JPH08230324A - Thermal recording material - Google Patents

Abstract

PURPOSE: To enhance water resistance, plasticizer resistance and oil resistance, in a thermal recording material wherein a thermal color forming layer and a protective layer are formed on a support, by adding carboxyl modified polyvinyl alcohol, an aldehyde compd. and a polyamide epoxy resin to the protective layer. CONSTITUTION: In a thermal recording material constituted so that the thermal color forming layer formed on a support is heated by a thermal head or laser beam to instantaneously react a color former in the color forming layer to form a recording image and a protective layer is provided on the thermal color forming layer, as the component constituting the protective layer, a crosslinking agent selected from carboxy modified polyvinyl alcohol, an aldehyde compd. and a polyamide epoxy resin is added. At this time, glyoxal is pref. used as the aldehyde compd. and polyamide epichlorohydrin is used as the polyamide epoxy resin. By this constitution, glyoxal generates intermolecular crosslinking to develop water resistance.

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 a protective layer provided on the heat-sensitive recording layer.

[0002]

2. Description of the Related Art A thermosensitive recording medium generally comprises a support and a thermosensitive coloring layer formed on the support, and the thermosensitive coloring layer is heated by a thermal head, a heating pen, a laser beam or the like to produce a thermosensitive coloring. The color developing agent in the layer is instantly reacted to form a recorded image, which has been widely known from the past, for example, from Japanese Patent Publication No. 43-4160 and Japanese Patent Publication No. 45-14039. .

Such a thermosensitive recording medium has the advantages that a recorded image can be formed with a relatively simple device, that the maintenance is easy, and that no noise is generated during recording. It has been applied to a wide range of fields such as, facsimiles, measurement recorders, terminal printers such as computers, vending machines, and bar code labels.

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. Therefore, strict characteristics that have not been a problem in the past have begun to be demanded.

In other words, the characteristics required for the heat-sensitive recording material are, of course, resistance to discoloration of the recorded image and background stain due to weather resistance, chemical resistance and the like, as well as for gas and electric meter reading recording. In such applications, since it may be used outdoors and in rainy weather, it is required to have excellent water resistance.

On the other hand, the conventional heat-sensitive recording material has the drawback that the recorded image is discolored or the background is colored when it comes into contact with a plasticizer, oils and fats in a vinyl chloride case, an organic solvent and the like. In order to overcome such drawbacks, a protective layer has been conventionally provided on the thermosensitive coloring layer, and components constituting this protective layer include, for example, water-soluble polymers such as polyvinyl alcohol and starch. Is used as the main component.

Therefore, as a method for imparting water resistance to a thermosensitive recording medium, a crosslinking agent which reacts with such a water-soluble polymer is used in combination. However, it is not possible to apply heat that causes a sufficient crosslinking reaction during the formation of the protective layer, and if a highly reactive crosslinking agent is used, a crosslinking reaction will occur in the coating liquid, and There is a problem that the viscosity is remarkably increased and the coating becomes impossible. For these reasons, the present situation is that a heat-sensitive recording material having water resistance and having excellent plasticizer resistance and oil resistance has not yet been obtained.

In order to solve such a problem, it has been proposed to introduce a functional group which enhances reactivity into a water-soluble polymer (JP-A-56-126193 discloses carboxy-modified PVA and JP-A- In JP-A 59-106995, acetoacetylated PVA and acrylonitrile-PVA copolymer, and in JP-A-59-169885, acrylic acid amide / acrylonitrile-modified PVA) are still insufficient.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat-sensitive recording material which overcomes the above problems and is excellent in water resistance, plasticizer resistance and oil resistance.

[0010]

DISCLOSURE OF THE INVENTION The present inventors have proposed a thermosensitive recording medium comprising a support, a thermosensitive recording layer formed on the support, and a protective layer formed on the support. It was found that the problem can be solved by containing polyvinyl alcohol and a crosslinking agent selected from an aldehyde compound and a polyamide epoxy resin.

Japanese Unexamined Patent Publication (Kokai) No. 3-155985 proposes to use a carboxy-modified polyvinyl alcohol which is a film-forming component and a polyamide epoxy resin which is a cross-linking agent, but this protective film is sufficiently cured (time and High performance can be obtained by heat treatment in which heat is applied to the protective film to complete the reaction.)
If curing is insufficient, satisfactory performance cannot be obtained.

