As painting quality becomes more stringent, faulty HAJIKI (cissing) and BUTSU (particle)are two major problems that have been difficult to solve since the painting began. This page is to introduce some of these two failure cases, together with some of the factors involved, and our products to suppress these failures.
- Example of a HAJIKI (cissing)
- Example of a BUTSU (particles)
|Product name||General name||Cissing||Particles||Feature|
|DUSTORON||Water-soluble gel coating agent||-||○||・ Apply to walls, nets, robotic suits, etc. to collect dust and worms.|
|SUKKILIN||Electrostatic clothes cleaning agents used in painting operations||-||○||・ Clean and remove paint without damaging the fibers of electrostatic clothes.|
|STRIAL||Removing agent for paint coat on painting jigs||-||○||・Remover for cured coating film of the coating jig|
|POLYCERAGUARD AG||Pre-coating agent for painting jigs||-||○||・ Prevent rust and residual paint particle from scattering by coating paint jig after removing paint film.
・ Paint removal time can be shortened by the effect of pre-coating film.
|POLYCERAGUARD M||Remover for gratings||-||○||・ Pre-coating agent for making remove paint adhering to gratings in paint booth easy.|
|PLACLEAN||Cleaning agent for resin molded products by hand wiping.||○||○||・ Remove dirt such as mold release agent to reduce HAJIKI (cissing).
・ Reducing the amount of electrostatic after wiping and BUTSU (particles).
|SL-Series||Paint pipe cleaning agent||-||○||・ Reduce defective BUTSU (particles) by removing paint that could not be removed by cleaning thinners.
・ For periodic maintenance of bell cups, paint piping, etc.
|Thinner||Cleaning of paint and degreasing||○||○||・ Wide line-up from those used in color change to those used for retarding two-component urethane paints.|
Example of a HAJIKI (cissing)
HAJIKI (cissing) is a phenomenon in which a flowable paint comes into contact with a factor substance having a lower surface tension than that of the paint, and the factor substance spreads by being pulled by the paint, and the film thickness of the part becomes thinner.
This phenomenon is similar to HAJIKI (cissing), uncured paint mist falls on the paint film and dissolves by the thinner in the paint film, causing the paint on the surface of the paint film to dissolve while being displaced.
Case 1) Mold release agent for resin molded products and its removal process
In general, when painting injection-molded products made of resin, the condensing substances of the external mold releasing agent sprayed on during molding and the internal mold releasing agent contained in the resin pellet can be cited as the causative substances.
Paintable mold release agents are usually used as external mold release agents if it is going to be painted later.
The internal mold releasing agent is blended in advance with antistatic agents used for countermeasures against static electricity in the pellet so that the external mold releasing agent does not need to be used. These mold releasing agents do not generate HAJIKI (cissing) if they are sufficiently thinner and smaller than the thickness of the paint film, but they generate HAJIKI (cissing) if they are condensed into large aggregates.
1. Example of HAJIKI (cissing) at complicated shapes and edges of injection molded products.
When an external mold releasing agent is used in injection molding process, a large amount of mold releasing agent is often applied more carefully to complicated shape parts and edge parts than to flat parts in order to improve mold separation.
In addition, even if the mold is released using an internal mold releasing agent, a small amount of external mold releasing agent may be applied to the part where the mold release is poor only in the initial stage because the mold releasability is inferior in the startup of the injection molding machine or after cleaning of the mold.
These initial startup products and stored molded products may be splashed with external release agent mist, resulting in an error. It is recommended to check not only the painting process but also the injection molding process and storage process.
2. Example of HAJIKI (cissing) caused by cleaning of molded products.
In order to remove dirt, dust, etc. adhering to the surface of resin injection molded products, when the surface of molded products is wiped and cleaned by cloth, sponge, etc. with IPA (isopropanol) or a wiping agent (thinner mixture), HAJIKI (cissing) like splash and stripe may appear on flat surface.
The spots where the splash HAJIKI (cissing) occurs coincide with the spots where the operator applied the cloth to the molded article and the spots where the cloth was stopped. In both of these areas, the wiping agent remains in like splash, and the dirt component is condensed more than in other areas, which makes it easier for the wiping agent to generate HAJIKI (cissing).
Multiple stripe HAJIKI (cissing) often appear on a flat surface. This is because too much wiping agent is infiltrated in the cloth, and the wiping agent dries with wiping stripes.
