Figure 4.1 - Special cutting, sheeting, perforating, punching and slitting tools
Each of the specialized tools itemized in the flow chart will now be examined in more detail:
PIN EJECT DIES
Small die cut areas can stay in the die and accumulate to the point of putting pressure on the inside edges of the cutting blades. Internal pressure will cause the cutting blades to break. Pin eject dies were developed as a solution to prevent this build-up. It can also assist in the removal of the waste from the converted web.
Figure 4.2 - A pin eject die courtesy of RotoMetrics
Pin eject dies contain a special compressible core material that allows the hardened ejector pins to compress into the die upon anvil contact. As the pins rotate off the anvil surface the unique engineered core will force the pins back out of cavity, removing the waste slug from the cutting die.
This revolutionary new product (developed by RotoMetrics) has not only improved current manufacturing methods, but has opened the door to new markets that require small die-cut shapes.
The feature provides a proven solution for metal to metal cutting challenges and will also allow the die cutting of small irregular shaped parts that need to be retained on the carrier liner. Adhesive displacement caused by the cutting action of the blades has made this all but impossible in the past. Using this technology, these cavities can now be cut clean and forced back into place utilizing the pin eject system.
Applications include disposable medical products, automotive gaskets, pharmaceutical applications, laser sheets, no waste boarding passes and tea bags to mention just a few.
Figure 4.3 - A RotoMetrics spring eject die
Spring eject dies are designed to prevent waste build-up inside die cavities and assist with waste removal out of the web. Since it uses spring-loaded pins to eject material out of the web on dies cutting through to the anvil, Spring-Eject Dies do not need compressed air.
Figure 4.4 - Shows a dedicated RotoMetrics air eject cylinder
AIR-EJECT CYLINDER DIES
Air-eject cylinder dies use compressed air to blow cutter waste out of the cavities during the cutting process, avoiding the build-up of waste inside smaller cutting cavities. The force of the air blowing through each individual hole is determined by the number of holes on the cylinder and the capacity of the air compression being used. Different types of air eject dies are available according to specific requirements, namely:
Standard air eject dies use compressed air forced through a shaft bore to blow air out of all holes drilled in the various cavities. The force of the air is determined by the capacity of the air compressor and the also the number of holes on the die. For these types of cylinders there is little control over the waste ejection.
Dedicated air eject cylinder dies make use of a special probe that fits precisely into the shaft bore and enables compressed air to be directed only to one row of labels/cavities across the web. See Figure 4.4.
Multi-port air eject cylinder. Developed as an alternative to the more expensive male and female cutting system for long runs and the solid rotary die-cutter with rubber inserts and without any waste control, shock air systems make use of so-called air forks to blow air into channels. These air channels, are linked to bores in the cavities.
Figure 4.5 - RotoMetrics Multi-port air eject cylinder
Air eject cylinders are usually used in conjunction with an extraction or waste collection unit which has been specially designed to collect the small pieces of material blown out of the die in order to avoid the waste collecting in the gears or on the surface of the anvil cylinder.
Die-cutting of the holes and blowing out of the waste into a stainless steel vacuum box or waste collection device is done simultaneously. Finally, the collected waste will be sucked away by an industrial vacuum cleaner.
VACUUM (THROUGH SHAFT BORE) ROTARY CYLINDERS
Vacuum rotary die cylinders provide an alternative to air eject cylinders. Instead of blowing the waste material out, the vacuum cylinders actually suck the cut-out waste particles into the die. It is then removed through the journals with the use of a vacuum extraction system.
Quite simply, vacuum dies feature a series of interchangeable punches which pick up waste from the web and pull it through the die journal with the assistance of a vacuum attachment. They are specially designed to cleanly remove even the smallest pieces of waste from the web, and are said to be the cleanest way of removing waste from the web when die-cutting.
The size, shape and number of cavities to be vacuumed all determine whether or not this type of product should be used. Vacuum dies also require the use of a vacuum waste assist block. Extra punches may be ordered with the tool and operators can quickly and easily replace any punch in-house, minimizing downtime.
