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Selection of Raw Materials for Tin-Free UV Resins

Release time:

2026-08-24 23:19

The selection of raw materials for tin‑free UV resins involves a systematic approach, spanning oligomer backbones, alternative catalytic systems, reactive diluents, and additives. Unlike conventional UV resins, the hallmark of tin‑free formulations lies in employing non‑tin catalysts to synthesize polyurethane acrylates, while integrating environmentally friendly attributes—such as waterborne formulation, benzene‑free composition, low MEHQ content, and bio‑based components—into the recipe design. The choice of each raw material directly influences the resin’s catalytic efficiency, product transparency, and the performance characteristics of the resulting coating.

I. Oligomer Backbone

Oligomers are film-forming substances that do not contain tin and serve as the base resin, determining the fundamental performance of the coating. Depending on their functionality, these products span a broad range, from difunctional to dec functional.

High‑functionality aliphatic polyurethane acrylates are suitable for high‑hardness, highly wear‑resistant coating formulations. These multi‑functional products outperform standard grades in scratch resistance, abrasion resistance, and hardness, while maintaining excellent flexibility. Free of tin, they are recommended for high‑hardness coating formulations used in in‑mold decoration, as well as for film coatings on window films and flat‑panel displays, and for automotive plastic interior components.

Medium- and low‑functionality systems emphasize flexibility and adhesion. Bis‑functional aliphatic polyurethane methacrylates exhibit low intrinsic viscosity, facilitating formulation, and are free of harmful substances such as organotin compounds and heavy metals. Bis‑functional polyurethane acrylates are suitable for both clear and pigmented coatings on a wide range of substrates, including wood, plastics, and metals.

Our waterborne dispersion products utilize swellable particle technology, offering both excellent adhesion and flexibility. They can be directly applied to a wide range of plastic substrates and are suitable for consumer electronics, automotive interiors, and flooring materials.

II. Alternative Catalytic Systems

The alternative catalytic system is the technological core of tin-free products. Conventional polyurethane synthesis relies on organotin catalysts, which are subject to stringent restrictions under numerous environmental regulations.

The bismuth‑salt catalytic system, comprising bismuth salts in combination with specific acids, enables the synthesis of tin‑free, radiation‑curable aqueous polyurethane dispersions, which react with organic polyisocyanates in the presence of bismuth salts and acids.

Highly compatible bismuth catalysts address the poor compatibility between conventional organobismuth compounds and polyester polyols, which typically causes resin turbidity and haze. The resulting UV‑curable resins exhibit excellent transparency and light coloration, with catalytic activity comparable to that of organotin catalysts.

The hydrolysis‑resistant, environmentally friendly catalyst is free of tin and complies with environmental regulations. It exhibits excellent compatibility with both polyester and polyether polyols and remains stable during long-term storage in aqueous formulations. It is recommended for the synthesis of UV‑curable polyurethane–acrylic resins.

III. Reactive Diluents

Reactive diluents are used to adjust resin viscosity and participate in the curing reaction. Tin-free UV resins employ a solvent-free formulation, replacing organic solvents with reactive monomers.

Common diluents include various acrylic ester monomers; some products use specific monomers as diluents, while others explicitly state that no particular monomer is used to minimize skin irritation. Water-based dispersion products use deionized water as the diluent, achieving zero VOC emissions.

IV. Other Raw Material Components

In terms of photoinitiators, the tin-free UV resin is compatible with a wide range of photoinitiator systems and can cure under various energy sources, including UV mercury lamps and LED‑UV. The waterborne dispersion products are formulated with a neutral or mildly alkaline pH and exhibit excellent compatibility with numerous photoinitiators.

In terms of functional additives, aliphatic isocyanates impart non‑yellowing properties and outdoor durability to the resin. Some formulations are free of hydroquinone and MEHQ to minimize skin sensitization. Epoxy acrylate systems can incorporate both acrylate and epoxy functionalities, enabling dual curing via a hybrid radical–cationic photoinitiator system.

V. Conclusion

The selection of raw materials for tin‑free UV resins involves a systematic integration of oligomer backbones, alternative catalytic systems, reactive diluents, and additives. High‑functionality aliphatic systems deliver hardness and abrasion resistance, while low‑functionality systems emphasize flexibility; the substitution of organotin catalysts with bismuth salts and non‑tin alternatives represents a key differentiator; and solvent‑free formulations and waterborne dispersions enable low VOC levels. As environmental regulations continue to tighten, the development of tin‑free UV resin feedstocks is increasingly oriented toward higher bio‑based content, lower VOC emissions, and broader curing windows.

