Temporary protective film layer for high-strength low-emissivity glass and method for manufacturing the same

Abstract

This invention relates to the field of temporary protective materials for glass processing, specifically a high-strength, low-emissivity temporary protective film for glass and its preparation method. The protective film is a core-shell nanoparticle-reinforced waterborne polyurethane composite film with a gradient crosslinking structure, composed of the following components: 100 parts by weight of waterborne polyurethane matrix resin, 10-20 parts by weight of a low-temperature unblocking crosslinking agent, 5-20 parts by weight of core-shell nanoparticles, and 0.5-2 parts by weight of additives. The protective film has a gradient crosslinking structure along its thickness direction, with a higher crosslinking density on the surface near the air side than on the bottom surface near the glass side. This invention significantly improves the film's density through the synergistic reinforcement of the gradient crosslinking structure and core-shell nanoparticles, achieving a surface water contact angle of over 90°. Even after 72 hours in a high-humidity environment, it maintains its integrity and good protective performance, effectively solving the technical problem of traditional water-soluble films easily absorbing moisture and softening.

Description

Technical Field

[0001] This invention relates to the field of temporary protective materials for glass processing, specifically a temporary protective film for high-strength, low-emissivity glass and its preparation method. Background Technology

[0002] High-strength low-emissivity glass (tempered Low-E glass) is widely used in building curtain walls, the automotive industry, and smart homes due to its excellent energy-saving effect and mechanical strength. The production of this type of glass typically follows a "coating first, tempering later" process: first, multiple layers of nanoscale metal oxide functional films (especially silver layers) are deposited on the surface of the glass substrate using magnetron sputtering; then, cold processing such as cutting and edge grinding is performed; finally, high-temperature tempering (680-720℃) is applied to obtain the final product. However, the silver layer in the Low-E film is chemically reactive and easily oxidized or physically damaged during storage, transportation, and cold processing due to contact with humid air, cutting dust, or mechanical scratches, leading to deterioration of the glass's optical properties or even rendering it unusable.

[0003] To address these issues, the industry commonly employs temporary protective films to protect the surface of coated glass. Traditional technologies fall into two main categories: one is polyethylene (PE) protective film, which needs to be manually removed before tempering, resulting in high labor intensity, significant waste, and the risk of residual contamination if not removed promptly; the other is water-soluble protective film, which can be automatically removed during the cleaning process, significantly improving automation. However, existing water-soluble protective films generally suffer from poor environmental adaptability: in high humidity environments, the film easily absorbs moisture and softens, losing its protective ability; in low temperature environments, the film becomes brittle and the dissolution rate decreases, severely affecting removal efficiency. Furthermore, existing films also struggle to meet the demands of high-end glass processing in terms of mechanical strength and transparency.

[0004] To address the aforementioned issues, researchers both domestically and internationally have conducted extensive work. A search revealed existing methods, such as US20090044897A1, which discloses a temporary protective coating method for heat-treated coated glass products. This technique involves coating a water-based acrylic polymer dispersion (such as EC-44) onto the surface of Low-E glass, providing temporary protection after heat treatment (such as tempering), and removing it with an alkaline solution (such as GS-40 conversion solution). The protective film produced by this method is insoluble in water, can resist corrosion to a certain extent in high-humidity environments (such as 50°C / 95%RH), and can withstand mechanical damage from Taber abrasion tests. However, this technology has limitations. After the protective film is applied, it cannot provide protection for the Low-E film layer during cold processing stages such as glass cutting and edge grinding. Furthermore, the removal of the protective film requires the use of a special alkaline conversion solution, which increases the complexity and cost of the process. Secondly, although the stability under high temperature and high humidity conditions has been tested, the risk of brittleness and dissolution performance of the film layer under low temperature conditions (such as -10°C) has not been addressed, and the antioxidant protection of the silver layer in the Low-E film layer has not been directly verified.

[0005] In the field of crosslinking agent technology, CN114230764B discloses a water-based blocked polyisocyanate curing agent using bisulfite as the blocking agent. It features a low unblocking temperature (down to 70°C) and excellent water dispersibility, primarily used in the preparation of water-based polyurethane coatings. CN113201110A discloses an end-capped, multi-branched water-based polyurethane crosslinking agent using sodium bisulfite for end-capping. It can unblock at suitable temperatures and crosslink with active groups on fibers, mainly used in the field of functional finishing of textiles to improve the wash fastness of water-repellent finishing agents. While these technologies demonstrate promising applications in their respective fields, none involve the application of temporary protective films for glass processing.

