Common problems and solutions for alcohol-soluble inorganic zinc silicate primers

This paper introduces the common defects in the construction of alcohol-soluble inorganic zinc silicate primer, and analyzes the causes from the construction environment, surface treatment and construction process, and puts forward a solution.
key words: inorganic zinc silicate primerCrackingadhesionpinholes bai rust
0
foreword
inorganic zinc-rich primer is divided into water-based inorganic zinc-rich and alcohol-soluble inorganic zinc-rich primer, ethyl silicate as hydrolytic solution of the alcohol-soluble inorganic zinc-rich primer also known as inorganic zinc silicate primer, is a kind of electrochemical and chemical protection dual function of the extremely protective antiseptic primer. Can be cured at room temperature, can be constructed in a humidity environment, and alcohol as a solvent, less toxicity, coupled with its high temperature resistance, in the steel plate welding cutting paint film will not be affected, can be used as welding primer. Therefore, it is widely used in bridges, storage tanks, petrochemical steel structures, ocean-going ships, marine engineering and power facilities, such as anti-corrosion aspects. However, this kind of coating on the construction environment, surface treatment, construction technology and other requirements are high, in the actual use of the process often appear a variety of defects, such as cracking, poor adhesion, fog, foaming, pinholes, white rust and other defects. In this paper, the causes of these defects from inorganic zinc-rich primer corrosion-proofing, construction environment and construction process to do some analysis and discussion, in order to play a role in the future anti-corrosion construction.
1
Inorganic
ZnSio3
primer anti-corrosion
to partially hydrolyzed ethyl silica as a film substance, zinc powder as a rust pigment, in the volatile alcohol solvent at the same time, ethyl silica alkyl absorption of moisture in the air and hydrolyzed reaction, cross-curing into zinc silicate and iron silicate compound salt. The molecular structure of ethyl silica is
Si (OC2H2CH3) 4
, which is partially hydrolysed to make a positive ethyl silica liquid containing a certain hydroxyl, and then mixed with zinc powder, coated into a film, part of the hydrolytic ethyl silicate continues to hydrolyte and shrink, eventually becoming a mesh high polyester.2
Common defects and causes analysis
(
1
) adhesion is divided into substrate and substrate adhesion, primer and middle layer or paint between the layer adhesion.
(1) primer and substrate adhesion is not good. Mainly the surface treatment measures in the early stage is not appropriate, by inorganic zinc primer corrosion-proofing system can be known, its zinc powder in the reaction with film-forming material at the same time with the substrate metal iron reaction. Residual oxidizing skin, rust, etc. on the substrate surface will prevent zinc powder from touching the potions on the steel surface, and reduce the chemical and polar attachment of the coating. In addition, the substrate is too smooth and can cause mechanical attachment of the coating. Therefore, the substrate surface should have a suitable cleanliness and roughness. Generally speaking, sand blasting rust removal up to
Sa2.5
level or more, surface roughness of
40 to 75
μ
m
. Excessive roughness can affect the flatness of the coating and the protective effect at the peak.
(2) layer adhesion is not good. In the inorganic zinc silicate primer coated with acetate paint, polyurethane paint, the primer is powdery, the paint is blocky off, the damage is not easy to repair. The main reason is that the primer is not solidified enough to paint the middle or finish. Inorganic zinc-rich primer pigment content is high, just painted when the cohesion is not good, if the solvent-based paint is painted too early, the solvent in the paint penetrates into the uncovered primer, softening the primer. When the finish is cured, the volume shrinks to produce stress that is passed on to the uncarified primer, allowing it to internalize the split and de-layer. If the backpaint coating is thick and contains more solvents, the greater the shrinkage stress that is generated when it cures, the more severe the
.
the curing rate of inorganic zinc-rich primers is greatly affected by air humidity, and the curing time is
12
to
24h
when the relative humidity is at least
50%
or more and the temperature is above
20
degrees C. In order to speed up its curing, after spraying
about
4 hours to start sprinkling water to speed up its curing process. Even at high relative humidity, such as
70%
or more, sprinkle water to accelerate its curing to ensure faster curing of the coating.
(
2
) coating cracking: too high a dry film thickness can cause the coating to crack. In particular, the inner angle weld of the steel structure and the abdominal plate and wing edge of the
H
steel are the most likely to cause the coating to crack. Different steel structures have different dry film thickness design requirements for inorganic zinc-rich primers. Rust-proof primers require
40
to
80
μ
m
, and a single coating thickness system (e.g. tank inner wall) requires
75
to
100
μ
m
. It is generally
that
μ
125
is safe. For complex structures, the risk of cracking is greater with multiple gun sprays using small nozzle nozzles. It is recommended to use a large nozzle gun. If it is found that the paint film has a tendency to thick flow, immediately brush flat with a brush.
