A two-color erasable thermal paper and its preparation method

Abstract

This invention relates to a two-color erasable thermal paper and its preparation method, belonging to the field of printing consumables technology. The two-color erasable thermal paper includes, from top to bottom, a protective layer, a thermal coating layer, a base layer, and a substrate. The components of the thermal coating layer, by weight, include: 10-20 parts of filler B, 20-40 parts of color developer, 30-50 parts of adhesive resin B, 10-20 parts of dye, and 10-20 parts of temperature-regulating agent. The addition of a temperature-regulating agent to the thermal coating layer of this invention enables reversible erasing and writing, while improving its color retention performance, eliminating the need for sensitizers. The heat-insulating filler used in the base layer layer of this invention is a high-hollow-ratio material, which can enhance heat insulation and improve the heat resistance and sensitivity of the thermal two-color reversible erasable paper.

Description

Technical Field

[0001] This invention relates to the field of printing consumables technology, specifically to a two-color erasable thermal paper and its preparation method. Background Technology

[0002] Thermal paper was first developed by 3M in the 1850s. With the continuous development of thermal technology, coating technology, and printing equipment, as well as changes in the market and industry, it is now widely used in various scenarios related to people's daily lives, especially in variable information fields such as shopping mall checkouts, entertainment tickets, supermarket labels, express delivery labels, medical electrocardiogram charts, movie tickets, boarding passes, and warehousing and logistics transportation. Ordinary thermal paper generally consists of three layers: the bottom layer is the paper base layer, the second layer is the thermal coating layer, and the third layer is the thin film protective layer. The thermal layer generally contains two substances: one is a colorless dye, also known as a latent dye, which is a colorless or nearly colorless solid that develops color when it encounters acid or electron acceptor compounds; the other is a color developer, which reacts with the colorless dye under heating conditions to produce a color reaction, thus recording information. However, currently, the vast majority of thermal paper is used for single purposes. When these thermal papers used to record text or images are no longer needed, they are treated as garbage or waste, resulting in a huge waste of resources and pollution to the environment.

[0003] Currently, erasable information storage for identification cards utilizes thermal erasable technology, but its single-color design fails to meet office needs. While dual-color irreversible thermal technology is relatively mature, its disposable nature exacerbates environmental pollution and resource waste, limiting its widespread use. Therefore, developing dual-color thermal erasable paper to enrich its application scenarios is of great significance. In view of this, this invention provides a dual-color erasable thermal paper and its preparation method. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a two-color erasable thermal paper and its preparation method. The aim is to provide a reversible red and black two-color thermal erasable paper that can significantly improve the color density of the color layer at low printing density.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] In a first aspect, a two-color erasable thermal paper is provided, wherein the two-color erasable thermal paper includes a protective layer, a thermal coating layer, a base coating layer and a substrate arranged from top to bottom;

[0007] The components of the protective layer, by weight, include: 20-40 parts of filler A, 8-15 parts of lubricant, 8-15 parts of thermal conductive agent, and 20-40 parts of adhesive resin A;

[0008] The components of the thermosensitive coating, by weight, include: 10-20 parts of filler B, 20-40 parts of color developer, 30-50 parts of adhesive resin B, 10-20 parts of dye, and 10-20 parts of temperature-regulating agent.

[0009] The components of the base coating, by weight, include: 30-50 parts of thermal insulation filler, 30-55 parts of adhesive resin C, and 10-30 parts of filler C.

[0010] The beneficial effects of this invention are as follows: the addition of a temperature-regulating agent to the thermal coating of this invention enables reversible erasure and writing while improving its color retention performance; the color developer, combined with a certain proportion of temperature-regulating agent, eliminates the need for a sensitizer; the heat-insulating filler used in the base coating of this invention is a high-hollow material, which can enhance heat insulation and improve the heat resistance and sensitivity of the thermal dual-color reversible erasure paper.

[0011] Based on the above technical solution, the present invention can be further improved as follows.

[0012] Furthermore, the thermal coating comprises a red thermal coating and a black thermal coating disposed sequentially; the red thermal coating is disposed between the black thermal coating and the protective layer;

[0013] The red thermosensitive coating comprises, by weight, 10-20 parts of filler B, 20-40 parts of color developer, 30-50 parts of adhesive resin B, 10-20 parts of red dye, and 10-20 parts of temperature-regulating agent.

