Stretch-hood Film At this moment the stretch wrapping foil is dominating the pallet packaging market. Stretch wrapping foil has to be turned under tension around the pallet. With the help of its memory, the foil tries to get back its original form. By doing this the pallet is being held together strongly. This type of pallet packaging can be done manually either machinally. Another way of pallet packaging is using a shrink hood. Here a plastic hood with a size a bit larger than the pallet is sliced over the pallet. When done the foil needs to be heated in order to shrink. By shrinking the foil, the goods are strongly kept together onto the pallet. This type of packing can be done manually (but you still need a heater of course) either on fully automated lines. Since more than ١٠ years a new type of pallet packaging has been developped. This new packaging technology was possible thanks to narrow cooperation between packaging machine constructors and polyolefin manufacturers. The result is a revolutionary packing way having the pallet packed hermetically, strongly, cheaply and fastly. Next paragraphs describe principles of Stretch hood wrapping technology, compare with other types of wrapping and offer Bocedi wrapping machines. Era-pack, s.r.o. is exclusive sales representative of company Bocedi for Czech Republic. Packing principles Opening Winding Tension Cover Packed When a pallet of goods is completed, it is moved to the stretch hood installation. This can be done either by roller conveyors or the pallet can be put directly on to the stretch hooder with a fork lift. Note that the pallet is put on a kind of piedestal. Thanks to this piedestal the machine will be able to cover the pallet with stretch hood foil until under the pallet which makes the pallet completely hermetic from the outside world! Once positionned on the machine an electronic eye is measuring the height of the pallet. Some more sofisticated stretch hood lines are also looking at the dimensions of the pallet. In function
of this information the machine will choose which stretch hood foil to use (in that case two foil formats are mounted on the line). Note that with one size of stretch hood foil you can pack several formats of pallets, but when they differ to much you need to use different foil sizes (e.g. for ٦٠٠x٨٠٠ mm and ١١٠٠x١٣٠٠ mm pallets you should better use two formats of tubular stretch hood foil). With all these dimensional informations the machine will roll of the needed length of the correct stretch hood foil. Once the length reached, the foil is sealed together and cut of the roll. The foil has been rolled of on four mechanical arms. This process is very important because it influences a lot the end result of the packed pallet. When badly positioned on the arms, the stretch hood will show up wrinkles or it will not be put equally over the four sides of the pallet. The mechanical arms are going down until under the pallet, by doing this the stretch hood is placed nicely over the pallet and from the moment that the stretch hood foil leaves the mechanical arms the foil comes back to its original format helding the pallet together! The smaller the original stretch hood size was, the higher the tension will be on to the pallet. For some applications a maximal tension is desired (eg. stone bricks), but for other applications this has to be avoided (eg too much tension on a tetra pak milk pallet could deform the boxes). The job is done, the arms are going up again and the pallet can be taken of the stretch hood line, ready to be piled up in the warehouse and to be shipped safely all over the world! Comparison between different packing systems Stretch hood packaging technology means improved packaging quality! Pallets packed by stretch hoods are absolutely waterproof: the foil covers the entire pallet and goes until under the pallet. When using a plastic sheet on the pallet before piling up the goods, the pallet will even be waterproof from under to up the pallet! With stretch wrapping foil you have only horizontal tension to keep the pallet together, with stretch hoods you have tension in both horizontal and vertical directions, this means that the goods are pressed downwards on to the pallet. Moreover the holding force on the goods is higher than with shrink hoods or stretch wrapping foil. Stretch hood technology doesn't need an oven to be warmed. By consequence energy consumption is very low. This also means more safety on the workfloor and lower insurance fees due to lower fire risk!
