JPH0141513B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-color recording paper on which recording is performed using a thermal head.

Conventionally, the method of two-color recording using a thermal head was developed by Nakano and Nagai (Oki Electric Research and Development No. 111).
As reported in vol. 47, No. 2, pp. 43-48), there is a method of obtaining two-color recording using heat-sensitive recording paper that develops red and blue colors depending on the difference in heating temperature. This method has the advantage of being able to distinguish between high-temperature and low-temperature heating and record two colors, red and blue, simply by adjusting the power applied to the heat head, but when recording red at high temperatures, the surrounding area becomes colder. The drawback was that the image quality deteriorated due to fringing caused by the blue color developed by heating.
In addition, a carbon paper-like film coated with black ink that melts and transfers when heated is layered on thin paper and thermosensitive recording paper that turns red when heated. The film is heated with a thermal head and black ink is transferred onto thermal paper to obtain an image.If a red record is to be obtained, the carbon paper-like film is removed and then removed.
There is a method of obtaining a red color by directly heating thermal paper with a thermal head. Although this method requires two thermal heads, one for black and one for red, it is not possible to record continuously, but it is characterized by good color separation between red and black and the ability to obtain clear images without mixing red and black. However, there is a drawback that the used carbon paper-like film remains as waste after recording.

The present invention aims to solve the drawbacks of conventional two-color recording, such as poor color separation and generation of waste.

First, the principle of the present invention will be explained. The heat-sensitive recording paper used in the present invention is novel in that it uses a mixture of a heat-sensitive coloring agent whose main ingredients are leuco dye and color developer, which have been widely used in recent years, and a heat-sensitive coloring agent whose main ingredients are diazonium and coupler. There is sex.

Next, it will be explained using figures. FIG. 1 is a cross-sectional view of recording paper used in the present invention, where recording paper 1 is base paper 2.
and a recording layer 3, in which a diazo compound, a coupler, a leuco dye, and a color developer each exist as independent particles and are held by a binder. When the recording paper shown in FIG. 1 is heated with a thermal head, the heated portion develops a first color to form an image 4. At this time, a color reaction between the diazo compound and the coupler and a color reaction between the leuco dye and the color developer occur simultaneously, and the first color is a mixture of the two colors.

FIG. 2 shows an operation in which the entire surface of the recording paper partially colored in FIG. 1 is irradiated with light to decompose the diazo compound by light. Due to this photodecomposition of the diazo compound, the coloring reaction between the diazo compound and the coupler does not occur upon subsequent heating. In FIG. 3, after the operation shown in FIG. 2 is performed, the image is heated again by a thermal head to form an image 5 of a second color. At this time, only the coloring reaction between the leuco dye and the color developer occurs, and an image with a color clearly different from that of the first image can be formed.

The important point of this recording method is that it solved the problem that conventionally it was extremely difficult to form a single recording layer containing four types of diazo compound, coupler, leuco dye, and color developer. It is in.
The reason for this will be explained next. In a color-forming reaction system in which a leuco dye and a color developer are combined, since both are insoluble in water, each was dispersed in water as fine particles, and a coating solution was formed in which the two did not substantially come into contact with each other. For this reason, the two are physically separated in the recording layer on the recording paper, and the coloring reaction is stopped, and when one of them melts during heating, they melt together and the coloring reaction progresses. A recorded image could be obtained. On the other hand, in the reaction caused by the combination of a diazo compound and a coupler, the conventional diazo compound was dissolved in water, so when both were added to water, the coloring reaction proceeded, and a coating liquid dispersed in water could not be formed. However,
The present inventors have discovered that when a diazo compound is treated with an organic boron compound such as a tetraphenyl boron salt or a triphenyl fluoroborate salt, it becomes insoluble in water and a coating liquid in which fine particles of the diazo compound and coupler are dispersed can be prepared. Ta. For this reason, at least 4 of the diazo compound coupler, leuco dye, and color developer.
It is now possible to create a coating liquid that contains seeds and is dispersed in water. Since this coating liquid became available, it became possible to create a recording paper having the structure shown in FIG. 1, and to perform two-color recording by intervening light irradiation.

