Why 3-zone chamber technology is superior to traditional single zone?
Traditional chamber systems, which we will broadly categorize as "single zone" chambered systems, differ not only in cavity geometry but in fluid dynamics as well. Typically they have one or more supply and multiple exhaust ports depending on the vendor and whether they intend to coat or print. In this type of design, the leading doctor blade breaks the boundary layer of air on the engraved cylinder's face, and ink or coating agitates against the cell face as the cylinder rotates, much like it did in the older ink-pan systems. A second blade meters excess ink or coating from the face of the cylinder as it exits the head. Excess ink/ coating, air or foam vents through a return port to the supply source.
The unique cavity design of the InkJector TM 3-zone chamber has but one focus: fill each cell 100% every time. Easy to say-tough to do.
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U.S. patents granted
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Each revolution of the engraved roll causes each cell to come in contact with the substrate (film, paper, foil etc.) and transfer its little dab of coating/ink. Assuming the cell itself is uniform in size, depth, angle of cell wall, and surface roughness this dab of coating/ink will be surprisingly exact. The major enemy to deal with is air in the now mostly empty cell. As an empty cell leaves the substrate air fills the balance of the cell and a layer of air surrounds the whole roll surface as it turns. The faster the roll turns the tighter this layer of air becomes until at some speed say 100 fpm to 165 fpm (30- 50 mpm) it forms a boundary difficult to penetrate.
This boundary layer will follow the roll surface right into a conventional open pan causing foaming and bubbling and in the process preventing the coating from entering and filling the cell completely. It is the purpose of the 3 zone chamber to eliminate this problem. The first step is for the first blade (called the trailing or dragging blade) to knife off the boundary layer of air, which it does quite effectively given the normal operating pressure of the blade against the engraved roll surface.
3-zone InkJectorTM chamber
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This then leaves the surface of the cell exposed but the cell volume is full of air. As this cell travels through the first zone the surface of the roll is covered with coating/ink. However, beneath that coating/ink layer small irregular amounts of air still reside in the bottom of the cell representing 20% to as much as 70% of the volume of the cell. This irregularity is the culprit. If it is possible for any air to remain in the cell, then it is possible for varying amounts to remain and, of course, any variation directly causes an equal variation in the amount of coating/ink actually applied.
Nonetheless, we desire the residual trapped remain in the cell through the first zone (supply zone) so that foam is not generated. The air is driven out of the cell as it passes across the second zone called the injection flat. The heavy layer of coating/ink picked up by the roll in the first zone follows the roll surface across the injection flat and is squeezed as the distance decreases between the radius of the roll surface and the straight line of the injection flat itself. This squeezing action causes a hydraulic spike to occur which creates a positive force on the fluid stream, which in turn pushes the air out of the cell with a positive force. This pushing action is aided by an increase in fluid stream velocity across the injection flat, tending to create a slight vacuum on any air in the cell. These two forces, therefore, create a push-pull effect which in combination, result in very highly reliable air from every cell every rotation. These forces become stronger with increased roll surface speed (RPM) which more than compensate for reduced dwell time of a cell within the InkJector itself.
Single zone G1TM chamber
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Having looked at the design concept used in all single zone chamber systems including our own G1TM single zone design and considering the principles at work you can begin to understand why traditional single zone chambers have long had problems of achieving uniform transfer and filling of the anilox cell. The degree to which the cell is not filled 100% is the degree to which the user will experience printing defects and variations.
Liquid forces present in the single zone chamber are:
1. Column pressure,
2. Turbulence and Splashing,
3. Diffusion.
Of these forces or conditions, the most important is turbulence and splashing because they are at least active forces, although they are random and accidental in nature. The other two are passive conditions more than forces and are substantially dwell time dependent.
At low to moderate speeds the single zone enclosed chamber is less problematic particularly in solvent based applications. Foaming tends to be a problem with water based systems as a result of the turbulence/splashing and large chamber cavity volume designs of many of the single zone designs. In both solvent and water base applications speed increases begin to lead to a reduction in coat weight and an increase in various printing defects and variations such as pin holes, ghosting ,streaks etc.
The 3-zone InkJector and single zone G1TM can be configured with a wide variety of “scaleable” user specified system options.
InkJectorTM chamber system features/options
G1TM chamber system features/options
For more detailed technical papers on 3-zone vs single zone chambers go to our Technical Library
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