Polymers in Flexible Packaging Jayshree Khangar, Sonia Rana #
Indian Institute of Packaging E-2, Midc Area, Andheri East Mumbai-400 093 Maharastra India
[email protected] [email protected] Abstract The main aim of this report is to understand the Flexible Packaging Industry and the Polymers used. The Industry - wise break up of Flexible Packaging market. Types of polymers used in Flexible Packaging and their compatibility for different industries like Food & Retail, cosmetic, Pharmaceutical, and Industry products etc. Choosing the right polymers, their manufacturing and printing process. Various Barrier films used in flexible packaging with different laminated structure. Benefits and contributions of the flexible packaging industry and its products. Various advantages like waste reduction, saving energy and reducing greenhouse gas emissions, extended shelf life, easy storage, microwave ability and reseal ability. A comparative analysis of Flexible Packaging Polymers with other packaging material like Rigid Plastic, Glass and Aluminium. New Developments in flexible packaging films such as Breathable properties, Biodegradable films, High-barrier resins, MAP & CAP vacuum packaging, Gas flush packaging resulting in Microwavable pouches, Reseal able Stand-up pouches, Retort pouches and Pouring Spouts are also covered.
B.
Materials TABLE 1 LIST OF PACKAGING MATERIALS
Material Paper & Paper based products
Form Cartons Boxes Bags Wrappers
Plastics
Bag Wrappers Pouches Cartons Bottles Containers
Aluminium
Collapsible Tube Foil Containers Cans Closure
Glass
Bottles Jars Jugs
I. INTRODUCTION A. Packaging Packaging is the technique of storing or placing a product in liquid, solid or powdered form into a protective container or wrapper to protect, carry, identify and merchandise the product. Packaging of any product is a vital link between the manufacturer and the consumer for the safe delivery of the product through the various stages, starting from manufacturing, storing, transporting, distribution to marketing. India’s packaging market is about Rs 40,000 Cr. with an average growth of 15 percent per annum. On an average, packaging costs constitute 45 percent of the final price of the product.
Advantage Low Cost Relative Weightlessness Easy Disposal Easy Availability Ease of Fabrication Highly Versatile Light Weight Highly Corrosion Resistant Ease of Decoration Highly Energy Saving Good Barrier Properties Greaseproof Shrink Proof Tasteless, Odor less Hygienic Transparent Good Strength Higher Rigidity Excellent Gas & Water Vapour Barrier Chemically Inert
Disadvantage Low Tear Strength Low Wet Strength Less Durability
Poor Strength Temperature Sensitive Environment Sensitive Higher Shrinkage Poor Creep Behavior
Not suitable for Microwave oven More Transportation Cost More Shelf Space Higher Weight Fragile High Energy Consumption Light sensitive
Tinplate
Cans Containers
Laminates
Pouches Films Tubes Bags
Good Strength Excellent Barrier Properties Eco-Friendly Longest Shelf Life Good Strength Good Barrier Properties Grease Resistance Heat Seal Property
Higher Weight Corrosive More Shelf Space
Environment Sensitive Temperature Sensitive Lesser Shelf Life
Toothpaste Tubes
Metal
Soaps
Paper
Fertilizers Retail Carrier Bags Oil
Jute Paper, Jute Tinplate, Plastic Rigid Containers
F le x ib le P ac k a g in g C o n s u m p tio n P a tte rn
S nac k s 6%
C.
Flexible Packaging
Rigid vs Flexible
Raw Materials Consumption Sizes Storage & Space Re-use Energy Conservation Reseal ability Disposal
E.
Flexible Light Exact performance requirement by Composite Structure Very less (1 kg pouch weighs 8gm) Suitable for Smaller Packs 60-70% less Not possible 30-40% less (Manufacturing, Transportation ) Possible Easy
Rigid Heavy Better by Composite Technology More (1 kg container takes 40gm) Suitable for Bigger Packs More Can be Re-Used More Not Possible Difficult
Shift in Packaging Trends
Pharmaceuticals
Conventional Glass Glass, Tinplate, Aluminium Paper, Glass
Current Film Pouches PET PVC, HDPE, PP Laminated tubes
O ther N on-F ood 30%
Fig 1 Consumption Pattern
Growth Drivers for Flexible Packaging
Food packaging, stand-up pouches, CAP/MAP, improved barrier properties using barrier resins like EVOH, PVDC, SiO2 Convenience features such as spout, re-closable lid etc. Larger use of laminates with barrier enhancement properties without foil and metallising by using materials like films with plasma coated SiO2 on PET or BOPP as well as nano materials. Biodegradable and renewable resource materials like starch and PLA for avoiding the ecological problems. Solvent less lamination. G.
Key Drivers for Flexible Packaging
The demand for Multilayer films in increasing on account of gradual shift from Loose to Packed products Rigid to Flexible packaging providing lower costs & weight Small pack and shelf appeal
TABLE 3 SHIFTS IN PACKAGING TRENDS Product Milk Beverage
C hew ing Tobac c o 32%
C onfec tionery 6% F ood S taples 6%
F.
TABLE 2 RIGID VS FLEXIBLE Parameters Weight Performance
O ther F ood 11%
Tea 3%
B is c uits 6%
Flexible Package is a material like foil or paper or plastic films sheeting which, when filled and sealed, acquires pliable shape and is used to form products like bags, envelopes, pouch, sachets and wraps Polymers play a vital role in the field of packaging and flexible packages in the form of laminates and multilayer coextruded films are expected to dominate the field. These are mainly used in Retail applications. D.
HDPE, LLDPE, PP Polyester film, PVC PP Woven Sacks LDPE, HDPE PE, LDPE, Nylon Laminates
II. MANUFACTURING PROCESS A.
Extrusion
In the extrusion of plastics, raw thermoplastic material in the form of small beads (often called resin in the industry) is gravity fed from a top mounted hopper into the barrel of the extruder.
The material enters through the feed throat (an opening near the rear of the barrel) and comes into contact with the screw. The rotating screw (normally turning at up to 120 rpm) forces the plastic beads forward into the barrel which is heated to the desired melt temperature of the molten plastic (which can range from 200 °C (392 °F) to 275 °C (527 °F) depending on the polymer). In most processes, a heating profile is set for the barrel in which three or more independent PID controlled heater zones gradually increase the temperature of the barrel from the rear (where the plastic enters) to the front. This allows the plastic beads to melt gradually as they are pushed through the barrel and lowers the risk of overheating which may cause degradation in the polymer Fig 3 Co-Extrusion Process
C.
Blown Film Extrusion
Blown film extrusion is the process by which most commodity and specialized plastic films are made for the packaging industry. The film blowing process basically consists of a extruding a tube of molten thermoplastic. Plastic melt is extruded through an annular slit die, usually vertically, to form a thin walled tube. Air is introduced via a hole in the centre of the die to blow up the tube like a balloon. Mounted on top of the die, a high-speed air ring blows onto the hot film to cool it. The tube of film then continues upwards, continually cooling, until it passes through nip rolls where the tube is flattened to create what is known as a ' lay-flat' tube of film. Fig 2 Extrusion Process
B. Co-Extrusion Co-extrusion is the extrusion of multiple layers of material simultaneously. This type of extrusion utilizes two or more extruders to melt and deliver a steady volumetric throughput of different viscous plastics to a single extrusion head (die) which will extrude the materials in the desired form. This technology is used on any of the processes described above (blown film, over jacketing, tubing, and sheet). The layer thicknesses are controlled by the relative speeds and sizes of the individual extruders delivering the materials.
Fig 4 Basic Blown Film
D. Cast film process Polymer is plasticized & homogenized in the extruder. Melt is passed through coat hanger die. The extrudate comes out of a die as thin, wide curtain of the film. Molten film is quenched in water tank or onto a chilled roll. Finally film is corona treated, slit and rolled.
B.
An alternate bonding method is ultrasonic sealing. In ultrasonic sealing, mechanical oscillations are transferred under force into a polymeric material, which results in heat friction, as well as intermolecular and boundary friction, at the joint to be sealed. The friction causes a build-up of heat and melts the material at the joint. The melted polymer molecules intermingle, also forming a strong bond after the material has cooled and re solidified. An advantage of ultrasonic sealing is that it provides a quick melting of the polymeric material. Further, ultrasonic seals are readily monitored for quality control and can be formed even through any contamination present on the polymeric material. C.
