JPH0679872B2 - Thermal recording material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having excellent color stability and other recording properties and having good image stability.

[Prior art]

A general heat-sensitive recording material is a colorless or light-coloring coloring dye such as leuco dye as a coloring agent on a support such as paper or film, and a phenolic compound (especially bisphenol A) as a color developing agent for coloring the same when heated. A thermosensitive coloring layer in which a binder, a filler, a sensitivity improver, a lubricant, and other auxiliaries are dispersed in a coloring system made of an acidic substance such as an organic acid.For example, JP-B-43-4160, Kosho 45-14039,
It was introduced in Japanese Patent Laid-Open No. 48-27736 and is widely put to practical use. This type of heat-sensitive recording sheet obtains a color image by a momentary chemical reaction between a color developer and a color developer at the time of heating (a thermal printer or a facsimile having a thermal head is used for heating). Therefore, compared to other recording materials, recording can be obtained in a short time with a relatively simple device without performing complicated processing such as development and fixing, there is little noise and environmental pollution, and cost is low. Because of its advantages such as low price, it is useful for copying books, documents and the like, and is also useful as a recording material for various information and measuring instruments such as electronic calculators, facsimiles, telexes and medical measuring instruments.

However, in the case of this type of leuco thermal recording material,
The stability of the recorded image is poor, and when it comes into contact with oils or a plasticizer such as dioctyl phthalate contained in the plastic film, the recorded image is easily erased.

Conventionally, in order to enhance the stability of the recorded image, for example, a thermosensitive coloring layer containing a large amount of water-resistant and chemical-resistant resin, or a thermosensitive coloring layer containing a resin that is cured by heat or light,
Alternatively, a resin protective layer formed on the surface to protect the thermosensitive coloring layer from the action of chemicals or water has been proposed, but the process becomes complicated, the cost becomes high, and the thermal responsiveness also deteriorates. Have the problem.

In order to solve this problem, the present inventors have made diligent efforts, and as a result, first, by using an antipyrine complex of zinc thiocyanate represented by the following formula (I) as a developer for a leuco dye, It has been found that a heat-sensitive recording material having extremely high image stability, which is free from coloration of the background portion and decolorization of the coloration portion upon contact with a plasticizer or the like, can be obtained.

On the other hand, in recent years, along with the development of society, there has been an increasing demand for high speed recording and high density recording. For this reason, it is strongly desired to develop a recording material capable of coping with the speedup of the recording apparatus itself. Conventionally, in order to make a heat-sensitive recording material suitable for high speed recording, for example, JP-A-53-39
139, JP-A-53-26139, JP-A-53-5636, JP-A-53-5636
As described in JP-A-53-11036, various thermosensitive coloring materials such as waxes, fatty acid amides, alkylated biphenyls, substituted biphenylalkanes, coumarins, and diphenylamines are added to the thermosensitive coloring layer. There is a method of adding as a sensitizer (or melting point depressant). However, when these methods are applied to a heat-sensitive recording material that uses an antipyrine complex of zinc thiocyanate as a developer, it is still insufficient in terms of color density, color sensitivity, background whiteness, water resistance of images, etc. It is hard to say that it is a thing.

〔Purpose〕

The object of the present invention is that the color density and color sensitivity are sufficient, suitable for high-speed recording, and that the background whiteness is high, and further, even when contacted with oils and plasticizers, the color formation and color development of the background part It is an object of the present invention to provide a heat-sensitive recording material having extremely high practicability, which does not cause decoloration and does not reduce the image density even when it comes into contact with water such as immersion in water.

〔Constitution〕

According to the present invention, in a heat-sensitive recording material utilizing a color-developing reaction between a leuco dye and its color developer, an antipyrine complex of zinc thiocyanate represented by the following formula (I) is used as the color developer. Provided is a heat-sensitive recording material characterized by using at least one selected from diester compounds represented by the following general formulas (II) and (III) as an auxiliary component.

