JPH09263047A - Thermosensitive recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermosensitive recording medium with high water resisting property which is free from a blocking phenomenon, if used outdoors in the rain by using starch with a specific value of average molecular weight or its derivative and further, a curing agent in a protecting layer, in a recording medium consisting of a support formed sequentially of a thermosensitive coloring layer and the protecting layer. SOLUTION: When using a thermosensitive recording medium with a protecting layer outdoors in the rain, a problem arises in which a thermosensitive recording face adheres to its rear face or the thermosensitive recording faces adhere to each other, if the thermosensitive recording media after recording come into contact with each other immediately after they are moistened with water. Therefore, in order to give water resisting property to the protecting layer of the thermosensitive medium, starch with an average molecular weight of at least, 50,000 or its derivative is used in the protecting layer. In addition, a curing agent is added as a constituent and thus the protecting layer is formed. The blending amount of this curing agent is set to a range of at least, 5-30 pts.wt. preferably 10-15 pts.wt based on 100 pts.wt. of the starch and/or its derivative. In addition, the curing agent is preferably epichlorhydrin.

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 improving the blocking property of a protective layer provided on the 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 by heating the thermosensitive coloring layer with a thermal head, a heating pen, a laser beam, etc., a color is developed in the thermosensitive coloring layer. The agent reacts instantly to form a recorded image. For example, Japanese Patent Publication No. 43-4160 and Japanese Examined Patent Publication No.
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 drawback that the recorded image is discolored or the background part is colored by contact with the oils and fats, or the organic solvent such as ethyl alcohol and toluene. In order to overcome such drawbacks, it has been conventionally performed to provide a protective layer on the thermosensitive coloring layer, and as a component constituting this protective layer, a water-soluble polymer such as polyvinyl alcohol or starch is used. Used as the main component.

For this reason, when the 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 being wet with water, the thermal recording surface and its back surface or the 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 for 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 the 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, etc. have been proposed, but the blocking properties are insufficient even if these modified polyvinyls are used. Further, the use of a protective layer of cationic starch is disclosed in JP-A-61-102287, but even if the cationic starch (Aminofax 15) used in the examples is used, the blocking property is not good.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat-sensitive recording material having excellent water resistance which does not cause problems such as blocking even when used outdoors in the rain.

[0011]

Means for Solving the Problems As a result of intensive studies by the present inventors, in a heat-sensitive recording material in which a heat-sensitive recording layer is provided on a support and a protective layer is further provided thereon, the protective layer has an average value. By using starch and / or starch derivatives having a molecular weight of 50,000 or more and further using a curing agent, the crosslinking effect can be enhanced, and the addition of a curing agent further increases the film-forming property than when not in use and improves the barrier property. It has been found that a particularly excellent water resistant protective layer can be obtained.

When the molecular weight of starch is 50,000 or less, the barrier property required for the overcoat layer is remarkably inferior, the blocking property, and the increase of the residue adhered to the thermal head by the running test are observed. Further, the crosslinking reaction by the crosslinking agent also takes a long time, which is a drawback in production.

The average molecular weight of starch can be measured by calculating the molecular weight distribution by a liquid chromatographic method and then using the result of the molecular weight distribution. For details, for example DSJACKSON, Cer
eal Chem. 65 (6), p.493-496,1988, JAU-YI CHUANG, Jo
f Applied Polymer Science. 34, p. 1739-1748, 1987, M.
See Papantonakis, Tappi. 63 (5), p.65-69, 1980.

The present invention provides 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, wherein the protective layer has an average molecular weight of 50,000 or more. Is a starch and / or its derivative, and a curing agent is further used.

Further, the present invention provides 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, wherein the protective layer has an average molecular weight of 5 It is a heat-sensitive recording material characterized by using more than 10,000 starches and / or derivatives thereof and further using epichlorohydrin as a curing agent.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The starch and its derivatives used in the present invention have a molecular weight of 50,000 or more, for example, Oji Ace A (oxidized starch) manufactured by Oji Corn Starch, MS # 3800 manufactured by Nippon Food Processing Co. (Oxidized starch), manufactured by Oji Corn Starch: Ace P120 (phosphate esterified starch), Ace P130 (phosphate esterified starch), Ace P240 (phosphate esterified starch), OSA1250 (acetylated starch), HES4 (hydroxylated starch). Etc. are selected.

Further, by adding a crosslinking agent to the protective layer, the crosslinking rate can be improved and the film-forming property of the protective layer can be promoted. In particular, when epichlorohydrin is used together as a cross-linking agent, the effect is particularly likely to be exhibited.

The blending amount of the starch used in the protective layer and the curing agent used in the derivative thereof is 5 parts by weight or more with respect to 100 parts by weight of starch and the derivative thereof.
In the range of 0 parts by weight or less, preferably 10 parts by weight to 15 parts by weight
Parts by weight are used.

Further, the protective layer has improved runnability and writability,
Inorganic or organic pigments may be added for the purpose of imparting imprintability, and the pigment used may be kieselguhr,
Inorganic pigments such as talc, kaolin, calcined kaolin, calcium carbonate, aluminum hydroxide, magnesium carbonate, titanium oxide, zinc oxide and amorphous silica, and organic pigments represented by urea resins are used. In this case, it is sufficient that the pigment is contained in an amount of 5 to 45% by weight based on the total solid content of the protective layer.

