Method for the production of thermally stable polyoxymethylene copolymers with low formaldehyde emission

Abstract

The present invention relates to a method for obtaining polyoxymethylene copolymers (cPOM) with stable Melt volume-flow rate (MVR) and low formaldehyde emission levels by providing thermal stability and shear stress stability through the addition of a hydroxylamine compound to a crude cPOM comprising an acidic catalyst. Moreover, the present invention relates to a method to produce a polymer molding composition comprising a polyoxymethylene copolymer (cPOM).

Description

[0001] 240992

[0002] Method for the production of thermally stable polyoxymethylene copolymers with low formaldehyde emission

[0003] Field of the invention

[0004] The present invention relates to a method for obtaining polyoxymethylene copolymers (cPOM) with stable Melt volume-flow rate (MVR) and low formaldehyde emission levels by providing thermal stability and shear stress stability through the addition of a hydroxylamine compound to a crude cPOM comprising an acidic catalyst.

[0005] Moreover, the present invention relates to a method to produce a polymer molding composition comprising a polyoxymethylene copolymer (cPOM).

[0006] Background

[0007] Polyoxymethylene copolymers are known for a long time. These polymers have a number of outstanding properties so that they are suitable for a wide variety of industrial applications. Polyoxymethylene copolymers are engineering thermoplastics and are used in various applications of transportation, electrics, electronics and consumer industries. Polyoxymethylene copolymers are also known as acetal resins, polyacetals and polyformaldehydes. To produce polyoxymethylene copolymers, formaldehyde is generally converted to its cyclic oligomer, preferably to 1 ,3,5-trioxane. Polyoxymethylene copolymers can be obtained by the polymerization of the cyclic oligomers of formaldehyde, preferably 1 ,3,5-trioxane, and the comonomer / s in the presence of an acid catalyst. The polymerization can be carried out as a bulk polymerization, for example in a melt kneader. After the polymerization reaction, raw polyoxymethylene copolymer is obtained which still contains the acid catalyst. If the acid catalyst remains in the polyoxymethylene copolymer, it can catalyze the depolymerization reaction of the polyoxymethylene copolymer to formaldehyde which leads to an unstable polyoxymethylene copolymer with very limited usability.

[0008] Therefore, after the polymerization, the acid catalyst typically is deactivated and the raw polyoxymethylene copolymer is typically further stabilized by the removal of residual monomers and the removal of unstable end groups in order to obtain the finished polyoxymethylene copolymer.

[0009] For the deactivation of the acid catalyst contained in the raw polyoxymethylene copolymer, normally a deactivation agent is added to the raw polyoxymethylene copolymer. As a deactivation agent, generally basic compounds like (functional) amines are used. The basic compound which is used as a deactivation240992

[0010] 2

[0011] agent generally forms an acid-base product, in other words, a complex of the acid catalyst and the basic compound that remains in the polymer matrix of the polyoxymethylene copolymer.

[0012] The methods to produce polyoxymethylene copolymers and the deactivation agents used in the state of the art, however, lead to finished polyoxymethylene copolymers which in most cases show insufficient stability. Moreover, in some cases, the polyoxymethylene copolymers obtained by the production methods described in the state-of-the-art show formaldehyde emissions which are too high.

[0013] Therefore, a stabilization process is performed. The stabilization process is mainly carried out using a degassing extruder. The principle of stabilization involves applying shear stress to the polymer melt in a degassing extruder, which generates heat to remove unstable chain ends and removes formaldehyde set free by thermal decomposition of the instable end groups.

[0014] The German patent application DE 19633708 discloses a method to produce polyoxymethylene copolymers, wherein the acid catalyst is deactivated with ammonia, trimethylamine, dimethylamine or triethylamine.

[0015] The US patent US 7,893,140 discloses a method to produce polyoxymethylene copolymers, wherein the acid catalyst is deactivated with triethylamine, tributylamine, triethanolamine or tri butanol amine.

[0016] However, the high shear stress and elevated temperature during a stabilization process in a degassing extruder even in the absence of an active acidic catalyst still can induce cleavage of polymer chains, leading to a decrease in molecular weight, corresponding to a decrease in melt viscosity, which might lead to an explicit alteration of the mechanical properties of a molded polymer article.

[0017] Generally, to prevent melt viscosity loss, the person skilled in the art will try to compensate these adverse effects by reducing shear stress, by reducing the polymer processing temperature or residence time in the degassing process, but this may result in inefficient removal of residual formaldehyde. Consequently, the produced POM exhibits high formaldehyde emissions, rendering it unsuitable for use in interior materials, or other odor sensitive applications.

[0018] Therefore, the underlying objective of the present invention is to produce polyoxymethylene copolymers under conditions of high shear stress, high processing temperature, and sufficient degassing time without suffering from the disadvantages mentioned in the prior art. In particular, the method should lead to polyoxymethylene copolymers showing an improved thermal and hydrolytic stability, lower formaldehyde emission, good color as well as good mechanical properties, being appropriate for interior or other odor sensitive applications.240992

[0019] 3

[0020] Detailed Description of the Invention

[0021] In a first aspect, the present invention relates to a method for producing polyoxymethylene copolymers comprising the steps of:

[0022] A. adding a catalyst deactivator to a first mixture (M1) comprising a polyoxymethylene copolymer and an acidic catalyst to obtain a second mixture (M2), wherein the catalyst deactivator is an alkanolamine; and

[0023] B. performing a melt degassing, wherein the second mixture (M2) is brought in contact with a hydroxylamine thereby obtaining the third mixture (M3).

[0024] It has surprisingly been found that the addition of hydroxylamine compounds can improve the properties of a finished polyoxymethylene copolymer (cPOM), especially with respect to its thermal and hydrolytic stability, lower formaldehyde emission and low migration of the deactivation agent to meet specific migration limits as set out for example in the Commission Regulation (EU) No 10 / 201 l and, therefore, especially enabling its use for use in interior materials, or other odor sensitive applications, even for applications demanding contact to food or drinking water.

[0025] In step A, a first mixture (M1) is provided, comprising the polyoxymethylene copolymer (cPOM) and the acid catalyst, which is deactivated with a specified amount of an alkanolamine.

[0026] Alkanolamines are also known as amino alcohols. Alkanolamines are organic compounds that contain both hydroxyl (-OH) and amino (-NH2, -NHR, and -NR2) functional groups on a hydrocarbon backbone.

[0027] Alkanolamines may be primary amines, secondary amines or tertiary amines comprising at least one hydroxyl group. Non limiting examples for may be triisopropanolamine, N-methyl diethanolamine, aminoethoxyethanol, monoisopropylamine, diethanolamine, ethanolamine, triethanolamine, diisopropanolamine, N,N-dimethylethanolamine N,N-diethylethanolamine.

[0028] According to a further embodiment, the catalyst deactivator is alkanolamine. In a certain embodiment, alkanolamine is added to the first mixture (M1) to deactivate the acid catalyst and in orderto obtain a second mixture (M2) comprising the polyoxymethylene copolymer (cPOM), a complex of the acid catalyst and alkanolamine.240992

[0029] 4

[0030] The alkanolamine can be added in pure form or in form of a solution which comprises the alkanolamine and an organic solvent. Preferably, the alkanolamine in step a) is added to the first mixture in form of a solution which comprises the alkanolamine and an organic solvent. Suitable organic solvents are for example cyclohexane, methanol, ethanol, acetone, methylethylketone, ethyl acetate or benzene, wherein benzene and ethyl acetate are preferred. Ethyl acetate is most preferred.

[0031] If the alkanolamine is added in form of a solution, the concentration of the alkanolamine is typically in the range of 1 to 50 % by weight, preferably in the range of 5 to 60 % by weight, more preferably in the range of 2 to 30 % by weight, and particularly preferred in the range of 3 to 10 % by weight, based on the total weight of the solution which comprises the alkanolamine and the organic solvent.

[0032] Moreover, in step A., in another embodiment, the alkanolamine may be added in a mixture with at least one other deactivation agent selected from the group consisting of ammonia, triethylamine, tri-n-butylamine and triethanolamine. However, in a preferred embodiment, in step B. alkanolamine is the only deactivation agent added.

