Field of the invention
[0001] The present invention relates to a substantially light-insensitive thermographic
material comprising a subbing layer with a low concentration of leachable non-fluoro-halide
ions.
Background of the invention.
[0002] Thermal imaging or thermography is a recording process wherein images are generated
by the use of thermal energy.
[0003] In thermography three approaches are known:
1. Direct thermal formation of a visible image pattern by image-wise heating of a
recording material containing matter that by chemical or physical process changes
colour or optical density.
2. Image-wise transfer of an ingredient necessary for the chemical or physical process
bringing about changes in colour or optical density to a receptor element.
3. Thermal dye transfer printing wherein a visible image pattern is formed by transfer
of a coloured species from an image-wise heated donor element onto a receptor element.
[0004] Most of the "direct" thermographic materials are of the chemical type. On heating
to a certain conversion temperature, an irreversible chemical reaction takes place
and a coloured image is produced. A wide variety of chemical systems has been suggested
some examples of which have been given on page 138 of "Imaging Systems" by Kurt I.
Jacobson-Ralph E. Jacobson, The Focal Press - London and New York (1976), describing
the production of a silver metal image by means of a thermally induced oxidation-reduction
reaction of a silver soap with a reducing agent.
[0005] JP 57-69,095 discloses a support coated with a subbing layer containing an ionomer,
and then coated with a heat-sensitive recording layer whose solubility in water decreases
upon heating to give a thermographic sheet. EP-A 496 017 discloses a heat-sensitive
recording medium, comprising: (a) a synthetic-resin support; (b) an ionomer-resin
layer on said support; and (c) a heat-sensitive recording layer on said ionomer resin
layer.
[0006] GB 2 114 767 discloses a thermosensitive recording sheet comprising: a support material;
a primer layer formed on the support material and comprising a filler and a binder
agent; a thermosensitive colouring layer formed on the primer layer and comprising
a colourless light-coloured leuco dye, and an acidic material which colours the leuco
dye upon application of heat hereto; and a protective layer formed on the thermosensitive
colouring layer and comprising a water-soluble agent and a filler.
[0007] US-P 5,006,451 discloses in the specification that "polymeric subbing layers used
to promote the adhesion of coating compositions to polyester film supports are very
well known in the photographic art. Useful compositions for this purpose include interpolymers
of vinylidene chloride such as vinylidene chloride/acrylonitrile/acrylic acid-terpolymers
or vinylidene chloride/methyl acrylate/itaconic acid-terpolymers".
[0008] However, the inventors of the present invention found that the light-stability and
archivability of substantially light-insensitive thermographic materials coated from
aqueous media were surprisingly, considering their thinness relative to the thickness
of the thermosensitive element thereof, dependent upon the choice of subbing layer
and that, moreover, polymer subbing layers used to promote adhesion between polyester
support and conventional photographic emulsion layers were in the main unusable (see
COMPARATIVE EXAMPLE 2) due to prohibitive light-sensitivity and poor archivability.
There is therefore a need for subbing layers for use on the supports of thermographic
materials, which have no adverse effect upon the light-stability and archivability
of thermographic materials.
Objects of the invention.
[0009] It is therefore an object of the present invention to provide thermographic materials
coatable from aqueous media which exhibit improved archivability and/or improved light
stability, while maintaining high maximum density and low minimum density levels upon
printing.
[0010] Further objects and advantages of the invention will become apparent from the description
hereinafter.
Summary of the invention
[0011] Thermographic materials adhere poorly to unsubbed polyethylene terephthalate, as
is shown in COMPARATIVE EXAMPLE 1. In the photographic art adhesion of the gelatinous
silver halide emulsion layers to a polyethylene terephthalate support is attained
by the use of a subbing layer consisting of two sub-layers, one to render the polyethylene
terephthalate support sufficiently hydrophilic to adhere to a gelatinous layer to
which gelatinous silver halide emulsion layers would adhere. COMPARATIVE EXAMPLE 2
shows that such a subbing layer indeed provides good adhesion between the polyethylene
terephthalate support and gelatinous thermographic materials, but at the expense of
poorer archivability and lower light stability. It is surprising that the composition
of a subbing layer for the polymeric or polymer-coated support on the same side of
the support as the thermosensitive element has a considerable influence on the light-stability
and archivability of a substantially light-insensitive black and white thermographic
material despite the thinness of a subbing layer compared to that of the thermosensitive
element. In particular certain ingredients such as silica, whether colloidal or non-colloidal,
have, above a concentration of 20% by weight, and the presence of non-fluoro-halide
ions leachable into water at a concentration of 0.6mg/m
2 or more have been found to have a prohibitive effect on the light-stability and archivability
of thermographic materials coated from aqueous media.
