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Coil binding, also known as spiral binding, is a commonly used book binding style for documents. This binding style is known by a number of names including spiral coil, color coil, colorcoil, ez-coil, plastic coil, spiral binding, plastikoil and coilbind. Documents bound with helical coil (usually called spiral coil) can open flat on a desk or table and offer 360 degree rotation for easy note taking. This binding style is durable and is often used for documents that need to be mailed. Spiral coil binding spines are also available in more colors and sizes than other binding styles.
The most common hole pattern used with coil binding is a 4:1 pitch hole pattern (6 mm outside the US), which has four holes per inch along the binding edge of the sheets of paper. The holes for this style are usually either round or oval shaped and depending on the size and spacing of the hole pattern, there will be 43 or 44 holes on an eleven-inch binding edge. Supplies for binding documents with 4:1 pitch spiral coil are available in sizes ranging from 6 mm up to 50 mm in diameter. This allows for binding documents that are up to two inches thick.
A .2475-inch pitch spiral is similar to the 4:1 pitch plastic spiral; the difference is .0005 inch per loop. This pitch was designed to slightly modify the 4:1 pitch punch pattern to perfectly center 44 holes on an 11-inch binding edge and still use the 4:1 pitch coil. This makes it easier to automate the coil insertion process. Some manufacturers make the coil specifically in the .2475-inch pitch to make it even easier. Coil is available in 6 mm to 30 mm in .2475-inch pitch.
Although not as common as 4:1 pitch coil, some printers and binderies use 5:1 pitch coil. With five holes per inch, 5:1 pitch coil is more tightly wound and provides a neat and tidy appearance. However, the tight spacing of the coil and the smaller size of the holes used by this pattern limit the size of spines that are available. Spiral coil with 5:1 pitch is available in diameters ranging from 5 mm up to 25 mm. This means that documents larger than one inch thick cannot be bound using this hole pattern.
Spiral coil with 3:1 pitch is less common than either 5:1 or 4:1 pitch coils. It is designed for the hole pattern used in wire binding or with GBC Proclick. Three to one pitch spiral coils are slightly easier to use for large diameter books because there are fewer holes to insert the coil through. Supplies for this hole pattern are available in sizes ranging from 6 mm up to 56 mm.
Coil with 2.5:1 pitch, also known 0.400 pitch coil, and is used with a hole pattern that has 2.5 holes per inch. However, many users choose to use this hole pattern with the hole pattern that is produced for 2:1 pitch wire binding. This type of spiral coil uses a larger filament diameter and is specifically designed for binding thick documents. Spirals in this pitch pattern are available in diameters ranging from 20 mm up to 76 mm. This means that 2.5:1 pitch coil can be used to bind documents that are thicker than any of the other pitches of spiral coil.
Coil with 3.2:1 pitch is also known as .3125 inch pitch. This pitch is also most common for the larger books because of the larger holes and the wider pitch. Coil sizes available in this pitch are 23 mm to 50 mm.
One of the strengths of spiral coil binding is that the supplies are available in a variety of lengths. Most users purchase spiral coils in twelve inch lengths. This spine is inserted onto an eleven-inch document and the excess length of coil is cut and crimped at each end of the book. However, the forming process for creating spiral coil binding elements allows them to be created in virtually any length. Many binderies and print shops choose to purchase coils in 36 in lengths in order to have the flexibility to bind custom document sizes and to reduce waste. For binding documents shorter than eleven inches it is also possible to purchase shorter lengths of spiral coil in order to save time and money.
Spiral coil is sometimes made from low-carbon steel.
Spiral coil binding supplies are also available in a wide variety of colors. In fact there are more than sixty standard colors available for binding documents with spiral coil. This makes spiral coil binding an excellent choice for marketing agencies and design firms that want to match the spine of the document to a specific color palette. It is even possible to get a Pantone color match for organizations that want their spines to match the exact colors used in their printed materials.
Coil binding spines are normally measured in millimeters and not inches. Coils are available in sizes as small as 5 mm (1⁄4 in) and as large as 76 mm depending on the pitch of coil chosen. However it is important to note that binding thick documents using spiral coil can be difficult. When a large document is punched for coil binding the path through the holes will be straight. However, the coil binding spines are curved. This means that it is necessary to shape the spine of the document into a curve in order to allow the coil to travel smoothly through the holes. Special tools are generally used for this purpose.
Plastic spiral binding is a three-step process: punch, insert, crimp. First, a punch creates holes along the edge of the document. Second, a coil inserter spins the coils through the holes. Third, a pair of coil crimping pliers or a crimping machine is used to cut off the excess coil and crimp the end to prevent the coil from coming loose from the document. There are also more automated systems that will insert and cut and crimp the coil in one process and even some fully automated systems that will punch, insert, and crimp for the very high volume users. Light volume or personal users may choose to buy a single machine that does all of these features or may even choose to spin the coils onto their books by hand. Higher volume users will often choose to separate these three functions to help increase productivity.
In general, coil manufacturers purchase quantities of raw PVC beads, melt the beads into a single mass, and extrude a single long 'string' of semi-flexible PVC material. This PVC string is wound about a spool much like thread. When an order is received for any specific size and color combination, these long strands of PVC are heated to roughly 120 degrees Fahrenheit by a forming machine and are wrapped around a mandrel which matches the specific width desired. Once cooled and cut to size, the PVC material maintains the coil shape and is ready to be used for binding.