GB2125796A - Flame retarding extruded plastics foam compositions - Google Patents

Abstract

A flame retarding extruded plastic foam composition comprising a minor amount up to 5 weight percent, and preferably from 1 to 2 weight percent, pentabromochlorocyclohexane.

Description

SPECIFICATION Flame retarding extruded plastics foam compositions This invention relates to extruded plastics foam compositions. One aspect of the invention relates to extruded plastics foam compositions having improved flame retarding characteristics. A further aspect of the invention relates to the use of pentabromochlorocyclohexane to reduce flame spread, fuel contribution and smoke density when extruded plastics foam compositions are subjected to an open flame.

Extruded plastics foam compositions have become recognized and appreciated as important materials for the manufacture of a wide variety of commercial products including, for example, thermal and acoustic insulation products, cushioning and packaging materials, furniture components, building materials, and the like. However, problems have been encountered by those of ordinary skill in the art in producing plastics foam compositions that resist burning and, when employed as building materials, that comply with the codes and standards established by such widely recognized organizations as the International Congress of Building Officials (ICBO), the Southern Building Congress International (SBCC) and the Building Officials and Code Administrators International (BOCA).Thus, numerous extruded plastics foam compositions otherwise suitable for various uses and applications have either been rejected or else have received limited use because of their inability to retard or inhibit burning.

According to the present invention, extruded plastics foam compositions are provided that demonstrate unexpected and significantly improved resistance to burning when compared to compositions commercially available or disclosed in the prior art. The compositions of the invention generally exhibit lower flame spread, fuel contribution and smoke density when subjected to an open flame than have previously been obtained with otherwise comparable, commercially available products.

According to one embodiment of the invention there is provided an improved flame retarding extruded plastics foam composition comprising a minor amount up to 5 weight percent, and preferably from 1 to 2 weight percent, pentabromochlorocyclohexane.

According to another embodiment of the invention there is provided an improved flame retarding extruded plastics foam composition comprising a minor amount up to 2 weight percent of pentabromochlorocyclohexane in combination with minor effective amounts of either calcium silicate or 2,2 bis-stearamide, or both. In one such embodiment, the improved flame retarding extruded plastics foam composition comprises from 1 to 2 weight percent pentabromochlorocyclohexane and from 0.3 to 0.7 weight percent calcium silicate. In another preferred embodiment of the invention, the improved flame retarding extruded plastics foam composition comprises from 1 to 2 weight percent pentabromochlorocyclohexane, from 0.3 to 0.7 weight percent calcium silicate, and from 0.3 to 0.4 weight percent 2,2 bis-stearamide.

According to yet another preferred embodiment of the invention, there is provided a low density, extruded plastics foam pipe insulation comprising from 2 to 7 weight percent of a styrene-butadiene block copolyment, from 0.3 to 10 weight percent nucleator further comprising from 1 to 2 weight percent pentabrnmochlorncyclohexan-e, from 0.1 to 1.5 weight percent lubricant fruther comprising from 0.3 to 0.4 weight percent 2,2 bis-stearamide, from 10 to 19 weight percent blowing agent, and the remainder being at least one thermoplastics resin such as low density polyethylene.

Extruded plastics foam compositions falling within the scope of the invention generally comprise at least one thermoplastic resin, a nucleator, a lubricant, a blowing agent, and a flame retarding component comprising a minor amount up to 5 weight percent pentabromochlorocyclohexane as disclosed herein. In addition to these components, it is understood that the compositions of the invention can also include without limitation such optional ingredients as rubbers, ionomer resins, coloring agents, ultraviolet light stabilizers, and the like.

Satisfactory thermoplastics resins for use in the compositions of the invention include both crystalline and amorphous polymeric materials such as, for example, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene, polyethylene, polypropylene, and terephthalates. Although it is understood that formulations, process variables, and operating conditions can vary according to the thermoplastics resin employed and the particular end product desired, the types and quantitiies of flame retarding components disclosed herein as preferred for making the compositions of the invention are substantially the same in each instance, and will therefore be described in relation to a preferred extruded flame retarding plastics foam composition comprising low density polyethylene.

Conventional extruded low density polyethylene foam compositions typically comprise at least one nucleator, lubricant, blowing agent, and thermoplastics resin. More recently, superior low density polyethylene foam compositions have been discovered that comprise from 2 to 7 weight percent rubber, from 0.3 to 10 weight percent nucleator, from 0.1 to 1.5 weight percent lubricant, from 10 to 19 weight percent blowing agent, and the remainder low density polyethylene. Satisfactory rubbery materials for use in such low density polyethylene foam compositions include, for example, polybutadiene, polyisoprene, polyisobutylene, styrenebutadiene block copolymers, and other copolymers having a high butadiene content. The rubber is preferaly provided in pellet or particle form, such pellets or particles being comparable in size to those of the polyethylene resin employed therewith.Compositions containing less than about 2 weight percent rubbery material generally do not exhibit the degree of flexibility that is considered to be desirable for many applications, while compositions containing more than about 7 weight percent rubber may fail to achieve adequate homogeneity during extrusion, with some discrete rubber particles carrying through into the final composition. In some cases, an ionomer resin is blended with the polyethylene and rubber in an amount ranging up to about three parts per hundred of the polyethylene component by weight. The ionomer resin functions as a wall improver in the compositions, contributing to better elongation in the melt during extrusion and better stretch and barrier characteristics in the cell walls of the resulting product.A minor amount of carbon black can also be included in the compositions to function as both a coloring agent and an ultraviolet light absorber. The use of about 1 weight percent of carbon black dispersed in polyethylene has proven particularly satisfactory for this purpose.

