Knowledge about color-coated plates! Popularize!
When many people buy color-coated plates, they don’t know where the difference between a really good color-coated plates and a poor color-coated plates is,
because the surface is almost the same, and it will not be a problem if it is not used for a while.
There are many factors to consider when choosing a coating. It mainly includes the type of coating, coating thickness, coating color and coating gloss.
In addition, sometimes the primer and back coating requirements of the coating are also considered.
The types of coatings currently used for color coated steel sheets are polyester coating (PE), fluorocarbon coating (PVDF), silicon modified coating (SMP),
high weather resistant coating (HDP), acrylic coating, Polyurethane coating (PU), plastisol coating (PVC), etc.
Common coating types color-coated plates
(1)polyester (PE, Polyester)
PE coating has good adhesion to materials, color coated steel plate is easy to process and form, cheap and many products, and the choice of color and gloss is large.
Polyester coatings are not ideal for UV resistance and powdering resistance of coatings. Therefore, the use of PE coatings still needs to be limited.
It is generally used in areas where air pollution is not serious or products that require multiple molding processes.
▲ Applicable industry
Ordinary industrial plants and warehouse logistics warehouses do not corrode the color-coated plates themselves.
The requirements for corrosion resistance and anti-aging of color plates are not high. More consideration is given to the practicality and cost-effectiveness of plant construction.
(2), Silicon Modified Polyester (SMP, Silicone Mobified Polyester)
Since the polyester contains an active group -OH/-COOH, it is easily reacted with other macromolecular substances.
In order to improve the sunlight resistance and pulverization of PE, the chromic retention and heat resistance of the Silicone resin are denatured. ,
The denaturation ratio of PE and PE can be between 5% and 50%. SMP provides better durability of the steel color-coated plates, and its corrosion protection period can be as long as 10-12 years.
Of course, its price is also higher than PE.
However, because the adhesion and processing formability of the Silicone resin is not ideal, the SMP color-coated plates is not suitable for applications requiring multiple molding processes, and is mostly used for building roofs and exterior walls.
(3) high weather resistant polyester (HDP, High durable Polyster)
For the shortcomings of PE and SMP, HYDRO (now acquired by BASF) and BECKER of Sweden developed a 60-80% weatherable HDP polyester coating that can achieve PVDF coating in early 2000, and is superior to ordinary silicon modification.
The polyester coating has an outdoor weather resistance of 15 years.
The high weathering polyester resin is synthesized by using a monomer containing a cyclohexane structure to achieve flexibility, weather resistance and cost balance of the resin,
and the aromatic-free polyol and polybasic acid are used to reduce the absorption of UV light by the resin.
To achieve high weather resistance of the coating.
UV coatings and hindered amines (HALS) are added to the coating formulation to improve the weather resistance of the film.
High weathering polyester coil coatings have been recognized in the market abroad, and the cost performance of this coating is very prominent.
▲ Applicable industry
Metallurgical and power industry non-ferrous metal smelters (copper, zinc, aluminum, lead, etc.) are the most challenging years of use of color plates. Steel plants, power plants, etc. will also produce corrosive media, and have high corrosion resistance requirements for color plates.
(4) PVC plastic sol (PVC Plastisol)
PVC resin has good water resistance and chemical resistance, and is generally coated with a high solid content, and its coating thickness is between l00 and 300 μm.
It can provide smooth PVC coating or light embossing treatment as embossing coating; because PVC coating is thermoplastic resin,
it has high film thickness and can provide good protection of steel plate. However, PVC has weak heat resistance.
It was used more in Europe in the early days, and it is currently used less and less because of its relatively poor environmental protection.
Due to the strong bond energy between the chemical bonds and chemical bonds of PVDF, the coating has very good corrosion resistance and color retention.
It is the most advanced product in the color coating steel coating for construction industry.
The molecular weight is large and the direct bond type structure, so in addition to chemical resistance, mechanical properties, ultraviolet resistance and heat resistance are also prominent.
In the general environment, the corrosion protection period can reach 20-25 years. In recent years, fluorine-containing resins copolymerized with chlorotrifluoroethylene and vinyl ester monomers have been popular in China, and are widely used in exterior walls and metal sheets of buildings.
Since the content of easily hydrolyzable vinyl ester monomer and fluorine is about 30% lower than that of PVDF, there is a certain gap between the weather resistance and PVDF.
The fluorocarbon coating produced by Baosteel has a PVDF content of not less than 70% (others are acrylic resins).
▲ Applicable industry
Chemical industry products have volatile characteristics, and are prone to volatile or volatile substances such as acid or alkaline.
When exposed to water, dewdrops are easily attached to the surface of the color plate, causing corrosion to the coating of the color plate and possibly further corrosion.
To the zinc layer or even the steel plate.
Comparison of performance of different coatings
There are two most important factors in the choice of primer.
One considers the adhesion of the primer and topcoat and the substrate,
The second is that the primer provides most of the corrosion resistance of the coating.