Fig 5 Cast Film Process
Ultrasonic Sealing
Impulse sealing
The process of joining thermoplastic sheets by pressing them between elements equipped to provide a pulse of intense thermal energy to the sealing area for a very short time, followed immediately by cooling. The heating element may be a length of thin resistance wire such as Nichrome, or an RF heated metal bar which is cored for water cooling. It is also known as Thermal Impulse Sealing.
III. SEALING METHODS Flexible films, packages, and methods of making the same are provided where the film is capable of being sealed to itself or to other films by more than one sealing method, including thermal sealing and ultrasonic sealing. A method for sealing a film includes the steps of providing a multilayer film having at least a sealant layer and an outer layer, folding the multilayer film to provide a folded film including at least three layers of multilayer film, and applying mechanical oscillations to seal the folded film flexible plastic packaging for foods and beverages is well known. A.
Thermal sealing
Typically, thermoplastic material can be thermally sealed to itself or another polymeric material. Specifically, heat and pressure are applied to the thermoplastic material for a period of time, referred to as the "dwell time," to melt the polymers. The liquefied polymer molecules at the joint are thus allowed to intersperse, forming a strong bond once the polymeric materials cool and resolidify. Thermal sealing may be easily performed in a continuous manner and is inexpensive to incorporate into a machine design.
IV. POLYMERS IN FLEXIBLE PACKAGING A.
Desirable Attributes of Commonly Used Flexible Materials TABLE 4 FLEXIBLE SUBSTRATES & ATTRIBUTES
Flexible Substrates Paper Foil Cellophane LDPE EVA HDPE BOPP Polyester PVC Nylon Coating Materials Paraffin Waxes PVDC Ionomer
Primary Functions Stiffness and Printability Barrier Properties & Aesthetic Appeal Clarity & Printability Heat Seal ability & Barrier properties Strength & Heat Seal ability Stiffness & Low EVTR Clarity & Barrier properties Impact & Barrier properties Economy & Versatility in uses Strength, Grease & Oil Resistance Primary Functions Low Temperature Seal ability Grease Resistance & Barrier properties Heat Seal ability & Grease resistance
Lacquer
Gloss
C.
Flexible Packaging Polymers
Permeability to Gases
P ET 10%
TABLE 6 PERMEABILITY TO GASES PP 31%
PE 59%
Fig 6 Flexible Packaging Polymers
B.
Mechanical Properties of Polymers TABLE 5 MECHANICAL PROPERTIES OF POLYMER
Propert y Thickne ss Yield (per kg of 25 micron) Tensile Strength
Uni t Mic ron m2
Elongati on
%
Tear Strength
45
HD PE 0.95 5 42.5
LD PE 0.92 5 43.5
Cellop hane 1.4 1.5 27 29
PVC 1.2 1.5 28 - 32
190
150 200
800 1000
200560
-
10-50
25-60
812
-
10
10
100
-
1012
20-12
30-40
Gloss
g/25 mic ron Mul len/ poin ts %
200 800 50200
785
76-82
Haze
%
2
2-4
8-198
Heat Seal Range
0C
90140
075 450 120 200
120175
175215
85
040 1050 135 200
N2 7 18 15 0.06 50 1 80 5 20 3 25
O2 35 90 75 0.3 250 5 400 25 15 100 125
H2O 140 360 300 300 1000 20 1600 100 60 400 500
CO2 175 450 375 1.5 1250 25 2000 125 75 500 625
SO2 280 720 600 2.4 2000 40 3200 200 120 800 1000
10
50
200
250
400
All figures in g cm / cm2 h (mm Hg ) *10^12 D.
Monolayer – Shrink Films TABLE 7 MONOLAYER SHRINK FILMS
100 0150 0 70100
Burstin g Strength
Kg/ cm2
BO PP 0.81
Films BOPP PP HDPE PVDC LDPE PVC EVA Cellophane PS Nylon11 Cellulose Acetate Cellophane
Film Type PE (Low Density)
Advantages Strong Heat Seals Low Temperature Shrink Lowest Cost
PP
High Stiffness High Shrink Force Good Durability
PP (Copolymers)
Strong Heat Seals Good Optical Appearance High Shrink Force
PVC
Lowest Shrink Temperature Excellent Optic Lowest Shrink Force for Wrapping Fragile products
Possible Problems Narrow Shrink Temperature Range Low Stiffness, Poorer Optical Contamination High Shrink Temperature Not suitable for Fragile products Brittle Seals Higher Heat Seal Temperature Lower Film Slip Higher Shrink Temperature Weakest range seals Corrosive Gas Emission from Heat Sealing Low Film Slip
E.
Multilayer Films – Two Layer Films TABLE 8 MULTILAYER FILMS
Material Combination LLDPE/EVA PP/EVA
EVA/HDPE
Properties
Applications
Easily Welded Seal ability Can be Sterilized Transparency Stiffness Seal ability High Strength Sterilisable
Stretch Wrap Medical Articles Baked Goods Food Stuff Tomato Purce Pet Foods Corn Flakes Blood Plasma Baked Food Packaging Film for Bread, Jam, Dairy Products Packaging film for Meat, Cheese Coconuts Cocktail Snacks Milk Bags General Packaging
PP/PP
Easily Weld able Easily Printable Smooth Surface
PA6/Ionomer
Good Seal ability Gas & Aroma Tight Grease proof
EVA/Ionomer LDPE/LDPE
Micro pore Sealed Multi Colored
Fig 7 Multilayer Film Structure
G. F.
Multilayer Films – Three Layer Films
Structure TABLE 9 STRUCTURE OF LAYERS
3 layer
Outer layer Middle layer Inner layer Outer layer Bonding layer
5 layer
Middle layer Bonding layer Inner layer
Printing, Seal ability, strength & barrier Strength, barrier mainly gas aroma retention Seal ability, Machine ability, strength barrier Printing, Seal ability, Strength Good bond strength, compatibility Gas barrier strength Good bond strength Machine ability, Seal ability, Strength, Hot Tack Strength.
TABLE 10 2 LAYER FILMS Material Combination PP/ PP + Chalk/PP
PP/ PP + Regernate /PP LDPE/EVA/PP
EVA/LLDPE/LDPE
Ionomer /PA/ Ionomer
Properties
Applications
Low Shrinkage Smooth Outer Layer Easily Printable Low Temperature Resistance Low Material Cost High Impact Resistance Non Stick Outer Layer Good Transparency High Extensibility Good Adhesive Properties
Precooked Packaging
Good Seal ability Good Transparency Reduced tendency to Roll
Deep Packs
Food
Freeze
Blood Packaging Bag Production
Stretch film for Palette Packaging Adhesive Packaging Sheet Vacuum Packaging
H.
Materials used in making packaging pouches are Polyvinyl Chloride, Polyolefin, PP, Polyester etc.
Multilayer Films – Five Layer Films TABLE 11 MULTILAYER FILMS
Material Combination LDPE/ION/PA/ION/L DPE LDPE/BA/EVOH/BA/ LDPE LDPE/Bonding/PA6/B onding/LDPE
I.
Types of packaging pouches
Properties
Applications
Gas, Steam & Aroma Tight No tendency to curl Gas, Steam & Aroma Tight Moisture Barrier Moisture Barrier Good Seal ability Good Transparency
Meat, Fish, Cheese
Milk Powder Wine Packaging Fish Vacuum Packaging Packaging of Sausage, Meat, Ham
Packaging Polymers in Different Industries
TABLE 12 POLYMERS IN DIFFERENT INDUSTTRIES Industry Polymers Used Pharma •Nylon/Foil Laminates •Paper/Foil Laminates •Polyester/Foil Laminates •LDPE foils •PVC-coated Paper •Aluminum foil laminates •Tube laminates •Sachet/pouch laminates •Blister lidding •Cold formed laminate etc Food Packaging of fresh PET, Nylon, PE Laminates, and frozen food Aluminium foil Ready-to-eat Films coated with Aluminium or packages (PVDC) or metalized and clear PP films Diary •Metalized plastic films •PVDC coated films •Laminates – Polyolefin, PP, LDPE/PE, LLDPE/PE •Nylon •LDPE
V. TYPES OF FLEXIBLE PACKAGING A.
Packaging Pouch
The packaging pouches are used for packing all kinds of items but not large quantities. The packaging pouches or sachets provide sealing safety. The greatest advantages of pouches are that they have excellent print ability with easy tearing material.
