graphics products- techniques & processes

Finishing techniques

Laminating

Laminating involves applying a transparent plastic film to paper and board.Useslaminating has a wide range of uses across the whole spectrum of printed products due to its properties- for example menus in restaurants.Propertieslaminating gives good gloss and strength, as well as having the advantage of being low in cost.

In commercial heated roller laminating, a PP film is glued to the paper as it is fed through a heating wedge under high pressure. Heating the glue before applying the film to the paper or board makes the application of the film faster. As the adhesive materials are non adhesive until exposed to heat, they are much easier to handle. The glue is solid at room temperature, so lamination of this type is less likely to shift or warp after applying. 

Varnishing

Varnish is applied to paper and board to give it a high gloss finish, as on the pages of glossy magazines, to give the paper a quality feel.

A fine varnish is sprayed onto the surface of the paper or board. Once dry, this gives a gloss finish which helps to protect the printing underneath

The varnishing process can only take place after the colour printing is completed, as the oil or water based varnished used t take at least two hours to dry completely. This is a major disadvantage as other finishing processes have to be delayed until the varnish dries. For example a brochure cannot be collated, folded and bound too early or the pages will stick together.

UV varnishing

.. can be used to speed up the drying process; Special varnishes dry almost straight away if they are exposed to UV light. The varnish is sprayed onto the paper in the same way as other varnishes. However after spraying the paper passes under UV lights which dry the varnish almost instantaneously.Printed materials can move quickly onto other finishing processes. One disadvantage is that this type of machinery is expensive to purchase. However it produces the ultimate in gloss finishes to paper and board.

Varnishing can also be applied by the screenprinting process- this is usually just for spot varnishing.Spot varnishing applies UV varnish to selected areas of a printed image to enhance product impact 

Hot foil blocking

Hot foil blocking also known as foil blocking or hot foil printing is used to produce true 'reflective metal' printing, and other effects impossible with normal metallic printing inks. Hot foil blocking can be used to enhance and add value to conventionally printed materials.In the hot foil blocking process, a foil coating is transferred to paper or board by the means of a heated die. A roll of foil with a polyester backing is continuously fed over the paper or board, and a heated die presses the foil onto its surface.The visual impact comes at a cost, so designers must weigh up whether the cost is worth the added visual appeal.

Printing processes

Photocopying

Photocopying is a widely available printing process, both in schools and through copy centres on the high street Full colour copying using expensive digital photocopiers is now commonplace. However even the simplest copier has a number of stages involved

Stages of photocopying

Charging- inside the photocopier is a cylindrical drum that is electro-statically charged. The drum has a coating of photoconductive material that will conduct electricity when exposed to light.

Exposure- an intense beam of light illuminates the original document and the white areas of it reflect the light onto the surface of the photo-conductive drum. The areas of the drum that are exposed  to light become conductive; the areas which aren't exposed remain negatively charged. The result is an electrical image on the surface of the drum

Developing- The photocopier holds a fine black powder known as toner, which is positively charged.  When toner is applied to the drum to develop the image it is attracted to and sticks to the areas that are negatively charged.

Transfer- the toner image produced on the surface of the drum is transferred from the drum onto a piece of paper using a higher negative charge than the drum.

Fusing- the toner is melted and bonded to the paper by heat and pressure rollers

Cleaning- The drum is wiped clean with a rubber blade and completely discharged by light.

Usesgeneral applications such as business documents, handouts, posters

Advantages-widely available- good colour reproduction-automatic collation and stapling of documents if required-can easily print double sided-low cost per copy for small batches-fast printing speeds

Disadvantages-not cost effective for long print runs-poor reproductive quality when toner is running low-image fades over time

Offset lithography

Lithography works on the principle that oil and water do not mix but repel eachother.

