Fluororesin coating and steel-plastic composite barrel
Shanghai Xugong Coating Technology Co., Ltd. Xu Guoxing
The fluororesin is a general term for a resin containing a fluorine atom in a polymer structure. In 1934, F. Schlofer and O. Scherer invented polyvinyl fluoride and in 1938, Pr. J. Plunkett discovered the refrigerant of halothane. Teflon has been counted for more than half a century.
The fluororesin is prepared by homopolymerization or copolymerization of a fluorine monomer such as tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride and ethylene. In the initial stage, although there were only two varieties of polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE), it was found to have excellent properties such as heat resistance, low temperature resistance, chemical resistance, weather resistance and resistance. Aging, pollution resistance, non-stickiness, low coefficient of friction, electrical insulation properties, etc. Therefore, people have been highly valued from the beginning. However, at the same time, it has also found its Achilles heel, such as poor machinability, insoluble, refractory, and it is difficult to have pinholes even if it is made into a coating. Later, as technicians continue to work hard to develop new varieties of fluororesins that overcome these weaknesses and have excellent performance, such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (Teflon PFA), it is called "fusible." Sexual PTFE."
Today, fluororesin products from all over the world have grown to more than a dozen varieties, such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE). ), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), ethylene-chlorotrifluoroethylene copolymer (E-CTFE), ethylene-tetrafluoroethylene copolymer (E-TFE), tetrafluoroethylene-perfluoro An alkyl vinyl ether copolymer (Teflon PFA), a vinylidene fluoride-chlorotrifluoroethylene copolymer (VDF-CTFE), a tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (Teflon EPE), Perfluorosulfonic acid resin (XR resin) and vinylidene fluoride-hexafluoroisobutylene copolymer (CM-I resin) and the like. The annual production capacity of global fluororesin has reached 75,000 tons 10 years ago. 20% of it is used in coatings. Therefore, fluororesin coatings are one of the main uses of fluororesins.
Second, fluororesin coating
The fluororesin coating has a dispersion type, a enamel type, a powder type, and the like in terms of its form. From the perspective of its functional use, it can be divided into anti-corrosion, weather-resistant, anti-stick, anti-wear and other coatings. Its application fields are very wide, such as household appliances, electric irons, non-stick pans, food utensils, molds, construction industry, chemical anti-corrosion, light-transparent weather-resistant roofs for large sports fields, exterior decorative coatings, etc. Now, the fluororesin which has been used as a coating material is polytetrafluoroethylene, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene. Ethylene-perfluoroalkyl vinyl oxime ether copolymers, polyvinyl fluoride and the like.
At present, some fluororesin coating grades and manufacturers available abroad are listed in Table 1.
Table 1 Manufacturer's brand number and manufacturer of some fluororesin coatings
Third, the performance and application of chlorine resin coatings
1. PTFE coating
Polytetrafluoroethylene English abbreviation PTFE. Polytetrafluoroethylene resin is extremely resistant to chemical corrosion. In addition to metal sulphate, fluorine and its compounds have erosive effects, other chemicals such as strong acids, alkalis, greases, detergents and organic solvents do not work for it, so it is known as plastic king, it can withstand boiling Various concentrations of hydrofluoric acid. It can remain soft below -1Â°C, and can maintain dimensional stability at 25Â°C. The 0.1mm thick PTFE film has been exposed to outdoor for more than six years, and its appearance and performance have not changed significantly. It is excellent in chemical stability and aging resistance.
There are two types of PTFE coatings, decentralized and enamel. Generally, it can be applied by spraying or dipping. Since polytetrafluoroethylene has a very high melt viscosity at the processing temperature, it is difficult to apply without pinholes, and the adhesion between the coating film and the object to be coated is also poor. Therefore, pure PTFE resin coatings are generally not used in anti-corrosion applications, but in non-stick, lubricated applications, such as frozen food trays, baked food molds, various industrial molding dies, electric irons, non-stick pans. And lubricating coatings for mechanical parts.
