Thermosensitive recording medium

Abstract

To provide a heat-sensitive recording medium that can prevent contamination of a thermal head at the time of printing without providing a top coat layer thereon.SOLUTION: A heat-sensitive recording medium 1 is not provided with an intermediate layer or a top coat layer and has a base material 2 having a heat-sensitive recording layer 3 put thereon. The heat-sensitive recording layer 3 has, as lubricants, paraffin and zinc stearate. The content of the lubricant is 30 mass% or less relative to the total of the heat-sensitive recording layer 3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a thermal recording medium, and more particularly to a thermal recording medium having an excellent function of preventing contamination of a thermal head.

Background Art

[0002] A thermal recording medium develops color by a chemical reaction by heating with a thermal head or the like, and a recorded image can be obtained. It is used not only as a recording medium for facsimiles, automatic ticket vending machines, and scientific measuring instruments, but also widely used as a thermal recording label for POS systems in retail stores and the like (for example, see Patent Document 1).

[0003] In recent years, a thermal recording medium without a protective layer provided on a thermal recording layer has been proposed. More specifically, for example, a thermal recording medium having a thermal recording layer provided on a base material, the thermal recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer, and containing an alkyl ketene dimer (AKD) has been proposed. And it is described that by containing such an alkyl ketene dimer (AKD), sufficient film strength and print running property (anti-sticking property) can be ensured without providing a protective layer (top coat layer) on the thermal recording layer (for example, see Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the thermal recording medium described in Patent Document 2 above, since the protective layer is not provided, there is a problem that the thermal head is contaminated during printing.

[0006] Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a thermal recording medium that can prevent contamination of the thermal head during printing without providing the above-described top coat layer or intermediate layer.

Means for Solving the Problems

[0007] In order to achieve the above object, in the first invention, on the premise of a thermal recording medium in which a thermal recording layer is laminated on a base material (however, excluding those provided with an intermediate layer and a top coat layer), the thermal recording layer contains paraffin and zinc stearate as lubricants, and the content of the lubricant in the entire thermal recording layer is 10% by mass or more and 30% by mass or less.

[0008] According to the above configuration, it is possible to prevent contamination of the thermal head during printing without providing a top coat layer.

[0009] Further, in the second invention, in the first invention, the thermal recording layer contains a pigment, and the content of the pigment in the entire thermal recording layer is 24% by mass or more and 43% by mass or less.

[0010] Further, in the third invention, in any one of the first to second inventions, the pigment is calcium carbonate.

[0011] Further, in the fourth invention, in any one of the first to third inventions, an undercoat layer is provided between the base material and the thermal recording layer.

Effects of the Invention

[0012] According to the present invention, it is possible to prevent contamination of the thermal head during printing without providing an intermediate layer and a top coat layer.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the following embodiments.

[0015] FIG. 1 is a cross-sectional view for explaining the thermal recording medium of the present embodiment.

[0016] As shown in FIG. 1, the thermal recording medium 1 of the present embodiment has a structure in which a thermal recording layer 3 that develops color by heating is laminated on a sheet-like base material 2. Note that the thermal recording medium 1 of the present embodiment does not include an intermediate layer and a top coat layer, and the thermal recording layer 3 is exposed.

[0017] As the base material 2, fine paper, other paper base materials, synthetic paper, resin, etc. can be used from the viewpoint of ensuring the physical strength of the thermal recording paper. Note that these can be selected from the viewpoints of required strength, thickness, weight, durability, etc., and can be used alone or in combination of two or more.

[0018] The material for forming the thermal recording layer 3 includes a color former that develops color by heating, a developer, a binder, a lubricant, a pigment, and the like.

[0019] Specifically, examples of the dye as the color former include 2 - aniline - 3 - methyl - 6 - (N - methyl - P - toluidino) fluoran, 3 - dibutylamino - 6 - methyl - 7 - anilinofluorane, etc., and their particle diameters are preferably 0.1 to 1.0 μm. Here, the particle diameter refers to the 50% average particle diameter measured by a microtrack laser analysis / scattering type particle size analyzer.

