Thermoplastic resin composition

Abstract

Thermoplastic resin compositions of improved lubricity and wear resistance are prepared without sacrificing the excellent moldability which is inherent in thermoplastic resins which compositions comprise a base resin, a lubricant and an ethylene-vinyl acetate copolymer.

Description

BACKGROUND OF THE INVENTION

In order to improve the lubricity and the wear resistance of thermoplastic resins such as nylon and polyacetal which have been used as bearing materials, etc., it has been the practice to incorporate into these resins liquid or solid lubricants such as molybdenum disulfide, graphite and polytetrafluoroethylene.

However, molybdenum disulfide, polytetrafluoroethylene and the like are expensive and do not achieve the desired results to a high degree. Moreover, their presence adversely affects the moldability of the resin. A particular problem is that when nylon, polyacetal or similar thermoplastic resin with an added lubricant is subjected to a molding process such as by extrusion molding or screw injection molding technique, the blend fails to fill the molding cavity completely and conform faithfully to its contours. Consequently, the desired molded products are not obtained. To avoid the difficulty, compression molding or the method whereby a sintered resin is immersed in a liquid lubricant are normally employed. With these methods, however, it is difficult to efficiently produce large numbers of molded products of complicated shapes.

Recently a method has been disclosed which enables an oil to be incorporated in nylon or polyacetal (Japanese Official Gazette of Patent Publication No. 5321/1971). This method requires the resin to be treated at an elevated temperature for an extended period of time in the lubricant oil. Unfortunately, this gives rise to the possiblity of degradation of the resin. In addition, this method requires special mechanical equipment which increases the cost and decreases the productivity. Moreover, pellets produced by this method, when subjected to extrusion molding or screw injection molding, tend to bleed out the lubricant which seriously impairs the efficiency of the molding machine. This method, despite elaborate precautions produces molded products in which the surface is wet with lubricant.

It has now been discovered that the addition of a third component, namely an ethylene-vinyl acetate copolymer substantially alleviates the problems aforesaid, and permits the production of molded products of complicated design which have excellent lubricity without a wet surface, and excel in wear resistance. Moreover, the products can be produced at high production rates.

SUMMARY OF THE INVENTION

The compositions of this invention are novel resin compositions excelling in moldability, lubricity and wear resistance, which composition comprise from 55 to 99.5 percent by weight of thermoplastic resin, from 0.3 to 25 percent by weight of a lubricant and from 0.2 to 20 percent by weight of an ethylene-vinyl acetate copolymer in such amounts to make up 100 percent by weight.

DETAILED DESCRIPTION OF THE INVENTION

Any of a wide variety of thermoplastic resins may be employed as the principal component of the compositions of this invention. These include, for example, polyacetal, nylon, polyethylene, polypropylene, polyphenylene sulfide and polysulfone. The invention is particularly useful with polyacetals or nylons which are used in bearings and gears and have excellent solvent resistance. Typically useful polyacetals include homopolymers or copolymers containing 1 to 10 mol % of a cyclic ether. Typically useful nylons include nylon 6, nylon 6.6, nylon 6.10 or nylon 6.12.

When the compositions contain appreciably more than 99.5 percent by weight resin the desired effect of the lubricant upon lubricity and wear resistance is not achieved. When less than 55 percent by weight is employed the products are not sufficiently rigid. The preferred compositions contain from 70 to 98 percent by weight, respectively based on the weight of the composition.

Substantially any liquid lubricant which does not dissolve the resin can be used. These include, for example, paraffins of the type which are solid at normal room temperature and which become liquid during the production of the composition of this invention. Typical examples of desirable liquid lubricants include paraffin, naphthene, and aromatic type oils, polyalkylene glycol type oils, ester type oils, e.g. mono- and polyalcohol esters of organic and inorganic acids such as monobasic fatty acids, dibasic fatty acids, phthalic acid and phosphoric acid. Blends of these oils may also be employed.

The amount of the lubricant is generally from 0.3 to 25 percent, preferably between 1 to 15 percent, by weight based on the weight of the composition. When the amount of the lubricant is appreciably less than 0.3 percent by weight, the lubricant's effort upon lubricity and wear resistance is substantially lost. If the amount substantially exceeds 25 percent by weight, however, the stiffness of the finished composition is seriously affected.

