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Print Process Descriptions: Printing Industry Overview: Postpress

Cutting

The machine typically used for cutting large web-type substrates into individual pages or sheets is called a guillotine cutter or "paper cutter". These machines are built in many sizes, capacities, and configurations. In general, however, the cutter consists of a flat bed or table that holds the stack of paper to be cut. At the rear of the cutter the stack of paper rests against the fence or back guide which is adjustable. The fence allows the operator to accurately position the paper for the specified cut. The side guides or walls of the cutter are at exact right angles to the bed. A clamp is lowered into contact with the top of the paper stack to hold the stack in place while it is cut. The cutting blade itself is normally powered by an electric engine operating a hydraulic pump. However, manual lever cutters are also still in use.

To assist the operator in handling large reams of paper which can weigh as much as 200 pounds, some tables are designed to blow air through small openings in the bed of the table. The air lifts the stack of paper slightly providing a near frictionless surface on which to move the paper stack.

The cutter operator uses a cutting layout to guide the cutting operation. Typically, the layout is one sheet from the printing job that has been ruled to show the location and order of the cuts to be made. Though cutting is generally considered a postpress operation, most lithographic and gravure web presses have integrated cutters as well as equipment to perform related operations such as slicing and perforating.

Folding

Folding largely completes postpress operations for certain products such as simple folded pamphlets. Other products are folded into bunches, known as signatures, of from 16 to 32 pages. Multiple signatures are then assembled and bound into books and magazines. Though folding is generally considered a postpress operation, most lithographic and gravure web presses are equipped with folders.

Three different folders are used in modern print shops. They range in complexity from the bone folder to the buckle folder. Bone folders have been used for centuries and are made of either bone or plastic. These folders are simple shaped pieces of bone or plastic that are passed over the fold to form a sharp crease. Today, they continue to be used, but only for small, very high quality jobs.

Knife folders use a thin knife to force the paper between two rollers that are counter-rotating. This forces the paper to be folded at the point where the knife contacts it. A fold gauge and a moveable side bar are used to position the paper in the machine before the knife forces the paper between the rollers. The rollers have knurled surfaces that grip the paper and crease it. The paper then passes out of the folder and on to a gathering station. Several paper paths, knives and roller sets can be stacked to create several folds on the same sheet as it passes from one folding station to another.

Buckle folders differ from knife folders in that the sheet is made to buckle and pass between the two rotating rollers of its own accord. In a buckle folder, drive rollers cause the sheet to pass between a set of closely spaced folding plates. When the sheet comes in contact with the sheet gauge, the drive rollers continue to drive the paper causing it to buckle over and then pass between the folding rollers.

Assembly

The assembly process brings all of the printed and non-printed elements of the final product together prior to binding. Assembly usually includes three steps: gathering, collating, and inserting. Gathering is the process of placing signatures next to one another. (A signature is a bunch of printed sheets ranging from 16 to 32 pages.) Typically, gathering is used for assembling books that have page thicknesses of at least 3/8 inch. Collating is the process of gathering together individual sheets of paper instead of signatures. Inserting is the process of combining signatures by placing or "inserting" one inside another. Inserting is normally used for pieces whose final thickness will be less than one-half inch.

Assembly processes can be manual, semiautomatic or fully automatic. In manual assembly operations, workers hand assemble pieces from stacks of sheets or signatures laid out on tables.

Sheets or signatures are picked up from the stacks in the correct order and either gathered, collated, or inserted to form bindery units. Some printers use circular revolving tables to assist in this process. However, due to the high cost of labor, manual assembly is used only for small jobs.

Semiautomatic assembly is completely automated except that stacks of sheets or signatures must be manually loaded into the feeder units. During semiautomatic inserting, operators at each feeder station open signatures and place them at the "saddlebar" on a moving conveyer. The number of stations on the machine is determined by the number of signatures in the completed publication. Completed units are removed at the end of the conveyer and passed on to the bindery.

Automatic assemblers are similar to semiautomatic units except that a machine and not a person delivers the sheets or signatures to the feeder station and places them on the conveyor. In order to improve efficiency, automatic assemblers are typically placed in line with bindery equipment.

Binding

Binding is categorized by the method used to hold units of printed material together. The three most commonly used methods are adhesive binding, side binding, and saddle binding. Three types of covers are available to complete the binding process: self-covers, soft-covers, and casebound covers.

Binding Methods

Adhesive binding, also known as padding, is the simplest form of binding. It is used for note pads and paperback books, among other products. In the adhesive binding process, a pile of paper is clamped securely together in a press. A liquid glue is then applied with a brush to the binding edge. The glue most commonly used in binding is a water-soluble latex that becomes impervious to water when it dries.