The stretch hood foil has the advantage that it follows narrowly the form of the pallet. This is very important when you work with irregular pallets. Stretch hoods don't stick to the goods piled on the pallet! With shrink hoods you could be confronted with melted plastic on the shrink foil underneath (example cans in shrinkfoil or plastic bags on pallet packed with a shrink hood). With stretch hoods this problem cannot occur! Stretch hood technology has the opportunity of being very fast. With one single performant line you can easily pack more dan ١٥٠ pallets an hour! With one foil size you can wrap different sizes of pallets! Their are certain limitations but with two dimensions you should be able to cover most of the standard pallet, going from half an europallet (٦٠٠ x ٨٠٠ cm) until a double europallet (١٢٠٠ x ١٦٠٠ cm). The optical properties of the stretch hoods are much better. It's possible to produce film with an excellent transparancy and a very high brillance. Foil consumption is lower with stretch hoods than with shrink hoods. Since stretch hoods are being used thinner and thinner it becomes even more economic as stretch wrapping foil! Using less materials for a same packaging is also more ecological! Another interesting point of using stretch hoods are the low maintenance costs of the machine due to less moving parts and less heated parts than other packaging systems! Comparison between different packaging systems Property Stretch hood Shrink hoods Stretch foil Holding strength Highest High High Energy consumption Low High Low Roll changes Fewest Few Many Film consumption Low High Low Optical properties Highest High Low Manual wrapping No Yes Yes Automated wrapping Yes Yes Yes Water proof Yes Yes No Packaging speed <٢٠٠ pallets/h <١٠٠ pallets/h <١٠٠ pallets/h Safety at packaging High Low High Ability to recycle foil High High Low Investment cost Medium High Low Printability High High Low Pallet diversity Medium Low High
THE GLOBAL FLEXIBLE PACKAGING MARKET, NOW AND ٢٠١٥, PIRA, BRUSSELS ٢٠٠٥ PIRA, Brussels ٢٠٠٥ Flexible Packaging ٢٠٠٥ PIRA ٥th International Conference ١٩th-٢٠th October ٢٠٠٥, Brussels Belgium Types of films and materials The processing of any plastic into a film calls for the plastic to be melted, fed into a shaping exit die at a metered rate, cooled and fed to a wind-up station. Many variants and complexities can be added to this simple concept. The die can be flat or annular for either cast or tubular films. All flexible packaging, films, laminates, paper, foil, cartons, cases, bags, pouches, labels, all start as material on a reel. Then the converters add value by printing, shaping, coating, metallizing, laminating, stamping, slitting, forming, folding. Plastics for films A wide variety of plastics materials are used, plus the combinations of these films, as multilayers by all the processes to obtain them, whether the final films are all plastics or a combination of plastics and other materials such as paper, cardboard and aluminium foil. Polyethylene films The PE films are the largest tonnage of all plastics films. Originally, low density polyethylene PE-LD, were the first plastics films in current use, back in the ١٩٥٠s. In spite of down gauging, increasing environmental requirements and the greater use of recycled materials, the average annual growth rate of PE films ranges ١-٣ % in the industrialized countries. In the rest of the world, the rate of growth is much higher, up to ١٠ % a year. Consumption of PE films in Europe, all types, in thousands of tons, estimates in ٢٠٠٥ Types of films Consumption Shrink films, collating and pallets ١٠٠٠ Stretch films, hand and machine ٩٠٠ Film for automatic machine wrap ٦٠٠ Other films for coating, lamination, multilayers ٧٠٠ Heavy duty bags ٤٥٠ Other industrial bags, large bags, liners ٤٥٠ Shopping, retail, household bags ٧٠٠ Refuse bags ٥٠٠ Films for agriculture ٥٠٠ Films for building construction ٤٠٠ All other films, diapers, ٦٠٠ Total estimated ٦٨٠٠ Sources: various, Pardos Marketing estimates, PE producers, film industry, etc.
