Packaging Insight

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

Understanding Flexographic Printing

Flexographic printing is defined as a method of direct rotary printing that uses special rubber or photopolymer material. The printing plates are affixed to plate cylinders of various repeat lengths, which are inked by a cell structure (anolox roll) which is used to meter the flow of the ink on roll. It carries a fast drying fluid ink to the plates that print on a variety of substrates (paper / plastic / nylon / polypropylene / cellophane / LDPE / LLDPE / etc.).

Flexographic printing is a rotating method for every revolution of the printing plate cylinder an image is produced. If the image is stepped several times around a cylinder several images may be produced in one revolution.

Due to the nature of the printing process there are factors that don’t exist with other print methods such as offset and gravure. Because flexographic employs a flat but flexible printing plate that is stretched around a curved cylinder and the image on the plate distorts when the plate is mounted on the printing cylinder. A circle shape for example distorts into an egg shape. The amount of distortion depends on many factors including cylinder size, plate size, and the amount of distortion depends on a number of factors, including cylinder size, plate size, and the amount of adhesive mounting tape used to attach the plate cylinder.

Another aspect of flexographic printing is the solids (line art) print differently than screens (dot patterns). That is because the printing plate is relatively soft and the ink on its surface must be pressed against the substrate to print. Thus the amount of pressure applied to the printing plate is critical For example more pressure is needed to print a dense and heavy solid than to print a screen tint.

Whichever method used to set up the printing press, one design implication must remain clear is that you may not be able to successfully print one color screens and solids on the same printing plate or printing station. This is very different from offset printing where the solids and screens of a given color can be printed with a single printing plate.

dbanig@prflexbag.com

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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

Corona Surface Treatment allows for effective Flexo Printing on Plastic Film and other Substrates.

With corona treating, the goal is to increase the materials surface energy to provide wet ability and adhesion. But, treating a plastic film or substrate can be ineffective when the system is not properly run and maintained. So you must be aware of how to effectively process the various materials or substrates.

Over or under corona treating can transfer too much energy to a plastic substrate which is where a lot of problems could occur when printing or converting of plastic material. When attempting to obtain satisfactory printing results on under treated material can result in the use of excessive amounts of ink in an effort to try to make up for the low treatment levels. Over treatment can result in damage to the material itself as well as problems with the plastic film or plastic tubing blocking together.

Poor ink adhesion, or low dyne levels can occur. How you can establish a good starting point is with the power level. You begin by working your way u until the anticipated dyne level is achieved this is done through quality assurance checks of the plastic film. Once the power level is established for the given product at the given speed, note the power level so when your next time you run the same material and machine speeds you will have a set standard and can be assured of desired repeatability.

Plastic film converters can achieve proper treat levels through trial and error. Testing protocols which include adhesion and bond strength measurements at a variety of power levels should be used to determine the acceptable power level for each substrate or material type, material thickness, and even material suppliers are all variables which can impact the appropriate power level. Once determined, the appropriate power settings should become a permanent part of the job specification.

Accurate web tension effects plastic film treatment which if not controlled properly can cause variances in surface treatment. With too much tension the material can wrinkle or snap whereas a lack of tension creates air gaps between the material and roll. In both cases the material can become unevenly treated. Also can cause another problem called backside treating.

Materials that do not come in close contact with the treater roll under the electrode or back up roller can affect the treatment process. Wrinkles in the material or air getting trapped under the material can result in some treatment of the back side of the material which will result in reduce treatment level in respect to the top part of the material and may cause the material to stick together or block.

There are ways to ensure proper tension is to consider nip rolls as they will eliminate concerns with developing an air pocket between the back up roll and the plastic film. Also in some cases you may want to have a spreader roll or a crowned roll to help eliminate any wrinkles especially at higher production speeds.

Maintaining the surface treatment equipment is very important to help reduce long production downtimes. Proper cleaning of the equipment will reduce this downtime.

Many materials tend to clog up or coat the electrodes or air take away systems for example materials like slip and other additives during the corona treatment process.

The material acts like dirt and can be deposited on the rollers or electrodes. The dirt build up can contribute to producing backside treating causes high and low spots on the treater roll which allows for air gaps that changes the variance in the levels of treatment.

This is one thing plastic converters can do is maintain the treater equipment. Inspect the rollers and electrodes when you have a web break, inspect the rollers for un-wanted particles. Assure your exhaust and cooling air is working properly especially during high humidity months. With a little care and designed scheduled maintenance your equipment will last a long time but best of all product quality.

 

dbanig@prflexbag.com                                                      www.prflexbag.com

Static Shielding Bags

Static Bags making the right choice!

Static Shielding, Moisture Barrier, Dissipative Poly Bags (Pink)

Scuffing one’s shoes on the carpet and touching a person, metal door handle produces a shock. Drying synthetic clothing in the cloths dryer will often produce “static cling”. The static electricity behind these common events can destroy modern electronic circuits and devices.

As electronic circuits and their connecting pathways have continued to shrink in size, their susceptibly to damage from static electricity has increased.

Protective handling and packaging techniques have been adopted by the electronics industry from the chip foundry to production floor.

Bags

One of the most common static preventive measures is a bag. The use of protective bag began in the 60’s with introduction 0f “Pink Poly Bags”. Static shielding bags were introduced in the late 70’s and while the military has used moisture barrier bags. The surface mount technology has greatly increased usage.

Static Threats

Electronic device needs to be protected from 3 primary static threats:

1)      Direct Discharge (ESD): A discharge directly to a bag can subject the device inside to high current, melting or fusing the circuit.

