JP3177926B2 - Thermal recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having excellent dot reproducibility in a low density region and suitable for halftone recording.

[0002]

2. Description of the Related Art Thermosensitive recording materials are widely used for recording various printers, facsimile machines, measuring instruments, and the like because they do not require a development / fixing step after printing colors, and are easy to maintain. ing. Recently, there have been devices that apply a thermosensitive recording medium to record halftones such as television images. In order to perform such halftone recording, the thermosensitive recording medium has a dot reproducibility, especially a low density. Dot reproducibility in the area has been required.

Conventionally, to improve such dot reproducibility, a method of smoothing the surface of a recording material (Japanese Patent Publication No. 52-20142)
), A method using undercoated paper as a support (Japanese Patent Application Laid-Open No. 54-83841), a method of setting the surface roughness and gloss of a recording medium to a specific range (Japanese Patent Application Laid-Open No. 55-156086), and the like. Although it is known, dot reproducibility in a low density region was not always satisfactory.

Japanese Patent Application Laid-Open No. 61-98585 discloses a method for obtaining a thermosensitive recording medium which is excellent in dot reproducibility and suitable for halftone recording.
The invention discloses a thermosensitive recording medium using paper containing at least 10% by weight. However, when the precipitated calcium carbonate is added to the paper in an amount of 30% by weight or more, the paper strength is reduced, and the paper is easily cut at the time of paper making and when the heat-sensitive paint is applied. There was a problem that it became easy.

Conventionally, high-quality paper has been used as a support for a heat-sensitive recording medium. This high-quality paper has a low oil absorption of 20 to 40 ml / 100 g, such as clay and talc, according to the Kokura method. About 10 to 15% by weight. However, when these high-quality papers were used as a support for a thermosensitive recording medium, dot reproducibility in a low density region was extremely poor as it was.

[0006]

SUMMARY OF THE INVENTION The present invention provides a thermosensitive recording material which has excellent dot reproducibility, is suitable for halftone recording, has sufficient strength and productivity, and generates little paper dust. The purpose is to:

[0007]

As a result of research for solving the above-mentioned problems, calcium carbonate having a large oil absorption amount was reduced to 1%.
By using a paper containing 5 to 30% by weight as a support, a decrease in surface strength and paper strength of the support is reduced, and troubles such as paper breakage at the time of paper making or heat-sensitive coating are reduced.
Further, it is possible to eliminate powder dropping in the auto cutter portion of the facsimile, and at the same time, it has been found that a thermosensitive recording medium having excellent dot reproducibility and suitable for halftone recording can be obtained. A heat-sensitive recording medium was obtained.

The present invention relates to a thermosensitive recording medium having a thermosensitive coloring layer mainly composed of a leuco compound and a color-developing substance capable of coloring the leuco compound when heated, which is provided on a support. Oil absorption by the method is 70-140ml / 100g
The present invention provides a heat-sensitive recording material characterized by being paper containing 15 to 30% by weight of calcium carbonate having a specific surface area of 10 to 38 m ² / g. The calcium carbonate used in the present invention has an oil absorption of 70 to 140 ml as measured by the Kokura method.
/ 100 g of calcium carbonate. Commercially available calcium carbonate corresponding to this condition includes, for example, Univer 70
(Shiraishi Kogyo, oil absorption 70ml / 100g , specific surface area 1
3m ² / g ), Callite SA (manufactured by Shiroishi Central Research Laboratory, oil absorption 90 ml / 100 g , specific surface area 10 m ² / g ), Callite KT (manufactured by Shiroishi Central Research Laboratory, oil absorption 140 ml /
100 g , specific surface area 38 m ² / g ) and KK-12 (manufactured by Shiroishi Central Research Laboratory, oil absorption 120 ml / 100 g , specific surface)
Product 20 m ² / g ).

[0009] The amount of the calcium carbonate is 15 to 30% by weight relative to the total weight of the support, preferably 20
３０30% by weight. The oil absorption by the Ogura method of the present invention is 7
The reason that the use amount of calcium carbonate of 0 to 140 ml / 100 g is limited is that the content is about 10% by weight based on the weight of the support, but it is practically necessary to add 15% by weight or more of the halftone. It is necessary for clear recording, but on the other hand, the upper limit is limited to 30% by weight in order to maintain the surface strength of the paper and to maintain the strength that does not cause breakage during papermaking and thermal coating. is there. That is, if the calcium carbonate content exceeds 30% by weight, the strength of the paper decreases.

