Text 3 Offset lithography

V. Compose a plan and write a short summary of the text.

IV. Speak about the advantages and disadvantages of the letterpress printing, using the following information.

Adjust, creasing, plane, curved, jobbing, length, web-fed

I. Read the sentences and discuss if they are true or false. If they are false, correct them.

1) In the letterpress the raised surface is inked before printing.

2) The text and the pictures are printed from metal type.

3) A ‘plate’ means the same as ‘the set of elements assembled together’.

4) The printing surface is made up of pieces of type, blocks and spacing.

5) Letterpress blocks of photographs don’t require a high-quality art paper.

6) The ink for letterpress process is water-based or spirit-based.

7) There are a lot of wastes in letterpress printing process.

II. Find the equivalents of the following terms:

1. rigid frame a) пробільний елемент

2. letterpress block в) набір

3. spacing с) шрифт

4. 'squash' d) рама для заключки

5. origination e) кліше для високого друку

6. typesetting f) травлення

7. non-printing background g) розбавляти

8. typeface h) заключати

9. denseness i) ореол (дефект друку)

10. 'relief' process j) виготовлення набору і фотоформи

11. to dilute k) рельєфний процес

12. chase l) жорстка рама

13. etching m) густота

14. to impose n) незадруковане тло

III. Fill the gaps using the following words:

1. The platen press consists of two … surfaces.

2. Flat-bed cylinders machine are today used for cutting and ….

3. Rotary press prints from a … or flexible metal or plastic plate.

4. On a platen press is very easy to adjust the….

5. The belts vary in … depending on the number of pages in the book.

6. Platen presses are used for … work such as stationary,.tickets and leaflets.

7. Rotary press can be sheet-fed or ….

Advantages: Disadvantages:

• Dense ink • High cost of printing surface

• Good printing of type for high- • Costlier paper needed to get same
quality books results as other processes

• No problems with ink and water • Sheet-fed machines run slowly
balance • Modem origination methods suit

• Less paper wastage than other other processes better
processes

This is the predominant process used in printing today, being used for a wide range of items from letterheads to books and magazines. The basic process of lithography was invented by Senefelder in Bavaria in 1798, but it was only when the offset principle was applied early this century that lithography started to be used for commercial printing, and only in the 1960s that it started to overtake letterpress as the major printing process. Prior to its commercial development, it was used mainly in the field of art, with prints made from stone printing surfaces.

The development of the process for commercial use was held back by the problems of achieving the right balance between ink and water: the water had a tendency to dilute the ink and this resulted in a rather weak and dull appearance. Now developments in inks, presses and techniques have allowed the process to exploit its obvious advantages.

The lithography process Lithography (generally known simply as 'litho') is a 'planographic¹ process, as the printing surface is flat rather than raised, as in letterpress, or recessed, as m gravure. The area to be printed is treated chemically so that it accepts grease (ink) and rejects water, while the non-image, or background, area is treated to accept water and reject grease. The whole surface has both ink and water applied to it. When the inked and dampened plate is then pressed against paper, only the image area is printed.

The offset lithography principle Where lithography is used it is nearly always as offset lithography. This means that the inked image on the metal plate is 'offset' (printed) onto a rubber blanket wrapped around a rotating metal cylinder; the image is transferred from the blanket onto the paper, One reason for using the blanket is to prevent the delicate litho plate from coming into contact with the more abrasive paper surface, which would wear the plate more significantly.

An advantage of the offset principle is that less water comes into contact with the paper than in direct lithography. Moreover, the rubber responds to irregularities of surface so that it is possible to print on to a wide variety of surfaces, including metal, for cans and boxes: special inks are used for this, and the printed metal is heat-treated after printing to give a rub- and scratch-resistant surface.

Dry offset printing This version of the offset process is also known as 'indirect letterpress' or 'offset letterpress', There is no dampening, and the zinc or aluminium plate has a slightly raised surface — it is, in effect, a letterpress plate. This prints on to a rubber blanket and the image is then printed on to the paper.

Platemaking costs are high, as plates are made by etching. The process is used for specialist work, such as for colouring books where the colour appears when water is applied or for carton work where very strong, solid colours are required. It is also used for certain kinds of security work, such as banknotes and cheques.

Exercises:

Дата добавления: 2014-12-23