Process for the production of polyurethane sandwich elements

Abstract

The present invention relates to a process for the continuous production of polyurethane sandwich elements comprising an upper outer layer and a lower outer layer and a layer of cellular polyurethane lying in between, which is firmly bonded to the outer layers. This invention also relates to an apparatus suitable for the production of polyurethane sandwich elements as described above.

1 . A process for the continuous production of polyurethane sandwich elements comprising an upper outer layer, a lower outer layer and a layer of cellular polyurethane lying in between and which is firmly bonded to the outer layers, said process comprising:
 a) continuously conveying the two outer layers in the longitudinal direction such that a gap extending in the longitudinal direction of the outer layers is formed between the outer layers,   b) applying the polyurethane reaction mixture pro rata from a position above the upper side of the lower outer layer and onto the upper side of the lower outer layer, and from a position below the under-side of the upper outer layer and onto the under-side of the upper outer layer,   c) feeding the outer layers with the polyurethane reaction mixture into a shaping zone in which the thickness of the polyurethane sandwich element is established and in which the polyurethane reaction mixture reacts,   and   d) removing the resultant polyurethane sandwich element off the conveying means,   wherein the ratio of the material flow of the polyurethane reaction mixture applied to the upper outer layer to the material flow of the polyurethane reaction mixture applied to the lower outer layer is between 0.001:1 and 0.2:1.   
   
   
       2 . The process of  claim 1 , wherein the ratio of the material flow of the polyurethane reaction mixture applied to the upper outer layer to the material flow of the polyurethane reaction mixture applied to the lower outer layer is between 0.002:1 and 0.1:1. 
   
   
       3 . The process of  claim 1 , wherein the ratio of the material flow of the polyurethane reaction mixture applied to the upper outer layer to the material flow of the polyurethane reaction mixture applied to the lower outer layer is between 0.005:1 and 0.05:1. 
   
   
       4 . The process of  claim 1 , in which applying of the polyurethane reaction mixture to the upper outer layer is by spraying with a spray mixing head, and the spray zone is demarcated by films or paper webs which move at an average advance of 0.1 to 10 m/h, in a plane parallel to the upper outer layer. 
   
   
       5 . The process of  claim 4 , in which any scattered aerosols or scattered mists formed during spraying are sucked off at the narrow sides of the spray zone. 
   
   
       6 . The process of  claim 4 , in which the spray mixing head oscillates transversely to the direction of movement of the upper outer layer, the translatory distance covered by the spray mixing head being set smaller than the width of the upper outer layer and the spray mixing head being swiveled outwards at the ends of the distance covered, such that the edge regions of the upper outer layer are also sprayed. 
   
   
       7 . The process of  claim 1 , in which a first mixing head and a second mixing head apply the reaction components to the outer layers with the reaction components conveyed to the first mixing head and to the second mixing head with common metering units and the division of the material flows for the first mixing head and for the second mixing head is effected by a flow distributor. 
   
   
       8 . The process of  claim 7 , in which the common metering units and flow distributor are adjustable. 
   
   
       9 . The process of  claims 1 , in which an auxiliary substance is injected online into one or more of the reaction components before the mixing of the reaction components in the first or second mixing head. 
   
   
       10 . The process of  claim 9 , wherein said auxiliary substance comprises a catalyst. 
   
   
       11 . The process of  claim 1 , in which the polyurethane reaction mixture is applied to the upper and the lower outer layer with a time interval, such that the polyurethane reaction mixture remains longer on the upper outer layer than on the lower outer layer, before both outer layers enter into the shaping zone. 
   
   
       12 . The process of  claim 1 , in which the polyurethane reaction mixture is applied to the upper outer layer by the dipping process. 
   
   
       13 . An apparatus for the continuous production of polyurethane sandwich elements comprising an upper outer layer, a lower outer layer, and a layer of cellular polyurethane lying in between the outer layers and which is firmly bonded to the outer layers, and which comprises a circulating upper belt for guiding the upper outer layer, a circulating lower belt for guiding the lower outer layer, a feed device for feeding the upper outer layer onto the circulating upper belt, a feed device for feeding the lower outer layer onto the circulating lower belt, a first mixing head arranged above the lower outer layer to apply the polyurethane reaction mixture to the lower outer layer, a second mixing head arranged below the upper outer layer to apply the polyurethane reaction mixture to the upper outer layer, a metering device to meter the reaction components to the first mixing head, to the second mixing head, and to the lines between the metering device and the first and the second mixing heads, with the second mixing head being a spray mixing head wherein the spray zone in which the scattered mists caused by the spraying form are demarcated from the environment by films or paper webs. 
   
   
       14 . The apparatus of  claim 13 , additionally comprising a length-cutting device for the polyurethane sandwich element. 
   
   
       15 . The apparatus of  claim 13 , in which the films or paper webs are moved at an average advance of 0.1 to 10 m/h in a direction perpendicular to the direction of movement of the upper layer, and this movement is either continuous or intermittent. 
   
   
       16 . The apparatus of  claim 15 , in which the films or paper webs are in a plane parallel to the upper outer layer and in which suction devices are arranged at the open narrow sides of the spray zone. 
   
   
       17 . The apparatus of  claim 16 , having a total of four suction devices, with the first two suction devices being arranged such that these are on opposite sides of the spray mixing head with one suction device being at the open narrow side of the spray zone close to the outer edges of the upper outer layer, and the last two suction devices being arranged such that these are on opposite sides of the spray mixing head with one suction device being in front of the spray mixing head and the other being behind the spray mixing head. 
   
   
       18 . The apparatus of  claim 13 , in which the second mixing head oscillates transversely to the direction of movement of the upper outer layer, with the translatory distance covered by the second mixing head being adjustable, and in which the second mixing head swivels outwardly at the end points of the distance covered. 
   
   
       19 . The apparatus of  claim 13 , in which the second mixing head ( 34 ) and, optionally, the films or paper webs which limit the spray region can be moved away or swiveled away. 
   
   
       20 . The apparatus of  claim 13 , in which the metering device for each reaction component comprises only one common metering unit with which the reaction component is conveyed to the first and to the second mixing head, and one flow distributor with which the metered material flow of reaction component is distributed to the first and the second mixing head. 
   
   
       21 . The apparatus of  claim 20 , in which the metering units and flow distributors are adjustable. 
   
   
       22 . The apparatus of  claim 13 , additionally comprising means for injecting additional auxiliary substances in which the means for injecting are arranged in the lines between the metering device and the first and/or the second mixing heads.