- Email: [email protected]
High-versus low-solids coatings and VOC compliance
atings and
HIGH-SOLIDS
VERSUS LOW-SOLIDS
COATINGS
Is there any difference in product quality and appearance when one compares high-solids and lowsolids coatings?
When you refer to ‘high-solids” coatings I presume you are referring to coatings that meet EPA limits such as 3.5 lb/gal, 2.8 lb/gal, etc. Similarly, when you speak of “low-solids” coatings, I assume that these are noncompliant coatings with higher VOCs? During the 1980s and 1990s the paint industry made an all-out effort to develop compliant coatings that did not compromise the physical and chemical performance properties that we enjoyed with the existing noncompliant coatings. To a great extent the paint vendors met this challenge, and there are some technologies in which the manufacturers even surpassed the performance properties of the “old” systems. On the other hand, the application properties were often compromised. Even current compliant coatings are often more difficult to apply than their noncompliant cousins of the 1980s and 1990s. It’s no secret that high-solids coatings are more difficult to apply at low film thicknesses than we could achieve with low-solids coatings. Further, many painters still struggle to apply these coatings using HVLP guns without getting “orange peel” finishes. Consequently, during the past 15 years the public has unconsciously come to accept that many nonautomotive finishes simply come with the orange peel appearance. Autobody shops often complain that they cannot achieve automotive finishes with high-solids coatings and this is a problem with fussy customers. Other application problems also exist. For instance, high-solids coatings often need longer curing times; they easily produce runs and sags if the application is not well controlled, and plural-component coatings tend to have shorter pot lives. To summarize, for the most part, you can expect the chemical and physical properties to be much the same as the old systems, but in many cases appearance and application properties have been compromised. Ron Joseph is an independent Calif. E-mail, [email protected].
December
2001
coating
consultant
in San Jose,
RELATIONSHIP
BETWEEN VAPOR PRESSURE AND VOC
Why is acetone an exempt VOC (smog former) even though its vapor pressure is approximately 58 mm Hg. What is the cutoff point in making this determination?
Vapor pressure and the smog-forming tendencies of a solvent are not related. Years ago the EPA used a vapor pressure of 0.1 mm Hg as the threshold for determining whether or not a VOC should be considered to be a precursor to the formation of smog (ozone). The EPA assumed that if an organic compound had a vapor pressure equal to or greater than 0.1 mm Hg, it should be considered a VOC, where VOC implied that it contributed to the formation of ozone (0,). It is true that acetone has a high vapor pressure; however, already in the 1980s (and perhaps even before) companies, such as Dow Chemical, demonstrated that certain stable VOCs do not form smog with any ease. The EPA confirmed that compounds, such as l,l,l trichloroethane, acetone, methyl acetate, methyl siloxanes, and many fluor-chloro hydrocarbons, have a negligible tendency to react with nitrogen oxides (NOx) in the presence of sunlight to form ozone; therefore, the EPA called such compounds “exempt.” They do not form ozone easily and are not considered a threat to air pollution, at least as far as smog is concerned. These organic compounds are volatile, as demonstrated by their high vapor pressures, but they are not VOCs or smog formers. If you find a compound listed on an MSDS that has a vapor pressure less than 0.1 mm Hg it is most likely that the compound is not sufficiently volatile to be considered a “VOC.” While the EPA used this threshold value as the determining factor many years ago, the current requirement is to evaluate the compound in accordance with EPA Method 24 or 24a. If one of these methods provides results that show the compound to be even partially volatile, then unless it is on the list of exempt compounds, it is considered by default to be a smog former. SPRAYBOOTH EFFICIENCY
AIR VELOCITY AND CAPTURE
A company that I work with uses electrostatic bells and is permitted by OSHA to reduce the air velocity 43
through its spraybooths to 60 fpm. is required by the state air quality at least 90% of the VOCs emitted operations and abate them in a How does the reduced air velocity efficiency of the spraybooth?
