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Films and Other Packaging



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Webster defines a barrier as a "material object or set of objects that separates, demarcates, or serves as a barricade." But today, barrier materials, when used in packaging, offer so much more that the topic is worth a little elaboration.


Barrier material consists of base material such as polypropylene, polyester, aclar, foil, paper, tyvek and nylon, that is laminated for additional strength and protection to polyethylene, ethylene acrylic acid, and Surlyn (lonomer).  The laminating process extends the versatility of the barrier by providing additional protection against water, grease, acid, chemicals, corrosion and atmospheric changes. The material can be formed into bags, or can be used as sheets, blankets, or shrouds.


The three functional elements of today's flexible packaging are barrier, machineability, and sealability. Barrier packaging seldom has one single substrate satisfy all of these functional requirements. Consequently, you must combine various materials to meet specific needs.


The work horse of the laminations business is paper/polyethylene/ aluminum foil/polyethylene.  Examination of this structure in light of the three functional elements shows:


Barrier - Aluminum foil is the most cost-effective gas and water vapor barrier material. It has no inherent strength .


Machineability - Paper is the most cost-effective material which has the physical strength and stiffness for machineability.


Sealability - Polyethylene is the most cost-effective heat sealing material.


Typical base substrates used in barrier laminations in ascending order of cost are: Paper, Polypropylene, Polyester, Nylon, and Tyvek. Typical sealants used in flexible packaging in ascending order of cost are: Polyethylene, Linear Low Density PE, Ethylene Acrylic Acid, and Surlyn (lonomer).


Made with any number of flexible barrier materials, custom pouches or bags are used extensively commercially in the pharmaceutical, electronic, chemical, dried food, photographic, bulk vitamin and packaged powder industries. Heat sealing the bag provides the ability to store an item for an indefinite period of time, fully protected according to product specifications.


Some pouches offer moisture-vapor protection and, when combined with a material impervious to light, are widely used in the packaging of light sensitive chemicals and photography supplies.  Other pouches provide a flexible, heat-sealed barrier material, for applications that require protection against the build-up or retention of Electro-Static charges. These pouches are especially suitable for packaging electronic parts and equipment for storage and shipment.




MIL B-117 covers heat sealable, interior packaging bags, sleeves and tubing required by the Military Services for the protection of supplies during transportation and storage under all climatic conditions.


Intended Use. The bags, sleeves and tubing covered by this specification are intended for use as containers to provide various degrees of protection to the contents. Transparent bags are intended for use where transparency is desired to facilitate visual inspection of the enclosed product.


Bags shall be formed using two sheets or by folding one sheet of material. Heat sealable surfaces of the specified material shall be placed face to face. Heat sealing along both sides and the bottom edge. Transparent bags fabricated by the side weld process shall be folded and have two side seams. The side seams shall be parallel to each other and the outer edge of the bag. The bottom seam shall be at right angle to the side seam. When specified, bags 12 inches or less in length, with a mouth opening of 10 inches or less, shall be provided with a lip by extending one edge of the mouth 1/8 inch ( + 1/16 inch) beyond and parallel to the outer edge. The length of the lip shall not be included in the dimensions of the bag. Bags fabricated from sleeves or tubing shall consist of a bottom seam and do not require a lip.




A variety of competitive loose fill and free-flowing materials are available. The vast majority are made of expanded polystyrene and their cost per cubic foot is lower than most other packaging materials.


Flowable cushioning floats your product to prevent damage during transit. Millions of tiny air bubbles in the foam act as shock absorbers to cushion bumps and jars. Most flowable cushioning interlock to hold your product securely in position. There is no shifting or settling to expose an item to damage.


Flowable cushioning eliminates the need for a variety of expensive packaging materials such as die-cut inserts, corner blocks and molded foam parts. Many products, regardless of size, shape or weight, can be easily and economically packed in standard carton sizes with loose fill flowable cushioning.


Shrink Wrapping


By Richard Buchau National Sales Manager Shanklin Corporation


Shrink wrapping is placing a tightened wrap around a product and/or group of products.


