JPS6131143B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to improved fiber reinforced polyoxymethylene molding compositions. Specifically, the present invention relates to fiber reinforced polyoxymethylene molding compositions that produce composites with improved physical properties. As is well known, polyoxymethylene or polyacetal is a thermoplastic resin widely used for producing molded objects. Particularly strong and tough molded bodies are obtained when polyoxymethylene resins are intimately mixed with various reinforcing materials. However, it has been discovered that various additives are necessary to impart the desired physical properties to molded objects made from reinforced polyoxymethylene polymers. Poor physical properties are usually attributed to poor adhesion between the polyoxymethylene polymer and the fibrous reinforcement. Thus, for example, the reinforced polyoxymethylene polymers described in US Pat. No. 3,455,867 use chemical coupling agents to increase the strength of molded objects. British Patent No. 993,600 discloses polyoxymethylene compositions containing carbodiimides which are primarily useful for anti-aging purposes. Although this patent broadly suggests the use of mono- and poly-carbodiimides, specific examples include 2,6,2',6'-tetraisopropyldiphenylcarbodiimide and 1.
3,5-triisopropyl-benzene-2,4-
The use is limited to highly hindered carbodiimides such as diisocyanate polycarbodiimides. U.S. Pat. No. 3,901,846 discloses that incorporation of small amounts of certain high molecular weight phenoxy resins into intimate mixtures of polyoxymethylene polymers and reinforcements provides desirable improved physical properties and improved surface effects in molded objects. It is being announced. Different uses of carbodiimides in the production of polyoxymethylene polymers are described in U.S. Patent No.
Also published in issues 3170896 and 3135718. Conventional polycarbodiimides have also been used as thermal and hydrolytic stabilizers for polyesters and in U.S. Pat.
No. 3835098, serial number 715946 published on August 19, 1976, and serial number published on December 22, 1976.
753384, British Patent Nos. 1056202, 1231975 and 1330036, Japanese Patent Publication 75-00044 (Chem.
Abstract, 17232W, 82 volumes 1975), Belgian Patent No.
No. 626176 (Chem.Abstract, 2054f, vol. 61 1964)
and W. Neumann and P. Fitschier, “Preparation of carbodiimides from isocyanates”
(Anqew.Chem.Internat.Edit.625, 1962). In view of the prior art, it is an object of the present invention to provide improved reinforced polyoxyethylene molding compositions capable of producing composites with improved physical properties. Another object of the present invention is to provide a reinforced polyoxymethylene composite having physical properties superior to those of conventional phenoxy-modified and fiber-reinforced polyoxymethylene bodies. Yet another object of the present invention is to improve reinforced polyoxymethylene molding resins with improved physical properties using a well-defined class of polycarbodiimides not hitherto used in this field. To provide a methylene molded object. Other objects of the invention will become apparent from the following description of embodiments. In accordance with the present invention, a special class of polycarbodiimides, in particular unhindered aromatic polycarbodiimides having up to one methyl substituent per aromatic ring and at least three carbodiimide groups per molecule, is now a polyoxymethylene and a total composition weight It has been discovered that the physical properties of the resulting fiber-reinforced composites are improved when incorporated with fiber reinforcement in an amount of about 0.5 to 5% by weight, based on the weight of the material. In another form of the invention, the polycarbodiimide can be used in admixture with high molecular weight thermoplastic phenooxy resins, which are well known in the art to improve the physical properties of reinforced polyoxymethylene polymers. have been found to provide a synergistic improvement in the physical properties of, in particular, glass-reinforced polyoxymethylene objects. As used herein, "polyoxymethylene" is intended to include both homopolymers and copolymers, including so-called capped homopolymers, ie, acylated polymers. This class of polymers, which can be produced by methods well known in the art, repeats -
It has OCH ₂ - units and is generally prepared by polymerization of anhydrous formaldehyde or trioxane. Particularly useful in the present invention are polymers having at least one chain with repeating oxymethylene (-OCH ₂ -) units, interspersed with -OR- groups, and in which the R's are directly bonded to each other. is a divalent group having at least two carbon atoms, and is located between two valent atoms in the chain, and has an inert substituent on the R group, that is, a substituent that does not cause undesired reactions. It is a polyoxymethylene copolymer, which is a group that can be used as a base. Preferred copolymers contain from about 60 to about 99.6 mole percent repeating oxymethylene groups. In a preferred embodiment R is, for example, an alkylene or substituted alkylene group having at least 2 carbon atoms. The copolymer utilized in the present invention has the formula: (However, in the formula, n is zero or an integer from 1 to 5, and R ₁
and R ₂ represent inert substituents, ie, substituents that do not cause undesired reactions. ) has a structure consisting of repeating units. In the above formula, n is zero in 60 to 99.6% of the repeating units. A preferred type of copolymer has 60 to 60 repeating units.
