JPH07157630A - Polyacetal resin composition - Google Patents

Abstract

PURPOSE:To obtain a sliding member excellent in friction and wear properties, moldability and delamination, etc., by incorporating a specific block copolymer, a fatty ester, an inorg. filler and a potassium titanate fiber into a polyacetal resin. CONSTITUTION:(A) 100 pts.wt. polyacetal resin is kneaded together with (B) 0.5-40 pts.wt. graft or block copolymer of at least one olefin is polymer selected from among polyethylene, polypropylene and ethylene-propylene copolymers with at least one vinyl (co)polymer selected from among polymethyl methacrylate, acrylonitrile-styrene copolymers and polystyrene, (C) 0.1-20 pts.wt. ester of a 16C or higher fatty acid with at least one alcohol selected from among 16C or higher fatty alcohols, ethylene glycol, etc., (D) 0.5-30 pts. wt. inorg. filler of at most 30mum in average particle size, (E) 1-70 pts.wt. potassium titanate fiber, and a variety of additive (s) to obtain a compsn., which is then molded to obtain a sliding member.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyacetal resin composition having excellent friction and wear characteristics and good moldability and machinability, and a sliding member formed by molding the same. .

[0002]

BACKGROUND OF THE INVENTION Polyacetal resins have well-balanced mechanical properties.
It is widely used in the fields of automobiles, electric / electronic products, etc. due to its excellent friction / wear resistance, chemical resistance, heat resistance, and electrical characteristics. However, the required properties in such fields are becoming more sophisticated, and as an example, further improvement in sliding properties as well as general physical properties is desired. Such sliding characteristics include not only the friction coefficient and the specific wear amount, but also sliding noise (squeaking noise) is taken up as one of the important characteristics. In particular, sliding noises (squeaking noises) are often a problem particularly in sliding components such as cams and switch components that have a small contact area of sliding portions and are in an extreme pressure state. For the purpose of improving such sliding properties, addition of fluororesin or polyolefin resin to polyacetal resin, and addition of lubricating oil such as fatty acid, fatty acid ester, silicone oil, various mineral oils, etc. Addition of fluororesin or polyolefin resin improves sliding characteristics including sliding sound characteristics to some extent, but since these resins have poor compatibility with polyacetal resin, peeling may occur on the surface of the molded product, or molding may occur. Precipitates are easily generated on the mold. Also, the addition of lubricating oil is effective in reducing the friction coefficient and the specific wear amount, but is insufficient for improving the sliding noise,
Further, there are various problems such as difficulty during extrusion processing and exudation during use. The present inventors, from the results of the improvement study of the above problems, a specific graft copolymer to the polyacetal resin, by further adding a lubricant,
It was found that a polyacetal resin composition excellent in friction and wear properties and other general physical properties was obtained, and a patent application was made (JP-A-2-138357). By such a method, the performance of a general sliding member is dramatically improved. However, the addition of the graft copolymer and further the lubricant causes a decrease in the surface hardness of the molded product, and the conditions such as the cam mechanism and the switch parts where the sliding pressure is locally applied or the friction such as the friction at an extremely high speed are severe. Under various conditions, it was found that various problems such as local deformation and increase in the amount of wear occur.
Furthermore, due to the tendency of parts to become light, thin, short, and small, under such severe conditions, the sliding member itself is often deformed and, for example, the sliding pin is disengaged from the cam groove, and in many cases does not function as a mechanical part. It was required to have higher rigidity as well as slidability. Generally, in order to improve the rigidity of a resin material, glass fiber is used for reinforcement, but when glass fiber is used, friction and wear characteristics are significantly deteriorated and it cannot be put to practical use.

[0003]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies on the development of a polyacetal resin composition having excellent sliding properties and good performance in other properties. By adding and using a specific graft copolymer, fatty acid ester, specific inorganic powder and potassium titanate fiber to the resin, it is possible to balance all of friction and wear characteristics, moldability, surface peeling, surface hardness and mechanical characteristics. The present invention has been accomplished by finding that a polyacetal resin composition having excellent performance is obtained. That is, the present invention is (A) polyacetal resin
100 parts by weight of (B) (b-1) olefin polymer, (b-2)
Graft or block copolymer obtained from at least one vinyl polymer 0.5 to 40 parts by weight, (C) fatty acid ester 0.1 to 20 parts by weight, (D) inorganic powder having a weight average particle size of 30 μ or less 0.5 to 30 parts by weight And (E) 1 to 70 parts by weight of potassium titanate fiber, a polyacetal resin composition, and a polyacetal resin sliding member formed by molding the composition.

