The trend in the painting industry is moving toward very high solids products to meet VOC regulations. The way we handle, store and apply these products is as much a change as the products themselves. There are a whole new set of rules and problems that this paper presents to help us all deal with the new technology and make it work.
Abstract: The trend in the painting industry is moving toward
very high solids products to meet VOC regulations. The way we handle, store
and apply these products is as much a change as the products themselves. There
are a whole new set of rules and problems that this paper presents to help us
all deal with the new technology and make it work.
For many years, one way to determine whether too much paint had been applied
to a vertical surface was by looking for runs and sags. Paint products had enough
solvent in them from the factory to give the proper flow characteristics needed
for application. On top of this, the old time painter also added a glug or two
of thinner to make the product work even better. VOC regulations have caused
the industry to make a big change. Many of yesterday’s tricks are no longer
The workhorse products of the industry have become epoxies, urethanes and acrylics.
The reason is that the epoxies and urethanes have been somewhat easier to formulate
as either high solids or water reducible systems. The acrylics or modified acrylic
products are either water reducible or low enough in solids that they usually
do not cause application or handling problems.
High solids epoxies have been around for some thirty plus years. Some of the
epoxies from that era were one hundred percent. These products were usually
very difficult to apply. They required special plural component equipment because
of their short pot life. Most maintenance contractors would not have this expensive
equipment in their possession. This limited the use of these products to fixed
application sites such as fabrication and manufacturing plants. Some paint manufacturing
companies supplied the equipment to the contractor to apply their products.
These were usually specialized applications such as riveted tank seam sealing.
The new generation high solids epoxies of today still cause field application
problems. It is very common to have an intermediate coat be an epoxy with volume
solids of seventy, eighty or even ninety percent. The epoxy resin technology
has progressed to give us products with higher solids and lower viscosity. This
has helped with the application properties, but with the higher resin solids
it also requires more pigmentation, which raises the viscosity. The raw material
suppliers, coatings manufacturers, application equipment manufacturers, owners
and paint contractors have all had to change to meet these requirements.
In addition to the raw material suppliers and coatings manufacturers, the application
equipment manufacturers have also met the challenge of high solids products.
There are two very significant changes made in equipment that have allowed us
to properly apply the higher solids products. One change is that the newer airless
spray pumps have higher-pressure ratios. The old standard thirty to one pump
had difficulty supplying 2500 pounds of pressure at the tip. This was sufficient
pressure to break up the old lower solids products. Even some of the 70% volume
solids products require 2800 hundred pounds of tip pressure to properly atomize
the material with a production size tip. The new airless pumps on the market
easily supply up to 5,000 pounds of pressure at the tip. This allows the equipment
to handle the products using a variety of lengths of fluid hose, a variety of
tip sizes and additional guns on each pump. In addition, equipment people have
made great strides in designing equipment to handle the higher-solids products.
The newer High Volume Low Pressure spray guns can handle most of the products.
And, because of the low atomization pressures used, there is much less orange
peel. It may be necessary to starve the gun of fluid and make more passes to
obtain the higher film builds of the higher solids materials, but with experience
the thickness required can be achieved.
The other significant change with application equipment is the introduction
of power roller systems that actually work. The pumps, hoses and valves are
the same as those used for spray application but the roller, handle and cover
are much improved. The high pressures needed to pump the high solids products
no longer blow the seals on the newer handles. The power rollers allow the applicator
to achieve the 5 to 7 dry mils usually recommended for these products. It has
been documented in at least one instance, that a paint crew can role a large
tank faster than they can spray it. It is no longer necessary to specify two
thin coats of high build epoxy to achieve the desired thickness when roller
applying. Paint contractors in the maintenance business have had to learn and
train their crews to roller apply even the high builds in one pass to remain
The coatings formulators have made changes to meet the requirements. With the
introduction of the equipment to handle the higher solids, the requirement for
longer pot life has surfaced. The pot life of some typical 100% solids products
today is 45 minutes at 75°F. This is not a long time, but with the proper
training a paint crew can spray apply the material with the standard single
component pumps. The old products typically had a pot life of no more than 20
minutes. The older products have been hot potted, but there were more problem
applications than there were good applications.
