CA2226388C - Thermoplastic composition with improved wear properties - Google Patents
Thermoplastic composition with improved wear properties Download PDFInfo
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- CA2226388C CA2226388C CA002226388A CA2226388A CA2226388C CA 2226388 C CA2226388 C CA 2226388C CA 002226388 A CA002226388 A CA 002226388A CA 2226388 A CA2226388 A CA 2226388A CA 2226388 C CA2226388 C CA 2226388C
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L59/00—Compositions of polyacetals; Compositions of derivatives of polyacetals
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L101/00—Compositions of unspecified macromolecular compounds
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2555/00—Characteristics of bituminous mixtures
- C08L2555/40—Mixtures based upon bitumen or asphalt containing functional additives
Abstract
A self-lubricating polymeric composition, characterized as a melt blend of a thermoplastic polymer and a lubricating system containing ultra high molecular weight polyethylenes, a polyester, acid metal salts, calcium salts, antioxidants and stabilizers. The composition may be prepared into shaped articles which exhibit improved surface wear resistance and coefficients of friction.
Description
THERMOPL?.STIC POLYMER COMPOSITION
WITH IMPROVED WElrR PROPERTIES
F'~ELD OF THE TNVENTION
The present invention relates to self-lubricating, low wear compositions containing a thermoplastic polymer and lubricating system suitable for use as a molding resin to prepare shaped articles. Shaped articles prepared from the composition exhibit low friction properties as well as reduced surface wear under loads.
g,grK~ROLrrln OF TT3E INVENT_rON
Thermoplastic polymers, e.g., polyamides, polyesters, polyphenylene sulfide, polyvxymethylene, polyolefins, styrene polymers, and polycarbonates, are characterized as polymersw that exhibit exceptional mechanical and electrical properties, as well as good moldability and chemical resistance. However, these polymers may exhibit inadequate tribological properties when utilized in some friction environments, e.g..
plastic to metal, and plastic to plastic interfaces.
While many lubricating compositions have been applied to thermoplastic polymers to improve friction and wear properties of shaped articles prepared therefrom, some applications prohibited the use of certain lubricants because of possible contamination, e.g., faod handling, clothing preparation and volatile environments.
Attempts have been made to improve the friction properties and reduce the surface wear of articles prepared from thermoplastic polymers by incorporating lubricants directly into the polymer matrix prior to the fabrication of shaped articles therefrom. Many materials, including solid lubricants and fibers (e.g., graphite, mica, silica, talc, boron nitride and molybdenum sulfide), paraffin waxes, petroleum and S synthetic lubricating oils, and other polymers (e. g., polyethylene and polytetrafluoroethylene) have been added to thermoplastic polymers to improve friction and wear properties. However, the addition of many of these additives in various combinations to thermoplastic polymers, while improving tribological properties have reduced other desirable physical and mechanical properties. Some additives have proven satisfactory for short terms at low speeds and loads. However, friction characteristics of many of these lubricants significantly deteriorate over long periods of time under increased Loads.
There is a desire for a non-toxic, self-lubricating thermoplastic compositions possessing surface wear resistance and low friction properties under increasing loads over long periods of time. A suitable composition, when fabricated into a shaped article, should maintain the desired mechanical and physical properties long associated with thermoplastic polymers, and be safely utilized in food handling and clothing manufacturing industries.
S TtrtMARY OF THE TNVENTZON
The present invention relates to a self-lubricating a composition suitable for forming a low friction, shaped article, characterized as a melt blend of from about ~0 , to about 99.5 weight percent of a thermoplastic polymer, WO 97!31055 PCT/US96I0259I
WITH IMPROVED WElrR PROPERTIES
F'~ELD OF THE TNVENTION
The present invention relates to self-lubricating, low wear compositions containing a thermoplastic polymer and lubricating system suitable for use as a molding resin to prepare shaped articles. Shaped articles prepared from the composition exhibit low friction properties as well as reduced surface wear under loads.
g,grK~ROLrrln OF TT3E INVENT_rON
Thermoplastic polymers, e.g., polyamides, polyesters, polyphenylene sulfide, polyvxymethylene, polyolefins, styrene polymers, and polycarbonates, are characterized as polymersw that exhibit exceptional mechanical and electrical properties, as well as good moldability and chemical resistance. However, these polymers may exhibit inadequate tribological properties when utilized in some friction environments, e.g..
plastic to metal, and plastic to plastic interfaces.
While many lubricating compositions have been applied to thermoplastic polymers to improve friction and wear properties of shaped articles prepared therefrom, some applications prohibited the use of certain lubricants because of possible contamination, e.g., faod handling, clothing preparation and volatile environments.
Attempts have been made to improve the friction properties and reduce the surface wear of articles prepared from thermoplastic polymers by incorporating lubricants directly into the polymer matrix prior to the fabrication of shaped articles therefrom. Many materials, including solid lubricants and fibers (e.g., graphite, mica, silica, talc, boron nitride and molybdenum sulfide), paraffin waxes, petroleum and S synthetic lubricating oils, and other polymers (e. g., polyethylene and polytetrafluoroethylene) have been added to thermoplastic polymers to improve friction and wear properties. However, the addition of many of these additives in various combinations to thermoplastic polymers, while improving tribological properties have reduced other desirable physical and mechanical properties. Some additives have proven satisfactory for short terms at low speeds and loads. However, friction characteristics of many of these lubricants significantly deteriorate over long periods of time under increased Loads.
There is a desire for a non-toxic, self-lubricating thermoplastic compositions possessing surface wear resistance and low friction properties under increasing loads over long periods of time. A suitable composition, when fabricated into a shaped article, should maintain the desired mechanical and physical properties long associated with thermoplastic polymers, and be safely utilized in food handling and clothing manufacturing industries.
S TtrtMARY OF THE TNVENTZON
The present invention relates to a self-lubricating a composition suitable for forming a low friction, shaped article, characterized as a melt blend of from about ~0 , to about 99.5 weight percent of a thermoplastic polymer, WO 97!31055 PCT/US96I0259I
and from about 30 to about 0.5 weight percent of a lubricating system, wherein said lubricating system :nay be characterized as an ultra high molecular weight polyolefin, pentaerythritol tetrastearate (PETS) and S calcium carbonate. Processing aids that do not extract from the characteristics of the invention may be added to the composition to enhance physical properties and processing, e.g., dispersion of the lubricating system within the polymer matrix.
I0 The composition may be formed into self-lubricating shaped articles, e.g., bearings, gears, cams, rollers, sliding plates, pulleys, levers, guides, conveyor links, etc., which exhibit good friction properties and are useful in numerous applications wherein parts exhibiting I5 low friction and reduced wear properties are desirable.
D.TATLED DESCRTpTTON OF THF ~T~NTION
The invention is directed to a self-lubricating composition which may be fabricated into shaped articles exhibiting good friction properties. Generally, the 20 composition may be characterized as an ac~ixture 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 contain from about 85 to about 99 weight percent of the 25 thermoplastic polymer and from about ZS 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 lubricating system, based on the total weight of the 30 composition.
I0 The composition may be formed into self-lubricating shaped articles, e.g., bearings, gears, cams, rollers, sliding plates, pulleys, levers, guides, conveyor links, etc., which exhibit good friction properties and are useful in numerous applications wherein parts exhibiting I5 low friction and reduced wear properties are desirable.
D.TATLED DESCRTpTTON OF THF ~T~NTION
The invention is directed to a self-lubricating composition which may be fabricated into shaped articles exhibiting good friction properties. Generally, the 20 composition may be characterized as an ac~ixture 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 contain from about 85 to about 99 weight percent of the 25 thermoplastic polymer and from about ZS 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 lubricating system, based on the total weight of the 30 composition.
