(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:346)(cid:410)(cid:400)(cid:3)(cid:396)(cid:286)(cid:400)(cid:286)(cid:396)(cid:448)(cid:286)(cid:282)(cid:856)(cid:3)
`(cid:69)(cid:381)(cid:3)(cid:437)(cid:374)(cid:258)(cid:437)(cid:410)(cid:346)(cid:381)(cid:396)(cid:349)(cid:460)(cid:286)(cid:282)(cid:3)(cid:282)(cid:349)(cid:400)(cid:272)(cid:367)(cid:381)(cid:400)(cid:437)(cid:396)(cid:286)(cid:3)(cid:381)(cid:396)(cid:3)(cid:396)(cid:286)(cid:393)(cid:396)(cid:381)(cid:282)(cid:437)(cid:272)(cid:410)(cid:349)(cid:381)(cid:374)(cid:854)(cid:3)(cid:367)(cid:349)(cid:272)(cid:286)(cid:374)(cid:400)(cid:286)(cid:282)(cid:3)(cid:410)(cid:381)(cid:3)(cid:393)(cid:437)(cid:396)(cid:272)(cid:346)(cid:258)(cid:400)(cid:286)(cid:396)(cid:3)(cid:381)(cid:374)(cid:367)(cid:455)(cid:856)
`
`0601
`
`EX1008 (Part 3 of 3)
`Yita v. MacNeil
`IPR2020-01139
`
`

`

`8.2 Forming Thin Films
`
`585
`
`Double Bubble
`
`Collapsing Frame
`
`
`
`Blown Film Bubble
`
`
`
`Frost Line
`
`
`
`
`External Air Ring~.
`
`Extruder
`
` =|___. IntarnalAir Inlet
`
`Figure 8.1 Typical blown film tower with optional double bubble stretching section [2]
`
`Regrind isdifficult to accommodatein calendering, and dirt, gels and contamination
`can be a problem.
`Films are also produced by solution casting, Any polymerthat can be solvated or
`dissolved in a carrier can be cast
`into film. Typically, polymers that cannot be
`extruded or melt processed are solution cast into films. Examples include polyimides,
`polyazoles and latexes. Solution casting is usually a manual batch process although
`
`(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:346)(cid:410)(cid:400)(cid:3)(cid:396)(cid:286)(cid:400)(cid:286)(cid:396)(cid:448)(cid:286)(cid:282)(cid:856)(cid:3)
`© 1996 Carl Hanser Verlag. All rights reserved.
`(cid:69)(cid:381)(cid:3)(cid:437)(cid:374)(cid:258)(cid:437)(cid:410)(cid:346)(cid:381)(cid:396)(cid:349)(cid:460)(cid:286)(cid:282)(cid:3)(cid:282)(cid:349)(cid:400)(cid:272)(cid:367)(cid:381)(cid:400)(cid:437)(cid:396)(cid:286)(cid:3)(cid:381)(cid:396)(cid:3)(cid:396)(cid:286)(cid:393)(cid:396)(cid:381)(cid:282)(cid:437)(cid:272)(cid:410)(cid:349)(cid:381)(cid:374)(cid:854)(cid:3)(cid:367)(cid:349)(cid:272)(cid:286)(cid:374)(cid:400)(cid:286)(cid:282)(cid:3)(cid:410)(cid:381)(cid:3)(cid:393)(cid:437)(cid:396)(cid:272)(cid:346)(cid:258)(cid:400)(cid:286)(cid:396)(cid:3)(cid:381)(cid:374)(cid:367)(cid:455)(cid:856)
`No unauthorized disclosure or reproduction; licensed to purchaser only.
`
`0602
`
`0602
`
`