[0012] The above-mentioned objects are realized with a substantially light-insensitive black
and white thermographic material comprising a polymeric or polymer-coated support,
a subbing layer on the support and on the same side of the support as the subbing
layer a thermosensitive element containing a substantially light-insensitive organic
silver salt, a reducing agent therefor in thermal working relationship therewith and
a binder, characterized in that the subbing layer contains a binder, less than 20%
by weight of silica and covalently bonded acid groups in said binder, if present,
are either substantially present as free acid or substantially present as acid salts
and has a leachable non-fluoro-halide ion content into water at room temperature over
a period of 120 minutes of less than 0.6mg/m
2.
[0013] A process is also provided for producing the above-referred to substantially light-insensitive
thermographic material comprising the steps of: coating the support with a subbing-layer
composition thereby forming the subbing layer; producing one or more aqueous coating
compositions together containing the substantially light-insensitive organic silver
salt, the reducing agent and the binder; and applying the one or more aqueous coating
compositions to the same side of the support as the subbing layer thereby forming
after drying the thermosensitive element.
[0014] Preferred embodiments of the present invention are disclosed in the detailed description
of the invention.
Detailed description of the invention.
Subbing layer
[0015] The subbing layer used in accordance with the present invention the subbing layer
contains a binder, less than 20% by weight of silica and covalently bonded acid groups
in the binder, if present, are either substantially present as free acid or substantially
present as acid salts and the leachable non-fluoro-halide ion content into water at
room temperature of the subbing layer is less than 0.6mg/m
2 over a period of 120 minutes. The subbing layer used in accordance with the present
invention may consist of one or more sub-layers. The leachable non-fluoro-halide ion
is preferably a chloride ion.
[0016] By the term ionic group is meant an ionized group, for example carboxylate, sulfinate,
sulfonate, quaternary ammonium, quaternary phosphonium, ternary sulfonium and phosphate
groups. Suitable binders include any natural, modified natural or synthetic resins,
polysilicic acid, hydrolyzed polyalkoxysilanes etc. or mixtures thereof.
[0017] The preferred leachable non-fluoro-halide ion content of the subbing layer used in
accordance with the present invention is less than 0.5mg/m
2, with less than 0.4mg/m
2 being particularly preferred.
[0018] Preferred ingredients for the subbing layer used in accordance with the present invention
are a polymer latex, polyethylene wax and hydrolyzed polyalkoxysilanes. By the term
polyalkoxysilane is meant a silane with a least two hydrolyzable alkoxy-groups. Particularly
preferred polymer latexes for use in the subbing layer of the present invention are
producible with monomers selected from the group consisting of acrylates, methacrylates,
vinyl esters, acrylic acid, methacrylic acid, itaconic acid, vinylidene chloride,
polyisocyanates, aromatic polycarboxylic acids and polyols.
[0019] Suitable ingredients for use in the subbing layer in accordance with the present
invention are:
- 3-glycidoxypropyltrimethoxysilane hydrolyzed in the presence of polystyrene sulfonic
acid;
- a copolymer consisting of 80% by weight of ethyl acrylate and 20% by weight of methacrylic
acid;
- a copolyester consisting of 26.5 mol% of terephthalic acid, 20 mol% of isophthalic
acid, 3.5 mol% of sulfo-isophthalic acid and 50 mol% of ethylene glycol;
- polyethylene wax;
- melamine-formaldehyde resin;
- polymethylmethacrylate particles; and
- silica up to 20% by weight of the subbing layer.
Aqueous
[0020] 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, octanol, cetyl alcohol etc.; glycols e.g. ethylene glycol;
glycerine; N-methyl pyrrolidone; methoxypropanol; and ketones e.g. 2-propanone and
2-butanone etc.
