JPH0573599B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a heat-sensitive recording material capable of developing two colors. More specifically, the present invention relates to a heat-sensitive recording material that can develop two different colors at different heating temperatures. BACKGROUND OF THE INVENTION In recent years, thermal recording methods have been developed that can form single-color image records by utilizing chemical or physical changes in substances caused by thermal energy.
This method has advantages over other recording methods in that it does not generate noise and does not require development and fixing processing. For this reason, thermal recording methods have come to be widely applied not only to recording books and documents, but also to recording measuring instruments, recording computer output, printing on facsimile machines, printing on automatic ticket vending machines, etc. Furthermore, recently, attempts have been made to obtain multicolor recording by utilizing differences in heating temperature and thermal energy, and various multicolor thermosensitive recording materials have been proposed accordingly. Examples of multicolor thermosensitive recording materials include recording materials in which two types of coloring components that develop different tones at different coloring temperatures are mixed in the same thermosensitive coloring layer (see Japanese Patent Publication No. 49-69); Depending on the coloring temperature of the coloring component, a high-temperature heat-sensitive coloring layer and a low-temperature heat-sensitive coloring layer are used separately, and these two layers are sequentially laminated on a support.
15540), and between the high temperature and low temperature thermosensitive coloring layers, when forming an image in the high temperature thermosensitive coloring layer, it exhibits a decoloring effect on the coloring component in the low temperature thermosensitive coloring layer corresponding to the image forming area. Two-layer structure recording materials provided with a color erasing layer (see Japanese Patent Application Laid-open No. 48-8251) and so-called color erasing-coloring systems using organic bases (see Japanese Patent Publication No. 51-29024) are known. There is.
However, all of these conventional multicolor thermosensitive recording materials have some problems and are still unsatisfactory. That is, the above-mentioned conventional multicolor thermosensitive recording material has the following problems. (a) When the low-temperature coloring layer is colored at a low temperature, the high-temperature coloring layer also develops a slight color, and the separation of the colors corresponding to the heating temperature is insufficient. (b) Recording bodies containing a color erasing agent or layer and recording bodies having a color erasing-color developing system have insufficient color image storage stability. (c) Fog (background stain) is likely to occur on the recording surface of the thermal recording medium. This is because, as thermal recording speeds have increased in recent years, recording planes have been made smoother and heat-sensitive coloring materials have been made finer in order to bring closer contact between the heat-sensitive recording medium and the recording head. Problems to be Solved by the Invention In a two-color thermosensitive recording material, the color separation between the low-temperature coloring layer and the high-temperature coloring layer corresponding to the heating temperature is improved, the coloring image is made clearer, and the storage stability of the coloring image is improved. The objective is to increase the sensitivity and reduce the occurrence of scumming on the recording surface. Means and Effects for Solving the Problems The two-color thermosensitive recording material of the present invention comprises: 1. a support; a color-forming first layer formed on one surface of the support;
a first coloring layer containing a leuco dye; a color developer layer formed on the first coloring layer and containing a color developer capable of reacting with the first leuco dye to develop color by heating; and a second coloring layer formed on the color developer layer and containing a second leuco dye that reacts with the color developer by heating to develop a color tone different from the color tone of the first coloring layer. and selected from waxes, terephthalic acid esters, aromatic condensed ring derivatives, biphenyl compound derivatives, and aromatic amide compound derivatives that do not cause color development of the first and second leuco dyes only in the second coloring layer. The present invention is characterized in that it contains a non-developing sensitizer containing at least one type of color-developing sensitizer. The recording medium of the present invention will be explained with reference to the accompanying drawings. In the accompanying drawings, a first coloring layer 1, a color developer layer 2, and a second coloring layer 3 are sequentially formed on a support 4. The first coloring layer 1 contains a coloring first leuco dye,
The second color developing layer 3 includes a second leuco dye that develops a color different from the first leuco dye and a non-color developing sensitizer, and the color developer layer includes the first and second leuco dyes. Contains a color developer that can react with each color by heating to develop a color. Since only the second coloring layer contains a non-color developing sensitizer together with the second leuco dye, it can develop color at a relatively lower temperature (for example, 70°C to 100°C) than the first coloring layer. That is, when a heat source comes into contact with the second coloring layer, the sensitizer melts at a relatively low temperature, and the second leuco dye in the second coloring layer and the color developer in the developer layer are mixed into this melt. The agents instantly dissolve and react with each other to develop color. In response to the above-mentioned low-temperature heating, the color developer layer has the effect of inhibiting heat conduction to the first coloring layer.
