Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-02-12
2003-03-04
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S708000, C252S609000, C558S080000, C558S092000, C558S093000, C558S200000
Reexamination Certificate
active
06528559
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to crosslinked phenoxyphosphazene compounds, a process for the preparation thereof, flame retardants, flame-retardant resin compositions and moldings of flame-retardant resins.
BACKGROUND ART
Synthetic resins are widely used in various fields such as electric and electronic products, office automation equipment, office equipment and communications equipment because of their excellent molding processability, mechanical properties, appearance and the like. The resins used in certain applications are required to have flame retardancy for protection against the heat and ignition of internal parts in devices and appliances.
In order to impart flame retardancy to synthetic resins, a flame retardant is generally added to the resin prior to molding of the resin. Flame retardants are roughly classified into two groups, i.e., halogen-containing flame retardants and halogen-free flame retardants.
Examples of halogen-containing flame retardants include tetrabromobisphenol-A and like organic halogen compounds; tris(chloroethylphosphate), tris(2,3-dibromopropyl)phosphate and like halogen-containing organic phosphorus compounds. Halogen-containing flame retardants produce high flame-retardant effects but also reduce heat stability of matrix synthetic resins, cause deterioration and discoloration of the resins and further have the following drawbacks. Halogen-containing flame retardants undergo thermal decomposition to generate hydrogen halide, thereby causing corrosion of metallic molds, and further produce low molecular weight toxic halogen compounds as byproducts during molding or burning.
Examples of halogen-free flame retardants include magnesium hydroxide, aluminum hydroxide and like inorganic metal hydroxides; triphenyl phosphate (TPP), resorcinol bis(diphenylphosphate)(RDPP), trixylyl phosphate (TXP) and like organic phosphorus compounds (EP Patent No. 174,493, Dutch Patent No. 8,802,346, Japanese Unexamined Patent Publication No. 1,079/1993 and U.S. Pat. No. 5,122,556).
The inorganic metal hydroxides exhibit flame retardancy due to water generated by thermal decomposition. Since water merely produces low flame retardant effects, the inorganic metal hydroxide must be added in a large amount to provide a sufficient level of flame retardancy. However, such a large amount addition entails a disadvantage that the inherent properties of synthetic resins (e.g., mechanical properties) are impaired.
The organic phosphorus compounds produce comparatively high flame-retardant effects. However, since these compounds are liquid or low melting solid and have a high volatility, it is necessary to use a low temperature for molding a resin composition containing an organic phosphorus compound, and there always arise problems such as blocking during kneading, and migration of the organic phosphorus compound to the surface (juicing) during kneading or molding. Moreover, resin compositions containing said organic phosphorus compound have the drawback of dripping (falling of molten resin droplets) during burning and spreading of a fire due to the dripping. Consequently, in order to obtain a rating of V-0 (flaming does not continue for more than a specified period, and there are no molten resin drips which ignite cotton) in a flame retardancy test UL-94 (Testing for Flammability of Plastic Materials for Parts in Devices & Appliances, which is a standard test for evaluating flame retardancy), by adding an organic phosphorus compound to a resin, it is necessary to add a fluorine-containing resin such as polytetrafluoroethylene (PTFE) as an agent for preventing dripping of molten resin during burning. However, the fluorine-containing resin contains halogen and evolves toxic gases during combustion.
Known as flame retardants are phenoxyphosphazene compounds obtained by reacting dichlorophosphazene with a monohydroxy compound such as phenol. For example, proposed is adding a phenoxyphosphazene compound to a thermoplastic resin, such as polyamide resin (Japanese Examined Patent Publication No. 53,746/1981), polycarbonate resin (Japanese Unexamined Patent Publication No. 37,149/1976), polycarbonate or a mixture of polycarbonate and other thermoplasitic resins (Japanese Unexamined Patent Publication No. 292,233/1995) or a mixture of aromatic polycarbonate and rubber-styrene resin (Japanese Unexamined Patent Publication No. 53,009/1997), or to a thermosetting resin such as epoxy resin (Japanese Unexamined Patent Publication No. 225,714/1996).
Such incorporation of phenoxyphosphazene may increase the limit oxygen index (LOI) value (an index of flame retardancy) but does not impart sufficiently improved flame retardancy to the resin and inevitably reduces heat resistance and mechanical properties of the resin.
Further, Japanese Unexamined Patent Publication No. 47,042/1976 proposes using as a thermoplastic aromatic polyester flame retardant a phosphazene compound prepared by substituting chlorine atoms of dichlorophosphazene with monohydroxy compounds (e.g., alkali metal phenolate) so as to have a substitution degree of 3.9 to 6 (based on the dichlorophosphazene trimer) and further substituting the residual chlorine atoms with alkali metal diphenolate (e.g., an alkali metal salt of 4,4′-isopropylidene diphenol).
However, when the phosphazene compound prepared by the production method disclosed therein is incorporated into a thermoplastic resin such as polyester or polycarbonate, the molecular weight of the thermoplastic resin decreases and moldings of the resulting resin composition will have low mechanical properties and low heat resistance and fail to have a sufficiently high flame retardancy. This tendency becomes more evident with the lapse of time from the production of the resin moldings.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a novel phosphazene compound which can greatly improve flame retardancy.
Another object of the invention is to provide a flame retardant which, when incorporated into a thermoplastic resin or a thermosetting resin, does not reduce the molecular weight of the resin and thus does not impair the mechanical properties or heat resistance of the resin.
A further object of the invention is to provide a process for preparing the foregoing phosphazene compound.
Other features of the present invention will become apparent from the following description.
The present inventors carried out extensive research to achieve the above objects, and finally succeeded in producing a new crosslinked phenoxyphosphazene compound which is useful as a flame retardant for synthetic resins, and completed the present invention.
According to the present invention, there is provided a crosslinked phenoxyphosphazene compound characterized in that:
at least one phosphazene compound selected from the group consisting of a cyclic phosphazene compound represented by the formula (1)
(wherein m is an integer of 3 to 25 and Ph is a phenyl group) and a straight- or branched-chain phosphazene compound represented by the formula (2)
(wherein X
1
represents a group —N═P(OPh)
3
or a group —N═P(O)OPh, Y
1
represents a group —P(OPh)
4
or a group —P(O)(OPh)
2
, and n is an integer of 3 to 10000 and Ph is as defined above)
is crosslinked with at least one crosslinking group selected from the group consisting of o-phenylene group, m-phenylene group, p-phenylene group and bisphenylene group represented by the formula (3)
(wherein A is —C(CH
3
)
2
—, —SO
2
—, —S— or —O— and z is 0 or 1);
(a) each of the crosslinking groups is interposed between the two oxygen atoms left after the elimination of phenyl groups from the phosphazene compound;
(b) the amount of the phenyl groups in the crosslinked compound is 50 to 99.9% based on the total amount of the phenyl groups in said phosphazene compound represented by the formula (1) and/or said phosphazene compound represented by the formula (2); and
(c) the crosslinked phenoxyphosphazene compound has no free hydroxyl groups in the molecule.
According to the present inv
Nakacho Yoshifumi
Nishioka Yoichi
Tada Yuji
Yabuhara Tadao
Otsuka Chemical Co. Ltd.
Sanders Kriellion A.
Sughrue & Mion, PLLC
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