JP2014533770A - Modification of polyoxymethylene with imidized acrylic resin - Google Patents

Abstract

(A) 92 to 99% by weight of polyoxymethylene having a number average molecular weight of 65,000 to 250,000 g / mol; (b) 1 to 8% by weight of an imidized acrylic resin obtained by treating an acrylic polymer with a monoalkylamine. Wherein the weight percentages of a and b are percentages of their total weight, and the monoalkyl group has 1 to 5 carbon atoms and the degree of imidization is 20% to 100%. Described herein are compositions having an acid level of 0 to about 2% by weight relative to the imidized acrylic resin. This composition has a significantly higher heat deflection temperature than pure polyoxymethylene. A method for increasing the heat deflection temperature of a POM composition described herein by blending (a) and (b), wherein the resulting melt blend composition is the same melt blend lacking (b) A method having a 200% or greater increase in time to 5% creep strain compared to the composition.

Description

  The present invention relates to the use of imidized acrylic resins as polyoxymethylene modifiers that improve their high temperature properties.

  Polyoxymethylene [POM] compositions comprise formaldehyde homopolymers or cyclic oligomers of formaldehyde such as trioxane, and / or copolymers of formaldehyde or cyclic oligomers of formaldehyde. POM homopolymers have end groups that are end-capped by esterification or etherification. In the POM copolymer, the oxyalkylene group has at least two adjacent carbon atoms in the backbone, and the end group can be hydroxyl terminated or end-capped by esterification or etherification. The proportion of comonomer can be up to 20% by weight.

  Using a POM composition having a relatively high molecular weight, i.e. a POM of 50,000-100,000, any of the techniques commonly used in thermoplastic materials, such as compression molding, injection molding, extrusion molding, blowing Articles can be produced by molding, melt spinning, stamping and thermoforming. Articles made from such relatively high molecular weight POM compositions have desirable physical properties such as stiffness, strength, toughness, dimensional stability and solvent resistance.

  POM compositions are commercially available from DuPont under the trade name Delrin® and are used in the automotive, industrial, electronic and consumer goods industries.

  Unmodified POM has a heat deflection temperature [HDT] of about 97 ° C. to 100 ° C. and a bending modulus of about 3000 megapascals [MPa]. For many industrial applications, the height of these two properties is not sufficient. The conventional method for increasing the rigidity and HDT of POM has been to add glass fibers. Although HDT is increased, the addition of glass fiber increases the weight, promotes anisotropy such as deterioration in appearance, difficulty in molding, and shrinkage, and decreases toughness.

  US Pat. No. 2,146,209; US Pat. No. 3,284,425; US Pat. No. 4,169,924 and US Pat. No. 4,246,374 include: Polyglutarimides, also known as imidized acrylic polymers or imides of polyacrylic acid, are disclosed. U.S. Pat. No. 4,246,374 and U.S. Pat. No. 4,217,424 include imidized acrylic polymers, impact modifiers, pigments, fibers, stabilizers, lubricants, etc. Combinations with materials are described. U.S. Pat. No. 4,255,322; U.S. Pat. No. 4,595,727 and U.S. Pat. No. 5,502,111 include polyglutarimide and PVC with improved heat deflection temperature. And blends are disclosed.

  Imidized acrylic resins have been used to modify polyamides to improve their melt flow, melt strength, tensile strength, and modulus. The compatible polymer blend of polyamide and imidized acrylic resin has improved impact resistance and ductility compared to pure imidized acrylic resin. When a high service temperature imidized acrylic resin is added to a low service temperature nylon, the service temperature of the nylon is improved. A compatible polymer blend of an imidized acrylic resin with nylon and a conventional impact modifier has improved impact response compared to an imidized acrylic resin modified with an equivalent amount of a conventional impact modifier. (See U.S. Pat. No. 4,415,706 and U.S. Pat. No. 4,874,817).

  The imidized acrylic resin is blended with a composition comprising POM and thermoplastic polyurethane to improve molding shrinkage while maintaining a useful balance of properties such as stiffness, elongation, and toughness (US Patent) No. 5,318,813 and EP 0424755). US Pat. No. 4,727,117; US Pat. No. 4,954,574; US Pat. No. 5,004,777; and US Pat. No. 5,264,483 A 50/50 blend of POM and imidized acrylic resin is disclosed. Japanese Patent Application Publication No. 1990-015585 discloses a blend of polyglutarimide and polyacetal that provides impact resistance and fluidity while maintaining the thermal deformation temperature of polyglutarimide. German Patent Application No. 4132638 discloses a blend of POM and imidized acrylic resin.

  Polyoxymethylene compositions having increased heat deflection temperature, increased stiffness / modulus at room temperature and higher temperatures below the melting point of polyoxymethylene, increased upper working temperature at a given stiffness and reduced long term creep at elevated temperatures. Development is desired. It is also desirable to develop compositions having these properties with improved heat resistance and resistance to decomposition at high temperatures.

(A) about 92 to about 99% by weight of polyoxymethylene having a number average molecular weight of 20,000 to 250,000 g / mol, based on the total weight of (a) and (b);
(B) from about 1 to about 8% by weight of an imidized acrylic resin obtained by treating the acrylic polymer with a monoalkylamine, based on the total weight of (a) and (b);
A thermoplastic composition comprising, consisting essentially of or produced from, wherein the monoalkyl group has 1 to 5 carbon atoms, the degree of imidization is 20% to 100%, and the acid Described herein are thermoplastic compositions whose levels are from 0 to about 2% by weight of the imidized acrylic resin. Of note, the composition is substantially free of thermoplastic polyurethane. Preferably, the imidized acrylic resin is obtained by treating polymethyl methacrylate with methylamine. Preferably, the imidized acrylic resin is present in the composition in an amount of about 1 to about 5% by weight.

  Articles comprising the compositions described herein are also described herein. The article has a heat deflection temperature determined in accordance with ASTM D-648, which exceeds the heat deflection temperature of a comparative standard article, and the molded article and comparative standard article are comparative standards. It has the same shape and structure except that the article is made from a polyoxymethylene composition that does not contain an imidized acrylic resin.

(1) A step of melt blending a first polyoxymethylene composition with an imidized acrylic resin to provide the above-mentioned molten thermoplastic composition, wherein the first polyoxymethylene resin is the component (a) A process as described, wherein the imidized acrylic resin is as described in component (b) above;
(2) forming a molten composition into a desired shape;
(3) a step of cooling the molten composition to obtain a molded article;
A molded article comprising a composition, wherein the molded article has a heat deflection temperature determined in accordance with ASTM D-648, which is the temperature of the comparative standard article. The molded article and the comparative standard article have the same shape and structure, except that the comparative standard article is made from a first polyoxymethylene composition that does not contain an imidized acrylic resin. Are also described herein.

