Coating may produce various defects during storage and use. After drying the surface of the product to form a film, or even after the product is used in the hands of the user for a period of time, it will produce defects of one kind or another. These defects seriously affect the decorative mass and painting efficiency of the surface of wood products. Therefore, try to avoid or analyze the causes of defects after they occur, and take appropriate measures to ensure the smooth progress of the painting process.
There are many reasons for painting defects, mainly including painting materials, properties and states of substrates, painting environment, painting technology, coating process, etc. Defects that appear immediately after painting are mainly caused by painting technical problems, while defects that appear after a long time are mostly caused by poor Coating quality. Here, the types, causes and treatment methods of defects caused by painting technical problems are mainly introduced.
Brushing defects and treatment methods
When brushing, due to manual operation, due to operation technology, construction environment, Coating selection and other reasons, there are many defects. The causes and treatment methods are as follows.
I. sag
1. Phenomenon
Coating flows at the grooves on the perpendicular surface or line corners. The thickness of the paint film is uneven, such as hanging curtain sagging in severe cases, and beaded tear stains in mild cases.
2. Reasons
Excessive thinner, Coating viscosity is lower than the normal construction requirements, the paint can not be attached to the surface of the falling flow;
The construction site temperature is too low, Coating drying speed is too slow, and in the film formation flowability is large;
The selected paint brush is too large, the hair is too long, too soft or too much paint is dipped when painting, so that the thickness of the paint surface varies, and the thicker part will flow;
The uneven brushing surface or the grooves of the edges, corners, and line corners of the object can easily cause uneven brushing and different thicknesses, and the thicker parts will flow;
The surface to be painted is unclean, with oil, water and other dirt, and it cannot be well attached and flowing after painting;
Coating contains a large proportion of pigment and uneven pigment dispersion.
3. Prevention and control measures
Select excellent Coating materials and appropriate amount of thinner;
Environmental temperature and Humidity should be appropriate.
The selected paint brush and bristles should have resilience, thick roots and fine tips. The bristles are thick and the mouth is even. The paint brush dipped in paint should be dipped less frequently;
During construction, the substrate should be made flat as much as possible and the edges and corners should be ground off. When brushing, brush hard, brush vertically first, then horizontally, and do not smear horizontally. Gently connect the corners and corners of the lines with a paint brush, and dip the excess Coating in to avoid the paint film being too thick and flowing;
Coating thinner should be selected;
Effectively clean up the debris, oil, water and other debris on the coated surface;
When the paint film is not through drying, Coating falls on one side or one surface part, the excess Coating can be removed with a spatula, and then brushed again. If the paint film has been through drying, for light scattered falling, it can be smoothed with sandpaper. For large-area falling, it can be smoothed with water sandpaper.
Ⅱ. Rough paint film
1. Phenomenon
Coating is painted on the surface of the object, and there are many granular protrusions in the paint film, which are rough and not smooth.
2. Reasons
Dust, sand and other debris are mixed into the Coating.
Coating, the resulting bubbles in the paint solution without dissipation that construction, especially in cold weather prone to bubble can not be scattered phenomenon, so that the surface of the film after drying rough.
Construction environment is not clean, there are dust, sand falling in the coating, or paint brush and other brushing tools are not clean, sticky debris.
The substrate treatment is not suitable, the sanding is not smooth, and the dust and sand are not cleaned.
3. Prevention and control measures
Coatings need to be sieved filtrated before brushing to remove debris.
After the Coating is prepared, it should stand for 10 to 20 minutes, and then use it after the bubbles disperse.
It is not suitable for construction in windy weather or dusty places, and the coatings just finished should be protected from dust and soil pollution.
The uneven part of the substrate should be filled with putty, then sanded with sandpaper to smooth, and then brushed coatings after wiping off the dust.
The surface of the paint film has been rough, sanding can be used to smooth, and then brush the topcoat again. For advanced decoration, sanding can be used to smooth, and finally waxed, polished, and polished.
Ⅲ. Bubble and pinholing
1. Phenomenon
Bubbles are small bubbles that do not run away from the surface of the paint film.
Pinholing is a sinkage-penetrating pinhole phenomenon on the surface of the paint film. This pinhole-like pinhole is like a pinprick hole with a pore size of about 100 microns.
2. Reasons
Coating entrained air, wood moisture content is too high. In the process of brushing and drying the film entrained air failed to escape and form bubbles in the film.
