CA2322286A1 - Synergist for flame retardant nylons - Google Patents

Abstract

Antimony-free polyamide molding compositions are disclosed having improved flame resistance. These compositions comprise, in with percent, 20-77 % polyamide having a melting point of 215-340 ~C; 10-60 % inorganic filler; 1035 % of a flame retardant having 50-70 % bormine; 3-10 % zinc borate; and, 0-2 % of a heat stabilizer.

Description

TITLE
SYNERGIST FOR FLAME RETARDANT NYLONS
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. Provisional Application No.
60/078,392 filed March 18, 1998.
BACKGROUND OF THE INVENTION
Field of the Invention The invention relates to polyamide molding compositions having improved flame resistance. More particularly, the invention relates to antimony-free polyamide compositions with superior physical properties.
Description of Prior Art Typically industry uses a variety of antimony compounds (antimony oxides and sodium antimonate) as a synergist to promote the effectiveness of halogen containing flame-retardants and in nylon molding compositions.
Industry has been trying for years to eliminate the toxic heavy metal antimony in flame retardant compositions, but has been unable to develop anything nearly as effective as antimony compounds.
While looking for improved thermal stability in flame retarded high temperature nylons, it was surprisingly found that zinc borate could be used as a direct (equally effective) replacement for antimony compounds in polyamide compositions.
Another unexpected side benefit of this discovery is a significant improvement in physical properties (i.e. tensile strength and elongation to break) by using the zinc borate as a synergist.
SUMMARY OF THE INVENTION
There is disclosed and claimed herein antimony-free polyamide molding compositions with improved flame resistance, comprising, in weight percent, (a) 20 - 77% polyamide, having a melting point of 215 - 340°C, (b) 10 - 60% inorganic filler, (c) 10 - 35% of a flame retardant having SO - 70% bromine, (d) 3 - 10% zinc borate, and (e) 0 - 2% of a heat stabilizer There is further disclosed and claimed herein processes for improving the temperature stability and flame resistance of polyamide resins, comprising the steps of providing a molding composition as above and molding this composition to make a molded part. Molded parts made from such processes are also disclosed.
DETAILED DESCRIPTION OF THE INVENTION
The polyamide used in this invention may be 20-77% (all percentages are weight percent unless designated otherwise) of any polyamide that has a melting point of from about 215°C to about 340°C. An example of a suitable polyamide is a copolyamide composed of 20-80 mole % of units derived from hexamethylene terephthalamide and 80-20 mole % of units derived from hexamethylene adipamide. This polyamide is referred to hereinafter as 6T/66 copolymer. Other suitable polyamides include polyamides composed of 20-80 mole % of units derived from hexamethylene terephthalamide and 80-20 mole % of units derived from hexamethylene sebacamide, hexamethylene dodecamide, hexamethylene isophthalamide, 2-methylpentamethylene terephthalamide, or mixtures thereof.
"Synthetic polyamide," as used herein, includes a polymer which is made by man, and does not include natural fibers such as woofs or silks. By an "aliphatic polyamide" is meant a polymer which has repeat units which include amide groups in the main chain, and in which at least some, preferably at least SO
mole percent, of these amide groups (through the nitrogen atoms andlor carbonyl carbon atoms of the amide groups) are connected to aliphatic carbon atoms.
Preferred polyamides include nylon-6,6, nylon-6, nylon 6,12, and copolymers of nylon-6,6 and nylon 6. Nylon-6,6 and nylon-6, and copolymers thereof, are especially preferred and nylon-6,6 is more preferred.
There are no particular limitations on the process for the production of the copolyamide used in the composition of the present invention. It may be produced easily by ordinary melt polymerization. One method to produce the copolymer of this invention is an autoclave one-step polymerization process taught in US Patent No. 5,378,800 which is incorporated by reference herein.
That process includes feeding to a reactor an aqueous salt solution of an admixture of desired diacids and diamines, heating the solution under pressure, reducing the pressure, maintaining the reaction mixture at a pressure that is not greater than about atmospheric pressure, and discharging the polyamide from the reactor. An alternative process includes preparing a prepolymer and subjecting the prepolymer to solid-phase polymerization or melt-mixing in an extruder to increase the degree of polymerization. The prepolymer is prepared by heating at 150°C-320°C an aqueous solution containing 6T salt (a salt formed from hexamethylenediamine and terephthalic acid) and 66 salt (a salt formed from hexamethylenediamine and adipic acid). An alternative process consists of subjecting 6T salt and 66 salt directly to solid-phase polymerization at a temperature lower than the melting point.
The composition of the present invention contains 10-60% of an inorganic S filler or reinforcing agent that includes, for example, fibrous reinforcement such as glass fiber and carbon fiber, glass beads, talc, kaolin, wollastonite and mica.
Preferable among them is glass fiber. Glass fibers suitable for use in the present invention are those generally used as a reinforcing agent for thermoplastics resins and thermosetting resins. Preferred glass fiber is in the form of glass rovings, glass chopped strands, and glass yarn made of continuous glass filaments 3-20 micron meters in diameter.
The resin composition of the present invention contains 10-3S% of a flame retardant. It is a flame retardant based on brominated polystyrene and/or brominated poly-phenylene ether containing SO-70% by weight bromine. The 1 S polystyrene has a weight-average molecular weight higher than 5000, preferably higher than 20,000, and more preferably higher than 28,000. The ether has a molecular weight of at least 6000. A preferred flame retardant is brominated polystyrene or polydibromostyrene.
As described above, the present compositions comprise 3-10% zinc borate, but no antimony compounds.
Also present may be up to 2% of a heat stabilizer such as copper iodide.
The copolyamide resin of the present invention may have incorporated in it a variety of additives such as an impact modifier, a viscosity modifier, pigment, dye, antioxidant, and heat resistance improver, in such amounts that they do not 2S harm its characteristic properties.
Moreover, the copolyamide resins of the present invention may include up to S% of color concentrate (such as carbon black) as well as up to 1% of lubricant.
Drip suppressants may also be present in amounts of up to S%.
EXAMPLES
The present invention is illustrated by the following examples and comparative examples.
Samples of various compositions were produced on a commercial scale S8°mm twin screw extruder (Werner and Pfleiderer, Ramsey, New Jersey) at 600 pounds per hour. Product was analyzed on a thermogravimetric analyzer (DuPont 3 S Instruments [Series 9S 1 ], DuPont Company, Wilmington, Delaware) measuring weight retention at 340°C after a 30 minute hold. Also samples were tested for standard physical properties following standard ASTM methods.