Further , in the present invention, together with calcium carbonate having an oil absorption of 70 to 140 ml / 100 g according to the Ogura method, a filler having an oil absorption of 70 ml / 100 g or less, for example, clay, talc, calcium carbonate, aluminum hydroxide,
It is also possible to use zinc oxide or the like in combination. The Ogura method used in the present invention is described in "Pigments, Supplies, and Inks" (Junzo Matsumoto, Masateru Ogura, Kyoritsu Shuppan Co., Ltd., 4th Edition, 1950, pp. 66-67). JIS K 5421, using cooked linseed oil).

In a thermal facsimile, a thermal printer, or the like, when a thermal recording medium is heated by a thermal head or the like to perform color printing, a color sensitivity adjusting agent such as a higher fatty acid amide or the like adheres to the thermal head or the like as scum and prints. Decreases sharpness. Calcium carbonate exhibits a so-called scum removal effect of suppressing and preventing such scum adhesion. In particular,
Calcium carbonate with high oil absorption and water absorption (120
(ml / 100 g or more) has a high effect, and it is known that such calcium carbonate is added to the heat-sensitive recording layer or the undercoat layer (Japanese Patent Application Laid-Open No. 1-230424). The heat-sensitive recording material of the present invention is completely different from the above-mentioned heat-sensitive recording material because the support contains calcium carbonate. However, in the present invention, the oil absorption is 120 ml / 100 by the Ogura method.
When calcium carbonate of g or more is used, the debris removing effect is improved.

The pulp used for producing the support of the present invention is not particularly limited, but for example, KP, S
CP, TMP, waste paper pulp and the like can be mentioned. The basis weight of the paper used for the support is 20 to 300 g / m ^2, and preferably 30~200 g / m ^2. Examples of the leuco dye used in the heat-sensitive recording layer of the present invention include a triallylmethane dye, a thiazine dye, a spiro dye, a lactam dye and various fluoran compounds.

Further, in the present invention, the developer used for causing the leuco dye to develop a color when heated is not particularly limited, but has a property of liquefying, vaporizing or dissolving with an increase in temperature, and Various developers having the property of developing color upon contact with the leuco dye. Developers that can be mentioned as typical specific examples include, for example, 4-
tert-butylphenol, bisphenol A, m-terphenyl, α-naphthol, 4-acetylphenol,
Hydroquinone monobenzyl ether, 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, 4-
Aromatic carboxylic acids such as methyl hydroxybenzoate, terephthalic acid and the like, and phenolic compounds, salts of aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel, etc. Organic acid substances.

In preparing a coating solution containing these components, water is generally used as a dispersion medium, and a leuco dye and a developer are dispersed together or separately using a ball mill, an attritor, a sand grinder or the like, or a pulverizer. Prepared as a coating solution. In such a coating solution, usually as a binder starches, hydroxyethylcellulose, methylcellulose,
Carboxymethylcellulose, gelatin, casein, gum arabic, polyvinyl alcohol, styrene / maleic anhydride copolymer salt, styrene / butadiene copolymer emulsion, etc. are 2 to 40% by weight of the total solid, preferably 5 to 25% by weight. Used in proportion. Further, various auxiliaries can be added to the coating liquid as needed.
For example, dispersants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium salt of lauryl alcohol sulfate, metal salts of fatty acids, and the like, other antifoaming agents, fluorescent dyes, coloring dyes, and the like.

In the heat-sensitive recording medium of the present invention, the method for forming the heat-sensitive recording layer is not particularly limited, and the heat-sensitive recording layer can be formed according to a conventionally well-known technique.
For example, in a method of applying a heat-sensitive coating solution to a support, an appropriate coating device such as an air knife coater or a blade coater is used. The coating amount of the coating liquid is not particularly limited, but is generally in the range of ^{2 to} 15 g / m ² , preferably 3 to 10 g / m ² in terms of dry weight.

Further, an intermediate layer using an inorganic pigment such as calcined kaolin or silica or an organic pigment such as a plastic pigment can be provided between the support and the heat-sensitive recording layer.
Various known techniques in the thermal recording medium field can be added.

