GB2120266A - Floorcoverings made from plastics materials - Google Patents

Abstract

Floorcovering is made from thermoplastic plastics material at least part of which is cross-linked. In a particularly preferred embodiment the cross linking is achieved by exposing processed sheeting made from a thermoplastics material (such as PVC) mixed with a polyfunctional acrylate to electron beam irradiation.

Description

SPECIFICATION Floorcoverings made from plastics materials This invention relates to floor coverings made from plastics materials.

Plastics floorcoverings in sheet and tile form made from thermoplastics materials, such as polyvinyl chloride (PVC), are well known and widely used. However, these floorcoverings suffers from certain well-recognised disadvantages. In particular, due to their thermoplastic properties they can be easily damaged by stubbed cigarettes. Also, shrinkage may occur after laying due to plasticiser loss and relaxation of stresses induced during processing; and resistance to certain solvents may be poor. Traditional linoleum floorcoverings can demonstrate more desirable properties particularly in relation to resistance to melting, but plastics floorcoverings are generally preferred due to their more advantageous properties with regard to flexibility, abrasion resistance and cost and convenience of manufacture.

An object of the present invention is to provide an improved plastics floorcovering having advantageous properties with regard to dimensional stability and resistance to melting and solvent attack.

According to the invention therefore there is provided a floorcovering formed from thermoplastic plastics material characterised in that at least a portion of said plastics material is cross-linked.

As a consequence of this cross-linking it is possible to achieve advantageous physical properties, particularly with regard to dimensional stability and resistance to melting and solvent attack, in the context of a floorcovering formed from plastics material.

The plastics material may be polyvinylchloride, polyvinyl chloride/polyvinyl acetate copolymer, polythene polypropylene or any other suitable polymer, copolymer or mixture thereof.

Most preferably the cross-linking is effected through the intermediary of a polyfunctional acrylate such as a di-acrylate (e.g. tetraethylene glycol dimethacrylate), or a tri-acrylate (e.g. trimethylol propane trimethacrylate), or a tetra-acrylate (e.g.pentaerythritol tetra-acrylate), although any other suitable substance or combination of substances may be used.

Cross-linking may be effected by any suitable technique. A preferred technique involves the use of electron beam irradiation and this may be particularly advantageous in so far as a desired depth and extent of crosslinking can be conveniently achieved by appropriate control of the application of such radiation to the thermoplastic material. It is however also possible to use other techniques including for example the incorporation of a free radical initiator such as a peroxide (e.g. t-butylperbenzoate, dicumyl peroxide, di-t-butyl peroxide) in conjunction with a crosslinking intermediary, such as a polyfunctional acrylate as described above, whereby cross-linking occurs with elapse of time after admixture of the initiator and cros-linking intermediary and/or following application of heat thereto or otherwise.

The floorcovering of the invention may be in the form of large sheets or small tiles with or without adhesive backing as desired. The floorcovering may be wholly of the "homogeneous" kind i.e. of a substantially uniform nature throughout the entire thickness thereof. However, the floorcovering may alternatively be laminated or coated or otherwise of a non-homogeneous nature. The effect of the cross-linking would normally be such as to give a hard surface to the floorcovering and also such as to increase its rigidity. The extent of these effects may be selected as desired.Thus, although it may be preferred that the floorcovering is of sufficient flexibility to enable this to be rolled around a former for transport and/or storage purposes in accordance with customary practice in relation to conventional thermoplastic floorcoverings, if desired, the floorcovering of the invention may be of a hard inflexible nature.

The floorcovering of the invention would normally incorporate one or more additives such as are conventionally used in the formulation of PVC floorcoverings including: plasticisers (e.g. di-octylphthalate, benzyl butyl phthalate, trixylyl phthalate), extending oils (e.g. the oil sold by l.C.l. Limited under the Trade Mark CERECLOR), stabilizers (e.g. metal salts), pigments, and fillers (e.g. ground limestone, or other finely divided inorganic materials such as mica, slate, china clay.

