PLANT AND PROCESS FOR PRODUCING A COATED MINERAL FIBRE ELEMENT

Abstract: A plant and a process for producing a mineral fibre element comprising a mineral fibre base layer having a surface coating in the form of a fibrous non-woven fabric formed of a thermoplastic polymer material, the surface coating covering at least part of the surface of the base layer, wherein the plant comprises one or more coating devices, means for melting a thermoplastic polymer material, means for supplying the polymer melt obtained to the coating devices, wherein each coating device comprises a number of dispensing units comprising a number of orifices, means for extruding the polymer melt obtained through the orifices and distributing the extruded polymer material on the surface of a mineral fibre base layer, and means for directing one or more high pressure gas streams closely past the orifices in order to elongate the extruded polymer material so as to form thin filaments and/or fibres, and wherein the distance between the orifices and the surface of the base layer is from 50 mm to 150 mm.

Description: Plant and process for producing a coated mineral fibre element. The present invention relates to a plant for producing a mineral fibre element comprising a mineral fibre base layer having a surface coating in the form of a fibrous non-woven fabric formed of a thermoplastic polymer material, the surface coating covering at least part of the surface of the base layer, wherein the plant comprises one or more coating devices, means for melting a thermoplastic polymer material, means for supplying the polymer melt obtained to the coating devices, wherein each coating device comprises a number of dispensing units comprising a number of orifices, means for extruding the polymer melt obtained through the orifices and distributing the extruded polymer material on the surface of a mineral fibre base layer, and means for directing one or more high pressure gas streams closely past the orifices in order to elongate the extruded polymer material so as to form thin filaments and/or fibres . Mineral fibre material is used i.a. for thermal and acoustic insulation in a number of connections. In order to increase the tactility of the mineral fibre material used during the handling and mounting thereof it may be coated with a surface layer, e.g. consisting of a non-woven sheet fabric of polymer fibres. Furthermore, such a surface coating serves to reduce or eliminate the release of fibre wads or single fibres from the mineral fibre material to the surroundings before, during and/or after mounting. WO 93/16874 discloses a process and an apparatus for applying a coating in the form of a fibrous netting of a thermoplastic polymer material onto the surface of a mineral fibre material. The apparatus used may be a so- called "melt blowing apparatus" or a "hot melt spray apparatus". The distance between the polymer discharge orifices of the apparatus and the surface of the mineral fibre material is from 0,3 to 0,5 m. US-A-5501872 discloses a method of preparing a six-sided fibrous batting which is coated with a non-woven polymeric material by passing the batt sequentially through three coating stations using melt blowing technology. Four sides of the batt are coated in the first two stations, and after the batt has been turned 90°, the final two sides are coated. The distance between the orifices of the dispensing chamber and the upper side of the fibrous batting is typically from 6 to 9 inches ( 15.2 - 22.9 cm) . The temperature of the polymer in the dispensing chamber was 250 °C and the temperature of the air was 260 °C The prior art methods suffer from the drawback that the adhesion of the polymer coating to the mineral fibre material is insufficient, i.e. the coating is liable to loosen partly or completely from the mineral fibre material during further processing, handling, storage and use. Thus the object of the present invention is to provide an apparatus of the type defined in the preamble to claim 1, which is capable of producing mineral fibre elements, wherein the adhesion of the polymer coating to the mineral fibre material is improved compared to a product produced by the prior art apparatuses. This object is obtained by the apparatus of the invention which apparatus is characterized in that the distance between the orifices and the surface of the base layer is from 50 mm to 150 mm. The inventors have examined the influence of a number of process parameters, such as type of polymer used, the temperature of the polymer melt and the high pressure gas streams, the distance between the orifices and the base layer and the weight of the extruded polymer material, on the strength of the adhesion of the polymer coating to the base layer. The studies have surprisingly shown that one parameter is decisive in determining the adhesion strength, viz. the distance between the orifices and the base layer. Thus, it has been found that a greatly improved adhesion may be obtained by using a specific distance range. It is believed that the improved adhesion obtained is due to the fact that the polymer fibres/filaments at the point of impingement with the mineral fibre material has a higher kinetic energy than when larger distances are used and that this high kinetic energy causes the