JPH03146391A - Thermal recording material - Google Patents

Abstract

PURPOSE:To improve the reproducibility of a printing pixel in every range from a low density to a high density by providing a thermal recording layer on cast-coated paper having a dynamic wet value adjusted to be in a specific range. CONSTITUTION:A cast-coated layer having a dynamic wet value of -0.15 to 0.00g is provided on a substrate, and on the cast-coated layer a thermal recording layer is provided. If the dynamic wet value is higher than 0.00g, a printing recording density is reduced. On the other hand, if it is less than -0.15g, the poor adhesion between the cast-coated layer and the thermal recording layer prevents the elimination of a repelling phenomenon and the rubbing-off of the thermal recording layer. It is particularly desirable that a light calcium carbonate having a BET specific surface area of 10g/m<2> or higher is used in the range of 40-100wt.% of the total pigment in the cast-coated layer. In this manner, an adjustment to the above wet value can be facilitated, and an improvement effect is obviously shown in coating characteristics of the thermal recording layer or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a heat-sensitive recording medium, and particularly to a heat-sensitive recording medium that has excellent print pixel reproducibility and high recording density.

``Prior art'' Conventionally, a colored image is obtained by utilizing a color reaction between a coloring agent and a coloring agent and bringing the two substances into contact with each other using heat.

Thermosensitive recording media made of the same type of heat-sensitive materials are well known. Such heat-sensitive recording media are relatively inexpensive, and the recording device is compact and maintenance is relatively easy, so they are used in a wide range of fields as recording media for facsimiles and computers.

With the diversification of applications, thermal recording materials have excellent reproducibility of printed pixels in any range from low density to high density, and can produce recorded images of high quality comparable to silver halide photography. The demand for this is increasing. Furthermore, as recording equipment becomes faster, there is an increasing demand for heat-sensitive recording materials with excellent dynamic recording sensitivity.

In order to obtain such a heat-sensitive recording medium with high sensitivity and high image quality, an intermediate layer made of an oil-absorbing inorganic pigment is provided (Japanese Patent Application Laid-open Nos. 59-155097 and 61-44683). Recording bodies composed of multiple layers to improve smoothness and heat insulation (JP-A-61-11286, JP-A-61-1)
No. 93880) etc. have been proposed.

However, when a highly oil-absorbing inorganic pigment such as amorphous silica or calcined kaolin is used as a pigment, the specific surface area of the pigment increases, leading to surface activation of silicic acid, etc., especially when acidic paper base paper is used as a support. Another drawback is that a phenomenon called background fog 1 occurs, in which the whiteness of the recording medium decreases.

In addition, recording materials with improved smoothness using art paper, coated paper, or cast coated paper as a support (Japanese Patent Laid-Open No. 54
-83841) has been proposed.

However, when art paper or coated paper is used, the insulation properties are low and it is difficult to achieve high sensitivity.

When using cast-coated paper, when applying the heat-sensitive recording coating liquid onto the cast-coated paper, the coating liquid tends to repel, and the adhesion between the cast-coated paper and the heat-sensitive recording layer is poor. Therefore, there was a problem that the heat-sensitive recording layer would rub off when the surface of the heat-sensitive recording layer was rubbed.

"Problems to be Solved by the Invention" The present invention aims to solve the above problems and provide a thermal recording medium with excellent reproducibility of printed pixels in all areas from low density to high density. do.

"Means for Solving the Problems" The present invention provides a support with a dynamic wetting value of -0.15 to 0. OOg
A heat-sensitive recording material is provided with a cast coating layer, and further provided with a heat-sensitive recording layer on the cast coating layer.

"Function" The present inventors have solved the drawbacks such as insufficient coating suitability of a coating liquid for a heat-sensitive recording layer and insufficient surface strength of the formed heat-sensitive recording layer when a heat-sensitive recording layer is provided on a cast coated paper. As a result of extensive research, the dynamic wettability value of cast coated paper was reduced to -0,
It has been found that the above-mentioned drawbacks can be overcome by adjusting the amount within the range of 15 to 0.00 g.

That is, the dynamic wettability value (cast coating layer surface) of cast coated paper is -0.15 to 0. By providing the heat-sensitive recording layer on cast coated paper whose OOg is adjusted to a range of -0.10 to 0.00 g, the coating suitability of the coating liquid for the heat-sensitive recording layer and the coatability of the heat-sensitive recording layer are improved. Defects such as insufficient surface strength can be effectively eliminated.

The dynamic wettability value of cast coated paper is determined by the change in the adhesive force against water over time as a measure of wettability. It is expressed as a value measured using a

Specifically, a 2 cm x 5 cm test piece with insulating tape pasted on the back side of cast-coated paper was immersed in water at a speed of 16 mm/sec to a depth of 12 mm for 10 seconds. ), and the magnitude of wetting (ie, dynamic wetting value) indicates that the smaller the value, the harder it is to get wet, and conversely, the larger the value, the easier it is to get wet.

It should be noted that the wettability value measured by a dynamic wettability tester after 1 second of immersion in water has a large influence on the repellency of the coating liquid for the heat-sensitive recording layer and the rubbing off of the recording layer. The term "dynamic wetting value" refers to the dynamic wetting value 1 second after immersion in water.