Formula (I): General formula (II): General formula (III): In the general formula (II), R ₁ represents an alkylene group, a phenylene group or —CH ₂ PhCH ₂ —. The alkylene group includes those having about 1 to 10 carbon atoms such as methylene, ethylene, propylene, hexamethylene, decamethylene and the like. R ₂ and R ₃ represent a benzyl group.

The diester compounds represented by the general formulas (I) and (II) used together as an auxiliary component in the present invention have a melting point of 40 to 150 ° C. from the viewpoint of storage stability and sensitivity as a thermal recording material.
Those of 50 to 120 ° C. are particularly preferable.
Specific examples of the diester compound of the present invention are shown below, but the present invention is not limited thereto.

The leuco dyes used in the present invention may be used alone or as a mixture of two or more, and as such leuco dyes,
What is applied to this kind of heat-sensitive material is arbitrarily applied, and for example, leuco compounds of dyes such as triphenylmethane type, fluorane type, phenothiazine type, auramine type and spiropyran type are preferably used. Specific examples of such leuco dyes include those shown below.

3,3-bis (p-dimethylaminophenyl) -phthalide, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet letolactone), 3,3-bis ( p-Dimethylaminophenyl) -6-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3-bis (p-dibutylaminophenyl) phthalide, 3-cyclohexyl Amino-6-chlorofluorane, 3-dimethylamino-5,7-dimethylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7,8-benz Fluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3- (Np-tolyl-N-ethylamino) -6-methyl- -Anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 2- {N- (3'-trifluoromethylphenyl) amino} -6-diethylaminofluorane, 2- {3, 6-bis (diethylamino) -9- (o-chloroanilino) xanthylbenzoic acid lactam}, 3-diethylamino-6-methyl-7- (m-trichloromethylanilino) fluorane, 3-diethylamino-7- (o-chloroanilino ) Fluoran, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3-N-methyl-N-amylamino-6-methyl-7-
Anilinofluorane, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3- (N, N-diethylamino) ) -5-Methyl-7- (N, N
-Dibenzylamino) fluorane, benzoyl leuco methylene blue, 6'-chloro-8'-methoxy-benzoindolino-pyrrolispirane, 6'-bromo-3'-methoxy-benzoindolino-pyrrolispirane, 3- (2'-hydroxy) -4'-Dimethylaminophenyl) -3- (2'-methoxy-5'-chlorophenyl)
Phthalide, 3- (2'-hydroxy-4'-dimethylaminophenyl) -3- (2'-methoxy-5'-nitrophenyl)
Phthalide, 3- (2'-hydroxy-4'-dimethylaminophenyl) -3- (2'-methoxy-5'-methylphenyl)
Phthalide, 3- (2'-methoxy-4'-dimethylaminophenyl) -3- (2'-hydroxy-4'-chloro-5'-
Methylphenyl) phthalide, 3-monofolino-7- (N-propyl-trifluoromethylanilino) fluorane, 3-pyrrolidino-7-trifluoromethylanilinofluorane, 3-diethylamino-5-chloro-7- (N- Benzyl-trifluoromethylanilino) fluorane, 3-pyrrolidino-7- (di-p-chlorophenyl) methylaminofluorane, 3-diethylamino-5-chloro-7- (α-phenylethylamino) fluorane, 3- (N-ethyl-p-toluidino) -7- (α-phenylethylamino) fluorane, 3-diethylamino-7- (o-methoxycarbonylphenylamino) fluorane, 3-diethylamino-5-methyl-7- ( α-phenylethylamino) fluorane, 3-diethylamino-7-piperidi Fluoran, 2-chloro-3-(N-Echirutoruijino)-7-(p
-N-butylanilino) fluorane, 3- (N-benzyl-N-cyclohexylamino)-
5,6-benzo-7-α-naphthylamino-4′-bromofluorane, 3-diethylamino-6-methyl-7-mesitidino-
4 ', 5'-benzofluorane and the like.

