Erasable color thermal paper and method for producing the same

Abstract

The present application relates to a kind of erasable color thermosensitive paper and its preparation method, erasable color thermosensitive paper includes protective layer, thermosensitive coating and substrate layer, thermosensitive coating includes yellow thermosensitive coating, first intermediate layer, magenta thermosensitive coating, second intermediate layer and cyan thermosensitive coating from top to bottom sequentially, yellow thermosensitive coating is equipped with the protective layer, cyan thermosensitive coating is arranged on substrate layer;Yellow thermosensitive coating, magenta thermosensitive coating, cyan thermosensitive coating between the color development temperature difference is not less than 25 DEG C;Yellow thermosensitive coating, magenta thermosensitive coating and cyan thermosensitive coating are all added with heat-conducting aid.The erasable color thermosensitive paper of the present application, heat is isolated by intermediate layer;By making the color development temperature difference of yellow thermosensitive coating, the magenta thermosensitive coating, the cyan thermosensitive coating not less than 25 DEG C, full-color printing can be realized by superimposing three colors;By adding heat-conducting aid of different particle sizes, more efficient erasing effect is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field related to printing consumables, and in particular to erasable color thermal paper and a preparation method thereof. Background Art

[0002] Thermal recording compounds are formed by the color reaction between electron-donating color-forming compounds (leuco dyes) and electron-accepting compounds (developers). With the continuous development of thermal technology, coating technology, and printing equipment, they have now been widely used in various scenarios of people's food, clothing, housing, transportation, and work. Especially in variable information fields such as shopping mall cashiers, entertainment tickets, supermarket labels, express delivery labels, medical electrocardiograms, movie tickets, boarding passes, warehousing and logistics transportation, they have a large market size.

[0003] Color, non-erasable thermal paper is already commercially available. Zink paper consists of a layer of crystals containing yellow, magenta, and cyan dyes, a protective surface coating, and a paper base. This paper enables truly inkless printing. Zink paper is produced by paper mills as large-format rolls and then cut into various sizes and specifications according to user needs. Zink paper can also be processed onto plastic sheets and self-adhesive backings, offering a wide range of applications. The specialized paper contains crystals containing yellow, magenta, and cyan dyes that change color when heated, resulting in the appearance of different colors on the paper. However, Zink paper cannot be reused, and discarded photos pollute the environment and waste resources. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the current commercial inkless printing paper is a disposable product, which is not environmentally friendly and wastes resources. In order to solve this technical problem, the present invention provides a rewritable color thermal paper and a preparation method thereof.

[0005] The present invention solves the above-mentioned technical problem with the following technical solution: a rewritable color thermal paper comprising a protective layer, a thermal coating layer, and a substrate layer, wherein the thermal coating layer comprises a yellow thermal coating layer, a first intermediate layer, a magenta thermal coating layer, a second intermediate layer, and a cyan thermal coating layer, arranged in order from top to bottom; the protective layer is provided on the yellow thermal coating layer, and the cyan thermal coating layer is provided on the substrate layer; the color development temperature difference between the yellow thermal coating layer, the magenta thermal coating layer, and the cyan thermal coating layer is not less than 25°C;

[0006] Heat-conducting additives are added to the yellow heat-sensitive coating, the magenta heat-sensitive coating and the cyan heat-sensitive coating.

[0007] The beneficial effects of the present invention are as follows: the erasable color thermal paper of the present invention can achieve efficient monochrome printing by isolating heat through the intermediate layer; by making the color development temperature difference of the yellow thermal coating, the magenta thermal coating, and the cyan thermal coating not less than 25° C., full-color printing can be achieved by superimposing the three colors; and by adding thermal conductive additives of different particle sizes, a more efficient erasing effect is obtained.

[0008] On the basis of the above technical solution, the present invention can also be improved as follows.

