Heat-sensitive recording material

Details Heat-sensitive recording material Heat-sensitive recording material

2003-05-23

2004-05-04

Edwards, N. O. (Department: 1774)

Record receiver having plural interactive leaves or a colorless

Having a colorless color-former, developer therefor, or...

Identified organic electron acceptor other than phenolic resin

C503S200000

Reexamination Certificate

active

06730632

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat-sensitive recording material, specifically, a heat-sensitive recording material giving a high color development density and having excellent storage stability.
2. Description of the Related Art
In recent years, heat-sensitive recording materials, onto which heat is supplied from a thermal head or the like so as to record images, have been spreading since the materials are relatively inexpensive and recording device for the materials are simple and high in reliability and require no maintenance.
Under such a situation, in particular, improvement in performances thereof, for example, improvement in the image quality and storage stability thereof has been highly demanded in recent years. Thus, eager research on the color development density, the image quality, the storability and other properties of the heat-sensitive recording materials has been conducted.
As a heat-sensitive recording material having a high sensitivity, for example, Japanese Patent Application Laid-Open (JP-A) No. 11-342676 describes an example in which 2,4-bis(phenylsulfonyl)phenol is used as a color developing agent (electron-accepting compound). However, even the heat-sensitive recording material described in this publication cannot satisfy recently increasing market demands for high sensitization and the like. In particular, there is a room for improvement in the water resistance of heat-sensitive recording materials, and the sticking resistance thereof, which is concerned with fraction between the materials and a thermal head.
SUMMARY OF THE INVENTION
The inventors have found out that performances of a heat-sensitive recording material are improved by appropriately selecting the kind of an electron-accepting compound added to a heat-sensitive color developing layer, selecting a binder incorporated, together with an electron-donating colorless dye and the electron-accepting compound, added to the heat-sensitive color developing layer, and selecting an appropriate additive added to an outermost layer.
An object of the invention is to provide a heat-sensitive recording material which has a high sensitivity, gives a high print density, is superior in storage stabilities (heat resistance, humidity resistance and plasticizer resistance (solvent resistance)) of image portions and non-image portions (background portions) and head break resistance, and is particularly superior in water resistance, stamping ability and sticking resistance.
Some embodiments of the present invention for solving the above-mentioned problems are shown as follows:
A first aspect of the invention provides a heat-sensitive recording material which comprises, on a substrate, at least one heat-sensitive color developing layer comprising an electron-donating colorless dye, 2,4-bis(phenylsulfonyl)phenol as an electron-accepting compound, and a sulfonic acid-modified polyvinyl alcohol and at least one modified polyvinyl alcohol other than the sulfonic acid-modified polyvinyl alcohol as binders, an outermost layer of the heat-sensitive recording material comprising a lubricant.
A second aspect of the invention provides a heat-sensitive recording material according to the first aspect, wherein the heat-sensitive color developing layer comprises an acetoacetyl-modified polyvinyl alcohol as the modified polyvinyl alcohol other than the sulfonic acid-modified polyvinyl alcohol
A third aspect of the invention provides a heat-sensitive recording material according to the first or second aspect, wherein the lubricant is an aliphatic acid metal salt, or an aliphatic acid amide compound having a melting point of 105° C. or more.
DETAILED DESCRIPTION OF THE INVENTION
The heat-sensitive recording material of the present invention is a heat-sensitive recording material which comprises, on a substrate, at least one heat-sensitive color developing layer comprising an electron-donating colorless dye, 2,4-bis(phenylsulfonyl)phenol as an electron-accepting compound, and a sulfonic acid-modified polyvinyl alcohol and at least one modified polyvinyl alcohol other than the sulfonic acid-modified polyvinyl alcohol as binders, an outermost layer of the heat-sensitive recording material comprising a lubricant.
In the heat-sensitive recording material of the invention, its heat-sensitive color developing layer comprises an electron-donating colorless dye, 2,4-bis(phenylsulfonyl)phenol as an electron-accepting compound, a sulfonic acid-modified polyvinyl alcohol, which may be referred to as a “sulfonic acid-modified PVA” hereinafter, and at least one modified polyvinyl alcohol other than the sulfonic acid-modified polyvinyl alcohol, which may be referred to as a “different modified PVA” hereinafter, and further an outermost layer of the heat-sensitive recording material comprises a lubricant, thereby making it possible to improve various performances of the heat-sensitive recording layer, for example, sensitivity, print density, storage stability (heat resistance, humidity resistance and plasticizer resistance (solvent resistance)) of image portions and non-image portions (background portions) and head break resistance, and further improve the water resistance of the heat-sensitive recording material, the stamping ability thereof, and the sticking resistance thereof, which is related to fraction between the material and a thermal head.
The “outermost layer” of the heat-sensitive recording material, which comprises the lubricant in the invention, means a layer disposed as the outermost layer on the recording side in the heat-sensitive recording material. This layer is brought into direct contact with a thermal head when images are printed by the thermal head. For example, when only the heat-sensitive color developing layer is formed on the substrate, the heat-sensitive color developing layer is the outermost layer. When a protective layer is formed on the heat-sensitive color developing layer, the protective layer is the outermost layer. The “sticking resistance” means performance against defects, such as noises (adhesion sounds) at the time of printing images, and white spots, in which a part of a printed image is missing, the defects resulting from fraction between the thermal head and the surface of the heat-sensitive recording material.
The following will describe the heat-sensitive recording material of the invention in detail.
The heat-sensitive recording material of the invention comprises at least one heat-sensitive color developing layer on or over a substrate. A plurality of the layers may be disposed; some other layer such as an undercoat layer or a protective layer may be formed when necessary.
Heat-Sensitive Color Developing Layer
The heat-sensitive color developing layer comprises an electron-donating colorless dye, 2,4-bis(phenylsulfonyl)phenol as an electron-accepting compound, and a sulfonic acid-modified PVA and at least one different modified PVA as binders. If necessary, this layer comprises some other component such as a heat-melting material or an image stabilizer.
Electron Acceptable Compound
In the heat-sensitive recording material of the invention, 2,4-bis(phenylsulfonyl)phenol is used as an electron-accepting compound which makes an electron-donating colorless dye exhibit color. The electron-donating colorless dye will be described later in detail. By the use of 2,4-bis(phenylsulfonyl)phenol as the electron-accepting compound, the heat-sensitive recording material has superior storage stability.
In order to improve the sensitivity and give a high color development density, 2,4-bis(phenylsulfonyl)phenol is dispersed in the binder, which comprises the sulfonic acid-modified PVA and the different modified PVA, in the heat-sensitive color developing layer so as to have preferably a volume-average particle size of 0.4 to 1.0 &mgr;m, and more preferably 0.4 to 0.8 &mgr;m. If the volume-average particle size is less than 0.4 &mgr;m, the fog density of background portions in the resultant printed material may rise during storage. If the size is more than 1.0 &

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