The biggest difference between UV cured digital inkjet and UV cured printing ink lies in viscosity and rheology. Printing ink has relatively high viscosity and belongs to pseudoplastic fluids, while inkjet requires low viscosity and high tension, with rheology as close as possible to Newtonian fluids and good fluidity. In addition, the particle size requirement for inkjet colorants (mainly pigments) is less than 0.25 microns, and the particle size distribution must be strictly controlled within a very narrow range. LD50 is less than 0.2 micron and LD90 is less than 0.35 micron. The quality of domestically produced inkjet printers varies greatly, especially in terms of particle size. The author has conducted measurements and found that most self proclaimed nanoscale inkjet printers have pigment particle size distributions ranging from 0.1-0.6 microns, while the actual product requires a particle size distribution of 0.045-0.15 microns This is the main reason why some inkjet printers often clog the nozzle during use.
Complete selection plan for UV curing digital inkjet dispersant
UV cured digital inkjet printing strictly prohibits small molecule and ionic dispersants, and only 100% solid polymer block hyperdispersants (steric hindrance type) can be used; Core: Anchor group matching pigment+solvation chain matching UV acrylic monomer/resin+no yellowing, no impact on curing, particle size below 0.25 microns, low viscosity anti clogging.
1、 First, select a dispersant based on the type of pigment
1. Inorganic pigments (titanium dioxide, iron oxide, fillers, white ink), selected phosphate/carboxylic acid anchoring type (acidic anchoring point adsorbs metal oxide hydroxyl groups), with pigment viscosity reduction and anti settling aggregation; Recommended dispersants HR-4013, HR-4039AC, HR-4057, dosage: Titanium dioxide 5% to 12% (pigment mass ratio)
2. Organic pigments (red/yellow/blue/purple, PR254, PY150, PB15:3, etc.), selected with aromatic rings/amides/polyamines multi-point anchoring (including benzene ring anchoring segments), matched with the aromatic ring structure of the pigment, have the property of depolymerization, and the pigment does not aggregate or become coarse; Recommended dispersants HR-4039AC, HR-4057, HR-4062, dosage: organic powder 15% to 30% (pigment ratio)
3. Carbon black (black ink is the most difficult to disperse), choose a high polarity multi anchor block dispersant (multi-point adsorption of carbon black pores), which has the performance of reducing the viscosity and flocculation of the system pigment, and prevents pigment precipitation and thickening; Recommended dispersant HR-4057, HR-4061C0 dosage: carbon black 20% to 35% (pigment ratio)
2、 Match solvation chains according to UV system (carrier resin/monomer)
UV systems are divided into three categories, with the optimal solvent chain molecular weight of 2000-8000, insufficient steric hindrance due to short chains, and increased viscosity due to long molecule entanglement:
1. Polyurethane acrylic PU system (high elasticity soft ink, leather/roll printing): Polyester solvent chain dispersant (HR-4057, HR-4060BC)
2. Epoxy acrylate (high hardness glass/sheet UV): polyether modified polyester dispersant (HR-4029)
3. Pure monomer and low resin formula (high flow industrial sprinkler ink): narrow molecular weight acrylate block dispersant to avoid system gel thickening
Hard taboos: use white ink with caution when containing large amounts of primary amine dispersants → UV curing amine promotes yellowing; White ink priority amine free dispersant (HR-4031, HR-4036, HR-4029)
3、 The core of piezoelectric nozzle adaptation selection lies in matching the requirements of application scenarios for accuracy, speed, ink compatibility, and stability, and prioritizing the locking of nozzle types
1. Industrial piezoelectric nozzles (Ricoh, Konica, Kyocera, high-precision<5pl ink droplets)
The requirement is to be a non flocculent, Newtonian fluid, non thixotropic, with a D50 of 120-220nm after grinding, stored at 70 ℃ for 7 days, and viscosity fluctuation<20% to prevent clogging of the nozzle due to flocculation.
Recommended dispersant HR-4039AC, HR-4057
2. Desktop XP600/5th generation nozzle (mid to low end UV machine), recommended HR-4062 dispersant, control particle size<300nm.
4、 Add quantity and test verification (selection and implementation steps)
1. Add benchmark (pigment mass%)
Titanium dioxide: 5-13% | Organic pigments: 15-35% | Carbon black: 20-40%; First, conduct a gradient test with a tolerance of ± 3%
2. Four mandatory screening tests
① Grinding particle size: D50 ＜ 250nm, D99 ＜ 800nm (excessive plug)
② Thermal storage stability: 70 ℃ oven for 7 days, viscosity increase<25%, no layered precipitation
③ Curing test: equivalent photoinitiator, curing speed, hardness, white ink yellowing test
④ Printing machine: continuous ink output without interruption, oblique spraying, and flying ink
5、 List of commonly used dispersants
HR-4062 (Universal), HR-4061C0, HR-4061BC (Full Color Ace), HR-4035, HR-4029 (High Color Carbon Black)
