A PROCESS FOR THE PREPARATION OF A LAYERED INSULATING BOARD, AND A LAYERED BOARD AND A USE OF THIS BOARD

Abstract: The present invention relates to a process for the preparation of a mineral fibre insulating board, which insulating board comprises at least one high density layer and at least one low density layer. The process comprises provision of a primary web comprising a binding agent, and compression of the primary web in one or more longitudinally extending zones comprising an added compression aid, doubling of the primary web under formation of a secondary web, and curing and optional compression of the secondary web.

Description: A PROCESS FOR THE PREPARAΗON OFA LAYERED INSULATING BOARD, ANDA LAYERED BOARD AND A USE OF THIS BOARD The present invention relates to a process for the preparation of an insulating board having at least one high density layer, wherein a primary web of mineral fibre material is provided, where the primary web is compressed m at least one longitudinally extending zone in which the primary web is made to overlap itself under formation of a secondary web, and where the secondary web is cured and optionally compressed. Boards of mineral fibre material for insulation purposes can be prepared with various properties depending on the desired field of application. In order to increase the dimensional stability of the insulating boards, the mineral fibre material will often comprise an amount of binding agent, e.g. in the form of phenol formaldehyde urea which is cured when the secondary web passes through a curing owen. When erecting new constructions, thermal insulation is often performed with mineral fibre material m the cavity wall. In certain forms of new construction, the inner wall is erected first, whereafter it is clad with a layer of insulating material before the outer wall is erected. The insulating material will typically be secured to the inner wall by means of wall ties which are anchored in the wall and extend throughout and beyond the insulating material. The wall ties retain the insulating material secured to the wall by means of retaining clips in the form of plate shaped end pieces which urge against the outer layer of the insulating material. Thus, it is important that the insulating material possesses sufficient rigidity to be fixed m this way. Further, insulating boards are often subjected to rough handling during mounting, and consequently it is generally desirable with respect to handling that insulating boards of mineral wool have at least one comparatively dimensionally stable surface. Finally, the outer wall with the insulating material mounted thereon may risk being exposed to weathering conditions for a prolonged period until the outer wall is erected. Consequently, it is desirable to be able to prepare an insulating board which also has a suitably weather-resistant surface, i.e. a hard or high density layer. On the other hand, as it is, the outer side of an inner wall is often rather uneven. In order to avoid formation of ducts through which e.g. cold air may flow, it is consequently desirable to be able to prepare an insulating board which essentially is conformable to the contours of the wall, i.e. a soft or lower density layer. Further, it is generally desirable to keep the average density of the insulating material down m view of transport and production economy, as well as for reasons of handling. It is i.a. known from patent specifications Nos. CA 1 057 183, EP 0 451 186 Bl, and DE 3 701 592 C2 to prepare insulating boards comprising layers having different characteristics by gluing or curing a separate compressed layer and another non-compressed or less compressed layer together so as to form one web. Danish utility model No. DK 92 00033 U3 discloses an insulating board thus prepared which is intended for insulating buildings having ventilated outer wall, or as facade cladding. The insulating board is prepared from mineral wool and comprises a thin layer of about 30 mm having a relatively high density of about 90 kg/m 3 , and a comparatively thick layer of about 70 mm having a relatively low density of about 45 kg/m 3 . According to the utility model, the insulating board may be prepared on a dual-density apparatus, e.g. as described in US 4 950 355, and according to the utility model the insulating board may contain 0.5-15 weight-% binding agent, and preferably 0.5- 5 weight-%. In the above processes for the preparation of insulating boards comprising several layers having different properties, it has been found that the initial costs are very high. Further, in connection with the particular insulating boards problems of delamination may arise, so that after some time the layers come apart. Further, as it is, if it is a matter of products having low density, the individual layers will not get to cohere sufficiently, because the compression resistance in the light non-cured mineral wool is too low. If sufficiently good bonding between the layers is to be obtained, the light wool layer will be compressed excessively. Hereby the layer gets too thin, which will result in too poor insulating capacity. It is not possible either to prepare products with thin layers having high density by several of the above processes, since it is not possible to cut off a sufficiently thin layer from the secondary mineral fibre web. The cut off, thin non-cured fibre web will further be unable to cohere sufficiently for the web to be treated by the above processes. From Danish published application No. 155 163 B it is known to prepare mineral fibre webs having a zone with a higher degree of hardness than the rest of the web. This is achieved by compressing a part of the primary web before distribution by a pendulum conveyor, and where the compressed part at the pendulum distribution is made to partly overlap the compressed part of a number of the preceding layers. Hereby a zone of compressed primary web is established which extends in the longitudinal and horizontal direction of the secondary web. By e.g. compressing a zone along the edge of the primary web it is possible by this process to obtain a secondary web of mineral fibre containing insulating material having a high density layer positioned at one of the surfaces. However, it