Suggestions for the use of screen printing ink leveling agent
Suggestions for the use of screen printing ink leveling agent
Screen printing ink leveling agent is a key additive to improve the printing performance of ink. Its use needs to be adjusted comprehensively according to the ink system, printing process and target effect. The following are specific usage suggestions:
I. Selection of applicable system
Solvent-based ink
Preferably use polyether-modified silicone or polyester-modified silicone leveling agents, such as Dow Corning DC-51. Such additives can reduce the surface tension to 20-25mN/m, improve the wettability of ink on low surface energy substrates, and reduce defects such as shrinkage cavities and pinholes.
UV-curing ink
It is necessary to select a leveling agent that is resistant to UV curing, such as KMT-5510S. Its polyether siloxane copolymer structure can withstand a curing temperature of 120-150℃, avoiding performance failure caused by the decomposition of the leveling agent during the curing process.
Water-based ink
It is recommended to use polydimethylsiloxane leveling agents, such as Dow Corning DC-51 water-based dispersion. Its 80% active ingredients can provide a 0.1-0.3% addition window, which improves the smoothness while maintaining the transparency of the ink.
II. Addition Control
Conventional Addition
It is recommended to add 0.2-0.8% for solvent-based inks, 0.1-0.5% for water-based inks, and 0.05-0.3% for UV inks. The fineness of the ink needs to be tested by a scraper fineness meter. When the leveling agent reduces the fineness from 25μm to below 15μm, it can be considered that the optimal addition amount has been reached.
Special process adjustment
For high screen count printing (>300 lines/inch), the addition amount needs to be increased to the upper limit; for thick film printing (>25μm), the addition amount needs to be reduced to the lower limit to balance the leveling and drying speed.
III. Use process optimization
Pre-dispersion treatment
The leveling agent needs to be pre-diluted with a solvent of 5-10% of the total ink amount and stirred at a speed of 200-400r/min for 15-20 minutes. For UV ink, it is necessary to pre-disperse it under light-proof conditions to prevent the leveling agent from curing prematurely.
Timing of addition
It is recommended to add it after grinding and in the ink adjustment stage. For two-component inks, the leveling agent needs to be mixed before the curing agent is added to avoid reaction with isocyanate curing agents.
Equipment matching
When using a scraper grinder, the amount of leveling agent added needs to be increased by 10-15%; when using a three-roll grinder, the amount can be reduced by 5-10% to compensate for the effect of different grinding methods on leveling.
IV. Performance verification method
Leveling test
Using ISO 2838 standard, at 23℃ and 50%RH environment, by observing the change in the mirror reflectivity of the 30μm wet film, when the reflectivity increases from 60% to more than 85%, it can be considered that the leveling meets the standard.
Anti-adhesion test
The printed samples were stacked for 24 hours at 40℃ and 80%RH. When the peel force dropped from >200g/25mm to <50g/25mm, it showed that the leveling agent effectively improved the anti-adhesion performance.
Friction resistance test
The weight loss rate after 100 turns was tested with a load of 500g using a Taber abrasion tester. When the leveling agent reduced the weight loss rate from >8mg to <3mg, it was considered to have achieved the effect of increasing slip and wear resistance.
V. Solutions to common problems
Pitting problem
If pores with a diameter of >0.5mm appear, the compatibility of the leveling agent and the resin needs to be checked. 0.1-0.3% of a silicone defoamer (such as BYK-052N) can be added for synergistic improvement.
Uneven gloss
When the gloss deviation is >5GU, the HLB value of the leveling agent needs to be adjusted. For water-based inks, 0.2-0.5% non-ionic wetting agent (such as TEGO Wet 270) can be added to enhance substrate wetting.
Migration phenomenon
If the leveling agent is found to migrate to the ink surface, a high molecular weight (>100,000) polydimethylsiloxane product should be selected and the amount added should be controlled within the recommended lower limit.
VI. Precautions
Storage conditions
The leveling agent should be sealed and stored at 5-35°C to avoid contact with strong acids and strong bases. For silicone leveling agents, special precautions should be taken to prevent contact with heavy metal ions such as tin and lead.
Compatibility test
When developing new formulas, a 72-hour thermal storage stability test (50°C) is required. When the viscosity change is <5% and the fineness change is <2μm, the leveling agent can be considered compatible with the ink system.
Safety regulations
When operating silicone leveling agents, nitrile gloves and goggles must be worn. For water-based leveling agents, pay attention to their pH value (usually 6.5-7.5) and avoid mixing with strong alkaline substances.