Full-color thermal paper, its preparation method and application

Abstract

This invention provides a full-color thermal paper, its preparation method, and its application, relating to the field of thermal paper technology. The full-color thermal paper comprises, from bottom to top, a base paper, a base coating, an RGB microcapsule color-developing layer, and a top coating. The RGB microcapsule color-developing layer is a single-layer structure containing red (R) capsules, green (G) capsules, and blue (B) capsules, as well as fumed silica thermal barrier filler filling the gaps between the microcapsules. The red (R) capsules, green (G) capsules, and blue (B) capsules are arranged in a two-dimensional array in a horizontal plane. The two-dimensional array consists of multiple array periodic units, each containing one red (R) capsule, two green (G) capsules, and one blue (B) capsule arranged in the R-G-B-G sequence. This invention's design replaces traditional multi-layer coating with a single-layer planar integration, significantly reducing thickness and improving thermal response speed. Simultaneously, the fumed silica filler effectively suppresses thermal diffusion between adjacent microcapsules.

Description

Technical Field

[0001] This invention relates to the field of thermal paper technology, and in particular to a full-color thermal paper, its preparation method, and its application. Background Technology

[0002] Thermal paper is an information recording material with a thermally sensitive coloring material coating on its surface, which can develop color upon excitation by a thermal signal. Traditional thermal paper typically only has monochrome (black or blue) color development capability, and its basic structure consists of a base paper, a base coating, a thermally sensitive color developing layer, and a top coating. The color developing layer contains components such as colorless dyes, color developers, and sensitizers. When heated, the color developer releases protons, causing a structural change in the dye and thus producing color.

[0003] The existing technologies for preparing colored thermal paper mainly include the following: (1) Multi-layer overlay color development layer: Three thermal color development layers of cyan (C), magenta (M), and yellow (Y) are sequentially coated on the paper, each corresponding to a different unsealing temperature. Layered color development is achieved by controlling the heating temperature. This scheme has a large coating thickness, low thermal conductivity, and limited color saturation.

[0004] (2) Microcapsule encapsulation technology: Different colored thermosensitive dyes are encapsulated in microcapsules, and the capsules are broken by mechanical pressure or heat source to reveal the color. However, most existing solutions use random mixing and coating, which cannot achieve precise pixel-level color control.

[0005] Therefore, existing technologies still face the following challenges: 1. How to achieve precise arraying of RGB three-color microcapsules within the same planar layer; 2. How to achieve pixel-level independent color control without being affected by lateral thermal diffusion; 3. How to construct a printing heat source system that matches the requirements of full-color display.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The primary objective of this invention is to provide a full-color thermal paper that achieves high resolution and pixel-level independent color control by combining RGBG periodic array arrangement with thermal barrier filler within the same planar layer, thereby solving the problems of traditional color thermal paper having a large coating thickness, blurred color edges due to lateral thermal diffusion, and inability to achieve pixel-level accurate color rendering.

[0008] The second objective of this invention is to provide a method for preparing full-color thermal paper.

[0009] A third objective of this invention is to provide an application of full-color thermal paper.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The present invention provides a full-color thermal paper, which comprises, from bottom to top, a base paper, a bottom coating layer, an RGB microcapsule color developing layer, and a top coating layer; The RGB microcapsule color layer is a single-layer structure, which includes red R capsules, green G capsules and blue B capsules, as well as fumed silica thermal barrier filler filling the gaps between the microcapsules to achieve thermal isolation between the microcapsules. The red R capsule, green G capsule, and blue B capsule are arranged in a two-dimensional array in a horizontal plane. The two-dimensional array consists of multiple array periodic units. Each array periodic unit contains one red R capsule, two green G capsules, and one blue B capsule arranged in RGBG order. The distribution density of the green G capsule is greater than that of the red R capsule and greater than that of the blue B capsule. The red R capsule, green G capsule, and blue B capsule are all single-layer capsule wall structures with the core material covered by the wall material.

[0011] Furthermore, the red R capsule is coated with a photothermal conversion agent to absorb the first wavelength, the green G capsule is coated with a photothermal conversion agent to absorb the second wavelength, and the blue B capsule is coated with a photothermal conversion agent to absorb the third wavelength, and the first wavelength, the second wavelength, and the third wavelength are different from each other; Furthermore, the first wavelength is 800~820nm, the second wavelength is 970~990nm, and the third wavelength is 1050~1080nm; Furthermore, the glass transition temperatures (Tg) of the wall materials of the red R capsule, green G capsule, and blue B capsule are respectively a first temperature, a second temperature, and a third temperature, and the first temperature, the second temperature, and the third temperature are different from each other. Furthermore, the glass transition temperature of the wall material of the red R capsule is 75~85℃, the glass transition temperature of the wall material of the green G capsule is 115~125℃, and the glass transition temperature of the wall material of the blue B capsule is 145~155℃. Furthermore, the wall thicknesses of the red R capsule, the green G capsule, and the blue B capsule are the first wall thickness, the second wall thickness, and the third wall thickness, respectively, and the first wall thickness < the second wall thickness < the third wall thickness. Furthermore, the wall thickness of the red R capsule is 1.5~2.5μm, the wall thickness of the green G capsule is 3.0~4.0μm, and the wall thickness of the blue B capsule is 4.5~5.5μm; Furthermore, the thermal response time constant of the red R capsule is 0.5~1.0 ms, the thermal response time constant of the green G capsule is 2.0~3.0 ms, and the thermal response time constant of the blue B capsule is 4.0~6.0 ms.

[0012] Furthermore, the red R capsule is a single-layer capsule wall structure in which the core material is covered by the wall material, and the wall material is a modified polyurethane with a low glass transition temperature. The modified polyurethane with a low glass transition temperature is a flexible long-chain polyether diol modified polyurethane, and the glass transition temperature of the modified polyurethane is 75~85℃. The core material of the red R capsule includes rhodamine B lactone, bisphenol A, butyl stearate, and gold nanorods, which absorb laser light with a wavelength of 800-820 nm.

[0013] Furthermore, the green G capsule is a single-layer capsule wall structure in which the core material is covered by a wall material, and the wall material is cross-linked polymethyl methacrylate or polyurea with a glass transition temperature of 115~125℃. The core material of the green G capsule includes zeaxanthin-based green leuco dye, bisphenol S, tetradecyl alcohol, and copper sulfide nanosheets, which absorb laser light with a wavelength of 970-990 nm.

[0014] Furthermore, the blue B capsule has a single-layer capsule wall structure in which the core material is covered by a wall material, and the wall material is a highly cross-linked polyurethane or an aromatic polyurea. Furthermore, the highly crosslinked polyurethane increases its glass transition temperature by adding a crosslinking agent, and the aromatic polyurea contains a rigid aromatic ring structure in its molecular backbone to increase its glass transition temperature; the glass transition temperature of the highly crosslinked polyurethane or aromatic polyurea is 145~155℃. The core material of the blue B capsule includes crystal violet lactone (CVL), benzyl benzoate, and copper sulfide nanosheets, which absorb laser light with a wavelength of 1050-1080 nm.

[0015] Furthermore, the thickness of the RGB microcapsule color-developing layer is 22~32μm; Furthermore, the fumed silica thermal barrier filler in the RGB microcapsule color layer has a particle size of 7~40nm, a specific surface area of ​​200~400m² / g, and a filling amount accounting for 10~20% of the total mass of the RGB microcapsule color layer; Furthermore, the center-to-center distance between adjacent microcapsules in the RGB microcapsule color development layer is 40~45μm, and the diameter of a single microcapsule is 18~35μm, preferably 20~30μm; Furthermore, the base coating comprises hollow plastic pigment, calcined kaolin, styrene-butadiene latex and polyvinyl alcohol, with a coating amount of 4~6 g / m² and a thickness of 5~6 μm; Furthermore, the top coating comprises modified polyvinyl alcohol, crosslinking agent, fumed silica filler and lubricant, with a coating amount of 1~2 g / m² and a thickness of 1.5~2 μm.

[0016] The present invention provides a method for preparing the above-mentioned full-color thermal paper, the method comprising the following steps: (A) Forming a base coating on the base paper; (B) Using piezoelectric inkjet microarray coating technology, a first dispersion containing red R capsules, a second dispersion containing green G capsules, and a third dispersion containing blue B capsules are sprayed onto the base layer in an RGBG periodic unit array to form a single-layer RGB microcapsule color layer, wherein the R, G, and B capsules in the single-layer RGB microcapsule color layer are arranged in a two-dimensional array in the horizontal plane. The RGBG sequence is used as the periodic unit and sprayed in an array onto the base layer to form a single-layer RGB microcapsule color development layer. (C) The microcapsule gaps of the RGB microcapsule color layer are filled with fumed silica thermal barrier filler; (D) A top coating is formed on the RGB microcapsule color development layer.

[0017] Furthermore, the piezoelectric inkjet microarray employs three piezoelectric inkjet printheads, each loaded with the first dispersion, the second dispersion, and the third dispersion.

