Hydrophilic coatings applied to medical devices provide lubricity, which improves medical device efficiency, and reduces tissue damage during operational procedures. The benefits of hydrophilic coatings for medical devices is unquestioned. However, the best way to dry and cure these coatings is up for debate. When it comes to medical coatings, there are two main ways they can be dried and cured. These are thermal curing and UV curing. The question becomes, which one should you pick: UV coating vs Thermal coating? If you are unsure which type of coating to choose for your application, you are in the right place.
In this article we cover the difference between curing coatings with UV light and with heat. We will dive deep into these two application methods, pros and cons of each, and learn how to choose the best coating application option based on various scenarios.
What is Thermal Coating?
Thermal coating is a process of drying or curing liquid coating in the presence of heat. Thermal curing accelerates the hardening time of the thermoset resin with the help of large thermal ovens, hot air dryers, or IR lamps.
In general, powder or thick viscous liquids of materials (ex. Bakelite) are heated under high pressure. This results in the cross-linking of polymer chains to form a solid surface coating. Sometimes, a chemical catalyst is added to boost the processing time. In addition filler materials can be added to improve the quality and properties of the final product.
Similar to UV coating, it is another method of solidifying a liquid or semi-solid substance. Thermal coatings can be applied to papers, plastics, metals, and composites and are found in many industries, from automotive to medical, including coatings for medical devices.
Thermal curing coatings is still among the best choices for applying a hydrophilic coating to medical devices.
Pros of Thermal Coating
- Extremely lubricious
- Flexible
- Extra strength and durability
- Mechanical and chemical stability
- Impressive heat resistance
- Biocompatible
- It can be applied to materials with complex shapes
- The properties of the final product can be adjusted with the help of additives and filler material
Cons of Thermal Coating
- Longer processing vs UV curing
- Higher energy consumption
- Curing equipment has a large footprint
- Heat-sensitive materials are easily damaged
- VOC emissions
What is UV Coating?
Ultraviolet coating, commonly known as UV coating, is a process in which a liquid coating is cured in the presence of ultraviolet light.
UV-curable resins, including photoinitiators, react with ultraviolet light and are dried instantly through a chemical process called polymerization. This results in an evenly spread transparent coating with a 100% solid formulation. The process is faster and cleaner than traditional thermal coating. It can be applied to paper, plastic, glass, wood, etc.
It is commonly used for printing marketing materials such as business cards, flyers, catalogs, booklets, sales sheets, and postcards. The brilliant, glossy appearance of the underlying material makes UV coating one of the best choices for printing.
In addition, the UV curing method is also used in a wide range of other applications. These range from medical coatings to industrial coatings.
Such a coating also protects the material from harmful UV radiation. UV-coated supportive or decorative metals can withstand harsh marine and coastal environments. It blocks radiation and preserves material strength and appearance.
Pros of UV Coating
- Quicker cure / processing and require less space vs thermal coatings
- Excellent glossy finish
- Impressive clarity
- Environmentally friendly – primarily low VOC emissions and reduced energy consumption
Cons of UV Coatings
- Not suitable for complex shapes and structures
- Inability to cure inner diameters
- Adherence issues with specific substrates
- Higher initial cost
- Ineffectiveness with thicker coatings due to limited penetration (cure depth) – this is an issue where thicker coatings are needed
- Typically require stricter storage conditions due to chemicals
- Require stricter application conditions
Comparison of UV Coating vs Thermal Coating
UV coating have become popular as of late. However, thermal coating still proves to be the best choice under some circumstances.
Here’s a quick table comparing UV coating vs. Thermal coating.
| Attribute | UV Coating | Thermal Coating |
|---|---|---|
| Process | Photosensitive liquid coating is dried instantly in the presence of ultraviolet light. | Heat is used to solidify thermoset resins under high pressure. |
| Speed | Liquid coating is dried instantly. | Thermal curing takes minutes or hours, depending on the shape and size of the substrate. |
| Batch size | Larger batch sizes, useful for larger batches. | Smaller batch sizes. |
| Energy Consumption | Less energy consumption due to UV lamps and faster processing time. | Solidifying the liquid coating requires a lot of energy for a more extended time. |
| Durability | Excellent abrasion, scratch, and smudge resistance. | Enhanced abrasion, scratch, and smudge resistance. |
| Consistency | High consistency and 100% solid formation on smooth surfaces. | Maintaining temperature at a given value throughout the curing process becomes challenging, which may result in poor consistency. |
| Complex Shapes | Evenly coated surfaces cannot be achieved on objects with complex shapes. | Even if the material has a complex shape, a comparatively better coating is achieved vs UV coatings. |
| Heat Sensitivity | Suitable for heat-sensitive material. | Heat-sensitive materials may get damaged during the process. |
| Finish | Glossy, shiny finish with high vibrancy. | Glossy, matte, or textured finish. |
| Eco-friendly | It is a safe and eco-friendly method as no volatile organic compounds (VOSs) are included and produced. | Thermal curing may produce volatile organic compounds (VOSs) based on the application. |
UV Coating or Thermal Coating: Which one should you choose?