The ethylene-vinyl acetate copolymer absorbs the lubricant and swells, but does not dissolve in the lubricant at normal room temperature. Ethylene-vinyl acetate copolymers used in this invention normally contain from 15 to 50 percent, preferably 19 to 28 percent, by weight of vinyl acetate comonomer. Melt index (MI) of the copolymer is typically from 0.1 to 300 g/10 min. as measured by ASTM D1238.

The amount of ethylene-vinyl acetate copolymer employed in the compositions of the invention is normally from 0.2 to 20 percent, preferably from 1 to 15 percent, by weight. When the amount of ethylene-vinyl acetate copolymer is noticeably less than 0.2 percent by weight, the ability of the composition to provide good transporting property of the screw during the molding operation is decreased. When the amount appreciably exceeds 20 percent by weight, however, the stiffness of the composition is seriously lowered.

In addition to the base resin, the lubricant and the ethylene-vinyl acetate copolymer described hereinabove, the compositions of this invention can include the usual reinforcing agents, extenders, additives, etc., which are generally employed with such resins. These may also include solid lubricants such as graphite, molybdenum disulfide, fluorocarbon resins and metallic soaps; inorganic filters; glass fiber; pigments; flame retardants; antistatic agents and various stabilizers.

The combination of the aforementioned three essential components, that is, base resin, lubricant and ethylene-vinyl acetate copolymer, must be selected properly bearing in mind their respective properties. When resins such as polyphenylene sulfides or polysulfones which have relatively high molding temperatures are employed as the base resin, the lubricant selected should be capable of withstanding high molding temperatures.

The mixer utilized for producing the compositions of this invention may be any of those readily available mixers which have the necessary heat production and mixing capabilities. For example, high-speed fluid mixing devices such as the Henschel mixer, ribbon blenders and the like are advantageously used. Devices which are not adapted to permit heating may be used if the individual components of the resin composition are heated in advance.

In one typical method employed for producing the compositions of this invention, the base resin in the form of powder or pellets, the lubricant and the ethylene-vinyl acetate copolymer in the form of powder or pellets are agitated and mixed at a temperature below the melting point of the base resin or, in the case of a noncrystalline resin, at a temperature below the point at which the resin melts and coagulates, until the lubricant has thoroughly been absorbed by the ethylene-vinyl acetate copolymer. This usually requires about ten minutes, although it may vary appreciably depending on the quantities of the components, the rate of mixing, the particular resin and lubricant selected and the temperature. The composition thus produced may be pelletized in an extruding device and the pellets thereafter molded. In this case, the amount of the lubricant employed is from 0.2 to 8 times that of the ethylene-vinyl acetate copolymer, so as to obtain the desired results with respect to friction property and wear resistance and transporting property of the screw of the extruding device.

Alternatively, the compositons may be prepared by initially mixing the base resin and the ethylene-vinyl acetate copolymer, and subsequently introducing the lubricant dropwise into the resultant mixture while under agitation so that it may be absorbed into the mixture.

The compositions may also be produced by first introducing the lubricant dropwise into the ethylene-vinyl acetate copolymer while under agitation and, after the lubricant has thoroughly been absorbed, adding the base resin to the resultant mixture. Thus, the sequence of mixing, the method of addition of the lubricant, the method of heating the mixture, etc., may advantageously be selected from a variety of possibilities.

For optimum convenience, the base resin and the ethylene-vinyl acetate copolymer selected for the production of the compositions of this invention are normally in the form of finely divided particles capable of passing a sieve of a mesh size 10. This is not essential, however, They may be used in the form of pellets.

The pellets formed by any of the methods described above may be utilized directly for extrusion or injection molding. It is not necessary to form the compositions into pellets, however, since they can be formed and utilized in any of a variety of geometrical configurations.

Compared with the lubricant-containing resin obtained by the sintering method or the method disclosed by the Japanese Official Gazette of Patent Publication No. 5321/1971 which has heretofore been used, the pelletized composition of the present invention suffers far less from the phenomenon of heat degradation due to prolonged heating. Moreover, since no special equipment is required, molded products can be produced in large quantities in a short period of time.

