Coating with covering and thermochromic characteristics, thermosensitive chromophoric material, and preparation process and application of thermosensitive chromophoric material

Abstract

The invention belongs to the technical field of thermosensitive color development materials, and particularly relates to a coating with covering and thermochromic characteristics, a thermosensitive color development material and a preparation process and application thereof.The coating is prepared from, by mass, 80-99 parts of polymer hollow spheres A, 1-20 parts of polymer hollow spheres B, 5-60 parts of scattering particles, 1-30 parts of adhesive and 0-3 parts of water repellent agent, 0-20 parts of a coalescing agent and 0-1 part of a lubricant; the Tg of the polymer hollow sphere A is 50-90 DEG C, and the Tg of the polymer hollow sphere B is greater than 90 DEG C; and the melting point of the scattering particles is 50-150 DEG C. A coating layer prepared from the coating has better covering performance and shows higher whiteness and lower color density value before color development, meanwhile, the lowest color development temperature is larger than or equal to 85 DEG C, and production scrapping caused by color development in advance on a production line is avoided.

Description

Technical Field

[0001] This invention belongs to the field of thermosensitive color-developing materials technology, specifically relating to a coating, thermosensitive color-developing material, preparation process and application with covering and thermochromic properties. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Thermal materials, as a type of information recording material that uses a heat-sensitive coating to generate color, are widely used in fields such as ticket printing and label marking. Traditional thermal materials are mainly composed of a base layer (base paper or film, etc.) and a thermal coating (containing colorant, developer, sensitizer, etc.). In some application scenarios, a protective top coating is added to improve waterproof, oil-proof, wear-resistant, and alcohol-proof properties. Its color generation principle is: when the print head is heated, the colorless dye in the coating reacts chemically with the developer to form a visible color. The disadvantages of traditional thermal materials generally include the following aspects: (1) Poor preservation stability: Traditional thermal materials rely on chemical color development reactions. Under light, high temperature, and humidity, the color molecules are easily decomposed or oxidized, causing the writing to fade. For example, the shelf life of ordinary thermal paper at room temperature is usually only 1-2 years, and the shelf life is even shorter in high temperature and high humidity environments, which cannot meet the long-term preservation needs of archives, medical records, etc.; (2) Insufficient environmental protection: Bisphenol A (BPA) is commonly used as a developer in traditional coatings. It has endocrine interference properties and poses potential hazards to human health and the ecological environment. In addition, some sensitizers and adhesives contain volatile organic compounds (VOCs), which can easily cause pollution during the production process.

[0004] Currently, the industry is trying to improve the performance of traditional thermosensitive materials in the following ways: (1) Adding antioxidants or ultraviolet absorbers: Although they can delay fading, they have limited effect on inhibiting molecular decomposition under high temperature and high humidity conditions; (2) Developing BPA-free color developers: such as using bisphenol S (BPS) to replace BPA, but BPS still has similar toxicity risks; (3) Multi-layer composite coating design: By adding a barrier layer, environmental tolerance can be improved, but the process is complicated and the cost is high.

[0005] Other approaches abandon chemical color-developing principles and develop physically color-developing thermosensitive materials. For example, a layer of porous polymer particles is placed on a colored carrier under dry conditions. By applying heat, the opacity of selected areas is reduced, thereby forming an image. Some existing technologies require the polymer particles to have a first polymer inner shell with a Tg of 40-130℃ and a second polymer outer shell with a Tg of -55-50℃. However, an unreasonable cavity collapse temperature in the coating can result in lower coating opacity and a lower color-developing temperature. This poses a risk of online drying and color development during actual production, or limits its use in heat-contact scenarios such as hot drinks and hot meals, and also affects the color-developing performance of the material. Simultaneously, a low softening temperature in the coating can also result in low cavity pressure resistance, making it prone to color development through friction or slight pressure. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a coating, a thermosensitive colorant, and its preparation process and application with covering and thermochromic properties.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a coating having covering and thermochromic properties, comprising, by weight, the following components: 80-99 parts of polymer hollow spheres A, 1-20 parts of polymer hollow spheres B, 5-60 parts of scattering particles, 1-30 parts of adhesive, 0-3 parts of water-resistant agent, 0-20 parts of film-forming aid, and 0-1 part of lubricant. The Tg of the polymer hollow sphere A is 50-90℃, and the Tg of the polymer hollow sphere B is >90℃. The melting point of the scattering particles is 50-150℃.