[0006] In summary, the existing technology lacks a temporary protective film that can simultaneously meet the following requirements: (1) It can be applied before heat treatment to effectively protect the integrity of the film layer of Low-E glass during cold processing such as cutting and edge grinding; (2) It has excellent moisture-proof performance and does not absorb moisture or soften in high-humidity storage environments; (3) It has good low-temperature adaptability, does not crack in cold environments and has a controllable melting rate; (4) It has sufficient mechanical strength to resist cutting dust and mechanical abrasion; (5) It can be completely removed by warm water in the regular cleaning process without the need for special chemical reagents; (6) It can directly verify the antioxidant protection effect on the silver layer. How to achieve the synergistic improvement of the above properties through structural design and material innovation is still a technical problem that needs to be solved in this field.

[0007] Therefore, we propose a temporary protective film for high-strength, low-emissivity glass and its preparation method. Summary of the Invention

[0008] The purpose of this invention is to provide a temporary protective film for high-strength, low-emissivity glass and its preparation method. The film features a gradient cross-linking structure design and core-shell nanoparticle reinforcement, which significantly improves the moisture-proof performance and low-temperature adaptability of the film while maintaining excellent water solubility and removability. This solves the technical problem of balancing protective performance and environmental adaptability in the prior art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a temporary protective film layer for high-strength, low-emissivity glass, wherein the protective film layer is a core-shell nanoparticle-reinforced waterborne polyurethane composite film with a gradient cross-linking structure, and is composed of the following components: 100 parts by weight of waterborne polyurethane matrix resin, 10-20 parts by weight of low-temperature unblocking crosslinking agent, 5-20 parts by weight of core-shell structured nano-reinforcing particles, and 0.5-2 parts by weight of additives; The protective film layer has a gradient cross-linking structure along the thickness direction, and the cross-linking density of the surface region near the air side is higher than that of the bottom surface region near the glass side.

[0010] A coating liquid, wherein the coating liquid is a mixture of the components described in claim 1, has a solid content of 25-35%, and a viscosity of 150-300 mPa·s at 25°C. Preferably, the low-temperature unblocking crosslinking agent is a hexamethylene diisocyanate trimer modified with sodium 2-[(2-aminoethyl)amino]ethanesulfonate and blocked with sodium bisulfite, with an unblocking temperature of 65±2℃.

[0011] Preferably, the core-shell structured nanoparticles have a core of monodisperse silica modified with γ-methacryloxypropyltrimethoxysilane and a shell of polymethyl methacrylate, with a particle size of 55-75 nm and a shell thickness of 10-15 nm.

[0012] Preferably, the crosslinking density of the surface region of the gradient crosslinking structure is 1.3 to 1.5 times that of the crosslinking density of the bottom region, characterized by the ratio of the 1530 cm⁻¹ amide II peak to the 2940 cm⁻¹ C-H stretching peak determined by micro-infrared spectroscopy.

[0013] Preferably, the additives consist of a wetting agent, a defoamer, and a leveling agent.

[0014] A method for preparing a temporary protective film layer for high-strength, low-emissivity glass includes the following steps: Step 1: Prepare waterborne polyurethane matrix resin; Step 2: Prepare a low-temperature unsealing crosslinking agent; Step 3: Prepare core-shell structured nanoparticles; Step 4: Mix 100 parts by weight of waterborne polyurethane matrix resin, 10-20 parts by weight of low-temperature unblocking crosslinking agent, 5-20 parts by weight of core-shell structured nano-reinforcing particles and 0.5-2 parts by weight of additives, stir evenly, and prepare coating liquid. Step 5: Apply the coating liquid evenly to the surface of the high-strength, low-emissivity glass, controlling the wet film thickness to 25-35 μm; Step 6: Dry using a gradient temperature drying process to form a gradient cross-linked structure.

[0015] Preferably, the gradient temperature drying process in step 6 includes: First, dry at 45±2℃ for 8 minutes, then at 65±2℃ for 12 minutes, and finally at 40±2℃ for 5 minutes.

[0016] A high-strength, low-emissivity glass with a temporary protective film layer, wherein the glass surface is covered with the temporary protective film layer, or a temporary protective film layer prepared by the method.

[0017] The application of the coating liquid in the preparation of a high-strength, low-emissivity temporary protective film layer for glass.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention significantly improves the density of the film layer through the synergistic enhancement of gradient cross-linking structure and core-shell nanoparticles, and the surface water contact angle reaches more than 90°. It can still maintain its integrity and good protective performance after being placed in a high humidity environment for 72 hours, effectively solving the technical problem of traditional water-soluble film layers being prone to moisture absorption and softening.

[0019] 2. The polymer shell of the core-shell structured nanoparticles of this invention has good compatibility with the polyurethane matrix and can still maintain flexibility in low-temperature environments without brittleness of the film. At the same time, the gradient cross-linking structure ensures that the film still has a controllable dissolution rate in low-temperature cleaning water, and the removal efficiency is not affected.

[0020] 3. The core-shell structured nanoparticles of this invention are uniformly dispersed in a polyurethane matrix, which significantly improves tensile strength, enhances surface hardness, and significantly improves resistance to cutting dust and mechanical scratches. At the same time, the light transmittance of the film layer is maintained above 90%, which facilitates visual inspection during the processing.

