Chlorinated Rubber Resin Paints for Concrete and Metal Surfaces

Introduction

Important binders derived from natural rubber or, nowadays, mostly from synthetic rubber are cyclized rubber and chlorinated rubber. Chlorinated polyolefins have properties similar to chlorinated rubber, but are prepared differently from saturated polymers such as polyethylene or polypropylene. Low molecular weight polybutadienes (oligobutadienes) with different steric structures and certain functional groups have similarly established a firm place in the paints sector in recent years. Work on the development of diene-styrene copolymers based on the use of vulcanization mechanisms (production of permanent elastic masses through cross-linking with sulfur during heating) or peroxide cross-linking reactions has been explained. Chlorinated rubber and related chlorinated polymers form paint films through physical drying. However, without the addition of plasticizers or resins, the paint film is brittle. Chlorinated rubber is a product derived by modifying natural rubber through chlorination. It finds broad application in paints, inks and adhesive production. Chlorinated rubber is a film-forming resin that can have molecular weights ranging from 3,500 to 20,000. It is a commercial product containing approximately 65% chlorine, prepared by chlorinating rubber in solution. It is used as the primary binder in air-dry paints where chemically resistant products are required. Since the polymer is a brittle solid, chlorinated rubber resin requires plasticizers in paint applications. Chlorinated rubber resins are compatible with alkyds as well as used in combination with other resins. Chlorinated rubber-based paints have been used for buildings, rendered surfaces, swimming pools, road markings and maritime purposes. In wall paints, a solution prepared with a mixture of chlorinated rubber and poly(vinyl chloride) provides good resistance to attack and can be used as the basis for wall coatings with a typical service life of 10 to 15 years.

Production

Chlorinated rubber products are manufactured by dissolving natural rubber in chlorinated organic solvents followed by a series of processes including chlorination synthesis, chemical neutralization, hydrolytic analysis, centrifugation, washing and drying. Chlorinated rubber is a product derived by modifying natural rubber through chlorination. To produce chlorinated rubber (CR) resin, natural or synthetic rubber such as polyethylene, polypropylene or polyisoprene is reduced to low molecular weight compounds through the addition of radical formers or mastication and dissolved in carbon tetrachloride (CTC) to form a solution. Chlorinated rubber is produced by treating a natural rubber solution in carbon tetrachloride with chlorine. (The rubber takes up a large amount of chlorine; approximately 67% of chlorinated rubbers is chlorine). The reaction is carried out with reflux; after the reaction is complete, the solution is treated with hot water and the chlorinated rubber is precipitated. The product is washed and dried. (Rubber)n + Cl2 ⇒ (Trichloro derivative)_n 61.3% chlorine + (Tetrachloro derivative)_n 68.2% chlorine The chlorine percentages it contains are typically 64-68% by weight. Chlorine gas is supplied to this solution and reacted with the raw material to form CR. The solution is then added to boiling water. CR is precipitated and the solvent evaporates. CR is separated from water, rinsed, dried and ground to a white powder, the saleable product. After removal of water, chlorine, hydrochloric acid and other impurities, the solvent is reused. In addition to CTC entering and affecting the ozone layer, CTC emissions from modern facilities are nearly zero. The CTC content in chlorinated rubber produced in these facilities is as low as 10 ppm (Bayer). Chlorinated rubber produced in older or substandard facilities contains up to 10% CTC. This product and products manufactured with it must be labeled in accordance with relevant regulations in different countries. Recently, an aqueous process has been developed to produce CR. Unfortunately, the carbon tetrachloride released in this process results in a CTC content of 100-500 ppm in CR. Chlorinated rubber paints are produced by conventional methods. Plasticizers, resins and in some cases a portion of the chlorine rubber are first dissolved in solvent. A solvent with a high boiling point in the formulation is more suitable for this stage. Hydrogenated castor oil is then added and the resulting mixture is dispersed in a solvent in a dissolver. To achieve optimum dispersion, the recommendations of the castor oil manufacturer must be strictly followed and the temperature must not be allowed to exceed approximately 60°C. Dispersion is followed by formation of a paste with pigments and fillers, and dispersion is then carried out in a machine. Conventional equipment such as dissolvers is suitable as dispersion equipment. Grinding with steel balls should be avoided, as the resulting iron dust can cause gelation of the final paint after prolonged storage. The dispersed and ground paste is then added to the prepared chlorinated rubber solution. In summary, chlorinated rubber products are manufactured by dissolving natural rubber in ODS-free (Ozone Depleting Substances) organic solvents followed by a series of processes including chlorination synthesis, chemical neutralization, hydrolytic analysis, centrifugation, washing and drying.

