JPH04261893A - Multicolor thermal recording material - Google Patents

Abstract

PURPOSE:To reproduce a natural color without generating color shift even in the reproduction of black line drawing by using at least a part of the color forming components contained in a transparent color forming single layer in an encapsulated state. CONSTITUTION:A cyan color forming layer, a magenta color forming layer and an yellow color forming layer are successively provided to one surface of a transparent support and a black color forming layer is provided to the other surface of the support. Then, a color forming component is contained at least in a three-layer transparent color forming single layer other than the remotest layer on a recording image looking side. The material to be used is a component generating color forming reaction based on the contact with a substance due to heating, concretely, a combination of an acidic substance and an electron donating dye precursor, a combination of an azo compound and a coupling compound or other additive. At least the electron donating dye precursor or diazo compound among those components is encapsulated from the aspects of the enhancement of transparency, raw preservability (fog prevention) and the control of color forming sensitivity before use.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor heat-sensitive recording material, and more particularly to a multicolor heat-sensitive recording material suitable for recording full-color images.

0002

[Prior Art] The thermal recording method has three main features: (1) development is not required; (2) when the support is paper, the paper quality is similar to that of ordinary paper; and (3)
) Easy to handle, (4) High color density, (5
) The recording device is simple and inexpensive, and (6) there is no noise during recording, so it has rapidly become popular in the fields of black and white facsimiles and printers. In the recording field as well, with the rapid development of the information industry, there is an increasing demand for easily obtaining color hard copies from information equipment terminals such as computers and facsimiles.

However, when trying to increase the number of color hues in a direct coloring type thermal method, for example, it is possible to cope with this by simply increasing the number of fractions of applied heating energy and widening the energy difference between each of them. It is possible to design a heat-sensitive recording material that has multiple heat-sensitive coloring layers on the same support, but in reality, if the applied heating energy is extended to a lower range than before, the shelf life of the recording material itself ( On the other hand, if the imprint heating energy is extended to a high area, problems may occur such as poor print runnability (e.g. sticking) due to image scorching or fusion, and shortening of the life of the thermal head. A serious new problem arises. Therefore, in the past, the maximum allowable fraction of the applied heating energy was actually about 2 fractions in order to satisfy the color separation property.

[0004] As a heat-sensitive recording material which solves the above-mentioned drawbacks of the conventional heat-sensitive recording material, a heat-sensitive recording material in which cyan, magenta, and yellow coloring unit layers are already provided on one side of the support (Japanese Patent Application No. 1987-1
62361) and a heat-sensitive recording material in which cyan, magenta, and yellow coloring unit layers are provided on both sides of a transparent support (Japanese Patent Application Laid-Open No. 63-45084) have been developed.

[0005]

[Problems to be Solved by the Invention] These multicolor thermosensitive recording materials are excellent in being able to reproduce multicolor images close to full color, but they suffer from color shift when reproducing black images that are often used in line drawings. There was a drawback that it occurred.

[0006] As a result of intensive studies to solve the above-mentioned drawbacks, the inventors of the present invention laminated a layer that develops heat color in cyan, magenta, and yellow hues on one side of a transparent support, and also laminated a layer on the other side of the transparent support. The present inventors have discovered that very good results can be obtained by providing a layer that thermally develops black to reproduce a black image with a single black color, and have thus arrived at the present invention.

[0007] Accordingly, the first object of the present invention is to provide a multicolor heat-sensitive recording material that does not cause color shift even when reproducing black line drawings. A second object of the present invention is to provide a multicolor thermosensitive recording material that enables better reproduction of natural colors than ever before.

[0008]

[Means for Solving the Problems] The above-mentioned objects of the present invention are to have a set of color-forming unit layers thermally coloring each hue of cyan, magenta, and yellow on one side of a transparent support, and on the other side. A multicolor thermosensitive recording material having a coloring unit layer that thermally develops a black color on its surface, wherein at least three of the coloring unit layers other than the layer furthest from the side where a recorded image is viewed are substantially transparent; , at least a diazo compound or an electron-donating dye precursor among the combination of a diazo compound and a coupler or the combination of an electron-donating dye precursor and a color developer and other additives contained as a color-forming component in the transparent color-forming unit layer. This was achieved using a multicolor thermosensitive recording material characterized by being encapsulated in microcapsules.

Next, a method for easily obtaining a good multicolor image using the multicolor heat-sensitive recording material (hereinafter abbreviated as heat-sensitive material) of the present invention will be explained with reference to the drawings. FIG. 1 shows a heat-sensitive material of the present invention in which a cyan coloring layer, a magenta coloring layer, and a yellow coloring layer are sequentially stacked on one side of a transparent support, and a black coloring layer is provided on the other side.

In this case, in order to develop color in each layer independently and make the recorded multicolor image close to natural colors, the color development layer includes:
It is preferable to employ a system of a coupling coloring reaction of a diazo compound and a light fixing reaction as disclosed in JP-A-61-40192.

That is, first, the black layer on the outer surface of one side of the support was independently colored by thermal recording with low thermal energy, and then
The uppermost yellow layer on the other side is colored independently using the same low thermal energy. Thereafter, photofixing is performed using a light source with a specific wavelength that selectively photodecomposes only the yellow diazo compound. Next, the inner magenta layer, which has low thermal sensitivity, is thermally recorded with relatively higher thermal energy than the previous time to cause the magenta layer to develop its color independently, and then a high source of a specific wavelength is used to selectively photodecompose only the magenta diazo. Photofixing is performed using Furthermore, the cyan layer located inside the magenta layer is thermally recorded with higher thermal energy than the previous time, causing it to develop color independently. In this case, the cyan layer at the bottom of the three layers does not necessarily require photofixing.

[0012] The recording of the black layer may be performed at any stage of the recording process, and may or may not be of the optical fixing type. When a photofixable diazo compound is used in the black layer, the recording stage of the black layer can be made arbitrary by providing an ultraviolet absorbing layer between the black layer and the cyan layer. Therefore, in the present invention, since cyan, magenta, yellow, or black can be independently developed on both sides of the support, good natural colors without color shift can be reproduced.

[0013] In this case, if all the coloring layers are substantially transparent layers, it is also possible to view the resulting image as a transmitted image.
In addition to being able to be viewed by projecting it like a HP, it can also be viewed as a reflected image by placing it on a white sheet.

