Print101NAIJA: Printing Process

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Prepress and Postpress- Very Important for Every Graphic Designer

print101naija August 18, 2018

Printing process includes a lot of steps and every step has its own importance. There are a lot of activities even before the printing like Design, Preflighting and after the actual printing is over, like cutting, folding, assembling and binding. But it is not always necessary that all printed items are subjected to these processes. For example, advertising pamphlets does not require binding.

Three important printing processes are:

PrePress
Press
PostPress

What is PrePress?

Prepress is the terminology used to define processes that happens before printing and finishing. Since several publications nowadays are published both in print and electronic media, many shared processes are referred to as premedia services instead.

PrePress Processes

The prepress processes which are mentioned below may take place at single location, like large publishing or printing house, or at different places. Generally, few tasks happen at a publisher end while few take place at a dedicated prepress company (which are also known as service bureaus or trade shops).

Design: Since the advent of desktop publishing, several people in the printing industry don’t take design to be a prepress task. The design process includes following things
- Preparation of data, which comprises of copyediting and product photography, for example for a mail order catalogue.
- Making the layout is done by using one of the principal computer design application such as Adobe InDesign or QuarkXPress. Sometimes people take usage of tools like Microsoft Office or Publisher. There is also a extensive range of specialized applications are available for tasks like database publishing.
- The rectification sequence contains processes like proofreading and image retouching, for which Adobe Photoshop is the best application available in the market.
- Preflighting: Before finished pages go through the rest of the processes, a validation needs to be done to check if all the data meet the critical production requirements.
- Proofing: During the design phase, page proofs were already being created. Proofs are also done by the company which is responsible for the printing. This is done for internal checks of the impositioning as well as for the customers who need to sign off the proofs for approval. Hardcopy proofing is still very popular in the case of adequate time for it and for color critical or expensive jobs.
- Imposition: Number of pages will be united into signatures as per the final output device.
- To output data, pages or complete flats have to be ripped or rendered. This process also includes:
  - transparency flattening: transparency effects like drop shadows behind text need to be fixed.
  - screening
  - trapping
  - managing colors
  - color partition

Some people delay the above-mentioned processes to the last moment. This is commonly known as late binding.

Most of the above-mentioned processes are automated nowadays, with the help of either stand-alone applications or prepress workflow systems. The automation process also allows for more intricate communication processes:

Exchanging data like the final layout can still happen with the help of a DVD. Earlier people used to use the original layout file(s) and all associated images, fonts and other data. Nowadays, instead PDF files are used instead.
Nowadays use of internet has increased for submitting jobs. This is also known as web-to-print.
- When the data exchange is purely dependent on page content, solutions like FTP server or e-mail or file sharing tools such as DropBox or YouSendIt are used. A more sophisticated web portal can add functions such as preflighting and page approval.

What is Press?

After prepress, the next phase is Press. During printing, accuracy is crucial for both quality and timely delivery, so projects only go to press after they have passed the pre-press and plate making stages, which will result in cutting out any need for costly reprints.

There are several different kinds of printing process and the choice of process depends on the kind of job. Machine printers may specialise in one particular printing process. Most machines are computer controlled. A machine printer's tasks can include:

preparing the paper or card so that it runs smoothly through the machine
positioning the printing plates in the press and taking trial prints to ensure everything is correctly placed
loading the machine with inks and making sure colours are reproduced correctly
maintaining quality checks during the running of the press
looking out for problems, such as paper jams, to avoid machine downtime
routine maintenance and cleaning of the press.

What is PostPress?

PostPress is a crucial part of any printing process and it takes place after the actual printing. It helps in determines the final look, shape and feel of the printed product.

Post press consists of several sub processes that are implemented depending upon the type of the project and the job being handled. Some of the basic types of post press operations in printing industry which are often used are as follows:

Cutting: This is one of the most common operations of post press which is used in almost all projects. For this purpose, the machines which used are known as “guillotine cutter” or "paper cutter". These are special machines which are used for cutting large substrates of web-type into different sheets or pages. These machines differ in sizes, features, abilities, capacities and configurations; because they are built for individual purposes.
Folding: This activity is performed mostly in printing workshops for pamphlets, magazines and product boxes. There are mainly three types of folders used in print shops – bone folder, knife folder and buckle folder.
- Bone folder is the one of the oldest among its peers that are made either of bone or plastic. Today they are used occasionally only for high quality jobs.
- Knife folders use knife to force the paper getting into the roller for folding.
- Buckle folder will convert a sheet into buckle so as to pass it between the two rotating rollers.
Assembling: In assembly, there are three main steps which should be followed - gathering, collating and inserting.
- Gathering is a method of placing bunch of sheets one after another. This is done for assembling books with page thicknesses ranging between 3 to 8 inches.
- Collating is a process of gathering individual sheets of paper instead of bunch of papers. The last step will be inserting involves the process of combining signatures or bunch of papers by “inserting” one into another.
- Inserting is done for the papers with signature pieces having final thickness less than one-half inches.
Biding: In this category, the printed material or pages are stick together. Three most common binding techniques which are used are- adhesive binding, side binding and saddle binding. For completing binding process, three individual types of covers are used. They are –
- self-covers
- soft-covers
- case-bound covers.

