Field of the invention
The present invention relates to thermographic recording
materials with improved stability to incident light and improved
archivability.
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 containing matter that by
chemical or physical process changes colour or optical density.
Such recording materials become photothermographic upon
incorporating a photosensitive agent which after exposure to UV,
visible or IR light is capable of catalyzing or participating in a
thermographic process bringing about changes in colour or optical
density.
Examples of photothermographic materials are the so called "Dry
Silver" photographic materials of the 3M Company, which are reviewed
by D.A. Morgan in "Handbook of Imaging Science", edited by A.R.
Diamond, page 43, published by Marcel Dekker in 1991.
In US 2,910,377 the following statement is made in the
description in column 7, lines 23-27: "Stability towards exposure to
light is improved by selecting highly purified materials; freedom
from halides and sulphides is particularly important in the case of
compositions involving silver salts". The disclosure in US
2,910,377 concerned thermographic recording materials coated from
solvent media.
WO 94/16361 discloses a multilayer heat-sensitive material which
comprises: a colour-forming layer comprising: a colour-forming
amount of finely divided, solid colourless noble metal or iron salt
of an organic acid distributed in a carrier composition; a colour
developing amount of a cyclic or aromatic organic reducing agent,
which at thermal copy and printing temperatures is capable of a
colour-forming reaction with the noble metal or iron salt; and an
image-toning agent; characterized in that (a) the carrier
composition comprises a substantially water-soluble polymeric
carrier and a dispersing agent for the noble metal or iron salt and
(b) the material comprises a protective overcoating layer for the
colour-forming layer. WO 94/16361 concerns thermographic materials
coated from aqueous media.
Ever tighter solvent emission regulations and measures to avoid
solvent explosions, make the avoidance of solvent coating desirable.
However, thermographic materials of the type disclosed in WO
94/16361 while being coatable from aqueous media exhibit an
inadequate archivability for many applications. Furthermore, the
presence of chloride ions in the ingredients has been found to cause
poor light stability. There is therefore a need for thermographic
recording materials coatable from aqueous media based on
substantially light-insensitive organic silver salts with improved
shelf-life and stability to light, whose prints exhibit improved
archivability and stability to incident light.
Objects of the invention.
It is therefore an object of the present invention to provide
thermographic recording materials coated from aqueous media with
improved stability to incident light.
It is therefore another object of the present invention to
provide thermographic recording materials which are capable of
producing thermographic prints with improved archivability and
stability to incident light.
Further objects and advantages of the invention will become
apparent from the description hereinafter.
Summary of the invention
It is known that conversion of organic silver salts into silver
non-fluoro-halides renders thermographic materials photosensitive,
since this is the basis of photothermographic materials. This
conversion would be expected to occur more readily in aqueous media
due to the non-fluoro-halide ions being more mobile in a highly
polar medium such as water. The statement made in US 2,910,377 to
the effect that the use of highly purified materials improves the
light-stability of thermographic materials and in particular freedom
from halides and sulphides, concerns thermograpahic materials coated
in solvent media in which the mobility of non-fluoro-halide ions is
much lower than in water.
It is therefore surprising that in the presence of gelatin and
despite the greater potential for silver halide formation in aqueous
media, the expected light instability due to non-fluoro-halide ions
only becomes significant, relative to the general stability of the
material concerned (dependent upon choice of reducing agent and
other ingredients), at non-fluoro-halide ion concentrations above
700ppm with respect to the gelatin present. This invention enables
the use of ingredients in thermographic materials without the
exhaustive removal of non-fluoro-halides.
The above objects of the present invention are realized by
providing a thermographic recording material comprising a support
and a thermosensitive element containing a substantially light-insensitive
silver salt of an organic carboxylic acid, a reducing
agent therefor in thermal working relationship therewith and at
least one proteinaceous binder, characterized in that the
thermosensitive element contains between 700ppm and 5ppm of a non-fluoro-halide
ion with respect to the proteinaceous binders in the
thermosensitive element and the thermographic recording material is
thermally developable under substantially water-free conditions.
A process for producing a thermographic recording material as
described above is further provided by the present invention
comprising the steps of: producing an aqueous dispersion of the
substantially light-insensitive silver salt of an organic carboxylic
acid; producing one or more aqueous coating compositions containing
together the aqueous dispersion of the substantially light-insensitive
silver salt of an organic carboxylic acid, the reducing
agent and the proteinaceous binder(s); and applying the one or more
aqueous coating compositions to the support thereby forming after
drying the thermosensitive element.
Preferred embodiments of the present invention are disclosed in
the detailed description of the invention.
Detailed description of the invention.
In a preferred embodiment the substantially light-insensitive
thermographic recording materials of the present invention are black
and white thermographic recording materials.
Definitions
The term aqueous for the purposes of the present invention
includes mixtures of water with water-miscible organic solvents such
as alcohols e.g. methanol, ethanol, 2-propanol, butanol, iso-amyl
alcohol etc.; glycols e.g. ethylene glycol; glycerine; N-methyl
pyrrolidone; methoxypropanol; and ketones e.g. 2-propanone and 2-butanone
etc.
By substantially light-insensitive is meant not intentionally
light sensitive. By substantially solvent-free aqueous medium is
meant that solvent, if present, is present in amounts below 10% by
volume of the aqueous medium.
Heating in a substantially water-free condition as used herein,
means heating at a temperature of 80 to 250°C. The term
"substantially water-free condition" means that the reaction system
is approximately in equilibrium with water in the air, and water for
inducing or promoting the reaction is not particularly or positively
supplied from the exterior to the element. Such a condition is
described in T.H. James, "The Theory of the Photographic Process",
Fourth Edition, Macmillan 1977, page 374.
