Mark J. Kirwan Paper and Paperboard Packaging Technology
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PAPERBOARD-BASED LIQUID PACKAGING
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Most of the brick-shaped packages have a rectangular cross section, as
shown in Figure 13.3, but it is possible to have a square cross section, as shown in
Figure 13.9.
13.4.4 Pouch
Tetra Fino is a paperboard-based pouch (Fig. 13.10). This pack and the associated
packaging machinery provide a low cost and low investment system. It also
places a lower demand for personnel, training and spare parts compared with other
systems.
13.4.5 Wedge
The wedge shaped is a stand-up pouch (Fig. 13.11). An example is the Tetra
Wedge which, with a straw, is a convenient-to-use drinks pack.
Figure 13.9 Tetra Brik – Square. (Reproduced, with permission, from Tetra Pak.)
Figure 13.10 Tetra Fino – Pouch shaped liquid package. (Reproduced, with permission, from Tetra Pak.)
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PAPER AND PAPERBOARD PACKAGING TECHNOLOGY
13.4.6 Multifaceted and curved designs
Designs have emanated from all the leading companies in paperboard-based
liquid packaging in order to meet specific needs with respect to life style and
product differentiation. Designs have been produced for people on the move
which fit easily into bags, into their hands and have both convenient to open and
drink from features. Elopak has issued a pack with a hexagonal design named
Diamond Pure-Pak
®
.
Other examples are as follows:
•
Tetra Prisma is an eight-faceted design as illustrated in Figure 13.12
•
Combishape is the concept that can be customised to meet specific customer
and market needs – see three alternatives in Figure 13.13.
Figure 13.11 Wedge shaped paperboard-based package. (Reproduced, with permission, from
Tetra Pak.)
Figure 13.12 Tetra Prisma. (Reproduced, with permission, from Tetra Pak.)
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13.4.7 Square cross section with round corners
Tetra Top (Fig. 13.14) is a container with a square cross section modified with
rounded corners and a plastic top.
This design is differentiated by the range of tops which are discussed in Section
13.5 and shown in Figure 13.22.
13.4.8 Round cross section
The Walcican 250 Aseptic is a round cross section container manufactured by
Lamican Oy. It is a ‘drink from the can’ container, with a foil ring-pull or peel-tab
opening (Fig. 13.15). An aluminium-free specification is also available. A well-known
tea company has marketed 12 flavours of iced tea in this container.
Figure 13.13 Combishape designs. (Reproduced, with permission, from SIG Combibloc.)
Figure 13.14 Tetra Top. (Reproduced, with permission, from Tetra Pak.)
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13.4.9 Bottom profile for gable top carton
This is not a carton design as such, but a modification to an existing design with
a technical or performance-related benefit. This is the Sahara bottom which reduces
water absorption by the raw edge in the bottom design of the Tetra Rex carton.
It is a feature which can be applied on the forming and filling machine. It has
the effect of raising the uncoated paperboard edge in the sealed bottom of Tetra
Rex away from contact with the surface, which may be wet, on which the bottom
of the carton is resting. The raised area of the base is shown in Figure 13.16. It is
Pull tapePull tape
LidLid
PolymerPolymer
PolymerPolymer
PaperPaper
PrintPrint
BottomBottom
Alufoil or
polymer barrier
Alufoil or
polymer barrier
GlueGlue
BoardBoard
Figure 13.15 Walcican 250 Aseptic. (Reproduced, with permission, from Lamican Oy.)
Figure 13.16 Modified carton base profile – Sahara design for Tetra Rex. (Reproduced, with
permission, from Tetra Pak.)
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claimed that raising the exposed edge by 1mm reduces the uptake of water by the
raw edge of paperboard by 80% and prevents the bottom of the carton from
becoming saturated with water, i.e. soggy (Packaging, 2000).
13.5 Opening, reclosure and tamper evidence
The main disadvantage of liquid food and beverage cartons has, until compara-
tively recently, been the absence of convenient and safe ways of opening them.
Though many packs, particularly the smaller ones, were considered to be one-shot
packs, reclosure was a poorly addressed feature, particularly for the larger pack
sizes, and this became a barrier to developing the use of these containers in some
product markets.
The early gable top cartons from Ex-Cell-O were to be opened ‘with a knife or
scissors’. Clips were used to reclose gable tops. In 1955, the ‘Pitcher Pour’ built-in
pouring spout concept replaced the perforated tabs and openings covered by paper
patches (Robertson, 2002, p. 48).
The sequence of recommended steps that should be taken to open a gable top
carton are shown in Figure 13.17, where one is advised to ‘press back two of the
wings and compress them to form a spout’.
