Traditional offset lithography depends on the fact that oil and water repel each other. The image area of a traditional lithographic plate attracts the oily ink and repels the dampening solution (water and alcohol), while the non-image area attracts water and repels the oily ink. When the commercial printer achieves the correct ink/water balance, the press can accurately print type and images from the planographic (flat surfaced) printing plates.
Unfortunately, offset lithography has its environmental drawbacks:
- It wastes a huge amount of water.
- It takes a lot of makeready time for the commercial printer to achieve the ink/water balance, so paper waste is high.
- The custom printing vendor’s dampening solution contains VOCs (volatile organic compounds such as alcohol) that are hazardous to the environment.
But There Is an Alternative: Waterless Custom Printing
Waterless printing, originally patented by 3M in the ’60s as “Driography,” is based not on chemistry but on the physical properties of the plate coating, the plate surface, and the ink. In contrast, offset lithography distinguishes between image area and non-image area based on the mutually exclusive chemical properties of oil and water.
Unlike offset lithography, waterless custom printing uses silicon-coated plates. Silicon repels ink (ink slips right off is surface). Therefore, by exposing the printing plate with a laser and removing the silicon in the image areas, the commercial printer can produce a plate on which ink will only be attracted to the type, line art, and photos. (More specifically, UV light travels through the silicon and activates the underlying photopolymer layer of the plate, breaking the bond with the silicon and allowing it to slough off.)
Unlike the flat plates of offset lithography, waterless plates are intaglio in nature (they have recessed image areas) once the silicon has been removed. This allows waterless presses to carry and deposit a greater volume of ink than traditional offset presses (a stiffer, thicker, and more viscous ink with a higher tack, since no water is involved). And the ability to print a greater volume of thicker ink yields a larger color spectrum than can be achieved with traditional offset lithography.
Where Can You Find Waterless Presses?
Waterless lithography has been around since the 1960s, but it is not a pervasive technology. Direct Imaging presses are waterless. These would include the Heidelberg Quickmaster DI (as well as Presstek’s, Screen’s, and KBA’s direct imaging presses).
In addition, some presses are hybrids. These can be used for offset lithography and waterless printing, but they must include a special cooling apparatus, in which hollow tubing carries water through rollers in the ink train to maintain a constant ink temperature. Otherwise, the thicker ink would cause friction in the ink rollers and press plates, raising the overall ink temperature and compromising its viscosity.
Why Choose Waterless Printing?
Waterless offset provides a number of benefits:
- The process allows for higher halftone screen rulings since the ink is stiffer, tackier, and more viscous than offset press ink. This yields better halftone dot reproduction and hence better image definition.
- The higher screen rulings allow commercial printers to achieve increased print contrast and a wider color range while eliminating the halftone rosette patterns of traditional offset lithography.
- A waterless press will hold a tonal range from a .5 percent halftone dot to a 95.5 percent halftone dot. This greater tonal range provides more mid-tone and shadow detail than traditional offset lithography.
- Waterless printing produces less dot gain (spreading of the ink on the paper), so there is greater image detail, particularly in shadows and midtones. Reduced dot gain also allows the custom printing vendor to use a thicker ink film, which yields brighter colors.
- The thicker, tackier ink allows for exceptional ink holdout on a multitude of coated and uncoated printing stocks (i.e., the ink sits up on the surface of the press sheet).
- Since the commercial printer does not need to maintain a stable ink/water balance, he can reduce paper waste and improve the efficiency of the custom printing job. The commercial printer can also hold more consistent color throughout the press run once he has achieved optimal color on press.
- Eliminating the dampening solution also eliminates the paper stretch that results from wet paper. The higher dimensional stability of the paper affords the custom printing vendor better control over color register on press.
- The environmental benefits include the elimination of water waste, reduced paper waste, and the elimination of hazardous chemicals.
This entry was posted
on Tuesday, March 13th, 2012 at 4:23 pm and is filed under Digital Printing, Offset Printing, Printing.
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