FILLER-CONTAINING POLYURETHANE BINDER AND SANDWICH PANEL COMPRISING SAME

Abstract: A polyurethane based binder prepared from a polyether diol having an average molecular weight of 800 - 3000 and containing a particulate filler in an amount of at least 40 weight.-%, in which at least 75 % of the filler have a particle size above 2 mu m, and that the filler has an average particle size of 3 - 8 mu m.

Description: Filler-containing polvurethane binder and sandwich panel comprising same The present invention relates to a polyurethane based binder containing a particulate inorganic filler, and in particular a binder for use for gluing coating layers onto an insulation layer of e.g. mineral wool so as to form a sandwich panel. In order for sandwich panels of the above kind to be usable for construction purposes, they must comply with certain requirements concerning fire resistance, laid down in EU directive 89/106/EEC. For example, the calorific value of any glue joints with primer in such sandwich panels must not exceed 4 MJ/m 2 in order for the panels to obtain A2-classification. The calorific value of a material indicates the amount of energy released from the material in case of fire. The calorific value is determined according to ISO 1716 in a bomb calorimeter. Polyurethane (PUR), which is typically used as basic component in binders for the preparation of sandwich panels of the kind stated in the preamble, has a calorific value of approx. 30 MJ/kg, and for the preparation of good quality panels it is normally required that the polyurethane binder be used in an amount of at least 300 g/m 2 . It is known to add inorganic fillers, such as calcium carbonate, to poly- urethane based binders in an amount of 20-30 weight-% in order to lower the calorific value of the binder. Hereby, binders with a calorific value of 18-20 MJ/m 2 have successfully been obtained, which, for the preparation of sandwich panels, however, allows use of the binder in an amount of only up ttoo 220000 gg//mm 22 wwhheenn tthhee ccaalloorriiffiicc vvalue of a primer on the coating layer or layers is also to be taken into account Attempts at further lowering the calorific value by using larger amounts of inorganic filler have entailed an increase in the viscosity of the binder to such extent that such binders cannot be used in connection with the existing glue application methods and plants. It is the object of the invention to provide a binder having a lower calorific value than that of the known ones, and having at the same time a low viscosity suited for application purposes and a good stability, i.e. good resistance to filler sedimentation. It is another object of the invention to provide a binder which can be used in an amount of at least 300 g/m 2 for the preparation of sandwich panels, which are to be compilable with the requirements concerning fire resistance pursuant to EU directive 89/106/EEC. It has surprisingly been found that these objects are obtainable with a poly- urethane based binder of the kind stated in the preamble, which binder is characterized in that the polyurethane is prepared from a polyether diol having an average molecular weight of 200-4000, that the filler content constitutes at least 40 weight-%, and that at least 75 % of the filler have a particle size of more than 2 μm, and that the filler has an average particle size of 3-8 μm. For the preparation of sandwich panels of the kind stated in the preamble, so-called 1 K-polyurethane binders are widely used, viz. prepolymers formed by reaction between a polyol and an isocyanate. Such prepolymers constitute a reactive system which is sensitive to additives and water. It has surprisingly been found that if the prepolymer is prepared using the above diol, it is possible to admix filler in an amount of up to and above 60 weight-% while obtaining a viscosity allowing use of known methods and plants for application of the binder. At the same time, by use of suitable particle sizes it is ensured that no filler sedimentation occurs. Also by use of so-called 2K-binders, i.e. binders being prepared immediately prior to the use in reaction between isocyanate and polyol, the invention offers the advantage that increased amounts of filler can be used, resulting in a reduction of the calorific value of the binder. When using the binder according to the invention for formation of glue joints in sandwich panels of the above mentioned kind, the calorific value of the glue joint and primer can be reduced to below 4 MJ/m 2 , even when the binder is applied in an amount in excess of 300 g/m 2 , e.g. between 300 and 350 g/m 2 , and the sandwich panels can thus be made to comply with the requirement for obtaining an A2-classification. The polyether diol used for the preparation of the polyurethane preferably has an average molecular weight of between 1500 and 3000. The polyether diol can be used together with other low-molecular organic hydroxy compounds, such as polyether triol. The isocyanate component for use for the preparation of the polyurethane prepolymer is preferably an aromatic polyisocyanate, such as diphenyl- methane diisocyanate. Preferably, the filler is used in an amount of between 40 and 60 weight-%, but even larger amounts, viz. 70 weight-% or larger, are also usable. The filler is preferably constituted by calcium carbonate, but also other inorganic fillers, such as barium sulphate, quartz powder, and dolomite, are usable. The filler preferably has a particle size of between 4 and 6 μm. The binder according to the invention may also contain commonly used additives, such as a moisture absorbent, a catalyst for the catalysis of the reaction between prepolymer and water, a dispersant for dispersing the filler particles in the polyurethane binder, and a foam inhibitor. When using 1 K-binders, the curing of the binder is effected by the influence of water, e.g. atmospheric moisture. The rate of curing is temperature dependent. When using particularly large amounts of filler, e.g. more than 60 weight-%, there may be a need for using a diluent in the form of a low-viscous organic liquid with a low vapour pressure at room temperature, such as acetyl acetate. The invention furthermore relates to a sandwich panel comprising an inorganic insulation layer having on at least one side a glued on coating layer. The sandwich panel according to the invention is characterized in that the glue joint between the insulation layer and the coating layer consists of a polyurethane based binder as described above. In the following the invention is described in more detail with reference to the examples below. EXAMPLE 1 A mixture of the following components was prepared: Polymeric diphenylmethane diisocyanate 19.5 parts by weight Polyether diol (average molecular weight: 2000) 15 Catalyst (dibutyltin laurate) 0.5 Diluent 5 Calcium carbonate (average particle size 5 μm, 75 % > 2 μm) 6 ( 3 "_ Total 100.0 The mixture had a viscosity of approx. 12 Pa.s. The calorific value of the binder thus formed was 10.5 MJ/kg, and could therefore - aside from the primer - be used in an amount of 381 g/m 2 without transgressing the threshold of 4 MJ/m 2 for calorific value laid down in EU directive 89/106/EEC. EXAMPLE 2 A basic mixture of the following components was prepared: Polyether diol (average molecular weight: 2000) 18 parts by weight Polyether triol (average molecular weight: 200) 6 Castor oil 6 Calcium carbonate (average particle size 5 μm, 75 % > 2 μm) 68 Total 100.0 The mixture was added with a curing agent in the form of polymer diphenyl- methane diisocyanate in a weight ratio of 20 parts by weight of curing agent per 100 parts by weight of basic mixture with 1 hour of mixing so as to obtain complete dispersion of the curing agent in the basic mixture. The mixture had a viscosity of approx. 15 Pa.s. The calorific value of the binder thus formed was 11.2 MJ/kg, which allows use of the binder in an amount of 337 g/m 2 without transgressing the above threshold value of 4 MJ/m 2 . COMPARATIVE EXAMPLE Three binders 1 , 2 and 3 were prepared by a method as described in example 1. The filler in binder 1 had an average particle size of 5 μm, and 76 % of the filler particles had a particle size above 2 μm. In binder 2, the average particle size of the filler particles was 6 μm, and less than 71 % of the filler particles had a particle size above 2 μm. Binder 3 contained filler particles with an average particle size of 12 μm, and more than 85 % of the filler particles had a particle size above 2 μm. The viscosity of the three binders was determined upon holding at 23 °C for 3, 17 and 24 days, and the stability was determined upon holding at 50 °C for 4, 12 and 19 days in a settler. During holding of the binders, an uppermost limpid layer, an intermediate turbid layer, and a lowermost sediment layer are formed. The stability of the binders was determined by measuring the thickness of the sediment layer and of the limpid layer (=sedimentation). In the studies of the three binders, the results set forth in tables 1 and 2 below were obtained: TABLE 1 TABLE 2 As apparent from the results in table 1 and table 2, binder 1 and binder 3 have better viscosity properties than binder 2, while the stability properties of binder 3 are significantly poorer than for binder 1 and binder 2. Binder 1 thus has a significantly better combination of viscosity and stability properties than the two other binders.

