JP2531956B2 - Thermal recording material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material utilizing a color development reaction between a leuco dye and a color developer.

[Prior art]

It has been known for a long time that colorless or pale-colored leuco dyes and color developers such as organic acidic substances develop a color by melting when heated, and examples of applying this color reaction to recording paper Are JP-B-43-4160 and JP-B-45-14039.
And is publicly known. These thermal recording sheets have been applied to a wide range of fields, such as measurement recorders, terminal printers such as computers, facsimile machines, automatic ticket vending machines, and bar code labels. According to
The required quality of the heat-sensitive recording sheet has also become higher. For example, as the thermal head speeds up, there is a demand for a thermal recording sheet capable of recording a clear image with high density even with a small amount of heat energy and having good head matching properties such as sticking and head residue.

The color development of the heat-sensitive recording sheet is one in which both or one of the color-forming leuco dye and the developer is dissolved and reacted by the heat energy supplied from the thermal head. As a method of adding a compound that melts at a lower temperature than the leuco dye and the developer and has a high ability to dissolve both (generally called a heat-fusible substance), various methods are widely known. Is disclosed in the following publication. For example, JP-A-49-3484
No. 2 discloses a nitrogen-containing compound such as acetamide, stearamide, m-nitroaniline, and dinitrile phthalate.
JP-A-52-106746 discloses acetoacetic acid anilide and JP-A-53-39139 discloses alkylated biphenylalkanes.

However, in recent years, especially in the field of thermal facsimile, the speed has been increased and the thermal head has been driven at a high speed. In this case, the background portion of the thermal recording sheet may be colored during continuous recording due to heat storage around the head. (Remaining heat coloring) and the like, there is a need to increase the dynamic coloring sensitivity without lowering the coloring start temperature. However, with the above compounds, the static color development sensitivity is improved, but sufficient dynamic color development sensitivity cannot be obtained unless a large amount is added to the thermosensitive color development layer. 2), sticking occurs, or the melting point is too low, the storage stability (background fog) of the heat-sensitive recording sheet is deteriorated, and a satisfactory result cannot be obtained.

Further, as one method of improving the dynamic color sensitivity, to improve the smoothness of the surface of the thermosensitive coloring layer, or to reduce the content of components that do not participate in the coloring reaction in the coloring layer, for example, the content of fillers and binders, There is also a method of increasing the density of the coloring component. In order to improve the surface smoothness, it can be easily achieved by calendering usually with a super calender or the like, but the background is colored or the surface glossiness is increased, and the appearance of the recording paper is significantly impaired. . In addition, in order to keep the whiteness of the background normally in the thermosensitive coloring layer, and to prevent the adhesion of dust on the head, sticking, etc., calcium carbonate, clay, a filler such as urea-formalin resin is added, or a coloring component or a component thereof. A water-soluble binder is added for fixing the additive to the support, but reducing the content of these causes the quality of the above-mentioned deterioration, and causes inconvenience. I can't get a good result.

Furthermore, for the purpose of effectively utilizing the energy from the thermal head, between the support and the thermosensitive coloring layer,
Providing a heat insulating layer is disclosed in, for example, JP-A-55-164192 and
It is proposed in each of the publications such as 59-5903 and 59-171685. However, since the smoothness of the surface of the heat insulating layer may be impaired, it cannot be said that sufficiently satisfactory results are obtained.

[Purpose] An object of the present invention is dynamic coloring capable of recording a clear image with high density even with a small amount of heat energy without impairing other properties such as sticking or head matching properties, background whiteness, and heat resistant storage stability. It is to provide a heat-sensitive recording material having a high density.

〔Constitution〕

According to the present invention, a thermosensitive color developing layer is provided on a support through a layer having fine hollows, or a thermosensitive color developing layer containing fine hollow particles is provided. Provided is a heat-sensitive recording material characterized in that it is 0.85 g / cm ³ or less and the Bekk smoothness of the surface of the heat-sensitive color forming layer is 1,000 seconds or more.