Substantially
[0021] 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.
Thermosensitive element
[0022] According to the present invention, a thermographic material is provided comprising
a thermosensitive element including a substantially light-insensitive organic silver
salt, an organic reducing agent therefor in thermal working relationship therewith
and a binder. The 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 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 substantially light-insensitive
organic silver salt particles so that reduction of the organic silver salt can take
place.
Organic silver salts
[0023] Preferred substantially light-insensitive organic silver salts used in the thermographic
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
materials of the present invention.
Production of particles of organic silver salts
[0024] A process for producing a suspension of particles containing a substantially light-insensitive
organic silver salt is disclosed in EP-A 754 969.
Organic reducing agents
[0025] Suitable organic reducing agents for use in the thermographic materials of the present
invention for the reduction of the substantially light-insensitive organic silver
salt, are organic compounds containing at least one active hydrogen atom linked to
O, N or C, such as is the case with: catechol; hydroquinone; aminophenols; METOL™;
p-phenylenediamines; alkoxynaphthols, e.g. 4-methoxy-1-naphthol described in US-P
3,094,417; pyrazolidin-3-one type reducing agents, e.g. PHENIDONE™; pyrazolin-5-ones;
indan-1,3-dione derivatives; hydroxytetrone acids; hydroxytetronimides; hydroxylamine
derivatives such as for example described in US-P 4,082,901; hydrazine derivatives;
and reductones e.g. ascorbic acid; see also US-P 3,074,809, 3,080,254, 3,094,417 and
3,887,378.
Auxiliary reducing agents
[0026] 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. sterically hindered phenols,
such as described in US-P 4,001,026; bisphenols, e.g. of the type described in US-P
3,547,648; sulfonamidophenols, such as described in Research Disclosure, February
1979, item 17842, in US-P 4,360,581 and 4,782,004, and in EP-A 423 891; 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; and organic
reducing metal salts, e.g. stannous stearate described in US-P 3,460,946 and 3,547,648
or organic reducing metal salts, e.g. stannous stearate described in US-P 3,460,946
and 3,547,648. The auxiliary reducing agents may be present in the imaging layer or
in a polymeric binder layer in thermal working relationship thereto.
Binder
[0027] The thermosensitive element of the thermographic 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.
[0028] 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, 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
acids, acrylic acids, vinyl esters, styrenes and alkenes; or mixtures thereof.
[0029] Suitable water-soluble film-forming binders are: polyvinyl alcohol, polyacrylamide,
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.
[0030] 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. Preferred
water-dispersible binders for use according to the present invention are water-dispersible
film-forming polymer with covalently bonded ionic groups selected from the group consisting
of sulfonate, sulfinate, carboxylate, phosphate, quaternary ammonium, tertiary sulfonium
and quaternary phosphonium groups. Water-dispersible binders with crosslinkable groups,
e.g. epoxy groups, aceto-acetoxy groups and crosslinkable double bonds are also preferred.
[0031] Further preferred water-dispersible binders for use in the present invention are
polymer latexes. Compositions of polymer latexes suitable for use in the present invention
are given in the table below:
polymer latex nr. |
B [% by wt.] |
IP [% by wt.] |
BA [% by wt.] |
S [% by wt.] |
MMA [% by wt.] |
IA [% by wt.] |
AA [% by wt.] |
1 |
47.5 |
- |
- |
- |
47.5 |
5 |
- |
2 |
45 |
- |
- |
- |
45 |
10 |
- |
3 |
49 |
- |
- |
- |
49 |
2 |
- |
4 |
- |
47.5 |
- |
- |
47.5 |
5 |
- |
5 |
- |
- |
50 |
50 |
- |
- |
- |
6 |
- |
- |
47 |
- |
53 |
- |
- |
7 |
- |
- |
51 |
- |
49 |
- |
- |
8 |
- |
55 |
44 |
- |
- |
- |
1 |
9 |
50 |
- |
- |
- |
50 |
- |
- |
where:B = butadiene; IP = isoprene; BA = butyl acrylate; S = styrene; MMA = methyl
methacylate; IA = itaconic acid; and AA = acrylic acid. |
[0032] The binder to organic silver salt weight ratio is preferably in the range of 0.2
to 6, and the thickness of the recording layer is preferably in the range of 1 to
50 µm.
