Adhesives based on polyurethane prepolymers having a low residual monomer content

Claim 2

An isocyanate terminated polyurethane prepolymer having a low content of free isocyanate residual monomers which is the reaction product of (A) a low viscosity first stage prepolymer having free NCO moieties and free OH moieties which is itself the reaction product of (a) a first diisocyanate containing NCO moieties of differing reactivity and (b) a polyhydric alcohol, in an OH:NCO ratio of about 0.55-4:1, so that only the more reactive NCO moieties are reacted with some of the OH moieties; and (B) a second diisocyanate containing NCO moieties which are more reactive than the less reactive NCO moieties of the first diisocyanate, in an OH:NCO ratio of from equimolar to an excess of NCO, so that the NCO moieties of said second diisocyanate react with said remaining free OH moieties of said first stage prepolymer, to form said isocyanate terminated polyurethane prepolymer.

Claim 3

The polyurethane prepolymer of claim 1 wherein said first diisocyanate is an aliphatic and/or aromatic asymmetrical diisocyanate.

Claim 4

The polyurethane prepolymer of claim 2 wherein said first diisocyanate is monocyclic.

Claim 5

The polyurethane prepolymer of claim 1 wherein said first diisocyanate is a tolylene diisocyanate, isophorone diisocyanate, or any mixture thereof.

Claim 6

The polyurethane prepolymer of claim 1 wherein said polyhydric alcohol is an aliphatic alcohol containing from 2 to 6 hydroxyl moieties.

Claim 7

The polyurethane prepolymer of claim 1 wherein said polyhydric alcohol is a primary or secondary aliphatic alcohol containing from 2 to 4 hydroxyl groups.

Claim 8

The polyurethane prepolymer of claim 1 wherein said polyhydric alcohol is selected from at least one of: C 2-5 diols; C 3-6 triols; C 4-8 tetraols; OH-functional polyesters having a number-average molecular weight of about 200 to 10,000; or OH-functional polyethers having a number-average molecular weight of about 100 to 10,000.

Claim 9

The polyurethane prepolymer of claim 1 wherein said polyhydric alcohol is a polypropylene glycol.

Claim 10

The polyurethane prepolymer of claim 1 wherein said second diisocyanate is an aliphatic and/or aromatic symmetrical diisocyanate.

Claim 11

The polyurethane prepolymer of claim 9 wherein said second diisocyanate is dicyclic.

Claim 12

The polyurethane prepolymer of claim 1 wherein said second diisocyanate is 4,4-diphenylmethane diisocyanate, 4,4-dicychlohexylmethane diisocyanate, or a mixture thereof.

Claim 13

The polyurethane prepolymer of claim 1 wherein: said first diisocyanate is at least one aliphatic and/or aromatic asymmetrical monocyclic diisocyanate; said polyhydric alcohol is at least one primary or secondary aliphatic alcohol containing from 2 to 6 hydroxyl moieties; and said second diisocyanate is at least one aliphatic and/or aromatic symmetrical dicyclic diisocyanate.

Claim 14

The polyurethane prepolymer of claim 1 wherein: said first diisocyanate is a tolylene diisocyanate, isophorone diisocyanate, or any mixture thereof; said polyhydric alcohol is a polypropylene glycol; and said second diisocyanate is 4,4-diphenylmethane diisocyanate, 4,4-dicyclohexylmethane diisocyanate, or a mixture thereof.

Claim 15

The polyurethane prepolymer of claim 1 wherein the OH:NCO ratio of polyhydric alcohol to first diisocyanate is about 0.6-1:1.

Claim 16

The polyurethane prepolymer of claim 1 wherein the OH:NCO ratio of first stage prepolymer to second diisocyanate is about 0.5:1:1.

Claim 17

The polyurethane prepolymer of claim 1 wherein the OH:NCO ratio of first stage prepolymer to second diisocyanate is about 0.6-0.8:1.

Claim 18

The polyurethane prepolymer of claim 12 wherein the OH:NCO ratio of polyhydric alcohol to first diisocyanate is about 0.6-1:1 and the OH:NCO ratio of first stage prepolymer to second diisocyanate is about 0.5-1:1.

Claim 19

The polyurethane prepolymer of claim 13 wherein the OH:NCO ratio of polyhydric alcohol to first diisocyanate is about 0.6-1:1 and the OH:NCO ratio of first stage prepolymer to second diisocyanate is about 0.6-0.8:1.