The coloring layer does not develop color, and only the second coloring layer develops color, forming a clear image. Coloring start temperature of the second coloring layer (i.e. heat sensitivity)
can be defined to a desired value by changing the type of sensitizer (that is, by changing the melting point), thereby making it possible to respond to the recent increase in speed of thermal recording. When a heat source at a relatively high temperature (for example, 100°C to 150°C) is brought into contact with the second coloring layer, the second coloring layer immediately develops color, and the heat passes through the color developer layer and reaches the first coloring layer. This can be colored. At this time, since the first coloring layer and the second coloring layer have different color tones, these two colors are mixed to form an image having a color tone different from that of the second coloring layer. The first and second leuco dyes used in the first and second coloring layers of the heat-sensitive recording material of the present invention are colorless to very light-colored, and include triphenylmethane-based, fluoran-based, phenothiazine-based, auramine-based, You can choose from leuco dyes such as spiropyran dyes. Examples of these leuco dyes are as follows. Crystal violet lactone 3,3-bis(p-dimethylaminophenyl)-
6-dimethylaminophthalide 3,3-bis(p-dimethylaminophenyl)phthalide 3,3-bis(p-dimethylaminophenyl)-
6-diethylaminophthalide 3,3-bis(p-dimethylaminophenyl)-
6-chlorophthalide 3-(N-P-tolyl-N-ethylamino)-6-
Methyl-7-(N-phenylamino)fluoran 3-diethylamino-7,8-benzfluoran 3-cyclohexylamino-6-methylfluoran 3-diethylamino-6-methyl-7-chlorofluoran benzoylleucomethylene blue 6'- Chloro-8'-methoxy-benzoindolino-
Birilosbilane 6'-bromo-8'-methoxy-benzoindolino-
Birilosbilane 2-[3,6-bis(diethylamino)-9-(0
-Chloroanilino) As the first leuco dye of the color forming layer, it is preferable to use a leuco dye whose color tone overlaps with the color tone of the second leuco dye to form black or a color tone close to black. That is, it is preferable that the various color tones of the second leuco dye form a complementary color or black to the color tone of the second leuco dye of the second color forming layer. The leuco dye is used in each coloring layer at a desired concentration, preferably from 20 to 80% by weight. The color developer used in the color developer layer is made of one or more substances that can react with the first and second leuco dyes to develop color when heated, and is made of phenolic substances and organic acidic substances. You can choose. As phenolic substances, α-naphthol,
β-naphthol, 4-t-butylphenol, 4
-t-octylphenol, 4-phenylphenol, 2,2'-bis(p-hydroxyphenyl)
Propane, 2,2'-bis(p-hydroxyphenyl)butane, 4,4'-cyclohexylidene diphenol, 2,2'-bis(2,5-dibrom-4-
hydroxyphenyl)propane, 4,4'-isopropylidene bis(2-t-butylphenol),
Examples include 2,2'-methylenebis(4-chlorophenol) and benzyl p-hydroxybenzoate. Acidic substances include boric acid, oxalic acid, maleic acid, tartaric acid, citric acid, succinic acid, benzoic acid,
Stearic acid, gallic acid, salicylic acid, 4-oxy-2-naphthoic acid, 0-oxybenzoic acid, 2-
Oxy-p-toluic acid, m-oxybenzoic acid,
