Packaging Insight

Woven Polyproplene Bags

A majority of pet owners have experienced the convenience of buying pet food in bulk: it means fewer trips to the store and in most cases a significant cost savings. But for many people, these benefits are quickly forgotten when they go to lift a bag of pet food, only to have the bag rip and spill all over the floor, while still at the retail location, or even later when they have already purchased the item and transported it home.

 

The traditional paper bags used to hold pet food can be endlessly aggravating – for consumers and retailers alike. Consumers can be frustrated by overly-heavy bags that rip and tear too easily, and retailers and suppliers are oftentimes forced to absorb the extra costs that come with replacing defective product, and cleaning up after the inevitable spill.

 

Packaging manufacturers are all too familiar with these frustrations, and have developed a product specifically designed to overcome some of the annoying drawbacks of large, multi-wall paper sacks. Woven polypropylene bags consist of thousands of strands of plastic woven together to form a fabric-like sheet that is very strong and extremely durable, and capable of carrying well over fifty pounds without any problems. They are also extremely stable, and rarely will they rip or burst when dropped.

 

In recent years, woven polypropylene bags have been extensively adopted by the agricultural and manufacturing industries, most commonly used to hold animal feed, sand, produce, grain, minerals, salt, chemicals, fertilizers, cement, coffee, sugar, wood pellets, bio-mass and much more. The bags can be custom printed with a logo and text on one or two sides and come in a variety of sizes. They can also be readily customized with gussets, anti-slip coatings, laminations, and treated to be UV-resistant. Many manufacturers of pet products have been particularly pleased with smaller bags, as their weight can be kept at a reasonable amount so that women, the largest buyers of pet food, can handle them more readily.

 

While paper bags have been the traditional packaging used in selling pet food, manufacturers of these types of products have grown weary of absorbing the costs that come with the need to replace bags on retailers’ floors. In addition, woven polypropylene bags are made from plastic, so they are inherently water-resistant. They will not smudge, sag, or get soggy, so they will still be sellable even after inclement weather. This is good news for retailers, many of whom have been looking to put pet food outside the store to make room for more profitable items within. Packaging that is weather-resistant increases retailers’ merchandising options, and decreases the risk of damaged product.

 

Heavey Duty shipping sacks are changing to woven polypropelene bags to eliminate waste especially dealing in big box stores. Improved flexo printing and lamination on woven polypropelene makes a very attractive package.

Wood Pellets - Renewable Energy

What is Pellet Fuel?

Pellet fuel is a renewable, clean-burning and cost stable home heating alternative currently used throughout North America. It is a biomass product made of renewable substances – generally recycled wood waste. There are approximately 800,000 homes in the U.S. using wood pellets for heat, in freestanding stoves, fireplace inserts and even furnaces. Pellet fuel for heating can also be found in such large-scale environments as schools and prisons. North American pellets are produced in manufacturing facilities in United States and Canada, and are available for purchase at fireplace dealers, nurseries, building supply stores, feed and garden supply stores and some discount merchandisers.

In short, pellet fuel is a way to divert millions of tons of waste from landfills and turn it into energy

Printed Stand Up Pouches - What Material Sructure Do I Really Need?

The first step when considering printed stand up pouches was to ask the question and clearly understand what you were packaging.  Step two goes deeper to explore the type of structure you’ll need based upon your criteria for the particular printed stand up pouch or stand bag.  Your criteria delves deeper into the weight you plan to put into the pouch, the conditions the stand up pouch will be subjected to, what the ultimate use will be for the stand bag, and even who the end user will be.  The information below will shed some light onto the advantages and disadvantages of the different barrier film structures available.

 Your Criteria determines the thickness of your pouch.

Your Criteria + the thickness + the quantity needed = the price per pouch

 Clear Structures and Metalized Film Structures:  are usually very close in price when everything else is equal (your criteria).  Both can be made with excellent barrier properties, excellent strength and durability too.

Aluminum Foil Structures:  these tend to be more expensive, as they generally have superior barrier properties over clear and metalized film.  Remember, aluminum foil is just one part, one layer of the overall structure.  It all depends on your criteria.

Boilable Structures:  these can be made from clear film, metalized film, and foil structures.  As mentioned above, clear and metalized films tend to be very close in price points whereas aluminum foil tends to be more expensive. It all depends on your criteria.

Microwaveable Structures:  are made from clear films that are laminated to provide barrier properties and the strength to withstand microwave heating elements.  Anything metalized wouldn’t work in a microwave.  The price points for microwaveable clear films are in line with other clear films and are based on your criteria.