[0021] 4. The present invention adopts a gradient cross-linking structure, which enables the membrane layer to dissolve layer by layer from bottom to top under conventional cleaning conditions. The removal process is stable and controllable, with no residue. The removal speed can be precisely controlled by adjusting the cleaning water temperature, adapting to different seasons and process requirements.

[0022] 5. After aging for 7 days in a humid and hot environment of 85%RH and 50℃, the sheet resistance of the silver layer of this invention changes by less than 2%, which is far superior to the uncoated sample and effectively protects the Low-E film from oxidation and corrosion. Attached Figure Description

[0023] Figure 1 Transmission electron microscope image of the core-shell structured nano-reinforcing particles of the present invention; Figure 2 This is a microscopic infrared scan of the gradient cross-linked structure of the protective film layer of the present invention; Figure 3 The curves showing the change in water contact angle of the protective film layer of this invention and the comparative example under different humidity levels are shown. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0025] Please see Figures 1-3 As shown, the present invention provides a temporary protective film layer for high-strength, low-emissivity glass. The protective film layer is a core-shell nanoparticle-reinforced aqueous polyurethane composite film with a gradient cross-linking structure, characterized by being composed of the following components: (A) 100 parts by weight of waterborne polyurethane matrix resin with a solid content of 30% is prepared by reacting poly(1,4-butanediol adipate), isophorone diisocyanate, dimethylolpropionic acid and triethylamine. (B) 10-20 parts by weight of a low-temperature unblocking crosslinking agent, wherein the crosslinking agent is a hexamethylene diisocyanate trimer modified with sodium 2-[(2-aminoethyl)amino]ethanesulfonate and blocked with sodium bisulfite, the unblocking temperature is 65±2℃, and the solid content is 40%; (C) 5-20 parts by weight of core-shell structured nanoparticles, wherein the core-shell structured nanoparticles have a core of monodisperse silica modified with γ-methacryloyloxypropyltrimethoxysilane (KH-570) and a shell of polymethyl methacrylate, with a particle size of 55-75 nm, a shell thickness of 10-15 nm, and a solid content of 20%; (D) 0.5-2 parts by weight of additives, wherein the additives consist of wetting agents, defoamers and leveling agents.

[0026] The protective film has a gradient cross-linking structure along the thickness direction: the cross-linking density of the surface region near the air side is higher than that of the bottom region near the glass side, and the cross-linking density of the surface region is 1.3 to 1.5 times that of the bottom region. This is characterized by the ratio of the 1530 cm⁻¹ amide II peak to the 2940 cm⁻¹ C-H stretching peak determined by micro-infrared spectroscopy.

[0027] The preparation method of the low-temperature unblocking crosslinking agent includes: mixing 100 parts of hexamethylene diisocyanate trimer with 15 parts of sodium 2-[(2-aminoethyl)amino]ethanesulfonate, and reacting at 50°C for 1 hour in the presence of 0.1 parts of dibutyltin dilaurate catalyst, so that the amino group in the sulfonate reacts with the isocyanate group, and the sulfonic acid group is introduced into the polyisocyanate molecular chain, so that it has water dispersibility; After the reaction was completed, 25 parts of sodium bisulfite were added to carry out the blocking reaction. The reaction temperature was controlled at 40℃ and the reaction time was 2 hours to obtain an aqueous blocked polyisocyanate crosslinking agent with a deblocking temperature of 65±2℃.

[0028] The preparation method of the core-shell structured nanoparticles includes: (1) Surface modification: Take 500g of monodisperse silica aqueous dispersion (solid content 20%), add 500g of ethanol for dilution, adjust the pH to 9-10 with ammonia, add 15g of γ-methacryloyloxypropyltrimethoxysilane (KH-570), react at 50℃ for 6 hours, centrifuge after the reaction, wash with ethanol 3 times, redisperse in deionized water to obtain modified silica dispersion with surface grafted double bonds, solid content 20%; (2) Shell polymerization: 100 parts of the above modified silica dispersion were added to the reactor, along with 15 parts of methyl methacrylate monomer and 0.3 parts of potassium persulfate. After replacing the air with nitrogen, the temperature was raised to 75℃±2℃ and reacted for 4 hours to obtain a core-shell structured nanoparticle aqueous dispersion.

