JP2003276330A - Process for manufacturing thermal recording sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording sheet which has a back coating layer having a good compatibility with a pressure-sensitive adhesive, has a high level of whiteness and, at the same time, possesses excellent anti-curling property and storage stability. <P>SOLUTION: This thermal recording sheet includes: a support; a thermal recording layer which is provided on the support and is composed mainly of a colorless or light-colored electron-donating dye, an electron-accepting acidic material capable of developing color from the dye upon hating, and an adhesive; a protective layer which is provided on the thermal recording layer and is composed mainly of a water-soluble or water-dispersible binder, and a pigment; and a back coating layer which is provided on the backside of the support and is composed mainly of a binder. The process for manufacturing the thermal recording sheet is characterized in that the binder of the back coating layer is a core-shell-type acrylic resin and, after the application of the thermal recording layer and the protective layer, the back coating layer is applied. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a heat-sensitive recording sheet, and more specifically, a heat-sensitive recording sheet having a good backing property suitable for use as a pressure-sensitive adhesive for a label. The present invention relates to a method for producing a heat-sensitive recording sheet having a layer, having high whiteness, curling properties and storage stability.

[0002]

2. Description of the Related Art A heat-sensitive recording sheet generally comprises a support and a heat-sensitive recording layer containing a colorless or light-colored electron-donating dye and an electron-accepting acidic substance as main components. By heating with a pen, laser light, etc.,
An electron-donating dye and an electron-accepting acidic substance react with each other in an instant to form a color image, which is disclosed in JP-B-43-4160 and JP-B-45-14039.

Generally, such a heat-sensitive recording sheet has advantages that a color image can be obtained by a relatively simple device, that it is easy to maintain and that noise is not generated. It is widely used in a wide range of fields such as printers, computer terminals, label printers, tickets, and vending machines. In particular, the type of product, the price,
When applying the heat-sensitive recording sheet to applications such as product labels that display quality, capacity, etc., mailed items, labels that display the address attached to courier, etc., improve the water resistance of the heat-sensitive recording layer, and in high temperature environments. There is a demand for image stability against background fog, sunlight, plasticizer, oil, etc. when exposed.

Among these image stability, in order to improve storage stability against plasticizers, oils, etc., a recording method using an electron-donating dye and an electron-accepting acidic substance which are usually used in a heat-sensitive recording layer as a color-forming component. In place of the above, a heat-sensitive recording method using an aromatic isocyanate and a color-forming component of an imino compound (Japanese Patent Laid-Open No. 58-38733, Japanese Patent Laid-Open No. 58-104959, etc.) has come to be used. Color density and heat resistance (background fog) are not sufficient for a thermal recording sheet. Further, various proposals have been made to improve the above-mentioned drawbacks by providing a protective layer containing a water-soluble polymer, a water-dispersible polymer or the like as a main component on the heat-sensitive recording layer. (JP-A-55-95
593, JP-A-57-188392, JP-A-58-122892, JP-A-59-1797, JP-A-59-45191, and JP-A-60-1.
15484, JP-A-62-42884, etc.).

However, even if these water-soluble polymer substances are provided in the protective layer, a small amount cannot provide sufficient image stability, so that the amount of the protective layer must be increased. Further, for label applications, it is used in the form of providing a pressure-sensitive adhesive layer on the back surface of the support, but it is necessary to provide a backing layer on the back surface of the support to prevent background fog and discoloration of recorded images due to this pressure-sensitive adhesive. There is. In this case, if a thermosensitive recording layer and then a protective layer are applied after applying the backing layer first, a protective layer with a certain thickness is essential to maintain image stability. There is no escape area for the protective layer to swell or puncture, resulting in deterioration of appearance and image storability. Furthermore, there is no escape area for water vapor, and the whiteness is reduced due to wet heat fog, and both become products that cannot be marketed as products. On the other hand, in the case of a hydrophilic support such as paper, since the water-based paint curls on the side where the coating is finally applied, if the backing layer is applied first, it will curl on the side of the coloring surface. The heat-sensitive recording sheet of the present invention is provided with a heat-sensitive recording layer on one surface of a support and a protective layer on the heat-sensitive recording layer, and a pressure-sensitive adhesive layer on the other surface of the support to attach a release paper to form a label. In order to
The paper becomes very thick. Therefore, if curling occurs on the color surface side, the paper will be jammed in the printer, which will hinder the conveyance. Therefore, the thermal recording sheet for labels is required to be as flat as possible or slightly curled toward the pressure-sensitive adhesive surface.