[0017]

EXAMPLES The present invention will be described in detail with reference to examples. Example 1 C.I. S. F. LBKP5 with a freeness of 300 ml
0 parts by weight and C.I. S. F. NBKP5 with a freeness of 300 ml
In a 0 part by weight pulp slurry, calcium carbonate (Kallite KT (BET specific surface area 38 m ² / g, water content 3%, average particle diameter 2.3μ)) having an oil absorption of 140 ml / 100 g according to the Ogura method manufactured by Shiroishi Central Research Institute ) And 38 parts by weight of a neutralizing sizing agent (Hercon W, manufactured by Dick Hercules)
0.3 parts by weight, 3 parts by weight of cationized starch (manufactured by Nichiden Chemical),
Anionic polyacrylamide (Polystron 117,
After adding and mixing 0.2 parts by weight of Arakawa Chemical,
g / m ² paper was made and lightly calendered.
This gives a thickness of 55 μm and a surface Beck smoothness of 300
Seconds, a paper with a Steckigt sizing degree of 5 seconds and a filler content of 25% by weight was obtained. Formation of thermosensitive coloring layer The following solution A and solution B were prepared respectively.

A solution of acrylamide-based water-soluble resin (TY-121, solid content 12
%) And 30 parts by weight of an aqueous dispersion of 30% zinc stearate, and 20 parts by weight of an amorphous silicate (oil absorption: 150 ml / 100 g) was gradually added thereto. And mixed. Next, 150 parts by weight of the solution B was added to the solution A, and 35 parts by weight of water were further added to obtain a thermosensitive coloring liquid.

Liquid A color-forming leuco dye (3- (N-ethyl-N-isoamyl)
Amino-6-methyl-7-anilinofluoran) [S-205 manufactured by Yamada Chemical] 10 parts by weight Polyvinyl alcohol 30 parts by weight (12% aqueous solution) Polystyrene acrylic acid 2 parts by weight Ammonium (20% aqueous solution) Water 8 parts by weight The above components were dispersed and prepared by a sand grinder until the average particle size became 1 μm.

Liquid B Bisphenol A 18 parts by weight m-terphenyl 22 parts by weight Polyvinyl alcohol (12% aqueous solution) 50 parts by weight Ammonium polystyrene acrylate (20% aqueous solution) 3 parts by weight Water 57 parts by weight The above components are subjected to a sand grinder. It was prepared by dispersion until the average particle size became 1 μm.

The thermosensitive coloring solution prepared in this manner is applied on the paper so that the weight after drying is 6 g / m ^2, and after drying, the Bekk smoothness is further reduced to about 600 seconds. A heat-sensitive recording medium was obtained by performing a calendering process. Example 2 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that 30 parts by weight of callite KT of calcium carbonate was added to the pulp slurry, and the content of calcium carbonate in the support was changed to 20% by weight. Was manufactured. [Example 3] As a filler, oil absorption by the Kokura method was 90 ml.
/ 100g of calcium carbonate (Callite SA (BET
Specific absorption surface area 10 m ² / g, moisture 3%, average particle size 3.3
μ), manufactured by Shiroishi Central Laboratory) was added to the pulp slurry in an amount of 40 parts by weight, and the content of calcium carbonate in the support was 28%.
A thermosensitive recording medium was manufactured in the same manner as in Example 1 except that the amount was changed to% by weight. Comparative Example 1 A thermosensitive recording medium was prepared in the same manner as in Example 1, except that 14 parts by weight of calcium carbonate callite KT was added to the pulp slurry, and the content of calcium carbonate in the support was changed to 10% by weight. Was manufactured. Comparative Example 2 A thermosensitive recording medium was prepared in the same manner as in Example 1, except that 70 parts by weight of calcium carbonate callite KT was added to the pulp slurry, and the content of calcium carbonate in the support was changed to 40% by weight. Was manufactured. [Comparative Example 3] As a filler, the oil absorption by the Ogura method was 60 ml.
/ 100 g of calcium carbonate Pz (manufactured by Shiraishi Calcium Co., Ltd.) was added to the pulp slurry by 45 parts by weight, and the content of calcium carbonate in the support was changed to 30% by weight. A thermal recording medium was manufactured. [Comparative Example 4] As a filler, oil absorption by the Ogura method was 300
Example 1 Same as Example 1 except that 30 parts by weight of silica (P-527, manufactured by Mizusawa Chemical Co., Ltd.) was added to the pulp slurry at a concentration of 20% by weight, and the content of calcium carbonate in the support was 20% by weight. A thermosensitive recording medium was produced by the method. [Comparative Example 5] 100 parts by weight of Kallite KT, casein 4
A slurry of 0 parts by weight and 320 parts by weight of water was mixed with a basis weight of 50 g /
It was applied to dry paper having a dry solid weight of 8 g / m ^{2 on} high quality paper of m ² and dried. The same heat-sensitive paint as in Example 1 was applied thereon, and a heat-sensitive recording medium was manufactured. Comparative Example 6 A thermosensitive recording medium was produced in the same manner as in Example 1 except that a support mainly composed of pulp was used without using Callite KT.

