Color masterbatch production process principle
The most typical production process of masterbatcher is a high-speed mixer and twin-screw extruder. The surface of the pigment is treated with additives, and the pigment is sheared, dispersed, and stabilized by different combinations of screws. It involves the uniform mixing and dispersion of pigments and the control of the screw extrusion molding process.
1. Pigment uniform mixing and dispersing process
The uniform mixing and dispersion of filler masterbatch are mainly completed by the high-speed mixer.
When the high-speed mixer is working, the high-speed rotating impeller makes the material move tangentially along the impeller by means of the friction between the surface and the material and the thrust of the side against the material. At the same time, due to the centrifugal force, the material is thrown to the inner wall of the mixing chamber and rises along the wall. When it rises to a certain height, due to the action of gravity, it falls back to the center of the impeller and then is thrown up again. The combination of this upward movement and tangential movement makes the material actually in a continuous spiral up and down movement state.
Due to the high rotational speed of the impeller, the moving speed of the material is also very fast, and the rapidly moving particles collide and rub against each other, causing the agglomerates to be broken, and the temperature of the material rises accordingly, and at the same time, the interactive mixing is carried out rapidly. These actions promote the homogeneous distribution of components and absorption of liquid additives.
The baffles in the mixing chamber further disturb the flow of the material, causing the material to form random motions and creating a strong vortex near the baffles. For high-mounted impellers, the material forms a continuous cross-flow above and below the impeller, resulting in faster mixing. After mixing, the cooling medium passes through the jacket, and the cooled material is discharged from the discharge port under the action of the impeller.
2. Screw extrusion molding process
The extrusion molding process is a type of thermal processing. Under the action of the rotating screw, the mixed material is continuously transported forward, during which the material is continuously compressed and propelled by the pressure. With the friction, shearing, and heat generation between the materials, between the materials and the screw barrel, and at the same time by external heating, the phase structure of the materials changes and gradually melts into a viscous fluid melt. Then, under the action of the extrusion system, the homogenized plastic melt is extruded through the extruder head and dies at a constant temperature and pressure, and enters the next step of setting, cooling, pulling, and pelletizing.
In order to achieve good dispersion of the pigment and maintain dispersion stability, in addition to controlling the formulation composition and extrusion temperature and speed, the length-diameter ratio of the screw and the reasonable arrangement and combination of the screw are also very important. At the same time, the extrusion temperature is set according to the thermal performance parameters of the carrier resin in the masterbatch. Different mixing and dispersing effects can be achieved by changing the arrangement and combination of screw elements in the screw.
(1) Arrangement of threaded components and their process settings
a. The screw can be divided into five sections from the structural principle
Conveying section: convey materials to prevent overflow.
Melting section: Through heat transfer and frictional shearing, the material is fully melted and homogenized.
Mixing section: The material components are further refined and uniform to form an ideal structure with good distribution and dispersion.
Exhaust section: discharge impurities such as water vapor and low molecular weight substances.
Homogenization (metering) section: conveying and pressurizing, establishing a certain pressure, so that the material at the die mouth has a certain density, and at the same time, it is further mixed, and finally the purpose of smooth extrusion and granulation is achieved.
b. Sections of distributive (distributive) mixing and dispersive mixing
Distribution (distribution) mixing: The melt is divided and reorganized, and the spatial distribution of each component is uniform. It is mainly realized by the displacement of flow by stress such as separation, stretching (alternating compression and expansion), twisting, and fluid activity reorientation.
Dispersion and mixing: The components are broken into particles or the size of the incompatible two-component dispersed phase reaches the required range, which is mainly achieved by shear pressure and tensile stress.
(2) Comparison of the dispersion and distribution capabilities of threaded components
The dispersion ability of the same length and different staggered angles is 60°>45°>30°>90° (the value here represents the staggering angle), and the distribution ability is 30°>45°>60°>90°.
The dispersing ability of the same staggered angle, the same length, and different meshing sheet thicknesses is: the thick sheet is greater than the thin sheet; the distribution capacity is: the thin sheet is greater than the thick sheet.
3. Detailed description of the production process of masterbatch
a. Formula design: select raw materials and confirm the ratio according to product requirements.
b. Weighing: Prepare the raw and auxiliary materials of the color masterbatch according to the composition of the product formula through the weighing scale to ensure that the various raw and auxiliary materials meet the formula requirements.
c. Material pre-mixing: The raw materials weighed in a certain proportion are put into the high-speed mixer in turn according to the process requirements, and are stirred and mixed until uniform.
d. Melt extrusion: The premixed material is automatically fed into the extruder screw through the extruder feeding system, and then melted and blended through the screw conveying, compression, heating, shearing, friction, and other functions. Various pigments and additives are uniformly dispersed in the polymer matrix, and the polymer melt is extruded from the die hole of the extruder die under the action of the screw.
e. Cooling, drying, and dicing
Cold cutting method: Pull out the polymer melt strip extruded from the die head of the extruder, and cool it into a solid plastic strip by water cooling and air cooling. The plastic strip is pulled to the hob of the pelletizer for pelletizing, and the plastic masterbatch is obtained.
Hot cutting method: The melt-extruded by the extruder is directly cut into pellets, cooled by water circulation, and air-dried to obtain plastic masterbatches.
f. Screening: Through the vibrating screen, the plastic particles that are too long or too short, or too thick and too fine, which do not meet the particle size requirements, are separated from the plastic masterbatches from the pelletizer, and plastic particles that meet the particle size requirements are obtained. Masterbatch products.
g. Masterbatch homogenization and mixing: The particles are sent to the mixer for homogenization and mixing, and try to ensure that the differences between the color masterbatches produced at different times are minimized.
h. Inspection: The quality inspection of the produced products is carried out by means of sampling inspection, and sampling inspection is carried out on the particle appearance, color effect, dispersibility, and other performance requirements of the product. During the production process, a sampling inspection is carried out at regular intervals, and the products that finally meet the quality requirements will enter the next process, and the products that do not meet the requirements will be adjusted or scrapped.
i. Packaging and identification, storage
Pack the plastic masterbatch products according to the specified weight, and make a mark on the outer bag of the package (indicate the product name, specification type, weight, production batch number, shelf life, and other information), and then store it in storage.
