MXPA97006539A - Improved composition of polymer thermoplastic self-soluble - Google Patents

Abstract

A self-lubricating composition containing at least about 70 to about 99.5% by weight of a thermoplastic polymer and about 30 to about 0.5% by weight of a lubricant system, wherein the lubricant system contains high molecular weight polyethylene and low, polyethylene waxes, metal salts, antioxidants and stabilizers, the composition is suitable for the manufacture of shaped articles, eg, gears, pulleys, rollers and bearings, which have improved friction and surface wear properties

Description

IMPROVED COMPOSITION OF AUTOLUBRICATED THERMOPLUSTIC POLYMERS FIELD OF THE INVENTION The present invention relates to low wear self-lubricating compositions characterized in that they contain a tenepoplastic polymer and a lubricating system. The shaped articles prepared from the composition exhibit low friction properties as well as reduced surface wear under loads.

BACKGROUND OF THE INVENTION Thermoplastic polymers, for example, polyamides, polyesters, polyphenylene sulfide, polyoxyethylene, polyolefins, styrene polymers and polycarbonates, are characterized by exceptional mechanical and electrical properties, as well as good molding properties and chemical resistance. However, these polymers can exhibit inadequate tribological properties when used in some friction environments, for example, on adjoining surfaces of plastic with metal and plastic with plastic. Although many lubricant compositions have been applied to thermoplastic polymers to improve the friction and wear properties, some applications prohibited the use of certain lubricants due to possible contamination, for example, food handling, clothing preparation and volatile environments. Attempts have been made to improve the friction properties and reduce the wear on the surface of articles prepared from thermoplastic polymers by directly incorporating lubricants into thermoplastic polymers before manufacturing the articles configured therefrom. Many materials in different combinations, including lubricants and solid fibers (eg, graphite, mica, silica, talc, boron nitride and rnolibdenum sulfide), paraffin waxes, petroleum and synthetic lubricating oils, and other polymers (eg, polyethylene) and polytetrafluoroethylene), have been added to thermoplastic polymers to improve lubrication properties. However, the addition of many of these additives in various combinations to the thermoplastic polymers, while improving the tribological properties, has reduced other desirable physical and mechanical properties. Some additives have proven to be satisfactory in the short term at low speeds and loads; however, the friction properties of many of these lubricants deteriorate significantly over long periods under increased loads. There is a desire to obtain compositions that possess properties of resistance to surface wear and low friction under increasing loads over long periods. An appropriate composition, when manufactured in a shaped article, must maintain the desired mechanical and physical properties associated with thermoplastic polymers, and be non-contaminating when used in food handling and clothing manufacturing.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a self-lubricating composition suitable for use in the manufacture of shaped articles having slippery surfaces, characterized in that it contains: (a) from about 70 to about 99.5% by weight of a thermoplastic polymer, (b) around from about 30 to about 0.5% by weight of a lubricant system, characterized as: (i) at least about BO to about 70% by weight of a very high molecular weight polyethylene, characterized in that it has a molecular weight of at least 500,000, a density of at least about 0.94 g / crn3, and a mold flow index (MFI) of about 0.4 to about 2.2 g / 10 min; (ii) at least about 20 to about 30% by weight of a high density polyethylene copolymer or copolymer characterized in having a density of about 0.95 g / crn3 and an MFI of about 3.0 g / 10 in; (iii) at least about 0.05% by weight of an acid metal salt of calcium stearate or zinc stearate; (iv) at least about 0.05% by weight of a non-polar low molecular weight polyethylene wax, characterized in that it has a molecular weight of from about 5,000 to about 10,000; (v) about 0.05% by weight of a wax of fatty amide selected from bis-stearoethylenediarnide and bis-palmitoylethylenediarnide; and (vi) at least about 0.05% by weight of phenolic antioxidant / phosphite co-stabilizer, based on the total weight of the lubricant system; at least about 0.8% by weight of calcium ricinoleate or calcium hydroxystearate, (d) at least about 0.1% by weight of a hindered phenol; (e) at least about 0.2% by weight of oxyethylene copolymer crosslinked with diepoxide; and (f) at least about 0.01% by weight of N, N'-ethylene-bis-stearamide, based on the total weight of the composition. The invention also relates to a method for improving the lubricity of thermoplastic articles, characterized by the manufacture of the article from a self-lubricating composition by mixing at least about 0.5% by weight of the lubricating system and the thermoplastic polymer, based on the weight total of the composition, to produce a self-lubricating composition, and the manufacture of the composition in a shaped article, wherein the article has improved surface and friction properties. The composition is suitable for numerous friction applications such as gears, pulleys, bearings, cams, sliding plates, guides, levers, rollers, conveyor belt links, etc.