The structure of the present invention will be described in detail below. First, as the polyacetal resin (A) used in the present invention, both a polyacetal homopolymer and a polyacetal copolymer in which the main chain is mostly an oxymethylene chain can be used. Also, a polyacetal modified by crosslinking or graft copolymerization by a known method can be used as the base resin, and the degree of polymerization is not particularly limited as long as it can be molded.

Next, the graft or block copolymer used as the component (B) in the present invention is obtained from (b-1) an olefin polymer and (b-2) at least one vinyl polymer, Olefin-based polymer and vinyl-based polymer,
Branched or cross-linked A structurally chemically bonded graft or block copolymer. Here, as a specific example of the (b-1) olefin polymer constituting the main chain portion of the component (B),
Low density polyethylene, ultra low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, polypropylene, homopolymers of polyα-olefins such as polybutene, hydrogenated products of polybutadiene, and those containing these as the main components. A copolymer is mentioned. As the copolymer, ethylene / propylene copolymer, ethylene / 1-
Examples include butene copolymers. Of these, various polyethylenes, polypropylenes and ethylene-propylene copolymers can be particularly preferably used. Next, as the vinyl polymer (b-2) to be graft- or block-copolymerized with this olefin polymer (b-1), polymethyl methacrylate, polyethyl acrylate, polyacrylic acid ethyl, polyacrylic acid can be used. Examples thereof include butyl, poly (2-ethylhexyl acrylate), polystyrene, polyacrylonitrile, acrylonitrile-styrene copolymer, butyl acrylate / methyl methacrylate copolymer, butyl acrylate / styrene copolymer and the like. Particularly preferred are polymethyl methacrylate, acrylonitrile-styrene copolymer and the like. The graft or block copolymer (B), which is a feature of the present invention, is the above-mentioned (b) which constitutes the main chain portion.
-1) an olefin polymer and (b-2) a vinyl polymer,
Graft or block copolymer having a chain, branched or crosslinked structure in which a polymer (b-1) and a polymer (b-2) having different properties are chemically bonded at at least one point, rather than being used alone. By having such a feature in that, and by having such a graft or block structure as described below, a remarkable effect that cannot be obtained by simply blending (b-1) or (b-2) alone is obtained. is there. The method for preparing the graft or block copolymer comprising the (b-1) segment and the (b-2) segment is not particularly limited, but can be easily prepared by a well-known radical reaction. For example, a method of melt kneading by adding a radical catalyst to the polymers (b-1) and (b-2), or the polymer (b-1) or (b
It is prepared by a method in which a free radical is generated by a peroxide or the like in any one of -2) and this is melt-kneaded with other component polymers. Further, the graft or block copolymer may be prepared by a method such as hydrogenation of styrene-butadiene rubber.
(B) is prepared. Here, the ratio of (b-1) and (b-2) for constituting the graft or block copolymer of the component (B) is appropriately 95: 5 to 40:60. If the component (b-1) exceeds the component (b-2) in excess of the ratio of 95: 5, the separation of the polyolefin component from the polyacetal becomes remarkable, and the peeling and abrasion properties deteriorate. Also, beyond the ratio of 40:60
When the amount of the component (b-1) is less than that of the component (b-2), the effect of modifying the surface of the polyacetal by the polyolefin component becomes insufficient, and the effect of improving the friction coefficient is not exhibited. The above-mentioned (B) graft or block copolymer can be obtained from the market, for example, MODIPER A1400, A1200, A1100 (trade name) manufactured by NOF CORPORATION.
Etc. are commercially available. In addition, the component (B) is the component (A)
The amount is preferably 0.5 to 40 parts by weight, more preferably 1 to 30 parts by weight, based on 100 parts by weight. If the amount of the component (B) is too small, the effects of improving the sliding characteristics and moldability that are the objectives of the present invention cannot be obtained, and if it is too large, surface peeling occurs and the appearance of the molded product deteriorates, which is not preferable.