Claims: Claims: 1. A polyurethane based binder containing a particulate inorganic filler, characterized in that the polyurethane is prepared from a polyether diol having an average molecular weight of 800-20000, that the filler content constitutes at least 40 weight-%, that at least 75 % of the filler have a particle size above 2 μm, and that the filler has an average particle size of 3-8 μm. 2. A binder according to claim 1, characterized in that the poly- urethane is prepared from a polyether diol having an average molecular weight of 1500-3000. 3. A binder according to claim 1 or 2, characterized in that the polyurethane is prepared from a mixture of polyether diol and at least one other low-molecular organic hydroxy compound. 4. A binder according to any of the claims 1-3, characterized in that the filler constitutes from 40 to 60 weight-% of the binder. 5. A binder according to any of the claims 1-4, characterized in that in that the filler is constituted by calcium carbonate particles. 6. A binder according to claim 5, characterized in that the filler particles have an average particle size of between 4 and 6 μm. 7. A binder according to any of the preceding claims, characterized in that it additionally contains a diluent. 8. A sandwich panel comprising an inorganic insulation layer having on at least one side a glued on coating layer, characterized in that the glue joint between the insulation layer and the coating layer consists of a polyurethane based binder according to any of the claims 1-7.

Inventors: MUNK UFFE DAMGAARD, RASMUSSEN JEPPE, MUNK, UFFE, DAMGAARD, RASMUSSEN, JEPPE
Applicants: CASCO AS, MUNK UFFE DAMGAARD, RASMUSSEN JEPPE, CASCO A/S, MUNK, UFFE, DAMGAARD, RASMUSSEN, JEPPE
Application year: 2001
Main classification: C09J175
IPC codes: C08G18