[0006]

DISCLOSURE OF THE INVENTION The present invention comprises applying a heat-sensitive layer and a protective layer and then applying a backing layer,
The present invention is intended to produce a heat-sensitive recording sheet having high whiteness and excellent image stability and curl.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies on a method for producing a heat-sensitive recording sheet having high whiteness, excellent image stability and curl, and as a result, have completed the present invention. . That is, the present invention provides a heat-sensitive recording layer mainly composed of a colorless or light-colored electron-donating dye, an electron-accepting acidic substance that develops the color of the dye by heating, and an adhesive on the heat-sensitive recording layer. A water-soluble or water-dispersible binder,
And a thermal recording sheet provided with a protective layer containing a pigment as a main component and a backing layer containing a water-dispersible binder as a main component on the back surface of the support, wherein the binder of the backing layer is a core-shell type acrylic resin. And a backing layer is applied after the heat-sensitive recording layer and the protective layer are applied.

The second invention of the present invention is the heat-sensitive recording sheet for labels according to the first invention, wherein the heat-sensitive recording sheet has a release paper attached to the backing layer surface via a pressure-sensitive adhesive layer. It is a method of manufacturing a sheet.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As the support used in the present invention, a hydrophilic support such as paper containing wood pulp as a main component is particularly effective. Further, synthetic paper, metal foil, laminated paper made of polyethylene or the like, film made of polyethylene terephthalate, or the like may be used alone or in combination. In the case of paper, curling to the side of the thermosensitive recording layer tends to increase due to evaporation of water when coating the thermosensitive recording layer and protective layer, and curling can be corrected by applying the backing layer after the protective layer. it can. As an apparatus used for coating the heat-sensitive recording layer, the protective layer and the back coating layer, an air knife coater, a gravure coater, a roll coater, a rod coater, a curtain coater, a die coater, a lip coater, a blade coater and the like are used.

The backing layer of the present invention is applied to the back surface of the support after coating a heat-sensitive recording layer and a protective layer on one surface of the support, and the layer is a water-dispersible core-shell type acrylic resin. It is contained as a main component, and a water-proofing agent or a defoaming agent can be added as necessary to improve water resistance. The coating amount of the core-shell type acrylic resin for maximizing the effect of preventing penetration of the pressure-sensitive adhesive and the effect of improving the barrier property by the backing layer is 1 to 3 g / m ² .

The thermal recording layer generally contains water as a dispersion medium,
Leuco dye, electron-accepting acidic substance, sensitizer if necessary,
A ball mill, together with or separately from the preservability improver,
Use an attritor, sand mill, etc.
After finely pulverizing so that the average particle size is 2 μm or less,
Support the coating solution for the thermal recording layer prepared by adding a binder
It is formed by applying and drying on one side of the
The amount is usually 2-8g / m ², Preferably 4-6 g / m²degree
Is. Also, the surface of the heat-sensitive recording layer is a super calendar,
Smoothing process with gloss calendar, machine calendar, etc.
To improve recording density and sensitivity
You can

