JP2002293023A - Heat-sensitive recording sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-sensitive recording sheet having a light weight and an excellent color developing sensitivity. SOLUTION: The heat-sensitive recording sheet comprises a heat-sensitive color developing layer provided on a support. In this sheet, the support contains a low-densifying chemical. The recording sheet further comprises an undercoating layer provided between the support and the color developing layer.

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 sheet which is lightweight and has excellent color sensitivity.

[0002]

2. Description of the Related Art In general, a heat-sensitive recording sheet having a heat-sensitive coloring layer mainly composed of a colorless or light-colored dye precursor and a color developing agent which reacts with the dye precursor by heating to form a color is disclosed in
It is disclosed in Japanese Patent Publication No. 14039 and widely used. A thermal printer with a built-in thermal head is used for recording on the thermal recording sheet, and is widely used in facsimile and computer fields, various measuring instruments, labels and the like with the development of the information industry. With the diversification and high performance of these recording devices, the required quality of the heat-sensitive recording sheet has become higher, and the coloring sensitivity is high, even with a small amount of heat energy. It is required that an image be obtained.

In order to satisfy these demands, it is important to use heat efficiently.
JP-184875 describes that the thermal conductivity between a thermal head and a support is increased by including a cationic softening agent in the support. Also, JP-A-10-219588
The publication describes the use of a low-density sheet containing, as a support, fine fibers having a specific range of a binding reinforcing factor and curled fibers having a specific range of a wet curl factor. However, when these low-density papers are used as a support for a heat-sensitive recording sheet, sufficient coloring properties may not always be obtained.

[0004] On the other hand, low-density paper has been attracting attention in recent years in conjunction with an increase in environmental protection, and it has been attempted to conserve resources of paper pulp manufactured from forest resources and to handle it during distribution. There is a strong demand for reducing the weight of paper from the viewpoint of improving the properties. Here, to reduce the weight of paper means to reduce the density while maintaining the thickness and strength of the paper, that is, to make the paper low density (bulky).

[0005] As a method for reducing the density (bulking) of paper,
Studies include papermaking pulp, which is a main raw material of paper, and fillers, which are contained next to pulp. Wood pulp is generally used as papermaking pulp.It is manufactured by grinding wood with a refiner or grinder without using chemicals, compared to chemical pulp obtained by extracting lignin, a reinforcing material in fibers, with chemicals. The mechanical pulp to be used has more rigid fibers, which is advantageous for lowering the density. In addition, although the pulp for papermaking usually makes the fibers soft and fibrillates by beating treatment, the beating treatment is a process contradictory to bulking, and it is desirable that the beating be performed as little as possible for bulking.

Among mechanical pulp, ground pulp (G
P) greatly contributes to lower density. However, in the case of high-quality paper, the use of GP and thermomechanical pulp (TMP) has many problems in terms of standards, and there are defects in paper quality and quality such as fading with the passage of time. Therefore, chemical pulp is preferably used. Also, the density of paper is greatly affected by the type of pulped wood, and the lower the density, the coarser the wood fibers themselves. For example, gumwood, maple, birch and the like can be mentioned as tree species that can be made relatively low-density in hardwoods.
However, it is difficult to identify and collect only these tree species, especially in the tide of environmental protection.

[0007] Japanese Patent Application Laid-Open No. 5-339898 describes that a filler contains a hollow synthetic organic substance capsule. There is also known a synthetic organic foaming filler which expands due to heat in a dryer section at the time of papermaking to increase bulk. However, methods using these fillers have problems such as difficulty in setting drying conditions, low surface strength, and low print gloss.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording sheet which is reduced in weight and excellent in color sensitivity regardless of the type of pulp and filler constituting the support.

[0009]

An object of the present invention is to provide a thermosensitive recording sheet having a heat-sensitive coloring layer provided on a support, wherein the support contains a low-density chemical, and the support and the heat-sensitive coloring layer This was achieved by providing an undercoating layer between the above.

The present invention provides a support having a reduced density (hereinafter referred to as a support).
In the case of low-density base paper or simply base paper), when the heat-sensitive coloring layer coating is applied, the coating easily penetrates into the base paper due to the voids, and when subjected to calendering for the purpose of imparting smoothness, it becomes bulky. It has been found that, by focusing on the fact that the property is likely to be lost, the above-described configuration can provide a heat-sensitive recording sheet having high coloring sensitivity while maintaining light weight.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The support used in the heat-sensitive recording sheet of the present invention is a chemical pulp (bleached or unbleached kraft pulp of softwood, bleached or unbleached kraft pulp of hardwood) or a mechanical pulp as a raw material pulp. Ground pulp, thermo-mechanical pulp, chemi-thermo-mechanical pulp, etc.), deinked pulp, etc. can be used alone or in a mixture at an arbitrary ratio.
It is manufactured according to a conventionally known manufacturing method by adding various papermaking chemicals such as a sizing agent, a paper strength enhancer, a retention enhancer, a colorant, and an antifoaming agent.