DETAILED DESCRIPTION OF THE INVENTION The self-lubricating composition of the present invention generally contains a thermoplastic polymer and a lubricant system. The composition is characterized in that it contains from about 70 to about 99.5% by weight of the thermoplastic polymer and from about 30 to about 0.5% by weight of the lubricant system, based on the total weight of the composition. Typically, the composition contains from about 85 to about 99% by weight of the thermoplastic polymer and from about 15 to about 1% by weight of the lubricant system based on the total weight of the composition. Preferably, the composition contains about 98% by weight of the thermoplastic polymer, about 2% by weight of the lubricant system. The lubricant system is generally prepared before being added to the polymers and can be added together with suitable processing additives to the thermoplastic polymer. Processing additives that do not degrade the lubricant system or the physical and mechanical properties of the polymer can be added thereto to aid dispersion of the lubricant system within the polymer prior to the combination, extrusion and manufacture of shaped articles. Although the invention is generally directed to improving the surface wear and lubricity of the thermoplastic resins selected from polyarynides, polyesters, polyphenylene sulfide, polyoxymethylene, polyolefins, styrene polymers and polycarbonates, a particularly preferred class of thermoplastic resins are polyoxirne Ines . The oxymethylene polymers, ie polymeric acids or polyoxymethylenes, useful in the invention are generally characterized as having repeating oxymethylene repeating units of the general formula: 0 CH2 The polymeric acetals useful in the preparation of the lubricant composition of the present invention generally have a high content of oxymethylene units, i.e., generally greater than about 85%. These materials are commercially available from a number of manufacturers such as homopolymers, copolymers, terpolymers and the like. These highly crystalline cells, which are described briefly below, are well known in the art and have been extensively reviewed. For example, a review of polymeric acetals entitled "Acetal Resins, by T. J. Dolce et al.