Although it is not necessarily clear why the effect of the present invention can be obtained by setting the dynamic wetting value of the cast coated paper to a specific value, it is possible to obtain the effects of the present invention by increasing the wettability of the cast coated paper. It becomes difficult for the coating liquid to repel, and the coating liquid for the heat-sensitive recording layer easily penetrates into the cast coating layer, so the adhesion between the heat-sensitive recording layer and the cast coating layer improves, and the heat-sensitive recording layer It is assumed that this will eliminate the rubbing off.

Incidentally, when the dynamic wetting value exceeds O,-00g, a decrease in print recording density is observed. It is presumed that this is because the coating liquid for the heat-sensitive recording layer penetrates into the cast coating layer significantly.

In addition, when producing cast coated paper, the cast coat layer tends to stick to the cast drum, resulting in a phenomenon called drum pick, where part of the cast coat layer sticks to the cast drum surface. This makes it difficult to produce cast coated paper.

On the other hand, if it is less than -0.15 g, the adhesion between the CAST coating layer and the heat-sensitive recording layer is poor, making it impossible to eliminate the repelling phenomenon and the rubbing off of the recording layer.

Methods for controlling the dynamic wetting value of cast coated papers include kaolin, aluminum hydroxide, titanium dioxide, satin white, heavy calcium carbonate, light calcium carbonate, talc,
Types of pigments such as acid clay and plastic pigments, average particle diameter, particle size distribution, specific surface area and compounding ratio, type and amount of adhesive, type and amount of release agent, casting method, composition of rewetting liquid and gelling liquid There are many factors such as these, and it is possible to achieve this by appropriately combining these methods depending on the characteristics of the heat-sensitive recording material.

Among these, light calcium carbonate having a BET specific surface area of 10 g/m'' or more is preferably used in an amount of 40 to 100% by weight, more preferably 50 to 100% by weight of the total pigment in the cast coating layer.
When used in the range of 100% by weight, the wetting value can be easily adjusted to the above-mentioned value, and a remarkable improvement effect is observed in the coating properties of the heat-sensitive recording layer.

As the adhesive, a synthetic latex containing butadiene, such as a styrene-butadiene latex or a methacrylic acid derivative-butadiene latex, is preferably used. The synthetic latex adhesive containing butadiene is preferably used in an amount of 5 to 25 parts by weight based on 100 parts by weight of the total pigment contained in the cast coating layer, from the viewpoint of the surface strength of the heat-sensitive recording layer.

If there is less adhesive, the adhesion of the pigment particles will decrease.
New problems may occur, such as paper dust being more likely to be generated when cutting with a cutter.

On the other hand, if there is a large amount of adhesive, penetration of the heat-sensitive recording layer into the cast coating layer becomes poor, and the surface strength of the heat-sensitive recording layer may decrease.

It should be noted that no correlation could be found between the contact angle of the cast coated paper with water, the value of the water absorption tester, etc., and the repellency or rubbing off of the heat-sensitive recording layer.

The cast coating layer can contain pigments and adhesives that are generally used in the field of cast coating and heat-sensitive recording materials, within a range that does not impede the effects of the present invention.

In addition to the above-mentioned light calcium carbonate, examples of pigments include clay, kaolin, argonium hydroxide, titanium oxide, barium sulfate, zinc oxide, satin white, plastic pigment, and pigments with an oil absorption of 80 cc based on the JIS K 5101 method. /100g or more of various oil-absorbing pigments can also be selected and used as appropriate. Calcined kaolin for oil-absorbing pigments,
Examples include micronized talc, amorphous silica, polystyrene fillers, and amino resin fillers. One or more of these may be used as appropriate.

In addition to base latex containing butadiene, adhesives include natural adhesives such as starch, modified starch, casein, and soybean protein, acrylic emulsion latex, latex such as styrene-acrylic acid copolymer, and polyvinyl alcohol. , methyl cellulose, carboxyethyl cellulose, hydroxyethyl cellulose, and water-soluble synthetic polymers such as polyacrylic acid.

Furthermore, in the cast coating layer, release agents such as fatty acids such as stearic acid, oleic acid, and palmitic acid, and their salts such as sodium, calcium, ammonium, and zinc, sulfated castor oil, polyethylene wax, and alkyl phosphorous are used. One or more of various known mold release agents, such as sucrose higher fatty acid ester, lecithin, and various surfactants, may be used as appropriate.

Furthermore, various auxiliary agents such as a dispersant, a waterproofing agent, a preservative, a dye, an antifoaming agent, and a flow modifier can be added to the cast coating layer as required.

A coating liquid for a cast coating layer is usually prepared by dispersing or dissolving the various components described above in water as a medium.

The support for cast coated paper is not particularly limited, but acidic or neutral paper made using a fourdrinier machine, twin wire machine, Yankee machine, etc., which is generally used for cast coated paper and heat-sensitive recording media, etc. High-quality paper, single-sided glossy paper, etc. are used.

In addition, if necessary, a general pigment coating composition may be pre-coated on one or both sides of the support, and in that case, the coating amount is 4 to 30 g/m in terms of dry weight per side. degree is preferred.