The low-density chemical used in the present invention is added to the pulp slurry when the base paper is made. Incorporation in a larger amount than necessary not only increases the cost, but also tends to significantly impair the balance of physical properties of the base paper. If the amount is too small, the desired effect cannot be obtained.
The blending amount can be appropriately determined by experiments depending on the properties of the low-density chemical, the properties of the pulp and various chemicals to be simultaneously blended, and the purpose of blending. 0.0%, preferably 0.4 to 1.5%.

The low-density chemical used in the present invention can be selected by the following tests. Using a pulp slurry in which an organic compound to be tested is added to a pulp composition constituting a target paper in an amount of 0.3 part by weight based on 100 parts by weight of the absolutely dry pulp of the pulp composition, an orientation tester for experiment is used. Paper is made at a rotational speed of 900 rpm (manufactured by Kumagai Riki Co., Ltd.), pressed according to the method of JIS8209, and dried at 50 ° C. for 1 hour by a blow dryer to obtain test paper. When the density of the test paper obtained in this way is lower than the density of the paper containing no organic compound, the organic compound can be used as the low-density chemical of the present invention. Is preferably used as a low-density chemical.

Specific examples of the low-density chemicals of the present invention include oil-based nonionic surfactants, sugar alcohol-based nonionic surfactants, sugar-based nonionic surfactants, and polyhydric alcohol-type nonionic surfactants. Surfactants such as surfactants which are commercially available or classified, higher alcohols, ethylene oxide or propylene oxide adducts of higher alcohols or higher fatty acids, fatty acid polyamidoamines, and aliphatic quaternary ammonium salts can be exemplified. . More preferably, it is a polyhydric alcohol type nonionic surfactant. Further, the low-density chemical of the present invention can be used in combination with amorphous silica, amorphous silicate, or the like, which is a bulky filler.

The heat-sensitive recording sheet of the present invention can be obtained by providing a heat-sensitive coloring layer on base paper containing the above-mentioned low-density chemical. The formation of the heat-sensitive coloring layer may be performed according to a conventionally known production method, and usually, a heat-sensitive coloring layer coating solution containing an organic developer, a basic colorless dye, a binder, a pigment, and other necessary additives is prepared. It is formed by coating and drying on a support.

The organic color developer used in the present invention includes:
Although not particularly limited, for example, Japanese Patent Application Laid-Open
No. 07688, JP-A-5-24366, etc., bisphenol A, 4-hydroxybenzoic acid ester, 4-hydroxyphthalic acid diester, phthalic acid monoester, bis- (hydroxyphenyl) sulfide, -Hydroxyphenylaryl sulfones, 4
-Hydroxyphenylarylsulfonates, 1,3
-Di [2- (hydroxyphenyl) -2-propyl]-
Benzenes, 4-hydroxybenzoyloxybenzoic acid esters, bisphenol sulfones, JP-A-8-59
No. 603 is exemplified.

The basic dye used in the present invention includes:
There is no particular limitation, triphenylmethane,
Conventionally known compounds such as fluoran, azaphthalide, and fluorene can be used. These basic dyes can be used alone or in combination of two or more.

The binder in the thermosensitive coloring layer is a completely saponified polyvinyl alcohol having a polymerization degree of 200 to 1900, a partially saponified polyvinyl alcohol, a carboxy-modified polyvinyl alcohol, an amide-modified polyvinyl alcohol, a sulfonic acid-modified polyvinyl alcohol, a butyral-modified polyvinyl alcohol. Modified polyvinyl alcohol such as alcohol, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose,
Cellulose derivatives such as acetyl cellulose, styrene-maleic anhydride copolymer, styrene-butadiene copolymer, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylate, polyvinyl butyral, polystyrene and their copolymers , Polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin, and cumarone resin. These high-molecular substances can be used by dissolving them in solvents such as water, alcohols, ketones, esters, and hydrocarbons.Also, they can be used in emulsified or paste-like form in water or other media. You can also.

As fillers in the thermosensitive coloring layer, silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth,
Talc, titanium oxide, zinc oxide, aluminum hydroxide,
Polystyrene resin, urea-formalin resin, styrene-
Examples thereof include methacrylic acid copolymers, styrene-butadiene copolymers, and inorganic or organic fillers such as hollow plastic pigments.

In addition, a sensitizer, an image stabilizer, a release agent such as a fatty acid metal salt, a lubricant such as a wax, a benzophenone-based or triazole-based ultraviolet absorber, and a water-resistant material such as glyoxal are used in the heat-sensitive coloring layer. Agents, dispersants, defoamers,
Antioxidants, fluorescent dyes and the like can be added.

The amounts of the organic developer and the basic dye used in the present invention and the types and amounts of other various components are determined according to the required performance and recording suitability, and are not particularly limited. For 1 part of the basic dye, 1 to 8 parts of an organic developer and 1 to 20 parts of a filler are used, and an appropriate binder is 10 to 25% of the total solid content.