Thermal solvents
[0033] 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
[0034] In order to obtain a neutral black image tone in the higher densities and neutral
grey in the lower densities, thermographic 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. 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.
Surfactants and dispersants
[0035] The thermographic materials of the present invention may further contain one or more
surfactants. These surfactants may be anionic, non-ionic or cationic surfactants.
Examples of suitable surfactants are:
- Surfactant Nr. 1 =
- HOSTAPAL™ BV, a sodium trisalkyl-phenyl-polyethyleneglycol(EO 7-8)sulphate from Hoechst;
- Surfactant Nr. 2 =
- MERSOLAT™ H80, a sodium hexadecyl-sulfonate from Bayer;
- Surfactant Nr. 3 =
- ULTRAVON™ W, a sodium arylsulfonate from Ciba-Geigy;
- Surfactant Nr. 4 =
- TERGITOL™ 4, a sodium 1-(2'-ethylbutyl)-4-ethylhexylsulfate;
- Surfactant Nr. 5 =
- MARLON™ A-396, a sodium dodecylphenylsulfonate from Hüls;
- Surfactant Nr. 6 =
- HOSTAPAL™ W, a nonylphenylpolyethylene-glycol from Hoechst;
- Surfactant Nr. 7 =
- AKYPO™ OP 80, supplied by CHEMY as an 80% con-centrate of an octyl-phenyl-oxypolyethylene-glycol(EO
8)acetic acid;
- Surfactant Nr. 8 =
- ammonium dodecylphenyl sulfonate;
- Surfactant Nr. 9 =
- hexadecyl-dimethylammonium acetic acid.
In the thermographic materials of the present invention the surfactant requirement
is mainly that required to disperse the substantially light-insensitive organic silver
salt.
[0036] The thermographic materials according to the present invention may also contain dispersants.
Suitable dispersants are: natural polymeric substances, a synthetic polymeric substances
and finely divided powders, e.g. silica.
Stabilizers and antifoggants
[0037] In order to obtain improved shelf-life and reduced fogging, stabilizers and antifoggants
may be incorporated into the thermographic materials of the present invention.
Other ingredients
[0038] In addition to said ingredients the thermographic material may contain other additives
such as free fatty acids, surface-active agents, 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
[0039] The support for the thermographic material according to the present invention is
polymer or polymer-coated and may be transparent, translucent or opaque and is preferably
a thin flexible carrier made e.g. from 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 made of an opacified resin composition.
Protective layer
[0040] A protective layer may also be provided for the thermo-sensitive 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 said 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.
[0041] A slipping layer, being said 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 EP 138 483, EP 227 090, US-P 4,567,113, US-P 4,572,860, US-P 4,717,711, EP-A 311
841, 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
[0042] The coating of any layer of the thermographic 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
[0043] 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.
[0044] 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 1.0 ms, 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.
[0045] 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 said thermal printing heads may proceed through a contacting but removable
resin sheet or web wherefrom during said heating no transfer of recording material
can take place.
[0046] 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, e.g. magnetic disc or tape or optical disc
storage medium, optionally linked to a digital image work station wherein the image
information can be processed to satisfy particular needs.
[0047] 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 pulse-wise. When used in
thermographic recording operating with thermal printheads said thermographic 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 said material. Image-
or pattern-wise heating of the thermographic material may also proceed by means of
pixel-wise modulated ultra-sound, using e.g. an ultrasonic pixel printer as described
e.g. in US-P 4,908,631.
Industrial applications
[0048] Thermographic 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.
[0049] The following examples and comparative examples illustrate the present invention.
The percentages and ratios used in the examples are by weight unless otherwise indicated.
