Mark J. Kirwan Paper and Paperboard Packaging Technology

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of the window. The film is cut automatically from a reel and applied over the

adhesive. The carton is then sent to a straight-line gluer for folding and gluing.

The windowing machine can also be used with attachments to apply flexible

packaging tubular material for bag-in-box cartons. Specially designed windowing

machines, which can also make creases in plastic film, are available to make

paperboard cartons with windows on three or four panels.

10.4.7.2 Waxing

In addition to making cartons from paperboard impregnated with wax during

paperboard manufacture, it is also possible to apply wax to one or both sides of a cut

and creased flat carton blank. Wax can be applied in patterns and can be kept off

glue flaps.

Waxing in this way is either ‘dry’ waxing, where the wax solidifies on the

surface giving a matte appearance, or ‘wet’ waxing, where the carton passes under

heaters which remelt the wax before the blank is carried on belts through refrigerated

water. The shock cooling produces a high-gloss finish on the surface of the wax.

With appropriate wax blends, cartons which are high gloss waxed can be heat

sealed. Waxed cartons are used for frozen foods, ready meals and ice cream.

Cartons with tapered sides in tub and conical shapes and with a round or square

cross section can be waxed after forming. The first liquid-packaging cartons were

made in this way.

10.5 Packaging operation

10.5.1 Speed and efficiency

Cartons are erected, filled and packed by product manufacturers, also known as

end-users or packer/fillers. There are, additionally, contract packers who provide

a packaging service, which includes cartonning, to manufacturers, particularly in

order to meet promotional and test marketing needs.

Carton packing may be either manual, partly manual and mechanically assisted,

or fully automatic. Speeds vary considerably from, for example, 10–1000 cartons

per minute (cpm), though not many would be running at speeds in excess of 500 cpm.

Mechanical cartonning with manual product-assisted loading is possible up to

40–60 cpm. Fully automatic cartonners start at speeds of around 60cpm and most

cartonning machinery manufacturers offer equipment which can run at higher speeds,

such as 120–240cpm. Higher speeds are possible in the range of 250–400 cpm,

thereafter the machinery is designed with specific products in mind, and in this

respect, cigarette cartonning is unique. Packets of 20 cigarettes (sticks) in the

special style of carton with a flip-top – also known as a hinged lid, and incorpor-

ating a three-sided inner frame – are running at 400–700 cpm. A new generation

of cigarette-cartoning machine running at 1000cpm was launched in 2002 (A-B

Journal, 2002).

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PAPER AND PAPERBOARD PACKAGING TECHNOLOGY

Whatever be the speed and overall output needs of a particular operation, there

will be a choice of cartonning machinery to meet the needs of the business. Some

manufacturers may prefer three machines rated at 60 cpm to one machine rated

at 180cpm. Several factors will influence the choice, such as:

•

factory layout or features of the production process

•

need to pack several sizes of product concurrently

•

need to pack different products concurrently.

The sequence of operations on a packing line is:

•

feeding and erecting the cartons from a box or magazine

•

filling with the product

•

closing the carton

•

checkweighing and metal detection depending on the product

•

end-of-line operations preparing the product for distribution.

A survey (unpublished) of different types of packing line in several locations

by a multinational FMCG manufacturer revealed that problems associated with the

in-feed section of packing machines were the most prevalent cause of stoppages.

10.5.2 Side seam–glued cartons

Side seam glued cartons are placed in a magazine from which they are removed

one at a time by vacuumised suckers (pads). There are two basic methods by

which cartons are extracted from the magazine and erected. In the first, the suckers

pull on one panel and transfer the cartons into the moving pockets of a flighted

conveyor. The length of each pocket, which is controlled by the flights, reduces

automatically to the width of the carton and, in so doing, erects the carton by

pressing on the two opposite, folded creases. This method is referred to as ‘diagonal’

loading. The other method is to use suckers on adjacent panels and pull the carton

in opposing directions such that the carton assumes a rectangular cross section by

the time it is dropped into the pocket of the flighted conveyor. This is known as

‘rotational loading’. Another mechanical opening method inserts knives from both

sides which are twisted as the carton is eased into the flighted conveyor in a diagonal

loading mode.