Also, the floorcovering may be processed in conventional manner involving for example steps such as: mixing, calendering or extruding, and surface treatment, to give sheet material which can then be cut to size as desired. By incorporation of pigments and admixture of chips of differently pigmented plastics material a desired marbled or other decorative finish can be obtained.

Where an electron beam technique is utilised, the floorcovering can be exposed to the radiation at any suitable stage, preferably, as a final or late processing stage in the manufacure thereof. Such exposure may be effected by feeding processed sheeting forming the floorcovering continuously beneath a radiation source which may be such as to subject the sheeting to a fixed curtain or a moving scanning beam of electron radiation. Such irradiation may take place as part of a continuous floorcovering manufacturing process whereby the processed sheeting is fed directly from a preceding processing stage (such as a calendering or extruding, or surface treatment stage) to the radiation source. Alternatively, such irradiation may be applied (preferably to the otherwise completely processed sheeting) on a later occasion, even after long storage thereof.

Where cross-linking is effected by incorporation of a free radical initiator, such initiator may be added with other ingredients at an initial mixing stage and the arrangement may be such that cross-linking occurs gradually to give sufficient time for all processing steps to be performed before cross-linking is completed.

As indicated above, the floorcovering may be cut to length and rolled or cut into tiles and this may be effected either before or after irradiation as desired.

The invention will now be described further with reference to the following Example.

Example The following ingredients are blended in conventional manner in an internal mixer such as a Banbury mixer, all parts being by weight.

PVC or PVC/PVA copolymer 100 Plasticiser 10 to 50 Extending Oil 0two30 Stabilizer 0.5 to 3 Pigment 1 to 3 Filler 50 to 500 Polyfunctional Acrylate 5 to 30 The first six of the above ingredients may be the same as those conventionally used in the manufacture of thermoplastic floorcovering. Some examples of suitable substances have already been given. Reference has also already been made by way of example to suitable polyfunctional acrylates.

The blending is carried out at a temperature slightly higher than the melting range of the mixed ingredients, say at or above about 1 500C, and the resulting molten mixture is milled to give strip material.

This strip material is further milled together with differently pigmented plastics chips (to impart a desired marbling or other decorative effect to the final end product), and the material is then calendered or extruded to give sheeting of any desired thickness (say 1 mm to 3mm) and width (say up to two metres). The calendered sheeting is reheated and subjected to mechanical treatment (e.g. embossing flat) to give a desired surface finish. The sheeting is then cooled. The properties of the cooled sheeting depend on the proportion of ingredients. Thus, sheeting made with 500 parts by weight of filler and 30 parts by weight of plasticiser (softener) will be very rigid and brittle whereas sheeting made with higher levels of plasticiser and lower levels of filler will be softer and more flexible.

The procedure so far described (apart from the incorporation of the polyfunctional acrylate) is conventional.

Contrary to conventional practice, however, as a final processing step, the sheeting is subjected to electron beam irradiation. This may be effected as a final or late step in a continuous manufacturing process in which case the sheeting may be fed continuously to electron beam irradiation equipment (e.g. on a conveyor belt at say five to 15 metres/min) from the above-mentioned final mechanical treatment stage (via a cooling station and/orvia a sufficiently long pathway to allow for cooling).Alternatively, the sheeting may be cooled and stored (e.g. in rolled form) and then subjected to electron beam irradiation subsequently when required and as convenient Electron beam irradiation can be effected by passing the sheeting beneath an electron beam outlet of electron beam irradiation equipment (such as the equipment sold by Radiation Dynamics Inc. under the Trade Mark DYNAMITRON). The equipment has an electron-emitting filament at one end of an evacuated accelerator tube to which a very high voltage is applied. Emitted electrons are accelerated to high velocities down the tube to form an intense, high energy, pencil beam which can be scanned backwards and forwards (under the influence of a constantly changing magnetic field) so as to emerge through a thin metallic window as a vertically downwardly directed fan-shaped radiation configuration.

