JPH05221137A - Thermal recording material - Google Patents

Abstract

PURPOSE:To enhance sensitivity and applicability by sequentially laminating an undercoat mainly composed of spherical hollow plastic particles containing inorganic thickener and a thermal coloring layer mainly composed of leuco dye and developer therefor on a support. CONSTITUTION:Spherical hollow plastic particles composed of thickener, e.g. swelling fluoromica ore, polystyrene, and the like having an average grain size of 0.2-20mum are added to an undercoat layer forming liquid and then it is applied onto a support to form an undercoat layer. Consequently, spherical hollow plastic particles are prevented from floating and aggregating, compactness on the surface of the undercoat is enhanced, and the sensitivity is improved. A thermal coloring layer composed of leuco dye of triphenylmethane and a developer of 4,4-isopropyliden bisphenol, for example, is then formed on the undercoat layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having various properties improved by providing an undercoat layer between a support and a heat-sensitive color forming layer.

[0002]

2. Description of the Related Art Recently, various recording materials have been researched and developed and put to practical use in the information recording field in response to social demands such as diversification and increase of information, resource saving and pollution-free. Among them, the heat-sensitive recording material is (1) that a color image is recorded by simply heating it and a complicated developing step is not necessary, (2) it can be manufactured using a relatively simple and compact device, and further the obtained recording The material is easy to handle and the maintenance cost is low. (3) In many cases, paper is used as the support. In this case, not only the support cost is low, but also the feel of the obtained recording material is improved. Because of its advantages such as being close to plain paper, it can be used for computer output, calculators and other printer fields, medical measurement recorder fields, low and high speed facsimile fields, automatic ticket vending machines, thermal copying fields, POS system Are widely used in the label field and the like of the beam.

The above-mentioned thermosensitive recording material is usually produced by coating a substrate such as paper, synthetic paper or synthetic resin film with a thermosensitive coloring layer solution containing a coloring component capable of causing a coloring reaction by heating and drying. The heat-sensitive recording material thus obtained records a color image by heating it with a hot pen or a thermal head. As a conventional example of such a heat-sensitive recording material, for example, a heat-sensitive recording material disclosed in JP-B-43-4160 or JP-B-45-14039 can be cited. Responsiveness was low, and sufficient color density was not obtained during high speed recording. As a method for improving such a defect, for example, JP-A-49-38424 discloses a nitrogen-containing compound such as acetamide, stearamide, m-nitroaniline and dinitrile phthalate, and discloses JP-A-52-1067.
No. 46 discloses acetoacetic acid anilide, and JP-A-53-1
No. 1036 discloses an N, N-diphenylamine derivative,
Benzamide derivatives and carbazole derivatives are disclosed in
Japanese Patent Laid-Open No. 3-39139 discloses alkylated biphenyls and biphenylalkanes, and Japanese Laid-Open Patent Publication No. 56-144193 discloses p-hydroxybenzoic acid ester derivatives, thereby increasing the speed and increasing the sensitivity. Although disclosed, it was the current situation that none of the methods provided sufficiently satisfactory results. Further, as another method, a method of making a leuco dye having a high melting point amorphous to lower the melting point to increase the sensitivity is disclosed in JP-A-56-164890. However, since the surface of the amorphized dye is activated and is highly reactive, there is a problem in that the fog in the heat-sensitive color developing coating liquid or the heat-sensitive recording material or the background fog is large and the whiteness is poor.

Therefore, in order to suppress the background fog and enhance the dynamic color development sensitivity, the thermal conductivity of the support is set to 0.04 Kca.
1 / mh ° C. or lower (JP-A-55-164192), or a layer containing fine hollow sphere particles as a main component is provided on a support (JP-A-59-5093 and 59-225).
987) and the like, and a method of using non-expandable fine hollow particles of 5 μm or less made of a thermoplastic resin for the intermediate layer (Japanese Patent Laid-Open No. 62-5886).
Is proposed.

[0005]

However, the heat-sensitive recording materials proposed in the above-mentioned JP-A-55-164192 and JP-A-59-5093 are insufficient in foaming property and flexible to the wall material. In some cases, there is a lack of heat resistance, insufficient heat insulation, or insufficient adhesion between the thermal head and the thermal recording material.Therefore, it is said that satisfactory results are obtained. Further, since the hollow hollow particles do not break and the specific gravity is small, the undercoat layer forming liquid containing the particles easily separates into layers and has a problem of poor coatability. Further, the heat-sensitive recording material proposed in the above-mentioned JP-A No. 62-5886 does not provide sufficiently satisfactory results.

