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First of all, the production of powder coating is to add solid materials such as resins, curing agents, pigments, fillers and additives to the mixer according to the formula proportion, and then add them to the extruder for melt mixing after mixing and dispersing
.
Then it is pressed into thin sheets on the tablet press cooling machine, cooled and broken into thin sheets, and then fed into air grading and grinding, crushed and sieved through a certain mesh screen to obtain the finished product
.
It can be seen that the whole production process of powder coating is a physical mixing process, and the extruder is the main mixing extrusion equipment for the production of powder coating, the premixed solid raw materials are transported through the barrel, and the material is heated during the process, so that the material is subjected to strong extrusion and shear coating online coatingol.
com
in a molten state.
To fully mix and disperse the components of the raw material, in order to obtain a better dispersion effect, it is very important
to select the extruder and adjust the appropriate parameters of the extruder.
Because extrusion is the core process of powder production, it has a decisive impact on the quality of powder, and the mixing effect of the extruder is not good, which will reduce the gloss of the product, the leveling will deteriorate, and there will be uneven color mixing, local gelatinization, the formation of plate particles and other drawbacks
.
The inherent parameters of the extruder, such as power, screw structure, length-diameter ratio, maximum torque, operation mode, etc.
, different specifications and uses, are considered
according to the needs of the enterprise at the early stage of purchase.
In the face of the equipment that we already have, we adjust the variable, screw revolution, heating temperature, and feeding speed to maximize its ability and make a good product
.
Through the following experimental data, a reasonable equipment adjustment parameter is found for the extruder, and the material test process of the equipment used is as follows:
(1) Experimental extruder, temperature control plus or minus one degree, frequency conversion main motor up to 50HZ, power 5.
5KW rated current 11.
7A;
(2) High-gloss white material 5KG (epoxy resin 30 polyester resin 30 precipitated barium 13 rutile titanium dioxide 25 general leveling agent 1 brightener 0.
8 benzoin 0.
4);
(3) Matte black material 5KG (epoxy resin 33 polyester resin 27 precipitated barium 34 physical matting agent 3 general leveling agent 1 brightener O.
8 benzoin O.
4 carbon black O.
8);
(4) Low temperature curing material 5KG (epoxy resin 30 polyester resin 29 precipitated barium 38 low temperature curing accelerator 0.
2 general leveling agent 1 brightener 0.
8 benzoin 0.
4 carbon black 0.
8);
(5) Thermometer 0-300 degrees; (6) A universal crusher; (7) Standard sieve 200 mesh, standard sieve tray, cover a set; (8) THE MAXIMUM WEIGHT OF ELECTRONIC SCALE IS 15KG, AND THE INDEXING VALUE IS 0.
1G; (9) Constant temperature drying box, plus or minus 1 degree; (10) Experimental electrostatic spray gun
.
According to the ratio listed in 2#3#4#, accurately weigh the materials, mix and reserve, (epoxy resin softening point 90 polyester resin softening point 112 used in the experiment) extruder settings, adjust the temperature of extruder area 1 and 2 according to the temperature shown in Table 1, and turn on the cooling water to ensure the accuracy of the
extrusion temperature.
When starting, the number of screw revolutions and feeding revolutions are set according to the corresponding settings in Table 1, and after the material is extruded, the corresponding heat record
is read out by placing a thermometer in the fluid at the discharge port.
After the material passes through the pressure roller, the middle sheet is taken from the head and tail, crushed with a universal crusher, passed through the 200 mesh screen, the powder obtained, sprayed the standard sample, baked according to the corresponding baking temperature time in Table 1, after the sample is cooled, the thickness gloss impact strength is measured, and the surface of the coating film is evaluated
.
The surface difference of these three samples is not very large, the mechanical properties are basically the same, and the temperature change when the screw and feeding revolution number are fixed does not have a great
impact on the gloss and mechanical properties.
Although the temperature of the set screw barrel is 20 degrees, the temperature of the material outflow is similar, but the current of the main motor decreases with the increase of temperature, that is, the resistance of the material becomes smaller, which seems to save electricity
.
Among the three plates, A4-2#, the screw has the lowest number of revolutions, so the current is high, the feeding is relatively fast, the shear force becomes larger, but too much material makes its dispersion effect not too good, and the gloss does not reach the brightness it should be, so the speed
of the screw should be increased as a high-gloss powder.
