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is a mark-to-pulse system. These systems are

time based. A shaft encoder, which generates

a series of high-frequency pulses, is used to

precisely measure line-shaft revolution.

Sensors at each print position detect register

marks on the plate cylinders. The timing of

the register marks are measured against the

pulse chain to determine register. To avoid

overreacting, both mark-to-mark and mark-

to-pulse systems use an averaging algorithm

to determine register error. If they did not,

and transient errors were responded to, the

system would quickly begin to chase itself.

On some narrow-web presses, register

corrections affect web velocity and tension.

This effect occurs when the plate roll and

impression roll, or the die and anvil roll,

have a common drive. In these situations,

the momentary velocity change to the plate

cylinder or die, done to effect a register cor-

rection, also creates a momentary velocity

change to the impression roll or anvil roll.

The transient disruption of tension usually

will not result in a noticeable misregister on

pressure-sensitive materials or on board

stock. However, it can affect register on

extensible film materials.

Drying and Curing

Narrow-web presses either dry or cure the

ink after each print station. This interstation

drying eliminates the need to wet-trap colors,

and allows multiple converting and finishing

operations to be done in-line. Drying of flexo-

graphic inks requires the removal, through

evaporation or absorption, of a portion of the

ink blend. Curing of UV flexo inks is a photo-

chemical process, that is, a chemical reaction

is initiated by the ultraviolet light and instant-

ly proceeds to link the reactive components

of the ink blend. Many narrow-web presses

have both drying and curing capabilities at all

or some of the print stations.

Drying on narrow-web equipment is done

in chambers, or tunnels, located after each

print position. The volatile components of the

ink or coating are vaporized by heated, high

velocity air directed at the web. Ty p i c a l l y, the

air is heated with electric heating elements.

Some designs incorporate infrared (IR) lamps

to radiate heat energy to the web. Occa-

s i o n a l l y, natural gas will be used to heat the

a i r. The airflow in the tunnel must create tur-

bulence around the wet ink. As it passes

through the press, the web pulls a thin stream

of air with it that forms a vapor barrier, which

in turn prevents the evaporated particles

from escaping from the ink. Turbulence is

used to break down the vapor barrier.

Ultraviolet curing. For UV curing, ultraviolet

radiation (light) must be generated. Ultra-

violet light is usually generated with a mer-

cury lamp. When the lamp is turned on, the

mercury droplets are vaporized to a gaseous

state. When excited to a gas form, mercury

naturally emits radiation in the ultraviolet

f r e q u e n c y. Either an electrical current or

microwave radiation can be used to vaporize

the mercury. Polished reflectors are used to

direct the light at the web. For better, deep-

er or faster curing of some colors or of some

specialty formulations, other materials may

be added to the mercury in the lamp to alter

the spectral “signature” or wavelength pro-

file of the emitted light.

Laminating and Va rn i s h i n g . Some products

look better and are more durable with a

glossy surface finish. This finish can be

accomplished by laminating a film with a

pressure- or heat-sensitive adhesive to the

web, or by applying an overprint varnish.

Most converters use varnish, since it is gener-

ally considered cheaper than laminating.

Ultra-violet curable varnishes are particularly

popular because of their durability and gloss.

When laminating, either a self-wound or

l i n e r-backed material can be used. If the lam-

inating material has a liner, then this must be

rewound on a waste spindle. The laminate

film is applied to the web by pressure from a

rubber roll in one of the die cutting stations.

As well as giving gloss to the product, lami-

PRESSES AND PRESS EQUIPMENT 23

24 FLEXOGRAPHY: PRINCIPLES & PRACTICES

nates and varnishes provide more durability

and scuff resistance.

Die-cutting Stations

Narrow-web presses are converting sys-

tems that combine printing with die-cutting

and other finishing operations. Die cutting r e-

quires extreme precision and exacting toler-

ances. Its mechanics have been compared to

using an ax to cut wood to a prescribed depth

repeatedly and consistently. The increased

use of film materials for labels requires that

the analogy be modified to include precisely

cutting plastic as well as wood.