has proved to be difficult to obtain products having sufficiently high density-ratios between layers formed by zones having been pre-compresεed and zones not having been pre-co pressed. Essentially it is difficult to obtain sufficiently both thin and dense layers by the above mentioned method. Even by extreme pre-compression of the primary web, the pre-compressed zones tend to release some of the compression during handling and before fixation by the curing step, resulting eventually in an insufficient density in the layers formed by the pre- compressed zones. Furthermore, by subjecting the primary web to such extreme pre-compression, one might damage the individual fibres in the web, which generally has a disadvantageous influence on the properties of the final product, e.g. in terms of decreased tensile strength. Accordingly, it is an object of the present invention to provide a process of the kind stated in the preamble of claim 1, wherein an insulating board comprising at least one hard, easy-to-handle and weather-resistant layer, and at least one soft and conformable layer, may easily be prepared and without the use of excessive pre-compression. This object is achieved by the process according to the invention which is characterized in that a compression aid is supplied to the longitudinally extending pre- compression zone. The invention is based on the recognition that by supplying a compression aid to the zones of the primary web to be pre-compressed, it is possible to essentially maintain the pre-compression until the product is cured, thus resulting in the pre-compressed zones forming layers having a significantly higher density relative to the degree of pre-compression, than corresponding layers not having been subjected to the application of such compression aid. Accordingly it is an advantage of the present invention that it enables an increased density-ratio between layers constituted by pre-compressed zones and layers constituted by zones not having been pre-compressed. It is a further advantage of the present invention that due to the improved properties of the high density layer of the insulating boards produced by present method the high density layers may be produced thinner using less mineral fibres and thus enabling that the average density of the insulating board may be lowered. Accordingly both costs of production and transport may be reduced. It is a yet further great advantage of the present invention, that the necessary amount of ordinary binding agent normally supplied to the primary web in order to improve hardness of the high density layer may be reduced, thus further reducing cost. The compression aid is preferably substantially in the form of a liquid, which is added to the pre-compression zones of the primary web before, during and/or shortly after the pre-compression force is applied. Dry newly formed fibres tend to resemble very frosty snow, in the way that it is very hard to keep in compressed state. Surprisingly it has been found that liquids have the ability to make the fibres act m a melting snow-like fashion, facilitating the maintenance of the applied compression, by keeping the individual fibres together. The amount of such liquid necessary to obtain the desired effect depends on the nature of the liquid in question. The practical lower limit is determined by the minimum amount where an actual effect can be noticed, and the upper limit is more or less determined by whether and/or to which extent compression aid is to be removed at a later stage. However, in practice it is generally preferred to use an amount of 0,1-10 weight-?, liquid compression aid, more preferably 0,5-5 weιght-% compression aid. Applicable substantially liquid compression aids comprises most organic and inorganic based liquids, comprising e.g. oils (organic as well as preferably silicon-based oil) , water, surfactants, suspension or solutions comprising dye or one or more coloring agents, suspensions of binding agents (e.g. phenol formaldehyde resin or mela me resin), colloidal suspensions and/or the like, or any mixture thereof. Surprisingly water has proven to be very suitable for the purpose of compression aid, and is therefore for economical and environmental reasons a particularly preferred liquid compression aid. Water, in terms of pre-compression aid, is preferably added in an amount of about 0,2-2 weιght-%, or added m an amount so that the total amount of water m the pre- compression zones is about 0,8-3 weιght-%. In another preferred embodiment of the method according to the invention an oil is used as compression aid. Applicable oils comprise any oil capable of keeping the fibers together, i.e. maintaining the pre-compression effect. For reasons of fire-safety the used oil is preferably silicon-based. The oil is preferably added to the pre-compression zone of the primary web in a total amount of about 0,2-2 weight- percent. However, the entire primary web may for other reasons comprise an amount of oil in which case, the oil is added to the pre-compression zone is preferably added in an amount corresponding to about 0,4-1 weight-percent- points more than the average amount of oil in the zones of the primary web not to be pre-compressed. In order to provide an essentially dry product, the excess part of the applied liquid compression aid may be removed from the product or transformed immediately before, during and/or at any time after the curing of the product. Depending on the nature of the compression aid, it may be e.g. evaporated, combusted, hardened or cured. Apart from the substantially liquid compression aids, substantially non-liquid compression aids may be applied. Such substantially non-liquid compression aids may comprise adhesives, derivatives of cellulose or acrylates, water-soluble polymers, thermoplastic polymers, surfactants, colloidal substances, diatomite, gels (e.g. silicagel or water glass) , dye or coloring agents, or mixtures thereof. The here-mentioned substances may also be applied in combination with one or more substantially liquid substances, e.g. in the form of one of the above mentioned substantially liquid substances. It is an advantage of the above mentioned essentially non- liquid compression aids, that in most cases