For beginners of silk screen silicone, controlling quality is the key to ensuring that products meet requirements and improve market competitiveness. The following introduces the methods of controlling quality in detail from three stages: preparation before silk screen printing, key points of operation during silk screen printing, and quality inspection after silk screen printing:
Preparation before silk screen printing
Material selection
Silicone ink: Choose the appropriate silicone ink according to the use environment and requirements of the product. For example, silicone ink used for outdoor products must have good weather resistance and be able to resist ultraviolet rays, wind and rain erosion; ink used for food contact products must meet food safety standards to ensure non-toxic and harmless.
Screen: The mesh count of the screen determines the amount of ink passing through and the fineness of the printed pattern. Beginners should choose the appropriate mesh count of the screen according to the detailed requirements of the printed pattern. Generally speaking, for products with thicker printed lines and simple patterns, a screen with a lower mesh count (such as 80-120 mesh) can be selected; if you want to print fine patterns and text, you need to use a high mesh screen (such as 200-300 mesh). At the same time, ensure that the tension of the screen is uniform and there is no obvious looseness and tightness to ensure that the ink can be evenly transmitted during the printing process.
Substrate: Check whether the surface of the substrate is flat and clean, and free of defects such as oil, dust, and scratches. If there are impurities on the surface of the substrate, it will affect the adhesion of the ink, causing the printed pattern to fall off and blur. For some products that require high surface flatness, such as mobile phone keypad silicone covers, the substrate needs to be pre-treated, such as polishing and cleaning.
Equipment debugging
Screen printer: Adjust the scraper pressure, angle, and speed of the screen printer. If the scraper pressure is too small, the ink cannot evenly penetrate the screen, resulting in a light and unfull color of the printed pattern; if the pressure is too high, it is easy to scratch the screen, affecting the service life of the screen, and may also cause ink leakage, making the edge of the pattern blurred. Generally speaking, the angle between the scraper and the screen is more suitable between 70° and 80°, and the scraper speed should be adjusted according to the size and complexity of the pattern, usually between 20 and 40cm/s.
Curing equipment: If it is a heat-curing silicone ink, ensure that the temperature and time of the curing furnace are set accurately. If the temperature is too high or the curing time is too long, the silicone ink will age, discolor, and even deform the substrate; if the temperature is too low or the curing time is insufficient, the ink cannot be completely cured, the adhesion is poor, and it is easy to fall off. For example, the curing temperature of common silicone ink is between 150℃-180℃, and the curing time is about 3-5 minutes.
Key points of operation during screen printing
Ink mixing
Proportion control: Strictly follow the formula ratio provided by the ink supplier to mix and avoid the degradation of ink performance due to imbalance of proportion. For example, some silicone inks need to be mixed with curing agents in a certain proportion. If too much curing agent is added, the ink will cure too quickly and block the mesh on the screen; if too little is added, the ink will not cure completely, affecting the product quality.
Stir evenly: Use a stirrer to stir the ink evenly to ensure that the pigment, resin, solvent and other components in the ink are fully mixed. The stirring time is generally not less than 3-5 minutes. During the stirring process, be careful to avoid too many bubbles, otherwise it will affect the printing effect.
Printing operation
Accurate positioning: Place the substrate accurately on the workbench of the screen printer and use the positioning device to fix it to ensure that the position of each print is consistent. For some products that require multi-color overprinting, positioning accuracy is particularly important. Excessive deviation will lead to inaccurate color registration, ghosting, misalignment and other problems.
Scraping operation: When scraping, keep the angle and pressure of the scraper and the screen plate stable, and scrape at a uniform speed. During the scraping process, pay attention to observe the penetration of the ink. If the ink penetration is uneven, adjust the scraper pressure or angle in time. At the same time, avoid repeated scraping at the same position to avoid ink accumulation and uneven pattern thickness.
Quality inspection after screen printing
Appearance inspection
Pattern integrity: Check whether the printed pattern is complete, whether there are missing strokes, broken strokes, missing prints, etc. For example, when printing a brand's logo, make sure that all parts of the logo are clearly visible and not missing.
Color consistency: Compare the color of the printed product with the standard color sample to check whether there is color difference. A colorimeter can be used for precise measurement, and the color difference ΔE is generally required to be ≤1.5 (the requirements for color difference in different industries may vary).
Surface quality: Observe whether the printed surface is smooth and flat, and whether there are defects such as bubbles, particles, and orange peel. Bubbles and particles will affect the appearance quality of the product, and the orange peel phenomenon will make the pattern surface look uneven and affect the feel.
Performance test
Adhesion test: Use a hundred-grid knife to cut 10×10 1mm×1mm small squares on the printed pattern, and then use 3M tape to stick tightly on the small squares, quickly tear off the tape in the vertical direction, and check the pattern shedding. According to the standard requirements, the pattern shedding area should be less than 5% to be qualified.
Wear resistance test: Use a wear tester to perform a friction test on the printed pattern, set a certain number of frictions and pressures, and observe the wear of the pattern. For example, after 500 frictions, the pattern can still remain clear and there is no obvious wear, which means that the wear resistance meets the requirements.
Chemical resistance test: According to the use environment of the product, select the corresponding chemical reagent to test the printed pattern. For example, soak the printed material in solvents such as alcohol and gasoline for a period of time, and then observe whether the pattern changes color or falls off to evaluate its chemical resistance.