METHOD OF MANUFACTURING A PLASTIC MAT

Abstract: A continuous base layer (1) of plastic material having been made electroconductive is coated by spread-coating with a surface layer (2) of a non-plastified plastic mass (3). Electroconductive grains (6) are supplied to the surface layer, the size of the grains being at least equal to the thickness of the surface layer (2). By heating and smooth-hobbing a plastic mat is brought about which is electroconductive, in that the grains (6) extend across through the surface layer.

Description: Method of manufacturing a plastic mat This invention relates to a method of manufacturing an electroconductive flooring of plastic material. Floorings of plastic material easily are charged with static electricity. The sparking possibly resulting therefrom is at times of discomfort and can in certain cases, for example at the presence of explosive gases, even cause serious explosion accidents. In some kind of rooms, for example operating-rooms in hospitals, it is, therefore, requested that the floor must be electroconductive to some extent. The conductivity of the floor, thus, shall be sufficient to discharge static electricity, but must be restricted so as to prevent electric shocks by spark-over to the floor when conatct is made with material, which has become live. Floorings of plastic can be utilized in such cases when the floorings are made electroconductive by admixing to them electroconductive substances, usually acetylene soot. For obtaining the necessary conductivity, however, the soot content must be so high, 10 to 20 per cent, that the plastic material unavzdably gets black, This is regarded a disadvantage, as in many cases the floorings are desired to be light and/or coloured. Many solutions for overcoming this disadvantage have been proposed. The electroconductive acetylene soot, as one example, is not admixed to the entire base material, but is concentrated to points, lines or networks in a plastic material, which in general is light and/or coloured. It has not been possible, however, to satisfactorily manufacture such floorings in the form of contnuous mats. This problem is solved according to the present invention which, thus, relates to a method of continuously manufacturing floorings of plastic in web shape, by which method the flooring can be given the desired colour, in that the conductivity has been concentrated to small defined points. The characterizing features of the invention become apparent from the attached claims. The invention is described in greater detail in the following, with reference to the attached Figs. 1 and 2 showing by way of example two embodiments of the method according to the invention. An electroconductive base layer l of plastic material is manufactured conventionally, for example, by rolling, calendering, extrusion etc. of a plastic material, for example PVC (polyvinyl chloride), containing a substantial content of an electroconductive substance, for example 10 to 20 per cent acetylene soot. The thickness of the base layer can be about 1 to 3 mm. The conductivity is adjusted by the acetylene suot content. The base layer, for example, may have the following approximate composition: PVC (polyvinyl chloride) 100 parts Dioctylphtalate 55 parts Heat stabilizer (basic lead carbonate) 5 parts Calcium carbonate 100 parts Acetylene soot 40 parts On the base layerla surface layer 2 is applied by spread-coating with a plastic mass 3 of viscous consistency, for example a PVC paste. The plastic mass then is in a non-plasticized state. The spread-coating is carried out by means of a doctor blade when the base layer is passing over a support surface 5. The thickness of the surface layer varies according to the application field, but can be about 0.4 to 1 mm. The plastic mass, for example, may have the following approximate composition: PVC (polyvinyl chloride) 100 parts Dioctyl phtalate 20 parts Butyl benzyl phtalate 20 parts Heat stabilizer '2 parts Pigment 2 parts In order to obtain electroconductivity across through the surface layer, electroconductive grains 6 are applied to the surface layer. The grain size is at least equal to the thickness of the surface layer. According to Fig. l, the grains 6 are admixed to the plastic mass 3 prior to the spread-coating operation. According to Fig. 2, the spread-coating is carried out at first. Thereafter the grains 6 are applied to the surface layer from a separate supply means 7. The grains 6 may consist of electroconductive material, such as metal or plastic having been made electroconductive. Another alternative is that the grains 6 consist of electrically insulated material, which has been coated with electroconductivt material. For example mineral with a surface layer of electroconductive thermoset. In the mat formed, i.e. the base layer 1 coated with the surface layer 2 and grains 6, plastification of the surface layer 2 is brought about by heating by means of a heating device 8, for example in the form of a furnace or a heat radiation device. The heating temperature may be 150 to 2000C. The mat thereafter is smooth-hobbed by passing it in heated state through a hobbing unit 9 with a hobbing roll 10 and a counter-pressure roll 11. The smooth-hobbing operation is carried out substantially without reduction of the mat thickness. When the grains 6 have been applied to the surface layer 2 subsequent to the spread-coating (Fig. 2), the grains are pressed down through the surface layer 2 into contact with the base layer 1. When the grains 6 were admixed to the plastic mass 3 already prior to the coating (Fig. 1), the smooth-hobbing yet ensures the function of the grains as electric conductors across through the surface layer 2 by depressing possible upward projecting tops. The invention, of course, is not restricted to the embodiments set forth above, but can be varied within the scope of the invention. idea.

Claims: Claims 1. A method of manufacturing an electroconductive continuous plastic mat comprising a continuous base layer of plastic material, which has been made electrically conductive, c h a r a c t e r i z e d i n that the base layer (1) by spread-coating is coated with a surface layer (2) of a non plastified plastic mass (3), that electroconductive grains (6) are supplied so as to be distributed in the surface layer (2), the size of the grains being at least equal to the thickness of the surface layer, and that thereafter the surface layer (2) is plastified by heating and finally is smooth-hobbed in a hobbing unit (9), so that the grains get into contact with the base layer (1). 2. A method as defined in claim l, c h a r a c t e r i z e d i n that the grains (6) are supplied to and distributed in the plastic mass (3) prior to the coating. 3. A method as defined in claim l, c h a r a c t e r i z e c i n that the grains (6) are applied to the surface layer (2) subsequent to the coating. 4. A method as defined in any one of the claims 1 - 3 f c h a r a c t e r i z e d i n that the grains (6) consist of an electroconductive material. 5. A method as defined in any one of the claims 1 - 3, c h a r a c t e r i z e d i n that the grains (6) consist of an electrically insulating material with a coat of electroconductive material.

Inventors: MARTELL, KARL RUNE
Applicants: HOLMSUND GOLV AKTIEBOLAG
Application year: 1981
Main classification: H05F3
IPC codes: B29C70, H05F3