Non-fluoro-halide ion concentration in the thermosensitive element
According to the present invention a thermographic recording
material is provided comprising a support and a thermosensitive
element containing a substantially light-insensitive silver salt of
an organic carboxylic acid, a reducing agent therefor in thermal
working relationship therewith and at least one proteinaceous
binder, characterized in that the thermosensitive element contains
between 700ppm and 5ppm of a non-fluoro-halide ion with respect to
the proteinaceous binders in the thermosensitive element. In a
preferred embodiment the non-fluoro-halide ion concentration in the
thermosensitive element is between 500ppm and 5ppm of a non-fluoro-halide
with respect to the proteinaceous binders in the
thermosensitive element, with between 300ppm and 5ppm of a non-fluoro-halide
ion with respect to the proteinaceous binders in the
thermosensitive element being particularly preferred and between
150ppm and 5ppm being especially preferred. The non-fluoro-halide
ion is preferably the chloride ion.
Proteinaceous binders
The non-fluoro-halide ions present in the thermosensitive
element may be non-exclusively or exclusively present in the
proteinaceous binder(s) used in the thermosensitive element of the
thermographic and photothermographic recording materials of the
present invention. Therefore the proteinaceous binders in the
thermosensitive element may together contain between 700ppm and 5ppm
of non-fluoro-halide ions and preferably between 500ppm and 5ppm and
particularly preferably between 300ppm and 5ppm and especially
between 150ppm and 5ppm.
The alkali metal ion concentration of the proteinaceous
binder(s) used in the thermosensitive element of the thermographic
and photothermographic recording materials of the present invention
together of 100ppm or less.
Suitable proteinaceous binders include gelatin, modified
gelatins such as phthaloyl gelatin, zein etc, with gelatin being
preferred. Table 1 shows that the chloride ion concentration
present in gelatin as determined by ion chromatography using a
DIONEX QIC ANALYSER ion chromatograph varies according to gelatin
type from 5300 to 17ppm:
GELATIN type | general description | chloride ion concentration [ppm] | sodium ion concentration [ppm] |
GEL01 | low viscosity | 5300 | - |
GEL02 | hydrolyzed gelatin | 2900 | 1700 |
GEL03 | calcium-free, low viscosity | 1270 | - |
GEL04 | calcium-free, medium viscosity | 17 | <100 |
GEL05 | calcium-free, low viscosity | <40 | 2600 |
GEL06 | calcium-free, low viscosity | <40 | <100 |
GEL07 | calcium-containing, medium viscosity | ≤ 250 | - |
GEL08 | calcium-free, high viscosity | ≤ 200 | - |
GEL09 | calcium-free, medium viscosity | ≤ 150 | - |
GEL10 | calcium-containing, low viscosity | 150-300 | - |
Thermosensitive element
According to the present invention, a substantially light-insensitive
thermographic recording material is provided comprising
a thermosensitive element containing a substantially light-insensitive
silver salt of an organic carboxylic acid, an organic
reducing agent therefor in thermal working relationship therewith
and a binder. The thermosensitive element may comprise a layer
system in which the ingredients are dispersed in different layers,
with the proviso that the substantially light-insensitive silver
salt of an organic carboxylic acid and the organic reducing agent
are in thermal working relationship with one another i.e. during the
thermal development process the reducing agent must be present in
such a way that it is able to diffuse to the particles of
substantially light-insensitive silver salt of an organic carboxylic
acid so that reduction of the silver salt of an organic carboxylic
acid can take place. The thickness of the thermosensitive element
is preferably in the range of 1 to 50 µm.
In a preferred embodiment of the present invention the
thermosensitive element further contains a photosensitive silver
halide, making thermographic recording material photothermographic.
Silver salts of an organic carboxylic acid
Preferred substantially light-insensitive silver salts of an
organic carboxylic acid used in 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". Other silver salts of an
organic carboxylic acid 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 silver salt of an organic
carboxylic acids may also be used in the present invention.
Auxiliary film-forming binders of the thermosensitive element
Suitable water-dispersible binders for use as auxiliary binders
in the thermographic and photothermographic recording materials of
the present invention may be 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. Preferred
water-dispersible binders for use according to the present invention
are water-dispersible film-forming polymers with covalently bonded
ionic groups selected from the group consisting of sulfonate,
sulfinate, carboxylate, phosphate, quaternary ammonium, tertiary
sulfonium and quaternary phosphonium groups. Further preferred
water-dispersible binders for use according the present invention
are water-dispersible film-forming polymers with covalently bonded
moieties with one or more acid groups.
Thermal solvents
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.
Organic reducing agents
Suitable organic reducing agents for the reduction of silver
salt of an organic carboxylic acid particles are organic compounds
containing at least one active hydrogen atom linked to O, N or C.
Catechol-type reducing agents, i.e. reducing agents containing
at least one benzene nucleus with two hydroxy groups (-OH) in ortho-position
are preferred with those described in EP-B 692 733 and EP-A
903 625 being particularly preferred. Other suitable reducing
agents are sterically hindered phenols, bisphenols and
sulfonamidophenols.
Combinations of reducing agents may also be used that on heating
become reactive partners in the reduction of the substantially
light-insensitive silver salt of an organic carboxylic acid. For
example, combinations of sterically hindered phenols with 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; and 2-substituted
malonodialdehyde compounds as disclosed in US-P
5,654,130.
Toning agents
In order to obtain a neutral black image tone in the higher
densities and neutral grey in the lower densities, the thermographic
and photothermographic 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 silver salt of an organic carboxylic acid and
reducing agents during thermal processing. Any known toning agent
from thermography or photothermography may be used. Suitable toning
agents are the phthalimides and phthalazinones within the scope of
the general formulae described in US-P 4,082,901 and the toning
agents described in US-P 3,074,809, US-P 3,446,648 and US-P
3,844,797. 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.
Stabilizers and antifoggants
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.
Polycarboxylic acids and anhydrides thereof
According to the recording material of the present invention the
thermosensitive element may comprise in addition at least one
polycarboxylic acid and/or anhydride thereof in a molar percentage
of at least 15 with respect to all the silver salt of an organic
carboxylic acid(s) present and in thermal working relationship
therewith. The polycarboxylic acid may be aliphatic (saturated as
well as unsaturated aliphatic and also cycloaliphatic) or an
aromatic polycarboxylic acid. These acids may be substituted e.g.
with alkyl, hydroxyl, nitro or halogen. They 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.
