Study on the stability of Bonding metal powder for aluminum profiles.

Author
Wen/Qin Xiangyu, Cai Jinshu, Cai Yingjin
Guangdong Huajiang Powder Technology Co., Ltd.
Summary
by elaborating on the basic principles of Bonding, it is explained that the factors affecting the stability of Bonding are mainly formulas and Bonding processes. Through the thermal bonding bonding test, using infrared spectroscopy, X-ray, electron mirror, dry particle size instrument and other detection means, it is verified that the Bonding process is the surface softening of powder particles, bonded together with the metal effect pigment, and the effect of Bonding process and formula on Bonding effect is explained by different comparative tests.
0 Foreword
With the improvement of people's living standards, people's decorative requirements are also higher and higher, metal effect powder coating in the entire powder coating applications in the rapid growth of

. However, the stability of the production of metal effect powder still bothers the major domestic powder manufacturers, the reason is that the understanding of the Bonding principle is more vague, in the process of Bonding, the micro-change state of powder particles, metal effect pigments and powder particles how to interact with the cognition or relatively one-sided, the principle of unclear cognition is leading to a deviation in the direction of research, so as to do more than half the work, poor people.
production process of metal effect powder is mainly three kinds: normal temperature dry mixing, melt extrusion heat mixing, Bonding thermal bonding mixing. This paper mainly studies bonding technology of Bonding thermal bonding.
1 Bonding production technology introduction
1.1 Bonding principle
powder coating Bonding technology is also known as thermal bonding technology, mainly through friction heating or jacket heating way to make the surface of powder particles have a certain degree of viscosity, so that the metal effect pigment and powder base powder combined, specifically through Bonding machine mixing paddle high-speed Rotation, so that between the powder and powder, metal effect pigments, powder and Bonding machine (stirring oars, cylinder wall) between high-speed collision, friction, in a certain period of time, the surface temperature of powder particles rose to a certain extent, powder surface softening, metal effect pigment particles and powder coating particles bonded together, so that static spraying to obtain a stable coating with metal effect. In order to make the coating effect relatively stable, under a certain metal effect pigment content, bonding technology is adopted to make more metal effect pigments and powders tightly combined to ensure the stability of construction.
powder coating is a mixture of resins, curing agents, pigments, additives and fillers. The resins in the formula are polymerized from polyols and polyic acids. Glassing temperature is the temperature at which a polymer changes from a high-ballistic to a glass state, which refers to the transition temperature of a non-stereotyped polymer (including the amorphous part of a crystalline polymer) from a glass state to a high-e-bullet state or by the latter forward, and is the lowest temperature of free movement of the large molecular band of a non-stereotyped polymer, usually expressed in Tg, with the method and conditions of the determination varying somewhat. Above this temperature, the high-polymer shows elasticity, and below this temperature, the high-cluster shows brittleness. As shown in Figure I, it is the morphological-temperature curve of polymers.
Bonding process of the setting conditions mainly include Bonding temperature, heating speed, insulation speed, insulation time, metal effect pigments and powder particles bonded together because the powder particle surface has softened phenomenon, or even the phenomenon of stickiness, at this time the powder particle surface instantaneous temperature has reached the softening point. In the friction between the mixing oar and the material, the stirring oar to the material to do part of the work into the material's dynamic energy, part into thermal energy, so that the surface of the powder particles instantaneous temperature reached Tg point, or higher than Tg point, at this time due to the huge force of the mixing oar on the material, powder particles and metal effect pigment tightly bonded together. The electro-mirror diagram of Bonding powder products is shown in Figure II.
general product powder coating is composed of resins, curing agents, pigments, fillers and additives. Products obtained by premixed, melted extruded, cooled, crushed, finely crushed, graded screened. Therefore, the mixing effect of better products, can be regarded as each powder coating particle composition is basically the same, the same charge performance, under the high-pressure electrostic action powder particles with uniform charge. According to Coulomb's law, in a certain period of time, the powder coating particles have the following relationship:
so the same powder coating in the spray baked out of the color, appearance and performance of the coating film is consistent, recycled powder in repeated use, coating color and appearance and performance is also basically stable.
