A Brief Discussion on Chlorinated Rubber Coatings
Natural rubber or synthetic rubber itself is a highly unsaturated high molecular weight polymer with high viscosity, slow film formation, and easy aging, so it is not suitable for making coatings. After chlorination modification, its molecular weight is reduced and the unsaturation of the molecular structure is changed to make natural rubber derivatives – chlorinated rubber or cyclized rubber. Among them, chlorinated rubber is an odorless, non-toxic white powder or fine flaky solid, non-irritating to human skin. After being dissolved, it is a slightly yellow solution. The coating film formed has good adhesion, chemical corrosion resistance, quick drying, water seepage resistance and flame retardancy.
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Composition of Chlorinated Rubber Paint
- Chlorinated rubber resin
The chlorine content of industrial chlorinated rubber is generally between 62% and 67%. Before chlorinated rubber is made into paint, it needs to be dissolved into a resin solution with a solvent. It is soluble in aromatic hydrocarbons, esters, ketones (except acetone), ethers and chlorinated hydrocarbon solvents, but insoluble in aliphatic hydrocarbons, alcohols and water. Generally, chlorinated rubber resin is dissolved in xylene into a 40% solution for paint making. Modified resin
Chlorinated rubber paint usually uses some natural resin or synthetic resin to improve the performance of the paint film, such as gloss and light stability, mechanical properties and construction properties. Resins that can be used with chlorinated rubber resin include: medium and long oil alkyd resins, polyurethane resins, acrylic resins, epoxy resins, phenolic resins, rosin, glycerol rosin esters, etc. It is incompatible with cellulose acetate, ethyl cellulose, cellulose nitrate and vinyl acetate copolymer.The type and amount of modified resin have a great influence on the performance and cost of chlorinated rubber paint. The amount of added resin is generally: chlorinated rubber: modified resin: plasticizer = 1~3:1:0.5.
Plasticizer
Chlorinated rubber molecules contain many six-membered rings, and the coating film formed by it alone is brittle, so plasticizers must be added for modification. Correct selection and addition of plasticizers play a very important role in changing the performance of the paint film. Since chlorinated rubber is an inert resin, the requirements for plasticizers are obvious plasticizing effects and can basically approach the performance of chlorinated rubber (inert) to ensure the stability of the base material. Many plasticizers are compatible with chlorinated rubber, so the selection range is relatively wide, such as: chlorinated paraffin, chlorinated biphenyl, dibutyl phthalate, dioctyl phthalate, tricresol phosphate and drying oil (linseed oil, tung oil, soybean oil and epoxidized soybean oil). Among them, chlorinated paraffin is the most suitable plasticizer for chlorinated rubber paint. In addition to the above requirements, it also has excellent pigment wettability and dispersibility, miscibility with other coating resins and excellent chemical resistance. In addition, phthalates can also be used as plasticizers in topcoats that require good weather resistance.The ratio of chlorinated rubber to chlorinated paraffin has a great influence on the tensile strength, elongation, flexibility, water vapor permeability and adhesion of the paint film. To obtain a balance of various properties, the most suitable ratio range is very narrow. Due to the different types and amounts of pigments and fillers, the ratio of plasticizer to chlorinated rubber is also different, and experiments are required to test the ratio. Generally speaking, when the ratio of chlorinated rubber to chlorinated paraffin with a chlorine content of 42% is about 70:30, the flexibility and adhesion of the paint film reach the maximum value and maintain good water vapor permeability resistance.
- Anti-settling agent
In order to prevent and improve the precipitation and agglomeration of pigments in chlorinated rubber paint, an appropriate amount of anti-settling agent should be added to the paint, such as organic bentonite, fumed silica, hydrogenated castor oil, etc., among which hydrogenated castor oil has a significant thickening and anti-settling effect. Amide-modified hydrogenated castor oil is often used as a thixotropic agent when preparing thick paste paint. Other additives
Chlorinated rubber resin itself has poor dispersibility for pigments and fillers, and modified resins or chlorinated paraffin are generally used to disperse pigments. In order to improve the dispersibility, storage stability and surface state of the pigment in the paint, a small amount of wetting dispersant is sometimes added, such as BYK-P104S and Deqian’s Disponer904S.During roller coating or high-pressure airless spraying, especially for thick paste chlorinated rubber paint, the paint film is prone to bubbles, so an appropriate amount of defoamer, such as EFKA-2035, BYK-066N, etc., should be added to the paint during production.
Chlorinated rubber paint modified with alkyd resin also needs to add an appropriate amount of organic acid metal soap drier, i.e., dry material, to accelerate the oxidation drying time of the paint.
Chlorinated rubber is a highly chlorinated polymer. If there are iron ions or aluminum, copper and other chlorides (except aluminum chloride and copper chloride) in the paint liquid, the paint liquid will often undergo chemical reactions during storage due to the effects of high temperature, moisture, etc. to generate products such as ALCl3 and FeCl3, release HCl gas, and form double bonds in the molecules to cross-link, release heat to increase the paint temperature, increase viscosity until gel, especially iron red chlorinated rubber paint is prone to this situation in summer. In order to ensure the storage stability of the paint, in addition to adding necessary dispersants, stabilizers must also be added to the paint, such as zinc oxide, magnesium oxide, zinc cyclohexane solution, low molecular weight epoxy resin, epoxidized soybean oil, triphenyl phosphite, etc. The amount used is generally about 1% of the amount of pigment.
