JPS63134281A - Thermal recording material - Google Patents

Abstract

PURPOSE:To improve an image contrast by providing a thermosensitive layer and a transparent layer on a substrate by applying a coating liquid wherein microcapsules containing a basic dye precursor and a developer are emulsified and dispersed. CONSTITUTION:A dispersion liquid wherein microcapsules containing a basic dye precursor and a developer dissolved in an organic solvent difficult to be solved or insoluble in water are emulsified and dispersed is applied to an dried on a substrate to provide a thermosensitive layer. Further, a transparent layer that is turned opaque by heat and/or pressure is laminated on the thermosensitive layer to obtain a thermosensitive recording material. Triaryl methane compound, diphenylmethane compound or the like is preferable as the basic dye precursor. The developer, for example, for leuco dye includes phenol compound, triphenylmethane compound, sulfur-containing phenolic compound and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a heat-sensitive recording material. More specifically, the present invention relates to a heat-sensitive recording material with excellent optical readability.

(Prior art) The thermal recording method has three advantages: (1) no development is required; (2) when the support is paper, the quality of the paper is similar to that of ordinary paper; (3) it is easy to handle; and (4) color density is high. (5) The recording device is simple and inexpensive, and (6) There is no noise during recording, so it has rapidly become popular in the field of facsimiles and printers in recent years, and the applications of thermal recording are also expanding. are doing.

Against this background, in recent years, in order to adapt to multicolor, overhead projectors (
It is desired to develop transparent heat-sensitive recording materials that can be directly recorded with a thermal recorder for use in OHP applications.

Therefore, in recent years, emulsified dispersions in which microcapsules containing a colorless or light-colored basic dye precursor and a color developer dissolved in an organic solvent that is sparingly soluble or insoluble in water are emulsified and dispersed on a support have been developed. A heat-sensitive recording material has been proposed in which a coating liquid is coated and dried.

(Problems to be Solved by the Invention) However, from the viewpoint of use in 0) IP or color reproduction in multicoloring, further improvements in image contrast have been desired.

Therefore, an object of the present invention is to provide a heat-sensitive recording material that has even better image contrast than conventional heat-sensitive recording materials.

(Means for Solving the Problem) The above object of the present invention is to provide microcapsules containing a colorless or light-colored basic dye precursor, and a color developer dissolved in an organic solvent that is sparingly soluble or insoluble in water. A heat-sensitive layer obtained by emulsifying and dispersing the above, applying and drying a coating solution containing the obtained emulsified dispersion, and a transparent layer that becomes opaque by heat and/or pressure are laminated on a support. Achieved by heat-sensitive recording materials.

(Function) As described above, when a layer that develops color when heated and a layer that becomes opaque are laminated, the image area is not only colored but also becomes opaque by thermal printing by the thermal head. The image contrast is better than in the case of a heat-sensitive recording material having each heat-opaque layer individually, and this effect is particularly remarkable when the heat-sensitive record of the present invention is produced for OHP use using a transparent support.

In the present invention, the layer that becomes opaque by heat and/or pressure (heat-sensitive/pressure-sensitive opaque layer) includes, for example, JP-A-61
Layers of polymer mixtures which phase separate and become opacified by heat, such as those described in US Pat. Water-soluble polymers such as acid copolymer hydrolyzate, styrene-maleic anhydride copolymer Hafestel hydrolyzate, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, polyacrylamide derivatives, polyvinylpyrrolidone, sodium polystyrene sulfonate, sodium alginate, etc. Polymers such as water-insoluble polymers such as styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex, polyvinyl acetate emulsion, preferably rubber latexes, styrene/maleic acid copolymers A layer that has a layer on top that becomes apparently transparent because the surface flatness is disturbed by heat and/or pressure, a layer that contains fine particles that foam when exposed to heat, or a layer that itself foams when exposed to heat. The layers obtained can be mentioned.

