and nucleating agents.

[0037] The additives described above may be added before, during, or after polymerization. Preferably, the additives are added to the raw polyoxymethylene copolymer (rPOM) after polymerization and after the addition of the deactivating agent. The additives can be added to any known device. The additives are preferably added to a mixing device.

[0038] Suitable antioxidants are, for example, sterically hindered phenols, such as triethylene glycol bis(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate (e.g. Irganox 245 from BASFSE). When an antioxidant is used, it is added in an amount such that the colored polyoxymethylene copolymer (cPOM) contains 0.001 to 10% by weight, preferably 0.002 to 5% by weight, more preferably 0.005 to 3% by weight (based on the total weight of the colored polyoxymethylene copolymer (cPOM)) of antioxidant.

[0039] A suitable formaldehyde scavenger is, for example, a condensate of melamine, formaldehyde and polyamide. When a formaldehyde scavenger is used, it is added in an amount such that the colored polyoxymethylene copolymer (cPOM) contains 0.001 to 10% by weight, preferably 0.002 to 5% by weight, more preferably 0.005 to 3% by weight (based on the total weight of the colored polyoxymethylene copolymer (cPOM)) of formaldehyde scavenger.

[0040] Suitable polyamides are, for example, copolyamides based on caprolactam, hexamethylenediamine, p,p'-diaminodicyclohexylmethane and adipic acid, which may further comprise monofunctional polymeric compounds (e.g. propionic acid or triacetonediamine) as components for adjusting the molar mass. Examples are Ultramid® 1C and Ultramid® C31 from BASFSE. When using polyamide, it is added in such an amount that the colored polyoxymethylene copolymer (cPOM) comprises 0.001 to 2% by weight, preferably 0.005 to 1.99% by weight, more preferably 0.01 to 0.08% by weight (based on the total weight of the colored polyoxymethylene copolymer (cPOM)) of polyamide.

[0041] Suitable UV absorbers include, for example, hindered amine light stabilizers (e.g., those having the polymer structure: [ka] (wherein n is an integer ranging from 5 to 50). (Hindered amine represented by the formula:

[0042] When a hindered amine is used, it is added in an amount such that the colored polyoxymethylene copolymer (cPOM) contains 0.001 to 10% by weight, preferably 0.002 to 5% by weight, more preferably 0.005 to 2% by weight (based on the total weight of the colored polyoxymethylene copolymer (cPOM)) of hindered amine.

[0043] Suitable release agents are, for example, esters or amides of saturated or unsaturated aliphatic carboxylic acids having 10 to 40 carbon atoms, preferably 16 to 22 carbon atoms, with polyols or aliphatic saturated alcohols or amines having 2 to 40 carbon atoms, preferably 2 to 6 carbon atoms. When using esters or amides, they are added in such an amount that the colored polyoxymethylene copolymer (cPOM) contains 0.01 to 5% by weight, preferably 0.09 to 2% by weight, in particular 0.1 to 0.7% by weight (based on the total weight of the colored polyoxymethylene copolymer (cPOM)) of the release agent. Thus, preferred esters or amides are glyceryl distearate, glyceryl tristearate, ethylenediamine distearate, glyceryl monopalmitate, glyceryl trilaurate, glyceryl monobehenate, and pentaerythrityl tetrastearate.

[0044] Suitable acid scavengers are, for example, alkali or alkaline earth carbonates, hydroxides or silicates. When an acid scavengers is used, it is added to the colored polyoxymethylene copolymer (cPOM) in an amount comprising 0.001 to 2% by weight, preferably 0.002 to 1% by weight, in particular 0.003 to 0.7% by weight (based on the total weight of the colored polyoxymethylene copolymer (cPOM)).

[0045] Suitable nucleating agents are, for example, melamine cyanurate, silicic acid, branched polyoxymethylene and talcum. When a nucleating agent is used, it is added in an amount comprising 0.005 to 5% by weight, preferably 0.01 to 2% by weight, in particular 0.02 to 0.7% by weight (based on the total weight of the colored polyoxymethylene copolymer (cPOM)).

[0046] When present, the additives are added in the usual manner (eg, individually or together, as a solution or suspension, as a masterbatch).

[0047] In step a), component (A1) is provided in particulate form. Thus, after polymerization and optionally after addition of additives, the untreated polyoxymethylene copolymer (rPOM) can be, for example, crushed to obtain the untreated polyoxymethylene copolymer (rPOM) in particulate form. Crushing the untreated polyoxymethylene copolymer (rPOM) gives the untreated polyoxymethylene copolymer (rPOM) in powder form. The particles thus have an irregular morphology, and thus the particle size of component (A1) is, for example, in the range of 10 μm to 2 mm. The average particle size is determined using Fraunhofer diffraction using a Mastersizer 3000.

