JPH09300818A - Thermal recording body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve water resistance and prevent a problem such as blocking from occurring when used outdoors on a rainy day, by using two kinds of inorganic pigments each having a different average grain size at a specified weight compounding ratio when a protective layer is provided on a thermal coloring layer formed on a supporting body. SOLUTION: In a thermal recording body made by providing a thermal recording layer on a supporting body and providing a protective layer thereon, as pigments used for the protective later, an inorganic pigment whose average grain size is 1 to 3μm and one whose grain size is 4 to 20μm are used jointly. On such occasion, the compounding amount of a total inorganic pigment can be 5 to 45% and the weight compounding ratio of an inorganic pigment whose average grain size is 1 to 3μm and that whose average grain size is 4 to 20μm should be 90/10 to 10/90, preferably 80/20 to 30/70. If necessary, an intermediate layer whose main components are a pigment and a binder or a back layer such as a curl-adjusting or antistatic layer is provided between the supporting body and the thermal coloring 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 material capable of recording an image by a heat-sensitive recording method, and more particularly to improvement of blocking property and dot reproducibility of a protective layer provided on a heat-sensitive recording layer.

[0002]

2. Description of the Related Art Generally, a thermosensitive recording material has a thermosensitive coloring layer formed on a support, and the thermosensitive coloring layer is heated by a thermal head, a heating pen, a laser beam or the like to form a thermosensitive coloring layer in the thermosensitive coloring layer. A color forming agent is reacted instantaneously to form a recorded image. For example, Japanese Patent Publication No. 43-4160 and Japanese Examined Patent Publication No. 4160.
It has been widely known from the past, for example, in Japanese Patent Laid-Open No. 5-14039.

These thermosensitive recording media have the advantages that a recorded image can be formed with a relatively simple device, maintenance is easy, and noise during recording is small. It is applied in a wide range of fields such as recorders, facsimiles, terminal printers such as computers, POS printers, automatic ticket vending machines, and bar code label printers.

Particularly in recent years, the use of the thermal recording material has been expanded to various kinds of tickets, receipts, ATMs of banks, meter reading of gas and electricity, and so on. Then, strict characteristics that have not been a problem are beginning to be required.

That is, the characteristics required for a thermal recording material are, of course, resistance to fading of recorded images and background fogging due to weather resistance, chemical resistance, etc., as well as gas and electric meter reading. In some applications, it may be used outdoors and in the rain, and resistance to water is also required.

On the other hand, conventional heat-sensitive recording materials include plasticizers such as phthalic acid diesters typified by phthalic acid dibutyl ester contained in a vinyl chloride case, aliphatic dibasic acid esters, phosphoric acid triesters, salad oil, hand cream, etc. There is a defect that the recorded image is discolored or the background part is colored by contact with the above-mentioned oils and fats or organic solvents such as ethyl alcohol and toluene.

In order to overcome such drawbacks, a protective layer has been conventionally provided on the heat-sensitive color developing layer, and the component constituting this protective layer is highly soluble in water such as polyvinyl alcohol and starch. Molecules are used as the main component.

For this reason, when a thermal recording medium having a protective layer is used outdoors even in rainy weather, if the thermal recording mediums after recording come into contact with each other immediately after getting wet with water, the thermal recording surface and its back surface or thermal recording surface are Adhere to each other, and in the worst case, the heat-sensitive recording paper peels from the paper layer, which causes a problem that the recorded information cannot be read, or water drops fall on the side of the winding before recording and the heat-sensitive surface and its Since the back surface is adhered with water drops, blocking occurs, resulting in a problem such as a defective feeding of the recording paper.

In order to solve this, as a method of imparting water resistance to the protective layer of the thermosensitive recording medium, a crosslinking agent which reacts with such a water-soluble polymer is used in combination. However, in the formation of the protective layer, it is not possible to impart heat energy that causes a sufficient crosslinking reaction, and if a highly reactive crosslinking agent is used, a crosslinking reaction will occur in the coating liquid and the coating liquid There is a problem that the viscosity is remarkably increased and coating cannot be performed.

