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    Home > Coatings News > Paints and Coatings Market > Talk about the development and status quo of lead-free paint technology

    Talk about the development and status quo of lead-free paint technology

    • Last Update: 2020-11-29
    • Source: Internet
    • Author: User
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    Reducing lead pollution and promoting lead-free paint is one of the trends in the development of paint, this paper introduces the source of lead-containing components in coatings and the development of new lead-free alternative technology, and expounds the technical difficulties in the development of lead-free paint and the direction of prevention.
    Keywords Lead poisoning, lead paint, lead pigment substitutes, alternative technology
    1 The source of lead paint
    lead resources are widely distributed on Earth, because of its "easy extraction, easy processing" characteristics, mankind as early as 7000 years ago has begun to recognize and use this resource, in the Western Bible, Egypt has been mentioned. China has a wealth of lead pigment resources, including red lead dan, yellow yellow dan, lead gray lead sulfide and a variety of white lead pigments such as lead white, phosphorus lead ore, horn lead ore, lead chloride, lead sulfate, etc. , in China on their development and use history is also a long time
    China

    Modern coating products are usually composed of film-forming substances, dispersion media, pigments and additives, wherein the main source of lead components is the paint production process added lead-containing raw materials (mostly color pigments, rust-proof pigments and a small amount of lead-containing additives), or its raw materials processing process lead residue caused, which brought into the paint more lead-containing pigments and color pigments.
    Lead-containing compounds as one of the effective ingredients in pigments and additives used in coatings, in the paint has a long application history, and the use of lead compounds has indeed played a role to a certain extent, to increase the speed of paint drying, improve the durability of the paint, maintain a fresh appearance, and has a protective decorative role against moisture, prevent corrosion.
    And lead is the only trace element that the human body does not need, it is a stable non-degradable pollutant, can accumulate in the environment for a long time, it will have an impact on the body's blood system, immune system, digestive system, nervous system, etc. , while lead on a number of central and peripheral nervous system in the specific nerve structure has a direct toxic effect.
    Lead poisoning is caused by acid-soluble lead, the so-called acid-soluble lead refers to the acidic conditions of the human stomach fluid can be dissolved and absorbed by the human body lead ions;
    2 Application of lead pigments and their alternative techniques
    Modern archaeologists have found that lead pigments have been widely used in ancient frescoes in northwest China, and rich varieties of lead pigments have been found in Tiantaishan Grottoes, while the Macy's Grottoes use a large number of phosphorus lead ore-arsenic lead mineral pigments;
    Based on many years of experience abroad, for lead-containing rust-proof pigments, mainly through the development of new non-toxic anti-rust pigments to replace it, and for lead-color inorganic pigments, there are more ways to replace, such as: the use of the corresponding color of organic pigments, the use of organic pigments and non-toxic cover type inorganic pigments stitched together, the use of new non-toxic inorganic pigments, the use of organic-inorganic composite pigments.
    2.1 Anti-rust pigments
    main function of anti-rust pigments is to prevent metal corrosion and improve the protective effect of paint film on metal surfaces. The role of rust-proof pigments can be divided into two categories: physical anti-rust and chemical anti-rust, in which chemical anti-rust pigments can be divided into corrosion-reprieve and electrochemical action type two pigments.
    2.1.1 Lead-containing rust-proof pigments
    The usual lead-containing rust-proof pigments commonly used in coatings are: red dan, yellow dan, alkaline lead silicate, calcium lead and lead carbon nitride, etc. , most of which are corrosion-repulsive rust-proof pigments, used in the production and processing of anti-corrosion coatings such as rust-proof primers. At present, the market commonly used lead rust-proof pigments are as follows:
    2.1.1.1 red dan
    red dan also known as lead Dan, changdan, chemical name is lead pb3O4, molecular form Pb3O4, red dan appearance orange powder, relative density of 8.6g/cm3. Red dan insoluble in water and alcohol, soluble in overheated alkali, partially dissolved under acidic conditions to produce water and salt, precipitation part is PbO2.
    Red Dan used in the paint has a long history, as a rust-proof pigment has been used to date, after painting has a strong adhesion and cover, especially and linen oil preparation of anti-rust paint, its resulting lead soap can play a corrosion-repulsion effect, anti-rust performance is very good, it is characterized by steel surface treatment requirements are not high, applied to the surface with residual rust is still very good anti-rust effect.
