Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-08-14
2004-01-06
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S445000, C524S446000, C524S515000, C524S847000, C524S913000
Reexamination Certificate
active
06673855
ABSTRACT:
The present invention concerns polyolefin compositions with high flame resistance. These compositions are suitable to be used in several applications, e.g. as insulating material in electric wires and cables, as extruded sheets for waterproofing roofs and tunnels, in manufacturing raceways and pipes, general purpose extruded articles and gaskets. Said compositions comprise a thermoplastic olefin polymer in admixture with an elastomeric olefin polymer, an inorganic hydrated filler capable to release water at the combustion temperature of the composition, an organic nitrogen-containing flame retardant compound and preferably an inorganic anhydrous filler. The polymeric components are preferably modified with a small amount of a functional monomer to improve the compatibility with the fillers. No crosslinking treatment is made on the compositions of the invention. It is known that inorganic hydrated fillers, such as magnesium hydroxide and aluminum hydroxide, when present in suitable amount in the polyolefin compositions afford to reach a good level of flame resistance.
In particular, said hydrated inorganic fillers improve the flame resistance of polyolefins as shown for instance by values of the L.O.I. (limiting oxygen index) as high as or even higher than 24-25%. To perform so effectively, the inorganic hydrated fillers must be present in relatively high amount, which involves a worsening of the physical mechanical properties, surface appearance of the extruded articles and electrical properties, in particular volume resistivity.
Inorganic anhydrous fillers are well-known inexpensive fillers, useful to improve physical mechanical properties and extrusion properties without a significant impairing of the excellent electrical properties of the olefin polymers.
Inorganic anhydrous and hydrated fillers do not produce smoke during combustion, are not corrosive and are not released from compositions if exposed to water or humidity.
Nitrogen containing organic compounds are also known for their flame retardant activity. Melamine in particular is used as organic filler to fire retard polymeric materials. Its action is supposed to be based on the dilution of the combustible gases from thermal degradation of the polymeric matrix with incombustible gases from sublimation and decomposition of melamine itself. The use of melamine has also the advantage to decrease the specific weight of the fire retarded materials. On the other hand, melamine is slightly soluble in hot water and is a relatively soft filler, which affects abrasion resistance of final items and mechanical properties. The combined use of inorganic hydrated fillers, inorganic anhydrous fillers and melamine compounds is shown in the Japanese published patent application Hei 7 (1995) 330980. This application describes compositions consisting of at least an elastomeric and usually crosslinked copolymer selected from ethylene/alpha-olefin, ethylene/alpha-olefin/diene and ethylene/vinyl acetate copolymers and of a mixture of additives able to give a high flame resistance, such a mixture comprising per 100 parts of polymer by weight:
from 50 to 300 parts by weight of an hydrated metal oxide,
from 1 to 40 parts by weight of a melamine compound,
from 1 to 50 parts by weight of talc.
The compositions disclosed in said patent application contain therefore from 21 to 75% by weight of hydrated metal oxide and from 0.2 to 21% by weight of the melamine compound referred to the total weight of the composition, the ratio of the percentage amounts of these compounds ranging therefore from about 1 to about 375.
In the working examples of the same patent application the minimum amount of hydrated metal oxide is about 46% referred to the total weight of the composition and the minimum ratio of the percentage amount of the hydrated metal oxide to the percentage amount of the melamine amount is about 4.7.
The total amount of the fillers in the polymeric compositions of said patent application is kept at a still acceptable low level, so avoiding an extreme worsening of the physical mechanical properties and of the volume resistivity. The obtained compositions are usually crosslinked to reach the best balance of the physical mechanical properties and can be used in typical applications of the elastomeric polymers.
On the other hand it is desirable to get a good balance of the flame resistance and physical mechanical properties also in the non-crosslinked polyolefin compositions comprising thermoplastic and elastomeric polymers.
Now the applicant has found that the best balance of flame resistance, physical mechanical properties, extrusion properties and volume resistivity in the case of non-crosslinked polyolefin compositions is obtained when the amount of inorganic hydrated fillers is less than or at most equal to 40% by weight with reference to the total weight of the composition. The present invention concerns in particular polyolefin compositions comprising (percent by weight):
A) from 20 to 60%, preferably from 30 to 45% by weight of a heterophasic olefin polymer composition comprising a crystalline olefin polymer (a) and an elastomeric olefin polymer (b), said composition (A) being optionally modified with at least one functional monomer in an amount from 0.005% to 0.6% by weight, preferably from 0.01% to 0.3%, referred to the total weight of the total composition;
B) from 15 to 40%, preferably from 18 to 35% by weight of one or more than one inorganic hydrated fillers;
C) from 12 to 40%, preferably from 22 to 35% by weight of one or more than one organic flame retardants containing nitrogen in the molecule;
D) from 0 to 40%, preferably from 10 to 25% by weight of one or more than one inorganic anhydrous fillers.
The compositions of the instant invention can be worked with the machines, in particular the extruders, normally used to work the thermoplastic polymers, without undergoing any subsequent thermosetting reaction. Moreover the compositions of the instant invention typically have a limiting oxygen index higher than or equal to 25 and are classified V0. V1 or V2 according to the UL 94 method (Underwriters Laboratories, “vertical burning test method”), keeping at the same time a good level of the other desired properties.
The heterophasic olefin polymer composition A) preferably comprises: (a) a portion consisting either of a crystalline propylene homopolymer, in particular isotactic polypropylene, or of one or more than one crystalline copolymers of propylene with ethylene and/or other alphaolefins, in particular C
4
-C
10
alphaolefins e.g. 1-butene, 1-hexene, 1-octene and 4-methyl-1-pentene, or of a mixture of said homopolymer with said copolymers; and (b) a portion consisting of elastomeric olefin copolymer(s). Examples of said elastomeric olefin copolymers are ethylene-alphaolefin copolymers and ethylene-alphaolefin-diene terpolymers, wherein the alphaolefin preferably has 3 to 10 carbon atoms, e.g. propylene, 1-butene, 1-hexene, 1-octene and 4-methyl-1-pentene and the diene preferably is 1,3-butadiene, 1,4-hexadiene or 5-ethylidene-2-norbornene. In said elastomeric copolymers the ethylene content can range between 20 and 70% by weight whereas the diene, if present, is usually less or at most equal to 10% by weight. Particular examples of heterophasic compositions suitable as component A) are the heterophasic compositions comprising (percent by weight):
a) 10-60%, preferably 20-50%, of a propylene homopolymer with an isotacticity index value (determined as percent by weight of the polymer insoluble in xylene at 25° C.) higher than 80, preferably between 90 and 98, or a propylene crystalline copolymer with ethylene and/or C
4
-C
10
alphaolefins containing at least 85% of propylene and having an isotacticity index value of at least 80 or a mixture thereof;
b) 0-40%, preferably 2-40%, more preferably 2-25%, of a copolymer fraction containing ethylene and insoluble in xylene at 25° C.;
c) 15-90%, preferably 15-78%, more preferably 30-75%, of an ethylene copolymer with propylene and/or C
4
-C
10
alphaolefins and optionally a diene, conta
Braga Vittorio
Goberti Paolo
Marchini Roberta
Zucchelli Ugo
Basell Poliolefine Italia S.p.A.
Cheung William
Wu David W.
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