Simple description of the pre-coating coils of metal packaging

Amino alkyd coating
As a precoated coil coating. The amino alkyd coating has the longest history. At the same time because of its low price and outdoor weather resistance is better. So it is still in use today. It is often a short oil alkyd containing no oil. With cyanide resin as a cross-linking agent. In order to improve the film forming processability, corrosion resistance, adhesion and chemical resistance. A third resin component such as epoxy resin or vinyl resin may also be added. However, outdoor weatherability should be fully considered at this time.
Dry oil or semi-dry oil modified alkyd resin is added with a trace amount of dry material and then amino resin. It can also be used as a top coat for pre-coated coils. However, due to yellowing problems and poor outdoor weather resistance. Therefore, it is not used as a top coat in most cases. The amino alkyd resin containing non-drying oil or synthetic non-drying oil is characterized by good construction performance. Consider from price. Relatively speaking, its weather resistance is good. However, due to poor processing and corrosion resistance. So gradually replaced by polyester or acrylic resin. Its proportion in the precoating of coil topcoats is declining year by year.
Plastisols and organosols
Plastic sols and organosols are also known as plastisol and diluting plastisol. It is customary to refer exclusively to PVC-based plastisols or organosols. Polyfluorocarbons are also used as a pre-dissolved form. But not included.
The sol-grade polyvinyl chloride powder is dispersed in a plasticizer and a volatile diluent that does not dissolve the resin at room temperature. Together with stabilizers, pigments and so on. This kind of paint is called organic solvent paint. Does not contain volatile diluents. Only dispersed in the plasticizer is called plastisol coating. The two coatings are baked at temperatures above 180 °C for a short time. The resin is swelled, melted, and melted by the plasticizer. A uniform and tough coating film is formed.
Plasticizers are the key ingredients for the preparation of plastisols and organosols. Its amount has a great influence on the film performance. It is generally 1-40% plasticizer. Plasticizers are high boiling, chemically stable, and thermally stable organic liquids. Phthalate esters, adipic acid esters, sebacic acid esters, sebacic acid esters and phosphoric acid esters are among the types thereof. When selecting plasticizers, factors such as end-use requirements, rheological properties, degassing, gelling and plasticization, and cost must be considered. Volatile solvents can reduce the viscosity of the plastisol. Make it suitable for a variety of coating processes. These solvents are divided into dispersants and thinners. The organosol is affected in slightly different ways. Diluted solvating power is low and can be used alone or in combination with dispersants with higher solvating power. The more commonly used diluent is a cheap aliphatic hydrocarbon solvent. Its boiling range is relatively wide. Representative dispersants such as ketones and aromatic hydrocarbon solvents. Its polarity is stronger. Usually volatile. Solvents can be added directly to the plasticizer either at the time of preparation or before use.
Organic solution compared with solution type vinyl resin coating. The paint cost per unit area is low. Hardness, adhesion, flexibility, etc. are good. Can be sutured, embossed, die and other processing. The volume fraction of the plastisol is very high, up to 97-100% and there is no volatile solvent. Therefore, it is most suitable for thick coating. Due to the poor adhesion of plastisol and metal substrates. Therefore, it is generally necessary to first coat vinyl chloride/vinyl acetate copolymers with carboxyl groups. Or first coat acrylic, phenolic, epoxy polyester polyurethane and other primers. Bake at 260C for 60 sec.
Then apply plastisol on it. Thick coatings like this are suitable for embossing. With plasticizers different. Elongation is also different. But even if the plasticizer content is small. The plastisol coating also has an elongation of 180%. Therefore, all processing methods can be used.
Solution type vinyl resin coating
Solution-type vinyl coatings feature vinyl chloride-vinyl acetate copolymers as the main film-forming material. The components of the paint include plasticizers, stabilizers, solvents, and thinners. It is a volatile coating. The suitable baking conditions are 230-260 °C for 60 sec. Solution type vinyl paint features:
1 easy coating can roll coating, diffuse coating, spraying, flow coating;
2 stable chemical resistance to alkali, strong inorganic acid resistance. Resistant to alcohol, grease, petroleum, grease and hydrocarbons. Intolerant ketone and aromatic hydrocarbons;
3 has good adhesion, flexibility and elasticity (for joints, curling, deep drawing, rolling, molding and other processing. Film does not damage);
4 does not change for a long time. Hardness, elasticity and little change from the beginning after storage;
5 good water resistance;
6 If the pigment is selected properly. It has excellent weather resistance;
7 resin color is light. It can be made into a transparent coating;
8 is not mildew;
Due to the excellent elasticity of solution type ethylene coatings. Therefore, it can perform harsh processing and molding. Through long-term test and practical use, it proves that solution type ethylene coating has excellent weatherability. Good adhesion to the substrate during natural exposure. Adhesion remains unchanged for a long time. Difficult to chalk up. Do not fade, no mildew. These properties fully satisfy the necessary conditions for precoating coil coatings.
Acrylic paint
Acrylic resin coatings have good stain resistance, gloss, hardness, and excellent weather resistance and chemical resistance. The disadvantage of acrylic prepaints is poor formability. Generally cannot withstand deep processing. Acrylic resin is generally made of the following four monomers with different properties of the copolymer: 1 hard monomer: such as phenyl ethyl ester, vinyl toluene, methyl methacrylate and so on. 2 soft monomers: such as ethyl acrylate, butyl acrylate, butyl acrylate, 2-ethylhexyl acrylate and so on. 3 functional group containing monomers: such as acrylamide, hydroxymethylated acrylamide (meth) acrylic acid 0 hydroxyalkyl ester. Acrylic acid, methacrylic acid, monoalkyl maleate, and the like. In the design of the acrylic resin formulation, the comonomer should be selected according to the requirements of the pre-coating material for the performance of the paint film. Synthesis of the desired polymer.
The commonly used cross-linking method can be basically divided into: 1 self-crosslinking of acrylic resin, reaction of hydroxymethyl or partial ether compound of acrylamide contained in the polymer with hydroxyl group, amide group; 2 combination of amino resin one by one Hydroxymethyl or alkoxymethyl amino resin and polymer hydroxyl, amide and other reactions; 3 and epoxy resin epoxy resin and epoxy resin, amide group reaction. Or the hydroxyl group of the epoxy resin reacts with the hydroxymethyl group of the polymer. Cross-linking method 1 is characterized by excellent gloss and processability. But often outdoor durability is poor. Mode 2 is better in outdoor weather resistance and corrosion resistance. However, the processability is poor. When using mode 3. The weatherability problem must be considered. Among the pre-coating acrylic paints worth mentioning is the electron beam cured acrylated coating. It is characterized by extremely fast curing (curing at room temperature in just 0.1 seconds). High efficiency, energy saving and pollution-free. The electron beam curing method initiates the polymerization reaction by allowing electrons to generate free radicals in the monomer or prepolymer in the film. Acrylic coatings that cure the film by electron beam curing are suitable for pre-thickness steel plates. The disadvantage is that the mechanical properties of the paint film are poor. It is difficult to meet the pre-coated steel plate processing and use requirements. Plasticizing resins are often added to improve the impact resistance, adhesion and elasticity of the paint film.
Waterborne coatings
In recent years. The importance of environmental pollution control and energy conservation and the shortage of petrochemical products, flux prices rose. Promote the development of water-based paint. Waterborne coatings for precoating coils have also been developed accordingly. Pre-coating water-based paint mainly includes two types. Latex paints and water-soluble paints. Among the most successful are polyesters and acrylics. For the latter. The vast majority are cross-linked (self-crosslinking and cross-linking agents) acrylic latex paints. Both types of resins are preferably hexamethoxymethyl melamine resins as crosslinking agents. Acrylic latex paint in addition to pollution, energy saving, safety advantages. Because of its much larger molecular weight than solvent-based acrylic paints. So durability is also better than solvent-based acrylic paints.
Use water as a solvent. It will inevitably bring some shortcomings. The surface tension of water is large. It is difficult to wet the surface of the steel plate. The latex paint has pseudoplastic rheological properties. This means that the paint does not flow under low shear. The ribs are easily formed after the paint roll is applied to the strip. When the shear force is high. The viscosity is too low and sticky on rollers. Cause broken paint. The addition of suitable additives can increase the viscosity under high shear without affecting the fluidity of the paint and even form a smooth film under low shear forces.
In addition. Even if the water-based paint is a film, there is a disadvantage that the water-based paint is more hydrophilic than the solvent-based paint. Pre-coated steel plate with water-based paint. When used as an overpack. If the overlapping part of the steel plate has accumulated water. The film will expand slightly due to water. 5. Overlapped steel plates are bound to shrink due to temperature changes. The friction between the steel plates due to this expansion and contraction may damage the expanded and soft paint film.
Burners are generally installed in baking systems in Japan and the United States. The organic solvent evaporated in the oven is discharged into the combustion furnace to be burned, and the generated heat is reintroduced into the oven. This eliminates pollution and makes full use of heat. Therefore, if the water-based paint does not show much superiority in economy or certain performance. It restricts its development in certain procedures.