JPH02141278A - Thermal recording material - Google Patents

Abstract

PURPOSE:To enhance sensitivity by constituting the base paper used as a support of base paper respectively having specific air permeability and a specific sizing degree. CONSTITUTION:In a thermal recording material wherein a thermal color forming layer containing an electron donating leuco dye and an electron acceptive compound is formed on a support, as the base paper for the support, base paper having a sizing degree wherein air permeability is 20sec or less by an Oken-type air permeability meter and Cobb water absorption due to JIS P-8140 is 10 - 20g/m<2> is used. As the electron donating leuco dye and electron acceptive compound contained in the thermal color forming layer formed on the support, usual ones can be used. By this method, the thermal recording material having high sensitivity can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a heat-sensitive recording material, and more particularly to an i-thermal recording material with good thermal responsiveness.

[Prior Art] Thermosensitive recording paper is popular because it can produce colored images by simply heating it, and the recording device can be made relatively simple and compact, so it is widely used as a variety of information recording paper. It is used for.

Particularly in recent years, improvements have been made in the equipment of thermal facsimile machines and thermal printers that use such thermal recording bodies, and high-speed recording, which was difficult in the past, has become possible.

As the speed of such equipment and hardware increases, the thermal recording paper used is also required to have improved recording sensitivity, and many proposals have been made in this regard.

For example, with the aim of improving sensitivity by increasing the smoothness of the surface of thermal recording paper and improving its adhesion with the thermal head, Bekk smoothness can be increased to 200% by calendering such as super calender, machine calender, or cross calender.
~1000 seconds (Special Publication No. 52-20142)
, or the surface roughness Ra should be 1.2 μ or less and the gloss level should be 25% or less (Japanese Patent Application Laid-Open No. 55-156086).
No. 2) has been proposed.

However, depending on this method, even if the smoothness is improved by calendering, the voids in the undercoat layer or the base paper are reduced, and as a result, a sufficient sensitivity improvement effect cannot be expected.

JP-A No. 56-867921 proposes to improve the smoothness by applying a super calender after applying the undercoat layer, but since supercalendering also damages the heat insulation properties of the undercoat layer, the result is that the smoothness is not sufficiently improved. Sensitivity improvement effect cannot be expected.

On the other hand, in order to increase the voids in the layer below the heat-sensitive layer, the heat in the heat-sensitive layer is prevented from escaping due to the insulating properties of air.
An intermediate layer is provided between the heat-sensitive layer and the base paper, and hollow fine particles are contained in the intermediate layer (JP-A-59-5093, JP-A-60-248390, JP-A-62-176877).
No. 2) has been proposed.

However, the intermediate layer only accounts for 10% or less of the total thickness of the thermal recording paper, and even if a large amount of air is included in the intermediate layer to improve heat insulation, the insulation effect cannot be said to be sufficient.

In addition, the thermal conductivity of the support was set to 0.04 Kcal/mh°C (2
There are proposals to lower the temperature below 0°C, but
(No. 92) The sensitivity of the transparent thermosensitive recording paper cannot be sufficiently improved by simply increasing the heat insulation properties of the support.

[Problems to be Solved by the Invention] An object of the present invention is to improve the drawbacks of the prior art and provide a heat-sensitive recording material that exhibits high sensitivity.

[Means/effects for solving the problems] The present invention provides a heat-sensitive recording material in which a heat-sensitive coloring layer containing an electron-donating colorless dye and an electron-accepting compound is formed on a support, which can be used as a base paper for the support. , its air permeability is 20 seconds or less using an Oken air permeability meter, and JIS P-81.
The paper is characterized in that it uses a base paper having a size of 10 to 20 g/m 2 in terms of water absorption according to the standard.

In heat-sensitive recording materials, the support on which a heat-sensitive coloring layer containing an electron-donating colorless dye and an electron-accepting compound is formed may be base paper alone or a base paper with an intermediate layer formed thereon. There is. That is, a typical thermosensitive recording paper has a two-layer structure of a heat-sensitive recording layer and a base paper, or a three-layer structure of a heat-sensitive recording layer, an intermediate layer, and a base paper. In either case, the thickness of the base paper accounts for more than 80% of the total thickness of the thermal recording paper, and improving the heat insulation properties of the base paper is important for increasing the sensitivity of the thermal recording material. have an influence.

The present invention focused on the heat insulation properties of the base paper in this heat-sensitive recording material, and discovered that the high heat insulation properties are closely related to the air content, and the present invention was completed. That is, the thermal conductivity of air is one to two orders of magnitude lower than that of the fibers, resins, pigments, etc. that make up the base paper.