`

`586
`
`Producing Sheet and Film
`
`[Refs. on p. 644]
`
` Two-RollMill +) ©
`
`"L" Calender Roll Stack
`
`Inverted "L" Calender Roll Stack
`
`Figure 8.2 Two calendering roll stack configurations. Redrawn from [3] and used with permission of
`copyright owner
`
`Two-RollMill C+) S
`
`RAY
`
`CA
`
`+)
`
`"FE" Calender Roll Stack
`
`"2" Calender Roll Stack
`
` Two-Rall Mill
`
`= =,
`
`&
`
`Figure 8.3 Two calendering roll stack configura-
`tions. Redrawn from [4] and used with permission
`of copyright owner
`
`the resulting films are quite
`latex casting has been automated. With proper care,
`uniform in thickness and properties. Films having thicknesses of | mil, 0.001 in or
`25 um or less are common.Solvent cast films are usually quite expensive. Residual
`solvent can be a serious problem during reheating of the film in the forming
`operation.
`Thin films are also needed when coextruded sheet is required. In this case, the
`polymeris melt-extruded with a secondary extruder into a special multilayer die. This
`is discussed below.
`
`(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:346)(cid:410)(cid:400)(cid:3)(cid:396)(cid:286)(cid:400)(cid:286)(cid:396)(cid:448)(cid:286)(cid:282)(cid:856)(cid:3)
`© 1996 Carl Hanser Verlag. All rights reserved.
`(cid:69)(cid:381)(cid:3)(cid:437)(cid:374)(cid:258)(cid:437)(cid:410)(cid:346)(cid:381)(cid:396)(cid:349)(cid:460)(cid:286)(cid:282)(cid:3)(cid:282)(cid:349)(cid:400)(cid:272)(cid:367)(cid:381)(cid:400)(cid:437)(cid:396)(cid:286)(cid:3)(cid:381)(cid:396)(cid:3)(cid:396)(cid:286)(cid:393)(cid:396)(cid:381)(cid:282)(cid:437)(cid:272)(cid:410)(cid:349)(cid:381)(cid:374)(cid:854)(cid:3)(cid:367)(cid:349)(cid:272)(cid:286)(cid:374)(cid:400)(cid:286)(cid:282)(cid:3)(cid:410)(cid:381)(cid:3)(cid:393)(cid:437)(cid:396)(cid:272)(cid:346)(cid:258)(cid:400)(cid:286)(cid:396)(cid:3)(cid:381)(cid:374)(cid:367)(cid:455)(cid:856)
`No unauthorized disclosure or reproduction; licensed to purchaser only.
`
`0603
`
`0603
`
`

`

`The criteria for judging the quality of thin films are the same as those for heavier
`gage sheet. These are discussed below. With thin films,
`there is a greater concern
`about gels, fish-eyes and other occlusions in the sheet simply because the dimensions
`of these defects may be equal to or greater than the thickness of the film.
`
`§.3 Forming Sheet
`
`587
`
`8.3 Forming Sheet
`
`As noted, calendering is used to produce thin-gage sheet to 50 mils, 0.050 in or
`1250 pm in thickness. Its use is usually restricted to polymers that require fluxing or
`masticating and those that are thermally sensitive. Polyviny] chloride is the domi-
`nant polymer produced as calendered sheet. High molecular weight polymethyl
`methacrylate is sought for clarity and chemical resistance in pools, spas, shower
`stalls, and most glazing applications. It is produced by cell casting [5]. Generally,
`methyl methacrylate monomer with its hydroquinone inhibitor removed is mixed
`with benzoyl peroxide catalyst and heated to 90-95°C. The catalyzed syrup is cast
`between two highly polished plates separated by flexible polyvinyl chloride or
`polyviny] alcohol gaskets. The plates are held against the gaskets with carefully
`calibrated spring-loaded clips since the polymer increases in density or decreases in
`volume as its molecular weight increases. Temperature is maintained at 40°C early
`in the polymerization but gradually raised to 95-97°C after several hours to allow
`the polymerization to proceed to completion. The sheet
`is then cooled to below
`40°C, removed from the plates and annealed for up to 2 hours at 140°C to minimize
`internal stresses.
`Although the original batch processis still used to produce sheets with special
`sizes and thicknesses or acrylics that are lightly crosslinked, the continuouscell-cast
`process dominates the production of most commercial glazing acrylic sheets. The
`continuous process uses a monomer/polymer syrup containing up to 20% high-
`molecular weight polymer. Although the abrasion and chemical resistances are
`thought
`to be somewhat
`inferior to the batch cell-cast product,
`this product
`is
`substantially less expensive. Continuouscell-cast acrylic can also be crosslinked to
`improve impact strength. With proper temperature control, lower molecular weight
`polymethyl methacrylate pellets and granules are extruded into sheets using conven-
`tional single-screw extruders. Such products have lowered abrasion,
`impact and
`scratch resistances and may not have the surface quality and clarity of higher
`molecular weight acrylics. And extrusion-grade acrylics are usually not crosslinked.
`Extrusion through a slot die is
`the primary method of producing sheet
`of thicknesses from 10 mils, 0.010 in or 250 pm to 500 mils, 0.500 in or 12 mm
`or more. Table 8.2 lists the scope of continuous screw extrusion techniques.
`Plasticating single-screw extruders and twin-screw extruders dominate production of
`sheet for thermoforming. Of the rest, two-stage and tandem extruders are used to
`produce foam sheet. This is covered in some detail in Chapter 9 on forming foam
`sheet.
`
`(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:346)(cid:410)(cid:400)(cid:3)(cid:396)(cid:286)(cid:400)(cid:286)(cid:396)(cid:448)(cid:286)(cid:282)(cid:856)(cid:3)
`© 1996 Carl Hanser Verlag. All rights reserved.
`(cid:69)(cid:381)(cid:3)(cid:437)(cid:374)(cid:258)(cid:437)(cid:410)(cid:346)(cid:381)(cid:396)(cid:349)(cid:460)(cid:286)(cid:282)(cid:3)(cid:282)(cid:349)(cid:400)(cid:272)(cid:367)(cid:381)(cid:400)(cid:437)(cid:396)(cid:286)(cid:3)(cid:381)(cid:396)(cid:3)(cid:396)(cid:286)(cid:393)(cid:396)(cid:381)(cid:282)(cid:437)(cid:272)(cid:410)(cid:349)(cid:381)(cid:374)(cid:854)(cid:3)(cid:367)(cid:349)(cid:272)(cid:286)(cid:374)(cid:400)(cid:286)(cid:282)(cid:3)(cid:410)(cid:381)(cid:3)(cid:393)(cid:437)(cid:396)(cid:272)(cid:346)(cid:258)(cid:400)(cid:286)(cid:396)(cid:3)(cid:381)(cid:374)(cid:367)(cid:455)(cid:856)
`No unauthorized disclosure or reproduction; licensed to purchaser only.
`
`0604
`
`0604
`
`

