Paint And Coating Manufacturing

Paints and coatings include paints, varnishes, lacquers, stains, printing inks, etc. Traditional coatings consist of pigment particles dispersed in a vehicle, which consists of a film-forming agent or binder (usually an oil or resin) and a diluent (usually a volatile solvent). In addition, there can be a wide variety of fillers and other additives. Varnish is a solution of oils and natural resins in organic solvents. Synthetic resins can also be used. Lacquer is a coating in which a film dries or hardens entirely by the evaporation of a solvent.

Traditional coatings have less than 70% solids content, with most of the remainder being solvents. Air pollution regulations that limit the amount of solvents that can be emitted into the atmosphere have led to the development of a variety of alternative coatings that contain low or no organic solvents. These include: water-based latex paints; two-part catalyzed coatings (e.g., epoxy and polyurethane systems); high-solids coatings (more than 70% solids), including plastisol coatings, which consist primarily of pigments and plasticizers; Radiation Cured coatings; and powder coatings.

According to the National Institute for Occupational Safety and Health (NIOSH 1984), approximately 60% of paint manufacturers employ fewer than 20 workers, and only about 3% employ more than 250 workers. These statistics are expected to be representative of global coatings manufacturers. This shows the dominance of small shops, most of which do not have in-house health and safety expertise.

manufacturing process

Generally speaking, the manufacturing of paints and other coatings is a series of unit operations using a batch process. Little or no chemical reactions; operations are mostly mechanical. Manufacturing includes the assembly, mixing, dispersing, diluting and conditioning of raw materials, filling of containers and warehousing.

coating

The raw materials used to make paints are liquids, solids, powders, pastes and slurries. These are hand weighed and pre-mixed. The agglomerated pigment particles must be reduced to the original pigment size, and the particles must be wetted with a binder to ensure dispersion in the liquid matrix. This dispersion process, called grinding, is accomplished through various types of equipment, including high-speed shaft-impeller dispersers, dough mixers, ball mills, sand mills, three-roll mills, mixers, etc. The initial run can take up to 48 hours, then the resin is added to the paste and the grinding process is repeated for a shorter period of time. The dispersed material is then transferred by gravity to a discharge tank, where other materials, such as coloring compounds, can be added. For water-based paints, the binder is usually added at this stage. The paste is then diluted with resin or solvent, filtered, and transferred again by gravity to the canning area. Filling can be done manually or mechanically.

After the dispersion process, the tank and grinder may need to be cleaned before introducing a new batch. This may involve hand and power tools, as well as alkaline cleaners and solvents.

paint

The production of paint is usually carried out in closed equipment such as tanks or mixers to minimize the evaporation of solvents, which can cause dry paint films to be deposited on processing equipment. Otherwise, lacquer is produced in the same way as paint.

Varnish

The manufacture of oil-based varnishes involves cooking oils and resins to make them more compatible, developing high molecular weight molecules or polymers, and increasing solubility in solvents. Older plants may use portable open kettles for heating. Add the resin and oil or resin separately to the kettle and heat to approximately 316oC. Natural resin must be heated before adding oil. Pour the ingredients over the top of the kettle. During cooking, the kettle is covered with a fire-resistant vent hood. After cooking, the kettle is moved to the room and cooled quickly, usually by spraying water, and then thinner and desiccant are added.

Modern plants use large closed reactors with capacities of 500 to 8,000 gallons. These reactors are similar to those used in the chemical processing industry. They are equipped with stirrers, sight glasses, lines for filling and emptying the reactor, condensers, temperature measuring devices, heat sources, etc.

In both old and modern factories, the diluted resin is filtered as a final step before packaging. This is usually done while the resin is still hot, often using a filter press.

powder coating

Powder coatings are solvent-free systems based on the melting and fusion of resin and other additive particles on the surface of a heated object. Powder coatings can be thermoset or thermoplastic and include resins such as epoxy, polyethylene, polyester, polyvinyl chloride and acrylics.