In order to make the polytetrafluoroethylene resin coating fully exert its chemical corrosion resistance and aging resistance, the polytetrafluoroethylene resin may be modified or blended to make up that the resin is too soft and has poor adhesion to the coated object. The coating film is easy to have pinhole weakness. Resins for modifying polytetrafluoroethylene abroad include phenolic, acrylate, epoxy, polyimide, polyurethane, p-hydroxybenzoic acid polymers and the like. The modified polytetrafluoroethylene coatings are satisfactory in various fields and are therefore welcomed in various fields.
Here, it is important to introduce a polymer that has the potential to apply a modified polytetrafluoroethylene coating to steel drums, called polyphenylene sulfide (PPS), also known as polyphenylene sulfide, with a molecular formula of . This is a thermoplastic resin that is resistant to strong acids and bases such as sulfuric acid, hydrochloric acid, phosphoric acid, sodium hydroxide, potassium hydroxide, hydrogen peroxide, etc., and is insoluble in common organic solvents. It can be used continuously at 28 Â° C, and can be heat resistant to 600 Â° C or more after chemical crosslinking. It has excellent adhesion and good adhesion to glass, ceramics and metals. As a coating, it has excellent adhesion and adhesion to metals. It is a highly heat-resistant, chemically resistant coating, but its film is hard. Pure polyphenylene sulfide as a coating appears to be hard and brittle. However, when polytetrafluoroethylene is blended with polyphenylene sulfide to form a coating, it compensates for its weaknesses, and the advantages of this mixed coating are well exerted. The C-4012 "PPS/PTFE" coating from Japan's Hodogaya Chemical Industry is made of polyphenylene sulfide as the precursor, with titanium dioxide, and then added with PTFE for blending and sanding.
2. Polychlorotrifluoroethylene coating
Polychlorotrifluoroethylene English abbreviation PCTFF. It is known from the name of polychlorotrifluoroethylene that it has three fluorine atoms and one chlorine atom in its molecule. Compared with polytetrafluoroethylene, one of the four fluorine atoms is replaced by a chlorine atom, which causes the polarity of the molecular structure, so its heat resistance and chemical resistance are slightly lower than that of polytetrachloroethylene. However, in addition to the fluorine-containing gas at high temperature, highly halogenated solvent and molten alkali metal, it can still withstand all other acids, bases and solvents, and its film is air, water, 28% ammonia, 50% sodium oxyhydride, 37% hydrochloric acid, benzene, methanol, etc., have excellent barrier properties. It also has good cold flow resistance, high compressive strength, good wear resistance and dimensional stability, and can withstand tests from -200 Â° C to +200 Â° C for a long time. Its coating can be applied as a thick, pinhole-free coating. The permeability of this coating to various gases and chemicals is the smallest of all fluororesins. Therefore, it is the most commonly used anti-corrosive fluororesin coating. For example, adding polychlorotrifluoroethylene resin to graphite powder or chromium oxide and formulating a suspension dispersion with a concentration of 30% to 40% in ethanol is a good coating for spraying, dip coating and pouring. Coating, brushing, etc. After the coating, the solvent (ie, ethanol) is volatilized and then melt-plasticized at 300 Â° C to become a very good anti-corrosion coating. Shanghai Shuguang Chemical Factory has a reaction tower with 1-2% sulfuric acid and 25% ammonium sulfate. It used to be 6mm lead lining for anti-corrosion. It needs to be replaced after 2000 hours. It is coated with polychlorotrifluoroethylene and used. 5000 hours is still good. There is also a water-washing tower with a medium of 10% hydrochloric acid and a trace of hydrogen fluoride and a working temperature of 80 Â°C. It was originally lined with phenolic plastic and asbestos mortar. It will be replaced in just a few months and replaced with polychlorotrifluoroethylene. It remains the same for more than two years.