Next, as the (C) fatty acid ester used in the present invention, a fatty acid having 16 or more carbon atoms and an aliphatic alcohol having 16 or more carbon atoms, ethylene glycol, propylene glycol, trimethylolpropane, glycerin or pentaerythritol is used. An ester with one or more alcohols selected is preferable. Examples of fatty acids having 16 or more carbon atoms include straight-chain and / or branched unsaturated fatty acids such as palmitic acid, stearic acid, isostearic acid, arachidic acid, behenic acid, and montanic acid. Further, as the aliphatic alcohol having 16 or more carbon atoms, cetyl alcohol, stearyl alcohol, isostearyl alcohol, behenyl alcohol, erucyl alcohol,
Hexyldecyl alcohol, octyldodecyl alcohol and the like can be mentioned. The ester of such fatty acid and alcohol is preferably used, but particularly preferably, stearyl stearate, behenyl behenate, ethylene glycol mono (di) stearate, ethylene glycol mono (di) behenate, glycerin mono (diester). ,
Tri) stearate, glycerin mono (di, tri) behenate. In the present invention, one or more selected from these fatty acid esters are preferably used. In the present invention, the amount of the fatty acid ester (C) added is 0.1 to 20 parts by weight per 100 parts by weight of the component (A). If the amount is less than 0.1 part by weight, the effect of improving the slidability cannot be expected, and conversely, if the amount is more than 20 parts by weight, the properties of the base polyacetal resin may be significantly impaired. Preferably, 0.5 to 10 parts by weight is blended.

In the present invention, as the component (D), an inorganic powder having a weight average particle size of 30 μm or less is used. It is preferable that the weight average particle diameter is 30 μm or less, and the proportion of particles having a particle diameter of 50 μm or less is 90% or more, particularly preferably the weight average particle diameter is 10 μm or less. As the particle size of the inorganic powder becomes larger, unevenness is formed on the surface of the molded product, and the so-called sliding surface is damaged due to so-called increase in surface roughness. Therefore, it is not preferable that the weight average particle size exceeds the above range. The inorganic powder used is not particularly limited,
Particularly preferred is at least one selected from the group consisting of calcium carbonate, talc, silica, clay, mica and carbon.

Such an inorganic powder is surface-treated,
Although any untreated surface can be used, it is more preferable to use one that has been surface-treated in terms of smoothness of the molding surface and mechanical properties. The surface treatment agent is not particularly limited in terms of chemical structure as long as it can almost cover the powder surface, and all known agents can be used, such as silane-based agents, titanate-based agents, aluminum-based agents, and zirconium-based agents. Examples of various coupling treatment agents are Specifically, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, isopropyltristearoyl titanate, diisopropoxyammonium ethyl acetate,
Examples thereof include n-butyl zirconate. Further, granules of these inorganic powders are particularly preferable because they are much more excellent in operability during compounding than those not granulated. In the present invention, the amount of the inorganic powder (D) added is 0.5 to 30 parts by weight per 100 parts by weight of the component (A). If the amount is less than 0.5 parts by weight, the effect of improving slidability cannot be expected, and
If the amount is more than 30 parts by weight, the friction coefficient may be deteriorated and the surface of the molded product may be roughened to damage the mating material.

In the present invention, potassium titanate fiber is blended as the component (E). The compounding amount is (A) component 1
It is 1 to 70 parts by weight with respect to 00 parts by weight. If the amount is less than 1 part by weight, the reinforcement hardening is poor and not practical, and if it exceeds 70 parts by weight, the surface appearance is deteriorated, the friction coefficient is remarkably increased, and the thermal stability of the composition is lowered, which is not preferable. Practically, 10 to 50 parts by weight is preferable, and 20 to 40 parts by weight is particularly preferable. As for the shape of the fibers, both whisker-like and fiber-like ones can be used. As a typical example, the average fiber diameter is 0.03 to 10μ, and the fiber length is 2 to 30.
Examples include μ. From the aspect of rigidity, the aspect ratio
Although 10 or more are particularly preferable, the present invention is not limited to these fiber shapes. Such potassium titanate fibers are surface-treated, unsurface-treated,
Any of these can be used, but from the viewpoint of the smoothness of the molding surface and the mechanical properties, it is more preferable to use a surface-treated product. The surface treating agent is not particularly limited in terms of chemical structure as long as it can almost cover the powder surface, and all known ones can be used. The above-mentioned silane-based, titanate-based, aluminum-based, zirconium Examples include various coupling treatment agents such as a system.