Ty p i c a l l y, die cutting is done with rotary

tools. However, flatbed die cutting is often

used for folding cartons and in some inter-

national markets. Special male/female tools

are also used for folding cartons and for foil

lids. These applications require that the

desired shape be fully cut out of the web.

Since male/female tools provide a shear cut-

ting action, as opposed to the crush or burst-

ing action obtained with standard rotary and

steel rule dies, less force is required and a

cleaner cut is produced. Die life is also

greater with male/female systems.

A typical rotary die station (Figure

)

consists of parallel slots milled in the front

and rear frames of the press; a rotating, dri-

ven roller used as an anvil; a pressure assem-

bly consisting of a pressure bridge and an

assist assembly; and a waste matrix removal

system. Removable bearing blocks are

placed on the journals of the die to position

and maintain it in the parallel slots.

A typical rotary die

station consists of

parallel slots milled in

the front and rear

frames of the press;

a rotating, driven roller

used as an anvil;

a pressure assembly

consisting of a

pressure bridge and an

assist assembly; and a

waste matrix removal

system.

The rotary die is typically engraved in the

desired pattern from high-grade steel. In

some cases, electronic discharge machining,

EDM, is used to create the cutting shapes.

This process uses an electrical spark to

erode material from the steel roll. It creates a

very durable cutting edge and is used for

long-run applications and when through-cut-

ting to the anvil. Thin steel, etched plates or

“flexible dies” are also used for die cutting.

These flexible dies are mounted on magnetic

cylinders of the appropriate circumference

to match the desired repeat length. The cost

of the magnetic cylinders has limited the use

of this form of die cutting because a separate

cylinder is required for each repeat size. This

method is used most frequently for EDP

labels and stickers and other applications

that have a small number of standard shapes.

Bearers are also machined on the die. The

height of the engraved cutting area relative to

the bearers determines the depth of the cut.

Different dies are usually required for differ-

ent liner materials. However, special anvil

rolls are sometimes used to allow the same

die to be used with a variety of liners. These

anvils have a different diameter on the main

body of the roll than in the area of the roll

contacted by the die bearers. This difference

in diameter changes the relationship of the

bearers and cutting blades to the material

being cut. These special anvil rolls are called

“stepped anvils.” Usually these are fixed

dimensions and one anvil is substituted for

another as the liner material is changed.

Anvil rolls have also been introduced that

allow the operator to adjust the depth of the

cut without changing the anvil roll.

The anvil rolls must be rigid enough to

resist deflecting under the force created by

the die-cutting operation. They must be

mounted in bearings adequate for the load

and the station frames must be rigid. The

pressure assembly must also be rigid and

must not compress or deflect. Many press

designs incorporate a pressure beam or a

roller beneath the anvil to increase the struc-

tural integrity of the die station and to assist

in carrying the load. Increasingly, die pres-

sure systems are used to observe the force

on both bearer areas and to obtain quantified

data for SPC or other quality programs.

Die-cutting Basics

Because of the many factors that affect the

outcome of what is broadly termed die cut-

ting, the process remains more art than sci-

ence. What may in certain situations be a

solution to a problem may, in other circum-

stances, make the problem worse. For exam-

ple, in some cases, waste removal (stripping)

problems caused by a difficult adhesive

release may be improved by heating the web,

but a thin plastic substrate will be difficult to

die cut if it is overheated.

Die cutting on narrow-web presses is very

much like using an old fashioned cookie cut-

ter on a thin layer of dough. In the case of

flatbed die cutting, forward speed of the web

and the die are matched by slowing or stop-

ping the web and/or moving the die in an

orbital pattern as the web slows.

Since, in flatbed cutting, all the cutting

edges contact the web at the same time, var-

ious approaches are used to reduce the

extreme pressures involved. The dies are

either kept small or, in some presses, the

amount of cutting edge in contact is reduced

by using a moving anvil roller under the web

to create the cutting action.

To get a picture of the rotary application,

imagine our cookie cutter being wrapped

around a cylinder, with the cylinder’s surface

speed matched to the speed of the web.

While the entire process is properly called

“die cutting,” it would be well to remember

that it really is a two-fold activity. One step is

the cutting of a material to a predetermined

shape, and the other is the removal or sepa-

ration of the product from the waste or the

waste from the product.