[0014] Furthermore, by providing an opaque protective layer containing a white pigment on the outside of the outermost coloring layer (black layer or yellow layer in FIG. 1) on the side opposite to the side on which the image is viewed, the white sheet can be The image can be reproduced as a reflected image without using it. Similarly, when the purpose is to reproduce a reflected image, the coloring layer furthest from the side from which the image is viewed may be made opaque. It should be noted that those skilled in the art can easily understand that intermediate colors can be appropriately reproduced by controlling the color development of each unit by appropriately adjusting the applied heating energy. Above, an example of the multicolor coloring process of the present invention has been schematically shown,
Next, each material used in the present invention will be explained.

The material used for thermal recording according to the present invention is a component that causes a coloring reaction based on contact of substances by heating, and specifically, a combination of an acidic substance and an electron-donating dye precursor or a coupling with a diazo compound. It is a combination of compounds.

The electron-donating dye precursor in the former combination has the property of donating electrons or accepting protons such as acids to develop color.
Although not particularly limited, it is generally colorless and has partial skeletons such as lactones, lactams, sultones, spiropyrans, esters, and amides, and these partial skeletons ring-open or cleave when contacted with a color developer. A compound is used. Specifically, crystal violet lactone, benzoylleucomethylene blue, malachite green lactone, rhodamine B lactam, 1,3,3-trimethyl-6
'-Ethyl-8'-butoxyindolinobenzospiropyran and the like.

Color developers for these color formers include:
Acidic substances such as phenol compounds, organic acids or metal salts thereof, and oxybenzoic acid esters are used. The color developer preferably has a melting point of 50°C to 250°C, especially one with a melting point of 6
Phenols and organic acids that are poorly soluble in water and have a temperature of 0°C to 200°C are desirable. Specific examples of these color developers are, for example,
No. 0-132990.

The other diazo compound of the heat-sensitive recording color forming material according to the present invention is a compound that develops a desired hue by reacting with a color developer called a coupling component, which will be described later. When exposed to light, it decomposes and no longer has the ability to develop color even when a coupling component acts on it. The hue in this coloring system is mainly determined by the diazo dye produced by the reaction between the diazo compound and the coupling component. Therefore, as is well known, the coloring hue can be easily changed by changing the chemical structure of the diazo compound or the chemical structure of the coupling component, and almost any coloring hue can be obtained depending on the combination. be able to. For this reason, it is possible to contain various diazo compounds in one layer and also incorporate one type of coupling component and other additives into the same layer. In this case, each unit coloring group has a different diazo compound. It is composed of compounds, common coupling components and other additives.

There are also combinations in which separate coupling components are included in several layers and the same diazo and other additives are incorporated into each layer. At this time, each unit coloring group is composed of a different coupling component and a common diazo compound and additive. In any case, each unit coloring group is composed of one or more diazo compounds, one or more coupling components, and other additives that are combined so that the coloring hues are different.

The photodegradable diazo compound in the present invention mainly refers to aromatic diazo compounds, and more specifically refers to compounds such as aromatic diazonium salts, diazosulfonate compounds, and diazoamino compounds. Hereinafter, explanation will be given mainly using diazonium salt as a representative example.

The diazonium salt has the general formula ArN2 +
It is a compound represented by X- (wherein Ar represents a substituted or unsubstituted aromatic moiety, N2 + represents a diazonium group, and X- represents an acid anion).
.

It is generally said that the photodecomposition wavelength of a diazonium salt is its maximum absorption wavelength. It is also known that the maximum absorption wavelength of diazonium salts varies from about 200 nm to about 700 nm depending on its chemical structure ("Photodegradation and chemical structure of photosensitive diazonium salts" by Takahiro Tsunoda and Ao Yamaoka, Nippon Photo) Academic Journal 29(4) 197-2
05 page (1965)). That is, if a diazonium salt is used as a photodegradable compound, it will be decomposed by light of a specific wavelength depending on its chemical structure, and if the chemical structure of the diazonium salt is changed, it will be decomposed by light of a specific wavelength depending on its chemical structure. The hue of the pigment also changes.

In the present invention, one of the preferred embodiments is to use diazonium compounds having different photodecomposition wavelengths, but as compounds having photodecomposition wavelengths around 400 nm, 4-diazo-1-dimethylaminobenzene, 4-diazo-1-dimethylaminobenzene, 4-diazo-1-dimethylaminobenzene, -Diazo-1-diethylaminobenzene, 4-diazo-1-dipropylaminobenzene, 4-diazo-1-methylbenzylaminobenzene, 4-diazo-1-dibenzylaminobenzene, 4-diazo-1-ethylhydroxyethyl Aminobenzene, 4-diazo-1-diethylamino-3
-methoxybenzene, 4-diazo-1-dimethylamino-2-methylbenzene, 4-diazo-1-benzoylamino-2,5-diethoxybenzene, 4-diazo-1-
Morpholinobenzene, 4-diazo-1-morpholino-2
, 5-diethoxybenzene, 4-diazo-1-morpholino-2,5-dibutoxybenzene, 4-diazo-1-anilinobenzene, 4-diazo-1-tolylmercapto-2,5-diethoxybenzene, 4-Diazo-1,4-
Examples include methoxybenzoylamino-2,5-diethoxybenzene.

Compounds having a photolysis wavelength of 300 to 370 nm include 1-diazo-4-(N,N-dioctylcarbamoyl)benzene, 1-diazo-2-octadecyloxybenzene, 1-diazo-4-(4 -tert
-octylphenoxy)benzene, 1-diazo-4-(
2,4-di-tert-amylphenoxy)benzene,
1-Diazo-2-(4-tert-octylphenoxy)benzene, 1-diazo-5-chloro-2-(4-te
rt-octylphenoxy)benzene, 1-diazo-2
, 5-bis-octadecyloxybenzene, 1-diazo-2,4-bis-octadecyloxybenzene, 1-diazo-4-(N-octylteuroylamino)benzene, and the like. The photodecomposition wavelength of the aromatic diazonium compounds typified by the examples listed above can be varied widely by arbitrarily changing the substituents.

Specific examples of acid anions include Cn F2
n + 1 COO- (n represents 3 to 9), C
Examples include compounds represented by m F2 m +1 SO3 − (m represents 2 to 8). A large number of diazosulfonates that can be used in the present invention are known and can be obtained by treating each diazonium salt with a sulfite.