(A) 1-8% by weight of an imidized acrylic resin obtained by treating an acrylic polymer with a monoalkylamine having an acid level and a degree of imidization and having a monoalkyl group;
(B) 92-99% by weight of polyoxymethylene having a number average molecular weight of 50,000-250,000 g / mol;
(C) optionally one or more other additives;
A method of increasing the heat deflection temperature comprising the steps of melt mixing and forming a melt mixed composition comprising:
The weight percentages of (a) and (b) are based on the total weight of (a) and (b), respectively,
The monoalkyl group has 1 to 5 carbon atoms,
The degree of imidization is 20% to 100%,
The acid level is from 0 to about 2% by weight of the imidized acrylic resin; and the time to creep strain of the molten blend composition as determined by ISO 899-1 up to 5% of the same composition lacking (a) Methods are also described herein that are over 200% longer in comparison.

Definitions and Abbreviations The following definitions and abbreviations are used to interpret the meaning of the terms set forth in the specification and claims.

  As used herein, “one” refers to one and more than one and does not necessarily limit the subject noun to the singular.

  As used herein, the terms “about” and “at” or “about” can be the value or the other value at which the amount / value in question is the specified value, or approximately or approximately the same. Means that. The term is intended to mean that a similar value facilitates an equivalent result or effect as recited in the claims.

  As used herein, “comprises”, “comprising”, “contains”, “contains”, “has”, “having” ) ”,“ Consisting essentially of ”, and“ consisting of ”or any other variation thereof may mean either non-exclusive inclusion or exclusive inclusion. Where these terms mean non-exclusive inclusion, a process, method, article, or device that includes a list of elements is not limited to elements of the list, but other elements that may not be specifically mentioned or may be specific May also be included. Furthermore, unless otherwise specified, “or” means inclusive, rather than exclusive, unless otherwise specified. For example, condition A or B is as follows: A is true (or present) and B is false (or does not exist), A is false (or does not exist) and B is true ( Or both) are satisfied by either one of A and B being true (or present).

  When these terms mean more exclusive inclusion, these terms limit the scope of the claimed materials and processes to substantially affect the novel elements of the described invention.

  Where these terms mean completely exclusive inclusion, these terms exclude elements, steps or ingredients not specifically recited in a claim.

  As used herein, the term “article” means an unfinished or finished product, object, object, or an element or feature of an unfinished or finished product, object or object. When an article is an unfinished product, the term “article” as used herein refers to an article, thing, or object that is included in the finished product and / or undergoes further processing to become a finished product. , Element, device, and the like. When an article is an unfinished product, the term “article” as used herein refers to an article, thing, object, element that has been processed and completed to suit a particular application / purpose. Means a device, etc.

  The article may include an assembly having one or more elements or assemblies that are partially completed and awaiting further processing, or other elements / assemblies that together contain the finished product. Further, as used herein, the term “article” may refer to a system or configuration of articles.

  As used herein, terms describing a molecule or polymer follow the terminology in the September 7, 2009 IUPAC Compendium of Chemical Termination version 2.15 (International Union of Pure and Applied Chemistry).

  As used herein, the term “additive” is an additional component added to the polyoxymethylene composition described herein and is different from the imidized acrylic resin described herein. Means ingredients.

  Unless otherwise specified, all percentages, parts, ratios, amounts, etc. are defined by weight.

  As used herein, the expressions “known to those skilled in the art”, “conventional” or synonyms or synonymous phrases are used in the conventional or known manner of materials, methods, and apparatus. It means an explanation that represents something that is known or known to those skilled in the art at the time of filing this application.

  As used herein, the term “polymer” means a polymer or collection of polymers that differ by the number of repeating units, such as oligomers, homopolymers, or copolymers.

  As used herein, the term “copolymer” refers to a polymer comprising copolymerized units resulting from the copolymerization of a plurality of comonomers. A copolymer may be described herein by its constituent comonomer, such as “a copolymer comprising ethylene and 18% by weight acrylic acid” or by the amount of its constituent comonomer. Such a description of the copolymer indicates that the copolymer contains (in the specified amount, if specified) copolymerized units of the specified comonomer. The term “terpolymer” means a polymer consisting essentially of three monomers.

As used herein, the terms “polyoxymethylene”, “polyoxymethylene polymer” and “polyacetal polymer”, abbreviated as POM, refer to one or more of the repeating units —CH ₂ O—. By homopolymer, copolymer and mixtures thereof are meant. The end groups of these polymers are derived by initiating, terminal, or chain transfer groups such as water or alcohols, or by chemical reactions that result in ester or ether groups such as acetate, acetyl, methyl and methoxy groups.

  As used herein, the term “acrylic resin” means a polymer of an acrylate ester (alkyl acrylate) or a methacrylate ester (alkyl methacrylate), or a combination thereof.

  As used herein, the terms “imidized acrylic polymer”, “imidized acrylic” and “polyglutarimide” are used interchangeably and refer to the following chemical structure:

Structure I: Imidized acrylate or methacrylate polymer:

In which R ₁ is C ₁ -C ₅ alkyl;
R ₂ is H or CH ₃ .

Structure II: Imidized methacrylate polymer

In the formula, R ₁ is C ₁ -C ₅ alkyl.

  As used herein, the term “highly acid imidized acrylic [IA]” means an IA having 5% by weight or more of acid.

  As used herein, the term “low acid IA” means an IA having no more than 4% by weight, preferably less than 1% by weight of acid.

As used herein, the term "weight average molecular weight" is abbreviated as M _w or Mw. As used herein, the term “number average molecular weight” is abbreviated as M _n or Mn.

  As used herein, the terms “polymer melt mass flow rate”, “melt flow rate” or “melt flow index”, abbreviated as “MFR” or “MFI”, refer to the heat containing the melt of the polymer composition. It means a measure of the ease of flow of the plastic polymer melt. As the mass (grams) of polymer flowing in a capillary of a specific diameter and length in 10 minutes, with a pressure applied through a preselected selective weight at a predesignated selective temperature. Defined. This method is described in standard ASTM D1238-04c. Polymer melt mass flow rates are reported in grams per 10 minutes unless otherwise specified and are conducted at 190 ° C./2.16 kg.

