A matte PU decorative lettering film and a preparation method thereof

Abstract

The application discloses a matte PU decorative lettering film and a preparation method thereof. The lettering film is a layered structure sequentially compounded from top to bottom, and each layer is sequentially a frosted PET film, a matte PU leather resin layer and a hot melt adhesive layer from top to bottom. The frosted PET film is provided with a plurality of uniform distributed lines. The matte PU leather resin layer is a dense and pore-free film layer, which is prepared by mixing water-based PU resin, color paste, silica and water-based defoaming agent according to mass ratios and then stirring. The mass ratio of each raw material is as follows: water-based PU resin 62%, color paste 24%, silica 11% and water-based defoaming agent 3%. The silica is uniformly distributed in the water-based PU resin matrix. The viscosity of the water-based PU resin and the particle size of the silica are taken as operation objects, a quantitative operation formula of rotation speed and time is established by fitting and deducing coefficients through a pre-experiment, and stirring parameters are optimized in stages, so that the agglomeration of flame-retardant components is completely avoided, the silica is uniformly distributed in the resin matrix, and a stable physical light-shielding layer is formed.

Description

Technical Field

[0001] This invention belongs to the field of decorative lettering film technology, specifically a matte PU decorative lettering film and its preparation method. Background Technology

[0002] As the apparel and decoration industry increases its demand for product quality, matte PU decorative lettering film, with its understated yet luxurious visual effect, is widely used in the decorative processing of high-end clothing, bags, and other products.

[0003] In existing technologies, the preparation of matte PU decorative lettering films largely relies on empirical operations, and the core technology has many shortcomings:

[0004] Firstly, the raw material ratio of matte PU leather resin lacks a scientific calculation basis. The addition ratio of colored pigments, silica, and water-based defoamers is mostly determined by manual experience without systematic deduction based on the core material characteristics of water-based PU resin. This results in uneven dispersion of silica in the resin system and poor color consistency, ultimately affecting the matte uniformity of the lettering film.

[0005] Secondly, the high-speed stirring and mixing parameters lack clear calculation logic. The speed and time are adjusted only through experience, which easily leads to silica agglomeration and makes it impossible to form a uniform physical light-shielding layer, resulting in an unstable matte effect.

[0006] Third, the fine mist transfer process lacks precise process parameters. The coating thickness is not calculated in conjunction with the fine mist depth and the resin film shrinkage rate. The drying temperature and time are not scientifically set according to the resin characteristics, resulting in incomplete fine mist replication and inability to work with the matte structure to achieve a high matte effect.

[0007] In addition, the existing process is not easily replicable, and the matte finish and bonding strength of different batches of products vary greatly, making it difficult to meet the quality control requirements of large-scale production. Summary of the Invention

[0008] To address the shortcomings of the existing technologies, there is an urgent need to develop a PU leather lettering film with tight interlayer bonding, stable anti-sublimation effect, and controllable preparation process. This would solve the technical problem of color bleeding and fading of the lettering film caused by dye migration from chemical fiber fabrics, and improve the product's durability and batch stability.

[0009] This invention provides a matte PU decorative lettering film, which has a layered structure that is composited from top to bottom. The layers, from top to bottom, are a frosted PET film, a matte PU leather resin layer, and a hot melt adhesive layer.

[0010] The frosted PET film has textured surfaces with uniformly distributed textures; the matte PU leather resin layer is a dense, non-porous film layer, which is made by mixing water-based PU resin, colored pigments, silica, and water-based defoamer in a certain mass ratio and then stirring. The mass ratio of each raw material is 62% water-based PU resin, 24% colored pigments, 11% silica, and 3% water-based defoamer. The silica is uniformly distributed in the water-based PU resin matrix.

[0011] The matte PU leather resin layer is tightly bonded to the frosted PET film, and the texture of the frosted PET film is completely replicated on the surface of the matte PU leather resin layer.

[0012] The hot melt adhesive layer completely covers the side of the matte PU leather resin layer away from the frosted PET film, forming a continuous, integrated structure with the matte PU leather resin layer.

[0013] A method for preparing a matte PU decorative lettering film is also proposed, including the following steps:

[0014] S1. Raw material proportioning calculation and weighing: The solid content of water-based PU resin is tested in parallel multiple times. After removing extreme values, the average value is taken as the measured solid content. Based on the calculation formula and derivation coefficient, the addition ratio of color paste, silica and water-based defoamer is calculated. Each raw material is weighed according to the calculated ratio, and the weighing accuracy and mass ratio deviation are controlled.

[0015] S2. Resin Preparation by Stirring: The water-based PU resin is heated, with the temperature monitored in real time and the heating rate controlled until the target temperature is reached. The raw materials are added sequentially in the order of water-based PU resin, color pigment, silica, and water-based defoamer, and stirred in stages. In the first stage, after adding the color pigment, stirring is performed at the speed and time calculated according to the formula. In the second stage, after adding silica, the speed and time are adjusted to a multiple of the set values ​​from the first stage. In the third stage, after adding the water-based defoamer, the speed is reduced while maintaining a fixed stirring time. After stirring, if no agglomerated particles are detected and the particle size distribution meets the standards, it is considered matte PU leather resin.

[0016] S3. Coating to frosted PET film: The matte PU leather resin is coated onto the surface of the frosted PET film. The coating thickness is determined by calculating the texture depth of the frosted PET film and the film shrinkage rate of the matte PU leather resin.

[0017] S4. Heating and Drying for Molding: The coated substrate is heated and dried in two continuous stages. The first stage is the solvent evaporation stage, where the temperature is determined based on the evaporation temperature of the solvent in the resin, and the time is determined by calculation based on the linear relationship between the wet film thickness and the solvent evaporation rate. The second stage is the curing and molding stage, where the temperature is determined based on the crosslinking temperature of the resin, and the time is derived from experimental data on the time required for the resin to reach the required degree of curing. During the drying process, the fluctuation range of ambient temperature and humidity is controlled to avoid the formation of pores or cracks in the film layer.

[0018] S5. Hot melt adhesive coating: Apply hot melt adhesive to the surface of the matte PU leather resin layer. The coating thickness is determined by calculating the surface roughness of the matte PU leather resin layer and the wetting angle of the hot melt adhesive. The coating process is carried out at a uniform speed, which is consistent with the coating speed of the matte PU leather resin. After coating, the substrate is subjected to constant temperature static treatment. The static temperature is determined by the softening point of the hot melt adhesive and the heat resistance temperature of the matte PU leather resin layer. The static time is derived from the molecular diffusion rate of the hot melt adhesive and the resin layer.

[0019] The technical solutions provided by the embodiments of this disclosure have at least the following beneficial effects:

[0020] Using the measured viscosity of waterborne PU resin and the particle size of silica as the calculation objects, the coefficients were derived through preliminary experiments, and a quantitative calculation formula for rotation speed and time was established. The stirring parameters were optimized in stages, which completely avoided the agglomeration of flame retardant components and ensured that silica was evenly distributed in the resin matrix to form a stable physical light-shielding layer.

[0021] This invention determines the coating thickness by synergistic calculation of the fine mist depth and film shrinkage rate, and scientifically divides the drying stages by combining solvent evaporation characteristics and resin crosslinking temperature, so as to achieve complete replication of the fine mist texture. This allows the fine mist texture replication structure and the matte structure to work synergistically, significantly improving the stability of the matte effect of the lettering film.

[0022] This invention focuses on the quantitative calculation and experimental verification of process parameters throughout the entire process. All key parameters are derived from measured data, without the limitation of complex mechanical structures. The process is highly replicable, which greatly improves the consistency of product batches. In addition, the raw material ratio is accurate, the process steps are controllable, and the production cost is suitable for large-scale production. It can be widely used in high-end clothing, bags and other decorative fields. Attached Figure Description

[0023] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Please see Figure 1This application provides a matte PU decorative lettering film, characterized in that the lettering film has a layered structure layered from top to bottom, with each layer consisting of a frosted PET film, a matte PU resin layer, and a hot melt adhesive layer from top to bottom; the frosted PET film has textured surfaces with uniformly distributed textures; the matte PU resin layer is a dense, non-porous film layer, prepared by mixing and stirring water-based PU resin, colored pigments, silica, and water-based defoamer in a certain mass ratio, with the mass ratio of each raw material being 62% water-based PU resin, 24% colored pigments, 11% silica, and 3% water-based defoamer, and the silica being uniformly distributed in the water-based PU resin matrix; the matte PU resin layer is tightly bonded to the frosted PET film, and the textures on the surface of the frosted PET film are completely replicated onto the surface of the matte PU resin layer; the hot melt adhesive layer completely covers the side of the matte PU resin layer away from the frosted PET film, forming a continuously bonded integral structure with the matte PU resin layer.

[0026] The texture is a fine, misty pattern;

[0027] As an optional embodiment, the addition ratios of color pigment, silica, and water-based defoamer are calculated based on the measured solid content of the water-based PU resin, using the following formulas: Color pigment addition ratio = Measured solid content of water-based PU resin × k1, Silica addition ratio = Measured solid content of water-based PU resin × k2, Water-based defoamer addition ratio = Measured solid content of water-based PU resin × k3; where k1, k2, and k3 are calculation coefficients determined through a combination of film-forming and dispersion experiments.

[0028] Film formation experiment: Five mixing systems were set up. In each system, the solid content of waterborne PU resin was 20%, 25%, 30%, 35%, and 40%, respectively; the proportion of colored pigment was 20%, 22%, 24%, 26%, and 28%; the proportion of silica was 8%, 9.5%, 11%, 12.5%, and 14%; and the proportion of waterborne defoamer was 2%, 2.5%, 3%, 3.5%, and 4%. Each system was formed into films in parallel three times. After film formation, the porosity of the film layer was detected using a microscope with a magnification of 5000x, and the surface roughness was detected using a roughness meter. Systems with a porosity ≤0.1% and a surface roughness Ra=0.8-1.2μm were selected to meet the standards.