[0048] To provide component (A1) in particulate form, all known mills may be suitable. Particularly suitable mills include, for example, roller mills or bar mills.

[0049] Coloring agent; component (A2) Further, in step a), component (A2) is provided which comprises a colorant.

[0050] The colorant may be a colorant of any color. However, within the context of the present invention, component (A2) preferably comprises at least one black colorant. At least one black colorant in this case is understood to mean only one black colorant and a mixture of two or more black colorants. The at least one black colorant is preferably selected from the group consisting of carbon black, activated carbon, carbon nanotubes, graphene black, nigrosine, and perylene dyes. Preferred black colorants are selected from the group consisting of carbon black and activated carbon, with carbon black being particularly preferred. The colorant may be provided in pure form, generally in the form of a powder or compact. In this embodiment, component (A2) consists of a colorant.

[0051] In a preferred embodiment, component (A2) is provided in the form of a masterbatch, in which the colorant is dispersed in a polymer, the polymer forming the continuous phase and the colorant forming the dispersed phase.

[0052] In a more preferred embodiment as a polymer for the masterbatch, a polyoxymethylene copolymer (POM) is used. In a further preferred embodiment as a polymer for the masterbatch, a polyoxymethylene copolymer (POM) is used which forms the basis for the colored polyoxymethylene copolymer (cPOM) produced by the process of the present invention.

[0053] Preferably, component (A2) contains a colorant and a polyoxymethylene copolymer (masterbatch). More preferably, component (A2) contains 5-30% by mass of at least one black colorant described above and 95-70% by mass of a polyoxymethylene copolymer.

[0054] The masterbatch can be produced, for example, in an extruder where the colorant is mixed with the polymer. Preferably, the black colorant is carbon black and the polymer is a polyoxymethylene copolymer.

[0055] In a preferred embodiment, component (A2) is provided in the form of granules. The particle size of the granules is preferably in the range of 2 to 3 mm. The particle size is determined as described above for determining the particle size of component (A1).

[0056] Degassing Equipment The degassing device preferably comprises, in the direction of flow, a melter and a degasser.

[0057] Melting Device The melter comprises at least one melting zone. At least one melting zone in the context of the present invention means only one melting zone as well as two or more melting zones. Preferably, the melter comprises only one melting zone. In this preferred embodiment, the melter is equal to the melting zone.

[0058] The melter is operated at a temperature of 130-220°C, preferably 150-210°C, most preferably 150-200°C. As melter, all known devices capable of melting and mixing components (A1) and (A2) can be used. It is clear that only meltable components are melted in the melter. If the colorant is, for example, carbon black, the skilled person understands that carbon black only disperses and does not melt. The same is true if component (A1) contains additives that cannot be melted, such as fillers or reinforcing agents.

[0059] The energy for operating the melter at temperatures between 130 and 220° C. comes from friction, so in a preferred embodiment there is no need to heat the melter externally.

[0060] No vacuum is applied in the melter. A preferred melting zone of the melter in a preferred embodiment comprises, in the flow direction, conveying elements, kneading elements, optionally mixing elements and flow restriction elements. Preferably, the melter is implemented as an extruder. In this case, the melter comprises, in the flow direction, conveying elements, kneading elements, optionally mixing elements and flow restriction elements. Suitable conveying elements, kneading elements, mixing elements and flow restriction elements are known to those skilled in the art.

[0061] The conveying elements serve to convey the ingredients contained in the extruder forward. The shear rate acting on the ingredients in the extruder through the conveying elements is usually lower than the shear rate acting on the ingredients in the extruder through the kneading or mixing elements. Suitable conveying elements are known to those skilled in the art, for example screw conveying elements, preferably twin screw conveying elements.

[0062] The kneading element serves to mix the individual components contained in the extruder. At the same time, it can grind additives (such as colorants, carbon black, or fillers or reinforcing agents), for example.

[0063] The shear rate acting on the components in the extruder through the kneading elements is usually higher than the shear rate acting on the components through the mixing and conveying elements. Suitable kneading elements are known to those skilled in the art, for example kneading screws. More preferred are twin-screw kneaders.

[0064] The mixing element serves to mix the individual components contained in the extruder. The shear rate acting on the components in the extruder through the mixing element is usually smaller than the shear rate acting on the components through the kneading element. Suitable mixing elements are known to those skilled in the art, for example, two mixing elements or screw mixing elements. A preferred mixing element is a twin screw mixing element.

