Mark J. Kirwan Paper and Paperboard Packaging Technology
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11 Corrugated fibreboard packaging
Joël Poustis
11.1 Introduction
11.1.1 Overview
Corrugated fibreboard packaging is, in terms of tonnage, by far the commonest
type of paper and paperboard-based packaging. It fulfils two main functions:
•
it is a medium which displays printed information
•
it is a protective or structural entity, particularly in the distribution of goods.
The relative split between these functions by product type is shown in Figure 11.1.
The basic function of corrugated fibreboard packaging is the same as for any
packaging – namely to protect products during distribution until the product is
removed from the package. It may also protect the environment from the product – for
example in the distribution of dangerous goods and liquids in glass or plastic containers.
The growing use of palletization in warehousing and distribution requires
corrugated boxes with good stackability. Corrugated board is an appropriate material
for achieving high stackability, forming a lightweight rigid structure composed of
liners separated by corrugated fluting papers. Moreover, the corrugated-board
package is designed to contain products during distribution. Product containability
and cost-effective adaptation to logistics systems in packing and distribution are
important issues in corrugated-board transport-packaging design.
Physical property
Information
content
Books
Consumer packaging
Distribution packaging
Magazines
Industrial products
Figure 11.1 Relative positioning of functions of information provision and protection. Source: Pira
International – Nigel Jopson – June 2001.
Paper and Paperboard Packaging Technology
Edited by Mark J. Kirwan
Copyright © 2005 by Blackwell Publishing Ltd
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PAPER AND PAPERBOARD PACKAGING TECHNOLOGY
Corrugated fibreboard boxes are erected and packed manually or automatically.
The packaging can be either erected, filled and closed, or formed around the product
and closed. To ensure packing-line efficiency, corrugated fibreboard boxes, also
referred to as ‘cases’ and ‘cartons’, have to present flatness, structural stability and
suitability for closure.
Today, packaging is used not only as a protection for the products contained
but as advertising and brand promotional support. It is a communication medium,
carrying information and artwork, and printing quality has been developed to meet
these promotional needs. The attractiveness of the print can be decisive in catching
the customer’s eye.
11.1.2 Types of corrugated fibreboard packaging
The most commonly used corrugated fibreboard package is the case (box or
carton) with a rectangular cross section together with top and bottom flaps. This
is known as a regular slotted container (RSC) as shown in Figure 11.2. Slots
have to be cut between adjacent flaps to facilitate neat folding when the case is
closed. When corrugated packaging is discussed, creases are often referred to
as ‘scores’. The manufacturer’s joint can be glued, taped or stitched with wire
staples. Gluing provides strong seals and can be carried out at high speeds. Stitch-
ing is not normally used in food packaging or allowed into food manufacturing
factories.
An alternative to the RSC is a wraparound design where the manufacturer sup-
plies a flat blank to the packer. This is folded around the product and the overlap
sealed, Figure 11.3.
Shrink or stretch wrapping, usually with polyethylene (PE) film, is a popular
form of transit packaging. It is cost effective and provides product visibility in
storage and distribution. Product visibility is an important requirement for packs
bought by small shopkeepers in ‘Cash and Carry’ wholesaling, where the quant-
ities purchased do not justify direct supply from the manufacturers. Many products
Figure 11.2 Regular slotted container.
CORRUGATED FIBREBOARD PACKAGING
319
still require a shallow tray to contain a number of unit, or primary, packs. The use
of a shallow tray, Figure 11.4, also facilitates palletization.
A U-shaped fitting to provide increased stacking strength may be used in
combination with a tray and stretch or shrink wrapping, Figure 11.5.
Considerable ingenuity is possible in pack design to produce one-piece packaging
to meet specific market needs. An example, shown in Figure 11.6, is the carry-home
pack for six bottles of wine. This would be supplied as a flat one-piece pack which
is erected by hand on demand.
Figure 11.3 Wraparound case.
Figure 11.4 Corrugated fibreboard tray.
Figure 11.5 Tray with U-shaped fitting.
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PAPER AND PAPERBOARD PACKAGING TECHNOLOGY
Corrugated fibreboard is also used for shock amelioration in various forms,
for example as full-depth interlocking dividers or cells to protect labelled bottles
in a corrugated case, Figure 11.7. Corrugated fibreboard is also used in the form of
pads and fittings to locate and protect vulnerable product components.
A specific in-store use of corrugated fibreboard is the point of purchase (POP)
display stand, Figure 11.8. These stands may be combined with plastic components.