[0018] Furthermore, the red R capsule, green G capsule, and blue B capsule are each prepared independently through the following steps: S1: Prepare wall material solution and core material dispersion separately, mix and emulsify the core material dispersion and wall material solution to form an emulsion, and use the emulsion to form a wall-forming reaction such as solvent evaporation deposition, suspension polymerization or interfacial condensation to form a capsule wall on the surface of the core material droplet; S2: After the product in S1 is solidified and shaped, it is washed, purified, sieved and classified to obtain microcapsules with uniform particle size. The microcapsules are redispersed in a dispersion medium to prepare a dispersion for piezoelectric inkjet printing. Furthermore, the red R capsule has a sieve particle size of 20~30μm, the green G capsule has a sieve particle size of 18~28μm, and the blue B capsule has a sieve particle size of 22~32μm.

[0019] The present invention provides the application of the above-mentioned full-color thermal paper or the full-color thermal paper prepared by the above-mentioned preparation method of the present invention in the preparation of laser selective color printing.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a full-color thermal paper. The full-color thermal paper achieves precise spatial positioning and thermal isolation of the RGB three-color display units on the same plane by setting red, green, and blue microcapsules arranged in an RGBG matrix array within a single planar layer, and filling the gaps between the microcapsules with fumed silica thermal barrier filler. This structure replaces the traditional multi-layered color-developing layer, significantly reducing the overall thickness of the color-developing layer. The two-dimensional array arrangement ensures uniform distribution and periodic regularity of the color microcapsules in the horizontal direction, which is beneficial for precise control of printing resolution and color consistency. The RGBG sequential arrangement within each array periodic unit matches the high sensitivity of the human eye to the green spectrum, improving image visual sharpness. The single-layer capsule wall structure simplifies the construction of the color-developing unit, which is beneficial for improving thermal response speed and color uniformity. The fumed silica thermal barrier filler effectively suppresses lateral thermal diffusion between adjacent microcapsules, ensuring the reliability of pixel-level color control. Furthermore, by combining different microcapsules with gradient differences in light absorption wavelength and glass transition temperature of wall material, precise selective triggering with spatiotemporal synchronization is achieved, further ensuring the high fidelity and reliability of full-color display.

[0021] This invention provides a method for preparing full-color thermal paper. The method involves sequentially constructing a base coating layer on a base paper and precisely depositing a microcapsule dispersion arranged in the RGBG order using piezoelectric inkjet microarray coating technology. This achieves the structured integration of RGB three-color display units in the same plane. This process avoids the superposition of color layer thickness and thermal conduction delay caused by traditional multi-layer coating, ensuring the precise controllability of microcapsule spatial position and pixel-level independence of thermal response, while also taking into account the repeatability of the production process and industrial adaptability.

[0022] The full-color thermal paper provided by this invention can be widely used in laser selective color printing. The full-color thermal paper of this invention combines its single-layer RGBG array structure with wavelength photothermal response characteristics, so that lasers of different wavelengths can independently and accurately excite the corresponding color microcapsules for color development. Without the need for filters or mechanical switching devices, it can achieve direct writing, high resolution, and low latency output of full-color images. Attached Figure Description

[0023] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1This is a schematic diagram of the structure of the full-color thermal paper provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the array coating of microcapsules achieved by piezoelectric inkjet microarray printing according to Embodiment 1 of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] According to one aspect of the present invention, a full-color thermal paper comprises, from bottom to top: a base paper, a bottom coating layer, an RGB microcapsule color developing layer, and a top coating layer; The RGB microcapsule color layer is a single-layer structure, which includes red R capsules, green G capsules and blue B capsules, as well as fumed silica thermal barrier filler filling the gaps between the microcapsules to achieve thermal isolation between the microcapsules. The red R capsule, green G capsule, and blue B capsule are arranged in a two-dimensional array in a horizontal plane. The two-dimensional array consists of multiple array periodic units. Each array periodic unit contains one red R capsule, two green G capsules, and one blue B capsule arranged in RGBG order. The distribution density of the green G capsule is greater than that of the red R capsule and greater than that of the blue B capsule. The red R capsule, green G capsule, and blue B capsule are all single-layer capsule wall structures with the core material covered by the wall material.

[0027] This invention provides a full-color thermal paper. The full-color thermal paper achieves precise spatial positioning and thermal isolation of the RGB three-color display units on the same plane by setting red, green, and blue microcapsules arranged in an RGBG matrix array within a single planar layer, and filling the gaps between the microcapsules with fumed silica thermal barrier filler. This structure replaces the traditional multi-layered color-developing layer, significantly reducing the overall thickness of the color-developing layer. The two-dimensional array arrangement ensures the uniform distribution and periodic regularity of each color microcapsule in the horizontal direction, which is beneficial for precise control of printing resolution. The RGBG sequential arrangement within each array periodic unit matches the high sensitivity of the human eye to the green spectrum, improving image visual sharpness. The single-layer capsule wall structure simplifies the construction of the color-developing unit, which is beneficial for improving thermal response speed and color uniformity. The fumed silica thermal barrier filler effectively suppresses lateral thermal diffusion between adjacent microcapsules, ensuring the reliability of pixel-level color control. Furthermore, by combining different microcapsules with gradient differences in light absorption wavelength and glass transition temperature of wall material, precise selective triggering with spatiotemporal synchronization is achieved, further ensuring the high fidelity and reliability of full-color display.

[0028] In a preferred embodiment of the present invention, the red R capsule is coated with a photothermal conversion agent for absorbing a first wavelength, the green G capsule is coated with a photothermal conversion agent for absorbing a second wavelength, and the blue B capsule is coated with a photothermal conversion agent for absorbing a third wavelength, and the first wavelength, the second wavelength, and the third wavelength are different from each other.

[0029] As a preferred embodiment, the red R capsule, green G capsule, and blue B capsule of the present invention are respectively configured with photothermal conversion agents that selectively absorb different wavelengths, so that each colored microcapsule generates a thermal response only under laser excitation of the corresponding wavelength, thereby achieving precise targeted delivery of laser energy.

[0030] Preferably, the first wavelength is 800~820nm, the second wavelength is 970~990nm, and the third wavelength is 1050~1080nm.

[0031] In a preferred embodiment of the present invention, the glass transition temperatures of the wall materials of the red R capsule, the green G capsule, and the blue B capsule are respectively a first temperature, a second temperature, and a third temperature, and the first temperature, the second temperature, and the third temperature are different from each other. In a preferred embodiment, the glass transition temperatures of the wall materials of the red R capsule, green G capsule, and blue B capsule of the present invention are gradient differences, resulting in different thermally induced desealing thresholds for the three. This design constructs a temperature difference threshold isolation mechanism in the temperature dimension. Even if limited thermal diffusion occurs during laser heating, adjacent microcapsules remain closed because the softening temperature of the wall material does not reach the threshold, thereby effectively preventing color crosstalk.

[0032] Preferably, the glass transition temperature of the wall material of the red R capsule is 75~85℃, the glass transition temperature of the wall material of the green G capsule is 115~125℃, and the glass transition temperature of the wall material of the blue B capsule is 145~155℃. In a preferred embodiment of the present invention, the wall thicknesses of the red R capsule, the green G capsule, and the blue B capsule are respectively a first wall thickness, a second wall thickness, and a third wall thickness, and the first wall thickness < the second wall thickness < the third wall thickness.

[0033] In a preferred embodiment, the wall thickness of the red R capsule, green G capsule, and blue B capsule of the present invention increases in a gradient, resulting in different thermal response time constants for the three. This design introduces a time-dimensional response isolation mechanism, which can achieve time-selective control of the color development process of each color unit by matching the thermal inertia of different microcapsules with the laser pulse width.

[0034] Preferably, the wall thickness of the red R capsule is 1.5~2.5μm, the wall thickness of the green G capsule is 3.0~4.0μm, and the wall thickness of the blue B capsule is 4.5~5.5μm.

[0035] In a preferred embodiment of the present invention, the thermal response time constant of the red R capsule is 0.5~1.0 ms, the thermal response time constant of the green G capsule is 2.0~3.0 ms, and the thermal response time constant of the blue B capsule is 4.0~6.0 ms.

[0036] In a preferred embodiment, the thermal response time constants of the red R capsule, green G capsule, and blue B capsule of the present invention are significantly different. This difference allows only the target microcapsule to complete thermal accumulation and unsealing and color development within the pulse duration under laser excitation with a set pulse width, while adjacent microcapsules with slower response remain uncolored because the heat has not been fully conducted to the core. This enhances the independence and precision of color control in the time dimension.

[0037] In a preferred embodiment of the present invention, the red R capsule is a single-layer capsule wall structure in which the core material is covered by the wall material, and the wall material is a modified polyurethane with a low glass transition temperature. The modified polyurethane with a low glass transition temperature is a flexible long-chain polyether diol modified polyurethane, and the glass transition temperature of the modified polyurethane is 75~85℃. The core material of the red R capsule includes rhodamine B lactone, bisphenol A, butyl stearate, and gold nanorods, which absorb laser light with a wavelength of 800-820 nm.

[0038] In a preferred embodiment, the red R capsule of the present invention uses modified polyurethane with a low glass transition temperature as the wall material. Its glass transition temperature is precisely set to 75~85℃ through flexible segment control, ensuring that the capsule wall softens and the core material is released at a relatively low temperature. In the core material, rhodamine B lactone and bisphenol A undergo a color reaction after heating, butyl stearate acts as a phase change permeation promoter to promote the migration of color-developing components, and gold nanorods efficiently absorb 800~820nm laser light and convert it into local heat, together ensuring rapid, sensitive and high-contrast red color development.

