Treatment of the surface spraying failure of the h

2022-08-14
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Treatment methods for spraying faults on the surface of plastic products

oxidation polymerization paint, alkyd resin and primer of nitro paint or aminoalkyd resin with more pigment components are easy to peel during storage

. Generally, carbonates and oximes can be added as effective anti scaling agents. Each kind of

only needs to add less than 1% of the amount

the viscosity of the coating will increase during storage. This phenomenon is called thickening or delayed thickening. If further developed, the coating

will lose its fluidity and form a gelatinous state. For oily coatings, the amount of desiccant should be appropriately reduced and oxidation polymerization prevention agent should be added. However, it should be noted that this will affect the drying performance of the coating, and the reduction must be limited. For the coating material of amino alkyd resin, alcohol polar solvent with hydroxyl should be added, which has a significant effect on skinning

the coating surface forms a colloid after skinning, and if it develops further, it often hardens and produces bonding. Generally, color carriers with low acid value should be selected, and fatty acid esters or amines can also be added to prevent hardening and bonding. It is worth noting that alkyd resin does not harden and bind to high

acid value color carriers, but harden and bind to low acid value color carriers

generally, pigment particles are suspended and dispersed in the polymer solution of the coating. Due to the different specific weights of the solution and pigment particles,

pigments often precipitate and are in a metastable state, It leads to uneven film color or surface gloss difference due to insufficient stirring during the coating process, as well as blockage of the coating during pipeline transportation. In order to prevent precipitation and separation, appropriate surfactants should be selected,

keep the dispersant at a certain viscosity, and reasonably determine the composition of the solvent. If the coating has been deposited and separated, good dispersion equipment and dispersion methods should be used. After fully stirring the film sagging on the vertical plane, columnar or wavy stripes will be generated. Long columnar stripes are called trickle, and curtain stripes are called sagging

dripping and sagging are caused by the fluidity of the paint, which is directly related to the type and amount of pigment in the paint and the presence or absence of additives

and has a great impact on it. Generally, coatings with good fluidity, slow curing speed and solvent evaporation speed are prone to

trickle. In addition, because the paint containing pigment is easy to show thixotropy, the paint with mechanical stirring is easy to produce sagging. The viscosity of the coating has a certain influence on the dripping. Generally, the higher the viscosity of the coating, the harder it is to drip. However, the dripping property of coatings with the same viscosity

is also different, which is mainly affected by the thixotropy of coatings and the volatility of solvents. In order to prevent coating dripping

and sagging, the solvent with good volatility can be considered. The coating should be sprayed as thin as possible, and the dilution ratio of diluent should be adjusted appropriately. For example, the viscosity of the coating should be appropriately reduced, and the distance and running speed of the spray gun should be reasonably controlled

the white atomization phenomenon on the surface of the coating during or after drying is called albinism. The main reason for albinism is that when the solvent in the coating evaporates rapidly, although the ambient temperature is high, the temperature of the coating liquid drops below the dew point, and the water vapor in the air will condense into water and enter the material liquid, making the polymer in the coating either precipitate or evaporate due to the evaporation of condensed water. The coating film is full of gas, and after drying, a small white mark will appear on the film surface

under the condition of high temperature and humidity, if a bright paint system coating containing a large amount of fast volatile solvent is used for coating, the volatilization of the solvent will suddenly take away a large amount of heat, resulting in the decrease of the surface temperature of the coating liquid, condensing and mixing the moisture in the air, causing the polymer precipitation in the coating material and whitening. In addition, if the thinner with weak solubility is used to dilute the coating, the solvent with strong solubility will evaporate quickly, increasing the proportion of non solvent components in the coating, resulting in the precipitation of dissolved polymers and whitening. It can be seen from

that bleaching mainly depends on factors such as relative humidity, temperature difference between coating and surrounding environment, solvent and polymer type. For example,

it is very easy to produce whitening when painting bright paint under the condition of relative humidity of more than 80%. At this time, 20% - 30% high boiling solvent, i.e. slow drying diluent, should be added to the lacquer diluent

, and the coated products should be preheated for a certain time before spraying

it is worth noting that if the slow drying diluent is used excessively, it is easy to produce poor drying, and after the diluent with weak solubility is used, polymer components will precipitate during the drying process. In addition, the water content in compressed air and the amount of solvent with low boiling point should be reduced as much as possible. The phenomenon that the coating film decomposes on the surface in the outdoor environment, turns into powder and loses luster is called chalking. In this regard, when spraying white

color paint, an appropriate amount of zinc oxide or antimony and barium sulfate can be added. An appropriate amount of ultraviolet absorbent can also be added as an auxiliary agent

the bottom coating or bottom color exudes from the surface coating, and the phenomenon of discoloration of the surface coating is called surface discoloration. In addition, when pigments with a capacity of

that are easy to cause surface bleeding are used, the pigments often precipitate from the coating, which is called frosting

the cause of surface bleeding and frosting is mainly because the coloring substances contained in the bottom coating or bottom color are dissolved by the dissolving agent of the surface coating. Generally, inorganic pigments will not produce surface bleeding, and organic pigments such as red or maroon lake pigments are easy to cause surface bleeding. Therefore, the solubility of organic pigments should be improved. In order to prevent surface bleeding and frosting, first, try not to use pigments that cause bleeding in the primer