[0008] In a second aspect, the present invention provides a thermosensitive color-emitting material, comprising a substrate and a thermosensitive coating, wherein the thermosensitive coating is attached to the substrate and the thermosensitive coating is prepared by coating with a coating having covering and thermochromic properties; The color layer is placed between the substrate and the heat-sensitive coating, or the substrate itself is colored, or the heat-sensitive coating itself is colored; Before printing and color development, the color of the color layer is partially or completely covered by a thermal coating.

[0009] Thirdly, the present invention provides a method for preparing the heat-sensitive color-emitting material, comprising the following steps: mixing polymer hollow spheres A, polymer hollow spheres B, dispersing particles, adhesive, water-resistant agent, film-forming aid and lubricant in proportion to obtain a coating; The coating is applied to a substrate with a color layer and dried to obtain the final product. Alternatively, color particles can be added to the coating, mixed well, applied to the substrate, and dried to obtain the final product.

[0010] Fourthly, this invention provides the application of the aforementioned thermal color-emitting material in the preparation of information recording materials. This invention relates to thermal paper (materials) such as label paper and cash register paper, which, in practical applications, can be used as labels to adhere to hot beverage packaging or for heating while maintaining information integrity.

[0011] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: The coating prepared by the paint of the present invention has better hiding performance, which is manifested by higher whiteness and lower color density value before printing and color development, while the minimum color development temperature is ≥85℃, avoiding premature color development on the production line and thus production scrap.

[0012] The coating has better opacity: the paper whiteness is increased while the color density is reduced, indicating better coverage of the base color. This helps to improve the color contrast during printing and improve the printing effect.

[0013] This invention has a lower color density at 100℃ and a higher color development temperature, which can avoid the waste caused by color development during the drying stage of the production process. It also makes the product more suitable for use in hot beverage and microwave oven scenarios. Attached Figure Description

[0014] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0015] Figure 1 This is the first method of setting the color layer in this embodiment of the invention; Figure 2 This is the second method of setting the color layer in this embodiment of the invention; Figure 3 This is the third way to set the color layer in this embodiment of the invention. Detailed Implementation

[0016] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0017] Paper whiteness is the ability of paper to reflect visible light (especially blue light band), and it is a key indicator for measuring the whiteness of paper. It is usually measured by a whiteness meter according to the national standard GB / T 7974 Determination of the blue light diffuse reflectance factor D65 brightness of paper, paperboard and pulp (diffuse / vertical method, outdoor daylight conditions)

[0018] The color density of paper is the density of the paper sample tested using a reflectance densitometer (compliant with GB / T23649 requirements), representing the depth of color.

[0019] Dynamic saturation color density is an indicator for measuring the dynamic color development performance of thermal materials. It adopts the "GBT28210-2024 Thermal Paper - Appendix B Determination of Dynamic Color Development". In the thermal color development material of this invention, dynamic saturation color density reflects the maximum color development capability of the material under dynamic heating conditions simulating actual printing (such as rapid heating of the print head): the higher the value, the darker the printed text color and the higher the clarity.

[0020] Color density at 100℃ is an indicator of the degree of color development of a thermosensitive material at 100℃. The lower the value, the less likely the material is to develop color prematurely at 100℃. A lower color density at 100℃ can prevent color development during the drying stage of production, which could lead to scrapping. At the same time, it can improve the applicability of the product in high-temperature contact scenarios such as hot drinks and microwave ovens. It adopts the standard GB / T 28210-2024 Thermal Paper - Appendix A Determination of Static Color Development.

[0021] The static color development curve represents the relationship between the color development density of the thermal material and the printing temperature. The static saturated color development density represents the highest color development density. The method used is "GBT28210-2024 Thermal Paper - Appendix A Determination of Static Color Development".

