You will see all of these processes on your plant tour today, except for cast films sheet extrusion and rotogravure printing.
Basic Extrusion
Resin
Screw
Barrel To Die
Presenter
Presentation Notes
1. Resin is loaded into the hopper. 2. Resin drops onto the rotating screw inside the barrel of the extruder. 3. Flights convey resin forward along the heated barrel as the screw rotates. 4. The screw generates heat and pressure so the resin is melted, mixed, and at the right pressure and temperature by the time it reaches the end. 5. Resin passes through screens to filter out foreign matter. 6. Goes through a circular (or flat) die and into the next process. (Give typical back pressure and temps)
Basic Extrusion
– Resin is fed into rotating screw
– Heat (external & shear) and pressure melt the resin
– Molten polymer is forced through a screen pack to remove foreign matter, create back pressure, and aid in mixing
– Melt from extruder flows into die to provide the desired and a uniform thickness of film
– Flat die or annular (circular) die
Presenter
Presentation Notes
Monoxial films are oriented in the machine direction only. In Biaxially oriented films, each polymer has a natural orientation ratio. Orientation ratio is defined as percent stretch in each direction
Basic Extrusion
– Critical region in extrusion is in the transition of solid to melt phase
– Gels (unmelted or crosslinked polymer) can develop randomly due to:
• Incorrect temperatures, poor screw design
• Poor incoming resin, polymer buildup
– In regions where polymer flow is slow, oxidized polymer can exist (carbon)
– Carbon can randomly discharge into melt stream
Blown Film
Primary Nip Roll
Resin Blenders
Hopper
Extruder
Guide Rolls
Blown Tube
Windup Rolls
Air Ring
Treater
Presenter
Presentation Notes
Molten resin enters a circular die, and is extruded in the form of a thick-walled tube. The tube is expanded into a bubble by forcing air into it. As the tube is stretched, the thickness of the plastic is reduced. During the process, the top nip slowly rotates to distribute film thickness variations. Without rotation, gauge bands would build up in one place on the roll of film as it winds. At the top of the process the bubble is gradually pinched together. The film then winds downward through several rollers which guide the web and prevent it from wandering. The film is cut into two separate, continuous layers of film which are each wound onto separate rolls.
Gauge Bands/Baggy Film
Blown Film Extrusion - Blenders
Blown Film Extrusion
Blown Film Extrusion
Blown Film Extrusion – Gauge Control
Blown Film Extrusion – Gauge Control (IGC)
Non-contact (air cushion) Nuclear Gauge - Measures thickness around the bubble
Vertically Sliding Teeth - Adjusts airflow through ¼” gap
Sliding Teeth Actuator - Raises or lowers teeth
Live Ring – Oscillates the thickness sensor around the bubble
Bubble
Blown Film Extrusion – Gauge Control (IGC)
Profile Control System Off
Profile Control System On
Blown Films - Process Basics
Blown Film Extrusion – Top Nip
Blown Film Coextrusion
• Up to 9 independent extruders feed the die
• Each discrete melt stream can be made up of a blend of polymers and additives
• Allows for optimization of performance properties vs. cost
Die
Molten Resin
Top View
Cross Section
Presenter
Presentation Notes
Allows us to combine up to 7 different resins in the same film. Each extruder supplies molten resin to the same die. All resins must melt and flow at same temperatures. Resins do not mix resulting in a single film with multiple layers. Common uses Sealant films, Ice ® films This process produces films with: * Little gauge variation * Good puncture resistance * Lower cost—one operation creates a multi-layer film
Blown Film Extrusion
• Monolayer die has a single melt stream
• Coextrusion die combines multiple melt streams to create a single film with multiple layers
• Melt exits die at 350-550ºF (177-288ºC)
• Bubble immediately cooled with chilled air
• Bubble oscillates to distribute caliper variation
• Bubble is collapsed and surface treated
• Thickness is controlled by extruder speed, line speed, die gap
Corona Treatment of Film
• Film is corona treated to enhance surface energy • Generates an electrical discharge which oxidizes the
polymer surface • Treatment improves adhesion properties required for
subsequent laminating or printing processes • Base polymers have varying initial levels of surface
tension:
Material Surface Tension ( dynes/ cm 2) Polypropylene (PP) 29Polyethylene (PE) 31Polyester (PET) 43Polytetrafluorethylene ( “Teflon”) 19
Corona Treament
Primary Nip Roll
Resin Blenders
Hopper
Extruder
Guide Rolls
Blown Tube
Windup Rolls
Air Ring
Corona Treater
Presenter
Presentation Notes
Molten resin enters a circular die, and is extruded in the form of a thick-walled tube. The tube is expanded into a bubble by forcing air into it. As the tube is stretched, the thickness of the plastic is reduced. During the process, the top nip slowly rotates to distribute film thickness variations. Without rotation, gauge bands would build up in one place on the roll of film as it winds. At the top of the process the bubble is gradually pinched together. The film then winds downward through several rollers which guide the web and prevent it from wandering. The film is cut into two separate, continuous layers of film which are each wound onto separate rolls.
Corona Treatment
Treatment Level Determination
• Dyne pens or dyne solutions are utilized to determine treatment level
Sheet Extrusion
Extruder
Resin Additives
Blender / Mixer
Die Windup
Cooling Roll
Cooling Roll
Cooling Roll
Produces materials from 10-60 mil thick Typically used for thermoforming applications (trays) Can be mono-layer or co-extrusion
Presenter
Presentation Notes
Schematic of how we make thick gauge films, typically from 10 - 60 mils thick. Can go as thin as 6 mils on this set up. The die is horizontal. The gap between the chill rolls controls thickness. The most common rigid materials we promote are PET, HIPS and PP. Fremont has 2 sheet lines and 5 thermoformers.
Orientation Basics
Orientation enhances several key properties: – Tensile strength – Impact strength – Heat resistance – Oxygen and water barrier – Abrasion resistance – Gloss and clarity
Presenter
Presentation Notes
Monoxial films are oriented in the machine direction only. In Biaxially oriented films, each polymer has a natural orientation ratio. Orientation ratio is defined as percent stretch in each direction
M.D. Orientation Annealing
T.D. Orientation Extrusion
OVEN
Tenter Frame Process
Presenter
Presentation Notes
This is another process used to make OPET and BOPP. (Curwood does not use this process.) Film is extruded and cast onto a chill roll. It is then sequentially oriented in the machine direction and transverse direction. Tenter process is the industry standard. Machine direction speed is what causes first stretching. Advantage of double bubble is balanced physical properties--better flex crack and tensile properties. Lines are typically very wide (up to 10 meters finished film width) and produce over 20 million pounds per line per year.
Orientation Basics
• Oriented films are highly stretched and heat stabilized
• Polymer is initially extruded into a thick sheet
• Thick sheet is re-heated and stretched in both machine and transverse directions:
– Orientation stretch ratios from 12X - 40X
• After orienting, the film travels through an annealing oven to relieve internal stresses and heat stabilize
Remember to give examples, don’t just read the characteristics.. Applications/ Why Snacks:Moisture barrier & flex crack resistance Cheese:Good flex crack resistance BOPP can also be used as an interior layer on cheese films because it provides good flex crack resistance. Show samples. 1 mil oriented polyprop has barriers of: O2TR = 150cc/100in2/day MVTR= 0.45 gr/100in2/day