; The second is to paint the surface layer after the bottom coating is completely cured; Third, for the bottom coating or bottom color that is easy to produce surface color bleeding, first coat the surface with a coating containing alcohol soluble polyvinyl butyral or aluminum powder, cover the color bleeding surface, and then coat the surface coating

in order to match a variety of colors, the coating is mostly composed of more than two kinds of pigments. Due to the different lubrication degree, particle size, specific gravity and cohesion of various pigments, there will be differences in sedimentation rate during coating, resulting in the different color of the surface layer and the bottom layer when the coating film is formed. This phenomenon is called floating color or surface color separation. For example, coating with cyan

cyan and yellow lead should form a green film, but due to the continuous precipitation of yellow lead, the yellow tone is lost, and the film only shows a strong cyan tone. In addition, if there is no difference between the color of the surface layer and the bottom layer of the film, but there is a color difference in the part of the film or the so-called color unevenness is called blooming or color floating

surface floating color and blooming mostly occur in gray, blue and green systems, which is closely related to the dispersion stability of pigments and the vortex and convection phenomena of

in the process of solvent volatilization. With the convection phenomenon of evaporation of coating solvent, the pigment with small particles is easy to flow, and the pigment with large particles is difficult to flow. Therefore, in the process of convection, fine and relatively low density pigments move to the surface layer, and coarse and

relatively high density pigments move to the bottom layer, thus showing the phenomenon of color separation. Generally, the coating liquid has high viscosity, is not easy to flow, and the convection is small; The viscosity of the coating liquid is low, the convection phenomenon is serious, and it is easy to produce color separation. In addition, in the process of convection, the pigment particles in the flow

conflict with each other, and the particles with unstable interface agglutinate and become large particles, which are distributed in the bottom layer of the coating

as the causes of surface floating color and blooming are quite complex, there are no effective measures to prevent this phenomenon. Before the project, it is mainly to reasonably select pigments, color developing agents and solvents, especially to mix appropriate additives. The research shows that adding soybean emulsifier or lead naphthenate can prevent blooming. The addition of lubricants such as castor fatty acid can reduce the agglutination of titanium dioxide, increase the agglutination of cyanosis, maintain the balance of sedimentation, and prevent the color from floating out. Adding an appropriate amount of silicone oil can also prevent the surface from being scratched, which is suitable for rapid and nondestructive qualification inspection of seamless steel pipes,

this is due to the surface viscoelasticity generated by the adhesion of silicone oil to the coated surface, which mechanically inhibits the convection of eddy currents in the coating. In addition to this

, the paint should be fully stirred and carefully filtered before use, and it should be evenly stirred after adding diluent. The oil stain on the surface of the product must be washed away

and cleaned; Metallic coatings cannot be painted too thick

there are three main reasons for the discoloration of the film after coating: first, the color of the film migrates to other colors, such as the Yellow

color film containing yellow lead turns black after contacting hydrogen sulfide; Second, the color pigment of the coating film becomes lighter and loses its primary color, such as the coating

film containing organic red pigment loses its red and turns white after exposure to sunlight; Third, the coating film of white or light color and transparent paint turns yellow or brown due to the action of sunlight, artificial light

line or heat. Therefore, discoloration and fading are mainly caused by paint factors and environmental factors or the combination of the two factors. Usually, when the temperature is high, the discoloration phenomenon is more obvious. The adhesion of dust or soot, mold or substrate shadow

will also cause the film to change color. The light resistance of organic pigments is poor, and its coating is easy to fade after being exposed to light. Inorganic colored pigments

have poor acid-base resistance, and their coatings are easy to change color after being eroded by acid and alkali or contacting acid or alkaline gases. The film with phenol formaldehyde or oxyindene resin with high unsaturation

as binder and lead white, lithopone white and titanium dioxide as pigments is easy to turn yellow. When the desiccant is added too much, it is also easy to cause discoloration or yellowing. In order to prevent the film from discoloration, pigments should be selected and combined reasonably. After coating, the surface coating film of the product should be kept clean.

the gloss of the coating film with the advantage that ordinary plastic profiles cannot be replaced is called gloss loss in the short term after coating. Some of the loss of light is caused by the environment, such as

the film is eroded by the discharged ammonia, hydrogen sulfide, carbon dioxide and other chemical gases, or the humidity of the spraying environment is high, and the condensation of water in the film produces loss of light. The amount of diluent in the coating solution has a great impact on the surface gloss of the film, and the proportion of use must be appropriate

when spraying, the temperature and environmental humidity of the coating liquid must be adjusted reasonably.

when spraying on the surface of soft PVC or cellulose products, there is a problem that the coating film becomes brittle due to softening or adhesion, delaying drying or the loss of softness of bright

paint film. This phenomenon is called migration

the main reason for migration is that the plasticizer in the product is transferred to the film or the plasticizer in the lacquer film is absorbed

and received in the product. In order to prevent migration, the first is to appropriately reduce the amount of plasticizer during product molding; Second, plastic varieties without plasticizers

are used to replace plastic varieties with a large amount of plasticizers, that is, the varieties of raw materials used to make products are replaced; Third, try to use non

migratory plasticizers; Fourth, when choosing the variety of raw materials, the type of plasticizers and designing the formula of coatings, we should take into account the compatibility of the three

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