[0022] In order to solve the technical problems described in the background art, the present invention provides a coating having covering and thermochromic properties, comprising the following components by weight: 80-99 parts of polymer hollow spheres A, 1-20 parts of polymer hollow spheres B, 5-60 parts of scattering particles, 1-30 parts of adhesive, 0-3 parts of water-resistant agent, 0-20 parts of film-forming aid, and 0-1 part of lubricant; The Tg of the polymer hollow sphere A is 50-90℃, and the Tg of the polymer hollow sphere B is >90℃. The melting point of the scattering particles is 50-150℃.

[0023] Thermochromic properties refer to the fact that in the unprinted state, the coating is a porous scattering layer with air filling the pores or interparticle gaps, exhibiting a strong light scattering effect. The color surface of the base paper is obscured, appearing light-colored. During printing, the print head is locally heated. At temperatures close to or higher than the glass transition temperature (Tg) of hollow sphere A, polymer hollow sphere A softens and collapses, losing its hollow structure and reducing its covering power. Meanwhile, polymer hollow sphere B retains its hollow structure, adsorbing some molten scattering particles to reduce light scattering, thus losing some of its covering power while maintaining a certain level of compressive strength. This reduced covering power means the base paper colorant develops, resulting in darker printed information.

[0024] Specifically, the glass transition temperature (Tg) of polymer hollow sphere A, as the main thermotropic component of the coating, determines the color trigger temperature. When the printhead is heated to near or above its Tg, hollow sphere A softens and collapses, losing its hollow structure. This weakens the coating's opacity, allowing the base color (color layer or substrate color) to develop. Setting the Tg of polymer hollow sphere A to 50-90℃ ensures its structural stability under normal production drying temperatures, preventing premature collapse.

[0025] The high glass transition temperature of polymer hollow sphere B allows it to maintain a hollow structure in printing heating or heat contact scenarios (such as hot beverage packaging), thus preserving the mechanical strength of the coating and preventing overall collapse.

[0026] The hollow structure of polymer hollow spheres B enhances light scattering through air pores. Non-hollow materials reduce the porosity of the coating, leading to decreased light scattering ability, reduced paper whiteness, and increased color density. If replaced with non-hollow materials, air gaps cannot be formed, weakening the ability to cover the substrate or color layer, making the base color easily visible before printing.

[0027] The high Tg of polymer hollow spheres B can suppress structural changes at high temperatures. If replaced with non-hollow materials, the color density at 100℃ may increase significantly due to differences in thermal expansion or thermal conductivity. Moreover, non-hollow materials cannot adsorb molten scattering particles, resulting in incomplete elimination of light scattering and a possible decrease in dynamic saturation color density, affecting print clarity.

[0028] Polymer hollow spheres B maintain their hollow structure during printing heating, preserving the coating's mechanical strength. Replacing them with non-hollow materials may lead to excessive rigidity or lack of elasticity, causing the coating to crack or collapse under thermal stress. Non-hollow materials cannot buffer external forces, reducing the coating's compressive strength and making it more susceptible to color development triggered by friction or slight pressure.

[0029] Before printing, the scattering particles are dispersed in the coating as solid particles, forming a porous structure with the hollow spheres. They cover the base color through the light scattering effect of air pores and particle gaps, resulting in high whiteness and low color density. During printing, they melt under heating (close to the Tg of hollow sphere A), filling the pores of the hollow spheres or particle gaps, eliminating light scattering, further reducing the covering power, and enhancing the contrast of the base color development. Some scattering particles (such as stearamide and polyethylene wax) can provide lubrication, wear resistance, non-sticking, or waterproof properties.

[0030] Scattering particles mask the base color through light scattering effects in air pores and between particles. Their absence weakens the coating's light scattering ability, leading to decreased paper whiteness and increased color density. They also fail to effectively mask the base color or color layer, resulting in the base color appearing before printing, affecting product aesthetics and user experience. While melting scattering particles can fill pores and enhance the contrast of the base color development, their absence reduces this contrast. Furthermore, the coating's thermal stability decreases at high temperatures, making it prone to premature color development during drying or heat-contact processes, leading to product scrap.

