Organic Silicon Resin Heat-resistant Coating Pigments
Aug 1, 2024
When preparing organic silicon high-temperature resistant coatings, fillers (such as mica powder, talc powder, calcium carbonate, etc.), pigments (such as aluminum powder, zinc powder, carbon black, etc.), and catalysts (such as octanoates or cyclic carbonates of zinc, diamond, magnesium, iron, etc.) should be added to the silicone resin. The types of pigments and fillers have a significant impact on the heat resistance of the formulated coatings. Pigments and fillers used in heat-resistant coating formulations should not only have general properties, but also have high temperature stability, that is, they should not decompose or change color under high temperature for a long time. Therefore, inorganic pigments and fillers are often used.
(1) White pigment
There are mainly Qinbai, zinc oxide, zinc barium mortar, and oxide ladder. Qinbai is a commonly used white pigment with excellent thermal stability. Ruiqin type Qinbai has better heat resistance and adhesion to the bottom layer at high temperatures than Jin Hong Shi Qinbai. It is suitable for long-term heat resistance at 250℃ and can withstand 350-400℃ without discoloration when combined with organic silicon. It turns yellow brown at 600℃ and irreversible black brown at 1200-1300℃. Zinc oxide has good heat resistance, with a heat resistance of 250-300℃. When combined with organic silicon, it can be used for a long time at 370℃, but its covering power is low. Oxidized brocade is resistant to light, heat, and has low powdering properties, mainly used in fireproof coatings. Lide powder is suitable for long-term heat resistance at 250℃. Zinc sulfide is suitable for long-term heat resistance at 200℃.
(2) Yellow pigment
There are mainly Dehuang and Guohuang. SrCr01 is a commonly used yellow pigment in organic silicon heat-resistant coatings. It has good heat resistance and is suitable for long-term heat resistance at 200℃. It has passivation and rust prevention ability for metals, but has low coverage. It is suitable as a heat-resistant primer pigment for light metals (magnesium, aluminum metals). CdS has a bright color, good covering power, and is resistant to light and heat. It is suitable for heat resistance at 1200℃ and stable when heated to 700℃. At higher temperatures, it turns brown, and at 980℃, it turns pale red.
(3) Red pigment
There are mainly pickaxe red and iron oxide red. Hao Hong (3CdS • 2CdS) has a bright red color, good covering power, light resistance, and heat resistance, and is suitable for long-term heat resistance at 250℃. Iron oxide red (Fe203) has good coverage, light resistance, and heat resistance, and is suitable for long-term heat resistance at around 250℃, but its color is not bright enough.
(4) Blue pigment
There are mainly Diamond Blue, Qunqing, and Oujing Blue. Diamond Blue CC0Al201 is heat-resistant and suitable for long-term heat resistance at 500℃, with good light resistance but low coverage. Qunqing is an aluminum silicate blue pigment containing sodium polysulfide and having a special structure. It is resistant to light and heat, and is suitable for long-term heat resistance at 200℃. The color fades slightly above 250℃, but the covering power is poor. Youjing Blue is suitable for heat resistance below 200℃.
(5) Green pigment
There are mainly two types: oxidized Minglv and Youjing Green. They are resistant to light, heat, acid, and alkali, and can withstand temperatures up to 260℃ in silicone resin. However, they are hard and difficult to grind, and have slightly poor covering power. Trioxide is suitable for long-term heat resistance at 250℃.
(6) Black pigment
There are mainly carbon black, graphite, manganese dioxide, and lead iron black. Carbon black has strong covering power and chemical resistance, so it has a certain degree of heat resistance. Suitable for long-term heat resistance at 250℃. If the temperature is higher than 300℃, the color will fade and it will be difficult to disperse in the paint. Suitable for heat-resistant coatings below 350℃. Graphite series is composed of flake like crystalline carbon elements, black with gray luster, soft and smooth in texture, good in heat resistance, suitable for long-term heat resistance above 300℃, and can withstand 650℃ when combined with other pigments. It has good acid resistance and is commonly used to prepare acid and heat resistant coatings. Manganese dioxide is a brownish black pigment with good heat resistance, suitable for long-term heat resistance at 300℃. Mingtie Black is a pigment composed of a mixture of iron oxide, oxidized iron oxide, and dioxide, which is highly heat-resistant and remains unchanged at 800℃. It is a good black pigment in high-temperature resistant coatings. Ceramic black has low covering power and is suitable for long-term heat resistance above 1000℃. Iron oxide black is also used at low temperatures.
