Several analytical tests should be performed daily to enhance the performance and stability of your electrocoat paint bath. These tests include percent solids, pigment to binder ratio, pH, and conductivity. Additional tests may be necessary as well, such as acid/base titrations and solvent analyses, depending on the type of electrocoat product you use. Your paint supplier should assign specification ranges for each test, and every effort should be taken to operate the paint tank within these specifications. Maintaining your electrocoat bath within the recommended ranges will enable you to obtain the best possible performance on line.

Many factors can be impacted by operating your tank in specification, including appearance, hiding, gloss, color control, film coalescence, bath solubility, cure response, filter bag and ultrafilter performance, part rinsing, throwing power, and, most importantly, cost! It is important when testing your paint bath that proper instrumentation and test methods be used to ensure accurate results. An electrocoat tank that is properly maintained will experience minimal downtime and re-working of parts, as well as avoid potentially expensive activities associated with problem solving and corrective action.

Laboratory Equipment and Instrumentation
A number of instruments are used to perform the tests that are necessary to control your electrocoat paint bath. The following table lists the basic equipment needed. Detailed descriptions of the laboratory equipment can be found in the individual test methods at the end.

Table 1. Laboratory Instruments
Test	Equipment/Instruments Needed
Percent Solids by Weight	Analytical balance, forced-air convection oven
Pigment to Binder Ratio	Same as solids, plus muffle furnace
pH	pH meter and probe, buffer solutions
Conductivity	Conductivity meter, beaker cell, calibration solution

It is important to note that all laboratory instruments should be properly maintained and kept in good working order. Routine calibrations and periodic maintenance need to take place to ensure that accurate data can be generated.

Instrument Calibration and Verification/ISO Considerations
Analytical laboratories are easy targets for ISO and QS inspectors, who closely scrutinize data generation and instrument calibration under elements 4.9 Process Control, 4.11 Inspection, Measuring, and Test Equipment, and 4.18 Training. You must be able to prove to an auditor that your laboratory instruments are working properly, and that the personnel involved with conducting the tests are trained to perform them correctly. Therefore, it is important to initiate and execute a workable control plan at your facility. This document tells the auditor what facets of your operation you plan to control to assure quality. Your control plan is also the document that the auditor will reference when conducting an audit. A simple guideline to survive an ISO or QS audit of your analytical laboratory is to “say what you do, and do what you say.”

Some laboratory instruments require more frequent calibration and/or verification than others do. The following table provides a general guideline to ensure that your equipment is operating properly.

Table 2. Calibration/Verification Frequency
Instrument	Calibration/Verification Frequency
Analytical Balance	Monthly
Convection Oven	Monthly
Muffle Furnace	Monthly
pH Meter	Daily
Conductivity Meter	Daily

Any activity associated with instrument calibration or verification should be recorded on detailed log sheets. Be certain your operators are properly trained and competent to perform these functions. Use certified buffer solutions and calibration standards for your pH and conductivity meters and make sure to dispose of these materials when the shelf life expires. Use NIST traceable weights when calibrating your balance and certified temperature probes to verify your solids oven and muffle furnace. If one of your laboratory instruments is not working properly or cannot be calibrated, place an “out-of-service” tag on it until it the instrument is repaired and can be brought back into compliance. Signing and dating any lab record proves that the activity occurred, so this aspect is critical.

Use unique identification labels for any samples being tested in the laboratory. The ID of the sample should match the ID indicated on the daily log-sheet that is used to record test data. Keep your test methods on-hand so you can show an auditor that everyone involved with testing samples follows the same methods to generate data.

Above all, whether calibrating your instruments or recording test data, do not attempt to “fudge” numbers. ISO auditors are like bloodhounds, and once they get on the trail of a questionable record they will trace it to its source in an attempt to discover if the paper trail is complete. You can risk losing your ISO or QS status if an auditor discovers falsified records during an audit.