[0009] Furthermore, the thermal conductive agent is at least one of magnesium oxide, zinc oxide, aluminum oxide and boron nitride; and the particle size of the thermal conductive agent is 1 to 20 μm.

[0010] The beneficial effect of adopting the above further solution is that by providing a thermal conductive agent and controlling the particle size of the thermal conductive agent, various colors with higher color density and clarity can be stacked, and the erasing effect is better.

[0011] Furthermore, the single-color printing time of the yellow thermosensitive coating and the magenta thermosensitive coating is less than 100ms. The single-color printing time of the yellow thermosensitive coating is the shortest, and the single-color printing time of the magenta thermosensitive coating is shorter than the single-color printing time of the cyan thermosensitive coating.

[0012] Furthermore, a first temperature regulating agent is added to the magenta heat-sensitive coating, and a second temperature regulating agent is added to the cyan heat-sensitive coating. The difference in melting points between the first temperature regulating agent and the second temperature regulating agent is not less than 25°C.

[0013] The beneficial effect of adopting the above-mentioned further scheme is that the color development temperature of the yellow thermal-sensitive coating, magenta thermal-sensitive coating and cyan thermal-sensitive coating can be adjusted to high, medium and low by adding a temperature regulating agent, yellow monochrome printing can be achieved by short-term high-temperature heating, magenta monochrome printing can be achieved by short-term medium-temperature heating, and cyan monochrome printing can be achieved by low-temperature heating. At the same time, full-color printing can be achieved by superimposing three colors.

[0014] Furthermore, the first temperature regulating auxiliary agent and the second temperature regulating auxiliary agent are respectively at least one of naphthyl urea compounds, naphthyl amide compounds, naphthyl ester compounds, and naphthyl amino acid ester compounds.

[0015] Furthermore, the yellow heat-sensitive coating, the magenta heat-sensitive coating, and the cyan heat-sensitive coating all include a developer, and the developer has the following structure: Where p=12~37.

[0016] Furthermore, the yellow thermosensitive coating includes a yellow thermosensitive dye, and the yellow thermosensitive dye is at least one of the following structures:

[0017] Or / and, the magenta thermosensitive coating comprises a magenta thermosensitive dye, and the magenta thermosensitive dye is at least one of the following structures:

[0018] Or / and, the cyan thermosensitive coating includes a cyan thermosensitive dye, and the cyan thermosensitive dye is at least one of the following structures:

[0019] Preferably, the color of the red thermosensitive dye is at least one of orange and pink.

[0020] The beneficial effects of adopting the above further solution are: under heating conditions, the dye and the color developer are mixed to produce a color development reaction, the particle size of the thermal conductive additive is controlled, and color printing with higher color density and efficient erasing effects are achieved.

[0021] Furthermore, the yellow thermosensitive coating comprises the following raw materials in parts by weight: 10 to 45 parts of a developer, 2 to 15 parts of a yellow thermosensitive dye, 30 to 50 parts of an adhesive, 20 to 30 parts of a polyamide curing agent, and 1 to 20 parts of a thermal conductive agent, wherein the particle size of the thermal conductive agent is 1 to 20 μm;

[0022] The magenta heat-sensitive coating comprises the following raw materials in parts by weight: 10 to 45 parts of a developer, 2 to 15 parts of a red heat-sensitive dye, 30 to 50 parts of an adhesive, 20 to 30 parts of a polyamide curing agent, 1 to 20 parts of a thermal conductive agent, and 2 to 15 parts of a temperature regulating agent, wherein the particle size of the thermal conductive agent is 1 to 20 μm.

[0023] The cyan thermosensitive coating comprises the following raw materials in parts by weight: 10 to 45 parts of a developer, 2 to 15 parts of a cyan thermosensitive dye, 30 to 50 parts of an adhesive, 20 to 30 parts of a polyamide curing agent, 1 to 20 parts of a thermal conductive agent, and 2 to 15 parts of a temperature regulating agent, wherein the particle size of the thermal conductive agent is 1 to 20 μm.