From this perspective, epoxy is the best choice.
If you consider flexibility and consider UV resistance, you can also choose a polyurethane primer.
For the back coating, the most correct choice is to choose a two-layer structure if the color coated steel sheet is used in a single board.
It is a layer of back primer and a back side finish. The primer is the same as the front, and the topcoat is a polyester with a light color (such as white).
If the color coated steel sheet is used in a composite or sandwich panel, the back surface is coated with an epoxy resin excellent in adhesion and corrosion resistance.
Coating gloss selection
The glossiness of the enamel is not a performance indicator of the coating. Like the color, it is just a characterization. In fact, coatings (coatings) are easier to achieve high gloss.
However, high-gloss surface glare causes high light reflectance during the day, which causes light pollution (many do not use glass curtain walls now because of light pollution).
The high-gloss surface has a small coefficient of friction and is easy to slip. It is easy to bring safety hazards during roof construction.
The aging of color-coated steel sheets when used outdoors is firstly indicating that the light is lost.
If maintenance is required, the old and new steel sheets are easily distinguishable.
If the back paint is high-gloss, when there is light in the room, it will easily cause halo and cause visual fatigue.
Therefore, under normal circumstances, the color coated steel sheets for construction use low to medium gloss (30-40 degrees).
Coating thickness selection color-coated plates
Microscopically, the coating is a long empty tissue. Water in the air, corrosive media (chloride ions, etc.) will invade through the weak part of the coating,
causing corrosion under the film, and the coating will foam and flake off.
In addition, even with the same coating thickness, the secondary coating is denser than the primary coating.
According to foreign reports and related corrosion test results, the front coating can effectively prevent the intrusion of corrosive media by more than 20μm.
Due to the different corrosion protection mechanisms of the primer and the topcoat, it is necessary to specify not only the total film thickness but also the thickness of the primer (“5 μm” and the topcoat (“15 μm”).
Only in this way can the different parts of the painted steel plate be ensured.
Corrosion resistance is balanced.
PVDF products require a thicker coating film. Because of the longer lifespan guarantee.
The requirements for the backside coating depend on the application, and the sandwich panel requires only a layer of bondable primer.
The formed steel sheet is also required to be coated with two layers due to the indoor corrosive environment.
The thickness is at least 10 μm or more.
The choice of coating color (marked!)color-coated plates
The choice of color is mainly considering the matching with the surrounding environment and the owner’s hobby,
but from the perspective of using technology,the choice of pigments for light color paints is large,
You can choose inorganic coatings with superior durability (such as titanium dioxide), and the coating has strong heat reflection ability (reflection coefficient is double that of dark paint).
The temperature of the summer coating itself is relatively low, which is the extension of coating life. benefit.
In addition, even if the coating is discolored or pulverized, the contrast of the light color coating film with the original color is small, and the effect on the appearance is small.
The dark colors (especially the brighter colors) are mostly organic colors, which are easily faded when exposed to ultraviolet light, and become color in the shortest 3 months.
According to relevant experimental data, the white surface is 10 degrees lower than the blue surface temperature and 19 degrees lower than the black surface
when the ambient temperature is highest at noon in summer.
The ability of different colors to reflect sunlight is different. The following table lists the reflective capabilities of different colors.
Color reflectance reflection
In the case of color-coated steel sheets, the thermal expansion rates of coatings and steel sheets are usually different,
especially the linear expansion coefficients of metal substrates and organic coatings are large.
When the ambient temperature changes, the substrate and the coating bond interface will undergo expansion or contraction stress,
and if it is not properly released, the coating crack will occur.
Baosteel has done the same coating variety in Hainan, the same coating supplier,
8 years of exposure test of different colors,
and the results also confirmed that the color of the light color paint is small. The following table compares the different color exposure tests.
Gloss chromatic aberration original thickness thickness
Coating gloss selection
In addition, here are two points to explain the current misunderstandings in the domestic market:
First, there is a large amount of white primer in the country.
The purpose of the white primer is to reduce the thickness of the topcoat because the corrosion-resistant primer for normal construction is yellow-green
(and therefore has a strontium chromate pigment) and must have sufficient topcoat thickness for good hiding power.
In this way, the corrosion resistance is very dangerous. First, the primer has poor corrosion resistance, and the topcoat is greatly reduced to less than 10 microns.
Such a color-coated steel plate looks glamorous, and in a few years it will cause corrosion in different places (cutting, bending, under-film, etc.).
Second, the color coated steel plate for construction engineering uses different manufacturers and different batches of color-coated steel plates.
It seems to have the same color in the construction, but after several years of sunlight, the color changes of different coatings are different.
Different trends,There are so many examples that lead to serious chromatic aberrations.
Even if the products of the same supplier, it is strongly recommended that the same project be ordered once.
Because different batches are likely to use products from different coating suppliers, the possibility of chromatic aberration is increased.
Reasonable material selection not only improves the service life of buildings,
but also reduces costs, thus truly achieving environmental friendliness and resource conservation.