[0014] The components of the black thermosensitive coating, by weight, include: 10-20 parts of filler B, 20-40 parts of color developer, 30-50 parts of adhesive resin B, and 10-20 parts of black dye.

[0015] Furthermore, the filler B includes at least one of aluminum hydroxide, light calcium carbonate, porcelain clay, silica, and kaolin.

[0016] The color-developing agent is an alkylphenol, wherein the alkyl chain length of the alkylphenol is 12-37, the number of phenyl groups is 1-2, and the number of phenolic hydroxyl groups on each phenyl group is 1-2. The phenol and the alkyl group can be linked by carboxyl, amide, or urea groups. Where P = 12~37;

[0017] The adhesive resin B includes at least one of polyvinyl alcohol (PVA), polyurethane, and polyacrylic acid resin;

[0018] The temperature-regulating agent includes one or two of monoaromatic amides, polyaromatic amides, and pyrrolidine amide derivatives; the alkyl chain length in the temperature-regulating agent is 12-45, and the number of phenyl or tetrahydropyrroles is 1-3; the alkyl chain and the benzene or tetrahydropyrrole are linked by amide or urea.

[0019] The beneficial effect of adopting the above-mentioned further solution is that it allows red to be printed at a lower print density while black remains unseen, thus achieving two-color writing.

[0020] Furthermore, the temperature-regulating agent comprises at least one of formulas I to VIII: In equations I to VIII, n ranges from 12 to 45.

[0021] Furthermore, the red layer dye includes at least one of scarlet, peach, and orange-red; its structural formula is as follows:

[0022]

[0023] The black layer dye includes at least one of ODB2, s205, and b15; its structural formula is as follows:

[0024] .

[0025] Furthermore, the filler A includes at least one of TiO2, ZnO, SiO2, and Fe2O3;

[0026] The lubricant includes at least one of zinc stearate, calcium stearate, and magnesium stearate;

[0027] The thermal conductive agent includes at least one of polyethylene wax emulsion, zinc oxide (ZnO), magnesium oxide (MgO), and titanium dioxide;

[0028] The adhesive resin A includes at least one of PVA, acrylic resin, vinyl chloride, and ethylene-vinyl acetate copolymer.

[0029] The beneficial effect of adopting the above-mentioned further solutions is that the overall printing density requirement is reduced.

[0030] Furthermore, the insulating filler includes at least one of glass microspheres, expanded polystyrene, and polyurethane foam;

[0031] The adhesive resin C includes at least one of PVA, acrylic resin, vinyl chloride, and ethylene-vinyl acetate copolymer;

[0032] The filler C includes at least one of calcium carbonate, montmorillonite, and hydrotalcite.

[0033] The beneficial effects of adopting the above-mentioned further solutions are: further improving heat utilization efficiency and achieving low-energy printing.

[0034] Furthermore, the substrate includes at least one of PVC substrate, white cardboard, grey board, coated paper, offset paper, corrugated paper, and kraft paper.

[0035] Furthermore, the thickness of the protective layer is 1-3 μm; the thickness of the thermosensitive coating is 3-6 μm; the thickness of the base coating is 1-2 μm; the thickness of the substrate is 100-130 μm; the thickness of the red thermosensitive coating is 3-7 μm; and the thickness of the black thermosensitive coating is 4-8 μm.

[0036] Secondly, a method for preparing two-color erasable thermal paper includes the following steps:

[0037] S1: Prepare the components of the base coating into a coating liquid, apply the coating liquid to the substrate, and dry it to obtain the base coating on the substrate;

[0038] S2: Prepare a coating liquid for red thermosensitive coating by taking the components of red thermosensitive coating; prepare a coating liquid for black thermosensitive coating by taking the components of black thermosensitive coating; coat the coating liquid for black thermosensitive coating and the coating liquid for red thermosensitive coating onto the base coating in sequence, and dry to obtain thermosensitive coating.

[0039] S3: Prepare the coating liquid of the protective layer by the components of the protective layer, coat it on the heat-sensitive coating, and dry it to obtain the protective layer;

[0040] S4: The substrate, base coating, thermal coating and protective layer are composited by hot pressing process to obtain two-color erasable thermal paper.