[0029] This invention also provides a method for preparing the above-mentioned temporary protective film layer for high-strength, low-emissivity glass, comprising the following steps: Step 1: Preparation of waterborne polyurethane matrix resin: Add 100 parts of poly(1,4-butanediol adipate) (molecular weight 2000) and 45 parts of isophorone diisocyanate to a reaction vessel, react at 80℃±2℃ for 2 hours, and take a sample to determine that the NCO content reaches the theoretical value (about 3.2%). Before adding dimethylolpropionic acid, 80 parts of acetone were added to reduce the viscosity of the prepolymer and control the solid content of the system to about 70%. Then, 8 parts of dimethylolpropionic acid and 5 parts of triethylamine were added to carry out a hydrophilic chain extension reaction for 1 hour. Cool to 40°C, add 200 parts of deionized water, and emulsify at 1000 rpm for 30 minutes. After emulsification, the mixture was transferred to a rotary evaporator and acetone was removed by vacuum distillation at 45°C and -0.08 MPa to obtain an aqueous polyurethane emulsion with a solid content of 30%. Step 2: Preparation of low-temperature unblocking crosslinking agent: Mix 100 parts of hexamethylene diisocyanate trimer with 15 parts of sodium 2-[(2-aminoethyl)amino]ethanesulfonate, add 0.1 parts of dibutyltin dilaurate catalyst, and react at 50℃±2℃ for 1 hour; Add 25 parts of sodium bisulfite and react at 40℃±2℃ for 2 hours to block the reaction; add 225 parts of deionized water and stir at 800 rpm for 30 minutes to obtain a water-based blocked polyisocyanate crosslinking agent with a solid content of 40%. Step 3: Preparation of core-shell structured nanoparticles: (3a) Surface modification: Take 500g of monodisperse silica aqueous dispersion (solid content 20%) with a particle size of 40nm, add 500g of ethanol to dilute, and adjust the pH to 9-10 with ammonia. Add 15g of γ-methacryloxypropyltrimethoxysilane (KH-570) and react at 50℃ for 6 hours; After the reaction was completed, the mixture was centrifuged, washed three times with ethanol, and redispersed in deionized water to obtain a modified silica dispersion with surface-grafted double bonds and a solid content of 20%. (3b) Shell polymerization: 100 parts of the above modified silica dispersion were added to the reactor, along with 15 parts of methyl methacrylate monomer and 0.3 parts of potassium persulfate. After replacing the air with nitrogen, the temperature was raised to 75℃±2℃ and reacted for 4 hours to obtain an aqueous dispersion of core-shell structured nanoparticles with a solid content of 20%. Step 4: Prepare the coating solution: Mix the components according to the following weight ratio: 100 parts of waterborne polyurethane emulsion (30%), 10-20 parts of low-temperature unblocking crosslinking agent (40%), 5-20 parts of core-shell structured nanoparticle dispersion (20%), 0.5 parts of wetting agent, 0.2 parts of defoamer, and 0.3 parts of leveling agent. Stir at 600 rpm for 30 minutes, filter through a 200-mesh filter to obtain the coating solution with a solid content of 25-35% and a viscosity of 150-300 mPa·s at 25℃. Step 5: Apply the coating liquid evenly to the surface of the high-strength, low-emissivity glass: use a roller coating method with a roller speed of 20 rpm, a coating gap of 0.1 mm, and control the wet film thickness to be 30 ± 2 μm; Step 6: Drying is carried out using a gradient temperature drying process: The coated glass is sent into a three-section drying tunnel. The temperature of the first section is 45℃±2℃, and the dwell time is 8 minutes to allow the moisture to evaporate initially and the film to set. The second drying tunnel temperature is 65℃±2℃, and the dwell time is 12 minutes, which allows the cross-linking agent to be unsealed and react with the polyurethane. The temperature of the third drying tunnel is 40℃±2℃, and the dwell time is 5 minutes. The temperature is slowly reduced to prevent film stress. The film thickness after drying is 10±0.5μm.

[0030] The formation mechanism of the gradient crosslinking structure: During the first stage of low-temperature drying (45℃), the surface moisture of the film layer evaporates preferentially, which leads to a rapid increase in the concentration of surface resin and crosslinking agent, forming a concentration gradient. When entering the second stage of high-temperature zone (65℃), the crosslinking agent is unsealed, and the high concentration of crosslinking agent on the surface quickly reacts with polyurethane to form a surface layer with high crosslinking density. However, in the interior of the film layer (near the glass side), the crosslinking agent concentration is lower due to the slow evaporation of moisture, and some crosslinking agent migrates to the surface after unsealing, resulting in a lower internal crosslinking density. This concentration gradient and reaction degree difference from the surface to the inside ultimately forms a gradient crosslinking structure with a high surface and low interior.

[0031] The present invention will be further illustrated below with reference to embodiments and comparative examples, but these are not intended to limit the scope of the invention.