[0024] The protective layer comprises the following raw materials in parts by weight: 10 to 50 parts of thermal conductive additive, 1 to 10 parts of anti-ultraviolet additive, 1 to 5 parts of lubricant, 30 to 80 parts of adhesive resin, and 40 to 60 parts of polyurethane curing agent. The particle size of the thermal conductive additive is 1 to 10 μm.

[0025] The first intermediate layer comprises the following raw materials in parts by weight: 10 to 50 parts of thermal insulation additive, 30 to 80 parts of adhesive resin, and 40 to 60 parts of polyurethane curing agent;

[0026] The second intermediate layer comprises the following raw materials in parts by weight: 10-50 parts of thermal insulation additive, 30-80 parts of adhesive resin, and 40-60 parts of polyurethane curing agent;

[0027] The substrate layer is at least one of coated paper, white cardboard, kraft paper, offset paper, glassine paper, stone paper, and PVC paperboard;

[0028] In the yellow heat-sensitive coating, the magenta heat-sensitive coating, and the cyan heat-sensitive coating, the adhesive comprises at least one of epoxy resin, polyurethane, and acrylate respectively;

[0029] In the protective layer, the anti-ultraviolet additive includes at least one of salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, and triazines; the lubricant includes at least one of zinc stearate, mineral lubricants, silicone oil, fatty acid amide, oleic acid, polyester, synthetic ester, and carboxylic acid; and the adhesive resin includes at least one of PVA, polyacrylate, and polyurethane.

[0030] In the first intermediate layer and the second intermediate layer, the adhesive resin includes at least one of PVA, polyacrylate and polyurethane; the thermal insulation auxiliary agent includes at least one of glass fiber, montmorillonite, rare earth heat-resistant agent, porous silica, porous titanium dioxide, porous carbon, their composites or the like.

[0031] The beneficial effect of adopting the above further solution is that by limiting the components of the protective layer, the heat conduction effect is ensured while reducing the cost.

[0032] By limiting the components of the yellow thermal coating, a higher color density of yellow can be achieved, avoiding the insufficient yellow density in current thermal photographic paper. By limiting the components of the magenta thermal coating, a higher color density of magenta can be achieved, avoiding the insufficient magenta density in current thermal photographic paper. By limiting the components of the cyan thermal coating, a higher color density of cyan can be achieved, avoiding the insufficient cyan density in current thermal photographic paper. This facilitates the printing of separate yellow, magenta, and cyan colors, and facilitates the printing of high-density yellow, magenta, and cyan colors.

[0033] By limiting the components of the middle layer, a heat-insulating effect is achieved, which prevents the magenta thermal-sensitive coating from developing color when yellow is printed at high temperature.

[0034] Furthermore, the thickness of the yellow heat-sensitive coating is 5 to 8 μm; the thickness of the magenta heat-sensitive coating is 6 to 10 μm; and the thickness of the cyan heat-sensitive coating is 8 to 14 μm.

[0035] The thickness of the protective layer is 1 to 3 μm; the thickness of the first intermediate layer is 2 to 6 μm; the thickness of the second intermediate layer is 2 to 6 μm; and the thickness of the base material layer is 100 to 140 μm.

[0036] A method for preparing the above-mentioned erasable color thermal paper comprises the following steps:

[0037] S1: preparing a yellow heat-sensitive coating liquid, a magenta heat-sensitive coating liquid, a cyan heat-sensitive coating liquid, a protective liquid, a first intermediate layer coating liquid, and a second intermediate layer coating liquid;

