The Applications of bonding layer resins can be broadly classified as:
- Flexible packaging;
- Rigid packaging;
- Laminate applications; and - Other - Applications
Flexible packaging includes cheese packaging, meat packaging, multi-layer bottles, HDPE co-extruded films, and other flexible packaging applications (cardboard coating, bag-in-box packaging, bubble wrap, barrier extrusion). Rigid packaging applications include multi-layer bottles, barrier sheets and automotive fuel tanks. Composite applications include nylon modification, PP and wood plastic composite (WPC) coupling agents. Other applications include multi-layer pipe applications, pipe coating applications and metal coatings.
Flexible packaging/ Restorative composite- Cheese packaging
Typical applications: One of the key technical requirements for cheese packaging is a high barrier to oxygen. Binding layer resins are the natural choice for the cheese industry due to their oxygen barrier properties and are therefore the largest end use in the cheese industry. Binding layer resins are used to package cheeses of different sizes.
Cheeses of different sizes, chopped aged or unaged natural cheeses (cheddar, Swiss, mozzarella, etc.). Depending on the technical requirements of the cheese to be packaged, the structure used can be from three to seven layers.
Technical requirements: Multi-layer packaging products use a "gauge" as a measure of thickness (mil). Typical thicknesses of films used to package cheese range from 1.6 to 210 mil (40 to 55 microns). The most common types of films used for this purpose are clear, laminated or co-extruded multilayer structures. Some of the important properties needed in a film are:
- Oxygen barrier;
- Water vapor barrier;
- Low temperature heat seal;
- High tensile strength;
- Good puncture resistance;
- Good sealing bond;
- High flex-crack resistance; and
- processability on high speed lines
Typical structure of cheese packaging: A typical example of a multi-layer film structure for cheese packaging is shown below:
- Natural cheese packaging: (Note: TLR = Tie Layer Resin)
- PET/PVDC/TLR/LLDPE-EVA blend - PET/PEL/PE/TLR/EVOH/TLR/m-PE - PET/TLR/OPP/TLR/m-PE
- Salted cheese packaging:
- Nylon/PVDC, LDPE/TLR/m-PE - LLDPE/TLR/PA/TLR/LLDPE
- Swiss cheese packaging:
Competition between materials: The most common binding layer resins used in cheese packaging are LLDPE-based binding layer resins. They compete with LDPE and EVA based binding resins. Competition is based on price, but in some cases, competition is based on the specific and unique properties they offer to the product.
The competition is based on price, but in some cases it is based on the specific and unique properties they offer to the product. EVA-based bonding resins offer better adhesion and, in some cases, lower cost than co-extruded structures based on LLDPE and LDPE resins. Competition among resins comes down to the technical requirements of the product and is achieved in a cost effective manner. Figure 4-2 illustrates the multi-attribute analysis for cheese packaging. Multi-property analysis is a useful tool for qualitatively comparing the ranking of competing materials in end use. This tool helps to "visualize" important attributes and helps to "conceptualize" the relative position of each product.
4.2.2 Meat packaging
Typical Application: One of the most important factors in meat packaging is the shelf life of the product. Co-extruded film structures provide longer shelf life for processed ready-to-eat meat and often meet the requirements of the meat packaging industry. The most commonly packaged meats are "salami" sausages, ham, deli meats, poultry, bacon, sausage, etc. Common resin materials used for this type of meat packaging are nylon and EVOH (bonded by a binding layer resin) or polyester bonded to EVOH (bonded by a binding layer resin). Depending on the required barrier properties of the packaged product, the structure can be as little as three layers.
Depending on the required barrier properties of the packaged product, the structure can be as little as three layers or as many as 11 layers. The meat is vacuum-packed to remove any moisture and oxygen that may cause low shelf life.
Technical requirements: Typical film thickness for packaging ready-to-eat meat is 1 to 3 mil (30 to 78 microns). Some of the technical properties required for films used in meat packaging are:
- Resistance to aroma or odor of the packaged meat;
- organoleptic properties of the resin (must not smell like plastic); - clarity of the package;
- moisture resistance;
- resistance to oxygen;
- sealability of the film at low temperatures;
- good puncture resistance;
Typical structures for meat packaging: Nylon, PVDC, EVOH, LDPE, PP and ionomers are commonly used as binding layer resins in meat packaging. Example: (Note: TLR = Tie Layer Resin)
- Red meat packaging:
- PET/TLR/PE/TLR/EVOH/TLR/Sealant (EVA or ionomer)
- Nylon/TLR/EVOH/TLR/LDPE or ionomer
- PVDC/TLR/LDPE or ionomer
- Cooked ham packaging:
- Poultry meat packaging:
- Deli meats:
Most packaging films consist of polyolefins; however, they need to be bonded with other epoxy resin to form multilayer structures in order to achieve the desired functionality. Binding layer resins are typically used to bond the inner and outer layers of a multilayer structure.
Competition between materials: The most common bonding layer resins used in this application are LLDPE and EVA-based resins. These two resins compete with each other in the market. EVA is cost effective and offers good heat sealability and adhesion to certain resins. LLDPE has low-temperature impact strength (important as all meat is refrigerated), good flex-crack resistance and toughness. Each resin has its advantages and the choice depends on the requirements of the final product. Figure 4-3 shows a multi-property analysis of meat packaging.
4.2.3 HDPE Coextruded Films
Typical applications: A common example of a co-extruded film application is the packaging of cereals, cereals, crackers, chips and snack foods. The binding layer resin is co-extruded with a polyolefin resin to achieve a multilayer structure for packaging. Cereals, cereals and crackers are packaged in film and then placed in cartons typically found on market shelves. Snack foods with higher fat and oil content and lower moisture content place greater demands on film structured packaging. Snack foods also contain salt, which is a catalyst for oxidative rancidity and can damage packaging films. Therefore, films with low water vapor and oxygen transmission rates are preferred for snack food packaging.
Technical Requirements: Typical thicknesses of this packaging film range from 1.2 to 3 mil (32 to 78 microns). Some of the technical requirements for the film structure used in this application are:
- Good organoleptic properties;
- Sealability at low temperatures;
- Resistance to grease and oil;
- Moisture resistance;
- good oxygen barrier properties; and
- light transmission.
The inner layer of the film used to package these products is usually made of EVA copolymer. Copolymers with high EVA (decided %VA) have good sealing properties at low temperatures, good sealing strength and thermal adhesion.
Typical structure of HDPE co-extruded films: HDPE co-extruded films for packaging are as follows: (Note: TLR = Tie Layer Resin)
- Cereal/biscuit/flake cookie liners:
- HDPE/TLR/Nylon or EVOH/Ionomer
- HDPE/TLR/Nylon or EVOH/TLR/EVA blend
- HDPE/TLR/EVOH/TLR/Ionomer - Meat snacks:
Traditionally, wax-coated film structures were used to package snack foods. With the advent of binding layer resins, it has revolutionized the industry. The HDPE / TLR / Nylon structure has replaced the wax-coated structure. Better handling and cost effectiveness were the main factors in the switch. Flavored grains are packaged in nylon or EVOH resins because of their good aromatic barrier properties. Metallocene-based polyolefin resins can compete with EVA for snack food packaging.
Intermaterial Competition: In this application, HDPE-based binding layer resins compete with LLDPE-based binding layer resins. HDPE-based resins typically offer benefits such as high temperature resistance, toughness, and cost effectiveness. Figure 4-4 shows a multi-generic analysis of HDPE co-extruded films.