Some of the job profiles in this field are:

Printing Worker,
Prepress Technician,
Press workers and Software designer for print industry.

A digital print press operator uses digital printing machines and software programs to efficiently create materials as per client requirements. In fulfilling these requests, operators may change many variables in the printing press set-up, such as dimension, color or contrast.

The best way to learn these concepts is by joining a professional graphic design institute which can provide training in advanced level concepts of Pre-Press and Post Press. That is why print101naija is there for you. Join us today to start expanding your career.

Printing Process

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Introduction to printing processes

print101naija August 02, 2018

There are a wide variety of technologies that are used to print stuff. The main industrial printing processes are:

Offset lithography
Flexography
Digital printing: inkjet & xerography
Gravure
Screen printing

Additional printing techniques were developed for very specific applications. These include flock printing, letterpress, intaglio, pad printing, and thermography.

Why a certain job is better printed using one of these processes mentioned can be read on this page about choosing a printing process.

Offset

In offset lithography a printing plate, which is most often made from aluminum, contains an image of the content that needs to be printed. When the plate is inked, only this image part holds ink. That inked image is subsequently transferred (or offset) from the plate to a rubber blanket and then to the printing surface. The process can be used to print on paper, cardboard, plastic or other materials, but these have to have a flat surface.

Below is a picture of a 4 color sheetfed printing press. At the far end is the intake where individual sheets of paper are automatically fed into the press. The 4 towers or printing units each print one color, typically black get printed first, followed by cyan, magenta and yellow. The stack of printed sheets is visible on the front of the machine, underneath the press console & monitor which the press operator uses to control the press.

For higher volume work offset presses use rolls of paper. The picture below shows such a much larger web press. It is so fast that the printed paper needs to be force dried. The black unit at the end of the press is an oven.

Offset is nowadays the most widely used printing technique for an extensive range of products such as books, newspapers, stationery, corrugated board, posters, etc.

There is a trend that printing promotional material is gradually migrating to digital printing while some packaging printing is moving to flexo.

You can find more information on the page dedicated to offset printing.

Flexo

In flexography the content that needs to be printed is on a relief of a printing plate, which is made from rubber. This plate is inked and that inked image is subsequently transferred to the printing surface. The process can be used to print on paper as well as plastics, metals, cellophane and other materials. Flexo is mainly used for packaging and labels and to a lesser extent also for newspapers.

Some packaging printing is moving from flexo to digital.

Digital printing

Digital printing can be done in various ways. Two technologies dominate the industry:

Inkjet – In an inkjet printer the image that needs to be printed is created by small droplets of ink that are propelled from the nozzles of one or more print heads. Inkjet devices can print on a wide range of substrates such as paper, plastic, canvas or even doors and floor tiles. Inkjet printing is used a lot for posters and signage. It is also economical for short run publications such as photo books or small runs of books. In-line inkjet printers are sometimes combined with other types of presses to print variable data, such as the mailing addresses on direct mail pieces. The press shown below is the HP PageWide C500, meant for printing on corrugated board.
Xerography – In xerographic printers, such as laser printers, the image that needs to be printed is formed by selectively applying a charge to a metal cylinder called a drum. The electrical charge is used to attract toner particles. These particles are transferred to the media that is being printed on. To make sure the toner is fixed properly, the substrate passes through a fuser that melts the toner into the medium. Laser printers are not only used in offices but also for small run printing of books, brochures and other types of document. These printers are also used for transactional printing (bills, bank documents, etc) and direct mail.

In 2009 both techniques jointly accounted for around 15% of the total volume of print.

Digital printing is increasingly utilized for print jobs that were previously printing using offset, flexo or screen printing.

In short run small format (A3 size) printing, digital is taking over from offset for both color and B&W printing. Quick printers and copy shops print digitally on presses from vendors like Xerox, HP, Canon, and Konica Minolta.
Labels are also increasingly being printed digitally.
Billboard and point-of-sale or point-of-purchase jobs are being done by wide-format inkjet devices.
There is a wide range of small format printers used to print on phone cases, mugs and other products.
In book printing publishing companies start to rely more on print-on-demand. The Espresso Book Machine pictured below is well suited for that job.

