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Types of UV Resins with Poor Adhesion to Substrates (I)

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2026-09-29 07:13

Types of UV Resins with Poor Adhesion to Substrates (I)

UV resins for difficult-to-bond substrates can be classified in various ways, with categorization by substrate type offering a straightforward and practical framework. Different plastic substrates exhibit significant differences in surface energy, crystallinity, chemical inertness, and micro‑morphology, each of which dictates distinct priorities in resin formulation. Polyolefin substrates require solutions to wetting and physical anchoring challenges, polyester substrates demand control of curing‑induced shrinkage stresses, and fluoropolymers necessitate specialized low‑surface‑energy compatibility systems. Understanding resin types from the perspective of their intended substrates helps quickly identify the most suitable product for a given application.

I. Polyolefin-Specific Type

The polyolefin‑specific type is one of the more mature categories within UV‑curable resins for difficult‑to‑adhere substrates, primarily targeting polypropylene and polyethylene. These substrates typically exhibit surface energies lower than the surface tension of conventional coatings, resulting in poor wetting, large contact angles, and challenging spreading. Moreover, polyolefins are highly crystalline and have smooth surfaces, lacking the micro‑roughness necessary for mechanical anchoring.

Polyolefin‑specific resins typically use chlorinated polyolefins as the core component. Chlorinated polypropylene shares a molecular structure similar to that of polypropylene, enabling it to form strong interfacial adhesion with the substrate in accordance with the principle of “like dissolves like.” Chlorinated polyolefins can penetrate the substrate surface, creating physical entanglements and forming surface crystallization, thereby enhancing peel strength. By grafting polar functional groups such as maleic anhydride onto chlorinated polypropylene, its compatibility with UV‑curable resins and its reactivity can be further improved.

Depending on the application, polyolefin‑specific formulations can be further categorized into primer‑type and one‑step formulation types. Primer‑type systems are applied to the substrate surface prior to UV coating as adhesion promoters, forming a bridging layer. These treatment agents enhance substrate wettability and surface energy while strengthening the bond between the substrate and the UV coating, thereby ensuring a robust connection between the paint film and the substrate. In contrast, one‑step formulations incorporate chlorinated polyolefins directly into the UV resin matrix, enabling the coating to achieve adhesion to the substrate concurrently during curing. This approach simplifies the application process but places higher demands on formulation design. A blended system of chlorinated polyolefins and acrylic resins is compatible with both polypropylene and ABS substrates, allowing for co‑line spraying and reducing the time required for line changeovers and adjustments.

II. Polyester-Specific Type

The polyester‑specific formulation is designed to meet the coating requirements of polyester films and sheets. Although the surface tension of polyester is slightly higher than that of polyolefins, its high crystallinity and chemical stability likewise make adhesion challenging. During UV curing, the primary challenge for polyester is not inadequate wetting but rather interfacial stresses arising from volumetric shrinkage of the coating.

During UV curing, as the resin transitions from a liquid to a solid state, volumetric shrinkage occurs, generating internal stresses. These stresses concentrate at the interface between the coating and the substrate; when the stress exceeds the interfacial adhesion strength, the coating delaminates from the substrate. For polyester substrates, the root cause of adhesion issues often lies in the interfacial stresses induced by volumetric shrinkage.

Polyester‑specific formulations reduce coating volume shrinkage by incorporating cyclic acrylates. The cyclic structure buffers volumetric changes during polymerization, thereby lowering the cure‑shrinkage rate and correspondingly reducing interfacial stresses. Monomers such as isobornyl acrylate, which possess bulky, rigid side groups, can significantly minimize short‑chain and long‑chain branching during polymerization; the resulting molecular regularity helps to mitigate shrinkage‑induced stresses. For substrates like polyester films that are highly sensitive to shrinkage stress, low‑shrinkage characteristics constitute a critical prerequisite for ensuring adhesion. Moreover, the surface of polyester substrates contains ester groups and terminal hydroxyls, which can form hydrogen bonds or chemical bonds with polar functional groups in the resin; this property can be leveraged in formulation design to further enhance interfacial bonding.

