Mark J. Kirwan Paper and Paperboard Packaging Technology
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the functional needs of the pack. Such scope arises in, for example, confectionery
packaging for chocolate assortments, Easter Eggs or chocolate bar cartons with
after-use play value. Examples exist in other end use areas, for example cartons
for luxury cosmetics and gift packs of all kinds.
The structural design is facilitated by the strength and toughness of paperboard
and by the ease with which paperboard can be accurately and cleanly cut, creased,
folded and glued.
Several comprehensive guides on the mainstream types of carton construction
are available. The ECMA (European Carton Makers Association) Code and ‘The
Packaging Designer’s Book of Patterns’ (Lászlo Roth and George L. Wybenga),
published by John Wiley & Sons, Inc., from which several examples are quoted
below (see ‘References’ for full description). Computer-aided-design (CAD)
packages are also available.
As already noted, the most common shape of folding carton is based on a
rectangular or square cross section. It has four rectangular or square panels. There
is a fifth, narrow panel which when fixed, using an adhesive, to the underside of
the first panel creates a tube. This structure is said to be side seam glued and it is
folded flat by the carton maker for shipment to the packer.
The packer usually erects this style mechanically. The product is loaded,
either horizontally, or from the vertical direction, and the end flaps are closed
either by tucking, locking slits or with the help of an adhesive. It is referred to
as an ‘end load’ or tube-style carton. An example of this design is shown in
Figure 10.1.
Another popular rectangular shape is based on a tray style. In this instance, the
carton maker supplies a flat blank. The base of the tray is a flat area of paperboard
to which four panels are attached by creases. The tray is erected mechanically by
folding these four panels through 90°. This structure is secured either by the use of
a hot-melt adhesive or with locking, hook-shaped tabs which fit into slots in the
adjacent panels. There are many variations to this style. Lids can be incorporated
as extra panels and both lids and side panels can have extensions which are folded
Figure 10.1 End load carton. (Reproduced, with permission, from Alexir Packaging Ltd.)
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into position after the product has been loaded, as in Figure 10.2. In the case of the
lids, they can be closed by tucking in a folded extension to the lid or by hot-melt
gluing one or three closure flaps. This style is often referred to as a ‘top load’ car-
ton. A point worth considering is that, depending on the product, it makes sense to
load the product through the largest opening.
A simple tray style is the shallow tray with side walls 25–38-mm deep with
glued or locked corners, which are used to collate groups of cartons for stretch or
shrink wrapping, as in Figure 10.3.
The side walls do not necessarily have to be vertical – they may be tapered as
shown in Figure 10.4.
Where these trays are plastic extrusion coated with PE, PP or PET they can be
erected by heat-sealing. The method of corner-folding and heat-sealing makes this
design leak-proof as shown in Figure 10.5.
Trays can also be made by pressing and deep drawing, as shown in Figure 10.6.
This process places high demands on the paperboard. The normal depth of drawing
Figure 10.2 Top load carton. (Reproduced, with permission, from Alexir Packaging Ltd.)
Figure 10.3 Shallow-depth tray with locked corners. (Reproduced, with permission, from Alexir
Packaging Ltd.)
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is around 25 mm, and with additional moisture application and two-stage drawing,
it is possible to extend this to 45–50mm. Deep drawing can be used with paper-
board extrusion coated with PET, which can be used to pack food products that are
cooked and/or reheated in the pack. Reheating is possible using microwave or
radiant heat. The trays can be lidded with plastic snap-on lids, heat-sealed plastic
film or heat-sealed plastic-coated paperboard.
By changing the cutting and creasing of the paperboard carton blank and by
corner-gluing, tray designs can be made by the carton maker, which are folded for
Figure 10.4 Tapered carton with lid. (Reproduced, with permission, from Alexir Packaging Ltd.)
Figure 10.5 Tray with tapered sides and heat sealed corners. (Reproduced, with permission, from
John Wiley & Sons, Inc.)
Figure 10.6 Deep-drawn, pressed trays. (Reproduced, with permission, from Iggesund Paperboard.)
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packing and shipment to the carton user who then erects these cartons by hand.
These can be four corner–glued or six corner–glued, the latter, which incorporates
a lid, being traditionally used by cake shops (Fig. 10.7).
A modification of the tray design with hollow walls and a double-thickness lid,
as shown in Figure 10.8, is a popular choice for chocolate assortments. This carton
can be erected mechanically on the packing line. The hollow walls provide excel-
lent rigidity, enabling the carton to be held by one corner when offering the
contents around. The double-thickness lid results in the same high-quality printing
Figure 10.7 Six corner–glued cake box. (Reproduced, with permission, from Alexir Packaging Ltd.)