These developers, dyes and materials to be added as needed are pulverized by a pulverizer such as a ball mill, an attritor, a sand grinder or an appropriate emulsifying device to a particle size of several microns or less, and a binder and Various coating materials are added according to the purpose to form a coating liquid.
Examples of the coating method include hand coating, size press coater method, roll coater method, air knife coater method, blade coater method, flow coater method, comma direct method, gravure direct method, gravure reverse method, reverse roll coater method and the like. . After spraying, spraying or dipping, drying may be performed.

In the heat-sensitive recording sheet of the present invention, an undercoat layer is provided between the support and the heat-sensitive coloring layer. The undercoat layer usually contains a binder and a filler, and as the binder and the filler, the materials exemplified as the components of the thermosensitive coloring layer can be appropriately used according to the required quality. The method for preparing the undercoat layer coating solution is not particularly limited, and is generally prepared by using water as a dispersion medium and adding various additives as necessary in addition to the binder and the filler. The method for forming the undercoat layer is not particularly limited, either, and the undercoat layer is formed by a method such as applying and drying the undercoat layer coating solution on the thermosensitive coloring layer in the same manner as the thermosensitive coloring layer.

Further, in the heat-sensitive recording sheet of the present invention, an overcoat layer of a polymer substance or the like can be provided on the heat-sensitive coloring layer for the purpose of enhancing the storage stability.

[0025]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto. “Parts” and “%” indicate “parts by weight” and “% by weight”, respectively. [Manufacture of base paper] Hardwood bleached kraft pulp (LBKP, freeness CSF 320 ml) is used as a pulp raw material, and a polyhydric alcohol-type nonionic surfactant (KB110, manufactured by Kao Corporation) is used as a low density chemical. 0 per pulp.
8% by weight, 17% by weight of calcium carbonate as a filler (ash content in paper) of 17% by weight of paper and amorphous silicate (hydrated aluminum silicate soda, bulk specific gravity 0.25g /
paper), which was adjusted to 8% by weight, and 0.2% by weight of an alkyl ketene dimer as a neutral sizing agent, based on the paper weight. A low-density base paper having a basis weight of 78 g / m ² was obtained. Next, starch 100 for coating was used as a water-soluble polymer.
A 7.5% surface treatment aqueous solution consisting of 1 part by weight of a sizing agent and 1 part by weight of a sizing agent was applied to the base paper so as to have a coating amount of 4 g / m ² by a two-roll size press to obtain a base paper for a heat-sensitive recording sheet. .

[Example 1] An undercoat layer and a thermosensitive coloring layer having the following compositions were sequentially provided on the base paper produced as described above.・ Undercoat layer Calcined kaolin 100 parts Styrene / butadiene copolymer latex (solid content 48%) 11 parts 10% aqueous solution of polyvinyl alcohol 10 parts Water 150 parts The above coating solution was applied to one side of the base paper to 8.0 g / m ² . It was applied and dried to form an undercoat layer. -Thermosensitive coloring layer A liquid (developing agent dispersion liquid) 4-hydroxy-4'-isopropoxydiphenylsulfone 6.0 parts 10% aqueous polyvinyl alcohol solution 18.8 parts Water 11.2 parts The above composition is sand-grindered. Milled to an average particle size of 1 micron. Liquid B (dye dispersion liquid) 3-di (n-butyl) amino-6-methyl-7-anilinofluoran 2.0 parts 10% aqueous polyvinyl alcohol solution 4.6 parts water 2.6 parts Grinding was performed with a sand grinder to an average particle diameter of 1 micron. Liquid C (sensitizer dispersion liquid) Parabenzylbiphenyl 6.0 parts 10% aqueous polyvinyl alcohol solution 18.8 parts Water 11.2 parts The above composition was ground with a sand grinder to an average particle diameter of 1 micron. Subsequently, the dispersion liquid was mixed at the following ratio to obtain a coating liquid. Liquid A 36.0 parts Liquid B 9.2 parts Liquid C 36.0 parts Kaolin clay (50% dispersion) 12.0 parts Each of the above coating liquids is applied onto the undercoat layer in an amount of 6.0 g / m ² . The coating was dried as described above to form a thermosensitive coloring layer to obtain a thermosensitive recording sheet.

Comparative Example 1 A thermosensitive recording sheet was obtained in the same manner as in Example 1 except that no undercoat layer was provided.

[Color sensitivity test] TH- manufactured by Okura Electric Co., Ltd.
Using a PMD, printing was performed on the prepared thermosensitive recording medium at an applied energy of 0.30 mJ / dot and 0.39 mJ / dot, and measurement was performed with a Macbeth densitometer (using an amber filter).

[0029]

[Table 1]

[0030]

The heat-sensitive recording sheet of the present invention is light in weight, has high coloring sensitivity, and is extremely excellent in practical use.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yoshihide Kimura 5-21-1, Oji, Kita-ku, Tokyo Nippon Paper Industries Co., Ltd. F-term (reference) 2H026 AA07 BB02 BB24 DD01 DD02 DD43 DD58 FF01 FF15

Claims (1)

[Claims] 1. A thermosensitive recording sheet having a thermosensitive coloring layer provided on a support, wherein the support contains a low-density chemical and an undercoat layer is provided between the support and the thermosensitive coloring layer. A heat-sensitive recording sheet characterized by the following.