JPH02269092A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a transparent heat-sensitive layer enhanced in sensitivity and available for OHP by using a specific compound and a bisphenol compound as at least a part of a color developer. CONSTITUTION:On a substrate, a heat-sensitive layer at least having microcapsules containing an electron donative dye precursor and a color developer is formed. As at least a part of the color developer, a compound shown by a formula I and a bisphenol compound are used. In the formula I: R1 represents hydrogen atom, halogen atom, alkoxy group, alkyl group, and phenyl group; and R2 represents alkoxycarbonyl group which may have substituents, phenoxycarbonyl group, or alkyl group which may have substituents. Hydrogen atom, halogen atom, and alkyl group are preferable among the substituents shown by R1. In this manner, a thermal recording material having a transparent heat-sensitive layer can be efficiently produced with good reproducibility, and the obtained thermal recording material is improved in transparency.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a heat-sensitive recording material having a transparent heat-sensitive layer,
In particular, it relates to a heat-sensitive recording material with excellent transparency and stability of the heat-sensitive layer.

(Prior art) Thermal recording methods are: (I) does not require development; (2) when the support is paper, the quality of the paper is similar to that of paper; (3) it is easy to handle; and (4) it develops color. Due to its advantages such as high density, (5) simple and inexpensive recording device, and (6) no noise during recording, it has rapidly become popular in the fields of facsimiles and printers, and has also been used for thermal recording. It is expanding.

Against this background, in recent years, in order to adapt to multicolor, overhead projectors (
It has become desirable to develop a transparent heat-sensitive recording material that can be directly recorded with a thermal head for use in OHP.

For example, Japanese Unexamined Patent Application Publication No. 63
-265682, 64-11884, 64-2
As detailed in No. 0190, etc., a combination of a colorless or light-colored electron-donating dye precursor and a color developer is adopted as a coloring system, and the former is contained in microcapsules, and the latter is sparingly soluble or insoluble in water. A transparent heat-sensitive recording material has been reported that can be obtained by dissolving and emulsifying and dispersing the two in an organic solvent, mixing the two, and coating the mixture on a support.

However, it has been found that the transparency of the above-mentioned heat-sensitive recording material is significantly influenced by the emulsion stabilizer of the emulsion in the heat-sensitive layer. It has become clear that benzyl hydroxybenzoic acid ester has significant drawbacks in terms of transparency, such as easy crystallization in the heat-sensitive layer and easy fogging.

As a result of intensive studies to solve the above-mentioned drawbacks, the present inventors discovered that precipitation of the color developer from the heat-sensitive layer can be prevented by combining a specific color developer, and arrived at the present invention. .

(Object of the Invention) Therefore, an object of the present invention is to provide a heat-sensitive recording material having a transparent heat-sensitive layer that has high sensitivity and can be used for OHP.

(Means for Solving the Problems) The above-mentioned aspects of the present invention provide a heat-sensitive recording material in which a heat-sensitive layer having microcapsules containing at least an electron-donating dye precursor and a color developer is provided on a support. This was achieved by a heat-sensitive recording material characterized by using a compound represented by the general formula (I) or (II) and a bisphenol compound as at least a part of the color developer.

In the above formula, R5 represents a hydrogen atom, a halogen atom, an alkoxy group, an alkyl group, or a phenyl group, and R2 represents an alkoxycarbonyl group that may have a substituent, a phenoxycarbonyl group, or a substituent. It represents an alkyl group, and R1 represents an alkyl group, an alkoxycarbonyl group, or an acyl group which may have a substituent.

Among the substituents represented by R1 in general formula (I), preferred are a hydrogen atom, a halogen atom, and an alkyl group.

Hff CI! .

Among the substituents represented by R2, preferred ones are represented by the following general formula (IV).

+C00±"R, (IV) In the general formula (U), ! represents O or 1, and R4 represents a branched or straight-chain alkyl group or a substituent of the general formula (V).

In general formula (V), m represents an integer of 1 to 8, n represents 0 or 1, and Rs represents a hydrogen atom, a halogen atom, an alkyl group, or an alkoxy group.

Particularly preferred examples of R3 in general formula (I) are shown below.

CH3 General formula (II) R1 preferred in Below is an example of Regarding bisphenol compounds, General formula (Vl) It is expressed as

C-Ht-ya.

m-0~2, n 2-1 In the general formula (Vl), CJ*a*+ C@H1a** Preferred examples are shown below.

-(, (CL)s, HCHlh"CH2, -beCHth"CH2, Next, the electron-donating dye precursor that gives a colored product when contacted with the above-mentioned color developer will be described.