Extruded low density polyethylene foam compositions generally comprise from 0.3 up to 10 weight percent nucleator material. Conventional nucleators include, for example, talc, powdered metals, pigments, where other similar powder type materials whose particles can serve as nuclei on which the tiny droplets of blowing agent can condense as it is injected into the extruder. The particle size of the nucleator material must be extremely fine, and should preferably be able to pass through a 325 mesh screen.

According to the present invention, flame retarding extruded plastics foam compositions are made by incorporating into the nucleator material a minor amount up to 5 weight percent pentabromochlorocyclohexane, preferably in combination with minor effective amounts of either calcium silicate or 2,2 bis-stearamide, or both. Pentabromochloroglycohexane, calcium silicate and 2,2 bis-stearamide are all available in powder form and, together with the primary nucleator such as, for example, magnesium silicate, are easily admixed or blended with the thermoplastic resin and other components prior to introducing them into the extruder. The preferred flame retarding extruded plastic foam compositions of the invention comprise a minor amount up to 5 weight percent, and preferably from 1 to 2 weight percent pentabromochlorocyclohexane.One preferred embodiment of the invention comprises from 1 to 2 weight percent pentabromochlorocyclohexane and from 0.3 to 0.7 weight percent calcium silicate.

Another preferred embodiment of the invention comprises from 1 to 2 weight percent pentabromochlorocyclohexane, from 0.3 to 0.7 weight percent calcium silicate, and from 0.3 to 0.4 weight percent 2,2 bis-stearamide. In each case, the disclosed amount of flame retarding components is preferably included with the other nucleator material in the extrusion process to make the flame retarding extruded plastic foam compositions of the invention.

According to a particularly preferred embodiment of the invention there is provided a flame retarding low density, extruded plastic foam pipe insulation comprising from 2 to 7 weight percent of a styrenebutadiene block copolymer, from 0.3 to 10 weight percent nucleator further comprising from 1 to 2 weight percent pentabromochlorocyclohexane, from 0.1 to 1.5 weight percent lubricant further comprising from 0.3 to 0.4 weight percent 2,2 bis-stearamide, from 10 to 19 weight percent blowing agent, and the remainder being at least one thermoplastic resin such as low density polyethylene.

In the preferred embodiment comprising a flame retarding low density, extruded plastic foam pipe insulation, from 0.1 to 1.5 weight percent lubricant is combined with the thermoplastic resin, rubber and nucleator prior to extrusion. In this regard, it should be noted that the preferred lubricants for use with the compositions of the invention are themselves powders, and therefore serve to some degree as nucleators during the extrusion process. Satisfactory lubricants for use in the compositions of the invention include without limitation any of the powdered lubricants commonly employed for similar applications in the plastics industry.According to one preferred embodiment of the invention, the lubricant comprises a mixture of about four parts by weight calcium stearate per part of Acrowax C (a powdered synthetic wax manufactured by Glyco Chemicals, Inc. of Greenwich, Connecticut) which is believed to be a 2,2 bis-stearmide. In this embodiment the 2,2 bis-stearmide is believed to function as both a lubricant and nucleator, in addition to contributing to the flame retarding characteristics of the extruded product. In some cases, the lubricity achieved through the use of synthetic waxes aione may be so great that the cell to cell fusion in the end product is adverseiy affected. However, by employing a mixture of another powdered lubricant such as calcium stearate in combination with the synthetic wax in the suggested proportions, this tendency is successfully controlled.

The composition of the preferred low density polyethylene foam pipe insulation further comprises from 10 to 19, and preferablyfrom 12 to 15 weight percent of a blowing agent. Satisfactory blowing agents for use in the invention include methyl chloride, carbon dioxide, ammonia, air, normal pentane, isopentane, fiuorocarbons, and mixtures thereof. A preferred blowing agent for use in the flame retarding low density polyethylene foam pipe insulation is a mixture comprising 80 weight percent Freon 114 and 20 weight percent Freon 11. (Freaon 114and Freon 11 aretrademarksforfluorocarbon products manufactured by Du Pont de Nemours, E.l., Co., Wilmington, Delaware). The blowing agent expands rapidly as the plastic foam composition exits from the extruder, creating the individual cells characteristic of the end product. In general, increasing the volatility of the blowing agent will increase the rate at which the expansion takes place and the size of the cells formed. However, where the volatility of the blowing agent is too great and exceeds the tensile strength of the material comprising the cell wails at the exit temperature, a significant number of cells may overexpand, thereby adversely affecting the product. Plastic foam compositions made with highly volatile blowing agents suffer the further disadvantage of cell shrinkage or partial collapse as the foamed product begins to cool downstream of the extrusion die. Taking these factors into consideration, desirable results have now been achieved by empioying a major amount of a less volatile blowing agent together with a minor amount of blowing agent having higher volatility.Upon exiting the extrusion die, the more volatile component will rapidly expand to increase the cell size without rupturing the cell wall. Then, as thje plastic foam composition begins to cool, the heavier blowing agent component will aid substantially in preventing undesirable cell shrinkage or collapse.

