Powder coatings information
Powder coating – fine-dispersed polymeric dry powder on the base of:
• polymeric resins (base, film forming)
• hardners (polymerization – congelation)
• pigments (color)
• target modifying agents (getting special properties), which being heated in the furnace to t° = 140-200°C are polymerized (congelated) and make uniform, heavy-duty cover with very high degree of adhesion with coated surface.
Powder coatings are classified to:
1. resin type: epoxy
• epoxy-polyester
• polyester
• acrylic
• polyurethane
2. formed surface type:
• flat (plain)
• shagreen (thick orange skin) moire (small abrasive paper)
3. formed surface glliter degree type (%):.
• glossy (from 70 %)
• semigloss (50%-70%)
• semimatt (25%-50%)
• matt (to 25%)
On color:
There is several color and tint coding standards in the world. The most popular among them is RAL standard designed in German Guarantee Of Quality And RAL Certification Institute. Every tint of any color has a digital index of its own within this standard.
Kinds of industrial and powder coatings
Powder coatings are heavy dispersed layout which consist of film forming materials (resins), hardeners, pigments, fillers and target agents. Powder coatings are produced with the components being mixed, melted with further grinding. Powder coatings are differ with their properties, content, cover forming conditions, assignment and are divided into two big groups:
1. Thermoplastic - there is a solid polymeric film on the item after fusing and blending of the particles, under heat of coated powder, which function protectively after cooling-down. The coating of thermoplastic lacquer being heated repeatedly – is fused again. Among thermoplastic powder coatings are: based on butyral resin polyfluoroolefin, polyethylene.
2. Thermosetting - there is a solid polymeric film, under heating of applied powder coating after fusing and blending of the particles, and polymerization reaction after which has irreversible and that is why being heated repeatedly there is no flowing of polymeric film. Coatings, being got in such a way, as a rule, are very lasting and durable. Among thermosetting powder coatings are: coatings based on epoxy and polyester resins, acrylic and polyurethane.
There are such types of curing by method and regime as:
1. Powder coatings solidificated being heated (usual and accelerated)
2. Powder coatings solidificated with ultraviolet light – flowing (coatings of photochemical curing) of a powder is made after being heated to t° = 90 - 110îC and polymerization – with powerful ultraviolet light within a couple of seconds.
Industrial powder coatings characteristics
Polyester lacquers.
Polyester-urethane contents are combinations of hydroxyl – containing polyesters and blocked polyisocyanate. Coating forming should be at t° about 170îC. It is coated of not large thickness (25-27mkm). There is a complex of value properties in polyester-urethane coatings: firmness with high steadiness to chips, steadiness to weather conditions and chemical steadiness. They are steady in diluted acid solutions, salt environments, withstand aromatic and aliphatic hydrocarbon effects, patrol and grease oils; thin layers of these coatings protect metals from corrosion well.
Polyester-urethane coatings usage area – sports ground and gardens equipment protection, conditioners, electrical equipment, auto details, metallic furniture. Coatings are good protection for different pigmented coatings, including fluorescent ones.
Polyester coatings, solidificated with triglycidylezocyanurate, are produced based on carboxyl-containing polyester. Coatings (thickness 75mkm) are formed at lower temperatures, than polyester-urethane. Peculiarity of these lacquers is an ability to cover well, without drippage, sharp-edged; it is easy to get grain-oriented (orange skin-like) coating by means of them. The coatings have good mechanical properties, excellent light fastness and are weather proved. On adhesion and anticorrosive properties – they are close to Polyester-urethane coatings, although their steadiness to chemical substances and solvents is evidently worse.
Typical usage areas of polyester coatings with hardener TGIC - aluminum shape protection, disks, wheels, transformers, conditioners, lawn and metallic fences equipment.
Polyacrylic coatings.
Polyacrylic coatings analogically to polyester-urethane need a high temperature and time for forming a coating (minimum unblocking temperature is 180îC). Coated products on weatherproof and on chemical resistance are better then ones coated with polyester-urethane, which is fitted to polyacrylic properties. They have a good spreading and absolutely plain surface with very little thickness. Their maximum thickness needed for votalization of unblocking agent is 75 mkm. According to their mechanical properties – flexibility and impact fastness, poly acrylic urethane are considerably worse then polyester- urethane. These coatings usage area – wheel disk protection, slot-machine coating, sheet, rolled metal of aluminum.
Hybrid acrylic coatings are produced on mixtures of acrylic and epoxy resins, that is why they are considered to be analogs of hybrid epoxy-polyester coatings. They are substantially better then polyacrylic-urethane coatings. There is better atmosphere fastness. Hybrid acrylic lacquers are the most widely used for coating of metal furniture and lightning equipment.
Glycidol-containing polyacrylic compositions are characterized rather fast condensation; the coating well withstand to weather impacts. Achromous coatings are differ with its surface condition and film transparency, that is why they perfectly fit for brass glazing and chromed items. Pigmented coatings have a nice appearance as well. Acceptable thickness of the coating lies in wide ranges; but in thick layers, flexibility of coatings may be reduced.
Epoxy coatings.
