GB2066813A - Liquid Polyisocyanate Compositions - Google Patents

Abstract

A liquid polyisocyanate composition which is stable to storage at low temperatures is prepared by reacting one equivalent proportion of 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 from 10 to 90% on a weight basis, with from 0.01 to 0.4 equivalent proportions of a monohydric alcohol of the formula: A-OH wherein A represents an alkyl radical containing from 9 to 16 carbon atoms or a radical of the formula: <IMAGE> wherein R represents a C1-12 alkyl group, R<1> represents hydrogen or C1-3 alkyl group and x is an integer of from 1 to 58, the reaction being performed at a temperature of from 100 to 250 DEG C and in the presence of a catalyst for the NCO/0H reaction.

Description

SPECIFICATION Liquid Polyisocyanate Compositions This invention relates to liquid polyisocyanate compositions and in 'particular to compositions containing diphenylmethane diisocyanate and to the use of such compositions in the manufacture of polyurethanes.

It is welt know to manufacture polyurethanes, of a cellular or non-cellular nature, by reacting an organic polyisocyanate with an organic polyol in the presence of additives of various kinds. Many organic polyisocyanates have been proposed for use in making polyurethanes but, since many polyurethanes manufacturing processes involve the rapid mixing of materials at room temperature, it is preferred to use polyisocyanates that are liquid at room temperature and that remain in the liquid state without significant deposition of solid materials even when stored at relatively low temperatures such as may be encountered in winter.

One of the polyisocyanates which has been used commercialiy in the manufacture of polyurethanes is diphenylmethane diisocyanate which is generally available either in a substantially pure form or in admixture with related polymethylene polyphenyl polyisocyanates of higher functionality such as may be represented by the general formula:

wherein n has an average value b e or more. The latter mixtures are commonly referred to in the trade as "crude MDI" and are made b12 the phosgenation of a mixture of polyamines obtained by the acid condensation of aniline and formaldcyde.

The manufacture of both the polyamine mixtures and the polyisocyanate mixtures is well known.

The condensation of aniline with formaldehyde In the presence of strong acids such as hydrochloric acid gives a reaction product containing diaminodip.tenylmethane together with polymethylene polyphenylpolyamines of higher functionality, the precise composition depending in known manner on the aniline/formaldehyde ratio. The polyisocyanates are fnade by phosgenation of the polyamine mixtures and the various proportions of diamines, triamines and higher polyamines give rise to related proportions of diisocyanates, triisocyanates and high polyisocyanates.

The relative proportions of diisocyanate, triisocyanate and high polyisocyanates in the crude diphenylmethane diisocyanate compositions determine tha average functionality of the compositions, that is the average number of isocyanate groups per molecuie. By varying the proportions of starting materials, the average functionality of the polyisocyanate compositions can be varied from little more than 2 to 3 or even higher. The lower functionality compositions, useful in the manufacture of polyurethane elastomers and flexible foams, have high diphenylmethane diisocyanate contents, especially the 4,4'- and 2,4'-isomers which have melting points of 42 OC and 360C respectively. There is a tendency, therefore, for these materials to deposit crystals when stored or transported at low temperatures.When this happens, the whole material has to be heated to melt the crystals and then thoroughly re-mixed. The higher functionality compositions, useful in the manufacture of polyurethane and polyisocyanurate rigid foams have lower diphenylmethane diisocyanate contents but crystallisation can still occur under winter conditions in some cases.

The present invention provides liquid polyisocyanate compositions which are stable to storage at low temperatures and which provide polyurethane and polyisocyanurate foams having excellent properties.

Thus, according to the invention, there is provided a method for the preparation of a liquid polyisocyanate composition which comprises reacting one equivalent proportion of a polymethylene polyphenyl polyisocyanate composition consisting essentially of diphenylmethane diisocyanate and polymethylene polyphenyl polyisocyanates of functionality greater than two, the diphenyimethane diisocyanate content of the composition being from 10 to 90% on a weight basis, with from 0.01 to 0.4 equivalent proportions of a monohydric alcohol of the formula: A-OH wherein A represents an alkyl radical containing from 9 to 16 carbon atoms or a radical of the formula::

wherein R represents an alkyl group containing from 1 to 1 2 carbon atoms, R1 represents hydrogen or an alkyl group containing from 1 to 3 carbon atoms and Xis an integer of from 1 to 58, the reaction being performed at a temperature of from 100 to 2500C and in the presence of a catalyst for the NCO/QH reaction.

When the monohydric alcohol is one in which A is an alkyl radical having 9 to 1 6 carbon atoms, it may be linear or branched but the latter is preferred. Alcohols having from 10 to 14 carbon atoms are especially suitable. A mixture of alcohols may be employed and in fact many of the alcohols are most readily available as isomer mixtures.

When the monohydric alcohol is a monoalkoxy glycol, R is preferably an alkyl group containing from 1 to 5 carbon atoms, for example methyl or ethyl. R1 is preferably hydrogen or methyl, the material then being a monoalkoxy (poly)ethylene or (poly)propylene glycol. The formula includes copolymeric monoalkoxy polyalkylene glycols, for example copolymers derived from ethylene and propylene oxides. The integer n is preferably less than 44. Mixtures of monoalkoxy glycols may be used.

Under the conditions specified for the performance of the method of the invention, the urethane formed by the reaction of the monohydric alcohol with the isocyanate groups of the polymethylene polyphenyl polyisocyanate composition reacts with further isocyanate to form an allophanate. It will be appreciated, however, that the reaction product may contain a minor proportion of material that has not reacted beyond the urethane stage as well as higher functionality material where the reaction has gone beyond the allophanate stage.

