Metal effect powder coating preparation process.

Foreword
metal effect powder coating, in the whole decorative powder, the application of more and more wide, is currently the mainstream of fine art powder.
can be used in powder coatings there are many varieties of metal pigments, generally divided into four categories. That is, aluminum and silver powder pigments, pearlescing pigments, copper and gold powder pigments and other metal pigments (such as nickel powder, stainless steel powder, etc.)

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each type of metal pigment also contains a lot of color products, applied to powder coatings, so that the powder colorful, greatly enriched the variety and decorative powder coatings.
the 4E properties of powder coatings, more and more liquid coatings are moving towards powder coatings. Metal effect powder coating is now mainly used in domestic and foreign metal furniture, lamps, handicrafts, smoke machines, strollers, sports equipment and automobiles and other industries.
production process of metal effect powder coating can be divided into: melt extrusion method, postmix method, thermal bonding method. And the latest chemical bonding method. The fluidized bed bonding method has also attracted the interest of researchers.
1, metal effect powder coating production process
1.1 molten extrusion method
the metal material and substation, additives together through the extruder shear mixture extrusion. Make it all capsules during heating, melting and mixing.
This method makes aluminum sheet in a good dispersion at the same time get a solid bonding force, after spraying easy to obtain a uniform metal flash effect, and the amount of metal material is greatly reduced, the requirements of spray equipment is also significantly reduced.
but loses its metallic luster during mixing and high-speed crushing. When the amount of sheet metal is relatively large. The problem is even more pronounced, not only losing the metallic sheen, but also endangering weather resistance.
in the subsequent crushing phase, the sheet metal may be broken, exposing the metal to the air, increasing the risk of fire and dust explosion.
1.2 after mixing
the base powder is crushed and dried with the aluminum powder at low speed stirring. Does not damage metal flakes. However, in construction applications, it is easy to separate from powder coating substations due to the small or non-sticking of metal particles and the large differences in the charged properties and specific gravity of metal particles and base powders.
often results in the separation of atomized materials when electrostectrectile spraying, resulting in uneven coating and "mirror frames". These paint film defects are caused by changes in the corona discharge voltage.
disadvantage of this method is that the over-spraying powder of dry mixed metal powder coating cannot be recycled. The powder rate is low and the color difference between batches is large.
addition of metal powder is too high to produce spitting powder and blocking the gun head phenomenon, too low there is no mirror effect, the general amount of its dosage is 0 to 3. 0% 。
1.3 thermal bonding method
since the metal powder bonding technology was recorded in 1977. Thermal bonding technology has come a long way. First, metal powder manufacturer Benda-lutz provided thermal bonding services, and later powder coatings companies including AkzoNobel and Tiger successfully applied thermal bonding technology to the production of powder coatings.thermal bonding method is composed of dry mixing method and heat treatment method. In this technique, the powder coating base is heated above the glass temperature, under the protection of inert gas, metal powder is added under stirring, so that it is bonded to the surface of softened powder coating particles, avoiding the powder coating clinging to metal, increasing the reaction activity of the polymer.
this process is usually done in a high-speed mixer with a temperature control jacket metal "bonding", in a short period of time to apply a high shear force, there is no obvious temperature rise.
if too high shear force will be applied there will be a tendency to break the sheet metal, in order to produce high-quality products, the process conditions are best controlled within a certain range.of thermal bonding metal effect powder coating made by the i-inch cyclone separator to measure its loss shows that: the loss of thermal bonding method is less, easy to obtain a uniform metallic color. Other advantages include powder utilization of nearly 100%, as with regular powders.
no metal pigment stacking or blocking the muzzle when spraying with Corona electrostectoral guns. There are no border problems caused by atomization or spraying. The metal pigment selection range is wide.
can be very high, and some powder coatings have a metal effect that is close to or greater than liquid coatings. There is no separation problem between the metal pigment and the base powder.
1.4 Chemical Bonding
forms chemical bonds by adding polymers between metal powders and powder coating base powders, known as chemical bonding.
Alcoa powder company's research report that: the surface of the metal powder silicone chemical modified and then half-branched a certain amount of official energy group or resin encapsulation metal powder to form capsules, these function groups can form a bond with the resin in the powder coating, at this time the metal powder and powder coating base powder form a consistent charge.
can make metal powder react with powder coating base powder or fuse by selecting the official energy group. Some of these official groups participate in the crosslinking of powder coatings to form a collocational coating film.
for different systems of powder coatings, its modified official group is not the same, can include: amines, isocyanates, carboxy acids, hydroxy compounds and so on.
design of different ernum groups to handle metal powder according to the resin type of base powder in powder coating. This method improves the compatibleness of metal-effect powder coatings through the close connection between metal powder and resin. This improves the flatness and color stability of the metal effect powder coating.
1.5 fluidized bed bonding method
recently described a new method in a paper presented by researchers at the Hosokawa Powder Technology Institute. This new method involves bonding the ingredients to the fluidized bed with the appropriate substation and operating at a temperature lower than the glassy temperature of the powder coating.
the material used in the study was polyester powder varnish with an average particle size of 35 btm, and the average cross-section of the polymer-coated non-stripped aluminum sheet was 16/-tm, with a thickness of 10 to several hundred nanometers.
liquid substation is an anionic hydroponic PU emulsion with an average particle size ;p of 130 nm; O;20 degrees C viscosity of 160mPa.s, can be diluted with water, and the selected powder coating is matched.the
fluidized bed bonding device consists of a cylindrical device with a nozzle, at the bottom of which a device for the flow of hot air is embedded, and a pulsed oscillating bag filter is installed above the bed to capture small particles and return the recovered particles to the fluidized bed.
