Direct image and electrostatic

Direct image

This is the simplest form of the plate processes and origination is placed onto a paper plate directly from a typewriter. The plate is then treated with gum and phosphoric acid solution in preparation for printing. Being suitable only for short-run work, this type of plate barely comes within the scope of the commercial printer (print run: approx 1,000).

Electrostatic

There are two types of platemaking process involved here, one is transfer and the other is direct. The transfer system employs a selenium plate; the selenium is photoconductive and can be used more than once. The photoconductive plate is positively charged in special units necessary to the process. It is then exposed in a camera, where reductions and enlargements are possible. The white light reflected from the background areas of the original disperses the positive charge in the corresponding area on the plate, which is then dusted with a negatively charged powder which sticks to the image areas. A suitable printing plate is then placed onto the selenium plate and the image transferred. Finally, the powder is fused onto the printing plate to complete the process.

An alternative method of platemaking using the electrostatic principle is produced directly from copy. The special surface layer is of an organic photo-conductive nature. The plate itself is charged positively and exposed. The latent image is then developed by passing thorough the image-forming pigment. At this stage alterations can be made to copy simply by wiping away the powder. The powder is then heat-fused to the image for 30 sec at 170⁰C. The coating in the non-image areas must be removed with the appropriate de-coating fluid before the process is complete (print run: approx 100,000 on metal plates).

Chemical transfer

In this process, also known as transfer diffusion, a silver-halide negative and original are exposed together. Light passes through the negative from the back and reflects from the original onto the negative coating to obtain a latent image. Exposure can be obtained through transmitted light for translucent or clear originals. The original is placed over a light box, the side to be copied facing upwards and the negative with emulsion side up.

The resulting negative is then fed into a processor with a specially coated plate where it is developed and then rolled into contact with the plate. The unexposed emulsion areas on the negative are therefore transferred onto the plate where they diffuse into the surface coating. The plate is then developed and fixed to produce an image of firmly adhered silver.

The plate processes used incorporate both exposing and processing units, thereby eliminating the need for dark-rooms and special plumbing (print run: approx 10,000-100,000).

Ink series in web offset

The buyer of web offset inks, and also the printer at the offset rotation, is often faced with the question as to which of the many ink series offered on the market is best suited to his requirements. The various factors which have to be taken into account so as to make the right choice, and the reasons for the existence of varying ink formulations, are explained below.

The demands placed on the processing properties of an ink are ultimately oriented towards the customer's wishes, i.e. towards the expectations placed on the printed product. We can say with certainty that the conveying of information, be it the portrayal of a landscape in a travel brochure or of a food, e.g. meat or fruit in a newspaper supplement for a supermarket, or the design of a packaging, be it for a tin of food or a pack of potato crisps, has to be as authentic as possible. This ensures that the observer is able to recognize the image being portrayed, even if in part only sub-consciously, and that the observer feels that he is being addressed directly.

The first factor to impact on the result of a print is without doubt the choice of substrate. The surface structure, i.e. the glossiness or roughness of the paper surface, as well as the inherent color of the paper, which may range from a bright white to a more or less yellowish color, have a considerable impact on the quality of image reproduction. Smooth, glossy papers allow much more brilliant, high-resolution image reproduction than slightly yellowish, uneven substrates, where the paper fiber structure is still visible after printing.

Another - invisible - paper quality also has a not inconsiderable impact on the printing result. The capillary structure of the paper determines the extent to which the ink is absorbed, and this has a decisive impact on the color strength of the printed ink on the paper.

The surface solidity of the substrate has major consequences for the ink to be used. Any damage to the paper surface, e.g. the picking of paper fibers or coating particles, has a negative impact on the visual appearance of the printed matter, as well as on the continuous production run, and in particular with larger print runs.

An unsmooth full-surface print caused by the build-up of paper dust from paper fibers on the printing plate can only be overcome by repeated washing. While the rubber blanket is cleaned, the washing procedure also affects the printing plate, from which the contaminants are carried away via the paper web when the press cylinder is reset.

When evaluating the picking susceptibility of a paper, it is not only the tendency of the dry paper web to form dust which is of significance, but rather the property of the paper surface after contact with the water of the damping system. In the case of papers which tend to pick, individual paper fibers are very often straighten up to the surface after contact with the water of the damping system and come away from the surface of the paper. As a result they can easily be torn out due to adhesion with the rubber blanket and are then passed on to the printing plate by re-separation. Here they accumulate, particularly if there is also a lesser degree of material transport of ink towards the web due to low ink consumption.

In these cases the ink needs to be adjusted with respect to its tack in such a way that, on the one hand, it is not too sticky, so that this does not lead to increased picking of paper fibers, and so that, on the other hand, it has sufficient adhesion/cohesion so as to guarantee the continuous transport of paper dust via the printed paper web. In this respect one also has to consider that at this stage of the printing process the ink is in an emulsified state with fountain solution. There are findings that the water of the damping system is not only present in the ink in an emulsified state, as so-called "interior water", but also as so-called "surface water" where the ink and air come into contact.

Библиографический список

1. Кузнецова С.А., Мусницкая Е.В., Павлова К.Г. Программа курса иностранного языка для вузов неязыковых специальностей. М.: МГЛУ, Учеб.-метод. объединение по образованию в области лингвистики. Центральный кабинет методики обучения иностранным языкам, 2004. – 75 с.

2. Журналы «British Printer», «Print», «American Ink Maker», «Print Week», 2006-2008.

3. Siegwerk Group International «Offset Printing Inks». – Germany; Siegburg, 2004. – 30 с.

4. Сборник научных трудов. Выпуск № 454. Профессиональная ком-муникация как цель обучения иностранному языку в неязыковом вузе. – М.: МГЛУ, 2000. – 134 с.

5. Вестник МГЛУ. Выпуск 467. - М.: МГЛУ, 2002, – 148 с.

6. Вестник МГЛУ. Выпуск 477. - М.: МГЛУ, 2003, – 162 с.

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Редактор Т. А. Москвитина

 

Компьютерная верстка, дизайн обложки – Е. В. Беспалова

 

ИД № 06039 от 12.10.2001 г.

 

Подписано в печать 23.01.09. Формат 60×84 ¹/₁₆. Бумага офсетная.

Отпечатано на дупликаторе. Усл. печ. л. 5,5. Уч.-изд. л. 5,5.

Тираж 100. Заказ 128.

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