[0041] The advantages of adopting the above solution are: by leveraging the mature thermal paper technology, it is beneficial to reduce costs. Attached Figure Description

[0042] Figure 1 This is a physical image of a two-color erasable thermal paper according to the present invention;

[0043] Figure 2 This is a schematic diagram of the two-color erasable thermal paper of the present invention. Figure I ;

[0044] Figure 3 This is a schematic diagram of the two-color erasable thermal paper of the present invention. Figure II . Detailed Implementation

[0045] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0046] The raw materials used in the embodiments of this invention, except for the color developer and temperature-regulating agent, are all commercially available raw materials; the temperature-regulating agent is designed in-house.

[0047] The synthetic route of the color developer is as follows: octadecyl isocyanate and p-aminophenol are added to a beaker containing toluene, reacted in a water bath at 60°C until stirring is impossible, filtered, recrystallized, and dried to obtain the color developer.

[0048] The current method for synthesizing temperature-regulating agents involves adding octadecyl isocyanate and aminophenol to a beaker containing 100 mL of toluene, reacting them in a water bath at 60°C until they cannot be stirred, filtering, recrystallizing, and drying to obtain the temperature-regulating agent.

[0049] Example 1:

[0050] This embodiment relates to a two-color erasable thermal paper, which includes, from top to bottom, a protective layer, a thermal coating layer, a base coating layer, and a substrate (paper base layer); the thermal coating layer includes a red thermal coating layer and a black thermal coating layer arranged sequentially, with the red thermal coating layer disposed between the black thermal coating layer and the protective layer. Figure 1-3 );in:

[0051] The protective layer comprises, by weight, 20 parts calcium carbonate, 50 parts PVA resin, and 8 parts polyethylene wax emulsion;

[0052] The components of the red thermosensitive coating, by weight, include: 10 parts zinc oxide, 20 parts color developer, 25 parts PVA resin, 25 parts red pigment, and 20 parts octadecylureabenzene.

[0053] The components of the black heat-sensitive coating, by weight, include: 10 parts zinc oxide, 20 parts color developer, 25 parts PVA resin, and 25 parts ODB-2.

[0054] The base coating consists of 30 parts glass microspheres, 55 parts PVA resin, and 30 parts TiO2.

[0055] This embodiment also provides a method for preparing two-color erasable thermal paper, including the following steps:

[0056] S1: Prepare the components of the base coating into a coating liquid, apply the coating liquid to the substrate, and dry it to obtain the base coating on the substrate;

[0057] S2: Prepare a coating liquid for red thermosensitive coating by taking the components of red thermosensitive coating; prepare a coating liquid for black thermosensitive coating by taking the components of black thermosensitive coating; coat the coating liquid for black thermosensitive coating and the coating liquid for red thermosensitive coating onto the base coating in sequence, and dry to obtain thermosensitive coating.

[0058] S3: Prepare the coating liquid of the protective layer by the components of the protective layer, coat it on the heat-sensitive coating, and dry it to obtain the protective layer;

[0059] S4: A two-color erasable thermal paper is obtained by laminating a substrate, a base coating, a thermal coating, and a protective layer through a hot-pressing process. For example... Figure 1 This is a picture of a two-color erasable thermal paper.

[0060] The protective layer has a thickness of 2 μm; the thermosensitive coating has a thickness of 4 μm; the base coating has a thickness of 1.5 μm; the substrate has a thickness of 120 μm; the red thermosensitive coating has a thickness of 5 μm; and the black thermosensitive coating has a thickness of 5 μm.

[0061] Example 2:

[0062] This embodiment relates to a two-color erasable thermal paper, which includes a protective layer, a thermal coating layer, and a substrate (paper base layer) arranged from top to bottom; the thermal coating layer includes a red thermal coating layer and a black thermal coating layer arranged sequentially, with the red thermal coating layer disposed between the black thermal coating layer and the protective layer; wherein:

[0063] The components of the protective layer, by weight, include:

[0064] The protective layer comprises, by weight, 20 parts calcium carbonate, 50 parts PVA resin, and 8 parts polyethylene wax emulsion;

[0065] The components of the red thermosensitive coating, by weight, include: 10 parts zinc oxide, 20 parts color developer, 25 parts PVA resin, 25 parts red pigment, and 20 parts octadecylureabenzene.

[0066] The components of the black heat-sensitive coating, by weight, include: 10 parts zinc oxide, 20 parts color developer, 25 parts PVA resin, and 25 parts ODB-2.