In the present invention, in order to bond and support the leuco dye, the color developer and the auxiliary component on the support, various conventional binders can be appropriately used, and examples thereof include polyvinyl alcohol, starch and its derivatives, and methoxy. Cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose and other cellulose derivatives, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide / acrylic acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid terpolymer , Styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate,
Water-soluble polymers such as gelatin and casein, polyvinyl acetate, polyurethane, styrene / butadiene copolymer,
Polyacrylic acid, polyacrylic acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, styrene / butadiene /
A latex such as an acrylic copolymer can be used.

Further, in the present invention, together with the leuco dye, the color developer, and the auxiliary component, if necessary, further, an auxiliary additive component commonly used in this type of heat-sensitive recording material, for example, a filler, a surfactant, a heat-fusible component It is possible to use together a volatile substance (or a lubricant) and the like. In this case, as the filler, for example, calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, inorganic fine powder such as surface-treated calcium or silica, etc. ,
Examples include organic fine powders such as urea-formalin resin, styrene / methacrylic acid copolymer, and polystyrene resin.

The heat-sensitive recording material of the present invention is produced, for example, by applying a heat-sensitive layer-forming coating liquid containing the above-mentioned components onto a suitable support such as paper, synthetic paper, or plastic film, and drying. In this case, the amounts of leuco dye, color developer, and color-sensitivity increasing agent used are 5-40% by weight and 20-60%, respectively.
%, 20-60% by weight are suitable.

[Effect]

The heat-sensitive recording material of the present invention has improved sensitivity, is suitable for high-speed recording, has a high background whiteness, and even when contacted with oils and plasticizers, the background color and color are developed. There is no decolorization of the part, and the image density does not decrease even when it comes into contact with water such as immersion in water.
These effects are obtained by using the antipyrine complex of zinc thiocyanate represented by the formula (I) in combination with a specific diester compound.

〔Example〕

Next, the present invention will be described in more detail with reference to examples. The parts and% shown below are based on weight.

The antipyrine complex of zinc thiocyanate used in the examples described later was synthesized as follows.

Zinc sulfate _{(ZnSO 4 · 7H 2 O)} 14.4g of potassium thiocyanate
29.2 g was dissolved in 200 ml of water. Separately, a solution prepared by dissolving 8.8 g of antipyrine in 200 ml of water was prepared, and a white precipitate was immediately formed when the solution was added dropwise to the above solution under stirring. The precipitate was separated by filtration, washed with water and dried, and the obtained white powder was recrystallized with a water-ethanol mixed solvent to obtain 24.2 g of white crystals of an antipyrine complex of zinc thiocyanate having a melting point of 118 to 120 ° C.

Example 1 A mixture having the following composition was separately pulverized and dispersed for 2 days using a magnetic ball mill to prepare the following liquids [A] to [D].

[Liquid A]

3- (N-cyclohexyl-N-methylamino-6-methyl-7-anilinofluorane 20 parts 10% aqueous solution of hydroxyethyl cellulose 20 parts water 60 parts [solution B] antipyrine complex of zinc thiocyanate 20 parts methyl cellulose 5 % Aqueous solution 20 parts water 60 parts [C liquid] tetramethylene glycol dibenzoate (compound of compound example No. 4, melting point 81 to 82 ° C.) 20 parts 5% aqueous solution of methylcellulose 20 parts water 60 parts [D liquid] urea-formalin resin Fine powder of 20 parts Methyl cellulose 5% aqueous solution 20 parts Water 60 parts Next, solution A 10 parts, solution B 30 parts, solution C 30 parts, solution D 20 parts and 20% aqueous solution of isobutylene-maleic anhydride copolymer 10% Parts to prepare a thermosensitive color forming layer forming liquid, and a basis weight of 50 g /
After coating and drying on high-quality paper of cm ^{2 so} that the dry adhesion amount becomes 4 to 5 g / cm ² , a thermosensitive coloring layer is provided, and then the surface of the layer is calendered so that the surface smoothness becomes 500 to 600 seconds. Then, a thermal recording material (a) was prepared.

