Selection principle and scheme of water-based ink (ink wash) dispersant
I、 Three main types of dispersants (ink specific)
1. Anionic polyacrylate dispersant (low-cost)
Representative: RK-4046
-Features: Fast viscosity reduction, low price, good dispersion effect of inorganic pigments such as titanium dioxide/calcium carbonate
-Disadvantages: poor water resistance, pigment particles are easy to flocculate when encountering calcium and magnesium ions, carbon black/phthalocyanine has poor color development, and foam is too large
-Addition amount (pigment powder): inorganic 3%~10%; Organic 10%~20%; Carbon black is not recommended as an alternative
-Applicable: Low end corrugated cardboard boxes with acrylic ink, white filler ink, and paper products without water resistance requirements
-Prohibited: Soft packaging PU ink, food ink, high water resistance film coating system
2. Polymer polyurethane block copolymer (with strong steric hindrance, suitable for high-end main players)
Representative: RK-4039AC, RK-4057
-Advantages: Its molecules contain highly binding adsorption groups, which can firmly grasp surface inert and easily agglomerated high difficulty pigments (such as carbon black, phthalocyanines, quinacridone), thereby achieving efficient and stable dispersion; Stable storage in a wide range of acid-base and salt environments (pH 4-11), long-lasting pigment dispersion, and high gloss color performance after film formation, with good water resistance and film adhesion.
-Disadvantage: Higher unit price
-Addition amount: 12%~30% for ordinary organic pigments; Phthalocyanine/high pigment carbon black 30%~75%
-Applicable: Soft packaging BOPP/PET ink, high gloss cardboard, resin free color paste, food grade ink
3. Non ionic polyether dispersant (compound auxiliary/non ion sensitive system)
Representative: RK-4061ED low foam wetting and dispersing two in one
-Features: Good low foaming performance, avoiding defects such as pinholes and fish eyes in the coating; Simultaneously compatible with cationic and anionic additives, no reaction occurs; It will not cause demulsification of PU lotion and has good re solubility.
-Disadvantage: Insufficient strength of dispersed high pigment carbon black alone, generally used as a synergistic additive
-Addition amount: 0.2%~0.7% of the total formula for compound use
-Applicable: PU film ink, transparent varnish, dye ink, easy foaming high-speed printing system
II、 Match according to the ink resin system
1. Rosin modified acrylic acid (low-grade ink for corrugated cardboard boxes)
Prioritize the use of polycarboxylates for cost; Export/High gloss cardboard boxes switched to polyurethane type
2. Pure acrylic acid/styrene (cardboard, labels, high gloss paper)
Polyurethane polymer dispersant enhances the blackness, glossiness, and storage stability of the system
3. Water based PU polyurethane ink wash (BOPP/PET/PE flexible packaging)
It is prohibited to use a large number of anionic salts, which may cause lotion demulsification and viscosity explosion; We mainly promote non-ionic/amphoteric polyurethane dispersants to improve boiling resistance and stabilize the composite adhesion of different substrates
4. Resin free concentrated color paste
Specialized non-ionic polymer polyurethane dispersant achieves technical characteristics of low viscosity during high solid content grinding and long-term storage without thickening or delamination through multi-point anchoring and long-chain steric hindrance mechanism
III、 Accurate selection based on pigments (core matching criteria)
1. Inorganic pigments (titanium dioxide, iron oxide, calcium carbonate) - Low cost cardboard box: anionic polycarboxylate dispersant;
-Film coating/high water resistance white ink: modified polyurethane dispersant to avoid later water absorption and whitening
2. Ordinary organic pigments (bright red, medium yellow, perpetual yellow)
Universal polyurethane dispersant; Adding a small amount of anionic compound can reduce costs when the budget is limited
3. Difficult to disperse organic pigments (phthalocyanine blue/green, permanent violet)
High anchoring polyurethane/polyester dispersants must be selected to prevent floating color coagulation, insufficient dispersion, difficulty in meeting fineness standards, and poor glossiness.
4. Carbon black (ink is the most difficult to disperse) - Low pigment carbon black (ordinary black ink for cardboard boxes): Anion+polyurethane compound
-High pigment furnace black/groove black (thin film high gloss black): a polymer polyurethane dispersant specifically designed for carbon black
The larger the specific surface area of charcoal black, the higher the amount of dispersant added, up to 80% of the pigment
IV、 Screening by post printing process of printing substrate
1. Corrugated paper and absorbent paper
Low water resistance requirements and the most cost-effective anionic dispersant; Export food cardboard boxes to replace polyurethane dispersants
2. BOPP and PET plastic films (requiring dry lamination)
Full process polyurethane dispersant, strictly controlling the residual content of low molecular weight anionic additives to prevent adhesion failure (delamination) and surface hardness decrease (poor friction resistance) between the film layer and substrate due to migration aggregation, moisture absorption plasticization, and interface repulsion.