When the feeding is increased, the current increases significantly, and at the same time increases the working pressure of the screw, the torque becomes larger, easy to cause screw deformation In actual production, adjust the feeding speed, not exceeding 95% of the rated current as well, if to improve work efficiency, the screw speed and the temperature of the screw barrel increase together
.
Low-gloss products have relatively low requirements for mixing and dispersion, low temperature, low speed and high feeding, which can obtain relatively lower gloss, but for matting agents requiring good dispersion, it can only improve the mixing effect, and the gloss will also increase
significantly.
For low-temperature curing powder, it should be low-temperature fast extrusion, the shorter the residence time of the material in the screw barrel, the better, its activity is high, and the temperature of the material flowing out of the production is higher than the display temperature of about 30, so as to prevent the material from reacting in the screw barrel at this time, gelatinizing, affecting the coating performance
.
According to the above, the higher the temperature within a reasonable range, the lower the viscosity of the material, the lower the current, and the higher the gloss of the product, indicating that the dispersion effect is also good, and the feeding speed is appropriately increased, which can increase the output and save power energy
.
The screw has high speed, high material pass rate, fast speed, due to the short residence time of the material in the screw barrel, suitable for low-temperature curing products, screw low-speed overfeeding when the amount is large, suitable for low-light and texture products with low mixing requirements
.
Feeding speed, for different products, fast speed can improve work efficiency, slow can make the material stay in the screw barrel for a slightly longer time, mixing more uniformly, suitable for most high-gloss products
.
For the temperature setting, the feeding section is the lowest, it is necessary to cool down with water, keep the material dry, in order to achieve the role of continuous forward transportation, the temperature of the plasticizing section, based on the lowest softening point of the resin, keep the temperature constant, can melt the material, and maintain the best viscosity to enhance the shear force and dispersion effect
.
The temperature of the mixing section can be set to the polyester softening point temperature, the mixing section is the most critical part of the extruder, the screw sleeve and the mixing block are precisely meshed, there is a good mixing and dispersion effect, and the effective shearing effect is an important guarantee for
the production of high-quality powder coatings.
In production, because the screw is longer, the material passing through the extruder is 20 to 30 degrees higher than the display temperature of the screw barrel, so when producing powder, it is more appropriate
to set the temperature of the plasticizing section to about 90.
The temperature of the mixing section of the second zone should not be higher than 110, so as not to produce gelatinized sheets, the material retained by the screw or screw gap at high temperature, the reactivity becomes larger, it is easy to partially gelatinize or solidify, once it is taken out and crushed, particles
are formed on the surface of the paint film.
The speed of the screw is generally set to 70%-95% of the maximum speed, the speed is low, the material passing rate is low, the production capacity is low, the screw torque increases, and it is easy to cause screw deformation
.
When the speed is high, due to the heat generated by its own friction and shear materials, it is easy to gelatinize the highly active materials and produce particles, which are coordinated with the feeding speed and adjusted to the most suitable position feeding speed to match the needs to set
.
Fast feeding speed, high production capacity, greater shear force, general mixing effect, low light or texture, low temperature class suitable, observe the host current, to not exceed the rated current
.
The feeding speed is slow, the material stays in the screw barrel for a long time, and it is easy to produce gelatinized particles, but the mixing effect is good, suitable for high-gloss powder or requires better dispersion (such as pigment dispersion is not good color @ production of high-gloss powder, the temperature setting is equivalent to the softening point temperature of the resin, the rotation of the screw is adjusted to 85% of the maximum revolution, and the feeding speed is debugged, and the current does not exceed 90% of the rated current as the best
.
To produce matting or texture powder, the set temperature should be 10 degrees lower than the normal temperature, the screw rotation number should be about 70% of the highest revolution, and the feeding speed should be adjusted, subject to the current of the main engine
.
Low temperature curing powder production, the temperature setting depends on the specific situation, in general can be the same as the setting of matting powder, fast feeding, it is best not to stop
halfway.
High-gloss products, high temperature and high speed feeding; Low-light texture products, low-temperature medium-speed large-scale feeding; Anti-corrosion low-temperature products, low-temperature high-speed large-scale feeding
.
In summary, controlling the three points of the extruder, extrusion temperature, screw speed, feeding speed, through the adjustment of the three variables, with reference to the change of the host current, can be realized on the same equipment, produce different products that meet the requirements, and reduce the cost
of purchasing equipment for enterprises.
Through continuous experimentation and learning, find the most suitable method for yourself, do more with half the effort, produce products that can meet market demand, and make a little contribution
to the development of the powder coating industry.