`

`588
`
`Producing Sheet and Film
`
`[Refs. on p. 644]
`
`Table 8.2 Types of Continuous Screw Extruders
`
`
`
`Single-screw extruders
`
`
`Mullti-screw extruders
`
`
`Melt fed or plasticating
`Twin screw
`
`Single stage
`Gear pump
`Multi-stage
`Planetary gear
`
`Plastic
`Multi-screw (>2)
`Rubber
`
`
`Single-Screw Extrusion
`
`Figure 8.4 is a cut-away schematic of a conventional single-screw extruder. The basic
`elements are:
`
`Constant diameter flighted screw,
`Constant bore barrel,
`Zoned heater bands,
`Keyed bearing block,
`Feed hopper,
`Venting ports,
`
`Barrel (EEELLLCLLa(agea4
`
`Screw
`
`Gear Box EDD
`
`Heater Band
`
`SS
`
`Figure 8.4 Schematic of single-screw extruder for thermoplastics
`
`(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:346)(cid:410)(cid:400)(cid:3)(cid:396)(cid:286)(cid:400)(cid:286)(cid:396)(cid:448)(cid:286)(cid:282)(cid:856)(cid:3)
`© 1996 Carl Hanser Verlag. All rights reserved.
`(cid:69)(cid:381)(cid:3)(cid:437)(cid:374)(cid:258)(cid:437)(cid:410)(cid:346)(cid:381)(cid:396)(cid:349)(cid:460)(cid:286)(cid:282)(cid:3)(cid:282)(cid:349)(cid:400)(cid:272)(cid:367)(cid:381)(cid:400)(cid:437)(cid:396)(cid:286)(cid:3)(cid:381)(cid:396)(cid:3)(cid:396)(cid:286)(cid:393)(cid:396)(cid:381)(cid:282)(cid:437)(cid:272)(cid:410)(cid:349)(cid:381)(cid:374)(cid:854)(cid:3)(cid:367)(cid:349)(cid:272)(cid:286)(cid:374)(cid:400)(cid:286)(cid:282)(cid:3)(cid:410)(cid:381)(cid:3)(cid:393)(cid:437)(cid:396)(cid:272)(cid:346)(cid:258)(cid:400)(cid:286)(cid:396)(cid:3)(cid:381)(cid:374)(cid:367)(cid:455)(cid:856)
`No unauthorized disclosure or reproduction; licensed to purchaser only.
`
`0605
`
`0605
`
`

