Mark J. Kirwan Paper and Paperboard Packaging Technology
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simplest, this comprises a colour patch which can change colour if the temperature
rises above specified limits.
In practice, there are several ways of ensuring a satisfactory carton performance
in distribution. One of the considerations is the level of moisture resistance required.
Moisture condenses on the surface of cartons when they are removed from the
cold environment. Moisture will also affect cartons of chilled foods as they are
stored in an environment with high RH.
Paperboard absorbs moisture on the surface and through cut edges. The effect is
visual and results in distortion of the surface and loss in strength. Surface treatments,
such as printing and UV varnishing, slow down moisture adsorption. Hard sizing
also slows down moisture adsorption. Plastic coatings can be applied to one or
both sides of the paperboard. Low density polyethylene is the most commonly
used plastic. High density polyethylene (HDPE) has a better moisture vapour
barrier. If additional performance needs are required, then there are additional
choices. PET or PETE provides additional product resistance, and can also be used
where the product is reheated in microwave and conventional radiation heated
ovens. PP is satisfactory for reheating in convection steam heated ovens. PET
(PETE), PP and HDPE have good grease/fat resistance. All these plastics are
heat sealable, and this property is frequently made use of by forming trays with
the plastic on the inside. These trays can be lidded with peelable film and plastic
coated paperboard.
Care must be taken with exported goods which may be containerised and which
pass through extremely warm conditions. In these instances, hot-melt adhesives
used to erect and/or close cartons must be replaced on the packaging machines
because hot-melt adhesives can soften and the adhesion fails at high temperatures.
The hazards associated with distribution comprise:
•
shock, for example due to dropping
•
compression – both static, slow rate of loading, and dynamic, fast rate of loading
•
vibration in transport causing destabilisation of the pallet and product damage
(FOPT, 1999).
These factors can be studied in the laboratory. Safety factors are applied to static
compression loading results because, in practice, the box compression of the
carton depends on:
•
the structural design
•
direction of loading
•
whether contents support the carton, as with a bottle or jar, or not, for example
breakfast cereals in pouches
•
type of transit pack, for example corrugated fibreboard case
•
storage, palletisation, stacking and climatic conditions
•
paperboard properties, such as grammage, thickness, moisture content,
stiffness and short-span compression strength.
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PAPER AND PAPERBOARD PACKAGING TECHNOLOGY
Complaints of carton damage need to be investigated carefully to find the real
cause of the problem, because some examples of transit damage would not have
been avoided even if the paperboard used to make the carton had been twice as
thick and therefore much stronger. Everyone wants to reduce packaging and
clearly a balance must be achieved where the carton is strong enough without
being open to criticism of overpackaging. This is best achieved with practical tests
and by considering the whole packaging system, as it may be better to improve
a situation by changing the specification of the transit pack or pallet arrangement
rather than the specification of the carton.
A vast amount of work has been reported on the subject of relationships
between paperboard properties and observed box compression strength (Hine,
1999, pp. 111–139). An example of this research is that carried out by Fellers et al.
(STFI, 1983). This research showed that the compression of a panel, minimum
size 60 mm × 90 mm, is described by the relationship
where F
p
is the panel compression strength; F
c
is the compression strength
(short span) in the direction of loading; S
MD
is the MD stiffness; S
CD
is the CD stiff-
ness; and c is a constant. is known as the geometric mean stiffness. It is
recognised as an important strength-related feature of paperboard.
Under certain conditions and for a range of panel sizes, it was found that the
constant c has a value 2π or 6.28. On the basis of that, for a complete box of four
panels, the compression would be F
B
= 4 × F
p
. Then:
This shows that the box compression strength is dependent on paperboard
stiffness and the short-span compression strength. Figure 10.40 shows the
relationship between measured panel compression strength (N) and the predicted
value based on stiffness and short-span compression using this equation, and the
agreement is very good.
The importance of this work, in the author’s opinion, is not that it is predic-
tive, within limits, with respect to box compression, but that it shows that stiffness
and short-span compression are important paperboard performance-related
properties.
The short-span compression is measured by compressing a sample which is
only 0.7 mm long. If a longer sample length is chosen, as would be the case with
a tensile test, then under compression it would merely bend and buckle. When
0.7 mm is compressed, the failure point occurs when the fibres slide in relation to
F
p
= cF
c
S
MD
S
CD
×
S
MD
S
CD
×
F
B
=4 F
p
× =8π F
c
S
MD
S
CD
×
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each other. This is an interesting phenomenon, bearing in mind the fibrous
structure and interfibre bonding. The range in length of the fibres present in any
given sample is also relevant, bearing in mind that the thickness of hardwood
fibres is around 1.0mm and softwood 3.0–3.5mm.
