JP5908777B2 - Thermal recording material - Google Patents

Description

  The present invention relates to a thermal recording material, and more particularly to a thermal recording material excellent in oil resistance.

  The thermal recording medium is colored by a chemical reaction when heated by a thermal head or the like, and a recorded image is obtained. It is not only used as a recording medium for facsimiles, automatic ticket vending machines, and scientific measuring instruments, but also for POS labels and medical measurement. Widely used in applications such as recorders.

  When a recorded image formed on such a heat-sensitive recording material comes into contact with a plasticizer, the color density decreases, and in an extreme case, the recorded image is completely lost. For example, when a heat-sensitive label provided with an adhesive layer on the back side of the heat-sensitive recording material is attached to a resin film or the like, the plasticizer contained in the film moves from the back side of the label to the heat-sensitive recording layer of the heat-sensitive recording material, There is a problem that the plasticizer is transferred from the film that is in direct contact with the surface to the heat-sensitive recording layer, and the color density of a recorded image such as a barcode or a character printed on the label is lowered and cannot be read.

  For this reason, a heat-sensitive recording layer is provided with a barrier layer comprising a water-soluble polymer substance such as polyvinyl alcohol or methylcellulose and a water-resistant agent such as formaldehyde or glyoxal that makes the water-soluble polymer substance water resistant. Recording labels have also been proposed (see, for example, Patent Document 1).

Japanese Utility Model Publication No.59-9909

  With the expansion of the field of use of the thermal recording material, there is a demand for a thermal recording material excellent in preservability with respect to oil such as edible oil. However, in Patent Document 1, the oil resistance is not sufficient, and the improvement Was desired.

  The present invention has been made in view of the above points, and an object thereof is to provide a heat-sensitive recording material having improved oil resistance.

  In order to achieve the above object, the present invention is configured as follows.

(1) The heat-sensitive recording material of the present invention is a heat-sensitive recording material in which at least a heat-sensitive recording layer and a non-radiation curable protective layer are laminated on a substrate, and includes the heat-sensitive recording layer and the protective layer. In the meantime, a bentonite layer containing no resin binder is provided.

  The heat-sensitive recording material of the present invention may be provided with at least three layers of a heat-sensitive recording layer, a protective layer, and a bentonite layer on the base material, and other layers may be added. Is not particularly limited. For example, another layer may be interposed between the thermosensitive recording layer and the baitnite layer, or between the bentonite layer and the protective layer.

The bentonite layer should just be a bentonite layer which does not contain a resin binder, and it is preferable to consist only of bentonite.

  According to the heat-sensitive recording material of the present invention, since a bentonite layer is provided between the heat-sensitive recording layer and the protective layer, oil such as edible oil that has penetrated from the protective layer on the surface side of the heat-sensitive recording material is caused by the bentonite layer. The penetration into the heat-sensitive recording layer can be suppressed, and the oil resistance is improved.

The reason why the bentonite layer improves the oil resistance is not clear in detail, but because bentonite absorbs and retains water and swells, the moisture absorbed in the bentonite layer repels the oil and makes thermal recording. It is thought to prevent the penetration of oil into the layer.
(2) In a preferred embodiment of the present invention, the bentonite layer is a bentonite-only layer.

( 3 ) In a preferred embodiment of the heat-sensitive recording material of the present invention, the bentonite layer is made of natural bentonite.

  According to this embodiment, since the bentonite layer is made of natural bentonite, the oil resistance is further improved compared to the case of synthetic bentonite.

( 4 ) In another embodiment of the heat-sensitive recording material of the present invention, an undercoat layer is provided between the substrate and the heat-sensitive recording layer.

  According to this embodiment, it is possible to improve the heat insulating property for preventing the heat dissipated from the thermal head and to improve the print quality by enhancing the cushioning property.

( 5 ) In another embodiment of the heat-sensitive recording material of the present invention, the undercoat layer contains hollow particles.

