Water paint and oil paint deployment, construction, performance comparison
"Waterborne coating" had been put forward nearly 20 years ago actually, but at that time only at verbal talk endowment, the position of waterborne coating is not like now so "scene is infinite".There are two main reasons for the difference between water-based coatings in the past and the present :(1) limited to the scientific and technical level, such as the pending hydrolysis problem of water-based polyester resin, the lack of high-performance water-based resin with excellent construction performance, efficient paint film performance and stable storage capacity;A "red sea" (2) the paint market, under the present situation of domestic numerous facilities are usually in line with the "use, good enough is" simple, rough logic, water-based paint is concept of the "old", but "new product", usually selling price will be higher than the traditional solvent coating, high cost, paint factory to coating of ability in instinctive rejection.In addition, also responsible for the construction of spray paint, difficult to adapt to changing patterns of previous spraying and coating consumption related consumer environmental protection concept of weak and some factory for the banner of "water paint" but could not provide the qualified water-based coating product, causing negative impression of water-based coating industry, etc., many factors contributed to coating of ability in development "thunder, little rain" awkward situation.
Look at the development circumstance of coating of ability in swimming nearly two years on the other hand, we discover coating of ability in swimming is consistent with "environmental protection card" play than ever before beautiful!Among them, of course, with the Chinese government to change the mode of economic growth of the administrative guidance role inseparable;The so-called "striking iron also needs its own hard", the more important reason is that the waterborne paint and used as the base material of the waterborne resin synthesis process level greatly improved.
Water-based coatings and water-based resins used as base materials have their own characteristics.Divided according to the application field, coating system is numerous, the following will only which has been widely applied in industry as an example of the lacquer that bake, respectively from the deployment of resin, paint, coating (including construction viscosity, base material processing, etc) and physical properties of the paint film is introduced, and moderate comparing with the traditional solvent coating is introduced, in order to play a "topic".
1. The resin
At present, the main resin used as the water-based industrial baking paint is mainly acrylic resin or modified acrylic resin, mainly considering the high hardness and excellent adhesion characteristics of acrylic resin, and there are some waterborne resins modified by polyurethane in the market.When considered for finish coating, due to the pure acrylic resin has other resin incomparable excellent weather resistance, became the first choice for varnish varnish.
Acrylic resin as the main resin coating, paint film after film, in addition to the above high hardness, excellent adhesion and pure acrylic resin has excellent weather resistance, there are inherent shortcomings, especially for water-based coating.
Acrylic resin as a result of the existence of strong dilution peak, water-based acrylic coating on dilution, at some point in dilution curve of linear decline, viscosity are more sensitive to the amount of adding water, in order to reduce because of the existence of dilute the peak effect on the viscosity of coating, and increase the solubility in water, often need to add some glycol ethers hydrophilic oleophilic parents of cosolvent.Want to dilute coating to spray construction viscosity, still need to add a lot of water, with water based acrylic coating original paint as 1 look, usually the amount of water added to reach 0.8-1.2.The addition of a large amount of water dilutes the solid content of acrylic resin in the film.So, paint film can appear normally burnish is inferior, plump the malpractice with inferior degree.
Common metal roasting paint, in order to adapt to processing, molding and other aspects of the need, usually on the film flexibility will have varying degrees of requirements.Because acrylic resin carbon-carbon double bond (C=C) is not easy to rotate, acrylic resin film coating is often flexible is its obvious shortcoming.
At present, some domestic resin manufacturers produce high performance polyester resin for industrial paint.The resin usually has excellent fullness, glossiness and flexibility, as well as excellent weather resistance, repainting and other properties.
The water's surface tension is about 72.8 mN/m (20 ℃), far more than the surface tension of the common solvents (common solvent surface tension for 28-35 mN/m), the deployment of paint additives are usually added in the process of some low surface tension of surfactant.Generally, the larger the surface tension deviation between the dispersing medium and the surfactant, the more easily bubbles are generated.Therefore, under the same operating conditions, the water-based coatings with water as the dispersion medium are more likely to produce bubbles than the traditional solvent coatings.The existence of bubbles will have different negative effects on the final film appearance.Therefore, in the deployment of water-based coating, it is necessary to pay more attention to the high-speed disperser speed, the location of the rotary table and other easy to bring into the bubble operation.
