GB2041953A - Rigid polyisocyanurate foams - Google Patents

Abstract

A process for the manufacture of rigid polyisocyanurate foams which comprises reacting an organic polyol or polyol mixture having a hydroxyl equivalent weight greater than 100 with a polymethylene polyphenyl polyisocyanate composition consisting essentially of diphenylmethane diisocyanate and polymethylene polyphenyl polyisocyanates of functionality greater than two, the diphenylmethane diisocyanate content of the composition being less than 30% on a weight basis, in the presence of a catalyst for the trimerisation of isocyanates and a blowing agent, the initial polyisocyanate/polyol equivalent ratio being in the range 3:1 to 10:1. The foams have excellent mechanical properties together with a high level of resistance to fire and high temperatures.

Description

SPECIFICATION Polymeric materials This invention relates to polymeric materials and more particularly to the manufacture of rigid polyisocyanurate foams.

It is already known to make rigid polyisocyanurate foams by reacting an organic polyol with an excess of an organic polyisocyanate in the presence of a trimerisation catalyst and a blowing agent. Polyisocyanates that have been used in the reaction include polymethylene polyphenyl polyisocyanate compositions which are available commercially under various trade names. In general, the foams have good fire properties as measured by various well known standard tests but sometimes some of their mechanical properties, for example degree of friability, are not completely satisfactory. Various organic polyols have been examined in this reaction as have various polymethylene polyphenyl polyisocyanate compositions in attempts to provide foams having even better fire properties together with a higher level of mechanical properties.

It has now been found that polyisocyanurate foams having excellent mechanical properties together with a high level of resistance to fire and high temperatures may be prepared by using the poly/polyisocyanate combinations hereinafter described.

Thus, according to the invention, there is provided a process for the manufacture of rigid polyisocyanurate foams which comprises reacting an organic polyol or polyol mixture having a hydroxyl equivalent weight greater than 100 with a polymethylene polyphenyl polyisocyanate composition consisting essentially of diphenylmethane diisocyanate and polymethylene polyphenyl polyisocyanates of functionality greater than two, the diphenylmethane diisocyanate content of the composition being less than 30% on a weight basis, in the presence of a catalyst for the trimerisation of isocyanates and a blowing agent, the initial polyisocyanate/polyol equivalent ratio being in the range 3:1 to 10:1.

The organic polyol used in the process of the invention may be any organic polyol having a hydroxyl equivalent weight greater than 100 although for convenience it is preferred to use a polyol or polyol mixture that is liquid at the start of the reaction, the reaction most commonly being started at or about ambient temperature.

The polyol may be a diol having a molecular weight greater than 200, a triol having a molecular weight greater than 300 or a polyol of higher functionality and correspondingly higher molecular weight. Suitable polyols include polyether polyols, such as may be prepared by reacting one or more alkylene oxides with a compound containing a plurality of active hydrogen atoms, and polyester polyols such as may be prepared by reacting polyhydric alcohols with polycarboxylic acids. Polyether and polyester polyols having equivalent weights greater than 100 and methods for their preparation have been fully described in the prior art, especially the prior art relating to the manufacture of polyurethane and polyisocyanurate foams.

Mixtures of polyols may be used in the process of the invention and these may be mixtures of polyols differing in chemical constitution and/or equivalent weight. Mixtures of polyols of different equivalent weight may include polyols having equivalent weights of 100 or less so long as the equivalent weight of the mixture is greater than 1 00. Thus, it is often convenient to dissolve the trimerisation catalyst in a polyol of low equivalent weight such as ethylene glycol. Moreover, low molecular weight polyesters having average equivalent weights greater than 100 will contain significant proportions of polyol species having equivalent weights less than 100.

Polyisocyanate compositions useful in the process of the invention may be prepared by phosgenation of mixtures of polyamines obtained by the acid condensation of aniline and formaldehyde. The manufacture of such polyamine mixtures and polyisocyanate compositions is known. The condensation of aniline with formaldehyde in the presence of strong acids such as hydrochloric acid gives a reaction product containing diaminodiphenylmethane together with polymethylene polyphenyl polyamines of higher functionality, the precise composition depending in known manner on the aniline/formaldehyde ratio. The various proportions of diamines, triamines and higher polyamines give rise on phosgenation to related proportions of diisocyanates, triisocyanates and higher polyisocyanates.

Thus polymethylene polyphenyl polyisocyanate compositions having a diphenylmethane diisocyanate content of less than 30% by weight can be prepared by appropriate choice of the aniline/formaldehyde ratio. Such compositions can also be prepared by starting with a higher aniline/formaldehyde ratio and then removing the excess difunctional material, either as diamine before phosgenation or as diisocyanate afterwards by an appropriate method such as distillation.

The polymethylene polyphenyl polyisocyanate composition is used in an amount to provide from 3 to 10, and preferably from 4 to 6.7, isocyanate groups for each hydroxyl group present in the polyol or polyol mixture.