J. A. Grates, can be found in the second edition of Encyclopedia of Polymer Science and Engineering, John Uiley and Sons, New York, 1985, Vol. 1, pp. 42-61. More information on acetal polymers can be found in French Patent No. 1,221,148, as well as in the US Patents. commonly assigned Nos. 3,027,352, 3,072,069, 3,147,234 and 3,210,318. Typically, acetal polymer furnaces can be prepared by polymerizing anhydrous formaldehyde or trioxane. The homop > Oximene oligomers are regularly stabilized against thermal degradation by blocking at the terminus, for example, with ester or ether groups, such as those derived from alkanoic anhydrides (eg, acetic anhydride) or dialkyl ethers (eg, dimethyl ether), or incorporating the stabilizing compounds in the homopoly e o. The commercially available acetal opolymer is obtained by polymerizing anhydrous formaldehyde in the presence of an initiator after which the polymer is blocked at its ends by acetylation of the hemiacetal end groups with acetic anhydride in the presence of a sodium acetate catalyst. Methods for producing blocked acetal homopolymers at their ends are taught in the U.S. Patents. Nos. 2,786,994 and 2,998,409. Acetal homopolymers are well known in the art and are commercially available under the trade names DELRIN * and TENAC. Polymeric acetals which have been found to be especially suitable for use in the composition of the present invention are crystalline oxymethylene copolymers having repeating units consisting essentially of oxymethylene groups interspersed with higher oxyalkylene groups of the general formula: R2 R2 -0-Ci- ~ CI - (- R3--) wherein each Ri and R2 is hydrogen, a lower alkyl group, or a lower alkyl group substituted with halogen, each R3 is an ethylene group, Oxymethylene, Rethylene substituted with halogenoalkyl or lower alkyl or oxymethylene substituted with halogenalkyl or lower alkyl, and n is zero or an integer from one to three, inclusive. Each lower alkyl group preferably contains one or two carbon atoms. Oxymethylene groups will generally constitute from 85 to 99.9% of the recurring units in said copolymers and are generally incorporated by ring-opening polymerization of trioxane in the presence of acid catalyst. The higher oxyalkylene groups are incorporated into the polymer by copolymerizing a typical or formal cyclic ester having at least two adjacent carbon atoms in the ring in addition to trioxane. The cyclic ether or formal are incorporated by the coating of an oxy-carbon bond. The preferred higher oxyalkylene group is oxyethylene, which has the formula: --O - CH2 - CH2 - The oxyethylene can be incorporated into the polymer by copolyzing ethylene oxide or 1,3-dioxolane with trioxane. Preferred crystalline acetal copolymers, as described above and having a structure consisting essentially of oxymethylene and oxyethylene groups, have a melting point of at least 150 ° C. They can usually be milled or processed at temperatures ranging from about 175 ° C to about 230 ° C and are usually highly crystalline, having a polymer crystallinity of about 40% to about 90% or more. Typically, oxymethylene copolymers are stabilized after manufacture by degradation of the unstable molecular ends of the polymer chains to a point where a relatively stable carbon-carbon bond prevents further degradation of each end of the polymer chain. Said degradation of the unstable molecular ends is generally effected by hydrolysis, as described, for example, in the U.S. patent. No. 3,219,623 of Berardinelli. The oxymethylene copolymer can also be stabilized by endblocks, again using techniques well known to those skilled in the art, such as by acetylation with acetic anhydride in the presence of a sodium acetate catalyst. A particularly preferred class of oxymethylene copolymer is commercially available under the tradename CELCON * acetal copolymer. Typically, CELCON acetal copolymers are copolymers of approximately 98% by weight of trioxane and about 2% of dioxalan. CELCON is a registered trade name of Hoechst Celanese Corporation. The compositions of the present invention can be obtained using any commercial grade of CELCON acetal, including CELCON grades U-10, M-25, M-95, M-270 and M-450. The CELCON M-25 acetal copolymer has a melt flow rate of approximately 2.5 g / 10 min when tested in accordance with ASTM D1238-82. The CELCON M-90 acetal copolymer has a molecular weight and molten bath viscosity less than CELCON M-25. CELCON M-270 has a molecular weight and molten bath viscosity even lower than CELCON M ~ 25. The oxymethylene terpolyners can also be used to obtain the self-lubricating compositions of the present invention. These terpolymers contain oxymethylene groups, oxy (higher alkylene) groups such as those corresponding to the general formula: R2 - R2 -0- í_i_. (- R3--) Rl Ri and a different third group that has been interpolymerized with the oxymethylene and higher oxyalkylene groups. A terpolyner as described above is typically obtained by reacting trioxane with a cyclic ether or cyclic acetal and a third monomer which is a bi-functional compound, such as a diglycide of the formula: H2 C CH- -CH2 - -Z - CH2 - -CH- -CH2 \ / \ / 0 0 wherein Z represents a carbon-carbon bond, an oxygen atom, an oxyalkoxy group of 1 to 8 carbon atoms, inclusive, preferably 2 to 4 carbon atoms, an oxycycloalkoxy group of 4 to 8 carbon atoms, inclusive, or a lower oxypolialkoxy group, preferably one having from 2 to 4 recurring lower alkoxy groups each having 1 or 2 carbon atoms. Examples of suitable bi-functional compounds include the diglycidyl ethers of ethylene glycol of 1,2-propanediol and 1,4-butanediol, with diglycidyl ether of 1,4-butanediol being preferred. In general, when preparing such terpolymers, ratios of 89.0 to 99.89% by weight of trioxane, 0.1 to 10% by weight of the cyclic ether or cyclic acetal, and 0.01 to 1% by weight of the bifunctional compound, based on the total weight of the monomers used to form the terpolymer. A particularly preferred oxymethylene terpolymer commercially available from UlO Hoechst Celanese Corporation under the name CELCON UlO acetal polymer; a terpolymer of 1,4-butanediol, dioxolane and trioxane diglycidyl ether containing about 0.05% by weight, 2.0% by weight, and 97.95% by weight, respectively, of repeating units derived from these three onomers, based on weight total of the terpolymer. Oxymethylene-based terpolymers are obtained and stabilized by methods well known in the art which are generally analogous to those used from the manufacture of the copolymers. More detailed descriptions of the methods for producing oxymethylene-based terpolymers and their compositions can be found in previously cited patents. The oxymethylene polymers can be combined in various proportions by melt blending in extruders or similar apparatus to form suitable resins to prepare the self-lubricating composition of the invention. In general, the polymers can be mixed at temperatures of at least about 170 ° C to about 230 ° C. The lubricant system can be prepared by mechanically mixing, that is, by combining, a polyolefin composition containing: (a) from about 60 to about 98% by weight of a very high molecular weight polyethylene, characterized in that it has a molecular weight of 500,000 to about 600,000, a density of about 0.94 to about 0.99 g / cm 3, and a mold flow index (MFI) of about 0.4 to about 2.2 g / 10 rnin; (b) from about 20 to about 40% by weight of homopolymers or high density polyethylene copolymers, characterized in that they have a density of about 0.95 g / cm3 and an MFI of about 3.0 g / 10 min; (c) from about 0.05% to about 1.00% by weight of an acid metal salt of calcium stearate or zinc stearate; (d) from about 0.05% to about 5.00% by weight of a non-polar low molecular weight polyethylene wax, characterized in that it has a molecular weight of from about 5,000 to about 10,000; (e) from about 0.05 to about 5.00% by weight of N, N'-ethylene-bis-stearamide, characterized in that it has a melting point of 143 ° C, and (f) from about 0.05 to about 3.00% in phenolic antioxidant weight / phosphite co-stabilizer, based on the total weight percent of the lubricant system Other processing additives that can be mixed with the self-lubricating composition of the invention are hindered phenols, calcium ricinoleate or calcium hydroxystearate, a copolymer Oxymethylene entangled with diepoxide, and N, N'-ethylene-bis-stearamide The hindered phenols which are used in the present invention are generally known as antioxidants or free radical inhibitors, at least one of which may be used. '-methylenbys (4-methyl-6-t-butylphenol), bis (3, 5-di-t-butyl-4-hydroxyhydrocinnamate) of hexarnetylene glycol, tetrabismethylene (3,5-di-t-butyl-4-hydroxyhydrocin-mato)] methane, triethylene glycol bis-3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionate, 1,3 , 5-trimethyl-2,4,6,6-tris (3,5-di-t-butyl-4-hydroxy-benzyl) benzene, 3- (4'-hydroxy-3 ', d-di-t-butylphenpropionate p-octadecyl, 4,4'-methylenebis (2,6-di-t-butyl phenol), 4,4'-butylidene-bis- (6-t-butyl-3-methylphenol), bis-C3- (2,4-di-t-butyl-4-hydroxyphenyl-3-propionate 2,2-thiodiethyl, 3,5-di-t-butyl-4-hydroxybenzylphosphonate di-stearyl and 6- (3-t-butyl) -5-methyl-2-hydroxybenzyl) -4-methylphenyl-2-t-butyl acrylate However, useful hindered phenols are not limited to these compounds, other hindered or stereo-obstructing phenols of the same type are also effective. described above, the bis- (3,5-di-t-butyl-4-hydroxyhydrocinnamate) of hexaethylene glycol, for example Irganox "259 available from Ciba-Geigy, tetrakismethylene. 5-di-t-butyl-4-hydroxyhydrocinnamate) Imeta-no, for example plo Irganox 1010 manufactured by Ciba-Geigy, and bis-3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionate tetraethylene glycol, for example Irganox 245 manufactured by Ciba-Geigy. A preferred hindered phenol is bis (3,5-di-t-buityl-4-hydroxy-hydrocinnamate) of hexamethylene glycol. The N, N'-ß-ethyl-bis-stearamide useful in the invention is marketed under the tradename Acrawax® C by Lonza, Inc. A preferred embodiment of the invention comprises preparing the polyoxymethylene composition of the self-lubricant useful for the manufacture of shaped articles. having slippery surfaces, characterized by the steps of: (a) selecting an oxymethylene polymer from the group consisting of: (i) oxymethylene homopolymers; (ii) oxymethylene copolymer comprising from about 85 to about 99.9% of oxymethylene repeating units interspersed with repeating units of the formula: 0 wherein each Ri and R2 is selected from the group consisting of hydrogen, lower alkyl radicals and lower alkyl radicals substituted with halogen, said lower alkyl radicals each having 1 to 2 carbon atoms, each R3 is selected from the group consisting of ethylene, oxymethylene, methylene substituted with halogenalkyl and lower alkyl, and oxymethylene radicals substituted with halogenalkyl and lower alkyl, and n is an integer from 0 to 3, inclusive; (iii) oxymethylene terpolymer, which is the product or reaction of trioxane, a cyclic ether and / or cyclic acetal, and a diglycidyl ether of the formula: H2C CH - CH2 - Z - CH2 - CH - CH2 \ / \ 0 0 where Z is selected from the group consisting of a carbon-carbon bond, oxygen, an oxyalkoxy unit of 1 to 8 carbon atoms carbon, and a lower oxypolylalkoxy unit; and (iv) mixtures of (i), (ii) and (iii). b) mixing from about 70 to about 99.5% by weight of the polymer with from about 30 to about 0.5% by weight of a lubricant system, based on the total weight of the composition, which contains: (i) about 60 to about 70% by weight of a very high molecular weight polyethylene, characterized in that it has a molecular weight of about 500,000, to about 600,000 and a density of at least about 0.94 g / cm 3; (ii) at least about 20 to about 30% by weight of high density polyethylene copolymers or copolymers, iii) at least about 0.05% by weight of an acid metal salt; iv) at least about 0.05% by weight of a non-polar polyethylene wax characterized in that it has a molecular weight of from about 5,000 to about 10,000; v) about 0.05% by weight of a wax of fatty amide; and (vi) at least about 0.05% by weight of phenolic antioxidant containing phosphite and phosphonite co-stabilizers, based on the total weight of the lubricant system; (c) further mixing with the polyoxymethylene and the lubricant system at least 0.05% by weight of calcium ricinoleate or calcium hydroxystearate, at least about 0.1% by weight of a hindered phenol, at least about 0.1% by weight of oxymethylene copolymer crosslinked with diepoxide, and at least about 0.8% by weight of N, N'-ethylene-bis-stearamide, based on the total weight of the composition to form a well dispersed self-lubricating composition; and (d) forming a self-lubricating composition wherein the system is well dispersed within the composition. Numerous additives known to those skilled in the art can also be included in the self-lubricating composition as long as, however, the tribological and wear properties of the composition are not compromised. These additives, which can provide desirable properties to the composition, include mold lubricants, plasticizers, glass fibers, nucleating agents, antioxidants, formaldehyde scavengers, chain cutting inhibitors, ultraviolet light inivers, impact modifiers, acid scavengers. , dyes, etc. The composition can be formed into self-lubricating shaped articles, e.g., bearings, gears, cams, rollers, sliding plates, pulleys, levers, guides, links of conveyor belts, etc., which are useful in numerous applications ranging from machines commercial to automotive parts and electrical appliances, including machines for food handling and for fabric manufacture, or where the properties of low friction and reduced wear are desirable. Test discs were prepared for wear and friction properties by cleaning in a sonic bath of methanol, drying in air and weighting to one tenth (1/10) milligram. The discs were tested for tribology properties in accordance with a pin-on-disc wear test. According to the test, a machined Nylatron nylon pin with a tip radius of approximately .475 cm was mounted on the upper spindle of a Falex wear and friction test apparatus, approximately 1.19 cm from the center of the test disk, which was mounted on the lower spindle thereof. A force of approximately 9 kg was applied to the test disk by means of an air cylinder and the disk was pressed against the spherical tip of the pin. A rotational speed of approximately 425 rpm was applied to the test disk by means of an air cylinder an impeller motor. During the test, an air current of 1,132 liters per hour normal (1 / hr normal) and a distance of 5.08 cm was directed against the surface of the disk to remove debris. Test times ranged from around 0.5 to about 65 hrs. After the test, the tip of the pin and disc were separated so that they were not in contact and the disc was cleaned of debris by blowing the surface with compressed air, and the disc was weighed again for weight loss. The torque (D, measured during the test, was converted to a coefficient of friction (f) by applying the equation, based on the load and velocity placed on the apparatus as follows: The results of surface wear and friction coefficients are given in four 1, below. The following examples are general illustrations of methods for preparing the polymeric composition and shaped articles of the invention. They are provided for illustration purposes only as they are appreciated from the above description.

