Substantially light-insensitive thermographic recording...

Details Substantially light-insensitive thermographic recording... Substantially light-insensitive thermographic recording...

1999-10-13

2001-01-30

Hess, Bruce H. (Department: 1774)

Coating processes

Transfer or copy sheet making

C427S152000, C503S202000, C503S210000

Reexamination Certificate

active

06180165

ABSTRACT:

DESCRIPTION
1. Field of the Invention
The present invention relates to a substantially light-insensitive thermographic recording material with improved stability.
2. Background of the Invention
Thermography is concerned with materials which are substantially light-insensitive, but are sensitive to heat or thermographic. Most of the “direct” thermographic recording 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 the book “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.
In U.S. Pat. No. 2,910,977 the following statement is made in the description in column 7, lines 23-27: “Stability towards exposure to light is improved by selecting highly purified materials; freedom from halides and sulfides is particularly important in the case of compositions involving silver salts.” The disclosure in U.S. Pat. No. 2,910,977 concerned thermographic recording materials coated from solvent media.
WO 94/16361 discloses a multilayer heat-sensitive material which comprises: a colour-forming layer comprising: a colour-forming amount of finely divided, solid colourless noble metal or iron salt of an organic acid distributed in a carrier composition; a colour developing amount of a cyclic or aromatic organic reducing agent, which at thermal copy. and printing temperatures is capable of a colour-forming reaction with the noble metal or iron salt; and an image-toning agent; characterized in that (a) the carrier composition comprises a substantially water-soluble polymeric carrier and a dispersing agent for the noble metal or iron salt and (b) the material comprises a protective overcoating layer for the colour-forming layer.
Coating of thermographic recording materials from aqueous media is preferred over coating from solvent for ecological and economic reasons. However, the inventors of the present invention found that the choice of surfactants used in the production of thermographic recording materials using aqueous dispersions and solutions had a substantial effect upon the stability of the thermographic recording materials produced and on prints produced therewith.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide thermographic recording materials coated from aqueous media which exhibit improved stability.
It is therefore another object of the present invention to provide thermographic recording materials which are capable of producing thermographic prints which exhibit improved stability.
Further objects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
In view of the statement made in U.S. Pat. No. 2,910,977 to the effect that freedom from halides is particularly important it is surprising that the halide concentration in the totality of surfactants present in thermographic recording materials coated from aqueous media can be as high as 500 ppm without adversely affected the light-stability of thermographic recording materials coated from aqueous media.
A substantially light-insensitive thermographic recording material substantially exclusive of cationic surfactants is provided in which at least one non-cationic surfactant is present, the thermographic recording material comprising a support and a thermosensitive element containing a substantially light-insensitive organic silver salt, a reducing agent therefor in thermal working relationship therewith and a binder, wherein all the non-cationic surfactants present in the thermographic recording material together have a non-fluoro-halide ion concentration of 1500 ppm or less.
A process for producing the substantially light-insensitive thermographic recording material referred to above is also provided comprising the steps of: producing an aqueous dispersion of the substantially light-insensitive organic silver salt; producing one or more aqueous coating compositions containing together the aqueous dispersion of the substantially light-insensitive organic silver salt, the reducing agent and the binder; and applying the one or more aqueous coating compositions to the support thereby forming after drying the thermosensitive element, characterized in that one or more of the aqueous dispersion of the substantially light-insensitive organic silver salt and the one or more aqueous coating compositions aqueous contain a non-cationic surfactant.
Preferred embodiments of the present invention are disclosed in the detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment the substantially light-insensitive thermographic recording materials of the present invention are black and white thermographic recording materials.
Aqueous
The term aqueous for the purposes of the present invention includes mixtures of water with water-miscible organic solvents such as alcohols e.g. methanol, ethanol, 2-propanol, butanol, iso-amyl alcohol etc.; glycols e.g. ethylene glycol; glycerine; N-methyl pyrrolidone; methoxypropanol; and ketones e.g. 2-propanone and 2-butanone etc.
Substantially
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.
Non-cationic Surfactants
Surfactants are surface active agents which are soluble compounds which reduce the interfacial tension between a liquid and a solid. Cationic surfactants have not been found to be useful for this application due to their photographic activity and the use of halide counterions in most commercial surfactants.
Non-cationic surfactants aid the dispersion of ingredients which are insoluble in the particular dispersion medium. The thermographic recording materials of the present invention contain at least one non-cationic surfactant, which may be anionic, non-ionic or amphoteric.
In the present invention the expression: “all the non-cationic surfactants present in the thermographic recording material together have a particular non-fluoro-halide ion concentration in ppm's”, means 10
6
multiplied by the sum of the quantities of non-fluoro-halide ions in the different non-cationic surfactants present divided by the sum of the quantities of all the non-cationic surfactants present in the same units of weight as that used for the quantities of non-fluoro-halide ions.
In a preferred embodiment of the present invention all the non-cationic surfactants present in the thermographic recording material together have a non-fluoro-halide ion concentration of 1000 ppm or less, with 500 ppm or less being particularly preferred and 200 ppm being especially preferred. It is also preferred that all the non-cationic surfactants present in the thermographic recording material together have an alkali metal ion concentration of 200 ppm or less. The alkali metal ions are: sodium, potassium, lithium, rubidium and caesium.
The chloride ion and sodium ion concentrations determined by ionic chromatography for commercial non-cationic surfactants according to the present invention are given in table 1.
TABLE 1
Surfactant
[Cl
−
]
Nr
Type
SURFACTANT
[ppm]
[Na
+
] [ppm]
S01
A
HOSTAPAL ™ B
<50
S02
A
MARLON ™ A365
<40
4300
S03
A
dodecyl sulfonic acid
<40
<1000
S04
A
ULTRAVON ™ W
700
74468
S05
A
HOSTAPUR ™ SAS 60
<40
S06
A
MARLON ™ AS3
<200
<200
S07
N
ANTAROX ™ CO 880
<40
S08
N
SURFYNOL ™ CT111
<40
S09
N
ARKOPAL ™ N 060
<20
S10
N
GAFAC ™ RM 710
<40
<1000
S11
A
ALKANOL ™ XC
1600
S12
A
sodium dodecyl sulfate
6400
S13
A
DOWFAX ™ 2A1
2700
S14
A
NIAPROOF ™ AN

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