Powder coating is a completely different form from general coatings. It exists in the form of fine powder.Because no solvent is used, it is called powder coating.The main characteristics of powder coatings are: harmless, efficient, resource saving and environmental protection.
There are many classification standards, and the names of various powders on the market are uneven.according toFilm-forming substanceIts properties can be divided into two categories: thermoplastic powder coatings and thermosetting powder coatings.Or according to the appearance of the film-forming material, it can be divided into: extinction type, highlight type, art type, etc.You can also pressUse environmentIt is divided into indoor and outdoor types.
type
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Although the varieties of powder coatings are not likeSolvent based paintThere are many of them, but they can be used as powder coatingspolymerThere are also many resins.Generally, it can be divided into thermosetting type and thermoplastic type.[2]
1. Thermosetting powder coating refers toThermosetting resinAs a film-forming material, addCrosslinking reactionAfter heating, the hardener of can form a hard coating with non melting texture.No matter how high the temperature is, the coating will not be likeThermoplasticityThe coating softens like that and can only decompose.Since the resin used for thermosetting powder coating isDegree of polymerizationLowerPrepolymer, the molecular weight is low, so the coatingLevelnessGood, with good decoration, and the low molecular weight prepolymer can form a network cross-linkedmacromoleculeTherefore, the coating has goodCorrosion resistanceAnd mechanical properties.Therefore, thermosetting powder coatings have developed rapidly.
one point oneEpoxy powder coating。Because of its excellentAdhesive forceCorrosion resistance, hardnessflexibilityandimpact strength Therefore, it is the first type of thermosetting powder coating.Epoxy powder coating is prepared byepoxy resin(Epoxy Resin), curing agent, pigment, filler and other additives.The powder formed by these component pairsCoating performanceA suitable formula is actually the result of coordination of various components.
1.2 Polyester powder coating.Compared with other types of powder coatings, polyester powder coatings have unique properties.Performance inWeatherability, UV rotation resistance ratio[2]Good epoxy resin.In addition, due topolyester resinhavePolar groupTherefore, the powder loading rate is higher than that of epoxy resin, and it is not easy to bakeyellowingHigh gloss, good leveling, full paint film, light color and other characteristics, so it has good decoration.Usually used in refrigerators, washing machinesVacuum cleanerInstrument shell, bicycle, furniture and other fields.
one point threeAcrylatePowder coating.acrylic resin Powder coatings are thermoplastic and thermosetting.Thermosetting acrylic resinThe biggest advantage of powder coating is excellent weather resistanceChromaticity, ResistanceContamination, MetaladhesionStrong, excellent film appearance, suitable for decorative powder coatings.
2. Thermoplastic powder coating.Thermoplastic powder coating appeared in 1950. It dissolves at spraying temperature and solidifies to form film when cooling.Because the processing and spraying methods are simple, the powder coating only needs to be heated and melted, leveled, cooled or extracted and solidified to form a film, and does not need a complex curing device.Most of the raw materials used are common polymers in the market, which can meet most conditionsPerformanceRequirements.But there are also some shortcomings, such asMelting temperatureHigh, low coloring level, poor adhesion with metal surface, etc.Nevertheless, the commonly used thermoplastic powder coatings still show some unique properties, among whichpolyolefinPowder coating has excellentSolvent resistance；Polyvinylidene fluorideThe coating has outstanding weather resistance;polyamideWith excellentAbrasion resistance；PVC has good price/performance ratio;Thermoplastic polyester powder coating has the advantages of beautiful appearance and high artistry.These characteristics make thermoplastic powder coatings occupy a large proportion in the coating market.
2.2 PolyethylenePowder coatingIt has excellent corrosion resistance, chemical resistance and excellentElectrical insulationAnd resistance to ultraviolet radiation.The disadvantages aremechanical strengthNot high, poor adhesion to the substrate.It can be used for chemical tank, impeller, pump, pipe inner wall, instrument shell, metalboard, refrigerator inner mesh plateAuto partsEtc.
two point threenylonPowder coating.Nylon is also called polyamide, because the N atom of the chlorine group on the molecular chain is adjacent toChain segmentOnhydrogen atomEasily formedhydrogen bond, soPolyamide resinThe melting point of is generally high.Nylon has high mechanical strength, impact resistance, hardness, wear resistance andfriction coefficientSmall, low dust absorption and other advantages, can be used for parts with special requirements.If used forPump impeller、textile machinery PartsDiesel engineStarting piston partsMotorboatpropellerImpeller, automobile wheel, motorcycle bracket, agricultural machinery, construction andSports equipmentEtc.In addition, because nylon is resistant to salt water andmould. The inertia of bacteria is very suitable for making coatings immersed in or in contact with sea water. At the same time, nylon powder coating is non-toxic, odorless, not corroded by mold, not promoting the growth of bacteria, and is very suitable for sprayingfood industryComponents, drinking water pipes andFood packagingEtc.