Your Criteria

a)  What you are packaging (is it a powder, a paste, a liquid, sharp, heavy, oily, greasy, etc?)

b)   Do you want to be able to see your product or have a clear window on your pouch?

c)   How much weight you are packaging into the pouch (150 grams, 1 pound, 5 pounds, etc)?

d)  What style pouch do you want (will it be a Stand Up Pouch and need to stand, or will it be a flat pouch that hangs in a display, a gusseted pouch, a tamper evident pouch that loads from the bottom, etc)?

e)  What features do you want (ziplock, tear notch, hang hole, liquid pour spout, etc)?

f)   What kind of conditions will the pouch will be subjected to (will it be in a chemical factory and thrown off of a pallet, will it be used by a consumer who will open it and place it back into his/her pantry, will it be used in a dirty, greasy industrial plant, or will it be used in a clean-room electronic facility, etc)?

g)   What price point do you want/need to be at.  Do you want the cheapest possible price to keep your product fresh for 30 days, or do you want something that will keep your product fresh for one year and withstand high temperatures, a drop from 15 feet, etc?

IMPORTANT:  As far as cost is concerned, all of these factors (above) play a role into the film structure and ultimately the thickness of the film we propose to the client.  Is clear film the cheapest?  Not necessarily.  The thickness of your pouch means how much material your pouch will require/use and this will play the largest part of your price followed closely by the actual materials (aluminum foil, polyester metalized film, clear film, etc) used in the different layers.

 Clear Structures

Advantages:

1. You can see thru it…and/or print it with a clear window

2. Excellent barrier properties available
3. Strong, puncture resistant film structures available
4. Lots of choices based upon the use and needs of the client (your criteria)
5. Cost effective (not always the cheapest…this depends on the overall thickness and the other layers chosen, but clear is always cost effective).
   

Disadvantages:

1. You can see thru it.  This is not a typo.  Some clients choose a clear structure based upon what they are packaging, their cost structure, the style of pouch, etc (see below).  If the product going into the pouch is sensitive to light, we will need to under-print the pouch with a solid color to make it opaque and prevent light from affecting the product(s) inside.

2. If you are printing this pouch and/or printing everything but a “clear window” area, consider under-print the rest of the pouch (except the clear window area).  This may add a minimal amount to the per piece price, however, if this is not done, the printing would look translucent, drab, dull, and boring.

Metalized Film Structures

 Metalized film is not foil (aluminum).  Metalized film is made from polyester and is just one part, one layer of the overall structure.

Advantages:

1. Opaque, doesn’t allow light to product inside

2. Because of this opacity, the printing naturally POPS without the need of any under-printing.
3. Excellent barrier properties
4. Cost effective
5. Strong, puncture resistant structures available
6. Lots of combinations available depending on your criteria.
   

Disadvantages:

1. Opaque, cannot see thru to contents inside

Aluminum Foil Structures

 Advantages:

1. Opaque, doesn’t allow light to product inside

2. Because of this opacity, the printing naturally POPS without the need of any under-printing.
3. Strong, puncture resistant structures available
4. Lots of combinations available based upon your criteria.

 Disadvantages

1. Tends to be more expensive than other structures

In closing, there are many things to keep in mind when considering printed stand up pouches.  Some of the information above pertains to the overall cost; some to print capability, and some to the strength and durability required.  This information should be helpful as you start this journey.  As always, your packaging professional will be instrumental to helping you navigate the road ahead.  Counting on them will save you time, aggravation, and money.

UV Coating what is it?

I want to explain what UV coatings are and all the other various coatings.

The two most common reasons for adding a coating over your printed piece are for protection: to avoid scuffing the ink, if you have included areas of heavy ink coverage; and for aesthetic reasons: to draw the reader's eye to particular items, to add depth and interest to your printed piece. First consider why you are coating your job.

When making a decision, keep in mind the following:

1. Dried inks show fingerprints and scuffing, especially in dark solids.

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2. Press coatings (like varnish) cost less than bindery (off-press) coatings (like UV coating and laminates) since bindery coatings are applied over dry ink at slow speeds. Because the chemicals used in aqueous coating damage press rollers, this coating is more expensive for the printer/binder to apply than varnish; therefore, the extra cost is passed on to the client.

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3. Varnish is the least effective way to prevent scuffing, particularly when publications are multiply shrink-wrapped (as opposed to singly shrink-wrapped) prior to shipping. Bindery coatings like UV coating and laminates are far better for protecting loose books in transit. Even aqueous coating is much stronger than varnish and can therefore withstand books shifting around in transit without scuffing.

