Metamerism

In the context of the printing industry, metamerism describes a situation whereby prints of an original and a matched ink, when viewed under a standard illuminant (D50 for example) prove a good visual match. Whereas, if the same samples are viewed under an alternative illuminant (a fluorescent light source for example), the visual match is poor. This is called a metameric match.

To understand what causes a match to be metameric, it’s important firstly to appreciate that it occurs not as result of a variation in the state of the viewer (in this case the human eye), but a change in the viewing conditions.

It’s important to establish that different illuminants (light sources) have a specific spectral energy distribution, or wavelength and that any object (in this case a colour sample) interacts with the illuminant uniquely, absorbing some and reflecting the remaining spectral energy and thereby determining the colour of the object as interpreted by the human brain and eye.

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Gas Ghosting

Also often referred to as Gloss or Chemical Ghosting, the term refers to the appearance of a “ghost” image from the reverse side of one printed sheet on the face of the adjacent sheet. The ghost may appear as a variation in gloss level, or density and although many research projects have been carried out, it remains a complex problem.

We know that rather than the migration of any ink/varnish components through the substrate, ghosting occurs as a result of the oxidation by-products of the first pass sheet’s printed ink film, either altering the surface energy (surface tension) of the substrate - which then impacts on the transfer of ink during the second pass (backing up), and/or the same oxidation by-products interfering with the drying of the subsequently printed ink film on an adjacent sheet in the stack.

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Calcium and it Effects on the Printing Process

The paper industry's switch from acidic to alkaline paper, coupled with an increase in the pH and alkalinity of municipally supplied water, has created a new set of problems for today's printer. Many of these problems can be directly traced to the increased presence of calcium in the printing environment. In the following article we share our experience in observing, analyzing and solving these problems. The article covers:

• These new problems and how they can be recognized;
• Recommend steps which the printer can take to minimize their effect
• Cover the sources of calcium, and why paper and water are changing
• Discuss the role that fountain solution can play in minimizing calcium's    effects.

These new problems and how they show up in the printing process.

Rollers

A uniform white haze develops on the surface of rollers in either the inking or dampening trains. This interferes with the ability of these rollers to carry uniform ink and/or water films, and leads to poor ink transfer, roller stripping or sensitive water rollers. In extreme cases, a hard band of white calcium compounds builds up at roller ends, and roller settings cannot be properly maintained.

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Roller Maintenance Program

What causes roller problems?

Rubber rollers are manufactured with ‘hills’ and ‘valleys’ ground into their surface, so that the ink transfers easily down the roller train to the plate surface. To check their condition, use your senses of sight and touch. Rollers should have a dull, velvety appearance, and they should feel velvety smooth as you drag your finger across the roller’s surface.

If the rollers look shinny and have a glassy smooth feel to them, they are glazed. When rollers are glazed, their surface cannot transfer ink effectively. This means that you will need to run more ink and water on the press to achieve the required ink densities. Higher levels of ink and water can result in dot gain, mottled solids, hickies, ink drying problems, etc.

 

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Improve profits by improving your environment

As the economic downturn bites harder printers are looking at saving costs wherever possible. Improvements to the environment are not an obvious place to look for savings but there are huge benefits in looking in this area.

Take a look in the pressroom at the consumables used and identify the most flammable and volatile material in use. Isopropanol Alcohol is a VOC (Volatile Organic Compound) that evaporates fast and has a flash point of only 12 degrees. You might also be surprised at how much you are spending on a product that just evaporates and pollutes our atmosphere.

So why do we use so much in the press damping system?
IPA added to the fountain solution will reduce the surface tension and make the water wetter and more efficient in dampening the plate. It will also increase the viscosity, and act as a disinfectant and anti foaming agent, that’s the only good news.

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