As described above, when the internal mold releasing agent and antistatic agent are kneaded in the resin in advance and the wiping agent remains on the resin surface without drying for a long time, these additives are extracted into the wiping agent, and are condensed together with drying to form HAJIKI (cissing) substances.
The cloth after infiltrating with the wiping agent must be squeezed hard, and cleaning must be performed without stopping the cloth on the surface of the molded article.
The wiping agent should be designed to spread easily and dry uniformly. Wiping agents should be reviewed if they do not spread and dry in splash state, leaving a watermark.
In addition, it is necessary to frequently replace the wiping agent so that the dirt concentration in the wiping agent does not become too high. Note that when using IPA in high humidity or when water is mixed into it by 15% or more (condensation water due to latent heat of evaporation), water remains when drying, and may be visually recognized as a watermark after coating and drying the paint.
For wiping cloths, the material, shape, and knitting of the fibers are also important, and should be selected after confirming the compatibility with the cleaning agent.
If the clothes in the molding department and the painting department are washed in the same washing machine and dryer, the mold release agent in the molding department may adhere to the clothes in the painting department.
Case 2) Surrounding environment
In the vicinity of the painting environment, there are many substances that are used without knowing that they contain HAJIKI (cissing) substances and that have an impact on paint quality.
Silicone, a well-known causative substance of HAJIKI (cissing) in painting, is used in various products such as shoe-polishing creams, glass cleaners, anti-foaming agents, car waxes, heat-resistant greases, and edible oils. It is necessary to take countermeasures with understanding the use of silicone in these products.
1. HAJIKI (cissing) that occurs frequently right after the start of work or after a break time
If the following silicone remains attached to the body at the start of painting work, it may cause a HAJIKI (cissing) problem.
|Silicone in wax||Car waxing|
|Silicone in shoe polish cream||Leather shoe polishing|
|Silicone to improve combing||Hair styling|
|Silicone on the printing surface||Reading of magazines and flyers|
|Silicone in a glass cleaner||Cleaning offices and booth|
3. Example of HAJIKI (cissing) caused by wind
There is HAJIKI (cissing) that occurs only when direction of the wind is toward the painting site with gentle breeze, and it is not raining.
|Silicone for defoaming in frying oil||SEdible oils for frying in cafeterias and cooking rooms|
|Silicone in defoaming agent||Defoaming agent used for defoaming the cooling tower|
|Phenyl-silicone||Heat-resistant lubricating oil and grease used in high-temperature drying ovens and baking ovens.|
|Phenylsilicone used for heat-resistant lubrication||Waste oil heater|
|Silicone in the mold release agent||Aluminum die casting plant|
|Silicone for improving combing in hair-shaping spraying||Rest rooms and lavatories|
Reference: "Do not use hair-styling sprays in the vicinity of the oil fan heater" is because the silicone contained in the hair-styling agent burns and affects the flame sensor. It is also advisable to investigate the positional relationship between the location where these troubles occur and the air intake to the painting booth.
Case 3) Using paints of different manufacture
et-on-wet paints are designed to lower the surface tension from undercoating to overcoating, and to spread paints to be painted later better. The topcoat has the lowest surface tension.
he design differs among paint manufacturers and even with the same topcoat, there is a difference in surface tension between manufacturers.
1. Example of HAJIKI (cissing) in case of painting paints from different manufacturers in the same paint booth.
In the case of simultaneous painting in the same painting booth using paint from Company A and Company B, paint mist may splash on the painting surface of other manufacturers due to turbulence of air flow caused by poor maintenance of the painting booth.
The generation of HAJIKI (cissing) is limited to on paints which has higher surface tension between company A and B. Semi-dried mist that has adhered to paint booth walls, robots, hoses, etc. may splash on the products and cause the same HAJIKI (cissing).
Instead of asking paint manufacturers for improvements, the maintenance for air flow and simultaneous painting of the paint booth should be reviewed.
2. Example of HAJIKI (cising) in which any paint of undercoating, intermediate coating, or top coating is replaced with paint of another manufacturer
As described above, paint manufacturers design lower surface tensions in the order of undercoating, intermediate coating, and top coating. When one of the undercoating and intermediate coating is replaced with the paint of another paint manufacturer, the paint film coated thereon may generate HAJIKI (cissing). (Due to the fact that the surface tension did not become low in the order of undercoating, intermediate coating, and top coating)
3. Example of HAJIKI (cissing) caused by inadequate cleaning of tools such as can-cutter.
If a paint can is opened using a tool such as a can cutter and the paint adhered to the can cutter is used in another paint can without washing off the paint, paint with low surface tension may mix with paint with high surface tension, causing HAJIKI (cissing). Failure to wash the funnel may also cause HAJIKI (cissing).
