What Is a Film Coating?
Film coating refers to a thin protective film formed on the surface of plastic or another synthetic resin.
These functional films offer improved weather and stain resistance, among other enhancements, compared to conventional films.
Types of Film Coatings
There are different types of film coatings, each tailored for specific applications. Choosing the appropriate coating method based on the required performance is crucial. Generally, there are four main types of film coatings.
1. Water-Soluble Coating
Water-soluble coatings form a protective film by applying a water-based solution and allowing it to dry. The solution often includes resins like polyvinyl alcohol, polyvinyl acetate, polyvinyl chloride, vinylidene chloride copolymer, silicone resin, and rubber latex.
2. Solvent-Based Coating
Solvent-based coating involves dissolving a coating agent in an organic solvent before application. This method forms a protective film more rapidly than water-soluble coatings. However, due to the flammable nature of solvents, careful handling is required.
3. Thermal-Melting Coating
Thermal-melting coating is a process where a stable protective film is formed by melting materials such as wax or resin, and then cooling them after application. Common materials for coating agents include paraffin wax, rubber compounds, polyethylene, vinyl, and ethylene.
4. Extrusion Coating
In extrusion coating, melted resin is applied and then pressed against a die. This method forms a protective film by cooling and crimping, and is often used for polyethylene lamination.
Principle of Film Coatings
A typical film coating machine mainly consists of a feeder, a coating unit, a drying unit, and a take-up unit. The production volume can be adjusted by changing the coating unit, for instance, to a dual-stage type, based on the required performance and conditions.
Take-Out Device
There are two types of take-out devices: one integrated with the main unit’s frame, and another mounted independently. The choice is influenced by the device’s weight; heavier devices require a separate frame. Different types of brakes, such as manual, mechanical, and electric, are used to adjust the film feed rate.
Coating Equipment
The coating equipment can be adapted based on specific conditions, with the best equipment selected according to the coating agent’s amount and viscosity. Using a coater as a single head without changing equipment limits the production to a consistent process over time. A multifunctional head is generally recommended for a range of products.
Heads for coating equipment include reverse rolls, blade coaters, spray coaters, gravure coaters, air knives, and Myer bars.
Drying Equipment
Drying equipment is utilized to dry water and solvents after coating, ensuring the stabilization of the protective film.
Take-up Equipment
Take-up equipment is necessary for forming the coating and winding the finished product at a consistent speed and tension. There are two types of systems: center drive and surface drive. Recently, the center method has become more popular due to its resilience against weight changes and other factors.