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4. All printers can apply varnish, but not all printers can apply laminates, UV coating, or aqueous coating.

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5. You cannot print (ink-jet or by hand), glue, or foil stamp over coatings, so you need to leave an uncoated window if you want to do any of these (coatings should be the final finishing step on a printed piece).

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6. You should only varnish coated stock, or the coating will seep into the paper and be lost.

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7. Some coatings deepen the ink color they cover, yellow with age, and/or discolor white paper.

VARNISH
Varnish is essentially ink without pigment. It requires its own printing unit on press. It can be wet-trapped (printed in-line at the same time other inks are laid down), or dry-trapped (run as an additional pass through the press after the initial ink coating has dried). The latter often provides a glossier finish. Varnish comes in gloss, dull, and satin (in-between dull and gloss), and can be tinted by adding pigment to the varnish.

From an artistic standpoint, you can play a dull-varnished portion of the sheet against a portion without varnish or with a gloss varnish. This contrast can give emphasis to certain areas and/or give the impression of depth.

UV COATING
UV Coating is a clear liquid spread over the paper like ink and then cured instantly with ultraviolet light. It can be a gloss or dull coating, and can be used as a spot covering to accent a particular image on the sheet or as an overall (flood) coating. UV coating gives more protection and sheen than either varnish or aqueous coating. Since it is cured with light and not heat, no solvents enter the atmosphere. However, it is more difficult to recycle than the other coatings.

UV coating is applied as a separate finishing operation as a flood coating or (applied by screen printing) as a spot coating. Keep in mind that this thick coating may crack when scored or folded.

AQUEOUS COATING
Aqueous coating is more environmentally friendly than UV coating because it is water based. It has better hold-out than varnish (it does not seep into the press sheet) and does not crack or scuff easily. Aqueous does, however, cost twice as much as varnish.

Since it is applied by an aqueous coating tower at the delivery end of the press, one can only lay down a flood aqueous coating, not a localized "spot" aqueous coating. Aqueous comes in gloss, dull, and satin.

LAMINATE
Laminates come in two types: film and liquid, and can have a gloss or matte finish. As their name suggests, in one case a clear plastic film is laid down over the sheet of paper, and in the other case a clear liquid is spread over the sheet and dries (or cures) like a varnish. Laminates protect the sheet from water (including perspiration from the hands) and are therefore good for coating items like menus and book covers. For more money, one can even specify a porous, lay-flat laminate (the interior of which is covered with numerous "V"-shaped cuts in the plastic that minimize the "curl" one often sees on paperback book covers due to moisture seeping into the uncoated side and causing it to expand). Laminates are slow to apply and costly but provide a strong, washable surface. They are the superior choice for protecting loose books in transit.

What kind of coating you should get depends of course on what you're printing and what that printing is intended for.

www.prflexbag.com

dbanig@prflexbag.com

Star Seal

The star seal is the most common type of seal in HDPE trash bag market.

Designed without gussets, the star seal eliminates gaps along the seal

where leaks can occur. This allows the bag to more easily conformed to

the shape of the container and distributes refuse weight evenly inside the

bag.

Star seal liners maximize the bag's carrying capacity and virtually eliminate

leaks.
Star seal liners are designed in two dimensions, 40 x 46

Gusset Bag

A flat style bag manufactured with both sides tucked in to form gussets.
Where indented, the bag is sealed through four layers of film while in
the middle of the bag has only two. This leads to a potentially weak
bottom seal.

Gusseted seal liners are designed in three dimensions, 23 x 17 x 46.

Flat Bag / Side Weld or Bottom Seal

A flat seal is a two-dimensional bag with a bottom seal or two side seals,

much like a pillow case. Flat seals are generally leak proof but are clumsy to handle.
Also, they do not conform well to the shape of most trash receptacles or box liners.
Flat seal liners are designed in two dimensions, 40 x 46.

