Thermal transfer printing

Details Thermal transfer printing Thermal transfer printing

1996-06-11

1998-09-22

Tran, Huan H.

Incremental printing of symbolic information

Thermal marking apparatus or processes

Multicolor

347224, 347217, B41J 2325, B41J 2475, B41J 248

Patent

active

058121730

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION



BACKGROUND OF THE INVENTION

This invention relates to dye diffusion thermal transfer printing.
Dye diffusion thermal transfer printing is a generic term for processes in which one or more thermally transferable dyes are caused to transfer from a dye sheet to a receiver sheet in response to thermal stimuli. Using a dye sheet comprising a thin substrate supporting a dye coat containing one or more such dyes uniformly spread over an entire printing area of the dye sheet, printing can be effected by heating selected discrete areas of the dye sheet whilst the dye coat is pressed against a receiver sheet. The shape of the pattern transferred is determined by the number and location of the discrete areas which are subject to heating. Complex images can be built up from large numbers of very small pixels placed close together, the resolution of the final image being determined by the number, size and spacing of such pixels. Full colour prints can be produced by printing with different coloured dye coats sequentially in like manner. Usually, the dye sheet is In the form of a ribbon with the different coloured dye coats being in the form of discrete panels or stripes transverse to the axis of the ribbon in a repeated sequence along the ribbon, printing of the three colours being effected by moving the dye ribbon axially relative to the receiver sheet and whatever means are used to generate the thermal stimuli.
The thermal stimuli may be produced by a thermal printing head having a matrix of tiny heating elements (typically six or more to the millimeter) which are selectively energisable to transfer individual pixels. By programming the printing head to respond to electronic signals representing monochrome or full colour images (eg from a video camera, electronic still camera or computer), hard copies of those images can be produced. Alternatively, the thermal stimuli can be produced by means of a laser beam which is scanned across the dye coat in a raster pattern, the intensity of the beam being modulated in accordance with the aforesaid electronic signals to transfer the individual pixels. Use of a laser allows much greater resolution which is particularly important in respect of the use of thermal printing to prepare 35 mm slides (or transparencies) as an alternative to the conventional photographic method.
Conventionally, the dye coats are applied by gravure coating and as is well known, gravure coating relies on a roller the surface of which has been etched to provide a pattern of cells which pick up and transfer the coating and which inherently produce variations in the thickness of the dye coat which can cause variations in the optical density of the transferred image. Normally this is of little importance as such variations are invisible to the eye.
However, 35 mm slides can, of course, be magnified by a factor of 50 or more during projection and at this degree of magnification any variation caused by the cell pattern would be a serious drawback.
Moreover, for slide preparation it is essential to have a high dye coat weight so that the high transmission optical density required in final prints can be achieved and such weights cannot easily be achieved by gravure coating.
Although a better quality coating (ie without cell patterns) of higher weight can be achieved using continuous coating methods such as bead coating, such methods cannot be used to produce conventional panelled dye sheets.
In WO/14581 an attempt is made to overcome the problem by coating the substrate longitudinally with the dye coats and then cutting the resulting dye sheet into strips which are joined end to end to form a conventional dye ribbon with transverse dye coats. However, this is a cumbersome operation and such dye ribbons would have an inherent physical weakness.
To simplify terminology, hereinafter dye ribbons on which the dye coats are in the form of stripes extending along the longitudinal axis of the ribbon will be referred to as longitudinal dye ribbons and those on which the dye coats extend at righ

REFERENCES:
patent: 4611217 (1986-09-01), Iizuka et al.
patent: 5017547 (1991-05-01), DeBoer
patent: 5341157 (1994-08-01), Campagna et al.
patent: 5450117 (1995-09-01), Quanz
R.J. von Gutfeld, "Layered Structure For Decreasing Laser Energy For Beam-Addressable Memory", IBM Technical Disclosure Bulletin, vol. 16, No. 2 Jul. 1973 pp. 498-499.
Nash et al., "Ink Barrier For A Multicolor Printer Ribbon", IBM Technical Disclosure Bulletin, vol. 27, No. 3 Aug. 1984, p. 1824.

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