Figure 4.6 - Vacuum cylinder courtesy of RotoMetrics
Vacuum systems are also available for use with specially designed magnetic cylinders with an air system incorporated. In this case, the flexible die has holes in it, distributed across the plate as to line up with the holes in the magnetic cylinder, allowing the suction (or even air expulsion) of the die cut waste.
Figure 4.7 - Removable blade perforator or sheeter courtesy of RotoMetrics
REMOVABLE BLADE SHEETERS AND PERFORATORS
Removable blade perforators and sheeters come in a number of different formats, depending on the particular manufacture, and may be in the form of a removable blade or a floating blade . each of which can be made with multiple, precision-milled slots at equal or special locations around the roll. They are designed for cutting across a web to produce items such as A4 sheets, or to provide perforation. These lines of very small dashes are punched into a label surface enabling various parts of the perforated label to be separated from one another by simply tearing off along the dotted perforated lines.
Figure 4.8 - Sprocket hole punched and perforated computer labels
The blade seats are milled and precision-cut to ensure perfect location. The clamping bars and counter clamps ensure that blades are fixed securely. Fast and reliable blade assembly is guaranteed every time. For sheeting, blades are usually made for through cuts, but other heights can be made upon request.
The sheeter or perforator shown in Figure 4.7 is made for through-to-anvil (metal-to-metal) cutting only and does not require the placement of shims under the blades as in some manufacturers' units. It does, however, have shim stock to the side of the blade to accept the pressure of the screws holding the blade in the slot.
Any distortion from tightening the set screws is transferred to the shim then, instead of the blade. Slots can accept either a perforating blade or a sheeter/scorer blade. Perforating blades are also available in several standard cut and tie combinations, or can be custom made. Minimum distance between blades varies depending upon the diameter of these units.
Perforating and hole punching (described later) are often used together and have of course, long been used within the continuous and fan-fold sprocket hole punched business forms and computer label manufacturing sectors to carry labels through printing devices (Figure 4.8) using tractor-, pin- or sprocket-fed systems.
Perforations can be produced to be vertical or horizontal, and may go through the label only, through the carrier between the labels, or through both the label and the carrier.
Figure 4.9 - Perforating blade showing a typical cut and tie pattern
Perforations are available in a wide range of strengths, full or partial, depending on the size of the cut to the width of the connection (called the ‘tie’). The number of ties per inch and the width of the tie and the cut are based upon the weight of the liner, the type of printer used, the type of burster, and the kind of handling that the label will be exposed to.
Depending on the manufacturer, custom perforations may be available by size or length of perfs, or the number of dashes, reducing or increasing in size, and the quantity of perfs required.
Apart from continuous and fan-folded labels, tickets, tags and business forms, perforated labels are used for applications such as coupons, gift certificates, pharmaceutical labels, business, and industrial applications.
Perforated stickers are also often used for pull out security tags that need to stay intact until the stub tag is pulled off. Such labels can be used for sealing many products or projects including medical packaging, specialty groceries, software boxes, electronics, toys, CD cases, sleeves, and box seals.
LINEAL PERFORATING AND/OR CUTTING CYLINDERS
Lineal cutting and perforating cylinders are multipurpose and durable precision tools which provide an optimum solution for continuous lineal slitting and perforating and for edging trimming of material webs (Figure 4.10).
Figure 4.10 - Kocher+Beck lineal perforating/cutting cylinder
They are made from high-grade materials, machined on the latest CNC machines, and provide a multipurpose tool which is a durable and high-precision product.
Lineal, or vertical, perforations are likely to be required for hand separating and are placed between rows of multiple width labels (Figure 4.11) so that the rows can be torn apart to be handled individually. In this case, it may be necessary to run some tests to determine the proper perforation requirements.
A very light vertical perforation may be provided to guide the operator in positioning slitting wheels. However, vertical perforations are not normally required in the margins as there is no need to remove the line holes from the carrier sheet.
The number of possible types of perforation is almost unlimited, with perforations suitable for all pressure sensitive papers, self-adhesive foils, composite and mono materials, cardboard packaging and metalized materials. The range is extensive including coated papers, polyethylene, polypropylene, polyamide, polyester, recycled paper, thermal paper, Tyvek and metalized material.
