Introduction to CR Rubber
CR, or Chloroprene Rubber, is a synthetic polymer produced by the polymerization of chloroprene (2-chloro-1,3-butadiene) monomers, typically via emulsion polymerization. It was first developed by DuPont in the 1930s as one of the earliest synthetic rubbers, marketed under the trade name Neoprene. The chlorine content (about 40%) imparts unique properties like flame retardancy and oil resistance. CR can be homopolymerized or copolymerized with small amounts of other monomers for enhanced performance. It is compounded with fillers such as carbon black or silica, accelerators, and antioxidants. Grades vary by crystallization rate: fast-crystallizing for adhesives and slow-crystallizing for molded goods. Sulfur-modified grades offer better processing, while xanthate-modified ones provide superior heat resistance.
Characteristics of CR Rubber
CR offers a well-rounded set of properties, bridging the gap between general-purpose and specialty rubbers. Here are its key characteristics:
- Mechanical Properties: CR has good tensile strength (10-25 MPa), elongation at break (200-600%), and tear resistance. It exhibits excellent dynamic fatigue resistance and resilience, similar to natural rubber, but with better aging properties. It crystallizes under strain, enhancing strength in applications like belts.
- Chemical Resistance: Moderate resistance to oils, greases, and fuels (better than NR but less than NBR). It resists water, dilute acids, alkalis, and some solvents. However, it's susceptible to strong oxidizing agents, aromatic hydrocarbons, and ketones.
- Thermal Properties: Operates effectively from -40°C to +100°C (or up to +120°C for short periods). It has good low-temperature flexibility without plasticizers and resists heat aging well. Crystallization at low temperatures can cause stiffening, mitigated in certain grades.
- Durability and Aging: Outstanding resistance to ozone, UV, weathering, and atmospheric aging due to its polychloroprene structure. It has inherent flame retardancy (self-extinguishing) and low gas permeability. Compression set is moderate, improved with proper curing.
- Processing and Cost: Easy to process via extrusion, calendering, molding, and dipping. It has good green strength and adhesion to fabrics/metals. CR is more expensive than SBR or NR but cost-effective for its durability in harsh conditions.
- Other Properties: Good electrical insulation, vibration damping, and abrasion resistance in wet conditions. It can be vulcanized with metal oxides (e.g., zinc oxide) rather than sulfur, avoiding bloom. It's available in latex form for adhesives and coatings. However, it may have a slight odor and can degrade in high-humidity storage.
In formulations, CR is often blended with other rubbers (e.g., NR for cost reduction or NBR for better oil resistance) and requires protective agents against copper and manganese contamination.
Applications of CR Rubber
CR's weather and chemical resistance make it suitable for outdoor and industrial uses:
- Automotive and Transportation: Used in hoses, belts (e.g., timing and V-belts), seals, gaskets, and mounts for its oil and heat resistance in engines and suspensions.
- Construction and Building: In roofing membranes, window seals, expansion joints, and waterproofing due to its weatherproofing and flexibility.
- Marine and Outdoor Equipment: Essential for wetsuits, diving gear, boat seals, and cable jackets, leveraging its water and ozone resistance.
- Adhesives and Coatings: As a base in contact adhesives (e.g., for footwear and laminates) and protective coatings for corrosion resistance.
- Industrial Products: In conveyor belts, rollers, diaphragms, and gloves for chemical handling and abrasion resistance.
- Other Uses: Electrical insulation, orthopedic braces, mouse pads, and foam products. It's also in consumer goods like laptop sleeves and phone cases for shock absorption.
CR is produced globally in significant volumes, with eco-friendly variants emerging to reduce chlorine emissions. It's a reliable choice for applications demanding longevity in moderate to severe environments.
