Paint knowledge: paint lecture: diagnosis and analysis of 19 kinds of paint film cases

Core tips: 1 Crust is stored in the container in vain, and the phenomenon of paint crust formed on the liquid surface due to oxidative polymerization is called crust The reason for this is that the oxide dry coating, due to too many driers, contains a large number of excessive polymerization tung oil coating not filled or air leakage or too long storage temperature will produce skinning 2 The phenomenon that the viscosity of thickened coating increases in storage and becomes difficult to construct is called thickening The reason is that the acid value of the coating is too high, saponification occurs with the alkaline pigment, and air leakage occurs in the barrel Solvent volatilization; water mixed in the barrel or pigment containing water; high storage temperature makes the paint accelerate polymerization; low storage temperature, especially the water-based paint is prone to cold precipitation Shenyang steel structure fireproof coating construction expert punde Building Fire Engineering Co., Ltd Recommended introduction: since its establishment, Shenyang punde Construction Fire Engineering Co., Ltd has cultivated a group of professional construction teams with excellent equipment, rich experience and serious responsibility with advanced and scientific management methods and strict engineering quality assurance and after-sales service system It has undertaken a number of fire system installation projects, which has been praised by customers Every idea and special requirement of you will be fully considered by us and fully realized in the construction technology, which will become the cornerstone of our successful long-term development We are looking forward to your invitation, to provide you with quality services and high-quality technical support! All construction coatings have passed ISO9001 Paint Home News: 1 Crusting in vain in the container storage, due to the role of oxidative polymerization on the surface of the formation of paint skin phenomenon known as skinning The reason for this is that the oxide dry coating, due to too many driers, contains a large number of excessive polymerization tung oil coating not filled or air leakage or too long storage temperature will produce skinning 2 The phenomenon that the viscosity of thickened coating increases in storage and becomes difficult to construct is called thickening The reason is that the acid value of the coating is too high, saponification occurs with the basic pigment, and air leakage occurs in the barrel Solvent volatilization; water mixed in the barrel or pigment containing water; high storage temperature makes the paint accelerate polymerization; low storage temperature, especially the water-based paint is prone to cold precipitation Preventive measures: it can be adjusted by adding matching dilution, adding appropriate amount of butanol when there is water, mixing and adjusting the viscosity, the latter can be stored in the warm room for 2-8d to thaw and recover 3 A pathological condition in which particles of pigments, physical pigments, etc precipitate or dense lumps that are hard to be redistributed after agitation appear in the precipitated and agglomerated paint It can be caused by the poor grinding of pigments or system pigments, poor dispersion or physical and chemical reactions between pigments and paint base In the coating process, take out the sediment and grind it, then add it into the original mix, and use it after filtering 4 The phenomenon that the paint liquid flows downward when the coating is applied on the vertical surface is called sagging The reason is that the paint is too thin, viscosity is too low, drying is too slow, the heavy pigment in the paint is too much or uneven, the spraying distance is too close, the adhesion to the substrate is poor, the paint is too much, the paint film is too thick, the temperature is too high during the construction so that the quick drying paint can dry without leveling, etc., all of these are the reasons for sagging Preventive measures: increase the construction viscosity as appropriate, adjust the spraying pressure and properly increase the spraying distance, and control the thickness of one-time spraying at about 30um, which can prevent and reduce sagging 5 Undercut the phenomenon that the upper layer softens the coating of the lower layer and causes undercut is called undercut Causes: the primer is not completely dry, the solvent of the upper paint is too strong, and the primer and finish are not matched Preventive measures: apply the second coat of paint after the primer is dry or the surface is dry, and the solvent used for the second coat shall match with the primer 6 After the construction of slow drying and back adhesion coating, the phenomenon that the coating does not dry within the specified time or the back adhesion after drying is called slow drying and back adhesion Causes: poor volatility of solvent, topcoat before primer dries completely; too high construction temperature, too low temperature, unclean surface treatment, stained with oil, wax, turpentine, unsealed knots; disordered impurities in paint or omission of desiccant are the causes of slow drying and back adhesion Preventive measures: before painting, the surface texture shall be free of oil, water, dust and other impurities Each coating and diluent shall be matched When the relative temperature is too high or too low, coating construction shall be avoided Appropriate moisture-proof agent can be added according to the construction environment The two-component coating shall be strictly proportioned according to the proportion 7 After the construction of the pelletizing coating, the phenomenon that the surface of the coating is not smooth and produces small particles is called pelletizing The reason is that the pigment is not fine in the production process, it does not meet the specified fineness, or when there is agglomeration in the storage, the construction environment and tools are not clean, the paint and solvent do not match, and the speech produces microgel; the nozzle is small in caliber, the wind pressure is large, the spray distance is too large, the mixing is confused when the material is mixed, the filter is not filtered and the surface treatment is not clean Preventive measures can be taken according to the causes 8 The phenomenon that the whitened coating becomes white and loses light or produces no light spots after drying is called whiteness The main reason is that the construction humidity is too high (relative humidity > 80%) and the solvent volatilization is too fast, which makes the surface temperature of the film sharply drop The speech makes the water vapor condense on the film, which makes the resin or cellulose precipitate and cause the whitening phenomenon Generally, the quick drying volatile paint (such as nitro, perchloroethylene, thermoplastic acrylic acid, etc.) is easy to whiten because it contains a large number of low boiling point solvents and diluents It can prevent whitening by adjusting the solvent formula, improving the construction environment and removing the moisture in the compressed air Shellac coating will also turn white when contacting with hot articles (such as water cup filled with boiling water) It can be recovered by wiping the white place with cotton ball dipped in alcohol or dilute shellac solution 9 In the process of painting or dry film-forming, there are some uneven