JPH0651428B2 - Thermal recording paper - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat-sensitive recording paper for recording with a heat head, a heat ben, and the like, and more specifically, the binding between the heat head and the heat-sensitive coloring layer. The present invention also relates to a thermal recording paper which does not have piling on a thermal head, has good dot reproducibility even at high speed recording, and can obtain clear and high density recording.

(Prior art) In recent years, the development of fax machines, printers, etc. has been remarkable,
In particular, a heat-sensitive material coated with a colorless dye (hereinafter referred to as a color-developing agent) such as crystal violet letolactone and an acidic substance (hereinafter referred to as a color-developing agent) such as a phenol compound as described in JP-B-45-14039. A heat-sensitive recording method using a combination of recording paper and a thermal head is widely adopted in these devices.

This heat-sensitive recording method has many advantages such as that the recording paper has a primary color, no development is required, the recording device can be simplified, the cost of the recording paper and the recording device is low, there is no impact, and there is no noise. Yes, it has established itself as a low-speed recording system. However, a major drawback of heat-sensitive recording is that the recording speed is slower than other recording methods such as electrostatic recording, and it is the current situation that the adoption range does not reach to high-speed recording.

In thermal recording, the main reason why high-speed recording cannot be performed is that thermal conduction between the thermal head and the thermal recording paper in contact therewith is not sufficiently performed, and sufficient recording density cannot be obtained. The thermal head, which is a collection of dot-shaped electric resistance heating elements, generates heat in response to a recording signal, and the thermosensitive coloring layer in contact with the thermal head melts and develops color. In order to obtain clear and high-density recording, good dot reproducibility, that is, the thermal head and the thermosensitive coloring layer are in intimate contact with each other as efficiently as possible, the heat conduction is performed efficiently, and it is perfectly compatible with high-speed recording signals. It is necessary to form dots on the thermosensitive coloring layer, which are completely colored and correspond to the shape of the thermal heating dot heating element. But,
At present, only a few percent of the amount of heat generated by the thermal head is conducted to the thermosensitive coloring layer, and the thermal conduction efficiency is extremely low.

Several methods have been proposed for improving the smoothness of the heat-sensitive color developing layer so that the heat head and the heat-sensitive color developing layer are in close contact with each other as much as possible.

Japanese Examined Patent Publication No. 52-20142 describes that the surface of the thermosensitive coloring layer is surface-treated to have a Begg smoothness of 200 to 1000 seconds. Japanese Patent Application Laid-Open No. 54-115255 discloses that a surface smoothness of 200 to 1000 seconds can be applied only to a heat pulse of about 5 to 6 milliseconds, and for high speed recording of 1 millisecond or less, the surface of the thermosensitive coloring layer is coated. It is described that it is necessary to perform a smoothing treatment for smoothness of 1100 seconds or more.
If the flatness of the surface is set to 1100 seconds or more, color fog will occur due to the pressure.
Bek smoothness is improved to 500 seconds or more to prevent color fog. JP-A-53-156086 describes that the surface roughness Ra of the surface of the thermosensitive color developing layer is 1.2 μm or less and the glossiness is 25% or less.

All of the above-mentioned conventional techniques for improving the smoothness improve the smoothness of the heat-sensitive color developing layer only by a calendar treatment such as a super calendar, a machine calendar and a gloss calendar. The calendering is performed only on the base paper, or the base paper and the thermal paper, or only the thermal paper. Thermal paper with smoothness improved by these calender treatments has more staking and piling as the smoothness improves and the recording density improves. Therefore, the smoothness is actually suppressed to an appropriate level. Thus, the recording density, staging, and piling are properly balanced. The conventional technique is not practical for high-speed recording in terms of recording density or recording stability regardless of smoothness level.

With staking, the thermal head and the thermosensitive coloring layer adhere,
Peeling is a phenomenon in which peeling noise is generated or dot reproducibility is deteriorated.Piling is a phenomenon in which the thermal melt of the thermosensitive coloring layer accumulates on the thermal head, resulting in a decrease in recording density and dot reproducibility. Both are phenomena that disturb stable recording.

Another drawback of the calendering process for heat-sensitive paper is that color fog occurs due to pressure, and the density of the background portion of the recording paper increases. On the other hand, there is a limit to the calendering process for the base paper because of the occurrence of so-called beckles, streaks and the like due to uneven basis weight. As described above, the smoothing of the thermosensitive coloring layer and the improvement of the recording density by the calendering process are necessarily limited, and a satisfactory one for high speed recording cannot be obtained.

(Object of the Invention) An object of the present invention is to provide a thermal paper in which the above-mentioned drawbacks have been improved, that is, a thermal paper having a good dot reproducibility and a high recording density.

