Fire-retardant polyolefin compositions

Details Fire-retardant polyolefin compositions Fire-retardant polyolefin compositions

2001-02-27

2004-05-18

Szekely, Peter (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S127000

Reexamination Certificate

active

06737456

ABSTRACT:

FIELD OF THE INVENTION
This invention is in the field of flame-retardants. More particularly, it relates to fire-retardant polyolefin compositions.
BACKGROUND OF THE INVENTION
Brominated organic compounds are commonly used as additives for retarding and slowing the flammability of plastic compounds they are blended with. They may be blended alone or in combination with other brominated or non-brominated flame-retardants in a synergistic manner. Optionally, additional compounds may be added to the blend in order to achieve good flame-retarding results and maintain durability. In general brominated aliphatic compounds are more effective flame-retardants than brominated aromatic compounds since they tend to break down more easily (International Plastics Flammability Handbook, 2
nd
edition, Jurgen Troitzsch, p. 45).
GB 2,085,898 discloses a self-extinguishing polyolefin composition containing polypropylene, a brominated arene together with Sb
2
O
3
and a free radical initiator. JP 63/027,543 discloses a flame-retardant polyolefin composition comprising a blend of chlorinated polyethylene and polyethylene, together with an organic brominated compound and Sb
2
O
3
, a free radical initiator and a metal hydroxide. U.S. Pat. No. 4,430,467 discloses a self-extinguishing propylene polymer where the propylene polymer is blended with 5,6-dibromonorbornane and a free radical initiator. This flame-retardant has low bromine content and it is not melt blendable.
Another flame-retardant widely used in polyolefins is Tetrabromobisphenol A bis (2,3-dibromopropyl ether) (International Plastics Flammability Handbook, 2
nd
edition, Jurgen Troitzsch, p. 56), but it suffers from heavy blooming and has limited UV stability. By “blooming” it is meant that a separation of the additive from the polymer matrix occurs, which has a negative effect on the surface appearance of the plastic articles. Many of the above mentioned flame-retardants require the additional use of antimony trioxide as a synergist.
Another flame-retardant used in polyolefins is tris(tribromoneopentyl) phosphate, which is also known as tris(3-bromo-2,2(bromomethyl)propyl) phosphate. Some of the advantages of this flame-retardant are: minimal impact upon the properties and the processing of the polymer; easily extrudable with polypropylene; free flowing powder; melt and mix with polypropylene resin to give a uniform product; exceptional heat stability which results in processing stability, storage stability, and performance permanence; it can be used without antimony trioxide, for instance, for the production of fine denier polypropylene fibers (Proceedings of the Flame Retardants '96 Conference, p. 107).
Only a combination of very high loadings of tris(3-bromo-2,2 (bromomethyl) propyl) phosphate with antimony trioxide give rise to a composition that may pass the UL (Underwriters Laboratory) 94 V-0 test. Such a composition is not commercially competitive.
WO 98/17,718 discloses adding a halogenated flame-retardant having at least one halogen atom attached to an aliphatic carbon atom to tris(tribromoneopentyl) phosphate in order to achieve V-0 in the UL 94 test in a polyolefin at a low loading. U.S. Pat. No. 5,393,812 discloses a composition of polyolefin, a phosphate or phosphonate ester of a halogenated organic compound and a light stabilizer of a certain type.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide non-blooming flame-retardant polyolefin formulations having good flame-retardancy, excellent UV and light stability, and excellent thermal stability.
It is yet another object of the present invention to significantly improve the flame-retardancy of tris(tribromoneopentyl) phosphate, which is known to be less efficient than other commercial flame-retardants in similar applications (Proceedings of the Flame Retardants 2000 Conference, p. 82).
It is a further object of the present invention to achieve very short burning time in polypropylene objects.
Still yet another object of the present invention is to provide a polyolefin with a higher standard of flame-retardancy, such as UL 94 V-0, and excellent thermal stability with a low amount of halogenated aliphatic compounds and without the use of halogenated aromatic compounds.
In addition a further object is to provide a flame-retardant polyolefin formulation containing tris(tribromoneopentyl) phosphate and polyolefin that does not include antimony trioxide.
Thus, the flame-retardant polyolefin composition of the present invention comprises:
(a) At least one polyolefin;
(b) tris(tribromoneopentyl) phosphate; and
(c) free radical source
The polyolefin may be a polymer blend comprising at least 20% (w/w) polypropylene. It may either be a homopolymer or a copolymer. The amount of the tris(tribromoneopentyl) phosphate is preferably in the range of about 0.5% to about 20% (w/w) of the entire composition, and the amount of the free radical source is in the range of between about 0.01% to about 4% (w/w) and preferably in the range of between about 0.05% to about 2% (w/w).
The composition may further comprise another fire-retardant compound, which may serve as a synergist. In such a composition, the amount of the organic brominated compound may be reduced, thus leading to a lower amount of bromine in the composition, which makes the composition more economic.
DETAILED DESCRIPTION OF THE INVENTION
The present invention deals with flame-retardant polyolefin compositions, which, due to their unique additives to the polyolefin and the percentage in the composition, retain most of the physical characteristics of a pure polyolefin polymer while attaining strict fire-retardance standards. The flame-retardancy properties of the olefin composition are achieved by selecting an appropriate brominated compound and a free radical source. The brominated compound is tris(tribromoneopentyl) phosphate which is also known as FR-370 (manufactured by Dead Sea Bromine Group). The compound is a very stable brominated aliphatic compound, which does not undergo chemical reactions common to aliphatic brominated compounds. This stem from the fact that there is no hydrogen atom bound to the carbon atom, which is in the &bgr;-position in relation to the bromine, thus avoiding the possible elimination of HBr.
The free radical source in accordance with the present invention is an organic compound which is stable at processing temperatures of about from 150° C. to about 250° C., and decomposes above these temperatures (at about from 220° C. to about 350° C.) to give relatively stable free radicals. Examples of free radical initiators are 2,3-dimethyl-2,3-diphenyl-butane and 2,3-dimethyl-2,3-diphenyl-hexane.
The polyolefins useful in this invention (sometimes also referred to as “polyolefin resins”) may be derived from a variety of monomers especially from propylene, ethylene, butene, isobutylene, pentene, hexene, heptene, octene, 2-methyl propene, 2-methyl butene, 4-methylpentene, 4-methyl hexene, 5-methyl hexene, bicyclo (2,2,1)-2-heptene, butadiene, pentadiene, hexadiene, isoprene, 2,3 dimethyl butadiene, 3,1 methyl pentadiene 1,3,4 vinyl cyclo hexene, vinyl cyclohexene, cyclopentadiene, styrene and methyl styrene. The polyolefins include copolymers produced from any of the foregoing monomers and the like, and further include homopolymer blends, copolymer blends, and homopolymer-copolymer blends. The polyolefins may be in a molding grade, fiber grade, film grade or extrusion grade
The preferred polyolefins are polypropylene and polyethylene, including atactic, syndiotactic and isotactic polypropylene, low density polyethylene, high density polyethylene, linear low density polyethylene, block copolymers of ethylene and propylene, and random copolymers of ethylene and propylene. The polyolefins useful in this invention may be produced using a variety of catalytic processes including metallocene-catalyzed processes. The polymers may have a broad range of melt flow indexes (MFI) but will typically have MFI values in the range 0.5 to 30. The invention finds particular applications in polyme

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