Heat-sensitive recording material

Details Heat-sensitive recording material Heat-sensitive recording material

2002-03-20

2004-07-27

Hess, Bruce H. (Department: 1774)

Record receiver having plural interactive leaves or a colorless

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

C503S226000

Reexamination Certificate

active

06767861

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat-sensitive recording material, and, particularly to a heat-sensitive material which comprises a heat-sensitive recording layer and a protective layer on a support and a uniform coating.
2. Description of Related Art
Heat-sensitive recording has been developed in recent years because heat-sensitive recording devices are simple, highly reliable and require no maintenance. As heat-sensitive recording materials used for the heat-sensitive recording, for example, heat-sensitive recording materials which use a reaction between an electron-donating colorless dye and an electron-acceptable compound and those which use a reaction between a diazonium salt compound and a coupler are widely known.
In these conventional heat-sensitive recording materials, surface defects (coating nonuniformities) caused by the repulsion of a protective layer by a heat-sensitive recording layer occur at a certain rate.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a heat-sensitive recording material having reduced coating nonuniformities.
The inventors of the present invention have conducted earnest studies to attain the above object and, as a result, found that it is effective to add a specific surfactant to a protective layer, thus completing the present invention.
Accordingly, the present invention provides a heat-sensitive recording material comprising a heat-sensitive recording layer and a protective layer on a support, wherein the protective layer contains an acetylene glycol represented by the following formula (1):
wherein: R
1
to R
4
respectively represents a hydrogen atom, a branched, straight-chain or cyclic unsubstituted or substituted alkyl group having 1 to 8 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms; R
5
to R
8
respectively represents a hydrogen atom or a methyl group; and n and m independently denotes an integer from 0 to 50.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of a heat-sensitive recording material according to the present invention will be explained hereinafter.
The heat-sensitive recording material of the present invention is provided with a heat-sensitive recording layer and a protective layer on a support. The protective layer contains at least an acetylene glycol represented by the following formula (1):
In the above formula, n and m denote integers from 0 to 50 and preferably integers from 0 to 4.
Also, R
1
to R
4
respectively represent a hydrogen atom, a branched, straight-chain or cyclic unsubstituted or substituted alkyl group having 1 to 8 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms. Specific examples of the alkyl groups include a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group and cyclohexyl group. Specific examples of the aryl group include a phenyl group and naphthyl group. Examples of the substituent include an ether group and ester group.
It is preferable that R
2
and R
3
respectively be a methyl group, R
1
and R
4
respectively be an isobutyl group among these groups and n and m respectively be 0.
R
5
to R
8
respectively represents hydrogen atom or a methyl group.
Specific examples of the acetylene glycol represented by the formula (1) will be given below; however, these examples are not intended to limit the present invention.
Other Components
In addition to the aforementioned surfactant, the protective layer comprises binders, pigments, lubricants, dispersants, fluorescent whitening agents, metal soaps, hardeners, ultraviolet absorbers, crosslinking agents and the like.
Examples of the above binder include water-soluble polymers such as vinyl acetate-acrylamide copolymers, silicon-modified polyvinyl alcohol, starch, denatured starch, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, gelatins, gum arabic, casein, styrene-maleic acid copolymer hydrolysate, styrene-maleic acid copolymer half ester hydrolysate, isobutylene-maleic acid anhydride copolymer hydrolysate, polyacrylamide derivatives, polyvinylpyrrolidone, sodium polystyrenesulfonate and sodium alginate and synthetic rubber latexes and synthetic resin emulsions such as styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex and vinyl acetate emulsion.
Among the above binders, polyvinyl alcohol or its derivatives are preferable. Specific examples of these compounds are described in Japanese Patent Application Laid-Open (JP-A) No. 2000-118133.
Examples of the aforementioned pigments are not particularly limited, and include, kaolin, baked kaolin, talc, agalmatolite, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, zinc oxide, lithopone, amorphous silica, colloidal silica, baked gypsum, silica, magnesium carbonate, titanium oxide, alumina, barium carbonate, barium sulfate, mica, microballoon, urea-formalin filler, polyester particle and cellulose filler.
The content of the aforementioned binder is preferably 10 to 500 wt % and more preferably 50 to 400 wt % relative to the pigment in the protective layer.
It is effective to use a crosslinking agent and a catalyst that promotes the reaction of the crosslinking agent together to improve the water resistance. Examples of the crosslinking agent include an epoxy compound, blocked isocyanate, vinylsulfone compound, aldehyde compound, methylol compound, boric acid, carboxylic acid anhydride, silane compound, chelate compound and halogen compound. Among these compounds, those able to adjust the pH of a coating solution for a protective layer to be from 5.5 to 9.5 are preferable. Examples of the catalyst include known acids and metal salts, and, like the above, those able to adjust the pH of a coating solution for a protective layer to be from 5.5 to 9.5 are preferable.
Preferable examples of the lubricant include zinc stearate, calcium stearate, paraffin wax and polyethylene wax.
The protective layer may contain other surfactant. Preferable examples of the other surfactant include those which contain fluorine.
A coating solution for forming the protective layer (coating solution for a protective layer) is obtained by mixing each of the aforementioned components. A mold releasing agent, wax, water repellent agent and the like may also be added according to the need.
The dry coating amount of the protective layer is preferably 0.2 to 7 g/m and more preferably 1 to 4 g/m
2
If the dry coating amount is less than 0.2 g/m
2
, then the water resistance might not be maintained. Conversely, if the amount exceeds 7 g/m
2
, then the heat sensitivity might be significantly decreased. After the protective layer is formed by application, a calendering treatment may be carried out according to the need.
Heat-sensitive Recording Layer
The heat-sensitive recording layer comprises color developing components and may also comprise other components such as a binder and a base according to the need. Preferable examples of the aforementioned color developing component include (1) a combination of a diazonium salt compound and a coupler which has a coupling reaction with the diazonium salt compound to form a color and (2) a combination of an electron-donating dye precursor and an electron-acceptable compound which reacts with the electron-donating dye precursor to form a color.
Diazonium Salt Compound
Examples of the aforementioned diazonium salt compound are compounds represented by the following formula (2).
Ar—N
2
+
X
−
  (2)
wherein Ar represents a portion of an aromatic group and X
−
represents an acid anion.
The diazonium salt compound is a compound which has a coupling reaction with a coupler, the coupler to be explained later, when heated to form a color and which is decomposed by light. The maximum absorption wavelength of each of these compounds can be controlled by the position and type of substituent of the Ar.
Specific examples of diazoniums forming salts include

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