(Structure of the Invention) As a result of intensive studies to improve these drawbacks, the present inventors have found that (a) a white inorganic pigment and / or a white organic pigment (b) between the support and the thermosensitive coloring layer. The object of the present invention is achieved by providing an intermediate layer made of a resin cured by electron beam irradiation.

White inorganic pigments used in the present invention include calcined kaolin, kaolin, talc, light calcium carbonate, synthetic silica, barium sulfate, titanium oxide, and the like, and white organic pigments include urea formalin resin melamine formalin resin,
It is a fine powder of acrylic resin, styrene resin, or the like. The white pigment has a whiteness of 80% or more, more preferably 85% or more, and an oil absorption of 30 to 300 ml / 100 g is preferable.

Examples of the compound that is cured by the electron beam used in the present invention include a compound having a double bond in the molecule, preferably a compound having a plurality of double bonds in the molecule, more preferably an acryloyl group, a methacryloyl group, Examples thereof include compounds containing an acrylamide group, an allyl group, a vinyl ether group, a vinyl thioether group, and unsaturated polyesters.

In addition to the above electron beam curing compound and white pigment, a monomer and / or an organic solvent having at least one carbon-carbon unsaturated bond in the molecule may be contained, if necessary.
Examples of the monomer having one unsaturated bond in the molecule include acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, styrene, acrylonitrile, vinyl acetate and the like, and homologs thereof. In addition, as a compound having two or more unsaturated bonds in the molecule, "Photosensitive Resin Data Collection" (published by Soken Chemical Research Institute Co., Ltd.) 235-
The compounds exemplified on page 236 (1968) can be mentioned. Among these described compounds, ethylene diacrylate, glycerol diacrylate, pentaerythritol tetramethacrylate, 1,5 pentanediol dimethacrylate, glycerol trimethacrylate and the like are preferable.

As the organic solvent, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexane; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol monoethyl ether acetate; ethers, glycol monoethyl ether , Glycol ethers such as dioxane, benzene, toluene,
Tar-based materials such as xylene; hydrogen chlorides such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene can be selected and used. The ratio of the compound (including the monomer) cured by the electron beam to the inorganic pigment is 3/1 to 1 /
3 is preferable and the coating amount of the intermediate layer is 1 to 10 g / m ^2.
When it is out of this range, the color density is lowered and the curl balance is not preferable.

In the kneading of the coating liquid, the pigment and the above-mentioned components are all charged into the kneading machine simultaneously or individually. A dispersant may be added together with the pigment.

Various kneading machines are used for kneading and dispersing the composition. For example, two roll mill, three roll mill, ball mill, pebble mill, tron mill, sand glider, Sz
Egvari attritor, high-speed impeller disperser, high-speed stone mill, high-speed impact mill, Teisper, kneader, high-speed mixer, horgenizer, ultrasonic disperser and the like.

Techniques relating to kneading and dispersion are described in T.W. C. "Paint Flow and Pigment D" by Patton
"Ispersion" (1964, John Wi
published by ley & Sons).
Also, US Pat. Nos. 2,581,414 and 2,855
No. 156.

As a method of applying the above composition on a support, an air doctor coat, a blade coat, an air knife coat,
Squeeze coat, impregnation coat, reverse low coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray coat, spin coat, etc. can be used, and other methods are also possible, and these specific explanations are published by Asakura Shoten. "Coating Engineering", pp. 253 to 277 (published 46.320 of Showa), for details.

As the electron beam accelerator, a van de Graaff type scanning method, a double scanning method, or a curtain beam method can be adopted, but the curtain beam method, which is relatively inexpensive and can obtain a large output, is preferable. As the electron beam characteristics, the acceleration voltage is 100 to 1000 KV, preferably 1
0 to 300 KV and 0.5 to 20 as absorbed dose
Megarad, preferably 2 to 10 Megarad. When the accelerating voltage is 100 KV or less, the energy transmission amount is insufficient, and when the accelerating voltage exceeds 1000 KV, the energy efficiency used for polymerization is reduced, which is not economical. 0.5 as absorbed dose
If it is less than megarad, the curing reaction is insufficient and the desired quality cannot be obtained, and if it is more than 20 megarad, the energy efficiency used for curing is lowered, or the irradiated object generates heat.
Not preferable.

When the application surface is attached to a mirror roll such as electron beam irradiation, the application surface becomes smoother and the effect of the present invention can be further enhanced. It is also possible to peel off the resin composition once cured on another base and adhere it to a support to form an intermediate layer.

