Patent GB-954743-A (GB)
Title: Electrophotographic material
IPC: G03G5/05
Filed: 1962-10-18
Abstract: 954,743. Electrophotographic materials; printed circuits. KALLE A.G. Oct. 18, 1962 [Oct. 25, 1961], No. 39519/62. Headings H1K and H1R. [Also in Division G2] The photoconductive layer of an electrophotographic material includes one or more photoconductors and as a binder polyvinylacetate having an average molecular weight in the range 20,000 to 150,000. Mixtures of polyvinylacetates with molecular weights in this range may be used. The photoconductor: polymer ratio is preferably in the range 0.5 : 1 to 10: 1. Other film-forming resins such as polystyrene, styrene interpolymers, and polyacrylic esters may be included in the layer in quantities usually not greater than 10%. Any of the usual electrophotographic photo conductors may be used, for example the oxides and sulphides of zinc and cadmium, zinc oxide being a preferred material. Mixtures of inorganic photoconductors, mixtures of one or more inorganic photoconductors with one or more organic photoconductors, or organic photoconductors alone may be used. Suitable organic examples listed fall within the classes of diazoles, oxazoles, thiazoles, imidazolones, imidazolethiones, triazoles, oxadiazoles, triazines, hydrozones, and hydrazides. The photoconductive layer may contain unspecified pigments, fillers, and activators added in small quantities, and sensitizers such as known dyestuff sensitizers may be added to the mix before it is applied to a support or may be applied after coating. Suitable support materials include metal foils such as those of magnesium, zinc, aluminium, copper and brass; plastic foil to metal foil laminates; and plastic foils metallised by vapour deposition of one of the metals previously mentioned. Other common electrophotographic supports may be used including paper which should be water-proofed and provided with an hydrophilic electrically conductive pre-coat for example by treatment with a polyamide from an aqueous alcoholic solution or from a dispersion in a suitable vehicle. The dissolved or dispersed components of the photoconductive layers are applied to the support by spraying, painting, roller application, or by immersion of the support in the mix. The support may be rotated during application of the mix and the material is afterwards dried at an elevated temperature. For the production of printed circuits a support of metal foil-covered plastic sheet carries the photoconductive layer. This is electrostatically charged, exposed to an image, and developed with a material containing a toner which adheres to the image areas. Photoconductor material is dissolved from the non- toner covered parts to expose the metal foil which in these areas is subsequently etched away. (For example copper may be removed by iron chloride or ammonium persulphate solutions.) A suitable solvent is then used to remove the toner and remaining photoconductor to reveal the printed circuit. In the specific example directed to this application a layer containing zinc oxide and polyvinyl acetate is formed on a copper foil/phenolic resin laminate. The material is charged, with the copper foil earthed, and a contact exposure made using a transparent positive. A developer is used which uniformly colours solid areas, for example a mixture of an electrophotographic toner and iron particles. The toner is fixed by heating and the unprotected photoconductor areas dissolved away for example with aqueous iso-propanol (other solvents are suggested) and the bared copper etched away. The toner and remaining photoconductor are removed with a solvent such as methylene chloride.