MATERIALS | MEDICAL
COC grades, the elastomer is a high-purity resin with low leachables and extractables, and good chemical resistance. The company says E-140 also offers exceptional barrier properties compared with other elastomeric materials, allowing it to deliver additional product shelf life. Importantly, the elastomer is compatible in assemblies with a rigid COC, like grade 5013L-10. Among other advantages, this property facilitates multi-material moulding and eliminates concerns about cracking and other structural deficiencies that may develop from incompatible materials. The resin, which is also suitable for microfluidic applica- tions, offers good clarity, high flow without loss of material strength or optical properties, and heat resistance to 127°C. New product evaluations show that Topas Elastomer possesses strength and stiffness suitable for numerous flexible applications. Tensile modulus is reported at 6,400 psi while elongation at break is greater than 450%. In addition, the material’s low dielectric properties are comparable to some fluoroelastomers, providing strong electrical insulation performance. Another key feature is the material’s ability to maintain good ductility at temperatures below -90°C. The grade has an 89 Shore A hardness and meets USP Class VI require- ments for use in medical devices. It also complies with US FDA food-contact regulations as detailed in FDA FCN 1104. Elkem Silicones observes two main trends with plastics for medical application. “There is an increase in at-home care and diagnostics devices, which requires comfort and durability that can withstand consumer handling and care,” says
Table 1. Typical properties of two Teknor Apex medical grade TPEs for overmoulding on to polycarbonate and PC alloys
Medalist Medical TPE Compounds General-
Wearable Properties and Units Density, g/cm3
Hardness, Shore A (5 sec.) Tensile strength, psi/MPa Tensile elongation % 100% Modulus, psi/MPa
Tensile strength change % Tensile elongation change, %
Tensile strength change % Tensile elongation change, %
Source: Teknor Apex Company 42 INJECTION WORLD | January/February 2020 Purpose
MD-34969 1.10 73
907 / 6.25 562
454 / 3.13
Applications MD-36975
1.10 75
576 / 3.91 130
561 / 3.87
Chemical Resistance, 70% Isopropyl Alcohol Wipe Test -6.9 -7.3
1.4 5.4
Chemical Resistance, Suntan Lotion Wipe Test -8.8 -9.1
-4.9 0.0
Michael Goglia, Healthcare Market Manager for the Americas. “We also see an increase in wearable devices, which require softer, smaller and durable designs. Often wearable devices include wireless electronic reporting functions requiring batteries. These devices must be moulded at lower tempera- tures to avoid damage to the batteries. Other medical moulding issues include challenges in the industry for two-shot and overmoulding at low temperatures to maintain the integrity of the plastic, circuit board and battery, for example. Another challenge is friction or drag.” He continues: “In order to address the challeng-
es of two-shot and overmoulding, we have devel- oped and introduced Silbione LSR Select, which is a patented advanced system of LSR materials that enables users to achieve multiple capabilities all in one solution. These include low temperature cure. With LSR Select users can achieve cure at tempera- tures as low as 80°C and below. It also offers formulation flexibility. Users can now custom blend LSR Select in line to obtain desired durometer performance from 20 to 70 Shore A. Productivity improvements can also be achieved by enabling users to optimise cure kinetics resulting in im- proved cycle times up to 50% and beyond.” In order to address the challenge of friction and
drag of silicone in combination with plastics, Elkem Silicones has developed a healthcare grade self-bleeding series, Silbione LSR 4700. The company says that this medical grade LSR series, available in 45, 55 and 65 durometers, creates a lubricious surface on the moulded part after vulcanisation. The material is designed to minimise friction and prevent slit healing in applications. Built into the bulk LSR formulation, the self-bleed- ing lubricity of this product line eliminates the need for a secondary coating process to reduce coeffi- cient of friction, reducing costs and improving cycle time for the part manufacturer. Elkem Silicones has recently been involved with a customer looking to consistently deliver tight durometer specifications for a small part, just 2-3g, with a 25s cycle time. “The customer’s pain point was not necessarily cycle time, but rather tighten- ing the durometer consistency to ±3 points, over six different durometers,” says Goglia. “Thanks to the blending capability of LSR Select, we were able to achieve all six durometers blending just two base materials, a 20 Shore A and a 70 Shore A. We were able to hone in the desired specific durom- eters by fine tuning the blend in-line, enabling the part manufacturer to consistently achieve part specification parameters. As a bonus, we also improved cycle time by 32%. In addition to
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