Shrink packaging usually involves two steps: (1) wrapping the product in a full or bag wrap; (2) applying heat to shrink the film tight and neatly around the product.


Shrink-film usage involves two distinct groups: (1) polyolefin films and (2) polyvinyl chlorides (PVC). These are used for a normal retail application, where appearance is a major criterion. A shrink polyethylene is also available.  There is a wide variety of shrink films available with a range of properties and characteristics to allow the many options needed for performance and desirable economy. In normal applications, a three-dimensional item is placed into a flat two-dimensional pouch. This will produce excessive film in the corners that should be shrunk up tightly against the corners of the item being wrapped.


Semi-automatic, automatic, and form-fill-seal type wrapper are offered in single or two web film models. Major consideration in selecting a wrapper would be product size, pattern flow, cycles per minute, whether centerfold, flat, sleeve or a bag-type film, custom design and cost.


As for tunnels, factors to consider are size of tunnel, speed in feet per minute, heating method, air velocity, conveyor speed and cost.


Once the product has been properly wrapped, the next step is to shrink the film tightly around the item being wrapped. To do this, not only heat but air velocity or turbulence within the tunnel is needed from all directions. This will properly excite the air which will act as a temporary superstructure to raise and support the film away from the item so it can be heated to the proper temperature to release the shrink energy. If not, the item will act as a heatshrink and improper or partial shrinkage will result. An air hole in the sealed bag will allow gradual reduction of air pressure within the package and the film will draw tightly against the item.


Stretch Wrapping


By Patrick R. Lancaster IL. President Lantech, Incorporated


Stretch wrapping is the method of unitizing and protecting pallet loads or groupings of individual containers of product by applying layers of plastic film. The film is mechanically stretched to increase its yield and create a rubber band effect to keep the load unitized.


There are basically two approaches in stretch wrapping: pass-through and rotary.


In pass-through systems, a roll of film is located on each side of the conveyor system.  The ends of the rolls are joined by a heat seal, forming a film web across the conveyor and through which the pallet load passes. As the load moves through the wrap area, the film is pulled around the front and sides of the load.  The back of the load is covered as the sealing heads move together and seal the film ends.  Pass-through systems are typically automated and use webs of film which are approximately the same height as the loads being wrapped.  This method applies a single layer of film, typically ranging from 3/4 to 3 millimeters thick.


With rotary systems, the wrap cycle is accomplished by rotating the load on a mechanically driven platform and applying multiple layers of film, ranging from 1/2 to 1-1/2 millimeters thick.  Yield is between 20 and 300 per cent. Rotary systems can be either spiral or full web in terms of the manner in which they apply film.


The spiral approach uses a 20- or 30-inch film web which moves up and down the load during the rotation cycle.  This method provides the flexibility to accommodate loads of varying height.  It allows the operator to program the placement of the film on the load by regulating the speed of the up and down travel and selecting the wrap counts which apply additional layers of film to the top and bottom of the load. The full-web approach similar in some respects to the pass-through method, uses a web of film ranging from 40 to 85 inches in width. The web width is selected to match the height of the loads being wrapped. As the load rotates, a full web of film is applied, covering the entire surface of the load with each revolution.


Basically, there are two methods of elongating or stretching film--conventional or pre-stretch.


The conventional design uses a friction or magnetic brake on the film roll shaft or mounted against the film roll. The function of the brake is to restrict, to a degree, the unwind of the film. As the load rotates, it generates a pulling force on the film, and the difference between there restricting force of the brake and the pulling force of the load creates the film stretch.


In the pre-stretch method, the film is stretched primarily before it is applied to the load. The film passes between or around two rollers, the second turning faster than the first.  Generally, the rollers are mechanically connected or electronically controlled to regulate the speed differential. Pre-stretch isolates the load from a significant portion of the forces it takes to stretch film and consequently allows higher film stretch.


Stretch can be changed by altering the mechanical ratio of the two rollers and thereby increasing or decreasing the speed differential between them. The addition of a motor provides assistance to the roller rotation and produces a greater range of flexibility to adjust or regulate the amount of stretch force that is applied to the load by the film.


