FIELD OF THE INVENTION
[0001] The present invention concerns barrier layers for use in substantially light-insensitive
thermographic recording materials.
BACKGROUND OF THE INVENTION
[0002] Thermography is an image-forming process including a heating step and hence includes
photothermography in which the image-forming process includes image-wise exposure
and direct thermal processes in which the image-forming process includes an image-wise
heating step. In direct thermal printing a visible image pattern is produced by image-wise
heating of a recording material.
[0003] US 3,832,186 discloses in EXAMPLE 9 a heat developing-out
photosensitive material obtained by coating a polyethylene terephthalate film support with a composition
comprising polyvinyl butyral, silver benzotriazole, mercuric bromide, a benzoxazolidene
thiohydantoin sensitising dye, ascorbic acid monomyristate as reducing agent and 3-mercapto-5-phenyl-4-phenyl-1,2,4-triazole
and overcoating this composition with a vinyl chloride-vinyl acetate copolymer (weight
ratio 85:15).
[0004] US 3,933,508 discloses a heat developable
light-sensitive material comprising, on a support, (1) an organic silver salt, (2) a light-sensitive
silver halide or silver-halide prepared by reacting the organic silver salt with a
halide, (3) a reducing agent, (4) a binder, and (5) an overcoat layer overlying components
(1)-(4); said components (1)-(4) occurring in a single coated layer consisting essentially
of a polymer having a refractive index greater than about 1.45 at 20°C, having heat
resistance to temperatures greater than about 46°C, being colorless and soluble in
organic solvents, and providing increased transparency for said overcoat layer. Examples
of polymers used for the overcoat layer according to US 3,933,508, which are preferably
heat-resistant, colorless and soluble in solvents, are polyvinyl chloride, polyvinyl
acetate, copolymers of vinyl chloride and vinyl acetate containing more than 50 mol%
vinyl chloride but insufficient vinyl chloride to lower the heat resistance, polyvinyl
butyral, polystyrene, polymethyl methacrylate, benzyl cellulose, ethyl cellulose,
cellulose acetate butyrate, cellulose acetate, polyvinylidene chloride, polyvinyl
pyrrolidone, cellulose propionate, polyvinyl formal, cellulose acetate phthalate,
polycarbonates and cellulose acetate propionate. Moreover, gelatin, gelatin derivatives
such as phthalated gelatin, acrylamide polymers, polyisobutylene, butadiene-styrene
copolymers (no limitation on monomer proportions) and polyvinyl alcohol are preferred.
EXAMPLES 5, 10, 12 and 18 exemplify an overcoat comprising a vinyl chloride-vinyl
acetate copolymer (95 wt% vinyl chloride, 5wt% vinyl acetate).
[0005] GB-A 1,422,057 discloses a heat-developable
photosensitive material comprising, coated on a support, a layer of (1) an organic silver salt,
(2) a light-sensitive silver halide as grains of which at least 30 mole % is silver
iodide, (3) a reducing agent and (4) a spectrally sensitising dye adsorbed on the
surface of the silver halide grains, which sensitizing dye has an oxidation potential
not exceeding 1.00 volt and difference in values between its oxidation potential and
its reduction potential of at least 2.00 volts. EXAMPLE 4 discloses a silver benzotriazolate-containing
heat-developable photosensitive layer with a top-coat of a vinyl chloride-vinyl acetate
copolymer (85:15 by weight).
[0006] DE-A 24 39 460 discloses a thermally developable
photosensitive material, comprising coated on a support, (a) an organic silver salt, (b) a catalytic
quantity of a silver halide or photosensitive silver-halide prepared by reacting the
organic silver salt with a halide, (c) a reducing agent and (d) a binder, and an overcoat,
which comprises a polymer layer with kaolin dispersed therein. DE-A 24 39 460 discloses
the following overcoat polymers: (a) copolyesters; (b) nylon compounds; (c) vinylidene
dichloride copolymers; (d) ethylene-vinyl acetate-copolymers; (e) cellulose ethers;
(f) polyethylene; (g) synthetic rubbers; (h) cellulose esters; (i) polyvinylesters;
(j) polyacrylates and α-alkyl-polyacrylate esters; (k) high molecular weight polyethylene
oxides of polyglycols with an average molecular weight of about 4000 to 1,000,000;
(1) polyvinyl chloride and copolymers; (m) polyvinyl acetals; (n) polyformaldehydes;
(o) polyurethanes; (p) polycarbonates; (q) polystyrenes; (r) gelatins and their derivatives;
(s) polyvinyl alcohol; (t) naturally occurring colloids. EXAMPLE 4 discloses an overcoat
layer comprising a vinyl chloride-vinyl acetate copolymer (95:5 by weight).
[0007] US 4,197,131 discloses a
light-sensitive composition comprising an intimate mixture of a substantially light-sensitive silver
compound which upon reduction gives a visible change and sufficient of a silver halide
to catalyse said reduction to give a visible change in those areas where the silver
halide has been exposed to light and when the mixture is heated in the presence of
a reducing agent, and as a yellow acutance dye a 1-alkyl-4-nitromethylene-quinolane,
the alkyl substituent containing 1 to 4 carbon atoms. The EXAMPLES disclose overcoating
of the light-sensitive dispersion with a layer comprising a vinyl chloride-vinyl acetate
copolymer available from Union Carbide under the name VYNS.
[0008] The EXAMPLES of US 4,450,229 disclose the overcoating of a
photothermographic element comprising a binder, light sensitive silver halide in catalytic proximity
to a light insensitive silver source material in said element which contains a reducible
source of silver ions, a reducing agent for silver ion and an effective latent image
stabilizing of a particular class of compounds, with a layer comprising a vinyl acetate-vinyl
chloride copolymer (80 wt% vinyl acetate, 20wt% vinyl chloride).
[0009] US 4,558,003 discloses an unexposed
photothermographic article comprising a support, a silver containing layer comprising a binder, a silver
compound having reducible silver ions, silver halide in catalytic proximity to said
silver compound, and a reducing agent for silver ion, said binder comprising at least
25 percent by weight of a poly(vinyl acetal), said article being characterized by
the presence of an amount of borate ion, a boric acid salt, or a boric acid, alone,
or in combination with an isocyanate, sufficient to harden said binder. EXAMPLE 1
exemplifies a top coat of a poly(vinyl acetate)/poly(vinyl chloride)copolymer (80/20).
[0010] US 4,460,681 discloses a color
photothermographic imageable article comprising a substrate, a photothermographic emulsion layer, and
organic solvent soluble barrier layer, a second photothermographic emulsion layer
on a polymeric cover layer, wherein each of the photothermographic layers comprise
a reducible silver source, photosensitive silver halide, a reducing agent for silver
ion and solvent soluble binder, and further wherein each photothermographic layer
is sensitized to a portion of the spectrum at least 60 nm different from the other
photothermographic layer and each photothermographic layer contains a leuco dye which
when oxidized forms a feasible dye having a maximum absorbance at least 60 nm different
from that of the dye formed in the at least one other photosensitive layer, and the
barrier layer is between said photothermographic layers and is impermeable to the
solvent contained in the second photothermographic layer. Second layer "barrier" polymers
may, according to US 4,460,681, be maleic anhydride/vinyl methyl ether copolymers,
polyvinylidene chloride (SARAN™), or polyvinylpyrrolidone, with maleic acid copolymers
such as alkyl monoesters of poly(methyl vinyl ether/maleic acid) being preferred.
The "barrier" polymer, which is the fourth layer and preferably contains the color
reactants, is normally a methyl methacrylate polymer (preferably a hard polymer with
a Tukon hardness of 20 or more), copolymer, or blend with other polymers or copolymers
(e.g. copolymer with n-butyl acrylate, butyl methacrylate, and other acrylates such
as acrylic acid, methacrylic acid, acrylic anhydride, and the like), polystyrene,
or a combination of a polyvinyl chloride tripolymer with a butadiene-styrene copolymer.
The preferred polymer is a hard methyl methacrylate homopolymer blended with soft
methyl methacrylate copolymers. In EXAMPLE 5, a yellow/magenta barrier coating is
disclosed of a butadiene/styrene copolymer and a polyvinyl chloride/acetate/alcohol)
polymer (VAGH).
[0011] EP-A 0 536 955 discloses a heat developable
photothermographic article comprising: (a) an image-receiving element comprising a polymeric image-receiving
layer; and (b) strippably adhered to said image-receiving element, an imageable photothermographic
element comprising a plurality of emulsion layers, each of which emulsion layers comprises
a binder, a silver source material, and a leuco dye, and interposed between each pair
of said emulsion layers a dye-permeable interlayer. EP-A 0 536 955 further discloses
that the first interlayer must be impermeable to solvents to be used for applying
the subsequent coating; however, the polymer for forming the first interlayer can
be applied from any organic solvent. The polymer of the first interlayer is preferably
a thermoplastic polymer. Homopolymers of vinyl chloride or copolymers of vinyl chloride,
preferably having a glass transition temperature greater than 80°C, for example, a
copolymer of vinyl chloride (96%) and vinyl acetate (4%), a blend of poly(vinyl chloride)(90%)
and poly(vinyl acetate)(10%), can be used to form the first interlayer. EXAMPLE 1
exemplifies an interlayer comprising a terpolymer of vinyl chloride(83%), vinyl acetate(16%)
and maleic acid(1%).