In the COMPARATIVE and INVENTION EXAMPLES the following ingredients were used in addition
to those already mentioned above:
i) subbing layer ingredients:
PAREZ RESIN™ 707 |
a 80% solids melamine-formaldehyde resin from AMERICAN CYANAMID; |
HORDAMER™ PE02 |
a 40% aqueous dispersion of polyethylene from HOECHST; |
PSS |
polystyrene sulfonic acid |
R 10985 |
a calcium-containing medium viscosity gelatin from ROUSSELOT; |
MOBILCER™ Q |
a microcrystalline polyethylene wax from Mobil Oil |
KIESELSOL 100F |
a 36% aqueous dispersion of colloidal silica from BAYER; |
KIESELSOL 300F |
a 30% aqueous dispersion of colloidal silica from BAYER; |
PMMA |
a 20% aqueous dispersion of polymethylmethacrylate particles 2µm in diameter |
ii) thermosensitive element ingredients:
- K7598 =
- KOEPF™ Type 7598, a calcium-free gelatine;
- GEL01 =
- a calcium-free gelatin;
- AgBeh =
- silver behenate
- R01 =
- ethyl 3,4-dihydroxybenzoate
- T01
- = 7-(ethylcarbonato) benzo[e] [1,3]oxazine-2,4-dione
- T02 =
- benzo[e] [1,3]oxazine-2,4-dione
PREPARATION OF SUBBING LAYERS
SUBBING LAYER NUMBER C1:
[0050] A 0.34mm thick polyethylene terephthalate sheet was first coated to a wet thickness
of 7µm with a composition which after drying and longitudinal and transverse stretching
produced a 175µm thick support coated with a sub-layer with the following composition,
expressed as the coating weights of the ingredients present:
# terpolymer 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
[0051] The 175µm thick longitudinally stretched polyethylene terephthalate support was then
coated on one side with a composition which after drying at 130°C produced a second
sub-layer with the following layer composition, expressed as the coating weights of
the ingredients present:
# gelatin (R 10985): 380mg/m2
# colloidal silica (KIESELSOL™ 300F) : 341mg/m2
# PMMA: 1mg/m2
# an alkylpolyethylene glycol (Surfactant Nr. 6): 7mg/m2
# aryl sulfonate surfactant (Surfactant Nr. 3): 13mg/m2
# 4-chloro-3-methylphenol: 10mg/m2
# 1,2,6-trihydroxyhexane: 25mg/m2
These two sub-layers together form subbing layer number C1, which is used in the
photographic art as a subbing layer for providing adhesion between a polyethylene
terephthalate support and gelatinous silver halide emulsion layers.
SUBBING LAYER NUMBER C2:
[0052] A 0.34mm thick polyethylene terephthalate sheet was first coated to a wet thickness
of 7µm with a composition which after drying and longitudinal and transverse stretching
produced a 175µm thick support coated with a sub-layer with the following composition,
expressed as the coating weights of the ingredients present:
# terpolymer 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
[0053] The 175µm thick longitudinally stretched polyethylene terephthalate support was then
coated on one side with a composition which after drying at 130°C produced a second
sub-layer with the following layer composition, expressed as the coating weights of
the ingredients present:
# gelatin (R 10985): 380mg/m2
# colloidal silica (KIESELSOL™ 300F): 341mg/m2
# PMMA: 1mg/m2
# an alkylpolyethylene glycol (Surfactant Nr. 6): 7mg/m2
# aryl sulfonate surfactant (Surfactant Nr. 3): 13mg/m2
# hexylene glycol: 22mg/m2
# trimethylolpropane: 11mg/m2
These two sub-layers together form subbing layer number C2, which is used in the
photographic art as a subbing layer for providing adhesion between a polyethylene
terephthalate support and gelatinous silver halide emulsion layers.
SUBBING LAYER NUMBER C3:
[0054] 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 175µm thick support coated with the following subbing-layer composition of SUBBING
LAYER NUMBER C2 expressed as the coating weights of the ingredients present:
# terpolymer 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 01:
[0055] 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 175µm 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
SUBBING LAYER NUMBER 02:
[0056] A 0.34mm thick polyethylene terephthalate sheet was coated to a thickness of 7µm
with a composition which after drying and longitudinal and transverse stretching produced
a 175µm thick support coated with the following subbing-layer composition of subbing
layer number 02 expressed as the coating weights of the ingredients present:
# hexadecyldimethylammonio-acetic acid: 1mg/m2
# 3-glycidoxypropyltrimethoxy silane hydrolyzed in presence of PSS: 30mg/m2
# polystyrene sulfonic acid (PSS): 16mg/m2
# colloidal silica (KIESELSOL™ 300F from BAYER): 4mg/m2
# Mobilcer™ Q: 1mg/m2
Quantity of leachable non-fluoro-halide ions per unit surface of subbing layers
[0057] The chloride-ion content leachable during overcoating with an aqueous dispersion
or solution was simulated by placing a 10 x 5cm
2 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:
[0058] 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 01 and a small quantity in subbing layer C3.