The heat-sensitive recording material of the present invention is provided with a layer having fine hollows between the support and the heat-sensitive color forming layer, or a heat-sensitive color forming layer containing fine hollow particles is provided on the support to increase the density of the heat-sensitive recording material. Since it is 0.85 g / cm ³ or less and the Beck's smoothness of the surface of the thermosensitive coloring layer is 1,000 seconds or more, the heat insulating property is increased and the unevenness of the surface of the thermosensitive coloring layer is made uniform. Energy is effectively transferred to the thermosensitive coloring layer, and the dynamic coloring sensitivity is remarkably improved.

Heat-sensitive recording material of the present invention has a density is of 0.85 g / cm ³ or less, and preferably in the range of density 0.40~0.85g / cm ^3. When the density of the heat-sensitive recording material exceeds 0.85 g / cm ³ , the heat insulating property is insufficient and the heat sensitivity is low. The density of the heat-sensitive recording material of the present invention is preferably 0.90 g / cm ³ or less when only the layer portion (that is, the coating layer) formed on the support is used as a reference.

Further, the thermosensitive recording material of the present invention is required to have a Bekk smoothness of 1,000 seconds or more on the surface of the thermosensitive coloring layer. When the Beck's smoothness is less than 1,000 seconds, the unevenness of the thermosensitive coloring layer is not uniformed, the adhesion to the thermal head is deteriorated, and a product having high heat sensitivity cannot be obtained.

If the smoothness of the thermosensitive coloring layer is set to 1,000 seconds or more, the surface of the recording sheet may be colored or the surface gloss may be increased as described above, and the appearance of the recording paper may be deteriorated. Such a defect can be eliminated by reducing the density of the material to 0.85 g / cm ³ or less or the density of the thermosensitive coloring layer to 0.90 g / cm ³ or less.

In the present invention, a layer having fine hollows is provided between the support and the thermosensitive coloring layer, or a thermosensitive coloring layer containing fine hollow particles is provided on the support, and a method for providing these layers is provided. Examples of the method include (i) a method of adding inorganic fine hollow particles or fine hollow plastic fillers to a thermosensitive color forming layer forming solution, and (ii) inorganic fine hollow particles or fine hollow plastic fillers. Method of coating on a support, (iii) A layer containing a fine hollow foamable plastic filler containing a thermoplastic material as a shell and a low boiling point solvent inside is provided on the support, and heated to expand. Method, or (iv) by heating CO ₂ , N ₂ , N
Examples include a method of forming a layer containing a foaming agent that generates a gas such as H ₃ and O ₂ and a thermoplastic polymer on a support, and heating the layer to form a layer having a cell structure having a large porosity. However, the present invention is not limited to these.

More specifically, as the inorganic micro hollow particles used in the methods (i) and (ii), various conventionally known ones are used, for example, micro hollow particles formed of a material such as glass or ceramics. Specific examples thereof include borosilicate glass micro hollow sphere powder and aluminosilicate micro hollow sphere powder.

The micro hollow plastic filler used in the above methods (i) and (ii) is a foam micro hollow plastic particle containing a thermoplastic material as a shell and a low boiling point solvent inside, The expandable plastic filler used in the method (iii) is an unexpanded fine hollow plastic particle containing a thermoplastic material as a shell and a low boiling point solvent inside, and such a plastic filler is conventionally used. Various types of heat-sensitive recording materials are known and are known. The thermoplastic resin that serves as the shell of this plastic filler includes polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate,
Examples thereof include polyacrylic acid ester, polyacrylonitrile, polybutadiene, and copolymers thereof.
Further, propane, butane, etc. are generally used as the foaming agent contained in the shell.

