Collating | Folding | Binding | Coatings | Die-Cutting | Embossing
Collating or sorting is the process of assembling the components of a print application into the correct order. There are many digital printing devices that are able to collate pages automatically. This may be available as an option or it may be a standard feature on some models. Off-line equipment may also be used or signatures may be gathered by hand for smaller quantities.
As with collating, there are many digital printing devices that offer online folding as a standard feature or as an option. There may be limitations as to the number of folds that can be performed depending on the type and model of the digital printing device. Some of the more complicated folds may have to be performed on off-line equipment.
Regardless of the type of equipment that is used, the grain of the paper is a major factor determining the success of the fold. Paper that is folded parallel with the grain of the paper will fold much more cleanly. A cleaner fold is produced because the paper fibers (grain) are running in the same basic direction as the fold. Only a few of the fibers provide any resistance to the folding action which results in a high quality fold.
When a fold is applied perpendicular to the grain of the paper, the resulting fold may have a ragged appearance. A ragged fold is produced because all of the fibers are folded at one time creating resistance to the folding action. The ragged appearance of the fold is especially noticeable when folding heavy stocks.
A score is a crease which is applied to the substrate allowing the substrate to be easily folded for some type of assembly procedure. A score may be used to crease the cover of a publication allowing it to stretch around a group of pages to be bound together or it may be used to apply a light crease on internal pages to make the folding process easier, especially if the fold is against the grain of the paper.
When a score must be applied parallel to the direction that the stock travels through the equipment, a steel scoring wheel is used. The scoring wheel rolls along the stock and applies the score as the stock is pulled through the press. The scoring wheel has a blunt, flattened edge and comes in various widths to produce narrow or wide scores on the paper. Multiple scores can be applied at the same time.
For scores that must be perpendicular to the direction the paper travels through the equipment, steel scoring rules are used. The blunt steel rules are inserted into cylinders which stamp the score into the paper as the cylinders revolve.
|Parallel scores are described as scores that run in the same direction that the paper travels through the digital equipment and/or are parallel with the grain of the paper.
||Perpendicular scores run in the opposite direction that the paper travels through the digital equipment and/or are perpendicular to the grain direction of the paper.|
A knife fold is best used with heavy stocks and when the fold must be cross grain. A blunt steel blade pushes the internal part of the substrate at the desired location between two rollers to create the fold in the substrate.
To create a buckle fold, a document passes through a set of rollers and into a plate where the substrate stops at a backstop. When the substrate hits the backstop, it buckles and is forced downward and into a set of nip rollers. The nip rollers grab the sheet at the buckle and pull it through, compressing a fold into the sheet as it passes through the rollers. If several folds are desired, then the material is sent into another plate to repeat the process. The fold or buckle location is adjustable by altering the stop mechanism, allowing for different folds to occur depending upon the type required.
Types of Folds
Typically, there are only two basic types of folds, parallel and right-angle. Products having parallel folds have all of the folds running parallel to each other. Right-angle folds are folds at right angles to each of the preceding folds.
Common Parallel Folds
- 4-Page Standard / Single / Half
- 6-Page Standard / C-Fold / Business Letter
- 6-Page Standard / Gate
- 6-Page Accordion / Z-Fold
- 8-Page Parallel Map
- 8-Page Reverse Map
- 8-Page Parallel / Roll
- 8-Page Accordion
- 8-Page Double / Double Parallel
- 10-Page Accordion
- 16-Page Parallel Booklet
Common Right Angle Folds
- 8-Page Booklet with 2 Right Angle Folds (French Fold)
- 8-Page Right Angle - First Fold Short
- 12-Page Letter
- 12-Page Broadside - First Fold Short
- 16-Page Broadside
Off-line Folding Equipment
Some digital printing presses are able to fold documents with standard or optional online folding devices that have preset standard folds. Some applications may require special folds or the digital printing equipment may not be able to perform online folding, which means that the application must be folded as a separate operation. Off-line folders for digital on-demand printing applications offer a variety of preprogrammed folds and automatic settings.
Several methods can be used with digitally printed documents to bind together multiple pages of an application. Some methods may be accomplished as an inline operation which reduces the overall cost of the application, while other methods must be performed off-line.
Saddle stitched books are constructed with sheets that are printed front and back that represent four pages of a book. The sheets of four pages are stacked with other sheets in the correct page order and then stapled along the fold line or saddle. The stapling is accomplished on equipment that cuts staples from a continuous roll of wire mounted on the machine and inserts them into the paper. Some machines can do the folding and stitching in one operation. There are several digital press models that provide for online stitching as an option. Many booklet manufacturers use this multiple task equipment to increase efficiency.
The most popular method of binding books printed with digital technology is perfect binding. Most digital books are printed as stacks of single sheets rather than groups of folded sheets (signatures) as is the case with conventional printing. Perfect binding is an easy and inexpensive method of binding single sheets.
Books that are perfect bound must have square backs, smooth spines, and adequate binding strength to prevent the pages from being pulled from the binding. In the past, the only way to accomplish this was with large off-line production machines, which required lengthy make-ready periods and resulted in very expensive short run applications. The large off-line machines were better suited to larger print runs.
