Shrink Wrap 101
Shrink Wrap What?
Shrink wrap packaging applications.
Shrink Wrapping Printed Materials - This is still the largest of all market segments. Once dominated by PVC films, the introduction of the low shrink force polyolefin?s has dramatically eroded the PVC domination of this market.
Businesses involved in this segment range from small job shop printers up to large business form producers. Gone are the days of contracting these jobs out, as most now perform the packaging within their own facilities.
Shrink Wrap Film For Toys, Games and Sporting Goods - Shrink is used here to assure product integrity and offer the consumer visual appeal. Plastic models, puzzles and games all benefit from the security of shrink film.
Shrink Packaging For Hardware and House ware - A broad category with a tremendous variety of product being over wrapped. From tools to plastic bowls, shrink fulfills the need once served by corrugated and blister packaging.
Shrink Wrap For Packaged Foods - Major applications include frozen pizza, ice cream and frozen foods. The fastest growing trend is the process of multi-packing products for sale at wholesale type stores. The use of shrink offers the benefits of enhanced visual appeal; tamper evidence and prolonged shelf life, through the prevention of freezer burn.
Shrink Wrapped Stationary, Cards and Gift Wrap - PVC films are still widely used to protect these easily damaged products and improve appearance. Today?s soft shrink films afford the opportunity to introduce polyolefin films into this market.
Shrink Wrap Packaging For Pharmaceuticals - Spurred by the need for tamper-evidence, this market has grown in recent years. Lower cost alternatives, i.e. PVC shrink bands, control most of the individual product need, however, shrink offers the ability reduce costs through multipacking with film vs. other packaging alternatives.
Shrink Wrap For Video Tapes and CD's - These products all benefit from some sort of film over wrap. Video is predominately shrink wrapped where CD is usually done with a non-shrink process such as tuck and fold. More and more CD producers have turned to shrink as they are updating equipment.
Shrink wrapping is widely used across the spectrum of industries and is finding its way into new segments daily. The retail appeal and security offered insures growth for the future.
Shrink Wrap How?
Shrink wrap is manufactured and processed.
All Blopane film products are co-extruded films. Polymer resins are loaded into hoppers at the rear of extrusion equipment. These resins are then pushed through a heated barrel by a screw. When forced down the barrel the resins are melted and compacted then finally forced through a circular die.
Bollore uses multiple extruders to feed into one die. The resin from each of these extruders is then layered over one another as the melt exits the die. This results in a multilayered product.
The extruded structure in the form of a tube is then turned upward, then back downward and filled with air. This process converts the tube into a bubble. This bubble is then stretched on both axis, horizontally by the airflow and vertically by means of a set of pinch rollers drawing the tube down. The act of stretching the film tube on both axis is known as bi-axial orientation. A bi-axial orientation gives the film many of the required strengths of a shrink film.
The pinch rollers collapse the bubble into sheet form where it is then rolled onto a core. This roll of material is called a mill log.
The mill logs are then converted into the finished product. Conversion entails slitting of the film to width and folding in the case of centerfold film. Preperforation is completed during this conversion process.
Shrink Wrap Sizing
Shrink film quantity calculated by package size.
Shrink wrap sizing also known as package sizing is the act of determining the appropriate size film for over wrapping of a specific package with shrink film. Many factors must be considered when sizing the film requirements. The actual product dimensions, the orientation of the package as it will introduce into the film and the type of equipment to be used are all required information. Failure to obtain this information or incorrect specifications may result in inappropriate film size being calculated.
Each package has three dimensions, which must be known. These measurements should be made with the orientation (positioning) of the package as it enters the film identified.
- Product Width: The dimension of the product in the Transverse (parallel to the cut-off or cross seal) direction.
- Product Length: The dimension of the product in the Machine (parallel to the fold of the film, in cases of centerfold film) direction.
- Product Height: The actual height of the product. In cases of products with uneven surfaces, the height should be considered from the bottom to the highest point of the package.
- Product Orientation: When measuring a product for film sizing, remember to use the longer dimension as the product width (bearing in mind, it must not surpass the seal dimensions of the equipment being used).
- Less shrink waste: By orienting the package using the shortest possible dimension as the product length results in the smallest amount of waste, in cases of centerfold use or side seal applications.
- Increased packaging speed: A shorter product length results in faster cycling of products into and out of the sealing area. Over the course of a production shift this incremental time savings can produce large dividends.