  According to this embodiment, since the undercoat layer contains hollow particles, the absorption of oil into the undercoat layer is suppressed as compared with the case of containing an inorganic filler. Oil permeation into the heat-sensitive recording layer is suppressed and oil resistance is improved.

( 6 ) In still another embodiment of the heat-sensitive recording material of the present invention, an adhesive layer may be provided on the lower surface side of the substrate .

  According to this embodiment, since the pressure-sensitive adhesive layer is provided on the lower surface side of the substrate, that is, the back surface side of the thermal recording material, it can be suitably used as a thermal recording label.

  According to the present invention, since the bentonite layer is provided between the heat-sensitive recording layer and the protective layer laminated on the base material, oil such as edible oil that has penetrated from the protective layer is absorbed by the bentonite layer. Can be prevented from penetrating into the oil and oil resistance is improved.

FIG. 1 is a schematic sectional view of a thermosensitive recording material according to an embodiment of the present invention. FIG. 2 is a grayscale image showing the color development state before and after the oil resistance test of the example and the comparative example. FIG. 3 is a schematic cross-sectional view of a thermosensitive recording material according to another embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view of a thermal recording material according to an embodiment of the present invention.

  In the thermal recording material 1 of this embodiment, an undercoat layer 3, a thermal recording layer 4 that develops color by heating, a bentonite layer 5, and a protective layer 6 that protects the thermal recording layer 4 are formed on a sheet-like substrate 2. It has a laminated structure.

  As the base material 2, for example, paper, non-woven fabric, synthetic resin film, metal foil, and a composite sheet combining these can be used.

  The undercoat layer 3 functions as a heat insulating layer for preventing the dissipation of heat given from the thermal head to develop the color of the thermosensitive recording layer 4 and as an elastic layer for providing cushioning properties.

  For the undercoat layer 3, the heat-sensitive recording layer 4 and the protective layer 6, publicly known materials can be used.

  As a material for forming the undercoat layer 3, a filler is added to a binder, and additives such as a crosslinking agent, a dispersant, an antifoaming agent, a water-resistant agent, and an ultraviolet absorber are added as necessary. Is used.

  Examples of the binder for the undercoat layer 3 include polyvinyl alcohol, modified polyvinyl alcohol, starch, modified starch, casein, gelatin, glue, gum arabic, polyamide, polyacrylamide, modified polyacrylamide, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose. , Hydroxypropyl cellulose, polyvinyl acetate, polyacrylate, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, diisobutylene-maleic anhydride copolymer, vinyl acetate-maleic anhydride copolymer Polymer, methyl vinyl-maleic anhydride copolymer, isopropylene-maleic anhydride copolymer, styrene-butadiene copolymer, maleic acid copolymer, polyvinyl chloride, polyvinyl chloride , Vinyl chloride - vinyl acetate copolymer, polyurethane, polystyrene, polyvinyl pyrrolidone, acrylic acid esters, acrylonitrile, can be used by selecting one or more water-soluble resin or emulsion, such as methyl vinyl ether.

  In addition, the fillers include aluminum hydroxide, aluminum oxide, aluminum silicate, heavy calcium carbonate, light calcium carbonate, titanium oxide, barium sulfate, silica gel, activated clay, talc, clay, kaolinite and other kaolin, diatomaceous earth. , White carbon, magnesium carbonate, magnesium oxide, magnesium hydroxide, zinc oxide, polystyrene resin particles, urea-formalin resin particles, polyolefin resin particles and the like can be selected and used.

  As the filler, known hollow particles that are generally used may be used. Examples of the material of the hollow particles include polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylate, Thermoplastic resins such as acrylonitrile, polybutadiene, and copolymers thereof can be used.

  As a material for forming the heat-sensitive recording layer 4, a sensitizer, a lubricant, and the like can be contained in addition to a color former, a developer, a filler, and a binder that develop color by heating.

