Field of the invention
[0001] The present invention concerns black and white substantially light-insensitive thermographic
recording materials containing a substantially light-insensitive organic silver salt
and a novel reducing agent.
Background of the invention
[0002] Thermal imaging or thermography is a recording process wherein images are generated
by the use of thermal energy. Most of the "direct" thermographic recording materials
are of the chemical type in which upon heating an irreversible chemical reaction takes
place and a coloured image is produced.
[0003] EP-A 248 405 discloses a thermal recording material with a colour-developing layer,
which contains an electron acceptor and an electron donor in addition to the usual
additives, characterized in that the electron acceptor is a metallic double salt of
a long-chain fatty acid with 16 to 35 carbon atoms and the electron donor is a polyhydric
aromatic compound of formula (I):
wherein R is an alkyl group with 18 to 35 carbon atoms,
wherein R
1 is a C
18- to C
35-alkyl group, n is an integer of 2 or 3, -X- is -CH
2-, -CO
2-, -CO-, -O-, -CONH-, -CO(R')N- (wherein R' is a C
18- to C
35-group), -SO
2-, -SO
3- or -SO
2NH-. Example 4 concerns a thermosensitive recording material with a colour-developing
layer containing silver aluminium double salt of octadecyl 2,3,4-trihydroxybenzoate.
[0004] EP-A 599 580 discloses a thermal recording sheet comprising, in order: (a) a substrate;
(b) an intermediate layer which comprises a pigment having an oil absorption according
to Japanese Industrial Standard (JIS) K501 of 100mL/100g or less; and (c) a thermal
color developing layer which comprises a leuco dye type chromogenic component consisting
of a leuco dye and an organic color developer and a metal chelate type chromogenic
component consisting of an electron acceptor and an electron donor, wherein: the organic
color developer is at least one of compounds of formula (I) and formula (II):
wherein R is propyl, isopropyl, or butyl;
the electron acceptor is a metal double salt of a fatty acid having 16 to 35 carbon
atoms; and the electron donor is a polyhydric aromatic compound of formula (III),
which is the same as formula (I) of EP-A 248 405.
[0005] JP 09142029 discloses a recording layer containing at least one kind of aminobenzene
sulfonamide derivative shown by formula I, at least one kind of multi-value phenolic
compound, shown by formula II [same formula as formula I of EP-A 248 405 wherein X
= -CH
2-, -CO
2-, -CO-, -O-, -CONH-, -CON(R')-] and a high class aliphatic metallic salt, is formed
on the supporting body of a heat sensitive recording body.
[0006] The thermosensitivity of organic silver salt/reducing agent systems is dependent
upon the choice of reducing agent. However, increased thermosensitivity is generally
associated with poorer image gradation i.e. dependence of image density upon applied
thermal energy, reduced stability and poorer image colour. There is therefore a need
for reducing agents which increase the thermosensitivity of organic silver salt/reducing
agent systems without substantially affecting the gradation, stability and image colour
of prints made therewith.
Objects of the invention.
[0007] It is therefore an object of the present invention to provide thermographic recording
materials with increased thermosensitivity without significantly affecting the gradation,
stability and image colour of prints made therewith.
[0008] Further objects and advantages of the invention will become apparent from the description
hereinafter.
Summary of the invention
[0009] Surprisingly it has been found that prints of thermographic recording materials containing
novel 3,4-dihydroxyphenyl compounds exhibit increased thermosensitivity without significantly
affecting the gradation, stability and image colour of prints made therewith. In fact
there is even a marginal improvement in image colour.
[0010] The above-mentioned objects are realized by a substantially light-insensitive black
and white monosheet thermographic recording material comprising a support and a thermosensitive
element containing a substantially light-insensitive organic silver salt, 1,2-dihydroxyphenyl-compound
in thermal working relationship therewith and a binder, characterized in that the
1,2-dihydroxyphenyl-compound is represented by formula (I):
where n is 0 or 1; R is -(C=O)R
1, -(C=O)NR
1R
2, -CN, -SO
3R
2, -SO
2R
2, -SOR
2, -SO
2NR
2R
3 or -PO
3R
2R
3; R
1 is H or a substituted or unsubstituted alkyl group with 12 or less carbon atoms;
and R
2 and R
3 are independently H or an alkyl, a substituted alkyl, an aryl or a substituted aryl
group; and R
1 and R
2 can together provide the atoms to close a carbocyclic or heterocyclic ring; and R
2 and R
3 can together represent the atoms to close a carbocyclic or heterocyclic ring.
[0011] A recording process is also provided comprising the steps of: (i) providing the above-described
substantially light-insensitive black and white monosheet thermographic recording
material; (ii) bringing an outermost layer of the recording material into proximity
with a heat source; (iii) applying heat from a heat source image-wise to the recording
material while maintaining proximity to the heat source to produce an image; and (iv)
removing the recording material from the heat source.