[0065] A flow restriction element differs from a conveying element in that it has a counter conveying effect, so that it restricts the flow of the ingredients contained in the extruder. Commonly used flow restriction elements are conveying elements that are mounted so that their conveying direction is opposite to the flow direction.

[0066] The extruder is defined by the following parameters: d is the diameter of the extruder screw; N is the rotation speed of the extruder screw; Δ is the difference in width between the outer wall of the screw (screw tip) and the inner wall of the extruder.

[0067] The diameter (d) of the screw of the melter is usually in the range of 70 to 360 mm, preferably in the range of 120 to 250 mm, and particularly in the range of 150 to 230 mm.

[0068] The rotation speed (N) of the screw in the melter is, for example, in the range of 80 to 200 rpm, preferably in the range of 110 to 180 rpm, and particularly preferably in the range of 130 to 160 rpm.

[0069] The width difference (Δ) in the melter is usually in the range of 3 to 12 mm, and preferably in the range of 4 to 8 mm.

[0070] In the melter, the walls of the melter, preferably the walls (casing) of an extruder, preferably a twin screw extruder, are closed, so that no vacuum is applied in the melter.

[0071] Since there is no equipment capable of extracting gaseous components, the melter preferably has a screw diameter in the range of 70 to 360 mm.

[0072] The ratio (L / d) of the length (L) of the melter (preferably the melting zone when the melter is equivalent to the melting zone) to the diameter (d) of the extruder screw of the melter (preferably the melting zone when the melter is equivalent to the melting zone) is generally 3-10.

[0073] In the melter, components (A1) and (A2) are melted at the temperatures mentioned above, which are measured at the casing of the extruder.

[0074] In step b), components (A1) and (A2) are preferably fed simultaneously to the melt zone of the degasser. Preferably, the components are fed simultaneously to the melt zone of the degasser in particulate form. Component (A2) is preferably fed to the melt zone of the degasser in an amount such that the colored polyoxymethylene copolymer (cPOM) comprises an amount of colorant in the range of 0.01-2% by weight, preferably in the range of 0.01-1.5% by weight, more preferably in the range of 0.05-1.0% by weight, most preferably in the range of 0.1-0.3% by weight (based on the total weight of the colored polyoxymethylene copolymer (cPOM)).

[0075] Preferably, components (A1) and (A2) are fed simultaneously to the melter of the degasser.

[0076] In a preferred embodiment, in the direction of flow, the melter is the foremost part of the degasser. Preferably, the melter of the degasser consists of one melting zone. In general, components (A1) and (A2) are fed to the melting zone via feeds that are not part of the degasser.

[0077] Degasser The degasser generally comprises, in the direction of flow, a first degassing zone, a second degassing zone and optionally a third degassing zone. In a preferred embodiment, the degasser comprises, in the direction of flow, a first degassing zone, a second degassing zone and a third degassing zone.

[0078] Preferably, the degasser of the degasser comprises a first degassing zone, a second degassing zone and a third degassing zone.Accordingly, another object of the present invention is a method for producing a colored polyoxymethylene copolymer, in which the degasser comprises a melter comprising a melting zone and a degasser comprising a first degassing zone, a second degassing zone and a third degassing zone.

[0079] The first degassing zone generally comprises, in the direction of flow, conveying elements, possibly kneading zones, mixing elements and flow restriction elements. For the conveying elements, kneading elements, mixing elements and flow restriction elements in the first degassing zone, the above explanations for the melter (melt zone) apply accordingly. The same applies to the preferred embodiment.

[0080] Thus, the conveying, mixing and flow restricting elements in the first degassing zone are preferably implemented as a twin screw extruder.

[0081] The first degassing zone is preferably implemented as a twin screw extruder. The twin screw extruder of the first degassing zone can be defined by the following parameters:

[0082] The above mentioned parameters d, N and Δ of the first degasser are as follows:

[0083] The diameter (d) of the screw in the first degassing zone is usually in the range of 70 to 360 mm, preferably in the range of 120 to 250 mm, in particular in the range of 150 to 230 mm.

[0084] The rotation speed (N) of the screw in the first degassing zone is, for example, in the range of 80 to 200 rpm, preferably in the range of 110 to 180 rpm, and particularly preferably in the range of 130 to 160 rpm.

[0085] The difference (Δ) in the width of the first degassing zone is usually in the range of 3 to 12 mm, preferably in the range of 4 to 8 mm.

[0086] The ratio (L / d) of the length (L) of the first degassing zone to the diameter (d) of the extruder screw in the first degassing zone is generally 3-15.

