Welcome to Discount Plastic Film!

WHAT ARE PLASTIC FILMS?

PLASTIC FILM is a thin sheet of material with a thickness less than 2.5mm/10 mils/1000 gauge, averaging between 0.7 mils to 1.5 mils. It is (usually plastic and transparent) used as a packaging medium to cover or wrap things. A mil is 0.00l inch.

Plastic film also can be clear or colored, printed or plain, single- or multilayered and combined with other materials such as aluminium and paper.

HOW IT IS MADE?

• Extrusion - hot, melted plastic resin is forced through a circular die, forming a thin tube. Air is introduced, expanding the size of the cooling tube which is then flattened as it passes through converging slats and rollers.
• Extrusion coating - resin is melted and forced through a long, slit-shaped die. The sheet of plastic falls evenly onto a continually moving roll of material, such as paper, cardboard, aluminium foil or fabric. The plastic cools and sets on the material.
• Coextrusion - this involves complex die design and multiple extruders, allowing two or more melt streams to be combined. Increasingly, up to five or seven layers are now being used.
• Calendering - this process follows the principle of squeezing laundry out in an old mangle. Hot plastic is poured and evenly squeezed between rollers.

IN WHAT APPLICATIONS ARE FILM USED?

Another reason why it is somewhat difficult to get a grasp on plastic film is because it is used in such a wide range of products and packages. Typically, its usage is divided into two general categories—packaging and nonpackaging—that can also be broken down into smaller components. For example, there are three types of packaging applications in which film is used: food, nonfood and other. It is important to keep in mind that within each of these categories, plastic film can vary by resin and color; it also may be made of one layer of plastic or as many as ten layers depending on the complexity of the package. In addition, other materials—such as aluminium or paper—may be used in combination with plastic film in order to impart special properties. Therefore, even the following categories of film are themselves made up of many diverse types of film.

• Food Packaging

Food packaging film is used in such things as in-store bags for produce (such as apples and potatoes); all nonfrozen baked goods (such as rolls and breads); bakery bread and bun bags; tray covers for institutional deliveries of bakery products; bags-in-a-box (film used to contain fluid in a supportive box, such as boxed wine); boil-in-bags (film used to contain food prepared by keeping it in the package and placing it in boiling water); candy and confection bags and wrappers; carton liners (for such products as cake mixes); and meat, poultry and seafood wraps (such as hot dog and bacon film).

As mentioned in the section on film generation, the only data available on the use of film in food packaging applications are restricted to the polyethylene family, despite the fact that other resins are used in food packaging as well.

It is worth pointing out that LDPE is the polyethylene resin used most often in food packaging; it accounts for 65.5 percent of the total, with LLDPE making up 25.6 percent and HDPE making up 8.9 percent

• Nonfood Packaging

Nonfood packaging film refers to such things as industrial liners (film used to line supported structures such as gaylord boxes, frozen pork box liners and liners for shipments of nuts and bolts), shipping sacks (film used to protect and/or contain contents such as bark and mulch bags), bubble packing, envelopes, multiwall sack liners, overwrap, and rack and counter bags. Again, data on film used in nonfood packaging applications are confined to the polyethylene family. As Exhibit 3 shows, LDPE is the polyethylene resin used most frequently in nonfood packaging applications. It composes 54.9 percent of the polyethylene used in nonfood packaging, whereas LLDPE composes 35.5 percent and HDPE composes 9.6 percent.

• Other Packaging

The other types of packaging in which film is found are stretch and shrink wrap. Stretch wrap is a strong, highly flexible film that can be stretched to take the shape of a product or products. It is used in a variety of applications ranging from overwrapping fresh meats to securing shipping cartons to pallets. Stretch wrap usually is made of co-extruded LLDPE and LDPE, although it can be made from individual plastic resins, such as LLDPE, LDPE and PVC.

Shrink wrap, on the other hand, is a plastic film that is applied loosely around products, sealed by heating the seams and shrunk through a heating process to take the shape of the products. In shipping, it can be used to bind multiple packages of less than pallet size together (such as five 20-ounce cans of beans or three juice boxes) or used over an entire pallet of packages. In these applications, shrink wrap typically is made of LDPE, although it can be made from other resins as well, such as LLDPE and PP. In addition to shipping applications, shrink wrap also can be used for bundling purposes, such as bundling magazines and papers, and it can be used to protect and display such products as albums and compact disks.

There are several ways to tell stretch wrap and shrink wrap apart: stretch wrap usually feels somewhat tacky to the touch and is very flexible, whereas shrink wrap may be more brittle (or crinkly) to the touch and does not stretch when pulled. In addition, stretch wrap usually is wrapped around products, whereas shrink wrap will enclose the product (that is, have a top and bottom cover), which makes it an attractive choice for shipping products in extreme weather conditions or for products that need extra protection.

Data compiled by Modern Plastics show that a total of 1,074 million pounds of polyethylene film were used in “other” packaging applications in 1995. (Again, data are not available for nonpolyethylene resins or for HDPE.) As Exhibit 4 shows, LLDPE is used most often in stretch wrap applications (at 802 million pounds) and LDPE is used most often in shrink wrap applications (at 192 million pounds).

• Nonpackaging Applications

Of course, a great deal of film also is found in a category the industry refers to as nonpackaging applications. For example, it is commonly used to produce grocery, T-shirt and trash bags; can liners; agricultural film (such as greenhouse, fumigation and mulch films, haysleeve covers and silage bags); construction film (such as vapor barriers in walls, moisture barriers under concrete, paint drop cloths and drapes); medical and health care film (such as garbage and hazardous material bags, I.V. bags and sterile wrap); garment bags; self-service bags; household wrap; and as a component of disposable diapers.