An alternative to the large off-line binding devices and the online binders is smaller, less expensive, off-line perfect binders which are specially designed for small digital print applications. They are capable of producing perfect bindings that are nearly the same quality as the larger machines. The labor rates are much less than the larger machines and the make-ready time is greatly reduced.
Even more efficient are digital printing devices that are equipped with units capable of performing the perfect binding online, which saves time and expense. Even though the cost of the digitally printed book may be reduced, the quality of the binding may not always be of the same standard as the perfect binding applied on the large, expensive, off-line equipment.
There are several other methods used for binding digitally printed applications including loose leaf or ring binding, plastic spiral binding, sewn soft cover binding, and hardcover or case binding. These methods are usually accomplished with off-line equipment and are more expensive than stitching or perfect binding. Your print provider will be able to assist you in selecting the best method of binding for your application.
Several types of coatings can be applied to digitally printed documents in order to liven up the color and design. Coatings may be used to provide emphasis to a particular area of the document or to the entire application. They are most often used to provide protection to the printed piece, especially to documents with large areas of color.
Applied during the printing process or as an off-line process, overprint varnishes are much like a solvent based inks. They are usually colorless, but sometimes they are tinted to achieve a desired effect. Varnishes can be applied as an all-over coat or in spots to highlight a specific area of a printed piece.
Varnishes are available in glossy, dull, or satin finishes. Gloss varnish creates a smooth surface over the paper, filling in any voids or irregularities that may be on the surface. Dull varnish also fills in irregularities to form a smooth surface, but it diffuses light that reflects back to our eyes, which creates a dull appearance. A nearly 3-D effect can be created by applying gloss varnish to a subject and dull or satin varnish to the background. The subject will appear to jump off the page. In addition to applying varnish as a solid coat, it can also be printed as a halftone (series of dots) in order to provide subtle effects and to give objects a more dimensional appearance. The effects that can be achieved are endless when using different combinations of varnish, paper, and colorant.
Besides design effects, another important aspect of varnish is the protection it provides. A coating of varnish over a printed piece protects it from the wear and tear that is part of every day handling, allowing the document to last much longer than one that is unvarnished. An all-over coat of satin varnish will protect the printed surface without drawing attention to the fact that varnish was used for protection purposes.
A disadvantage of varnish is that many of them are solvent based. A solvent varnish emits VOCs while it is being applied, which can be a health hazard for the press operator unless the proper safety precautions are followed. Another disadvantage is that varnishes tend to yellow over time if they are formulated with tung or linseed oil. Varnishes with alkyd formulations will not yellow, but they are not as glossy or as hard as tung or linseed oil.
Some digital press manufacturers may offer optional components for the application of special coatings. For example, some manufacturers offer an automatic UV coater which adds a high gloss UV coating to applications printed with digital equipment. Some coaters can be used inline, depending on the application. A greater range of products can be produced with digital equipment with the addition of the UV coater, such as glossy posters and brochures, book covers, labels, and packaging products.
Aqueous coatings are usually applied during the printing process and can be applied as an all-over coat or in patterns or spot coatings. Like varnishes, they offer protection for the printed document and provide numerous effects for print applications. Aqueous coatings are available in gloss, matte, and satin finishes. Among the advantages that aqueous coatings have over solvent base varnishes is that they will not yellow over time and they are less toxic and emit fewer VOCs.
Lamination is the process of covering a printed document with a thin coating of clear plastic material in order to provide protection for the document. Lamination is a good method of providing protection for placemats and extending the life of menus. Booklets with laminated covers will last much longer than unprotected booklets.
Lamination may help correct an oversight in the design process such as when a cover has been designed with large solid areas of print in the area where the cover will be folded. The laminate will prevent heavy areas of toner from flaking off, especially along the fold where it is more likely to happen. It is important to make sure that the laminate is compatible with the toner and the type of paper used so that no problems will occur with toner lifting from the substrate or with paper curl.
Die cutting involves the use of metal dies constructed of knife-edge cutting blades formed into a pattern or die. A machine presses the die into the substrate to produce the desired shape. Almost any shape can be created and applied to a diverse array of raw materials. Labels, envelopes, folders, cartons, and documents are only a few of the many printed products that can be die cut for added functionality. Die cutting on digitally printed applications is an off-line process which may add a significant cost to the job.
Often used in combination with foil stamping, embossing is a process that applies pressure to the back side of a material to alter the surface, giving it a three dimensional or raised effect. The procedure involves the use of two dies, one fitting into the other so that the raised die forces the stock into the recessed die to create the embossed impression. A die maker engraves the desired image or copy into several metal plates, which are the embossing dies for use on an embossing press. Thoroughly understanding the process will enable a more successful result. Generally, embossing is the process most often employed to attract attention or convey a high quality textural contrast in relation to the surrounding area of the stock.
Debossing is the term used to describe the opposite process or effect, which involves applying pressure to the front side of a substrate forcing the material away or down from the surface. Although it is not commonly used, it is occasionally used to provide a different effect or appearance that fits a particular theme. Embossing and debossing on digitally printed applications is an off-line process, which may add a significant cost to the job.
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