Among these compounds, preferred compounds include 2-methoxy, 2-phenoxy, and 2-methoxy-
4-phenoxy, 2,4-dimethoxy, 2-methyl-4
Benzenediazosulfonate having a substituent such as -methoxy, 2,4-dimethyl, 2,4,6-trimethyl, 4-phenyl, 4-phenoxy, 4-acetamide, etc., or also 4-(N-ethyl, N-benzylamino), 4-
(N,N-dimethylamino), 4-(N,N-diethylamino), 4-(N,N-diethylamino)-3-chlor, 4-pyrodinino-3-chlor, 4-morpholino-2
-methoxy, 4-(4'-methoxybenzoylamino)
-2,5-dibutoxy, 4-(4'-trimercapto)
It is a benzenediazosulfonate having a substituent such as -2,5-dimethoxy. When using these diazosulfonate compounds, it is desirable to irradiate the diazosulfonate with light to activate the diazosulfonate before printing.

[0027] Other diazo compounds that can be used in the present invention include diazoamino compounds. The diazoamino compound is a compound in which a diazo group is coupled with dicyandiamide, sarcosine, methyltaurine, N-ethylanthranic acid-5-sulfonic acid, monoethanolamine, diethanolamine, guanidine, or the like.

The color developer for the diazo compound used in the present invention is a coupling component that couples with the diazo compound (diazonium salt) to form a dye. Specific examples include 2-hydroxy-3-naphthoic acid anilide, resorcinol, and
Examples include those described in No. 287485.

Furthermore, by using two or more of these coupling components in combination, an image of any color tone can be obtained. Since the coupling reaction between these diazo compounds and the coupling component is likely to occur in a basic atmosphere, a basic substance may be added to the layer.

As the basic substance, a poorly water-soluble or water-insoluble basic substance or a substance that generates an alkali when heated is used. Examples include inorganic and organic ammonium salts, organic amines, amides, urea and thiourea and their derivatives, thiazoles, pyrroles, pyrimidines,
Piperazines, guanidines, indoles, imidazoles, imidazolines, triazoles, morpholines, piperidines, amidines, formazines,
Examples include nitrogen-containing compounds such as pyridines. Specific examples of these are described, for example, in Japanese Patent Application No. 60-132990. Two or more basic substances may be used in combination.

Materials that cause the above color reaction are selected from the viewpoint of improving the transparency of the heat-sensitive layer, from the viewpoint of shelf life (fogging prevention) such as preventing contact between the color forming agent and the color developer at room temperature, and from the viewpoint of desired printing heating. Some of the ingredients are encapsulated and used from the viewpoint of controlling color development sensitivity such as color development using energy.

[0032] A preferred microcapsule is one in which at room temperature the material isolation effect of the microcapsule wall prevents contact between the material inside and outside the capsule, and the permeability of the material increases only when heated above a certain temperature. Due to this phenomenon, the permeation start temperature can be freely controlled by appropriately selecting the capsule wall material, capsule core material, and additives. In this case, the transmission start temperature corresponds to the glass transition temperature of the capsule wall (eg, Japanese Patent Application Laid-Open No. 59-91438, Japanese Patent Application No. 190886-1986, Japanese Patent Application No. 59-99490, etc.).

[0033] In order to control the glass transition point specific to the capsule wall, it is necessary to change the type of capsule wall forming agent. Examples of the wall material of the microcapsule include polyurethane, polyurea, polyester, polycarbonate, urea-formaldehyde resin, melamine resin, polystyrene, styrene methacrylate copolymer, styrene-acrylate copolymer, gelatin, polyvinylpyrrolidone, polyvinyl alcohol, etc. . In the present invention, two or more of these polymeric substances can also be used in combination. In the present invention, among the above-mentioned polymeric substances, polyurethane, polyurea, polyamide, polyester, polycarbonate, etc. are preferable, and polyurethane and polyurea are particularly preferable.

The microcapsules used in the present invention can be microencapsulated by emulsifying a core material containing a reactive substance such as a coloring agent, and then forming a wall of a polymer material around the oil droplets. Preferably, in this case a reactant forming a polymeric substance is added to the interior of the oil droplet and/or to the exterior of the oil droplet. Details of microcapsules that can be preferably used in the present invention, such as a preferred method for producing microcapsules, are described in, for example, JP-A-59-222716.

[0035] The organic solvent for forming the oil droplets can generally be appropriately selected from high-boiling point oils, but in particular an organic solvent suitable for dissolving the color developer described below is used. In this case, it is preferable because it has excellent solubility in the color former, increases color density and color development speed during thermal printing, and reduces fog. Moreover, an organic solvent having a boiling point of 150° C. or lower can be used instead of the high boiling point oil. When making microcapsules, they can be made from an emulsion containing 0.2% by weight or more of the component to be microencapsulated.

[0036] For 1 part by weight of the diazo compound, the amount of the coupling component is 0.1 to 10 parts by weight, and the amount of the basic substance is 0.1 to 2 parts by weight.
Preferably, it is used in a proportion of 0 parts by weight. On the other hand, for 1 part by weight of the electron-donating dye precursor, add 0.3 parts of the color developer.
It is preferred to use ~160 parts by weight, preferably 0.3 to 80 parts by weight.

The preferred microcapsules produced as described above are not destroyed by heat or pressure as used in conventional recording materials, and the reactive substances contained in the core and outside of the microcapsules are It can penetrate through the microcapsule wall and react.

[0038] In the present invention, it is also possible to use a color development aid. The color development aid that can be used in the present invention is a substance that increases the color density during thermal printing or lowers the minimum color development temperature, and includes a coupling component, a basic substance, a color former, a color developer, or a diazo This is to create a situation where diazo, basic substances, coupling components, color formers, and color developers are more likely to react by lowering the melting point of the compound or the softening point of the capsule wall.

Coloring aids include phenolic compounds, alcoholic compounds, amide compounds, sulfonamide compounds, etc. Specific examples include p-tert-octylphenol, p-benzyloxyphenol, phenyl p-oxybenzoate, Benzyl carbanylate, phenethyl carbanylate, hydroquinone dihydroxyethyl ether, xylylene diol, N-hydroxyethyl-
Compounds such as methanesulfonic acid amide and N-phenyl-methanesulfonic acid amide can be mentioned. These may be contained in the core material or may be added outside the microcapsules as an emulsified dispersion.