`

`8.3 Forming Sheet
`
`589
`
`Table 8.3 Typical Compression Ratios Single-Screw
` Extruders
`
`Polymer
`
`Compression ratio
`
`Regrind polyethylene fiuff
`Polyethylene powder
`Regrind polystyrene foam
`Other amorphous powders
`Polypropylene pellets
`PYC pellets
`Polystyrene pellets
`ABSpellets
`Crystalline PET pellets
`Polyamide (nylon) pellets
`
`4.5:1
`4.0:1
`4.03
`3.5:1
`3.0:1
`2.531
`2,5:1
`25:1
`2.0:1
`1.5:1
`
`e Electric motor,
`*
`Power coupling between motor and flighted screw, and
`* Temperature and speed controls.
`
`The most common screw is single-flighted. The screw serves to advance the polymer
`from the hopper to the die end, compressing, melting and increasing the pressure on
`it as it advances. The screw root increases along the screw, compressing and pressing
`the polymer against the heated barrel inner wall. The amount of compressionis the
`compression ratio, Table 8.3 gives typical compression ratios for some polymers. The
`function of the screw is intellectually divided into three segments (Fig. 8.5) [6]:
`
`«
`
`Solids conveying. where the plastic pellets or powder is augered from the hopper
`into the barrel. Energy transfer to the polymer is minimal. Friction between the
`semi-solid polymer and the barrel and screw surfaces dominates. Typically the
`screw root dimension does not change in this zone.
`
`Metering SectionelETheNtoringSeteFeed Section Transition Section
`
`
`
`
`
`
`
`-s|
`
`Key
`
`Screw Flight
`
`
`
`Screw Tip
`
`Channel DepthShank Screw Diameter
`
`
` |AAPPETTITTTTY
`Pubs | Ne
`Pitch
`
`
`Helix Angle Screw Root Screw Flight~Channel Width
`
`Figure 8.5 Schematic of screw for single-screw extruder with identification of various screw ele-
`ments. Redrawn from [6] and used with permission of copyright owner
`
`(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:346)(cid:410)(cid:400)(cid:3)(cid:396)(cid:286)(cid:400)(cid:286)(cid:396)(cid:448)(cid:286)(cid:282)(cid:856)(cid:3)
`© 1996 Carl Hanser Verlag. All rights reserved.
`(cid:69)(cid:381)(cid:3)(cid:437)(cid:374)(cid:258)(cid:437)(cid:410)(cid:346)(cid:381)(cid:396)(cid:349)(cid:460)(cid:286)(cid:282)(cid:3)(cid:282)(cid:349)(cid:400)(cid:272)(cid:367)(cid:381)(cid:400)(cid:437)(cid:396)(cid:286)(cid:3)(cid:381)(cid:396)(cid:3)(cid:396)(cid:286)(cid:393)(cid:396)(cid:381)(cid:282)(cid:437)(cid:272)(cid:410)(cid:349)(cid:381)(cid:374)(cid:854)(cid:3)(cid:367)(cid:349)(cid:272)(cid:286)(cid:374)(cid:400)(cid:286)(cid:282)(cid:3)(cid:410)(cid:381)(cid:3)(cid:393)(cid:437)(cid:396)(cid:272)(cid:346)(cid:258)(cid:400)(cid:286)(cid:396)(cid:3)(cid:381)(cid:374)(cid:367)(cid:455)(cid:856)
`No unauthorized disclosure or reproduction; licensed to purchaser only.
`
`0606
`
`0606
`
`