As the basic dye precursor used in the heat-sensitive coloring layer of the present invention, a colorless or light-colored one is appropriately selected from known compounds that develop color by donating electrons or accepting protons such as acids. Such compounds have partial skeletons such as lactones, lactams, sultones, spiropyrans, esters, and amides, and these partial skeletons are ring-opened or cleaved upon contact with a color developer. Preferred compounds include Examples include triarylmethane compounds, diphenylmethane compounds, xanthine compounds, thiazine compounds, and spiropyran compounds.

A particularly preferred compound is a compound represented by the following general formula.

In the formula, R1 is an alkyl group having 1 to 8 carbon atoms, R2 is an alkyl group having 4 to 18 carbon atoms, an alkoxyalkyl group, or a tetrahydrofurfuryl group, and R3 is a hydrogen atom or an alkyl group having 1 to 15 carbon atoms. Alternatively, the halogen atom and R4 represent a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

As the substituent for R4, an alkyl group having 1 to 5 carbon atoms, an alkoxy group, a halogenated alkyl group, and a halogen atom are preferable.

In the present invention, by encapsulating the above-mentioned coloring agent in microcapsules, it is possible to prevent fogging during the production of heat-sensitive materials, and at the same time, to improve the shelf life and archival properties of heat-sensitive materials. can. In this case, it is possible to increase the image density during recording by selecting the wall material and manufacturing method of the microcapsule.The amount of color former used is preferably 0.05 to 5.0 g/m2.

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 are preferably 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. In this case, a polymeric material is formed or an actant 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.

Here, the organic solvent for forming the oil droplets can be appropriately selected from those generally used as pressure-sensitive oils, but in particular, organic solvents that have been used to dissolve the color developer described below are used. In this case, it is preferable because it has excellent solubility in leuco dyes, increases the color density and speed of color development during thermal printing, and also reduces fogging.

In the present invention, the size of the microcapsules is preferably 2 μm or less, particularly preferably 1 μm or less, as measured by the measurement method described in JP-A No. 60-214990.

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

In the present invention, the wall material of the microcapsule is selected,
If necessary, a glass transition point adjusting agent (for example, Japanese patent application 1986-
119862) to prepare microcapsules consisting of walls with different glass transition points, and by selecting combinations of basic dye precursors with different hues and their color developers, multicolored It is possible to achieve intermediate colors. Therefore, the present invention is not limited to single-color thermal paper, but can also be applied to two-color or multi-color thermal paper and thermal paper that has been subjected to gradation image recording.

Further, if necessary, a photofading inhibitor described in, for example, Japanese Patent Application No. 60-125470, Japanese Patent Application No. 60-125471, and Japanese Patent Application No. 60-125472 can be appropriately added.

The color developer used in the present invention, which causes a color-forming reaction by thermal melting with the basic dye precursor, can be appropriately selected from known ones. For example, color developers for leuco dyes include phenolic compounds, triphenylmethane compounds, sulfur-containing phenolic compounds, carboxylic acid compounds, sulfonic acid compounds, urea or thiourea compounds, etc. is described, for example, in Paper and Pulp Technology Times (1985), pages 49-54 and 65-70. Among these, especially those with a melting point of 50℃~
250°C is preferable, especially 60°C to 200°C,
Phenols and organic acids that are poorly soluble in water are preferred, and the use of two or more color developers in combination is preferred because solubility increases.

Among the color developers used in the present invention, particularly preferred ones are represented by the following general formulas (1) to (IV).

[1] m-0 to 2, n=2 to 11 [■] H R1 is an alkyl group, an aryl group, or an aralkyl group, and a methyl group, an ethyl group, and a butyl group are particularly preferred.

(III) R2 is an alkyl group, especially a butyl group, a pentyl group,
Heptyl and octyl groups are preferred.

(IV) R3 is an alkyl group or an aralkyl group.

In the present invention, a color developer is dissolved in an organic solvent that is sparingly soluble or insoluble in water, and then mixed with an aqueous phase containing a surfactant and having a water-soluble polymer as a protective colloid to emulsify and disperse it. Use in the form of a dispersion.