The most common manufacturing methods include dry blending of powder ingredients and extrusion melt blending (see Figure 1). The dry resin or binder, pigments, fillers and additives are weighed and transferred to the premixer. The process is similar to dry mixing operations in rubber manufacturing. Once mixed, the material is placed in an extruder and heated until melted. The molten material is extruded onto a cooling conveyor and then transferred to the coarse granulator. The granular material is passed through a fine grinder and then screened to achieve the desired particle size. The powder coating is then packed.

Figure 1. Flow chart of powder coating manufacturing by extrusion melt mixing method

Hazards and their prevention

Generally speaking, the main hazards associated with paint and coating manufacturing involve material handling; toxic, flammable, or explosive substances; and physical factors such as electric shock, noise, heat, and cold.

Manual handling of boxes, barrels, containers, etc. containing raw materials and finished products is a major source of injuries from improper lifting, slips, falls, dropped containers, etc. Precautions include engineering/ergonomic controls such as material handling aids (rollers, jacks and platforms) and mechanical equipment (conveyors, cranes and forklifts), non-slip flooring, personal protective equipment (PPE) such as safety shoes and appropriate Training in manual lifting and other material handling techniques.

Chemical hazards include exposure to toxic dusts, such as lead chromate pigments, which can occur during weighing, filling of mixer and grinder hoppers, operation of unenclosed equipment, filling of powder coating containers, equipment cleaning, and container spills. The manufacture of powder coatings results in significant dust exposure. Precautions include replacing powders with pastes or slurries; local exhaust ventilation (LEV) for opening powder bags (see Figure 2) and processing equipment, equipment enclosures, spill cleanup procedures and respiratory protection where necessary.

Figure 2. Bag dust control system

A variety of volatile solvents are used in the manufacture of paints and coatings, including aliphatic and aromatic hydrocarbons, alcohols, ketones, and others. The most volatile solvents are usually found in lacquers and varnishes. Exposure to solvent vapors may occur during the dilution process in solvent-based coating manufacturing processes; when charging reaction vessels (especially older kettle types) in varnish manufacturing processes; during filling of all solvent-based coatings; and during use During manual cleaning of process equipment with solvents. Enclosures for equipment such as varnish reactors and paint mixers generally involve lower solvent exposure, except in the case of leaks. Precautions include process equipment enclosures, LEVs for dilution and canning operations, and respiratory protection and confined space procedures for cleaning containers.

Other health hazards include inhalation and/or skin contact with isocyanates used in the manufacture of polyurethane paints and coatings; with acrylates, other monomers and photoinitiators used in the manufacture of radiation-curable coatings; acrolein and other gaseous emissions from cooking of varnishes; As well as curing agents and other additives in powder coatings. Precautions include enclosures, LEVs, gloves and other personal protective clothing and equipment, hazardous materials training and good work practices.

Flammable solvents, combustible powders (especially nitrocellulose used in lacquer production) and oils all present a fire or explosion hazard if ignited by sparks or high temperatures. Ignition sources may include faulty electrical equipment, smoking, friction, open flames, static electricity, etc. Oil-soaked rags can be a source of spontaneous combustion. Precautions include connecting and grounding containers when transferring flammable liquids, grounding equipment such as ball mills that contain combustible dusts, ventilating to keep vapor concentrations below the lower explosion limit, covering containers when not in use, removing sources of ignition, using Spark-proof non-ferrous tools and good housekeeping practices around flammable or combustible materials.

Noise hazards may be associated with the use of ball mills, high-speed dispersers, vibrating screens for filtration, etc. Preventative measures include vibration isolators and other engineering controls, replacement of noisy equipment, good equipment maintenance, isolation of noise sources, and hearing protection programs in the presence of excessive noise.

Other hazards include inadequate machine guarding, a common source of injury around machinery. Electrical hazards are a particular problem without proper lockout/tagout procedures for equipment maintenance and repairs. Burns can occur from hot varnished cooking vessels and splashing materials, as well as from hot-melt adhesives used in packaging and labeling.