Stretch ability is the measure of how far a given film can be stretched over a given load profile. To the load, stretchability is important because the amount the film is stretched determines the force exerted by the film on the load.


Often overlooked, restretch force is the measure of the force available to restrict further movement of the load once it is encapsulated in film.


The higher the restretch force, the more effective the load unitization.


Film strength or breaking strength is another important film load-holding property.  Quite simply, film strength is the measure of the ultimate force which can be brought into holding the load before film failure. Strength is especially important in sustaining or arresting the forces of impact. The strength value of film is generally expressed in terms of pounds per square inch of cross-sectional area, or simply psi. And, depending upon the film type, strengths may range from 2,500 to 7,000 psi.


Stretch-wrap equipment


Today's stretch-wrap equipment offers a broad range of machine configurations, production capabilities, features and operator requirements.


The simplest method involves a hand-held roll of film, 10 to 20 inches in width, with a mechanical stretch mechanism for spiral wrap or top banding applications. The operator walks around the load and applies the film.  There are also wheel-mounted assemblies which can be pushed around the load generally for full web applications, and turntables or platform devices which are foot-pedal controlled to rotate the load as the operator applies film from a hand-held dispenser.


Platform-turntable units vary greatly in price, performance and operating features.  The load is placed on a turntable by a fork lift or pallet jack. The operator attaches the film to the load and then activates the wrap cycle.  The turntable rotates, and the film, either spiral or full web depending on the model, is applied to the load.


Several variations of the platform approach allow the pallet to remain stationary while the film-dispensing mechanism moves around the load. "Straddle-type" models are designed with an overhead-mounted film arm which rotates around the load, and robot models that travel around the perimeter of the load.


Gravity roller and powered conveyorized semi-automatic models are intermediate in operation and price between platform and fully automatic systems. Loads are fed by conveyor into the wrapping zone, wrapped and discharged to an exit staging conveyor.  These systems are typically loaded and unloaded by forktruck. They require an operator to sequence the pallets, attach the film to the load and activate or control the wrap cycle. Their greatest advantage is the increased production capability they offer over platform units.


Fully automated conveyorized systems are available in pass-through and spiral or full-web rotary models. Product loads are fed into the infeed conveyor system by palletizer, load former, robot or fork truck. The loads are staged on the infeed conveyor system and automatically sequenced into the wrapping station.  The load is wrapped and then discharged onto the exit conveyor system. The entire program is automatic, and no operator is required.


Of growing interest is stretch bundling, the unitizing with stretch film of a group of individual products, in less than pallet-load quantities. Generally, two or more bags, cartons, rolls or sheets are stretch wrapped together to create a bundle. As with pallet overwrap applications, the film holds the bundle together and, at the same time, provides product protection from contamination or damage. This form of stretch bundling has become a popular replacement for more expensive corrugated and heavy or specially treated kraft containers.


Shrink Films


By Fred Calmes Films Market Development Manager Cryovac Division, W.R. Grace & Company


Most shrink films are manufactured from polyolefin resins (primarily polyethylenes, ethylene-propylene copolymers, polypropylenes and ethylvinylacetates) or polyvinyl chlorides. The types of films produced from these resins range from industrial commercial grades, such as shrink polyethylene, to specialized commercial products such as polyvinyl chlorides, blended monolayer polyolefins and co-extruded polyolefins.


Generally speaking, the shrink polyethylenes are used in bundling, individual case wrapping, carton palletizing and other non-retail applications. Polyvinyl chlorides and polyolefins tend to be used in retail display items which need the special marketing and merchandising attributes these films exhibit.


Shrink films were first introduced in the early 1960's and were generally used to contain products and prevent pilferage or as dust covers to keep products clean. One of the early marketing break throughs brought record albums from behind the counter into a self-service, mass-market concept. The clarity and gloss of the new films also enhanced the graphics of the record jacket. Previously, LPs had been wrapped in a hazy, non-shrink polyethylene.