According to the appearance requirements of the coating film, the general metal effect pigment is added to the powder coating with dry mixing method, this powder in the high-pressure electrostectrulation effect with static electricity, the charge effect of metal powder and metal effect pigment and the charge effect of the powder is very different, so the ratio of powder adsorbed to the work piece to the metal effect pigment, Unlike the proportion in the original powder and the effect is not stable, this will lead to the proportion of metal effect pigment in the recovery powder and the metal content in the new powder is not consistent, and with the increase in the number of recovery, the difference between the metal content is increasing, so when adding the recycled powder for spraying, the coating color and appearance change with the spray time, resulting in the spray product coating film quality instability.
In order to ensure that metal powder (metal effect pigments) in electrostitive spray products coating appearance and quality stability, must take a special process to powder coating to ensure the quality of metal powder (metal effect pigments), this process is called "bonding" (bonding), so in the production of products with metal effects (aluminum powder, pearl powder, copper powder, nickel powder, zinc powder), must be bonded treatment.
in the process of electrostectrectrectrectrative spraying, the force of powder coating particles in addition to electric field force has its own gravity, air resistance, air pressure. Therefore, the combined (1) can be known to affect the powder charge Qs factors are dielec meter constant, particle size of powder particles, electric field strength. The dielecyte constant is mainly affected by the material of the powder and the stability of bonding, and the electric field strength is influenced by voltage and gun distance. In the process of spraying, in order to maintain the stability of the spray effect, it is possible to make each powder particle subject to gravity, electric field force, air resistance, air pressure size is equal, the same direction.
the stability of the spray are Bonding stability (the degree of binding of powder with metal effect pigment), voltage, current, and air pressure. Therefore, the hand spray gun can be sprayed with different voltages, air pressure to observe the color of the coating film, metal effect is consistent to judge the stability of Bonding. The factors affecting Bonding stability are Bonding temperature, Bonding time, operating frequency, transition frequency, feeding order, base powder resin amount, base powder particle size, type of metal effect pigment, metal effect pigment amount.
Bonding process is the general name of Bonding temperature, Bonding time, heating frequency, transition frequency, cooling time, feeding order, in order to add metal effect pigment powder coating in the static powder spray to obtain a stable coating quality, under certain temperature conditions, so that metal effect pigment particles adhere to the powder coating particles, in electrostation spray, so that the metal effect pigment in accordance with a certain proportion of uniform and stable adsorption to the work surface, to ensure stable appearance of the coating. And the temperature setting is the main factor of Bonding, mainly according to the glass temperature of powder base powder set, the general flat metal powder Bonding temperature is a few degrees higher than the glacification temperature.
In general, if the metal powder is not Bonding, because the metal effect pigment with static electricity and substrate is different, the content of the metal effect pigment in the recovery powder will gradually increase with the increase in the number of recovery and the difference between the metal content of the new powder, the use of recycled powder spray or add recycled powder spray unevenly will cause the original powder spray appearance is not the same, will cause the appearance and quality of the coating film instability.
1.2 Bonding effect detection method
(1) spray plate observation method: take The powder product, according to different voltages, air pressure spray plate, to observe whether the plate effect is uniform and stable.
(2) horizontal spray line simulation: according to the process of small spray line to simulate the customer on-site spraying process, observe the difference between the plate effect and the standard.
(3) visual observation method: with a clean transparent polyethylene plastic bag to pick up a small half-bag of Bonded powder, half-bag air hand-held after shaking a few times lifted, gently patting the first half of the plastic bag without powder. If Bonding is warm enough, the powder state in the bag can be seen through the eyes. The inner surface of the silver powder adsorption plastic bag is not able to see through the condition of the bag.
(4) instrument detection method: magnifying glass, microscope, electron mirror to observe powder status and plate conditions.
(5) particle size analysis method: according to the particle size distribution measured by the dry particle size meter, observe whether the fine powder before and after Bonding significantly reduced, whether the particle size distribution is more concentrated, if the fine powder significantly reduced, the particle size distribution is more concentrated, then Bonding effect is good.
(6) electro-mirror map: According to the Bonding base powder and metal effect pigment mixed electro-mirror map and Bonding powder electro-mirror comparison, the more metal effect pigment bonded on the powder particles, the better the Bonding effect.
2 Bonding experiment and law summary
In order to explore the main factors affecting the stability of Bonding, the main factors affecting Bonding stability were tested using thermal conduction heating test machine, and the design experiments according to the main factors affecting Bonding stability were as follows: Experiment I, Bonding temperature, Bonding time, running frequency, transition frequency on stability;
method of determining whether the bonding process has reached the end point is to observe the state of the powder, the actual spray effect and the microscopic particle size distribution: First, the degree of powder clumping, the sticky cylinder. Second, the fluctuation of Bonding electromechanical flow. Third, different voltage pressure spray plate, to observe whether there is a color difference, metal effect pigment amount is uniform. Fourth, compared with the base powder, dry mix, Bonding finished product dry particle size to observe the particle size distribution.
