How to ensure the uniformity of the coating during the surface treatment of the thermos cup?
1. Preliminary preparation
1.1 Surface cleaning and pretreatment
Surface cleaning and pretreatment are key steps to ensure the uniformity of the coating of the thermos cup, which directly affects the adhesion and uniformity of the coating.
Surface cleaning: Oil, dust and impurities on the surface of the thermos cup will seriously affect the adhesion and uniformity of the coating. Using an ultrasonic cleaner to clean the thermos cup can effectively remove tiny particles and oil on the surface. The cleaning temperature is set at 40℃~60℃, the power is between 60kHz~120kHz, and the cleaning time is controlled at 10~15 minutes, which can ensure that the surface cleanliness reaches more than 95%.
Pretreatment: Pretreatment includes surface grinding and chemical treatment. Grinding can remove the oxide layer and scratches on the surface, making the surface smoother and easier for coating adhesion. Using 400-600 mesh sandpaper for grinding can form a uniform texture and improve the adhesion of the coating. Chemical treatment usually uses acid or alkaline washing to remove rust and residues on the surface, further improving the cleanliness and activity of the surface.
Effect evaluation: After cleaning and pretreatment, use a surface tension tester to detect the cleanliness and activity of the surface. The surface tension should reach 35~40 dynes/cm to ensure that the coating can be evenly spread.
2. Coating process selection
2.1 Spray painting process
Spray painting process is a common surface treatment method for thermos cups. Liquid paint is evenly sprayed on the surface of the thermos cup to form a protective film and decorative layer. The uniformity of its coating is affected by many factors:
Equipment and process parameters: The use of automated spray painting equipment, such as a 4-gun 6-axis multi-function coating machine, can achieve multi-angle and uniform spraying. The spraying speed is controlled at 0.5~1.5 m/s, and the distance between the spray gun and the surface of the thermos cup is maintained at 15~25 cm, which can effectively ensure uniform coating thickness. At the same time, the viscosity of the paint needs to be controlled within 20~30 seconds (apply - 4 cups) during the painting process to ensure good fluidity of the paint and avoid sagging and accumulation.
Coating thickness control: Through multiple spraying and drying, the wet film thickness of each spray is controlled at 20~30 microns, and the final dry film thickness reaches 60~80 microns, which can ensure uniform coating and strong adhesion. Multiple spraying can also reduce the risk of uneven coating and cracking caused by excessive thickness of one spray.
Environmental factors: The temperature of the painting environment should be controlled at 20℃~30℃, and the relative humidity should be between 50%~70%. Too high or too low temperature will affect the drying speed and adhesion of the paint, and humidity will affect the leveling of the paint. In a suitable environment, the paint can be spread better to form a uniform coating.
Advantages and limitations: The advantages of the spray painting process are diverse appearance effects, rich color choices, and high gloss or special texture. However, the spray painting process has a greater impact on the environment, contains volatile organic compounds (VOCs), and has relatively low durability and is easy to scratch or peel off.
2.2 Powder spraying process
The powder spraying process is to spray the powdered paint onto the surface of the thermos cup by electrostatic or pressure, and then bake it at high temperature to form a coating. The uniformity of its coating is also affected by many factors:
Equipment and process parameters: Using electrostatic spraying equipment, the powder coating is evenly attached to the surface of the thermos cup by electrostatic adsorption. The spraying voltage is controlled at 60~80 kV, and the spraying distance is maintained at 10~20 cm to ensure the uniform adhesion of the powder coating. The baking temperature is generally controlled at 180℃~220℃, and the baking time is 10~15 minutes to ensure that the powder is melted into a uniform film.
Powder coating characteristics: The particle size distribution of powder coating is crucial to the uniformity of the coating. Powder coatings with a particle size between 30~100 microns can form a uniform and smooth coating. In addition, the fluidity of powder coating will also affect the spraying effect. Powder coating with good fluidity can better cover the surface of the thermos cup and reduce the unevenness of the coating thickness.
Coating thickness control: The coating formed by the powder spraying process is usually thicker, and the dry film thickness can reach 60~120 microns. The thicker coating not only improves the wear resistance and impact resistance of the thermos cup, but also effectively reduces the risk of coating shedding due to local uneven thickness.
Environmental factors: The powder spraying process has relatively low environmental requirements, but the workshop still needs to be kept clean to avoid dust and impurities from mixing into the coating. Compared with the painting process, the powder spraying process does not involve solvents, is environmentally friendly, and the coating has stronger wear resistance and impact resistance.