no special action has to be taken in order to remove a carrier agent or the compression aid itself neither during nor after the curing of the product. The benefits of the present invention may be obtained by any process of the above kind where part of the primary web is compressed before the primary web, e.g. by pendulum distribution or by preceding cutting off in sections as described in EP 0 297 111 Bl, is made to overlap itself under formation of a secondary web which is optionally compressed and eventually cured. It is possible by the present invention that the amount of binding agent in weight-% of the cured end-product can be the same in all layers requiring an amount of binding agent. Thus, during the production of the insulating boards to dose the binding agent in an essentially uniform amount across the entire primary web or to those of the primary web zones requiring binding agent. However, it is also possible in a first step to dose a uniform amount of a binding agent composition to all the zones of the primary web, requiring an amount of binding agent, and in another step to dose an additional amount of binding agent composition to the pre-compression zones, thus using the further added binding agent composition as a compression aid. This latter embodiment gives the advantage of only having to handle one type of composition, which is supplied in different amounts and/or concentrations to the different zones of the primary web. A further advantage of this particular embodiment of the process according to the invention is that an increased level of binding agent in the pre-compression zones eventually will result in the high density layers being even harder and more weather- resistant. Such compositions applicable as both binding agent and compression aid comprise any composition comprising a curable binding agent in a liquid suspension, any curable binding agent being a liquid at the supply-temperature and any substantially non-liquid composition having an adhesive effect at the supply-temperature and being curable. However, preferably such a double-functioning composition is an aqueous suspension of phenol- formaldehyde-urea . The applied binding agent may be supplied before, under or after appliance of the compression a d and/or the compression force. According to a preferred embodiment of the process according to the invention, 1-3 weight-o binding agent are added to the zones of the primary web which are to constitute the low density layers of the insulating board, and 1.3-5 weight-" binding agent to the zones of the primary web which are to constitute the high density layers of the insulating board, i.e. the pre-compression zones. All binding agent weight-percentages is relative to the cured end-product. According to another preferred embodiment of the process according to the invention an average amount of binding agent of 2-3 weιght-% is added to the primary web. It is possible directly to prepare a mineral fibre web having a high density layer positioned at one of its surfaces, and a low density layer positioned at the other surface, and where the insulating boards prepared by the process according to the invention can be obtained by cutting off in suitable lengths from the web. This is achievable by a particularly preferred embodiment of the process according to the invention wherein the primary web is compressed in a longitudinally extending zone along one of its edges. However, it is also possible by the process according to the invention to prepare the above insulating boards by first preparing a mineral fibre web having an easy-to- handle and weather-resistant layer on both sides, whereafter the web is divided symmetrically or asymmetrically in the vertical direction so as to obtain two webs having one easy-to-handle and weather-resistant side and one soft and conformable side, respectively. Fibre webs may also be prepared where the primary web is compressed at another site or several other sites than along the edges, and the web may be divided into one or more planes parallel to the upper and lower surface in a suitable way so as to obtain insulating boards having the desired combinations of layers with different properties. The pre-compression of the primary web may be performed using any known means of compression, e.g. rollers, continuous bands and the like. The surface of the pre- compression means may be smooth or curved or having a pattern. Furthermore the applied pressure may be constant or varied over time and/or the pre-compression zone. Preferably rollers are used for applying a constant pressure to the entire pre-compression zone. The invention also relates to an insulating board obtainable by the process according to the invention. In addition to the above advantageous properties, the insulating board according to the invention offers the advantage that it can be packed more densely than conventional insulating boards without suffering damage. Hereby transport and handling of the final packaged products are facilitated. Further, the insulating boards might be prepared using a lower amount of binding agent than similar conventional boards. As described above, the insulating boards according to the invention exhibit an improved tensile strength over conventional insulating boards. An insulating board according to the invention having a high density layer positioned at one surface of the board, and a low density layer positioned at the other surface of the board, is particularly suited for cavity wall insulation where the insulating board is secured with the soft and conformable surface of the insulating board to the outer side of the inner wall by means of wall ties, and where the outer wall is erected at a distance from the insulating boards so as to establish a cavity between the insulating material and the inner side of the outer wall. A particularly preferred embodiment of the insulating board according to the invention comprises a low density layer positioned at one surface of the board, and a high density layer positioned at the other surface of the board. Another particularly preferred embodiment of the insulating board according to the invention is prepared by dividing m the vertical direction a mineral fibre web having several