[0031] In some embodiments, the Tg of polymer hollow sphere B is ≥120℃, and the Tg of polymer hollow sphere A is 60-80℃.

[0032] The preparation method of the aforementioned polymer hollow spheres A and B can be found in patent CN1269850C. The hollow spheres are produced through core-shell polymerization, where a core containing numerous carboxyl groups is encapsulated within the particle. Then, through acid-base neutralization, the carboxyl groups are opened, allowing a large amount of water to fill the particle's interior. After drying, the water evaporates from the particle, leaving an air-filled space, thus forming particles with a hollow structure.

[0033] By selecting the monomers and their amounts, polymers with the desired glass transition temperature (Tg) can be obtained through polymerization. The glass transition temperature (Tg) is referred to as... g The FOX formula can be used for approximate estimation. Its mathematical expression is: ; In the formula, T g It is the glass transition temperature of the copolymer, K; T gi It is the glass transition temperature (K; W) of the homopolymer of comonomer i. i It is the mass fraction of comonomer i in the total amount of monomers.

[0034] In some embodiments, the particle size of the polymer hollow sphere A is 200-1500 nm; the particle size of the polymer hollow sphere B is 1000-3000 nm.

[0035] The core function of polymer hollow spheres B is to maintain the hollow structure at high temperatures (such as printing heating and thermal contact scenarios), providing mechanical support for the coating and preventing overall collapse. Larger particle sizes (1000-3000nm) can form a more stable skeletal structure, enhancing the coating's compressive strength and deformation resistance, preventing cracking or damage due to the loss of support after the collapse of polymer hollow spheres A. In contrast, polymer hollow spheres A, as a thermally responsive component, need to soften and collapse rapidly upon heating; smaller particle sizes are more conducive to a uniform response to temperature changes, synergistically filling pores with the scattering particles.

[0036] Polymer hollow spheres B (large particle size) provide macroscopic pores, scattering visible light through the air-particle interface and improving overall opacity; polymer hollow spheres A (small particle size) fill the gaps between large particles, refine the pore structure, further enhance the uniformity of light scattering, and avoid local light transmission caused by excessively large pores. The combination of the two can achieve higher paper whiteness and lower color density.

[0037] In some embodiments, the coating having covering and thermochromic properties comprises, by weight, the following components: 80-95 parts of polymer hollow spheres A, 5-20 parts of polymer hollow spheres B, 5-60 parts of scattering particles, 10-30 parts of adhesive, 1-3 parts of water-resistant agent, 5-20 parts of film-forming aid, and 0.3-1 parts of lubricant.

[0038] Preferably, the coating having covering and thermochromic properties comprises, by weight, the following components: 85-93 parts of polymer hollow spheres A, 5-15 parts of polymer hollow spheres B, 10-40 parts of scattering particles, 10-30 parts of adhesive, 1-3 parts of water-resistant agent, 5-20 parts of film-forming aid, and 0.3-1 part of lubricant.

[0039] Preferably, the scattering particles are selected from at least one of fatty acids, fatty acid amides, fatty acid salts, waxes, DPS (diphenyl sulfone), DPE (1,2-diphenoxyethane), and BON (2-naphthol benzyl ether).

[0040] Light-scattering particles, typically added to coatings in the form of aqueous dispersions, are applied to paper. As the moisture in the coating evaporates, the particles remain discontinuously dispersed within the coating due to the coating temperature being below its melting point. Gaps exist between the particles, giving them light-scattering properties and thus a certain degree of masking ability. However, during printing, the print head heats them, causing them to soften and melt, filling the gaps between the particles or the pores of the hollow spheres. This eliminates light scattering and the masking ability is lost, allowing for development. Their synergistic effect with the hollow spheres provides contrast before and after printing, while also facilitating heat transfer and improving color development. Some dispersed particles can also provide lubrication, wear resistance, anti-sticking properties, and water resistance.