According to figures from Modern Plastics, approximately 3,730 million pounds of polyethylene film were used in nonpackaging applications in 1995. Exhibit 5 shows how that film was distributed by polyethylene resin type.

It is important to remember that the figures presented in this section focus only on polyethylene films because data are collected in this manner only for members of the polyethylene family. That does not mean, however, that only polyethylene is used in these applications. For example, in the nonpackaging category, PP films are used in such things as diapers and in the packaging categor y, polyester and polypropylene films are used in sterilization wrap.

Review of Nine Important Resins used to make Plastic Films

1. Polyethylene (polyethene): The ethylene polymer, polyethylene, is the most important of all the plastic packaging materials today. Polyethylene is classified into three main groups:
   LDPE: Low Density Polyethylene 0.910 - 0.925 g/cm3
   MDPE: Medium Density Polyethylene 0.926 - 0.940 g/cm3
   HDPE: High Density Polyethylene 0.941 - 0.965 g/cm3
   
   • Low Density Polyethylene (LDPE) is the dominant type of PE and the most commonly used. It finds its greatest use in film form as a basis for bag making. LDPE is readily heat sealed and is also the cheapest type of PE. The range of low density PE includes those with a variety of slip and antiblock agents, such as required in bulk packaging where low slip for good stackability is needed. Bags for soft goods, where high slip is desired for easy packing, are other applications of LDPE. Low density polyethylene is flexible and tough.
   
   
   • Medium Density Polyethylene (MDPE) is used for film formulations or other applications where a higher stiffness or higher softening temperature than LDPE is necessary. The MDPE material is a little more expensive than LDPE.
   
   
   • High Density Polyethylene (HDPE) is more rigid than the two previous types. HDPE can be subjected to temperatures of up to 120°C and, therefore, this type can be used for packages to be sterilized by steam. HDPE can also be slit into narrow tapes to make woven plastic sacks. However, polypropylene is a more commonly used material for this purpose.

   The different PE types have some interesting properties, which make them all very suitable as packaging materials. First, PE has good moisture and water barrier properties, the better these properties the higher the density. Polyethylene also has very good heat sealing characteristics and will retain its flexibility at very low temperatures - it can be used under freezing conditions down to –50°C (-58°F). It has a comparatively even viscosity curve with varying temperatures and is, therefore, easy to handle and convert. Physiologically, there are no disadvantages connected with PE. When it burns, it produces only carbon dioxide and water. There are certain disadvantages, however. The material has a rather high oxygen permeability, its aroma barrier properties are limited and it also has a fairly low resistance to fats, especially in the case of LDPE. There is a risk of unpleasant smell if the plastic is converted incorrectly, e.g. extruded at temperatures that are too high. Some packaging machines may not work well with LDPE, because of its rather low rigidity.

   Polyethylene can be transparent if it is cooled rapidly after extrusion. In other cases, the material is characterised by a somewhat milky appearance. Polyethylene is used a great deal for film extrusion for further converting into wraps, bags and sacks. It is also extruded as coatings onto paper or paperboard and it is the most used material for the blow moulding of containers like bottles and jars. It is further used for flexible tubes, trays, boxes, drums, beverage carriers, etc. One very important application is for various types of closures. The chemical inertness of PE is also worth mentioning in this context. Oriented and pre-stretched PE film is used a great deal in shrink and stretch wrapping.

   The properties of polyethylene vary substantially from one manufacturer to another. However, some typical figures are presented below in order to demonstrate how the properties change by going from low density to high density material.

   Polyethylene can be transparent if it is cooled rapidly after extrusion. In other cases, the material is characterised by a somewhat milky appearance. Polyethylene is used a great deal for film extrusion for further converting into wraps, bags and sacks. It is also extruded as coatings onto paper or paperboard and it is the most used material for the blow moulding of containers like bottles and jars. It is further used for flexible tubes, trays, boxes, drums, beverage carriers, etc. One very important application is for various types of closures. The chemical inertness of PE is also worth mentioning in this context. Oriented and pre-stretched PE film is used a great deal in shrink and stretch wrapping.

   The properties of polyethylene vary substantially from one manufacturer to another. However, some typical figures are presented below in order to demonstrate how the properties change by going from low density to high density material.

   Type of PE	Moisture Vapour Transmission Rate*	Gas transmission** O2	Gas transmission** CO2	Tensile Strength***
   LDPE	1.4	500	1350	1.700
   MDPE	0.6	255	500	2.500
   HDPE	0.3	15	350	4.000

   * g/100 sq.in./24h/l mil
   ** cc/100 sq.in/24h/l mil
   *** lbs/sq.in/1 mil
   

2. Polypropylene (PP) is another of the olefin plastics. It is much stiffer than PE and it has better tensile strength and higher transparency. It also has low moisture permeability values. Because of its high crystallinity, the softening temperature is as high as 150°C and, therefore, it can be successfully used in connection with autoclave sterilization of medical products, etc. PP can be used as a packaging material for ready-made food to be warmed in a convection oven or by boiling. It is also commonly used for injection moulding of closures.

   The density of polypropylene is as low as 0.90 g/m3 and its higher strength makes it possible to use thinner films, which makes it competitive to certain forms of PE for special uses. It has also taken over many applications from regenerated cellulose film (cellophane), e.g. for the wrapping of cigarette packs. There is a tendency for PP to become brittle at low temperatures, and this can, to some extent, be overcome by copolymerizing a small amount of ethylene into the propylene.

