Scratch-resistant anti-decoloration thermo-sensitive paper and preparation method thereof

Abstract

The invention belongs to the technical field of heat-sensitive paper, and discloses scratch-resistant and anti-decoloration heat-sensitive paper and a preparation method thereof.The scratch-resistant and anti-decoloration heat-sensitive paper is formed by compounding three layers of structures including a base layer, a heat-sensitive coating and a scratch-resistant protective layer. Synergistic application of the nano silicon dioxide particles and the ultraviolet curing technology becomes the key to break through the traditional performance bottleneck. Nano silicon dioxide with the particle size of 50-100 nm serves as a rigid reinforcing phase and is evenly dispersed in a waterborne polyurethane resin system according to the mass ratio of 2: 5: 1, and particles and a resin molecular chain form a tightly-wound microstructure due to the high specific surface area characteristic of the nano silicon dioxide. When the coated paper enters ultraviolet light curing equipment, 365nm ultraviolet light accurately excites a 1173 photoinitiator, and under high-intensity irradiation of 800-1000mW / cm < 2 >, a rapid cross-linking reaction between resin and hydroxyl groups on the surfaces of nanoparticles can be initiated within 3-5 seconds to form a three-dimensional net-shaped curing layer.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal paper, and in particular relates to scratch-resistant and discoloration-resistant thermal paper and a preparation method thereof. Background Art

[0002] As the wave of digitalization sweeps the globe, sectors like the Internet of Things (IoT), smart retail, and medical receipts are experiencing explosive growth. Thermal paper, with its ready-to-print, ink-free nature, has become the preferred printing consumable across various industries. Thermal paper plays an indispensable role in high-frequency receipt printing in smart retail, precise medical inspection report generation, and the massive logistics labeling required in IoT scenarios.

[0003] However, the disadvantages of traditional thermal paper are obvious in actual applications. Its wear resistance is insufficient. During the frequent handling and friction during logistics and transportation, or during daily contact with medical equipment, scratches are very likely to appear on the surface of the paper, making the information difficult to recognize; at the same time, the problem of information fading is prominent. Environmental factors such as high temperature and humidity will accelerate the oxidative decomposition of dyes and color developers in the thermal coating, causing the key information on the bill to become blurred and disappear in a short period of time. In the existing technology, although there are attempts to improve the wear resistance by adding nanoparticles or to enhance the density of the coating by using UV curing technology, the former often causes brittle coating due to uneven particle dispersion, and the latter is prone to shedding of the protective layer due to the lack of interlayer bonding optimization. Both fail to solve the synergistic problems of "scratch resistance" and "anti-fading" at the same time. This performance defect makes it impossible to effectively trace logistics labels and difficult to archive medical records for a long time, which seriously restricts the promotion of thermal paper in high-end application scenarios. Summary of the Invention

[0004] The object of the present invention is to provide a scratch-resistant and discoloration-resistant thermal paper and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0005] Compared with the prior art, the innovation of the present invention is:

[0006] Constructing a composite structure of "transition layer + scratch-resistant protective layer". The transition layer is made of acrylic resin and polyurethane resin in a 1:1 ratio, solving the technical problem of insufficient bonding between traditional heat-sensitive coatings and protective layers.

[0007] The scratch-resistant protective layer uses a specific ratio (2:5:1) of 50-100nm nano-silica, water-based polyurethane resin and 1173 photoinitiator, combined with 365nm ultraviolet light for rapid curing, to form a three-dimensional network structure that is both rigid and flexible, overcoming the coating embrittlement problem caused by the addition of single nanoparticles.

[0008] In order to achieve the above objectives, the present invention provides the following technical solutions: a scratch-resistant and discoloration-resistant thermal paper, which is composed of a three-layer structure, including a base layer, a heat-sensitive coating and a scratch-resistant protective layer.

[0009] Preferably, the specific steps of the method for preparing the scratch-resistant and discoloration-resistant thermal paper are as follows:

[0010] S1: Pretreatment of the substrate: Select qualified rolls of base paper according to specifications, verify the batch and quality inspection report, and reject any damaged or damp paper. Load the base paper onto the unwinding device of the coating machine, adjust the position, and set a tension of 5-10N to ensure smoothness. Remove surface impurities with an electrostatic eliminator or brush. In special cases, perform a light corona treatment before proceeding to the subsequent coating process.

[0011] S2: Preparation of thermosensitive coating: First, the raw materials are proportioned and pretreated, and fillers such as calcium carbonate, kaolin, and hollow balls are weighed according to the formula ratio. The fillers are sieved to remove lumps, and the functional additives such as color developers, dispersants, and lubricants are dissolved or made into aqueous dispersions. Then enter the wet dispersion process, mix the fillers and additives in a high-speed disperser at a speed of 2000-3000rpm for 30 minutes, and then grind them with zirconium oxide beads in a sand mill 2-3 times to make the particle size ≤1μm, then slowly add the latex and stir evenly at a low speed. Finally, the viscosity, pH value, solid content and other properties of the coating liquid are adjusted, and the viscosity is controlled at 2000-3000cP, the pH value is adjusted to 6-8, the solid content is controlled at 50-60%, and impurities are removed through a 10-20μm bag filter. The prepared coating liquid is transported to the coating machine at a constant temperature to prepare for the subsequent coating process;