Therefore, an object of the present invention is to provide a heat-sensitive recording material having high sensitivity and excellent coatability of the undercoat layer.

[0007]

According to the present invention, an undercoat layer containing plastic spherical hollow particles as a main component, a leuco dye, and a color developing agent capable of coloring the leuco dye when heated are contained as a main component on a support. A heat-sensitive recording material comprising a heat-sensitive color forming layer and a heat-sensitive color forming layer, which are successively laminated, wherein the undercoat layer contains an inorganic thickener.

The undercoat layer containing the spherical hollow particles of the present invention and the inorganic thickener acts as a heat insulating layer, and improves the coloring sensitivity by efficiently utilizing the heat energy from the thermal head or the like. In addition, the addition of the above-mentioned inorganic thickener improves the liquidity of the undercoat layer forming liquid containing the spherical hollow particles.

The plastic spherical hollow particles used in the present invention have a thermoplastic polymer as a shell and contain air or other gas inside, and are fine hollow particles which have already been foamed, and have an average particle diameter. Is 0.2 to 20 μm
What is used. This average particle diameter (particle outer diameter) is 0.
If it is smaller than 2 μm, it is difficult to make it to have an arbitrary hollowness and there is a production problem, and if it is larger than 20 μm, the smoothness of the surface after coating and drying is deteriorated. Therefore, the touchability with the thermal head is reduced, and the sensitivity improving effect is reduced. Therefore, it is desirable that such a particle distribution has a particle diameter within the above range and a uniform distribution peak with little variation.

Further, the plastic spherical hollow particles used in the present invention have a hollowness of 40% or more,
Since those having a hollowness of less than 40% have low heat insulating properties, heat energy from the thermal head is released to the outside of the heat-sensitive recording material through the support, and the effect of improving sensitivity becomes insufficient. The hollowness referred to here is the ratio of the outer diameter to the inner diameter of the hollow particles, and is represented by the following formula.

The plastic spherical hollow particles used in the present invention are easily and inexpensively made of polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylic acid ester, polyacrylonitrile, polybutadiene or copolymer resins thereof. Can be manufactured.

Further, in the undercoat layer of the present invention, an inorganic thickener is blended, and particularly preferable thickeners include swelling fluoromica minerals, montmorillonite clay minerals and structural formulas. (OH ₂ ) ₄ (OH)
Etc. sepiolite represented by _{4 Mg 8 Si 12 O 30 ·} 6~8H 2 O and the like.

In this case, the swelling fluoromica-based mineral is colloidal hydrous magnesium silicate / lithium or colloidal hydrous magnesium silicate / sodium, and specific examples thereof include Na tetrasilicic mica NaMg ₂ . ₅ (Si
₄ O ₁₀ ) F ₂ Na or Li teniolite (Na, Li) Mg ₂ Li
(Si ₄ O ₁₀ ) F ₂ Na or Li hectorite (Na, Li) 1 / 3Mg ₂ 2 /
_{3Li1 / 3 (Si 4 O 10} ) F 2 and the like are known.

These swellable fluoromica-based minerals have a property that when water is absorbed, water molecules are drawn between the crystal layers to swell, and at the most developed stage of this swelling property, the crystals are cleaved to form ultrafine particle flake. It forms a stable sol in water and has reversible thixotropic flow characteristics against shear stress.

Further, montmorillonite clay minerals are part cationic substitution of colloidal hydrous aluminum _{silicate, Al 2 O 3 · 4SiO 2} · H 2 O · nH 2 O of Al
There are various types, for example, by replacing Mg with Si and Al with Al. For example, magnesium bentonite partially replaced with Mg, calcium bentonite replaced with Ca, and hydrogen bentonite replaced with H for all adsorbed ions are referred to as hydrogen bentonite. In addition, natural bentonite contains a large amount of montmorillonite clay minerals.

[0016] These montmorillonite clay minerals have a structural viscosity such that when they absorb water, their crystal lattice swells and the volume increases up to about 16 times.
It has reversible thixotropic fluidity.

