As the saying goes, "three paint, seven construction", waterborne industrial paint will encounter various problems in the construction process, most of which are similar to the problems encountered in the paint construction. However, waterborne industrial paint and paint belong to completely different systems, with their own characteristics and characteristics, internal factors determine external factors, and corresponding problems encountered in the construction will also have corresponding solutions Surface is a common pathological phenomenon in the construction of waterborne industrial paint and its prevention.
(1) Problem phenomenon
Blistering occurs between the coated surface and the paint film, or between two layers of paint film; after the paint film is dry, there are protuberant round bubbles of different sizes, which are called blisters. If the fracture is not even, the hole will burst. If there is a small hole, it is called a pinhole. There is a kind of pinpoint pinhole phenomenon on the surface of paint film. The pinprick hole is like a pinprick hole with an aperture of about 100 am.
(2) Causes
① The substrate treatment is not up to the requirements, such as oil stain and dust on the surface of the base material, high moisture content of the wood, or the rosin and aromatic oil contained in the wood are not removed, which will cause blistering when it volatilizes naturally; the surface treatment of the board is not good, there are many wood hairs and thorns, so it is difficult to fill; the moisture content of the wood is high; the joints and apertures of the wood are not filled, and there are apertures, etc. ② The construction environment temperature is high, the humidity is low, or the drying room temperature is too high, and the surface drying is fast. ③ If the bottom layer is not sufficiently dry, the construction will be carried out for the second time. ④ The viscosity of the coating is too high, and the bubbles are not eliminated; or the one-time construction is too thick. ⑤ When brushing, drag the brush back and forth, and the bubbles generated are not eliminated. ⑥ The prepared paint is not allowed to stand for a period of time, and the air is stirred into the paint at high speed. (3) To solve the problem, the substrate treatment shall meet the requirements, and the oil and dust shall be removed; the blank of the Board shall be polished and leveled, and then sealed with a sealing primer: before construction, the wood shall be dried to a certain moisture content, generally 10% - 12%; ② construction shall not be carried out when the temperature and humidity are high; the temperature of the drying room shall be adjusted to a proper range, generally 35-50 ℃. Reduce the temperature of drying channel and let the leveling time be longer. ③ In case of multiple construction, the interval of recoating shall be sufficient, and the construction shall be carried out for the second time after the lower layer is fully dry; the viscosity of the coating shall be adjusted to a proper level, and the spraying shall be carried out according to the standard, instead of one-time thick coating. In case of multiple spraying, the drying time of the bottom layer shall be strengthened, and multiple thin spraying shall be conducted; during brushing, do not drag back and forth, first horizontally, then vertically, and finally straighten along the direction of wood grain. ④ The prepared coating shall be allowed to stand for a period of time to completely eliminate bubbles before construction. ⑤ When there are many bubbles in paint or paint liquid, which affect the use, there are many defoamers to choose. Products with air bubbles shall be carefully polished before repainting. For products with slight air bubbles, after the paint film is completely dry, sandpaper shall be used to polish them and then finish. In case of serious bubbles, first break the bubbles, carefully polish them with sandpaper and clean them, and then repair them layer by layer according to the coating process.
(1) Problem phenomenon
Flash rust (or Flash corrosion) is caused by the contact between the water in the coating and the iron surface (such as nail head, steel, etc.). When the coating is applied in general environment (such as humid climate), the possibility of flash corrosion is more likely to occur, which mainly occurs at the corroded interface or recently activated steel surface.
(2) Causes
The treatment of floating rust or oxide skin on the workpiece surface is not clean; the temperature is low, the humidity is high, the speed of water volatilization is slow, the paint film is thick, and the paint film is dry slowly; The formation of flash rust may be related to the dissolution and precipitation of iron compounds. The severity of flash rust depends on the paint system. When the paint, such as polyvinyl acetate emulsion, is at low pH, low temperature and high humidity, the contact time between water and substrate is prolonged, and flash rust is easy to occur; no anti flash rust agent is added to the paint products.
