Optimizing the viscosity and solid content of silicone ink is a key step to improve printing effects (such as thick ink layer, three-dimensional effect, adhesion), which requires comprehensive control from the aspects of formula design, raw material selection, process adjustment and test verification. The following are specific optimization methods:
1. Viscosity optimization strategy
Viscosity directly affects the fluidity, ink permeability and printability of the ink, and needs to be adjusted according to the printing method (screen printing, pad printing, molding) and ink layer thickness requirements.
1. Adjust the viscosity of basic silicone
Low viscosity silicone:
Applicable scenarios: thick plate printing with high ink permeability (such as ink layer above 0.3mm).
Adjustment method:
Add diluent (such as xylene, cyclohexanone), but the amount added needs to be controlled (≤5%) to avoid affecting the curing performance.
Choose low molecular weight silicone (such as 107 glue), which has low initial viscosity and good fluidity.
High viscosity silicone:
Applicable scenarios: fine dot printing or preventing ink from flowing.
Adjustment method:
Add thickener (such as fumed silica, polyamide wax) to increase viscosity through physical filling.
Choose high molecular weight silicone (such as 110 glue), which has a long molecular chain and higher viscosity.
2. Add rheological additives
Thixotropic agent:
Function: Keep the ink at high viscosity when it is still (to prevent flowing), and reduce the viscosity when scraping (good ink permeability).
Recommended materials: hydrogenated castor oil, bentonite, added at 1%-3%.
Viscosity reducer:
Function: Reduce ink viscosity and improve fluidity.
Recommended materials: non-ionic surfactants (such as BYK-346), added at 0.5%-1%.
3. Process parameter matching
Printing speed:
High viscosity ink needs to reduce the printing speed (such as screen printing speed ≤30m/min) to ensure sufficient ink penetration.
Scraper angle:
High viscosity ink uses a sharp angle scraper (such as 60°) to increase the ink pressure; low viscosity ink uses a blunt angle scraper (such as 90°) to prevent ink flying.
2. Solid content optimization strategy
Solid content directly affects the thickness of the ink layer, curing speed and durability, and it is necessary to balance printing efficiency and performance requirements.
1. Adjust the basic formula ratio
Increase the solid content:
Method: Increase the proportion of silicone resin (such as MQ resin) or pigment, and reduce the amount of solvent.
Goal: Solid content ≥ 60% (screen printing thick plate ink) to reduce the number of printing times.
Reduce the solid content:
Method: Add solvent (such as toluene, ethyl acetate) to dilute, but the evaporation rate needs to be controlled (to avoid too fast to cause orange peel).
Goal: Solid content 40%-50% (fine dot printing) to prevent blocking.
2. Use high-solid raw materials
Silicone resin:
Choose high-solid MQ resin (such as 80% solid content) to replace traditional low-solid resin to directly increase the solid content of ink.
Pigment:
Select highly dispersible pigments (such as organic pigments), reduce the amount of dispersant, and indirectly increase the solid content.
3. Curing agent matching
Two-component system:
Add an appropriate amount of curing agent (such as platinum catalyst) to promote silicone cross-linking and increase the density of the ink layer after curing.
The curing agent ratio must be strictly in accordance with the supplier's recommendation (such as 10:1) to avoid incomplete or too fast curing.
Single-component system:
Curing by heating (such as baking at 150℃ for 30 minutes) to ensure that the solvent is completely volatilized and improve the utilization rate of solid content.
III. Coordinated optimization of viscosity and solid content
1. Thick plate printing scenario
Goal: high viscosity (8000-12000mPa·s), high solid content (60%-70%).
Formula example:
Basic silicone: 100 parts (low viscosity 107 glue)
Thickener: 3 parts of fumed silica
Pigment: 20 parts (highly dispersible organic pigment)
Curing agent: 10 parts of platinum catalyst
Solid content: 65%
Process:
Print in 5-8 times, bake at 80℃ each time to dry, and the cumulative thickness is 0.5mm.
2. Fine dot printing scenario
Goal: low viscosity (3000-5000mPa·s), moderate solid content (45%-55%).
Formula example:
Basic silica gel: 100 parts (high molecular weight 110 glue)
Viscosity reducer: BYK-346 0.8 parts
Pigment: 15 parts (fineness ≤ 5μm)
Solvent: ethyl acetate 10 parts
Solid content: 50%
Process:
Use 300 mesh screen to achieve clear dots in one printing.
IV. Testing and verification
1. Viscosity test
Instrument: Rotational viscometer (such as NDJ-1).
Standard:
Silk screen thick plate: 8000-12000mPa·s (25℃).
Fine printing: 3000-5000mPa·s (25℃).
Adjustment: Increase or decrease thickener or diluent according to test results.
2. Solid content test
Method:
Weigh 10g of ink and place it in a 105℃ oven for 2 hours.
Weigh the mass of the residue and calculate the solid content = (residue mass/initial mass) × 100%.
Standard:
Ink for thick boards: ≥60%.
Fine ink: 40%-50%.
3. Verification of printing effect
Thick ink layer: Check whether the edge of the ink layer is neat, without flowing or cracking.
Adhesion: Pass the hundred grid test (ASTM D3359) to ensure that it reaches level 5B (no falling off).
Washability: Simulate 40℃ water washing for 50 times, and the ink layer does not fade or fall off.
V. Common problems and solutions
Problem Cause Solution
Ink viscosity is too high Silicone molecular weight is large or thickener is excessive Add diluent or reduce the amount of thickener
Ink viscosity is too low Too much solvent or low viscosity of basic silicone Add high viscosity silicone or reduce the amount of solvent
Insufficient solid content Incomplete solvent evaporation or wrong formula ratio Extend baking time or adjust formula ratio
Ink layer cracking Solid content is too high or incomplete curing Reduce solid content or increase curing agent dosage
Ink flows after printing Low viscosity or poor thixotropy Add thixotropic agent or increase scraper pressure