  Melt flow rate is an indirect measure of molecular weight, with a high melt flow rate corresponding to a low molecular weight. At the same time, melt flow rate is a measure of the ability of molten material to flow under pressure. It should be borne in mind that although the melt flow rate is inversely proportional to the melt viscosity at the test conditions, the viscosity of such materials will vary depending on the force applied. The ratio of two melt flow rate values for a single material at different weights is often used as a measure of the breadth of the molecular weight distribution.

  As used herein, the expression “substantially free of thermoplastic polyurethane” means that the thermoplastic polyurethane in the composition is less than 1% by weight, preferably less than 0.5% by weight. .

  As used herein, the terms “heat deflection temperature”, “heat distortion temperature”, abbreviated as HDT, mean the temperature at which a polymer or plastic sample deforms under a specified load.

  As used herein, the term “degree of imidization” of the imidized acrylic resin described herein refers to the molar amount of ester groups that react with an amine to form a cyclic imide moiety. This term is also described with respect to the weight percent of cyclic imide groups in the resulting copolymer.

  As used herein, the terms “creep resistance”, “creep strain” and “time to creep strain X%” mean the same or equivalent properties that are a measure of the ability of a material to withstand creep. . Specifically, creep occurs as a result of prolonged exposure to high levels of stress that is less than the yield strength of the material, where the solid material tends to move slowly or permanently deform under the influence of stress. . Since creep always increases with temperature, it is more severe with materials that have been exposed to heat close to the melting point for extended periods of time. Thus, the term “time to creep strain X%” is a measure of the time it takes for a material to experience X%, such as 5% or 7% creep strain, and is itself a secondary or steady state creep. It is a measure of the creep strain rate in stages.

  As used herein, the term “storage modulus E” refers to a modulus elastic element of a material, as opposed to a viscous element.

  As used herein, the terms “MPa”, “mPA”, “mPa” mean a measure of pressure, megapascal or megapascal. As used herein, the terms “kPa”, “kPA”, “kPa” mean kilopascal (Kilopascal).

  As used herein, the symbol “%” means percent.

  As used herein, the terms “in”, “m”, and “cm” mean inches, meters, and centimeters, respectively.

  As used herein, the terms “hr”, “min”, and “sec” mean hours, minutes, and seconds, respectively.

  As used herein, the terms “lb”, “oz”, “gm”, “kg” mean pounds, ounces, grams and kilograms, respectively.

  As used herein, the term “Tg” means glass transition temperature.

  As used herein, the term “CHN analyzer” refers to the three major elements that determine the elemental composition of a sample and are measured by the device: carbon (C), hydrogen (H) and nitrogen (N). Means a device that derives its name from. Sulfur (S) and oxygen (O) can also be measured.

  As used herein, the term “Std. Dev.” Means standard deviation.

Ranges The ranges specifically described herein include their endpoints unless specifically stated otherwise. Regardless of whether such a pair is disclosed separately herein, the description of an amount, concentration, or other value or parameter as a range is specifically based on the upper limit of the range and the lower limit of the range. Disclose all ranges formed. The methods and articles described herein are not limited to the specific values disclosed in the scope definitions in the specification.

Preferred Variations Any variation relating to materials, methods, steps, values, and / or ranges, etc., whether or not identified as preferred variations of the methods, compositions and articles described herein. Are specifically intended to disclose methods and articles comprising any combination of such materials, methods, steps, values, ranges, and the like. For the purpose of providing precise and sufficient assistance to the claims, any combination so disclosed is specifically intended to be a preferred variation of the methods, compositions, and articles described herein. Is done.

SUMMARY POM compositions comprising an imidized acrylic polymer (IA) are described herein. Also described is a method of increasing the creep resistance of relatively high molecular weight POM compositions, ie having a Mn of 50,000 to 250,000, by adding a low acid imidized allyl polymer.

  These compositions and methods have improved heat resistance, including increased heat deflection temperature, increased Vicat temperature, increased stiffness / modulus at room temperature and higher temperatures below the melting point of POM, and increased upper working temperature at a given stiffness. Have sex. Because IA has a much higher glass transition temperature than polyoxymethylene, blends of IA and polyoxymethylene improve the heat resistance and mechanical properties of the POM composition, such as tensile strength and thermoplastic processability. Surprisingly, the benefits of increased heat deflection temperature and increased stiffness / modulus are achieved using very low levels of IA.

Polyoxymethylene ["POM"]
The polyoxymethylene in the compositions described herein is a homopolymer of formaldehyde or a cyclic oligomer of formaldehyde whose end groups are end-capped by esterification or etherification, and formaldehyde or formaldehyde. Copolymers of cyclic oligomers and other monomers that give an oxyalkylene group having at least two adjacent carbon atoms in the main chain (the end groups of the copolymer are hydroxyl-terminated or end-capped by esterification or etherification) Can be included).

  The polyoxymethylene can be branched or linear and generally has a number average molecular weight (Mn) in the range of 20,000 to 250,000 g / mol. Useful POMs for the compositions described herein have a Mn of 50,000 to 100,000, more preferably 50,000 to 80,000. Polyoxymethylene having a number average molecular weight of about 65,000 is particularly preferred. The weight average molecular weight (Mw) of the POM used in the blend can be from 50,000 to about 150,000 g / mol, preferably from 100,000 to 150,000 g / mol.

  The molecular weight can conveniently be measured by gel permeation chromatography in m-cresol at 160 ° C. using a bimodal column kit with a nominal pore size of 60 and 1000 Å [Å].

  As an alternative to number average molecular weight, melt flow rate also characterizes the POM used herein. Suitable polyoxymethylene in the compositions described herein is 0.1 to 40 grams measured at 190 ° C. using a weight of 2.16 kg according to ASTM-D-1238 Procedure A. It has a melt flow rate of / 10 minutes. Preferably, the POM in the compositions described herein has between 0.5 and 35 grams / 10 minutes. More preferably, the POM used herein is linear and has a melt flow rate of about 1 to 20 grams / 10 minutes. POM having a melt flow rate of about 1-5 grams / 10 minutes or about 10-20 grams / 10 minutes is particularly preferred.

  The POM in the compositions described herein can be a homopolymer, a copolymer, or a mixture thereof. POM homopolymer is preferred because of its rigidity and strength. Preferred polyoxymethylene homopolymers include polymers whose terminal hydroxyl groups are end-capped by chemical reaction to form ester or ether groups, preferably acetate or methoxy groups, respectively. US Pat. No. 2,998,409 describes a process for preparing acetate end-capped POM homopolymers.