[0012] S3: Transition layer coating: To address the issue of insufficient bonding between the heat-sensitive coating and the scratch-resistant protective layer, a transition layer process is introduced. Acrylic resin and polyurethane resin are precisely mixed in a 1:1 mass ratio. The two complement each other, with the former providing good flexibility and the latter imparting excellent wear resistance. Ethyl acetate diluent is then added and thoroughly stirred to form a uniform transition layer coating solution. The coating solution is evenly applied to the heat-sensitive coating using a doctor blade coating method with a precisely controlled thickness of 1-2 μm. The solution is then dried at 70-80°C for 10-15 minutes to ensure a tight fit between the transition layer, forming a solid bond between the heat-sensitive coating and the scratch-resistant protective layer.

[0013] S4: Preparation of scratch-resistant protective layer: In the preparation of the scratch-resistant protective layer, nano-silica particles with a particle size of 50-100nm, water-based polyurethane resin, and 1173 photoinitiator are carefully selected and mixed according to the precise mass ratio of 2:5:1. Nano-silica gives the coating hardness, water-based polyurethane resin ensures flexibility and film-forming properties, and photoinitiator is the key to subsequent curing. After adding deionized water, it is dispersed at a speed of 3000-4000 rpm in a high-speed disperser for 30-40 minutes, fully mixed to form a uniform coating, and finally a roller coater is used to coat the coating at a speed of 10-15g / m 2 Apply the standard coating amount to evenly cover the surface of the transition layer;

[0014] S5: UV curing: In the UV curing process, the paper coated with the scratch-resistant protective coating is accurately fed into the UV curing equipment. A UV lamp with a wavelength of 365nm is selected as the light source. This wavelength can effectively stimulate the activity of the 1173 photoinitiator at 800-1000mW / cm 2 Under high-intensity irradiation, the photoinitiator quickly absorbs light energy and decomposes to produce free radicals, triggering a polymerization reaction between the waterborne polyurethane resin and the nano-silica particles. Within 3-5 seconds of instantaneous irradiation, the coating can quickly solidify from a liquid state into a three-dimensional network structure, forming a dense protective layer with uniform thickness and a hardness of more than 3H. Its intermolecular bonding strength is 40% higher than that of traditional coatings, significantly enhancing the surface's scratch resistance.

[0015] S6: Post-processing: After the coating and curing of the scratch-resistant and anti-fading thermal paper are completed, the paper needs to undergo a key post-processing step and be placed in an environment with a temperature of 25-30°C and a humidity of 40%-60% for 24 hours. This natural aging process can promote further cross-linking and fusion of molecules between the coating materials in the paper, eliminate internal stress, and thus significantly improve the stability of the overall performance of the paper. After the aging is completed, the paper is precisely cut and finally packaged. At this point, the complete scratch-resistant and anti-fading thermal paper preparation process is successfully completed.

[0016] Preferably, pre-treatment of the base layer in S1 involves selecting a standard raw paper roll according to the required specifications, verifying the batch information and quality inspection report, and avoiding the use of damp or damaged paper. The roll is then mounted on the unwinding device of the coating machine, adjusted in position, and set to an appropriate tension of 5-10N to ensure smooth and stable unwinding. If dust or other impurities are found on the surface of the paper, it can be cleaned with an electrostatic eliminator or a soft brush. In special cases, a mild corona treatment can be applied to the surface to increase the surface energy. After treatment, the paper is ready for the subsequent coating process.

[0017] Special cases are when the base paper surface is found to have obvious oil stains or wrinkles caused by uneven tension;

[0018] Mild corona treatment is defined as a corona power of 3-5 kW and a treatment time of 1-2 seconds.

[0019] Preferably, the specific steps of preparing the thermosensitive coating in S2 are as follows:

[0020] Step 1: Raw material processing and mixing: First, the raw materials are proportioned and pre-treated. Calcium carbonate, kaolin, and hollow ball filler are weighed according to the formula ratio. The mass ratio of the three is 3:2:1. The lumps are removed by sieving, and functional additives are dissolved or prepared. At the same time, the color developer (bisphenol A is selected, accounting for 6% of the total mass of the filler), the dispersant (sodium polyacrylate is selected, accounting for 2% of the total mass of the filler), and the lubricant (zinc stearate is selected, accounting for 1% of the total mass of the filler) are pre-treated. The lubricant is made into a 5% mass concentration aqueous dispersion. It is mixed at a speed of 2000-3000rpm in a high-speed disperser for 30 minutes. It is ground with zirconium oxide beads in a sand mill for 2-3 times to make the particle size ≤1μm. Then, the latex is slowly added and stirred at a low speed.

[0021] After grinding, the particle size D50 is controlled at 0.5-0.8μm and D90 ≤ 1μm, ensuring that the particles are evenly dispersed and avoiding agglomeration that affects the smoothness of the coating.