The largest applications of PE films in Europe are shrink and stretch films that account for more than ١.٥ million tons of PE, or ٢٥ % of the total PE film consumption. The agricultural segment grows in hot house films and goes down in silage and covering films. Shopping and carrier bags are severely attacked on environmental grounds and are imported from Asia, increasingly. In general the consumption, extrusion of PE films in Europe, has remained stagnant at best, this being due to a number of reasons: Decrease of thickness, up to ٥ % per annum, with increasing use of PE-LLD Massive imports of low priced finished products, such as shopping and retail bags Polypropylene There are two types of PP films, oriented and cast. There are more than ٢٠٠ BOPP film producers worldwide, the ten largest accounting for ٤٠ % of the market. The recent increases in BOPP film capacity have been in China, with a proliferation of small plants, often for in-house manufacturing of capacitor films, tapes, labels, and packaging. While the BOPP film industry is quite fragmented in China, there are a few larger scale players emerging. The global BOPP film demand is to grow an average ٧% per annum, the demand in Asia accounting for more than half of this global growth. World consumption of BOPP should reach ٦ million tons by ٢٠١٠, of which China will be at least ١ million tons. The main uses of OPP films are: Food packaging is the main application٧٠ % of total OPP consumption Adhesive tapes ١٥ % Tobacco ٣ %, and going down All other applications, including capacitors ١٢ % BOPP films dominate snack food packaging and provide effective barrier when layered with EVOH or metallized. Other important applications are chips, biscuit, confectionery, dry and fresh bread. In spite of strong growth in demand, the industry has tended to suffer from poor margins, as producers have sought to increase or protect their market share. The competition has been particularly active in Asia and South America, where overcapacity in PET film production has kept the price low with greater competition with BOPP films. As the packaging industry is becoming increasingly global, and major food producers want to deal with as few as possible suppliers that can operate on a world wide basis, the regional players have to specialize or consolidate. PVC One of the earliest plastics produced in quantity was PVC, and it is still an important film material, although fast decreasing. The distinction between film and sheet is slightly blurred as there is a large category of thin rigid films that can be thermoformed, yet thin enough to be
called film. As a rule, the suppliers, for each of their products, offer a thickness range of ٥٠ to ٩٠٠ microns and over, making the distinction between film and sheet quite uncertain, and only applicable through detailed analysis of each of the very many applications. The split of thin PVC film applications in Europe, about ٤٠٠ ٠٠٠ tons total, is estimated: ٧٠ %, for food, non food, visual packaging, display shrink, pharmaceutical Packaging total blisters Adhesive tapes ٩ % Technical ٢١ %, print, stationery, furniture, cards, others applications With technical applications such as furniture coverings, the safety aspect of fire resistance plays an important role, as the chlorine atom present in the PVC molecule has built-in flame retardancy. Polystyrene and derivatives BOPS, bi-axially oriented PS, was first developed in the mid ١٩٣٠s for use in electrical applications, capacitors, and it was the first polymer to use a biaxial orientation system. Then the primary use became packaging. The global OPS film production capacity is currently estimated at ٥٠٠ ٠٠٠ tons, interestingly only in the US and Asia, Europe hardly present. BOPS sheet can be used in many applications, but its primary use is in packaging. The film /sheet are used for cookie and candy trays, bakery product containers, salad containers, cup lids. It is widely used for prepared fresh food containers, in supermarket and delicatessen, as thin and transparent thermoformed containers. PET PET film is generally produced by the producers of resins and not by the plastics processing industry. From its origins in the forties, by Hoechst, it was one of the very first products to be very concentrated with world producers. Polyester film is a global business, dominated by a small number of international producers that went through several major mergers and acquisitions in the last three years. The total consumption of PET film in the world was estimated at ٢.٢ million tons in ٢٠٠٥, up from ١.٢ million in ١٩٩٧, because of sustained growth in packaging applications. Out of this total consumption, the captive market is estimated at ٢٥٠ ٠٠٠ tons, held by photographic, reprographic and magnetic tape making. The merchant market develops most of the growth, because of the very active demand in packaging. The outlook for the years ٢٠٠٥ to ٢٠١٥ gives an average annual growth of ٥% led by new applications in packaging, the growing demand in Asia and less developed countries, and slowed down by downgauging in packaging, sharp decline in magnetic tape, stagnation in other applications.
