Answer: Common paint problems and their solutions.

Causes of symptoms:

1. Too much dilution water was added.

2. Too much and too thick painting each time, and improper repainting time.

3. The surface of the object is uneven, unclean, complex in shape and contains oil and water.

4. The nozzle is too big and the distance between the nozzle and the surface of the object is too close.

5. The spraying speed is uneven and the interlayer spacing is not enough.

Solution to symptoms

1. Add diluent in proportion.

2. Spray it twice, ten minutes apart each time, and not too thick each time.

3. Treat the sprayed surface without water or oil.

4. Select the diameter of the spray gun correctly, and the spray gun should keep a distance of 20-25cm from the object.

5. Adjust the viscosity of spray brush and master the brush speed.

Common symptoms and solutions of paint orange peel

Causes of symptoms:

1. The paint is too thick, the thinner is too much, and the spraying pressure is too high and too close.

2. The construction site temperature is too high or too low.

3. The substrate is uneven or the diluent volatilizes too fast.

4. One layer is too thick.

Solution to symptoms:

1. Add diluent in proportion, mix curing agent, and adjust the pressure and distance of spray gun.

2. Adjust the temperature of the construction site.

3. The base should be as flat as possible.

4. Each layer should not be too thick.

Common symptoms and solutions of paints and coatings: pinhole

Causes of symptoms:

1. Too much dilution water was added.

2. Too much and too thick painting each time, and improper repainting time.

3. The surface of the object is uneven, unclean, complex in shape and contains oil and water.

4. The nozzle is too big and the distance between the nozzle and the surface of the object is too close.

5. The spraying speed is uneven and the interlayer spacing is not enough.

Solution to symptoms

1. Add diluent in proportion.

2. It should be sprayed twice, with an interval of ten minutes for each single pass, and the coating should not be too thick for each pass.

3. Treat the sprayed surface without water or oil.

4. Select the diameter of the spray gun correctly, and the spray gun should keep a distance of 20-25cm from the object.

5. Adjust the spray viscosity and master the brushing speed.

Common symptoms and solutions of paints and coatings: pinhole

Causes of symptoms:

1. Too much dilution water was added.

2. Too much and too thick painting each time, and improper repainting time.

3. The surface of the object is uneven, unclean, complex in shape and contains oil and water.

4. The nozzle is too big and the distance between the nozzle and the surface of the object is too close.

5. The spraying speed is uneven and the interlayer spacing is not enough.

Solution to symptoms

1. Add diluent in proportion.

2. It should be sprayed twice, with an interval of ten minutes for each single pass, and the coating should not be too thick for each pass.

3. Treat the sprayed surface without water or oil.

4. Select the diameter of the spray gun correctly, and the spray gun should keep a distance of 20-25cm from the object.

5. Adjust the spray viscosity and master the brushing speed.

Preventive measures of paint film whitening

After the coating is dried and the film is formed, the film appears cloudy and white, which leads to dullness and turbidity. Preventive and control measures are as follows:

1. Only when the relative humidity is 80% and the ambient temperature is lower than 5℃ can the construction be started. If it is urgent, you can use an infrared lamp to heat around the object to be painted, and then paint it after the ambient temperature rises.

2. Strictly prevent moisture from mixing in paint production.

3. The condensed water in the spraying equipment must be completely removed, and the water separation of the oil-water separator should be checked.

4. The coated substrate shall be dry and coated with sealing primer.

5. The main paint, curing agent and diluent are strictly proportioned to prevent the polymer from precipitating in the brushing process. Diluents must be used reasonably.

6. For the whitening phenomenon of paint film, the coated object can be slowly heated, or a thin layer of moisture-proof agent can be sprayed, or the two methods can be combined. For the paint film that is severely white and beyond repair, you can gently polish the stone with fine sandpaper to remove dust and repaint it in a suitable environment.

Common faults of paints and coatings and their treatment methods-blackening and yellowing. The blackening of polyester furniture paint products has nothing to do with the quality of the paint itself. Often due to the black spots on the wood itself, it becomes obvious after painting. When wood encounters moisture, the yellowing degree of paint is mainly related to the composition of paint and the environment in which it is used. Judging from the composition of the coating, the yellowing degree is nitrocellulose in turn. TDI or its derivative? Other components of the resin. The addition of nitrocellulose, a white pigment, on the one hand can improve the brushing performance of polyester paint, on the other hand, it also brings the disadvantage that the paint film is easy to yellow under the irradiation of sunlight and ultraviolet rays. For example, Byron semi-dumb formula paint will turn yellow seriously if it is exposed to the sun for half a day in summer. B aromatic urethane bonds are decomposed and oxidized under ultraviolet irradiation to produce quinone chromophore, which makes the paint film yellow. Which is represented by TDI. Due to the difference of production technology, the color of these curing agents using TDI as raw materials changed from water white to brown yellow, but all of them turned yellow to overvoltage under ultraviolet irradiation. Super yellow-resistant curing agents and other polyester curing agents belong to this kind of curing agents. Besides the ultraviolet rays of the sun, the yellowing of C is also related to the baking time of paint film. The longer the baking time and the higher the temperature, the easier the paint film will turn yellow. For white or light-colored polyester and polyurethane paints, if the curing agent is TDI products. Therefore, when using white enamel outdoors, please avoid using S04- 1 white poly, or choose C04-42 white alkyd enamel, A04-9 white amino baking enamel, white acrylic amino baking enamel or white acrylic biuret polyester enamel with component A added.