phenomena (such as yellowing, floating color, gold, etc.) in the color and tone of the paint film, which is called blooming This is mainly due to the different density and particle size of pigment, poor lubricity, high moisture absorption, large oil absorption and partial dissolution of color (such as red powder) In case of this situation, dry materials can be added for replacement To improve this situation, appropriate amount of protective glue (ethyl cellulose, polyvinyl alcohol, etc.) or lubricating oil (methyl silicone oil) can be added for improvement and solution 10 In addition to the initial wrinkles, the film shrinks sharply outside the drying process, which is called wrinkles If the drying is not properly matched or added too much, the film will not dry outside and inside, the film will be too thick, the outer layer of the existing conjunctiva, the film will wrinkle under the sun or the baking temperature is too high In this case, dry materials can be replaced Some amino resins can be added to alkyd resin to prevent wrinkling 11、 Orange peel is the surface of the coating film formed many semicircles such as orange peel disease The reason is that the viscosity is too high, the pressure is too large, the caliber is too small, the spraying distance is too close, and there are too many solvents with low boiling point when they volatilize rapidly so that the paint liquid can not be leveled before orange peel is produced Improve; Select the appropriate solvent, the construction viscosity, pressure, nozzle size, spraying distance should be appropriate, the baking temperature should not be too fast, the surface of the coating should be below 50 ℃, the construction thickness should be controlled at 20-30um.12, shrinkage After coating construction, the surface of the coating shrinks, as if water is smeared on wax paper, and the phenomenon of exposing the primer is called shrinkage, also known as "laughing" and "pockmarks" It is mainly caused by the poor lubricity of the coating on the surface of the object to be coated, so that it can not form a uniform film, but shrink to a bead shape; the surface is too smooth, the gloss of the primer is too large, the object surface is stained with oil or smoked; the spraying equipment is mixed with oil or water; the solvent volatilizes too fast, the film is not even; the spraying density is too large, splashing occurs, etc., which will cause the film shrinkage Shrinkage is common in varnishes, red lead, polyurethane, epoxy and pure phenolic coatings The phenomenon of coating shrinkage can be improved by adding proper additives 13 The surface of pinhole coating after drying presents pinhole like pinhole, which is called pinhole Causes: the drying is too fast, the coated materials quickly enter the high temperature baking, the bottom layer is not dry, the top coat is applied, the construction viscosity is too high, the surface treatment is not clean and contains oil, water, dust and other impurities Preventive measures: dry in strict accordance with the drying temperature and time specified in the coating process When drying, gradually enter the high temperature area from the low temperature area According to the spraying method, prepare the appropriate viscosity of the coating The thickness of the first spraying should not be too thick The pre-treatment should be clean and free of impurities It is not allowed to mix impurities such as oil, water and dust into the coating or solvent The existing pinholes can be puttied The way to remedy 14 The phenomenon of bubbles with different sizes and shapes on the surface of the blister film is called blistering The main reason for this is that it enters into high temperature baking immediately after coating, and the bottom layer is coated with the top coat before it is dry The construction viscosity is too high, and the surface treatment is not clean and contains oil, water, dust and other impurities Preventive measures: dry in strict accordance with the drying temperature and time specified in the coating process When drying, gradually enter the high temperature area from the low temperature area Prepare the appropriate viscosity of the coating according to the spraying method The thickness of the first spraying should not be too thick The pretreatment should be clean and free of impurities It is not allowed to mix impurities such as oil, water and dust into the coating or solvent The coating and solvent used should be matched 15 The phenomenon that the color paint can't cover the color of the substrate after the coating is dry and film-forming is called exposed bottom The main reason is that the pigment in the paint is not enough or the covering power is too poor; too much thinner is added during the construction; the paint liquid is not stirred evenly, and the coating is too thin Improve; select the pigment with strong covering power, fully mix evenly when using, mix the construction viscosity properly, and control the coating thickness at 20-30um 16 Infiltrate color top coat dissolves primer, make the color of primer permeate to the surface is called infiltrate color, also called bite color This phenomenon often occurs when light colored paint is applied on red primer or asphalt The main reason is that the primer is not dry, and the top coat dissolves the primer film; the primer contains dye, and the asphalt does not have the sealing layer, which will appear color penetration after the top coat is applied Preventive measures: the diluent of each coating shall be matched, and the bottom layer shall be coated with two layers after drying, and the color difference between the middle layer and the surface layer shall not be too large 17 The phenomenon that the gloss of the matt coating disappears slowly after drying and film forming for a short time (several hours or days) is called Matt Outdoor paint film, after a long period of exposure and loss of light is not included in this list Main reasons: insufficient or incompatible oil and resin consumption and improper polymerization degree; too much diluent consumption; construction in cold or high temperature weather; after paint drying, diluent will enter the drying room before it reaches a certain extent; after painting, it will encounter atmospheric smoke; surface treatment will not be done or the primer will not dry out, etc Preventive measures: the diluent of each coating shall be matched; the drying shall be carried out in strict accordance with the drying temperature and time specified in the coating process, and the drying shall be carried out from low temperature to high temperature; the grinding time shall be suitable abrasive cloth and grinding piece, and the residual dust shall be removed after grinding; the front part shall be free of oil, embroidery, water and dust impurities 18 The surface color of the powdered and peeled off paint film is dull after drying, and the phenomenon that it is stuck on the hand when touched by hand is called powdering The main reasons are: the surface treatment is not clean, there are oil, water, and other pollutants; the drying stability is too high or fast into the high temperature baking, the primer is not dry and the top coat is not applied; the diluent is not used; the viscosity of the coating is large and the coating is too thick; the viscosity of the coating is too low and too thin; the coating is not resistant to high temperature baking and the coating is zoomed and powdered off Preventive measures; thorough pre-treatment