Ensuring the uniformity of ink during the ink mixing process is crucial to the final quality of screen printing silicone. If the ink is not mixed evenly, it may cause the printed pattern to have different shades, spots or stripes, and even affect the adhesion and curing effect of the ink. The following is a detailed description of the methods to ensure uniform ink from three aspects: preparation before mixing, operation during mixing, and inspection and treatment after mixing:
Preparation before mixing
Choose the right tool
Container: A clean, dry container with no impurities should be selected. The container material is preferably glass or stainless steel. Avoid using plastic containers, because some plastic materials may react with ink components, and the plastic surface is prone to static electricity and dust absorption, affecting the purity of the ink mixing. The size of the container should be selected according to the amount of ink to be mixed, ensuring that there is enough space for stirring to prevent ink overflow.
Stirring equipment: For manual stirring, a glass rod or a plastic stirring rod should be used. The surface of the stirring rod should be smooth and without sharp edges to avoid scratching the container or introducing impurities. If mechanical stirring is used, a suitable stirrer should be selected, such as an electric stirrer or a disperser, and the speed and shape of the stirring paddle of the stirrer should be adjusted according to the viscosity of the ink and the mixing amount. For high-viscosity inks, anchor or frame-type stirring paddles can be used; for low-viscosity inks, propeller-type stirring paddles are more suitable.
Confirm the formula and raw materials
Accurate formula: Strictly follow the ink formula provided by the supplier to prepare, and clarify the proportion of each component such as the main agent, curing agent, and diluent. For example, a silicone ink formula requires a mass ratio of the main agent to the curing agent of 10:1, and the amount of diluent added is 15% of the total mass. Each component must be accurately weighed to avoid changes in ink performance due to ratio deviation.
Raw material inspection: Before preparation, carefully check the appearance, color and smell of the ink raw materials. If the raw materials are found to have abnormal conditions such as stratification, precipitation, discoloration or odor, it means that the raw materials may have deteriorated or been contaminated and cannot be used. At the same time, ensure that the raw materials are within the shelf life and avoid using expired raw materials.
Preparation process operation
Reasonable order of adding materials
Main first, then auxiliary: Usually add the main agent first, and then add auxiliary ingredients such as curing agent and diluent in turn. Take the preparation of silicone ink as an example. First, pour the main agent into the container, then slowly add the curing agent, stirring while adding, so that the curing agent and the main agent are fully mixed. Finally, add the diluent as needed to adjust the viscosity of the ink.
Step-by-step addition: For some inks that need to add pigments or additives, they should be added in steps. For example, first add a small amount of pigment, stir evenly, and then gradually increase the amount of pigment to ensure that the pigment can be evenly dispersed in the ink. When adding additives, it should also be done in accordance with the principle of small amounts and multiple times to avoid adding too much at one time, which will cause the ink performance to be unstable.
Fully stir
Stirring time: Stirring time is one of the key factors to ensure the uniformity of the ink. Different ink formulas and stirring equipment require different stirring times. Generally speaking, the manual stirring time is not less than 5-10 minutes, and the mechanical stirring time can be appropriately adjusted according to the stirring speed and ink viscosity, usually about 3-8 minutes. For example, using an electric stirrer to stir low-viscosity silicone ink at a speed of 500-800 rpm, stirring for about 5 minutes can achieve good uniformity; for high-viscosity inks, the stirring time may need to be extended to 8-10 minutes.
Stirring method: During the stirring process, a suitable stirring method should be used to ensure that all parts of the ink can be fully mixed. When stirring manually, the stirring rod should make a circular motion along the wall of the container, and the ink should be turned up and down at the same time to avoid dead corners. When stirring mechanically, the stirring direction and speed should be adjusted according to the shape of the stirring paddle and the flow characteristics of the ink to make the ink form a good circulation flow. For example, when using a disperser for stirring, you can first stir at a low speed to initially mix the components, and then gradually increase the speed to fully disperse the particles in the ink.
Eliminate bubbles: Bubbles are easily generated during the stirring process, and bubbles will affect the printing effect and curing quality of the ink. Bubbles can be eliminated by the following methods:
Standing defoaming: After stirring, let the ink stand for a period of time to allow the bubbles to rise and burst naturally. The standing time depends on the viscosity of the ink and the size of the bubbles, generally 15-30 minutes.
Vacuum degassing: For inks with high viscosity and bubbles that are difficult to eliminate naturally, a vacuum degassing machine can be used for degassing. Put the container containing ink into the vacuum degassing machine and keep it at a certain vacuum degree (usually -0.08 - -0.1MPa) for 10 - 20 minutes to effectively remove bubbles in the ink.
Post-mixing inspection and processing
Appearance inspection
Color uniformity: Pour the prepared ink on white paper or glass plate to observe whether its color is uniform. If there are different shades, spots or stripes, it means that the ink is not mixed evenly and needs to be re-stirred or the formula adjusted.
Fineness: Dip a small amount of ink with a scraper or glass rod, scrape it on a flat surface, and observe the fluidity and fineness of the ink. Uniform ink should have good fluidity, and the surface should be smooth after scraping, without obvious particles or agglomeration.
Viscosity detection
Use a viscometer: Use a suitable viscometer (such as a rotational viscometer, a coating - 4 cup viscometer, etc.) to measure the viscosity of the ink. After calibrating the viscometer according to the operating procedures, pour the ink sample into the measuring container of the viscometer and read the viscosity value. According to the use requirements and process parameters of the ink, determine whether the viscosity is within the qualified range. If the viscosity does not meet the requirements, it can be adjusted by adding diluent or thickener.
Take the average value of multiple measurements: In order to improve the accuracy of viscosity measurement, the ink should be measured multiple times at different locations and the average value should be taken as the final result.
Remedial measures for uniformity
Re-stirring: If the appearance inspection or viscosity test finds that the ink is unevenly mixed, the ink can be poured back into a clean container and stirred again. During the stirring process, the stirring speed and time can be adjusted appropriately to ensure that the components of the ink are fully mixed.
Filtration treatment: For inks with fine particles or impurities, a suitable filter can be used for filtration. The pore size of the filter should be selected according to the size of the particles in the ink. Generally, a filter of 100-200 mesh can be selected. Pour the ink slowly during filtration to avoid clogging of the filter.