[0039] In a preferred embodiment of the present invention, the green G capsule is a single-layer capsule wall structure in which the core material is covered by a wall material, wherein the wall material is cross-linked polymethyl methacrylate or polyurea; The core material of the green G capsule includes zeaxanthin-based green leuco dye, bisphenol S, tetradecyl alcohol, and copper sulfide nanosheets, which absorb laser light with a wavelength of 970-990 nm.

[0040] In a preferred embodiment, the green G capsule of the present invention uses cross-linked polymethyl methacrylate or polyurea as the wall material, with its glass transition temperature set at 115~125℃, forming a gradient difference with the red R capsule and blue B capsule, ensuring stable unsealing in the mid-temperature range; the xanthan green leuco dye in the core material reacts with bisphenol S after heating to develop color, tetradecanol acts as a phase change permeation enhancer to improve color development efficiency, and copper sulfide nanosheets specifically absorb 970~990nm laser light and generate heat efficiently, together achieving high selectivity, high saturation and good stability of green color development.

[0041] In a preferred embodiment of the present invention, the blue B capsule is a single-layer capsule wall structure in which the wall material covers the core material. The wall material of the blue B capsule is a highly cross-linked polyurethane or aromatic polyurea. The highly cross-linked polyurethane or aromatic polyurea increases the glass transition temperature to 145~155°C by increasing the amount of cross-linking agent or introducing a rigid aromatic ring structure. The core material of the blue B capsule includes crystal violet lactone (CVL), benzyl benzoate, and copper sulfide nanosheets, which absorb laser light with a wavelength of 1050-1080 nm.

[0042] In a preferred embodiment, the blue B capsule of the present invention uses highly cross-linked polyurethane or aromatic polyurea as the wall material, and its glass transition temperature is precisely increased to 145~155℃ through structural control, constituting the highest unsealing temperature threshold among the three-color capsules, ensuring that the blue color development is independently triggered in the high-temperature range; in the core material, crystal violet lactone (CVL) and benzyl paraben undergo a color development reaction after heating, while copper sulfide nanosheets specifically absorb 1050~1080nm laser light and efficiently convert it into heat energy, together achieving high heat resistance, high color purity and good photostability of the blue color development.

[0043] In a preferred embodiment of the present invention, the thickness of the RGB microcapsule color layer is 22~32μm.

[0044] As a preferred embodiment, the thickness of the RGB microcapsule color development layer of the present invention is controlled within the range of 22~32μm (determined by the maximum particle size of the single-layer densely packed microcapsules). This ensures the complete coverage of the microcapsule array structure and the effective carrying capacity of the color development components. Furthermore, by replacing the traditional multi-layer coating with a single-layer densely packed structure, it is beneficial to improve the thermal conductivity, shorten the color development response time, and enhance the flexibility and curl adaptability of the thermal paper.

[0045] In a preferred embodiment of the present invention, the particle size of the fumed silica thermal barrier filler in the RGB microcapsule color layer is 7~40nm, the specific surface area is 200~400m² / g, and the filling amount accounts for 10~20% of the total mass of the RGB microcapsule color layer.

[0046] In a preferred embodiment, the fumed silica thermal barrier filler of the present invention has a particle size of 7~40nm and a specific surface area of ​​200~400 m² / g, and fills the gaps between microcapsules at a ratio of 10~20% of the total mass of the RGB microcapsule color layer, thereby forming a continuous and dense nanoscale thermal barrier network. While ensuring the mechanical strength and surface smoothness of the coating, it effectively suppresses lateral heat conduction between adjacent pixels, providing a stable thermal field isolation basis for pixel-level independent color display.

[0047] In a preferred embodiment of the present invention, the center-to-center distance between adjacent microcapsules in the RGB microcapsule color development layer is 40~45μm.

[0048] In a preferred embodiment, the center-to-center spacing between adjacent microcapsules of the present invention is set to 40~45μm, thereby forming a close but non-overlapping regular array structure on the plane, which not only ensures the spatial independence and thermal isolation margin of each color sub-pixel, but also achieves high-density arrangement.

[0049] In a preferred embodiment of the present invention, the base coating comprises hollow plastic pigment, calcined kaolin, styrene-butadiene latex and polyvinyl alcohol, with a coating amount of 4~6 g / m² and a thickness of 5~6 μm.

[0050] In a preferred embodiment, the base coating of the present invention is composed of hollow plastic pigment, calcined kaolin, styrene-butadiene latex and polyvinyl alcohol, with a coating amount of 4~6 g / m² and a thickness of 5~6 μm. This forms a transition layer between the base paper and the color developing layer, which has the functions of heat insulation, surface smoothing and component barrier, effectively reducing the loss of printing heat to the base paper, improving heat utilization efficiency, and providing a flat and stable support interface for microcapsule array coating.

[0051] In a preferred embodiment of the present invention, the top coating comprises modified polyvinyl alcohol, crosslinking agent, fumed silica filler and lubricant, with a coating amount of 1~2 g / m² and a thickness of 1.5~2 μm.

[0052] In a preferred embodiment, the top coating of the present invention is composed of modified polyvinyl alcohol, crosslinking agent, fumed silica filler and lubricant, with a coating amount of 1~2 g / m² and a thickness of 1.5~2 μm. This forms a highly transparent, dense, smooth and weather-resistant protective barrier on the surface of the RGB microcapsule color development layer, effectively resisting friction, scratching, moisture and organic solvent erosion, while reducing the frictional resistance between the print head and the paper surface, ensuring the stability of the high-precision laser scanning process and the consistency of imaging quality.

[0053] It should be noted that the fumed silica in this invention has two functions: (1) filling the gaps between microcapsules in the RGB microcapsule color layer as a thermal barrier filler to achieve thermal isolation between microcapsules; the RGB microcapsule color layer includes red R capsules, green G capsules and blue B capsules and fumed silica thermal barrier filler filling the gaps between each capsule; the fumed silica thermal barrier filler is used to form a thermal barrier path between adjacent capsules to achieve thermal isolation between each capsule; (2) filling the top coating layer, the fumed silica can be used as a non-functional filler.

[0054] According to one aspect of the present invention, a method for preparing the above-mentioned full-color thermal paper includes the following steps: (A) Forming a base coating on the base paper; (B) Using piezoelectric inkjet microarray coating technology, a first dispersion containing red R capsules, a second dispersion containing green G capsules, and a third dispersion containing blue B capsules are sprayed onto the base layer in an RGBG periodic unit array to form a single-layer RGB microcapsule color layer, wherein the R, G, and B capsules in the single-layer RGB microcapsule color layer are arranged in a two-dimensional array in the horizontal plane. (C) The microcapsule gaps of the RGB microcapsule color layer are filled with fumed silica thermal barrier filler; (D) A top coating is formed on the RGB microcapsule color development layer.

[0055] This invention provides a method for preparing full-color thermal paper. The method involves sequentially constructing a base coating layer on a base paper and then precisely depositing a microcapsule dispersion arranged in the RGBG sequence using piezoelectric inkjet microarray coating technology. This achieves the structured integration of RGB three-color display units within the same plane. The two-dimensional array arrangement, achieved through piezoelectric inkjet microarray coating, ensures the periodic and regular arrangement and precise spatial positioning of the microcapsules in the horizontal direction, guaranteeing the positional accuracy and uniform distribution of each color microcapsule, thus providing a technological foundation for high-resolution color development. This process avoids the layer thickness accumulation and thermal conduction delays associated with traditional multi-layer coating, ensuring precise controllability of the microcapsule spatial position and pixel-level independence of thermal response, while also considering the repeatability and industrial applicability of the production process.

[0056] In a preferred embodiment of the present invention, the piezoelectric inkjet microarray employs three piezoelectric inkjet printheads respectively loaded with the first dispersion, the second dispersion, and the third dispersion.

[0057] As a preferred embodiment, the piezoelectric inkjet microarray of the present invention employs three independent piezoelectric inkjet printheads, each loaded with R, G, and B microcapsule dispersions. This achieves synchronized, programmed, and non-contact dot matrix deposition of the three colors of microcapsules, ensuring the geometric accuracy and batch consistency of the RGBG matrix arrangement, while avoiding cross-contamination and performance degradation caused by mechanical mixing.

[0058] In a preferred embodiment of the present invention, the red R capsule, the green G capsule, and the blue B capsule are each prepared independently through the following steps: S1: Prepare a wall material solution and a core material dispersion separately, and mix and emulsify the core material dispersion and the wall material solution to form an emulsion; The emulsion is subjected to wall-forming reactions such as solvent evaporation deposition, suspension polymerization, or interfacial condensation to form a capsule wall on the surface of the core material droplet; S2: After solidifying and shaping the product of S1, it is washed, purified, sieved and classified to obtain microcapsules with uniform particle size. The microcapsules are then redispersed in a dispersion medium to prepare a dispersion for piezoelectric inkjet printing.

[0059] In a preferred embodiment, the red R capsules, green G capsules, and blue B capsules of this invention are prepared independently. Wall material solutions and core material dispersions adapted to their color development characteristics and thermal response requirements are prepared separately. These are then emulsified and undergo a wall-forming reaction to form the capsule walls. Finally, the capsules are cured, washed, and sieved to obtain microcapsule products with uniform particle size. This independent preparation process ensures precise differential control of the glass transition temperature, wall thickness, type of photothermal conversion agent, and color development system of the three types of microcapsules, providing a structurally and performance-controllable raw material basis for subsequent array coating and selective laser color development.

