Many of the finishing operations mentioned above may be carried out in different ways. For example, die-cutting may take place using flatbed cutting dies, solid rotary dies or flexible wrap-around dies . even laser cutting today. Perforating may also be undertaken from a flat die or a rotary die. The same applies to embossing or hot foiling where there may also be segmented dies.
The challenges involved in manufacturing and using cutting, perforating, foiling, embossing or punching dies is that labels . and unsupported film . may frequently be required to be produced using different types of paper, film, foil, metallic, etc., substrates, with different types of liners to cut to, as well as different types of adhesive. Some substrates and adhesives may well be more abrasive or challenging to cut than others, perhaps requiring different cutting angles or bevels.
Understandably therefore, the manufacture of the different types of dies and tooling is a highly specialized and quite complex process, or sequence of processes, using hardened metals and coatings or surface treatments to give different types of quality, performance and cutting profiles.
Many or most of the different types of cutting, punching or perforating dies need an accurate solid surface to cut against, . called an anvil or base roll . or additionally, in the case of flexible dies, a magnetic cylinder on which they are held firmly in position. In some printing processes, flexible printing plates may be used, again held in place on a magnetic print cylinder, or perhaps they are in the form of a sleeve fitted onto a sleeve cylinder. Gear wheels and bearers may need to form part of these various cylinder constructions.
The flexographic printing process has an additional requirement for an anilox roll that carries the fluid ink from the ink tray or pan to the printing cylinder. Again, precision made, anilox rolls are quite complex in their manufacture and requirements and have a significant impact on the quality of printing that can be produced.
The manufacture and production of many of these ancillary manufactured products used on a pressure-sensitive roll-label and some other narrow-web presses is commonly known as tooling and the items themselves as tools. Put together and depending on the specific supplier or sector, tooling can generally be categorized under one or more of the headings shown in the following flow chart (Figure.1.1):
Figure 1.1 - Flow chart showing the main types of tooling available for narrow- to mid-web label and related presses
The nature, role and function of each of these types of tooling is outlined below.
THE NATURE, ROLE AND FUNCTION OF TOOLING
Before moving on to understand the materials, technology and production of the different types of tooling it would be of value to a know a little more about each type of tool and to be able to recognize what they look like and how, when and where they are used in label printing and converting operations, starting with the various types of label die-cutting tools.
Die-cutting tools are used in the process of cutting a label to size and shape with a die. Most self-adhesive labels have to be die-cut to shape as part of their manufacturing and finishing procedure. Depending on the type of label and the printing and/or die-cutting requirement, this operation may be performed using flexible dies, solid rotary dies or flat dies or, most recently, with digital laser die-cutting technology.
Historically, flat die-cutting tools were the dominant technology used on the intermittent feed and semi-rotary presses of the 1970s and 1980s. As rotary printing started to become the major label printing process so the industry moved to solid rotary dies. More recently, flexible dies have become the die-cutting process of choice, overtaking solid tools.
Today, flexible dies are said to account for more than 80 percent of all label dies used in Europe and around 70 percent in North America, largely due to their much easier transportation, storage and handling, as well as not insignificant cost savings. An increasing trend towards shorter run lengths has also influenced the trend towards flexible dies.
Figure 1.2 - Magnetic cylinder and flexible die. Source- RotoMetrics
Flexible dies are thin plates made from spring steel that have the die-cutting configuration etched over the surface and milled to the right dimensions. They are then mounted for use by wrapping the thin steel around a magnetic cylinder.
Figure 1.3 - Solid milled rotary die. Source- RotoMetrics
Solid milled rotary dies are engraved from a cylinder of steel so as to leave the cutting edge standing proud around the cylinder circumference.
Each of the types of flexible or rotary die require some form of final finishing following on from the machining or etching, which is undertaken using computer-guided equipment and which sets the seal on the final quality on the die.