In the present invention, the polyacetal resin (A)
In addition, the effect of adding and using the copolymer (B) and the fatty acid ester (C) together is to significantly improve the friction and wear characteristics of a general sliding member. However, the combined use of the component (B) and the component (C) has a limitation in adaptability to a special sliding member due to the decrease in surface hardness as described above. Also, copolymer (B)
When using a combination type of fatty acid ester with a certain type of ester, especially when a large amount of ester is used, there is a drawback that surface peeling easily occurs in part of the molded product depending on the molding conditions or the shape of the molded product, and the physical properties are significantly May be damaged. Therefore, in the present invention, the components (A), (B), and (C) are added to (D) an inorganic powder having a specific particle size, and the rigidity is significantly improved without further lowering the sliding characteristics (E) Titanium. It is characterized by blending potassium acid fiber, such (A), (B), (C), (D),
By blending the five components of (E), the above-mentioned drawbacks are greatly improved, and a well-balanced sliding member having excellent sliding properties, moldability, mechanical properties, and practicality can be obtained. I found that. Such performance is (A) above
, (B), (C) components, (D) a specific particle size of the inorganic powder, and (E) potassium titanate fiber can not be obtained by blending them individually, but realized by using both together It is what is done. According to the present invention, not only the performance generally required for a sliding member but also the special sliding characteristics required for a cam component for controlling a tape running mechanism such as a VTR or 8 mm video and a switch for a keyboard are satisfied, It is possible to provide a sliding member suitable for these parts.

Various known stabilizers may be added to the resin composition of the present invention to reinforce the stability. Further, various known additives may be further added in order to improve the physical properties depending on the intended use within a range that does not affect the effects of the present invention. Examples of additives include various coloring agents, release agents (other than the above-mentioned (C) fatty acid ester),
Nucleating agents, antistatic agents, other surfactants, heterogeneous polymers (other than (B) graft or block copolymers mentioned above)
Etc. In addition, as long as it does not significantly reduce the performance of the composition intended by the present invention, the fibrous shape of the inorganic, organic, metal, etc. outside the range defined by the present invention ((D) and (E) components) It is also possible to use one kind or a mixture of two kinds of powdery, granular or plate-like fillers. Next, the composition of the present invention is easily prepared by a known method generally used as a conventional resin composition preparation method. For example, after mixing each component, a method of preparing pellets by kneading and extruding with a single-screw or twin-screw extruder, once preparing pellets (masterbatch) having different compositions, and mixing a predetermined amount of the pellets (dilution) Any of these methods can be used. Further, in the preparation of such a composition, it is preferable to pulverize a part or all of the base polyacetal resin, mix this with other components, and then carry out extrusion or the like in order to improve the dispersibility of the additive. This is the preferred method. Further, when a particularly liquid one is used as the (C) fatty acid ester, it may be mixed with the (B) graft or block copolymer in advance and then impregnated, followed by kneading with the polyacetal resin, followed by extrusion and the like. It is a preferred method from the viewpoint of facilitating preparation of the composition and improving processability and slidability. The sliding member of the present invention is used by molding the composition prepared by such means into a desired shape by various methods such as molding, extrusion and cutting. The characteristics of (1) are not impaired at all, and are preferably used without being limited by any processing method.