[0022] Functional additive pretreatment method: the color developer is stirred and dissolved in deionized water at 50-60℃, with a stirring speed of 1000-1500rpm, until it is completely dissolved; the dispersant is first mixed with deionized water at a mass ratio of 1:3, and pre-dispersed at a speed of 800-1200rpm for 5-10 minutes;

[0023] Step 2: Performance Adjustment and Delivery: The coating liquid is then adjusted to maintain viscosity between 2000-3000 cP, a pH between 6-8, and a solids content between 50-60%. Impurities are removed using a 10-20 μm bag filter. Styrene-butadiene latex (45% solids) is used as the latex, adding 12% of the total filler weight. The delivery temperature is controlled at 40 ± 2°C, maintaining this constant temperature. The prepared coating liquid is then delivered to the coating machine, providing a qualified thermally sensitive coating solution for subsequent coating steps.

[0024] Preferably, the specific steps of coating the transition layer in S3 are as follows:

[0025] Step 1: Preparation of transition layer raw materials: Weigh acrylic resin and polyurethane resin in a 1:1 mass ratio. The flexibility of the former and the wear resistance of the latter complement each other. Add ethyl acetate as a diluent and stir thoroughly in a stirring device to evenly mix the two resins and the diluent to form a transition layer coating liquid with good fluidity and uniform texture, ready for subsequent coating.

[0026] The amount of ethyl acetate added is 15%-20% of the total mass of acrylic resin and polyurethane resin, which can adjust the viscosity of the coating liquid to 50-80 cP, ensuring uniformity and fluidity during blade coating;

[0027] Experimental verification shows that the acrylic resin and polyurethane resin in a 1:1 mass ratio can make the transition layer adapt to both the surface properties of the heat-sensitive coating and the adhesion requirements of the scratch-resistant protective layer, achieving a stable bond between the two layers.

[0028] Step 2: Transition layer coating operation: Use the doctor blade coating method to evenly cover the prepared transition layer coating liquid on the surface of the thermal coating. By precisely adjusting the height and angle of the doctor blade, the thickness of the transition layer is strictly controlled at 1-2μm to ensure that the transition layer is flat and evenly distributed on the paper surface. This ensures the bonding effect between the coatings without affecting the overall performance due to excessive thickness, and ensures that the transition layer initially adheres to the thermal coating.

[0029] Step 3: Drying of the transition layer: After coating, place the paper in an environment of 70-80°C and dry it for 10-15 minutes. Under these temperature and time conditions, diluents such as ethyl acetate evaporate quickly, and the acrylic resin and polyurethane resin further cross-link and solidify, so that the transition layer fits tightly on the heat-sensitive coating, becoming a solid bond between the heat-sensitive coating and the scratch-resistant protective layer, thereby enhancing the bonding strength between the coatings.

[0030] Preferably, the specific steps of preparing the scratch-resistant protective layer in S4 are as follows:

[0031] Step 1: Raw Material Proportioning for the Scratch-Resistant Protective Layer: To prepare the scratch-resistant protective layer, carefully selected nano-silica particles with a particle size of 50-100nm, water-based polyurethane resin, and 1173 photoinitiator are weighed and mixed in a precise mass ratio of 2:5:1. The nano-silica acts as a hardness-enhancing core, imparting scratch resistance to the coating; the water-based polyurethane resin ensures the coating's flexibility and excellent film-forming properties; and the photoinitiator provides the key conditions for the subsequent curing reaction. Together, these three ingredients lay the foundation for a high-quality protective layer.

[0032] Step 2: Mixing and dispersing the scratch-resistant protective coating: Add an appropriate amount of deionized water to the prepared raw materials and pour into a high-speed disperser. Set the disperser speed to 3000-4000 rpm and continue dispersing for 30-40 minutes. Under high-speed stirring, the nanoparticles are evenly dispersed in the resin system, and all the ingredients are fully blended to form a scratch-resistant protective coating with uniform texture and stable performance, ready for coating;

[0033] The proportion of deionized water: 15%-25% of the total mass of nano-silica, waterborne polyurethane resin and 1173 photoinitiator;

[0034] The optimal ratio of deionized water is 20%, and the reasonable adjustment range of 15%-25% is suitable for different coating environments, which can ensure the uniformity of nanoparticle dispersion.

[0035] Step 3: Scratch-resistant protective layer coating: Use a roller coater to evenly coat the prepared scratch-resistant protective coating on the surface of the transition layer, and strictly control the coating amount to 10-15g / m 2 The roller coater ensures that the coating is evenly covered on the paper surface through the extrusion and rotation of precision rollers, forming a coating with uniform thickness, which provides a guarantee for subsequent UV curing and the final formation of a protective layer with high scratch resistance.

[0036] Preferably, the UV curing in S5 refers to the process of accurately conveying the paper coated with the scratch-resistant protective coating to a professional UV curing device in the UV curing step, and selecting a UV lamp with a wavelength of 365nm as the core light source. This specific wavelength is highly consistent with the absorption peak of the 1173 photoinitiator, which can efficiently activate its activity at 800-1000mW / cm 2 Under high-intensity irradiation, the photoinitiator quickly absorbs light energy and decomposes to produce free radicals, which quickly triggers a polymerization reaction between the water-based polyurethane resin and the nano-silica particles. Within 3-5 seconds, the liquid coating completes the transformation into a three-dimensional network structure, forming a dense protective layer with uniform thickness and a hardness of more than 3H, which greatly enhances the scratch resistance of the thermal paper surface.