Performance Characteristics of Chlorinated Rubber Coatings
Advantages of chlorinated rubber coatings
- Not limited by temperature during construction: chlorinated rubber coatings can be applied in an environment of -20-50℃, and are not limited by seasons or temperature.
- Easy to use: Most chlorinated rubber coatings are single-can packaging systems, and do not require temporary preparation of other components at the construction site. Just open the packaging iron barrel and stir it evenly before use.
- Quick drying: chlorinated rubber coatings are physical film-forming coatings that evaporate and dry with solvents, and the solvent release rate is fast. After coating, they quickly dry and form a film. After an interval of 4 to 6 hours at room temperature, the second coat of coating can be applied.
- Thicker coatings can be obtained: For chlorinated rubber thick paste coatings, if high-pressure airless spraying is used, the dry film thickness of each coat can reach about 55 to 85µm, and the maximum dry film thickness of one coat can reach 120µm, so a thick coating can be obtained with fewer coats, and the construction cycle is short.
- Excellent adhesion: Chlorinated rubber coating has good adhesion to the surface of steel and metal. At the same time, the solvent in the film-forming material can penetrate between the coatings, making them adhere to the lower layer, thereby strengthening the adhesion between the coatings.
- Good corrosion resistance: Since chlorinated rubber itself is a chemically inert film-forming material, the permeability of the coating to water vapor and oxygen is extremely low, only 1/10 of that of alkyd, and it has good resistance to moisture, salts, acids, alkalis, oxidants, and various corrosive gases.
- Easy maintenance: There is no need to remove the solid old paint film during maintenance. The new and old paint films can be mutually dissolved due to the penetration of solvents, and the adhesion is particularly strong. Chlorinated rubber paint can also be applied on some other types of paint films, so maintenance is very convenient.
- Good anti-toxic and flame retardant properties: Since the chlorinated rubber coating component contains a high level of “chlorine” polymers, it has the ability to inhibit the growth of toxic bacteria. If the surface of the equipment encounters a fire source, the coating can decompose chlorine gas and have a certain flame retardant effect.
Disadvantages of chlorinated rubber coatings
- Poor solvent resistance: They are soluble coatings, which can be considered a positive feature, but it can also be a negative feature. Its positive impact will be the dominant factor in most cases, because the solubility gives a flexible coating time interval, and basically there is no risk of peeling between each coating. The negative impact is that chlorinated rubber products are not resistant to most solvents, which means that strong solvents may damage the paint film, especially alkyd-modified chlorinated rubber coatings.
- Poor temperature resistance: Chlorinated rubber is a thermoplastic coating, and it starts to decompose when the temperature is higher than 130°C in a dry environment, and it starts to decompose at 60°C in a humid environment, so the use temperature cannot be higher than 60-70°C.
- Poor decorative properties: Chlorinated rubber itself has low gloss, and it needs to be modified with other resins to improve the gloss.
- Poor outdoor weather resistance: Chlorinated rubber contains chlorine in its structure. After long-term outdoor exposure, the paint film turns yellow, which has a great impact on the decorativeness of the topcoat. Topcoats that require good weather resistance, such as white paint, are generally modified with acrylic resin and phthalates as plasticizers.
- Environmental pollution: Chlorinated rubber itself is non-toxic and odorless, but the chlorinated rubber products produced by the solvent method contain 3% to 8% carbon tetrachloride residues, which then evaporate into the air, causing harm to the human body and destroying the ozone layer in the atmosphere.
Usual Applications of Chlorinated Rubber Coatings
Chlorinated rubber coatings have countless beneficial applications as a result of their toughness and protective homes. It is extensively used to shield products in extreme atmospheres, such as ships, offshore systems, bridges, docks, containers, automobile chassis, road indications and chemical devices. Additionally, high-viscosity chlorinated rubber is utilized to create high-strength adhesives or included in other rubber products to improve their quality. The following is a list of the most usual applications:
Marine and Industrial Makes Use Of
Chlorinated rubber coverings are commonly utilized to coat aquatic devices such as ships, anchors and buoys. It shields versus rust from salt water and weathering.It is also generally made use of in the manufacture of commercial equipment such as tanks, pipes and structural steel. Its chemical resistance protects against contact with solvents, acids and antacids.
- Roofing Coatings
Chlorinated rubber coatings can be used as roof covering coatings to secure and secure the roofing system surface. It is adaptable enough to expand and contract with temperature level modifications, protecting against fracturing. Its water resistant properties help protect against leakages and dampness damages. Metal roofings and level roofing systems are commonly coated with chlorinated rubber layers. - Swimming Pools
The water resistance and toughness of chlorinated rubber finishings make them suitable for coating pool and swimming pool devices. It safeguards concrete swimming pools and metal components like ladders, handrails and pumps from lasting exposure to chemically treated swimming pool water.
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References
What Is Chlorinated Rubber Used For & Its Advantages? by | Jun 21, 2023
Chlorinated Rubber CAS 9006-03-5 | Look Chemical
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