There is no particular limitation on the method of coating the coating liquid for the cast coating layer thus obtained on the support, and examples include air knife coater, pure blade coater, rondo blade coater, bill blade coater, roll coater, and brush. Various coating devices such as coaters and size presses are used as appropriate.

The coating amount of the cast coating layer is also not particularly limited and may be adjusted as appropriate depending on the desired characteristics of the recording medium, but generally the thickness of the cast coating layer is about 5 to 40 μm. It is preferable to adjust the dry coating amount to about 4 to 35 g/m''.Furthermore, the cast coating layer is not limited to a single layer structure, but can also have a multilayer structure of 2N or more.

After coating the coating liquid for the cast coating layer, the coating layer, while still in a plastic state containing water, is pressed against the cast drum surface and dried, and after the moisture in the coating layer has substantially evaporated. The mold is released from the cast drum to form a cast coating layer.

Various known methods such as a wet casting method, a rewetting casting method, and a gelling casting method are applied to the production method of such cast coated paper.

A heat-sensitive recording layer is formed on the cast coating layer thus formed, but the method of forming the heat-sensitive recording layer is not particularly limited, and the combination of the coloring agent and the coloring agent constituting the heat-sensitive recording layer can also be Any combination can be used as long as the two come into contact with each other due to heat and a color reaction occurs. For example, combinations of colorless or light-colored basic dyes and inorganic or organic acidic substances, combinations of higher fatty acid metal salts such as ferric stearate and phenols such as gallic acid, diazonium compounds, couplers, and bases. A thermosensitive recording layer containing a combination of a basic dye and an acidic substance can be appropriately selected and used, but a combination of a basic dye and an acidic substance is particularly preferred.

Various types of colorless to light-colored basic dyes are known, and examples include the following.

3.3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3.3-bis(p-dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl)-3-(1,2 -dimethylindol-3-yl)phthalide, 3-(p-dimethylaminophenyl)-
3-(2-methylindol-3-yl)phthalide, 3
．． 3-bis(1,2-dimethylindol-3-yl)
-5-dimethylaminophthalide, 3,3-bis(1゜2
-dimethylindol-3-yl)-6-dimethylaminophthalide, 3,3-bis(9-ethylcarbazole-
3-yl)-6-dimethylagonophthalide, 3,3-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-'; methylanophenyl-3-(1-methylpyrrole triallylmethane dyes such as -3-yl)-6-dimethylaminophthalide, 4
．． 4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoolamine, N-
diphenylmethane dyes such as 2,4,5-)lichlorophenylleucoolamine, thiazine dyes such as benzoylleucomethylene blue and p-nitrobenzoylleucomethylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, Spiro dyes such as 3-phenyl-spirodinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho-(6'-methoxybenzo)spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine-B ani Lactam dyes such as linolactam, rhodagon (p-nitroanilino) lactam, rhodamine (0 nichloroanilino) lactam, 3-dimethylamino-7-methoxyfluoran, 3-diethylamino-6-methoxyfluoran, 3-
Diethylamino-7-medoxyfluorane, 3-diethylamino-two-chlorofluorane, 3-diethylamino-6-methyl-two-chlorofluorane, 3-diethylamino-6,7-dimethylfluorane, 3-(N -ethyl-p-1luidino)-7-methylfluorane, 3-diethylamino7-N-acetyl-N-methylagonofluorane, 3-diethylamino-7-N-methylaminofluorane, 3-diethylamino 7-dipendylanofluorane, 3-diethylamino-7-N-methyl-N
-benzylaminofluorane, 3-diethylamino-7
-N-chloroethyl-N-methylaminofluorane, 3
-diethylamino-7-N-diethylaminofluorane, 3-(N-ethyl-p-)luidino)-6-methyl-
7-phenylaminofluorane, 3-(N-cyclopentyl-N-ethylamino)-6-methyl-7-anilinofluorane, 3-(N-ethyl-p-toluidino)-6-
Methyl-7-(p-1-luidino)fluoran, 3-diethylamino-6-methyl-7-phenylaminofluoran, 3-diethylamino-7-(2-carbomethoxy-phenylamino)fluoran, 3-(N- Ethyl-N
-Isoatamino)-6-methyl-7-phenylaminofluorane, 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluorane, 3-pyrrolidino-6-methyl-7 -phenylaminofluorane, 3-piperidino-6-methyl=7-phenylaminofluorane, 3-diethylamino-6-methyl-
7-xylidinofluorane, 3-diethylamino-7-
(o-chlorophenylamino)fluoran, 3-diethylamino-7-(0-chlorophenylamino)fluoran, 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluorane, 3-N-methyl-N-tetrahydrofuran Furylamino-6-methyl-7-anilinofluoran, 3-N-ethyl-N-tetrahydrofurfurylamino-6-methyl-7; fluoran dyes such as anilinofluoran, but of course, these It is not limited to these dyes, and two or more types can be used in combination.

Various types of inorganic or organic acidic substances that develop color upon contact with basic dyes are also known, and examples thereof include the following.