(3) Solutions
The substrate shall be cleaned, and the coating surface shall be free of serious rust, rust spots, oxide skin, sundries, etc.; measures shall be taken to improve the drying time of the paint film, strengthen ventilation, thin coating, etc.; the pH value of the paint shall be increased; flash corrosion inhibitors (such as sodium nitrite, sodium benzoate and sodium tetraborate) shall be used to inhibit the flash corrosion; In case of flash rust, a layer of antirust paint shall be applied after the paint film is dry and properly polished, otherwise the rust spots will continue to migrate to the surface.
(1) Problem phenomenon
During the use of the coating, there are discontinuous appearance changes, and the drying coating produces visible linear, polygonal, or indefinite cracks or cracks. The cracks are from small to large, from shallow to deep, and finally the coating is completely damaged. Crack is a serious defect. According to the depth of crack, it can be divided into: fine crack (thin and shallow surface crack and generally distributed on the film with regular pattern), small crack (similar to fine crack, but its crack is relatively deep and wide), deep crack (the crack at least penetrates through the crack form of the coating, and eventually leads to complete damage of the film), crack (wide crack and similar to one of turtle shell or crocodile skin) The crack pattern is similar to that of crow claw.
(2) Causes
The moisture content of wood is too high, the base has cracks, or it is too loose and rough, and the treatment is poor; when spraying for many times, the bottom coating is not fully dry, that is to say, another spraying is carried out, or the amount of one-time spraying is too much, or the viscosity is too high, and the shrinkage cracks are caused; the matching between the coatings is poor, for example, the hard coating is applied on the elastic coating, or the coatings with different properties are mixed; The coating is too thin to resist cracking due to the excessive dilution of the coating; the coating is applied at low temperature, or in case of strong wind, or the surface temperature of the workpiece is low, and the coating is not well cracked due to the drying and film formation; the coating has too much pigment or powder, and the film formation is poor.
(3) Solutions
① Test whether the moisture content of the wood is more than 14%; strengthen the treatment of the base material. The primer shall not only remove oil, rust and dirt, but also have a certain roughness. If necessary, use fine sandpaper to slightly polish. When treating the wood, it is necessary to remove the resin, clean it with ethanol, and paint after the resin part is closed. ② One time coating of the film shall not be too thick (except for thick film coating, which can ensure certain mechanical strength). The thickness of the bottom and surface coating shall be strictly controlled according to the process requirements. There shall be a certain coating interval for the coating. The primer shall be completely dry before the finishing coat. ③ Strengthen the compatibility between the coatings, emphasize that the expansion performance of the base coating and the top coating should be close, adopt the principle of "hard bottom and soft surface", and select the coating with compatible properties when using a variety of coatings. ④ Dilute with water according to the construction requirements. Excessive dilution will result in incomplete coating. ⑤ Do not work in bad weather, and control the temperature of workpiece to be higher than the minimum film forming temperature. ⑥ Adjust the formula and control the appropriate ratio of pigment to base. ⑦ The film has been wrinkled and can be re coated after being polished with water sandpaper. For cracks visible to the naked eye, the coating film has lost its protection function. All the failed coating films shall be removed and repainted.
(1) Problem phenomenon
Shrinkage cavity refers to the local shrinkage on the surface of the coating film, and the uneven pockmarks like fish eyes appear on the surface of the coating, as if water is sprinkled on the wax paper, and the pockmarks show the flower like phenomenon of the bottom layer, also known as fish eyes. "Shrinkage" refers to the small and round defects on the surface of the coating, which looks like a crater, and the shrinkage is different from the blast hole.
(2) Causes
There are oil stains or oily waxes on the surface of the coating; the spraying facilities and spraying tools are unclean, and the air compressor and pipeline are oily; the environment of the coating line is polluted, and the air contains oil or wax, etc.; the oil or wax and other unclean substances are mixed in the coating; the defoamer and other chemicals are added excessively.
