Imaging method using deposition of dots of plastic to form a rel

Details Imaging method using deposition of dots of plastic to form a rel Imaging method using deposition of dots of plastic to form a rel

1997-09-26

1999-11-23

Tran, Huan

Incremental printing of symbolic information

Thermal marking apparatus or processes

Pre or post image recording treatment

347171, B41J 232

Patent

active

059909188

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for forming an image on a surface, and articles on which such images have been formed.
Thermal transfer printing is a well known printing technique, whereby a dye, resin wax or similar transferable pigments are transferred from a thin carrier film to a receiver media by means of thermal impulses from a thermal array printhead. The pigments may be any colour but are commonly black, yellow, cyan or magenta.
In this process, the thermal array printhead comprises a linear array of several hundred small heater elements, in intimate contact with the carrier film, the pigmented surface of which is pressed against the receiver media.
When selected heater elements on the surface of the thermal printhead are given short pulses of electrical energy, this raises their surface temperature to a value where pigment is transferred from the carrier film to the receiver media to form a pixel or coloured spot on the receiver media. Following this transfer, the carrier film and receiver film are moved relative to the thermal printhead, by a distance equivalent to the diameter of the spot. By a process of repeating this sequence of heat impulses followed by media movement, any desired image is built up. The cycle times for printing a linear array of pixels or colour spots is generally five milliseconds or less. Half tone images are produced by printing a dither pattern of dots and spaces. True photographic quality images are produced by controlling the energies of the heat impulses in conjunction with a suitable diffusion type of dye film. This type of printing is known as dye sublimation or dye diffusion printing.
In certain applications, such as the printing of colour images onto PVC cards for identity purposes, it is necessary to protect the images from damage due to abrasion and wear. The most common method is for a thin, transparent plastic coating to be applied to the printing media. A special plastic overlay film is used, which consists of a thin carrier film coated with a layer of a clear plastic material. The said material may be transferred to the top surface of the printed receiver media by means of a heated roller, or by means of a thermal printhead, in the same manner as the pigment layer is transferred as described above. Essentially all of the plastic material is transferred to the surface of the receiver media, which results in a glossy finish protective overlay, of maximum thickness, to protect the underlying image.


BRIEF SUMMARY OF THE INVENTION

According to the present invention an image is formed as a relief or textured image on a surface by depositing pixels or dots of plastics material of differing thickness or texture on said surface.
In particular a method of forming an image on a surface according to the invention consists in using a thermal printhead with multiple heater elements, and a carrier film coated with a layer of plastics material, the heating elements serving to heat the carrier film with the plastics coating in contact with said surface so that the plastics material is transferred to said surface in those areas adjacent to energised heater elements. The heater elements may be energised selectively so that they conduct or attain different levels of heat and cause a variation in the thickness of plastics material transferred to said surface at different points. It is thus possible to produce a desired surface pattern in the form of a relief image.
The heater elements may be energised so that the plastics material is applied as a continuous layer over the whole of an area to be coated, and may serve as a protective coating.
Energisation of the heater elements may be controlled continuously or discretely over a range of energy levels to produce a coating that varies continuously or discretely in thickness over said surface. In one example, each heater element may be energised at one or the other of two energy levels so as to transfer either a maximum thickness or a lesser thickness, nominally 50% of the plastics ma

REFERENCES:
patent: 5387573 (1995-02-01), Oldfield et al.
Ohya et al., "Gray-Scale Printing on Plain Paper Using Thermal Ink--Transfer Imaging", Journal of Imaging Technology, vol. 10, No. 2, Apr. 1984 pp. 57-63.

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