Inorganic acidic substances such as activated clay, acid clay, acpulgite, bentonite, colloidal silica, aluminum silicate, 4-tert-butylphenol, 4-hydroxyphenoxide, α-naphthol, β-naphthol, 4
-Hydroxyacetophenol, 4-tart-octylcatechol, 2,2'-dihydroxydiphenol,
2.2'-methylenebis(4-methyl-6-terL-
isobutylphenol), 4.4'-isopropylidene bis(2-tert-butylphenol), 4. 4
"-5ec-butylidenediphenol, 4-phenylphenol, 4.4'-isopropylidenediphenol, 2.2'-methylenebis(4-chlorophenol)
, hydroquinone, 4,4'-cyclohexylidene diphenol, benzyl 4-hydroxybenzoate, dimethyl 4-hydroxyphthalate, hydroquinone monobenzyl ether, 4-hydroxy-4'-isopropyloxydiphenyl sulfone, 3'4'-tetra Methylene-
4-hydroxydiphenylsulfone, 4.4'-(
1,3-dimethylbutylidene)bisphenol, 4.4
'-(1-phenylethylidene) bisphenol, 4°4'-(p-phenylene diisopropylidene) diphenol, 4.4'-(m-phenylene diisopropylidene) diphenol, novolak type phenol resin, phenol polymer Phenolic compounds such as benzoic acid, p
-tert-butylbenzoic acid, trichlorobenzoic acid,
Terephthalic acid, 3-5ec-butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3.5-dimethyl-4-hydroxybenzoic acid, salicylic acid, 3-isoprobylsalicylic acid, 3-tert −
Butylsalicylic acid, 3-benzylsalicylic acid, 3-(α
-methylbenzyl) salicyl M, 3-ri0O-5=(α
-methylbenzyl)salicylic acid, 3,5-di-tert
Aromatic carboxylic acids such as -butylsalicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3゜5-di-α-methylbenzylsalicylic acid, and these phenolic compounds, aromatic carboxylic acids, etc. Examples include organic acidic substances such as salts with polyvalent metals such as zinc, magnesium, aluminium, calcium, titanium, manganese, tin, and nickel.

The proportion of the basic colorless dye and the acidic substance in combination is not necessarily limited and may be adjusted depending on the materials used, but it is generally 1 to 10 parts by weight, preferably 1 part by weight, per 1 part by weight of the basic colorless dye. On the order of .5 to 7 parts by weight of acidic material is used. Note that, of course, two or more types of acidic substances may be used in combination as necessary.

To prepare a coating solution containing these substances, generally, water is used as a dispersion medium, and dyes, acidic substances, etc. are added together or separately using a ball mill, attritor, vertical or horizontal sand mill, etc., or stirring or grinding machine. It is prepared by dispersing, etc.

Such coating liquids usually contain starches and binders as binders.
Hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, gum arabic, polyvinyl alcohol, diisobutylene/maleic anhydride copolymer salt, styrene/maleic anhydride copolymer salt, ethylene/acrylic acid copolymer salt, styrene/
Acrylic acid copolymer salt, natural rubber emulsion, styrene/butadiene copolymer emulsion, acrylolitrile/butadiene copolymer emulsion, methyl methacrylate/butadiene copolymer emulsion, polychloroprene emulsion, vinyl acetate emulsion, ethylene/acetic acid Vinyl emulsions etc. have a total solid content of 10~
It is added in an amount of about 40% by weight, preferably about 15 to 30% by weight.

Furthermore, various auxiliary agents can be added to the coating liquid.
For example, dispersants such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, alginates, fatty acid metal salts, ultraviolet absorbers such as benzophenone and triazole, and foaming agents thereof. Examples include fluorescent dyes and colored dyes.

In addition, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax, calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, and sulfuric acid may also be used as necessary. Inorganic pigments such as zinc, talc, kaolin, clay, fired clay, colloidal silica, styrene microballs,
Nylon powder, polyethylene powder, urea/formalin resin filler, organic pigments such as raw starch, fatty acid amides such as stearic acid amide, stearic acid methylene bisamide, oleic acid amide, pargotic acid amide, coconut fatty acid amide, dibenzyl terephthalate), 1.2-
Di(3-methylphenoxy)ethane, 1.2-diphenoxyethane, 4.4'-ethylenedioxy-bis-benzoic acid diphenylmethyl ester, 1.1.3-1-IJ
(2-Methyl-4-hydroxy-5-tert-butylphenyl)butane, 2,2'-methylenebis(4-methyl-5-tert-butylphenol), 4°4'-
Hindered phenols such as butylindenbis (5-tert-butyl-3-methylphenol) and various known thermofusible substances can also be added.

When an inorganic or organic pigment is contained in the recording layer, it is preferable to use a pigment with a particle size as small as possible, and it is particularly desirable to use a pigment with an average particle size of 2 μm or less.

In the present invention, the method of forming the heat-sensitive recording layer is not particularly limited, and examples thereof include an air knife coater, a vinyl blade coater, a rond blade coater, a short dwell time coater, a flexo coater, a gravure coater, an offset gravure coater, and a roll coater.
It is formed by applying a coating liquid onto a cast coating layer and drying it using a coating device equipped with various coater heads such as the above.

Furthermore, the coating amount of the coating liquid is not particularly limited, and is usually 2 to 12 g/m'' in terms of dry weight, preferably 3 to 10 g/m.
``Adjusted within a range of degrees.