The opening of side seam glued cartons has been studied in depth, and the

carton opening force measured using methods which replicate both diagonal and

rotational loading. For a full treatment, see Hine (1999, pp. 111–139). This reference

relates carton gluing, crease prebreaking, and the variation in carton opening force

with storage time.

An important conclusion of this work is that with diagonal loading, carton

opening force increases rapidly after gluing and packing by the carton maker during

the first 6 days of storage, levelling out after two or three months. However, with

rotational loading, there was no significant rise in carton opening–force torque

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with storage, suggesting that this is a superior method of carton erection. Another

conclusion is that for both methods of carton erection, the main resistance to opening

comes from the pre-folded creases, indicating the importance of this aspect of

folder gluer operation.

An additional aspect of folder/gluer operation is the effect of compression on

the folded creases. This can be assessed by measuring the height of a given

number of cartons at the end of the gluing operation. The higher the compression

pressure, the lower the height and the greater likelihood that the carton will be

difficult to open on the packing line. If, however, the compression is too low, the

side-seam adhesion may be impaired and, in addition, it would be difficult to load

the cartons into the magazine of the cartonning machine. In practice, for a given

carton, this height should be maintained within a range established by correlation

with the acceptable range of heights at the cartonning stage, i.e. after storage. This

height feature is also referred to as the ‘bounce’.

One of the main causes of carton-feeding problems at the packing stage is the

distortion of folded cartons which may occur in storage. In particular, the shape

distortion, which is described as a ‘banana’ or ‘armchair’ shape, is virtually impos-

sible to open. Another form of distortion produces an ‘S’ shape. Hence the recom-

mendation is that cartons are stored on edge and isolated from stacking pressure in

non-returnable corrugated fibreboard outer cases. The resulting rows of cartons

should not be too tight. Hanlon suggests that the combined thickness of the row –

calculated as three times the paperboard thickness, i.e. the thickness at the glue

flap, multiplied by the number of cartons and adding 15% of the result – should be

used as the internal length dimension of the case (Hanlon et al., 1998).

Consideration of carton opening force has led in some case to changes in the

way the gluing of cartons is organised. Cartons may be printed and cut and creased

in large batches, taking account of the cost-benefit of longer production runs. The

gluing, however, has been organised in much smaller batches to minimise the risk

of a high carton opening force and/or distortion in storage. In some cases, the gluing

has virtually been organised on demand in a location and facility remote from the

carton manufacturer and adjacent to the cartonning operation. Alternatively, some

cartonning machines have included a simply designed side-seam gluer actually

attached to the infeed.

Side seam–glued cartons may be filled horizontally or vertically (see Figure 10.36),

depending on the product. A free-flowing product which is apportioned gravimet-

rically would have an integral weigh filler with many filling heads. This type of filler

can progressively fill the cartons vertically as the filling heads travel around a

semicircular (carousel) track. This type of filling can run at high speed, for example

hundreds of cartons per minute.

Some cartonning machines are fitted with a pre-feeder. The object is to extend

the time given to erecting the carton under controlled conditions. This can be done

by designing a circular pre-feeder and fitting it alongside the cartonning machine

infeed whereby erected cartons are transferred to the flights (pockets) of the cartonning

machine.

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Carton machinery, where the product is free-flowing and filled vertically, can

incorporate carton tare weighing and product top-up features to achieve very high

accuracy in fill weight. This is beneficial when filling expensive products.

The closing of side seam–glued cartons is by hot-melt sealing, as shown in

Figure 10.37, tuck-in-flaps or locking tabs. Sealed closures would usually have

an easy-opening feature, the design of which would be dependent on whether

a reclosure feature is also required.

10.5.3 Erection of flat carton blanks

Flat carton blanks are erected by the packer/filler using one of the following

methods:

Figure 10.36 Vertical filling and sealing operation. (Reproduced, with permission, from Iggesund

Paperboard.)

Hot-Melt

Application

Nozzle

Hot-Melt

Storace Tank

Open Time

Setting Time

Compressing Time

CompressingClosing

Figure 10.37 Carton closing using hot-melt adhesive (courtesy of M-Real).

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•

Using a reciprocating tool which is pressed against the base panel thereby

forcing the side panels through 90° into the vertical (usually, there are

exceptions) position. The side panels are then secured in this position, forming

a tray shape either by means of interlocking tabs or by hot-melt adhesive

(Fig. 10.38).

