JPH08143748A - Polyacetal resin composition - Google Patents

Abstract

PURPOSE: To obtain a polyacetal resin compsn. which is suitable for a conductive bearing having an earthing function necessary in the audio-visual and office automation fields by compounding a polyacetal resin with a conductive carbon black, a specific graft copolymer, and a lubricant. CONSTITUTION: This resin compsn. comprises 100 pts.wt. polyacetal resin, 5-30 pts.wt. conductive carbon black, 2-30 pts.wt. graft copolymer obtd. from an ethylene-α,β-unsatd. acid ester copolymer and at least one vinyl polymer, and 0.5-10 pts.wt. at least one lubricant selected from among an α-olefin oligomer, a fatty acid ester, and an alkylated diphenyl ether in a wt. ratio of the graft copolymer to the lubricant of 0.40 or higher. The carbon black is pref. an acetylene black and/or an oil furnace black having a DBP absorption of 300ml/100g or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has excellent friction and wear characteristics, good electrical conductivity, good moldability and machinability, and is a ground required in the AV and OA fields. The present invention relates to a polyacetal resin composition suitable for a conductive bearing having a function, and further to a conductive bearing comprising such a composition.

[0002]

BACKGROUND OF THE INVENTION Polyacetal resins have well-balanced mechanical properties.
It is widely used in the fields of automobiles, electric and electronic parts, etc. due to its excellent friction and wear characteristics, chemical resistance, heat resistance and electric 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. Furthermore, in copying machines, facsimiles, and other devices, it is important to maintain the insulation around the developing section and the thermal drum. Therefore, the occurrence of static electricity is often a problem. It is often handled by using a metal or resin coated with a conductive coating for grounding. However, these bearings have little cost advantage, and there is an increasing demand in the market for materials having both conductivity and slidability. For the purpose of simultaneously improving the conductivity and sliding characteristics,
It is generally known that carbon fiber or graphite is mixed with polyacetal resin, but carbon fiber is expensive and has a relatively high contact resistance due to an increase in the surface roughness of the material, which is practically sufficient. In many cases, excellent conductivity cannot be obtained. Further, graphite has a remarkable decrease in physical properties at a compounding amount sufficient to improve conductivity, and causes deterioration of wear, and neither of them can exhibit sufficient performance in practical use. On the other hand, the composite of carbon black and various sliding modifiers,
It is generally known, however, that the thermal decomposition of the base resin by conductive carbon with a large specific surface area and the adsorption of the liquid sliding modifier on the carbon itself cause the sliding modifier to not exhibit its full effect. There was a problem. In addition, although polyolefin-based copolymers and carbon black are also commonly compounded, polyolefins that have poor affinity with the matrix polyacetal can be used to remove polyolefin components when molding small gate molds and other products. Tended to cause gate clogging and mold deposit (mold deposit). Under such circumstances, there is a strong demand in the market for a material having conductivity, slidability, and moldability suitable for a conductive bearing and the like.

[0003]

[Means for Solving the Problems] The inventors of the present invention have earnestly studied the development of a polyacetal resin composition having excellent conductivity, sliding properties, moldability, and other properties as well. As a result, by adding and using a conductive carbon black, a specific graft copolymer and a specific lubricant in the polyacetal resin,
The inventors have found that a polyacetal resin composition having excellent performance in which conductivity, friction / wear characteristics, moldability, surface peeling, and mechanical characteristics are well balanced can be obtained, and have reached the present invention. That is, the present invention relates to (A) 100 parts by weight of polyacetal resin, (B) conductive carbon black 5 to
30 parts by weight, (C) ethylene-α, β unsaturated acid ester copolymer (c-1), and at least one vinyl polymer (c-2)
2 to 30 parts by weight of the graft copolymer obtained from (1) and 0.5 to 10 parts by weight of one or more lubricants selected from the group consisting of (D) α-olefin oligomer, fatty acid ester and alkyl-substituted diphenyl ether. And (C)
The present invention provides a polyacetal resin composition having a ratio by weight (C) / (B) of the component to the component (B) of 0.40 or more, and a conductive bearing comprising 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. The improvement of conductivity and slidability which is the object of the present application is not limited in any way,
190 ℃ for molding process such as thermal stability when using carbon together
Melt flow index (load 2060g) 9g / mi
A polyacetal copolymer having a fluidity of n or more is particularly preferably used.

