Floor coverings

Details Floor coverings Floor coverings

2000-02-01

2001-09-11

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

Composite

Of addition polymer from unsaturated monomers

C428S523000, C428S203000, C428S204000, C427S372200, C427S358000, C427S428010, C427S385500

Reexamination Certificate

active

06287706

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to floor coverings and more particularly to durable tile or sheet form floor coverings made of one or more layers of polymers suitable for e.g. pedestrian traffic in domestic and/or other situations over an extended period of time.
DESCRIPTION OF THE RELEVANT PRIOR ART
Most floor coverings of this type are based on polyvinylchloride (PVC) polymer. In more detail, PVC polymer resin is generally mixed with a plasticiser (solid or liquid) (usually with various other additives such as fillers, polymer stabilisers, and processing aids) to form a spreadable paste which can be formed into sheets by spread coating using knife or roller coater equipment and then thermally cured e.g. by oven heating.
The use of PVC does however raise significant environmental problems due to the use of chlorine and there is accordingly a need for floor coverings based on alternative polymers. Polyalkene polymers are generally preferred from an environmental point of view but the use of conventional polyalkenes presents significant processing problems and they are not suitable for use in floor covering manufacturing facilities based on spread coating and calendering technology. In addition a particular problem in employing conventional polyalkene polymers in floor coverings, is that they do not provide the necessary physical characteristics required in the final product. In more detail floor coverings produced using conventional polyalkenes have been known to give insufficient tensile and tear strength, abrasion and stain resistance, and elastic recovery.
SUMMARY OF THE INVENTION
It is an object of the present invention to avoid or minimize one or more of the above disadvantages.
It has now been found that a particular class of polyalkenes, which are produced by single site catalysed polymerisation, can be successfully used in floor covering manufacture based on more or less conventional spread coating or calendering technology. More particularly, suitable polyalkenes in accordance with the present invention are those having a relatively narrow molecular weight distribution (MWD) and, a small amount of long chain branching and produced by single site catalysed polymerisation, and having the following characteristics:
a) Melt Index (MI) of from 0.1 to 100
b) Density of from 0.86 to 0.97; and
c) a DRI of from 0.1 to 6.0, preferably from 0.4 to 5.5.
As used herein the following terms have the meanings indicated:
Melt Index (MI) or I
2
is the amount (in grams) of polymer resin which is extruded in a predetermined period of time (10 minutes) as measured in accordance with ASTM (American Standard Testing Method) D-1238 (190/2.16).
Molecular Weight Distribution (MWD) is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (i.e. Mw/Mn).
Density is the mass (in grams) of 1 cubic centimetre of resin as measured in accordance with ASTM D-792 standard.
Dow Rheology Index (DRI) is an index of long chain branching measured by comparing the shift to the right (due to a longer relaxation time), relative to a polymer resin with zero long-chain branching (LCB), in a plot of zero shear viscosity against relaxation time (both from a cross viscosity equation).
Other abbreviations used herein which are common in the art include:
PHR—parts per hundred parts by weight of polymer resin (or principal polymer resin component).
Suitable polyalkenes in accordance with the present invention may also comprise a polyalkene having a relatively narrow molecular weight distribution (MWD) and, a small amount of long chain branching and produced by a single site catalysed polymerisation of at least one, linear, branched or cyclic, alkene having from 2 to 20 carbon atoms. Conveniently the polyalkene comprises a copolymer produced by copolymerisation of two or more alkenes comprising a first linear or branched, alkene having from 2 to 8 carbon atoms and, a second, linear, branched or cyclic, alkene having from 2 to 20 carbon atoms. This allows for greater design flexibility in relation to obtaining sheet materials with particular desired combinations of physical characteristics. In general there may be used up to 15 mole percent of said second monomer. It will of course be understood that where cyclic alkenes are used these may have more than one carbon ring and thus include bicyclic and tetra-cyclic alkenes such as norbornene and tetracyclododecene.
In another aspect the present invention provides a sheet material suitable for use in or as a floor covering and comprising a polyalkene resin in intimate admixture with one or more additives selected from a filler and a spread coating processing aid, wherein said polyalkene resin has a relatively narrow molecular weight distribution (MWD), preferably less than 3.0, and, a small amount of long chain branching and produced by single site catalysed polymerisation, and having the following characterisrics:
a) Melt Index (MI) of from 0.1 to 100
b) Density of from 0.86 to 0.97; and
c) a DRI of from 0.1 to 6, preferably 0.4 to 5.5.
One of the very versatile features of metallocene catalysts is the range of comonomer which may be incorporated into polymeric chains by using such catalysts in the single site polymerisation of alkenes. Metallocene catalysts are, for example, capable of incorporating into polymer chains cyclic monomers, advantageously polycyclic monomers, including cyclic monomers such as norbornene (C
7
H
10
). Thus, for example it is possible to incorporate materials such as norbornene into copolymers with ethylene, which has the benefit of raising the toughness and melting point over conventional PE resins.
The new sheet materials provided by the present invention have the further advantage of suitability for incorporating various design features. It may be possible to incorporate graphic images into the flooring in a manner which will give an image with depth perception. Systems using ion projection technology are well known in the art. These systems use an electrostatic charge corresponding to the desired image. This image is deposited on the material with a drum or belt. The material bearing the electrostatic image is moved through a developer station where a toning material opposite charge adheres to the charged areas of the dielectric surface to form a visible image. Another layer of polymer may be deposited on top of this, and another image produced in this layer. By adding successive layers, each with its own image, it is possible to built a structure with an image depth perception. This art, using conventional resins, is explained in U.S. Pat. No. 5347296.
One advantage of using polymer prepared using metallocence-derived catalysts comes about during the image process. More particularly the use of metallocene catalysts permits the incorporation of boron containing end groups and/or very high levels of unsaturation. These end groups may be functionalized to provide additional means for facilitating imaging. Images may be created either via electrostatic projection systems or by functionalizing these end groups so the polymer chains will better combine with toner or pigments.
In another aspect the present invention provides a sheet material suitable for use in or as a floor covering and comprising a polyalkene resin in intimate admixture with at least one additive comprising a filler, wherein said polyalkene resin has a relatively narrow molecular weight distribution (MWD) and, a small amount of long chain branching and produced by single site catalysed polymerisation of a first, linear or branched alkene having from 2 to 8 carbon atoms and, preferably a second, linear, branched or cyclic, alkene having from 2 to 20 carbon atoms.
Whilst processing aids may be used in the new materials of the present invention, to adjust or accentuate particular processing characteristics such as reduced energy requirements and/or increased processing speed, it is a feature of the polyalkene resins used in the present invention that they do not require the use of a plasticiser thereby significantly reducing e

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