Powder Coating Storage And Handling

Powder Coating Storage And Handling

Powder, like any coating material must be shipped, inventoried, and handled in its journey from the powder coating manufacturer to the point of application. Manufacturers’ recommendations, procedures, and cautions should be followed. Although various powders may have specific requirements, some universal rules apply. It is important that powders should always be:

• Protected from excess heat;
• Protected from humidity and water;
• Protected from contamination with foreign materials, such as other powders, dust, dirt, etc.

These are so important, they deserve more elaborate explanations.

Excess Heat

Powders must maintain their particle size to allow handling and application. Most thermosetting powders are formulated to withstand a certain amount of exposure to heat in transit and in storage. This will vary according to types and formulation, but can be estimated at 100-120°F (38-49°C) for short-term exposure. When these critical temperatures are exceeded for any length of time, one or all of the following physical changes may happen. The powder can sinter, pack, andor clump in the container. Pressure of powder weighing on itself (Le., large tall containers) can accelerate packing and clumping of the powder toward the bottom of the container.

Manufacturers recommend long-term storage temperatures of 80°F (27’C) or lower. Unless its exposure to heat has been excessive over an extended period of time, powder that has experienced such changes can usually be broken up and rejuvenated after being passed through a screening device.

Powders with very fast or low-temperature curing mechanisms may undergo a chemical change as a result of exposure to excess heat. These powders may partially react or “B stage.” Even though these powders may be broken up, they will not produce the same flow and appearance characteristics as unexposed powders. They will have, and irreversibly retain, restricted flow, even to the point of a dry texture.

Powders formulated with chemical blocking agents to prevent curing below certain trigger temperatures do not typically “B stage” at temperatures below 200°F (93°C).

Protect from Humidity and Water

Water and powder do not mix when the intent is to spray as a dry powder. Exposure to excessive humidity can cause the powder to absorb either surface or bulk moisture. This causes poor handling, such as poor fluidization or poor gun feeding, which can lead to gun spitting and eventually feed hose blockage. High moisture content will certainly cause erratic electrostatic behavior, which can result in changed or reduced transfer efficiency and, in extreme conditions, affect the appearance and performance of the baked coating film.

Contamination

Because powder coating is a dry coating process, contamination by dust or other powders cannot be removed by filtering, as in liquid paint. It is imperative, therefore, that all containers are closed and protected from plant grinding dusts, aerosol sprays, etc.

POWDER COATING STORAGE RECOMMENDATIONS

Storage stability properties of powder coatings need not cause problems at the end user’s facility, provided that a few simple precautions are taken. Among these precautions are:

• 1. Control temperature, 80°F (27°C) or less. Remember that powder requires minimal storage space. For example, a semi-tractortrailer-sized area can accommodate 40,000 lbs. (1 8,143 kg) of powder, which is approximately equal to 15,000 gallons (56,775L) of liquid paint at applications solids.
• 2. Efficiently rotate the stored powder to minimize inventory time. Powder should never be stored for a period exceeding the manufacturer’s recommendation.
• 3. Avoid having open packages of powder on the shop floor to preclude possible moisture absorption and contamination.
• 4. Precondition powder prior to spray application by providing preconditioning fluidization, as is available on some automatic systems, or by adding virgin powder through reclaim system. These techniques will break up the powder if minor agglomeration has occurred in the package.
• 5. Maximize powder transfer efficiency in the booth to avoid problems associated with recycling large quantities of powder.
• 6. Minimize the amount of powder coating material held on the shop floor if temperature and humidity

SAFETY

Powder coatings contain polymers, curing agents, pigments, and fillers that require safe operator handling procedures and conditions. Pigments may contain heavy metals, such as lead, mercury, cadmium, and chromium. The handling of materials containing such elements is controlled by OSHA regulations. End use may be restricted according to Consumer Product Safety Commission Regulations.

Under some circumstances, OSHA regulations require the applicator to inform employees of the hazards associated with handling certain components or powder coatings. The applicator is advised to obtain this information from the supplier in the form of a Material Safety Data Sheet. Powder coatings should be handled in a manner as to minimize both skin contact and respiratory exposure consistent with particular Material Safety Data Sheet recommendations. Obvious health reactions attributed to any powder coating operation should be referred to a physician as soon as possible.

Opening, emptying, and handling powder containers, such as boxes and bags, often present the greatest worker exposure, even with welldesigned systems. Engineering practices, personal protective equipment, and good personal hygiene should be used to limit exposure. In a welldesigned spray operation, there should be negligible exposure of employees to dust. Powder coatings, because of their fine particle size and frequently large percentage of TiO,, will absorb moisture and oil readily.

If powder is left in contact with the skin for extended periods, it tends to dry out the skin. To prevent this, gloves and clean clothing should be worn by the workers. Operators of manual electrostatic guns must be grounded. To prevent carrying powder away from work, workers should change clothes prior to leaving the workplace. If powder does get on the skin, it should be washed off at the earliest convenient time, at least by the end of the day. Workers who show skin reactions on exposure to powder must be especially careful to wash frequently. Washing the sfin with organic solvents is an unsafe practice that should be forbidden. Generally, cleansing with soap and water is the appropriate hygienic practice. Additional information should be obtained from the supplier’s Material Safety Data Sheet.

Powder Coating Storage And Handling