Record receiver having plural interactive leaves or a colorless – Having a colorless color-former – developer therefor – or... – Method of use – kit – or combined with marking instrument or...
Reexamination Certificate
2000-01-05
2001-03-27
Hess, Bruce H. (Department: 1774)
Record receiver having plural interactive leaves or a colorless
Having a colorless color-former, developer therefor, or...
Method of use, kit, or combined with marking instrument or...
C503S202000, C503S212000, C503S226000
Reexamination Certificate
active
06207614
ABSTRACT:
DESCRIPTION
1. Field of the invention
The present invention relates to thermographic recording materials whose prints have improved image tone.
2. Background of the invention
Thermal imaging or thermography is a recording process wherein images are generated by the use of thermal energy. In direct thermal thermography a visible image pattern is formed by image-wise heating of a recording material containing matter that by chemical or physical process changes colour or optical density. 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.
According to U.S. Pat. No. 3,080,254 a typical heat-sensitive (thermographic) copy paper includes in the heat-sensitive layer a thermoplastic binder, a water-insoluble silver salt and an appropriate organic reducing agent.
EP 669 876 discloses a recording material comprising on a support (i) a heat sensitive layer comprising a substantially light insensitive organic silver salt, (ii) a protective layer containing a thermomeltable particle dispersed in a binder and (iii) a reducing agent being present in the heat sensitive layer and/or any other layer of the recording material on the same side of the support carrying the heat sensitive layer. According to EP 669 876, the thermomeltable particles are waxes such as e.g. amide waxes, bees wax, polyethylene wax, polytetrafluoroethylene wax, Carnauba wax etc.
EP-A 775 595 discloses a recording material comprising at least one thermosensitive element, comprising a substantially light-insensitive organic silver salt and an organic reducing agent therefor in thermal working relationship therewith, on a support, characterized in that an outermost layer of the recording material comprises at least one solid lubricant having a melting point below 150° C. and at least one liquid lubricant in a binder, wherein at least one of the lubricants is a phosphoric acid derivative. Solid lubricants which can be used according to EP-A 775 595 include ester waxes e.g. fatty acid esters, and amide waxes e.g. fatty acid amides.
EP 669 876 and EP-A 775 595 concern the use of waxes in the protective layers of thermographic materials which overcoat a layer containing organic silver salts i.e. the waxes and organic silver salts are not in the same layer.
Prior art substantially light-insensitive black and white thermographic recording materials exhibit an insufficiently neutral image colour due to the thermal development process in which temperatures up to 300 to 400° C. are reached for a heating time which may be less than a 1.0 ms. However, image tone is particularly important for thermographic recording materials for medical diagnostic applications for which image tone requirements are particularly severe, particularly at low optical densities. There is therefore a need for thermographic materials which produce more neutral image tones upon image-wise thermal development.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide substantially light-insensitive black and white thermographic recording materials whose prints exhibit a more neutral image tone.
Further objects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
Surprisingly it has been found that substantially light-insensitive black and white monosheet thermographic recording materials with a thermosensitive element containing substantially light-insensitive mixed crystals of at least one organic silver salt and at least one organic fatty acid derivative in an inner layer exhibit a more neutral image tone than thermographic recording materials with crystals of a substantially light-insensitive organic silver salt.
The above mentioned objects are realized by a substantially light-insensitive black and white monosheet thermographic recording material comprising a support and a thermosensitive element which is optionally provided with a protective layer, wherein the thermosensitive element contains substantially light-insensitive mixed crystals of at least one organic silver salt and at least one organic fatty acid derivative, an organic reducing agent for the organic silver salt in thermal working relationship therewith and a binder and wherein the substantially light-insensitive mixed crystals are present in an inner layer of the thermographic recording material.
A recording process is further provided according to the present invention comprising the steps of: (i) bringing an outermost layer of the above-mentioned thermographic recording material in proximity with a heat source; and (ii) applying heat from the heat source imagewise to the recording material while maintaining proximity to the heat source to produce an image; and (iii) removing the recording material from the heat source.
Preferred embodiments of the invention are disclosed in the dependent claims.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment of the recording process, according to the present invention, the heat source is a thermal head with a thin film thermal head being particularly preferred.
DEFINITIONS
By substantially light-insensitive is meant not intentionally light sensitive.
An inner layer is a layer which is not the outermost layer of a material.
A mixed crystal is a mixture of at least two species in which only a single species can be detected by an X-ray diffractometer (XRD), which may be one of the components with slightly shifted XRD-lines reflecting the take-up of one of the components in the crystal lattice of the other.
A fatty acid is an organic monobasic acid of the general formula C
n
H
2n+1
COOH derived from the saturated series of aliphatic hydrocarbons e.g. arachidic acid, behenic acid, stearic acid, palmitic acid and myristic acid, but also includes unsaturated hydrocarbon groups as in the case of erucic acid, oleic acid, linoleic acid, elaidic acid, vaccenic acid and arachidonic acid.
Tallow is animal fat containing as glycerides oleic acid, palmitic acid, stearic acid, myristic acid, linoleic acid and small quantities of cholesterol, arachidonic, elaidic and vaccenic acids and has a solidification point which ranges from 40 to 46° C.
Organic Fatty Acid Derivatives
The term organic fatty acid derivatives as used herein refers to derivatives of one or more saturated or unsaturated fatty acids such as esters, amides etc. or mixtures thereof, which do not contain metallic atoms. The term does not include fatty acids. Preferred organic fatty acid derivatives are ester and amide waxes or mixtures thereof. The esters may have one or more ester groups depending on whether the alcohols forming the esters have one or more esterifiable hydroxy groups in addition to other functional groups. Examples of alcohols with more than one esterifiable hydroxy group are glycerine, sorbitan etc. Examples of ester and amide waxes suitable for use in the substantially light-insensitive thermographic recording materials of the present invention are:
WAX01: glycerine tristearate;
WAX02: glycerine monostearate;
WAX03: methyl stearate;
WAX04: N-(2-hydroxy-1-propyl)-lauramide, C
11
H
23
CONHCH
2
CHOHCH
3
;
WAX05: glycerine monopalmitate;
WAX06: oleamide;
WAX07: erucamide;
WAX08: glycerine monotallow acid ester; (RILANIT™ GMS from HENKEL AG);
WAX09: sorbitan monostearate (SPAN™ 60 from ICI PLC);
WAX10: sorbitan tristearate (SPAN™ 65 from ICI PLC);
WAX11: sorbitan monopalmitate (SPAN™ 40 from ICI PLC);
WAX12: POE-(4)-sorbitan monostearate (TWEEN™ 61 from ICI).
Preferred ester- or amide-waxes for use in the present invention are selected from the group consisting of: glycerine tristearate, glycerine monostearate and N-(2-hydroxy-1-propyl)-lauramide.
Substantially Light-Insensitive Mixed Crystals of Organic Silver Salts with Organic Fatty Acid Derivatives
Substantially light-insensitive mixed crystals of at least one organic silver salts with at least one organic fatty acid derivative exhibit the X-ray diffraction pattern of the organic
Defieuw Geert
Loccufier Johan
Van-den Bergh Armand
AGFA-GEVAERT
Baker & Botts L.L.P.
Hess Bruce H.
LandOfFree
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