Thermoplastic polymer useful in the self lubricating composition of the present invention may be, generally, selected from polyamides, polyesters, polyphenylene sulfides, polyolefins, polyoxymethylenes, styrene polymers, and polycarbonates. Particular preferred thermoplastic polymer of the invention is polyoxymethylenes, i.e., polymeric acetals or oxymethylene polymers. Polyoxymethylenes exhibit physical and mechanical properties that make them suitable for many industrial applications.
Polyoxymethylenes, i.e., polyacetals or oxymethylene polymers useful in the present invention are generally characterized as havinq recurring oxymethylene units of the general formula:
~2 Polyoxymethylenes that are useful in making composition of the invention generally have a fairly high content of oxymethylene units, i.e., generally greater than about 85 percent. These materials are commercially available from a number of manufacturers as homopolymers, r copolymers, terpolymers, and the like. These highly crystalline acetals, described briefly hereinbelow, are well known in the art and have been reviewed extensively.
WO 9?/31055 PCT/US9b/02591 For example, a review of polymeric acetals entitled, "Acetal Resins," by T. J. Dolce and J. A. Grates, may be found in the Second Edition of E~clopedia of Pol:cne_r ° Sc,'_ence and EnQ~-n ring, John Wiley and Sons. New York, 5 1985, Vol. 1, pp. 42-61. Additional information on acetal polymers can be found in French Patent No.
1,221,148 as well as commonly assigned U.S. Patent Nos.
3,027,352, 3,072,069, 3,14?,234, and 3,210,318.
Typically, acetal homopolymers may be prepared by polymerizing anhydrous formaldehyde or trioxane.
Oxymethylene homopolymers are typically stabilized against thermal degradation by end-capping with, for example, ester or ether groups, such as those derived from alkanoic anhydrides (e.g., acetic anhydride) or dialkyl ethers, (e.g., dimethyl ether) or by incorporating stabilizer compounds into the homopoly~er.
Co~ercially available acetal homopolymer is made by polymerizing anhydrous formaldehyde in the presence of an initiator after which the polymer is end-capped by acetyiation of the hemiacetal end groups with acetic anhydride in the presence of sodium acetate catalyst.
Methods for making end-capped.acetal homopolymers are taught in U.S. Patent Nos. 2,786,994 and 2,998,409.
Acetal homopolymers are well know in the art and are coitQnercially available under the trademarks DELRIN~ and TENAC~_ Polymeric acetals which have been found to be especially suitable far use in the composition of the ° present invention are crystalline oxymethylene copolymers having repeat units which consist essentially of WO 97!31055 PCT/US96/02591 oxymethylene groups interspersed with oxy(higher alkylene) groups of the general formula: "
-~~R3~
R3 Ri wherein each R1 and RZ is hydrogen, a lower alkyl group, or a halogen substituted lower alkyl group, each R3 is a S methylene, oxymethylene, lower alkyl or haloalkyl substituted methylene or lower alkyl or haloalkyl substituted oxymethylene group, 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 generally will constitute from about 85 to 99.9 percent of the recurring units in such copolymers and are generally incorporated by ring-opening polymerization of trioxane in the presence of an acidic catalyst. The oxy(higher alkylene) groups are incorporated into the polymer by copolymerizing a cyclic ether or cyclic formal having at least two adjacent carbon atoms in the ring in addition to trioxane. The cyclic ether or formal is incorporated by the breaking of an oxygen-to-carbon linkage. The preferred oxy(higher alkylenel group is oxyethylene, having the formula:
~2 ~2 Oxyethylene may be incorporated into the polymer by copolymerization of ethylene oxide or 1,3-dioxolane with trioxane.
The preferred crystalline acetal copolymers, as ' described above which have a structure consisting essentially of oxymethylene and oxyethylene groups, are S thermoplastic materials having a melting point of at least 150°C. They normally are millable or processible at temperatures ranging from about 175°C to about 230°C.
These copolymers are normally highly crystalline and exhibit a polymer crystallinity from about 40 percent to about 90 percent or greater.
Typically, oxymethylene copolymers are stabilized after manufacture by degradation of unstable molecular ends of the polymer chains to a point where a relatively stable carbon-to-carbon linkage prevents further degradation of each end of the polymer chain. Such degradation of unstable molecular ends is generally effected by hydrolysis, as disclosed, for example, in U.S. Patent No. 3,219,623 to Berardinelli. Oxymethylene copolymer may also be stabilized by end-capping, again using techniques well known to those skilled in the art, as for example by acetylation with acetic anhydride in the present of a sodium acetate catalyst.
A particularly preferred class of oxymethylene copolymers is co~anercially available under the trade name CELCONc9 acetal copolymer. CELCON acetal copolymers " typically are copolymers of about 98 weight percent of trioxane and about 2 percent of dioxolane. CELCON is a r registered trademark of Hoechst Celanese Corparatian.
The compositions of the current invention may be made using any commercial grade of CELCON acetal, including CELCON grades U-10, M-25, M-90, M-270 and M-450. CELCON
M-25 acetal copolymer has a melt index of about 2.5 g/IO
min when tested in accordance with ASTM D1238-82. CELCON
M-90 acetal copolymer has a lower molecular weight and melt viscosity than CELCON M-25. CELCON M-270 has an even lower molecular weight and melt viscosity than CELCON M-25.
Oxymethylene terpolymers may also be used in making IO 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:
~~~R3~
Ri R1 and a different third group which has been interpolymerized with the oxymethylene and oxy(higher alkylene) groups. A terpolymer as described above is typically made by reacting trioxane with a cyclic ether or cyclic acetal and a third monomer which is a bifunctional compounds, such as a diglycide of the 2 0 .f ozznuia H2~-~Q3-Wi2 Z ~2 O O
WO 97/31055 PCTlCTS96/02591 wherein Z represents a carbon-to-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 an oxypoly(lower alkoxy) group, preferably one having from 2 to 4 recurring lower alkoxy groups each with 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 the I0 diglycidyl ether of 1,4-butanediol being preferred.
Generally, when preparing such terpolymers, ratios of from 99.89 to 89.0 weight percent trioxane, 0.1 to 10 ' weight percent of the cyclic ether or cyclic acetai, and 0.01 to I weight percent of the bifunctional compound are preferred, based on the total weight of monomers used in forming the terpolymer. A particularly preferred oxymethylene terpolymer is commercially available from Hoechst Celanese Corporation under the name CELCON U10 acetal polymer, made from 1,4-butanediol diglycidyl ether crossiinker, dioxolane and trioxane containing about 0.05 weight percent, 2.0 weight percent, and 97.95 weight percent, respectively, of repeating units derived from these three monomers, based on the total weight of the terpolymer. The oxymethylene-based terpoiymers are made and stabilized by methods well known in the art, such as by the addition of antioxidants and formaldehyde and acid scavengers. More detailed descriptions of the methods for making oxymethylene-based terpolymers and their " compositions can be found in previously cited patents.
These oxymethylene polymers may be combined in various proportions by melt blending in extruders or similar apparatus to form suitable polymers for preparation of the self-lubricating composition of the present invention. Generally, polyoxymethylene polymers are readily blended with the lubricating system and processing aids when 5 the polymer is in the molten state, i.e., at temperatures of at least about 170°C.
