Rapid advances in sources and materials, vacuum technology and network layer manipulation have generated interest in several product conversion industries, including clear glass coatings and abrasion/anti-reflective coatings for windows, solar cells, and packaging films and sheets. Glass barrier plastic films produced by plasma deposition and plasma polymerization processes offer new options for the coatings industry.
The coating on the protective/anti-reflection film should have these physical properties: index of refraction 1.4 (lower is better) in the range of 1.3; thickness for visible wavelengths of 0.25, at least the top layer if the material is multilayered or has a gradient index of refraction; hard surfaces; low coefficient of friction; and resistance to weather and contamination for glass applications.
Source and deposition environments are designed to match the desired material, material structure and coating level. Barrier and protection/increasing from high speed by oxide coating, using three plasmas: plasma cleaning of the substrate and ionization of a large portion of deposited material near the plasma source providing good nucleation and adhesion to polar surfaces necessary Mobility and close packing energy for adatoms, and tightly packed plasma annealed coatings.
The coating process usually takes place under high vacuum to avoid interacting background gases and material deposition. A high vacuum helps avoid electrons and photons from heating the substrate. Due to good nucleation, the low lateral stress oxide barrier has an elongation of about 5% and can be processed through a web machine. Poor nucleation results in a nonbarrier, columnar structure, even though the coating is amorphous. The barrier properties of plasma-activated SiO2 on polyester can be improved by an order of magnitude by plasma pretreatment of helium or methane. Pretreatment is preferably done in-line, but does not preclude the need for corona treatment at atmospheric pressure.
The high vacuum in the plasma CVD process prevents nucleation in the gas phase, and in the electron beam deposition process, the low pressure allows atoms with high kinetic energy and electron excitation energy to reach the substrate.
The main differences between plasma activated CVD and e-beam processes are as follows:
1. The electron beam process requires cleaning and separating the plasma from the nuclear matrix, ionizing the atoms, and annealing the coating . During plasma activated CVD, these three plasmas are combined into one.
2. The pressure of plasma CVD is higher than that of electron beam deposition, so when the electron beam coating is deposited in front of the eye to form dust particles around the pinholes, plasma CVD tends to push the dust particles into the coating .
3. High-pressure plasma CVD allows the background inert gas to eliminate most of the condensation heat before reaching the substrate, so the modified effect of CVD plasma treatment does not require a cold drum.
There are two ways to improve the barrier performance of SiO2: modification of deposition material and modification of deposition source. Modifiers or substitutes for silica can reduce its porosity, melting point, and solubility, and can change its nucleation density or refractive index to match that of adjacent materials.
Silica is the preferred main component because of its unusual glass-forming ability, resistance to crystallization on cooling and consequent high elastic elongation. Some materials that have been shown to enhance one or more properties of SiO include oxides of magnesium, carbon, barium, boron, aluminum, germanium, zinc, and titanium.
For example, glass containing 35% magnesia and 65% SiO2 has a lower melting point, allowing the film to anneal and increase its bulk density after annealing. Silica dissolves slowly in water, and about 10% zirconium prevents acid and alkali attack. Its X-factor varies from 1.55 to 1.8 in SiO-X, the oxygen permeability coefficient varies from 0.1 to 0.4, and the film turns yellow as the barrier properties increase.
High-speed deposition techniques other than electron beam, which are suitable for new methods of production of barrier and protective/anti-reflective coatings, including cardiovascular disease. These plastic coatings can be produced by two closely related processes: plasma-activated CVD and plasma polymerization. Both processes use similar equipment.
For applications requiring high refractive index, tetraalkoxytitanium compounds are non-volatile and non-toxic, so they can replace siloxanes as raw materials for yielding intermediate refractive index titanium dioxide coatings. These processes offer three major advantages of e-beam coatings: they are conformal because they are made at relatively high pressures; and because of a wider range of raw materials and reaction conditions, a wider range of chemical bond structures can be produced in coatings , or the coating can target the flexibility of the polymer or the hardness of the oxide; the thermal load on the plastic coating is lower, so cooling is unnecessary. This is due to atoms condensing in the gas phase into liquid particles that are large enough to greatly reduce the heat of condensation on the substrate, energetic enough to allow atomic mobility for annealing and close packing, but small enough to prevent "snow" formation.
The main disadvantage is that most plasma CVD coating materials are often highly toxic and sometimes pyrophoric.
Materials that have been plasma polymerized include methane, ethane, ethylene, tetrafluroethylene, acrylic acid and other monomers such as methyl methacrylate. Plasma-polymerized coatings differ from bulk polymers made from the same monomers because they are highly cross-linked, making them harder than their lower elastic counterparts. Barriers to plasma polymerization have been reported with oxygen permeability less than 0.01.
One of the advantages of plastic film with a glass barrier is that it can be recycled. Glass-coated plastic films can be reextruded, whereas composite polymer barriers cannot. Most likely, SiO 1.8 is still the main component of glass barrier coatings. Its bonds are flexible in angle and length, which endows the coating with high elastic elongation and resistance to crystallization when coated. It has a low refractive index, so it doesn't add glare to plastic films. It is also relatively insoluble. The oxygen transmission rate of the coating film at 2 days/100 days is 0.02 cubic meters/100, the water vapor transmission rate at 2 days/0.06 days is 0.05 g/100, and the 2 days/2 days is 0.07 g/100.
In many cases, reactive magnetron sputtering is the deposition process of choice. This is a well-established industrial deposition process for coating webs such as Kapton films. Reactive sputtering enables maximum control over the coating process and high deposition rates. Variations of this process are quite possible, including plasma deposition (introducing additional silicon in silane to increase the deposition rate) and plasma polymerization.
Figure 32.14 shows a cross-section of a sputter roll coater. A roll of film is released from a vacuum, passed through a cold drum to stabilize the film coating by one or several magnetron sputtering sources, the properties of the coating are monitored and in-line before film back. This configuration allows for continuous monitoring and feedback control of the coating process and performance. Different optical and electrical properties can be monitored depending on the fabricated coating.
