FEATURE FASTENINGS & ADHESIVES
A quality bond for medical devices
In order to achieve a good quality bond, designers need to consider such aspects as the substrates,
joint design, surface preparation, application and cure. In the medical industry, where there is
zero tolerance for failure, technology which helps affirm that assemblies are being bonded to the
specified quality are needed, as Peter Swanson, managing director of Intertronics, explains
light indicates absence or presence of the material in the bondline, correct location and even some qualitative idea of quantity. In some circumstances, the fluorescent response can be measured by a sensor, allowing an automatic check. Commonly used fluorescing agents in this technology emit blue light. These agents normally absorb UV
light in the same region of the spectrum as is required during curing, limiting the quantity of fluorescing agent that can be incorporated into the adhesive without affecting the cure. This then limits the fluorescent response or glow. To help overcome this, Dymax developed Ultra-Red technology. Because it does not absorb the same
Within the medical industry, a highly reliable and consistent bond is essential. To help ensure the quality of the finished product, in-process measures and checks are necessary, including whether the correct amount of adhesive has been dispensed
W
ithin the medical industry, a highly reliable and consistent bond is
essential, and this is why UV light curing medical device adhesives are often specified. Suitable for joining medical plastics as well as bonding metal to glass and metal to plastic, these are used in applications such as the bonding of needles, syringes and cannulas, reservoirs and housings, tube sets and fittings, surgical instruments and catheters. To help ensure the quality of the
finished product, however, in-process measures and checks are necessary. These include whether the correct amount of adhesive has been dispensed, whether it has been applied in the right location, and whether the material has completely cured.
FLUORESCENCE BENEFITS UV light curing adhesives or coatings can be formulated with fluorescing agents. Fluorescence – a well- established technique in forensics and non-destructive testing (NDT) – involves a substance which fluoresces under the ‘black light’ emitted from a lamp, generating long wave UV and little or no visible light, producing a glow which is visible to the naked eye. The adhesives response to this black
8 MAY 2020 | DESIGN SOLUTIONS
wavelengths used to cure the adhesive, adhesives formulated with Ultra-Red technology often have faster, deeper, cures than blue fluorescing products, and emit a very strong red glow under black light, which is easy to see. Red fluorescing technology is particularly useful when bonding plastics that naturally fluoresce blue themselves, such as PVC and PET, providing a contrasting and more detectable response. One-part UV curing adhesives are
often suited to high-volume high-speed automated medical device assembly, due to their rapid curing and bonding properties. Fluorescing properties enhance the performance of automated sensing and vision systems in detection of material coverage and volume. Missing dispense cycles, undersized or oversized applied volumes, air bubbles, blocked dispensing equipment or material reservoir depletion can be detected in-process and quickly rectified with minimal production losses.
QUALITY ASSURANCE To provide further assurance that the cure is being adequately completed, medical device manufacturers can opt for light curable adhesives with See-Cure technology. These are bright blue in colour prior to cure, enabling the user to confirm adhesive placement. As the blue colour is extremely visible, simple vision systems may be incorporated into
assembly processes prior to curing in order to easily identify adhesive coverage and profile. During the light-curing process, the blue colour disappears and the adhesive becomes clear, confirming the adhesive has received the sufficient dose of energy to reach full cure. These simple visible process indicators provide extra assurance that the adhesive is correctly applied and cured. It is also important to ensure the
correct amount of adhesive is being dispensed. To help, the Flowplus16 compact inline fluid sensor installs readily into an adhesive dispense system, with luer fittings at each end and a short, straight fluid path with no dead spaces. The piezoresistance pressure sensor uses an elastomer to transfer the system pressure to a measuring cell, which outputs a simple voltage signal, providing precise monitoring of flows up to 100ml/min. Because the fluid channel in the sensor is coated with FDA compliant perfluoroelastomer, it is inert and therefore suitable for food and biochemical applications. The sensor can identify whether
there are any issues affecting material flow, such as unwanted air bubbles in the material, contamination, clogging caused by agglomeration of fillers, variable feed pressure or an empty material reservoir. These can all lead to inaccurate or inconsistent application of adhesive, reducing the integrity and performance of the product and leading to non-compliance with regulations and risks to health. The sensor can be connected to a PLC and enable alarms in an automated system. Flowplus16 can be easily connected
to syringes, drain tubes, infusion tubes, catheters, injection needles and similar devices to monitor many other fluid systems. For laboratory or analytic work, it will deliver pressure and flow information, and can analyse static and dynamic application flow mechanics using the output and appropriate software.
Intertronics
www.intertronics.co.uk
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