Figure 1.4 - Flat rule die. Source- Wink
Flat dies are most commonly produced by bending lengths of accurately fashioned steel rule, which has been finished to a cutting bevel along one or both edges. This rule is around 0.4mm (0.0157”) in thickness and nominally 12mm (0.472”) in height.
To form a cutter, the rule, once bent to shape using a special bending tool, is placed in a base into which the shape or shapes of the label(s) has been cut. In this way the rule is supported during use in the die-cutting and is able to retain a high degree of accuracy.
A magnetic base and a flat flexible cutting die may also be used for some die-cutting applications.
Figure 1.5 - UEI Falcontec Unisphere aluminium rotary embossing dies (left) and flat brass embossing die (right)
Embossing tools. Embossing tool dies are used to shape/set the surface of a substrate to create a raised (embossed) or recessed (debossed) design. Embossing can be achieved with a matched male die and female counterforce (flat or rotary). The female counterforce has the required image incised into the surface; the male die has a matched raised image. An offset is applied to one or both images to enable the dies to accommodate the thickness of the material being embossed.
During the embossing process, the two dies are pressed together through a substrate to create a raised image.
In the process of debossing - which is the reverse of embossing - the positions of the relief die and the counter die are reversed.
Male/female embossing dies have their widest application in rotary embossing, although other approaches may be used for certain applications.
For less detailed images, more economic single male or female embossing dies used in conjunction with a hard rubber coated anvil may well achieve the desired result.
Embossing dies are produced to run in both dedicated embossing units or in an available cutter station.
Figure 1.6 - Solid rotary hot foiling cylinder. Source- Kocher+Beck
Foiling tools. Hot foiling or hot stamping is a dry printing process which uses very thin metalized foil in a variety of metallic colours – such as gold, silver, red or blue – rather than inks from which to print. The hot-foil printing process is achieved by transferring the colored metallic pigment coating from a ribbon of plastic material known as the ‘carrier’ onto the surface of the label material to be printed using a solid or flexible printing die or plate which bears the image to be hot-foiled.
The transfer is achieved through the application of heat, pressure, and the length of time the heated coating area is in contact with the substrate – known as the dwell time. The balance and control of these elements is critical and must be individually calculated for the surface to be printed, and the type of ribbon or foil being used.
The printing plate used for hot foil blocking needs to be of a hard material and have a raised image similar to that used by the letterpress process. The fact that image transfer relies upon both heat and pressure restricts plate materials to either a very hard thermoformed plastic plate for very short runs or plates produced from brass, copper, magnesium, steel, or zinc, for the longer runs.
Figure 1.7 - Econofoil/Unisleeve hot-foiling flexible dies designed to run on low cost aluminium mandrels. Source- UEI Falcontec
Hot-foil blocking/stamping is used on both short and long runs today. Further, traditionally hot foil stamping was used on rotary presses with cylinders; however, today flexible dies are used on rotary presses and flat dies are used on other narrow web presses.
Figure 1.8 - A (cross) perforation cylinder/sheeter. Source- RotoMetrics
Perforating and sheeting tools. In rotary form, perforation tools are cylinders that contain removable or floating blades that can be used to produce perforated or cut lines (sheeting or scoring). They are designed for cutting or perforating across a web to produce items such as A4 sheets, or to provide perforation lines that are punched into a label surface for, say, fan-folding.
The perforating and cutting blades themselves are able to be positioned equally stepped, or freely positioned around the circumference of the cylinder to provide for production flexibility. The blades are held in place by clamping or counter bars and set screws.
Figure 1.9 - Hardened steel anvil roller. Source- Kocher+Beck
Anvil rollers. An anvil roller is a hardened steel roller upon which the bearers of a rotary die, magnetic cylinder or perforation cylinder run.
Normally, this cylinder is placed in the bottom position of a die station. However, for some jobs it is necessary to place the anvil roller in the top and the cutting cylinder in the bottom position. In case of a support roller the anvil roller would be in the middle position.
Anvil cylinders/rollers (see Figure 1.9) are characterized by their exemplary hardness and run-out accuracy, whether in use as a standard diameter or a plus or minus cylinder so as to compensate for a wide range of backing papers.