While die cutting is a large factor in the

PRESSES AND PRESS EQUIPMENT 25

26 FLEXOGRAPHY: PRINCIPLES & PRACTICES

success or failure of the entire converting

operation, the interaction of the various parts

of the converting process (printing, drying or

o v e r-laminating) often causes the difficulties.

The components of this interaction are: the

specifications for the products to be pro-

duced, whether it is tags, labels or specialty

items; the capability and condition of the

press and auxiliary equipment, such as an air

compressor; the environment in which the

process will take place; and the condition,

adequacy and quality of the die being used.

Individual components, such as the material

to be converted or the die, frequently meet

specifications of their own, but when used in

combination and influenced by other parts of

the process, may have to change to attain

needed or expected production rates.

The die station anvil is another significant

influence on the results of the cutting process.

Of the three variables that interact during the

cutting process – the liner, the die and the

anvil – the anvil is the easiest to inspect and

maintain. It must be perfectly round and

smooth, and its die-supporting surface has to

be concentric to its axis of rotation.

Even though anvils are made of steel and

hardened, like all components, they will wear

with use. Unfortunately, this wear is neither

uniform nor predictable. As with all cylinders

on a press, frequent detailed inspection of

anvils with appropriate measuring instru-

ments is advisable. It is preferable to take

some of these measurements while the load

is applied to the system, so that eccentricities

caused by faulty gears, bearings or support-

ing components can also be detected.

To best understand rotary die cutting

action, particularly with lines perpendicular

to the length of the web, think of the process

as driving an ax into a piece of wood. The

sharper the blow and the more rugged the

support, the more likely it is to produce a

thorough cut. The lighter the ax or the weak-

er the force of the blow, the more likely it is

to glance off the target and not penetrate suf-

ficiently to do its job.

Consider this definition of narrow-web die

cutting: “the process of cutting a prescribed

shape in register while printing on diverse

substrates moving at high speeds, without

adversely affecting the integrity of the carri-

er and while separating waste.” It is a simple

enough statement for a process that can be

very frustrating when problems crop up.

Additional details about the key aspects of

die cutting are discussed below.

Substrate Influence

The two most important traits to consider

when die cutting are the substrate’s ability to

be die cut with a wedge-like tool, as in rotary

die cutting, and sufficient strength in the

part that becomes waste, to resist the stress

of subsequent waste rewinding. In the case

of pressure-sensitive laminates (Figure

1 )

) ,

the adhesive bond to the release liner, called

the release factor, adds significantly to the

strength requirements of the waste portion,

as does the product’s configuration. To a

lesser degree, the impact tear strength of the

waste material is also important, since the

removal and rewind process tension often is

i r r e g u l a r.

Many materials besides paper are now

used in converting on narrow-web flexo

presses. Some of these materials are readily

This cross-section

of a pressure-sensitive

laminate shows the

layer where the adhe-

sive bonds the release

liner, which provides

the additional strength

needed to resist the

stress of subsequent

waste rewinding.

1 )

affected by environmental conditions when

it comes to being die cut and having waste

removed. For example, some thin plastic

films are affected by heat and/or ink sol-

vents, making them extrude under the die

edge instead of parting.

The liner of a pressure-sensitive laminate,

sometimes called the carrier sheet, is as

important to the die-cutting process as the

label material itself. Since the liner, along

with the anvil roller, becomes the surface

supporting the die-cutting action, it is impor-

tant that it be uniform in all characteristics

throughout the lot, particularly in thickness

and compressibility.

For many years, paper coated with a thin

layer of silicone to allow easy removal of the

adhesive was the material of choice for lin-

ers. As the variety of label materials grew

and the demands on the strength and perfor-

mance of the liner increased, plastic liners or

composites also came to be used.

