Laser dye thermal transfer printing

Details Laser dye thermal transfer printing Laser dye thermal transfer printing

1996-06-10

1999-01-26

Le, N.

Incremental printing of symbolic information

Light or beam marking apparatus or processes

Scan of light

347252, B41J 247, G01D 1514

Patent

active

058643567

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a method of operating a laser source to effect dye thermal transfer printing. There are three main types of dye thermal transfer printing methods, in which dye is transferred by melting, diffusion and sublimation respectively.
In the diffusion method, a dye donor ribbon and a dye receiver ribbon, comprising a dye layer and a receiver layer, respectively, on a supporting substrate, are held in contact with one another, and a localized source of energy is used to heat selected pixel regions of the dye layer to cause dye in those regions to become thermally mobile and diffuse into the adjacent receiver layer to produce a pattern of printed pixels therein. A desired print may be produced by heating an appropriate selection of pixel regions in the dye layer. By applying more or less energy to a pixel region of the dye layer, more or less dye is transferred to the receiver layer, and so darker or lighter printed pixels are produced. This allows for continuous tone printing.
Laser sources are often selected as the energy source, because they can provide an intense, highly directional and controllable output. When laser sources are selected, laser light absorbing material is normally provided in the dye ribbon, either as a separate layer or dispersed within the dye layer, to convert the laser energy to heat.
Typically, the output of a laser source is scanned across the donor ribbon at a set speed, and the laser source output is pulsed on and off. A heated pixel region is produced in the dye layer whenever the output is pulsed on, and the darkness of a printed pixel depends upon the amount of dye transferred to it from the corresponding heated pixel region in the dye layer, which in turn, depends upon the power and length of the laser pulse applied to that pixel region. The spacing between adjacent printed pixels depends upon the scan rate of the laser output across the dye layer and on the time between the start of the pulses producing the printed pixels.
A region of darkness may be produced in a print by printing a line of adjacent dark pixels, and it is known to select the scan rate and laser pulse rate so that each printed pixel partly overlaps those adjacent it in the scan direction. This ensures that the printed dark region is of constant optical density, and compensates for the fact that each printed pixel is slightly darker at its centre than at its periphery due to the gaussian cross-sectional profile of a typical laser output. The overlap generally coincides with the half width points of the laser beam profile (measured at l/e of maximum profile intensity) when projected onto the printed pixels.


SUMMARY OF THE INVENTION

The present invention relates to the more efficient operation of a laser source in dye thermal transfer printing, and recognizes the advantages of optimized modulation and control of laser pulse times and overlap, in contrast to the prior art, which does not.
From a first aspect, the invention provides a method of laser dye thermal transfer printing in which the output of a pulsed laser source is scanned across a dye donor element to heat selected pixel regions of the donor element to effect transfer of dye to a dye receiving element, wherein the scan rate of the output across the donor element and the delay time between the start of successive laser pulses which apply heat to respective adjacent heated pixel regions are set such that the adjacent heated pixel regions overlap in the scan direction, and wherein the delay time is further set such that a significant amount of residual heat from a first heated pixel region, which produces a printed pixel of the darkest shade, is still present in that region at the time of application of heat to the adjacent heated pixel region.
The term "adjacent heated pixel regions" should be taken to define a pair of heated pixel regions which are at the minimum spacing for the particular scan rate and delay time used in the method, and should not be taken to cover two heated regions what are

REFERENCES:
patent: 4383262 (1983-05-01), Noguchi
patent: 4772582 (1988-09-01), DeBoer
patent: 4903042 (1990-02-01), Kaufl et al.
patent: 5036040 (1991-07-01), Chapman et al.
patent: 5066962 (1991-11-01), Sarraf
patent: 5241328 (1993-08-01), Sarraf et al.

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