fibres/filaments to penetrate deeper into the surface layer of the mineral fibre material and hence become more entangled therewith. The kinetic energy (E kιn = Η. m-V 2 , wherein m is the mass and V is the velocity) depends primarily on the velocity, and it is believed that the velocity of the extruded polymer material is closely related to the distance from the orifices, which is i.a. due to the fact that the high pressure gas streams carrying the polymer material is dispersed in a fan-shaped zone from the orifice. In order to increase the kinetic energy of the extruded polymer material it has been attempted to increase the velocity of the high pressure gas streams. However, such an increase of gas velocity has not been successful, since it causes the polymer fibres/filaments to become too thin to form a suitable coherent non-woven fabric, i.e. the coating formed is fluffy and tend to adhere to surfaces, with which it is brought into contact. However, it has further surprisingly been found that the said distance cannot be reduced to below a certain limit of 50 mm, since below the said limit, the non-woven coating obtained becomes too brittle to resist handling. When the heated, liquid polymer melt is extruded from the dispensing unit it is gradually cooled in the surrounding air as a function of the distance from the orifices of the dispensing unit, whereby the polymer melt gradually solidifies. It is believed that the brittleness of the coating, which occurs at small distances, is due to the fact that at small distances the extruded polymer melt is not sufficiently cooled and hence solidified at the point of impingement with the mineral fibre material. Thus, the distance range of 50-150 mm according to the invention is the result of two factors, which point in opposite directions. On the one hand the smaller the distance is, the stronger the adhesion between the polymer material and mineral fibre material is, and on the other hand the higher the distance is, the less brittle the coating formed is. The distance range of 50- 150 mm is the range, wherein an acceptable adhesion may be obtained while at the same time avoiding brittleness of the coating, the optimum distance being about 90 mm. In connection with the present invention the term "extruding the polymer melt through the orifices" means pressing out the polymer melt through the orifices by means of an extruder, a pump or another mechanical device or allowing the gravitation to make the polymer melt run through the orifices. As used in the present invention the term "mineral fibres" includes rock fibres, glass fibres, slag fibres and mixtures thereof. As used in the present invention the term "thermoplastic polymer material" means any natural or synthetic thermoplastic polymer, copolymer or polymer blend. A thermoplastic material is characterized by that it is solid or partially solid at room temperature or at temperature of use, that it melts when heated and that it solidifies or resumes a solid or partially solid form when cooled. The term "thermoplastic polymer material" also includes such materials which are ordinarily referred to as "thermoplastic hot melt adhesives" or "hot melt adhesives" or simply "hot melts". By way of examples thermoplastic polymer materials are polymers of ethylenically unsaturated monomers, such as polyethylene, polypropylene, polybutylenes, polystyrenes, poly (a-methyl styrene) , polyvinyl chloride, polyvinyl acetate, polymethyl methacrylate, polyethyl acrylate, polyacrylonitrile, etc; copolymers of ethylenically unsaturated monomers, such as copolymers of ethylene and propylene, ethylene and styrene, polyvinyl acetate, styrene and maleic anhydride, styrene and methyl methacrylate, styrene and ethyl acrylate, styrene and acrylonitrile, methyl methacrylate and ethyl acrylate etc; polymers and copolymers of conjugated dienes, such as polybutadiene, polyisoprene and polychloroprene and polymers of bi- polyfunctional monomers, such as polyesters, polycarbonates, polyamides and polyepoxides . Examples of natural thermoplastic polymer materials are wax and bitumen. Particularly preferred thermoplastic polymer materials are polyesters, polyamides, polypropylene and polyvinyl acetate. The thermoplastic polymer material as used in the invention may contain up to 30 % by weight of additives. The thermoplastic polymer material to be used in the plant of the invention should have such a low viscosity in its molten heated state so that it is capable of flowing freely through the dispensing unit and so that the extruded polymer material is capable of being drawn out readily by the high pressure gas streams. The base layer used in the invention is made from Man- Made Vitreous Fibres (MMVF) . The coated element produced by the plant of the invention may be used as thermal or fire insulation or protection, for noise reduction or regulation, or as a horticultural growing medium. The base layer used in the invention may be in any form and typically it has the form of an endless web, a web, a mat, a sheet, a slab or a tube, e.g. a pipe insulation, such as a circular pipe section, i.e. a pipe insulation having an annular cross section and a longitudinal slit. Preferably, the distance between the orifices and the base layer is from 70 mm to 120 mm. The surface weight