Next, specific components will be explained.

The diazo salt used has an anion component such as tetraphenylboron [B(C ₆ H ₅ ) ₄ ] ^- , [B(C ₆ H ₄ F) ₄ ^- or triphenylfluoroborate salt [B(C ₆ H ₅ )] ₃ F] ^- is a water-insoluble compound composed of organic boron compounds such as -. These water-insoluble diazonium salts can be extracted as a precipitate by mixing an aqueous solution of a water-soluble diazonium salt with an aqueous solution of an organic boron compound such as sodium tetraphenylboron. Water-soluble diazonium salts that can be used at this time include conventionally known ones, such as p-diazo-N-ethyl-N-hydroxyethylaniline chloride zinc chloride, p-diazo-
N,N-dimethylaniline chloride zinc chloride,
p-diazo-N,N-diethylaniline chloride zinc chloride, 4-benzamido-2,5-diethoxybenzenediazonium chloride zinc chloride,
2-methoxy-4-morpholinobenzenediazonium chloride zinc chloride, 4-morpholino-2,
5-dibutoxybenzenediazonium chloride, zinc chloride, etc.

Note that these water-insoluble diazonium salts can be used alone or in combination of two or more.

The coupler used in the present invention is, for example, a water-insoluble compound represented by the following general formula.

R ₁ and R ₂ may be a C ₁ to C ₄ alkyl group, or R ₁ and R ₂ may form a heterocycle together with the N atom to which they are bonded.

etc. These couplers can be used alone or in combination of two or more.

Leuco dyes include triphenylmethane-based leuco dyes (A) or fluoran dye bases (B) represented by the following general formula, and lactam compounds.

Rx, Ry, Rz: hydrogen, hydroxyl group, halogen, alkyl group, nitro group, aryl group, amino group, dialkylamino group, monoalkylamino group, allyl group, Z: O in atoms necessary to form a heterocyclic ring , S
shows.

Specific examples are as follows.

As a triphenylmethane dye, 3,3-bis(p-dimethylaminophenyl)
-6-nitrophthalide, 3,3-bis(P-dibutylaminophenyl)
-phthalide, 3,3-bis(P-dimethylaminophenyl)
-4,5,6,7-tetrachlorophthalide.

3,3-bis(P-dimethylaminophenyl)
-phthalide, 3,3-bis-(P-dimethylaminophenyl)
-6-dimethylaminophthalide (crystal violet lactone), 3,3-bis(P-dimethylaminophenyl)
-6-aminophthalide, etc.

Fluoran dyes include 3-dimethylamino-5,7-dimethylfluoran, 3-diethylamino-5,7-dimethylfluoran, 3,6-bis-β-methoxyethoxyfluoran, 3,6-bis-β -cyanoethoxyfluoran, 3-dimethylamino-6-methoxyfluoran, 7-acetamino-3-dimethylaminofluoran, and the like.

Examples of lactam compounds include:

lactam of 9-P-nitroanilino-3,6-bis(diethylamino)-9-xanthenyl-O-benzoic acid (rhodamine B lactam),
Lactam of 9-P-nitroanilino-3,6-bis(dimethylamino)-9-thioxanthenyl-O-benzoic acid.

A phenol compound or an organic acid can be used as a color developer.

Phenolic compounds include 3,5-xylenol, thymol, 4-tert-butylphenol, 4-hydroxyphenoxide, methyl-4-hydroxybenzoate, 4-hydroxyacetophenone, α-naphthol, β- Naphthol, catechol, resorcinol, hydroquinone, 4-tert-octylcatechol, 4,4'-secondary-butylidenedienol, 2,2'-dihydroxydiphenyl, 2,
2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-bis(4'-oxyphenyl)propane, 4,4'-isopropylidene bis(2-tert-butylphenol),
4,4'-Secondary butylidene diphenol,
Examples include pyrogallol, phloroglycin, and phloroglucin carboxylic acid.

