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Why Our Inks are Good
The idea of a jet printer has its roots in the last century when the two British Lords, Kelvin and Raleigh structured the mathematical equations describing the conditions under which a stream of liquid can break into droplets.
However, most of the research that made the current jet printers possible began in 1968 and the first working bubble jet printer saw the light in 1977.
Jet printers can be classified according to the way the ink is handled. There are three basic systems:-
Continuous Ink -
Electrostatic -
Drop-on-Demand
Most printers on the market are of the Drop-on-Demand type and these can be further classified into:-
Thermal Bubble -
Piezoelectric
"Drop-on-Demand" means exactly what it says - on the printhead receiving a specific electrical pulse the "demanded" ink drop is formed and delivered to paper. Shown here is how a bubble is formed and ejected from a cartridge. Ink is first heated by voltage pulses. As the ink begins to vaporize, a bubble is formed and begins to grow. The pressure formed from the expanding bubble forces the ink out of the nozzle. The bubble then cools and contracts creating a vacuum. The vacuum, in turn, pulls more ink into the nozzle and a new cycle is ready to start.
"Thermal Bubble"
Bubble Jets, Hewlett Packard Deskjets, Thinkjet and Designjet printers belong to this category.
In piezoelectric Drop-on-Demand printers droplets are produced by a transducer, shown here. The Epson Stylus Color Printer is an example of this design concept.
Print Quality
Good print quality, as we can expect, depends on two parameters: Ink and Paper. The higher the DPI (dots per inch) of the printer, the more critical is the paper (to achieve the number of dots per inch that the printer can deliver). The way paper is actually made is also important - for example, the amount of fiber clumping as observed by holding a piece of paper to a strong light. In general, the coating and substrate of the paper must match the resolution of the printer. A 600 dpi printer printing on plain paper will not yield a 600 dpi print, and a 720 dpi printer printing on 300 dpi paper will not deliver 720 dpi.
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Difference in dot spreading between coated paper (left) and uncoated paper (right)
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Coated paper is expensive and the better the coating the higher the cost. Fortunately, unless you are dealing with special applications not yet routinely handled by jet printers, such as photographic reproduction, etc. you can print on standard paper and have quite good results. From on e point of view, having paper with less resolution may actually be an advantage. For example, the unmagnified side of the letter M in the sketch will actually appear darker and have more eye impact than the left portion, composed of discernible and independent dots.
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Ink spreads and penetrated. Here is illustrated (not to scale) the effects of printing on ideal (coated papers) and on other papers. Spread is more accentuated when using our water resistant inks, but this is quite acceptable. Looking at the print with a magnifying glass, you would see a continuous line rather than a string of minute dots.
The Ink Jet Design Challenge
You are probably using (or know that millions use) ink jet printers. The specifications of a jet ink appear tough and almost forbidding. Below is listed under four separate headings: Ink, Material Compatibility, Drop Ejection and Print, the parameters that must be considered and weighed when formulating a jet ink.
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Jet Ink
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Material Compatibility
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Drop Ejection
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Print
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Good Stability
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Non-Corrosive
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Inform Drop Size
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High Optical Density
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Low Viscosity
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Plastics Compatible
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High Drop Velocity
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Color Quality
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High Surface Tension
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Adhesives Compatible
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High Drop Frequency
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Fading Resistance
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Conductivity
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No Particulate Formation
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No Orifice Wetting
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Lightfastness
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Long Shelf Life
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Non-Crusting
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Waterfastness
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Non-Flammable
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Non-Clogging
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Solvent Resistance
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Non-Toxic
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Smear Resistance
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No Biological Growth
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Off-Setting
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Dye Solubility
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Crack Resistance
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Media Sensitivity
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Spreading
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Feathering
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Dry Time
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In general, the final product is, as always, a compromise. The ink ingredients are such as to ensure the optimal medium between print quality, dry time, and nozzle performance. The better the print, the longer the drying time. The shorter the drying time, the more likely the ink will dry on the nozzle when the printer is not in operation.
Ink is first analyzed for color tone, feathering, intercolor bleed, laydown, text sharpness, and performance on plain paper, coated paper and transparencies. Then viscosity, surface tension and pH are measured. The interaction of these factors determines print quality and short and long term stability. Long term stability is purely an experimental factor - we can now say that our inks will be stable in a bottle for at least three years.
After the ingredients, the solvents, the glycol content and the proportions have been established and tested, the ink is filtrated through a long process down to 0.2 microns. After filtering the ink is tested again to check that the properties have been maintained. After three experimental batches have been successfully prepared and tested for Consistency, the formulation and procedure are formalized and the ink goes into production.
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