Ultraviolet (UV) curable coatings are used on a variety of substrates, including plastics, paper, wood, metal, glass, and composite materials. For plastic substrates, UV coatings may impart more strength, rigidity, color, and other attributes. As coating technologies advance, UV coating will continue to grow as a popular solution for improving the quality of plastic goods. Other coatings require complex heating and curing cycles that can be cost-prohibitive or too time-consuming. For example, they may require a binary curing system of the resin itself and a hardening chemical. However, UV coatings harden and cure quickly when exposed to UV light.
Learn more about the science behind UV coatings for plastics, their benefits, how they compare to other types of coatings, and Toagosei’s UV coating chemicals.
The Science Behind UV Coatings
UV curable coatings are formulated primarily with a blend of monomers and oligomers. A small percentage of the compound includes photoinitiators, pigments, and many other additives (e.g. processing aids, application aids, performance enhancers, etc.). Though only comprising a small percentage of the overall formula, the photoinitiator (sometimes called a light trigger or UV activator) is the key ingredient lending the coating its UV curing properties.
When exposed to a source of UV radiation, the photoinitiator acts as a sort of catalyst triggering the cross-linking of molecules and ultimate hardening or curing of the coating, adhesive, or sealant within a relatively short period of time. This cross-linking creates a strong polymerized network, locking the coating molecules together.
UV curing is a type of energy curing, which also consists of visible light curing and electron beam curing. UV curing occurs at wavelengths ranging from 200 to 400 nm, while visible light curing occurs at wavelengths ranging from 380 to 700 nm. Thinner coatings use shorter wavelengths, while thicker coatings require longer wavelengths for deeper penetration. The quickest, most effective wavelength for a specific UV curing application often depends on how well the LED bulb’s wavelength matches the peak of the absorption profile of the coating.
The exact curing time will vary based on the area being cured, the thickness of the resin, and the strength of the UV light. The quantity of photoinitiator used will also speed up curing time, though it may have negative consequences such as discoloration or brittleness.
Benefits of Using UV Coatings for Plastics
UV-curable resins present numerous advantages over other types of resins that either require complex curing cycles or start to harden as soon as they’re exposed to air. Some of the benefits of choosing UV coatings for plastics include:
- Aesthetic Appeal: UV coatings can be produced with a wide range of colors and visual characteristics. Coating machinery can apply the coatings in intricate patterns and designs without concerns about the products curing in the middle of the application. Once the UV coating cures, it has a glossy finish.
- Cost-Effectiveness: UV coatings can cure in very short windows of time and don’t require much manual processing or manufacturing footprint. This reduces labor costs, production cycle times, and energy consumption, making this method more cost-effective.
- Durability: As UV coatings harden, they transform into a hard, durable surface that resists scratches, abrasions, and impact damage. UV coatings can also resist various chemicals and solvents.
- Environmental Friendliness: Epoxy, binary, and solvent coatings produce harmful vapors or volatile organic compounds (VOCs), which can leach into soil and groundwater. From there, VOCs can intrude into buildings and negatively impact indoor air quality. Exposure to VOCs can also result in various adverse health effects, such as respiratory irritation, nausea, headaches, and damage to the nervous system, kidneys, or liver. UV coatings produce low to no VOC emissions, so they are better for the environment and human health, due to the lack of drying equipment and lower energy consumption when LEDs are utilized.
Industries That Rely on UV Coatings
Because UV coatings present so many advantages, they’re commonly used in a wide array of consumer, commercial, and industrial applications. Some of the industries that rely most on UV-curable resins include:
- Automotive: Car manufacturers can use UV coatings to finish plastic components for car interiors, like touchscreens, dashboard instrument panels and displays, door components, consoles, and control knobs and buttons. Aftermarket refinish products also depend on UV-curable coatings for body fillers and headlight lenses.
- Electronics: Manufacturers can apply UV coatings to protect phones, tablets, and other electronic surfaces. Our UV conformal coating, Aronix® UVX-5800, protects PCBs and FPCs from water, dust, and other contaminants to prevent short circuits.
- Food and Beverage: Manufacturers use UV coating technology to apply designs and labels to metal beverage cans and other containers.
- Wood Flooring: Manufacturers of UV coatings produce impact and scratch-resistant coatings for wood flooring.
- Furniture Coatings: Manufacturers of UV coatings supply coatings that increase gloss and scratch resistance in the furniture market.
Comparing UV Coatings With Other Coating Types
UV-curable resins are just one option manufacturers can use to finish goods. Potential limitations of UV coating include the need for specialized equipment and the possibility of shadowing issues during application. However, UV coatings present many advantages over other options, such as:
- Powder Coatings: This option doesn’t work on many plastic materials, and the finished coating can degrade with exposure to UV light and other elements. Powder coating also requires more preparation in the form of surface pretreatment, priming, and masking.
- Solvent-based Coatings: Solvent-based coatings are designed to cure via evaporation when exposed to oxygen. These solvents produce more VOCs and require longer cure times than UV coatings, producing a potential bottleneck in your operations. This method is best saved for specialty applications when no other coating is an option.
- Water-based Coatings: While water-based coatings can be more environmentally friendly, they don’t last as long and don’t offer the same protective benefits. Water-based coatings also take longer to cure than UV coatings.
Toagosei’s UV Coating Offerings
Toagosei develops a growing range of UV coating chemicals for different commercial and industrial applications. Our popular UV coating chemicals for plastics include:
- DPHA: Our DPHA chemicals used in plastic coatings include M-404 and M-940.
- Urethane Adducts: Our urethane adducts have good transparency, hardness, and a narrow viscosity range.
- THEICs: M-313 or M-923 can be mixed with M-5300, M-5400, or M-5700 for improved adhesion to plastics. M-313 and M-923, in addition to urethane acrylates like Aroni TJ-UA 20024, are often used in automotive lens coatings.
- Oxetanes: Used in UV-cured epoxies, oxetanes adhere well to a range of plastics as well as “direct to metal” for beverage cans and other decorative or protective metal applications.
| UV Coating Chemical | Properties | Applications |
|---|---|---|
| DPHA: M-404, M-940 | High transparency | Plastics Flexographic plates Lithographic inks |
| Urethane Adducts | Good transparency and hardness Narrow viscosity range | Plastics |
| THEICs: M-313, M-923 | High transparency Low film curl Good adhesion | Plastics Hard protective coatings |
| Oxetanes | Cationic curable resins used in UV-cured epoxy chemistries High reactivity Good adhesion | Plastics Metal |
Transform Your Products With Toagosei’s UV Coating Expertise
UV coatings can produce a hard protective surface layer, cure faster, and have more aesthetic appeal than most other coating options. In the future, UV coating technology will continue to become more energy-efficient and speed up curing times, growing in popularity as an eco-friendly alternative to traditional coating methods. Contact Toagosei America for help finding the right UV coating chemical for your next project.