A matte traceless tattoo sticker and a preparation method thereof

Abstract

This invention relates to the field of polymer materials technology and discloses a matte, traceless tattoo sticker and its preparation method. The coating of the tattoo sticker is made of anionic aliphatic aqueous polyurethane emulsion, pre-dispersed silica slurry, hydrophobically modified ethoxylated polyurethane, defoamer, neutralizer, and deionized water. The preparation method includes: mixing and maturing the above raw materials to obtain a composite liquid; using a 1.0 MHz megahertz wave to treat the composite liquid to remove the powder solvent layer; after coating and forming a film, passing it sequentially through a first temperature-controlled drying tunnel with steam for humidity control, and a second drying tunnel with a dehumidification system for high-temperature curing. This invention uses high-frequency sound field demasking and dual temperature and humidity control to induce physical convection, driving the matte powder to migrate vertically and concentrate on the surface, effectively avoiding lateral eddies and demulsification problems, and solving the defects of traditional coatings such as easy whitening during stretching and easy formation of orange peel pores on the surface.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a matte, traceless tattoo sticker and its preparation method. Background Technology

[0002] In the preparation of matte temporary tattoos, inorganic powders such as fumed silica are typically added to the waterborne polyurethane system as matting agents. Currently, the main technical problem with existing waterborne polyurethane matte coatings is the inability to achieve controlled directional migration of matting powders to the coating surface while maintaining emulsion stability and coating smoothness. This results in stress whitening of the coating under tensile stress, accompanied by a decrease in mechanical properties.

[0003] Specifically, in conventional formulation and film-forming processes, rigid silica particles are uniformly dispersed within a flexible polyurethane bulk phase. Due to the physical difference in their elastic moduli, when the coating is subjected to tensile stress during skin movement, the stress concentrates at the inorganic particle interface. The polyurethane matrix cannot deform synchronously with the particles, causing physical separation between the resin and particles and the formation of micropores within the coating. Light is scattered when passing through these micropores, resulting in a whitening of the coating.

[0004] To address this stress-induced whitening problem, theoretically, it's necessary to induce vertical phase separation of silica particles towards the coating surface, allowing the polyurethane bulk phase to remain in the underlying layer to dissipate mechanical energy. However, in practice, fumed silica readily forms hydrogen bonds with the solvent, increasing steric hindrance. If conventional high-shear or low-frequency ultrasonic methods are used to forcibly disrupt these bonds, mechanical shear stress or cavitation effects will damage the double-layer structure of the waterborne polyurethane latex particles, leading to demulsification and gelation. Furthermore, in conventional hot air drying processes, rapid moisture evaporation causes premature cross-linking and surface drying on the coating surface, blocking the physical channels for powder to float. Simultaneously, uncontrolled fluid convection triggered by moisture evaporation causes lateral shearing and spreading on the coating surface, resulting in orange peel and pinholes in the cured coating. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a matte, seamless tattoo sticker and its preparation method, resolving the contradiction between the requirements for powder surface enrichment and fluid processing stability in existing technologies.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a matte, seamless tattoo sticker, wherein the coating of the tattoo sticker is made from the following raw materials in parts by weight: Anionic aliphatic waterborne polyurethane emulsion: 70-85 parts; Pre-dispersed silica slurry: 15-25 parts; Hydrophobically modified ethoxylated polyurethane: 0.3~1.0 parts; Polyether-modified polysiloxane defoamer: 0.1~0.4 parts; Neutralizing agent: 0.08~0.2 parts; Deionized water: 0.5~2.0 parts; The neutralizing agent is N,N-dimethylethanolamine.

[0007] Preferably, the pre-dispersed silica slurry contains hydrophilic fumed silica, which has not undergone surface hydrophobic modification and has a specific surface area of ​​185 m². 2 / g~215m 2 / g, with a native particle size of 12nm~14nm; The hydrophobically modified ethoxylated polyurethane is a block copolymer formed by polymerizing polyethylene glycol and diisocyanate, with a number average molecular weight of 30,000 to 50,000, and the main chain is double-capped with hexadecyl long-chain aliphatic hydrocarbons at both ends.

[0008] Preferably, the anionic aliphatic waterborne polyurethane emulsion is prepared from raw materials comprising polycaprolactone diol with a number average molecular weight of 2000, 2,2-dimethylolpropionic acid, isophorone diisocyanate, and a salting agent.

[0009] Preferably, the composite liquid used to prepare the coating film has a dynamic yield stress between 0.5 Pa and 1.0 Pa at 25°C; the surface gloss of the cured coating film is less than 3.0 at an incident angle of 60°, the elongation at break is greater than 450%, and the lightness difference under 100% tensile strain does not exceed 2.0.

[0010] A method for preparing a matte, seamless temporary tattoo includes the following steps: S1. Mix anionic aliphatic waterborne polyurethane emulsion with polyether-modified polysiloxane defoamer, add pre-dispersed silica slurry, add a neutralizer to adjust the pH value, add hydrophobically modified ethoxylated polyurethane and deionized water and stir to mature and obtain a composite liquid. S2. The composite liquid obtained in step S1 is sent into the acoustic field reaction chamber for continuous flow treatment. S3. Coat the material processed in step S2 onto the surface of the base paper to form a wet film; pass the base paper with the wet film through the first temperature-controlled drying tunnel where steam is introduced for humidity and temperature control, and the second drying tunnel where the dehumidification system is turned on for high-temperature curing. After cross-linking curing and cooling and winding, the matte traceless tattoo sticker is obtained.