III. Specialized Type for Fluoropolymers

The fluoropolymer‑specific formulation is developed for ultra‑low surface energy substrates such as polytetrafluoroethylene. These substrates exhibit extremely low surface energy, making them completely unwettable and non‑adhesive to conventional UV‑curable resins; even specialized polyolefin‑compatible resins often fail to deliver satisfactory adhesion.

Fluoropolymer‑specific formulations, through the use of specialized fluorinated monomers or fluorinated resin systems, enable coatings to wet fluoropolymer surfaces. Fluorinated polyurethane acrylate oligomers can reduce the coating’s surface tension, promoting effective spreading on fluoropolymer substrates. Fluorinated acrylate monomers are also commonly employed to modulate the system’s surface energy. During film formation, these resins ensure that fluorinated segments selectively enrich at the coating–air interface, with the wetting behavior governed by a thin fluorinated surface layer while the bulk properties remain intact.

In terms of adhesion mechanisms, fluoropolymer‑specific systems typically rely on a dual strategy that combines chemical and physical anchoring. Some formulations introduce specific functional groups that can interact with the fluoropolymer surface, forming chemical bonds at the interface. Simultaneously, by carefully controlling curing conditions, the coating develops an appropriate degree of penetration and anchoring structure on the substrate surface, thereby enhancing physical adhesion.

IV. General Purpose

The universal UV resin for difficult-to-bond substrates is designed to accommodate a wide range of low-surface-energy materials, including polyethylene, polypropylene, polyester, and thermoplastic polyurethane. In actual production, a single production line may need to process multiple substrates; a universal formulation helps minimize quality fluctuations caused by substrate changes.

These resins typically employ either organosilicon‑modified systems or composite adhesion promoters. Organosilicon‑modified systems leverage the low surface tension of polysiloxanes, while acrylate‑modified polydimethylsiloxane combines the low surface tension of organosilicon with the photocurable reactivity of acrylates, enabling wetting and adhesion on a wide range of low‑surface‑energy substrates. Composite adhesion promoters, by contrast, rely on the synergistic interplay of multiple mechanisms to meet the adhesion requirements of diverse substrates. Although general‑purpose formulations may exhibit slightly inferior adhesion on single substrates compared with specialized products, their broad compatibility facilitates production models characterized by multiple product varieties and small batch sizes.

V. Conclusion

Based on the substrate type, UV‑curable resins for difficult-to-bond substrates can be categorized into polyolefin‑specific, polyester‑specific, fluoropolymer‑specific, and general‑purpose formulations. Polyolefin‑specific resins use chlorinated polyolefins as the core to address wetting and physical anchoring issues; polyester‑specific resins employ cyclic acrylates to control curing‑induced shrinkage stresses; fluoropolymer‑specific resins incorporate a specialized fluorine‑containing system to match ultra‑low‑surface‑energy substrates; and general‑purpose formulations leverage organosilicon modifications or composite accelerators to accommodate a wide range of substrates. When selecting a formulation, it is essential to strike a balance between substrate specificity and versatility, taking into account both the substrate type and the production line configuration.

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Bossin Related Product Recommendations – Membrane Materials
Difficult to adhere to the substrate
Product Model/English Abbreviation	Product Name/Product Type	Product Features
B-186	Modified epoxy acrylate	Boil-resistant, excellent adhesion, high-temperature resistant, chemically resistant
B-509B	Polyester acrylate	Good adhesion, good flexibility, and excellent pigment wetting.
B-531	Polyester acrylate	Good adhesion, impact resistance, excellent flexibility, and yellowing resistance.
B-546	Polyester acrylate	Good adhesion, fast curing, and excellent flexibility.
B-590	Polyester acrylate	Good adhesion, fast curing, and excellent pigment wetting.
BM2224 (EO-HDDA)	Ethoxylation of 1,6-hexanediol diacrylate	It exhibits excellent adhesion to plastics, good dilutability, and low volatility.

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Types of UV Resins with Poor Adhesion to Substrates (Part II)

Main directions for UV resins on difficult-to-adhere substrates