Also, the company agency to capture from the painting carbon adsorber. affect the capture
The answer really depends on the spraybooth design rather than on the velocity. If the booth is properly designed and maintained, air turbulence will be minimal and all or most of the air entering the booth will move to the filters from where the solvent-laden air can be directed to the abatement device. If the booth is poorly designed or poorly maintained, airflow through the booth will be turbulent regardless of the air velocity. In this case, the solvent-laden air will be able to escape from the booth through conveyor openings, even from the back of the booth where access doors might be located; therefore, the key to having a high capture efficiency is to insure that the booth is designed so that one
Getting YGC & HAP information fmm d MS&
’
Value of EPA Method 24 for validating VKX-IAP data Calculations for VOC/HAP in Ibslgal, k&gal solids, lbslgal solids applied, Ibs VOC/lb coating, mass balances, and more Transfer efficiency-the
most effective P2 strategy
New MACT regulations for Misc. Metal Parts and Plastic Parts. .!,a “. Measuring compliance of Fl_P arx$
can always keep the airflow in balance. I have written several columns in recent years on this topic and encourage you to read about the many parameters that affect this property. CALCULATING CHEMICAL
POTENTIAL TO EMIT FOR A BATCH
PROCESS
work with a company that manufactures resins in a batch process. The permit requires that the company calculate the maximum process rate, yet no two batches are of the same size nor is the residence time in the reactor the same. How can such a calculation
I
be accomplished?
A review of the company’s manufacturing records should easily be able to identify the maximum batch size that has been processed over the past year or two. Similarly, for QC purposes the operators usually keep records of the process times, and it should easily be possible to get a reasonable range of the shortest and longest times. Perhaps you can even
T&J Industries specializes in anodizing racks and rack components. Our broad line of products include: l Formed Disc Racks l Discs l Fishbone Racks l Utility Racks l Panels l Clips l Slotted Hangers l Pierced Hole Hangers l Angle Bars l Cross Members & Hardware For a FREE catalog call our Minnesota office at (952) 226-1’792, or E-mail [email protected], OR call our California office at (805) 23743101,or E-mail [email protected].
General NESHAP
www.tj-industries.com
Circle 002 on reader card or go to www.thru.to/webconnect 44
Circle 039 on reader card or go to www.thru.to/webconnect Metal Finishing
find a correlation between the batch size and the process times. I assume that this question relates to calculating the Potential to Emit (PTE) for a Title V facility. If this is so, the company environmental representative and the agency’s permitting engineer should be able to agree on the maximum values to be used. If both parties are flexible it won’t be necessary to search for the ultimate maximum. Surely an approximate figure will suffice? QUICK AND COMPLIANCE
DIRTY
METHOD
TO DETERMINE
VOC
This question relates to situations in which a company is required to comply with a specific VOC limit for its coatings. Is there a short and simple method for determining if a mixed coating is likely to have been overthinned by the painter(s)? For instance, can one use coating viscosity or density to make a quick and dirty determination?
Viscosity is inversely proportional to temperature. As temperature increases, viscosity decreases; however, be aware that this is not a linear relationship. If you set up precise standards for different mixing ratios at a specified constant temperature you should be able to determine the viscosity at which the coating is likely to exceed the VOC limit. If you choose this method, be aware that you will need a sophisticated, sensitive laboratory instrument to measure the viscosity and I very much doubt that a simple Zahn cup will do the trick. Further, even if you can determine the viscosity at
Kushner Electroplating
which the VOC is exceeded, this would not be legally acceptable for citing the company for noncompliance. The only legal method for determining compliance is EPA Method 24, which in itself comprises several ASTM methods, none of which includes viscosity. In the case of plural component coatings, such as polyurethanes and epoxies, the problem becomes considerably more difficult, because the viscosity starts to increase immediately after the components are mixed. Initially, the viscosity increases almost imperceptibly, but as the coating ages the viscosity rises ever more rapidly until the coating becomes a solid. Moreover, the reaction time is also a function of temperature, with viscosity increasing rapidly as the temperature increases; therefore, for plural component coatings it seems most unlikely that you would want to use viscosity as your quick and dirty tool to screen for potentially out-of compliance coatings. Density is definitely a method that you could consider for screening both single and plural-component coatings. As with viscosity, temperature must be taken into account, but I don’t believe density is quite as sensitive to temperature fluctuations. With properly established standards it is possible that you can use this method to perform your quick and dirty screening. Try both methods and see if they work, but always remember that the only legal method for determining compliance is EPA Method 24. MF
School
“Training Electroplaters Since 1947”
TkAlAVNG
FOR BETTER
ELECTROPLATING a/
METAL
FINISHING
KNOW
HOW II
CORRESPONDENCE PROGRAMS d
GROUP TRAINING PROGRAMS c/ ON-SITE TRAINING PROGRAMS d
CUSTOM TRAINING PROGRAMS 732 Glencoe Court, Sunnyvale, CA 94087 (408) 749-8652 . Fax (408) 749-0176 E-mall: [email protected] www.plotlngschool.com
Circle 026 on reader card or go to www.thru.to/webconnect December
2001
Circle 004 on reader card or go to www.thru.to/webconnect 45
HIGH-SOLIDS
VERSUS LOW-SOLIDS
COATINGS
Is there any difference in product quality and appearance when one compares high-solids and lowsolids coatings?