The air in the wood is expanded by heat, migrates into the paint film, fails to escape and forms bubbles and causes pinholing;
The surface of the paint film is drying too fast, and the solvent vapor that is too late to escape can also form bubbles and cause pinholing;
Brushing is too thin, Coating wettability is not good is also the cause of pinholing;
Coating and solvent are not matched, the amount of curing agent is too much, or the type of curing agent is wrong;
The substrate is not handled well, and the wood hair is not removed cleanly;
Coating drying of the lower layer is insufficient, that is, the upper layer is coated, and the surface layer dries too fast;
The initial temperature of heating drying is too high, the standing time is short, and the solvent is not fully volatilized;
The tube hole is not filled, there is air in the hole, and the coating is too thick
Improper brushing method, the brush produces bubbles when going back and forth
Environmental temperature is too high (more than 30 ℃) or relative humidity is too high (more than 80%) wind speed is too fast.
3. Prevention and control measures
When preparing Coating, the paint liquid should be stirred evenly. The stirring speed should not be too fast or too hasty to avoid the formation of bubbles, and the thinner should be added according to the dosage specified in the product manual. The Coating should be fully left standing and the appropriate viscosity of the Coating should be controlled, otherwise the paint film is too thin;
The surface of the coated substrate should be cleaned up, and no moisture or oil stains should remain. The wood should be dried to a certain moisture content (generally between 8 and 12%) before painting, and the wood pipe holes should be carefully filled when doing the bottom treatment. When brushing, wait for the previous paint to be fully dried before applying the next one;
When preparing and using Coatings, moisture should be prevented from mixing in. It is not suitable for construction on windy days and windy days;
When brushing, the brush back and forth should not be too hard to facilitate the escape of bubbles in the Coating;
For the pinholing paint film, after drying, lightly sanding with water sandpaper and then spraying a primer locally, then spraying a topcoat.
Select the matching Coating and matching solvent, adjust the amount of curing agent;
Control the temperature (15 ℃~ 25 ℃), Humidity (less than 80%) and wind speed of the construction site
Master the correct painting method
Ⅳ. Brush marks
1. Phenomenon
There are traces of bristles left on the paint film, and after drying, a trace of uneven brush pattern appears, making the thickness of the paint film uneven.
2. Reasons
The viscosity of the paint is too high and the evaporation rate of the diluent is too fast;
In the brushing of wood products, there is no parallel operation in the direction of wood grain;
The selected paint brush is too small or the bristles are too hard or the paint brush is not well kept to make the bristles uneven or dry;
The absorption capacity of the surface to be coated is too strong, and it is difficult to brush.
3. Prevention and control measures
Adjust the application viscosity of the paint and select the matching diluent;
When brushing construction, the first paint should be brushed in the direction of wood grain;
To use a softer oil brush, the operation should be light. After the paint brush is used, wash it with a thinner. Keep it properly, and paint brushes with uneven bristles should not be used as much as possible;
Seal the substrate with a sealing primer, and then brush the primer and topcoat;
The paint selected for brushing should have good leveling, and a diluent with suitable volatilization rate should be selected;
When you find brush lines, apply water sandpaper to gently smooth, clean the dust with a clean rag, and then brush the paint again.
Ⅴ. Slow dry, after tack
1. Phenomenon
After Coating brushing, if the curing time exceeds the specified curing time of Coating technical requirements, the paint film is still not drying, which is called slow drying. If the paint film has been formed, after a period of time, there will be a sticky hand phenomenon, which is called after tack. It makes the surface of the paint film easy to break or stain, which prolongs the construction period.
2. Reasons
If the coating is too thick, the oxidation will not reach the inside of the paint layer and the bottom layer will not dry for a long time. Too thick scraping of oily putty can also cause the paint film to dry slowly;
The surface to be coated is unclean, with oil stains, wax, alkali or salt, etc., and the surface of the substrate is not cleaned by Resin;
The first paint is not dry and the second paint is applied;
Coating is stored for too long, beyond the service life or poor sealing, the solvent has evaporated and livering, although this kind of Coating can be painted after adding thinner, but the paint film is not drying or easy after tacking;
Construction in rain, humidity, darkness, sun exposure and other harsh climate conditions.