- Increased film roll bag yield: Although a product requires the same square inches of film regardless of orientation, the amount of scrap produced is decreased.
Another consideration when recommending film size is production speed. In many cases, the formula to calculate required film size turns out not to be a whole number. Although 1/2" increments are available, most users opt for a standard inch size, usually rounding down in an attempt to save money. Many times this practices actually costs more than the cost had they rounded up and increased the film size. By trying to use the narrowest film size possible, users may actually make an operator's job more difficult, reducing production speed and increasing the overall package cost.
Once package orientation and dimensions are established, the next consideration is the type of equipment upon which the package is to be wrapped. Specific types of equipment dictate the use of either center folded or single wound film. Furthermore, some types of machinery demand the use of wider film sizes than others due to the mechanics of their operation.
When using the film sizing formulas to calculate film sizes, be sure to use the formula for the type of equipment it is to be used on.
Shrink Wrap Costing
Shrink wrap costing formula and process.
The end-user of shrink film purchases the product by means of roll cost. A roll of 60 ga. film costs $XX.xx. Many times a person would like to know how much the amount of film on each package is costing them.
For example; a small manufacturer is over wrapping his product on a manual L-bar sealer. His current supplier has recommend he use 8" centerfold film in a 60 ga. material.
- The dimensions of his package are 2" tall x 4" x 8".
- Obviously, he is wrapping his package by orientating it with the 8" side in the machine direction. In doing so, each cycle is producing a scrap tail 11" long by approximately 2". That calculates out to 22 sq.inches of scrap per package. (2 layers of scrap, 1" wide. Centerfold!)
- Industry standard put-up is 4370 feet of film per roll. That equates to 52,440 inches in length. (Feet x 12 = number of inches)
- Dividing 52,440 by 11 ( bag length or cut-off) equals 4767. That is the maximum number of packages obtained from each roll of film.
- Dividing the price paid per roll of film by 4767 determines the cost per package.
- Remember that 22 sq.in. Of film wasted each cycle? Multiplied by 4767 (total # of packages per roll) the total amount of wasted material is 104,874 sq.inches.
- In the case of an 8" centerfold, a roll with a total area of 839,040 sq.inches, his current scrap waste is 12.5% of the total amount of film purchased!
- Lets re-orientate this package and check the savings.
- Turning the package 900 results in the need of 12" film. The cut-off however is reduced to 7" That results in a total waste of 14 sq. inches of film per package. The net result is 35% less scrap!
With the new situation, the total amount of scrap generated equals 8% of film purchased. By simply turning the product this shrink wrap customer has saved 4% per roll. In addition to the savings this shrink wrap customer will benefit a higher package yield from a single roll (7491 pkgs / per roll) and increased production speed.(the new package is 35% shorter than the old method allowing faster through-put.)
Shrink Wrap Systems
Shrink wrap equipment and shrink wrap machines.
Choosing the right shrink wrap equipment for your packaging needs is a very important step in designing an effective and efficient packaging operation. There are many different types of shrink wrap systems designed for different applications, performance levels and budget. When shopping for a shrink wrap system, take into consideration what your needs are now and in the future.
Questions to Consider Before Purchasing A Shrink Wrap System
What do you want to shrink wrap?
There are many types of shrink wrap film that are suited for specific types of applications. Shrink wrap films should be considered when shopping for a shrink wrapper system to ensure no shrink film issues arise later.
Shrink wrap packaging speed?
Shrink wrapping systems vary widely in the packaging speed. Know your wrapping output needs and compare systems. For example some shrink wrappers pack several products an hour while others pack 35 products per minute and more. Once volume levels are determined, degree of automation can be considered as well, choices are: manual shrink wrappers, semi-automatic shrinkwrappers or fully automatic shrink wrapper systems.
Shrink wrap system in the BIG Picture.
Is the shrink wrapper to be integrated into an automated packaging production line? If so, not all shrink wrap systems are suited for integrated packaging operations and add on systems like conveyors will need to be carefully selected for flexibility and suitability for the packaging processes involved.
Shrink wrap packaging size?
Like most things, shrink wrap systems, machines and applicators come in different sizes. If your packaging units are large, likely your shrink wrap system will be too.
Do you have work space limitations?
