Abstract:
A bituminous coating sheet for a base, and a method for the manufacture of a bituminous coating sheet for a base is provided that includes a bitumen-impregnated core material that has been coated with a top-face bitumen and a rear-face bitumen and which has an outermost layer of welding bitumen arranged in zones on a side of the sheet to be adhered to the base. The layer of rear-face bitumen has thereon a layer of a grainy mineral material in a matrix including a thermoplastic polymer. The grainy mineral material layer is between the rear-face bitumen and the outermost layer of welding bitumen and provides a barrier for melted rear-face bitumen when heat energy is applied to the welding bitumen during application of the sheet. Ninety-five percent by weight of the grainy mineral material consists of grains that are smaller than 0.15 mm.

Description:
[0001]     This is a continuation application of co-pending application U.S. Ser. No. 10/363,126, filed Oct. 9, 2003 which is a nationalization of PCT/DK01/00575, filed Sep. 5, 2001 and published in Danish, which is entitled to and claims the priority from and benefit of Danish Application No. PA 2000 01327, filed Sep. 6, 2000 and published in Danish. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a method for the manufacture of a bituminous coating sheet for a base in which a bitumen-impregnated core material, on which a layer of rear-face bitumen has been applied, is caused to contact one or more rotating bodies during the manufacturing process, and in which welding bitumen is subsequently applied in zones in order to enable, during application of the sheet on the base, the establishment of pressure equalization channels between the layer of rear-face bitumen and the base. The invention also relates to a coating sheet manufactured by the method.  
         [0004]     2. Description of the Related Art  
         [0005]     Danish patent No 150,586 discloses a coating sheet of this kind, wherein an additional bituminous layer that constitutes a welding bitumen is arranged on the layer of rear-face bitumen in accordance with a predetermined pattern. Hereby separate zones are formed, by which the sheet can be secured to the base. Following laying out of the sheet on the base it is possible, in this manner, to provide a number of pressure-equalization channels, whereby it can largely be avoided that, while under sub-atmospheric pressure, humidity and air accumulate in closed-off areas of the coating sheet when the sheet has been laid out on the base. The coating sheet comprises a layer of sand that is, in practice, relatively coarse-grained and that prevents ia that the sheet adheres to the base in the areas between the zones, ie at the bottom of the pressure equalization channels. However, the sand layer significantly increases the weight of the coating sheet, and the sand layer may give rise to delamination.  
         [0006]     It is known from WO99/43499 to manufacture a coating sheet wherein a bitumen-impregnated core material with a layer of rear-face bitumen is conveyed across one or more cooling rotating bodies during the manufacturing process, wherein the sheet is, in a final step, provided with a fully coating welding bitumen on the one side. An initial application of a layer of slip material that is melted away during the application of the fully coating welding bitumen makes it possible to avoid that the sheet adheres to the rotating body during advancement of the sheet.  
       SUMMARY OF THE INVENTION  
       [0007]     It is the object of the present invention to provide a method for the manufacture of an improved bituminous coating sheet with pressure-equalization channels, wherein the coating sheet does not adhere to the rotating bodies in the production equipment and wherein the danger of delamination is minimized. By the invention, the risk of the pressure-equalization channels being blocked by the layer of rear-face bitumen unintentionally causing the sheet to firmly adhere to the base at the bottom of the channel is efficiently avoided. This is obtained according to the inventive method in that a mixture is provided of a slip material dispersed, emulsified or dissolved in a liquid and a filler material having a grain size that essentially does not exceed 0.15 mm. The mixture is applied to the layer of rear-face bitumen on the side that is to be caused to contact a rotating body, the liquid is evaporated prior to contact with the rotating body, and welding bitumen is applied in zones on the side provided with the mixture.  