[0060] In a preferred embodiment of the present invention, the target particle size for sieving the red R capsule is 20-30 μm, the target particle size for sieving the green G capsule is 18-28 μm, and the target particle size for sieving the blue B capsule is 22-32 μm.

[0061] According to one aspect of the present invention, the above-described full-color thermal paper is used in the preparation of laser selective color printing.

[0062] The full-color thermal paper provided by this invention can be widely used in laser selective color printing. The full-color thermal paper of this invention combines a two-dimensional array arrangement structure of red R capsules, green G capsules and blue B capsules with wavelength-division photothermal response characteristics, so that lasers of different wavelengths can independently and accurately excite the corresponding color microcapsules to develop color, and full-color image output can be achieved without filters or mechanical switching devices.

[0063] The technical solution of the present invention will be further described below with reference to the embodiments.

[0064] Example 1 Figure 1 This is a schematic diagram of the structure of the full-color thermal paper provided in this embodiment.

[0065] Depend on Figure 1 As can be seen, the full-color thermal paper provided in this embodiment includes, from bottom to top: base paper, bottom coating layer, RGB microcapsule color development layer and top coating layer.

[0066] A method for preparing full-color thermal paper, the method comprising: (I) Preparation of microcapsules: 1. Preparation of red R capsules: (1) Preparation of red R capsule wall material solution: Take 20 parts by mass of flexible long-chain polyether diol modified polyurethane with a low glass transition temperature (glass transition temperature of 80℃), dissolve it in 200L of xylene, stir at 300rpm for 2h at 60℃ to prepare a wall material solution with a concentration of 10wt%, and control the solution viscosity within the range of 100mPa·s for later use.

[0067] (2) Preparation of red R capsule core material dispersion: Take 10 parts by mass of rhodamine B lactone leuco dye, 15 parts by mass of bisphenol A color developer, 5 parts by mass of butyl stearate sensitizer and 2 parts by mass of PEG-coated gold nanorods (length-to-diameter ratio 4:1, longitudinal surface plasmon resonance absorption peak 808nm) and disperse them in 100L of ethyl acetate. Sonicate for 30min to form a uniform oil phase core material dispersion.

[0068] (3) Core material mixing and emulsification: The core material dispersion obtained in step (2) is slowly added to the wall material solution obtained in step (1) and mixed to form an oil phase. The oil phase is then injected into 500L of deionized water containing 2wt% polyvinyl alcohol emulsifier. The emulsion is then emulsified at 3000rpm at 60℃ for 30min to form an O / W type emulsion. The droplet size of the emulsion is controlled within the range of 25μm.

[0069] (4) Solvent evaporation deposition and solidification: The emulsified system was reacted at 60℃ and 800rpm for 2 hours, and the organic solvent was gradually removed by distillation, allowing the polyurethane wall material to deposit on the surface of the core material droplets to form a single-layer capsule wall. Subsequently, it was cured at 75℃ (below the Tg of the wall material and below the color development trigger temperature of the core material) for another 2 hours to complete the cross-linking and shaping of the capsule wall, thus preventing the core material from developing color prematurely during the preparation stage.

[0070] (5) Washing and purification: After curing, the product is cooled to below 60°C and collected by centrifugation (4000 rpm, 10 min). The microcapsules are first washed twice with anhydrous ethanol to remove unreacted monomers and residual solvents, and then rinsed three times with deionized water until the washing solution is clear (the washing temperature is lower than the wall material Tg to prevent the capsule wall from softening and deforming).

[0071] (6) Screening and grading: After washing, the R capsules are passed through a 400-mesh standard sieve (approximately 38 μm in pore size) to remove oversized particles. The undersized particles are then passed through a 600-mesh standard sieve to remove undersized particles, resulting in a target product with uniform particle size, with a target particle size range of 25 μm.

[0072] (7) Preparation of red R capsule dispersion: The sieved R capsules were redispersed in deionized water, the solid content was adjusted to 20 wt%, 0.8 wt% sodium polyacrylate dispersant was added, and the capsules were ultrasonically dispersed for 30 min to make them uniformly suspended. The viscosity of the dispersion was adjusted to 8 mPa·s and set aside for later use.

[0073] Finished product quality inspection: The R capsules were tested and found to have an average particle size of 25 μm, a wall thickness of about 2.0 μm, a glass transition temperature of 80℃, a thermal response time constant of about 0.8 ms, qualified suspension stability, and a photothermal conversion efficiency of about 65% at a wavelength of 808 nm.

[0074] 2. Preparation of Green G Capsules: (1) Preparation of green G capsule wall material solution: Take 16 parts by mass of methyl methacrylate monomer, 3 parts by mass of ethylene glycol dimethacrylate crosslinking agent and 1 part by mass of azobisisobutyronitrile initiator (total 20 parts by mass), dissolve them in 200L of xylene, prepolymerize at 300rpm for 30min at 70℃ (conversion rate controlled below 10%), and prepare a 10wt% wall material solution, namely crosslinked polymethyl methacrylate solution (Tg 120℃). Control the solution viscosity within the range of 120mPa·s, and keep it under nitrogen protection or vacuum for later use.

[0075] (2) Preparation of dispersion of green G capsule core material: Take 8 parts by mass of xanthan green leuco dye, 12 parts by mass of bisphenol S color developer, 4 parts by mass of tetradecyl alcohol sensitizer and 3 parts by mass of copper sulfide nanosheets (particle size about 15nm, absorption peak 980nm) and disperse them in 100L of ethyl acetate. Disperse them by ultrasonication for 30min to form a uniform oil phase core material dispersion.

[0076] (3) Core material mixing and emulsification: The core material dispersion obtained in step (2) is slowly added to the wall material solution obtained in step (1) and mixed to form an oil phase. The oil phase is then injected into 500L of deionized water containing 2wt% polyvinyl alcohol emulsifier. The emulsion is then emulsified at 4000rpm at 50℃ for 40min to form an O / W type emulsion. The droplet size of the emulsion is controlled within the range of 22μm.

[0077] (4) Suspension polymerization and curing: The emulsified system was transferred to a reactor and heated to 70°C under nitrogen protection to initiate a suspension crosslinking polymerization reaction. The system was continuously stirred at 300 rpm to prevent droplet aggregation, and the reaction time was 3 hours, allowing the wall material to form a monolayer capsule on the surface of the core material droplets. Subsequently, the solvent was removed under vacuum at 75°C (120°C below the wall material's Tg and below the core material's color development trigger temperature), and the system was cured and set for 1.5 hours.

[0078] (5) Washing and purification: Cool down to below 60℃, centrifuge (3500 rpm, 12 min) to collect microcapsules, wash twice with anhydrous ethanol, and then rinse three times with deionized water.

[0079] (6) Screening and grading: Large particles are removed by passing the material through a 400-mesh standard sieve, and small particles are removed by passing the material through a 600-mesh standard sieve to obtain a green G capsule product with a target particle size range of 22μm.

[0080] (7) Preparation of Green G Capsule Dispersion: The sieved G capsules were redispersed in deionized water, the solid content was adjusted to 20 wt%, 0.8 wt% sodium polyacrylate dispersant was added, ultrasonically dispersed for 30 min, and the viscosity of the dispersion was adjusted to 8 mPa·s for later use.

[0081] Finished product quality inspection: The test results showed that the average particle size of the green G capsules was 22 μm, the wall thickness was about 3.5 μm, the glass transition temperature was about 120℃, the thermal response time constant was about 2.5 ms, and the photothermal conversion efficiency at a wavelength of 980 nm was about 55%.

[0082] 3. Preparation of blue B capsules: (1) Preparation of blue B capsule wall material solution: Take 12 parts by mass of the polyisocyanate component (isophorone diisocyanate and diphenylmethane diisocyanate mixed in a mass ratio of 1:1) and dissolve it in 150L of xylene. Stir at 300rpm for 2 hours at 50℃ to prepare an oil phase wall material solution with a concentration of about 10wt%. Control the viscosity of the solution in the range of 120 to 180mPa·s for later use.

[0083] (2) Preparation of blue B capsule core material dispersion: Take 12 parts by mass of crystal violet lactone CVL leuco dye, 18 parts by mass of benzyl p-hydroxybenzoate color developer and 4 parts by mass of copper sulfide nanosheets (particle size about 40 nm, absorption peak 1064 nm) and disperse them in 100 L of ethyl acetate. Disperse them by ultrasonication for 40 min to form a uniform oil phase core material dispersion.

[0084] (3) Core material mixing and emulsification: The core material dispersion obtained in step (2) is slowly added to the wall material solution obtained in step (1) and mixed to form an oil phase. Then, it is injected into 500L of deionized water phase (the pH is adjusted to 8-9 with sodium carbonate to suppress the hydrolysis side reaction of isocyanate) containing 2wt% polyvinyl alcohol emulsifier and 8 parts by mass of aromatic diamine component (4,4'-diaminodiphenylmethane, which is pre-dissolved by stirring at 50℃). The emulsion is emulsified at 5000rpm at 50℃ for 40min to form an O / W type emulsion. The droplet size of the emulsion is controlled within the range of 35μm.