Further, the structural formula (OH ₂ ) ₄ (OH) ₄ Mg ₈ Si
Sepiolite represented by ₁₂ O ₃₀ · 6 to 8 H ₂ O has a crystal structure in which talc bricks are alternately stacked. Therefore, since sepiolite has such a crystal structure, that is, a three-dimensional chain structure, it does not cause a swelling phenomenon unlike ordinary layered clay (montmorillonite). In addition, the voids formed in the chain-like gaps show a large surface area, and when the sepiolite is slurried, high viscosity and thixotropy are brought about.

By the way, the liquid for forming the undercoat layer containing the spherical hollow particles tends to float and aggregate because the specific gravity of the spherical hollow particles is small, and the layers are easily separated in a short time.
The surface of the formed undercoat layer also tends to become rough.

However, when an inorganic thickening agent such as a swelling fluoromica mineral, a montmorillonite clay mineral, or sepiolite is added to such an undercoat layer forming liquid,
Since the floating agglomeration of spherical hollow particles is prevented and the surface of the undercoat layer formed during coating is densified, the heat-sensitive recording material obtained by coating the undercoat layer forming liquid is very sensitive. Will be improved.

The weight ratio of the spherical hollow particles to the inorganic thickening agent is preferably 0.5 to 0.005, more preferably 0.1 to 0.01, relative to the spherical hollow particles 1. When this weight ratio exceeds 0.5, the heat insulating effect becomes insufficient, and conversely, when it is less than 0.005, the liquid property improving effect is lost.

To form the undercoat layer on the support, the plastic spherical hollow particles and the inorganic thickener are dispersed in water together with a binder such as a known water-soluble polymer or aqueous polymer emulsion. It is obtained by applying this to the surface of a support and drying. in this case,
The coating amount of the plastic spherical hollow particles is at least 1 g, preferably about ^{2 to} 15 g per 1 m ² of the support, and the coating amount of the binder resin may be such that the undercoat layer is strongly bonded to the support. Usually, it is 2 to 50% by weight based on the total amount of the plastic spherical hollow particles and the binder resin.

In the present invention, the binder used when forming the undercoat layer is appropriately selected from conventionally known water-soluble polymers and / or aqueous polymer emulsions. Specific examples thereof include water-soluble polymers such as polyvinyl alcohol, starch and derivatives thereof, methoxycellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose,
Cellulose derivatives such as ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylic acid ester copolymer, acrylamide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / Maleic anhydride copolymer alkali salt, polyacrylamide,
Examples include sodium alginate, gelatin, and casein. Examples of the aqueous polymer emulsion include latex of styrene / butadiene copolymer, styrene / butadiene / acrylic copolymer, vinyl acetate resin, vinyl acetate / acrylic acid copolymer, styrene / acrylic ester copolymer. , Emulsions of acrylic acid ester resins, polyurethane resins and the like.

In the undercoat layer of the present invention, together with the plastic spherical hollow particles, the inorganic thickener and the binder, if necessary, an auxiliary additive component commonly used in this type of heat-sensitive recording material, for example, , A filler, a heat-fusible substance, a surfactant and the like can be used in combination. In this case, as specific examples of the filler and the heat-fusible substance, various ones described in connection with the thermosensitive coloring layer component in the following will be mentioned.

Further, in order to make the surface of the undercoat layer formed on the support as described above smoother, the surface may be smoothed by a calendering process after the formation of the undercoat layer.