[0038] S2: applying a cyan thermal-sensitive coating liquid on one side of the substrate layer, and then drying to form a cyan thermal-sensitive coating layer; applying a second intermediate layer coating liquid on the cyan thermal-sensitive coating layer, and then drying to form a second intermediate layer; applying a magenta thermal-sensitive coating liquid on the second intermediate layer, and then drying to form a magenta thermal-sensitive coating layer; applying a first intermediate layer coating liquid on the magenta thermal-sensitive coating layer, and then drying to form a first intermediate layer; applying a yellow thermal-sensitive coating liquid on the first intermediate layer, and then drying to form a yellow thermal-sensitive coating layer; finally, applying a protective liquid on the red thermal-sensitive coating layer, and drying to form a protective layer;

[0039] S3: Compounding the substrate layer, the cyan thermal-sensitive coating, the second intermediate layer, the magenta thermal-sensitive coating, the first intermediate layer, the yellow thermal-sensitive coating, and the protective layer through a hot pressing process to obtain a color erasable thermal paper.

[0040] The beneficial effects of the present invention are as follows: the erasable color thermal paper prepared by the preparation method of the present invention has only a slight deviation in its color coordinates after repeated erasure 100 times, and can be reused many times, which greatly saves resources, reduces pollution and is environmentally friendly. In addition, the existing inkless printing paper has insufficient color vividness and low erasing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the layered structure of the erasable color thermal paper of the present invention.

[0042] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0043] 1. Base material layer; 2. Cyan thermal-sensitive coating; 3. Second intermediate layer; 4. Magenta thermal-sensitive coating; 5. First intermediate layer; 6. Yellow thermal-sensitive coating; 7. Protective layer. DETAILED DESCRIPTION

[0044] The principles and features of the present invention are described below. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this field or the product instructions are used. Where the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be purchased through regular channels.

[0045] The raw materials used in the embodiments of the present invention can all be purchased commercially. The color developer and the temperature control auxiliary agent can also be purchased commercially or synthesized using the following method.

[0046] The optional synthesis route of the color developer is: 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.

[0047] An optional synthesis method for the currently used temperature-regulating agent octadecylureidophenol is as follows: octadecyl isocyanate and aminophenol are added to a beaker containing 100 mL of toluene, reacted in a water bath at 60°C until stirring is impossible, filtered, recrystallized, and dried to obtain the temperature-regulating agent.

[0048] An optional synthesis method for the currently used temperature-regulating agent naphthyl octadecyl ester is as follows: 1-naphthylamine and octadecyl isocyanate are dissolved in 100 mL of toluene, reacted in a water bath at 60°C until stirring is impossible, filtered, recrystallized, and dried to obtain the temperature-regulating agent.

[0049] Example 1

[0050] This embodiment relates to a rewritable color thermal paper, such as Figure 1 As shown, the device comprises a protective layer 7, a thermosensitive coating layer, and a substrate layer 1. The thermosensitive coating layer comprises, from top to bottom, a yellow thermosensitive coating layer 6, a first intermediate layer 5, a magenta thermosensitive coating layer 4, a second intermediate layer 3, and a cyan thermosensitive coating layer 2. The protective layer 7 is provided on the yellow thermosensitive coating layer 6, and the cyan thermosensitive coating layer 2 is provided on the substrate layer 1. The color development temperature difference between the yellow thermosensitive coating layer 6, the magenta thermosensitive coating layer 4, and the cyan thermosensitive coating layer 2 is no less than 25°C. A thermal conductive agent is added to each of the yellow thermosensitive coating layer 6, the magenta thermosensitive coating layer 4, and the cyan thermosensitive coating layer 2. The single-color printing time of the yellow thermosensitive coating layer 6 and the magenta thermosensitive coating layer 4 is less than 100ms.

[0051] The substrate layer is made of 80g coated paper.

