JPS59179396A - Thermal recording material - Google Patents

Abstract

PURPOSE:To improve discoloration property and decoloration property of a recorded image, by a method wherein an undercoat layer comprising a specified hydroxynaphthoic acid compound, a filler and a binder is provided between a base and a thermal color forming layer, and a p-hydroxybenzoic acid ester is used as a part of a color developer incorporated in the thermal color forming layer. CONSTITUTION:In a thermal recording material wherein a thermal color forming layer comprising a leuco dye and a color developer is provided on a base, an undercoat layer comprising a hydroxynaphthoic acid compound of the formula (wherein R is H, halogen or lower alkyl, and [A] is naphthalene ring), a filler and a binder is provided between the base and the color forming layer. In the undercoat layer, the weight ratio of the filler to the binder is preferably 1:9-9:1, and the hydroxynaphthoic acid compound is used preferably in a quantity of 0.5-4pts.wt. per 1pt.wt. of the leuco dye contained in the color forming layer. The undercoat layer is favorably applied in a quantity of not smaller than 3g/m<2>. The color forming layer comprises the leuco dye and the color developer as main constituents, and the color developer comprises a p-hydroxybenzoic acid ester. With the undercoat layer provided, ground fogging is prevented, a recorded image improved in discoloration property and decoloration property can be obtained, and ruggedness of the surface of the base is smoothened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a heat-sensitive recording material that utilizes a color-forming reaction between a leuco dye and a color developer.

[Prior art]

Recently, various recording sheets have been researched and developed and put into practical use in the information recording field in response to social demands such as the diversification and increase of information, resource conservation, and pollution-free technology.Among them, thermal recording sheets are (1) A colored image is recorded simply by heating, eliminating the need for a complicated development process; (2) It can be manufactured using a relatively simple and compact device;
Furthermore, the resulting recording sheet is easy to handle and maintenance costs are low; (3) paper is often used as a support; in this case, not only is the support cost low; Because of its advantages, such as the feel of the recorded sheet being similar to that of plain paper, it is useful in the fields of computer output, printers such as tabletops, recorders for medical measurement, low and high speed facsimiles, automatic ticket filling machines, and thermal copying fields. It is widely used in etc.

The above-mentioned thermosensitive recording sort is manufactured by applying and drying a thermosensitive coloring layer solution containing a coloring component that can develop color or cause a reaction when heated, on a support such as ordinary paper, synthetic paper, or synthetic oil-celled film. A colored image is recorded on the heat-sensitive recording sheet thus obtained by heating it with a thermal pen or a thermal head. Conventional examples of such heat-sensitive recording sheets include, for example, the heat-sensitive recording sort disclosed in Japanese Patent Publication No. 43-4160 or Japanese Patent Publication No. 45-14039; Responsiveness was low and sufficient color density could not be obtained during high-speed recording.

As a method to improve such drawbacks, for example, Japanese Patent Application Laid-open No. 49
JP-A-34842 discloses nitrogen-containing compounds such as acetamide, stearamide, m-nitroaniline, diphthalate, etc., and JP-A-52-106746 describes acetoacetanilide. No. 11036 discloses N,N-diphenylaminylamine derivatives, benzamide derivatives, cargusol derivatives, and JP-A No. 5
No. 3-39139 discloses an alkylated hiphenyl or vinylalkane, and JP-A-56-144193 discloses that high sensitivity is achieved by incorporating a p-oxybenzoic acid ester derivative in a heat-sensitive coloring layer. Among the methods disclosed, the use of a p-oxybenzoic acid ester derivative as a color developer is the most effective method.

However, these color developers deteriorate the stability of the recorded image, causing the recorded image to fade naturally, or if fingerprints (finger sebum components), oil, cosmetics, etc. adhere to the area, the color of the recorded image may fade. As a method to improve these drawbacks, Japanese Patent Application Laid-Open No. 57-83495 discloses
The combined use of a color developer such as 2,2'-methylenebis(4-m5-6-t-butylphenol) has been shown, but its effectiveness is still insufficient. I can't do it.

