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Automotive Coatings Chemistry 101

To be honest chemistry wasn’t my favorite class at school. Probably it was because of the teacher, but I didn’t succeed in getting an A on chemistry no matter what. However, life is unpredictable, and sometimes things you wish to avoid, become part of your life or career. I began my entrepreneurial path with trading chemical raw materials for coatings manufacturing, and now I am in automotive refinishing business, where the greater part of products are chemicals. I don’t know if you experienced my difficulties with chemistry, but if you use or supply automotive painting products, then chemistry is important for your work too.

Chemistry is an exact science

You may wonder what this article is about? Well, I intend to stress the importance of understanding and respecting chemistry as science, and not just any science, but an exact one. Chemistry is in the heart of the automotive refinishing industry. Paints, clears, primers, bodyfillers, sealants and other paint related materials are developed based on the fundamental rules of the applied chemistry. We all know that.

The exact sciences are characterized by accurate quantitative expression, meaning that the reaction between the chemical elements happens in accordance with the quantitative parameters of these elements.

You do not need to know the chemical formulas, but understanding the essentials is the key to success in our trade. Failing to do so will cost you money and reputation. Below you can find the most common examples how chemistry can “punish” you if you didn’t learn the lesson.

Adhesion problems

Unfortunately adhesion problems are very common paint defects in collision repair works. Painters many times fail to understand that adhesion of one material on another depends on two parameters: mechanical bond (this is why we use abrasives to create the right scratch pattern for the subsequent coating’s bonding) and chemical bond, which happens on the molecular level. If you do not remove the waxes and release agents from the new OEM bumper, for instance, it will cause flaking. Similarly, silicone particles can not mix with any other liquid, therefore the so-called “fish-eye” defect will appear on the contaminated surface. Proper surfaces preparation and following the TDS will help to avoid unpleasant situations of poor adhesion.

Problems with curing of 2K materials

If a clearcoat’s technical data sheet says that the mixing ratio is 2 parts of clear to 1 part of hardener without any thinner (or “reducer” as our American colleagues call it), it means exactly that. Not 5%, not 10%, not “I am used to do it like that all the time!” Period.

Similarly, if you add more benzoyl peroxide hardener to polyester-based body filler, it will not speed up the curing process, simply because the crosslinking between hardener and resin can happen only given a certain amount of available styrene and polyester molecules. More benzoyl peroxide will not “find” free elements and just stay unused, causing problems like bleeding.

Problems with expired products

You wouldn’t eat smelly meat or drink expired milk, would you? Just like we respect the shelf-life of our food, we must respect the indicated storage times on your fillers or clearcoats.  I have seen dozens of times how easily painters mix and use coatings, which are expired. While sometimes one can get away with this, in the majority of cases problems are almost guaranteed. It is worth mentioning that even similar products, but from different suppliers may greatly vary as to the shelf-life of the materials. You can find in the market primers ranging from 12 to 36 month’s storage. Needless to say that treating all the primers the same way is a big error. Careful stock management and implementation of the logistic practices like FIFA (first in, first out) will save money both for the bodyshop and coatings supplier.

Incompatibility of the coatings

In chemistry there are two main scenarios how two substances can react in case of contact: no reaction or intermixing or some kind of reaction. In the paint shop we observe both of them. When hardener is mixed with clearcoat, we have chemical reaction, which leads to fast curing of the mixture and crystallization. This is a desirable outcome. On the flip-side, we do not want any chemical reaction between bodyfiller and primer, for example. What happens if we spray etch-primer over the bodyfiller? Aggressive acids in the etch-primer will react with bodyfiller, causing lifting and adhesion failure.

Problems caused by using wrong thinner/reducer

Many products in the market are designed to be used with certain thinners (reducers) in order to get the desirable viscosity. Unfortunately, not all thinners are created equal. In the paint workshop you can find different types of thinners: acrylic thinner, base coat thinner, nitro thinner and epoxy. All of them have different base and purpose. One of the most common mistakes I have observed is using of nitro-based solvent in the 2K primers and clears (for the cost reasons mainly). The vast majority of 2K materials in the collision repair shop are made on the acrylic-urethane resins. If you use nitro thinner, for example, which is much faster than acrylic ones, it may cause gloss reduction and orange peel effect.

Good news

When you are taking exam at school, you are not allowed to use any help or source of the information. The good news is that in our business not only we have the cheat sheets available, but we are encouraged to use them as we wish. I am talking about TDSs or technical data sheets. I am confident that if every painter used TDS whenever doubtful, the amount of the paint defects and costly re-sprays would have dropped significantly. Nowadays, thanks to the internet connection and smart phones, you can find the needed information within just a few minutes. TDS is the best source of information for every single product you use. Chemists and technicians worked hard to put the necessary information together for you, so use it. No need to re-invent bicycle… Well bicycles are more about physics, but this is another subject though…

 

 

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