[0011] Preferably, before step S1, the pre-dispersed silica slurry is prepared in advance, specifically by the following method: Anhydrous ethyl acetate, propylene glycol methyl ether, polyether-modified heptamethyltrisiloxane, and hydrophilic fumed silica were mixed and stirred to obtain a preliminary dispersion slurry. The preliminary dispersion slurry was continuously pumped into a pipeline high-shear emulsifier for homogenization and shearing treatment. After the material was discharged, it was directly cooled by a plate heat exchanger with a cooling medium temperature of 5℃~10℃ and collected for later use.

[0012] Preferably, the jacket heating temperature of the inline high-shear emulsifier is set to 60℃~65℃, and the shear rate at the stator and rotor is controlled at 10000s. -1 ~12000s ~1 The residence time of the slurry in the homogenization chamber is 10-20 seconds; the outlet temperature of the material after being cooled by the plate heat exchanger is 15℃-20℃.

[0013] Preferably, in step S2, the acoustic field reaction cavity is a pipeline megasonic reaction cavity, the megasonic emission frequency is set to 1.0MHz, the volumetric power density is set to 30W / L~50W / L, and the exposure time of the fluid in the megasonic reaction cavity is 5 seconds~10 seconds.

[0014] Preferably, in step S3, the ambient air temperature of the first temperature-controlled drying tunnel is set to 40℃~50℃, saturated steam is introduced into the drying tunnel to dynamically maintain the relative humidity at 75%~85%, the advection wind speed is controlled at 1.5m / s~2.5m / s, and the residence time is 10 seconds~15 seconds; the ambient air temperature of the second drying tunnel is set to 80℃~100℃, the entire dehumidification system is turned on, the impact wind speed is controlled at 3.0m / s~5.0m / s, and the residence time is 60 seconds~120 seconds.

[0015] Preferably, in step S1, the ambient temperature during the addition of the pre-dispersed silica slurry is controlled at 20°C to 25°C, and the addition time is 15 min to 20 min; a neutralizing agent is added to adjust the pH of the mixture to 8.2 to 8.5; and the maturation stirring time after adding the hydrophobically modified ethoxylated polyurethane is 30 min to 45 min.

[0016] This invention provides a matte, seamless temporary tattoo and its preparation method. It has the following beneficial effects: 1. This invention uses 1.0MHz mega-sonic waves to treat the composite liquid, causing the solvent layer on the surface of the pre-dispersed silica to peel off. The mechanical high-frequency acoustic flow at this specific frequency is gentle and does not easily damage the double electric layer structure of the waterborne polyurethane latex particles. This solves the problem that conventional low-frequency ultrasonic treatment can easily cause transient cavitation, leading to demulsification and gelation of the system. It improves the migration ability of powder in the film-forming stage while maintaining the stability of the emulsion.

[0017] 2. This invention controls the relative humidity to 75%~85% during the initial drying stage of the coating film. By inhibiting moisture evaporation and promoting the preferential escape of low-boiling-point solvents, it drives the directional migration of silica particles to the coating surface. This process achieves vertical phase separation of the powder, resulting in a silica-rich surface layer for a matte finish, while the underlying layer retains the pure polyurethane bulk phase to maintain flexibility. This solves the problem of edge whitening and interface peeling that easily occur in traditional homogeneous coating films under stress and tension.

[0018] 3. The present invention adds hydrophobically modified ethoxylated polyurethane with double end capping to the formulation, so that the composite liquid has a dynamic yield stress of 0.5Pa~1.0Pa. This stress condition restricts the lateral flow of the fluid on the coating surface, while allowing silica particles to float in the vertical direction. This solves the problem of lateral spreading caused by solvent evaporation convection during the drying process and avoids surface defects such as orange peel and pinholes after the coating is cured. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the process steps of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. 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.

[0021] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0022] Polycaprolactone diol, with a number average molecular weight of 2000, CAS number 24980-41-4.

[0023] 2,2-Dihydroxymethylpropionic acid, with a purity of not less than 99.0%, CAS number 4767-03-7.

[0024] Isophorone diisocyanate, with a purity of not less than 99.0%, CAS number 4098-71-9.

[0025] Hydrophilic fumed silica, without surface hydrophobic modification, has a specific surface area of ​​185 m². 2 / g~215m 2 / g, with a native particle size of 12nm~14nm, and CAS number 112945-52-5.

[0026] Polyether-modified heptamethyltrisiloxane, with the R group being -C3H6O-(C2H4O).x -(C3H6O) y -H polyethylene oxide-propylene oxide copolyether with a single end group, a hydrophilic-lipophilic balance value of 6.0~8.0, a surface tension of no more than 22mN / m at 25℃, and CAS number 27306-78-1.

[0027] Hydrophobically modified ethoxylated polyurethane is a block copolymer of polyethylene glycol and diisocyanate with a number average molecular weight of 30,000 to 50,000. The main chain is double-capped at both ends with hexadecyl long-chain aliphatic hydrocarbons.

[0028] Preparation Example 1: This preparation example provides a method for preparing anionic aliphatic waterborne polyurethane emulsion, including the following steps: 100 parts by weight of polycaprolactone diol and 5.5 parts by weight of 2,2-dimethylolpropionic acid were added to a reactor equipped with a condenser and a vacuum device. The mixture was heated to 105°C and vacuum dehydrated for 2 hours under an absolute pressure of 0.08 MPa. The mixture was then cooled to 60°C.