The sheeting is advanced continuously (e.g. on a conveyor belt) under this metallic window within a screened irradiation chamber with the sheeting horizontal and the entire width of the upper surface thereof exposed to the radiation beam. The concentration of electrons is defined by the "dose rate", and this is typically five to eight mega rads for PVC. The energy or penetrating power of the electron beam is determined by the electron voltage and ampage and these are typically 1.5 x 105 ##to 3 x 106eV and 10-5 to 10-4 amps (i.e. between .150 and 1.5 mega electron volts and 10 to 100 milliamps.

The radiation is capable of penetrating into the body of the sheeting and the degree of penetration and duration of irradiation are selected in accordance with the desired nature of the end product. Thus where a high degree of hardness and inflexibility is required, the arrangement may be such that the sheeting is irradiated throughout its thickness and for an appreciable period of time. Where softness and flexibility are important the sheeting may be su bjected to shorter duration irradiation and/or lower energy radiation such that only the surface region of the sheeting is appreciably irradiated. Where irradiation is confined to a surface layer, this may be only at the top surface of the sheeting. Alternatively, the irradiation process may be applied (e.g. in successive procedures) to both the top and the bottom surfaces of the sheeting.

The sheeting may be cut to length and rolled or cut into tiles after irradiation as required.

It is of course to be understood that the invention is not intended to be restricted to the above details which are described by way of example only. Thus, for example, in place of (or in addition to) the irradiation technique, cross-linking may be effected by incorporation of an initiator (as discussed hereinbefore) for example in the range 0.05 to 3 parts by weight in addition to the above ingredients of the Example.

Claims (16)

1. A floor covering formed from thermoplastic plastics material characterised in that at least a portion of said plastics material is cross-linked.

2. A method of forming a floorcovering according to claim 1, wherein ingredients including thermoplastic plastics material are mixed and further processed to give sheet material which is then cut to size, characterised in that at least a portion of said plastics material is cross-linked.

3. A method according to claim 2, wherein the plastics material is selected from polyvinylchloride, polyvinylchloride/polyvinylacetate copolymer, polythene, and polypropylene.

4. A method according to claim 2 or 3, wherein the cross-linking is effected through the intermediary of a polyfunctional acrylate.

5. A method according to claim 4, wherein the said acrylate is selected from diacrylates, such as tetraethylene glycol dimethacrylate, triacrylates, such as trimethylol propane trimethacrylate, tetraacrylates such as pentaerythritol tetraacrylate.

6. A method according to any one of claims 2 to 5, wherein said ingredients include one or more additives selected from plasticisers, extending oils, stabilizers, pigments and fillers.

7. A method according to any one of claims 2 to 6, wherein said cross-linking is effected by a technique involving exposure to electron beam radiation.

8. A method according to claim 7, wherein said exposure is effected by feeding processed sheeting forming the said floorcovering continuously beneath a radiation source.

9. A method according to claim 8, wherein said radiation source subjects the sheeting to a fixed curtain of radiation.

10. A method according to claim 8, wherein said radiation source subjects the sheeting to a moving scanning beam of radiation.

11. A method according to any one of claims 8 to 10, wherein the processed sheeting is fed directly from a preceding processing stage to the radiation source.

12. A method according to any one of claims 8 to 10, wherein the irradiation is applied to the processed sheeting after storage thereof.

13. A method according to any one of claims 2 to 7, wherein said cross-linking is effected by a technique involving incorporation of a free radical initiator in conjunction with a cross-linking intermediary.

14. A method according to claim 13, wherein said initiator is added with other ingredients at an initial mixing stage so that cross-linking occurs gradually during subsequent processing steps.

15. A method according to claim 2, substantially as hereinbefore described in the Example.

16. Floorcovering when formed by the method of any one of claims 2 to 15.