Powdery flame retardant

Details Powdery flame retardant Powdery flame retardant

2001-02-14

2003-09-30

Medley, Margaret (Department: 1714)

Compositions

Fire retarding

C252S604000, C524S116000, C524S127000

Reexamination Certificate

active

06627122

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a novel powdery flame retardant.
BACKGROUND ART
Flame retardants for synthetic resins such as phosphazen compounds, phosphoric ester compounds or the like are generally liquid or intrinsically solid. Nevertheless, these flame retardants tend to be produced as a mixture in a liquid or viscous solid state due to homologues or analogues produced as a by-product in the course of production. The flame retardants show the same tendency even if they have a high purity of, e.g. 98% or above.
When the flame retardant is added to a synthetic resin and the like, a powdery substance can be more easily handled and can be more expediently supplied, as a matter of course, than a liquid or viscous solid substance. Further, a powdery substance is more advantageous in packaging or transporting.
To pulverize a liquid or viscous solid substance, a purification method such as recrystallization using an organic solvent or fractional distillation is generally carried out. However, such methods have drawbacks that not only the methods require special equipment and energy as a heat source, but also it is unavoidable to recover and re-use the organic solvent.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a novel powdery flame retardant free from the foregoing prior art problems.
Another object of the invention is to provide a novel powdery flame retardant prepared by pulverizing a flame retardant which is liquid or a viscous solid at ordinary temperature by a simple method free from the prior art problems.
Other objects and features of the invention are apparent from the following description.
According to the invention, there is provided a powdery flame retardant prepared by mixing a flame retardant which is liquid or a viscous solid at ordinary temperature with an inorganic fibrous substance to adhere or adsorb the flame retardant to the fibrous substance, the powdery flame retardant comprising 5 to 70 wt. % of the flame retardant and 95 to 30 wt. % of the fibrous substance.
The present inventors conducted extensive research to achieve the foregoing objects and found that a powdery flame retardant is obtained by merely mixing a flame retardant which is liquid or a viscous solid at ordinary temperature with an inorganic fibrous substance to adhere or adsorb the flame retardant to the fibrous substance, namely that it is obtained by the simple process without impairing the performance of the flame retardant as the starting material.
The present invention was completed based on this novel finding.
The powdery flame retardant of the present invention comprises as effective components a flame retardant which is liquid or a viscous solid at ordinary temperature and an inorganic fibrous substance. The term “liquid at ordinary temperature” used herein refers to a liquid having a viscosity of about 0.3 mpa·s to about 10 Pa·s at 25° C. The term “a viscous solid at ordinary temperature” used herein means a solid having a viscosity of about 10 Pa·s or more at 25° C.
Conventional flame retardants can be used as the flame retardant which is liquid or a viscous solid at ordinary temperature, namely as the raw material for the powdery flame retardant of the invention.
Preferred flame retardants for use as the starting material are, for example, phosphazene compounds, phosphoric ester compounds, organic halogen compounds and the like which are useful in producing a powdery flame retardant in a favorably powdery state. The term “in a favorably powdery state” used herein means a state wherein the powder has a substantially uniform particle size, scarcely solidifies even when stored for a long term and raises no dust in use.
Phosphazene compounds and phosphoric ester compounds are especially preferred as the starting flame retardant because they are free of halogen element which generates a harmful gas or compound on exposure to a high temperature. When a flame retardant resin composition is prepared from the powdery flame retardant of the invention and a synthetic resin, the flame retardant of the invention containing at least one of these starting flame retardants and an inorganic fibrous substance can attain a V-0 level flame retardancy in a test according to the method of flame retardancy test UL-94 (Test for Flammability of Plastic Materials for Parts in Devices and Appliances UL-94, Fourth Edition) without addition of a dripping inhibitor (inhibitor for preventing dripping of flaming particles) such as polytetrafluoroethylene or the like. Consequently the flame retardant of the invention is significantly suitable as a powdery flame retardant for a completely halogen-free flame retardant resin composition.
Phosphazene compounds useful as the starting flame retardant can be any of conventional compounds disclosed in patent publications, literature, etc., specifically in James E. Mark, Harry R. Allcock and Robert West, “Inorganic Polymers” (Prentice-Hall International, Inc., 1992), pp. 61-140.
Stated more specifically, the following compounds (1) to (4) can be exemplified.
(1) A cyclic phosphazene compound represented by the formula (1)
wherein m is an Integer of 3 to 25, two R
1
groups are the same or different and each represents a phenyl group substituted with at least one group selected from an alkyl group having 1 to 6 carbon atoms and an allyl group, or an unsubstituted phenyl group.
(2) A straight-chain phosphazene compound represented by the formula (2)
wherein n is an integer of 3 to 1,000, R
1
is as defined above, X represents a group —N═P(OR
1
)
3
or a group —N═P(O)OR
1
, and Y represents a group —P(OR
1
)
4
or a group —P(O)(OR
1
)
2
.
(3) A crosslinked phosphazene compound wherein at least one of the foregoing phosphazene compounds (1) and (2) is crosslinked with at least one crosslinking group selected from the class consisting of o-phenylene group, m-phenylene group, p-phenylene group, biphenylene group and a group represented by the formula
wherein A is a group —SO
2
—, a group —S—, a group —O— or a group —C(CH
3
)
2
—, each of said crosslinking groups being interposed between the two oxygen atoms left after the elimination of group R
1
from the phosphazene compound (1) or (2), and the amount of the R
1
groups in the crosslinked phosphazene compound being 50 to 99.9% based on the total number of R
1
groups in said phosphazene compound prior to crosslinking.
(4) At least one phosphazene compound selected from the group consisting of a cyclic phosphazene compound represented by the formula (3)
wherein R
2
is a cyano-substituted phenyl group; R
3
is an alkyl group having 1 to 18 carbon atoms or an aryl group having 6 to 10 carbon atoms; these groups may be substituted with at least one group selected from alkyl groups having 1 to 10 carbon atoms, allyl group and aryl groups; when two or more R
3
groups exist, the R
3
groups may be the same or different; p and q are numbers which fulfill the requirements that p>0, q≧0, and p+q=2; and r is an integer of 3 to 25, and a straight-chain phosphazene compound represented by the formula (4)
wherein R
2
, R
3
, p and q are as defined above; s is an integer of 3 to 1,000; X′ is a group —P(OR
2
)
4
, a group —P(OR
2
)
3
(OR
3
), a group —P(OR
2
)
2
(OR
3
)
2
, a group —P(OR
2
)(OR
3
)
3
a group P(OR
3
)
4
, a group —P (O)(OR
2
)
2
, a group —P(O)(OR
2
)(OR
3
), or a group —P(O)(OR
3
)
2
; and Y′ is a group —N═P(OR
2
)
3
, a group —N═P(OR
2
)
2
(OR
3
), a group —N═P(OR
2
)(OR
3
)
2
, a group —N═P(OR
3
)
3
, a group —N═P(O)OR
2
or a group —N═P(O)OR
3
.
These phosphazene compounds can be used either alone or in combination and include a mixture of cyclic and straight-chain phosphazene compounds.
Specific examples of the cyclic phosphazene compound (1) and the straight-chain phosphazene compound (2) include a mixture of phosphazene compounds in which phenoxy groups and/or alkoxy groups are introduced as substituents and which are obtainable from a mixture of cyclic and straight-chain chlorophosphaz

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