[0012] In order to exhibit such excellent performance, a great deal of curing is required, so that the background is covered,
It has been found that there is a drawback that the product cannot be manufactured immediately after manufacturing if it is gently cured so as not to cover the skin. The performance after sufficient curing is excellent, so as a result of studying how to improve the initial performance with gentler curing, the initial performance can be achieved without using the aldehyde compound in combination with the aldehyde compound. It was found that it could be done.

PVA and / or modified PVA and / or P
It has been known that an aldehyde compound alone is used as a cross-linking agent for a VA copolymer. However, when an aldehyde compound and a polyamide epoxy resin are used together, curing is not performed by leaving the aldehyde compound at room temperature. However, it is not known until now that water resistance is developed due to the progress of the cross-linking reaction with the polyamide-epoxy resin, and among the aldehyde compounds, glyoxal from the viewpoints of the expression of action effects, yellowing, economical efficiency, etc. Are particularly preferably used.

In particular, when glyoxal is used, a cross-linking reaction effectively occurs and good water resistance is imparted to the film without curing, but when glyoxal is used alone, it can be stored for a long time. The present inventors have found that there is a very serious drawback that performance is rapidly deteriorated (especially when placed in a high temperature dry state) and water resistance is lost. This phenomenon similarly occurs in the reaction with the carboxy-modified polyvinyl alcohol used in the present invention.

The present inventors have conducted various studies on methods for improving these properties, and as a result, by combining these cross-linking agents, excellent water resistance can be exhibited immediately after coating without curing and any long-term It was found that it is possible to obtain a film that retains its excellent water resistance even under storage conditions. Presuming this action, glyoxal causes intermolecular cross-linking through the hydroxyl group of carboxy-modified PVA to develop the initial water resistance, and then the reaction between the polyamide epoxy resin and the carboxyl group proceeds over time to finally It seems that it became possible to obtain a film with excellent water resistance. That is, when stored for a long period of time (especially when placed in a high temperature dry state), the water resistance due to glyoxal deteriorates, but the water resistance due to the polyamide epoxy resin does not deteriorate, so a film with excellent water resistance is finally obtained. be able to.

Specific examples of the aldehyde compound include aldehyde starch, glutaraldehyde, glyoxal, and other resins having an aldehyde group. Among them, glyoxal is particularly excellent not only in the manifestation of its action and effect but also in the amount of supply and the price.

The polyamide epoxy resin is obtained by acting epihalohydrin on a polyamide resin obtained by condensation of an alkylpolyamine compound and an alkyldicarboxylic acid, and has an epoxy group in the molecule. Examples of the epihalohydrin include epichlorohydrin, epibromohydrin, and epiiodohydrin, and as the resin, particularly polyamide epichlorohydrin exhibits an excellent effect.

If desired, other crosslinking agents may be used as long as they do not impair the effects of the present invention. For example, 1) N-methylol compound N-methylurea, N-methylmelamine, N-methylolethyleneurea 2) Active vinyl compound divinylsulfone, bis (β-hydroxyethylsulfone) 3) Polycarboxylic acid compound Dicarboxylic acid, dicarboxylic acid Chloride, methyl vinyl ether-maleic acid copolymer 4) diisocyanate compound toluylene diisocyanate, diphenylmethane diisocyanate 5) aziridine compound trimethylolpropane-tri-β-aziridinyl propionate, N, N′-hexamethylene-1,6 -Bis (1-aziridinecarboxamide), tetramethylolmethane-tri-β-aziridinylpropionate 6) Complexing agent Compounds such as Cu, B, Al, Ti, Zr, Sn, V and Cr.

Paper, plastic film, synthetic paper and the like are mainly used as the support of the thermal recording material of the present invention having the above-mentioned constitution, and further various kinds of non-woven fabrics, metal foils and the like, or composite sheets or the like in combination thereof. Can also be used. An undercoat layer may be formed on the surface of the support before forming the thermosensitive coloring layer.

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, and examples thereof include an electron-accepting property represented by leuco dyes and phenolic substances. Due to reaction with substances,
Those obtained by the reaction of an imino compound and an isocyanate compound, those obtained by the reaction of a long-chain fatty acid iron salt with a polyhydric phenol, and the like can be used. Specific examples of these combinations are described in, for example, JP-A-54-118845.