The pelletized compositions of this invention can be utilized for injection, extrusion, or blow molding and similar procedures, with the transporting property of the screw improved to a great extent. The compositions in a pulverized form can be used in rotational molding.

In addition to improved moldability, other factors which contribute to the value of the novel compositions of this invention are improved lubricity and wear resistance. Conventional compositions include only the resin and the lubricant. The products of this invention, however, additionally contain an ethylene-vinyl acetate copolymer system. The copolymer retains the lubricant in an abosorbed state so that bleed out of the lubricant on the resin surface is minimized. The lubricity and wear resistance offered by this composition immediately after molding is equivalent to that of the conventional systems. However, even after a prolonged service, the surface of the molded product is wetted only slightly as a result of bleeding out of the lubricant. Thus, the surface does not become sticky and the abrasion resistance is not degraded.

The mold shrinkage and impact resistance of the compositions obtained in accordance with the present invention are also excellent.

the following non-limiting examples are given by way of illustration only.

Examples 1 and 2 and Comparative Examples 1-1, 1-2, 1-3, 2-1, 2-2 and 2-3:

Polyacetal homopolymer (MI 7.0 g/10 min. 190.degree. C.) or nylon 6 (relative viscosity is sulfuric acid 2.5) in the powdered form was used as the thermoplastic resin, a paraffin type oil (SUS 460 100.degree. F.) or naphthene type oil (SUS 370 100.degree. F.) was used as the lubricant, and ethylene-vinyl acetate copolymers (EVA MI 150 g/10 min. and having a vinyl acetate content of 19 percent by weight; MI 15 g/10 min. and having a vinyl acetate content of 28 percent by weight) in the powdered form were used as the ethylene-vinyl acetate copolymer, respectively in amounts to give percent compositions shown in Table 1. Each charge was mixed while heating in a Henschel mixer at temperatures below the point at which the resins would be melted and converted into a viscous solidified mass. The resultant mixture composition was pelletized by means of an extruder.

In Comparative Examples 1-2, 2-2 and 2-3, the preparation of pellets was carried out in accordance with the method disclosed in the Japanese Official Gazette of Patent Publication No. 5321/1971.

These pellets and pellets of polymers used as base resins were subjected to injection molding. The results are shown in Table 1. As is clear from this table, the pellet compositions according to this invention could be injection molded in the same way as the pellets of base resins to afford test pieces with good lubricity, wear resistant and high dimensional accuracy, whereas the pellet compositions of the resin + lubricant system could not be injection molded because of inferior transporting property of the screw. Consequently, wear resistant test pieces with good lubricity were obtained from these compositions by using the compression molding technique.

The results of the lubricity and wear resistance test performed on such test pieces are shown in Table 1. As is clear from this table, the compositions according to this invention are superior to the conventional lubricant-containing resin compositions in molding property, particularly in terms of transporting property of the screw and decreased bleed out. As concerns the properties of lubricity and wear resistance, they showed a lower friction coefficient than the base resins. The state of wear was satisfactory and equivalent to that of the conventional lubricant-containing resin composition. Thus, the improved properties of the resin compositions of this invention were evident.

Examples 3-1, 3-2, 3-3, 3-4, 3-5, 3-6, 3-7, 3-8, 3-9, 3-10, 3-11, and Comparative Examples 3-1, 3-2, 3-3, 3-4, 3-5, 3-6, 3-7 and 3-8:

The compositions of the formulations shown in Example 1 and Example 2 were combined with the other formulations shown in Table 2-1 and Table 2-2, subjected to test molding, and thereafter tested for physical properties.

For comparison, compositions having the proportions of components varied so as to be outside of the stated range of formulation were subjected to the same test. The results are included in said table.

As is apparent from Table 2-1 and Table 2-2, molded products of compositions using resins in amounts smaller than the lower limit of said range exhibited lower stiffness and those of compositions using lubricants in amounts smaller than the lower limit failed to produce the effect of lubricant upon lubricity and wear resistance. It is also apparent that the transporting property of the screw was adversely affected when the ratio of lubricant and ethylene-vinyl acetate copolymer were increased beyond their respective upper limits and that the lubricant's effect upon lubricity and wear resistance was lost when their ratio were decreased below their respective lower limits.