(7) Metallic pigments
There are mainly aluminum powder, zinc powder, and stainless steel powder. Aluminum powder is a granular or flaky metallic aluminum pigment with silver luster, which is generally used as aluminum powder in pine perfume. Aluminum powder has good heat resistance and strong covering power. Its melting point is about 600℃. Coatings combined with organic silicon resin can be used for a long time at 540℃. Aluminum powder penetrates into high temperature steel surfaces to form alloys, which can be maintained for a long time without damage. But it is susceptible to alkali or inorganic acid erosion, has poor chemical resistance, and aluminum powder paint is prone to precipitation. If it is prepared for too long, the color will darken and lose its luster. It is best to prepare and use it now. Zinc powder has a melting point of about 420℃ and vaporizes at 900℃, so its heat resistance is not as good as aluminum powder. Coatings made with organic silicon can be used for a long time at 400℃. Zinc powder has an electrochemical protective effect on the surface of steel and is commonly used as a heat-resistant and rust proof primer for steel surfaces. Stainless steel powder generally contains 18% Ming and 8% Zhu, and has high heat resistance, suitable for 300-400℃ heat resistance. It is also relatively stable to chemical corrosion. Organic silicon coatings using it as a pigment have good heat resistance and corrosion resistance, and are often used together with aluminum powder and other pigments. Zinc powder, copper powder, and zinc oxide can also be used to enhance the heat resistance of silicone resin, and can be used at 370-480℃.
(8) Constitutional fillers
There are mainly talc powder, mica powder, asbestos powder, heavy stone powder, silica powder, and glass powder, all of which are suitable for long-term heat resistance above 300℃. The chemical composition of talc powder is mainly 3Mg0 • 4S heart. Talc powder and asbestos powder are both fibrous pigments that can strengthen the connection between coating structures in heat-resistant coatings. When heated at high temperatures, they can improve the thermal elasticity and crack resistance of the coating. However, when used in large quantities, they are prone to loss of gloss or even powdering at high temperatures. According to reports, adding talcum powder or asbestos powder instead of 10% pigment to the enamel formula can increase the heat resistance to micro cracking time of the paint film by 50%. Barite powder is suitable for heat resistance below 300℃ and can improve coating hardness. The chemical composition of mica powder is mainly composed of Di 0 • 3Al203 • 6Si2 • 2H core and flakes. It can improve the strength of the paint film in heat-resistant coatings, and has good resistance to powdering and insulation. The chemical composition of asbestos powder is mainly a mixed salt of calcium and magnesium silicate. Generally, asbestos is burned at 400℃ and ground into powder for use. It has high thermal stability and can provide high resistance to cracking of the paint film at high temperatures. Silicon dioxide powder, naturally quartz powder steel, has a hard texture that is not easy to grind. Artificial silica powder, also known as white carbon black, is divided into precipitation method silica and gas-phase method silica according to production methods. The former is mostly used as heat-resistant fillers, while the latter is lightweight and used as thickeners and anti precipitation agents in coatings. Glass powder has a better melting point range of 400~700℃. When combined with organic silicon coatings, when organic silicon decomposes at high temperatures, the glass powder melts and forms a bundled ceramic coating with organic silicon and other pigments and fillers, which can withstand higher temperatures.
(9) Rust proof pigment
Blunt yellow, zinc phosphate. Avoid using pigments containing lead, calcium, and chromium in the formula. It is necessary to test their gelling properties to prevent the gelation of organic silicon. Lead pigments can also reduce the heat resistance life of the coating. Generally, the principle of using pigments is to meet the covering power of the coating, and the amount of bulk pigments should be minimal.
(10) Other
The silicone resin used for baking is resistant to dilute hydrochloric acid, sulfuric acid, acetic acid, and caustic soda solutions, and has good weather resistance. Drying agents can use organic acid salts of zinc and diamond, and lead should not be used. Lead welding iron cans are also not suitable for packaging silicone paint.
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