[0052] In parts by weight, the protective layer 7 comprises: 5 parts of benzotriazole as an anti-ultraviolet additive, 3 parts of talc as a solid lubricant, 75 parts of epoxy resin adhesive, 50 parts of polyurethane curing agent, and 5 parts of boron nitride (particle size 5 μm); the thickness is controlled at 3 μm;

[0053] In parts by weight, the yellow thermosensitive coating 6 comprises: 36 parts of developer, 9 parts of yellow thermosensitive dye, 30 parts of epoxy resin adhesive, 30 parts of polyamide curing agent and 6 parts of boron nitride (particle size 10 μm), and the thickness is controlled at 6 μm; the yellow thermosensitive dye is The color developer is Where P = 18;

[0054] In parts by weight, the magenta heat-sensitive coating 4 comprises: 24 parts of a color developer, 6 parts of a heat-sensitive red dye, 30 parts of an epoxy resin adhesive, 30 parts of a polyamide curing agent, 6 parts of a temperature-regulating agent, 18-naphthyl octadecyl ester, and 6 parts of a boron nitride filler (particle size 10 μm), with a thickness controlled at 6 μm; the heat-sensitive red dye is The color developer is Where P = 18;

[0055] In parts by weight, the cyan heat-sensitive coating 2 comprises: 36 parts of developer, 9 parts of cyan heat-sensitive dye, 30 parts of epoxy resin adhesive, 30 parts of polyamide curing agent, 9 parts of temperature-regulating auxiliary agent octadecyl urea phenol and 6 parts of boron nitride filler (particle size 10 μm), and the thickness is controlled at 8 μm; the cyan heat-sensitive dye is The color developer is Where P = 18;

[0056] In parts by weight, the first intermediate layer and the second intermediate layer each comprise: 40 parts of zinc oxide, 75 parts of epoxy resin adhesive resin, and 50 parts of polyamide curing agent, and the thickness is controlled at 3 μm.

[0057] The method for preparing multi-color and multi-layered erasable thermal paper involved in this embodiment comprises the following steps:

[0058] S1: preparing a cyan thermosensitive coating coating liquid from the components of the cyan thermosensitive coating; preparing a magenta thermosensitive coating coating liquid from the components of the magenta thermosensitive coating; preparing a yellow thermosensitive coating liquid from the components of the yellow thermosensitive coating; preparing an intermediate layer coating liquid from the components of the intermediate layer; applying the cyan thermosensitive coating liquid, the intermediate layer coating liquid, the magenta thermosensitive coating liquid, the intermediate layer coating liquid, and the yellow thermosensitive coating liquid on a substrate in sequence, and drying to obtain a thermosensitive coating;

[0059] S2: preparing the components of the protective layer into a coating liquid for the protective layer, applying the liquid on the heat-sensitive coating, and drying the liquid to obtain the protective layer;

[0060] S3: Compounding the substrate, the heat-sensitive coating, and the protective layer through a hot pressing process to obtain a color thermal erasable thermal paper based on multi-color and multi-layer superposition.

[0061] Example 2

[0062] In this embodiment, the particle size of the boron nitride in the yellow heat-sensitive coating is set to 20 μm. The particle size of the boron nitride in the magenta heat-sensitive coating is set to 20 μm. The particle size of the boron nitride in the cyan heat-sensitive coating is set to 20 μm. The rest is the same as in Example 1.

[0063] Example 3

[0064] In this embodiment, the protective layer is removed and the rest is the same as in embodiment 2.

[0065] Example 4

[0066] In this embodiment, the coating components are as follows, and the rest are the same as in Example 1.

[0067] In parts by weight, the protective layer 7 comprises: 5 parts of benzotriazole as an anti-ultraviolet additive, 3 parts of talc as a solid lubricant, 75 parts of epoxy resin adhesive, 50 parts of polyurethane curing agent, and 5 parts of boron nitride (particle size 5 μm); the thickness is controlled at 3 μm;

[0068] In parts by weight, the yellow thermosensitive coating 6 comprises: 36 parts of developer, 9 parts of yellow thermosensitive dye, 30 parts of epoxy resin adhesive, 30 parts of polyamide curing agent and 6 parts of boron nitride (particle size 10 μm), and the thickness is controlled at 6 μm; the yellow thermosensitive dye is The color developer is Where P = 18;