Example 2 A thermosensitive recording material (b) was prepared in the same manner as in Example 1 except that the following solution [E] was used instead of the solution [C] in Example 1.
It was created.

[E] Liquid p-xylylene glycol dibenzoate (compound of compound example No8, melting point 86-87 ° C.) 20 parts 10% aqueous solution of methylcellulose 20 parts water 60 parts Example 3 [C] liquid of Example 1 Thermal recording material (c) was prepared in the same manner as in Example 1 except that the following liquid [F] was used.
It was created.

[F] Liquid dibenzyl terephthalate (compound of compound No. 10; melting point 94-96 ° C.) 20 parts 10% aqueous solution of methylcellulose 20 parts water 60 parts Comparative Example 1 [C] liquid of Example 1 was replaced with water. Example 1 except that
Thermal recording material (d) was prepared in the same manner as in (1).

Comparative Example 2 A thermosensitive recording material (e) was prepared in the same manner as in Example 1 except that the following [G] solution was used instead of the [C] solution of Example 2.

[G] liquid 20 parts stearic acid amide 5% aqueous solution of methylcellulose 20 parts water 60 parts Example 4 All the same as in Example 1 except that the following [H] liquid was used instead of the [C] liquid of Example 1. Thermal recording material (f)
It was created.

[H] liquid Methylene glycol benzoate 20 parts (Compound of compound No. 1 compound, melting point 99-100 ° C) 5% aqueous solution of methylcellulose 20 parts Water 60 parts Thermal recording materials (a) to ( f)
Head thermal power 0.45W / dot, 1 line recording time 20 in a thermal printing experimental device with a thin film head manufactured by Matsushita Electronic Components Co., Ltd.
Printing was performed with a pulse width of 1.6, 2.0, and 2.4 (msec) under the condition of msec /, scanning line density 8 × 3.85 dots / mm, and the print density was measured with a Macbeth densitometer RD-514 (filter W-106). The results are shown in Table-1.

Next, the thermal recording materials (a) to (f) were printed with a thermal inclination tester (manufactured by Toyo Seiki) under the conditions of pressure 2 kg, contact time 1 second and 150 ° C., and cut out in a 4 cm square centering on the printed part. , One piece of polyvinyl chloride film (Polyrap V-300 manufactured by Shin-Etsu Polymer Co., Ltd.) was placed on top of this, and after applying a load of 500 g / cm ² for 24 hours at room temperature, it was taken out and the density of the background part and the color part It was measured with a Macbeth densitometer (RD-514) and compared with the density before the test. The results are shown in Table-2.

Next, when cotton seed oil was thinly applied to the background and colored areas of the sample printed in the same manner and stored at room temperature for 24 hours, all of the samples (a) to (f) showed no color development in the background area and decolorization in the colored area. It was never seen.

Next, a sample printed in the same manner was cut out in a 4 cm square centering on the printed portion, immersed in a 100 ml beaker containing 80 ml of tap water at room temperature for 24 hours, taken out and dried, and then the change in the density of the colored portion was measured. The results are shown in Table-3.

From the above, the heat-sensitive recording material of the present invention has high sensitivity and high background white color, and even when contacted with oils and plasticizers, there is no color development of the background part, no decolorization of the color development part, immersion in water, etc. It can be seen that the image density does not decrease even when it comes into contact with water, which is extremely practical.

Claims (1)

[Claims] 1. A heat-sensitive recording material utilizing a color-forming reaction between a leuco dye and a color developing agent thereof, wherein an antipyrine complex of zinc thiocyanate represented by the following formula (I) is used as the color developing agent: A heat-sensitive recording material comprising at least one selected from diester compounds represented by the following general formulas (II) and (III) as an auxiliary component. Formula (I): Formula (II): (In the formula, R ₁ is an alkylene group, phenylene, or —CH ₂ PhC.
Represents H ₂ −. ) Formula (III): (In the formula, R ₂ and R ₃ represent a benzyl group.)