[0087] The first degassing zone is operated at a temperature of 155 to 270° C., preferably 160 to 240° C., in particular 170 to 230° C. The first degassing zone is preferably operated at a pressure of 0.1 mbar to 10 bar, preferably 10 mbar to 2 bar, in particular 10 mbar to 1 bar, most in particular 10 mbar to 400 mbar.

[0088] In the context of the present invention, "bar" means absolute pressure (absolute bar). Absolute pressure bar uses an absolute scale and is zero-referenced to a perfect vacuum. Usually, bar is equal to gauge pressure plus atmospheric pressure.

[0089] The first degassing zone of the degasser has a volume of gas phase in the range of 80-20% by volume, preferably 70-30% by volume, more preferably 50-40% by volume. The volume of the gas phase is defined as follows: Volume of gas phase = available volume in the first degassing zone - available melt volume in the first degassing zone.

[0090] In the above formula, the available volume is defined as: Available volume = volume in the casing of the first degassing zone - volume of the elements contained in the first degassing zone (conveying elements, possibly kneading elements, mixing elements and flow restriction elements)

[0091] Preferably, the first degassing zone is implemented as a twin screw extruder as described above. The casing of the twin screw extruder preferably includes one or more degassing openings for applying a vacuum to the first degassing zone. In the first degassing zone, the unstable end groups of the raw polyethylene copolymer (rPOM) are depolymerized. The reaction product of the depolymerized end groups is gaseous and is removed through one or more degassing openings of the first degassing zone.

[0092] Thus, a vacuum is applied to the first degassing zone. In the first degassing zone, at least 50 mol %, more preferably 60 mol %, in particular at least 70 mol % (based on the total molar amount of unstable end groups contained in the untreated polymethylene copolymer (rPOM)) of the unstable end groups are depolymerized and removed. The depolymerized product (formaldehyde) is removed from one or more degassing openings of the first degassing zone. Furthermore, in the first degassing zone, unreacted residual monomers are removed. The unreacted residual monomers include trioxane and formaldehyde.

[0093] The at least partially depolymerized melt is conveyed from the first degassing zone to a second degassing zone.

[0094] The settings of the second degassing zone are essentially the same as those of the first degassing zone. However, the screw design, temperature, pressure, vacuum of the elements may differ. The parameters d, N, Δ and L / d of the second degassing zone are within the ranges defined above for the first degassing zone. These parameters of the second degassing zone can be the same as those of the first degassing zone or can be changed as long as they are within the ranges defined above.

[0095] The volume of the gas phase in the second degassing zone is preferably in the range of 70 to 30% by volume, more preferably in the range of 50 to 30% by volume, where the volume of the gas phase is respectively as defined above for the second degassing zone.

[0096] In the second degassing zone, the remaining unstable end groups are depolymerized and removed through one or more degassing openings.

[0097] Furthermore, in the second degassing zone, unreacted residual monomers are removed through one or more degassing openings. The residual monomers are typically trioxane and formaldehyde, which may further include forms of α-ω-hydroglycols, which may be substituted with cc chains.

[0098] In the second degassing zone, at least 50%, preferably at least 75%, more preferably at least 85%, in particular at least 95% (based on the total amount of unreacted residual monomers contained in the untreated polyoxymethylene copolymer (rPOM)) of the unreacted residual monomers is removed.

[0099] The settings of the third degassing zone are essentially the same as those of the first degassing zone, except for the screw design of the elements, temperature, pressure, vacuum. The parameters d, N, Δ and L / d of the third degassing zone are within the ranges defined above for the first degassing zone. These parameters of the third degassing zone can be the same as those of the first degassing zone or can be changed, as long as these parameters are within the ranges defined above.

[0100] The volume of the gas phase in the third degassing zone is preferably in the range of 30-0 vol.%, preferably in the range of 10-0 vol.%. At the end of the third degassing zone the volume of the gas phase is preferably 0. The volume of the gas phase in the third degassing zone is defined as described above for the first degassing zone.

[0101] In another preferred embodiment, the first degassing zone of the degasser has a volume of gas phase in the range of 80-20% by volume, the second degassing zone of the degasser has a volume of gas phase in the range of 70-30% by volume, and the third degassing zone of the degasser has a volume of gas phase in the range of 30-0% by volume.

[0102] The depolymerized and at least partially degassed melt is preferably conveyed from the second degassing zone to a third degassing zone.

[0103] In the third degassing zone, any remaining residual unreacted monomer is removed through one or more degassing openings.

[0104] A preferred arrangement of the degasser is shown in FIG.

[0105] According to step c), at the end of the third degassing zone, which preferably forms the last part of the degasser (preferably the degasser), the coloured polyoxymethylene copolymer (cPOM) is removed from the degasser.