Common faults of coatings and their treatment methods-color bleeding

After the topcoat is coated on the primer, the color of the primer penetrates to the surface due to the effect of the topcoat solvent, which is called "color bleeding". Most topcoats are light in color, and it is easy to appear when the primer is dark in color.

1) The primer contains oil-soluble pigments or dyes.

For example, when painters spray A04-9 red amino paint, in order to save money, they often pour the red thinner of the sprayer into F06- 1 red-gray phenolic primer or other red primers, thinking that they are all red anyway, which often leads to the phenomenon of redness when spraying light-colored topcoat.

2) Paint containing strong solvent, such as nitrocellulose paint, is sprayed on the primer that is not completely dried.

Common faults of paints and coatings and their treatment methods-biting the bottom

It means that the solvent in the topcoat can easily soften the paint film of the primer and even affect the adhesion between the primer and the surface of the object. After the top coat is applied, the phenomenon of biting off the primer is called "undercut", and the slight undercut is very similar to the wrinkle of the paint film.

1) Apply topcoat before the primer is completely dried.

For example, H06-2 iron red epoxy primer and F53-3 1 red lead antirust paint have excellent performance at high temperature in summer, but with the decrease of temperature, especially in winter, there are more and more complaints about wrinkling and undercut caused by topcoat on them, mainly because the drying speed of these two paints has a great relationship with temperature. Take iron red epoxy as an example. It usually takes one day in summer when the temperature is high. The topcoat containing strong solvent will not bite and wrinkle when sprayed, but it will take 5 days or even longer to dry itself at low temperature in winter, and it is easy to bite when topcoat is applied the next day. We suggest that the iron red epoxy primer should be dried at 120℃ and 1 hour in winter. If there is no drying equipment, it is recommended to extend the drying time or choose other quick-drying primers.

2) Primer and topcoat are not compatible.

If the primer itself is a paint that is not resistant to strong solvents, such as red lead phenolic antirust paint or iron red phenolic antirust paint, and the top coat is a strong polar solvent, such as nitroaldehyde paint and polyurethane paint, even after the primer is dried, it will still cause undercut.

3) The curing agent of the two-component coating leaks air, which leads to a certain degree of resin gelatinization or painting after the coating is prepared for a long time, which reduces the final film-forming quality of the coating, resists the penetration of the topcoat solvent and reduces the swelling ability, thus causing undercut.

4) The bottom layer is made of volatile putty or paint with poor solvent resistance, and the top layer is made of polyester and polyurethane thermosetting resin paint. This undercut often occurs not when the first coat of paint is painted, but when the second coat of paint is painted after the first coat of paint is completely dried. The main reason is that the second layer of paint has strong solvent penetrating into the first layer of paint, which makes the volatile putty expand and produces undercut.

Common faults of coatings and their treatment methods-particles

1) construction tools are not clean, dust is newly brushed, old paint brushes are not cleaned in time, paint skin is left, and paint containers are not clean.

2) The construction environment and construction personnel are not clean, the paint is not clean, or the construction weather and surrounding environment are bad, so that impurities such as dust, mesh sand and yarn wool fall into the paint, or are soaked in the wet paint film, which makes the paint film granular.

3) Poor dilution ability of paint thinner leads to precipitation of some resin components in the paint. For example, when the semi-matte transparent top coat or transparent primer and diluent leak or have poor dilution ability, the particle phenomenon will occur.

Solution: Add strong solvents such as butyl acetate and cyclohexanone into thinner, then mix with paint and filter.

Common faults of paints and coatings and their treatment methods-wrinkling

1) If the drier is improperly matched or added too much, the inner and outer layers will dry unevenly and wrinkle.

2) Thick coating and pouring coating, of which C04-42 alkyd enamel is the most representative. Poor coating of C04-42 alkyd enamel will lead to wrinkling and slow drying.

3) After painting, the baking temperature in strong sunlight is too high.

4) Bite the bottom slightly.

Common faults of paints and coatings and their treatment methods-paint shrinkage

1) has pollution (dust, sweat, oil stain, wax, etc. ) and the moisture on the surface of the coated object. For steel workpieces, clean them with solvent and then paint them. For wooden furniture, first clean it with soap and water mill, then wipe it with clear water to dry it, and then finish it.

2) The injected compressed air contains oil or water.

3) The surface of the coated object is too smooth, and the surface has been pretreated by sandblasting and polishing.

4) Two-component coatings are sometimes painted immediately after uneven mixing, and contraction fermentation will also occur. After paint mixing, fully stir and solidify, and then brush.