The compression strength is two to three times lower than the tensile strength
and prior compression in this way does not affect the tensile measurement. This
discussion explains how creasing and folding can occur, given the internal stresses
withstood by fibres in tension and compression in close proximity. The various
factors which are involved in studying compression strength are shown in
Figure 10.41.
10.7 Point of sale, dispensing, etc.
The consumer eventually takes possession of the cartonned product. As noted in
Paragraph 10.1, this can take place in a number of ways depending on the product
and the intended market. In some situations, for example self-service retailing, the
appearance of the pack is extremely important – a damaged or faded carton is
unlikely to be purchased and an attractive carton may result in an impulsive
purchase. In some situations, such as in the dispensing of a prescription medicine,
the carton may play no part in the transaction, but nevertheless the brand owner
would still want the carton to have an hygienic, quality image. Hence the printed
Figure 10.40 Panel compression strength, measured vs calculated (Fellers, de Ruvo, Htun, Carlsson,
Engman and Lundberg). (Reproduced, with permission, from Iggesund Paperboard.)
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PAPER AND PAPERBOARD PACKAGING TECHNOLOGY
appearance should be maintained, and the carton should be strong enough with
an adequate box compression strength, good rub resistance, etc.
In the supermarket, the transit pack should be a conveniently handleable unit,
easy to open and recycle. The cartons should be easy to merchandise, i.e. easy to
stack and display, at the point of sale. The integrity of the pack is important to
demonstrate that the product has not been tampered with.
An important consideration for the consumer today is that the product is genuine,
i.e. not a counterfeit product. Several techniques are available to detect this:
•
Printing an identification on the carton using a clear, transparent varnish
containing an ingredient which is only visible under UV illumination.
•
Incorporating a clear mark in the paperboard that is similar to a watermark.
A recently published system can provide a mark which may be either visible
to the naked eye or only visible under UV illumination (Tobacco Reporter,
2002a).
•
‘Fingerprinting’ the approved paperboard using near infrared spectroscopy
(NIR) (Tobacco Reporter, 2002b). Every paperboard has an individual
spectrum depending on the ingredients used in its manufacture and which
will remain the same unless any of the ingredients are changed.
•
Use of RFID labels on pallet loads and transit packs (Paper Technology,
2003a). RFID labels are discussed in Section 4.5.3. This is a rapidly develop-
ing area mainly depending on reduction in the cost of the electronic
components.
Figure 10.41 Compression testing. (Reproduced, with permission, from Iggesund Paperboard.)
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10.8 Consumer use
Quality aspects of packaging which are particularly noticeable to the consumers
generally relate to such features as the ease of handling, any form of damage
including security against pilferage, ease of opening and ease of reclosure (where
relevant). If the reclosure uses a tuck-in-flap, then the durability of the lid-hinge
crease is critical. The print should not be rubbed when handled – wet rub is a critical
requirement for cartons used for frozen food, chilled food and ice cream. The
printed instructions should be easy to read and unambiguous.
Convenience in the use of packaging is a feature that consumers respond to and
manufacturers seek to provide. One of the more technically innovative develop-
ments which provides convenience in several ways has been the development of
the PET (or PETE) extrusion coated paperboard tray for microwaveable and
radiant oven reheating of frozen and chilled convenience ready meals at temperatures
up to 200 °C. To achieve this, several technologies have been brought together
in a ‘system’.
The extrusion coating process has already been described. For the best results,
the coating is applied to the reverse side of SBB which can be formed into a tray by
one of two methods. In using the first method, a tray format can be cut and creased
and formed on a tray erector, by either heat sealing or interlocking corners.
A leakproof tray-erected heat-sealed, web cornered style is also possible (Fig.
10.5). Alternatively, the tray can be formed by deep drawing using metal tool-
ing (Figs 10.6 and 10.42). Depths up to 25mm can be formed in one operation
and if the paperboard is moistened, a second draw to a depth of 45–50mm can be
achieved with heat and pressure, as noted in 10.3.2.
These tray designs can incorporate flanges to which plastic film or plastic
coated paperboard can be applied with peelable seals. Initially, microwave-heated
foods provided convenience and rapid reheating (Fig. 10.43). The system could not
Figure 10.42 PET-lined paperboard deep-drawn tray with flange for applying lid. (Reproduced, with
permission, from Iggesund Paperboard.)