    2.1.1.2 Calcium lead-acid
    Calcium lead-acid has a similar chemical structure to red dan, with the molecular form 2CaO-PbO2, which is the result of an attempt in the early 1950s to find a substitute material with low lead content and a rust-proof effect similar to red dan. Calcium leadate is made from calcium oxide or calcium carbonate and lead oxide, which react at a high temperature of 700 degrees C.
    lead-acid appearance of milky yellow powder, relative density 5.71, lead content of 59%, mainly used in place of red dan preparation rust-proof paint.
    2.1.1.3 Alkaline lead silicate
    alkaline lead silicate is a nuclear pigment, the core part is SiO2, the surface part is PbCrO4-PbO and PbSiO3-3PbO, i.e. silicone dioxide particles as the core, on its surface to produce alkaline lead chromate and tri-alkali-γ-lead silicate. This is a generation of red dan rust-proof pigment developed in the 1960s, the production method is based on fine quartz powder (silicon dioxide) as the core, with lead oxide and chromate on the surface of its particles, to produce a layer of alkaline lead chromate (PbCrO4) PbO and PbCrO4-4PbO) precipitation, after high-temperature calcination, quartz powder particles and their surface precipitation form a solid coating of PbCrO4-PbO and PbSiO3-3PbO.
    alkaline lead silicate appearance is orange powdered, lead content of 43%, with excellent rust resistance, sulfur dioxide has a very high stability, good light resistance and poor covering and weak coloring. The pigment is insoluble in water and alcohol and other organic media, compared with other lead pigments have a smaller density, good chemical stability, not easy to form carbonate and fade, good adaptability to a variety of paint materials, the production of paint rust resistance, water resistance and weather resistance are very good.
    2.1.1.4 lead white
    lead white also known as white lead powder, the main component is secondary lead oxide, mixed with a small amount of lead oxide, molecular Pb3 (OH) 4CO3 density 6.14g/cm3,400c decomposition, has good weather resistance, but in contact with air containing hydrogen sulfide, due to the production of lead sulfide from white.
    Lead white appearance is white powder, its rust-proof effect and purity, fineness and surface state are related, lead white and fatty acids are very strong chemical force, reaction results make the paint film more tough, can adapt to a variety of paint materials, rust-proofing similar to red Dan.More than
    lead anti-rust pigments in a considerable period of time, become an essential addition to the rust-proof coating system, they all have excellent anti-corrosion function, while its good price-performance ratio so that it still has a larger market space, but with the improvement of people's awareness of lead pollution, the use of such products also began to be limited.
    2.1.2 lead-free rust-proof pigment technology
    In recent years, with the progress of science and technology, people in the development of non-toxic anti-rust pigments have also achieved certain results, has developed zinc phosphate, aluminum polyphosphate, ion exchange rust-proof pigments and other new non-toxic anti-rust pigments, for the traditional lead anti-rust pigment replacement, providing a strong technical guarantee.
    2.1.2.1 Selection of lead-free rust-proof pigments
    Coating manufacturers have been allowed to use a variety of non-toxic anti-rust pigments (e.g. iron red, mica iron oxide, aluminum powder, glass scales, boric acid) Zinc, modified boric acid, zinc phosphate, aluminum tripolyphosphate, etc.), through physical shielding, chemical passivation corrosion and other multi-directional technology to select design, preparation to achieve and better than the traditional lead-containing rust-proof pigment lead-free anti-rust coating. According to its anti-corrosion properties, the anti-rust pigments in
    coatings are composed of the following three categories:
    (1) physical anti-rust pigments
    Commonly used non-toxic physical rust-proof pigments are iron oxide red, mica iron oxide, mica powder, glass scales, stainless steel scales, aluminum powder and aluminum powder.
    (2) Chemical rust-proof pigment
    Chemical anti-rust pigment based on its own chemical activity, in the process of metal corrosion, with the metal ion reaction on the metal surface to produce a dense passivation film phosphate film to inhibit its corrosion process, or according to electrochemical principles, by sacrificing anodes to achieve the purpose of protecting metal. Rust-resistant pigments can also be chemically reacted with the ingredients in certain paints to produce compounds with stable properties and good water resistance with low permeability. Some pigments form corrosion-resistant conjunctivations during film formation, which improves the anti-rust effect. Commonly used non-toxic chemical anti-rust pigments are: phosphates, palladium salts, borates, ion exchange pigments and so on.
    (3) integrated anti-rust pigment
    integrated anti-rust pigment has both physical anti-rust and chemical anti-rust process, with more excellent corrosion resistance. Commonly used integrated non-toxic anti-rust pigments are: flaky zinc powder, flaky zinc aluminum alloy, composite iron titanium powder and so on.