There are a number of other digital printing processes that are geared towards specific niche markets:

Dye-sublimation is a printing process in which heat is used to transfer a dye onto the substrate. Dye-sub printers are mainly used for printing on textiles, for proofing and for producing photographic prints. Some printers can print on a variety of materials such as paper, plastic, and fabric.
In the direct thermal printing process heat is used to change the color of a special coating that has been applied to paper. This process is used in cash registers but also to add markings, such as serial numbers, to products. For this a transparent ink is used that changes color when a laser applies heat to it.
In the thermal ink transfer printing process heat is used to melt print off a ribbon and onto the substrate. It is used in some proofing devices but seems to be gradually disappearing off the market.

Gravure

Also known as rotogravure, this is a technique in which an image is engraved into a printing cylinder. That cylinder is inked and this ink subsequently transfers to the paper. Gravure is used for high volume work such as newspapers, magazines, and packaging.

Gravure is gradually losing market share to offset for publication printing and to flexo for packaging applications.

Screen printing

As its name implies, this printing technique relies on a screen, which is a woven piece of fabric. Certain areas of this mesh are coated with a non-permeable material. In the remaining open spaces ink can be pushed through the mesh onto a substrate. The advantage of screen printing is that the surface of the recipient does not have to be flat and that the ink can adhere to a wide range of materials, such as paper, textiles, glass, ceramics, wood, and metal.

The image below shows a screen printing press that is used to print t-shirts.

Increasingly screen printing is being replaced by digital printing.

Additional printing processes

Letterpress – Once a dominant printing technique, letterpress is now used for business cards, wedding invitations,…
Flocking – used to add a (colored) velvet-like texture to paper, textiles, etc.
Pad printing – used to print on 3-dimensional surfaces.
Intaglio – nowadays mainly used for used stamps and paper currency.
Thermography – This is more of a finishing process than an actual printing process. It produces raised lettering on the printed side of the paper and is used for wedding invitations, letterheads, business cards,…

Printing Process

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What is Thermography in printing process?

print101naija July 26, 2018

Thermography is the process of spreading thermal powders on the wet ink of a print application and heating it in order to melt the powder into a single solid mass which is raised above the printed surface. It is also known as "imitation engraving", however an engraving die is not needed with thermography. The process is faster than engraving and it is less expensive.

Applications

Thermography can add value to many ordinary print applications. Among the many applications that can benefit from thermography are letterheads, greeting cards, invitations, business cards, marketing applications, announcements, and envelopes. Thermography can make the appearance of many print applications more distinctive, providing a customized appearance that cannot be achieved with any other method.

Thermographic Process

Thermography is successful when the powdered resins are applied to a printed surface on which the printing ink is still wet. This enables the powder to stick to the printed areas. Any powder on non-image areas and any excess powder on the image areas is suctioned off the substrate before the heating takes place.

The heat is produced with electric heating elements that are placed inside an oven or tunnel. The powdered substrate passes into the heat tunnel where the powder melts onto the heated substrate and is fused with the wet ink. The substrate must be raised to the temperature of the melting point of the powder in order for the process to work correctly. When the heating process is complete, the sheet is cooled and the melted powder hardens into the raised thermographic image.

Important points to consider when designing a project for the thermographic process include:

Thermography will not improve or mask the flaws of a poor design or a poorly printed application.
Type sizes less than 6 point should not be avoided because they can fill in. Type faces that are very fine can also fill in.
Large solid areas and very small type should be avoided on the same page because each of the elements requires a different type of resin.
Many print applications using thermography may require special techniques for trimming because the raised print makes it difficult to cut stacks of thermographed sheets using a standard guillotine cutter. The cost of trimming thermographic applications may be more expensive than print projects without thermography. Some applications such as business cards (which are printed with many per sheet) are sent through special slitting machines in order to be separated.
Large wholesale thermography companies handle large volumes of standard items and are the most cost effective source for standard products, but they may not offer specialized or customized thermography.

Thermographic Powders

Thermographic powders are made from plastic resins which were introduced in the 1970's. They have taken the place of resin materials that were traditionally manufactured with a base made from ground tree sap. There are a wide range of thermographic powders available that produce an endless variety of effects. The powders come in many particle sizes to suit any application. A choice of finishes, such as gloss, semi-gloss, semi-dull, and matte are also available.

Types of Powder
In addition to standard powders, the following types of thermographic powders are available:

Metallic Resin: Metallic resin powders produce a metallic sheen after being melted and they are less expensive than foil stamping. Metallic resins are unaffected by the color of the paper stock and they are well suited for dark colored paper stocks. Applications include presentation folders, advertising, and announcements. Metallic resins come in silver, gold, bronze, and copper.
Glitter: Glitter can be added to thermal resins to produce a sparkling effect after processing. Depending on the application, the glitter can be varied for different effects.
Varnish: Varnish can be applied as an all over coat on applications such as four color process jobs to give the four color images a thermographic appearance.
Pearlescent Resin: Special ingredients are contained in pearlescent resin along with pigments to produce a pearlescent sheen after the application is processed.
Static Resistant: The build up of static electricity on the application is reduced with the use of static resistant powders.
High Viscosity: A high viscosity powder is used to maintain the detail on images that are made up of fine lines.
Laser Safe Powders: One drawback with standard resins is that the raised coatings on applications such as letterheads can remelt if they come in contact with other heat producing equipment such as laser printers and photocopiers. Laser safe resins are treated with ultraviolet light after they are applied and melted on the substrate. This gives the resins the ability to be unaffected by additional heat sources.