The leuco dyes used in the thermosensitive coloring layer of the present invention may be applied alone or in admixture of two or more, and as such leuco dyes, those applied to this type of thermosensitive material are arbitrarily applied. For example, leuco compounds of dyes such as triphenylmethane type, fluorane type, phenothiazine type, auramine type, spiropyran type and indolinophtalide type dyes 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 lactone), 3,3-bis ( p-dimethylaminophenyl) -6-diethylaminophthalide,
3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3-bis (p-dibutylaminophenyl) phthalide, 3-cyclohexylamino-6-chlorofluorane, 3-dimethylamino-5,7 -Dimethylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-methylfluorane, 3-
Diethylamino-7,8-benzfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-
(Np-tolyl-N-ethylamino) -6-methyl-
7-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) fluorane, 3-di- n-Butylamino-7- (o-chloroanilino) fluorane, 3-N-methyl-N, 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-spiropyran, 6 '
-Bromo-3'-methoxy-benzoindolino-spiropyran, 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'-diethylaminophenyl) -3- (2'-methoxy -5'-
Methylphenyl) phthalide, 3- (2'-methoxy-4 '
-Dimethylaminophenyl) -3- (2'-hydroxy-4'-chloro-5'-methylphenyl) phthalide, 3-
(N-ethyl-N-tetrahydrofurfuryl) amino-
6-methyl-7-anilinofluorane, 3-N-ethyl-N- (2-ethoxypropyl) amino-6-methyl-
7-anilinofluorane, 3-N-methyl-N-isobutyl-6-methyl-7-anilinofluorane 3-morpholino-7- (N-propyl-trifluoromethylanilino) fluorane, 3-pyrrolidino- 7-trifluoromethylanilinofluorane, 3-diethylamino-5-chloro-7- (N-benzyl-trifluoromethylanilino) fluorane, 3-pyrrolidino-7- (di-p-chlorophenyl) methylaminofluor Oran, 3-
Diethylamino-5-chloro-7- (α-phenylethylamino) fluorane, 3- (N-ethyl-p-toluidino) -7- (α-phenylethylamino) fluorane, 3-diethylamino-7- (o-methoxy Carbonylphenylamino) fluorane, 3-diethylamino-
5-Methyl-7- (α-phenylethylamino) fluorane, 3-diethylamino-7-piperidinofluorane, 2-chloro-3- (N-methyltoluidino) -7-
(Pn-butylanilino) fluorane, 3-di-n-
Butylamino-6-methyl-7-anilinofluorane,
3,6-bis (dimethylamino) fluorene spiro (9,3 ′)-6′-dimethylaminophthalide, 3- (N
-Benzyl-N-cyclohexylamino) -5,6-benzo-7-α-naphthylamino-4'-bromofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3-diethylamino-6- Methyl-7-mesitidino-4 ', 5'-benzofluorane, 3-N-methyl-N-isopropyl-6-methyl-7-anilinofluorane, 3-N-ethyl-N-isoamyl-6-methyl −
7-anilinofluorane, 3-diethylamino-6-methyl-7- (2 ', 4'-dimethylanilino) fluorane and the like.

As the developer used in the thermosensitive color developing layer of the present invention, various electron-accepting compounds that cause the leuco dye to develop color upon contact, or oxidizing agents are applied. Such a material is conventionally known, and specific examples thereof include the following.

4,4'-isopropylidene bisphenol, 4,4'-isopropylidene bis (o-methylphenol), 4,4'-secondary butylidene bisphenol 4,4'-isopropylidene bis (2-tert-butylphenol) ), Zinc p-nitrobenzoate, 1, 3,
5-tris (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanuric acid, 2,2
-(3,4'-dihydroxydiphenyl) propane, bis (4-hydroxy-3-methylphenyl) sulfide,
4- {β- (p-methoxyphenoxy) ethoxy} salicylic acid, 1,7-bis (4-hydroxyphenylthio)
-3,5-dioxaheptane, 1,5-bis (4-hydroxyphenylthio) -5-oxapentane, phthalic acid monobenzyl ester monocalcium salt, 4,4'-cyclohexylidene diphenol, 4,4 ' -Isopropylidene bis (2-chlorophenol), 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 4,4'-butylidenebis (6-tert-butyl-2-methyl) phenol, 1, 1,3-Tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-Tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 4,4 ′ -Thiobis (6-tert-butyl-2)
-Methyl) phenol, 4,4'-diphenol sulfone, 4-isopropoxy-4'-hydroxydiphenyl sulfone, 4-benzyloxy-4'-hydroxydiphenyl sulfone, 4,4'-diphenol sulfoxide,
Isopropyl P-hydroxybenzoate, benzyl P-hydroxybenzoate, benzyl protocatechuate, stearyl gallate, lauryl gallate, octyl gallate,
1,3-bis (4-hydroxyphenylthio) -propane, N, N'-diphenylthiourea, N, N'-di (m
-Chlorophenyl) thiourea, salicylanilide, bis- (4-hydroxyphenyl) acetic acid methyl ester, bis- (4-hydroxyphenyl) acetic acid benzyl ester, 1,3-bis (4-hydroxycumyl) benzene,
1,4-bis (4-hydroxycumyl) benzene, 2,
4'-diphenol sulfone, 2,2'-diallyl-4,
4'-diphenol sulfone, 3,4-dihydroxyphenyl-4'-methyldiphenyl sulfone, 1-acetyloxy-2-naphthoate zinc, 2-acetyloxy-
Zinc 1-naphthoate, zinc 2-acetyloxy-3-naphthoate, α, α-bis (4-hydroxyphenyl)-
α-Methyltoluene, zinc thiocyanate antipyrine complex, tetrabromobisphenol A, tetrabromobisphenol S, 4,4′-thiobis (2-methylphenol), 4,4′-thiobis (2-chlorophenol) and the like.