[0037] 365nm ultraviolet light excites 1173 photoinitiator to generate free radicals, which trigger the cross-linking of waterborne polyurethane resin molecular chains and hydroxyl groups on the surface of nano-silica, forming a uniformly distributed three-dimensional network structure and improving the density of the coating.

[0038] Preferably, the post-processing in S6 refers to the completion of the coating and curing of the scratch-resistant and discoloration-resistant thermal paper. The post-processing link is the key to ensuring the stability of paper performance. The paper is placed in an environment with a temperature of 25-30°C and a relative humidity of 40%-60% for 24 hours. This natural aging process provides ideal molecular interaction conditions for each coating material. During this period, the molecules between the coatings are further cross-linked and fused, and the internal stress is effectively eliminated, making the overall structure of the paper more stable, and the mechanical and chemical properties are significantly improved. After the aging is fully completed, the paper is accurately cut by high-precision equipment to make its size specifications meet the requirements of different usage scenarios such as logistics labels and medical receipts. Finally, it is packaged with moisture-proof and dust-proof professional packaging materials. At this point, the complete scratch-resistant and discoloration-resistant thermal paper preparation process is completed.

[0039] The beneficial effects of the present invention are as follows:

[0040] 1. The present invention uses the synergistic application of nano-silica particles and UV curing technology in the innovative construction of the scratch-resistant protective layer, which becomes the key to breaking through the traditional performance bottleneck. Nano-silica with a particle size of 50-100nm is used as a rigidity-enhancing phase and is evenly dispersed in the water-based polyurethane resin system at a mass ratio of 2:5:1. Its high specific surface area allows the particles and the resin molecular chains to form a tightly entangled microstructure. When the coated paper enters the UV curing equipment, 365nm UV light accurately excites the 1173 photoinitiator at 800-1000mW / cm 2 Under high-intensity irradiation, a rapid cross-linking reaction between the resin and the hydroxyl groups on the surface of the nanoparticles can be triggered within 3-5 seconds to form a three-dimensional network solidified layer. The intermolecular bonding strength of this structure is greatly improved compared to traditional coatings.

[0041] 2. The present invention enhances the bonding strength between the thermal coating and the scratch-resistant protective layer by providing a transition layer between the two layers. At the same time, the scratch-resistant protective layer can effectively block the erosion of the thermal coating by external oxygen, moisture, etc., and inhibit the oxidation reaction of the dye and color developer in the thermal coating, thereby significantly improving the anti-fading performance of the thermal paper. The information retention time of this thermal paper far exceeds that of traditional thermal paper, greatly meeting the application scenarios that require long-term information preservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a flow chart of the method for preparing the scratch-resistant and discoloration-resistant thermal paper of the present invention. DETAILED DESCRIPTION

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0044] like Figure 1 As shown, an embodiment of the present invention provides a scratch-resistant and discoloration-resistant thermal paper and a preparation method thereof. The scratch-resistant and discoloration-resistant thermal paper is composed of a three-layer structure, including a base layer, a heat-sensitive coating layer and a scratch-resistant protective layer.

[0045] The specific steps of the method for preparing the scratch-resistant and discoloration-resistant thermal paper are as follows:

[0046] S1: Pretreatment of the substrate: Select qualified rolls of base paper according to specifications, verify the batch and quality inspection report, and reject any damaged or damp paper. Load the base paper onto the unwinding device of the coating machine, adjust the position, and set a tension of 5-10N to ensure smoothness. Remove surface impurities with an electrostatic eliminator or brush. In special cases, perform a light corona treatment before proceeding to the subsequent coating process.

[0047] S2: Preparation of thermosensitive coating: First, the raw materials are proportioned and pretreated, and fillers such as calcium carbonate, kaolin, and hollow balls are weighed according to the formula ratio. The fillers are sieved to remove lumps, and the functional additives such as color developers, dispersants, and lubricants are dissolved or made into aqueous dispersions. Then enter the wet dispersion process, mix the fillers and additives in a high-speed disperser at a speed of 2000-3000rpm for 30 minutes, and then grind them with zirconium oxide beads in a sand mill 2-3 times to make the particle size ≤1μm, then slowly add the latex and stir evenly at a low speed. Finally, the viscosity, pH value, solid content and other properties of the coating liquid are adjusted, and the viscosity is controlled at 2000-3000cP, the pH value is adjusted to 6-8, the solid content is controlled at 50-60%, and impurities are removed through a 10-20μm bag filter. The prepared coating liquid is transported to the coating machine at a constant temperature to prepare for the subsequent coating process;

[0048] S3: Transition layer coating: To address the issue of insufficient bonding between the heat-sensitive coating and the scratch-resistant protective layer, a transition layer process is introduced. Acrylic resin and polyurethane resin are precisely mixed in a 1:1 mass ratio. The two complement each other, with the former providing good flexibility and the latter imparting excellent wear resistance. Ethyl acetate diluent is then added and thoroughly stirred to form a uniform transition layer coating solution. The coating solution is evenly applied to the heat-sensitive coating using a doctor blade coating method with a precisely controlled thickness of 1-2 μm. The solution is then dried at 70-80°C for 10-15 minutes to ensure a tight fit between the transition layer, forming a solid bond between the heat-sensitive coating and the scratch-resistant protective layer.