In the present invention, when providing a substantially transparent heat-sensitive coloring layer, the color developer for the electron-donating dye precursor or diazo compound, which is the coloring agent, is an organic solvent that is sparingly soluble or insoluble in water. After being dissolved, this is mixed with an aqueous phase containing a surfactant and having a water-soluble polymer as a protective colloid, and used in the form of an emulsified dispersion.

The organic solvent used in this case can be appropriately selected from high boiling point oils. In addition to esters, preferred oils include compounds represented by the following general formulas (1) to (3), triallylmethane (e.g., tritolylmethane, tolyldiphenylmethane), and terphenyl compounds (e.g., terphenyl). ), alkyl compounds (eg, terphenyl), alkylated diphenyl ethers (eg, propyl diphenyl ether), hydrogenated terphenyl (eg, hexahydroterphenyl), diphenyl ether, and the like.

[Chemical formula 1]

In the formula, R1 represents hydrogen or an alkyl group having 1 to 18 carbon atoms, and R2 represents an alkyl group having 1 to 18 carbon atoms. p1 and q1 represent integers of 1 to 4, and
The total number of alkyl groups is 4 or less. Furthermore, R1 and R
The alkyl group of 2 is preferably an alkyl group having 1 to 8 carbon atoms.

[Case 2]

In the formula, R3 is a hydrogen atom or has 1 to 1 carbon atoms.
The alkyl group of 2 and R4 represent an alkyl group having 1 to 12 carbon atoms. n represents 1 or 2. p2 and q2 represent integers from 1 to 4. When n=1, the total number of alkyl groups is 4 or less, and when n=2, the total number of alkyl groups is 6 or less.

[Chemical formula 3]

In the formula, R5 and R6 are hydrogen atoms or
It represents the same or different alkyl groups having 1 to 18 carbon atoms. m represents an integer from 1 to 13. p3 and q3 are 1~
represents an integer of 3, and the total number of alkyl groups is 3 or less. In addition, the alkyl group of R5 and R6 is particularly preferably an alkyl group having 2 to 4 carbon atoms.

Examples of compounds represented by formula (Chemical formula 1) are:
Examples include dimethylnaphthalene, diethylnaphthalene, diisopropylnaphthalene, and the like. Examples of the compound represented by formula (Chemical formula 2) include dimethylbiphenyl, diethylbiphenyl, diisopropylbiphenyl, and diisobutylbiphenyl.

Examples of the compound represented by the formula (Chemical formula 3) are:
Examples include 1-methyl-1-dimethylphenyl-1-phenylmethane, 1-ethyl-1-dimethylphenyl-1-phenylmethane, and 1-propyl-1-dimethylphenyl-1-phenylmethane. Among these, it is particularly preferable to use esters from the viewpoint of emulsion stability of the emulsified dispersion.

Examples of esters include phosphate esters (for example, triphenyl phosphate, tricresyl phosphate, butyl phosphate, octyl phosphate, cresyl diphenyl phosphate), phthalate esters (dibutyl phthalate, 2-ethylhexyl phthalate, phthalate). Ethyl, octyl phthalate, butyl benzyl phthalate) dioctyl tetrahydrophthalate,
Benzoate esters (ethyl benzoate, propyl benzoate, butyl benzoate, isopentyl benzoate, benzyl benzoate), abietate esters (ethyl abietate, benzyl abietate), dioctyl adipate, isodecyl succinate, dioctyl azelate, Oxalate esters (dibutyl oxalate, dipentyl oxalate),
Diethyl malonate, maleate esters (dimethyl maleate, diethyl maleate, dibutyl maleate),
Tributyl citrate, sorbate esters (methyl sorbate, ethyl sorbate, butyl sorbate), sebacate esters (dibutyl sebacate, dioctyl sebacate), ethylene glycol esters (formate monoesters and diesters, butyrate monoesters and diesters) , lauric acid monoesters and diesters, palmitic acid monoesters and diesters, stearic acid monoesters and diesters, oleic acid monoesters and diesters), triacetin, diethyl carbonate, diphenyl carbonate, ethylene carbonate, propylene carbonate, boric acid esters tributyl, tripentyl borate), etc.

Among these, it is preferable to use tricresyl phosphate alone or in combination because the emulsion dispersion stability of the color developer is particularly good. It is also possible to use the above oils together or with other oils.

In the present invention, an auxiliary solvent may be added to the above-mentioned organic solvent as a low-boiling solubilizing agent. Particularly preferred examples of such co-solvents include ethyl acetate, isopropyl acetate, butyl acetate and methylene chloride. Optionally, no high boiling oil can be included and only a low boiling cosolvent can be used.

The water-soluble polymer to be contained as a protective colloid in the aqueous phase to be mixed with the oil phase containing these components is appropriately selected from known anionic polymers, nonionic polymers, and amphoteric polymers. However, polyvinyl alcohol, gelatin, cellulose derivatives, etc. are preferred.

[0051] The surfactant to be contained in the aqueous phase may be appropriately selected from anionic or nonionic surfactants that do not interact with the protective colloid to cause precipitation or aggregation. can. Preferred surfactants include sodium alkylbenzene sulfonate, sodium alkyl sulfate, dioctyl sodium sulfosuccinate, polyalkylene glycol (eg, polyoxyethylene nonylphenyl ether), and the like.

[0052] The emulsified dispersion in the present invention is produced by combining an oil phase containing the above components and an aqueous phase containing a protective colloid and a surfactant using means commonly used for fine particle emulsification, such as high-speed stirring and ultrasonic dispersion. It can be mixed and dispersed easily.

The ratio of the oil phase to the aqueous phase (oil phase weight/aqueous phase weight) is preferably from 0.02 to 0.6, particularly from 0.02 to 0.6.
．． It is preferable that it is 1-0.4. If it is less than 0.02, the aqueous phase is too large and diluted, and sufficient color development cannot be obtained;
．． On the contrary, if it is 6 or more, the viscosity of the liquid increases, resulting in inconvenience in handling and decreased stability of the coating liquid.

The light and heat sensitive recording material of the present invention can be coated using a suitable binder. As a binder, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose,
Various emulsions such as gum arabic, gelatin, polyvinylpyrrolidone, casein, styrene-butadiene latex, acrylonitrile-butadiene latex, polyvinyl acetate, polyacrylic acid ester, and ethylene-vinyl acetate copolymer can be used. The amount used is 0.5 to 5 g/m2 in terms of solid content.

In the present invention, in addition to the above-mentioned materials, acid stabilizers such as citric acid, tartaric acid, oxalic acid, boric acid, phosphoric acid, and pyrophosphoric acid can be added. The heat-sensitive layer provided as described above has extremely good transparency.

Further, the heat-sensitive material of the present invention can be viewed as a transmitted image or a reflected image from one side of the transparent support, but especially in the latter case, if the back side of the background part is visible, the image will not be visible. Since it is dull, a white pigment may be added to the heat-sensitive layer to make it look white, or a layer containing a white pigment may be additionally applied. In either case, it is effective to perform this on the outermost layer on the reflective side from the side where the recorded image is viewed.

Examples of preferred white pigments include talc, calcium carbonate, calcium sulfate, magnesium carbonate, magnesium hydroxide, alumina, synthetic silica, titanium oxide, barium sulfate, kaolin, calcium silicate, urea resin, and the like.

Furthermore, when the outermost coloring layer itself is made opaque by using a coloring component other than diazo, a color developer component, etc. used in the present invention, it is preferable to use a solid dispersion using a sand mill or the like. . In this case, each is separately dispersed in a water-soluble polymer solution. Preferred water-soluble polymers include water-soluble polymers used when making microcapsules. At this time, the concentration of water-soluble polymer is 2~
30% by weight, and coloring components other than diazo and color developer are added in amounts of 5 to 40% by weight, respectively, to this water-soluble polymer solution.

The dispersed particle size is preferably 10 μm or less. Also, the coating amount of the heat-sensitive layer is 3g/m2 to 20g/m2.
m2, particularly preferably between 5 g/m2 and 15 g/m2. If it is less than 3 g/m 2 , sufficient sensitivity cannot be obtained, and even if it is applied more than 20 g/m 2 , no improvement in quality is observed, which is disadvantageous in terms of cost.

[0060] At least one of the heat-sensitive layers in the present invention must be substantially transparent in order to improve color separation. The term "substantially transparent" as used herein means that the haze (%) (measured with an integrating sphere HTR meter manufactured by Nippon Seimitsu Kogyo Co., Ltd.) must be 40% or less. Preferably it is 30% or less, more preferably 20% or less. However, the transparency of an actual heat-sensitive layer test sample is greatly influenced by light scattering due to minute irregularities on the surface of the heat-sensitive layer. Therefore, the inherent transparency of the heat-sensitive layer, which is a problem in the present invention,
That is, when measuring the transparency inside the heat-sensitive layer using a haze meter, a simple method is to attach a transparent adhesive tape onto the heat-sensitive layer and evaluate the measured value by substantially excluding surface scattering.

In the present invention, the protective layer that may be provided on top of the heat-sensitive layer is preferably made of at least silicon-modified polyvinyl alcohol and colloidal silica if transparency is required.

The silicon-modified polyvinyl alcohol used in the present invention is not particularly limited as long as it contains a silicon atom in the molecule, but usually the silicon atom contained in the molecule is an alkoxyl group or an acyloxyl group. Alternatively, it is preferable to use one having a reactive substituent such as a hydroxyl group or an alkali metal salt thereof obtained by hydrolysis or the like. Details of the method for producing modified polyvinyl alcohol containing silicon atoms in the molecule are given in JP-A-58-
It is described in Public Relations No. 193189.

The colloidal silica used in the present invention is used as a colloidal solution in which ultrafine particles of silicic anhydride are dispersed in water using water as a dispersion medium. The particle size of colloidal silica is 10 mμ to 100 mμ, and the specific gravity is 1.1 to 1.
3 is preferred. In this case, the colloidal solution preferably has a pH value of about 4 to about 10.

When the above-mentioned protective layer is provided on the surface of the heat-sensitive recording material, the surface scattering phenomenon is suppressed as in the case where the above-mentioned transparent adhesive tape is applied, and the transparency of the protective layer is extremely good. The transparency of the entire material can be further improved. In addition, when this protective layer is provided as the outermost layer of the recording material, it improves the mechanical strength of the surface of the heat-sensitive layer, and when it is provided as an intermediate layer between heat-sensitive layers, it serves to prevent unnecessary color mixing between the layers. can also play an additional role.

A suitable blending ratio of silicon-modified polyvinyl alcohol and colloidal silica in the present invention is 0.5 to 3 parts by weight, more preferably 1 to 3 parts by weight of colloidal silica to 1 part by weight of silicon-modified polyvinyl alcohol.
2 parts by weight. If the amount of colloidal silica used is less than 0.5 parts by weight, the effect of improving transparency will be small, and if it is used more than 3 parts by weight, cracks will occur in the protective layer, and the transparency will be reduced.

The protective layer may further contain one or more polymers. Specific examples of polymers that can be used in combination include:
Methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, starches, gelatin, gum arabic, casein, styrene-maleic anhydride copolymer hydrolyzate, styrene-maleic anhydride copolymer half ester hydrolyzate, polyvinyl alcohol, carboxy-modified polyvinyl Water-soluble polymers such as alcohol, polyacrylamide derivatives, polyvinylpyrrolidone, sodium polystyrene sulfonate, sodium alginate, etc., and styrene-butadiene rubber latex, acrylonitrile-bradiene rubber latex, methyl acrylate-butadiene rubber latex, polyvinyl acetate emulsion, etc. Examples include water-insoluble polymers. The amount used in combination is preferably 0.01 to 0.5 parts by weight per 1 part by weight of silicon-modified polyvinyl alcohol.

Pigments, metal soaps, wax, crosslinking agents, etc. are added to the protective layer for the purpose of improving matching with the thermal head during thermal printing and improving the water resistance of the protective layer. Pigments include zinc oxide, calcium carbonate, barium sulfate,
Examples include titanium oxide, lithopone, talc, Rouseki, kaolin, aluminum hydroxide, amorphous silica, etc., and the amount added thereof is 0.05 to 2 times the total weight of the polymer, particularly preferably 0.1 to 0.5 times. That's double the amount. If the amount is less than 0.05 times, it will not contribute to improving the matching performance with the head;
If the amount is more than double the amount, the transparency and sensitivity of the heat-sensitive recording material will drop significantly, impairing its commercial value.