  Here, as the color former that develops color by heating, a commonly used known leuco dye can be used. As this leuco dye, for example, 3- (N-isopentyl-N-ethyl) amino- 6-methyl-7-o-chloroanilinofluorane, 3-dipentylamino-6-methyl-7-anilinofluorane, 3-jetylamino-6-methyl-7-p-toluidinofluorane, crystal violet Lactone, 3- (N-ethyl-N-isopentyl) amino-6-methyl-7-anilinofluorane, 3-jetylamino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N- p-toluidino) -6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino 6-methyl-7-anilinofluorane, 3- (N-cyclohexyl-N-methyl) amino-6-methyl-7-anilinofluorane, 3-jetylamino-7- (o-chloroanilino) fluorane, 3- Dibutylamino-7- (o-chloroanilino) fluorane, 3-jetylamino-7- (m-trifluoromethylanilino) fluorane, 3-dimethylamino-5-methyl-7-methylfluorane, 3- (N-methyl) -Nn-propyl) amino-6-methyl-7-anilinofluorane, 3- (N-isobutyl-N-ethyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethoxy) Propyl-N-ethyl) amino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-bromofluorane, 3-jet Amino-6-methyl-8-methyl-fluoran, 3- Jechiruamino-7-chloro-fluoran and the like may be used alone or in combination of two or more.

  In addition, as the developer, various electron accepting substances that react with the leuco dye as described above when heated to develop color can be used. For example, commonly used bentonite , Zeolite, acid clay, activated clay, silica gel, zinc oxide, zinc chloride, zinc bromide, aluminum chloride, salicylic acid, 3-tert-butylsalicylic acid, 3,5-di-tert-butylsalicylic acid, di-m-chlorophenylthio Urea, di-m-trifluoromethylphenylthiourea, di-phenylthiourea, salicylanilide, 4,4'-isopropylidenediphenol, 4,4'-isopropylidenebis (2-chlorophenol), 4,4 ' -Isopropylidenebis (2,6-dibromophenol), 4,4'-isopropylidenebis (2,6-di) Rolophenol), 4,4′-isopropylidenebis (2-methylphenol), 4,4′-isopropylidenebis (2,6-dimethylphenol), 4,4′-isopropylidenebis (2-tert-butyl) Phenol), 4,4′-sec-butylidene dipheseal, 4,4′-cyclohexylidenebisphenol, 4,4′-cyclohexylidenebis (2-methylphenol), 4-tert-butylphenol, 4 Phenylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, dimethyl 5-hydroxyphthalate, methyl-4-hydroxybenzoate, 4-hydroxyacetophenone, novolak type phenol resin, 2,2 ′ -Thiobis (4,6-dichlorophenol), catechol, resorcin, Loquinone, pyrogallol, phloroglycin, phloroglysin carboxylic acid, 4-tert-octylcatechol, 2,2'-methylenebis (4-chlorophenol), 2,2'-methylenebis (4-methyl-6-tert-butylphenol) 2,2′-dihydroxydiphenyl, ethyl p-hydroxybenzoate, propyl p-hydroxybenzoate, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, p-hydroxybenzoate-p-chlorobenzyl, p -Hydroxybenzoic acid-o-chlorobenzyl, p-hydroxybenzoic acid-p-methylbenzyl, p-hydroxybenzoic acid-n-octyl, benzoic acid, zinc salicylate, 1-hydroxy-2-naphthoic acid, 2-hydroxy- 6-naphthoic acid, 2-hydroxy-6-naphtho Zinc, 4-hydroxydiphenyl sulfone, 4,2'-diphenol sulfone, 4-hydroxy-4'-chlorodiphenyl sulfone, 4-hydroxy-4'-benzyloxydiphenyl sulfone, 4-hydroxy-4'-iso Propoxydiphenylsulfone, 4-hydroxy-4'-isobutyloxydiphenylsulfone, bis (4-hydroxyphenyl) sulfide, 2-hydroxy-p-toluic acid, zinc 3,5-di-tert-butylsalicylate, 3,5 -Tin di-tert-butylsalicylate, tartaric acid, oxalic acid, maleic acid, citric acid, succinic acid, stearic acid, 4-hydroxyphthalic acid, boric acid, biimidazole, hexaphenylbiimidazole, carbon tetrabromide, methylenebis- (Oxyethylenethio) diphenol, ethylenebis- (Oxyethylenethio) diphenol, bis- (4-hydroxyphenylthioethyl) ketone, bis- (4-hydroxyphenylthioethyl) ether, m-xylylenebis (4-hydroxyphenylthio) ether and the like can be used.