The lubricating system of the present invention may be characterized as containing ultra high molecular weight polyolefin, pentaerythritol tetrastearate and a 10 calcium carbonate. The ultra high molecular weight polyolefin may be a linear polyethylene exhibiting a crystallinity of at least about 40 percent, a weight-average molecular weight of at least about 3x106 (typically from about 5x106 to about 6x106), an intrinsic viscosity of at least about 28 dl/g (measured by ASTM No. D4020), a bulk density of at least about 0.5 g/cm3 (measured by ASTM
No. D1895), and a specific gravity of about 0.93 g/cm3. A
particular preferred ultra high molecular weight (UHMW) polyethylene, meeting FDA/USDA compliance, is Hostalen~
GUR 415 UHMW polyethylene distributed by Hoechst Celanese Corporation of Somerville, New Jersey. Generally, the lubricant system of the present invention is characterized as containing at least about 0.1 weight percent of UHMW
polyethylene, at least about 0.1 weight percent of PETS, and least about 0.1 weight percent of the calcium carbonate, based on the total weight of the composition. Typically, the lubricant system is characterized as containing from about 0.2 to about 10.0 weight percent of UHMW polyethylene, from about 0.25 to about 2.0 weight percent of PETS, and from about 0.25 to about 4.0 weight percent of the calcium carbonate, based on the total weight of the composition. Preferably, the lubricating system is characterized as containing about 1.5 weight percent of UHI~4V polyethylene, 1.0 weight percent of PETS, and about 1.0 weight percent of the calcium carbonate, based on the total weight of the composition.
Several additional components may be added to the composition of the present invention to aid lubricity and processing. Generally, the additives may be combined proportionally with the lubricating system and admixed as a package with the thermoplastic polymer or they may be added directly to the composition. These additives may be selected from: (a) at least about 0.1 weight percent of a polyoxymethylene terpolymer; (b) at least about 0.1 weight percent of a hindered phenol; and (c) at least about 0.05 weight percent of calcium ricinoleate or calcium hydroxystearate, based on the total weight percent of the composition. Typically, these additives may be admixed with the self-lubricating composition in amounts selected from: (a) from about 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; and (c) from about 0.05 to about 0.3 weight percent of calcium ricinoleate or calcium hydroxystearate, based on the total weight percent of the composition. Preferably, these additives are admixed with the composition in amounts of: (a) about 0.5 weight percent of a polyoxymethylene terpolymer; (b) about 0.4 weight percent of a hindered phenol; and (c) 0.01 weight percent of calcium ricinoleate or calcium hydroxystearate, based on the total weight percent of the composition. The addition of these processing aids will typically result in a cenccmitanc adjustment in the amount of thermoplastic resin. Other processing aids known to those skilled in the art, such as silicone or fluoropolymer mold sprays may be used to aid molding.
The calcium carbonate useful in the invention is characterized as exhibiting a particle size of about 0.5 um, a surface area of about 7 mz/gm, a bulk density of about 25 lb/ft', and a specific gravity of about 2.7. A
preferred calcium carbonate is Super-Pflex~ 200 available from Pfizer, Inc.
The hindered phenol useful in the present invention are generally known as antioxidants or free radical inhibitors. At least one of 2,2~-methylenebis(4-methyl-6-t-butylphenol), hexamethyleneglycol-bis(3,5-di-t-butyl-35 4-hydroxyhydrocinnamate), tetrabis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane, triethyleneglycol-bis-3-t3-t-butyl-4-hydroxy-5-methylphenyl) propionate, I,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxy-benzyl)-benzen, p-octadecyl-3-(4~-hydroxy-3',S'-di-t-butyl-phenol)propionate, 4,4~-methylenebis(2,6-di-t-butylphenoi), 4,4'-butylidene-bis-(6-t-butyl-3-methylphenol), 2,2'-thiodiethyl-bis-[3-(3,5-di-t-butyl-4-hydroxyphenol)]propionate, di-stearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate and 2-t-butyl-6-t3-t-butyl-5-methyl-2-hydroxybenzyl)-4-methylphenylacrylate may be used. However, the useful hindered phenols are not limited to these compounds. Other hindered or stereo-obstructing phenols of the same kind as the above described ones are effective. Of them, hexamethyleneglycol-bist3,5-di-t-butyl-4 -hydroxyhydrocinnamate), for example Irganox~ 259 available from Ciba-Geigy, tetrakis(methylene(3,5-di-t-butyl-4-hydrox~~hydrocinnamate))methane, for example Irganox 1010 made by Ciba-Geigy and triethyleneglycol-bis-3-(3-t-butyl-4-hydroxy-5-methylphenyl) propionate, for example Irganox 245 made by Ciba-Geigy are effective.
A preferred hindered phenol is hexamethyleneglycol-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamate).
The following examples are general illustrations of methods for preparing the polymeric composition of the invention. They are provided for purposes of exemplification only as should be appreciated from the foregoing discussion.
To prepare a blend of the self-lubricating composition, containing 7.9 weight percent of the lubricating system, the following components were utilized:
a) 90 lbs. of polyoxymethylene copolymer unstabilized flake;
b) 4.9 lbs. of UHMw polyethylene;
c) 1.5 lbs. of polyoxymethylene terpoiymer;
d) 1.0 lbs. of pentaerythritol tetrastearate (PETS);
e) 2.0 lbs. of calcium carbonate;
f) 0.1 lbs. of calcium ricinoleate; and g) 0.5 lbs. of preferred hindered phenol The components were tumbled in a barrel followed by high speed mixing for 30 sec. in a Henschel mixer to form a mixture. The mixture was extruded into strands in a Werner and Pfleiderer twin screw ZSK extruder, heated and purged with polyacetal pellets. The extruder zones were operated at 372° to 387°F, the melt temperature was 415°F and under a vacuum of 27 in. Hg, and the screw speed was 150 rpm.
Strands of extrudate were produced at a rate of 38 lbs/hr.
Thereafter, the strands were quenched in cold water and cut into pellets. The pellets were injection molded at conventional pressure, velocity and cycle time settings, a nozzle temperature setting of 360° to 420°F, and barrel temperature setting of 350° to 420°F to form 1.25 in diameter disks, each weighing about 7 gm, for mechanical and tribological analyses.
The disks were prepared for surface wear resistance and torque analyses by cleaning in a bath of methanol, drying in air, and weighing to about one-tenth (1/10) of a milligram. These disks were tested according to a Pin-on-Disk Wear Test. In performing the tests, a machined Nylatron NYLON pin with a spherical tip having a radius of 0.187 inches was mounted on the upper spindle of a Falex Friction and Wear Test Machine, Model Multi-Specimen at a distance of 0.469 inches from the center of the test disks, which was mounted on the lower spindle. A load of 20 pounds was applied to the test disks by means of an air cylinder pressed the disk against the spherical pin tip.
The rotational velocity was 425 rpm (104.3 ft/min). During the test, a stream of air at 40 standard cubic feet per hour (SCFH) and a distance of 2 inches was directed against the disk surface to remove debris. Testing times ranged from 0.5 to 65 hours. After testing, the pin tip and disk were separated from contact brushed to remove loose debris, and weighed for weight ~ loss, i.e., surface wear.
Torque (r), measured during the test, was converted into a coefficient of friction (f) by application of the 5 equation:
f = I" (2.137/20) The factor 2.137 is a specific coefficient for this machine. Results of surface wear and coefficients of friction are in Table I.
10 Cam~narativ .x m~
As a comparative example, a polymeric composition was prepared by substituting I.5 wt~
polytetrafluoroethylene (PTFE) for the lubricating system of Example 2, the following components were utilized:
IS a) 213.84 lbs of polyoxymethylene copolymer unstabilized flake (97_2 wt$);
b) 1.1 lbs of polyoxymethylene copolymer pellets (0.5 wt$);
c) 199.76 gm of N,N~-ethylene bis-stearamide t0.2 wt$);
d) 1.1 lbs of preferred hindered phenol (0.5 wt$);
e) 99.88 gm of calcium ricinoleate (0.1 wt$); and f) 3.3 lbs of the PTFE (1.5 wt$ of total composition!
