MXPA00000585A - Thermoplastic polymer composition exhibiting improved wear - Google Patents

Abstract

A low wear polymeric composition exhibiting improved surface wear resistance and coefficients of friction characterized as a melt blend of a thermoplastic polymer and a lubricating system containing PTFE, pentaerythritol tetrastearate and fine particle, stearate coated calcium carbonate, a hindered amine, N, N'-ethylene bis-stearamide, and calcium ricinoleate. The composition is suitable for the preparation of shaped articles for use in frictional environments.

Description

COMPOSITION OF THERMOPLASTIC POLLERO THAT PRESENTS REDUCTION BÍ IMPROVED WEAR FIELD OF THE INVENTION The present invention relates to thermoplastic polymer compositions with improved wear reduction properties. The composition contains a thermoplastic polymer and a lubricant system suitable for use as a moldable resin for preparing shaped articles. The shaped articles prepared from the composition exhibit low friction properties as well as reduced surface wear when subjected to loads.

BACKGROUND OF THE INVENTION Thermoplastic polymers, for example polyamides, polyesters, polyphenylene sulfide, polyoxymethylene, polyolefins, styrene polymers, and polycarbonates, are characterized as polymers having exceptional mechanical and electrical properties, as well as good molding ability and chemical resistance. However, these polymers can exhibit inadequate tribological properties when used in friction environments, for example, adjoining surfaces of plastic to metal, and plastic to plastic. Although many lubricating compositions have been applied to thermoplastic polymers to improve the friction and wear properties of shaped articles prepared therefrom, some applications prohibit the use of certain lubricants due to possible contamination, for example food handling, dressing preparation and volatile environments. Attempts have been made to improve the friction properties and reduce the wear of the surface of articles made of thermoplastic polymers by incorporating lubricants directly into the polymer matrix prior to the manufacture of shaped articles thereof. Many materials, including solid lubricants and fibers (eg, graphite, mica, silica, talc, boron nitride and molybdenum sulfide), paraffin waxes, petroleum and synthetic lubricating oils, and other polymers (eg, polyethylene and polytetrafluoroethylene) have been added to thermoplastic polymers to improve friction properties and wear reduction. However, the addition of many of these additives in various combinations to thermoplastic polymers, while increasing the tribological properties have reduced other desirable physical and mechanical properties. Some additives have been found to be satisfactory for short periods at low speeds and loads. However, the friction characteristics of many of these lubricants deteriorate significantly over long periods of time under increased loads. There is a need for low-wear, non-toxic thermoplastic compositions that possess surface wear resistance and low friction properties when subjected to increased loads over long periods of time. A suitable composition, when manufactured in a shaped article, should maintain the desired mechanical and physical properties associated with thermoplastic polymers, and should be used safely in the handling of food and clothing manufacturing industries.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a low wear polymer composition suitable for forming a low friction shaped article, characterized as a melt mixture of about 70 to about 99.5 weight percent of a thermoplastic polymer, and about 30 to 50 weight percent. about 0.5 weight percent polytetrafluoroethylene, pentaerythritol tetrastearate (PETS), and calcium carbonate coated with fine particle stearate. Processing aids that do not deviate from the features of the invention can be added to the composition to improve the physical properties and processing, for example the dispersion of the lubricant system within the polymer matrix. The composition may be formed into low wear shaped articles, for example bearings, gears, cams, rollers, sliding plates, pulleys, levers, guides, conveyor links, etc., which exhibit good friction properties and are useful in numerous applications in where the parts exhibiting low friction and reduced wear properties are desirable.