  Examples of the filler for the heat-sensitive recording layer 4 include aluminum hydroxide, aluminum oxide, aluminum silicate, heavy calcium carbonate, light calcium carbonate, titanium oxide, barium sulfate, silica gel, activated clay, talc, clay, and kaolinite. Select one or more of kaolin, diatomaceous earth, white carbon, magnesium carbonate, magnesium oxide, magnesium hydroxide, zinc oxide, polystyrene resin particles, urea-formalin resin particles, polyolefin resin particles, etc. Can do.

  Further, as the binder for the heat-sensitive recording layer 4, known ones that are generally used can be used. For example, polyvinyl alcohol, modified polyvinyl alcohol, starch, modified starch, casein, gelatin, glue, gum arabic, Polyamide, polyacrylamide, modified polyacrylamide, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl acetate, polyacrylate, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, diisobutylene -Maleic anhydride copolymer, vinyl acetate-maleic anhydride copolymer, methyl vinyl-maleic anhydride copolymer, isopropylene-maleic anhydride copolymer, styrene-butadiene copolymer, Vinyl chloride, polyvinylidene chloride, vinyl chloride - vinyl acetate copolymer, polyurethane, polystyrene, polyvinyl pyrrolidone, acrylic acid esters, acrylonitrile, can be used singly or two or more aqueous resin such as methyl vinyl ether.

  Further, as the sensitizer and the lubricant contained in the heat-sensitive recording layer 4, known ones that are generally used can be used. Examples of the sensitizer include 1,2-bis- (3-methylphenoxy) ethane, waxes, higher fatty acids, higher fatty acid amides, higher fatty acid anilides, naphthol derivatives, naphthalene derivatives, aromatic ethers, aromatics. Carboxylic acid derivatives, aromatic sulfonic acid ester derivatives, carbonic acid or oxalic acid diester derivatives, biphenyl derivatives, polyether derivatives, terphenyl derivatives, sulfone derivatives, etc., solids at room temperature, preferably those having a melting point of about 70 ° C. or higher Can be used. Examples of the lubricant include fatty acids such as paraffin wax and oleic acid, polyolefin waxes such as polyethylene wax, metal soaps such as zinc stearate, ester waxes such as carnauba wax, and oils such as silicon oil and whale oil. These can be used alone or in combination of two or more.

  The protective layer 6 contains a filler, a binder, a crosslinking agent, a lubricant and the like.

  As the filler, binder and lubricant of the protective layer 6, the same materials as those of the above-mentioned heat-sensitive recording layer 4 can be used.

  As the crosslinking agent for the protective layer 6, ammonium zirconium carbonate, polyamide polyamine epichlorohydrin resin, formalin, glyoxal, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, carboxy group-modified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, pectin, casein, gelatin, Water-soluble polymers such as starch, polyacrylic acid, alkali salt of acrylic acid / styrene copolymer, polyvinyl acetate, vinyl chloride / vinyl acetate copolymer, polystyrene, polyacrylic ester, polyurethane, styrene / butadiene / acrylic Select one or more types of hydrophobic polymer compound emulsions such as acid ester copolymers, epoxy compounds, melamine-formalin resins, etc. Can.

  In this embodiment, a baitnite layer 5 is provided between the heat-sensitive recording layer 4 and the protective layer 6 in order to improve the storage stability of the color image with respect to oil such as edible oil, that is, oil resistance.

  The bentonite layer 5 is a kind of clay mainly composed of montmorillonite and swells when water is added.