It has a structure consisting of circulating units, of which 99.6% are oxymethylene units. This copolymer has trioxane and structure: (In the formula, n is 0, 1 or 2.) It is produced by copolymerization with a cyclic ether. Other preferred examples of polymers include copolymers of trioxane and cyclic ethers having at least two contiguous carbon atoms, such as those described in US Pat. No. 3,027,352. Ethers that can be used include ethylene oxide, 1,3-dioxolane, 1,3,5-trioxepane, 1,3-dioxane, trimethylene oxide, pentamethylene oxide, 1,2-
These include propylene oxide, 1,2-butylene oxide, neopentyl formal, pentaerythritol diformal, paraldehyde, tetrahydrofuran, and butadiene monooxide. Preferred polymers for use in accordance with the invention include an average molecular weight of at least about 35,000, a melting point of at least 150°C and an intrinsic viscosity of at least about 0.8 (in p-chlorophenol containing 2% by weight alpha-pinene).
It was made into a 0.1% by weight solution and measured at 60°C. ) is a moldable thermoplastic material. Usually polyoxymethylene polymers are substantially pre-stabilized. This stabilization method takes the form of stabilizing the polymer chain by decomposing the molecular ends until a relatively stable carbon-to-carbon bond exists at each end of the polymer chain. This degradation can be accomplished by melt hydrolysis as described in US Pat. No. 3,318,848 or by solution hydrolysis as described in US Pat. No. 3,219,623. Of course, mixtures of polyoxymethylene polymers stabilized by melt hydrolysis and polyoxymethylene polymers stabilized by solution hydrolysis can also be used. The polyoxymethylene may also contain conventional stabilizers such as antioxidants and/or acid scavengers. Generally, these stabilizers may be present in a total amount up to about 3% by weight based on the weight of the polyoxymethylene polymer. The polycarbodiimides which can be used in the present invention are selected from a specifically defined group. (a) derived from one or more aromatic diisocyanates with up to one methyl substituent or no substituents on each aromatic ring; and (b) at least one per polycarbodiimide molecule. It has been found that only polycarbodiimides with 3 carbodiimide units produce the desired results. It is believed that the specific polycarbodiimides specified herein, alone or in combination with thermoplastic phenooxy resins, improve the adhesion between the chemical reactivity of the oxymethylene polymer chains and the fibrous reinforcement primarily through a complex mechanism. However, the mechanism cannot be easily explained. Carbodiimides having less than 3 carbodiimide units per polycarbodiimide molecule are not suitable for use in the compositions of the present invention because they are too volatile for practical use at the temperatures of typical molding, ie, injection molding operations and are susceptible to evolution during molding. Furthermore, such carbodiimides have the property of not mixing well with polyoxymethylene. The polycarbodiimide must have the property of being miscible with polyoxymethylene in the molten state. Polycarbodiimides useful in the present invention generally have an average molecular weight of about 450 to 10,000, typically about 800 to about 8,000, preferably about 1,000 to about 6,500.
