Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2000-09-15
2003-04-08
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S031000, C528S032000, C528S033000, C528S034000, C528S035000, C525S100000, C525S393000, C525S474000, C525S477000, C525S478000
Reexamination Certificate
active
06545116
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a flame retardant for thermoplastic resins and a flame retardant resin composition.
BACKGROUND ART
Thermoplastic resins have been widely used in electric and electronic parts, office automation devices, household articles and building materials. However, thermoplastic resins have the defect that they are generally inflammable. Therefore, the improvement has been attempted by incorporation of various flame retardants. For instance, incorporation of organic halogen-containing compounds or organic phosphorus compounds has been widely conducted for this purpose. However, most of the organic halogen-containing compounds and organic phosphorus compounds have a problem in toxicity. In particular, organic halogen-containing compounds have the problem that they generate a corrosive gas at the time of burning.
In order to solve these problems, it has been investigated to impart a flame resistance by incorporation of polyorganosiloxane compounds (hereinafter also referred to as “silicone”). For example, Japanese Patent Publication Kokai No. 54-36365 discloses that a flame retardant resin is obtained by kneading a non-silicone polymer with a silicone resin composed of monoorganopolysiloxane.
Japanese Patent Publication Kokoku No. 3-48947 discloses that a mixture of a silicone resin and a salt of a group IIA metal imparts a flame retardancy to thermoplastic resins.
Japanese Patent Publication Kokai No. 8-113712 discloses a process for obtaining a flame retardant resin composition by dispersing into thermoplastic resins a silicone resin prepared by mixing 100 parts by weight of a polyorganosiloxane with 10 to 150 parts by weight of a silica filler.
Japanese Patent Publication Kokai No. 10-139964 discloses that a flame retardant resin composition is obtained by incorporating a solvent-soluble silicone resin having a weight average molecular weight of 10,000 to 270,000 into a non-silicone resin containing an aromatic ring.
However, although the silicone resins disclosed in the above publications impart a flame retardancy to some extent, they lower the impact resistance of resin compositions if incorporated in an excess amount and, therefore, it has been difficult to obtain flame retardant resin compositions having well-balanced flame resistance and impact resistance.
It is an object of the present invention to provide a flame retardant of low environmental load which does not generate a harmful gas when burns.
A further object of the present invention is to provide a flame retardant thermoplastic resin composition of low environmental load which does not generate a harmful gas when burns and which has an excellent impact resistance.
DISCLOSURE OF INVENTION
The resent inventors have found, as a result of making an intensive study in order to achieve the above objects, that crosslinked particles of a specific polyorganosiloxane can be used as a flame retardant for thermoplastic resins, and thermoplastic resin compositions containing the polyorganosiloxane crosslinked particles are excellent not only in flame resistance but also in impact resistance.
The present invention provides a flame retardant for thermoplastic resins comprising crosslinked particles of a polyorganosiloxane which have a toluene-insoluble matter content of at least 50% by weight and an average particle size of 0.01 to 2,000 &mgr;m.
Preferably, the polyorganosiloxane crosslinked particles are prepared by emulsion polymerization of a mixture of 50 to 99.5% by weight, especially 60 to 98.5% by weight, of an organosiloxane and/or a difunctional silane compound, 0.5 to 50% by weight, especially 0.5 to 39% by weight, of a silane compound having a functionality of at least 3, and 0 to 40% by weight, especially 0.5 to 30% by weight, of a polymerizable vinyl group-containing silane compound.
Further, the present invention provides a flame retardant resin composition comprising a thermoplastic resin and 0.1 to 50 parts by weight of the above-mentioned flame retardant per 100 parts by weight of the thermoplastic reisn.
BEST MODE FOR CARRYING OUT THE INVENTION
The flame retardant for thermoplastic resins of the present invention comprises crosslinked particles of a polyorganosiloxane which have a toluene-insoluble matter content of not less than 50% by weight and an average particle size of 0.01 to 2,000 &mgr;m.
The term “polyorganosiloxane” as used herein indicates a polyorganosiloxane, a modified polyorganosiloxane wherein 1 to 20% by weight, preferably 1 to 10% by weight, of a polyorganosiloxane is replaced with an organic polymer having no polyorganosiloxane segment (e.g., butyl acrylate polymer, styrene-butyl acrylate copolymer, styrene-acrylonitrile copolymer, or methyl methacrylate polymer), and the like. The modified polyorganosiloxane includes a modified polyorganosiloxane wherein a polyorganosiloxane and an organic polymer having no polyorgaosiloxane segment are chemically bonded, and a modified polyorganosiloxane wherein a polyorganosiloxane and an organic polymer having no polyorgaosiloxane segment are merely coexist. The content of the organic polymer in the modified polyorganosiloxane is not more than 20% by weight, preferably not more than 10% by weight.
The content of toluene-insoluble matter in the polyorganosiloxane crosslinked particles measured by immersing 0.5 g of the crosslinked particles in 80 ml of toluene at room temperature for 24 hours is from 50 to 100% by weight, preferably 60 to 100% by weight. Also, the average particle size of the crosslinked particles obtained by a light scattering method or electron microscopic observation is from 0.01 to 2,000 &mgr;m, preferably from 0.01 to 1,000 &mgr;m. If the content of toluene-insoluble matter is small, the flame resistance-impact resistance balance tends to be deteriorated. If the average particle size is too small or too large, the flame resistance-impact resistance balance tends to be deteriorated.
It is preferable from the viewpoint of good flame resistance-impact resistance balance that the variation coefficient in particle size distribution of the above-mentioned average particle size (100×standard deviation/average particle size (%)) is from 10 to 100%, especially 20 to 80%. It is difficult to obtain the particles having a variation coefficient of less than 10%. If the variation coefficient is too large, the flame resistant effect tends to be lowered.
The polyorganosiloxane crosslinked particles can be prepared, for instance, by polymerizing a polyorganosiloxane-forming component comprising (a) an organosiloxane and/or a difunctional silane compound, (b) a silane compound having a functionality of at least 3, and optionally (c) a polymerizable vinyl group-containing silane compound. Preferably, the polyorganosiloxane crosslinked particles is prepared by polymerizing, for instance, a polyorganosiloxane-forming component comprising (a-1) an organosiloxane having an aromatic group and/or a difunctional silane compound having an aromatic group, (a-2) an organosiloxane having no aromatic group and/or a difunctional silane compound having no aromatic group, (b) a silane compound having a functionality of at least 3, and (c) a polymerizable vinyl group-containing silane compound.
The component (a-1) serves to impart a flame resistance. As the component (a-1) is used at least one member selected from the group consisting of organosiloxanes having an aromatic group and difunctional silane compounds having an aromatic group. Examples of such an organosiloxane are, for instance, cyclic siloxanes such as trimethyl-triphenylcyclotrisiloxane and tetramethyltetraphenylcyclotetrasiloxane. Examples of the difunctional silane compound are, for instance, diphenyldimethoxysilane, diphenyldiethoxysilane, diphenyldichloro-silane, phenylmethyldimethoxysilane, phenylmethyldichlorosilane, and the like. Of these, diphenyldimethoxysilane and diphenyldichlorosilane are preferably used from the viewpoints of economy and reactivity.
The component (a-2) constitutes the main backbone of polyorganosiloxane chain, and as the component
Hamaguchi Shigeki
Miyatake Nobuo
Nakamori Daisuke
Takikawa Kazunori
Armstrong Westerman & Hattori, LLP
Kaneka Corporation
Szekely Peter
LandOfFree
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