  The bentonite layer 5 can be formed by applying an aqueous solution of bentonite onto the thermal recording layer 4 and drying it.

  As bentonite, natural bentonite or synthetic bentonite can be used, and both bentonites may be mixed and used.

  Examples of natural bentonite include Kunipia-F (trade name) manufactured by Kunimine Industry Co., Ltd., and Kunipia-F is a high-purity montmorillonite powder obtained by purifying bentonite produced in nature. As the synthetic bentonite, for example, smecton SA (trade name), which is a synthetic inorganic polymer having a saponite structure manufactured by Kunimine Industry Co., Ltd., can be mentioned.

  Both natural bentonite and synthetic bentonite are effective in improving oil resistance, but natural bentonite is more preferable.

  The concentration of the bentonite aqueous solution is preferably about several percent by weight from the viewpoint of coatability, and is preferably about 2 percent by weight, for example.

The coating amount is preferably about 0.2 g / m ^{2 by} weight after drying.

  Thus, since the bentonite layer 5 is provided between the heat-sensitive recording layer 4 and the protective layer 6, oil such as edible oil that permeates from the protective layer 6 that is the surface of the heat-sensitive recording body 1 penetrates the heat-sensitive recording layer 4. Therefore, the bentonite layer 5 acts so as to prevent the disappearance of the color image of the heat-sensitive recording layer 4 and the oil resistance is improved.

  Next, based on an Example and a comparative example, this invention is demonstrated still in detail.

  As shown in Table 1 below, Examples having a natural bentonite layer 5 in five sample configurations A to E in which the materials of the base material 2, the undercoat layer 3, and the heat-sensitive recording layer 4 are different from each other, The comparative example which does not have a bentonite layer was created, and oil resistance was evaluated. In addition, the structure of the protective layer 6 is the same also in any sample AE of an Example and a comparative example.

  As shown in Table 1, as the base material 2, high quality paper was used in samples A to C, pure white paper was used in sample D, and a synthetic resin film was used in sample E.

  For the undercoat layer 3, samples A to C are undercoat layers containing organic hollow particles, sample D is an undercoat layer containing calcined kaolin, and sample E based on a synthetic resin film is base 2 In order to enhance the adhesion between the heat-sensitive recording layer 4 and the heat-sensitive recording layer 4, an anchor layer was used.

  For the heat-sensitive recording layer 4, Sample A.3 is used. B was a heat-sensitive recording layer containing a preservability improver, and Samples C to E were heat-sensitive recording layers not containing a preservative improver.

In the example, in the configuration of each of the samples A to E described above, an aqueous solution of 2% by weight of natural bentonite is applied on the thermosensitive recording layer 4 and dried to form the bentonite layer 5. A protective layer 6 was formed. The bentonite was coated such that the dry weight was 0.2 g / m ² .

  In the comparative example, the same protective layer 6 as in the example was formed on the heat-sensitive recording layer 4 without forming a bentonite layer in the configurations of the samples A to E described above.

The heat-sensitive recording materials of the examples and comparative examples having the above-described structure were heated and colored for 1 second at 140 ° C. and a pressure of 1 kg / cm ² using a thermal gradient tester HG-100 manufactured by Toyo Seiki Co., Ltd. It was measured with a Macbeth reflection densitometer RD-914 (manufactured by Sakata Inx Engineering Co., Ltd.).

  This measured value was used as the color density before the test (Macbeth density), and as a corrosion resistance test, salad oil (Nisshin Oilio Group Co., Ltd.) was applied, and the color density after 1 hour was applied to the Macbeth reflection densitometer RD-914. The measured value was used as the color density after the test.

  Further, a color density remaining ratio {= (color density after test / color density before test) × 100}, which is a ratio of the color density after the test (after 1 hour of salad oil application) to the color density before the test, was calculated. .

  The results are shown in Table 2 below.