[0106] In a preferred embodiment, the colored polyoxymethylene copolymer (cPOM) is subsequently granulated. Thus, the colored polyoxymethylene copolymer (cPOM) is preferably fed from the third degassing zone to the granulator. More preferably, the colored polyoxymethylene copolymer (cPOM) is fed from the third degassing zone to a melt pump (preferably a gear pump), then passes through a melt filter and subsequently to the granulator.

[0107] According to step (c), the colored polyoxymethylene copolymer (cPOM) is removed from the degasser, preferably from the third degassing zone of the degasser. Generally, after the third degassing zone, the colored polyoxymethylene copolymer (cPOM) is granulated.

[0108] The granulated colored polyoxymethylene copolymer (cPOM) can be optionally dried and deodorized. The colored polyoxymethylene copolymer (cPOM) is then stored in a silo.

[0109] Another object of the present invention is the colored polyoxymethylene copolymers (cPOM) obtainable by the process of the present invention.

[0110] Colored polyoxymethylene copolymers (cPOM) typically contain 60-99.9% by weight of at least one polyoxymethylene copolymer, 0.01%-2% by weight of at least one colorant, and optionally 0-39.99% by weight of at least one additive selected from the group consisting of antioxidants, formaldehyde scavengers, UV absorbers, release agents, acid scavengers, and nucleating agents.

[0111] Another object of the present invention is the use of the colored polyoxymethylene copolymer (cPOM) obtained by the method of the present invention for the manufacture of molded parts. The use of the present invention leads to molded parts that exhibit a uniform distribution of the colorant, i.e., very bright colors. Furthermore, the use of the present invention leads to molded parts with low formaldehyde emissions. EXAMPLES

[0112] The present invention is illustrated below with reference to examples, but is not limited thereto.

[0113] Analysis method Weight loss N 2 (Weight loss measurement under nitrogen atmosphere) To test the thermal stability, the weight loss at 222°C under N2 is determined, which is the percentage weight loss of a weighed sample of approximately 1.2 g of pellets when heated at 222°C under nitrogen for 2 hours. After cooling, the sample is reweighed and the weight loss is calculated.

[0114] MVR (DIN EN ISO 1133-1:2012-03) Melt volume-flow rate (MVR) is determined by extruding molten material from the plastometer cylinder through a die of specific length and diameter under preset conditions of temperature (190°C) and load (2.16 kg or 10 kg).

[0115] Residual formaldehyde content (GC Headspace Chromatography) Residual formaldehyde content in colored polyoxymethylene copolymer pellets was determined by headspace gas chromatography. A capillary gas chromatograph (GC 7890 B, Agilent) equipped with an autosampler (PAL COMBI-xt, CTC Analytics), a thermal conductivity detector, and a fused silica capillary (polydimethylsiloxane, DB-1, Agilent) using helium as carrier gas was used. 3,00 g of test items were weighed into a 20 ml headspace vial previously filled with argon. The vial was then tightly sealed with a septum cap. The vial was kept at 140 °C for 30 min. A gas volume of 500 μl was then injected using a split ratio of 15:1.

[0116] Oven temperature: 40℃ for 5 minutes; 40℃→200℃, 8K / min; isothermal at 200 °C for 2 min.

[0117] The amount of formaldehyde was calculated based on the detector signal of formaldehyde (peak area in mV) and a calibration curve. The calibration curve was performed by total evaporation of five stock solutions of formaldehyde in ethanol. The formaldehyde content is shown relative to the dry weight of the pellet (µg / g = ppm).

[0118] Formaldehyde Emissions (VDA 275, 1994 edition, July 1, 1994) The preparation of the test pieces (test samples) was carried out as follows: In an injection molding machine (Arburg Allrounder 320M), colored polyoxymethylene copolymer pellets were injected into an injection molding plate (40 × 100 × 2.5 mm 3 The test samples are molded in a PE bag for 1 day before inspection. The injection molding machine is operated with the following parameters: mass temperature: 200°C; tool wall temperature: 90°C; screw diameter: 30 mm; screw speed: 170 (1 / min); injection speed: 50 mm / sec. The test samples are stored in PE bags for 1 day before inspection.

[0119] For the measurement, the test specimens are placed in distilled water in a sealed (closed) 1 L polyethylene bottle and fixed at a constant temperature (60 ° C) for 3 hours. After that, the 1 L polyethylene bottle is cooled and the formaldehyde content in the distilled water is determined as follows. A photometric analysis using the so-called acetylacetone method is used. Thus, formaldehyde is converted into diacetyldihydrolutidine using acetylacetone and ammonium acetate. The concentration of diacetyldihydrolutidine is determined photometrically (the maximum absorption value of diacetyldihydrolutidine is 412 nm).

