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This is the third article in a series of blogs intended to educate users new to flow wrapping as well as to help experienced users looking for a quick reference. It explains the basic calculations used to determine film dimensions to flow wrap a specific product.  (Read the other articles in this series Principle of Operation of a Horizontal Flow Wrapper and Sealing Fundamentals of Horizontal Flow Wrapping)

Cut-off Length (package length)
First of all it is important to determine the correct cut-off length. This is especially critical for registered film that incorporates graphics that need to be centred on each package. The diagram and formula below explain how to calculate this distance.

Cut-off length

Cut-off Length = Product Height divided by 0.86603 + Total Crimper Width + Total Product Length

 

Web Width
Secondly, you must determine the film web width.  Again, one the key inputs for this calculation is the product dimensions. For products with more variable dimensions, such as bakery products, the film width must be increased to allow for bigger variations. This however, creates looser packs with wider finseal areas.

product dimensions

Web Width = 2 x (Product Width + Product Height + Fin Seal Roller Height + 5mm)

The 5mm (o.2″) can be explained by the distance (including the height and thickness of the deckplates) from the product to the fin seal rollers and some extra film to assure good tracking in the fin seal rollers.  Common fin seal roller heights are 6, 9 and 15 mm.  Together with the 5mm of film for tracking purposes, this results in finseal widths of 11, 14 and 20 mm respectively.

Use the formulas mentioned in this blog for a starting point only. Testing on your machine with actual product and film is necessary to determine film sizing and cut off.

More explanation on the basic calculations used to determine the film dimensions and flow wrapper configuration can be found in Bosch’s Guide to Flow Wrapping. Feel free to download it under the “Links and Downloads” section on the Pack 101 flow wrapper webpage on the Bosch Packaging website. This guide contains other sections to assist users in initially setting up their wrapper, changing over to new products, or solving problems common in flow wrapper operation.

Turning on the No Jam feature on your Pack 101 can be done in just three easy steps. The No Jam feature senses when product is in the way of the crimper. It allows the crimper to remain open while a designated number of products pass through before running production again.


Summary:

Step 1: In the HMI, select “Recipe”, then “Crimper”
Step 2: Turn the No Jam feature to “ON”
Step 3: Select the number of “No Jam” cycles

Watch for more tech tips and instructional videos for your Bosch equipment. For questions or technical support, contact us.

This is the second in a series of blog articles intended to educate users new to flow wrapping and serve as a quick reference for experienced users .  It explains the sealing fundamentals of horizontal flow wrapping. This is useful in selecting the general type of packaging material and determining the machine settings that can be adjusted to influence the seal quality. (Read the first article in the series “Principle of Operation of a Horizontal Flow Wrapper“)

Generally speaking, two types of film can be distinguished: (1) heat seal film and (2) cold seal film. The choice of using heat or cold seal film depends on a variety variables, such as:

  • Product characteristics
  • Material costs
  • Required capacity/speed
  • Necessary barriers (Ultraviolet, Oxygen, etc.)
  • Hermetic seal strength or integrity

 Cold seal films consists of a base material (carrier) and a thin layer of glue. The sealing of this type of film is achieved by pressing the two layers of glue together. One of the advantages of this film is that it can be used at higher film speeds than heat seal films.   It also requires no heat to seal, so the lack of hot machine surfaces may be beneficial when dealing with temperature sensitive products, such as chocolate. However, there are some disadvantages.  Primarily that they can never offer the same protection and hermetic seal qualities as heat seal film.  They also need to be stored in a climate controlled room and lastly, the cost is generally higher than that of heat seal film. Therefore this type of film is less common than heat seal film.

Heat seal jaws cutting and sealing packages on a Pack 101 flow wrapper.

Heat seal jaws cut and seal packages on a Pack 101 flow wrapper.

Heat seal films are often multi-layered and consist of an outer coating that prevents the film from melting,  the core of the film such as polypropylene, and a sealant layer on the interior which has a lower melting temperature and bonds to seal the package together.  When high integrity seals are required, heat seal film offers the best alternative.  Generally, it is also less expensive than cold seal films.   Heat seal films are also offered in a wide range of laminations so that barrier properties can be optimized to meet product protection requirements.

The three important factors that should be kept in mind and controlled when producing a seal are:
(1) Heat: Temperature of the sealing surfaces (heat is not necessary with cold seal film)
(2) Dwell: Amount of time the machine jaws are in contact with the sealing material
(3) Pressure: Amount of pressure applied to the sealing material

Whenever a change is made in any one of these factors, one or both of the other two factors must be adjusted to compensate for this change. For example, when machine speed increases significantly, the dwell time will drop, so the temperature (and sometimes pressure) may need to be increased to compensate for this.