         [0008]     It has thus been found that by applying a layer of the mixture featured in the claim, a favorable barrier for melted rear-face bitumen is obtained when heat energy is applied to activate the zones of welding bitumen during application of the sheet. This energy is usually applied by means of a welding torch simultaneously with the sheet being unrolled. The layer of the stated mixture will thus in general and to a wide extent form the bottom surface of the pressure equalization channels following the welding of the sheet onto the base. There is thus in normal conditions no risk of the sheet also adhering to the base in the area between the zones of welding bitumen, i.e. at the bottom of the pressure equalization channels, and thereby giving rise to blocking of the channels. The slip material that forms a matrix for the filler material also provides an increased guarantee against delamination of the finished product. Thereby the risk is avoided that eg roof coverings, bridge coatings and the like membrane coatings will, in case of vehement outer impacts, such as influences of wind, be exposed to pulls in the surface that may give rise to a delamination of the bituminous coating sheet. The consequence of such delaminations may be leaks with ensuing damage to the roof construction and/or remaining parts of the building or the plant.  
         [0009]     In accordance with the invention, when 95% by weight of the filler material consists of grains that are smaller than 0.15 mm, particularly suitable properties are obtained. The filler material being selected such that 95% by weight of the filler material consists of grains that have a grain size of less than 0.045 mm allows the mixture to conveniently be sprayed out by means of conventional nozzles.  
         [0010]     Preferably the supplied amount of the mixture and the advancement rate of the core material through the process plant are selected such that the finished product appears with at least 0.3 cm 3  of the filler material per m 2  of the sheet.  
         [0011]     In accordance with the features of the present invention, the supplied amount of the mixture and the advancement rate of the grain material through the process plant being selected such that the finished product will appear with a maximum of 200 cm 3  of the filler material per m 2  of the sheet, preferably between 1 cm 3  and 40 cm 3 , more preferably between 3 cm 3  and 20 cm 3  of the filler material per m 2  of the sheet, ensures that the rear-face bitumen layer  4  will, in case of a particular, intensive heating of the underside of the coating sheet, for example by means of a welding torch, within a relatively short period of time, still melt and appear between the zones of welding bitumen, whereby overlapping joints between two adjoining sheets can be provided transversally to the longitudinal direction.  
         [0012]     The mixture of filler material and the slip material that has been dispersed, emulsified or dissolved in a liquid is preferably applied to the coating sheet at such distance from the first rotating body that said liquid will, to a large extent, have evaporated prior to contact with the first rotating body. Hereby a permanently, non-adhesive surface layer consisting of the slip material and the filler material is provided. In that context it is important that, during application of the mixture, the bituminous material has a suitable temperature. Conveniently it is between 100 and 200° C., however, preferably between 120 and 160°. The relatively elevated temperature effects a swift evaporation of the liquid in which the slip material has been dispersed, emulsified or dissolved, which entails an advantageous cooling of the bituminous coating sheet that increases the viscosity of the bitumen material. optionally additional coolant can be supplied to the surface of the bituminous layer.  
         [0013]     By the method a slip material in the form of a polymer is preferably used, eg a thermoplastic polymer that can be acrylic-based and that has been dispersed, emulsified or dissolved in a liquid. PVB (Polyvinyl Butyral) can also be used, to which a softener and a pigment material can be added.  
         [0014]     Upon melting, these substances can be dissolved in the layer of welding bitumen, the oils in the bitumen material dissolving the dried film of polymer at a relatively low temperature. Thus, during application of the welding bitumen layer, dissolution of the polymer will occur and due to this, increased delamination strength will result, the welding bitumen layer being caused to be in direct contact with the rear-face bitumen layer.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The method, an apparatus for exercising the method and the coating sheet produced by the method will be explained in further detail in the following with reference to the drawing, wherein  
         [0016]      FIG. 1  is a schematical cross-sectional view through a coating sheet according to the invention;  
         [0017]      FIG. 2  shows the one side of the embodiment of the sheet coating shown in  FIG. 1 ;  
         [0018]      FIG. 3  shows the one side of a second embodiment of the coating sheet; and  
         [0019]      FIG. 4  is a schematical view of a production plant for the manufacture of a coating sheet in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.  
         [0021]     In  FIG. 1 a  cross-sectional view through a coating sheet is shown. The coating sheet is constructed form a core material  3 , that may consist eg of a woven synthetic-fibre material, such as polyester fibre. The core material  3  is impregnated with bitumen. On the top face of the core material  3 , a bituminous layer  2  is provided on which a layer of grainy protective material has been distributed, eg crushed slate. On the underside of the core material a further bituminous layer  4  is provided, a so-called rear-face bitumen, and underneath this rear-face bitumen  4 , is a thin layer  5  consisting of a slip material in the form of a thermoplastic polymer material and a fine-grained filler material. The filler material has a grain size that essentially does not exceed 0.15 mm. However, the maximal grain size may particularly advantageously be comprised between 0.01 and 0.045 mm.  
         [0022]     Underneath the layer  5 , a partially coating layer  6  of welding bitumen is provided that has been applied in accordance with a pre-selected pattern. Besides, the coating sheet is downwardly provided with a film  7 , whereby it is avoided that the welding bitumen layer adheres to other surfaces before the sheet is taken to use.  
         [0023]      FIG. 2  shows how the layer  6  of welding bitumen has been applied to form elongate zones  200  of welding bitumen are provided, whose longitudinal direction coincides with the longitudinal direction of the material. At its left edge, the shown sheet has a coherent strip  300  of welding bitumen or some other kind of adhesive by which the coating sheet can be connected to an adjoining sheet by overlapping. The strip  300  is applied continuously during advancement of the core material through the process equipment, and the bitumen material that is used to form the strip  300  can optionally have other properties than the material used for forming the zones  200 .  
         [0024]      FIG. 3  shows an alternative coating sheet with a large number of zones  600  of welding bitumen, of which the major part are rectangular and has a longitudinal expanse that extends transversally of the sheet. Additionally the sheet  500  has, at its left edge, an uninterrupted strip  700  of welding bitumen or some other kind of adhesive for use in the securing of the sheet to an adjoining sheet.  
         [0025]     Preferably the material in the zones  200 ,  600  is deposited on the sheet  100 ,  500  by means of an anti set-off roller.  
         [0026]     It will appear from the above disclosures that, between the zones  200 ,  600 , areas or channels  6 ′ will appear that contain no welding bitumen, which means that, during application of the sheets on a base, pressure-equalization channels are provided that are of the same kind as described in Danish patent No. 150,586 B3. Following application of the sheet these channels serve to perform the same functionality as described in said disclosure.  
         [0027]     During mounting of the sheet, the sheet is slowly unrolled on top of the base while simultaneously the zones  200 ,  600  of welding bitumen  6  is, in a conventional manner, heated by means of a welding torch that is conveyed across the surface for a brief duration. In this case the slip material and the filler material form a sealing and effective barrier for the rear-face bitumen material that prevents the rear-face bitumen material from adhering to the base and thereby ensures the integrity of the channels. When the sheet has been applied and a sealing connection is to be established to a subsequent sheet to be applied in extension of the sheet, a continuous heating of the underside of the coating sheet is performed, along the transversal edge of the sheet, whereby the slip material in the layer  5  is decomposed while simultaneously the rear-face bitumen layer  4  melts. Hereby the rear-face bitumen layer  4  is able to diffuse into the areas between the zones  200 ,  600 . In this manner, it is possible to provide a welding of the two adjoining sheets transversally of the longitudinal direction by the welding bitumen layer  6  adhering, jointly with the rear-face bitumen material  4 , to the top face of the subsequent sheet.  