As the electron-donating dye precursor used in 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.

Particularly preferred compounds are those 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 R1 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 color forming agent in microcapsules, it is possible to prevent fogging during the production of the photosensitive material, and at the same time, to improve the raw and record storage properties of the heat-sensitive material. In this case, by selecting the wall material and manufacturing method of the microcapsules, it is possible to increase the image density during recording.The amount of color former used is preferably 0.05 to 5.Og/rrr. .

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. 0 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. 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.

Here, as an organic solvent for forming oil droplets, 1. It can be appropriately selected from those commonly used as pressure sensitive oils. Among these, preferred oils include triarylmethane, terphenyl compounds, diphenyl ethers, chlorinated paraffins, dialkylnaphthalenes, dialkylbiphenyls, diphenylalkanes, and the like. These are described in detail in Japanese Patent Application Laid-Open No. 2002-120000, cited in the prior art section.

It is also possible to use the above oils together or with other oils.

In the present invention, the size of the microcapsules is preferably 4 microns or less, as measured by the volume average particle size measured, for example, by the measurement method described in JP-A No. 60-214990.

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 Can react by penetrating walls.

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.

In addition to the above-mentioned compounds, other known color developers may be appropriately used as the color developer that causes a color reaction upon application of heat with the electron-donating colorless dye used in the present invention. Color developers for dyes include phenolic compounds, triphenylmethane compounds, sulfur-containing phenol compounds, metal salts of aromatic carboxylic acids, sulfone compounds, urea or thiourea compounds, etc.
For details, see, for example, Paper and Pulp Technology Times (I985
2013), pages 49-54 and 65-70.

Among these, those with a melting point of 50°C to 250°C are particularly preferred, and among them, phenols and organic acids that are poorly soluble in water and have a melting point of 60°C to 200°C are preferred.When two or more color developers are used in combination is preferable because it increases solubility.

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 that dissolves the color developer may be sparingly soluble or insoluble in water.
The melt can be appropriately selected from among the melts, but it is particularly preferable to use an organic solvent with a boiling point of 150°C or less because it has good thermal sensitivity. Examples of these organic solvents include ethyl acetate, isopropyl acetate, , butyl acetate and methylene chloride.

In the present invention, these organic solvents can be mixed with high-boiling esters or the pressure-sensitive oil as appropriate, but esters are particularly preferred from the viewpoint of stability of the developer emulsion dispersion. It is preferable.

These compounds are described in detail in JP-A-Sho, cited in the prior art section.

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 preferable, especially partially saponified polyvinyl alcohol, especially saponification degree of 75 to 90%.
Preferably.

Further, as the surfactant to be contained in the aqueous phase, a surfactant that does not cause precipitation or aggregation when used in combination with the above-mentioned protective colloid can be appropriately selected from anionic or nonionic surfactants. .

Preferred surfactants include sodium alkylbenzenesulfonate (for example, sodium dodecylbenzenesulfonate), sodium alkylsulfate, dioctyl sodium sulfosuccinate, polyalkylene glycol (for example, polyoxyethylene nonylphenyl ether), and the like. Ruru.

°The emulsified dispersion containing partially saponified polyvinyl alcohol of a color developer in the present invention is prepared by mixing an oil phase containing the color developer and an aqueous phase containing a protective colloid and a surfactant by high-speed stirring, ultrasonic dispersion, etc. It can be easily obtained by mixing and dispersing using the means used for ordinary fine particle emulsification.

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 like whose melting point is lowered by this are used at the same location.If they are added to different locations, it is preferable to add them in an amount 1 to 3 times the above-mentioned 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 0.5 to 5 g/n as solid content. The heat-sensitive recording material of the present invention is a partially saponified dispersion of polyvinyl alcohol in which microcapsules containing a color former and at least a color developer are emulsified and dispersed. A coating solution containing a substance and other additives such as a binder is prepared, and the coating solution is coated and dried on a support such as paper or a synthetic resin film by a coating method as described below, so that the solid content is 2.5 to 25 g. /rtt.The heat-sensitive layer of the heat-sensitive material thus produced surprisingly has very good transparency, although the reason is not clear.

Transparency here refers to Integrating Sphere Method HT manufactured by Nippon Seimitsu Kogyo ■.
It can be expressed as haze (%) measured with an R meter. 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, when measuring the inherent transparency of the heat-sensitive layer, which is a problem in the present invention, that is, the transparency inside the heat-sensitive layer, a simple method is to attach a transparent adhesive tape on top of the heat-sensitive layer, and then Evaluation is made using the measured value with almost all scattering removed.

