Analysis of the essential characteristics of waterborne industrial coatings!

The essential properties of waterborne industrial coatings

Basic properties of water

Non-combustible, non-toxic, non-polluting Economical, sustainable resources Freezing at 0°C, boiling at 100°C Highly polar, dissolving and dispersing ionic substances Dissolving small amounts of oxygen and other gases Neutral, acidic or alkaline environmental versatility High chemical reactivity, hydrolysis and corrosion Bio-essential.

The nature of water

Two elements, three atoms; The four hybrid orbitals come from the oxygen 2S, 2Px, 2Py and 2Pz atomic orbitals, pointing outward from the oxygen nucleus to the angle of the tetrahedron; asymmetric charge distribution, becoming polar molecules (α=114°29′, β=104°27′); Intermolecular hydrogen bonding, in which the hydrogen nucleus interacts with the lone pair of negative charges of neighboring water molecules, produces a hydrogen bond
with an energy of about one-tenth of the O-H bond of the molecule.

Aqueous solution structure

Liquid water is a highly structured substance coated online coatingol.
com
.
The detailed arrangement of
molecules in liquid water is uncertain.
Based on a hexagonal ice structure, each water molecule is connected
to four adjacent water molecules.
Derived from the structure of ice, some additional molecules occupy the gap space to exchange molecules in the hydrogen bond network, and the average number of adjacent molecules of water molecules increases from 4 in ice to 4.
4 in the liquid freezing point
.
Water is denser than ice
.
Water has one of the highest known dielectric constants, at 25°C at 78
.
The higher the dielectric constant, the lower the energy required to separate the opposite charge, making water an effective solvent for ionic substances
.

Water-based principle of organic resin

Principle of water-based technology: polymer molecules are coated with hydrophilic substances/chemically grafted hydrophilic groups, and (or after neutralization) can be diluted
with water.

External emulsification: add an emulsifier (ionic or non-ionic) to form micelles in the aqueous phase, and polymerize into latex by emulsion; Or add hydrophilic substances, obtained by reverse emulsification
.
Often referred to as an emulsion
.

Self-emulsification: grafting hydrophilic groups (-COOH, -CH2-CH2-O-,-NH2, etc.
) on polymer molecules, which can be diluted
with water (or neutralized).
Often referred to as a dispersion
.

Waterborne resin macro morphology

Macromorphology (emulsions, micro-transparent dispersions, transparent solutions)

Most water-soluble resins are not really soluble in water (except polyvinyl alcohol, cellulose, polyacrylic acid), but after the amine salt solution of the organic solvent is diluted with water, a relatively stable polymer colloidal dispersion solution
is formed.

Micromorphology of waterborne resins

Heterogeneous systems: latex particles, polymer aggregate particles

Free hydrophilic substances, neutralizing agents, co-solvents, etc

Dilution viscosity change of waterborne resin—aqueous dispersion, waterborne resin

There are viscosity peaks during the waterborne resin dilution process

Aqueous dispersions do not have viscosity peaks and vary greatly compared to resin solutions

Water-based resin dilution viscosity change - waterborne resin

The viscosity of waterborne resins is also related
to molecular weight, co-solvent polarity and quantity.

Distribution of solvents in aqueous resins

The solvent is not evenly distributed in the aqueous phase and the polymer phase; Affects system viscosity, particle aggregation into film, moisture volatilization and stability

Waterborne industrial coating drying process

The strong interaction between water and organic solvent volatilization deviates from Raoul's law, relative humidity affects water volatilization, has little effect on solvent, and the heat capacity and heat of vaporization of water are abnormally large (boiling point, butyl acetate (126 °C) volatilizes faster than n-butanol (118 °C)), and the volatilization rate of mixed solvent in the wet stage is controlled by factors such as vapor pressure, surface temperature, relative humidity, air velocity, and surface area to volume ratio
.
It is a one-time relationship
with the thickness of the paint film.
The volatilization rate of the mixed solvent in the dry stage is determined by the diffusion rate of
the solvent molecules.
It is a quadratic relationship
with the thickness of the paint film.

Water-based paint coating film compactness

The film-forming process involves interparticle and intermolecular diffusion

Heterogeneous films (as opposed to solventborne coatings)

Structure and composition of waterborne coating film

Heterogeneous dense coating film; the presence of enrichment zones of different substances; Hydrophilic substances/groups remain partially in the
coating film.

Flash rust concept and evaluation

ISO12944-4 defines flash rusting as 'slight rust formation on a prepared steel surface soon afterpreparation' Translation: Minor rust that forms quickly on the surface of the treated steel

ASTMD 610-85 (1989) Standard Test Method for Evaluating the Degree of Rust on the Surface of Painted Steel

Factors influencing "flash rust" of coatings Waterborne polymer type (important factor) Relative humidity in the film forming process (very important factor) System pH (low importance factor) Metal type (important factor) Metal weld (submerged arc welding) > cast iron > carbon steel

A classic example of waterborne industrial coating applications – electrophoretic coating

Adapt to complex shape parts comprehensive coating, uniform film formation, thin film, high performance, automation
.