those produced on the floorings of motor showrooms by rubber tyres.
as
The scuff markings first referred to can be removed by rubbing with scouring powder and fine steel wool and, on materials other than thermo- plastic tiles. by wiping with a cloth moistened with turpentine or white spirit. The markings in motor show. rooms, however. are indelible they are caused by interaction be- tween the antioxidants in the rub. ber tyres and the floor finish. Here. prevention is the only real answer, although careful choice of pattern in the flooring can help to mask the effect. Mats, metal strips, or thin sheets of polyethylene are effective safeguards in preventing contact be- tween tyres and floors.
COMPOSITION
Thermoplastic binders
These are termed thermoplastic because they soften when heated and harden again on cooling. At nor- mal temperatures they are usually brittle unless blended with plasticiz
ers.
Large quantities of flooring employ the following binders:
Pitch and petroleum bitumen
dark brown to black substances obtained from the distillation of coal and petroleum respec- tively.
―
Gilsonite a dark brown natural- ly occurring asphaltic material. Coumarone resins
pale yellow substances found in coal tar naphtha. Extensive processing, including polymerization, necessary before they can be used for flooring.
Vinyl resins
is
white resins
synthesized from acetylene. Im- portant members of this group are polyvinyl chloride (PVC), copolymers of vinyl chloride and vinyl acetate containing up to 15% of the acetate, and copolymers of vinyl chloride and vinylidene chloride.
Plasticizers
Plasticiers are usually oily liquids having high boiling points and low volatility. They are used to in- crease the pliability of the binder during the manufacturing process and to provide some measure of
126
control over the flexibility of the finished product.
Fillers
These are used mainly to reduce material costs but they have sub- sidiary uses. e.g. carbon black may sometimes act as a reinforcing agent or even as a means of providing an electrically conducting material, and asbestos fibre helps to improve the handling properties of hot material during the manufacturing process. Most of the powdered fibres used are of mineral origin, e.g. calcium carbonate and china clay. Cellulosic fillers such as sawdust are seldom used since products containing them are more sensitive to moisture; fur- ther, they sometimes lead to high dirt retention by the finish.
Stabilizers
Stabilizers are used mainly to pre- vent degradation of some of the thermoplastic binders during manu- facture. but they also protect the finished flooring subsequently when this is exposed to strong sunlight.
MANUFACTURE AND AVAILABILITY
Thermoplastic flooring tiles
Thermoplastic tiles, as first pro- duced in Britain in 1947, were of almost identical composition with the American asphalt tile': indeed, the first British tiles were sold under the American name. But this type of tile was confused with the totally different compressed rock asphalt tiles already in in Britain (B.S. 1324 and B.S. 1325), and this led to the adoption of the 'thermoplastic tile, although it is generally realised that this term is not entirely appropriate.
use
name
Thermoplastic tiles are made by heating and masticating binders, plasticizers, short-fibre asbestos, powdered mineral fillers and pig.
ments.
The resulting hot mass is passed between rollers, which com- bine heat and pressure, to produce a sheet of appropriate thickness from which the tiles are produced, usually by die-cutting. At ordinary tempera. tures the material is brittle so that it cannot be marketed in sheet form. The binders range from petrolemin bitumen and pitch in the very dark coloured tiles through gilsonite to
coumarone-indene
and coumarone-
styrene resins in the lightest colours. The dark binders and their associat- ed fillers and pigments are cheapest and this is reflected in the lower cost of the dark tiles. The tiles are usually 9 in. square by in. thick, but 3/16 in. thick tiles are also made, as are 6 in. square and 12 in. square units. They are produc- ed in a variety of plain colours and marbled patterns; other patterns, e.g. one simulating the grain and colour of timber, have been made.
PVC (vinyl) asbestos tiles
PVC (vinyl) asbestos tiles, com- monly known as vinyl asbestos tiles, formed a natural development from thermoplastic tiles. They are manu- factured in the same way with ap proximately the same ratio of binder to filler; the difference lies in the binder which consists mainly of vinyl chloride polymer or of copoly mers of vinyl chloride with vinyl acetate. The binder allows the pro- duction of tiles having clearer.
colours and brighter
greater flexibility than thermoplastic tiles, though the material is too inflexible to allow of its marketing in sheet form. There is no relationship be tween colour and price as there is with thermoplastic tiles. Vinyl as-
bestos tiles are produced in four thicknesses, 0.062 in., 0.080 in.. 0.100 in. and 0.125 in.; the standard size is 9 in. square.
Flexible PVC flooring
Flexible PVC flooring is made in both sheet and tile form and in the same thicknesses as vinyl asbestos tiles. The tiles are usually 12 in. square; sheet material is produced in 36-in., 54-in. and 72-in. widths. The binders used are polyvinyl chloride.
of copolymers
vinyl chloride or blends of these. It should be noted that although the binding medium may not be entirely poly- vinyl chloride it is common practice to refer to the binders as PVC; to avoid confusion this description will be used here. Powdered minerals are the most commonly used fillers but some flooring contains a small proportion of asbestos fibre. The ratio of binder (plasticized resin) to filler can vary very widely; some materials contain as much as 85% (Turn to page 128)
THE HONG KONG & FAR EAST BUILDER-VOLUME 18, NUMBER 2