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a reduced wear polymer composition which can be manufactured in shaped articles having good frictional properties. In general, the composition can be characterized as a mixture of from about 70 to about 99.5 weight percent of a thermoplastic polymer and from about 30 to about 0.5 weight percent of a lubricating system. Typically, the composition may comprise from about 85 to about 99 weight percent of a thermoplastic polymer and from about 15 to about 1 weight percent of the lubricating system. Preferably, the composition contains about 98 weight percent of the thermoplastic polymer and about 2 weight percent of the lubricant system, based on the total weight of the composition. The thermoplastic polymer useful in the reduced wear composition of the present invention can generally be selected from polyamides, polyesters, polyphenylene sulfides, polyolefins, polyoxymethylenes, styrene polymers, and polycarbonates. The preferred thermoplastic polymer in particular of the invention is polyoxymethylene, ie polymeric acetals or oxymethylene polymers. Polyoxynilenes have physical and mechanical properties that make them suitable for many applications in the industry. The polyoxymethylenes, ie polyacetals or oxymethylene polymers useful in the present invention are generally characterized in that they have recurring oxymethylene units of the general formula: - (- O-CHg -) - The polyoxymethylenes that are used to make the composition of the invention generally have a high content of oxymethylene units, that is to say generally more than about 85 percent. These materials are available commercially from a large number of manufacturers such as homopolymers, copolymers, terpolymers and the like.

These highly crystalline cells, which are briefly described below, are well known in the art and have been extensively reviewed. For example, a review of polymeric acétales titled, "Acetal Resins", by T.J. Dolce and J. A. Grates, can be found in the second edition of the Encvclopedia of Polvmer Science and Enqineerinq, John Wiley and Sons, New York, 1985, Vol. 1, pp. 42-61. It is possible to find additional information on acetal polymers in French patent No. 1, 221, 148 as well as the patents of E.U.A. Commonly assigned Nos. 3,027,352, 3,072,069, 3,147,234, and 3,210,318.

Typically, acetal homopolymers can be prepared by polymerizing anhydrous trisodium or folmaldehyde. Oxymethylene homopolymers are usually stabilized against thermal degradation by blocking at the end with, for example, ester or ether groups, such as those derived from alkanoic anhydrides (eg acetic anhydride) or dialkyl ethers, (e.g. dimethyl ether) or incorporating stabilizing compounds in the homopolymer. The commercially available acetal homopolymer is made by the polymerization of anhydrous formaldehyde in the presence of an initiator after which said polymer is blocked at the end by acetylation of the hemiacetal end groups with acetic anhydride in the presence of sodium acetate catalyst. . Methods for making acetal homopolymers blocked at the end are presented in the U.S. Patents. Nos. 2,786,994 and 2,998,409. Acetal homopolymers are known in the art and are available commercially under the trade names Delrin® and Tenac®. Polymeric acetals which have been found especially suitable for use in the composition of the present invention are crystalline oxymethylene copolymers having repeating units generally consisting of oxymethylene groups interspersed with oxy (higher alkylene) groups of the general formula: wherein each Ri and R2 is hydrogen, a lower alkyl group, or a lower alkyl group substituted with halogen, each R3 is a methylene group, oxymethylene, methylene substituted with lower alkyl or haloalkyl or oxymethylene group substituted with lower alkyl or haloalkyl, and n is zero or an integer from 1 to 3, inclusive. Each lower alkyl group preferably contains 1 or 2 carbon atoms. Oxymethylene groups will generally constitute from about 85 to 99.9% of the recurring units in said copolymers and are generally incorporated by trioxane ring opening polymerization in the presence of an acid catalyst. The oxy (higher alkylene) groups are incorporated into the polymer by copolymerizing a cyclic or cyclic formal ether having at least two adjacent carbon atoms in the ring in addition to trioxane. The ether or cyclic formal is incorporated by breaking an oxygen to carbon bond. The preferred oxy (higher alkylene) group is oxyethylene, which has the formula: - O-CHg-CHg - Oxyethylene can be incorporated into the polymer by copolymerization of ethylene oxide or 1,3-dioxolane with trioxane. Preferred crystalline acetal copolymers, as described above having a structure consisting essentially of oxymethylene and oxyethylene groups, are thermoplastic materials having a melting point of at least 150 ° C.