[0012] US 4,942,115 discloses a thermally processable imaging element comprising a support
bearing a thermally processable hydrophobic imaging layer and, on the side of the
imaging layer away from the support, an overcoat layer comprising poly(silicic acid)
and a hydrophilic monomer or polymer, wherein the element comprises a polymeric adhesion
promoting layer between the overcoat and the imaging layer. US 4,942,115 discloses
that polymers that are useful in the polymeric adhesion promoting layer are: (1) terpolymers
of 2-propenenitrile, 1,1-dichloroethene, and propenoic acid, such as disclosed in
US 3,271,345; and (2) terpolymers of 2-propenoic acid, methyl ester, 1,1-dichloroethene
and itaconic acid as disclosed in, for example, US 3,437,484, with a polymeric adhesion
layer comprising poly(2-propenenitrile co-1,1-dichloroethene-co-2-propenoic acid)
or poly(2-propenoic acid, methyl-ester-co-1,1dichloroethene-co-itaconic acid) being
preferred and poly(2-propenenitrile co-1,1-dichloroethene-co-2-propenoic acid) being
exemplified.
[0013] US 6,352,819 discloses a high contrast black-and-white
photothermographic material comprising a support having thereon: (a) a thermally developable, high contrast
imaging layer(s) comprising a binder and in reactive association, photosensitive silver
halide, a non-photosensitive source of reducible silver ions, a reducing composition
for said non-photosensitive source reducible silver ions, and a high contrast agent,
and (b) a barrier layer that is on the same side but farther from said support than
said high contrast imaging layer(s), said barrier layer comprising a film-forming
polymer and being impermeable to or reactive with any components that are diffusible
from said image-forming layer(s) at a temperature greater than 80°C. US 6,352,819
further discloses but does not claim a high contrast black-and-white
thermographic material comprising a support having thereon: (a) a thermally developable and non-photosensitive,
high contrast imaging layer(s) comprising a binder and in reactive association, a
non-photosensitive source of reducible silver ions, a reducing composition for said
non-photosensitive source reducible silver ions, and a high contrast agent, and (b)
a barrier layer that is farther from the support than the high contrast imaging layer(s),
the barrier layer comprising a film-forming polymer and being impermeable to or reactive
with any components that are diffusible from said image-forming layer(s) at a temperature
greater than 80°C. The term thermographic material is a generic term which includes
photothermographic materials and the recitation of the high contrast thermographic
material does not exclude the presence of photosensitive species such as photosensitive
silver halide. There is therefore no specific disclosure in US 6,352,819 concerning
substantially light-insensitive thermographic materials and moreover US 6,352,819
contains no examples devoted to substantially light-insensitive thermographic materials.
Some particularly useful barrier materials, according to US 6,352,819, include polyvinyl
alcohol, a styrene polymer (including polymers of styrene derivatives), a vinyl halide
polymer, a vinyl acetate polymer [such as polyvinyl acetate, poly(ethylene-co-vinyl
acetate) or a copolymer of a vinyl halide and vinyl acetate], a polyvinyl pyrrolidone,
a water-soluble or water-dispersible polyester, and gelatin (including deionised and
acid processed gelatin) or a gelatin derivative (such as phthalated gelatin and carbamoylated
gelatin, with the styrene polymers, vinyl acetate polymers and polyvinyl alcohol being
preferred. EXAMPLE 12 discloses a barrier layer comprising poly(vinyl chloride-co-vinyl
acetate), EXAMPLE 32 discloses a barrier layer comprising poly(styrene-co-acrylonitrile)
(75:25 weight), EXAMPLE 33 discloses a barrier layer comprising U CAR VYNS poly(vinyl
chloride-co-vinyl acetate) from Union Carbide and EXAMPLE 34 discloses a barrier layer
comprising U CAR VAGH poly(vinyl chloride-co-acetate-co-vinyl alcohol) from Union
Carbide.
[0014] It has been found that, in order to achieve a neutral image tone in substantially
light-insensitive black and white monosheet thermographic materials, reducing agents
and toning agents are required which diffuse to the surface of the material despite
the presence of an outermost protective layer both during storage before printing
and after printing and results, in extreme cases, in the user visually observing deposits
of reducing agents, toning agents and reaction products of the imaging-forming process
on the surface of the materials. Substantially light-insensitive black and white monosheet
thermographic materials are therefore required which exhibit an acceptably neutral
image tone, but do not exhibit the formation of such deposits of reducing agents,
toning agents and reaction products of the imaging-forming process.
ASPECTS OF THE INVENTION
[0015] It is therefore an aspect of the present invention to provide a substantially light-insensitive
black and white monosheet thermographic material, which exhibits acceptably neutral
image tone, but do not exhibit the formation of surface deposits comprising, for example,
reducing agent, toning agent and carboxylic acid.
[0016] Further aspects and advantages of the invention will become apparent from the description
hereinafter.
SUMMARY OF THE INVENTION
[0017] US 6,352,819 teaches the barrier layer comprises a film-forming polymer(s) that reacts
with or acts as a physical barrier to diffusible by-products resulting from the presence
of high contrast agents such as acrylonitrile co-developers, hydrazide co-developers
and isoxazole codevelopers. It has been surprisingly found that prints of substantially
light-insensitive black and white monosheet thermographic materials with thermosensitive
elements not containing a high contrast agent and containing at least one substantially
light-insensitive silver salt of a carboxylic acid, ortho-dihydroxy-benzene derivatives
as reducing agents in combination with a barrier layer comprising a copolymer comprising
vinyl chloride units and vinyl acetate units and/or vinyl alcohol units and/or a copolymer
comprising styrene units and acrylonitrile units inserted between the outermost protective
layer and the thermosensitive element exhibit acceptably neutral image tones, as characterized
by CIELAB a* and b* values, and that surface deposits are neither formed prior to
printing nor after printing. The L*, a* and b* CIELAB-values were determined by spectrophotometric
measurements according to ASTM Norm E179-90 in a R(45/0) geometry with evaluation
according to ASTM Norm E308-90.
[0018] Aspects of the present invention are realized with a substantially light-insensitive
black and white monosheet thermographic recording material has a support and on one
side of the support comprises a thermosensitive element, a barrier layer and an outermost
protective layer, the thermosensitive element being exclusive of a high contrast agent
and containing comprising a substantially light-insensitive silver salt of a carboxylic
acid, at least one reducing agent therefor in thermal working relationship therewith,
at least one toning agent and a binder, characterized in that the at least one reducing
agent is an ortho-dihydroxy-benzene derivative and the barrier layer comprises a copolymer
comprising vinyl chloride units and vinyl acetate units and/or vinyl alcohol, a copolymer
comprising styrene units and acrylonitrile units, a copolymer comprising cationic
units and/or a copolymer comprising styrene units and maleic acid units.
[0019] Preferred embodiments of the present invention are disclosed in the detailed description
of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
[0020] The term alkyl means all variants possible for each number of carbon atoms in the
alkyl group i.e. for three carbon atoms: n-propyl and isopropyl; for four carbon atoms:
n-butyl, isobutyl and tertiary-butyl; for five carbon atoms: n-pentyl, 1,1-dimethylpropyl,
2,2-dimethylpropyl and 2-methyl-butyl etc.
[0021] The term acyl group as used in disclosing the present invention means -(C=O)-aryl
and -(C=O)-alkyl groups.
[0022] The L*, a* and b* CIELAB-values are defined in ASTM Norm E179-90 in a R(45/0) geometry
with evaluation according to ASTM Norm E308-90.
[0023] Substantially light-insensitive means not intentionally light sensitive.
[0024] The term "high contrast agent", which are sometimes identified as "co-developers"
or "auxiliary developers", have as their main function an increase in the contrast
of the material by reducing most or all of the reducible silver ions in the substantially
light-insensitive silver salt of a carboxylic acid in the radiation-exposed areas
e.g. acrylonitrile co-developers, hydrazide co-developers and isoxazole co-developers
as disclosed in US 6,352,819 herein incorporated by reference.
[0025] Heating in association with the expression a substantially water-free condition as
used herein, means heating at a temperature of 80 to 250°C. The term "substantially
water-free condition" as used herein 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.
Thermosensitive element
[0026] The term thermosensitive element as used herein is that element which contains all
the ingredients, which contribute to image formation. According to the substantially
light-insensitive black and white monosheet thermographic recording material, according
to the present invention, the thermosensitive element contains at least a substantially
light-insensitive silver salt of a carboxylic acid, an ortho-dihydroxy-benzene derivative
reducing agent therefor in thermal working relationship therewith, a toning agent
and a binder. The thermosensitive element may comprise a layer system in which the
above-mentioned ingredients may be dispersed in different layers, with the proviso
that the substantially light-insensitive silver salt of a carboxylic acid is in reactive
association with the ortho-dihydroxy-benzene derivative reducing agent 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 the substantially light-insensitive silver
salt of a carboxylic acid, so that reduction to silver can occur. Such materials include
the possibility of the substantially light-insensitive silver salt of a carboxylic
acid and/or the ortho-dihydroxy-benzene derivative reducing agent therefor being encapsulated
in heat-responsive microcapsules, such as disclosed in EP-A 0 736 799 herein incorporated
by reference.
Substantially light-insensitive silver salt of a carboxylic acid
[0027] According to a first embodiment of the substantially light-insensitive black and
white monosheet thermographic recording material, according to the present invention,
the substantially light-insensitive silver salt of a carboxylic acid is not a double
organic salt containing a silver cation associated with a second cation e.g. magnesium
or iron ions.