`

`590
`
`Producing Sheet and Film
`
`[Refs. on p. 644)
`
`Molten Polymer Film
`
`Barrel
`
`SS SS
`
`PTE
`
`Mall Poo!
`
`Solid Polymer Granular Bed
`
`Figure 8.6 Schematic of the interrelationship of solid and melt polymer and screw and barrel in the
`plastication region for single-screw extruder [7]
`
`« Plasticating or melting, where the compressed cake melts against the barrel surface
`and the melt is continuously conveyed into a pool at the front ofthe trailing flight
`(Fig. 8.6) [7]. In this zone, the screw root dimension linearly increases.
`e Melt pumping, where the molten polymer is homogenized and compressed to build
`pressure necessary to flow through the extrusion sheet die. In this zone, the screw
`root dimension remains constant.
`
`These extruders are usually described in terms of screw diameter and the screw
`length-to-diameter ratio, L/D. In the US, screw diameters are given in inches as 1,
`14, 2, 25, 35, 45, 6, 8, 10, 12 and so on. In Europe and other metric areas, screw
`diameters are given in mm as 20, 25, 30, 35, 40, 50, 60, 90, 120, 150 and so on. L/D
`ratios are as low as 12:1] to 16:1 for rubber and thermoplastic elastomeric polymers
`to 20:] to 36:] for most commercial extruders to 48:1 for certain olefinic extruders.
`24:1 and 30:1 extruders make up the bulk of sheet extrusion capability in the US
`while most European extruders are typically 30:1 to 36:1. Increased L/D allows for
`improved solids conveying and melt homogenization but increases the residence time
`and shear history on the polymer melt. Table 8.4 gives an overview of the capacities
`of extruders of various diameters [8], Extruder throughput rates are also dependent
`on the type of polymer, as seen in Table 8.5 [9]. These rates represent extruder
`capacity when the flow rate through the die is not controlling. This is the case for
`most heavy-gage sheet extrusion. For thin-gage sheet extrusion, on the other hand,
`extruder throughput rates may be reduced by flow resistance through the die, as seen
`in Table 8.6 for the extrusion of 15 to 80 mil, 0.015 to 0.080 in or 400 to 2000 pm
`flat sheet of certain polymers [10]. Example 8.1 showsthe relative output for a given
`extruder screw diameter.
`
`(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:346)(cid:410)(cid:400)(cid:3)(cid:396)(cid:286)(cid:400)(cid:286)(cid:396)(cid:448)(cid:286)(cid:282)(cid:856)(cid:3)
`© 1996 Carl Hanser Verlag. All rights reserved.
`(cid:69)(cid:381)(cid:3)(cid:437)(cid:374)(cid:258)(cid:437)(cid:410)(cid:346)(cid:381)(cid:396)(cid:349)(cid:460)(cid:286)(cid:282)(cid:3)(cid:282)(cid:349)(cid:400)(cid:272)(cid:367)(cid:381)(cid:400)(cid:437)(cid:396)(cid:286)(cid:3)(cid:381)(cid:396)(cid:3)(cid:396)(cid:286)(cid:393)(cid:396)(cid:381)(cid:282)(cid:437)(cid:272)(cid:410)(cid:349)(cid:381)(cid:374)(cid:854)(cid:3)(cid:367)(cid:349)(cid:272)(cid:286)(cid:374)(cid:400)(cid:286)(cid:282)(cid:3)(cid:410)(cid:381)(cid:3)(cid:393)(cid:437)(cid:396)(cid:272)(cid:346)(cid:258)(cid:400)(cid:286)(cid:396)(cid:3)(cid:381)(cid:374)(cid:367)(cid:455)(cid:856)
`No unauthorized disclosure or reproduction; licensed to purchaser only.
`
`0607
`
`0607
`
`

`

`8.3 Forming Sheet
`
`591
`
`Table 8.4 Typical Extruder Capacities [8]
`
`
`
`
`Extruder size
`Barrel heater
`Average power
`Output
`
`
`(HP)
`
`(kW)
`
`
`
`(Ib/h) (kg/h)
`
`
`
`
`7.5
`23-74
`is
`10-15
`50-75
`
`21
`54-73
`24
`20-30
`120-160
`
`
`
`45
`113—181
`33
`40-75
`250-400
`
`
`
`75
`181-318
`4!
`80.125
`400-700
`140
`6
`150-225
`800-1200
`363-544
`
`8
`680-9071500-2000 225
`300-500
`
`
`
`
`
`
`Example 8.1 Extrusion Capacity
`
`Your thermoforming operation requires 40 in x 52 in x 0.060 in ABS sheet. Deter-
`niine the number af 100 sheet pallets that can be produced from a 4-in extruder.
`Compare the output with the maximum output of that extruder. Determine the
`weight of each pallet.
`
`From Table 8.6, the 45-in extruder with a sheeting die can produce 1320 to
`1430 Ib/h ABS. Thespecific gravity of ABS is 1.05 g/cm* = 65.5 lb/ft’. Thus
`the volumetric output is 20 to 22 ft?/h. The volume of each sheet is 124.8
`in? = 0.072 ft®. Therefore the extruder will produce 275 to 300 sheets per
`hour or 2.75 to 3 pallets per hour. The plastic on each pallet weighs 470 Ib.
`According to Table 8.5, a 44-in extruder can plasticate 1170 to 1430 Ib/h.
`Therefore, the extruder with a sheeting die is running at maximum capacity.
`
`Manysingle-screw extruders have venting ports or vents at some location along
`the barrel. Some polymers contain small amounts of volatiles. These are removed
`prior to the sheeting die to eliminate foaming and to minimize microbubbles,pits and
`poresin the finished sheet. Venting screws usually have a decompression or let-down
`region just ahead of the vent, as seen in Fig. 8.7 [Il]. Vented or devolatilizing
`extruders usually have L/Ds of 30:1 or more. Although vents can be plugged and the
`extruder run unvented, the screw is usually not optimum and so the polymer may be
`subjected to higher than normal shear and residence time at melt temperature. Vented
`extruders should not be used to dewater polymers. Polymers having high moisture
`level potentials should be thoroughly dried prior to being charged to the extruder.
`
`Filtering the Polymer
`
`A filter screen is usually placed between the end of the extruder and the die to catch
`contaminants, unmelted polymer and somegel particles. The generic screen is a plate
`with regularly spaced holes. Screens with different sized holes are usually grouped
`together to form a screen pack. A typical screen pack might have several 100 mesh
`
`(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:346)(cid:410)(cid:400)(cid:3)(cid:396)(cid:286)(cid:400)(cid:286)(cid:396)(cid:448)(cid:286)(cid:282)(cid:856)(cid:3)
`© 1996 Carl Hanser Verlag. All rights reserved.
`(cid:69)(cid:381)(cid:3)(cid:437)(cid:374)(cid:258)(cid:437)(cid:410)(cid:346)(cid:381)(cid:396)(cid:349)(cid:460)(cid:286)(cid:282)(cid:3)(cid:282)(cid:349)(cid:400)(cid:272)(cid:367)(cid:381)(cid:400)(cid:437)(cid:396)(cid:286)(cid:3)(cid:381)(cid:396)(cid:3)(cid:396)(cid:286)(cid:393)(cid:396)(cid:381)(cid:282)(cid:437)(cid:272)(cid:410)(cid:349)(cid:381)(cid:374)(cid:854)(cid:3)(cid:367)(cid:349)(cid:272)(cid:286)(cid:374)(cid:400)(cid:286)(cid:282)(cid:3)(cid:410)(cid:381)(cid:3)(cid:393)(cid:437)(cid:396)(cid:272)(cid:346)(cid:258)(cid:400)(cid:286)(cid:396)(cid:3)(cid:381)(cid:374)(cid:367)(cid:455)(cid:856)
`No unauthorized disclosure or reproduction; licensed to purchaser only.
`
`0608
`
`0608
`
`