The components were mixed, extruded and molded according to the process of Example 1 to form 7 gm disks for weight loss and coefficient of friction analyses. Results of ' the analyses are in Table I.
J
C'om~ara l ~r xamnl a '~
As a comparative example, a polymeric composition was prepared by substituting 3.0 wt~ PTFE for the lubricating system of Example 1, the following components were utilized:
a) 210.54 lbs of polyoxymethylene copolymer unstabilized flake;
b) 1.1 lbs of polyoxymethylene copolymer pellets;
c) 199.76 gm of N,N'-ethylene bis-stearamide;
d) 1.2 lbs of preferred hindered phenol;
e) 99.88 gm of calcium ricinoleate; and IS f> 6.6 lbs of the PTFE t3.0 wt$ of total composition) The components were mixed, extruded and molded according to the process of Example 1 to form 7 gm disks for weight loss and coefficient of friction analyses. Results of the analyses are in Table I.
Results of analyses illustrate that after 0.5 hours of pin-on-disk testing, Example 1 samples exhibited an average weight loss of 1.1 mg; after 1.5 hours of testing, the disks exhibited an average weight loss of 1.4 mg; after 17 hours, a coefficient of friction of 0.075; and after a total of 65 hours of testing, disks exhibited an average weight loss of 5.4 mg.
Results of wear testing of disks prepared from compositions containing PTFE, as the lubricating system, exhibited surface wear as well as coefficients of friction significantly higher than the invention.
i8 To demonstrate the the wear performance of the composition in the presence and absence of the lubricating system, several formulations were prepared in accordance with the method of Example 1, above, as S follows:
Exam~4 ~onent wt ~
polyoxymethylene copolymer 95.5 polyoxymethylene terpolymer 0.5 preferred hindered phenol 0.4 calcium ricinoleate 0.1 UF~IW polyethylene 1.5 PETS 1.0 calcium carbonate 1.0 polyoxymethylene copolymer 97 polyoxymethylene terpolymer 0.5 preferred hindered phenol 0.4 calcium ricinoleate 0.1 UHI~IW polyethylene 0 WO 97!31055 PCT/US96/02591 PETS 1.0 ' calcium carbonate 1.0 F~amnle 6 wt polyoxymethylene copolymer 96.5 polyoxymethylene terpolymer 0.5 preferred hindered phenol 0.4 calcium ricinoleate 0.1 UF~iW polyethylene 1.5 calcium carbonate 1.0 Examr~ 1 a 7 Cy iponent e,rt polyoxymethylene copolymer 96.5 polyoxymethylene terpolymer 0.5 preferred hindered phenol 0.4 calcium ricinoleate 0.1 UF3MW polyethylene 1.5 PETS 1.0 calcium carbonate 0 WO 97/31055 PCTlLTS96/02591 Exam Co~onc~n wt $
polyoxymethylene copolymer 98.7 polyoxymethylene terpolymer 0.5 preferred hindered phenol 0.5 calcium ricinoleate 0.1 N,N'-ethylene bis-stearamide 0.2 UHMW polyethylene 0 10 calcium carbonate 0 ion n wt ~
polyoxymethylene copolymer 96.6 polyoxymethylene terpolymer 0.5 15 preferred hindered phenol 0.4 calcium ricinoleate 0.1 L,TF~iW polyethylene 0.4 PETS 1.0 calcium carbonate 1.0 Coo ponent wt ~
polyoxymethylene copolymer 96.2 polyoxymethylene terpolymer 0.5 S preferred hindered phenol 0.4 calcium ricinoleate 0.1 ' UHMW polyethylene 0.8 PETS 1.0 calcium carbonate I.0 The compostions of Examples 4 through 10 were molded into test disks and wear tested according to a Pin-on-Disk Wear Test in accordance with the procedure of Example 1.
The results of the test are illustrated in Table II, below:
TABLE I
Wt. Loss , mgi/Coefficient of Friction a Ex Lub. Test Time, System, hrs.
wt~k 0.5 1.5 1 7.9 1.1 I.4 4.3/0.075 5.4 2 1.5 PTFE 8.1 15.9 122/0.14 181 3 3.0 PTFE 3.4 15.9 87/0.13 155 4 3.5 1.8 2.1 4.2 8.6 5 2.0 n dZ 2 45 n/d 6 2.5 n/d 4.1 167 n/d ~ 7 ~ 2.5 ~ n/d ~ 2.4 ~ 64 [ n/d [ 8 [ 0 ~ n/d ~ 113 ~ 260 ~ n/d [ 9 ~ 2.4 [ n/d i 3.0 ~ 6.9 X 30.1 L 10 2.8 [ n/d ~ 2.8 ~ 7.8 ~ 12.4 [
The Table illustrates that the composition of Examples 4, 9 and 10 containing UHMW polyethylene, 1@ load of 20 lbs; velocity of 104.3 ft/min n/d: no data SUBSTITUTE SHEET (RULE 26) WO 97!31055 PCT/CTS96/02591 calcium carbonate and PETS, provides superior lubrication properties after I7 and 65 hours of wear testing in 4 comparison to the composition containing less than all three components.
Polyoxymethylenes, i.e., polyacetals or oxymethylene polymers useful in the present invention are generally characterized as havinq recurring oxymethylene units of the general formula:
~2 Polyoxymethylenes that are useful in making composition of the invention generally have a fairly high content of oxymethylene units, i.e., generally greater than about 85 percent. These materials are commercially available from a number of manufacturers as homopolymers, r copolymers, terpolymers, and the like. These highly crystalline acetals, described briefly hereinbelow, are well known in the art and have been reviewed extensively.
WO 9?/31055 PCT/US9b/02591 For example, a review of polymeric acetals entitled, "Acetal Resins," by T. J. Dolce and J. A. Grates, may be found in the Second Edition of E~clopedia of Pol:cne_r ° Sc,'_ence and EnQ~-n ring, John Wiley and Sons. New York, 5 1985, Vol. 1, pp. 42-61. Additional information on acetal polymers can be found in French Patent No.
1,221,148 as well as commonly assigned U.S. Patent Nos.
3,027,352, 3,072,069, 3,14?,234, and 3,210,318.
Typically, acetal homopolymers may be prepared by polymerizing anhydrous formaldehyde or trioxane.
Oxymethylene homopolymers are typically stabilized against thermal degradation by end-capping with, for example, ester or ether groups, such as those derived from alkanoic anhydrides (e.g., acetic anhydride) or dialkyl ethers, (e.g., dimethyl ether) or by incorporating stabilizer compounds into the homopoly~er.
Co~ercially available acetal homopolymer is made by polymerizing anhydrous formaldehyde in the presence of an initiator after which the polymer is end-capped by acetyiation of the hemiacetal end groups with acetic anhydride in the presence of sodium acetate catalyst.
Methods for making end-capped.acetal homopolymers are taught in U.S. Patent Nos. 2,786,994 and 2,998,409.
Acetal homopolymers are well know in the art and are coitQnercially available under the trademarks DELRIN~ and TENAC~_ Polymeric acetals which have been found to be especially suitable far use in the composition of the ° present invention are crystalline oxymethylene copolymers having repeat units which consist essentially of WO 97!31055 PCT/US96/02591 oxymethylene groups interspersed with oxy(higher alkylene) groups of the general formula: "
-~~R3~
R3 Ri wherein each R1 and RZ is hydrogen, a lower alkyl group, or a halogen substituted lower alkyl group, each R3 is a S methylene, oxymethylene, lower alkyl or haloalkyl substituted methylene or lower alkyl or haloalkyl substituted oxymethylene group, 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 generally will constitute from about 85 to 99.9 percent of the recurring units in such copolymers and are generally incorporated by ring-opening polymerization of trioxane in the presence of an acidic catalyst. The oxy(higher alkylene) groups are incorporated into the polymer by copolymerizing a cyclic ether or cyclic formal having at least two adjacent carbon atoms in the ring in addition to trioxane. The cyclic ether or formal is incorporated by the breaking of an oxygen-to-carbon linkage. The preferred oxy(higher alkylenel group is oxyethylene, having the formula:
~2 ~2 Oxyethylene may be incorporated into the polymer by copolymerization of ethylene oxide or 1,3-dioxolane with trioxane.
