Talking about the Prevention of Common Defects of Water-based Anticorrosive Coatings

China Coatings Online News Information: The
research and development of water-based anti-corrosion coatings began in the 1980s. Due to well-known reasons, water-based anti-corrosion coatings have been slowly developed, applied in small quantities, and have been performing well for 30 years.
Since last year, the relevant departments of the state issued a series of documents, restricting the use of solvent-based coatings in some areas and projects, the VOC super-standard coatings to levy consumption tax, promulgated water-based acrylic, water-based polyurethane, water-based epoxy, water-based alcoholic acid and other resin coatings, water-based inormeric phosphate solvent-resistant anti-corrosion coating standards, and the above-mentioned paint harmful substances limit standards, environmental mark products including water-based coatings technical requirements. In this way, so that water-based paint materials research and development units have a direction, so that some paint enterprises see business opportunities, so that our water-based paint research and development of technical personnel have a basis. Since this year, water-based paint resins, pigments, additives more and more, many solvent-based coating enterprises began to busy with the "oil-to-water" boom, some coating enterprises are also more and more favor water-based paint. Since then, China's water-like industrial paint into a new period of development.
In recent years, Wuxi Taihu Anticorrosion Materials Co., Ltd. research and development and put into the market water-based inorganic zinc-rich anti-corrosion primer, general-purpose water-based acrylic anti-rust paint, packaging bucket water-based baking paint, water-based anti-corrosion series paint varieties have been increased to more than a dozen. At present, the development of water-powered auto parts paint has begun. The company's high-level strategy is: solvent-based coatings gradually reduce VOC and other harmful substances, water-based anti-corrosion coatings to increase research and development efforts, so that paint, water paint two-handed grasp.
1 Water-based anti-corrosion coating common defects
a just done and packaged paint, its advantages or defects are not clear, only to open the can, open the barrel, can see its appearance and stability of the situation, at this time the defects have floating water, under the lumps, surface blisters, bad mold and so on. Also, to the coating construction, can only see its effect, at this time the defects are paint flow, a poor cover force, membrane shrink holes, pinholes, uneven surface, the outside paint lack of plumpness and gloss. After a period of time, if the paint or coating quality is not good, there will be cracking, peeling, foaming, rust and other defects. Water-based paints may have more defects than solvent-based coatings due to their inherent weaknesses.
2 The cause of common defects in water-based preservatives
1) or too many hydro-friendly substances in the paint, water easily seeped in, producing air pressure, the paint film top up. With more foaming, the entire coating loses adhesion.
2) Coating film bubble holes: the main reasons are: desiccant selection and mismainting, the pulping and painting phase did not break the desiccant smooth, the paint when the paint is too low, spray gun when spraying is not adjusted to the best. There are bubble holes, no material cover in the hole, water and oxygen easily invaded, corrosion occurred.
3) coating shrink hole: the main reasons are: the coating system components failed to stir evenly, the surface of large-strength substances such as emulsion, spread poor mobility; There are many shrink holes, the primer is easy to rust, the paint appearance is poor.
4) Hardness problem: the main reasons are: Tg and addition of the base material, and the amount and amount of oil absorbed by the powder, and the environmental conditions in the process of film-forming, namely temperature and humidity. The coating film is too hard, flexibility, bending and impact resistance can not pass, the coating film is too soft, water penetration plastic and then residual corrosion effect is obvious.
5) poor water resistance (salt): the main reasons are: the film-forming, water-resistant whitening of the substrate is poor, solid particles are coarser; The surface strength, so the primer and substrate adhesion difference, there are foaming, shrink holes, pinholes and other fatal defects, some coatings cover the above defects, it is more water-resistant, salt-resistant water resistance, and even salt-fog resistance can be said.