Polycarbodiimides having a molecular weight of about 10,000 or more cannot be used in the present invention because they do not dissolve in polyoxymethylene melts. Polycarbodiimides useful in the present invention typically include poly(tolylcarbodiimide), poly(4.
4'-diphenylmethanecarbodiimide), poly(3,3'-dimethyl-4,4'-biphenylenecarbodiimide), poly(p-phenylenecarbodiimide), poly(m-phenylenecarbodiimide),
Poly(3,3'-dimethyl-4,4'-diphenylmethanecarbodiimide) and mixtures thereof. Preferred polycarbodiimides are poly(tolylcarbodiimide), poly(4,4'-diphenylmethanecarbodiimide), and mixtures thereof. Poly(4,4'-diphenylmethanecarbodiimide) is particularly preferred because its carbodiimide groups are most readily available for interaction between the oxymethylene polymer and the fiber reinforcement. It also only gives the mixture a pale yellow color. Poly(tolylcarbodiimide) has less availability of carbodiimide groups and provides more intense color to the mixture. Polycarbodiimides can be prepared by methods well known to those skilled in the art, such as by heating the aromatic diisocyanate compounds described above, with or without the presence of a solvent. The production of polycarbodiimide is accompanied by the generation of carbon dioxide gas. The polycarbodiimides useful in the present invention can be produced without the use of catalysts, but without catalysts, considerably high temperatures (about 300° C.) are required. Certain polycarbodiimides produce large amounts of by-products and colored products when such high temperatures are used. Polycarbodiimides are therefore generally described in U.S. Pat.
Chem. 27, 3851 (1962) by heating isocyanates in the presence of a catalyst such as the phosphorus-containing catalysts described in Chem. 27, 3851 (1962). J.Amer.Chem.Soc. of Kirambel et al.
84, 3673 (1962) are good catalysts. A particularly preferred catalyst is 1-ethyl-3-methyl-3-phosphorin-1-oxide. Since isocyanates react rapidly with water at elevated temperatures, it is preferred to conduct the polycarbodiimide forming reaction under argon or other dry inert gas to minimize the amount of water that comes into contact with the reactants. Aromatic diisocyanates that can be used to produce the desired polycarbodiimides include toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 3.
3'-dimethyl-4,4'-diphenylmethane diisocyanate, and mixtures thereof. Preferred aromatic diisocyanates are toluene diisocyanate, 4,4'-diphenylmethane diisocyanate and mixtures thereof. Aromatic diisocyanates are best used in essentially pure form, but with minimal amounts (i.e., less than about 2% by weight) of other compounds such as ureas, amines, and trace amounts of water and/or acids. May include.
"Toluene diisocyanate" means 2,4-toluene diisocyanate, 2,6-toluene diisocyanate or a mixture of these isomers. 2,4- and 2,6-isomer mixtures are usually 2,
80 parts by weight of 4-toluene diisocyanate and 2.6 parts by weight
-20 parts by weight of toluene diisocyanate or 2.4 parts by weight
-65 parts by weight of toluene diisocyanate and 2.6-
Consists of 35 parts by weight of toluene diisocyanate. Small amounts (i.e., 50% by weight or less) of aromatic monoisocyanates can also be used in conjunction with aromatic diisocyanates to prepare the polycarbodiimides used in the process of the invention. The monoisocyanates act as chain stoppers and help control the molecular weight and viscosity of the resulting polycarbodiimides. The amount of aromatic monoisocyanate used will depend on the particular diisocyanate used, but will generally be about 20 to about 50% by weight, typically about 25 to 45%, preferably about 30 to 40% by weight, based on the total weight of the isocyanate compound used. % by weight, and correspondingly the diisocyanate is generally about 50 to about 80
% by weight, typically from about 55 to about 75%, preferably from about 60 to about 70%. Aromatic monoisocyanates that can be used in this way include, for example, p-chlorophenyl isocyanate, m-chlorophenyl isocyanate, phenyl isocyanate, p-methoxyphenyl isocyanate, m-methoxyphenyl isocyanate, p-tolyl isocyanate, m-tolyl isocyanate, o-tolyl isocyanate, p-
These include nitrophenyl isocyanate, m-nitrophenyl isocyanate, and mixtures thereof. Phenyl isocyanate, p-chlorophenyl isocyanate, m-chlorophenyl isocyanate, and mixtures thereof are preferred monoisocyanates for use in the present invention. Polymerizable carbodiimides cannot be obtained even if monoisocyanates are heated alone, so monoisocyanates alone cannot be used to produce polycarbodiimides. The polycarbodiimide in the reinforced polyoxymethylene resin composition typically contains about
