Patent GB-1080308-A (GB)
Title: Electrically rupturable microcapsules
IPC: B01J13/22
Filed: 1965-03-25
Abstract: 1,080,308. Capsules; packages. MINNESOTA MINING & MANUFACTURING CO. March 25, 1965 [April 28, 1964], No. 12763/65. Headings B8C and B8P. [Also in Divisions B6, G2 and H1] Micro-capsules have an electrically continuous and conductive exterior surface enabling them to be thermally ruptured by passage of a current, to release their contents. The capsules may be of natural or synthetic polymers or of glass, with a coating of metal or carbon. Alternatively the surface of the capsule body may be modified, e.g. by impregnation, to render it conductive. Coating capsules with metal.-As an example of a process for silver coating, capsules formed from urea formaldehyde and containing a dye were added to a bath containing a solution of silver nitrate in water to which ammonia had been added gradually. A solution of anhydrous dextrose and one of potassium hydroxide, both in water, were added, one after the other. The mixture was stirred and the coated capsules removed. Applications: resin adhesive-hardener packages.-Resin mixed with capsules containing the hardener are packaged in a container, the mouth of which is obscured by a grid to which current may be applied when the contents are poured out. As emerging capsules contact the grid, they burst to release the hardener. Facsimile reproduction.-Capsules containing colour dyes or colour forming reactants are attached to a conductive backing sheet and transversed by the usual stylus which forms an electrode. The capsules which it contacts burst to produce the image. In the case of colour forming reactants, one reactant may be carried in a layer on the sheet in which the capsules are embedded, e.g. methyl yellow with capsules containing an acidic substance. Capsules may be further coated or covered with a photo-conductive material, e.g. indium oxide, either before or after attachment to the sheet so that, after exposure to a light image and contact with an electrode roller, brush or stylii, they will burst according to the degree of conductivity induced and reproduce the image. Capsules containing various coloured dyes may be coated with photo-conductive material sensitized to the corresponding colour and be attached, randomly dispersed, to the conductive sheet for treatment as above, so that colour prints may be produced. The coating thickness may be varied to produce tone graduations. Two sets of capsules containing resin and hardener, rendered photo-sensitive as above and attached to a sheet may produce a raised image after selective bursting, hardening and removal of unaffected material. The image may be transferred to a sheet or roller. If image and background areas have different wetting characteristics, plates or sheets so formed may be used as lithographic masters. Material from burst capsules may be stabilized by later application of heat with or without a catalyst. Co-reactants may be applied after release to such capsule contents as dye precursors. A second sheet containing co-reactant may be brought into contact with released capsule contents on a first sheet to provide an image on the second sheet. Multiple copies may be produced in this manner.