The present inventors have conducted various studies to improve the stability of recorded images, and found that when a hydroxynaphthoic acid compound and p-hydroxybenzoic acid ester are used in a mixed state, the fading and erasing properties of images are significantly improved. However, I found that
It has been confirmed that when both compounds are used in the same layer, the background tends to become foggy, which is still a practical problem.

〔the purpose〕

An object of the present invention is to solve the above-mentioned problems and provide a heat-sensitive recording material in which the fading and erasing properties of recorded images are improved and the background fog is reduced during production and storage.

〔composition〕

In a heat-sensitive recording material in which a heat-sensitive color forming layer containing a leuco dye and a color developer is provided on a support, there is a bond between the support and the heat-sensitive color forming layer of the general formula (wherein R1 is a hydrogen atom, a halogen or a lower In addition to providing an undercoat layer consisting of a hydroxynaphthoic acid compound represented by an alkyl group and (i) represents a naphthalene ring, a filler, and a binder,
There is provided a heat-sensitive recording material characterized in that p-hydroxybenzoic acid ester is used as at least a part of the color developer contained in the heat-sensitive coloring layer.

In the above, examples of the lower alkyl group representing R usually include those having 1 to 6 carbon atoms, and examples of the halogen include chlorine, bromine, and the like.

Examples of the hydroxynaphthoic acid compound represented by the above general formula used in the present invention include 1-hydroxy-2-naphthoic acid, 2-hydroxy-1-naphthoic acid, 2-hydroxy-3-naphthoic acid, -Hydroxy-3-naphthoic acid, 1,6-dibromo-2hydroxy-
Examples include 3-naphthoic acid, 1-methyl-2-hydroxy-3-naphthoic acid, 6-chloro-2-hydroxy-3-naphthoic acid, 6-methyl-2-hydroxy-3-naphthoic acid.

In the heat-sensitive recording material of the present invention, an undercoat layer consisting of the hydroxynaphthoic acid compound, a filler, and a binder is provided between the support surface 6- and the heat-sensitive coloring layer. In -, any inorganic or organic pigment used for membrane paper making or coating may be used, and specific examples include those listed below.

Calcium carbonate, kaolin, talc, bad lead oxide, aluminum hydroxide, silica, magnesium silicate, sr) +
) Styrene resin, urea-formaldehyde resin, etc.

As the binder, generally known water-soluble polymers and aqueous emulsions are used, and specific examples include those shown below.

Pholhynyl alcohol, methylcellulose, hydroxyethylcellulose, starch, tensin derivative, styrene-maleic anhydride copolymer, inbutylene-maleic anhydride copolymer, polyamide, SBR latex, polystyrene-acrylate emulsion, polyhinyl acetate emulsion etc.

The weight ratio of the filler and binder in this undercoat layer can be arbitrarily determined depending on the selected components, but is preferably 1:
The hydroxynaphthoic acid compound is preferably used in an amount of 0.5 to 4 times the weight of the leuco dye in the heat-sensitive coloring layer. Further, as for the coating amount of the undercoat layer, a coating amount of 1 ft/m'' or more is effective, but preferably a coating amount of 3y/rn'y or more is good.

The thermosensitive color forming layer used in the present invention has a leuco dye and a color developer as main components, and in this case, the color developer contains p-hydroxybenzoic acid ester at least in part. In this case, as the p-hydroxybenzoic acid ester, in addition to lower alkyl esters such as methyl, ethyl, propyl, and butyl, aromatic esters such as Hensyl ester are also applicable. In addition, for p-hydroxybenzoic acid ester, various conventionally known color developers can be used in combination, and color developers that are preferably used in combination include:
Examples include phenolic substances, such as those shown below.

4-phenylphenol, 2.2-bis(p-hydroxyphenyl)pronone, 2.2-bis(p-hydroxyphenyl)butane, 4.4'-cyclohexylidene diphenol, 4.4'
-isozolobylidene bis(2-t-butylphenol)
, 2.2'-methylenebis(4-methyl-6-butylphenol), 2.2'-methylenebis(4-ethyl-6-butylphenol), 4.4'-thiobis(3-methyl-6- butylphenol) etc.

These color developers that can be used in combination with p-hydroxybenzoic acid ester are used in an amount of 1 part by weight or less based on 1 part by weight of p-hydroxy7benzoic acid ester.