With the advent of larger stores and the increased emphasis on self-service, shrink films began to play a major role in merchandising thousands of products.  The optics and cleanliness of shrink film lent a quality image as its use expanded into hardware; household items; all types of paper goods including stationery, gift wrap and greeting cards; prepared foods such as fresh or frozen pizza, taco shells and dairy products; automotive accessories; and toys, games and hobby kits.


Shrink films are available in center-fold or single-wound form in thicknesses ranging from 50 to 150 gauge for polyolefins and up to 200 gauge for polyvinylchloride (PVC). Center-folded films are used on L sealer equipment. The package is placed on the loading tray and transferred into the seal area where a hot-wire seal is made on the open front and side of the film. A small vent hole is formed on the film to allow air to escape during the shrink process.  The product is then conveyed into a hot-air tunnel where the film initially balloons and then shrinks tightly to the package. Depending on product size, speeds of up to 15 packages per minute can be obtained on manual L sealers and up to 30 per minute on automatic L sealers.


Higher speeds can be attained using horizontal or vertical automatic form-fill-seal equipment with single-wound film. In this process, a specially designed forming shoe is used to wrap the film around the product.  It's secured with a static or thermal lap seal on the bottom or side of the package and by a hot-wire or hot-knife trim seal on the front and back. Complete and carefully designed packaging systems consisting of automatic infeeds, indexers, collators, high-speed shrink tunnels and collecting areas can reach speeds of up to 250 packages per minute.


Industrial grade polyethylene film may have a variety of end uses, especially when packaging speeds or film characteristics aren't critical. It's often used for bundling large cartons or over wrapping trays containing canned goods or beverages. Available in very thick gauges, it can also be used to protect heavy items during shipment. Since it is hazier than most other shrink films, it is not usually recommended for packaging retail items.


PVC resins, due to their high-density, amorphous molecular structure, enable manufacturers to create films with very specialized properties. For example, they're a good choice where low shrink tension is necessary.  The new soft-shrink polyolefins are also a viable option for such items as flat sheets of gift wrap, stationery, single-set sheets, pillow cases and other textile products.


Another feature of PVC is the ability, during the manufacturing process, to vary the shrink tension in longitudinal and transverse directions. Having a high percentage of shrink in one direction enables it to run on sleeve-wrap equipment, resulting in the common "bull's eye" package with circular openings at both ends. When produced with mono-axial shrink, it makes excellent neck bands for tamper-evident packaging.


Finally, PVC has very good clarity, a wide seal-temperature range and low-temperature shrink. The latter two characteristics enable this family of films to perform well on less expensive sealers and tunnels and/or poorly maintained equipment.


Some of the limitations encountered with PVC include loose packages due to low shrink tension, weak and charred seals marked with pinholes and film relaxation. In addition, the film must be stored at least at room temperature or below to prevent shrink-back. It can also become quite brittle at temperatures below freezing, causing problems when wrapping products that are frozen and/or shipped during the winter.  Unless seal temperatures are closely controlled and the packaging area vented, equipment corrosion is common.  Over a prolonged period of time, these films will also tend to become brittle and discolored.


Polyolefins, because of their crystalline molecular structure, offer a wide variety of characteristics. They usually appear in formulations of high-density or low-density polyethylenes, linear-low or linear medium-density polyethylenes, ethylene/propylene copolymers, ethyl vinyl acetate, or multilayered combinations. They are dimensionally stable and biaxially oriented to provide a balanced shrink. They are tough and clear.  And due to their higher shrink tension, they shrink very tightly to the product. When irradiated, the molecules become crosslinked to provide an even tougher and more abuse-resistant film.


Polyolefins are very stable under long term storage conditions. They are able to withstand a temperature of -60F. or lower, making them ideal for packaging frozen products. Due to the higher modulus of these materials, the resultant stiffness and flatness make them an excellent choice for high-speed automatic equipment. Finally, they produce clean, non-corrosive films that will not leave char marks, corrode equipment, discolor or relax and lose dimensional stability.


There are a few limitations of polyolefin films. These include the possible distortion of non-rigid products because of high shrink tension. However, new developments have lead to soft-shrink polyolefins. Some sealing difficulty may also be encountered when running the material on poorly maintained L sealers.  It may not shrink well when conveyed through tunnels with little air velocity or inadequate temperature controls.