Surfactants and dispersants
Surfactants are surface active agents which are soluble
compounds which reduce the interfacial tension between a liquid and
a solid. The thermographic and photothermographic recording
materials of the present invention may contain anionic, non-ionic or
amphoteric surfactants e.g.:
- Surfactant Nr. S01
- = ammonium dodecylphenylsulfonate;
- Surfactant Nr. S02
- = N, N-dimethyl-N-hexadecyl-ammonio-acetic acid;
- Surfactant Nr. S03
- = MARLON™ A-365, supplied as a 65% concentrate of
a sodium alkyl-phenylsulfonate by HÜLS.
- Surfactant Nr. S04
- = AKYPO™ OP 80, supplied by CHEMY as an 80% concentrate
of an octyl-phenyl-oxy-polyethylene-glycol(EO
8)acetic acid;
- Surfactant Nr. S05
- = hexadecyl-dimethylammonium acetic acid;
- Surfactant Nr. S06
- = acid form of ULTRAVON™ W from CIBA-GEIGY;
- Surfactant Nr. S07
- = ULTRAVON™ W, an aryl sulfonate from CIBA-GEIGY
- Surfactant Nr. S08
- = ARKOPAL™ N060 (previously HOSTAPAL™ W), a
nonylphenylpolyethylene-glycol from HOECHST
- Surfactant Nr. S09
- = SAPONINE QUILAYA, containing 10% of saponines,
15% of tannins, 11% of calcium oxalate and 64%
of starch from SCHMITTMANN;
- Surfactant Nr. S10
- = NIAPROOF ANIONIC™ 4, supplied as a 27%
concentrate of a sodium 1-(2'-ethylbutyl)-4-ethylhexylsulphate
by NIACET;
- Surfactant Nr. S11
- = ammonium salt of perfluoro-octanoic acid.
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
In addition to the ingredients the substantially light-insensitive
thermographic recording material may contain other
additives such as free fatty acids, silicone oil, ultraviolet light
absorbing compounds, white light reflecting and/or ultraviolet
radiation reflecting pigments, silica, and/or optical brightening
agents.
Support
The support for the substantially light-insensitive
thermographic recording 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. The support may be subbed with a subbing layer.
It may also be made of an opacified resin composition.
Protective layer
In a preferred embodiment of the thermographic recording
material according to the present invented the thermosensitive
element is provided with a protective layer. A protective layer
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. In a particularly preferred embodiment of the
thermographic recording material of the present invention, the
protective layer is exclusive of proteinaceous binders.
The protective layer may comprise a dissolved lubricating
material and/or particulate material, e.g. talc particles,
optionally protruding therefrom. Examples of suitable lubricating
materials are a surface active agent, a liquid lubricant, a solid
lubricant or mixtures thereof, which may be used with or without a
polymeric binder.
Layer on opposite side of the support to the thermosensitive element
The thermographic recording material according to the present
invention may be provided with a layer containing a second
proteinaceous binder on the opposite side of the support to the
thermosensitive element protective layer.
Photosensitive silver halide
The photosensitive silver halide used in the present invention
may be employed in a range of 0.1 to 100 mol percent; preferably,
from 0.2 to 80 mol percent; particularly preferably from 0.3 to 50
mol percent; especially preferably from 0.5 to 35 mol %; and
especially from 1 to 12 mol % of substantially light-insensitive
organic silver salt.
The silver halide may be any photosensitive silver halide such
as silver bromide, silver iodide, silver chloride, silver
bromoiodide, silver chlorobromoiodide, silver chlorobromide etc.
The silver halide may be in any form which is photosensitive
including, but not limited to, cubic, orthorhombic, tabular,
tetrahedral, octagonal etc. and may have epitaxial growth of
crystals thereon.
The silver halide used in the present invention may be employed
without modification. However, it may be chemically sensitized with
a chemical sensitizing agent such as a compound containing sulphur,
selenium, tellurium etc., or a compound containing gold, platinum,
palladium, iron, ruthenium, rhodium or iridium etc., a reducing
agent such as a tin halide etc., or a combination thereof. The
details of these procedures are described in T.H. James, "The Theory
of the Photographic Process", Fourth Edition, Macmillan Publishing
Co. Inc., New York (1977), Chapter 5, pages 149 to 169.
Spectral sensitization
The photosensitive silver halide in the photo-addressable
thermally developable element of the photothermographic recording
material, according to the present invention, may be spectrally
sensitized with a spectral sensitizer, optionally together with a
supersensitizer.
Antihalation dyes
The thermographic recording materials used in the present
invention may also contain antihalation or acutance dyes which
absorb light which has passed through the photosensitive thermally
developable photographic material, thereby preventing its
reflection. Such dyes may be incorporated into the photosensitive
thermally developable photographic material or in any other layer of
the photographic material of the present invention.
Coating
The coating of any layer of the substantially light-insensitive
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.
Thermographic printing
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. Heating takes place in a
substantially water-tree condition.
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 via the
Joule effect into heat, which is transferred to the surface of the
thermographic recording material wherein the chemical reaction
resulting in the development of a black and white image 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 1.0 ms,
the pressure contact of the thermal printhead with the recording
material being e.g. 200-500g/cm2 to ensure a good transfer of heat.
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.
The image signals for modulating the laser beam or current in
the micro-resistors of a thermal printhead are obtained directly
e.g. from opto-electronic scanning devices 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. 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 recording material can
also be carried out using an electrically resistive ribbon
incorporated into the material. Image- or pattern-wise heating of
the thermographic recording material may also proceed by means of
pixelwise modulated ultra-sound, using e.g. an ultrasonic pixel
printer as described e.g. in US-P 4,908,631.
Photothermographic printing
Photothermographic recording materials, according to the present
invention, may be exposed with radiation of wavelength between an X-ray
wavelength and a 5 microns wavelength with the image either
being obtained by pixel-wise exposure with a finely focused light
source, such as a CRT light source; a UV, visible or IR wavelength
laser, such as a He/Ne-laser or an IR-laser diode, e.g. emitting at
780nm, 830nm or 850nm; or a light emitting diode, for example one
emitting at 659nm; or by direct exposure to the object itself or an
image therefrom with appropriate illumination e.g. with UV, visible
or IR light.