         [0028]     A coating sheet as shown in  FIGS. 1, 2  and  3  may be manufactured, eg in a production plant as shown schematically in  FIG. 4 . For the sake of overview the machine frames, drive means, etc, are not shown. Such measures can readily be implemented by the person skilled in the art. The coating sheet is, in the example shown, conveyed from the left to the right. Starting from the left, the shown part of the production plant receives a sheet of impregnated core material  3 , on which a bituminous layer  2  has been applied to the top side, and a bituminous layer  4  has been applied to the underside. The sheet temperature is, at this point in time, 100-200° C., preferably 120-160° C. At a sanding station  8 , a grainy sanding layer of crushed slate is distributed on top of the bituminous layer  2  to protect the applied sheet against sunlight. The sheet is subsequently conveyed around a first rotating body  9 , where the sanded side of the sheet abuts on this rotating body  9 . The sanding  1  thus prevents adhesion of the sheet to the rotating body  9 .  
         [0029]     Immediately after the rotating body  9  a coating station  10  is provided for a slip material, such as a thermoplastic polymer that has been dispersed, emulsified or dissolved in a liquid, such as water that has been admixed with a filler material in the form of an inorganic, preferably mineral material having a grain size that essentially does not exceed 0.15 mm. The liquid with the slip material is admixed with the filler material in a mixing station and is conveyed to the surface of the bituminous layer  4 . The coating station  10  is, in the example shown, constituted by four spray nozzles arranged on a shared suspension device transversally to the sheet, such that the entire width of the sheet is covered by the sprayed-on dispersion/emulsion/solution containing the filler material. The application is preferably effected such that the finished product appears with at least 0.3 cm 3  and maximally 200 cm 3  of the filler material per m 2  of the sheet. Hereby the ranges for the thickness of the layer  5  are defined.  
         [0030]     At a distance from the coating station  10  the sheet is conveyed around a second rotating body  11  and further around a third and a fourth rotating body  12 ,  13 , where the side featuring the slip material  5  abuts on these three rotating bodies  11 ,  12 ,  13 . In that connection it is important that the liquid content of the applied dispersion, emulsion or solution has been essentially evaporated prior to contact with the first rotating body  11 , and that the temperature of the sheet has also been lowered to a suitable level, where the thermoplastic polymer does not become adhesive. Now the bituminous layer  4  appears with a surface where the polymer material bonds the fine-grained filler material to the surface  4  and simultaneously also bonds the fine-grained particles to each other.  
         [0031]     Now, the sheet is conveyed into a vessel  16  by means of two rotating bodies  14 ,  15 . In the vessel a layer of welding bitumen  6  is applied to the side provided with the slip material  5  in accordance with a pre-selected pattern for forming the zones  200 ,  600 . Hereby the layer of welding bitumen has a preferred temperature that causes a dissolution and/or adhesion of the thermoplastic polymer in those areas of the sheet where welding bitumen is applied. The remaining areas of the sheet outside the zones  200 ,  600  will continue to appear with a surface layer  5  that consists of the slip material and the filler material. The subsequently finished coating sheet is provided with an anti-adhesive film layer (not shown) and is, via a further rotating body  17 , conveyed to the final packaging and storage.  
         [0032]     It is to be added that the filler material can particularly advantageously be a pigment substance, such as iron oxide, whereby it can optionally be made easy for the end user to recognize the zones  200 ,  600  and thereby direct the welding torch for heating exactly zones  200 ,  600 . The properties of the slip material and the filler material are thus adapted to be such that the rear-face bitumen layer  4  is, in case of a continued heating of the underside of the coating sheet, able to melt and appear in the channels, whereby it is possible to provide overlapping joints between two adjoining zones transversally to their longitudinal direction.  
         [0033]     When the rear-face bitumen layer  4  appears in the surface of the coating sheet, the black colour of the bitumen material will be visible between the zones  200 ,  600  and thereby indicate that the surface in question is adhesive, following which the sheet can be adhered to an adjoining material sheet.  
         [0034]     The term ‘bitumen’ as used herein is intended to designate both bitumen alone and also mixtures consisting primarily of bitumen and having a desired content of additives, such as SBS or other polymer substances, and/or inert fillers, such as powdered lime.  
         [0035]     The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by one skilled in the art are intended to be included within the scope of the following claims.