Extrusion coating is a process of coating thermoplastic material on to a substrate such as woven fabric, paper, paperboard aluminum foil, PET, BOPP film etc., The resins that are most commonly used in extrusion coating are polyolefin’s such as polyethylene, ionomers, ethylene vinyl acetate copolymers and polypropylene. Widespread advantages of extrusion coatings include :
- Double sided coating can be done to achieve desired properties
- Solvent free
- Adhesive free
- Coating thickness can be varied depending on the end usage
- Provides moisture barrier properties
- Avoid direct contact to substrates
- Provides heat sealable characteristics
- Reduces loss of content
M Ajay Fabricators use up to date technology to manufacture high performance extrusion coating line and it consists of :
- Chrome plated chilled roll
- Backup roll
- Winders/un winders
Extruder contains the ability to convert solid pellets of thermoplastic resin into a uniform, homogenous melt. Die that are commonly used are flat type with adjustable die lip. Melt that is extruded through the die comes into the die lip that is formed by chrome plated chilled role and soft rubber coated back roll. This large diameter chilled roll in extrusion coating line provides enough contact time to cool the product to allow the film stripped from the roll without damage. The surface of the chilled role may be bright, dull and embossed depending on the desired surface characteristics.
Each and every factor of Extrusion Coating Line has its own influence on the performance
Melt Temperature – extrusion coating lines are normally operated at extreme temperatures. The resins for extrusion coating lines contain lower level of antioxidants. This higher melting temperature oxidizes the polymer partially and promotes good bonding to the substrate.
Air Gap – The gap between the die exit and chilled roll is said to be air gap which needs to be optimize with respect to the coating material. Higher gap leads to higher necking and cooling of the melt, leading to improper adhesion of the polymer to the substrate.
Chilled roll temperature – It influences on coating adhesion and stiffness.
The present market trend for extrusion coating line units is in the area of synthetic woven sacks and coating on non raffia substrates. Non raffia substrates include coating on paper, aluminum foils, PET and BOPP substrates. Typical applications of extrusion coating line unit is in plastic processing, pharmaceutical and food packaging industries.
Typical applications of extrusion coating
- Woven sacks for fertilizer packaging
- Coatings on conventional jute bags
- Pharmaceutical strip packaging
- Cable wraps
- Coating on paper