Polyacetal resin composition containing electrically conductive carbon black is improved in respect to stability to heat by incorporating thereinto an amide compound.

The present invention relates to a thermally stable, electrically 
conductive, polyacetal resin composition. 
Heretofore, compounding polyacetal resin with a sufficient amount of 
electrically conductive carbon black has been practiced as a method for 
imparting electrical conductivity to the resin. 
However, compounding polyacetal resin with a sufficient amount of 
electrically conductive carbon black to satisfactorily achieve desired 
performances will markedly reduce the thermal stability of polyacetal 
resin, resulting in notable interference with its moldability and also 
deterioration of its properties. 
The present invention relates to an electrically conductive polyacetal 
resin composition in which these drawbacks have been overcome through 
appreciable improvement in the thermal stability by adding an amide 
compound to the polyacetal resin composition compounded with electrically 
conductive carbon black. 
The electrically conductive carbon black used in this invention may include 
commercially available electrically conductive carbon black, e.g., Ketjen 
Black EC (a product of Lion-Akzo Co., Ltd.). 
Preferable electrically conductive carbon black should have a generally 
well developed structure, small particle size, high micro-porosity and 
large surface area. 
The amount of the electrically conductive carbon black added shall be 3-30 
weight % of the whole composition. With less than 3 weight %, the desired 
electric conductivity cannot be achieved and with more than 30 weight %, 
its compounding with polyacetal resin will become difficult. Accordingly, 
the preferable amount of addition, from the viewpoint of properties and 
formulation, should be 3-10 weight %. 
The amide compound used in this invention includes those of mono- or 
poly-carboxylic acids represented by the following general formula and 
ethylene oxide adducts thereof: 
##STR1## 
In this formula, R represents a carboxylic acid residue, which is a 
saturated or unsaturated hydrocarbon group having at least two carbon 
atoms, preferably one having 2-23 carbon atoms. Or R may be a group 
representing a basic unit of a vinyl polymer or a vinyl copolymer. n is an 
integer of 1 or larger, preferably 1-6. x and y are each 0 or an integer 
of 1 or larger, preferably 1-10. 
Accordingly, the amide compounds used in this invention include those of 
fatty acids, higher fatty acids, etc., or ethylene oxide adducts thereof 
and those of polymers of vinyl compounds or of copolymers mainly 
comprising vinyl compounds or ethylene oxide adducts thereof. Cited as 
such amide compounds employed in this invention are, for example, 
butyamide, caproamide, caprylamide, capramide, lauramide, myristamide, 
palmitamide, linolenamide, erucamide, natural higher fatty acid amides as 
a mixture of higher fatty acid amides, succinamide, adipamide, sebacamide, 
dodecanedicarboxylic acid diamide, 1,6-cyclohexanedicarboxylic acid 
diamide, propane-1,2,3-tricarboxylic acid triamide, benzamide, 
phthalamide, terephthalamide, trimellitamide, pyromellitamide, 
polyacrylamide, polymethacrylamide, and ethylene-acrylamide copolymer, and 
ethylene oxide adduct thereof. These amide compounds may be used alone or 
as a mixture of two or more of them. Preferable amide compounds are 
ethylene oxide adducts of higher fatty acid amides, especially those with 
the number of moles of ethylene oxide added being x+y=2-7 giving a 
prominent effect. 
The amount of these polyamide compounds added is 0.1-15 weight % of the 
whole polyacetal resin composition, more preferably 0.3-5 weight %. 
The polyacetal resin used in this invention refers to polyoxymethylene 
homopolymer or polyacetal copolymers with a major portion of its main 
chain composed of consecutive oxymethylene units. The polyacetal resin 
composition of this invention may be compounded with an additive such as 
well-known antioxidant or antiacid agent. 
Cited as such antioxidants are, for example, phenols such as 
2,2'-methylenebis-(4-methyl-6-t-butylphenol), hexamethylene glycol 
bis(3,5-di-t-butyl-4-hydroxyhydrocinnamate), tetrak 
methylene[(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]-methane, 
1,3,5-trimethyl-2,4,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-benzene, 
4,4'-methylenebis(2,6-di-t-butylphenol) and 
1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimenthylbenzyl)isocyanurate, and 
amines such as N-phenyl-N'-isopropyl-p-phenylenediamine, 
N,N'-diphenyl-p-phenylenediamine, 
4,4'-bis(4-.alpha.,.alpha.-dimethylbenzyl)diphenylamine, a condensate 
between diphenylamine and acetone, N-phenyl-.beta.-naphthylamine and 
N,N'-di-.beta.-naphthyl-p-phenylenediamine. 
Cited as antiacid agents are, for example, urea, dicyandiamide, melamine, 
polyamide and metal salts of lower and higher fatty acids, e.g., calcium 
stearate. 
These antioxidants and anti-acid agents may be used each alone or as a 
mixture of two or more of them. When stearamide or lauric acid 
diethanolamide is used as the amide compound of this invention, the resin 
composition of this invention which further contains antioxidant amine(s) 
such as alkyl-substituted diphenylamine shows an especially excellent 
thermal stability. 
In exercising this invention, joint use of an additive for improving the 
dispersion of carbon black, for example, an oligomer, besides the 
above-mentioned additives, is recommended. 
The oligomer is a low molecular weight polymer which per se gives only low 
moldability. For ease in the addition operation, it should preferably be 
in a solid state at normal temperature. 
As examples, paraffin wax, microcrystalline wax, polyethylene wax, 
polypropylene wax and other polyolefin waxes may be cited. 
Polyethylene wax may be manufactured by thermal decomposition of high 
molecular weight polyethylene resin produced by a high-pressure process or 
by direct polymerization of ethylene monomer. Generally, polyethylene 
waxes whose molecular weights are reduced by thermal decomposition at such 
a high temperature as above 300.degree. C. contain some branched and polar 
groups and, therefore, are particularly preferable in dispersibility, 
etc., to polyethylene waxes mainly composed of hydrocarbons obtained by 
direct polymerization. Cited as an example of conventional dispersants for 
carbon black is oil. These dispersants may be used as a mixture of two or 
more of them. With these dispersants which enable better dispersion of 
carbon black and reduction in the amount of amide compounds added, 
polyacetal resins having uniform mechanical properties are obtainable. The 
joint use of the amide compounds and polyethylene wax further improves the 
thermal stability. The amount of addition of such polyolefin wax as the 
aforementioned polyethylene wax is 0.3-3 weight % of the resin 
composition, preferably 0.5-2 weight %.