Figure 10.8 Carton with cavity walls and double thickness lid. (Reproduced, with permission, from
John Wiley & Sons, Inc.)
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which is expected with this type of application to be achieved on the inside surface
of the lid.
A popular way of providing product protection is to overwrap a folding carton
with a barrier-coated PP film with envelope folded and heat sealed end seals. Typ-
ical applications include cartons for chocolates, tea bags and cigarettes. Another
material used in this way is high-gloss wax-coated paper used to overwrap
unprinted cartons for frozen food.
A popular carton style is the hinged-lid cigarette carton as shown in Figure 10.9.
This carton is erected at high speed from a rectangular blank. It incorporates
a small additional piece of paperboard which provides strength and facilitates the
design of the closure.
Other shapes are, however, possible and are used to meet specific needs, for
example round, elliptical, triangular, pyramidal, hexagonal, domed, wallet shaped
(for retort pouches), etc. (Figs 10.10 and 10.11).
Where a product requires protection from moisture, oxygen, contaminating
odours and taints, etc., cartons may be lined by the carton maker with a flat tube of
a flexible barrier material which is inserted during carton manufacture. The flex-
ible material is usually heat sealable – examples include paper/aluminium foil/PE
Figure 10.9 Hinged-lid cigarette carton. (Reproduced, with permission, from John Wiley & Sons, Inc.)
Figure 10.10 Wallet or pillow design. (Reproduced, with permission, from John Wiley & Sons, Inc.)
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and laminations involving plastic films. The lined cartons are supplied folded
flat to the packing/filling machine. One end of the liner is heat sealed, the asso-
ciated carton flaps closed and then, after filling, the other end is sealed and the
carton flaps closed. This type of carton is used for ground coffee, dry foods and
liquids. Packing machines can vacuum pack or gas flush a product such as
ground coffee. A lined carton of this nature may be fitted with a plastic hinged
lid incorporating a moisture vapour barrier and tamper evident diaphragm
(Fig. 10.12).
Another type of lined carton, which can be formed by the packer on the packing
machine, takes flat carton blanks and a roll of the material to be used as the liner,
frequently bleached kraft paper. First, the liner is formed around a solid mandrel.
The side seam and base are either heat-sealed or glued with adhesive, depending
on the specification. The carton is then wrapped around the liner with the side
seam and base sealed with adhesive. The lined carton is removed from the mandrel,
the product is filled and both liner and carton are sealed/closed. This type of pack
Figure 10.11 Hexagonal design. (Reproduced, with permission, from Alexir Packaging Ltd.)
Figure 10.12 Lined carton. (Reproduced, with permission, from Alexir Packaging Ltd.)
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is suitable for the vertical filling of powders, granules and products such as loose
filled tea.
Folding cartons can have windows or plastic panels for product display, for
example spirits, toys, etc (Fig. 10.13).
A display outer is a carton which performs two functions. At the packing stage, it is
used as a transit pack or outer. When it arrives at the point of sale, the specially
designed lid flap is opened and folded down inside the carton at the back of the product
to become a display pack with a printed header display. This design of carton, as shown
in Figure 10.14, is used to pack a number of smaller items which are sold separately,
for example confectionery products, such as chocolate bars, also known as countlines.
Figure 10.13 Windowed carton. (Reproduced, with permission, from Alexir Packaging Ltd.)
Figure 10.14 Display outer. (Reproduced, with permission, from Alexir Packaging Ltd.)
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In the case of the end load or tube style carton, the carton flaps on the base are
closed by either tucking, locking, gluing or heat-sealing. A heat sealed closure
requires the presence of a thermoplastic layer, for example PE, PP or PET.
The crash lock base is made by the carton maker. The bottom flaps are creased
and glued in a special way which enables the carton maker to fold the carton flat
for shipment to the packer who erects the carton by hand in such a way that the
bottom flaps snap, or crash, into position irreversibly. This type of base can support
a considerable weight, for example bottle of alcoholic liqueur.
The lid flaps may be closed with a tuck-in-flap or flip top, or may be locked,
glued or heat sealed. Closures may be made tamper evident. The top may have an
easy opening device and where necessary, a reclosure feature. Closures which are
repeatedly opened and closed during the life of the contents, for example perfume,
require their creasing to have sufficient folding endurance. This requires careful
consideration of the type of paperboard used.
Additionally, cartons can have integral, internal display fitments or platforms,
sleeves can be used for trays of chilled ready meals and multipacks for bottles,
drinks cans (Fig. 10.16) and yoghurt pots (Fig. 10.15).
