Commercial Printing Methods

8/8/2019 Commercial Printing Methods

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Modern Printing Methods explained.

GCSE Graphic Products

What do we need to know for our exam????

The AQA (our examining board) specifies the following:

Quality checks such as colour registration marks, position marks.

Commercial printing methods- letterpress, lithography, flexography, gravure and

screen printing.

Varnishing (oil, spirit, UV and water).

Laminating, embossing and foil application.Multiple surface developments (nets) produced by die cutters and creasing bars.


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The five main types of printing are:

Relief- Letterpress, Block printing, Flexography (foil blocking)

Planographic (flat plate printing)- Lithography & offset lithography

Intaglio (etching) Gravure, Screen Printing

Xenography (dry printing)- Photocopying, Laser printing, commercial digital printing

Please note that while it is good to know what these are, not all are required for

the AQA syllabus.


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FlexographyFlexography is a form ofrelief(a raised profile) printing.

The image is slightly raised, inked and the printed straight onto the substrate

(technical term for paper, card or whatever is being printed on).

The plate is usually made from soft rubber or plastic and uses a quick drying ink.

This high speed process is well suited to a number of materials such as acetate

film, polyethylene (eg supermarket bags), brown paper and newsprint.

For more information visit:

http://graphics.tech.uh.edu/MatProcesses/Flexography.html

a rubber flexograph plate

Flexograph machine


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Offset LithographyOffset Lithography is by far the most common form of commercial printing. It accounts for

over 70 % of commercial printing.

Offset lithography works on a very simple principle: oil and water dont mix. Images (wordsand art) are put on plates which are damped first by water the by oil-based ink. The ink

sticks to the image area , the water to the non-image area which absorb moisture and

repel ink. Then the image is transferred to a rubber roller and then to the substrate. This

happens at an extremely fast speed as the plates are wrapped around a roller. The paper

is web fed (a continuous roll).


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What happens inside

An offset lithography machine has four of these presses, printing thecyan, magenta, yellow and black (CYMK) components of a print.


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Advantages of offset lithography:

Prints 4 colours onto flat materials

It is a high quality process

Very economical on medium to large production runs 500 - 500,000

It is a fast process speeds of up to 50,000 presses per hour can be acheived on

a web fed press!

Disadvantages of offset lithography

Less economic than rotogravure and flexography on high volume printing

1,000,000+

Less economic than digital printing on small to medium runs 50 -100,000(although

quality is slightly higher)

Limited to the type of materials it can print onto the surface must be flat. Litho

would not be accurate enough for newspaper print.


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Gravure

Gravure is a printing process that uses intaglio or engraved metal plates or cylinders.

The image to be printed is photo-etched onto the plate as microscopic dots.Rotogravure is a printing technique characterised by high print quality and large

numbers of copies hundreds of thousands or even many millions. Tiny ink volumes

are transferred from the gravure printing cylinder to printing dots on the paper. Millions

of printing dots show up to the human eye as letters/text or images

The "doctor blade" isangled against the cylinder

to wipe away the excess

ink, leaving ink only in the

cell wells


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The main application of gravure covers a wide range of commercial products.

Gravure is especially suited to work in the four colour process on relativelycheap papers in quantities over 250,000. The reason being the expense of the

original printing plates which can each run into thousands of pounds.

Example applications include

magazines

mail-order

catalogues

Board packaging products such as folding box cartons for food and cigarette

industries, also printed video cases.

Flexible packaging such as printed cellophane and polythene used in food

wrapping, display and production.


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Advantages of Gravure:

It can be used for the highest quality reproductions

It uses lower grade, lighter paper than lithography

High speed usually 6000-10,000 prints per hour

Automatic registration.

Disadvantages of gravure

Initial cost of rotogravure plates extremely high therefore it is only economic forvery high print runs

Colour correction is difficult


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Silk Screen Printing

Screen Printing is unlike any other process as it uses a stencil through which ink is

pushed. The process involves forcing ink through a fine mesh (screen) which helps to

spread the ink evenly.

Its easy to use, versatile and requires low

capital investment.

Relatively cheap on short and medium print

runs automated presses which can print,varnish or gum up to 6000 per hour.

Most importantly it can print onto curvrd and

uneven surfaces


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The main stages of modern print production

Prepress

origination

compostion

Colour separation

Plate production

print

sheet or web fed

4 colour printing

Quality control

Finishing

Stiching binding stapling

Embossing, blocking

Varnish and laquer

Die cutting and

creasing


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The main stages of modern print production

The basic stages of modern print production are:

1. Original artwork photographs, illustrations and text are scanned and enteredinto a computer

2. These elements are combined into a document using page makeup or desktoppublishing software

3. Full size films are output using a high-resolution imagesetter. These could beeither positives or negatives.

4. Printing plates are made from films using a photochemical process

5. The flexible plates are attached to the plate cylinders of a litho press and the job is

printed.


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Full Colour PrintingFor printing, and image is separated into its

colours Cyan, Magenta, Yellow and Black

(CMYK).Each colour is printed over the other as the

paper (or substrate) moves through the

presses. Each colour has its own press.

For the original go to

micro.magnet.fsu.edu/.../primarycolors/

colorseparation/

Cyan magenta yellow black


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Quality ControlThe two main quality checks are:

Registration

Colour Density

Registration can be checked by either eye or

automatically and are used to check that the 4

processes are aligned properly on the substrate.

Images out of alignment can appear blurred.

Colour density is checked using a Densitometer,

which is a hand held device that measures the

density of colour.

The densitometer is held over the colour bar (one

colour for each of the process colours and

greyscale.

Registration marks at about 10X magnification

A colour density bar


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BindingOnce printed the next stage is the binding of the product. The bindery is where the

printed product is completed. The huge rolls of now-printed paper are cut and put

together so that pages fall in the correct order. Pages are also bound together by,staples or glue, in this step of the process.

A machine called a stitcher takes the folded printed paper (called press signatures)

and collates them together.

The final components in the stitcher machine are the knives which trim the paper to its final delivered size.

A sticher machine Paper being cropped manually


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Cutting and Folding (creasing)

Most cartons (packages, boxes) require cut outs and creases in order for them to be

assembled. The machine tool used on modern presses is the die cutter.

Documents

Commercial Printing Methods