For this reason, as a result of research on the presence of air in base paper, it was found that when the air permeability of base paper is set to 20 seconds or less using an Oken air permeability meter, the heat insulating properties of base paper are significant. It has been found that the sensitivity of thermal recording paper is preferably high by using this method.

The value measured by the air permeability needle indicates the degree to which air passes under a certain pressure difference.If there is a lot of air in the base paper, air will easily pass through the base paper, and the air permeability Set the needle reading to a low value. For this reason, the Ohken type air permeability meter
It is believed that when a base paper with a heat resistance of 0 seconds or less is used as a support for a heat-sensitive recording material, a heat-sensitive recording material with high sensitivity can be obtained. When the measured value of the Oken air permeability meter exceeds 20 seconds, the sensitivity decreases significantly.

As explained above, such base paper that lasts for 20 seconds or less with an Oken air permeability meter contains a large amount of voids, so when coating a heat-sensitive coloring layer or intermediate layer on its surface, it is difficult to The coating liquid tends to fill the voids in the base paper. Therefore, in order to avoid this tendency, the water absorption of the base paper must be 20 g/II2 or less. However, if it is less than 10 fI/Rin2, the wettability of the coating liquid to the paper support will deteriorate, and if high-speed coating is performed, small uncoated areas will occur in some parts, which is not preferable. There must be.

As the colorless or light-colored electron-donating dye and electron-accepting compound contained in the heat-sensitive coloring layer formed on the support, commonly used ones can be used.

For example, representative examples of the former include the following color-forming lactone compounds.

Crystal violet lactone 3-(N-ethyl-N-isopentylamino)6-methyl-7-anilinofluorane.

3-diethylamino-6-methyl-7-anilinofluorane.

3-diethylamino-6-methyl-7-(o,p-dimethylanilino)fluoran.

3-(N-ethyl-p-)luidino)-6-methyl-7
-Anilinofluorane.

3-pyrrolidino-6-methyl-7-anilinofluorane.

3-dibutylamino-6-methyl-7-anilinofluorane.

3-(N-cyclohexine-N-methylamino)-6-
Methyl-7-anilinofluorane.

3-diethylamino-7-(0-chloroanilino)fluoran.

3-diethylamino-7-(m-1-lifluoromethylanilino)fluoran.

3-diethylamino-6-methyl-7-chlorofluorane.

3-diethylamino-6-methylfluorane.

The coloring agent made of 3-cyclohexylamino-6-chlorofluoranphenol or an organic acid may be the same (conventionally known ones), and the following are examples thereof.

Bisphenol A.

Benzyl P-droxybenzoate.

n-Butyl di(4-hydroxyphenyl)acetate.

Bisphenol S.

4-Hydroxy, 4°-isopropyloxydiphenyl sulfone.

1.1-di(4-hydroxyphenyl)cyclohexane.

1,7-Di(hydroxyphenylthio)-3,5=dioxahebutane As the so-called sensitizer, six thermofusible organic compounds with a melting point of 50-150°C are used. The following are typical examples.

p-Droxynaphthoic acid phenyl ester.

p-benzylbiphenyl.

Benzyl naphthyl ether.

Dibenzyl terephthalate.

Benzyl p-benzyloxybenzoate Diphenyl carbonate.

The organic or inorganic pigment used in the ditolyl carbonate coloring layer is not limited by oil absorption or the like, and includes, for example, calcium carbonate.

Silica, zinc oxide, l! ! In addition to inorganic fine powders such as titanium chloride aluminum oxide, zinc hydroxide, barium FA acid, clay, talc, and surface-treated calcium carbonate and silica, urea-formalin resin 1 styrene/methacrylic acid copolymer, polystyrene resin, etc. Organic fine powder etc. are used.

The heat-sensitive coloring layer may contain additional waxes as required. They may be known waxes such as paraffinamide waxes, bisimide waxes, and metal salts of higher fatty acids.

Adhesives include polyvinyl alcohol of various molecular weights, starch and its derivatives, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide, and acrylic acid ester copolymer. Coalescence, acrylamide/acrylic ester/methacrylic acid terpolymer, styrene/
Maleic anhydride copolymer alkali salt, polyacrylamide.

In addition to water-soluble polymers such as sodium alginate, gelatin, and casein, polyvinyl acetate, polyurethane, styrene/butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride/vinyl acetate copolymer, polybutyl methacrylate, Latexes such as ethylene/vinyl acetate copolymer, styrene/butathene/'acrylic copolymer, etc. can be used.