[0049] S4: Preparation of scratch-resistant protective layer: In the preparation of the scratch-resistant protective layer, nano-silica particles with a particle size of 50-100nm, water-based polyurethane resin, and 1173 photoinitiator are carefully selected and mixed according to the precise mass ratio of 2:5:1. Nano-silica gives the coating hardness, water-based polyurethane resin ensures flexibility and film-forming properties, and photoinitiator is the key to subsequent curing. After adding deionized water, it is dispersed at a speed of 3000-4000 rpm in a high-speed disperser for 30-40 minutes, fully mixed to form a uniform coating, and finally a roller coater is used to coat the coating at a speed of 10-15g / m 2 Apply the standard coating amount to evenly cover the surface of the transition layer;

[0050] S5: UV curing: In the UV curing process, the paper coated with the scratch-resistant protective coating is accurately fed into the UV curing equipment. A UV lamp with a wavelength of 365nm is selected as the light source. This wavelength can effectively stimulate the activity of the 1173 photoinitiator at 800-1000mW / cm 2Under high-intensity irradiation, the photoinitiator quickly absorbs light energy and decomposes to produce free radicals, which triggers a polymerization reaction between the waterborne polyurethane resin and the nano-silica particles. Within 3-5 seconds of instantaneous irradiation, the coating can be rapidly solidified from a liquid state into a three-dimensional network structure, forming a dense protective layer with uniform thickness and a hardness of more than 3H, significantly enhancing the surface's scratch resistance.

[0051] S6: Post-processing: After the coating and curing of the scratch-resistant and anti-fading thermal paper are completed, the paper needs to undergo a key post-processing step and be placed in an environment with a temperature of 25-30°C and a humidity of 40%-60% for 24 hours. This natural aging process can promote further cross-linking and fusion of molecules between the coating materials in the paper, eliminate internal stress, and thus significantly improve the stability of the overall performance of the paper. After the aging is completed, the paper is precisely cut and finally packaged. At this point, the complete scratch-resistant and anti-fading thermal paper preparation process is successfully completed.

[0052] The base layer pretreatment in S1 involves selecting a standard raw paper roll according to the required specifications, verifying batch information and quality inspection reports, and avoiding the use of damp or damaged paper. The roll is then installed on the coating machine's unwinding mechanism, adjusted, and set to an appropriate tension of 5-10N to ensure smooth and stable unwinding. If dust or other impurities are found on the paper surface, it can be cleaned with an electrostatic eliminator or a soft brush. In special cases, a mild corona treatment can be applied to the surface to increase surface energy. After treatment, the paper is ready for coating.

[0053] Among them, in the preparation process of the heat-sensitive coating in S2, the raw materials are first proportioned and pretreated. Fillers such as calcium carbonate, kaolin, and hollow balls are accurately weighed according to the formula, sieved to remove lumps, and ensure uniform particles; at the same time, functional additives such as color developers, dispersants, and lubricants are dissolved or made into aqueous dispersions to enhance their dispersibility and stability. Then, the wet dispersion process is entered, and the fillers and additives are initially dispersed in a high-speed disperser at a speed of 2000-3000 rpm for 30 minutes. The fillers and additives are then initially dispersed, and then ground 2-3 times with zirconium oxide beads in a sand mill to a particle size of ≤1μm. The sand mill speed is 1800-2200 rpm, and the zirconium oxide bead particle size is 0.8-1mm. The material temperature is controlled at ≤50°C during grinding to ensure a fine coating. After that, the latex is slowly added and stirred evenly at a low speed to form a uniform coating liquid. Finally, the coating liquid's key properties, including viscosity, pH value, and solid content, are adjusted. The viscosity is controlled at 2000-3000 cP, the pH value is adjusted to 6-8, and the solid content is controlled at 50-60%. Impurities are removed through a 10-20 μm bag filter, and the liquid is delivered to the coating machine at a constant temperature, laying the foundation for subsequent processes.

[0054] Latex type: Choose styrene-butadiene latex (solid content 40%-50%) or vinyl acetate latex (solid content 35%-45%), and add 10%-15% of the total mass of the filler;

[0055] The minimum film-forming temperature of styrene-butadiene latex is ≤5°C, ensuring the formation of a continuous film layer during the subsequent drying process.

[0056] The specific steps of coating the transition layer in S3 are as follows:

[0057] Step 1: Preparation of transition layer raw materials: Weigh acrylic resin and polyurethane resin in a 1:1 mass ratio. The flexibility of the former and the wear resistance of the latter complement each other. Add ethyl acetate as a diluent and stir thoroughly in a stirring device to evenly mix the two resins and the diluent to form a transition layer coating liquid with good fluidity and uniform texture, ready for subsequent coating.