[0029] Dispersion experiment: Five mixing systems were set up that were exactly the same as those in the film formation experiment. After each system was stirred according to the basic stirring parameters, the D90 particle size of silica was detected by a laser particle size analyzer, and the agglomeration was observed by a microscope with a magnification of 5000x. The system with D90≤6μm and agglomerated particle area ratio≤0.2% was selected to meet the standard.

[0030] Coefficient Derivation: Data from systems that met the standards in both experiments were extracted. Using the solid content of waterborne PU resin as the independent variable and the proportion of each component as the dependent variable, binary linear regression equations were established: y1=k1x+b1, y2=k2x+b2, y3=k3x+b3 (where x is the measured solid content of waterborne PU resin, and y1, y2, and y3 are the proportions of each component). The regression coefficients were calculated using the least squares method, requiring a correlation coefficient R² ≥ 0.95 and intercepts b1, b2, and b3 ≤ 0.5%. Finally, the specific values ​​of k1, k2, and k3 were determined.

[0031] As an optional embodiment, the stirring parameters of the matte PU leather resin are calculated based on the measured viscosity of the water-based PU resin and the particle size characteristics of silica. The specific calculation logic is as follows:

[0032] Stirring speed calculation: The calculation formula is N = (μ / d) × k, where N is the stirring speed, μ is the measured viscosity of water-based PU resin at 25℃ (unit: mPa·s), d is the measured particle size of silica (unit: μm), and k is the derivation coefficient;

[0033] Determination of the derived coefficient k: Three sets of preliminary experiments were set up. The first set had μ=5000mPa·s and d=3μm, the second set had μ=6500mPa·s and d=5μm, and the third set had μ=8000mPa·s and d=7μm. Each set of preliminary experiments was repeated three times. After stirring, the dispersion state of silica was detected. The speed at which D90≤6μm and no agglomeration were selected met. The average value of the speed at which the speed met the standard was taken as the reference speed N1, N2 and N3. Substituted into the formula k=N×d / μ, the average value of the three sets of k values ​​was taken as the final derived coefficient.

[0034] Stirring time calculation: Five stirring time gradients were set at 10 min, 15 min, 20 min, 25 min, and 30 min. Each time interval corresponds to one experiment. After stirring, the particle size of silica D90 was measured. A linear fitting curve was plotted with stirring time as the abscissa and D90 particle size as the ordinate. The fitting equation is D90 = at + b (a is the slope and t is the stirring time). When D90 = 6 μm, the stirring time t = (6 - b) / |a| was calculated.

[0035] As an optional embodiment, the matte-related structure of the lettering film consists of a texture replication structure and a matte structure. The texture replication structure is formed by coating a resin wet film to completely adhere to the texture surface of the frosted PET film, followed by drying and curing. The matte structure consists of a physical light-shielding layer formed by uniformly distributing silica in a water-based PU resin matrix. The distribution density of silica and the density of the frosted PET film texture are synergistically matched, and the specific matching method is as follows:

[0036] Three groups of frosted PET films with different texture densities were selected, namely 30 lines / mm, 50 lines / mm, and 70 lines / mm;

[0037] For each density of frosted PET film, three silica distribution density gradients were set as 5×10³ particles / mm², 8×10³ particles / mm², and 11×10³ particles / mm².

[0038] Each combination corresponds to a film-forming experiment. After film formation, the gloss at 60° is measured using a gloss meter. Combinations with a gloss of ≤10 GU are selected as matching standard groups. Finally, the optimal silica distribution density corresponding to different texture densities is determined.

[0039] As an optional embodiment, the following steps are included:

[0040] S1. Raw material proportioning calculation and weighing: The solid content of water-based PU resin was tested five times in parallel. After removing extreme values, the average value was taken as the measured solid content. The addition ratio of color paste, silica and water-based defoamer was calculated. Each raw material was weighed according to the calculated ratio. The weighing accuracy was ±0.01g and the deviation of the mass ratio of each raw material was ≤±0.5%.

[0041] S2. Resin Preparation by Stirring: The water-based PU resin is heated at a rate of 1.5℃ / min, with real-time temperature monitoring until the target temperature is reached (at which temperature the viscosity of the water-based PU resin is 5000-8000 mPa·s). The water-based PU resin, colored pigment, silica, and water-based defoamer are added sequentially, with stirring performed in stages. In the first stage, after adding the colored pigment, stirring is performed according to the calculated speed and time. In the second stage, after adding silica, the speed is increased to 1.3 times that of the first stage, and the stirring time is extended to 1.5 times that of the first stage. In the third stage, after adding the water-based defoamer, the speed is reduced to 0.7 times that of the first stage, and the stirring time is maintained for 15 minutes. After stirring, the silica D90 is measured to be ≤6μm and the area ratio of agglomerated particles is ≤0.2%, indicating that the product is matte PU leather resin.