Table 1:
subbed support |
concentration of leachable chloride ions [ppm] |
quantity of leachable chloride ions [mg/m2 surface] |
chlorine content with WDXRF [kcps] |
side 1 |
side 2 |
|
|
|
subbing layer number |
coverage [mg/m2] |
subbing layer number |
coverage [mg/m2] |
|
|
|
- |
0 |
- |
0 |
0 |
0 |
<2 |
C1 |
981.6 |
C1 |
981.6 |
1987 |
1.95 |
51,452 |
C2 |
979.6 |
C2 |
979.6 |
1633 |
1.6 |
- |
C3 |
204.6 |
C3 |
204.6 |
3177 |
0.65 |
27.5 |
01 |
48 |
C2 |
989.9 |
915 |
0.95 |
- |
02 |
52 |
- |
0 |
<9615 |
<0.25 |
|
The quantity of leachable chloride ions in the different subbing layers obtained
from these measurements are summarized in table 2:
Table 2:
Subbing layer number |
Quantity of leachable chloride ions [mg/m2 surface] |
C1 |
1.95 |
C2 |
1.60 |
C3 |
0.65 |
01 |
0.3# |
02 |
<0.5* |
- |
0* |
# calculated using results for the support with two C2 layers and for the support
with one C2 layer and one 01 layer = (0.95 x 2) - 1.6 = 0.3 mg/m2 |
* assuming that uncoated support has no leachable chloride ions on the basis of WDXRF
measurements |
COMPARATIVE EXAMPLES 1 to 3 and INVENTION EXAMPLES 1 & 2
Preparation of a silver behenate dispersion
[0059] 1125g of a 10% aqueous solution of Surfactant Nr 5 and 1500g of silver behenate were
added to 4875g of deionized water and the mixture stirred for 30 minutes with a HOMOREX™
stirrer. The resulting dispersion was then stirred for 15 minutes with an ULTRA-TURRAX™
stirrer after which it was stored for 24 hours in a refrigerator to allow the foam
to dissipate. The dispersion was then stirred for 10 minutes with an ULTRA-TURRAX™
stirrer and passed twice through a GUERIN homogenizer coupled with a MICROFLUIDICS™
microfluidizer at a pressure of 350 bar to obtain a finely divided aqueous silver
behenate dispersion.
[0060] A gelatin solution was produced by adding 660g of K7598 to 2319g of deionized water,
allowing the gelatin to swell for 30 minutes and heating the mixture to 50°C. The
gelatin solution was then added to the aqueous silver behenate dispersion with vigorous
stirring with a DISSOLVER™, after which the stirring was continued for a further 15
minutes producing a gelatinous aqueous dispersion of silver behenate containing: 14.3%
of silver behenate, 1.07% of Surfactant Nr. 5 and 6.28% of gelatin.
Preparation of a tone modifier dispersion
[0061] The tone modifier dispersion was prepared by first dissolving 8.8g of K7598 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 gelatin.
Preparation of the thermosensitive element
[0062] The coating dispersion was prepared by adding 324g of the gelatinous aqueous dispersion
of silver behenate to 165.7g of deionized water, heating the dispersion to 36°C, then
adding 81g of the tone modifier dispersion as flakes, followed by stirring for 15
minutes before adding with stirring 70.8g of a 30% latex dispersion of polymer latex
number 1 at pH 5, a further 5 minutes stirring was followed by the addition with stirring
of 103.24g of a 7.25% aqueous solution of boric acid at 50°C, 11.01g of R01 in 20.52g
of ethanol and 15.7g of a 3.7% aqueous solution of formaldehyde to produce a dispersion
containing: 5.85% of silver behenate, 0.44% of Surfactant nr 5, 3.47% of gelatin,
2.68% of polymer latex number 1, 1.39% of R01, 0.94% of boric acid, 2.05% of T01 and
0.07% of formaldehyde.
