Factors affecting the drying speed of water-based paint

The so-called drying is the process of changing from a fluid state to a solid state after the paint film is coated.

One of the biggest differences between water-based paint and oil-based paint is the difference in the drying process.

Whether it is water-based paint or oil-based paint, the drying process is mainly the volatile com" href="">paint of the dispersion medium (water, solvent) com" href="">online coatingol.

For oil-based paint, the volatilization rate is not greatly affected by the environmental temperature and humidity, and the purpose of adjusting the drying speed can be easily achieved by adjusting the fast/slow drying solvent; while the water-based paint is greatly affected by the environmental temperature and humidity, and the dispersion medium is water.

Therefore, the drying speed of water-based paint must consider many factors.

A dry environment

The drying environment is the most important factor influencing the drying of water-based paint.

It is like drying clothes in summer and drying out quickly, while clothes in winter often take a long time to dry.

The influence of humidity on the drying speed of water-based paint is also self-evident.

Temperature and humidity are also interrelated.

Second, the air flow rate on the surface of the paint film

In a windy environment, the paint film can dry faster.

Most of the commonly used drying auxiliary equipment has an exhaust function, but too fast air flow also has an adverse effect on the paint film, especially for thick paint films, which may crack or crust.

Three paint film thickness

The effect of paint film thickness on drying speed is obvious.

In addition, the increase in the thickness of the paint film will also increase the risk of many paint film defects such as cracking, sagging, and shrinking.

Four solvents

Water-based paint is generally not completely solvent-free, and generally contains about 5-10% solvent, which is much less than oil-based paint and water-soluble paint.

The role of the solvent in the water-based paint generally has the functions of dissolving, film forming, and antifreeze.
Solvents and water have different boiling points and volatilization rates, so they will also affect the dryness of water-based paints.

For example, ethanol has a boiling point of 78°C and a very small molecular weight of 46, so it is easy to take away water when it volatilizes, so ethanol is often used as a quick-drying aid when it is added.

Film-forming aids are generally based on alcohol-ether solvents with high boiling points.
The higher the boiling point, the slower the drying speed, the worse the water solubility, and the better the film-forming effect.
In addition, the film-forming aids generally do not greatly affect the volatilization of water, so the film-forming aids mostly affect the actual drying.
And the higher the boiling point, the slower the actual drying speed and the slower the hardness build-up.

Five solids, pigments and fillers

Water-based paint is a paint with water as the dispersion medium.
Water and solvents will leave the paint film during the drying process of the paint film, and the remaining part will form the paint film, that is, the solid part.

Under other conditions unchanged, if the solid content of the paint solution is increased, the drying speed of the paint film will also increase, which is obvious.
On the other hand, increasing the solid content is also conducive to increasing the fullness of the paint film and reducing the number of construction passes.

But the reality is that the market blindly requires low prices, and coating companies have to reduce the solid content, add more water and thickeners to reduce costs, so many properties, including drying speed, are virtually reduced.

Adding pigments and fillers is also a way to increase the solid content.
In addition, the pigments and fillers can absorb a certain amount of water to make the paint film dry faster.

Six additives

The commonly used additives are added in a small amount and have little effect on the surface dryness.
Such as wetting agents, defoamers, leveling agents, bactericides, etc.
, will not affect the drying of the paint film.
But there are also some additives that will have a certain impact, such as thickeners.

Cellulose is a very hydrophilic macromolecule.
It is used in many fields to retain water and thicken.
Therefore, cellulose must have a delaying effect on the drying of water-based coatings.
Fortunately, there are not many applications of cellulose in water-based industrial paints.

Alkali swelling thickeners can increase the viscosity by adsorbing water through the main chain, and will also have a certain impact on the drying speed of the coating.

In addition, after thickening such as cellulose and alkali swelling thickeners, the paint solution exhibits obvious pseudoplasticity, and its fluidity is reduced, resulting in a reduction in the microscopic flow of the paint film up and down, and it is also not conducive to surface drying.
Relatively speaking, polyurethane thickeners have some advantages.

Seven resin itself

The performance difference of the resin itself is also one of the important factors that affect the drying speed.

Summarized briefly:

a.
In the case of the same additive amount of film forming aids, the high Tg resin will dry faster.
However, high Tg resins need to add more film-forming aids to ensure film formation, which is another matter.

b.
Other conditions are the same, the resin with small particle size will dry faster.
One is that the small particle size resin usually has better fluidity and promotes water volatilization; the second is that the small particle size resin has a smaller average molecular distance and is easier to contact each other to form a film.

c.
The one-component type generally dries faster than the two-component type; the two-component emulsion type generally dries faster than the dispersion type.

to sum up

As can be seen from the above, there are various factors influencing the drying speed of water-based paint.
From raw material selection to formulation design, from the use of additives to construction applications, there is a big relationship.

But water-based paint is definitely not drying as fast as possible.
Our ultimate goal is to get a perfect paint film.
Water-based paint drying too fast may cause many disadvantages, such as cracking, orange peel, poor film formation, decreased adhesion, heat rash, hazy hair, etc.
While meeting the performance of the paint film, taking into account the production efficiency is the most important.