The organic solvent for dissolving the color developer can be appropriately selected from those commonly used as pressure-sensitive oils.
In particular, oils having two or more benzene rings and the number of heteroatoms equal to or less than the group constant are preferred. Such oils include compounds represented by the following general formulas (V) to (■) and triallylmethane. (e.g. tritolylmethane, tolyldiphenylmethane), terphenyl compounds (e.g.
terphenyl), alkylated diphenylethyl (eg, propyl diphenyl ether), hydrogenated terphenyl (eg, hexahydroterphenyl), diphenyl ether, and the like.

(V) In the formula, R1 is hydrogen or an alkyl group having 1 to 18 carbon atoms,
R2 represents an alkyl group having 1 to 18 carbon atoms, pl, q
l represents an integer of 1 to 4, and the total number of alkyl groups is 4
No more than 100 pieces.

In addition, the alkyl group of R1 and R2 is preferably an alkyl group having 1 to 8 carbon atoms.

(Vl) In the formula, R3 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, R4 represents an alkyl group having 1 to 12 carbon atoms, and n represents 1 or 2.

R2 and ql represent integers of 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.

(■) 1; Parable ・=・In the formula, R5,
R6 represents a hydrogen atom or the same or different alkyl group having 1 to 18 carbon atoms.

m represents an integer of 1 to 13, p3 and q3 represent integers of 1 to 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 the compound represented by formula (V) include dimethylnaphthalene, diethylnaphthalene, and diisopropylnaphthalene.

Examples of the compound represented by formula (VI) include dimethylbiphenyl, diethylbiphenyl, diisopropylbiphenyl, and diisobutylbiphenyl.

Examples of compounds represented by formula (■) include 1-methyl-
1-dimethylphenyl-1-phenylmethane, 1-ethyl-1-dimethylphenyl-1-phenylmethane, 1-
Propyl-1-dimethylphenyl-1-phenylmethane is mentioned.

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-point solubilizing agent. Particularly preferred examples of such co-solvents include ethyl acetate, isopropyl acetate, butyl acetate and methylene chloride.

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

Further, as the surfactant to be contained in the aqueous phase, one can be appropriately selected from anionic or nonionic surfactants that do not cause precipitation or aggregation by interacting with the above-mentioned protective colloid. .

Preferred surfactants include sodium alkylbenzenesulfonate (eg, sodium lauryl sulfate), dioctyl sodium sulfosuccinate, polyalkylene glycol (eg, polyoxyethylene nonylphenyl ether), and the like.

The emulsified dispersion of a color developer in the present invention is produced by mixing an oil phase containing a color developer and an aqueous phase containing a protective colloid and a surfactant by means of ordinary methods used for fine particle emulsification, such as high-speed stirring and ultrasonic dispersion. It can be easily mixed and dispersed using.

A melting point depressant for a color developer may be added to this emulsified dispersion as appropriate. Some of these melting point depressants are
It also functions as a glass transition point regulator for the capsule wall. Examples of such compounds include hydroxy compounds, carbamate ester compounds, sulfonamide compounds, aromatic methoxy compounds, etc. For details, see
For example, it is described in Japanese Patent Application No. 59-244190.

These melting point depressants can be used in an amount of 0.1 to 2 parts by weight, preferably 0.5 to 1 part by weight, per 1 part by weight of the color developer that lowers the melting point. It is preferable that the color developer and the color developer whose melting point is lowered thereby are used at the same location. When adding to different locations, it is preferable to add 1 to 3 times the above amount.

The heat-sensitive recording material of the present invention can be coated using a suitable binder.

Binders include polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxypropylcellulose, gum arabic, gelatin, polyvinylpyrrolidone, casein, styrene-butadiene latex, acrylonitrile-butadiene latex, polyvinyl acetate, polyacrylic acid ester, ethylene-vinyl acetate, etc. Various emulsions such as polymers can be used. The amount used is 0.2 to 5 g/m2 as solid content.

In the present invention, the order of stacking the heat-sensitive coloring layer and the heat-sensitive/pressure-sensitive opacifying layer is arbitrary, but from the viewpoint of being able to select the coloring hue of the image, It is preferable to laminate coloring layers. Therefore, in producing the heat-sensitive recording material of the present invention, first, a solution, latex, or emulsion of the polymer that becomes unfavorable when heated is coated with a bar or blade on a support such as paper or various synthetic resin films. , air knife application, gravure application, roll coating application, spray application,
After coating and drying using a coating method such as dip coating, microcapsules containing a color former and a dispersion containing at least a color developer are mixed so that the solid content after drying is 2.5 to 25 g/m2. It is preferable to provide a heat-sensitive coloring layer by coating a coating liquid containing the components and other additives such as a binder on the heat-sensitive/pressure-sensitive opacifying layer.