[0028] According to a second embodiment of the substantially light-insensitive black and
white monosheet thermographic recording material, according to the present invention,
said substantially light-insensitive silver salt of an carboxylic acid is a substantially
light-insensitive silver salt of an aliphatic carboxylic acids known as a fatty acid,
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 salts of an organic carboxylic acids may also be used in the present
invention, as disclosed in EP-A 964 300 herein incorporated by reference.
Ortho-dihydroxy-benzene derivative
[0029] According to a third embodiment of the substantially light-insensitive black and
white monosheet thermographic recording material, according to the present invention,
the ortho-dihydroxy-benzene derivative is selected from the group consisting of catechol,
3-(3,4-dihydroxyphenyl) propionic acid, 3,4-dihydroxybenzoic acid, 3,4-dihydroxybenzoic
acid esters, gallic acid, gallic acid esters, e.g. methyl gallate, ethyl gallate and
propyl gallate, 3,4-dihydroxy-benzaldehyde, 3,4-dihydroxy-acetophenone, 3,4-butyrophenone,
3,4-dihydroxy-benzophenone, 3,4-dihydroxybenzophenone derivatives, 3,4-dihydroxy-benzonitrile,
and tannic acid, as disclosed in EP-A 0 692 733, EP-A 0 903 625, EP-A 1 245 403 and
EP-A 1 245 404 herein incorporated by reference.
[0030] Combinations of reducing agents may also be used that on heating become reactive
partners in the reduction of the one or more substantially light-insensitive organic
silver salt. For example, combinations of sterically hindered phenols with sulfonyl
hydrazide reducing agents such as disclosed in US 5,464,738; trityl hydrazides and
formyl-phenyl-hydrazides such as disclosed in US 5,496,695; trityl hydrazides and
formyl-phenyl-hydrazides with diverse auxiliary reducing agents as disclosed in US
5,545,505, US 5,545,507 and US 5,558,983; acrylonitrile compounds as disclosed in
US 5,545,515 and US 5,635,339; and 2-substituted malonodialdehyde compounds as disclosed
in US 5,654,130.
Toning agent
[0031] According to a fourth embodiment of the substantially light-insensitive black and
white monosheet thermographic recording material, according to the present invention,
the at least one toning agent is selected from the group consisting of phthalazinone,
phthalazinone derivatives, benzoxazine dione, benzoxazine dione derivatives, naphthoxazine
dione and naphthoxazine derivatives, pyridazone, pyridazone derivatives, compounds
represented by formula (I) :
wherein R
1 is an alkyl group optionally substituted with a hydroxy, carboxy, carboxy ester,
acyl or carbonate group; X is S, O or N-R
6; R
6 is an optionally substituted alkyl group; R
2, R
3, R
4 and R
5 independently represent a hydrogen atom, a halogen atom or an alkyl, an alkoxy, a
thio-alkoxy, a nitro, a cyano, a carboxy, a carboxy ester, an acyl, an aldehyde, an
acylamido, a sulphonamido, an acylamino, a carbonate, a hydroxy or an aryl group or
at least one of R
2 and R
3, R
3 and R
4 and R
4 and R
5 independently represent the atoms necessary to form a carbocyclic or heterocyclic
group or at least one of R
1 and R
5 and R
2 and R
6 independently represent the atoms necessary to form a heterocyclic ring; compounds
represented by formula (II) :
wherein R
7 is an optionally substituted alkyl group; Y is S, O or N-R
10 ; R
10 is an optionally substituted alkyl group; R
8 and R
9 independently represent a hydrogen atom, a halogen atom or an alkyl, an alkoxy, a
thio-alkoxy, a nitro, a cyano, a carboxy, a carboxy ester, an acyl, an aldehyde, an
acylamido, a sulphonamido, an acylamino, a carbonato, a hydroxy or an aryl group or
R
8 and R
9 represent the atoms necessary to form a heterocyclic or a nonaromatic carbocyclic
ring or at least one of R
8 and R
10 and R
9 and R
7 independently represent the atoms necessary to form a heterocyclic ring; and both
R
8 and R
9 cannot both be an alkyl group; and compounds represented by formula (III):
wherein R
11 is a hydrogen atom or a C1 to C3 alkyl, a C1 to C3 alkenyl, a C1 to C3 alkynyl, a
cycloalkyl, an alkaryl, an aryl, a heterocyclic or a heteroaryl group all of which
may be optionally substituted; with the proviso that R
11 may not be a hydrogen atom if both R
12 and R
13 are both hydrogen atoms; R
12 and R
13 are independently a hydrogen atom or an amide, ester, carboxy, carbonato, alkyl,
alkenyl, alkynyl, cycloalkyl, alkaryl, aryl, heterocyclic or heteroaryl group all
of which may be optionally substituted; R
12 and R
13 may together represent the atoms necessary to complete an alicyclic, a heterocyclic
or a heteroaromatic ring which all may be optionally substituted; and X is a carbonyl
group, or is -N-R
14, where R
14 is an alkyl group.
[0032] Suitable optional substituents for the alkyl groups of R
1, R
6, R
7 and R
10 are independently include carboxy and carboxy ester groups. Suitable substituted
alkyl groups include: -CH
2COOH, -C
2H
4COOH and -C
2H
4COOC
2H
5.
[0033] Suitable benzoxazine dione toning agents for use in the thermographic material, according
to the present invention, are disclosed in GB 1,439,478, US 3,951,660 and US 5,599,647,
herein incorporated by reference.
Binder of the thermosensitive element
[0034] The film-forming binder of the thermosensitive element may be all kinds of natural,
modified natural or synthetic resins or mixtures of such resins, in which the at least
one organic silver salt can be dispersed homogeneously either in aqueous or solvent
media: e.g. cellulose derivatives, starch ethers, galactomannan, polymers derived
from α,β-ethylenically unsaturated compounds such as polyvinyl chloride, after-chlorinated
polyvinyl chloride, copolymers of vinyl chloride and vinylidene chloride, copolymers
of vinyl chloride and vinyl acetate, polyvinyl acetate and partially hydrolyzed polyvinyl
acetate, polyvinyl alcohol, polyvinyl acetals that are made from polyvinyl alcohol
as starting material in which only a part of the repeating vinyl alcohol units may
have reacted with an aldehyde, preferably polyvinyl butyral, copolymers of acrylonitrile
and acrylamide, polyacrylates, polymethacrylates, polystyrene and polyethylene or
mixtures thereof.
[0035] Suitable water-soluble film-forming binders for use in thermographic recording materials
according to the present invention are: polyvinyl alcohol, polyacrylamide, polymethacrylamide,
polyacrylic acid, polymethacrylic acid, polyvinylpyrrolidone, polyethyleneglycol,
proteinaceous binders, polysaccharides and water-soluble cellulose derivatives. A
preferred water-soluble binder for use in the thermographic recording materials of
the present invention is gelatine.
[0036] The binder to organic silver salt weight ratio is preferably in the range of 0.2
to 7, and the thickness of the thermosensitive element is preferably in the range
of 5 to 50 µm. Binders are preferred which do not contain additives, such as certain
antioxidants (e.g. 2,6-di-tert-butyl-4-methylphenol), or impurities which adversely
affect the thermographic properties of the thermographic recording materials in which
they are used.
Barrier layer
[0037] Aspects of the present invention are realized with substantially light-insensitive
black and white monosheet thermographic recording material has a support and on one
side of the support comprises a thermosensitive element, a barrier layer and an outermost
protective layer, the thermosensitive element being exclusive of a high contrast agent
and containing at least one substantially light-insensitive silver salt of a carboxylic
acid, at least one reducing agent therefor in thermal working relationship therewith,
at least one toning agent and a binder, characterized in that the at least one reducing
agent is an ortho-dihydroxy-benzene derivative and the barrier layer comprises a copolymer
comprising vinyl chloride units and vinyl acetate and/or vinyl alcohol units, a copolymer
comprising styrene units and acrylonitrile units, a copolymer comprising cationic
units and/or a copolymer comprising styrene units and maleic acid units.
[0038] According to a fifth embodiment of the substantially light-insensitive black and
white monosheet thermographic recording material, according to the present invention,
the barrier layer is interposed between the thermosensitive element and the outermost
protective layer.
[0039] The mechanism of the restraining influence of the barriers layers, according to the
present invention, upon the diffusion of ingredients and reaction products of the
imaging forming process to the surface of the protective layer is unknown, but it
is believed that these layers may perform a dual role in providing an impervious barrier
for certain of the ingredients and reacting with others of the diffusing species.
The copolymers used in the barrier layer of the thermographic material, according
to the present invention, all have a more polar species, e.g. vinyl chloride, acrylonitrile,
maleic acid and cationic units, and less polar species, e.g. styrene and vinyl acetate.
Such polar species could represent a barrier to the diffusion of non-polar species.
[0040] According to a sixth embodiment of the substantially light-insensitive black and
white monosheet thermographic recording material, according to the present invention,
the copolymer comprising vinyl chloride units and vinyl acetate units contains up
to 95% by weight of vinyl chloride. The weight ratio of vinyl chloride to vinyl acetate
has not been found to be critical. Further comonomers may be present, but have not
been found to be critical to the performance of the copolymer as a barrier to diffusion
of ingredients or reaction products from the image-forming process.
[0041] According to a seventh embodiment of the substantially light-insensitive black and
white monosheet thermographic recording material, according to the present invention,
the copolymer comprising styrene units and acrylonitrile units contains between 20
and 60% by weight of acrylonitrile.
