Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1992-12-14
1993-12-14
Welsh, Maurice J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524815, 524827, 524832, 524834, 524839, 524840, C08L 7504
Patent
active
052703835
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to aqueous polyurethane dispersions obtainable by reacting (a) dihydroxy compounds having a molecular weight of from 500 to 5,000, (b) diisocyanates and, if required, (c) chain extenders having at least two hydrogen atoms which are reactive toward isocyanate groups and a molecular weight of less than 300, which do not have any salt groups, in the melt or in the presence of a water-miscible, organic solvent (S) which is inert toward isocyanate groups and boils below 100.degree. C. to give a prepolymer having terminal isocyanate groups, then reacting the prepolymer with (d) salts of aliphatic aminocarboxylic or aminosulfonic acids or tertiary ammonium salts, which contain one or more hydrogen atoms which are reative toward isocyanate, the molar ratio of the components a : b : (c+d) being from 1:2:1 to 1:14:13 and dispersing the resulting polyuret hane in water, wherein, before the polyurethane obtained is dispersed in water, from 5 to 60 parts by weight, based on 100 parts by weight of the polyurethane, of a polymer (P) selected from the group consisting of polyvinyl acetate [sic], polyvinyl chloride, polymethyl methacrylate, polyamide, polyether, in particular polyetherdiol, polyester resin, in particular polyesterdiol, polurethane free of salt groups and phenacrylate and a mixture of at least two of these substances which is dissolved in a water-miscible solvent (S') inert toward isocyanate and boiling below 100.degree. C. is admixed.
The present invention furthermore relates to the use of the products, i.e. of the elastomeric polyurethanes, as adhesives or coating materials.
In this context, it should first be stated that it is known that the relevant polyurethane elastomers can be used as adhesives; cf. for example Kunststoff-Handbuch, Volume 7, July 1983, pages 588 to 590.
It is also known that, in the case of the polyurethanes known to date as adhesives, the low solubility in suitable solvents (acetone and methyl ethyl ketone) is a disadvantage, and large amounts of solvent therefore have to be evaporated off during adhesive bonding. Attempts have therefore long been made to convert elastomers into the form of aqueous dispersions; cf. for example the Kunststoff-Handbuch cited above, page 591 et seq. Aqueous dispersions are usually stabilized by means of incorporated ion groups. The disadvantage of these dispersions is that relatively high activation temperatures (80.degree. C. or higher) are required during adhesive bonding, in order to bring the dry adhesive film to the consistency required for adhesive bonding, or that the initial adhesive strengths of the system which were obtained at a given activation temperature are too low. The term initial adhesive strengths is understood as meaning the adhesive strengths measured immediately after brief activation and pressing together of the surfaces to be bonded.
It is also known that, in the case of polyurethane adhesives which are processed from organic solution, the initial adhesive strength can be improved by adding certain resins; cf. for example B. KujawaPencek et al., Adhasion (1984)3, 7-12.
There is no indication of an improved process for the preparation of polyurethane dispersions.
Aqueous polyurethane dispersions can be prepared by various methods; cf. for example D. Dieterich, Progress in Organic Coatings, 9 (1981), 281-340. The acetone process is relatively simple Here, a polyurethane ionomer is prepared in a plurality of steps in solution in acetone and then converted into an aqueous dispersion by adding water. The acetone still dissolved in the water is generally distilled off at the end under reduced pressure.
D. Dieterich, Angewandte Makromolekulare Chemie 89 (1981), 133-165, Kunststoff-Handbuch, Volume 7, Jul. 1983, page 591, and B. Kujawa-Pencek et al., Adhasion (1984) 3, 7-12, disclose that polymers dispersed in water can be added to aqueous polyurethane dispersions. However, these dispersions are frequently unstable. The products tend to exhibit loss of adhesion or poor adhesive strength.
DE-A 3903538 descri
REFERENCES:
Adhasion, vol. 3, pp. 7-12, 1984, B. Kujawa-Pencek, et al.
Progress in Organic Coatings, vol. 9, pp. 281-340, 1981, D. Dieterich.
D. Dieterich, "Angerwandte Makromolekulare Chemie", vol. 89, pp. 133-165, 1981.
Kunststoff Hanbuch, vol. 7, pp. 591-592, Jul., 1983.
Fisch Herbert
Maempel Lothar
BASF - Aktiengesellschaft
Welsh Maurice J.
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