[0033] In step A., preferably the alkanolamine is added in a molar excess in view of the acid catalyst contained in the first mixture (M1) from 25:1 to 1 :1, more preferably from 10:1 to 1.1 :1 and particularly preferred from 5:1 to 1.2:1.

[0034] In step A., the second mixture (M2) is obtained, comprising the polyoxymethylene copolymer (cPOM) and the complex of the acid catalyst and alkanolamine.

[0035] In one embodiment, the alkanolamine is a tertiary trialkanol amine.

[0036] In a further embodiment, the alkanolamine is selected from the group consisting of N,N-diethyl-ethanolamine, N-methyl-N-ethylethanolamine, N-ethyl-N-isopropylethanolamine, N-methyl-N-isopropylethanolamine, N-ethyl-N-butylethanolamine, N-methyl-N-butylethanolamine, N-ethyl-N-propylethanolamine, N-methyl-N-propylethanolamine, N-ethyl-N-methylpropanolamine, N-methyl-N-ethylpropanolamine and triisopropanolamine.

[0037] In a certain embodiment, the alkanolamine is triisopropanolamine.

[0038] Polyoxymethylene copolymers (cPOMs) are known perse. They are preferably prepared by polymerization of trioxane (as a monomer) and one or more comonomers. In general, the polyoxymethylene copolymer (cPOM) contained in the first mixture (M1) comprises from 60 to 99.99 mol-% of -CH2O- recurring units and from 0.01 to 40 mol-% of recurring units according to formula (I)240992

[0039] 5

[0040] R2R3

[0041] -O-C— c— (R )n—

[0042] R R(I),

[0043] where R1to R4are each, independently of one another, a hydrogen atom, a Ci-C alkyl group or a alkoxysubstituted alkyl group having from 1 to 4 carbon atoms, and R5is a chemical bond, a -CH2-, -OCH2-, a Ci-C4-alkyl- or Ci-C4-alkoxy-substituted methylene group or a corresponding polyoxymethylene group, and n is from 0 to 3, wherein the mol-% of the -CH2O- recurring units and the mol-% of the recurring units according to formula (I) are based on the total number of mols of recurring units contained in the polyoxymethylene copolymer (cPOM).

[0044] Preferably, the polyoxymethylene copolymer (cPOM) comprises 60 to 99.99 mol-%, more preferably 80 to 99.95 mol-%, even more preferably 90 to 99.9 mol-% and particularly preferred 94 to 99.5 mol-% of -CH2O- recurring units. Preferably, the polyoxymethylene copolymer (cPOM) comprises 0.01 to 40 mol-%, more preferably 0.05 to 20 mol-%, even more preferably 0.1 to 10 mol-%, and particularly preferred 0,5 to 6 mol-% of recurring units according to formula (I), wherein the mol-% in each case are based on the total number of mols of recurring units comprised in the polyoxymethylene copolymer (cPOM).

[0045] Therefore, in one embodiment of the present invention the polyoxymethylene copolymer (cPOM) comprises from 60 to 99.99 mol% of -CH2O- recurring units and from 0.01 to 40 mol% of recurring units according to formula (I)

[0046] R2 3

[0047] -O-C— C-(R5). —

[0048] R R(I)

[0049] where R1to R4are each, independently of one another, a hydrogen atom, a Ci-C4-alkyl group or an alkoxysubstituted alkyl group having from 1 to 4 carbon atoms and R5is a chemical bond, a -CH2-, -OCH2-, a Ci-C4-alkyl- or Ci-C4-alkoxy-substituted methylene group or a corresponding polyoxymethylene group and n is from 0 to 3.

[0050] The -CH2O- recurring units are generally introduced into the polyoxymethylene copolymer (cPOM) by a polymerization of at least one main monomer selected from the group of cyclic formals (cyclic oligomers of formaldehyde), wherein 1 ,3,5-trioxane is particularly preferred.240992

[0051] 6

[0052] The recurring units according to formula (I) can advantageously be introduced into the polyoxymethylene copolymer (cPOM) by ring-opening polymerization of at least one first comonomer selected from the group of those of the formula (II)

[0053] R2

[0054] R1— C— O

[0055] R3— C— (R5)n

[0056] R4CD

[0057] where R1to R5and n are as defined above for formula (I).

[0058] Preferably, the at least one first comonomer is selected from the group consisting of ethylene oxide, 1 ,2-propylene oxide, 1,2-butylene oxide, 1 ,3-butylene oxide, 1,3-dioxane, 1,3-dioxolane and 1,3-dioxepane, wherein 1,3-dioxolane is particularly preferred.

[0059] Optionally, the polyoxymethylene copolymer (cPOM) can comprise recurring units derived from at least one second comonomer. The second comonomer is preferably selected from the group consisting of cyclic ethers of the formula (III), or of acetals of the formula (IV)

[0060]

[0061] where Z is a chemical bond, -O-, -ORO- (R is Ci-Cs-alkylene or Cs-Cs-cycloalkylene), linear oligoformals and polyformals. Preferred second comonomers are selected from the group consisting of ethylene diglycide, diglycidyl ether and diethers derived from glycidyls and formaldehyde, dioxane or trioxane in a molar ratio of 2:1 and also diethers derived from 2 mol of a glycidyl compound and 1 mol of an aliphatic diol having from 2 to 8 carbon atoms, for example the diglycidyl ethers of ethylene glycol, 1 ,4-butanediol, 1,3-butanediol, cyclobutane-1 ,3-diol, 1 ,2-propanediol, 1,3-propanediol, cyclohexane-1,4-diol.240992

[0062] 7

[0063] If at least one second monomer is used, the at least second monomer is preferably used in such amounts that the recurring units derived therefrom are contained in the polyoxymethylene copolymer (cPOM) in amounts of 0.001 to 5%, preferably from 0.01 to 2%, wherein the mol-% in each case are based on the total number of mols of recurring units comprised in the polyoxymethylene copolymer -(cPOM).

[0064] The molecular weight of the cPOM is adapted to the needed melt viscosity of the resulting product using at least one chain transfer agent (CTA). As CTA, linear oligoformals like dimethoxymethane, diethoxymethane or dibutoxymethane can be used. Dimethoxymethane (CH3OCH2OCH3) is the preferred CTA.

[0065] The melting point of the polyoxymethylene copolymer (cPOM) contained in the first mixture (M1) is preferably in the range of from 150 to 200°C, more preferably the melting point is in the range of from 160 to 180°C. The melting point of the cPOM is determined with a heating and cooling rate of 20 K / Min according to DIN EN ISO 11357-3 (year 2018-07) and a sample weight of about 8.5 mg.

[0066] The molecular weight of the polyoxymethylene copolymer (cPOM) contained in the first mixture (M1) (weight-average Mw; determined as described below) can be adjusted within a wide range. The molecular weight Mwis preferably in the range of from 10000 to 240000 g / mol ± 10%, while the number-average molecular weight Mn(determined as described below) is preferably in the range of from 8 000 to 85000 g / mol. Preferably, the polyoxymethylene copolymer (cPOM) contained in the first mixture (M1) has a molecular weight (Mw) in the range of from 80 000 to 220 000 g / mol ± 10%, while its molecular weight (Mn) is preferably in the range of from 9000 to 38 000 g / mol. The Mw / Mn ratio (Polydispersity Index) of the polyoxymethylene copolymer (cPOM) contained in the first mixture (M1) is preferably in the range of from 1.4 to 14, the Mw / Mn is more preferably in the range of from 2.1 to 14.