They are usually crushed or processed at temperatures in the range of about 175 ° C to about 230 ° C. These copolymers are usually highly crphstalin and have a polymer crystallinity of from about 40% to about 90% or more. Typically, the oxymethylene copolymers are stabilized after their manufacture by degradation of non-stable molecular ends of the polymer chains to a point where a relatively stable carbon-to-carbon bond prevents further degradation of each end of the polymer chain. Said degradation of non-stable molecular ends is generally effected by hydrolysis, as described, for example, in the patent of E.U.A. No. 3,219,623 of Berardinelli. The oxymethylene copolymer can also be stabilized by end blocking, again using techniques well known to those skilled in the art, such as acetylation with acetic anhydride in the presence of a sodium acetate catalyst. A particularly preferred class of oxymethylene copolymers is commercially available under the tradename Celcon® acetal copolymer Hoechst Celanese Corporation, Hoechst Technical Polymers. Celcon acetal copolymers are typically copolymers of about 98% by weight of trioxane and about 2% dioxolane. Celcon® is a trade name of Hoechst Celanese Corporation. The compositions of the present invention can be made using any commercial grade of Celcon acetal, including Celcon U-10, M-25, M-90 ™, M-270 ™ and M-450 grades. The Celcon M-25 acetal copolymer has a melt index of about 2.5 g / 10 min when tested in accordance with ASTM D1238-82. The Celcon M-90 acetal copolymer has lower molecular weight and lower melt viscosity compared to Celcon M-25. Celcon M-270 has even lower molecular weight and melt viscosity than Celcon M-25. The oxymethylene terpolymers can also be used to make low wear polymer compositions of the present invention. These terpolymers contain oxymethylene groups, oxy (higher alkylene) groups such as those corresponding to the general formula: and a third different group that has been interpolymerized with the oxymethylene and oxy (higher alkylene) groups. A terpolymer such as the one described above is usually made by reacting trioxane with a cyclic ether or cyclic acetal and a third monomer which is a bifunctional compound, such as a diglycid of the formula: wherein Z represents a carbon to carbon bond, an oxygen atom, an oxyalkoxy group of 1 to 8 carbon atoms, preferably 2 to 4 carbon atoms, an oxycycloalkoxy group of 4 to 8 carbon atoms, *. ^ a? kJL * included, or an oxypoly (lower alkoxy) group, preferably from about 2 to 4 recurring lower alkoxy groups each having 1 or 2 carbon atoms. Examples of suitable bifunctional compounds include the diglycidyl ethers of ethylene glycol, 1,2-propanediol, and 1,4-butanediol, with diglycidyl ether of 1,4-butanediol being most preferable. In general, when preparing said terpolymers, scales of about 99.89 to 89.0 percent by weight of trioxane, 0.1 to 10 percent by weight of cyclic ether or cyclic acetal, and 0.01 to 1% by weight of the bifunctional compound are preferred. , based on the total weight of the monomers used to form the terpolymer. A particularly preferred oxymethylene terpolymer is commercially available from Hoechst Celanese Corporation, Hoechst Technical Polymers under the name polymer Acetal Celcon U10, made from the interlayer of diglycidyl ether 1,4-butanediol, dioxolane and trioxane containing about 0.05 weight percent, 2.0 weight percent, and 97.95 weight percent, respectively, of repeat units that are derived from these three monomers, based on the total weight of the terpolymer. Oxymethylene-based terpolymers are made and stabilized by methods known in the art, such as the addition of antioxidants and formaldehyde and acid scavengers. It is possible to find more detailed descriptions of the methods for making oxymethylene-based terpolymer and its compositions in patents cited above.