For the thermal development of image-wise exposed photothermographic
recording materials, according to the present invention, any
sort of heat source can be used that enables the recording materials
to be uniformly heated to the development temperature in a time
acceptable for the application concerned e.g. contact heating,
radiative heating, microwave heating etc.
Industrial application
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.
The following examples and comparative examples illustrate the
present invention. The percentages and ratios used in the examples
and compositions of the ingredients are by weight unless otherwise
indicated.
i) backing layer ingredients:
- KELZAN™ S,
- a xanthan gum from MERCK & CO., Kelco Division, USA,
which according to Technical Bulletin DB-19 is a
polysaccharide containing mannose, glucose and glucuronic
repeating units as a mixed potassium, sodium and calcium
salt;
- PERAPRET™ PE40,
- a 40% aqueous dispersion of polyethylene latex from
BASF;
- LATEX02,
- a 20% by weight dispersion of polymethyl methacrylate with
an average particle size of 88.8nm prepared as described in
US-P 5,354,613;
- LATEX03,
- a 15% dispersion of a terpolymer of 18 mol% methyl
acrylate, 79 mol% potassium salt of acrylic acid and 3 mol%
TAOE;
- LATEX04,
- a 20% dispersion of a 1µm polymethylmethacrylate latex;
- KIESELSOL™ 100F,
- a colloidal silica from BAYER;
- KIESELSOL™ 300F,
- a colloidal silica from BAYER;
- PLEXIGUM™ M345,
- a polymethylmethacrylate type from ROHM;
ii) thermosensitive element ingredients (in addition to those
mentioned above):
- AgBeh
- = silver behenate;
- R01
- = ethyl 3,4-dihydroxybenzoate, a reducing agent containing
470ppm of chloride ions;
- R02
- = propyl gallate, a reducing agent containing 654ppm of
chloride ions;
- T01
- = 7-(ethylcarbonato)benzo[e][1,3]oxazine-2,4-dione, a
toning agent containing 500ppm of chloride ions
- T02
- = phthalazinone containing less than 100ppm of chloride
ions;
- T03
- = benzo[e][1,3]oxazine-2,4-dione containing 0.7ppm of
chloride ions;
- LATEX 01
- = a terpolymer of 42% butyl acrylate, 53% styrene, 2%
itaconic acid and 3% of the ammonium salt of N-[(4'-sulfobenzamido)-oxo-decyl]methacrylamide;
- POLY01
- = POLYVIOL™ WX48 20, a polyvinylalcohol from WACKER CHEMIE,
contains 545ppm of chloride ions;
- POLY02
- = Polyvinylpyrrolidone, contains 1.5ppm of chloride ions;
and iii) in the protective layer:
- POLYVIOL™ WX48 20, a polyvinylalcohol from WACKER CHEMIE;
- RILANIT™ GMS, a glycerine monotallow acid ester, from HENKEL AG
- MICROACE TALC P3, an Indian talc from NIPPON TALC;
- SERVOXYL™ VPAZ 100, a mixture of monolauryl and dilauryl
phosphate, from SERVO DELDEN B.V.;
- SERVOXYL™ VPDZ 3/100, a mono[isotridecyl polyglycolether (3 EO)]
phosphate, from SERVO DELDEN B.V.;
- LEVASIL™ VP AC 4055, a 15% aqueous dispersion of colloidal
silica with acid groups predominantly neutralized with sodium
ions and a specific surface are of 500 m2/g, from BAYER AG has
been converted into the ammonium salt.
INVENTION EXAMPLES 1 to 3
THERMOGRAPHIC COMPOSITION I
Preparation of silver behenate dispersions
Silver behenate was added with stirring to an aqueous solution
of ammonium dodecylsulfonate (Surfactant Nr. S01) and the mixtures
stirred for 30 minutes with a KOTTHOFF™ stirrer. The resulting
dispersions were then ball-milled to obtain a finely divided 18.5%
by weight aqueous dispersion of silver behenate with 1g of a 0.1g of
ammonium dodecylsulfonate per g silver behenate.
Preparation of the thermographic recording materials
3.23g of GEL05 (gelatin) was allowed to swell in 15.986g of
deionized water for 30 minutes and the swollen GEL05 was heated up
to 36°C. The following ingredients were then added with stirring:
4.434g of a 20% aqueous solution of T02 followed by 5 minutes
stirring, then 24.20g of the silver behenate dispersion at a
temperature of 36°C followed by 10 minutes stirring, then 11.150g of
an aqueous solution containing 5.55% of boric acid, 8.17% of R01 and
15.23% of ethanol was added and finally 1.0g of an aqueous solution
containing 19.2% of formaldehyde and 6.75% of methanol. The
dispersions for INVENTION EXAMPLES 1 to 3 contained the
concentrations of chloride and sodium ions with respect to the
gelatin present given in table 2.
The resulting silver behenate dispersions were then doctor
blade-coated onto a 175µm thick subbed polyethylene terephthalate
support to produce the coating weights of silver given in table 2.
Thermographic printing
The printer was equipped with a thin film thermal head with a
resolution of 300 dpi and was operated with a line time of 19ms (the
line time being the time needed for printing one line). During this
line time the printhead 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
substantially light-insensitive thermographic recording materials of
INVENTION EXAMPLES 1 to 3.
The maximum densities, Dmax, and minimum densities, Dmin, of the
prints given in table 2 were measured through visible or blue
filters 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.
Light box test
The stability of the image background of the prints made with
the substantially light-insensitive thermographic recording
materials of INVENTION EXAMPLES 1 to 3 was evaluated on the basis of
the change in minimum (background) density measured through a blue
filter using a MACBETH™ TR924 densitometer upon exposure on top of
the white PVC window of a specially constructed light-box placed for
3 days in a VÖTSCH conditioning cupboard set at 30°C and a relative
humidity (RH) of 85%. Only a central area of the window 550mm long
by 500mm wide was used for mounting the test materials to ensure
uniform exposure.