0.5 to 5% by weight, typically about 1 to 3% by weight
used in amounts of Polycarbodiimide amount approximately 0.5
Within 5% by weight, extensive mixing with the polyoxymethylene is required to improve the desired physical properties, but above about 5% by weight, the physical properties are not improved much more than with small amounts, and the composition Easy to cause undesirable discoloration. Any of the polycarbodiimides described above can be used alone or mixed with other polycarbodiimides to achieve the desired effect. In a second form or embodiment of the invention, an improved thermoplastic reinforced polyoxymethylene composition is formed by mixing both a polycarbodiimide and a specific high molecular weight phenooxy resin into the composition. The phenooxy resin that can be used in accordance with the present invention is disclosed in U.S. Pat.
It is described in No. 3901846. This resin is a high molecular weight thermoplastic resin produced from 2,2'-bis-(4-hydroxyphenyl)propane and epichlorohydrin by the method described in U.S. Pat. No. 3,356,646. The basic chemical structure of phenooxy resin is the same as that of epoxy resin. However, it is a unique class of resins that differs from epoxy resins in a variety of important properties. 1 Phenoxy resin is a tough and flexible thermoplastic substance. This average molecular weight is about 15,000 to 13,000, compared to 340 to 13,000 for ordinary epoxy.
75,000, preferably about 20,000 to 50,000, which cross-link in the polymerization reaction. 2. Phenoxy resins do not have highly reactive terminal epoxy groups and are thermally stable and have a long shelf life. 3. Phenoxy resins can be used without further chemical changes. This requires no catalyst or hardener, making it a useful product, whereas epoxy resins require a catalyst or hardener to be used. The phenooxy resins used in the present invention have a repeating structure: and an average molecular weight of about 15,000 to 75,000. As can be seen, the terminal structure is completed with a hydrogen atom or a suitable end capping group. The polycarbodiimide and the phenooxy resin are combined in the reinforced polyoxymethylene composition in an amount of about 0.6 to 5% by weight, preferably about 1 to 3% by weight, based on the total weight thereof. Total amount of polycarbodiimide and phenoxy resin is approximately 0.6% by weight
If the amount is less, the desired improvement cannot be achieved or a long time mixing with polyoxymethylene is required. Amounts greater than about 5% by weight do not provide a significant improvement and are not approved. The ratio of polycarbodiimide to phenooxy resin usually ranges from about 1:16 to 50:1. It is preferred that the amount of polycarbodiimide used is at least the same as the amount of phenooxy resin used. If both polycarbodiimide and phenooxy resin are utilized, the minimum amount of polycarbodiimide should be about 0.5% by weight and the minimum amount of phenooxy resin should be about 0.1% by weight, based on the total composition weight. The physical properties of composite objects made from reinforced polyoxymethylene compositions containing both polycarbodiimide and phenoxy resin are significantly better than unmodified reinforced polyoxymethylene molding compositions and the same amount of polycarbodiimide alone as the combined amount of the two additives. or better than the physical properties of molded products made from reinforced polyoxymethylene molding compositions containing an amount of phenooxy resin alone (by weight). It appears that increasing the amount of polycarbodiimide for a given amount of phenooxy resin improves the physical properties of the molded product. The polyoxymethylene, the fibrous reinforcement and the polycarbodiimide and, in the second form of the invention, the phenooxy resin are mixed or compounded in any convenient manner. Thus, for example, in a preferred embodiment, the polycarbodiimide or polycarbodiimide and the phenooxy resin are simultaneously intimately mixed with the toughening agent and the oxymethylene polymer. Mixing times involving fibrous reinforcement should be minimized to avoid wear and tear of the fibrous reinforcement. For example, all ingredients may be mixed in a ZSK extruder with the ingredients at a melting temperature of approximately 400 to 405 mm.