In order to solve such a problem, it has been proposed to introduce a functional group which enhances reactivity into a water-soluble polymer. For example, JP-A-56-126193, JP-A-59-106995, and JP-A-59-1698.
No. 85, JP-A No. 62-264990 and the like have been proposed, but the characteristics that sufficiently satisfy the blocking characteristics have not been obtained.

On the other hand, Japanese Patent Application Laid-Open No. 2-175281 proposes a protective layer composed of at least one kind of silica and / or calcium carbonate having an average particle diameter of 0.1 μm and a water-soluble binder. By using these inorganic pigments having an average particle diameter of 0.1 μm or less, the reproducibility and sensitivity of dots can be improved by increasing the adhesiveness of the thermal head, but this proposal cannot satisfy the blocking characteristics. .

Further, in JP-A-1-255588, an average particle diameter is 4 to 20 μm and an oil absorption amount is 80 to 400 ml / 10.
A protective layer containing 0 g of a pigment has been proposed. By using pigments having these average particle diameters, it is possible to obtain a thermal recording material having a low surface gloss and further improved writability. Satisfaction has not been obtained in terms of sensitivity.

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermosensitive recording medium having excellent water resistance which does not cause problems such as blocking even when used outdoors in the rain, and has good dot reproducibility. To do.

[0014]

Means for Solving the Problems As a result of earnest studies by the present inventors, in a heat-sensitive recording material comprising a support, a heat-sensitive recording layer provided thereon, and a protective layer provided thereon, the heat-sensitive recording layer was used as the protective layer. It has been found that good blocking characteristics can be obtained by using as the pigment to be used an inorganic pigment having an average particle size of 1 to 3 μm and an average particle size of 4 to 20 μm and different in average particle size.

Regarding the measurement of the average particle size of the inorganic pigment used here, a 5% suspension of the pigment was prepared by T.K. K. 300 using Homomixer TYPE M
The mixture was dispersed at 0 rpm for 5 minutes, and then the median diameter obtained by setting the refractive index of the pigment was used by using a laser diffraction / scattering particle size analyzer LA-910 manufactured by Horiba Ltd.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION As an inorganic pigment having an average particle size of 1 to 3 μm used in the present invention, Mizukasil P-527 is used.
(Average particle diameter 2.5 μm: Mizusawa Chemical Industry Co., Ltd.), Mizukasil P-604 (average particle diameter 2.0 μm: Mizusawa Chemical Industry Co., Ltd.), Softon # 3200 (average particle diameter 2.4 μm: Shiraishi Industry Co., Ltd.) and the like are used. To be

On the other hand, as an inorganic pigment having an average particle size of 4 to 20 μm, Syloid ED-2 (average particle size 5.0 μm:
GRACE), Softon # 1200 (average particle size 4.
3 μm: Shiraishi Kogyo), Softon # 1000 (average particle size 5.9 μm: Shiraishi Kogyo), Callite SA (average particle size 5.2 μm: Shiraishi Kogyo), Callite KT (average particle size 5.8 μm: Shiroishi Kogyo) Made), Sipernat2
2S (average particle size 12.1 μm: made by Degussa Japan)
Are used.

It is sufficient that the total amount of the inorganic pigments used in the protective layer is 5 to 45% by weight, and the inorganic pigments used in the present invention have an average particle diameter of 1 to 3 μm.
The inorganic pigment and the inorganic pigment having an average particle diameter of 4 to 20 μm can be used in a weight mixing ratio of 90/10 to 10/90, but preferably 80/20 to 30/70.
Good range.

When an inorganic pigment having an average particle diameter of 1 to 3 μm is used alone, the reproducibility of dots of the heat-sensitive recording material obtained is good, but the blocking property is remarkably poor. On the other hand, when an inorganic pigment having an average particle diameter of 4 to 20 μm is used alone, the smoothness of the heat-sensitive surface is lowered and the blocking property is good, but the dot reproducibility and the sensitivity are lowered.

As the water-soluble binder used in the present invention, polyvinyl alcohol, modified polyvinyl alcohol, starch and the like are used. In addition to epichlorohydrin and glyoxal, as a cross-linking agent used for the protective layer, chromium alum, N-methylurea, active vinyl compound,
Polyvalent carboxylic acids, diisocyanate metal complexing agents, melamine-formaldehyde resins, polyamide-epichlorohydrin resins and the like can also be used. The addition amount is preferably 5 to 30 parts by weight with respect to 100 parts by weight of the water-soluble binder.