It is paradoxical that the liner on a pres-

sure-sensitive laminate is ultimately discard-

ed as waste, but during its life serves many

critical functions in the manufacture and

application of pressure-sensitive labels. The

liner function starts as a release-coated web

to which adhesive and label-face stock are

merged. Its next job is to provide a way to

store the label material until it is placed on

the press unwind, at which point it becomes

a carrier for the face stock, transporting it to

the various printing, coating and over- l a m i-

nating stations. When the web reaches the

die-cutting station, the liner functions as part

of the anvil against which the die cutting is

done. The liner then carries the die-cut label

as a conveyor through the waste-removing

station and onto the end of the press, where

it takes on a storage function again, either in

fan-folded, sheeted or roll form. Before

being disposed of, the liner performs its last

significant task, that of providing a way to

remove the label for transfer to its product

or other end use.

In many cases, the label is transferred to

its intended surface with automatic dispens-

ing equipment that relies a great deal on the

l i n e r ’s ability to release the label and with-

stand the high stresses of this dispensing

process. It is at this point that the quality of

the die-cutting process and its effect on line

integrity are most critical.

Since many pressure-sensitive labels are

automatically dispensed and applied in high

speed packaging lines, it is important that

while die cutting, the liner’s integrity be pre-

served. If the die cuts too deeply, it may dam-

age the liner’s release coating and sometimes

even the base material. Depending on the

location and severity of this damage, fouling

of the application equipment can occur and

cause interruptions of the production line.

Frequent and diligent monitoring of the die-

cutting process will prevent this downtime.

The most prevalent method of quality

assurance for liner integrity is visual inspec-

tion of the liner after removing the die-cut

parts from randomly selected portions of the

web. To enhance this difficult, very subjec-

tive evaluation, a dye or diluted ink solution

is spread over the release-coated side of the

l i n e r, where it will penetrate and highlight

areas where the coating has been damaged.

When it comes to quality, there are widely

varying standards for what to accept and

what to reject. It is crucial that the standards

are agreed upon between the customer and

the producer and clearly defined to the press

staff before each production run.

Since the quality of the label’s liner is such

a critical part of the product’s utility, the

matching of the die’s specification to the

liner thickness is critical. A great deal of the

potential success or failure of the die-cutting

process depends on the ability to maintain

tight control over the consistency of the

thickness (caliper) and compressibility of

the liner so the die can be produced to work

with a predetermined liner specification. Un-

expected variations in the die or the liner are

PRESSES AND PRESS EQUIPMENT 27

28 FLEXOGRAPHY: PRINCIPLES & PRACTICES

the most frequent causes for production

problems and resulting delays.

Cutting Modes

There are two basic modes of rotary die cut-

t i n g :

• Partway-through cutting, usually done to

the liner, without damaging it, when the

substrate is a multiple-layer laminate,

• Through-cutting, sometimes called

“steel-to-steel” cutting, cuts through the

whole web thickness.

Combinations of the two modes are some-

times used with the same die, which is called

a two-height or multi(ple)-height tool.

Other cutting modes sometimes are used

in narrow-web presses. For example, slitting

a straight cut along the web can be done in

several modes: with a through-cutting (steel-

to-steel) lineal rotating die against an anvil,

using razor blades held by a press attach-

ment against the web (substrate) as it moves

along; or with rotating shearing rings whose

edges overlap like scissors to sever the web.

On narrow-web presses, shear cutting

across the web is very rare, except in small-

hole cutting with special male/female attach-

ments. This example is yet another variation

of the basic cutting modes.

Prescribed Shapes

The easiest shape to define, specify and

die cut is a straight line along the web’s trav-

el direction. While it may seem that a

straight line in any direction would be equal-

ly simple, that is not the case in rotary die

cutting. Straight line cutting across the web

(perpendicular to web travel direction),

causes significant reactive stresses on the

die support members and the total die sta-

tion, including the anvil. These stresses can

be very significant as the length of cut across

the web approaches the full web-width

capacity of the press.

Examples of simple, across-the-web cut-

ting are a cross perforation used on comput-

er labels and buttcut labels, such as bumper

stickers. Circles are considered the easiest

shape to die cut because of the absence of

across-the-web straight lines, but there can

be a problem with waste removal.

There are many aspects of a product’s

shape that affect the ease of waste removal.

U n f o r t u n a t e l y, the converter is frequently not

given enough of a chance to affect the final

design. In addition to long, straight-across-

the-web lines, other hurdles to successful

waste removal without tearing the substrate

include small corner radii (under 1"), abrupt

changes in outline configurations and reverse

indentations in the product outline .