A duration of 0.5 to 3 minutes (eg 1 to 2 minutes) is sufficient. The reinforcement used can be intimately mixed with the other ingredients in an extruder, heated rolls or other mixer by dry mixing or melt mixing. Also, the reinforcement can be mixed with the monomer during the polymerization reaction as long as the polymerization reaction is not affected.
Fibrous reinforcement materials that can be used are those commonly known for thermoplastic molding resins and include synthetic fibers such as glass fibers (cut or continuous rovings), asbestos fibers, cellulose fibers, and graphite fibers. However, best results have been obtained using glass fiber reinforced polyoxymethylene compositions for polycarbodiimides and mixtures of polycarbodiimides and phenoxy resins. The amount of reinforcing material may range from about 2 to about 60% by weight, preferably from 5 to 50% by weight, based on the total molding composition weight. In addition to the polyoxymethylene polymers of this invention, the reinforced polyoxymethylene molding compositions of reinforcing agents and polycarbodiimides and optionally phenoxy resins also contain lubricants, dyes, and conventional antioxidants and acid scavengers. It may contain the minimum amount of additives commonly used in unreinforced polyoxymethylene molding compositions, both polymerizable and non-polymerizable. A typical molding composition with additives according to the invention includes, for example, 57 to 89.9% by weight polyoxymethylene, 10 to 40% by weight glass fiber, and 0.1% antioxidant.
2.0% to 2.0% by weight and acid remover 0.05 to 1.0% by weight
Consists of. A preferred composition improved by the present invention includes 69 to 79.8% by weight polyoxymethylene polymer, 20 to 30% by weight glass fiber, and 0.15% antioxidant.
0.5% to 0.5% by weight and 0.1 to 0.5% by weight of acid scavenger. For example, a mixture of 72.9 parts by weight of polyoxymethylene, 0.5 parts of antioxidant and 0.1 part of acid remover, 25 parts of glass fiber and 1.5 parts of polycarbodiimide
or polyoxymethylene resin mixed with 0.5 parts of antioxidant and 0.1 part of acid remover.
71.4 parts by weight may be mixed with 25 parts of glass fiber, 1.5 parts of polycarbodiimide, and 1.5 parts of phenooxy resin. However, the actual composition selected may vary depending on the desired properties of the molded object, as will be apparent to those skilled in the art. Molded objects made from thermoplastic reinforced polyoxymethylene molding compositions according to the invention have distinct physical properties when compared to objects made from polyoxymethylene reinforced with polycarbodiimide or polycarbodiimide and fibers free of phenoxy resin. This shows significant improvements. For example, compositions containing about 5 to 50% by weight of glass fibers and about 0.5 to 5% by weight of polycarbodiimide, based on the total weight of the composition, typically increase tensile strength by up to 70% and Izod impact value by up to 40%. The following examples illustrate the invention:
This is not limited to this. Example (1) A mixture of polyoxymethylene polymer, glass fiber, and polycarbodiimide, and (2) a mixture of polyoxymethylene polymer, glass fiber, polycarbodiimide, and phenoxy were put into a ZSK extruder in the respective proportions shown in the table below. and mixed for 1 to 2 minutes. The various compositions were then molded into drawbars at 21/2 oz. The conditions of the Statube molding machine are as follows: Cylinder temperature 410〓 Molding temperature 180〓 Cycle time Injection 10 seconds Cooling 20 seconds Other 2 seconds Total 32 seconds Screw 80RPM Injection pressure 9000-18000psi The polyoxymethylene polymer used in the example was It was a polyoxymethylene copolymer made from trioxane and 2% by weight of ethylene oxide and had an average molecular weight of about 68,000. The oxymethylene polymer was a polymer mixture consisting of 67 parts by weight melt hydrolyzed according to US Pat. No. 3,318,848 and 33% by weight solution hydrolyzed according to US Pat. No. 3,219,623. Polyoxymethylene polymer or pre-mix standard addition package and 0.5% 2.2'-
It had been "stabilized" or "pre-stabilized" by adding methylene-bis-(4-methyl-6-tert.butylphenol) antioxidant and 0.1% cyanoguanidic acid scavenger. The glass fibers were cut to 3/16 inch lengths and were 50 to 55 x 10 ^-5 inches in diameter. Glass fiber is Owens Corning fiber.