3. Tetrafluoroethylene hexafluoropropylene copolymer coating
Tetrafluoroethylene hexafluoropropylene copolymer, also known as polyperfluoroethylene propylene, FEP prepared in English. Its chemical stability is similar to that of polytetrafluoroethylene. Only elemental fluorine, alkali metal, oxygen difluoride, chlorine trifluoride, etc. at high temperature can interact with it. For other various concentrations of inorganic acids, bases, alcohols, Ketones, aromatic hydrocarbons, chlorinated hydrocarbons, detergents, greases, etc., have excellent corrosion resistance, and the long-term use temperature range is -85 Â° C to ten 205 Â° C. Since the melt viscosity is lower than that of polytetrafluoroethylene, the pinhole phenomenon of the coating is much better than that of polytetrafluoroethylene. Since its basic properties are similar to those of polytetrafluoroethylene, tetrafluoroethylene hexafluoropropylene copolymer can also be used in applications where PTFE can be used.
The tetrafluoroethylene hexafluoropropylene copolymer coating has two types of dispersion type and powder type. The dispersed coating can be processed by a general spraying method, and the powder coating is processed by electrostatic coating or bubbling bed dipping. Since the flow properties of the tetrafluoroethylene hexafluoropropylene copolymer coating are better than those of the same meltability, such as polyvinylidene fluoride, ethylene tetrafluoroethylene copolymer, and tetrafluoroethylene perfluoroalkyl vinyl ether copolymer, This paint is much more popular. In addition, the coating is partially repaired, and the film thickness can be up to 2000Î¼. Therefore, it is very suitable for anti-corrosion occasions.
4. Tetrafluoroethylene perfluoroalkyl vinyl ether copolymer coating
Tetrafluoroethylene perfluoroalkyl vinyl ether copolymer, also known as polyperfluoroalkoxy is a polymer of a "CF" chain backbone linked to a perfluorinated propoxy side chain through an oxygen bond. Abbreviated as PFA.
Tetrafluoroethylene perfluoroalkyl vinyl ether copolymer is similar to polytetrafluoroethylene in chemical resistance, non-stickiness, electrical properties, weather resistance, etc., but it can be thermoplastically processed, so it is called fusible polytetra Vinyl fluoride. Because its coatings are similar in properties to PTFE and can be applied as a smooth, pinhole-free coating, they are extremely versatile. It can be used in applications where PTFE coatings can be used. It can be used in applications where PTFE coatings can be used. It can also be used in chemical anti-corrosion coatings that cannot be applied in PTFE coatings. very popular.
5. Ethylene tetrafluoroethylene copolymer coating
The chemical composition of the ethylene tetrafluoroethylene copolymer, particularly a copolymer having a ratio of ethylene to tetrafluoroethylene of 1:1, is similar to that of polyvinylidene fluoride. However, polyvinylidene fluoride is soluble in dimethyl amide and dimethyl sulfoxide, and even crosslinked polyvinylidene fluoride can swell in these two solvents, whereas ethylene tetrafluoroethylene copolymer does not dissolve or swell. . It is written in English as ETFE. A copolymer having a ratio of ethylene to tetrafluoroethylene of 1:1 is referred to as F-40.
Ethylene tetrafluoroethylene copolymer combines the radiation resistance of polyethylene and the corrosion resistance of polytetrafluoroethylene. Its chemical corrosion resistance is similar to that of polytetrafluoroethylene, but its mechanical strength, toughness, creep resistance and wear resistance. Sex is much better than PTFE.
Ethylene tetrafluoroethylene copolymer coatings are also available in both dispersion and powder form. Among them, the electrostatic coating of powder coating is the best, the coating can be applied to any thickness, and the coating can be fully melted to form a continuous smooth pinhole-free coating film, which has good resistance. Penetration performance.
6. Ethylene chlorotrifluoroethylene copolymer coating
The ethylene chlorotrifluoroethylene copolymer is usually a polymer compound obtained by copolymerizing ethylene chlorotrifluoroethylene in a ratio of four, six or six or four. The molecular structure is abbreviated as F-30, and the English abbreviation is ECTFE. It was first produced by the American Allied Chemical Company in the 1960s. Its powder pellets are marketed under the name Halar. It has the mechanical strength of nylon, the corrosion resistance of fluoroplastics and the molding properties of high density polyethylene. In addition to being attacked by chlorinated solvents at elevated temperatures, there is no plasticizing agent at 120 Â°C. The coating is mainly a powder coating and is suitable for coating by electrostatic coating or boiling impregnation. However, the use of ethylene chlorotrifluoroethylene copolymer in coatings appears to be relatively small compared to its other applications.
7. Polyvinylidene fluoride coating
Polyvinylidene fluoride is a homopolymer of vinylidene fluoride, abbreviated as PVDF. Polyvinylidene fluoride has the inherent heat resistance and chemical resistance of the fluororesin series and the cracking stability in a very strong ultraviolet environment. It is resistant to most chemicals, solvents, oxidants, alkalis, halogens other than high-temperature elemental fluorine, but degraded in strong acids (such as fuming sulfuric acid) and strong organic bases (such as n-butylamine). It is swollen or partially dissolved in a solvent such as acetone, ethyl acetate or methyl ethyl ketone, and is dissolved in a colloidal solution in a strong polar organic solvent such as dimethylacetamide or dimethyl sulfoxide. Its use temperature is -70 Â° C to +150 Â° C.
Polyvinylidene fluoride can be dissolved in a polar organic solvent, so it is convenient to prepare an organosol coating which is dispersible, which is the biggest difference between polyvinylidene fluoride and the above fluororesins.
Polyvinylidene fluoride was commercialized in 1960 by Pennsalt. Dispersed coatings are applied by spray coating, and powder coatings are applied by electrostatic spraying or bubbling bed dipping. At present, all of the coatings used in steel drums are polyvinylidene fluoride dispersion type coatings in which dimethyl phthalate is used as a dispersion. Because this coating has been applied to domestic steel drums, it is more extensively described here.
Since polyvinylidene fluoride has good coloring properties, it can be made into various bright colored paints. Because of its flame retardancy and excellent weather resistance and radiation resistance, its coatings can be used in a variety of exterior applications in addition to chemical corrosion.
For the coating of polyvinylidene fluoride coatings, Pennselt has conducted special tests, of course, testing their company's polyvinylidene fluoride coating. However, it is not unreasonable to explain the performance of the coating film.
Table 2 Polyvinylidene-resistant chemical medium performance table
(1) Paint film exposure test: The tensile strength is maintained at 20,580 kPa, and the medium length is 5-10%, up to 30 years.
(2) Abrasion resistance: resistance to atmospheric dust, rain, snow, construction site damage, 30 to 60% stronger than the usual synthetic resin coating.
(3) Salt spray resistance: After 1000 hours of salt spray, there is no change in the color of the coating film, and even the scratched portion is excellent in adhesion and corrosion resistance.
(4) Accelerated aging: no change in 1000 hours, and the weight loss of the coating film after 4000 hours is one third of other synthetic resin coatings.
Our steel drum industry mainly uses its chemical resistance, so the chemical resistant medium of polyvinylidene fluoride listed below is expected to contribute to the application of polyvinylidene fluoride coating in our steel drum industry. As shown in Table 2.
8. Polyvinyl fluoride coating
Polyvinylidene fluoride, polyvinyl fluoride is a homopolymer of vinyl fluoride, abbreviated as PVF. Polyvinyl fluoride has particularly good weatherability. Because it does not absorb ultraviolet light from sunlight, it has excellent sun aging resistance and flexibility. Cooking in superheated water at 160 Â° C for 60 hours, the performance remains unchanged. It is immune to most boiling acids and bases and is resistant to at least 100 Â° C for many solvents. Reagents that can withstand one year are: 20% sulfuric acid, phosphoric acid, nitric acid, 10% sodium chloride and sodium hydroxide at room temperature, phenol; kerosene; 10% hydrochloric acid; n-hexane; benzene; 12 to 39% hydroxide Ammonium; acetone. The reagents that can withstand one month are: cresol phosphate at 75 Â° C; trichloroethylene; toluene; % sulfuric acid; 9% sodium sulfide; 10-54% sodium hydroxide; 5% phenol; 10-40% nitric acid, methyl ethyl ketone, 10-30% hydrochloric acid; ethanol; ethyl acetate; 10% ammonium hydroxide; glacial acetic acid. The above-mentioned "resistance" standard is that in the above reagents, there is no change in tensile, impact strength and elongation after exposure.