[0020] Examples of the above color former include 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone, etc., and their particle diameters are preferably 0.1 to 1.0 μm.

[0021] Examples of the above binder include styrene-butadiene copolymers, etc.

[0022] Examples of the above lubricants include paraffin, zinc stearate, and polyethylene, etc., and their particle diameters are preferably 0.5 μm or less. These lubricants can be used alone or in combination of two or more.

[0023] Also, from the viewpoint of preventing sticking between the thermal recording medium 1 and the thermal head, it is particularly effective to contain zinc stearate.

[0024] Examples of the above pigments include calcium carbonate, kaolin, calcined kaolin, aluminum hydroxide, aluminum oxide, aluminum silicate, heavy calcium carbonate, light calcium carbonate, titanium oxide, barium sulfate, silica gel, activated clay, talc, clay, kaolinite, diatomaceous earth, white carbon, magnesium carbonate, magnesium oxide, magnesium hydroxide, zinc oxide, polystyrene resin particles, urea-formalin resin particles, and polyolefin resin particles, etc. These pigments can be used alone or in combination of two or more.

[0025] Among these, from the viewpoints of improving whiteness and color development during printing without inhibiting the color development of the above color former, it is particularly effective to contain calcium carbonate. The particle diameter of calcium carbonate is preferably 0.1 to 1.0 μm or less.

[0026] Here, in the conventional thermal recording medium, as described above, since the protective layer is not provided, there has been a problem that the thermal head is contaminated during printing.

[0027] Therefore, the present inventors focused on this point and, in the thermal recording medium 1 not provided with the intermediate layer and the top coat layer, specified the type of the lubricant contained in the thermal recording layer 3 and adjusted the content thereof, thereby finding the conditions for preventing the contamination of the thermal head during printing.

[0028] More specifically, the thermal recording layer 3 of the present embodiment is characterized in that it contains paraffin and zinc stearate as lubricants, and the content of the lubricant with respect to the whole of the thermal recording layer 3 is 10% by mass or more and 30% by mass or less.

[0029] Since paraffin has a low melting point and is easily liquefied, it forms a thin liquid film on the heating zone when the thermal head generates heat, and can prevent the adhesion of deposits (such as carbides) caused by the above-described color former. As a result, during printing, contamination (black contamination) of the thermal head caused by the deposits can be prevented.

[0030] Also, the content of paraffin is 5% by mass or more and 14.5% by mass or less. This is because when it is less than 5% by mass, the function of preventing the adhesion of the above-described deposits (such as carbides) may not be sufficiently exhibited. Further, as the thermal head cools, paraffin also cools and becomes a white solid. Therefore, when it is more than 14.5% by mass, contamination (white contamination) of the thermal head caused by paraffin may occur.

[0031] Also, zinc stearate can prevent the sticking (adhesion) between the thermal recording medium 1 and the thermal head during printing, and as a result, contamination (white contamination) of the thermal head can be prevented.

[0032] Also, the content of zinc stearate is 5% by mass or more and 14.5% by mass or less. If it is less than 5% by mass, the above-mentioned sticking prevention function may not be sufficiently exhibited. Also, if it is more than 14.5% by mass, white stains may occur.

[0033] And in the thermal recording medium 1 of the present embodiment, since the content of the lubricant (that is, paraffin and zinc stearate) with respect to the whole thermal recording layer 3 is 30% by mass or less, it is possible to prevent the above-mentioned deposits and the contamination of the thermal head caused by paraffin when printing without providing an intermediate layer and a top coat layer.

[0034] Also, since the content of the lubricant with respect to the whole thermal recording layer 3 is 10% by mass or more, it is possible to surely prevent the wear of the thermal head.

[0035] Also, in the thermal recording layer 3 of the present embodiment, it is preferable to contain calcium carbonate as a pigment, and the content of the pigment with respect to the whole thermal recording layer 3 is preferably 24% by mass or more and 43% by mass or less.