It was OCF409 type commercially available from Glass. The polycarbodiimide used as an additive was poly(4,4'-diphenylmethanecarbodiimide) (commercially available from Apgeon Company, hereinafter referred to as PCDI) with an average molecular weight of approximately 5000, and the thermoplastic phenooxy resin was epichlorohydrin. and 2.2-
It was produced from bis(4-hydroxyphenyl)propane and had an average molecular weight of about 30,000. The physical properties of moldings produced from the formulations according to the invention are shown in the table. For comparison, instead of using polycarbodiimide, polycarbodiimide, and phenooxy, (1) phenooxy alone, (2) 2.
Diepoxide (hereinafter referred to simply as epoxide), which is a reaction product of 2'-bis(4-hydroxyphenyl)-propane and epichlorohydrin and has an average molecular weight of 8,000 to 12,000 and is commercially available under the trademark Epirets 560, A mixture with carbodiimide and (3) methylene diphenyl isocyanate (hereinafter referred to as MDI; conventionally used to improve the physical properties of reinforced polyoxymethylene compositions, but its use is dangerous due to its toxicity). The physical properties of molded products made from the same mixture were shown.

【table】

【table】

Table: Comparative results show that polycarbodiimide significantly improves physical properties over the unadded control and is also better than the use of phenooxy resin alone. The use of a mixture of polycarbodiimide and phenooxy resin provides a greater improvement than the use of either of these alone and the use of a mixture of polycarbodiimide and epoxy resin. Although moldings made from compositions according to the invention are slightly less improved than those made from compositions containing MDI additives, there are no toxicity problems inherent in the use of MDI. Also, the composition according to the invention may require the same molding conditions as would require a composition containing only the phenooxy additive. However, MDI modified compositions require high pressure molding. Similar remarkable results are obtained using other polyoxymethylenes, polycarbodiimides and phenooxy resins within the scope of the invention as previously defined. Concurrently filed U.S. Pat. A process is claimed for producing unreinforced polyoxymethylene molding compositions containing a small amount of polycarbodiimide that plays a different role (i.e., reduces molding deposits). Although the present invention has been described in terms of preferred embodiments, it is intended that the present invention not be limited thereto, but that the present invention may be practiced in any manner within the scope of the claims.

