Using Solvents to Your Advantage

Q: I run a job shop that uses liquid coatings and HVLP spray guns. We’ve been using the same formula for months, but recently started having problems with the paint being very thick and not spraying or looking as smooth as it used to. I know we need to adjust our solvents to account for the colder weather, but it’s hard to know where to start. Why are there so many variations of solvents and how do I figure out which ones I need while keeping costs down?

A: Selecting the right solvent to add can be a tricky process. There are a lot of factors to consider and hundreds of options available, from straight solvents to solvent blends. Ultimately, most formulas must be customized to fit your specific application. Hence, the variety of solvents available. Your supplier can help identify the best options for your shop, however there are guidelines to help you narrow things down.

Solvents can be broken up into five main categories: Aliphatic, Aromatic, Ketone, Ester and Exempt Solvents. Within these, there are three subcategories: fast, medium and slow. Determining which solvent should be incorporated depends on the paint’s composition, governmental regulations and the environmental conditions of your spray booth and shop.

When choosing a solvent, there are multiple main factors to consider.

Solvent selection is heavily influenced by climate. As we head into colder months, you’ll need to lower your viscosity to apply the coating successfully and dry it within a reasonable time. For this situation, a fast solvent may be all you need to achieve the correct flow and get a smoother application.

When the weather warms, you may start to see orange peel, sandy texture and reduced gloss, which are all signs that your paint is drying too quickly. This means you need a slower solvent to help reduce the rate of evaporation. Solvent blend choices are based on the coating’s technology. Some solvents will not work with specific formulas, so check with your supplier before you start testing.

Equipment considerations are typically straightforward enough. Your spray gun settings must be optimized for the correct flow and droplet size of your paint, which will change based on viscosity. High- and low-pressure application equipment tends to require different viscosities.

Paints designed for electrostatic applications are formulated to have a resistivity range safe for the application equipment. Added solvents can affect the electrical resistivity of the paint, so you’ll need one that keeps the paint within the recommended operating range. You can use an ohm meter to measure resistivity and ensure it’s within the working range of your equipment.

Government regulations must also be considered when adjusting your paint. Solvents are the main source of volatile organic compounds (VOCs) and hazardous air pollutants (HAP) emissions in paint. Local municipalities regulate VOC and HAP levels, so make sure to check and go through permitting as needed.

Applications needing low VOCs can be reduced with VOC-exempt solvents. These organic compounds are exempt from VOC restrictions in the United States and Canada because they are not expected to contribute to ozone formation or depletion. When exempt solvents cannot achieve VOC regulations, waterborne coatings are typically chosen.

Choice of cleaning solvent is another important factor to consider and it’s possible you’ll need a different strength for this purpose. Using a more powerful solvent for cleaning will help minimize VOC emissions and the amount of solvent needed, which helps keep total costs down.                                                    

A solvent still is another great way to reduce emissions and save money. These devices feed dirty clean-up solvent through a machine, separating it from paint sludge through evaporation and recollection so the reclaimed solvent can be reused for future cleaning. Solvent recycling can be an effective way to minimize waste, as they’re relatively inexpensive and can deliver significant long-term savings in materials and waste disposal costs. Check your local HSE regulations on the use of this equipment. 

No matter the issue, always start by adding minimal amounts of solvent and going up from there. Like salt when you’re cooking, solvents are easy to add in, but very difficult to remove. You don’t need to overcomplicate your mixture either. One or two solvents is typically enough. Once you start mixing more, formulas become impossible to recreate. Some suppliers offer pre-blended solvents, which could be an option as well. These typically cost more than straight solvents, but depending on your needs and challenges, the efficiency improvements can be well worth the higher price tag.

Whatever you do, do not just start mixing things. You’ll waste a lot of product, time and money that way. Your supplier should be able to provide the best guidance for your unique situation. Some distributors even customize different mixtures for the summer and winter months, so the best first step would be reaching out for some expert guidance.