EXAMPLE 1 To prepare the mixture of the self-lubricating composition containing 1% of the lubricant system, the following components were used: a) 97.58 kg of unstabilized polyoxymethylene copolymer flake (97.7% by weight); b) .499 kg of polyoxymethylene copolymer pellets, entangled with diepoxide (0.5% by weight); c) 90.69 g of N, N'-ethylene-bis-steararnide (0.2% by weight); d) .454 kg of bis- (3,5-di-t-butyl-4-hydroxyhydrocinnamate hexa ethylene glycol (0.5% by weight), - e) 45.34 g of calcium ricinoleate (0.1% by weight); and f) .998 kg of the lubricant system (1% by weight with respect to the total composition). The components were briefly stirred in a barrel followed by mixing at high speed for 30 seconds in a Henschel mixer to form a mixture. Subsequently, the mixture was destroyed in strips in a ZSK twin-screw extruder from Werner and Pfleiderer, previously heated and purged with polyacetal pellets. The extruder zones were operated at 188.8 to 197.2 ° C, the melting temperature was 212 ° C and under a vacuum of 68.58 cm Hg, and the screw speed was 150 rpm. Strips of extruded product were produced at a rate of 17.25 kg / hr. Subsequently, the strips were cooled in cold water and cut into pellets. The pellets were injection molded at temperatures of 82.2 to 93.3 ° C and to conventional pressure, speed and cycle time settings, a nozzle temperature setting of 182.2 to 215.5 ° C and a barrel temperature setting of 176.6 to 215.5 ° C to form 3.17 cm discs. in diameter, each weighing approximately 7 g. The discs were analyzed for weight loss and coefficient of friction after 0.5, 1.5, 17 and 65 hrs. The results of the analyzes are presented in Table I.

