Introduction of fluorocarbon coating

Among all kinds of plastics, fluorocarbon resin plastic has a large electronegativity of fluorine element and strong fluorocarbon bond bond, which makes fluorocarbon resin have particularly superior characteristics: weather resistance, heat resistance, low temperature resistance type , Chemical resistance, but also has a unique non-stick and low friction. These excellent characteristics make fluorocarbon resin widely used in various fields such as construction, chemical industry, electrical and electronic industry, machinery industry, aerospace industry, household goods and so on.

1. Types of fluorocarbon resin

There are four common types of fluorocarbon resin family: PTFE, PVDF, FEVE, and PVF.

PTFE (Poly tetra fluoro ethylene) is polytetrafluoroethylene resin, which was successfully developed in the United States in 1938. Its excellent anti-corrosion performance is known as the "plastic king". "Teflon" is another name. It is often in sugar, grease, salt and other components that can maintain non-stick and self-cleaning in complex environments with high temperature response. PTFE bearings do not require lubricating oil and are self-lubricating.

PVDF is polyvinylidene fluoride resin, which appeared in the 1960s, and is mainly used as a protective coating for metal decorative plates for architectural coatings. After thirty years of real test, the original appearance is basically maintained.

The two types of fluorocarbon-coated metal baking varnishes must undergo high temperature to form a film, and cannot be applied at normal temperature.

FEVE, which is polychlorotrifluoroethylene/vinyl ether resin, was successfully developed by Japanese scientists in 1982 using molecular chain design technology and membrane technology. It is a fluorocarbon coating that can be cured at room temperature. At normal temperature, the fluorocarbon coating is applied to the surface of various substrates by brushing, roller coating, spraying and other common coating methods to form a fluorocarbon protective coating, which greatly expands the scope of application of fluorocarbon coatings. Fluorocarbon coatings in daily life.

PVF, and polyvinyl fluoride, was invented by DuPont in 1940. This patented product is a film extruded from PVF interpolymer. The thickness is generally 12.5~50μm. This formation process guarantees The PVF decorative layer is dense and flawless, and there are no defects such as pinholes and cracks that often occur in the process of PVDF coating spraying or rolling. PVF film is used for building exterior walls by compounding with metal plates, and for space film structures by compounding with PVC films. Its good UV resistance also makes it widely used as a protective film for outdoor advertising posters.

(The extrusion arrangement of the molecular lattice in the vertical and horizontal directions during the PVF film manufacturing process greatly strengthens its physical strength, so:

• The PVF film has greater toughness. After the 180° bending test, the magnifying glass with a magnification of 43 times was used to observe that the PVF film had no cracks, but the PVDF coating showed obvious cracks. The reason is that the elongation of the PVF film can reach 100%, and No PVDF coating! )

2. Commonly used fluorocarbon resin for curtain wall materials

The fluorocarbon coating for curtain wall material coating is an organic coating based on fluorocarbon resin and metal particles or mica crystals as toner. Its PVDF (polyvinylidene fluoride) content is 70% (resin Mass ratio) above. The chemical structure of the fluorocarbon base material is bonded by a fluorine/carbon chemical bond, which is considered to be the most stable and strongest bond so far. Under normal circumstances, it has the following excellent performance:

² Weather resistance—It has the ability to resist bad weather and ultraviolet rays, so it can maintain color and gloss for a long time;

² Corrosion resistance—It is resistant to acid and liquid alkali and is not affected by air pollution and acid rain. The permeability of oxygen, moisture and corrosive particles is low, and it can withstand the harsh environment for a long time without corrosion.

² Mechanical properties—Excellent impact resistance, abrasion resistance and excellent paint film flexibility.

In the coating named KYNAR500@, the required weight ratio of KYNAR500@resin is ≥70%. The reason is that when the resin content is 70%, the performance of PVDF, especially the weather resistance and durability, can meet the higher requirements, and when it is greater than 70%, its performance impact is not large, basically 70% In the same performance state, and the primer content of 30% matches 70% of PVDF, the performance is the best. It is proved by scientific experiments that the performance of PVDF <70% of the coating is significantly reduced.

KYNAR500 @resin content is less than 70%, the name of KYNAR500 @paint is not allowed.

Commonly used fluorocarbon-coated curtain wall materials include fluorocarbon sprayed aluminum profiles, fluorocarbon sprayed aluminum veneer, fluorocarbon roller-coated aluminum veneer, and fluorocarbon roller-coated aluminum-plastic composite panel. At present, PVF perfluorocarbon coated aluminum veneer is also sold in the domestic market.

3. Painting of fluorocarbon resin paint for curtain wall materials

There are many coating methods for fluorocarbon resin coatings, which can be roller coating, spray coating or electrostatic powder coating. Different coating methods require different production equipment and substrate treatment requirements, and the resulting coating thickness and coating effect are also different. The treatment of fluorocarbon coatings is currently the most widely used in China. Roller coating is more popular abroad, and only a small amount of electrostatic powder is used.

3.1 Fluorocarbon resin coating spraying

Finished or semi-finished finished metal materials are subjected to surface treatment. For example, the aluminum veneer is sent to the spraying line for surface treatment after being processed by sheet metal, and the aluminum profile is extruded and then sprayed for surface treatment.

