Medical Design Briefs - May 2021 - 15

alyzed HCRs are supplied in a one-, twoor three-part system, which can be ideal
for a manufacturer that would like maximum flexibility to adjust work time,
table life, or cure profile directly on the
production floor.
More commonly, HCRs are supplied
precatalyzed in either a one- or two-part
system, using either a peroxide catalyst
or a platinum catalyst already incorporated in the system. Table 1 provides
technical characteristics to assess when
choosing between peroxide-cured and
platinum-cured HCRs:
Peroxide catalyzed. Peroxide-cured
HCRs have a long history in implant
applications. It's an excellent material
for low-volume device or parts production. This one-part system contains
either a vinyl, or a nonvinyl specific peroxide catalyst ready for use. In peroxidecatalyzed systems, curing is not initiated
until the HCR is exposed to heat. In
some peroxide cures, the process produces a mild acid as a byproduct, which
must be removed with a high-temperature post-cure.
Platinum catalyzed, addition cure.
Medical devices made with silicone material commonly use platinum-cure systems
due to the fact that, unlike peroxidecatalyzed systems, there are no by-products
of the cure mechanism, post cure is not
required, and the end product experiences less shrinkage. During the curing
process, platinum-catalyzed HCRs can
also be heat-accelerated for increased
throughput. Platinum-catalyzed systems
commonly consist of two components:
one with a platinum catalyst, and the
other with cross-linkers and inhibitors.
Since many factors can influence conditions required to successfully process
HCRs, optimizing these variables can
ensure the fastest and most repeatable
process possible. Temperature is critical
when optimizing cure times based on
processing needs. Formulation adjustments can customize the time needed
for a platinum-catalyzed HCR to cure at
a particular temperature. However, increasing or decreasing the processing
temperature can also change the time
required to achieve the desired state of
cure for any given formulation.
Figure 2 depicts how changes to temperature affect the time needed to cure
the silicone. There are practical limits to
increasing processing temperatures to
reduce cure time, so care must be taken
to avoid issues such as scorch.
Determining the optimal processing

temperature is commonly done through
experimental evaluation.
Understanding the Three Main
HCR Processing Methods
Based on the desired end component,
there are a variety of ways an HCR can
be processed. The most common HCR
processing methods include extrusion,
transfer or compression molding, and
calendaring.

Extrusion. If manufacturing continuous profiles, such as tubing, rod, or ribbon, extruding is often the ideal manufacturing process. Extrusion is a very
efficient and relatively low-cost way to
manufacture high-volume parts. Parts
produced through extrusion can have
typical wall thicknesses ranging from
less than 0.01 inches up to 3.00 inches
and have a wide range of elastomeric
properties.

Industrial Solutions.

Smart system solutions for needle bonding
UV curable adhesives and advanced LED curing systems
from one source. Panacol-USA provides:
* Fast curing, biocompatible adhesives
* Viscosity options for a wide range of hub designs
* High intensity LED curing systems for maximum
productivity
* Programmable process control with operational
feedback
Contact us today!

www.panacol-usa.com

Medical Design Briefs, May 2021

Free Info at http://info.hotims.com/79413-787

Cov

ToC

http://info.hotims.com/79413-787

Medical Design Briefs - May 2021

Table of Contents for the Digital Edition of Medical Design Briefs - May 2021