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First, the principle of dispersant
Most dispersants are used to disperse fillers through a process of wetting, grinding, dispersing, coupling and wrapping stabilization
.
In water-based coatings, due to cost control reasons, more expensive dispersants
cannot be used.
Most of the wetting and dispersing agents
on the market are anionic and non-ionic.
Their principle is to use low surface tension to quickly wet the pigment particles, and then through high shear forces, such as dispersing machines, grinding machines, etc.
, the pigment particles form a semi-flocculent (or controlled flocculation) dispersion
.
If the viscosity of the paint is relatively high at this time, there will be no phenomenon of pigment back-coarse and serious flocculation, but if the viscosity is not well controlled, over time, there will be problems; Some use coupling agents as dispersants to couple two different substances together
through their hydrophilic groups and sulfur water groups.
Like bridging, the advantages of this are: good comprehensive performance, good dispersion, less dosage, and can increase the adhesion of the coating, but the disadvantage is that it is not a deflocculation group, which is not suitable
for coatings with high requirements for color spread.
Second, the classification of water-based dispersants
There are many kinds of dispersants, and preliminary estimates show that there are more than 1,000 substances in the world that have a dispersive effect
.
Now according to its structure, it can be divided into:
(1) anionic type, (2) cationic type, (3) non-ionic type, (4) amphoteric type, (5) electroneutral type, (6) polymer type (including high, medium and low molecular weight) superdispersant
.
(1) Anionic surfactants: most of them are composed
of non-polar negatively charged lipophilic hydrocarbon chain parts and polar hydrophilic groups.
The two groups are at opposite ends of the molecule, forming an asymmetric hydrophilic and lipophilic molecular structure
.
Its varieties are; Sodium oleate, carboxylate, sulfate (R-O-SO3Na), sulfonate (R-SO3Na), etc
.
Anionic dispersants have good compatibility and are widely used
.
(2) Cionic type: It is a compound
with a positive charge of a non-polar base.
The variety has octadecenylamine acetate
.
Alkyl quaternary ammonium salt, aminopropylamine dioleate, quaternary amine salt, specially modified polyaminoamide phosphate, etc
.
The cationic surfactant has strong adsorption force and has a good dispersion effect on carbon black, various iron oxides and organic pigments, but it should be noted that it has a chemical reaction with the carboxyl group in the base material, and it should also be paid attention not to be used at the same time with the anionic dispersant, and the use should be cautious.
(3) Non-ionic type: can not be ionized, without charge
.
The adsorption on the surface of the pigment is relatively weak, and it is mainly used
in aqueous coatings.
The varieties include the adduct C17H33COO (CH2 CH2O)nH of the fatty acid ethylene oxide, polyethylene glycol polyol and polyethyleneimine derivative
.
Their role is to reduce surface tension and improve wettability
.
If you add some silicone oxanes, you can prevent flowering, floating color and improve the effect of
leveling.
(4) Amphoteric: It is a compound
composed of anions and cations.
Typical applications are phosphate-based polymers
.
These polymers have a high acid value and affect interlayer adhesion
.
It should be noted
.
(5) Electro-neutral type: the size of the anion and cationic organic group in the molecule is basically equal, and the whole molecule is neutral but polar.
Varieties: oleamyl oleate
(6) Polymer type (including high, medium and low molecular weight).
Among them, the more high-grade and stable is the polymer type
.
For example: a.
polyol-polyethyleneimine block copolymer, b.
dochongolide and triethylenetetramine's reactant, c.
polymerization with group transfer, first add methacrylate, and then add acrylate polymer made of glyceryl methacrylate
.
d.
Low molecular weight polyester prepared by polyhydroxystearic acid, various polyurethanes and polyacrylates
prepared by introducing anchor groups.
And so on, because their anchor groups are wound with resin at one end and adsorbed with pigment particles at the other
.
Therefore, the storage stability is better, of course, we should also pay attention not to use too strong solvents, because too strong solvents in the case of high shear force, will dissolve the anchor chain of these polymer superdispersants, and then cause the pigment to return to rough flocculation
.
III.
Recommendations
Through research and practice, it is recommended that you use some polymer types in water-based coatings with dispersants for deflocculation
.
Because the advantages of this are: good color exhibition, high brightness and good gloss of the color filler, it is also recommended that you try to use some thickeners that do not affect the gloss and will not thicken after when using thickeners
.
However, in pure emulsion systems, we recommend a dispersant
that enhances charge repulsion.
Such as electroneutral amine salts, polycarboxylate dispersants
.
Now there are some surfactants on the market that have been equipped with polyols, its wettability and penetration are very strong, you can try
.
Source: Chinese and foreign coatings
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.
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.
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