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
1999-09-02
2001-08-07
Niland, Patrick D. (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...
C524S492000, C524S493000, C524S494000, C524S495000, C524S496000, C524S590000, C525S399000
Reexamination Certificate
active
06271302
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a polyacetal resin composition for fuel-related parts comprising a polyacetal resin, glass fibers, a conductive carbon and a polyurethane resin, and having an excellent creeping resistance, a high conductivity and a high thermal stability in the kneading or molding step. It is also relates to fuel-related parts produced therefrom.
2. Background Art
A polyacetal resin is excellent in mechanical properties, fatigue resistance, friction and abrasion resistance, chemical resistance, oil resistance, thermal resistance and moldability. Therefore, it is used in a wide variety of fields such as automobiles, electrical and electronic equipment, other precision machines, and pipes for construction materials. As its use applications become wider, resin compositions having improved properties as materials are required and manufactured. As one of those resin compositions, a polyacetal resin containing a conductive carbon black for the purpose of giving conductivity thereto is used. For example, the polyacetal resins are used as fuel-related parts in consideration of their excellent chemical resistance. But in this case, since static electricity is generated by shearing of a fuel and the resin, the polyacetal resin is required to be conductive. Accordingly, the conductive carbon black is usually blended with the polyacetal resin.
However, the polyacetal resin has such a serious drawback that the blend of the carbon black noticeably decreases the toughness of the polyacetal resin. And so, when a pipe or the like as the above fuel-related part is continuously given a constant pressure or continuously loaded with a stress, a creep rupture occurs in a short period of time even if the stress is low.
On the other hand, in order to give the polyacetal resin both conductivity and a high mechanical strength, a surface-treated carbon fiber is added thereto. Such a polyacetal resin, however, cannot be used as general-purpose materials due to a highly increasing cost.
Therefore, there has been desired a polyacetal resin composition for fuel-related parts which can be manufactured at a low cost and which has a high conductivity, a high toughness, and in particular, an excellent creep resistance.
DISCLOSURE OF THE INVENTION
The present inventor has intensively investigated to obtain a polyacetal resin composition for fuel-related parts having excellent properties as described above. As a result, he has found that it is extremely effective to blend glass fibers, a conductive carbon and a polyurethane resin with a polyacetal resin and, in consequence, the present invention has been completed.
That is, the present invention relates to a polyacetal resin composition for fuel-related parts which is obtained by blending (A) a polyacetal resin with (B) glass fibers, (C) a conductive carbon and (D) a polyurethane resin, and which has a volume resistivity of 1×10
5
&OHgr;cm or less and, as a creep resistance, such a tensile creep strength that it is not ruptured under a stress of 20 MPa in 60° C. water for at least 200 hours.
In a word, the present invention relates to the composition containing the above-described (A), (B), (C) and (D) and having the volume resistivity and the tensile creep strength as described above, and the fuel-related parts produced therefrom.
DETAILED DESCRIPTION OF THE INVENTION
The constitutional components of the present invention will be described hereinafter.
The polyacetal resin (A) according to the present invention is a polymer having oxymethylene groups (—CH
2
O—) as the main repeating unit, and such a polyacetal resin includes polyoxymethylene homopolymers and polyacetal copolymers. The copolymers contain, other than the oxymethylene groups, oxyalkylene groups having about 2 to 6 carbon atoms, preferably about 2 to 4 carbon atoms (e.g., an oxyethylene group (—CH
2
CH
2
O—), an oxypropylene group, an oxytetramethylene group or the like). The content ratio of the oxyalkylene units having about 2 to 6 carbon atoms can be suitably selected in accordance with the application of the polyacetal, for example, 0.1 to 30 mol %, preferably 1 to 20 mol % based on the total polyacetal.
The polyacetal copolymer can be constituted of a plurality of components such as a copolymer consisting of two components and a terpolymer consisting of three components, and it may be a block copolymer. The polyacetal resin may be not only a linear one but one having a branched or cross-linked structure. Further, the terminals of the polyacetal resin may be stabilized by esterification with carboxylic acids such as acetic acid, propionic acid and butyric acid. The degrees of polymerization, branching and cross-linking of the polyacetal resin are not particularly restricted so long as the resin is meltable and moldable.
Preferable polyacetal resins include polyoxymethylene homopolymers and polyacetal copolymers (e.g., a copolymer comprising at least both an oxymethylene unit and an oxyethylene unit). Preference is given to the polyacetal copolymers from the standpoint of thermal stability.
A molecular weight of the aforesaid polyacetal resin is preferably as large as possible. The larger the molecular weight is, the more the creep resistance improves. Concretely, it is preferred that a melt index at 190° C. of the resin is not more than 9.0 g/10 min.
The aforesaid polyacetal resin can be produced by a conventional method, for example, by polymerizing aldehydes such as formaldehyde, paraformaldehyde and acetaldehyde, and cyclic ethers such as trioxane, ethylene oxide, propylene oxide and 1,3-dioxolane.
The glass fibers (B) usable in the present invention are not particular restricted. In view of handling, a chopped strand being cut into approximately 2 to 8 mm lengths is preferable. The glass fiber having a diameter of usually 5 to 15 &mgr;m, preferably 7 to 13 &mgr;m can be suitably used.
As the glass fiber, it is also preferred to use a surface pre-treated one. As a material for the surface treatment, polyurethane resins or oligomers are preferred. Such surface treated glass fibers can be easily handled.
The conductive carbon (C) used in the present invention is not restricted to particular ones. Any of Ketchen Black, acetylene black, channel black or various furnace type conductive carbons having an average particle size of 1-500 m&mgr;, preferably 10-100 m&mgr; can be used.
The polyurethane resin (D) used in the present invention is a polymer or an oligomer having an urethane linkage in the main chain. Generally, in many cases, a reactive functional group such as a hydroxyl group is present at the end of the polymer chain or a functional group including a hydroxyl group is suspending from the main chain. The polyurethane resin includes, for example, thermoplastic polyurethanes prepared by reacting a polyisocyanate component such as aliphatic, alicyclic or aromatic polyisocyanates with a polyol component such as a lower molecular weight polyol component, e.g., aliphatic, alicyclic or aromatic polyols, polyether diols, polyester diols and polycarbonate diols. In the preparation of the polyurethane, use may be made of a chain elongating agent such as diols or diamines. Furthermore, polyurethane elastomers may also be included in the polyurethane resin. These polyurethane resins may be used alone or in combination of two or more of them.
In the present invention, an addition of such a polyurethane resin results in the improvement of melt stability and processability of the conductive polyacetal resin. That depresses the decomposition during the molding or processing and enhances mechanical strength and creep resistance.
The polyurethane resin may be not only linear but also blanched or cross-linked as long as it can maintain thermoplasticity. Among these polyurethane resins, preference is given to the polyurethane and the polyurethane elastomer which are produced by reacting a diisocyanate component with a diol component.
A molecular weight of the polyurethane resin is not restricted. For example, from oligomers having a mole
Niland Patrick D.
Nixon & Vanderhye P.C.
Polyplastics Co. Ltd.
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