Figure 10.15 Sleeve for two plastic tubs. (Reproduced, with permission, from Alexir Packaging Ltd.)
Figure 10.16 Multipack for six beverage cans. (Reproduced, with permission, from Alexir
Packaging Ltd.)
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Cartons can incorporate dispensing devices, carrying handles and easy opening
tear strip features for convenience in handling and use. Cartons can be made into
non-rectangular, innovative shapes, such as packaging for Easter Eggs.
This chapter is not comprehensive. It is intended to indicate that folding cartons
can take many shapes and meet many packaging needs. A carton designer working to a
project brief has many options and considerable freedom to express imaginative and
creative ideas. The paperboard features that make this possible depend on the strength
and toughness of paperboard and its creasing, folding and glueability properties.
Reference has been made to the use of CAD packages – an added advantage of
CAD is that it can be linked to plotters which can quickly reproduce drawings and
even make actual samples for evaluation.
Together with an appropriate coating, lamination or separate carton lining,
paperboard can be used in conjunction with the design of the pack to produce
cartons, sleeves, trays and blisterpacks which meet demanding performance require-
ments, such as liquid tightness, siftproofness, heat sealability, grease resistance,
moisture and moisture vapour resistance, product release and reheating by micro-
wave, convection and radiant heat. Folding cartons can meet the needs of a wide
range of distribution, storage, packaging and use conditions, for example frozen,
chilled, ambient, tropical and wet conditions.
Once a specific type of paperboard has been selected, it is necessary to choose
the grammage (basis weight) and thickness to provide adequate carton strength at
each stage of the packing chain from packing through to use by the consumer.
The outcome of the design phase for both surface design and structure is to
provide one or more design proposals for evaluation by marketing, production,
R&D, costing and functionality at each stage of the packaging chain.
10.4 Manufacture of folding cartons
10.4.1 Printing
The main processes for carton printing today are offset lithography, flexography
and gravure. Letterpress and silk screen are used to a limited extent. The most
recently introduced process, digital printing, can be used for short print runs and
for customising packaging already pre-made in bulk.
All these processes are discussed in Sections 4.6.1–4.6.8.
The answer to the question as to which print process to use, is complicated. The
considerations are:
•
product, distribution and usage
•
quality of reproduction
•
run length
•
lead time
•
cost.
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Printing involves solid print, text, illustrations and diagrammatic repre-
sentations appropriate for the type of product concerned and its market pos-
itioning. As already noted, product positioning and specific brand values will
have a major influence on the print design and the quality of reproduction
required.
Functional needs of the packaging, depending on the product or method of
distribution, may impose constraints. Products such as detergents can be aggressive
to print, particularly in conditions of high humidity. Powdered products packed
hot may impose the need for highly scuff and rub resistant print surfaces. Products
such as chocolate and tobacco are sensitive to retained ink odours and this will
influence the choice of inks and print process. In every case, the overall needs should
be discussed with printing experts.
With respect to quality of reproduction, there is overlap in what can be
achieved today with the different printing processes.
It is used to be said that flexo was poor for solids, half tones, as required for
illustrations, and varnish gloss. This is not true today. Excellent results have also
been demonstrated using UV cured varnish. A flexo press with cutting and creasing
in-line was recently demonstrated for printing cigarette cartons, the printing of
which is currently dominated by gravure.
Gravure was considered the best for solids, and offset litho the best for half tones.
Offset gravure and conventional gravure with electrostatic assist may improve
gravure half-tone reproduction, but the benefits are academic if the capacity to
print large volumes is not available or if run lengths are too low to justify the high
cost of gravure cylinders.
There was a time when, for example a rose would be printed by offset litho
on a carton for chocolate assortments and the rest of the carton, with an overall
solid print, would be printed by sheet-fed gravure. There were specific reasons
for this. Gravure, provided the retained solvent level met the required standards,
was the better choice since in those days the residual odours from oxidation–
polymerisation drying oil-based litho inks were a potential hazard for chocolate
packaging. Moreover there was a risk of set-off and poor rub resistance with
litho on such large solid areas of print. Today there is a wide choice of offset
litho ink and drying systems, particularly with UV (ultraviolet) and EB (electron
beam) assisted drying.
It used to be the case that varnishing in-line by offset litho was poor in terms
of colour and gloss. Today, this no longer applies as presses are fitted with coating
units and can apply UV cured varnishes which are water clear, have high gloss and
rub resistance.
It still the case that the cylinders are relatively dearer for gravure than plates are
for litho and flexo, but they are longer lasting and hence are competitive when
long runs are required.
Silk screen printing has always been known for its ability to print thick films of
ink – it gives the best fluorescent effect, for example. It is possible to use UV