Talk about metal powder coatings for aluminum profiles.

Abstract
: This paper introduces the metal pigments, formulation design characteristics and detection methods commonly used in metal powder coatings for aluminum profiles, and makes a simple analysis of common problems in the production and spraying of metal powder coatings.
foreword . Metal powder coating refers to various types of powder coatings containing metal pigments (e.g. pearlescent pigments, aluminum silver powder, copper and gold powder, etc.). With the development of powder coatings and the improvement of technical level, powder coating varieties are becoming more and more abundant and perfect, metal powder coatings and other high-end powder coatings have also been greatly

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because it not only has outstanding protection function, but also has a brilliant, flashing charming appearance decorative, very popular in the market.with the increase in the use of metal powder coatings, people's quality requirements are getting higher and higher. This paper will combine the characteristics of metal pigments and the actual production experience of metal powder coatings, to explore how to improve the stability of metal powder coating production under the existing conditions, in order to improve product quality, inappropriate to ask colleagues to point out.
1, metal powder coating commonly used metal pigments
1.1 pearlescent pigments
pearl light is a natural mica thin skin covered with metal oxides produced by the pearl luster of the new pigment, relying on light refraction, reflection, transmission to show color and light, so that the appearance of the coating film more brilliant, bright.powder shows different effects in use, depending on the size of its particles. In general, the larger the particle, the stronger the flickering effect, and the weaker the cover force of the base color,
the smaller the particles, the stronger the cover of the base color, the softer the gloss. However, too thick particle size will lead to gravel on the surface of the coating film, affecting the flatness of the coating film, so coarse pearl light is not easy to add too much.
1.2 aluminum powder . Aluminum powder because of its silver-white metallic luster, so commonly known as aluminum silver powder or silver powder, its chemical composition is "aluminum", not "silver". The main two categories are floating silver and non-floating silver.
(1) floating silver by stearic acid treatment, with floating, easy to gather on the surface of the coating film, vulnerable to the impact of corrosive media, the smaller the particle size of the metal sense is stronger, the stronger the cover force, but the increase is too high when easy to produce vomit powder and block the phenomenon of the gun head, so for particle size less than 10um floating silver, the amount should not be more than 1%.
(2) non-floating silver usually has silicon dioxide coating, acrylic coating, etc. , can be evenly distributed in the entire coating film, because aluminum powder is wrapped in resin, so it has good antioxidant, wear resistance, better resistance to acid and alkalinity, and no handprint.
non-floating silver coating surface bright, and the color can be adjusted from the base powder, but the amount of addition is larger than floating silver, metal effect is not floating silver strong.
1.3 copper and gold powder . Copper gold pink is pure bright, strong metal sense, but its weather and temperature resistance is poor, is rarely used in aluminum profile users outside powder coating.
1.4 metal pigments are used in powder coatings . Metal powder coating composition is similar to ordinary powder coating, the formulation design follows the principle of simple manufacturing, stable spraying, excellent performance.metal powder coating formulation design, the fewer types of metal pigments, the better, the use of metal pigments with the least amount to achieve the best cover force is appropriate.
In order to achieve a certain metal effect, improve film performance or control costs, the formula design can be based on the particle size and performance of metal pigments, the use of pearl powder and pearl powder, pearl powder and silver powder, silver powder and silver powder mixed and matched.
because floating silver has not been modified treatment, its alkaline resistance is very poor, should not be used alone. When mixed with silver powder, the amount is not easy to exceed 1.5%.
Because most metal pigments in the extrusion process will destroy, break its structure, so that the metal effect is not obvious or metal-free effect, so the metal powder coating is mainly mixed with ordinary powder paint with metal pigments, through the Bonding process to bond it to achieve flashing metal Decorative effect, metal powder coating production process as follows:
2, metal powder coating Bonding process because of the silver powder particles in terms of shape, density and charge amount of differences with powder particles, in the spray will cause separation and affect the powder. Bonding powder coating with silver powder can significantly improve the spray stability and powder rate of metal powder coating.whether the full film surface metal effect has a direct impact, mainly manifested in the same amount of metal pigments appear different metal effects of the coating surface.
Bangding temperature impact: If Bonding temperature is too low, powder particles softening is not sufficient, surface adsorption force is small, metal pigments and base powder can not be fully bonded together, thus affecting the bonding effect of metal powder coating, so according to the different base powder and choose different Bonding temperature.
Generally speaking, the resin glass temperature selected for sand powder is higher, Bonding temperature can be set higher, the bonding temperature of the two-part powder is a little lower than the sand powder, and the flat flour Bonding temperature is significantly lower than the sand powder. operating frequency: It is important to determine the optimal operating frequency of the Bonding machine. If the operating frequency is too low, the Bonding effect is not sufficient, but too high will destroy the protective layer coated on the surface of silver powder, reducing the alkali resistance of the coating film. It also breaks the pearlescing powder, making the metal flicker less effective. time: Bonding time and Bonding operating frequency have similar effects on metal powder coatings, also need to choose the best time based on practical experience. the silver powder quality is very light, in order to bond the effect is uniform, not easy to add directly alone, silver powder and base powder premixed to add. At the same time, fire accidents caused by direct friction of silver powder can also be avoided.