[0042] According to an eighth embodiment of the substantially light-insensitive black and
white monosheet thermographic recording material, according to the present invention,
the copolymer containing cationic units contains quaternary ammonium, quaternary phosphonium
or ternary sulphonium units.
[0043] According to a ninth embodiment of the substantially light-insensitive black and
white monosheet thermographic recording material, according to the present invention,
the copolymer containing cationic units contains methacrylamidopropyltrimethylammonium
chloride or dimethyl-diallylammonium chloride units.
[0044] It has been found that the barrier layers exhibit an optimal restraining influence
upon the diffusion of ingredients and reaction products of the imaging forming process
when coated from coating solutions containing 5 to 20% by weight of the copolymer
and/or with wet layer thicknesses of 5 to 20 µm.
[0045] Suitable copolymers for use in the substantially light-insensitive black and white
monosheet thermographic recording material, according to the present invention, include:
Copolymer nr. |
Copolymer composition |
1 |
VINNOL™ E15 45, a vinyl chloride-vinyl acetate-copolymer (85:15 by weight) from Wacker
Chemie |
2 |
VINNOL™ E15 45M, a vinyl chloride-vinyl acetate-maleic acid anhydride-copolymer (80.9:18.5:0.6
by weight) from Wacker Chemie |
3 |
VINNOL™ E15 45A, a vinyl chloride-vinyl alcohol-copolymer (83.5:16.5 by weight) from
Wacker Chemie |
4 |
VINNOL™ H40 60, a vinyl chloride-vinyl acetate-copolymer (60:40 by weight) from Wacker
Chemie |
5 |
VINYLITE™ VAGD, a vinyl chloride-vinyl acetate-vinyl alcohol-copolymer (91:3:6 by
weight) from Rohm and Haas Company |
6 |
LUSTRAN™ SAN28, a styrene-acrylonitrile-copolymer (75:25 by weight) from BAYER |
7 |
LURAN™ 378P, a styrene-acrylonitrile-copolymer (67.5:32.5 by weight) from BASF |
8 |
LURAN™ 388S natur, a styrene-acrylonitrile-copolymer (67.8:32.2 by weight) from BASF |
9 |
LURAN™ 358N, a styrene-acrylonitrile-copolymer (64:36 by weight) from BASF |
10 |
LUSTRAN™ SAN CN25, a styrene-acrylonitrile-copolymer (54:46 by weight) from BAYER |
11 |
POVAL CM318, methacrylamidopropyl trimethylammonium chloride-vinyl acetate-vinyl alcohol-copolymer,
88.5 mol% gehydrolyseerd with 2.5 mol% N+, from Kuraray |
12 |
POVAL C118, a methacrylamidopropyl trimethylammoniumchloride-vinyl acetate-vinylalcohol-copolymer,
99.4 mol% hydrolyzed with 0.5 mol% N+ from Kuraray |
13 |
POVAL C506, a 75.5% hydrolyzed methacrylamidopropyl trimethylammoniumchloride-vinyl
alcohol-vinyl acetate-copolymer with 0.5 mol% N+ from Kuraray |
14 |
a styrene-maleic acid copolymer (50/50 mol%) as a 10% by weight aqueous solution with
pH 7 |
15 |
GOSHEFIMER K210, a 85.8-88% hydrolyzed vinyl acetate-vinyl alcohol with ca. 1 mol%
dimethyl-diallylammonium chloride-copolymer from Nippon Goshei |
Protective layer
[0046] In general the outermost 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.
A slipping layer, being the outermost layer, may comprise a dissolved lubricating
material and/or particulate material, e.g. talc particles, optionally protruding from
the outermost layer.
Examples of suitable lubricating materials are a surface-active agent, a liquid lubricant,
a solid lubricant or mixtures thereof, with or without a polymeric binder.
[0047] According to a tenth embodiment of the substantially light-insensitive black and
white monosheet thermographic recording material, according to the present invention,
the outermost protective layer comprises the reaction product of at least one hydrolyzed
polyalkoxysilane and a hydroxy-group containing polymer.
[0048] According to an eleventh embodiment of the substantially light-insensitive black
and white monosheet thermographic recording material, according to the present invention,
the outermost protective layer comprises the reaction product of a hydrolyzed tetra-alkoxysilane,
e.g. tetramethoxysilane or tetra-ethoxysilane, and polyvinyl alcohol.
Stabilizers
[0049] According to a twelfth embodiment of the substantially light-insensitive black and
white monosheet thermographic recording material, according to the present invention,
the thermosensitive element further contains a stabilizer.
[0050] According to a thirteenth embodiment of the substantially light-insensitive black
and white monosheet thermographic recording material, according to the present invention,
the thermosensitive element further contains a stabilizer selected from the group
consisting of benzotriazole; substituted benzotriazoles; aromatic polycarboxylic acid,
such as ortho-phthalic acid, 3-nitro-phthalic acid, tetrachlorophthalic acid, mellitic
acid, pyromellitic acid and trimellitic acid and anhydrides thereof; 1-phenyl-5-mercapto-tetrazole
compounds in which the phenyl group is substituted with a substituent containing an
optionally substituted aryl group, 1-(5-mercapto-1-tetrazolyl)-acetyl compounds represented
by formula (IV):
wherein R
15 is -NR
16R
17, -OR
18 or an optionally substituted aryl or heteroaryl group; R
16 is hydrogen or an optionally substituted alkyl, aryl or heteroaryl group; R
17 is an optionally substituted aryl or heteroaryl group; and R
18 is an optionally substituted aryl group; and compounds with two or more groups represented
by formula (V) :
where Q comprises the necessary atoms to form a 5- or 6-membered unsaturated heterocyclic
ring, A is hydrogen, a counterion to compensate the negative charge of the thiolate
group or two or more A groups provide a linking group between the two or more groups
represented by formula (V).
[0051] According to a fourteenth embodiment of the substantially light-insensitive black
and white monosheet thermographic recording material, according to the present invention,
the thermosensitive element further contains at least one optionally substituted aliphatic
or carbocyclic polycarboxylic acid and/or anhydride thereof in a molar percentage
of at least 15 with respect to all the organic silver salt(s) present and in thermal
working relationship therewith. The polycarboxylic acid may be used in anhydride form
or partially esterified on the condition that at least two free carboxylic acids remain
or are available during the heat recording step.
Surfactants and dispersants
[0052] Surfactants and dispersants aid the dispersion of ingredients, which are insoluble
in the particular dispersion medium. The substantially light-insensitive thermographic
material used in the present invention may contain one or more surfactants, which
may be anionic, non-ionic or cationic surfactants and/or one or more dispersants.
Suitable dispersants are natural polymeric substances, synthetic polymeric substances
and finely divided powders, e.g. finely divided non-metallic inorganic powders such
as silica. It has been found that the addition of a silicone oil to the coating solution
of the Copolymer endowed the barrier coating solution with improved wetting properties.
[0053] According to a fifteenth embodiment of the substantially light-insensitive black
and white monosheet thermographic recording material, according to the present invention,
the barrier layer contains a silicone oil.
Support
[0054] According to a sixteenth embodiment of the substantially light-insensitive black
and white monosheet thermographic recording material, according to the present invention,
the support is transparent or translucent. It is preferably a thin flexible carrier
made transparent resin film, e.g. made of a cellulose ester, e.g. cellulose triacetate,
polypropylene, polycarbonate or polyester, e.g. polyethylene terephthalate. The support
may be in sheet, ribbon or web form and subbed if needs be to improve the adherence
to the thereon coated thermosensitive element. The support may be dyed or pigmented
to provide a transparent coloured background for the image.
Coating techniques
[0055] The coating of any layer of the substantially light-insensitive thermographic material
used in the present invention may proceed by any coating technique e.g. such as described
in Modern Coating and Drying Technology, edited by Edward D. Cohen and Edgar B. Gutoff,
(1992) VCH Publishers Inc., 220 East 23rd Street, Suite 909 New York, NY 10010, USA.
Coating may proceed from aqueous or solvent media with overcoating of dried, partially
dried or undried layers.
Thermographic processing
[0056] Thermographic imaging is carried out by the image-wise application of heat either
in analogue fashion by direct exposure through an image or 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, with a substantially light-insensitive
thermographic material preferably containing an infra-red absorbing compound, or by
direct thermal imaging with a thermal head.
[0057] 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 operating temperature of common thermal printheads
is in the range of 300 to 400°C and the heating time per picture element (pixel) may
be less than 1.0ms, the pressure contact of the thermal printhead with the recording
material being e.g. 200-1000g/linear cm, i.e. with a contact zone (nip) of 200 to
300 µm a pressure of 5000 to 50,000 g/cm
2, to ensure a good transfer of heat.
[0058] In order to avoid direct contact of the thermal printing heads with the outermost
layer on the same side of the support as the thermosensitive element when this outermost
layer is not a protective layer, the image-wise heating of the recording material
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.
[0059] Activation of the heating elements can be power-modulated or pulse-length modulated
at constant power. EP-A 654 355 discloses 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. EP-A 622 217
discloses a method for making an image using a direct thermal imaging element producing
improvements in continuous tone reproduction.
[0060] Image-wise heating of the recording material can also be carried out using an electrically
resistive ribbon incorporated into the material. Image- or pattern-wise heating of
the recording material may also proceed by means of pixel-wise modulated ultrasound.
Industrial application
[0061] Thermographic imaging can be used for the production of reflection type prints and
transparencies, in particular for use in the medical diagnostic field in which black-imaged
transparencies are widely used in inspection techniques operating with a light box.