As the cross-linking agent used in the protective layer in the present invention, in addition to epichlorohydrin and glyoxal, chromium alum, N-methylurea, active vinyl compound, polyvalent carboxylic acid, diisocyanate metal complexing agent, melamine-
Formaldehyde resin, polyamide-epichlorohydrin resin and the like can also be used. The addition amount is preferably 5 to 30 parts by weight based on 100 parts by weight of starch and / or its derivative.

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.

The coating amount of the protective layer is 0.5 to 8 g / m ² , preferably 1 to 4 g / m ² , and the coating amount of the thermosensitive coloring layer is 2-1.
0 g / m ^2, preferably from 3 to 6 g / m ^2.

Blocking Test Method The obtained heat-sensitive recording material was cured for 24 hours in an environment of 40 ° C. and 15%, and then printed with a Canon Handy Terminal Printer HT9000 for testing. After recording, hang one drop of water on the recording surface of the thermosensitive recording medium, fold it in half so that the recording surface is on the inside, and apply a load of 100 g / cm ² onto the recording medium on which the water droplet has been dropped, at 20 ° C 65% RH. It was allowed to stand for 24 hours underneath, after which the recording surface was peeled off and blocking was evaluated. The evaluation criteria are as follows. ◯: 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

[0027]

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 Ammonium polystyrene 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 Part by weight Polystyrene ammonium acrylate: 20% aqueous solution 3.6 parts by weight Water 78 parts by weight For solution A, the average particle size is measured by a sand grinder (laser diffraction / scattering particle size analyzer manufactured by Horiba Ltd. [LA91
0] is the median diameter determined in [0]. same as below. ) Is 0.5
Liquid B was dispersed to an average particle size of 0.8 μm or less. Kuraray PVA-105 is used for polyvinyl alcohol. same as below. Polystyrene Ammonium Acrylate uses Polymaron 326 manufactured by Arakawa Chemical Co., Ltd. Solution A adjusted above: 59.6 parts by weight, Solution B: 2
01.6 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 coating amount of the air-dried and the resulting heat-sensitive coating solution on high quality paper of Beitsubo 50 g / m ² is coated on the test bar coater so as to be 5 g / m ^2, and dried to form a heat-sensitive recording layer.

Formation of Protective Layer A molecular weight of 7.0 was obtained as starch on the resulting thermosensitive recording layer.
Oxidized Starch Oji Ace A (14% aqueous solution: Oji Cornstarch Co., Ltd.) 500 parts by weight, silica (Mizukasil P-527: Mizusawa Chemical Industry Co., Ltd.) 20 parts, 30%
33.3 parts by weight of zinc stearate dispersion liquid (Hydrin D-523: manufactured by Chukyo Yushi Co., Ltd.), 72 parts by weight of an aqueous solution of epichlorohydrin WS-570: manufactured by Japan PMC Co., Ltd., and water 3
36.7 parts by weight of a protective layer coating solution prepared by mixing and stirring 46.7 parts by weight
A protective layer was formed by coating and drying with a test bar coater so as to obtain m ² .

After that, the Bekk smoothness of the surface is about 50.
Gross calendering was performed for 0 seconds to obtain a heat-sensitive recording material.

Example 2 In Example 1, instead of Oji Ace A, oxidized starch MS3800 having a molecular weight of 64,000 (manufactured by Nippon Shokubai Co., Ltd.)
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that was used.

Example 3 In the same manner as in Example 1 except that Oji Ace A was replaced with phosphate esterified starch ace P-120 (manufactured by Oji Corn Starch Co., Ltd.) having a molecular weight of 75,000. A thermosensitive recording medium was obtained.

Example 4 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that acetylated starch OSA1250 (manufactured by Oji Corn Starch) having a molecular weight of 69,000 was used in place of Oji Ace A. Obtained.

Comparative Example 1 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that, in place of Oji Ace A, oxidized starch Oji Ace B having a molecular weight of 47,000 (manufactured by Oji Corn Starch Co., Ltd.) was used. Got

Comparative Example 2 Oxidized starch MS3600 (manufactured by Nippon Shokubai Co., Ltd.) having a molecular weight of 44,000 instead of Oji Ace in Example 1
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that was used.

COMPARATIVE EXAMPLE 3 Heat sensitive material was prepared in the same manner as in Example 1 except that phosphoric acid esterified starch MS4600 (manufactured by Nippon Shokubai Co., Ltd.) having a molecular weight of 25,000 was used in place of Oji Ace A. I got a record.

COMPARATIVE EXAMPLE 4 In Example 1, 220 parts of Prince Ace A was completely saponified P
VA (PVA117: Kuraray Co., Ltd .: 12% water) 2 liquids
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 80 parts was used.

Comparative Example 5 Heat-sensitive material was prepared in the same manner as in Example 1 except that cation-modified starch Aminofax 15 (made by Matsutani Chemical Industry Co., Ltd.) having a molecular weight of 40,000 was used in place of Oji Ace A. I got a record.

Comparative Example 6 Epichlorohydrin aqueous solution WS-53 in Example 1
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 0 was not used.

[0041]

[Table 1]

[0042]

As is apparent from Table 1, the thermosensitive recording medium of the present invention is an excellent thermosensitive recording medium in which water-wetting blocking hardly occurs.

Claims (2)

[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, wherein the protective layer is a starch having an average molecular weight of 50,000 or more. And / or a derivative thereof and a curing agent are further used. 2. A heat-sensitive recording material according to claim 1, wherein epichlorohydrin is used as a curing agent for the protective layer.