Examples include 4-oxyphthalic acid. The developer concentration in the developer layer can be determined appropriately, but is generally used at a concentration of 20 to 80% by weight. As the non-color developing sensitizer in the second color forming layer, conventionally known ones can be used. Generally, waxes, terephthalic acid esters, aromatic condensed ring derivatives, biphenyl compound derivatives, aromatic amide compound derivatives, and the like, which do not cause color development of leuco dyes, are used as the non-developable sensitizer. The sensitizer is preferably one with a melting point of 70°C to 160°C, but is not necessarily limited to one having such a melting point. It can be selected as appropriate to match the design. Examples of substances that can be used as non-developing sensitizers include stearic acid amide, dimethyl terephthalate, dibenzyl terephthalate, benzyl naphthyl ether, benzyl naphthyl methyl ether, benzyl biphenyl, naphthyl biphenyl, and benzenesulfonamide. I can do it. The concentration of the non-color-developing sensitizer in the second coloring layer can be determined appropriately, but it is generally used at a concentration of 20 to 80% (by weight). In order to form the first and second color forming layers and the color developer layer, the necessary components of each layer are combined with a conventionally known binder such as starch, starch derivatives, cellulose derivatives, polyacrylic acid, polyvinyl alcohol, or polyvinylpyrrolidone, A coating liquid is prepared by grinding and mixing into fine particles using a dispersion mixer such as a ball mill, attritor, or sand mill, and then dispersing them in water. Using each coating liquid, support (e.g. paper, plastic film, synthetic system, etc.)
A first coloring layer, a color developer layer, and a second coloring layer are coated and dried on the surface of the substrate in this order. Fillers, brighteners, wetting agents, etc. are added to each layer as necessary.
A lubricant etc. can be added. Further, if chemical resistance is required, a chemical resistant layer may be coated on the surface of the second coloring layer. Examples The present invention will be further explained below with reference to Examples. [Example 1] Solutions [A] and [B] were prepared by grinding a mixture consisting of the following formulations in a magnetic ball mill for one day. [A] Liquid composition Crystal violet lactone 100g 10% polyvinyl alcohol aqueous solution 50g Water 350g [B] Liquid composition 3-(N-cyclohexyl-N-methyl-amino)
-6-Methyl-7-anilinofluorane 100 g 10% polyvinyl alcohol aqueous solution 50 g Water 350 g A mixture consisting of the following formulations was ground in a sand mill to prepare solutions [C] and [D]. [C] Liquid composition 2,2-bis(p-hydroxyphenyl)propane 100g 10% polyvinyl alcohol aqueous solution 50g Water 350g [D] Liquid composition p-benzyl-biphenyl 100g 10% polyvinyl alcohol aqueous solution 50g Water 350g Above [ B] 30g of liquid and 45% SBR latex 5
g and 10 g of water were mixed and stirred to prepare a coating liquid for the first coloring layer. This coating liquid was applied and dried on commercially available high-quality paper with a standard basis weight of 50 g/m ² using a selected wire bar so that the dry coating amount was about 2 g/m ² . On the formed first coloring layer, 30 g of [C] solution, 3 g of 45% SBR latex, and 5 g of 20% polyvinyl alcohol aqueous solution,
A developer layer coating solution prepared by mixing 10 g of water was applied and dried to a dry coating amount of about 3 g/m ² to form a developer layer. The resulting intermediate product was calendered. On the surface of the calendered developer layer, add 10 g of [Liquid A] and 10 g of [Liquid D].
, 6 g of 55% calcium carbonate aqueous dispersion, 2 g of 21% zinc stearate aqueous dispersion, 8 g of 20% polyvinyl alcohol aqueous solution, and 10 g of water were mixed to prepare a second coloring layer coating solution, and dried. The amount of application is about 3
g/m ² , dried, and further calendered. A two-color thermosensitive recording paper was obtained. This heat-sensitive recording paper is tested using a facsimile tester.
