Silicone screen printing on aramid fabrics needs to be combined with its high temperature resistance and flame retardant properties, and can be achieved by optimizing printing process parameters, selecting suitable materials and strictly controlling the operation process. The following are specific steps and precautions:
1. Material preparation and equipment selection
Analysis of aramid fabric characteristics
Aramid (such as meta-aramid) has excellent high temperature resistance (continuous use at 205℃), flame retardancy (limiting oxygen index>28%) and chemical stability, but the surface is smooth and has poor hygroscopicity, so silicone materials with strong adhesion need to be selected.
Silicone material selection
Type: Use two-component addition type silicone (need to be mixed with AB agent), whose temperature resistance can reach more than 200℃, which is in line with the use scenario of aramid.
Additives: Add 5%-8% color paste (high temperature resistant pigments are recommended) and 1%-3% curing agent, and avoid using solvent-containing diluents (which may corrode aramid).
Viscosity adjustment: Control the viscosity of silicone at 4000-8000 centipoise by funnel method or rotational viscometer to ensure moderate fluidity.
Equipment and tools
Screen: Use 80-120 mesh stainless steel screen, photosensitive glue thickness 0.1-0.3mm (adjusted according to the pattern thickness).
Scraper: Polyurethane material, hardness 70-80 degrees, angle 45°-60°.
Baking equipment: infrared tunnel oven or hot air circulation oven, temperature control accuracy ±5℃.
2. Printing process
Fabric pretreatment
Cleaning: Wipe the aramid surface with isopropyl alcohol with a dust-free cloth to remove oil and dust.
Roughening: Increase the surface roughness and improve adhesion through plasma treatment or sandblasting (particle size 50-100μm).
Coating: Spray a thin layer of silicone primer (thickness 1-2μm), and form a chemical bonding layer after drying.
Plate making and glue adjustment
Plate making: Use photosensitive plate making method, exposure time 8-12 minutes (adjusted according to the thickness of the photosensitive glue), and check the mesh permeability after development.
Glue adjustment: Mix AB agents in proportion, stir for 3-5 minutes until uniform, and vacuum degas for 10 minutes to eliminate bubbles.
Printing operation
Positioning: Use a positioning fixture to fix the aramid fabric to ensure the pattern alignment accuracy of ±0.1mm.
Primer: Print 1-2 layers of transparent silicone primer, each layer is 0.05-0.1mm thick, and the baking temperature is 120℃/5 minutes.
Color printing:
Each color is printed 3-4 times, and baked after each printing (120℃/3 minutes) to prevent color interpenetration.
For rounded patterns, the silicone needs to be diluted (add 10% diluent), and for right-angle patterns, the viscosity needs to be increased (reduce diluent).
Cover: Print 2 layers of transparent silicone protective layer to enhance wear resistance and color vividness, and the baking temperature is 150℃/10 minutes.
Post-processing
Vulcanization: Put the printed product into the vulcanizer at a temperature of 180℃/30 minutes to completely cure the silicone.
Inspection: Check whether the pattern edge is clear and burr-free, and test the adhesion (Baige method ≥ 4B grade).
3. Control of key process parameters
Parameter Recommended value Function
Printing pressure 4-5kg/cm² Ensure that the silicone fully penetrates the gap between aramid fibers
Scraper speed 20-30cm/s Balance printing efficiency and ink layer thickness
Baking temperature 120-150℃ Avoid high temperature causing discoloration or degradation of aramid
Vulcanization time 20-30 minutes Ensure that the silicone is completely cross-linked
4. Common problems and solutions
Insufficient adhesion
Reason: The aramid surface is smooth or the silicone is not fully cured.
Solution: Increase the roughening treatment or extend the vulcanization time to 40 minutes.
Blurred pattern
Reason: The viscosity of the silicone is too high or the scraper pressure is uneven.
Solution: Adjust the viscosity to 6000 centipoise and calibrate the parallelism of the scraper.
Color interpenetration
Reason: Insufficient drying between layers.
Solution: Increase the baking time to 5 minutes after each layer is printed.
5. Application Cases
A fire suit manufacturer prints reflective silicone logos on aramid fabrics and achieves mass production through the following optimizations:
Material: Use silicone and glass microbead reflective powder that can withstand high temperatures of 300°C.
Process: Use molded silicone transfer technology, first make a copper mold, and then use a vulcanizer to form it in one go, which increases efficiency by 50%.
Effect: The logo can be washed more than 50 times, and the reflective intensity meets the EN471 standard.