[0085] (4) Interfacial condensation and solidification: The emulsified system was reacted at 50℃ and 300rpm for 4 hours. The aromatic diamine component in the aqueous phase diffused to the interface of the oil phase droplets and underwent interfacial condensation with the polyisocyanate, forming a monolayer capsule wall of aromatic polyurea on the surface of the core material droplets (the polymerized molecular backbone contains a rigid aromatic ring structure, and the glass transition temperature is 150℃). Subsequently, the temperature was raised to 65℃ to remove residual solvent under vacuum, and the capsule wall was cured for 2 hours to complete the shaping. The high Tg of 150℃ of the capsule wall is guaranteed by the rigid aromatic ring cross-linking structure, and no high-temperature curing is required.

[0086] (5) Washing and purification: Cool to below 60℃, centrifuge (3000 rpm, 15 min) to collect microcapsules, wash twice with anhydrous ethanol, and finally rinse three times with deionized water.

[0087] (6) Screening and grading: Large particles were removed by passing the material through a 400-mesh standard sieve, and small particles were removed by passing the material through a 600-mesh standard sieve to obtain a blue B capsule product with a target particle size range of 28μm.

[0088] (7) Preparation of blue B capsule dispersion: The sieved blue B capsules were redispersed in deionized water, the solid content was adjusted to 20 wt%, 0.8 wt% sodium polyacrylate dispersant was added, ultrasonically dispersed for 30 min, and the viscosity of the dispersion was adjusted to 10 mPa·s for later use.

[0089] Finished product quality inspection: The test results showed that the average particle size of the obtained blue B capsules was 28 μm, the wall thickness was about 5.0 μm, the glass transition temperature was about 150℃, the thermal response time constant was about 5.0 ms, the suspension stability was qualified, and the photothermal conversion efficiency at a wavelength of 1064 nm was about 70%.

[0090] (II) Preparation of full-color thermal paper: 1. Base paper preparation: High-quality wood pulp thermal paper with a coating surface smoothness of not less than 90s is selected as the base material, with a basis weight of 58g / m² and a thickness of 58μm.

[0091] 2. Primer coating application: The primer coating was prepared according to the following weight ratio: 30 parts calcined kaolin, 50 parts hollow plastic pigment (polystyrene hollow spheres, d50=10μm, hollowness 80%), 10 parts styrene-butadiene latex, 8 parts polyvinyl alcohol PVA-0588, 3 parts calcium stearate, and 0.8 parts sodium polyacrylate dispersant. Using water as a solvent, the solid content was adjusted to 35%. The mixture was first dispersed at high speed (600 rpm) for 60 min, then stirred at low speed (100 rpm) for 20 min. A metering rod was used for coating at a rate of 4 g / m² (dry weight). After hot air drying at 80℃, the mixture underwent in-machine double-roll soft calendering. The measured thickness of the primer coating was 5.0 μm.

[0092] 3. RGB microcapsule array coating: The prepared red R capsules, green G capsules, and blue B capsules were redispersed in deionized water with a solid content adjusted to 20%. After ultrasonic dispersion for 30 minutes, they were pre-filtered through a 50μm precision filter to prevent nozzle clogging. A high-precision piezoelectric inkjet microarray printing system was used for array coating. The nozzle diameter was 100μm, and the inkjet frequency was 12kHz (matched to a feed speed of 0.5m / s, with a droplet spacing of 42μm). The droplet volume was controlled to 15pL by adjusting the voltage amplitude (50V) and pulse width (10μs) of the piezoelectric element, and the droplet position was adjusted by synchronously controlling the inkjet frequency and the base paper feed speed (0.5m / s). PenTile array coating was performed on the pre-coated base layer in a fixed "RGBG" matrix order, with a center-to-center spacing of 42μm between adjacent microcapsules. The coating environment temperature was 25℃, and the relative humidity was 50%.

[0093] Figure 2 This is a schematic diagram of the array coating of microcapsules achieved by piezoelectric inkjet microarray printing according to Embodiment 1 of the present invention.

[0094] See Figure 2 As can be seen, the method for achieving array coating of microcapsules in the piezoelectric inkjet microarray printing system of this embodiment includes: A high-precision three-channel piezoelectric inkjet microarray printing system is used to achieve array coating of microcapsules. The system mainly consists of the following parts: three piezoelectric inkjet printheads (each loaded with a microcapsule dispersion of red R capsules, green G capsules, and blue B capsules, equipped with independent nozzles, such as R nozzle, G nozzle, and B nozzle), microcapsule dispersion storage tanks (independent supply of R / G / B, constant temperature control at 25±2℃), base paper conveying system (servo motor driven, speed adjustable at 0.5m / s), piezoelectric drive controller (controlling the electrical pulse signals of the three PZT piezoelectric ceramic elements), and main controller.

[0095] Droplet volume adjustment: Droplet volume adjustment is primarily achieved through the piezoelectric control mechanism of the piezoelectric inkjet printhead. The printhead contains a PZT element. The main controller applies an electrical pulse signal to the piezoelectric element, causing it to mechanically deform and compress the microcapsule dispersion within the chamber, thus extruding droplets from the nozzle. By adjusting the voltage amplitude (adjustable 50V) and pulse waveform (pulse width 10μs, adjustable rise / fall slope) applied to the piezoelectric element, the deformation and compression force of the piezoelectric element can be precisely controlled, thereby accurately controlling the droplet volume of each ejection within the range of 15pL.

[0096] The method of adjusting the landing position: The precise control of the landing position is achieved through the following two methods: (1) Nozzle physical arrangement design: The R, G and B nozzles on the three printheads are fixedly arranged in physical space according to a specific spacing and order. The lateral offset between the nozzles is precisely controlled at 42μm to naturally form the RGBG order within the array periodic unit; (2) Synchronous matching of inkjet frequency and base paper speed: The base paper moves longitudinally at a uniform speed of 0.5m / s, and the printhead sprays at a frequency of 12kHz. The main controller controls the precise moment when the droplet leaves the nozzle by accurately calculating the moving speed of the base paper and the spray time difference of the nozzle, so that the droplet falls on the designated coordinate point on the base paper. Through the closed-loop feedback system of the encoder, the inkjet frequency and the base paper conveying speed are highly synchronized, thereby ensuring that the center distance between adjacent microcapsules is stable at about 42μm.

[0097] The array coating process is as follows: Using the aforementioned high-precision three-channel piezoelectric inkjet microarray printing system, three microcapsule dispersions (20% solid content) – red (R capsules), green (G capsules), and blue (B capsules) – are loaded onto a base paper with a pre-coated base layer and arranged in a fixed "RGBG" matrix order. Four microcapsule sub-pixels are arranged within an 84μm × 84μm array periodic unit, with a center-to-center spacing of 42μm between adjacent microcapsules. This RGBG PenTile arrangement doubles the density of the green sub-pixels, matching the highest visual sensitivity of the human eye to green, resulting in sharper color rendering at the same resolution. Simultaneously, the total number of capsules is reduced by approximately 25%, lowering material costs. The inkjet frequency is controlled at 12kHz, and the base paper feed speed is 0.5m / s.

[0098] 4. Vapor-phase SiO2 filling: An aqueous dispersion of fumed silica (Aerosil 200, particle size 30 nm, specific surface area 200 m² / g) (solid content 10%) was used to fill the intercellular spaces of the capsules by dip coating. The filling amount was approximately 1.5 g / m² (dry weight). According to the ash content method, this filling amount accounted for 10% of the total mass of the RGB microcapsule color development layer. Then, it was dried with hot air at 60 °C.

[0099] The RGB microcapsule color development layer prepared in steps 3 and 4 has a single-layer close-packed structure with a thickness of about 28 μm. The sieve particle sizes of the R / G / B microcapsules were adjusted to 25 μm, 22 μm, and 28 μm, respectively.

[0100] 5. Protective coating application: The protective coating was prepared according to the following weight ratio: 60 parts acetoacetyl-modified PVA, 8 parts polyazidopyridine crosslinking agent, 15 parts fumed silica, 8 parts zinc stearate, and 5 parts polyolefin polymer resin (water-resistant agent). The solid content was adjusted to 15%, and the mixture was stirred at low speed for 40 minutes. The coating was applied using a metering rod at a rate of 2 g / m² (dry weight). After drying with hot air at 70°C, the coating was calendered externally. The measured thickness of the resulting protective layer was 2.0 μm.

[0101] Example 2 This embodiment is identical to Embodiment 1, except that the thickness of the RGB microcapsule colorimetric layer is adjusted to the lower limit range. Details are as follows: By uniformly adjusting the droplet volume of the R / G / B channels of the piezoelectric inkjet printhead to 10 pL (15 pL in Example 1), and adjusting the sieve particle size of the R / G / B microcapsules to 20 μm, 18 μm, and 22 μm respectively, the other inkjet parameters, coating environment, and post-processing are exactly the same as in Example 1.

[0102] The thickness of the RGB microcapsule color development layer was measured to be 22 μm using a scanning electron microscope (SEM) cross-sectional image.

[0103] Example 3 This embodiment is identical to Example 1, except that the amount of fumed silica is increased to the upper limit. Details are as follows: An aqueous dispersion of fumed silica (Aerosil 200, specific surface area 200 m² / g) was used, with its solid content adjusted from 10% to 20%, and was filled into the gaps between RGB microcapsules by dip coating at a filling amount of 3.0 g / m² (1.5 g / m² in Example 1), and dried with hot air at 60°C.