3, metal powder coating detection method
3.1 coating performance detection acid-base resistance test cycle is short, simple operation, often used for metal powder coating film performance detection.
3.1.1 acid-base resistance
aluminum is a partial acidic metal, the acidic medium is dull, in general, acid-resistant 15min has no effect on the coating film. Aluminum is sensitive to alkaline media, so alkali resistance is a common method to judge the quality of aluminum powder and aluminum powder metal powder coatings.
3.1.2 Mortar resistance test
(1) according to aluminum alloy building profile Part 4: powder spray profile GB 5237.4-2008 in the test method: take JC/T480 specified raw lime 75g and standard sand 225g, and then add about 100g GB / T 6682 specified three-stage water mixed into a paste mortar.
put the paste mortar on the surface of the sample, stacked into a cylindrical shape with a diameter of 15mm and a thickness of 6mm±, placed 24h in a constant temperature and humidity of 95% ±5% at 38 degrees C±3 degrees C, removed the mortar, wiped the residue with a damp cloth, dried it, and examined the coating surface after the test, there should be no shedding or other obvious changes. (2) Although the national standard does not provide for the use of sodium hydroxide to detect alkali resistance, but in practice in order to be able to obtain test results within ten minutes.
Usually using 10% sodium hydroxide solution, drawing on acid resistance detection methods, the alkali resistance of the coating film is tested: sodium hydroxide solution (l-9) is configured with chemical pure sodium hydroxide and three-stage water, and 10 drops of sodium hydroxide test solution are dripped on the coating surface of the sample.
covered with surface dishes and placed at an ambient temperature of 15min at 18C-27C, wash and dry with tap water. Visual inspection of the coating surface after the test, requiring no obvious corrosion of the coating surface after the test. (3) silver powder corrosion resistance simple sorting: floating silver < resin coating products< silicon dioxide coating products< dense silicon dioxide coating products< composite coating products.
3.2 Spray Stability Detection
3.2.1 Manual Spray Plate Observation
The spray stability of metal powder coatings is mainly detected by electrostational spraying. Take the well-ordered powder, set different air pressure, voltage spray several models, spray process to observe whether the gun head silver accumulation.
the sprayed model all baked out to observe the different spray conditions of the model coating surface is normal, coating surface metal effect is consistent, so as to avoid the spray process on the effect of spraying.
3.2.2 Simulated pipeline construction spray gun test work parts method
Due to the difference between pipeline spraying and manual spraying effect, metal powder coating manufacturers need to simulate downstream customer spray conditions, with the pipeline automatic spray system for spraying, so as to ensure product quality stability.
4, metal powder coating production and spraying in the common problem analysis
4.1 different batches of metal effect is not consistent
Bonding process consistency directly affects the stability of different batches of metal powder coating, if bonding process is inconsistent, so that the degree of bonding is different, resulting in different metal effects of each stated, metal powder is more or less.
therefore, the bonding temperature, water supply time, operating frequency and bonding time of different batches of metal powder coatings need to be controlled under the same conditions.
4.2 poor fluidity
the overall fluidity of powder coatings can be reduced due to the good conductivity, significant ratio and bonding of metal particles to the base powder. Therefore, the metal powder coating in the electrostectrulative spraying process, the need for a moderate amount of increased voltage. At the same time, metal powder coatings need to be supplemented with flow aids to improve their mobility.
However, the addition of flow aids in the Bonding process often has no effect on the fluidity of powder coatings, because the operation of the Bonding machine stirring will destroy the structure of the flow aids, thereby invalidate the flow aids. Therefore, the flow aid is best added at the end of the added bonding.
4.3 Bonding after the film metal flicker effect decreased
Bonding after the film surface metal pigment particle size thinner, resulting in a decrease in the metal flicker effect of the film surface, which is mainly due to the long bonding time, too many return to the state fixed number or the frequency of operation is too high.
because the pearlescient pigment for mica powder high temperature calcination, the material is very brittle, in the process of Bonding easy to break and thin. Therefore, for pearl-shaped metal powder coating, it is necessary to reduce the operating frequency of bonding machine or shorten the bonding time.
4.4 Bonding after coating alkali resistance performance decreased
usually added aluminum silver powder pigment metal powder coating, Bonding after coating alkali resistance is worse than Before Bonding. This is due to increase the acid-base resistance of aluminum silver powder, aluminum silver powder is usually covered with silicon dioxide, acrylic resin and so on.
in bonding process, the operation of Bonding machine blades will break this layer of protective film, so that the metal powder coating film after Bonding alkali resistance performance decreased.
4.5 different batch color differences
in the bottom color, as far as possible to the base color close to the face color, which can reduce the impact of metal pigments on the final product color, thereby ensuring the stability of the product color between batches.
5, the . In summary, in order to ensure the quality of metal powder coatings, the quality of metal pigments and production, Bonding process control is very important. Improving the quality of metal powder coating products requires not only improving the stability of production technology, production equipment and construction facilities, but also strengthening the professional skills of technicians and operators.
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