1. Field of the Invention
This invention relates to a non-vinyl composition useful as a surface covering material. More particularly, it relates to a floor tile composition comprising a mineral filler and a binder that is a blend of a heteropolymer and an ionomer resin.
2. Description of the Prior Art
A widely used resinous binder material having particular utility in surface coverings is based on those polymers of vinyl chloride, such as the thermoplastic poly(vinyl cloride). When properly compounded with an assortment of plasticizers, heat and light stabilizers, fillers and pigments, the resultant vinyl composition displays satisfactory physical, traffic abrasion and stain resistance properties, such finding particular use as flooring materials. The economics of formulations employing these vinyl polymers particularly favors high filler loadings. However, the cavalier addition of filler materials to the vinyl resin binder is disadvantageous to those commercially important physical properties mentioned above. For example, one of the least expensive filler materials commonly used in vinyl compositions is calcium carbonate. Its sole use in vinyl formulations is generally deterimental to the compounding operation, requiring careful handling at slow speeds on sheet or calendar rolls. Fluidity of the resultant molten mass is generally so high that the melt strength is negligible and proper calendering is all but impossible. Lack of dimensional stability, as exhibited by sheet shrinkage upon removal from the calendar (nerve), is a further problem in these formulations. Of course, many difficulties with the calcium carbonate-only filled compositions can readily be resolved by the use of fibrous fillers, especially asbestos. Compositions containing such filler material display good melt strength, exhibiting the proper degree of viscous flow and melt elasticity, so that they can be readily sheeted, calendered and/or transported without excessive tearing or elongation in the manufacturing process. However, the use of asbestos has recently found a great deal of disfavor since various medical researchers and government officials have suggested that exposure to asbestos fiber-containing products may pose a serious health peril to the general public. At the preset time, many states and municipalities are contemplating or have preliminarily passed legislation to end the use of asbestos in the confines of their jurisdiction. The manufacturing of asbestos-free compositions has, therefore, become a prime goal in the flooring industry.
Additionally, vinyl chloride resins themselves have become subject to health hazard study. The monomer, vinyl chloride, is a noted carcinogen. This, in concert with the recent scarcity of the monomer-forming starting materials, suggests the importance of discovering non-vinyl resin binders.
In U.S. Letters Pat. No. 3,904,579, a novel flooring composition is disclosed that comprises a plasticized vinyl chloride polymer compounded with a terpolymer comprising vinyl chloride/vinyl C.sub.2 -C.sub.4 alkanoate/C.sub.2 -C.sub.4 alkene and filler. While the composition contains no asbestos, the terpolymer comprises at least 75% to 80% of the composition, such containing vinyl chloride. Chlorinated polyethylene is disclosed to be of use in place of, or along with, poly(vinyl chloride) in this formulation. However, the use of such does little to eliminate the use of vinyl chloride in the compounded composition.
Iononic copolymers, generally known as ionomers, are recognized as having unusual properties. However, their use in flooring compositions is severely restricted since they generally have disadvantageously low use temperatures. At normal room temperatures, these copolymers display extensive creep, such accompanied by a rapid decrease in modulus. Further, processing problems using these ionic materials are severe due to their great tenacity for metal surfaces.