JPH0236993A - Heat-sensitive recording medium - Google Patents

Abstract

PURPOSE:To obtain a heat-sensitive recording medium with high printing pixel reproducibility, high recording sensitivity and high degree of whiteness by adding kaolin with specific bulk density as pigment for an undercoat layer in a heat- sensitive recording medium consisting of the undercoat layer and a heat-sensitive recording layer laminated on a base. CONSTITUTION:A heat-sensitive recording medium contains kaolin with a bulk density of 0.35g/cm<2> or less in an undercoat layer. Kaolin with this kind of bulk density is manufactured by the secondary flocculation of kaolin. The binder for applying kaolin to the surface of a base is not particularly defined. However, its mixture percentage is 2-40% by weight of the total amount of solid component, and preferably about 5-20% by weight. In addition, such additives as a dispersant, defoaming agent, coloring dye, fluorescent dye and ultraviolet ray absorber can be mixed. The preferable coating amount is about 2-20g/m<2>, although not particularly specified.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a heat-sensitive recording medium, and particularly to a heat-sensitive recording medium that has excellent print pixel reproducibility, extremely high recording sensitivity (and high whiteness).

(Prior art) Conventionally, thermosensitive technology utilizes a color reaction between a color former and a color former that develops color when it comes into contact with the color former, and brings both colored substances into contact with each other using heat to obtain a colored image. Recording bodies are well known. Such heat-sensitive recording media are relatively inexpensive, and the recording equipment is compact and relatively easy to maintain.
It is used not only as a recording medium for facsimiles and various computers, but also in a wide range of other fields.

With the diversification of uses, there is an increasing demand for thermal recording materials that can provide high-quality recorded images with excellent reproducibility of printed pixels in any range from low density to high density. 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 high image quality and highly sensitive thermal recording medium,
For example, methods have been proposed to improve smoothness and heat insulation by providing various pigment layers between the support and the recording layer, but since each pigment has its own drawbacks, this is not always possible. No satisfactory results have been obtained.

For example, even if the undercoat layer contains pigments with high bulk density such as calcium carbonate, zinc oxide, titanium oxide, aluminum hydroxide, curcum, clay, etc., sufficient pixel reproducibility and recording density cannot be obtained.

Ancilenx (manufactured by Engelhart, bulk density 0.37) is the most common calcined kaolin with a relatively low bulk density.
g/cnJ), the purpose is not fully achieved. Furthermore, when a special pigment such as silicic acid is used, it causes fogging at the interface with the coloring layer, which has the disadvantage of reducing whiteness.

(Problems to be Solved by the Invention) An object of the present invention is to provide a heat-sensitive recording material that has excellent print pixel reproducibility, high recording sensitivity, and high whiteness without having the above-mentioned drawbacks. .

(Means for Solving the Problems) The above-mentioned object of the present invention is to provide a heat-sensitive recording material in which an undercoat layer and a heat-sensitive recording layer are sequentially laminated on a support, in which the pigment of the undercoat layer has a bulk density of 0. .35g/c
This is achieved by containing kaolin of +11 or less.

(Function) As described above, the heat-sensitive recording material of the present invention is characterized in that the undercoat layer contains kaolin having a bulk density of 0.35 g/cI11/or less.

Kaolin having such a bulk density is produced by secondary agglomeration of kaolin.

In addition, the bulk density in the present invention is expressed as the weight (g) per constant volume (c + 1i) by putting the pigment in a 10-female graduated cylinder, applying vibration until the volume becomes constant, and weighing the pigment accurately. is the value to be used.

Binders for coating the above-mentioned kaolin on the support include, but are not particularly limited to, starches, polyvinyl alcohol, cellulose derivatives such as hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, methoxycellulose, and ethylcellulose; Sodium polyacrylate, polyvinylpyrrolidone, amide acrylate 1/acrylic ester copolymer, amide acrylate 1
/acrylic acid ester/methacrylic acid three-dimensional copolymer,
Styrene/maleic anhydride copolymer alkali salt, isobutylene/maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, casein, and other water-soluble polymers, polyvinyl acetate, polyurethane, styrene/butadiene copolymer, etc. Polymers, polyacrylic acid, polyacrylic esters, vinyl chloride/monyl acetate copolymers,
Latexes such as polybutyl methacrylate-1-, ethylene/vinyl acetate copolymer, and styrene/butadiene/acrylic copolymer are used. Further, the amount used is about 2 to 40% by weight of the total solid content, preferably about 5 to 20% by weight.