Next, the (B) conductive carbon black used in the present invention has a large specific surface area, the distance between carbon particles becomes smaller with respect to the added amount, and the DBP (dibutyl phthalate) oil absorption amount is smaller. 300 ml / 100 g or more of oil furnace black or acetylene black starting from acetylene and having a chain structure developed is preferably used. Particularly preferably, it is preferable to use the conductive furnace black in which the oxygen-containing functional group, which is likely to be generated by normal incomplete combustion at high temperature in air, is reduced by incomplete combustion in an inert gas such as nitrogen. In such carbon black, the capture of π electrons is suppressed, and it is possible to realize high conductivity with a smaller amount. The existing amount of the oxygen-containing functional group is generally expressed by the pH value of the water slurry as a substitute, but carbon black having a pH value of 7 or more is preferably used. Specific examples of such conductive carbon black include Ketjen Black EC (Lion Akzo) and Ketjen Black EC-600JD.
(Lion Akzo Co., Ltd.), Black Pearls 2000 (Cabot Corp., USA) and the like, but not limited to these. The conductive carbon black as the component (B) is blended in an amount of 5 to 30 parts by weight, preferably 5 to 20 parts by weight, based on 100 parts by weight of the component (A). If the blending amount is less than 5 parts by weight, it is not sufficient to improve the desired conductivity, and if it is blended over 30 parts by weight, the viscosity of the polyacetal, which is the base resin, is significantly increased by the carbon and the flowability is increased. Toughness and toughness are greatly reduced and decomposition of polyacetal is accelerated, which is not preferable.

The component used as the component (C) in the present invention is an ethylene-α, β unsaturated acid ester copolymer (c-1).
And a graft copolymer obtained from at least one vinyl polymer (c-2), both of which are chemically bonded in a branched or crosslinked structure. Here, as the ethylene-α, β unsaturated acid ester copolymer (c-1) constituting the main chain component of the graft copolymer (C), ethylene / ethyl acrylate copolymer, ethylene / methyl acrylate An ethylene / acrylic acid ester copolymer represented by a copolymer is preferably used. The composition ratio of the α, β unsaturated acid ester unit and the ethylene unit is not particularly limited, but the α, β unsaturated acid ester component is contained in the main chain polyethylene copolymer in an amount of 5% or less.
A copolymer containing at least wt% is preferably used.
Practically preferably, it is 5 to 40% by weight. Next, as the monomer unit constituting the vinyl polymer (c-2), methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, acrylic acid Butyl, acrylate-2 ethylhexyl, acrylate-hydroxyethyl, acrylate-hydroxypropyl, and other esters of acrylic acid and methacrylic acid and their derivatives, styrene, aromatic vinyl compounds such as α-methylstyrene, and acrylonitrile. can give. Particularly preferable vinyl polymers are acrylonitrile-styrene copolymers and polystyrene. The graft copolymer which is a feature of the present invention, the (c-1) ethylene-αβ unsaturated acid ester copolymer constituting the main chain portion,
(c-2) The vinyl-based polymer has a feature in that it is a graft copolymer having a chain, branch or cross-linking structure chemically bonded at at least one point, and simply by having such a graft structure as described below ( This produces a remarkable effect that cannot be obtained by the single composition of c-1) or (c-2). Take (c
The method for preparing the graft copolymer comprising the -1) segment and the (c-2) segment is not particularly limited, but it can be easily prepared by a well-known radical reaction. For example, by grafting a polymer (c-1) and a radical catalyst such as peroxide to any of (c-2) to generate free radicals, and melt-kneading this with other component polymers. A copolymer (C) is prepared. Here, (c-1) and (c-2) for forming the graft copolymer of component (C)
The ratio of 95: 5 to 40:60 is suitable. If the component (c-1) exceeds the component (c-2) in excess of the ratio of 95: 5, the separation of the polyethylene component from the polyacetal becomes remarkable,
Peeling and wear characteristics deteriorate. Beyond the 40:60 ratio
When the amount of the component (c-1) is smaller than that of the component (c-2), the effect of modifying the surface of the polyacetal by the polyethylene component becomes insufficient, and the effect of improving the friction coefficient cannot be exhibited. The above-mentioned (C) graft copolymer can be obtained from the market, for example, MODIPER A manufactured by NOF CORPORATION.
It is commercially available as 5400, A5100 (trade name), etc. Further, the component (C) is 2 to 30 parts by weight with respect to 100 parts by weight of the component (A).
It is preferable that the amount is 4 parts by weight, more preferably 4 to 20 parts by weight. If the amount of the component (C) is too small, the sliding-improving performance aimed at by the present invention, the reduction of the deterioration of thermal stability due to carbon black, and the improvement effects such as moldability cannot be obtained. It is not preferable because it deteriorates the molding appearance and promotes the generation of mold deposits. Further, the graft copolymer of the component (C) preferably has a ratio by weight (C) / (B) of 0.4 or more to the conductive carbon black of the component (B). When the graft copolymer (C) / (B) ratio is less than 0.4 with respect to the conductive carbon black, the decomposition of the polyacetal itself is promoted, resulting in heat generation such as foaming during pellet extrusion and gas generation during molding. It is not preferable because the decomposition property (loss on heat) is deteriorated and the appearance of the molded product is deteriorated by the generated gas.