  The POM copolymer contains one or more comonomers commonly used in the manufacture of POM compositions. More commonly used comonomers include alkylene oxides of 2 to 12 carbon atoms and their cycloaddition products with formaldehyde. The amount of comonomer in the compositions described herein is no more than 20 wt%, preferably no more than 15 wt%, and most preferably about 2 wt%. Most preferred is ethylene oxide.

  The POM compositions described herein can contain additives, ingredients, and modifiers, such as stabilizers and antioxidants, commonly known to be added to polyoxymethylene.

Imidized acrylic resin The imidized acrylic polymer has the following chemical structure and formula:
Structure I: imidized acrylate or methacrylate polymer

In which R ₁ is C ₁ -C ₅ alkyl;
R ₂ is H or CH ₃ .

Structure II: Imidized methacrylate polymer

R ₁ is C ₁ -C ₅ alkyl. For example, U.S. Pat. No. 3,284,425: U.S. Pat. No. 4,246,374; U.S. Pat. No. 4,518,717; U.S. Pat. No. 4,727,117 and See U.S. Pat. No. 5,110.

  Of note, imidized acrylic resins contain cyclic imide units. Imidized acrylic polymers react with ammonia or primary amines with acrylate or methacrylate esters such as poly (methyl methacrylate) to form cyclic imide groups from the condensation of amines with two adjacent ester groups of the acrylic polymer. Manufactured by. The molar amount of ester groups that react with an amine to form a cyclic imide moiety is called the degree of imidization and can also be expressed as the weight percent of the cyclic imide group of the resulting copolymer.

  The preferred primary amine used for the acrylic polymer treatment in the imidation reaction described above is methylamine, but higher aliphatic amines may be used. Other amines include, for example, ethylamine, isopropylamine, and butylamine.

  The acrylic polymer can be poly (methyl methacrylate) or poly (methyl acrylate), preferably poly (methyl methacrylate). Other polymethacrylates or polyacrylate copolymers may be used in place of poly (methyl methacrylate), but this is undesirable because of its low glass transition temperature [Tg]. In addition to methacrylate or acrylate monomers, these polymers can have small amounts of additional ethylenically unsaturated comonomers that are copolymerized therewith. Such additional monomers can be, for example, styrene, acrylonitrile, vinyl acetate, ethylene, butadiene and methyl vinyl ether. When used to produce imidized acrylates, copolymers of methyl methacrylate or methyl acrylate with at least one further comonomer selected from styrene, acrylonitrile, vinyl acetate, ethylene, butadiene or methyl vinyl ether are preferably It contains at least about 40%, preferably at least 60%, more preferably at least 80% by weight of methacrylate or acrylate units.

  Suitable imidized polymers include imidized poly (methyl methacrylate) or poly (methyl acrylate), methyl methacrylate or an imidized copolymer of methyl acrylate and a comonomer as described above, preferably poly (methyl methacrylate) is Reacts with methylamine. The composition described herein, unlike the imidized acrylic resin in the PVC blend of US Pat. No. 4,255,322, generally has a molecular weight of 100,000 to 200,000 and a degree of imidization of 20 to 60%. The product is an imidization having a preferred molecular weight of 20,000 to 200,000 and a degree of imidization of 20 to 100%, preferably 60 to 100%, more preferably 80 to 100%, most preferably 90 to 100%. Has acrylic resin.

  The imidized acrylic polymers described herein can contain unconverted ester groups, carboxylic acid groups, and end-capped carboxylic acid groups, depending on the degree of imidization of the starting polymer. Anhydride groups and acid groups are formed on the polymer chain as a by-product of (meth) acrylic polymers by reaction with ammonia or primary amines and are reported to be intermediates in the formation of imide units. As the degree of imidization exceeds 95% and approaches 100%, the amount of acid and anhydride units present on the resulting imidized product decreases. If the degree of imidization of the imidized acrylic polymer described herein is 95% or less, as a general result of the reaction, the amount of acid and anhydride functional groups present in the polymer chain will vary depending on the properties of the polyimide. Undesirable due to general adverse effects. For example, the acid and anhydride functional groups of the imidized acrylic polymer described herein can change the miscibility of the polymer with other thermoplastic polymers.

  Reduction of the number of acid groups and anhydride groups on the imidized acrylic polymer is known, eg, US Pat. No. 4,727,117; US Pat. No. 4,954,574; US Pat. U.S. Pat. No. 5,110,877; U.S. Pat. No. 5,264,483; and U.S. Pat. No. 5,548,033 and U.S. Published Application. 2007/0055017. U.S. Pat. No. 4,727,117 discloses that residual acid and anhydride groups can be converted to non-acid or non-anhydride groups and cannot react with imide units. A method of treating with a reagent is disclosed. These reagents include alkylating and esterifying agents such as trialkyl orthoformate or dimethyl carboxylate. The acid level, indicated by the weight percent of acid groups (such as methacrylic acid units) present in the polymer, is 0 to 10 weight percent, preferably 0 to 2 weight percent.

  PARALOID® HT-510 grade blended with PVC and PARALOID® EXL-4000 grade blended with other engineering resins by Rohm and Haas Company (Philadelphia, PA), higher glass transition Several types of imidized acrylic resins have been provided in advance, such as a family of resins having a temperature (Tg). Depending on the degree of imidization of the starting acrylic polymer, the Tg of the imidized acrylic resin changes and increases as the degree of imidization increases. PARALOID® HT-510 has a fairly low Tg, about 130 ° C. The PARALOID® EXL-4000 family is reported to have a Tg of 140 ° C to 170 ° C. PARALOID® resin is blended with nylon 6, polycarbonate, acrylonitrile / styrene / butadiene and styrene / acrylonitrile resins, and poly (ethylene terephthalate) to increase the heat resistance or melt strength of the resulting composition and optical It improves the mechanical properties or serves as a carrier for pigments and other additives.

  PARALOID® EXL-4000 grade resin has less than 1% to about 10% carboxylic acid groups; some may also contain minor amounts of anhydride groups. As mentioned above, carboxylic acid groups are clearly formed during the imidization reaction and are probably inevitable. However, some grades of these resins probably have carboxylic acid groups capped by esterification.

Additives In addition to POM and imidized acrylic polymers, the compositions described herein include ingredients commonly used in the polymer field, such as other additives, modifiers, and stabilizers and co-stabilizers. U.S. Pat. No. 3,960,984; U.S. Pat. No. 4,098,843; U.S. Pat. No. 4,766,168; U.S. Pat. No. 4,814,397; U.S. Pat. Antioxidants, pigments, colorants, UV stabilizers, tougheners, nucleating agents, glass, minerals, such as the components disclosed in US Pat. No. 5,011,890; and US Pat. No. 5,063,263. , Lubricants, fibers, reinforcing agents, and fillers. Some pigments and colorants can adversely affect the stability of the polyoxymethylene composition, but have little effect on its physical properties. Preferred heat stabilizers are described in US Pat. No. 5,011,890, with polyacrylamide being most preferred.