These oxymethylene polymers can be combined in various proportions by melt blending in extruders or the like to form polymers suitable for the preparation of the reduced wear composition of the present invention. In general, polyoxymethylene polymers are easily mixed with the lubricant system and processing aids when the polymer is in the melting state, ie at temperatures of at least 170 ° C. The lubricant system of the present invention can be characterized in that it contains a lubricant amount, sufficient to reduce friction and wear, of polytetrafluoroethylene (PTFE), pentaerythritol tetrastearate (PETS), and calcium carbonate coated with fine particulate stearate. The components of the lubricant system can be mixed together with the desired polymer to form the lubricant composition or separately to form a lubricant system package that can subsequently be combined with the desired polymer to produce a thermoplastic composition having reduced wear properties. Generally, the lubricant system can be characterized in that it contains at least 0.5 percent by weight of PTFE, at least about 0.25 percent by weight of PETS, and at least 0.25 percent by weight of calcium carbonate coated with stearate in fine particles, based on the total weight of the composition. Typically, the lubricant system contains from about 0.5 to about 5 weight percent of PTFE, from about 0.25 to about 2.0 weight percent PETS, and from about 0.25 to about 2.0 weight percent calcium carbonate. coated with stearate in fine particles, based on the total weight of the composition. Preferably, the composition contains about 0.8 weight percent PTFE, about 0.5 weight percent PETS, and about 1.0 weight percent calcium carbonate coated with fine particulate stearate, based on the total weight of the composition. It is possible to add additional components to the composition of the present invention to aid lubrication and processing. Generally, the additives can be combined proportionally with the lubricant system and mixed as a package for addition to a thermoplastic polymer or can be mixed directly with the polymer. In general, these additives may be selected from: (a) at least 0.25 weight percent of a polyoxymethylene terpolymer; (b) at least 0.1 weight percent of a hindered phenol; (c) at least 0.5 weight percent of calcium ricinoleate; and, optionally, (d) at least 0.1 weight percent of N.sup.N'-ethylene bis-stearamide, based on the total weight percent of the composition. Typically, these additives can be mixed with the self-lubricating composition in selected amounts of: (a) from about 0.25 to about 2.0 weight percent of a polyoxymethylene terpolymer; (b) from about 0.1 to about 0.75 weight percent of a hindered phenol; (c) from about 0.5 to about 0.2 weight percent of calcium ricinoleate; and optionally, (d) from about 0.1 to about 0.5% by weight of bis-stearamide of N.N'-ethylene, based on the total weight of the% -position. Preferably, these additives are mixed with the composition in amounts of: (a) about 0.5% by weight of a poly-oxymethylene terpolymer; (b) about 0.5% by weight of a hindered phenol; (c) about 0.1% by weight of calcium ricinoleate; and optionally, (d) about 0.2% by weight of N, N'-ethylene bis-stearamide, based on the total weight percent of the composition. The addition of these processing aids will typically result in a concomitant adjustment in the amount of thermoplastic resin. Other processing aids known to those skilled in the art which do not depart from the improved wear properties of the composition, such as silicone and fluoropolymer molding sprinklers can be used to assist in the release of the mold when preparing shaped articles. A particularly preferred polytetrafluoroethylene (PTFE) compliant with the FDA / USDA, is Hostaflon® TF9203 distributed by Hoechst Celanese Corporation of Somerville, New Jersey. A pentaerythritol tetrastearate (PETS) is Glycolube P® distributed by Lonza, Inc. Calcium carbonate coated with fine particulate stearate, useful in the invention is characterized in that it exhibits a particle size of about 0.6 μm, a surface area about 7 m2 / gm, a mass density of about 122 kg / m3, and a specific gravity of about 2.7. A calcium carbonate coated with fine particulate stearate is Super-Pflex® 200 available from Pfizer, Inc. The hindered phenol useful in the present invention is generally known as an antioxidant or free radical inhibitor. It is possible to use at least one of 2,2'-methylenebis (4-methyl-6-t-butylphenol), bis (3,5-di-t-butyl-4-hydroxyhydrocinnamate) of hexamethylene glycol, tetrabis [methylene (3 , 5-di-t-butyl-4-hydroxyhydrocinnamate)] methane, triethylene glycol bis-3- (3-t-butyl-5-hydroxy-5-methylphenyl) propionate, 1, 3,5-tritymethyl- 2,4,6-tris (3,5-di-t-butyl-4-hydroxy-benzyl) -benzene, 3- (4'-hydroxy-3 ', 5'-di-t-butyl-phenol) p-octadecyl propionate, 4,4'-methylenebis (2,6-di-t-butylphenol), 4,4'-butylidene-bis- (6-t-butyl-3-methylphenol), bis- [3- (2,3-di-t-butyl-4-hydroxyphenol)] propionate of 2,2'-thiodiethylof 3,5-di-t-butyl-4-hydroxybenzylphosphonate di-stearyl and -6- (3-t- 2-t-butyl butyl-5-methyl-2- 10 hydroxybenzyl) -4-methylphenylacrylate. However, useful hindered phenols are not limited to these compounds. Other hindered phenols or stereo obstruction of the same type as those described above are effective. Of these, bis (3,5-di- t-butyl-4-hydroxy-dinacinnamate) of hexamethylene glycol, for example Irganox® 259 available from Ciba-Geigy, tetrakis [methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane, for example Irganox 1010 made by Ciba-Geigy and bis-3- (3-t-butyl-4-hydroxy-5- triethylene glycol methylphenyl) propionate, for example Irganox 245 prepared by Ciba-Geigy are effective. A preferred hindered phenol is bis (3,5-di-t-butyl-4-hydroxyhydrocinnamate) of hexamethylene glycol. The bis-stearamide of N, N'-20 ethylene which is used in the invention is known by the trade name Acrawax® C from Lonza, Inc. The following examples are general illustrations of methods for preparing the polymer composition of the invention. They are provided with the purpose of exemplifying only, as will be evident from the foregoing description.