3. Prevention and control measures
Each film should not be too thick, and the putty should not be scraped too thick at one time. It is better to scrape and apply several times, not to rush for success, and apply too thick at one time;
The treatment of the base layer needs to meet the requirements. After sealing the surface of the base layer with a closed primer, brushing primer or topcoat;
After the previous paint film is dry, brush the second paint layer;
Coatings that have expired should be avoided. For Coatings that have exceeded the service life, a small sample should be prepared first to prove that they meet the requirements before being put into use. Coatings that cannot be used up should be sealed reliably;
The construction environment shall not have acid, alkali, salt, fog or other chemical gases, and shall not be constructed under harsh climate conditions such as rain, fog, humidity, darkness, and scorching sun exposure. The construction site shall maintain air circulation;
When the paint film is slightly slow drying or sticky, it can be ventilated, appropriately increase the Environmental temperature, strengthen the protection, observe for a period of time, if it is really not drying the conjunctiva, then do treatment. If it is slow drying, after tacking is serious, wash it off with a strong solvent and scrape it again.
Ⅵ. Orange peel
1. Phenomenon
There are many semicircular protrusions on the surface of the film, which are shaped like orange peel markings.
2. Reasons
After brushing, the volatile solvent in the paint film evaporates sharply, resulting in strong convection, which breaks the film layer into small holes, and the surface has dried up before the second degree of flow to form orange peel;
Environmental temperature is too high or too low, can make the film produce orange peel phenomenon.
3. Prevention and control measures
In painting, it is necessary to ensure that there is a certain levelling time after Coating Spreader, and the solvent cannot evaporate too fast;
Environmental temperature is too high or too low should not be construction;
For coatings with orange peel, use water sandpaper to smooth the raised part, sinkage the putty part, and brush the paint layer again.
Ⅶ. Bite the bottom
1. Phenomenon
Bottom biting refers to the phenomenon that the solvent in the upper layer Coating softens and expands the bottom layer paint film, resulting in small adhesion of the bottom layer paint film, and peeling and uncovering the bottom.
2. Reasons
The primer is not applied through drying, and the solvent in the primer can easily dissolve and soften the primer, causing the bottom to bite;
The operation is not fast when brushing the topcoat, and the phenomenon of biting the bottom will occur if the number of repeated brushing is too much;
For greasy paint films and some synthetic resin paint films modified by dry oil without high oxidation and coalescence film formation, once they meet with strong solvents, the primer film will be eroded. If the primer uses phenolic paint and the topcoat uses nitro paint, the solvent in the nitro paint will bite the oily phenolic paint and separate it from the original adhesion base.
3. Prevention and control measures
Coating through drying should wait for the bottom layer, then brushing the surface layer Coating;
When brushing solvent Coatings, be skilled, operate accurately, quickly, and prevent repeated brushing;
Bottom Coatings and Surface Coatings should be used together;
For serious underbite, all coatings need to be removed, and the same kind of Coating should be used for brushing after the base layer is dried.
Ⅷ. Pour light, lose light
1. Phenomenon
Pouring refers to the phenomenon that there is Gloss after the paint film dries, but the Gloss decreases and disappears within a short period of time (hours to weeks). Loss of light refers to the phenomenon that there is no Gloss or insufficient Gloss after the varnish is cured into a paint film. Although there are differences in the phenomenon of pouring light and losing light, the reasons are roughly the same.
2. Reasons
Humidity of the air is too large or water vapor coacervation, coating moisture absorption, or moisture in the brushing tool.
The substrate contains alkaline vegetable glue that absorbs water, and white fog is generated after brushing the nitro paint, resulting in loss of light;
The coated surface or putty layer is not well sanding, the surface is too rough, and the paint film Gloss is dull;
Coating percent solids and excessive thinner;
Painting Environmental temperature is too low, water condensation in the dry coating;
After the water sand, it is polished without sanding, and the water is not dry after the water sand.
3. Prevention and control measures
It is not suitable for construction in rainy, cold weather or humid environment. Prevent painting tools from bringing moisture into the Coating;
The surface of the substrate should be cleaned before brushing, and there should be no dirt;
To be coated surface, sanding should be effective and clean the surface dust;
The thinner dosage should not be too much, and the temperature and Humidity of the construction environment should be reasonably controlled;
Before polishing, it needs to be sanded flat and fine;
Found that the paint film pouring or loss of light phenomenon, can be used Far infrared irradiation, to promote the paint film drying, if the pouring or loss of light is serious, should wait for the surface to dry with water sandpaper sanding, water sand after effective drying, brushing a layer of topcoat;
Light loss of light paint film can be used high boiling point solvent gently rubbing, can be improved, for serious can be repainted.
Ⅸ. Paint film cracking, checking
1. Phenomenon
There are different shades of crazing on the surface of the paint film. If the lower surface can be seen from the crazing, it is called "cracking"; if the paint film shows a small crazing like a tortoise pattern, it is called "checking".