[0012] Preferred embodiments of the present invention are disclosed in the detailed description
of the invention.
Detailed description of the invention.
[0013] According to a preferred embodiment of the recording process according to the present
invention the heat source is a thermal head.
Organic reducing agents
[0014] The organic reducing agent used in the thermographic recording materials of the present
invention is a 2,3,4-trihydroxyphenyl-compound represented by formula (I). In a preferred
embodiment the -(CH=CH)
nR group has a Hammett substituent constant σ
p greater than 0.25. Hammett substituent constants are, for example, listed on pages
28 and 29 of Advances in Linear Free Energy Relationships, edited by N. B. Chapman
and J. Shorter and published by Plenum Press, London in 1972. Particularly preferred
-(CH=CH)
nR groups are formyl, oxo-alkyl, oxo-aryl, cyano, carbamido, diphenoxyphosphoryl, alkylsulfinyl,
alkylsulfonyl and sulfonylamino groups.
[0015] Preferred reducing agents for use in the present invention are selected from the
group consisting of: consisting of: 2,3,4-trihydroxy-acetophenone, 2,3,4-trihydroxy-propionophenone,
2,3,4-trihydroxybenzaldehyde and 2,3,4-trihydroxybenzonitrile.
[0016] Compounds according to formula(I) are long known, the synthesis of a wide range of
2,3,4-trihydroxy-phenyl-oxo-derivatives, for example being described in Beilsteins
Handbuch der Organischen Chemie, Vierte Auflage, Achter Band, Springer Verlag, Berlin
(1925): p. 388, 393, 398, 399, 400, 417, 684 and 685. 2,3,4-trihydroxy-benzaldehyde,
2',3',4'-trihydroxyacetophenone, 2,3,4-trihydroxy-benzophenone are all commercially
available from Aldrich and can be used to produce other derivatives such as 2,3,4-trihydroxybenzo-nitrile
by methods known to synthetic chemists.
Auxiliary reducing agents
[0017] The reducing agents used in accordance with the present invention being considered
as primary or main reducing agents may be used in conjunction with so-called auxiliary
reducing agents. Such auxiliary reducing agents are e.g. hydroquinone or catechol
substituted with strongly electron-withdrawing groups such as sulfonic acid groups;
hydrazides such as disclosed in EP-A 762 196, sulfonyl hydrazide reducing agents such
as disclosed in US-P 5,464,738; trityl hydrazides and formyl-phenyl-hydrazides such
as disclosed in US-P 5,496,695; trityl hydrazides and formyl-phenyl-hydrazides with
diverse auxiliary reducing agents such as disclosed in US-P 5,545,505, US-P 5,545,507
and US-P 5,558,983; acrylonitrile compounds as disclosed in US-P 5,545,515 and US-P
5,635,339; 2-substituted malondialdehyde compounds such as disclosed in US-P 5,654,130.
[0018] In a preferred embodiment of the present invention the thermographic material comprises
a support and a thermosensitive element which further contains a 3,4-dihydroxyphenyl
compound with ethyl 3,4-dihydroxybenzoate, butyl 3,4-dihydroxybenzoate and 3,4-dihydroxybenzoic
acid being particularly preferred.
Substantially
[0019] By substantially light-insensitive is meant not intentionally light sensitive. A
substituted or unsubstituted alkyl group with 12 carbon atoms or less includes: methyl,
ethyl, n-propyl, isopropyl, n-butyl, tertiary butyl, secondary butyl, n-pentyl, n-hexyl,
cyclohexyl, n-heptyl, 2-ethylhexyl, n-octyl, n-nonyl, n-decyl, n-undecyl and n-dodecyl
groups.
Thermosensitive element
[0020] According to the present invention, a thermographic recording material is provided
comprising a thermosensitive element including a substantially light-insensitive organic
silver salt, a reducing agent according to formula (I) in thermal working relationship
therewith and a binder. The thermosensitive element may comprise a layer system in
which the ingredients may be dispersed in different layers, with the proviso that
the substantially light-insensitive organic silver salt and the reducing agent according
to formula (I) are in thermal working relationship with one another i.e. during the
thermal development process the reducing agent according to formula (I) must be present
in such a way that it is able to diffuse to the substantially light-insensitive organic
silver salt particles so that reduction of the substantially light-insensitive organic
silver salt can take place.