[0069] In parts by weight, the magenta heat-sensitive coating 4 comprises: 24 parts of a color developer, 6 parts of a heat-sensitive red dye, 30 parts of an epoxy resin adhesive, 30 parts of a polyamide curing agent, 6 parts of a temperature-regulating agent, 18-naphthyl octadecyl ester, and 6 parts of a boron nitride filler (particle size 10 μm), with a thickness controlled at 6 μm; the heat-sensitive red dye is The color developer is Where P = 18;

[0070] In parts by weight, the cyan heat-sensitive coating 2 comprises: 36 parts of developer, 9 parts of cyan heat-sensitive dye, 30 parts of epoxy resin adhesive, 30 parts of polyamide curing agent, 9 parts of temperature-regulating auxiliary agent octadecyl urea phenol and 6 parts of boron nitride filler (particle size 10 μm), and the thickness is controlled at 8 μm; the cyan heat-sensitive dye is The color developer is Where P = 18;

[0071] In parts by weight, the first intermediate layer and the second intermediate layer each comprise: 40 parts of zinc oxide, 75 parts of epoxy resin adhesive resin, and 50 parts of polyamide curing agent, and the thickness is controlled at 3 μm.

[0072] Example 5

[0073] In this embodiment, the particle size of the boron nitride in the yellow heat-sensitive coating is set to 1 μm. The particle size of the boron nitride in the magenta heat-sensitive coating is set to 1 μm. The particle size of the boron nitride in the cyan heat-sensitive coating is set to 1 μm. The rest is the same as in Example 1.

[0074] Comparative Example 1

[0075] In this embodiment, the weight proportions of the developer and the yellow thermosensitive dye in the yellow thermosensitive coating are changed to 24 parts and 9 parts respectively, and the rest are the same as in Example 1.

[0076] Comparative Example 2

[0077] In this embodiment, boron nitride is not added to the protective layer, and the rest is the same as in embodiment 2.

[0078] Comparative Example 3

[0079] In this embodiment, the thickness of the cyan thermosensitive coating is reduced from 8 μm to 6 μm, and the rest is the same as in Embodiment 3.

[0080] Test example

[0081] Printing method: CV80 printer prints yellow, magenta and cyan to test color density.

[0082] Erasing method: At 140℃, 1kgf / cm 2 Under pressure, using a hot sheet machine, the image was heated for 1 second to erase, and the retention rate was less than 10%, indicating that the reversibility was successful once.

[0083] Erasing efficiency: (color density after erasing - background color density) / (printing color density - background color density) * 100%.

[0084] Table 1 Performance comparison of Example 1 and Comparative Example 1

[0085]

[0086] As shown in Table 1, by comparing the color density of the yellow thermosensitive coating before erasing and after erasing 100 times in Example 1 and Comparative Example 1, it can be seen that reducing the amount of the developer and the yellow thermosensitive dye in the yellow thermosensitive coating will reduce the color density of yellow.

[0087] Table 2 Performance comparison of Example 2 and Comparative Example 2

[0088]

[0089] As can be seen from Table 2, by comparing the color density and erasure efficiency of each color of the thermal-sensitive coating before erasing and after erasing 100 times in Example 2 and Comparative Example 2, it can be seen that not adding a thermal conductive additive to the protective layer will reduce the color density of each color and reduce the erasure efficiency. From the comparison between Example 2 and Example 1, it can be seen that the addition of a high-particle-size thermal conductive additive can effectively improve the color density and erasure efficiency.

[0090] Table 3 Performance comparison of Example 3 and Comparative Example 3

[0091]

[0092] As shown in Tables 2 and 3, a comparison of the color density and erasure efficiency of the yellow thermosensitive coating after 100 erasures in Example 2 and Example 3 shows that, in Example 3, the yellow thermosensitive coating without a protective layer exhibits a significant decrease in yellow color density after 100 erasures, and the erasure efficiency is also low. A comparison of the color density and erasure efficiency of the cyan thermosensitive coating in Example 3 and Comparative Example 3 shows that reducing the thickness of the cyan color-developing layer reduces the cyan color density.