two point fourFluororesinPowder coating.FluoropolymersThere are many kinds of powder coatings that can be prepared, such asteflon（PTFE）、Polytrifluoroethylene(PTFCE), polyvinylidene fluoride（PVDF）Etc.The melting point of polytetrafluoroethylene is up to 327 ℃, which can be used for a long time in the range of - 250~250 ℃. In addition, it has excellentCorrosion resistance, even in aqua regia, excellentDielectric properties, extremely low friction coefficient and self lubrication“Plastic King”It is called.It is widely used in petroleum and chemical industryAnticorrosive coating, seal, bearingLubricating materials、Electronic appliancesMaterials, ship launching guide rails andnon-stick cookwareCoating, etc.Polytrifluoroethylene is cheaper than PTFE, the processing temperature can be reduced, the coating can be used for a long time below 130 ℃, and it is alkali resistant and resistantHydrogen fluorideThe ability of corrosion is better thanAcid resistant enamel, resistanthydrochloric acid、Dilute sulfuric acid、Hydrogen chlorideandchlorineThe ability of corrosion is better thanstainless steelEquipment.It has been widely used in chemical plantsInsecticide Factory、Pharmaceutical factory, detergent factory, etc.The greatest advantage of PVDF powder coating is its excellent weather resistance, high degradation resistance in outdoor exposure, no dust absorption, and easy to maintain the original luster.5 Chlorinated polyether powder coating.Chlorinated polyethers have excellentchemical stabilityThe coating film has good corrosion resistance and dissolution resistance to various acids, alkalis and solvents. Its chemical stability is second only to that of polytetrafluoroethyleneFriction performanceAlso very good.Chlorinated polyether powder coating is mainly used inChemical equipmentPipe lining, instrument equipment shell, etc.Its disadvantage is poor adhesion with metal.The adhesion with metal can be improved by adding additives.
2、Utilization rate of raw materialsHigh, powder produced by some famous brand powder suppliers, whose overspray powder can be recycledUtilizationIt can even reach more than 99%.
3. After pre-treatment of coated materials, one-time construction is not requiredPrime coat, enough thickness of coating film can be obtained, which is easy to realizeAutomated operation, high production efficiencycost reduction。
5. The storage and transportation of powder coatings are safe and convenient.
Powder sprayingConstruction technology and requirements: so-calledPowder electrostatic sprayingIt is the principle of using high-voltage electrostatic corona electric field.Connect the high voltage negative pole to the metal guide mark at the head of the spray gun, and the sprayed workpiece is grounded to form a positive pole, so that a strong positive pole is formed between the spray gun and the workpieceElectrostatic field。When the compressed air, as the carrier gas, sends the powder coating from the powder supply barrel through the powder pipe to the guide rod of the spray gun, the powder coating is produced due to the connection of the guide rod to the high-voltage negative polecorona discharge , densenegative charge, making the powder negatively charged and enteringelectric field intensityVery highelectrostatic field, onElectrostatic forceAnd carrier gasDouble effectThe powder will fly evenly to the surface of the grounding workpiece to form a thick and thin powder layer, which will be heated and solidified to form a durable coating.PaintingConstruction processPretreatment - drying and moisture removal - spraying - inspection - baking - inspection - finished product construction requirements General powder spraying construction requirements
(1) In order to give full play to the characteristics of powder coating and extend the service life of the coating film.
(2) When spraying, the coated object must be completely grounded to increase theSprayEfficiency.
(3) Check immediately after powder spraying. If any defect is found, deal with it in a timely manner. If any defect is found after curing, the scope is small and only local without affecting it. For surface decoration of the coated object, powder of the same color can be usedacetoneRepair after dilution, if the scope is large and affectssurface quality , sand paper is used for polishing, and then spray again orPaint removerRemove the coating, and then re Suo powder.
(4) Recycled powder must be screened to remove impurities, and then mixed withFresh powderMixed action。
(1) The input air pressure should not be too high during powder spraying,general control0.5-1.5kg/cm2 is good.Too much air pressure will cause patterndefinitionPoor or somePockmarks。The static voltage should not be too high, generally controlled at 60-70Kv.If the voltage is too high, the powder attached to the workpiece surface will rebound and pockmarks will appear.Poor leveling and other defects.
(2) Attention shall be paid to ensuring the thickness of the coating film, which is generally controlled between 70-100 μ m to facilitate the formation of obvious patterns and larger patterns. If the coating film is thin, the patterns are not obvious, and the patterns are small, and pockmarks will appear at the same timeExpose the bottomAnd other defects.