UV coating is commonly used in the medical industry today. However, UV coating is not always the best choice for every application. Thermal coating offers its own set of unique benefits that are worth exploring before finalizing the coating method for your medical devices.
The right choice ultimately depends upon various factors and specific applications, which we discuss in more detail below.
1. Processing time
UV coating reduces production time to seconds or several minutes. It is quicker and requires less energy. The credit goes to photosensitive liquid coating or compound that solidifies instantly when exposed to UV light.
On the other hand, thermal curing includes the time to activate curing agents and initiate the chemical reaction via heat. This timing largely depends upon the underlying material used as a coating.
2. Durability
Choose thermal cure coating if you want a more durable and flexible option. Due to the chemical reaction used to solidify it, thermal cure coatings can withstand higher temperatures and extreme environmental conditions.
UV-coated materials also offer excellent scratch and abrasion resistance properties but are more prone to cracks if folded or bent. The thermal coating ensures advanced protection from wear and tear.
3. Eco-friendly
UV coating is less time-consuming and eco-friendly than thermal cure coating. When curing it does not produce volatile organic compounds (VOCs) and hazardous air pollutants (HAPs).
As an example, printed papers coated with UV coatings are recycled using standard procedures like regular paper.
4. Medical Applications
Hydrophilic coatings need to possess very high lubricity, high durability, and low particulates for safe and life-saving medical procedures. The best choice to apply hydrophilic coatings on medical devices depends on factors such as substrate material and inner or outer layer.
As we learned, thermal coating is best suited for complex areas and shapes; it is an ideal choice for inner-diameter coating.
On the other hand, you should consider the device’s substrate. Specifically, avoid using thermal coating for heat-sensitive substrates, as it can alter the underlying material’s properties. In that case, go with the UV-cure coating.
When it comes to specific medical applications, the choice between UV curing and thermal curing will depend on the performance and requirements of the application itself.
When are Thermal Cure Coatings a Better Choice vs UV Coating?
UV coating has become popular over traditional thermal coating. As such, there may be a misconception that it is suitable for every application. However, there are certain applications where thermal coating is highly recommended over UV coating.
One of the major disadvantages of UV curing is the inability of UV to fully cure the coating in hard to reach places. This becomes an issue with devices or products that have complex geometries. It is also a major issue with applications that involve curing UV coatings on the inside diameters (ID) of devices or products. The reason is because it is very difficult to reach the inside diameter with UV.
In both cases, the UV is not able to fully cure the coating. As a result, the intended properties and durability of the UV coating are not achieved. This can cause significant performance issues or outright failure.
As such, it is recommended to use a properly formulated Thermal Coating for these and other specific applications.
Hydromer® Coatings
Choosing the optimal coating and curing method for your application may seem difficult. However, it does not have to be. Working with an experienced coating manufacturer like Hydromer, Inc. can simplify the process.
Hydromer Inc. is recognized as a leading hydrophilic coatings manufacturer providing a complete range of custom coatings and specialized services for both medical and industrial applications. Our company develops custom coatings formulated and tested for your product’s specific product needs. As a result, our team of coating experts can help you develop the right coating.
Hydromer® Coatings Services
What sets Hydromer®, Inc. apart from others is our full-service, start to finish approach. Hydromer does not just sell coatings, we help you develop the ideal coating solution based on your unique requirements and project goals. Our coating services range from expert consultation and technical service to R&D, coating process development, and technology transfer.
Our Coating services include but are not limited to:
- Technical and regulatory consulting and support
- Contract R&D and formulation
- Contract coating services
- Specialized analytical testing
- Technology transfer services
Please contact us for more information or to start your project with us.