Method of Increasing Heat Deflection Temperature An increase in creep resistance indicates an increase in the heat distortion temperature of polyoxymethylene. The increase in creep resistance varies with the addition of low acid IA. Therefore, when the low acid IA is added, the creep resistance is improved and the heat deflection temperature is increased.

  By applying a constant load to the rectangular specimen while imposing a steady temperature rise, the heat deflection temperature of the thermoplastic material is measured. The temperature at which the deflection of the beam loaded under bending reaches a preset value is called the heating deflection temperature (HDT). The actual strain experienced by the sample under these test conditions is usually less than 1% and is essentially a flexural strain. An increase in heat deflection temperature is consistent with an increase in stiffness retention with respect to the temperature of the composition.

  In order to improve the creep resistance of the POM composition, it is also necessary to improve the rigidity. Thus, the stiffness of the POM composition is improved during exposure to steadily increasing temperatures, thereby indicating both increased heat deflection temperature and improved creep resistance.

  The tensile creep measurement shown below was performed at high temperature and high load, 90 ° C. and 25 MPa. The reduction in deformation under these conditions corresponds to better retention of stiffness, similar to that observed during measurement of the heat deflection temperature.

  However, in contrast to HDT measurements, creep resistance was measured in the more stringent tensile mode herein and the entire cross section of the sample was subjected to the same load. In addition, testing was performed until the total cumulative strain reached at least 7%. This is a much larger strain than is generally confirmed in HDT tests. Thus, the measurement of creep resistance herein reflects a more stringent test of stiffness retention and therefore has a stronger impact on the increase in HDT for the compositions described herein.

The method for increasing the heat deflection temperature described herein includes:
(A) Acid level 1-8% by weight of an imidized acrylic resin obtained by treating an acrylic polymer with a monoalkylamine having a degree of imidization and having a monoalkyl group;
(B) 92-99% by weight of polyoxymethylene having a number average molecular weight of 50,000-250,000 g / mol;
(C) optionally one or more other additives;
Melt mixing to form a melt mixed composition,
% By weight of (a) and (b), respectively, based on the total weight of (a) and (b)
The monoalkyl group has 1 to 5 carbon atoms,
The acid level is from 0 to about 2% by weight, based on the imidized acrylic resin; and the same composition, as determined by ISO 899-1, up to 5% creep strain of the molten mixture composition lacking (a) It is 200% longer than that of the product.

  In addition to showing the time to creep up to 5% as described in the paragraph above, these processes are 20% as determined by ISO-751 / -2 compared to the same composition lacking (a). Higher heat deflection temperatures can also be shown. Further, in any of the methods described herein, the imidized acrylic resin may contain cyclic imide units and / or be present in the melt mixed composition in an amount of 1-5% by weight.

  Further, in any of the methods described herein, the imidized acrylic resin is from poly (methyl methacrylate); poly (methyl acrylate); methyl acrylate and styrene, acrylonitrile, vinyl acetate, ethylene, butadiene, or methyl vinyl ether. Copolymer of at least one additional comonomer selected; group consisting of copolymers of methyl methacrylate and at least one additional comonomer selected from styrene, acrylonitrile, vinyl acetate, ethylene, butadiene or methyl vinyl ether It is obtained by treating an acrylic polymer selected from In these processes, the preferred acrylic polymer is poly (methyl methacrylate) and / or the imidized acrylic resin can be obtained by treatment with methylamine poly (methyl methacrylate).

  Further, in any of the methods described herein, the polyoxymethylene has a number average molecular weight of 50,000 to 80,000 g / mol and is selected from the group consisting of homopolymers, copolymers, and mixtures thereof. obtain. Further, in any of the methods described herein, the degree of imidization can range from 60% to 100%, preferably from 80 to 100%, more preferably from 90 to 100%.

Production of the POM Compositions Described herein The POM compositions described herein are preferably produced by tumbling or mixing individual component pellets or the like with each other. Regardless of how they are mixed, the individual components are melt blended by a mixing device capable of producing high shear within a temperature range above the softening point of the polymer blend component and below the point of significant degradation. It should be. Examples of such devices include closed mixers such as rubber mills, “Banbury” and “Brabander” mixers, single or multiple blade closed mixers with cavities heated externally or by friction, “Ko- kneader ", multi-barrel mixers such as" Farrel continuous mixer ", injection molding machines, and extruders (both single and biaxial, either co-rotating or counter-rotating). These devices can be used alone or as a static mixer, mixing torpedo and / or various devices for increasing internal pressure and / or mixing strength, eg valves, gates or screws designed for this purpose Can be used together.

  It is preferred to use a continuous mixing device to achieve intimate mixing of the blend components with maximum efficiency, consistency and uniformity. Due to high throughput, possible modular construction and ease of assembly, many mixing screw options, and ease of process temperature control and maintenance, an extruder is the simplest to use. Particularly preferred are twin screw extruders, particularly extruders incorporating high strength mixing sections such as reverse pitch elements and kneading elements.

Articles comprising the POM compositions described herein Molded articles comprising the POM compositions described herein are compression molded, injection molded, extruded, blow molded, melt spun, cast film or blow molded film technology. Can be produced by any of several common methods, such as film formation and thermoforming. Examples of molded articles include sheets, profiles, rods, films, filaments, fibers, straps, tapes, tubing, pipes and complex shaped articles such as machine or engine parts. Such molded article can be processed by orientation, stretching, coating, annealing, painting, laminating and plating after it is initially shaped. Since the blend is a thermoplastic material, the article can be crushed and reshaped.

  The POM compositions described herein have an increased upper working temperature and can withstand creep without sagging at higher temperatures compared to pure POM, especially in automotive applications that are exposed to higher temperatures on a regular basis It can be used to manufacture parts such as gears and electronic devices, and in applications where high ductility retention and good heat resistance are desired. Other particularly useful applications include parts of conveyor systems that handle food, packaged or unpackaged food intake products, dietary supplements, pharmaceuticals, and the like.

  The following examples further illustrate the compositions described herein and set forth in the claims.

Material POM-500: commercially available from DuPont under the trade name DELRIN® 500P with a melt flow rate of 15 g / 10 min measured at 190 ° C., using approximately 30,000 Mn and a weight of 2.16 kg General purpose non-impact modified POM resin.

