COC reinforced polyolefin in food, medical equipment, packaging and other fields show their skills

COC reinforced polyolefin in food, medical equipment, packaging and other fields show their skills

Figure1 COCThe rigidity of the polyolefin blend can be increased, thereby enhancing the "straightening" performance of standing food bags, making them easier to fill and handle.

 

Cyclic olefin copolymer (COC) is an amorphous thermoplastic that can be used as an effective blending component in polyolefin packaging film applications in the medical, consumer and industrial markets to greatly improve the performance of packaging films.

As an amorphous thermoplastic, cyclic olefin copolymer (COC) is increasingly used as a blending component to enhance film properties in polyolefin packaging films for medical, consumer and industrial markets. Pure COC provides high transparency, excellent moisture resistance, high stiffness and strength, and excellent biocompatibility in applications such as medical devices, food and pharmaceutical packaging, optics, and electronics.

In polyolefin blends, cyclic olefin copolymers (COC) provide higher modulus, better heat resistance and increased barrier properties for packaging bags and thermoformed articles such as trays and the like. These blends can be processed in conventional cast and blown film lines using standard polyolefin process parameters.

Topas COC is a copolymer with ethylene and norbornene as monomers and polymerized with metallocene catalyst. Depending on the proportion of comonomers, this material may have a glass transition temperature (Tg) ranging from 33°C to 180°C. As an amorphous polymer, COC does not have a crystalline melting point, it begins to soften above Tg and gradually becomes fluid with increasing temperature. This colorless and transparent crystal-like material has a strong compatibility with traditional polyethylene (PE). It is most compatible with highly linear polyethylene, such as linear low density polyethylene (LLDPE), but can also be compatible with low density polyethylene (LDPE) and high density polyethylene (HDPE). Topas Advanced Polymers most commonly used COC grades for olefin blends are Topas 9903D-10(Tg 33°C), Topas 9506F-04(Tg 68°C) and Topas8007F-04(Tg 78°C). Higher Tg grades are sometimes used for special products or to improve the heat resistance of the film.

Figure2 COCPolyolefin blends for thermoformed film packaging can be provided with higher modulus and clarity. The leftmost pure polyethylene (PE) The tray looks rigid and sharp belowCOC/PEBlends (from left to rightCOCThe dosage is gradually increased, in turn.10％、15％、20% and30％）

Permissible thinning of rigidity

COC is one of the most commonly used blend components to increase the modulus and allow the thickness of the monolayer film to be reduced. In the modulus range of 2068MPa, the addition of 10% COC to linear low density polyethylene (LLDPE) can increase its modulus by 2 or 3 times while maintaining a low haze. In a simple monolayer film or as part of a co-extruded structure, the LLDPE/COC blend tends to provide thinner films with the same performance as before thinning, and thus reduces the cost per square meter of film, which can provide important sustainability advantages.

The use of higher Tg COC can make the blend have higher modulus even at high temperature (close to the Tg of COC), thus improving the hot filling performance and high temperature resistance of the film. It is important to remember that the addition of COC to linear low density polyethylene (LLDPE) greatly reduces the Elmendorf tear strength of the film, especially in the machine direction, although it improves the puncture resistance of the film. COC is commercially used as an additive to control the linear tear strength of films. In addition, many polyolefin/COC films are commercialized for thermoforming applications, and the amorphous nature of the COC can improve the consistency of the thermoforming process, and can improve the thickness control of the product in deep drawn parts and corners.

LLDPE/COC blends are also well suited for sealant films. The heat sealing properties of the film are usually expressed in terms of seal strength, hot tack strength and seal initiation temperature. An increase in the modulus of the COC blend typically results in a 10% to 20% increase in seal strength. As it cools, the cyclic olefin copolymer (COC) rapidly transitions from a rubbery material above Tg to a high modulus material below Tg. This sharp change usually increases the hot tack performance (seal strength after 0.1s of cooling) by up to 100%. Hot tack strength is important for the vertical form/fill/seal process. During this process, the packaged product falls into the bag while the closure is still hot. Cyclic olefin copolymer (COC) not only increases the overall modulus, but also enhances the "stand-up" performance of the stand-up pouch. This makes the bag easier to fill and handle.