Figure 4.11 - Vertical perforation between rows
Punching technology and high precision punching tools have been developed over many years and are today found in a wide range of label and related web converting applications, including:
Smooth and serrated punching for business forms and computer labels, datamailers, tea bags, specialized self-adhesive labels and price tags, etc.
Contour and profile punching for the corner cuttiing of ATB- and ATB2- tickets, boarding passes, wallets, parking tickets, banknotes, batteries/energizers, security labels, smart cards, solar panels, datacards, diagrams, test strips, file holes, meat tray inserts, film holes, security documents
Surface holes for fruit and vegetable wrapping foils, band aids
Opening features in packaging and even straw holes in liquid packaging
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. The module can also be installed in machines used for the production of business forms. Modification of the punch pattern or application of a security perforation can easily be achieved by changing the punch and die bars.
Holes punched for transporting purposes using sprocket or pin-fed labels (e.g. computer labels) are used to guide material in finishing lines or through dot matrix, continuous laser, thermal transfer or thermal direct printers (as seen in Figures 4.8 and 4.11). They can be realized in register to a printed web or with an equal pitch on non-printed materials. Round holes are preferred to minimize manufacturing costs as much as possible. In certain cases rectangular, oval or special shapes are used.
Although use of sprocket or pin-fed labels has declined over the years there is still a considerable residual demand for labels supplied in this format. Major printer manufactures such as OCE, Epson, Xerox and OKI still make and support printers which use this type of fan-folded sprocket stationary.
For thicker stocks such as tickets, tags, or cardstock, fanfold stationary is often preferred because it stays flat, unlike rolls which cause memory-effect curl on cardstock. Tags can be made available in various size configurations, on different stocks, and in a variety of card weights or colors for overprinting on thermal transfer printers. Finishing options include round or cut-out corners (Figure 4.12), perforating and hole punching. Tags and labels for harsh environments and outdoor use are also available. Fanfold labels, tickets and tags can be supplied in already finished, ready to use packs, or in a plain/blank or printed format ready for over-printing with fixed or variable data.
Figure 4.12 - Shows perforated and hole punched swing tags
Tractor feed index cards, also known as continuous feed index cards, are used for many purposes and in many different industries, businesses, and manufacturing processes. Index cards are used as a mailing tag, mailing card, production card, pull slip, controlled substance card, procurement card, production card, route card, inventory card, allocation card, water bills, pull ticket, transfer card, schedule card, gondola tags, strategic procurement card, maintenance card, history card, slicer ticket, student registration card, gift card, job card, notice card, transfer card, travel card, ledger card, and traffic ticket etc.
Tractor or sprocket hole punched and perforated tickets are also to be found in use as shelf-edge perforated tickets which may be used for retail shelf labelling or pricing cards in Electronic Point of Sale (EPoS) systems (Figure 4.13).
Figure 4.13 - Hole punched and perforated shelf-edge tickets
The non-adhesive blank cards are easily inserted into plastic and channelled shelf edge holders and are ideal for overprinting using laser and inkjet printing systems.
Figure 4.14 shows a typical punching/scoring tool which consists of a mandrel upon which a set of bearers and gear are fastened, plus then any combination of hole punch, score, slit, or perforation rings as required by the converter. The blades/punches are each held in place with a set screw, tightened into the ‘V’ groove on the mandrel. The bearer set screws are tightened into a pilot hole. The rings can be adjusted across the web and then the set screw re-tightened to the new position.
Figure 4.14 - A typical RotoMetrics punching/scoring tool
The hole cutting rings are milled and maintain standard die-cutter tolerances. As a norm, hole cuttings had been set at a distance of 1/2 inch center-to-center along the web to match the tractor feed mechanisms of the printers. The tool has evolved to include customer shapes and positioning now and can be tailored to the project as needed.
The punch, perforation or slitting rings are extremely resistant against wear and tear and can be adjusted axially, offering maximum accuracy of the perforation and slitting along the longitudinal axis. The number of rings that can be placed across the shaft is usually variable and can be adjusted to individual requirements.