The foaming agent used in the method (iv) above includes
For example, inorganic compounds such as sodium bicarbonate, ammonium bicarbonate, ammonium carbonate, nitroso compounds such as N, N-dinitrosopentamethylenetetramine, N, N'-dimethyl-N, N'-dinitrosoterephthalamide, and azodiene. Examples thereof include azo compounds such as carbon amide, azobisisobutyronitrile and barium azodicarboxylate, and sulfonyl hydrazide compounds such as benzenesulfonyl hydrazide and toluenesulfonyl hydrazide. The thermoplastic polymer used together with the foaming agent is softened by heating and expands by the gas generated by decomposition of the foaming agent to form a sponge. Examples of such a thermoplastic polymer include various polymers or copolymers similar to those described above for the thermoplastic resin serving as the shell of the plastic filler.

In the methods (ii) to (iv), in order to provide the layer having the fine hollows on the support, the fine hollow particles, the fine hollow plastic filler or the foaming agent and the thermoplastic polymer can be prepared by a known method. Dispersing in water with a binder such as a water-soluble polymer or aqueous emulsion, coating this on a support and drying, or in the case of the above (iii) and (iv), heating and foaming after coating. Obtained by

In the present invention, the binder used when forming the layer having the minute hollows is appropriately selected from conventionally known hydrophobic polymer emulsions and / or water-soluble polymers. That is, as the hydrophobic polymer emulsion, latex of styrene / butadiene copolymer, styrene / butadiene / acrylic copolymer, vinyl acetate resin, vinyl acetate / acrylic acid copolymer, styrene / acrylic ester copolymer Coalesced, acrylic ester resin,
Examples include emulsions of polyurethane resin and the like. Further, as the water-soluble polymer, for example, polyvinyl alcohol, starch and its derivatives, methoxycellulose, hydroxyethyl cellulose, carboxymethyl cellulose,
Methyl cellulose, cellulose derivatives such as ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone,
Acrylamide / acrylate copolymer, acrylamide / acrylate / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt,
Examples include isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein.

In the case of the method (i), inorganic fine hollow particles or fine hollow plastic fillers are used.
It may be added to the heat-sensitive color forming layer directly or by mixing with a binder such as the water-soluble polymer described above.

Further, in the present invention, in order to improve the surface smoothness, if necessary, a binder is provided between the support and the thermosensitive coloring layer containing fine hollow particles, or between the layer having fine hollows and the thermosensitive coloring layer. An undercoat layer containing a filler as a main component can be provided.

Examples of the binder used here include the various binders shown in connection with the formation of the layer having fine hollows. The filler used here is a conventionally known general filler such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, surface-treated calcium or silica. Other inorganic fillers such as urea-formalin resin, styrene / methacrylic acid copolymer, polystyrene resin, and other organic fillers.

In the present invention, the layer having the minute hollows may be formed alone or may be formed in plural. Also,
The same applies to a layer containing a binder and a filler as main components, which is provided as desired. Further, it is possible to carry out a calendering treatment after forming each layer. However, in any case, it is necessary to set the density of the thermal recording material to 0.9 g / cm ³ or less.

In the present invention, a known leuco dye and a color developer, which are commonly used, are used as a main component, on a support or on a layer having fine hollows, in some cases, on a layer containing a binder and a filler as main components. A thermosensitive coloring layer is provided.

The leuco dye used in the present invention is applied alone or as a mixture of two or more kinds. As such a leuco dye, those applied to this kind of heat-sensitive material are arbitrarily applied, for example, triphenylmethane And leuco compounds of dyes such as fluoran compounds, phenothiazine compounds, auramine compounds, spiropyran compounds and indolinophthalide compounds are preferably used. Specific examples of such leuco dyes include, for example, 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-dimethyl Aminophenyl) -6-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3-bis (p-dibutylaminophenyl) phthalide, 3-cyclohexylamino-6-chlorofurf Oran, 3-dimethylamino-5,7-dimethylfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-7-methylfluoran, 3-diethylamino-7,8-benzfluoran, 3-diethylamino -6-methyl-7-chlorofluoran, 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) Fluorane, 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-
Pyrirospirane, 6'-bromo-3'-methoxy-benzoindolino-
Pyrirospirane, 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-isoamyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-tetrahydrofurfuryl) amino-6-methyl-7- Anilinofluorane, 3- (N-ethyl-N-ethoxypropyl) amino-
6-methyl-7-anilinofluorane, 3- (N-methyl-N-isopropyl) amino-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) methylaminofluorane, 3-diethylamino-5-chloro-7- (α-phenylethylamino) ) Fluoran, 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-pi Rijinofuruoran, 2-chloro-3-(N-Mechirutoruijino) -7-
(Pn-butylanilino) fluoran, 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.