`

`592
`
`Producing Sheet and Film
`
`mdysnomyy
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`(Refs. on p. 644]
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`(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:346)(cid:410)(cid:400)(cid:3)(cid:396)(cid:286)(cid:400)(cid:286)(cid:396)(cid:448)(cid:286)(cid:282)(cid:856)(cid:3)
`© 1996 Carl Hanser Verlag. All rights reserved.
`(cid:69)(cid:381)(cid:3)(cid:437)(cid:374)(cid:258)(cid:437)(cid:410)(cid:346)(cid:381)(cid:396)(cid:349)(cid:460)(cid:286)(cid:282)(cid:3)(cid:282)(cid:349)(cid:400)(cid:272)(cid:367)(cid:381)(cid:400)(cid:437)(cid:396)(cid:286)(cid:3)(cid:381)(cid:396)(cid:3)(cid:396)(cid:286)(cid:393)(cid:396)(cid:381)(cid:282)(cid:437)(cid:272)(cid:410)(cid:349)(cid:381)(cid:374)(cid:854)(cid:3)(cid:367)(cid:349)(cid:272)(cid:286)(cid:374)(cid:400)(cid:286)(cid:282)(cid:3)(cid:410)(cid:381)(cid:3)(cid:393)(cid:437)(cid:396)(cid:272)(cid:346)(cid:258)(cid:400)(cid:286)(cid:396)(cid:3)(cid:381)(cid:374)(cid:367)(cid:455)(cid:856)
`No unauthorized disclosure or reproduction; licensed to purchaser only.
`
`0609
`
`0609
`
`
`

`

`8.3 Forming Sheet
`
`593
`
`
`
`
`
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`
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`
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`(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:346)(cid:410)(cid:400)(cid:3)(cid:396)(cid:286)(cid:400)(cid:286)(cid:396)(cid:448)(cid:286)(cid:282)(cid:856)(cid:3)
`© 1996 Carl Hanser Verlag. All rights reserved.
`(cid:69)(cid:381)(cid:3)(cid:437)(cid:374)(cid:258)(cid:437)(cid:410)(cid:346)(cid:381)(cid:396)(cid:349)(cid:460)(cid:286)(cid:282)(cid:3)(cid:282)(cid:349)(cid:400)(cid:272)(cid:367)(cid:381)(cid:400)(cid:437)(cid:396)(cid:286)(cid:3)(cid:381)(cid:396)(cid:3)(cid:396)(cid:286)(cid:393)(cid:396)(cid:381)(cid:282)(cid:437)(cid:272)(cid:410)(cid:349)(cid:381)(cid:374)(cid:854)(cid:3)(cid:367)(cid:349)(cid:272)(cid:286)(cid:374)(cid:400)(cid:286)(cid:282)(cid:3)(cid:410)(cid:381)(cid:3)(cid:393)(cid:437)(cid:396)(cid:272)(cid:346)(cid:258)(cid:400)(cid:286)(cid:396)(cid:3)(cid:381)(cid:374)(cid:367)(cid:455)(cid:856)
`No unauthorized disclosure or reproduction; licensed to purchaser only.
`
`0610
`
`0610
`
`
`€
`