[0093] Table 4 Performance comparison of Example 4 and Example 5

[0094]

[0095] As shown in Table 4, the color density of Comparative Example 4 and Example 5 decreases as the particle size of boron nitride decreases. As the particle size of the thermal conductive additive decreases, the thermal conductive effect decreases and the color density decreases.

[0096] In summary, the protective layer, the intermediate layer and the heat-sensitive coating work together to achieve three-color color development. By adding a thermal conductive additive and adjusting its particle size, efficient erasable color and full-color overlay can be achieved.

[0097] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0098] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A rewritable color thermal paper, characterized in that: The invention comprises a protective layer, a heat-sensitive coating layer and a substrate layer, wherein the heat-sensitive coating layer comprises a yellow heat-sensitive coating layer, a first intermediate layer, a magenta heat-sensitive coating layer, a second intermediate layer and a cyan heat-sensitive coating layer arranged in order from top to bottom, the protective layer is provided on the yellow heat-sensitive coating layer, and the cyan heat-sensitive coating layer is provided on the substrate layer; the color development temperature difference between the yellow heat-sensitive coating layer, the magenta heat-sensitive coating layer and the cyan heat-sensitive coating layer is not less than 25°C; A thermal conductive additive is added to the yellow thermal sensitive coating, the magenta thermal sensitive coating and the cyan thermal sensitive coating; The yellow heat-sensitive coating, the magenta heat-sensitive coating, and the cyan heat-sensitive coating all include a developer, and the developer has the following structure: , where p = 12~37; The yellow thermosensitive coating includes a yellow thermosensitive dye, and the yellow thermosensitive dye is at least one of the following structures: 、 ; The magenta thermosensitive coating includes a magenta thermosensitive dye, and the magenta thermosensitive dye is at least one of the following structures: 、 、 、 、 、 、 ; The cyan thermosensitive coating includes a cyan thermosensitive dye, and the cyan thermosensitive dye is at least one of the following structures: 、 、 、 、 、 ; The yellow thermosensitive coating comprises the following raw materials in parts by weight: 10-45 parts of a developer, 2-15 parts of a yellow thermosensitive dye, 30-50 parts of an adhesive, 20-30 parts of a polyamide curing agent, and 1-20 parts of a thermal conductive additive, wherein the particle size of the thermal conductive additive is 1-20 μm; The magenta heat-sensitive coating comprises the following raw materials in parts by weight: 10-45 parts of a developer, 2-15 parts of a red heat-sensitive dye, 30-50 parts of an adhesive, 20-30 parts of a polyamide curing agent, 1-20 parts of a thermal conductive agent, and 2-15 parts of a temperature regulating agent, wherein the particle size of the thermal conductive agent is 1-20 μm. The cyan heat-sensitive coating comprises the following raw materials in parts by weight: 10-45 parts of a developer, 2-15 parts of a cyan heat-sensitive dye, 30-50 parts of an adhesive, 20-30 parts of a polyamide curing agent, 1-20 parts of a thermal conductive agent, and 2-15 parts of a temperature regulating agent, wherein the particle size of the thermal conductive agent is 1-20 μm. The protective layer comprises the following raw materials in parts by weight: 10-50 parts of thermal conductive additive, 1-10 parts of anti-ultraviolet additive, 1-5 parts of lubricant, 30-80 parts of adhesive resin, and 40-60 parts of polyurethane curing agent. The particle size of the thermal conductive additive is 1-10 μm. The first intermediate layer comprises the following raw materials in parts by weight: 10 to 50 parts of thermal insulation additive, 30 to 80 parts of adhesive resin, and 40 to 60 parts of polyurethane curing agent; The second intermediate layer comprises the following raw materials in parts by weight: 10-50 parts of thermal insulation additive, 30-80 parts of adhesive resin, and 40-60 parts of polyurethane curing agent; The substrate layer is at least one of coated paper, white cardboard, kraft paper, offset paper, glassine paper, stone paper, and PVC paperboard; In the yellow heat-sensitive coating, the magenta heat-sensitive coating, and the cyan heat-sensitive coating, the adhesive comprises at least one of epoxy resin, polyurethane, and acrylate respectively; In the protective layer, the anti-ultraviolet additive includes at least one of salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, and triazines; the lubricant includes at least one of zinc stearate, mineral lubricants, silicone oil, fatty acid amide, oleic acid, polyester, synthetic ester, and carboxylic acid; and the adhesive resin includes at least one of PVA, polyacrylate, and polyurethane. In the first intermediate layer and the second intermediate layer, the adhesive resin includes at least one of PVA, polyacrylate and polyurethane; the thermal insulation additive includes at least one of glass fiber, montmorillonite, rare earth heat-resistant agent, porous silica, porous titanium dioxide and porous carbon.