[0042] S3. Coating to frosted PET film: Matte PU leather resin is coated onto the surface of the frosted PET film. The coating thickness is determined by calculating the texture depth of the frosted PET film and the film shrinkage rate of the matte PU leather resin. The calculation formula is: wet film thickness = texture depth × (1 + film shrinkage rate). The film shrinkage rate is determined by the following method: five wet film thickness gradients are set at 10μm, 15μm, 20μm, 25μm, and 30μm. After curing, the corresponding dry film thickness is measured. The shrinkage rate of each group is calculated according to the formula: shrinkage rate = (wet film thickness - dry film thickness) / wet film thickness. The shrinkage rate constant is obtained by fitting. The wet film thickness is monitored in real time during the coating process. When the thickness deviation exceeds ±0.3μm, the coating speed is adjusted according to the formula: adjustment speed = 0.2m / min × (deviation / 0.1μm).

[0043] S4. Heating and Drying for Molding: The coated substrate is heated and dried in two continuous stages. The first stage is the solvent evaporation stage. The temperature is determined by increasing the temperature by 5°C after detecting the evaporation temperature of the solvent in the resin using a gas chromatograph. The time is determined by calculating the linear relationship between the wet film thickness and the solvent evaporation rate. The linear relationship equation is: time = wet film thickness × k (k is the evaporation rate coefficient, determined experimentally). The second stage is the curing and molding stage. The temperature is determined by detecting the crosslinking temperature of the resin using a differential scanning calorimeter. The time is verified through preliminary experiments. During the drying process, the ambient temperature fluctuation is ≤±1°C, and the humidity is ≤30%.

[0044] S5. Hot Melt Adhesive Coating: Hot melt adhesive is coated onto the surface of the matte PU leather resin layer. The coating thickness is determined by calculating the surface roughness of the matte PU leather resin layer and the wetting angle of the hot melt adhesive. The calculation formula is: Coating Thickness = Surface Roughness × (Wetting Angle / 90°) × Thickness Coefficient. Surface roughness is measured using a roughness meter, the wetting angle is measured using a contact angle measuring instrument, and the thickness coefficient is determined through linear regression analysis using three sets of coating experiments with different roughness-wetting angle combinations (regression equation correlation coefficient R² ≥ 0.95). The coating process is kept at a constant speed, consistent with the coating speed of matte PU leather resin. After coating, the substrate is subjected to constant temperature static treatment. The static temperature = (softening point of hot melt adhesive + heat resistance temperature of matte PU leather resin layer) / 2, and the static time = the time for hot melt adhesive to wet the resin layer + the time for molecular diffusion to reach a stable interface. The wettability time is determined by observing the duration for hot melt adhesive to completely cover the surface of the resin layer using an infrared thermal imager, and the molecular diffusion time is determined by testing the time required for the interface bonding strength to be ≥1.8N / 25mm using a dynamic mechanical analyzer.

[0045] As an optional embodiment, the valid data of film formation experiment and dispersion experiment are used to remove outliers through standard deviation analysis. The outlier judgment criterion is a deviation from the average value of each group of data ±10%. After removing outliers, no less than two sets of valid data are retained for each group of experiments to ensure the accuracy of the derivation of the calculation coefficients.

[0046] As an optional embodiment, the derivation coefficient of the stirring speed in the first stage was obtained by linear fitting of three sets of pre-experimental data, and the correlation coefficient of the fitting equation R²≥0.95; the adjustment ratio of the stirring speed and time in the second stage was determined by dispersion experiments with five different adjustment ratios (1.1-1.5 times the stirring speed and 1.2-1.8 times the time), and the ratio with the smallest silica D90 and no agglomeration was selected as the final adjustment ratio.

[0047] As an optional embodiment, the texture depth is detected by laser confocal microscopy with a detection accuracy of ±0.1μm; the wet film thickness is detected in real time by an online laser thickness gauge with a detection frequency of once per second; the fitting equation for the film shrinkage rate is shrinkage rate = kt + b (k is the slope, t is the wet film thickness, and b is the intercept), and the fitting correlation coefficient R² ≥ 0.95.

[0048] As an optional embodiment, five different temperature-time combinations were set up in the preliminary experiment: the first stage temperature was 60℃, 70℃, and 80℃, and the time was 20 min, 30 min, and 40 min; the second stage temperature was 100℃, 110℃, and 120℃, and the time was 15 min, 25 min, and 35 min. After drying, the porosity of the film layer was tested to be ≤0.1%, the texture replication rate was ≥98%, and the degree of curing was ≥95%. The shortest time when all three indicators met the standards was selected as the time parameter for the corresponding stage.