A protective layer can be further provided on the heat-sensitive coloring layer thus produced.

In the protective layer, for the purpose of improving the matching property with the thermal head during thermal printing and improving the water resistance of Ho1JTra, etc.
It is preferable to add pigments, metal soaps, waxes, crosslinking agents, etc.

Pigments include zinc oxide, calcium carbonate, barium sulfate, titanium oxide, lithopone, talc, Rouseki, kaolin, aluminum hydroxide, amorphous silica, etc., and the amount added is 0.05 to 2.0% of the total weight of the polymer. The amount is particularly preferably 0.1 to 0.5 times. If the amount is less than twice the amount of O,OS, it is ineffective in improving the matching property with the head, and if the amount is more than twice the amount, the transparency and sensitivity of the heat-sensitive recording material will be significantly reduced, impairing its commercial value.

Metal soaps include emulsions of higher fatty acid metal salts such as zinc stearate, calcium stearate, and aluminum stearate, and contain 0.5 to 20 f of the total weight of the protective layer.
It is added in an amount of only % fi, preferably 1 to 1% by weight of OfI. Waxes include emulsions such as paraffin wax, microcrystalline wax, carnauba wax, methylolstearamide, polyethylene wax, and silicone, and the proportion thereof is 0.5 to 40% by weight, preferably 1 to 20% by weight of the total weight of the protective layer. is added in an amount of

Further, 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, sodium salts of di(2-ethylhexyl)sulfosuccinic acid, di(n-hexyl)sulfosuccinic acid, etc. Or ammonium salt etc.

Furthermore, a surfactant, a polymer electrolyte, etc. may be added to the protective layer to prevent charging of the heat-sensitive recording material. The solid coating amount of the protective layer is usually preferably 0.2 to 5 g/m2, more preferably Ig to 3 g/m2.

The paper used for the support is heat extracted pH 6 sized with a neutral sizing agent such as an alkyl ketene dimer.
~9 Neutral paper (described in JP-A-55-14281)
The use of is advantageous in terms of storage stability over time.

In order to prevent the coating liquid from penetrating the paper and to improve the contact between the recording heat head and the heat-sensitive recording layer, Japanese Patent Application Laid-Open No. 57-1166
Paper described in No. 87 (Metric Preface) and having a Beck smoothness of 90 seconds or more is advantageous.

Also, paper having an optical surface roughness of 8μ or less and a thickness of 40 to 75μ, described in JP-A-58-136492, JP-A-58-136492.
- Paper with a density of 0.9 g/cm 3 or less and an optical contact ratio of 15% or more, described in JP-A-69097, JP-A-58-
Canadian Standard Freeness (JIS P) described in No. 69097
8121) paper made from pulp beaten to 400 cc or more to prevent penetration of coating liquid, JP-A-58
-65695, the glossy side of base paper made by a Yankee machine is used as the coated surface to improve color density and resolution, and JP-A-59-35985 describes a method in which the base paper is subjected to corona discharge treatment. Papers and the like which have been coated to improve their coatability may also be used in the present invention with good results. In addition to these, any support commonly used in the field of heat-sensitive recording paper can be used as the support of the present invention.

In the present invention, a back layer may be provided on the back surface of the support for the purpose of curl correction, antistatic charge, and improvement in scratch resistance. As the constituent components of the back layer, it is preferable to use the same components as those of the protective layer.

(Effects of the Invention) Images obtained by thermal printing on the heat-sensitive recording material of the present invention have good image contrast even under normal recording conditions, and are particularly good for use as an OHP. Furthermore, even when the image is multicolored, the sharpness of the image is good and the color reproduction is also good.

