The present invention relates to homogeneous storable mixtures containing small quantities of salts and having a high mixed hydroxyl number or mixed hydroxyl/amine number and a high content of low molecular weight di- and/or polyfunctional hydroxyl compounds.
German Offenlegungsschrift No. 1,770,703 discloses that mixtures of polyols which are incompatible with one another can be used for the production of polyurethanes. End products having improved properties, such as high thermal stability and high impact strength, can be obtained in this way. German Offenlegungsschrift No. 2,309,861 extended this principle of using incompatible polyol mixtures to the production of polyurethane foam moldings having a compact surface.
However, the use of a mixture of incompatible polyols has many disadvantages in terms of storage and processing. Even after brief storage periods (i.e. from a few hours to 3 days) of thoroughly mixed polyol systems, the mixture separates into two phases. Therefore, the polyol mixtures have to be very intensively remixed or continuously mixed or kept in circulation to ensure that the mixing ratio between the components remains intact.
Various methods have been proposed for phase-stabilizing mixtures of this type. U.S. Pat. No. 3,945,939 for example, prevented the phases from separating by adding colloidal silica or a clay modified with an onium compound. Similarly, German Offenlegungsschrift No. 2,341,294 disclosed that the use of inert, surface-active materials having a specific surface of from 10 to 800 m.sup.2 /g (such as silica agglomerate and/or a chrysotile asbestos and/or an inorganic material corresponding in its mineral composition to chrysotile asbestos) would reduce separation of the polyols.
Another possible method for homogenizing several incompatible polyols is the use of liquid or soluble solution promoters. According to U.S. Pat. No. 4,141,952, mixtures of monomeric polyols having a molecular weight below 500 and polyether polyols having a molecular weight in the range from 1800 to 7000 are prevented from separating by the use of so-called graft polypropylene ether glycols having a molecular weight in the range from 1500 to 3500. U.S. Pat. No. 4,273,884 discloses that a stable emulsion of a high molecular weight polyol and ethylene glycol or 1,4-butane diol may be produced by using an ethylene oxide/propylene oxide copolymer (molecular weight &gt;12000).
German Offenlegungsschrift No. 2,759,398 describes mixtures of poly(oxypropylene/oxyethylene)-polyols (OH-number 20-60) having certain oxyethylene contents and ethylene glycol or butane diol. The polyols used are required to have a terminal oxyethylene content of from 10 to 30 wt % and an inner oxyethylene content of from 5 to 60 wt %. It is preferred for as much ethylene oxide as possible to be internally incorporated in the polyols.
According to U.S. published application Ser. No. B 471,405, mixtures of high molecular weight polyoxyalkylene polyols having OH-equivalent weights of from 650 to 3000 and, for example, ethylene glycol may be protected against separation by the use of soluble diol compounds, such as 1,2-butylene glycol, di-(1,2-butylene glycol), di-(1,2-propylene glycol) and tri-(1,2-propylene glycol).
Two-phase mixtures of incompatible polyols may also be phase-stabilized by the addition of emulsifiers, such as long-chain benzene alkyl sulfonates.
The prior art does not, however, disclose a fully satisfactory resolution of the separation problem. The use of solids as emulsion stabilizers can give rise to abrasion in mixing units, in addition to which the stabilizing effect generally falls off drastically after a few days. Use of asbestos-containing materials is objectionable on physiological grounds. Another factor which must be taken into account where surface-active materials are used is their natural catalytic activity, particularly when they are charged with onium compounds. Use of so-called "graft polyols", as proposed in U.S. Pat. No. 4,141,852, has the disadvantage that "graft polyols" such as these are expensive compared to polyols and thus adversely affect the economy of the process.
U.S. Pat. No. 4,273,884 discloses "fairly stable" emulsions which show at least some phase separation in the first 6 to 8 weeks.
Although, according to U.S. published application Ser. No. B 471,405, it is possible to produce phase-stable polyol mixtures by using di- and tripropylene glycol, use of these compounds produces a serious deterioration in the mechanical properties (particularly dimensional stability under heat) of polyurethane plastics produced from them.
The use of conventional emulsifiers for phase stabilization involves numerous disadvantages. The emulsifiers can separate in crystalline form from the polyol mixture over a period of time or they may accumulate at the surface. Further, the emulsifiers are capable of uncontrollably upsetting the catalytic balance of the system. Additionally, conventional emulsifiers are capable of exuding from the finished polyurethane molding and, hence, of seriously impairing its service properties.
An urgent commercial need for polyol or polyol-polyamine formulations which have an adequate shelf life (at least about 6 months), which are optically clear and which have a high mixed hydroxyl and, optionally, hydroxyl/amine number and a high content of, preferably, ethylene glycol and/or 1,4-butane diol still exists.
German Offenlegungsschrift No. 3,219,759 describes homogeneously storable mixtures of relatively high molecular weight polyoxyalkylene polyols having an OH number of from 20 to 210 and containing at least 5 wt % of predominantly terminal oxyethylene segments and ethylene-glycol-containing reaction products of ethylene glycol with from 0.1 to 0.5 mole of propylene oxide.
German Offenlegungsschrift No. 3,219,822 describes storable homogeneous polyol mixtures of relatively high molecular weight polyoxyalkylene polyols having an OH-number of from 20 to 210 and at least 5 wt % of predominantly terminal oxyethylene segments in admixture with reaction products of ethylene glycol and/or 1,4-butane diol and from 0.05 to 0.5 mole of alkyloxiranes, the mixture additionally containing ammonium or metal salts of C.sub.1 -C.sub.8 -monocarboxylic or polycarboxylic acids or hydrohalic acids as solution-promoting additives in quantities of from 0.01 to 5 wt %, based on the polyoxyalkylene polyols.
Although the polyol formulations disclosed in German Offenlegungsschriften No. 3,219,759 and 3,219,822 represent a significant advance over the prior art, these formulations are disadvantageous in that the short-chain crosslinking component (for example ethylene glycol or 1,4-butane diol) must be partially alkylated with an oxirane in a separate reaction step. It was therefore necessary to use an excess of diol in relation to the alkoxylation product. In addition, particular care had to be taken in the alkoxylation of the diols. It is therefore difficult to add dipropoxylated ethylene glycol to ethylene glycol, for example, to an extent such that the oxypropyl content would be the same as the corresponding mixture of monopropoxylated ethylene glycol with ethylene glycol. In addition, the alkoxylation products of the diols adversely affect many properties of the polyurethane plastic synthesized therewith, so that the polyol miscibility improved by the alkoxylation products is obtained at the expense of the properties of the polyurethane products.