This invention relates to solutions of separately-prepared oligo-urethane ethers containing terminal OH-groups in relatively high molecular weight polyethers containing terminal hydroxyl groups and to the use of these solutions as modified polyols in the production of polyurethane foams characterized by excellent high-frequency weldability and flame-laminatability.
Applications where high-frequency weldability is a particularly desirable property include, for example, the production of door linings for motor vehicles, in which sheets of foam have to be welded to one another or to other materials; the manufacture of articles with quilted surface appearances; or the production of moldings. In addition, flame lamination is used for the production of composite systems of foams with textiles, such as in upholstery backings which are subsequently profiled and/or formed by high-frequency (e.g. where the welding energy is provided by an electromagnetic field). (HF welding).
It is known that flame-laminatable and, to a certain extent, high-frequency-weldable foams can be produced from polyisocyanates and polyester polyols using suitable auxiliaries and additives. However, these foams can only be produced in special processing machines and are inferior in many properties to polyether-polyurethane foams. For example, their open-cell structure is poorer, their elasticity lower and their resistance to moisture and heat inferior.
Flame-laminatable and high-frequency-weldable polyurethane foams can be produced from polyether polyols, polyisocyanates, water and/or blowing agents in the presence of emulsifiers, stabilizers, catalysts and other auxiliaries, by the addition of special auxiliaries.
Thus, U.S. Pat. No. 3,205,120 describes the production of flame-laminatable polyether-polyurethane foams by the addition of a relatively small quantity of a polyol (particularly phosphorous-containing polyols, such as tris-(dipropylene glycol)-phosphite) having a molecular weight in the range from 200 to 1500. Disadvantages of this process include a deterioration in processing reliability, a certain tendency towards core-discoloration and a flame-lamination behavior which is distinctly inferior to that of a polyester-polyurethane foam because of the polyol quantities normally used.
U.S. Pat. No. 4,060,439 describes the cofoaming of small quantities of alkylene glycols containing from 2 to 8 carbon atoms, or triols containing from 3 to 10 carbon atoms, dialkanolamines containing from 2 to 10 carbon atoms with short-chain glycol ethers and polyhydric phenols into flexible polyether foam formulations. However, experience has shown that the co-foaming of compounds such as these makes foaming more difficult and, in particular, very considerably narrows the processing gap between an open-cell and a closed-cell structure.
In addition, U.S. Pat. No. 3,497,416 describes the foaming of a polyether polyol with a modified polyisocyanate (the reaction product of dipropylene glycol and/or dibutylene glycol with an excess of polyisocyanate) for the production of a weldable polyurethane foam. The disadvantage of this process lies in the fact that, to obtain sufficient open cells, dimethyl formamide --a toxicologically-unacceptable substance, has to be used as cell-opening agent. In addition, foams of this type have a high compression set, and polyether-NCO-prepolymers of this type used show only moderate stability in storage.
In view of the disadvantages of polyether-polyurethane foams which account for the fact that, on the whole, polyester-polyurethane foams are used for flame lamination and for high-frequency welding, there is a considerable need for a flame-laminatable and high-frequency (HF)-weldable polyether foam which can be manufactured safely.
Solutions of polyisocyanate-polyaddition compounds in polyols are also known. Thus, German Offenlegungsschrift No. 2,638,759 describes solutions of this type having solids contents of from 5 to 70%, by weight, which are obtained by either reacting diisocyanates with H-active compounds (including, among many others, diprimary diols) in polyhydric alcohols having a molecular weight of from 62 to 450 (but generally, from 62 to around 200) as reaction medium or by subsequently dissolving the powdered, separately-produced polyaddition compounds in the polyhydric alcohols.
Although solutions of this type may frequently be used as starting materials in the production of polyurethane plastics, they are not suitable for the production of flexible coatings and, in particular, flexible foams. The introduction of significant amounts of the polyaddition compound into the polyurethane foam formulation is only possible if relatively large quantities of the low molecular weight polyhydric alcohols (the solvents) are used at the same time. This seriously affects processing reliability in the manufacture of flexible foams (effecting the critical links between open-cell structure and shrinkage properties) or it makes the production of an open-cell flexible foam completely impossible.
It has now suprisingly been found that oligourethane ethers containing terminal OH-groups of diisocyanates and dihydric, relatively short-chain polyether diols form clear, stable solutions in relatively high molecular weight, polyhydric polyether polyols optionally at elevated temperature- and that solutions of this type may readily be processed into flexible foams characterized by good mechanical properties and by good high-frequency weldability.