Organic silver salts
[0021] Preferred substantially light-insensitive organic silver salts for use in the thermographic
recording materials, according to the present invention, are silver salts of aliphatic
carboxylic acids known as fatty acids, wherein the aliphatic carbon chain has preferably
at least 12 C-atoms, e.g. silver laurate, silver palmitate, silver stearate, silver
hydroxystearate, silver oleate and silver behenate, which silver salts are also called
"silver soaps". Silver salts of modified aliphatic carboxylic acids with thioether
group as described e.g. in GB-P 1,111,492 and other organic silver salts as described
in GB-P 1,439,478, e.g. silver benzoate, may likewise be used to produce a thermally
developable silver image. Combinations of different organic silver salts may also
be used in the thermographic recording materials of the present invention. A preferred
process for producing a suspension of particles containing a substantially light-insensitive
organic silver salt is disclosed in EP-A 754 969.
Binder
[0022] The thermosensitive element of the thermographic recording materials of the present
invention may be coated onto a support in sheet- or web-form from an organic solvent
containing the binder dissolved therein or may be applied from an aqueous medium using
water-soluble or water-dispersible binders.
[0023] Suitable binders for coating from an organic solvent are all kinds of natural, modified
natural or synthetic resins or mixtures of such resins, wherein the organic heavy
metal salt can be dispersed homogeneously: e.g. cellulose derivatives, cellulose esters,
carboxymethylcellulose, starch ethers, galactomannan, polyurethanes, polycarbonates,
polyesters, polymers derived from α,β-ethylenically unsaturated compounds such as
after-chlorinated polyvinyl chloride, partially hydrolyzed polyvinyl acetate, polyvinyl
alcohol, polyvinyl acetals, preferably polyvinyl butyral, and homopolymers and copolymers
produced using monomers selected from the group consisting of: vinyl chloride, vinylidene
chloride, vinyl esters, acrylonitrile, acrylamides, methacrylamides. methacrylates,
acrylates, methacrylic acid, acrylic acid, vinyl esters, styrenes, dienes and alkenes;
or mixtures thereof.
[0024] Suitable water-soluble film-forming binders are: polyvinyl alcohol, polyacrylamide,
polymethacrylamide, polyacrylic acid, polymethacrylic acid, polyethyleneglycol, polyvinylpyrrolidone,
proteinaceous binders such as gelatine modified gelatines such as phthaloyl gelatine,
polysaccharides, such as starch, gum arabic and dextran and water-soluble cellulose
derivatives.
[0025] Suitable water-dispersible binders are any water-insoluble polymer. It should be
noted that there is no clear cut transition between a polymer dispersion and a polymer
solution in the case of very small polymer particles resulting in the smallest particles
of the polymer being dissolved and those slightly larger being in dispersion.
[0026] The above mentioned binders or mixtures thereof may be used in conjunction with waxes
or "heat solvents" also called "thermal solvents" or "thermosolvents" improving the
reaction speed of the redox-reaction at elevated temperature.
Toning agents
[0027] In order to obtain a neutral black image tone thermographic recording materials according
to the present invention may contain one or more toning agents. The toning agents
should be in thermal working relationship with the substantially light-insensitive
organic silver salt and reducing agents during thermal processing. Any known toning
agent from thermography or photothermography may be used. Particularly useful toning
agents are the heterocyclic toner compounds of the benzoxazine dione or naphthoxazine
dione type described in GB-P 1,439,478, US-P 3,951,660 and US-P 5,599,647.
Polycarboxylic acids and anhydrides thereof
[0028] According to a preferred embodiment of the present invention the substantially light-insensitive
black and white monosheet thermographic recording material the thermosensitive element
further contains at least one polycarboxylic acid and/or anhydride thereof in a molar
percentage of at least 15 with respect to the substantially light-insensitive organic
silver salt and in thermal working relationship therewith. The polycarboxylic acid
may be aliphatic (saturated as well as unsaturated aliphatic and also cycloaliphatic)
as disclosed in US-P 5,527,758 or an aromatic polycarboxylic acid, may be substituted
and may be used in anhydride form or partially esterified on the condition that at
least two free carboxylic acids remain or are available in the heat recording step.
Stabilizers and antifoggants
[0029] In order to obtain improved shelf-life and reduced fogging, stabilizers and antifoggants
may be incorporated into the thermographic recording materials of the present invention.
Suitable stabilizers compounds are unsaturated carbocyclic or heterocyclic compounds
substituted with a -SA group where A is hydrogen, a counterion to compensate the negative
charge of the thiolate group or a group forming a symmetrical or an asymmetrical disulfide.
for use in the present invention may be further substituted, which substitution also
includes the atoms necessary to form an annulated unsaturated carbocyclic or heterocyclic
ring system. Preferred substituents include acylamido, aryl-SO
2NH-, alkyl-SO
2NH-, aryl-NHSO
2-, alkyl-NHSO
2-, arylamino, alkyl, aryl, nitro and cyano groups and halogen atoms. Preferred stablizer
compounds used in the present invention have an unsaturated 5- or 6-membered ring.