For note pads, the glue used is flexible and will easily release an individual sheet of paper when the sheet is pulled away from the binding. Adhesive bindings are also used for paperback books, but these bindings must be strong enough to prevent pages from pulling out during normal use. For paperback book binding, a hot-melt glue with much greater adhesive strength than a water-soluble latex is applied. A piece of gauze-like material is inserted into the glue to provide added strength.

In side binding, a fastening device is passed at a right angle through a pile of paper. Stapling is an example of a simple form of side binding. The three other types of side binding are mechanical, loose-leaf, and side-sewn binding.

A common example of a form of mechanical binding is the metal spiral notebook. In this method of binding, a series of holes are punched or drilled through the pages and cover and then a wire is then run through the holes. Mechanical binding is generally considered as permanent; however, plastic spiral bindings are available that can be removed without either tearing the pages or destroying the binding material. Mechanical binding generally requires some manual labor.

Looseleaf bindings generally allow for the removal and addition of pages. This type of binding includes the well known three-ring binder.

Side-sewn binding involves drilling an odd number of holes in the binding edge of the unit and then clamping the unit to prevent it from moving. A needle and thread is then passed through each hole proceeding from one end of the book to the other and then back again to the beginning point. This type of stitch is called a buck-stitch. The thread is tied off to finish the process. Both semiautomatic and automatic machines are widely used to perform side-stitching. The main disadvantage of this type of binding is that the book will not lie flat when opened.

In saddle binding one or more signatures are fastened along their folded edge of the unit. The term saddle binding comes from an open signature's resemblance to an inverted riding saddle. Saddle binding is used extensively for news magazines where wire stitches are placed in the fold of the signatures. Most saddle stitching is performed automatically in-line during the postpress operations. Large manually operated staplers are used for small printing jobs.

Another saddle binding process called Smythe sewing is a center sewing process. It is considered to be the highest quality fastening method used today and will produce a book that will lie almost flat.

Covers

Self-covers are made from the same material as the body of the printed product. Newspapers are the most common example of a printed product that uses self-covers. Soft covers are made from paper or paper fiber material that is somewhat heavier or more substantial than the paper used for the body of the publication. This type of cover provides only slight protection for the contents. Unlike self-cover, soft covers almost never contain part of the message or text of the publication. A typical example of the soft cover is found on paper-back books. These covers are usually cut flush with the inside pages and attached to the signatures by glue, though they can also be sewn in place.

Casebound covers are the rigid covers generally associated with high-quality bound books. This method of covering is considerably more complicated than any of the other methods. Signatures are trimmed by a three-knife trimming machine to produce three different lengths of signature. This forms a rounded front (open) edge to give the finished book an attractive appearance and provides a back edge shape that is compatible with that of the cover. A backing is applied by clamping the book in place and splaying or mushrooming out the fastened edges of the signatures. This makes the rounding operation permanent and produces a ridge for the casebound cover.

Gauze and strips of paper are then glued to the back edge in a process called lining-up. The gauze is known as "crash" and the paper strips are called "backing paper." These parts are eventually glued to the case for improved strength and stability. Headbands are applied to the head and tail of the book for decorative purposes. The case is made of two pieces of thick board, called binder's board, that is glued to the covering cloth or leather. The covering material can be printed either before or after gluing by hot-stamping or screen methods. The final step in case binding consists of applying end sheets to attach the case to the body of the book.

In-Line Finishing

Historically, the finishing operations described above were labor-intensive operations handled either in-house or by trade shops. Even when performed in-house, finishing operations generally were not integrated with the presses or with each other. Today, web presses are often linked directly to computer controlled in-line finishing equipment. Equipment is available to perform virtually all major post-press operations including cutting, folding, perforating, trimming, and stitching (Adams). In-line finishing equipment can also be used to prepare materials for mailing. The computer can store and provide addresses to ink-jet or label printers, which then address each publication in zip code order (Adams).

One of the most important results of computer in-line finishing is the introduction of demographic binding, the selective assembly of a publication based on any one or more of a number of factorsincluding geographic area, family structure, income, or interests. For example, an advertisement will appear only in those copies of a magazine intended for distribution in the advertisers selling area. Demographic binding has proven to be a successful marketing tool and is already widely used, especially by major magazines (Adams).

One comparison found that the use of in-line finishing equipment can reduce the number of operators and helpers required for an off-line finishing operation by almost half, while at least doubling the rate of production (Adams).

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