After coating and drying the heat-sensitive recording layer, it is possible to perform smoothing treatment such as super calendering as necessary, and it is also possible to provide an overcoat layer on the recording layer for the purpose of protecting the recording layer, or to coat the support. Of course, it is also possible to add various known techniques in the field of heat-sensitive recording materials, such as providing a coating layer on the back surface of the recording material.

The thus obtained heat-sensitive recording material of the present invention has a cast coating layer between the support and the heat-sensitive recording layer, which has a specific dynamic wettability value with excellent smoothness and heat insulation. Excellent pixel reproducibility is obtained in any range from high density to high density, there is no repelling of the coating liquid for the heat-sensitive recording layer, and the surface strength is also excellent.

"Example" The present invention will be described in more detail with reference to Examples below, but the present invention is of course not limited to these.

Further, unless otherwise specified, parts and % in the examples indicate parts by weight and % by weight, respectively.

For adhesives other than those indicated as aqueous solutions of specific concentrations, parts by weight are expressed in terms of solid content.

Example 1 [Preparation of cast coating layer coating liquid-1] Light calcium carbonate (BET specific surface area 12 g/m")
100 parts casein
10 parts acrylic acid/butadiene/methyl methacrylate (ratio: 2/33/65) copolymer latex 20 parts stearic acid 0.5 parts The above formulation was dispersed in water to a solid content concentration of 52% and cast coated. Layer coating liquid-1 was prepared.

[Manufacture of cast coated paper]

The obtained cast coating layer coating liquid-1 was applied at a weight of 50 g/m
'' was coated on the surface of high-quality paper, and finished by wet casting using the equipment shown in Figure 1.

That is, the first coating device (2) casts the coating liquid onto the surface of the high-quality paper (1) to a dry weight of 10 g/m.
Then, while this coating layer is in a wet state, immediately apply the same casting coating liquid as above in the second coating device (3) so that the dry weight becomes Log/m''. 3000 mm in diameter and passed through a press roll (4) with a diameter of 800 mm.
The paper was pressed against a cast drum (surface temperature: 90° C.) (5) of 1.5 mm in diameter, and peeled off after drying to obtain a cast coated paper (6).

[Preparation of heat-sensitive recording layer coating liquid]

1. Preparation of liquid A 3-(N-cyclohexyl-N-methylamino)6-methyl-7-phenylaminofluorane 10 parts 1.2-di(3-methylphenoxy) ethane 20 parts Methylcellulose 5% aqueous solution 15 Department water
80 parts of this composition was ground in a sand mill until the average particle size was 3 μm.

2. Bl preparation 4. 4'-isopropylidene diphenol 30 parts Methyl cellulose 5% aqueous solution 30 parts water
70 parts of this composition was ground in a sand mill until the average particle size was 2 μm.

125 parts of liquid A, 130 parts of liquid B, amorphous silica (oil absorption 1
80 cc/100 g), 150 parts of a 20% oxidized starch aqueous solution, and 55 parts of water were stirred and mixed to prepare a recording layer coating liquid.

[Formation of heat-sensitive recording layer]

The obtained recording layer coating liquid was applied onto the above-mentioned cast coated paper using a rondo blade coater and dried so that the coating weight after drying was 5 g/m'', followed by supercalendering to obtain a heat-sensitive recording paper.

Example 2 A thermosensitive recording paper was obtained in the same manner as in Example 1, except that the cast coating layer coating liquid-1 of Example 1 was changed to cast coating N coating liquid-2 having the following composition.

[Preparation of cast coating layer coating liquid-2] Light calcium carbonate (BET specific surface area 12 g/m")
45 parts calcined kaolin (oil absorption: 110cc/loog) 20
35 parts kaolin 35 parts casein
10 parts acrylic acid, butadiene, methyl methacrylate (ratio: 2/33/65) copolymer latex 6 parts stearic acid 0.5 parts The above formulation was dispersed in water to a solid concentration of 52% and cast coated. Layer coating liquid-2 was prepared.

Example 3 A thermosensitive recording paper was obtained in the same manner as in Example 1, except that the cast coating layer coating liquid-1 of Example 1 was changed to cast coating layer coating liquid-3 having the following composition.

[Preparation of cast coating layer coating liquid-3] Light calcium carbonate (BET specific surface area 12 g/m")
30 parts calcined kaolin (oil absorption: 110cc/100g) 50
1 part kaolin 20 parts casein
10 parts acrylic acid, butadiene,
Methyl methacrylate (ratio 1/33/65) copolymer latex 8 parts Stearic acid 0.5 parts The above formulation was dispersed in water to a solid content concentration of 52% to prepare cast coating layer coating liquid-3. did.

Example 4 Heat-sensitive recording paper was prepared in the same manner as in Example 1, except that the light calcium carbonate in the cast coating layer coating liquid-1 of Example 1 was changed to light calcium carbonate having a BET specific surface area of 7 g/m''. Obtained.

Example 5 Acrylic acid/butadiene/methyl methacrylate (ratio: 2/33/
65) A thermosensitive recording paper was obtained in the same manner as in Example 2, except that the copolymerized latex was changed to 4 parts.

Example 6 Light calcium carbonate of cast coating layer coating liquid-1 of Example 1 had a BET specific surface area of 20 g/m'', and acrylic acid/butadiene/methyl methacrylate (ratio 1/33/65) A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the copolymerized latex was changed to 26 parts.

