Toluene-Free Conformal Coatings: Alternatives to Aromatics

Posted by Dan Griffin on Dec 20, 2023 11:28:35 AM
Dan Griffin
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Toluene and Xylene: solvents that have shown value and utility within the adhesives and coatings industries for decades. However, they often serve as a double-edged sword, offering superior solvent and drying capabilities but accompanied by some negative health and environmental impacts.

Many traditional conformal coatings used to protect PCBs have been formulated with the use of aromatic solvents such as Toluene and Xylene. The popularity of these specific solvents is due to several factors important to the manufacture of adhesives and coatings including-

  • Relatively low cost
  • Excellent compatibility with organic polymers
  • Slow evaporation/drying rate

This last property, slow evaporation, is one of great value in industrial coating as it minimizes premature drying and skinning of a coating which can entrap bubbles and defects.

Whether by choice or by government fiat, you and your organization may be considering moving away from aromatic solvents in your processes. It’s our goal to help you find viable alternatives that aren’t just sufficient replacements but superior ones.


Why Do We Use Toluene?

Xylene and Toluene are two common aromatic solvents encountered in the adhesives and coatings industries. They have been safely used for decades, so long as they are used with the proper protection. This includes standard PPE: gloves, masks, and proper workplace ventilation. Still, there are growing efforts for environmental conservatism and mitigating personal health risks that call for the discontinuation (or limiting) of these solvents.

We at Humiseal use solvents in the production of our conformal coatings. Conformal coatings must be sprayed on a PCB and flow well to form an even film; base polymers are far too viscous to spray or form an even film on their own. Solvents serve the main function of “thinning” the polymers from a thick paste-like consistency to a sprayable and flow-able liquid. Conformal coating thinner solvents are—in fact—only a processing aid and serve no part in the function of the finished protective film. They are evaporated away during the drying phase.

Related Article: Conformal Coating Viscosity Explained


Why Consider Toluene-Free Coatings?

So why would anyone consider or request a change? The answer has mainly to do with national, state, and local regulations and limitations on the use of aromatic solvents. These limitations are based on continued and evolving knowledge of some of the potential health hazards and environmental risks associated with organic solvents. All organic solvents have health and environmental considerations, but some governing bodies consider aromatic solvents for additional regulatory control or elimination.

Aromatics such as Toluene and Xylene pose potential risks to:

  • Personal health and safety
  • Environmental hazards: toxicity to fish and wildlife and damage to the ozone layer

Regarding personal health and safety, aromatic solvents pose potential risks due to their flammability as well as due to issues related to toxicity. Toxicity sounds scary. Even if the risks can be overblown at times, it certainly must be considered. Industrial hygiene can easily be maintained through the use of personal protective equipment as well as through the use of “adequate ventilation”.

Any chemical (even water!) can be toxic. The important consideration is the route of entry as well as the concentration and dosage. Nevertheless, some companies have chosen a no-aromatics policy; and in these cases, alternative solvents can be found.

As it relates to the overall environment, aromatic solvents can risk contamination in the air, soil, or water if not handled properly. In the air, risks can include odors and ozone issues. If spilled or disposed of improperly, solvents will of course risk contamination of soil and water affecting both humans and wildlife.

Fortunately, we at HumiSeal have a wide range of recommendations for alternatives to aromatic solvents if necessary.

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Aromatic Solvent Alternatives: Specialty Solvents, Silicones, and UV-Curables 

Humiseal offers three primary alternatives to aromatic solvent-borne conformal coatings:

Regarding alternative solvents, HumiSeal has a diverse range of non-aromatic solutions. In many cases, these alternative thinners have the same protective property results as standard Toluene solvents. You may choose one of these chemical thinners should you continue to use solvent-based conformal coatings.

A few examples include:

It's important to note that each aromatic-free thinner has a specific list of compatibilities and should be selected based on the conformal coating used by your operation.

Another method of moving away from aromatics is silicone coatings for PCBs. These coatings can be manufactured at appropriate viscosities for spraying without the use of intervening solvents. The right silicones have a 100% solids rate, leaving the entirety of the coating on the PCB.

An increasingly popular option for the elimination of processing solvents is environmentally conscious UV-curable conformal coatings. These coatings, similar to silicones, are supplied at 100% solids without the need for solvents to achieve viscosity. Unlike solvent-based processes, there is no chemical byproduct or risk to personal and environmental safety when handling these materials.

As a supplier of all major forms and chemistries of conformal coatings, Chase Corporation and HumiSeal® can help you with an unbiased approach to evaluating your application and process. We’ll show you how to maximize efficiency, minimize cost, and improve product reliability. Our outstanding manufacturing and technical support groups can provide your organization with reliable global supply, unmatched quality, and superior technical support.

Please contact us today for a customized solution to your electronics coatings needs.

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Topics: Aromatic Free, toluene

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