Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-09-07
2001-07-17
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S495000
Reexamination Certificate
active
06262165
ABSTRACT:
This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/JP98/00934 which has an International filing date of Mar. 6, 1998, which designated the United States of America.
TECHNICAL FIELD
The present invention relates to a polyacetal resin composition which is excellent in electrical conductivity, mechanical properties and releasability, and a method for producing the composition. Particularly, it relates to a polyacetal resin composition used for automobile components, and a molded article.
BACKGROUND OF THE INVENTION
Polyacetal resins are widely used, for example, as a component of automobile parts, electronic and electrical parts, and working parts or exterior parts of other industrial apparatuses because of their excellent mechanical strength, creep characteristics, lubrication characteristics, and electric characteristics. However, when polyacetal resins are used as a component in bracketing materials for in-tank type fuel pump apparatuses as disclosed, for example, in JP-A-8-279373, the resin is simultaneously required to have the properties of electrical conductivity for the inhibition of static electricity formation caused by contact with fuel, high mechanical strength for operation at high pump pressure, and excellent releasability for smooth releasing from molds of complicated shapes produced by injection molding.
The following prior art teaches polyacetal resins having improved electrical conductivity characteristics. JP-A-63-210162 discloses a composition comprising a polyoxymethylene resin, a specific carbon black, and an epoxy compound, but this composition only has improved antistatic properties, not improved mechanical properties.
JP-A-49-37946 discloses compositions comprising a polyacetal resin containing a carbonaceous carbon fiber, and mentions, in the examples, that the fiber length of the carbon fiber in the injection molded products is in the range of 0.10-0.20 mm, and the electrical conductivity improves as the amount of the carbon fiber contained therein increases. It further discloses that mechanical strength, elastic modulus and frictional characteristics of the compositions are equal to or higher than those of polyacetal. However, the compositions have high anisotropy, and when they are injection molded (especially when they are molded into relatively large articles such as brackets of in-tank type fuel pump apparatuses). They show non-uniform shrinking behavior in the mold resulting in clamping of the mold and deterioration of releasability from the mold.
JP-A-62-267351 discloses a polyacetal resin composition containing one or two or more of carbon materials selected from the group consisting of carbon black, carbon fiber and graphite in an amount of 0.1-30% by weight based on the whole composition and one or two or more compounds selected from the group consisting of alkali metal compounds and alkaline earth metal compounds in an amount of 0.0005-2% by weight based on the whole composition. The publication states that the heat stability of the polyacetal resin containing the carbon materials is improved by the addition of the alkali metal compounds and/or the alkaline earth metal compounds, but makes no mention of the examples where they are used in combination, and fails to disclose excellent effects in all of the electrical conductivity, the mechanical properties and the releasability as attained in the present invention.
JP-A-6-240049 discloses a thermoplastic resin composition comprising a carbon fiber of 1-6 &mgr;m in diameter contained in an amount of 3-30 wt % in the thermoplastic resin and carbon black contained in an amount of 0-20 wt % in the thermoplastic resin. As the thermoplastic resin, a polyoxymethylene resin is mentioned, and examples including it are given, but all of the examples use only carbon fiber as the carbon material. Thus, naturally, the effects obtained in the present invention are not shown.
SUMMARY OF THE INVENTION
As a result of an intensive research conducted by the inventors in an attempt to provide polyacetal resin compositions which have excellent electrical conductivity, mechanical properties and releasability, and the molded articles obtained by molding the polyacetal resin compositions, (especially as automobile components), it has been found that the above objects can be attained by using a polyacetal resin, an electrically conductive carbon black, and a carbon fiber of 120-350 &mgr;m in average fiber length, and, if necessary, a lubricant.
That is, the present invention relates to a polyacetal resin composition comprising (A) 100 parts by weight of a polyacetal resin, (B) 1.0-30 parts by weight of an electrically conductive carbon black, and (C) 1.0-30 parts by weight of a carbon fiber of 120-350 &mgr;m in average fiber length, and, if necessary, 0.001-5 parts by weight of a lubricant.
The present invention further relates to a method for producing a polyacetal resin composition which comprises melting a polyacetal resin, adding simultaneously 1.0-30 parts by weight of an electrically conductive carbon black and 1.0-30 parts by weight of a carbon fiber to 100 parts by weight of the molten polyacetal resin, and kneading them.
The present invention further relates to molded articles obtained by molding the above composition, particularly as automobile components.
DETAILED DESCRIPTION OF THE INVENTION
The polyacetal resins used in the composition of the present invention include oxymethylene homopolymers prepared by polymerizing formaldehyde, or cyclic oligomers such as trioxans which are trimers of formaldehyde or tetraoxans which are tetramers of formaldehyde and then capping the end of the resulting polymers with an ether group or an ester group, and oxymethylene copolymers obtained by copolymerizing formaldehyde, trioxans or tetraoxans with cyclic ethers such as ethylene oxide, propylene oxide, 1,3-dioxolane, and 1,4-butanediol formal; these oxymethylene homopolymers or copolymers into which a crosslinkage or a branched molecular chain is introduced; and oxymethylene block copolymers containing a segment comprising an oxymethylene unit and a segment of different component, the end of which is capped with an ether group or an ester bond. Preferred are oxymethylene homopolymers and oxymethylene copolymers obtained by using ethylene oxide or 1,3-dioxolane as a comonomer component. More preferred are oxymethylene copolymers obtained by using ethylene oxide or 1,3-dioxolane as a comonomer component.
Melt index (hereinafter referred to as “MI”) of the polyacetal resins is not limited, but preferred are those which can stand the usual molding processes and have the mechanical strength inherent to the polyacetal resins. In the composition of the present invention, MI is preferably 0.1-200 g/10 min, and more preferably 0.1-120 g/10 min. The melt index here is measured in accordance with ASTM-D1238 at a temperature of 190° C. and under a load of 2160 g and expressed by the unit of g/10 min.
The electrically conductive carbon blacks used in the present invention are not limited, but preferred are those which are small in particle size or large in the surface area per unit weight and developed in a chain structure.
The surface area per unit weight of an electrically conductive carbon black is usually measured using the absorption of dibutyl phthalate (hereinafter referred to as “DBP”) oil. In the present invention, an electrically conductive carbon black having a DBP oil absorption of 200 ml/100 g or more is preferred. This DBP oil absorption is a measure which indicates the degree of development of structure of carbon black, and the DBP oil absorption increases as the structure develops, and the electrical conductivity increases. The DBP oil absorption can be obtained by subjecting a given amount of carbon black, which agitated by a kneader mixer, to titration with DBP using an automatic burette. That is, in this titration, when carbon black is filled with DBP in its voids absorbs the DBP to a maximum, powders which freely flow until then become semi-plastic to cause an abr
Ariyasu Hideyuki
Tsuji Hironori
Asahi Kasei Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Cain Edward J.
LandOfFree
Polyacetal resin composition does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polyacetal resin composition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polyacetal resin composition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2518473