of the non-woven fabric is preferably 2-50 g/m 2 , more preferably 2-15 g/m 2 , and most preferably 4-10 g/m 2 . The temperature of the high pressure gas streams measured in °C is preferably 0-15 % higher than the temperature of the dispensing unit measured in ° C, more preferably from 5 % to 10 %. Such temperature levels help to reduce the cooling of the polymer melt leaving the nozzles, the temperature of the polymer melt approximately corresponding to that of the dispensing unit, and hence to facilitate the drawing out of the polymer strands extruded from the orifices. Preferably, the plant of the invention comprises means for supporting and conveying the base layer. The supporting and conveying means may e.g. have the form of any suitable transport means, such as rotatable rolls, e.g. a roller belt or a roller path, a conveyor belt or a conveyor path or a combination thereof, preferably rotatable rolls. A preferred embodiment of the invention is characterised in that it comprises one or more suction devices, preferably suction boxes, disposed vis-a-vis the coating devices. Such suction devices serve mainly to remove excess polymer material, i.e. polymer fibres/filaments which are not deposited on the mineral fibre base layer and to remove polymer vapours contained in the emitted high pressure gas streams. The base layer in the plant of the invention may be placed in horisontal position, in an inclined position or in vertical position, preferably in horizontal position. Correspondingly, the coating devices may be placed in horizontal position, in an inclined position or in vertical position. A preferred embodiment of the invention is characterised in that it comprises six coating sections disposed in sequence and designed so as to be able to coat all sides of a six-sided base layer, wherein each coating section comprises one coating device, a number of rotatable rolls for supporting and conveying the base layer and a suction device disposed vis-a-vis the coating device, wherein two coating devices are disposed at one side of the base layer and two coating devices are disposed at the opposite side of the base layer, the said four coating devices all being disposed in such a manner that the polymer material is extruded in a substantially horizontal direction, wherein one coating device is disposed above the base layer in such a manner that the polymer material is extruded in a downward substantially vertical direction, and wherein one coating device is disposed below the base layer in such a manner that the polymer material is extruded in an upward substantially vertical direction. Preferably, one or more of the coating sections of the above-described six coating sections embodiment comprises holder means for keeping the base layer in place, the holder means being disposed on the upper side of the base layer. The holder means preferably have the form of rolls, which abut on the upper surface of the base layer. The high pressure gas streams used in the plant of the invention need to have such a kinetic energy that they may cause a lifting of the base layer from the support rolls in the coating section having the coating device placed below the base layer. Such a lifting is undesirable, since it increases the distance between the orifices and the base layer resulting in a reduced adhesion strength of the coating to the base layer. Also, the gas streams may cause a transverse displacing of the base layer on the support in the coating sections having the coating devices placed at the side of the base layer. Such a displacement is undesirable, since as a result a part of the base layer side to be coated will not be coated, and since part of the polymer material will be deposited on the rolls, which should be avoided, because the deposited polymer material tend to adhere to the coating of the following mineral fibre elements and hence to tear up the said coating. It has been found that the above-mentioned holder means placed above the base layer prevent both the lifting and the transverse displacement of the base layer. A preferred embodiment of the invention is characterised in that the coating devices are melt blowing die apparatuses comprising an oblong polymer dispensing chamber which via a pump is in liquid communication with the melting means and which at its distal end comprises a number of closely spaced orifices, two gas chambers located along the two side walls of the dispensing chamber and at the distal end of which a longitudinal slot is formed, and means for directing a high pressure gas stream through the said gas chambers and out through the slots. Another preferred embodiment of the invention is characterised in that the coating devices are hot melt spray nozzle apparatuses each comprising a number of individual spray nozzles which via a pump are in liquid communication with the melting means, and which comprise means for directing one or more high pressure gas streams past the orifices of the nozzles. Yet another preferred embodiment of the invention is characterised in that the coating devices are spun bond apparatuses . With respect to the structure and operation of "melt blowing die apparatuses" and "hot melt spray nozzle apparatuses", reference is made to international application No. WO 93/16874, which is