Properties

Films that dry through solvent evaporation have non-convertible film characteristics. Chlorinated rubber paints are classified physically as air-dry systems. Chlorinated rubber systems are thermoplastic. Film formation occurs through solvent evaporation. Therefore, their drying is physical. They are affected by all organic solvents except low alcohols and aliphatic hydrocarbon solvents. They do not undergo chemical reactions or are not affected by environmental conditions during short drying times. Although chlorinated rubber finds an important application area in chemically resistant paints, it has a somewhat unstable structure. At 125°C, it decomposes by generating hydrochloric acid. This can also occur at ambient temperatures, and therefore chemical stabilizers are frequently used. Lead compounds and epoxy compounds are effective stabilizers in this regard. The disadvantages of pure CR resulting from its high chlorine content are low temperature resistance (60°C wet, 90°C dry) due to the elimination of hydrochloric acid. Chlorinated rubber also tends to yellow when exposed to atmospheric influences. Chlorinated rubber is a synthetic chlorinated rubber that provides many functional and practical advantages due to its extremely high chemical resistance and excellent film-forming properties. The characteristic advantages of chlorinated rubber provide a property that best combines high quality with a well-balanced economy. Chlorinated rubber is a single-component system. This eliminates all problems associated with weighing different components in the correct proportion and subsequently mixing them. Chlorinated rubber paints have practically unlimited shelf life in containers, independent of temperature and humidity. It is possible to compensate for any solvent lost due to evaporation in unsuitable storage conditions by adding fresh solvent immediately before application. Chlorinated rubber paints can be applied as low or high build systems. Temperature and humidity are only effective under extreme conditions. When chlorinated rubber solution is applied to metal, concrete, paper and similar surfaces, the solvent easily evaporates at room temperature and forms a transparent, hard and glossy glassy film layer. This thin film can prevent the ingress of water vapor and oxygen. After aging, they have excellent overcoat adhesion. As with many organic pigments, they can be used with virtually all inorganic pigments and fillers.

Table 1: Viscosity grades of Pergut, an example of a commercial chlorinated rubber product

* Measured in a 20% solution in toluene at 23°C in a Hoppler viscometer (DIN 53015). ** Measured by combination of gel permeation chromatography and viscometry.

Solubility:

They exhibit good solubility in virtually all conventional solvents except water, aliphatic hydrocarbons and alcohols. Chlorinated rubber dissolves easily in aromatic hydrocarbons, esters and ketones.

Compatibility:

Shows good compatibility with a wide variety of paint resins and plasticizers. Chlorinated rubber is not only used as an additive in paints for fast drying and chemical resistance, but also has versatile mixtures. For example, when mixed with alkyd, acrylic and hydrocarbon resins, it dissolves easily in organic solvents such as toluene and xylene to form a colorless or yellowish transparent solution. Can be mixed with acrylic resin, alkyd and other esters. In addition, it can be combined with phenolic and vinyl resins as well as with tar, bitumen and oils.

Fire resistance:

Since chlorinated rubber is non-flammable and inert to bacteria and molds, it can generally be added to other paint systems for non-flammability properties. Chlorinated rubber systems are non-flammable and do not support combustion. However, they decompose at high temperatures and lose adhesion.

Chemical resistance:

Show good resistance to normal acids and alkaline conditions. However, they are sensitive to concentrated nitric acid and acetic acid as well as to animal and vegetable fatty acids. Not recommended against sulfur dioxide or concentrated NH4OH solutions. Can show high resistance to oxidizing agents (e.g., ozone or peroxide), water, inorganic salts, acids, alkalis and gases.

Anti-corrosive properties:

Chlorinated rubber paints are resistant to air, water and chemicals. This property provides excellent corrosion prevention effect. Chlorinated rubber has good resistance to weather conditions, excellent adhesion properties, high chemical stability, excellent salt water resistance and good UV resistance. However, in exterior systems, they can be balanced against UV degradation with UV absorbers and certain pigments. Chlorinated rubber and chlorinated paraffin degrade in heat and UV. For this reason, paints made from them should not be stoved at temperatures of 108°C or above. They should not be immersed in liquids at temperatures of 60°C or above. Paints can be applied in adverse high humidity atmospheric conditions such as low temperatures below the dew point. Zinc-rich, anticorrosive, toxic paints, architectural and fire-retardant paints can be formulated. Paints can be stored for very long periods in well-closed containers in a cool, dry place. High degree of chlorination greatly changes the properties of the polymers. A hard, granular white powder with the following properties is obtained.

