Mark J. Kirwan Paper and Paperboard Packaging Technology
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Standards are prepared under the guidance of representative committees and
are widely circulated before they are authorised for publication. They include
glossaries of terms, definitions, quantities, units and symbols, test methods, speci-
fication for quality, safety and performance, preferred sizes and types, codes
of practice, etc. Examples include ‘Recommendations for informative labelling of
textile floor coverings’ or ‘Standards relating to the testing and performance
of labels for use in maritime conditions’ or those for ‘Safety signs and colours’.
It is always advisable to check for possible legislative or standardisation
requirements when designing or developing labels for new applications, requirements
or markets.
4.11 Specifications, quality control and testing
4.11.1 Introduction
Almost all label buyers and label end-users today will expect that the labels they
purchase and use will meet key materials, colour, print, label line and end-user
performance criteria. These criteria will be established with the label printer and
set out in the label specifications prior to the commencement of the job and before
the ordering of the label materials, inks, varnishes, etc.
Many packaging and label end-user organisations undertake their own tests
during the development of new labelling solutions to ensure that the specifications
they draw up for the label printer and converter will meet:
•
all the necessary brand identity and image requirements
•
brand or house colour criteria
•
label line, handling, distribution and end-usage needs in terms of rubbing,
scuffing, durability
•
any product or usage resistance demands
•
any legislative requirements (such as three months immersion in seawater)
•
safety, waste or environmental demands.
Once established in the specifications, the materials suppliers (inks, papers or
films), label printers and converters and application companies will be expected to
check, test and confirm that all criteria and specifications are met throughout the
label order.
Test procedures that are accepted by brand owners, label buyers, packaging and
printing companies, paper and film suppliers, ink manufacturers and the like have
been established over a long period of time by organisations such as Pira, Technical
Association for the Pulp, Paper and Converting Industries (TAPPI), American Society
for Testing and Materials (ASTM International), Graphic Arts Technical Foundation
(GATF), or by the relevant trade or industry associations, such as FINAT, (the Inter-
national Federation of Manufacturers and Converters of Self-adhesive and Heat Seal
Materials on Paper and other Substrates) or Tag & Label Manufacturers Institute Inc.
(TLMI). Some of the more common test procedures or requirements are set out below.
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4.11.2 Testing methods for self-adhesive labels
Testing of pressure-sensitive adhesives has evolved from the subjective
evaluations used in the early days of the industry to the standardised tests now
used throughout the world. Standard tests to assess the adhesive properties of a
self-adhesive label are now published by FINAT (see test methods below) and the
European Association for the Self Adhesive Tape Industry (Afera) in Europe and
by TLMI and ASTM in America. Test methods to measure the three fundamental
properties – 180° peel, shear and quick stick – are described, plus a test for
adhesive-coat weight, which is important not only for performance but also for
commercial reasons.
4.11.2.1 Peel adhesion test method
Designed to quantify the performance or peelability of pressure-sensitive materials,
peel adhesion is measured using a tensile tester, or similar machine, which is capable
of peeling a laminate through an angle of 180° with a jaw separation rate of 300mm
per minute with an accuracy of ±2%. Adhesion is measured 20 min and 24 h after
application – the latter being considered as the ultimate adhesion.
4.11.2.2 Resistance to shear test method
Designed to measure the ability of an adhesive to withstand static forces applied in
the same plane as the labelstock, resistance to shear is defined as the time required
for a standard area of pressure-sensitive coated material (using at least three strips) to
slide from a standard flat surface in a direction parallel to the surface. The resistance
to shear is expressed as the average time taken (for the three strips) to shear from
the test surface.
4.11.2.3 Quick-stick test methods
Designed to allow end-users to compare the ‘initial grab’ or ‘tack’ of different
laminates, the quick-stick value is the force required to separate, at a specific speed,
a loop of material (adhesive outermost) which has been brought into contact with a
specified area of a standard surface. It is tested using a tensile tester, or similar
machine, with a reversing facility and a vertical jaw-separation rate of 300mm per
minute with an accuracy of ±2%. It is an extremely useful test for those working
with automatic labelling equipment where a ‘grab’ or ‘tack’ value is of particular
importance.
4.11.2.4 Adhesive coat weight test method
Designed to determine the amount of dry adhesive material applied to the surface
of a pressure-sensitive label construction, adhesive coat weight is expressed as the
weight of dry adhesive on a standard area of material – in grams per square metre
(g/m
2
). It is tested using a template to cut samples, a circulated hot-air oven and
accurate balance and a beaker of solvent.