   Polypropylene is used as a film, which is comparatively rigid and has a range of applications much like cellophane, primarily because of its high clarity. PP film is often oriented (OPP), which means that it has been stretched in one or two main directions, producing better rigidity and strength.

   OPP film is rigid enough to be easily handled on many packaging machines, it is completely transparent and has good barrier properties against moisture. However, it is difficult to heat seal, which can be overcome by co-extrusion with polyethylene.

   PP is also greatly used for closures and finds successful applications where PE may show stress-cracking of the surface under the influence of certain surfaceactive substances. A common application for polypropylene is as a raw material for woven sacks.

3. Polystyrene (PS) is produced from petroleum by polymerization of styrene. This plastic is completely transparent but it has poor barrier properties against moisture and gases. The material as such is rigid but has inferior resistance to impacts and, therefore, synthetic rubber, butadiene, is blended into it to give additional shock strength. However, adding butadiene destroys the transparency, and shock resistant PS (HIPS) is therefore opaque, usually white.

   PS is very easy to process for packaging purposes. It can be blow and injection moulded, extruded, thermoformed, etc. Its use for packaging is limited by its poor diffusion performance and it is mostly used for thermoformed trays or cups. Typical uses are packing of vegetables and fresh meat on trays, and yogurt and other milk products in cups. As film, polystyrene is used for the overwrapping of fruits and vegetables, such as tomatoes and lettuce. Biaxial orientation gives the film increased strength and toughness. It is then called Oriented Polystyrene film (OPS).

   Expanded Polystyrene (EPS) is manufactured from specially treated polystyrene pellets. Heating the pellets in steam will expand the pentane contained in the material very rapidly and thus a cellular structure is formed. EPS is used for shock-absorbing inner parts for packages containing delicate machinery, etc., being moulded to fit exactly the form of the object to be packed. It has also found wide use for insulating trays and packs for fresh meat and fish, fresh fruit, bakery products, eggs, etc.

4. Polyester or linear ester plastics are manufactured by condensation like the polyamides. It is mostly extruded to form a film, and the film is biaxially stretched in both directions. Polyester has an exceptionally high mechanical strength, together with a temperature resistance of up to 300°C. This film has low moisture and gas permeability values and the resistance to organic solvents is good. It has poor heat sealing properties and is, therefore, often extrusion coated with polyethylene.

   Polyester film can be coated with PVDC and will then become even less permeable to gases and aroma. Combined with aluminium foil and PE, polyester makes an excellent material for the packing of ground coffee in vacuum packs and for meat products, etc. It is sometimes used for boil-in-bag packages, where the contents are heated by boiling directly in the bag. This becomes possible because of the high temperature resistance of the material. Polyester film can be thermoformed to a limited extent and there is a shrinkable version of this material as well. A recent, very interesting application is to use a particular type of polyester: Polyethylene terephthalate (PET) for carbonated beverage bottles.

5. Polyamide (PA) or Nylon has a very good mechanical strength with excellent heat resistance properties. There are varieties of PA with melting points of up to 250°C. PA is used as a component in several laminate types, with PE in particular, which are used especially in web-fed vacuum thermoforming machines for packing of sliced meat products, fresh meat and cheese. The laminate used has polyamide as the inner layer. PA is widely used for sterilizable packaging of hospital articles.

6. Polyvinylchloride (PVC) is produced in two varieties: rigid and plasticized. Rigid, non-softened PVC has good moisture and gas barrier properties along with good resistance to fats. Rigid PVC is used a lot for thermoforming of packages for butter, margarine, etc. It is also transparent and makes good bottles for mineral water, cosmetics, edible oils and fruit juices.

   Plasticized PVC in film form is mainly used for the packaging of fresh fish and meat, fruit and vegetables, and other fresh goods. It can be used for pallet wrapping to secure whole pallet loads to the pallet by stretch film winding. There are also PVC shrink films for use as overwraps, e.g. for gramophone records, where a pilferproof package is required.

   PVC as such has rather inferior temperature stability and to make it possible to extrude PVC through an extruder, special stabilizers have to be added. Some countries do not accept tin-based PVC stabilizing agents, and in most countries there are strict regulations about the maximum amount of residual vinyl monomer in the final product.

7. Polyvinylidene chloride (PVDC) is usually copolymerized with vinyl chloride and is often then called by the trade name Saran (registered trade mark). PVDC has a very low water vapour, oxygen and carbon dioxide permeability. It also has good resistance to fats and chemicals. A shrinkable PVDC film is manufactured under the name of Cryovac (registered trade mark). Production of PVDC film is done by extrusion into a water bath, after which the resulting tube is blown up by air to a very large diameter; this orients the film biaxially. Then the film is laid flat, cut lengthwise and made into reels.

   PVDC is also much used in dispersion from (i.e. dispersed in water) for coating of paper and paperboard. Multiple layers are necessary for good results.

   PVDC is mainly used for products which demand a very dense packaging material, like cheese and poultry, often vacuum packed in shrinkable PVDC. It can be heat sealed by high frequency sealers or by impulse sealers.

   PVDC, being the plastic material with one of the best barrier properties of all commercially available plastics, will always find its use when there are high barrier property requirements. Some examples are PVDC lacquered cellophane for biscuits and other moisture sensitive products. PVDC is also used a lot as a component in sophisticated laminates for meat packing; a co-extruded PE/PVDC/PE is an important material.