The lubricant (D) used in the present invention is α
One or more kinds selected from the group consisting of olefin oligomer, aliphatic ester and alkyl-substituted diphenyl ether are used. α-olefin oligomers are mainly
C _{6 to} C ₂₀ α-olefin alone, or ethylene and C ₃ to
It is an aliphatic hydrocarbon having a structure in which a C ₂₀ α-olefin is copolymerized. In the present invention, the number average molecular weight is 400
Approximately 4000 ethylene / α-olefin oligomers are preferably used. As an aliphatic ester, 1 with C ₁₆ or higher
An ester composed of a monovalent saturated fatty acid and a C ₁₆ or more monovalent saturated aliphatic alcohol or a polyhydric alcohol, and C ₁₆
An ester composed of the above monovalent saturated aliphatic alcohol and polyvalent carboxylic acid is preferably used. Examples of C ₁₆ or more monovalent saturated fatty acids constituting the aliphatic ester include palmitic acid, isopalmitic acid, stearic acid,
Examples thereof include isostearic acid, behenic acid, lignoceric acid, cethylonic acid, heptacosanoic acid, montanic acid, melissic acid, laxeric acid, cetoleic acid and erucic acid. Also
Examples of the C ₁₆ or more monovalent saturated aliphatic alcohol include cetyl alcohol, stearyl alcohol, isostearyl alcohol, behenyl alcohol, erucyl alcohol, hexyldecyl alcohol, and octyldodecyl alcohol. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, butanediol, glycerin, erythritol, pentaerythritol, sorbitan and the like. Further, phthalic acid and adipic acid are typical examples of the polyvalent carboxylic acid. A partial ester in which a part of alcohol is esterified with a fatty acid and most of hydroxy groups remain has a large bleed-out and tends to deteriorate the appearance of the molded product, but the conductivity, sliding property and moldability are deteriorated. It is usable, not detrimental. Among the aliphatic esters consisting of such carboxylic acids and alcohols, particularly preferable are stearyl stearate, behenyl behenate, ethylene glycol distearate, in view of price, availability (synthesis and purification), and friction and wear characteristics. Trimethylolpropane triisostearate, trimethylolpropane tristearate, pentaerythritol tetrastearate, distearyl adipate, distearyl phthalate and the like. As the alkyl-substituted diphenyl ether, as shown by the following formula (1), at least one or more C ₁₂ or more aliphatic chains are introduced into phenyl of diphenyl ether in the form of a substituent selected from an alkyl group, an ether group and an ester group. The compound is shown. There is no particular restriction on the molecular weight, and any alkyl-substituted diphenyl ether is preferably used. Such a substituent may be introduced at any position of the phenyl group, but from the viewpoint of synthesis and economy, it is particularly preferable that the substituent be at any of the 2,4,6,2 ′, 4 ′, 6 ′ positions. Is an alkyl-substituted diphenyl ether that is particularly preferred, and a disubstituted product at the 4,4 ′ position is particularly preferred.

