Summary: The application, advantages and disadvantages of chlorinated rubber coatings are introduced, and the severe challenges such as environmental protection, VOC reduction and application range are emphasized.
Key words: heavy anticorrosion coating, chlorinated rubber coating, high durability
Development of chlorinated rubber coatings
1.1 period of prosperity Chlorinated Rubber resins are made from natural Rubber and other materials in chloroform or tetrachloromethane solvents at 80-100 °C. In the 1950s, chlorinated rubber coatings gradually replaced nitrocellulose coatings, perchloroethylene coatings, low-grade alkyd coatings and so on. Especially after 1960s, with the appearance of thick-film chlorinated rubber coatings and the use of airless spraying technology, the film thickness of a spray increased from 35um to 80um, and chlorinated rubber coatings began to be widely used in the field of Hyundai Heavy Industries. 1.1.1 shipping The application of chlorinated rubber coating in marine industry is the most common. From 1960s to 1970s, Ministry of chemical industry and navy organized “418”marine coatings to develop chlorinated rubber anti-corrosion coatings for ship bottom. Chlorinated rubber coating is widely used in new ship hull paint, water line paint up to G other ship accessories.
1.2 Ship repair as a two-year overhaul, until now still a large number of applications of chlorinated rubber coating. 1.1.2 containers Since the first container in 1960, all the containers in the world have been coated with chlorinated rubber. Before 2000 in the container industry, the outer side of the container with chlorinated rubber finish had to pass the test of 8 items and 13 Tests in the KONSTTENDT laboratory of the United States, with a total score of more than 120 points （out of 130 points） , to make an international standard container. Container Paint Quality Target: 5 Years 10% IS04628 RI3 grade 1.1.3 bridges From 1993 to 2004, chlorinated rubber coating was used as topcoat in bridge industry. Example 1: Zhaobao Mountain Bridge, Ningbo （concrete structure, design unit, Tianjin Municipal Design Institute） , opened in 1995. The coating matching scheme is shown in Table 1, and the effect is good. The first major overhaul did not begin until late 2017,22 years later. Table 1: Coating Scheme for Ningbo Zhaobao Mountain Bridge Table 1 Coating matching schema of Ningbo zhaobaoshan Bridge Matching scheme Specified film thickness UM Epoxy sealant 30 Chlorinated rubber coating 80
1.3 Chlorinated rubber topcoat 80 Total 190
Example 2: Huangpu River: the coating schemes of 4 bridges are shown in Table 2. Table 2 coating schemes for 4 bridges on Huangpu River Table 2 Coating matching schema of 4 bridges on the Huangpu River Completion time Bridge name Matching scheme Overhaul time 1993 Nanpu Bridge Epoxy zinc-rich primer + epoxy mica medium coat + chlorinated rubber topcoat 2010 1995 Xupu Bridge Water-borne inorganic zinc-rich primer + epoxy cloud iron coating + chlorinated rubber topcoat 2016 1996 Yangpu Bridge Epoxy zinc-rich primer + epoxy mica medium coat + chlorinated rubber topcoat 2018 2004 Lupu Bridge Epoxy zinc-rich primer + epoxy cloud iron coating + polyurethane topcoat 2018 As can be seen from Table 2, the steel truss girders of the three bridges have been coated for more than 15 years, of which the Nampho Bridge is the best: during major repairs, 30% ~ 40% chlorinated rubber topcoat is still firmly attached to the surface of steel beam （pull-off adhesion > 3.0 MPA） . According to the investigation of different bridges, different low surface treatment coatings are selected for overhaul. The application of low surface treatment coating is attributed to the anticorrosion of chlorinated rubber coating, which achieves the effect of energy saving and environmental protection. 1.2 consolidation stage CCL4 was used as a solvent in the traditional production process of chlorinated rubber resin. CCL4 is an ozone depleting substance, which pollutes the atmosphere and is restricted by environmental protection in many countries. In 1991, our country signed into law the London Amendment to the Montreal Protocol, according to the provisions of the amended Montreal Protocol, our commitment to the global phase-out of the production and consumption of ozone-depleting substances by phasing out and limiting the use of CCL4 in the production of chlorinated rubber and completely eliminating the use of CCL4 by 2010, shut down the apparatus for producing chlorinated rubber coatings with CCL4. Because the supply of chlorinated rubber resin in China has dropped sharply, some industries have stopped using chlorinated rubber. International Container Standardization Committee: stop using chlorinated rubber topcoat to use acrylic topcoat; foreign owners have also cancelled the use of chlorinated rubber paint, replaced by acrylic paint, polyurethane paint; The domestic bridge uses acrylic acid, polyurethane, fluorocarbon, polysiloxane topcoat, the construction steel structure also uses acrylic acid, polyurethane, fluorocarbon, polysiloxane topcoat. The development of chlorinated rubber coating is in the consolidation stage. 