8. Regenerated cellulose (cellophane), is the dominant material in the group of cellulosic materials used for the same purposes as plastic films. Cellophane was the first commercially exploited packaging film and for a long time it was also the leading one in quantity. The polyolefins, and particularly polypropylene, have taken over a lot of ground from cellophane, but the latter still remains an important packaging material for certain purposes.

   Production of cellophane starts with highly purified chemical cellulose pulp, which is brought to a syrup-like consistency by added solvents. This "viscose" is extruded from a long narrow orifice into a regeneration bath to form a film. This material, therefore, is called regenerated cellulose. The word "Cellophane" is actually a registered brand name which has acquired a generic meaning. There are great many varieties of cellophane, tailor-made for several different uses. The coding system, designed to differentiate between the various types of cellophanes is explained in section 4 of this note.

   The most used type of cellophane is MSAT, which means a quality that is moisture-proof, heat sealable, anchored and transparent. Cellophane is often lacquered with nitrocellulose or PVDC (Saran) lacquer. This lacquer layer provides a good moisture barrier and heat sealability while the base material in itself is a good barrier, when dry, against gases and aroma. Due to its transparency and rigidity, which makes it possible to run this film on very fast packaging machinery, cellophane is very widely used in the textile and confectionery industries. Sometimes, cellophane lacquered on one side only is used for wrapping fresh met or processed meat products.

   A problem with PVDC lacquered cellophane, in comparison with homogenous plastic film types, is that the heat seal bond is not particularly strong, as it is limited to the adherence of the lacquer to the surface of cellophane. This material has low tear resistance and a seal can easily be torn open. This is sometimes actually an advantage, e.g. for pouches of sweets. Cellophane has very good printing properties and can be successfully printed by all suitable printing methods.

   There is a certain amount of water contained in the cellophane and it is this moisture content that gives the film its flexibility. If it is allowed to get too dry, it will consequently become brittle and tear easily. For freezing temperatures it is absolutely necessary to choose the correct grade of cellophane, since a grade not specially built to withstand low temperatures will easily fail in use.

   Cellophane is mostly used for foodstuffs, tobacco, textiles and sweets. For sweets a laminate composed of cellophane-wax-cellophane or cellophane-gluecellophane is mainly used, in both cases with the printing trapped between the two layers. Other important uses are as laminates for vacuum packaging of meat products, cheese, fish, pickled vegetables, mustard, etc.

9. Cellulose acetate (CA) has a brilliant transparency and is therefore used a lot as a window material for bags and cartons, as well as for covers for gift boxes, etc. Cellulose acetate can be used successfully for skin and blister packages by the thermoforming method. CA is dimensionally very stable in varying moisture conditions and, therefore, replaces cellophane as a laminate with paper, such as that used for book covers, brochures, record sleeves, etc.

THE BENEFITS OF PLASTIC FILM

The use of plastic film has grown steadily over time. According to data compiled by SPI, only 8,690 million pounds of plastic were used to manufacture film in 1990; by 1994, that number had increased nearly 20 percent, to 10,375 million pounds. A brief discussion of some of the benefits of using plastic film, all of which have contributed to its recent growth in packaging applications, follows.

• Source Reduction

Perhaps one of the biggest and most overlooked benefits of plastic film is its ability to substantially reduce the amount of material needed to make a product or package. How does it do that? Plastic has a high strength to weight ratio, which means that manufacturers can use less material when making a product or package. For example, in rigid packaging, a 16-ounce soft drink container can be made with only 30 grams of plastic whereas the same size container would require 200 grams of glass.3 That means that substantially less packaging is needed to produce a package when a manufacturer uses plastic instead of glass.

Plastic film, however, has an even higher strength to weight ratio than rigid plastic, which means that manufacturers need even less material to make a package. For example, a plastic film pouch used to deliver concentrated fabric softener is 85 percent lower in weight and volume than a comparable plastic bottle, yet it delivers the same quantity of softener to the consumer. 4 The material minimization benefits that plastic film provides are among the reasons it has become a popular choice for packaging. In addition, if a package requires less material on the front end, it also creates less waste on the back end (i.e., waste minimization), which also makes plastic film desirable to manufacturers. (For more information on source reduction and waste minimization, see page 10.)

• Cost

Plastic film's high strength to weight ratio also plays a significant role in a manufacturer’s bottom line. Because very little plastic film is needed to produce a highly functioning flexible package (thicknesses generally range between .0005 and .003 inches), the manufacturer has to purchase less material for the package, which translates into lower costs.

Using flexible packaging also can reduce costs in other ways. It takes less energy to produce; it takes up less space in stores and in production facilities; its light weight helps reduce transportation and fuel costs; because the packages are smaller, it requires fewer trucks for shipment; and distribution losses are minimized because it is easy to handle and does not break.5

One example of the cost benefits of using plastic film is reflected in DuPont’s Mini-Sip™ package. The company, which provides packaged milk to schools across the countr y, recently decided to switch from using standard and slim-line milk cartons to using the Mini-Sip™ flexible pouch. The cartons require 13.3 and 10.2 grams of material respectively, whereas the pouch requires only 2.3 grams of material to deliver the same amount of milk. As a result of the switch,

1. significantly less packaging material was needed to make the pouch;
2. the energy used to produce the package decreased 72 percent;
3. refrigeration space utilization increased 50 percent (at the dair y, on trucks and in schools); and
4. there were fewer product losses because the pouches were hermetically sealed.

