Process for making flexible foams

Details Process for making flexible foams Process for making flexible foams

1998-12-14

2001-08-07

Cooney, Jr., John M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S114000, C521S116000, C521S130000, C521S139000, C521S155000, C521S159000, C521S174000

Reexamination Certificate

active

06271277

ABSTRACT:

The manufacture of polyurethane flexible foams by reacting organic polyisocyanates such as toluene diisocyanates (TDI) or diphenyl methane diisocyanates (MDI) with polyether polyols in conjunction with a foaming agent is well established. The polyethers are usually polyoxypropylene polyols derived from propylene oxide or poly(oxypropylene-oxyethylene) polyols derived from various combinations of propylene and ethylene oxides. Ethylene oxide tipped polyoxypropylene polyols wherein the oxyethylene groups constitute a minor proportion of the total oxyalkylene residues are particularly important because of their enhanced reactivity towards isocyanates.
Polyols having higher oxyethylene contents, for example 50% or more on a weight basis, are often employed as minor additives to ensure that the foams have an open-cell structure. The use of these polyethers at very high concentrations in conjunction with the usual isocyanates is not as usual because then, instead of having a cell-opening effect, they result in closed cell foam.
In co-pending application PCT/EP94/01659 it has been found that flexible foam having valuable properties can be successfully made from formulations containing high concentrations of polyols having high oxyethylene contents if substantially pure 4,4′-MDI or a derivative thereof is employed as the polyisocyanate, water being used as the blowing agent. The preparation of hydrophilic flexible foams has further been described in U.S. Pat. No. 4,137,200 and U.S. Pat. No. 4,828,542.
Surprisingly it has now been found that hydrophilic foams may be obtained when the prepolymer, made from a polyisocyanate and a polyol having a high oxyethylene content, and the water are used at different temperatures.
Thus according to the invention, there is provided a process for the preparation of flexible foams by reacting a prepolymer having an NCO value of 3-15% by weight, which is the reaction product obtained by reacting an excessive amount of a polyisocyanate with a polyether polyol or a mixture of such polyols, said polyol or mixture having an average nominal hydroxyl functionality of from 2 to 6 and preferably of from 2 to 4, an average hydroxyl equivalent weight of from 500 to 5000 and preferably from 1000 to 5000 and an oxyethylene content of at least 50% by weight, with water, the amount of water being 15-500 parts by weight per 100 parts by weight of prepolymer, characterised in that at the start of the reaction the temperature of the prepolymer is 10-50° C., preferably 15-30° C. and most preferably room temperature and the temperature of the water is 10-50° C., preferably 20-45° C. higher than the temperature of the prepolymer. The temperature of the water is 25-90° C., preferably 40-70° C., most preferably 55-65° C.
A preferred embodiement of the invention is a method for the preparation of flexible polyurethane foams by reacting a prepolymer, having an NCO value of 3-10% by weight which is the reaction product obtained by reacting an excessive amount of a polyisocyanate containing at least 65, preferably at least 90, and more preferably at least 95% by weight of 4,4′-diphenyl methane diisocyanate or a variant thereof with a polyether polyol or a mixture of said polyols, said polyol or mixture having an average nominal hydroxyl functionality of from 2.5 to 3.5, an average hydroxyl equivalent weight of from 1000 to 3000, and an oxyethylene content of from 50 to 85% by weight, with water, the amount of water being 30-300 parts by weight per 100 parts by weight of prepolymer, characterised in that at the start of the reaction the temperature of the prepolymer is 10-50° C., preferably 15-30° C. and most preferably room temperature and the temperature of the water is 25-90° C., preferably 40-70° C. and most preferably 55-65° C. and the temperature of the water is 10-50° C., preferably 20-45° C. higher than the temperature of the prepolymer.
Surprisingly it has been found that good quality hydrophilic flexible foams can be obtained having a low density and hardness while the density and the hardness of the foam become less or even hardly dependent upon the amount of water used than in case the prepolymer and the water are reacted while having both the same or a similar temperature at the start of the reaction. For the sake of convenience the word average in the present application is not further specified but refers to number average unless explicitly used otherwise.
Polyisocyanates used for preparing the prepolymer may be selected from aliphatic, cycloaliphatic and araliphatic polyisocyanates, especially diisocyanates, like hexamethylene diisocyanate, isophorone diisocyanate, cyclohexane-1,4-diisocyanate, 4,4′-dicyclohexylmethane diisocyanate and m- and p-tetramethylxylylene diisocyanate, and in particular aromatic polyisocyanates like toluene diisocyanates (TDI), phenylene diisocyanates and most preferably methylene diphenylene diisocyanates (MDI) and its homologues having an isocyanate functionality of more than two, like crude MDI and polymeric MDI.
Preferred polyisocyanates are methylene diphenylene diisocyanates selected from pure 4,4′-MDI, isomeric mixtures of 4,4′-MDI and 2,4′-MDI and less than 10% by weight of 2,2′-MDI, and modified variants thereof containing carbodiimide, uretonimine, isocyanurate, urethane, allophanate, urea or biuret groups, like uretonimine and/or carbodiimide modified MDI having an NCO content of at least 25% by weight and urethane modified MDI obtained by reacting excess MDI and a low molecular weight polyol (MW up to 1000) and having an NCO content of at least 25% by weight.
Mixtures of the isocyanates mentioned above may be used if desired. The polyisocyanate may contain dispersed urea particles and/or urethane particles prepared in a conventional way, e.g. by adding a minor amount of an isophorone diamine to the polyisocyanate. The most preferred polyisocyanate used in preparing the prepolymer is a polyisocyanate containing at least 65%, preferably at least 90% and more preferably at least 95% by weight of 4,4′-diphenyl methane diisocyanate or a variant thereof. It may consist essentially of pure 4,4′-diphenyl methane diisocyanate or mixtures of that diisocyanate with one or more other organic polyisocyanates, especially other diphenyl methane diisocyanate isomers, for example the 2,4′-isomer optionally in conjunction with the 2,2′-isomer. The most preferred polyisocyanate may also be an MDI variant derived from a polyisocyanate composition containing at least 65% by weight of 4,4′-diphenylmethane diisocyanate. MDI variants are well known in the art and, for use in accordance with the invention, particularly include liquid products obtained by introducing uretonimine and/or carbodiimide groups into said polyisocyanates, such a carbodiimide and/or uretonimine modified polyisocyanate preferably having an NCO value of at least 25% by weight, and/or by reacting such a polyisocyanate with one or more polyols having a hydroxyl functionality of 2-6 and a molecular weight of 62-1000 so as to obtain a modified polyisocyanate, preferably having an NCO value of at least 25% by weight.
The polyether polyol or mixture of polyether polyols used in preparing the prepolymer preferably has an average nominal hydroxyl functionality of 2-4 and most preferably of 2.5-3.5 and an average hydroxyl equivalent weight of 1000-3000 and an oxyethylene content of from 50-85% by weight.
Polyether polyols include products obtained by the polymerisation of ethylene oxide optionally together with another cyclic oxide like tetrahydrofuran and—preferably—propylene oxide in the presence, where necessary, of polyfunctional initiators. Suitable initiator compounds contain a plurality of active hydrogen atoms and include water, butanediol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, ethanolamine, diethanolamine, triethanolamine, toluene diamine, diethyl toluene diamine, phenyl diamine, diphenylmethane diamine, ethylene diamine, cyclohexane diamine, cyclohex

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