More details on optimizing sealing parameters and an overview of  different packaging films and their uses can be found in Bosch’s Guide to Flow Wrapping. It’s available for free download under the “Links and Downloads” section on the Pack 101 flow wrapper webpage on the Bosch Packaging website. This guide contains other sections to assist users in initially setting up their wrapper, changing over to new products, or solving problems common in flow wrapper operation.

This is the first article in a series of blog articles intended to educate users new to flow wrapping as well as to help experienced users looking for a quick reference.   It covers the basic operational principles of horizontal flow wrapping. These principles are the same for every horizontal flow wrapper, often referred to as horizontal form fill and seal (HFFS) machines.

Every wrapper has an infeed conveyor, a film feed assembly (backstand), a film forming area (former), bottom seal (finseal), a cutting head and a discharge area. Food and non-food products created by processing equipment, are placed on the infeed conveyor of the flow wrapper. This can be done by hand feeding or by using an automated feeding solution. As the infeed conveyor delivers product to the forming area, film is drawn from the film feed assembly into the forming area, where a film tube is formed around the product and a finseal is created. The film tube and the product are then delivered to the cutting head. The cutting head creates the end seals while it cuts apart adjoining wrapped products into individual packages, and delivers the packages to the discharge area. From the discharge area, the packages can be either cartoned at a packing station or accumulated for packing at a later time.

Flow Wrapper Principle

 

More details on the basic principles of horizontal flow wrapping can be found in Bosch’s Guide to Flow Wrapping.  Download your copy today under the “Links and Downloads” section on the Pack 101 flow wrapper webpage on the Bosch Packaging website. This guide contains other sections to assist users in initially setting up their wrapper, film selection, changing over to new products, or solving problems common in flow wrapper operation.

A common question raised by first-time manufacturers or manufacturers launching a new product is “What type of flexible packaging film is best for my product?”  While there is a large variety of films available today, we’ve listed the top 10 that we see used in horizontal form fill seal (flow wrapper) applications.  The most popular film for flow wrapping by far is Polypropylene.  It is used in some form in almost 90% of applications.

Top 10 FilmsPolypropylene  (PP – OPP) Film

Polypropylene is the most commonly used film for horizontal form fill and seal.  It is used to over wrap snack foods, candy, baked goods, etc.  The common make-up of this film consists of an outer layer, a polypropylene core and a sealant layer on the interior.  The outer layer is commonly acrylic coated to prevent the film from melting on the crimping jaws and also to reduce friction on contacted surfaces.

Polypropylene film over wrap provides a containment seal and protection from dirt and dust.  It also provides some degree of protection from moisture and oxygen, but over time this film does allow exchange of atmosphere.

Polypropylene film can come in literally hundreds of laminations depending on your specific needs.  Unprinted polypropylene is a clear film that provides complete visibility of the product inside.

Polypropylene film can be supplied with several types of heat seal layers or with a cold seal adhesive layer.  Sealant layers such as metallocene, surlyn or EVA melt at lower temperatures than most sealant layers and tend to increase line speeds.

Polypropylene films can be laminated with other materials such as low density polyethylene and used for Modified Atmosphere Packaging or gas flush applications.  These gas flush applications require a barrier film and “hermetic” seals. Barrier films will not allow for exchange of atmosphere from the inside of the package to the outside or vice versa.  In modified atmosphere packaging the oxygen inside the package is replace with nitrogen, carbon dioxide or a blend of both gases. This inhibits the growth of mold and extends the shelf life of the product inside the package.

Polypropylene film is also available as an opaque film.  This film provides a nice white appearance and also provides for very attractive graphics when printed.  This film is commonly used for chocolate bars and ice cream treat over wraps. This film can also be either heat sealable or cold seal.  The white layer helps to slow product deterioration due to light sources.

A third type of polypropylene film is metalized.  This film has a vacuum deposited aluminum layer applied when the film is produced.  The metallization of film enhances the film’s ability to protect the product from outside oxygen and moisture.  It also provides some degree of protection from light deterioration of the product.

Metalized opp is used for candy bars, breakfast bars and in some applications pharmaceutical applications where it replaces foil laminates.

Most polypropylene films run in a temperature range of 225F – 425F, depending on thickness of film, sealants, coatings and speed.

Polyester (PET) Film

Polyester films are commonly used as an outer layer in laminations with other materials.  Polyester has good heat resistance which performs well in high speed applications.  This film will not shrink due to high temperatures like polypropylene will.  The polyester layer in a laminate also adds some structure strength to the film.

Light gauged polyester has become the standard over wrap material for toaster pastries.  Because of its heat resistance, polyester wrapped products can be heated in microwaves.  There is also a variety of polyester that can be used in ovens.  This material is used to wrap products such as French bread.  It is also used for lidding material on most frozen trayed products.  These products can go directly from freezer to oven!

48 gauge polyester along with a sealant layer of LDPE is widely used for moist towelettes and baby wipes.

Polyester films will typically accept temperature settings as high as 500F +.

Polyethylene (PE) Film

 Polyethylene film comes in two common versions:

  1. Low Density Polyethylene (LDPE) commonly used in shrink applications such as pizzas, soap bars for South America and a variety of other shrink bundle applications.  LDPE can also run on a fin seal type horizontal wrapper if the film is produced with a sealant layer on the inside.  Typically EVA is used for a sealant layer.  This film is primarily used for wrapping plastic cutlery, syringes for the pharmaceutical industry and literature over wrap. Sealing temperatures for LDPE with an inside sealant layer are usually in the 225F – 250F range.  Linear Low Density Polyethylene (LLDPE) is used in laminations of materials to add tear resistant properties to the finished film structure.  It can also be used as a sealant layer in laminated films.
  2. High Density Polyethylene (HDPE) requires a sealant layer in order to seal on a fin seal type horizontal wrapper.  It is used as an outer layer along with LDPE and an EVA sealant layer for wrapping Waffles, crackers and plastic cutlery, to name a few applications.  Sealing temperatures for HDPE blends are typically in the 250F -300F range.

Foil Laminations

 Foil laminations are made up of an aluminum alloy sheet sandwiched between another film layer and an inside sealant layer.  These laminations can be several layers thick depending on the desired film properties.  Thickness of the foil layer can also vary widely.

Foil laminations are used for pharmaceutical products and light sensitive products. The outer layer of a foil lamination may be paper, polyester, nylon and polypropylene or others.

Foil laminates have the highest barrier properties of any material used for over wrap.

Seal temperature for foil laminations can range from 300F-500F depending on thickness, outers layer and sealant layer.

Foil laminations often require extended dwell wrappers to seal properly.

Paper/polyethylene laminations

Paper/poly laminations are commonly used to wrap gauze bandages.  Several frozen food products such as pot pies and burritos are wrapped in paper/poly films.  Some manufacturers have added a thin metalized layer to the film; this is called “suseptor” film.  The suseptor layer works in the microwave to help brown or promote crispness of the product.

Paper/poly films typically do not run at high rates of speed due to the insulating factor that the paper creates.

Typical heat ranges are 350F – 500F and may require preheat in order to attain line speeds required.

Glassine Film

Glassine is a grease resistant paper with an inner sealant layer.  It is typically use for fried products such as fruit pies found in vending machines.  This type of film is being phased out in favor of other materials that run faster and are not a prone to tearing.

Valeron Film

This is a name that has been given to a film that was developed for its superior tear strength properties.  It is used for wrapping most chlorine tablets for toilet tank and swimming pool use.  This film provides an excellent moisture barrier, but its highest asset is its very high resistance to punctures and tears. These qualities make it child resistant which is a requirement for commercial chlorine products.

This film typically will not seal at speeds above 450 inches per minute.  The film also has a very narrow sealing window.  This means the temperature window between good seals and melting the film is very narrow!

Shrink Film

There are several films that fall into the shrink film category and include films made from polyethylene. Low density polyethylene and linear low density polyethylene films are common along with some polypropylenes. Shrink films can also be made from an ethylene-propylene copolymer and multi-layer polyolefin.

These films are always run on a wrapper using a lap bottoms and a hot knife end seal.

Product wrapped using shrink films are: compact disks, candles, greeting cards, box over wrap and trays of frozen product.

Polyvinyl Chloride (PVC)

Also included in the shrink film category is Polyvinyl Chloride (PVC).  PVC is used because of its high clarity and stiffness.  It is used in place of polyolefin film where very high clarity is desired.

PVC films are run using a lap seal that is usually a static seal.  The end seal is created by a special PVC knife that seals and separates the packages. These films are also used to wrap candles, greeting cards and compact disks.

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