  POM-100: Commercially available from DuPont under the trade name DELRIN® 100P with a melt flow rate of 2.5 g / 10 min measured at 190 ° C. using about 65,000 Mn and a weight of 2.16 kg. General-purpose non-impact modified POM resin.

  Plexiglas® V920: PMMA acrylic resin having a melt flow rate of 8.0 g / 10 min measured according to ASTM D1238 at 230 ° C. using a weight of 3.8 kg.

  Ultraform® E3320: a terpolymer polyacetal commercially available from BASF.

  Denka Boron Nitride SP-3: Fine particle boron nitride commercially available from Denki Kagaku Kogyo.

  Irganox® 1098: a sterically hindered phenolic antioxidant with a molecular weight of 637 g / mol, commercially available from Ciba.

Allantoin: having the formula _{C 4 H 6 N 4 O 3} , International Specialty Products, available from Wayne NJ.

apparatus:
Compounding extruder: 30 mm co-rotating twin-screw extruder with mixing and melting zones, equipped with a 0.187 inch diameter two-hole strand die and commercially available from Coperion Corporation, Ramsey, NJ USA Injection molding: 6 ounce reciprocating screw injection molding unit commercially available from Nissei Corporation, Japan.

Test Methods For Imidized Acrylic [IA] Polymers Two types of IA polymers, both “high scale” IA and “low acid” IA, both made on a “laboratory scale” were used in the study. As used herein, high acid IA has 5% or more by weight of acid, and low acid IA has 4% or less, preferably less than 1% by weight of acid. The IA was prepared using the following procedure:

  Using a 25 mm diameter single screw extruder, the starting resin was melted and metered into a 15 meter long, 12.5 mm diameter stainless steel transfer line tube. The pressure of the transfer line was adjusted using a polymer valve at the end of the transfer line. A 25 mm twin screw extruder with two vacuum hole vent ports used to pump polymer into the strand die and remove excess amine and reaction byproducts before cutting the strands into pellets. It was downstream from the polymer valve. The amine source was injected into the polymer melt using a dual syringe pump system at the beginning of the transfer line. After IA was produced in a twin screw extruder and volatiles were removed, the IA product contained carboxylic acid groups, anhydride groups, and some unreacted esters in addition to imide groups. The initially produced IA generally has at least 5% by weight of acid groups. The “low acid” version of IA is produced by passing the first produced IA through the extruder a second time and adding dimethyl carbonate to esterify the acid groups of the polymer chain.

  The IA sample is Plexiglas (registered) using the screw speed of a single screw extruder at a speed of 50 rpm, estimated to correspond to a PMMA resin feed rate of 97 g / min and a monomethylamine injection rate of 43 ml / min. Trademark: V920 was prepared by reacting with monomethylamine. The oil temperature setting value of the jacket around the transfer line was 280 ° C., and the measured polymer melting temperature was 260 ° C. The discharge pressure to the polymer valve was controlled at 800-900 psig (5.5-6.2 mPa). The methylamine injection pressure was recorded as 900-1200 psig (6.2-8.3 mPa). In the twin screw extruder, the vacuum at the vent port was recorded to be 17 (Hg) or 58 kPa. The polymer melting temperature recorded on the pelletizing die of the twin screw extruder was 245 ° C. By DSC and nitrogen analysis, the Tg was determined to be 163 ° C. and the nitrogen content was 7.5% by weight. Several small batches performed under the same nominal conditions were blended together to produce high acid IA's such as IA-HA-1.

  Low acid IA (such as IA-LA-1) was extruded again at a set point of 100 ° C. overnight in a dry high acid material (adsorption hopper dryer) manufactured under the nominal conditions described above) Prepared by treatment with dimethyl carbonate. The screw speed of the single screw extruder is 74 rpm, which is estimated to correspond to a feed rate of about 140 g / min. The syringe pump was filled with dimethyl carbonate and injected into the transfer line at a rate of 14 ml / min to reduce the amount of acid present in the polymer. The set point of the oil heater that heats the oil covering the transfer line was set at 280 ° C. The discharge pressure at the end of the transfer line was controlled at 250-440 psig (1.7-3 mPa). The injection pressure of the syringe pump was 640 to 880 psig (4.4 to 6 mPa). The melt temperature of the high acid polymer recorded with an adapter between the single screw extruder and the transfer line was 270 ° C. The melting temperature of the low acid IA in the pelletizing die of the twin screw extruder was 235-265 ° C. By DSC and nitrogen analysis, the Tg of the low acid material was determined to be 151 ° C. and the nitrogen content was 7.5% by weight. Several small batches were combined with each other to obtain a low acid IA.

  A blend of small batches of imidized acrylic material was analyzed and the results are shown in Table A below.

  The number of nitrogen as a weight percent of IA polymer nitrogen was determined by standard combustion using a CHN analyzer, Carlo Erba Model 1108. The percent imidization (by weight) of the polymer was calculated based on the number of nitrogens. The 100% imidized PMMA resin produced using monomethylamine has a nitrogen number of 8.4. As the molecular weight of the amine source increases, the 100% imidation nitrogen number decreases.

  The weight percent of methacrylic acid in the IA polymer was determined by titrating and calculating the amount of methacrylic acid from the molar amount of neutralized acid. The weight percent of ester groups can be calculated by subtracting imide weight percent and acid weight percent from 100. Since the anhydride could not be detected by IR, the amount of anhydride was considered negligible.

  The glass transition temperature [“Tg”] of the IA polymer is equilibrated at 0 ° C., heated to 200 ° C., cooled to 0 ° C., and again heated to 200 ° C. at 10 ° C./min to ASTM D3418 (0-200 ° C) as determined by differential scanning calorimetry {"DSC"] and Tg was recorded during the second heating.

  All components of the following various samples were first dry blended in the required proportions and then fed to a twin screw extruder to obtain a uniformly melt mixed sample. Specifically, IA samples were separately incorporated into either POM-500 or POM-100 by melt blending in an 18 mm Coperion twin screw extruder. Two separate feeders were used to feed the IA and POM components to the back of the extruder. Prior to blending, the IA pellets were dried at 100 ° C. for 5 hours. A relatively strong screw design was used to achieve the desired amount of shear and mixing. Upon exiting the extruder die, the emerging strand was quenched in a water bath and then cut into 3 mm long pellets with a conventional strand cutter. The pellets were then dried overnight at 80 ° C. and injection molded on a 1.5 ounce Arburg injection molding machine to form test specimens.

  The compounding and injection molding process went smoothly without difficulty except that specimens made from pure IA polymer were very brittle.