Straight anvils are used for most standard daily operations, and stepped anvils are used to extend the life of a die when most needed and to provide the flexibility to run dies on liners other than those for which they were made, or to compensate for worn cutting tools.
Hole punching tools. A hole punching (pin feed) tool was historically used for making EDP (electronic data processing) holes but other shapes are also possible. The holes, which were used to guide material in finishing lines through dot matrix, continuous laser or thermal printers, are cut by using either a male/female system or using a shaft with movable EDP rings. The latter is used in anvil position to cut up to the face material, with the waste being removed by the waste matrix system when stripping the face.
Figure 1.10 - Hole punching shaft with movable EDP rings. Source- RotoMetrics
The punches are held in position with a set of screws, tightened into a groove. Rings can be adjusted across the web.
There are also microhole punching tools which are designed to create tear-off holes in postage stamps. The punched waste is removed through the hollow die cylinder with working widths up to 500 mm. The modules are connected mechanically or electronically to the converting machine.
Figure 1.11 - A RotoMetrics printing cylinder with bearers and gear wheel
Printing cylinders. Standard printing cylinders form the basis of every label printing machine. These cylinders, together with hot foiling and embossing cylinders, are all manufactured with the greatest care and finite precision in order to guarantee optimum fit and run-out accuracy.
In the flexographic, letterpress and litho processes the printing plates are located on the print cylinders. Each cylinder needs to have accurate and even contact with the inking rollers and the surface of the substrate, or in the case of the litho process, the offset blanket.
Printing cylinders (see Figure 1.11) used in the roll-label industry include plate cylinders, blanket cylinders and impression cylinders and these are made from solid aluminium or steel, or produced as a tube with end rings fitted, and with spur or helical gears.
There are also a number of suppliers offering unique coatings applied directly onto existing or newly manufactured printing cylinders. These coatings can provide additional surface protection thereby potentially increasing the life of the cylinder.
Figure 1.12 - Magnetic cylinder and flexible die. Source- Kocher+Beck
Magnetic cylinders and bases. Magnetic cylinders used with flexible dies provide an economic alternative to standard rotary die cutting tools. They are manufactured on CNC machines from high tensile and high alloyed stainless tool steel with fully hardened bearers. Hard ferrite or ceramic and rare earth permanent magnets, hardened bearings seats as well as bearing necks (journals) with fully hardened centering sleeves are usually standard. Higher-strength magnet configurations are available based on the application.
Magnetic cylinders are available for a full range of label presses and converting machinery, allowing converters to use flexible dies in many different applications.
Figure 1.13 - A RotoMetrics magnetic flat base (left) and a close up of a section from a Kocher + Beck magnetic base (right)
Where flexible dies are used in flat die-cutting systems, then flat magnetic bases can be provided by a number of suppliers. Magnetic bases are used for a variety of different applications, particularly those involving intricate patterns or shapes and can offer a more accurate total die height when compared to most types of steel rule dies.
Flatbed magnetic base systems can also be used for hot stamping and embossing but for foil stamping, they would need to be a heated base.
Figure 1.14 - RotoMetrics RD razor slitter
Slitting of label webs. Once printed and die-cut using flat, rotary or flexible cutting dies, the web of labels (2, 3, 4 or more) printed labels across the web needs to be subsequently converted into individual label widths so that each individual label can be removed from the backing liner in the subsequent label application process. This is because most label presses, depending on label size, are producing more than one label across the web width, which means that the printed and die-cut web will need slitting lengthwise at some stage into individual web widths for rewinding into the final applicator-sized reels.
Figure 1.15 - An ABG International scissor knife slitting unit in operation
Some webs may also need an unwanted edge on either side of the printed web to be removed, commonly known as edge trim. Slitting operations, either in-line on the press or off-line on a slitter rewinder, are commonly undertaken in a slitting unit which utilizes cutting heads that can be of a crush cut, razor (shown in Figure 1.14) or rotary scissor construction. Figure 1.15. shows a typical scissor knife slitting unit found in operation on a roll-label press or on a finishing line.