Comparative Example 1 A thermosensitive recording paper was obtained in the same manner as in Example 1, except that the cast coating layer coating liquid-1 of Example 1 was changed to cast coating layer coating liquid-4 having the following composition.

[Preparation of cast coating layer coating liquid-4] Light calcium carbonate (BET specific surface area 7 g/m")
30 parts kaolin
70 parts casein
15 parts acrylic acid, butadiene, methyl methacrylate (ratio: 2/33/65) copolymer latex 22 parts stearic acid 1.0 part The above table was dispersed in water to a solid content concentration of 52% and cast coated. N coating liquid-4 was prepared.

Comparative Example 2 A thermosensitive recording paper was obtained in the same manner as in Example 1, except that the cast coating layer coating liquid-1 of Example 1 was changed to cast coating layer coating liquid-5 having the following composition.

[Preparation of cast coating layer coating liquid-5] Light calcium carbonate (BET specific surface area 20 g/m")
50 parts calcined kaolin (oil absorption: l 1Occ/100g) 5
0 parts casein 8 parts acrylic acid
Butadiene methyl methacrylate (ratio? 2/33
/65) Copolymer latex 3 parts Stearic acid 0.2 parts The above formulation was dispersed in water to a solid content concentration of 52% to prepare cast coating FJ coating liquid-5.

Example 7 A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the coating solution for the cast coating layer and the production of the cast coated paper were carried out as described below.

[Preparation of cast coating layer coating liquid-6] Light calcium carbonate (BET specific surface area 15 g/m")
100 parts casein
4 parts styrene/butadiene (ratio:
55/45) Copolymer latex 2
3 parts ammonium stearate 0.3 parts zinc sulfate 2 parts sodium polyacrylate 0.5 parts tributyl phosphate
Cast coating layer coating liquid-6 was prepared by dispersing 0.5 parts of the above formulation in water to a solid content concentration of 45%.

[Manufacture of cast coated paper]

The obtained cast coating layer coating liquid-6 was mixed into 5Q g
/m'' high-quality paper was finished by rewet casting using the apparatus shown in FIG.

That is, the surface of the high-quality paper (7) has a dry weight of 20 g/m! The above coating liquid was applied using an air knife coater (8) and dried using an air floating dryer (9).

Next, a press roll (10) with a diameter of 750 mm and a chrome-plated cast drum (11) with a diameter of 1500 mm are added.
) is passed through a press nip (12) formed by a nozzle (13), where the surface of the coating layer is rewetted with a rewetting liquid (0.3% concentration) consisting of a polyethylene emulsion supplied from a nozzle (13). The paper was pressed against a cast drum with a surface temperature of 105°C at a press nip pressure of 200 kg/cm, dried, and then peeled off from the cast drum with a take-off roll (14) to obtain a cast coated paper (15).

Example 8 A thermosensitive recording paper was obtained in the same manner as in Example 7, except that the cast coating layer coating liquid-6 in Example 7 was changed to the following cast coating layer coating liquid-7.

[Preparation of cast coating layer coating liquid-7] Light calcium carbonate (BET specific surface area 15 g/m2)
45 parts Baked Kaolin (Oil absorption: 110cc/100g) 20 parts Kaolin 35 parts Casein
5 parts styrene butadiene (
Ratio: 55/45) copolymer latex
9 parts Ammonium stearate 0.5 parts Zinc sulfate 2 parts Sodium polyacrylate 0.5 parts Tributyl phosphate 0.5 parts The above formulation was dispersed in water to a solid concentration of 45% to form a cast coating layer. Coating liquid-7 was prepared.

Example 9 A thermosensitive recording paper was obtained in the same manner as in Example 7, except that the cast coating layer coating liquid-6 in Example 7 was changed to the following cast coating layer coating liquid-8.

[Preparation of cast coating layer coating liquid-8] Light calcium carbonate (BET specific surface area 15 g/m2)
35 parts Kaolin (oil absorption: 110cc/100g) 30
45 parts kaolin 45 parts casein
5 parts styrene butadiene (
Ratio: 55/45) copolymer latex
9 parts Ammonium stearate 0.5 parts Zinc sulfate 2 parts Sodium polyacrylate 0.5 parts Tributyl phosphate 0.5 parts The above formulation was dispersed in water to a solid concentration of 45% to form a cast coating layer. Coating liquid-8 was prepared.

Example 10 A thermosensitive recording paper was obtained in the same manner as in Example 7, except that the BET specific surface area of light calcium carbonate in the cast coating layer coating liquid-6 of Example 7 was set to 7 g/m<2>.

Example 11 A thermosensitive recording paper was obtained in the same manner as in Example 8, except that 4 parts of the styrene-butadiene copolymer latex in the cast coating layer coating liquid-7 of Example 8 was used.

Example 12 A thermosensitive recording paper was obtained in the same manner as in Example 7, except that the styrene-butadiene copolymer latex in the cast coating layer coating liquid-6 of Example 7 was changed to 27 parts.

Comparative Example 3 A thermosensitive recording paper was obtained in the same manner as in Example 7, except that the cast coating layer coating liquid-6 in Example 7 was changed to the following cast coating N coating liquid-9.

