UV Flexo Ink Formulation Analysis

Date: Mar 25 2025 From: Star Color Views:

UV flexographic inks (ultraviolet-curable flexographic printing inks) are a type of ink that achieves rapid curing through chemical reactions initiated by ultraviolet (UV) light. They are characterized by fast drying speed, good environmental friendliness, and strong printing adaptability, widely used in packaging printing, label printing, and other fields. Their formulations mainly consist of resins (prepolymers), reactive diluents (monomers), photoinitiators, pigments, fillers, and additives, with the roles and common types of each component detailed below:

Typical UV Flexo ink Formulation Example (for Plastic Film Printing)

Component	Content (%)	Function Description
Polyurethane acrylate prepolymer	40–50	Provides flexibility and adhesion
Tri-functional monomer (TMPTA)	20–25	Increases crosslink density and curing speed
Photoinitiators (Irgacure 184 + TPO)	3–5	Rapid curing initiation, yellowing resistance
Organic pigment (e.g., phthalocyanine blue)	8–12	Imparts color
Silica filler	2–5	Adjusts thixotropy
Leveling agent (silicone-based)	0.5–1	Improves leveling
Adhesion promoter	1–2	Enhances adhesion to PP films

1. Resins (Prepolymers) — Film-Forming Matrix

Resins are the core component of inks, determining the basic properties of the ink (such as adhesion, hardness, flexibility, gloss, etc.) and forming a continuous ink film after curing.

Common Types:
1. Acrylate-Based Prepolymers
  - Epoxy acrylates: High hardness and strong adhesion, commonly used for substrates like paper and plastics, but with poor flexibility.
  - Polyurethane acrylates: Excellent flexibility and wear resistance, suitable for substrates requiring tensile resistance, such as films and metal foils.
  - Polyester acrylates: High gloss and chemical resistance, often used in high-gloss products or packaging printing requiring solvent resistance.
2. Other Types: Such as siloxane acrylates (low surface energy, suitable for difficult-to-adhere substrates) and water-based acrylates (environmentally friendly, low VOCs).
Functions:
- Provide film-forming properties and mechanical strength to the ink.
- Regulate ink viscosity, leveling, and printability.

2. Reactive Diluents (Monomers) — Viscosity Adjustment and Crosslinking

Reactive diluents are low-molecular-weight compounds with reactivity, used to reduce ink viscosity (for easy printing) and participate in photopolymerization reactions, affecting curing speed and film properties.

Common Types:
- Mono-functional monomers: Such as 2-ethylhexyl acrylate (EHA), with strong diluting ability, slow curing speed, and improved film flexibility.
- Di-functional monomers: Such as 1,6-hexanediol diacrylate (HDDA), balancing diluting ability and curing speed while enhancing film hardness.
- Multi-functional monomers: Such as trimethylolpropane triacrylate (TMPTA), with fast curing speed and high film hardness, but lower flexibility.
Functions:
- Adjust ink viscosity to improve printing fluidity (e.g., adapting to the transfer characteristics of anilox rollers in flexography).
- Increase crosslink density in the system, influencing post-cure wear resistance and chemical resistance.

3. Photoinitiators — Core of Curing Reaction

Photoinitiators generate free radicals or cations under UV irradiation, initiating crosslinking reactions between prepolymers and monomers to cure the ink.

Common Types:
1. Free Radical Photoinitiators
  - Benzophenones: Such as benzophenone (BP), requiring amine co-initiators, suitable for dark-colored inks (strong light absorption).
  - α-Hydroxyketones: Such as 1-hydroxycyclohexyl phenyl ketone , with high initiation efficiency, suitable for transparent or light-colored inks.
  - Acylphosphine Oxides: Such as 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO), suitable for thick film layers or white inks (excellent yellowing resistance).
2. Cationic Photoinitiators: Such as aromatic diazonium salts and triarylsulfonium salts, used in special systems (e.g., epoxy-based inks) with oxygen-inhibition-free curing.
Functions:
- Determine curing speed, curing depth, and adaptability to different substrates.
- Need to match the UV light source wavelength (e.g., 365nm, 395nm) of printing equipment.

4. Pigments and Fillers — Color and Performance Enhancement

Pigments:
- Types: Organic pigments (e.g., azo, phthalocyanine, vibrant colors) and inorganic pigments (e.g., titanium dioxide, carbon black, high hiding power).
- Functions: Provide ink color, hiding power, and gloss, affecting ink fluidity and curing speed (e.g., dark pigments may absorb more UV light, slowing curing).
Fillers:
- Types: Silica, calcium carbonate, talcum powder, etc.
- Functions: Adjust ink thixotropy and wear resistance, reduce costs (e.g., used in matte inks or to increase film thickness).

5. Additives — Key to Performance Optimization

Additives are used to improve ink printability, curing performance, or special functions, typically accounting for 0.1%–5% of the formulation.

Common Types and Functions:
1. Leveling agents: Such as silicone or acrylate-based agents, improving ink leveling and reducing craters and orange peel effects.
2. Defoamers: Silicone or non-silicone types, eliminating bubbles generated during ink production and printing.
3. Adhesion promoters: Such as silane or titanate coupling agents, enhancing ink adhesion to substrates (e.g., low-surface-energy materials like PE, PP).
4. Dispersants: Preventing pigment agglomeration, improving pigment dispersion stability, and enhancing ink hue and gloss.
5. Inhibitors: Such as hydroquinone, inhibiting spontaneous crosslinking of prepolymers during storage to extend shelf life.
6. Plasticizers: Such as phthalates, improving film flexibility and preventing cracking (note environmental regulatory restrictions).
7. Antistatic agents: Reducing electrostatic accumulation during printing, suitable for insulating substrates like plastic films.

Zhongzhixing Color has been dedicated to the sustainable development of the printing industry for many years, constantly improving ink formulations and developing more environmentally friendly printing inks. In UV flexo ink research and development, our continuous innovation has received widespread user acclaim in practical applications. Contact us today to obtain the FDA test report for our UV flexographic ink.