The preferred crystalline acetal copolymers, as ' described above which have a structure consisting essentially of oxymethylene and oxyethylene groups, are S thermoplastic materials having a melting point of at least 150°C. They normally are millable or processible at temperatures ranging from about 175°C to about 230°C.
These copolymers are normally highly crystalline and exhibit a polymer crystallinity from about 40 percent to about 90 percent or greater.
Typically, oxymethylene copolymers are stabilized after manufacture by degradation of unstable molecular ends of the polymer chains to a point where a relatively stable carbon-to-carbon linkage prevents further degradation of each end of the polymer chain. Such degradation of unstable molecular ends is generally effected by hydrolysis, as disclosed, for example, in U.S. Patent No. 3,219,623 to Berardinelli. Oxymethylene copolymer may also be stabilized by end-capping, again using techniques well known to those skilled in the art, as for example by acetylation with acetic anhydride in the present of a sodium acetate catalyst.
A particularly preferred class of oxymethylene copolymers is co~anercially available under the trade name CELCONc9 acetal copolymer. CELCON acetal copolymers " typically are copolymers of about 98 weight percent of trioxane and about 2 percent of dioxolane. CELCON is a r registered trademark of Hoechst Celanese Corparatian.
The compositions of the current invention may be made using any commercial grade of CELCON acetal, including CELCON grades U-10, M-25, M-90, M-270 and M-450. CELCON
M-25 acetal copolymer has a melt index of about 2.5 g/IO
min when tested in accordance with ASTM D1238-82. CELCON
M-90 acetal copolymer has a lower molecular weight and melt viscosity than CELCON M-25. CELCON M-270 has an even lower molecular weight and melt viscosity than CELCON M-25.
Oxymethylene terpolymers may also be used in making IO 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:
~~~R3~
Ri R1 and a different third group which has been interpolymerized with the oxymethylene and oxy(higher alkylene) groups. A terpolymer as described above is typically made by reacting trioxane with a cyclic ether or cyclic acetal and a third monomer which is a bifunctional compounds, such as a diglycide of the 2 0 .f ozznuia H2~-~Q3-Wi2 Z ~2 O O
WO 97/31055 PCTlCTS96/02591 wherein Z represents a carbon-to-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 an oxypoly(lower alkoxy) group, preferably one having from 2 to 4 recurring lower alkoxy groups each with 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 the I0 diglycidyl ether of 1,4-butanediol being preferred.
Generally, when preparing such terpolymers, ratios of from 99.89 to 89.0 weight percent trioxane, 0.1 to 10 ' weight percent of the cyclic ether or cyclic acetai, and 0.01 to I weight percent of the bifunctional compound are preferred, based on the total weight of monomers used in forming the terpolymer. A particularly preferred oxymethylene terpolymer is commercially available from Hoechst Celanese Corporation under the name CELCON U10 acetal polymer, made from 1,4-butanediol diglycidyl ether crossiinker, dioxolane and trioxane containing about 0.05 weight percent, 2.0 weight percent, and 97.95 weight percent, respectively, of repeating units derived from these three monomers, based on the total weight of the terpolymer. The oxymethylene-based terpoiymers are made and stabilized by methods well known in the art, such as by the addition of antioxidants and formaldehyde and acid scavengers. More detailed descriptions of the methods for making oxymethylene-based terpolymers and their " compositions can be found in previously cited patents.
These oxymethylene polymers may be combined in various proportions by melt blending in extruders or similar apparatus to form suitable polymers for preparation of the self-lubricating composition of the present invention. Generally, polyoxymethylene polymers are readily blended with the lubricating system and processing aids when 5 the polymer is in the molten state, i.e., at temperatures of at least about 170°C.
The lubricating system of the present invention may be characterized as containing ultra high molecular weight polyolefin, pentaerythritol tetrastearate and a 10 calcium carbonate. The ultra high molecular weight polyolefin may be a linear polyethylene exhibiting a crystallinity of at least about 40 percent, a weight-average molecular weight of at least about 3x106 (typically from about 5x106 to about 6x106), an intrinsic viscosity of at least about 28 dl/g (measured by ASTM No. D4020), a bulk density of at least about 0.5 g/cm3 (measured by ASTM
No. D1895), and a specific gravity of about 0.93 g/cm3. A
particular preferred ultra high molecular weight (UHMW) polyethylene, meeting FDA/USDA compliance, is Hostalen~
GUR 415 UHMW polyethylene distributed by Hoechst Celanese Corporation of Somerville, New Jersey. Generally, the lubricant system of the present invention is characterized as containing at least about 0.1 weight percent of UHMW
polyethylene, at least about 0.1 weight percent of PETS, and least about 0.1 weight percent of the calcium carbonate, based on the total weight of the composition. Typically, the lubricant system is characterized as containing from about 0.2 to about 10.0 weight percent of UHMW polyethylene, from about 0.25 to about 2.0 weight percent of PETS, and from about 0.25 to about 4.0 weight percent of the calcium carbonate, based on the total weight of the composition. Preferably, the lubricating system is characterized as containing about 1.5 weight percent of UHI~4V polyethylene, 1.0 weight percent of PETS, and about 1.0 weight percent of the calcium carbonate, based on the total weight of the composition.
Several additional components may be added to the composition of the present invention to aid lubricity and processing. Generally, the additives may be combined proportionally with the lubricating system and admixed as a package with the thermoplastic polymer or they may be added directly to the composition. These additives may be selected from: (a) at least about 0.1 weight percent of a polyoxymethylene terpolymer; (b) at least about 0.1 weight percent of a hindered phenol; and (c) at least about 0.05 weight percent of calcium ricinoleate or calcium hydroxystearate, based on the total weight percent of the composition. Typically, these additives may be admixed with the self-lubricating composition in amounts selected from: (a) from about 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; and (c) from about 0.05 to about 0.3 weight percent of calcium ricinoleate or calcium hydroxystearate, based on the total weight percent of the composition. Preferably, these additives are admixed with the composition in amounts of: (a) about 0.5 weight percent of a polyoxymethylene terpolymer; (b) about 0.4 weight percent of a hindered phenol; and (c) 0.01 weight percent of calcium ricinoleate or calcium hydroxystearate, based on the total weight percent of the composition. The addition of these processing aids will typically result in a cenccmitanc adjustment in the amount of thermoplastic resin. Other processing aids known to those skilled in the art, such as silicone or fluoropolymer mold sprays may be used to aid molding.
The calcium carbonate useful in the invention is characterized as exhibiting a particle size of about 0.5 um, a surface area of about 7 mz/gm, a bulk density of about 25 lb/ft', and a specific gravity of about 2.7. A
preferred calcium carbonate is Super-Pflex~ 200 available from Pfizer, Inc.