[0041] More preferably, the particle size of the scattering particles is 500-5000 nm, and more preferably 700-1500 nm.

[0042] More preferably, the fatty acid is stearic acid or palmitic acid; Fatty acid amides are stearamides or palmitamides; The fatty acid salt is zinc stearate; The wax is paraffin wax, polyethylene wax, or oxidized polyethylene wax.

[0043] More preferably, the scattering particles are stearamide or polyethylene wax.

[0044] In some embodiments, the adhesive is selected from at least one of polyvinyl alcohol, styrene-acrylic latex, styrene-butadiene latex, polyurethane, acrylic latex, and starch.

[0045] In some embodiments, the water-repellent agent is selected from zirconium carbonate, glyoxal, amino resin, PAPU polyamide polyurea resin, or PAE resin.

[0046] Preferably, the amino resin is glyoxal resin.

[0047] The water-resistant agent is used to improve the water resistance of the coating.

[0048] In some embodiments, the film-forming aid is selected from alcohols, alcohol ethers, alcohol esters, or alcohol ether esters.

[0049] Preferably, the alcohol is ethylene glycol, propylene glycol, hexanediol, or benzyl alcohol; The alcohol ethers are dipropylene glycol monopropyl ether (DPnB), ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol n-butyl ether, or propylene glycol phenyl ether. The alcohol esters are alcohol ester-12 or alcohol ester-16; The alcohol ether esters are hexanediol butyl ether acetate or ethyl 3-ethoxypropionate.

[0050] Film-forming aids are used to improve film-forming properties.

[0051] In a second aspect, the present invention provides a thermosensitive color-emitting material, comprising a substrate and a thermosensitive coating, wherein the thermosensitive coating is attached to the substrate and the thermosensitive coating is prepared by coating with a coating having covering and thermochromic properties; The color layer is placed between the substrate and the heat-sensitive coating, or the substrate itself is colored, or the heat-sensitive coating itself is colored; Before printing and color development, the color of the color layer is partially or completely covered by a thermal coating.

[0052] The color layer must have sufficient color density to ensure adequate color density after color development.

[0053] In some embodiments, the coating amount on the substrate is 1-10 gsm, preferably 2-4 gsm.

[0054] In some embodiments, the substrate is paper or film.

[0055] In some embodiments, a heat-insulating coating is further included, which is attached to the substrate and a color layer is disposed on the heat-insulating coating.

[0056] Preferably, the heat-insulating coating contains colorant particles such as carbon black. In this case, the coating can simultaneously function as a heat-insulating layer and a colorant layer.

[0057] The heat-insulating coating reduces heat transfer to the substrate, improving print quality.

[0058] Preferably, the material of the heat-insulating coating comprises, by weight, the following components: 100 parts pigment, 5-25 parts colorant, and 5-30 parts adhesive.

[0059] More preferably, the pigment is selected from calcined kaolin, hollow sphere pigment, silica, or aluminum silicate; the adhesive is selected from starch, latex (including styrene-butadiene latex and styrene-acrylic latex), styrene-acrylic latex, PVA and its modified forms, or polyurethane.

[0060] Hollow sphere pigments and silica have high porosity. After the coating dries, air fills the pores. Since air is a poor conductor of heat, it can reduce the heat from the printhead being transferred to the substrate, thereby improving thermal printing performance.

[0061] More preferably, the pigment is a hollow sphere pigment and calcined kaolin in a ratio of 10:90-40:60, and the adhesive is latex.

[0062] Thirdly, the present invention provides a method for preparing the heat-sensitive color-emitting material, comprising the following steps: mixing polymer hollow spheres A, polymer hollow spheres B, dispersing particles, adhesive, water-resistant agent, film-forming aid and lubricant in proportion to obtain a coating; The coating is applied to a substrate with a color layer and dried to obtain the final product. Alternatively, color particles can be added to the coating, mixed well, applied to the substrate, and dried to obtain the final product.

[0063] Fourthly, the present invention provides the application of the thermosensitive color-emitting material in the preparation of information recording materials.

