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Tips on Using a New Adhesion Additive in LSR Molding

( 11/17/2020 ) Written by: Anonymous

In Part I of our blog series introducing Chemlok 3Stream (3S), “New Adhesion Additive Technology Eliminates Expensive Self-Bonding Liquid Silicone Rubber," it was shown that this breakthrough technology allows molders to easily bond standard LSR grades to substrates—a task that has previously been laborious and expensive. Compared to self-bonding LSRs, standard LSRs are inexpensive, have a longer shelf life, are widely available and have short lead times. Chemlok 3S-902 is the first adhesion additive in our product portfolio. By adding Chemlok 3S-902 via a third-stream pump—in quantities as low as 0.5 wt% in LSR—you can transform regular LSR into self-bonding LSR. This translates not only to cost savings, but to greater supply chain and design flexibility. In fact, molders can save up to 50 percent in raw material costs (compared to self-bonding LSRs), while still having the ability to bond to nearly all LSRs across a wide range of durometers. 

The Chemlok 3Stream additive achieves bonding between LSRs and clean metals or thermoplastics with little to no change in the physical properties of the LSR. In addition, Chemlok 3S modified systems retain curing performance within a normal expected range for LSR. Tests on Chemlok 3S-902 have shown that in most cases, the bond strength achieved by using the additive with a standard LSR is equivalent to, or greater than, the bond strength achieved with the commercially available self-bonding LSR grades tested. Repeated experiments have shown excellent tear strength results—i.e, the bond strength exceeded that of the silicone material itself. Tests have also shown that Chemlok 3S-902-modified LSRs show superior adhesion and better strength retention when exposed to hot and hot/humid environments, attributable to the additional curing that takes place in these environments. 

Overall, experimentation has shown that the main processing parameters that affect bonding performance of Chemlok 3S additive are cure temperature and cure time Better bonding is achieved at higher temperatures and longer cure cycles. Although time and temperature improve adhesion, it is not necessarily required to change your current manufacturing process. Chemlok 3S-902 can bond to various substrates at a minimum bonding temperature of 125C, and cycle times will be dependent on the curing profile of the standard LSR used. Depending on your application and bonding requirements,  postbaking parts may be recommended to achieve optimal adhesion, but is not necessarily required. 

Prior to using Chemlok 3Stream, organic materials (such as grease, dirt and oils) should be removed from substrates by solvent or alkaline cleaning. Cleaning can be accomplished using either mechanical or chemical processes, or a combination of both. Check out our application guide for more information.

Patent-pending Chemlok 3S is a revolutionary product that will lead to dramatic efficiencies in injection-molding LSRs. It is easy to add to existing manufacturing processes, generating self-bonding properties in LSRs without giving up quality or performance. Check out the full white paper or learn more about Chemlok 3Stream

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