FEATURE Materials Handling & Conveying
Outsourcing plasma treatments for surface modifi cation
Manufacturers turn to contract processors for plasma treatments to enhance the value of products, writes Jeff Elliott, technical writer based in the US
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n manufacturing, plasma treatments are often utilised to solve problems that can’t be solved otherwise. Whether improving adhesion of dissimilar materials, depositing coatings, cleaning surfaces, applying a protective coating that repels water or biological fl uids, or enhancing surface wettability or functional coating, plasma treatments often add signifi cant value to products. For many manufacturers the application of plasma-applied coatings and surface treatments can play a signifi cant role in new product development. As a result, the industry is investigating and applying plasma to products that require a treatment step for cleaning and decontamination, surface conditioning or to promote adhesion. “Manufacturers are continuously looking for unique ways to technologically advance their products to be the market leader,” says Michael Barden of PVA TePla, a company that designs and manufactures plasma systems, provides surface modifi cation research, and serves as a contract processing centre. “Often, the top-tier products incorporate some form of advanced coating to functionalise the surface.” However, when manufacturers want plasma-treated parts or components without having to invest in in-house equipment, the solution is to utilise a contract processor. In this approach, parts are sent in, treated and returned within 1-2 days, or up to a week for larger volumes. For small or infrequent batches, this can lower the price per part signifi cantly. The most common application for contract processing is to improve the bonding power of chemical adhesives, whether metal to plastic, silicone to glass, polymers to other polymers, biological content to microtiter plates and even bonding to PTFE. However, it is also used often to clean, activate, chemically graft and deposit a wide range of chemistries on the surface of parts or components.
16 July/August 2021 | Automation
According to Barden, the companies that tend to opt for contract processing generally fall into two categories. The fi rst has little or no experience with plasma treatments, but may have heard that it can resolve issues or add value to products. “For many customers, plasma is not the fi rst thing they have tried but have read or heard that it can be used to solve a specifi c problem,” explains Barden. “They have a target for their material or the chemistry, but very often they don’t know exactly how to get there, so it can be somewhat experimental.”
When this is the case, the initial capital costs may be a deterrent; even large manufacturers may opt to avoid purchasing equipment initially if the product is new or a new version, and production quantities are unknown. The other type of enquires are from companies for which outsourcing is a core concept, but also for those that want to develop a product, but only assemble and do fi nal packaging in-house, along with contract sub-assemblers.
Plasma treatments According to Barden, many contract- processing projects involve using plasma to create a high-energy surface to resolve bonding issues with chemical adhesives. Plasma treatments are used to increase the surface-free energy of the material to be bonded.
When a substrate has a high surface
energy, it tends to attract. For this reason, adhesives and other liquids often spread more easily across the surface. This wettability promotes superior adhesion. Adhesion promotion can be achieved
by increasing the surface-free energy through several mechanisms, including precision cleaning, chemically or physically modifying the surface, increasing surface area by roughening, and primer coatings. The net eff ect is a tremendous improvement in bonding – in some cases, up to a 50 times bond strength
Many contract processing projects involve using plasma to create a high-energy surface to resolve bonding issues with chemical adhesives
improvement can be achieved. On the other hand, substrates that have low surface energy, such as PTFE, are diffi cult to adhere to other materials without fi rst selectively altering the surface to increase the free energy. “When a surface is really hydrophobic,
like Tefl on, it’s very diffi cult to bond to it,” says Barden. “If you apply a liquid or adhesive, by nature it pools and will not spread eff ectively across the surface.” There are several plasma methods employed to increase surface energy, including physical and chemical plasmas along with PECVD coating surfaces. Silicone, another material widely used in the industry for its low surface energy, is often used as an over-moulding compound to protect electronic boards from extreme conditions. Unfortunately, the topography of a PCB means the silicone must bond to many types of materials, including polymers, metals, alloys, ceramics and the
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