[0067] This embodiment also provides a method for preparing two-color erasable thermal paper, including the following steps:

[0068] After the black thermal coating liquid is applied to the paper base and dried, the red thermal coating liquid is applied on the black thermal coating and dried, and then a protective layer is applied; finally, it is bonded together with the paper base, color layer and protective layer through a hot pressing process.

[0069] The protective layer has a thickness of 2 μm; the thermosensitive coating has a thickness of 4 μm; the substrate has a thickness of 120 μm; the red thermosensitive coating has a thickness of 5 μm; and the black thermosensitive coating has a thickness of 5 μm. Example 3:

[0070] This embodiment relates to a two-color erasable thermal paper, which includes a thermal coating layer, a base coating layer, and a substrate (paper base layer) arranged from top to bottom; the thermal coating layer includes a red thermal coating layer and a black thermal coating layer arranged sequentially, with the red thermal coating layer disposed between the black thermal coating layer and a protective layer; wherein:

[0071] The components of the red thermosensitive coating, by weight, include:

[0072] The components of the red thermosensitive coating, by weight, include: 10 parts zinc oxide, 20 parts color developer, 25 parts PVA resin, 25 parts red pigment, and 20 parts octadecylureabenzene.

[0073] The components of the black heat-sensitive coating, by weight, include: 10 parts zinc oxide, 20 parts color developer, 25 parts PVA resin, and 25 parts ODB-2.

[0074] The base coating consists of 30 parts glass microspheres, 55 parts PVA resin, and 30 parts TiO2.

[0075] This embodiment also provides a method for preparing two-color erasable thermal paper, including the following steps:

[0076] The base coat is applied to the paper substrate and dried to obtain the base coat. Then, the obtained black thermal coating liquid is applied to the base coat and dried to obtain the color layer. Next, the red thermal coating liquid is applied to the black thermal coating and dried. Finally, the base coat, the paper substrate, and the color layer are bonded together through a hot pressing process.

[0077] The thickness of the thermal coating is 4 μm; the thickness of the base coating is 1.5 μm; the thickness of the substrate is 120 μm; the thickness of the red thermal coating is 5 μm; and the thickness of the black thermal coating is 5 μm.

[0078] Example 4:

[0079] This embodiment relates to a two-color erasable thermal paper, which includes a thermal coating and a substrate (paper base layer) arranged from top to bottom; the thermal coating includes a red thermal coating and a black thermal coating arranged sequentially, with the red thermal coating disposed between the black thermal coating and a protective layer; wherein:

[0080] The components of the red thermosensitive coating, by weight, include:

[0081] The components of the red thermosensitive coating, by weight, include: 10 parts zinc oxide, 20 parts color developer, 25 parts PVA resin, 25 parts red pigment, and 20 parts octadecylureabenzene.

[0082] The components of the black heat-sensitive coating, by weight, include: 10 parts zinc oxide, 20 parts color developer, 25 parts PVA resin, and 25 parts ODB-2.

[0083] This embodiment also provides a method for preparing two-color erasable thermal paper, including the following steps:

[0084] The components of the red thermosensitive coating are prepared into a coating liquid for the red thermosensitive coating; the components of the black thermosensitive coating are prepared into a coating liquid for the black thermosensitive coating; the coating liquid for the red thermosensitive coating and the coating liquid for the black thermosensitive coating are sequentially coated onto a paper substrate and dried to obtain a thermosensitive coating.

[0085] Two-color erasable thermal paper is obtained by combining the paper base layer with the thermal coating through a hot-pressing process.

[0086] The thickness of the thermal coating is 4 μm; the thickness of the substrate is 120 μm; the thickness of the red thermal coating is 5 μm; and the thickness of the black thermal coating is 5 μm.

[0087] Comparative Example 1:

[0088] The difference from Example 1 is whether or not polyethylene wax is added to the protective layer; otherwise, it is the same as Example 1.

[0089] Comparative Example 2:

[0090] The difference from Example 1 is that the temperature regulating agent is changed to 10 parts; the rest are the same as in Example 1.

[0091] Comparative Example 3:

[0092] The difference between Example 4 and Example 2 is the presence or absence of polyethylene wax in the protective layer; otherwise, they are the same as Example 2. Comparative Example 4:

[0093] The difference from Example 2 is that the temperature regulating agent is changed to 10 parts; the rest are the same as in Example 2.