  As shown in Table 2, in any sample configuration of A to E in which the materials of the base material 2, the undercoat layer 3, and the thermosensitive recording layer 4 are different, the example having the bentonite layer 5 is the bentonite layer 5. It can be seen that the color density remaining rate is higher than that of the comparative example having no odor, and the storage stability to edible oil is improved.

  In the example having the bentonite layer 5, the color density after the test was higher than the color density before the test except for the sample D because the gloss was generated by the oil. In the comparative example which does not have, since the oil penetrates into the inside, the color density after the test is lower than that before the test.

  In addition, FIG. 2 shows grayscale images of the states of the examples and comparative examples of the samples A to E before and after the test.

  As shown in FIG. 2, in any of the sample configurations A to E in which the materials of the base material 2, the undercoat layer 3, and the thermosensitive recording layer 4 are different, the comparative example having no bentonite layer has a color density. It can be seen that the color image is hardly deteriorated in the example having the bentonite layer 5 while it is decolored by being lowered.

  In Table 2 and FIG. 2, the color density of sample D is lower than that of the other samples, but this is not only because the oil is not only from the protective layer 6 on the surface side of the thermal recording body 1. In the sample D, the undercoat layer 3 contains calcined kaolin, which is an inorganic filler, and therefore, it absorbs oil more easily than the sample containing organic hollow particles. It is considered that the concentration has decreased. Also in this sample D, it can be seen that in the example, the decrease in color density is less than that in the comparative example, and the oil resistance is improved.

  As described above, in the example having the bentonite layer 5, a decrease in the color density is suppressed as compared with the comparative example, and the color image is less likely to deteriorate with respect to oil such as edible oil, and the oil resistance is improved. It could be confirmed.

  Although details of the reason why the bentonite layer 5 improves the oil resistance is not clear, bentonite easily absorbs and retains water. Therefore, the water retained by the bentonite layer 5 repels the oil and transfers the oil to the thermosensitive recording layer 4. It is thought that it is because it can suppress soaking.

  In addition to the oil resistance test described above, the dynamic sensitivity characteristics of the sample A and the comparative example were measured.

  The dynamic sensitivity characteristics were obtained by stepwise changing the printing energy using L2000 manufactured by Ishida Co., Ltd. to perform color printing and measuring the color density with the Macbeth reflection densitometer RD-914. The results are shown in Table 3.

  As shown in Table 3, it was confirmed that the example in which the bentonite layer 5 was provided also had the same dynamic sensitivity characteristics as the comparative example and was not inferior.

  Thus, when using the thermosensitive recording material of this invention which is excellent in oil resistance as a label, as shown in FIG. 3, for example, as shown in FIG. The release paper (not shown) may be attached to the pressure-sensitive adhesive layer 8 so as to be peelable. The barrier layer 7 prevents the components of the pressure-sensitive adhesive layer 8 from diffusing into the heat-sensitive recording layer 4 through the substrate 2 or the like, but the barrier layer 7 may be omitted.

  Although the undercoat layer 3 is provided in the above-described embodiment, the undercoat layer 3 may be omitted as another embodiment of the present invention.

DESCRIPTION OF SYMBOLS 1 Thermal recording body 2 Base material 3 Undercoat layer 4 Thermal recording layer 5 Bentonite layer 6 Protective layer 7 Barrier layer 8 Adhesive layer

Claims (5)

A heat-sensitive recording material in which at least a heat-sensitive recording layer and a non-radiation curable protective layer are laminated on a substrate,
A bentonite layer not containing a resin binder is provided between the thermosensitive recording layer and the protective layer.
A heat-sensitive recording material. The bentonite layer is a bentonite only layer,
The heat-sensitive recording material according to claim 1. The bentonite layer is made of natural bentonite,
The heat-sensitive recording material according to claim 1 or 2. An undercoat layer is provided between the substrate and the thermosensitive recording layer.
The heat-sensitive recording material according to any one of claims 1 to 3 . The undercoat layer contains hollow particles;
The heat-sensitive recording material according to claim 4 .