[0067] The molecular weight of the polymers was determined via size-exclusion chromatography in a SEC apparatus (size exclusion chromatography). This SEC apparatus was composed of the following combination of separating columns: a preliminary column of length 5 cm and diameter 7.8 mm, and two linear columns (length 30 cm and diameter of 7.8 mm). The separating material in each column was PL-HFIP gel from Polymer Laboratories. The detector used comprised a differential refractometer from Agilent 1100. A mixture composed of hexafluoroisopropanol with 0.05% of potassium trifluoro acetate was used as eluent. The flow rate was 1 ml / min, the column temperature being 35 degrees C. 50 microliters of a solution of 3 g sample per liter of eluent were injected. This specimen solution had been filtered in advance through a Millipor Millex FG (pore width 0.2 micrometers). Narrowly distributed PMMA standards from PSS (Mainz, DE) with molecular weight M from 800 to 2.220.000 g / mol were used for calibration. Polydispersity index is defined as the weight average molecular weight divided by the number average molecular weight.240992

[0068] 8

[0069] The molecular weight distribution of the polyoxymethylene copolymer (cPOM) contained in the first mixture (M1) may be monomodal or essentially monomodal. It may also have a multimodal molecular weight distribution. It may be possible that cPOM has a bimodal molecular weight distribution.

[0070] In step A., the first mixture (M1) is provided which comprises the polyoxymethylene copolymer (cPOM) and the acid catalyst. The term “acid catalyst” in the present invention is understood to mean exactly one acid catalyst and mixtures of two or more acid catalysts. Preferably, the first mixture (M1) comprises one acid catalyst. The term “acid catalyst” in the present invention, moreover, is understood to comprise the acid catalyst itself as well as catalytic active transformation products of the acid catalyst.

[0071] The acid catalyst may preferably be at least one, e.g. two, more preferred one halide of boron, tin, titanium, phosphorous, antimony or arsenic. Thereby it may be preferred that the halide is a chloride or fluoride or that the halide contains both. Examples thereof are boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentafluoride, phosphorous pentachloride, antimony pentafluoride and arsenic pentafluoride, and especially also their complex compounds.

[0072] The acid catalyst may preferably be at least one halide of boron, in particular boron trifluoride, e.g. boron trifluoro hydrate, or at least one, more preferred one coordination compound of boron halide and at least one, more preferred one organic compound comprising at least one oxygen or sulfur atom or both. Thereby it may be more preferred that the organic compound comprises only at least one, in particular one oxygen atom. Said organic compound to form a coordination compound of boron halide may for instance be an alcohol, ether or sulfide.

[0073] Preferably the acid catalyst is selected form the group consisting of boron halide in coordination with an ether, in particular an alkyl ether, such as a Ci to C4 alkyl ether may be most preferred. The coordination compound of boron trifluoride with an ether, in particular a dialkyl ether, such as a Ci to C4 dialkyl ether, may be most preferred, in particular inter alia, boron trifluoride dibutyl etherate, boron trifluoride diethyl etherate or boron trifluoride dimethyl etherate or a mixture thereof. Boron trifluoride diethyletherate may most preferably be used.

[0074] According to another embodiment, the acid catalyst is at least one acid catalyst selected from the group consisting of boron trifluoride, a coordination complex of boron trifluoride with water, a coordination complex of boron trifluoride with a dialkylether and catalytic active transformation product of the aforementioned acid catalysts.

[0075] In a particularly preferred embodiment, the first mixture (M1) comprises boron trifluoride diethyletherate as an acid catalyst.240992

[0076] 9

[0077] The amount of the acid catalyst in the first mixture (M1) is not specifically limited. Typically, the amount of the acid catalyst in the first mixture (M1) is from 10 to 150 ppm, preferably from 20 to 140 ppm, more preferably from 30 to 130 ppm, and in particular preferred from 40 to 100 ppm, in each case based on the total weight of the main monomers and comonomers, preferably based on the total weight of the first mixture. Lower amounts may lead to slower reaction initiation, and higher amounts usually do not lead to a faster reaction.

[0078] In a preferred embodiment, the provision of the first mixture (M1) in step a) comprises step a1 ), namely the polymerization of at least one main monomer selected from the group of cyclic formals, preferably 1 ,3,5-trioxane, and at least one first comonomer selected from the group of those of formula (II) and, optionally, at least one second comonomer in presence of the acid catalyst.

[0079] According to another embodiment, step A. comprises the step:

[0080] A1 ) polymerization of at least one main monomer selected form the group of cyclic formals, and at least one first comonomer selected from the group of those of the formula (II)

[0081]

[0082] <

[0083] where R1to R5and n are as defined above, and optionally at least one second comonomer, in the presence of the acid catalyst, to provide the first mixture (M1) comprising the polyoxymethylene copolymer (cPOM) and the acid catalyst.

[0084] Generally, the polymerization in step AI) can be carried out using diverse methods. Such methods are known to the person skilled in the art or are accessible to him by application of his general knowledge. It is preferred that the first mixture (M1) is produced via cationic polymerization. During cationic polymerization, the polyoxymethylene copolymer (cPOM) can be formed in bulk (i.e. without or essentially without solvent).

[0085] The polymerization may be carried out at temperatures, pressures and in equipment generally known to the person skilled in the art or accessible to him by application of his general knowledge. For instance, it may be performed in an extruder or a cascade of two or more extruders such as of twin-screw type, such as of the self-cleaning type. It may also be possible to carry out the process disclosed herein in a kneader or a cascade of two or more kneaders, such as of the self-cleaning type. Generally, it may be advantageous to240992

[0086] 10

[0087] carry out the polymerization at temperatures as low as possible to avoid waste of energy and at temperatures high enough to sustain the polymerization and to ensure good blending, in particular by way of sustaining the at least one monomer and, if present, also the at least one comonomer in the liquid state. Thus, it may be preferred to carry out the polymerization at a temperature of from 50 to 150 °C, whereby temperatures of from 60 to 120°C may be more preferred. Thereby the temperatures refer to the temperature in the bulk.

[0088] In one embodiment, the first mixture (M1) can further contain unreacted residual monomers in amounts from 2 to 30% by weight. The unreacted residual monomers are typically selected from the above-mentioned main monomers, the comonomers and formaldehyde.

[0089] In a preferred embodiment, the first mixture (M1) comprises:

[0090] 70 to 98% by weight of polyoxymethylene copolymer (cPOM),

[0091] 2 to 30% by weight of unreacted residual monomers, and

[0092] 10 to 150 ppm acid catalyst,

[0093] based on the total weight of the first mixture (M1).

[0094] For the polyoxymethylene copolymer (cPOM) and the further optionally contained components like, for example, the unreacted residual monomers, the aforementioned descriptions and preferences apply analogously.

[0095] In step B., a melt degassing is performed, wherein the second mixture (M2) is brought in contact with a hydroxylamine thereby obtaining a third mixture (M3).

[0096] In general, the degassing is carried out using a degassing extruder. The principle of degassing involves applying shear stress to the polymer melt in a degassing extruder, which generates heat to remove unstable chain ends and removes formaldehyde set free by thermal decomposition of the instable end groups.

[0097] The addition of a hydroxylamine to the crude polyoxymethylene copolymer mixture (M2) leads to polyoxymethylene copolymers showing an improved thermal and hydrolytic stability, lower formaldehyde emission, good color as well as good mechanical properties, being appropriate for interior or other odor sensitive applications.

[0098] Moreover, the crude polyoxymethylene copolymer mixture (M2) can be processed under conditions of high shear stress and high temperature without the final product suffering from high formaldehyde emission and240992

[0099] 11

[0100] decreased thermal stability. This allows a reducing of the degassing time without suffering from the disadvantages as explained above and in the prior art cited.

[0101] Due to these advantages, the addition of a hydroxylamine leads to a more time efficient and thus an improved process for producing a polyoxymethylene copolymer. In addition, the polyoxymethylene copolymer derived from said process has improved properties, especially lower formaldehyde emission as well as an improved thermal and hydrolytic stability.

[0102] According to any embodiment, the hydroxylamine is represented by general formula (V)

[0103] K?1

[0104] HO — N

[0105] R(V)

[0106] wherein R1and R2each independently represents a hydrogen atom or a C1-C40 hydrocarbon group.

[0107] In one embodiment, R1and R2each independently represents a hydrogen atom or alkyl-substituted C1-C40 hydrocarbon group. In a further embodiment, R1and R2each independently represents an alkyl-substituted C10-C40 hydrocarbon group. In a certain embodiment, R1and R2each independently represents a C10-C40 alkyl group.

