JP2005103824A - Thermosensitive recording body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermosensitive recording body having high recording sensitivity and capable of obtaining a high quality recording image. <P>SOLUTION: The thermosensitive recording body, which is provided on a support with an undercoating layer comprising a pigment and a binder as main components and a thermosensitive recording layer comprising a colorless or a light-colored basic colorless dye and a color developing agent developing a color by reacting with the basic colorless dye as main components, is characterized in that the undercoating layer contains 0.1 to 25 pts.wt. of hydroxy alkyl etherified starch to 100 pts.wt. of a pigment. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat-sensitive recording material utilizing a color development reaction between a basic colorless dye and a developer.

  In general, a heat-sensitive recording medium is usually a colorless or light-colored basic colorless dye and an organic developer such as a phenolic compound, which are ground and dispersed into fine particles, and then mixed together to form a binder and a packing. A coating obtained by adding an agent, a sensitivity improver, a lubricant and other auxiliary agents is applied to a support such as paper, synthetic paper, film, plastic, thermal head, hot stamp, heat Color is generated by an instantaneous chemical reaction by heating with a pen, laser light or the like, and a recorded image is obtained. Thermosensitive recording media are widely used in facsimiles, computer terminal printers, automatic ticket vending machines, measuring recorders, and the like. In recent years, with the diversification of recording devices and the advancement of performance, high-speed printing and high-speed image formation have become possible, and higher quality is required for the recording sensitivity of the thermal recording medium. Further, with the diversification of applications, it is also required to obtain a high-quality recorded image in any region from low density to high density.

As a method for satisfying these requirements, it is generally performed to increase the smoothness of the surface of the heat-sensitive recording layer by using a super calender or the like, but it is not always possible to obtain a satisfactory image quality. Further, it is known that the coating uniformity of the undercoat layer is important for high image quality. For example, it is known that the smoothness of the undercoat layer is improved by a super calendar. Furthermore, in order to provide a thermosensitive recording material having excellent dot reproducibility, for example, Patent Document 1 proposes a method of laminating a first intermediate layer and a second intermediate layer.
JP 2000-108518 A

  However, in the method based on the super calender, the calender pressure impairs the porosity of the undercoat layer and loses the heat insulation, resulting in a decrease in sensitivity. Moreover, the method of laminating the first intermediate layer and the second intermediate layer is disadvantageous in production because the process is complicated. Accordingly, an object of the present invention is to provide a heat-sensitive recording material that has a high recording sensitivity and can obtain a high-quality recorded image without causing these problems.

  The above-mentioned problems include, as a main component, an undercoat layer containing a pigment and a binder as main components on a support, a colorless or light basic colorless dye, and a developer that reacts with the basic colorless dye to develop a color. The heat-sensitive recording material provided with the heat-sensitive recording layer contained as a heat-sensitive recording material was achieved by forming the undercoat layer into a heat-sensitive recording material containing hydroxyalkyl etherified starch.

  According to the present invention, a thermal recording material having high recording sensitivity and excellent image quality can be obtained by containing hydroxyalkyl etherified starch in the undercoat layer.

Embodiments of the present invention will be described below.
The undercoat layer in the present invention contains a pigment and a binder as main components, and it is important to contain a hydroxyalkyl etherified starch as a binder. As the hydroxyalkyl etherified starch used in the present invention, hydroxyethyl etherified starch (hereinafter sometimes referred to as hydroxyethylated starch) and hydroxypropyl etherified starch are practical, and the former is particularly preferable. The hydroxyalkyl etherified starch in the present invention preferably has a molecular weight of 200,000 to 1,000,000, more preferably 500,000 to 850,000, and a substitution degree of 0.02 to 0.065.
The hydroxyalkyl etherified starch is preferably contained in an amount of 0.1 to 25 parts by weight based on 100 parts by weight of the pigment. More preferably, it is 1 to 10 parts by weight with respect to 100 parts by weight of the pigment. The hydroxyalkyl etherified starch used in the present invention is considered to have the effect of improving the water retention of the coating solution and suppressing the penetration of the coating material. When the number of the hydroxyalkyl etherified starch is too small, sufficient water retention cannot be obtained, and conversely, when it is too large, the ratio of the calcined clay is relatively low. The effect will be reduced.