The reaction mixture may also contain other materials which contain active hydrogen atoms and are therefore capable of reacting with the polyisocyanate. Examples of such materials include moisture and surfactants containing hydroxyl groups. Any such materials should be present only in minor amounts on an equivalents basis so that the overall ratio of isocyanate groups to active hydrogen atoms is not significantly different from the aforementioned ratio of isocyanate groups to hydroxyl groups present in the polyol.

Catalysts for the trimerisation of isocyanates have been fully described in the prior art relating to the reactions of isocyanates and the preparations of polyisocyanurates.

Particularly suitable catalysts include alkali metal salts of weak acids, for example potassium acetate. The catalyst is suitably employed in an amount of from 0.1 to 5% by weight based on the weight of the polyisocyanate composition.

Suitable blowing agents have been described in the prior art relating to polyurethane and polyisocyanurate foams and include inert liquids of low boiling point which vaporise under the influence of the exothermic reactions which take part. Trichlorofluoromethane is a particularly suitable liquid blowing agent. If desired, gaseous blowing agents such as dichlorodifluoromethane may be incorporated under pressure into one or more components of the reaction mixture. The blowing agent is used in an amount appropriate for the desired foam density.

In addition to the materials already mentioned, the foam-forming reaction mixture may contain other conventional ingredients of such reaction mixtures. Thus, it may contain one or more catalysts for the reaction between the isocyanate groups and the hydroxyl groups although in some cases this may not be necessary because the trimerisation catalyst will also catalytic the urethane-forming reaction. Other useful additives are surfactants, for example siloxane-oxyalkylene copolymers, flame-retardants, fillers and antioxidants.

The invention is illustrated by the following Example 1 in which all parts and percentages are by weight. Examples 2 and 3 are included for the purpose of comparison.

Example 1 A foam to illustrate the invention is prepared by mixing the following components: 100 Parts of a polymethylene polyphenyl polyisocyanate containing 28% of diisocyanatodiphenylmethane isomers and having an isocyanate group content of 29.2%, 1 5 parts of trichlorofluoromethane, 1.5 parts of a solution of potassium acetate in ethylene glycol, 3.8 parts of an ethylene oxide tipped poly(propy lene glycol), 0.7 parts of a siloxane-oxyalky lene copolymer commercially available as Silicone L5340, and 1 9.4 parts of a hydroxylended polyester having a hydroxyl number of 360 and an equivalent weight of 1 56. The mean equivalent weight of the hydroxyl-containing components is 1 57.

The foam is fine-pored with a density of 40 kg m-3, and has a compression modulus in the rise direction of 13.15 MNm-2, an oxygen index of 26.3, and a weight retention in the Butler Chimney test of 91.9%.

The polyester used in this Example is prepared by reacting 7 moles of adipic acid with 10 moles of diethylene glycol and 2 moles of glycerol.

Example 2 To demonstrate the superiority of the above polymeric isocyanate composition, a foam is prepared from 95 parts of a polymethylene polyphenylene polyisocyanate containing 50% of diisocyanate diphenylmethane isomers and having an isocyanate group content of 30.8%, and other components as described in Example 1.

The foam has a density of 38.0 kg m-3, and has a compression modulus in the rise direction of 10.6 MNm-2, an oxygen index of 25.2, and a weight retention in the Butler Chimney test of 90.7% Example 3 A further foam is prepared for comparison purposes by using 100 parts of the polymethylene polyphenylene polyisocyanate described in Example 1, and mixing with 1 5 parts of trichlorofluoromethane, 1.5 parts of a solution of potassium acetate in ethylene glycol, 1.8 parts of an ethylene oxide tipped poly(propylene glycol), 0.4 part of a siloxaneoxyalkylene copolymer commercially available as Silicone Us340, 4.7 parts of a polyester having a hydroxyl number of 500 and an equivalent weight of 11 2. The mean equivalent weight of the hydroxyl-containing components is 82.

The foam has a density of 39.7 kg m-3, a compression modulus in the rise direction of 11.9 MNm-2, an oxygen index of 25.8 and a weight retention in the Butler Chimney test of 82.6%.

The polyester used in this Example is pre pared by reacting 1 mole of adipic acid with 2.85 moles of diethylene glycol.

Claims (5)

1. A process for the manufacture of rigid polyisocyanurate foams which comprises reacting an organic polyol or polyol mixture having a hydroxyl equivalent weight greater than 100 with a polymethylene polyphenyl polyisocyanate composition consisting essentially of diphenylmethane diisocyanate and po lymethylene polyphenyl polyisocyanates of functionality greater than two, the diphenyl methane diisocyanate content of the composition being less than 30% on a weight basis, in the presence of a catalyst for the trimerisation of isocyanates and blowing agent, the initial polyisocyanate/polyol equivalent ratio being in the range 3:1 to 10:1.

2. A process as claimed in claim 1 wherein the initial polyisocyanate/polyol equivalent ratio is in the range 4:1 to 6.7:1.

3. A process as claimed in claim 1 or claim 2 wherein the catalyst is an alkali metal salt of a weak acid.

4. A process as claimed in claim substantially as hereinbefore described with reference to Example 1.

5. Rigid polyisocyanurate foams whenever manufactured by a process claimed in any one of the preceding claims.