[0108] In another embodiment, R1and R2each independently represents a hydrogen atom or alkyl-substituted C10-C30 hydrocarbon group. In a further embodiment, R1and R2each independently represents an alkyl-substituted C10-C30 hydrocarbon group. In a certain embodiment, R1and R2each independently represents a C10-C30 alkyl group.

[0109] In a further embodiment, R1and R2each independently represents a hydrogen atom ora C14-C24 alkyl group. In yet a further embodiment, R1and R2each independently represent a linear C14-C24 alkyl group. In a certain embodiment, R1and R2each independently represents a linear C16-C21 alkyl group. In another certain embodiment, R1and R2each independently represents a linear C14-C18 alkyl group. In a particular embodiment, R1and R2each independently represents a linear C16-C18 alkyl group.

[0110] According to any embodiment, a composition comprising one or more hydroxylamines is added in step B. In other words, the hydroxylamine is a composition comprising one or more hydroxylamines. In one embodiment, the hydroxylamine is a composition comprising a plurality of hydroxylamines.

[0111] According to a further embodiment, R1and R2are the alkyl mixture found in dehydrogenated tallow)amine. It is clear that the dehydrogenated tallow)amine originating from animal sources may well vary somewhat in240992

[0112] 12

[0113] the specific distribution of alkyl substituents, but the dehydrogenated tallow)amine contains major amounts of N,N-dihexadecylamine, N,N-dioctadecylamine and N-hexadecyl-N-octadecylamine. The individual components of the mixture can be separated by distillation under high vacuum.

[0114] In a certain embodiment, the hydroxylamine is the mixture of hydroxylamines having the CAS No 143925-92-2 bis(hydrogenated tallow C16-18-alkyl)hydroxylamine.

[0115] In one embodiment, the hydroxylamine is obtained by adding to step b) an amine-oxide represented by general formula (VI):

[0116]

[0117] wherein R1and R2are as defined for formula (V) and wherein R3is a C1-C10 hydrocarbon group.

[0118] In a further embodiment, R3is a C1-C5 alkyl group.

[0119] In a certain embodiment, R3is selected from methyl, ethyl, propyl, iso-propyl, butyl and iso-butyl. In a particular embodiment, R3is methyl or ethyl. In one more particular embodiment R3is methyl. In yet one more particular embodiment R3is ethyl. In one more particular embodiment R3is propyl. In one more particular embodiment R3is butyl.

[0120] According to any embodiment, a composition comprising one or more amine-oxides is added in step B. In other words, the amine-oxide is a composition comprising one or more amine-oxide. In one embodiment, the amine-oxide is a composition comprising a plurality of amine-oxide.

[0121] The amine-oxide is the mixture of rape oil based amine-oxides. In a certain embodiment, the amine-oxide is the mixture of amine-oxides having the CAS No 204933-93-7.

[0122] In another embodiment, the hydroxylamine is formed in situ from the corresponding amine-oxide. In a further embodiment, the hydroxylamine of formula (V) is obtained by in situ formation from its corresponding amine-oxide according to formula (VI).

[0123] In a further embodiment, the hydroxylamine is obtained by thermal treatment of the corresponding amine-oxide brought in contact with the second mixture (M2). In yet a further embodiment, the thermal treatment of the corresponding amine-oxide takes place at temperature of at least 100°C. In a certain embodiment, the thermal treatment of the corresponding amine-oxide takes place at temperatures above 100°C. In240992

[0124] 13

[0125] another certain embodiment, the thermal treatment of the corresponding amine-oxide takes place at 100 to 250°C, preferably at 120 to 210°C. The use of an N-oxide is particularly advantageously, since the conversion temperature to obtain the corresponding hydroxyl amine is well in line with the temperature used in the melt and degassing processes as described herein. In practical terms, this means that if a process is already operating at certain temperatures for melting and degassing, the conversion of the N-oxide to hydroxylamine can be conducted without having to change the operational conditions. This can lead to reduced energy costs, less equipment wear, and a more streamlined production workflow.

[0126] In one embodiment, the hydroxylamine or amine-oxide is added in step B. together with a pentaerythritol-based tetra-ester. In other words, pentaerythritol is the alcohol moiety of each ester functional group in the pentaerythritol-based tetra-ester molecule. Pentaerythritol (IUPAC name 2,2-Bis(hydroxymethyl)propane-1,3-diol) is a commonly known tetra-alcohol having the formula C(CH2OH)4. As can be seen from said formula, a tetra-alcohol is an alcohol having four hydroxyl groups.

[0127] In a further embodiment the pentaerythritol-based tetra-ester has the formula C(CH2OX)4, wherein each X represents independently an organic acid moiety. It is to be understood that the organic acid moiety in the related ester is the carbonyl substituent derived from the acid component.

[0128] X may be a hindered phenol. Hindered phenols serve a role in disrupting the ongoing process of hydrogen extraction from molecular chains by peroxide radicals. When hindered phenolic antioxidants are introduced, they offer hydrogens that can be more readily removed compared to those from the polymer itself. This action helps to preserve the integrity of the materials involved.

[0129] In one embodiment each X represents independently a 4-hydroxy-3,5-dialkyl-benzylic acid moiety wherein the alkyl groups in 3 and 5 position are selected from the group consisting of a methyl, ethyl, i-propyl and / or t-butyl. In a certain embodiment, the alkyl groups in 3 and 5 position are the same. In a certain embodiment, the alkyl groups in 3 and 5 position are different.

[0130] There is a synergistic effect between the hydroxylamine and the pentaerythritol-based ester. The combination of hydroxylamine and pentaerythritol-based ester strongly improves the thermal and hydrolytic stability, lower formaldehyde emissionand allows to achieve a good color as well as good mechanical properties of the polyoxymethylene copolymer (cPOM). In addition, the crude polyoxymethylene copolymer mixture (M2) can be processed under conditions of significantly higher shear stress and higher temperatures without suffering from high formaldehyde emission and decreased thermal stability. This allows a significant reducing of the degassing time without suffering from the disadvantages as explained above and in the prior art cited.240992

[0131] 14

[0132] In a certain embodiment, the pentaerythritol-based ester is pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate).

[0133] In one specific embodiment, step B. is a melt degassing, wherein the second mixture (M2) is brought in contact with bis(hydrogenated tallow C16-18-alkyl)hydroxylamine having the CAS No 143925-92-2 and pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate) thereby obtaining the third mixture (M3).

[0134] A second aspect of the present invention is a method for the production of a polymer molding composition (PM) the steps:

[0135] a) providing an oxymethylene copolymer obtainable by the method according to the invention;

[0136] b) optionally adding at least one additive to the second mixture (M2);

[0137] c) adding at least one filler and / or additive to the third mixture (M3).

[0138] In one embodiment, step a) of the method for the production of a polymer molding composition (PM) comprises the steps:

[0139] a1 ) polymerization of at least one main monomer selected form the group of cyclic formals, and at least one first comonomer selected from the group of those of the formula (II)

[0140] R2

[0141] R1— C— O

[0142] R3— C— (R5)n

[0143] R4

[0144] RCD

[0145] where R1to R5and n are as defined above in claim 2, and optionally at least one second comonomer, in the presence of the acid catalyst, in order to provide the first mixture (M1) comprising the polyoxymethylene copolymer (cPOM) and the acid catalyst,

[0146] a2) adding triisopropanolamine to the first mixture (M1) to deactivate the acid catalyst in order to obtain a second mixture (M2) comprising the polyoxymethylene copolymer (cPOM) and a complex of the acid catalyst and triisopropanolamine,

[0147] a3) adding a specified amount of M2 and a hydroxylamine to obtain a third mixture (M3).240992

[0148] 15

[0149] For steps a1), a2) and a3) of the method to produce the polymer molding composition (PM) the aforementioned descriptions and preferences in view of the method for the deactivation of an acid catalyst during the production process of a polyoxymethylene copolymer (cPOM) apply analogously.