Further, various auxiliary agents such as a dispersant, an antifoaming agent, a colored dye, a fluorescent dye, and an ultraviolet absorber can be added as necessary.

Coating methods include, but are not particularly limited to, air knife coating, blade coating, hard coating, gravure coating, curtain coating, and the like.

Furthermore, the coating amount is not particularly limited, but is 2 to 20 g/rr.
A coating amount of about f is preferable.

The heat-sensitive color forming layer in the present invention is composed of a combination of a leuco dye and a color developer, and any leuco dye that is applied to this type of heat-sensitive material can be used.

Various kinds of basic dyes are known, for example,
The following are examples.

3.3-bis(p-dimethylaminophenyl)6-dimethylaminophthalide, 3.3-bis(dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl)-3-(1,2- Dimethylindol-3-yl)phthalide, 3-(p-dimethylaminophenyl)-3
-(2-methylindol-3-yl)phthalide, 3.
3-his(1,2-dimethylindol-3-yl)5
-dimethylaminophthalide, 3,3-bis(12-dimethylindol-3-yl)-6-dimethylaminophthalide I, 3,3-his(9-ethylcarbazol-3-
yl)-6-dimethylaminophthalide, 33-bis(2
-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-(
Triallylmethane dyes such as 1-methylpyrrol-3-yl)-6-dimethylaminophthalide, 4.4bis-dimethylaminohenzhydrylhenzyl ether, N-halophenyl-leucoolamine, N-2/I 5 -1
~Diphenylmethane dyes such as dichlorophenyl leuco auramine, thiazine dyes such as hendiyl leucomethylene blue, ρ-2I-lopenzoyl leucomethylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3 - Spiro dyes such as phenyl-spirodinaphthopyran, 3-pendyl-spirodinaph I-pyran, 3-methyl-naphtho(6'-methoxyhenzu)spiropyran, 3-proyl-spirodinaphthobilan, rhodamine B-ani Linolactam, Rhodamine (p-nitroanilino)lactam, Rhodamine (0
-lactam dyes such as chloroanilino)lactam, 3-
Dimethylamino-7-medoxyfluorane, 3-diethylamino-6-me1-hexyfluorane, 3-diethylamine-7-me1-xyfluorane, 3-diethylamine-7-chlorofluorane, 3-diethylamino-6-methyl-7 -Rirorofluorane, 3-diethylamino-6
, 7-dimethylfluorane, 3-(N-ethyl-p-toluidino)-7methylfluorane, 3-diethylamino-7-N-acetyl-N-methylaminofluorane, 3-diethylamino-7-N-methylamino Fluorane, 3-
Diethylamino-7-dihendylaminofluorane, 3
-diethylamino-7-N-methyl-N-behenruaminofluorane, 3-diethylamino-7-N-amethyl-N-methylaminofluorane, 3-diethylamino-7-N-diethylaminofluorane, 3-( N-ethyl P-toluidino)-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-p-+.luidino)-
6-Methyl-7-(p-l-luidino)fluoran, 3
-diethylamino-6-methyl-7phenylaminofluorane, 3-dibutylamino-6-methyl-7-phenylaminofluorane, 3-diethylamino-7-(2-
Carbomethoxyphenylamino)fluorane, 3-(N
-cyclohexyl-N-methylamine)-6-methyltwophenylaminofluorane, 3-pyrrolidino6-methyl-7-phenylaminofluorane, 3-piperidino-
6-Methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl 7-xylidinofluorane, 3
-diethylamine/-7=, (o-')lorophenylamino)fluoran, 3-dibutylamino-7, -(0-
chlorophenylamino)fluorane, 3-pyrrolidino-
6-methyl-7-p-butylphenylaminofluorane,
3-(N-methyl-Nn-amyl)amino6-methyl-7-phenylaminofluorane, 3-(N-ethyl-
N-n-amyl)amino-6methyl-7-phenylaminofluorane, 3(N-ethyl-N-isoamyl)amino-6-methyl-7-phenylaminofluorane, :3
-(N-butyl-N-n-hexyl)amino-6-methyl-7-phenylaminofluorane, 3-(,N-ethyl-
N-n-hexyl)amino-6-methyltophenylaminofluorane, 3-(N-ethyl-N-β-ethylhexyl)amino-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-N -te+-rahitrofurfuryl)amino6-methyl-7-phenylaminofluorane, 3-(N-ethyl-N-cyclopentyl)amino6-
Fluoran dyes such as methyl-7-phenylaminofluorane, etc. Of course, the present invention is not limited to these dyes, and it is also possible to use two or more kinds of dyes in combination.