Operator Training and Test Methods
How do you know your operators in the laboratory are performing the tests properly? The best way to achieve this is to create and use Standard Operating Practices (SOP’s) that reference accepted test methods prescribed by the American Society for Testing and Materials (ASTM International). If everyone conducting tests at your facility uses the same test methods, the chances of duplicating results between operators and controlling your paint tank properly are greatly increased. Operators should be trained using your laboratory ’s SOP ’s to guide them through each test procedure. Training checklists can be created for anyone conducting tests in the lab, and laboratory operators should demonstrate competence in each test to be considered fully trained.

The test methods we follow in our laboratory can be found at the end of this report. All of these tests should be performed at least once per day, or preferably once per shift to maintain the best possible control over your electrocoat paint bath. Samples should be run in duplicate to ensure the results are accurate before making any adjustments to the paint tank. Properly trained operators using approved test methods are essential to a successful electrocoat finishing operation.

Interpretation of Results/Paint Bath Adjustments
How do you interpret and respond to the data you have generated? It is important to know what makes your paint bath “tick” to properly interpret the data. There are three primary components of your electrocoat paint bath: pigment, resin, and solvent. The solvents found in electrocoat are deionized water and significantly smaller quantities of organic co-solvents, which are typically glycol ethers. There are numerous relationships that occur between the various paint components, and the analytical tests you perform can provide valuable insight into these relationships. The results you generate are used to make adjustments to your paint bath, so accuracy and precision are critical to ensure proper paint bath adjustments will take place.

Solids
The solids portion of your electrocoat paint bath is comprised of the pigment and resin components, therefore: %Solids = %Pigment + %Resin. Electrocoat paint is generally low in solids at 10--20% by weight. The remainder is primarily water, hence the viscosity of an electrocoat paint bath is “water-thin” and the solids have a tendency to settle. The paint tank needs to be constantly agitated to keep the solids particles in suspension. The same principle holds true for the sample being tested for solids. It needs to be representative of the electrocoat bath and should be well agitated before testing. If settled material remains in the bottom of the sample container, the solids result will be erroneous. In general, pigment solids tend to settle more readily than resin solids.

Bath solids play a major role in the overall health of your electrocoat system. Baths running in spec for solids have better inherent stability than baths whose solids are low. Low-solids paint baths tend to be less robust and are more prone to problems associated with contamination, as contaminants tend to have an amplified effect on a low-solids bath. Additionally, low solids tanks are more likely to experience difficulty building film and film appearance may be poor. A common cure for many electrocoat paint problems is to add fresh feed, since higher solids impart more robustness to the system and tend to dilute contaminants.

If your solids result is low, add the appropriate amount of fresh resin and paste components (i.e. feed) to bring the value into specification. If the solids result is high, coating parts will effectively lower the solids. If your bath solids are significantly high, it may be necessary to transfer a portion of the electrocoat bath into a storage tank and add deionized water to the tank to lower the solids. This type of action is rarely necessary though, and should only be performed as a “last resort.”

Pigment to Binder Ratio (P/B)
The P/B result is used to determine how much pigment is in your electrocoat paint bath. The percentage of pigment present is usually shown in relationship to the amount of resin or binder, therefore: %Pigment to Binder Ratio = %Pigment ÷ %Binder.

The higher the pigment to binder ratio, the more pigmentation is in the system; the lower the pigment to binder ratio, the less pigmentation is in the system. Some of the factors impacted by the amount of pigment present in the paint bath include hiding, gloss, color control, and cure.

Dark colors generally need less pigmentation to achieve hiding than lighter colors, so the tendency for pigments to settle out of the paint bath is somewhat diminished. As in solids testing, the sample needs to be well agitated before conducting the test.

Typical P/B ratios for black electrocoat paints range from 0.05 to 0.20; typical P/B ratios for white and light gray electrocoat paints range from 0.35 to 0.55.