EXAMPLE 1 To prepare a mixture of the reduced wear polymer composition, containing 3.4% by weight, based on the total weight of the composition, of the lubricant system, the following components were used: a) 96.1% by weight flake not stabilized polyoxymethylene copolymer; b) 0.5% by weight of polyoxymethylene terpolymer; c) 0.8% by weight of PTFE; d) 1.0% by weight of PETS; e) 1.0% by weight of calcium carbonate; f) 0.1% by weight of calcium ricinoleate; and g) 0.5% by weight of preferred hindered phenol. The components were stirred in a barrel and then mixed at high speed for 30 seconds in a Henschel mixer to form a mixture. The mixture was fed into a ZSK twin-screw extruder from Werner and Pfleiderer and extruded into strips. The zones of the extruder were operated from 188.8 ° to 192.2 ° C, the melting temperature was 212.7 ° C and under vacuum of 68.58 cm Hg, and the screw speed was 150 6 rpm. Strips of extruded material were produced at a rate of 17.25 kg / hr. Afterwards, the strips were extinguished in cold water and cut into pellets. The pellets were injection molded at pressure, speed and conventional time cycles, a nozzle temperature setting from 182.2 ° to 215.5 ° C, 5 and a temperature setting in the barrel from 176.6 ° to 215.5 ° C to form discs of 3.17 cm in diameter, each weighing 7 grams, for mechanical and tribological analysis. The discs were prepared for analysis of wear resistance of the surface and torque by cleaning in an isopropanol bath, drying with air, and weighing them to about a tenth (1/10) of a milligram. The discs were tested in accordance with the Pin-on-Disk Wear Test. When performing the tests, a Nylatron pin machined with a spherical tip of a radius of 0.47 cm was mounted on the upper spindle of a Falex Friction machine and Wear Test Machine, Model Multi-Specimen at a distance of 1.19 cm from the center of the test discs, which were mounted in the lower spindle. A load of 9.08 kg was applied to the test discs by an air cylinder that pressed the disc against the tip of the spherical bolt. The rotation speed was 425 rpm (31.79 meter / min). During the test, a current of air at 1.12 cubic meters per hours (SCFH) and at a distance of 5.08 cm from the disk went to the surface of the disk to remove the debris. The test times were on a scale of 0.5 to 65 hours. After the tests, the tip of the bolt and disc were separated and the disc was removed, brushed with air to remove loose waste, and weighed to assure weight loss, ie, surface wear. The torque (r), measured during the test, was converted into a coefficient of friction (? By application of the equation: f = T (2.137 / 20) The factor 2.137 is a specific coefficient for this machine. Surface wear and friction coefficients are shown in Table II.

EXAMPLE 2 In another example, a low wear composition containing 3.0% by weight of polytetrafluoroethylene (PTFE) was prepared in the lubricant system, wherein the lubricant system comprised 4.6% by weight of the composition. The following components were used: Components a) 94.9% by weight of unstabilized flake of polyoxymethylene copolymer; b) 0.5% by weight of polyoxymethylene terpolymer; c) 3.0% by weight of PTFE; d) 0.5% by weight of PETS; e) 0.5% by weight of calcium carbonate; | f) 0.1% by weight of calcium ricinoleate; and g) 0.5% by weight of preferred hindered phenol The components were mixed, extruded and molded according to the procedure of Example 1 to form 7.5 gram discs for analysis of weight loss and coefficient of friction. The results of the analyzes are presented in table II.

