Coating production process

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Coating Production Process Chapter 1: Coating Manufacturing Process I. Basic components of coatings: Resin, pigments, solvents, additives II. Manufacturing process: Pre-dispersion – Grinding – Mixing and adjustment – Color tuning – Testing – Filtration and packaging III. Manufacturing process diagram Note: QC1 refers to raw materials； QC2 is process quality control ； QC3: Finished product inspection – Serial number, quality issues, main causes, solutions, preventive measures. 5. Thickening of color paste (fineness issue): 1. Failure to stir immediately after adding the cleaning solution, or excessive amount of cleaning solution used; 2. Failure to stir immediately after making up the mixture; 3. Thickening and thickening during storage. Solution: Re-grind. 1. Follow the operating procedures strictly, and monitor the fineness at three key points: before discharge, after cleaning, and after making up the mixture; 2. Control the inventory of color paste to minimize storage time; 3. The technical department should re-test the stored color paste regularly. 6. Unacceptable fineness of colored paint (fineness issue): 1. The fineness of the color paste or paint is unacceptable, with missed or incorrect inspections before coloring; 2. Incorrect dilution method – the ingredients are not added slowly while stirring, resulting in pigment precipitation; 3. Wrong type of paint used, or different paints in different color pastes, leading to poor resin compatibility and thus unacceptable fineness; 4. Unclean working tanks or impurities introduced by other auxiliary materials. Solutions: 1. If acceptable to the customer, approve the product despite the issue; 2. If not acceptable, re-grind it or use it in flash paint; 3. If poor resin compatibility is the cause, appropriate solvents can be added after testing to improve compatibility. 1. It is necessary to check the fineness of the color paste and paint before adding them to the mixture; 2. Operate carefully to avoid introducing impurities or causing precipitation; 3. The formula should be well-designed, taking into account compatibility issues. II. Painting production equipment: The production process for colored paint is as follows: pre-dispersion – grinding – coloring and formulation – filtration and packaging. The production equipment will now be described based on this process. Chapter 1: Pre-dispersion Equipment Pre-dispersion allows pigments to be mixed with a portion of the paint, resulting in a semi-finished product in the form of a pigment paste. It is the first step in pigment slurry production. Purpose: ① To mix the pigments evenly ； ②To partially moisten the pigment ； ③Initially break up large pigment aggregates. It mainly functions through mixing, providing some degree of dispersion to prepare for the subsequent grinding process. The quality of the pre-dispersion effect directly affects the quality and efficiency of grinding and dispersion. The main equipment used is a high-speed disperser. In addition to being used as a dispersion device, high-speed dispersers can also be employed as equipment for producing colored paints. For example, if the pigments used in such paints are easy to disperse, or if the required fineness of the colored paint is not high, then a high-speed disperser can be used directly to disperse the materials and produce the colored paint. Its structure is shown in Figure 2-1. (For floor-standing high-speed dispersers) It consists of a machine body, a transmission device, a main shaft, and impellers. Figure 2-1 shows the external appearance of the floor-mounted high-speed disperser. The machine body is equipped with hydraulic lifting and rotating mechanisms; the hydraulic lifting function is achieved by a gear oil pump that supplies pressure oil to raise the head, while it descends due to its own weight. The descending speed is controlled by a stroke throttle valve. The rotating mechanism allows the head to turn 360°, and a handle is provided to lock it in place after rotation. The drive mechanism is powered by a motor via a V-belt; the motor can operate at three speeds or two speeds, or it may feature variable-speed control via a belt or frequency conversion. The rotation speed ranges from a few hundred revolutions per minute to tens of thousands of revolutions per minute, while the power varies from several dozen to over a hundred kilowatts. The key component of a high-speed disperser is the serrated disc impeller, as shown in Figure 2-2. Figure 2-2 Schematic diagram of the impeller in a high-speed disperser. The diameter of the impeller is directly related to the size chosen for the mixing tank; empirical data show that the optimal dispersion effect is achieved when the diameter of the mixing tank is φ=2.8–4.0D (where D is the impeller diameter). The high-speed rotation of the impeller creates a rolling circulation in the paint slurry, generating a large vortex. At a distance of 2.5–5 cm from the edge of the impeller, a turbulent zone is formed; in this zone, the pigment particles are subjected to strong shear and impact forces, which cause them to disperse rapidly within the paint slurry. A satisfactory dispersion effect can be achieved when the rotational speed of the impeller results in a circumferential velocity of about 20 m/s. If it is too high, it will cause the paint slurry to splash and increase power consumption. Vmax=20--30m/s. There are two ways to install dispersers: floor-mounted types, which are suitable for cylinder drawing operations, and those mounted on stands, allowing one disperser to be used with several fixed tanks. At present, there are many modified versions of high-speed dispersers available, each with its own characteristics, which broaden the range of applications for these dispersers. For example: twin-shaft twin-impeller high-speed disperser, see Figure 2-3 ； Two-speed high-speed dispersers (two-axis single-impeller dispersers, two-axis two-speed mixers), etc. Figure 2-3 Two-axis double-impeller high-speed disperser. Chapter 2: Grinding and Dispersing Equipment. Grinding equipment is a key type of equipment used in the production of colored paints. There are two basic categories: those that use grinding media, such as sand grinders and ball mills, and those that do not use any grinding media and rely on frictional forces for dispersion, such as three-roll mills and single-roll mills. Equipment equipped with grinding media relies on the impact force and shear force generated by the grinding media (such as glass beads, **, pebbles, etc.) during impact as well as mutual rolling or sliding to carry out grinding and dispersion. It is commonly used in the production of medium and low-viscosity paint pastes with good fluidity, offering high production volumes and efficient dispersion. A grinding and dispersing device without abrasive media can be used for the production of materials with very high viscosity, even those in paste form. Now, the vertical sand mill and the three-roll mill will be introduced separately. Section 1: Vertical Sand Mill. Its external structure is shown in Figure 2-4; it consists of a machine body, a main motor, transmission components, a cylinder, a disperser, a feeding system, and an electrical control system. Figures 2–4: Schematic diagram of the structure of a vertical sand grinder. 1 – Discharge port for the sand ； 2—Cooling water inlet ； 3—Feed pipe ； 4—Continuously variable transmission ； 5—Feeding pump ； 6—Speed control handwheel ； 7—Control button panel ； 8—Disperser ； 9—Centrifugal clutch ； 10—Bearing housing ； 11—Screen ； 12—Simplified version: For the working principle, see Figure 2-5. The pre-dispersed paint slurry is fed in from the bottom by a feed pump; the flow rate can be adjusted. The bottom valve 8 is a special check valve that prevents the glass beads from flowing back after the pump stops operating. Once the paint is fed in, the sanding machine is started; the dispersion shaft drives the dispersion disk 5 to rotate at high speed, with the circumferential speed at the outer edge of the dispersion disk reaching around 10 m/s (the rotation speed of the dispersion shaft is between 600 and 1500 rpm). The paint slurry and glass beads near the dispersion disk are driven by viscous forces to move along with the rotation of the disk; they are thrown against the walls of the sanding machine and then return to the center. As a result, the pigment particles are subjected to shear and impact forces, thereby becoming dispersed within the paint. The dispersed paint slurry overflows from the outlet through a screen, while the glass beads are retained by the screen. Figures 2–5 Schematic diagram of the principle of a conventional sand mill; 1—water jacket ； 2—Typical flow pattern of the paint slurry trapped between the two dispersion discs (double annular rolling grinding action): 3—Screen ； 4—Slurry outlet after dispersion ； 5—Dispersion disc: 6--Mix of paint slurry and grinding medium: 7—Balancing wheel ； 8—Bottom valve ； 9—Premixed paint slurry inlet: If the slurry does not meet the required fineness level after one round of dispersion, it can be ground in a sand mill again until it meets the standards. Several (2–5) sanding machines can also be used in series. Grinding can achieve a size of around 20μm. The glass beads have a diameter of 1–3 mm; they should be regularly cleaned, screened, and replenished due to wear. During operation, sand grinding generates a large amount of heat due to friction; therefore, a jacket is built around the barrel body to cool it with cooling water. Laboratory sand grinders are generally