The P/B test method involves the use of a muffle furnace, which incinerates all organic components of the paint. Paints with high concentrations of organic pigments, such as carbon-based blacks and reds, require the use of a correction factor, which inherently reduces the accuracy of the test. It may be necessary to use an alternate test method for these types of paints. The muffle furnace method works well for paints that contain mostly inorganic pigments, such as whites and grays.

If your P/B result is low, add the appropriate amount of pigment paste to bring the value into spec. If your P/B result is high, add resin. Note that paste and resin additions associated with P/B adjustments will also cause an increase in overall solids, but this increase tends to be relatively small unless copious amounts are added.

It should be mentioned that P/B testing is not necessary for one-component electrocoat products, since the pigment levels are controlled as part of the manufacturing process. Hence, one-component technology is advantageous from a cost standpoint given that the daily P/B test can be eliminated, and a muffle furnace is not needed in the analytical laboratory.

pH
In electrocoat, pH is an indication of overall bath solubility. For cationic electrocoat, pH is acidic (<7.0); for anionic electrocoat, pH is basic (>7.0). Note that the pH result is on a logarithmic scale, so what may appear to be a small change in pH actually represents a large change in the overall chemistry of the paint bath. The following table represents pH results obtained from a cationic epoxy electrocoat paint bath:

Table 3.pH Results
Sample Number	Test	Specification Range	Result
1	pH	5.7 to 6.0	5.27
2	pH	5.7 to 6.0	6.33

The out-of-spec low result obtained from Sample 1 indicates that excess acid is present in the paint tank. Since cationic electrocoat paints are solubilized by acidic species, excess acid can lead to aggressive post rinses and the occurrence of film re-dissolution; i.e. the deposited paint film can be dissolved back into the paint bath. If your film builds are low under normal coating conditions, check the bath pH; it may be detrimentally low (or high, for anionic electrocoat).

Conversely, the out-of-spec high result obtained from Sample 2 indicates that insufficient acid is present in the paint system. This can cause the electrocoat bath to “kick-out,” which is manifested as settled material on horizontal surfaces of parts and/or abnormal bag filter and ultrafilter fouling.

In cationic electrocoat systems, high pH can be adjusted down by adding appropriate acids into the paint bath. Low pH can be adjusted up by regulating the conductivity set point on the anolyte system. Basic materials should never be added to a cationic electrocoat bath, as they are incompatible and will cause the bath to kick-out immediately. Acidic species are imparted into cationic paint baths as part of the coating process, and the anolyte system is used to remove acidic materials from the paint. Adjusting the anolyte conductivity set point to a low value will remove more acid from the paint bath (so the pH of the bath will go up); a high anolyte conductivity set point will remove less acid from the paint bath (so the pH of the bath will go down). Ideally, the conductivity set point of the anolyte is adjusted to maintain a relatively constant bath pH within the specification range.

For anionic (basic) electrocoat systems, high pH can be adjusted by directing permeate into the waste stream, since the basic materials used to solubilize the paint system are water miscible and can be removed through ultrafiltration. Care must be taken not to over-purge the paint bath though, as this can actually lead to even higher pH through the removal of excess acidic species.

If the pH is low, add amine until the pH is in spec. Acidic materials should never be added to an anionic electrocoat bath, as they are incompatible and will cause the bath to kick-out.

Conductivity
In electrocoat, DC electricity is used to drive the paint to the part, so the paint bath must be capable of conducting electricity. The conductivity result is used to determine how conductive your electrocoat paint bath is. The process of deionizing water implies that any ionic components present in the water will be removed; therefore the conductivity of deionized water should be relatively low. For electrocoating purposes, the conductivity of deionized water should be less than 10 µmhos/cm.

