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High Solids
High solids coatings were first introduced to comply with the amplifying VOC regulations and Clean Air Act in the United States, we can expect similar regulations here in Canada in the very near future. Traditional coatings systems have a composition that is about 25% solids and 60% solvents. The high solids coatings introduce a different concept by adding little to no solvent to the composition. In comparison to traditional systems these coatings have a much higher percentage of solids, around 65% to 80%. Very high solids coatings have as much as 100% solid content. Due to this increased solids content and lack of solvent, these coatings have much higher viscosities, 3 to 4 times thicker. The removal of solvents, which are used in traditional paints to compensate for viscosity, flow and curing, require the new coatings to have very different characteristics and require new methods of handling.
These coatings not only provide reduced VOC emissions, they also provide increased corrosion resistance, coating thickness and edge retention. They provide a higher level of performance, requiring less surface preparation and the ability to self-prime. The thickened coating provides the advantage of fewer required coats, reducing cost per application.
The coatings are produced as both single and dual component systems. For dual component systems, the two parts are mixed at application to minimize some of the problems encountered with the reduced solvent and high solids. After the dual component system is mixed the chemical reaction begins and heat within the mixture rises. This new composition causes three main challenges, reduced pot life due to quick reaction time, temperature sensitivity during application and high viscosities, requiring new application methods.
The use of typical application equipment does not provide the adequate pressure levels to deliver a smooth layer of paint. Higher-pressure pumps were then introduced as a solution to the viscous mixture. Problems encountered range from pump clogging, pump seal leakage, excessive pump down time and finally, extensive flushing and clean up requirements after each use. Additional issues included high pressure spray gun, accessories and tip problems. Paint mixing problems became an issue due to viscosity and the short pot life of the materials. Temperature sensitivity and personnel exposure problems were also reported.
Next, the plural component spray equipment was introduced. This equipment not only produces the increase in pressure needed to properly atomize the coating but also provides the added advantage of increased production rates due to the product delivery rate increase. In addition, with reduced solvent content coatings, thickness per coat can be increased; therefore fewer coats are needed to obtain the specified dry film thickness. Selecting the appropriate equipment for the job is essential to the successful application of these coatings.
Single Component Spray Equipment (High Pressure)
Advantages
Using higher-pressure single component paint spray equipment to apply two component high solids coatings has its advantages. Primarily the initial equipment set up cost is much less. Training for equipment operators is minimized(mainly safety related for operating higher pressure equipment), major process modifications are not required, and it gets the job done.
Disadvantages
The two primary disadvantages are the short pot life management and the advantages of bulk product supply cannot be realized. The short pot life, in some cases 3045 minutes, will always be a process issue and product mixing and product tending will remain labor intensive. Personnel are exposed to the products during the mixing process. Paint waste and delivery container (5 gallon cans) waste stream is costly. Mixing ratios and homogeneity can be an issue; small quantities of the coating cannot be easily produced. In some cases 5 gallons must be mixed to deliver the final few pints of product required. Equipment must be flushed and cleaned after each operation (large quantities of solvent are used, along with higher solvent emissions to the environment, and many man-hours expended). An equipment or process hold up can result in equipment damage due to product solidifying while still in the pump. Rapid cure technology is not feasible. In the final analysis larger paint teams are required, more product is wasted, risk of production delays is real and it is the more expensive application method.
Plural Component Equipment (High Pressure)
Advantages
With the introduction of Plural Component Systems into the application process, numerous process improvements can be instituted and production and economic advantages realized. These improvements not only provide a manpower savings but also can dramatically reduce application costs. The advantages can be divided into four main categories. 1. Reduction in Material Costs.2. Reduction in Labor Costs 3. Environmental Concerns. 4. Production Efficiencies.
Reduction in Material Costs
Coating materials can be drawn from large, recyclable, space-saving containers (drums, tanks, etc.).There is no loss of material due to spillage or residual left in emptied paint cans. The expensive disposal of paint cans with residue (hazardous materials) is eliminated. No material is lost due to excess premixed paint and short pot life losses. Small quantities of paint needed for finishing a job or touch up can be dispensed. Solvent cost savings are realized when cleaning the system, since only those parts that come in contact with mixed material must be flushed. Material is also saved, especially when using long hoses, by use of an attached high-pressure flush pump that enables mixed material still located in the spraying hoses to first be applied before flushing the system at the end of the application.
Reduction in Labor Costs
No extra personnel are required for manually mixing the materials to be sprayed, scraping material from the sides and bottoms of containers, and managing the hot potting evolution. No logistics trail of supplying paint cans to the site, and then removing and storing these cans for disposal. Labor costs are also reduced, since each component in the system is transferred separately. Less work is necessary for cleaning, since only those parts that come in contact with mixed material must be flushed. Equipment does not have to be cleaned after each application because the 2 components are not mixed until the mixing manifold, which can be positioned near the final spray point. Paint teams could possibly be reduced by 1 or 2 personnel.
Environmental Concerns
Hazardous waste is reduced through the use of large recyclable containers (no more paint cans with residual material needing disposal).No solvents are necessary to apply coatings. Solvents used for clean up are drastically reduced since only those parts that come in contact with mixed material must be cleaned.
Production Efficiencies
Delays due to poor management of product premixing are eliminated. Production delays due to work slow down, and equipment clogging due to material curing in the single component pump, are gone. Inaccurate proportioning due to personnel error is eliminated. Eliminating manual agitation ensures an accurate homogenous mixture. Pre-heating the components with in-line heaters is possible, thereby contributing to efficient atomization of the mixed coating at lower pressures. Coatings go on easier with less over-spray. The lower pressures also provide a safer work environment for applicators and less equipment wear and tear. In some cases colder weather applications are possible. Pump clean up after every painting evolution is not required, and equipment down time is reduced. Containerized, climate controlled units can be positioned on or near the job site. Rapid cure coatings can be utilized.
Disadvantages
The initial equipment start up cost is the biggest detractor for shifting to plural component equipment. The units are larger and heavier. Plural systems are slightly more complicated to operate and operator training (generally provided by the equipment manufacturer) is required.
PROCESS
Single Component Equipment Process Overview
(Application of high solids coatings)
Application of two component high solids coatings utilizing higher-pressure single component equipment presents several challenges to the application process. The viscosity of the paint makes it not only a challenge to spray but manual mixing can be a problem. The base must first be stirred and then the hardener manually mixed in at the specified mixing ratio to make a homogeneous mixture prior to the pump. The short pot life prevents pre mixing and staging, as well as requiring constant attention and coordination with applicators to prevent production delays or material wastage. The mixed product then enters the pump and exits through the hose to the paint gun. All parts of the pump from the suction on are exposed to the mixed material and must be thoroughly cleaned after each application.
Plural Component Equipment Process Overview
When applying two component high solids coatings by high-pressure plural component equipment, the base and hardener are stored separately in bulk supply containers that can be refilled without interrupting production. These containers can be supplied with level indicators, agitators and pre-heaters if desired. Each product is supplied separately to its individual pump fluid end. The products do not come in contact with each other until the mixing manifold, or in some cases, at the spray gun itself. No mixed product goes through the pump, thereby eliminating clogging or solidification of product in the pump. Coating specified mixing ratios could be set by mechanically changing out the lower end of a fixed ratio unit or by adjusting the stroke on a variable ratio pump.
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