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 results are summarized in table 2.
The results of the thermographic evaluation of the thermographic
recording material of INVENTION EXAMPLES 1 to 3 show no significant
photo-instability in the light-box test indicating that up to a
chloride ion concentration of 201ppm with respect to the gelatin
present there is no adverse effect of the chloride ion content upon
the light stability of thermographic recording materials with the
very stable THERMOGRAPHIC COMPOSITION I used.
Invention example number | AgBeh coverage [g/m2] | gelatin | concentrations of ions with respect to gelatin present | fresh | Light box: ΔDmax/ΔDmin blue after 3 days at 30°C/85%RH |
| | | [Cl-] [ppm] | [Na+] [ppm] | Dmax blue | Dmin blue |
1 | 3.4 | GEL05 | 201 | 44 | 2.26 | 0.05 | +0.14/+0.01 |
2 | 3.7 | GEL05 | 167 | 22 | 2.63 | 0.05 | -0.07/+0.01 |
3 | 3.7 | GEL05 | 140 | 4 | 2.43 | 0.05 | +0.22/+0.02 |
COMPARATIVE EXAMPLES 1 & 2 and INVENTION EXAMPLES 4 to 6
THERMOGRAPHIC COMPOSITION II
Preparation of a tone modifier dispersion
The tone modifier dispersion was prepared by first dissolving
8.8g of GEL05 in 71.4g of deionized water by first adding the
gelatin, then allowing the gelatin to swell for 30 minutes and
finally heating to 50°C. 20 g of T01 was added with ULTRA-TURRAX™
stirring to this gelatin solution at 50°C, and the stirring
continued for a further 5 minutes. Finally the resulting dispersion
was pumped through a DYNOMILL™ for 2 hours to produce the final tone
modifier dispersion containing: 20% of T01 and 8.8% of GEL05.
Preparation of thermographic recording materials
Aqueous silver behenate dispersion was first prepared as
described for INVENTION EXAMPLES 1 to 3 except that the surfactant
used was Surfactant Nr. S03 and was present at a concentration of
0.1g/g silver behenate and the silver behenate concentration was
16.9%.
The coating dispersion for the thermosensitive element was
produced by first adding 2.059g of gelatin (for the type see table
3) to 7.64g of deionized water or in the case of COMPARATIVE EXAMPLE
1 2.059g of gelatin (for the type see table 3) together with 1.949g
of GEL02 to 13.11g of deionized water, allowing the gelatin to swell
for 30 minutes and then heating the mixture to 36°C then adding the
following solutions and dispersions with stirring while maintaining
a temperature of 36°C: 6.93g of the toner modifier dispersion as
flakes (contains GEL05), then for COMPARATIVE EXAMPLE 2 and
INVENTION EXAMPLES 4 to 6: 7.430g of a 26.2% dispersion of LATEX 02,
then 30.72g of the aqueous silver behenate dispersion followed by
stirring, then 12.35g of an aqueous solution containing 2.78% of
boric acid, 8.17% of R01 and 15.23% of ethanol and finally 2.88g of
a 3.7% aqueous solution of formaldehyde. The chloride and sodium
ions present in the dispersion only arise from the gelatin used.
The coating dispersion was doctor-blade coated at a pH of Ca.
5.4 onto a 175µm thick subbed polyethylene terephthalate support to
provide, after drying in a drying cupboard at 50°C, the
thermographic recording materials of COMPARATIVE EXAMPLE 1 & 2 and
INVENTION EXAMPLES 4 to 6 with the silver behenate coating weights
given in table 3 below.
Comparative example number | AgBeh coverage [g/m2] | binder % as LATEX 02 | GELATIN | total [Cl-] vs gelatin [ppm] | fresh | Light box: ΔDmax/ΔDmin blue after 3 days at 30°C/85%RH |
| | | type | [Cl-] [ppm] | | Dmax blue | Dmin blue |
1 | 4.35 | 0 | (38%) GEL02 | 2900 | 3153 | 3.57 | 0.10 | +0.52/+0.07 |
| | (62%) GEL05 | <40 |
2 | 4.21 | 38 | GEL03 | 1270 | 1707 | 3.26 | 0.10 | +0.19/+0.10 |
Invention example number |
4 | 4.24 | 38 | (76%) GEL04 | 17 | 454 | 3.15 | 0.10 | +0.24/+0.01 |
| | (24%) GEL05 | <40 |
5 | 4.11 | 38 | GEL05 | <40 | 437 | 3.38 | 0.10 | +0.03/+0.01 |
6 | 4.35 | 38 | (76%) GEL06 | <40 | 437 | 3.18 | 0.10 | +0.17/+0.02 |
| | (24%) GEL05 | <40 |
The results of the thermographic evaluation of the thermographic
recording materials of COMPARATIVE EXAMPLES 1 & 2 show a significant
increase in Dmin i.e. 0.07 and 0.10 respectively after the light box
test as can be seen from table 3, whereas the thermographic
recording materials of INVENTION EXAMPLES 4 to 6 show increases in
Dmin of 0.02 or less after the light box test indicating that for
chloride concentrations above 1500ppm with respect to gelatin,
thermographic recording materials of THERMOGRAPHIC COMPOSITION II
exhibit significant photo-instability in the light-box test, whereas
at chloride ion concentrations of 500ppm or less with respect to
gelatin, there is no significant photo-instability during this test.
COMPARATIVE EXAMPLE 3 and INVENTION EXAMPLE 7
THERMOGRAPHIC COMPOSION III
Aqueous silver behenate dispersions were prepared as described
for INVENTION EXAMPLES 1 to 3 except that the surfactant used was
that given in table 3 and was present at a concentration of 0.1g/g
silver behenate and the silver behenate concentration was 21%.
