Fluorinated resin coating performance and environmental protection of the coordinated development of China from the 1980s began to develop fluorine resin coatings, the current research and production units have grown to more than 70. It is predicted that the use of fluorocarbon coatings in China will increase at a rate of 30% to 40% per year.
First, thermosetting fluororesin coating Fluorine resin can resist UV attack, is an important condition for excellent weather resistance, the fluorine content of the resin determines the weather resistance of fluororesin. For example, the polyvinylidene fluoride (PVDF) resin has a fluorine atom content of 59.3% and forms an organic plastisol with a thermoplastic acrylic resin. The fluorine atom accounts for 38%-44% of the total film forming material, and has excellent weather resistance. According to the accelerated weather resistance test (EMMAQUA method), the optical retention rate in the wild after 20 years of exposure is still above 80%.
Hydroxy-containing fluororesin (FEVE) is used for curing at room temperature or medium temperature. Its fluorine atom content is 27%-29%, and its gloss retention is slightly better than that of PVDF. Domestic synthetic FEVE resin products after sampling test, its molecular weight distribution is wide, after 3000 hours of artificial aging of coating film, the loss of light is obvious, the resistance to salt spray is also poor, and there is a big gap with the Japanese comparison sample. Although the fluorine atom content is above 26%, due to the unreasonable structure of the resin, the performance is far from the requirement.
In fact, the performance of foreign companies' FEVE industrial products cannot meet the weather resistance level proposed by the data. It is also obvious that the coating film loses light after some artificial aging of FEVE resin for 4000 hours, because the molecular structure and molecular weight distribution are not easy to control. Therefore, it needs to be modified by atmospheric pressure synthesis to change the monomer structure of the fluoroolefin and make it a liquid product.
Second, fluorine-containing resin water dispersion coating 1. General fluorine resin water dispersion coating Solvent-based fluorine-containing resin coating VOC usage, does not meet the requirements of environmental protection, even if the performance is excellent, the development of life is limited. Japan began to study water-based fluororesin coatings, the most effective species for reducing VOCs. More than 100 patents have been issued since 1982. Representatives from Asahi Glass, DIC, and Daikin represent three companies.
1 Thermoplastic one-component fluororesin aqueous dispersion coating Daikin developed ZEFFLE SE series fluoropolymer aqueous dispersion, which is a vinylidene fluoride (VDF) copolymer with polymethyl methacrylate (PMMA) at the molecular level On the mixture. Due to the strong interaction between the ester group and the PVDF unit of PMMA, the ester group can be protected by PVDF, so the coating has good water resistance and excellent weather resistance. The company used this series of coatings to conduct exposure tests in the Japanese island of Toshima. After five years of exposure to white paint at a temperature of 30°C, the company used scanning electron microscopy and Fourier transform infrared spectroscopy (FTIR) to analyze the changes in color and gloss of the sample surface. As a result of the evaluation, the coating film still maintained its initial state, indicating that the water-based fluorocarbon coating has excellent weatherability and durability, and at the same time, the film-forming material in the coating film as a control sample has been degraded.
2Room Temperature Cross-linked Fluorine Resin Water Dispersion Coating Asahi Glass Co., Ltd. used seed emulsion polymerization technology to synthesize single-component room-temperature cross-linked PFEVE and carbonyl-containing diacetone acrylamide and other acrylic monomer polymers. This type of resin is abbreviated as FEVE. -AC. FEVE is thermally polymerized with an acrylic polymer to give a copolymer having a core-shell structure capable of forming a homogeneous, transparent coating, while physically mixed FEVE and acrylic emulsions form separate opaque coatings. In the FEVE-AC coating, even if the acrylic monomer content accounts for 15% of the total amount, the gloss retention rate after 8 hours is maintained by the SWM aging test for 4000 hours. The curing agent used is a C1-C10 dicarboxylic acid-derived dihydrazide such as malonic dihydrazide, azelaic acid dihydrazide, etc., which undergo curing cross-linking reaction with the carbonyl group of the reactive functional group in the fluoropolymer emulsion. The dosage is 0.01%-10%, the pH of the system is adjusted to alkaline, and storage stability.