[0064] The present invention will be further described below with reference to the embodiments.

[0065] Example 1 The coating, which has hiding and thermochromic properties, comprises the following components by weight: 90 parts of polymer hollow spheres A, 10 parts of polymer hollow spheres B, 20 parts of stearamide scattering particles, 20 parts of polyvinyl alcohol adhesive, 2 parts of glyoxal water-resistant agent, 10 parts of dipropylene glycol monopropyl ether film-forming aid, 0.5 parts of zinc stearate lubricant, and the remainder being water solvent.

[0066] Polymer hollow sphere A is a commercially available product from Foshan Rosef Technology Co., Ltd.; hollow sphere HT-3000; glass transition temperature Tg is 65℃.

[0067] Polymer hollow sphere B is a commercially available product from Foshan Rosef Technology Co., Ltd.; hollow sphere HN-2100 has a glass transition temperature (Tg) of 120℃.

[0068] The particle size of polymer hollow sphere A is 400-1000 nm; the particle size of polymer hollow sphere B is 1500-2000 nm; and the average particle size of stearamide scattering particles is 3000 nm.

[0069] The preparation method of the thermosensitive color-developing material includes the following steps: Polymer hollow spheres A, polymer hollow spheres B, dispersing particles, adhesive, water-repellent agent, film-forming aid, and lubricant are mixed in proportion to obtain a coating. The coating is applied to paper with a colored layer at a rate of 4 gsm, and then dried.

[0070] Example 2 The coating, which has opacifying and thermochromic properties, comprises the following components by weight: 95 parts of polymer hollow spheres A, 5 parts of polymer hollow spheres B, 40 parts of polyethylene wax scattering particles, 20 parts of styrene-butadiene rubber latex adhesive, 1 part of ammonium zirconium carbonate water-resistant agent, 5 parts of ethylene glycol film-forming aid, 0.5 parts of calcium stearate lubricant, and the remainder being water solvent.

[0071] Polymer hollow sphere A is a commercially available product from Foshan Rosef Technology Co., Ltd.; hollow sphere HT-3000; glass transition temperature Tg is 65℃.

[0072] Polymer hollow sphere B is a commercially available product from Foshan Rosef Technology Co., Ltd.; hollow sphere HN-2100 has a glass transition temperature (Tg) of 120℃.

[0073] The particle size of polymer hollow sphere A is 400-1000 nm; the particle size of polymer hollow sphere B is 1500-2000 nm; and the average particle size of polyethylene wax scattering particles is 1000 nm.

[0074] The preparation method of the thermosensitive color-developing material includes the following steps: Polymer hollow spheres A, polymer hollow spheres B, dispersing particles, adhesive, water-repellent agent, film-forming aid, and lubricant are mixed in proportion to obtain a coating. The coating is applied to paper with a colored layer at a rate of 3 gsm, and then dried.

[0075] Example 3 The coating, which has both covering and thermochromic properties, comprises the following components by weight: 85 parts of polymer hollow spheres A, 15 parts of polymer hollow spheres B, 30 parts of diphenyl sulfone (DPS) scattering particles, 25 parts of polyvinyl alcohol adhesive, 2 parts of glyoxal water-resistant agent, 10 parts of alcohol ester-12 film-forming aid, 0.5 parts of zinc stearate lubricant, and the remainder being water solvent.

[0076] Polymer hollow sphere A is a commercially available product from Foshan Rosef Technology Co., Ltd.; hollow sphere HT-3000; glass transition temperature Tg is 65℃.

[0077] Polymer hollow sphere B is a commercially available product from Foshan Rosef Technology Co., Ltd.; hollow sphere HN-2100 has a glass transition temperature (Tg) of 120℃.

[0078] The particle size of polymer hollow sphere A is 400-1000 nm; the particle size of polymer hollow sphere B is 1500-2000 nm; and the average particle size of diphenyl sulfone (DPS) scattering particles is 2000 nm.