Bag-in-box, two-or-three litre, wine packs are widely used. They combine:
•
product-barrier protection against the effects of oxygen and light through the
use of heat-sealable, metallized plastic laminates
•
selection of plastic material provides leak-proof sealing
•
a bag which collapses as the wine is withdrawn so that air does not enter and
cause deterioration
•
stacking and handling strength through the use of corrugated fibreboard
•
tamper evidence and convenience in use with spouts (taps) and caps
•
high quality printed graphics.
Bag-in-box suppliers support their customers through the supply of all the necessary
pack components and filling equipment.
Figure 11.6 Carry-home pack for six wine bottles.
Figure 11.7 Full depth divider for bottles in case.
CORRUGATED FIBREBOARD PACKAGING
321
Large, heavy and bulky products, particularly in the automotive, chemical,
engineering and electrical industries, are packed in heavy-duty corrugated fibreboard
packaging. The weight of the product on a pallet can be as high as one tonne and
pallets may be stacked two or three high. This often involves packaging which
combines other materials such as plastic foam, plastic components, plywood and
timber, for example corner posts. Heavy-duty corrugated is based on double
and triple wall corrugated fibreboard, high grammage liners, for example 400 or
440g/m
2
, and wet-strength adhesives. Wire stitching and heavy-duty tape can also
be used for the manufacturer’s joints.
Generally, the most common printing used with corrugated fibreboard packaging is
flexo – either as post-print, i.e. after the corrugated board has been made or as pre-print
where it is printed, reel to reel, prior to use on the corrugator. However, other print
processes are used appropriately, for example offset litho for the high quality required
with some, usually branded, higher value, retail packaging; or silk screen for short runs
of POP-display packaging. High-quality printed self-adhesive labels may also be used.
11.2 Corrugated board – definitions
11.2.1 Structure
Corrugated board has a sandwich material structure. It comprises a central paper
(called the corrugating medium, or, simply, the ‘medium’) which has been formed,
using heat, moisture and pressure, in a corrugated, i.e. fluted, shape on a corrugator
Figure 11.8 Point of Purchase display stand.
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PAPER AND PAPERBOARD PACKAGING TECHNOLOGY
and one or two flat papers (called liners) have been glued to the tips of the corru-
gations. The sandwich can be formed in several ways. If one liner is used, the
product is known as ‘single faced’ (Fig. 11.9a). If two liners are used, one on
either side of the fluting, the product is known as ‘single wall’, or double faced
(Fig. 11.9b). The combination of two media, or flutings, and three facings is called
double wall (Fig. 11.9c) and the combination of three media and four facings is
called triple wall (Fig. 11.9d).
Corrugated board is normally made in one of the nine flute sizes, i.e. D, K,
A, C, B, E, F, G and O. The flute size is defined by the pitch, the number of flutes
per unit length and the take-up factor. The pitch is the distance between two
fluting tips.
The take-up factor defines the length of the medium (fluting) material used in
a corrugated fibreboard structure compared with the length of the facings (Table 11.1).
(a)
(b)
(c)
(d)
Figure 11.9 Corrugated boards: (a) single face; (b) single wall; (c) double wall; and (d) triple wall.
Table 11.1 Corrugating flutes’ profiles
Source: ‘Technical Corrugating Roll Data’, BHS Corrugated brochure
by Edmund Bradatsch and Lothar Jobst – July 2000.
Flute
Average number
of flutes per metre Pitch (mm) Take-up factor
D 75 14.96 1.48
K 95 11.70 1.50
A 110 8.66 1.53
C 129 7.95 1.42
B 154 6.50 1.31
E 295 3.50 1.24
F 310 2.40 1.22
G 350 1.80 1.21
O 360 1.25 1.14
CORRUGATED FIBREBOARD PACKAGING
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The properties and specifications of a corrugated board are defined as follows.
11.2.1.1 Weight per unit area (grammage) and thickness (calliper)
The grammage is the weight of one square metre of corrugated board (unit is g/m
2
and measured under standard conditions: 23°C – 50% RH). It can be evaluated
from the component paper grammages using a simple linear formula. For a single
wall corrugated fibreboard, the relation is
Grammage = L
1
+ (a × F) + L
2
where L
1
and L
2
are the liners, F is the medium, with all the measurements being
made in g/m
2
and ‘a’ is the take-up factor.
In the European countries, for a single-wall corrugated quality, the average
grammage is 500g/m
2
and for a double wall, it is around 750 g/m
2
.
The thickness (calliper) is measured under 20kPa pressure. Average values are
reported in the Table 11.2. In North America, weight per unit area is reported in
pounds per 1000 square feet.
