Printing high density effect heat transfer silicone labels requires combining material properties with process parameter control. The following are the specific operation procedures and key technical points:
1. Material and equipment preparation
Silicone material selection
Use high viscosity, slow-drying silicone (such as Shore hardness A30-A50) to ensure that it is not easy to flow during printing and form a thick glue layer after curing.
Add 3%-5% silicone thickener (such as fumed silica) to improve the stiffness of the material and avoid printing collapse.
Screen and equipment
Use 100-120 mesh stainless steel screen to ensure that the silicone passes through the screen smoothly and the edges are clear.
Equipped with a constant temperature oven (temperature accuracy ±2℃) and an infrared leveling machine to control the thermal expansion coefficient during the curing process.
2. Printing process
Base glue printing
Use a base glue special for thick plate silicone (such as polyurethane modified silicone) and print 2-3 layers, each layer thickness 0.1-0.15mm.
After each layer is printed, bake it in an 80℃ infrared leveling machine for 3-5 minutes to ensure that the glue layer is uniform and free of bubbles.
Surface glue printing
When preparing the surface glue, the ratio of silicone to curing agent is strictly controlled at 10:1 (weight ratio), and 0.5%-1% fluorescent color paste or pearl powder is added to enhance the visual effect.
Print in 3-4 times, bake at 80℃ for 5 minutes after each printing, and control the final thickness at 0.3-0.5mm.
Thermal transfer parameters
Temperature: 160-170℃ (10-15℃ higher than ordinary transfer), to ensure that the silicone is completely melted.
Pressure: 0.3-0.4MPa. Too low pressure may lead to incomplete silicone transfer, and too high pressure may crush the substrate.
Time: 15-20 seconds, adjusted according to the thickness of the silicone and the material of the substrate.
3. Key technical control
Anti-collapse treatment
Add 0.2%-0.3% fibrous filler (such as glass fiber) to the silicone to enhance the deformation resistance of the glue layer.
After printing, immediately put it in the 0℃ cold air channel for rapid cooling for 1 minute to solidify the surface structure.
Edge sharpening technology
The edge of the screen is chamfered with 0.1mm to reduce the accumulation of silicone during printing.
After printing, use a scraper to gently press the edge at a 45° angle to squeeze out excess silicone.
Weather resistance enhancement
Add 2% UV absorber (such as benzotriazole) and 1% antioxidant (such as hindered phenol) to the surface adhesive. After 800 hours of xenon lamp aging test, the color difference ΔE≤2.
4. Quality inspection standards
Thickness inspection
Use a laser thickness gauge to take 5 points at the four corners and center of the label, and the thickness deviation is ≤±0.05mm.
Adhesion test
According to ASTM D3359 standard, a hundred-grid knife test is used, the scratch spacing is 1mm, and the residual area after the tape is peeled off is ≥95%.
Washability test
After 50 times of 40℃ water washing (containing 4g/L neutral detergent), the label does not fall off, crack or fade significantly.
5. Solutions to common problems
Silicone residue
Cause: transfer temperature is too low or pressure is insufficient.
Countermeasures: Increase the transfer temperature to 170℃ and the pressure to 0.4MPa.
Edge warping
Reason: Incomplete curing of silicone or insufficient surface tension of substrate.
Countermeasures: Extend the baking time to 10 minutes, and pre-coat the surface of the substrate with silicone treatment agent (such as Dow Corning DC-1200).
Bubble generation
Reason: The humidity of the printing environment is too high (>60%) or air is mixed in the silicone.
Countermeasures: Control the humidity of the workshop ≤50%, and vacuum degas the silicone before printing (vacuum degree -0.095MPa, 10 minutes).