Particularly suitable compounds are represented by formula (II):
where Q are the necessary atoms to form a 5- or 6-membered aromatic heterocyclic
ring, A is selected from hydrogen, a counterion to compensate the negative charge
of the thiolate group or a group forming a symmetrical or an asymmetrical disulfide.
Surfactants and dispersants
[0030] Surfactants and dispersants aid the dispersion of ingredients which are insoluble
in the particular dispersion medium. The thermographic recording materials of the
present invention may contain one or more surfactants, which may be anionic, non-ionic
or cationic surfactants and/or one or more dispersants. Suitable dispersants are natural
polymeric substances, synthetic polymeric substances and finely divided powders, for
example finely divided non-metallic inorganic powders such as silica.
Other ingredients
[0031] In addition to the ingredients the thermographic material may contain other additives
such as free fatty acids, antistatic agents, e.g. non-ionic antistatic agents including
a fluorocarbon group as e.g. in F
3C(CF
2)
6CONH(CH
2CH
2O)-H, silicone oil, ultraviolet light absorbing compounds, white light reflecting
and/or ultraviolet radiation reflecting pigments, silica, and/or optical brightening
agents.
Support
[0032] The support for the thermographic material according to the present invention may
be transparent, translucent or opaque and is preferably a thin flexible carrier made
e.g. from paper, polyethylene coated paper or transparent resin film, e.g. made of
a cellulose ester, e.g. cellulose triacetate, polypropylene, polycarbonate or polyester,
e.g. polyethylene terephthalate. The support may be in sheet, ribbon or web form and
subbed if needs be to improve the adherence to the thereon coated heat-sensitive recording
layer. The support may be made of an opacified resin composition.
Protective layer
[0033] In a preferred embodiment of the present invention a protective layer is provided
for the thermosensitive element. In general this protects the thermosensitive element
from atmospheric humidity and from surface damage by scratching etc. and prevents
direct contact of printheads or heat sources with the recording layers. Protective
layers for thermosensitive elements which come into contact with and have to be transported
past a heat source under pressure, have to exhibit resistance to local deformation
and good slipping characteristics during transport past the heat source during heating.
[0034] A slipping layer, being the outermost layer, may comprise a dissolved lubricating
material and/or particulate material, e.g. talc particles, optionally protruding from
the outermost layer. Examples of suitable lubricating materials are a surface active
agent, a liquid lubricant, a solid lubricant or mixtures thereof, with or without
a polymeric binder. Suitable slipping layer compositions are described, for example,
in US 5,587,350, US 5,536,696, US 5,547,914, WO 95/12495, EP-A 775 592 and EP-A 775
595.
Coating techniques
[0035] The coating of any layer of the thermographic recording materials of the present
invention may proceed by any coating technique e.g. such as described in Modern Coating
and Drying Technology, edited by Edward D. Cohen and Edgar B. Gutoff, (1992) VCH Publishers
Inc., 220 East 23rd Street, Suite 909 New York, NY 10010, USA. Coating may proceed
from aqueous or solvent media with overcoating of dried, partially dried or undried
layers.
Thermographic printing
[0036] Thermographic imaging is carried out by the image-wise application of heat either
in analogue fashion by direct exposure through an image of by reflection from an image,
or in digital fashion pixel by pixel either by using an infra-red heat source, for
example with a Nd-YAG laser or other infra-red laser, or by direct thermal imaging
with a thermal head.
[0037] In thermal printing image signals are converted into electric pulses and then through
a driver circuit selectively transferred to a thermal printhead. The thermal printhead
consists of microscopic heat resistor elements, which convert the electrical energy
into heat via Joule effect. The electric pulses thus converted into thermal signals
manifest themselves as heat transferred to the surface of the thermal paper wherein
the chemical reaction resulting in colour development takes place. Such thermal printing
heads may be used in contact or close proximity with the recording layer. The operating
temperature of common thermal printheads is in the range of 300 to 400°C and the heating
time per picture element (pixel) may be less than 1.0ms, the pressure contact of the
thermal printhead with the recording material being e.g. 200-500g/cm
2 to ensure a good transfer of heat.
[0038] In order to avoid direct contact of the thermal printing heads with a recording layer
not provided with an outermost protective layer, the image-wise heating of the recording
layer with the thermal printing heads may proceed through a contacting but removable
resin sheet or web wherefrom during the heating no transfer of recording material
can take place.
[0039] The image signals for modulating the laser beam or current in the micro-resistors
of a thermal printhead are obtained directly or from an intermediary storage means,
optionally linked to a digital image work station wherein the image information can
be processed to satisfy particular needs.