[0120] Formaldehyde content is expressed in ppm and is calculated by dividing the formaldehyde in mg by the dry weight of the test specimen in kg.

[0121] Molecular weight determination by size exclusion chromatography The molecular weight of the polymer was determined via size exclusion chromatography on a SEC (size exclusion chromatography) apparatus. The SEC apparatus consisted of the following combination of separation columns: a preparatory column of 5 cm length and 8 mm diameter; a second linear column of 30 cm length and 7.5 mm diameter; a third column of 30 cm length and 7.5 mm diameter. The separation material of column 1 was HFIP-LGGuard, while columns 2 and 3 were PL-HFIP gel. The detector used consisted of an Agilent 1100 differential refractometer. A mixture of hexafluoroisopropanol and 0.05% potassium trifluoroacetate was used as the eluent. The flow rate was 1 ml / min and the column temperature was 35° C. 50 microliters of solution (concentration of 1.5 g sample per liter of eluent) was injected. The sample solution was prefiltered through Millipor Millex GF (0.2 micrometer pore width). For calibration, narrowly distributed PMMA standards (with molecular weights M ranging from 800 to 2.2 million g / mol) from PSS (Mainz, DE) were used. The polydispersity index is defined as the weight average molecular weight divided by the number average molecular weight.

[0122] Average Particle Size The volume-based mean particle size (Dv50) (mm) was determined using a Mastersizer3000.

[0123] Residual monomer content (% by weight: based on the total weight of untreated polyoxymethylene copolymer (rPOM)) The residual monomer content of the untreated polyoxymethylene copolymer (rPOM) was determined by extracting 50 g samples in a Soxhlet extractor for 6 hours in chloroform. The chloroform extract was analyzed by gas chromatography using a flame ionization detection (FID). The content of formaldehyde, 1,3,5-trioxane, and 1,3-dioxolane was determined by utilizing a calibration curve using the corresponding standard samples. The residual monomer content in mass % shown in Table 1 is the sum of formaldehyde, 1,3,5-trioxane, and 1,3-dioxolane relative to the total mass of the untreated polyoxymethylene copolymer (rPOM).

[0124] Carbon black content (%) The carbon black content was determined according to DIN EN ISO 3451-1:2008 by incineration of 3.0 g samples at 625° C. for 9 min. The carbon black content in % is calculated based on the measured residue after incineration relative to the sample amount x 100.

[0125] Molding of black test specimens for measuring gloss and color The test pieces (test samples) were prepared as follows: In an injection molding machine (Arburg Allrounder 320M), colored polyoxymethylene copolymer pellets were placed in an injection molding plate (60 x 60 x 2 mm 3 , cold runner, 2-cavity). The injection molding machine operates with the following parameters: mass temperature: 200 °C; tool wall temperature: 90 °C; thread diameter: 30 mm; screw speed: 100 (1 / min); injection speed: 90 mm / s.

[0126] Molded plaque gloss The gloss of black molded plaques was measured according to ISO 2813:2014 (= DIN EN ISO 2813:2015) using a "Byk-Gardner Haze-Gloss" instrument. By using the reflectance measurement mode, the determined gloss values ​​at the sample surface are correlated with the visual gloss impression. The gloss of a sample is determined by the ratio of the gloss of the sample to a polished black glass plate with a fixed refractive index (1.567 at 587.6 nm wavelength) x 100. The measurement angle is 60°, which is suitable for semi-glossy surfaces such as injection molded plaques.

[0127] Molding plaque color The color of the molded plaques was determined according to DIN 53236:2018, which describes the measurement and evaluation conditions for determining color differences in plastics. The color coordinates X, Y, Z of the test specimens are measured and transferred to the CIE 1976 L*a*b* color space, which is specified in ISO 11664-4:2008. The color coordinates were measured using method B of DIN 53236 with a Byk-Gardner spectrophotometer Color-View and a backed white standard test specimen in daylight D65-10 with measurement geometry R45 / 0.

[0128] Additives and chemicals used -Irganox 245 FF / Ethylenebis(oxyethylene)bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)-propionate) (CAS number 36443-68-2), BASF SE; -Synthetic magnesium silicate (CAS number 1343-88-0), PQ Corporation; -Talc (CAS number 14807-96-6): hydrous magnesium silicate, Mondo Minerals BV; -EBS / N, N'-ethylene distearamide (CAS number 110-30-5), Lonza Ltd.; -BF3xOEt2, boron trifluoride-diethyl ether, BASF SE; -Triisopropanolamine (CAS number 122-20-3), assayed by GC >99%, BASF SE; -Methylal, assayed by GC >99%, Lambiotte Cie sa; -Calcium hydroxide (assay >90%) and ethyl acetate (assay >99% by GC), purchased from a chemical distributor.