When you refer to ‘high-solids” coatings I presume you are referring to coatings that meet EPA limits such as 3.5 lb/gal, 2.8 lb/gal, etc. Similarly, when you speak of “low-solids” coatings, I assume that these are noncompliant coatings with higher VOCs? During the 1980s and 1990s the paint industry made an all-out effort to develop compliant coatings that did not compromise the physical and chemical performance properties that we enjoyed with the existing noncompliant coatings. To a great extent the paint vendors met this challenge, and there are some technologies in which the manufacturers even surpassed the performance properties of the “old” systems. On the other hand, the application properties were often compromised. Even current compliant coatings are often more difficult to apply than their noncompliant cousins of the 1980s and 1990s. It’s no secret that high-solids coatings are more difficult to apply at low film thicknesses than we could achieve with low-solids coatings. Further, many painters still struggle to apply these coatings using HVLP guns without getting “orange peel” finishes. Consequently, during the past 15 years the public has unconsciously come to accept that many nonautomotive finishes simply come with the orange peel appearance. Autobody shops often complain that they cannot achieve automotive finishes with high-solids coatings and this is a problem with fussy customers. Other application problems also exist. For instance, high-solids coatings often need longer curing times; they easily produce runs and sags if the application is not well controlled, and plural-component coatings tend to have shorter pot lives. To summarize, for the most part, you can expect the chemical and physical properties to be much the same as the old systems, but in many cases appearance and application properties have been compromised. Ron Joseph is an independent Calif. E-mail, [email protected].
December
2001
coating
consultant
in San Jose,
RELATIONSHIP
BETWEEN VAPOR PRESSURE AND VOC
Why is acetone an exempt VOC (smog former) even though its vapor pressure is approximately 58 mm Hg. What is the cutoff point in making this determination?
Vapor pressure and the smog-forming tendencies of a solvent are not related. Years ago the EPA used a vapor pressure of 0.1 mm Hg as the threshold for determining whether or not a VOC should be considered to be a precursor to the formation of smog (ozone). The EPA assumed that if an organic compound had a vapor pressure equal to or greater than 0.1 mm Hg, it should be considered a VOC, where VOC implied that it contributed to the formation of ozone (0,). It is true that acetone has a high vapor pressure; however, already in the 1980s (and perhaps even before) companies, such as Dow Chemical, demonstrated that certain stable VOCs do not form smog with any ease. The EPA confirmed that compounds, such as l,l,l trichloroethane, acetone, methyl acetate, methyl siloxanes, and many fluor-chloro hydrocarbons, have a negligible tendency to react with nitrogen oxides (NOx) in the presence of sunlight to form ozone; therefore, the EPA called such compounds “exempt.” They do not form ozone easily and are not considered a threat to air pollution, at least as far as smog is concerned. These organic compounds are volatile, as demonstrated by their high vapor pressures, but they are not VOCs or smog formers. If you find a compound listed on an MSDS that has a vapor pressure less than 0.1 mm Hg it is most likely that the compound is not sufficiently volatile to be considered a “VOC.” While the EPA used this threshold value as the determining factor many years ago, the current requirement is to evaluate the compound in accordance with EPA Method 24 or 24a. If one of these methods provides results that show the compound to be even partially volatile, then unless it is on the list of exempt compounds, it is considered by default to be a smog former. SPRAYBOOTH EFFICIENCY
AIR VELOCITY AND CAPTURE
A company that I work with uses electrostatic bells and is permitted by OSHA to reduce the air velocity 43
through its spraybooths to 60 fpm. is required by the state air quality at least 90% of the VOCs emitted operations and abate them in a How does the reduced air velocity efficiency of the spraybooth?