6) Paint film appearance defects: as far as the exterior paint is concerned, the main reasons are: paint film uneven, less abundance, is due to the paint surface strength, internal non-flowing spread, poor film flatness;
3 Prevention and control of common defects in water-based anti-corrosion coatings
According to the experience of research and development practice, we have taken the following measures to prevent and control these defects:
1) from the source of the formula to prevent and control, that is, to try to reduce the surface pressure of the coating. The main difference between water-based coatings and solvent-based coatings is that the dispersed dilution medium used is different, resulting in different surface pressure of the two coatings, water-based paint problems than solvent-based paint. Therefore, water-based anti-corrosion paint, whether high-grade or low-grade, should reduce the surface pressure of the coating to improve the adhesion of the coating in the first place. This requires the choice of road additives: First, the use of low-volume high-performance substrate wetting agents, such as BYK's 300 series of products, TEGO's 4000 series of products, the original Corning H110, H140, H188A and other varieties. With H204, 3275 and other high-efficiency dispersants, complete the first step to reduce the surface pressure of the coating. The second is to add water-based coatings with adhesion promoters. Silane coupled agent has a strong mobility, can be freely migrated to the organic / inorganic interface, so emulsion is the addition of silane attachment system, and the most effective attachment agent on the steel surface is the two oxygen-based energy silane, more expensive. Titanate concedes have the performance of wetting substrates, as well as auxiliary deblistering and leveling. Such as Jiangnan plant jN one ll5A, is a chelated type of titanium-ester coupling agent, can increase polyester and steel, acrylic and iron bonding. Dosing in about 1%, cost-effective. Nanjing Shuguang, Taiwan Deqian, Germany have this kind of products, these additives as long as the right choice, will become another sharp weapon to reduce surface stress. Third, the use of high-efficiency low surface pressure leveling agents, such as BYK 345, 346, the original Corning DSX-2000, not only can expand the primer on the substrate spread surface, increase its attachment point, but also conducive to the flow leveling of the coating surface, reduce the appearance of filling. Fourth, to supplement a certain amount of different volatile rate of alcohol ether combination to help solvents, on the one hand to better help the substation film, on the other hand can also reduce the surface pressure of the coating, but to take into account the relationship between addition and drying and construction. The main positioning of these additives, synergy, the surface pressure of the coating will be reduced, adhesion will be increased.
Reasonable to take the above measures, those self-drying primer or baking paint peeling, foaming, attachment is not secure and other defects, the outside paint surface is uneven, not smooth, not full and other defects, paint life is not long and other defects can be effectively prevented and resolved.
For the soft, flowing, uneven surface of the packaging barrel water-based paint and other issues, we by screening the appropriate resin and adjust the proportion, the replacement of reduced surface pressure, anti-flow hanging leveling additives to solve. Before doing a product, performance is very good, only voc more than 100g / L, customers can not pass. Later, a low-content dispersion of voc was used to meet the customer's requirements.
To the general-purpose water-based paint rough, multi-bubble, shrink hole, poor appearance, thickening or thinning later and other defects, we use the "four two" additive use method to overcome. "Four two", that is, more than two moisturizing dispersants, more than two anti-foaming anti-foaming agents, more than two membrane-assisted solvents, more than two rheumoid aids. More than two wetting dispersants, in order to polish out a sufficient fine slurry, for the coating film to provide adhesion, fineness, gloss, anti-fouling, etc. , the original Corning H1140 is a low foam, flow, strong surface pressure reduction substrate wetting Agent, suitable for hard-to-wet metal substrates, similar in performance to BYk345, half the price; Sioxane 154, BASF molecular grade A-34, etc., in order to provide the surface of the paint film bubble-free, pinhole-free, non-shrinking performance and smooth, smooth, decorative performance; Propylene emulsion with TExANOL, and then with different volatile rate of alcohol ether-assisted solvents, such as propylene glycol methyl ether, butyl ether, etc., is conducive to the formation of coating continuous complete dense film, thus providing adhesion, water resistance, aging resistance, stain resistance and other properties for the coating film More than two kinds of fluidization aids, such as polyether, polyurethane, fluorine-containing leveling agent, hydrophobic modified alkali-soluble thickening agents, such as Haichuan D3200, D3380, DOW 2020, 8W, TT935, etc., are good fluidizers, can provide fluidity, gloss and fullness for the coating film.
2) Water-based paint defect prevention and control, but also depends on a reasonable production process. Our approach is to put the "three pass" good. One is the fine pass. The slurry dispersion grinding is not thorough, the fineness is not fine, there will be uneven paint film, loss of light and other problems; Water-based coatings should be maintained in a alkaline state in order to make emulsion stable, paint unchanged quality, and third, viscosity, viscosity, related to construction and storage stability, should be paid attention to. The amount of fluidizer given in the formula is only a subjective data, the actual production process, the production staff need flexible grasp, now test.
3) there is a formal coating management, there is a qualified coating team, there is a standard coating process, there is an effective coating equipment, these are also important links to prevent and control paint defects. Once encountered a thing, there is a winter, low temperature and humidity high, a construction team in the use of our primer added a lot of water, brush later electricity said, this paint cover is not good, and rust, there is poor adhesion, film under. I went to observe, found a few problems, first of all, the surface of the iron plate rust powder, not treated on the paint; Construction defects are all concentrated here. Adhesion is the fundamental premise of coating and coating, therefore, spraying the first paint on the iron plate, first to clean the substrate, and then find a way to make the paint dry, to ensure that the paint, plate firmly combined, in order to continue the construction. The so-called "skin does not exist, Mao will be attached to", that is, this truth.