Polyvinyl fluoride coatings are also available in both dispersion and powder coatings. The coating method is the same as the two coatings of polyvinylidene fluoride. Polyvinyl fluoride coatings are the most widely used in the steel drum industry. The reason is that it is much lower than other fluororesin coatings, and its chemical resistance is better than other synthetic resin coatings. At present, all the polyvinyl fluoride coatings used in various barrel factories in China are all polyvinyl fluoride dispersion coatings produced by Zhejiang Chemical Research Institute using dimethyl phthalate as a dispersion. According to the institute, the polyvinyl fluoride coatings they produce can be applied to the packaging of the following chemical and pesticide products:
1 pesticides: jinggangmycin, marathon, methamidophos, rice glutinous rice, different rice glutinous rice, fenthion, trithiaphos, chlorpyrifos, pyrethroid, chrysanthemum, insecticidal double, Xin phosphorus, dimethoate, omethoate, quercetin, Jiuxiaoling, enemy anti-linger, herbicide.
2 spices, food, pharmaceuticals: glucose, honey, part of animal and vegetable oil, ginger oil, sassafras oil, eucalyptus oil, leaf oil, iLI scorpion oil, amine shell oil, turpentine, white oil, bay oil, pine Oil, silicone oil.
3 hydrocarbons and halogenated hydrocarbons: carbon tetrasulfide, tetrachloroethane, tetrachloroethylene, pentafluoroethane, cyclohexane, chlorinated paraffin, gasoline, light diesel oil, Daqing crude oil, tar, chloroprene latex, perchlorine Ethylene, chloroform.
4 alcohols, ethers, ketones, aldehydes: methanol, ethanol, n-propanol, ethylene glycol, propylene glycol, glycerol, n-butanol, isoxalate, terpineol, diphenyl ether, formaldehyde, furfural, butyraldehyde , benzaldehyde, glyoxal, cyclohexanone, methyl ethyl ketone.
5 acid, ester, amine: oleic acid, oxalic acid, low phosphoric acid, vinyl acetate, butyl acetate, dimethyl phthalate (diethyl ester, dibutyl ester, dioctyl ester), ethyl acetate, Monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, dimethylformamide, butyrolactone, tributyl phosphate, diphenyl sulfite, lactic acid.
8 benzene, benzene derivatives, heterocyclic compounds: benzene, toluene, xylene, benzyl alcohol, phenol, tetrahydrofuran, quinoline, pyridine, tannin, o-nitrotoluene, epichlorohydrin, OP emulsifier, 801 glue , wallpaper adhesive, softener, dimethyl sulfoxide.
7 inorganic compounds: cerium oxide, ferric chloride, saturated sodium chloride solution, sodium sulfate solution, 5% sodium chloride solution, sodium hydroxide solution, 30% sulfuric acid, 1O% nitric acid, 83% phosphoric acid, dichromic acid Potassium solution, 20% chromic acid, 50% 6 potassium chloride, 50% potassium oxychloride.
Fourth, fluororesin coating and steel-plastic composite barrel
Steel-plastic composite barrels, as the name implies, are barrels made of steel and plastic composite. This barrel has been introduced in the previous article "Polyethylene powder coating and steel-plastic composite barrel", except that the inner coating of the steel barrel is polyethylene plastic, and the fluororesin plastic is introduced in this paper.