[0029] 40 parts by mass of isophorone diisocyanate and 0.07 parts by mass of dibutyltin dilaurate were added dropwise to a reaction vessel, and the mixture was heated to 85°C and reacted at this temperature for 3 hours. The temperature was then lowered to 60°C, and 2.5 parts by mass of 1,4-butanediol and 40 parts by mass of anhydrous acetone were added, and the mixture was reacted at this temperature for 1.5 hours. The temperature was then lowered to 35°C, and 3.8 parts by mass of N,N-dimethylethanolamine were added and stirred for 15 minutes to form a salt. 250 parts by mass of deionized water were added dropwise at a stirring speed of 1200 rpm, and the mixture was dispersed for 30 minutes. The material was transferred to a vacuum distillation vessel, and acetone was removed by vacuum distillation at 45°C. The emulsion was then filtered through a 200-mesh filter to obtain an anionic aliphatic waterborne polyurethane emulsion.

[0030] Preparation Example 2: This preparation example provides a method for preparing a pre-dispersed silica slurry, including the following steps: In a sealed mixing vessel, 120 parts by weight of anhydrous ethyl acetate, 30 parts by weight of propylene glycol methyl ether, and 10 parts by weight of polyether-modified heptamethyltrisiloxane were added sequentially. The mixture was stirred at 300 rpm for 5 minutes. Subsequently, 20 parts by weight of hydrophilic fumed silica were added in batches and stirred to obtain a preliminary dispersion slurry. The preliminary dispersion slurry was continuously pumped into a pipeline high-shear emulsifier with a jacket heating temperature set at 65°C, and the stator and rotor shear rates were controlled at 10,000 s. -1 The feed pump flow rate is adjusted to ensure that the material's residence time in the homogenization chamber is 15 seconds per cycle. After the material exits from the inline high-shear emulsifier, it flows directly through a plate heat exchanger with a cooling medium temperature of 5°C. The flow rate is controlled to ensure that the material's residence time in the plate heat exchanger is 3 seconds. The outlet temperature is monitored and reduced to 15°C. The material is then collected and left to stand for later use to obtain a pre-dispersed silica slurry.

[0031] Example 1: This example provides a method for preparing a matte, seamless temporary tattoo. See attached document. Figure 1 It includes the following steps: Eighty parts by mass of the anionic aliphatic aqueous polyurethane emulsion prepared in Preparation Example 1 and 0.2 parts by mass of the polyether-modified polysiloxane defoamer were added to a paint mixing tank. Under stirring conditions of 200 rpm and 25°C, 18 parts by mass of the pre-dispersed silica slurry prepared in Preparation Example 2 were added dropwise at a uniform rate over a period of 15 minutes. After the slurry addition was complete, 0.12 parts by mass of N,N-dimethylethanolamine were added dropwise to the paint mixing tank to adjust the pH of the mixture to 8.3. Then, 0.6 parts by mass of the hydrophobically modified ethoxylated polyurethane and 1.2 parts by mass of deionized water were added to the paint mixing tank, and the mixture was stirred at 250 rpm for 40 minutes to obtain a composite liquid.

[0032] The composite liquid is pumped into the pipeline megasonic reaction chamber through a volumetric pump. The megasonic emission frequency is set to 1.0MHz and the volumetric power density is set to 40W / L. The fluid pumping speed of the volumetric pump is adjusted so that the fluid is exposed in the megasonic reaction chamber for 8 seconds. After the megasonic treatment, the material flows out directly and is transported to the feeding tank of the microgravure coating machine.

[0033] A micro-gravure coating machine is used to evenly coat the material in the feed trough onto the surface of a base paper with a water transfer release layer, controlling the wet film thickness on the base paper surface to be 20μm. The base paper with the wet film on its surface is then conveyed to the first temperature-controlled drying tunnel, where the ambient air temperature is set to 45℃. Saturated steam is introduced into the drying tunnel to dynamically maintain the relative humidity at 80%, and the advection air velocity is controlled at 2.0m / s. The base paper's residence time in the first temperature-controlled drying tunnel is 12 seconds. Subsequently, the base paper is continuously conveyed to the second drying tunnel, where the ambient air temperature is set to 90℃. The entire dehumidification system of the second drying tunnel is activated, and the impact air velocity is controlled at 4.0m / s. The base paper's residence time in the second drying tunnel is 90 seconds. After the solvent and moisture are removed and the polyurethane cross-links and cures, the paper is cooled and wound up to obtain a matte, traceless tattoo sticker product.

[0034] Example 2: This example provides a method for preparing a matte, seamless temporary tattoo, including the following steps: In a sealed anhydrous mixing vessel, 13.9 parts by weight of anhydrous ethyl acetate, 2.0 parts by weight of propylene glycol methyl ether, and 0.5 parts by weight of polyether-modified heptamethyltrisiloxane were added sequentially. The mixture was stirred at 300 rpm for 5 minutes. Then, 1.5 parts by weight of hydrophilic fumed silica were added in batches, and the mixture was stirred to obtain a preliminary dispersion slurry. The preliminary dispersion slurry was continuously pumped into a pipeline high-shear emulsifier with a jacket heating temperature set to 60°C, and the shear rate at the stator and rotor was controlled at 10000 s⁻¹. -1The feed pump flow rate is adjusted to ensure that the slurry's residence time in the homogenization chamber is 10 seconds per cycle. After exiting the inline high-shear emulsifier, the material flows directly through a microchannel plate heat exchanger with a cooling medium temperature of 10°C. The flow rate is controlled to ensure that the material's residence time in the microchannel plate heat exchanger is 5 seconds. The outlet temperature is monitored and reduced to 20°C, and the pretreated slurry is collected for later use.

