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Essential Characteristics for Rapid Access & Hard Dot Graphics Films
Derek Pullen
B&W Platform Director
Eastman Kodak Company
Essentially Digital
Graphics films are essentially digital, they determine for the subsequent printing process where ink will “print” or “not print”. The essential requirements for film are therefore that it clearly defines image and non-image areas.
It should provide:
- Clear low-density areas, which guarantee short exposures to printing plates
- Significant density-differential between the clear and black areas so as to ensure complete in-depth exposure of the printing plate
- A clearly defined image / non-image interface ( i.e. high contrast ).
Thirty years ago Kodak introduced the first Rapid Access film, Kodaline Rapid Film. This class of film became known as rapid access because the processing access time was significantly less than the Lith films commonly used at that time.
This category of film became popular with those that liked the rapid, robust processing it offered and were prepared to make accommodations in their manufacturing processes for the somewhat lower image quality provided in comparison with Lith films.
In 1982 Kodak introduced the first Hard Dot film system, Ultratec. This provided an image quality better than that of Lith films, but with a much more user-friendly processing regime.
| Figure 1 - Photomicrographs of: |
Rapid Access
(note the "softer" edges)
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Hard Dot
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| Figure 2 - Density profile shots of: |
| Rapid Access |
Hard Dot |
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| Photomicrograph of a Rapid Access Image |
Photomicrograph of a Hard Dot Image |
Kodak has continued to support and improve these two film technologies providing a choice for the printing industry world-wide.
This continuing commitment has resulted in:
- Films to suit every available imagesetter whatever the light source, width or writing speed.
- No need for a darkroom as films available in roomlight loading packaging.
- Compatibility with a wide range of processors,
- On-line transport links between all significant imagesetters and processors,
- Significant enhancements in physical robustness (easier to transport, scratch resistant, etc.),
- Superior batch-to-batch consistency,
- mproved image discrimination (no dye stain, higher densities),
- Improved stability of unexposed and imaged films.
Rapid Access Films
The performance of Rapid Access films is primarily dependent on the construction of the silver halide crystals that are the light sensitive elements within the emulsion. Their solid state electronic properties are determined as they are grown to approximately one tenth of a micron in size. Just a few atoms of elements such as Rhodium and Iridium are doped into each crystal to ensure high-contrast and appropriate responses to sub-microsecond exposures. The electronic properties of these light receptors are optimised for maximum light sensitivity by subsequent surface treatments.
During 1998 the Kodak Gen 5 film family was introduced. These advanced rapid access performance by incorporating new proprietary technology, enhancing both image quality and ease-of-use compared with previous films of this type. Process times of less than one minute are now achievable, enhancing productivity.
The major benefit which users see from Rapid Access films is their forgiving processing characteristics. The output produced is very consistent; in many cases even when the processing system is not well managed.
Hard Dot Films
Hard Dot films, such as the current Kodak Recording 2000 film family, utilise similar emulsion technology to that described above, but with the addition of other components which deliver the very desirable high-contrast which results in their “Hard Dot” designation. Complex molecules, known as "nucleators" inject electrons into the silver halide crystals in areas where exposure has occurred; ensuring that they all develop, yielding high density and clear differentiation between image and non-image areas. Typical of the molecules used is the hydrazide shown below:
Figure 3 - Hydrazide molecule
The design of these molecules is optimised to facilitate speed and robustness in processing of hard dot films. The nucleation phenomenon, which these materials produce, results in small amounts of image area-wise growth, which can be exploited beneficially in imagesetting applications.
Benefits
What benefits do users see from Hard Dot films?
In subsequent contacting steps, for example to plate, the desire is to retain the image information stored on the film. This becomes easier if the image record is as near to digital as possible. On the other hand, if the dots are very “soft”, tone reproduction can be difficult to maintain and there is a risk that some information, say in the highlights, is lost. These issues become more critical at higher screen rulings and with stochastic screening. If the dots are not hard, then exposures in those subsequent stages need to be well controlled. Hard Dots give significantly greater assurance that the image information will be faithfully retained.
In imagesetting applications there are additional factors. Lower-cost imagesetters which tend to have poorer quality optics, tend to image softer dots. However, when these devices write on Hard Dot films the poorer optics are no longer apparent, since these films appear to “sharpen” the dots. The lower cost machines also tend to use a single writing spot size; independent of the resolution. In some circumstances this can be challenging to Rapid Access films, making it difficult to produce smooth edged and uniformly high-density dots. The nucleating process and associated image growth referred to earlier naturally “smooths” over these artefacts. Hard Dot technology can make films from a $ 20k imagesetter look like those from a $100k machine.
Many users want the best possible Linearity from their imagesetter/film combination. The high contrast characteristics of Hard Dot films naturally deliver this. Generally Hard Dot films are more linear than their Rapid Access counterparts.
Optimum performance
The “furthest point north” in film performance to date has been that exhibited by the Kodak Advantage/EZ media. These systems are an integration of film, hardware and software; co-designed with hardware partners. These media use Recording 2000 film technology. Communication between the film, imagesetter and processor linked to an algorithm provides intelligent system performance. By this means hard dot quality is provided consistently, and the process is managed transparently to the user, by the algorithm. Additionally in the most popular version, the processing components are supplied in cartridges and the processor requires no connections to water or drain giving excellent ease-of-use.
From both a users and film manufacturing point-of-view we would prefer to have one technology which offers the best features of these two film families…… that is our ultimate goal.
As we work towards this goal, we are conducting R&D to provide:
The highest image quality
with the greatest ease-of-use,
to maximise productivity in the printing industry.
Kodak graphics films have benefits to suit all applications.
These can be found in our conventional rapid access and hard dot films:
And in the newcomer to the family
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