[0150] In step a2), optionally at least one additive is added to the second mixture (M2). However, in a preferred embodiment, the second mixture (M2) contains, as described above, 2 to 30% by weight of unreacted residual monomers and 50 to 700 ppm of the complex of the catalyst and the triisopropanolamine. The polyoxymethylene copolymer, moreover, may contain unstable end groups. In a preferred embodiment, therefore, the second mixture (M2) is thermally treated in order to remove the residual monomers and to depolymerize the unstable end groups. The removal of the residual monomers and the unstable end groups is usually done in the melt using a kneading and a degassing device. This finishing process is generally known to a person skilled in the art.

[0151] To the thus obtained finished polyoxymethylene copolymer (cPOM) at least one filler and / or additive is added in step c).

[0152] The filler may be selected from suitable fillers known in the art. In the following, non-limiting examples of suitable additives are described.

[0153] Fillers can be selected from particulate or fibrous inorganic materials (mineral fillers), e.g. basalt, kaolin, wollastonite. Possible fibers include glass fibers, carbon fibers, Kevlar fibers, carbon nanotubes.

[0154] Particulate fillers include talc, carbon black, alumina, titania, silica and mixed oxides thereof.

[0155] The additive may be selected from any suitable additive know in the art. It is to be understood that the following non-limiting examples of suitable additives may be added to any of processes and products as disclosed herein. In particular, the additives may be added to any mixture (M1), (M2) and (M3). The additives may be added to the method for the production of polyoxymethylene copolymers as disclosed herein. The additives may also be added to the method for the production of a polymer moulding composition as disclosed herein.

[0156] Suitable antioxidants are for example sterically hindered phenols, such as triethylene glycol bis(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate. In case an antioxidant is used, it is added in such an amount that the polyoxymethylene copolymer (cPOM) comprises from 0.001 to 10 % by weight, preferably from 0.002 to 5% by weight, more preferred from 0.005 to 3% by weight antioxidant(s) based on the total weight of polyoxymethylene copolymer (cPOM).240992

[0157] 16

[0158] Suitable formaldehyde scavengers are for example amines, amino-triazine compounds, benzoguanamine, amino-acids, hydrazides, urea or urea derivatives, allantoin, guanamines, hydantoin, (modified) melamines orcondensates of melamine and formaldehyde and polyamides, or mixtures thereof. In case aformaldehyde scavenger is used, it is added in such an amount that the polyoxymethylene copolymer (cPOM) comprises from 0.001 to 10 % by weight, preferred from 0.002 to 5% by weight, more preferred from 0.005 to 3% by weight formaldehyde scavenger(s) based on the total weight of polyoxymethylene copolymer (cPOM).

[0159] Suitable polyamides are for example copolyamides based on caprolactam, hexamethylenediamine, bis(4-aminocyclohexyl)methane and adipic acid, which can further comprise monofunctional polymerizing compounds such as propionic acid or triacetonediamine as components to regulate the molar mass. Examples are Ultramid® 1C and Ultramid® C31 from BASF SE. In case a polyamide is used, it is added in such an amount that the polyoxymethylene copolymer (cPOM) comprises from 0.001 to 2% by weight, preferably from 0.005 to 1.99% by weight, more preferably from 0.01 to 0.08% by weight of polyamide(s) based on the total weight of polyoxymethylene copolymer (cPOM).

[0160] Suitable UV absorbants are for example hindered amines light stabilizer such as a hindered amine of the polymeric structure, wherein n is an integer in the range of 5 to 50,

[0161]

[0162] In case a hindered amine is used, it is added in such an amount that the polyoxymethylene copolymer (cPOM) comprises from 0.001 to 10 % by weight, preferred from 0.002 to 5% by weight, more preferred it may be of from 0.005 to 2% by weight of hindered amine(s) based on the total weight of polyoxymethylene copolymer (cPOM).

[0163] Suitable mold-release agents are for example esters or amides of saturated or unsaturated aliphatic carboxylic acids having from 10 to 40 carbon atoms, preferably from 16 to 22 carbon atoms, with polyols or aliphatic saturated alcohols or amines having from 2 to 40 carbon atoms, preferably from 2 to 6 carbon atoms. In case an ester or amide is used, it is added in such an amount that the polyoxymethylene copolymer (cPOM) comprises from 0.01 to 5% by weight, preferably from 0.09 to 2% by weight and in particular from 0.1 to 0.7% by weight mold-release agents, based on the total weight of polyoxymethylene copolymer (cPOM). Preferred esters or amides are accordingly glyceryl distearate, glyceryl tristearate, ethylenediamine distearate, glyceryl monopalmitate, glyceryl trilaurate, glyceryl monobehenate and pentaerythrityl tetrastearate.240992

[0164] 17

[0165] Suitable acid scavengers are, for example, alkaline or earth alkaline carbonates, hydroxides, (hydroxy)stearates or silicates. In case an acid scavenger is used, it is added in such an amount that the polyoxymethylene copolymer (cPOM) comprises from 0.001 to 2% by weight, preferably from 0.002 to 1% by weight, and particularly from 0.003 to 0.7% by weight acid scavengers, based on the total weight of the polyoxymethylene copolymer (cPOM).

[0166] Suitable nucleation agents are, for example, melamine cyanurate, melamine formaldehyde condensate, silica acid, branched polyoxymethylene and talcum. In case a nucleation agent is used, it is added in such an amount that that the polyoxymethylene copolymer (cPOM) comprises from 0.005 to 5% by weight, preferably from 0.01 to 2% by weight, and particularly from 0.02 to 0.7% by weight nucleation agents, based on the total weight of the polyoxymethylene copolymer (cPOM).

[0167] If present the additives are added in a customary manner, for example individually or together, in pure form, as a solution or suspension or as a masterbatch.

[0168] In a third aspect, the present invention relates to use of the the polymer molding composition according to the second aspect for the production of molded parts.

[0169] The molded parts may be used for automotive applications. The molded parts may be suitable for use in any further industrial application.

[0170] In a fourth aspect, the present invention relates to use of hydroxylamines to lowerthe formaldehyde emission in a process for producing polyoxymethylene copolymers.

[0171] It is to be understood that the lowering of the formaldehyde emission is to be seen in the difference of formaldehyde emission of a polyoxymethylene copolymer (cPOM) produced according to the process of the present invention compared to a polyoxymethylene copolymer (cPOM) produced according to the same process without addition of the hydroxylamine.

[0172] Thus, in one embodiment, the lowering of the formaldehyde emission is between a polyoxymethylene copolymer (cPOM) produced according to the process of the present invention compared to a polyoxymethylene copolymer (cPOM) produced according the same process without addition of the hydroxylamine.

[0173] Suitable hydroxylamines are those described hereinabove for the first aspect. As further described hereinabove for the first aspect, the hydroxylamines may be generated from the corresponding amine oxide.240992

[0174] 18

[0175] Particularly suitable are hydroxylamines according to formula (V) and / or amine oxides according to formula (VI) as described hereinabove.

[0176] One embodiment relates to the use of hydroxylamines to lower the formaldehyde emission in a process for producing polyoxymethylene copolymers, wherein the hydroxylamine is generated from the corresponding amine oxide. In other words, the embodiment relates to use of amine oxide to lower the formaldehyde emission in a process for producing polyoxymethylene copolymers.

[0177] In a certain embodiment, an amine oxide is used to lower the formaldehyde emission in a process for producing polyoxymethylene copolymers, wherein the amine oxide undergoes a thermal treatment. In a certain embodiment, the amine oxide is converted in situ to the corresponding hydroxylamine by thermal treatment. The thermal heat treatment is described in the first aspect of the present invention.

[0178] In another embodiment, the formaldehyde emission of the polyoxymethylene copolymer (cPOM) is between 0.1 ppm and 20 ppm. In one more embodiment, the formaldehyde emission of the polyoxymethylene copolymer (cPOM) is between 0.2 ppm and 18 ppm. In one more embodiment, the formaldehyde emission of the polyoxymethylene copolymer (cPOM) is between 0.3 ppm and 16 ppm. In one more embodiment, the formaldehyde emission of the polyoxymethylene copolymer (cPOM) is between 0.4 ppm and 4 ppm.

