Non-label printing process for direct thermal imaging...

Details Non-label printing process for direct thermal imaging... Non-label printing process for direct thermal imaging...

1999-11-30

2002-04-23

Yan, Ren (Department: 2854)

Typewriting machines

Typing by other than type-face or type-die

Thermal

C347S191000

Reexamination Certificate

active

06375371

ABSTRACT:

FIELD OF THE INVENTION
The present invention concerns a non-label-printing process for the printing of substantially light-insensitive thermographic monosheet materials.
BACKGROUND OF THE INVENTION
Thermal imaging or thermography is a recording process wherein images are generated by the use of thermal energy. In direct thermal printing a visible image pattern is produced by image-wise heating of a recording material e.g. image signals can be converted into electric pulses and then via a driver circuit selectively transferred to a thermal printhead, which consists of microscopic heat resistor elements, thereby converting the electrical energy into heat via the Joule effect. This heat brings about image formation in the thermographic material.
EP-A 754 564 discloses a heat sensitive recording material comprising a support and, provided thereon, a heat sensitive recording layer containing a colorless or light colored dye precursor and an electron accepting color developer which reacts with the dye precursor upon heating to cause color formation of the dye precursor, where the heat sensitive recording material contains at least one water-insoluble resin selected from the group consisting of an aromatic resin, a resin having a low or no acid value and a resin having a carbonyl group and an alicyclic unit. Different printing tests described in the invention examples of EP-A 754 564 disclose applied energy per unit area in the ranges of 20-140 mJ/mm
2
, 80-140 mJ/mm
2
, 30-50 mJ/mm
2
, 80-100 mJ/mm
2
, 30-35 MJ/mm
2
and 20-200 mJ/mm
2
; as well as specific energies of 30 mJ/mm
2
, 40 mJ/mm
2
, 80 mJ/mm
2
and 90 mJ/mm
2
.
EP 736 799A discloses a recording material comprising a support having provided thereon at least a recording layer comprising (a) a heat-responsive microcapsule having encapsulated therein an organic silver salt; (b) a developer for the organic silver salt and (c) a water-soluble binder. A heat recording energy per unit area of 60 mJ/mm
2
is disclosed in the invention examples.
EP 622 217 discloses a method for making an image by means of a direct thermal imaging element, comprising on a support a thermosensitive layer containing an organic silver salt and a reducing agent, the imaging element being imagewise heated by means of a thermal head having energizable heating elements, characterised in that the activation of the heating elements is executed line by line with a line-duty-cycle A representing the ratio of activation time to total line time, according to the equation
P≦P
max
=3.3W/mm
2
+(9.5 W/mm
2
×&Dgr;)
where P
max
is the maximal value over all heating elements of the time averaged power density P (expressed in W/mm
2
) dissipated by a heating element during a line time.
A major problem with black and white substantially light-insensitive thermographic monosheet materials is the production of high densities with a sufficiently neutral image tone.
OBJECTS OF THE INVENTION.
It is therefore an object of the present invention to provide a non-label-printing process for producing prints with high densities and a more neutral image tone.
Further objects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
It has been surprisingly found that the image density of black and white substantially light-insensitive thermographic monosheet materials is primarily dependent upon the heating energy used to produce a image dot, regardless of how the heating power is supplied.
The above-mentioned objects are realised by a printing process for a substantially light-insensitive thermographic monosheet material having two edges parallel to one another and >12 cm apart (non-label) for obtaining a desired optical density and a desired colour tone comprising:
selecting a thermographic monosheet material, the selected thermographic monosheet material being a black and white thermographic monosheet material having a support and a thermosensitive element;
supplying image data to a processing unit of a thermal printer including a printhead having energizable heating elements arranged in a column C;
converting the image data which are not zero into at least one activation pulse per pixel to be printed;
energising the heating elements printing-line by printing-line adjacent to the selected thermographic monosheet material thereby producing an image;
transporting the selected thermographic monosheet material past and adjacent to the printhead in a transport direction with a transport system;
forming an image dot with a heat energy of 50 to 200 mJ/mm
2
of heating element surface area;
wherein the thermosensitive element contains a substantially light-insensitive organic silver salt, a reducing agent therefor in thermal working relationship therewith and a binder; and the thermosensitive element excludes a colourless or light coloured dye precursor and also excludes an encapsulated organic silver salt in a heat-responsive microcapsule. With the black and white substantially light-insensitive thermographic monosheet material, a desirable colour tone is a neutral tone as defined by CIELAB a* and b*-values and a desirable optical density, D
vis
is above 1.2 and even more desirably above 1.5.
Preferred embodiments of the present invention are disclosed in the detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
Certain terms used in disclosing the present invention are defined below.
A non-label for the purposes of the present invention is a sheet material having two edges parallel to one another and >12 cm apart. A preferred shape of non-label according to the present invention has two parallel edges separated by a distance of >12 cm measured perpendicular to the parallel edges.
Dot energy is the heating energy used to produce a dot.
A printhead PH comprises a t least one column C having a first number (e.g. s=3) of sections S, each section having a second number (e.g. se=10) of heating elements Hi.
Perceptible printed characters are composed of printed dots each dot representing a print pixel.
A line LL may be parallel or non-parallel to the direction of transportation of the substantially light-insensitive thermographic monosheet material. On a landscape non-label, for example, the line LL is substantially parallel to and on a portrait non-label the line LL is substantially perpendicular to the direction of transportation. Each line may be composed of a plurality of printing-lines PL. Examples of a printing-line PL are “-----------” and “-- ---- -”.
A printing-line PL is printed by a column C of heating elements Hi. The printing-line PL is substantially parallel to the column C; but the printing-line PL may be parallel or non-parallel to a line LL. Each printing-line is generated by a printing cycle of activation pulses in which all heating elements of a column can be activated at least once. The time taken to print a printing-line PL is a line-time LT.
Each activation pulse may either have an “off-state” (corresponding to a logical zero “0”) or an “on-state” (corresponding to a logical one “1”).
A line-duty-cycle &Dgr; is the ratio of activation time to total line time for the heating elements which can be activated in producing a printing-line.
A printing-line may comprise several printing-sublines. Each printing-subline SL takes a time-slice or a time-step or a column-time (being the time wherein all heating elements of at least one section of a column can be activated once). A column-duty-cycle ∇ is the ratio of the sum of all activation-times during a column-time of all heating elements of a printing-subline divided by the column-time.
A transport system can consist of a moving belt, motor-driven drums, capstans etc.
Substantially light-insensitive means not intentionally light sensitive.
The descriptor aqueous in the term aqueous medium for the purposes of the present invention includes mixtures of water-miscible organic solvents such as alcohols e.g. methanol, ethanol, 2-propanol, butanol, iso-amyl alcohol etc.; glycols e.g. ethylene

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