incorporated herein by this reference. Spun-bond fibres of thermoplastic polymers and apparatus for making them are disclosed in US-A-3, 692, 618, US-A-5, 213, 881 and EP-B1-0, 480, 550, which are incorporated herein by this reference. The temperature of the polymer melt to be extruded and the temperature of the high pressure gas streams depend primarily on the type of polymer used. In general, it is desirable to keep the temperature of a polymer melt as low as possible while maintaining it flowable, since most polymers tend to decompose at high temperatures. On the other hand, the melt to be extruded should have a sufficiently low viscosity so as to be able to be drawn out by the high pressure gas streams. The temperature of the polymer melt in the plant is conveniently controlled by setting the temperature of the dispensing unit, i.e. e.g. a melt blowing die or a hot melt spray nozzle, to a desired level selected with due consideration to the specific polymer used, preferably 180-240 °C, and then adjusting the temperature of the polymer melt in the polymer melt supply means at the point of entry into the dispensing unit to a level of from +5 % to -25 %, more preferably from 0 % to -10 %, relative to that of the dispensing unit. Also, the temperature of the high pressure gas streams is controlled on the basis of the temperature of the dispensing unit, and preferably the former is adjusted to be from 0 % to 15 % of the latter, more preferably from 5 % to 10 %. The gas in the high pressure gas streams is preferably air. The present invention further relates to a process for producing a mineral fibre element comprising a mineral fibre base layer having a surface coating in the form of a fibrous non-woven fabric formed of a thermoplastic polymer material, the surface coating covering at least a part of the surface of the base layer, the process comprising the steps of melting a thermoplastic polymer material and supplying the polymer melt obtained to one or more coating devices comprising a number of dispensing units having a number of orifices, extruding the polymer melt through the orifices while directing one or more high pressure gas streams closely past the orifices in order to elongate the extruded polymer material so as to form thin filaments and/or fibres and so as to distribute the extruded polymer material on the surface of a mineral fibre base layer. The process of the invention is characterised in using a distance between the orifices and the surface of the base layer of from 50 mm to 150 mm. The invention will now be described in further details with reference to the drawings, wherein Fig. 1 is a perspective view of a preferred embodiment of the plant according to the invention. Fig. 2 shows a cross sectional view of the lower part of a melt blowing die apparatus situated above a mineral fibre base layer. Fig. 1 shows a plant according to the invention comprising six coating sections 1-6 placed in a line, wherein each coating section 1-6 comprises a melt blowing die apparatus 7, a suction box 8 and a bed of rotatable rolls 9 for supporting and conveying a six-sided rectangular mineral fibre mat 10. The six apparatuses 7 each comprises a die housing 11-16 and a polymer melt supply conduit 17 and a high pressure air supply conduit 18. The conduits 17 are via pumps (not shown) connected to a single extruder (not shown) , which supplies polymer melt to all six apparatuses 7. Correspondingly, the conduits 18 are connected to a single air compressor (not shown) , which supplies high pressure air to all six apparatuses 7. Alternatively, each melt blowing die apparatus 7 may be supplied with polymer melt and/or high pressure gas from individual extruders with or without the use of pumps and from individual gas compressors, respectively. The die housings 11-14 of the first four coating sections 1-4 are disposed alternately at different sides of the mat 10 in a vertical position and the suction boxes 8 of the coating sections 1-4 are disposed at the sides opposite to the die housings 11-14 in a vertical position. Between coating sections 2 and 3 an intermediate bed 19 of rotating rolls is placed, in which bed 19 the mat 10 is rotated 90 around the axis of a vertically disposed rod 20 extending from the upper surface of the rotating rolls. The die housings 15 and 16 are disposed horizontally on the upper and lower side, respectively, of the mat 10 and in a transverse direction in relation to the direction of movement of the mat 10. The suction boxes 8 of the coating sections 5 and 6 are disposed on the lower and upper side, respectively, of the mat 10 vis-a-vis the die housings 15 and 16, respectively. In coating sections 1-4 two holder rolls 21 is placed on the upper side of the mat 10 at the site of the die housings 11-14. The holder rolls 21 only extend across a smaller part of width of the bed 9. In coating section 6 two holder rolls 22 is placed on the upper side of the mat 10 vis-a-vis the die housing 16, the holder rolls 22 extending across the entire width of the bed 9. The mode of operation of the above described plant is as follows: The mat 10 is conveyed continuously through the plant on a roller path consisting of the six beds of rolls 9 and the intermediate bed of rolls 19. In coating sections 1 and 2, the mat 10 is coated