[0094] Comparative Example 5:

[0095] The difference from Example 3 is that the temperature regulating agent is changed to 10 parts; the rest are the same as in Example 3.

[0096] Comparative Example 6:

[0097] The difference from Example 4 is that the temperature regulating agent is changed to 10 parts; the rest are the same as in Example 4.

[0098] Experimental example:

[0099] (1) Method for detecting static saturated color density:

[0100] Calibrate the reflectance densitometer according to the instrument manufacturer's instructions, then heat the static colorimeter, gradually increasing the temperature from low to high. Use 70°C as the starting temperature, with each 10°C increment as a heating interval. Once the desired temperature is reached and stabilized, place the sample flat on the heating plate of the static colorimeter, with the colored side of the sample facing the heating plate. Cover with the upper pressure plate and start timing simultaneously. After heating for 10 seconds, remove the sample. At least three samples of each type should be colored at each temperature. After the statically colored samples have been placed for 120 minutes, measure the optical density using the reflectance densitometer. Measure three samples of each type, taking measurements at three points on each sample. The average of the nine measurements is used to represent the optical density value of that type of sample. When the optical density value of the sample reaches its maximum, it indicates saturated color development, and the corresponding color development temperature is the static saturated color development temperature of that type of sample.

[0101] (2) Static saturated color density after 3 hours of ethanol protection test: First, place the sample on a flat glass plate with the colored side facing up. Then, place the liquid collector on each saturated colored sample and add 1.0 mL of ethanol to the liquid collector. After placing the sample at room temperature for 3 hours, remove the liquid collector from the sample and gently absorb the ethanol remaining on the sample surface with filter paper. After drying the sample with a hairdryer in cold air, measure its optical density value.

[0102] (3) Method for detecting image retention rate; by using 80℃ and 1kgf / cm 2 Under pressure, using a heat gun, heat the image for 1 second, (erased image color density value / original color density) * 100%.

[0103] (4) Testing of reversible erasure and rewrite performance

[0104] Zebra printer with a density of 30 write, through 140℃ and 1kgf / cm 2 Under pressure, using a heat gun, the image is erased after heating for 1 second. If the retention rate is less than 10%, it indicates that the reversibility was successfully achieved once.

[0105] Note: Except for (4), which is a self-defined standard, (1), (2), and (3) are based on GB / T 28210—2011.

[0106] Table 1 Performance comparison of Example 1 and Comparative Examples 1 and 2

[0107]

[0108] As can be seen from Table 1, adding polyethylene wax to the protective layer will reduce the color density, and reducing the amount of temperature-regulating additives will reduce the design density.

[0109] Table 2 Performance comparison of Example 2 and Comparative Examples 3-4

[0110]

[0111] Table 3 Performance comparison of Example 3 and Comparative Example 5

[0112]

[0113] As can be seen from Table 3, reducing the temperature-regulating additive will significantly reduce the durability of thermal paper. A comparison of Tables 1, 2 and 3 shows that without a protective layer, the initial color density decreases, but the durability decreases very significantly.

[0114] Table 4 Performance comparison of Example 4 and Comparative Example 6

[0115]

[0116] As can be seen from Table 4, reducing the temperature-regulating additives will significantly reduce the durability of thermal paper. A comparison of Tables 1, 2, 3 and 4 shows that the absence of a protective layer and a base coating significantly reduces the durability of thermal paper.

[0117] In summary, the addition of a temperature-regulating agent to the thermal coating of this invention enables reversible erasure and writing while improving its color retention performance; the use of a color developer in combination with a certain proportion of temperature-regulating agent eliminates the need for a sensitizer; the heat-insulating filler used in the base coating of this invention is a high-hollow material, which can enhance heat insulation and improve the heat resistance and sensitivity of the thermal dual-color reversible erasure paper.