New technologies in co-extrusion have made possible multilayer shrink films, allowing the creation of products specifically tailored to meet a packager's needs. High oxygen, moisture or aroma barriers and solvent resistance are just a few possibilities utilizing this technique. Special additives, blended in during production, are also making possible antifog and antistatic films.


Linear low-density polyethylenes (LLDPE) have contributed greatly to improved abuse-resistance of shrink films.  They've also reduced the energy requirements of packaging lines by sealing and shrinking at lower temperatures.  Although usually available as a monolayer product, LLDPE may find its greatest use in coextruded films.


Co-extrusion allows the incorporation of the positive aspects of various polymers into a single multiply material. The toughness of LLDPE can be combined with the excellent machinability of ethylene/propylene copolymers to make a very strong film that can easily run on high-speed automatic machinery


The 1980s have seen an explosion in market demand for shrink films. They've become an excellent choice for tamper-evident packaging, which is increasingly important to the pharmaceutical and food industries. Printing the surface with a company logo provides even greater protection. Additional advantages have been derived because film enhances the appearance of the package, creating a premium image. Dairy products such as ice cream, cottage cheese and yogurt have been quick to capitalize on these points.


With the recent introduction of automatic collating equipment, shrink film can eliminate trays or boxes, saving literally tens of thousands of dollars. The rapid growth of the warehouse discount-club concept and its demand that many items be sold in multiple units have greatly increased the need for this type of unitized packaging. Contract packagers, sheltered workshops and food processors have been quick to accommodate this market.


Home entertainment applications such as video cassettes and compact discs, and commercial products such as floppy discs and computer software are among the newest markets for shrink films. They've adopted films to protect sensitive surfaces from microscopic contaminants--a major hazard in their business--and to improve package appearance. Antistatic films are a natural fit in this market.


Stable electrostatic dissipative films, designed to package and protect circuit boards, semiconductors and other static-sensitive products have recently been introduced in the market place. These materials are generally noncorrosive, transparent and compatible with the polycarbonates that are used as "boards" in the electronic industry. These are part of a new generation of specific characteristic protective products that go far beyond the traditional uses of shrinkable films.


The new barrier films are another example of these highly sophisticated products. Barriers can be engineered to contain the smell of naturally aromatic products such as mothballs, or prevent off-odors from contaminating sensitive consumer items such as chocolates and beverages. Recent work even promises that they can help retain important nutrients in foods during storage.


Another sophisticated new product is a microwavable, antifog film that's currently being used for consumer-sized packages of fresh-cut, trayed vegetables. Its respiration rate is keyed to match that of the product. Its antifog characteristic keeps the vegetables clearly visible for maximum consumer impact --an important asset for high-moisture, refrigerated products.


The markets for shrink film will continue to expand as new technologies develop products with more specialized characteristics.  We're fast approaching the day when "designer films" can be manufactured to meet the most demanding requirements.


Stretch Films


By Bob W. Griggs Marketing Manager Bemis Company, Incorporated


Stretch films can be stretched to varying degrees depending upon the item or products being unitized. Stretch films are applied to bundles, pallets of goods and single items to provide product protection and maintain the integrity of the items or loads.


Several different kinds of stretch films are used. Low-density polyethylene, ethylene vinyl acetate, linear low-density polyethylene and EVA-LLDPE blends are dominant.  LDPE films, introduced in the early '70s, represent a small segment of the market today. EVA, a copolymer stretch film, was introduced in the mid 1970s. The major requirements for a good film include stretch, cling, strength and stress retention--all of these properties are good to excellent in this film group. LLDPE films, introduced in the late 1970s, have very good to excellent properties of stretch, strength and stress retention.


Film properties have a bearing on how the unit is wrapped, stored, shipped and received at its final destination.


Cling is the tackiness that causes the film to stick to itself. Cling provides load integrity by keeping the end of the film stuck to the wrap, and causes the layers of film to laminate to each other on the load. This layer-to-layer adhesion of the film holds the load together.