with a non-woven fabric on opposite short side surfaces 23. On the intermediate bed of rolls 19, the mat 10 is then rotated 90 ° by means of the rod 20 so as to bring the mat 10 into a position, where the coated short side surfaces 23 are placed perpendicularly to the direction of movement of the mat 10. In coating sections 3 and 4, the mat 10 is coated on opposite long side surfaces 24, and in coating sections 5 and 6 the mat 10 is coated on its upper main surface 25 and lower main surface, respectively. The melt blowing die apparatuses 7 are operated in a discontinuously manner, i.e. polymer material is extruded from the apparatuses 7 only during the period of time, wherein the mat 10 passes past the apparatus 7. The initiation and ending of extrusion of polymer material are controlled by means of photoelectric cell technology (not shown) . The suction boxes 8 serve to remove excess polymer material, which is not deposited on the surface of the mat 10 so as to minimise the amount of polymer fibres/filaments, which are spread to the surrounding room. Also, the suction boxes 8 serve to remove the air from the high pressure air streams so as to remove the polymer vapour contained therein and so as to prevent that the air streams make turbulence, which is undesirable, since it may affect the coating process adversely. The holder means 21 are disposed so as to exert a small pressure on the upper surface of the mat 10. Although the holder means 21 are placed on the upper side of the mat 10 and only extend across a smaller part of the width of the mat 10, the holder means 21 are capable of preventing that the kinetic energy of the high pressure air streams displaces the mat 10 in the transverse direction of the roller path. The holder means 22 is also placed so as to exert a small pressure on the upper surface of the mat 10. Fig. 2 shows the lower part of a melt blowing apparatus 30 disposed above a mineral fibre mat 31. The apparatus 30 comprises a thermoplastic polymer channel 32, which ends in an orifice 33, from which a polymer melt P is extruded. At both sides of the channel 32, high pressure gas chambers 34 are disposed, from which a gas G is ejected. Finally, Fig. 2 shows the distance D between the lower end of the orifice 33 and the upper surface 35 of the mat 31. Example 1 A stone fibre mat having the dimensions 90 cm x 60 cm x 10 cm (length x width x height) was coated with a non- woven fabric using a melt blowing die apparatus disposed at the distances of 90 mm, 110 mm and 130 mm between the orifices of the die apparatus and the surface of the mat. The non-woven fabric consisted of polypropylene and the intended surface weight of the fabric coating was 10 g/m 2 . The mat was conveyed on a roller path at a speed of 20 m/min. The temperature of the melt blowing die was set to 200 °C, and the temperature of the polymer melt entering the die was 190 °C. The pressure and temperature of the high pressure gas stream being supplied to die apparatus was 80 psi and 210 °C, respectively. The strength of the adhesion between the coating and the stone fibre mat was subsequently measured using the following test method: A rectangular iron frame having an internal size of 100 x 200 mm was heated to a temperature of about 200 °C, and the heated frame was used to burn away the coating around a rectanangular piece of coating having the dimensions of 100 x 200 mm. Then, the said piece of coating was peeled off from the mineral fibre mat using a dynamometer while maintaining a vertical direction of pulling throughout the process of peeling off. The resulting measurement was calculated as the mean value of the process. The results obtained appear from Table 1. As will appear from Table 1, the adhesion strength decreases strongly with increasing distance between the orifices and the mat surface. TABLE 1 Example 2 A stone fibre mat having the dimensions 90 cm x 60 cm x 10 cm (length x width x height) was coated with a non- woven fabric using a melt blowing die apparatus disposed at the distances of 90 mm, 10 mm and 130 mm between the orifices of the die apparatus and the surface of the mat. The non-woven fabric consisted of polypropylene and the intended surface weight of the fabric coating was 8 g/m 2 . The mat was conveyed on a roller path at speeds of 20 m/min, 30 m/min and 40 m/min. The temperature of the melt blowing die was set to 180°C, and the temperature of the polymer melt entering the die was 170 °C . The pressure and temperature of the high pressure gas stream being supplied to die apparatus was 80 psi and 200 °C, respectively. The strength of adhesion between the coating and the stone fibre mat was then measured using the same test method as described under Example 1. The results obtained appear from Table 2. As will appear from Table 2, the adhesion strength increases with increasing mat conveying speed and it decreases with increasing distance between the orifices and the mat surface. TABLE 2