2.1 Raw materials and instruments
polyester resin (allnex); isocyanuric acid triglycerides (Huahui); sabbath (Ningbo South China Sea); brighteners (flatter); leveling agents (flattering); boosters (Shanghai Sox Chemical Co., Ltd.); Bonding additives (octo degrees); mobile additives (Degusai); sulfate (Guixiang); aluminum powder (domestic, Aika); metal effect (domestic).
instruments: dry particle size BT-2001, extruder (E×30), grinder (ACM-05F), Bonding machine (BD11819X), fully automatic spray line, experimental spray gun (CQ-SJ5), oven (101-3AS type).
2.2 This paper tests the reference standard
2.3 The effect of different Bonding process on Bonding effect
Affected by the speed, the amount of base powder resin, different Bonding process directly affects the final Bonding effect, so this experiment carried out the following experimental design of this parameter:
2.3.1 Bangding time on bonding effect
A metal effect pigment in the same quality of the same base powder, with a special Bonding process for Bonding, each Bonding 2kg, follow the principle of a single variable, specific Bonding process such as Table 2-3-1:
Bonding process:
<6>A, B, C are 3 mixtures of the same base powder and metal effect pigments, respectively, according to 3 processes to Bonding, with Bonding after the product is measured dry particle size distribution, dry particle size test statistical results such as Table 2-3-2:
put three powders with the same spray process spray plate, from the plate effect, B's pearly powder volume is higher than C, more shiny, indicating that the stirring time is too long resulting in thick pearl powder by the mixing oar fine or covered, not flash enough. From the table 2-3-2 particle size distribution, extended Bonding time, fine powder Bonding efficiency is higher, coarse powder has become more, so Bonding time is extended, pearl powder is easy to break, but also easy to be better covered by powder, not so flashing.
2.3.2 Effect of different frequencies of the mixing paddle on bonding effect
The metal effect pigment is bonded to the powder particles because the surface of the powder particles has softened, or even become sticky, at this time the instantaneous temperature of the surface of the powder particles has softened the surface of the powder particles. When the mixing oar and the material friction, the stirring oar to the material to do part of the work into the material's dynamic energy, part into thermal energy, so that the surface of the powder particles instantaneous temperature reached the softening point, or slightly lower than the softening point, at this time due to the rapid speed of the mixing oar, the material collision produced a huge force, powder particles and metal effect pigment tightly bonded together. Therefore, in the actual production process, the change in control speed is very critical, generally in the process of heating up the speed is faster (30-40Hz), when the temperature rises to a certain extent, the current produces abnormal fluctuations, the speed drops to (22-28Hz), maintain a period of time (2-5min), cooling discharge. When the general metal effect pigment is fine, a higher speed can be used, and when the metal effect pigment is thicker, a relatively low speed is used.
2.3.3 Bangding temperature on the effect of Bonding
the glass temperature of resin is generally 63-67 degrees C, at this temperature the resin has not softened, and the actual Bonding temperature is generally around the glacification temperature, different models of Bonding machine Bonding temperature differences, if the temperature of the powder particle surface is Bonding display temperature, powder particles will not produce the phenomenon of wrapped metal effect pigment particles. The actual phenomenon of powder particles have been bonded with the metal effect pigment, or even wrapped, so bonding temperature is much higher than the set Bonding temperature, powder particle surface due to high-speed friction with the mixing paddle has reached a softening point. Therefore, the actual set state temperature is an empirical value, in the actual production as a reference value.
In actual production, the key is to make the temperature of the upper and lower Bunding machine uniform, in order to be the powder and metal effect pigment particles binding uniform, to prevent a part of the metal effect pigment is not bonded with powder particles, and powder particles have been a large number of adsorption bonding together, the phenomenon of clinging, resulting in Bonding instability.
2.3.4 Effect of discharge temperature on product quality
In the actual production process, Bondi has three stages of heating-insulation-cooling, and the discharge temperature is also an important parameter of product quality, generally placed from the hot cylinder to the cold cylinder below 40 degrees C. In, the temperature is too high during the shutdown, due to high stationary time and more material may cause material lumps, or even damage the motor;