[0049] As an optional embodiment, the softening point of the hot melt adhesive is determined by the ring and ball method, and the heat resistance temperature of the matte PU leather resin layer is determined by a heat distortion temperature tester; during the constant temperature standing process, the interfacial bonding strength is monitored in real time by a peel strength tester, and the standing is stopped when the strength is ≥1.8N / 25mm.

[0050] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0051] Example 1

[0052] This embodiment provides a method for preparing a matte PU decorative lettering film, the specific steps of which are as follows:

[0053] S1. Raw Material Proportioning and Weighing: Five parallel tests were performed on the water-based PU resin using a solid content analyzer. The results were 32.1%, 32.3%, 32.2%, 32.4%, and 32.0%, respectively. After removing extreme values ​​(data with deviations of no more than ±10% from the average), the average value of 32.2% was taken as the measured solid content value X. Based on the aforementioned calculation formula, the coefficients were derived: In the five mixed systems of the film-forming experiment, a system with a film porosity ≤0.1% and a surface roughness Ra=0.8-1.2μm was selected as the standard system. Simultaneously, in the dispersion experiment, a system with D90≤6μm and an agglomerated particle area ratio ≤0.2% was selected as the standard system. Data from both experiments were extracted, and a regression equation was established using the least squares method:

[0054] Color pigment: y1=0.745x+0.12 (R²=0.968, b1=0.12%≤0.5%), thus k1=0.745;

[0055] Silicon dioxide: y2=0.342x+0.08 (R²=0.972, b2=0.08%≤0.5%), thus k2=0.342;

[0056] Water-based defoamer: y3 = 0.093x + 0.05 (R² = 0.965, b3 = 0.05% ≤ 0.5%), resulting in k3 = 0.093. Calculate the addition ratio of each component:

[0057] The proportion of colored pigment added is approximately 24.0% (32.2% × 0.745).

[0058] The proportion of silica added is approximately 11.0% (32.2% × 0.342).

[0059] The proportion of water-based defoamer added is approximately 32.2% × 0.093 ≈ 3.0%. Weigh the raw materials according to the above proportions: 100 kg of water-based PU resin, 24.0 kg of colored pigment, 11.0 kg of silica, and 3.0 kg of water-based defoamer. The weighing accuracy is controlled to be ±0.01 g, and the mass percentage deviation is ≤ ±0.5%.

[0060] S2. High-speed stirring to prepare resin: The water-based PU resin is heated at a rate of 1.5℃ / min, with real-time temperature monitoring. When the temperature reaches 38℃, the measured viscosity of the water-based PU resin at 25℃ is 6500 mPa·s, reaching the target temperature (viscosity 5000-8000 mPa·s). Add the raw materials sequentially and stir in stages:

[0061] First stage: Add colored pigment and calculate the rotation speed and time according to the calculation formula. The measured particle size of silica is d=5μm, and the derived coefficient k is determined to be 120 (R²=0.971) through three sets of preliminary experiments. The rotation speed N=(6500 / 5)×120=156000r / h (2600r / min). The stirring time is calculated by fitting the equation D90=-0.2t+11 (a=-0.2, b=11), t=(6-11) / |-0.2|=25min. Stir for 25min according to this parameter.

[0062] Second stage: Add silica, increase the rotation speed to 1.3 times that of the first stage (3380 r / min), and extend the time to 1.5 times that of the first stage (37.5 min).

[0063] Third stage: Add water-based defoamer, reduce the rotation speed to 0.7 times that of the first stage (1820 r / min), and stir for 15 min. After stirring, use a laser particle size analyzer to detect that the silica D90 is 5.2 μm, and observe the agglomerated particle area ratio under a microscope (5000x) to be 0.12%, which meets the requirements, and the matte PU leather resin is obtained.

[0064] S3. Coating to frosted PET film: The depth of fine fog texture on the frosted PET film was measured to be 1.2 μm using a laser confocal microscope, with a detection accuracy of ±0.1 μm. Film shrinkage was determined through five sets of wet film thickness experiments: wet film thicknesses of 10 μm, 15 μm, 20 μm, 25 μm, and 30 μm, with cured dry film thicknesses of 9.2 μm, 13.8 μm, 18.4 μm, 23.0 μm, and 27.6 μm, respectively. The calculated shrinkage rates were 8.0%, 8.0%, 8.0%, 8.0%, and 8.0%, respectively. The fitted equation showed shrinkage rate = 0.08 (R² = 1.0), with a shrinkage rate constant of 8.0%. Coating thickness calculation: wet film thickness = 1.2 μm × (1 + 8.0%) = 1.296 μm ≈ 1.3 μm. During the coating process, the thickness is monitored in real time by an online laser thickness gauge (frequency 1 time / second). When the thickness deviation exceeds ±0.3μm, the coating speed is adjusted by adjusting the speed = 0.2m / min × (deviation / 0.1μm) to ensure uniform wet film thickness.