[0036] Since calcium carbonate is a hard pigment, by containing 24% by mass or more with respect to the whole thermal recording layer 3, it is possible to scrape off the paraffin that has become the above-mentioned white solid adhering to the surface of the thermal head, and thus it is possible to further prevent the contamination (white contamination) of the thermal head.

[0037] However, if the content of calcium carbonate is more than 43% by mass, the heat generating zone of the thermal head is scraped and worn by the hard calcium carbonate, which is not preferable.

[0038] That is, by setting the content of calcium carbonate with respect to the whole thermal recording layer 3 to 24% by mass or more and 43% by mass or less, it is possible to further prevent the contamination (white contamination) of the thermal head without causing wear of the thermal head.

[0039] In addition, the heat-sensitive recording layer 3 may further contain additives other than the above-described color former, developer, etc. Examples of such additives include surfactants and ultraviolet absorbers.

[0040] Also, the above embodiment may be modified as follows.

[0041] In the above embodiment, the heat-sensitive recording body 1 composed only of the base material 2 and the heat-sensitive recording layer 3 was given as an example. However, as in the heat-sensitive recording body 10 shown in FIG. 2, an undercoat layer 4 may be provided on the upper layer side of the base material 2 (between the base material 2 and the heat-sensitive recording layer 3).

[0042] This undercoat layer 4 has functions such as heat insulation and cushioning properties that prevent the dissipation of heat given from the thermal head. For example, it is formed by adding hollow particles as a filler to a modified styrene-butadiene copolymer as a binder.

[0043] And by providing the undercoat layer 4 having heat insulation properties, the printing sensitivity is improved, so that an increase in the applied voltage of the thermal head can be suppressed. As a result, burning of the thermal head can be suppressed.

[0044] In addition, other than hollow particles may be used as the filler. For example, fired kaolin, aluminum oxide, aluminum silicate, heavy calcium carbonate, light calcium carbonate, titanium oxide, barium sulfate, silica gel, activated clay, talc, clay, kaolinite, diatomaceous earth, white carbon, magnesium carbonate, magnesium oxide, magnesium hydroxide, zinc oxide, polystyrene resin particles, urea-formalin resin particles, and polyolefin resin particles can be mentioned. Also, these fillers can be used alone or in combination of two or more.

Example

[0045] Hereinafter, the present invention will be described based on examples. It should be noted that the present invention is not limited to these examples, and these examples can be modified and changed based on the gist of the present invention, and they are not excluded from the scope of the invention.

[0046] (Examples 1 - 5, Comparative Examples 1 - 5) (Production of Thermal Recording Medium) <Thermal Recording Layer> The coating liquid for forming the thermal recording layer shown in Table 1 was prepared, and the prepared coating liquid for forming the thermal recording layer was applied to high-quality paper with a thickness of 80 μm as the base material, and the coating amount was 6 g / m 2 in terms of dry weight. After coating, drying was performed to form a thermal recording layer. In Table 1, the numerical values of each compounding agent represent the mass ratio (mass %) during drying.

[0047] Also, as compounding materials, paraffin with a melting point of 75 °C and a particle diameter of 1.0 μm, and zinc stearate with a melting point of 120 °C and a particle diameter of 5.5 μm were used as lubricants. Additionally, calcium carbonate with a particle diameter of 0.4 μm was used as the pigment.

[0048] By the above method, thermal recording media of Examples 1 - 5 and Comparative Examples 1 - 5 were produced.

[0049] <Evaluation of Thermal Head Contamination> Next, for each of the produced thermal recording media of each example and each comparative example, a commercially available thermal printer (manufactured by Teraoka Seiko Co., Ltd., product name: HP - 3600) was used, and continuous printing of 20 m was performed under the conditions of a printing speed of 100 mm / sec and a duty of 53%. Then, the presence or absence of contamination of the thermal head after printing was visually evaluated. The above results are shown in Table 1.

[0050] <Evaluation of Thermal Head Wear> Also, in the thermal recording media of each example and each comparative example, using a shape analysis laser microscope (manufactured by Keyence Corporation, product name: VK - X1000), the height H before the above - mentioned 20 m continuous printing in the heat - generating zone at a predetermined position of the thermal head 1and the height H after 500 consecutive printings 2 Measure them, and calculate the difference in their heights (H 2 - H 1 ). Based on the following criteria, evaluate the wear of the thermal head after printing. The above results are shown in Table 1. ○: The difference in height (H 2 - H 1 ) is 0.3 μm or less ×: The difference in height (H 2 - H 1 ) is greater than 0.7 μm

[0051] Note that, as described later, in Comparative Example 1, contamination of the thermal head and sticking between the thermal recording medium and the thermal head occurred, so the wear evaluation of the thermal head was not performed.

[0052] Also, as described later, in Comparative Examples 2 and 5, contamination of the thermal head occurred, so the wear evaluation of the thermal head was not performed.

[0053] <Sticking Evaluation> Also, in the thermal recording media of each example and each comparative example, after printing at the maximum applied energy using a direct thermal printer (manufactured by Teraoka Seiko Co., Ltd., product name: ALP - 750), observe the printed area using a microscope, and evaluate the sticking between the thermal recording medium and the thermal head based on the following criteria. The above results are shown in Table 1.

[0054] ○: No distortion or peeling occurred in the printed area ×: Distortion or peeling occurred in the printed area

[0055]

Table 1

[0056] As shown in Table 1, it can be seen that in the thermal recording media of Examples 1 to 5 in which the content of the lubricants (paraffin and zinc stearate) with respect to the entire thermal recording layer is 30% by mass or less, contamination of the thermal head can be prevented during printing. Further, since the content of the pigment (calcium carbonate) with respect to the entire thermal recording layer is 24% by mass or more and 43% by mass or less, it can be seen that contamination of the thermal head can be prevented without causing wear of the thermal head.

[0057] On the other hand, in Comparative Example 1, since the content of paraffin is high, it can be seen that contamination (white contamination) of the thermal head due to paraffin has occurred.

[0058] Further, in Comparative Example 2, since paraffin is not contained, adhesion of deposits (carbides, etc.) due to the color former cannot be prevented, and it can be seen that contamination (black contamination) of the thermal head due to the deposits has occurred.

[0059] Further, in Comparative Examples 3 to 4, since the content of calcium carbonate is high, it can be seen that the heat generating zone of the thermal head has been scraped and worn by hard calcium carbonate.

[0060] Further, in Comparative Examples 1 and 3, since zinc stearate is not contained, it can be seen that sticking has occurred between the thermal recording medium and the thermal head.

[0061] Further, in Comparative Example 5, since the content of the lubricants (paraffin and zinc stearate) with respect to the entire thermal recording layer is more than 30% by mass and the content of paraffin is high, it can be seen that contamination (white contamination) of the thermal head due to paraffin has occurred.

Industrial Applicability

[0062] As described above, the present invention is particularly useful for a thermal recording medium not provided with a top coat layer.

Explanation of Signs

[0063] 1 Thermal recording medium 2 Substrate 3 Thermal recording layer 4 Undercoat layer 10 Thermal recording medium

Claims

1. A thermal recording medium having a thermal recording layer laminated on a substrate, not provided with an intermediate layer and a top coat layer, and the thermal recording layer being exposed, wherein the thermal recording layer contains paraffin and zinc stearate as lubricants, the thermal recording layer contains calcium carbonate as a pigment, the content of the lubricant with respect to the whole of the thermal recording layer is 10% by mass or more and 30% by mass or less, and the content of the calcium carbonate with respect to the whole of the thermal recording layer is 38% by mass or more and 43% by mass or less. A thermal recording medium characterized by this.

2. The thermal recording medium according to claim 1, characterized in that an undercoat layer is provided between the substrate and the thermal recording layer.

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