3 Two-Component Room Temperature Curing Fluorine Resin Water Dispersion Coating Asahi Glass Co., Ltd. has developed FE-4200, 4400 and other two-component room temperature curing water-dispersed fluororesin coatings. Incorporation of polyoxyethylene ether macromonomer (EOVE) with internal emulsification in FEVE structure to prepare emulsion-type FEVE resin for two-component coating, which is also alternating between chlorotrifluoroethylene (CTFE) and vinyl ether Structural copolymers. Curing agents commonly used hydrophilic modified polyisocyanate can get similar performance with solvent-based FEVE resin. In addition to concrete, cement board and other inorganic building materials (such as exterior paint), can also be used for metal substrates, excellent performance.
To sum up, water-based fluororesin coating is a kind of product that is highly recommended for its coordinated development of high performance and environmental protection. In recent years, domestic research in this field has also started. Enterprises such as Dalian Zhenbang and Shanghai Weikewei are all developing and promoting their own waterborne fluororesin coatings.
2. Water-based fluoroelastomer coatings Fluoroelastomer-based coatings are mainly used for coating metals, fabrics, cements, plastics and rubber. However, solvent-based fluoroelastomer coatings use ketones as solvents, solids content is 20% to 40%, curing agents are generally amines and aminosilanes, and the service life (activation period) is short. Only 2-4 hours, the coating must use double packaging. The newly developed water-based fluoroelastomer polymer introduces a functional group that may undergo cross-linking reaction within the molecule or between molecules. A partially hydrolyzed aminosilane is used as a curing agent, and its amount is optimized, and the single package can be stored stably for 4 months. Water-based fluoroelastomer coatings reduce the amount of VOCs and can replace solvent-based coatings in automotive, chemical, aerospace and other industrial applications.
Third, ultra-low surface free energy Fluorine-containing polymer coating PTFE is the lowest surface free energy resin, use this feature to make a series of anti-stick coating, because it is not easy to adhere to food, can be longer at high temperature Application, odorless, non-toxic, widely used in aluminum, aluminum alloy castings, stainless steel, iron and bakelite materials, as a variety of kitchen interior paint, can also be used in the range hood, bakelite handle.
By using the relationship between the structure of the fluorine compound and the surface free energy, a new, lower surface free energy fluorine-containing resin is designed, and many new types of coatings can be further developed. For example, people began to study the application of ultra-low surface energy fluorine-containing resins in self-cleaning coatings (architectural coatings, aluminum coatings). When the wetting angle is greater than 160°C, water droplets can easily roll off. The self-cleaning function depends on the surface roughness, in addition to the surface free energy. The smaller the roughness, the better self-cleaning.
The ultra-low surface free-energy fluorine-containing coating can also be used for underwater anti-fouling of ships at sea, no need for anti-fouling agents, and the problem of pollution prevention of seawater by anti-fouling agents is eliminated. Another potential use is as a coating for blood-blendable materials, such as dialysis membranes, artificial blood vessels, medical implants, etc. Since the adsorption of proteins in human blood is minimal, the compatibility with blood can be improved.
In addition, people have used the characteristics of good translucency, chemical inertness, and incombustibility of fluororesin to launch photocatalytic coatings, fluorescent coatings, flame retardant coatings, etc., which have also become a hot topic in the coatings industry.
Reproduction of Silicon-Containing Coatings The current national production volume of solvent-borne silicone coatings is about 4000t/a, and research and development focuses are mainly on water-based, coupling agents, new organic silicon monomers, and waterborne inorganic coatings containing silicon.
A. Silicone-modified Acrylic Water Dispersion Coatings Silicone-modified Acrylic Water Dispersion Coatings combine the advantages of two resins, with excellent weather resistance, scrub resistance, and stain resistance, while being water-based coatings that will be high The combination of performance and environmental protection is a hot topic at home and abroad. The focus of silicone modified coatings research is to improve the stability of silicone-acrylic emulsion polymerization, increase the content of silicone in the modified resin, and obtain excellent performance of silicone-acrylic emulsion.
In foreign countries, silicone-acrylic coatings with good durability and anti-staining properties have been developed for more than 10 years. Some domestic units are promoting silicone-modified acrylic emulsions with 15% to 25% organic silicon content. However, from the analysis of technical indicators, the improvement in performance is not large, the minimum film formation temperature is high, the VOC content is high, and the cost performance is difficult to accept. . Because the process of emulsion polymerization of silicone-modified acrylic acid is very complicated and involves many factors, only a stable emulsion containing more than 10% of silicone is obtained macroscopically, which is not necessarily the best structure of the emulsion, so it is still to be further studied in order to catch up with foreign standards. .