EXAMPLE 2 To prepare the mixture of the polymer composition containing 2% of the lubricant system, the following components were used: a) 96.58 kg of non-stabilized polyoxymethylene copolymer flake; b) .499 kg of polyoxiornethylene copolymer pellets, entangled with diepoxide; c) 90.69 g of N, N'-ethylene-bis-stearnary; d) .499 kg of bis- (3,5-di-t-butyl-4-hydroxyhydro-cinnamate) of hexamethylene glycol; e) 45.34 gr of calcium ricinoleate; and f) 1.99 kg of the lubricant system (2% by weight with respect to the total composition). The components were mixed, destroyed and molded according to the procedure of Example 1 to form nominal discs of 7 g for analysis of weight loss and coefficient of friction. The results of the analyzes are presented in table I.

EXAMPLE 3 To prepare the mixture of the self-lubricating composition containing 3% of the lubricant system, the following components were used: a) 95.58 kg of unstabilized flake of polyoxy ethylene copolymer (97.7% by weight); b) .499 kg of polyoxyethylene ethylene copolymer pellets, entangled with diepoxide; c) 90.69 g of N, N'-ethylene-bie-stearamide; d) .499 kg of bis- (3,5-di-t-butyl-4-hydroxyhydro-cinnamate) of hexamethylene glycol; e) 45.34 gr of calcium ricinoleate; and f) 2.99 kg of the lubricant system (3% by weight with respect to the total composition). The components were mixed, destroyed 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 presented in table I.