Cyclic olefin copolymers (COCs) are also increasingly being used in polyolefin blends to produce barrier films for packaging. COC is one of the polymers with the best moisture barrier properties of all polymers. Its performance is better than low density polyethylene (LDPE)4 to 5 times. In the blend, if the COC content exceeds 70%, the barrier properties of the blend can generally reach 90% of the barrier properties of pure COC, and the haze is maintained low. COC also has excellent barrier properties against many other polar solvents, such as ethanol in hand sanitizers and antiseptic sponges. Compared with linear low density polyethylene (LLDPE), its ethanol barrier performance can be 35 times higher. Typically, these high COC content blends are used in laminated coextruded films where the outer layers are linear low density polyethylene (LLDPE), which do not require a tie layer.

Figure3 AddCOCCan improve the rigidity of various polyolefin film resins

Cyclic olefin copolymers (COC) are also typically 5 to 10 times more resistant to fragrance and aroma penetration than linear low density polyethylene (LLDPE). Although it is believed that COC does not have high gas permeation resistance, it is still significantly better than polyethylene (PE) and can be used to tailor blends to meet the specific O2 and CO2 permeation resistance required for fresh produce packaging.

Minimal process adjustment

COC is compatible with all types of polyethylene in any ratio of 0% to 100% in the blend. However, the best compatibility is with more linear polyolefins, such as linear low density polyethylene (LLDPE). Blends of COC with these materials have little or no increase in haze. When selecting PE grade, the processor should choose according to the processing viscosity and the final required performance. Polyethylene (PE) with melt index of 1.0~6.0g/10min at 190 ℃ has been proved to have good blending effect with COC. The COC does not need to be dried, and its storage temperature should be below Tg to avoid caking of the resin particles.

For film production, the COC and PE granules should be uniformly mixed to produce a "salt and chili"-like granule mixture. When processing COC/polyolefin blends, the melting temperature usually depends on the Tg of COC, and the extrusion temperature is generally 130~150 ℃, above the Tg of COC.

To obtain a high quality melt in production to ensure the high quality of the final film, the key is good mixing during the extrusion process. The recommended extruder screw speed is at least 50r/min. If lower speeds must be used to accommodate throughput requirements, a denser screen can be used to produce higher extruder discharge pressures (>10MPa) to enhance mixing. It is recommended that the extruder have a length to diameter (L/D) ratio of at least 24:1 and a low compression screw design. The barrier-type mixing screw is the best in use, and its Maddock mixing zone has proven to be very effective, but it is not necessary. In terms of dies, typical coat-rack cast film dies and spiral blown film dies can be used.

Figure4 Addition in polyolefin film resinsCOCThe rigidity can be increased, thereby improving the heat resistance of the heat-filled bag. The figure shows two different grades addedTopasCOCofLLDPEModulus at different temperatures

Other process parameters for cast and blown films are consistent with conventional PE film production. In blown film production, the increased stiffness resulting from higher levels of COC may pose challenges to achieving wrinkle-free bubble rupture and unfolding. In general, it is helpful to maintain a certain temperature in the portion where the film breaks. Equipment specializing in the production of high-density polyethylene (HDPE) and nylon rigid films generally produces better results when used to produce rigid films with high COC content

Topas COC is a thermally stable resin that prevents gel formation. Of course, it is best to clear the COC when switching products or shutting down equipment. In general, a typical cleaner stock may consist of 50% 1-MI linear low density polyethylene (LLDPE) and 50% standard PE scavenging compound.

Meets food and medical requirements

Topas COC grade meets all major regulatory food contact requirements today. In the United States, they comply with FDA Regulation 21 CFR 177.1520 "Olefin Polymers" (3.9). According to US FDA FCN#75 and #405, the material can be used in films, sheets and other articles in direct contact with food. This applies to all types of food and all conditions of use. Some product grades may not be suitable for use in certain higher temperature food applications due to their Tg limitations.

In Europe, Topas COC can also be used in contact with food, and the monomers used in its production are listed in the EU Plastics Directive 2002/72/EC1/2 (August 6, 2002). Manufacturers using the Topas COC should check any restrictions and seepage restrictions on the finished product.

Topas COC is also approved for use in the medical and pharmaceutical sectors. Most TopasCOC grades have established a US FDA Drug Master File (DMF#12132) and a Device Master File (MAF#1043). Most grades also meet USP Class VI.