As the leuco dye used in the present invention, conventionally known colorless or slightly light-colored leuco dyes can be used, but triphenylmethane-based, fluoran-based, phenothiazine-based, auramine-based, and spiropyran-based leuco dyes can be used. For convenience, specific examples of these are shown below.

(a) Leuco compound of triphenylmethane dye represented by the following general formula: (wherein Rx, Ry and Rz are hydrogen, hydroxyl group,
They are halogen, alkyl group, nitro group, amino group, dialkylamine group, monoalkyl group, and allyl group. ) Specific examples of the above leuco compounds are as follows.

3.3-bis(p-dimethylaminophenyl) = 10
- - Phthalide 3. a-Bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as crystal violet lactone) 3.3-bis(p-1 methylaminophenyl)-6-dibutylaminophenyl 3.3-bis( T)-dimethylaminophenyl)-6-
Chlorphthalide 3.3-Bis(p-dibutylaminophenyl)phthalide←) Leuco compound of fluoran dye represented by the following general formula: Rz In the formula, RX, Ry and Rz are the same as in the above (a).

” Specific examples of bipartite compounds are as follows.

3-Cyclohexylamino-6-chlorofluorane 3-(N,N-diethylamino)-3-methyl-7-(
N,N-dibenzylamino) fluoran 3-dimethylamino-5,7-dimethylfluoran 3-diethylamino-7-methylfluoran 3-diethylamine-7,8 nipenzfluoran (c) Fluoran dye leuco Compound: 3-diethylamino-6-methyl-7-chlorofluoran 3-pyrrolidino-6-methyl-7-anilinofluoran 2 (N-(3'-)IJ fluoromethylphenyl)
amine)-6-dinithylaminofluorane 2-(3,6-bis(diethylamino)-9-(0-chloroanilino)xanthylbenzoic acid lactam) A generally known method for producing the thermal recording sheet of the present invention can be used.

First, at least the leuco compound and color developer are separated, and an aqueous solution of a water-soluble polymer such as polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, an alkali salt of styrene/maleic anhydride copolymer, starch, or a starch derivative is added. After pulverization and dispersion using a dispersing machine such as a Diru Mill, Attritor, or Zand Mill until the dispersed particle size becomes 1 to 3 μm, the mixture is blended into a certain formulation to prepare a heat-sensitive coloring layer solution.

Separately, the hydroxynaphthoic acid compound is added to an aqueous medium, for example, the aqueous solution of the water-soluble polymer, and after being pulverized and dispersed using a disperser, a filler and a binder aqueous solution are added and mixed and stirred. and prepare an undercoat layer solution.

Next, the undercoat layer solution is coated and dried on a support such as paper, film, synthetic paper, etc., and then the heat-sensitive coloring layer solution is coated and dried on top of the undercoat layer solution, followed by calendering. A thermosensitive recording sheet of the invention is obtained.

At this time, the heat-sensitive coloring layer liquid contains inorganic and organic fillers such as calcium carbonate clay, silica, aluminum hydroxide, urea-formaldehyde resin, etc., in order to improve head matching (sticking residue adhesion) and whitening effect. A surfactant and an antifoaming agent can also be added to improve coating properties.

〔effect〕

Since the heat-sensitive recording material of the present invention contains p-hydroxybenzoic acid ester in the heat-sensitive coloring layer and contains a hydroxynaphthoic acid compound in the undercoat layer together with a filler and a binder, the problem of background fog does not occur. figure,
Moreover, it provides recorded images with improved fading and erasing properties,
Furthermore, the undercoat layer smoothes the unevenness on the surface of the support and reduces the penetration of the thermosensitive coloring layer liquid into the support, resulting in very good thermal sensitivity.

14- [Example] Next, the present invention will be explained in more detail with reference to Examples. Note that all departments and sections shown below are based on weight.

Examples 1 to 4 Liquids (8) were prepared by pulverizing and dispersing mixtures having the following component compositions in a magnetic mill for two days.

