Silver paint coating defects and prevention methods

is also known as aluminum powder paint, mainly refers to aluminum powder and resin paint composed of paint. Aluminum powder has excellent rust resistance and good shielding, fine aluminum scales in the paint can form more than a dozen layers of parallel arrangement of the structure, visible light, ultraviolet, infrared and radiation heat has a strong reflective function, can effectively delay the aging damage of ultraviolet rays, etc. , but also can prevent the passing of water, gas and ions, so as to effectively protect the paint film. Therefore, it has better weather resistance and corrosion resistance than general color paint, widely used in general weather-resistant heat and temperature-resistant places
China
. However, in the process of use of silver paint brush marks, flowers and other common surface diseases, not only affect the appearance of the paint decorative effect, but also will cause the quality of anti-corrosion coating decline. Controlling the morbid occurrence of film surface is an important problem in silver powder coating.
The composition of silver powder paint
the main pigment used in silver powder paint is aluminum powder, generally do not mix with other pigments, because when mixing with other coloring pigments, the brightness and saturation of the paint film color will have a greater attenuation. Silver paint has a strong cover.the classification of
metallic aluminum powder
the metallic aluminum pigment is characterized by its geometric shape and particle size distribution, and the main difference with other pigments is that it is neither crystals, nor sprub-shaped or other-shaped particles, but the extension body, in the form of tiny scales. The thickness is 0.1 to 2 m and the diameter is between 10 and 200 m. Industrial aluminum powder is sold in the form of aluminum powder. Aluminum powder contains 65% aluminum powder and 35% solvent. According to its floating properties, it can be divided into floating aluminum powder and non-floating aluminum powder.
1. Floating aluminum powder
floating aluminum powder is also known as floating silver pulp, it is aluminum powder in ball grinding processing using hard fat acid and other saturated fatty acids as a lubricant, is adsorbed to the surface of aluminum pigment flakes, so that aluminum pigment hydrophobic and oil-dependent, thus forming a floating aluminum pigment. Floating aluminum silver slurry always floats on the outerst side of the coating in the coating film, forming a multi-layer continuous film layer parallel to the directional arrangement of the substrate. In order to keep the hydrophobic layer intact, floating aluminum silver slurry does not need sufficient wetting when mixing and dispersing, but there must be sufficient shear force to disperse the scales to ensure their floating nature. Grinding should therefore be avoided when dispersing. Floating aluminum powder is mostly used in anti-corrosion paint, which is the focus of this paper.
2. Non-floating aluminum powder
non-floating aluminum powder, also known as non-floating silver pulp, is aluminum powder in ball grinding processing, the use of lysate and other unsaturated fatty acids as a lubricant obtained material. It is not directed on the surface of the coating film, but evenly and evenly distributed throughout the coating film. Non-floating silver paste should be completely moisturized when mixing to ensure its complete optical properties, such as coloring force, covering force, gloss, brightness and so on. In the paint is used in rust-proof primer and hammer paint and other varieties with special effects.
resin lacquer liquid
1. Physical film-forming
silver powder and many resins have good compatible, physical film-forming resins are many, commonly used resin varieties are: alkyd resin, chlorinated rubber resin, chlorinated polyolefins, acrylic acid, fluorocarbons and so on. They are generally dried into film by the volatile of solvents. Among them, the alkyd silver paint with its low price and general weather-resistant decorative effect (the initial gloss is better), in the low end of the anti-corrosion coating market occupies a larger share. Chlorinated rubber and chlorinated polyolefin silver powder paint is widely used in engineering corrosion prevention because of its anti-corrosion effect, but because of its environmental protection problems, it is gradually replaced by silver acrylic paint. Fluorocarbon coatings are high-end products.
2. Reaction curing type
such film-forming materials are mainly epoxy resin, polyurethane resin, silicone resin, etc., coatings are divided into two or three groups, must have curing agent to participate in film-forming. Silver epoxy paint is mostly used indoors because of its poor weather resistance. Silicone silver paint is mostly used in heat- and temperature-resistant areas. Polyurethane is widely used in anti-corrosion engineering sites that require good weather resistance, high gloss and high decoration.
the surface of silver powder paint is sick and the cause
the surface of silver paint is sick many, of which brush marks, hair flowers are the two most common diseases. Brush marks refer to the paint film dry, paint film left a ridge-like streak phenomenon, is due to the paint film level is not good caused. Hair flower is a kind of disease formed when the coating is filmed, refers to the uneven distribution of pigments in the coating film, in the coating film is honeycomb-like or striped spots.
Coating film-forming mechanism
the surface pathology of the coating film is formed in the process of coating drying into the film, so the analysis of the pathogenic causes of the coating surface, we must start with the process of analyzing the coating drying into the film. It is generally believed that the coating drying film is divided into 3 stages: the initial coating film solvent or dispersant content is more, the system viscosity is low, the solvent or medium at a constant evaporation rate of evaporation, when with the movement of solvent molecules, pigment particles may be solvent molecules clamped together to the coating surface movement. Medium-term pigment particles begin to come into contact with each other, not easy to move with solvent molecules, so that the surface layer polymer concentration increased. The late solvent can only be diffused to the coating surface, and the resin begins to form a film or react to cure into a film.
main cause of the morbidity of the surface of the silver powder coating
1. Causes of flowering on the surface of silver powder paint
The main reason for flowering on the surface of silver powder paint is the difference in particle size and density of pigment fillers and the difference in surface stress between solvents and substrates. Because the surface pressure of the solvent is generally lower than the substrate, so with the evaporation of the coating surface solvent, the surface pressure rises, resulting in the surface layer and the inner coating surface pressure difference, the surface pressure of the lower coating movement to the surface, while carrying pigments to move together to form the Benaud vortex. Pigment particle size has a certain distribution, and different types of pigment particles particle particles particle particles are very different particle size, smaller pigment particles are more likely to flow with solvents, if the pigment particle size difference is larger, smaller particles are easier to be transported by solvent, in the Benaud vortex finer pigment particles more concentrated to hexo-shaped edges, resulting in honeycomb-like plaque, that is, causing flowering. For silver powder paint, the main cause of flowering is the surface stress of solvents and resins due to the absence of the effects of other pigment fillers and their own unique floating characteristics.