[0118] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0119] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A two-color erasable thermal paper, characterized in that, The two-color erasable thermal paper includes, from top to bottom, a protective layer, a thermal coating layer, a base coating layer, and a substrate; The components of the protective layer, by weight, include: 20-40 parts of filler A, 30-50 parts of adhesive resin A, 8-15 parts of lubricant, and 8-15 parts of thermal conductive agent; The thermal coating comprises a red thermal coating and a black thermal coating arranged sequentially, with the red thermal coating disposed between the black thermal coating and the protective layer; the thermal coating does not include a sensitizer. The red thermosensitive coating components, by weight, include: 10-20 parts filler B, 20-40 parts color developer, 30-50 parts adhesive resin B, 10-20 parts red dye, and 10-20 parts temperature-regulating agent. The components of the black heat-sensitive coating, by weight, include: 10-20 parts of filler B, 20-40 parts of color developer, 30-50 parts of adhesive resin B, and 10-20 parts of black dye. The components of the base coating, by weight, include: 30-50 parts of thermal insulation filler, 30-55 parts of adhesive resin C, and 10-30 parts of filler C; The color developer is an alkylphenol, wherein the alkyl chain length of the alkylphenol is 12-37, the number of phenyl groups is 1 or 2, the number of phenolic hydroxyl groups on each phenyl group is 1 or 2, and the phenol and the alkyl group are connected by carboxyl, amide or urea groups. The temperature-regulating agent includes one or two of monoaromatic amides, polyaromatic amides, and pyrrolidine amide derivatives; the alkyl chain length in the temperature-regulating agent is 12-45 cm, and the number of phenyl or tetrahydropyrroles is 1-3; the alkyl chain and the benzene or tetrahydropyrrole are linked by amides or ureas; The thermal conductive agent includes at least one of polyethylene wax emulsion, ZnO, and MgO.

2. The two-color erasable thermal paper according to claim 1, characterized in that, The filler B includes at least one of aluminum hydroxide, light calcium carbonate, porcelain clay, silicon dioxide, and kaolin. The adhesive resin B includes at least one of polyvinyl alcohol, polyurethane, and polyacrylate.

3. The two-color erasable thermal paper according to claim 2, characterized in that, The temperature-regulating agent comprises at least one of formulas I to VIII: , In equations I to VIII, the values ​​of n range from 12 to 45.

4. The two-color erasable thermal paper according to claim 1, characterized in that, The red layer dye includes at least one of scarlet, peach, and orange; the black layer dye includes at least one of ODB2, S205, and b15.

5. The two-color erasable thermal paper according to claim 1, characterized in that, The filler A includes at least one of TiO2, ZnO, SiO2, and Fe2O3; The lubricant includes at least one of zinc stearate, calcium stearate, and magnesium stearate; The adhesive resin A includes at least one of PVA, polyacrylic acid resin, vinyl chloride, and ethylene-vinyl acetate copolymer.

6. The two-color erasable thermal paper according to claim 1, characterized in that, The thermal insulation filler includes at least one of glass microspheres, expanded polystyrene and polyurethane foam; The adhesive resin C includes at least one of PVA, acrylic resin, vinyl chloride, and ethylene-vinyl acetate copolymer; The filler C includes at least one of titanium dioxide, calcium carbonate, and zinc oxide.

7. The two-color erasable thermal paper according to claim 1, characterized in that, The substrate includes any one of PVC substrate, white cardboard, grey board, coated paper, offset paper, corrugated paper, and kraft paper.

8. The two-color erasable thermal paper according to claim 1, characterized in that, The thickness of the protective layer is 1-3 μm; the thickness of the thermosensitive coating is 3-6 μm; the thickness of the base coating is 1-2 μm; the thickness of the substrate is 100-130 μm; the thickness of the red thermosensitive coating is 3-7 μm; and the thickness of the black thermosensitive coating is 4-8 μm.

9. A method for preparing a two-color erasable thermal paper according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1: Prepare the components of the base coating into a coating liquid, apply the coating liquid to the substrate, and dry it to obtain the base coating on the substrate; S2: Prepare a coating liquid for red thermosensitive coating by taking the components of red thermosensitive coating; prepare a coating liquid for black thermosensitive coating by taking the components of black thermosensitive coating; coat the coating liquid for black thermosensitive coating and the coating liquid for red thermosensitive coating onto the base coating in sequence, and dry to obtain thermosensitive coating. S3: Prepare the coating liquid of the protective layer by the components of the protective layer, coat it on the heat-sensitive coating, and dry it to obtain the protective layer; S4: The substrate, base coating, thermal coating and protective layer are composited by hot pressing process to obtain two-color erasable thermal paper.

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