Fluoropolymer Pre-Bonding Etchant.

Since 1958, Acton Technologies has helped thousands of customers worldwide with the process of making fluoropolymers bondable to other materials or to themselves. The technique is rather simple when you follow our recommended procedures.

Do you want to do your own etching? Perhaps you don't want to, but your production cycle requires "in-house" etching. Acton can provide innovative advice, introduce the most appropriate techniques, suggest the right tank design, and offer additional chemistry to optimize your results.

The Need for Bonding Fluoropolymers.

Fluoropolymers such as PTFE, FEP, PFA, ETFE and others are well known for their chemical resistance, heat resistance, exceptional dielectric properties, weather resistance, toughness and flexibility, negligible moisture absorption and low coefficient of friction

.

Their chemical resistance has made the fluoropolymers very useful in the chemical process industry as linings for vessels and piping. The bio-medical field uses fluoropolymers in the human body as both implantable parts and devices such as catheters with which to perform diagnostic and therapeutic procedures. Fluoropolymers have replaced asbestos as high temperature wire insulation. High performance automotive and aircraft bearings and seals are now commonly made from fluoropolymers.

The dielectric properties of these unique polymers have encouraged a whole new theory of printed circuit board technology. This concept is responsible for the very latest in high-speed, high-frequency radar and communications found in the newest defense systems as well as in the next generation of ultra high speed computers.

Each of these applications requires adhesion to the fluoropolymer and this can only be accomplished by etching. Fluoropolymer film and sheet must be etched on one side to bond it to the inside of tanks and piping; the OD of small diameter, thin wall fluoropolymer tubing must be etched in order to bond to an over-wrap or over-extrusion resulting in a fluoropolymer-lined guide catheter.

Fluoropolymer jacketed high temperature wire has to be etched to allow the printing of a color stripe or other legend such as the gauge of the wire and/or the name of the manufacturer. PTFE-based printed circuit boards require etching to permit the metallization of through-holes creating conductive paths between both sides of a double sided board or connecting several circuits in a multilayer configuration.

To enable the use of fluoropolymers in these applications, their surface must be altered enough to promote bondability without changing their other very desirable characteristics. The active metals are the only chemicals known to react with the fluoropolymers. Sodium is the most commonly used material. It is a safe and environmentally sound process.

The etching process is in fact a chemical reaction between the sodium in the etchant and the fluorine in the polymer. Sodium strips the fluorine from the carbon backbone and promotes its replacement with hydroxyl, carbonyl and carboxyl groups which are the organic species responsible for adhesion.

This reaction takes place to a depth of only a few angstroms leaving the bulk of the polymer unaffected but rendering the surface completely bondable with conventional adhesives. The surface energy is increased to more than 70 dynes/cm2 and is easily verified with a water wettability test.

FluoroEtch® Safety Solvent does not require refrigeration, is safe and easy to handle (its flash point is 70°C) and offers the user significant quality, safety, efficiency and industrial hygiene advantages over the competition. It has a shelf life of at least one year at room temperature.

Due to the hygroscopic nature of sodium-containing solutions, the most effective application of FluoroEtch® is by immersion. This permits the reaction to take place in a closed or nearly closed container. A thirty to sixty second exposure to warm etchant (50°C to 60°C) is recommended. Agitation of the parts during immersion enhances the etching effect. This is sufficient to affect a color change to dark brown (in the case of PTFE and PFA; FEP and ETFE show a very slight color change) indicating a more carbonaceous layer at the surface and rendering the fluoropolymer completely water-wettable and bondable. Following the etching process, the parts should be washed in an isopropyl or methyl alcohol bath, washed in hot water with a detergent, rinsed well and dried thoroughly.

Technology for Tomorrow.

Acton Technologies, Inc. has been involved with fluoropolymer etchants and etching since 1958 and has developed a unique expertise in this surface chemistry. The close association of Acton with its customers and with various university research projects in fluoropolymers has led the company into the development of the next generation of treatments for these polymers.

This process, electronic in nature, is a replacement for the traditional chemical etching procedure for some but not all applications. It goes a step further by tailoring the fluoropolymer surface to the next, very specific process. So, a given fluoropolymer that is to be bonded to stainless steel or molded into an elastomer or adhered to another polymer would receive distinctly different treatments to provide the specific functionality required for each use.

Aging tests have proven this new treatment to be extremely durable and show no degradation of bondability after well over one year. There is no color change with this process such as is the rule for sodium etching so the fluoropolymer retains its original color. This process is very end-use specific and capital intensive so its advantages are best seen in large volume applications.

As a supplementary, integral process, a seed layer of a metal or an oxide can be deposited onto the treated surface without exposing the material to atmospheric contamination. This system is capable of producing the unique group of metal or oxide clad fluoropolymers that are opening new vistas in the computer, electronics, biomedical and many other fields.