Which coatings can be used as topcoat

In the construction of color coating, finish paint has the most critical function of product performance.It not only provides the decorative color coated board, but also makes the color coated board with a variety of practical functions.Color coated board with different topcoat can be used in different fields, such as building materials for color coated board, home appliances for color coated board, automotive color coated board.Therefore, the study of top coat in coil coating is the most thorough kind of coating.At present, there are mainly the following types of coil topcoat in industrial production.

A polyester finish

By definition, polyester resin refers to the polymer materials containing ester bonds on the main chain of molecules, including three types: alkyd tree, saturated polyester and unsaturated polyester.Polyester used in the coil industry refers to saturated polyester.

The coating film formed by polyester resin has excellent comprehensive properties and a wide adjustable range of properties, and can be made into different application forms, such as solvent, water, powder, drying or self-drying coating products.It is widely used in the industries of home appliances, automobiles, metal furniture, building materials and canning.Polyester resin for rolling materials is mainly composed of aromatic dibasic acid aliphatic dibasic acid and aliphatic polyol by condensation polymerization.

Polyester topcoat for color coated board is a coating made from polyester.Crosslinked resin is mainly butanol etherified melamine formaldehyde resin (amino resin).Amino resin cured polyester topcoat has good flexibility, hardness and durability, as well as good processability.Therefore, it is the most widely used coil finish at present.

B polyurethane finish

Polyurethane coatings are widely used in different fields because of their excellent comprehensive properties.In 1972, the polyurethane coating composed of closed polyisocyanate and hydroxyl polyester was first used as the pre-coated coil topcoat for aluminum coils in Germany.In 1997, polyurethane finish has accounted for 5% of pre-coated coil finish, and in 1999, it ranked fourth in synthetic resin for pre-coated coil coating, mainly used in coating building materials, household appliances and vehicle pre-coated metal coils.Polyurethane topcoats (especially those made of aliphatic and aliphatic polyisocyanates) have a better balance of flexibility, hardness, and durability than amino polyester topcoats.Another characteristic of polyurethane finish is that it can be either baking or self-drying at room temperature.For the same formula of the coating, the use of multiple isocyanic acid components are closed for pre-coated coil production line, and not closed for self-drying two-component coating, the final structure and performance of the same paint film, which is very beneficial to building materials with pre-coated coil in the use of the site repair work.

C polyacrylate finish

Polyacrylate coating is a kind of coating with wide application.The main chain of polyacrylate resin is carbon-carbon bond, which is very stable to light, heat, acid, alkali and so on. The coating made with it has excellent outdoor durability and light retention and color retention. In addition, through the copolymerization of various acrylate, the mechanical properties of the resin can be adjusted.

At present, there are three main types of polyacrylate coatings for color coating: solvent-based heat-cured polyacrylate coatings, water-diluted polyacrylate coatings and radiation-cured polyacrylate coatings.

Solvent-based thermal curing polyacrylate coating has good anti-fouling, scratch resistance, high gloss and hardness, as well as excellent weather resistance and chemical resistance, the shortcomings of this kind of coating is difficult to get hardness and toughness at the same time meet the requirements of the product.When the hardness meets the requirements, the film generally can not undergo deep processing molding.At present, this kind of coating is mainly used as a matching primer for PVC plastic-sol topcoat.

In order to further improve the outdoor durability of polyacrylate coatings, organosilicone modified polyacrylate coatings were developed in the mid-1960s, in an attempt to replace fluorine-containing coatings with part of the price advantage, for the manufacture of pre-coated metal coils for external walls and roofing.In the practical application, it is found that the introduction of organosilicone will reduce the processability while improving the weatherability, and this contradiction is difficult to find a satisfactory balance point, and the improvement of weatherability is not worth the increased cost, so this kind of coating has been less used in the production of color coated board.

D. PVC organic sol and plastisol topcoat

PVC organic sol and plastisol is the sol grade polyvinyl chloride powder dispersed in the organic solvent and plasticizer mixture or only dispersed in plasticizer dispersion, the former is called organic sol, the latter is called plastisol, and then with pigment and additives into the corresponding coating.Sol coating is a dispersion, the solid content is much higher than solvent coating.The solid content of the organic sol is 50%~70%, and the plastisol can be as high as 95%, which can coat the paint film with a thickness of 200 nm at one time.It is widely used in northern Europe and the United Kingdom as a roofing board.In addition, the use of the paint film is thermoplastic this characteristic, can be embossed on the paint film and have a better decorative effect, as the outer shell of electrical appliances and instruments, luggage and boat interior decorative board.

E - chlorine-free disperse finish

The so-called chlorine-free dispersion coating is actually non-chlorine other high polymer powder, such as polyester, polyolefin, polyacrylate and other relatively high molecular weight resin powder in plasticizer into plastisol.Chlorine-free organosol is a solution - based dispersion coating made by dispersing chlorine-free polymer powder in a resin solution.Resin solution generally consists of hydroxyl terminated polyester or polyacrylate and closed polyisocyanate plus solvent.

The mechanical properties of this kind of coating can be adjusted by the varieties and proportions of different polymerized monomers, so the overall performance is often good.At present, this kind of coating has been pre-coated metal coil industry recognized, is gradually replacing PVC organic sol, production performance better products.

F fluorinated resin topcoat

Fluorine-containing resin coating refers to the coating made with the polymer containing fluorine atoms as a film-forming material.Due to the introduction of fluorine atom, the paint film has excellent weather resistance, solvent resistance, chemical resistance, abrasion resistance, processing and anti-fouling.Outdoor service life up to 15~20 years, mainly used for external walls, roofing, road signs and highway guardrail and other occasions requiring high durability.Fluororesin for color coating can be divided into three categories: polyfluoroolefin, fluoroolefin and other olefin copolymer, fluoropolyether resin.

G powder coatings topcoat

In the early 1990s, in order to protect the environment and save resources, people tried to use the powder coating without solvent in the coil production line. In 1995, the first color coating board production line using powder coating was put into industrial operation in the United States.Due to the limitation of coating speed and the paint film is too thick, the powder coating in the pre-coated coil production line did not get the expected development, in 1999 only consumed 70,000 t, less than 1/10 of the total amount of powder coating.In 2001, less than 10 of the more than 60 pre-coated coil production lines in Europe used powder coatings.The key to the development of powder coatings for color coating production line lies in the improvement and innovation of coating formula, coating equipment, curing method and equipment to improve the coating speed and reduce the thickness of paint film.Now there are breakthroughs on both fronts.

At present, the powder coatings used in the production of color coated board mainly include polyester, polyurethane and polyacrylate coatings, etc. Epoxy resin powder coatings, due to poor weather resistance, are generally not directly used as pre-coated coil topcoat, but commonly used as curing agent of polyester resin or polyacrylate resin powder coatings.