Process for encapsulating dissolved reactants of color-reaction systems, the capsules obtainable therefrom as well as their use in color-reaction papers

Abstract

A process is described for encapsulating a solution of color reactants of color-reaction systems present in an aqueous emulsion accomplished by means of conventional microencapsulation processes, in which the color reactant is first dissolved in a solvent and a non-dissolver, which may insignificantly dissolve the color reactant, is mixed into the resulting solution in an amount that establishes a supersaturated solution while mixing at high speed, the supersaturated solution is emulsified immediately in the aqueous phase while mixing at high speed, and immediately thereupon the encapsulation is performed. A vegetable oil C 1 -C 8 alkyl ester is used as the solvent. This process has economic and technological advantages. For example, it can be used to produce microcapsules that have an advantageous narrow monomodal particle distribution, which results in improved writing performance.

1 - 17 . (canceled)  
   
   
       18 . Microcapsules for pressure-sensitive color-reaction systems, wherein the microcapsules are obtained from a process comprising: 
 dissolving a color reactant in a solvent;    high speed mixing a non-dissolver into the resulting solution in an amount that establishes a supersaturated solution;    emulsifying the supersaturated solution immediately in the aqueous phase while mixing at high speed; and    encapsulating the supersaturated solution immediately;    wherein the color-reactant within the microcapsules is present in a supersaturated system that contains a vegetable oil C 1 -C 8  alkyl ester as the solvent and a non-dissolver.    
   
   
       19 . Microcapsules of  claim 18 , wherein approximately 0.5 to 4 wt. parts non-dissolver is used per one weight part solvent mixture.  
   
   
       20 . Microcapsules of  claim 18 , wherein the vegetable oil C 1 -C8 alkyl ester is present in the form of a vegetable oil methyl ester, comprising a rapeseed oil methyl ester.  
   
   
       21 . The microcapsules of  claim 18 , wherein the supersaturated system also contains a good solvent that dissolves the color reactant better than the vegetable oil C 1 -C 8  alkyl ester.  
   
   
       22 . The microcapsules of  claim 21 , wherein approximately 0.1 to 9 wt. parts vegetable oil C 1 -C 8  alkyl ester are used per 1 wt. part good solvent.  
   
   
       23 . The microcapsules of  claim 21 , wherein the good solvent is present in the form of an aromatic solvent and/or chlorinated paraffin.  
   
   
       24 . The microcapsules of  claim 23 , wherein the aromatic solvent is present in the form of alkylated biphenyls, alkylated naphthalenes, alkylated terphenyls, arylated xylenes, and/or in the form of diarylalkane compounds.  
   
   
       25 . The microcapsules of  claim 18 , wherein the non-dissolver is present as a nonaromatic solvent, in particular in the form of an aliphatic and/or cycloaliphatic hydrocarbon.  
   
   
       26 . The microcapsules of  claim 18 , wherein a basic color-producing substance is encapsulated as a color reactant.  
   
   
       27 . The microcapsules of  claim 26 , wherein a lactone derivative, fluorane derivative, phthalide derivative, diphenylmethane derivative, triphenylmethane derivative, oxazin derivative, and/or spiropyrane derivative is encapsulated as a basic color-producing substance.  
   
   
       28 . The microcapsules of  claim 18 , wherein an acid reactant of the basic color-producing substance of the color-reaction system is encapsulated.  
   
   
       29 . The microcapsules of  claim 28 , wherein an acidic phenolic compound, a zinc-modified salicylic acid derivative, and/or acid-activated clay minerals are encapsulated as the acidic reactant.  
   
   
       30 . Microcapsules of  claim 18 , wherein at room temperature (20° C.) the degree of supersaturation of the encapsulated system is at least 5%.  
   
   
       31 . The microcapsules of  claim 30 , wherein the supersaturation is more than 50 wt. %.  
   
   
       32 . The microcapsules of  claim 18 , wherein the average particle diameter of said microcapsules lies between approximately 3 and 5.  
   
   
       33 . The use of the microcapsules of  claim 18  with an encapsulated microdispersion of a basic color-producing substance, which produces a color by means of the reaction with acidic reactants, in color-reaction papers.