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Are Batch-to-Batch Paint Variations Self-Inflicted?

Posted by Rob Gladstone

Dec 11, 2019 11:04:00 AM

At an event recently, we struck up a conversation with an Account Manager at one of the major paint suppliers. During our conversation we discussed the batch-to-batch variation of the paints they supply. He said what we often hear from paint suppliers, “Our paints don’t vary much from batch to batch.” When we asked why their customers often have a different perception he said, “Most of the variations that they see are self-inflicted.” That prompted us to request a more in-depth conversation so we could better understand how end users may be unknowingly creating their own batch variations. We thought his insights were helpful, so we decided to share a summary of them here.

Drums - smallerHis first observation was that end users sometimes ignore FIFO, (First in First out). Paint properties shift over time. The amount of change varies by formulation and is the result of the reactions between the myriad chemicals that make up a specific paint. Add to this list that small volume of air in the top of each drum. Those companies that adhere to FIFO are less likely to suffer from changes that take place as those paints age.

His second observation was that the paint is often not tumbled before it is used. The resin, pigments, and solvents can, and do, separate as the paint sits stagnant. A simple tumbling before using the paint helps blend everything and put the pigment back in suspension to promote consistent color application.

His third observation was that the paint needs to be agitated. He admitted that most end users do an adequate job of agitation. While tumbling and agitation serve much the same purpose, tumbling mixes the paint before it is used, whereas agitation mixes the paint as it is being used. Another important difference is that agitation can entrap air in the paint – and how much depends on the degree of agitation and how long it continues – whereas tumbling limits air exposure to that already in the drum. This is an important distinction as oxidation is one of the primary forms of degradation for most chemicals.

His fourth and perhaps most significant observation concerned solvent additions combined with arbitrary process adjustments. (For purposes of this summary, we will use solvent to refer to both solvent in solvent-based paints and water in water-borne paints). There are times where an operator needs to add solvent. For example, after a long break period, it may be necessary to replenish the solvent that has been lost due to evaporation. However, he observed that paint can be altered to suit an operator’s preference and is often done in conjunction with other process adjustments, (i.e. flow rate, atomization, gun speed, etc.). This is where you can generate issues that ultimately create the appearance of paint batch variation. If you do need to make a solvent addition, he recommended that you record when you made the addition, how much you added, and why you added it. (Given our knowledge of viscosity change as a function of temperature, we would add temperature to that list.) At a minimum, you are setting up the next operator with a more complete understanding before he or she begins making adjustments or additions.

We produced a one-minute video on altering paint which does a nice job highlighting this issue. You can find that video by clicking here. The key point in the video is that if you maintain consistent application conditions, the need to add solvent and make process adjustments can be minimized – often eliminated.

As you’re working with your paint supplier to create the perfect formulation, ensuring the right color, gloss and adhesion properties, it would be ideal if you could maintain predictable properties all the way through your application process. Analyzing and maintaining consistent application conditions is something we can help with.

While we understand that painting at the OEM or Tier 1 level is dramatically more complex than just maintaining consistent application conditions, having fewer things to consider and adjust to get the right finish can certainly give you an advantage. It may also cut down on your self-inflicted batch-to-batch variations.

Topics: painting, automotive painting, industrial painting, temperature control systems, Paint Temperature Control Series, robotic painting, paint temperature control, paint surface finish, automotive paint finishing

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