(3) Curing must be carried out at the specified temperature and time.If the temperature is too low and the time is too short, the powder will not form a pattern, and the curing is not completeMechanical propertiesIt has also dropped significantly.In addition, due to the fine pattern powderProduction processThe pattern will become smaller or have no obvious change after re spraying with recycled powder, so it is generally recommended not to use recycled powder of fine arts powder.It must also be tested before use.From the above, although the construction requirements are strict, it is believed that as long as the above factors are well grasped in the coating process, the ideal satisfactory effect will be achieved.
advantage
1. Health and environmental protection.
Various liquid chemicals added to achieve coating performance are omitted, which are harmful to film forming, dispersion, wetting, leveling and anti-corrosionAntifungalAnd other additives.
2. Convenient transportation and storage
Ordinary coatings contain about 20-50% water or solvent, while powder coatings contain neither water nor solvent. They are completely solid and are easy and safe to transport. In addition, coatings containing water or solvent tend to freeze when the temperature of transport and storage is lower than 0 ℃. This problem does not exist in powder coatings.
In the traditional liquid paint, food containing both water and bacteria is easy to be contaminated by bacteria.Therefore, in order to prevent deterioration, preservatives should be addedEmulsion powder coatingNo bacterial contamination, no preservatives required
4. Paint odor
Compared with the traditional paint smell residue, this paint can be dispersed quickly, which can be said to be "instant painting and instant elimination".
Due to the progress in the preparation technology of automobile powder coatings abroad, the coatings for automobile glazing, wood and plastics are the most dynamicpotential market。The automobile industry will be a major consumer,Greece、turkeyandEastern EuropeThe growth momentum of powder coating market is very good,Asia Pacificmarket potentialLarger, it has been considered as the fastest growing region in the world.
Manufacturing process
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The coating is made of special resin, pigments and fillers, curing agent and other additives, mixed in a certain proportion, and then prepared by hot extrusion, crushing and sieving.They are stable in storage at room temperatureElectrostatic spraying, friction spraying (thermosetting method) orFluidizing Bed Dipping (Thermoplastic method), reheating and bakingMelting solidificationTo form a smooth and brightPermanentCoating to achieve the purpose of decoration and anti-corrosion.
Construction requirements
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Electrostatic spraying (refer to the coating process of powder coating for details)
(1) In order to give full play to and extend the characteristics of powder coatingfilmService life, the surface of the coated object shall be strictly treated firstPretreatment。
(2) During spraying, the coated object must be completely grounded to increase the spraying efficiency of powder coating.
(3) Yes, it is largeSurface defectThe coated object of shall be coated with conductiveputty To ensure the smoothness and smoothness of the film.
(4) After spraying, the objects need to be heated and solidified. The curing conditions are powder productsTechnical indicatorsSubject to full assurancecuring temperature And time to avoid insufficient curingquality accident 。
(6) The recovered powder must be screened to remove impurities, and then mixed with the new powder in a certain proportion.
(7) Powder supply bucketPowder spraying roomAnd the recovery system should avoid the pollution of other powders with different colors, so it must be purged every time when changing colors.
matters needing attention
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1. Keep away from fire source and direct sunlight, and place it in a well ventilated place with temperature below 35 ℃.
