Using UV curable masking materials in orthopedic implant manufacturing

Kevin Brownsill, Head of Technology: Learning & Development intertronicsDiscusses how temporary masking challenges can be overcome with UV curable materials.

During the manufacture of orthopedic implants, temporary masks are used to protect surfaces from metal finishing processes. Their tenacious adhesion seals and protects machined, ground or polished surfaces during tumbling, peening, abrasive or cleaning processes to help achieve the desired surface finish in various areas of the implant. However, masking can present a challenge to medical device manufacturers due to the properties of masking materials.

Around 200,000 people have hip or knee replacements in England and Wales each year, and they are generally highly effective. Research from the University of Bristol found that eight out of ten knee implants and six out of ten hip replacements last up to 25 years. To ensure long-term success, orthopedic implants must be precisely manufactured to specific surface finishes to achieve the required biological, chemical and mechanical properties – for example, to reduce friction and wear.

Orthopedic implant manufacturers typically achieve the desired surface finish with several stages of processing. During these steps, maskants are applied to protect some surfaces from processes such as anodization, plasma treatment, or shot blasting, while they are applied to surfaces that remain exposed. Once the process is complete, the mask is removed, usually through peeling, which may require soaking the material in water to soften or burnish it, and then mask additions where necessary. as the product passes through various processing stages.

Approach to temporary masking

Traditional methods of implant masking include tapes, boots, waxes, and lacquers. However, each of these techniques comes with benefits and challenges. Because orthopedic implants typically have complex geometries, accurately masking them with shoes and tape is difficult and time-consuming. Another challenge with boots and tapes is that they can deform – for example, if the edge of the tape lifts up, this can result in less than optimal edge definition. Applying these materials is typically done manually, which is time consuming and prone to human error.

These challenges can be overcome by using a liquid mask such as lacquer or wax. If their viscosity is low, they can be difficult to apply accurately, and may drip or flow into additional areas of the implant, leading to poor edge definition. In addition, they can take minutes to hours to cool or cure, and may require process work, which can slow down manufacturing.

If there is a problem during the masking process, such as lifting of the edges of the tape, misplacing the mask, or not applying the mask correctly, there is a possibility of rework or scrapping. Implants are high-cost parts, and therefore avoiding them is of utmost importance for manufacturing profitability.

Benefits of UV Curable Materials

UV curable liquid masks are an attractive option for concealing orthopedic implants. The speed and simplicity of their process leads to increased productivity, while overcoming the challenges associated with traditional masking approaches – they can reduce labor, rework and scrap.

A major reason for this is that UV curable materials cure “on demand”, usually in seconds. Since the material will not cure until exposed to the correct wavelength and intensity of UV light, the manufacturer can be extremely precise. If the process goes wrong for some reason, the creator can easily erase the content and start again. The faster cure time also means that the masked implant can be quickly moved to the next stage of processing, reducing work in progress.

building masking process

A wide variety of UV curable masking materials are available in low, medium and high viscosity formulations and with varying adhesion properties, so manufacturers can choose the material that best suits their application. Diamax Speedmask, for example, is a popular choice for orthopedic implant masking, and is available in burn off and peelable grades to keep surfaces residue free. These materials conform to complex shapes, providing reliable coverage in a single layer, eliminating the time spent waiting for layers to dry.

UV curable materials are single component and solvent free, which means they are easy and safe to handle, without any mixing. Depending on the requirements of the application, UV curable materials can be dispensed with varying levels of precision, from simple time pressure dispensing to volumetric dispensing, such as using the Preflow Eco-PEN, which is ±1%, > Provides an accuracy of 99% of the time. For surfaces with complex geometry or variation, manufacturers may wish to consider contactless applications using jetting valves or spraying. The application is more easily automated than other options, reducing the risk of application errors.

When selecting a UV curable material it is important to note that, for optimum results, it must be matched with the proper curing system. LED curing systems bring a number of advantages compared to traditional mercury arc systems, in particular their lower energy consumption. They require no warm-up and cool down time, so users can switch them on and off on demand for immediate use. Plus, there’s no need to change bulbs, which can lead to cost savings over time.

To confirm cure, some materials, such as Diamax 726-C, have color-changing technology, which means the mask is tinted blue and tinted pink for an added safety factor.

Orthopedic implant surgeries are typically highly cost-effective, and maintaining an accurate, productive manufacturing process is critical to ensuring patients receive the treatment they need. With UV curable massage materials, manufacturers can overcome challenges associated with other techniques, helping to fabricate precision implants more efficiently.