[0179] In a certain embodiment, the formaldehyde emission of the polyoxymethylene copolymer (cPOM) is less than 15 ppm. In another certain embodiment, the formaldehyde emission of the polyoxymethylene copolymer (cPOM) is less than 13 ppm. In another certain embodiment, the formaldehyde emission of the polyoxymethylene copolymer (cPOM) is less than 9 ppm. In another certain embodiment, the formaldehyde emission of the polyoxymethylene copolymer (cPOM) is less than 6 ppm. In another certain embodiment, the formaldehyde emission of the polyoxymethylene copolymer (cPOM) is less than 5 ppm.

[0180] In the present invention, the formaldehyde emission is estimated according to VDA 275, 1994 Edition, July 1, 1994. A more detailed description for estimating the formaldehyde emission is estimated according to VDA 275, 1994 Edition, July 1, 1994 is provided hereinbelow in the analytic methods section.

[0181] In a fifth aspect, the present invention relates to use of hydroxylamines to improve the thermal stability and / or melt viscosity stability and / or shear stress stability of polyoxymethylene copolymers.

[0182] Suitable hydroxylamines are those described hereinabove for the first aspect. As further described hereinabove for the first aspect, the hydroxylamines may be generated from the corresponding amine oxide.240992

[0183] 19

[0184] Particularly suitable are hydroxylamines according to formula (V) and / or amine oxides according to formula (VI) as described hereinabove.

[0185] One embodiment relates to the use of hydroxylamines to improve the thermal stability and / or melt viscosity stability and / or shear stress stability of polyoxymethylene copolymers, wherein the hydroxylamine is generated from the corresponding amine oxide.

[0186] In a certain embodiment, an amine oxide is used to improve the thermal stability and / or melt viscosity stability and / or shear stress stability of polyoxymethylene copolymers, wherein the amine oxide undergoes a thermal treatment. In a certain embodiment, the amine oxide is converted in situ to the corresponding hydroxylamine by thermal treatment. The thermal heat treatment is described in the first aspect of the present invention.

[0187] In one embodiment, the improvement of the thermal stability and / or melt viscosity stability and / or shear stress stability of polyoxymethylene copolymers is determined between a polyoxymethylene copolymer (cPOM) produced according to the process of the present invention compared to polyoxymethylene copolymer (cPOM) produced according to the same process without addition of the hydroxylamine.

[0188] Improvement of the thermal stability and / or melt viscosity stability and / or shear stress stability of polyoxymethylene copolymers may be determined by melt volume-flow rate (MVR). In other words, the polyoxymethylene copolymer (cPOM) produced according to the process of the present invention has a lower melt volume-flow rate (MVR) compared to polyoxymethylene copolymer (cPOM) produced according to the same process without addition of the hydroxylamine.

[0189] The melt volume-flow rate (MVR) is determined according to DIN EN ISO 1133-1:2022-10. In particular, the melt volume-flow rate (MVR) is determined by extruding molten material from the cylinder of a plastometer through a die of specified length and diameter under preset conditions of temperature (190°C) and load (2.16 kg).

[0190] In other words, the present invention relates to use of hydroxylamines to improve the MVR of polyoxymethylene copolymers.

[0191] In one embodiment, the improvement of the MVR of polyoxymethylene copolymers is determined between a polyoxymethylene copolymer (cPOM) produced according to the process of the present invention compared to polyoxymethylene copolymer (cPOM) produced according to the same process without addition of the hydroxylamine.240992

[0192] 20

[0193] In another embodiment, improvement of the MVR means that the MVR of a polyoxymethylene copolymer (cPOM) produced according to the process of the present invention is lower compared to polyoxymethylene copolymer (cPOM) produced according to the same process without addition of the hydroxylamine.

[0194] In a certain embodiment, the MVR of a polyoxymethylene copolymer (cPOM) produced according to the process of the present invention is at least 10 % lower compared to polyoxymethylene copolymer (cPOM) produced according to the same process without addition of the hydroxylamine, based on the MVR of copolymer (cPOM) produced according to the process of the present invention.

[0195] In another certain embodiment, the MVR of a polyoxymethylene copolymer (cPOM) produced according to the process of the present invention is between 10 and 60 % lower compared to polyoxymethylene copolymer (cPOM) produced according to the same process without addition of the hydroxylamine, based on the MVR of copolymer (cPOM) produced according to the process of the present invention.

[0196] In another certain embodiment, the MVR of a polyoxymethylene copolymer (cPOM) produced according to the process of the present invention is between 10 and 50 % lower compared to polyoxymethylene copolymer (cPOM) produced according to the same process without addition of the hydroxylamine, based on the MVR of copolymer (cPOM) produced according to the process of the present invention.

[0197] In another certain embodiment, the MVR of a polyoxymethylene copolymer (cPOM) produced according to the process of the present invention is between 10 and 47 % lower compared to polyoxymethylene copolymer (cPOM) produced according to the same process without addition of the hydroxylamine, based on the MVR of copolymer (cPOM) produced according to the process of the present invention.

[0198] In another certain embodiment, the MVR of a polyoxymethylene copolymer (cPOM) produced according to the process of the present invention is between 20 and 37 % lower compared to polyoxymethylene copolymer (cPOM) produced according to the same process without addition of the hydroxylamine, based on the MVR of copolymer (cPOM) produced according to the process of the present invention.

[0199] In another certain embodiment, the MVR of a polyoxymethylene copolymer (cPOM) produced according to the process of the present invention is between 24 and 32 % lower compared to polyoxymethylene copolymer (cPOM) produced according to the same process without addition of the hydroxylamine, based on the MVR of copolymer (cPOM) produced according to the process of the present invention.

[0200] According to a sixth aspect, the present invention relates to a polyoxymethylene copolymer (cPOM) comprising 10 to 1000 ppm of a hydroxylamine and / or a hydroxylamine complex, based on the total weight of the polyoxymethylene copolymer (cPOM).240992

[0201] 21

[0202] In one embodiment, the polyoxymethylene copolymer (cPOM) comprises less than 1000 ppm of a hydroxylamine and / or a hydroxylamine complex. In another embodiment, the polyoxymethylene copolymer (cPOM) comprises less than 800 ppm of a hydroxylamine and / or a hydroxylamine complex, n yet another embodiment, the polyoxymethylene copolymer (cPOM) comprises less than 600 ppm of a hydroxylamine and / or a hydroxylamine complex. In yet another embodiment, the polyoxymethylene copolymer (cPOM) comprises less than 500 ppm of a hydroxylamine and / or a hydroxylamine complex. In yet another embodiment, the polyoxymethylene copolymer (cPOM) comprises less than 400 ppm of a hydroxylamine and / or a hydroxylamine complex. In yet another embodiment, the polyoxymethylene copolymer (cPOM) comprises less than 100 ppm of a hydroxylamine and / or a hydroxylamine complex. In yet another embodiment, the polyoxymethylene copolymer (cPOM) comprises less than 70 ppm of a hydroxylamine and / or a hydroxylamine complex. In yet another embodiment, the polyoxymethylene copolymer (cPOM) comprises less than 54 ppm of a hydroxylamine and / or a hydroxylamine complex. In yet another embodiment, the polyoxymethylene copolymer (cPOM) comprises less than 36 ppm of a hydroxylamine and / or a hydroxylamine complex. In yet another embodiment, the polyoxymethylene copolymer (cPOM) comprises less than 21 ppm of a hydroxylamine and / or a hydroxylamine complex. In yet another embodiment, the polyoxymethylene copolymer (cPOM) comprises less than 12 ppm of a hydroxylamine and / or a hydroxylamine complex. In yet another embodiment, the polyoxymethylene copolymer (cPOM) comprises less than 10 ppm of a hydroxylamine and / or a hydroxylamine complex.