Advantages and limitations: The advantages of the powder spraying process are environmental protection, no VOCs, strong coating durability, good abrasion resistance and impact resistance. However, the color and effect selection of the powder spraying process is relatively limited, and the initial investment cost and equipment cost are high.
3. Coating uniformity control method
3.1 Spraying equipment and parameter optimization
The optimization of spraying equipment and process parameters is the key link to ensure the uniformity of the coating of the thermos cup. By accurately controlling the parameters of the spraying equipment, the uniformity, adhesion and appearance quality of the coating can be effectively improved.
Equipment selection and optimization:
Automated spraying equipment: The use of automated spraying equipment, such as a 4-gun 6-axis multifunctional coating machine, can achieve multi-angle and uniform spraying. This equipment can accurately control the movement trajectory and spraying angle of the spray gun to ensure that the coating is evenly distributed on the surface of the thermos cup.
Spray gun parameter adjustment: The distance between the spray gun and the surface of the thermos cup should be kept at 15~25 cm, and the spraying speed should be controlled at 0.5~1.5 m/s. The spray gun pressure is also an important factor affecting the uniformity of the coating, which is usually controlled at 0.4~0.75 MPa. The precise control of these parameters can effectively avoid the coating being too thick or too thin and ensure the uniformity of the coating.
Paint property control: The viscosity of the paint has a significant effect on the uniformity of the coating. During the painting process, the viscosity of the paint needs to be controlled within 20~30 seconds (apply - 4 cups) to ensure good fluidity of the paint and avoid sagging and accumulation. In addition, the solid content and concentration of the paint should also be adjusted according to the specific process to meet different spraying requirements.
Process parameter optimization:
Coating thickness control: Through multiple spraying and drying, the wet film thickness of each spraying is controlled at 20~30 microns, and the final dry film thickness reaches 60~80 microns. Multiple spraying can not only reduce the risk of uneven coating and cracking caused by excessive spraying at one time, but also improve the adhesion and wear resistance of the coating.
Environmental factor control: The temperature of the spraying environment should be controlled at 20℃~30℃, and the relative humidity should be between 50%~70%. Suitable environmental conditions can ensure the drying speed and adhesion of the paint, while avoiding coating defects caused by temperature and humidity changes.
Baking process optimization: Baking temperature and time are crucial to the curing and uniformity of the coating. For example, the baking temperature of the powder spraying process is generally controlled at 180℃~220℃, and the baking time is 10~15 minutes. By optimizing the baking process, the coating can be uniformly cured and the problem of uneven coating caused by local overheating or underheating can be reduced.
3.2 Coating thickness detection and adjustment
The detection and adjustment of coating thickness is a key link to ensure the uniformity of the coating. By real-time monitoring of the coating thickness and timely adjustment of the spraying parameters, the uniformity and quality of the coating can be effectively improved.
Detection method:
Online thickness monitoring system: Modern coating machines are usually equipped with online thickness monitoring systems, such as laser thickness gauges or optical measuring devices. These devices can detect the coating thickness in real time during the coating process and feed the data back to the control system. Based on these data, the system can automatically adjust the coating parameters (such as speed, pressure, etc.) to achieve dynamic thickness correction and ensure the uniformity of the coating.
Offline detection: In addition to online detection, offline detection methods can also be used, such as using a coating thickness gauge to sample the coating. The coating thickness gauge can accurately measure the thickness of the coating, and the detection range is usually between 5~200 microns. Through offline detection, the coating thickness can be analyzed in more detail, and the uneven coating thickness problem can be discovered in time.
Adjustment method:
Parameter adjustment: According to the test results, the parameters of the spraying equipment, such as spray gun pressure, spray speed, paint viscosity, etc., can be adjusted in time. For example, if the coating is detected to be too thick, the spray gun pressure can be appropriately reduced or the spray speed can be increased; if the coating is too thin, the spray gun pressure can be appropriately increased or the spray speed can be reduced.
Process optimization: In addition to adjusting equipment parameters, the coating uniformity can also be improved by optimizing the process flow. For example, increase the drying time of the coating to ensure that the coating is completely dry before spraying the next layer. In addition, the baking process can be adjusted to ensure that the coating is uniformly cured.