Table 2: Properties of Chlorinated Rubber Resin

Table 3: Property Differences According to Resin Types

Paint Composition

The binder used in the paint contains approximately 65% chlorinated rubber (usually low viscosity types) and 35% plasticizer. As plasticizers, chlorinated paraffins, ICI (Cereclor) and Clariant Muttens (CH) can be given. If necessary, specially hydrolyzed plasticizers can also be given, these are plasticizers such as bisphenoxyethylformal (Desavin, Bayer) or resin-modified phenyl alkyl sulfonates (Leromoll, Bayer). Such a composition provides "non-hydrolyzability" which gives the binder resistance to water, acid and alkali. If hydrolyzable phthalate or adipate plasticizers are used, this property is not achieved. Non-hydrolyzable resins such as cumaron-indene resins or other hydrocarbon resins are sometimes given as filler resins. Red lead has proven to be exceptionally suitable as a pigment in initial primer coats of steel surfaces and is fully effective in chlorinated rubber paints. Due to environmental protection and occupational health, the use of toxic lead compounds is declining. Although not having the same corrosion protection effect, zinc phosphate is used instead. Lead dust, aluminum, bronze and zinc dust, like traditional metal pigments, are used in producing diffusion-resistant paints with good mechanical properties. In the case of aluminum, bronze and zinc dust use, the paint must be stabilized to prevent gelation. Iron oxide, chromium oxide and titanium dioxide pigments commonly used in the paint industry are suitable for topcoats. Zinc oxide, white lead and lithopone are not suitable. All inert minerals are suitable as fillers. Carbonate-containing fillers, however, can only be used where strict requirements for resistance to water and chemicals are not necessary. Solvent selection is practically unlimited. Xylene or other alkyl benzenes are generally recommended. Ester mixtures and white spirit can be used to avoid mandatory warning labels. Hydrogenated and modified castor oil is used as an additive to adjust viscosity. Therefore, it facilitates the application of the paint by brush or spraying (pressurized air or airless) in film thicknesses of up to 100 μm.

Application Fields

Chlorinated rubber paint can be applied with all conventional paint application equipment. However, manufacturer's instructions should be noted as chlorinated rubber paints are specifically formulated for recommended application equipment. These types of paints can be applied by brush, roller, dipping, flow coating and spraying. These paints can be applied even in adverse environments such as temperatures above the dew point and high humidity atmospheric conditions. They show very high stability against a wide variety of chemicals (e.g., acid, alkali, etc.), while also protecting the base substrate, preventing corrosion and serving as a decorative topcoat. Additionally, because this product has very high chlorine content and therefore good flame resistance. Zinc-rich, anticorrosive, toxic paints, architectural and fire-retardant paints can be formulated. Due to their high water resistance, chlorinated rubber paints are used as underwater steel and concrete surface paints in places such as water storage tanks, swimming pools, sewage systems, harbor facilities and docks. In mines using aqueous solutions of inorganic chemicals, in storage areas, tanks and structural components used in chemical plants and similar locations, they are used to provide chemical resistance. Due to the alkaline nature of the concrete surface, concrete paints require chlorinated rubber as a binder. Another main application area for chlorinated rubber paints is underwater paints in ships. The suitable properties for this application are high water resistance, fast drying independent of ambient temperature in the shipyard, mutual good adhesion of independent films and easy renewal of old paint layers.

Table 4: Application Fields of the Resin

Chlorinated rubber types are versatile and particularly suitable for use in a wide range of applications in the corrosion prevention sector. They are used wherever the protection they provide is superior to decorative effect and give equally excellent results on steel, iron and zinc as well as on concrete and other mineral building materials. Chlorinated rubber paints are widely applied on ships, offshore platforms, bridges, docks, containers, vehicle chassis, road markings, chemical equipment and in surface protection of materials for severe environmental conditions. Additionally, high viscosity chlorinated rubber is used in the production of high-strength adhesives. In addition, it is also given to other rubber products to improve their quality. Low viscosity chlorinated rubber is suitable for quality ink production. Chlorinated rubber coatings provide lasting and reliable protection against corrosion both in air and underwater, thus providing adequate protection to coated objects for many years. Chlorinated rubber has been successful in the following application areas for years:

Application fields by types

Commercial Chlorinated Rubber Resins

Commercial products, chlorinated rubber resin from natural rubber or synthetic polyisoprene, are produced by only a few manufacturers. These are given in the table below.   M. Namık Kayaalp Chemical Engineer Ecelak Boya Kimya Ltd. Şti.      

References: 1. Paint and Surface Coatings, Theory and Practice Second edition, R. Lambourne and T. A. Strivens. 2. Journal Oil Color Chemist Association, London, 1970. 3. Organic Coating Technology, V:II, H.F. Payne, John Wiley & Sons Inc. 1961. 4. ULLMANN's Encyclopedia of Industrial Chemistry, 1991, B. Elvers, J. F. Ransaville, G.Shulz. 5. Michael and Irene Ash, Formulary of Paints and Other Coatings, George Godwin 1978. 6. Pergut, BAYER A.G. Coatings and Colorants, Leverkusen, Edition 2002, Germany. 7. Fenghua Yuron Chemical Industry Material Co., Ltd Houge, Xikou, Fenghua , Zhejiang, China.