hard and/or low density layers. Finally, it may for certain types of insulation purposes be expedient to have an insulating board having two hard surfaces with a soft core, or two soft surfaces with one hard core. Yet another particularly preferred embodiment of the insulating board according to the invention is characterized by having a high density layer on both surfaces. Still another preferred embodiment of the insulating board according to the invention has a low density layer on both surfaces. In this way the insulating board is conformable to uneven surfaces on both sides, simultaneously with it still being easy-to-handle due to a firm core in the form of a high density layer. The term insulating board as used herein comprises any board or sheet formed insulating material intended for thermal insulation, sound insulation or sound regulation, fire retardant purposes, or the like. The term mineral fibre as used herein comprises all types of man-made mineral fibres, such as rock, glass or slag fibres, in particular fibres used in materials for the above purposes, and as filler in cement, plastics or other substances, or which are used as culture medium for plants . The term binding agent as used herein comprises any material which is suited as binding agent in mineral fibre materials for the above products, e.g. phenol formaldehyde urea, acrylic-copolymer, resorsinole, furan or melamine resin. Such binding agents are preferably supplied to the mineral fibre material in the form of aqueous suspensions. The term layer as used herein denotes areas which essentially exhibit uniform characteristics within the area; but the term comprises both layers which are sharply delimited, and areas in which there is a stepwise or continuous transition to any neighboring layers. The expression high density layer as used herein denotes a layer which has a density which is higher than the average density of the product, i.e. high density layers are hard layers . The expression low density layer as used herein denotes a layer which has a density which is lower than the average density of the hard layers, i.e. low density layers are softer layers. The expressions substantially liquid and substantially non-liquid is meant in combination to denote the hole continuous range of states from liquid state to solid state. Accordingly the expression substantially liquid denotes compositions being primarily liquid, and the expression substantially non-liquid denotes compositions being primarily solid. The expression building surface denotes any surface of a building, comprising e.g. inner and outer walls, the inside of cavity walls, roofs and ceilings. All percentages, where not specified otherwise, is to be understood as weight-% of the mineral fibre web. However, percentages referring to binding agent is relative to the cured end-product. In the following the invention will be described in more detail by way of an example. Example 1: Mineral fibres are obtained by spinning in a spinning chamber, and are made to deposit on a conveyor belt under formation of a primary web having a width of about 1.8 m, and a surface weight of about 500 g/ιr.2. A binding agent comprising phenol formaldehyde urea in aqueous suspension is continuously distributed to the fibres in the air in the spinning chamber prior to the fibres settling on the conveyor belt, the binding agent being added in an amount corresponding to a final concentration of phenol formaldehyde urea in the primary web of about 2.1 % of the weight of the web. A zone along both edges of the primary web having a width of about 30 cm is sprayed with a further amount of pure water corresponding to a final concentration of water of app . 1,8 weιght-% m the sprayed zones, and the zones are rolled by means of 2 rollers each urging against the web at a pressure of 1600 kg. The primary web is laid out by pendulum distribution under formation of a secondary web having a width of about 2 m, the secondary web as seen m cross-section comprising about 12 layers of primary web. The secondary web obtained is compressed to a height of 200 mm, and cured in a curing owen, whereafter the secondary web is divided symmetrically in the vertical direction into 2 webs having a height of 100 mm. Finally, the insulating boards are provided by cutting off in the desired sizes from the divided secondary web. Insulating boards prepared by the process according to the example have a high density layer of about 15 mm positioned at one surface, and a low density layer of about 85 mm positioned at the other surface. The high density layer has a density of about 60 kg/m 3 , and the low density layer has a density of about 26 kg/m 3 , the average density of the insulating board being about 29.9 kg/m 3 . Example 2: Mineral fibres are obtained by spinning in a spinning chamber, and are made to deposit on a conveyor belt under formation of a primary web having a width of about 1.8 m, and a surface weight of about 500 g/m 2 . A binding agent comprising phenol formaldehyde urea m aqueous suspension is continuously distributed to the fibres in the air in the spinning chamber prior to the fibres settling on the conveyor belt, the binding agent being added m an amount corresponding to a final concentration of phenol formaldehyde urea in the primary web of about 2 weιght-% of the weight of the web. A zone along one edge of the primary web having a width of about 30 cm is sprayed with a further amount of an aqueous suspension comprising phenol formaldehyde urea corresponding to a final concentration of binding agent of app. 3 weιght-% in the sprayed zone, and the zone is rolled by means of 2 rollers each urging against the web at a pressure of 1600 kg. The primary web is laid out by pendulum distribution under formation of a secondary web having a width of about 2 m, the secondary web as seen in cross-section comprising about 12 layers of primary web. The secondary web obtained is compressed to a height of 200 mm, and cured m a curing owen. Finally, the insulating boards are provided by cutting off in the desired sizes from the divided secondary web. s mentioned, insulating boards prepared by the process according to the invention exhibit better properties than conventional insulating boards.