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4.11.3 Testing methods for wet-glue labels
A wide range of equipment and apparatus is available for carrying out various test
procedures to establish individual wet-glue label properties. In practice, however,
most bottling and packaging plants only need to apply a limited number of tests.
The more important tests for wet-glue labels and label papers include the following:
4.11.3.1 Tear strength test method
Designed as a simple test for use by bottling plants and small printing companies,
tear strength testing is normally carried out using a tensile testing machine and a
10 or 15 mm wide paper strip.
4.11.3.2 Water absorption capacity test method
Designed to ensure that labels bond quickly and positively, water absorption is
measured by the ‘Cobb’ test. Suitable labels should have an absorption capacity of
between 7 and 11g/m
2
after 60 s of water contact. Labels with a low absorption
capacity may have problems due to the edges lifting after application. Labels with
excessive water absorption capacity will tend to curl excessively. The standard
time for water contact is 60s, but when comparing more absorbent papers a
shorter time may be preferred. In all cases, the time for water contact used in the
test must be recorded.
4.11.3.3 Caustic soda resistance test method
Designed to test the resistance of the label to the effect of caustic soda, resistance can
be tested by placing 120cm
2
of label paper in a sealed measuring vessel containing
20cl of 1.5% sodium hydroxide solution and shaking vigorously (around 30
times). A sample with adequate caustic soda resistance will not disintegrate, while
there should be no contamination of the solution caused by ‘pulping’ of the fibres.
4.11.3.4 Paper weight test method
Designed to test the weight per unit area (basis weight) of a label paper, testing can
be determined with sufficient accuracy by the use of pocket scales. Thickness or
calliper can be measured using a standard micrometer or a special paper micrometer.
4.11.3.5 Bending stiffness test method
Designed to measure the flexural stiffness, i.e. bending strength of paper and
labels, bending stiffness is measured using a bending stiffness tester, e.g., Thuring-
Albert Tester, which provides a comparison of the bending strength of new labels
with that of labels known to handle satisfactorily in labelling machines.
4.12 Waste and environmental issues
Waste and environmental issues have been well to the fore in the label and pack-
aging sectors for several decades and have acquired some notoriety, partly due to
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the high level of visibility that post-consumer packaging and label waste ‘litter’
arouses.
The driving force behind the prominence of environmental issues for packaging
and labelling is threefold: governments, commercial factors and consumers/
consumer groups.
•
Governments around the world, particularly in western Europe and North
America, have introduced measures ranging from container deposits, packaging
levies, bans on certain types of packaging and mandatory recycling rates.
•
Commercial factors and supply-chain issues are playing a role as companies
respond to the environmental challenge. Some retail chains have banned
what they consider to be environmentally unacceptable types of packaging.
They are also responding to pressures from customers and governments.
•
Consumers and consumer groups are showing ever more interest in the
environmental credentials of the products that people buy and the companies
that they buy them from.
Environmental legislation, bringing these various issues together, has been a key
issue for the packaging and labelling industry from the late 1980s, through the
1990s and into the current decade. This existing, and forthcoming new, legislation
is likely to be one of the most important external drivers on the rigid plastics,
metal, glass and paper-based packaging and labelling sectors in the coming years.
Labels and labelling environmental and waste issues follow from an EU Directive
on Packaging and Packaging Waste, as well as from schemes and requirements
introduced by individual countries.
Websites
www.aferta.co
www.gain.net/PIA_GATF/non_index.html
www.finat.com
www.tappi.org
www.tlmi.com
5 Paper bags
Welton Bibby & Baron Ltd
5.1 Introduction
Paper bags, in all their different forms, make an essential contribution to industry
and are a vital part of everyday shopping. Made from a renewable and natural
resource, paper bags are a proven packaging medium – part of the High Street
scene beyond living memory.
Paper offers strength, rigidity, breathability and versatility, and is cost-effective.
This chapter traces the development and use of paper bags from the development
of the early prototype machines right up to the multi-million pound industry into
which it has grown in the first years of the twenty-first century.
The earliest record of machines to make paper bags dates back to 1850. The
leaders in the new emerging market appear to have been Bibby & Baron of Bury,
Manchester. Prior to that many products were probably wrapped in paper and
secured with string.
