Trouble shooting of the surface spraying of the ho

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Troubleshooting of plastic product surface spraying fault

fault name

causes and Countermeasures

coating surface scaling

oxidation polymerization paint, alkyd resin and nitro paint or ammonia alkyd resin primer with more pigment components are easy to scale during storage. Generally, carbonates and oximes can be added as effective anti scaling agents. For each kind of coating, only less than 1% of the amount should be added. The viscosity of coating gel will increase during storage. This phenomenon is called thickening or delayed thickening. If further developed, the coating

will lose its fluidity and form a gel state. For oily coatings, the amount of desiccant shall be appropriately reduced and oxidation polymerization prevention agent shall 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 materials of amino alkyd resin, alcohol polar solvent with hydroxyl should be added, which has a significant effect on skinning.

the coating hardens and binds.

the coating forms a colloid after skinning. If it is further developed, it often hardens and produces bonding. Generally, the color carrier with

low acid value should be selected, and fatty acid ester or amine can also be added to prevent hardening and bonding. It is worth noting that alkyd resins do not harden and bind to high acid value color carriers, but harden and bind to low acid value color carriers.

pigment deposition and separation

generally, pigment particles are suspended and dispersed in the polymer solution of the coating. Due to the different specific gravity of the solution and pigment particles, the pigment is often precipitated and in a metastable state, It leads to uneven film color or surface gloss difference due to insufficient stirring during coating, and the coating can be blocked during pipeline transportation as a qualification item. In order to prevent precipitation and separation, appropriate surfactants should be selected to maintain a certain viscosity of the dispersant and reasonably determine the composition of the solvent. If the coating has been deposited and separated, good dispersing equipment and dispersing methods shall be used to fully stir the sagging or sagging of the coating film. The sagging or sagging of the coating film on the vertical plane will produce columnar or wavy stripes. The long columnar stripes are called trickle, and the curtain stripes are called sagging

the cause of dripping and sagging is the fluidity of the coating, which is directly related to the type and amount of pigments in the coating and the presence or absence of additives, and has a great impact on it. Generally, coatings with good fluidity, slow curing speed and solvent volatilization speed are easy to produce

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 impact on the trickle. Generally, the more dynamic the coating viscosity analyzer is, the more difficult it is to trickle because it is a new type of impact analyzer that can instantly measure and record the characteristic curve of the material in the process of impact and analyze the characteristics of the material. However, the drips of coatings with the same viscosity

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

and sagging, the solvent with good volatility can be considered. The coating should be sprayed as thin as possible. 5) testmdb folder experimental data and sample information files; If many experiments have been done to adjust the dilution ratio of diluent, properly reduce the viscosity of the coating, reasonably control the distance and running speed of the spray gun

coating whitening

the phenomenon of white atomization on the surface of the coating during or after drying is called whitening. The main reason for whitening is that when the solvent in the coating evaporates rapidly, the temperature of the coating liquid drops below the dew point despite the high ambient temperature, and the water vapor in the air will condense into water and enter the material liquid, causing the polymer in the coating to either precipitate or volatilize due to the evaporation of the condensed water. The coating film is full of gas. 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 volatile solvent will suddenly take away a large amount of heat, resulting in a drop in the surface temperature of the coating liquid, causing the moisture in the air to condense and mix into it, resulting in 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 volatilize 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 whitening 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 point solvent, i.e. slow drying diluent, shall be added to the lacquer diluent

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

it should be noted that if the slow drying diluent is used excessively, poor drying will easily occur, and polymer components will be separated out during the drying process after the diluent with weak solubility is used. In addition, the water content in compressed air and the amount of solvent with low boiling point shall be reduced as much as possible. Coating pulverization. The phenomenon that the surface of the coating decomposes into powder and loses luster in the outdoor environment is called pulverization. In this regard, when spraying white

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

surface bleeding and frosting

the bottom coating or bottom color seeps from the surface coating film, and the phenomenon that the surface coating film changes color is called surface bleeding. In addition, when pigments with a capacity of

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

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

; 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, the surface shall be coated with the coating containing alcohol soluble polyvinyl butyral or aluminum powder, and then the surface coating shall be carried out after covering the color bleeding surface. Due to the different lubrication degree, particle size, specific gravity and cohesiveness of various pigments, there will be differences in sedimentation rate during coating, resulting in different color of surface layer and bottom layer during the formation of coating film. This phenomenon is called floating color or surface color separation. For example, if the paint containing cyan

cyan and yellow lead is used for coating, a green film should be formed. However, 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 coating, but there is color difference or so-called color unevenness in the coating, it is called blooming or color floating

surface floating color and blooming

surface floating color and blooming often 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. Maybe he wants to know the definition, concept and corresponding common sense of search engine; Or maybe he wants to know which search engines are currently related. With the convection phenomenon of solvent volatilization, the pigments with small particles are easy to flow, and the pigments with large particles are difficult to flow. Therefore, in the convection process, the fine and relatively low density pigments move to the surface layer, and the 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 coating liquid is low, convection phenomenon is serious, and color separation is easy to occur. In addition, in the convection process, the pigment particles in the flow

conflict with each other, and the unstable particles at the 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 oil acid can reduce the agglutination of titanium dioxide, increase the agglutination of cyanosis, maintain the balance of sedimentation, and prevent color floating. Adding an appropriate amount of silicone oil can also prevent the surface from blooming,

this is due to the surface viscoelasticity caused by the adhesion of silicone oil to the coating surface, which mechanically inhibits the convection of eddy current in the coating liquid. In addition, the coating shall be fully stirred and carefully filtered before use, and it shall be evenly stirred after adding diluent. The oil stain on the surface of the product must be cleaned; Metallic coatings shall not be painted too thick

surface discoloration and fading

there are three main reasons for film discoloration 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, for example, the coated

film containing organic red pigment loses its red color and turns white after exposure to sunlight; Third, white or light color

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