Common preventive measures countermeasures for application faults
I. Treatment of appearance problems
1. Viscosity is one of the control indexes of product delivery. Viscosity is within a certain range. The viscosity of the same product varies with the temperature. It is no direct relationship with solid content and buildiness.
2. Appearance is a joint reflection of resin and filler. Appearance has no direct relationship with quality. The storage time also affect product appearance, especially for nitro-cotton system.
3. Skinning is a pure quality problem which relates with resin.
4. Swell is caused by CO2 generated by reaction of curing agent and the air in the container. In case of swell, if the curing agent has not apparently thickened or muddy and is normal after test, it can be used; otherwise, it cannot be used any more.
Wrinkling is the phenomenon when the paint film surface has protuberance like ridge.
The main reason of this phenomenon is that the paint film is too thick and the drying speed of the film is not the same. The surface dries faster and the inside dries slower. It is common in floor paint.
The reasons of wrinkling
1. During coating application, the one-time coat is too thick.
2. The application environment is over ventilated.
3. The solvent release performance of the coating is bas and the volatile speed of solvent is not proper.
4. The coating viscosity is too low and the work piece is not placed on a flat surface and the paint film runs.
Countermeasures for wrinkling
1. Use coating which dries fast for inside and slower for surface.
2. The viscosity of coating shall be proper and the coat thickness shall be well controlled.
3. Use proper coating.
4. Control the ventilation rate in the application environment.
5. Before the viscosity of paint film is increase to a certain degree, work piece of large area shall be placed flat.
III. Brush marks
There are brush marks on the paint films after the coat dries, making the thickness and gloss of the paint film uneven.
The reasons of brush marks
1. The viscosity of coating is too high and the volatile speed of the thinner is too large.
2. The backward brushing time is too long.
3. The coating brushing and applying of wooden products did not follow the direction of wood grain.
4. The paint brush is too small or the brush hair is too hard, or the brush is not well kept, the brush hair is of different length or hard and dry.
5. The substrate surface absorbs too much coating, which makes application difficult.
6. The application performance of the coating is poor.
Countermeasures for brush marks
1. Adjust the application viscosity of coating and select the matching thinner.
2. Brush following the wood grain direction for first layer of coating.
3. Use brush with soft hair and the brushing action shall be light and skillful. After the brush is used, use thinner to wash it and keep it well. Do not use brush with different brush hair length.
4. Seal the substrate with sealer and then brush primer or top coating.
5. The coating selected shall have good levelling property and the selected thinner shall have proper volatile speed.
6. When brush marks are found, used sand paper to polish and then clean the dust with clean cloth and then brush/spray once again.
IV. Rough hand feeling
1. The reason is almost the same with those of granule.
2. The temperature of application environment is too high, and the thinner dries fast, causing over-spray phenomenon.
3. The layout of drying room and spray room is not reasonable, or the ventilation of the spray room is not good and the painting mist in the spray room enters drying room.
4. The performance of the coating is poor.
Countermeasures of rough hand feeling
1. If the reason of rough hand feeling is granule, please refer to the counter measures of granule.
2. If the rough hand feeling is caused by over-spray, add isophorone to extend the opening hours of paint film.
3. Improve the ventilation system of the spray room and arrange the location of the drying room to avoid the painting mist to enter the drying room.
4. Change the coating variety.
5. For paint film already with rough hand feeling, polish it and spray the top coat again.
Precipitation is obvious precipitation phenomenon of fillers or other solid content during storage and use process of coating.
Precipitation is often seen when diluting primer, flashing paint or matte top coat.
Reasons of precipitation
1. Too much thinner is added or the system viscosity is too low.
2. The coating is placed for too long after adding the thinner.
3. The anti-precipitation performance of the coating is poor.
Countermeasures of precipitation
Dilute the coating through adding each component according to the required ratio. The amount of thinner cannot be too much. It can be less.
The diluted coating cannot be placed for a long time. It shall be used as soon as possible. If it is placed for a long time, the coating must be stirred with proper interval.
Change coating with better anti-precipitation performance.
VI. Poor sanding property
Poor sanding property refers to the phenomenon that it is not easy to sand the coat to powder after it is dried or within normal process period, which is accompanied with adhesion to the sand paper.