[0129] Preparation of untreated polyoxymethylene copolymer (rPOM) [Component (A1)] For the preparation of the raw polyoxymethylene copolymer, 96.5% by weight of 1,3,5-trioxane and 3.5% by weight of 1,3-dioxolane (based on the total amount of monomers used) were used. As a solvent, 1% by weight of ethyl acetate based on 1,3,5-trioxane was used. The polymerization was initiated using 85 ppm of BF3OEt2 based on 1,3,5-trioxane, and dimethoxymethane was used as a molecular weight regulator. The polymerization was carried out in a kneader reactor with a polymerization temperature profile of 60-80 °C. The polymerization was stopped by adding 400 ppm of tri-iso-propanolamine based on 1,3,5-trioxane as a 10% by weight solution in ethyl acetate at the outlet of the reactor. The raw POM was ground and transported with nitrogen to a storage vessel. The rPOM had the following properties:

[0130] [Table 1]

[0131] To the untreated polyoxymethylene copolymer (rPOM) of Table 1, the following additives (for 105 parts of rPOM) were added and mixed uniformly: 0.01 parts Ca(OH)2; 0.35 parts Irganox 245 FF; 0.15 parts N,N'-ethylene distearamid; 0.05 parts talc; and 0.05 parts synthetic magnesium silicate.

[0132] Coloring agent [Component (A2)] Component (A2) was used as a carbon black masterbatch, and the pellet shape was limited (size: 2-3 mm). The carbon black masterbatch was a 79.92% by mass polyoxymethylene copolymer (MVR=25 cm 3 A2 was produced by melt compounding in a twin-screw extruder (ZS60MAXX; conditions: barrel temperature 165-220°C, screw speed 400 rpm, total throughput 400 kg / h) of 20.0% by weight of 100% propylene glycol (A2b) / 10 min, according to ISO 1133 (190°C / 2.16 kg) with 20.0% by weight of carbon black beads and 0.08% by weight of potassium carbonate. The polymer melt leaving the twin-screw extruder was pelletized using a water ring pelletizer device. In the final step, the pellets were heated at 120°C for 4 hours with hot air as a deodorizing means to obtain a final product with low levels of residual volatile components (especially formaldehyde). Carbon black, PRINTEX® F80 beads (A2b), and PRINTEX® 90 beads (A2a) were purchased from Orion.

[0133] [Table 2]

[0134] Preparation of colored polyoxymethylene copolymers (cPOM) Examples 1 to 4 of the present invention Untreated polyoxymethylene copolymer with additives (rPOM; component (A1)) was added at a feed rate of 2000 kg / h, and colorant (A2) was added at a feed rate of 20 kg / h in barrel C1 (total L / D=56, screw diameter d=96 mm) of a twin-screw extruder from JSW. The twin-screw extruder consisted of the following defined zones, as shown in Table 3. In the first, second and third degassing zones a vacuum (p=40 mbar) was applied.

[0135] [Table 3]

[0136] The polymer melt leaving the twin screw extruder was pelletized using a water ring pelletizer device. In a final step, the pellets were heated with hot air at 140°C for 6 hours as a deodorizing means to obtain a final product with low levels of residual volatile components (especially formaldehyde).

[0137] [Table 4]

[0138] Comparative examples 1a, 2a, 3a, 4a Comparative Examples 1a, 2a, 3a, 4a were prepared by secondary compounding of finished uncolored polyoxymethylene copolymer with colorant (A2) in a twin screw extruder.

[0139] Preparation of finished uncolored polyoxymethylene copolymer: In a first step, uncolored polyoxymethylene copolymers were prepared under the same conditions as A1a / Example 1 (POM UN(1)) and A1b / Example 3 (POM UN(3)), except that no colorant (A2) was added. The properties obtained are shown in Table 5.

[0140] [Table 5]

[0141] In the second step, 99% by weight of POM UN was melt-kneaded together with 1.0% by weight of colorant (A2) in a twin-screw extruder (type ZSK90) under conditions (barrel temperature of 140-210°C, screw speed of 150 rpm, total throughput of 350 kg / hr). The molten polymer leaving the twin-screw extruder was pelletized using a water ring pelletizer device. In the final step, the pellets were heated at 120°C for 4 hours by hot air as a deodorizing means to obtain a final product with low levels of residual volatile components (especially formaldehyde). The resulting material had the properties as shown in Table 6.