[0068] Metal soaps include emulsions of higher fatty acid metal salts such as zinc stearate, potassium stearate, and aluminum stearate.
．． It is added in a proportion of 5 to 20% by weight, preferably 1 to 10% by weight. Waxes include emulsions such as paraffin wax, microcrystalline wax, carnauba wax, methylroll stearamide, polyethylene wax, silicone, etc., and the amount is 0.5 to 0.5 of the total weight of the protective layer.
It is added in an amount of 40% by weight, preferably 1-20% by weight.

Furthermore, in order to uniformly form a protective layer on the heat-sensitive layer, a surfactant is added to the coating solution for forming the protective layer. Surfactants include sulfosuccinic acid-based alkali metal salts, fluorine-containing surfactants, etc. Specifically, di-(2-
Examples include sodium salts or ammonium salts of ethylhexyl)sulfosuccinic acid, di-(n-hexyl)sulfosuccinic acid, and the like.

Further, a surfactant, a polymer electrolyte, etc. may be added to the protective layer to prevent charging of the heat-sensitive recording material. The solid content coating amount of the protective layer is usually 0.2 to 5 g/m
2 is preferable, and more preferably 1 g/m2 to 3 g/m2. If transparency is not required for the protective layer, a known protective layer may be provided as appropriate.

Next, the transparent support used in the present invention will be described. The transparent supports mentioned here include polyester films such as polyethylene terephthalate and polybutylene terephthalate, cellulose derivative films such as cellulose triacetate films, polystyrene films, polypropylene films, polyolefin films such as polyethylene, etc. It can be used alone or in combination. The thickness of the transparent support is 2
0 to 200 μm is used, especially 50 to 100 μm.
m is preferred.

In the present invention, an undercoat layer can be provided between the transparent support and the heat-sensitive layer in order to enhance the adhesion between the two layers.As the material for the undercoat layer, gelatin, synthetic polymer latex, Nitrocellulose and the like are used. The coating amount of the undercoat layer is preferably in the range of 0.1 g/m2 to 2.0 g/m2, particularly 0.2 g/m2 to 1.0 g/m2.
A range of g/m2 is preferred.

If it is less than 0.1 g/m2, the adhesion between the support and the heat-sensitive layer is insufficient, and even if it is increased to 2.0 g/m2 or more, the adhesion between the support and the heat-sensitive layer has reached saturation. Therefore, it is disadvantageous in terms of cost.

The undercoat layer is hardened using a hardening agent, since the image quality of the heat-sensitive layer may deteriorate if the heat-sensitive layer swells due to the water contained in the heat-sensitive layer when it is coated thereon. It is desirable to

[0075] As hardeners that can be used in the present invention, the following can be mentioned. (1) Divinylsulfone N,N'-ethylenebis(vinylsulfonylacetamide), 1,3-bis(vinylsulfonyl)-2-
Propanol, methylene bismaleimide, 5-acetyl-1,3-diacryloyl-hexahydro-s-triazine, 1,3,5-triacryloyl-hexahydro-
s-triazine, 1,3,5-trivinylsulfonyl-
Active vinyl compounds such as hexahydro-s-triazine.

(2) 2,4-dichloro-6-hydroxy-s-triazine sodium salt, 2,4-dichloro-
6-methoxy-s-triazine, 2,4-dichloro-6
-(4-sulfoanilino)-s-triazine sodium salt, 2,4-dichloro-6-(2-sulfoethylamino)-s-triazine, N-N'-bis(2-chloroethylcarbamyl)piperazine active halogen compounds such as

(3) Bis(2,3-epoxypropyl)
Methylpropylammonium p-toluenesulfonate, 1,4-bis(2',3'-epoxypropyloxy)butane, 1,3,5-triglycidyl isocyanurate, 1,3-diglycidyl-5-(γ -acetoxy-
Epoxy compounds such as β-oxypropyl) isocyanurate.

(4) Ethyleneimino compounds such as 2,4,6-triethylene-s-triazine, 1,6-hexamethylene-N,N'-bisethyleneurea, and bis-β-ethyleneiminoethylthioether.

(5) Methanesulfonic acid ester compounds such as 1,2-di(methanesulfonoxy)ethane, 1,4-di(methanesulfonoxy)butane, and 1,5-di(methanesulfonoxy)pentane.

(6) dicyclohexylcarbodiimide,
1-Cyclohexyl-3-(3-trimethylaminopropyl)carbodiimide-p-trienesulfonate, 1
- Carbodiimide compounds such as ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride.

(7) Isoxazole such as 2,5-dimethylisoxazole perchlorate, 2-ethyl-5-phenylisoxazole-3'-sulfonate, 5,5'-(paraphenylene)bisisoxazole system compound. (8) Inorganic compounds such as chromium alum and chromium acetate.

(9) Dehydrated condensed peptide reagents such as N-carboethoxy-2-isopropoxy-1,2-dihydroquinoline and N-(1-morpholinocarboxy)-4-methylpyridinium chloride; N,N'- Active ester compounds such as adipoyldioxydisuccinimide and N,N'-terephthaloyldioxydisuccinimide.

(10) Isocyanates such as toluene-2,4-diisocyanate and 1,6-hexamethylene diisocyanate. (11) Glutaraldehyde, glyoxal, dimethoxyurea, 2,3-dihydroxy-
Aldehydes such as 1,4-dioxane.

Among these, dialdehydes such as glutaraldehyde and 2,3-dihydroxy-1,4-dioxane, and boric acid are particularly preferred. The amount of these hardeners added is in the range of 0.20% to 3.0% by weight based on the weight of the undercoat material, and the appropriate amount should be selected depending on the application method and desired degree of curing. Can be done.

If the amount added is less than 0.20% by weight, the degree of curing will be insufficient no matter how long it is allowed to last, and the undercoat layer will swell when the heat-sensitive layer is applied. If the amount is more than 1, the degree of curing will proceed too much, and the adhesion between the undercoat layer and the support will deteriorate, resulting in the disadvantage that the undercoat layer will become film-like and peel off from the support.

Depending on the curing agent used, if necessary, the pH of the solution can be made alkaline by adding caustic soda, or the pH of the solution can be made acidic by using citric acid or the like. It is also possible to add an antifoaming agent to eliminate foam generated during coating, or to add an activator to improve liquid leveling and prevent coating streaks. .

Furthermore, before applying the undercoat layer, it is desirable to activate the surface of the support by a known method. Activation treatment methods include acid etching treatment,
Flame treatment using a gas burner, corona treatment, glow discharge treatment, etc. are used, but from the point of view of cost or simplicity, US Pat. No. 2,715,075, US Pat.
No. 846,727, No. 3,549,406, No. 3
, 590, 107, etc., is most preferably used.