There were major advances in the growth of the industry from 1850 until World
War II during which period the basic shapes of bags and the machinery to make them
were invented and were being developed. These shapes are flat, satchel (with side
gussets) and – most importantly for the future of the industry – square-bottom
bags, which were free standing. Section 5.4 examines these shapes in more detail.
Printing techniques were also being developed. We again hear the name Bibby
& Baron as the inventors of the flexographic printing process in Liverpool in 1890
(Wmich, 2004). This company appears to have been central to the direction of
packaging manufacture throughout the nineteenth and twentieth centuries. Inter-
estingly, they still trade today as Welton Bibby & Baron in Midsomer Norton,
Somerset, England.
By now, large quantities of paper bags were required for the packaging of
staple foods, such as dried fruit, flour, sugar, tea and coffee. Other products, which
used millions, even billions of paper bags, included coins, potato crisps, ice-lollies
and gramophone records.
Expansion of the industry was checked during World War II. Paper was scarce and
a quota system continued for several years after the war was over.
Manufacture of paper bags continued its inexorable expansion in subsequent
years. Paper-bag makers increased production, new factories were opened and
engineering companies were constructing more advanced machines to make and
print paper bags. Coupled with this, a parallel industry emerged making machinery
for the automatic opening, filling and sealing of paper bags in food processing
factories.
Paper and Paperboard Packaging Technology
Edited by Mark J. Kirwan
Copyright © 2005 by Blackwell Publishing Ltd
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Today, bags are widely used for catering foods, ingredients, pet food, bread,
potatoes, sterilisation packs, vacuum cleaners and the travel industry. They are
also increasingly in evidence at point of sale in the High Street.
The paper bag displays resilience as a form of packaging, quickly adapting to
constantly changing needs and fashions.
5.1.1 Paper bags and the environment
Paper is increasingly recognised by consumers and governments as not only a
natural, but also a renewable and recyclable resource from which to manufacture
high performance packaging.
Paper recycling schemes have become widespread since the 1990s and there is
increasing demand for packaging to be made from previously used materials. In
addition, managed forestry in Europe and North America ensures that we have
a secure future source of supply.
Legislation in the Republic of Ireland in 2002 imposed a levy on plastic carrier
bags and this had an immediate and visible effect of litter reduction. In department
stores, the paper carrier bag has provided a popular and economic replacement.
Other EU nations are considering similar action as they strive to comply with
collection and recycling targets.
5.2 Types of paper bags and their uses
5.2.1 Types of paper bag
The Introduction, Section 5.1 above, gave details of the main shapes of paper
bags, which have been developed over the past 150 years. This section examines
these shapes in more detail with illustrations of the types of bag, their main appli-
cations and the materials used. The main types of paper bags are:
•
Flat and satchel
•
Strip window
•
SOS bags – pre-packed
•
SOS bags – point of sale
•
SOS carrier bags – pre-packed
•
SOS carrier bags – retail/point of sale.
5.2.2 Flat and satchel
5.2.2.1 Flat bags
This is the most basic form of paper bag (Fig. 5.1). It is two-dimensional, and its
use is confined almost entirely to retail point of sale. Much favoured in the retail
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sector by greengrocers, confectioners, bakers, clothes shops, pharmacies and iron-
mongers, most of these bags are produced from white (bleached) or brown kraft.
5.2.2.2 Satchel bags – bags with side gussets
The construction of these bags is similar to the flat bag but additional paper is
folded on each side to form the gussets – hence the term ‘satchel’ (Fig. 5.2).
Figure 5.1 Flat bag.
Figure 5.2 Satchel bag.
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Satchel bags, when opened, have the advantage of being three-dimensional and
provide greater ease of handling and filling compared with a flat bag. Their use is
mainly in point of sale in the same retail sectors as flat bags. Although three-
dimensional, satchel bags are not ‘free-standing’ and therefore have limited use in
factories for pre-packed food and other products. Most satchel bags are produced
from kraft paper but may have a coating or inner ply of a protective material if
required for hot or greasy products, for example bakery and hot snacks.
5.2.2.3 Medical and hospital bags
An important and specialised application for flat and satchel shaped paper bags is
sterilisation packs for medical and hospital use. Bleached white kraft is the preferred
material. Due to the stringent requirements of the sterilisation process, the bag and
the paper must have special properties, which are described in Section 5.3.4.
