Have you solved the delamination problem of water-based coatings?

So what is the cause of the delamination of the paint?

How can we solve this situation?

This is what we are going to discuss today~

Phenomenon classification

First of all, we need to figure out that paint delamination is mainly divided into three different phenomena:

Water separation (synthesis) during paint storage

Emulsion separation during paint storage

Settling during paint storage

01 During the coating storage process-water separation

Symptom:

After the paint is stored for a period of time, a part of transparent light yellow or colorless transparent mucus is separated on the surface of the paint

02 During the coating storage process-separate emulsion

Symptom:

The surface layer of the paint separates a certain amount of liquid, sometimes the liquid has some blue light, in most cases the separated liquid is milky white

03 During coating storage-sedimentation

Symptom

During the storage of the finished paint, the uniformity of the paint changes.

In the above three cases, the separation of water emulsion is usually accompanied by sedimentation

Stratification factors

1 The influence of thickeners

We know that the types of commonly used thickeners are mainly divided into cellulose (HEC), alkali swelling (ASE), hydrophobically modified alkali swelling (HASE) and non-ionic polyurethane (HEUR)

Everyone should be familiar with the principle of thickening.

Cellulose thickeners or common alkali swelling thickeners only thicken the water phase, and their concentrated "thickening network" has nothing to do with the particles of the system, and presents a separate phase

Hydrophobic modified alkali swelling (HASE) and non-ionic polyurethane (HEUR) thickeners.

Cause Analysis

01 Improper matching of hydration-type thickeners and associative thickeners in types and dosages leads to incompatibility and rejection of coatings during storage
.
If the compatibility of the two networks in the system is not good, one is too hydrophobic and the other is too hydrophilic, using such a thickener to match, the water separation phenomenon is difficult to control
.
Usually only the "concentrated network" that thickens the water phase shrinks and dissociates and causes water separation on the surface of the coating
.

02 Cellulose and alkali swelling thickeners can swell only under alkaline conditions (pH>7), so we must pay attention to adjusting the pH of the system
.

Avoid using ammonia as a pH adjuster, because it has poor durability and is easy to volatilize, which will cause the pH to drop, and it will have a certain odor
.
For industrial paints, cellulose and alkali swelling thickeners have a great influence on water resistance.
Therefore, such thickeners should be used as little as possible
.

03 The association between the associative thickener and the emulsion particles is not strong, so that the associated emulsion particles are desorbed and separated during storage, suspended on the surface of the paint, and the paint is divided into emulsion
.

04 If the low-shear viscosity of the coating is too low, it will also cause delamination
.

Everyone should be very familiar with this picture.
For the storage of paint, we must ensure that it has a certain low shear viscosity to effectively prevent its delamination
.

Regarding the choice of thickeners, it is generally to choose several different thickeners to make the coating have suitable high, medium and low shear viscosities.
If necessary, use the anti-settling agent described below
.
Under the premise of stable storage, better workability is guaranteed
.

2 Influence of dispersant

Whether the pigment is well dispersed and stable, whether there is flocculation, etc.
, will affect many properties
.
Pigments and fillers have poor dispersibility, and particles agglomerate into large particles, thereby accelerating sedimentation
.

The influence of different dispersants on anti-settling

The above picture shows the anti-settling effect of mixed and ground color pastes using different dispersants after storage
.
Many people may take it for granted that anti-settling must rely on anti-settling agents.
In fact, this is one-sided
.
If the ground color paste is flocculated, the pigment particles become larger and the specific gravity increases, and it will settle quickly, especially the organic pigments
.
If a suitable dispersant is selected, the anti-settling agent can be omitted or added less
.

Therefore, if sedimentation occurs, consider replacing the dispersant
.
A high molecular weight multi-branched dispersant can be used to adsorb on the surface of the pigment and filler particles to increase its steric hindrance, increase repulsive force, and reduce sedimentation
.

Precautions

The dispersant and the associative thickener are in the same aqueous medium and have competitive adsorption on the surface of the pigment and emulsion particles.
There is a complicated competitive relationship between the two.
Whether their combination is reasonable or not directly affects the performance and performance of the coating.
The problem of stratification
.

3 Choice of anti-settling agent

In many cases, regarding the problem of delamination, everyone still chooses to add anti-settling agents to the paint, that is, to introduce a loose network thixotropic structure into the paint, which can make the pigment and filler particles suspend without agglomeration and prevent the pigment from settling
.
So, how should we choose different types of anti-settling agents?