The fact that your paint bath is conductive indicates that one of the primary ingredients in the paint is also conductive. Since we use deionized water for electrocoat, this rules out conductivity of water as the source. In fact, the resin portion of the paint imparts the majority of the conductivity to the paint system. As such, increases in bath solids through resin additions will lead to an increase in overall bath conductivity. Now that we have established a relationship between bath solids and conductivity, let’s discuss how to interpret conductivity data. Consider the following example:

Table 4.Conductivity Results
Test	Specification Range	Result
%Solids	14.0 to 16.0	15.62
Conductivity (µmhos/cm)	950 to 1,250	1,475

In this case, the conductivity of the sample in question is high out-of-spec, while the solids are in spec. Assuming the test method used to generate the data is correct, the high conductivity of this sample is an indication that ionic species have contaminated the bath. The paint bath responds by showing an increase in overall conductivity and can also respond by coating parts with inferior film appearance (typically “patchy roughness”) and substandard properties. Several sources of ionic contamination are common, but the most typical is highly conductive pretreatment chemicals being carried into the electrocoat bath by way of the part being coated. Another frequent source is poor quality water. Unless corrective action is taken, serious implications can result and costs will be incurred.

One important point to note is that the temperature of the sample is critical when measuring conductivity. Sample temperature and the corresponding conductivity result move together on a nearly linear scale, so the lower the sample temperature, the lower the conductivity result; the higher the sample temperature, the higher the conductivity result. Our conductivity test method describes a procedure in which 25C (77F) is the proper sample temperature to use.

If the conductivity result is high, direct the permeate flow into your waste stream. This will remove water and any components that are soluble in water, including ionic materials, certain co-solvents, and various acidic and basic species. For some paints, solvent and meq acid and base levels should be tested after purging the electrocoat bath, as they may need to be replenished. If the conductivity result is low (which can occur if your paint bath is over-purged), add resin until the conductivity result is in spec.

Note that resin additions will also affect bath solids and P/B ratio, so these parameters may need to be adjusted as well.

Record Keeping/Database Operations
Data generated from each test should be stored in some fashion. Daily log sheets or laboratory worksheets are useful to record information about the sample, and copies can be kept near the coating station for quick reference. A variety of computer applications may also be used to store and manipulate analytical data. The following graph depicts pH results over a three-month period.

Figure 1. Example of a pH Graph
Graphical interpretations of data can be useful tools in detecting trends. The graph shows periods where bath pH increased and decreased over time. The assumption can be made that these trends prompted action from the operator to avoid a potentially detrimental and costly situation.

Addressing Discrepancies Between Labs
Identical samples tested in different laboratories by different operators rarely generate identical data. Knowing that there is variation inherent to any test performed tells us we should not be surprised if questionable results are obtained in one lab and not in another. Following the same test methods and using laboratory instruments that are properly calibrated can minimize test variation and experimental error. It is important to know that your equipment is functioning correctly. In addition, running tests with multiple samples in duplicate or triplicate increases the statistical accuracy and precision of the data generated.

Proper maintenance of your electrocoat paint bath through analytical testing is critical to managing a cost-effective coatings system. Trained operators using approved test methods will enable appropriate adjustments to be made to your paint bath to keep things running smoothly with minimal downtime and re-working of parts. Performing the following tests on a daily basis and adjusting your electrocoat bath accordingly will enable you to realize significant cost savings at your facility.

Test Methods

Percent Solids Determination

Scope
This method describes the procedure for determining solids content of electrocoat paint baths using a forced-air convection oven.

Safety

• This test procedure may involve hazardous materials, operations, and equipment. This procedure does not purport to address all of the safety concerns associated with its use. It is the responsibility of the users of this procedure to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
• Safety goggles and solvent resistant gloves should be worn when working with wet samples.
• Heat resistant gloves should be worn when removing samples from oven.
• Personnel using this method should be familiar with the safety and handling precautions of the test materials and apparatus used.