1)
Vacuum Pouch
Vacuum pouches help preserve the sealed product in cold and hot temperatures and are used in conjunction with vacuum packaging equipment. These pouches reduce the atmosphere in a package to protect and preserve the freshness of food products, like meat and poultry, seafood, cheese etc. They are also used to keep other non-food products like medical and pharmaceutical items sterile and to prevent oxidation. This vacuum packaging and can be UV resistant. They extend the shelf life of products as the vacuum slows down the oxidation process. 2) Stand-Up Pouch Also known as SUPs have actually changed the face of consumer packaging for various products like coffee, milk, fruit juice, and soup mixes. They have a definite use for industrial applications as well Stand up pouches give retailers new opportunities to display products and maximize shelf space. Manufacturers can also reduce their packaging costs by eliminating the original style of bag-ina-box method of packaging. The wide face of the SUP is perfect for an elaborate label or high quality print design. Stand up pouch with spout is just perfect for beverage packaging. 3)
High Temperature Retort Pouch
High temperature retort pouches are considered to be good barrier to gas, moisture, smell and light, and used to pack vegetable, bamboo, Ready to eat food etc. They are resistant to oil and contamination. These pouches are made from high quality raw materials like Aluminium, PET, PE, composite, laminated, strong, and can be high temperature cooked. They can be heat sealed. They are suitable for gas conditioning packaging and microwaveable food packaging and processed foods. Due to the flexible pouch being thinner and heating more efficiently, process time is shorter and processing temperature lower. B.
Packaging Bags
Packaging bags are available in a wide variety of shapes, styles and materials. These bags are used for holding objects in bulk. They are used in a variety of applications. Packing bags are meant for everyday use. They are convenient to use and protect various contents through safe storage. They have visual appeal. Materials used in making packaging bags are Plastic, Nylon, and Polyester etc.
Types of packaging bags B. 1) Vegetables Bag Specially designed to store vegetables and fruits in refrigerators. They are breathable bags to keep vegetables and fruits fresh. 2) Vacuum Bags A good packaging bag to pack frozen food, red meat, bread and process meat and which also which lengthens the shelf life of the food. 3) Woven Packaging Bags Woven bags in both laminated and un-laminated variety are capable of bearing heavy weight. 4) Courier Packaging Bags Such bags are high quality, water-proof packaging bags which find wide application in the postal departments and courier agencies.
C. Laminated Tubes Laminated Tube has a sleeve comprising even up to 10 layers. A threaded or a plug-type, which is injectionmoulded is also provided. TABLE 13 TYPICAL STRUCTURE From Outside to Inside Layer LDPE & Antistat LDPE/Printing Ink White pigmented LDPE Paper LDPE Ethylene Acrylic Acidic Copolymer Aluminium Foil/Met Films Ethylene Acrylic Acidic Copolymer LDPE
Function Dust Preventive Printed Cover Back-up for Printed Surface Non-stretch web-base Paper Lamination/Primer Bonding Layer Barrier Bonding Layer Sealant Layer
VI. NEW DEVELOPMENTS A.
MAP
The Shelf-life extension is achieved by ‘Modifying the atmosphere inside the structure. Generally this is done by injecting gas mixture inside the container – either Carbon – Dioxide, Nitrogen or Oxygen. In most MAP applications, conventional Multilayer, high barrier films such as a 5 layer LDPE blown film with EVOH, Nylon, PVDC as barrier layer is used. This is mainly used for Perishable Foods.
CAP
Intentional alteration of the natural gaseous environment and maintenance of that atmosphere, at a specified condition through out the distribution cycle regard less of the temperature or other environmental variations. C.
Bag – in – Box
Bag-in-Box is bulk packaging system for both solids and liquids. It consists of a collapsible bag housed in a rigid outer container. The bag actually consists of 2 bags: an inner bag to contain the liquid and an outer one to provide barrier properties. The inner bag is heat sealed around the edges to the outer bag. A tubular spout is heat sealed onto the inner and outer bags during the bag manufacturing process and is fitted with a valve through which the product is filled and dispensed. Combination of LDPE, HDPE, LLDPE, VLDPE, EVA, Metalized Polyester and Nylon are most commonly used for most bag applications.
D.
High Barrier Resins –
Polyolefin Plastomers Performance Superior Seal Ability High Hot Tack & Heat Seal Strength Low Heat Seal Initiation Temperature Excellent Optics Very Good Toughness Good Process Ability Cost Efficiency
E.
Benefits Package Integrity & Faster Filling Speeds
Consumer appeal Package Integrity Can run on LLDPE lines Much lower cost than Ionomers
Vacuum Packaging
The vacuum environment removes atmospheric oxygen, protecting the food from spoiling by limiting the growth of aerobic bacteria or fungi, and preventing the evaporation of volatile components. Vacuum packing is commonly used for long-term storage of dry foods such as cereals, nuts, cured meats, cheese, smoked fish, coffee, and crisps. It is also for storage of fresh foods such as vegetables, meats, and liquids such as soups in a shorter term because vacuum condition cannot stop bacteria from getting water which can promote their growth. Vacuum packaging food can extend its life by up to 3-5 times. The mainly used polymers are EVOH, PC, PVDC, Nylon etc. F.
Slider Zipper
The printed and laminated stand up pouches with zip lock are provided smooth and stable finish with wide sealing, temperature tolerance. These features make it compatible to store contents on extreme temperature. These pouches have been provided such dimensions that can be used to position these pouches straight in display. G.
Spouts
The pouch can contain a multitude of liquid and semiviscous products, including a wide variety of condiments such as tomato ketchup, mayonnaise, sauces, gravies and beverages. The current non-food applications are for products such as shampoo, lotions, detergents, motor oil and paint. The spout closure may be applied and positioned in the top corner, top centre or front panel. A spout can even be sealed into the top or bottom gusset of the pouch, depending on the specific design attributes of the application. I.
aluminum foil
Breathable Films
“Films allowing the transfer of the gases at moderate to high transmission rates are considered as breathable.” Breathable films are capable of transmitting water vapor but resistant to the passage of water in a liquid form. A film is called as "breathable" if it has a water vapor transmission rate of at least 100 g mil / day / m2, measured using ASTM E96-93 method, with minor variations as described in the test. (7, 8, 9) . Breathable films are produced by compounding a PP or PE resin with mineral filler.
J.
Retort Packaging
Retort able Flexible packaging materials are defined by the ASTM as ‘those capable of withstanding specified thermal processing in a closed retort at temperature above 100 degree C. The polymers used are PET, PC, and PP. It is preferred for low acid food with moderate to large-size particles because of ease of removing oxygen from the head space by gas flushing and also because a crisp texture obtained through freezing is possible only with the retort packaging system. K.
Aseptic Packaging
Aseptic Packaging involves a sterile product that is sealed into a sterile package under sterile conditions thus eliminating the need to sterilize the product package system after filling. The commonly used polymers are PET, PVC, and PVDC. These are used for packaging of Jams, Jellies, and Sausages etc. VII. REFERENCES [1] Library Reference Indian Institute of Packaging, Mumbai Indian Plastic Institute, Mumbai [2] URL http://packartpackaging.tradeindia.com http://www.packaging-films.com http://www.marketresearch.com/product http://www.medicalpackagingindia.com/industry http://www.expresspharmaonline.com www.flexpackmag.com www.flexpack.org
TABLE 14 BREATHABLE FILMS
Breathability testing The gases which are most commonly used to describe the breathability of films are water vapor (moisture vapor) and oxygen. The water vapor transmission test (WVTR) and oxygen transmission test (OTR) are used to measure the mass or volume of gas transported through the crosssection of the film in a given unit of time at a defined set of environmental conditions. (6) This test procedure follows the Modified ASTM E96-93 test. (4)
petri dish
water
Press to Close Zipper
The Double Zipper ensures complete bag closure and provides added seal security to lock out air and keep foods fresh. It features two sets of interlocking profiles strategically spaced to guide consumers' fingers along a path when closing a package. As a result, the closure mechanism is more easily aligned, providing a complete seal each time the product is used. H.
25 cm3 sample
[3]
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