Anilox rolls. Anilox tools or rolls consist of an engraved metal or ceramic-coated roll used to meter ink to the raised (image) areas on the relief printing plate used in the flexographic inking system. Each type of flexographic press uses an anilox roll, the surface of which is engraved at one of three angles with a pattern of tiny cells of fixed size and depth that transfer the ink to the plate. The cells are so small that they can only be seen under magnification. The size and number of these cells determine how much ink will be delivered to the image areas of the plate, and ultimately to the substrate. An anilox roll today is either copper-engraved and then chrome-plated, or ceramic-coated steel with a laser-engraved cell surface.
Anilox tools are carefully selected for specific types of printing, substrates, and customer requirements. The printer may well perform test runs to determine the ideal anilox for producing the desired ink distribution for halftones, spot color and solids.
There is also some use of anilox sleeves. These are not new. They have been under development, testing, trials and use for a number of years, with many manufacturers of ‘gearless’ presses particularly looking at the benefits of sleeve technology, such as ease of register, overall quality, low weight, maintenance, etc., as well as lower shipping costs and storage capabilities.
Figure 1.16 - An anilox sleeve. Source- Harper
Although early attempts at anilox sleeve manufacture were somewhat hit-and-miss due to a variety of reasons there have subsequently been dramatic improvements in the material, construction and stability of anilox sleeves.
In use, sleeves need to be expanded to fit securely on the press mandrels. This may be undertaken with a mechanical mandrel that expands by hydraulic action, or through the use of a press mandrel with an inner compressible layer, or bladder, that is activated by air.
Mandrels used with anilox sleeves are critical to the success of the process, with diameter, circularity and concentricity all important.
CONFIGURING TOOLING IN A LABEL PRESS
Modular presses are the most common form of label press configuration used by the label converter today. Such presses start with an unwind unit and web infeed, incorporate web tension control and are then followed by the various printing units and processes that make up the converter’s press specification. Almost any printing process may be used, either on its own as a dedicated ‘single’ process machine or in the form of a multi-process combination press that is capable of total process interchangeability.
Within the printing section of the label press the ‘basic’ tooling products that can be seen are the print cylinders, anilox rolls in flexo presses.
Most common of the ‘finishing, embellishing and other converting processes’ which are compatible with the pressure-sensitive label printing processes and found to some degree on almost all label printing and converting lines are:
Die-cutting is carried out in a cutting station or unit, which may be flatbed, semi-rotary or rotary depending on the particular type of label press, and this is followed by the removal of the matrix waste. A diagram showing a rotary die cutting unit and matrix waste removal can be seen in the following illustration (Figure 1.17).
The die-cutting tools will cut against an anvil roller (crush cut) and the two cylinders are typically stacked on top of each other in a conventional cutting unit. Typically, there is a support roller below the anvil roller.
Figure 1.17 - A typical rotary die-cutting and matrix rewinding unit
The repeat size of the cutting cylinder will vary from job to job. A cutting unit is generally constructed so that the cutting cylinders are relatively easy to replace.
Put together, it can be readily seen that a variety of highly accurate and specialized tooling is needed to produce pressure-sensitive labels on a roll label press.
A typical press construction and location of some of the more commonly used tooling is shown in the Figure 1.18.
This series of articles are primarily concerned with tooling that is used at the finishing end of a label press rather than the manufacture and use of print cylinders and anilox rolls that are used in the analog or digital press section.
The nature and use of cutting, embossing and foiling dies, speciality dies and tooling, slitting wheels or blades, as well as magnetic cylinders and anvil rollers, are all set out in the following pages, together with guidelines for optimizing the cutting processes and for handling, storage and health and safety in the use of tooling.
Figure 1.18 - Shows in diagrammatic form the construction of a flexographic roll-label press and where some of the most common forms of tooling would be found