Thermographic recording material with improved image tone

Details Thermographic recording material with improved image tone Thermographic recording material with improved image tone

2002-06-27

2004-02-17

Hess, B. Hamilton (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...

C503S212000

Reexamination Certificate

active

06693062

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to thermographic recording materials whose prints have 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 material.
EP 692 733 discloses a direct thermal recording process wherein a direct thermal recording material is heated dot-wise and the direct thermal recording material comprises on a substrate an imaging layer containing uniformly distributed in a film-forming polymeric binder (i) one or more substantially light-insensitive organic silver salts being no double salts, the silver salt(s) being in thermal working relationship with (ii) an organic reducing agent therefor, wherein the reducing agent is a benzene compound the benzene nucleus of which is substituted by no more than two hydroxy groups which are present in 3,4-position on the nucleus and have in the 1-position of the nucleus a substituent linked to the nucleus by means of a carbonyl group.
EP-A 903 625 discloses a substantially light-insensitive black and white monosheet thermographic recording material is provided comprising a support and a thermosensitive element containing a substantially light-insensitive organic silver salt, a 1,2-dihydroxybenzene-compound in thermal working relationship therewith and a binder, characterized in that the 1,2-dihydroxybenzene-compound is represented by formula (I):
where R is —P(═O)R
1
R
2
, —SO
x
R
3
, —CN, —NO
2
or —CR
4
═NR
5
when n is 0; R is —P(═O)R
1
R
2
, —SO
x
R
3
, —CN, —NO
2
, —CR
4
═NR
5
or —COR
6
when n is an integer; R
1
and R
2
are independently an alkyl, a substituted alkyl, an aryl, a substituted aryl group, an alkoxy, a substituted alkoxy, an aryloxy, a substituted aryloxy, a hydroxy group, an amino group or a substituted amino group; R
3
is an alkyl, a substituted alkyl, an aryl, a substituted aryl, an amino or a substituted amino group; R
4
is an alkyl, a substituted alkyl, an aryl or a substituted aryl group or hydrogen; R
5
is an alkyl, a substituted alkyl, an aryl, a substituted aryl, a hydroxy, an alkoxy, an aryloxy, an acyl, an amino or a substituted amino group; R
6
is an alkyl, a substituted alkyl, an aryl, a substituted aryl, an alkoxy, a substituted alkoxy, an aryloxy, a substituted aryloxy, a hydroxy, an amino or a substituted amino group or hydrogen; x is 1, 2 or 3; and the benzene ring of the 1,2-dihydroxybenzene-compound represented by the formula (I) may be further substituted.
Unpublished European Patent Application Nr. EP01000096.6 disclosed a monosheet black and white substantially light-insensitive thermographic recording material comprising a thermosensitive element and a support, the thermosensitive element containing a substantially light-insensitive organic silver salt, a 3,4-dihydroxybenzene compound in thermal working relationship therewith and a binder, characterized in that the 3,4-dihydroxybenzene compound is an aryloxo-3,4-dihydroxybenzene compound in which the aryl-group is substituted with at least one substituent having a &sgr;
m
-value greater than 0; or a heteroaryloxo-3,4-dihydroxybenzene compound in which the heteroaryl group has a unified aromaticity index I
A
greater than 53 and is optionally substituted with at least one group selected from the group consisting of aryl, hydroxy, carboxy, sulfo, sulfoalkyl, sulfoaryl, sulfonylalkyl, sulfonylaryl, annulated aryl, annulated heteroaryl, carboxyalkyl, carboxyaryl, oxoalkyl, oxoaryl, halogen, nitro, cyano and mercapto-alkyl groups; and a thermographic recording process therefor.