Examples 4, 5 and 6 and Comparative Examples 4-1, 4-2, 4-3, 5-1, 5-2, 5-3, 6-1, 6-2 and 6-3.

The procedures of Examples 1 and Comparative Examples 1-1, 1-2 and 1-3 were repeated, except polyacetal homopolymers containing glass fiber, molybdenum disulfide (MoS.sub.2) and graphite respectively were used in place of base polymers. The resultant compositions were tested for moldability and physical properties.

The results are shown in Table 3. From the table, the effects of the Compositions (Example 4, 5 and 6) according to the present invention were evident as in the case of Example 1.

Examples 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 and 18:

The procedures of Example 1 and Example 2 were repeated, except aromatic type oil (having aromatic content of 50% by weight, 15 cst, 100.degree. F.), polyalkylene glycol oil (35 cst, 100.degree. F.), butyl stearate, dioctyl sebacate, dioctyl phthalate and tricresyl phosphate were used in place of the lubricants of Example 1 and Example 2. The resultant compositions were tested for moldability and physical properties.

The results are shown in Table 4. From the table, the effects of the compositions were evident as in the case of Example 1 and Example 2.

Examples 19, 20, 21, 22 and 23:

The procedures of Example 2 were repeated, except acetal copolymer (copolymer of trioxan and cyclic ether, MI 13.0 g/10 min. 190.degree. C.), nylon 6.6 (relative viscosity in sulfuric acid 2.5), nylon 6.10 (relative viscosity in sulluric acid 2.6) nylon 6 containing glass fiber and nylon 6.6 containing graphite were used in place of nylon 6. The resultant compositions were tested for moldability and physical properties.

The results are shown in Table 5. From the table, the effects of the compositions were evident as in the case of Example 1.