The hindered phenol useful in the present invention are generally known as antioxidants or free radical inhibitors. At least one of 2,2~-methylenebis(4-methyl-6-t-butylphenol), hexamethyleneglycol-bis(3,5-di-t-butyl-35 4-hydroxyhydrocinnamate), tetrabis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane, triethyleneglycol-bis-3-t3-t-butyl-4-hydroxy-5-methylphenyl) propionate, I,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxy-benzyl)-benzen, p-octadecyl-3-(4~-hydroxy-3',S'-di-t-butyl-phenol)propionate, 4,4~-methylenebis(2,6-di-t-butylphenoi), 4,4'-butylidene-bis-(6-t-butyl-3-methylphenol), 2,2'-thiodiethyl-bis-[3-(3,5-di-t-butyl-4-hydroxyphenol)]propionate, di-stearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate and 2-t-butyl-6-t3-t-butyl-5-methyl-2-hydroxybenzyl)-4-methylphenylacrylate may be used. However, the useful hindered phenols are not limited to these compounds. Other hindered or stereo-obstructing phenols of the same kind as the above described ones are effective. Of them, hexamethyleneglycol-bist3,5-di-t-butyl-4 -hydroxyhydrocinnamate), for example Irganox~ 259 available from Ciba-Geigy, tetrakis(methylene(3,5-di-t-butyl-4-hydrox~~hydrocinnamate))methane, for example Irganox 1010 made by Ciba-Geigy and triethyleneglycol-bis-3-(3-t-butyl-4-hydroxy-5-methylphenyl) propionate, for example Irganox 245 made by Ciba-Geigy are effective.
A preferred hindered phenol is hexamethyleneglycol-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamate).
The following examples are general illustrations of methods for preparing the polymeric composition of the invention. They are provided for purposes of exemplification only as should be appreciated from the foregoing discussion.
To prepare a blend of the self-lubricating composition, containing 7.9 weight percent of the lubricating system, the following components were utilized:
a) 90 lbs. of polyoxymethylene copolymer unstabilized flake;
b) 4.9 lbs. of UHMw polyethylene;
c) 1.5 lbs. of polyoxymethylene terpoiymer;
d) 1.0 lbs. of pentaerythritol tetrastearate (PETS);
e) 2.0 lbs. of calcium carbonate;
f) 0.1 lbs. of calcium ricinoleate; and g) 0.5 lbs. of preferred hindered phenol The components were tumbled in a barrel followed by high speed mixing for 30 sec. in a Henschel mixer to form a mixture. The mixture was extruded into strands in a Werner and Pfleiderer twin screw ZSK extruder, heated and purged with polyacetal pellets. The extruder zones were operated at 372° to 387°F, the melt temperature was 415°F and under a vacuum of 27 in. Hg, and the screw speed was 150 rpm.
Strands of extrudate were produced at a rate of 38 lbs/hr.
Thereafter, the strands were quenched in cold water and cut into pellets. The pellets were injection molded at conventional pressure, velocity and cycle time settings, a nozzle temperature setting of 360° to 420°F, and barrel temperature setting of 350° to 420°F to form 1.25 in diameter disks, each weighing about 7 gm, for mechanical and tribological analyses.
The disks were prepared for surface wear resistance and torque analyses by cleaning in a bath of methanol, drying in air, and weighing to about one-tenth (1/10) of a milligram. These disks were tested according to a Pin-on-Disk Wear Test. In performing the tests, a machined Nylatron NYLON pin with a spherical tip having a radius of 0.187 inches was mounted on the upper spindle of a Falex Friction and Wear Test Machine, Model Multi-Specimen at a distance of 0.469 inches from the center of the test disks, which was mounted on the lower spindle. A load of 20 pounds was applied to the test disks by means of an air cylinder pressed the disk against the spherical pin tip.
The rotational velocity was 425 rpm (104.3 ft/min). During the test, a stream of air at 40 standard cubic feet per hour (SCFH) and a distance of 2 inches was directed against the disk surface to remove debris. Testing times ranged from 0.5 to 65 hours. After testing, the pin tip and disk were separated from contact brushed to remove loose debris, and weighed for weight ~ loss, i.e., surface wear.
Torque (r), measured during the test, was converted into a coefficient of friction (f) by application of the 5 equation:
f = I" (2.137/20) The factor 2.137 is a specific coefficient for this machine. Results of surface wear and coefficients of friction are in Table I.
10 Cam~narativ .x m~
As a comparative example, a polymeric composition was prepared by substituting I.5 wt~
polytetrafluoroethylene (PTFE) for the lubricating system of Example 2, the following components were utilized:
IS a) 213.84 lbs of polyoxymethylene copolymer unstabilized flake (97_2 wt$);
b) 1.1 lbs of polyoxymethylene copolymer pellets (0.5 wt$);
c) 199.76 gm of N,N~-ethylene bis-stearamide t0.2 wt$);
d) 1.1 lbs of preferred hindered phenol (0.5 wt$);
e) 99.88 gm of calcium ricinoleate (0.1 wt$); and f) 3.3 lbs of the PTFE (1.5 wt$ of total composition!
The components were mixed, extruded and molded according to the process of Example 1 to form 7 gm disks for weight loss and coefficient of friction analyses. Results of ' the analyses are in Table I.
J
C'om~ara l ~r xamnl a '~
As a comparative example, a polymeric composition was prepared by substituting 3.0 wt~ PTFE for the lubricating system of Example 1, the following components were utilized:
a) 210.54 lbs of polyoxymethylene copolymer unstabilized flake;
b) 1.1 lbs of polyoxymethylene copolymer pellets;
c) 199.76 gm of N,N'-ethylene bis-stearamide;
d) 1.2 lbs of preferred hindered phenol;
e) 99.88 gm of calcium ricinoleate; and IS f> 6.6 lbs of the PTFE t3.0 wt$ of total composition) The components were mixed, extruded and molded according to the process of Example 1 to form 7 gm disks for weight loss and coefficient of friction analyses. Results of the analyses are in Table I.
Results of analyses illustrate that after 0.5 hours of pin-on-disk testing, Example 1 samples exhibited an average weight loss of 1.1 mg; after 1.5 hours of testing, the disks exhibited an average weight loss of 1.4 mg; after 17 hours, a coefficient of friction of 0.075; and after a total of 65 hours of testing, disks exhibited an average weight loss of 5.4 mg.
Results of wear testing of disks prepared from compositions containing PTFE, as the lubricating system, exhibited surface wear as well as coefficients of friction significantly higher than the invention.
i8 To demonstrate the the wear performance of the composition in the presence and absence of the lubricating system, several formulations were prepared in accordance with the method of Example 1, above, as S follows:
Exam~4 ~onent wt ~
polyoxymethylene copolymer 95.5 polyoxymethylene terpolymer 0.5 preferred hindered phenol 0.4 calcium ricinoleate 0.1 UF~IW polyethylene 1.5 PETS 1.0 calcium carbonate 1.0 polyoxymethylene copolymer 97 polyoxymethylene terpolymer 0.5 preferred hindered phenol 0.4 calcium ricinoleate 0.1 UHI~IW polyethylene 0 WO 97!31055 PCT/US96/02591 PETS 1.0 ' calcium carbonate 1.0 F~amnle 6 wt polyoxymethylene copolymer 96.5 polyoxymethylene terpolymer 0.5 preferred hindered phenol 0.4 calcium ricinoleate 0.1 UF~iW polyethylene 1.5 calcium carbonate 1.0 Examr~ 1 a 7 Cy iponent e,rt polyoxymethylene copolymer 96.5 polyoxymethylene terpolymer 0.5 preferred hindered phenol 0.4 calcium ricinoleate 0.1 UF3MW polyethylene 1.5 PETS 1.0 calcium carbonate 0 WO 97/31055 PCTlLTS96/02591 Exam Co~onc~n wt $
polyoxymethylene copolymer 98.7 polyoxymethylene terpolymer 0.5 preferred hindered phenol 0.5 calcium ricinoleate 0.1 N,N'-ethylene bis-stearamide 0.2 UHMW polyethylene 0 10 calcium carbonate 0 ion n wt ~
polyoxymethylene copolymer 96.6 polyoxymethylene terpolymer 0.5 15 preferred hindered phenol 0.4 calcium ricinoleate 0.1 L,TF~iW polyethylene 0.4 PETS 1.0 calcium carbonate 1.0 Coo ponent wt ~
polyoxymethylene copolymer 96.2 polyoxymethylene terpolymer 0.5 S preferred hindered phenol 0.4 calcium ricinoleate 0.1 ' UHMW polyethylene 0.8 PETS 1.0 calcium carbonate I.0 The compostions of Examples 4 through 10 were molded into test disks and wear tested according to a Pin-on-Disk Wear Test in accordance with the procedure of Example 1.