With a pot life of 45 minutes, you must be very efficient in the mixing procedures.
There is no longer the easy box method or break a branch from the nearest tree
and stir the paint. A power mixer is an absolute must. The power mixer has to
have sufficient power to mix a paste consistency, as most of these products
tend to gel up in storage. It is beneficial to have longer handles installed
on the mixer. It may even become necessary to have some sort of device to clamp
the pail or container so it will not spin with the powerful mixing motor. Complete
mixing of each component separately is a must if both of them are in a gel state.
This usually breaks down the gel and makes mixing the two components faster
and more efficient. Do the mixing in the area of the paint pump so time is not
lost in transporting the mixed material. Do not over mix as this creates heat
that will shorten the pot life.
It may be necessary to make some changes to the paint pump when working with
this high viscosity paint. Paint pumps are usually set up with a pick up hose
of up to one inch inside diameter. This inside diameter tends to get smaller
as the pump is used and cured paint builds up on the walls. This will cause
the pump to starve or overwork in picking up the product. This hose can be removed
and a short length of pipe added to the bottom of the foot to reach the bottom
of the pail or the pail can be raised to the bottom of the pump. The pump filter
should be changed to a thirty mesh. A sixty or one hundred mesh filter may lower
the pressure too much. With the use of a self-cleaning spray tip and good house
keeping around the mixing area, there should not be too much trouble with tip
stoppage. Use a front fed type of spray gun. The type with springs or filters
in the handles may cause too much restriction or pressure loss. The old rule
to remove fingers from the spray pattern was to lower tip size or increase the
pump pressure. With these high solids products, that may no longer be the way
to remove the fingers. It may be necessary to use a larger tip allowing the
material to atomize properly.
Transportation and storage of the newer products is more involved than the
storage we were used to. When paint was delivered to the job site it was usually
stored in the open, near the unit to be painted. If that happened to be out
in the sun or out in the cold weather, it did not matter. The temperature of
the product is going to affect the properties of the product. The increased
temperature of storing the material in the sunlight will most certainly shorten
the pot life of the mixed material. Cold temperature can cause the material
to increase in viscosity to the point that it cannot be mixed properly. If either
of these conditions is encountered in transporting the material from the factory
to the job site, the material should be stored to allow it to reach the 75°F
range before application is attempted. The material should be kept in the climate-controlled
storage until just before its use.
The owners of the units have had to become more involved in the coatings procedure.
Most often, the proper storage of the material can only be supplied by the owners.
This has increased involvement in the project by the owners, but it has also
been a benefit to them. The one hundred percent volume solids has allowed single
coat tank linings, faster cure times for faster return to service, and less
overall waste for the owner to deal with.
There is still a requirement for plural component equipment in the coatings
industry. Many of the one hundred percent solids urethanes on the market have
a very short pot life. Some of them have a pot life of 7 to 10 seconds. The
applicator cannot release the trigger on the gun until it has been flushed with
solvent. These products usually have very specialized services such as in storage
of aggressive commodities, secondary containment for aggressive products and
external maintenance for buried piping. The plural component pumps can be made
to be portable. They are usually truck or trailer mounted along with a power
generator as some of the products have to be heated to be pumped. This equipment
is usually owned and operated by a contractor that specializes in this type
of work. This equipment requires more and better maintenance to function properly.
Another area that plural component equipment is used is in the fabrication
industry. Where the same products are used every day, plural component equipment
can reduce labor costs along with the cost of lost material. The material is
mixed as it is needed.
In conclusion, the present day coating products are successful because of cooperation
from all parties concerned. Without this cooperation, we would not be able to
meet the regulations that are so needed for our environment The raw material
suppliers met the need for the low viscosity, high solids raw materials and
the paint suppliers were able to formulate products from these raw materials
that met the chemical resistance and regulation requirements. The application
equipment manufacturers were able to supply the equipment to handle the higher
solids products. The contractors and owners had to work together to test apply
the products and find ways to deal with the increased participation required
by all. The industry has learned some very valuable information in the past
few years that will help all of us deal with the field problems we will encounter
with the even newer generation of coatings.
Source: SSPC, The Society of Protective Coatings