Cycloolefin, English name: Cyclo-Olefin Copolymer, abbreviated as COC, is a copolymer of cycloolefin and ethylene or α-olefin. COC resins are typically prepared by polymerization with Ziegler-Natta and metallocene catalysts. Ethylene is first subjected to a Diels-Alder addition reaction with cyclopentene to form norbornene intermediate (norbornene) and then copolymerized with ethylene under a metallocene catalyst to form COCs. Since regularity of molecular chain of copolymer is broken, COC is an amorphous polymer. The COC molecular chain has a ring structure, so it has high rigidity, high material hardness and modulus.
COC has high transparency, as transparent as water and glass, and similar to methyl methacrylate (PMMA). In near ultraviolet and visible regions of light, transparency is above 90%. Due to irregularity of molecular chain of COC, it does not have ability to crystallize, therefore, even after stretching orientation, induced crystallization will not occur, which is confirmed by birefringence data. After PC resin is stretched, since molecular chain is oriented in direction of external force, molecular chain is induced to recrystallize, so there is a difference in transverse and longitudinal refractive index (i.e., birefringence); while COC is stretched No, there is also birefringence, so its transparency does not change when orientation is extended. In addition to difference in optical properties, COC is less polar than amorphous PC and PMMA resins and therefore has a lower adsorption capacity for water vapor.
COC friction coefficient is much lower than other resins, especially at high temperature, COC friction coefficient is only about 0.3 at 80°C. For other resins, general rule is that higher temperature, greater coefficient of friction. COC is resistant to acids, alkalis and polar solvents at room temperature. The polarity of COC is low, so it has high resistance to polar solvents, and its chemical stability is better than that of PC, PMMA, PS and PVC. The electrical properties of COC are also excellent, with very low dielectric losses. The molecular chain of COCs is rigid and its Tg is much higher than room temperature. It is in a glassy state at room temperature, and segments or groups of molecular chain are frozen, so loss modulus is small, and dielectric constant is also small. The Tg of COC increases with amount of norbornene cyclic monomer. COC itself is a non-polar resin, so it has high barrier properties for water, etc., but poor barrier properties for oxygen.
The most unique advantage of COC is its high water resistance, which is 10 times that of PVC and twice that of PVDC coated PVC; its film has a high transmittance (especially in near ultraviolet range) and good dimensional stability. And it can produce vapor-deposited metal film; mechanical properties of COC resin are also very excellent, modulus of elasticity reaches 2600 MPa; COC resin has very little dissolved solids, meets USP Class VI and FDA standards, and can be used for food packaging. . Just because COC has so many benefits, its annual consumption growth is 5%.
After COC and PE are melt-blended, film can be extruded or composite film can be made by multi-layer co-extrusion. For example, a 3-layer composite structure (A-B-A) and a 5-layer co-extrusion (A-bond-B-bond-A) COC structure as base material can be used as a blister pack. Blister packs can be made using extrusion-molding-filling-heat sealing process. COC blister packaging has good moisture-proof effect, good moldability, high purity, no halogen, and high transparency.
In field of food packaging, COC is used for following purposes.
1. Stand-up pouch: increased rigidity, reduced thickness, high transparency and gloss, controlled tearing;
2. Blister packaging: excellent formability, increased strength, increased puncture resistance, reduced thickness;
3. Sterilization packaging: no shrinkage, high water resistance, excellent moldability after treatment at 120°C for 20 minutes;
4. Shrink film for flexible packaging: highi Shrinkage rate, low shrinkage force, low processing temperature, tight fit to body with good transparency;
5. Easily tearable film: easy to open, controlled tearing, increased rigidity;
6. Coated paper: moisture resistance several times higher than polyethylene, less curl, lower recycling costs;
7. Foaming Material: It has good heat resistance, high strength and toughness, low density and good thermoformability.
There are also many COC composite films, such as nine-layer COC composite film with high rigidity, high transparency, heat resistance, used for packing fresh meat, cheese and other food; PP-COC-PP composite film is resistant to water vapor. It has high barrier properties. There are reasons to believe that prospects for use of COCs will be ever wider.
Source: Membrane Communication