EXAMPLE 4 To prepare the mixture of the self-lubricating composition containing 4% of the lubricant system, the following components were used: a) 94.58 kg of unstabilized flake of polyoxymethylene copolymer; b) .499 kg of polyoxymethylene copolymer pellets, entangled with diepoxide; c) 90.69 g of N, N'-ethylene-bis-stearamide; d) .499 kg of bis- (3J5-di-t-butyl-4-hydroxyhydro-cinnamate) of hexa ethylene glycol; e) 45.34 gr of calcium ricinoleate; and f) 3.99 kg of the lubricant system (4% by weight with respect to the total composition). The components were mixed, destroyed 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 presented in table I.

EXAMPLE 5 To prepare the mixture of the self-lubricating composition containing 5% of the lubricant system, the following components were used: a) 83.85 kg of unstabilized flake of polyoxymethylene copolymer; b) .454 kg of polyoxymethylene copolymer pellets, entangled with diepoxide; c) 82.44 g of N, N * -ethylene-bis-stearamide; d) .454 kg of bis- (3,5-di-t-butyl-4-hydroxyhydrocin ate) of hexamethylene glycol; e) 41.22 gr of calcium ricinoleate; and f) 4.54 kg of the lubricant system (5% in comparison with the total composition).

The components were mixed, destroyed 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 presented in table I.

COMPARATIVE EXAMPLE 6 As a comparative example, a polyrnical composition was prepared by replacing the lubricant system of Example 1 with polytetrafluoroethylene (1.5% by weight of PTFE) HOSTAFLON® TF 9203, using the following components: a) 97.68 kg of unstabilized flake of polyoxymethylene copolymer; b) .499 kg of polyoxymethylene copolymer pellets, entangled with diepoxide; c) 90.69 g of N, N'-ethylene-bis-eeteararnide; d) .499 kg of bis- (3,5-di-t-butyl-4-hydroxyhydro-cinnamate) of hexamethylene glycol; e) 45.34 g of calcium ricinoleate; and f) 1.49 kg PTFE < 5% by weight with respect to the total composition). The components were mixed, destroyed 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 presented in the O K picture I.

COMPARATIVE EXAMPLE 7 As another comparative example, a polymer composition was prepared by replacing the lubricant system with 3.0% by weight of PTFR, using the following components: a) 95.58 kg of unstabilized flake of polyoxirnethylene copolymer; b) .499 kg of polyoxymethylene copolymer pellets, entangled with diepoxide; c) 90.69 g of N, N'-ethylene-bis-stearnary; d) .499 kg of bis- (3,5-di-t-butyl-4-hydroxyhydro-cinnamate) of hexamethylene glycol; e) 45.34 gr of calcium ricinoleate; and f) 2.99 kg of PTFE (3.0% by weight with respect to the total composition). The components were mixed, destroyed 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 presented in table I.

COMPARATIVE EXAMPLE 8 As a comparative example, a polymer composition without the addition of the lubricant system (0 wt.% Of the lubricant system) was prepared using the following components: a) 98.58 kg of unstabilized polyoxyethylene copolymer flake; b) .499 kg of polyoxymethylene copolymer pellets, entangled with diepoxide; c) 90.69 g of N, N'-ethylene-bis-stearamide; d) .499 kg of bis- (3,5-di-t-butyl-4-hydroxyhydro-cinnamate) of hexarnetylene glycol; e) 45.34 gr of calcium ricinoleate; and f) 0 kg of the lubricating system. The components were mixed, destroyed and molded according to the procedure of Example 1 to form 7 g discs for weight loss analysis and coefficient of friction. The results of the analyzes are presented in table I.

TABLE I i Load of 9.8 kg, speed of 31.8 m / min, material pin is nylon. 2 No data

Claims (21)

NOVELTY OF THE INVENTION CLAIMS

1. - A self-lubricating composition suitable for use in the manufacture of shaped articles having slippery surfaces, characterized in that it contains: a) from about 70 to about 99.5% by weight of a terrnoplastic polymer, b) from about 30 to about 0.5% by weight weight of a lubricating system, characterized as: (i) at least about 60 to about 70% by weight of a very high molecular weight polyethylene, characterized in that it has a molecular weight of at least 500,000, a density of at least about 0.94 g / cm 3, and a mold flow index (MFI) of about 0.4 to about 2.2 g / 10 min; ii) at least about 20 to about 30% by weight of a high density polyethylene homopolymer or copolymer, characterized in that it has a density of about 0.95 g / cm 3 and an MFI of about 3.0 g / 10 min; iii) at least about 0.05% by weight of a metal salt; iv) at least about 0.05% by weight of a non-polar low molecular weight polyethylene wax, characterized in that it has a molecular weight of from about 5,000 to about 10,000; v) of about 0.05% by weight of a wax of fatty amide selected from bis-stearoylethylenedia ida and bis-palmitoylethylenediamide; and (vi) at least about 0.05% by weight of phenolic antioxidant / phosphite co-stabilizer, based on the total weight of the lubricant system; (c) at least about 0.8% by weight of calcium ricinoleate or calcium hydroxystearate, (d) at least about 0.1% by weight of a hindered phenol; (e) at least about 0.2% by weight of oxynenetylene copolymer crosslinked with diepoxide; and (f) at least about 0.01% by weight of N, N'-ethylene-bis-eatera ida, 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, polyoxymethylene, polyolefins, ether 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) oxymethylenepolymer; (ii) oxymethylene copolymers comprising from about 85 to about 99.9% repeating units of oxymethylene interspersed with repeating units of the formula: R2 - -R2 -0- • (- a -) "Rl Ri wherein each Ri and R2 is selected from the group consisting of hydrogen, lower alkyl radicals and lower alkyl radicals substituted with halogen, said lower alkyl radicals each having 1 to 2 carbon atoms, each R3 is selected from the group consisting of of methylene, oxymethylene, substituted methylene with halogenalkyl and lower alkyl, and oxymethylene radicals substituted with halogenalkyl and lower alkyl, and n is an integer from 0 to 3, inclusive; (iii) oxyrnethylene terpolyners, which are the product or reaction of the trioxane and, a cyclic ether and / or cyclic acetal, and a diglycidyl ether of the formula: H2C CH - CH2 - Z - CH2 - CH - CH2 \ / \ / 0 0 wherein Z is selected from the group consisting of a carbon-carbon bond, oxygen, an oxyalkoxy unit of 1 to 8 carbon atoms, and an oxypolylCalkoxy unit lower); and (iv) mixtures of (i), (ii) and (iii).