As the color-forming dye used in the present invention, a colorless to light-colored electron-donating dye capable of reacting with an electron-accepting acidic substance under heating to form a color can be used. For example, 2,2 bis {4- [6 '-(N-cyclohexyl-
N-methylamino) -3'-methylspiro (phthalide-
3,9'-xanthene) -2'-ylamido] phenyl} propane, 3-diethylamino-6-methyl-7-
Anilinofluorane, 3-piperidino-6-methyl-7
-Anilinofluorane, 3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluorane, 3-diethylamino-7-chloroanilinofluorane, 3- [N-ethyl-N -(P-Methylphenyl) amino] -6-methyl-7-anilinofluorane, 3-diethylamino-7- (metatrifluoromethyl) anilinofluorane, 3- (N-ethyl-N-tetrahydrofurfuryl ) Amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isopentyl) amino-6
-Methyl-7-anilinofluorane, 3- (N, N-dibutyl) amino-6-methyl-7-anilinofluorane, and other fluorane dyes are available, and the dyes are not limited to these and two The above can also be used together.

The electron-accepting acidic substance used in the heat-sensitive recording layer is, for example, 4,4'-isopropylidenediphenol, 4,4'-cyclohexylidenediphenol,
2,2-bis (4-hydroxyphenyl) -4-methylpentane, benzyl 4-hydroxybenzoate, 2,4 '
-Dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, bis (3-allyl-
4-hydroxyphenyl) sulfone, 4-hydroxy-
4′-methyldiphenyl sulfone, bis (p-hydroxyphenyl) butyl acetate, methyl bis (p-hydroxyphenyl) acetate, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [ Phenolic compounds such as α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene and 1,3-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, N- (p- Toluenesulfonyl) carbamoyl acid p
-Cumylphenyl ester, N- (p-toluenesulfonyl) carbamoyl acid p-benzyloxyphenyl ester, N- (o-toluoyl) -p-toluenesulfoamide, 4,4'-bis (Np-toluenesulfonyl) Aminocarbonylamino) diphenylmethane, etc.
Those having SO ₂ NH-bond, zinc p-chlorobenzoate, zinc 4- [2- (p-methoxyphenoxy) ethyloxy] salicylate, zinc 4- [3- (p-tolylsulfonyl) propyloxy] salicylate, 5, -[P- (2
-P methoxyphenoxyethoxy) cumyl] salicylic acid zinc salt and the like.

The heat-sensitive recording layer may contain a storability improver for increasing the storage stability of a recorded image and a sensitizer for increasing the recording sensitivity. Specific examples of such a preservability improving agent include, for example, 2,2′-ethylidene bis (4,6-di-tert-butylphenol), 4,
4'-thiobis (2-methyl-6-tert-butylphenol), 1,1,3-tris (2methyl-4hydroxy-5-tert-butylphenyl) butane, 1,
Hindered phenol compounds such as 1,3-tris (2methyl-4hydroxy-5-cyclohexylphenyl) butane and 2,2-bis (4hydroxy-3,5-dimethylphenyl) propane, 1,4-diglycidyloxy Benzene, 4,4'-diglycidyloxydiphenyl sulfone, 4-benzyloxy-4 '-(2-methylglycidyloxy) diphenyl sulfone, diglycidyl terephthalate, cresol novolac type epoxy resin, phenol novolac type epoxy resin, bisphenol A type Epoxy compounds such as epoxy resin, N, N′-di-2-naphthyl-p-phenylenediamine, sodium or polyvalent metal salt of 2,2′-methylenebis (4,6-di-tert-butylphenyl) phosphate, Bis (4-ethyleneiminocarbonylami) Nophenyl) methane and the like.

Specific examples of the sensitizer include stearic acid amide, methylenebisstearic acid amide, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, 2-naphthylbenzyl ether, m-ta-phenyl and p-benzyl. Biphenyl, p-tolyl biphenyl ether, di (p-methoxyphenoxyethyl) ether, 1,2-di (3-methylphenoxy) ethane,
1,2-di (4-methylphenoxy) ethane, 1,2-
Di (4-methoxyphenoxy) ethane, 1,2-di (4
-Chlorophenoxy) ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2- (3-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p
-Acetotoluidide, p-acetophenetidide, N-acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, oxalic acid di-p-chlorobenzyl ester, oxalic acid di-p-methylbenzyl ester, oxalic acid Dibenzyl ester etc. are illustrated.

