Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-06-08
2003-08-26
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S157000, C524S236000, C524S425000
Reexamination Certificate
active
06610767
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an antistatic inorganic filler which has an antistatic effect by itself and which can impart antistatic properties to plastic and rubber materials when the inorganic filler is incorporated into these materials; a resin composition containing the inorganic filler; and a method for preparing the inorganic filler.
Fillers, which have conventionally been used in plastic and rubber materials, are surface-treated with a hydrophobic substance such as stearic acid or oleic acid prior to use in order to improve the compatibility to a matrix such as a plastic material. Since the plastic and rubber materials, to which these fillers are incorporated, are quite susceptible to electrification, it has been common to additionally add an antistatic agent to plastic and rubber materials. In addition, it has recently been proposed to previously treat the surface of fillers for incorporating into plastic and rubber materials with an antistatic agent, as described in, for instance, Japanese Un-Examined Patent Publication (hereinafter referred to as “J. P. KOKAI”) Nos. Sho 56-136849 and Sho 59-138267. However, the use of antistatic agents suffers from problems such as those described below. If an antistatic agent is specially added, the surface resistivity and/or volume resistivity of these materials are not, in fact, sufficiently reduced and any satisfactory antistatic effect is not always expected in case of, in particular, plastic materials such as polyethylene and polypropylene, which are quite susceptible to electrification. Even if the surface resistivity or the like is reduced or a desired antistatic effect can be obtained, most of the antistatic agent is gradually transferred to the surface of these materials and therefore, the effect thereof is only temporary and is not a long-lasting one.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an antistatic inorganic filler which can serve as a filler and can simultaneously impart long-lasting and excellent antistatic properties to substances such as plastic and rubber materials when the filler is added to these materials.
Another object of the present invention is to provide a resin composition comprising the inorganic filler.
A still another object of the present invention is to provide a method for preparing an antistatic inorganic filler.
The present invention has been developed on the basis of such findings that if an inorganic filler is wet-pulverized in the presence of a dispersant or a water-soluble surfactant and then treated with an antistatic agent, the surface of the inorganic filler is in order covered with the dispersant and the antistatic agent and that the foregoing problems associated with the conventional techniques can effectively be eliminated by the use of the inorganic filler having such a double adsorption layer structure (double layer).
According to a first aspect of the present invention, there is provided an antistatic inorganic filler wherein an organic dispersant is applied onto the surface of an inorganic filler and an organic antistatic agent is then applied onto the layer of the organic dispersant.
According to a second aspect of the present invention, there is provided a resin composition which comprises the foregoing inorganic filler.
According to a third aspect of the present invention, there is also provided a method for preparing an antistatic inorganic filler which comprises the steps of wet-grinding an inorganic filler in the presence of an organic dispersant, drying the pulverized filler, mixing it with an organic antistatic agent.
According to a fourth aspect of the present invention, there is also provided a method for preparing an antistatic inorganic filler, which comprises the steps of wet-grinding an inorganic filler in the presence of an organic dispersant, adding an organic antistatic agent to the resulting slurry of the pulverized filler and then drying the mixture.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will hereunder be described in more detail with reference to the following preferred embodiments.
Examples of inorganic fillers to be used in the present invention are various kinds of inorganic substances such as ground calcium carbonate (G.C.C.), precipitated calcium carbonate (P.C.C.), talc, sericite, calcium sulfate, montmorillonite, zeolite, calcium sulfite, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfate and kaolin, which may be used alone or in any combination. In this connection, calcium carbonate, in particular, ground calcium carbonate is preferably used.
In the present invention, such inorganic fillers may directly be wet-ground, but it is preferred that they are previously dry-ground prior to the wet-grind. In this respect, it is preferred to pulverize the inorganic filler to a particle size of not more than 40 mm and preferably to an average particle size of from about 2 mm to 2 &mgr;.
In the method of the present invention, an organic dispersant is first applied onto the surface of the foregoing inorganic filler. The application of the dispersant may be carried out by a variety of methods, but the inorganic filler is preferably wet-ground in the presence of the organic dispersant to obtain an organic dispersant-coated inorganic filler.
More specifically, the application of an organic dispersant is performed by adding an aqueous medium (preferably water) to an inorganic filler in a weight ratio: inorganic filler/aqueous medium ranging from 70/30 to 30/70 and preferably 60/40 to 40/60; adding a dispersant to the resulting dispersion in an amount, as expressed in terms of the solid content, ranging from 0.01 to 5 parts by weight (solid content) and preferably 0.01 to 0.7 part by weight (solid content) per 100 parts by weight of the inorganic filler and then wet-grinding the filler according to the usual method. Alternatively, an inorganic filler is admixed with an aqueous medium in which a dispersant is dissolved in advance in such an amount that the content of the dispersant falls within the range specified above, followed by wet-grind of the filler according to the usual method. The wet-grind may be batch-wise or continuous type one and it is preferred to use media mills which make use of grinding media such as a sand mill, an atrittor, a ball mill. If the inorganic filler is wet-ground in this manner, the resulting filler has an average particle size of not more than 2 &mgr;m and preferably 1 to 0.3 &mgr;m.
Examples of organic dispersants usable in the present invention are (A) water-soluble cationic surfactants, (B) water-soluble anionic surfactants and (C) water-soluble nonionic surfactants.
The water-soluble cationic surfactant (A) used herein as the organic dispersant may be, for instance, primary, secondary and tertiary amine salt type cationic low molecular weight or high molecular weight surfactants and quaternary ammonium salt type cationic low molecular weight or high molecular weight surfactants.
Specific examples of the primary to tertiary amine salt type surfactants are higher alkylamine salts, higher alkylamine ethylene oxide adducts, higher alkylamine ethylene oxide/propylene oxide adducts, SOROMINE A (former I.G. product) type amine salts, SAPAMINE A (former Ciba; now Ciba Geigy Corp. product) type amine salts, AHCOVEL A (Arnold Hoffman Co. product) type amine salts and imidazoline type amine salts.
The quaternary ammonium salt type low molecular weight surfactants may be, for instance, higher alkyl trimethyl ammonium salts, alkyl dimethylbenzyl ammonium salts, SAPAMINE type quaternary ammonium salts, imidazoline type quaternary ammonium salts and alkyl pyridinium salts.
The primary to tertiary amine salt type high molecular weight surfactants may be, for instance, polyethylene imines, polyalkylene polyamine salts, salts of polyamine-dicyandiamide condensates and polydiallylamine salt. The quaternary ammonium salt type high molecular weight surfactants may be, for instance, polystyrene methylaminotrimethyl ammonium salts polydiallyl dimethylammon
Itoh Ryoji
Katayama Seiji
Matsushige Toshiaki
Mita Koji
Takase Yumiko
Burns Doane , Swecker, Mathis LLP
Fimatec Ltd.
Mulcahy Peter D.
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