GB1042596A - Pressure-sensitive record sheets - Google Patents

Abstract

A pressure-activatable, self-generating-image-forming sheet material includes normally separated image-forming coreactants which form visible images on contact with one another. One of the coreactants is in a water-immiscible liquid fill contained in minute, hollow, rupturable capsules that are insoluble but dispersible in water and have shells of urea-formaldehyde polymer. The second colour-reactant is carried on the sheet material adjacent to the capsules to produce the distinctive colour when the capsules are ruptured. The sheet material may be formed by adding the capsules and the second reactant to an aqueous slurry of sheet-material-forming solids and then depositing the slurry, e.g. on a paper-making machine, to form the sheet material. The second reactant may be present as a filler or as a sizing for the sheet, or may be applied as a coating to the capsules or as a coating or impregnant for a preformed sheet containing the capsules. It may be preformed or formed in situ by the successive addition to the slurry of two substances, e.g. sodium rosinate and nickel sulphate that react to form it. The sheet-forming solids may be rag- or wood-pulp, "fibrids", mica or synthetic fluorine mica, or man-made fibres of rayon, polyacrylonitriles, polyesters or polyamides. A layer of web-forming solids without capsules may be first formed, and a second layer of web-forming solids containing capsules then laid on top. The preferred capsule fill is a solution of dithioxamide (DTO) or its N, N1-disubstituted derivatives, and the other reactant a rosinate of a metal, e.g. nickel, cobalt, copper or silver or a mixture thereof. In the Examples: (2) capsules containing N, N1-dibenzyl-dithioxamide (DBDTO) and nickel stearate were added to a wood-pulp slurry and formed into paper of a bluish colour which marked where typed upon; (3) a similar slurry was applied to a wet web formed from wood-pulp alone, purple images could be formed by stylus pressure; (4) to wood-pulp were added successively sodium rosinate, capsules containing DBDTO, and nickel sulphate, the paper formed was off-white and gave blue-purple marks when typed upon; (5) to wood-pulp were added sodium rosinate, capsules containing DBDTO and oleic acid, and cupric nitrate, the paper formed was light green and gave a green image when typed upon; (6) cobalt nitrate was substituted for the cupric nitrate of example 5, the paper formed was light grey and gave yellow images; (7) a mixture of nickel sulphate and cupric nitrate was substituted for the simple salts of examples 5 and 6, the paper was off-white with a greenish tint and gave a metallic-brown image; by varying the proportions of nickel and copper salts the colour could be varied from brown to purple; (8) to wood-pulp were added a mixture of sodium rosinate and sodium oleate, nickel sulphate and capsules containing DBDTO and oleic acid, the paper formed had little if any background colour and formed blue-purple images; by replacing a small proportion of the nickel sulphate with cupric nitrate, the colour of the images was changed to lavender; (9) to pulp were added capsules as in Example 5, nickel rosinate and nickel oleate, the paper was white and formed blue images; (10) capsules as in Example 5 were coated with nickel rosinate and incorporated into the paper slurry; (11) the slurry contained wood-pulp and fluorine synthetic mica, to this were added capsules containing a solution of crystal violet lactone and p, p1-methylene-bis-(N, N1-dimethylaniline), the paper formed blue images; (12) the capsules contained solutions of lauroylpyrogallol or ortho-dihydroxy-spiroindane and were used with paper pulp, sodium rosinate, ferric sulphate and alum, the paper was yellow to tan and formed black images; lighter yellow sheets were obtained by reacting the sodium rosinate and ferric sulphate before adding them to the slurry; when silver was substituted for iron, the sheet was light pink to white and the image dark brown; when octadecylamine vanadate was substituted for the metal rosinate, the sheet was white and the image blue-black. The Specification also refers to the use with DTO or its derivatives of (C2H5)2 AuBr, Ni(H2NCH2CH2NH2)3 and Ni(CH3NH2)2, to the use of Malachite green lactone, orthohydroxybenzalacetophenone, 2, 4-bis-(paradimethylaminoazo) -aniline-6-hydroxysymmetrical-triazine, and Michler's hydrol with alum or siliceous compounds, and to the use of other siliceous compounds such as magnesium trisilicate, zeolite, attapulgite and bentonite, or attapulgite clay and synthetic fluorine mica in combination, flocculated by barium nitrate. The paper may also contain other additives of known kind, or may be sized with antioxidants such as thiourea, hydroquinone, or phenylbetanaphthylamine to reduce fading or change of colour in the images.