Developments in Barrier Coatings for Paper and Board Packaging

78 Pages·0.642 MB·English

by  Pira International Ltd

Developments in Barrier Coatings
for Paper and Board
Edward M. Petrie
Published by
Pira International Ltd
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Pira International Ltd 2006
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Contents
List of tables v Extrusion versus lamination 37
6
List of figures vi
Executive summary vii
1
Liquid coatings 39
Water-soluble materials 39
Introduction 1 EVOH 39
Paper and board barrier packaging 1 PVOH 40
Objective, scope, methodology 4 Emulsion coatings 41
2
Acrylic emulsions 44
Vinyl copolymers 45
Other aqueous coatings 47
Other liquid coatings 47
7
Current approaches to barriers 7
Consumer requirements 7
Major materials 7
Web or substrate 8
Barrier coatings 11 Nanocomposites 49
Barrier principles 16 Inorganic–organic coatings 49
Barrier classifications 22 Ormocers 49
3 NanoTech Coatings 51
Other nanocoatings 51
InMat 51
Foster 52
Waxes and wax emulsions 23 Triton Systems 52
Hot-melt wax coatings 24 Nanophase and Altana 52
Wax emulsions 24 Avery Dennison 53
Repulpability and recyclability 25 STFI-Packforsk 53
4
Nanofilms 53
8
Metallised papers and films 27
5
Biopolymer barriers 55
Waxes 55
PLA 57
9
Hot-melt, extrusion and laminate
coating 31
Hot-melt coating 31
Extrusion coating 31 Other methods 59
Lamination 35 Fluorochemicals 59
Adhesive lamination 35 Vapour-phase coatings 60
Extrusion laminating 36 Other additives 60
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Advances in High-speed Digital Colour Printing
Contents
1 0
Current and future markets 63
Growth trends 64
Barriers to barriers 64
Emerging trends 64
Stakeholders 65
References 69
Page iv © Copyright Pira International Ltd 2006
List of tables
1.1 Barrier packaging technologies and 5.2 Common extrusion coatings for
applications 3 paper and paperboard packaging 33
2.1 Paper packaging constructions for 5.3 Extrusion coating, extrusion
food use 8 laminating and adhesive
2.2 Advantages and disadvantages of lamination 37
paper packaging 8 6.1 PVdC and PVOH coatings: OTR and
2.3 Some common paper packaging MVTR 40
products 10 8.1 PLA: properties and packaging
2.4 Typical papers and paperboards used improvements 57
in food packaging 11 8.2 Grease resistance of conventional
2.5 Some laminated barrier structures 12 coated papers 57
2.6 Polymer barriers: OTR and WVTR 13 8.3 Grease and oil resistance of PLA-
3.1 Waxes: properties and coated paper 58
characteristics 23 10.1 US patents on barrier-coated paper
4.1 Films with 500nm metallisation: OTR packaging 63
and WVTR 29 10.2 Leading stakeholders in barrier
5.1 Packaging uses of ethylene-based coatings for paper packaging 66
extrusion coatings 32
Page v © Copyright Pira International Ltd 2006
List of figures
1.1 Typical permeance ranges for food 4.1 OTRs and WVTRs for metallised
packaging materials 2 films 29
1.2 Common barrier coatings used for 5.1 Extrusion coating 31
paper and paperboard packaging 4 5.2 Plastic-coated paperboard with a foil
2.1 Solution, diffusion and barrier for aseptic cartons 34
permeation 17 6.1 WVTR for paper substrates with
2.2 Gas permeates only through the 100μm emulsion coatings 42
amorphous phase 18 6.2 Effect of relative humidity and
2.3 Oxygen permeability versus coating thickness on WVTR 43
temperature 19 7.1 Ormocer processing for coatings 50
2.4 WVTR versus temperature 20 8.1 Cumulative carbon loss in soils 56
2.5 Oxygen barrier versus relative
humidity for non-oriented films 21
Page vi © Copyright Pira International Ltd 2006
Executive summary
Barrier properties are enormously important to any packaging for perishable contents.
The permeation of gases (e.g. O , CO ) and vapours (e.g. H O, aromas and flavours)
2 2 2
through polymers is an important packaging problem, and plastic producers can use
several technologies to solve it. One of these technologies is barrier coatings, the
subject of this report. Over the past few decades, several barriers have been used to
reduce the permeation rate of gases and vapours through paper or paperboard. They
include new additives to the pulp and coatings that can be applied on the wet end
of the papermaking machine. Foil and polymeric laminates can be manufactured and
bonded to paper stock to provide the barrier function. Coatings can be applied as hot
melts, extruded polymers or low-viscosity liquids. Barrier coatings can even be applied
to individual cellulose fibres by vapour deposition. All these barrier solutions have some
drawbacks, such as cost, humidity sensitivity, opacity and environmental restrictions.
Consequently, the process of selecting the correct barrier packaging material is often
rather difficult.
