PKG Lecture 10 Notes
PKG Lecture 10 Notes PKG 101
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This 6 page Class Notes was uploaded by Samantha Shea on Thursday October 13, 2016. The Class Notes belongs to PKG 101 at Michigan State University taught by p. koning in Fall 2016. Since its upload, it has received 6 views. For similar materials see Principles of Packaging in Packaging Science at Michigan State University.
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Date Created: 10/13/16
Lecture 10 Thursday, October 13, 201612:45 PM Plastics Packaging Plastics Defined • Plastics are based on synthetic resins or modified polymers of natural origin. • They are solid in the finished state, but can be molded using controlled heat and pressure at relatively low temperatures, compared to glass and metals. • Plastics are sub -‐classified in to two categories 1. Thermoplastics: materials which soften when heated and harden again when cooled. This process can be repeated indefinitely. Because of this behavior, thermoplastics are recyclable to some extent. 2. Thermosets: thermoset materials harden when heated or, in some cases, when they are treated with certain chemicals. After the initial set, thermoset materials no longer soften when heated. They are not recyclable except as inert fill in concrete or other materials. Plastic History and Trends 1933-‐ Polyethylene • Other polymer development followed • Waterproofing electronic-‐ s1930s • A significant early application was the use of polyethylene to waterproof the wires and other components in RADAR, SONAR, and similar equipment that was first used during WWII. Applications of Plastics • Plastic containers have replaced many metal, glass, paper, and wood packages that were formerly used. • The U.S. produces more plastic than steel, aluminum, and copper combined. Plastic packaging • Packaging is the largest market for plastics The Nature of Plastics • The ability of plastics to be shaped is an important property which results from their molecular structures. • Synthetic polymers are nearly always considered to be plastics Growth of Plastic Packaging • The growth of plastic packaging has accelerated rapidly since the 1970s, largely because of four characteristics of plastics: 1. Low density their molecular structures. • Synthetic polymers are nearly always considered to be plastics Growth of Plastic Packaging • The growth of plastic packaging has accelerated rapidly since the 1970s, largely because of four characteristics of plastics: 1. Low density 2. Formability 3. Strength and damage resistance 4. Economics Characteristics of plastics 2. Formability: easy to form into shapes 3. Strength and damage resistance • Light weight but strong. High strength to weight ratio • Damage resistance, flexibility • Chemical resistant • Relatively inert materials • No corrosion Raw materials for plastic • Naphtha, the primary raw material • Natural gas is the second most common raw material • Bio based materials Small Percentage usage • Packaging uses a fraction of this percentage Packaging Plastics • Big Six ○ Polyethylene (PE) § LDPE § HDPE ○ Polypropylene (PP) ○ Polyethylene Terephthalate (PET) ○ Polystyrene (PS) ○ Polyvinyl Chloride (PVC) ○ Others (covered in advanced PKG courses) § Society of Plastic Industry (SPI) Container Coding System #1 Polyethylene Terephthalat -PET (polyester) • Excellent clarity/ transparen-‐tsparkle = replacing PVC applications ○ Clear or colored • Good tensile/toughness/ tear strength = strapping • Can resist internal pressure from carbonation • All soda bottles up to 3 liters • "Fair" gas barrier • Metalized PET film for coffee vacuum packs • PREMIUM Soft Drink Bottling • Can resist internal pressure from carbonation • All soda bottles up to 3 liters • "Fair" gas barrier • Metalized PET film for coffee vacuum packs • PREMIUM Soft Drink Bottling • Soft drink bottlers switched from aluminum and glass to plastic because of the advantages of plastic ○ Weigh less ○ Variety of shapes and sizes ○ Transparent or colored (over metal, not glass) Less damage and breakage ○ ○ Most local curbside collection recycling systems accept PET containers = increasing popularity • Reduced shelf life of beverage products in plastic containers ○ Shelf life of carbonated beverages is only about 6 to 8 weeks when packaged in PET compared to months or even years when packaged in glass or aluminum containers • Necessary to re -‐structure the entire warehousing, distribution, and retail system Polyethylene • The polyethylene family is the most widely used type of plastics • #2-‐ High Density Polyethylene -‐ HDPE • #4-‐ Low Density Polyethylene -‐ LDPE #2 -‐ High Density Polyethy- DPE • HDPE may be clear like LDPE, but it often has a Translucent, white, milky appearance • Biggest use is as plastic jugs or milk, fruit juice, and water #3 -‐ Polyvinyl Chloride -‐PVC • Tough film • Excellent clarity- sparkle • Non-‐food: e.g. Shampoo bottles • Thermoformed blisters and clamshells • Food: low O2 barrier = film for red meats, cling wrap • Negative influences = almost obsolete in US for bottling food/beverage. Losing market to PET #4 Low Density PolyethyleneL DPE • A primary application -‐ bags • Stretch wrap for unitizing loads #5 Polypropylene -‐ PP • Less dense than PE, and stiffer • Excellent clarity and sparkle like PS • Clear or colored • High temperature tolerate for hol = HOT • Examples #5 Polypropylene -‐ PP • Less dense than PE, and stiffer • Excellent clarity and sparkle like PS • Clear or colored • High temperature tolerate for hol = HOT • Examples ○ Over-‐wraps ○ Closures (plastic caps) ○ Excellent living hinge properties: injection molded boxes, containers and closures • Another common use of polypropylene is snack food packaging such as pretzels and potato chips. Often the PP in those applications has had a thin layer of aluminum added to improve the barrier. We refer to this material as metalized film (specifically, metalized PP, in this case) #6 Polystyrene-‐ PS • Clear food service, colored or opaque cups -‐ PS • Foamed (expanded) cushion material -‐ EPS ○ Molded and loose-‐fill cushioning • Crystal clear rigid jewel boxes, cosmetics -‐ PS • Crystal clear film -‐PS • Superior clarity similar to PET & PP Environmental concerns about EPS • EPS has also been a target of certain environmental groups Society of Plastic Industry (SPI) Container Coding System • Developed to help states recycling efforts • Some states written the coding system into law • Not based on federal law • Being used in similar form in other countries The Most Common Forming Methods for Packaging Plastics • Extrusion • Lamination-‐extruded sheet or film (rigid and felxible) • Thermoforming-‐ extruded sheet • Injection molding ○ Injection blow molding (IBM) ○ Injection Stretch Blow Molding (ISBM) Extrusion • Basic machine that is used in the beginning of the process of all plastic formation • Heat and pressure • Mixes and melts plastic • Forces molten plastic out through die Silt ○ ○ Ring ○ Other shapes • Heat and pressure • Mixes and melts plastic • Forces molten plastic out through die ○ Silt ○ Ring ○ Other shapes Injection Molding • Special Extruder: accumulates a "shot" of melted plastic, then injects into the mold • Mold filled, cooled to shape, plug pulled out, finished object pushed out • 'Witness' tiny rough point, faint circular markings Plastic Bottles • Characteristics of a Bottle ○ Hollow vessels ○ Manufactured from thermoplastic material ○ Finish that has a smaller diameter than the body ○ Requires a blow molding process where air pressure is used with a mold to create the shape Blow Molding Process 1. Injection Blow Molding (IBM) ○ Injection Stretch Blow Molding (ISBM) 2. Extrusion Blow Molding (EBM) ○ Extrusion blow mol-‐fill-‐seal process Injection Blow Molding • Injection blow molding is used for the production of bottles in large quantities • The injection blow molding process produces bottles of superior visual and dimensional quality compared to extrusion blow molding • No flash • When injection and blowing are done on a single machine, the process is described as "one-‐step" Injection Blow Molding (IBM) Process • Injection -‐ Preform • Blowing • Ejection Injection Blow Molding • More precise control -‐ good for items with tight dimensions • No scrap (flash) • Little limitation of polymer materials that can be used • Better distribution of material • No commercially successful handles (they must be glued on in a second operation) Injection Stretch Blow Molding • Overview ○ Injection stretch blow moldings used for the production of large volume • Better distribution of material • No commercially successful handles (they must be glued on in a second operation) Injection Stretch Blow Molding • Overview ○ Injection stretch blow moldings used for the production of large volume containers. ○ Preform and container can be molded at different times, in different places • Materials ○ Polyethylene -‐ Terephthalate PET Injection Stretch Blow Molding (ISBM) Typical Product Packages Produced • Carbonated and soft drink bottles Injection Stretch Blow Molding Process • Injection • Molten polymer flows into the injection cavity to produce the desired shape of the PREFORM • Ejection/Discharge Injection Stretch Blow Molding Process cont. • Preheat Preform • Stretching and Blowing (biaxial orientation created) • Ejection Injection Stretch Blow Molding (ISBM) Animation • Normal plastic bottles have uniaxial orientations (horizontally) when blown • To get biaxial orientation, it needs to also be stretched vertically • Results: Biaxially oriented PET bottles perform much better Injection Stretch Blow Molding (ISBM) • Advantages ○ High clarity ○ Improved gas barrier ○ Improved stiffness ○ Permits thinner walls ○ Absence of any trim and scrap • Container and its Preform • Blow molding mark on the container bottom. The point where the plastic injected into the mold was cut off
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