Theoretically, coatings applied by the UNICARB system are no different than conventionally applied coatings. In a cured coating film, the delivery solvent rarely plays a role. Its only purpose is to lower the viscosity so that the material can be sprayed. After application, the delivery solvent evaporates and leaves the film. Supercritical CO2 is used by the UNICARB system to replace the organic delivery solvents. Other solvents and materials such as the resin system, pigment package, and other additives remain unchanged. The CO2 supplies an atomization mechanism and is vaporized from the coating during the atomization process.

For material to be used in the UNICARB system, the coating supplier must know of the intent to use supercritical CO2 as the solvent. Testing is required to ensure the CO2 will properly dissolve in the organic coating material, provide adequate solvent properties, and is compatible with the other materials. Other major components of the coating system remain unchanged.

The UNICARB equipment is more complex than conventional spray systems although its operation is as simple. Operators and facility maintenance personnel would require three days of training with the equipment. Operators would need to be trained on the aspects of airless sprayers, specifically the effect of nozzle selection on spray pattern and application rate. Typical spray practices will need to be followed. The operator would be able to select the correct nozzle (spray pattern) for different parts, and personnel spraying preferences.

Once the ratio of paint to CO2 is set for a given coating, it will not require changing. However, regular maintenance is necessary to ensure correct calibration of critical measurement components. If these components are neglected, an improper mixture of coating and CO2 could occur, resulting in application problems. One 50-lb CO2 cylinder should supply the needs of 19 trailers.

Use of the UNICARB CO2 system results in the following compliance benefits:

• Elimination or significant reduction of VOCs used as solvents in paints, which are associated with the formation of smog typically regulated by state and local air pollution control districts.
  
• Elimination of hazardous air pollutants (HAPs) used as solvents in paints, which are regulated by federal, state, and local regulations including the National Emissions Standards Hazardous Air Pollutants (40 CFR 63).
  
• Elimination of all SARA Title III reporting substances from coating process (40 CFR 300, 355, 370, and 372; and EO 12856).
  
• Reduced generation of coating waste and cleaning solvents that may need to be handled and disposed as hazardous waste under 40 CFR 260 and related sections.
  
• Reduced occupational exposures that are regulated under 29 CFR 1910.

Compliance benefits include: 1) elimination of recordkeeping and reporting requirements under the Title V, NESHAP Program and SARA programs, 2) reduced administrative burden associated with hazardous waste (i.e., tracking, plans, reports, and training), and 3) reduced administrative burden associated with OSHA (i.e., training and recordkeeping).

According to an Environmental Protection Agency (EPA) legal opinion dated April 10, 1998, the agency has the authority to regulate CO2 as a pollutant under the Clean Air Act. Currently the EPA has no plans to do this. However, the UNICARB process does not produce any new CO2 emissions that would be regulated. Rather, existing CO2 is used for the process and returned to the environment; additionally, the volume emitted from a UNICARB spray operation would be considered infinitesimal in comparison to other major CO2 emitters (such as power plants).

The Compliance Benefits listed here are only meant to be used as a general guideline and are not meant to be strictly interpreted. Actual Compliance Benefits will vary depending on the factors involved, e.g., the amount of workload involved.

No materials compatibility issues were identified. However, as with all coatings, coatings used by the UNICARB system require a well prepared, clean surface for optimum adhesion and protection performance.

The UNICARB system may be used in conjunction with an electrostatic paint spray system. Electrostatic spray guns operate at high voltages (30 to 150 kV). Hence, operator safety is a major concern. All items in the work area must be grounded, including the operators, the paint booth, the application equipment (unless applying conductive coatings), and conveyors. Ungrounded items should be removed from the work area. Removing paint buildup from the paint booth helps ensure that workpieces are grounded. Workers should never wear rubber- or corked-soled shoes (special shoe-grounding devices are available). Adequate skin contact is required when using hand-held guns. Painters should grasp the gun with bare hands or use gloves with fingertips and palms cut out.

Proper design, operation, and maintenance of the equipment is required for its safe use. The spray booth must be well ventilated. Additional health concerns depend on the coating being applied. Solvent-based coatings can irritate the lungs and mucous membranes. Prolonged exposure can affect the respiration system and/or the central nervous system. Proper personnel protective equipment should be worn, if required.

Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing any of these technologies.

• Reduced environmental impact associated with hazardous solvents and solid/hazardous waste generated for disposal.
• Improved health and safety working conditions and decreased health-related costs (liability risks, protective equipment costs, and monitoring costs) compared to the use of VOC-containing coatings.
• Reduced manufacturing costs as a result of less raw material usage due to the higher transfer efficiency.
• Produces larger spray patterns, provided that the fluid delivery rate is uniform, which can provide faster, more efficient coating of a given surface area.

• Based on data from an industrial painting line at Rock Island Arsenal (RIA), IL
• Topcoat is a single component, moisture-cure urethane coating (MIL-C-53039)
• Electrostatic spray gun (Graco manual spray gun) with a nozzle featuring a 6" spray pattern
• Mixture ratio: 3.3 ml of paint to 1 g of CO2
• Temperature 60 °C
• Pressure 1500 psig
• On average, 3-5 wet mils were achieved to meet baseline operations.
• 4 trailers were used, with temperatures ranging from 83-88 °F and relative humidity ranging from 46-67.

Material costs are shown in Table 1.

Item	Cost ($)	Usage/trailer
2.8 lb/gal VOC coating	75-100/gal	0.77 gal
3.5 lb/gal VOC coating	60/gal	~2.75 gal
50 lbs CO2 cylinder CO2 cylinder rental 30/yr	6.5 1.92 lbs	N/A

• Due to a decrease in spraying times, RIA could save 156 labor hours per year at a production rate of 12 trailers per week.
  
• The UNICARB system used an average of 0.77 gallons of coating per trailer vs. 2.5-3 gallons baseline.
  
• Spraying times for the UNICARB system was 39 minutes per trailer vs. 45-60 minutes baseline.

Note: Utility costs were not included, and could be considered insignificant.

• Average cost savings per trailer was in excess of 50 percent.
  
• The simple return on investment to recover the cost of equipment is 0.8 years.
• RIA would emit 7.4 lbs. of VOC less per trailer than baseline operation.
• Because RIA would require almost two gallons of paint less per trailer, the installation would require storage, procurement, and spraying of 1235 gallons less of paint per year.
• Due to decrease in spraying times, RIA could save 156 labor hours per year.

Approval is controlled locally, and the technology should be implemented only after engineering approval has been granted. Major claimant approval is not required.

None identified.

James E. Tardoni
Concurrent Technologies Corporation
100 CTC Drive
Johnstown, PA 15904
Phone: (814) 269-2540

Anna Wojcheichowski
Tank-automotive and Armaments Command
US Army-TACOM
Warrant MI 48397-5000
(810) 574-5954

Jeff Goad
Dow Chemical Corp
3200 Kanawha Turnpike
P.O. Box 8361
South Charleston, WV 25503
(304) 747-4549

Theron Sherman
Linden EMB
137 Ascot Pkwy
Cuyahogia Falls
OH 44223
(330) 928-4064

Concurrent Technologies Corporation. UNICARB CO2 Painting Demonstration for Rock Island Arsenal (RIA). Demonstration Data Analysis/Report. October 16, 1998.

A simplified schematic of the Linden system is presented below: