Waterborne coatings are not a single product type, but represent a multitude of products with different formulations that can meet a wide range of needs, and the production process must also be adapted to these different needs. But only the most basic elements of production are discussed here. Usually, the production process of water-based paint and solvent paint is not substantially different, the main difference is that their respective basic principles lead to different production processes. The production process can be divided into several separate steps, the key step being the dispersion of pigments and fillers in the liquid phase (water or binder/water). Proceed as follows:
① Production of premix; ② Dispersion process; ③ All mixed and placed; ④ Testing, calibration and final adjustment; ⑤ Sieving and packing.
The first step is to prepare the premix for dispersion. Most of the additives have been added here, including sizing and dispersing agents, anti-settling agents and thickening agents, anti-mold agents, anti-foaming agents, erosion agents and film-forming agents. For water-soluble resins, the next steps are neutralization, pH adjustment, addition of auxiliary solvents, and then the addition of pigments and fillers with agitation. The solid components should be added under slow stirring, and in order to remove air bubbles and limit the generation of air bubbles at a lower viscosity, the finest components should be added first, and the composition of the premix must be precisely adjusted to the dispersion process. the required composition. Aqueous resin solutions can generally be used directly in the dispersion process because they are shear stable and exhibit good wetting properties. Appropriate shear force can greatly improve the dispersion effect, which is beneficial to the whole production.
The second step of decentralized operations consists of three separate but closely related processes:
① dispersion of pigments and fillers (as good as possible); ② good wetting of the surface; ③ reaching a steady state to prevent their re-agglomeration.
Simple mixing of solid and liquid components without any hassle, pigments and fillers are initially composed of basic particles that stick together in the dry state, which is called agglomeration. The dispersion force breaks up these agglomerates, restoring them to their original basic particle state as much as possible. To break the agglomeration of basic particles, it is necessary to overcome the adhesive force between them, which depends on the application of mechanical energy to the coating by the dispersion tool, which is essentially the action of pressure and shear force, and its propagation depends on turbulent flow (such as dissolution device) or laminar flow (three grinders). In addition, grinding media, such as ball milling, sand milling, etc., can also be introduced.
The third step is to enter the placement stage after the dispersion operation is completed. At this point the remaining binder, water and other auxiliary components are added to finalize the coating formulation. It is beneficial to add a certain amount of defoamer after the grinding is completed. Or defoaming the mixture in a vacuum mixer.
The fourth step is to adjust and test. If necessary, some adjustments should be made to the composition and properties of the coating, that is, the initial formula is not strict enough, and fine-tuning can be done after the inspection, which is to ensure the quality of the product. And need to carry out the final test, the standard test method is as follows:
① Density control (especially important when packaging is measured by volume);
② Determination of solid content;
③ To measure viscosity, both flow time and rheological properties can be measured;
④ Determination of pH value;
⑤ After the dispersion process, check whether the grinding reaches the required fineness;
⑥ Before packaging, the sieve residue should be measured every time, so as not to block the sieve and pump;
⑦ The general water-soluble system is always threatened by bacteria, so the determination of the number of bacteria must be carried out routinely;
⑧ Generally, the color and gloss must be measured for the paint.
Usually indoor dispersion coatings are very cheap, but still require the following properties:
① Hiding; ② Whiteness; ③ Matting; ④ Scrub resistance.
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