Process Principle and Formula Design of UV Vacuum Plating Coatings

Abstract

This paper details the application process of UV vacuum plating coatings, with a focus on analyzing the formula design of primers and topcoats, including the selection of oligomers, adaptation of reactive diluents, application of photoinitiators, and optimization of additives.  It also discusses the coating adaptability of different plastic substrates.  In addition, an in-depth analysis of the functional requirements for topcoats is conducted, providing theoretical guidance for the development and application of UV vacuum plating coatings.

UV vacuum plating coatings are a high-performance coating technology developed based on UV plastic coatings.  By applying a primer, vacuum plating a metal layer, and coating a topcoat on plastic substrates, they endow products with a metallic luster and excellent performance.  This technology not only conserves metal resources and reduces weight but also finds wide application in fields such as cosmetic packaging, automotive lighting, wine bottle caps, and electronic products.

I. Application Process of UV Vacuum Plating Coatings

 ✿   1. Pre-treatment of Workpieces

 ✿   2. Spraying of UV Primer

 ✿   3. Room-Temperature Leveling

 ✿   4. Infrared Leveling

 ✿   5. UV Curing

 ✿   6. Cooling of Workpieces

 ✿   7. Vacuum Plating

 ✿   8. Spraying of UV Topcoat

 ✿   9. Room-Temperature Leveling

 ✿   10. Infrared Leveling

 ✿   11. UV Curing

 ✿   12. Off-line Inspection and Packaging

II.  Formula Design of Primer for Photocurable Vacuum Plating Coatings

Main Functions of the Primer:

 ✿   1. Sealing the plastic substrate to prevent volatile impurities from precipitating during vacuum plating, which would otherwise affect the plating quality.

 ✿   2. Providing a smooth and flat mirror-like surface finish.

 ✿   3. Enhancing adhesion to low-polarity plastic substrates.

 ✿   4. Acting as a thermal buffer for plastic substrates with poor heat resistance.

Key Points for Primer Formula Design:

 ✿   1. Oligomer Selection:

Bifunctional or trifunctional urethane acrylates are usually used, and amino acrylates are combined to improve adhesion to plastics.

 ✿   2. Reactive Diluent Adaptation:

Monomers with low surface tension, low volume shrinkage, and the ability to moderately swell plastics should be selected.   The adaptive monomers for different substrates are as follows:

❖ PC  : HDDA, Urethane Monoacrylate, NPG(PO)2DA, DPGDA, Ethoxylated Phenoxy Acrylate

❖ ABS  : HDDA, NPG(PO)2DA

❖ PMMA  : HDDA, Urethane Monoacrylate, NPG(PO)2DA, DPGDA, Ethoxylated Phenoxy Acrylate

❖ PVC  : HDDA, Urethane Monoacrylate, Ethoxylated Phenoxy Acrylate, Lauryl Acrylate, EHA

❖ PS  : HDDA

❖ PE/PP  : Octadecyl Acrylate (ODA)

 ✿   3.  Photoinitiators

The main photoinitiators used are 1173 and 184;  benzophenone and tertiary amines can be added to alleviate oxygen inhibition and improve surface drying performance.

III.  Key Properties of Topcoat for Photocurable Vacuum Plating Coatings

The topcoat is a protective layer applied on the vacuum-plated film, which must meet the following requirements:

 ✿   1.  Excellent adhesion to the metal plating film;

 ✿   2.  Good wear resistance, scratch resistance, and chemical resistance;

 ✿   3.  No components that corrode the metal plating film;

 ✿   4.  High transparency and gloss to highlight the metallic texture.

The formula design of the topcoat needs to balance functionality and decorativeness.   The technical details of photocurable metal coatings will be further discussed in subsequent sections.

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