Claim 20

In an adhesive composition for bonding plastics, comprising a polyurethane prepolymer and at least one of a hardener, moisture, organic solvent, or an accelerator, the improvement wherein said polyurethane prepolymer has a low content of free isocyanate residual monomers and comprises the reaction product of (A) a low viscosity first stage prepolymer having free NCO moieties and free OH moieties which is itself the reaction product of (a) a first diisocyanate containing NCO moieties of differing reactivity and (b) a polyhydric alcohol, in an OH:NCO ratio of about 0.55-4:1, so that only the more reactive NCO moieties are reacted with some of the OH moieties; and (B) a second diisocyanate containing NCO moieties which are more reactive than the less reactive NCO moieties of the first diisocyanate, in an OH:NCO ratio of from equimolar to an excess of NCO, so that the NCO moieties of said second diisocyanate react with said remaining free OH moieties of said first stage prepolymer.

Claim 21

In an adhesive composition for bonding plastics, comprising a polyurethane prepolymer and at least one of a hardener, moisture, organic solvent, or an accelerator, the improvement wherein said polyurethane prepolymer has a low content of free isocyanate residual monomers and comprises the reaction product of (A) a low viscosity first stage prepolymer having free NCO moieties and free OH moieties which is itself the reaction product of (a) a first diisocyanate containing NCO moieties of differing reactivity and (b) a polyhydric alcohol, in an OH:NCO ratio of about 0.55-4:1, so that only the more reactive NCO moieties are reacted with some of the OH moieties; and (B) a second diisocyanate containing NCO moieties which are more reactive than the less reactive NCO moieties of the first diisocyanate, in an OH:NCO ratio of from equimolar to an excess of NCO, so that the NCO moieties of said second diisocyanate react with said remaining free OH moieties of said first stage prepolymer.

Claim 22

The adhesive composition of claim 19 wherein, in said polyurethane prepolymer: said first diisocyanate is at least one aliphatic and/or aromatic asymmetrical monocyclic diisocyanate; said polyhydric alcohol is at least one primary or secondary aliphatic alcohol containing from 2 to 6 hydroxyl moieties; and said second diisocyanate is at least one aliphatic and/or aromatic symmetrical dicyclic diisocyanate.

Claim 23

The adhesive composition of claim 20 wherein, in said polyurethane prepolymer the OH:NCO ratio of polyhydric alcohol to first diisocyanate is about 0.6-1:1 and the OH:NCO ratio of first stage prepolymer to second diisocyanate is about 0.5-1:1.

Claim 24

A process for synthesizing an isocyanate terminated polyurethane prepolymer having a low content of free isocyanate residual monomers, comprising reacting: (A) a low viscosity first stage prepolymer having free NCO moieties and free OH moieties which is itself synthesized by reacting: (a) a first diisocyanate containing NCO moieties of differing reactivity with (b) a polyhydric alcohol, in an OH:NCO ratio of about 0.55-4:1, so that only the more reactive NCO moieties are reacted with some of the OH moieties; with (B) a second diisocyanate containing NCO moieties which are more reactive than the less reactive NCO moieties of the first diisocyanate, in an OH:NCO ratio of from equimolar to an excess of NCO, so that the NCO moieties of said second diisocyanate react with said remaining free OH moieties of said first stage prepolymer, and form said isocyanate terminated polyurethane prepolymer.

Claim 25

A process for synthesizing an isocyanate terminated polyurethane prepolymer having a low content of free isocyanate residual monomers, comprising reacting: (A) a low viscosity first stage prepolymer having free NCO moieties and free OH moieties which is itself synthesized by reacting: (a) a first diisocyanate containing NCO moieties of differing reactivity with (b) a polyhydric alcohol, in an OH:NCO ratio of about 0.55-4:1, so that only the more reactive NCO moieties are reacted with some of the OH moieties; with (B) a second diisocyanate containing NCO moieties which are more reactive than the less reactive NCO moieties of the first diisocyanate, in an OH:NCO ratio of from equimolar to an excess of NCO, so that the NCO moieties of said second diisocyanate react with said remaining free OH moieties of said first stage prepolymer, and form said isocyanate terminated polyurethane prepolymer.

Claim 26

The process of claim 22 wherein: said first diisocyanate is at least one aliphatic and/or aromatic asymmetrical monocyclic diisocyanate; said polyhydric alcohol is at least one primary or secondary aliphatic alcohol containing from 2 to 6 hydroxyl moieties; and said second diisocyanate is at least one aliphatic and/or aromatic symmetrical dicyclic diisocyanate.

Claim 27

The process of claim 23 wherein the OH:NCO ratio of polyhydric alcohol to first diisocyanate is about 0.6-1:1 and the OH:NCO ratio of first stage prepolymer to second diisocyanate is about 0.5-1:1.

Claim 28

The process of claim 22 wherein both stages of the synthesis are conducted at temperatures of about 40° to 100° C.

Claim 29

The process of claim 22 wherein both stages of the synthesis are conducted at temperatures of about 80° to 95° C.