All of the above powders can be used alone or they can be combined in various ways to produce multiple effects. For example, adding glitter to metallic resin produces a sparkling effect on the metallic finish. Most resins can be mixed with a variety of substances such as tinsel, sequins, and diamond dust to create even more effects.

Particle Sizes
Different particle sizes are available ranging from fine to course. Fine powder is used on images with fine detail and thin lines. Heavier images can be processed with course powder.

Extra Fine: Used for fine details and type sizes 14 point and smaller.
Fine: A fine particle can be used for most purposes except the finest details and it works well with type sizes from 12 to 30 points.
Medium: Used for solids and types sizes from 24 to 42 point.
Course: Large solids and type sizes over 36 point are well suited for course powder.

Equipment

Table Top Models
Table top machines were developed in the 1970's which made it easier for more print manufacturers to offer thermography as an option for their customers. Some table top models involve mostly manual operations to produce the thermographic images. The powdered resins are applied to the printed sheet by hand and the excess is shaken off the sheet. The sheet is placed in the thermographic unit which is basically a heat tunnel. The sheet is removed and another sheet is placed in the machine. This can be a very time consuming process and may not be economical to use on runs over a few hundred unless a job is printed with many images per sheet such as a business card application.
Floor Models
Larger floor models are fully automated and are attached to and synchronized with press equipment in order to eliminate manual procedures. The printing press may need to be equipped with slow down pulleys in order to be properly synchronized with the thermographic unit. The desired speed of the equipment depends upon the design of the application, the materials used, and the type of equipment used for printing the application and for producing the thermographic image.

Paper Stock

Some points to consider when selecting a paper stock suitable for thermography are weight, moisture content, color, and texture. Don't assume that any paper stock can be used. Some paper stocks are not suitable for thermography mainly because of the high temperature required for the process. Paper stocks must be able to be heated to at least 250 degrees Fahrenheit in order for the process to work properly because the heat on the paper is what melts the resin. Paper stocks such as 20 lb. bond cannot handle the high temperature without adverse effects. The amount of thermographic raise that is achieved also changes depending on which paper stock is used.

Paper stocks should have a hard surface and a low moisture content. Excessive moisture in the paper can cause the paper to curl when it is subjected to high temperatures. Curling can also occur when uneven heating is applied to the paper. Curling often happens when one side of the paper is heated more intensely than the other side. Excessive moisture content in the paper can also leave the thermographic image with a cloudy appearance as a result of moisture being released from the paper during the heating process and being trapped in the thermal coating. Paper that has a moisture content which is too low may absorb the ink so fast that the thermographic powder may not stick to the ink.

The heavier and thicker the paper, the more heat is required to raise the temperature of the paper to the melting point of the thermal powder. Some heavily textured stocks may require special resins in order to produce a smooth thermographic finish over the printed areas.

Ink

The quality of the ink and the quality of the printed image are directly related to the degree of quality that can be expected when applying thermography to the application. The ink should be tacky (sticky) when entering the thermographic device. The tackiness of the ink is what causes the thermographic powder to adhere to the printed surface before it is melted. If the ink is not tacky enough, the vacuum used to remove excess powder from the non-image area can also remove some of the powder from the image area resulting in substandard thermography. The press operator may have to run more ink and/or less water than normal to achieve the proper ink coverage and ink tackiness required for thermography and yet the coverage must not be so great as to produce set-off on the back side of the printed sheet. Thermography works best when as much ink as possible is laid down on the paper with a minimum amount of impression. Inks with little or no drier additives are well suited to thermography because the ink stays wet longer and the ink acts as the adhesive for the thermal powder.

Printing Process

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What is screen printing?

print101naija July 26, 2018

Description

Screen printing has been used for centuries and although there have been many improvements with the technology, the process still consists of forcing ink through a stencil covered fabric or wire mesh which has been mounted in a sturdy frame. The ink goes through only the open areas of the stencil and is deposited onto a printing surface positioned below the frame. Screen printing is very versatile and it is often the only printing process capable of handling certain applications.

The equipment costs for screen printing are lower than other printing processes, but the rate of production is usually slower. Manual screen printing can be accomplished with only a few simple items: a sturdy frame, screen fabric, stencils, squeegees, and ink. Automatic press equipment is available which greatly speeds up the process, but it is no match for the output delivered by press equipment used for other print processes.