The thermosensitive coloring layer containing the coloring component is
Similar to the thermosensitive coloring layer in a conventional thermosensitive recording medium, a coating material for forming a thermosensitive coloring layer containing an aqueous solution of a water-soluble polymer compound and / or an aqueous emulsion of a hydrophobic polymer compound as a binder is provided at a predetermined position. It is obtained by applying it by a coating method or a printing method and then drying it.

As the resin used for the protective layer in the present invention, carboxy-modified polyvinyl alcohol is used as described above. The carboxy-modified polyvinyl alcohol includes polyvinyl alcohol, fumaric acid, phthalic anhydride,
Reactants with polycarboxylic acids such as mellitic anhydride and itaconic anhydride, or esterification products of these reactants, and further vinyl acetate and maleic acid, fumaric acid, itaconic acid,
It is obtained as a saponified product of a copolymer with an ethylenically unsaturated dicarboxylic acid such as crotonic acid, acrylic acid and methacrylic acid. Specifically, for example, the manufacturing method illustrated in JP-A-53-91995 can be adopted.

As long as the effects of the present invention are not impaired, other various water-soluble polymer compounds and / or hydrophobic polymer compounds can be used in combination, if necessary. Specific examples thereof include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, various modified polyvinyl alcohols, and styrene as long as they are water-soluble polymer compounds.
Maleic anhydride copolymer, ethylene-maleic anhydride copolymer and the like. Further, if it is an aqueous emulsion of a hydrophobic polymer compound, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, methyl acrylate-
Examples thereof include butadiene copolymer.

In the protective layer in the present invention, if necessary, diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide and hydroxide may be added together with the above-mentioned resin and crosslinking agent. Inorganic and organic pigments such as aluminum and urea-formalin resins, higher fatty acid metal salts such as zinc stearate and calcium stearate, paraffin,
It is possible to add a head wear preventing agent / sticking preventing agent and the like composed of waxes such as paraffin oxide, polyethylene, polyethylene oxide, stearic acid amide, and castor wax.

Further, various addition auxiliaries usually used in the production of thermosensitive recording materials, for example, dispersants such as sodium dioctylsulfosuccinate, surfactants such as defoaming agents, fluorescent dyes such as coloring agents, etc. are desired. It is used according to.

The preferred amounts of the constituent materials used in the present invention are 0.1 to 30 parts by weight (particularly preferably 1 to 25 parts by weight) of aldehyde compound and 100 to 100 parts by weight of carboxy-modified polyvinyl alcohol, and polyamide epoxy resin. 0.1 to 30 parts by weight (particularly preferably 1 to 25 parts by weight)
Can be used together.

The coating amount of the protective layer is 0.5 to 8 g / m ² (particularly preferably 1 to 5 g / m ² ), and the coating amount of the thermosensitive coloring layer is 2 to 2.
Sufficient effect can be obtained with 10 g / m ² (particularly preferably 3 to 6 g / m ² ).

[0028]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In addition, "part" and "%" in the examples represent "part by weight" and "% by weight", respectively, unless otherwise specified.

Example 1 Solution A Preparation 3-Dibutylamino-6-methyl-7-anilinofluorane (leuco compound) 10 parts 20% aqueous solution of polyvinyl alcohol (Kuraray Povar 1
05: Made by Kuraray ........ 10 parts Water ........ 20 parts The composition with the above composition was pulverized with a sand mill, and the average particle diameter (laser diffraction / scattering particle size distribution manufactured by Horiba, Ltd.) A median diameter obtained by a measuring device [LA910] is the same. The same shall apply hereinafter) to obtain a liquid A having dispersed particles of 0.8 μm.

Preparation of liquid B 4,4'-diisopropylidenediphenol (developing agent)
..... 10 parts 20% polyvinyl alcohol aqueous solution (Kuraray Poval 1
05: manufactured by Kuraray Co., Ltd .... 10 parts Water ... 20 parts The composition having the above composition was pulverized by a sand mill to obtain a liquid B made of dispersed particles having an average particle size of 1.5 μm. .

Preparation of liquid C Metaterphenyl (sensitizer) ... 10 parts 20% aqueous polyvinyl alcohol solution (Kuraray Poval 1
05: made by Kuraray Co., Ltd .... 10 parts Water ... 20 parts The composition having the above composition was pulverized by a sand mill to obtain a liquid C with dispersed particles having an average particle diameter of 1.0 μm. .