2)      Static Fields: Fields can induce destructive currents in circuit conductors. Field differentials can break down the circuit dielectric.

3)      Tribocharging: Friction between the bag and the device can produce damaging static voltage and fields.

Below, the protection abilities, construction, and applications of several of the most common bag types are described.

Pink Poly Bags or Dissipative Poly Bags

The bag has the ability to dissipate a static charge to ground. This keeps static electricity from building up on the package or device. The material is also antistatic, suggesting that it will not charge up (tribocharge) when rubbed against other materials. Unfortunately these bags have no shielding ability. A static field or discharge occurring outside the bag will penetrate the bag and damage electronics inside.

Construction: Pink Poly Bags consist of polyethylene (plastic) that has been loaded or surface coated with a chemical called antistat. The “Pink Poly” is only a colorant that was added to differentiate static control materials from standard packaging.

Applications: Pink Poly Bags are useful for packaging items that have no static susceptibility. Their primary use is to package support or processing material that will be close proximity to static sensitive devices. This keeps static generating packaging materials away from sensitive areas. Poly bags are also known as type ll bags from the

U.S.

military standard Mil-B-81705.

Black Conductive Poly Bags

Black Poly is very conductive and will dissipate a charge very fast. Unfortunately this fast dissipation also means that a charged person or object can spark (ESD) to its surface. The general idea in static control is to swap charges at a slow so as to allow a static build up. Because the material is conductive it does provide some small measure of shielding. However there is no plastic layer (dielectric) to isolate a device inside a bag. The charge may be transferred through the thickness of the material to the device instead of around the material to ground.

Construction: Black Poly Bags are a polyethylene plastic that is loaded with a conductive form of carbon. The material is black and opaque in appearance.

Applications: Black Poly was used as a barrier between pink poly and shield bags because of the slightly lower cost offering some shielding as opposed to non with pink poly. However, as the price of shield bags continues to drop the usage of black poly will likely drop as well. Because black poly bags are opaque the bags contents must be removed for identification. This creates a new opportunity for static damage.

Shielding Bags

Shield Bags provide the dissipative and antistatic attributes of the poly bag but add a metal shield and polyester dielectric to stop static from entering the bag.  The test for shielding demonstrates the difference between the various bags. Shield Bags will generally stop 97% of a 1,000 volt static pulse applied to the outside of the bag from reaching the inside. Pink Poly will stop only about 10% and black poly about 30%.

Construction: Static Shielding Bags consist of several layers. Dissipative poly laminated to metalized polyester. The outside polyester has an antistatic coating. The metal is vapor deposited in a vacuum chamber. Aluminum is the metal most used in this process, with nickel and copper also being used. The structure of a shield bag has metal between two layers of plastic.

Applications: Static Shield Bags should be used for all electronic components, boards, assemblies. Shield bags are referred to as TYPE lll under MIL-B81705C.

Moisture Barrier Bags

Moisture Barrier Bags provide dissipation, antistatic properties, static shielding, and add a moisture vapor barrier. The moisture barrier protects moisture sensitive items and improves long term storage.

Construction: Type of bag is physically stronger than a shield bag. Moisture barrier bags are similar in structure to the shield bags. The two types are “foil and tyvek” and heavy metallization.

The heavy metallization structure is essentially that of a shield bag but with opaque, thick aluminum metallization or multiple layers of metallization. Nylon may be used in place of Tyvek or polyester. It provides the needed strength at a lower cost than tyvek. Both foil and metalized moisture barriers provide a good product.

Applications: The moisture barrier bag is used when barrier protection is needed or when maximum shielding protection is desired but transparency is not an issue.

The moisture barrier bag is also referred to as Mil-B81705 TYPE l.

Summary:

Static protective bags are an integral part of a static control program. Selecting the right bag can help reduce static damage and save money on costly repairs and rework. Thee cost of static protective packaging is insignificant when compared to the protection it affords the costly items placed in the package.

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dbanig@prflexbag.com

Rubber and Tire Industrial Applications

Protective Release Film

We call all of our materials used for release liners R" series.

R-1 & R-20 represent a new generation of protective release film for the rubber and tire industry. We special formulated polyethylene compounds that do not interact with other materials present in the various rubber compounds. R-series is specialty formulated film that is a substitute for the regular embossed film. You wonder what the benefits might be? It is easy to clean release and peeling, retaining freshness and stickiness of the rubber compound, prevents pollution and improves mechanical features, economizes volume and storage and enables 100% recycling with high resistance to heat especially the R-20.

The film is much more cost effective up to 10 times than that of regular embossed film. The use of this material increases the number of feet per roll which reduces the number of roll changes saving time and cost and in the mean time increases productivity. The R-1 & R-20 film comes in a variety of width, length, thickness and not to mention a variety of colors.

R-1 Cold Calendaring process (up to 40 degrees C)

R-15 Hot Compounds / Rich rubber Cobalt and Sulfur compounds such as steel calendaring / (Hot Compounds).R-15 absorbs the sulfur and cobalt incorporated in the compound.

R-20 Hot Compounds

Advantages of release film in comparison to Liners.

*Length of the film in a roll is about 10 times more than a liner roll with the same diameter.

* Change to a jumbo roll which decreases the number of roll changes.

*Reduce storage space.

*Excellent product quality

*Taylor made to desired width, length, thickness,and color.

This product is a new generation of material that helps in reducing waste, storage, cost, etc.

dbanig@prflexbag.com