Plastic Poly Bag / Technical Information

Here is technical information on plastic bags.  Plastic bags are created from plastic resins through polymerization , the process in which a chemical reaction links together monomers to form a polymer. A monomer consists of molecules from the same organic substance. When linked together, monomers create polymers , solid substances composed of repeating units. In the plastics industry, the term polymer is synonymous with plastic. Polyethylene and polypropylene are two plastic resins frequently used in the production of plastic bags. Polyethylene (PE), a light, chemically resistant thermoplastic used in packaging and insulation, represents the most common plastic resin. The polymerization of ethylene, a flammable, gaseous hydrocarbon found in petroleum, results in the production of polyethylene resin. Polyethylene resins used in the production of plastic bags include low density, linear low density, and high density resins. Low Density polyethylene (LDPE) remains the most common and least expensive plastic bag material. The resin is created through the polymerization of ethylene at very high temperatures and pressures. LDPE maintains its durability, flexibility, water resistance, and clarity under low temperatures, and its low melting point make it ideal for heat sealing. Linear Low Density polyethylene (LLDPE) is produced at lower temperatures and pressures than LDPE through copolymerization, the polymerization of two distinct monomers. Copolymerization results in LLDPE’s crystalline structure, which provides LLDPE greater stiffness and a higher melting point than LDPE. Although it is more difficult to process, LLDPE maintains greater tensile strength and a greater resistance to stress cracking than LDPE. High Density polyethylene (HDPE) maintains greater strength, resistance, and stiffness than either LDPE or LLDPE. Polypropylene (PP) is a light, durable thermoplastic often used in packaging. Polypropylene contains polymers of propylene, a colorless, combustible gas found in petroleum. Although more expensive to process than polyethylene, processing of polypropylene remains quite easy. In addition, polypropylene is denser, stiffer, and stronger than polyethylene, and maintains a high melting point. In addition to various resins, we have numerous sizes, shapes, styles, and features from which to choose. Common plastic bag shapes include flat and gusseted. Flat bags provide versatile plastic packaging for items of many shapes and sizes. Flat bags are heat sealed on either the side or the bottom of the bag. Bottom-sealed bags provide extra support for heavier items. Gusseted bags contain folds or pleats called gussets, which allow the bag and the bag opening to expand in order to accommodate large or bulky items. Gusseted bags consist of either bottom sealed, side gusseted bags or side sealed, bottom gusseted bags. STYLES Countless flat bag and gusseted bag styles exist. Some of the most familiar bags include those used in retail, food storage, and waste removal storage. Retail bags include all bags used to store and carry merchandise. Supermarkets, department stores, and specialty shops offer different bag styles for employee and customer convenience. A few of the most common retail bag styles include the following: T-shirt bags , often found in grocery stores, are gusseted bags containing long handles to accommodate shoppers; the material of choice is high density polyethylene. Die-cut bags are flat bags containing a hole at the top of the bag for carrying; die-cut bags are common in retail settings and trade shows. Patch handle bags are flat bags with a die-cut handle reinforced by a heat-sealed patch for added strength; patch handle bags are useful in carrying heavy items like books. Drawstring bags contain either plastic or cotton drawstrings inserted inside the rim of the bag. The drawstrings allow for easy closure and provide handles with which to carry the bags. TERMS Additive – substance added to a polymer to increase the effectiveness, but not the strength, of the polymer. Strength increase is achieved by adding a reinforcement. Examples of additives include flame-retardants, anti-static compounds, pigments, and lubricants.   Blow extrusion – common process of creating plastic bags in which compressed air fills an extruded plastic tube in order to enlarge and thin out the resin.   Copolymer – a polymer made up of two monomers in which each repeating unit in the chain consists of units of both monomers.   Crazing - very thin cracks in a polymeric material caused by chemicals or other agents, such as ultraviolet radiation. Degree of polymerization – the length of the molecular or monomeric units in a polymer chain; this length determines the properties of the polymer. EVA (ethylene vinyl acetate ) – copolymer produced through the chemical reaction of ethylene and vinyl acetate; often added to plastic resins to increase the strength of the resin in temperatures below freezing. Glass transition temperature (Tg )–reflects the temperature when a substance changes from a hard, glass to a rubber consistency; polymers become weak at temperatures below their transition temperature.   Grade – polymers originating from the same chemical family and produced from the same company; however, they vary in weight, additives, reinforcements, and the manner in which they are processed.   Heat sealing – fusing together two or more thermoplastic films, such as low density polyethylene, through the application of heat and pressure.   Light-weighting – the process of decreasing the weight of plastic by using less resin, while retaining the plastic’s strength and effectiveness.   Melting point – the temperature at which a substance converts from a solid into a liquid.   Monomer – the most basic polymeric unit, usually a liquid or a gas, consisting of molecules from the same organic substance; chained together, momomers form solid polymers.   Plasticizer – a chemical additive added to plastic resins to increase the plastic’s flexibility.   Polymer – two or more monomers bonded together through a chemical reaction; each polymer consists of a chain of repeating monomers.   Polyethylene – light, chemically resistant thermoplastic used in packaging and insulation.  Polyethylene contains polymers consisting of ethylene, a colorless, odorless organic gas found in petroleum; ripening fruit also produces ethylene in order to regulate growth.   Polypropylene – light, durable thermoplastic with a high melting point often used in packaging. Polypropylene contains polymers consisting of propylene, a colorless, combustible gas found in petroleum.   “Poly bags” – bags derives from polyethylene or polypropylene, although it usually refers to polyethylene bags.   Reinforcement – substance added to a polymer to increase the strength of the plastic. Examples include clay, mica, and glass fibers.   Resin – a class of polymers, or plastics, chemically different to naturally occurring resin, a sticky substance obtained from certain trees and plants. Examples of resins include polyethylene, polyurethane, and acrylics.   Stress cracking – cracking occurring as a result of mechanical stress. In most cases, tiny cracks caused from exposure of the plastic to chemicals or ultraviolet radiation are already present. When stress is applied to the plastic, the cracks enlarge and spread, creating a greater fracture.   Terpolymer - a polymer made up of three monomers in which each repeating unit in the chain consists of units of all three monomers.   Thermoforming – the process of applying heat, pressure, or suction to create plastic sheets according to certain sizes and shapes.   Thermoplastic - category of plastics that have the potential to soften and reform when heated, and harden again during cooling; during the process, the plastic’s physical makeup does not change.   Thermoset – category of plastics that can not be reformed upon reheating; thermosets remain permanently hard.   UVI (ultraviolet inhibitor ) – plastic additive that increases the plastic’s resistance to the harmful effects of ultraviolet radiation, which include fading of color and strength decrease.   Vapor corrosive inhibitor – thermoplastic coating or film that safeguards sensitive items from harsh environmental conditions through the release of a vapor that forms a protective layer on the surface of the thermoplastic. www.prflexbag.com dbanig@prflexbag.com

Benefits Of Using Batch Inclusion Bags To Help The Environment

Batch Inclusion film or bags derive their name from the fact the bag itself,along with contents,is actually included in the production batch or during rubber compounding. The bag, once melted and dispersed, becomes part of the product being made. Batch inclusion bags typically hold chemical additives for large scale industries, such as synthetic rubber and plastic compounding. Often the additives involved are difficult to handle, weigh to little or are used to hard to dispense automatically. These could include colorants, fillers, resins and even some polymers for large scale mixing. Because the bag and its contents become part of the batch, the user will realize a cleaner environment, along with other benefits such as reduce labor cost, reduce disposal cost and clean up cost, better hygiene. The bags or film has a number of benefits like more efficient use of raw materials and a more consistent mixtures of compounds. Also, you will find the use of material in a sealed bag allows for a reduction in storage space when compared to an open container, such as metal containers or plastic and sometimes paper bags. As sealed bags can pile in a bin, cardboard boxes, tubs, or carts.

Benefits of using Batch Inclusion Bags are they improve quality and batch uniformity insures 100% compound ingredients go into the mixing of the material when doing in house weighing, batch inclusion bags eliminate the risk of cross-contamination due to chemical residue in tubs and weighing containers. Will increases productivity and eliminates the need to weigh ingredients in-house through the use of having the product weighed and ready to be thrown into a batch of rubber also eliminates the need to clean out tubs and weighing containers. Reduces the amount of solid waste disposal going into the land fills. You will have less product loss due to spillage and minimizes the accumulation of costly additives in the dust collectors. The idea is to minimizes worker exposure to hazardous materials.

dbanig@prflexbag.com http://www.prflexbag.com

What is slip and how does it work in manufacturing plastic film and bags.

What is slip and how does it work in manufacturing plastic film and bags. Slip is an organic chemical that is added to the blend during film extrusion process to modify the coefficient of friction (COF). COF is a measurement of the amount of friction between two surfaces as they begin to slide and as they continue to drag against one another.

The amount of energy it takes to put an object in motion is always greater than the amount of energy that it takes to keep it moving while it is in motion.

Although there are a number of chemicals that are used to modify the COF the two main ones used in Polyethylene and Polypropylene are Erucamide (which is considered a slow bloom) and Oleamide ( which is a fast bloom. The materials are sometimes called primary amides.

Slip is a very efficient molecule it has been added to a plastic film in very low concentrations typically 500 to 1500 parts per million (PPM). The slip additive can be let down at the levels of 1 to 3% by weight in blending while extruding the plastic film.