Furthermore, various compounds are known as coloring agents used in combination with the above-mentioned basic dyes, and the following are exemplified.

4-tert-butylphenol, α-naphthol, β
~Naphthol, 4-acetylphenol, 4tert-
Octylphenol, 44'-3θG-funaridenediphenol, 4-phenylphenol, 44'-dihydroxy-diphenylmethane, 4°4'-isopropylidenediphenol, 22bis(4-hydroxyphenyl)-
4-methylpentane, hydroquinone, 4,4'-cyclohexylidene diphenol, 44'-(1,3-
dimethylbutylidene) bisphenol, 4,4'dihydroxydiphenyl sulfide, 4,4'thiobis(6
tert-butyl-3-methylphenol), 4.4'
-dihydroxydiphenylsulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-
4'-methoxydiphenylsulfone, 4-hydroxy-
4'-isopropoxydiphenyl sulfone, 4-hydroxy 3'/I'-1-rimethylene diphenyl sulfone, 4-hydroxy-3', 4'-tetramethylene diphenyl sulfone, 3,4-dihydroxy-4' medyl Diphenyl sulfone, bis(3-allyl 4-hydroxyphenyl) sulfone, 1,3 di(2-(4-hydroxyphenyl)-2-propyl) Hensen, l diF quinone monobenzyl ether, bis(4-hydroxy phenyl)acetic acid butyl ester, 4-hydroxyhenduphenone, 24-dihydroxyhenduphenone, 2,4.4'
Trihydroxybenzuphenone, 2.2',44'-tetrahydroxyhensiphenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, utyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, 4- 5ec-butyl hydroquinobenzoate, methyl 4-hydroxybenzoate, phenyl 4-bitoroxybenzoate, hensyl 4-hydroxybenzoate, 4-hydro-1
Tolyl cybenzoate, 4-hydroquine chlorophenyl benzoate, phenylproyl 4-hydroxybenzoate, 4-
Phenethyl hydroxybenzoate, p-chlorohensyl 4-hydroxybenzoate, p-methoxyhensyl 4-hydroxybenzoate, novolac type phenolic resin, phenolic compounds such as phenol polymers, benzoic acid, p-
tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-sec-butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,
5-dimethyl-4-hydroxobenzoic acid, salicylic acid,
3-isoprobylsalicylic acid, 3tert-butylsalicylic acid, 35-disilicyl-L-butylsalicylic acid, 3
-Hensylsalicylic acid, 3(α-methylhensyl)salicylic acid, 3-chlor■ 5-(α-methylhensyl)salicylic acid, 3phenyl-
5-(α,α-dimethylhensyl)salicylic acid, 3,5
- Aromatic carboxylic acids such as di-α-methylbenzyl salicylic acid, and these phenolic compounds, aromatic carboxylic acids such as di-α-methylbenzyl salicylic acid,
Organic acidic substances such as salts of bonic acid and polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel. Note that, of course, two or more of these coloring agents can be used in combination if necessary.

The usage ratio of the basic dye and coloring agent is selected appropriately depending on the type of dye and coloring agent used, and is not particularly limited, but generally the basic dye is 100% 100 to 700 parts by weight, preferably 150 parts by weight
A loading portion of about ˜400 parts by weight is used.

Preparation of coating liquids containing these generally uses water as a dispersion medium,
It is prepared by dispersing the dye and coloring agent together or separately using a stirring/pulverizing machine such as a ball mill, attritor, or sand mill.