In addition, the schools that used the new milk pouch reduced the amount of waste in their trash cans because the uncompacted Mini-Sip™ took up 70 percent less space than the milk cartons and the amount of waste going from the schools into area landfills decreased by 90 percent because the compact - ed pouch took up even less space

• Functionality

Another benefit of plastic film is that it can fulfill all of the necessary functions of a package, including containing and protecting a product as well as providing convenience and information to the consumer.

Containment: Containment simply means that a package must be able to hold a product and give the consumer a convenient way to transport it. For example, it would be very difficult and time consuming to move a dozen apples, 12 rolls of toilet paper, or frozen peas from the grocery store shelf, into the shopping cart, through the check out lane, out to the car and into the home without a surrounding package. Because a film package can contain these and other products in the package and allows for easy transportation, it meets the packaging requirement of containment.

Protection: Protection comes in a variety of forms. For example, a film package used to contain clothing at a retail outlet protects it from dirt so that it is clean when the consumer buys and wears it. Similarly, the film around lunch meat helps keep the product free from bacteria; the film around potato chips keeps the product fresh and protects it from exposure to oxygen, moisture and light; and the film around fresh fruit protects it from insects and helps keep it clean. In these instances, the package made with plastic film is protecting the product from exterior influences that could harm and/or devalue the product.

A good package also helps preserve products. For example, the film around meat extends the product’s life beyond what it would be in a case at the butcher shop. Similarly, the plastic film used to package cheese, fresh vegetables and bakery goods preserves the products inside because exposure to oxygen would substantially shorten their lives.

Convenience: Film in packaging and nonpackaging applications also provides convenience to consumers. For example, film can be clear, which allows consumers to see a product before they buy it or colored to protect the product from too much exposure to light. It can be fabricated in a variety of sizes—from a one-ounce candy bag to a 2,000-pound bulk bag used to hold powdered chemicals—which makes it ideal for very small and large products or products that are oddly shaped. Plastic film also can conform to the product, which helps save valuable shelf space at home and in the store. In nonpackaging applications, such as retail and storage bags, plastic film can be formed into packages with handles and drawstrings for easy carrying and zip-lock tops for repeated opening and closing. Plastic film also can be used as a mechanism to provide evidence of tampering with a product or package, important for consumer safety.

Information: Finally, plastic film can be printed, which means that manufacturers of a product can relay important information to the consumer, such as the name of the product, its ingredients and its value. In addition, instructions on how to use and/or prepare the product can be printed on the film package. These examples demonstrate that plastic film can fulfill the necessary functions of a package, which, in turn, has contributed to the growth of its use in packaging and nonpackaging applications.

• Versatility

Another benefit of plastic film is that it is versatile; it can be used alone, used in conjunction with other plastic resins or even used in conjunction with other materials, such as paper and aluminum. This versatility allows manufacturers to create packages that can perform very specific functions. Following are some examples of such packages.

Single-resin, single-layer packages: A produce bag that contains apples or potatoes is an example of a single- layer, single-resin package. It usually is made of one layer of LDPE or LLDPE and a metal crimp or twist tie is used as a closure device.

Multi-resin, multilayer packages: Some products, such as frozen vegetables, are designed to be cooked while still in a package. The bag used in this application— commonly referred to as a boil-in-bag—is made of three materials (two of which are film) and draws on the properties of different resins. It typically consists of a PET layer, which provides strength at the temperature of boiling water, and a polyethylene layer, which is needed for heat sealing. An adhesive is then used to hold the two layers of film together. Bubble packaging is another example of a multi-resin, multilayer film package, which is made with a combination of two nylon layers and one polyethylene layer.

Multi-resin, multilayer films are sometimes referred to as co-extruded films because they are made in a manufacturing process called co-extrusion. In this process, separate extruders are used to produce layers of different polymers. The layers are joined together in the liquid state just before the extrusion die. The combined layers then pass through the die to be cast or blown into one multilayer film.7 Co-extrusion is desirable because it can take the best properties of different resins and join them together into a common structure that performs better than its individual parts.

Multi-material packages: Skin packages, which are increasingly used in hardware stores and retail outlets, are a good example of multi-material packaging. In these packages, products such as nuts and bolts are placed on paperboard. A thin layer of plastic film (usually modified polyethylene) is heated and placed over the product and paperboard. The heat-softened film is then drawn down by vacuum to stick to the paperboard, thus sealing the product inside. This multi-material package, made of both paperboard and plastic film, is desirable because it is easy to handle (which helps reduce distribution losses), it cuts down on excess inventories and helps reduce clerical costs and pilferage at the retail level.8

Metallized packages: Some packages appear to be made with more than one material, but actually are made with just one specialized plastic film. A potato chip bag is a good example. Although it looks like it has an aluminum inner layer, it really is a micro-thin deposit of aluminum on the polypropylene, which is vaporized into the film (like a coating). This is referred to as “metallized” polypropylene. The aluminum coating is needed to block out ultraviolet rays, which would cause product degradation, and the polypropylene is needed to resist oxygen, which would turn the fats in the product rancid.9

All of the benefits discussed in this section of the report demonstrate why plastic film is used in packaging and nonpackaging applications and why its use has grown over time. Plastic film helps reduce waste at the source and in trash containers and landfills. It helps reduce costs during production, distribution and use. It minimizes product loss because of its unique properties and its ease of handling and storing. It performs all the functions required of a highquality package. And, its versatility allows manufacturers to design packages to perform in very specific and necessary ways.