2. Silane Coupling Agents and Precursors Used in Coatings 1. Silane Coupling Agents In recent years, Europe, America and Japan have passed silane coupling agents and silica sols (solute with SiO2 as the basic unit) and other metal oxides and organic synthetic resins. Sol-gel technology has developed a series of organic-inorganic hybrid coatings that can be applied to the coating of metals, cements, plastics, and wood. The paint has good gloss, high hardness, strong flame retardancy, weather resistance comparable to fluororesin coatings, acid resistance, alkali resistance, and corrosion resistance superior to epoxy coatings; outstanding heat resistance, long-term workability at 500°C, maximum Can withstand 800 °C; for internal and external wall coatings with self-cleaning and antibacterial function; due to the use of silane coupling agent, the coating and the substrate is more solid, its comprehensive performance greatly exceeds solvent-based silicone coatings. The problem is that there is only 90 days of single-package storage at 30°C. In addition, the higher silane coupling agent price also leads to higher coating prices. At present, some companies in Taiwan are promoting such products in the mainland.
2. Silane precursors In sol-gel technology, tetraethoxysilane (TEOS) is commonly used as a precursor, in addition to modified polyester resins, it can also be used for the modification of polyacrylates, epoxy resins, etc. The obtained coating film is dense and uniform, but the coating film is too thin (about 1 μm) and is not suitable for a single coating. Someone has developed a new silane precursor, which is controlled by trimethyltrimethylcyclotetrasiloxane coupling agent under alkaline conditions with HSiCl2CH3 to obtain the pure and colorless liquid of polyethoxysilane. Polycondensation reaction, a new multifunctional sol-gel oligomer precursor can be obtained. This oligomer precursor has excellent storage stability (storage time, 3 years), and also has better film-forming properties. It can be formulated as automotive varnish, coating film from 4μm to 25μm, without cracking; Good transparency on glass, hardness 5H, no yellowing, good gloss retention.
Compared with the synthetic process of silicone-modified other resins, the sol-gel method can easily prepare Si02 (inorganic phase)-organic resin composite film forming materials. The composite materials of Si02 and polysiloxanes, polyacrylates, polyesters, epoxy resins, polycarbonates, and rubbers have been studied in foreign countries, with excellent uniformity, dense coating, and increased chemical resistance. , wear resistance, weather resistance. Although the sol-gel method for the preparation of composite film formers is still in the experimental stage, but foreign experts pointed out that it is a new method of coating chemistry, for the preparation of excellent performance paint composite film shows a new prospect .
Nano, cleaning and other coatings are increasingly active First, nano-materials modified coatings nano-materials will enhance its many functions in the coating, such as nano-TiO2 for photocatalytic coatings, have the function of air purification; nano-SiO2 modified architectural coatings can improve resistance Scrubbing, antibacterial and self-cleaning properties; nano-modified stealth coatings have been officially used on aircraft and other aircraft. Other functional nanocomposite coatings and general-purpose nanocomposite coatings have been reported at home and abroad. Due to excessive speculation of nanometers in previous years, the image of nano-modified coatings was greatly damaged, but from a scientific point of view, nano-modified coatings are still an important direction of development.
Second, Hyperbranched Polymers Hyperbranched polymers with dendritic structures have attracted attention both at home and abroad due to their special properties. The hyperbranched polyester resin has a spherical shape, low viscosity, good coating performance, and potential applications in high solids coatings. Hyperbranched polyester acrylic copolymers are used in UV-curing coatings without any photosensitizers, which can reduce the cost of UV-curable coatings by 10% to 40%, making the study of hyperbranched polyesters and modified copolymers highly desirable.
Third, the clean coating technology, such as automotive paint If you use solvent-based paint, will produce a lot of VOC, and there are problems such as heavy metal pollution. European automotive coatings (such as Daimler-Benz) use coating technology instead of painting, using water-based and powder coatings as much as possible to achieve VOC emissions of 7g/m2 for car body painting, which is far below European emission regulations (from 60g/m2 dropped to 35g/m2). Some advanced automotive paint production lines further propose the concept of zero VOC emissions.
The development of simplification of phosphating and chromium passivation processes in foreign countries has made great progress in research and development. Waterborne alkyd coating and phosphating and passivation processes have been successfully applied. This not only simplifies the process, but also removes Cr6+-containing heavy metals. Passivation; Developed a successful epoxy primer, VOC-free acrylic latex