[0040] Activation of the heating elements can be power-modulated or pulse-length modulated
at constant power. EP-A 654 355 describes a method for making an image by image-wise
heating by means of a thermal head having energizable heating elements, wherein the
activation of the heating elements is executed duty cycled pulsewise. When used in
thermographic recording operating with thermal printheads the thermographic recording
materials are not suitable for reproducing images with fairly large number of grey
levels as is required for continuous tone reproduction. EP-A 622 217 discloses a method
for making an image using a direct thermal imaging element producing improvements
in continuous tone reproduction. Image-wise heating of the thermographic material
can also be carried out using an electrically resistive ribbon incorporated into the
material. Image- or pattern-wise heating of the thermographic material may also proceed
by means of pixel-wise modulated ultra-sound.
Industrial application
[0041] Thermographic recording materials according to the present invention may be used
for both the production of transparencies, for example in the medical diagnostic field
in which black-imaged transparencies are widely used in inspection techniques operating
with a light box, and reflection type prints, for example in the hard copy field.
For such applications the support will be transparent or opaque, i.e. having a white
light reflecting aspect. Should a transparent base be used, the base may be colourless
or coloured, e.g. with a blue colour for medical diagnostic applications.
[0042] The following examples and comparative examples illustrate the present invention.
The percentages and ratios used in the examples are by weight unless otherwise indicated.
The following ingredients were used in the thermosensitive element in addition to
those mentioned above:
- AgBeh
- = silver behenate;
- BR 18
- = PIOLOFORM BR 18, a polyvinyl butyral from WACKER CHEMIE;
- CR01
- = ethyl 3,4-dihydroxybenzoate, according to US-P 5,582,953;
- CR02
- = propyl gallate;
- CR03
- = propyl 2,3,4-trihydroxybenzoate;
- CR04
- = 3,4-dihydroxybenzonitrile, according to EP-A 903 625;
- CR05
- = 3,3,3',3'-tetramethyl-1,1'-spirobisindane-5,5',6,6'-tetrol, according to EP-A 599
369;
- R01
- = 2,3,4-trihydroxy-acetophenone;
- R02
- = 2,3,4-trihydroxy-propionophenone;
- R03
- = 2,3,4-trihydroxy-benzaldehyde;
- R04
- = 2,3,4-trihydroxy-benzophenone;
- S01
- = tetrachlorophthalic anhydride;
- S02
- = 3'-decanoylamino-1-phenyl-1H-tetrazole-5-thiol
- T01
- = 7-(ethylcarbonato)benzo[e][1,3]oxazine-2,4-dione;
- Oil
- = Baysilon™ MA, a silicone oil from BAYER AG.
COMPARATIVE EXAMPLES 1 to 4 and INVENTION EXAMPLE 1
Preparation of a silver behenate dispersion
[0043] 72kg of a 25% solution of BR 18 in 2-butanone, 180kg of silver behenate and 455kg
2-butanone were mixed for in a ball mill. After 4 days 72kg of a 25% solution of BR
18 in 2-butanone and 22kg of 2-butanone were added and then mixed in the ball mill
for several days more. 576kg of a 25% solution of BR 18 in 2-butanone, 0.684kg of
oil, 326.2kg of 2-butanone and 10.08g of T01 were then added and the mixture further
mixed for 10 hours in the ball mill. The final 2-butanone dispersion contained 10.5%
of silver behenate, 10.5% of BR 18, 0.59% of T01 and 0.04% of oil.
Preparation of the thermosensitive element
[0044] The subbed 120µm thick polyethylene terephthalate support was doctor blade-coated
with a composition containing 2-butanone as solvent/dispersing medium so as to obtain
thereon, after drying for 30 minutes at 50°C, a thermosensitive element with the compositions
summarized in table 1 below:
Table 1
Comparative example nr |
AgBeh coverage [g/m2] |
reducing agent |
BR 18 [g/m2] |
Oil [g/m2] |
T01 [g/m2] |
S01 [g/m2] |
S02 [g/m2] |
|
|
type |
[g/m2] |
|
|
|
|
|
1 |
5.35 |
CR01 |
1.091 |
5.35 |
20.4 |
0.300 |
0.128 |
0.117 |
2 |
5.35 |
CR02 |
1.274 |
5.35 |
20.4 |
0.300 |
0.128 |
0.117 |
Invention example nr |
|
|
|
|
|
|
|
|
1 |
5.40 |
R02 |
1.126 |
5.40 |
20.6 |
0.302 |
0.130 |
0.118 |
Thermographic printing
[0045] During printing of the recording materials of COMPARATIVE EXAMPLES 1 & 2 and INVENTION
EXAMPLE 1 the print head was separated from the imaging layer by a thin intermediate
material contacted with a slipping layer of a separable 5µm thick polyethylene terephthalate
ribbon coated successively with a subbing layer, heat-resistant layer and the slipping
layer (anti-friction layer) giving a ribbon with a total thickness of 6µm.