[0012]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Examples 1 to 10 and Comparative Examples 1 to 12 As shown in Table 1, (A) polyacetal resin (manufactured by Polyplastics Co., Ltd., trade name DURACON), (B) various olefinic copolymers, (C) various Fatty acid ester, (D)
Various inorganic powders and (E) potassium titanate whiskers were mixed at the ratios shown in Table 1, and then melt-kneaded by a twin-screw extruder to prepare pelletized compositions. Then, a test piece was prepared by injection molding using this pellet and evaluated. The results are shown in Table 1. For comparison, as shown in Table 2, (B) graft copolymer, (C) fatty acid ester, (D)
Inorganic powder and (E) If any one of the potassium titanate whiskers is not added, or if an inorganic powder outside the range specified in this application is added as the (D) component, (E)
The same evaluation was performed in the case where glass fiber was added as a component. The results are shown in Table 2. The evaluation items and evaluation methods are as follows.・ Friction coefficient, wear amount, appearance change after sliding Using a Suzuki type friction / wear tester, as shown in Fig. 1, high surface pressure (load 10kg), low speed (2cm / sec), sliding at 30,000 revolutions The friction coefficient and the amount of wear were measured. The measurement was performed using the same material molded from the resin composition for both the pin and the ring molded piece. In addition, the state of deformation of the sliding surface edge portion of the ring molded piece (cylindrical inner diameter 18 mm, outer diameter 22 mm) after the measurement was evaluated in five levels. -General physical properties The flexural modulus was measured according to ASTM D 790.

The component (B) and its constituents (b-
The substances used as 1) and (b-2) are as follows.
-In Table 2, it is indicated by abbreviations. (b-1) PE: low-density polyethylene (b-2) AN / S: acrylonitrile-styrene copolymer PS: polystyrene PMMA: polymethylmethacrylate (B) PE-g-AN / S: PE (50) Graft copolymer with AN / S (50) PE-g-PS: PE (50) and PS (50) graft copolymer PE-g-PMMA: PE (50) and PMMA (50) Graft copolymer

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

As is apparent from the above description and Examples, the specific graft or block copolymer (B), the fatty acid ester (C), the specific inorganic powder (D) and the specific polyacetal resin (A) are used. The polyacetal resin composition of the present invention containing the fibrous filler (E) is superior in sliding (wear) performance to that obtained by simply adding a graft or block copolymer and a fatty acid ester. Further, the rigidity is remarkably improved, and further, there is no peeling of the surface layer on the surface of the injection-molded product, which is preferable as a sliding member. In addition, the composition of the present invention does not have particular problems such as separation of components and bleeding, which have been problems of materials of this type. Since the resin composition of the present invention has excellent properties as a sliding material as described above, audio- and video-related parts such as VTR, 8 mm video gears, cams, lever guide rollers, guide poles, etc. It is suitable for the sliding member. Besides, it is preferably used for mechanical parts of various office automation equipment such as textile machines, cameras, radios, facsimiles and computers.

[Brief description of drawings]

FIG. 1 is a view showing a sliding test piece used in Examples.

[Explanation of symbols]

 1 Suzuki type test piece 2 pin 3 load

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Claims (6)

[Claims] 1. A graft or block copolymer obtained from (A) 100 parts by weight of a polyacetal resin (B) (b-1) an olefin polymer and (b-2) at least one vinyl polymer. -40 parts by weight, (C) 0.1 to 20 parts by weight of fatty acid ester, (D) 0.5 to 30 parts by weight of inorganic powder having a weight average particle size of 30 μ or less, and (E) 1 to 70 parts by weight of potassium titanate fiber. A polyacetal resin composition comprising: 2. The (B) graft or block copolymer comprises: (b-1) one or more olefinic polymers selected from polyethylene, polypropylene and ethylene-propylene copolymers; and (b-2) a poly (olefin). The polyacetal resin composition according to claim 1, which is obtained from at least one vinyl (co) polymer selected from methyl methacrylate, acrylonitrile-styrene copolymer and polystyrene. (C) The fatty acid ester (C) is a fatty acid having 16 or more carbon atoms and at least one selected from aliphatic alcohols having 16 or more carbon atoms, ethylene glycol, propylene glycol, trimethylolpropane, glycerin and pentaerythritol. The polyacetal resin composition according to claim 1 or 2, which is an ester with alcohol. 4. The polyacetal resin according to claim 1, wherein the inorganic powder (D) is one or more selected from the group consisting of calcium carbonate, talc, silica, clay, mica and carbon. Composition. 5. A polyacetal resin sliding member formed by molding the composition according to any one of claims 1 to 4. 6. The polyacetal resin sliding member according to claim 5, wherein the sliding member is a cam component or a switch component.