  The reason why an excellent effect can be obtained in the present invention is considered as follows. One reason for the deterioration in image quality is that the solid content concentration of the undercoat layer coating solution in the heat-sensitive recording material is better than the coating layer coating solution of a general printing coated paper being 60 to 70%. In order to obtain high quality and dispersibility of the coating liquid, it may be about 40% or less depending on the material used. Since the concentration is low, the binder component migrates downward after coating. Cheap. As a result, the binder distribution and pigment orientation in the coating layer become non-uniform, and when a thermal recording layer is provided and recorded on this, the thermal energy is not transmitted uniformly, resulting in uneven dots and poor image quality. Conceivable. On the other hand, in the present invention, the hydroxyalkyl etherified starch functions as a part of the binder, thereby improving water retention and fluidity, thereby preventing binder migration and uniform coating. It is considered that a construction layer is obtained and effective. In addition, when the amount of the hydroxyalkyl etherified starch is as low as 2 parts or less, that is, even when the function as a binder is not exhibited, the water retention is improved, so it is effective to add it as an auxiliary agent to the paint It is.

In the undercoat layer of the present invention, in addition to the hydroxyalkyl etherified starch, water-soluble polymers such as starch, polyvinyl alcohol, methylcellulose, carboxymethylcellulose, styrene / maleic anhydride, styrene / butadiene copolymer, acrylic Contains synthetic resin emulsions such as acid copolymers.
In forming this undercoat layer, the coating amount is about 1 to 15 g / m ² , and it is applied on a support made of an appropriate material such as paper, recycled paper, plastic film, synthetic paper, etc. using a normal coating machine. It is easily done by applying. As a coating method, any of known coating methods such as an air knife method, a blade method, a gravure method, a roll coater method, and a curtain method may be used, but high concentration coating is possible and the coating liquid is applied to the support. It is preferable that the undercoat layer is formed by blade coating because it does not easily penetrate and a uniform layer structure is formed.

Examples of the pigment contained in the undercoat layer include (baked) kaolin, calcium carbonate, aluminum oxide, titanium oxide, magnesium carbonate, amorphous silica, aluminum silicate, magnesium silicate, calcium silicate, and the like. In particular, a calcined kaolin having an oil absorption (based on the JIS K 5101 method) of 80 cc / 100 g to 120 cc / 100 g is most preferable because a heat-sensitive recording material excellent in the balance between color development sensitivity and image quality can be obtained. By using such calcined kaolin, a sufficient heat insulating effect is given and the sensitivity is increased, and the binder is not absorbed in a large amount by the pigment, so that a uniform coating layer is formed and good image quality is obtained. It is thought that. On the other hand, when calcined kaolin is used, it is generally inferior in fluidity of the paint compared to round calcium carbonate or the like because of its flat shape, and since it is calcined, the surface has silanol OH groups. (Hydroxyl group) does not exist, and it is thought that the water-retaining property is weakened and the water retention of the paint tends to decrease. On the other hand, in this invention, it is thought by the effect | action of a hydroxy alkyl etherified starch that the paint suitability at the time of using calcined kaolin is improved.
If necessary, a dispersant, a wax, a thickener, a surfactant, an ultraviolet absorber, an antioxidant, a water / oil repellent and the like may be added to the coating solution for the undercoat layer.
The heat-sensitive recording layer formed on the undercoat layer is formed by a conventionally known production method.

As the colorless or light-colored basic colorless dye used in the heat-sensitive recording material of the present invention, all known ones in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used and are not particularly limited. Phenylmethane compounds, fluorane compounds, fluorene compounds, divinyl compounds and the like are preferable. Specific examples of typical colorless or light-colored basic colorless dyes are shown below. These basic colorless dyes may be used alone or in combination of two or more.
<Triphenylmethane leuco dye>
3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone)
3,3-bis (p-dimethylaminophenyl) phthalide (also known as malachite green lactone)

<Fluoran leuco dye>
3-diethylamino-6-methylfluorane 3-diethylamino-6-methyl-7-anilinofluorane 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane 3-dibutylamino-6- Methyl-fluorane 3-dibutylamino-6-methyl-7-anilinofluorane 3-dibutylamino-6-methyl-7- (o, p-dimethylanilino) fluorane 3-dibutylamino-7- (o-chloroanilino ) Fluorane 3-dibutylamino-7- (o-fluoroanilino) fluorane 3-n-dipentylamino-6-methyl-7-anilinofluorane 3- (N-ethyl-N-isoamylamino) -6-methyl -7-anilinofluorane 3- (N-ethyl-N-isoamylamino) -6-chloro-7-anilinofluor Lan 3-cyclohexylamino-6-chlorofluorane