`

`594
`
`Producing Sheet and Film
`
`[Refs. on p. 644]
`
`Constant Taper
`
`GRADHA
`
`Constant Taper Screw
`
`Fead
`
`Transition
`
`
`Metering
`
`
`
`a_iwaaaaaaaa dese
`
`be Feed TransitionwihMetering iale Decompression ot Metering |
`
`
`
`
`
`WAAAY?
`
`
`
`Two-Stage Vented or Gas Injection Screw
`
`Figure 8.7 Schematics of various screw configurations for single-screw extruders. Figure redrawn
`from [11] and used with permission of copyright owner
`
`screens placed against several 50 mesh screens. The screen packis then placed against
`a breaker plate. Screens can be plates with drilled holes, welded wire mesh, woven wire
`cloth or porous sintered metal. Filter screens are used throughout the sheet extrusion
`industry and are especially important when running large percentages of regrind,
`particularly if the polymeris an intrinsic gel former such as polyethylene terephthalate,
`polyamide,
`low-density polyethylene, polypropylene and rigid polyvinyl chloride.
`Pigmented polymers can also cause substantial filtering problems, particularly in
`regrind. Pressure drop across the filter screen must be continually monitored to
`determine when the screen has clogged and needs to be replaced. Continuous screen
`changers are expensive but useful if the polymer is heavily contaminated.
`
`Flow Improvement Devices
`
`In recent years, there has been great progress in improved plastication and homoge-
`nization of the polymer melt, primarily through improved screw design and motor
`drive and thermal feedback controls. Some typical plasticating and mixing screw
`sections are shown in Fig.8.8 [12], Surging, the bane of quality sheet production, has
`been greatly reduced. Gear pumps andstatic mixers are used to further improve melt
`quality prior to the die. Figure 8.9 is a schematic of an extruder having these
`features. Static mixers are dissipative devices that
`improve laminar mixing by
`separating the melt stream into many layers,
`reorienting the layers and then
`
`(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:346)(cid:410)(cid:400)(cid:3)(cid:396)(cid:286)(cid:400)(cid:286)(cid:396)(cid:448)(cid:286)(cid:282)(cid:856)(cid:3)
`© 1996 Carl Hanser Verlag. All rights reserved.
`(cid:69)(cid:381)(cid:3)(cid:437)(cid:374)(cid:258)(cid:437)(cid:410)(cid:346)(cid:381)(cid:396)(cid:349)(cid:460)(cid:286)(cid:282)(cid:3)(cid:282)(cid:349)(cid:400)(cid:272)(cid:367)(cid:381)(cid:400)(cid:437)(cid:396)(cid:286)(cid:3)(cid:381)(cid:396)(cid:3)(cid:396)(cid:286)(cid:393)(cid:396)(cid:381)(cid:282)(cid:437)(cid:272)(cid:410)(cid:349)(cid:381)(cid:374)(cid:854)(cid:3)(cid:367)(cid:349)(cid:272)(cid:286)(cid:374)(cid:400)(cid:286)(cid:282)(cid:3)(cid:410)(cid:381)(cid:3)(cid:393)(cid:437)(cid:396)(cid:272)(cid:346)(cid:258)(cid:400)(cid:286)(cid:396)(cid:3)(cid:381)(cid:374)(cid:367)(cid:455)(cid:856)
`No unauthorized disclosure or reproduction; licensed to purchaser only.
`
`0611
`
`0611
`
`