Applications

Screen printing can be performed on almost any type of material including paper, glass, fabric, plastic, wood, and metal. Products as varied as signs, posters, circuit boards, mugs, clothing, and soft drink bottles can be printed using the process. Screen printing is very useful when an image needs to be wrapped around an object or when images need to be printed onto oddly shaped manufactured objects.

Screen Fabrics

Fabrics for screen printing are selected because of several properties. One type of fabric may be suitable for one application and not another. Fabrics are classified according to the following properties:

Filament refers to the type of thread that makes up the fabric. The thread can be multifilament or monofilament of which monofilament provides the best quality. The multifilament threads produce images with more jagged edges than the monofilament thread, but they are not as expensive as monofilament.
Mesh Count is the number of threads per linear inch. A higher mesh count produces finer details and higher quality in the product.
Strength is determined by the diameter of the thread. A larger thread diameter will provide greater strength to the fabrics, but the print quality will decrease.
Weave Patterns for screen printing fabrics are based on three types: plain, which can be used for most applications, gauze, which is selected for long runs because of its strength, and twill, which is chosen for its low cost and when quality is not an issue.

Most fabrics used for screens are made from one of the following materials:

Silk used to be the most common fabric because of its durability, but it is not used as much today because other fabrics, especially synthetics, have proven to be as good or better and are less expensive.
Organdy is inexpensive and is good for short and medium runs.
Nylon is the most durable fabric (synthetic or natural). It is a good choice for print applications involving convex or concave surfaces
Polyester is widely used for its durability and versatility.
Metal Mesh is made of stainless steel, copper, bronze, or brass and is used when plastic substrates are printed with heated inks.

Stencil Types

Knife cut stencils are created with manual cutting and can be paper, water soluble, or lacquer soluble.

Paper: Stencils cut from paper are used for basic designs and short runs.
Water Soluble: Water soluble gelatin is cut away from the plastic base of the stencil. The cut away portions of the gelatin represent the image areas. The plastic base and remaining gelatin are placed on the screen material and water is used to adhere the gelatin layer to the screen. The plastic base can then be peeled off from the gelatin layer which remains adhered to the screen fabric.
Lacquer Soluble: A lacquer soluble stencil is used much the same way as the water soluble stencil except that the stencil is adhered to the screen material with lacquer solvents.

Photographic stencils are made of photosensitive materials and require the use of film positives for exposure. There are three types of photographic stencils: indirect, direct, and direct/indirect.

Indirect: An indirect stencil is a photographic stencil which is produced independent of the screen fabric and is applied to the screen after exposure.
Direct: A direct stencil is one in which the photosensitive material is applied to the screening fabric so that after exposure, the stencil becomes part of the fabric. It is very durable and is useful for long runs.
Direct/Indirect: A direct/indirect stencil is a combination of the two stencil types. It lasts longer than an indirect stencil, but it cannot match its quality.

Ink

There is a wide variety of inks available for use with screen printing. The ink for some applications may need to be resistant to ultra-violet light or they may need to be scratch, fade, or chemical resistant for other applications. Most of the inks for screen printing are applied with a heavy coverage so the ink layer takes a long time to dry. The printed products can be air dried on racks if the number of printed pieces is small, but most often a heat source is used to speed up the drying, especially if the screen printing is performed with higher speed, automatic equipment.

Press Types

Most large volume screen printing is performed on automatic printing equipment which makes the process much more efficient and cost effective. Manual screen printing is still used for many of the smaller runs or for specialized applications. The basic press types are listed below:

Flatbed: A flatbed press is used for printing on flat substrates.
Flatbed Cylinder: A flatbed cylinder press is much like a letterpress flatbed cylinder press and is used for longer runs of flat applications.

Cylinder: A cylinder press is used for printing on round or oval objects.
Textile: T-shirts and other clothing items are printed on a textile press.
Precision Flatbed: One of the major uses for the precision flatbed press is circuit board printing.
Rotary: Higher production rates are a benefit of the rotary presses. The ink is pumped into the printing cylinder and a squeegee on the inside of the cylinder controls the flow of the ink.

Printing Process

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Offset process explained in detail

print101naija July 26, 2018

Description

Offset lithography is the most widely used print process. About 40% of all print jobs are produced with offset printing. It is an indirect printing process which means that an image is transferred, or offset, from one surface to another. A printing plate mounted on a cylinder transfers the image to a rubber blanket mounted on another cylinder. The image is then transferred from the blanket cylinder to the substrate as the substrate passes between the blanket cylinder and an impression cylinder. The image on the plate is "right reading" and when the image is transferred to the blanket it becomes "wrong reading". When the image is transferred to the printing surface it becomes right reading again.

The image area and non-image area of the offset plate are on the same plane and work on the principle that oil and water do not mix. The non-image areas of the plate attract a wetting agent (fountain solution) and repel ink made from an oil base. The image areas attract the ink and repel the fountain solution.