The coating dispersion for the thermosensitive element was
produced by first adding 0.31g of boric acid and 3.942g of gelatin
(for the type see table 4) to 19.46g of deionized water, allowing
the gelatin to swell for 30 minutes and then heating the mixture to
36°C then adding the following solutions and dispersions with
stirring while maintaining a temperature of 36°C: 4.93g of the toner
modifier dispersion as flakes, then a solution of 1g of R01 in 3g of
deionized water and 1g of ethanol at 50°C then 1.98g of deionized
water and finally by 23.36 of a 21% dispersion of silver behenate
with 0.1g of surfactant/g silver behenate. The chloride and sodium
ions present in the dispersion only arise from the gelatin used.
The coating dispersion was doctor-blade coated at a pH of ca.
5.0 onto a 175µm thick subbed polyethylene terephthalate support to
provide, after drying in a drying cupboard at 50°C, the thermographic
recording materials of COMPARATIVE EXAMPLE 3 and INVENTION
EXAMPLES 7 with the silver behenate coating weights given below.
Thermographic evaluation
Thermographic evaluation was carried out as described for
INVENTION EXAMPLES 1 to 3 and the results are given in table 4
below. The results of INVENTION EXAMPLE 5 cannot be directly
compared with those of INVENTION EXAMPLE 7, because THERMOGRAPHIC
COMPOSITION II of INVENTION EXAMPLE 4 to 6 and COMPARATIVE EXAMPLES
1 & 2 is more stable than THERMOGRAPHIC COMPOSITION III of INVENTION
EXAMPLE 7 and COMPARATIVE EXAMPLE 3. However, the trend observed
for the results with THERMOGRAPHIC COMPOSITION II is also to be
found in the results obtained with THERMOGRAPHIC COMPOSITION III
i.e. that the thermographic recording material of COMPARATIVE
EXAMPLE 3 with a chloride ion concentration greater than 1500ppm
exhibited significant photo-instability in the light-box test,
whereas the thermographic recording material of INVENTION EXAMPLE 7
with less than 500ppm of chloride ions with respect to the gelatin
exhibited no significant photo-instability in the light-box test in
the context of the lower general stability of THERMOGRAPHIC
COMPOSITION III.
Comparative example number | AgBch coverage [g/m2] | binder % as LATEX 01 | GELATIN | total [Cl-] vs gelatin [ppm] | fresh | Light box: ΔDmax/ΔDmin blue after 3 days at 30°C/85%RH |
| | | type | [Cl-] [ppm] | | Dmax blue | Dmin blue |
3 | 4.53 | S03 | (89%) GEL01 | 5300 | 5544 | 2.66 | 0.10 | +0.17/+0.63 |
| | | (11%) GEL05 | <40 |
Invention example number |
7 | 4.40 | 502 | GEL05 | <40 | 244 | 2.95 | 0.10 | +0.02/+0.04 |
INVENTION EXAMPLES 8 and 9
THERMOGRAPHIC COMPOSITION IV
PREPARATION OF SUBBING LAYERS
SUBBING LAYER NUMBER 01:
A 0.34mm thick polyethylene terephthalate sheet was coated to a
thickness of 0.1mm with a composition which after drying and
longitudinal and transverse stretching produced a 175mm thick
support coated with the following subbing-layer composition
expressed as the coating weights of the ingredients present:
# terpolyrner latex of vinylidene chloride/methyl acrylate/itaconic acid (88/10/2): | 162mg/m2 |
# colloidal silica (KIESELSOL™ 100F from BAYER): | 38mg/m2 |
# alkyl sulfonate surfactant (Surfactant Nr. 2): | 0.6mg/m2 |
# aryl sulfonate surfactant (Surfactant Nr. 3): | 4mg/m2 |
SUBBING LAYER NUMBER 02:
A 0.34mm thick polyethylene terephthalate sheet was coated to a
thickness of 0.1mm with a composition which after drying and
longitudinal and transverse stretching produced a 175mm thick
support coated on with the following subbing-layer composition of
subbing layer number 01 expressed as the coating weights of the
ingredients present:
# copolymer of terephthalic acid/isophthalic acid/sulfo-isophthalic acid/ethylene glycol 26.5/20/3.5/50): | 37.0mg/m2 |
# copolymer latex of ethyl acrylate/methacrylic acid (80/20): | 3.0mg/m2 |
# HORDAMER™ PE02: | 1.0mg/m2 |
# PAREZ RESIN™ 707: | 7.0mg/m2 |
Quantity of leachable non-fluoro-halide ions per unit surface of
subbing layers
The chloride-ion content leachable during overcoating with an
aqueous dispersion or solution was simulated by placing a 10 x 5cm2
piece of subbing layer-coated polyethylene terephthalate in 25mL of
deionized water for a period of 2 hours and determining the quantity
of chloride ions leached out by injecting samples of the leaching
water directly into a DIONEX QIK ANALYSER ion chromatograph The
detection limit with these measurements was limited to 0.1ppm by the
deionized water used in the leaching experiments, which had a
chloride ion concentration of 0.02 to 0.06 ppm. The results obtained
are given below in table 1:
Wavelength dispersive X-ray fluorescence (WDXRF) measurements
were carried out on some of the supports to obtain a qualitative
estimate of the total chlorine constant of the supports i.e. both
covalently bound chlorine and chloride ions. These showed no
detectable chlorine in an uncoated support, a very small quantity in
subbing layer number 02 and a small quantity in subbing layer 01.
The quantity of leachable chloride ions in the different subbing
layers obtained from these measurements are summarized in table 5:
Subbing layer number | Quantity of leachable chloride ions [mg/m2 surface] |
01 | 0.65 |
02 | 0.3 |
Preparation of the silver behenate dispersion
The silver behenate dispersion was produced as follows:
dispersing 25kg (73.5M) behenic acid was dispersed with stirring at
80°C in 100L of a 10% solution of Surfactant Nr 5/g behenic acid
made up to 250L with deionized water at a temperature of 80°C; then
36.75L of a 2M aqueous solution of sodium hydroxide was added over a
period of 10 to 20 minutes to give a clear solution substantially
containing sodium behenate; then 25L of a 2.94M aqueous solution of
silver nitrate was added with stirring at a rate of 0.163moles/moles
silver behenate·min to convert the sodium behenate completely into
silver behenate; and finally ultrafiltration was carried out with a
500000 MW polysulfone cartridge filter at room temperature to
concentrate the resulting silver behenate dispersion, the final
AgBeh-concentration was 16.7% with 0.07g of Surfactant Nr 5/g AgBeh,
the residual conductivity was 1.0mS/cm.
