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Contents

Rotary PrintingOther Print MethodsColourHalf TonesTintsOverprintingKnockoutsStockVarnishingFoil Blocking

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Print Methods

Rotary PrintingRotary printing categorizes the methods to printing which involve wrapping printing plates around a cylinder. There are 3 examples of this: Offset Lithography, Rotogravure and Flexography.

Offset LithographyHis makes use of etched aluminium plates. Ink is transferred to an “offset” rubber blanket roller and then onto the substrate.

The stock can be web or sheet fed. The web offset machines work at high speeds and often have finishing and folding built into it.

Note: Offset = transfer1. Paper2. Impression cylinder3. Dampening system4. Inking system5. Print plate cylinder6. Rubber cylinder

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RotogravureThe plates used for rotogravure are made from copper and hold the mirror image. They transfer the ink straight onto the desired surface. The plates for this process are much more durable and are therefore ideal for newspapers and magazines.

FlexographyA positive mirror image rubber polymer plate transfers sticky ink onto a surface. The sticky ink used makes it a suitable process for carrier bags, wrappers, labels etc.

1. Paper2. Counterpressure cylinder3. Printing plate4. Inking system

1. Paper2. Counterpressure cylinder3. Printing plate4. Inking roller5. Ink6. Doctor blade

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Other Print Methods

Digital PrintThis is the reproduction of digital images onto a surface by using a device that translates digital code, without the need for an intermediate physical process. This method is suitable for short or special runs.

Pad PrintingThis method allows for transfer of a 2D image to a 3D object. The image is transferred from the printing plate via a silicone pad onto the substrate.

Screen PrintingA screen is made using woven mesh, followed my a stencil becoming exposed onto the screen. The ink is then forced through the stencil. This method of printing is not suitable for high volume printing, as each colour has to apply before applying the next. If you are planning to screen printing a full colour image, the image should be split into the 4 channels. This means that 4 screens will need to be exposed.

Example of digital print

Example of pad printing

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Opposite: Example of colour channels

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RGB

CMYK

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ColourPrint uses a colour mode referred to as CMYK (Cyan, Magenta, Yellow, Key). This is known as a subtractive colour system, as opposed to projected colour – which is additive colour (RGB).

One way to remember these names is:Subtractive – SubstrateAdditive – Add to make white

Theoretically all visible colours can be formed with the additive primary colours, this can’t be said for CMYK. However spot colours can be produced using process colour to print colours that can’t be mixed. For example, fluorescents, golds and silver

To find out whether the colours in your design can be printed software such as Photoshop offer a gamut warning feature, that will indicate any colours unprintable through CMYK.

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Halftones are images made up of dots, which collec-tively replicate the continuous tone of a photograph. The dot’s can be different in shape, size, spacing and angle depending on which effect you want. Varying the size or spacing of the dots has a direct influence on image brightness.

When printing halftone a series of screens will be used to print each colour, gaining the photographic tone. Otherwise each of the dots will just be printed on top of each other.

Halftones

TintsBy adding white to a colour, tints can be created. This means that lots of different tones can be created using just one colour. This is a particularly useful technique for one, two or three colour jobs. Another way to add an extra colour without using ink is to use coloured stock.

cyan 105yellow 90magenta 75black 45

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Over PrintingOverprinting refers to when an ink is printed on top of another ink. A colour can only be overprinted if it’s already printed.

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KnockoutsA knockout is the purposefully blank area on a layer, left so that the layer overlapping it can fill in the gap. This can cause flashes however, which are unprinted white areas. Reasons for flashes occurring include; incorrect adjustment of the press or perhaps the shape of the paper changing during printing. You can reduce the risk of these by overprinting/overlapping areas of colour by 3mm (standard). This is known as ink trapping.

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StockSeveral considerations should be taken when choosing a stock; to ensure it will support the design, whether you have a budget to work to and it’s GSM (and how this will affect postage costs).

Colour reproduction will differ depending on what stocks are chosen, when working on a project it is likely that the designs will be printed on a number of stocks and perhaps a colour palette suitable for this should be decided on.

The GSM (gram per square meter) can give an indication of how thick or stiff stock is. This can have a direct affect on how successful folding mechanics are. Sometimes thicker card or board is measured in a different unit – microns. A micron is 1000th of a millimetre.

A coated stock has an improved surface smoothness, gloss, whiteness and printability. Resulting in brighter and sharper images. Coated stocks are typically used for brochures, leaflets and posters.An uncoated stock is much more absorbent and is likely to be used for business stationery.

As well as the usual A sizes, printers also use SRA sizes. These are slightly larger versions of the original A sizes, allowing for trimming, grip and bleeds. An example of this would be:A0 – 841x1189SRA0- 900x1280

Opposite is an example of two stocks that have been bonded together, so that their are different colours and texture. This is called duplexing.

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Finishing

applied onto a wet layer of ink, therefore they both absorb into the stock at the same time. This will reduce the impact of the varnish effect. Dry refers to applying the varnish layer once the printed ink has dried. Also note that, varnish performs better on a coated surface. Once printed there are a number of finishing techniques available to apply to a design. These finishing techniques can be both decorative and functional.

VarnishingThis takes place in the last printing stage. It is the application of a colourless, glossy or matt, drying layer of varnish. Applying varnish will alter the original texture of the stock and has the ability to change the hue of the printing ink. It also speeds up the drying process. Spot varnishing refers to varnishing that happens in just a particular area and is treated like a separate colour. The varnish can be applied “wet” or “dry”. By wet, this means a wet layer of varnish is

Once printed there are a number of finishes available to apply to a design. These finishing techniques can be toh decorative nd functional.

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Foil Blocking

Hot foil stamping is useful for applying colour that may not be available through printing methods such as digital printing, such as metallic colours. The foil is originally on a polyester film and is applied to a stock through heat and pressure. The foil will stick to the stock depending on where the glue is – usually transferred through a stencil.

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