As a result of the surface tension of water is greater than the air around the substrate, water-based coating in addition to the viscosity after spraying is too thin, paint film is too thick and other improper operation, will form a clear outline in the corner of the substrate, and the coating has obvious retraction phenomenon, called the "border effect"."Border effect" can be solved by adding additives and adjusting construction viscosity.
Most of the polymer materials used in water-based coatings are those with carboxylate (-coor) after neutralization with ammonia (such as water-based saturated polyester resin, water-based acrylic resin, etc.).Amino resins, additives and pigments added in the later stage of waterborne coating system are mostly soluble in water.Therefore, the operator needs to pay special attention to the water solubility of the resin after adding the main resin of the film-forming substance.A simple way to judge the water solubility of the resin is to test the pH value (such as pH meter method, pH test paper method) and empirical method (specifically: dip a small amount of resin in your fingers, rinse with tap water, if there is no obvious greasy feeling, the resin is considered to have a good water solubility).It can be said that how to emphasize the acid base value of waterborne resins used in waterborne coatings is not too much.If the PH value of the resin itself is lower than 7, a small amount of ammonia neutralizer can be added to continue to adjust the water solubility of the resin until the water solubility is good.After determining that the resin has a good water solubility, then add additives, water color paste, and adjust the final paint factory viscosity.Let the paint continue to mix in a high speed disperser for 10-15 minutes before packaging.In comparison, the traditional solvent coatings do not pay much attention to the concept of acid base value of the resin, and regardless of water paint or solvent coatings deployment process is basically the same.
3. The coating
Waterborne coating and traditional solvent coating before coating, need to carry out simple derusting, oil removal, drying treatment of the substrate, the pre-treatment of the substrate on the two are much the same.The difference between the two in coating is mainly the difference of construction viscosity.
As a dispersive medium of water on the solubility of high branch polymer than the solvent, the same construction viscosity, the solid content of water-based coating will be lower than the solvent coating.After this is in paint film dry, in order to have the dry film thickness that is equivalent with traditional solvent sex coating, the construction viscosity of water borne coating is met slightly tall.The latent heat of water is much higher than that of solvent.In order to take into account the dry film solid content and paint film without hanging, according to the coating method of spraying as an example, the traditional solvent paint construction viscosity is usually 14-18 seconds of viscosity, water paint construction viscosity is recommended for 22-25 seconds, of course, the specific viscosity may also need to depend on other comprehensive conditions.
Due to the pressure type used in the traditional manual spraying gun in painting and coating efficiency is poorer, now most of the manual spraying change for electrostatic spray gun, electrostatic generator through making coating particles carry electric charge, when spraying coating particles to metal substrate with heterogeneous charge directional movement, has the advantages of paint film is uniform, due to the conductivity of the water-based paint far higher than that of common organic solvents, spraying paint fog with higher rate, smaller mist spraying workshop, improve the operating environment from the coating.
Is the use of water paint and traditional solvent coating electrostatic spraying equipment is completely the same?In fact, this is also a lot of want to turn "water-based" business owners, engineers and technicians are very concerned about the problem, which involves the equipment may bring about cost increases.
Since water and oil are not directly compatible, and the conductivity of water-based coating is much higher than that of solvent coating, there are several aspects of electrostatic equipment that need attention as follows:
Low supply water paint, solvent coating paint tube cannot mix;
Low electrostatic spraying device of feed pump using a water-based coating, instead of the insulation, and this is the only "cost center" in equipment modification, fortunately, the transformation cost is very low.
QuanZhou Neweco High Polymer Material Co.,Ltd.
Neweco is one of the leading unsaturated polyester resin manufacturers and suppliers,widely used in automobiles, ships, rail transit, wind power generation, pipe cans, heat and corrosion protection, building materials, stone repair, sanitary ware, artificial stone and other industries. Suitable for hand lay-up, spray, pultrusion, winding, molding, vacuum introduction / RTM, casting and other molding processes. Neweco Resin is committed to excellence and focuses on the application of composite materials to provide customers with comprehensive solutions.