Specific examples of the binder used in the heat-sensitive recording layer of the present invention include starch derivatives, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, casein, gelatin, polyvinyl alcohol, carboxy modified polyvinyl alcohol and acetoacetyl group. Modified polyvinyl alcohol, silicon polyvinyl alcohol, diisobutylene-maleic anhydride copolymer salt, styrene-maleic anhydride copolymer salt, ethylene-acrylic acid copolymer salt, styrene-acrylic acid copolymer salt, urea resin, Examples thereof include melamine resin, amide resin, urethane resin latex, acrylic resin latex, and styrene-butadiene resin latex.

Further, various auxiliary agents may be added to the coating liquid for the heat-sensitive recording layer, if necessary, and examples thereof include kaolin, light (heavy) calcium carbonate, calcined kaolin, titanium oxide and magnesium carbonate. Aluminum hydroxide, amorphous silica, pigments such as urea-formalin resin filler, sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, dispersant for fatty acid metal salt, zinc stearate, calcium stearate, polyethylene Examples thereof include waxes such as wax, carnauba wax, paraffin wax and ester wax, defoaming agents and coloring dyes.

A protective layer is provided on the heat-sensitive recording layer in order to enhance the chemical resistance and water resistance of the recording portion. Such a protective layer is formed by applying a coating liquid for a protective layer containing a water-soluble or water-dispersible binder as a main component (preferably adding a pigment) onto the heat-sensitive recording layer and drying it.

The adhesive contained in the coating liquid for the protective layer includes completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, diaceto-modified polyvinyl alcohol. Polyvinyl alcohols such as starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, casein, gelatin, diisobutylene-maleic anhydride copolymer salt, styrene-maleic anhydride copolymer salt, ethylene-acrylic acid copolymer salt. , Styrene-acrylic acid copolymer salt, urethane latex, acrylic latex, styrene-butadiene latex and the like, preferably those having film-forming property.

A pigment is preferably added to the protective layer of the present invention, and as the pigment, kaolin, silica, clay, calcined kaolin, talc, calcium carbonate, aluminum hydroxide, magnesium carbonate, titanium oxide, zinc oxide, silica. Examples thereof include aluminum oxide, polystyrene resin, polyacrylic resin, melamine resin, urea resin and the like. If the addition amount is usually less than 5% by weight, sticking tends to occur and the thermal head matching property tends to be poor, and if it is more than 30% by weight, infiltration of chemicals or the like cannot be sufficiently prevented. Therefore, 5 to 30% by weight of the protective layer
It is preferable to use a pigment in the range of. The protective layer further has a water-proofing agent such as formaldehyde, polyamide-epichlorohydrin resin, melamine resin, melamine-formaldehyde resin, polyamide resin, or ammonium chloride, which is made water-resistant by reacting with a hydrophobic polymer, and higher fatty acids and higher fatty acids. Amides, higher fatty acid metal salts, paraffin wax, microcrystal wax, carnauba wax, and other lubricants, defoaming agents, surfactants and the like can be added.

The protective layer is coated in one layer to several layers. When the coating amount is too large, the color developability tends to be poor, and when the coating amount is too small, a uniform layer cannot be obtained and the effect as a protective layer tends to be difficult to obtain. Therefore, the coating amount is preferably 1 to It is 4 g / m ² .

As the binder used for the backing layer, generally the binder used for the protective layer is used as it is, or a water-soluble binder is used, and the backing layer is peeled off via a pressure-sensitive adhesive layer. A heat-sensitive recording sheet for labels with paper attached can be obtained. However, it should be noted that some of these binders do not have sufficient adhesive strength as a label because the amount of transfer of the pressure sensitive adhesive to the backing layer surface is small due to its excellent film forming property. is there. Also, food labels are often used while the food is immersed in water, so if the water resistance of the backing layer binder is insufficient, the backing layer binder will dissolve in water. Problems such as peeling off only the printed label occur. Therefore, the binder of the backing layer is required to have a function of preventing color development and desensitization by the pressure-sensitive adhesive, as well as an appropriate amount of transfer and sufficient water resistance. In addition, proper film forming property is also required.