The main reason is that the paint film is too hard, too soft or the polishing additive is insufficient.
The reasons of poor sanding property
1. The temperature is too low and the paint film fails to be fully cured within normal process period.
2. The curing agent is not added according to the required ratio or the curing agent is not matching.
3. The solvent volatilizes too slow or the paint film is too thick and the solvent is not fully volatilized.
4. The performance of the coating is poor.
The countermeasures of poor sanding property
1. Improve drying environment and take appropriate heating measures in low temperature.
2. Extend the drying time for paint film.
3. The paint film cannot be too thick in one application.
4. Use curing agent and thinner which can dry fast.
5. Use correct coating, especial avoid to use coating designed for summer in winter.
VII. Spoiled curing agent
PU curing agent makes the coating cannot be used or affects its quality before or during use.
The main reason is that the curing agent has had chemical reaction (molecular weight is larger and the tolerance is smaller).
Reasons of spoiled curing agent
1. The coating quality is poor.
2. The sealing of packing is poor.
3. The temperature of the storage environment is too high.
Countermeasures of spoiled curing agent
If the curing agent is not obviously thickened or muddy, without performance changes after it is mixed with coating, the curing agent can be used; otherwise, it shall be replaced.
The coating of work piece runs on non-horizontal surface or grooves of corners, resulting in uneven thickness of the paint film.
The main reason is the liquidity of the coating is too strong or the wet film is too thick.
The reasons of sagging
1. Too much thinner is added, the application viscosity is too low, one-time paint film is too thick or the interval is too short.
2. The spray distance is too small and moving speed is slow. The amount of paint sprayed is too large and the spray pressure is not uniform.
3. The coating lacks thixotropy.
4. The surface of substrate is too smooth.
5. The solvent in the coating volatilizes too slowly.
6. It is more possible to happen when the environment temperature is low; the temperature difference of coating and the substrate in the application room is large.
7. Pigments of large content are in the coating without fully stirred.
Countermeasures for sagging
1. Adjust proper viscosity and the one-time spray coat cannot be too thick.
2. According to the actual situation, the diameter of spray gun is usually1.5～2mm; during application, the air compressor shall keep stable air pressure; the spray distance is about 300mm and the speed of spray gun is 60cm/s; control the amount of paint sprayed and control the interval of recoating.
3. Give proper thixotropy to the coating.
4. Keep appropriate roughness of the substrate surface, and polish carefully before reapplication.
5. Install ventilation equipment; reduce the temperature difference of the coating and substrate in the application room. The temperature of application room shall be 15 to 30℃.
6. During application, the coating shall be stirred fully for many times.
IX. Insufficient abrasion resistance
After the paint film is fully dried, appearance change is easily happen under exogenic action, for example, scratch or reduced gloss, etc, which is called abrasion. If the paint film has not enough resistance to abrasion, it is called insufficient abrasion resistance.
The reasons of insufficient abrasion resistance
1. The temperature of application environment is low, the solvent volatiles too slow, or the surface drying time is too long.
2. The amount of curing agent is not enough or the coating dries slow.
3. One-time coat is too thick.
4. The PU coating is mixed with water of the humidity of application environment is too high.
5. The performance of the coating is poor.
The countermeasures of insufficient abrasion resistance
1. Use materials with good abrasion resistance, for example, PU paint with glass powder or AC paint.
2. Use curing agent and thinner which can dry fast.
3. One-time coat cannot be too thick.
4. Avoid application under too high or low temperature.
Yellowing refers to the phenomenon that partial or the whole paint film becomes yellow obviously after the coating is applied for some time.
The main reason is that the paint film has oxidizing reaction and generates coloring substance under the action of light or chemical substance.
The reasons of yellowing
1. Coating without yellowing resistance is used and the paint film ages decomposed under direct sunlight.
2. The acid or base substance on the substrate is not cleaned.
3. The white primer has bleeding phenomenon or the substrate is applied putty.
The countermeasures of yellowing
1. Avoid direct sunlight before the paint film is fully dried.
2. Use anti-yellowing coating to reduce yellowing.
3. Make proper treatment to the substrate, for example, using sealer to seal or detergent to clean.
The paint film surface has cracks of different sizes and if the underlying coat can be seen from the cracks, it is called "cracking"; if the paint film has fine cracks like tortoise back pattern, it is called "checking".