[0058] The amount of ethyl acetate added is 15%-20% of the total mass of acrylic resin and polyurethane resin, and the viscosity of the coating liquid is adjusted to 50-80 cP;

[0059] Step 2: Transition layer coating operation: Use the doctor blade coating method to evenly cover the prepared transition layer coating liquid on the surface of the thermal coating. By precisely adjusting the height and angle of the doctor blade, the thickness of the transition layer is strictly controlled at 1-2μm to ensure that the transition layer is flat and evenly distributed on the paper surface. This ensures the bonding effect between the coatings without affecting the overall performance due to excessive thickness, and ensures that the transition layer initially adheres to the thermal coating.

[0060] Step 3: Drying of the transition layer: After coating, place the paper in an environment of 70-80°C and dry it for 10-15 minutes. Under these temperature and time conditions, diluents such as ethyl acetate evaporate quickly, and the acrylic resin and polyurethane resin further cross-link and solidify, so that the transition layer fits tightly on the heat-sensitive coating, becoming a solid bond between the heat-sensitive coating and the scratch-resistant protective layer, thereby enhancing the bonding strength between the coatings.

[0061] First, acrylic resin and polyurethane resin are weighed in a 1:1 mass ratio. The former imparts flexibility, while the latter provides wear resistance. The two complement each other. After adding an appropriate amount of ethyl acetate diluent, they are fully mixed in a stirring device to form a transition layer coating liquid with good fluidity and uniform texture. Then, the coating operation is carried out. By using the doctor blade coating method, the coating liquid is evenly applied to the surface of the heat-sensitive coating with a thickness of 1-2μm by precisely controlling the height and angle of the doctor blade, ensuring that the transition layer is evenly distributed, which not only guarantees the bonding effect between the coatings, but also avoids the impact of excessive thickness on performance. Finally, a drying process is carried out. The paper is placed in an environment of 70-80℃ and dried for 10-15 minutes to promote the volatilization of ethyl acetate. At the same time, the acrylic resin and polyurethane resin are further cross-linked and cured, so that the transition layer is closely attached to the heat-sensitive coating, becoming a solid link connecting the heat-sensitive coating and the scratch-resistant protective layer, significantly enhancing the bonding strength between the coatings.

[0062] The specific steps for preparing the scratch-resistant protective layer in S4 are as follows:

[0063] Step 1: Raw Material Proportioning for the Scratch-Resistant Protective Layer: To prepare the scratch-resistant protective layer, carefully selected nano-silica particles with a particle size of 50-100nm, water-based polyurethane resin, and 1173 photoinitiator are weighed and mixed in a precise mass ratio of 2:5:1. The nano-silica acts as a hardness-enhancing core, imparting scratch resistance to the coating; the water-based polyurethane resin ensures the coating's flexibility and excellent film-forming properties; and the photoinitiator provides the key conditions for the subsequent curing reaction. Together, these three ingredients lay the foundation for a high-quality protective layer.

[0064] The waterborne polyurethane resin is an anionic resin with a molecular weight of 15,000-20,000; the nano-silica particles are hydrophobic particles modified with a silane coupling agent (surface hydroxyl content 2.0 mmol / g); the purity of the 1173 photoinitiator is ≥99%;

[0065] Step 2: Mixing and dispersing the scratch-resistant protective coating: Add an appropriate amount of deionized water to the prepared raw materials and pour into a high-speed disperser. Set the disperser speed to 3000-4000 rpm and continue dispersing for 30-40 minutes. Under high-speed stirring, the nanoparticles are evenly dispersed in the resin system, and all the ingredients are fully blended to form a scratch-resistant protective coating with uniform texture and stable performance, ready for coating;

[0066] Step 3: Scratch-resistant protective layer coating: Use a roller coater to evenly coat the prepared scratch-resistant protective coating on the surface of the transition layer, and strictly control the coating amount to 10-15g / m 2 The roller coater ensures that the coating is evenly covered on the paper surface through the extrusion and rotation of the precision roller, forming a coating of uniform thickness, which provides a guarantee for the subsequent UV curing and the final formation of a highly scratch-resistant protective layer;

[0067] Roller coating machine parameters: roller speed 60-80m / min, roller pressure 0.2-0.25MPa, ensure coating amount deviation ≤±0.5g / m 2 ;

[0068] First, select nano-silica particles with a particle size of 50-100nm, water-based polyurethane resin, and 1173 photoinitiator, and weigh them according to the precise mass ratio of 2:5:1. Nano-silica acts as a hardness reinforcement core to impart scratch resistance, water-based polyurethane resin ensures flexibility and film-forming properties, and photoinitiator provides key conditions for the curing reaction. Then add an appropriate amount of deionized water to the prepared raw materials, pour into a high-speed disperser, and continue dispersing at a speed of 3000-4000 rpm for 30-40 minutes to evenly disperse the nanoparticles in the resin system to form a scratch-resistant protective coating with a uniform texture. Finally, use a roller coater to evenly apply the coating on the surface of the transition layer, strictly controlling the coating amount to 10-15g / m 2 , through precision roller extrusion and rotation, the paint is ensured to be evenly covered, forming a coating of uniform thickness, laying the foundation for subsequent UV curing and the formation of a protective layer with high scratch resistance.