•

Applying an adhesive to a side seam and folding the carton blank around a

mandrel. This is usually preceded by wrapping paper, paper coated with a

barrier coating, such as PE or PVdC, an oriented polypropylene film (OPP)

with PVdC coating or a film laminate around the mandrel, sealing the side

seam and base.

•

Forming the hinged lid blank together with a reinforcing inner frame – a

design mainly confined to the packing of cigarettes.

•

Applying adhesive to the side seam as the first operation on the packing line

using a simplified side seam gluing unit.

The efficiency of operation, where the cartons are presented in the form of flat

blanks, mainly depends on the flatness of the paperboard blanks being maintained.

This is because a blank which has a curl or twist can easily misfeed and cause

a stoppage. For example, if the carton blank is pulled out of the magazine, print

face downwards, onto a short conveyor, the lugs which are supposed to push the

(back) edge of the board, instead, pass under the upturned edge. Curl may also

prevent a tuck-in-flap from being pushed in accurately.

The tray-type carton is top loaded, either by hand or mechanically by an automatic

‘pick and place’ action. The integral lid is closed and sealed on one or three sides

with hot-melt adhesive. Where the product is filled hot, water-based adhesives

based on PVA, starch or dextrine are required. The efficiency of water-based adhe-

sives depends on the absorbency of the surfaces being sealed and the compression

time to allow the adhesive to set, i.e. to become tacky enough so that unrestrained

joints do not open.

Plastic-coated trays are usually erected and lidded by heat sealing but plastic coated

end-loaded cartons are usually sealed, though not always, using hot melt adhesive.

Blank

Corner sealed or locked

Tray erect Top load product Close lid Seal or tuck lid

Hot melt adhesive

Figure 10.38 Erection of tray-style carton for top loading and closing. (Reproduced, with permission,

from Iggesund Paperboard.)

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An important precaution in the use of hot-melt adhesives is that they must not

be exposed to air for long periods at the working temperature when the machine is

not in production. This will cause heat degradation and subsequent loss of adhesion.

A situation was investigated where the packer claimed that the surface of the

paperboard was defective because the hot-melt adhesive would not close the cartons

permanently. It was found that the heat supplied to the adhesive reservoir had not

been switched off when the machine had been left unattended overnight and at the

weekend. This, it was claimed, had been standard practice to ensure a quick start-up

when production was resumed. There was evidence of severe carbonisation in the

adhesive system. The hot-melt adhesive had been degraded. The solution was to

use time switches set to remelt the adhesive a short while before packing was

required to recommence. Today, pressurised on-demand nozzle applicators are

preferred to open-to-air glue pots.

10.5.4 Carton storage

Reference has been made to the fact that paperboard will absorb moisture when

exposed to high humidity and lose moisture in low humidity. Moisture content

changes are usually accompanied by changes in flatness (shape). Hence reasonable

precautions should be taken at all stages where the paperboard may be exposed to

changes in RH. The carton manufacturer should provide moisture protection for

storage and transit. The packer/filler (end-user) must ensure that cartons are not

unwrapped until they have attained temperature equilibrium with the area in which

the packaging is carried out.

Problems have been observed where unwrapped pallets of cartons awaiting

packing have been left near exits to the outside environment. Also cold cartons

have been found to affect the efficiency of hot-melt adhesion due to the fact that

the adhesive open time is reduced by being applied to a cold surface and the

tackiness is lost before the surfaces being sealed are brought together.

Packer/fillers should also replace moisture-resistant wrappings to pallets and

boxes of cartons left unused at the end of a production run and over a weekend.

This is especially important in dry (low RH) packing areas handling dry food

products, such as tea and baked products, for example biscuits and cereals. In this

dry environment, unprotected flat paperboard carton blanks are likely to develop

downcurl, i.e. curl away from the print and this will cause problems on cartonning

machines.

10.5.5 Runnability and packaging line efficiency

Good runnability is essential. The requirements of good runnability are many and

varied. Good runnability is difficult to define, but everyone knows when it is missing.

In a general way, it describes a packaging operation running with minimum dis-

ruption, at a specified level of efficiency, which can be measured and monitored.

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Packing line efficiency is dependent on:

•

the machine(s), or method of packaging in the case of a manually operated line

•

reliability and maintenance of the machinery

•

the product

•

the operators, level of training, etc.

•

quality of the cartons.

The packer/filler’s aim is to avoid, or minimise, the production of damaged packs,

wasted product, wasted packaging and to achieve the rated output of the packing

line. The efficiency of a packing line is given by,

In establishing ‘expected output’, it is important to base this on the real time

available for packing. This means that setting-up time and routine maintenance

must be eliminated from overall production time.

A packaging line may comprise several, linked, packaging machines, for

example form/fill/seal pouch or sachet machine, cartonning machine and case

packer. If the efficiency of each machine is 90% then the efficiency of the line as

a whole would be the product of these individual machine efficiencies, in this

example 72.9%. This must be taken account of when planning a packaging system.

A mistaken poor efficiency complaint arose when a packer reported high carton

wastage. The line was fed from a carton erector fitted with a counter which

counted every vertical cycle. The carton erector could erect cartons faster than the

rest of the packing line could pack and close the cartons – it itself a good feature.

When the line was full of partially loaded cartons, an automatic switch stopped the

carton feed into the carton erector. However, the carton erector continued to cycle

automatically even though no cartons were being erected. The counter ticked away

and at the end of the shift the counter figure was taken as the number of cartons

erected, clearly this was erroneous. The production of filled cartons was much

lower than the figure from the carton erector and the difference was interpreted as

high carton wastage! Eventually, the correct usage was established by reconcilia-

tion with the quantities of cartons in, and issued by, the warehouse, but not before

someone had initiated an investigation by the supplier of the cartons and the

paperboard!

Some examples of features which affect runnability are more nebulous than

others, and one which comes into this category is ‘timing’. This relates to the settings

on a cartonning machine within which an established carton specification can

be run with a satisfactory packing-line efficiency. Settings control mechanical

movement whereby the machine interacts with the carton and the paperboard.

Some settings can be advanced or retarded in response to, for example, the paper-

board stiffness or the resistance to folding or spring back of carton creases.

Line efficiency %=

Actual output

Expected output

------------------------------------------

100×

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PAPER AND PAPERBOARD PACKAGING TECHNOLOGY

The importance of timing was highlighted by the following example which

occurred when an alternative carton specification was trialled on a well-established

packaging line. The alternative paperboard specification was significantly different

in that it was based on FBB from a machine fitted with Foudrinier wires whilst the

established carton was based on recycled board, WLC, made on a modified vat

machine, and the thickness of the two boards was the same which meant that the

FBB was 23% lower in grammage.

The cartons were medium to large in size. They were erected for horizontal

end-loading of the product which was already packed in a PE coextruded film bag.

The cartons were therefore moving in the same direction as the MD of the paper-

board. There was a large difference between the MD stiffness of the WLC and that

of the FBB, with the MD stiffness of the WLC being about 25% higher. This

mainly resulted from the difference in forming on the paperboard machine. The

MD/CD stiffness ratio for the WLC was 2.8 and for the FBB 2.1. When the

settings which suited the carton made from WLC were used for the FBB cartons,

the machine quickly jammed. This could have been the end of the trial and the

result recorded as a failure. However, with the co-operation of engineering personnel

new settings and timings were found for chains, flights and conveyors, which

enabled the FBB cartons to run satisfactorily.

Today all settings and adjustments can be logged and retained electronically so

that cartonning machines can be quickly reset after size changes. Machines are

also fitted with technical support visual displays for troubleshooting to minimise

the effect of any stoppages which may occur.

Coefficient of friction, measured in the dynamic mode as opposed to the static

mode, is frequently found to be involved in runnability investigations. A note of

caution should be made when deciding which surfaces to use in the test method.

As the guide rails and ploughs on the machine are likely to be made of steel or

aluminium, it is likely that the particular metal surface involved is used in checking

the coefficient of friction against the carton surface. This, however, has been

found to yield confusing results. It should be recognised that the metal surfaces on

the machine can become coated with material which transfers from the cartons,

and account of this should be taken.

Surface friction resulting from inks and varnish can be modified with the

help of the respective suppliers. The inclusion of silicones, or wax, to

improve rub resistance can lower coefficient of friction or angle of slide. It

can also reduce gloss levels and hence care is necessary when any changes

are contemplated.

