Acknowledgements 6
Contents 8
Introduction 12
1Materials for Blown Film 16
1.1Polymers 16
1.1.1Polyethylene (PE) 17
1.1.2Low Density Polyethylene (LDPE) 17
1.1.3High Density Polyethylene (HDPE) 19
1.1.4Linear Low Density Polyethylene (LLDPE) 20
1.1.5Metallocene Polyethylene (mPE) 21
1.1.6Polypropylene (PP) 21
1.1.7Polystyrene (PS) 22
1.1.8Ethylene Vinyl Acetate (EVA) 23
1.1.9Ethylene Vinyl Alcohol (EVOH) 24
1.1.10Polyvinyl Chloride (PVC) 24
1.1.11Polyvinylidene Chloride (PVDC) 25
1.1.12Polyamide (PA) 25
1.1.13Polyurethane (PU) 26
1.2Additives 26
1.2.1Antiblocking Agents 27
1.2.2Antioxidants 27
1.2.3Antistatic Agents 27
1.2.4Colorants 28
1.2.5Lubricants 29
1.2.6Reinforcements and Fillers 29
1.2.7Stabilizers 31
1.2.8Tackifiers 31
2Extrusion Overview 34
2.1Extruder Hardware Systems 34
2.1.1Drive System 36
2.1.1.1Motor 36
2.1.1.2Speed Reducer 36
2.1.1.3Thrust Bearing 37
2.1.2Feed System 39
2.1.3Screw/Barrel System 41
2.1.3.1Screw 41
2.1.3.2Barrel 43
2.1.4Head/Die System 44
2.1.4.1Head Assembly 45
2.1.4.2Adapter 45
2.1.4.3Breaker Plate 45
2.1.4.4Melt Filter 46
2.1.4.5Die 48
2.1.5Instrumentation and Control System 49
2.1.5.1Temperature Control 50
2.1.5.2Head Pressure 53
2.1.5.3Motor Current 54
2.2Extrusion Functional Zones 55
2.2.1Solids Conveying 56
2.2.1.1Gravity-Induced Region 56
2.2.1.2Drag-Induced Region 57
2.2.2Melting 58
2.2.3Melt Pumping 60
2.2.4Mixing 62
2.2.4.1Distributive Mixing 63
2.2.4.2Dispersive Mixing 63
2.2.4.3Mixing Devices 64
2.2.5Degassing 66
2.2.6Die Forming 67
3Hardware for Blown Film 72
3.1Upstream Components 73
3.2Grooved Feed Throat 75
3.3Screws for Blown Film Extrusion 77
3.4Blown Film Dies 78
3.5Bubble Geometry 83
3.6Bubble Cooling 86
3.7Bubble Stabilization 91
3.8Collapsing Frames 91
3.9Haul-off 92
3.10Winders 94
3.11Film Treatment 95
3.12Line Control 96
4Processing 102
4.1Process Variables vs. Bubble Geometry 103
4.2Characteristic Bubble Ratios 105
4.3Process/Structure/Property Relationships 108
4.4Double Bubble Processing 110
5Coextrusion 112
5.1Dies 113
5.2Interfacial Instabilities 115
5.3Product Applications 116
5.3.1Breathable Packaging 116
5.3.2Shrink Film 117
5.3.3High Barrier Film 118
6Film Properties 120
6.1Tensile Strength (ASTM D882) 122
6.2Elongation (ASTM D882) 124
6.3Tear Strength (ASTM D1004, ASTM D1922, and D1938) 124
6.4Impact Resistance (ASTM D1709, D3420, and D4272) 126
6.5Blocking Load (ASTM D3354) and Coefficient of Friction (ASTM D1894) 127
6.6Gel (Fisheye) Count (ASTM D3351 and D3596) 128
6.7Low Temperature Brittleness (ASTM D1790) 128
6.8Gloss (ASTM D2457) 129
6.9Transparency (ASTM D1746) 129
6.10Haze (ASTM D1003) 130
6.11Density (ASTM D1505) 130
6.12Melt Index (ASTM D1238) 131
6.13Viscosity by Capillary Rheometry (ASTM D3835) 133
7Troubleshooting 136
7.1Extruder Problems 137
7.1.1Surging 137
7.1.2High Melt Temperature 138
7.1.3Excessive Cooling 140
7.1.4Low Output 141
7.2Film Problems 142
7.2.1Melt Fracture 142
7.2.2Thickness Variation 143
7.2.3Die Lines 147
7.2.4Gels 148
7.2.5Low Mechanical Properties 149
7.2.6Poor Optical Properties 150
7.2.7Wrinkles 151
Appendix A: The Blown Film Extrusion Simulator 152
A.1Introduction 152
A.2Installation 153
A.3Running the Program 154
A.4Worksheet 161
Appendix B: Useful Equations 164
References 172
Subject Index 176

6 Film Properties (S. 109-110)

This chapter covers many of the most important properties measured by producers of blown film. These include mechanical, thermal, optical, physical, electrical, and rheological properties. The first five in this list apply primarily to the extruded film and the last one applies to the molten polymer inside the extruder and die. By obtaining the measurement values for these properties, manufacturers gain assurance that their resin or film will perform adequately, whether during manufacture (extrusion or conversion) or in final product form as used by the customer. It is vital that manufacturers document and maintain baseline data on the performance of their incoming materials and the film that they produce. This information provides the most efficient means for solving many problems that may arise in a manufacturing plant. Many extrusion performance issues are related to even slight modifications in raw material composition or processing properties.

These modifications are easily identified when prior baseline data is available. In addition, film performance deficiencies as measured by a reduction in some property, such as impact strength, may lead the technical staff to identify an undesirable drift in processing conditions. Another important reason for maintaining baseline data is that many customers require it. Tests for resin and film property values can be performed in-house, by an outside testing facility, or by a supplier. There are advantages and disadvantages to each. The most important consideration is the accuracy of the data collected. After that, consideration must be given to costs associated with the amount of data needed (equipment, consumables, training, labor, etc.) and the frequency of measurement required.

To suitably compare measurement values obtained at different times or locations, there must be assurance that the tests were performed under identical conditions. To accomplish this, a committee of experts in each particular subject area develops standardized test methods. The methods establish the exact conditions for all test parameters by all parties conducting tests to measure the property of interest. A major publisher of test methods covering polymer resins and plastic films is the American Society for Testing and Materials (ASTM), West Conshohocken, PA, USA. In this chapter, ASTM method reference numbers are included in parentheses at the beginning of each property description section.

Although publicly published test methods are invaluable for comparing measurement results, not all tests must conform to published standards. In many cases, processors, their suppliers, or their customers will design and perform customized tests in an attempt to best simulate actual product conditions. An example would be a grocery sack manufacturer that performs a routine quality check by loading a finished bag with a specified weight and then dropping the load onto the floor from a specified height to check for bag failure. Many in-house tests like this are designed and conducted regularly to best model actual use, shipping, or handling conditions. It is crucial, however, that test procedures are documented and followed identically every time so that results comparisons are valid.