Process for producing microcapsules
A process for producing microcapsules containing a shell and a core of a liquid water-insoluble material is disclosed. The microcapsules are prepared using a bifunctional isocyanate, an anionically modified diisocyanate, a bifunctional amine, and a protective colloid. The protective colloid is a polyvinyl alcohol copolymer having hydrolysis degrees from 85 to 99.9%.
1. A process for producing microcapsules which contain a shell and a core of a liquid water-insoluble material, comprising
(a) preparing a premix (I) from water and a protective colloid;
(b) preparing a further premix (II) from a water-insoluble liquid component and at least one bifunctional isocyanate (A) or a mixture of two or more different isocyanates containing (A) and an anionically modified diisocyanate (B) is used, wherein the anionically modified diisocyanates (B) are selected from the group which contain at least one sulfonic acid group in the molecule;
(c) mixing the two premixes (I) and (II) together until an emulsion is formed; and
(d) then pouring at least a bifunctional amine into the emulsion from step (c); and
(e) then heating the emulsion to at least 50° C. until the microcapsules are formed,
wherein the protective colloid is a polyvinyl alcohol copolymer having hydrolysis degrees from 85 to 99.9%; and
wherein the polyvinyl alcohol copolymer contains 0.1 to 30 mol % comonomers with anionic groups.
2. The process as claimed in claim 1 , wherein the polyvinyl alcohol copolymer has hydrolysis degrees between 85 to 95%.
3. The process as claimed in claim 1 , wherein the polyvinyl alcohol copolymer contains 0.1-30 mol % comonomers with sulfonic and/or carboxylate groups as anionic groups.
4. The process as claimed in claim 1 , wherein the at least one bifunctional isocyanate (A) is selected from the group consisting of hexane 1,6 diisocyanate, hexane 1,6 diisocyanate biuret, oligomers of hexane 1,6 diisocyanate, and dicyclohexanemethylene diisocyanate.
5. The process as claimed in claim 1 , wherein the weight ratio between the isocyanates (A) and (B) is in the range from 10:1 to 1:10.
6. The process as claimed in claim 1 , wherein the at least one bifunctional amine used is a polyethyleneimine.
7. The process as claimed in claim 1 , wherein the core-shell ratio (w/w) of the microcapsules is 20:1 to 1:10.
8. The process as claim in claim 3 wherein the polyvinyl alcohol contains 0.1 to 15 mol % comonomers with sulfonic and/or carboxylate groups as anionic groups.
9. The process as claim in claim 8 wherein the polyvinyl alcohol contains 0.1 to 10 mol % comonomers with sulfonic and/or carboxylate groups as anionic groups.
10. The process as claimed in claim 4 wherein the at least one bifunctional isocyanate (A) comprises a trimer of hexane 1,6 diisocyanate or dicyclohexanemethylene diisocyanate.