Hard Coating Systems
Hard Coating Systems
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By utilizing a primer in conjunction with hardcoats, performance and versatility can see a significant enhancement. This combination of hardcoat and primer is commonly referred to as a hardcoating system. Primers provide strong adhesion to various substrates, impact resistance, and the ability to be tinted. Meanwhile, the hardcoat delivers abrasion and scratch resistance, among other beneficial properties. It is essential for labs and manufacturers to collaborate closely with their hardcoating suppliers to select the most suitable primer and topcoat, optimizing the overall effectiveness of the hardcoating system.
Thermal vs. UV:
Coatings are typically cured through either UV light or thermal heat exposure. Selecting between these two curing methods depends largely on the coating's chemical properties. Each class of coatings possesses its own set of advantages and disadvantages. Below is a general overview:
Thermally Cured Coatings:
Thermally cured coatings were originally used exclusively by lens manufacturers, often labeled as factory coatings or the front coatings on semi-finished lens blanks. These coatings exhibit excellent abrasion resistance and compatibility with AR. They permit the use of primers for enhanced adhesion and impact resistance. Primarily designed for adhesion to a single substrate, these coatings are particularly useful in lens manufacturing environments. However, incorporating a primer allows for compatibility across multiple substrates or even as an overcoat. Consequently, the adoption of thermally cured coatings has surged in labs and retailers. Generally, these coatings display greater compatibility with AR and mirror coatings and can be applied via spin or dip coating methods. Cure times typically range from one to four hours, with limited substrate compatibility.
UV Cured Coatings:
Conversely, UV cured coatings are primarily utilized in laboratory settings and by certain lens manufacturers. Their main advantages include rapid curing times and compatibility with various substrates, making them particularly suited for environments that demand quick turnaround times. Application methods for UV cured coatings include spin coating, dip coating, and in-mold coating, with spin coating being the most prevalent. While UV cured coatings display decent resistance to abrasion, they often fall short in performance compared to thermally cured coatings during the Bayer Abrasion Test.
Hybrid Coatings:
This emerging category aims to merge the strengths of both thermally and UV cured coatings. They undergo initial curing through UV light, followed by a brief thermal cure, resulting in a coated surface that combines the abrasion resistance and AR compatibility of thermally cured coatings with the quicker cure times associated with UV curing.
Overcoating:
Overcoating is the method of applying a hardcoat atop an existing one. This enables the application of the same coating to both the front and back surfaces of a lens that already possesses a factory coating. This practice allows labs or retailers to apply a premium hardcoat that provides uniform performance on all surfaces and substrates. A primer is used to ensure effective adhesion across various factory coatings and bare substrates, followed by the application of a thermally cured coating. This technique empowers labs and retailers to manufacture lenses with robust abrasion resistance, optical clarity, and AR compatibility on all surfaces. Some coating systems may require factory hardcoating to be removed using an acid wash before the overcoating process.
Surface Protection: Soft or Hard Ceramic Coating
Coatings serve a broad array of applications, from surface protection to aesthetic enhancements, bringing diverse benefits. Two primary categories exist: soft and hard coatings. Both types offer their unique advantages, though distinctions between them are considerable.
Soft or Hard Coating: Which is Right for the Job?
What are Soft Coatings?
Soft coatings, generally composed of organic polymers like urethane, exhibit lower surface hardness. They are often employed to bolster surface performance and durability. Soft coatings create excellent adhesion with substrates, ensuring a robust bond, and they also possess superior flexibility, ideal for applications involving frequent flexing, bending, or impact. Moreover, they resist chemicals, dynamic abrasion, cavitation, and corrosion, making them suitable for rugged environments like pump impellers and mill circuit chutes, which often face cavitation and dynamic abrasion issues.
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What are Hard Coatings?
On the other hand, hard coatings consist of inorganic materials, such as ceramics, characterized by high surface hardness. Their primary function is to safeguard surfaces against linear wear and scratch damage. Hard ceramic coatings excel in applications with significant linear wear but minimal impact damage. While offering some corrosion resistance, these coatings are ideally suited for challenging environments.
Typical applications for hard ceramic coatings involve situations necessitating the reshaping of solid structures or cases of considerable linear erosion, such as in transfer vessels that experience low turbulence but handle aggressive slurry transfers.
Difference Between Soft and Hard Coatings
The definitive distinction between soft and hard ceramic coatings lies in their hardness levels. Soft coatings are flexible and low in hardness, while hard coatings exhibit rigidity and high hardness. The choice between the two types hinges on the specific application and the surface of the substrate. Generally, soft coatings are best suited for scenarios where flexibility, impact resistance, cavitation resistance, and chemical resilience are paramount. In contrast, hard coatings prime in linear wear and abrasion resistance applications.
Notably, soft coatings may offer a degree of self-healing, allowing for automatic repair of minor damages, while hard coatings tend to lack this capability but provide superior scratch and wear resistance.
Which MetaLine Product is Soft or Hard Coating?
As highlighted, soft and hard coatings deliver varying benefits. Soft coatings from the Global Pumps MetaLine 700 series are recognized for flexibility, chemical resistance, and a certain level of self-healing. Conversely, hard coatings such as the Global Pumps MetaLine XL Series boast rigidity, superior linear abrasion, and scratch resistance, making them suitable for reinforcement in worn areas.
With an extensive selection of MetaLine products and access to in-house coating specialists, Global Surface Protection can guide you in selecting the optimal soft or hard coating tailored to your specific application and surface needs.
Contact our product manager, Steve, for more information today.
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