Plastic Bags

About Plastic Bags and Plastic Bag Manufacturers Including: Baggies, Clear Plastic Bags, Medical Bags, Plastic Merchandise Bags, Polyethylene Bags, Polypropylene Bags. Poly Bags, Printed Plastic Bags, Resealable Plastic Bags, Shopping Bag, Vinyl Bags, & Zip Lock Bags.

Plastic bags, often referred to as poly bags, remain a popular choice for packaging because of the advantages to manufacturers and consumers, which include cost effectiveness, flexibility, durability and insulation. The flexibility of plastic allows plastic bag manufacturers to produce a wide range of sizes and shapes, including plastic merchandise bags like shopping bags, clear plastic bags, resealable plastic bags  like zip lock bags, vinyl bags and plastic baggies. Plastic bags are waterproof and chemically resistant and also provide ample thermal and electrical insulation. In addition to various sizes, shapes and styles, plastic bag features often include color and custom printing. Because of their versatility, plastic bags abound in almost every industry, providing utility in various applications in the medical, pharmaceutical, engineering/construction, automotive, electronic, computer and retail industries.

Plastic bag manufacturers create plastic bags from plastic resins through polymerization, the process in which a chemical reaction links together monomers to form a polymer. In the plastics industry, the term polymer is synonymous with plastic. Polyethylene (PE) and polypropylene (PP) are two plastic resins frequently used in the production of plastic bags. There are a few types of polyethylene, which have distinct advantages, depending on the application. High density polyethylene (HDPE) is non-porous and non-stretching, creates a moisture and vapor barrier and usually is about half the cost of low density polyethylene (LDPE). HDPE is perfect for general packaging applications and trash storage, although HDPE bags are susceptible to tears and are non-recyclable. LDPE is porous and somewhat stretchable, has good clarity and is great for everyday packaging needs and all-purpose trash collection. Linear low density polyethylene (LLDPE) is non-porous, very stretchable, puncture and tear resistant and about 15-50% less costly than LDPE. LLDPE serves the same purposes as LDPE. Metallocene is a new-generation polyethylene resin that is very tough and extremely tear resistant, much more so than LDPE. Polypropylene is very different than polyethylene. It is non-porous, super transparent, non-stretching and typically stronger and more rigid than types of PE. PP is utilized in food packaging and retail displays. Many plastic bag manufacturers now specialize in biodegradable packaging films, including biodegradable polymer bags.

There are several determining factors in determining which type of plastic bag is right for a specific application. Once the size of the bag is determined (length x height x diameter), materials must be chosen based on application requirements for tear resistance, strength, durability, recyclability and cost. Other considerations include side-sealed bags or bottom-sealed bags, closure type (if any) such as slider grip, zipper or draw-string and handle requirements, which will be determined by the bag's expected weight capabilities. Printed logos may be chosen to display brand or store names. Anticipated storage and use environments, such as warehouse storage or consumer shopping must also be considered when determining plastic bag specifications.

The non-recyclable nature of plastic bags has become a major environmental concern across the globe. Only 0.5% of consumer plastic is recycled. In the United States, four out of five grocery bags used are plastic. South Africa has banned grocery bags, as Americans know them, and has replaced them with a thicker, recyclable plastic. Germany and Sweden have taken steps to phase out the use of plastic bags by retailers, and Australia is beginning to follow suit. A progressive company in India has been taking plastic bags, pressing them into colorful sheets and using those sheets to create trendy fashion accessories, such as handbags and wallets. Other uses for the pressed plastic sheets include tablemats and notepad covers. Several U.S. plastic bag manufacturers have made strides in creating biodegradable polymer films and polymer alternatives, although these have yet to see significant exposure on the mainstream market.

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Plastic Bag Types

• Anti-static bags contain an anti-static additive that disseminates static electrical charges. Anti-static bags are ideal for short-term storage.
  
• Baggies are thin, disposable plastic bags used for storage, packing, and food preparation.
• Clear plastic bags are used for promotion, product display, retail, furniture covers, food storage, dry cleaning garment bags and many other applications in business and consumer industries. Clear bags are typically extruded from LDPE, although clear plastic totes can be made from thicker acrylic sheets, while "crystal clear plastic" bags are extruded from a polyester resin.
• 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.
  
• 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.
  
• Electrically conductive bags, which provide exterior protection from static charges, are made from carbon-impregnated polyethylene.
  
• Flap lock bags, commonly known as "sandwich" bags, have a lip that is folded back with side seals.
  
• Flat bags provide versatile plastic packaging for items of many shapes and sizes that are heat-sealed on either the side or the bottom of the bag. Bottom-sealed bags provide extra support for heavier items.
  