The binder used in the backing layer of the present invention is a copolymer emulsion containing acrylonitrile / butyl acrylate as a core particle as a main monomer and a copolymer emulsion containing styrene / 2-ethylhexyl acrylate as a main monomer. It is a core-shell type acrylic emulsion obtained by copolymerizing methacrylamide and an unsaturated monomer component copolymerizable with methacrylamide in the presence of. The coating amount of the backing layer is preferably 1 to 3 g / m ^{2, and when it} is too small, chemicals and the like permeate from the back surface of the support, and there is a tendency that background fogging of the thermal recording layer and fading of recorded images cannot be prevented.

As the pressure-sensitive adhesive layer and the release paper provided on the side of the backing layer, any of those used for conventional release labels can be used. For example, as the adhesive, a styrene-butadiene polymer, Acrylic ester-based polymer or the like is used, and the release paper is formed by a paper or the like having a release layer such as a silicone resin provided on a backing paper.

Further, in order to improve color development sensitivity and recording image quality, an undercoat layer containing an oil-absorbing pigment or hollow particles as a main component may be provided between the support and the heat-sensitive recording layer, or various layers may be formed and then smoothed by a super calendar. It can also be subjected to a chemical treatment.

An undercoat layer is provided if necessary, but if the coating amount is too small, its effect is small, and if it is too large, the strength of the paper is weakened and it is not economical. The layer is usually 3 to 20 g / m ² , especially 5 to 10
It is provided with a coating amount of g / m ² .

As the support used in the present invention, paper is used. However, synthetic paper, metal foil, laminated paper made of polyethylene or the like, film made of polyethylene terephthalate or the like may be used alone or in combination. I can. As an apparatus used for coating the undercoat layer, the heat-sensitive recording layer and the protective layer, an air knife coater, a gravure coater, a roll coater, a rod coater, a curtain coater, a die coater, a lip coater, a blade coater and the like are used.

[0028]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
In addition, the part and% in an Example show a mass part and the mass%.

Example 1 [Preparation of Coating Liquid for Undercoat Layer] Ansilex (Engelhard, calcined kaolin) 100 parts 10% sodium hexametaphosphate 4 parts 48% styrene-butadiene latex 40 parts 20% phosphoric ester modified starch aqueous solution Water was added to 30 parts or more of the mixture and stirred to prepare an undercoat layer coating liquid with a solid content concentration of 40%. Apply 60 g / m ² of base paper with a blade coater to a dry coating amount of 10 g / m ² and dry.
An undercoat layer was obtained.

[Preparation of Dispersion] Liquid (A) 3-Dibutylamino-6-methyl-7-anilinofluorane 100 parts 10% sulfonation-modified PVA aqueous solution 80 parts water 100 parts A liquid is Dynomil (Shinmaru Enterprises). S) was used to pulverize the particles until the volume average particle diameter became 0.5 μm. (B) Liquid bis- (3-allyl-4-hydroxyphenyl) sulfone 50 parts 2-benzyloxynaphthalene 70 parts 1,1,3-tris- (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane 20 Parts 10% sulfonation-modified PVA aqueous solution 70 parts water 160 parts B liquid was pulverized using Dynomill (manufactured by Shinmaru Enterprises Co., Ltd.) until the volume average particle diameter became 1 μm. (C) Liquid light calcium carbonate 10 parts 10% sodium hexametaphosphate 1 part water 14 parts

[Preparation of coating liquid for heat-sensitive recording layer] A coating liquid for heat-sensitive recording layer was prepared by the following formulation. Solution (C) 25 parts (B) solution 75 parts 10% aqueous polyvinyl alcohol solution 100 parts 50% zinc stearate emulsion 8 parts solution (A) 18 parts water 20 parts Using this thermosensitive recording layer coating liquid, the undercoat layer is formed. An air knife coater was used to apply a dry coating amount of 5 g / m ² and the mixture was dried to obtain a heat-sensitive recording layer.