Further, as the developer used in the present invention, various electron-accepting substances that react with the leuco dye upon heating to develop the color are applied, and specific examples thereof include phenol as shown below. And organic or inorganic acidic substances or their esters and salts.

Gallic acid, salicylic acid, 3-isopropylsalicylic acid, 3-cyclohexylsalicylic acid, 3,5-di-tert-
Butyl salicylic acid, 3,5-di-α-methylbenzyl salicylic acid, 4,4′-isopropylidene diphenol, 4,4 ′
-Isopropylidene bis (2-chlorophenol), 4,
4'-isopropylidene bis (2,6-dibromophenol), 4,4'-isopropylidene bis (2,6-dichlorophenol), 4,4'-isopropylidene bis (2-methylphenol), 4,4 ′ -Isopropylidene bis (2,6-
Dimethylphenol), 4,4'-isopropylidene bis (2-tert-butylphenol), 4,4'-sec-butylidene diphenol, 4,4'-cyclohexylidene bisphenol, 4,4'-cyclohexyl Denbis (2-methylphenol), 4-tert-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide, α
-Naphthol, β-naphthol, 3,5-xylenol,
Thymol, methyl-4-hydroxybenzoate, 4-
Hydroxyacetophenone, novolak type phenolic resin, 2,2'-thiobis (4,6-dichlorophenol), catechol, resorcin, hydroquinone, pyrogallol,
Phloroglysin, phloroglysin carboxylic acid, 4-tert
-Octylcatechol, 2,2'-methylenebis (4-chlorophenol), 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 2,2'-dihydroxydiphenyl, p-hydroxybenzoic acid Ethyl, propyl p-hydroxybenzoate, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, p-chlorobenzyl p-hydroxybenzoate, o-chlorobenzyl p-hydroxybenzoate, p-hydroxybenzoic acid −
p-methylbenzyl, p-hydroxybenzoic acid-n-octyl, benzoic acid, zinc salicylate, 1-hydroxy-
2-naphthoic acid, 2-hydroxy-6-naphthoic acid, 2
Zinc-hydroxy-6-naphthoate, 4-hydroxydiphenyl sulfone, 4-hydroxy-4'-chlorodiphenyl sulfone, bis (4-hydroxyphenyl) sulfide, 2-hydroxy-p-toluic acid, 3,5 -Ge-t
Zinc ert-butyl salicylate, tin 3,5-di-tert-butyl salicylate, tartaric acid, oxalic acid, maleic acid, citric acid, succinic acid, stearic acid, 4-hydroxyphthalic acid, boric acid, thiourea derivative, 4- Hydroxythiophenol derivative, bis (4-hydroxyphenyl) acetic acid,
Methyl bis (4-hydroxyphenyl) acetate, bis (4
-Hydroxyphenyl) ethyl acetate, n-propyl bis (4-hydroxyphenyl) acetate, n-butyl bis (4-hydroxyphenyl) acetate, phenyl bis (4-hydroxyphenyl) acetate, benzyl bis (4-hydroxyphenyl) acetate Phenethyl bis (4-hydroxyphenyl) acetate, bis (3-methyl-4-hydroxyphenyl) acetic acid, methyl bis (3-methyl-4-hydroxyphenyl) acetate, bis (3-methyl-4-hydroxyphenyl) acetic acid Ethyl, n-propyl bis (3-methyl-4-hydroxyphenyl) acetate, 1,7-bis (4-hydroxyphenylthio) 3,5-dioxaheptane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, dimethyl 4-hydroxyphthalate, 4-hydroxy-4'-methoxydiphenyl Sulfone, 4-hydroxy-4'-ethoxy diphenyl sulfone, 4-hydroxy-4'-isopropoxy diphenyl sulfone, 4-hydroxy-4'-n-propoxy diphenyl sulfone, 4
-Hydroxy-4'-n-butoxydiphenyl sulfone, 4-hydroxy-4'-isobutoxydiphenyl sulfone, 4-hydroxy-4'-sec-butoxydiphenyl sulfone, 4-hydroxy-4'-ter butoxydiphenyl sulfone, 4 -Hydroxy-4'-benzyloxydiphenyl sulfone, 4-hydroxy-4'-phenoxydiphenyl sulfone, 4-hydroxy-4 '-(m
-Methylbenzyloxy) diphenylsulfone, 4-hydroxy-4 '-(p-methylbenzyloxy) diphenylsulfone, 4-hydroxy-4'-(o-methylbenzyloxy) diphenylsulfone, 4-hydroxy-4'-
(P-chlorobenzyloxy) diphenyl sulfone and the like.