In the thermosensitive color developing layer of the present invention, various conventional binders can be appropriately used for coating the leuco dye and the color developer on the undercoat layer. Specific examples thereof include: The same as those exemplified in the above-mentioned undercoat layer coating can be mentioned.

In the thermosensitive coloring layer of the present invention, an auxiliary additive component, such as a filler or a heat-fusible compound, which is commonly used in the thermosensitive recording materials of this type, may be added together with the above-mentioned leuco dye and developer. It is possible to use together a substance and a surfactant. In this case, as the filler, for example,
Calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay,
Inorganic fine powders such as talc and surface-treated calcium and silica, as well as organic fine powders such as urea-formalin resin, styrene / methacrylic acid copolymer, and polystyrene resin can be mentioned. Examples of the functional substance include higher fatty acids or esters, amides or metal salts thereof, various waxes, condensates of aromatic carboxylic acids and amines, benzoic acid phenyl esters, higher linear glycols, 3,4- 5 such as epoxy-dialkyl hexahydrophthalate, higher ketones, other heat-fusible organic compounds
Those having a melting point of about 0 to 200 ° C. can be mentioned.

In the present invention, a layer containing a filler, a binder, a heat-fusible substance or the like may be provided as an intermediate layer between the undercoat layer and the thermosensitive color developing layer, if necessary. In this case, specific examples of the filler, the binder and the heat-fusible substance include the same as those exemplified in connection with the thermosensitive coloring layer or the undercoat layer.

Further, in the heat-sensitive recording material of the present invention, a protective layer may be provided on the heat-sensitive color developing layer for the purpose of improving the matching property of a thermal head or the like and further improving the storability of recorded images. In this case, the above-mentioned filler, binder, surfactant and heat-fusible substance can also be used as the component constituting the protective layer.

The heat-sensitive recording material of the present invention is produced, for example, by applying the above-mentioned coating liquid for forming each layer on a suitable support such as paper, synthetic paper, plastic film, etc., and drying it. Applied in the recording field.

[0034]

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

Example 1 [Liquid A] 3- (N-methyl-3-N-cyclohexyl) amino 20 parts-6-methyl-7-anilinofluorane 10% aqueous solution of polyvinyl alcohol 20 parts water 60 parts

[Solution B] Benzyl p-hydroxybenzoate 10 parts Polyvinyl alcohol 10% aqueous solution 25 parts Calcium carbonate 15 parts Water 50 parts

The mixture consisting of the above composition was dispersed using a sand mill so that the average particle diameter was 2 μm or less, to prepare [solution A] and [solution B].

[Liquid C] Plastic spherical hollow particle dispersion 30 parts (solid content concentration 31%) (average particle size 7 μm, hollowness 95%) Na tetrasilicic mica dispersion 6 parts (Topy Industry Co., Ltd .: NaTSS) (Solid content 5%) Styrene / Butadiene copolymer latex (Solid content 47%) 10 parts Water 54 parts

An undercoat liquid was prepared by stirring and dispersing the mixture having the above composition with a disper, and the weight of the undercoat liquid on the surface of commercially available high-quality paper (basis weight: 52 g / m ² ) was 6 after drying.
An undercoat paper was obtained by coating and drying so as to obtain g / m ² .