EXAMPLE 3 In another example, a reduced wear polymer composition containing 3.0% by weight of PTFE and 4.1% by weight of the lubricant system was prepared. The components were mixed according to example 1, as indicated: Components a) 95.4% by weight flake non-stabilized polyoxymethylene copolymer; b) 0.5% by weight of polyoxymethylene terpolymer; c) 3.0% by weight of PTFE; d) 0.25% by weight of PETS; e) 0.25% by weight of calcium carbonate; f) 0.1% by weight of calcium ricinoleate; and g) 0.5% by weight of hindered phenol preferred The components were mixed, extruded and molded according to the procedure of Example 1 to form 7 g discs for analysis of weight loss and coefficient of friction. The results of the analyzes are shown in table II. To demonstrate the wear performance of the composition in the presence of the PTFE lubricant system not containing pentaerythritol tetrastearate and calcium carbonate, two (2) formulations were prepared according to the method of Example 1, as follows: COMPARATIVE EXAMPLE 4 Components a) 97.2% by weight of non-stabilized flake of polyoxymethylene copolymer; b) 0.5% by weight of polyoxymethylene terpolymer; c) 1.5% by weight of PTFE; d) 0% by weight of PETS; e) 0% by weight of calcium carbonate; f) 0.1% by weight of calcium ricinoleate; g) 0.5% by weight of preferred hindered phenol; and h) 0.2% by weight of bis-stearamide of N.N'-ethylene SER * .i. ^ ^ «3 ^ ^ COMPARATIVE EXAMPLE 5 Components a) 95.7% by weight of non-stabilized flake of polyoxymethylene copolymer; b) 0.5% by weight of polyoxymethylene terpolymer; c) 3.0% by weight of PTFE; d) 0% by weight of PETS; e) 0% by weight of calcium carbonate; f) 0.1% by weight of calcium ricinoleate; g) 0.5% by weight of preferred hindered phenol; and h) 0.2% by weight of N.sub.N'-ethylene bis-stearamide The percentages by weight of the components of the compositions of examples 1 to 5 are summarized in Table I. Comparative examples 4 and 5 contain PTFE in the system lubricant, but do not contain PETS or calcium carbonate.

TABLE I The wear test results of the discs prepared from the PTFE-containing compositions, such as the lubricant system, showed surface wear as well as friction coefficients significantly greater than those of the invention. While the lubricant system containing a combination of PTFE, pentaerythritol tetrastearate and calcium carbonate showed superior wear reduction properties after several hours of testing. Table II illustrates the results of the wear tests for the examples. After 0.5 hours of pin-on-disk test, the composition of Example 1 exhibited an average weight loss of 2.6 mg after 1.5 hours of wear test, 17 mg of weight loss after 17 hours of wear test, and 44.8 mg of weight loss after 65 hours of testing. Similarly, Example 2 presented 9 mg of weight loss after 1.5 hours of testing, and Example 3 presented 19.6 mg of weight loss after 1.5 hours of attrition test. However, comparative examples 4 and 5 showed more significant weight losses of 29 and 24.3 mg, respectively, after 1.5 hours of wear tests.

TABLE II no data

Claims (21)

NOVELTY OF THE INVENTION CLAIMS

1. A polymer composition of reduced wear suitable for forming a low friction shaped article comprising, a melt mixture of about 70 about 99.5% by weight of a thermoplastic polymer, and about 30 to about 0.5% by weight of a lubricating system comprising, polytetrafluoroethylene, pentaerythritol tetrastearate, and calcium carbonate coated with stearate in fine particles, based on the total weight of the composition.

2. The composition according to claim 1, further characterized in that the thermoplastic polymer is selected from the group consisting of polyamides, polyesters, polyphenylene sulfide, polyoxymethylenes, styrene polymers, and polycarbonates.