Specialized Tooling

There are two manufacturing processes

that generate the cutting edges on rotary dies.

One uses conventional machining, sometimes

called engraving because the cutters are so

small. The other uses electrical discharge

machining: the controlled erosion of material

with an electric spark. Whatever the process,

the crucial results are shape, included angle,

sharpness and consistency of cutting edge

height in relation to the bearer.

Besides the conventional rotary die pro-

duced from a steel bar with raised cutting

edges and machined to conform to the press,

there are also now in use thin, sheet-steel

etched dies mounted to magnetic cylinders.

But their use is limited by the availability of

varying repeats of costly magnetic cylinders.

In addition to shape-cutting rotary dies,

other special tools used in the die-cutting sta-

tions of narrow-web presses are described

b e l o w.

Removable Blade Crosscut To o l s. These tools

cut straight across the web and by changeing

blades, allow the removal and replacement

of the cutting edge as it wears. These tools

also allow a change from straight cut to var-

ious interrupted cuts, called perforations,

and changes in cut spacing.

Adjustable lineal cutting and scoring tools.

These tools permit across-the-web position

adjustment of the lineal cut, while the press

is stopped. After loosening a set screw, the

cutting blade is repositioned and then

relocked. Often, these tools come with extra

blades and some perforating wheels. When

repaired, all parts originally supplied with

them must be refurbished at the same time.

Pinfeed hole-cutting tools. For use with pres-

sure-sensitive laminates, these tools are

available as either fixed-position or adjus-

table across-the-web tooling. Usually, they

are installed in the anvil position of the die

station, cutting the liner up against the face

material, and allowing removal of the small

liner waste on the pressure-sensitive waste

m a t r i x .

For some other applications, where small

holes are required in the liner, such as feed

slots for some labeling equipment, the same

principle as for pinfeed hole cutting can be

used. Frequently, the die labeling is then no

longer adjustable but is dedicated to that

a p p l i c a t i o n .

A i r-assisted dies. When cutting through a sin-

gle-layered substrate or all the way through

a multilayered web, compressed air is fre-

quently used to keep the die clean and help

separate waste from web. Air-assisted dies

are made with air passages leading from the

cutting cavities to the hollow center of the

tool, which is connected to a compressed-air

source. Waste accumulating in the cavities is

a common culprit in die damage.

Two kinds of air-assisted dies are in wide

use today: the standard air-eject, with all

passages open at the same time; and dies

incorporating a unique valving system that

uses air more efficiently to greatly boost the

capabilities of air-assisted tooling while

reducing some of the disadvantages.

To further help with waste collection and

removal, industrial vacuums, brushes and

various other mechanical devices are

e m p l o y e d .

Male/female tooling. This tooling is employed

on web presses if product quantities are large

enough to amortize the cost. The rotary

attachments use two large, geared rings run-

ning opposed to one another with the web

between them (Figure

1 !

). The lower ring

usually carries the female or die portion and

the upper carries the punch, which penetrates

the substrate and forces waste into the die.

Cutting is achieved by a shearing action.

U s u a l l y, waste is removed from the lower ring

with a vacuum, creating the most positive cut-

ting and waste removal system in rotary die

cutting. A flat die-cutting attachment is some-

times available for reciprocating male/female

cutting, depending on press or unit design.

Care and Handling of

Rotary Tooling

Rotary dies represent a major investment.

They are very expensive, perishable tools

and can be resharpened several times. Their

service life is directly related to the sub-

stances being cut, the ink through which cuts

are made, and the care the tool gets. Given

the precision nature of these tools, even stor-

age habits have to be considered in prevent-

ing damage.

It is sad but true that die repair is mandat-

ed more often by mishandling or damage in

storage rather than by wear. Much has

already been written about ways to avoid die

damage. The essentials can be reduced to

common sense practices that apply to any

machine part.

Shafts and bearers should be clean and

well-lubricated. Die surfaces must be kept

clean and protected from unexpected

sources of damage, such as rings or belt

buckles worn by the operator. Keeping the

die protected while stored, installed in the

press or otherwise handled should become a

routine pressroom practice.