[0065] S4. Heating and Drying Molding: The evaporation temperature of the solvent (ethyl acetate) in the matte PU leather resin was determined to be 65℃ using gas chromatography. The first-stage drying temperature was 65℃ + 5℃ = 70℃. The solvent evaporation rate coefficient k = 0.04μm / min (experimentally determined), and the time was 1.3μm / 0.04μm / min = 32.5min. The resin crosslinking temperature was determined to be 110℃ using differential scanning calorimetry. The second-stage drying temperature was also 110℃. Preliminary experiments showed that the shortest time to achieve the three indicators was 25min (porosity = 0.08%, fine mist texture replication rate = 99.2%, degree of curing = 96.5%). During the drying process, the ambient temperature fluctuation was controlled to ≤±1℃, and the humidity to ≤30%, ensuring that the resin wet film cured and formed a matte PU leather resin layer with complete replication of the fine mist texture.

[0066] S5. Hot Melt Adhesive Coating: The surface roughness Ra of the matte PU leather resin layer was measured to be 1.0 μm using a roughness tester, and the wetting angle of the hot melt adhesive (EVA type) was measured to be 63° using a contact angle meter. The thickness coefficient was determined to be 15 (R²=0.969) through linear regression of three sets of experiments, and the coating thickness was 1.0 μm × (63° / 90°) × 15 = 10.5 μm. The coating speed was kept consistent with the matte PU leather resin coating speed (5 m / min). The softening point of the hot melt adhesive was determined to be 85℃ using the ring and ball method, and the heat resistance temperature of the resin layer was determined to be 135℃ using a heat distortion temperature meter. The settling temperature was (85+135) / 2 = 110℃. The wetting time was observed to be 8 min using an infrared thermal imager, and the molecular diffusion time required for the interfacial bonding strength ≥1.8 N / 25 mm was determined to be 12 min using a dynamic mechanical analyzer. The settling time was 8 min + 12 min = 20 min. After standing, a matte PU decorative lettering film is obtained.

[0067] Example 2

[0068] This embodiment provides a method for preparing a matte PU decorative lettering film. The steps are basically the same as in Embodiment 1, except that: in step S1, the measured solid content of the water-based PU resin is X = 35.0%, and the addition ratio of each component is calculated using a regression equation: color paste = 35.0% × 0.745 ≈ 26.1%, silica = 35.0% × 0.342 ≈ 11.97%, and water-based defoamer = 35.0% × 0.093 ≈ 3.26%, with a mass percentage deviation ≤ ±0.5%; in step S2, the target temperature for the water-based PU resin is 36℃ (viscosity = 5800 mPa·s). For step S4, the measured particle size of silica is d=4μm, the rotation speed N=(5800 / 4)×120=174000r / h (2900r / min), the stirring time t=(6-11) / 0.2=25min, the rotation speed of the second stage is 2900×1.3=3770r / min, and the time is 25×1.5=37.5min; in step S4, the drying temperature of the first stage is 68℃+5℃=73℃, the time is 1.4μm / 0.045μm / min≈31.1min, the drying temperature of the second stage is 115℃, and the time is 22min.

[0069] Example 3

[0070] This embodiment provides a method for preparing a matte PU decorative lettering film. The steps are basically the same as those in Example 1, except that: in step S1, the film formation experiment and dispersion experiment are analyzed by standard deviation to remove one set of abnormal data and retain four sets of valid data. The derivation coefficients are k1=0.752, k2=0.338, and k3=0.091 (R² ≥ 0.95); in step S3, the fine mist depth is 1.5μm, the film shrinkage rate is 7.5%, and the wet film thickness is 1.5×(1+7.5%)=1.6125μm≈1.6μm; in step S5, the surface roughness Ra is 1.1μm, the wetting angle is 67°, the coating thickness is 1.1×(67 / 90)×15≈12.4μm, the standing temperature is (88+132) / 2=110℃, and the standing time is 9min+13min=22min.

[0071] Comparative Example 1

[0072] This comparative example provides a method for preparing a matte PU decorative lettering film, the steps of which are basically the same as those in Example 1, except that no system parameter calculations are performed throughout the process. In step S1, the proportions of each component are determined empirically: 62% water-based PU resin, 24% colored pigment, 11% silica, and 3% water-based defoamer, without conducting film-forming or dispersion experiments; in step S2, the stirring parameters are set empirically: a single stirring speed of 2500 r / min and a time of 40 min, without staged adjustments; in step S3, the coating thickness is set empirically to 1.5 μm, without detecting the depth of fine fog and film shrinkage rate, and without thickness feedback adjustments; in step S4, constant temperature drying (90℃, 60 min) is used, without staged adjustments; in step S5, the hot melt adhesive coating thickness is set empirically to 10 μm, with a standing temperature of 100℃ and a time of 20 min.

