What is MDO Film?
Machine-direction orientation (MDO) film represents one of the great technological innovations of the 21st century. In this process, a polymer film is heated to a temperature slightly below its melting point and stretched in a particular orientation. The film can be cast on an MDO machine, or this step introduced as the last stage in the manufacture of blown films.
We’ve been living with MDO since the 1960s, but it is only recently that this process has started to fulfil its potential.
The benefits of MDO are numerous. The process enhances the qualities of the film as a packing material, and reduces immediate costs by stretching it, sometimes by more than 1,000%. Of course this results in a host of knock-on advantages: less raw material is used, leading to reduced mass and lower transportation costs. Perhaps best of all, MDO film can improve your company’s green credentials by shrinking your carbon footprint.
But it’s not just about the bottom line, because the MDO process produces a superior product. Stretched film exhibits greatly enhanced optical properties, which can be tailored to your requirements. If you require a film with low or high gloss, polarisation or haze, these options are achievable by scaling the MDO machine settings. And film treated in this way also has better mechanical properties such as improved puncture resistance and easy tearing in a particular direction.
A Technical Challenge
Because the process also confers resistance to moisture, MDO products are not only used as packing materials, but as the impermeable layer in nappies, sanitary products and incontinence pads. Some of the films are even made from natural biodegradable compounds. They are clearly indispensable, so why are we only now beginning to see them emerge into different areas of the marketplace?
The answer to this lies in the magnitude of the technical challenge that is MDO stretching. The process can very easily go wrong. It consists of four separate stages, and selecting the wrong settings at any one of them can produce a film that is too brittle. MDO sounds simple, but works profound changes on the properties of the material treated.
The first step in the MDO process is preheating, where a film is fed into the stretching unit and evenly warmed to the desired temperature. This is followed by orientation, where the film is stretched between a series of rollers that are revolving at different speeds. Next, during the annealing stage, the film’s new properties are locked in and made permanent before cooling, when the film is brought back to near room temperature.
In the past, machinery for producing MDO products was specific to the outcome required. So self-adhesive labels were produced on one machine, cling film on another and fibrous ribbon for weaving synthetic sacks on yet another. This was expensive and space inefficient, so 21st century manufacturers sought to bring together the capability for different products in a single machine. They were largely successful, but this advance brought with it a fresh set of difficulties.
Nowadays, issues arise because the equipment used to produce MDO film has an almost infinitely varied number of settings. This level of flexibility is an asset, but it requires expert operators who have enough experience to possess a feel for the likely outcome whenever variables are changed. Also, they need to know their materials, since the draw ratio for the finished film depends upon the original polymer. Some materials cannot be MD oriented at all because their composition results in a film with very poor tensile strength.
When all is said and done, MDO film is one of this century’s engineering triumphs. The process not only results in the decreased use of raw materials and improved transportation costs, but produces films with varied mechanical and optical properties, making them suitable for purposes from nappies to synthetic woven sacking. As MDO technology and materials science advances, expect this indispensable process to dominate industry to an ever greater extent in the future.
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