Such coating liquids usually contain other binders such as hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, arahia gum, polyvinylalnylene, styrene/maleic anhydride copolymer salt, and styrene/acrylic acid copolymer salt. Polymer salt, styrene butadiene copolymer emulsion, etc. are 2 to 40% by weight, preferably 5 to 25% by weight of the total solids.
It is expressed in weight%.

Furthermore, various auxiliary agents can be added to the coating liquid.
Examples include dispersants such as dioctyl sulfonylium, sodium dodecylhensensulfonate, lauryl alcohol sulfate/sulfur/lium salts, fatty acid metal salts, other antifoaming agents, fluorescent dyes, and coloring dyes. It will be done.

In addition, to improve the adhesion to the recording head, we also use kaolin, clay, cruzi, carbonic acid, fired resin, etc.
Inorganic pigments such as titanium oxide, diatomaceous earth, particulate anhydrous silica, and activated clay may also be added. Further, a dispersion or emulsion of stearic acid, polyethylene, carnauba wax, paraffin socks, zinc stearate, calcium stearate, ester wax, etc. can be added to prevent sticking from occurring due to contact with a recording device or a recording head.

Further, fatty acid amides such as stearic acid amide, stearic acid methylene bisamide, oleic acid amide, palmitic acid amide, . -methyl-5-tertbutylphenol), L4
Hindered phenols such as -butylidene bis(6-tert-butyl-3-methylphenol), 1.1.3-1~lis(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, p -Hensylbiphenyl, 1,2-bis(phenoxy)ethane, 1,2-bis(4-methylphenoxy)ethane, 1,2-bis(3
-methylphenoxy)ethane, ethers such as 2-naph l-ruhensyl ether, esters such as dihenzyl terephthalate, 1-hydroxy-2naphthoic acid phenyl ester, 2-(2'hydroxy-5'- methylphenyl)henzo] ~ riazole, 2-hydroxy-4-
UV absorbers such as penzyloni-1-cyhenzophenone,
Various known thermofusible substances can also be used as sensitizers.

In the method of the present invention, the method of forming the recording layer is not particularly limited, and can be formed according to conventionally well-known and commonly used techniques. For example, a suitable coating device such as an air knife coater, a fiber coater, a bar coater, a gravure coater, a curtain coater, etc. can be used to apply the coating liquid for the heat-sensitive recording layer onto the base paper.

Furthermore, the amount of coating liquid to be applied is not particularly limited, and is generally 2 to 12 g/I, preferably 3 to 12 g/I in terms of dry weight.
It is adjusted within the range of 10g/rl.

Further, as the support, paper, plastic film, synthetic paper, etc. can be used, but paper is most preferably used in terms of cost, coating suitability, etc.

It is also possible to provide an overcoat layer on the recording layer for the purpose of protecting the recording layer, etc., and it is possible to provide a protective layer on the back side of the base paper or apply adhesive processing, etc. in the field of thermal recording material manufacturing. Various known techniques can be added.

The heat-sensitive recording material of the present invention obtained in this manner has an undercoat layer containing kaolin having a bulk density of 0.35 g/crA or less between the support and the heat-sensitive recording layer, and therefore has a high dynamic recording sensitivity. It is a thermal recording material with excellent printing pixel properties and high whiteness.

(Example) The present invention will be specifically described below with reference to Examples.
Of course, it is not limited to these.

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

Example 1 ■ Preparation of undercoat paint Secondary agglomerated kaolin (bulk density 0.318/cnt, trade name: SAMTON 471, manufactured by HUBER)
100 parts SBR Latinx 10
1 part polyvinyl alcohol 3 parts A paint with a paint concentration of 25% is prepared using the above formulation.

■ Preparation of heat-sensitive coloring layer paint (a) Preparation of liquid A 3 to (N-cyclohexyl-N-methylamine)-6-
Methyl-7-phenylaminofluorane
10 parts 1,2-bis(4-methylphenoxy)ethane
25 parts methyl cellulose 5% water soluble? &20 :'+(+water
30 parts of this composition was ground in a Santo mill until the average particle size was 2.0 μm.