Table 1__________________________________________________________________________Test for moldability and physical properties (1) Friction property and wear resistance test (test condition-resin- to-resin under load of 2 kg/cm.sup.2) Formulation Friction SurfaceTest for (percent by weight) Moldability coefficient wetting ofmoldability Ethylene- Cylinder (.mu.) molded& physical vinyl temper- Cycle (linear product withproperties Base acetate Molding ature time speed 1 Condition bleeded out(1) resin Lubricant copolymer process (.degree. C) (sec) cm/sec) of wear oil__________________________________________________________________________Example 1 Poly- Paraffin EVA Injection 200 (45) 0.10 - 0.15 Absolutely Practically acetal type oil (vinyl molding no wear no wetting (90) (5) acetate observed. content 19% by weight) (5)Comparative Poly- -- -- Injection 200 (45) 0.30 - 0.35 Worn NoneExample 1-1 acetal molding powder (100) appeared over about 10 cm/secComparative Poly- Paraffin -- Injection 200 (.infin.) -- -- --Example 1-2 acetal type oil molding Poor (95) (5) trans- porta- tionComparative Poly- Paraffin -- Compres- -- -- 0.10 - 0.15 Absolutely UnusuallyExample 1-3 acetal type oil sion no wear heavy (95) (5) molding observed. wetting observedExample 2 Nylon Naphthene EVA Injection 210 (60) 0.05 - 0.10 Absolutely Practically (90) type oil (vinyl molding no wear no wetting (5) acetate observed. content 28% by weight) (5)Comparative Nylon -- -- Injection 210 (60) 0.40 - Worn5 NoneExample 2-1 (100) molding powder appeared over about 10 cm/sec.Comparative Nylon Naphthene -- Injection 210 (.infin.) -- -- --Example 2-2 (95) type oil molding Poor (5) trans- porta- tionComparative Nylon Naphthene -- Compres- -- -- 0.05 - 0.10 Absolutely UnusuallyExample 2-3 (95) type oil sion no wear heavy (5) molding observed. wetting observed.__________________________________________________________________________ Table 2-1__________________________________________________________________________Test for moldability and physical properties (2-1) Friction property and wear resistance test (test condition-resin Formulation to-resin, under load (percent by weight) of 2 kg/cm.sup.2) EVA Moldability Friction SurfaceTest for (vinyl (by injection coefficient wetting ofmoldability Paraf- acetate Degree of molding) (.mu.) molded& physical fin content: pelletiza- Cylinder Cycle (linear product withproperties Poly- type 19% by Oil (wt%) tion of tempera- time speed Condition bleeded out(2-1) acetal oil weight) EVA (wt%) composition ture (sec) 1 cm/sec.) of wear oil__________________________________________________________________________Example 3-1 90 5 5 1 Good 200 45 0.10 - 0.15 Absolutely Practically no wear no wetting observed.Comparative 99.9 0.05 0.05 1 Good 200 45 0.30 - 0.35 Worn NoneExample 3-1 powder appeared over 10 cm/sec.Example 3-2 99 0.5 0.5 1 Good 200 45 0.20 - 0.25 Absolutely None no wear observed.Example 3-3 70 15 15 1 Good 200 45 0.10 - 0.15 Absolutely Practically no wear no wetting observed.Comparative 40 30 30 1 Pelletization 200 50 0.15 - 0.20 Sample WettingExample 3-2 was was difficult deformed because of because of low stiffness low stiffness.Comparative 90 9.9 0.1 99 No trans- -- -- -- -- --Example 3-3 portation was obtained with extruder.Example 3-4 90 6.7 3.3 2 Good 200 45 0.10 - .015 Absolutely Practically no wear no wetting observed.Example 3-5 90 3.3 6.7 0.5 Good 200 45 0.10 - 0.15 Absolutely Practically no wear no wetting observed.Comparative 90 0.1 9.9 0.01 Good 200 45 0.30 - 0.35 Worn NoneExample 3-4 powder appeared over 15 cm/sec.__________________________________________________________________________ Table (2-2)__________________________________________________________________________Test for moldability and physical properties (2-2) Lubricity & wear resist- ance test (test condi- tion-resin- to-resin under load of 2 kg/ cm.sup.2) Formulation Fric- (percent by weight) Moldability tion EVA (by injec- coef-Test for (vinyl tion molding) ficient Surfacemoldability Paraf- acetate Oil Degree of Cylind- (.mu.) wetting of& physical fin content (wt %) Pelletiz- er temp- Cycle (linear molded prod-properties Nylon type 19% by EVA ation of erature time speed Condition uct from(2-2)6 oil weight) (wt %) composition (.degree. C) sec 1 cm/sec) of wear bleed out__________________________________________________________________________ oilExample 90 5 5 1 Good 230 60 0.05- Absolute- Practically3-6 0.10 ly no wear no wetting observed.Compara- 99.9 0.05 0.05 1 Good 230 60 0.35- Worn powd- Nonetive Ex- 0.40 er appear-ample 3-5 ed over 10cm/sec.Example 99 0.5 0.5 1 Good 230 60 0.20- Absolute- None3-7 0.25 ly no wear observed.Example 70 15 15 1 Good 230 60 0.05- Absolute- Practically3-8 0.10 ly no wear no wetting observed.Compara- 40 30 30 1 Pelletiz- 230 80 0.05- Sample was Wettingtive Ex- ation was 0.10 deformedample 3-6 difficult because of because of low stiffness. low stiffnessCompara- 90 9.9 0.1 99 No trans- -- -- -- -- --tive Ex- portationample 3-7 was ob- tained with extruderExample 90 6.7 3.3 2 Good 230 60 0.05- Absolute- Practically3-9 0.10 ly no wear no wetting observed.Example 88 9 3 3 Good 230 60 0.05- Absolute- Practically3-10 0.10 ly no wear no wetting observed.Example 90 3.3 0.7 0.5 Good 230 60 0.10- Absolute- None3-11 0.15 ly no wear observed.Compara- 90 0.1 9.9 0.01 Good 230 60 0.30- Worn powder Nonetive Ex- 0.35 appeared overample 3-8 10cm/sec.