2. The cause of paint film brush marks
From the thermodynamics, the leveling of the brush marks is a spontaneous process, i.e. the surface can be reduced, the driving force of the leveling is gravity and surface tension, but the premise of the leveling is that the coating must have fluidity. From a dynamic point of view, the time required for leveling is shorter than the drying time of the coating, i.e. the time to lose fluidity, otherwise brush marks will be left. Brush marks or other uneven surface formation factors are viscosity, surface stress, coating thickness, brush geometry and so on. From this point of view, the coating to have a better leveling, must have low viscosity, long drying time, and has a large gravity or high surface pressure. In general, the higher the viscosity, the longer the time required for leveling (except for plastic structures), the lower the viscosity is conducive to leveling, and also extends the drying time, with a longer leveling time. The higher the gravity or surface pressure, the higher the surface energy of the brush marks and the greater the driving force of the level. However, the higher the surface pressure, the greater the surface stress difference due to solvent volatility, which can lead to severe Benaud's nest. In addition, large coating thickness and small brush marks of waveforms are also good for coating leveling. For aluminum paint and other coatings with high cover, the coating thickness is very small, in order to get a better leveling effect, we have to rely on low viscosity and a longer leveling time and suitable surface pressure to solve.
The sick solution of the surface of silver powder paint
To solve the surface disease of silver powder paint, we must choose the appropriate aluminum powder, control the viscosity of the coating, drying time and other physical performance indicators, add appropriate additives to reduce surface pressure, improve the construction process and so on.
1. Choice of aluminum powder
Floating aluminum silver paste always floats on the outerst side of the coating in the coating film, forming a multi-layer continuous film layer parallel to the directional arrangement of the substrate.
because of its good stretching, it has a great effect on the surface leveling and flowering of the coating film.
we choose aluminum powder requires a plate diameter, thin thickness uniform, scattered floating good. Thin and large scales have a high floating nature, and their floating characteristics also depend on the overall density of the scales, but also affected by surface treatment agents. General saturated fatty acids and non-polar solvents treat lower levels of unsaturated fatty acids and polar solvents have a good floating force. Although floating is not an important indicator for non-floating aluminum powder, it also affects film flowering, in addition, non-floating aluminum powder should have good wetting dispersion.
2. Control of the physical properties of coatings
the viscosity and drying time of coatings have a great impact on the construction performance of coatings and the performance of coatings. The viscosity is low, generally speaking, the resin dilution is large, the resin content is low, which is fatal to the aluminum paint with strong cover, the result is a short-term de-powdering, corrosion resistance decreased. Long drying time is good for coating film leveling and floating arrangement and deblistering of aluminum silver paste. However, low viscosity and long-term drying are the key to the production of coating film flow, so in the production must strictly control the viscosity of the coating and drying time and other indicators. However, different types of paint or resin lacquer liquid, its physical properties are different. For the physical drying film resin, the table drying is slow, its surface disease is less; Table drying time can be improved by adjusting the solvent. For reactive curing resin, the drying time is moderately adjusted by controlling the amount of curing agent, and the appropriate addition of additives can do more with less.
3. Selecting the right additive
leveling agent is a class of surfactants with low surface stress, which is lower than that of most coatings and solvents. Its limited solubility with the system makes it form a single molecular layer on the coating surface, so that the surface temperature of the coating surface is much lower than the surface stress of the coating system, reducing the interface between the coating and the base, greatly improving the wetting with the base. When the solvent in the coating is volatile and the surface stress increases, it does not produce a surface stress difference on the surface. Even if a vortex may be generated within the coating due to poor surface pressure, it will not cause surface ills.
to solve the problem of low viscosity, long drying time of the construction flow, in addition to strict control of production, comprehensive balance, the practice of appropriate addition of leveling aids, can achieve good results. Coatings have suitable tentacles, not only to prevent flow hanging, but also a certain leveling effect on pigments also have a certain degree of anti-sinking, conducive to uniform dispersion.
the wetting of aluminum powder is not a problem, but dispersion in resin lacquer is the key. Dispersion is basically the process of crushing pigments with a polymer. Fully dispersed aluminum powder has a great influence on the performance of aluminum powder. Usually when the viscosity of the coating is low, the wetting is good, but the shear force is very small, the dispersion effect is very poor. In keeping the paint low viscosity, to achieve a good wetting and dispersing effect, the appropriate addition of dispersants is required.
4. Improving the construction
the construction process can be improved for surface pathology caused by brushing tools. Change the brush to roller coating or spray, improve the construction environment, and sometimes easy to get a smooth and smooth high decorative coating.
Aluminum powder paint construction after the surface state is an important performance index of the coating, in order to get a uniform, flat and smooth high decorative anti-corrosion coating, first of all, we must start from the selection of materials, choose the appropriate aluminum powder particle size and can meet the requirements of the resin paint liquid; Among them, the selection of
additives is also an element of controlling surface disease, and again, improving the construction process to avoid man-made surface disease.