Further aspects will become clear from the following detailed description of the invention.
EXAMPLE 1
Microcapsules consisting of polyurea-formaldehyde containing the precursor of the epoxy resin were prepared by curing in situ in a water-oil emulsion. 400 mL of deionised water and 100 mL of an aqueous solution of an EMA copolymer were mixed in a 2 L beaker at ambient temperature (25° C.). 10 g of urea, 1.0 g of ammonium chloride and 1.0 g of resorcinol were dissolved in the solution under stirring. The pH was increased from 2.6 to 3.5 by adding NaOH and HCl drop by drop. A slow flow of 120 ml of epoxy oligomer was added to form an emulsion, and stabilised for 10 min. After stabilisation, 25 g of an aqueous solution of formaldehyde was added. The emulsion was heated at the rate of 1° C. a minute to 55° C. After 4 hours' continuous stirring the heating was switched off and the mixture cooled. The suspension of microcapsules was separated under vacuum, and the microcapsules were rinsed and dried for 48 hours. The SEM image of the microcapsules obtained is shown in FIG. 1.