The paper support used in the present invention is mainly made of wood pulp, but it is also possible to partially mix synthetic fibers or synthetic pulp. As the wood pulp, either a softwood pulp or a hardwood pulp can be used, but a hardwood pulp having short fibers and easily exhibiting smoothness is more preferable. The water content of the pulp is preferably 200 to 500 cc (C.S.F.), and more preferably 300 to 400 cc. Also, sizing agents such as rosin, paraffin wax, higher fatty acid salts, alkenyl succinates, fatty acid anhydrides, styrene maleic anhydride copolymers, alkyl ketene dimers, epoxidized fatty acid amides, and maleic anhydride copolymers as softening agents. Of polyalkylene polyamine with quaternary substance, quaternary ammonium salt of higher fatty acid, polyacrylamide as starch, starch, polyvinyl alcohol, melamine formaldehyde condensate, gelatin, sulfuric acid band as fixing agent, polyamide polyamine epichlorohydrin, and other dyes It is also possible to add a fluorescent dye, an antistatic agent, etc., if necessary, and replace the paper support with synthetic paper or a plastic film, if necessary.

Next, the heat-sensitive coating liquid used in the present invention will be described.

In the heat-sensitive coating liquid, a color-developing agent and a color-developing agent are generally separately dispersed in a water-soluble polymer solution using a means such as a ball mill. In order to obtain a finely divided product of the color former or the developer, for example, a ball mill is used, which is achieved by using balls having different particle diameters at an appropriate mixing ratio and dispersing them for a sufficient time. It is also effective to use a model sand mill (trade name: Dyno Mill).

The resulting dispersion of the color-developing agent and the color-developing agent is mixed, and an inorganic pigment, waxes, higher fatty acid amide, metal soap, and if necessary, an ultraviolet absorber, an antioxidant, a latex binder, etc. are added to obtain a coating liquid. And These additives may be added at the time of dispersion.

The coating liquid generally has a coating amount of 0.2 g / m ² as a color former.
To 1.0 g / m ² on the support.

The color forming agent used in the present invention is not particularly limited as long as it is used in general pressure sensitive recording paper, heat sensitive recording paper and the like. Specific examples include (1) triarylmethane compounds such as 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3- (p -Dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide, 3 , 3-bis- (p-ethylcarbazole-3
-Yl) -3-dimethylaminophthalide, 3,3-bis- (2-phenylindol-3-yl) -5-dimethylaminophthalide, etc .: (2) diphenylmethane compounds such as 4,4 -Bis-dimethylaminobenzhydrin benzyl ether, N-halophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine, etc .: (3) Xanthene-based compound, for example, rhodamine B-anilino Lactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-
Butylaminofluorane, 3-diethylamino-7-
(2-chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7-ani Rinofluorane, 3-cyclohexyl-methylamino-6-methyl-
7-anilinofluorane, 3-diethylamino-6-chloro-7- (β-ethoxyethyl) aminofluorane,
3-Diethylamino-6-chloro-7- (γ-chloropropyl) aminofluorane, 3-diethylamino-6-
Chloro-7-anilinofluorane, 3-N-cyclohexyl-N-methylamino-6-methyl-7-anilinofluorane, 3-diethylamino-7-phenylfluorane, etc .: (4) thiazine compound, For example, benzoyl leuco methylene blue, p-nitrobenzoyl leuco methylene blue, etc .: (5) Spiro compounds, for example, 3-methyl-spiro dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-benzyl spiro-dinaphthopyran, 3
-Methylnaphtho- (3-methoxy-benzo) -spiropyran or the like, or a mixture thereof can be mentioned. These are determined by the application and the desired properties.

The color developer used in the present invention is a phenol derivative,
Aromatic carboxylic acid derivatives are preferable, and bisphenols are particularly preferable. Specifically, as phenols, p
-Octylphenol, p-tert-butylphenol, p-phenylphenol, 2,2 bis (p-hydroxy) propane, 1,1-bis (p-hydroxyphenyl) bentane, 1,1-bis (p- Hydroxyphenyl) hexane, 2,2-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) -2-ethyl-hexane, 2,2-bis (4-hydroxy-3) , 5-dichlorophenyl) propane and the like.

As the aromatic carboxylic acid derivative, p-hydroxybenzoic acid, propyl p-hydroxybenzoate, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate,
Examples of 3,5-di-α-methylbenzyl salicylic acid and carboxylic acid include polyvalent metal salts thereof.

These color developers are added as a eutectic with a low-melting heat-fusible substance in order to cause a color reaction by melting at a desired temperature, or the low-melting compound is added to the surface of the color developer particles. It is preferable to add it in the state of being fused to the.

Examples of waxes include paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, and higher fatty acid amides such as stearic acid amide, ethylene bis stearoamide, and higher fatty acid ester.

Examples of the metal soap include higher fatty acid polyvalent metal salts, that is, zinc stearate, aluminum stearate, calcium stearate, zinc oleate and the like.