The results of the test are illustrated in Table II, below:
TABLE I
Wt. Loss , mgi/Coefficient of Friction a Ex Lub. Test Time, System, hrs.
wt~k 0.5 1.5 1 7.9 1.1 I.4 4.3/0.075 5.4 2 1.5 PTFE 8.1 15.9 122/0.14 181 3 3.0 PTFE 3.4 15.9 87/0.13 155 4 3.5 1.8 2.1 4.2 8.6 5 2.0 n dZ 2 45 n/d 6 2.5 n/d 4.1 167 n/d ~ 7 ~ 2.5 ~ n/d ~ 2.4 ~ 64 [ n/d [ 8 [ 0 ~ n/d ~ 113 ~ 260 ~ n/d [ 9 ~ 2.4 [ n/d i 3.0 ~ 6.9 X 30.1 L 10 2.8 [ n/d ~ 2.8 ~ 7.8 ~ 12.4 [
The Table illustrates that the composition of Examples 4, 9 and 10 containing UHMW polyethylene, 1@ load of 20 lbs; velocity of 104.3 ft/min n/d: no data SUBSTITUTE SHEET (RULE 26) WO 97!31055 PCT/CTS96/02591 calcium carbonate and PETS, provides superior lubrication properties after I7 and 65 hours of wear testing in 4 comparison to the composition containing less than all three components.
Claims (20)
1. A self-lubricating composition for forming a low friction, shaped article, comprising a melt blend of from 70 to 99.5 weight percent of a thermoplastic polymer and from 30 to 0.5 weight percent of a lubricating system comprising an ultra high molecular weight polyolefin, pentaerythritol tetrastearate and calcium carbonate, wherein the thermoplastic polymer is selected from the group consisting of polyamides, polyesters, polyphenylene sulfide, polyolefins, polyoxymethylenes, styrene polymers, and polycarbonates.
2. The composition according to claim 1, wherein the thermoplastic polymer is polyoxymethylene.
3. The composition according to claim 2, wherein the polyoxymethylene is selected from the group consisting of:
(i) oxymethylene homopolymers;
(ii) oxymethylene copolymers comprising 85 to 99.9 percent oxymethylene repeat units interspersed with repeat units of the formula:
wherein each of R1 and R2 is selected from the group consisting of hydrogen, lower alkyl radicals and halogen-substituted lower alkyl radicals, each R3 is selected from the group consisting of methylene, oxymethylene, lower alkyl or haloalkyl-substituted methylene, and lower alkyl or haloalkyl-substituted oxymethylene radicals, the lower alkyl radicals each having from 1 to 2 carbon atoms, and n is an integer from 0 to 3, inclusive;
(iii) oxymethylene terpolymers, which are the reaction product of trioxane and, a cyclic ether and/or a cyclic acetal, and a diglycidyl ether crosslinker 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 oxypoly(lower alkoxy) unit; and (iv) mixtures of (i), (ii) and (iii).
(i) oxymethylene homopolymers;
(ii) oxymethylene copolymers comprising 85 to 99.9 percent oxymethylene repeat units interspersed with repeat units of the formula:
wherein each of R1 and R2 is selected from the group consisting of hydrogen, lower alkyl radicals and halogen-substituted lower alkyl radicals, each R3 is selected from the group consisting of methylene, oxymethylene, lower alkyl or haloalkyl-substituted methylene, and lower alkyl or haloalkyl-substituted oxymethylene radicals, the lower alkyl radicals each having from 1 to 2 carbon atoms, and n is an integer from 0 to 3, inclusive;
(iii) oxymethylene terpolymers, which are the reaction product of trioxane and, a cyclic ether and/or a cyclic acetal, and a diglycidyl ether crosslinker 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 oxypoly(lower alkoxy) unit; and (iv) mixtures of (i), (ii) and (iii).
4. The composition according to any one of claims 1 to 3, comprising from 85 to 99 weight percent of the thermoplastic polymer and from 15 to 1 weight percent of the lubricating system.
5. The composition according to any one of claims 1 to 4, wherein the ultra high molecular weight polyolefin is a linear, ultra high molecular weight polyethylene.
6. The composition according to claim 5, wherein the polyethylene exhibits a crystallinity of at least 40 percent, a weight-average molecular weight of at least 3×10 6, an intrinsic viscosity of at least 28 dl/g, a bulk density of at least 0.5 g/cm3 and a specific gravity of at least 0.93.
7. The composition according to claim 5 or 6, wherein the lubricating system comprises at least 0.1 weight percent of the ultra high molecular weight polyethylene, at least 0.1 weight percent of pentaerythritol tetrastearate and at least 0.1 weight percent of calcium carbonate, each based on the total weight of the composition.
8. The composition according to claim 5 or 6, wherein the lubricating system comprises 0.2 to 10.0 weight percent of the ultra high molecular weight polyethylene, 0.25 to 2.0 weight percent of pentaerythritol tetrastearate and 0.25 to 4.0 weight percent of calcium carbonate, each based on the total weight of the composition.
9. The composition according to any one of claims 1 to 8, further comprising: (a) at least 0.1 weight percent of a polyoxymethylene terpolymer; (b) at least 0.1 weight percent of a hindered phenol; and (c) at least 0.05 weight percent of calcium ricinoleate or calcium hydroxystearate, each based on the total weight percent of the composition.
10. A shaped article prepared from the self-lubricating composition according to any one of claims 1 to 9, exhibiting a weight loss of about 4.2 mg after 17 hours of wear at a revolutionary velocity of 104.3 ft/min and an applied load of 20 lbs, and a coefficient of friction of about 0.075.
11. A method of improving the surface wear resistance of a thermoplastic shaped article, comprising the steps of:
(a) preparing a melt blend composition, comprising from 70 to 99.5 weight percent of a thermoplastic polymer, and from 30 to 0.5 weight percent of a lubricating system, wherein the lubricating system comprises an ultra high molecular weight polyolefin, pentaerythritol tetrastearate and calcium carbonate; and (b) fabricating the composition into a shaped article, wherein the article exhibits an improved coefficient of friction and surface wear resistance.
(a) preparing a melt blend composition, comprising from 70 to 99.5 weight percent of a thermoplastic polymer, and from 30 to 0.5 weight percent of a lubricating system, wherein the lubricating system comprises an ultra high molecular weight polyolefin, pentaerythritol tetrastearate and calcium carbonate; and (b) fabricating the composition into a shaped article, wherein the article exhibits an improved coefficient of friction and surface wear resistance.
12. The method according to claim 11, wherein the thermoplastic polymer is selected from the group consisting of polyamides, polyesters, polyphenylene sulfide, polyoxymethylenes, styrene polymers, and polycarbonates.
13. The method according to claim 11, wherein the thermoplastic polymer is polyoxymethylene selected from the group consisting of:
(i) oxymethylene homopolymers;
(ii) oxymethylene copolymers comprising 85 to 99.9 percent oxymethylene repeat units interspersed with repeat units of the formula:
wherein each R1 and R2 is selected from the group consisting of hydrogen, lower alkyl radicals and halogen-substituted lower alkyl radicals, each R3 is selected from the group consisting of methylene, oxymethylene, lower alkyl or haloalkyl-substituted methylene, and lower alkyl or haloalkyl-substituted oxymethylene radicals, the lower alkyl radicals each having from 1 to 2 carbon atoms, and n is an integer from 0 to 3, inclusive;
(iii) oxymethylene terpolymers, which are the reaction product of trioxane and, a cyclic ether and/or a cyclic acetal, and a diglycidyl ether crosslinker 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 oxypoly(lower alkoxy) unit; and (iv) mixtures of (i), (ii) and (iii).