  Mechanical and thermal tests were performed using the ASTM test method. The bending modulus was determined according to ASTM D-790. Notched Izod impact strength was determined according to ASTM D-256. Charpy impact strength was determined according to ISO 179 at 23 ° C. The Vicat temperature was determined according to ASTM D1525 with a temperature rise rate of 2.0 ° C./min, a force of 10 Newtons and a penetration of 1 mm. The heat deflection temperature (HDT) was determined at 264 psi (1.8 MPa) in each case according to ASTM D-648. Dynamic mechanical analysis (DMA) was performed to evaluate the increase in modulus at high temperature and the increase in upper working temperature at constant stiffness.

  Table 1 shows the heat deflection temperatures of blends of POM-500 with high acid IA and low acid IA.

  At 5% by weight of IA-HA-1 (high acid) in POM-500 (Comparative Example C2), HDT was somewhat reduced compared to pure POM-500. In the case of low acid IA-LA-1, HDT increased slightly.

  Table 2 shows the heat deflection temperatures for various POM-100 blends and various IAs. IA-LA-1 was very brittle and could not produce HDT test specimens, and the HDT of IA-LA-1 was estimated based on its Tg.

  HDT of POM-100 modified with 5% by weight of high acid IA-HA-2 showed very little improvement (Comparative Example C5 compared to Comparative Example C3). However, HDT was significantly increased using, for example, up to about 5 weights of low acid IA-LA-1. With a low acid IA loading of about 1 to about 8% by weight based on the total amount of POM and IA, the HDT increased from about 5% to about 35% compared to the pure POM composition.

  As shown in Table 2, blending the low acid IA at only 2.5% and 5% by weight increased the HDT from 97.6 ° C in the control sample to 124 ° C and 128 ° C, respectively; That is, an increase of 26 ° C. and 31 ° C., or an increase of 27% and 31%, respectively. Examples up to about 8% by weight of low acid IA showed no further improvement.

  When IA-LA-2 was used at an addition rate of 5% by weight, a similar increase in HDT was observed. From a series of samples using IA-LA-3, it was found that the greatest increase in HDT was achieved at an IA addition rate of 5-10 wt%. The HDT of the sample with IA-LA-3 in an amount of 10-40% by weight was essentially the same (Comparative Examples C6-C10). The weight percentage of imide in IA-LA-3 was lower than that of IA-LA-1 as well as its Tg. Without being bound to a particular theory, the lower HDT, confirmed at an IA-LA-3 addition level of 5% by weight, can be explained by these factors.

  In general, the results in Table 2 demonstrate a significant and surprising improvement in the heat resistance of the POM compositions described herein by incorporating very small amounts of IA, particularly low acid IA. HDT increases at an IA addition rate of about 1 to about 40% by weight; the effect is most apparent at an addition rate of 1-8% by weight, especially about 2 to about 5% by weight. The increase in HDT achieved by adding about 8 to about 40% by weight of IA is not particularly significant. When IA exceeds about 40% by weight, especially at IA 50-100% by weight, the continuous phase in the blend can change from POM to IA, and then the main properties of the blend change. Specifically, as the IA of the blend increases, the HDT may increase again to a pure IA HDT. IA samples with acid levels above about 2% by weight showed significantly less HDT increase than the 5% by weight level.

  Comparing Examples 1 and 5, it was found that even when low acid IA was added to low molecular weight POM-500, the remarkable improvement was not obtained as in the case where similar low acid IA was added to high molecular weight POM-100. I understand.

  The stiffness of POM-100 also increased with an addition rate of about 1% to about 8% by weight. From Tables 3 and 4, in the IA range of 2.5-7.5% by weight, both the bending modulus at room temperature (under a small crease) and secant modulus (under a small strain) increase by about 30%. I understand that. When the IA was more than about 8% by weight and up to about 40% by weight, there was little further improvement in bending modulus.

  The addition of IA did not adversely affect the tensile strength. In contrast, Table 5 shows that the tensile strength increased slightly up to IA 5 wt%. Table 5 shows a low level of elongation reduction, but the results show that the sample still maintains reasonably good ductility to meet end use requirements. In particular, samples with IA of 20% by weight or more did not yield in these tensile tests, and the fracture strain was remarkably reduced.

  Dynamic mechanical analysis (DMA) results showed a significant improvement in storage modulus (stiffness). The storage modulus E 'represents the elastic element of the modulus of the material as opposed to the viscous element. From Table 6, in the temperature range of 70 ° C., 80 ° C., 90 ° C., and 100 ° C., Example 5 having 5% by weight of IA has a storage modulus of 24-34% of the storage modulus of the control at the same test temperature. It can be seen that it has an increasing range. Samples with a range of IA 5-8% by weight showed a slight further improvement.

  From Table 7, it can be seen that for IA modified blends compared to glass fiber reinforced POM-100 (C11): (1) percent elongation was maintained; (2) there was less reduction in Charpy impact.

  From Table 8, in a long term high temperature creep test conducted at 90 ° C. for 60 minutes with a force of 2 MPa, a POM composition comprising POM-100 modified with IA 2.5 wt% and 5 wt% is It can be seen that the creep reduction was about 20% by weight compared to the unmodified POM.

  Table 9 shows that thermogravimetric analysis ["TGA"] of the test samples showed that inclusion of IA in the POM compositions described herein improved its thermal stability. Molded specimen specimens are heated from 30 ° C. to 230 ° C. at 10 ° C./min in a nitrogen atmosphere and subsequently maintained at 230 ° C. for 60 minutes. Infrared spectroscopy was used to detect the gas generated during the temperature rise. Off-gas material was collected and analyzed for formaldehyde generation during the entire heating period. From the TGA results, it is shown in Table 9 that the total weight loss of the sample is small and the generation of formaldehyde is small compared to the pure POM.

  Table 10 shows test results for improved creep resistance for additional POM compositions described herein. Creep resistance is a term equivalent to the time to creep strain X%. All components of the sample in Table 10 were first dry blended in the required proportions and then fed to a twin screw extruder to obtain a uniformly melt mixed sample. The composition was formulated using a barrel temperature of 200-210 ° C. and a throughput of 30 pounds / hour at 150 rpm. The resulting melt extrudate was quenched in a 25 ° C. water bath and pelletized into cylindrical pellets having a length of about 0.25 inch [1 cm] and a diameter of 0.125 inch [0.5 cm]. The pellets were then dried under vacuum at 80 ° C. for 4 hours.