When we set the voltage to 19V and performed low-temperature thermal recording with a current application time of 1.5msec, a clear blue image was obtained. When we changed the current application time to 3.8 msec and performed high-temperature thermal recording, a clear black image was obtained. [Example 2] In solution [C] of [Example 1], benzyl p-hydroxybenzoate was used instead of 2,2-bis(p-hydroxyphenyl)propane to prepare [C].
-2] A two-color thermosensitive recording paper was obtained in the same manner as in Example 1, except for the liquid. When low-temperature recording was performed on this two-color thermosensitive recording paper under conditions of a voltage of 16 V and a current application time of 1.8 msec, clear blue recording was obtained. In addition, when we changed the current application time to 4 msec and recorded at high temperatures, a clear black recorded image was obtained. [Example 3] Dibenzyl terephthalate was used in place of p-benzyl-biphenyl in [D] solution of [Example 1] to make [D-2] solution, and the rest was the same as [Example 2]. A two-color thermosensitive recording paper was obtained. When this two-color thermosensitive recording paper was subjected to low-temperature and high-temperature recording under the same conditions as in Example 2, clear blue and black recorded images were obtained, respectively. [Comparative Example 1] 10 g of liquid C from [Example 1] was added to the first coloring layer coating solution from [Example 1] to obtain a first coloring layer coating solution, and the dry coating amount was about 3 g/m ^{2 .} On the obtained coated paper, liquids A and D of [Example 1] were applied.
10 g of each solution, 20 g of solution C, and additives, polyvinyl alcohol, and water were added in the same manner as [Example 1] to prepare a second coloring layer coating solution, and the dry coating amount was about 3 g/m ²
The mixture was coated and dried, and then calendered to obtain a two-color thermosensitive recording paper. When recording was carried out in the same manner as in [Example 1], clear two colors could not be obtained. [Comparative Example 2] When 20 g of solution [C] was added to the coating solution for the second coloring layer of [Example 1], the solution developed a blue color, and a practically usable thermosensitive recording paper could not be obtained. [Table-1] Examples 1 to 5 and Comparative Examples 1 and 2
Recording results and storage stability (40℃-30%RH 1 day)
Here are the test results.

【table】

[Table] Effects of the Invention The two-color thermosensitive recording material of the present invention has the following excellent effects. (a) Excellent color separation between two colors. (b) Since the two coloring layers and the color developer layer are separated, the degree of whiteness is high and there is no background smearing. (c) It has excellent storage stability because it does not contain a decolorizing agent.

[Brief explanation of the drawing]

The accompanying drawings are cross-sectional explanatory views showing the structure of the two-color thermosensitive recording material of the present invention. DESCRIPTION OF SYMBOLS 1...First color-developing layer, 2...Color developer layer, 3...Second color-developing layer, 4...Support.

Claims (1)

[Scope of Claims] 1. a support; a color-forming first layer formed on one surface of the support;
a first coloring layer containing a leuco dye; a color developer layer formed on the first coloring layer and containing a color developer capable of reacting with the first leuco dye to develop color by heating; , a second coloring layer formed on the color developer layer and containing the color developer and a second leuco dye that reacts with heating to develop a color tone different from the color tone of the first coloring layer; and a wax, a terephthalic acid ester, an aromatic condensed ring derivative, a biphenyl compound derivative, and an aromatic amide compound derivative, which do not cause the first and second leuco dyes to develop color only in the second coloring layer. A two-color thermosensitive recording material, characterized in that it contains at least one selected non-color developing sensitizer. 2. The heat-sensitive recording material according to claim 1, wherein the color developer comprises one or more selected from leuco dye color-developing phenolic substances and organic acid substances. 3. The second leuco dye of the second coloring layer is blue,
The heat-sensitive recording material according to claim 1, which develops a red or green tone. 4. The thermal recording material according to claim 1, which exhibits black or a color tone similar to black when the color tone of the first leuco dye of the first color layer overlaps with the color tone of the first color layer. . 5. The heat-sensitive recording material according to claim 1, wherein the content of the non-color developing sensitizer in the second coloring layer is within the range of 20 to 80% by weight.