[0063] The resulting emulsion was then doctor blade-coated to a wet thickness of 60µm with
the blade at a setting of 100µm onto an unsubbed 100µm thick polyethylene terephthalate
support in the case of COMPARATIVE EXAMPLE 1 and a 175µm thick polyethylene terephthalate
supports coated with different subbing layers in the cases of COMPARATIVE EXAMPLE
2 & 3and INVENTION EXAMPLES 1 & 2 and dried for 10 minutes at 50°C, producing a silver
behenate coverage of 3.8g/m
2.
Adhesion test
[0064] The adhesion of the thermosensitive element to the polyethylene terephthalate support
was evaluated for the thermographic materials of COMPARATIVE EXAMPLES 1 to 3 and INVENTION
EXAMPLES 1 & 2 using a tape test. In carrying out the test a 10 x 10 cm
2 sample was prepared and laid flat on a table and a section of TESAPACK™ 4122 tape,
available from BEIERSDORF AG, Hamburg, Germany, was placed across the width of the
sample and smoothed out by hand to ensure uniform adhesion. Upon manually removing
the tape, the area of thermosensitive element removed from the polyethylene terephthalate
support was estimated and related to adhesion as follows:
- poor adhesion
- = more than 50% of the thermosensitive element removed
- moderate adhesion
- = 20 to 49% of the thermosensitive element removed
- good adhesion
- = 1 to 19% of the thermosensitive element removed
- excellent adhesion
- = none of the thermosensitive element removed
Thermographic printing
[0065] During printing of the recording materials of COMPARATIVE EXAMPLES 1 to 3 and INVENTION
EXAMPLES 1 & 2 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.
[0066] 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 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 materials of COMPARATIVE EXAMPLES 1 to 3 and INVENTION EXAMPLES
1 & 2.
Image evaluation
[0067] The maximum densities, D
max, and minimum densities, D
min, of the prints given in table 3 for COMPARATIVE EXAMPLES 1 to 3 and INVENTION EXAMPLES
1 & 2 respectively were measured through a blue filter with a MACBETH™ TR924 densitometer
in the grey scale step corresponding to data levels of 255 and 0 respectively and
are also given in table 3.
Archivability test
[0068] The achivability of prints made with the thermographic materials of COMPARATIVE EXAMPLES
1 to 3 and INVENTION EXAMPLES 1 & 2 was evaluated on the basis of the observed changes
in minimum density upon heating the prints at 35°C in a relative humidity (RH) of
80% for 3 days in the dark. The results of these tests are given in table 3.
Light box test
[0069] The stability of the image background of the prints made with the thermographic materials
of COMPARATIVE EXAMPLES 1 to 3 and INVENTION EXAMPLES 1 & 2 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.
[0070] 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 3.
Table 3:
Comparative example number |
AgBeh cover age [g/m2] |
subbing layer |
FRESH |
Archivability ΔDmin vis/blue after 3d at 35°C/80% RH |
Light box ΔDmin vis/blue after 3d at 30°C/85% RH |
|
|
nr |
adhesion |
Dmax vis/blue |
Dmin vis/blue |
|
|
1 |
3.68 |
- |
poor |
3.12/3.23 |
0.07/0.08 |
0.00/0.00 |
0.06/0.11 |
2 |
4.13 |
C1 |
excellent |
3.40/3.55 |
0.08/0.10 |
0.00/0.00 |
0.10/0.28 |
3 |
3.58 |
C3 |
excellent |
2.65/2.71 |
0.08/0.09 |
0.00/0.00 |
0.06/0.14 |
Invention example number |
|
|
|
|
|
1 |
3.87 |
01 |
excellent |
3.05/3.13 |
0.08/0.09 |
0.00/0.00 |
0.05/0.12 |
2 |
3.84 |
02 |
excellent |
2.82/2.87 |
0.08/0.09 |
0.00/0.00 |
0.06/0.13 |
The results of the thermographic evaluation of the thermographic material of COMPARATIVE
EXAMPLE 1 demonstrate the excellent archivability and light box stability (= reduced
ΔD
min values) with unsubbed PET, but also the poor adhesion of the thermosensitive element
thereon.