[0046] The printer was equipped with a thin film thermal head with a resolution of 300 dpi
and was operated with a line time of 6.5ms (the line time being the time needed for
printing one line). During this line time the print head received constant power.
The average printing power, being the total amount of electrical input energy during
one line time divided by the line time and by the surface area of the heat-generating
resistors was 1.6 mJ/dot being sufficient to obtain maximum optical density in each
of the thermographic recording materials of COMPARATIVE EXAMPLES 1 & 2 and INVENTION
EXAMPLE 1.
[0047] The maximum and minimum densities of the prints given in table 2 were measured through
a visible or blue filter with a MACBETH™ TR924 densitometer in the grey scale step
corresponding to data levels of 64 and 0 respectively and are given in table 2.
[0048] For evaluating the steepness of the gradation of the thermographic recording materials
of COMPARATIVE EXAMPLES 1 & 2 and INVENTION EXAMPLE 1 the numerical gradation value
(NGV) corresponding with the quotient of the fraction
was determined, wherein E
2.5 is the energy in Joule applied in a dot area of 87 µm x 87 µm of the imaging layer
that obtains by the energy an optical density value of 2.5, and E
(1.0 + Dmin) is the energy in Joule applied in a dot area of the imaging layer material that obtains
by the energy an optical density value of (1.0 + D
min). The applied energy in Joule is actually the electrical input energy measured for
each resistor of the thermal head. The NGV's for the thermographic recording materials
of COMPARATIVE EXAMPLES 1 & 2 and INVENTION EXAMPLE 1 are given in table 2.
Light box test
[0049] The light stability of the image background of the prints made with the thermographic
recording materials of COMPARATIVE EXAMPLES 1 & 2 and INVENTION EXAMPLE 1 was evaluated
on the basis CIELAB-values. The CIELAB-values were determined by spectrophotometric
measurements according to ASTM Norm E179-90 in a R(45/0) geometry with evaluation
according to ASTM Norm E308-90. The light box test consisted of first heating the
thermographic materials of COMPARATIVE EXAMPLES 1 & 2 and INVENTION EXAMPLE 1 for
2 days at 57°C and 34% relative humidity and then exposing them on top of the white
PVC window of a specially constructed light-box for 3 days in a VÖTSCH conditioning
cupboard set at 30°C and a relative humidity of 80%. Only a central area of the window
550mm long by 500mm wide was used for mounting the test materials to ensure uniform
exposure.
[0050] The stainless steel light-box used was 650mm long, 600mm wide and 120mm high with
an opening 610mm long and 560mm wide with a rim 10mm wide and 5mm deep round the opening,
thereby forming a platform for a 5mm thick plate of white PVC 630mm long and 580mm
wide, making the white PVC-plate flush with the top of the light-box and preventing
light loss from the light-box other than through the white PVC-plate. This light-box
was fitted with 9 PLANILUX™ TLD 36W/54 fluorescent lamps 27mm in diameter mounted
length-wise equidistantly from the two sides, with the lamps positioned equidistantly
to one another and the sides over the whole width of the light-box and with the tops
of the fluorescent tubes 30mm below the bottom of the white PVC plate and 35mm below
the materials being tested. The a* and b* CIELAB of the thermographic recording materials
of COMPARATIVE EXAMPLES 1 & 2 and INVENTION EXAMPLE 1 determined after the light box
test are summarized in table 2.
Table 2
Comparative example number |
reducing agent nr |
fresh print |
2d at 57°C/34% RH in dark then 3d at30°C/85%RH on light box |
|
|
Dmax/Dmin (vis) |
NGV |
at Dmin |
|
|
|
|
|
|
a* |
b* |
a* at Dmin |
b* at Dmin |
1 |
CR01 |
2.70/0.05 |
13.5 |
0.00 |
1.14 |
0.04 |
3.19 |
2 |
CR02 |
3.64/0.05 |
21.6 |
0.03 |
1.28 |
0.61 |
9.07 |
Invention example nr |
|
|
|
|
|
|
|
|
|
1 |
R02 |
|
4.08/0.05 |
22.3 |
-0.15 |
1.88 |
0.20 |
6.25 |
[0051] Colour neutrality on the basis of CIELAB-values corresponds to a* and b* values of
zero, with a negative a*-value indicating a greenish image-tone becoming greener as
a* becomes more negative, a positive a*-value indicating a reddish image-tone becoming
redder as a* becomes more positive, a negative b*-value indicating a bluish image-tone
becoming bluer as b* becomes more negative and a positive b*-value indicating a yellowish
image-tone becoming yellower as b* becomes more positive.