An intermediate layer can be provided on the base paper if necessary, and in this case as well, the effect of increasing the severity can be observed.

The intermediate layer can usually contain a resin and/or a pigment (organic/inorganic), and the resin may be a known water-soluble polymer substance, aqueous emulsion, etc., and can be used, for example, in the heat-sensitive coloring layer of the present invention. Adhesives that can be used can be selected from those listed above.

As the pigment, known organic and inorganic pigments can be used alone or in a mixture of two or more, and specifically, among the pigments exemplified as pigments that can be used in the heat-sensitive coloring layer of the present invention, You can choose and use it.

There is no particular restriction on the amount of adhesive used, but it is preferable to use a small amount within a range that does not impede the oil absorption of the intermediate layer and as long as it satisfies the adhesive strength. It is preferable to use it in a range of 30% by weight.

[Example] Next, the present invention will be explained using a specific example.

In addition, unless otherwise specified, parts and percentages in steel indicate parts by weight or percentages by weight, respectively.

Examples 1-3. Comparative Example 1.2 Using the pulp and sizing agent shown in Table 1, a base paper having the air permeability and water absorption shown in Table 1 was obtained. All papers were made using a Fourdrinier paper machine with a basis weight of 40 and Og/2.

For each of the surfaces of the obtained base paper, an intermediate layer having the composition shown below was coated on the negative part, and a heat-sensitive coloring layer was directly coated on the other parts to obtain a heat-sensitive recording paper.

These thermal recording papers were subjected to a thermal recording process and the recording densities were measured, and the results are shown in Table 2. As is clear from Table 2, the coating method and method for measuring heat-sensitive recording density are as shown below.0 Heat-sensitive recording material using base paper having air permeability and sizing within the range of the present invention as a support. The sensitivity of
It is clear from the same table that the air permeability and size are clearly higher than when using base paper with air permeability and size outside this range.

Table 1 Preparation method for intermediate layer coating liquid 100 parts water 50 parts talc (MPIO-52, manufactured by Pfizer MSP) 50 parts heavy calcium carbonate (NS23)
After dispersing 10 parts of 101 polyvinyl alcohol aqueous solution (Nippon Gosei GLO5) by a homogenizer for 5 minutes, 50 parts of 10% polyvinyl alcohol (Nippon Gosei GH17) was mixed to prepare an intermediate layer coating solution. .

How to apply the intermediate layer coating liquid: 7 g/m solids on one side of the base paper using an air knife coater.
' and dried in a hot air dryer at 80°C.

Preparation method of heat-sensitive recording layer coating liquid Dispersion liquid A 3-(N-isopentytoethylamihar 6-methito7
- 20 parts 7 = linoalurothene polyvinyl alcohol 10 parts water 70 parts This composition was ground with a sand grinder to an average particle size/μ ring.

Dispersion B ρ-human a%'i besidyl benzoate 20
Part polyvinyl alcohol
10 parts water
70 parts of this composition was ground in a sand grinder to an average particle size/μ steel.

75 parts of liquid A, 125 parts of liquid B, 30 parts of calcium carbonate, 1
A coating liquid was prepared by mixing and stirring 200 parts of 0% polyvinyl alcohol, 17 parts of a 30% paraffin dispersion, and 17 parts of a 30% zinc stearate dispersion.

Coating method for heat-sensitive recording layer coating solution: Coat with an air knife onto base paper or a support provided with an intermediate layer at a coating weight of 5 g/m2 on one side, dry in a hot air dryer at 60°C, and apply a machine calender. Ta.

Method for measuring heat-sensitive recording density Measurement was carried out using an actual heat-sensitive facsimile machine modified for testing purposes.

1 line recording time 10m5/line, scanning line density 8x8
The pulse was modulated under the conditions of dot/■, the applied energy per dot was adjusted to 0.44 mJ, and 64 lines were printed.

The color density at that time was measured using a Macbeth densitometer RD-514, and was taken as a value representative of recording sensitivity.

Table 2 [Effects of the Invention] According to the present invention, a heat-sensitive recording material with high sensitivity could be provided.

Claims (1)

[Claims] 1. In a heat-sensitive recording material in which a heat-sensitive coloring layer containing an electron-donating colorless dye and an electron-accepting compound is formed on a support, the base paper used for the support has an air permeability of Oken style air permeability. 20 seconds or less on a meter, and its size is JISP-
A heat-sensitive recording material characterized in that it is a base paper having a cup water absorption of 10 to 20 g/m^2 according to 8140.