3. The composition according to claim 2, further characterized in that the thermoplastic polymer is polyoxymethylene.

4. The composition according to claim 3, further characterized in that the polyoxymethylene is selected from the group consisting of: (i) oxymethylene homopolymers; (ii) oxymethylene copolymers comprising from about 85 to about 99.9% oxymethylene repeating units interspersed with repeating units of the formula: wherein each Ri and R2 is selected from the group consisting of hydrogen, lower alkyl radicals, and lower alkyl radicals substituted with halogen, each said lower alkyl radical has from 1 to 2 carbon atoms, each R3 is selected of the group consisting of methylene, oxymethylene, methylene substituted with lower alkyl or haloalkyl, and oxymethylene radicals substituted with lower alkyl or haloalkyl, and n is an integer from 0 to 3, inclusive; (iii) oxymethylene terpolymers, which are the reaction product of trioxane, a cyclic ether and / or cyclic acetal, and a diglycidyl ether linker of the formula: wherein Z is selected from the group consisting of a carbon to carbon bond, oxygen, an oxyalkoxy unit of 1 to 8 carbon atoms, and an oxipoly (lower alkoxy) unit; and (iv) mixtures of (i), (ii), and (iii).

5. The composition according to claim 4, further characterized in that it comprises from about 85 to about 99 weight percent of the polyoxymethylene and from about 15 to about 1 weight percent of the lubricant system, based on the total weight of the composition.

6. - The composition according to claim 5, further characterized in that the lubricant system comprises at least 0.5 weight percent PTFE, at least about 0.25 weight percent PETS, and at least 0.25 weight percent of calcium carbonate 5 coated with stearate in fine particles, based on the total weight of the composition.

7. The composition according to claim 6, further characterized in that it comprises: (a) at least 0.25 weight percent of a polyoxymethylene terpolymer; (b) at least 0.1 percent in 10 weight of a hindered phenol; (c) at least 0.05 weight percent of calcium ricinoleate; and (d) at least 0.1 weight percent of N.N'-ethylene bis-stearamide, based on the total weight percent of the composition.

8.- A configured item that is prepared from the The self-lubricating composition according to claim 7, which has a weight loss of about 78.1 mg after 17 hours of wear at a rotation speed of 31.79 meter / min and an applied load of about 9.08 kg and a coefficient of friction of approximately 0.13.

9. A method for improving the wear resistance of the surface of a thermoplastic shaped article, comprising the steps of: (a) preparing a fused mixed composition, comprising from about 85 to about 99% by weight of the polymer thermoplastic and from about 15 to about 1% by weight of the lubricant system, wherein said lubricant system contains polytetrafluoroethylene, PETS, and calcium carbonate coated with fine particulate stearate; and (b) manufacturing said composition in a shaped article having improved coefficient of friction and wear resistance of the surface.

10. The method according to claim 9, further characterized in that the thermoplastic polymer is selected from the group consisting of polyamides, polyesters, polyphenylene sulfide, polyoxymethylene, styrene polymers, and polycarbonates.

11. The method according to claim 10, further characterized in that the thermoplastic polymer is polyoxymethylene.

12. The method according to claim 11, further characterized in that the polyoxymethylene is selected from the group comprising: (i) oxymethylene homopolymers; (ii) oxymethylene copolymers comprising from about 85 to about 99.9% oxymethylene repeating units interspersed with repeating units of the formula: wherein each Ri and R2 is selected from the group consisting of hydrogen, lower alkyl radicals, and lower alkyl radicals substituted with halogen, each said lower alkyl radical has from 1 to 2 carbon atoms, each R3 is selected of the group consisting of methylene, oxymethylene, methylene substituted with lower alkyl or haloalkyl, and oxymethylene radicals substituted with lower alkyl or haloalkyl, and n is an integer from 0 to 3, inclusive; (iii) oxymethylene terpolymers, which are the reaction product of trioxane, a cyclic ether and / or cyclic acetal, and a diglycidyl ether linker of the formula: wherein Z is selected from the group consisting of a carbon to carbon bond, oxygen, an oxyalkoxy unit of 1 to 8 carbon atoms, and an oxipoly (lower alkoxy) unit; and (v) mixtures of (i), (ii), and (ii).

13. The method according to claim 12, further characterized in that the composition comprises from about 85 to about 99 weight percent of the polyoxymethylene and from about 15 to about 1 weight percent of the lubricant system.

