Record receiver having plural interactive leaves or a colorless – Having a colorless color-former – developer therefor – or... – Method of use – kit – or combined with marking instrument or...
Reexamination Certificate
2000-05-31
2002-01-08
Hess, Bruce H. (Department: 1774)
Record receiver having plural interactive leaves or a colorless
Having a colorless color-former, developer therefor, or...
Method of use, kit, or combined with marking instrument or...
C503S202000, C503S209000, C503S212000
Reexamination Certificate
active
06337303
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to thermographic recording materials with improved image tone.
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 thermography a visible image pattern is formed by image-wise heating of a recording. On heating to a certain conversion temperature, an irreversible chemical reaction takes place and a coloured image is produced.
U.S. Pat. No. 3,074,809 discloses a heat sensitive copy-sheet useful in providing dense dark-colored image areas of pleasing appearance in the thermographic copying of differentially radiation-absorptive originals, the copy-sheet including a visibly heat-sensitive layer comprising: a normally solid organic silver salt of a noble metal; a cyclic organic reducing agent for the noble metal ions, which reducing agent has an active hydrogen atom attached to an atom, selected from the class of oxygen, nitrogen and carbon atoms, directly attached to an atom of the cyclic ring; and as a third significant component and in significant small amount within the approximate proportions of one to 10 percent of the composition, an organic carboxylic acid toner compound having a carboxyl group and at least one other group, from the class consisting of carboxyl and hydroxyl groups, in position to permit condensation reaction with the carboxyl group and with formation of a heterocyclic ring structure having 5-6 members in the ring.
EP-A 687 572 discloses a direct thermal imaging process wherein a non-photosensitive direct thermal recording material is heated dot-wise, and the direct thermal recording material comprises an imaging layer containing uniformly distributed in a film-forming polymeric binder (i) one or more substantially light-insensitive organic silver salts, the silver salt(s) being uniformly in thermal working relationship with (ii) one or more organic reducing agents therefor, however neither including 3,5-dihydroxybenzoic acid as acidic reagent nor di-tert-butyl-p-cresol as a sole organic reducing agent, wherein the imaging layer contains at least one polycarboxylic acid and/or anhydride thereof in a molar percentage of at least 20 with respect to the silver salt(s).
In printing with thermographic materials for medical applications with viewing with a light box, the materials should exhibit a fairly flat response of image density to heat applied (sensitometry) as provided by the thermographic materials disclosed in EP-A 687 572. However, optimum diagnosis requires a blue-black image tone so that higher ability of the human eye to distinguish detail with such image tone can be exploited, thereby improving the diagnostic value of such prints. A blue-black image tone is often obtained by coating the thermographic material on a support pigmented with a blue pigment, making the intrinsic image tone of thermographic material less critical. However, in the case of thermographic materials coated on a non-pigmented support, the intrinsic image tone of the thermographic material is very important. Image tone can be assessed on the basis of the L*, a* and b* CIELAB-values, the desired blue black image tone corresponding to a b* value<0.
Imaging materials for medical applications are also produced using a support with a particular blue pigment e.g. MACROLEX™ BLUE 3R from BAYER. The colour of such supports can also be defined in terms of L*, a* and b* CIELAB-values. Representative supports used for medical imaging materials have CIELAB-a* values and -b* values given in the table below.
a*
b*
Dvis
MEDICAL IMAGING MATERIAL SUPPORT 1
−7
−13.82
0.172
MEDICAL IMAGING MATERIAL SUPPORT 2
−7.22
−13.02
0.174
MEDICAL IMAGING MATERIAL SUPPORT 3
−6.86
−14.46
0.181
MEDICAL IMAGING MATERIAL SUPPORT 4
−7.92
−16.62
0.195
However, the background colour and the colour of an image is a combination of the colour of the support and the colour of the image background and the image of the particular material upon printing and b* values<−8 at D=1.0 are preferred.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide substantially light-insensitive black and white thermographic recording materials using a non-pigmented support capable of producing prints with a blue-black image tone.
It is therefore a second object of the present invention to provide substantially light-insensitive black and white thermographic recording materials whose prints have a higher diagnostic value.
Further objects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
It has been surprisingly found that thermographic materials containing particular polycarboxylic acids and combinations thereof produce prints with a markedly improved image tone i.e. a blue-black image tone without the need for a support pigmented with a blue pigment. ,
The above mentioned objects are realized by a substantially light-insensitive black and white thermographic recording material comprising a thermosensitive element and a support, the thermosensitive element containing at least one substantially light-insensitive organic silver salt, at least one organic reducing agent therefor in thermal working relationship therewith, a binder, at least one stabilizer and optionally an &agr;,&ohgr;-alkyldicarboxylic acid with a straight chain alkyl group having at least 4 carbon atoms which may be substituted, however neither including 3,5-dihydroxybenzoic acid as acidic reagent nor di-tert-butyl-p-cresol as a sole organic reducing agent, wherein the at least one stabilizer is represented by formula (I):
R
1
—(O═C)—R
2
—(C═O)—R
3
(I)
wherein R
2
is a divalent straight chain saturated hydrocarbon group with 2 or 3 carbon atoms which may be substituted with one or more of ═O, ═S, ═CR
4
R
5
, an alkyl group, a cycloalkyl group, a hydroxy group, a thiol group, a —(C═O)R
6
group or two of the substituents of R
2
may together form a closed non-aromatic carbocyclic or heterocyclic ring; R
4
and R
5
are independently hydrogen or an alkyl, hydroxy, thiol, —(C═O)R
7
group or R
4
and R
5
together may form a closed carbocyclic or heterocyclic group; R
1
, R
3
, R
6
and R
7
are independently a hydroxy or —NHR
8
group or R
1
and R
3
together is an oxygen atom forming an anhydride group; R
8
is hydrogen or a hydroxy, alkyl, aryl or —SO
2
R
9
group; R
9
is an alkyl, cycloalkyl, heterocyclic, aryl, heteroaryl, an —OR
10
, or a —NR
11
R
12
group; R
10
and R
11
are independently an alkyl, cycloalkyl or aryl group; R
12
is hydrogen or an alkyl, cycloalkyl or aryl group; and R
11
and R
12
may together form a closed carbocyclic or heterocyclic group; and wherein the concentration of the at least one stablizer and the &agr;,&ohgr;-alkyldicarboxylic acid, if present, is together at least 20 mol % with respect to the organic silver salts.
A recording process is also provided by the present invention comprising the steps of: (i) bringing an outermost layer of a thermographic recording material as described above into proximity with a heat source; (ii) applying heat from the heat source imagewise to the thermographic recording material in a substantially water-free condition while maintaining proximity to the heat source to produce an image; and (iii) removing the thermographic recording material from the heat source.
Preferred embodiments of the present invention are disclosed in the dependent claims.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment of the thermographic recording process, according to the present invention, the heat source is a thermal head with a thin film thermal head being particularly preferred.
DEFINITIONS
The term alkyl means all variants possible for each number of carbon atoms in the alkyl group i.e. for three carbon atoms: n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl and tertiary-butyl; for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl,
Dooms Philip
Geuens Ingrid
Michiels Peter
Agfa-Gevaert
Hess Bruce H.
Leydig , Voit & Mayer, Ltd.
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