[Preparation of cast coating layer coating liquid-9] Light calcium carbonate (BET specific surface area 7 g/m")
30 parts kaolin 70 parts casein
10 parts styrene/butadiene (ratio:
55/45) Copolymer latex 2
7 parts Ammonium stearate 1.0 parts Zinc sulfate 2 parts Sodium polyacrylate 0.5 parts Tributyl phosphate 0
．． Cast coating layer coating liquid-9 was prepared by dispersing 5 parts of the above formulation in water to a solid content concentration of 45%.

Comparative Example 4 A thermosensitive recording paper was obtained in the same manner as in Example 7, except that the cast coating layer coating liquid-6 in Example 7 was changed to the following cast coating layer coating liquid-1O.

[Preparation of cast coating layer coating liquid-10] Light calcium carbonate (BET specific surface area 20 g/m2)
70 parts calcined kaolin (oil absorption: 110
cc/100g) 30 parts force, zein 4 parts styrene-butadiene (ratio: 55/45) copolymer latex 4 parts ammonium stearate 0.1 part zinc sulfate
2 parts Sodium polyacrylate 0.5 parts Tributyl phosphate 0.5 parts The above formulation was dispersed in water to a solid content concentration of 45% to prepare a cast coating layer coating liquid-1O.

Example 13 A thermosensitive recording paper was obtained in the same manner as in Example 1, except that the coating liquid for the cast coating layer and the method for producing the cast coated paper were as follows.

[Preparation of cast coating layer coating liquid-11] Light calcium carbonate (BET specific surface area 15 g/m")
100 parts casein
9 parts styrene/butadiene (ratio: 60/40)
Copolymer latex 7 parts lecithin 0.3 parts sodium pyrophosphate
0.5 part Sodium polyacrylate
0.5 parts tributyl phosphate 0.5
A cast coating layer coating liquid-11 was prepared by dispersing the above formulation in water to a solid content concentration of 55%.

[Manufacture of cast coated paper]

The obtained cast coating N coating liquid-11 was added to 50 g/
A cast finish was applied to the surface of a high-quality paper of 100 mm by a gel casting method using the apparatus shown in FIG.

That is, the surface of the high-quality paper (16) has a dry weight of 20. g/m”
The above coating liquid was applied using a roll coater (17), and then a calcium formate aqueous solution with a concentration of 0.5% (
18) to gel the coating liquid.

Subsequently, it was pressed against a cast drum (20) with a diameter of 3000 mm at a press pressure of 180 kg/cm, and after drying, it was peeled off from the cast drum with a take-off roll (21) to obtain a cast coated paper (22).

Example 14 A thermosensitive recording paper was obtained in the same manner as in Example 13, except that the cast coating layer coating liquid-11 in Example 13 was changed to the following cast coating layer coating liquid-12.

[Preparation of cast coating layer coating liquid-12] Light calcium carbonate (BET specific surface area 15 g/m2)
50 parts Yaizu Kaolin Oil N: 110cc/100g) 20
30 parts kaolin 30 parts casein
10 parts styrene/butadiene (ratio: 60/40) copolymer latex
7 parts Lecithin 0.5 parts Sodium pyrophosphate 0.5 parts Sodium polyacrylate 0.5 parts Tributyl phosphate 0.5 parts The above formulation was dispersed in water to a solid concentration of 55% and cast coated. Layer coating liquid-12 was prepared.

Example 15 A thermosensitive recording paper was obtained in the same manner as in Example 13, except that the cast coating layer coating liquid-11 in Example 13 was changed to the following cast coating layer coating liquid-13.

[Preparation of cast coating layer coating liquid-13] Light calcium carbonate CBET specific surface area 15 g/m")
35 parts Calcined kaolin (oil absorption: 110cc/100g) 30
45 parts kaolin 45 parts casein
10 parts styrene butadiene (
Ratio: 60/40) copolymer latex
7 parts Lecithin 0.5 parts Sodium pyrophosphate 0.5 parts Sodium polyacrylate 0.5 parts Tributyl phosphate 0.5 parts The above formulation was dispersed in water to a solid concentration of 55% and cast coated. Layer coating liquid-13
was prepared.

Example 16 Cast coating layer coating liquid-11 of Example 13 except that the BET specific surface area of light calcium carbonate was 7 g/m''.
A thermosensitive recording paper was obtained in the same manner as in Example 13.

Example 17 A thermosensitive recording paper was obtained in the same manner as in Example 14, except that 4 parts of the styrene-butadiene copolymer latex was used in the cast coating layer coating liquid-12 of Example 14.

Example 18 Thermosensitive recording paper was obtained in the same manner as in Example 13, except that 4 parts of casein and 26 parts of styrene-butadiene copolymer latex were used in the preparation of cast coating layer coating liquid-11 of Example 13. Ta.

Comparative Example 5 A thermosensitive recording paper was obtained in the same manner as in Example 13, except that the cast coating layer coating liquid-11 in Example 13 was changed to the following cast coating layer coating liquid-14.

[Preparation of cast coating layer coating liquid-14] Light calcium carbonate (BET specific surface area 7 g/m")
30 parts kaolin 70 parts casein
15 parts styrene/butadiene (ratio: 60/40) copolymer latex 2
6 parts Lecithin 1.2 parts Sodium pyrophosphate 0.5 parts Sodium polyacrylate 0.5 parts Tributyl phosphate 0
．． Cast coating layer coating liquid-14 was prepared by dispersing 5 parts of the above formulation in water to a solid content concentration of 55%.