(
3
) blisters and pinholes. Inorganic zinc-rich primer surfaces are porously uneven. When solvent-based rear-channel paint is sprayed on a pore-filled surface, part of the solvent penetrates into the pore. Surface temperature is reduced due to decompression and instantaneous solvent volatility. The temperature then rises sharply, expanding the gas and air. Thus, the solvent in the pores has a volatile trend, while the air contained in the uneven surface of the primer to break through the paint surface release. These effects combine to form bubbles or pinholes. The higher the ambient temperature, the more severe this phenomenon is.
in order to eliminate this defect, thin intermediate transition layer paint can be used to completely penetrate the uneven surface of the paint closed, play a good anchoring role and reduce foaming phenomenon.
(
4
) is white rust. Because the primer contains a large amount of zinc powder, that is, single zinc. The low potential of zinc determines its vibrancy, single zinc and pure water contact and air with little or no air will form a large amount of zinc salt
Zn (OH) 2
, that is, white rust, this
Zn (OH) 2
is a two-sex oxide, very unstable, slightly soluble in water, will not form a closed film, there is no protective effect. If the thickness of the upper layer paint is not enough, the moisture enters from the thinner part of the upper paint film to form zinc salts, causing the coating to fall off.
, be sure to remove zinc salts before painting. The removal method can be rinsed with high-pressure water, or it can be brushed with a nylon brush and then rinsed with clean water. Severe can be removed with mechanical tools.
3
construction method
3.1
surface treatment
(
1
) before construction must be strict surface treatment of the coated surface, so that the surface is free of oil, dust and other contaminants.
(
2
) blasts the steel surface to
Sa2.5
grade (surface reveals a metallic gloss) and forms a certain roughness, which should generally be controlled at
50 to 75
μ
m
.
(
3
) blast is complete, remove all sand and dust by vacuum cleaning.
(
4
) should not be left exposed for too long after treatment, generally not more than
24
hours, to ensure that the painted surface meets the prescribed painting requirements as a principle.
3.2
and diluted
(
1
) shall not be changed arbitrarily as required. The hydrolyte should be sealed and stored after it has been left behind to prevent failure.
(
2
) slowly add the colorless transparent ingredients to the zinc-containing paste with stirring and stir thoroughly until the texture is even.
(
3
) conditions allow,
60 to 80
filter coatings can be used. Shake or stir the paint thoroughly or evenly before mixing
(
4
) depending on the operating procedure, steel surface temperature and processing speed, etc., it may be necessary to add thinners.
(
5
) airless spray thinner is generally
0 to 5%
, brushing and air spraying up to
15%
.
(
6
) after mixing at room temperature for
8 to 10
hours, once the use time is exceeded, even if there is no change on the surface, the remaining mixed coatings must not be used.
3.3
Application method
(
1
) airless spray or traditional spray, repair can be used brush coating, construction is best to continue mechanical stirring paint solution.
(
2
) inorderable spray guidance parameters: nozzle pressure:
8 to 12MPa
, nozzle aperture:
0.43 to 0.63mm
. Spray:
60 to 80 cm
, filter: check to keep clean.
(
3
) spray is suspended, it is possible that the paint should circulate in the hose to avoid precipitation.
should be used to thoroughly clean the entire construction equipment with matching thinner immediately after construction, and when the equipment is not in use, the diluent should be left in the hose.
3.4
the relative humidity of
(
1
) air is not less than
50%
, preferably more than
65%
.
(
2
) inorganic zinc-rich primer requires moisture to cure, and when humidity is low, it can gently spray water on the paint surface after
24
hours of construction to accelerate curing or artificially increase the humidity of the surrounding air.
3.5
curing time
(
1
) curing speed is affected by humidity, temperature, air circulation and film thickness.
(
2
) construction paint, inorganic zinc-rich primers must be completely cured, otherwise the adhesion of the paint will not reach the desired state.
(
3
) paint film is fully cured can be detected by the following method: scrub the paint surface with a thinner-soaked cloth, if the paint film is not damaged. The description has reached full curing.
3.6
paint
(
1
) no zinc salts and other dirt
(
2
) no The paint film of the machine zinc-rich primer is porous, because the porousness is affected by the climatic conditions and construction technology at the time of construction, when the repainting air in the pores will escape from the surface of the new paint film, resulting in bubbles and pinholes in the paint. In order to avoid this situation, and in order to improve the adhesion of the paint, it is recommended to use mist spray paint
/
coating technology: that is, paint dilution
30
to
60%
of the paint to fill the pores in the primer, after a few minutes to apply to the specified film thickness.
4

(
1
) inorganic zinc-rich primer after spraying, the relative humidity in the air is best maintained at
65%
. If the ambient humidity does not reach, it can artificially increase the humidity.
(
2
) inorganic zinc-rich primer must be fully cured before it can be coated with a backdoor coating. The primer table drys quickly and gives the illusion that it has been dried. The degree of dryness can be tested with a coarse cotton strip of butyl ketone to wipe the primer. If the color on the cloth is heavier, it is not dry.
(
3
) inorganic zinc-rich primer surface is porous, requiring the use of special closed paint or spray technology
(
4
) inorganic zinc-rich primer for coating thickness has strict requirements, too high dry film thickness will lead to coating cracking, in general, dry film thickness does not exceed
125
μ
m
.
(
5
) inorganic zinc-rich primer because of its rigidity, poor adhesion, must be used on the blast surface, therefore, not suitable for repair primers.
。