[0008]

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(R is an alkyl group, ether group or ester group introduced at part or all of the 2 to 6-position and 2'to 6'-position) As the substituent of the alkyl-substituted diphenyl ether, dodecyl group and tetradecyl group can be used. Group, straight chain alkyl group such as hexadecyl group and octadecyl group, and the following formula (2)
And branched alkyl groups shown in.

[0010]

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(N and m are integers of 0 or more and n + m ≧ 11) In the present invention, one or more selected from these lubricants are used. The amount of the (D) lubricant added is 0.5 to 10 parts by weight based on 100 parts by weight of the component (A). If the amount is less than 0.5 parts by weight, the effect of improving the slidability cannot be expected, and conversely, if the amount is more than 10 parts by weight, the properties of the polyacetal resin as the substrate may be significantly impaired. Preferably, 2 to 8 parts by weight is blended.

As an optional component, the present invention further comprises at least one (E) inorganic powder selected from the group consisting of calcium carbonate, silica, mica, and wollastonite, thereby providing friction and wear characteristics as a bearing. Is further improved. The inorganic powder (E) used for this purpose has an average particle size of 50 μm or less, and preferably a particle size of 100 μm or less in a proportion of 95% or more. Particularly preferably, the average particle size is 30 μm or less and the particle size is 50 μm.
The ratio of the following is 90% or more, and more preferably the average particle size is 10 μm or less. Inorganic powder having a large particle diameter exceeding the above value is not preferable because it greatly increases the surface roughness of the molded product and deteriorates the wear characteristics. As such an inorganic powder, one which has been surface-treated with a coupling agent such as a silane type, titanate type or aluminum type can be particularly preferably used. In the present invention, the preferable addition amount of the inorganic powder (E) is 0.5 to 20 parts by weight with respect to 100 parts by weight of the polyacetal resin.

The composition of the present invention can be further reinforced by adding various known stabilizers. Further, in order to improve the physical properties depending on the intended use, various known additives may be further added. If you show an example of an additive,
Various colorants, release agents (other than the above lubricants), nucleating agents, antistatic agents, other surfactants, different polymers (other than the above graft copolymers), and the like. Further, as long as it does not significantly reduce the performance of the composition of the present invention, one kind of other inorganic, organic, metal, etc. fibrous, plate-like filler or other powdery or granular filler is used. It is also possible to use a mixture of two or more kinds. Next, the composition or molded article of the present invention can be easily prepared by a known method generally used as a conventional resin composition preparation method. For example, after mixing the respective components, kneading and extruding with a uniaxial or biaxial extruder to prepare pellets, a predetermined amount of the pellets are mixed (diluted) and subjected to molding, and a molded article of the target composition is molded. Any method such as a method of obtaining can be used. Further, in the preparation of such a composition, it is preferable to pulverize a part or all of the polyacetal resin which is the substrate, 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.

[0014]

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 28 and Comparative Examples 1 to 13 As shown in Tables 1 to 3, (A) component is a polyacetal copolymer (manufactured by Polyplastics Co., Ltd., trade name DURACON), and (B) is a conductive carbon black, ( After mixing various graft copolymers as the component C), various lubricants as the component (D), and optional components, and optionally inorganic powders as the component (E) in the proportions shown in Tables 1 to 3, a twin-screw extruder is used. Were melt-kneaded to prepare a pelletized composition. Then, a test piece was prepared by injection molding using this pellet and evaluated. The results are shown in Tables 1 to 3. Further, for comparison, as shown in Tables 4 to 5, the same evaluations were made for the compositions in which any one of the components or the two components were not blended. The results are also shown in Tables 4-5. The following were used as the α-olefin oligomer and the alkyl-substituted diphenyl ether.・ Α-Olefin / Ethylene cooligomers (Mitsui Petrochemical Co., Ltd., Lucant HC40, HC600) ・ Alkyl-substituted diphenyl ethers (Matsumura Petrochemical Research Institute, Moresco High Loop) On the street.・ Polyolefin graft copolymer (C-1) Ethylene-ethyl acrylate copolymer (50wt%)
Graft copolymer of acrylonitrile / styrene copolymer (50wt%) (C-2) Ethylene-ethyl acrylate copolymer (50wt%)
Copolymer of ethylene and polystyrene (50wt%) (C-3) Ethylene-ethyl acrylate copolymer (70wt%)
Graft copolymer of acrylonitrile / styrene copolymer (30 wt%) The evaluation items and evaluation methods are as follows. -Pyrolysis property (heat loss) The weight change (wt%) was measured by TGA under the condition of 210 ° C x 30 minutes (in a nitrogen atmosphere).・ Molded product surface condition (molded product appearance) A test piece for evaluation (50 mm × 50 mm × 1 mm; center pin gate method) is molded under the following molding conditions, and the peeling condition of the surface (especially in the vicinity of the gate) is evaluated in 5 levels. did. Molding conditions Cylinder temperature (℃) 190 Injection pressure (kg / cm ² ) 750 Injection speed (m / min) 3 ・ Surface resistivity (conductivity) φ80 × 3t flat plate It was used and evaluated according to a conventional method. Advantest R6450 Digital Multimeter R12702A RESISTIVITY CHAMBER ・ Frictional coefficient, specific wear amount Using a Suzuki type friction / wear tester, under pressure (10 kg / c
m ² ), linear velocity 300 mm / sec, contact area 2.0 cm ² , S55C
The dynamic friction coefficient and the specific wear amount were measured using steel as the counterpart material.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