    In the above non-toxic anti-rust pigments, most pigments have been put into production and put on the market, began to replace lead pigments in different coating systems, so that paint manufacturers can according to different anti-corrosion environment and requirements, calmly choose the required non-toxic environmental protection anti-rust pigments.
    2.1.2.2 Some emerging anti-rust pigment technology
    (1) ion exchange anti-rust pigment
    ion exchange anti-rust pigment is a new type of non-toxic anti-rust pigment, including calcium ion exchange silicone and rare earth ion exchange silicone, its action is very different from the above-mentioned ordinary rust-proof pigment. When the corrosive electrolyte enters the coating film, that is, in contact with the rust-proof pigment, the latter intercepts the corrosive ions on this silicon dioxide surface, and releases the corresponding calcium ions and rare earth ions and transfers them to the metal substrate, and as this process continues, the calcium ion layer and the rare earth ion layer are stacked on the metal coating interface, thus acting as a barrier and protecting the substrate and enhancing the coating adhesion. This makes ion exchange pigments have some unique advantages: corrosion-reprieve ions are released "on demand" and can be fully utilized, silicone is insoluble in the coating, and its exchange reaction occurs at the molecular level on the surface of the oxide carrier, without affecting the shape of the pigment, which can maintain the integrity of the coating for a longer period of time.
    Domestic Zhou Qin and others carried out systematic research on these two ion exchange pigments, found that rare earth ion exchange silicone has excellent corrosion resistance, its production process is non-polluting, reaction mother liquid can be reused, in the paint developed, rare earth ion exchange silicone anti-penetration performance and corrosion resistance is better than calcium ion exchange silicone, and has a late anti-corrosion performance.
    (2) flaky zinc powder
    zinc powder has been used in the preparation of anti-corrosion coatings for decades, because of its excellent corrosion resistance, has become the steel components anti-corrosion field and workshop primer field of one of the most commonly used rust-proof primers. At present, the actual use of zinc-rich primers in domestic and foreign projects is mostly spqueer zinc powder, but with the development of the market, zinc powder gradually to the direction of scales. the corrosion-resistant structure of
    flaky zinc powder is based on the following aspects: (1) zinc has a lower potential than the base iron, which can protect the steel substate from corrosion by sacrificing the cathode electrochemical protection of the anode; Alkaline zinc carbonate and zinc-iron compound salts, deposited between zinc powder particles, filled the gap between pigments, and do not conduct electricity, thus playing a closed role in the coating;
    Domestic in Xiaohui and other developed a scale-based zinc-based zinc-based zinc-rich zinc-rich heavy anti-corrosion coating, breaking the traditional anti-corrosion paint only anti-corrosion and ant decorative performance, and when used on the metal surface can be rusted operation, compared with the traditional zinc-rich primer has many advantages: the amount of flaky zinc powder in the coating is only 1/3 to 1/2 of the dosage of spout zinc powder, the overall cost is reduced, with stronger adhesion, corrosion resistance and good storage performance.
    (3) niobate series
    vanadium anti-rust pigment is white, with better coloring and covering force, often used in primers, can also be used as paint. MoO42-MoO42, a niobium-acid root ion released by these pigments, is attached to the surface of the steel metal and forms a complex with ferrous ions. Because of the action of oxygen in the air, the ferrous ions into high-speed rail ions, the formation of the compound is insoluble, so the metal surface to create a protective film, resulting in the metal surface passivation, play a corrosion-proof role.
    research on pigments in China is rare, and foreign countries have applied them to high-performance corrosion-resistant coatings. Sherwin-Williams has successfully developed a range of tantalum pigments, of which the second generation of modified tantalum anti-rust pigment Moly-White MZAP (zinc phosphate calcium phosphate) anti-rust performance is better than chromate. B.Del.Amo et al. studied the properties of coatings made of zinc phosphate in various resins, and the results showed that they showed the best anti-rust properties in epoxy resins and chlorinated rubber resin coatings. L. Veleva et al. studied the use of zinc phosphate and zinc oxide in the formulation of epoxy coatings, and the results showed that, in the presence of zinc oxide, the system's rust resistance was improved by preventing zinc oxide from producing zinc hydroxide and zinc phosphate by attracting positive charges on the surface of niobium anion and zinc oxide particles.
    (4) calcium phosphate
    calcium phosphate anti-rust pigment is a new type of high-efficiency non-toxic anti-rust pigment, less research in China. Foreign countries in the 90's developed calcium phosphate, the United States, Japan have patents to report the application of calcium phosphate in coatings research, China in recent years has carried out the preparation and performance of calcium phosphate pigment research.
    hydroxyphosphorite
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