It is also likely that the advent of aseptic liquid-packaging cartons actually set
back concerns about opening liquid food and beverage cartons, as a balance has to
be struck between the opening convenience and the integrity of the contents. There
were also the questions of what sort of closure is needed, how it would be applied
and what would it cost.
One is invited to open brick-shaped packs with the aid of scissors. In another
example, a pull tab is sealed across the access point, as shown in Figure 13.18.
The simplest approach to drinking the contents of paperboard-based liquid
packaging is by means of a straw, wrapped in film, attached to the body of the carton.
A hole is punched in the paperboard prior to applying aluminium foil and PE. This
provides an easy entry point for pushing the straw into the carton. The position of
the hole is covered with a pull tab. The straw is packed in a film sachet and
attached to the carton with a spot of hot-melt adhesive (Fig. 13.19).
The Tetra Prisma, described in Section 13.4.6, is fitted with a pull-tab closure,
which when removed reveals a large drinking aperture that also is excellent for
removing the contents by pouring (Fig. 13.20).
Figure 13.17 Opening a gable top carton. (Reproduced, with permission, from Elopak.)
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In recent years, a wide range of recloseable injection-moulded plastic closures
has been launched with built-in tamper evidence.
Figure 13.21 shows Recap 3 from Tetra Pak. This has a flexible aluminium
foil-based diaphragm seal over the carton opening. This has to be removed in
order to access the product and is therefore a tamper-evident feature. The hinged
overcap can be used to reclose the container with a sharp click.
Figure 13.18 Opening indications on brick shaped cartons. (Reproduced, with permission, from Tetra Pak.)
Figure 13.19 Drinking straw attached to carton. (Reproduced, with permission, from Tetra Pak.)
PAPERBOARD-BASED LIQUID PACKAGING
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There are several types of screw-type closure. CombiTop from SIG Combibloc
was the first, launched in 1994. There are designs which are applied over an area
of the carton from which the paperboard was removed prior to extrusion coating
and laminating with aluminium foil. When this cap is removed for the first time,
the foil/plastic material is perforated and pushed away from the opening. Others
have external tamper-evident security plastic rings, which have to be broken in
order to remove the cap, as shown in Figure 13.22. Improved pourers and wide
apperture closures have been incorporated where they are considered appropriate
(Ayshford, 2001).
Tetra Top, the pack with the square cross section and rounded corners, is
offered with a family of alternative plastic closures integrated with the fibreboard-
based body of the container. Each closure is designed to meet specific market
needs. The closures are described below and are shown in Figure 13.23:
•
grand tab, a lift-off closure for a container, which is easy to drink from directly
•
total top, fitted with a ring pull which removes the entire top of the container
making it suitable for foods which are eaten from the container such as
soups, yoghurt and other desserts
•
screwcap, with a tamper-evident seal
•
ringpull, which is easy to open and close effectively.
Figure 13.20 Pull tab closure and wide drinking aperture. (Reproduced, with permission, from
Tetra Pak.)
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Figure 13.21 Tamper evident closure with reclosure, Recap3. (Reproduced, with permission, from
Tetra Pak.)
Figure 13.22 Screw cap with security ring. (Reproduced, with permission, from Tetra Pak.)
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13.6 Aseptic processing
In the aseptic packaging process, ultraheat treatment (UHT), in-line food steri-
lisation thermal processing is followed by packing in a sterilised container
whilst still within the sterile environment, also known as the aseptic zone. The
liquid food or drink is sterilised or pasteurised in a continuous process as it travels
through a heat exchanger, after which it is cooled and filled. Meanwhile, the
packaging machine shapes the container and sterilises the packaging material.
Figure 13.23 Four closure designs for Tetra Top. (Reproduced, with permission, from Tetra Pak.)
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This is significantly different to the procedure adopted when sterilising food
after it has been packed in a sealed container, such as a processed food can. This
difference is demonstrated in Figure 13.24.
Typical temperatures and holding times in a UHT process are of the order of
140 °C for a few seconds, for example 3–15s (Tucker, 2003). Sterilisation of the
packaging is carried out using hydrogen peroxide, UV and sterile hot air. The
system is purged with an overpressure using a sterile air system. A typical flow
line is illustrated in Figure 13.25.
Micro-organisms
(bacteria)
Product
Filling and
sealing
Sterilisation of the
sealed pack
Packed
sterilised product
Pack
Aseptic
zone
Aseptically
packed product
Filling and
sealing
Sterilisation
Product
Sterilisation
Pack
Figure 13.24 Comparison between aseptic packaging and sterilising a packed product. (Reproduced,
with permission, from SIG Combibloc.)