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| Intelligent Inkjet Solutions: Digital Ink Reference Guide | |||||||||||||||
| Your complete guide to understanding inks used in digital printing | |||||||||||||||
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| Posted: 11/5/2008 | |||||||||||||||
 Just as there are many different inkjet printers in the market, there are many choices of inks to utilize in those printers. The purpose of this article is to discuss the types of inks available and their applications in the commercial marketplace.
Background: Before the advent of the digital inkjet printer; the litho, commercial, and screen-printing industries used high viscosity ink, also known as paste ink. These industries used impression-based technology to print this type of ink on paper or other substrates. As inkjet printing evolved, the types of ink needed to change as well. This medium requires low viscosity or liquid inks to be used in non-impression printing techniques. Non-impression, or in this case inkjet printing, uses a print head to drop or fire the ink onto the media or substrate. Manufacturers had to devise inks that would fire through the print heads and maintain a dot structure to produce a print. All inkjet printers use a print head in the printer. A print head is the part of the print engine in which the ink travels through nozzles to print the image. There are hundreds of nozzles in these print heads, which provides the resolution on respective printers. Ink Construction: Different types of inkjet inks have evolved over the years and it is important to understand the types of ink available. There are water-based , oil-based , solvent-based and UV curable inks. The construction of digital inks is essentially the same. The inks are made using several different ingredients all mixed together to form liquid or low viscosity ink. Three (3) elements are combined to form digital ink: Carrier fluid (mixed with a co-solvent), Additives, and Colorants (dye or pigment). Ink Types and their respective ingredients: Water Base – Water base ink is the most widely used ink for ink jet printing in narrow format (desktop) and wide format printers. There are two different types of water-based inks, which consist of dye or pigmented versions. • Dye, water- base – This type of ink uses a carrier that is water based and is mixed with dye for the colorant and additives. The purpose of the dye is to form the color that is printed on the substrate. Dye is a colorant completely dissolved in the carrier fluid and should not separate out. Dye inks were the first to be used in inkjet printing for graphics. Dye inks dry by evaporation and are not water resistant. Most other inks have evolved from the knowledge of dye base inks. • Pigmented, water-base - Pigmented water base inks are constructed similarly to dye; however, these use a pigment instead of a dye to form the colorant. The construction of pigmented water-base inks consists of a carrier, additives and pigments for the colorant. These inks are most widely used today in the production of wide format graphics and photo quality inkjet printing. (Hewlett-Packard (HP) prefers to call their water-base pigmented ink UV ink . Pigmented inks offer a higher resistance to UV rays than dye but HP UV ink is not UV cured.) Oil-base - Some of the first wide format inkjet printers made for long term or outdoor graphics used oil base inks. Oil was used as the carrier fluid, with additives and pigment added to produce color. Oil-base inks worked well for their time; however, controlling dot gain is a problem. This is accomplished by using coated media on oil based inkjet printers. Before solvent-based printing developed to its wide use today, oil base inkjet printers were the printer of choice for outdoor graphics. Solvent-base – Solvent base inkjet inks are constructed similarly to other inkjet inks. They use a standard set of colors which is C,M,Y,K, and Lc, Lm, Ly, Lk. As piezo head technology developed and the need for durable outdoor graphics grew, piezo heads allowed for the jetting of solvent base inks. These inks use a mixture of solvents as the carrier and pigments as the colorant. Once the image is printed, the media passes over a drier on the printer and the solvents are flashed off leaving behind the pigments adhered to the media. The great thing about solvent inkjet printing is the ability to use uncoated media because the dot gain is controlled by many settings on the printer but the main source of control is the drier or heater. Eco-Solvent inks are a derivative of solvent-base inks, but have a lower VOC (Volatile Organic Compound) emissions. The advancement of Eco-Sol inks has come a long way in the past 6 months with greater color gamut and better adhesion to a wider variety of uncoated media. UV cured - UV inks are very popular today. The demand for UV inks is growing because they use a much different procedure to dry the ink. Water, oil and solvent base inks have to dry or flash off the carrier fluid (solvents, co-solvents), which leave behind the colorant. UV inks work differently. The inks are jetted through print heads onto the media and then exposed to UV light, which cures the ink or makes it dry. The benefit to UV inks is realized when a desire to print to media or substrates is required beyond what solvent base inks can do. For instance, UV inks can print direct to rigid media and stick because there is no need to heat the media and flash off any solvent. In the case of UV ink, the ink is printed and exposed immediately to UV light by lamps on the carriage, therefore controlling the dot gain. UV inks come in the standard set of C,M,Y,K, and/or Lc, Lm, and white. The use of white ink provides the option to print spot or flood white directly to a colored substrate. The white ink is printed onto the substrate and then colored ink can be printed on top of the white to produce the desired spot or image color. This happens simultaneously as the inkjet printer prints the file. Ink and Media Compatibility: The success of applications is based upon the ink and media combination. Not all media is compatible with the different ink types mentioned above. Call your local Piedmont representative for assistance in choosing the correct products for your specific requirements. The following chart can be used as a guideline for applications. Applications and their suggested Ink Types:
The Future: The world of inkjet inks is rapidly changing. Ink manufacturers are continually working to bring improvements to meet the demands of the imaging industry. Be on the look out for safer solvent-base inks and inks with greater versatility, such as water-base inks that can print direct to uncoated media, and biodegradable inks derived from agricultural products.  Please visit our Digital Product Line. homepage for more information. For a printable version of this document, click here. | |||||||||||||||
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