Low monomer polyurethane prepolymer and process therefore
First Claim
1. A low-monomer polyurethane prepolymer containing free isocyanate groups obtained by reacting one or more polyhydric alcohols and two or more diisocyanates, wherein the polyhydric alcohol is first reacted with at least one non-symmetrical diisocyanate having a first NCO group which has a slower rate of reaction with the polyhydric alcohol than a second NCO group, wherein a ratio of a number of OH groups to a number of first and second NCO groups is form 4:
- 1 to 0.55;
1, to form a reaction product having free OH groups and free first NCO groups, and reacting the reaction product with at least one second diisocyanate having NCO groups which have a faster rate of reaction with the polyhydric alcohol than the first NCO groups wherein a ratio of a total number of first and second NCO groups of the non-symmetrical diisocyanate to a number of NCO groups of the second diisocyanate is greater than 6;
1 and the second diisocyanate is added in an amount less than an equivalent of free OH groups in the reaction product.
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Accused Products
Abstract
A low-monomer PU prepolymer containing free NCO groups which is obtained from polyhydric alcohols and diisocyanates differing in their reactivity and which is distinguished by the ratio of the NCO groups of the partly slower-reacting diisocyanate to the NCO groups of the faster-reacting diisocyanate. It is greater than 6:1. Nevertheless the prepolymer according to the invention cures more quickly than a known prepolymer predominantly containing fast-reacting NCO groups. In a preferred embodiment, TDI is used as the partly slower-reacting diisocyanate while MDI is used as the faster-reacting diisocyanate. The prepolymer is produced in two stages. The prepolymer according to the invention is suitable for bonding plastic articles, metals and paper, especially films. The accelerated absence of migration is particularly noticeable in this regard.
68 Citations
18 Claims
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1. A low-monomer polyurethane prepolymer containing free isocyanate groups obtained by reacting one or more polyhydric alcohols and two or more diisocyanates, wherein the polyhydric alcohol is first reacted with at least one non-symmetrical diisocyanate having a first NCO group which has a slower rate of reaction with the polyhydric alcohol than a second NCO group, wherein a ratio of a number of OH groups to a number of first and second NCO groups is form 4:
- 1 to 0.55;
1, to form a reaction product having free OH groups and free first NCO groups, and reacting the reaction product with at least one second diisocyanate having NCO groups which have a faster rate of reaction with the polyhydric alcohol than the first NCO groups wherein a ratio of a total number of first and second NCO groups of the non-symmetrical diisocyanate to a number of NCO groups of the second diisocyanate is greater than 6;
1 and the second diisocyanate is added in an amount less than an equivalent of free OH groups in the reaction product. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 15, 16, 17, 18)
- 1 to 0.55;
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10. A process for producing a low-monomer polyurethane prepolymer containing free isocyanate groups comprising the steps of:
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(a) reacting one or more non-symmetrical diisocyanates, each containing a first NCO group which has a slower rate of reaction than a second NCO group, with one or more polyhydric alcohols in an OH;
NCO ratio of 4;
1 to 0.55;
1 until at least substantially all of the second NCO groups, but substantially none of the first NCO groups, have reacted with the OH groups of the polyhydric alcohols to form a reaction product having free OH groups and free first NCO groups;
(b) reacting the reaction product of step (a) with at least one symmetrical diisocyanate, each containing NCO groups which have a faster rate of reaction than the first NCO groups of the non-symmetrical diisocyanates, to form the low-monomer polyurethane prepolymer, wherein said symmetrical diisocyanates are added in an amount less than equivalents of free OH groups present in said reaction product of step (a) and a ratio of a total number of first and second NCO groups of the non-symmetrical diisocyanate to a number of NCO groups of the symmetrical diisocyanate is greater than 6;
1.- View Dependent Claims (11, 12, 13, 14)
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Specification