Method of printing onto pressure-sensitive record materials

Details Method of printing onto pressure-sensitive record materials Method of printing onto pressure-sensitive record materials

1995-05-04

1998-04-21

Mullis, Jeffrey

Plastic and nonmetallic article shaping or treating: processes

Encapsulating normally liquid material

101288, 101491, B41M 500

Patent

active

057414475

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION OF INVENTION

This invention relates to a method of printing onto pressure-sensitive record materials of the kind comprising a base sheet, typically of paper, coated with a rupturable material confining droplets of a solution of colour-forming substances, which when released by rupture of the material undergo a colour-forming reaction to produce an image either on the base sheet itself or on a further, receptor sheet in face-to-face contact with the coated face of the base sheet.
In particular, but without limitation, the invention is applicable to so-called "carbon-less" copy papers which rely on two coatings formed respectively on the contiguous faces of superimposed sheets of paper, namely a coating containing the colour-forming substance in the micro-capsules, on the back of the uppermost sheet (usually known as a CB coating) and a coating of a receptor layer on the front of the lowermost sheet (usually known as a CF coating). Colour-forming chemicals are typically dissolved in an oily solvent and encapsulated by well known techniques, and when such capsules are ruptured by mechanical pressure, as by impact of a type bar of a typewriter, the chemicals are released and react to form a visible mark on the CF coating of the adjacent sheet.
Conveniently, paper for use in such copying systems is of three types, distinguished by their coatings, namely CB sheets having a CB coating on the underside to form the top sheet of the set, CF sheets having a CF coating on the upper side to form the bottom sheet of a set, and optionally CFB sheets having a CF coating on the upper side and a CB coating on the underside to form one or more intermediate sheets of a set where required. Such coatings are normally applied by a continuous process to cover the entire area of the appropriate face of the sheet.
In recent years, there has been a demand for printing onto such coated paper as the recipient material in toner-based printing systems in which an image is transferred to the recipient material electrostatically, a process sometimes known as "xerographic, electronic or laser printing". However, difficulties have been experienced in such electrostatic printing systems when the recipient material comprises such coated papers. In particular, it appears that the handling of CB and CFB material, either before or during the printing process, may rupture some of the capsules containing the colour-forming chemicals, and this is particularly liable to lead to "poisoning" of the electrostatic transfer drum or loop and also contamination of paper-feed, fuser and pressure rollers so that the printing apparatus fails to perform satisfactorily after a short period of operation using such CB (or CFB) sheets.
Conventional colour-formers, e.g. various leuco-dye stuffs, have normally been dissolved in a range of organic solvents, typically aromatic solvents, which afford adequate solubility for conventional colour-formers and enable a good image to be produced. However, such conventional solvents appear to be mainly responsible for the above-mentioned problems with any printing apparatus, which incorporates components made of rubber (natural or synthetic) elastomers and/or polymers (i.e. such materials as nitriles, urethanes, EPDM, and particularly thermally conductive polydinethylfiloxane materials as used for fuser rolls), especially When operating above ambient temperatures. In addition synthetic and other capsules are brittle and are more readily fractured. This can lead to a build-up of micro-capsule dust which will damage mechanical parts of such electronic printing systems.
Proposals have been made with regard to the use of alternative encapsulation systems but so far no wholly acceptable alternative system has been found. It has been suggested that the micro-capsule is treated in such a way as to decrease the risk of premature rupture of the micro-capsules, but this results in a decrease in the imaging sensitivity of the material in subsequent use. Moreover, such specially treated coatings are inherently unsafe since i

REFERENCES:
patent: 4783196 (1988-11-01), Eckstein et al.
patent: 4859650 (1989-08-01), Hilterhaus et al.
patent: 4996240 (1991-02-01), Osipow et al.
patent: 5464803 (1995-11-01), McGuinness et al.
Derwent Abstract #74-31778v abstracting JP 49-013456 (1974).
Sanders et al. "Carbonless Paper for Xerographic Duplicator/Printers" Proceedings The 6th International Congress on Advances in Non-Impact Printing Technologies pp. 739-745, Oct. 1990.

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