Claims (1)

Claims: 1. (1) a polyoxymethylene polymer, (2) about 2 to 60% by weight fibrous reinforcement, based on the total weight of the composition, and (3) 1 per (a) aromatic ring. from about 0.5 to 5% by weight, based on the total weight of the composition, derived from aromatic isocyanates substituted or unsubstituted with up to 3 methyl groups and (b) having at least 3 carbodiimide units per polycarbodiimide molecule. 1. An improved fiber-reinforced polyoxymethylene molding composition capable of producing a composite with improved physical properties characterized in that it comprises a mixture of polycarbodiimides. 2. The composition of claim 1, wherein the fibrous reinforcement is glass fiber in an amount of about 5 to 50% by weight, based on the total weight of the composition. 3 The polyoxymethylene polymer has an intrinsic viscosity of at least 0.8 (p containing 2% by weight alpha-pinene)
- 0.1% by weight solution in chlorophenol at 60℃
It was measured with ), an average molecular weight of at least 35000 and a melting point of at least 150°C. 4 Polyoxymethylene polymer is about 60 to about 99.6
4. A composition according to claim 3, which is a copolymer with mole % of repeating _-OCH2- groups. 5 Polyoxymethylene polymer is component (2) and (3)
5. A composition according to claim 4, which has been previously stabilized by melt hydrolysis before being mixed with the composition. 6. The composition according to claim 4, wherein the polyoxymethylene polymer is pre-stabilized by the addition of an antioxidant and an acid scavenger. 7 The antioxidant is 2,2'-methylene-bis-(4
-methyl-6-tert.butylphenol) and the acid scavenger is cyanoguanidine. 8 Polycarbodiimide is poly(tolylcarbodiimide), poly(4,4'-diphenylmethanecarbodiimide), poly(3,3'-dimethyl-4,
4′-biphenylenecarbodiimide), poly(p-
phenylenecarbodiimide), poly(m-phenylenecarbodiimide), poly(3,3'-dimethyl-4,4'-diphenylmethanecarbodiimide) and mixtures thereof. A composition according to scope item 4. 9. The composition of claim 2, wherein the polyoxymethylene polymer is a mixture of a polymer stabilized by melt hydrolysis and a polymer stabilized by solution hydrolysis. 10 (1) a polyoxymethylene polymer, (2) about 2 to 60% by weight of a fibrous reinforcement based on the total weight of the composition, and (3) (a) substituted with up to one methyl group per aromatic ring. or from about 0.6 to 5% by weight, based on the total weight of the composition, of a polycarbodiimide and a high molecular weight thermoplastic phenooxy resin derived from an unsubstituted aromatic isocyanate and (b) having at least 3 carbodiimide units per polycarbodiimide molecule. It consists of a mixture and the weight ratio of polycarbodiimide to phenoxy resin is 1:16 to 50:
1. An improved fiber-reinforced polyoxymethylene molding composition capable of producing a composite object with improved physical properties characterized by a range of 1. 11 Phenoxy resin has a repeating structure: and an average molecular weight of about 15,000 to 75,000. 12. The composition of claim 11, wherein the fiber reinforcement is glass fiber in an amount of about 5 to 50% by weight based on the total composition weight. 13 The polyoxymethylene polymer is at least 0.8
(measured as a 0.1% by weight solution in p-chlorophenol containing 2% by weight of alpha-pinene at a temperature of 60°C), an average molecular weight of at least 35000 and a melting point of at least 150°C. A composition according to claim 12. 14 Polyoxymethylene polymer is about 60 to 99.6
14. The composition of claim 13, which is a copolymer with mole % of repeating _-OCH2- groups. 15 Polyoxymethylene polymer is component (2) and
15. A composition according to claim 14, which has been previously stabilized by melt hydrolysis before being mixed with (3). 16. The composition according to claim 14, wherein the polyoxymethylene polymer is previously stabilized by the addition of an antioxidant and an acid scavenger. 17 The antioxidant is 2,2'-methylene-bis-
(4-methyl-6-tert.butylphenol) and the acid scavenger is cyanoguanidine. 18 Polycarbodiimide is poly(tolylcarbodiimide), poly(4,4'-diphenylmethanecarbodiimide), poly(3,3'-dimethyl-4,
4′-biphenylenecarbodiimide), poly(p-
phenylenecarbodiimide), poly(m-phenylenecarbodiimide), poly(3,3'-dimethyl-4,4'-diphenylmethanecarbodiimide),
and mixtures thereof. 19 Claim 12, wherein the polyoxymethylene polymer is a mixture of a polymer stabilized by melt hydrolysis and a polymer stabilized by solution hydrolysis.
The composition described in Section.