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Typical Defects of UV Resins on Difficult-to-Bond Substrates (Part 1)

Release time:

2026-10-08 06:36

Typical Defects of UV Resins on Difficult-to-Bond Substrates (Part 1)

Insufficient adhesion is a typical defect in the application of UV‑curable resins to difficult‑to‑bond substrates, manifesting as coating delamination or lifting from the substrate surface. Although these resins are specifically formulated to address adhesion challenges on low‑surface‑energy plastics, substandard adhesion can still occur in practice due to various factors. This defect directly results in unacceptable product appearance and reduced reliability, making it a critical issue that requires close attention during the coating process.

I. Manifestations of Insufficient Adhesion

Insufficient adhesion manifests as inadequate interfacial bonding between the coating and the substrate, leading to delamination of the coating from the substrate surface under external forces. Delamination may initiate at the edges and progress inward, or it may occur as large‑area, sheet‑like detachment. Warping, on the other hand, is characterized by the coating edges lifting away from the substrate surface, creating visible gaps. Insufficient adhesion can become apparent immediately after coating application or may gradually emerge during subsequent processing or service. In cases where initial adhesion is adequate but durability is lacking, the underlying causes often include unstable chemical bonding at the interface or excessive shrinkage stresses arising during coating curing.

II. Improper Dosage of Adhesion Promoter

Improper dosage of adhesion promoters is a common cause of insufficient adhesion. For substrates that are difficult to bond, UV‑curable resins rely on adhesion promoters to establish interfacial adhesion between the coating and the substrate; the amount of promoter used directly affects the strength of the interfacial bond.

When the dosage is too low, the accelerator fails to generate sufficient interfacial adhesion, resulting in inadequate interfacial bonding between the coating and the substrate and leading to easy delamination under external forces. Conversely, when the dosage is excessive, the surplus accelerator may compromise the coating’s intrinsic cohesive strength, turning the internal structure into a weak link; failure then occurs within the coating rather than at the interface, again manifesting as poor adhesion. Therefore, the amount of accelerator must be carefully controlled to strike a balance between interfacial adhesion and the coating’s internal cohesive strength.

III. Insufficient Curing Energy

Insufficient curing energy is another major cause of inadequate adhesion. Adhesion promoters must fully participate in the curing reaction to firmly anchor their functional groups within the polymer network and effectively facilitate interfacial bonding.

When the curing energy is insufficient, the photoinitiator decomposes incompletely, resulting in a low free-radical yield and an inadequate degree of polymerization. The adhesion promoter fails to participate fully in the curing reaction, leading to incomplete chemical bonding at the interface and an interfacial bond strength that falls short of the desired level. Moreover, the coating itself exhibits insufficient crosslinking density and reduced cohesive strength; even if interfacial adhesion remains acceptable, the coating may still suffer internal failure.

4. Uneven surface treatment of the substrate or degradation of its performance

Surface treatment of the substrate is a critical step in coating on difficult-to-bond substrates, and its effectiveness directly influences adhesion. For polyolefin substrates, corona treatment or plasma treatment can increase surface energy, thereby enhancing paint wetting and adhesion.

When surface treatment is uneven, the surface energy varies across different areas of the substrate, leading to poor wetting and inadequate adhesion in regions with lower surface energy. The effectiveness of the treatment diminishes over time; if the treated substrate is not coated within the specified timeframe, its surface energy declines, making it difficult to achieve satisfactory adhesion—even when using UV‑curable resins designed for challenging substrates. In high‑humidity environments, the degradation of treatment performance accelerates, imposing stricter requirements on production scheduling.

V. Areas for Improvement

To address the issue of insufficient adhesion, improvements can be pursued from two perspectives: formulation design and process control. In terms of formulation, optimize the dosage and type of adhesion promoters to strike a balance between interfacial bonding strength and coating cohesive strength. From a process standpoint, ensure that the curing energy is adequate and stable, and regularly verify the output energy of the light source. Surface treatment of the substrate should be uniform, and coated promptly after treatment to prevent degradation of the treatment effect. For applications with stringent adhesion requirements, consider combining a primer with an integrated formulation to enhance interfacial bonding through multiple mechanisms.

VI. Conclusion

Insufficient adhesion is a typical defect in UV‑curable resin applications on difficult‑to‑bond substrates, arising from factors such as improper dosage of adhesion promoters, inadequate curing energy, and uneven or degraded surface treatment of the substrate. The amount of promoter must be precisely controlled to strike a balance between interfacial bonding strength and coating cohesion; sufficient and stable curing energy is essential to ensure complete participation of the promoter in the reaction; and surface treatment should be uniform and completed promptly before coating to prevent loss of effectiveness. In practical production, systematic troubleshooting—addressing both formulation optimization and process control—is required to ensure a strong, durable bond between the coating and the substrate.

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.

Boxing 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, excellent flexibility, and superior 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	Excellent adhesion to plastics, good dilutability, and low volatility.

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Typical Defects of UV Resins on Difficult-to-Adhere Substrates (Part 2)

Applications of UV Resins on Difficult-to-Bond Substrates