5. The composition according to claim 4, further characterized in that the lubricant system comprises about 70% by weight of high molecular weight polyethylene and about 30% by weight of high density polyethylene copolymer.

6. The composition according to claim 5, further characterized in that the acid metal salt is selected from the group consisting of zinc stearate, calcium stearate and mixtures thereof.

7. The composition according to claim 6, further characterized in that the composition consists essentially of about 1% by weight fine-wax waxes.

8. The composition according to claim 7, further characterized in that the fatty acid amide wax is selected from the group consisting of bis-eethearoethylendia ida and bis-palmitoylethylenediamide.

9. The composition according to claim 8, further characterized in that the hindered phenol is bis (3,5-di-t-butyl-4-hydroxyhydrocinnamate) of hexamethylene glycol.

10. The composition according to claim 9, further characterized in that the polyoxymethylene is oxymethylene copolymer comprising about 85 to about 99.9% of oxymethylene repeating units interspersed with repeating units of the formula: R2 - R2 -0- C (--R3 -) n Rl Ri wherein each Ri and R2 is selected from the group consisting of hydrogen, lower alkyl radicals and lower alkyl radicals substituted with halogen, said lower alkyl radicals each having 1 to 2 carbon atoms, each R3 is selected from the group that it consists of methylene, oxymethylene, halogenalkyl-substituted lower alkyl, and oxykenylene substituted with halogenalkyl and lower alkyl, and n is an integer from 0 to 3, inclusive.

11. A method for preparing a self-lubricating polymeric thermoplastic composition useful for the manufacture of shaped articles having slidable surfaces, comprising the steps of: (a) selecting a thermoplastic polymer selected from the group > or consisting of polyamide, polyesters, polyphenylene sulfide, polyoxymethylene, polyolefins, styrene polymers and polycarbonates; (b) mixing from about 70 to about 99.5% by weight of the polymer with from about 30 to about 0.5% by weight of a lubricant system, based on the total weight of the composition, which contains: (i) from about 60 to about 70% by weight of a very high molecular weight polyethylene, characterized in that it has a molecular weight of from about 500,000 to about 600,000, and a density of at least about 0.94 g / cm 3; (ii) at least about 20 to about 30% by weight of high density polyethylene homopolymers or copolymers, iii) at least about 0.05% by weight of an acid metal salt of calcium stearate or zinc stearate; iv) at least about 0.05% by weight of a non-polar polyethylene wax characterized in that it has a molecular weight of from about 5,000 to about 10,000; v) about 0.05% by weight of a wax of fatty amide; and (vi) at least about 0.05% by weight of phenolic antioxidant containing phosphite and phosphonite co-stabilizers, based on the total weight of the lubricant system; (c) further mixing with the polyoxymethylene the lubricating system at least 0.05% by weight of calcium ricinoleate or calcium hydroxystearate, at least about 0.1% by weight of a hindered phenol, at least about 0.1% by weight of copolymer of oxiradylene crosslinked with diepoxide, and at least about 0.8% by weight of N, N'-ethylene bis-eetheramide, based on the total weight of the composition to form a well dispersed self-lubricating composition.

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

13. The method according to claim 12, 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% repeating units of oxynethylene interspersed with repeating units of the formula: Rl Rl wherein each Ri and R2 is selected from the group consisting of hydrogen, lower alkyl radicals and lower alkyl radicals substituted with halogen, said lower alkyl radicals each having 1 to 2 carbon atoms, each R3 is selected from the group that consists of methylene, oxymethylene, methylene substituted with halogenalkyl and lower alkyl, and oxymethylene radicals substituted with halogenalkyl and lower alkyl, and n is an integer from 0 to 3, inclusive; (iii) oxymethylene terpolymers, which are the product or reaction of the trioxane and a cyclic ether and / or cyclic acetal, and a diglycidyl ether of the formula: H2C CH - CH2 - Z - CH2 - CH - CH2 \ / \ / 0 0 wherein Z is selected from the group consisting of a carbon-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).

