Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-06-04
2003-06-17
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S079000, C521S096000, C521S098000
Reexamination Certificate
active
06579911
ABSTRACT:
The present invention relates to fire retardant or fire resistant styrene polymer foams and in particular, relates to fire resistant or fire retardant styrene polymer foams having reduced brominated fire retardant.
Over the past several decades, polymer foams have become available in a wide variety of forms, either in answer to a material need in industry, or as a developmental expansion of commercialized precursors. Some of the more popular forms of foamed polymer. compositions take the shape of films, sheets, slabs and profiles. Generally, these products are produced by extrusion methods in which the polymer is converted by heat and pressure into a homogeneous melt and forced through a die into the desired shape. To obtain a cellular structure, the plastic usually incorporates a blowing agent that decomposes under the heat of the extrusion process and releases gases that cause the shape to expand. It is also possible to inject propellants directly into the melt.
Because of the favorable combination of properties, price and ease of processing, styrene polymers, especially polystyrene, are widely used in preparing foam sheets, films and slabs for such divergent end uses as packaging, pipe and tubing, construction and insulation. For example, expanded styrene polymers such as polystyrene are widely used in the insulation of freezers, coolers, truck bodies, railroad cars, farm buildings, roof decks and residential housing. Styrene polymer foams are also used as the core material for structural sandwich panels used in refrigerated truck bodies, mobile homes and recreational vehicles.
There is an increasing demand for improving the fire retardant properties of materials used in vehicles, the building trades and consumer goods, such as furniture, radio and television cabinets, appliance housing, electrical motor housings, and switch boxes. To meet this demand, various steps have been taken to improve the fire retardant properties of thermoplastic polymers in order to make them slower to ignite and to retard flame propagation. Thermoplastic polymers can be rendered flame retardant by compounding with fire retardant additives, including halogenated organic compounds and inorganic compounds such as antimony oxide.
Brominated organic compounds have been used in both foamed and nonfoamed styrene polymer compositions, with most ignition-resistant styrene polymer foam products being made with a brominated fire retardant, optionally including a radical generator synergist or flow promoter. Of the various brominated organic compounds, typically only brominated aliphatics are utilized with vinylaromatic foams, with hexabromocyclododecane (HBCD) being the most common.
While effective in improving flame retardancy, the incorporation of flame retardant additives into thermoplastic polymer compositions can negatively impact the strength of the foam, particularly at higher levels of such additives. In non-foamed polymers, the bromine content is typically quite high, for example, in excess of 5 parts of bromine per 100 parts of styrene polymer. However, in foamed styrene polymers, the degree of bromine loading has to be significantly lower to avoid detrimentally impacting the structural qualities and skin quality of the foam.
For example, when utilizing HBCD as a fire retardant in a styrene polymer foam, a high level of HBCD is required in order to meet fire retardancy requirements, particularly the stringent European fire retardancy tests. Depending on the foam characteristics (for example, density, blowing agents, etc.), the amount of HBCD typically required to meet fire retardancy requirements is from 2.5 percent to 4 percent by weight of the styrene polymer (the higher the foam density, the higher the percentage of HBCD). However, the incorporation of HBCD into the styrene polymer foam at these levels may result in 1) a poor dispersion of the HBCD in the foam, resulting in non-uniform expansion and poor skin quality and 2) a high degree of degradation of the styrene polymer and of the regrinded material in the extrusion process due to excessive heating, resulting in reduction of the molecular weight of the styrene polymer foam and of the regrinded styrene polymer and a resultant drop in physical properties.
Therefore, there remains a need in the art for fire-retardant styrene polymer foams which utilize hexabromocyclododecane (HBCD) as the fire retardant, which meet fire retardancy requirements, and which are amenable to extrusion processes, but which do not exhibit poor structural qualities and/or skin qualities.
Those needs are met by the present invention. Thus, the present invention provides extruded, flame retardant, foamed styrene polymer compositions which utilize hexabromocyclododecane (HBCD) as the fire retardant, which meet fire retardancy requirements, and which are amenable to extrusion processes, but which do not exhibit poor structural qualities and/or skin qualities. The extruded, flame-retardant, foamed styrene polymer compositions of the present invention utilize a fire retardant formulation which is comprised of a mixture of hexabromocyclododecane (HBCD) and a phosphorous compound. The use of the phosphorous compound in the fire retardant formulation allows the use of less than about 2.5 percent of HBCD while maintaining a high level of fire resistance. Because a lower level of HBCD is utilized, the foams of the present invention do not suffer from poor structural qualities and/or skin qualities. Furthermore, the use of such a fire retardant composition allows a production of polystyrene foam with lower foam density, thus effecting appreciable cost savings.
Thus, in one embodiment of the present invention, there is provided a polymer foam composition comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than about 2.5 percent by weight, based on 100 percent of styrene polymer, of HBCD; and 2) from 0.1 percent to 4.0 percent by weight, based on 100 percent of styrene polymer, of a phosphorous compound.
In another embodiment, there is provided a polymer foam composition comprising: a) a styrene polymer; and b) a fire retardant formulation comprising: 1) less than about 2.5 percent by weight, based on 100 percent of styrene polymer, of HBCD; and 2) from 0.1 percent to 4.0 percent by weight, based on 100 percent of styrene polymer, of a phosphorous compound; and c) 0.01 percent to 0.2 percent by weight based on 100 percent of styrene polymer, of a flow promoter.
The present invention provides an extruded, fire-retardant, styrene polymer foam in which the fire retardant formulation is comprised of a mixture of HBCD and a phosphorous compound. The use of the phosphorous compound in the fire retardant formulation allows the use of less than about 2.5 percent of HBCD while maintaining a high level fire resistance. Because a lower level of HBCD is utilized, the HBCD is well dispersed in the foam and the foam is uniformly expanded with good skin quality. In addition, the presence of the phosphorous compound results in a lower density foam. A foam with lower density is formed even though the foaming temperature is lowered to account for the lowering of the glass transition temperature of the styrene polymer (due to the higher solubility of the phosphate compound in the styrene polymer).
The flame retardant foamed polymer compositions of the present invention comprise: a) a styrene polymer; b) a fire retardant formulation comprising HBCD and a phosphorous compound; and optionally, c) a flow promoter.
Suitable styrene polymers for use in the present invention include polystyrene or a copolymer formed from styrene monomer and copolymerizable ethylenically unsaturated co-monomers. The co-monomer content is typically less than about 50 percent, and preferably less than about 20 percent based upon the weight of the styrene polymer. Examples of copolymerized compounds include &agr;-methylstyrene, acrylonitrile, acrylic or methacrylic acids having one to eight carbon atoms, esters of acrylic or methacrylic acid with alcohols having one to eight carbon atoms,
Boukami Sylvie
Vo Chau Van
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