Problems and Countermeasures of Bicycle Coating

Analysis: If the water-based bicycle coating needs electrostatic coating, it is necessary to install a water-oil general feeding system to replace the previous oil-based special feeding system.
No need to replace other parts such as nozzles, which can save the cost of modification:

Figure 1.
Water and oil universal feeding system

Figure 1.
Water and oil universal feeding system

Precautions during use: After the paint is diluted, the paint bucket must be placed on the plane of the red dot in Figure 1 during use, otherwise it will not function as insulation and electrostatic spraying will not achieve the desired effect.
The other setting parameters of the equipment are basically the same as the oiliness, and most do not need to be changed.

2.
Questions and answers about water-based paint coating:

(1) Waterborne spraying is easy to sag, how to solve it?

Analysis: The volatilization speed of water is slower than that of solvents (ethyl acetate, methyl ethyl ketone, etc.
), so the same spraying parameters such as spraying viscosity will have different spraying effects, so we need to increase the spraying viscosity to prevent sagging problems.
, At present, the electrostatic spraying viscosity of oil-based paint is about 12~13s (NK2#), and manual spraying is 13~14s (NK2#).
The spray viscosity of water-based paint is 25~30s (NK2#), or even higher.
Some people may ask such questions: Will the leveling of water-based paint spray so high (compared to oil-based paint)? Here, we have an in-depth discussion on this issue: the key to thinning and spraying of oil-based paint is that it evaporates quickly, and the open time of the paint film is very short.
If the viscosity is adjusted to a thicker point, it will cause appearance defects such as orange peel; while water-based paint is more volatile than oily The paint is slow, so the paint film of the water-based paint has a longer openness.
Even if it enters the high-temperature oven, it also has sufficient leveling time.
Therefore, the high spraying viscosity of the water-based paint will not cause orange peel and other phenomena, but sometimes it is more Oil-based paint has better leveling properties.
As for other factors that cause sagging: such as thick painting, excessive air pressure, uneven painting, spraying distance, etc.
, we will not discuss them here, because these factors also have the same effect on oil-based paint, and we will not discuss them here.

(2) Water-based paint is easy to foam:

Analysis: The phenomenon of blistering is a problem that we cannot avoid when using water-based paint.
The dispersion medium of water-based paint is mainly composed of water, and there is a certain amount of hydrophilic slow-drying solvent such as BCS as the cosolvent of the resin, so the water-based paint is overall The volatilization speed is slow.
If the sprayed element enters the high-temperature furnace, it will indeed cause the water to bump, and then produce many pits, resulting in defective products.
The oil-based paint is basically fast-drying solvent as the main solvent, and then matched with some medium and high boiling point solvents to form a good volatilization gradient.
After the spraying is completed, the solvent is basically volatilized in a short time, and there is almost no solvent residue.
, So there will be no obvious blistering in high-temperature baking.

Then the water-based solvent must be water as the main solvent, is there no way to overcome this problem? No.
There is also a way to break through it: since water as the main solvent is something we cannot change, we need to choose a water-based resin with good wettability before designing the coating formula, and the resin with good wettability can be well balanced.
The foaming tendency helps the bubbles to overflow quickly.
The high molecular weight water-based polyester produced by Southern Resin has this function; it can also be improved by adding a certain amount of high boiling point solvent in the formulation or during the paint mixing process: but adding a high boiling point solvent Before, we need to understand the temperature of baking and the length of time to make the best choice.
For example, many bicycle coating lines operate at 140℃*20~30min, then we need to prevent water-based paint from foaming, we can add a certain amount of BCS (boiling point 171℃) to suppress the bumping of water at 100℃; if When we are working under the condition of 180℃*5min, if we still use BCS to adjust the foaming of the system, it is not very suitable.
We should use DBCS (boiling point 230℃) to adjust, the principle is the same as before, here No longer discuss.

The baking temperature of bicycle spraying line is basically in the range of 120~180℃.
We can choose different slow-drying solvents to adjust according to different operating conditions.
The two hydrophilic slow-drying solvents introduced above can basically adjust the foaming of water-based paint.
problem.
Finally, it should be noted that the addition amount of slow-drying solvent is about 3~5%, which will not ultimately affect the VOC content.
You can rest assured to use this method.

(3) Is the spraying efficiency of water-based paint worse than that of oil-based paint?

Analysis: Oil-based paint has low viscosity.
The atomization is excellent, and the viscosity of water-based paint is higher than that of oil-based paint.
Will it affect the atomization and cause less paint discharge? This problem will directly affect the production efficiency.
Here we will answer your questions: water-based paint has high coating viscosity, but the spraying air pressure and flow rate are also larger than those of oil-based paint, so from the point of view of paint discharge, it is not less than oil-based paint.
Because of the high viscosity of water-based paint and high solid content of the coating, when the same film thickness is sprayed on the plain parts, the number of spraying times of water-based paint is less than that of oil-based paint, because the viscosity of oil-based paint is thin, the open-thin ratio is large, and the working solid content is small cause.
From a comprehensive analysis, we can draw the following conclusions: oil-based paints are thinner than water-based paints (the difference is very small), while water-based paints have high viscosity and high painting efficiency.
From the perspective of production efficiency, water-based paints and oil-based paints can be considered It is basically equivalent, even more efficient than oil-based paint.

(4) Does water-based paint require harsh operating conditions?

Analysis: The production process and raw materials of water-based paint are basically similar to those of oil-based paint, and even the amino curing agents used are the same, such as 325, 303, etc.
The difference is that the resin, additives and color paste are hydrophilic materials.
Therefore, from the perspective of baking conditions, due to the use of the same curing agent, the water-based paint can achieve the same baking temperature and time as the oil-based paint, and there is no need to increase the temperature and extend the baking time.
Our craftsmanship is also developed from the customer's point of view, and does not increase the customer's burden.

(5) Is the cost of using water-based paint high?

Analysis: On the whole, the unit price of water-based paint is a bit more expensive or the same as oil-based paint.
However, it is not a small expense to dilute oil-based paint with solvent; while water-based paint can be dilute with tap water, and there is almost no diluting cost.
Therefore, even if the dilution cost is taken into account, although the water-based paint is a bit inferior to the paint in the dilution ratio, the overall coating cost is almost the same as the oil-based paint, and even cheaper than the oil-based paint.
The comparison of spraying efficiency of water paint and paint has been introduced above, and combined with the cost of paint dilution, it can be said that the cost of water paint is the same as that of oil paint, or even lower.
Therefore, customers who are currently waiting for transformation do not need to worry too much about the increase in costs after using water-based paint.

Other construction ills:

Analysis: Other coating defects such as shrinkage, orange peel, pinholes, and floating colors are basically the same as oil-based paint: surface pollution, air compressor or gas pipeline oil or water, surface tension, etc.
This will not be discussed one by one.

to sum up

After years of technological development, especially the exploration and improvement of construction technology, water-based paint has caught up with oil-based paint in terms of performance and ease of construction, and the use efficiency and cost are even better than oil-based paint; The modification of the equipment is also a very small part of the modification.
If the DISK coating is used, the water-based universal feeding system can be installed, and other places do not need to be modified; if it is traditional high-pressure gas spraying, no modification is required.
The most important thing is the equipment.
The modification and debugging can be completed in a very short time without delaying the production of the guests.
Therefore, in the case of extremely low performance, cost, construction, equipment modification, etc.
, we should realize the transformation of water-based as soon as possible.
(Source: Global Coatings Network) (For more information, please log in: Global Coatings Network http:// )