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Understanding thermoformable hard coatings

Thermoformable hard coatings have revolutionized the way industries approach surface protection and design for various plastic products. At the forefront of this innovation is ViewTec, the tradename under which Zweko Optics offers its range of specialty coating solutions. A prime example of this advanced technology is ViewTec’s thermoformable hard coatings, which enhance production efficiency while providing superior protection for plastic surfaces. This blog delves into the benefits, applications, and challenges of using thermoformable hard coatings and explains why UV-curable coating systems are preferred.

Why use thermoformable hard coatings?

Thermoformable coatings offer a unique advantage in that they allow manufacturers to produce formed parts with a scratch-resistant coating without the need to apply a coating after forming. This approach not only improves the cost-effectiveness of production but also allows for coating larger surfaces in a single step, eliminating the need for one-by-one post-coating and 3D-machining. Once coated, these sheets can be cut and thermoformed into multiple finished parts, making the production process more streamlined and efficient. 

Potential applications for thermoformable hard coatings are vast and include products such as:

• Visors and windscreens for vehicles
• Laminated safety glass
• Machine covers
• Display covers for electronic devices

Moreover, ViewTec coatings can be applied to a variety of transparent plastics, including polycarbonate (PC), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyphenylsulfone (PPSU), and styrene acrylonitrile (SAN).

Why choose UV-curable coatings?

While some ViewTec coatings cure under thermal exposure, such as the ViewTec FRD antifog, our focus is primarily on UV-curable coating systems. UV curing is favored due to its numerous benefits:

• High productivity: UV-curable coatings cure rapidly, allowing for faster processing and higher production throughput.
• Low-temperature processing: This reduces the risk of damaging heat-sensitive substrates.
• Environmentally friendly: These coatings either reduce or eliminate volatile organic compounds (VOCs), making them a safer choice for both workers and the environment. Furthermore, energy consumption is a fraction compared to thermal coatings.
• Enhanced scratch and chemical resistance: UV-cured coatings provide a durable protective layer that extends the lifespan of plastic products.

Challenges of UV-curable coatings in thermoforming

Despite the advantages, UV-curable coatings come with technical challenges, especially during thermoforming. A significant issue arises from the shrinkage of the coating during the UV curing process, which can cause stress between the cured coating and the substrate. This stress becomes more pronounced when the plastic part is thermoformed, as the thermoplastic material expands and increases the tension at the coating-substrate interface, potentially leading to delamination.

To address these challenges, ViewTec coatings incorporate unique chemistry that ensures formability. This involves careful selection of the binder, molecular weight, and photo initiator to achieve the desired flexibility and adhesion. A crucial aspect of the coating’s performance is the strength of the covalent bonding between the coating and the substrate. Proper adhesion is maintained even during the thermoforming process, preventing delamination and ensuring long-lasting durability.

Ensuring proper adhesion: surface energy and bonding

The success of UV-curable coatings largely depends on quantifying and understanding the surface energies of both the wet coatings and the substrates. For strong adhesion, there must be an optimal interaction between the polar and disperse surface energies of the coating and the substrate, symbolized by a „handshake“ between the two. 

A case in point is the development of a new formable hard coat for PPSU sheet substrates. The coating is designed to withstand thermoforming temperatures of up to 275°C, a condition that would cause delamination if the adhesion were inadequate. The ViewTec development team was able to formulate a coating solution that performs exceptionally well on PPSU without the need for a primer, keeping the process both simple and cost-effective.

The ViewTec advantage: expertise in coatings and chemistry

At Zweko Optics, we excel in understanding the intricate chemistry and physics behind coatings and substrates. Our expertise enables us to develop tailored solutions that meet our customers’ specific needs, even under the most challenging circumstances. Whether it’s a new application or a particularly demanding production process, we are ready to take on the challenge and deliver results that exceed expectations.

If you are looking for advanced coating solutions that simplify your manufacturing process and offer outstanding performance, look no further than ViewTec. Let us put our expertise to the test and find the right coating solution for your needs.

For more information on ViewTec thermoformable hard coatings or to discuss your project, get in touch with us today.