[0142] [Table 6]

[0143] Comparative examples 1b, 2b, 3b, 4b Comparative Examples 1b, 2b, 3b, 4b were produced by self-coloring the finished uncolored polyoxymethylene copolymer from Table 5 with colorant (A2) in an injection molding machine. Thus, homogeneous dry blend pellet mixtures of 99% by weight POM UN and 1.0% by weight component (A2) were prepared, as summarized in Table 7.

[0144] [Table 7]

[0145] Table 8 shows the final properties of the molded parts of Examples 1 to 4 of the present invention, Comparative Examples 1a to 4a, and Comparative Examples 1b to 4b.

[0146] [Table 8]

[0147] The examples based on pigmented rPOM exhibit lower L values ​​and higher gloss values ​​compared to Comparative Examples 1a-4a and 1b-4b. Thus, the examples based on pigmented rPOM exhibit a deeper, more vibrant black color compared to Comparative Examples 1a-4a and 1b-4b. Additionally, the examples of the present invention based on pigmented rPOM exhibit low levels of formaldehyde emissions.

[0148] As a result, the method of the present invention provides a simple and cost-effective method for producing colored polyoxymethylene copolymers. Moreover, molded articles obtained from the colored polyoxymethylene copolymers have low formaldehyde emissions and exhibit excellent deep, vivid black color.

Claims

1. a) providing component (A1) and component (A2), where component (A1) comprises an untreated polyoxymethylene copolymer in particulate form, the untreated polyoxymethylene copolymer comprising a polyoxymethylene copolymer and 2 to 30 weight percent unreacted residual monomer (based on the total weight of the untreated polyoxymethylene copolymer), and component (A2) comprises a colorant in particulate form; b) simultaneously feeding components (A1) and (A2) to a degasser, in which the untreated polyoxymethylene copolymer is melted and mixed with component (A2), thereby at least partially removing the unreacted residual monomers from the untreated polyoxymethylene copolymer to obtain a colored polyoxymethylene copolymer; c) removing the colored polyoxymethylene copolymer from the degasser, the degasser comprising a melter consisting of a melting zone and a degasser consisting of a first degassing zone, a second degassing zone and a third degassing zone, the degasser operating at a temperature of 155-270° C. and a pressure of 0.1 mbar to 10 bar; A method for producing a colored polyoxymethylene copolymer, comprising:

2. 2. The process of claim 1, wherein said components (A1) and (A2) are fed simultaneously to the melter of said degasser.

3. 3. The method according to claim 1 or 2, wherein in the direction of flow, the melter is the foremost part of the degasser.

4. The method according to any of claims 1 to 3, wherein at least said degasser is implemented as a twin screw extruder.

5. The process according to any one of claims 1 to 4, wherein the melter is also implemented as a twin screw extruder.

6. 6. The method according to claim 1, wherein the first degassing zone of the degasser has a volume of gas phase in the range of 80 to 20% by volume, the second degassing zone of the degasser has a volume of gas phase in the range of 70 to 30% by volume, and the third degassing zone of the degasser has a volume of gas phase in the range of 30 to 0% by volume.

7. The method according to any one of claims 1 to 6, wherein the melter operates at a temperature of 130 to 220°C without the application of a vacuum.

8. The method according to any of the preceding claims, wherein the degasser operates at a temperature between 160 and 240°C and a pressure between 10 mbar and 2 bar.

9. The method according to any one of claims 1 to 8, wherein the colorant is at least one black colorant selected from the group consisting of carbon black, activated carbon, carbon nanotubes, graphene black, black organic pigments, and black organic dyes.

10. The polyoxymethylene copolymer is at least 50 mol % -CH ２ O-repeat units and up to 50 mol % of formula (I): 【Chemistry 1】 (In the formula, R １ ~R ４ are each independently a hydrogen atom, C １ ~C ４ an alkyl group or an alkoxy-substituted alkyl group having 1 to 4 carbon atoms, R ５ is -CH ２ --, --CH ２ O-, C １ ~C ４ Alkyl or C １ ~C ４ a methylene group substituted with alkoxy or the corresponding oxymethylene group, and n is 0 to 3. The method according to any one of claims 1 to 9, comprising a repeating unit represented by the formula:

11. 11. The method according to any one of claims 1 to 10, wherein the unreacted residual monomers are trioxane, formaldehyde and / or formals of α-ω-hydroxyglycols, optionally substituted with a C-C chain.

12. A coloured polyoxymethylene copolymer obtainable by the process according to any one of claims 1 to 11.

13. 13. Use of the colored polyoxymethylene copolymer according to claim 12 for producing molded parts.

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