Unpublished European Patent Application Nr. EP01000095.8 disclosed a monosheet black and white substantially light-insensitive thermographic recording material comprising a thermosensitive element and a support, the thermosensitive element containing a substantially light-insensitive organic silver salt, a 1,2-dihydroxybenzene-compound in thermal working relationship therewith and a binder, characterized in that the 1,2-dihydroxybenzene-compound is represented by formula (I): R
1
SO
2
R
2
, wherein R
1
is an optionally substituted aryl group and R
2
is selected from the group consisting of a 3,4,5-trihydroxyphenyl group, a 3-alkoxy-4,5-dihydroxyphenyl group and a 3-aryloxy-4,5-dihydroxyphenyl group; or the 1,2-dihydroxybenzene-compound is represented by formula (II): R
3
COOR
4
, wherein R
3
is a 3-alkoxy-4,5-dihydroxyphenyl group or a 3-aryloxy-4,5-dihydroxyphenyl group; and R
4
is an alkyl group or an aryl group; and a thermographic recording process therefor.
U.S. Pat. No. 3,028,254 discloses heat-sensitive copy-sheets comprising a substantially light-insensitive organic silver salt, a reducing agent therefor and a binder. Specifically in Example 1 molar ratio of molar hydroxy-equivalents of reducing agents to molar silver-equivalents of the substantially light-insensitive organic silver salts of 1.78 and 1.33 are disclosed with respect to 3,3,3′,3′-tetramethyl-1,1′-spiro-bis-indane 5,5′,6,6′-tetrol and behenyl pyrogallol and silver behenate; and 3,3,3′,3′-tetramethyl-1,1′-spiro-bis-indane 5,5′,6,6′-tetrol and silver behenate respectively.
U.S. Pat. No. 3,031,329 discloses heat-sensitive copy-sheets comprising a substantially light-insensitive organic silver salt, a reducing agent therefor and a binder. Specifically in Examples 1 and 2 molar ratios of molar hydroxy-equivalents of reducing agents to molar silver-equivalents of the substantially light-insensitive organic silver salts of 7.29 and 4.13 are disclosed respectively with respect to 3,3,3′,3′-tetramethyl-1,1′-spiro-bis-indane 5,5′,6,6′-tetrol, 3,4-dihydroxybenzoic acid and silver behenate; and methyl gallate and silver behenate respectively.
U.S. Pat. No. 3,074,809 discloses heat-sensitive copy-sheets comprising a substantially light-insensitive organic silver salt, a reducing agent therefor and a binder. Specifically in Examples 1, 2 and 3 molar ratios of molar hydroxy-equivalents of reducing agents to molar silver-equivalents of the substantially light-insensitive organic silver salts of 5.725, 5.725 and 2.310 are disclosed respectively with respect to hydroquinone and silver behenate; hydroquinone and silver behenate; and methyl gallate, 2,3-dihydroxybenzoic acid and silver behenate respectively.
U.S. Pat. No. 3,103,881 discloses heat-sensitive copy-sheets comprising a substantially light-insensitive organic silver salt, a reducing agent therefor and a binder. Specifically in Example 3 a molar ratio of molar hydroxy-equivalents of reducing agents to molar silver-equivalents of the substantially light-insensitive organic silver salts of 2.95 is disclosed with respect to 3,4-dihydroxy-benzoic acid and silver behenate.
U.S. Pat. No. 3,107,174 discloses heat-sensitive copy-sheets comprising a substantially light-insensitive organic silver salt, a reducing agent therefor and a binder. Specifically in Example 1 a molar ratio of molar hydroxy-equivalents of reducing agents to molar silver-equivalents of the substantially light-insensitive organic silver salts of 3.29 is disclosed with respect to methyl gallate and silver behenate.
Typical X-ray images with conventional silver halide radiographic film have an image tone corresponding to CIELAB-values of a*=−4.62 and b*=−8.86 for D=1.0 and a*=−2.53 and b*=−4.41 for a density of 2.0 and exhibit excellent archivability both as regards stability of image density and stability of image tone. Prints produced with prior art thermographic recording materials which exhibit acceptable archivability exhibit a reddish image tone and prior art thermographic recording materials which exhibit clinically acceptable neutral (a*=b*=0) to bluish image tone (a*=0 to −7; b*<0) exhibit unacceptable archivability. This problem is particularly a

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