Next, the above [solution A] and [solution B] were mixed and stirred at a weight ratio of 1: 8 to prepare a thermosensitive color forming layer-forming solution, which was applied to the surface of the above undercoated paper. After drying, a thermosensitive coloring layer is provided by coating and drying so that the weight becomes 7 g / m ^2, and then supercalendering is performed so that the Beck smoothness becomes 500 to 600 seconds to obtain the thermosensitive recording material of the present invention. It was

Example 2 [Liquid D] Plastic spherical hollow particle dispersion 30 parts (solid content concentration 31%) (average particle size 7 μm, hollowness 95%) Na hectorite dispersion 6 parts (Lapport Industry Co., Laponite) RD) (Solid content 5%) Styrene / Butadiene copolymer latex (Solid content 47%) 10 parts Water 54 parts

An undercoat liquid was prepared by stirring and dispersing the mixture having the above composition with a disper, and the weight of the undercoat liquid on the surface of commercially available high-quality paper (basis weight: 52 g / m ² ) was 6 after drying.
An undercoat paper was obtained by coating and drying so as to obtain g / m ² .

Next, the same thermosensitive coloring layer forming liquid used in Example 1 was applied to the surface of the above-mentioned undercoat paper so as to have a dry weight of 7 g / m ² and dried to form a thermosensitive coloring layer. After that, a super calendering treatment was further performed so that the Beck's smoothness was 500 to 600 seconds to obtain a heat-sensitive recording material of the present invention.

Example 3 [Liquid E] Plastic spherical hollow particle dispersion 30 parts (solid content concentration 31%) (average particle diameter 7 μm, hollowness 95%) Sodium montmorillonite dispersion 6 parts (Kunipine Industry Co., Ltd .: Kunipia) -F) (solid content 5%) Styrene / Butadiene copolymer latex (solid content 47%) 10 parts Water 54 parts

An undercoat liquid was prepared by stirring and dispersing the mixture having the above composition with a disper, and the undercoat liquid was applied to the surface of a commercially available high-quality paper (basis weight: 52 g / m ² ) to give a weight of 6 after drying.
An undercoat paper was obtained by coating and drying so as to obtain g / m ² .

Next, the same thermosensitive color forming layer-forming liquid as that used in Example 1 was applied to the surface of the above-mentioned undercoat paper so as to have a dry weight of 7 g / m ² and dried to form a thermosensitive color forming layer. After that, a super calendering treatment was further performed so that the Beck's smoothness was 500 to 600 seconds to obtain a heat-sensitive recording material of the present invention.

Example 4 [F liquid] Plastic spherical hollow particle dispersion 30 parts (solid content concentration 31%) (average particle diameter 7 μm, hollowness 95%) Purified bentonite dispersion 6 parts (Murakami Clay Mining Co., Ltd .; Fine) Gel) (solid content 5%) Styrene / Butadiene copolymer latex (solid content 47%) 10 parts Water 54 parts

The undercoat liquid was prepared by stirring and dispersing the mixture having the above composition with a disper, and the undercoat liquid was applied to the surface of a commercially available high-quality paper (basis weight: 52 g / m ² ) to give a weight of 6 after drying.
An undercoat paper was obtained by coating and drying so as to obtain g / m ² .

Next, the same thermosensitive color forming layer-forming liquid as that used in Example 1 was applied to the surface of the above-mentioned undercoat paper so as to have a dry weight of 7 g / m ² and dried to form a thermosensitive color forming layer. After that, a super calendering treatment was further performed so that the Beck's smoothness was 500 to 600 seconds to obtain a heat-sensitive recording material of the present invention.

Example 5 [Liquid G] Plastic spherical hollow particle dispersion (solid content concentration 31%) 30 parts (average particle size 7 μm, hollowness 95%) Sepilite dispersion (Made by Mizusawa Chemical Co., Ltd .: Aed Plus) (solid) 5%) 6 parts Styrene / Butadiene copolymer latex (solid content 47%) 10 parts Water 54 parts

An undercoat liquid was prepared by stirring and dispersing the mixture having the above composition with a disper, and the weight of the undercoat liquid on the surface of commercially available high-quality paper (basis weight: 52 g / m ² ) was 6 after drying.
An undercoat paper was obtained by coating and drying so as to obtain g / m ² .

Next, the same thermosensitive color forming layer-forming liquid as that used in Example 1 was applied to the surface of the above-mentioned undercoat paper so as to have a dry weight of 7 g / m ² and dried to form a thermosensitive color forming layer. After that, a super calendering treatment was further performed so that the Beck's smoothness was 500 to 600 seconds to obtain a heat-sensitive recording material of the present invention.