Applications

The types of printed materials that can be produced with offset lithography are numerous and varied. Some of the items include: newspapers, magazines, books, continuous business forms, unit sets, advertising pieces, brochures, posters, greeting cards, business cards, folders, mailers, laser sheets, integrated products, coupons, and art reproductions.

Press Types

Offset presses can be put into two categories: sheet-fed and web-fed.

Sheet-fed: A sheet-fed press prints an image on single sheets of paper as they are fed individually into the press. The print quality and sheet to sheet registration is often better than web-fed printing, but it is often more economical to produce very large runs on web presses because of their higher running speeds.
Sheet-fed presses can be divided into three categories: small, medium, and large sheet presses.

Small Sheet-fed: The small sheet-fed press can print sheets up to 14" x 17". They are used primarily for short runs of one or two colors for such items as business forms, letterheads, and business cards and are popular for instant print companies.
Medium Sheet-fed: Sheet sizes of up to 25" x 38" can be printed on a medium sheet-fed press. The presses are used for runs up to 20,000 and are common equipment for many medium and large printers. Products such as brochures, business forms, medium press runs of color work are produced with the mid-size press.
Large Sheet-fed: The largest runs (usually 100,000 or more) and the most complex jobs are reserved for the large format sheet-fed presses. They can accommodate a paper size of up to 49" x 74" and they may have several printing towers so that multiple colors can be printed with one pass.

Web-fed: A web-fed press prints images on a continuous web of paper fed into the press from a large roll of paper. The web of paper is then cut into individual sheets after printing or as with continuous business form applications, it is left in web form and is perforated for later separation into individual sheets.
Like sheet-fed presses, web-fed presses come in many types and sizes. Some smaller web presses are capable of printing only on narrow width paper rolls and can only print one or two colors on the front side of the paper. Other web presses can handle large width webs and can print on the front and the back side of the paper in one pass through the press. There may be 8 or more printing units so that applications requiring full color on the front and back can be printed.

Press Components

Offset presses (sheet-fed and web-fed) are made up of some common components that work together to carry out the offset printing function. Some of the common components include a device for feeding paper into the press, a set of cylinders that create the printed impression on the paper, a roller train for distributing ink and for dampening non-image areas of the plate, and a system for removing the printed paper from the printing system.

Feeding System: The feeding system is the device that feeds the paper into the press. There are different types of feeding systems for sheet-fed and web-fed presses.

Sheet-fed: The paper is usually stacked in a tray at the front end of the press where it is pulled into the press one sheet at a time. Vacuum devices called "sucker feet" pick up each sheet of paper from the stack. As paper is fed into the press, the tray of paper automatically raises up so that there is no interruption in the paper feed until the tray is empty.

Web-fed: A mechanism called a "rollstand", which accommodates a large continuous roll of paper, is used with the web-fed system. As the paper is fed through the press, another system maintains proper tension on the paper web as the roll of paper gets smaller in the rollstand. Some presses have automatic roll changers which splice in a second roll of paper as soon as the first roll is nearly out of paper.

Printing System: The printing system for offset presses contain 3 major components: the plate cylinder, blanket cylinder, and the impression cylinder. The circumference of the cylinders determine the size of the applications that can be printed on the press. For example, a press with printing cylinders of 17" in circumference is able to print applications with a depth of 17", 8 1/2", 4 1/4", and so on. For an 8 1/2" application, there would be two separate 8 1/2 inch pieces printed per revolution of the cylinders. Presses are often named for the circumference of their cylinders, such as a "17 inch press", or a "22 inch press".

Plate Cylinder: The plate cylinder contains a slot or "plate gap" into which the lead edge of the plate is inserted. The plate is wrapped around the cylinder and then the tail end of the plate is inserted into the slot. The plate ends are then locked into the slot.
Some sheet-fed presses utilize plates the are punched at both ends. The plate cylinder gap contains two sets of pins that the punched ends of the plate fit over. The pins are tightened do that that the plate remains stationary on the cylinder.
Blanket Cylinder: The blanket cylinder is much the same as the plate cylinder except instead of holding a plate, a compressible rubber blanket is mounted on it. The blankets vary in type and thickness depending on the type of press on which it is used.
Impression Cylinder: The impression cylinder is usually a seamless, hardened steel cylinder that provides a surface for the print impression to take place. The paper passes between the blanket cylinder and impression cylinder where just the right amount of squeeze between the two cylinders allows for the transfer of the image onto the paper.

Note: The gaps in the plate and blanket cylinders are "non-printable" areas. Allowances must be made with the overall image size so that the image on the plate does not extend into the plate gap when the plate is installed. The slot in the blanket cylinder, known as the "blanket gap" is usually wider than the plate gap, so even though the image may look correct on the plate, a sliver of the image may not be offset to the blanket because of its wider gap. For this reason, the image allowance is usually based on the non-printable area of the blanket cylinder. The non-printable gap is also known as the "lock-up" dimension and it varies between different types of presses.