[0062] The invention is illustrated hereinafter by way of comparative examples and invention
examples. The percentages and ratios given in these examples are by weight unless
otherwise indicated.
Subbing layer Nr. 01 on the emulsion side of the support has the composition:
copolymer of 88% vinylidene chloride, 10% methyl acrylate and 2% itaconic acid |
79.1 mg/m2 |
Kieselsol® 100F, a colloidal silica from BAYER |
18.6 mg/m2 |
Mersolat® H, a surfactant from BAYER |
0.4 mg/m2 |
Ultravon® W, a surfactant from CIBA-GEIGY |
1.9 mg/m2 |
Ingredients in the thermosensitive element in addition to the above-mentioned ingredients:
BL5HP |
S-LEC BL5HP, a polyvinyl butyral from SEKISUI; |
Oil |
BAYSILON, a silicone oil from BAYER; |
VL |
DESMODUR VL, a 4,4'-diisocyanatodiphenylmethane from BAYER |
Reducing agents:
[0063]
R01 |
3,4-dihydroxybenzonitrile; |
R02 |
3,4-dihydroxybenzophenone; |
R03 |
ethyl 3,4-dihydroxybenzoate |
Stabilizers:
[0064]
S01 |
glutaric acid |
S02 |
tetrachlorophthalic acid anhydride |
S03 |
benzotriazole |
S04 |
adipic acid |
Compositions of thermosensitive elements used:
|
Thermosensitive element types |
|
1 |
2 |
3 |
4 |
5 |
AgBeh [g/m2] |
3.94 |
4.150 |
3.960 |
4.15 |
4.42 |
BL5HP [g/m2] |
15.32 |
16.601 |
15.841 |
16.60 |
16.796 |
R01 [g/m2] |
0.595 |
0.439 |
- |
- |
0.618 |
R02 [g/m2] |
0.566 |
0.894 |
- |
- |
- |
R03 [g/m2] |
- |
- |
0.940 |
0.845 |
0.515 |
BOD01 [g/m2] |
- |
- |
0.216 |
- |
- |
BOD02 [g/m2] |
0.111 |
- |
0.111 |
0.116 |
0.226 |
BOD03 [g/m2] |
0.156 |
0.246 |
- |
- |
- |
BOD04 [g/m2] |
- |
- |
- |
0.269 |
- |
S01 [g/m2] |
0.256 |
0.294 |
0.283 |
0.297 |
0.287 |
S02 [g/m2] |
0.126 |
0.130 |
0.125 |
0.132 |
0.139 |
S03 [g/m2] |
0.105 |
0.109 |
0.103 |
0.110 |
0.116 |
VL [g/m2] |
0.175 |
0.190 |
- |
- |
- |
Oil [g/m2] |
0.035 |
0.037 |
0.035 |
0.037 |
0.039 |
Ingredients in the barrier layers:
Polymer nr |
Copolymer composition |
1 |
reaction product of hydrolyzed tetramethoxy-silane and polyvinyl alcohol (ERCOL™ 48
20) [0.166:2 by weight] |
2 |
reaction product of hydrolyzed tetramethoxy-silane and polyvinyl alcohol (ERCOL™ 48
20) [1.690:2 by weight] |
3 |
reaction product of hydrolyzed tetramethoxy-silane and polyvinyl alcohol (ERCOL™ 48
20) [3.379:2 by weight] |
4 |
reaction product of hydrolyzed tetramethoxy-silane and polyvinyl alcohol (ERCOL™ 48
20) [5.069:2 by weight] |
5 |
cellulose acetate butyrate |
6 |
S-LEC BL5HP, a polyvinyl butyral from Sekisui |
7 |
S-LEC BL16, a polyvinyl butyral from Sekisui |
8 |
S-LEC B DSG12, a polyvinyl butyral from Sekisui |
9 |
S-LEC KW23, a vinyl butyral-vinyl acetate-vinyl alcohol terpolymer from Sekisui |
10 |
S-LEC KW3, a vinyl butyral-vinyl acetate-vinyl alcohol terpolymer from Sekisui |
11 |
ALMACRYL™ EB56, an isophthalic acid/adipic acid/ethylene glycol polymer (75-80:25-20:100
on molar basis) from Image Polymers |
12 |
DEGALAN™ M345, a poly(methyl methacrylate) from Degussa |
13 |
JAGOTEX EM2245, a polyacrylate from E. Jäger Fabrik GmbH |
14 |
SARAN™ F2202, a vinylidene chloride-acrylonitrile-copolymer [80/20 by weight] from
Dow Chemical Co. |
15 |
HIMER™ ST95, a polystyrene from Sanyo Chemical Industries |
16 |
Polystyrene 158K, a polystyrene from BASF |
17 |
ERCOL™ 48 20, a polyvinylalcohol from ACETEX EUROPE |
18 |
CELVOL™ 203, a polyvinyl alcohol from Celanese Chemicals |
19 |
POVAL™ R2105, a 98% hydrolyzed silanol-modified vinyl alcohol-vinyl acetate-copolymer
from Kuraray |
20 |
POVAL™ R2130, a silanol-modified vinyl alcohol-vinyl acetate-copolymer from Kuraray |
21 |
POVAL™ 405, a vinyl alcohol-vinyl acetate-copolymer from Kuraray |
Ingredients in the protective layer:
ERCOL™ 48 20 |
a polyvinylalcohol from ACETEX EUROPE; |
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; |
ULTRAVON™ W |
75-85% concentrate of a sodium arylsulfonate from Ciba Geigy converted into acid form
by passing through an ion exchange column; |
SYLOID™ 72 |
a silica from Grace; |
SERVOXYL™ VPDZ 3/100 |
a mono[isotridecyl polyglycolether (3 EO)] phosphate, from SERVO DELDEN B.V.; |
SERVOXYL™ VPAZ 100 |
a mixture of monolauryl and dilauryl phosphate, from SERVO DELDEN B.V.; |
MICROACE TALC P3 |
an Indian talc from NIPPON TALC; |
RILANIT™ GMS |
a glycerine monotallow acid ester, from HENKEL AG |
TMOS |
tetramethylorthosilicate hydrolyzed in the presence of methanesulfonic acid. |
COMPARATIVE EXAMPLES 1 to 24 and INVENTION EXAMPLES 1 to 31
[0065] The substantially light-insensitive thermographic materials of COMPARATIVE EXAMPLES
1 to 24 and INVENTION EXAMPLES 1 to 31 were prepared by coating a dispersion with
the following ingredients of thermosensitive element type 1 in 2-butanone onto a 175µm
thick blue-pigmented polyethylene terephthalate support with CIELAB a*-and b*-values
of -9.5 and -17.9 respectively subbed on the emulsion-coated side with subbing layer
01 giving type 1 thermosensitive elements after drying at 50°C for 1h in a drying
cupboard, for composition see above. The type 1 thermosensitive elements were then
coated with a barrier layer from a 2-butanone solution, for type of copolymer used
and coating weight see Tables 1A and 1B. The barrier layers were then further coated
with an aqueous composition with the following ingredients, which was adjusted to
a pH of 3.8 with 1N nitric acid, to a wet layer thickness of 85 µm and then dried
at 50°C for 15 minutes to produce a protective layer PRO-L with the composition:
ERCOL™ 48 20 |
2.1g/m2 |
LEVASIL™ VP AC 4055 |
1.05g/m2 |
ULTRAVON™ W |
0.075g/m2 |
SYLOID™ 72 |
0.09 g/m2 |
SERVOXYL™ VPDZ 3/100 |
0.075g/m2 |
SERVOXYL™ VPAZ 100 |
0.075g/m2 |
MICROACE TALC P3 |
0.045g/m2 |
RILANIT™ GMS |
0.15g/m2 |
TMOS |
0.87g/m2 (assuming that the TMOS was completely converted to SiO2) |
After coating the protective layer was hardened by heating the substantially light-insensitive
thermographic material at 45°C for 7 days at a relative humidity of 70%.
Thermographic printing
[0066] The substantially light-insensitive thermographic recording materials of COMPARATIVE
EXAMPLES 1 to 24 and INVENTION EXAMPLES 1 to 31 were printed using a DRYSTAR™ 4500
printer from AGFA-GEVAERT with a resolution of 508 dpi which had been modified to
operate at a printing speed of 14 mm/s and a line-time of 3.5 ms instead of 7.1 ms
and in which the 75 µm long (in the transport direction) and 50 µm wide thermal head
resistors were power-modulated to produce different image densities. The maximum densities
of the images (D
max) measured through a visible filter with a MACBETH™ TR924 densitometer were all greater
than 2.0.
[0067] Assessment of diffusion of ingredients and reaction products of the imaging forming
process to protective layer surface
[0068] The diffusion of ingredients and reaction products of the imaging forming process
to the surface of the protective layer was assessed visually according to a scale
of 0 to 5 with the following criteria:
diffusion assessment of 0: |
no diffusion |
diffusion assessment of 1: |
first indication of diffusion upon examination under an intense lighting after rubbing
with a paper tissue |
diffusion assessment of 2: |
visible in daylight after rubbing with a paper tissue |
diffusion assessment of 3: |
just visible in daylight without rubbing with a paper tissue |
diffusion assessment of 4: |
moderately strong deposition without rubbing with a paper tissue |
diffusion assessment of 5: |
very strong deposition without rubbing with a paper tissue |
The results for unprinted and printed materials after different times under ambient
conditions (25°C) are given in Tables 1A and 1B below for COMPARATIVE EXAMPLES 1 to
24 and INVENTION EXAMPLES 1 to 31 respectively.