Example 6 [Liquid H] Plastic spherical hollow particle dispersion (solid content concentration 31%) 30 parts (average particle diameter 7 μm, hollowness 95%) Sepiolite dispersion (Showa Mining Co .: Milcon) 6 parts ( Solid content 5%) Styrene / Butadiene copolymer latex (solid content 47%) 10 parts Water 54 parts

An undercoat liquid was prepared by stirring and dispersing the mixture having the above composition with a disper, and the weight of the undercoat liquid on the surface of commercially available high-quality paper (basis weight: 52 g / m ² ) was 6 after drying.
An undercoat paper was obtained by coating and drying so as to obtain g / m ² .

Next, the same thermosensitive color forming layer-forming liquid as that used in Example 1 was applied to the surface of the above-mentioned undercoat paper so as to have a dry weight of 7 g / m ² and dried to form a thermosensitive color forming layer. After that, a super calendering treatment was further performed so that the Beck's smoothness was 500 to 600 seconds to obtain a heat-sensitive recording material of the present invention.

Comparative Example 1 A thermosensitive recording material for comparison was obtained in the same manner as in Example 1 except that the Na tetrasilicic mica dispersion of [C liquid] was omitted.

Comparative Example 2 In Comparative Example 1, instead of the plastic spherical hollow particles, plastic spherical non-hollow particles (manufactured by Mitsui Toatsu Co., Ltd .: SPM) were used.
A thermosensitive recording material for comparison was obtained in the same manner as in Comparative Example 1 except that M-HS: solid content concentration 40%) was used.

Each of the thermosensitive recording materials obtained as described above was tested for dynamic color development sensitivity. The results are shown in Table 1. The test was conducted as follows.

Dynamic color-developing: Head thermal power of 0.4 in a thermal printing experimental apparatus having a thin film head manufactured by Matsushita Electronic Components Co., Ltd.
Under the conditions of 5 w / dot, 1 line recording time of 20 msec / l, scanning line density of 8 × 3.85 dots / mm, printing with pulse widths of 0.3, 0.4, 0.5 and 0.6 msec,
The print density was measured with a Macbeth densitometer RD-914.

Further, with respect to each of the above-mentioned undercoat layer forming liquids, a test regarding liquid properties was conducted. The results are shown in Table 2.
Shown in. This test was conducted as follows.

Liquidity: Each undercoat layer forming liquid was prepared and allowed to stand for 18 hours, and the state of the liquid was observed.

[0062]

[Table 1]

[0063]

[Table 2]

From the results shown in Tables 1 and 2, it can be seen that the heat-sensitive recording material of the present invention has high sensitivity and the liquidity of the undercoat forming liquid is improved.

[0065]

The heat-sensitive recording material of the present invention comprises a support, an undercoat layer containing plastic spherical hollow particles as a main component, a leuco dye, and a developer containing, as a main component, a color developer capable of coloring the leuco dye when heated. In a heat-sensitive recording material in which a color-forming layer is sequentially laminated, the undercoat layer contains an inorganic thickener (for example, a swelling fluoromica-based mineral, a montmorillonite-based clay mineral, and sepiolite). Therefore, the color development sensitivity is very excellent. Further, since the undercoat layer forming liquid used in the present invention has a constitution in which the plastic spherical hollow particles are mixed with an inorganic thickener, the liquid property is improved.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroshi Yaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (4)

[Claims] 1. An undercoat layer containing plastic spherical hollow particles as a main component, a leuco dye and a heat-sensitive color developing layer containing a color developer which develops a color of the leuco dye when heated are sequentially laminated on a support. The heat-sensitive recording material according to claim 1, wherein the undercoat layer contains an inorganic thickening agent. 2. The heat-sensitive recording material according to claim 1, wherein the inorganic thickening agent is a swelling fluoromica-based mineral. 3. The heat-sensitive recording material according to claim 1, wherein the inorganic thickener is a montmorillonite clay mineral. 4. The inorganic thickener has a structural formula (OH ₂ ).
The thermal recording material according to claim 1, which is a sepiolite represented by ₄ (OH) ₄ Mg ₈ Si ₁₂ O ₃₀ · 6 to 8H ₂ O.