The thin PET film continues to grow very actively in Asia, particularly India and Indonesia. The growth in packaging is slightly slower in the industrialized countries, yet kept up with a number of niches and specific applications such as metallized films for packaging. Derivatives of PET films, with niches of their own, are PETG and PEN films. Polyamides Polyamide is widely used as one functional element in flexible food packaging and multilayer films, due to a unique combination of properties, toughness, transparence, medium barrier. There are three categories of nylon films: Oriented PA, bi-axially, or BOPA, and mono oriented PA, OPA, altogether ١٠%/y growth Cast PA films, used for lamination with PE, in medium barrier multi-layer films stagnant PA ٦ resin used for coextrusion with PE, growing, yet more slowly than the ٣ % BOPA films Nylon film is not really threatened by other plastic films in its specific market niches. The oriented laminates are particularly appreciated for the good mechanical resistance, against puncture and tearing. A ١٥ µm OPA film has twice the puncture resistance of a ١٢ µm PET film. The production of oriented nylon films has long been, and still is, a fairly small club. There have long been licenses, for the machines, that have limited the entry of new producers. The world consumption of nylon films, all types, is estimated at ٣٢٠ ٠٠٠ tons, split as: BOPA and OPA nylon ٦ films, for ١٢٠ ٠٠٠ tons lamination Non oriented cast film, for lamination ٦٠ ٠٠٠ PA ٦ coextruded with other plastics ١٤٠ ٠٠٠ There are a relatively limited number of applications. The main uses are: Hard cooked cheese, about ٤٥ % of total Other cheese, about ٥% Coffee ٥% Processed meat, fish, smoked salmon, lidding ٣٠ % Other food ٥ % Non food packaging ١٠ % Cellophane This material is considered closer to nature than plastics. Indeed from its wood base, cello biodegrades in six weeks, and can be disposed off in land fills or composting, like paper. From the ١٩٣٠s to the entry of OPP films, cellophane had dominated the transparent flexible packaging materials. OPP film replaced cello within a ١٥ year span, ١٩٧٠-١٩٨٥, because of lower cost, source reduction, strength and higher barrier properties. Back in ١٩٨٣, the world cellophane consumption reached its maximum with a total world tonnage of ٦٠٠ ٠٠٠ tons. From that date OPP films started to substitute, so that, by ١٩٩٠, the cello film total was down to ٣٠٠ ٠٠٠ tons, to ٢٠٠ ٠٠٠ tons in ١٩٩٤, to ١٤٠ ٠٠٠ tons in ١٩٩٧, of which ٤٠ ٠٠٠ tons in Europe and
still ٦٠ ٠٠٠ tons in Japan. Now the total world consumption has dwindled down to less than ٧٠ ٠٠٠ tons, a perfect case of the replacement of one material by another, as PP films have taken over all the cello markets, plus all the growth, leaving only a few niche applications, in the last twenty five years. About ٧٥ % of cellophane is used in food packaging and the balance in non food, cosmetics, medicals/pharmaceuticals packaging and pressure sensitive tapes. Many other materials play a role in films, whether alone or associated with other materials. Without a long description, just a list, probably not exhaustive: Ethylene copolymers, acid copolymers also used as tie-layers, in flexible packaging that require interpolymer adhesion between materials in a multi-layer structure, for instance involving inter contact between PE and EVOH as a barrier layer. Main materials, with ethylene basis, are, EVA, EAA, EMAA, EEA, EBA, EMA, etc. Ionomers Cyclo olefin copolymers, COC Polyvinyl butyral PVB, not used in packaging Polyvinyl Alcohol, PVOH Liquid crystal polymers LCP Polyarylamide MXDC ٦ Amorphous PA Polyimides Fluoropolymers Barrier materials The concept of barriers applies to a protection against external agents that attack and deteriorate the contents of any product supposed to be protected by its plastics envelop or container. The barrier concept most frequently applies to packaging, to protect the product inside and lengthen its useful life, but it may also apply to other containers, such as gas tanks in cars or other equipment such as pipes, outside of the film industry. The rise of new packaging materials is closely linked to barriers, search for a lasting protection of packaging contents against external agents, particularly gases, mainly oxygen, water vapor water, fats, chemicals, odors and flavors, aromas as well as preventing gases, water vapor, odors from escaping the package. The search for packaging materials with improved barrier properties is driven by the pressure to beat the degradability process of foods, and to make their trade and distribution more efficient and cost effective. This explains the interest for two major trends in food processing and packaging: Rapidly growing use of modified atmosphere packaging systems, MAP Increasing needs to provide shelf-stable conditions for foods, or slightly extended life of chilled foods. With the exception of pinhole free aluminium foil, all flexible packs have some level of permeability to oxygen, carbon dioxide and water vapor. It is rarely economic to use solid single