Table 1A:
Comparative Example Nr. |
Polymer |
Assessment of diffusion |
|
nr |
coverage [g/m2] |
prior to printing |
after printing |
|
|
|
0 d |
10 d |
20 d |
30 d |
0 d |
10 d |
20 d |
30 d |
1* |
- |
- |
5 |
5 |
5 |
5 |
3 |
5 |
5 |
5 |
2 |
- |
- |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
2 |
3 |
1 |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
2 |
3 |
4 |
2 |
2 |
0 |
0 |
0 |
0 |
1 |
2 |
2 |
2 |
5 |
3 |
2 |
0 |
0 |
0 |
0 |
1 |
3 |
3 |
3 |
6 |
4 |
2 |
0 |
0 |
0 |
0 |
1 |
2 |
2 |
2 |
7 |
5 |
2 |
0 |
0 |
0 |
0 |
0 |
1 |
2 |
2 |
8 |
6 |
2 |
0 |
0 |
0 |
0 |
0 |
2 |
2 |
2 |
9 |
7 |
2 |
0 |
0 |
0 |
0 |
0 |
2 |
2 |
2 |
10 |
8 |
2 |
0 |
0 |
0 |
0 |
0 |
3 |
2 |
3 |
11 |
9 |
2 |
0 |
0 |
1 |
1 |
0 |
3 |
3 |
3 |
12 |
10 |
2 |
0 |
0 |
0 |
0 |
0 |
3 |
3 |
3 |
13 |
11 |
2 |
0 |
0 |
0 |
0 |
2 |
2 |
2 |
2 |
14 |
12 |
2 |
0 |
0 |
0 |
0 |
0 |
2 |
2 |
2 |
15 |
13 |
2 |
0 |
0 |
0 |
0 |
0 |
1 |
2 |
2 |
16 |
14 |
2 |
0 |
0 |
0 |
0 |
0 |
1 |
2 |
2 |
17 |
15 |
2 |
0 |
0 0 |
|
0 |
1 |
2 |
2 |
2 |
18 |
16 |
2 |
0 |
0 |
0 |
0 |
0 |
2 |
2 |
2 |
19 |
18 |
2 |
0 |
0 |
0 |
1 |
0 |
3 |
4 |
3 |
20 |
18 |
1 |
0 |
0 |
0 |
1 |
0 |
3 |
3 |
4 |
21 |
19 |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
2 |
2 |
22 |
19 |
1 |
0 |
0 |
0 |
0 |
0 |
1 |
2 |
3 |
23 |
20 |
2 |
0 |
0 |
0 |
0 |
2 |
2 |
2 |
2 |
24 |
21 |
1 |
0 |
0 |
0 |
0 |
0 |
3 |
4 |
4 |
* without a protective layer |
Table 1B:
Invention Example nr. |
Copolymer |
Assessment of diffusion |
|
nr |
coverage [g/m2] |
prior to printing |
after printing |
|
|
|
0 d |
10 d |
20 d |
30 d |
0 d |
10 d |
20 d |
30 d |
1 |
1 |
2.0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
2 |
1 |
1.0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
3 |
1 |
0.5 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
4 |
1 |
0.25 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
5 |
2 |
2.0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
6 |
2 |
1.0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
7 |
2 |
0.5 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
8 |
2 |
0.25 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
9 |
3 |
2.0 |
0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
10 |
3 |
1.0 0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
11 |
3 |
0.5 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
12 |
3 |
0.25 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
13 |
6 |
2.0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
14 |
6 |
1.0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
15 |
6 |
0.5 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
16 |
6 |
0.25 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
17 |
7 |
2.0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
18 |
7 |
1.0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
19 |
7 |
0.5 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
20 |
7 |
0.25 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
21 |
8 |
2.0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
22 |
8 |
1.0 |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
23 |
8 |
0.5 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
24 |
8 |
0.25 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
25# |
11 |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
26# |
11 |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
27# |
12 |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
28# |
12 |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
29# |
13 |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
30# |
14 |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
31# |
14 |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
* without a protective layer, printing was carried out with a thin foil between the
thermosensitive element and the thermal head of the printer
# coated from an aqueous solution |
[0069] The results of COMPARATIVE EXAMPLE 1 show that there is very considerable diffusion
of ingredients and reaction products of the imaging forming process to the surface
even prior to printing. The results for COMPARATIVE EXAMPLE 2 show that the protective
layer used based on the reaction product of polyvinyl alcohol with hydrolyzed tetramethoxysilane
was able to prevent further transport to the surface of the protective layer prior
to printing, but after printing considerable diffusion of ingredients and reaction
products of the imaging forming process could be detected after 20 days.
[0070] The results of COMPARATIVE EXAMPLES 3 to 24 show that the ability of barrier layers
of Polymer nr. 1 to 21, all outside the scope of the present invention, to prevent
diffusion to the surface of the protective layer was inferior to the situation without
a barrier layer. It is notable that Polymer nr. 1 to 4 together with a protective
layer based on the reaction product of polysilicic acid and a hydroxy-containing polymer
was reported in US 5,264,334 to provide an effective barrier to ingredient diffusion.
[0071] The results for INVENTION EXAMPLES 1 to 31, on the other hand, show that Copolymers
nr. 1 to 3, 6 to 8 and 11 to 14, according to the present invention, are surprisingly
able, at coverages from below 0.25 g/m
2 to above 2 g/m
2, to prevent diffusion of ingredients and reaction products of the imaging forming
process to the surface of the protective layer over periods of 30 days under ambient
conditions (25°C) both before and after printing.
[0072] These copolymers can be grouped into copolymers comprising vinyl chloride and vinyl
acetate units (Copolymers nr. 1 to 3), copolymers comprising styrene-acrylonitrile
(Copolymers nr. 6 to 8), copolymers with cationic units (Copolymers nr. 11 to 13)
and styrene-maleic acid copolymers (Copolymer nr. 14).
COMPARATIVE EXAMPLES 25 to 29 and INVENTION EXAMPLES 32 to 38
[0073] The substantially light-insensitive thermographic materials of COMPARATIVE EXAMPLES
25 to 29 and INVENTION EXAMPLES 32 to 38 were prepared as described for COMPARATIVE
EXAMPLES 1 to 24 and INVENTION EXAMPLES 1 to 31 except for the barrier layers, which
are given in Tables 2A and 2B for COMPARATIVE EXAMPLES 25 to 29 and INVENTION EXAMPLES
32 to 38 respectively.
[0074] The diffusion of ingredients and reaction products of the imaging forming process
to the protective layer surface for COMPARATIVE EXAMPLES 25 to 29 and INVENTION EXAMPLES
32 to 38 was assessed as described for COMPARATIVE EXAMPLES 1 to 24 and INVENTION
EXAMPLES 1 to 31 prior to printing and after printing as described for COMPARATIVE
EXAMPLES 1 to 24 and INVENTION EXAMPLES 1 to 31. The results of the diffusion experiments
are also given in Table 2.
[0075] The results of the diffusion experiments in Table 2 confirm the findings of INVENTION
EXAMPLES 1 to 31, that copolymers 1 to 3 and 6 to 8 are able to prevent diffusion
of ingredients and reaction products of the imaging forming process to the surface
of the thermographic material both before and after printing for a period of 30 days
under ambient conditions (25°C).
Table 2:
Comparative Example nr. |
Polymer |
Assessment of diffusion |
|
nr |
coverage [g/m2] |
prior to printing |
after printing |
|
|
|
0 d |
10 d |
20 d |
30 d |
0 d |
10 d |
20 d |
30 d |
25 |
- |
- |
0 |
0 |
0 |
0 |
0 |
1 |
2 |
2 |
26 |
- |
- |
0 |
0 |
0 |
1 |
0 |
1 |
2 |
2 |
27 |
6 |
2 |
0 |
0 |
0 |
0 |
0 |
3 |
2 |
3 |
28 |
17 |
1 |
0 |
0 |
0 |
0 |
1 |
1 |
2 |
2 |
29 |
17 |
2 |
0 |
0 |
1 |
1 |
1 |
2 |
1 |
2 |
Invention Example nr. |
Copolymer |
|
|
nr |
coverage [g/m2] |
|
32 |
1 |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
33 |
1 |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
34 |
2 |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
35 |
3 |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
36 |
6 |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
37 |
7 |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
38 |
8 |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
Evaluation of thermographic properties
[0076] For a barrier layer to be usable in substantially light-insensitive thermographic
materials, it is important that it is not only able to restrain the diffusion of ingredients
and reaction products of the imaging forming process to the surface of the protective
layer but also has no adverse effect on the image tone of the prints.
[0077] The image tone of fresh prints made with the substantially light-insensitive thermographic
recording materials of COMPARATIVE EXAMPLES 25 to 29 and INVENTION EXAMPLES 32 and
38 was assessed on the basis of the L*, a* and b* CIELAB-values at optical densities,
D, of 1.0 and 1.5 and the results are given in Table 3.
[0078] The results in Table 3 show that barrier layers of copolymer nr. 1 to 3 and 6 to
8 shifted the CIELAB b*-values of fresh prints with barrier layers slightly negatively
with respect to the corresponding thermographic material of COMPARATIVE EXAMPLES 25
and 26, which renders the image tone more acceptable to a radiologist.
