The main purpose of the coating is to protect the surface along with providing an aesthetic appeal. For example, the automotive coating protects the car body from corrosion and it also enhances the appearance of the car body by providing color and gloss. Automotive coatings consist of several coatin...
The main purpose of the coating is to protect the surface along with providing an aesthetic appeal. For example, the automotive coating protects the car body from corrosion and it also enhances the appearance of the car body by providing color and gloss. Automotive coatings consist of several coating layers including primer, basecoat, and clearcoat on the steel substrate. Clearcoat is the outermost layer of coatings which needs to be of high gloss, transparency, scratch resistance, and water resistance. The common material that meets these requirements of clearcoat is acrylate-based polyurethane polymer. Urethane bonding is widely used for metal protection, due to its properties such as good adhesion to the substrates, abrasion resistance, and tensile strength.
As environmental regulations become more stringent, attempts now are to make more environmentally friendly coatings by replacing the organic solvent with water. Waterborne coating is one of the common methods for reducing volatile organic compounds (VOCs) in coating technology.
However, waterborne coatings have inferior mechanical properties and appearance quality than solvent-borne counterparts. The main reason for these limitations can be found in the difference in the film formation process of waterborne and solvent-borne coating. In solvent-borne coatings, when the solvent evaporates, the polymer chains become entangled and a uniform film is easily formed. However, water-based coatings are a more complex process. In waterborne coatings, polyols and polyisocyanate (PIC) are present in the form of particles. When water evaporates on heating, the particles get closer and polymer chains diffuse across the particles interface producing deformation and coalescence of particles. The entanglements are formed between the polymer chains and finally, the films are formed. In this complex process, the coalescences of polyol and PIC particles are, however, not often complete resulting in phase separation and a heterogeneous non-uniform film. In addition, the film has a low gloss and inferior chemical and physical properties due to low cross-linking density.
To overcome these limitations of waterborne coatings, here a unique acrylate polymer that bears blocked isocyanate moieties was synthesized by secondary dispersion processes. The film formation process of self-crosslinking is shown in Scheme 1. A special blocked isocyanate monomer (Karenz MOI-BP) was used for a homogeneous distribution of polyol and PIC. The self-crosslinking polymer was synthesized through free radical polymerization and characterized by SEC and 1H NMR. Using DLS and TEM, it was confirmed that the particle had a size of 100 nm with no other aggregations. The self-crosslinking clearcoat had a high gloss of 84.0 at 20°. Due to excellent optical and physical properties in addition to simple, and inexpensive preparation method and the synthesized polymer can be useful for waterborne coatings and contribute to environmental protection.
The main purpose of the coating is to protect the surface along with providing an aesthetic appeal. For example, the automotive coating protects the car body from corrosion and it also enhances the appearance of the car body by providing color and gloss. Automotive coatings consist of several coating layers including primer, basecoat, and clearcoat on the steel substrate. Clearcoat is the outermost layer of coatings which needs to be of high gloss, transparency, scratch resistance, and water resistance. The common material that meets these requirements of clearcoat is acrylate-based polyurethane polymer. Urethane bonding is widely used for metal protection, due to its properties such as good adhesion to the substrates, abrasion resistance, and tensile strength.
As environmental regulations become more stringent, attempts now are to make more environmentally friendly coatings by replacing the organic solvent with water. Waterborne coating is one of the common methods for reducing volatile organic compounds (VOCs) in coating technology.
However, waterborne coatings have inferior mechanical properties and appearance quality than solvent-borne counterparts. The main reason for these limitations can be found in the difference in the film formation process of waterborne and solvent-borne coating. In solvent-borne coatings, when the solvent evaporates, the polymer chains become entangled and a uniform film is easily formed. However, water-based coatings are a more complex process. In waterborne coatings, polyols and polyisocyanate (PIC) are present in the form of particles. When water evaporates on heating, the particles get closer and polymer chains diffuse across the particles interface producing deformation and coalescence of particles. The entanglements are formed between the polymer chains and finally, the films are formed. In this complex process, the coalescences of polyol and PIC particles are, however, not often complete resulting in phase separation and a heterogeneous non-uniform film. In addition, the film has a low gloss and inferior chemical and physical properties due to low cross-linking density.
To overcome these limitations of waterborne coatings, here a unique acrylate polymer that bears blocked isocyanate moieties was synthesized by secondary dispersion processes. The film formation process of self-crosslinking is shown in Scheme 1. A special blocked isocyanate monomer (Karenz MOI-BP) was used for a homogeneous distribution of polyol and PIC. The self-crosslinking polymer was synthesized through free radical polymerization and characterized by SEC and 1H NMR. Using DLS and TEM, it was confirmed that the particle had a size of 100 nm with no other aggregations. The self-crosslinking clearcoat had a high gloss of 84.0 at 20°. Due to excellent optical and physical properties in addition to simple, and inexpensive preparation method and the synthesized polymer can be useful for waterborne coatings and contribute to environmental protection.
주제어
#폴리우레탄[polyurethane] 코팅[coating]
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