Microcapsules with a defined opening temperature, a process for their production and their use
AssigneeBayer Aktiengesellschaft
InventorsHildegard Schnoring, Bruno Bomer, Manfred Dahm
Life of this patent
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Abstract
Microcapsules having a defined release temperature and being formed of gelatin or a mixture of gelatin with gum arabic, carboxymethylcellulose and/or anionic polymers, the gelatin having been hardened with a natural and/or synthetic tanning agent and with a carbonyl compound, and the process for making said microcapsules.
Claims18
In microcapsules of the type wherein a shell wall encloses a core material, the improvement comprising said shell wall being formed of gelatin mixed with carboxymethylcellulose and anionic polymers, which polymers consists of (a) a copolymer, the structural units of which consist to the extent of 65 to 90 mole %, relative to the polymer, of randomly distributed radicals of acrylamide and to the extent of 10 to 35 mole % of radicals of maleic acid or maleic anhydride, and which have an intrinsic viscosity of 0.05 to 1.0, and (b) a copolymer, the structural units of which consist of randomly distributed polymerized radicals of acrylamide, arylic acid and maleic acid, the maleic acid radicals being at least partly present in salt form, and which has an intrinsic viscosity of 0.05 to 1.5 and contains a total of 65 to 90 mole %, relative to the polymer, of radicals of acrylamide and of acrylic acid, and 10 to 35 mole % of radicals of maleic acid, the weight ratio of a:b being 1:2 to 20:1, and said wall material being hardened with a natural or synthetic tanning agent, or a mixture thereof and glutarodialdehyde for a period of time sufficient to raise the opening temperature to a predetermined desired temperature, to form a microcapsule with a defined release temperature.
A process for the production of microcapsules of the type wherein a shell wall encloses a core material, comprising the steps of coacervating gelatin in an aqueous medium in the presence of the core material by mixing the gelatin with a polymer of acrylamide and maleic anhydride, in approximately equal amounts by weight in about a 10% aqueous solution at 50.degree. C.;
- emulsifying the core material in the gelatin solution until the average droplet is size 10 to 15 .mu.m, and thereafter, adding a solution, warmed to 50.degree. C., of carboxymethylcellulose;
- pre-hardening the shells of the microcapsules by adding, as a tanning agent, Tannigan QF in acidic water with stirring, and thereafter cooling the mixture to between 5.degree. C. and 10.degree. C. and stirring for three hours;
- hardening the shell of the microcapsule by adding to the mixture an aqueous solution of glutarodialdehyde, and stirring for 2 to 3 minutes, thereafter adjusting the pH value to 6.5 with 10% strength aqueous sodium hydroxide solution and stirring the resulting slurry at room temperature for 16 hours;
- and thereafter
- drying the resulting capsules in a fluidized bed or in a spray-drier to give a free-flowing powder which is easily dispersed in water.
Dependencies are inferred from the claim text.