<Divinyl leuco dye>
3,3-bis- [2- (p-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrabromophthalide 3,3-bis- [2- ( p-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrachlorophthalide 3,3-bis- [1,1-bis (4-pyrrolidinophenyl) ethylene -2-yl] -4,5,6,7-tetrabromophthalide 3,3-bis- [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2-yl]- 4,5,6,7-tetrachlorophthalide

<Others>
3- (4-Diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide 3- (4-diethylamino-2-ethoxyphenyl) -3- (1 -Octyl-2-methylindol-3-yl) -4-azaphthalide 3- (4-cyclohexylethylamino-2-methoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4- Azaphthalide 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide 3,6-bis (diethylamino) fluorane-γ- (3'-nitro) anilinolactam 3,6-bis (diethylamino) Fluorane-γ- (4′-nitro) anilinolactam 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminopheny L) -ethenyl] -2,2-dinitrileethane 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2-β -Naphthoylethane 1,1-bis- [2 ', 2', 2 ", 2" -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2,2-diacetylethanebis- [2,2,2 ', 2'-tetrakis- (p-dimethylaminophenyl) -ethenyl] -methylmalonic acid dimethyl ester

As the developer used for the heat-sensitive recording material of the present invention, a conventionally known developer that develops a colorless or light basic dye can be used in combination. Examples of the color developer include bisphenol A, 4-hydroxybenzoic acid esters, 4-hydroxyphthalic acid diesters, and phthalic acid monoesters described in JP-A-3-207688 and JP-A-5-24366. Esters, bis- (hydroxyphenyl) sulfides, 4-hydroxyphenylaryl sulfones, 4-hydroxyphenylaryl sulfonates, 1,3-di [2- (hydroxyphenyl) -2-propyl] -benzenes, Examples include 4-hydroxybenzoyloxybenzoate and bisphenol sulfones.
In the heat-sensitive recording material of the present invention, conventionally known sensitizers can be used in the same manner as conventional heat-sensitive recording materials. Examples of such sensitizers include fatty acid amides such as stearamide and palmitic acid amide, ethylene bisamide, montanic acid wax, polyethylene wax, 1,2-di- (3-methylphenoxy) ethane, p-benzylbiphenyl, β- Benzyloxynaphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, dibenzyl oxalate, di (p-chlorobenzyl) oxalate, di (p-methylbenzyl) oxalate, Dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, o-xylene-bis -(Phenyl ether), 4- (m-methyl) Ruphenoxymethyl) biphenyl, 4,4′-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2-di (3-methylphenoxy) ethylene, bis [2- (4-methoxy- Examples thereof include, but are not limited to, phenoxy) ethyl] ether, methyl p-nitrobenzoate and phenyl p-toluenesulfonate. These sensitizers may be used alone or in combination of two or more.

In addition, as an image stabilizer showing the oil resistance effect of the recorded image,
4,4'-butylidene (6-tert-butyl-3-methylphenol)
2,2'-di-t-butyl-5,5'-dimethyl-4,4'-sulfonyldiphenol 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane 1, 1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane and the like can also be added.
In addition, release agents such as fatty acid metal salts, lubricants such as waxes, UV absorbers such as benzophenone and triazole, water resistance agents such as glyoxal, dispersants, antifoaming agents, antioxidants, fluorescent dyes, etc. Can be used.

The types and amounts of basic colorless dyes, developers, and other various components used in the heat-sensitive recording material of the present invention are determined according to required performance and recording suitability, and are not particularly limited. The developer is used in an amount of 0.5 to 10 parts and a filler of 0.5 to 10 parts per 1 part of the colorless dye.
By applying the coating liquid having the above composition to any support such as paper, recycled paper, synthetic paper, film, plastic film, foamed plastic film, non-woven fabric, etc., the desired thermal recording material can be obtained. Moreover, you may use the composite sheet which combined these as a support body.