The excellent properties of fluororesin coatings have been previously described. It is precisely because of the excellent performance shown by the fluorine paint, it has received the attention of all countries. However, in China, although most varieties of fluororesins such as polytetrafluoroethylene, polychlorotrifluoroethylene, tetrafluoroethylene hexafluoropropylene copolymer, tetrafluoroethylene perfluoroalkyl vinyl ether copolymer, ethylene tetraoxyethylene copolymer Polyfluoroethylene, polyvinylidene fluoride, etc. have been developed, and the application development in coatings is much weaker. Even the fluororesin coating used in the steel drum industry in China so far has only one type of polyvinyl fluoride. Although it is also useful for polyvinylidene fluoride coatings, the amount of use is negligible due to price factors. Moreover, both of these fluororesin coatings use dimethyl phthalate as a dispersion. Dimethyl phthalate is a plasticizer for nitrocellulose plastics, acetate plastics and synthetic rubber. The price is about 20,000 yuan per ton. It is used as a dispersion, which increases the cost invisibly. And, more importantly, although it is toxicologically much safer than other toxic solutions, it is used as a dispersion to produce a large amount of dense smoke during the baking of fluororesin coatings. The impact on environmental protection is conceivable. Shanghai Chemical Co., Ltd. once wanted to launch the PTFE inner coating barrel and the polyvinylidene fluoride inner coating barrel twice, all of which had to be dismantled due to too much smog.
Therefore, the research and development of domestic fluororesin coatings should be done with a little effort. At least for our steel drum industry, the development of such coatings should be very urgent.
V. Looking forward to new varieties of fluororesin coatings for steel-plastic composite barrels
At present, most of the fluororesin products used in China's coatings have been produced, but as mentioned earlier, there are few fluororesin coating products. However, it is worthy of relief that the development of this new coating has been taken seriously, and the use of the following three fluororesin coatings on steel drums is not a long way off.
1. Fluororesin powder coating. The coating is made by blending and polishing a fluororesin, a filler, a modification aid, and a pigment. Since it is completely solvent-free, it can be sprayed in a powder form and formed into a coating after baking, thus completely eliminating environmental pollution. Such coatings have long been used in foreign countries and have begun to be applied in other industries in China.
2. A dispersion type fluororesin coating of a low boiling point dispersion. The dispersion type fluororesin coating is a coating formed by uniformly dispersing a fluororesin, a filler, and an auxiliary agent in a dispersion liquid with extremely fine particles as a dispersion. After the coating film is formed by spraying or other coating method, the dispersion is volatilized and then plasticized into a film by baking. If the dispersion is of a high boiling point (such as dimethyl phthalate as described above), the volatilization of the dispersion is subject to high temperature baking. If the dispersion has a very low boiling point, it can be volatilized at normal temperature.
An example of a polychlorotrifluoroethylene coating herein is the use of ethanol as a dispersion. The dispersion of the dispersion type paint can be volatilized at normal temperature, so that a large amount of smoke is not generated during the baking and plasticizing process of the fluororesin. Moreover, if this kind of fractional liquid is used in our steel-plastic composite barrel, it is not cheap.
3. Room temperature curing type fluororesin coating. The fluorinated resin coating can be self-cured at room temperature to form a film by introducing a reactive functional group through a vinyl long chain of a fluororesin, and then reacting with a compound capable of reacting with the functional group to react with it. solidified.
The room temperature curing type fluororesin coating has not been reported in China, and it has only recently begun to supply products in foreign countries. Such as the fluororesin coating developed by Asahi Glass Co., Ltd. called "Lumiflon". The fluororesin molecules of such coatings form a fluorine-rich olefin and a vinyl ether-rich, reactive hydroxyl group by a suitable selection and combination of the kind and amount of vinyl ether side chain structure, and have a highly alternating polymer structure. When it is used as a coating material, a compound such as isocyanate or melamine is mixed with a group such as a reactive hydroxyl group to form a crosslinked network structure molecule, thereby achieving curing.
The application of fluororesin coatings in steel-plastic composite barrels has already begun well. It is hoped that in the near future, the fluororesin coatings with improved performance and superior performance will produce more fruitful results in the application of steel-plastic composite barrels.
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