| 摘要 |
A suspension of a particulate material in an inert electrical insulating liquid, e.g. an organic solvent, is treated with another particulate substance which may also be in the form of a suspension bearing an electrostatic charge of opposite polarity to the suspended material whereby the charges are modified <PICT:0879464/III/1> and the suspension is precipitated. The charge may be reduced, by control of the material added, so that a relatively large deposit is formed. The process is applied to the precipitation of pigments to develop images on an electrostatic surface as described in Specification 835,044. For example, particles 1, Fig. 1, suspended in an insulating liquid 2 are mixed with a suspension of oppositely charged larger particles 4 in another liquid compatible with liquid 2. The proportions of oppositely charged materials may be such that on mixing the iso-electric point is reached and precipitation occurs, and is collected, e.g. on a filter 7. By using different proportions the iso-electric point is not reached, and the suspension of mixed particles bearing a reduced charge may be used as a developer of electrostatic images, and is referred to as a "triggered" developer. Such a developer containing pigment particles partly reduced charge, will deposit relatively large number of particles to neutralize the charge on the electrostatic image. A close control over the image is thus available. The electric charge on the suspended particles may also be stimulated by an electric field. Examples are given of (1) a mixture of synthetic resins, solvent, and carbon black, re duced to 0.5 micron in particle size, and the pigment suspension is then coated and precipitated by adding a suspension of "Monolite" (Registered Trade Mark) red pigment; a suspension of antimony sulphide and calcium fluoride in carbon tetrachloride is separated into distinct layers by adding beeswax particles thereto. As coating and precipitating agents there may be used a powdered wax, gum or synthetic resin, or an oil.
|