In the present invention, in order to bind and support the leuco dye and the color developer on the support, various conventional binders can be appropriately used, and examples thereof include polyvinyl alcohol, starch and its derivatives, methoxycellulose, and hydroxy. Ethyl cellulose, carboxymethyl cellulose,
Methyl cellulose, cellulose derivatives such as ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone,
Acrylamide / acrylate copolymer, acrylamide / acrylate / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt,
Isobutylene / maleic anhydride copolymer Alkaline salt, polyacrylamide, sodium alginate, gelatin, casein, and other water-soluble polymers, as well as polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid ester, vinyl chloride / vinyl acetate An emulsion such as a polymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, or a latex such as styrene / butadiene copolymer or styrene / butadiene / acrylic copolymer can be used.

In the present invention, together with the leuco dye and the developer, if necessary, auxiliary additives commonly used in this type of heat-sensitive recording material, for example, fillers, surfactants, heat-fusible substances ( Or a lubricant) can be used in combination. In this case, examples of the filler include inorganic and / or organic fillers similar to those exemplified in relation to the binder and the layer containing the filler as a main component, and as the heat-fusible substance, For example, in addition to higher fatty acids or their esters, amides or metal salts, various waxes, condensates of aromatic carboxylic acids and amines, phenyl benzoates, higher linear glycols, 3,4-epoxy-hexahydrophthalic acid Dialkyl, higher ketone,
Other examples include those having a melting point of about 50 to 200 ° C., such as other heat-fusible organic compounds.

〔effect〕

The heat-sensitive recording material of the present invention can use the heat energy from the thermal head with an increased efficiency in the melting reaction of the heat-sensitive coloring layer by adopting the above-described configuration, and as a result, the heat sensitivity of the product is improved. It will be.

〔Example〕

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

Example 1 [Liquid A] was prepared by thoroughly stirring and dispersing a mixture having the following composition with a homomixer.

[Liquid A]

Thermally expandable micro hollow particles [Micropearl F30 manufactured by Matsumoto Yushi Co., Ltd.] 10 parts 10% aqueous solution of polyvinyl alcohol 10 parts Water 80 parts The above [liquid A] in an unfoamed state has a basis weight of 52 g / m ² . After coating on the surface of commercially available high-quality paper to a coating amount of 5 g / m ² after drying and drying, the coated surface is brought into contact with the surface of a rotary dryer heated to 110 ° C to heat foam, and further calendered. By processing, an undercoat layer-coated paper was obtained.

Next, a mixture having the following composition is pulverized and dispersed [B
Solution] and [C Solution] were prepared.

[Liquid B]

3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluorane 30 parts 10% aqueous solution of polyvinyl alcohol 30 parts water 40 parts [C liquid] benzyl p-hydroxybenzoate 15 parts 2, 2'-Methylenebis (3-methyl-6-t-butylphenol) 5 parts Calcium carbonate 10 parts 10% aqueous solution of polyvinyl alcohol 20 parts Water 50 parts Next, [solution B]: [solution C] = 1: 8 by weight. Both were mixed and stirred so that a thermosensitive color developer coating liquid was obtained.