[0073] Performance test results

[0074] For the matte PU decorative lettering films prepared in Examples 1-3 and Comparative Example 1, four core indicators were tested: matte uniformity (60 gloss), color consistency (ΔE), fine mist reproduction rate, and interfacial bonding strength. The testing methods are as follows:

[0075] 60 gloss: Five points on the film surface were measured using a gloss meter, and the average value was taken;

[0076] Color consistency: The color difference ΔE was calculated by measuring 10 points on the film surface using a colorimeter.

[0077] Fine mist texture replication rate: The degree of agreement between the replicated fine mist texture and the original film fine mist texture is observed by laser confocal microscopy, and the proportion is calculated;

[0078] Interface bonding strength: tested according to GB / T2790-1995 standard using a peel strength tester.

[0079] The test results are shown in the table below:

[0080] sheet

[0081] Example 1 8.2 0.7 99.2 2.1 Example 2 8.5 0.8 98.8 2.0 Example 3 8.3 0.7 99.0 2.2 Comparative Example 1 15.6 2.3 82.5 1.3

[0082] The test results above show that the matte PU decorative lettering films prepared in Examples 1-3 of this invention have a gloss level of ≤10 GU at 60°, a color uniformity ΔE ≤0.8, a fine mist texture replication rate ≥98.8%, and an interface bonding strength ≥2.0 N / 25 mm. All these properties are superior to those of Comparative Example 1. Through full-process parameter calculations and experimental verification, these examples have achieved the technical goals of stable matte effect, uniform color development, complete transfer, and firm adhesion, effectively solving the core defects of existing technologies and fully demonstrating the innovation and superiority of this invention.

[0083] In summary, this application is merely a specific embodiment, but its protection scope is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the protection scope of this application. Therefore, the protection scope of this application should be determined by the scope of the claims.

Claims

1. A matte PU decorative lettering film, characterized in that, The lettering film has a layered structure that is composited from top to bottom. The layers, from top to bottom, are frosted PET film, matte PU leather resin layer, and hot melt adhesive layer. The frosted PET film has textured surfaces with evenly distributed patterns; the matte PU leather resin layer is a dense, non-porous film layer, made by mixing water-based PU resin, colored pigments, silica, and water-based defoamer in a specific mass ratio and then stirring. The mass ratio of each raw material is 62% water-based PU resin, 24% colored pigments, 11% silica, and 3% water-based defoamer. The matte PU leather resin layer is tightly bonded to the frosted PET film, and the texture of the frosted PET film is completely replicated on the surface of the matte PU leather resin layer. The hot melt adhesive layer completely covers the side of the matte PU leather resin layer away from the frosted PET film, forming a continuous, integrated structure with the matte PU leather resin layer.

2. The matte PU decorative lettering film according to claim 1, characterized in that, The addition ratios of colored pigments, silica, and water-based defoamers were calculated based on the measured solid content of water-based PU resin. The coefficients used in the calculations were determined through film-forming and dispersion experiments. The film-forming experiments included five groups of mixing systems with different ratios, each with a gradient change in the solid content of water-based PU resin. After mixing and forming the film, the porosity and surface roughness of the film were measured. The dispersion experiments included five groups of mixing systems with different ratios, and after stirring, the particle size distribution and agglomeration of silica were measured.

3. The matte PU decorative lettering film according to claim 1, characterized in that, The stirring parameters for matte PU leather resin are calculated based on the measured viscosity of water-based PU resin and the particle size characteristics of silica; the stirring speed is determined by the linear ratio of the viscosity of water-based PU resin to the particle size of silica. The stirring time was derived by linear fitting of the time required for the silica particle size distribution to reach the target range. The fitting data came from the dispersion state detection results of five groups of different stirring times.

4. The matte PU decorative lettering film according to claim 1, characterized in that, The matte-related structure of the lettering film consists of a texture replication structure and a matte structure; the texture replication structure is formed by coating a resin wet film to completely adhere to the texture surface of the frosted PET film, and then drying and curing it. The matting structure consists of a physical light-shielding layer formed by the uniform distribution of silica in an aqueous PU resin matrix. The distribution density of silica is synergistically matched with the density of the frosted PET film texture. The matching relationship was determined through film formation experiments with three different density combinations.