As the inorganic pigment, kaolin, calcined kaolin, talc,
Examples thereof include wax, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium carbonate, titanium oxide and barium carbonate.

These inorganic pigments preferably have an oil absorption of 60 ml / 100 g or more and an average particle diameter of 5 μm or less. For the oil-absorbing inorganic pigment, the dry weight in the recording layer is 5 to 50% by weight,
It is desirable to add 10 to 40% by weight.

These are dispersed and applied in a binder. As the binder, water-soluble ones are generally used, and polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer. , Polyacrylic acid, starch derivative casein, gelatin and the like.

Further, a water-proofing agent (gelling agent, cross-linking agent) is added to these binders for the purpose of imparting water resistance, or a hydrophobic polymer emulsion, specifically, styrene-butadiene rubber latex, acrylic resin emulsion, etc. Can also be added.

The binder reacts in the recording layer at a dry weight of 10 to 30% by weight. Further, various auxiliaries such as defoaming agents, fluorescent dyes, and coloring dyes can be appropriately added to the coating liquid as needed.

The coating liquid for forming such a recording layer is a blade coating method,
Conventionally known coating methods such as an air knife coating method, a gravure coating method, a roll coating coating method, a spray coating method, a dip coating method, a bar coating method and an extrusion coating method can be used.

The coating amount of the coating liquid for forming the recording layer on the support is not limited, but is usually 3 to 15 g / m ² in dry weight,
It is preferably in the range of 4 to 10 g / m ² .

(Effects of the Invention) The thermosensitive recording paper according to the present invention in which an intermediate layer composed of a white pigment and a resin cured by electron beam irradiation is provided on a support, the smoothness of the base paper is deteriorated because the intermediate layer is not water-based coating. The extremely small amount of (return) results in remarkably good flatness after coating of the intermediate layer, and thus high recording density and good dot reproducibility at the time of thermal recording.

(Examples of the Invention) Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

Example 100 parts of LBKP was beaten to 350 cc of Canadian freeness, 0.2 parts of polyamide polyamine epichlorohydrin and 0.1 part of alkyl ketene dimer were added, and a base paper having a basis weight of 45 g / m ² and a thickness of 50 μ was prepared with a Fourdrinier paper machine. Paper-made. The composition shown in Table 1 was applied to the above base paper so that the applied amount after drying was 5 g / m ² and dried. No. 1 to No.
For 3 is 2 Mrad at an acceleration voltage of 200 KV.
Was irradiated with an electron beam to obtain a heat-sensitive support. Next, a heat-sensitive coating liquid was applied to these supports to obtain heat-sensitive recording paper. Thermal recording was performed on these samples and the recording density was measured.

The results are shown in Table 2.

The method for producing the heat-sensitive coating liquid, the coating method, and the method for measuring the heat-sensitive recording density are shown below.

Method for producing heat-sensitive coating liquid 20 kg of crystal bio-leptlactone was dispersed with a 10% aqueous solution of polyvinyl alcohol (saponification degree: 98%, polymerization degree: 500) in a 300-ball mill overnight. Similarly, 2,2-bis (4-hydroxyphenyl) propane 2
0 kg together with 10% polyvinyl alcohol aqueous solution 30
It was dispersed all day and night in a 0 ball mill. Both dispersions were mixed so that the ratio of crystal violet lactone and 2,2-bis (4-hydroxyphenyl) propane was 1: 5 by weight, and 5 kg of light trace carbonic acid was added to 20 kg of the mixed solution. Calcium was added and sufficiently dispersed to obtain a coating liquid.

Coating method of heat-sensitive coating liquid 6g / m in solid content on one side of base paper with air knife coater
^It was applied so that it would be ² , dried in a hot-air dryer at 50 ° C., and machine-calendered.

Thermal recording density measuring method Recording speed 2 ms per dot, recording density main scanning method 5
Solid color was developed at a dot / mm, a sub-scanning direction of 6 dots / mm, and a thermal head energy of 50 mm / mm ² . The recording density was a reflection density of 610 nm.

From the results shown in Table 2, it is clear that the thermosensitive recording paper according to the present invention has excellent properties in terms of both color density and dot reproducibility.

Claims (2)

[Claims] 1. A thermosensitive recording paper having a thermosensitive coloring layer on a support, wherein (a) a white inorganic pigment and / or a white organic pigment and (b) electron beam irradiation are provided between the support and the thermosensitive coloring layer. A heat-sensitive recording paper having an intermediate layer made of a resin cured by. 2. The heat-sensitive recording paper according to claim 1, wherein the support is a paper made of wood pulp and / or a synthetic pulp, or a plastic film.