Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-10-23
2002-09-03
Henderson, Christopher (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S096000, C524S100000
Reexamination Certificate
active
06444736
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a flame-retardant polyolefin composition. Precisely, it relates to a composition of good flame retardancy, which comprises a specific polypropylene composition and a flame retardant not containing a halogen atom (hereinafter referred to as a non-halogen flame retardant) added thereto.
More precisely, the invention relates to a flame-retardant polyolefin composition having the advantages of high melt tension, good retention of shape even in burning, much improved flaming drip resistance (flaming drip is meant to indicate the property of resin that will drip when burned according to the vertical burning test of UL94), generation of neither corrosive gas nor toxic gas, good moldability, and good mechanical strength of its moldings.
BACKGROUND ART
The resin for electric appliances shall be a non-combustible resin, a flame-retardant resin or a self-extinguishable resin for protecting them from ignition, combustion or firing to be caused by some electric troubles, and any of such resins are used in producing electric appliances depending on their necessary properties. In particular, polypropylenes are much used for electric appliances, as having the advantages of good impact resistance, stiffness, appearance and moldability, and various proposals have been made for flame retardation of such polypropylenes. Specifically, as in the United States UL Standards (Underwriters Laboratories Incorporation; UL Subject 94), the products themselves or the indicated members of electric appliances are required to have high flame retardancy. For exports to the United States, therefore, the materials must satisfy the requirements stipulated in the UL Standards. Not only in the United States but also in Japan and many other countries including West European countries, electric appliances are required to have high-level flame retardancy. To meet the requirements, various flame-retardant polypropylene resin compositions have been proposed.
Compositions containing a halogen compound that serves as a flame retardant therein generally have good moldability and their moldings have relatively high mechanical strength, and their moldings have high-level flame retardancy, but are problematic in that they often generate corrosive gas and toxic gas while molded or when burned.
Japanese Patent Laid-Open No. 147050/1984 discloses a flame-retardant polypropylene resin composition that contains an ammonium polyphosphate and a triazine compound both serving as a flame retardant therein. The composition has the advantages of good moldability and high mechanical strength of its moldings, and, while molded or when burned, it does not generate so much harmful gas. However, in the vertical burning test of UL Subject 94, “Flammability Test for Plastic Materials for Machine Members” (hereinafter referred to as UL94 burning test), the resin composition disclosed is in the rank V-2 for combustion resistance of {fraction (1/32)} inch-thick test pieces, and can hardly clear the high-level flame retardancy for the rank V-0.
For increasing the flaming drip resistance of polypropylene compositions, it may be taken into consideration to increase and elevate the melt tension and the crystallization temperature of the compositions. For increasing and elevating the melt tension and the crystallization temperature of polypropylene compositions, disclosed are a method of reacting a crystalline polypropylene, while in melt, with an organic peroxide and a crosslinking agent (Japanese Patent Laid-Open Nos. 93711/1984, 152754/1986, etc.); a method of reacting a semi-crystalline polypropylene with a peroxide having a low decomposition temperature, in the absence of oxygen, to produce a polypropylene having free long-chain branches and not containing gel (Japanese Patent Laid-Open No. 298536/1990), etc. Apart from these, other methods have been proposed for increasing the melt viscoelasticity including melt tension of polypropylene compositions by formulating different types of polyethylene or polypropylene that differ in the intrinsic viscosity or in the molecular weight, or by producing the compositions through multi-stage polymerization.
For example, disclosed are a method of producing a composition by adding from 2 to 30 parts by weight of an ultra-high-molecular-weight polypropylene to 100 parts by weight of an ordinary polypropylene followed by extruding the resulting mixture at a temperature falling within a range between the melting point of the mixture and 210° C. (Japanese Patent Publication No. 28694/1986); a sheet produced through extrusion of a two-component polypropylene composition which is prepared in a multi-stage polymerization process and in which the two polypropylene components each have a different molecular weight and the limiting viscosity ratio of the two is at least 2 (Japanese Patent Publication No. 12770/1989); a method for producing a polyethylene composition that comprises three different types of polyethylene each having a different viscosity-average molecular weight and contains from 1 to 10% by weight of high-viscosity, high-molecular-weight polyethylene in a process of melt-kneading or multi-stage polymerization (Japanese Patent Publication No. 61057/1987); a method for producing a polyethylene composition that contains from 0.05 to less than 1% by weight of an ultra-high-molecular-weight polyethylene having an intrinsic viscosity of at least 20 dl/g, through multi-stage polymerization in the presence of a high-activity titanium-vanadium solid catalyst component (Japanese Patent Publication No. 79683/1993); a method for producing a polyethylene composition that contains from 0.1 to 5% by weight of an ultra-high-molecular-weight polyethylene having an intrinsic viscosity of at least 15 dl/g, through multi-stage polymerization in a specific series of polymerization reactor units in the presence of a high-activity titanium catalyst component having been processed for prepolymerization with 1-butene or 4-methyl-1-pentene (Japanese Patent Publication No. 8890/1995), etc.
Also disclosed are a method for producing a polypropylene having high melt tension through polymerization of propylene in the presence of a pre-activated catalyst that comprises a titanium-containing solid catalyst component held on a carrier and an organoaluminium compound component and has been processed for prepolymerization with ethylene and a polyene compound (Japanese Patent Publication No. 222122/1993); and a method for producing a polyethylene-containing ethylene-&agr;-olefin copolymer having an intrinsic viscosity of at least 20 dl/g through copolymerization in the presence of a pre-polymerized catalyst of the same type as above but having been processed for prepolymerization with ethylene alone (Japanese Patent Laid-Open No. 55410/1992).
The above-mentioned proposals for polyolefin compositions and for methods of producing them will be effective for increasing the melt tension of polyolefin compositions in some degree, but are still problematic in that the crosslinked products of the polyolefin compositions proposed are not recyclable and are not stiff at high temperatures. Another problem with the polyolefin compositions containing high-viscosity polyethylene is that the motor load current to be applied to molding machines for them shall increase and the electric power to be consumed for molding them shall therefore increase, and that their productivity and thermal stability are low. These problems with the polyolefin compositions proposed must be solved.
The multi-stage polymerization method in which the step of producing a minor amount of a high-molecular-weight polyolefin is integrated with the essential step of ordinary olefin polymerization is problematic in that it is difficult to delicately control the production condition in forming such a minor amount of a high-molecular-weight polyolefin, and that the method requires a low polymerization temperature for forming such a polyolefin having a satisfactorily high molecular weight. To solve the problems, the apparatus for the proces
Touhara Mitsuhiro
Yamauchi Akira
Chisso Corporation
Henderson Christopher
McDermott & Will & Emery
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