Whilst high surface friction is sometimes the cause of poor runnability, it is

unlikely that the carton surface will be too slippy as this would give other problems,

such as making it difficult to handle a bundle of cartons.

Another property of paperboard where problems have arisen in the past is air

permeability (porosity). In a particular case study, the carton blanks were supposed

to be picked out of a pile, one at a time, by rubber vacuumised suckers which

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contacted the reverse unprinted side of the paperboard. A problem arose resulting in

misfeeds or partial pick-up which led to misalignment and jamming in the infeed

section of the cartonning machine.

The carton was made from mineral pigment-coated paperboard. This is virtually

impermeable to the rapid passage of air. In this case, the vacuumised suckers were

set quite close to the cut edge of the carton. As a result, air was being sucked in

through this edge into the middle plies of the paperboard, and from there to the

point where the suction was applied. The problem was solved by adjusting the

position of the suckers away from the edge of the carton blank.

Where uncoated and unlined, thin paperboard is used, less frequently today

compared to years ago, it has been known that the suckers can pull air through two

sheets causing a double feed and a machine jam.

The study of cartons and cartonning machine interactions is important and

co-operation between the manufacturers of cartons, paperboard, packers and

machinery companies should be encouraged. It must always be appreciated that

there is an explanation to every problem and the real explanation must be found if

the problem is to be understood and solved. This is often difficult when problems

interfere with production.

Sometimes a repetitive sequence is detected in the occurrence of a specific

fault. For example, the problem may be associated with one particular carton die

station, it may be associated with a damaged flight on a packaging-machine

conveyor or it may be due to a damaged carton-forming mandrel. Sometimes

the cause of a problem is related to some aspect of either the packing machine or

the carton, or to some obscure interaction between the two; but it cannot be

observed because the speed is too fast or the suspected position is difficult to access.

In these cases, high-speed video should be used to observe the features in slow

motion.

In his summary of carton–machine interactions, Hine (1999, p. 182) lists the

important paperboard and carton properties in relation to the efficiency of the

various machine functions and carton movements.

The properties and features listed are porosity, smoothness (roughness), friction,

adhesion, dimensions (accuracy thereof), cut quality, paperboard stiffness, fold

stiffness, carton opening force and flatness (Hine, 1999, p. 182: Table 8).

The machine and operation features which were related to these properties of

the paperboard and features of the carton are the efficiency of:

•

loading the carton feed magazine

•

extracting the cartons from the magazine

•

erecting the carton

•

conveying the carton through the machine

•

filling of the product

•

closing of the flaps

•

collating the cartons as they leave the machine.

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10.6 Distribution and storage

Cartons are usually collated or grouped together and packed in secondary packaging

for distribution and storage. Typical distribution packs, Figure 10.39, are as follows:

•

Unsupported blocks of cartons are stretch or shrink-wrapped – the cartons

may be packed in shallow-depth paperboard trays prior to stretch or shrink-

wrapping.

•

The blocks of cartons may be protected with a wraparound corrugated fibre-

board sleeve and then stretch or shrink-wrapped. There are other designs

which make use of corrugated fibreboard in this way. One of the objectives

is to ensure that some cartons are visible so that the pack has good visual

appeal when displayed in cash-and-carry type warehouses from which many

small traders obtain their bulk supplies.

•

Regular slotted containers (RSC) are made from corrugated fibreboard. The

cases may have tear tapes to facilitate opening and displaying the contents at

the point of sale. The case can be a wraparound blank erected in situ at the

end of the packaging line.

All these examples may be accompanied by the use of automatic equipment to

collate the cartons and erect/pack the trays or corrugated fibreboard packaging.

When the transit packing is completed, the packs are palletised, sometimes

automatically.

The specification of all packaging components must take account of any special

environments involved in the distribution, storage and merchandising at the point

of sale.

Typical examples of special environments are those for frozen food (−40 to −20°C),

and chilled food (0 to +3 °C). An aid to monitoring that these products are not

exposed to higher temperatures exists in the form of temperature monitors. At its

Primary

container

Shipping

(secondary container)

Unit load

(tertiary container)

Figure 10.39 Packaging for distribution and storage. (Reproduced, with permission, from The

Institute of Packaging.)