This thermosensitive coloring agent coating liquid is applied to the undercoated layer-coated paper surface with a wire bar so that the coating amount after drying is 5 g / m ^2, and after drying, the smoothness is adjusted to about 2000 seconds. A thermosensitive recording material of Example 1 was prepared by calendering with a nip pressure as low as possible.

Example 2 [D liquid] was prepared by dispersing a mixture having the following composition with a homomixer.

[D liquid]

Barium sulfate 20 parts Styrene / butadiene copolymer 20 parts Water 60 parts The above [solution D] was applied to the surface of the undercoat layer-coated paper obtained in the same manner as in Example 1 to give a coating amount of 3 g / m ² after drying. After providing the second undercoat layer as described above, a thermal recording material of Example 2 was prepared in the same manner as in Example 1.

Example 3 [Solution E] was prepared by dispersing a mixture having the following composition with a homomixer.

[Liquid E]

Benzenesulfonyl hydrazide 1 part 48% emulsion of styrene / acrylic acid ester copolymer 20 parts 10% aqueous solution of polyvinyl alcohol 48 parts water 31 parts The above [solution E] is used instead of [solution A] of Example 2. A thermosensitive recording material of Example 3 was prepared in the same manner as in Example 2 except that the above was used.

Example 4 [F liquid] was prepared by dispersing a mixture having the following composition with a homomixer.

[F liquid]

Micro hollow particles [Boncoat pp1000 manufactured by Dainippon Ink and Chemicals, Inc.] 30 parts 10% aqueous solution of polyvinyl alcohol 10 parts water 60 parts The above [F solution] was used in place of [A solution] of Example 2. A heat-sensitive recording material of Example 4 was prepared in the same manner as in Example 2 except that the heat-foaming treatment was not performed.

Comparative Example 1 A thermosensitive recording material of Comparative Example 1 was prepared in the same manner as in Example 1 except that the undercoat layer was not foamed.

Comparative Example 2 A thermosensitive recording material of Comparative Example 2 was prepared in the same manner as in Example 4 except that the smoothness in Example 4 was changed to 500 seconds.

Regarding the above thermal recording materials, the densities of the thermal recording material and the coating layer are determined by the basis weight (JIS-P
After determining from (according to -8124) and paper thickness (according to JIS-P-8118), tests were conducted for dynamic color development sensitivity, background density and heat resistance. The results are shown in the table. The test was conducted as follows.

(1) Dynamic color development sensitivity ...... Matsushita Electronics Co., Ltd., thermal power printing experiment device with thin film head, head power 0.60 W /
Dot, 1 line recording time 5ms / l, scanning line density 8 × 3.85
Pulse width of 0.1, 0.2, 0.3 and 0.4mse under dot / mm condition
Printing was performed with c, and the printing density was measured with a Macbeth densitometer RD-514 (filter-W-106).

(2) Background density: Measured with a Macbeth densitometer RD-514 (filter-W-106).

(3) Heat resistance: The background density was measured after storage for 24 hours under a dry condition of 60 ° C.

As is apparent from the table, the heat-sensitive recording material of the present invention is excellent in color development during high-speed recording, and is also excellent in whiteness of the background and heat-resistant storage stability.

Claims (2)

(57) [Claims] 1. A heat-sensitive recording material comprising a support and a heat-sensitive color-forming layer provided through a layer having fine hollows, or a heat-sensitive color-forming layer containing fine hollow particles, wherein the density of the heat-sensitive recording material is 0.85. A heat-sensitive recording material having a g / cm ³ or less and a Bekk smoothness of the surface of the heat-sensitive color forming layer of 1,000 seconds or more. 2. The thermal recording material according to claim 1, wherein the density of the portion of the thermal recording material excluding the support is 0.90 g / cm ³ or less.