GB823897A - Luminescent transfer paper - Google Patents

Abstract

823,897. Luminescent materials and uses thereof. KEE LOX MANUFACTURING CO. Oct. 7, 1957, No. 31278/57. Class 39(1). [Also in Group XVI] A transfer element comprises a paper support coated with a readily transferable copying layer containing wax and a luminescent substance which is substantially invisible in ordinary light but which fluoresces when exposed to energy having a wavelength different from that re-emitted by the luminescent substance. The preferred coating mixture comprises 32% carnauba wax, 21% mineral oil and 47% luminescent substance such as zinc sulphide activated by gold, copper, silver, bismuth or manganese. Ten thousand parts of pure zinc sulphide may be ground in a porcelain ball mill with one part of the activator and heated to about 1050‹C. to form a crystal structure. The luminescent material instead of being mixed with wax may be coated onto the surface of a wax coating on a sheet of tissue paper. The transfer element may be placed between two sheets of paper to provide a normally invisible copy on the underlying sheet of matter printed on the overlying sheet, or to provide a normally invisible "negative" copy on the under surface of the overlying sheet. The element may also carry a conventional carbon coating either on the other side of the paper support or between the paper and the luminescent layer or may combine these arrangements as shown in Fig. 4. In the latter case, if the carbon copy is erased or obliterated the underlying, normally invisible copy is stated to be unharmed. The exciting radiation may be electromagnetic, sound or invisible light waves. The luminescent material may be rhombohedral crystals of Willemite (Zn2 SiO4 : Si) excited by magnetic fields; tetragonal crystals of ZnF2: Mn, cubic crystals of ZnS : Mn, or Ca2 P 2 O 7 : Dy excited by sonic or ultrasonic vibrations ; or cubic crystals of Sr (S : Se) : SrSO 4 : CaF2 : Sm : Eu excited by infra-red radiations.