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brown or provide a degree of crispness, i.e., until a way was found to overcome
the deficiency. This was achieved by including a susceptor inside the pack.
Susceptors work by absorbing microwave energy which is made available to the food
in the vicinity, causing localised browning and crispness. The susceptor is made
from aluminium metallised PET film. They are also made using iconel (nickel/chro-
mium), which can induce even higher temperatures (ASTM, 2003).
Another example of innovative paperboard packaging is provided by the fol-
lowing ‘intelligent packaging’ application (Paper Technology, 2003b). In this
example, an SBB, chosen for its high security against cracking when the creases
are folded, was printed with a conductive ink containing an embedded micro-
chip, antenna and electronic circuitry. The application is a pharmaceutical blister
pack. The microchip detects the removal of a pill, records the time of the event
and can be programmed to bleep when the next pill is due to be taken. In add-
ition, there is a row of buttons which enable the patient to enter feedback on the
side effects of the pill. The information, which is encrypted, is stored in the chip,
which includes the Internet address to which the information can be sent. When
the pack is empty, it can be scanned and the information downloaded to a PC.
Alternatively, the data can be retrieved on a doctor’s computer and viewed on
screen.
Procedures are operated by paperboard manufacturers, carton makers and
end-users to ensure that the consumer’s needs in terms of product safety are met,
particularly where the paperboard is in direct contact with, or in close proximity
to, food, or other flavour or aroma-sensitive product.
Two of the best-known authorities in this field are:
•
United States, Food and Drugs Administration (FDA)
•
Germany, Bundesgesundheitsamt (BgVV) (German Federal Institute for
Consumer Protection and Veterinary Medicine Regulations).
There are particular regulations which apply to certain products, for example in
Europe EN71 Safety of Toys, Part 3 sets limits for the migration of certain elements
Figure 10.43 PET-lined paperboard trays stored in deep freeze and reheated in microwave oven.
(Reproduced, with permission, from Iggesund Paperboard.)
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which are applied to packaging. There are requirements for plastics in the EC Plas-
tics Food Packaging Directive 128 EEC and subsequent amendments.
The Confederation of European Paper Industries (CEPI) Food Contact Group
is co-operating with the Council of Europe with respect to food contact safety. It is
expected that the work will result in a European Union Directive.
The protection of products from loss of taste, flavour or aroma is critical
for some products. Chocolate confectionery, tea and tobacco are all particu-
larly sensitive in this respect, and paperboard and paperboard cartons are
regularly evaluated to ensure that they meet customer specifications in
respect of odour and taint. There are several potential sources of contamin-
ation. These comprise:
•
synthetic binders used in mineral-pigmented coatings
•
pulp – chemical, mechanical and recycled: whilst the fibres comprise
cellulose fibre which is tasteless and odourless, some fibres contain additional
materials; there is the possibility of the oxidation of residual organic fatty acids
to aldehydes and internal microbiological activity
•
ink and varnish residues, such as residual solvents, products arising from
oxidation–polymerisation of drying oils and unreacted components of radiation
curing
•
contamination as a result of pallets, and conditions in transit and storage.
The human sensations of taste and smell are most sensitive. These faculties are
used to test paperboard and printed cartons organoleptically. Panels of observers
whose taste and smell faculties are normal test the samples for odour and taint.
There are procedures for choosing panel members, and there are comprehensive
standards issued by the main Standards organisations, for example ISO, ASTM,
CEN, BS, DIN, etc. Topics covered include sensory testing and analysis. Many
new and updated standards have been issued between 1995 and 2005, and an
up-to-date search is recommended. The main methods involve Triangular and
Pairs testing for difference in both taint and odour evaluation as well as methods
which allocate scores quantitatively, for example DIN 10955 for which a new standard
was issued on 1 June 2004 (also known as the ‘Robinson’ test).
In addition, gas chromatography is carried out. Samples of the headspace of
jars containing fixed amounts of paperboard conditioned for a fixed period at a fixed
temperature are passed through a gas–liquid chromatograph (GLC). This separates
the various components, indicates their relative volumes on a chart recorder
(Figs 10.44 and 10.45), and measures their concentration in the material. It is possible to
split the contents of the column and have an observer check the smell against the
indications on the chart recorder. It is also possible to pass the eluted material from
the gas chromatograph to a mass spectrometer (MS) and thereby identify the actual
volatile materials arising from the original sample.