The nylon used in Examples E 1- E 22 and Comparative Examples CE I -CE 3 was nylon 66/6T (45/55 molar %) with a melting point of about 315°C and in Example E 23 and Comparative Example CE 4 was nylon 66, melting point approximately 265°C. The antimony compound used is 70% antimony trioxide in 66 nylon.
The flammability rating was conducted using UL Test No. UL-94 dated April 19, 1995.

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Claims (7)

What is claimed is:

1. An antimony-free polyamide molding composition with improved flame resistance comprising, in weight percent, (a) 20-77% polyamide, having a melting point of 215-340°C, (b) 10-60% inorganic filler, (c) 10-35% of a flame retardant having 50-70% bromine, (d) 3-10% zinc borate, and (e) 0-2% of a heat stabilizer.

2. The composition of Claim 1 wherein the polyamide (a) is a copolyamide composed of 20 - 80 mole % of units derived from hexamethylene terephthalamide and 80 - 20 mole % of units derived from hexamethylene adipamide.

3. The composition of Claim 1 wherein the inorganic filler (b) is selected from the group consisting of glass fiber, carbon fiber, glass beads, talc, kaolin, wollastonite and mica.

4. The composition of Claim 1 wherein the flame retardant (c) is either brominated polystyrene or polydibromostyrene.

5. The composition of Claim 1 wherein the heat stabilizer (e) is copper iodide.

6. A process for improving the flame retardance of a polyamide resin, comprising the steps of:
providing a molding composition of Claim 1, and molding the molding composition to make a molded part.

7. A molded part made from the process of Claim 6.