__________________________________________________________________________ Table 3__________________________________________________________________________Test for moldability and physical properties (3) Friction property and wear resistance test (test condition resin-to-resin under load of 2 kg/cm.sup.2) Friction coef- SurfaceTest for Formulation (percent by weight) Moldability ficient wetting ofmoldability Ethylene Cylinder (.mu.) molded& physicalvinyl tempera- Cycle (linear product withproperties Base acetate Molding ture time speed 1 Condition bleeded out(3) resin Lubricant copolymer Additive process (.degree. C) (sec) cm/sec) of wear oil__________________________________________________________________________Example 4 Poly- Paraf- EVA Glass Injection 200 (50) 0.10-0.15 Absolutely Practically acetal fin (VA fiber molding no wear no wetting (80) type oil content (10) observed. (5) 19% by weight) (5)Comparative Poly- Paraffin -- Glass Injection 200 (.infin.) -- -- --Example 4-1 acetal type oil fiber molding No (85) (5) (10) trans- porta- tionComparative Poly- Paraffin -- Glass Compres- -- -- 0.10-0.15 Absolutely UnusuallyExample 4-2 acetal type oil fiber sion no wear heavy (85) (5) (10) molding observed. wetting observed.Comparative Poly- -- -- Glass Injection 200 (50) 0.35-0.40 Worn NoneExample 4-3 acetal fiber molding powder (90) (10) appeared over 5 cm/secExample 5 Poly- Paraffin EVA (VA MoS.sub.2 Injection 200 (45) 0.10-0.15 Absolutely Practically acetal type oil content (2) molding no wear no wetting (88) (5) 19% by observed. weight (5)Comparative Poly- Paraffin -- MoS.sub.2 Injection 200 (.infin.) -- -- --Example 5-1 acetal type oil (2) molding No (93) (5) trans- porta- tionComparative Poly- Paraffin -- MoS.sub.2 Compres- -- -- 0.10-0.15 Absolutely UnusuallyExample 5-2 acetal type oil (2) sion no wear heavy (93) (5) molding observed. wetting observed.Comparative Poly- -- -- MoS.sub.2 Injection 200 (45) 0.30-0.35 Worn NoneExample 5-3 acetal (2) molding powder (98) appeared over 10 cm/sec.Example 6 Poly- Paraffin EVA (VA Graphite Injection 200 (45) 0.10-0.15 Absolutely Practically acetal type oil content (5) molding no wear no wetting (85) (5) 19% by observed. weight) (5)Example 6-1 Poly- Paraffin -- Graphite Injection 200 (.infin.) -- -- -- acetal type oil (5) molding No (85) (5) trans- porta- tionExample 6-2 Poly- Paraffin -- Graphite Compres- -- -- 0.10-0.15 Absolutely Unusually acetal type oil (5) sion no wear heavy (85) (5) molding observed. wetting observed.Example 6-3 Poly- -- -- Graphite Injection 200 (45) 0.30-0.35 Worn None acetal (5) molding powder (85) appeared over 20 cm/sec.__________________________________________________________________________ Table 4__________________________________________________________________________Test for moldability and physical properties (4) Friction property and wear resistance test (test condition-resin to-resin, under load Formulation of 2 kg/cm.sup.2) (percent by weight) Friction EVA Moldability coef- SurfaceTest for (vinyl Degree of (by injection ficient wetting ofmoldability acetate pelletiza- molding) (.mu.) molded& physical content: tion of Cylinder Cycle (linear product withproperties Base Lubri- 19% by Oil (wt %) compo- temper- time speed Condition bleeded out(4) resin cant weight) EVA (wt %) sition ature (sec) 1 cm/sec.) of wear oil__________________________________________________________________________Example 7 Poly- Aromatic 5 1 Good 200 45 0.10-0.15 Absolutely Practically acetal type oil no wear no wetting 90 5 observed.Example 8 Poly- Poly- 5 1 Good 200 45 0.10-0.15 Absolutely Practically acetal alkylene no wear no wetting 90 glycol observed. oil 5Example 9 Poly- Butyl 5 1 Good 200 45 0.10-0.15 Absolutely Practically acetal stearate no wear no wetting 90 5 observed.Example 10 Poly- Dioctyl 5 1 Good 200 45 0.10-0.15 Absolutely Practically acetal sebacate no wear no wetting 90 5 observed.Example 11 Poly- Dioctyl 5 1 Good 200 45 0.10-0.15 Absolutely Practically acetal phthalate no wear no wetting 90 5 observed.Example 12 Poly- Tricresyl 5 1 Good 200 45 0.10-0.15 Absolutely Practically acetal phosphate no wear no wetting 90 5 observed.Example 13 Nylon Aromatic 5 1 Good 230 60 0.05-0.10 Absolutely Practically 90 type oil no wear no wetting 5 observed.Example 14 Nylon Poly- 5 1 Good 230 60 0.05-0.10 Absolutely Practically 90 alkylene no wear no wetting glycoloil observed.Example 15 Nylon Butyl 5 1 Good 230 60 0.05-0.10 Absolutely Practically 90 stearate no wear no wetting 5 observed.Example 16 Nylon Dioctyl 5 1 Good 230 60 0.05-0.10 Absolutely Practically 90 Sebacate no wear no wetting 5 observed.Example 17 Nylon Dioctyl 5 1 Good 230 60 0.05-0.10 Absolutely Practically 90 phthalate no wear no wetting 5 observed.Example 18 Nylon Tricresyl 5 1 Good 230 60 0.05-0.10 Absolutely Practically 90 phosphate no wear no wetting 5 observed.__________________________________________________________________________ Table 5__________________________________________________________________________Test for moldability and physical properties (5) Lubricity & wear resist- ance test (test condi- tion-resin- to-resin under load of 2kg/ cm.sup.2) Formulation Fric- (percent by weight) Moldability tion EVA (by injec- coef-Test for (vinyl tion molding) ficient Surfacemoldability acetate Oil Degree Cylind- (.mu.) wetting of& physical content: (wt %) of pelleti- er temp- Cycle (linear molded pro-properties Base Naphthene 28% by EVA zation of erature time speed Condition duct from(5) resin type oil weight) (wt %) composition (.degree. C) (sec) 1cm/sec) of wear bleed out__________________________________________________________________________ oilExample 19 Acetal 5 5 1 Good 200 45 0.10-0.15 Absolutely Practically Copolymer no wear no wetting 90 observed.Example 20 Nylon 6.6 5 5 1 Good 280 60 0.05-0.10 Absolutely Practically 90 no wear no wetting observed.Example 21 Nylon 6.10 5 5 1 Good 240 60 0.10-0.15 Absolutely Practically 90 no wear no wetting observed.Example 22 Nylon 6 5 5 1 Good 230 60 0.10-0.15 Absolutely Practically contain- no wear no wetting ing 20 wt observed. % glass fiber 90Example 23 Nylon 66 5 5 1 Good 280 60 0.05-0.10 Absolutely Practically containing no wear no wetting 10 wt % gra- observed. phite 90__________________________________________________________________________