2. The erasable color thermal paper according to claim 1, characterized in that: The thermal conductive agent is at least one of magnesium oxide, zinc oxide, aluminum oxide and boron nitride; and the particle size of the thermal conductive agent is 1 to 20 μm.

3. The erasable color thermal paper according to claim 1, characterized in that: The monochrome printing time of the yellow thermosensitive coating and the magenta thermosensitive coating is less than 100 ms.

4. The erasable color thermal paper according to claim 1, characterized in that: A first temperature regulating agent is added to the magenta heat-sensitive coating, and a second temperature regulating agent is added to the cyan heat-sensitive coating. The difference in melting points between the first temperature regulating agent and the second temperature regulating agent is not less than 25°C.

5. The erasable color thermal paper according to claim 4, characterized in that: The first temperature regulating auxiliary agent and the second temperature regulating auxiliary agent are respectively at least one of naphthyl urea compounds, naphthyl amide compounds, naphthyl ester compounds, and naphthyl amino acid ester compounds.

6. The erasable color thermal paper according to claim 1, characterized in that: The thickness of the yellow heat-sensitive coating is 5-8 μm; the thickness of the magenta heat-sensitive coating is 6-10 μm; the thickness of the cyan heat-sensitive coating is 8-14 μm; The thickness of the protective layer is 1-3 μm; the thickness of the first intermediate layer is 2-6 μm; the thickness of the second intermediate layer is 2-6 μm; and the thickness of the substrate layer is 100-140 μm.

7. A method for preparing the erasable color thermal paper according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1: preparing a yellow heat-sensitive coating liquid, a magenta heat-sensitive coating liquid, a cyan heat-sensitive coating liquid, a protective liquid, a first intermediate layer coating liquid, and a second intermediate layer coating liquid; S2: coating a cyan thermal-sensitive coating liquid on one side of the substrate layer, and then drying to form a cyan thermal-sensitive coating layer; coating a second intermediate layer coating liquid on the cyan thermal-sensitive coating layer, and then drying to form a second intermediate layer; coating a magenta thermal-sensitive coating liquid on the second intermediate layer, and then drying to form a magenta thermal-sensitive coating layer; The first intermediate layer coating liquid is coated on the magenta heat-sensitive coating layer, and then dried to form the first intermediate layer; the yellow heat-sensitive coating liquid is then coated on the first intermediate layer, and then dried to form the yellow heat-sensitive coating layer; finally, the protective liquid is coated on the red heat-sensitive coating layer, and then dried to form the protective layer; S3: Compounding the substrate layer, the cyan thermal-sensitive coating, the second intermediate layer, the magenta thermal-sensitive coating, the first intermediate layer, the yellow thermal-sensitive coating, and the protective layer through a hot pressing process to obtain a color erasable thermal paper.

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