[0032] Example 1, 1. Raw materials and equipment Main ingredients: Poly(1,4-butanediol adipate): Industrial grade, molecular weight 2000, Yantai Wanhua Isophorone diisocyanate: Industrial grade, Evonik Germany Dimethylolpropionic acid: Industrial grade, Pastor, Sweden Triethylamine: Analytical grade, Sinopharm Group Acetone: Industrial grade, Sinopharm Group Hexamethylene diisocyanate trimer: Industrial grade, Bayer, Germany Sodium 2-[(2-aminoethyl)amino]ethanesulfonate: Industrial grade, CAS No. 34730-58-2, Tokyo Chemical Industry Co., Ltd. Sodium bisulfite: analytical grade, Sinopharm Group Monodisperse silica: Industrial grade, 40nm particle size, Zhejiang Yuda γ-Methacryloxypropyltrimethoxysilane (KH-570): Industrial grade, Nanjing Shuguang Methyl methacrylate: Industrial grade, Nippon Shokubai Potassium persulfate: analytical grade, Sinopharm Group BYK-346 wetting agent: Industrial grade, BYK (Germany) BYK-024 Defoamer: Industrial grade, BYK (Germany) BYK-333 Leveling Agent: Industrial Grade, BYK (Germany) Main equipment: 5L stainless steel reactor: equipped with stirrer, thermometer, and condenser. Shanghai Yanzheng. High-speed emulsifier: FLUKO FM200, Shanghai Fluk Rotary evaporator: RE-2000A, Shanghai Yarong Roller Coating Machine: CB-650, Hebei Chibang Three-section hot air drying duct: Custom-made, 12m long, Suzhou Huitong Constant temperature and humidity chamber: HS-80L, Shanghai Hecheng Universal Testing Machine: UTM2102, Shenzhen Sansi Contact angle measuring instrument: JC2000D, Shanghai Zhongchen Spectrophotometer: UV-2600, Shimadzu, Japan Micro-infrared spectrometer: Nicoleti N10, Thermo Fisher Scientific, USA Transmission electron microscope: JEM-2100, Japan Electronics Co., Ltd. Differential scanning calorimeter: DSC250, TA Instruments, USA X-ray photoelectron spectrometer: ESCALAB250Xi, Thermo Fisher Scientific, USA 2. Preparation process (1) Preparation of waterborne polyurethane matrix resin: 1000g of poly(1,4-butanediol adipate) diol was added to a 5L reactor, and the temperature was raised to 80℃. 450g of isophorone diisocyanate was added, and the reaction was maintained at 80℃±2℃ for 2 hours. The NCO content was determined by the di-n-butylamine method and found to be 3.18%, close to the theoretical value of 3.22%. 800g of acetone was added to reduce the viscosity of the prepolymer. 80g of dimethylolpropionic acid and 50g of triethylamine were added, and the reaction was continued for 1 hour. The temperature was lowered to 40℃, and 2000g of deionized water was added. A high-speed emulsifier was turned on, and emulsification was carried out at 1000rpm for 30 minutes. After emulsification, the mixture was transferred to a rotary evaporator, and acetone was removed by vacuum distillation at 45℃ and -0.08MPa to obtain a milky white aqueous polyurethane emulsion with a solid content of 30% and a particle size of approximately 80nm.

[0033] (2) Preparation of low-temperature unsealing crosslinking agent: 200g of hexamethylene diisocyanate trimer, 30g of sodium 2-[(2-aminoethyl)amino]ethanesulfonate, and 0.2g of dibutyltin dilaurate were added to a 1L reactor and reacted at 50℃±2℃ for 1 hour. Then, 50g of sodium bisulfite was added and reacted at 40℃±2℃ for 2 hours. Finally, 450g of deionized water was added, and the mixture was stirred at 800rpm for 30 minutes to obtain an aqueous blocked polyisocyanate crosslinking agent with a solid content of 40%. The deblocking temperature was measured using differential scanning calorimetry at a heating rate of 10℃ / min. The results showed a significant endothermic peak at 65.2℃, corresponding to the deblocking of the blocked groups.

[0034] (3) Preparation of core-shell structured nanoparticles: (3a) Surface modification: Take 500g of monodisperse silica aqueous dispersion (solid content 20%), add 500g of ethanol for dilution, and adjust the pH to 9-10 with ammonia. Add 15g of KH-570 and react at 50℃ for 6 hours. After the reaction, centrifuge, wash 3 times with ethanol, and redisperse in deionized water to obtain a modified silica dispersion with surface grafted double bonds and a solid content of 20%.

[0035] (3b) Shell polymerization: 500g of the modified silica dispersion was added to a reactor, along with 75g of methyl methacrylate and 1.5g of potassium persulfate. After purging with nitrogen to replace the air, the temperature was raised to 75℃±2℃ and reacted for 4 hours to obtain an aqueous dispersion of core-shell structured nanoparticles with a solid content of 20%. Transmission electron microscopy showed that the particles had a regular core-shell structure with a particle size of about 60-70nm and a shell thickness of about 12nm. No pure PMMA homopolymer microspheres were observed in the field of view (pure PMMA microspheres appear as spherical particles with a single contrast in TEM), indicating that MMA monomers underwent graft polymerization on the modified SiO2 surface.

