Analysis of the cause of foaming of the coating

Here said "foaming", different from "bubbles", refers to the construction of normal, paint film after a period of time bubble phenomenon.
, foaming form
1, according to the bubble medium classification
(1) the presence of liquid (wet foam)
(2) the presence of air / gas (dry foam)
(3) the presence of crystals (3) Wet and dry first
2, space classification of foaming (1)
between coating and substrate (2)
between coating and coating(3)


environmental classification (1)
humidity/atmospheric environment
(2) impregnated environment (3)
dry atmosphere environment
in a single coating(4)
the water surface
(5) corner(6)
pick-up or wetting
2, foaming cause analysis
1. Moisture-absorbing substances or moisture residues
These substances include soluble pigments in the coating under (1)
; Because these primers usually contain active (reactive) pigments and are only part of the protective coating system, they must be coated to effectively isolate the environment
.(2)
soluble salts on the substrate or coating surface, mostly caused by abrasives and environmental pollution. Zinc-rich primers also produce soluble zinc salts when exposed.(3)
other moisture-absorbing substances may include corrosion inhibitors/rust inhibitors, inappropriate surface treatment agents or cleaning agents, etc.(4)
with water, ice and surface dew on the surface.
due to the presence of moisture-absorbing substances, water vapor through the paint film, the formation of a relatively concentrated solution inside, resulting in the osmosis pressure-guided foaming, the typical characteristics of this bubble is that there is liquid inside.
2, surface impurities
these surface impurities, in addition to the soluble salts mentioned above may cause oozing foaming, but also include surface oil, dust, paraffin and other non-absorbent substances, the presence of these substances will lead to the production of weak parts of the coating, moisture will penetrate into the coating low adhesion and foaming.
3, inappropriate matching
including:
(1) inappropriate workshop primer (2)
coating containing corrosion inhibitors for the non-applicable environment (3)
hydrogen corrosion occurred
NACE, IMO and other relevant organizations have a full understanding of this, therefore, in PSPC and other relevant standards, it is recommended to use corrosion inhibitors for environmental impregnation. The corrosion inhibitor is translated from the English word "Inhibitor, corrosioninhibitors". It is not a single-finger additive, it covers the "cathode protection, shielding and corrosion" in the three anti-rust principles, to corrosion-proofing as the anti-rust agent of the paint material.
4, cathode protection is not compatible
cathode protection is too much or the coating is resistant to cathode peeling performance is poor, the steel plate produces enough hydrogen, resulting in pressure build-up and foaming (dry foam).
5, pitting pits
the steel (C, D grade), or rusty surface, very soluble residual soluble salts and oxidation products. Corrosive gases, such as sulfur dioxide, acid, carbon dioxide, etc., pass through the coating and are absorbed and blistered. This foaming occurs in the latter stages of coating service (wet and dried).
6, solvent residue
solvent residue will cause foaming in two cases:
- solvent sensitive to water and make the coating film increase water absorption, if the coating adhesion is not strong, it will cause
blisters;
7, internal stress
coating curing contraction produces internal stress, when the coating is too thick, the coating interval is short, the rear channel coating is faster than the previous coating curing, the internal stress will pull the coating off the substrate surface and foam. This bubble is a large "dry bubble" that concentrates on the inner corner.