[0104] Calculations using the ash content method show that this filler content accounts for 20% of the total mass of the RGB microcapsule color development layer. Thermal conductivity measurements show that the thermal conductivity of the coating after filling is 0.028 W / (m·K). Thermal diffusion model calculations, taking a 4ms laser pulse from the G capsule as an example, show that the lateral thermal diffusion length of the color development layer, L≈(α·t)^½≈15μm (where α is the equivalent thermal diffusivity of the low thermal conductivity coating), is significantly smaller than the 42μm center-to-center distance between adjacent microcapsules. This verifies the role of the fumed silica thermal barrier filler in ensuring pixel-level independent color development from a heat transfer perspective.

[0105] Example 4 This embodiment is identical to Embodiment 1, except that the thickness of the base coating is adjusted to the upper limit. Details are as follows: The coating was prepared according to the primer formulation of Example 1, with the coating weight increased from 5 g / m² to 6 g / m² (dry weight, coating solid content maintained at 35%), while the proportions of other components, dispersion process, and coating conditions remained unchanged. The thickness of the resulting primer coating was measured to be 6.0 μm.

[0106] Example 5 This embodiment is identical to Embodiment 1, except that the top coating thickness is adjusted to the lower limit. Details are as follows: The coating was prepared according to the formulation of Example 1 for the topcoat layer, with the coating weight reduced from 2.0 g / m² to 1.0 g / m² (dry weight, coating solid content maintained at 15%), while the proportions of other components, stirring time, and coating conditions remained unchanged. The thickness of the resulting topcoat layer was measured to be 1.5 μm.

[0107] Example 6 In this embodiment, except that the particle size of the R / G / B microcapsules is taken as the lower limit of its respective range, the rest is the same as in Example 1. Specifically: The R / G / B microcapsule dispersions prepared in this embodiment were passed through a 400-mesh standard sieve (pore size 38 μm), and then centrifuged (3000 rpm, 15 min). The R capsules were divided into 20 μm fractions, the G capsules into 18 μm fractions, and the B capsules into 22 μm fractions. The three were then redispersed in deionized water, the solid content was adjusted to 20%, sonicated for 30 min, and then filtered through a 50 μm precision filter.

[0108] The same three-channel piezoelectric inkjet microarray printing system as in Example 1 was used for RGBG array coating (center distance 42μm), with no nozzle clogging or droplet offset, and the array structure was intact.

[0109] Example 7 Except for the lower limit of each range, this embodiment is the same as Embodiment 1. Specifically: (a) Preparation of microcapsules: The R / G / B microcapsule dispersions prepared in this embodiment were passed through a 400-mesh standard sieve (pore size 38 μm), and then centrifuged (3000 rpm, 15 min). The 20 μm fraction of the red R capsules, the 18 μm fraction of the G capsules, and the 22 μm fraction of the B capsules were taken. The three were redispersed in deionized water, the solid content was adjusted to 20%, sonicated for 30 min, and then filtered through a 50 μm precision filter.

[0110] The same three-channel piezoelectric inkjet microarray printing system as in Example 1 was used for RGBG array coating (center distance 40μm). There was no nozzle clogging or droplet offset, and the array structure was intact.

[0111] The obtained red R capsules had an average particle size of 20 μm, a wall thickness of 1.5 μm, a glass transition temperature of approximately 75℃, a thermal response time constant of approximately 0.5 ms, and satisfactory suspension stability. Their photothermal conversion efficiency at 800 nm was approximately 21%. The obtained green G capsules had an average particle size of 18 μm, a wall thickness of 3.0 μm, a glass transition temperature of approximately 115℃, a thermal response time constant of 2.0 ms, and satisfactory suspension stability. Their photothermal conversion efficiency at 970 nm was approximately 30%. The obtained blue B capsules had an average particle size of 22 μm, a wall thickness of 4.5 μm, a glass transition temperature of approximately 145℃, a thermal response time constant of 4.0 ms, and satisfactory suspension stability. Their photothermal conversion efficiency at 1050 nm was approximately 33%.

[0112] (II) Preparation of full-color thermal paper: 1. Preparation of base paper, same as in Example 1.

[0113] 2. Primer coating application: The coating was applied using metering rods at a rate of 4.0 g / m² (dry weight), and then dried with hot air at 80°C before undergoing in-machine double-roll soft calendering. The thickness of the resulting base coating was measured to be 5.0 μm.

[0114] 3. RGB microcapsule array coating: By uniformly adjusting the droplet volume of the three channels R / G / B of the piezoelectric inkjet printhead to 10 pL (15 pL in Example 1), and matching the microcapsules prepared in this example accordingly to avoid jet clogging, the remaining inkjet parameters, coating environment and post-processing are exactly the same as in Example 1.

[0115] 4. Vapor phase SiO2 filling: An aqueous dispersion of fumed silica (Aerosil 200, particle size 7nm, specific surface area 200m² / g) (solid content 10%) was used to fill the intercapsule spaces by dip coating. The filling amount was approximately 0.96g / m² (dry weight). According to the ash content method, this filling amount accounted for 10% of the total mass of the RGB microcapsule color development layer. Then, it was dried with hot air at 60℃.

[0116] Cross-sectional images obtained by scanning electron microscopy (SEM) show that the RGB microcapsule colorimetric layer prepared in steps 3 and 4 has a single-layer close-packed structure with a thickness of approximately 22 μm.

[0117] 5. Protective coating application: The protective coating was prepared according to the following weight ratio: 60 parts acetoacetyl-modified PVA, 8 parts polyazidopyridine crosslinking agent, 15 parts fumed silica, 8 parts zinc stearate, and 5 parts polyolefin polymer resin (water-resistant agent). The solid content was adjusted to 15%, and the mixture was stirred at low speed for 40 minutes. The coating was applied using a metering rod at a rate of 1 g / m² (dry weight). After drying with hot air at 70°C, the coating was calendered. The measured thickness of the resulting protective layer was 1.5 μm.

[0118] Example 8 This embodiment is identical to Embodiment 1 except for the upper limit of each range. Specifically: (a) Preparation of microcapsules: The R / G / B microcapsule dispersions prepared in this embodiment were passed through a 400-mesh standard sieve (pore size 38 μm), and then centrifuged (3000 rpm, 15 min). The 30 μm fraction of the red R capsules, the 28 μm fraction of the G capsules, and the 32 μm fraction of the B capsules were taken. The three were redispersed in deionized water, the solid content was adjusted to 20%, sonicated for 30 min, and then filtered through a 50 μm precision filter.

[0119] The same three-channel piezoelectric inkjet microarray printing system as in Example 1 was used for RGBG array coating (center distance 45μm), with no nozzle clogging or droplet offset, and the array structure was intact.

[0120] The obtained red R capsules had an average particle size of 30 μm, a wall thickness of 2.5 μm, a glass transition temperature of approximately 85℃, a thermal response time constant of approximately 1.0 ms, and satisfactory suspension stability. Their photothermal conversion efficiency at 820 nm was approximately 23%. The obtained green G capsules had an average particle size of 28 μm, a wall thickness of 4.0 μm, a glass transition temperature of approximately 125℃, a thermal response time constant of 3.0 ms, and satisfactory suspension stability. Their photothermal conversion efficiency at 990 nm was approximately 32%. The obtained blue B capsules had an average particle size of 32 μm, a wall thickness of 5.5 μm, a glass transition temperature of approximately 154℃, a thermal response time constant of 6.0 ms, and satisfactory suspension stability. Their photothermal conversion efficiency at 1080 nm was approximately 36%.

[0121] (II) Preparation of full-color thermal paper: 1. Preparation of base paper, same as in Example 1.

[0122] 2. Primer coating application: The coating was applied using metering rods at a rate of 6.0 g / m² (dry weight), and then dried with hot air at 80°C before undergoing in-machine double-roll soft calendering. The thickness of the resulting base coating was measured to be 6.0 μm.

[0123] 3. RGB microcapsule array coating: By uniformly adjusting the droplet volume of the three channels R / G / B of the piezoelectric inkjet printhead to 20 pL (15 pL in Example 1), and matching the microcapsules prepared in this example accordingly to avoid jet clogging, the remaining inkjet parameters, coating environment and post-processing are exactly the same as in Example 1.

[0124] 4. Vapor phase SiO2 filling: An aqueous dispersion of fumed silica (Aerosil 400, particle size 40 nm, specific surface area 400 m² / g) (solid content 20%) was used to fill the intercapsule spaces by dip coating. The filling amount was approximately 3.8 g / m² (dry weight). According to the ash content method, this filling amount accounted for 20% of the total mass of the RGB microcapsule color development layer. Then, it was dried with hot air at 60 °C.

[0125] Cross-sectional images obtained by scanning electron microscopy (SEM) show that the RGB microcapsule colorimetric layer prepared in steps 3 and 4 has a single-layer close-packed structure with a thickness of approximately 32 μm.

[0126] 5. Protective layer coating: Same as in Example 1.

[0127] Comparative Example 1 Except for the use of calcium carbonate (CaCO3) instead of fumed silica as a thermal barrier filler, the base paper, base coating, RGB microcapsules, piezoelectric inkjet array coating parameters, and protective layer in this comparative example are completely the same as in Example 1.