Comparative Example 6 A thermosensitive recording paper was obtained in the same manner as in Example 13, except that the cast coating layer coating liquid-11 in Example 13 was changed to the following cast coating layer coating liquid-15.

[Preparation of cast coating layer coating liquid-15] Light calcium carbonate (BET specific surface area 20 g/m")
55 parts calcined kaolin (oil absorption: 110cc/100g) 45
1 part casein 5 parts styrene/butadiene (ratio: 60/40) copolymer latex
4 parts lecithin 0.
2 parts Sodium pyrophosphate 0.5 parts Sodium polyacrylate 0.5 parts Tributyl phosphate 0.5 parts The above formulation was dispersed in water to a solid content concentration of 55% to prepare a coating solution for the cast coating layer. 15 was prepared.

Comparative Example 7 A thermosensitive recording paper was obtained in the same manner as in Example 2, except that instead of forming a thermosensitive recording layer on the cast-coated paper of Example 1, high-quality paper provided with the following intermediate layer was used.

[Preparation of intermediate layer coating liquid] Calcined kaolin (oil absorption: 110 cc/100g)
100 parts styrene-butadiene (ratio: 60/40) copolymer latex 15 parts polyvinyl alcohol aqueous solution 2 parts The above formulation was dispersed in water to a solid content concentration of 35% to prepare an intermediate layer coating solution.

[Formation of intermediate layer]

The obtained intermediate layer coating liquid was dried on a 50 g/m2 high-quality paper using a Rondo blade coater, and the coating amount was 20 g10+"
It was coated and dried so that it looked like this.

The 25 types of thermal recording paper thus obtained were printed and recorded using a practical facsimile UF-60 manufactured by Matsushita Electric Transmission Co., Ltd., and the reproducibility of the printed image quality and color density were measured using a Macbeth densitometer (R).
D-100R model (using an amber filter), the results are shown in the table.

In addition, we evaluated the dynamic wetting value of the cast coated paper, the repellency of the coating liquid when the heat-sensitive recording layer coating liquid was applied to the cast-coated paper, and the rubbing off of the heat-sensitive recording layer (friction resistance suitability).
The results are also listed in the table.

The quality of the printed image, the repellency of the coating liquid, and the rubbing off of the heat-sensitive recording layer (friction resistance suitability) were each evaluated using the following evaluation methods.

[Print image quality]

The reproducibility of prints recorded using a facsimile UF-60 manufactured by Matsushita Electric Transmission Co., Ltd. was visually evaluated using the following criteria.

O: Very good print reproducibility.

Δ: The reproducibility of printing is slightly inferior, but there is no problem in practical use.

×: Poor print reproducibility.

[Coating characteristics of heat-sensitive recording layer]

The degree of repellency when the heat-sensitive recording layer coating liquid was coated on the 25 types of cast coatings or intermediate layers obtained above was visually evaluated based on the following criteria.

○: There is no repellency of the coating liquid at all.

Δ: Slight repellency of the coating liquid is observed.

×: Significant repellency of the coating liquid.

[Abrasion resistance suitability of heat-sensitive recording layer]

When the surface of the heat-sensitive recording material was rubbed with a finger, the degree of rubbing off of the heat-sensitive recording layer was evaluated based on the following criteria.

○: There was no rubbing off of the heat-sensitive recording layer.

Δ: Slight rubbing off of the heat-sensitive recording layer is observed.

X: Significant rubbing off of the heat-sensitive recording layer was observed.

[Cutting suitability]

The generation of paper dust was evaluated when the recording section and the blank section of the recording paper were each cut with a cutter. The evaluation criteria were as follows.

○: No generation of paper dust and no peeling of the heat-sensitive recording layer.

Δ: No paper dust was generated, but slight peeling of the heat-sensitive recording layer was observed.

x: Significant paper dust was generated, and the heat-sensitive recording layer often peeled off.

"Effects" As is clear from the results in Tables 1 and 2, the thermal recording paper of the present invention has high recording density, good print quality, and excellent thermal recording without repelling or rubbing off the thermal recording layer. It was the body.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 are schematic diagrams showing a method for producing cast coated paper used in Examples and Comparative Examples of the present invention. (1), (7), 06) Two high-quality paper (Anwaingu) (
2): First coating device (3): Second coating device (4), 00), 09) Nibbles roll (5), (11
), c! 0: Cast drum (6), 05), (22)
: Cast coated paper (8): Air knife coater (9): Air floating dryer Press nip rewetting liquid Take-off roll roll coater Gelling solution

Claims (2)

[Claims] (1) A heat-sensitive recording material in which a cast coating layer having a dynamic wetting value of -0.15 to 0.00 g is provided on a support, and a heat-sensitive recording layer is further provided on the cast coating layer. (2) The cast coating layer has a BET specific surface area of 10 g/m^
The heat-sensitive recording material according to claim 1, characterized in that the cast coating layer contains two or more light calcium carbonates in an amount of 40 to 100% by weight based on the total pigment contained in the cast coating layer.