Preparation of the thermosensitive element
175µm thick blue pigmented polyethylene terephthalate supports
coated with subbing layer numbers 01 & 02 were coated with an
aqueous coating composition and the following ingredients so to
obtain thereon after drying, a thermosensitive element containing:
- * AgBeh:
- 4.94g/m2
- * GEL05:
- 4.96g/m2
- * formaldehyde
- 0.2g/m2
- * Surfactant Nr. S01
- 0.32g/m2
- * Surfactant Nr. S04
- 0.004g/m2
- * Surfactant Nr. 505
- 0.13g/m2
- * R01
- 1.00g/m2
- * T03
- 0.53g/m2
- * boric acid
- 0.18g/m2
- * ammonium tetraborate
- 0.48g/m2
and to produce the thermographic recording materials of INVENTION
EXAMPLES 8 and 9 respectively in which the thermosensitive elements
contain, taking into account the leachable chloride ions from the
subbing layers used of 239ppm and 168ppm of chloride ions with
respect to gelatin.
Evaluation
Thermographic evaluation was carried out as described above for
COMPARATIVE EXAMPLES 1 to 3 and INVENTION EXAMPLES 1 & 2 except the
archivability tests were carried out for 4 days at 45°C and 70%
relative humidity instead of 3 days at 35°C and 80% relative
humidity. The results are summarized in table 6.
Invention example number | AgBeh coverage [g/m2] | Total Cl- ions versus gelatin [ppm] | Leachable Cl--ions from subbing layer | FRESH | Archivability: ΔDmin vis/blue after 4d at 45°C/70% RH | Light box ΔDmin vis/blue after 3d at 30°C/85% RH |
| | | layer nr | mg/m2 | Dmax vis/blue | Dmin vis/blue |
8 | 4.94 | 239 | 01 | 0.65 | 3.12/3.23 | 0.23/0.10 | 0.01/0.02 | 0.02/0.04 |
9 | 4.94 | 168 | 02 | 0.30 | 2.65/2.71 | 0.21/0.10 | 0.00/0.01 | 0.01/0.01 |
These results are consistent with those of INVENTION EXAMPLES 1
to 7 and show that these thermographic recording materials of
THERMOGRAPHIC COMPOSITION IV with chloride ion concentrations below
500ppm (239 and 168ppm respectively) with respect to gelatin exhibit
no significant photo-instability in the light-box test.
INVENTION EXAMPLES 10 to 12 and COMPARATIVE EXAMPLES 4 to 6
THERMOGRAPHIC COMPOSITION V
175µm thick polyethylene terephthalate supports coated with
subbing layer number 01 was coated with an aqueous coating
composition and the following ingredients to obtain thereon after
drying thermosensitive elements compositions of the thermographic
recording materials of COMPARATIVE EXAMPLES 4 to 6 and INVENTION
EXAMPLES 10 to 12 as given in table 7:
Comparative example nr. | binder | AgBeh [g/m2] | Surfactant Nr S03 [g/m2] | R01 [g/m2] | R02 [g/m2] | tone modifier |
| type | coverage [g/m2] | | | | | type | [g/m2] |
4 | POLY01 | 3.78 | 4.11 | 0.411 | - | 0.975 | T01 | 1.038 |
GEL05 | 0.33 |
5 | POLY01 | 3.83 | 4.16 | 0.416 | - | 0.986 | T02 | 0.611 |
GEL05 | 0.33 |
6 | POLY02 | 3.01 | 4.93 | 0.493 | 1.010 | - | T03 | 0.809 |
GEL05 | 0.39 |
Invention example nr. |
10 | GEL05 | 4.00 | 4.00 | 0.400 | - | 0.948 | T01 | 0.893 |
11 | POLY02 | 1.93 | 4.48 | 0.448 | 0.917 | - | T03 | 0.735 |
GEL05 | 2.55 |
12 | GEL05 | 3.95 | 3.95 | 0.395 | - | 0.937 | T02 | 0.580 |
Thermographic evaluation
Thermographic evaluation was carried out as described for
INVENTION EXAMPLES 1 to 3 and the results are given in table 8.
Comparative example number | AgBeh coverage [g/m2] | non-gelatin binder | GELATIN | total [Cl-] vs gelatin [ppm] | fresh | Light box: ΔDmax/ΔDmin blue after 3 days at 30°C/85%RH |
| | type | % | type | [Cl-] [ppm] | | Dmax blue | Dmin blue |
4 | 4.11 | POLY01 | 92 | GEL05 | <40 | 11717 | 4.00 | 0.17 | -0.20/+0.43 |
5 | 4.16 | POLY01 | 92 | GEL05 | <40 | 8279 | 3.50 | 0.21 | +0.20/+0.28 |
6 | 4.93 | POLY02 | 92.6 | GEL05 | <40 | 1680 | 2.90 | 0.13 | -0.60/+0.41 |
Invention example number |
10 | 4.00 | - | - | GEL05 | <40 | 429 | 4.10 | 0.12 | -0.10/+0.08 |
11 | 4.48 | POLY02 | 43 | GEL05 | <40 | 257 | 3.60 | 0.11 | -0.30/+0.09 |
12 | 3.95 | - | - | GEL05 | <40 | 320 | 4.10 | 0.08 | +0.40/+0.06 |
The light-box results for the thermographic recording materials
of COMPARATIVE EXAMPLES 4 to 6 with chloride ion concentrations with
respect to gelatin above 1500ppm with ΔDmin-values of 0.28 to 0.43
show much stronger photo-instability than with the thermographic
recording materials of INVENTION EXAMPLES 10 to 12 with chloride ion
concentrations below 500ppm with respect to gelatin with ADmin-values
of 0.06 to 0.09. This is attributable to the higher concentration
of chloride ions therein.