[0128] Specifically, in step 4, an aqueous dispersion of calcium carbonate (particle size 2μm, thermal conductivity 2.7 W / m·K) (solid content 10%) is used to fill the gaps between capsules by dip coating, with a filling amount of about 1.5 g / m², and then dried with hot air at 60°C.

[0129] Comparative Example 2 This comparative example is identical to Example 1 except that it uses conventional doctor blade coating to randomly mix and coat the R / G / B microcapsules.

[0130] Specifically, the R capsules, G capsules and B capsule dispersions prepared in Example 1 were mixed in a mass ratio of 1:1:1 and coated onto the base layer using a doctor blade. The coating amount was adjusted to be similar to the total solid content of the color development layer in Example 1. The RGBG sequence was not followed, and there was no fixed center-to-center spacing.

[0131] The subsequent vapor phase SiO2 filling and protective layer coating were the same as in Example 1.

[0132] Comparative Example 3 Except for the glass transition temperature of the wall material of both R capsule and B capsule being adjusted to 120℃ (i.e., the Tg gradient is eliminated and the Tg of G capsule is unified), this comparative example is completely the same as Example 1.

[0133] Specifically, the wall material of capsule R was changed to cross-linked PMMA, and the wall material of capsule B was also changed to cross-linked PMMA. The unsealing temperature for all three was 120°C. The remaining parameters for microcapsule preparation were the same as in Example 1. The average particle sizes of the resulting capsules were R: 25 μm, G: 22 μm, and B: 28 μm, and the wall thicknesses were R: 2 μm, G: 3.5 μm, and B: 5 μm, respectively.

[0134] The subsequent array coating, vapor phase SiO2 filling, and protective layer coating are the same as in Example 1.

[0135] Comparative Example 4 This comparative example is exactly the same as Example 1, except that the order of the "RGBG" matrix is ​​changed to an alternating arrangement of "RGB" with equal density.

[0136] Specifically, in step 3, the nozzle arrangement code of the piezoelectric inkjet printhead is changed to an "RGB" cycle, meaning each repeating unit contains one R, one G, and one B, with equal distribution densities for the three types of capsules. The center-to-center spacing between adjacent capsules remains 42 μm, and the diameter of a single capsule is approximately 25 μm. Subsequent vapor-phase SiO2 filling and protective layer coating are the same as in Example 1.

[0137] Comparative Example 5 This comparative example is identical to Example 1 except that the single-layer RGB color layer is replaced with a double-layer color layer structure.

[0138] Specifically, step 3 is modified as follows: First, a layer of R capsule dispersion (20% solid content) is coated onto the base coating using a doctor blade. After drying, an R colorimetric layer (approximately 30 μm thick) is formed. Then, a layer of mixed G / B capsule dispersion (G:B mass ratio 1:1, 20% solid content) is coated onto this layer using a doctor blade. After drying, a second colorimetric layer (approximately 30 μm thick) is formed. Vaporized SiO2 is not filled between the two layers; it is only filled above the second colorimetric layer. Finally, the top coating is applied.

[0139] Comparative Example 6 This comparative example is identical to Example 1, except that the same broad-spectrum absorber (carbon black) is used in the R / G / B capsule core material to replace the original wavelength-separated absorption nanomaterials.

[0140] Specifically, in the R capsule core material, 2 parts by mass of carbon black (50 nm particle size) replace gold nanorods; in the G capsule, 2 parts by mass of carbon black replace copper sulfide nanosheets; and in the B capsule, 2 parts by mass of carbon black replace copper sulfide nanosheets.

[0141] The parameters for wall material, emulsification, and curing are the same as in Example 1; the subsequent array coating, vapor phase SiO2 filling, and protective layer coating are the same as in Example 1.

[0142] Comparative Example 7 This comparative example is identical to Example 1 except that the gas phase SiO2 filling step is omitted.

[0143] Specifically, step 4 of Example 1 is omitted. After the RGB microcapsule array coating is completed in step 3, the protective layer coating in step 5 is directly applied. The gaps between the capsules are filled with air, and the top coating partially penetrates into the gaps.

[0144] Experimental Example In this experiment, the full-color thermal paper prepared in Examples 1-8 and Comparative Examples 1-7 was tested for color development using a laser selective color development printing device.

[0145] Test conditions: Three laser beams were combined using an optical beam combiner, and the two-dimensional motion trajectory of the light spot on the paper was controlled by an XY scanning galvanometer system. The laser beams were set to 808nm / 1W (pulse width 1ms), G laser 980nm / 1W (pulse width 4ms), and B laser 1064nm / 1.5W (pulse width 8ms), with a spot diameter of 30μm. A point-by-point dwell exposure mode was used: the spot displacement during the pulse duration did not exceed 1 / 3 of the spot diameter (equivalent dwell scanning speed ≤0.03m / s). Combined with the rapid pixel-by-pixel addressing of the XY galvanometer, this ensured the formation of clearly defined 125μm pixels. The pulse width was matched to the thermal response time constant of each capsule (R approximately 0.8ms, G approximately 2.5ms, B approximately 5.0ms) to ensure that the target capsule completed thermal accumulation and color development within the pulse duration.

[0146] The specific test results are shown in Tables 1 and 2.

[0147] Table 1. Detection results of the examples

[0148] Table 2 Comparative test results

[0149] As shown in Tables 1 and 2 above, the test results of Example 1 are as follows: (1) Monochrome color density: R≥1.2OD, G≥1.0OD, B≥1.1OD (measured by Macbeth densitometer); (2) Resolution test: Line pairs of patterns at 203dpi (125μm pixels) can be clearly distinguished; (3) Color gamut coverage: The CIE 1976 color gamut area reaches about 75% of the sRGB standard; (4) Color crosstalk test: When only R laser is turned on, there is no obvious color development in the G and B areas (density change <0.05OD), proving that the double insurance mechanism is effective; (5) Water resistance: After the printed sample is immersed in water for 24h, the color density retention rate is >90%.

[0150] The above test data demonstrates that the single-layer capsule wall microcapsules prepared using this invention can produce thermal paper that meets the requirements of actual production, solving the drawback of traditional color-developing microcapsules requiring multiple layers to be stacked. It also shows that the RGB microcapsule array coating using piezoelectric inkjet printing technology proposed in this invention not only solves the problem of the inability of traditional coating methods to accurately arrange the positioning of microcapsules, but also allows for the precise arraying of three types of microcapsules in the same planar layer in a precise "RGB" matrix sequence, so that each capsule acts as an independent sub-pixel, and full-color display is achieved by controlling the color depth (0-255 gray levels) of each sub-pixel.

[0151] In Example 2, by reducing the volume of the piezoelectric inkjet droplet from 15 pL to 10 pL, the thickness of the color development layer was reduced to 22 μm, the thermal response was further accelerated, and the monochrome color development density decreased slightly but was close to the level of Example 1. According to the above results, it can be seen that when the thickness of the color development layer is taken to the lower limit, the color development performance and response speed can still be taken into account. In Example 3, by increasing the fumed silica filling amount to the upper limit of 3.0 g / m², the thermal conductivity of the coating decreased to 0.028 W / (m·K), and the anti-color bleeding performance was optimal (density change <0.03 OD). Based on the above results, it can be concluded that 20% filling amount is the upper limit of the optimal value for thermal insulation effect. Example 4: By increasing the coating amount of the base layer from 5 g / m² to 6 g / m² (dry weight), the heat utilization rate is improved and the color density of the single color is increased by about 5% to 8%. According to the above results, the upper limit of the base layer thickness is beneficial to improving the heat utilization efficiency and color density. Example 5 shows that by reducing the top coating amount from 2.0 g / m² to 1.0 g / m² (dry weight), the light transmittance is optimal, the color density is the same as in Example 1, and the water retention rate is slightly reduced to about 88%. Based on the above results, it can be seen that the lower limit thickness of the top coating can take into account both optical transparency and protective performance. Example 6 shows that by controlling the particle size of R / G / B microcapsules to 20μm, 18μm, and 22μm (lower limits of each range), the accuracy of the spray landing point is improved, there is no nozzle clogging or droplet deviation, the array structure is intact, and the resolution is maintained at 203dpi. According to the above results, the lower limit of particle size is beneficial to further improve the array accuracy and resolution. Example 7 shows that by taking the lower limits of the respective ranges for all parameters of the R / G / B microcapsules and coatings, the prepared full-color thermal paper has the thinnest and lightest structure, the fastest thermal response (the thermal response time constant of the R capsule is only 0.5ms), high spraying accuracy, no nozzle clogging or droplet deviation, complete array structure, and a resolution of 203dpi; the monochrome color density is R≥1.1 OD, G≥0.9 OD, B≥1.0 OD, and the anti-color bleeding performance is <0.05 OD. All indicators meet the application requirements.

[0152] Example 8, by taking the upper limit of each range for all parameters of the R / G / B microcapsules and each coating, achieved the highest total amount of color-developing dye per unit area, the highest single-color color density among all examples, and a color gamut coverage of approximately 76% sRGB; the SiO2 filling ratio was increased to 20%, which enhanced the thermal insulation between microcapsules and improved the anti-color bleeding performance to <0.04 OD; the thickest top coating ensured the best water resistance, while maintaining a resolution of 203 dpi.

[0153] In summary, the results of Embodiments 1 to 8 of the present invention collectively verify that the upper and lower limits of the parameter ranges of the present invention are indeed feasible, and that the parameters can be adjusted to flexibly balance between thinness and speed and high density and high color gamut, thus meeting the needs of different application scenarios.