1.3 setting sail again Since 2006, Xiangshui Ruize Chemical Co. , Ltd. （the predecessor of Jiangsu Ruihe New Material Co. , Ltd.） has successfully developed a new process for producing chlorinated rubber resin by non-Carbon tetroxide method through solvent screening and compounding, the production process of the process realizes the closed-circuit circulation, and the whole production process has no waste water. Through the domestic expert authentication and Environmental Protection Appraisal, in 2007 obtained the national invention patent, filled the domestic blank. The company’s annual output of chlorinated rubber resin is as high as 5000t, which is continuously supplied to the paint manufacturers of “Kailin”， “Yangtze River”， “Fish boy”， “Flywheel”， “Flying whale”， “Haiyue”， “Nanjing”and “Goldfish”， about 30,000 tons of chlorinated rubber coating can be produced every year. Chlorinated rubber coatings are back on the fast track:
（1） a large number of chlorinated rubber coatings have been applied in the new shipbuilding and ship-repairing industry in China. Such as Zhejiang Zhonghong Shipping Co. , Ltd. using “Yutong”paint coating system: YUTEP 856 epoxy low surface treatment primer; YUTEP 852 epoxy bonding paint; YUTAF 933 self-polishing antifouling paint; Yutcr 915 chlorinated rubber antirust paint; Yutcr 916 chlorinated rubber antirust paint; Yutcr 960 chlorinated rubber topcoat.
（2） petrochemical works: In 2016 Hebei Zhengyuan Chemical Company overhaul EPC project, Donghua Engineering Company designated the use of chlorinated rubber paint.
（3） concrete bridges: In the winter of 2017, Shenyang Jinfeima Coating Engineering Company undertook the following supporting schemes for the concrete bridge project: Epoxy sealant 30um Chlorinated rubber intermediate paint 140um Chlorinated rubber topcoat 80um Total 250um The disadvantage of low temperature was overcome, and the project construction was smooth.
（4） when the Tianjin Ocean Design Institute discusses the ocean platform coating overhaul plan, also involves uses the construction performance fine chlorinated rubber paint.
（5） other industries Since 2017, Kunming Zhonghua paint has undertaken a large number of hydropower station gate projects, such as the Longkaikou Dam steel structure using the following supporting schemes: Epoxy zinc phosphate primer 60 m Chlorinated Rubber Topcoat 80m Total 140m Nuozhadu eight gates new power station, using the following supporting program: Epoxy zinc-rich primer 80m Epoxy cloud iron coating 100 m Chlorinated Rubber Topcoat 80m Total 260m Advantages and disadvantages of 2 chlorinated rubber coating 2.1 pros The use of chlorinated rubber coating and related supporting, has the following advantages: Good water resistance and corrosion resistance, its coating to water, gas permeability is low, only one tenth of alkyd resin coating. Chlorinated rubber coatings are included in the coating package specified in part 5 of IS012944-2007. In C5-1, severe corrosive environment, chlorinated rubber coatings have a supporting coating life of more than 15 years. Chlorinated rubber coatings can also be used on steel structural surfaces, such as hull and concrete surfaces, in dry and wet alternate zones. Good adhesion. The adhesion between chlorinated rubber primer and steel treated by sand blasting is good, the adhesion between chlorinated rubber primer, Topcoat and epoxy primer is also good, and the maintenance of chlorinated rubber coating is convenient, can be coated with chlorinated rubber, acrylic, oil-based coatings and various anti-fouling coatings. Excellent chemical resistance. Due to the chemical inertness of chlorinated rubber coating, its coating has excellent acid resistance, alkali resistance, and even can be used directly on alkaline substrates such as concrete. Excellent construction performance. Chlorinated rubber is a one-component coating that dries quickly. The application temperature ranges from-5 °C to 40 °C without the limit of maximum painting interval. It is suitable for airless spraying. When necessary, it can be heated and sprayed. The temperature of paint can be controlled in the range of 35 ~ 40 °C. Chlorinated rubber coatings can be “Wet-to-wet”sprayed on an automatic spray line to improve production efficiency. Excellent resistance to cathodic protection. 2.2 disadvantages In view of the chemical characteristics of chlorinated rubber coating itself, as an anti-corrosion coating has its shortcomings; in dry environment, it will decompose at 130 °C; in wet environment, it will start to decompose at 60 °C, the use temperature should not be higher than 60-70 °C. Chlorinated rubber coating not resistant to aromatic hydrocarbons and certain solvents; can not be long-term contact with animal and vegetable oils and fats, or the film will be softened expansion. The coating is easy to fade and change color. Chlorinated rubber coatings should not be used on the inner walls of chemical tanks and chemical equipment. Some chemicals may damage the coatings. Chlorinated rubber coating basically can not be “Water-based”， conventional products VOC （volatile organic compounds） content of 460 ~ 500g/L. The severe challenge to chlorinated rubber coating 3.1 chlorinated rubber resins must be prepared in accordance with environmental regulations At present, there are only two methods to meet the environmental requirements in China:
（1） Carbon tetroxide new solvent technology Jiangsu Ruihe New Material Co. , Ltd. has the exclusive development of this technology and the National Patent Authorization. The new process uses a new solvent instead of the tetrachloromethane solvent. Solid natural chlorinated rubber is fully plasticized and dissolved in the solvent. An initiator is added to open the double chain and the chlorine substitution reaction is carried out, without emulsifier and dispersant, the reaction process is uniform and sufficient, the relative molecular weight is controlled accurately, and the miscibility with other resins is strong. The new recovery process uses multi-stage condensation （- 50 ~-15 °C） to recover solvent, the recovery rate of solvent is more than 99.5% , the whole production process has no waste water, realizes the closed-circuit circulation, basically achieves zero discharge, and is friendly to the environment. At the same time, the new process achieved a breakthrough in the tetrachloromethane method, which can not produce super high viscosity chlorinated rubber resins. The chlorinated rubber resin with very low viscosity has been successfully developed by Ruihe New Process, which can be used to prepare chlorinated rubber coatings with high solid content and low VOC emission, see Table 3. Table 3 VOC emissions from several coatings Table 3 VOC emissions of several coating Brand Name Viscosity/KU Solid/% by volume VOC emission/（g.L-1） Chlorinated rubber coating 90 71 289 Epoxy paint 92 80.5 196 Polyurethane coating 90 68 314 Acrylic paint 91 50 480
（2） water-phase method for chlorinated rubber （i. e. aqueous suspension method） In the process of aqueous suspension, emulsifier, dispersant and initiator are added to latex and low concentration （< 10%） hydrochloric acid aqueous solution, and stirred to make the solution appear as suspension emulsion state, then the acid is washed by water, neutralized, and then deacidified and dried. The process produces a large amount of acidic and organic waste water after dehydration, which increases the environmental protection treatment burden. On the other hand, the chlorination reaction of the aqueous suspension method is different from the homogeneous chlorination reaction of the solvent method, therefore, the use of water-phase chlorinated rubber resin to replace solvent-based chlorinated rubber resin, but also in the modification and application of further improve and improve. 3.2 strengthen the research of chlorinated rubber coating and expand its application Types of chlorinated rubber coatings: Primer: Chlorinated Rubber Iron Red antirust paint, chlorinated rubber aluminum powder iron antirust paint, chlorinated rubber mid-coat paint. Topcoat: Alkyd modified chlorinated rubber topcoat, acrylic modified chlorinated rubber topcoat, epoxy ester chlorinated rubber topcoat. Scope of application: Marine （new shipbuilding, ship repair） paint, road marking paint, container paint （Belt and Road-RRB- , elevator steel structure primer, construction steel, chemical industry （new and overhaul） offshore platforms, bridges （concrete bridges） . At present, concrete accounts for one-third of the painting area of bridges, and various concrete structures requiring repair are gradually increasing. Especially when the ambient temperature is below 0 °C, water-based coatings and solvent-based epoxy coatings can not be applied, chlorinated rubber coating can play its advantages, smooth construction. Table 4 complete sets of chlorinated rubber coatings for concrete surfaces Table 4 Chlorinated rubber coating matching for concrete surface Serial number Paint type Specified film thickness um Number of channels Persistence 1 Epoxy sealant 40 1 Over 15 years 2 Epoxy putty 3 Chlorinated rubber coating 100 2 4 Chlorinated rubber topcoat 80 2 Conclusion In heavy anti-corrosion industry, the quality of supporting coating is the key to ensure the quality of coating, to achieve the specified age, is the largest energy conservation and environmental protection. The corresponding coating systems of ISO 12944C 4 and C 5 are shown in tables 5 and 6 respectively. Table 5 coating systems corresponding to C4 corrosion grades Table 5 Coating scheme corresponding to C4 corrosion grade System number Matching scheme NDFTum Expected durability Primer um Medium coat um Topcoat um C4-03 Chlorinated rubber primer 80 Chlorinated rubber intermediate paint 100 Chlorinated rubber topcoat 80 260 H （15-25 years） C4-11 Epoxy zinc-rich primer 80 2 coats 100 for chlorinated rubber or 100 for epoxy Chlorinated rubber topcoat 80 260 VH （> 25 years） Table 6 coating schemes corresponding to C5-1 corrosion grades Table 6 Coating scheme corresponding to C5-1 corrosion grade System number Matching scheme NDFTum Expected durability Primer um Medium coat um Topcoat um C5-02 Epoxy primer 80 Ring