The heat-sensitive recording material of the present invention is produced by preparing a coating liquid containing microcapsules encapsulating an electron-donating dye precursor or a diazo compound, a dispersion in which at least a color developer is emulsified and dispersed, and other additives such as a binder. , bar coating, blade coating, air knife coating, gravure coating, roll coating coating on supports such as synthetic resin films,
It is manufactured by coating and drying by a coating method such as spray coating or dip coating to provide a heat-sensitive layer having a solid content of 2.5 to 25 g/m2.

[0089] If necessary, US Pat. No. 2,761,7
No. 91, No. 3,508,947, No. 2,941,
No. 898, and the specification of No. 3,526,528, Yuji Harasaki, "Coating Engineering", p. 253 (published by Asakura Shoten, 1973), etc., by dividing into two or more layers and applying them simultaneously. is also possible, and an appropriate method can be selected depending on the coating amount, coating speed, etc.

[0090] Adding pigment dispersants, thickeners, flow modifiers, antifoaming agents, foam inhibitors, mold release agents, colorants, etc. to the coating liquid used in the present invention, as necessary, is a characteristic feature. There is no problem as long as it does not damage the

The heat-sensitive material of the present invention can be used as a printer sheet for facsimiles and electronic computers that require high-speed recording. In this case, unlike ordinary facsimiles and printers, it is desirable to use a device that has so-called double-sided thermal heads that can perform thermal recording on both sides simultaneously. It is also possible to record on one side using a conventional single thermal head and then turn the sheet over to thermally record the opposite side. Further, when a diazo compound is used as a coloring component, an exposure zone for photolysis is provided.

There are roughly two types of methods for arranging print heads and exposure zones. One is to perform photolysis light irradiation after printing once, and before and after this light irradiation, the recording material is in a state where it is ready for printing so that it can be printed again at the place where it was printed once by the feeding mechanism of the recording material. There is a so-called one-head multi-scan method in which the recording material returns to its original position, then prints again, then irradiates the light again, and the recording material returns to its original position. This is a so-called multi-head one-scan method that has a light irradiation zone between them, and both methods may be combined as necessary, or the thermal energy applied to the head may be changed as necessary. It's okay.

As a light source for photolysis, various light sources that emit light of a desired wavelength can be used, such as various fluorescent lamps, xenon lamps, xenon flash lamps, mercury lamps at various pressures, photographic flashes, Various light sources such as strobes can be used. Further, in order to make the optical fixing zone compact, the light source section and the exposure section may be separated using an optical fiber. In some cases, it is also possible to obtain a multicolor sample by placing the printed recording material under sunlight or a fluorescent lamp, fixing it mainly with light in the visible light range, and then printing again.

[0094]

[Effects of the Invention] As detailed above, in the present invention,
Since black images can be reproduced using a single black color, it is possible to produce multicolor images with excellent hue, excellent color separation without color shift, and good image storage stability that could not be obtained using conventional thermal recording methods. Obtainable. Furthermore, the present invention is of great significance because the obtained image can be either a transmission image or a reflection image, and it opens the way to the formation of natural color images using non-silver halide photography. Furthermore, since an inexpensive leuco coloring agent can be used to reproduce black, an economical multicolor thermosensitive recording material that can reproduce good natural color images can be produced using inexpensive materials.

[0095]

[Examples] The present invention will be further explained with reference to Examples below, but the present invention is not limited thereto. Note that "parts" indicating the amount added represent "parts by weight."

Example 1. Preparation of capsule liquid A

[Table 1] Diazo compounds represented by the following (Chemical formula 4)
3.4 parts

[C4
] Tricresyl phosphate

6 parts methylene chloride

12 parts trimethylolpropane trimethacrylate 18
Takenate D-110N (75% by weight ethyl acetate solution) (manufactured by Takeda Pharmaceutical Co., Ltd. (trade name))
24 copies

[
[0097] The components shown in Table 1 above were mixed, added to an aqueous solution consisting of 63 parts of an 8% by weight aqueous solution of polyvinyl alcohol and 100 parts of distilled water, and then emulsified and dispersed at 20°C.
An emulsion with an average particle size of 2 μm was obtained. Next, the obtained emulsion was continuously stirred at 40° C. for 3 hours. After cooling this liquid to 20°C, 100 cc of Amberlite IR-120B (manufactured by Rohm and Haas (trade name)) was added, stirred for 1 hour, and then filtered to obtain capsule liquid A.

Preparation of coupler/base dispersion A (emulsified dispersion) 1. Polyvinyl alcohol 4% by weight aqueous solution
170 copies

[Table 2] 2. A coupler represented by the following (Chemical formula 5)
14 parts

[Chemical formula 5] Triphenylguanidine (base)
6
Part Coloring aid represented by the following (Chemical formula 6)
14
Department

[Chemical formula 6] Tricresyl phosphate
1
0 parts ethyl acetate

20 copies

The above solution 2 was added to the aqueous solution 1 and emulsified and dispersed at 20°C to obtain an emulsified dispersion. Preparation of capsule liquid B

[Table 3] Basic colorless dye (Bl
ue #200 Yamada Chemical Co., Ltd.) 14 copies

[Chemical formula 7] 1-phenyl-1-xylylethane
55 copies
methylene chloride

55 parts Sumisorb 200 (ultraviolet absorber manufactured by Sumitomo Chemical Co., Ltd.)
2 parts Takenate D-110N (manufactured by Takeda Pharmaceutical Co., Ltd. (trade name)) 60 parts

0100
] The components shown in Table 3 above were mixed, added to an aqueous solution consisting of 100 parts of an 8% by weight aqueous solution of polyvinyl alcohol and 40 parts of distilled water, and then emulsified and dispersed at 20°C to form an emulsion with an average particle size of 1μ. I got the liquid. Next, the obtained emulsion was heated at 40°C.
Stirring was continued for 3 hours to obtain Capsule Liquid B.

Preparation of capsule liquid C Diazo compound represented by the following (Chemical formula 8)

Capsule liquid C was obtained in the same manner as capsule liquid A using [Image Omitted].