Table 3:
Comparative Example nr. |
Copolymer |
CIELAB values of fresh print at |
|
nr |
coverage [g/m2] |
D = 1.0 |
D = 1.5 |
|
|
|
a* |
b* |
a* |
b* |
25 |
- |
- |
-4.12 |
-4.45 |
-2.62 |
-4.92 |
26 |
- |
- |
-4.44 |
-4.44 |
-2.71 |
-4.53 |
27 |
6 |
2 |
-4.41 |
-3.69 |
-2.58 |
-3.97 |
28 |
17 |
1 |
-4.19 |
-4.85 |
-2.56 |
-3.94 |
29 |
17 |
2 |
-4.33 |
-3.57 |
-2.39 |
-2.75 |
Invention Example nr. |
Copolymer |
|
|
nr |
coverage [g/m2] |
|
32 |
1 |
2 |
-4.72 |
-6.29 |
-3.12 |
-5.65 |
33 |
1 |
2 |
-4.56 |
-5.74 |
-2.95 |
-5.86 |
34 |
2 |
2 |
-4.61 |
-6.76 |
-3.01 |
-6.24 |
35 |
3 |
2 |
-4.65 |
-6.24 |
-3.15 |
-5.99 |
36 |
6 |
2 |
-4.68 |
-6.97 |
-3.06 |
-6.36 |
37 |
7 |
2 |
-4.73 |
-6.94 |
-3.08 |
-6.19 |
38 |
8 |
2 |
-4.74 |
-6.90 |
-3.01 |
-6.21 |
COMPARATIVE EXAMPLE 30 and INVENTION EXAMPLES 39 to 50
[0079] The substantially light-insensitive thermographic materials of COMPARATIVE EXAMPLE
30 and INVENTION EXAMPLES 39 to 50 were prepared by coating a dispersion with the
ingredients of thermosensitive element type 2 in 2-butanone onto a 175µm thick blue-pigmented
polyethylene terephthalate support with CIELAB a*-and b*- values of -9.5 and -17.9
respectively subbed on the emulsion-coated side with subbing layer 01 giving type
2 thermosensitive elements after drying at 85°C for 3 minutes in a drying cupboard,
for composition of the type 2 thermosensitive element see above. The type 2 thermosensitive
elements were then coated with a barrier layer from a 2-butanone solution, for copolymer
type used and coating weight see Table 4. The barrier layers were then provided with
the same protective layer as for the substantially light-insensitive thermographic
materials of COMPARATIVE EXAMPLES 1 to 24 and INVENTION EXAMPLES 1 to 31.
[0080] The diffusion of ingredients and reaction products of the imaging forming process
to the protective layer surface for COMPARATIVE EXAMPLE 30 and INVENTION EXAMPLES
39 to 50 was assessed as described for COMPARATIVE EXAMPLES 1 to 24 and INVENTION
EXAMPLES 1 to 31 after subjecting prints to 3, 6, 9, 12, 15 and 18 days at 57°C and
34% relative humidity, which provided a more rigorous test of the ability of these
barrier layers to restrain diffusion of ingredients and reaction products of the imaging
forming process to the surface. The results of these diffusion experiments are also
given in Table 4.
Table 4:
Comparative Example nr. |
Polymer |
Assessment of diffusion for |
|
nr |
coverage [g/m2] |
prints subjected to 57°C/34%RH for |
|
|
|
|
3 d |
6 d |
9 d |
12 d |
15 d |
18 d |
30 |
- |
- |
|
2 |
2 |
4 |
5 |
5 |
5 |
Invention Example nr. |
Copolymer |
|
|
nr |
wet layer thickness [µm] |
coverage [g/m2] |
|
39 |
2 |
45 |
1 |
0 |
1 |
- |
- |
- |
- |
40 |
2 |
20 |
1 |
0 |
0 |
- |
- |
- |
- |
41 |
2 |
20 |
0.5 |
0 |
0 |
- |
- |
- |
- |
42 |
2 |
20 |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
43 |
2 |
20 |
0.6 |
0 |
0 |
0 |
0 |
0 |
0 |
44 |
2 |
20 |
0.5 |
0 |
0 |
0 |
0 |
0 |
0 |
45 |
2 |
20 |
0.4 |
0 |
0 |
0 |
0 |
0 |
1 |
46 |
2 |
20 |
0.3 |
0 |
0 |
0 |
0 |
0 |
2 |
47 |
7 |
50 |
1 |
0 |
0 |
- |
- |
- |
- |
48 |
7 |
45 |
1 |
0 |
1 |
- |
- |
- |
- |
49 |
7 |
20 |
1 |
0 |
0 |
- |
- |
- |
- |
50 |
7 |
20 |
0.5 |
0 |
0 |
- |
- |
- |
- |
[0081] The results in Table 4 show that barrier layers of Copolymer nr. 2, a vinyl chloride-vinyl
acetate-maleic acid anhydride copolymer, provides excellent restraint of the diffusion
of ingredients and reaction products of the imaging forming process to the surface
even under these more rigorous conditions and that barrier layers of Copolymer nr.
7, a styrene-acrylonitrile copolymer, also provided satisfactory restraint of the
diffusion of ingredients and reaction products of the imaging forming process to the
surface under these conditions.
Evaluation of thermographic properties
[0082] For a barrier layer to be usable in substantially light-insensitive thermographic
materials, it is important that it is not only able to restrain the diffusion of ingredients
and reaction products of the imaging forming process to the surface of the protective
layer but also has no adverse effect on the image tone of the prints.
[0083] The image tone of fresh prints made with the substantially light-insensitive thermographic
recording materials of COMPARATIVE EXAMPLE 30 and INVENTION EXAMPLES 39 to 50 was
assessed on the basis of the L*, a* and b* CIELAB-values at optical densities, D,
of 1.0 and 1.5 and the results given in Table 5.
Table 5:
Comparative Example nr. |
Polymer |
CIELAB values of fresh print |
|
nr |
wet layer |
coverage |
D = 1.0 |
D = 1.5 |
|
|
thickness [µm] |
[g/m2] |
a* |
b* -7.07 |
a* |
b* |
30 |
- |
|
- |
-4.95 |
|
-3.26 |
-5.74 |
Invention Example nr. |
Copolymer |
|
|
nr |
wet layer thickness [µm] |
coverage [g/m2] |
|
39 |
2 |
45 |
1 |
-5.31 |
-8.99 |
-4.04 |
-8.75 |
40 |
2 |
20 |
1 |
-5.49 |
-8.98 |
-4.19 |
-8.54 |
41 |
2 |
20 |
0.5 |
-5.35 |
-9.40 |
-3.78 |
-9.06 |
42 |
2 |
20 |
1 |
-5.53 |
-9.15 |
-4.10 |
-8.03 |
43 |
2 |
20 |
0.6 |
-5.43 |
-8.99 |
-4.03 |
-8.14 |
44 |
2 |
20 |
0.5 |
-5.42 |
-8.93 |
-4.07 |
-8.09 |
45 |
2 |
20 |
0.4 |
-5.36 |
-8.72 |
-3.93 |
-7.88 |
46 |
2 |
20 |
0.3 |
-5.03 |
-7.78 |
-3.22 |
-6.83 |
47 |
7 |
50 |
1 |
-5.16 |
-8.90 |
-3.45 |
-8.61 |
48 |
7 |
45 |
1 |
-5.19 |
-8.71 |
-3.40 |
-8.36 |
49 |
7 |
20 |
1 |
-5.43 |
-8.85 |
-3.85 |
-8.43 |
50 |
7 |
20 |
0.5 |
-5.18 |
-8.83 |
-3.72 |
-8.60 |
[0084] The results in Table 5 show that barrier layers of copolymer nr. 2 and 7 shifted
the CIELAB b*-values of fresh prints with barrier layers slightly negatively with
respect to the corresponding thermographic material of COMPARATIVE EXAMPLE 30, which
rendered the image tone more acceptable to a radiologist. Furthermore, it was found
that the attainable D
max decreased for a given barrier layer coverage with decreasing wet layer thickness
i.e. with increasing concentration of the Copolymer in the coating solution. A wet
layer thickness above 30µm had no further influence upon D
max for copolymer-coverages of less than 0.4 g/m
2 and a wet layer thickness of 20µm was possible for copolymer-coverages of less than
0.3 g/m
2.
COMPARATIVE EXAMPLE 31 and INVENTION EXAMPLES 51 to 62
[0085] The substantially light-insensitive thermographic materials of COMPARATIVE EXAMPLE
31 and INVENTION EXAMPLES 51 to 62 were prepared as described for COMPARATIVE EXAMPLE
30 and INVENTION EXAMPLES 39 to 50 except that type 2 thermosensitive elements were
used and for the barrier layers, which are given in Table 6.
Table 6:
Comparative Example nr. |
Polymer |
assessment of diffusion for prints subjected to 57°C/34%RH for 3d |
|
nr |
coverage [g/m2] |
|
31 |
- |
- |
5 |
Invention Example nr. |
Copolymer |
|
|
nr |
coverage [g/m2] |
|
51 |
2 |
1 |
0 |
52 |
3 |
1 |
0 |
53 |
4 |
1 |
0 |
54 |
5 |
1 |
0 |
55 |
5 |
1 |
0 |
56 |
6 |
1 |
0 |
57 |
7 |
1 |
0 |
58 |
9 |
1 |
0 |
59 |
10 |
1 |
0 |
60* |
11 |
1 |
0 |
61* |
12 |
1 |
0 |
62# |
14 |
1 |
0 |
* coated from an aqueous solution at pH 3.8 |
# coated from aqueous solution at pH 7 |
[0086] The diffusion of ingredients and reaction products of the imaging forming process
to the protective layer surface for COMPARATIVE EXAMPLE 31 and INVENTION EXAMPLES
51 to 62 was assessed as described for COMPARATIVE EXAMPLES 1 to 24 and INVENTION
EXAMPLES 1 to 31 after subjecting prints to 3 days at 57°C and 34% relative humidity.