These tools are generally used as under-cutters to make cuts into the liners. The feed slot or hole is cut up to the face stock, and the waste is removed by the waste matrix when stripping the face stock. Punch wheels are adjustable across the web.
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. Most label presses, depending on label size, converters 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.
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 re-winder, are commonly undertaken in a slitting unit which utilizes cutting heads that can be of a rotary, razor or crush cut construction. Figure. 4.15 shows a typical scissor knife slitting operation on a roll-label press.
Figure 4.15 - ABG International scissor knife slitting unit in operation
These three main slitting options can be further amplified as follows:
Rotary shear slitting. This method of slitting uses male and female circular slitting knives (typically referred to as the top and bottom blades) that may or may not overlap (depending on the material being slit) and are in contact with each other (Figure 4.16). They rotate in opposite directions to provide a scissors cutting effect. Rotary shear slitting is used to shear a wide range of materials, and similarly there are a wide range of blade designs for both the top and bottom slitter blades. The blade material also varies depending on the material to be cut, cutting application, and other factors.
However, blade profile can be a key factor in overall slitting quality. Shear slitting is able to produce a good quality edge at high line speeds with little dust.
Figure 4.16 - These two illustrations show the principle of rotary shear slitting.png
Crush cut slitting. In rotary crush cut slitting a hardened steel disc cuts against a rotating, hardened cylinder, anvil roller or segment (Figure 4.17). The discs or knives that are used are dulled or ‘rounded’ so as to crush the substrate, rather than actually cut it. When the knife is pressed against a backing roll with sufficient pressure to crush through the substrate, then ‘slitting’ is achieved. For best results the web, backing roller and crush roller must all be moving at the same speed. Crush cutting, also known as score cutting, can be economical if speed and edge quality are less critical.
The simplicity of score slitting is one of its main attractions, but slit-edge quality is highly dependent on important variables that must be addressed.
Figure 4.17 - Principle of crush cut slitting. Right shows the score knife profile and the crushing process.png
Razor slitting is ideal for thin plastic films and is very simple and quick to set. Razor slitting units enable the fixing of sharp razor type blades which cut the substrate as it passes through the unit. See Figure 4.18. Although the razor blades are low cost, they do need to be frequently changed to ensure a good quality slit edge. Razor slitting has the lowest installed cost, being the simplest and cheapest method. It can be easily adapted to almost any machine, in almost any location and is potentially the cleanest method of slitting, assuming the appropriate materials are being slit.
Figure 4.18 - Illustrations show the principle of a razor slitting unit and slitting process
Variables to analyze for each type of slitting application include the placement of slitting knives, which can be shaft mounted, mounted in individual holders on a bar, or mounted in a combination of the two. Blade materials can be anything from high chrome steel to carbide or ceramic; bevel and grind angles of the slitting blades can be varied, as can cutting angles, while the most important variable is the blade holder. Modern slitting units are capable of automatically positioning the top and bottom cutters, working from a digital program, so eliminating the need for manual setting of the slitters.
On a label press the slitting unit is normally positioned in the press prior to the press rewind unit, but may also be positioned at the unwind end of a press to ensure accurate web widths enter the press. The slitting unit will be adjacent to a waste removal or extraction unit which is used to take away the unwanted edge trim waste.
Figure 4.19 - A fully automated slitting module from ABG International
Slitter rewinders are normally used to slit printed label webs, plastic films, paper and metal foils. An unwind unit holds the roll stable and allows it to spin; it is either braked or driven to maintain accurate tension in the material. Some machines have a driven unwind which reduces the effect of inertia when starting to unwind heavy rolls or when the material is very tension-sensitive.
If the holder cannot maintain the proper settings, the entire slitting operation will be problematic. Decisions to be made before slitting are based on the process material’s characteristics, such as weight, thickness, flexibility or abrasiveness. Machine working width, slit width, operational speed, the number of cuts to be made, the quality required, and even the number of set-ups per shift and the number of shifts, are also important.
It should also be noted that slitting is also undertaken on jumbo rolls of label stock that need to be slit into narrower rolls prior to printing and converting on narrow-web presses.