There are several things that: can affect the cling characteristics of a film. They are heat, humidity, dust, dirt and the amount of stretch applied to the film before it is applied to the unit or pallet. Film may have adequate cling before it is stretched but not after.


The stiffness of a film also has a bearing on its ability to stick to itself or maintain adequate cling. Stiffer films are more difficult to stick to themselves since they tend to pull away from the next layer. Generally, softer films exhibit better cling characteristics.


Stretch is a film's ability to elongate when a pulling force is applied. This pulling force is applied either by the braking action on a stretch-wrapping machine or manually. Generally as the percent of stretch increases, the narrowing of width tear properties and the force to the load increase while the gauge decreases. Most new stretch-wrap equipment is designed to permit films to be used at higher stretch levels while reducing neckdown and the force to the load.


Puncture and tear resistance are a measure of a film's ability to resist being punctured. If punctured, as often happens in handling and shipping, it is a measure of the film's ability to resist zippering to a point where the film breaks.


Stress retention is the ability of a film to retain the holding force that is applied to the load or unit at the time it is being wrapped.  All films relax after they are put on the loads.  The amount of relaxation varies from film to film. The critical factor is that the relaxation is not so great to cause the load to lose its unitized integrity.


Yield means how much effective stretch can be obtained from a film and still satisfy the other requirements. The maximum yield obtained will vary depending on such things as the weight, height and configuration of the load as well as storage and shipping conditions.


Differential cling means that one side of the film has more cling or tack the other side. This permits the loads to have good load integrity or good layer-to-layer adhesion with less cling on the outside of the film. This low cling outside prevents the loads from blocking or sticking to each other during storage and shipping.


In general, as the temperature decreases, the cling characteristics of a film decrease. In refrigerated and frozen food application there is a need for good cling in temperature as low as 0F. to -20F. Some stretch films maintain reasonable cling characteristics ill those conditions.


Anti-static stretch film is used in environments requiring a quick decay of static charges generated during the wrapping) process. This property is required in places such as aerosol packaging, paint manufacturing, explosives and highly volatile environments.


Virtually all types, shapes:, sizes and weights of unit loads are stretch wrapped both with and without pallets or slip sheets.  Stretch films are also used to bundle many sizes, shapes and weights of goods which are shipped as a bundle.


There are many ways to apply stretch films to the pallets, units, bundles, etc. These methods run all of the way from simple, inexpensive hand-held devices to expensive fully automatic machines tied into fully automatic palletizing, and conveyor systems. To get maximum benefit from your system, the equipment must be properly designed and then properly adjusted and maintained.


Load configuration is a factor to consider when selecting the best film for the job. A film that can adequately wrap a regular shaped load may not be strong enough or have the puncture resistance required to handle an irregularly shaped load. Even a regularly shaped load that is smaller than the pallet will require a stronger film if the load is to be tied to the pallet. The prestretch systems on the newer equipment can lessen some of the load-shape problems.


The make-up of the load can influence the type of film used as well as the force applied to the load. A very light, fragile, low-density load that can be easily crushed will require a different film type, gauge and number of wraps applied to the unit than a heavier, rigid, high-density load.


The type of equipment to apply the film can have a bearing on the type of film used.  New machines are demanding of the films in terms of prestretch, the system used, the speed of film application and forces applied to the loads. All equipment changes have a bearing on the films used.


You must test a film and its application methods to select the proper film. Your products must be wrapped on your equipment and shipped by your normal methods to determine film effectiveness and cost efficiency.  These wrapping tests should be done with the film supplier present during the wrapping.





Desiccant is used in packages to protect products from damage caused by humidity and water vapor. Desiccant is an extremely effective moisture absorbing agent and is non-corrosive. It is inert, odorless, tasteless and non-toxic. It meets Method II packaging standards described in Mil P-116, which covers the basic requirements of military packaging methods of preservation.  Method II involves packaging an item within a sealed water- and vapor-proof package, enclosure. or container and providing desiccant inside to prevent rust, corrosion or mildew.  By enclosing desiccant, the unit is held below 40% relative humidity for at least 18 months to two years.