The photoinstability (ΔDmin increase) in the light-box test with
the thermographic recording materials of INVENTION EXAMPLES 10 to
12, with less than 500ppm of chloride ions with respect to gelatin,
is not dependent upon the chloride ion concentration and hence can
be attributed to the lower stability of the THERMOGRAPHIC
COMPOSITION V in general and not to the chloride ion concentration
in particular. Therefore in the context of the lower stability of
THERMOGRAPHIC COMPOSITION V, there is no significant photo-instability
attributable to the chloride ion concentration in the
light-box test results for the thermographic recording materials of
INVENTION EXAMPLES 10 to 12 with less than 500ppm of chloride ions
with respect to gelatin.
Therefore, the trend observed with the results obtained with
THERMOGRAPHIC COMPOSITIONS II and III is also to be found in the
results obtained with THERMOGRAPHIC COMPOSITION V i.e. the
thermographic recording materials of COMPARATIVE EXAMPLES 4 to 6
with chloride ion concentrations greater than 1500ppm with respect
to gelatin exhibited significant photo-instability in the light-box
test due to the presence of chloride ions, whereas there was no
photo-instability in the light-box tests for the thermographic
recording materials of INVENTION EXAMPLES 10 to 12 with chloride ion
concentrations below 500ppm with respect to gelatin, which is
directly attributable to the presence of chloride ions.
INVENTION EXAMPLES 14 and 15
Backside layers
A 175µm thick polyethylene terephthalate support coated on both
sides with subbing layer 01 was coated on one side with backside
layer B01 with the following composition:
KELZAN™ S | 10mg/m2 |
polyethylenedioxythiophene | 5mg/m2 |
polystyrene sulfonic acid | 10mg/m2 |
Surfactant Nr. S07 | 21mg/m2 |
PERAPRET™ PE40 | 10mg/m2 |
KIESOLSOL™ 100F | 20mg/m2 |
PMMA latex | 200mg/m2 |
LATEX02 | 30mg/m2 |
A 175µm thick polyethylene terephthalate support coated on both
sides with subbing layer 01 was also coated on one side with
backside layer packet B02. First a layer with the following
composition was coated:
GEL07 | 380mg/m2 |
KIESELSOL 300F | 340.7mg/m2 |
Surfactant Nr S07 | 13.3mg/m2 |
Surfactant Nr. S08 | 6.7mg/m2 |
2-methyl-2,4-pentanediol | 22.2mg/m2 |
Trimethylolpropane | 11.1mg/m2 |
PMMA latex | 1mg/m2 |
then with a layer with the following composition:
GEL05 | 300mg/m2 |
LATEX03 | 450mg/m2 |
Surfactant Nr S10 | 3mg/m2 |
Surfactant Nr S11 | 1mg/m2 |
Polystyrene sulfonic acid | 8mg/m2 |
and finally with a layer of composition:
GEL08 | 1266mg/m2 |
GEL09 | 100mg/m2 |
GEL10 | 130mg/m2 |
Surfactant Nr S09 | <5 mg/m2 |
Surfactant Nr S10 | 80mg/m2 |
Surfactant Nr S11 | 3mg/m2 |
anti-bacterial agent | 50mg/m2 |
LATEX04 | 100mg/m2 |
PLEXIGUM™ M345 | 50mg/m2 |
dioctadecyl phthalate | 5mg/m2 |
formaldehyde | 106mg/m2 |
sodium sulphate | 1mg/m2 |
Thermosensitive element
A 175µm thick polyethylene terephthalate support with an
uncoated subbing layer 01 on one side and backing layer B01 on the
other was used for the thermographic recording material of INVENTION
EXAMPLE 14 and a 175µm thick polyethylene terephthalate support with
uncoated subbing layer 01 on one side and backing layer B02 on the
other was used for the thermographic recording material of INVENTION
EXAMPLE 15.
A thermosensitive element of the following composition was
applied in each case to the side coated with subbing layer 01:
| thermosensitive element of INVENTION EXAMPLE 14 | thermosensitive element of INVENTION EXAMPLE 15 |
AgBeh | 5.031g/m2 | 5.268g/m2 |
Surfactant Nr. 1 | 0.503g/m2 | 0.527g/m2 |
GEL05 | 2.66.g/m2 | 2.785g/m2 |
LATEX 01 | 1.843g/m2 | 1.929g/m2 |
R01 | 0.956g/m2 | 1.001g/m2 |
T01 | 1.132g/m2 | 1.185g/m2 |
Boric acid | 0.325g/m2 | 0.340g/m2 |
HCHO | 0.192g/m2 | 0.201g/m2 |
Protective layers
The thermosensitive elements of the thermographic recording
materials of INVENTION EXAMPLES 14 and 15 were then coated with a
protective layer with the following composition:
POLY01 | 2.31g/m2 |
SYLOID™ 72 | 0.08g/m2 |
SERVOXYL™ VPDZ 3/100 | 0.07g/m2 |
SERVOXYL™ VPAZ 100 | 0.07g/m2 |
MICROACE™ TALC P3 | 0.04g/m2 |
RILANIT™ GMS | 0.13g/m2 |
LEVASIL™VP AC 4055 | 0.50g/m2 |
Formaldehyde | 0.52g/m2 |
Curl evaluation experiments
Curl evaluation experiments were carried out by hanging 24x30
cm
2 sheets for 4 hours at 20°C and 10% and 85% relative humidity
respectively in analogy with ISO Norm 4330 - 1979 (E) and then
evaluating the dgree of curl with a curl-meter The curl values in
table 9 are the reciprocal of the curl radius in metres.
Invention example number | Curl at room temperature & 10% RH | Curl at room temperature & 85% RH |
14 | 10 | 3.3 |
15 | 6.6 | 4.5 |
From these tests it is clear that the thermographic recording
material with the gelatin backing layer INVENTION EXAMPLE 15
exhibits significantly less curl than the thermographic recording
material with the polymethylmethacrylate-based backing layer of
INVENTION EXAMPLE 14.
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.