[0203] In one embodiment, the polyoxymethylene copolymer (cPOM) comprises 202 to 1000 ppm of a hydroxylamine and / or a hydroxylamine complex. In another embodiment, the polyoxymethylene copolymer (cPOM) comprises 300 to 800 ppm of a hydroxylamine and / or a hydroxylamine complex. In yet another embodiment, the polyoxymethylene copolymer (cPOM) comprises 400 to 700 ppm of a hydroxylamine and / or a hydroxylamine complex.

[0204] In one embodiment, the polyoxymethylene copolymer (cPOM) comprises 20 to 200 ppm of a hydroxylamine and / or a hydroxylamine complex. In another embodiment, the polyoxymethylene copolymer (cPOM) comprises 30 to 170 ppm of a hydroxylamine and / or a hydroxylamine complex. In yet another embodiment, the polyoxymethylene copolymer (cPOM) comprises 50 to 100 ppm of a hydroxylamine and / or a hydroxylamine complex.

[0205] According to an eight aspect, the present invention relaters to a polymer moulding composition comprising a polyoxymethylene copolymer (cPOM) and 1 to 1000 ppm of a hydroxylamine complex, based on the total weight of the polymer moulding composition.240992

[0206] 22

[0207] In one embodiment the polyoxymethylene copolymer (cPOM) is a polyoxymethylene copolymer (cPOM) according to the seventh aspect. In one more aspect the polyoxymethylene copolymer (cPOM) is a polyoxymethylene copolymer (cPOM) obtainable according to the process of the first aspect.

[0208] In another embodiment, the polymer moulding composition is obtainable from the process according to the third aspect.

[0209] In one embodiment, the polymer moulding composition comprises up to 1 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 2 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 3 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 4 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 5 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 6 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 7 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 8 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 9 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 10 ppm of a hydroxylamine and / or a hydroxylamine complex.

[0210] In one embodiment, the polymer moulding composition comprises up to 100 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 460 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 670 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 840 ppm of a hydroxylamine and / or a hydroxylamine complex. In one embodiment, the polymer moulding composition comprises up to 1000 ppm of a hydroxylamine and / or a hydroxylamine complex.

[0211] It is to be understood that all advantages and embodiments described for one aspect also apply for any of the further aspects.

[0212] In the following, the present invention will be illustrated by non -limiting Examples.

[0213] a. Analytical methods

[0214] Weight loss N2 (determination of the weight loss under nitrogen atmosphere):240992

[0215] 23

[0216] For testing the heat stability, the weight loss at 220°C under N2 is determined. It is the weight loss in percent of a weighed sample of about 1.2 g of pellets on heating for 2 h at 220°C under nitrogen. After cooling, the sample is weighed again and the weight loss is calculated.

[0217] MVR (DIN EN ISO 1133-1:2022-10):

[0218] The melt volume-flow rate (MVR) is determined by extruding molten material from the cylinder of a plastometer through a die of specified length and diameter under preset conditions of temperature (190°C) and load (2.16 kg).

[0219] Extractable Formaldehyde (FA) content:

[0220] The extractable FA content in cPOM granulate is determined as follows. 50 g cPOM granulate and 70 ml water are filled into an Erlenmeyer flask and stirred under reflux for 50 min. After rapid cooling, the FA content is determined on a Metrohm Titroprozessor 682. Therefore, the pH value is adjusted to pH 9.4 using n / 10 sodium hydroxide solution (5ml) and subsequently, if necessary, n / 10 sulfuric acid. Subsequently 5 ml of sodium sulfite solution (136 g Na2SC>3 dissolved in 1 kg deionized water) are added. After the reaction between Na2SO3and FA the solution is back-titrated to pH 9.4 using n / 10 sulfuric acid.

[0221] The Calculation of the FA content is carried out as follows:

[0222] mass FA [mg] = consumption H2SO4 x 2 x concentration H2SO4 x mass formaldehyde

[0223] FA content [%] = mass FA [mg] / net weight [g, cPOM granulate] x (1 000000 / 1 000)

[0224] x means multiplying operator

[0225] It is assumed, that the reaction follows the reaction scheme shown hereinafter

[0226]

[0227] Formaldehyde content (FA gas GC)

[0228] 3 g of pellet sample were placed in 20 mL headspace vials and tempered for 30 minutesat 140°C. Formaldehyde was analyzed via gas chromatography (GC) using a thermal conductivity detector (TCD). Calibration was carried out via the total evaporation of formaldehyde reference solutions in ethanol.

[0229] Formaldehyde emission (VDA 275, 1994 Edition, July 1, 1994):

[0230] The manufacture of specimen (test sample) was carried out as follows: In an injection molding machine the cPOM granulate is formed into injection molded plates (40 x 100 x 2,5 mm), an injection molding machine is utilized with the following parameters; mass temperature: 200°C, tool wall temperature: 90°C. The test samples are stored before examination in a PE-bag.

[0231] For the determination, the specimens are fixed over distilled water in a sealed (closed) 1 -L polyethylene bottle at constant temperature (60 °C) for a defined time. Afterwards 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 acetylaceton method is applied. Therefore, the formaldehyde is converted to diacetyldihydrolutidine using acetylacetone und ammonium acetate. The concentration of the diacetyldihydrolutidine is measured photometrically (the maximum of absorption of diacetyldihydrolutidine is at 412 nm).

[0232] The formaldehyde content is given relative to the dry weight of the specimen (mg / kg = ppm).

[0233] Tensile test (DIN EN ISO 527-2, Juni 2012):

[0234] Tensile bars were injection molded in an injection molding machine at a melt temperature of 200°C and a mold temperature of 90°C. The tensile test was conducted according to DIN EN ISO 527-2. Mean values of the tensile modulus, the tensile stress at yield, the tensile stress at break, the elongation at yield, the elongation at break and the nominal elongation at break were obtained from ten tensile bars. Exclusively specimens of type 1A were used for all tensile test measurements

[0235] Color of pellets (DIN EN ISO 11664-4, June 2012):

[0236] The color L, a, b of a pellet sample or injection molded specimen (plate size: 40 x 100 x 2,5 mm) was measured with a LabScan colorimeter from Hunter lab in r45 mess geometry.

[0237] b. Materials

[0238] The following components were used:

[0239] (1) Raw cPOM (M1):

[0240] Raw cPOM is taken from a kneader reactor of a polyoxymethylene copolymer production. For the production of the raw cPOM 96.5% by weight of trioxane and 3.5% by weight of dioxolane is used, based on the total amount of the used monomers. The raw cPOM contains beside cPOM, 85 ppm BF3xOEt2, 3% by weight ofunconverted trioxane and 3% by weight of thermally unstable endgroups, based on the total weight of raw cPOM

[0241] (2) Used amines for the deactivation:

[0242] Triisopropanolamine: technical grade, assay min. 99% by GC, by BASF SE

[0243] (3) Additives:

[0244] Ethylenebis(oxyethylene)bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl)-propionate) (antioxidant, CAS No: 36443-68-2), Pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (tetra-ester, CAS No: 6683-19-8), bis(hydrogenated tallow C16-18-alkyl)hydroxylamine (CAS No: 143925-92-2), Talkum, synthetic Magnesium silicate (CAS No. 1343-88-0), N,N’-ethylenebis(stearamide) (lubricant) and polyethylene glycol Mw=8000 (PEG, CAS No: 25322-68-3). Calcium hydroxide (Ca(OH)2).

[0245] c. Preparation of the materials

[0246] The mixture M2 was prepared by deactivation of M1 with 400ppm Triisopropanolamine for 2 hrs at elevated temperature. The Triisopropanolamine was added to M1 diluted with 90% of ethyl acetate. In a next step, hydroxylamine and other additives were added to 5 kg of M2, for shear, heat, and MVR stabilization (table 2). Afterward, the mixture is subjected to degassing in a twin-screw extruder (TEX-30, L / D = 40, Cp = 27 mm) to obtain M3. For efficient degassing, all three vent zones were maintained under vacuum.

[0247] To achieve high shear stress, the extrusion is carried out as single step extrusion at a significantly lower throughput rate of 5 kg / h and 200 rpm, compared to the usual output of 20-30 kg / hr. The temperatures of the six barrels with venting zones are set as shown in Table 1 for effective gas removal.