[0079] The preparation method of the thermosensitive color-developing material includes the following steps: Polymer hollow spheres A, polymer hollow spheres B, dispersing particles, adhesive, water-repellent agent, film-forming aid, and lubricant are mixed in proportion to obtain a coating. The coating is applied to paper with a colored layer at a rate of 5 gsm, and then dried.

[0080] Comparative Example 1 The difference from Example 1 is that the polymer hollow sphere B is replaced with polymer hollow sphere A, and the scattering particles are omitted; otherwise, they are the same as in Example 1.

[0081] Comparative Example 2 The difference from Example 1 is that polymer hollow sphere B is replaced with polymer hollow sphere A, while everything else is the same as in Example 1.

[0082] Comparative Example 3 The difference from Example 1 is that: 10 parts of polymer hollow sphere A and 90 parts of polymer hollow sphere B are used, while all other parts are the same as in Example 1.

[0083] Comparative Example 4 The difference from Example 1 is that: 50 parts of polymer hollow sphere A and 50 parts of polymer hollow sphere B are used, while all other parts are the same as in Example 1.

[0084] Comparative Example 5 The difference from Example 1 is that the scattering particles are omitted, but everything else is the same as Example 1.

[0085] The relevant properties of the thermosensitive color-emitting materials prepared in Examples 1-3 and Comparative Examples 1-5 are shown in Table 1.

[0086] Table 1 Paper indicators Paper whiteness % Paper color density Dynamic saturation color density Color density at 100℃ Static saturation color density Example 1 54.23 0.37 0.84 0.13 1.09 Example 2 55.2 0.40 0.92 0.15 1.15 Example 3 58.2 0.30 0.87 0.08 1.12 Comparative Example 1 50.41 0.44 0.79 0.38 1.08 Comparative Example 2 51.92 0.42 0.85 0.32 1.12 Comparative Example 3 58.42 0.27 0.62 0.07 0.77 Comparative Example 4 59.31 0.20 0.67 0.02 0.45 Comparative Example 5 52.61 0.39 0.62 0.06 0.58 Compared to Comparative Examples 1 and 2, the paper prepared in Examples 1-3 has increased whiteness and decreased color density, indicating better coverage of the background color. This helps to improve the color contrast during printing and improve the printing effect. In terms of color density at 100°C, the thermosensitive color-emitting material of the examples has a lower color density at 100°C. This can avoid color development during the drying stage of production, which would lead to scrap or overall color development and loss of printing information when used for hot beverage labels.

[0087] Compared to Example 1, the thermal color-developing materials prepared in Comparative Examples 3 and 4 have an excessively high content of hollow sphere B, resulting in higher paper whiteness and lower color density, indicating better coverage of the base color. However, because hollow sphere B has a higher glass transition temperature (Tg) and its color development temperature exceeds 100°C, the printed color density is lower, leading to a decrease in printing quality.

[0088] Compared to Example 1, the thermal color-emitting material prepared in Comparative Example 5 removed scattering particles, resulting in increased paper color density. This indicates a decrease in the coverage of the base color, leading to a decrease in color contrast during printing and a decline in printing quality.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A coating with covering and thermochromic properties, characterized in that: By weight, it includes the following components: 80-99 parts of polymer hollow spheres A, 1-20 parts of polymer hollow spheres B, 5-60 parts of scattering particles, 1-30 parts of adhesive, 0-3 parts of water-resistant agent, 0-20 parts of film-forming aid, and 0-1 part of lubricant. The Tg of the polymer hollow sphere A is 50-90℃, and the Tg of the polymer hollow sphere B is >90℃. The melting point of the scattering particles is 50-150℃.

2. The coating with covering and thermochromic properties according to claim 1, characterized in that: The Tg of polymer hollow sphere B is ≥120℃, while the Tg of polymer hollow sphere A is 60-80℃. Preferably, the particle size of the polymer hollow sphere A is 200-1500 nm; the particle size of the polymer hollow sphere B is 1000-3000 nm.