[0035] 80 parts by mass of the anionic aliphatic waterborne polyurethane emulsion prepared in Preparation Example 1 and 0.1 parts by mass of polyether-modified polysiloxane defoamer were added to a paint mixing tank. The pretreated slurry was added dropwise to the mixing tank at a constant speed of 150 rpm and a temperature of 20°C for 20 minutes. After the pretreated slurry was added, 0.10 parts by mass of N,N-dimethylethanolamine was added dropwise to the mixing tank to adjust the pH of the mixture to 8.2. Then, 0.4 parts by mass of hydrophobically modified ethoxylated polyurethane and 1.6 parts by mass of deionized water were added, and the mixture was stirred at 250 rpm for 30 minutes to obtain a composite liquid.

[0036] The composite liquid is pumped into the pipeline megasonic reaction chamber by a volumetric pump. The megasonic emission frequency is set to 1.0MHz and the volumetric power density is set to 30W / L. The fluid pumping speed is adjusted so that the fluid is exposed in the megasonic reaction chamber for 10 seconds. The material after megasonic treatment flows out directly and is transported to the feeding tank of the microgravure coating machine.

[0037] A micro-gravure coating machine is used to evenly coat the material in the feed trough onto the surface of a base paper with a water transfer release layer, controlling the wet film thickness on the base paper surface to be 15μm. The base paper with the wet film on its surface is then conveyed to the first temperature-controlled drying tunnel, where the ambient air temperature is set to 40℃. Saturated steam is introduced into the drying tunnel to dynamically maintain the relative humidity at 75%, and the advection air velocity is controlled at 1.5m / s. The base paper's residence time in the first temperature-controlled drying tunnel is 15 seconds. Subsequently, the base paper is continuously conveyed to the second drying tunnel, where the ambient air temperature is set to 80℃. The entire dehumidification system of the second drying tunnel is activated, and the impact air velocity is controlled at 3.0m / s. The base paper's residence time in the second drying tunnel is 120 seconds. After the solvent and moisture have completely evaporated, the paper is cooled and wound up to obtain a matte, seamless temporary tattoo product.

[0038] Example 3: This example provides a method for preparing a matte, seamless temporary tattoo, including the following steps: In a sealed anhydrous mixing vessel, 15.0 parts by weight of anhydrous ethyl acetate, 4.0 parts by weight of propylene glycol methyl ether and 1.5 parts by weight of polyether-modified heptamethyltrisiloxane were added sequentially and mixed at a stirring speed of 300 rpm for 5 min. Then, 2.5 parts by weight of hydrophilic fumed silica were added in batches and stirred to obtain an initial dispersion slurry.

[0039] The initially dispersed slurry was continuously pumped into a pipeline high-shear emulsifier with a jacket heating temperature set at 65°C, and the shear rate at the stator and rotor was controlled at 12000 s / s. -1 The feed pump flow rate is adjusted to ensure that the slurry's residence time in the homogenization chamber is 20 seconds per cycle. After exiting the inline high-shear emulsifier, the material flows directly through a microchannel plate heat exchanger with a cooling medium temperature of 5°C. The flow rate is controlled to ensure that the material's residence time in the microchannel plate heat exchanger is 2 seconds. The outlet temperature is monitored and reduced to 15°C, and the pretreated slurry is collected for later use.

[0040] 75.0 parts by mass of the anionic aliphatic aqueous polyurethane emulsion prepared in Preparation Example 1 and 0.3 parts by mass of polyether-modified polysiloxane defoamer were added to a paint mixing tank. The pretreated slurry was added dropwise to the mixing tank at a constant speed of 250 rpm and a temperature of 25°C for 15 minutes. After the pretreated slurry was added, 0.15 parts by mass of N,N-dimethylethanolamine was added dropwise to the mixing tank to adjust the pH of the mixture to 8.5. Then, 0.8 parts by mass of hydrophobically modified ethoxylated polyurethane and 0.9 parts by mass of deionized water were added, and the mixture was stirred at 250 rpm for 45 minutes to obtain a composite liquid.

[0041] The composite liquid is pumped into the pipeline megasonic reaction chamber through a volumetric pump. The megasonic emission frequency is set to 1.0MHz and the volumetric power density is set to 50W / L. The fluid pumping speed is adjusted so that the fluid is exposed in the megasonic reaction chamber for 5 seconds. After the megasonic treatment, the material flows out directly and is transported to the feeding tank of the microgravure coating machine.

[0042] A micro-gravure coating machine is used to evenly coat the material in the feed trough onto the surface of a base paper with a water transfer release layer, controlling the wet film thickness on the base paper surface to be 25μm. The base paper with the wet film on its surface is then conveyed to the first temperature-controlled drying tunnel, where the ambient air temperature is set to 50℃. Saturated steam is introduced into the drying tunnel to dynamically maintain the relative humidity at 85%, and the advection air velocity is controlled at 2.5m / s. The base paper's residence time in the first temperature-controlled drying tunnel is 10 seconds. Subsequently, the base paper is continuously conveyed to the second drying tunnel, where the ambient air temperature is set to 100℃. The entire dehumidification system of the second drying tunnel is activated, and the impact air velocity is controlled at 5.0m / s. The base paper's residence time in the second drying tunnel is 60 seconds. After the solvent and moisture have completely evaporated, the paper is cooled and wound up to obtain a matte, seamless temporary tattoo product.

[0043] Comparative Example 1: Compared with Example 1, the difference is that in the pre-dispersed silica slurry preparation stage, after the material is discharged from the pipeline high-shear emulsifier, it is not cooled by a plate heat exchanger, but is directly collected in a container and naturally cooled to room temperature. All other aspects are the same.

[0044] Comparative Example 2: Compared with Example 1, the difference is that the step of pumping the composite liquid into the pipeline megasonic reaction chamber for processing is omitted, and the composite liquid after maturation and stirring is directly delivered to the feeding tank of the microgravure coating machine. All other aspects are the same.