Further, in the protective layer, various additives usually used in heat-sensitive recording materials, for example, dispersants such as sodium polyacrylate, surfactants such as sodium dioctylsulfosuccinate, antifoaming agents such as fatty acid monoglycenide, fluorescent Dyes, color pigments, waxes such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, steric acid amide, and castor wax can also be added.

The support used in the present invention is not particularly limited and includes, for example, high-quality paper, recycled paper, glossy paper, oil resistant paper, coated paper, art paper, cast coated paper, lightly coated paper, resin laminated paper, Polyolefin synthetic paper, synthetic resin film and the like can be used as appropriate.

If necessary, an intermediate layer containing a pigment and a binder as a main component may be provided between the support and the thermosensitive coloring layer, and a back layer for curl adjustment and antistatic treatment may be provided.

The color-forming component of the thermosensitive color-forming layer on the support may be any one as long as it can form a recorded image by heating, for example, an electron-accepting substance typified by leuco dyes and phenolic substances. It is possible to use those by the reaction with, the reaction between the imino compound and the isocyanate compound, the reaction between the long-chain fatty acid iron salt and the polyhydric phenol, and the like. Specific examples of these combinations are described in, for example, JP-A-54-118845.

[0025] Although the coating amount of the protective layer is 0.5 to 8 g / m ^2, to secure the barrier properties of the protective layer, in order to increase the sensitivity of the thermal recording body, and 2 to 4 g / m ² Is preferred. The coating amount of the thermosensitive color developing layer is ^{2 to} 10 g / m ² , preferably 3 to 6 g / m ² . As a coating method, a known coating apparatus such as various bar coaters, roll coaters, blade coaters and air knife coaters can be used.

Blocking Test Method The obtained heat-sensitive recording material was cured at 40 ° C. and 15% for 24 hours, and then printed with a Canon Handy Terminal Printer HT950 for testing. After recording, drop one water drop on the recording surface of the thermosensitive recording medium, fold it in half so that the recording surface is on the inside, and put 1 drop on the recording material.
A load of 00g / cm ² is applied, and 24 at 20 ° C and 65% RH.
After leaving for a period of time, the recording surface was peeled off and blocking was evaluated.

Evaluation criteria. ◯: No blocking Δ: No blocking but peeling noise X: Blocking occurred and part of the recording layer was broken, making it difficult to read the recording XX: Large blocking, peeling from the paper layer

Dot Reproducibility Test Method Canon Handy Terminal Printer HT-950
The dot reproducibility was evaluated by recording the test pattern obtained by selecting the high speed mode as the print mode using.

Evaluation criteria. ○: Good printing quality △: Slightly inferior printing quality ×: Inferior printing quality

[0030]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

Example 1 Preparation of heat-sensitive coating liquid Liquid A: 3-dibutylamino-6-methyl-7-anilinofluorane 10 parts by weight Polyvinyl alcohol: 12% aqueous solution 26.7 parts by weight Polystyrene ammonium acrylate: 20 % Aqueous solution 1.6 parts by weight water 21.3 parts by weight solution B: 4-hydroxy-4′-isopropoxydiphenyl sulfone 30 parts by weight di (p-methylbenzyl) oxalate 30 parts by weight polyvinyl alcohol: 12% aqueous solution 60 Parts by weight Polystyrene ammonium acrylate: 20% aqueous solution 3.6 parts by weight Water 78 parts by weight

For the liquid A, the average particle diameter (which is the median diameter determined by a laser diffraction / scattering particle size analyzer [LA-910] manufactured by Horiba, Ltd., the same applies hereinafter) with a sand grinder is 0.5 μm or less. The liquid B was dispersed until the average particle size became 0.8 μm.

Solution A prepared above: 59.6 parts by weight, B
Liquid: 201.6 parts by weight and 83.3 parts by weight of 12% polyvinyl alcohol and 21.3 parts by weight of water were mixed and stirred to prepare a heat-sensitive coating liquid.