The foregoing examples illustrate the remarkable results which are achieved with a variety of polyacetals and nylons in accordance with the practice of this invention. Similar results are achieved in other specific examples with additional thermoplastic resins including polyethylene, polypropylene, polyphenylene sulfide and polysulfone.

Claims

1. A thermoplastic resin composition having excellent lubricity and wear resistance comprising from 55 to 99.5 percent by weight of thermoplastic polyacetal, from 0.3 to 25 percent by weight of a liquid lubricant which does not dissolve the resin, and from 0.2 to 20 percent by weight of an ethylene-vinyl acetate copolymer which contains from 15 to 50 percent by weight of vinyl acetate comonomer.

2. A composition as in claim 1 wherein the lubricant is selected from the group consisting of paraffin type oils, naphthene type oils, aromatic type oils, polyalkylene glycol type oils and ester type oils.

3. A composition as in claim 1 wherein the ethylene-vinyl acetate copolymer contains from 19 to 28 percent by weight of vinyl acetate comonomer.

4. A composition as in claim 1, wherein the polyacetal resin is selected from the group consisting of acetal homopolymer and acetal copolymer containing 1 - 10 mol % of cyclic ether.

5. A composition as in claim 1, wherein the thermoplastic resin content is from 70 to 98 percent by weight, the lubricant content is from 1 to 15 percent by weight, and the ethylene-vinyl acetate copolymer content is from 1 to 15 percent by weight.