The main reason is the multi-component coating system has insufficient film-forming cross-link, the single-component coating system has poor performance of the substrate cracks.
The primer and top coat does not match. The paint film is affected by external force (mechanical action or temperature changes) to have shrinkage stress, causing checking or cracking of paint film.
The PVC value of the primer is too light and top coat is too hard.
The wooden substrate has rosin which will permeate paint film and cause local checking.
The water content of the wood is too high and it may have deformation which causes cracks.
Too much curing agent is added or the wrong curing agent is used.
The coat is too thick or the film-forming cross-link is insufficient.
The application environment is very bad with high temperature difference and high humidity. The paint film is cooled and heated to have shrinkage, which causes checking.
Countermeasures of cracking
The primer and top coat shall be matched and the primer and substrate shall be matched.
Use coating of proper variety. Coating used in outdoor shall have excellent weather resistance.
Remove the rosin on the wood substrate and wipe it with alcohol and seal it the sealer.
Apply according to the required ratio.
Do not make thick coat.
Apply under appropriate environment conditions and stir the paint fully before application.
The water content of the wood shall be lower than 12%.
Collapsing refers to the phenomenon that after whole sealing application, the paint film has irregular or following substrate texture shrinkage.
The main reason is that the volatile of residual solvent of paint film causes shrinkage.
The reasons of collapsing
The amount of curing agent added in the primer is not sufficient.
Too much slow-drying solvent is used, or the dissolving capacity of top coat solvent is too large.
The primer is applied too thick at one time and the residual solvent is too much.
The application interval is too short and the primer did not dry completely.
Coating with low solid content is used.
The water content of wood is too high, the shrinkage is too large and the soft wood absorbs too much coating.
In the whole application process, the paint film is too thin.
Countermeasures of collapsing
Apply the top coat after the underlying coat is fully dry, Apply many times to get thick coat and have larger intervals.
Use thinner which can dry faster. No thinner residue shall be in the paint film.
Use power primer to cure the wood, or use more curing agent.
Use PE or UV as primer.
The wood shall be fully dried before application. Use wood with appropriate water content and shrinkage rate (the water content of substrate shall be equivalent to that of local wood).
XIII. Show-through (no-hiding)
It refers to the phenomenon that during solid color coating application, the paint applied on the substrate (whether coated or not) shows the color of the substrate after drying.
The main reason is the covering power of top coat is insufficient or the coat is not thick enough.
The reasons of show-through
1. The content of pigments in the coating is low, causing insufficient covering power.
2. The coating is not fully stirred with pigment.
3. The thinner dries slowly, the paint film has strong fluidity and the coat of edge is too thin.
4. There is holiday during operation.
5. The color of primer is darker while the color of top coat is lighter.
Countermeasure of show-through
1. Use proper coating.
2. Stir fully before application.
3. Rise the coating viscosity or use thinner which dries faster. Increase the thickness of edges.
4. Adopt the application method of "thin application in many times".
5. Operate in a certain order to avoid holiday.
6. The color difference of primer and top coat cannot be too large. The color of primer is better to be lighter.
XIV. Color difference
Color difference refers to the inconsistency between the color of finished application and the color of sample plate.
The main reason is the color difference in different batches of coatings or substrates, or the dye penetration performances of primers are different.
The reasons of color difference
1. There is color difference between different batches of coatings.
2. In transparent application process, the thickness of colorful coat is not the same or the color of substrate is different.
3. The primer bleeds, affecting the color of top coat.
4. The solid color coat floods, the thickness of different coats is different or different application methods are used.
The countermeasures of color difference
1. Use color coating of the same batch in large-scale application or make color test before application.
2. Tinting shall be operated by the same person or enhance tinting operation management.
3. Use coating with good anti-bleeding and flooding performance.
4. Evaluate the color of substrate.
After the matte varnish dries, there is uneven gloss in the shapes of flakes or stripes.