Examples of organic acids include boric acid, oxalic acid, maleic acid, tartaric acid, citric acid, succinic acid, benzoic acid, stearic acid, gallic acid, salicylic acid, 1-oxy-2-naphthoic acid, 2-oxy-P-toluic acid, Examples include O-oxybenzoic acid and 4-oxyphthalic acid.

Further, the coupler is a phenol and can be used as a coupler for diazo as well as a color developer for leuco dye.

Recording paper is prepared by coating it with a suitable binder.

Examples of the binder include generally known water-soluble polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxypropylcellulose, polyvinylpyrrolidone, gum arabic, gelatin, casein, starch, styrene-maleic anhydride copolymer salt, and polyacrylic acid. Water-soluble binders such as salts, latexes such as styrene-butadiene latex, acrylonitrile-butadiene latex, various emulsions such as polyvinyl acetate, polyacrylic acid ester, ethylene-vinyl acetate copolymer, ethyl cellulose, nitrocellulose, Polyvinyl acetate, polystyrene, polymethacrylate,
Various resins such as polyester, terpene resin, and cyclized rubber can be used.

Other additives that may be added include cyclic agents that prevent coloration due to oxidation after photodecomposition of the diazonium salt, such as thiourea, ascorbic acid, and allyl isothiocyanate. Zinc chloride is also added as a stabilizer for the diazonium salt. moreover,
Guanidine sulfate, pentaerythritol, and the like, which contribute to promoting thermal color development, can also be added.

Known inorganic pigments such as silica, barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide, and calcium carbonate, styrene beads, urea-melamine resin, and styrene are used to prevent staining on heat heads and to improve writing properties. - It is also possible to use fine powders such as maleic anhydride copolymers.

In the present invention, various waxes can be used by adjusting the coloring sensitivity. Examples include paraffin wax, microcrystalline wax, montan acid wax, montan acid ester wax, amide wax, and the like.

Next, an example will be explained.

Synthesis Example 1 While stirring 200 g of a 5% aqueous solution of p-diazo-N,N-dimethylaniline chloride zinc chloride,
5 of sodium tetraphenylborate in it.
% aqueous solution was slowly poured into the mixture at room temperature.
The resulting yellow precipitate was filtered off by suction, washed with water, and then sandwiched between paper and air-dried. The yield was 16.5g.

Example 1 The following paints were prepared.

20% aqueous dispersion of diazonium tetraphenyl boron salt of Synthesis Example 1 10 parts by weight 20% aqueous dispersion of 2-hydroxy-3-naphthoic acid-morpholinopropylamide 10 〃 20% aqueous dispersion of rhodamine lactam 10 〃 20% aqueous dispersion of bisphenol A 10 〃 10% aqueous solution of polyvinyl alcohol 30 〃 This paint was applied on high-quality paper with a basis weight of 65 g/m ² 60
The mixture was dried with hot air at ℃ to produce a heat-sensitive recording paper with a dry coating weight of 7 g/m ² . A thermal head with 1728 130Ω heating elements in contact with this recording paper was heated at a voltage of 12V at 5
When m·sec was applied, a black image with a recording density of 1.2 was obtained.

On the other hand, when the recording paper was left under room light for about an hour or exposed under an ultraviolet lamp for about 10 seconds and then recorded under the same conditions as above, the recorded density was
A red image of 0.9 was obtained.

As explained above, when the recording paper of the present invention is used, there is an advantage that the recording of different colors before and after light irradiation is well separated, and no waste is generated.

[Brief explanation of drawings]

1, 2, and 3 are cross-sectional views of recording paper showing the recording process of the present invention. 1...Recording paper, 2...Base paper, 3...Recording layer,
4, 5...Recorded image.

Claims (1)

[Claims] 1. A two-color thermosensitive recording paper comprising a water-insoluble diazo compound, a water-insoluble coupler, a leuco dye, a color developer, and a binder in a single recording layer.