Material adjustment: The characteristics of the coating material also have an important influence on the uniformity of the coating. By adjusting the physical properties of the paint, such as viscosity, solid content and concentration, the fluidity and spreadability of the coating can be optimized. For example, using high-viscosity paint can reduce the sagging phenomenon of the coating, while low-viscosity paint is easier to form a uniform coating.
Through the above spraying equipment and parameter optimization as well as coating thickness detection and adjustment methods, the uniformity of the thermos cup coating can be effectively improved to ensure the quality and performance of the coating.
4. Process improvement and innovation
4.1 Application of new coating materials
The application of new coating materials is an important way to improve the uniformity of the thermos cup coating. These materials have shown significant advantages in performance and application effects.
Nanocomposite coating materials: Nanocomposite coating materials have attracted much attention due to their unique physical and chemical properties. For example, coating materials with the addition of nano-silicon dioxide (SiO₂) can significantly improve the hardness and wear resistance of the coating. Studies have shown that when the particle size of nano-silicon dioxide is between 10 and 50 nanometers, the uniformity and adhesion of the coating are optimal. In addition, nanocomposite coating materials also have good UV resistance and can extend the service life of the coating.
Self-healing coating materials: Self-healing coating materials can automatically repair themselves when damaged by the outside world to maintain the integrity and uniformity of the coating. This material usually contains microcapsules or nanoparticles. When the coating is damaged, these microcapsules or nanoparticles will release repair agents to fill the damaged area. For example, the self-healing coating material containing polyurea microcapsules can achieve a scratch repair rate of more than 80%, effectively reducing the problem of uneven coating caused by scratches.
Environmentally friendly coating materials: With the enhancement of environmental awareness, environmentally friendly coating materials are increasingly widely used. Water-based coatings and high-solid coatings are among the representatives. Water-based coatings use water as a solvent, do not contain volatile organic compounds (VOCs), and are harmless to the environment and human health. Studies have shown that the coating uniformity of water-based coatings is comparable to that of traditional solvent-based coatings, and has better adhesion and weather resistance. High-solid coatings increase the solid content of the coating by reducing the use of solvents, thereby reducing the unevenness of the coating thickness.
4.2 Optimization of coating curing technology
The optimization of coating curing technology is a key link to ensure the uniformity and performance of the coating. Different curing technologies have a significant impact on the performance and uniformity of the coating.
Photocuring technology: Photocuring technology is a fast and efficient coating curing method that cures the coating quickly by ultraviolet or visible light irradiation. The curing speed of light-cured coatings is more than 10 times faster than that of traditional heat-cured coatings, which can significantly improve production efficiency. In addition, the uniformity of light-cured coatings is also better because the shrinkage rate of the coating is lower during the light-curing process. Studies have shown that the surface hardness and adhesion of UV-cured coatings with a wavelength of 365-405 nanometers can reach 1.5 times that of traditional coatings.
Optimization of thermal curing technology: Although traditional thermal curing technology is widely used, it has the problems of long curing time and high energy consumption. By optimizing the thermal curing process, the uniformity and performance of the coating can be significantly improved. For example, the curing process is divided into multiple stages by using a segmented temperature rise curing process, and the temperature and time of each stage are precisely controlled. This process can effectively reduce the stress inside the coating and improve the uniformity and adhesion of the coating. Studies have shown that the segmented temperature rise curing process can improve the uniformity of the coating by more than 20%.
Plasma curing technology: Plasma curing technology is an emerging coating curing method that quickly cures the coating through the high energy of plasma. Plasma curing technology can not only increase the curing speed of the coating, but also significantly improve the surface properties of the coating. For example, the surface roughness of plasma-cured coatings can be reduced to 1/3 of that of traditional coatings, thereby improving the uniformity and glossiness of the coating. In addition, plasma curing technology can also achieve coating curing at low temperatures, which is suitable for temperature-sensitive thermos cup materials.
5. Quality inspection and evaluation
5.1 Coating appearance quality inspection
The coating appearance quality is an important indicator of the surface treatment of thermos cups, which directly affects the aesthetics and market competitiveness of the product. The coating appearance quality inspection mainly includes the following aspects:
Color uniformity: The coating color should be uniform and consistent, without obvious color difference or color spots. The color uniformity of the coating is detected by a colorimeter, and the color difference value should be controlled within ΔE≤1.5. For example, in the same batch of thermos cups, 10 samples were randomly selected for inspection, and the color difference values were all within the range of ΔE≤1.5, indicating that the coating color uniformity is good.