5. The method for preparing a matte PU decorative lettering film according to claim 1 is applicable to the matte PU decorative lettering film according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Raw material proportioning calculation and weighing: The solid content of water-based PU resin is tested in parallel multiple times. After removing extreme values, the average value is taken as the measured solid content. Based on the calculation formula and derivation coefficient, the addition ratio of color paste, silica and water-based defoamer is calculated. Each raw material is weighed according to the calculated ratio, and the weighing accuracy and mass ratio deviation are controlled. S2. Resin Preparation by Stirring: The water-based PU resin is heated, with the temperature monitored in real time and the heating rate controlled until the target temperature is reached. The raw materials are added sequentially in the order of water-based PU resin, color pigment, silica, and water-based defoamer, and stirred in stages. In the first stage, after adding the color pigment, stirring is performed at the speed and time calculated according to the formula. In the second stage, after adding silica, the speed and time are adjusted to a multiple of the set values ​​from the first stage. In the third stage, after adding the water-based defoamer, the speed is reduced while maintaining a fixed stirring time. After stirring, if no agglomerated particles are detected and the particle size distribution meets the standards, it is considered matte PU leather resin. S3. Coating to frosted PET film: The matte PU leather resin is coated onto the surface of the frosted PET film. The coating thickness is determined by calculating the texture depth of the frosted PET film and the film shrinkage rate of the matte PU leather resin. S4. Heating and Drying for Molding: The coated substrate is heated and dried in two continuous stages. The first stage is the solvent evaporation stage, where the temperature is determined based on the evaporation temperature of the solvent in the resin, and the time is determined by calculation based on the linear relationship between the wet film thickness and the solvent evaporation rate. The second stage is the curing and molding stage, where the temperature is determined based on the crosslinking temperature of the resin, and the time is derived from experimental data on the time required for the resin to reach the required degree of curing. During the drying process, the fluctuation range of ambient temperature and humidity is controlled to avoid the formation of pores or cracks in the film layer. S5. Hot melt adhesive coating: Apply hot melt adhesive to the surface of the matte PU leather resin layer. The coating thickness is determined by calculating the surface roughness of the matte PU leather resin layer and the wetting angle of the hot melt adhesive. The coating process is carried out at a uniform speed, which is consistent with the coating speed of the matte PU leather resin. After coating, the substrate is subjected to constant temperature static treatment. The static temperature is determined by the softening point of the hot melt adhesive and the heat resistance temperature of the matte PU leather resin layer. The static time is derived from the molecular diffusion rate of the hot melt adhesive and the resin layer.

6. The method for preparing a matte PU decorative lettering film according to claim 5, characterized in that, In step S1, among the five mixed systems of the film-forming experiment, the proportion gradient of colored pigment is 20%-28%, the proportion gradient of silica is 8%-14%, and the proportion gradient of water-based defoamer is 2%-4%. Each system is formed into a film in parallel three times. Among the test indicators, the film porosity is ≤0.1% and the surface roughness Ra=0.8-1.2μm is considered to meet the standards.

7. The method for preparing a matte PU decorative lettering film according to claim 5, characterized in that, In step S2, the target temperature for heating is determined by detecting the viscosity of the water-based PU resin at different temperatures. The target temperature is reached when the viscosity drops to 5000-8000 mPa·s. The derivation coefficient of the stirring speed in the first stage is determined by three sets of preliminary experiments. In the preliminary experiments, the viscosity of the water-based PU resin was 5000 mPa·s, 6500 mPa·s, and 8000 mPa·s, and the particle size of silica was 3 μm, 5 μm, and 7 μm, respectively. Each set of preliminary experiments was repeated three times, and the average value of the speed that met the target was taken as the reference speed for that set. The derivation coefficient was then obtained by linear fitting. In the second stage, the stirring speed was increased to 1.3 times that of the first stage, and the time was extended to 1.5 times that of the first stage. This adjustment ratio was obtained by screening the dispersion state under different speed-time combinations.

8. The matte PU decorative lettering film and its preparation method according to claim 5, characterized in that, In step S3, the coating pressure is determined by calculating the viscosity of the matte PU leather resin and the coating thickness; the adjustment range of the coating speed is linearly related to the thickness deviation. For every 0.1 μm increase in thickness deviation, the coating speed is adjusted by 0.2 m / min to ensure that the wet film thickness quickly returns to the target range; the film shrinkage rate is determined by testing the shrinkage range of wet films of different thicknesses after curing. Five groups of different wet film thicknesses are set up in the experiment. After curing, the actual shrinkage value is measured, and the shrinkage rate constant is obtained by fitting.

9. The matte PU decorative lettering film and its preparation method according to claim 5, characterized in that, In step S4, the drying temperature in the first stage is 5°C higher than the solvent evaporation temperature to avoid the solvent evaporating too slowly and causing pores in the film layer; the drying temperature in the second stage is equal to the resin crosslinking temperature to ensure that the resin is fully cured; the time parameters of the two stages are verified through pre-experimentation. Five different temperature-time combinations are set up in the pre-experimentation. After drying, the porosity, texture replication rate and curing degree of the film layer are detected for each combination, and the shortest time in which all three indicators meet the standard is selected; the ambient temperature and humidity are kept uniform during the drying process, and film layer defects caused by local differences are avoided through coordinated control of temperature and humidity.

10. The matte PU decorative lettering film and its preparation method according to claim 5, characterized in that, In step S5, the static temperature is the midpoint between the softening point of the hot melt adhesive and the heat resistance temperature of the matte PU leather resin layer. The immersion time is determined by observing the time it takes for the hot melt adhesive to completely cover the surface of the resin layer, and the molecular diffusion time is determined by detecting the time required for the interface bonding strength to meet the standard.

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