Stages of offset lithography

- The printing plate, made from flexible aluminium or polymer is fixed to the plate cylinder on the printing press. The printing plate carries the design, such as text and photographs formed using an oil based emulsion- Rollers apply water which covers the blank portions of the printing plate but is repelled by the emulsion of the design area-Ink, applied by other rollers is repelled by the water and only sticks to the emulsion of the design- The printing plate then rolls against a drum covered with a rubber blanket which squeezes away the water and picks up the ink- The paper rolls across the blanket cylinder which transfers the image to the paper.

The four coloured inks used in offset lithography are:cyan (blue)magenta (deep pink)yellow black

Usesbusiness stationery, brochures, posters, magazines, newspapers

Advantages- good reproduction quality, especially for photographs- inexpensive printing process- can print on a wide range of papers- high printing speeds- widely available

Disadvantages- colour variation may occur- paper can stretch due to dampening- set up costs make it uneconomic on short runs- can only be used on flat materials-requires a good quality surface

See below for diagrams of the processes

UV Varnishing

Laminating

Hot foil blocking

See Below for Diagrams

Photocopying

Offset lithography

Printing processes

Flexography

Flexography is the main printing process used to commercially print packaging materials including carton board containers, plastic bags and chocolate bar wrappers. Flexography uses a relief type printing plate with raised images; only the raised images come into contact with the paper during printing. Printing plates are made of a flexible material such as plastic, rubber or UV sensitive polymer so that it can be attached to the plate cylinder for ink application.Flexographic presses have a plate cylinder, a metering cylinder that applies ink to the plate and an ink pan. Some presses use a third roller as a fountain roll and some have a doctor blade for improved ink distribution.In the flexographic printing process, the paper is fed into the press from a roll. The image is printed as the paper is pulled through a series of print units. Each print unit is printed with a single process colour. As with gravure and lithographic printing, the various tones and shading are achieved by overlaying the four basic shades of ink.

Gravure

Gravure is a type of printing process where the image is engraved onto a copper plate cylinder. Gravure like offset and flexography uses a rotary printing press and the vast majority of presses print on reels of paper, rather than sheets of paper. Rotary gravure presses are the fastest and widest pressures used commercially and they can print everything from narrow labels to 12 feet wide rolls of vinyl flooring.On the gravure plate cylinder, the engraved image comprises of small, recessed cells that act as tiny ink wells. The depth and size of these wells control the amount of ink that gets transferred to the paper.A gravure printing press has one printing unit for each of the four process colours. There are five basic components in each colour unit: an engraved plate cylinder, an ink fountain, a doctor blade, an impression cylinder and a dryer.

Stages of gravure printing-the plate cylinder is partially immersed in the ink fountain, filling the recessed cells. As the cylinder rotates it draws ink out of the fountain with it- the doctor blade scrapes the cylinder before it makes contact with the paper removing ink from the non printing areas-The paper passes between the impression cylinder and the plate cylinder under pressure. Here, the ink is transferred from the recessed cells to the paper. The purpose of the impression cylinder is to apply force, pressing the paper onto the plate cylinder, ensuring even and maximum coverage of the ink.-The paper passes through a dryer because it must be completely dry before going through the next colour unit and absorbing another coat of ink.

Usespackaging, less expensive magazines, paperbacks, newspapers

Advantageshigh speed printing process, fast drying inks, inexpensive to set up, can print on same presses as letterpress

Disadvantagesdifficult to reproduce fine detail, colour may not be consistent, set up costs high so would rarely be used on print runs below 500,000

Useshigh quality art & photographic books, postage stamps, packaging, expensive magazines

Advantagesconsistent colour reproduction, high speed printing process, widest printing presses, ink dries fast, good results on all paper

Disadvantageshigh cost of engraved printing plates and cylinders, only efficient for long runs, image printed as dots which are visible, very expensive set up costs

Flexography diagram

Gravure diagram

See diagrams below

Printing processes

Screenprinting

Screen-printing is a widely used commercial printing process for producing many mass or large batch produced graphics such as posters or point of sale display stands. The screen is made of a piece of porous finely woven fabric stretched over a wooden or aluminium

finishing techniques

photocopying & Offset lithography

Flexography&Gravure

screenprinting