Basic colorless dye, color developer, and materials to be added as necessary are pulverized to a particle size of several microns or less by a pulverizer such as a ball mill, an attritor, a sand glider, or an appropriate emulsifying device, an acrylic emulsion, Colloidal silica and various additive materials are added according to the purpose to obtain a coating solution. The application means is not particularly limited, and can be applied according to well-known conventional techniques. For example, an off-machine coating having various coaters such as an air knife coater, a rod blade coater, a bill blade coater, a roll coater, and a curtain coater. A machine or an on-machine coating machine is appropriately selected and used. The coating amount of the heat-sensitive recording layer is not particularly limited and is usually in the range of ² to 12 g / m ^{2 by} dry weight.
The heat-sensitive recording material of the present invention is further provided with an overcoat layer such as a polymer material on the heat-sensitive recording layer for the purpose of improving the storage stability, or for the purpose of increasing the color development sensitivity. A coat layer can also be provided under the heat-sensitive recording layer. It is also possible to correct the curl by providing a backcoat layer on the opposite side of the support from the thermosensitive recording layer. Also, various known techniques in the heat-sensitive recording material field can be added as appropriate, such as applying a smoothing process such as supercalendering after coating each layer.

The thermosensitive recording material of the present invention will be described below with reference to examples. In the description, parts and% indicate parts by weight and% by weight, respectively. Various solutions, dispersions, or coating solutions were prepared as follows.
[Example 1]
A composition comprising the following composition was stirred and dispersed to prepare an undercoat layer coating solution.
U solution (undercoat layer coating solution)
Baked clay (trade name: Ansilex 90, manufactured by Engelhard)
<Oil absorption 90cc / 100g>)
100 parts Styrene-butadiene copolymer latex (solid content 48%) 40 parts Polyvinyl alcohol 10% aqueous solution 30 parts Hydroxyethylated starch 10% aqueous solution 10 parts Water 100 parts

Next, the undercoat layer coating solution was applied to one side of a support (60 g / m ² base paper) and then dried to obtain an undercoat layer having a coating amount of 10.0 g / m ² .
The developer dispersion liquid (liquid A) and the basic colorless dye dispersion liquid (liquid B) having the following composition were separately wet-ground with a sand grinder until the average particle diameter became 1 micron.
Liquid A (developer dispersion)
4-hydroxy-4'-isopropoxydiphenylsulfone 6.0 parts polyvinyl alcohol 10% aqueous solution 18.8 parts water 11.2 parts Liquid B (basic colorless dye dispersion)
3-Dibutylamino-6-methyl-7-anilinofluorane (ODB-2)
2.0 parts polyvinyl alcohol 10% aqueous solution 4.6 parts water 2.6 parts Subsequently, the dispersion was mixed at the following ratio to obtain a recording layer coating solution.
Recording layer coating liquid A (developer dispersion) 36.0 parts B liquid (basic colorless dye dispersion) 9.2 parts Kaolin clay (50% dispersion) 12.0 parts After coating on the undercoat layer of the undercoat layer-formed paper so as to have a coating amount of 6.0 g / m ² , drying is performed, and this sheet is processed with a super calendar so that the smoothness becomes 500 to 600 seconds. A heat-sensitive recording material was obtained.

[Example 2]
In the U liquid (undercoat layer coating liquid) of Example 1, the blending part number of the polyvinyl alcohol 10% aqueous solution was 20 parts, and the blending part number of the hydroxyethylated starch 10% aqueous solution was 120 parts. A heat-sensitive recording material was prepared.

[Comparative Example 1]
A heat-sensitive recording material was prepared in the same manner as in Example 1 except that hydroxyethylated starch was not added to the U solution (undercoat layer coating solution) of Example 1.
[Comparative Example 2]
A heat-sensitive recording material was prepared in the same manner as in Example 1, except that in the U solution (undercoat layer coating solution) of Example 1, the blended part of the 10% aqueous solution of oxidized starch was 120 parts instead of hydroxyethylated starch. .

<Recording sensitivity evaluation>
The produced thermal recording material was printed at a applied energy of 0.27 mJ / dot using a TH-PMD (equipped with thermal recording paper printing tester, Kyocera thermal head) manufactured by Okura Electric Co., Ltd. The recording density of the recording part was measured and evaluated with a Macbeth densitometer (RD-914, using an amber filter).

<Image quality evaluation>
The solid print portion was visually evaluated.
○: No white spots are observed.
Δ: Some white spots are observed.
X: There are many white spots.

Claims (2)

An undercoat layer containing a pigment and a binder as main components on a support, a heat-sensitive material containing as a main component a colorless or pale basic colorless dye and a color developer that reacts with the basic colorless dye to develop a color. A heat-sensitive recording material provided with a recording layer, wherein the undercoat layer contains a hydroxyalkyl etherified starch. The heat-sensitive recording material according to claim 1, comprising 0.1 to 25 parts of hydroxyalkyl etherified starch with respect to 100 parts by weight of the pigment.