[0045] Comparative Example 3: Compared with Example 1, the difference is that the transmission frequency of the pipeline megasonic reaction cavity is replaced with a low-frequency ultrasonic process of 20 kHz, and all other aspects are the same.

[0046] Comparative Example 4: Compared with Example 1, the difference is that in the first stage of temperature-controlled drying tunnel, saturated steam is not introduced, relative humidity is not dynamically controlled, and conventional dehumidification hot air drying is carried out directly. All other aspects are the same.

[0047] Comparative Example 5: Compared with Example 1, the difference is that the hydrophobically modified ethoxylated polyurethane thickener is not added to the formulation, but is replaced with an equal mass of deionized water, and all other aspects are the same.

[0048] Test Example 1: Emulsion Mechanical Stability and Demulsification Filtration Test This test was used to determine the gelation rate of the composite liquids in each embodiment and comparative example after acoustic field treatment, verifying the physical influence of process equipment parameters on the stability of waterborne polyurethane emulsions. The specific experimental steps are as follows: 500.0 grams of the composite liquid from Examples 1 to 3, Comparative Examples 2 and 3, after maturation and processing through corresponding pipeline procedures, were taken as test samples.

[0049] Assemble a vacuum filtration apparatus equipped with a 200-mesh standard stainless steel filter screen of known initial mass. Turn on the vacuum pump and control the absolute pressure of the filtration system to 0.08 MPa. Pour each of the above test samples into the filtration funnel at a uniform speed for filtration.

[0050] After the composite liquid in the funnel has completely passed through the filter screen, 50.0 g of deionized water is used to rinse the inner wall of the funnel and the surface of the filter screen three times to wash away any unbroken liquid adhering to the surface of the filter screen. The filter screen with the solid residue is then removed and placed flat in a vacuum drying oven to dry at a constant temperature of 60°C for 4.0 h.

[0051] After drying, remove the filter screens and place them in a desiccator to cool to room temperature (25°C) before precise weighing. Calculate the mass of the gel residue by subtracting the initial mass of the filter screens from the total mass of the dried filter screens containing the retained material. Divide this mass of the gel residue by the initial total mass of the test samples (500.0 g) and multiply by 100% to calculate the gelation rate of each sample.

[0052] Table 1. Emulsion demulsification and filtration test data for each example and comparative example.

[0053] According to the data in Table 1, the gelation rate test results of Examples 1 to 3 were all below 0.2%, which is on the same order of magnitude as the test data of Comparative Example 2, which omitted the megasonite reaction chamber treatment process, and no obvious abnormal residues were found. The gelation rate of Comparative Example 3, which replaced the emission frequency of the reaction chamber with 20kHz low-frequency ultrasound, reached 14.64%, and a large number of solid gel blocks were trapped on the filter screen, showing severe demulsification.

[0054] Waterborne aliphatic polyurethane emulsions primarily rely on hydrophilic groups on polymer molecular chains to construct an electric double layer structure in the aqueous phase, utilizing electrostatic repulsion between charges to maintain the thermodynamic metastable state of the system. Examples 1 to 3 employed a 1.0 MHz high-frequency megasonic wave to treat the fluid during flow processing. At this frequency, a steady-state acoustic flow effect was primarily generated in the medium. The microscopic dynamic shear stress generated by the acoustic radiation pressure driving the fluid could provide the mechanical energy to break the weak monomolecular hydrogen bonds between propylene glycol methyl ether and the silanol groups of fumed silica. However, this energy scalar did not reach the threshold for disrupting the electrostatic repulsion energy of the electric double layer on the surface of the waterborne polyurethane latex particles. Therefore, the hydrated layer on the polymer particle surface was preserved, the system did not flocculate, and the mechanical stability with a low gel rate was maintained.

[0055] The 20kHz sound wave used in Comparative Example 3 belongs to the low-frequency ultrasonic band, where the fluid undergoes a violent transient cavitation effect. The strong shock wave and local heat energy released by the cavitation microbubbles upon collapse far exceed the tolerance limit of the double electric layer of the waterborne polyurethane latex particles, forcibly disrupting the charge balance on the surface of the latex particles. The polyurethane molecular chains, stripped of their charge repulsion protection, undergo high-frequency collisions in the flow field, leading to irreversible aggregation and cross-linking. Macroscopically, this manifests as system demulsification and the generation of a large amount of solid gel residue that has lost its flowability. The test results confirm that a frequency parameter of 1.0MHz is the engineering physical boundary for achieving weak hydrogen bond exfoliation on the powder surface without compromising the stability of the polymer matrix.

[0056] Test Example 2: Rheological Dynamic Yield Stress Test This test was used to determine the steady-state rheological properties of the composite liquids in each example and comparative example, verifying the ability of the physical network constructed by the hydrophobically modified ethoxylated polyurethane in the system to interfere with the hydrodynamic boundary. The specific experimental steps are as follows: 100.0 g of each of the composite liquids from Examples 1 to 3 and Comparative Example 5, which had been cured but not coated, were taken as test samples. The samples were placed in a constant temperature water bath at 25°C for 30 min to eliminate the shear heat generated during the sampling process.

[0057] The viscosity of plastic polymers or resins, as liquids or as emulsions or dispersions, was determined using a rotational rheometer equipped with a coaxial cylindrical test geometry, in accordance with the international standard ISO 3219-1993. The test sample, after being kept at a constant temperature, was slowly injected into the test sleeve of the rheometer and allowed to stand for 5 minutes to allow the internal structure of the material to recover.

[0058] The shear rate scan range of the rotational rheometer was set to 0.01 s. -1 ~100s -1 Fifty data points were collected using a logarithmic distribution pattern. The test was initiated, and the corresponding shear stress values ​​at different shear rates were recorded.