Claims: C l a i s : 1. A process for the preparation of an insulating board having at least two layers, one having a higher density than the other, wherein a primary web comprising mineral fibre material and a curable binding agent is provided, wherein the primary web is compressed in at least one longitudinally extending pre-compression zone, wherein the primary web is made to overlap itself under formation of a secondary web, and wherein the secondary web is treated to cure the binding agent and optionally compressed, characterized in that a compression aid is supplied to the longitudinally extending pre-compression zone. 2. A process according to claim 1 characterized in that a substantially liquid compression aid is supplied to the longitudinally extending pre-compression zone. 3. A process according to any of the preceding claims characterized in that a substantially liquid compression aid is added to the longitudinally extending pre- compression zone in an amount of 0,1 - 10 weιght-%. 4. A process according to any of the preceding claims characterized in that a substantially liquid compression aid comprising water is added to the pre-compression zone. 5. A process according to any of the preceding claims characterized in that a substantially liquid compression aid consisting essentially of water is added to the pre- compression zone. 6. A process according to any of the preceding claims characterized in that a substantially liquid water- comprising compression aid is added to the longitudinally extending pre-compression zone in an amount resulting m a total water-moisture content of said zone of 0,6 - 3 weight- ?. . 7. A process according to any of the preceding claims characterized in that a substantially liquid compression aid comprising an oil is added to the pre-compression zone. 8. A process according to claim 7 characterized in that a substantially liquid oil-comprising compression aid is added to the longitudinally extending pre-compression zone in an amount resulting in a total oil content of said zone of 0,2 - 2 weight-?.- 9. A process according to any of the preceding claims characterized in that a substantially non-liquid compression aid is added to the pre-compression zone. 10. A process according to any of the preceding claims characterized in that a substantially non-liquid compression aid comprising one or more fixation agents is added to the pre-compression zone. 11. A process according to claim 10 characterized in that the one or more of the fixation agents is the same as the one or more of the binding agents. 12. A process according to any of the preceding claims characterized in that a binding agent-comprising compression aid is added to the longitudinally extending pre-compression zone in an amount resulting in a total binding agent content of said zone of 1.3 - 5 weight-?.. 13. A process according to any of the preceding claims characterized in that a substantially non-liquid compression aid comprising one or more adhesives is added to the pre-compression zone. 14. A process according to any of the preceding claims, characterized in that 1-3 weight-" binding agent is added to the zones of the primary web which are to constitute the low density layers of the insulating board, and 1.3-5 weight- binding agent to the zones of the primary web which are to constitute the high density layers of the insulating board. 15. A process according to any of the preceding claims, characterized in that the primary web is compressed in a longitudinally extending pre-compression zone along at least one of its edges. 16. A process according to any of the preceding claims, characterized in that the secondary web is divided in a plane parallel to the surface before or after the optional compression and curing. 17. An insulating board obtainable by any of the processes according to the preceding claims. 18. Use of an insulating board according to any of claim 17 for cladding building surfaces.

Inventors: CRIDLAND IAN, NOERGAARD LUIS, CRIDLAND, IAN, NOERGAARD, LUIS
Applicants: CRIDLAND IAN, NOERGAARD LUIS, ROCKWOOL INT, CRIDLAND, IAN, NOERGAARD, LUIS, ROCKWOOL INTERNATIONAL A/S
Application year: 1997
Main classification: E04B1
IPC codes: D04H13, E04C2