2. Reasons
The primer is not matched with the topcoat, and the film is subjected to cissing stress due to external action (mechanical action, temperature change, etc.), causing the paint film to check or crack;
The primer is not dry enough to apply (spray, brush, roller painting) topcoat; or the first layer of topcoat is too thick, and the second layer of topcoat is applied without drying, so that the inner and outer expansion of the two layers of paint is inconsistent;
Indoor paint for outdoor or metal surfaces Primer for wood;
The wood substrate contains turpentine without removal and treatment, and the paint film will be exudation over time, resulting in local checking;
Coatings were not sufficiently mixed before painting;
The environment is harsh, the temperature difference is large, and the paint film is expanded and retracted by cold and heat, causing checking;
The moisture content of the substrate is too high, and the substrate cracks during the drying process;
The amount of drying agent is too much, and the construction temperature is extremely low. When painting polyester paint, the initiator and accelerator are added too much.
3. Prevention and control measures
Primer and topcoat should be matched, primer and substrate should be matched;
After the primer is dry, the next paint is painted; the first layer of topcoat should be thin and thin, and then the second layer should be applied after drying;
Select the appropriate Coating varieties, especially outdoor and paint, to choose weathering resistance Coating;
The pine resin of the wood substrate should be removed, wiped clean with alcohol, and sealed with a closed primer;
Construction under suitable environment conditions, full mixing paints before painting;
Control the moisture content of the substrate;
Add an appropriate amount of drying agent, and add initiator and accelerator according to the formula;
For cracks, it can be sanded off or recoated after disbonding.
Ⅹ. Paint film flaking
1. Phenomenon
Due to poor adhesion and bonding between the layers of the paint film, pathological phenomena such as peeling, flaking, bulging and peeling of the paint film will occur.
2. Reasons
The bottom and topcoat are not matched, resulting in poor intercoat adhesion;
The surface is unclean, stained with oil, moisture or other dirt;
Improper surface treatment. The surface is puttying or painted without sanding, so that the oil of the topcoat is absorbed by it and causes peeling; the wood surface is not effectively closed;
The bottom layer is not dry enough to apply the topcoat, and it will crack due to the inconsistent cissing rate of the bottom layer over time, which will affect the adhesion therebetween. The primer is too hard or the primer is very smooth, and the topcoat is directly painted without sanding;
Outdoor paint weathering resistance, water resistance, high-low temperature cycle poor;
The construction temperature is too low.
3. Prevention and control measures
Choose matching primer and topcoat;
Substrate surface preparation should effectively remove oil, moisture or other dirt;
Substrate to be sanding, trimming and puttying. The primer must be dry and sanding before coating (brush, roll or spray) topcoat to increase intercoat adhesion.
Ⅺ. whitening
1. Phenomenon
The coating surface was white mist.
2. Reasons
Environmental temperature High Humidity (above 85%), rainy days in summer;
Environmental temperature is low, the wind speed is too fast;
The surface temperature of the substrate to be painted is lower than room temperature;
Too thick paint at one time;
The surface of the substrate to be painted or the container has moisture;
Coating solvent or thinner evaporates too quickly.
3. Prevention and control measures
Regulates Air Humidity and Temperature;
Increase the construction Environmental temperature, the wind speed is lower than 1.0m/s;
Make the substrate surface temperature greater than or equal to room temperature;
Avoid painting too thick at one time;
The surface of the substrate to be painted and the container should be fully dried;
Appropriately add moisture-proof agent (whitening water, anti-whitening water) or reduce the evaporation speed. The coating that has produced mild whitening can be heated to 30~ 40 ℃ for drying; the local whitening can be gently rubbed with thinner; the severely whitening can be sanded to remove the whitening paint film and then reapplied, or all washed off and reapplied.
Ⅻ. Discoloration
1. Phenomenon
Color of the film after painting does not match the required Color
2. Reasons
Coatings with poor light resistance are used;
Coating is inconsistent;
The substrate itself changes color;
Residual bleach reacts with Coatings;
Too much curing agent added;
Inappropriate colorant is used.
3. Prevention and control measures
Coatings with good lightfastness;
Selection of matching Coatings;
Choose a substrate that is not easy to change color;
Remove residues such as bleach;
The amount of curing agent should be added;
Select the appropriate colorant;
For slight discoloration, the topcoat can be reapplied after color matching treatment; for serious discoloration, the discoloration paint film can be completely sanded off, or washed off with solvent and replaced with lightfastness Coating for re-painting.