Shrink wrap machines come in different sizes and mobility. For example if you have small space, small items to package and need the system to move as your workspace demands, you may want to consider a compact straight l-bar sealer as your shrink wrap system of choice.
Shrink film terminology explained.
Angel hair - Thin strands of film appearing at the cut end of film resulting from sealing.
Ballooning - A pillow effect created when air is trapped within the shrinking bag.
Bead Seal - A thin round weld created when pressure and heat are applied to two layers of film.
Bi-Axial Orientation - Oriented along both X and Y-axis.
Blocking - A condition in which two layers of film adhere to one another.
Blown Film - A film extruded by air inflation.
Burn Through - A temperature or condition where a film becomes cloudy or burns in the shrink tunnel.
Centerfold Film - A film that has been folded in half, lengthwise.
Centerfolder - A mechanical device used to create centerfolded film.
Coextrusion - Two or more polymers extruded and combined in a die, each forming a distinct layer in the final film.
Cold Slip - The amount of force required to slide two surfaces against one another at ambient temperature.
Cold Flex (CF) - Ability of a film to perform at low temperatures without failure.
Copolymer - Result of two monomers being combined through polymerization.
Core - A paper tube on which film is wound.
Cross-Linking - A process which binds the polymer chains into a network. Significantly increasing a films heat stability and strength.
Crow's Feet - A series of wrinkles radiating out from a finished package's corners.
Dog-Ears - Triangular projections of unshrunk film at the corners of finished packages.
Drape - The softness of a film characterized by the ability to conform to irregular shapes.
Electron Beam - A device used in the cross-linking process.
Fish Eyes - A scalloped surface on a finished product surface.
Form-Fill-Seal - A type of equipment, which produces a tube of film into which packages are introduced.
Gauge - A term used to describe the thickness of a material.
Hole Punch - A mechanical device used to produce an air evacuation hole.
Hot Slip - The amount of force required to side two surfaces of heated film against on another.
Impulse Seal - A heat sealing technique where the element is pulsed with voltage during the sealing cycle.
L-Sealer - A term used to describe equipment where the seal area is in the shape of an "L".
Laminate - A general term used to describe structures comprised of two or more materials.
Lap Seal - A seal made with two layers of film overlapping one another.
Machinability - The ability to form and seal on over wrapping equipment.
Machine Direction (MD) - The direction the film is manufactured and moves through the sealing equipment.
Memory - The ability of a film to maintain its characteristics after shrinking.
Monoaxial - A film, which is oriented to shrink in only one direction.
Monolayer Film - A single layer film extruded from one or a blend of raw materials.
Mutilayer Film - A film comprised of more than one layer of similar or different polymers.
Opaque - Relatively impervious to light.
Orientation - The stretching technique used in the manufacturing of film.
Oriented - The stretching and aligning of a film's molecules at a temperature below its melting point.
Perforations - Air evacuation holes in a film made by pin perforators.
Pin Perforators - A device used to produce small holes in film to allow air to escape during the shrinking process.
Polyethylene - A simple thermoplastic polymer of ethylene.
Polymer - A material made through the process of polymerization.
Polymerization - A gas heated under pressure forms a solid.
Polyolefin - A generic term used to describe ethylene and/or propylene based plastics.
Polypropylene - A thermoplastic polymer of propylene.
Preferential Shrink - The characteristics of a film to shrink more or less in a specific direction.
PVC - Polyvinyl Chloride.
Selvage - Another term for trim waste.
Shrink - Defined as the ability to become smaller.
Shrink Tunnel - A type of equipment featuring a chamber producing heat and airflow designed to shrink film.
Singlewound Film (SW)- A single layer of shrink film wrapped around a core.
Slip - The quality of a film to move over surfaces with little resistance.
Static - An electrical charge built-up in plastic film.
Static Seal - A type of longitudinal seal used in FFS equipment. Overlapping film edges are adhered to one another via a static charge.
Tap Switch - An electrical device used to control the amount of voltage introduced to sealing elements.
Tear Initiation - The amount of force required to initiate a tear.
Tear Resistance - The ability of a film to resist the propagation of a tear.
Transverse Direction (TD) - The direction parallel to the film width.
Trim - The amount of excess film severed during the sealing process.
Trim Seal - A seal made by using a sealing wire element.
Unbalanced - Unequal orientation in the LD and TD.
Wind - The direction in which the film is wound on the core.