Radiation imagery chemistry: process – composition – or product th – Microcapsule – process – composition – or product
Reexamination Certificate
2002-06-12
2004-04-20
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Microcapsule, process, composition, or product
C430S157000, C430S171000, C430S172000
Reexamination Certificate
active
06723482
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat-sensitive recording material, more particularly to a diazo compound-based heat-sensitive recording material which can be fixed and which is excellent in preservability.
2. Description of the Related Art
Heat-sensitive recording materials for recording images by applying heat via a thermal head or the like are widely used since they are relatively cheap, a recording apparatus for use therewith is simple and highly reliable, and maintenance thereof is unnecessary. Under such conditions, there has recently been strong desire for high performance such as high image quality, improved preservation stability and the like, and studies of color developing density, image quality, preservability and other properties of heat-sensitive materials have been intensively conducted.
As heat-sensitive recording materials, those using a diazo compound as a color component for improving color developing density, image quality and preservability have been abundantly developed. In the case of the heat-sensitive recording materials containing diazo compound, an image is formed by heat, then, the diazo compound is thermally decomposed (fixed) with light, and image preservability can be significantly improved by encapsulating the diazo compound.
However, even with the above-mentioned heat-sensitive recording materials containing the diazo compound, a problem is observed in that, after printing an image, a color developed portion thereof becomes discolored over time during storage and image concentration decreases. This has been ascribed to crystallization of an azo dye in the color developed portion with the passage of time. To prevent discoloration of the image resulting from crystallization of this dye, a diazo compound which is not easily crystallized when an azo dye is formed can be effectively used. When the diazo compound which is not easily crystallized is used, however, a problem occurs in that there is a decrease in light resistance of the color developed portion.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-described problems of the prior art and specifically to provide a heat-sensitive recording material which suppresses discoloration over time without decreasing light resistance of a color developed portion and which has excellent image preservability.
A first aspect of the present invention provides a heat-sensitive recording material comprising a substrate having disposed thereon at least a heat-sensitive recording layer comprising:
microcapsules;
diazonium salt compounds contained within the microcapules and represented by the following general formula (I); and
a coupler which undergoes coupling-reaction with the diazonium salt compounds to cause color development,
wherein three or more of the diazonium salt compounds represented by the general formula (I) are contained in the same microcapsule:
(wherein R
1
, R
2
and R
3
each independently represents an alkyl group, a substituted alkyl group, an aryl group or a substituted aryl group; and X
−
represents a counter anion).
Further, a second aspect of the present invention provides the heat-sensitive recording material of the first aspect at least one of said diazonium salt compounds contained in the microcapsule is a compound represented by the following general formula (II):
(wherein R
1
and R
2
each independently represents an alkyl group, a substituted alkyl group, an aryl group or a substituted aryl group; R
4
represents an alkyl group; and X
−
represents a counter anion).
DETAILED DESCRIPTION OF THE INVENTION
A heat-sensitive recording material of the present invention will now be described in detail.
The heat-sensitive recording material of the present invention comprises a substrate having disposed thereon at least a heat-sensitive recording layer containing diazonium salt compounds represented by the general formula (I) listed below and a coupler which undergoes coupling reaction with the diazonium salt compound to cause color development, wherein three or more diazonium salt compounds represented by the general formula (I) are contained in the same microcapsule.
In the heat-sensitive recording material of the present invention, crystallization of an azo dye with the passage of time can be suppressed without decreasing light resistance, by allowing three or more diazonium salt compounds represented by the general formula (I) to be contained in the same microcapsule. As a result, discoloration of a color developed portion can be suppressed to improved image preservability. In the heat-sensitive recording material of the present invention, it is necessary that three or more diazonium salt compounds represented by the following general formula (I) are contained in the same microcapsule. Said diazonium salt compounds may be appropriately selected and a number of kinds contained determined so that each diazonium salt compound is contained in an amount of at least 5% by weight. From the standpoint of balancing cost performance and the like with the effect of the invention, however, three or four diazonium salt compounds are preferably contained.
The heat-sensitive recording material of the invention has at least the heat sensitive recording layer disposed on the substrate, and the heat sensitive recording layer may comprise a single layer or a plurality of layers, and, if necessary, other layers such as a light transmittance controlling layer, a protective layer and the like may further be provided.
Heat-Sensitive Recording Layer
The heat-sensitive recording material of the invention has at least the one heat sensitive recording layer containing microcapsules containing three or more diazonium salt compounds of the above-mentioned general formula (I).
In the above-mentioned general formula (I), R
1
, R
2
and R
3
each independently represents an alkyl group, a substituted alkyl group, an aryl group or a substituted aryl group. A total number of carbon atoms in R
1
, R
2
and R
3
is preferably 12 or more, and more preferably 14 or more.
Examples of the alkyl group include a methyl group, ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a t-butyl group, a pentyl group, an isopentyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, an octyl group, a t-octyl group, a 2-ethylhexyl group, a nonyl group, an octadecyl group and the like.
Examples of the substituent of the substituted alkyl group include alkoxy groups, alkoxycarbonyl groups, alkylsulfonyl groups, substituted amino group, substituted amide groups, aryl groups, aryloxy groups, halogen and the like. However, the scope of the invention is not limited thereto. Specific examples of the substituted alkyl group include a benzyl group, 4-methoxybenzyl group, triphenylmethyl group, ethoxycarbonylmethyl group, 2-ethylhexyloxycarbonylmethyl group, methoxyethyl group, ethoxyethyl group, butoxyethyl group, 2′,4′-diisopentylphenyloxymethyl group, 2′,4′-di-t-butylphenyloxymethyl group, dibenzylaminocarbonylmethyl group, 2,4-di-t-aminophenyloxypropyl group, ethoxycarbonylpropyl group, 1-(2′,4′-di-t-aminophenyloxy)propyl group, acetylaminoethyl group, 2-(N,N-dimethylamino)ethyl group, 2-(N,N-dimethylamino)propyl group, methanesulfonylaminopropyl group and the like.
Examples of the substituent of the substituted aryl group include, but are not limited to, alkyl groups, alkoxy groups, alkylthio groups, aryl groups, aryloxy groups, arylthio groups, acyl groups, alkoxycarbonyl groups, carbamoyl groups, carboamide groups, sulfonyl groups, sulfamoyl groups, sulfoneamide groups, ureide groups, amino groups, heterocyclic groups, halogens and the like.
Specific examples of the substituted aryl group include a 2-methylphenyl group, 2-chlorophenyl group, 2-methoxyphenyl group, 2-butoxyphenyl group, 2-(2-ethylhexyloxy)phenyl group, 2-octyloxyphenyl group, 3-(2,4-di-t-pentylphenoxyethoxy)phenyl group, 4-chlorophenyl group, 4-methylphenyl group, 4-methoxyphenyl group, 4
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