And, while plastic film use has grown in the past, it is expected to grow even more in the future. In Modern Plastics Encyclopedia (1996), Business Communications Company predicted an estimated 4 percent average annual growth rate in the demand for flexible plastic packaging until 1998. (The estimates are based on actual data from 1993 through mid-1995 and estimates for mid-1995 through 1998.)

Reference:www.plasticsresource.com - American Chemistry Council

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bags film ~ plastic film roll ~ polythene films ~



HOW TO EXPRESS THICKNESS OF PLASTIC FILMS

A plastic film is a web material with a thickness not exceeding 0.25 mm or 0.001 inch. Material over this thickness is considered as sheet material. There are several ways of designating thicknesses. The most common are:

A THICKNESS OF A PLASTIC FILMS ARE USUALLY MEASURED USING A MICROMETER
• millimetres (mm) = 0.039 inch
• microns or mu (u) = 0.001 mm or 0.000039 inch
• mil (or thou) = 0.001 inch, 25.4 microns or 100 gauge
• gauge (or gage) = 0.00001 inch, 0.254 micron

For Example:

mm	inch	gauge	mil	microns(mu)
0.0064	0.00025	25	¼	6.4
0.0127	0.0005	50	½	12.7
0.0254	0.001	100	1	25.4
0.0508	0.002	200	2	50.8



packaging film ~ plastic films ~ plastic film sheet ~



General Properties of Plastic Films

The most important properties of plastics films in packaging are:

1. Tensile strength represents the force required to break the material in relation to a given area. Polyester film or oriented PP both have high tensile strength, normally over 400 kp/cm2 (40 MPa), cellophane can reach values over 600 kp/cm2 (60 MPa), but LDPE lies between 100 and 200 (10-20(Mpa).


2. Tear strength is a very important feature and governs the end use of many types of packaging films. It is a guide to the applicability of the films for certain machine operations. For some packages, a low tear resistance may be useful (e.g. a bag of potato chips). PE has a high tear strength, whereas cellulose acetate films have low values in this respect.


3. Impact resistance is a useful property, particularly when packing heavy products in plastic films or for big containers, which are directly subjected to shocks during transport. The method of testing this property is to drop a weight on the material and measure the force needed for penetration or breakage.


4. Stiffness may be important in some machine applications where plastic film is used. But it is also important for bottles and other containers where a rigid package with minimum wall thickness but maximum strength properties is needed. Stiffness can be measured by weighing a stretched material and measuring the rate of deflection.


5. Temperature resistance for plastic materials is composed of several different factors: The softening point indicates the temperature at which the structure of a thermoplastic begins to be affected. It is measured by slowly heating a sample of the plastic at a controlled rate and determining the temperature at which a weighted needle penetrates one millimetre into the sample. This is called the Vicat softening point.

Melt index is a term used to indicate the rate of flow of a thermoplastic at a given temperature under a specific pressure and through a specific orifice dimension in a given time. The melt index expresses the amount of plastic that flows out through the orifice in grams per 10 minutes.

Heat seal strength expresses the force needed to pull two heat sealed surfaces apart from each other at right angles. Polyethylene produces a very high strength seal and cellophane a much weaker one. Sometimes, a strong heat seal bond is not required, as for instance in bags for sweets and potato chips.

Another factor to consider is whether the film gets brittle when subjected to low temperatures. This is important for frozen food packaging, where polyethylene is a better alternative than cellophane.

The material should also have a certain permanence, which may also mean ability to withstand extremely high temperatures. This may be necessary for so-called boil-in-bag applications. Permanence can be described as general ability to withstand changes in environment without loss of essential properties.

6. Moisture resistance is a factor which is often very important in determining the suitability of a plastic film for the packaging of many products. Some products need protection from outside air moisture, others require that the moisture contained should not be allowed to evaporate through the package. There are several methods of measuring this, the simplest one being to stretch a piece of a film over a container with water, which is then placed in a drying chamber containing a desiccant to absorb the water transmitted through the film. The water in the test container is weighed before and after the standard test period and the Water Vapour Transmission Rate (WVTR) or Moisture Vapour Transmission Rate (MVTR) is expressed in grams of water diffused through one square metre (or 100 square inches) of film in 24 hours (g/m2/24h or g/100 sq.in/24h) with indication of the temperature and the relative humidity on the two sides of the barrier.


7. Gas barrier properties are not the same as water vapour transmission resistance. In this case the transmission rates of specified gases like nitrogen, carbon dioxide and, especially, oxygen are measured. Fresh coffee, for instance, generates carbon dioxide, which should be allowed to escape from the container, as otherwise it may burst because of inside pressure. Oxygen, on the other hand, makes coffee stale and should be excluded from packs for this product. A material with low oxygen but high carbon dioxide permeability should, therefore, be selected. An example of packs requiring high oxygen transmission is packing fresh meat for immediate sales. Meat needs the presence of oxygen to preserve its bright red colour, so attractive to many customers. The procedure of measuring gas permeability is to determine how much of a given gas is diffused through the material in a given time, in principle the same method as for the measurement of WVTR above. The values given are in cubic centimetres of gas per one square metre or 100 square inches of material in 24 hours (cm/m2/24h or cc/100 sq.in./24h) with indication of the temperature at which the measurement is made. Some additional properties of plastic materials might also be listed and explained in this context:

Elongation is the degree to which a plastic material will stretch before it fractures. The more it stretches, the better it will absorb shock loading, making breaking less likely. This is important for many applications, such as heavy-duty plastic sacks.

Elongation is expressed in per cent of original length. Polyethylene and polypropylene have high values, up to 450 per cent and over, whereas polyester and polystyrene have very low elongation values.