(3) Solutions
① The coated material shall be free from pollution, the base material shall be cleaned and polished thoroughly. ② Construction equipment shall avoid pollution of oil, wax, etc.; oil-water separator shall be used for air compressor, and regular drainage shall be carried out to filter air pressure and reduce the possibility of air pollution. ③ The workplace shall be fully ventilated and exhaust, check and remove the pollution sources on the painting site, such as volatile solvents, butter, wax or contaminated containers, clothing and rags. ④ Avoid paint contamination, especially oil, wax, etc. ⑤ The paint products adopt the additives with good compatibility to prevent the additives from separating from the paint. ⑥ If "shrinkage" is found during brushing, stop brushing immediately and clean the "shrinkage" part. After the surface is dry, brush the coating again. If there is shrinkage in the coating line, stop the line immediately and clean the site. No more than 3% leveling agent can be added into the coating. Products with shrinkage shall be thoroughly polished before rework.
(1) Problem phenomenon
Flower refers to the uneven distribution of various pigments in the newly applied anticorrosive coating film, usually in the form of strip or honeycomb spots, which can be understood as the separation of pigments in the vertical direction. Floating color refers to the horizontal layer separation of pigments in the wet film after coating construction, that is to say, one or several kinds of pigments in the coating film are relatively dense on the surface of the coating film and uniformly distributed, but there are obvious color differences with the original formula. Therefore, the color of the paint surface is not the same, there are spots and stripes and other appearance defects with disordered colors. There are at least two kinds of pigment blooming phenomenon in the coating will be obvious; floating color refers to the surface color, but it is different from what should be. Make the color difference between the coating surface and the interior. Floating color is the most troubled with different degrees of construction conditions, the use of the same paint and have different colors.
(2) Causes
① The particle size of pigments and fillers has a certain influence on the floating color of the paint. The particle size distribution is wide, and the possibility of floating color is great. In the drying process, the fine particles are easy to float up, resulting in uneven distribution of color and filler, resulting in ② poor miscibility between white base paint and purchased color paste, which will lead to the phenomenon of color floating and blooming of paint film. ③ When the mixed pigment is not well wetted and dispersed, flocculation will occur, and the movement of the gathered large particles will be slow, and the movement speed of the mixed pigment particles will be poor with that of the unflocculated pigment particles, and the color distribution will be uneven, forming blooming and floating color; when the proportion of various pigments in the mixed pigment is different, the wetting and dispersion are not good, and the pigment with small density floats on the surface of the coating film, it will cause blooming and floating color. ④ Due to insufficient protection of pigment particles, pigment flocculation, or affinity flocculation, or there is bridge flocculation between pigment particles, resulting in floating color and blooming. ⑤ The thick wet film, the low viscosity of the base material and the slow volatilization speed will make the wet film keep longer in the low viscosity, and make the pigment settle more and make the floating color worse.
(3) Solutions
① Avoid flocculation with low-density fine pigment, use solvent with faster volatilization and base material with higher viscosity. When the wet film is dry, the uneven evaporation of solvent causes the surface tension difference and convection, which is the driving force of floating color. ② Verify the compatibility of base paint and color paste, and adjust to meet the standard requirements. ③ Select appropriate wetting and dispersing agent, replace the pigments with wide particle size distribution, and prevent the floating color caused by particle size difference; add powder with thixotropy, such as kaolin, wollastonite, quadruplex clay, bentonite, etc., to weaken the role of benaldo eddy current and weaken the floating color. (4) according to the types of pigment (color paste), emulsion type, thickener type, wetting dispersant and filler type, add the corresponding wetting dispersant. Follow the principle of "thin coating and multi-channel", avoid wet film too thick, avoid coating viscosity too low, adjust coating dry.
(1) Problem phenomenon
Undercut refers to the phenomenon that the solvent in the upper coating softens and swells the underlying paint film, resulting in poor adhesion of the underlying paint film, resulting in peeling and uncovering. When this happens, the coating will expand, shift, contract, wrinkle, bulge, even lose adhesion and fall off.
(2) Causes
(1)