[0036] (4) Preparation of coating solution: Weigh the following components according to their respective weights: 1000g of waterborne polyurethane emulsion, 150g of low-temperature unblocking crosslinking agent, 100g of core-shell structured nanoparticle dispersion, 5g of BYK-346 wetting agent, 2g of BYK-024 defoamer, and 3g of BYK-333 leveling agent. Add the above components sequentially to a mixing tank and stir at 600 rpm for 30 minutes. Filter through a 200-mesh filter to obtain the coating liquid. The viscosity at 25℃ is 215 mPa·s (Brookfield DV2T viscometer, rotor #2, 60 rpm), and the solid content is 28.5%.

[0037] (5) Coating and drying: One hundred cleaned Low-E glass sheets (size: 1000mm × 800mm, triple silver Low-E film) were coated using a roller coater. The coating roller speed was set to 20 rpm, the coating gap to 0.1mm, and the coating speed to 2m / min, controlling the wet film thickness to 30±2μm. The coated glass immediately entered a three-stage drying tunnel. Section 1 (length 4m): Temperature 45℃±2℃, dwell time 8 minutes Second section (6m in length): Temperature 65℃±2℃, dwell time 12 minutes Third section (2m in length): Temperature 40℃±2℃, dwell time 5 minutes The glass temperature at the outlet drops to room temperature, the film is completely dry, and the thickness is 10±0.5μm.

[0038] 3. Performance Testing Test Project Test methods Test conditions Test Results film thickness micrometer method Randomly select 10 points for measurement 10.2±0.4μm Light transmittance Spectrophotometer 550nm wavelength 92.8% Tensile strength Universal testing machine 25℃, 50mm / min 23.5MPa Elongation at break Universal testing machine 25℃, 50mm / min 188% Surface water contact angle Contact angle measuring instrument 25℃, deionized water 94.2° Adhesion 100-point test 2mm spacing 5B (No shedding) High humidity stability Constant temperature and humidity chamber 85%RH, 72h, observe appearance The film layer is intact, without softening or wrinkling. Low-temperature brittleness Low temperature test chamber -10℃, 2 hours, fold in half and observe. No cracks Dissolving time in warm water constant temperature water bath Soak in 45℃ warm water Completely dissolved in 48 seconds Dissolving time in cold water constant temperature water bath Soak in 20℃ warm water Completely dissolved in 125 seconds 4. Characterization of gradient crosslinking structure The film prepared in Example 1 was analyzed by line scanning along the thickness direction using a micro-infrared spectroscopy instrument. The film was then subjected to liquid nitrogen fracture, and the fracture surface was tested point by point from the air side to the glass side (step size 2 μm). The relative crosslinking density was characterized by the ratio of the intensity of the amide II peak at 1530 cm⁻¹ to the intensity of the CH stretching peak at 2940 cm⁻¹. The results are as follows: Test location (distance from the air side) Amide II / 2940cm⁻¹ ratio Relative crosslinking density (based on the bottom surface) Surface (0-2μm) 0.85 1.42 2-4 μm from the surface 0.76 1.27 4-6 μm from the surface 0.65 1.08 6-8 μm from the surface 0.58 0.97 Bottom surface (8-10μm) 0.60 1.00 Test results show that the film layer of the present invention forms a gradient cross-linking structure that decreases from the surface to the inside along the thickness direction, and the surface cross-linking density is about 1.42 times that of the bottom surface.

[0039] 5. Gel content test Carefully scrape 10 mg of each of the surface layer (0-3 μm) and near-glass layer (7-10 μm) of the membrane with a blade. Wrap the samples in a 200-mesh copper grid and extract with DMF in a Soxhlet extractor for 24 hours. After drying, weigh the samples and calculate the gel content. Sampling location Gel content (%) Surface layer (0-3μm) 82.3 Near the glass layer (7-10μm) 61.5 The surface layer gel content was 20.8 percentage points higher than that of the near-glass layer, consistent with the results of micro-infrared spectroscopy, thus providing double verification of the existence of the gradient cross-linked structure.

[0040] Examples 2-4 Following the preparation method of Example 1, the effects of varying the amount of core-shell nanoparticles and crosslinking agent on performance were investigated. The formulation and test results are as follows: Example Crosslinking agent dosage (parts) Dosage of core-shell particles (parts) Tensile strength (MPa) Water contact angle (°) Dissolving time at 45℃ (seconds) Dissolving time at 20℃ (seconds) Example 2 10 15 21.8 92.5 65 148 Example 3 20 5 22.6 95.3 35 98 Example 4 15 20 24.9 95.8 58 162 Comparative Example 1 Instead of adding core-shell structured nanoparticles, ordinary fumed silica (20 nm particle size, Degussa A200) with an equal solids content (2 parts) was directly blended, with the rest as in Example 1. Test results: tensile strength 17.2 MPa, water contact angle 86.5°, dissolution time at 45°C 72 seconds, dissolution time at 20°C 195 seconds, and light transmittance 88.2%.