The heat-sensitive recording material of the present invention contains silica, barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide,
Pigments such as calcium carbonate, fine powders such as styrene peas, urea-melamine resin, etc. can be added, but in order to maintain the transparency of the heat-sensitive layer, additives are added on top of the heat-sensitive layer mainly to improve storage stability and stability. Targeted protection! Details about the protective layer, which is preferably applied by known methods and added to this protective layer, can be found, for example, in Paper and Pulp Technology Times J.
(I985, September issue), pages 2-4.

Similarly, metal soaps can also be added to prevent sticking. The amount used is 0.2-7g1
It is 0f.

Furthermore, when a transparent support is used as a support, the heat-sensitive material of the present invention can be seen as a transmitted image or a reflected image from one side of the transparent support, but especially in the latter case, the background part can be seen as a transmitted image or a reflected image. If the back side is visible, the image will be dull, so 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 coated.

In either case, it is effective to perform this on the outermost layer on the opposite 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.

The dispersed particle size is preferably 1011 or less.

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 used is 20 to 200 .mu.m, particularly preferably 50 to 100 .mu.m.

In the present invention, an undercoat layer can be provided between the transparent support and the heat-sensitive layer in order to enhance adhesion between the two layers. Gelatin, synthetic polymer latex, nitrocellulose, etc. are used as the material for the undercoat layer. The coating amount of the undercoat layer is 0.
Ig/rrf~2. It is preferably in the range of 0.2 g/rd to 1.0 g/rd. A range of Og/rlf is preferred.

If it is less than 0.1 g/nf, the adhesion between the support and the heat-sensitive layer will not be sufficient; Even if it is increased beyond Og/rrf, the adhesive force between the support and the heat-sensitive layer has reached saturation, which is disadvantageous in terms of cost.

The undercoat layer is made of a hardening material because the image quality of the heat-sensitive layer may deteriorate if the undercoat layer swells due to the water contained in the heat-sensitive layer when the heat-sensitive layer is coated thereon. It is desirable to cure it.

These hardeners are described in detail in JP-A-Sho, cited in the prior art section.

Among these, dialdehydes such as glutaraldehyde, 2°3-dihydroxy-1,4-dioxane, and boric acid are particularly preferred.

The amount of these hardeners added is based on the weight of the base coat material.
An appropriate addition amount can be selected in the range of 0.20% by weight to 3.0% by weight depending on the coating method and desired degree of curing.

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.

Moreover, it is also possible to add an antistatic agent if necessary.

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, U.S. Pat.
No. 846,727, No. 3,549,406, No. 3
, No. 590.107 is most preferably used.

The heat-sensitive recording material of the present invention can, of course, be designed for OHP use, and can also be formed by forming two or more heat-sensitive layers on a support directly, each of which can develop a different color, or via the above-mentioned protective layer or undercoat layer. Furthermore, one layer selected from known photosensitive layers, heat-sensitive layers, and light-sensitive heat-sensitive layers is provided on the support, and furthermore, one layer selected from known photosensitive layers, heat-sensitive layers, and light-sensitive heat-sensitive layers is provided on the support, and furthermore, a layer as described herein that can develop a color different from that of this layer is provided. Various embodiments are possible depending on the use and purpose, such as the possibility of providing a substantially transparent heat-sensitive layer.

The coating liquid according to the present invention includes -a a well-known coating method,
For example, dip coating method, air knife coating method, curtain coating method, roller coating method, doctor coating method,
Coating can be performed by a wire barcode method, a slide coating method, a gravure coating method, or an extrusion coating method using a hopper as described in US Pat. No. 2,681.294. U.S. Pat. No. 2,761,791 and U.S. Pat. No. 3,508,947 as appropriate.
No. 2,941,898, and No. 3゜526.
Specification No. 528, Yuji Harasaki, "Coating Engineering" 25
It is also possible to apply the product simultaneously in two or more layers using the method described on page 3 (published by Asakura Shoten in 1973), and an appropriate method can be selected depending on the amount of application, application speed, etc. .

Pigment dispersants, thickeners, flow modifiers, antifoaming agents, foam inhibitors, mold release agents, and colorants may be appropriately added to the coating liquid used in the present invention as long as they do not impair the properties. There is nothing wrong with that.

(Effects of the Invention) According to the present invention, the dispersion stability of the color developer emulsion dispersion can be significantly improved, so that a heat-sensitive recording material having a transparent heat-sensitive layer can be efficiently produced with good reproducibility. Not only that, the transparency of the obtained heat-sensitive recording material is also extremely 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 2-aniline-3-methyl-6-N-ethyl-N-isobutylaminofluorane (koiro pigment, Takene) D-11ON (Takeda Pharmaceutical capsule wall material) 60
g and Sumisorb 200 (ultraviolet absorber manufactured by Sumitomo Chemical ■)
2 g was added to a mixed solution of 55 g of 1-phenyl-1-xylylethane and 55 g of methylene chloride and dissolved.