Hardness of plastic material is determined, for example, with a Rockwell tester, which has a steel ball of a specific diameter, weighed with varying loads. The depth of the indentation when the load has been removed is measured. The higher the Rockwell number, the harder the material tested.

Elasticity is an important factor to consider in plastic packages. What it really expresses is the ability of the material to return to its original shape and size after having been subjected to a load. One could describe it as "memory". Beyond the memory limit, however, the material stays stretched and no longer returns. Elasticity is expressed as a modulus of elasticity. Some materials, such as plasticized PVC, have a low elasticity modulus and stretch well, while others, like polystyrene, have a high elasticity modulus and stretch very little.

Dimensional stability can, in some cases, be heavily influenced by changes in the relative humidity surrounding the package. Some materials expand, and others actually shrink, while some remain relatively unaffected.

Film slip is the friction a film is subjected to in contact with another plastic surface or a machine part, etc. It can be measured by using an inclined plane, recording the angle where the weight of the sample overcomes the surface friction. The slip characteristics can be adjusted by additives to the film. As an example, there are principally three grades of slip for PE film:

1. high slip, coefficient 0.1 - 0.3
2. medium slip, coefficient 0.3 - 0.5
3. low slip, coefficient above 0.5

Grease and oil permeability is important when the packed product contains fat. The appearance of the package could be spoiled if the fat is allowed to migrate through the material to the surface of the pack.

Measuring of grease and oil permeability is carried out by placing a pile of fine sand saturated with an exactly measured amount of oil or turpentine on top of a film sample over a piece of absorbent paper. The time needed for the oil to penetrate the film and show up on the paper is recorded.

Haze and gloss are extremely important properties in plastic packages, since many users demand a highly transparent material with a glossy and brilliant appearance. Haze appears as milkiness, which lowers the transparency of the film. It can be measured by determining the amount of light diffused by the test sample, as well as the amount transmitted through the material. Gloss relates to the measurement of the amount of light reflected by the film. A light beam is projected against the surface at a known angle and the amount of light reflected is measured by a light meter.

Flammability, or ease of burning, can be very important in some applications. Some films burn readily, such as cellophane, others, like ionomers, burn slowly. Polyethylene burns slowly but melts at the same time and forms burning drops. Others are self-extinguishing, like PVDC; rigid PVC is very difficult to burn at all.

Reference: www.intracen.org - International Trade Centre UNCTAD/WTO


plastic bags ~ polythene bags ~ poly bags ~



Research News




Nucleation agent is key to new plastic film

Underlining its ongoing to commitment to plastic films, Milliken has launched a new nucleating agent that delivers optical improvements, an enhanced moisture barrier and improved mechanical properties for polyethylene (PE) resins. As a result, says the company, functionality in films and packaging can now be expanded.

Nucleating agents provide a physical, molecular-level trigger point around which highly-ordered crystalline structures called spherulites form rapidly. Known as Hyperform HPN-20E, this agent has recently been granted food contact notification (FCN), which opens up a range of new options for customers in the PE industry.

Target applications include monolayer and coextruded film for food packaging, agricultural applications and overwrap films. Early focus has been in the area of linear low density polyethylene (LLDPE) resins where optical enhancement is vital for shelf appeal. Traditionally this has been achieved through blending low density PE (LDPE) into LLDPE. Unfortunately, this can result in reduction of tear and impact strength of the resultant film. Nucleating LLDPE with HPN-20E can enhance optics without detriment to tear and impact, offering film producers a new and novel option for packaging film constructions.

In addition, the nucleating agent is showing some improvement in PE film hot-tack performance that can potentially speed up vertical form, fill, and seal lines (VFFS). It also permits potential down-gauging by enhancing stiffness and eliminating much of the reduction in tear and impact performance associated with LDPE blending. This presents potential new ways for cost effective film constructions.

According to Milliken, nucleating polyethylene with Hyperform HPN-20E is also showing exciting reductions in water vapour transmission rates (WVTR), hence enhancing the barrier properties of polyethylene film layers – high density PE (HDPE) and LLDPE – used in a range of different coextruded structures. WVTR reductions on the order of 40percent (LLDPE) and 20percent (HDPE) have been observed in trials.

A new, in-house blown film line underscores Milliken Chemical’s commitment to PE and film, both of which are relatively new initiatives for the company (Fig.1).

“Polyethylene and polyethylene film are a new area for Milliken,” said Martin Horrocks, global market manager, polyethylene additives, “but we are learning that nucleation can bring value to this polymer and our short term focus is to understand how the benefits of nucleation of PE can drive value for our customers. Polyethylene is a very difficult material to successfully nucleate and HPN-20E is the most efficient chemistry to achieve this. We want to help the market investigate the types of improvements this technology can deliver. Long term, we want to investigate other areas of PE outside of film where nucleation can create value. A first example of this involves cycle time reductions in blow molding high density polyethylene.”

Reference: www.engineerlive.com

Environmentally friendly plastic film of potato starch

Plastic made of potato starch is a promising material for packaging, which is a big new application for starch plastics. This is shown in Åsa Rindlav-Westling’s doctoral dissertation, which was carried out in Paul Gatenholm’s research team in polymer technology at Chalmers University of Technology, Sweden.