Meeting consumer packaging needs is the responsibility of packer/fillers,
carton manufacturers and the manufacturers of the raw materials used in carton
manufacture.
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PAPER AND PAPERBOARD PACKAGING TECHNOLOGY
10.9 Conclusion
The folding carton has been around from the 1880s and whilst traditional in concept
is the subject of constant innovation with respect to:
•
increased productivity at all stages of manufacture and use
•
manufacture and specification of paperboard, inks, varnishes, plastic coatings,
adhesives, etc.
•
surface and structural design
Figure 10.44 Chromatogram of unprinted paperboard. (Reproduced, with permission, from Iggesund
Paperboard.)
Figure 10.45 Chromatogram of paperboard printed with low odour offset litho ink. (Reproduced,
with permission, from Iggesund Paperboard.)
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•
printing and all conversion processes
•
packaging machinery and methods, including product handling
•
meeting new market needs and opportunities
•
taking account of societal needs in respect of the environment, product and
consumer safety.
References
A-B Journal, 2002, ‘High speed ControlLogix (Rockwell Automation) for Italian packaging machine’,
September.
ASTM International, 2003, Standard test methods for temperature measurement and profiling for
microwave susceptors, F874-98 (2003).
Atlas Die, 2004a, visit Website at www.atlasdie.com.
Atlas Die, 2004b, Reverse cut scores, visit Website at www.atlasdie.com.
Bernal, 2004, visit Website at www.bernaltech.com.
FCI, 1988, ‘Computer-based carton testing made easy’, Folding Carton Industry, January.
FCI, 1996, ‘Carton blank testing’, Folding Carton Industry, January/February.
FOPT, 1999, Fundamentals of Packaging Technology, Institute of Packaging, pp. 361–380.
Hanlon, J.F., Kelsey, R.J. & Forcino, H.E., 1998, Handbook of Package Engineering, Third Edition,
p. 175.
Hine, D., 1999, Cartons and Cartonning, Pira International.
Indocomp, 2004, ‘ACT II Carton testing’, visit Website at www.indocomp.com.
Packaging, 2004, ‘Rotary screen printing’, Packaging Magazine, vol. 7, no. 3, p. 22.
Paper Technology, 2003a, RFID Radio Tagging, vol. 44, no. 10, December, pp. 3–4.
Paper Technology, 2003b, ‘An SBB with ideal folding properties for ePackaging’, vol. 44, no. 10,
December, p. 5.
Pfaff, M., 1999, ‘Die styles, cutting methods give converters options’, Paperboard Packaging, November.
Pfaff, M., 2000, ‘Choosing the method of die style’, Paperboard Packaging, November.
Pro Carton, 1999, ‘Carton packaging Fact File’, p. 5.
STFI, 1983, Carton Board – the Profitable use of pulps and processes, Fellers, C. et al, Swedish Forest
Products Laboratory, 1983.
Tobacco Reporter, 2002a, ‘Anti-counterfeit development for paperboard’, December.
Tobacco Reporter, 2002b, ‘Identification of paperboard using NIR’, December.
Lászlo Roth, George L. Wyybenga, 1991, The Packaging Designer’s Book of Patterns, 1st edition,
John Wiley & Sons, Inc.
Further reading
Cartons and Cartonning by Dennis Hine, published by Pira International, ISBN 1 85802 179 0.
Fundamentals of Packaging Technology by Walter Soroka, revised UK edition by Anne Emblem and
Henry Emblem, published by The Institute of Packaging, ISBN 0 9464 6700 5.
Paperboard Reference Manual, published by Iggesund Paperboard.
The Carton Packaging Fact File, published by Pro Carton, UK.
The Packaging User’s Handbook, edited by F.A. Paine, published by Blackie & Son Ltd. Under the
authority of The Institute of Packaging, ISBN 0 216 92975 X.
Boardtalk Trouble Shooting, published by M-real Corporation.
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Websites
British Carton Association at www.britishprint.com/sigs/bca.asp.
European Carton Makers Association, ECMA at www.ecma.org.
National Paperbox Association (United States) at www.paperbox.org.
Packaging Machinery Manufacturers Institute (United States) at www.ppmi.org.
Paperboard Packaging Council (United States) at www.ppcnet.org.
Pro Carton at www.procarton.com.
Processing & Packaging Machinery Association (UK) at www.ppma.co.uk.