Particularly useful products are obtained when one equivalent proportion of the polyisocyanate composition is reacted with from 0.05 to 0.1 5 equivalent proportions of the monohydric alcohol.

The reaction between the polyisocyanate composition and the monohydric alcohol is preferably performed at a temperature in the range 1 00 to 2000C and is continued until a product of the desired constitution is obtained. The reaction. catalyst may be any catalyst known for the reaction between isocyanate and hydroxyl groups. Particularly suitable catalysts are tin and dialkyl tin salts of carboxylic acids, for example stannous octoate and dibutyl tin dilaurate.Other suitable catalysts are tertiary amines in which the nitrogen atom is not directly attached to an aromatic residue, for example 1,4 diaza-bicyclol2.2.2]octane. The monohydric alcohol is conveniently added slowly to the polyisocyanate and catalyst at the reaction temperature, but the reactants may alternatively be brought together at ambient temperature or at an intermediate temperature and then heated to the reaction temperature.

After the reaction is complete, it is preferable to deactivate the catalyst either chemically, for example by incorporating an acidic substance, or physically, for example by adsorption on to activated carbon. It is also possible in some cases to remove the catalyst by filtration or distillation.

The polyisocyanate compositions of the present invention are liquid compositions which are stable to storage, that is to say the compositions remain liquid at room temperature for long periods of time, sufficient in fact for all practical purposes, and can be transported or stored at low temperature without significant sedimentation of crystals of diphenylmethane diisocyanate. The compositions are suitable for use in the manufacture of polyurethane and polyisocyanurate foams using techniques fully described in the prior art.

Those compositions derived from polymethylene polyphenyl polyisocyanate compositions containing from 30 to 65% by weight of diphenylmethane diisocyanate are particularly suitable for use in the manufacture of polyurethane and polyisocyanurate rigid foams. It is found that the polyisocyanurate foams obtained have lower friability and higher compressive strength than corresponding foams obtained from unmodified polymethylene polyphenyl polyisocyanate compositions.

The invention is illustrated by the follow Example in which all parts and percentages are by weight.

Example To 1000 parts of a polymethylene polyphenyl polyisocyanate composition containing 50% diphenylmethane diisocyanate being stirred at 1 200C under dry nitrogen were added 2.0 parts of dibutyl tin dilaurate. 72 parts of the monomethyl ether of ethylene glycol were then added over 1 5 minutes maintaining the temperature at 1 200C. The reaction mixture was stirred for a further 36 hours at 1200C and then cooled to room temperature. During the cooling period, 0.5 part of salicylic acid was added. The product was a dark brown liquid having an NCO content of 23.6%.

Rigid polyisocyanurate foams were prepared from this modified polymethylene polyphenyl polyisocyanate composition and also from an unmodified composition using the formulations described below: A B Polyol composition 88.2 69.5 Trichlorofluoromethane 70.4 68.5 Unmodified polymethylene polyphenyl 352 polyisocyanate Modified polymethylene polyphenyl - 360 polyisocyanate Catalyst solution 2.8 3.5 The catalyst solution was obtained by dissolving 20 parts of potassium acetate in 20 parts of ethylene glycol and 1 part of water.

The polyol composition consisted of 20.4 parts of a glycerol/diethylene glycol/adipic acid polyester, (hydroxyl value 350 mg KOH/g), 4.0 parts of an oxyethylated polypropylene glycol having a hydroxy number of 56 and an ethylene oxide content of 10%, 0.8 part of Silicone L5340 and 1.0 part of the above mentioned catalyst solution.

The foams had the following properties: A B Density (kg/m3) 31.0 30.7 Stress at 10% strain parallel to direction of rise (kNm-2) 1 55 240 perpendicular to direction of rise , 55 75 (kNm-2) Compression modulus parallel to direction of rise (kNm-2) 5500 7500 perpendicular to direction of rise 1200 1700 (kN m-2) Friability (% wt. loss/min. on ball milling) 19 2.2 The foam made from the polyisocyanate composition of the invention is clearly superior in terms of strength and friability.

Claims (8)

Claims

1. A method for the preparation of a liquid polyisocyanate composition which comprises reacting one equivalent proportion of 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 from 10 to 90% on a weight basis, with from 0.01 to 0.4 equivalent proportions of a monohydric alcohol of the formula: A-OH wherein A represents an alkyl radical containing from 9 to 16 carbon atoms or a radical of the formula::

wherein R represents an alkyl group containing from 1 to 1 2 carbon atoms, R1 represents hydrogen or an alkyl group containing from 1 to 3 carbon atoms and X is an integer of from 1 to 58, the reaction being performed at a temperature of from 100 to 2500C and in the presence of a catalyst for the NCO/OH reaction.

2. A method according to claim 1 wherein A is an alkyl radical having 10 to 14 carbon atoms.

3. A method according to claim 1 wherein R is an alkyl group containing from 1 to 5 carbon atoms.

4. A method according to claim 1 or claim 3 wherein R' is hydrogen or methyl.

5. A method according to any one of the preceding claims wherein the polyisocyanate composition is reacted with from 0.05 to 0.1 5 equivalent proportions of the monohydric alcohol.

6. A method according to claim 1 carried out substantially as hereinbefore described with reference to the foregoing Example.

7. A liquid polyisocyanate composition whenever prepared by a method claimed in any one of the preceding claims.

8. A process for the preparation of a polyurethane or polyisocyanurate foam in which there is used a liquid polyisocyanate composition as claimed in claim 7.