Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-12-13
2002-04-30
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S124000, C523S128000, C524S013000, C524S014000
Reexamination Certificate
active
06380282
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electrically conductive molded plastic article and to a method of production thereof, and more particularly it relates to a molded article an electrically conductive, biodegradable and non-biodegradable plastic having blended therein an electrically conductive additive and coconut shell fiber powder to increase electrical conductivity for improving antistatic properties and to a method of production thereof.
BACKGROUND ART
Generally, plastics have high electric resistance and articles made thereof are readily charged by abrasion or contact, and hence they give a shock to human body and cause fire to be induced upon discharge or cause various troubles for production or electrostatic troubles such as erroneous action of IC in electric components. To cope with these, surface treatment with antistatic agents or addition of a conductive substance to the plastics for the purpose of providing conductivity has been performed, in particular carbon black or surfactants have been kneaded upon molding.
However, when a large amount of conductive substance is kneaded in the plastics, the additive bleeds out to make the surface sticky, the localization of additive inhibits the original physical properties of the synthetic resin. Thus, since the amount of the additive usage is limited, the development of a material that exhibits conductivity with only a small amount of additive has been expected.
On the other hand, biodegradable plastics, whose decomposability by bacteria has recently been paid much attention from the viewpoints of prevention of environmental destruction, are used as a raw material mainly for throw-away articles such as agricultural articles, medical materials, or sporting goods as well as to daily necessaries depending on the material. Biodegradable plastics can give a bright aspects in the problem of disposal of plastics materials after use in that they are degraded in the soil, etc. and return to the nature. However, the speed of their biodegradation is unsatisfactory so that the development of means for improving its degradation has been desired.
DISCLOSURE OF THE INVENTION
Objects of the present invention is to promote the effect of conductive additive mixed to remove electrostatic troubles and prevent electrical charging by decreasing electric resistance and improve the degradation of the biodegradable plastics.
As means for solving the above-described two objects, the present inventors have focused on coconut shell fiber powder and completed the present invention.
That is, the present invention relates to an article molded of a plastic mixture comprising the following components:
(A) a plastic: 98 to 59% by weight,
(B) a dry powder of a water-swelling fiber: 1 to 40% by weight, and
(C) a conductive additive: 1 to 20% by weight (wherein the sum of (B) and (C) is 2 to 41% by weight).
In one embodiment, the present invention relates to the molded plastic article, wherein the plastic is a biodegradable plastic.
In another embodiment, the present invention relates to the molded plastic article, wherein the plastic is a non-biodegradable plastic.
In a still further embodiment, the present invention relates to the molded plastic article, wherein the dry powder of water-swelling fiber is a dry powder of coconut mesocarp fiber residue.
In still another embodiment, the present invention further relates to the molded plastic article, wherein the dry powder of coconut mesocarp fiber residue is a coconut shell fiber powder obtained by processing a dry compressed fiber mass of the coconut mesocarp to have a powder having a particle diameter of about 1 to 80 &mgr;m and further hot-air drying the powder to obtain a coconut shell fiber powder having a water content within a range of less than about 3% by weight.
In a further embodiment, the present invention relates to the molded plastic article, wherein the conductive additive is a powder selected from the group consisting of carbon black, carbon fiber, a carbon nano tube, cationic surfactant, nonionic surfactant, and metal oxides.
Also, the present invention relates to a method of producing a conductive molded plastic article, comprising the steps of processing a dry compressed fiber mass of the coconut mesocarp to have a powder having a particle diameter of about 1 to 80 &mgr;m, further hot-air drying the powder to obtain a coconut shell fiber powder having a water content within a range of less than about 3% by weight, preparing a mixture of 98 to 60% by weight of the plastic and 1 to 40% by weight of the coconut shell fiber powder, and molding the resulting mixture into a desired article after blending the mixture with 1 to 20% by weight of a conductive additive.
Hereafter, the present invention will be described in detail.
First, the components of the molded plastic article of the present invention will be described.
<1> Plastic
As the plastic used in the molded plastic article of the present invention, either biodegradable plastics or non-biodegradable plastics may be used.
The biodegradable plastics used in the present invention are not limited particularly so long as they are those plastics degraded in the environment, particularly by the action of microorganism. More specifically, they include polylactic acid, polyhydroxyalkanoate (for example, 3-hydroxybutyric acid (PHB), 3-hydroxyvaleric acid (PHV)), lactone resins, aliphatic polyesters (polyester resins obtained from a low molecular weight aliphatic dicarboxylic acid and a low molecular weight aliphatic diol), complex materials such as cellulose acetate base, polycaprolactone base, complex materials such as modified starch, modified polyvinyl alcohol, etc., other complex materials, and the like.
Also, the non-biodegradable plastics are not limited particularly so far as they are plastics usually used in the production of molded plastic articles, including such as polyethylene, polypropylene, ABS, etc.
When the non-biodegradable plastics are used in the present invention, addition of a small amount of conductive additive can decrease the electric resistance of the plastics to prevent electrical charging. When the biodegradable plastics are used, the degradation of the biodegradable plastics can be improved in addition to the above-described effect.
(2) Dry Powder of Water-swelling Fiber
The dry powder of water-swelling fiber used in the present invention is a powder of a fiber whose volume increases when water is added thereto as compared with the dry state, and is not limited particularly so long as it has this property and can be used for molding of the plastic. In particular, it is preferred that it is biodegradable per se. Preferred dry powder of water-swelling fiber includes a dry powder of coconut mesocarp fiber residue (hereafter, also referred to as “coconut powder”) More preferably, it is coconut shell fiber powder obtained by processing a dry compressed fiber mass of the coconut mesocarp to obtain a powder having a particle diameter of about 1 to 80 &mgr;m and hot-air drying the powder to make its water content within a range of less than about 3% by weight.
FIG. 1
is a side cross-sectional view of a coconut fruit. Coconut is produced in the tropics and in the fruit (1), fiber contained in the mesocarp (
1
a
) (hereafter, referred to as a coconut shell fiber) is light in weight and resilient, and the compressed and dried one has a property that it is expanded to 5 to 6 times in volume when water is added thereto.
The coconut powder used in the present invention, more specifically, is produced as described below. That is, to obtain the coconut powder, the coconut mesocarp is exposed to fresh water to dissolve the coconut sarcocarp and thereafter collecting only a fiber, exposing the fiber to sun light for 1 to 3 years, preferably for 2 years or more, to remove the salt contents and tannin, and further forcible drying by hot air for about 8 hours to reduce its water content within a range of about 10%. Then, fine fragments of the fiber (fiber residue) were obtained, which were compressed subjected to compre
Kilpatrick & Stockton LLP
Szekely Peter
LandOfFree
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