[0041] Comparative Example 2 Instead of a gradient drying process, conventional constant temperature drying (65℃, 20 minutes) was used, with the rest of the process the same as in Example 1. Test results: tensile strength 22.1 MPa, water contact angle 89.3°, dissolution time at 45℃ 32 seconds (dissolution too fast), dissolution time at 20℃ 85 seconds. Micro-infrared analysis showed that the amide II / 2940 cm⁻¹ ratio was basically consistent across all locations in the film (0.62-0.68), with no obvious gradient.

[0042] Comparative Example 3 A commercially available brand of water-soluble glass protective film (acrylate system, film thickness approximately 12μm) was used for testing on the same glass substrate. Test results: tensile strength 11.8MPa, water contact angle 75.6°, high humidity stability test (85%RH, 24h) showed significant softening of the film layer, low temperature brittleness test (-10℃, 2h) showed microcracks, dissolution time at 45℃ was 40 seconds, and dissolution time at 20℃ was 110 seconds.

[0043] Example 5: Stability Test of Coating Solution The coating solution prepared in Example 1 was stored under different conditions to test its storage stability. Storage conditions Storage time Appearance Viscosity change Coating performance 25℃ sealed 3 months No sedimentation, no stratification +8% good 25℃ sealed 6 months No sedimentation, no stratification +15% good 5℃ 3 months No sedimentation, no stratification +5% good -5℃ freeze-thaw cycle 3 times - Slightly thickens, returns to normal after stirring. +22% Available Example 6: Test of the antioxidant protection performance of silver layer The protective film prepared in Example 1 was coated onto the surface of triple silver Low-E glass (sample A). A blank control without film (sample B) and a commercially available film control (sample C, comparative example 3) were also set up. All three groups of samples were placed in a constant temperature and humidity chamber and aged for 7 days at 85%RH and 50℃. Changes in the sheet resistance and optical properties of the silver layer before and after aging were tested. sample Block resistance before aging (Ω / □) Sheet resistance after aging (Ω / □) rate of change Changes in transmittance before and after aging (550nm) Sample A (This invention) 3.52 3.58 +1.7% -0.3% Sample B (without membrane) 3.54 4.86 +37.3% -8.5% Sample C (commercially available film) 3.53 3.92 +11.0% -2.8% The results show that the protective film of the present invention can effectively block the corrosion of the silver layer by the humid and hot environment, and the protective effect is significantly better than that of commercially available films.

[0044] Example 7: Scratch Resistance Test Pencil hardness was tested according to GB / T 6739-2006, and steel wool abrasion resistance was tested according to ASTM D1044 (500g load, 0000# steel wool, 10 cycles of reciprocating friction): sample Pencil hardness Change in haze after friction (%) Example 1 2H +1.2 Comparative Example 1 HB +3.8 Comparative Example 3 2B +7.5 Example 8: Test of resistance to media The film sample from Example 1 was immersed in cutting oil (Shell Garia 205M-22) and edge grinding coolant (5% emulsion) for 24 hours. After removal, the adhesion change was tested. medium Adhesion before soaking Adhesion after soaking Appearance changes Cutting oil 5B 5B No change coolant 5B 5B No change Example 9: XPS Verification of Residual Film Layer XPS analysis was performed on the glass surface after the film layer of Example 1 was cleaned with 45°C warm water, and compared with blank glass (uncoated, cleaned): sample C element content (at%) Nitrogen content (at%) Si element content (at%) Blank glass 4.8 Not detected 25.6 Glass after cleaning 5.2 Not detected 24.8 The results showed that the elemental composition of the glass surface after cleaning was basically the same as that of the blank glass, and no polyurethane characteristic nitrogen element was observed, indicating that the film layer was completely removed and there was no residue.