(i) oxymethylene homopolymers;
(ii) oxymethylene copolymers comprising 85 to 99.9 percent oxymethylene repeat units interspersed with repeat units of the formula:
wherein each R1 and R2 is selected from the group consisting of hydrogen, lower alkyl radicals and halogen-substituted lower alkyl radicals, each R3 is selected from the group consisting of methylene, oxymethylene, lower alkyl or haloalkyl-substituted methylene, and lower alkyl or haloalkyl-substituted oxymethylene radicals, the lower alkyl radicals each having from 1 to 2 carbon atoms, and n is an integer from 0 to 3, inclusive;
(iii) oxymethylene terpolymers, which are the reaction product of trioxane and, a cyclic ether and/or a cyclic acetal, and a diglycidyl ether crosslinker 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 oxypoly(lower alkoxy) unit; and (iv) mixtures of (i), (ii) and (iii).
14. The method according to claim 13, wherein the composition comprises from 85 to 99 weight percent of the thermoplastic polymer, and from 15 to 1 weight percent of the lubricating system.
15. The method according to claim 14, wherein the polyoxymethylene is oxymethylene copolymer comprising 85 to 99.9 percent oxymethylene repeat units interspersed with repeat units of the formula:
wherein each R1 and R2 is selected from the group consisting of hydrogen, lower alkyl radicals and halogen-substituted lower alkyl radicals, each R3 is selected from the group consisting of methylene, oxymethylene, lower alkyl or haloalkyl-substituted methylene, and lower alkyl or haloalkyl-substituted oxymethylene radicals, the lower alkyl radicals each having from 1 to 2 carbon atoms, and n is an integer from 0 to 3, inclusive.
wherein each R1 and R2 is selected from the group consisting of hydrogen, lower alkyl radicals and halogen-substituted lower alkyl radicals, each R3 is selected from the group consisting of methylene, oxymethylene, lower alkyl or haloalkyl-substituted methylene, and lower alkyl or haloalkyl-substituted oxymethylene radicals, the lower alkyl radicals each having from 1 to 2 carbon atoms, and n is an integer from 0 to 3, inclusive.
16. The method according to any one of claims 11 to 15, wherein the lubricating system comprises 0.25 to 10.0 weight percent of ultra high molecular weight polyethylene, 0.25 to 2.0 weight percent of pentaerythritol tetrastearate and 0.25 to 4.0 weight percent of calcium carbonate, each based on the total weight of the melt blend composition.
17. The method according to any one of claims 11 to 15, wherein the lubricating system comprises at least 0.1 weight percent of ultra high molecular weight polyethylene, at least 0.1 weight percent of pentaerythritol tetrastearate and at least 0.1 weight percent of calcium carbonate, each based on the total weight of the melt blend composition.
18. The method according to any one of claims 11 to 17, wherein the composition further comprises: (a) 0.25 to 2.0 weight percent of a polyoxymethylene terpolymer;
(b) 0.25 to 0.75 weight percent of a hindered phenol; and (c) 0.05 to 0.3 weight percent of calcium ricinoleate or calcium hydroxystearate, based on the total weight percent of the composition.
(b) 0.25 to 0.75 weight percent of a hindered phenol; and (c) 0.05 to 0.3 weight percent of calcium ricinoleate or calcium hydroxystearate, based on the total weight percent of the composition.
19. A shaped article prepared according to the method of any one of claims 11 to 18, wherein the article exhibits a weight loss of about 4.3 mg after 17 hours of wear at a revolutionary velocity of 104.3 ft/min at an applied load of 20 lbs, and a coefficient of friction of less than 0.05.
20. The shaped article according to claim 19, wherein the article is selected from the group consisting of bearings, gears, cams, rollers, sliding plates, pulleys, levers, guides and conveyor belt links.
Priority Applications (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/597,334 US5641824A (en) | 1995-02-28 | 1996-02-06 | Thermoplastic polymer composition with improved wear properties |
| EP96102566A EP0730004B1 (en) | 1995-02-28 | 1996-02-21 | Thermoplastic polymer composition with improved wear properties |
| DE0730004T DE730004T1 (en) | 1995-02-28 | 1996-02-21 | Thermoplastic resin composition with improved wear properties |
| CA002226388A CA2226388C (en) | 1995-02-28 | 1996-02-26 | Thermoplastic composition with improved wear properties |
| PCT/US1996/002591 WO1997031055A1 (en) | 1995-02-28 | 1996-02-26 | Thermoplastic polymer composition with improved wear properties |
| CZ972713A CZ271397A3 (en) | 1995-02-28 | 1996-02-26 | Thermoplastic polymer composition with enhanced wear properties, method of improving resistance to surface wear and shaped product therefrom |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US39604795A | 1995-02-28 | 1995-02-28 | |
| CA002226388A CA2226388C (en) | 1995-02-28 | 1996-02-26 | Thermoplastic composition with improved wear properties |
| PCT/US1996/002591 WO1997031055A1 (en) | 1995-02-28 | 1996-02-26 | Thermoplastic polymer composition with improved wear properties |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2226388A1 CA2226388A1 (en) | 1997-08-28 |
| CA2226388C true CA2226388C (en) | 2006-08-22 |
Family
ID=27170595
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002226388A Expired - Fee Related CA2226388C (en) | 1995-02-28 | 1996-02-26 | Thermoplastic composition with improved wear properties |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2226388C (en) |
| WO (1) | WO1997031055A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8759431B2 (en) | 2010-03-29 | 2014-06-24 | Min Aik Technology Co., Ltd. | Durable polyoxymethylene composition |
| CN106633695A (en) * | 2016-12-13 | 2017-05-10 | 株洲时代新材料科技股份有限公司 | High-molecular self-lubricating material, preparation method of high-molecular self-lubricating material, and plate spring flanged bushing made of high-molecular self-lubricating material |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1510237A (en) * | 1975-10-18 | 1978-05-10 | Takahashi H | Inorganic filler and resin compositions filled therewith |
| US4670508A (en) * | 1984-01-06 | 1987-06-02 | Mitsui Petrochemical Industries Ltd. | Thermoplastic resin composition |
| US4960813A (en) * | 1988-02-25 | 1990-10-02 | Hoechst Celanese Corporation | Internal lubricant for glass reinforced polyarylene sulfide |
| JP2993062B2 (en) * | 1990-07-02 | 1999-12-20 | 三菱瓦斯化学株式会社 | Oxymethylene copolymer composition |
| US5302651A (en) * | 1990-10-19 | 1994-04-12 | Dainippon Ink And Chemicals, Inc. | Polyarylene sulfide resin composition |
| JP2915168B2 (en) * | 1991-05-29 | 1999-07-05 | ポリプラスチックス株式会社 | Flame retardant polybutylene terephthalate resin composition |
| US5300552A (en) * | 1991-10-07 | 1994-04-05 | Phillips Petroleum Company | Poly(arylene sulfide) composition |
-
1996
- 1996-02-26 CA CA002226388A patent/CA2226388C/en not_active Expired - Fee Related
- 1996-02-26 WO PCT/US1996/002591 patent/WO1997031055A1/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| CA2226388A1 (en) | 1997-08-28 |
| WO1997031055A1 (en) | 1997-08-28 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| MKLA | Lapsed |