Note: Some applications may require that the printed image be slightly larger than what can be actually printed by the press. To accommodate the larger print size, the copy may have to be split and printed on two separate printing units. This is known as an "over image" job or a "split image" and should be taken into consideration when planning a print job.

Inking System: The inking system on offset presses consists of a fountain which holds the ink and a set of rollers, known as the roller train, which distribute the ink and carry it to the printing plate. A roller within the fountain draws the ink from the fountain into the roller train where it is milled into the proper thickness. It is then brought to the final rollers in the system called the "form rollers" which apply the ink to the plate.
The number and type of rollers in an inking system varies widely between different types of offset presses. A small duplicator press may have only a minimum number of rollers to supply the flow of ink to the plate as most of the applications printed on a duplicator press are very basic. A large web press used for printing complex applications in full color requires a larger number of rollers to mill the ink and several form rollers to apply the ink to the plate. The more rollers there are in an inking system, the better the ink will be distributed and the better the print quality will be.
Dampening System: The dampening system consists of a set of rollers that distribute the fountain solution to the plate. The fountain solution is necessary to keep the non-image areas of the plate free of ink. As with the inking system, the dampening system consists of a fountain which holds the dampening solution, a roller within the fountain that carries the solution into the dampening rollers, and form rollers that apply the dampening solution to the plate. Like inking systems, the type of dampening system can vary greatly between different types of presses.

Delivery System: Sheet-fed and web-fed presses each have different types of delivery systems, which are described below:

Sheet-fed: Printed sheets are carried from the printing units of a sheet-fed press to a delivery tray. The tray has guides which assist in delivering the sheets to the proper place on the tray. A jogging system helps to keep the printed sheets in a neat stack. The tray of the delivery system automatically lowers as it is filled with printed sheets.

Web-fed: The printed web is carried from the printing units to one of two types of delivery systems. A "roll-to-sheet" press has a mechanism for cutting the web into individual sheets. The sheets are then carried a short distance on belts to a delivery tray where they are automatically jogged and can be removed in predetermined increments by the press operator.

Another type of web-fed delivery system is found on a "roll-to-roll" press. The printed web is carried from the printing units to a "rewind" unit where it is wound onto a spool. There are several reasons why rewinding is necessary:

A multiple part business form may require off-line collating, so each part of the form would be printed separately and wound on rolls at the press. The rolls would then be mounted on a collating machine where the individual parts would be attached together.
The application may require additional features that cannot be applied at the press, so they are handled off-line on other web-fed equipment.
Some types of continuous business forms are supplied to customers on rolls so that the forms will work properly through certain types of statement rendering equipment.

Note: Besides the common components described above, many offset presses have other components for applying additional finishing functions that would otherwise have to be accomplished off-line. The addition of perforations, scoring, punching, and consecutive numbering are only a few of the additional functions that can be performed. Many presses are modular in that additional printing units and finishing units can be added to the basic press in order to provide added functionality.

Printing Process

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What is Letterpress in printing?

print101naija July 26, 2018

Description

The letterpress process is referred to as a "relief" process because the printed image is produced from a plate in which the image area is slightly raised above the non-image surface of the plate. It is a direct printing method in that the inked plate applies the image directly to the substrate. Letterpress is one of the oldest printing processes and was the most widely used process until the middle of the 20th century when advances in other printing processes made it obsolete. Flexography, which is an updated version of letterpress, is now the dominate relief printing process.

The letterpress process utilizes an ink that is thick in consistency and is well suited for relief printing. A set of rollers deposits the ink on the raised image area of the type or plate, but ink is not deposited on the non-image areas. For this reason, letterpress plates do not require any dampening in order to keep the non-image areas free of ink. This makes the process a simple one and allows for consistent results, but the process still cannot match the quality of more sophisticated print processes.

Applications

Because of the popularity of other printing processes, letterpress is a fast diminishing printing method. It is still used for publishing a few small town newspapers, several types of labels, packaging materials, and some narrow web printing.

An area where letterpress has greater usage than it does with actual printing is with some finishing operations. Old letterpress equipment is used for procedures such as embossing, die-cutting, numbering, perforating, and foil stamping. The types of products that can be finished using letterpress equipment include embossed business cards and government documents, die-cut labels and folders, numbered tickets and membership cards, perforated mailers, and foil stamped letterheads and invitations.

Press Types

There are four types of relief presses which are described below:

Platen Press: With platen press, movable metal type is locked into a frame called a chase. The chase is then placed in the press bed and it is also locked into position. During the printing process, grippers move a sheet of paper from the feedboard, which contains a stack of paper, to the platen, which is the surface where the print impression is made. A set of rollers applies ink to the type on the press bed and then the press bed and the platen are pressed together like a clamshell which produces the image on the paper. When the impression is complete, the platen and the press bed spread apart and the grippers remove the paper, placing it on a delivery tray.