Formation of thermosensitive recording layer 40 parts of solution A, 80 parts of solution B, 40 parts of solution C, 20% polyvinyl alcohol (Kuraray Poval 105 manufactured by Kuraray) 60
Parts and 50 parts of water were mixed and stirred to obtain a coating liquid for heat-sensitive recording layer. 4 g (dr) of the obtained coating liquid on a high-quality paper of 50 g / m ²
It was coated at a ratio of y) / m ² and dried to form a heat-sensitive recording layer.

Formation of Protective Layer Further, 10% carboxy-modified polyvinyl alcohol (KL-) was added as a water-soluble polymer compound on the thermosensitive recording layer.
318: made by Kuraray), 25 parts of 40% glyoxal and 50 parts of 10% polyamide epichlorohydrin as a cross-linking agent, 20 parts of silica (P-527: made by Mizusawa Chemical Co., Ltd.) as a filler and 200 parts of water are mixed and protected. A layer coating agent was applied and dried at a rate of 3 g (dry) / m ² to form a protective layer.

Then, calendering treatment was carried out so that the surface smoothness was about 500 seconds to obtain a heat-sensitive recording material as an example of the present invention.

Comparative Examples 1 to 5 Dispersions were prepared by the same steps corresponding to the examples except that the protective layer coating agent was changed to the water-soluble polymer compound, the crosslinking agent and the filler shown in Table 1. In all other steps, a thermal recording medium for comparison was obtained by the same steps as those corresponding to the examples.

[0036]

[Table 1]

Curing Treatment The thermal recording material obtained as described above was prepared 20
What was left in an atmosphere of 65 ° C, 65% RH for 24 hours (no curing) and what was left in an atmosphere of 40 ° C, 15% RH for 48 hours (with curing) were prepared. ． Was evaluated.

Storage test The sample which was not cured was further stored at 60 ° C. for 1 hour.
With respect to the sample left to stand in an atmosphere of 5% RH for 7 days, water was dropped on the following blocking test and the film was strongly rubbed with a finger to judge the degree of water resistance. Judgment Criteria ∘: No dissolution of the coating components, Δ: Some dissolution, ×: Some dissolution

Printing test After heat-sensitive recording was carried out by a commercially available printer (Nisshinbo: XP6250), the storability of the image recording part and the background part was tested. The density was measured using a Macbeth densitometer (Model RD-514, manufactured by Macbeth Co.).

Evaluation Items and Evaluation Method 1. Blocking test After immersing the thermosensitive recording medium in water for 1 minute, the thermosensitive recording surface and the thermosensitive recording surface were pressure-bonded with each other at a pressure of ² kg / m ² , and the temperature was 60 ° C. for 15 minutes.
After being stored in a% RH blower dryer for 12 hours and dried,
Both were peeled off and checked for blocking. Judgment Criteria ◯: No blocking, Δ: Partial blocking, ×: Blocking present and not removable. 2. Water resistance test After dipping the thermosensitive recording medium in water for 12 hours, 60 ° C, 15%
After drying with an RH blast dryer, the degree of cloudiness of the overcoat layer was examined. The degree of white turbidity was measured by measuring the recording density before and after the test, and the less the decrease, the less the white turbidity and the better the water resistance. 3. Plasticizer resistance test 200 g / side of plastic eraser (dragonfly: MONO eraser) for each of image recording area and background area
It is contacted with a load of m ² and the concentration after storage for 24 hours under the condition of 20 ° C. and 65% RH is measured. 4. Oil resistance test For each of the image recording part and the background part, test cottonseed oil is applied with a cotton swab, and the concentration after storage for 24 hours at 20 ° C. and 65% RH is measured.

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

[0044]

As is apparent from Table 2 Table 3 and Table 4, the thermosensitive recording medium provided with the protective layer of the present invention has sufficient water resistance without curing, and has characteristics even when left at high temperature and low humidity. It is a good product with no deterioration and excellent plasticizer resistance and oil resistance. The heat-sensitive recording material of the present invention has a high density of a recorded image and has water resistance capable of withstanding outdoor use, and further, it causes fog on the background and fading of a recording portion due to contact with a plasticizer and various oils and fats. The heat-sensitive recording material has high quality characteristics such as no background and excellent storage stability of recorded images.

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 carboxy-modified polyvinyl alcohol and an aldehyde compound. And a polyamide epoxy resin. 2. The heat-sensitive recording material according to claim 1, wherein the aldehyde compound is glyoxal and the polyamide epoxy resin is polyamide epichlorohydrin.