[0059] Export the rheological test data, use the Carson model to perform nonlinear regression fitting on the data points in the low shear region, calculate the intercept when extrapolated to the shear rate of zero, and record the intercept value as the dynamic yield stress of the system.

[0060] Table 2. Rheological dynamic yield stress test data for each embodiment and comparative example.

[0061] According to the data in Table 2, the dynamic yield stress of the composite liquids in Examples 1 to 3 at 25°C ranged from 0.58 Pa to 0.91 Pa. The dynamic yield stress of Comparative Example 5, which did not contain hydrophobically modified ethoxylated polyurethane, was only 0.04 Pa, and it basically did not exhibit yield confinement characteristics.

[0062] The polymer backbone of hydrophobically modified ethoxylated polyurethane has long-chain aliphatic hydrocarbon hydrophobic groups at both ends. In an aqueous system, these hydrophobic end groups spontaneously adsorb onto the hydrophobic regions of the waterborne polyurethane latex particles, forming an associated network. This physical network causes the liquid system to exhibit viscoelastic characteristics; the fluid must withstand an external shear force exceeding a specific threshold to achieve macroscopic flow, which is the dynamic yield stress. In Examples 1 to 3, this stress threshold was controlled within the range of 0.5 Pa to 1.0 Pa through proportioning control.

[0063] The drag force in the vertical direction of Marangoni convection induced by solvent evaporation can exceed the yield stress, allowing silica particles to overcome resistance and migrate upwards. However, the lateral shear spreading force of convection on the coating surface is less than the yield stress, preventing macroscopic flow of the fluid in the horizontal direction. Comparative Example 5 lacks a physical association network, and the fluid deforms under extremely low stress, failing to provide rheological constraints on the lateral diffusion of Marangoni convection.

[0064] Test Example 3: Evaluation Test of Coating Surface Gloss and Macroscopic Smoothness This test was used to determine the surface optical characteristics and physical contour morphology of the cured films in each embodiment and comparative example, and to verify the actual influence of various process parameters on the vertical migration of matte powder and the lateral shrinkage of the coating film. The specific experimental steps are as follows: One roll of matte, traceless temporary tattoo product prepared and cooled and rolled up from Examples 1 to 3 and Comparative Examples 1, 2, 4, and 5 was taken respectively. Five test samples with a size of 100mm × 100mm were randomly cut from each roll of product.

[0065] According to the national standard GB / T9754-2007 "Determination of 20°, 60° and 85° Specular Gloss of Paint Films Without Metallic Pigments", the optical reflectance of the test sample surface was measured using a multi-angle gloss meter. The incident angle of the instrument was set to 60°. Five different test points were evenly selected on the surface of each test sample to read the gloss values, and the arithmetic mean was calculated as the final gloss data for that sample.

[0066] According to the national standard GB / T10610-2009 "Rules and methods for evaluating surface structure by the surface structure profile method in product geometric technical specifications", the macroscopic flatness of the test sample was determined using a contact surface roughness tester. The probe scanning length was set to 15.0 mm, and the measurement speed was set to 0.5 mm / s. The arithmetic mean roughness data of the surface profile were recorded.

[0067] Table 3. Surface gloss and smoothness test data for each embodiment and comparative example.

[0068] According to the data in Table 3, the 60° gloss of the coating surfaces in Examples 1 to 3 was all below 3.0 GU, and the arithmetic mean roughness remained below 0.6 μm. Comparative Example 1, which omitted the plate heat exchanger cooling process, and Comparative Example 2, which omitted the megasonic treatment, had higher gloss levels, reaching 16.3 GU and 11.7 GU, respectively. Comparative Example 4, which eliminated relative humidity control, had extremely high gloss but increased roughness. Comparative Example 5, which did not add a rheology confinement agent, achieved low gloss, but the arithmetic mean roughness increased to 3.58 μm, and orange peel defects appeared on the surface.

[0069] The gloss of the coating surface depends on the distribution of matting powder on the surface, while the smoothness depends on the hydrodynamic stability during film formation. In Comparative Example 1, no cooling and quenching was performed; water molecules occupied the silanol groups on the surface of the fumed silica, preventing the sufficient adsorption of the polyether-modified heptamethyltrisiloxane. The silica lacked the surface energy to migrate to the coating surface and remained at the bottom of the coating. Comparative Example 2 lacked the shear energy provided by the 1.0MHz frequency band acoustic waves, failing to completely strip the propylene glycol methyl ether masking layer. The overall steric hindrance of the particles was too large, reducing the migration rate to the surface.

[0070] In Comparative Example 4, under conventional hot air dehumidification, rapid evaporation of water molecules caused cross-linking and curing of the coating surface, blocking the physical channels for the matte particles to move upwards. Simultaneously, the stress contraction within the wet film was not released, resulting in high surface roughness. Examples 1 to 3, by controlling high humidity to suppress moisture evaporation, allowed the surface tension gradient generated by the preferential evaporation of low-boiling-point solvents to drive the directional migration of silica particles to the surface, exhibiting low-gloss characteristics. Although Comparative Example 5 achieved upward particle migration, the lack of dynamic yield stress constraint led to the lateral spread of Bénard eddies generated by convection on the coating surface, resulting in macroscopic orange peel defects after curing, significantly increasing surface roughness.

[0071] Test Example 4: Evaluation Test of Coating Tensile Deformation and Stress Whitening This test was used to determine the mechanical elongation and changes in optical brightness under tensile conditions after curing into films in each example and comparative example, verifying the physical influence of vertical phase separation of matting powder on the mechanical dissipation capability of the polyurethane bulk phase. The specific experimental steps are as follows: Take the products prepared in Examples 1 to 3, and Comparative Examples 1 and 4 respectively. Immerse the products in deionized water to remove the base paper and obtain independent test coatings. Use a cutter to cut the coatings into standard test samples.