The heat-sensitive recording materials obtained in Examples 1 to 3 and Comparative Examples 1 to 6 were evaluated by a powder drop test, a scum adhesion test, a dot reproducibility test, and the like. Table 1 shows the evaluation results.
1 is shown. [Evaluation method] 1. Image density (D _p ) Printing power 0.7 W / dot. Pulse period 5.0 ms, pulse width 0.3 ms with commercially available thermal head KFT-216-8 MPD I (manufactured by Kyocera)
Was performed under the following conditions, and the density of the obtained image was measured with a Macbeth densitometer RD-914. 2. Scum adhesion test and dot reproducibility test After printing a checkerboard pattern with a black ratio of 50% continuously for 10 m using a commercially available FAX FACOMFAX2000 (manufactured by Fujitsu), the evaluation of the scum adhered to the thermal head was visually judged. The dot reproducibility at that time was visually determined. 4. Evaluation of printing unevenness Solid printing was performed, and macroscopic image density variations were visually determined. 5. Paper cut When paper was cut out after 50,000 m of paper making, it was evaluated as x. 6. Paper Powder The thermal paper was continuously recorded for 1000 m, and stain on the platen roll was visually determined.

[0023]

[Table 1] filler oil absorption content D _p dregs dot uneven piece of paper paper powder ─────────────────────────────────例 Example Carla 1 KT 140 25 1.31 ○ ○ ○ ○ ○ Example Carla 2 KT 140 20 1.29 ○ ○ ○ ○ ○ Example Carla 3 SA SA 28 28 1.30 ○ ○ ○ ○ ○ Comparative Example Carla 1 KT 140 10 1.15 △ △ ○ ○ ○ Comparative example Carlait KT 140 40 1.24 ○ ○ ○ × × Comparative example 3 Carbonic acid PZ 60 30 1.01 × × ○ ○ ○ Comparative example Silica 4 300 20 1.21 ○ ○ ○ × × Comparative Example Callite KT5 (Undercoat)-1.34 ○ ○ × None ○ Comparative Example 6-0.82 × × ○ ○ ○

[0024]

As is clear from Table 1, in the support,
If a filler with a large oil absorption such as silica, which is conventionally known, is used, troubles such as paper breakage and paper dust may occur.
When calcium carbonate having a small oil absorption was added, dot reproducibility was lowered, and even if the addition amount was 30% by weight or more, there was no effect.

On the other hand, the heat-sensitive recording material of the present invention was excellent in dot reproducibility, suitable for halftone recording, had sufficient strength and productivity, and generated little paper dust.

Continuation of the front page (56) References JP-A-62-5880 (JP, A) JP-A-2-258288 (JP, A) JP-A-2-76788 (JP, A) JP-A-63-74682 (JP) JP-A-61-98584 (JP, A) JP-A-62-138286 (JP, A) JP-A-2-172786 (JP, A) JP-A-2-1644583 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B41M 5/28-5/34

Claims (1)

(57) [Claims] 1. A thermosensitive recording medium comprising a leuco compound and a thermosensitive coloring layer mainly composed of a color-developing substance capable of coloring the leuco compound when heated, provided on a support. Oil absorption by 70-140ml / 100g,
Calcium carbonate having a specific surface area of 10 to 38 m ² / g
A heat-sensitive recording material comprising a paper containing 5 to 30% by weight.