5. All equipment used for painting shall be well grounded to eliminate static electricity.
6. Avoid endless discharge of the coating machine.
Identification method
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IAppearance identification method:
1. It feels silky smooth, loose and floatingThe hand feels rough, heavy and heavyGrab a handful of powder in your hand, and the powder will be smoother and looser, with good quality. On the contrary, the powder will feel rough and heavy, with poor qualityIt is not easy to spray, and there are many secondary powder drops, resulting in large waste
2. The larger the volumeFillerThe less, the higher the cost. The better the quality of the powderThe smaller the volume, the higher the filler in the powder coating, the lower the cost, and the worse the powder qualityFor the same carton, the larger the size of the powder, the better the powder, and the smaller the size, the worse the powderIt is not easy to spray, with more secondary powder falling, large waste, less spraying area and high use cost
threeStorage timeGood powder can be stored for a long time, and the powder leveling and other effects remain unchangedPoor powder cannot be stored for a long time. After 3 months, the leveling of poor powder becomes worse and other effects become worseNormal powder at room temperaturequality guarantee periodFor 12 months, the quality of low-end raw materials is unstable and easy to deteriorateThe powder produced with poor raw materials will accelerate the pulverization and aging of the sprayed surface half a year later, which will affect the customer's reputation. In addition, the powder is not easy to store, resulting in a large waste of powder and a lot of charges for customers
IIIdentification method of spraying area：
Spraying area of normal powderResin contentIt should be about 55-65%, the resin is about 20 yuan/KG, and the filler is about 2 yuanSome poor powder factories use resin content below 45% to replace defective ones, and increase filler to reduce cost and spray areaContrast method: Two same powder sprayingSame product, which company has more powder coating products, which company has less coating products, and the one with less coating products is poor,Usage costHighFor the user, if the spraying area is small, the use cost will be high. If the spraying area is 6 square meters per kilogram of powder, each less spraying area is equivalent to an extra payment of 3-6 yuan per kilogram of powder by the manufacturer. It is recommended that the manufacturer use authentic powder and carefully calculate its actual use cost
IIIOperation identification method for spraying personnel:
Powder loading rate,work efficiencyGood powder is very easy to spray. The substrate can be covered by spraying 1-3 guns. The secondary recovery of powder is less and the work efficiency is highPoor powder is not easy to be applied. The substrate can be covered only by spraying 3-5 guns. There are many secondary recovered powders, and the work efficiency is lowThe operator can determine the amount of powder falling by spraying the powder rateLess products are produced at the same time, and more powder is recovered at the second time, which increases the burden of operators and leads to low work efficiency
4、 Bake identification method:
There is no smoke to produce good powder. There is no large amount of smoke in the baking processPoor powder produces a lot of smoke during bakingGood powder raw materials do not produce a lot of smoke. Some manufacturers fill the raw materials with inferior onesThe amount of powder will increase,Square numberSpraying does not come out, which increases the use cost. The same amount of powder produces less products
5、 Identification method for appearance and gloss of finished products after baking:
Baked powder with good appearanceProduct appearanceDelicate, plump, transparent, strong three-dimensional sensePoor powder products are dull, stiff, foggy, opaque, and poor stereoscopicThe appearance of the two panels is poor, which affects customer reputation and product appearanceglossGood powder has good glossiness and can maintain relative gloss for a long timePoor powder gloss works well when it is just baked out. It will start to shine in a few monthsglossAppearance inspectionThe powder made of poor materials cannot maintain long-term gloss stability, and sagittal light, pulverization,DepaintingEtc
6、 Adhesion and aging identification method:
Good adhesive force and aging powder have strong adhesive force and toughness, and can keep away from pulverization and aging for several yearsPoor powder has poor adhesion and is very brittle. It begins to age and pulverize three months to half a year after sprayingCompare and test the adhesion and bending, and observe whether the product is aged and powdery after several monthsPoor adhesion and aging, products are prone to aging, pulverization, rust, shorten product service life, and affect customer reputation
VIIHigh temperature identification method:
At high temperature, adjust the temperature to 220-230 ℃ and keep it for 10-15 minutes. Good powder has good temperature resistance and weather resistance. After baking at high temperature, the color change is small and the gloss change is smallPoor powder, poor temperature and weather resistance, serious discoloration and dull luster after baking at high temperatureThis method is particularly effective in detecting outdoor light colored powderPoor powder, poor resin,Titanium dioxidePoor pigments and fillers, poor temperature and weather resistance, low cost, shoddy
SGSThe powder materials that have been tested for environmental protection are all produced by large factories, ensuring environmental protectionPoor materials and recycled powder can't guarantee environmental protection for a long timeEnvironmental protection SGS detected that environmental protection exceeded the standardExport enterprisesCause comparisonBig economyLoss
Powder coatings are processing consumables, and the investment threshold is relatively low,market competition The intense competition has also resulted in chaos in the powder coating market, serious jerry building, and the pursuit of short-term benefits, which has caused a relatively big impact on some genuine enterprises. In addition, the powder coatingPowdery substanceIt is not easy to identify, which has caused great economic losses to some powder enterprises. The actual consumption of the original product is 3 tons. By taking part in the fake materials, the price is cheap, and the powder consumption is increased to 4-5 tons, which has increased the cost of the powder enterprises. Most of the powder enterprises only care about the price of the powder, not the actual use cost, which has caused great losses to the enterprises
Storage mode
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1. Keep away from fire source and direct sunlight, and place it in a well ventilated place with temperature below 35 ℃.
2. Avoid storing it in water,Organic solvent, places polluted by oil and other materials.
3. The powder coating shall not be exposed to the air at will after use, and shall be capped or tightly wrapped at any time to avoid sundries from entering.
4. Avoid long-term contact with the skin. The powder attached to the skin should be washed with soapy water. Do not use solvents.Safety of painting construction site
5. All equipment used for painting shall be well grounded to eliminate static electricity.
6. Avoid endless discharge of coating machine
7. In the powder spraying room, the concentration of floating dust shall be controlled atSafe concentrationTo avoid the danger of dust ignition and explosion