Our huge quantities of refuse could be reduced and a greater proportion than today could be composted. Combustion of materials from oil, such as conventional plastics and fossil fuels, raise levels of carbon dioxide in the atmosphere, increasing the risk of the greenhouse effect and environmental problems. Starch polymers, extracted from potatoes, corn, and wheat, for instance, can be used as raw materials for biologically degradable plastics. Today the EU has a surplus of agricultural products, and a certain share could be used as raw materials in the production of plastics. At present disposable eating utensils and packaging chips are made from starch. A major new field of use for plastic films made of starch could be packaging. Starch films have excellent oxygen-barrier properties and in some cases can replace aluminium when it comes to protecting oxygen-sensitive foods.

Potato starch is produced from carbon dioxide and water with the help of energy from the sun when potatoes grow. Åsa Rindlav-Westling’s doctoral work deals with plastic films made from potato starch. Her work has involved studying starch-film structure, which affects its properties. By varying the conditions under which the film is produced, she has been able to control the structure. Slow formation of film results in starches that exhibit well-ordered films, and crystallinity is high. Film properties like strength and elasticity are affected by crystallinity.

The films exhibited excellent properties as oxygen barriers. In high humidity, however, both the barrier properties and the strength of the films deteriorated. This is due to softening caused by the penetration of moisture. A new theory is presented regarding how water is redistributed in the film after heating, thereby influencing properties. One way to prevent water from penetrating the film is to treat its surface, and experiments were made involving plasma treatment, in which a glass-like surface or a strongly water-repellent surface was formed. A further possibility is to add water-repellent substances to the film, which will deposit themselves on the surface. Proteins in the starch turned out to migrate to the surface, which thereby became more water-resistant.

The study shows that starch is an extremely promising material for use in biodegradable and renewable plastics. The knowledge yielded by this work will be of use the development of new and environmentally friendly plastics. The dissertation Crystallinity and Morphology of Starch Polymer of Films was publicly defended on March 15.

Reference:www.innovations-report.de

Growing wheat under plastic

Early results from field trials on wheat crops show that a special plastic film that goes over crops during planting accelerates plant growth and encourages vigorous, high-quality crops despite dry field conditions. The discovery was announced earlier this year at the launch of a new Polymer Cooperative Research Centre.

The low-cost plastic covering can be applied to rows of crops using a fully automated system. It provides a temporary greenhouse environment that warms the soil and retains existing moisture in the soil. The plastic eventually degrades in the sunlight.

Field trials with the plastic were conducted in conjunction with the Birchip Cropping Group in Birchip, Victoria, a dry area with marginal rainfall. The trials have shown that, compared to the control crop, wheat that germinated under the film had higher protein content and lower moisture content in seeds. Wheat with these two key qualities commands premium prices in the market.

The research on the films is being conducted in the Cooperative Research Centre for Polymers (CRC-P). Research partners include: the Queensland University of Technology, the University of Queensland and the Swinburne University of Technology. The commercial partner is Integrated Packaging Pty Ltd. The CRC-P is conducting further tests on different films developed using innovative polymer technology.

The technology relies on the plastic film being degraded by sunlight so that plants can penetrate the weakening film at a critical time in their growing cycle without physical damage, and before they suffer heat stress.

Agricultural plastic films are already commercially used overseas on maize crops, but the CRC-P scientists are developing technology that controls and adjusts the rate of film degradation to suit the growing pattern of Australian crops such as wheat, barley, and cotton.

Dr Ian Dagley, CEO of the CRC-P, said the research team was looking at improving the system by controlling degradation through the use of novel additives in films.

"The team has so far developed 45 films and is consolidating their understanding of the process and the variables that affect film performance and the interaction between plant and film", he said.

According to Dr Dagley, the scientists are also determining the critical time in the plant's growing cycle when they need to be able to break through the film, so that they can develop a film that will weaken at precisely the right time for a given crop.

"The aim is to produce a film that is completely broken down by harvest time", he said.

The research team is currently running four trials. In South Australia and NSW, the film is being tested on wheat. In Victoria, it is being tested on wheat and lentils, and in Queensland, on maize and sorghum. A fifth trial is being planned for use on cotton in Narrabri, NSW.

Research into agricultural plastic films is one in the suite of research being undertaken by the CRC-P which received $32 million from the latest round of funding from the Commonwealth's Cooperative Research Centres Programme.

Other projects for the Centre include: technology to manufacture blood products from cells; polymer-based materials that, on exposure to fire, transform into ceramic fire barriers; low-cost transformable polymer solar cells; and computer modelling software that allows better design of moulded components.

Reference:www.future.org.au

Mode of Action of Plastic Film in Extending Life of Lemon and Bell Pepper Fruits by Alleviation of Water Stress 1

The mechanism by which seal-packaging individual fruit in high density polyethylene film delays deterioration was investigated with lemon (Citrus limon [L.] Burm. f. cv Eureka) and bell pepper (Capsicum annuum L. cv Maor) fruits. Seal-packaging effects were due to the water-saturated atmosphere in the sealed enclosure around the fruit. Softening of fruit was highly correlated with declining water potential of fruit. Sealing drastically inhibited softening as well as changes in cell wall pectins. Sealing also delayed disintegration of membrane as shown by the inhibited leakage of amino acids, in particular, and electrolytes in general. All these effects of sealing were prevented or reduced by including hygroscopic CaCl2 in the sealed enclosure which reduced the ambient humidity. Furthermore, some of these effects of sealing could be achieved also by maintaining nonsealed fruit in water-saturated atmosphere. Sealing effects could not be related to a possible `modified atmosphere' mechanism in O2, CO2, or ethylene. This work supports the hypothesis that the mode of action of sealing in the polyethylene relates to the alleviation of water stress which exists in harvested fruit.

Reference:/www.plantphysiol.org

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