4) Example of HAJIKI (cissing) caused by non-compliance with paint and equipment adjustments
1. Case of HAJIKI (cissing) after passing through the preheat zone and cooling zone in wet-on-wet painting of water-based paint
A film-forming assistant (a solvent that is difficult to dissolve in water) is added to water-based paints (emulsion paints). This component vaporizes in the preheat zone, condenses in the cooling section of the heat exchanger in the cooling zone, and droplets are scattered by the wind and adhere to the coating material. As a result, HAJIKI (cissing) is appeared on the paint film that is subsequently painted.
2. Case of HAJIKI (cissing) caused from painting of general paints at painting facilities with a track record of Silicone- and fluoro- based paints.
In general, silicone paints and fluorine paints have low surface tension, and the mist of uncured paint is also a causative substance for HAJIKI (cissing). It is advisable that these paints should be used in the exclusive line.
1. Case of HAJIKI (cissing) due to the addition of large quantities of antifoaming agent for paint booths at a time
It is important that the antifoaming agent should be charged devidedly in small amount and not added further if the foam disappears.
2. Case of HAJIKI (cissing) arising from containers for storage and transport of parts for painting
When transportation box filled with flyers not to move parts, HAJIKI (cissing) might occur on the parts where the flyers touch.
3. Case of HAJIKI (cissing) in which SUS nets used for paint filtration were used without cleaning.
The SUS mesh is knitted with lubricant applied so that the SUS thin wire is slipped in the knitting process. Therefore, such lubricants must be cleaned and removed with a thinner or the like.
References: Methods for checking HAJIKI (cissing)
In identifying the causative substances of HAJIKI (cissing), it is necessary to distinguish which paint has lower surface tension. This section introduces how to distinguish HAJIKI (cissing) when evaluating liquid states and fine mist states.
1. Judgment of surface tension when sample is liquid
Apply a given amount of each liquid on the plate to a diameter of about 10mm, using a glass tube, onto a clean SUS plate so that two droplets are in contact with each other. (Plastic spots must not be used to make droplets.)
As shown in the figure, a liquid with a low surface tension is pulled to a liquid with a high surface tension. (In the figure, gray liquid is considered to have low surface tension and white have high surface tension, and gray liquid is considered to be a prone to make HAJIKI (cissing).)
2. Judgment of surface tension when sample is fine mist.
Apply black or silver metallic raw paint on a clean plate about 30 cm square, immediately transfer it into the HAJIKI (cissing) atmosphere, and observe the paint film for several minutes depending on the frequency of HAJIKI occurence. (Silver-metallic raw paint is the easiest color to check HAJIKI (cissing) and black paint is easy to check particles.)
If HAJIKI (cissing) appears on the surface of the paint film, it is judged that the causative substance is suspended.
When it is desired to investigate where the HAJIKI (cissing) substance is generated, this plate can be used to determine whether the HAJIKI (cissing) substance is generated when it is installed in a suspect place. In addition, it can be determined whether or not improvement has been achieved after the countermeasures have been taken.
Instead of observing the plate after collecting it after a certain period of time after leaving it, observe the surface immediately after applying the paint in situ for several minutes.
3. How to distinguish between HAJIKI and particles (concave and convex)
In some cases, it is difficult to distinguish HAJIKI from particles if HAJIKI is very small.
When a metallic spoon is illuminated with a rod-shaped fluorescent lamp, and the spoon is fixed, and the eye is moved up and down. When the eye is lowered, the illuminated rod-shaped fluorescent lamp moves forward when there is convex part, and when there is concave parts, it moves away.
Understanding this phenomenon and moving up and down the eyes under illumination make it possible to judge whether it is a HAJIKI or a particles.
Example of a BUTSU (particles)
Defects due to particles tend to be more serious due to paint-induced particles, dust, fiber scraps, insects, other minute materials and also due to electrostatic adsorption due to static electricity. Therefore, it is necessary to grasp and observe the conditions of the surrounding environment in order to solve these problems.
Case 1) paint and paint can
- Inclusion of dust deposited on the top plate of the paint can into the paint.
- The top plate of the paint can was released with a can-cutter, and an agitator blade scraped the inner wall of the paint can.
- The required amount was taken from the hardener can of the two-component urethane paint and some of the hardener cured in the can because the lid was closed without purging nitrogen.