[0071] The results of COMPARATIVE EXAMPLES 2 and 3 and INVENTION EXAMPLES 1 and 2 show that
although excellent adhesion was observed between the support and the common thermosensitive
element with all the subbing layers used, the choice of subbing layer, surprisingly,
because of the relative bulk of the subbing layer compared with that of the thermosensitive
element, had a considerable influence upon the archivability and light box stability
of the resulting thermographic materials. This is particularly marked with the thermographic
recording material of COMPARATIVE EXAMPLE 2 with subbing layer number C1 with 1.95mg/m
2 of leachable chloride ions and less marked with the thermographic recording material
of COMPARATIVE EXAMPLE 3 with subbing layer number C3 with 0.65mg/m
2 of leachable chloride ions, due to the poorish light stability of the thermosensitive
element itself, which largely masked any slight differences in the influence of the
subbing layers upon the light stability of the thermographic recording material as
a whole, as shown by the small differences in ΔD
min (blue) after the light box test between the thermographic recording materials of
COMPARATIVE EXAMPLE 3 with a subbing layer falling outside that used in the thermographic
recording material of the present invention and INVENTION EXAMPLES 1 and 2 with subbing
layer number 01 and 02 with 0.3mg/m
2 and <0.5mg/m
2 of leachable chloride ions respectively used in the thermographic recording materials
according to the present invention.
COMPARATIVE EXAMPLE 4 & INVENTION EXAMPLE 3
Preparation of the silver behenate dispersion
[0072] The silver behenate dispersion was produced as follows: dispersing 25kg (73.5M) behenic
acid was dispersed with stirring at at 80°C in 1g 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 AgB-concentration was 16.7% with 0.07g of Surfactant
Nr 5/g AgB, the residual conductivity was 1.0mS/cm.
Preparation of the thermosensitive element
[0073] 175µm thick blue pigmented polyethylene terephthalate supports coated with subbing
layer numbers C3 & 01 were coated with an aqueous coating composition and the following
ingredients so to obtain thereon, after drying at 18 to 20°C for 93s in a stream of
air with a flow rate of 950kg/min, a thermosensitive element containing:
* AgBeh: 4.94g/m2
* GEL01: 4.96g/m2
* formaldehyde 0.2g/m2
* Surfactant Nr. 7 0.004g/m2
* Surfactant Nr. 8 0.32g/m2
* Surfactant Nr. 9 0.13g/m2
* R01 1.00g/m2
* T02 0.53g/m2
* boric acid 0.18g/m2
* ammonium tetraborate 0.48g/m2
and to produce the thermographic recording materials of COMPARATIVE EXAMPLE 4 & INVENTION
EXAMPLE 3 respectively.
Evaluation
[0074] Thermographic evaluation and evaluation of the adhesion between the support and the
thermosensitive element 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 4.
Table 4:
Comparative example number |
AgBeh coverage [g/m2] |
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 |
|
|
nr |
adhesion |
Dmax vis/blue |
Dmin vis/blue |
|
|
4 |
4.94 |
C3 |
excellent |
3.12/3.23 |
0.23/0.10 |
0.01/0.02 |
0.02/0.04 |
Invention example number |
|
|
|
|
|
|
|
3 |
4.94 |
01 |
excellent |
2.65/2.71 |
0.21/0.10 |
0.00/0.01 |
0.01/0.01 |
A comparison of the ΔD
min-values both through visible and blue filters for the thermographic recording material
of INVENTION EXAMPLE 3 with that for the thermographic recording material of INVENTION
EXAMPLE 1 with the same subbing layer shows a substantial reduction, indicating a
substantial improvement in stability to light due to the use of a different, more
stable, thermosensitive element. With this more stable thermosensitive the thermographic
recording material of INVENTION EXAMPLE 3 using subbing layer number 01 with a leachable
chloride content of 0.3mg/m
2 exhibited a significantly lower sensitivity to light, reduced ΔD
min-values, compared with the thermographic recording material of COMPARATIVE EXAMPLE
4 using subbing layer number C3 with a leachable chloride content of 0.65 mg/m
2 outside the chloride content of the subbing layers used in the thermographic recording
material according to the present invention.
[0075] 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.