5) The high temperature in summer greatly increases the volatilization rate of solvent in the paint, resulting in uneven dispersion of additives in the paint film and shrinkage of the paint. The solution is to reduce the construction humidity or add a strong solvent with slow volatility, such as cyclohexanone.

6) The paints don't match. When different manufacturers' primers and topcoats are used in polyester paint, paint shrinkage sometimes occurs because the additives used by different manufacturers are not necessarily compatible systems.

Common Faults of Paints and Coatings and Their Treatment —— Cracking

1) The coating itself has poor weather resistance and is not easy to use outdoors. For example, after outdoor use in summer 1-2 months, cracks will appear.

2) Thick coating and pouring coating [size= 1em] When floor paint is used, thick coating will greatly increase the possibility of paint cracking. Generally speaking, the total amount of paint used per square meter does not exceed 0.8kg, which is unlikely to crack.

3) The proportion of curing agent is high, or the coating itself has high hardness and insufficient toughness.

4) The bottom layer itself is loose and cracked, which leads to peeling and cracking of the upper paint film.

Common faults of paints and coatings and their treatment methods-powder removal

1) too much diluent is added, which leads to the separation of resin and powder, resulting in powder removal.

2) The coating of white pigment has poor weatherability, which leads to pulverization when it is used outdoors.

3) The coating is not evenly mixed, and the coating with high powder content in the lower layer produces powder removal.

4) Quick-drying paint is used to spray large workpieces, and the paint mist in the air falls on the workpieces, producing dust, so this paint is generally not easy to spray large workpieces. In the actual construction process, there may be some problems such as rust, floating color and golden light, which will not be explained here.

In short, whether it is furniture polyester paint or ordinary industrial paint or latex paint, the following items should be paid attention to during the construction process:

1) The substrate must be clean to ensure the quality of pretreatment, without water, oil and dust.

2) Building coating bottom and surface matching and solvent matching.

3) Pay attention to the influence of construction environment and temperature on specific construction.

4) Two-component and three-component coatings are used now, and will be invalid when they expire. Color paints should be fully mixed before use.

5) For non-thick coating, reverse coating is not allowed to shorten working hours.

6) After the construction is completed, ensure that the paint film has a certain curing period, and do not use it immediately.

4) The bottom layer is made of volatile putty or paint with poor solvent resistance, and the top layer is made of polyester and polyurethane thermosetting resin paint. This undercut often occurs not when the first coat of paint is painted, but when the second coat of paint is painted after the first coat of paint is completely dried. The main reason is that the second layer of paint has strong solvent penetrating into the first layer of paint, which makes the volatile putty expand and produces undercut.

5) Thick coating

Thick coating of primer prolongs the drying time of primer, and at the same time, with the enhancement of solvent penetration resistance of primer, the swelling and softening ability decreases, thus greatly improving the probability of undercut. The thick coating of topcoat makes the solvent in topcoat penetrate into the primer, and the softening time is correspondingly prolonged. Since the primer is bitten, the probability of being bitten increases.

Common faults of paints and coatings and their treatment methods-slow drying and sticky.

1) The surface of the object contains oil and water vapor, which leads to slow drying, or the plasticizer in the plastic penetrates into the paint.

2) Improper use of diluent. For example, non-volatile substances such as engine oil and diesel diluent are brought into the paint, which may cause the paint film to become sticky and dry slowly.

3) The influence of thick coating on polyurethane paint is not very prominent, but it is very prominent on alkyd and phenolic resin. Under the condition of constant temperature and pressure, the 20 micron C04-42 white alkyd enamel can be painted for 18 hours, but when the film is 50 microns, it can't be painted completely for three days, and it is easy to wrinkle. For this kind of paint, you'd better apply an extra coat.

4) After the oxide primer, putty or primer is wetted, the second coating is applied, which leads to interlayer isolation, air drying and solvent volatilization being blocked, thus leading to slow drying of the paint film.

Common faults of paints and coatings and their treatment methods-peeling and peeling

1) After the primer is fully dried, a smooth and hard paint film is formed. Insufficient polishing when painting the upper layer paint, resulting in interlayer falling off. Theoretically, the shorter the construction interval between matching coatings, the stronger the adhesion between them. However, considering that the primer is too short and dry, it may bring the problem of undercut. Therefore, when painting the last coat, painters usually let the primer dry fully, which puts forward higher requirements for the polishing of the primer.

2) In addition, in order to improve the construction performance of modern coatings, adding a lot of additives also reduces the interlayer adhesion of coatings.

3) The bottom does not match the surface. For example, nitrocellulose wood lacquer is coated on polyester or polyurethane varnish which has formed a certain fullness. Even if the polyester paint coating is polished, it will still fall off between layers after a long time. It is also suitable for the combination of 93 1 1 quick-drying acrylic paint and polyurethane paint.

4) The bottom layer is not thoroughly treated, with floating dust, oil pollution or loose bottom layer. The phenomenon of loose bottom layer falling off accounts for a large proportion of the reasons for latex paint falling off.