Detergent composition

Cleaning and liquid contact with solids – Processes – Using solid work treating agents

Reexamination Certificate

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C134S022140, C134S022160, C134S022190, C134S039000, C134S042000, C510S188000, C510S245000, C510S362000, C510S400000, C510S466000, C510S475000, C510S511000

Reexamination Certificate

active

06551411

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a detergent for removing a resin itself as well as additives such as colorant contained therein which remain in a molding machine used for injection molding or extrusion molding of a thermoplastic resin (which may hereinafter be referred to simply as “resin”) after completion of process such as coloring, mixing or molding of the resin.
BACKGROUND ART
Generally, an extrusion molding machine or an injection molding machine is used for conducting such processes as coloring, mixing or molding of a resin. Upon completion of these processes, there remain in the molding machine the resin itself and the additives such as colorant contained therein. If a same molding machine is used successively for molding the resins of different types or different colors, the residues of the previous operations stay as contaminants in the molded product to impair its visual appearance.
For removing these residues from the molding machine, several methods have been proposed and practically used, including a method comprising manually taking-apart and cleaning of the molding machine, a method in which the molding machine is kept running and filled with a molding material to be used next after the end of every round of operations so as to gradually replace the residue, and a method comprising use of a detergent.
When a molding machine, after use, is cleaned with a detergent and before the next round of molding operation, it is common practice to displace the residual detergent with the next supply of molding material. Therefore, the detergent used for this purpose is required to meet both the requirement to show a high detergency for the molding material used in the preceding molding operation and the requirement to be easily and effectively displaceable by the molding material used for the next molding operation.
Also, since various types of resin are often treated by a same molding machine in the molding operations, the detergent used for such a molding machine needs to be capable of showing a high detergency as well as easy displaceability for such various types of resin.
The conventional detergents, however, have been mostly designed for high detergency alone, and therefore the development of a detergent having not only high detergency but also easy removability (displaceability) has been desired.
Some of the present inventors had previously proposed a detergent comprising a styrene-based resin and a specific graft polymer as a preparation having excellent detergency combined with easy displaceability, and they also proposed to contain a specified amount of water or to contain glass fiber or glass particles in the detergent to enhance its detergency (U.S. Pat. No. 5,298,078). However, inclusion of glass fiber or glass particles in the detergent has problems that such inclusion could damage the interior of the molding machine when cleaned or clog the filter portion of the molding machine, and that it is necessary to take appropriate measures to prevent adverse effects to the working environment such as stimulation to the worker's skin.
Some of the present inventors had also proposed a detergent comprising a thermoplastic resin and a thermoplastic ultra-high-molecular-weight polymer as a product with excellent detergency and easy displaceability (JP-A 8-155969). In this detergent, however, if compatibility between the thermoplastic resin and the thermoplastic ultra-high-molecular-weight polymer is poor, part of the thermoplastic ultra-high-molecular-weight polymer might separate away and stay as powder in the detergent. In such a case, when the detergent is supplied to the hopper of a molding machine, the ultra-high-molecular-weight polymer powder would adhere to the hopper and mix in the molding material charged into the hopper after cleaning, thus necessitating much time for displacing the residual detergent.
U.S. Pat. No. 5,236,514 discloses a detergent comprising a thermoplastic resin and a higher fatty acid metal salt, and especially proposes a cleaning resin composition containing this detergent and an abrasive material selected from diatomaceous earth, ceramic particles, aluminum oxide, calcium carbonate, titanium dioxide, silica, minerals such as kaolin, mica, wollastonite, and the like. This cleaning resin composition is described as being capable of efficiently cleaning away a fluoroelastomer remaining in an extruder used for the molding operations. In this composition, however, diatomaceous earth is actually used as the abrasive material, so that when this composition is used as a detergent, it is unable to show a satisfactory detergency especially when it is used for removing general-purpose resins such as styrene- or olefin-based resins or engineering resins such as polycarbonate or polyphenylene resins. This composition is also unsatisfactory in displace-ability.
U.S. Pat. Nos. 4,838,945 and 5,124,383 disclose the cleaning resin compositions comprising an inorganic compound such as powdery calcium silicate having a specific particle size and a water-repellent compound such as silicone, but these compositions still fall short of the satisfactory level of detergency and displaceability.
DISCLOSURE OF THE INVENTION
The present invention is addressed to the solution of the above outstanding problems in the art of detergents. That is, the present invention is intended to provide a detergent composition which, without using glass fiber or glass particles, is capable of effectively cleaning away a resin remaining in a molding machine after a molding operation and also shows high detergency and easy displaceability for the residues of various types of resins such as general-purpose resins and engineering resins.
As a result of intensive studies for solving the above problems, the present inventors found that the detergency and displaceability of a detergent can be remarkably improved in comparison with the conventional detergents by using a thermoplastic resin containing wollastonite and water, and this finding led to the attainment of the present invention.
Thus, the present invention provides a detergent composition effective for cleaning away a residual resin in a molding machine after a molding operation, said composition comprising a thermoplastic resin, water and wollastonite.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described in detail below.
The detergent composition of the present invention is characterized by containing a thermoplastic resin, water and wollastonite.
In the present invention, it is possible to use a wide variety of thermoplastic resins commonly used for injection molding or extrusion molding, and these resins can be used either alone or as a combination. Examples of the thermoplastic resins usable in this invention include styrene-based resins such as polystyrene, ethylene-based resins such as polyethylene, propylene-based resins such as polypropylene, methyl methacrylate-based resins such as polymethyl methacrylate, polyvinyl chloride, polyamide-based resins, polycarbonate, polybutene and the like. Of these resins, styrene-based resins are preferred.
The “styrene-based resins” refer to polystyrene and copolymers of styrene and one or more other monomers, of which the styrene content is 50% by weight or more. As the “other monomers” to be copolymerized with styrene, there can be used, for instance, acrylonitrile and butadiene. Examples of such styrene-based resins include polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer and the like. It is especially preferred to use a styrene-acrylonitrile copolymer, particularly the one of which the acrylonitrile content is 5% or more by weight and less than 50% by weight, because of high detergency and reduced tendency to remain in the molding machine.
The molecular weight of the thermoplastic resin used in the present invention, although not specifically defined, is preferably in the range of 200,000 to 300,000, and its melt flow rate is preferably 0.5 to 30 g/10 min, more preferably 0.5 to 10 g/10 min, even mo

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