[Preparation of protective layer coating liquid (E)] A protective layer coating liquid was prepared by the following formulation. 10% aqueous solution of polyvinyl alcohol 100 parts 50% zinc stearate emulsion 4 parts 20% silica (Mizukasil P527 manufactured by Mizusawa Chemical Industry Co., Ltd.) 5 parts Using this protective layer coating liquid, dry coating amount on the heat-sensitive recording layer with an air knife coater The heat-sensitive recording sheet was obtained by coating and drying to 2.5 g / m ^2, and smoothing with a calender to a Beck smoothness of 600 to 800 seconds.

[Preparation of Backing Layer Coating Liquid (F)] Water-dispersible polymerization by polymerizing methacrylamide and methacrylic acid in the presence of acrylonitrile / butyl acrylate / 2-hydroxyethyl methacrylate / methacrylic acid polymer emulsion. The product (synthetic product X) was obtained. A backing layer coating liquid (F) was prepared with the following composition. 20% water-dispersible polymer (synthetic compound X) 100 parts 25% polyamide-epichlorohydrin cross-linking agent 5 parts water 100 parts Using this backing layer coating liquid (F), the above heat-sensitive recording layer and heat-sensitive recording layer. On the opposite surface of the heat-sensitive recording sheet having a protective layer formed thereon, an air knife coater was applied and dried to give a coating amount of 2 g / m ² , and a backing layer was provided to obtain a heat-sensitive recording sheet for labels of the present invention.

Example 2 [Preparation of Backing Layer Coating Liquid (G)] Water-dispersible polymerization by polymerizing methacrylamide in the presence of acrylonitrile / butyl acrylate / 2-hydroxyethyl methacrylate / methacrylic acid polymer emulsion. The product (synthetic product Y) was obtained. A backing layer coating liquid (G) was prepared with the following formulation. 20% water-dispersible polymer (synthetic Y) 100 parts 25% polyamide-epichlorohydrin crosslinking agent 5 parts water 100 parts Using this backing layer coating liquid (G), thermal recording was carried out in the same manner as in Example 1. Layer and a thermosensitive recording sheet provided with a protective layer on the thermosensitive recording layer, dried by an air knife coater on the opposite surface to a coating amount of 2 g /
The coating was dried so as to have a surface area of m ² and a backing layer was provided to obtain a heat-sensitive recording sheet for labels of the present invention.

Comparative Example 1 [Preparation of Backing Layer Coating Liquid (H)] A backing layer coating liquid (H) was prepared with the following composition. 48% styrene-butadiene latex 100 parts water 380 parts The backing layer coating solution (F) of Example 1 was replaced with the backing layer coating solution (H).
A thermal recording sheet for labels was obtained in the same manner as in Example 1 except that the above was used.

Comparative Example 2 The thermosensitive recording for labels was carried out in the same manner as in Example 1 except that the coating solution (F) for the backing layer in Example 1 was completely saponified polyvinyl alcohol (Gosenol NM-11 manufactured by Nippon Gosei Co., Ltd.). Got the sheet.

Comparative Example 3 A thermosensitive recording sheet of the present invention was prepared in the same manner as in Example 1, except that the backing layer coating solution (F) in Example 1 was changed to phosphoric ester modified starch. It was

Comparative Example 4 The backing layer coating liquid (F) of Example 1 was first applied, and then the undercoat layer, the heat-sensitive recording layer and the protective layer similar to those of Example 1 were sequentially provided on the opposite surface to provide heat-sensitive labeling. A recording sheet was obtained.