[0154] In contrast, Comparative Example 1 used calcium carbonate (CaCO3) instead of fumed silica as a thermal barrier filler (CaCO3 has a thermal conductivity of 2.7 W / m·K, which is about two orders of magnitude higher than that of fumed SiO2), and the cross-color density changed by more than 0.15 OD. Based on the above results, it can be seen that low thermal conductivity nanofillers are indispensable for thermal insulation, which in turn proves the necessity of fumed silica. Comparative Example 2 uses traditional doctor blade coating to randomly mix and coat R / G / B microcapsules. The microcapsules cannot be positioned at the pixel level, the colors are turbid, and the resolution is less than 100 dpi. Based on the above results, it can be seen that piezoelectric inkjet array coating is a key means to achieve pixel-level color control. In Comparative Example 3, since the Tg gradient of the wall material was eliminated, the Tg of R capsules and B capsules were uniformly adjusted to 120℃. R capsules softened and developed color prematurely under G laser irradiation, and B capsules had insufficient unsealing threshold, resulting in a significant decrease in color purity and a change in cross-color density exceeding 0.10OD. Based on the above results, it can be seen that the Tg gradient is a necessary design to prevent false triggering of the temperature dimension. In Comparative Example 4, by changing the order of the "RGBG" matrix to an alternating arrangement of "RGB" with equal density, the density of green subpixels is halved, the green color density drops to about 0.7OD, and the visual sharpness of the image decreases. According to the above results, it can be seen that the green density in the RGBG arrangement doubles, which is more in line with the visual characteristics of the human eye and improves sharpness. Comparative Example 5 shows that by changing the single-layer RGB color layer to a double-layer color layer structure, the total thickness doubled, the thermal response delay increased, and the interlayer crosstalk exceeded 0.10 OD. Based on the above results, it can be seen that single-layer planar integration has advantages in thickness and response speed compared to multi-layer stacking. Comparative Example 6 uses general-purpose carbon black instead of wavelength-specific nanomaterials as photothermal conversion agents. Carbon black has a broad spectrum of absorption, and any wavelength of laser light causes the three-color capsules to show color simultaneously, completely losing wavelength selectivity. Based on the above results, it can be seen that the photothermal conversion agent with wavelength-specific absorption is the core to achieve selective color development. Comparative Example 7 omitted the fumed silica filling step, resulting in miscoloration of adjacent microcapsules, density changes exceeding 0.2 OD, and blurred color edges. Based on the above results, it can be concluded that the interstitial thermal barrier filler is indispensable for suppressing lateral thermal diffusion and ensuring pixel-level independent color development.

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A full-color thermal paper, characterized in that, From bottom to top, it includes: base paper, bottom coating, RGB microcapsule color development layer and top coating; The RGB microcapsule color layer is a single-layer structure, which includes red R capsules, green G capsules and blue B capsules, as well as fumed silica thermal barrier filler filling the gaps between the microcapsules to achieve thermal isolation between the microcapsules. The red R capsule, green G capsule, and blue B capsule are arranged in a two-dimensional array in a horizontal plane. The two-dimensional array consists of multiple array periodic units. Each array periodic unit contains one red R capsule, two green G capsules, and one blue B capsule arranged in RGBG order. The distribution density of the green G capsule is greater than that of the red R capsule and greater than that of the blue B capsule. The red R capsule, green G capsule, and blue B capsule are all single-layer capsule wall structures with the core material covered by the wall material.

2. The full-color thermal paper according to claim 1, characterized in that, The red R capsule is coated with a photothermal conversion agent to absorb the first wavelength, the green G capsule is coated with a photothermal conversion agent to absorb the second wavelength, and the blue B capsule is coated with a photothermal conversion agent to absorb the third wavelength, and the first wavelength, the second wavelength, and the third wavelength are different from each other. The first wavelength is 800~820nm, the second wavelength is 970~990nm, and the third wavelength is 1050~1080nm; And / or, the glass transition temperatures of the wall materials of the red R capsule, green G capsule and blue B capsule are a first temperature, a second temperature and a third temperature, respectively, and the first temperature, the second temperature and the third temperature are different from each other; And / or, the glass transition temperature of the wall material of the red R capsule is 75~85℃, the glass transition temperature of the wall material of the green G capsule is 115~125℃, and the glass transition temperature of the wall material of the blue B capsule is 145~155℃. And / or, the wall thicknesses of the red R capsule, green G capsule and blue B capsule are the first wall thickness, the second wall thickness and the third wall thickness, respectively, and the first wall thickness < the second wall thickness < the third wall thickness; And / or, the wall thickness of the red R capsule is 1.5~2.5μm, the wall thickness of the green G capsule is 3.0~4.0μm, and the wall thickness of the blue B capsule is 4.5~5.5μm; And / or, the thermal response time constant of the red R capsule is 0.5~1.0 ms, the thermal response time constant of the green G capsule is 2.0~3.0 ms, and the thermal response time constant of the blue B capsule is 4.0~6.0 ms.

3. The full-color thermal paper according to claim 1, characterized in that, The red R capsule is a single-layer capsule wall structure in which the core material is covered by the wall material, and the wall material is a modified polyurethane with a low glass transition temperature. The modified polyurethane with a low glass transition temperature is a flexible long-chain polyether diol modified polyurethane, and the glass transition temperature of the modified polyurethane is 75~85℃. The core material of the red R capsule includes rhodamine B lactone, bisphenol A, butyl stearate, and gold nanorods, which absorb laser light with a wavelength of 800-820 nm.

4. The full-color thermal paper according to claim 1, characterized in that, The green G capsule is a single-layer capsule wall structure in which the core material is covered by a wall material. The wall material is cross-linked polymethyl methacrylate or polyurea, and the glass transition temperature is 115~125℃. The core material of the green G capsule includes zeaxanthin-based green leuco dye, bisphenol S, tetradecyl alcohol, and copper sulfide nanosheets, which absorb laser light with a wavelength of 970-990 nm.

5. The full-color thermal paper according to claim 1, characterized in that, The blue B capsule is a single-layer capsule wall structure in which the core material is covered by a wall material, and the wall material is a highly cross-linked polyurethane or aromatic polyurea. The highly crosslinked polyurethane increases its glass transition temperature by adding a crosslinking agent, and the aromatic polyurea contains a rigid aromatic ring structure in its molecular backbone to increase its glass transition temperature; the glass transition temperature of the highly crosslinked polyurethane or aromatic polyurea is 145~155℃. The core material of the blue B capsule includes crystal violet lactone (CVL), benzyl benzoate, and copper sulfide nanosheets, which absorb laser light with a wavelength of 1050-1080 nm.

6. The full-color thermal paper according to claim 1, characterized in that, The thickness of the RGB microcapsule color-developing layer is 22~32μm; And / or, the particle size of the fumed silica thermal barrier filler in the RGB microcapsule color layer is 7~40nm, the specific surface area is 200~400m² / g, and the filling amount accounts for 10~20% of the total mass of the RGB microcapsule color layer; And / or, the center-to-center distance between adjacent microcapsules in the RGB microcapsule color development layer is 40~45μm; And / or, the base coating comprises hollow plastic pigment, calcined kaolin, styrene-butadiene latex and polyvinyl alcohol, with a coating amount of 4~6 g / m² and a thickness of 5~6 μm; And / or, the top coating comprises modified polyvinyl alcohol, crosslinking agent, fumed silica filler and lubricant, with a coating amount of 1~2 g / m² and a thickness of 1.5~2 μm.

7. A method for preparing full-color thermal paper according to any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: (A) Forming a base coating on the base paper; (B) Using piezoelectric inkjet microarray coating technology, a first dispersion containing red R capsules, a second dispersion containing green G capsules, and a third dispersion containing blue B capsules are sprayed onto the base layer in an RGBG periodic unit array to form a two-dimensional array of RGB microcapsule color layer, wherein the R, G, and B capsules in the RGB microcapsule color layer are arranged in a two-dimensional array in the horizontal plane. (C) The microcapsule gaps of the RGB microcapsule color layer are filled with fumed silica thermal barrier filler; (D) A top coating is formed on the RGB microcapsule color development layer.

8. The preparation method according to claim 7, characterized in that, The piezoelectric inkjet microarray uses three piezoelectric inkjet printheads, each loaded with the first dispersion, the second dispersion, and the third dispersion.

9. The preparation method according to claim 7, characterized in that, The red R capsule, green G capsule, and blue B capsule are each prepared independently through the following steps: S1: Prepare wall material solution and core material dispersion separately, mix and emulsify the core material dispersion and wall material solution to form an emulsion, and use the emulsion to form a capsule wall on the surface of the core material droplet through a wall-forming reaction; S2: After the product in S1 is solidified and shaped, it is washed, purified, sieved and classified to obtain microcapsules with uniform particle size. The microcapsules are redispersed in a dispersion medium to prepare a dispersion for piezoelectric inkjet printing. The red R capsules have a sieve particle size of 20-30 μm, the green G capsules have a sieve particle size of 18-28 μm, and the blue B capsules have a sieve particle size of 22-32 μm.

10. The application of a full-color thermal paper according to any one of claims 1 to 6 or a full-color thermal paper prepared by the preparation method according to any one of claims 7 to 9 in the preparation of laser selective color printing.

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