3.1.1 Spraying process

The spraying process mainly includes three processes: pretreatment (degreasing, pickling, chromization), spraying and solid-state (baking). According to the needs of material coating, two coatings, three coatings or four coatings can be selected. Two coats (primer + topcoat); three coats (primer + topcoat + topcoat); four coats (primer + barrier + topcoat + topcoat). In general, the thickness of the two-coat coating is ≥30μm±5μm, and the thickness of the three-coat coating is ≥40μm±5μm.

Pre-treatment:

Before the substrate is sprayed, the surface of the workpiece must be degreased and chemically treated to produce a chromated film, which increases the bonding force and oxidation resistance of the coating and the metal surface, which is beneficial to prolong the service life of the paint film.

Primer coating: As the primer coating of the closed substrate, its role is to improve the coating's resistance to penetration, enhance the protection of the substrate, stabilize the metal surface layer, strengthen the adhesion between the topcoat and the metal surface, and ensure the surface The color uniformity of the paint coating, the thickness of the paint layer is generally 5 ~ 10μm.

Topcoat coating: The topcoat coating is the key layer of the spray coating, which is to provide the decorative color required by the base material, make the appearance of the aluminum material meet the design requirements, and protect the metal surface from the external environment atmosphere, acid rain, pollutants Erosion, prevent UV penetration. Greatly enhance the anti-aging ability. The topcoat layer is the thickest layer of paint in spraying. The thickness of the paint layer is generally 20~30μm.

Overcoat paint coating: Overcoat paint coating is also called varnish coating. The main purpose is to more effectively enhance the ability of the paint layer to resist external erosion, protect the topcoat coating, increase the metallic luster of the topcoat color, and make the appearance more colorful. Dazzling, the thickness of the coating is generally 5 ~ 10μm.

Curing treatment: The three-spray layer generally needs to be cured twice, commonly known as three-coated two-baked. The substrate is processed in a curing furnace. The curing temperature is generally 180~250℃, and the curing time is 15~25 minutes. Different fluorocarbon coating manufacturers will provide the best temperature and time according to their own coatings. The fluorocarbon spraying plant also changed the two curings during the three spraying to one curing based on its own experience.

3.1.2 Equipment for spraying fluorocarbon resin

Domestic fluorocarbon spraying equipment is mostly designed for the United States, Germany, and Japan, and computer software is introduced, as well as different types of electrostatic spray guns from various countries.

According to different spraying production lines, spraying methods are fully suspended and semi-suspended.

Full suspension means that the pretreatment of the substrate, spraying and curing processes are suspended, the computer operates the workpiece to walk on the hoisting, cleaning, multiple spraying, curing until the spraying is completed. The length of this fully automatic line reaches 420m, not only can spray aluminum plates of various specifications and thickness, but also can automatically spray six meters long aluminum profiles.

Semi-suspended means that the pretreatment of the substrate is processed in several baths (such as anodized aluminum cleaning tank), chromization is also carried out in the bath, and then the substrate is suspended, and the workpiece is on the hanger Walk up and finish the spray curing process until the product is produced. This kind of production line is generally only more than 100 meters, relatively speaking, less investment.

Generally speaking, the full-hanging spraying method has high efficiency and stable quality, and the semi-hanging spraying method has low efficiency. Moreover, due to the problem of secondary pollution in tank washing, quality control is relatively difficult.

The spray gun is also an important equipment for spraying. The performance of the fluorocarbon coating itself requires that the spraying equipment must ensure an excellent atomization effect and ensure the uniformity of the sprayed layer. The distribution of metal particles in the fluorocarbon coating directly affects the appearance of the coating. . The coating is uniform, and the excellent quality fluorocarbon coating has metallic luster, bright colors, and obvious three-dimensional sense. Fluorocarbon spray coating with improper spray equipment will produce uneven color, shadow on the surface or poor coating. It greatly affects the decoration effect of fluorocarbon. In order to achieve a good spraying effect, high-voltage electrostatic electric spray guns are used.

3.1 Roller coating of fluorocarbon resin coating

Fluorocarbon resin roll coating is mostly used for surface treatment of metal sheet substrates, also known as pre-coating. Through the long process, the coil is placed on the production line for surface treatment, and then coated (rolled) with paint or bonded with an organic film and baked to form a product. The roll-coated coil generally needs two forming processes before use.

3.2.1 Fluorocarbon resin roller coating process

The production process of roller coating differs from spray coating in that it is coated and baked. Generally, it needs to be baked several times. Commonly used is three-coated three-baked, or two-coated two-baked. Generally, the thickness of the three-coat and three-bake coating is 40μm±4μm, and the thickness of the two-coat and three-bake coating is ≥25μm±4μm. Due to the material characteristics of the mechanical roll bending equipment and the substrate itself, the thickness of the roll coating material is limited, and the aluminum coil is generally within 2.5mm. In addition, due to the directionality of the roller coating, the refraction effect of its products under the sun will be different. When using it, pay attention to the consistency of the direction of use.

3.2.2 Fluorocarbon roller coated curtain wall material

    There are two main types of metal plates coated with fluorocarbon rollers for curtain walls. The first type is pre-coated plates for the surface layer of composite aluminum plates with a thickness of not less than 0.5 mm. The other type is pre-coated aluminum veneer with a thickness of 2mm or more, which is used after secondary molding.

4. Performance requirements of fluorocarbon resin coating for curtain wall

At present, there are clear regulations on the quality and performance of aluminum profiles and aluminum plate fluorocarbon coatings for building curtain walls. There are also clear regulations on the fluorocarbon roller coating of composite aluminum plates for external walls. The quality and performance of the two coatings are shown in the table.