Example of Anysil HD Silicone on PP fabric
Abstract: Polypropylene (PP) fabric is widely used in various fields due to its lightweight, corrosion resistance, and low cost, but its low surface energy and poor wettability bring great challenges to silicone screen printing. This paper briefly analyzes the key precautions in the process of silicone screen printing on PP fabric, including substrate pretreatment, silicone ink selection, printing process control, curing conditions, and safety and environmental protection, so as to improve the adhesion, durability and aesthetic property of the printed pattern, and provide practical guidance for actual production.
Keywords: PP fabric; silicone screen printing; pretreatment; ink selection; curing process
1. Introduction
Silicone screen printing has the advantages of good elasticity, wear resistance, high temperature resistance and water resistance, and is widely used in fabric printing. However, PP fabric has a non-polar molecular structure, low surface energy, and poor adhesion to silicone ink, which easily leads to problems such as poor pattern adhesion, peeling and blurring during the printing process. Therefore, mastering the key precautions in each link of silicone screen printing on PP fabric is crucial to ensure the printing quality and product performance.
2. Key Precautions for Silicone Screen Printing on PP Fabric
2.1 Pretreatment of PP Fabric
Pretreatment is the premise to ensure the adhesion of silicone ink to PP fabric, and the core is to improve the surface energy of the fabric and remove surface impurities. First, it is necessary to clean the PP fabric to remove dust, oil stains, mold release agents and other impurities on the surface, which can be wiped with alcohol-based cleaners or cleaned by ultrasonic waves, and then dried thoroughly to avoid affecting the ink adhesion. Second, surface activation treatment is required. Corona treatment is the most commonly used method. High-voltage electric sparks change the surface structure of PP fabric, increase surface roughness and surface energy, and enhance the wettability and adhesion between ink and fabric. It should be noted that the intensity and time of corona treatment should be controlled appropriately; excessive treatment will damage the fabric structure, while insufficient treatment will not achieve the activation effect. In addition, for some PP fabrics with high water repellency, an appropriate amount of adhesion promoter can be applied after activation to further improve the bonding performance between silicone ink and fabric.
2.2 Selection of Silicone Ink and Auxiliaries
The selection of silicone ink directly determines the printing effect and durability. It is necessary to choose silicone ink specially formulated for PP fabric, which should have good adhesion, flexibility and compatibility with PP material. At the same time, the ink should meet environmental protection standards, avoid using inks containing heavy metals and other harmful substances, and comply with ROHS and OEKO-TEX standards. When preparing the ink, it is necessary to mix the silicone ink base, catalyst and pigment in strict accordance with the manufacturer's proportion. Generally, the mixing ratio of component A (transparent silicone) and component B (catalyst) is 9:1 or 10:1, and the amount of pigment added should not exceed 15% to avoid affecting the curing effect and adhesion of the ink. In addition, vacuum defoaming treatment should be carried out after ink mixing to remove air bubbles in the ink, so as to prevent pinholes and unevenness in the printed pattern. It should be noted that the mixed ink has a limited pot life, so it should be used within the specified time to avoid ink waste and performance degradation.
2.3 Control of Screen Printing Process
The control of screen printing process is the key to ensure the clarity and uniformity of the printed pattern. First, the selection of screen mesh: due to the high viscosity of silicone ink, it is recommended to choose a screen with 80-120 mesh for the bottom layer to ensure sufficient ink deposition and improve adhesion; for the surface layer or fine pattern, a screen with 120-160 mesh can be selected to ensure the clarity of the pattern. The screen should use polyester monofilament material, and the screen tension should be maintained at 25-30 N/cm to improve ink release and reduce pattern smudging. Second, the adjustment of squeegee: the squeegee hardness should be 65 durometer, and the angle between the squeegee and the screen should be 75°, with a sharp blade to ensure uniform ink scraping. The printing speed should be controlled at 30 strokes per minute, and the pressure should be adjusted according to the mesh count; the 110-count mesh requires less pressure to avoid damaging the screen and fabric. In addition, the alignment of the fabric and the screen should be accurate. Test printing on paper can be carried out first to confirm the alignment, so as to ensure the consistency of the printed pattern and reduce errors.
2.4 Curing Conditions of Silicone Ink
Curing is an important link to ensure the adhesion and performance of silicone ink. The curing of silicone ink on PP fabric is mainly thermal curing, and the curing temperature and time should be strictly controlled according to the ink performance and pattern thickness. Generally, the flash curing temperature is 150-160℃, and the time is 20 seconds; the final curing temperature is 150-180℃, and the time is 1-2 minutes. The curing temperature should not be too high, otherwise it will cause the PP fabric to shrink and deform; if the temperature is too low or the time is insufficient, the ink will not be fully cured, resulting in poor adhesion and easy peeling. During the curing process, temperature strips or infrared thermometers can be used to monitor the temperature to ensure the stability of the curing effect. For multi-color printing, flash curing should be carried out between each color layer to avoid ink mixing and improve the layering of the pattern.
2.5 Safety and Environmental Protection Precautions
In the process of silicone screen printing, attention should be paid to safety operation and environmental protection. First, the operating environment should be well-ventilated to discharge volatile organic compounds (VOCs) generated during ink mixing and curing, and operators should wear gas masks, heat-insulating gloves and other protective equipment to avoid inhalation of harmful gases and scalds. Second, the storage of ink and auxiliaries: silicone ink and catalyst should be sealed and stored separately in a cool and dry place with a temperature not exceeding 25℃, away from open flames and direct sunlight; flammable diluents should be stored in explosion-proof cabinets and marked with warning signs. Third, the treatment of waste: waste silicone, waste screens and cleaning rags should be classified as hazardous waste and handed over to qualified institutions for treatment; waste water containing silicone should be neutralized and precipitated before discharge to avoid blocking the sewer. In addition, it is forbidden to mix silicone ink with acid or alkaline detergents to avoid chemical reactions producing toxic gases.
3. Conclusion
The silicone screen printing on PP fabric involves multiple links such as substrate pretreatment, ink selection, process control, curing and safety protection. Only by strictly controlling each link and following the corresponding precautions can the problems of poor adhesion, peeling and blurring of the printed pattern be effectively solved, and the printing quality and product durability be improved. In actual production, it is also necessary to adjust the process parameters according to the specific performance of PP fabric and silicone ink, and conduct pre-printing tests to ensure the stability and reliability of the printing effect. With the continuous improvement of printing technology, the application of silicone screen printing on PP fabric will be more extensive, and the mastery of relevant precautions will provide important support for the development of the industry.