2 non-fixed nozzles for adding liquid substations are also installed at the bottom of the fluid bed to spray the lO to 20 btm substituts into the fluidized bed., for example, powder coatings and aluminum sheets are made with a mass ratio of 95:5, with 40. C's hot air is fluidized, and then the liquid substation is sprayed into the fluidized bed at a flow rate of 4 mL/min, about 15 min, and the content of the substation is about 0. 3% 。
then used 6o. C's hot air drys the material in the bed by about 5 min, making the bed temperature up to 40. C, finally introducing room temperature air to lower the temperature to 30.
C or less, the product is made. It takes approximately 25 min to prepare a 1 kg powder coating sample with metal. Production-scale fluidized bed bonding systems produce approximately 150 kg of metallic powder coating per hour.
operated with experimental-scale equipment, 25 min per batch is required. The ratio of the material is 950 g for powder, 50 g for aluminum and 60 g for base material (solid water, solid base material is 2. 68 g).
production with production-scale equipment, each batch needs 60 min, raw material ratio of powder 142. 5 kg, aluminum powder 7. 5, solid base 402 g, i.e. 9,000 g emulsion. In order to facilitate comparison, the same aluminum sheet using dry mixed legal system preparation powder coating, the made of bonded powder coating sprayed on the stainless steel furniture door lock, by the respective systems collected powder spray, using inductively coupled plasma atom emission spectroscopy to determine the content of aluminum sheet.
spray powder coating bonded with fluidized bed at different voltages, the resulting film aluminum sheet is evenly distributed, and the appearance of the coating does not change with the voltage.
and dry-mixed paint, the resulting coated aluminum powder distribution is uneven, when the voltage increases, the metal sheet concentrated on the edge. The powder coating bonded with fluidized bed does not have the problem of dispersion and bonding fastness. aluminum sheets were arranged on the coating film at a high magnification, comparing solvent-based metallic paint, dry mixed powder coatings and fluidized bed bonding powder coatings.
can be seen from the photos of the cross-section of the metal plate coating: when the construction thickness of the liquid coating is 19 gm, the aluminum sheet is almost parallel, the coating has a high brightness and good metal effect.
contrast sample, powder coating film thickness of about 60 gm, dry mixing powder coating aluminum sheet is arranged in an unconventional arrangement, and fluidized bed bonding powder coating has a high concentration of aluminum sheet, aluminum sheet is usually arranged in parallel with the metal substrate, and dry mix coating film compared to a very prominent metal appearance, similar to liquid metal paint coating. study also found that if the concentration of large grain-size aluminum sheets in the formula was higher than 5%, and can be arranged in parallel, a better metal appearance can be obtained.
this may be caused by metal sheets interfering with each other during the curing cycle, and high concentrations can also increase the stability of the film interior. found in multi-batch production: about 98% of the bonding material can be recycled, greater than or equal to 120/, tm of aggregate coarse powder only 2%.
also studied the distribution status of aluminum sheets and powder coatings in fluidized beds, and used laser scanning technology to determine the particle size of dry mixing materials, laboratory fluidized bed bonding materials, and production scale fluidized bed bonding materials obtained from top, middle and bottom.
The average particle size of the dry mixing powder coating is smaller than that of the fluidized bed bonding powder coating, partly due to the separation of small aluminum sheets from the powder coating when determining the particle size
; Laboratory and industrially manufactured fluidized bed bonding powder coatings have shown that this process can be used to obtain good batch reproducing. The aluminum content remained the same in all samples. does not use liquid substations, the use of thermal bonding technology can also be made powder coating, this process requires the various parts in the 50012 fluidized bed to maintain 30 min, fluidization temperature and powder glass temperature (55 to C) is very close.
compared with the dry mixing method, the performance of the coating can be improved, and the aluminum sheet can be evenly distributed with thermal bonding material without forming a frame coating film. The aluminum content of each powder was then measured separately during construction, and they were compared after 5 cycles. dry mixed powder coating after the first spray, the loss content of aluminum powder by 4. 6% to 1. About 8%, after 5 cycles of loss, aluminum content reduced to 1. 1%; the content of the hot bonding powder at the time of the first collection was 4. 6% to less than 3%;
after 5 cycles, the aluminum powder content dropped to 1. 5%; the powder bonded with fluidized bed had the least loss, and the aluminum content was 4. 2% and 3. 9%, aluminum content dropped to only 2. 1%。 metal powder coating, to get a more satisfactory visual effect, the limit content of aluminum powder is 4. 0% 。 Assuming a transfer rate of 50%, adding 50% of the new powder to the recycled material will sustain the required aluminum powder content.
other types of powder coatings, such as epoxy polyester blend, acrylic powder coatings, the experimental results are similar to the above-mentioned pure polyester powder coatings. to polyester powder coatings with an average particle size of 8 ktm, which may contain 1. 5% of the shedding aluminum sheet, compared with the type that does not fall off, the shedding level can not be corrosion-resistant, the use of fluidized bed bonding corrosion resistance has been improved, the process also helps to prevent static spraying of electric sparks.
2, conclusion
overall, increasing the content of metal powder in metal effect powder coatings, as well as maintaining the stability between batches, increasing the utilization rate of powder coatings is still the goal of powder coating manufacturers. But so far, the melt extrusion method and the postmix method have become the main production method due to the low maintenance cost of equipment, and the thermal bonding method has become a hot spot in the production of metal-effect powder coating due to its stability and high load of metal powder.
only Qitong and Sanli companies in China have carried out research and development and equipment production. The research and development of chemical bonding method and fluidized bed bonding method is still in the laboratory stage and pilot degree.
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