[0045] Example 10: Industrial Application Testing The protective film prepared in Example 1 was applied to the actual production line of a glass deep processing enterprise for batch testing (test quantity: 200 pieces of Low-E glass, size: 2440mm×1830mm, film layer: triple silver Low-E): Testing phase Process conditions Evaluation indicators Test Results Warehousing Store at an ambient temperature of 25-35℃ and a humidity of 40-75%RH for 7 days. Membrane integrity and appearance changes All 200 pieces were intact, with no bubbles, softening, or peeling. Cutting process Automatic cutting machine, cutting speed 8m / min, lubricated with cutting oil. Edge film adhesion, cut quality The edges are free of curling or peeling, and the cut is neat. Edge grinding process Dual-axis edge grinding machine, water-cooled, grinding depth 0.5mm Local dissolution of the membrane layer and its edge protection effect Slight dissolution of the 1-2mm edge layer of the film does not affect the main protective layer. Cleaning process Roller brush cleaning machine, 45℃ spray cleaning, cleaning time 2.5 minutes. Membrane removal rate and cleaning effect 198 pieces were completely removed, and 2 pieces had trace amounts of residue at the edges (analysis showed this was due to uneven coating thickness, which can be resolved by optimizing the coating process). glass surface after cleaning Visual inspection + wiping with a white cloth Residual inspection No visible residue, no watermarks, and leaves no stains when wiped with a white cloth. Tempered glass quality Tempering furnace, 690℃, tempering time 3 minutes Low-E film optical properties, tempered surface flatness There was no difference compared to the unfilmed control area, which conforms to the national standard GB / T18915.2-2013. Example 11: Adaptability Test for Different Film Thicknesses Following the formulation in Example 1, the wet film thickness was adjusted, and the performance of different dry film thicknesses was investigated. Dry film thickness (μm) Tensile strength (MPa) Dissolving time at 45℃ (seconds) Pencil hardness Light transmittance (%) 5 18.6 25 H 94.2 10 23.5 48 2H 92.8 15 25.8 72 2H 91.5 The appropriate film thickness can be selected according to different processing scenarios: thin coating (5μm) is suitable for short-term protection and rapid removal scenarios; The standard coating (10μm) is suitable for routine processing; Thick coating (15μm) is suitable for harsh environments or long-term storage.

[0046] Example 12: Adaptability Test of Different Coating Methods In addition to roller coating, the suitability of curtain coating and spray coating methods was tested: Coating method process parameters Film thickness uniformity Appearance Performance consistency Spray coating Flow rate 2L / min, conveying speed 2m / min ±0.8μm good Consistent with roller coating Spraying Air pressure 0.3MPa, spraying distance 20cm ±1.2μm good Consistent with roller coating The results show that the coating liquid of the present invention has good process adaptability, and the appropriate coating method can be selected according to the production line configuration.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A temporary protective film layer for high-strength, low-emissivity glass, characterized in that: The protective film is a core-shell nanoparticle-reinforced aqueous polyurethane composite film with a gradient cross-linking structure, and is composed of the following components: 100 parts by weight of waterborne polyurethane matrix resin, 10-20 parts by weight of low-temperature unblocking crosslinking agent, 5-20 parts by weight of core-shell structured nano-reinforcing particles, and 0.5-2 parts by weight of additives; The protective film layer has a gradient cross-linking structure along the thickness direction, and the cross-linking density of the surface region near the air side is higher than that of the bottom surface region near the glass side.

2. The temporary protective film layer for high-strength, low-emissivity glass according to claim 1, characterized in that: The low-temperature unblocking crosslinking agent is a hexamethylene diisocyanate trimer modified with sodium 2-[(2-aminoethyl)amino]ethanesulfonate and blocked with sodium bisulfite, with an unblocking temperature of 65±2℃.

3. The temporary protective film layer for high-strength, low-emissivity glass according to claim 1, characterized in that: The core-shell structured nanoparticles have a core of monodisperse silica modified with γ-methacryloxypropyltrimethoxysilane and a shell of polymethyl methacrylate, with a particle size of 55-75 nm and a shell thickness of 10-15 nm.

4. The temporary protective film layer for high-strength, low-emissivity glass according to claim 1, characterized in that: The crosslinking density of the surface region of the gradient crosslinking structure is 1.3 to 1.5 times that of the bottom region, and is characterized by the ratio of the 1530 cm⁻¹ amide II peak to the 2940 cm⁻¹ C-H stretching peak as determined by micro-infrared spectroscopy.

5. The temporary protective film layer for high-strength, low-emissivity glass according to claim 1, characterized in that: The additives consist of wetting agents, defoamers, and leveling agents.

6. A coating liquid, characterized in that: The coating liquid is a mixture of the components described in claim 1, with a solid content of 25-35% and a viscosity of 150-300 mPa·s at 25°C.

7. A method for preparing a temporary protective film layer for high-strength, low-emissivity glass as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Prepare waterborne polyurethane matrix resin; Step 2: Prepare a low-temperature unsealing crosslinking agent; Step 3: Prepare core-shell structured nanoparticles; Step 4: Mix 100 parts by weight of waterborne polyurethane matrix resin, 10-20 parts by weight of low-temperature unblocking crosslinking agent, 5-20 parts by weight of core-shell structured nano-reinforcing particles and 0.5-2 parts by weight of additives, stir evenly, and prepare coating liquid. Step 5: Apply the coating liquid evenly to the surface of the high-strength, low-emissivity glass, controlling the wet film thickness to 25-35 μm; Step 6: Dry using a gradient temperature drying process to form a gradient cross-linked structure.

8. The method for preparing a temporary protective film layer for high-strength, low-emissivity glass according to claim 7, characterized in that: Step 6 describes a gradient temperature drying process that includes: First, dry at 45±2℃ for 8 minutes, then at 65±2℃ for 12 minutes, and finally at 40±2℃ for 5 minutes.

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