14. The method according to claim 13, further characterized in that the polyoxymethylene is an oxymethylene copolymer comprising from about 85 to about 99.9% of oxymethylene repeating units interspersed with repeating units of the formula: * > & $? $ • # & amp;: 'J i & Wherein each Ri and R2 is selected from the group consisting of hydrogen, lower alkyl radicals, and lower alkyl radicals substituted with halogen, each of said lower alkyl radicals has from 1 to 2 carbon atoms. carbon, each R3 is selected from the group consisting of methylene, oxymethylene, methylene substituted with lower alkyl or haloalkyl, and oxymethylene radicals substituted with lower alkyl or haloalkyl, and n is an integer from 0 to 3, inclusive.

15. The method according to claim 14, further characterized in that the lubricating system comprises at least 0.8 percent by weight of PTFE, about 0.5 percent by weight of PETS, and about 1.0 weight percent calcium carbonate coated with fine particle stearate, based on the total weight of the composition.

16. The method according to claim 15, further characterized in that the lubricating system comprises from about 0.5 to about 5.0 weight percent of PTFE, about

0. 25 to about 2.0% by weight of PETS, and from about 0.25 to about 2.0 percent by weight of calcium carbonate coated with stearate in fine particles, based on the total weight of the composition.

17. The method according to claim 16, further characterized in that the lubricating system comprises: (a) at least 0.25 to about 2.0 weight percent of a polyoxymethylene terpolymer; (b) from about 0.25 to about 0.75 weight percent of a hindered phenol; (c) at least 0.05 to about 0.2 weight percent of calcium ricinoleate; and optionally, (d) from about 0.1 to about 0.5 weight percent of N, N'-ethylene bis-stearamide, based on the total weight percent of the composition.

18. A shaped article prepared according to the method of claim 17, further characterized by having a weight loss of about 34 mg after 17 hours of wear at a rotation speed of 31.79 meters / min and a load applied of about 9.08 kg and a coefficient of friction of less than about 0.12.

19. The article configured according to claim 18, further characterized in that it is selected from the group consisting of bearings, gears, cams, rollers, sliding plates, pulleys, levers, guides and conveyor links.

20.- A suitable reduced wear polymer composition 15 to form a low friction shaped article comprising about 98 weight percent polyoxymethylene and about 2 weight percent lubricant system, comprising about 0.8 weight percent PTFE, about 0.5 weight percent PETS , about 1.0 weight percent of calcium carbonate coated with stearate in 20 fine particles, about 0.5 weight percent of a polyoxymethylene terpolymer, about 0.5 weight percent of a hindered phenol, about 0.1 weight percent of calcium ricinoleate, and optionally, about 0.2 weight percent of bis-stearamide of N.N'-ethylene, based on the total weight percent of the composition, wherein the polyoxymethylene is selected from the group consisting of: (i) oxymethylene homopolymers; (ii) oxymethylene copolymers comprising from about 85 to about 99.9% oxymethylene repeating units interspersed with repeating units of the formula: wherein each Ri and R2 is selected from the group consisting of hydrogen, lower alkyl radicals, and lower alkyl radicals substituted with halogen, each said lower alkyl radical has from 1 to 2 carbon atoms, each R3 is selected of the group consisting of methylene, oxymethylene, methylene substituted with lower alkyl or haloalkyl, and oxymethylene radicals substituted with lower alkyl or haloalkyl, and n is an integer from 0 to 3, inclusive; (iii) oxymethylene terpolymers, which are the reaction product of trioxane, a cyclic ether and / or cyclic acetal, and a diglycidyl ether linker of the formula: wherein Z is selected from the group consisting of a carbon to carbon bond, oxygen, an oxyhaloxy unit of 1 to 8 carbon atoms, and an oxypiol (lower alkoxy) unit; and (iv) mixtures of (i), (ii), and (iii).

21. A shaped article prepared from the composition according to claim 20, further characterized by having reduced wear on the surface and low coefficient of friction, said article is selected from the group consisting of bearings, gears, cams, rollers , sliding plates, pulleys, levers, guides and conveyor links. liffl B ^ "- '" "--¡-te-Mfe * ^ *