[0248] Similarly, the single step extrusion was carried out at a high temperature 260°C. In

[0249] general, such extrusion is carried out at 220 to 230°C.

[0250] Table 1 : barrel temp setting

[0251]

[0252] The cPOM for the inventive examples ex1 to ex6 and for the comparative examples com1 to cpm3 was prepared with the additives as disclosed in Tables 2 and 3.26

[0253] Table 2: Additives to M2 used in the inventive examples 1a and 1 (ex1a and ex1) and the comparative examples (com1 and com2).

[0254]

[0255] Table 3: Additives to M2 used in the inventive examples 2 to 4 (ex2 to ex4) and the comparative examples 3 to 5 (com3 to com5).

[0256]

[0257] d. Results

[0258] (1) Production of cPOM resins under high shear and temperature conditions with extended degassing time.

[0259] Table 4: MVR and FA emissions forexl and ex1a compared to com 1 and com2 according to the addition of hydroxylamine / antioxidant / tetra-ester

[0260]

[0261] 240992

[0262]

[0263] The results in Table 4 demonstrate that Comparative Example 1, using the conventional heat stabilizer I RG245, exhibited an high MVR of 75, indicating cleavage of polymer chains under high shear and high temperature conditions. In contrast, Example lashowed an MVR of 27.1 cm3 / 10min, representing a medium MVR range. FA (GC) and VDA275, indicators of FA emissions, significantly decreased in Example 1a compared to Comparative Example.

[0264] Example 1 demonstrates that there is a synergistic effect between the hydroxylamine and the pentaerythritol-based ester . The comparative examples do neither comprise the hydroxylamine or the pentaerythritol-based tetra-ester. Example 1a comprises the hydroxylamine and no pentaerythritol-based ester, thereby showing improved properties of the resulting polymer compared to the Comparative Examples. Example 1 comprise the hydroxylamine and the pentaerythritol-based tetra-ester, which further significantly improves the properties of the resulting polymer compared to Example 1a and the Comparative Examples. As can be seen in Table 4, the improvement of the polymer’s properties achieved by the combination of hydroxylamine and the pentaerythritol-based ester are much higher than one would expect when merely adding both components. In particular, Example 1 conditions showed a low MVR of 13.8 cm3 / 10min, representing a higher molecular weight range. FA (GC) and VDA275, indicators of FA emissions, significantly decreased in Example 1 compared to Example 1a and Comparative Example 1.

[0265] The results of FA demonstrate that despite harsh degassing conditions, Hydroxylamine stabilizes the MVR and effectively removes FA. As a result, weight loss is reduced, indicating improved thermal stability performance.

[0266] (2) The effect of hydroxylamine quantity under high shearand temperature conditions with extended degassing time.

[0267] The results in Table 5 show that Comparative Example 3, which used the conventional antioxidant, had an MVR of 34, indicating that the polymer chain underwent cleavage under high shear and high temperature conditions. Examples 2, 3, and 4 show the effects of adding Hydroxylamine at varying concentrations. The indicators of FA emission, VDA275 slightly decreased in Comparative Examples 4 and 5. However, the addition of hydroxylamine resulted in a dramatic decrease compared to Comparative Example 3.240992

[0268] 28

[0269] Table 5: MVR and FA emissions according to the different hydroxylamine concentration

[0270]

[0271] As can be seen from Tables 3 and 5, hydroxylamine can be used in small quantities to improve properties of the polymer. Even at low quantities of 250 ppm, the polymer in Example 2 show improved properties compared to the Comparative Examples. Example 2 showed an MVR of 10.7 cm3 / 10min, representing a low MVR product. VDA275, indicator of FA emission, is significantly decreased in Example 2 compared to Comparative Examples 3 to 5.

Claims

240992Claims1. Method for producing polyoxymethylene copolymers comprising the steps of:A. adding a catalyst deactivator to a first mixture (M1) comprising a polyoxymethylene copolymer and an acidic catalyst to obtain a second mixture (M2), wherein the catalyst deactivator is an alkanolamine;B. performing a melt degassing, wherein the second mixture M2 is brought in contact with a hydroxylamine thereby obtaining a third mixture (M3).

2. Method according to claim 1 , wherein the polyoxymethylene copolymer comprises from 60 to 99.99 mol% of -CH2O- recurring units and from 0.01 to 40 mol% of recurring units according to formula (I)where R1to R4are each, independently of one another, a hydrogen atom, a Ci-C alkyl group or an alkoxy-substituted alkyl group having from 1 to 4 carbon atoms and R5is a chemical bond, a -CH2-, -OCH2-, a Ci-C4-alkyl- or Ci-C4-alkoxy-substituted methylene group or a corresponding polyoxymethylene group and n is from 0 to 3.

3. Method according to claim 1 or 2, wherein step a) comprises the step:A1) polymerization of at least one main monomer selected form the group of cyclic formals, and at least one first comonomer selected from the group of those of the formula (II)R2R1— C— OR3— C-(R5)nR4CDwhere R1to R5and n are as defined above in claim 2, and optionally at least one second comonomer, in the presence of the acid catalyst, to provide the first mixture (M1) comprising the polyoxymethylene copolymer (cPOM) and the acid catalyst.

4. Method according to any of claims 1 to 3, wherein the acid catalyst is at least one acid catalyst selected from the group consisting of boron trifluoride, a coordination complex of boron trifluoride24099230with water, a coordination complex of boron trifluoride with a dialkylether and catalytic active transformation product of the aforementioned acid catalyst.

5. Method according to any of claims 1 to 4, wherein the acid catalyst in step a) is present in an amount of from 10 to 150 ppm based on the total weight of the first mixture (M1).

6. Method according to any of claimsl to 5, wherein the hydroxylamine, is added in step b) in an amount from 10 to 1000 ppm based on the total weight of the second mixture (M2), and optionally wherein the at least one hydroxylamine is present in an amount from 10 to 1000 ppm based on the total weight of the third mixture (M3).

7. Method according to any of claims 1 to 6, wherein the at least one hydroxylamine is represented by general formula (V)E R»1HO — NR(V)wherein R1and R2each independently represent a hydrogen atom or a C1-C40 hydrocarbon group, preferably, R1and R2represent a hydrogen atom or alkyl-substituted C1-C40 hydrocarbon group, more preferably R1and R2represent a hydrogen atom or alkyl-substituted C10-C30 hydrocarbon group and most preferably R1and R2represent a hydrogen atom or a C14-C24 alkyl group.

8. Method according to any of claims 1 to 7, wherein the at least one hydroxylamine is obtained by adding to step b) at least one amine-oxide represented by general formula (VI):wherein R1and R2are as defined in claim 8 and wherein R3is an optionally substituted C1-C10 hydrocarbon group, preferably a C1-C5 alkyl group and more preferably selected from methyl, ethyl, propyl, iso-propyl, butyl and iso-butyl.

9. Method according to any of claims 1 to 8, wherein the at least one hydroxylamine or amine-oxide is added in step B. together with a pentaerythritol-based tetra-ester, preferably pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate).

10. Method for producing a polymer moulding composition, comprising the steps of24099231a) providing a polyoxymethylene copolymer obtainable by the method according to any one of claims 1-9;b) optionally adding at least one additive to the second mixture (M2);c) adding at least one filler and / or additive to (M3)11. Polymer moulding composition obtainable by the method according to claim 10.

12. Polyoxymethylene copolymer comprising 10 to 1000 ppm of a hydroxylamine and / or a hydroxylamine complex, based on the total weight of the polyoxymethylene copolymer.

13. Polymer moulding composition comprising a polyoxymethylene copolymer and 1 to 1000 ppm of a hydroxylamine complex, based on the total weight of the polymer moulding composition.

14. Use of hydroxylamines to lower the formaldehyde emission in a process for producing polyoxymethylene copolymers.

15. Use of hydroxylamines to improve the thermal stability, melt viscosity stability and shear stress stability of polyoxymethylene copolymers.

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