(b) Preparation of Solution B 4.20 parts of 4-dihydroxydiphenyl ether 5% aqueous solution of methylcellulose 50 parts of water
20 parts of this composition was ground in a sand mill until the average particle size was 2.0 μm.

■ Formation of heat-sensitive recording material B: Apply the undercoat paint prepared in step (■) on a base paper of 50 g/n (meter square meter) so that the coating amount is 9.0 g/rtf after drying and dry to form an undercoat layer. Next, on top of the undercoat layer, 85 parts of liquid A and 90 parts of liquid B prepared in ① were added, and silicon oxide pigment (oil absorption ktl 60 m
j2/100 g) 10 parts, 10% oxidized starch aqueous solution 1
A coating liquid for heat-sensitive recording prepared by stirring and mixing 00 parts and 70 parts of water was coated and dried so that the coating amount after drying was 5 g/rl (after drying), and further supercalender treatment was performed to obtain a heat-sensitive recording material. Ta.

Example 2 In the preparation of the undercoat, secondary agglomerated kaolin (bulk density 0.31 g/c, trade name: SITON 471.1) was used.
111 manufactured by BER Co., Ltd.), use secondary agglomerated kaolin (bulk density 0.28 g/c%, trade name: SAmon TON).
581, HIJBEI? Example 1 except that
A thermosensitive recording material was obtained in the same manner as above.

Comparative Example 1 In the preparation of Undercoor I, secondary agglomerated kaolin (
Bulk density 0.31 g/cry, product name: 5A)IT
A thermosensitive recording material was obtained in the same manner as in Example 1, except that calcined kaolin (bulk density 0, 37 g/cJ, Kf product name: Anthylenox, manufactured by Engelhard) was used instead of ON 471, +1t manufactured by IBER. Ta.

Comparative Example 2 In preparing the undercoat, secondary agglomerated kaolin (bulk density 0.3], g/cffl, trade name + 5AI
The same procedure as in Example 1 was carried out except that kaolin (bulk density 1.01 g/cffl, trade name: UW-90, manufactured by Engelhardt) was used instead of ITON 471 and HU I (manufactured by E I1). A thermosensitive recording medium was obtained.

Comparative Example 3 In the preparation of Undercoat I-, secondary agglomerated kaolin (
Bulk density 0.31 g/cJ, product name: SAMTON
471, instead of H [manufactured by IBER], calcium carbonate (high density 1.18 g/ca, product name: Soft) ~
N1500. A heat-sensitive recording material was obtained in the same manner as in Example 1, except that a heat-sensitive recording material (manufactured by Bihoku Kakogyo Co., Ltd.) was used.

Comparative Example 4 In the preparation of an undercoat, secondary agglomerated carline (bulk density 0.31 g/cnt, trade name: SAMTON)
411.11 II B IE It was manufactured in the same manner as in Example 1 except that silicon oxide (bulk density 0.11 g/cJ, trade name: Fine Seal CMF, manufactured by Tokuyama Soda) was used. Obtained a record.

The six types of heat-sensitive recording materials obtained as described above were printed using an ultra-high-speed thermal printer (UP-103, manufactured by Sony Corporation) at a head voltage of 15.5 V and a pulse duration of 4 ms and 8 ms, and the image density was determined. , dot reproduction rate, and whiteness were evaluated as follows, and the results are shown in Table 1.

[Image density]

The recorded density was measured with a Maches densitometer (using an RD-1croR type amber filter).

[Dot recall rate]

Dot reproduction rate was used to evaluate the reproducibility of printed pixels.

The ratio of the area of the printed dot to the area of one dot of the thermal head was evaluated.

0186% or more ○ Near 6-85% △: 70-75% ×: 69% or less [Whiteness] The whiteness of the thermosensitive recording material was measured using a Hunter whiteness meter.

Table 1 (Effects) As is clear from the results in Table 1, the thermal recording material of the present invention had high dynamic recording sensitivity (and was a thermal recording material with excellent printing pixel properties and high whiteness). .

Claims (1)

[Claims] A heat-sensitive recording material formed by sequentially laminating an undercoat layer and a heat-sensitive recording layer on a support, characterized in that the undercoat layer contains kaolin having a bulk density of 0.35 g/cm^2 or less as a pigment. A thermosensitive recording material.