Nicoat

VOC Number

This is the third in a series of Tech Notes about volatile emissions and what printers can do to comply with regulations while maintaining high quality operations.

How VOC Emissions Are Figured

Annual VOC emissions are calculated based on how much solvent is contained in the products you use, multiplied by how much you use.

How Much Solvent Products Contain

The manufacturer can tell you, in one of two ways:

• Pounds of solvent per gallon of product; or
• Percentage of solvent in product.

The amount of solvent in pounds per gallon is the VOC number. This is the number the EPA says you must use to calculate annual VOC emissions.

VOC Number Accuracy

Unfortunately, VOC numbers aren't always accurate. The EPA's method for figuring VOC numbers is not accurate for products that contain very little solvent-like aqueous coatings.

The EPA method (called Method 24A) starts by removing all of the water from the product (fountain solutions, aqueous coating, etc.) through a process called titration. Then, a mathematical calculation is used to figure out how much of the remaining material is solvent. Basically, the calculation says, "If we take out all the water and subtract the solids, the remainder is solvent."

EPA Method Doesn't Work For Aqueous Coatings

The EPA method assumes that titration removes all of the water from the product being tested. That doesn't happen in the real world; there can be a significant margin of error. The EPA method doesn't take such errors into account: Any water that remains in the product after titration is counted as solvent.

For example, let's say we're testing an aqueous coating that contains 4 percent solvent. The titration procedure removes only 97 percent of the water. Remember, whatever water the titration fails to remove, in this case 3 percent, is counted as solvent in the test results.

Though the titration error is small, the impact is significant. The test results will show that the coating contains 7 percent solvent -- that is, the 4 percent solvent that is actually there, plus the 3 percent water that the titration missed. Because aqueous coatings contain so little solvent, a small margin of error in titration has an important effect on the final test numbers. That is why the EPA test method is not appropriate for aqueous coatings.

A More Accurate Measure

Nicoat lists the solvent percentage on the MSDS sheet. The solvent percent is a more accurate way to measure the amount of solvent in an aqueous coating.

A Better Way

It's called chromatography. This is a laboratory procedure that separates the solvents out of an aqueous coating, then weighs them. The procedure itself is straightforward, but it requires sophisticated equipment. For aqueous coatings, chromatography is generally considered more accurate than EPA's method. That's why Nicoat uses both Method 24A and chromatography to determine the solvent content of its coatings, which is listed on the MSDS.

However, you should know that, although chromatography is more reliable than Method 24A, and it is routinely used by chemical manufacturers, it has not yet been approved by the EPA. This means the EPA may consider you noncompliant if you rely on VOC numbers determined by chromatography rather than Method 24A.

Nicoat can provide you with both VOC numbers and percent solvent as determined through chromatography.

Figure The Solvent Percent

Remember that aqueous coatings are mostly water. To figure the solvent percent of an aqueous coating, you first have to subtract the water. After you have eliminated the water, you can calculate the actual VOC.

The calculation for products that are mostly solvent, like press varnish, uses a simpler version of the same equation: