Patent GB-750972-A (GB)
Title: Pressure rupturable record member
IPC: B41J13/10
Filed: 1954-05-29
Abstract: A record member is provided on one surface with a coating of microscopic, pressurerupturable oil-containing capsules of gelled hydrophilic colloid material, the capsules containing at least one colour-reactant substance and being arranged in contiguity with microscopic particulate solid material on said surface adapted to react with said colour-reactant substance when the capsules are ruptured so as to produce a distinctive colouration of the record member.  The solid particle reactant substance is coated on the base by use of binder material and the capsule coating applied thereafter in a water suspension and dried.  Alternatively, the coatings may be applied in reverse order, or the capsular material may be interspersed with a liquid suspension of the particulate material and the whole applied as a single coating.  The encapsulating material may be gelatin, gelatin and gum arabic or agar-agar.  The total coating thickness may be as little as 0.001 inches.  The colour-reactant substance contained in the oil is an organic electrondonor aromatic compound having a doublebond system, which acquires a distinctive colour upon taking part in an electron donor-acceptor chemical reaction with the solid particulate substance, which is an acid relative to the organic substance, and which is inorganic.  The particulate substance may be attapulgite, magnesium trisilicate or sodium aluminium silicate zeolite material, or mixtures thereof.  The organic substance may be or include one or more reactants of of the phthalide type, such as crystal violet lactone or malachite green lactone, and there may be included a colourless compound, such as benzoyl leuco methylene blue, which oxidizes on contact with the particulate substance to form a colour, and renders the marks produced permanent.  Example.  20 per cent starch in water is cooked at 93 DEG C. for 15 minutes and cooled to room temperature.  One part attapulgite is dispersed in 3 part water. Four parts of the attapulgite dispersion is mixed with 1 part of the starch solution.  The mixture is applied to the paper to a thickness of 0.0005 inches and allowed to dry.  Twenty grams gum arabic is dissolved in 160 grams water, and into the solution is emulsified 80 grams trichlorodiphenyl containing 3-6 per cent crystal violet lactone and benzoyl leuco methylene blue in equal amounts, until the drop size is from 2 to 5 microns.  Twenty grams gelatine is dissolved in 160 grams water and mixed with the emulsion, the gelatin having a pH of 8 and a jelly strength of 275 grams, as measured by the Bloom gelometer.  The pH of the mixture is adjusted to 6.5 with 20 per cent sodium hydroxide in water.  Three hundred grams of the adjusted mixture is diluted with 700 grams water at 50 DEG C. with agitation. The pH is lowered to 4.5 with 10 per cent acetic acid in water, which causes the colloid to be deposited around the oil droplets.  While still at 50 DEG C., 2.19 grams of a 37 per cent solution of formaldehyde in water is added.  Not more than 20 minutes should elapse from the start of dilution to this point. Gelation is then commenced by placing the mixture in an ice bath until it reaches 10 DEG C.  The pH is then adjusted to 9 with 20 per cent sodium hydroxide in water to harden the capsules.  The material is then coated on to the paper.  Alternatively, the encapsulating film may be made from a single colloid material, in which case 1 gallon of an oil-in-water emulsion of 20 parts trichlorodiphenyl containing the colour-reactants referred to above and 100 parts of a solution of 10 per cent gelatin in water is prepared, and kept at 50 DEG C., while 0.4 gallon of 20 per cent sodium sulphate in water is slowly and uniformly added.  To gell, the mixture is poured into 10 gallons of 7 per cent sodium sulphate in water at 19 DEG C., with agitation.  The material is filtered and washed to remove the salt, the temperature being kept below the melting point of the gelatin.  The filtered material is hardened by combining it with 2 gallons of 37 per cent solution of formaldehyde in water, and the hardened mass is filtered and washed to remove the residual formaldehyde.  The proper water content is then obtained by adding or removing water.  Instead of trichlorodiphenyl, any waterimmiscible oil which is inert to the other substances used in forming the capsules may be used, e.g. paraffin oil, castor oil, sperm oil, lard oil, or methyl salycilate, the reactant material being either dissolved or dispersed in the oil.