• Food storage bags are bags made from polyethylene resin to maintain the freshness of the food items and are often sealed with slider grips or zippers. Food storage bags, which include sandwich bags, freezer bags and produce bags, increase the life of perishable foods.
  
• 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 include bottom-sealed, side-gusseted bags and side-sealed, bottom-gusseted bags.
  
• Header bags are side-weld bags that are loaded and sealed from the bottom. Header bags have a continuous seal along the top, which is 2-3" below the fold, and a hang hole.
  
• Patch handle bags are flat bags with a die-cut handle reinforced by a heat-sealed patch for added strength.
  
• Poly bags are bags derived from polyethylene or polypropylene, although this term usually refers to polyethylene bags.
  
• Reclosable bags, which include zipper bags, are top-sealed. Reclosable bags can be made with or without a tamper-evident adhesive seal.
  
• Retail bags include all bags used to store and carry merchandise.
  
• Shopping bags are supplied by retailers for the transportation of purchased goods. They can have handles and are usually printed with the names of retail stores.
• Side weld bags are sealed on the side and have no bottom seal.
  
• Vinyl bags are receptacles made of thin plastic that are used to store goods.
• Waste removal bags include all trash can liners and bags, as well as bags used to remove hazardous waste. Waste removal bags are often manufactured from high density polyethylene resin because of the strength and cost-effectiveness of the resin, but may also be made out of linear low density resin because of its stretching ability.
  
• Zip lock bags are plastic bags with interlocking strips for sealing.

Plastic Bag Terms

Additive - Substance added to a polymer to increase the effectiveness, but not the strength, of the polymer. Examples of additives include flame-retardants, anti-static compounds, pigments and lubricants.
 
Alloy - Also referred to as a "blend" or "hybrid," it is two chemically dissimilar polymers bonded together to form a new substance. However, each polymeric unit is representative of only one monomer.
 
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.

Ethylene Vinyl Acetate (EVA) - A copolymer produced through the chemical reaction of ethylene and vinyl acetate. EVA is often added to plastic resins to increase the strength of the resin in temperatures below freezing.

Gauge - A term referring to the thickness of the material. The smaller the gauge number, the thinner the material.

Glass Transition Temperature (Tg) - Term that 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.
 
High Density Polyethylene (HDPE) - A plastic material whose thickness ranges from .941 -.965 g/cm³. HDPE is more expensive to process, but maintains greater strength, resistance and stiffness than either LDPE or LLDPE.
 
Light-Weighting - The process of decreasing the weight of plastic by using less resin, while retaining the strength and effectiveness of the plastic.
 
Linear Low Density Polyethylene (LLDPE) - A plastic material that is produced at lower temperatures and pressures than LDPE through copolymerization, resulting in a crystalline structure responsible for 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.
 
Lip - The longer side of the bag that allows the bag to be opened more easily.
 
Low Density Polyethylene (LDPE) - The most common and least expensive plastic bag material that maintains a density of .910-.925 g/cm³. LDPE maintains its durability, flexibility, water resistance and clarity under low temperatures, and its low melting point makes it ideal for heat sealing.
 
Melting Point - The temperature at which a substance converts from a solid into a liquid.
 
Metallocene - A puncture resistant material that is thinner and stronger than LDPE.
 
Monomer - The most basic polymeric unit, usually a liquid or a gas, consisting of molecules from the same organic substance. When chained together, monomers form solid polymers.
 
Plasticizer - A chemical added to plastic resins to increase the flexibility of the plastic.
 
Polyethylene (PE) - The most common plastic resin, it is a light, chemically resistant thermoplastic used in packaging and insulation. PE resins used in the production of plastic bags include low density, linear low density and high density resins.

Polymer - Two or more monomers bonded together through a chemical reaction. Each polymer consists of a chain of repeating monomers.
 
Polypropylene (PP) - Light, durable thermoplastic with a high melting point that is often used in packaging. PP contains polymers consisting of propylene, a colorless, combustible gas found in petroleum.
 
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.
 
Slip - An additive that aids in decreasing the slippage of stacked packaged goods and prevents bags from sticking together.
 
Star Seal - A bottom seal for liners that combines four sections into a star design. Star seals are the strongest seals, and they maximize carrying capacity.
 
Stress Cracking - Cracking that occurs 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.
 
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 specified sizes and shapes.
 
Thermoplastic - Category of plastics that has the potential to soften and reform when heated and to harden again during cooling. During the process, the physical makeup of the plastic does not change.
 
Thermoset - A category of plastics that cannot be reformed upon reheating. Thermosets remain permanently hard.
 
Ultraviolet Inhibitor (UVI) - A plastic additive that increases the resistance of the plastic to the harmful effects of ultraviolet radiation, such as 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.