3. The coating with covering and thermochromic properties according to claim 1, characterized in that: The coating having covering and thermochromic properties comprises, by weight, the following components: 80-95 parts of polymer hollow spheres A, 5-20 parts of polymer hollow spheres B, 5-60 parts of scattering particles, 10-30 parts of adhesive, 1-3 parts of water-resistant agent, 5-20 parts of film-forming aid, and 0.3-1 parts of lubricant. Preferably, the coating having covering and thermochromic properties comprises, by weight, the following components: 85-93 parts of polymer hollow spheres A, 5-15 parts of polymer hollow spheres B, 10-40 parts of scattering particles, 10-30 parts of adhesive, 1-3 parts of water-resistant agent, 5-20 parts of film-forming aid, and 0.3-1 part of lubricant; Preferably, the scattering particles are selected from at least one of fatty acids, fatty acid amides, fatty acid salts, waxes, DPS, DPE, and BON. Preferably, the particle size of the scattering particles is 500-5000 nm, and more preferably 700-1500 nm; Preferably, the fatty acid is stearic acid or palmitic acid; Fatty acid amides are stearamides or palmitamides; The fatty acid salt is zinc stearate; The wax is paraffin wax, polyethylene wax, or oxidized polyethylene wax; Preferably, the scattering particles are stearamide or polyethylene wax.

4. The coating with covering and thermochromic properties according to claim 1, characterized in that: The adhesive is selected from at least one of polyvinyl alcohol, styrene-acrylic latex, styrene-butadiene latex, polyurethane, acrylic latex, and starch.

5. The coating with covering and thermochromic properties according to claim 1, characterized in that: The water-resistant agent is selected from zirconium carbonate, glyoxal, amino resin, PAPU polyamide polyurea resin, or PAE resin; Preferably, the amino resin is glyoxal resin; Alternatively, the film-forming aid is selected from alcohols, alcohol ethers, alcohol esters, or alcohol ether esters; Preferably, the alcohol is ethylene glycol, propylene glycol, hexanediol, or benzyl alcohol; The alcohol ethers are dipropylene glycol monopropyl ether (DPnB), ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol n-butyl ether, or propylene glycol phenyl ether. The alcohol esters are alcohol ester-12 or alcohol ester-16; The alcohol ether esters are hexanediol butyl ether acetate or ethyl 3-ethoxypropionate.

6. A heat-sensitive color-developing material, characterized in that: It includes a substrate and a thermosensitive coating, wherein the thermosensitive coating is attached to the substrate and the thermosensitive coating is prepared by coating with a coating having covering and thermochromic properties as described in any one of claims 1-5; The color layer is placed between the substrate and the heat-sensitive coating, or the substrate itself is colored, or the heat-sensitive coating itself is colored; Before printing and color development, the color of the color layer is partially or completely covered by a thermal coating.

7. The thermosensitive color-developing material according to claim 6, characterized in that: The substrate is paper or film.

8. The thermosensitive color-developing material according to claim 6, characterized in that: It also includes a heat-insulating coating, which is attached to the substrate and has a color layer disposed on the heat-insulating coating; Preferably, the heat-insulating coating contains colorant particles; Preferably, the material of the heat-insulating coating comprises, by weight, the following components: 100 parts pigment, 5-25 parts colorant, and 5-30 parts adhesive; Preferably, the pigment is selected from calcined kaolin, hollow sphere pigment, silica, or aluminum silicate; the adhesive is selected from starch, latex, styrene-acrylic latex, PVA and its modifiers, or polyurethane. Preferably, the pigment is a hollow sphere pigment and calcined kaolin, and the adhesive is latex.

9. A method for preparing the thermosensitive color-developing material according to any one of claims 6-8, characterized in that: The process includes the following steps: mixing polymer hollow spheres A, polymer hollow spheres B, dispersing particles, adhesive, water-repellent agent, film-forming aid, and lubricant in a specific ratio to obtain a coating; The coating is applied to a substrate with a color layer and dried to obtain the final product. Alternatively, color particles can be added to the coating, mixed well, applied to the substrate, and dried to obtain the final product.

10. The use of the thermosensitive color-emitting material according to any one of claims 6-8 in the preparation of information recording materials.

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