[0072] According to the national standard GB / T1040.3-2006 "Determination of tensile properties of plastics - Part 3 Test conditions for films and sheets", the specimen was clamped in the upper and lower fixtures of the universal testing machine. The tensile speed was set to 50 mm / min, and the instrument was started to perform constant-speed tensile testing. The elongation at break of the specimen was recorded.

[0073] According to the national standard GB / T11186.2-1989 "Methods for measuring the color of coatings - Part II: Color Measurement", the initial lightness value of the sample under no stress was determined using a colorimeter. Subsequently, a new sample of the same specifications was clamped in a tensile testing machine and stretched until the strain reached 100%, then held in a locked position. The lightness value of the stressed area at the center of the sample was then measured using a colorimeter. The lightness difference was calculated by subtracting the initial lightness value from the stretched lightness value. The higher this difference, the more severe the whitening phenomenon of the coating under stress.

[0074] Table 4. Elongation at break and stress whitening test data of coatings in each example and comparative example.

[0075] According to the data in Table 4, the elongation at break of Examples 1 to 3 all exceeded 450%, and the lightness difference remained at 2.0 under 100% tensile strain. Within this range, no obvious whitening was observed by the naked eye. Comparative Example 1, which omitted the cooling and quenching process, and Comparative Example 4, which did not undergo dynamic control of relative humidity, showed a significant decrease in elongation at break to below 300%, and a sharp increase in brightness difference during the stretching process, exhibiting severe edge stress whitening.

[0076] The macroscopic mechanical properties of the cured coating are determined by its microscopic phase structure. In Examples 1 to 3, phase separation was achieved through Marangoni convection. Inorganic rigid fumed silica particles migrated directionally to the coating surface and accumulated, while the underlying layer retained a highly pure aqueous aliphatic polyurethane bulk phase. The pure polyurethane macromolecular segments have extremely low elastic modulus and extremely high deformation compliance. Under external tensile stress, the underlying layer can effectively absorb and dissipate mechanical energy through the unentanglement and slippage of molecular chains, thus maintaining a high elongation at break without damage to the optical structure.

[0077] In Comparative Example 1, the powder lacked surface energy to drive the process, while in Comparative Example 4, the rapid surface drying of the film was due to the blockage of physical channels. Both resulted in the uniform dispersion or disordered agglomeration of fumed silica particles within the polyurethane bulk phase. Under tensile stress, a significant modulus difference existed between the rigid silica and the flexible polyurethane matrix, leading to a high concentration of stress at the inorganic particle interface. The polymer matrix could not undergo synchronous deformation, causing physical separation between the particles and the resin interface, resulting in numerous μm-scale micropores within the coating. When external light penetrated the coating, strong refraction and scattering occurred at these micropore interfaces, macroscopically manifesting as a stress-induced whitening phenomenon with a dramatic increase in brightness. The test results confirm that the vertical phase separation structure of the powder is the physical basis for solving the deformation-induced whitening defect in the coating.

[0078] Test Example 5: Surface Spectroscopy and Orange Peel Defect Evaluation Test This test was used to determine the macroscopic spectral profile data of the cured films in each embodiment and comparative example, verifying the intervention results of rheology confinement agents and relative humidity control on the hydrodynamic stability of the film. The specific experimental steps are as follows: Take one roll of each of the products prepared in Examples 1 to 3, and Comparative Examples 4 and 5, after cooling and winding. Randomly cut five test samples with a size of 150mm × 150mm from each roll of product.

[0079] The surface of the test sample was optically profiled using a coating spectroscopy scanner. The laser scanning measurement length of the instrument was set to 100 mm.

[0080] Record the long-wave profile values ​​output by the instrument. The long-wave profile corresponds to surface undulations in the wavelength range of 1.2mm to 12mm. The undulations in this band closely match the orange peel and pinhole defects observed macroscopically by the human eye. Higher values ​​indicate poorer surface smoothness of the coating and more obvious macroscopic hydrodynamic defects.

[0081] Table 5. Surface spectral scanning test data of coatings in each embodiment and comparative example.

[0082] According to the data in Table 5, the long-wave profile values ​​of Examples 1 to 3 were all controlled below 4.0, and the coating surface was smooth and without macroscopic undulations. The long-wave profile value of Comparative Example 4, which did not undergo humidity control by introducing saturated steam, increased to 19.6. The long-wave profile value of Comparative Example 5, which did not add hydrophobically modified ethoxylated polyurethane, surged to 37.2, and the coating surface exhibited severe orange peel texture and pinhole defects visible to the naked eye.

[0083] The surface smoothness of the coated wet film during the heat drying process is controlled by the solvent evaporation kinetics and surface tension gradient within the liquid. Examples 1 to 3 maintained a relative humidity of 75%–85% during the initial drying stage, suppressing water evaporation in the system. This, combined with the vertical tension gradient generated by the escape of low-boiling-point solvents, induced stable upward convection. Simultaneously, the dynamic yield stress present in the system acted as a physical threshold, rheologically restricting the lateral spread of the fluid on the surface and interrupting the closed-loop path of the macroscopic Bénard vortex, thus ensuring macroscopic surface smoothness.