Case 2) Compounding tanks and their surrounding facilities
- Water condensed in a local exhaust duct connected to a paint supply tank for preparing a two-component urethane paint mixed into the supply tank and reacted with a curing agent (isocyanate) to form particles.
- The coagulated paint remaining on the mesh was dropped and mixed when the paint filtration mesh was replaced.
Case 3) Paint supply route
- Paint is deposited and cured on the dead space between the ball of the ball valve and the housing in the paint piping. (Selection of a valve without dead space or cleaning in a valve half-open state is recommended)
- Potential difference caused by different metal bonding occurred at the joint part of brass ball valve and the stainless steel piping, and water-based paint agglomerated.
- Paint sedimentation are generated in the piping due to long-term use without cleaning of the paint supply piping. If cleaning is insufficient even after cleaning of the paint piping, the deposited paint particles fall off and discharge. It is necessary to continue thorough cleaning of long-standing deposited paints over several days using powerful paint piping cleaners.
- Paint sedimentation are generated in the dead space (near the entrance and exit) inside the diaphragm pump for feeding paint.
- The water-based paint was washed with water after high-pressure air extrusion, but the water-based paint was not redissolved in water after drying. Brush using water-based paint is immersed in water immediately, and can be reused well by repeating leaving for ten minutes and washing with water."
- At the static mixer for two-part urethane paint, gels and particles are always generated. (Observation)
Case 4) Painting booths and their surrounding environment
- The spray air used to remove dust causes the resin parts to take more static, resulting in electrostatic adsorption of dust.
- Humidity in the painting booth was not controlled. Painting was carried out under a low humidity atmosphere, and dust was electrostatically adsorbed.
- The dust accumulated on the electrode of the static electricity removal device came off.
- Particles of paint adhering to the top plate of the painting booth drops off due to the howling (periodic vibration) of the painting booth.
- Powdery paint was scattered by the wind blown off toward the gratings and painting jigs, on which paint that easily pulverized adhered and accumulated.
- Dust deposited between the door and the door frame used to enter and exit the paint booth came off.
- The BOX tissue and roll paper were brought into the paint booth and paint preparation room. (Nonwoven fabric with dustproof cut surface is good.)
- Painting with reduced capacity of the exhaust fan in order to suppress foaming of painting booth water, painting mist during painting scattered through the booth.
- The amount of air supplied to the painting booth was small. When the door of the building was opened, dust in the room and from the outside scattered toward the painting booth.
- Mosquitoes that occur in a pool of water, such as a gutter. (Pesticides that prevent flies and mosquitoes from emerging from maggots to feathers are on the market.)
- The insects gathered in the street lighting around the painting room. (It is necessary to use UV cut lighting and UV lighting separately.)
- The electrostatic clothes were dried outdoors in the sun or washed and dried together with the gloves. Therefore, the electrostatic clothes were covered with waste thread and dust.
Reference: Static electricity
An antistatic agent or the like is kneaded in the resin pellets for molding, and the resin pellets are designed so that static electricity is hardly charged when the resin pellets are handled in a molding machine or the like.
Further, carbon, acetylene black, or the like may be kneaded so that the molded article is not charged.
An electrification series is shown as an index of the likelihood of electrostatic charge.
Under an environment of about 60% humidity or less, most resins are charged (-) by friction with air.
The cloth and the resin are charged to (+) or (-) depending on the electrification series of each material.
When a resin workpiece having an electrostatic pressure of several kilovolts in the air is placed on an object, the electrostatic pressure decreases to a level close to 0V. A few kV is shown when it is again located in the air. The electric lines of force when the workpiece is in the air are directed in all directions. However, on the object, because the electric lines of force are directed toward the object, the amount of charge is apparently low, and the amount of charge does not change unless the workpiece is neutralized. That is, when the resin workpiece is supported by a metal rod-shaped jig or the like, the electrostatic pressure on the surface of the workpiece is high, and if the static electricity is not removed by the static electricity removing air or the like, the dust or the like is electrostatically adsorbed. On the other hand, when the workpiece is supported by a planar jig, the workpiece becomes to take high electrostatic pressure immediately after the work is removed from the jig, and dust and the like are electrostatically adsorbed. Pay attention when transferring a workpiece from a jig for wiping to that of painting.
It is strongly recommended that you be aware of humidity in winter and that you use an electrostatic potential meter to monitor the charging condition and take measures against static electricity.