The novel compositions of the invention can be made on a conventional plastic foam extrusion apparatus by methods known to those of ordinary skill in the art. In the conventional process utilized in the plastics industry for extruding plastic foam compositions, the therm plastic and rubbery materials, together with the nucleator, lubricant, the flame retarding components disclosed herein, and other optional components including without limitation ionomer resin, coloring agent, ultraviolet light stabilizer, and the like are blended, placed in a feed hopper, and thereafter delivered to the feed zone of a tandem screw-type extruder.As the composition moves along the extruder screw, the components thereof are further mixed and blended, and the plastic and rubbery components are subjected to shearing and compressive forces that tend to heat the composition, forming it into a substantially continuous flowable mass. As the composition continues down the barrel of the first extruder, the blowing agent is injected into the barrel under high pressure such as, for example, 5000 psi. Once inside the barrel, the blowing agent is mixed with the thermoplastic composition and condenses around the nucleator particles contained therein. This condensation is enhanced by the fact that the nucleator particles, being very fine, are not sheared by the action of the extruder screw and remain cooler than the surrounding metal.According to the conventional process, the composition exiting from the first extruder is fed through another feed port into the second extruder. The barrel of the second extruder is typically jacketed and supplied with a circulating cooling medium to reduce the temperature of the composition passing through it. Upon reaching the end of the second extruder, the composition is forced through an annulus in an extrusion die, whereupon it rapidly expands. Expansion of the extrudate occurs since the external pressure is reduced to atmospheric level upon exiting the die, permitting the blowing agent to expand around each nucleator particle, thereby forming the individual cells.

The novel compositions disclosed herein demonstrate unexpected and significantly improved resistance to burning when compared to compositions commercially available or disclosed in the prior art.

The compositions of the invention generally exhibit lower flame spread, fuel contribution and smoke density when subjected to an open flame than has previously been obtained with otherwise comparable, commercially available products. More particularly, the subject compositions have consistently and significantly outperformed similar compositions which did not contain the flame retarding components disclosed herein when tested in accordance with the provisions of ASTM Designation E-84-75.

Although for illustrative purposes, the detailed description of how to make the compositions of the invention has been primarily directed to a flame retarding, low density plastic foam pipe insulation, it will be readily apparent to those of ordinary skill in the art that the same methods are generally applicable to the analogous flame retarding compositions comprising other component materials and ranges as are herein disclosed.

Claims (10)

1. A flame retarding, extruded plastics foam composition comprising a minor amount up to 5 weight percent pentabromochlorocyclohexane.

2. A composition according to Claim 1, wherein the pentabromochlorocyclohexane is present in an amount ranging from 1 to 2 weight percent.

3. A composition according to Claim 1 or 2, comprising a minor amount up to 2 weight percent of pentabromochlorocyclohexane in combination with minor effective amounts of calcium silicate and 2,2 bis-stearamide.

4. A composition according to Claim 3, wherein the calcium silicate is present in an amount ranging from 0.3 to 0.7 weight percent.

5. A composition according to Claim 3 or 4, wherein the 2,2 bis-stearamide is present in an amount ranging from 0.3 to 0.4 weight percent.

6. A composition according to Claim 5, comprising from 1 to 2 weight percent pentabromochlorocyclohexane, from 0.3 to 0.7 weight percent calcium silicate, and from 0.3 to 0.4 weight percent 2,2 bis-stearamide.

7. A flame retarding, extruded plastics foam composition according to Claim 1, substantially as hereinbefore described.

8. A flame retarding, low density, extruded plastics foam pipe insulation comprising from 2 to 7 weight percent of a styrene-butadiene block copolymer, from 0.3 to 10 weight percent nucleator further comprising from 1 to 2 weight percent pentabromochlorocyclohexane, from 0.1 to 1.5 weight percent lubricant further comprising from 0.3 to 0.4 weight percent 2,2 bis-stearamide, from 10 to 19 weight percent blowing agent, and the remainder being at least one thermoplastics resin selected from crystalline and amorphous polymeric materials.

9. A plastics foam pipe insulation according to Claim 8, wherein the thermoplastics resin is low density polyethylene.

10. Aflame retarding, low density, extruded plastics foam pipe insulation according to Claim 8 substantially as hereinbefore described.