  After drying, the pellets were fed into an injection molding unit and the barrel was heated to 200-210 ° C. The mold was heated to 90 ° C. An insertion mold having a shape defined by ISO527-2 / 1A was used. Prior to testing, the resulting specimens were equilibrated at 23 ° C. and 50% relative humidity for 48 hours.

  A tensile creep test was performed in accordance with ISO899-1. The tensile creep test was performed at 90 ° C. and an initial stress of 25 MPa. The tensile strain of the sample was measured using an extensometer. All samples were deformed to about 10% tensile strain.

  In Table 10, C-12, C-13, and C-14 are comparative examples, and Ex-8 and Ex-9 are examples of POM compositions described herein. From Table 10, Example 8 with 2.5% by weight of low acid IA has a high molecular weight POM but no IA, with 0.1% by weight boron nitride SP-3 and 0.05% by weight allantoin. It can be seen that it showed a 208% increase in creep resistance as reported herein as time to creep strain of 5% compared to the composition C-14. Specific results were: 720 seconds (C-14) versus 2220 seconds (Ex-8). Example 9 with a low IA of 5 wt% showed a dramatic 300% increase in creep resistance compared to C-14. Importantly, C-14 was the comparative example with the highest creep resistance of the three comparative examples tested, probably due to the addition of boron nitride and allantoin. Thus, comparing Examples Ex-8 and Ex-9 with C-14 demonstrates the smallest improvement in creep resistance.

  Suitably, comparing the time to 5% Ex-8 creep strain versus C-12 shows an increase of 1750%, or 120-2220 seconds. Ex-9 versus C-12 shows a 2450% increase in time to 5% creep, ie an increase of 120-3060 seconds.

  Similarly, excellent results were achieved in comparing the time of C-13 to Ex-8 and Ex-9 up to 5% creep strain. C-13 contains 2% by weight of Ultraform® 3320, which is reported to have an HDT of 105 ° C., and may have increased creep resistance compared to C-12. Ex-8 had an increase of 240-2220 seconds, an increase of 825%. Ex-9 had an increase of 240-3060 seconds, an increase of 1175%.

  Creep resistance can also be measured as the time up to 7% creep strain. When using measurements of creep resistance, the improvement of Ex-8 and Ex-9 over C-12 is 1463% and 2000%, respectively. The increase in time to 7% for Ex-8 and Ex-9 for C-13 is 681% and 950%, respectively. The increase in time to 7% creep strain for Ex-8 and Ex-9 relative to C-14 is 191% and 291%, respectively.

Claims (15)

(A) acid level;
1 to 8% by weight of an imidized acrylic resin obtained by treating an acrylic polymer with a monoalkylamine having a degree of imidization and having a monoalkyl group;
(B) 92-99% by weight of polyoxymethylene having a number average molecular weight of 50,000-250,000 g / mol;
(C) optionally one or more other additives;
Comprising a step of melt mixing and forming a melt mixed composition comprising:
The weight percentages of (a) and (b) are based on the total weight of (a) and (b), respectively,
The monoalkyl group has 1 to 5 carbon atoms;
The imidization degree is 20% to 100%,
The acid level is 0-2% by weight of the imidized acrylic resin; and the same composition, as determined by ISO 899-1, up to 5% creep strain of the molten mixture composition lacking (a) A method that is more than 200% longer than that of the object.   2. The method of claim 1 wherein the increase in heat deflection temperature as determined by ISO 75-1 / -2 is 20% or more higher than that of the same composition lacking (a).   The method according to claim 1, wherein the imidized acrylic resin includes a cyclic imide unit.   The method according to any one of claims 1 to 3, wherein the imidized acrylic resin is present in the melt-mixed composition in an amount of 1 to 5% by weight. The imidized acrylic resin is
Poly (methyl methacrylate); poly (methyl acrylate); copolymer of methyl acrylate and at least one additional comonomer selected from styrene, acrylonitrile, vinyl acetate, ethylene, butadiene or methyl vinyl ether; and methyl methacrylate and styrene A copolymer with at least one additional comonomer selected from: acrylonitrile, vinyl acetate, ethylene, butadiene or methyl vinyl ether; obtained by treating with methylamine an acrylic polymer selected from the group consisting of: The method as described in any one of -4.   The method according to claim 1, wherein the polyoxymethylene has a number average molecular weight of 50,000 to 80,000 g / mol.   The method according to any one of claims 1 to 6, wherein the polyoxymethylene is selected from the group consisting of homopolymers, copolymers, and mixtures thereof.   The method according to any one of claims 1 to 7, wherein the degree of imidization is 60 to 100%, preferably 80 to 100%, or more preferably 90 to 100%. (A) 92-99% by weight of polyoxymethylene having a number average molecular weight of 20,000-250,000 g / mol based on the total weight of (a) and (b); and (b) an acrylic polymer with a monoalkylamine From about 1 to about 8 weight percent based on the total weight of (a) and (b) of the imidized acrylic resin obtained by treating with
A thermoplastic composition comprising:
Thermoplastic composition wherein the monoalkyl group has 1 to 5 carbon atoms, the imidization degree is 20% to 100%, and the acid level is 0 to 2% by weight of the imidized acrylic resin. object.   The composition according to claim 9, wherein the imidized acrylic resin contains a cyclic imide unit.   The composition according to claim 9 or 10, wherein the polyoxymethylene has a number average molecular weight of 50,000 to 100,000 g / mol, preferably 50,000 to 80,000 g / mol. The imidized acrylic resin is obtained by treating an acrylic polymer with methylamine, and the acrylic polymer is
Poly (methyl methacrylate); poly (methyl acrylate); copolymer of methyl acrylate and at least one additional comonomer selected from styrene, acrylonitrile, vinyl acetate, ethylene, butadiene or methyl vinyl ether; and methyl methacrylate and styrene 12. A composition according to any one of claims 9 to 11 selected from the group consisting of: a copolymer with at least one additional comonomer selected from acrylonitrile, vinyl acetate, ethylene, butadiene or methyl vinyl ether.   The composition according to any one of claims 9 to 12, wherein the degree of imidization is 60% to 100%, preferably 80% to 100%, more preferably 90% to 100%.   The composition according to any one of claims 9 to 13, wherein the imidized acrylic resin is present in the composition in an amount of 1 to 5% by weight.   An article having a heating deflection temperature determined in accordance with ASTM D-648 that exceeds the heating deflection temperature of a comparative standard article, wherein the comparative standard article is from a polyoxymethylene composition that does not contain an imidized acrylic resin. 15. An article according to any one of claims 9 to 14, wherein the molded article and the comparative standard article have the same shape and structure except that they are manufactured.