Die wear caused by use is expected. The

die should be checked after each run to

PRESSES AND PRESS EQUIPMENT 29

30 FLEXOGRAPHY: PRINCIPLES & PRACTICES

decide if resharpening is required before

putting the die into storage, so it will be

ready to work well the next time.

Problem Areas

The rotary die-cutting process appears quite

simple under casual observation but in fact

relies heavily on the quality of tools, convert-

ing materials, the condition of the die station

and the press. In addition to control and

maintenance of appropriate web tension, the

press must be able to keep the web from

weaving, thus avoiding what can be one of

the major sources of die damage – tracking

of the web under the bearers.

The die-cutting process relies on the web

being under tension while supported by the

anvil. This anvil must be rigidly supported

against deflection because the forces during

die cutting change greatly as the cutting

edges move from along-the-web to across-

the-web cuts. If the die isn’t correctly loaded,

the die bearers and the cutting edge may

separate from the anvil, thus losing the criti-

cal positioning of the cutting edge in relation

to the anvil. This separation, referred to as

die liftoff, is often found to be the source of

diecutting difficulties that can’t be diag-

nosed by measuring the die, the straightness

of the anvil and the liner in use.

A similarly difficult-to-diagnose problem is

caused by die flexing and sometimes both die

and anvil flexing. In this situation, the bear-

ers do not necessarily leave the anvil surface,

but the forces during cutting are great

enough to bend the die, causing a movement

A typical rotary

male/female punching

unit, where the lower

ring usually carries the

female or die portion

and the upper carries

the punch. The gears

run opposed to one

another, with the

web between them,

penetrating the

substrate and forcing

waste into the die.

Cutting is achieved by a

shearing action.

1 !

of the cutting edge away from the anvil along

the center of the across-the-web cuts.

In early models of narrow-web presses,

the problems of die flexing, anvil flexing and

die liftoff were accentuated by the method

used to position and load the die against the

anvil; it was done by applying the load over

the shafts through bearing blocks. In mod-

ern presses, anvil diameters and shaft sup-

port bearings have been increased consider-

a b l y, and the method of loading the die

employs an assist system that applies the

pressure directly against the die bearers

while using the die shafts only to locate the

die in the required position to the anvil.

A frequently asked question about die

wage is: What is the correct operating load

for a die? There is no specific force that can

be stated, since the load varies with the

amount of cutting edge across the web, the

material to be cut and the sharpness of the

die. The best way to define the correct load

is to say that just enough pressure should be

applied to keep the die bearers from sepa-

rating from the anvil during any part of the

d i e ’s revolution.

Various devices for measuring the load

being applied to the die have been developed

and are useful in training and developing

operator skills. It is very important that the

load applied to each bearer be equal, since

uneven loading can be even more detrimen-

tal than incorrect total load. In the absence

of load-measuring devices, backing off and

reapplying load while observing the cutting

action of the die and looking for evenness of

cut across the web can indicate whether a

die is loaded correctly. It is important to

remember that as a die-cutting station is

used, it warms up and various parts expand

at different rates. It is critical for extending

die life and reducing overloading on various

parts of the system, particularly bearings,

that during the warm-up period, die load is

readjusted to reduce excessive loading

caused by thermal expansion.

When a rotary die is positioned in the die

station, axes of the die and anvil must be

perfectly parallel to each other and perpen-

dicular to the web. Use of worn or non-sym-

metrical bearing blocks can cause lack of

parallelism, which results in changes in the

cutting depth of the die, incorrect placement

of the desired label shape on the web and

premature die failure.

During the life of a rotary die, the bearers

are very seldom the exact size that its gear

and particular anvil circumference require

for exactly matching die bearer surface

speed to that of the anvil. Therefore a slip-

page between the die bearer and the anvil

surface on which it rides has to occur. To

minimize the effects of this differential

movement, it is imperative that the surfaces

of the hewer and the anvil be kept clean and

well lubricated. Many narrow-web presses

do this cleaning and lubrication by installing

wipers. Wipers are pieces of felt or similar

material that ride against the anvil and/or

die, wiping away paper dust and other

debris, and depositing oil on the wiped sur-

face. These wipers require constant atten-

tion to replenish their oil and to remove the

accumulated debris they pick up.