[0084] In Comparative Example 4, moisture was forced to evaporate rapidly under low-humidity and hot air conditions, resulting in drastic volume contraction and irreversible stress fluctuations on the surface. Comparative Example 5 completely removed the dynamic yield stress of the system. Upon reaching the liquid surface, the upward Marangoni convection, no longer constrained by rheological confinement resistance, underwent disordered lateral spreading and shearing, forming numerous large-scale Bénard hydrodynamic circulations. These circulations were frozen within the coating after solvent removal and resin cross-linking and curing, ultimately evolving into orange peel and pinhole structures with extremely high long-wavelength profile values. This data validates that introducing a thixotropic network with a specific threshold in complex volatile systems is a necessary means to shield the lateral interference flow field and maintain coating smoothness.

[0085] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A matte, seamless temporary tattoo sticker, characterized in that, The coating of the tattoo sticker is made from the following raw materials in parts by weight: Anionic aliphatic waterborne polyurethane emulsion: 70-85 parts; Pre-dispersed silica slurry: 15-25 parts; Hydrophobically modified ethoxylated polyurethane: 0.3~1.0 parts; Polyether-modified polysiloxane defoamer: 0.1~0.4 parts; Neutralizing agent: 0.08~0.2 parts; Deionized water: 0.5~2.0 parts; The neutralizing agent is N,N-dimethylethanolamine.

2. The matte, seamless temporary tattoo sticker according to claim 1, characterized in that: The pre-dispersed silica slurry contains hydrophilic fumed silica, which has not undergone surface hydrophobic modification and has a specific surface area of ​​185 m². 2 / g~215m 2 / g, with a native particle size of 12nm~14nm; The hydrophobically modified ethoxylated polyurethane is a block copolymer formed by polymerizing polyethylene glycol and diisocyanate, with a number average molecular weight of 30,000 to 50,000, and the main chain is double-capped with hexadecyl long-chain aliphatic hydrocarbons at both ends.

3. The matte, seamless temporary tattoo sticker according to claim 1, characterized in that: The anionic aliphatic waterborne polyurethane emulsion is prepared from raw materials including polycaprolactone diol with a number average molecular weight of 2000, 2,2-dimethylolpropionic acid, isophorone diisocyanate, and a salting agent.

4. The matte, seamless temporary tattoo sticker according to claim 1, characterized in that: The composite liquid used to prepare the coating film has a dynamic yield stress between 0.5 Pa and 1.0 Pa at 25°C; the surface gloss of the cured coating film is less than 3.0 at an incident angle of 60°, the elongation at break is greater than 450%, and the lightness difference under 100% tensile strain does not exceed 2.

0.

5. A method for preparing a matte, seamless temporary tattoo as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Mix anionic aliphatic waterborne polyurethane emulsion with polyether-modified polysiloxane defoamer, add pre-dispersed silica slurry, add a neutralizer to adjust the pH value, add hydrophobically modified ethoxylated polyurethane and deionized water and stir to mature and obtain a composite liquid. S2. The composite liquid obtained in step S1 is sent into the acoustic field reaction chamber for continuous flow treatment. S3. Coat the material processed in step S2 onto the surface of the base paper to form a wet film; The base paper with a wet film is passed sequentially through a first temperature-controlled drying tunnel where steam is introduced to control humidity and temperature, and a second drying tunnel where the dehumidification system is turned on for high-temperature curing. After cross-linking, curing, cooling, and winding, a matte, traceless tattoo sticker is obtained.

6. The method for preparing a matte, seamless tattoo sticker according to claim 5, characterized in that: Prior to step S1, the pre-dispersed silica slurry is prepared in advance, including the following steps: Anhydrous ethyl acetate, propylene glycol methyl ether, polyether-modified heptamethyltrisiloxane, and hydrophilic fumed silica were mixed and stirred to obtain a preliminary dispersion slurry. The preliminary dispersion slurry was continuously pumped into a pipeline high-shear emulsifier for homogenization and shearing treatment. After the material was discharged, it was directly cooled by a plate heat exchanger with a cooling medium temperature of 5℃~10℃ and collected for later use.

7. The method for preparing a matte, seamless tattoo sticker according to claim 6, characterized in that: The jacket heating temperature of the inline high-shear emulsifier is set to 60℃~65℃, and the shear rate at the stator and rotor is controlled at 10000s. -1 ~12000s -1 The residence time of the slurry in the homogenization chamber is 10 to 20 seconds; the outlet temperature of the material after being cooled by the plate heat exchanger is 15°C to 20°C.

8. The method for preparing a matte, seamless tattoo sticker according to claim 5, characterized in that: In step S2, the acoustic field reaction chamber is a pipeline megasonic reaction chamber, the megasonic emission frequency is set to 1.0MHz, the volumetric power density is set to 30W / L~50W / L, and the exposure time of the fluid in the megasonic reaction chamber is 5 seconds~10 seconds.

9. The method for preparing a matte, seamless tattoo sticker according to claim 5, characterized in that: In step S3, the ambient air temperature of the first temperature-controlled drying tunnel is set to 40℃~50℃, saturated steam is introduced into the drying tunnel to dynamically maintain the relative humidity at 75%~85%, the advection wind speed is controlled at 1.5m / s~2.5m / s, and the residence time is 10 seconds~15 seconds; the ambient air temperature of the second drying tunnel is set to 80℃~100℃, the entire dehumidification system is turned on, the impact wind speed is controlled at 3.0m / s~5.0m / s, and the residence time is 60 seconds~120 seconds.

10. The method for preparing a matte, seamless tattoo sticker according to claim 5, characterized in that: In step S1, the ambient temperature during the addition of the pre-dispersed silica slurry is controlled at 20℃~25℃, and the addition time is 15min~20min; a neutralizing agent is added to adjust the pH of the mixture to 8.2~8.5; the curing and stirring time after adding the hydrophobically modified ethoxylated polyurethane is 30min~45min.

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