Surface flatness: The coating surface should be flat and smooth, without obvious orange peel, sagging or particles. The roughness of the coating surface is detected using a roughness tester, and the roughness value should be controlled within Ra≤0.5μm. In the actual test, the coating surface was randomly sampled and tested, and the roughness values were all within the range of Ra≤0.5μm, indicating that the surface flatness of the coating meets the requirements.
Gloss: The gloss of the coating is one of the important indicators to measure the appearance quality of the coating. According to different product requirements, the gloss value should be controlled within a certain range. For example, the gloss value of the high-gloss coating should reach more than 90%, while the gloss value of the matte coating should be controlled between 10% and 20%. The coating is tested by a gloss meter to ensure that it meets the design requirements.
5.2 Coating performance test
Coating performance test is a key link in evaluating the surface treatment quality of the thermos cup. It mainly tests the adhesion, hardness, wear resistance, corrosion resistance and impact resistance of the coating:
Adhesion test: Coating adhesion is an important indicator to measure the bonding strength between the coating and the substrate. The adhesion test is carried out by the cross-cutting method. The coating is divided into 100 small grids, and the tape is pasted and then torn off to observe the shedding of the coating. The adhesion level is divided into 0~5 levels, 0 means that the coating has not fallen off, and 5 means that the coating has fallen off completely. In actual testing, the adhesion level of the thermos cup coating should reach 0~1, indicating that the coating is well bonded to the substrate.
Hardness test: The hardness of the coating reflects the ability of the coating to resist external forces. The pencil hardness method is used for testing. Pencils of different hardness are scratched on the surface of the coating to observe the scratches of the coating. The hardness of the coating should reach 3H or more to ensure that the coating has good wear resistance and scratch resistance.
Wear resistance test: The wear resistance test evaluates the durability of the coating under friction conditions. Use a wear tester to test, set a certain number of frictions and loads, and observe the wear of the coating. For example, after 1000 frictions, the wear depth of the coating should be less than 0.05mm, indicating that the coating has good wear resistance.
Corrosion resistance test: The corrosion resistance test evaluates the protective performance of the coating in a corrosive environment. The test was conducted by using the salt spray test method. The thermos cup was placed in a salt spray test chamber, the temperature was set to 35°C, the salt spray concentration was 5%, and the corrosion of the coating was observed after continuous spraying for 24 hours. There should be no obvious corrosion points or peeling on the coating surface, indicating that the coating has good corrosion resistance.
Impact resistance test: The impact resistance test evaluates the coating's ability to resist damage when impacted. The impact tester was used for testing, and a certain impact energy was set to impact the coating. The coating should be free of cracks, peeling or obvious deformation to ensure that the coating can withstand a certain impact force during use.
Through the above coating appearance quality inspection and performance test, the quality of the surface treatment of the thermos cup can be comprehensively evaluated to ensure that the coating uniformity, adhesion, hardness, wear resistance, corrosion resistance and impact resistance and other performance indicators meet the design requirements, thereby improving the product's quality and market competitiveness.
6. Summary
The uniformity of the surface coating of the thermos cup is a key factor affecting its appearance quality, performance and service life. Through in-depth research on surface cleaning and pretreatment, coating process selection, coating uniformity control methods, process improvement and innovation, and quality inspection and evaluation, the uniformity and overall performance of the thermos cup coating can be effectively improved.
In the surface cleaning and pretreatment stage, ultrasonic cleaning and appropriate grinding and chemical treatment can significantly improve the surface cleanliness and activity, providing a good foundation for coating adhesion. In terms of coating process selection, the painting process and powder spraying process have their own advantages and disadvantages. The painting process has a variety of appearance effects but slightly poor durability. The powder spraying process is environmentally friendly and durable but has limited color selection. By optimizing the spraying equipment and parameters, and detecting and adjusting the coating thickness, the coating uniformity can be effectively controlled. The application of new coating materials and the optimization of coating curing technology further improve the performance and uniformity of the coating. Finally, through strict coating appearance quality inspection and performance testing, the quality of the thermos cup surface treatment can be comprehensively evaluated to ensure that it meets the design requirements.
To sum up, ensuring the uniformity of the thermos bottle coating requires starting from multiple links, comprehensively considering factors such as process, materials, equipment and environment, and through scientific methods and strict quality control, achieving a dual improvement in coating uniformity and performance, thereby improving the overall quality and market competitiveness of the thermos bottle.