`

`8.3 Forming Sheet
`
`595
`
`
`
`Double-Wave Screw
`{Vo}
`
`
`
`UC or Maddock Mixing Screw Tip
`
`
`
`sare Screw
`iSSSSss3
`
`Parallel Interrupted Flight Screw
`
`Figure 8.8 Schematics of various mixing sections forWVRVWvy
`
`single-screw extruders. Figure redrawn from [12] and
`used with permission of copyright owner
`
`Ring Barrier Screw
`
`Screw
`
`Barrel
`
`Static Mixer
`
`Gear Pump
`
`
`Reet
`
`
`Extruder
`
`Figure 8.9 Schematic of extruder/static mixer/melt pump/die configuration
`
`recombining the layers in a different order, There are more than 30 types ofstatic
`mixers {13]. The mixing section of a Kenics mixer is shown in Fig. 8.10 [14].
`Improved homogenization or mixing efficiency must be weighed against increased
`shear history and pressure loss through these devices, Today, static mixers are used
`whenthe screw design is not optimum for the polymer, when the melt pumping zone
`on the screw is too short or when the overall extruder L/D is too short. Therelative
`effectiveness of many of these devices is reviewed elsewhere [15-18].
`Gear pumps or melt pumps are characterized as “closely intermeshing counter-
`rotating twin screw extruder(s)” [19]. Details are shown in Fig. 8.11 [20]. One gearis
`driven. It drives the other. The polymer melt is engaged by the gear teeth and forced
`
`(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:346)(cid:410)(cid:400)(cid:3)(cid:396)(cid:286)(cid:400)(cid:286)(cid:396)(cid:448)(cid:286)(cid:282)(cid:856)(cid:3)
`© 1996 Carl Hanser Verlag. All rights reserved.
`(cid:69)(cid:381)(cid:3)(cid:437)(cid:374)(cid:258)(cid:437)(cid:410)(cid:346)(cid:381)(cid:396)(cid:349)(cid:460)(cid:286)(cid:282)(cid:3)(cid:282)(cid:349)(cid:400)(cid:272)(cid:367)(cid:381)(cid:400)(cid:437)(cid:396)(cid:286)(cid:3)(cid:381)(cid:396)(cid:3)(cid:396)(cid:286)(cid:393)(cid:396)(cid:381)(cid:282)(cid:437)(cid:272)(cid:410)(cid:349)(cid:381)(cid:374)(cid:854)(cid:3)(cid:367)(cid:349)(cid:272)(cid:286)(cid:374)(cid:400)(cid:286)(cid:282)(cid:3)(cid:410)(cid:381)(cid:3)(cid:393)(cid:437)(cid:396)(cid:272)(cid:346)(cid:258)(cid:400)(cid:286)(cid:396)(cid:3)(cid:381)(cid:374)(cid:367)(cid:455)(cid:856)
`No unauthorized disclosure or reproduction; licensed to purchaser only.
`
`0612
`
`0612
`
`

`

`596
`
`Producing Sheet and Film
`
`(Refs. on p. 644]
`
`Figure 8.10. Kenics static mixer element configuration. Redrawn from [14] and used with permission
`of copyright owner
`
`
`
`Figure 8.1] Two views of gear or melt pump showing intermeshing gear rotation relative to flow
`direction [20]
`
`against the pump wall. The remeshing of the gear teeth forces the polymer from the
`pump. Gear pumps were originally employed to counteract surging and secondary
`flow effects from screw flights. Today they are used primarily to boost melt pressure
`prior to the die. Owing to leakage between the gear teeth and pump wall and
`between the edge of the gears and the pump wall,
`the pumps are not positive
`displacement pumps. Although the typical volumetric efficiency is 90% or so, low
`viscosity melts and high pressure drops can reduceefficiencies to 50% or less [20].
`Gear pumps are high shear devices. As a result,
`it
`is not unusual
`to see melt
`temperature increases of 10°C or more as the polymerpasses through the gear pump.
`These pumps are not
`recommended for
`thermally sensitive polymers such as
`polyethylene terephthalate and rigid polyvinyl chloride.
`
`Pressure and Temperature in an Extruder
`
`Thestated purpose of an extruder is to plasticate or melt the polymer and to deliver
`the conditioned, homogeneous polymer melt at a constant flow rate. The majority of
`
`(cid:926)(cid:3)(cid:1005)(cid:1013)(cid:1013)(cid:1010)(cid:3)(cid:18)(cid:258)(cid:396)(cid:367)(cid:3)(cid:44)(cid:258)(cid:374)(cid:400)(cid:286)(cid:396)(cid:3)(cid:115)(cid:286)(cid:396)(cid:367)(cid:258)(cid:336)(cid:856)(cid:3)(cid:4)(cid:367)(cid:367)(cid:3)(cid:396)(cid:349)(cid:336)(cid:3