GB1279448A - Marking instrument for activating invisible ink printing - Google Patents

Abstract

1279448 Invisible ink developers; wax markers MEREDITH CORP 29 Sept 1969 [17 Jan 1969] 47836/69 Headings C4A and C5W [Also in Division B6] A marking instrument for developing invisible ink comprises a waxy matrix in which discrete particles of a hydrophilic solution of a material reactive with the ink are uniformly dispersed. The waxy matrix comprises at least 50% by wt. of said instrument and may include a wax, a resin, an emulsifying agent, a plasticizer and a colouring agent. The dispersed phase includes a metal salt ion or other chemical indicator reactive with the invisible ink to produce a colour, a solvent therefor, and optionally a chelating agent for the salt ion, a pH buffer, and a colouring agent. The ingredients are melted together and may be shaped into a crayon or block or any desired shape from which the solution particles are released when the waxy matrix is subjected to abrasion. The major wax component constitutes 50-80% by wt. of the composition and may comprise one or more of paraffin wax, scale wax and micro-crystalline wax. This wax may be plasticized by stearin derivatives, fatty acids or alcohols or by beeswax, and strengthened 'by .a synthetic or natural resin. Sorbitan stearates and hexylene glycol act as emulsifying agents. The hydrophilic phase may include ferric ammonium sulphate dissolved in ethylene glycol and water, with ;N,N - di(hydroxy)ethyl glycine sodium salt as chelating agent for the ferric ion, and triethanolamine as pH buffer. In place offerric ammonium sulphate pH indicators such as thymolphthalein, bromphenol blue, thymol blue, brow cresol green or purple, o-cresol phthalein, alizarin, resazurin or congo red may be used. Applications 47835/69 and 47837/69 are referred to.