Comparative Example 5 After the undercoat layer and the heat-sensitive recording layer of Example 1 were sequentially provided, the back coating layer coating liquid (F) was smear dried on the opposite side with an air knife coater to a dry coating amount of 2 g / m ^2. Finally, a protective layer was provided on the surface of the thermosensitive recording layer to obtain a thermosensitive recording sheet for labels.

The thermal recording sheets for labels obtained in Examples 1 and 2 and Comparative Examples 1 to 5 were evaluated by the following methods.
The evaluation results are shown in Table 1. "Punk on the protective layer surface" Apply the coating liquid for the protective layer, and visually check for blister or puncture on the protective layer surface. In addition, ethanol was added dropwise, and the presence or absence of dot-like color development at the dropping location was evaluated. "Whiteness" The whiteness of the recording surface was measured according to JIS P8123. The larger the number, the higher the whiteness. 80 in practical use
If it is above, there is no problem. “Curl” The thermal recording sheet for labels obtained is 210
The sheet was cut into a size of mm × 297 mm in length, left standing in an environment of 23 ° C and 50% RH for an hour, and the lifting height of the sheet end surface was measured, and the average value at four points was taken. As for the display method, the positive curl is raised to the color development side, and the negative curl is raised to the opposite side. The backing layer side of the "adhesive" heat-sensitive recording sheet, a pressure-sensitive adhesive acrylic coating amount after drying was coated and dried so as to be 10 to 20 g / m ^2, of 60 mm × 40 mm label and Then, it was attached to a vinyl chloride resin sheet. 23 ° C / 50
It was left for 1 hour in an environment of% RH, the label was peeled off by hand, and the strength of adhesion was evaluated. The evaluation criteria are as follows. ◯: Adhesiveness to the sheet is good, and the label itself tears when trying to peel it off. Δ: When peeling, most of the peeling occurred from the vinyl chloride sheet, but part of the label was torn. X: When peeling, there is resistance, but the label peels from the PVC sheet without tearing. The label attached to the vinyl chloride sheet was immersed in pure water at 23 ° C. for 24 hours in the same manner as above, and the strength of adhesion was evaluated. The evaluation criteria are as follows. ○: The label itself tears if it is peeled off even after watering. Δ: The label is not peeled off, but peeled off by hand. X: The label comes off and floats on water. "Color development" Head resistance 280 with Okura Denki color development tester
A 0 ohm thermal head was used to develop color with a pulse width of 1.2 msec and the density was measured with a Macbeth reflection densitometer. The higher the number, the higher the concentration. There is no problem if it is practically 1.20 or more. "Plasticizer resistance" A vinyl chloride sheet containing 30% of dioctyl phthalate was superposed on a printed thermal recording sheet, left in a dryer at 40 ° C for 24 hours, and the decrease in the density of the colored portion after the treatment was visually evaluated. did. The evaluation criteria are as follows. ◯: Almost no decrease in density. Δ: Can be used although the concentration is slightly lowered. X: Large decrease in density.

[0041]

[Table 1]

[0042]

The heat-sensitive recording sheet of the present invention, when used as a heat-sensitive label paper, has good suitability for a pressure-sensitive adhesive and is excellent in whiteness, curl and storability.

Claims (2)

[Claims] 1. A heat-sensitive recording layer containing a colorless or light-colored electron-donating dye, an electron-accepting acidic substance capable of coloring the dye by heating and an adhesive as a main component is provided on the support, and the heat-sensitive recording layer is provided on the heat-sensitive recording layer. In a thermal recording sheet having a protective layer containing a water-soluble or water-dispersible binder as a main component and a backing layer containing a binder as a main component on the back surface of the support, the binder of the backing layer is a core-shell type A method for producing a heat-sensitive recording sheet, which is an acrylic resin and further comprises applying a backing layer after applying a heat-sensitive recording layer and a protective layer. 2. The method for producing a heat-sensitive recording sheet according to claim 1, wherein the heat-sensitive recording sheet is a heat-sensitive recording paper sheet having a backing layer surface and a release paper attached thereto via a pressure-sensitive adhesive layer.