11.2.1.2 Strength properties
Bursting strength
The measurement of burst strength is described in ISO 2759. The unit is kPa. The
burst strength of a corrugated board can be predicted using a simple formula. For
a single wall corrugated board, the following equation is applied:
Burst strength= L
1
+ L
2
+ 100
where L
1
and L
2
are the burst strengths of the liners in kPa.
Burst strength is a commonly used measurement for classifying the quality
of the corrugated board. Depending on the grammage and the nature of the liners,
i.e. whether they are made from virgin, recycled or blends of virgin and recycled
fibres, a large range of qualities from 800 to 8000kPa are available.
Table 11.2 Average calliper (thickness) for
different corrugated board grades
Flute Calliper thickness (mm)
D 8.0
K 6.5
A 4.8
C 4.2
B 2.8
E 1.7
F 1.2
G 1.0
O 0.7
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PAPER AND PAPERBOARD PACKAGING TECHNOLOGY
Rigidity or bending stiffness
Rigidity or bending stiffness relates the force required to deflect a flat specimen of
corrugated board through a given angle. Figure 11.10 shows a schematic of the
normal 3-point bending stiffness loading geometry.
On a standard dynamometer, the load (N ) is applied in the centre of the sample
and deflection (m) data are collected using a data acquisition system.
The specimens are cut with a width of b = 5 cm while the length used varies
for the machine direction (MD) or cross direction (CD). MD is the direction of
movement of the board through the corrugator.)
The expression of the 3-point bending stiffness is calculated using the slope of
the load–deflection curve at the origin and the dimensions of the structure by the
following formula:
Bending stiffness (MD or CD)=
where L is the distance between the anvils.
The standard unit is newton metre (Nm) and the corrugated board sample is
tested according to ISO 5628. Bending stiffness is fully expressed by a global
matrix which is described in Pommier & Poustis (1990).
The experimentation carried out with different grammages and qualities of
liners shows that:
•
C flute has a higher bending stiffness than B flute
•
corrugated fibreboard based on kraft liner has a higher bending stiffness
than test liner at the same grammage
•
bending stiffness increases with increasing liner grammage.
Edge crush test
The edge crush test (ECT) is used to evaluate the compression strength of the
corrugated board. The standard unit is kilonewton per metre (kN/m). The corru-
gated board sample is tested according to ISO 3037 for ECT on a sample of
board mounted vertically, with flutes running vertically, between horizontal
platens.
R
M
M
Figure 11.10 Loading principle and deflection for 3-point method.
Load
Defection
-----------------------
L
3
48b
---------
CORRUGATED FIBREBOARD PACKAGING
325
Puncture
The puncture test, Figure 11.11, illustrates the energy required to penetrate the
corrugated board. According to ISO 3036 standard, the measurement is expressed
in millijoule per metre (mJ/m).
Flat crush and hardness
One of the main criteria for the stability of corrugated board is its ability to retain
its structure and its geometry. The traditional flat crush test (FCT) makes it possible
to evaluate and classify the performance of the fluting in accordance with its type
and basis weight. The board sample is tested according to ISO 3035 for flat crush
as illustrated in Figure 11.12.
Flat crush values depend on the shape of the flute and the quality of the fluting.
There is about a 40% difference between semi-chemical fluting and recycled
fluting for a similar grammage (Table 11.3).
Flat crush testing gives the intrinsic performance of the flutes predicted by the
Concora Medium Test – CMT and by basis weight. The flat crush test thus records
how appropriate the fluting medium is for processing on the corrugator.
Figure 11.11 Puncture testing.
Figure 11.12 Flat crush corrugated board testing.
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PAPER AND PAPERBOARD PACKAGING TECHNOLOGY
The concora medium test (CMT) is described in ISO 7263. It is a test of the
compression of the paper after fluting in a fluting apparatus (A flute), shown in
Figure 11.13. The measurements made are CMT
0
, i.e. the compression strength
immediately after fluting, and CMT
30
, which is the compression strength after
30 min conditioning at 23 °C and 50% RH.
As a first approximation, there is a good relationship between the FCT of the
board and the CMT strength of the flutes (Fig. 11.14). Because the thickness
Table 11.3 Flat crush performances for C flute at 23 °C and 50% RH
Board combination
Liners Fluting Grammage (g/m
2
) Flat crush (kPa)
2 × 175 Kraft 140 Wellenstoff 580 260
2 × 175 Kraft 150 Semi-chemical 595 360
Figure 11.13 Concora Medium Test apparatus.
400
300
350
250
200
150
140 160 180 220200 240 260 280 300 320
CMT
30
(N)
FCT(kPa)
Figure 11.14 FCT and CMT relationship. Source: Database SWR-Europe – 1990/1997.