[0052] The results of the thermographic evaluation of the thermographic recording materials
of INVENTION EXAMPLE 1 and COMPARATIVE EXAMPLES 1 & 2 show that the thermographic
recording material of INVENTION EXAMPLE 1, incorporating a novel reducing agent in
the thermographic recording material according to the present invention, is clearly
more thermosensitive than the thermographic recording materials of COMPARATIVE EXAMPLES
1 & 2, as evidenced by its higher D
max value. Despite this higher thermosensitivity the thermographic recording material
of INVENTION EXAMPLE 1 exhibited a gradation (NGV value) comparable or superior to
that of the thermographic recording materials of COMPARATIVE EXAMPLES 1 & 2 and comparable
CIELAB a* and b* values.
COMPARATIVE EXAMPLES 3 to 5 and INVENTION EXAMPLES 2 and 3
[0053] The thermosensitive elements of the thermographic recording materials of COMPARATIVE
EXAMPLE 3 to 5 and INVENTION EXAMPLES 2 and 3 were prepared as described for COMPARATIVE
EXAMPLES 1 & 2 and INVENTION EXAMPLE 1. The compositions of the thermosensitive elements
are given in table 3 below.
Table 3
Comparative example nr |
AgBeh coverage [g/m2] |
reducing agent |
BR 18 [g/m2] |
Oil [mg/m2] |
T01 [g/m2] |
S01 [g/m2] |
S02 [g/m2] |
|
|
type |
[g/m2] |
|
|
|
|
|
3 |
6.27 |
CR01 |
1.279 |
6.27 |
23.9 |
0.351 |
0.150 |
0.137 |
4 |
6.59 |
CR02 |
1.570 |
6.59 |
25.1 |
0.369 |
0.158 |
0.144 |
5 |
6.06 |
CR03 |
1.444 |
6.06 |
23.1 |
0.339 |
0.145 |
0.132 |
Invention example nr |
|
|
|
|
|
|
|
|
2 |
6.14 |
R01 |
1.156 |
6.14 |
23.4 |
0.344 |
0.147 |
0.134 |
3 |
6.37 |
R02 |
1.328 |
6.37 |
24.3 |
0.357 |
0.153 |
0.139 |
[0054] The thermographic recording materials of COMPARATIVE EXAMPLES 3 to 5 and INVENTION
EXAMPLES 2 and 3 were evaluated as described above for COMPARATIVE EXAMPLES 1 & 2
and INVENTION EXAMPLE 1. The results are given in table 4 below.
Table 4
Comparative example nr |
reducing agent nr |
fresh print |
2d at 57°C/34% RH in dark then 3d at 30°C/85%RH on light box |
|
|
Dmax/Dmin (vis) |
NCV |
a* at Dmin |
b* at Dmin |
3 |
CR01 |
3.35/0.05 |
14.5 |
-0.17 |
8.84 |
4 |
CR02 |
4.09/0.05 |
24.0 |
-0.05 |
12.40 |
5 |
CR03 |
3.61/0.05 |
22.7 |
1.36 |
15.39 |
Invention example nr |
|
|
|
|
|
2 |
R01 |
4.63/0.05 |
25.7 |
-0.59 |
9.86 |
3 |
R02 |
4.43/0.05 |
24.2 |
-0.37 |
9.63 |
The results of the thermographic evaluation of the thermographic recording materials
of INVENTION EXAMPLE 2 and 3 and COMPARATIVE EXAMPLES 3 to 5 show that the thermographic
recording material of INVENTION EXAMPLES 2 and 3, incorporating novel reducing agents
in the thermographic recording material according to the present invention, exhibit
a higher thermal sensitivity (i.e. higher D
max-value) and comparable or higher gradations (i.e. higher comparable or higher NGV
values) to those of COMPARATIVE EXAMPLES 3 to 5. Despite their higher thermal sensitivies,
the thermographic recording materials of INVENTION EXAMPLES 2 & 3 exhibit comparable
or more neutral CIELAB a*- and b*-values after the light box test.
COMPARATIVE EXAMPLES 7 and INVENTION EXAMPLES 4 to 7
[0055] The thermosensitive elements of the thermographic recording materials of COMPARATIVE
EXAMPLE 6 and INVENTION EXAMPLES 4 to 7 were prepared as described for COMPARATIVE
EXAMPLES 1 & 2 and INVENTION EXAMPLE 1. The compositions of the thermosensitive elements
are given in table 5 below.