Preparation of coupler/base dispersion C (emulsified dispersion) 1. Polyvinyl alcohol 4% by weight
170 copies

[Table 4] 2. A coupler represented by the following (Chemical formula 9)
14 parts

[Chemical 9] Triphenylguanidine (base)
6
Part Coloring aid represented by the following (Chemical formula 10)
14 parts

[Chemical formula 10] Tricresyl phosphate

10 parts ethyl acetate

20 copies

The above solution 2 was added to the aqueous solution 1 above to obtain an emulsion-dispersed paper emulsion at 20°C. Preparation of capsule liquid D Leuco dye represented by the following (Chemical formula 11)

embedded image 0.5 part of trimethylolpropane (3:1) adduct of xylene diisocyanate and 3 parts of ethyl acetate or isopropyl acetate were mixed and dissolved.

The solution prepared above was emulsified and dispersed in a solution prepared by dissolving 0.26 parts of polyvinyl alcohol in 3 parts of water using a homogenizer (manufactured by Nippon Seiki Co., Ltd.). Next, 10 parts of water was added and heated to about 60° C. for 2 hours while stirring to obtain leuco dye capsule liquid D.

Preparation of color developer dispersion D

[Table 5] Bisphenol A

20 parts polyvinyl alcohol

Part 5 Water

100 copies

0106
] The above composition was dispersed overnight using a sand mill to obtain a dispersion having an average particle size of 3μ. Preparation of coating solution

[Table 6] (1) Preparation of coating liquid A (cyan) Capsule liquid B

5 parts Color developer dispersion A (emulsified dispersion)

10 parts distilled water

5th part

[0107] Each component shown in Table 6 above was stirred and mixed to prepare a coating liquid A. (3) Preparation of coating liquid B (magenta)

[Table 7] Capsule liquid C

4.9 parts Hydroquinone 5% by weight aqueous solution

0.2 parts coupler/base dispersion C (emulsified dispersion)
3.7 parts

0
[108] Each component shown in Table 7 above was stirred and mixed to prepare a coating liquid B. (5) Preparation of coating liquid C (yellow)

[Table 8] Capsule liquid A

4.9 parts Hydroquinone 5% by weight aqueous solution

0.2 parts coupler/base dispersion A (emulsion)
3.7 parts

[0109] Each component shown in Table 8 above was stirred and mixed to prepare a coating liquid C. (4) Adjustment of coating liquid D (black)

[Table 9] Capsule liquid D

5 parts Color developer dispersion D (emulsion)

10 parts distilled water

5th part

0110
] Preparation of Recording Sheet A A biaxially stretched polyethylene terephthalate film with a thickness of 75 μm was used as a transparent support, and after corona treatment was applied to both sides, coating solution A was applied to one side, and then an intermediate layer having the following composition was applied. Liquid B, intermediate layer, coating liquid C, and coating liquid D were applied to the opposite side in order, and the dry weight of each of coating liquids A, B, C, and D was 12 g/m2, and that of the intermediate layer was 2 g/m2. It was prepared so that Next, a protective layer having the same composition as the intermediate layer was provided on both sides at a thickness of 2 g/m 2 to obtain a recording sheet A.

Composition of intermediate layer (protective layer)

[Table 10] Silica-modified polyvinyl alcohol (PVA R2105, manufactured by Kuraray Co., Ltd.): 1 part (solid content) Colloidal silica (Snowtex, manufactured by Nissan Chemical Co., Ltd.)
30): 1.5 parts (solid content) Zinc stearate (Hydrin manufactured by Chukyo Yushi Co., Ltd.)
Z-7): 0.02 part (solid content) Paraffin wax (Hydrin manufactured by Chukyo Yushi Co., Ltd.
P-7): 0.02 part (solid content)

Preparation of recording sheet B (for comparison) Recording sheet B was prepared in the same manner as recording sheet A except that coating liquid D was not applied.
was created. When energy of 30 mJ/mm2 was applied to each side of recording sheet A at several random locations using a thermal head (manufactured by Kyocera Corporation), yellow and black colors appeared on both sides, respectively. Next, Ricopy Super Dry 100 type (manufactured by Ricoh Co., Ltd.)
After light irradiation (400 to 430 nm) was carried out for 10 seconds on the yellow coloring side using the same method, 60 mJ/mm2 of energy was applied from the yellow coloring side in the same manner, and the lower layer developed a magenta color. Next, light irradiation (340 to 380 nm) was performed using Ricopy Super Dry 100 type.
was applied to the yellow coloring side for 10 seconds, and then 100 mJ/m was applied from the yellow coloring side using a thermal head.
When an energy of m2 was applied, the lower layer developed a cyan color.

As described above, when printing at a low temperature before irradiation with light, both sides of the recording sheet are colored black and yellow, respectively.
Next, a magenta image was obtained by photodecomposing the diazo compound (yellow coloring layer) by irradiation with light and then printing at a somewhat high temperature. Furthermore, after the diazo compound in the magenta color-forming layer was photodecomposed by light irradiation, cyan color was developed by printing at an even higher temperature. As a result, when this sheet is viewed as a transparent image from one side, the color images are clear and vague in cyan, magenta, yellow, blue (cyan + magenta), green (cyan + yellow), red (yellow + magenta) and black. A colored image was obtained without the necessary color mixture, color bleeding, and black color shift. Even when a white sheet was placed on the black side of the obtained image and the image was viewed as a reflective image, a clear, reflective multicolor image without unnecessary color mixing, color blurring, or black color shift was obtained.

[0114]

[Comparative Example] Recording was performed on recording sheet B in the same manner as recording sheet A, but a multicolor image was obtained which was inferior in terms of black color shift.

[Brief explanation of the drawing]

FIG. 1 is a conceptual cross-sectional diagram showing the state of color development when thermal printing is performed on the heat-sensitive material of the present invention.

[Explanation of symbols]

Code 1 is green Code 2 is yellow code 3 is red Code 4 is black Code 5 is blue Code 6 is cyan Code 7 is magenta

Claims (1)

[Claims] [Claim 1] A multicolor thermosensitive recording having, on one side of a transparent support, a set of coloring unit layers that thermally develop colors in cyan, magenta, and yellow hues, and having a black coloring unit layer on the other side. A material in which at least three of the color-forming unit layers other than the layer furthest from the viewing side of the recorded image are substantially transparent, and a diazo compound is contained as a color-forming component in the transparent color-forming unit layer. and a coupler, or a combination of an electron-donating dye precursor and a developer, and other additives, at least a diazo compound or an electron-donating dye precursor is encapsulated in microcapsules. Heat-sensitive recording material.