5.2.3 Strip window bags
These bags are satchel shape but merit a separate classification because of their
special method of construction in which a paper reel is sealed to a reel of plastic
film on the bag machine to produce a strip window. Developed entirely for bread
and baguettes these bags (Fig. 5.3) are used in factory bakeries as well as in
‘in-store’ bakeries. The combination of paper and micro-perforated film ensures
the bread remains fresh. Bags are supplied to large scale factory bakeries in ‘wicketted’
bundles to meet the needs of automatic packing machines, as will be described in
paragraph 5.4.5.
Figure 5.3 Strip window bag.
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5.2.4 Self-opening satchel bags (SOS bags)
For a better appreciation of the uses of this shape of paper bag (Fig. 5.4), one
needs to consider two entirely separate applications:
•
pre-packed products
•
point of sale.
5.2.4.1 SOS bags for pre-packing
The introduction to this chapter emphasises the essential contribution that the
SOS shape of bag has made to manufacturing industry. Figure 5.4 shows the
SOS bag in the folded form as delivered from the bag machine (a), fully open (b)
and, lastly, filled and sealed (c). It shows that the SOS bag, when fully opened,
is free-standing and consequently is ideally suited to being opened, filled and
sealed on fully automatic machinery. Products packed in these bags comprise not
only many basic foodstuffs, for example flour, sugar, cereals, tea, coffee, biscuits
and confectionery, but also food mixes for both retail and catering requirements.
Numerous other industries are served including cat litter, small pet-food packs,
agrochemicals, horticulture and DIY.
The base material used is generally bleached kraft – brown kraft to a lesser
degree. However, a wide range of coatings, lacquers, laminations and protective
lining materials supplement the kraft paper with two main objectives:
•
On the outside of the bag, the aim may be to achieve the maximum visual
impact. This requires a coating on the paper to achieve the best print surface.
Use of gloss or matt over-lacquer or a layer of transparent film printed on
the underside for optimum effect.
•
Inside the bag, additions to the base paper are chosen according to the nature
of the product and protection required, for example length of shelf life, grease,
Figure 5.4 Self-opening satchel bags (SOS): (a) folded; (b) fully open; and (c) filled and sealed.
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flavour and odour protection. This is achieved through grease-resistant or
greaseproof papers, wet strength and plastic-coated papers. A lining of paper
or plastic film or foil is sometimes added to provide additional mechanical
strength or product protection.
5.2.4.2 SOS bags for use at point of sale
The SOS bag is constructed in such a manner that it forms a rectangular base and
can stand up unsupported. This feature, essential for use on automatic machinery
in factories, is also of benefit when used ‘in-store’ and at point of sale. It provides
‘stackability’. Significant markets in this sector include bags, often with windows
of various shapes, for doughnuts and cookies in supermarkets, popcorn bags in
cinemas, ‘pick “n” mix’ confectionery selection and bags for prescriptions await-
ing collection in pharmacies. Bleached kraft is the most popular material in this
sector. Whilst graphic design is important for instant visual impact and the mater-
ial must be compatible with the product, choice of material is less critical than that
described in Section 5.2.4.1. The bag is handed to the consumer very soon after
packing. ‘Shelf life’ can be measured in minutes rather than weeks and months.
5.2.5 SOS carrier bags with or without handles
This section is also divided into two separate categories:
1. pre-packed products
2. point of sale.
5.2.5.1 SOS carrier bags for pre-packing
A large proportion of carrier bags are delivered to factories for pre-packed products.
Due to the weight and bulk of the contents, handles are fitted for ease of carrying
(Fig. 5.5). Among the many products packed in these larger bags, pet foods, cat lit-
ter, potatoes, charcoal for barbeques and horticultural products predominate.
The range of papers used and the reasons for the selection of these materials is
largely as explained in Section 5.2.4. However, physical strength is an additional
factor. Two-ply bags made from strong papers are necessary for many of these
larger packs, which weigh up to 12.5 kg. Many pre-packed carriers have punched
windows using netting or plastic film – particularly those for the potato market,
which were developed by Welton Bibby & Baron.
5.2.5.2 SOS carriers for use at point of sale
This sector, more than any, provides the most public profile for the paper bag. An
attractive paper carrier bag offers excellent publicity for retail shops – a walking
advertisement in the High Street. Not only the retail trades but also manufacturers
who wish to promote their products make use of this powerful advertising medium
by distributing carrier bags to retail outlets. Exhibitions and shows offer an additional
means of publicity.