Table 5
Comparative example nr |
AgBeh coverage [g/m2] |
reducing agent |
BR 18 [g/m2] |
Oil [mg/m2] |
T01 [g/m2] |
S01 [g/m2] |
S02 [g/m2] |
|
|
type |
[g/m2] |
|
|
|
|
|
6 |
7.6 |
CR01 |
1.536 |
7.6 |
28.7 |
0.422 |
0.181 |
0.164 |
Invention example nr |
|
|
|
|
|
|
|
|
4 |
6.9 |
R01 |
1.286 |
6.9 |
26.1 |
0.383 |
0.164 |
0.148 |
5 |
10.5 |
R02 |
2.160 |
10.5 |
39.5 |
0.580 |
0.249 |
0.225 |
6 |
9.6 |
R03 |
1.633 |
9.6 |
3.61 |
0.529 |
0.227 |
0.205 |
7 |
8.9 |
R04 |
2.250 |
8.9 |
3.33 |
0.489 |
0.209 |
0.189 |
[0056] The thermographic recording materials of COMPARATIVE EXAMPLES 7 and INVENTION EXAMPLES
4 to 7 were evaluated as described above for COMPARATIVE EXAMPLES 1 & 2 and INVENTION
EXAMPLE 1. The results are given in table 6 below.
[0057] The results of the thermographic evaluation of the thermographic recording materials
of INVENTION EXAMPLE 4 to 7 and COMPARATIVE EXAMPLE 6 show that the thermographic
recording material of INVENTION EXAMPLES 4 to 7, incorporating novel reducing agents
in the thermographic recording material according to the present invention, have higher
thermosensitivities (i.e. higher D
max values) and higher gradations (i.e. higher NGV values) than those of the thermographic
recording material of COMPARATIVE EXAMPLE 6.
Table 6
Comparative example nr |
reducing agent nr |
fresh print |
|
|
Dmax/Dmin(vis) |
NGV |
6 |
CR01 |
3.40/0.05 |
12.0 |
Invention example nr |
|
|
|
4 |
R01 |
5.61/0.06 |
23.7 |
5 |
R02 |
5.50/0.05 |
25.6 |
6 |
R03 |
5.36/0.05 |
25.3 |
7 |
R04 |
4.42/0.04 |
21.4 |
COMPARATIVE EXAMPLES 7 to 9 and INVENTION EXAMPLES 8 & 9
[0058] The thermosensitive elements of the thermographic recording materials of COMPARATIVE
EXAMPLE 7 to 9 and INVENTION EXAMPLES 8 & 9 were prepared as described for COMPARATIVE
EXAMPLES 1 & 2 and INVENTION EXAMPLE 1. The compositions of the thermosensitive elements
are given in table 7 below.
Table 7
Comparative example nr |
AgBeh coverage [g/m2] |
reducing agent |
BR 18 [g/m2] |
Oil [mg/m2] |
T01 [g/m2] |
S01 [g/m2] |
S02 [g/m2] |
|
|
type |
[g/m2] |
|
|
|
|
|
7 |
5.51 |
CR02 |
1.312 |
5.51 |
20.9 |
0.309 |
0.132 |
0.120 |
8 |
5.48 |
CR04 |
0.829 |
5.48 |
20.8 |
0.307 |
0.132 |
0.119 |
9 |
5.58 |
CR05 |
2.127 |
5.58 |
21.2 |
0.312 |
0.134 |
0.122 |
Invention example nr |
|
|
|
|
|
|
|
|
8 |
5.58 |
R01 |
1.050 |
5.58 |
21.2 |
0.312 |
0.134 |
0.122 |
9 |
5.45 |
R02 |
1.112 |
5.45 |
20.7 |
0.305 |
0.131 |
0.119 |
[0059] The thermographic recording materials of COMPARATIVE EXAMPLES 7 to 9 and INVENTION
EXAMPLES 8 & 9 were evaluated as described above for COMPARATIVE EXAMPLES 1 & 2 and
INVENTION EXAMPLE 1. The results are given in table 8 below.
Table 8
Comparative example nr |
reducing agent nr |
fresh print |
|
|
Dmax/Dmin(vis) |
NGV |
7 |
CR02 |
4,12/0.05 |
26.11 |
8 |
CR04 |
2.97/0.05 |
19.42 |
9 |
CR05 |
2.76/0.05 |
16.75 |
Invention example nr |
|
|
|
8 |
R01 |
4.61/0.05 |
30.22 |
9 |
R02 |
4.35/0.05 |
32.36 |
[0060] The results of the thermographic evaluation of the thermographic recording materials
of INVENTION EXAMPLE 8 and 9 and COMPARATIVE EXAMPLES 7 to 9 show that the thermographic
recording material of INVENTION EXAMPLES 8 & 9, incorporating novel reducing agents
in the thermographic recording material according to the present invention, exhibit
higher thermosensitivities (i.e. D
max values) and high gradations (i.e. higher NGV values) than those of the thermographic
recording materials of COMPARATIVE EXAMPLES 7 to 9 using reducing agents according
to the teachings of US-P 5,582,953, EP-A 903 625 and EP-A 599 369 respectively.
[0061] Having described in detail preferred embodiments of the current invention, it will
now be apparent to those skilled in the art that numerous modifications can be made
therein without departing from the scope of the invention as defined in the following
claims.