Equipment

• Safety Glasses
• Heat Resistant Gloves
• Forced Air Convection Oven capable of maintaining constant temperature of 110C (230F), accurate to + 2C
• Disposable Aluminum Weighing Dishes (18 x 57mm, with handle)
• Disposable Transfer Pipettes
• Balance, accurate to 0.001g

Procedure
1.Place the aluminum dishes in an oven for 30 minutes at 110C (pre-bake).
2.Store conditioned dishes in a desiccator until needed.
3.Test two samples.
4.Number an aluminum-weighing dish for each sample.
5.Record the weight of the empty dish (B).
6.Add 4.0 grams of well-mixed sample to the dish and record the weight (A).
7.Place the sample dish on a panel in the oven for one hour at 110C (230F); the sample must lay flat to insure uniform evaporation; the oven must already be preheated to 110C (230F).
8.Remove the sample dish from the oven; place immediately in desiccator; allow to cool; record the weight (D).

Notes
Avoid touching dishes with your bare hands. Use tongs or pliers to move dishes when weighing. Oil present on your hands could affect results. If un-evaporated liquid is still present in dishes after one hour, verify oven temperature and repeat the test.

Calculation
D =Weight of Solids and Dish B =Weight of Empty Dish A =Weight of Sample and Dish

Pigment/Binder Ratio Determination (P/B)

Scope
This method covers the procedure for determining the pigment-to-binder ratio of electrocoat paint baths.

Safety

• This test procedure may involve hazardous materials, operations, and equipment. This procedure does not purport to address all of the safety concerns associated with its use. It is the responsibility of the users of this procedure to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
• Safety goggles and solvent resistant gloves should be worn when working with wet samples.
• Heat resistant gloves should be worn when removing samples from oven.
• Personnel using this method should be familiar with the safety and handling precautions of the test materials and apparatus used.

Equipment

• Safety Glasses
• Heat Resistant Gloves
• Forced-Air Convection Oven capable of maintaining constant temperature of 110C (230F), accurate to + 2C
• Disposable Aluminum Weighing Dishes (18 x 57mm, with handle)
• Disposable Transfer Pipettes
• Balance, accurate to 0.001g
• Muffle Furnace capable of maintaining constant temperature of 500C (932F), accurate to + 4C

Procedure
1.Place the aluminum dishes in an oven for 30 minutes at 110C (pre-bake).
2.Store conditioned dishes in a desiccator until needed.
3.Test two samples.
4.Number two aluminum weighing dishes for each sample.
5.Stack the dishes on top of each other and record the weight of both dishes (B).
6.Add 4.0 grams of well-mixed bath sample to only the top dish and record the total weight (A).
7.Place empty dish beside sample dish on a panel in the oven for one hour at 110C (230F); the sample must lay flat to insure uniform evaporation. Note: The oven should already be preheated to 110C.
8.Remove from oven; lace empty dish securely on top of paint sample dish. Fold over tabs on side of dishes to help secure dishes together; place immediately in desiccator; allow to cool; record the weight (D).
9.Place in muffle furnace and bake for 90 minutes at 500C. Note: The muffle furnace should initially be at ambient temperature. The 90-minute bake begins when the muffle furnace reaches 500C.
10.Remove from furnace; allow dishes to cool; record the total weight (H). Note: The solids and pigment/binder tests can be combined with the % solids calculated between Steps #5 and #8.

Calculation
H =Weight of Ash and Dish
B =Weight of Empty Dish
A =Weight of Sample and Dish
% Pigment = %Ash x Correction Factor*
N = %Pigment
G = %Solids

*The Correction Factor corrects for the amount of organic pigment present in the formulation, which is removed during ashing. Your coatings supplier should provide a Correction Factor, if applicable. The Correction Factor is primarily used for black or bright red coatings. Most other colors will have a correction factor of 1.0.

pH Determination

Scope
This method describes the procedure for determining pH of electrocoat paint baths.

Safety
This test procedure may involve hazardous materials, operations, and equipment. This procedure does not purport to address all of the safety concerns associated with its use. It is the responsibility of the users of this procedure to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Safety goggles and rubber gloves should be used. Personnel using this method should be familiar with the safety and handling precautions of the test materials and apparatus used.