[0069] Among them, the UV curing in S5 refers to the process of accurately transporting the paper coated with the scratch-resistant protective coating to the professional UV curing equipment in the UV curing process, and selecting a 365nm wavelength UV lamp as the core light source. This specific wavelength is highly consistent with the absorption peak of the 1173 photoinitiator, which can efficiently activate its activity at 800-1000mW / cm 2 Under high-intensity irradiation, the photoinitiator quickly absorbs light energy and decomposes to produce free radicals, which quickly triggers a polymerization reaction between the water-based polyurethane resin and the nano-silica particles. Within 3-5 seconds, the liquid coating completes the transformation into a three-dimensional network structure, forming a dense protective layer with uniform thickness and a hardness of more than 3H. The intermolecular bonding strength is increased by 40% compared with traditional coatings, greatly enhancing the scratch resistance of the thermal paper surface.

[0070] The paper coated with scratch-resistant protective coating is fed into the equipment, and a 365nm ultraviolet lamp is used as the light source at 800-1000mW / cm 2 After irradiation at high intensity for 3-5 seconds, the photoinitiator is activated to initiate a polymerization reaction, causing the liquid coating to solidify into a three-dimensional network structure, forming a dense protective layer with a hardness of more than 3H, and the anti-scratch performance is significantly enhanced.

[0071] Among them, the post-processing in S6 refers to the completion of the coating and curing of the scratch-resistant and anti-fading thermal paper. The post-processing link is the key to ensuring the stability of the paper performance. The paper is placed in an environment with a temperature of 25-30°C and a relative humidity of 40%-60% for 24 hours. This natural aging process provides ideal molecular interaction conditions for each coating material. During this period, the molecules between the coatings are further cross-linked and fused, and the internal stress is effectively eliminated, making the overall structure of the paper more stable, and the mechanical and chemical properties are significantly improved. After the aging is fully completed, the paper is accurately cut by high-precision equipment to make its size specifications meet the needs of different usage scenarios such as logistics labels and medical receipts. Finally, it is packaged with moisture-proof and dust-proof professional packaging materials. At this point, the complete scratch-resistant and anti-fading thermal paper preparation process is completed.

[0072] After coating and curing, the paper requires post-processing. It is left to mature naturally for 24 hours at 25-30°C and 40%-60% humidity to promote molecular cross-linking and eliminate stress. After aging, it is slit with high precision to suit different applications and then packaged with specialized moisture- and dust-proof materials, completing the entire production process.

[0073] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0074] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A scratch-resistant and discoloration-resistant thermal paper, characterized by: The scratch-resistant and discoloration-resistant thermal paper is composed of a base layer, a thermal coating, a transition layer and a scratch-resistant protective layer. The thermal coating contains calcium carbonate, kaolin, hollow ball filler, with a mass ratio of 3:2:1, and bisphenol A color developer, which accounts for 6% of the total mass of the filler. The transition layer is composed of acrylic resin and polyurethane resin with a mass ratio of 1:

1. The scratch-resistant protective layer contains nano-silicon dioxide with a particle size of 50-100nm modified by a silane coupling agent, a water-based polyurethane resin with a surface hydroxyl content of 2.0mmol / g and a molecular weight of 15000-20000, and an 1173 photoinitiator with a purity of ≥99%, with a mass ratio of 2:5:

1. The scratch-resistant protective layer is exposed to light with a wavelength of 365nm and an intensity of 800-1000mW / cm 2 After irradiation with ultraviolet light for 3-5 seconds, it solidifies to form a three-dimensional network structure.

2. A method for preparing scratch-resistant and discoloration-resistant thermal paper, characterized in that: The specific steps of the method for preparing the scratch-resistant and discoloration-resistant thermal paper are as follows: S1: Base pretreatment: Select qualified roll base paper, install the base paper on the unwinding device of the coating machine, adjust the position and set the tension of 5-10N to ensure flatness, and use an electrostatic eliminator or a brush to remove surface impurities; S2: Preparation of heat-sensitive coating: First, weigh the filler according to the formula and sieve it, pre-treat the functional additives, then mix it in a high-speed disperser, then grind it in a sand mill, then add latex and stir evenly, and finally adjust the coating liquid properties; S3: Transition layer coating: acrylic resin and polyurethane resin are precisely mixed, and then ethyl acetate diluent is added and stirred to form a transition layer coating liquid. The coating liquid is evenly applied to the heat-sensitive coating using a doctor blade coating method, and then dried at 70-80°C for 10-15 minutes; S4: Preparation of scratch-resistant protective layer: Nano-silica particles, water-based polyurethane resin, and 1173 photoinitiator were mixed in a mass ratio of 2:5:1, deionized water was added, and the mixture was dispersed using a high-speed disperser. Finally, the coating was evenly applied to the surface of the transition layer using a roller coater. S5: UV curing: The paper coated with the scratch-resistant protective coating is fed into a UV curing device. A UV lamp with a wavelength of 365 nm is selected as the light source. The UV lamp is irradiated for 3-5 seconds to rapidly cure the coating from a liquid state into a three-dimensional network structure, forming a dense protective layer. S6: Post-processing: After the coating and curing of the scratch-resistant and discoloration-resistant thermal paper are completed, it is left to stand for 24 hours. After the curing is completed, the paper is accurately cut and finally packaged.

