Difference between inorganic zinc silicate primer and inorganic zinc silicate workshop primer

Shop primer, also known as maintenance primer or pretreatment primer, is an anti-rust coating that is sprayed on steel plates or sections after they have been descaled through shot blasting, on an assembly line. Its function is to protect the surface of the steel that has undergone shot blasting treatment, preventing corrosion damage that could occur during processing and ship construction. It is widely used in the construction of ships and large steel structures. 　　Shop primer differs from ordinary coatings in terms of the following characteristics: 　　1. It is a temporary maintenance primer with certain capabilities to prevent rusting of steel plates; its effective protection period is generally 3 to 9 months. In areas where it is exposed to seawater for extended periods, such primers possess cathodic protection properties that prevent saponification. 　　2. It meets the requirements of automated assembly line operations well, as the paint film dries within 3 to 5 minutes. Under heated conditions, with a surface temperature of 40°C on the steel plates, the shop primer dries within 3 minutes, ensuring that the paint film remains intact during movement on conveyors and lifting operations. 　　3. The thickness of the shop primer film is relatively thin, allowing for even coating application using high-pressure airless spraying. The thickness of zinc-containing and zinc-free shop primers is respectively 15–20 um and 15–25 um； The film thickness of the shop primer is generally not included in the total film thickness of the ship’s coating. 4. When the actual painting of the ship’s sections takes place, the shop primer can be removed or left in place; this depends mainly on the integrity of the shop primer layer itself at that time, as well as the specific requirements of the first coat of paint regarding surface preparation, and it must be compatible with the paints that will be applied later. 5. The shop primer does not affect the welding properties of the steel plates, nor does it impact the welding strength. 6. The shop primer does not contain pigments made from arsenic, antimony, lead, chromium, or cadmium. The fumes and dust generated during cutting or welding are harmless to human health, and the concentration of any toxic or harmful substances released remains within the limits allowed by health standards. 7. The paint film has good mechanical properties; it can withstand friction and impacts during handling, as well as bending during processing, and it exhibits good interlayer adhesion with various paints that will be applied later. 8. The paint film also has good resistance to cathodic protection potentials. Characteristics of the inorganic zinc silicate shop primer: 1. Excellent spraying performance: It can be used in conjunction with the assembly line processes for steel plate pretreatment; it does not clog the nozzles during spraying, allowing for continuous spraying over long periods of time. The resulting paint film is smooth and has a uniform thickness. 2. Rapid-drying type: Within the specified thickness, the paint film can dry within 5 minutes. 3. Low level of pollution, meeting environmental protection requirements: Since the primer used in the zinc inorganic silicate production process contains no harmful heavy metals such as chromium and lead, and has a low zinc content, the amount of zinc vapor generated during heat treatment is below the environmental standards. Moreover, the solvents used in this paint are alcohols, which result in a mild odor during spraying and cause minimal environmental pollution. 4. Good rust resistance: In coastal areas or industrial zones with strong corrosive conditions, it does not rust easily even after 3 to 6 months of exposure; white rust formation is also very rare. It allows for smooth processing, and once turned into a finished product, the primer facilitates anti-corrosion treatment. With slight additional treatment, it can be applied over various types of base coats, thus reducing the need for secondary surface treatment. 5. Excellent compatibility with topcoats: It can be used in combination with both organic and inorganic resin-based topcoats; it is compatible with coatings such as chlorinated rubber coatings, epoxy resins, and aluminum powder asphalt anti-rust coatings. Therefore, the inorganic zinc silicate primer is a widely applicable primer for protecting workshops. 6. Excellent welding and cutting performance: When welding, it is not necessary to remove the primer on the groove; welding can be carried out directly with the paint in place, without affecting the mechanical properties of the weld. There are fewer pits and pores in the weld; moreover, the paint coating suffers little damage during heat treatment processes. Features of the inorganic zinc silicate primer: 1) Zinc powder provides cathodic protection and excellent rust resistance; it offers good welding and cutting properties, as well as superior heat resistance – the paint film can withstand high temperatures of up to 400°C, with minimal damage occurring during welding and cutting. 2) Excellent low-temperature curing performance, excellent solvent resistance, excellent impact resistance, excellent wear resistance, and moderate flexibility. It can be used with most painting systems. 3) During construction, the mixer should be used continuously to prevent zinc powder from settling. When working at temperatures above 30°C, it is necessary to add 0–10% of a diluent to avoid dry spraying. 4) When the dry film thickness is below the required level and it is necessary to apply another coat of zinc silicate inorganic primer, it should be diluted with 5% thinner before reapplication in order to enhance the interlayer adhesion of the paint film. To prevent pinhole corrosion, it is necessary to seal the zinc silicate inorganic primer with an epoxy sealing paint.