ADHESIVE

Abstract: The present invention provides a foaming polyurethane adhesive formed from a polyol, a polyisocyanate and at least 5 % by weight of water based on the total weight of adhesive.

Description: Adhesive The present invention relates to a foaming polyurethane adhesive for bonding substrates. Polyurethane adhesives are used in various applications and when there is a fire, smoke is generated by the adhesive. There are an increasing number of regulations relating to smoke generation, for example in the case of building panels there is an increasing need to meet the fire/smoke requirements of, e.g. DIN 4102-A2 or other comparable national standards. We have now found that the amount of smoke generated by a polyurethane adhesive can be reduced by the use of higher than normal amounts of water. Accordingly the present invention provides a foaming polyurethane adhesive formed from a polyol, a polyisocyanate and at least 5% by weight of water, based on the total weight of adhesive. The adhesive is preferably a two component polyurethane, one component being a polyol and the other being a polyisocyanate. Suitable polyols include polytetrahydrofurans, polycaprolactone diols, polyalkylene glycols such as polypropylene glycols and polyether polyols. The diisocyanate and maybe any of those commonly used to make polyurethanes such as isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane 4,4'- diisocyanate, toluene diisocyanate, diphenylmethane, 4,4'-diisocyanate, trimethyl hexamethylene diisocyanate, tetramethyl xylylene diisocyanate, phenyl diisocyanate, xylylene diisocyanate and naphthalene diisocyanate. When making foamed polyurethane using water as a blowing agent the amount of water used is usually about 1 -2%. According to the present invention we use at least 5% of water, preferably at least 10%, more preferably at least 20%, e.g. 35 to 40%. Amounts as high as 60% may be used. For a given amount of adhesive, the more water that is used, the less smoke is produced on burning. The use of higher amounts of water produces optimum foaming and allows the use of lower amounts of adhesive thereby reducing the amount of smoke further. When producing such articles as building panels comprising rockwool between two steel panels, the high foaming ensures that any gaps or spaces between the steel skins and the rockwool are filled. This is of benefit for the mechanical properties of the panels. A standard ratio of polyol risocyanate in a polyurethane adhesive is about 100:10 to 100:25. In the system according to the invention, more isocyanate is needed to additionally react with the water. A preferred ratio of polyo isocyanate is 100:75 to 100:175, although more or less isocyanate may be used if desired. The present invention also provides a method of adhering substrates which comprises applying to at least one of the substrates an adhesive as described above, bringing the substrates together and allowing or inducing the adhesive to foam and cure. The adhesive system may be applied by various procedures. For example the polyol and isocyanate may be mixed and applied to the substrate with the separate application of water. This may be achieved using two sprays, one of the polyol/isocyanate and one of the water. As an alternative the water and polyol may be premixed and applied together with separate application of the isocyanate. The amount of adhesive applied may be below 150g/m 2 , preferably about 120g/m or below and most preferably about 10Og/m 2 or below. After application, the substrates are brought together and the adhesive allowed or induced to foam and cure. e.g. by heating if necessary. The invention is illustrated by the following Examples. Example 1 Steel panels are coated with a two-part polyurethane adhesive. One part comprises a polyol which is a branched polyether from propylene oxide and a triol and has an OH content of about 1.06% and an OH equivalent of about 1600 and containing a halogenated phosphate ester as fire retardant and 1% of dibutyl tin dilaurate, and 0.8% of N,N,N 1 ,IM 11 ,N 11 - pentamethyl diethylene triamine as catalysts. The other part is based in 4,4 1 - diphenylmethane diisocyanate containing isomers and oligomers and having a functionality of about 2.7. The two parts are used in the ratio of 100:150 parts by weight. The adhesive is applied to two steel panels preheated to 50 °C and Rockwool at a weight of per interface 90 g/m 2 and water is applied at the same time at an amount of 5-10% by weight of the adhesive or at 35-40% by weight of the adhesive. The Rockwool is then adhered between the two panels. After the adhesive is cured at 50 °C for 5 minutes samples are prepared with steel on one side only and being 30mm x 30mm x 15mm in size and these samples are tested according to DIN 4102-A2 in accordance with NMP 852-12/83. In order to pass this test the smoke density should be below 15%. When using 5-10% water, the maximum mean value of the smoke density is 14.2%. When using 35-40% water, the maximum mean value of the smoke density is 7.3%. Examples 2-4 Example 1 is repeated using three different weights of adhesive and different amounts of water. The results obtained when the samples are tested according to DIN 4102-A2 are as follows: Example Adhesive Amount of Smoke Weight (g/m 2 ) Water (%) Density (%) 2 121 38 12.0 3 117 10 14.1 4 95 38 7.9

Claims: Claims 1. A foaming polyurethane adhesive formed from a polyol, a polyisocyanate and at least 5% by weight of water based on the total weight of adhesive. 2. An adhesive as claimed in claim 1 in which the amount of water is at least 10%. 3 An adhesive as claimed in claim 1 or 2 in which the amount of water is at least 20%. 4. An adhesive as claimed in any preceding claim in which the weight ratio of polyo isocyanate is from 100:75 to 100:175. 5. An adhesive as claimed in any preceding claim which is a two-component polyurethane adhesive. 6. A method of adhering substrates which comprises applying to at least one of the substrates, an adhesive as claimed in any one of claims 1 to 5, bringing the substrates together, and allowing or inducing the adhesive to foam and cure. 7. A method as claimed in claim 6 in which the adhesive is used at an application rate of less than 150g/m 2 . 8. A method as claimed in claim 7 in which the adhesive is used at an application rate of about 120g/m 2 or below. 9. A method as claimed in claim 7 in which the adhesive is used at an application rate of about 100g/m 2 or below. 10. The use of an adhesive as claimed in any one of claims 1 to 5 for adhering substrates.

Inventors: BALL ALAN, BALL, ALAN
Applicants: BALL ALAN, CIBA GEIGY AG, BALL, ALAN, CIBA SPECIALTY CHEMICALS HOLDING INC.
Application year: 1997
Main classification: C08G18
IPC codes: C08G18, C09J175