Desiccant is best utilized when used in conjunction with sealed barrels, containers or barrier bags. It is used effectively in the packaging of components and instruments for the aerospace, computer and electronics industries. Desiccant can also be used in packaging that does not strictly conform to MIL Specs.


When properly applied, desiccants can:


         Prevent corrosion and related damage to machine parts, optical equipment, tools, cameras, medical instruments, and a variety of other products.


         Prevent mildew and rot in clothing. food products and documents.


         Maintain the activity of moisture-sensitive chemicals and the potency of pharmaceuticals


         Absorb moisture that may lie on top of containers of chemicals or petroleum products.


         Enhance the handling properties of hydroscopic materials, such as maintaining powders and seeds in a free-flowing state


How do these tiny beads absorb the moisture?  The water vapor is attracted and held by the microscopic pores and capillaries of the desiccant particles. And, desiccant can be reactivated and reused many times, simply by heating it in its own bag or package, at 250F (120C) for 16 hours.


Definition of Desiccant Unit (MIL-D-3436D-3.3)


A desiccant unit is that quantity of desiccant which will absorb at equilibrium with air at 25C at least the following quantities of water vapor:


(A) 3.00 grams at 20 percent relative humidity and (B) 6.00 grams at 40 percent relative humidity.  In testing bagged desiccant an allowance will be made for normal manufacturing variations. In connection with such inspection testing, unit absorption capacity shall be at least:  (A) 2.85 grams at 20 percent relative humidity and (B) 5.70 grams at 40 percent relative humidity.




When using desiccant for long term storage of products in a sealed barrier bag or sealed rigid container, it is recommended to use Humidity Indicator cards or plugs. These are simple means of indicating it the Desiccant inside the bag or container is currently active.  If it is not, the container or bag should be opened, and the Desiccant replaced.





Aluminum Foil


By Flexible Packaging Division Reynolds Metals Company


Of the raw materials commonly available to produce flexible packaging, only aluminum foil can provide an absolute barrier to gas, moisture and light transmission. Further unlike other materials, these barrier properties are relatively independent of gauge, particularly when aluminum foil is combined with other materials. Aluminum foil's pleasing metallic surface provides an upscale or quality image to packaged products. Foil can be coated, laminated, printed and embossed in a variety of ways.


By definition, aluminum foil is any gauge or thickness less than 0.006 inches.  Bare foil for household and food service wrapping applications generally is less than 0.001 inches in gauge. Gauges for converter foil, which is combined with other materials to make flexible packaging products, are generally less than 0.0005 inches; foils currently being produced commercially go down to 0.0002 inches. In certain applications, such as lidding stock for plastic or aluminum containers, thicker foils of 0.001 to 0.003 inches may be used in combination with coatings, extrusions and/or films to provide a tough, high barrier , peelable lid.


Aluminum foil is produced from direct chill (or DC) cast ingot or from continuously cast sheet. In the former process, ingots produced by the DC method measure 15 or more feet in length, 6 feet or so in width, and up to 2 feet in thickness. These massive ingots are "soaked" at high temperature, hot rolled to an intermediate gauge, then cold rolled to foil gauges. In the continuously cast process, an aluminum sheet varying from 1/4 to 1/2-inch in thickness is produced from molten aluminum. This sheet is then cold rolled in a series of rolling mill passes to the final foil gauge.


For flexible-packaging applications, the aluminum used to produce foil is relatively pure with only minute amounts of silicon, iron, copper, magnesium or manganese added to produce desired properties. As the metal passes through the various stages of rolling, it work-hardens. This hardening can be relieved or tempered by annealing--reheating the metal to a point where the rolled-in stresses are relieved or eliminated by full recrystallization. Foil usually receives at least two anneals--one approximately midway through the rolling process and the second at finish gauge.


During the production of aluminum foil, in gauges below 0.001 inches, two webs of metal are fed together, or doubled, into the rolling mill and rolled to finish gauge simultaneously. They are then separated into two single rolls for slitting, spooling, annealing and shipment to the user packager. This practice produces a material that presents a different appearance on either side of the foil. The side that is next to the highly polished steel rolls of the mill develops a bright, shiny finish.  The other side, that next to the other sheet of aluminum foil, develops a satin sheen finish called matte. There is no major chemical or other difference between the two surfaces of the metal as received by the packager, but the two surfaces differ substantially in appearance.