The main reason is poor coating performance or different thickness in application, causing uneven dulling.
The reasons of ghosting
1. The spray gun sprays uneven paint or air.
2. Unskilled application causes uneven spray.
3. Overlapping spray span.
4. The primer paint film is thin or is punched, causing suction trap.
5. The quality of the coating is not good, or using too much slow-drying solvent, causing too small drying speed.
6. The substrate has residual glue.
Countermeasures for ghosting
1. Repair the spray gun to make sure the paint and the air can be sprayed smoothly.
2. Improve application skills and make proper operation.
3. Use thinner which dries faster.
4. Spray enough paint on the substrate and then polish it.
5. Use coating of better quality.
6. Seal the substrate.
7. For paint film with ghosting, polish to make it coarse and apply coating again.
XVI. Color changing and fading
It refers to the phenomenon of color change or fading after color paint film is used for a while.
The main reason is that the pigments or dyestuff has chemical changes after the action of light/heat/chemical substance.
The reasons of color changing and fading
1. The light/heat/chemical product resistance of the pigments or dyestuff is poor.
2. The color of substrate changes.
3. The use environment of the paint film has strong light or high temperature.
4. The weather resistance of the film-forming substance of the coating is poor.
The countermeasures of bleeding color changing and fading
Change coating with better weather resistance.
Improve the use environment of paint film, and avoid strong light, high temperature, acid or base.
Use pigments or dyestuff of better weather resistance.
For paint film with color change or fading, if it is solid color coat, respray can be made; if it is transparent colorful paint, the coat can be polished and respray it again.
XVII. Dissolving out
After each component is added according to the required ratio, flocculate like bean curd jelly appears within pot-life.
The main reason is that the solvent cannot dissolve resin.
The reasons of dissolving out
1. The thinner is not matching.
2. The curing agent is spoiled.
3. The temperature is too high.
4. Coating designed for winter is used in summer.
Countermeasures of dissolving out
1. Use matching thinner or add some powerful solvent.
2. Change fresher curing agent.
3. Use matching coating according to the season.
Bleeding refers to the phenomenon that some coloring materials of primer paint film permeate to the top coat film, changing the color of top coat film.
The main reason is that the coloring materials of the primer film are not migration resistance or the solvent resistance of the coat is insufficient.
The reasons of bleeding
The materials have original color difference or the influence of some darker colors.
Pigments not resistant to migration or stain are used in primer.
The amount of curing agent in the primer is not sufficient; or the primer is single-component coating; or the primer is much darker than the top coat.
Top coating is applied before the primer is fully dried.
The solvent of top coat dries slowly.
The countermeasures of bleeding
For substrate with darker color, use treating agent or special sealer to treat or seal and then make normal application; make pre-production sample test;
Use coloring agent with migration resistance and good stability;
The ratio of curing agent shall be precise; use the matching primer and top coat; the design process use primer and top coat of the same or similar colors, and the color of primer shall be lighter.
The drying time between coats must be enough.
Use thinner which dries faster.
XIX. Sandpaper marks
During the drying process of top coat, there is polishing or other treatment marks of primer surface due to the paint film's shrinkage.
The main reason is insufficient buildiness or top coat or the machining marks of the substrate are too obvious.
The reasons of sandpaper marks
Polish against the direction of wood grain.
The sand paper used for polishing is too coarse;
The paint film is polished before it is fully dried;
The solvent used dries too low, and the paint film cannot dry in a certain period;
The last layer of paint film is too thin;
The film is not cleaned thoroughly after polishing and the paint cannot permeate;
Due to the paint powder on the surface during the use of sand paper, some part loses sanding function and will leave moving marks.
The countermeasures of sandpaper marks
Use the most suitable sand paper. The sand paper used for first polishing will be more coarse and for second polishing, less coarse and the sanding marks on the last layer will be also polished.
Polishing shall be made following the direction of wood grain;
Polishing shall be made after the paint film dries and the paint dust powder shall be removed afterwards;
When a sand paper is used for a while, check if there is paint powder on it and change it;
Adjust the paint viscosity and control the spray thickness of the paint film which shall be enough to cover the sanding marks.