Solid-liquid composition 2-hydroxy-3-naphthoic acid 3o
o part 10% polyvinyl alcohol aqueous solution
150 u water
550 (8) Liquid composition 2-hydroxy-1-naphthoic acid 3o
o Part 10 Polyvinyl alcohol aqueous solution
150 water
55o〃C〃Liquid composition 10% polyvinyl alcohol aqueous solution 200〃Water
65
o True liquid silk benzyl p-hydroxybenzoate 10
0 parts calcium carbonate 100〃10
Polyvinyl alcohol aqueous solution 250 tt water
550〃
(g) Liquid composition Benzyl p-hydroxybenzoate 10
0 parts calcium carbonate 100〃10
Polyvinyl alcohol aqueous solution 250
〃water
520 Next, 2 parts of solid/liquid, 2 parts of 50% polystyrene filler aqueous dispersion, and 1 part of 48% SBR latex were mixed and stirred to prepare an undercoat layer coating liquid [A'].

An undercoat layer coating solution [B'] was prepared by mixing and stirring 2 parts of the solution (1), 2 parts of a 50 polystyrene filler, and 1 part of a 48% SBR latex.

Furthermore, 0 times and prison liquid 2 times each ■-〇〕: Hit-1:
6 (weight ratio) were mixed and stirred to prepare heat-sensitive coloring layer coating solutions [D'] and [E'].

These coating solutions were applied to commercially available high-quality paper with a basis weight of 521/g according to the contents shown in Table 1 below, and after drying, the Bekk smoothness was 500.
A heat-sensitive recording sheet of the present invention was prepared by calendering for 2000 seconds.

Comparative Example 1 A heat-sensitive recording sheet of Comparative Example 1 was produced in the same manner as in Example 1 except that the undercoat layer was removed.

Comparative Example 2 A heat-sensitive recording sheet of Comparative Example 2 was prepared in the same manner as in Example 2 except that 2-17-hydroxy-3-naphthoic acid in the solution was removed using Underco.

Comparative Example 3 A similar procedure was carried out in Comparative Example 2 except that 2-hydroxy-3-naphthoic acid was used instead of 2,2'-methylenebis(4-ethyl-6-t-butylphenol) in the heat-sensitive coloring layer. A thermosensitive recording sheet of Comparative Example 3 was produced.

Next, we examined the dynamic coloring density, storage stability (background coloring), fading of recorded images, and discoloration due to fingerprints for these heat-sensitive recording sheets.
The results are shown in Table 2.

However, the test was conducted as follows.

(1) Dynamic color density: Main scanning recording time was 20 m5ec/1ine using a dynamic property testing machine with a thin film thermal head for facsimile.

Pulse width 2.2 m5eC, applied voltage Under two conditions of 1.2V and 13V Record and measure dynamic color density did. As a concentration meter, Mac ~18- PES RD-51,4 (filtera Tuten-106) was used.

(2) Preservability (Skin color development) The skin density before the test and the skin density after being left at 60° C. for 24 hours were measured.

(3) Discoloration of recorded images... After recording the image using Ricoh's G-■ facsimile (Refax-3300), measure the density after filing at room temperature for 2 weeks, and measure the density reduction rate according to the formula below. P was calculated.

(4) Fingerprint resistance... After recording the image in the same manner as in (3) above, the fingerprint of the index finger was stamped on the solid area, and after filing for two weeks, the density of the stamped area was measured, The concentration reduction rate P was calculated in the same manner as above.

Table 2 As can be seen from the results shown in Table 2, the thermal recording sheet of the present invention has high dynamic color development sensitivity, less fogging during storage, and less fading and decoloring of recorded images. It is.

Patent applicant Ricoh Co., Ltd. Agent Patent Attorney Toshiaki Ikeura

Claims (1)

[Claims] (1) In a heat-sensitive recording material in which a heat-sensitive color forming layer containing a leuco dye and a color developer is provided on a support, the general formula (wherein R is a hydrogen atom, An undercoat layer consisting of a hydroxynaphthoic acid compound represented by (a halogen or lower alkyl group, the latter being a naphthalene ring), a filler, and a binder is provided, and at least one of the color developers contained in the heat-sensitive coloring layer is provided. As part of p-
A heat-sensitive recording material characterized by using hydroxybenzoic acid ester.