3. The method for preparing scratch-resistant and discoloration-resistant thermal paper according to claim 2, wherein: The base pretreatment in S1 refers to selecting a roll of raw material that meets the standards, checking the batch information and quality inspection report, installing the roll of raw paper on the unwinding device of the coating machine, adjusting the position and setting the appropriate tension of 5-10N to ensure that the paper is unwound smoothly and stably, and cleaning it with an electrostatic eliminator or a soft brush. After the treatment is completed, the paper can enter the subsequent coating process.

4. The method for preparing scratch-resistant and discoloration-resistant thermal paper according to claim 2, wherein: In the preparation process of the heat-sensitive coating in S2, the raw materials are first proportioned and pretreated, and calcium carbonate, kaolin, and hollow spheres are accurately weighed according to the formula in a mass ratio of 3:2:1, and lumps are removed by sieving to ensure uniform particles; at the same time, bisphenol A color developer, accounting for 6% of the total mass of the filler, sodium polyacrylate dispersant, accounting for 2% of the total mass of the filler, and zinc stearate lubricant, accounting for 1% of the total mass of the filler, are dissolved or made into an aqueous dispersion; then the wet dispersion process is entered, mixed in a high-speed disperser for 30 minutes, and then ground with zirconium oxide beads in a sand mill, and then styrene-butadiene latex, accounting for 12% of the total mass of the filler, is slowly added, and stirred evenly at a low speed. Finally, the key properties of the coating liquid, including viscosity, pH value, and solid content, are adjusted, and the viscosity is controlled at 2000-3000 cP, the pH value is adjusted to 6-8, the solid content is controlled at 50%-60%, and impurities are removed through a 10-20 μm bag filter, and the liquid is transported to the coating machine at a constant temperature.

5. The method for preparing scratch-resistant and discoloration-resistant thermal paper according to claim 2, wherein: The specific steps of coating the transition layer in S3 are as follows: Step 1: Preparation of transition layer raw materials: Weigh acrylic resin and polyurethane resin in a mass ratio of 1:1, add ethyl acetate as a diluent, and stir thoroughly in a stirring device to evenly mix the two resins and the diluent; Step 2: Transition layer coating operation: Use the doctor blade coating method to evenly cover the prepared transition layer coating liquid on the surface of the thermal coating, control the thickness of the transition layer to 1-2μm, and make the transition layer initially adhere to the thermal coating; Step 3: Drying of the transition layer: After coating, place the paper in an environment of 70-80°C and dry for 10-15 minutes. Under these temperature and time conditions, the ethyl acetate diluent evaporates quickly, and the acrylic resin and polyurethane resin further cross-link and solidify, so that the transition layer fits tightly on the heat-sensitive coating.

6. The method for preparing scratch-resistant and discoloration-resistant thermal paper according to claim 2, wherein: The specific steps for preparing the scratch-resistant protective layer in S4 are as follows: Step 1: Prepare the scratch-resistant protective layer by weighing modified nano-silica particles with a particle size of 50-100 nm, a water-based polyurethane resin with a surface hydroxyl content of 2.0 mmol / g and a molecular weight of 15,000-20,000, and an 1173 photoinitiator with a purity of ≥99%, in a mass ratio of 2:5:

1. Step 2: Mix and disperse the scratch-resistant protective coating: Add the prepared raw materials to deionized water, accounting for 20% of the total weight of the three, pour into a high-speed disperser, set the disperser speed at 3000-4000 rpm, and continue dispersing for 30-40 minutes; Step 3: Scratch-resistant protective layer coating: Use a roller coater to evenly coat the prepared scratch-resistant protective coating on the surface of the transition layer, and strictly control the coating amount to 10-15g / m 2 .

7. The method for preparing scratch-resistant and discoloration-resistant thermal paper according to claim 2, wherein: The UV curing in S5 refers to transporting the paper coated with the scratch-resistant protective coating to a professional UV curing device, using a 365nm wavelength UV lamp as the core light source, at 800-1000mW / cm 2 Under high-intensity irradiation, the photoinitiator quickly absorbs light energy and decomposes to produce free radicals, which quickly initiates the polymerization reaction between the waterborne polyurethane resin and the nano-silica particles.

8. The method for preparing scratch-resistant and discoloration-resistant thermal paper according to claim 2, wherein: The post-processing in S6 refers to placing the paper in an environment with a temperature of 25-30°C and a relative humidity of 40%-60% for 24 hours after the coating and curing of the scratch-resistant and discoloration-resistant thermal paper are completed. After the curing is fully completed, the paper is cut by equipment and finally packaged with moisture-proof and dust-proof professional packaging materials.

Images