Equipment

• pH Meter With Electrode(s)
• 250 ml Beaker

Reagents: Anionic Electrocoat

• Certified Buffer Solution, pH 7.0
• Certified Buffer Solution, pH 8.0
• Certified Buffer Solution, pH 10.0

Reagents: Cationic Electrocoat

• Certified Buffer Solution, pH 4.0
• Certified Buffer Solution, pH 6.0
• Certified Buffer Solution, pH 7.0

Note
Never pour reagents back into original container; dispose of after each use or maintain separate containers and change weekly. Observe expiration dates on buffer containers.

Procedure
Follow the manufacturer ’s instructions for operating the pH meter.

Notes
It is recommended that the slope of efficiency range on the pH meter to be within the range established by the manufacturer. A tight slope of efficiency setting generates more accurate results than a wide slope of efficiency.

It is recommended to run all pH readings with samples and buffers at 77F (25C).

1.For Anionic Electrocoat, standardize the instrument with the pH 7.0 and pH 10.0 buffer solutions. Verify calibration with pH 8.0 buffer.

1a.For Cationic Electrocoat, standardize the instrument with the pH 4.0 and pH 7.0 buffer solutions. Verify calibration with pH 6.0 buffer.

2.Rinse the electrodes with distilled or deionized water and blot dry with absorbent tissue (Kimwipe/paper towel).

3.Immerse the electrodes into the beaker containing the paint sample and read the pH on the meter scale. No calculation is necessary.

4.Rinse the electrodes thoroughly with deionized water first to remove the majority of the paint. Use acetone only if necessary after a thorough water rinse to remove any remaining paint on the electrodes.

Notes: For Anionic Electrocoat, the electrodes should be placed in pH 7.0 buffer solution when not in use. For Cationic Electrocoat, the electrodes should be placed in pH 4.0 buffer solution when not in use.

Conductivity Determination

Scope
This method describes the procedure for determining the conductivity of electrocoat paint baths and DI water.

Safety

• This test procedure may involve hazardous materials, operations, and equipment. This procedure does not purport to address all of the safety concerns associated with its use. It is the responsibility of the users of this procedure to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
• Safety goggles and solvent resistant gloves should be worn when working with wet samples.
• Personnel using this method should be familiar with the safety and handling precautions of the test materials and apparatus used.

Equipment

• Conductivity Meter capable of automatically setting K factor
• Conductivity Cell With a Cell Constant of 1.0
• Thermometer, handheld digital

Reagents

• Potassium Chloride Calibration Solution (1,000 µmhos/cm traceable conductivity calibration standard) Note: Never pour used KCl solution back into original container. Dispose of after each use; observe expiration date on bottle.

Calibration Procedure
Before determining the specific conductivity of the electrocoat bath, the conductivity meter must be calibrated by using a 1,000-µmhos/cm conductivity traceable calibration standard KCI solution.

1.Be sure cell is clean by rinsing with deionized water.

2.Pour precisely 25 ml of potassium chloride calibration solution (1,000 µmhos/cm) into a beaker and adjust temperature to 77F (25C).

3.Pour calibration solution into cell.

Note: The most important part of the conductivity test is assuring 77F (25C) temperature of all measured samples. A 5F difference in temperature can change the conductivity reading by 100 µmhos/cm or more. Conductivity can also vary if less than 25 ml of standard volume is used.

Sample Procedure
1.Be sure cell is clean by rinsing with deionized water.

2.Pour precisely 25 ml of paint bath into a beaker and adjust temperature to 77F (25C).
Note: Using the correct temperature is critical to obtain accurate results, as is having the proper volume of paint bath (25 ml). If less than 25 ml of standard volume is used, conductivity can vary.

3.Pour sample into conductivity cell.

4.Read conductivity measurement on the meter. No calculation is necessary.

5.Rinse cell thoroughly with deionized water and let clean deionized water sit in cell at all times when not in use.