Slip molecules are very low in molecular weight as compared to the polymer in which they are used. These molecules are somewhat incompatible because of their nature. This means the material is bi-polar and has one end that has a positive charge and the other has a neutral charge. This incompatibility causes the molecule to migrate referred to as bloom through the polymer to the surface of the plastic film.  The more slip that migrates on the surface the lower the COF and the more slippery the plastic film becomes.

The COF relates to packaging because the substrates used to package objects always come in contact with other surfaces or themselves. As most packaging operations are very high speed, COF plays a very large role. The packaging material must have just the right COF in order to track properly on the packaging machines. If a material is too slippery the film will not track properly and may cause issues such as bad sealing or cause a powder substance that builds up on the tracking rolls which will cause packaging failures. If a material becomes to sticky can have the opposite effect. It may not allow the film to un-wind properly and cause web brakes or other tracking problems. Either scenario can shut a packaging line down.

www.prflexbag.com

dbanig@prflexbag.com

Flexible Pouches Stand Up To Maximize Shelf Appeal

Flexible Pouches Stand Up to Maximize Shelf Appeal

Today’s retail markets are finding endless benefits to using stand up pouches as they have maximized how products can be displayed at retail stores. With the different types of material structures available you can package food products, liquids, chemicals, etc.

Pouches use much less material than other traditional packaging methods like corrugated cartons or laminated boxes. Pouches can be customized to fit any of your needs but you need to understand why stand up pouches can be so beneficial to your business. Once you really understand how they are made, as they can be cheaper and run more efficiently than you may think.

The first thing to remember stand up pouches is that they are made up of co-extruded material from 3- layer, 5-layer, 7-layer, 9-layer or the material can be a single mono layer and laminated with a number of other film structures from p.e.t., nylon, metalized p.e.t., foil etc. They can be printed any color up to 10 color line print to 10 color process print with your logo or design, so the potential to really make an impact on retail shelves is very high.

Pouches are made from a continuous web of material where the first step in manufacturing process of a stand up pouch happens when it goes through a set of plows that folds the material into a w-shape guesset into the bottom so the pouch will be able to stand up. Now if you want a re-closable zipper as part of your pouch it is sealed on the inside of the face of the web near the top edge of the material. Re-closable zippers are the most common method, but spouts, perforations, and other re-closable openings are also available.

Once the gusset is formed vertical seals are then made along the pouches side and the re-closable zipper is pressed into the same area to seal the ends and flattens out. The laminated pouch is then cut apart vertically through the center of the of the side seals to create the finished stand up pouch.

After the product is dispensed into the pouch it travels thru the filling station where the re-closable zipper is closed and the pouch is sealed above the zipper.

Stand up pouches are becoming more and more popular options for liquids, dry chemicals, pet foods, personal care products, granular products like cereal, sugar, salt.

The stand up pouch is very user friendly both for consumers and to help reduce packaging cost.

www.prflexbag.com

dbanig@prflexbag.com

Process of Rotating The Die While Processing Good Quality Film!

By rotation of the extrusion die these gauge bands can be moved around the surface of the film as the bubble is being extruded. The bubble itself does not rotate. In this fashion they are evenly distributed across the face of the roll at an evenly distributed wound as you would reel in fish line on a fishing reel and build a cylindrical roll of plastic film of perfect symmetry. Without rotation these faults would build up in one place on the roll of film it would create a roll of film whose surface would look like something got caught in the roll and make an un-even impression or bulge on the roll.

Unfortunately rotation of the die can introduce problems of its own that the bulge called a gauge band now gradually moves across the face of the collapsing frames. When you have such actions the web moves back and fourth between the two wood or plastic frames and the lay flat begins to wonder back and fourth in the down stream equipment starting at the nip rolls. With out pulling trim off of the both sides of the film a web guide would be required.

Generally gauge bands are caused by drafts of air or a heat rise off of the front of the extruder. As for a consequence the roll of film may be tapered or have a convex or concave face as the different thicknesses of film build up upon themselves in the roll.

Again as the bubble or die diameter is increased so is the transverse speed of the gauge bands across the face of the A-Frames which will also change the rotational speed. This can cause bubble instability, intermittent wrinkling in the nips and web wondering downstream that can be corrected by reducing the rotational speed.

However one rotation should never be less than the time it takes to build a roll of film or the gauge bands will not have time to be uniformly distributed across the entire face of the roll of film.

dbanig@prflexbag.com http://www.prflexbag.com