Disclaimer: The above content has been compiled from publicly available sources and is provided for reference only. If any infringement occurs, please contact us, and we will address it promptly.

Bossin Related Product Recommendations – Eco-Friendly
Tin-free
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-221X	Aliphatic polyurethane acrylate	Tin-free, fast-curing, and resistant to boiling water.
B-368X	Aliphatic polyurethane acrylate	Tin-free, excellent leveling, excellent flex resistance, and good heat resistance.
B-6211	Aliphatic polyurethane acrylate	Fast curing, high hardness, scratch-resistant, and free of organotin.
B-919BX	Aliphatic polyurethane acrylate	Tin-free, high hardness, chemically and abrasion-resistant, with excellent toughness.
Benzene-free
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-153	Modified epoxy acrylate	Good flexibility, excellent pigment wetting, and strong adhesion.
B-21	Active amine photosensitizing promoter	Low color number, benzene-free, antioxidant and polymerization inhibitor, enhances curing rate.
B-27	Active amine photosensitizing promoter	Low color number, benzene-free, low odor, antioxidant and polymerization inhibitor
B-371	Aliphatic polyurethane acrylate	Good surface drying, excellent flexibility, and excellent gloss retention.
B-574	Polyester acrylate	Benzene-free, low-odor, and VOC levels meet cigarette-packaging standards.
Low MEHQ
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-151DM	Modified epoxy acrylate	Low halogen, yellowing-resistant, excellent plating performance, and strong adhesion.
B-376	Aliphatic polyurethane acrylate	LED yellowing is minimal, and the nail polish formulation exhibits excellent stability.
BM1211 (HPMA)	Hydroxypropyl methacrylate	HEMA-free, high strength, low irritation, and excellent adhesion
Bio-based
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-106	Acrylated epoxidized soybean oil resin	The pigment exhibits excellent wettability and is biodegradable after curing.
B-296SW	Aliphatic polyurethane acrylate	Yellowing resistance, impact resistance, bio-based content > 40%
BM3384 (3PO-GPTA)	Propylene glycol triacrylate	Good flexibility, low irritation, and excellent pigment wetting.
No TMPTA
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-151DM	Modified epoxy acrylate	Low halogen, yellowing-resistant, excellent plating performance, and strong adhesion.
B-153	Modified epoxy acrylate	Good flexibility, excellent pigment wetting, and strong adhesion.
B-162	Epoxy acrylate	Fast curing, low odor, high gloss, and high fullness.
B-166A	Modified epoxy acrylate	Good flexibility and strong adhesion
B-166A-85	Modified epoxy acrylate	Good flexibility, excellent adhesion, contains 15% HEMA.
B-166A-85P	Modified epoxy acrylate	Good flexibility, excellent adhesion, contains 15% HEMA.
B-207X	Aliphatic polyurethane acrylate	Medium molecular weight, low odor, and excellent flexibility.
B-27	Active amine photosensitizing promoter	Low color number, benzene-free, low odor, antioxidant and polymerization inhibitor
B-296	Aliphatic polyurethane acrylate	Fast curing, chemical resistance, yellowing resistance, impact resistance
B-376	Aliphatic polyurethane acrylate	LED yellowing is minimal, and the nail polish formulation exhibits excellent stability.
B-412T-6	Aliphatic polyurethane acrylate	Good toughness, free of organotin compounds, and excellent stability of the nail polish formulation.
B-546	Polyester acrylate	Good adhesion, fast curing, and excellent flexibility.
B-619W	Aliphatic polyurethane acrylate	Fast curing, high hardness, excellent toughness, wear resistance, and chemical resistance.
No HEMA
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-151DM	Modified epoxy acrylate	Low halogen, yellowing-resistant, excellent plating performance, and strong adhesion.
B-162	Epoxy acrylate	Fast curing, low odor, high gloss, and high fullness.
B-207X	Aliphatic polyurethane acrylate	Medium molecular weight, low odor, and excellent flexibility.
B-27	Active amine photosensitizing promoter	Low color number, benzene-free, low odor, antioxidant and polymerization inhibitor
B-296	Aliphatic polyurethane acrylate	Fast curing, chemical resistance, yellowing resistance, impact resistance
B-376	Aliphatic polyurethane acrylate	LED yellowing is minimal, and the nail polish formulation exhibits excellent stability.
B-412T-6	Aliphatic polyurethane acrylate	Good toughness, free of organotin compounds, and excellent stability of the nail polish formulation.

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Synthesis process of tin-free UV resin

Key points for using tin-free UV resin