Because several technologies are available, the packaging designer must understand
not only the properties of the barrier material but also the service conditions of the
package. Using an expensive barrier coating in a liquid packaging application may not
be cost-effective if the permeation rises rapidly with humidity, if the barrier characteristics
will be lost due to package handling, or if there is inconsistent performance from lot
to lot. Barrier coatings are used in a wide range of plastic packaging products from
carbonated beverage containers and boil-in-bag food pouches to pharmaceutical blister
packs. They are one of several technologies to keep oxygen, moisture, carbon dioxide
and other infiltrating species out of a package to preserve the flavour, colour, odour and
freshness of its contents. They are continuing to evolve and complement emerging resins
and manufacturing processes. Coatings use only a small amount of material, which is an
advantage over the other barrier technologies as it reduces cost and improves recycling.
Their disadvantage is that they add a manufacturing step and the coating equipment is
often expensive. Because they are thin, coatings are susceptible to abrasion and other
mechanical stresses commonly experienced by packaging materials during manufacture
and use.
In the paper packaging industry, barrier coatings primarily include naturally occurring
waxes, organic coatings such as polyvinylidene chloride and ethylene--vinyl alcohol,
polymeric films and metal foils. There are many processes for applying these coatings. The
performance and cost of the ultimate barrier coating depend on the processing methods
as well as the coating materials. Nanotechnology is also providing materials and processes
that can be adapted for barrier coatings. The factors that drive barrier packaging are
primarily shelf life, cost and consumer requirements. Consumers using products away from
home means smaller sizes and more robust packaging. As the number of older consumers
increases, easy opening will become more important. In today’s security-conscious world,
packaging must also be tamper-proof or at least tamper-evident and must prevent the
premature spoilage of products such as food, beverages and drugs.
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Developments in Barrier Coatings for Paper and Board
Executive summary
The development of barrier coatings on paper packaging has been especially important
for milk and juice. These containers are coated with barrier materials to preserve freshness
and taste and to increase shelf life. A similar high-volume application will be needed
to drive further development of barrier coatings. Bag-in-box wine, condiment packages,
microwaveable foods, etc., may provide the required impetus. There is always a need for
a higher barrier at lower cost, especially in structures that maintain barrier properties
even after significant handling. Downgauging interests packaging designers because it
offers reduced cost, but also reduced weight and size. A recent trend has been towards
increasing the barrier properties of the package so that the wall material can be reduced.
This report looks at the current and future state of barrier coatings for paper and
paperboard packaging. It reviews the fundamental principles of barrier packaging
technology. Then it examines and compares existing and potential barrier products
plus their drivers and trends. It gives general coverage of all barrier technologies and
detailed coverage of these barrier coatings for paper and paperboard: waxes and wax
emulsions, metallised films, hot melts, extrusions, laminates, liquid polymeric coatings,
vapour depositions, barrier coatings based on nanotechnology, biopolymers, and chemical
additives that can be added to the pulp or during the papermaking process. Barrier
coating technologies are not only liquid coatings in the conventional sense of the term.
For example, additives can be included into the paper at the early papermaking stages to
provide barrier properties and thin films of plastic can be bonded to the paperboard stock
to provide a barrier function. Thus, the technologies discussed in this report can also
be classified functionally as (1) barrier additives to the paper and board itself, (2) barrier
coatings, and (3) barrier films or foils that can be laminated onto the board. All will be
considered as they perform similar functions. To get a clear picture of performance and
cost, this report considers the coating material and the manufacturing process together.
It highlights any problems with the manufacture and use of advanced barrier coatings
and offers some possible solutions. Chapter 10 considers the future of barrier coatings for
paper packaging and highlights some trends.
Page viii © Copyright Pira International Ltd 2006
1
Introduction
Paper is the oldest and most widely used form of packaging. Technical developments in
the paper and packaging industry have led to an evolution of packaging products to serve
many demanding markets. Among these developments are totally new paper and board
packaging with improved barrier properties.
Paper and board Barriers are important in paper packaging. They optimise product shelf life, but they also
barrier packaging reduce the need for preservatives, provide grease and moisture resistance, and serve as
a printing substrate – they preserve, protect and promote. Without barrier packaging,
perishable goods such as food, beverages and pharmaceuticals would be susceptible to
a wide range of deterioration processes. According to Hersko and Nussinovitch (1998),
more than 25% of freshly harvested fruit and vegetables are lost due to spoilage every
year. Barrier is one of the most important properties of paper containers. Packaging with
a high barrier has been widely used in meat preservation, fruit and vegetable protection,
and corrugated linerboard containers. Consumers increasingly demand convenience and
product safety, which speeds up growth in barrier packaging.
Barrier packaging developments have focused on food applications, but they are not
limited to food applications. The key area has been liquid packaging in cartons for milk,
juices and soups. Strong trends result from the increase in ready meals and takeaway
foods as well as in fast foods, the increasing use of portion packs, and the popularity of
sachet and bag packs for sauces and pet foods. Grease-resistant and greaseproof papers
are also favoured for food packaging. They may be coated for biscuit bags and pet food or
uncoated for sandwich and bakery wraps. Paper and paperboard barriers are experiencing
major competition from plastic films, especially from vacuum-coated and metallised
films in Europe. The paper and board industry is concerned about the continuing trend
to plastic for food packaging; it will need to be addressed if the sector is to remain
competitive. However, paper and board do provide several advantages in packaging and
for this reason the packaging industry consumes about 37% of all specialty papers.