film as barrier, although there are a number of more or less polymer barriers which provide suitable levels of performance for particular situations. The barrier properties of the so-called barrier materials can be used in three main ways: Homogeneous layers, as single materials, mixtures or blends Coextruded or laminated multilayer structures Coated barrier on the surface of a substrate. The first approach, single barrier material, is illustrated by PEN, which has a much better barrier performance than PET, and can be formulated in combination with this polymer to provide enhanced barrier performance. An advantage with this approach is that the single material can be recycled. Multilayer constructions, whether coextruded or laminated, are widely used, with PVDC, EVOH and PAMXD٦, among the most cost effective. The beauty of this approach is that the thickness of each layer can be precisely controlled and that the film material can be converted on the filling line. A downside is that the trim, or waste, can only rarely be recycled, an economic as well as environmental handicap. Surface coating can be the most resource effective method of all, with the important added benefit that the barrier coating often also provides a heat sealing function. The earliest coatings, nitro cellulose, PVDC, probably the most useful single material, now suffering from adverse reactions because of its chlorine contents, acrylics, PVOH, all have this combination of properties. They can be applied to many kinds of substrates, paper, metal foils or plastics films, from solutions or other liquid dispersions, or extrusion coated as appropriate to each substrate. When the coating is very thin, less than ٥ % of the total finished film thickness, the substrate may be regarded as a single layer material. Another way of providing high barrier properties is to coat the surface with an ultra thin layer of an impermeable inorganic material, such as metal, for metallized films, metal oxide, silicon oxide. The only truly barrier materials are metals, tin plate and aluminium thick enough, and glass. The barrier concept really applies to plastics whose performances approach total barrier but never achieve it. The barrier materials whose price is at least two or three times higher than that of traditional materials or of commodity plastics, can be used, for economical reasons, only sparingly, as a thin layer, in association with cheaper plastics, in multi-layer materials. Up to now, the new concept of barrier materials has been closely linked to the design of multi - layers. The idea of a barrier package is thus the search for a precise balance between a barrier requirement, for a precise shelf - life of the contents, at an acceptable cost. The search for barrier materials is driven by performance improvements in films, end-user diversified requirements, packaging requirements, long distance shipping. The main two external agents most commonly to be kept out with barriers are moisture and gases. Achieving a good moisture barrier is relatively easy for plastics. Barrier to gases is more difficult. Barriers are defined by a general measure of the amount of moisture or gases that the material let through at a defined temperature and pressure, for ٢٤ hours. The standard measure is the oxygen transmission rate, OTR, expressed in cubic centimeters, at ٢٠ C, for ١µm thickness, per m², per
٢٤ hours, at atmospheric pressure, with measure at ٦٥ % and ٨٥ % relative humidity, RH. The gas barrier is the most difficult to achieve, so that when referring to barrier it generally means gas barrier. The main material /processes to achieve barrier are: Aluminium foil, the oldest of barriers used in packaging, back to the ١٩٣٠s Polymeric systems, PVDC, EVOH, PVOH, PAN, MXD٦, LCP, coated, laminated or coextruded Metallized PET, and other plastics substrates as well Inorganic oxide coatings, alumina or silica Nanocomposites Plasma techniques In this narrower sense of barrier, to oxygen, the main plastics used in packaging can be arranged into three categories: Little or no barrier to oxygen, PS. PE, PP Average barrier, PVC, PA, PET High barrier, PVDC, EVOH, PAN, PAMXD٦ The first applications of barrier materials, whether in film or sheet, were for standard, long - known products. The coextruded barrier films, the dominating and still fastest growing segment at the moment, are used in: bag - in - box for wines, fruit juices, milk, tomato paste, medical products, from ٢ to ١ ٠٠٠ liters. wrap for processed meat, delicatessen packaging packages for the keeping and aging of cheese controlled atmosphere flush packs for supermarket fresh meat cuts. More generally, high barrier films are used for CAP, controlled atmosphere packaging, for all kinds of longer shelf life packaging under gas flush. Multilayer films There are innumerable constructions for coextruded multilayers, many that seem practically custom designed for their specific use. Simply put, the basic structure of multilayer films is made of three basic types of components: An outer layer, to provide protection against abrasion and scratches during processing and packaging operations. It must be printable, direct or reverse, and resistant to temperatures required to melt the sealant. The middle layer provides the barrier to gas permeation. It may be EVOH or PVDC and others. In the case of EVOH used with polyolefins, there must be tie-layer between the polyolefins and EVOH. The inner layer provides a hermetic seal by melting at selected temperatures. The most used sealants are PE, EVA and ionomers.
The requirements for the selection of multi-layers are unlimited. The key idea is that the price/performance ratio is better achieved with the synergy of the layers than with a single material.