[Table 4]

[0019]

[Table 5]

[0020]

As is apparent from the above description and Examples, the polyacetal resin (A) has a specific (B) conductive carbon black, a specific (C) ethylene-based graft copolymer, and (D) specific A polyacetal resin composition comprising a lubricant and, as an optional component, (E) a specific inorganic filler, which is dramatically superior in friction and wear characteristics, and has good conductivity. Is possible.
A conductive bearing formed by using such a composition is suitable for AV equipment such as OA equipment typified by printing equipment such as printers and facsimiles, which is easily affected by static electricity generation, and AV equipment typified by audio and image reproduction related equipment. To provide various bearing parts.

Claims (8)

[Claims] 1. (A) 5 to 30 parts by weight of conductive carbon black, (C) 100 parts by weight of polyacetal resin, (C) ethylene-α, β unsaturated acid ester copolymer (c-1)
And 2 to 30 parts by weight of a graft copolymer obtained from at least one vinyl polymer (c-2), (D) an α-olefin oligomer, a fatty acid ester, and an alkyl-substituted diphenyl ether 1
0.5 to 10 parts by weight of one or more lubricants are mixed, and
A polyacetal resin composition having a ratio (C) / (B) by weight of the component (C) and the component (B) of 0.40 or more. 2. The conductive carbon black (B) is acetylene black starting from acetylene and / or DB.
The polyacetal resin composition according to claim 1, which is an oil furnace black having a P oil absorption of 300 ml / 100 g or more. 3. The graft copolymer (C) is (c-1) one or more olefinic polymers selected from ethylene / acrylic acid ester copolymers and ethylene / methacrylic acid copolymers, (c-2) The polyacetal resin composition according to claim 1 or 2, which is obtained from at least one vinyl (co) polymer selected from the group consisting of acrylonitrile-styrene copolymer and polystyrene. 4. The (D) component α-olefin oligomer is
The polyacetal resin composition according to any one of claims 1 to 3, which is an ethylene / α-olefin cooligomer having an average molecular weight of 400 to 4000. 5. A full ester, wherein the aliphatic ester of the component (D) comprises a C ₁₆ or more monovalent saturated fatty acid and a C ₁₆ or more monovalent saturated aliphatic alcohol or a polyhydric alcohol.
And / or a full ester composed of a C ₁₆ or more monovalent saturated aliphatic alcohol and a polyvalent carboxylic acid.
The polyacetal resin composition according to claim 3. 6. The component (D), which is an alkyl-substituted diphenyl ether, has at least one or more saturated aliphatic substituents selected from an alkyl group having a C ₁₂ or more, an ester group, and an ether group in the phenyl group. The polyacetal resin composition according to any one of claims 1 to 3, which is an introduced compound. 7. The average particle diameter or the average fiber diameter is 50 μm.
m or less and at least one (E) selected from the group consisting of calcium carbonate, silica, mica, and wollastonite
The polyacetal resin composition according to any one of claims 1 to 6, which comprises 0.5 to 20 parts by weight of an inorganic powder. 8. A conductive bearing comprising the polyacetal resin composition according to claim 1 and having a surface resistivity of 10 ⁵ Ωcm or less.