Packaging made from paper and paperboard provides greater recyclability than
plastic films and is generally considered more environmentally friendly. Environment
friendliness underscores nearly all developments in alternative barrier coatings and
packaging materials. Paper and paperboard have one major difficulty in packaging
applications – their low barrier properties. In most cases, paper and paperboard must
be coated with waxes or plastics, or laminated to plastic films to give them barriers to
water, vapours, gases or odours. Paper food containers have customarily been formed
from paperboard extruded with a wax or a polymer layer, such as polyethylene (PE),
polypropylene (PP) or polyethylene terephthalate (PET). Other coatings have been
developed to make food cartons resistant to grease and moisture and for preventing
ink-printed graphics from leaching into the food they contain. Figure 1.1 is a hierarchy
of barrier materials commonly used for food packaging. It shows their permeance to
atmospheric oxygen and nitrogen. Metal and glass have almost zero permeance – they
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Developments in Barrier Coatings for Paper and Board
Introduction
can be permeated by some gases under extraordinary conditions – so the data is
presented on a logarithmic scale.
FIGURE 1.1 Typical permeance ranges for food packaging materials
(cid:31)(cid:18)(cid:17)(cid:13)(cid:17)(cid:17)(cid:17) (cid:39)(cid:70)(cid:77)(cid:85)(cid:84)(cid:13)(cid:1)(cid:71)(cid:74)(cid:77)(cid:85)(cid:70)(cid:83)(cid:84)
(cid:49)(cid:74)(cid:79)(cid:73)(cid:80)(cid:77)(cid:70)(cid:69)(cid:1)(cid:84)(cid:90)(cid:84)(cid:85)(cid:70)(cid:78)(cid:84)
(cid:18)(cid:13)(cid:17)(cid:17)(cid:17)
(cid:18)(cid:17)(cid:17)
(cid:34)(cid:78)(cid:80)(cid:83)(cid:81)(cid:73)(cid:80)(cid:86)(cid:84)(cid:1)(cid:81)(cid:77)(cid:66)(cid:84)(cid:85)(cid:74)(cid:68)(cid:84)
(cid:18)(cid:17)
(cid:37)(cid:70)(cid:79)(cid:84)(cid:74)(cid:71)(cid:74)(cid:70)(cid:69)(cid:1)(cid:81)(cid:66)(cid:81)(cid:70)(cid:83)(cid:84)(cid:1)(cid:66)(cid:79)(cid:69)
(cid:18) (cid:67)(cid:66)(cid:83)(cid:83)(cid:74)(cid:70)(cid:83)(cid:1)(cid:81)(cid:80)(cid:77)(cid:90)(cid:78)(cid:70)(cid:83)(cid:84)
(cid:36)(cid:80)(cid:66)(cid:85)(cid:70)(cid:69)(cid:1)(cid:68)(cid:70)(cid:77)(cid:77)(cid:80)(cid:81)(cid:73)(cid:66)(cid:79)(cid:70)(cid:13)
(cid:17)(cid:15)(cid:18) (cid:81)(cid:66)(cid:81)(cid:70)(cid:83)(cid:84)(cid:1)(cid:66)(cid:79)(cid:69)(cid:1)(cid:67)(cid:80)(cid:66)(cid:83)(cid:69)(cid:84)
(cid:41)(cid:74)(cid:72)(cid:73)(cid:14)(cid:67)(cid:66)(cid:83)(cid:83)(cid:74)(cid:70)(cid:83)(cid:1)(cid:81)(cid:80)(cid:77)(cid:90)(cid:78)(cid:70)(cid:83)(cid:84)
(cid:17)(cid:15)(cid:17)(cid:18)
(cid:17) (cid:46)(cid:70)(cid:85)(cid:66)(cid:77)(cid:84)(cid:13)(cid:1)(cid:72)(cid:77)(cid:66)(cid:84)(cid:84)
Source: Brown (1992: 305)
Barrier properties in paper and board products have been achieved in several ways.
The current methods and developing technologies are the subject of this report. These
barrier coatings include waxes, metallisations, hot melts, extrusions, laminates, organic
liquids (generally water-based but others too), vapour-deposited coatings and chemicals,
nanocomposites, biodegradable polymers, and chemicals added early in the papermaking
process. Liquid coatings are among the most attractive for the paper industry because
of their low raw material costs, processing costs, flexibility, weight reduction and
environmental compliance. The cost of the other barrier technologies may be justified
in some high-value applications. Several of these approaches have been challenged for
environmental and other reasons, but new aqueous barrier coatings for paper and board
products have enabled the sector to meet changing and growing end uses. Environmental
and health regulations continue to evolve and will influence future trends. They have
certainly contributed to growth in aqueous coatings.
Some specialised paper and board products for packaging applications have multiple
functions. For example, pet food outer liners must provide grease resistance as well as
gravure printability and even metallising properties. To add value to a converted paper or
board product, a coating should have these characteristics:
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