Claims: Claims 1. A plant for producing a mineral fibre element comprising a mineral fibre base layer having a surface coating in the form of a fibrous non-woven fabric formed of a thermoplastic polymer material, the surface coating covering at least part of the surface of the base layer, wherein the plant comprises one or more coating devices, means for melting a thermoplastic polymer material, means for supplying the polymer melt obtained to the coating devices, wherein each coating device comprises a number of dispensing units comprising a number of orifices, means for extruding the polymer melt obtained through the orifices and distributing the extruded polymer material on the surface of a mineral fibre base layer, and means for directing one or more high pressure gas streams closely past the orifices in order to elongate the extruded polymer material so as to form thin filaments and/or fibres c h a r a c t e r i z e d in that the distance between the orifices and the surface of the base layer is from 50 mm to 150 mm. 2. A plant according to claim 1, c h a r a c t er i z e d in that the base layer has the form of an endless web, a web, a mat or a sheet. 3. A plant according to claim 1 or 2, c h a r a c t er i z e d in that the base layer has the form of a pipe insulation. 4. A plant according to any of the preceding claims, c h a r a c t e r i z e d in that the distance between the orifices and the surface of the base layer is from 70 to 120 mm. 5. A plant according to any of the preceding claims, c h a r a c t e r i z e d in that the temperature of the high pressure gas measured in °C is 0-15 % higher than the temperature of the dispensing unit measured in °C. 6. A plant according to any of the preceding claims, c h a r a c t e r i z e d in that it further comprises means for supporting and conveying the base layer. 7. A plant according to claim 6, c h a r a c t e- r i z e d in that the supporting and conveying means is rotatable rolls. 8. A plant according to any of the preceding claims, c h a r a c t e r i z e d in that it comprises one or more suction devices disposed vis-a-vis the coating devices . 9. A plant according to any of the preceding claims, c h a r a c t e r i z e d in that it comprises six coating sections disposed in sequence and designed so as to be able to coat all sides of a six-sided base layer, wherein each coating section comprises one coating device, a number of rotatable rolls for supporting and conveying the base layer and a suction device disposed vis-a-vis the coating device, wherein two coating devices are disposed at one side of the base layer and two coating devices are disposed at the opposite side of the base layer, the said four coating devices all being disposed in such a manner that the polymer material is extruded in a substantially horizontal direction, wherein one coating device is disposed above the base layer in such a manner that the polymer material is extruded in a downward substantially vertical direction, and wherein one coating device is disposed below the base layer in such a manner that the polymer material is extruded in an upward substantially vertical direction. 10. A plant according to claim 9, c h a r a c t er i z e d in that one or more of the coating sections comprises holder means for keeping the base layer in place, the holder means being disposed on the upper side of the base layer. 11. A plant according to claim 10, c h a r a c t er i z e d in that the holder means are rolls which abut on the upper surface of the base layer. 12. A plant according to any of the preceding claims, c h a r a c t e r i z e d in that the coating devices are melt blowing die apparatuses comprising an oblong polymer dispensing chamber which via a pump is in liquid communication with the melting means and which at its distal end comprises a number of closely spaced orifices, two gas chambers located along the two side walls of the dispensing chamber and at the distal end of which a longitudinal slot is formed, and means for directing a high pressure gas stream through the said gas chambers and out through the slots. 13. A plant according to any of the claims 1-11, c h a- r a c t e r i z e d in that the coating devices are hot melt spray nozzle apparatuses each comprising a number of individual spray nozzles which via a pump are in liquid communication with the melting means, and which comprise means for directing one or more high pressure gas streams past the orifices of the nozzles. 14. A process for producing a mineral fibre element comprising a mineral fibre base layer having a surface coating in the form of a fibrous non-woven fabric formed of a thermoplastic polymer material, the surface coating covering at least a part of the surface of the base layer, the process comprising the steps of melting a thermoplastic polymer material and supplying the polymer melt obtained to one or more coating devices comprising a number of dispensing units having a number of orifices, extruding the polymer melt through the orifices while directing one or more high pressure gas streams closely past the orifices in order to elongate the extruded polymer material so as to form thin filaments and/or fibres and so as to distribute the extruded polymer material on the surface of a mineral fibre base layer, c h a r a c t e r i z e d in using a distance between the orifices and the surface of the base layer of from 50 mm to 150 mm.

Inventors: PETERSEN CONNY, PETERSEN, CONNY
Applicants: PETERSEN CONNY, ROCKWOOL INT, PETERSEN, CONNY, ROCKWOOL INTERNATIONAL A/S
Application year: 1998
Main classification: D04H1
IPC codes: B32B5, D04H1, D04H3, D04H13, E04B1