4) On the anti-rust properties of water-based coatings, such as coating film adhesion, water resistance, salt water resistance, acid and alkaline resistance and other defects, simply put, mainly from the three raw materials to solve.
First, to choose good water resistance, a certain hardness and flexibility, self-intersecting, with rust-proof base group of substrates, its representative is an imported 6750, can be used as a steel substrate passivant and rust-proof primer, the effect is very good. I have a piece of iron plate, brush a lotion, dry into 3% salt water for 1 week, no foam and no rust, and then put outdoors, has been eight years, still not rust. I like to use Jiangyin Guolian anti-rust silicone sol to change the emulsion, many benefits, can improve the density and adhesion of the coating, and coating hardness and water resistance, salt resistance, when using its activity. Last year I made a cost of 6.50 yuan iron-red primer, which added 10% silicone sol, painted two, test plate immersed in water and placed outdoors, so far a year, still normal. In 2004, I used an AP3128 pure propylene anti-rust emulsion from a factory in Guangdong with anti-rust pigment, made of iron-red primer, immersed in 3% salt water 1 month later, in the eradication of lacquer film, found that the surface of the iron plate produced dense, smooth, hard black oxide film, this iron plate for several years exposed, still rusty, hard-won, worthy of in-depth study. There is a U.S. technology pH neutral rust conversion agent, coated on the rust plate, you can obtain a black closed film, and with rust-proof primer, can be applied to the medium anti-corrosion project.
to highlight the issue of adhesion. In addition to using a good wetting agent and attachment agent, it is important to use a good base. I do acrylic primer, choose a very water-resistant emulsion, and then use silicone sol mixed to change, so that the film dense and hard, with the iron plate grip point more. Taihu factory, a medium-grey primer, cost 7 yuan, adhesion can be up to 1 to 0 levels, pencil hardness can be up to 2H (see model).
2 To choose high-efficiency and environmental protection of rust-proof pigments, I recently adopted a Taiwan called "zinc phosphate aluminum" (ZAP) composite rust-proof powder made of white rust-proof paint, resistant to 3% salt water has passed 240h, test board is still bubble-free rust-free, the effect is really good. The material does not contain heavy metals, is not toxic, is compatible with different resins, will not re-thicken, its content is easy to hydrolyzed to produce phosphate root ions, and iron ions chelate, thereby passivating the steel surface. ZAP-Ic does not contain zinc oxide and is suitable for water-based epoxy and water-based alicic acid resin systems. There are many new materials on the market now, enough to choose from.
to supplement the use of some anti-flash rust agents, corrosion inhibitors, auxiliary to play the role of anti-corrosion. Such as the United States FA-179, is an organic rust inhibitor containing metal soap, cost-effective, a Shanghai company agent abroad corrosion inhibitors, A-142, A-143DA, etc., are good results.
4 On the current paint enterprises "oil-to-water" view
Since last year, the relevant ministries and Beijing and other places, issued a consumption tax on over-standard voc paint, and restrictions on the use of paint, vigorously promote environmental protection paint, including water-based paint a series of documents. So some paint factory busy looking for relocation, some feel the pressure increased, and want to stop production, some see water-like paint is popular, and want to transfer production, and some think that water paint has not been popular, paint.
that objective decision-subjectivity, the existence of a sense of decision- to be divided into two places, with the development of the point of view of this issue. Solvent-based coatings and water-based coatings have their own advantages and disadvantages. Oily paint high gloss, high scratch resistance, high corrosion resistance, are currently water-based paint is not enough, heavy anti-corrosion engineering, or paint-based. But the high voc of oily paint, not environmentally friendly, is a Achilles heel. Society in the development, technology in progress, I believe that oily paint will improve, the advantages of the same need, the use of continued. The advantages of water-like paint environmental protection to carry forward, insufficient to improve, I believe that soon can also achieve the performance of paint.
Taihu anti-corrosion company is to do a good job of painting, see the situation, investigation and research, fully brewing on the basis of the decision to set up a water-based paint project. Therefore, I think, the paint factory does not necessarily have to "oil to water", first to make the paint more environmentally friendly, conditional and then consider increasing water-like paint projects. Water-like paint or not, how to go on, or to calm down, to think twice, let the time let the market let the ability to make a decision.