Duty coatings. Main application areas of such coatings are electrical isolation and protection from corrosion. Epoxy coatings appeared to be a good alternative to many kinds of electrical isolation, earlier being used in production, namely: taping, compounding, coating (impregnation) with liquid coatings, etc. Due to value properties complex, simplicity and low value of electro isolation epoxy powder coatings and compounds got dominant significance in electro technical industry. Also these coating widely used in metalworking and chemical industry where physical-chemical properties prevail over decorative ones.
Epoxy powder coatings are widely used with a purpose of anti-corrosion protection. The coatings are differ with low cost, simplicity of service and durable protection being in different aggressive environments. Flexibility, impact resistance, low permeability, good thermo stability and adhesion. Coatings may be applied with one or another method into cold or previously heated surface. They may be exploited for a long time at t° up to 150îC after solidification. As electro isolating they are considered to be of B class on heat resistance (130îC).
Protective-decorative coatings.
Unlike duty materials, this kind of coatings is intended to get a coating surface with little thickness. They are chosen according to certain requirements. Application areas of such compositions are different. In the first place, these are drum dyers, horticultural sundry, door furniture, microwaves, refrigerators details, stands, toys.
Epoxy polyester (hybrid) coatings.
These coatings are more tolerant to yellowing then epoxy which was caused overheating at the moment of the coating solidification. Chalking and color changing of the coatings while exploiting in atmospheric conditions are seen lesser. Nevertheless, hybrid coatings, like epoxy ones, are not recommended to use in conditions sunlight to impact. Mechanical properties (flexibility, hardness, impact resistance) of the coatings are mainly like epoxy ones have and resistance to chemicals impact is a bit lower. Epoxy polyester coatings have the same usage spheres, like epoxy of protective-decorative function. Stands are lacquered with them, water heaters, office metallic furniture, electro instrument, fire extinguishers, oil cleaners and many more.
Coatings of photochemical solidification.
This is new quickly developing class of powder materials. Unsaturated polyester of a fusion temperature at 100-125îC is its film former. The coating is made stepping two stages: powder content first, on the surface, by means of infrared heater radiation and is fused into monolithic coating, then it is exposed to ultraviolet rays which cause solidification of the coating. Solidification is put into effect due to polymerization reaction which is initialized by radicals, formed after photoinitiator decay; the last one is a component of powder compositions. The process last several minutes or seconds. The source of ultraviolet rays are mercury lamps of average pressure (radiant flux with surface density about 12kilowatt/m2).
This technology is recommended to apply coatings on wood, timber-based materials, plastic and other heat-sensitive materials.
Thermoplastic powder coatings.
Polymers with comparatively large molecular weight are basic material to get such coatings. That is why high temperatures are required to form coated surface (150-200îC). While coating in boiling bed – it is heated formerly, and after the powder to be coated – it is often provided with repeated heating for it to be fused better and the coating to be floated. Destruction of polymers is not eliminated as a result of high temperature effect, that is why it is necessary to follow technological regimes strictly.
Coatings made of thermoplastic powder, as a rule, have low or not high adhesion. That is why accurate preparation should be carried out: to use bead-blasting or sandblast cleaning of a surface, in some cases – its priming.
There is a short description of coats below, got of powder coatings based on the most used thermoplastic polymers.
Polyamides. Polyamide powder structures and coatings are the most widespread, based on polymer known under nylon trade name. Nylon – made coatings have many value properties. They have a good appearance, high thickness, deletion fastness, resistant to chemical substances and solvents effect. There are structures which do not need priming, and lacquer applied on formerly primed surface. In case of strength coatings (dishwashing machine basket, tubes, pump valves, chemical equipment, medical instruments autoclave treatment needed protection), as a rule, priming is held. Having suitable raw materials set, polyamide coatings may be received which can contact with food products. Polyamide lacquers are used not for inner works only but also for outer ones, for example for lighting devices, posts, benches coating.
Polyolefines. Powder structures based on polyolefines - polyethylene, polypropylene, also, as on poliamides, have long usage history. Polyethylene makes coatings soft, polypropylene, and some of their copolymer in particular, - are quite elastic. Both coatings are characterized with good chemical resistance. Contacting with some solvents and cleaning agents - splitting may take place as a result of tension inside. Another disadvantage of such coatings – low adhesion to metals.
To improve the properties above, there must be a preparation of a surface with modification of structures or using more durable to adhesion copolymers instead of individual polymers.
Plasticized polyvinylchloride. The coatings based on plasticized polyvinylchloride being soft like caoutchouc have a good resistance to washing material and water effect and keep the adhesion at such products as, for example, dishwashing machine basket while being applied. The compositions are applicable also for outer coatings; it is possible to get coatings permissible to contact with food substances if coating formulation is appropriate.
Polyesters. Coating based on thermoplastic polyester in its external appearance like nylon ones. But they do not have many properties nylon does, resistance to solvent effect in particular, steadiness to deletion. They are also characterized with good adhesion to different materials, they do not need surface priming. Many polyester coatings have a good resistance to outer effects, they are used for example, for garden furniture protection. Polyester structures did not become very popular on the market because of the difficulties while coating.
Polyvinylidene fluoride. Coatings based on polyvinylidene fluoride have exclusive resistance to outer effects. They overcome all the others coatings on their weather resistance, as a result of powder coatings, also have a good electrical insulating properties and resistance to chemical substances effect, except of some solvents. They are mainly used in chemical industry to protect pumps, valves, pipe-lines and other equipment. Surface priming is recommended because of low coating adhesion.
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