What aspects should be paid attention to in the selection of water-based coating additives?

Water-based coating additives are an important component of coating products.
They can improve the production process, improve product performance, improve coating construction performance, and play a very key role in improving and improving the performance of coatings and coating films.
People are paying more and more attention to environmental protection, water-based coatings have begun to develop rapidly, and water-based coating additives have been paid more and more attention by the industry
.
So what aspects should be paid attention to in the selection of additives for water-based coatings? Wetting and dispersing agent Wetting and dispersing agent has both wetting and dispersing effects.
It is often used to solve the problem of difficult pigment dispersion.
It is a surfactant with both lipophilicity and hydrophilicity
.
1.
Wetting phenomenon 1.
Wetting phenomenonWhen the solid and liquid contact, the original solid-gas interface disappears and a new solid-liquid interface is formed.
This phenomenon is called wetting
.
2.
Wetting effect and wetting agent 2.
Wetting effect and wetting agentWhen a liquid is used to wet the pigment filler and make it penetrate into the agglomerates and aggregates of the pigment filler, if a small amount of surfactant is added to the liquid, the wetting and penetration will be easier.
This is the wetting effect
.
Surfactants that wet or accelerate the wetting of pigment fillers are called wetting agents
.
This liquid in water-based paint is water
.
The surface properties of pigments and fillers, the type and amount of wetting and dispersing agents, and the effectiveness of the dispersion equipment are the main factors affecting dispersion
.
The stability or coagulation of the suspension dispersion system of pigments and fillers depends on the force, repulsion and attraction between the particles
.
Repulsion is the main factor of stability, and attraction is the main factor of aggregation
.
Antifoaming agent Antifoaming agent foam is produced.
Under the action of external force, when air enters the liquid containing the surfactant, the surfactant will be arranged directionally at the air-liquid interface
.
The hydrophobic group faces the air with bubbles, and the hydrophilic group faces the water, producing a lot of bubbles
.
The reasons for foaming in the paint are as follows: 1.
The air is entrained into the paint due to mechanical agitation during the paint production; 2.
The air brought in during the paint coating process, such as brushing, roller coating, high pressure and airless spraying
.
3.
For two-component coatings, stir the mixed air when mixing before construction
.
4.
There are many pores in the coated object, and air bubbles are driven out due to the infiltration of the paint, such as when painting on porous wood and cement walls
.
5.
Bubbles produced by chemical reactions, such as the reaction of polyisocyanate in two-component PU coatings with trace water to produce carbon dioxide
.
The foam is inherently unstable, and its breaking has to go through three processes, namely, redistribution of bubbles, thinning of the film thickness and rupture of the film
.
However, for a relatively stable foam system, it takes a long time to go through these three processes to achieve natural defoaming, and most of all production uses defoamers
.
It is generally believed that defoamers reduce the local surface tension of the foam liquid film and defoam
.
Because of the low surface tension of the defoamer itself, it always penetrates into the foam system in the form of particles to locally reduce the surface tension of the foam film
.
Since the liquid with low surface tension always flows to the liquid with high surface tension, the membrane wall gradually becomes thinner and is strongly drawn by the surrounding membrane layer with high surface tension, resulting in an imbalance of stress and finally causing the bubble to burst
.
Currently, there are three general types of defoamers: mineral oil defoamers, silicone defoamers, and silicone-free polymer defoamers
.
Choice of defoamerChoice of defoamerThe choice of defoamer, there are many factors in the coating formulation that have an impact on foaming and foam stabilization
.
1.
Surface tension 1.
Surface tensionThe surface tension of the coating has a greater impact on the defoamer.
The surface tension of the defoamer must be lower than the surface tension of the coating, otherwise it will not have the effect of defoaming and foam suppression
.
The surface tension of the coating is a variable factor, so when choosing a defoamer, the surface tension should be constant, and then the surface tension factor should be taken into account
.
2.
The influence of other additives 2.
The influence of other additivesMost of the surfactants used in coatings tend to be functionally incompatible with defoamers
.
Especially emulsifiers, wetting and dispersing agents, leveling agents, thickeners, etc.
will affect the effect of defoamers
.
Therefore, when using various additives together, we must pay attention to the relationship between different additives and choose the best balance point
.
3.
Baking temperature 3.
Baking temperatureWhen the coating enters high-temperature baking at room temperature, the viscosity will decrease at the beginning and the bubbles can move to the surface.
However, due to the volatilization of the solvent, the curing of the coating, and the increase of the surface viscosity, the bubble film will become more stable, and it will shrink when left on the surface.
Holes and pinholes, so the baking temperature, curing speed, and solvent volatilization rate also have an impact on the effect of the defoamer
.
4.
The solid content, viscosity, and elasticity of the coating 4.
The solid content, viscosity, and elasticity of the coatingHigh solids and thick coatings, high viscosity, and high elasticity coatings are very difficult to defoam.
In these coatings, the defoaming agent is difficult to diffuse, the microbubbles become large and the foam speed is slow, the migration ability of the foam to the surface decreases, and the foam film has high viscoelasticity.
There are many unfavorable defoaming factors
.
The foam in these coatings is quite difficult to eliminate, it is best to use defoamers and defoamers together
.
5.
Coating method and construction temperature 5.
Coating method and construction temperatureThere are many coating methods, such as brush coating, roller coating, curtain coating, blade coating, high-pressure airless spraying, screen printing and so on
.
The degree of blistering of different coatings varies with the coating method used
.
Brushing and roller coating have more foam than spraying and scraping.
The most foamy is the screen printing of ink, and it is not easy to eliminate
.
When the temperature is high, there will be more foam than when the temperature is low, but when the temperature is high, the foam is easier to eliminate than when the temperature is low
.
Use of defoamer Use of defoamer1.
It must be fully stirred before use, and mixed evenly
.
2.
Add defoamer while the paint is stirring
.
3.
Before use, there is generally no need to dilute with water and can be added directly
.
If some varieties need to be diluted, they need to be used together
.
4.
The dosage should be appropriate
.
Too much amount will cause shrinkage, shrinkage, poor brushability and poor recoatability, etc.
If the amount is too small, the defoaming effect will be poor
.
The best point should be determined
.
5.
It is best to add in two times, namely before grinding the pigment paste and adding after adding the emulsion paint
.
Generally, the addition amount is half of the total amount each time, and it can also be adjusted according to the foam condition
.
A defoamer with good foam suppression effect can be used in the phase of grinding the pigment paste, and a defoamer with good foam breaking effect can be used in the paint mixing stage
.
Experiments have shown that it is best to add silicone defoamer at the stage of grinding the pigment slurry, and add as little water as possible, so that it can be fully dispersed and the amount can be reduced to a minimum
.
It is advisable to add a non-silicon defoamer in the paint mixing stage
.
6.
After adding the defoamer, it takes at least 24 hours to reach the balance between defoaming performance and shrinkage and shrinkage
.
Therefore, the coating performance test must be carried out after 24 hours
.