(Examples) Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1 [Preparation of capsule liquid] 14 g of crystal violet lactone (leuco pigment)
, Takene) D-11ON (capsule wall material manufactured by Takeda Pharmaceutical Co., Ltd.) 60 g and Sumisorb 200 (ultraviolet absorber manufactured by Sumitomo Chemical ■) 2 g were mixed with 55 g of 1-phenyl-1-xylylethane.
g and 55 g of methylene chloride in a mixed solvent,
Dissolved. This leuco dye solution was mixed with 100 g of 8% aqueous polyvinyl alcohol solution, 40 g of water, and 1.4 g of 2% sodium salt of dioctyl sulfosuccinate (dispersing agent).
10. Mix with an aqueous solution and use an Ace homogenizer manufactured by Nippon Seiki ■. Emulsify at OOOrpm for 5 minutes, then add 15 ml of water.
0g was added and reacted at 40°C for 3 hours to produce a capsule liquid with a capsule size of 0.7μ.

[Preparation of developer emulsion dispersion]

Color developer represented by the following structural formula (a) 8g, (b) 4g
and (C) 30 g were dissolved in 8.0 g of 1-phenyl-1-xylylethane and 30 g of ethyl acetate. The obtained developer solution was mixed with 8% polyvinyl alcohol aqueous solution 1
00g, water 150g, and sodium dodecylbenzenesulfonate 0.5g aqueous solution and emulsified at 10,000γpm for 5 minutes at room temperature using an Ace homogenizer manufactured by Japan $W Machine to emulsify the particle size to 0.5μ. A dispersion was obtained.

Developing core a) Developing agent 3) Developing strip C) [Preparation of sample] 50 g of monide rubber (Beyer GmbH Belgate 310) was dissolved in 300 g of Dorol. 120 g of methyl methacrylate, 120 g of ethyl acrylate, 80 g of ethyl acrylate and 2 g of dilauryl peroxide were added, followed by polymerization at 70°C. More dollar all 100
g was added.

After the reaction was completed, the temperature was further maintained at 70°C for 2 hours.

The obtained solution was coated on a polyethylene terephthalate (PET') support with a thickness of 75 μm to a solid content of 3 g/m2 and dried to form a heat-sensitive/pressure-sensitive opacifying layer. 5.0 g of liquid, 10 g of U colorant emulsified dispersion, Og, and 5 g of water.

Stir and mix 0g and place on the heat/pressure sensitive opacifying layer.
Sample (1) was prepared by coating the sample to a solid content of 7 g/m 2 and drying it to form a heat-sensitive coloring layer, and then providing a 2 μm protective layer having the following composition.

[Composition of protective layer]

Polyvinyl alcohol 1 part by weight (solid content) Kaolin 0.2 part by weight Zinc stearate (Hydrin Z-7 manufactured by Middle East Yushi ■)
A comparative sample (0.1 part by weight (solid content)) was prepared in exactly the same manner as above except that no heat-sensitive/pressure-sensitive opacifying layer was provided.

The obtained sample was subjected to GI [I-mode Hifax 700]
(Newly manufactured by Hitachi) and the transmission density of the image area was measured using a Macbeth densitometer.
In the case of 1), it was 0.78, while in the case of the comparative sample it was 0.70, demonstrating that the heat-sensitive recording material of the present invention can obtain images with higher contrast. Ta.

Example 2 In Example 1, a styrene-maleic acid copolymer (Polymaron 38 manufactured by Arayo Kagaku ■) was used as the heat-sensitive/pressure-sensitive opacifying layer.
Sample (2) was prepared in the same manner as in Example 1, except that the sample (2) was applied so that the solid content was 2 g/m2.

The obtained sample (2) was thermally recorded in the same manner as in Example 1, and the transmission density was measured, and the transmission density of the image area was 0.76.

Claims (1)

[Claims] A coating liquid containing the obtained emulsified dispersion is obtained by emulsifying and dispersing microcapsules containing a colorless or light-colored basic dye precursor and a color developer dissolved in an organic solvent that is poorly soluble or insoluble in water. A heat-sensitive recording material comprising a coated and dried heat-sensitive layer and a transparent layer that becomes opaque by heat and/or pressure, which are laminated on a support.