PAINT BOOTH MAINTENANCE

WATER WASH CHEMICALS

Chemical treatment is required in most water wash paint booths. To meet these needs you have the most complete line of products of any chemical supplier. In the following we will take each need one by one, relate which products are applicable and explain the products' action in treating the need.

Paint Kill With Alkaline Treatment Products

The basic need for all water wash booths is for a product to kill the paint (eliminate tackiness) in the solution tank. If the booth does not contain a treatment product, the paint will stick and adhere to the solution tank, the nozzles and eventually clog the circulation system.

One type of paint kill is based on reaction of the paint with an alkaline treatment product. The alkali in the product reacts with acid sites in the paint resin. This usually requires a pH in the solution above 9.0. A bad side effect of this type of kill is that some of the resulting reactant products may be soaps and cause foam. That is why it is best to use only the minimum amount of treatment product necessary to achieve the desired killed condition.

The type of paints that are traditionally treated with these alkaline products are basically the solvent containing, oil based paints.

However, new laws of Federal and State Environmental Protection Agencies are inducing paint companies to put less solvent in paints. Because of these changes the traditional high solvent paints are gradually being eliminated in industrial accounts. They are being replaced with high solids and water borne paints.

The high alkalinity type paint kill is also used on the new high solid paints. However, the alkaline treatment products for high solid paints, have increased wetting properties. This is because the new high solid paints contain less solvent than the traditional paints and need increased wetting for proper treatment.

Paint Kill With Acid Treatment Products

As you just learned, in industry today, most paints are treated by an alkaline treatment product. However, there is another new type of paint coming into use, which can be treated by acid products. This paint is called water borne or water based. Resin systems in these paints are treated at a solution pH of 4 to 6.

Defoaming

The need for defoaming in water wash booths seems to be on the increase. This can be attributed to the gradual switching to the new type paints and to some of the newer type paint booths. The new high solids and water borne paints have the tendency to foam more than traditional paints. Also some of the new paint booths are attempting to achieve better break up of the paint particles with turbulent action in the solution tank.

The other source of foam, is the possible formation of soap resulting from the reaction of an alkaline treatment product with the paint.

It is important to note that foam helps to float paint. If the customer desires to float the paint, eliminating all foam may allow a heavy paint to sink.

In your standard line of treatment products, de-foaming properties have been put into the products. However, it is impossible and too expensive to have enough defoamer in the treatment products to adequately handle all foaming problems.

Excessive foaming in paint booths is best treated by using a separate defoam product in addition to the treatment product. Some standard organic solvents or oils are sometimes added to kill foam. A safer method is to use organic defoamers. These organic defoamers concentrate near the solution surface preventing the formation of foam bubbles.

NEVER USE SILICONES FOR DEFOAMING PAINT BOOTHS. A trace amount of silicone in the atmosphere can cause a serious paint coating problem referred to as "fish eyes". These are small spots over which the paint will not coat and have the appearance of fish eyes.

Paint Treatment With Flocculites

The furthering development of the Milanco Water Treatment Product Line has exhibited that some of the flocculants products in that line, can also effectively be used to aid in treating paint in water wash booths. The flocculant product is not normally used by itself, but is used as an additional product along with the paint kill product.

When a flocculant is used at low concentrations up to 50ppm, it will cause the killed paint particles to floc together. This helps to better separate the killed paint from the water and makes it easier to collect the killed paint. Dewatering of the paint is faster, thereby reducing the quantity of waste paint solids generated.

For heavy paints, flocculation into larger particles may cause the paint to sink, if this is desirable.

When a flocculant is used at higher concentrations, 300 to 1000 ppm, it reacts just the opposite as it did at low concentrations, and now causes the killed paint to defloc and break up into smaller particles. Killed paints that would normally sink, can be suspended longer with this defloccing treatment. This provides extended time and surface for the paint booth compound to kill the paint. This results in a more efficient use of the booth compound and an overall cleaner system.

However, not all killed paints are susceptible to flocculant treatment. This can be pre-tested with a flocculant test kit or by sending a paint sample to the Milanco for testing.

Floating Overspray

Paint overspray is normally heavier than water and thus has a strong tendency to sink. One action that helps to float the paint in some booths, is the churning action of the water. This causes air to be entrapped, thus suspending the killed paint. Foam also helps to float paint. Another method, if the paint is susceptible, is defloccing the killed paint into smaller particles with a flocculant.

With time most paints will eventually sink. Floating sludge should be removed at a rate which disallows sinking. The weight of the paint and how long booth conditions and treatment products can float it, will dictate if surface skimming is the optimum method of removal. The alternative is allowing the paint to sink and eventually removing the sludge from the tank bottom.

Sinking The Overspray

Surface skimming is the usual preferred method of paint removal, but there are times when a customer desires to sink the paint. To accelerate sinking If the paint is susceptible, floc the killed paint with a flocculate. This also achieves a more de-watered sludge. With some paints, an over-kill with higher concentrations of booth compound, may accelerate sinking.

There are two programs that promote the sinking of paint solids. The first actually detackifies the paint particles and keeps then in suspension. A centrifuge or hydrocyclone is then used to continually remove the solids from the booth water. The water is then returned to the booth with the unused detackifier, still active and ready to treat more paint overspray. These machines will only remove the paint particles that are heavier than water and big enough to see. The paint detackification program is very important to maintain because the paint particles may pass through the pump, manifold, risers, and spray nozzles many times before being removed by the centrifuge or hydrcyclone.

The second program is to simply allow the paint particles to sink to the bottom of the booth. The tank is drained periodically and shoveled out by hand, or periodically vacuumed out with an industrial paint solids vacuum that filters out the solids and returns the liquid back to the tank. The paint detackifier must keep the paint solids from sticking together so that the sludge on the bottom does not turn into a layer of "putty."

Paint which is allowed to sink can be removed in several ways. A centrifuge or hydrocyclone is used when the water is kept in constant motion and the paint particles aren’t heavy enough to stay on the bottom when the recirculation system is turned back on.

Booth Rust Preventation

Rust is prevented in two ways. If the alkalinity of the solution is kept at a pH of 9 or more, there is little chance of rusting. For those treatment compounds which work at a pH lower than 9, chemical rust inhibitors are used in the products.

Prevention of Micro-Organism Growth

Micro-organisms generally will not grow in environments of greater than pH 9.5. For solutions at pH below 9.5, a well maintained, clean booth with no blockage in the circulation system, will prevent micro-organisms growth. Chemicals which prevent micro-organisms growth are used in your booth compounds. However, there may be extreme conditions when a non-cleaned booth builds up stagnant material and causes a rotten egg odor.

Choosing The Treatment Products

Now that you have some idea of what type of products are used to treat the needs of a water wash solution, how do you decide which of the products to use?

The best answer to this is, have the Milanco Technical Service lab test the paint and tell you what products perform the best. This is done by sending in a quart sample of paint with a work order.

Besides water wash products, Milanco also has a complete line of Paint Booth Maskants. You can sell these for use on any type of booth and almost all paint booth customers use them.