The results are also given in Table 6.
[0087] No diffusion of ingredients and reaction products of the imaging forming process
to the surface was observed in the case of barrier layers of Copolymers nr. 2 to 7,
9 to 12 and 14 with a coverage of 1g/m
2. Most of these barrier layers were applied from 2-butanone solutions, but barrier
layers of Copolymer nr. 11, 12 and 14 were applied from aqueous solutions. These copolymers
can mainly be grouped into copolymers comprising vinyl chloride and vinyl acetate
units (Copolymers nr. 1 to 5), copolymers comprising styrene-acrylonitrile (Copolymers
nr. 6 to 10) and copolymers with cationic units (Copolymers nr. 11 and 12).
Evaluation of thermographic properties
[0088] The image tone of fresh prints made with the substantially light-insensitive thermographic
recording materials of COMPARATIVE EXAMPLE 31 and INVENTION EXAMPLES 51 to 62 was
assessed on the basis of the L*, a* and b* CIELAB-values at optical densities, D,
of 1.0 and 1.5 and the results given in Table 7.
Table 7:
Comparative Example nr. |
Polymer |
CIELAB values of fresh print |
|
nr |
coverage [g/m2] |
D = 1.0 |
D = 1.5 |
|
|
|
a* |
b* |
a* |
b* |
31 |
- |
- |
-2.67 |
-9.42 |
-0.45 |
-9.22 |
Invention Example nr. |
Copolymer |
|
|
nr |
coverage [g/m2] |
|
51 |
2 |
1 |
-2.58 |
-11.15 |
-0.82 |
-10.6 |
52 |
3 |
1 |
-2.68 |
-11.14 |
-0.63 |
-10.5 |
53 |
4 |
1 |
-3.04 |
-10.39 |
-0.8 |
-9.41 |
54 |
5 |
1 |
-3.05 |
-11.27 |
-1.32 |
-10.86 |
55 |
5 |
1 |
-2.17 |
-10.15 |
+0.54 |
-9.7 |
56 |
6 |
1 |
-2.34 |
-10.63 |
-0.03 |
-10.1 |
57 |
7 |
1 |
-2.4 |
-10.41 |
+0.16 |
-9.81 |
58 |
9 |
1 |
-2.54 |
-10.58 |
+0.12 |
-10.04 |
59 |
10 |
1 |
-2.53 |
-10.2 |
-0.15 |
-9.68 |
60* |
11 |
1 |
-2.32 |
-8.3 |
+0.33 |
-7.15 |
61* |
12 |
1 |
-2.14 |
-8.85 |
+0.77 |
-8.35 |
62# |
14 |
1 |
-2.73 |
-8.87 |
-0.14 |
-8.76 |
* coated from an aqueous solution at pH 3.8 |
# coated from aqueous solution at pH 7 |
[0089] The results in Table 7 show that certain barrier layers of copolymer nr. 2 to 7,
9 to 12 and 14 shifted the CIELAB b*-values of fresh prints with barrier layers slightly
negatively with respect to the corresponding thermographic material of COMPARATIVE
EXAMPLE 31 (e.g. barrier layers of Copolymer nr. 2 to 7 and 9 and 10), which enhances
the image tone, and others shifted the CIELAB b*-values slightly positively with respect
to the corresponding thermographic material of COMPARATIVE EXAMPLE 31 (e.g. barrier
layers of Copolymer nr. 11, 12 and 14, all coated from aqueous solutions).
he composition of barrier layers of copolymers containing vinyl chloride and vinyl
acetate units with various weight percentages of vinyl chloride and vinyl acetate
units (Copolymer nr. 2 to 5) did not have a significant influence upon image tone
i.e. for weight percentages of vinyl chloride units between 60 and 91 and for weight
percentages of vinyl acetate between 3 and 15.
[0090] The composition of barrier layers of copolymers containing styrene and acrylonitrile
with various weight percentages of styrene and acrylonitrile (Copolymer nr. 6, 7,
9 and 10) did not have a significant influence upon image tone i.e. for weight percentages
of styrene units between 54 and 75 and for weight percentages of acrylonitrile between
25 and 46.
COMPARATIVE EXAMPLES 32 to 39 and INVENTION EXAMPLES 63 to 74
[0091] The substantially light-insensitive thermographic materials of COMPARATIVE EXAMPLES
32 to 39 and INVENTION EXAMPLES 63 to 74 were prepared by coating dispersions containing
the ingredients for the appropriate thermosensitive element type (see Table 8 for
the thermosensitive element type used for the particular COMPARATIVE or INVENTION
EXAMPLE) in 2-butanone onto the support described for COMPARATIVE EXAMPLES 1 to 24
and INVENTION EXAMPLES 1 to 31 giving the particular type of thermosensitive element
for the particular COMPARATIVE or INVENTION EXAMPLE after drying at 85°C for 3 minutes
in a drying cupboard with the compositions given above. The thermosensitive elements
were then optionally coated with a barrier copolymer from a 2-butanone solution, see
Table 8 for copolymer type and coating weight. The barrier layers were then provided
with the same protective layer as for the substantially light-insensitive thermographic
materials of COMPARATIVE EXAMPLES 1 to 24 and INVENTION EXAMPLES 1 to 31.
[0092] The diffusion of ingredients and reaction products of the imaging forming process
to the protective layer surface for COMPARATIVE EXAMPLES 32 to 39 and INVENTION EXAMPLES
63 to 74 was assessed as described for COMPARATIVE EXAMPLES 1 to 24 and INVENTION
EXAMPLES 1 to 31 after subjecting fresh material and prints to different tests: 3
days and 6 days at 57°C and 34% relative humidity; and 7 days at 45°C and 70% relative
humidity. The results are given in Table 8.
Table 8:
Comparative Example nr. |
thermosensitive element type |
Polymer |
Assessment of diffusion to material surface |
|
|
nr |
coverage |
fresh material after 57°C/ 34%RH/ |
prints after 57°C/ 34%RH/ |
fresh material after 45°C/70%RH/ |
|
|
|
[g/m2] |
3 d |
6 d |
3 d |
6 d |
7 d |
32 |
2* |
- |
- |
0 |
0 |
5 |
5 |
5 |
33 |
2 |
- |
- |
0 |
0 |
5 |
5 |
5 |
34 |
3* |
- |
- |
0 |
0 |
5 |
5 |
5 |
35 |
3 |
- |
- |
0 |
0 |
5 |
5 |
3 |
36 |
4* |
- |
- |
0 |
0 |
5 |
5 |
5 |
37 |
4 |
- |
- |
0 |
0 |
5 |
5 |
0 |
38 |
5* |
- |
- |
0 |
0 |
5 |
5 |
5 |
39 |
5 |
- |
- |
0 |
0 |
5 |
5 |
5 |
Invention Example nr. |
|
Copolymer |
|
|
|
nr |
wet layer thickness [µm] |
coverage [g/m2] |
|
63 |
2* |
6 |
10 |
0.79 |
0 |
0 |
0 |
0 |
0 |
64 |
2* |
6 |
20 |
0.79 |
0 |
0 |
0 |
0 |
0 |
65 |
2* |
6 |
30 |
0.79 |
0 |
0 |
0 |
0 |
0 |
66 |
2* |
6 |
40 |
0.79 |
0 |
0 |
0 |
0 |
0 |
67 |
2* |
6 |
50 |
0.79 |
0 |
0 |
0 |
0 |
0 |
68 |
2 |
6 |
50 |
0.79 |
0 |
0 |
0 |
0 |
0 |
69 |
3* |
6 |
50 |
0.79 |
0 |
0 |
0 |
0 |
0 |
70 |
3 |
6 |
50 |
0.79 |
0 |
0 |
0 |
0 |
0 |
71 |
4* |
6 |
50 |
0.79 |
0 |
0 |
0 |
0 |
0 |
72 |
4 |
6 |
50 |
0.79 |
0 |
0 |
0 |
0 |
0 |
73 |
5* |
6 |
50 |
0.79 |
0 |
0 |
0 |
0 |
0 |
74 |
5 |
6 |
50 |
0.79 |
0 |
0 |
1 |
1 |
0 |
* without a protective layer, printing was carried out with a thin foil between the
thermosensitive element and the thermal head of the printer |
[0093] The experiments disclosed in Table 8 show whether the barrier layers of the present
invention could be used with different thermosensitive elements with different compositions.
On the basis of these experiments with a barrier layer of Copolymer nr. 6 with a coverage
of 0.79 g/m
2, it can be seen that this barrier layer provides an excellent restraint of the diffusion
of ingredients and reaction products of the imaging forming process to the surface
of the thermographic material. Moreover, the results for INVENTION EXAMPLES 63 to
67, 69, 71 and 73 show that the barrier layer as such provides this restraint, which
means that the choice of protective layer is not critical with respect to restraining
ingredient diffusion and that the protective layer can be solely designed to optimise
the mechanical interaction to the thermal printing head and the adhesion to the barrier
layer.
The present invention may include any feature or combination of features disclosed
herein either implicitly or explicitly or any generalisation thereof irrespective
of whether it relates to the presently claimed invention. In view of the foregoing
description it will be evident to a person skilled in the art that various modifications
may be made within the scope of the invention.