3. Matte low surface energy PE film
The combination of high anchoring polyurethane dispersant and low foaming non-ionic wetting agent can avoid two types of appearance defects during construction, namely, the shrinkage and exposure of the paint film edge (shrinkage edge) and the uneven distribution of pigments, which can form stripes (flower), ensuring the integrity and uniform color of the coating.
4. Food contact, cooking and water-resistant ink
Recommendation: APEO free, low VOC polyurethane dispersant, mineral oil compound anionic dispersant is prohibited
5. Water based varnish, transparent clear ink
Recommendation: Low foam polyurethane/non-ionic polyether dispersant; It means that in the preparation of optical transparent materials (such as films, coatings, electrolyte gel), it is necessary to control the concentration or aggregation state of free anions to prevent them from causing micro phase separation or the formation of scattering centers, which will lead to increased light diffusion and decreased transparency (increased haze).
V、 Standard addition amount and feeding sequence
Addition amount (based on the weight of pigment powder)
-Titanium dioxide/filler: 3%~7%
-Ordinary organic pigments: 12%~25%
-Phthalocyanine, high-end organic color powder: 18%~38%
-High pigment carbon black: 35%~75%
Optimal feeding sequence (maximizing dispersion effect)
Deionized water → dispersant → wetting agent → small amount of defoamer → stirring evenly → adding pigment powder → high-speed pre dispersion → sanding
It is strictly prohibited to add pigments first and then dispersants, as the powder cannot be fully wetted and directly coagulates and aggregates.
VI、Quick Selection Comparison Table
Ink painting scene
| Preferred dispersant type not available | Recommended Type |
Ordinary corrugated cardboard box, low-cost colored ink | Anionic polyacrylic acid salt | High-grade pure polyurethane |
High gloss cardboard, labels, export cartons | General polymer polyurethane | Small molecule anion |
BOPP/PET flexible packaging, dry composite | Bipolar/non-ionic polyurethane | High content anionic dispersant |
PE/PP difficult to adhere film black ink | Carbon black specific high anchoring polyurethane | Polycarboxylate salt |
Food, cooking, water-resistant ink | APEO free polymer polyurethane | Mineral oil complex anion |
Resin free high solid color paste | Multi functional non-ionic polyurethane | Low molecular weight anions |
Practical compounding techniques
1. Universal paper box ink compound: 30% polyurethane+70% anionic polycarboxylate, balancing cost and gloss stability;
2. Standard solution for film ink painting: 100% polyurethane dispersant, without anions, ensuring composite performance;
3. Testing principle: Gradient addition of dispersant, conduct thermal storage at 50 ℃ for 7 days to verify stability, fineness, color development, and film peeling before mass production.
VII、Corresponding selection plan for common drawbacks
1. The grinding fineness cannot be reduced, and the molecules cannot completely cover the surface of the pigment, resulting in the dominant attraction between particles and agglomeration: the amount of polyurethane dispersant is insufficient, so the addition ratio should be increased.
2. Water based ink storage for 7 days resulted in flocculation failure due to charge neutralization between anionic dispersants and positive ions in the system, leading to precipitation/stratification. The polyurethane polymer was replaced.
3. Floating color, color separation, and printing color difference occur in colored ink: Anionic dispersants simultaneously adapt to inorganic/organic pigments, resulting in poor stability during blending, causing floating color and color difference. Therefore, universal polyurethane should be used instead.
4. For the problem of too much grinding foam and clogging of filter screen/spray plate, increase the proportion of low foam non-ionic dispersant and reduce the amount of high foam anionic surfactant to inhibit the formation of foam and ensure the continuity of production.
5. Black ink graying and insufficient blackness: Carbon black specific polyurethane dispersant enhances the adsorption (anchoring) and spatial barrier (wrapping) of molecules on the surface of carbon black, allowing the carbon black to fully decompose and aggregate to release maximum blackness.
6. Poor adhesion and delamination of the film after printing: excessive addition of small molecule anionic dispersants reduces the amount of polycarboxylate used
