Description | Ties Per Inch | Perforation Types

Description

Perforations are classified by bursting strength and type. The bursting strength is referred to as "Ties Per Inch" or TPI. The type of perforations are horizontal or vertical, which can be full or partial.

Ties Per Inch (TPI)

The tie or tab is the part of the perforation where the paper does not get cut, but remains intact to "tie" the paper together. The ties alternate with cut areas to form the perforation. The tied areas of the perforation are usually narrower than the cut areas to allow for easier detachment of the sections separated by the perforation. The proper TPI to use is generally determined by the type of product and the function of the perforation on that product. The following are some of the common TPI and their uses on single sheet products:

• 4 TPI: A 4 TPI is used when one section of a single sheet document needs to detach easily from another section. It is not recommended on single sheets that must remain intact for long periods of time because the ties are so loose.
• 6 TPI: Because there are more ties per inch, the 6 TPI perf is stronger than the 4 TPI, but it is still too loose to be used for single sheet products that must remain intact for a long period of time.
• 8 and 10 TPI: The perforations in this category are stronger than the 4 or 6 TPI and help to keep the single sheet intact until it is ready to use. It is most often used as a perf within a document that allows the user to remove a section of the document.
• 12 TPI: The 12 TPI is also referred to as a "statement perf". It is most often used as a perf within a document that allows the user to remove a section of the documentt. For example, the top or bottom section of a "statement of account" form may be removed to be sent back with a payment. The 12 TPI perforation is durable and many times it is best to fold the document on the perf so that it detaches easier.
• 16 and 18 TPI: The 16 and 18 TPI perforations are stronger than the 12 TPI and must be folded to weaken the perforation so that it detaches more easily. They are often used on magazine inserts and mailers.
• Letteredge or Invisible Perf: As the name implies, the letteredge perf is nearly invisible and leaves a clean, smooth edge after the perf is detached. The most common ties per inch for letterhead perfs are 50, 66, and 72. Most print manufacturers use one of them as the standard for all of their letteredge perfs unless a specific TPI is requested. A letteredge perforation does not work well on heavier weight paper stock because it is too difficult to control the depth of the perforation. Using a letteredge perf on heavy weight paper may result in a perforation that does not detach properly. If you are unsure of which TPI to use, you should discuss the options with your supplier.

Perforation Types

 
Perforations can be applied to single sheet products in several ways:

1. When a perforation must be applied parallel to the direction that the paper travels through the printing press, a steel segmented wheel is used. The wheel rolls along the paper and applies the required cuts per inch as the paper is pulled through the press.
2. For perforations that must be perpendicular to the direction the paper travels through the printing press, steel perforation rules are used which are inserted into cylinders on the press. As the cylinders revolve, the perforations are stamped into the paper.
3. Perforations that are more complicated, such as a perf that borders a detachable business card within a larger sheet, can be applied with a perf cutting method which is accomplished much the same as die cutting. Perforating blades which contain cut and uncut areas are constructed into a die pattern. The cut area of the blade strikes through the material while the uncut segment or tie of the blade does not cut the paper, enabling the perforated area to remain attached to the document until it is to be removed.

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