Flatbed Cylinder Press: The type or plate is locked in a chase which is then mounted on the flatbed of the press. Grippers on a rotating impression cylinder pick up a sheet of paper and as the cylinder revolves, the paper is pulled around it. The inked flatbed containing the letterpress plate then moves under the impression cylinder. The squeeze between the impression cylinder and the flatbed creates the printed impression on the paper. When the impression is complete, the flatbed returns to its original position and is inked for the next impression.

Rotary Sheet-Fed Press: The plate is mounted on a cylinder where a roller system applies ink to the raised area of the plate. The paper passes between the plate cylinder and an impression cylinder where the resulting squeeze between the two cylinders produces the printed impression on the paper.
Rotary Web-Fed Press: The web-fed system also utilizes a plate cylinder and impression cylinder, but instead of individual sheets passing between the two cylinders, the paper is a continuous web unwound from a large roll. After printing, the web is cut into individual sheets. Web-fed presses are used for larger print runs. Like other printing processes, the letterpress web-fed press usually contains several printing units so that multiple colors can be printed from a single pass.

Printing Process

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What is Gravure in printing?

print101naija July 26, 2018

Description

Gravure is a high quality printing process capable of producing printed images which have a continuous tone effect similar to a photograph. The gravure process utilizes a metal printing cylinder onto which the image is etched. The gravure cylinder can be created with analog or digital plating processes.

Applications

Gravure is used for many packaging applications, magazines, and pressure sensitive labels. Gravure is the preferred method of producing magazines and catalogs that have large circulations. An example of a high volume, high quality publication that utilizes rotogravure is the "National Geographic" magazine.

There are also many specialty items that are created with rotogravure including gift wrap, wallpaper, plastic laminates, printed upholstery, imitation wood grain finishes, and vinyl flooring. Many of the specialty items are printed on very wide presses. Some of them, such as those that print patterns on floor coverings, are up to 150 inches wide.

A gravure sheet-fed process is used for smaller runs for such items as limited edition prints and other artwork, photographic books, high denomination postage stamps, stock certificates, and some advertising pieces.

Cells

The printing impression produced by the gravure process is accomplished by the transfer of ink from cells of various sizes and depths that are etched into a copper covered steel cylinder. The cells are different sizes and depths and the cylinder may contain as many as 22,500 cells per square inch. The various sizes and depths of the depressions create the different densities of the image. A larger or deeper depression, transfers more ink to the printing surface creating a larger and/or darker area. The areas of the cylinder that are not etched become the non-image areas.

Originally, the cells in a gravure cylinder were all equal in area but they were different in depth. Today, the cells that are engraved in the cylinders are different in area and depth or they can be the same depth but different in area. This allows for greater flexibility in producing high quality work for different types of applications. Cells that vary in area but are of equal depth are often used on gravure cylinders for printing packaging applications. The gravure cylinders with cells that vary in area and depth are reserved for the highest quality printing.

Printed images produced with gravure are of the highest quality because the thousands of ink cells appear to merge into a continuous tone image. One drawback with the cells is that the quality of small typefaces, although good, may not be as sharp as type printed with a process such as offset lithography. This is because the type is created with individual cells just like the rest of the image, instead of being printed as a continuous solid shape.

Printing Process

Because of the expense of the cylinders, gravure is largely performed as a rotary web process (rotogravure). It is most often used for very long runs of up to a million and many times the press runs are greater than that. For runs of a million or more, the cylinders are plated with chromium to provide extra durability. If the chromium begins to wear, it is removed from the cylinder and a new coating is applied.

During the printing process, the gravure cylinder revolves in an ink fountain where it is coated with a very fluid ink. A stainless steel blade (doctor blade) clears the ink from the unwanted areas, leaving the ink in the depressions of the cylinder. The substrate passes between the gravure cylinder and an impression cylinder covered in rubber. The substrate passes between the two cylinders and the ink from the cells is deposited onto the substrate.

Besides being very thin and fluid, the ink colors used with process color applications differ in hue than the inks used with other processes. Instead of the usual cyan, magenta, yellow, and black used with offset lithography, blue, red, yellow, and black are used. Standards have been established by the Gravure Association of America for the correct ink types and colors that should be used for different types of substrates and printing applications.

Gravure is a direct printing method so there is no need to utilize fountain solution to keep the non-image areas clean. Eliminating this variable allows for better print quality control and jobs can be run at higher speeds. Some applications can be run as high as 3,000 feet per minute. The microscopic depressions on the gravure cylinder create an almost continuous tone image on the printed surface, which is why it is often used for high quality image reproduction.

Printing Process

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Three important printing processes are:

Offset

Flexo

Digital printing

Gravure

Screen printing

Additional printing processes