Also, the company agency to capture from the painting carbon adsorber. affect the capture
The answer really depends on the spraybooth design rather than on the velocity. If the booth is properly designed and maintained, air turbulence will be minimal and all or most of the air entering the booth will move to the filters from where the solvent-laden air can be directed to the abatement device. If the booth is poorly designed or poorly maintained, airflow through the booth will be turbulent regardless of the air velocity. In this case, the solvent-laden air will be able to escape from the booth through conveyor openings, even from the back of the booth where access doors might be located; therefore, the key to having a high capture efficiency is to insure that the booth is designed so that one
Getting YGC & HAP information fmm d MS&
’
Value of EPA Method 24 for validating VKX-IAP data Calculations for VOC/HAP in Ibslgal, k&gal solids, lbslgal solids applied, Ibs VOC/lb coating, mass balances, and more Transfer efficiency-the
most effective P2 strategy
New MACT regulations for Misc. Metal Parts and Plastic Parts. .!,a “. Measuring compliance of Fl_P arx$
can always keep the airflow in balance. I have written several columns in recent years on this topic and encourage you to read about the many parameters that affect this property. CALCULATING CHEMICAL
POTENTIAL TO EMIT FOR A BATCH
PROCESS
work with a company that manufactures resins in a batch process. The permit requires that the company calculate the maximum process rate, yet no two batches are of the same size nor is the residence time in the reactor the same. How can such a calculation
I
be accomplished?
A review of the company’s manufacturing records should easily be able to identify the maximum batch size that has been processed over the past year or two. Similarly, for QC purposes the operators usually keep records of the process times, and it should easily be possible to get a reasonable range of the shortest and longest times. Perhaps you can even
T&J Industries specializes in anodizing racks and rack components. Our broad line of products include: l Formed Disc Racks l Discs l Fishbone Racks l Utility Racks l Panels l Clips l Slotted Hangers l Pierced Hole Hangers l Angle Bars l Cross Members & Hardware For a FREE catalog call our Minnesota office at (952) 226-1’792, or E-mail [email protected], OR call our California office at (805) 23743101,or E-mail [email protected].
General NESHAP
www.tj-industries.com
Circle 002 on reader card or go to www.thru.to/webconnect 44
Circle 039 on reader card or go to www.thru.to/webconnect Metal Finishing
find a correlation between the batch size and the process times. I assume that this question relates to calculating the Potential to Emit (PTE) for a Title V facility. If this is so, the company environmental representative and the agency’s permitting engineer should be able to agree on the maximum values to be used. If both parties are flexible it won’t be necessary to search for the ultimate maximum. Surely an approximate figure will suffice? QUICK AND COMPLIANCE
DIRTY
METHOD
TO DETERMINE
VOC
This question relates to situations in which a company is required to comply with a specific VOC limit for its coatings. Is there a short and simple method for determining if a mixed coating is likely to have been overthinned by the painter(s)? For instance, can one use coating viscosity or density to make a quick and dirty determination?
Viscosity is inversely proportional to temperature. As temperature increases, viscosity decreases; however, be aware that this is not a linear relationship. If you set up precise standards for different mixing ratios at a specified constant temperature you should be able to determine the viscosity at which the coating is likely to exceed the VOC limit. If you choose this method, be aware that you will need a sophisticated, sensitive laboratory instrument to measure the viscosity and I very much doubt that a simple Zahn cup will do the trick. Further, even if you can determine the viscosity at
Kushner Electroplating
which the VOC is exceeded, this would not be legally acceptable for citing the company for noncompliance. The only legal method for determining compliance is EPA Method 24, which in itself comprises several ASTM methods, none of which includes viscosity. In the case of plural component coatings, such as polyurethanes and epoxies, the problem becomes considerably more difficult, because the viscosity starts to increase immediately after the components are mixed. Initially, the viscosity increases almost imperceptibly, but as the coating ages the viscosity rises ever more rapidly until the coating becomes a solid. Moreover, the reaction time is also a function of temperature, with viscosity increasing rapidly as the temperature increases; therefore, for plural component coatings it seems most unlikely that you would want to use viscosity as your quick and dirty tool to screen for potentially out-of compliance coatings. Density is definitely a method that you could consider for screening both single and plural-component coatings. As with viscosity, temperature must be taken into account, but I don’t believe density is quite as sensitive to temperature fluctuations. With properly established standards it is possible that you can use this method to perform your quick and dirty screening. Try both methods and see if they work, but always remember that the only legal method for determining compliance is EPA Method 24. MF
School
“Training Electroplaters Since 1947”
TkAlAVNG
FOR BETTER
ELECTROPLATING a/
METAL
FINISHING
KNOW
HOW II
CORRESPONDENCE PROGRAMS d
GROUP TRAINING PROGRAMS c/ ON-SITE TRAINING PROGRAMS d
CUSTOM TRAINING PROGRAMS 732 Glencoe Court, Sunnyvale, CA 94087 (408) 749-8652 . Fax (408) 749-0176 E-mall: [email protected] www.plotlngschool.com
Circle 026 on reader card or go to www.thru.to/webconnect December
2001
Circle 004 on reader card or go to www.thru.to/webconnect 45