Waste Removal

Die cutting creates a waste matrix that

must be removed and accumulated for dis-

posal. With pressure-sensitive labels, the

waste matrix is a portion of the face stock

and adhesive. Frequently, an edge trim of the

liner is made with a scoring unit and this por-

tion of the liner is also removed with the

waste matrix. The most common removal

and disposal method for this waste is to strip

it from the material and to wind it on a core-

h o l d e r. The waste rewind unit consists of an

idler roll for stripping the waste; a capstan

roll driven through a clutch to pull the

matrix at a constant tension; and a clutched

core-holder on which to wind the waste. A

turret system may be used for waste winding

PRESSES AND PRESS EQUIPMENT 31

32 FLEXOGRAPHY: PRINCIPLES & PRACTICES

for continuous operation, as can a vacuum

removal system. These systems also incor-

porate the stripping idler and capstan roll.

The waste-rewind components are intended

to keep the waste matrix moving at the

speed of the web without hesitation or

excessive pull. Frequently, a driven capstan

roll is provided to assure uniform pull on the

waste matrix as the rewound waste roll

changes size during the cycle. The waste

rewind drive has a clutch to allow for the

torque variation caused by the size change

as it drives a core holder and lock.

Many experts consider the geometry of the

point of waste-from-web separation a very

critical factor in overcoming waste removal

problems. Therefore, to allow for the rela-

tionship between the web, the die anvil and

the point of waste separation to be optimized,

both diameter and position of the idling roll of

the waste removal section and the position of

the stripping bar must be adjustable.

The waste created in die cutting folding

cartons, lids, in-mold labels and other prod-

ucts that are fully cut out of the web, is han-

dled differently than a pressure-sensitive

waste matrix. Die cutting of these products

occurs in the sheeting position of the press,

and the die cut pieces are fed into a convey-

or or stacker. The waste matrix is the unused

portion of the full web and not simply a por-

tion of the face stock, as with a pressure-sen-

sitive construction. If the waste is a continu-

ous matrix, it will typically be rewound on a

standard product rewind. In some cases, the

shape of the product prevents a continuous

waste matrix from being formed. When this

occurs, the waste is vacuumed away. The

vacuum system may be used with a pin-

removal system to physically capture the

waste for deposit into the vacuum tube.

In addition to shape-cutting rotary dies,

there are a number of special tools that are

used to sheet, perforate, score and add holes

to the web. These tools sometimes are

mounted on special platforms in the press,

but are more often used in a die station.

Removable blade crosscut tools are used

to through-cut, perforate or score across the

web. The blades used for the different oper-

ations can be easily interchanged and

replaced when worn. Ty p i c a l l y, the tool is

made with multiple positions around the roll

for mounting of the blades. By adding or

removing blades in these positions, the spac-

ing of the cuts may be altered.

Lineal cutting and scoring tools cut, score

and perforate the web in the direction of its

travel. Through-cutting systems are normal-

ly located in a dedicated position on the

press and are crush-cutting circular knives.

These systems can also be used for perforat-

ing the web. Shear-cutting systems are also

available for through-cutting. These may be

mounted either in a die slot or in a dedicated

position, depending on the press design.

Lineal-scoring tools are used to cut or perfo-

rate only part way through a web, for exam-

ple, to cut through the liner but not the face

stock of a pressure sensitive web. These

tools usually are positioned to cut or perfo-

rate from the bottom side of the web. They

may be placed in a die slot, but frequently

are mounted with brackets directly to the

press frames.

Hole-cutting tools are used to create feed

slots or other holes in the web. These tools

can be placed in a die slot and used to cut

through the liner material of a pressure-sen-

sitive web. The liner waste is then removed

with the waste matrix. More typically, line

hole punching is done with a male/female

unit mounted in a special platform on the

press. The waste from these systems is vac-

uumed away. Air assist dies are sometimes

used for through-punching the web. These

tools use compressed air to eject the waste

chaff from the die.

Product Delivery and Collection

The most common delivery system on nar-

row-web presses is to rewind the product.