This Leuco Dye R solution was mixed with an aqueous solution of 100 g of 8% polyvinyl alcohol aqueous solution, 40 g of water, and 1.4 g of 2% sodium salt of dioctyl sulfosuccinate (dispersing agent), and mixed with an Ace homogenizer manufactured by Nippon Seiki ■. 10
．． Emulsify at OOOrpm for 5 minutes, add 150g of water, and react at 40°C for 3 hours until the capsule size is 0.7μ.
capsule liquid was produced.

[Preparation of developer emulsion dispersion]

Color developer represented by the following structural formula (a) 7 g, (b)
7 g, (c) 16 g, (d) ILg, 1.7 g of tricresyl phosphate, and 0.8 g of diethyl maleate were dissolved in 38 g of ethyl acetate. The obtained developer solution was mixed with 8
% polyvinyl alcohol (PVA205 manufactured by Kuraray):
saponification degree 87-89%) aqueous solution 100g and water 150g1
and 0.5 g of sodium dodecylbenzenesulfonate in an aqueous solution, and emulsified using an Ace homogenizer manufactured by Nippon Seiki ■ at 10.00 rpm at room temperature for 5 minutes to obtain a particle size of 0.5 g. A 5μ emulsified dispersion was obtained.

Color developer (a) Color developer (b) Color developer (C) CHt c! Hs"") CHt +rCH Color developer (Q [Preparation of heat-sensitive material Φ]) 5.0 g of the above capsule liquid, 10.0 g of color developer emulsion dispersion
, and 5.0g of water by stirring! ! ! ! After preparing the coating solution, the coating solution was left to stand for 1 hour and the v:m of the coating solution was observed, and the stability of the coating solution was confirmed. As mentioned above, 1
The coating liquid after being left for a period of time is a transparent polyethylene terephthalate (PET) film with a thickness of 70μ, and the solid content is f5g.
/ A and dried. A protective layer having the following solid content composition was further formed on the heat-sensitive layer at 2.5 g/po.

Silicon-modified polyvinyl alcohol 2 parts by weight (PVAR-2105 manufactured by Kura LJI) Colloidal silica 3 parts by weight (Snowtesix 30 manufactured by Nissan Chemical ■) Paraffin wax emulsion 0.91 parts (Cellsol 428 manufactured by Middle East Oil & Fats ■) Zinc stearate emulsion 0 ．． 2 parts by weight (Hydrin Z-7 manufactured by Middle East Oil Co., Ltd.) The transparency of this film was determined using integral sphere H manufactured by Nippon Seiki Kogyo Co., Ltd.
The haze was 8% as measured by a TR meter, demonstrating that it had very good transparency.When this film was printed by facsimile, a clear black image was obtained.

Example 2 In place of the color developer (b) used in preparing the color developer emulsion dispersion in Example 1, a color developer (2) represented by the following structural formula was used.
The test was conducted in exactly the same manner as in the example except that e) was used.

As a result, the haze was 9%, and when this film was printed by facsimile, a clear black image was obtained.

Color developer (e) CH3 Comparative Example Same as Example 1 except that color developer (c) was used instead of color developer IIq (d) used when preparing the color developer emulsion dispersion in Example 1. The test was conducted in exactly the same manner. As a result, some crystals precipitated from the emulsified dispersion, and some color developed when mixed with the capsule liquid by stirring. When this solution was applied to a transparent support, the film became opaque during the drying process.

Claims (1)

[Scope of Claims] 1) A heat-sensitive recording material in which a heat-sensitive layer having microcapsules containing at least an electron-donating dye precursor and a color developer is provided on a support, in which at least a part of the color developer A heat-sensitive recording material characterized by using a compound represented by the general formula (I) and a bisphenol compound. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (I) In formula (I), R_1 is a hydrogen atom, a halogen atom,
Represents an alkoxy group, an alkyl group, a phenyl group, R_
2 represents an alkoxycarbonyl group that may have a substituent, a phenoxycarbonyl group, or an alkyl group that may have a substituent. 2) The heat-sensitive recording material according to claim 1, wherein a compound represented by the general formula (I) and a compound represented by the general formula (II) are used as at least a part of the color developer. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (II) In formula (II), R_3 represents an alkyl group, an alkoxycarbonyl group, or an acyl group that may have a substituent.