What is Plasma Treatment?
How does plasma treatment work and what can it do for you?
Henniker Plasma Informational Poster
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What is PLASMA TREATMENT and HOW DOES IT WORK?
0.0 States of matter
Solid, liquid and gas are the three states of matter we are all familiar with. We can move between the states by adding or removing energy (e.g. heating/cooling). If we continue to add enough energy, gas molecules will become ionised (lose one or more electrons) and so carry a net positive charge. If enough molecules are ionised to effect the overall electrical characteristics of the gas the result is called a plasma. Plasmas are therefore, quite rightly, often referred to as the fourth state of matter. A plasma contains positive ions, electrons, neutral gas atoms or molecules, UV light and also excited gas atoms and molecules, which can carry a large amount of internal energy (plasmas glow because light is emitted as these excited neutral particles relax to a lower energy state). All of these species can and do interact with any surface placed in contact with the plasma. By choosing the gas mixture, power, pressure etc. we can quite precisely tune, or specify, the effects of the plasma upon the surface.
0.1, 0.2 & 0.3 Steps in the Plasma Treatment Process
Plasma treatments are performed in an evacuated enclosure, or chamber. The air is pumped out and a gas is allowed to flow in at low pressure before energy in the form of electrical power is applied. It’s important to note that these types of plasmas are actually low temperature, meaning that heat sensitive materials can be processed quite readily.
0.4 Surface Cleaning
Plasma cleaning is a proven, effective, economical and environmentally safe method for critical surface preparation. Plasma cleaning with oxygen plasma eliminates natural and technical oils & grease at the nano-scale & reduces contamination up to 6 fold when compared with traditional wet cleaning methods, including solvent cleaning residues themselves. Plasma cleaning produces a pristine surface, ready for bonding or further processing, without any harmful waste material.
0.5 Hydrophobic Coatings & Hydrophilic Coatings
In plasma coatings a nano-scale polymer layer is formed over the entire surface area of an object placed in the plasma. The plasma coating process takes just a few minutes. The coating produced is typically less than 1/100th thickness of a human hair, colourless, odourless and doesn’t affect the look or feel of the material in any way. It is a permanent coating too, being bound to the material surface on an atomic scale. Plasma coatings are one of the most exciting areas of plasma technology, offering enormous potential to enhance a material’s function and value over a wide range of applications. They deliver two main categories of surface property: totally liquid (water & oil) repellent, or totally wettable.
How Plasma Coatings Work
Monomers are introduced with the plasma feed gas. Monomers are small molecules which will, under the correct conditions, bond together to form polymers. Plasmas create the right conditions at the surface of the material for this to happen both quickly and efficiently. Different monomers are used to produce hydrophobic and hydrophilic surfaces.
0.7 Plasma Surface Activation
Plasma surface activation is effective at altering the surface of a polymer by attaching polar or functional groups to it. Many polymers, in particular polyolefins such as polyethylene and polypropylene, are chemically inert and cannot bond easily to other materials, displaying poor adhesion with inks, paint and glues. The reason for this is the absence of polar and reactive functional groups in their
structure. Plasma surface activation renders many polymers receptive to bonding agents and coatings. Oxygen is usually used as the process gas, however many plasma activations can also be carried out with just air. Parts remain active for a few minutes up to several months, depending on the particular material that has been plasma treated. Polypropylene for example can still be reprocessed several weeks after treatment.
How Plasma Surface Activation Works
UV radiation and active oxygen species from the plasma break up separating agents, silicones and oils from the surface. These are pumped away by the vacuum system. Active oxygen species (radicals) from the plasma bind to active surface sites all over the material, creating a surface that is highly ‘active’ to bonding agents.
0.8 Plasma Surface Etching
Plasma surface etching is a type of plasma treatment used to increase the surface area of a material on the microscopic scale. The surface of the component is etched with a reactive process gas. Material from the surface is etched away, converted to the gas phase and removed by the vacuum system. The surface area is greatly increased, raising the surface energy and making the material easily wettable. Plasma surface etching is used before printing, gluing and painting and is particularly useful for processing of e.g. POM & PTFE, which cannot otherwise be printed on or bonded without the use of aggressive chemicals.