At the final gauge, the aluminum foil is once again annealed to produce a final product with the desired softness or temper and to prepare the surface for its end use. Changing the final annealing practice can result in a range of metal hardness, from intermediate temper to "dead soft," required for most flexible-packaging applications. In the case of converter foil used inflexible-packaging applications, the final annealing step also removes residual oils from the rolling operation and produces a clean surface suitable for bonding to the inks, coatings and adhesives.  Aluminum foil is generally shipped in widths up to 72 inches in rolls.


Aluminum Foil in Packaging


Aluminum foil is used in flexible packaging as a plain metal or printed metal surface for appearance purposes or for its barrier properties, formability or other functional characteristics. Often both are combined in the final package.


Foil is often used to convey the look and feel of quality to a package. Many products utilize foil's aesthetically pleasing appearance; classic examples include cartons, labels and overwraps. Foil's appearance can be further enhanced by its ability to be printed, through rotogravure, flexographic, offset or letterpress processes. The foil surface may first be treated to promote ink adhesion. After printing it may be given a clear overcoat for protective purposes or to provide desired machinability. It may be partially printed to present a pleasing contrast or be completely covered with ink.


When foil is to be used in a packaging structure for its barrier properties, it is usually necessary to protect the foil from rough handling, external elements and/or the packaged product. A classic foil-bearing structure used in packaging is paper/polyethylene/foil/polyethylene. In this instance, polyethylene protects the foil and provides a heat-sealing medium. A whole host of other packaging structures are now in the marketplace utilizing foil with films, paper, extrusion coatings and laminations, etc.


Below thicknesses of 0.0010 inches, foil may contain occasional minute openings called pinholes. These are created during the rolling process and may result from inclusions in the foil, particles in the rolling fluids and a number of other factors. Actual pinhole counts can vary substantially in thinner gauge foils, but generally will tend to increase exponentially from virtually none at 0.001 inches to several hundred per square foot at ultra-thin gauges. As a benchmark, one popular commercial specification states a pinhole count of 65 per square foot or less at 0.000285 inches. As a secondary measurement of pinholes, the rate of water vapor or gas passing through bare foil will be a function of the combined areas of pinholes present. A chart in ASTM standard B479 shows typical water vapor transmission rates for 1145 plain aluminum foil at 100F and 96 percent relative humidity.





Typical water vapor transmission rates for 1145 plain aluminum foil at 100F and 96% relative humidity.


While larger numbers of pinholes may be expected in ultra-thin converter foils, the moisture and gas transmission rates are still substantially better than virtually any competing raw-material option.


A second physical concern in the use of foil in flexible packaging is "flex cracking" which can create the same type of barrier permeability as a pinhole. However, by properly sandwiching the foil in a protective structure, flex cracking can be significantly reduced or eliminated. Shipping tests, vibration tests, drop tests, etc., are generally performed on developmental foil-bearing structures where the prevention of flex cracking is of critical importance.


An even more complex issue than pinholes or flex cracking is the protection of foil from internal or external chemical attack. In a classic example, a foil-bearing structure may be desirable to fully protect a high-acid food product. However, if the high-acid food product reaches the foil, the foil will react, producing hydrogen gas. Similarly, highly basic materials penetrating to the foil surface can act to corrode the foil, thus hampering its barrier properties. Therefore, careful selection must be made to assure that internal (or external) films, coatings and adhesives are used so that the foil is protected from potentially damaging elements.


As with the testing done for flex cracking, a whole series of environmental and product compatibility tests are performed on developmental foil-bearing structures to ensure that a suitable barrier is maintained for the expected shelf life of the product.


The unique functional characteristics of aluminum foil and its aesthetically pleasing appearance assure its continued and growing use as a packaging material, particularly when combined with a rapidly increasing choice of other materials in composite packaging structures.

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