Organoclay/polymer compositions with flame retardant properties

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...

Reexamination Certificate

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Reexamination Certificate

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06610770

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to polymer compositions with flame retardant properties that are made from a polymer blended using a defined process with a smectite clay that has been reacted with a specified mixture of organic materials.
The inventive compositions have the property that when the organically modified clay is added to the polymer, a composite results which has flame-retardant properties.
This invention covers improved polymer compositions with increased char yield and fire retardancy. The use of organoclay is a new, environmentally-benign approach to improve the fire retardance of these polymers. Such polymers will find use, for example, as architectural and construction materials such as interior panels, home sidings, and roofing pads and shingles, automotive parts particularly for car interiors, and in ship and military uses where fire retardancy is required.
2. Background of the Invention
It has long been a goal when using plastic materials to render them resistant to burning. Building codes and other government rules issued by regulatory bodies often require that plastic materials used as structural members or other useful articles pass a series of precise tests to insure that they will not accelerate a fire. In the past, many flame retardant polymer formulations have been developed. These include several classes of materials such as halogenated additives, char chemical producers, and chemical water generators. Each of these prior art materials has its particular strengths and weaknesses as a fire retardant.
The use of synthetic polymers has grown dramatically over the last three decades, as have the research efforts of scientists on controlling polymer flammability. Research and development to that end has focused primarily on fire retardant additives. One way to improve fire resistance has relied on the introduction of aromatic rings into the polymer structure; an increase in the aromaticity yields higher char residues that normally correlate with higher oxygen index and lower flammability. The high cost of these specialized materials and the specialized processing techniques required have limited their use and makes the search for an effective additive even more focused.
The effectiveness of fire retardant fillers has also been limited because the large amounts required for effective performance make processing difficult and the additives often negatively affect some properties of the final polymer compositions. High loadings of fillers can cause problems in the plastic such as loss of strength and flexibility, and discoloration. The relatively high loading of fire retardants needed in some plastics to achieve sufficient reduction in flame spread can also be very expensive.
Particularly disadvantaged prior art materials used as fire retardants are additives containing halogens. Problems associated with these materials include high costs, high use levels, and potential environmental problems. Brominated aromatic compounds, for example, have been widely used as fire retardants for polyolefins and other thermoplastics. In addition to the poor economics of using these materials, other concerns include suspected negative environmental impact and their well-established tendency to generate corrosive by-products during processing or when exposed to fire.
These concerns have established the need for fire retardant systems for polymers with reduced halogen content. It is thus the object of the instant invention to provide a flame retardant blend comprising reduced levels of halogenated compounds.
3. Description of the Prior Art
In the past organoclays have been blended with polymers as fire retardants in circumstances where an additional fire retardant additive was used. Several general articles on polymer-clay blends have included in their discussion a section about fire retardancy—see for example Miller, B.;
Plastics World
, No.10, October 1997, pp. 36-38.
An early patent by Berk Ltd., U.S. Pat. No. 3,516,959, describes an organophilic clay used with at least one additional flame retardant. A variety of thermoplastic polymer composites is described. No attempt is made to show the effect of an organoclay by itself on flame retardancy nor how the degree of dispersion would influence this.
Several specific patents discuss clay-polymer composites in the context of fire retardance. U.S. Pat. No. 4,472,538 discloses clay treated with a chlorosilane to initiate polymerization with an adsorbed monomer to give a composite with excellent flame retardance. The use of silane initiator gives a polymer chemically bound to the clay surface. A second object of the patent is to create a uniformly dispersed polymer-clay composite. No flame testing was done to indicate the degree of flame retardance nor are there comparisons of differing levels of dispersion.
U.S. Pat. No. 5,854,327 by Bridgestone/Firestone discloses a roofing membrane that is made flame retardant by a complex mixture of ingredients. The clay component is treated to make it reactive with the EPDM rubber matrix but no specific flame-retardant properties are associated with the clay.
A General Electric patent, European Patent No. 899,301 A1, describes a non-halogenated flame retardant resin-molding polyester composition that contains organoclay, polysiloxane, and compounds of boron and phosphorus.
A number of authors have made statements in the literature that to achieve the best properties from a smectite clay-polymer composite, it is necessary to achieve the best dispersion possible. This can be described as completely exfoliating the smectite clay into individual platelets separated by the polymer matrix. It has been surmised that it is optimum that the platelets should be in insufficient contact to be chemically associated with each other. It is the fully dispersed state that is frequently held up as the ideal for all developments in the smectite clay/organoclay composite areas.
Several papers and patents explicitly mention the critical need for platelet interlayer distances to be greater than 70 Å to have complete exfoliation/delamination. These papers include: Giannelis, E. P.;
Polymer Layered Silicate Nanocomposites
. Advanced Materials 8, No. 1, pp. 29-35 (1996); and Kishnamoorti, R.; Vaia, R. A.; Giannelis, E. P.;
Structure and Dynamics of Polymer Layered Silicated Nancomposites
, Chemistry of Materials 8, No. 8, pp.1728, (1996).
Several prior art patents go into significant detail on the differences between incompletely exfoliated states and the benefits of fully delaminated clay-polymer composites. A Toyota patent, U.S. Pat. No. 4,739,007, asserts that the best improvements in mechanical properties are observed in composites with platelet spacings greater than or equal to 100 Å. It is clear from the prior literature that fully exfoliated clay-polymer systems have been the goal of researchers working in the field.
It is noted that several papers on flame-retardant polymer compositions not using organoclays show evidence that less than full exfoliation has benefits. For example, Nyden, M. R. and Gilman, J. W.;
Molecular Dynamics Simulations of the Thermal Degradation of Nano-Confined Polypropylene
, Computational and Theoretical Polymer Science, Vol. 7, No. 3/4, pp. 191-8 (1997), shows polypropylene confined by graphite. A minimum in the burning mass loss rate was calculated for polypropylene confined between the graphite sheets at 30 Å. The author did not show any experimental evidence to support the theoretical conclusions.
A United States patent based on a Japanese invention describes polymeric compositions using calcium carbonate and other materials including kaolin clays other than smectites as fire retardant additives to polymers—see U.S. Pat. No. 5,025,057. U.S. Pat. No. 5,091,462, also based on a Japanese invention, shows the addition of an inorganic filler to crystalline polypropylene to improve the heat resistance of the polypropylene in the form of a four or five ingredient resin composition. The inorganic filler can

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