The obtained heat-sensitive coating liquid was applied to a high-quality paper of 50 g / m ² by weight with a test bar coater so that the coating amount after air-drying would be 5 g / m ² , dried and coated to form a heat-sensitive recording layer. Formed.

Formation of Protective Layer T was added as a water-soluble binder on the obtained thermosensitive recording layer.
-215 (acetyl-modified PVA: manufactured by Nippon Synthetic Chemical Industry) 12
% Aqueous solution 500 parts by weight, as an inorganic pigment having an average particle size of 1 to 3 μm, 16 parts by weight of silica (Mizukasil P-527: manufactured by Mizusawa Chemical Industry Co., Ltd.) and an inorganic pigment having an average particle size of 4 to 20 μm (Cyroid ED-2: GRACE) 4 parts,
30% zinc stearate dispersion (Hydrin D-52
(3: Chukyo Yushi Co., Ltd.) 33.3 parts by weight, epichlorohydrin aqueous solution WS-570: Japan PMC) 72 parts by weight and 346.7 parts by weight of water were mixed and stirred to form 3 parts of the protective layer coating solution.
A protective layer was formed by coating and drying with a test bar coater so as to obtain g / m ² .

Thereafter, a gross calendering treatment was carried out so that the Oken type Beck's smoothness described in "Types of Paper Pulp and Its Testing Method" edited by Japan Pulp and Paper Institute is about 500 seconds to obtain a thermal recording material. Obtained.

Example 2 In the same manner as in Example 1 except that 10 parts by weight of Mizukacil P-527 and 10 parts by weight of Syloid ED-2 were used, under the gross calender conditions of Example 1. Gloss treatment was performed to obtain a heat sensitive recording material.

Example 3 In Example 1, 4 parts by weight of Mizukacil P-527,
A thermosensitive recording medium was obtained by performing gloss treatment under the gloss calender conditions in Example 1 in the same manner as in Example 1 except that 16 parts by weight of Syloid ED-2 was used.

Example 4 The gloss of Example 1 was the same as in Example 1 except that (Softon # 1200: Shiraishi Kogyo) was used as the inorganic pigment having an average particle size of 4 to 20 μm. Gloss treatment was performed under calendering conditions to obtain a thermosensitive recording medium.

Example 5 The gloss of Example 1 was the same as in Example 1 except that (Softon # 1000: Shiraishi Kogyo) was used as the inorganic pigment having an average particle size of 4 to 20 μm. Gloss treatment was performed under calendering conditions to obtain a thermosensitive recording medium.

Comparative Example 1 The same procedure as in Example 1 was carried out except that 20 parts by weight of Mizukacil P-527 was used and no Syloid ED-2 was used, and the gloss calendering conditions in Example 1 were used. Processing was performed to obtain a heat sensitive recording material.

Comparative Example 2 In the same manner as in Example 1 except that 20 parts by weight of Syloid ED-2 was used and Mizukasil P-527 was not used, the gloss calender conditions in Example 1 were used. Processing was performed to obtain a heat sensitive recording material.

Comparative Example 3 The gloss calender in Example 1 was used in the same manner as in Example 1 except that the average particle size of the siloid ED-2 treated in Example 2 was adjusted to 2 μm with a paint conditioner. Gloss treatment was performed under the conditions to obtain a thermosensitive recording medium.

Comparative Example 4 Gloss treatment was carried out under the gross calender conditions of Example 1 as in Example 1 except that 20 parts by weight of Softon # 1200 was used and Mizukasil P-527 was not used. Then, a thermosensitive recording medium was obtained.

[0045]

[Table 1]

[0046]

As is clear from Table 1, the thermosensitive recording medium of the present invention is an excellent thermosensitive recording medium which satisfies dot reproducibility and is less likely to cause water wetting blocking.

Claims (1)

[Claims] 1. A thermosensitive recording medium comprising a support, a thermosensitive color forming layer formed on the support, and a protective layer formed on the thermosensitive color forming layer. An average particle of an inorganic pigment used in the protective layer. The diameter is 1 to 3 μm, and the average particle diameter is 4 to 20 μm.
2. A heat-sensitive recording material, characterized in that the two pigments are used in a weight mixing ratio of 10/90 to 90/10.