Types of anti-settling agent

01 Organobentonite

Organobentonite usually does not exist as primary particles, but is generally agglomerates of multiple particles.
Primary particles can be produced through the process of wetting, dispersion and activation to form an efficient thixotropic effect
.
In the polar system, in addition to providing chemical energy to help the organic bentonite disperse, the polar activator makes countless bentonite flakes form a gel structure through the bridging of water molecules, and the hydrocarbon chains on the flake surface are solvated through its stronger solvation.
Ability to thicken the system and produce a thixotropic effect.
Under the action of external force, the structure is destroyed and the viscosity is reduced, while the elimination of external force will restore the original viscosity and structure.

What are the advantages and disadvantages of bentonite anti-settling?

advantage:

Large application range; small addition amount, high efficiency, stable processing performance; good thixotropy performance; low price
.

shortcoming:

It has an impact on gloss, and there will be haze and turbidity in the varnish; poor resistance to strong solvents; poor leveling and anti-sagging effects; due to the need for good dispersion to achieve the best anti-settling effect, Therefore, it is difficult to use for post-addition.
If post-addition is required, it needs to be prepared into a pre-coagulated slurry
.

02 Fumed silica

Fumed silica has the greatest thickening effect in non-polar media
.
Fumed silica is produced by hydrolyzing silicon tetrachloride in a hydrogen-oxygen flame
.
It has a small particle size, a large specific surface area, and has silanol groups on the surface
.
These silanol groups can interact with adjacent fumed silica particles to form hydrogen bonds, and form a thixotropic structure in a three-dimensional space through hydrogen bonding
.

advantage:

It does not need to be activated and can be used directly
.

shortcoming:

Light weight, inconvenient construction; thixotropic effect is not very ideal; used on the top coat affects the gloss and affects the leveling
.

03 Castor oil derivatives

Castor oil derivatives are dispersed and activated in a non-polar solvent, and the swollen long chains are entangled with each other to form a thixotropic structure and play a role in thickening
.
When subjected to shearing force, the winding is pulled apart, the structure is destroyed, and the viscosity will drop; when the shearing force disappears, the winding is re-wound
.
This re-winding process is slow, so the viscosity recovery is slower, allowing a longer flow time to level, and proper adjustment can make the paint still level to a certain extent at a larger sag limit thickness
.

advantage:

The thixotropic performance is relatively good; the leveling property is good; the effect on the gloss is small; the price is lower
.

shortcoming:

It needs to be activated in advance when in use; it is not suitable for strong solvent systems; it is easy to return to coarse
.

04 Polyamide wax

Through the intertwining of macromolecular chains to form a network structure, it has thixotropy.
When sheared, the entangled molecules are pulled apart and the viscosity decreases; when the shearing stops, the macromolecules re-twist and increase the viscosity
.
Because the process of this new winding is relatively slow, the speed of viscosity recovery is also slow, and there is a long time for the wet film to flow and level, but it will not cause the sag to lose control
.

The thixotropic properties of polyamide wax are less dependent on temperature, and still have a good anti-sagging effect when used at higher temperatures.
It is baking type coatings such as amino baking paint, acrylic baking paint, epoxy baking paint and high A very effective rheology modifier in solid coatings, metal coatings, and thick build coatings
.

advantage:

The best thixotropic properties; good leveling and anti-sagging properties; little effect on gloss; not easy to return to roughness
.

shortcoming:

It needs to be activated in advance when used; the price is relatively high
.

In addition to the points described above, there are actually many factors that will affect the delamination of the coating, such as improper selection of surfactants or excessive amounts, types and excessive amounts of co-solvents, the thickness and collocation of powders, and the composition of resins and emulsions.
species, PVC design, and so on
.
I won’t go into details here~

The problem of stratification should be prevention
.
For the new formula system, everyone should do a good job of storage experiment before production~

So, is there any remedy for the layered paint?

For the settled paint, it can be used after stirring evenly by hand or mechanically
.
For agglomeration, first pour out the flowable part, shovel the sediment from the bottom of the container with a spatula, grind it, and then pour the flowing medium back into the original bucket and mix it thoroughly
.
If it is still unable to mix according to this method, there is still dry precipitation, and the paint can only be scrapped or degraded for use
.