14. The method according to claim 13, further characterized in that the polyoxymethylene is oxymethylene copolymer comprising about 85 to about 99.9% of oxymethylene repeating units interspersed with repeating units of the formula: R2 - R2 -0- L_i_ - ((---- IR3 -) "Rl Ri wherein each Ri and R2 is selected from the group consisting of hydrogen, lower alkyl radicals and lower alkyl radicals substituted with halogen, said lower alkyl radicals each having 1 to 2 carbon atoms, each R3 is selected from the group that it comprises methylene, oxymethylene, methylene substituted with halogenalkyl and lower alkyl, and oxymethylene radicals substituted with halogenalkyl and lower alkyl, and n is an integer from 0 to 3, inclusive.

15. The method according to claim 14, further characterized in that the lubricant system comprises about 70% by weight of high molecular weight polyethylene and about 30% by weight of high density polyethylene homopolymer.

16. A method for preparing a self-lubricating polyoxymethylene shaped article suitable for slidable applications, comprising a polyoxymethylene composition intimately combined with a lubricant system, wherein the composition comprises from about 70 to about 99.5% by weight of polyoxyethylene and of about 30 to about 0.5% by weight of a lubricant system, based on the total weight of the composition, comprising the steps of: (a) preparing a polyoxymethylene selected from the group consisting of: (i) oxymethylenepolymer; (ii) oxymethylene copolymers comprising from about 85 to about 99.9% repeating units of oxyethylene intermixed with repeating units of the formula: -0- J wherein each Ri and R2 is selected from the group consisting of hydrogen, lower alkyl radicals and lower alkyl radicals substituted with halogen, said lower alkyl radicals each having 1 to 2 carbon atoms, each R3 is selected from the group that it consists of methylene, oxymethylene, methylene substituted with halogenalkyl and lower alkyl, and oxymethylene radicals substituted with halogenalkyl and lower alkyl, and n is an integer from 0 to 3, inclusive; (iii) oxymethylene terpolymers, which are the product or reaction of the trioxane and a cyclic ether and / or cyclic acetal, and a diglycidyl ether of the formula: H2C CH - CH2-- Z - CH2 - CH - CH2 \ / \ / 0 0 wherein Z is selected from the group consisting of a carbon-carbon bond, oxygen, an oxyalkoxy unit of 1 to 8 carbon atoms, and an oxy oxy unit (lower alkoxy); and (iv) mixtures of (i), (ii) and (iii); (b) mixing the polyoxymethylene and the seven to lubricant, which consists essentially of: (i) from about 60 to about 70% by weight of a high molecular weight polyethylene, characterized in that it has a molecular weight of at least 500,000. , and a density of at least about 0.94 g / cm3; (ii) at least about 20 to about 30% by weight of high density polyethylene homopolymers or copolymers, iii) at least about 0.05% by weight of an acid metal salt of calcium stearate or zinc stearate; iv) at least about 0.05% by weight of a non-polar polyethylene wax characterized in that it has a molecular weight of from about 5,000 to about 10,000; v) about 0.05% by weight of a wax of fatty amide; and Cvi) at least about 0.05% by weight of phenolic antioxidant containing phosphite and phosphonite co-stabilizers, based on the total weight of the lubricant system; (c) further mixing with the polyoxymethylene the seventh lubricant at least 0.05% by weight of calcium ricinoleate or calcium hydroxystearate, at least about 0.1% by weight of a hindered phenol, at least about 0.1% by weight of copolymer of oxiradylene crosslinked with diepoxide, and at least about 0.8% by weight of N, N'-ethylene-bis-stearamide, based on the total weight of the composition to form a well dispersed self-lubricating composition; and (d) forming a self-lubricating composition wherein the system is well dispersed within the composition.

17. An article configured according to claim 16, further characterized in that the self-lubricating composition comprises from about 85 to about 99% by weight of oxymethylene polymer and from about 15 to about 1% by weight of the seventh lubricant bathed in the total weight of the composition.

18. An article configured according to claim 17, further characterized in that the self-lubricating composition comprises about 98% by weight of oxymethylene polymer and about 2% by weight of the lubricant system based on the total weight of the composition.

19. An article configured according to claim 18, further characterized in that it has a wear rate of about 4.5 mg at a speed of about 30.5 m / min and a load of about 9.08 kg after about 17 hours.

20. - An article configured according to claim 19, further characterized in that it has a coefficient of friction of less than about 0.053.

21. An article configured according to claim 20, further characterized in that it is selected from the group consisting of bearings, gears, cams, rollers, sliding plates, pulleys, levers and guides.