Manufacturing Flexible Packaging

Materials, Machinery, and Techniques

Thomas Dunn

• Publisher: William Andrew
• Year: 2014
• ISBN:
  9780323265058
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Efficiently and profitably delivering quality flexible packaging to the marketplace requires designing and manufacturing products that are both "fit-to-use" and "fit-to-make". The engineering function in a flexible packaging enterprise must attend to these dual design challenges.

Flexible Packaging discusses the basic processes used to manufacture flexible packaging products, including rotogravure printing, flexographic printing, adhesive lamination, extrusion lamination/coating; and finishing/slitting. These processes are then related to the machines used to practice them, emphasising the basics of machines' control systems, and options to minimize wasted time and materials between production jobs.

Raw materials are also considered, including the three basic forms: Rollstock (paper, foil, plastic films); Resin; and Wets (inks, varnishes, primers). Guidance is provided on both material selection, and on adding value through enhancement or modification of the materials' physical features.

A 'measures' section covers both primary material features – such as tensile, elongation, modulus and elastic and plastic regions – and secondary quality characteristics such as seal and bond strengths, coefficient of friction, oxygen barrier and moisture vapour barrier.

• Helps engineers improve existing raw material selection and manufacturing processes for manufacturing functional flexible packaging materials.
• Covers all aspects of delivering high value packaging to the customer – from the raw materials, to the methods of processing them, the machines used to do it, and the measures required to gauge the characteristics of the product.
• Helps engineers to minimize waste and unproductive time in production.

1

Basics of Web Processes

This chapter summarizes common components of web-based processes. These processes involve long thin strips (“webs”) of various materials rolled onto a cylindrical core with length approximately equal to the width of the stip. The rolls will later be unwound for their eventual use. The mechanics of winding and unwinding observe very basic principles of physics. Tension, nip pressure, and torque are the physical forces used to control webs during various manufacturing processes. Understanding specific flexible packaging manufacturing processes requires at least a semiquantitative appreciation of the meaning and interactions of these forces. Industry measures including “yield” and “basis weight” must also be understood for further study of flexible packaging manufacturing.

Keywords

Cross-web variation; dimensional analysis; down web variation; nip pressure; rewind designation; roll length estimation; torque units of measure; web tension; web winding

Chapter Outline

Web Tension 2

Web Winding 3

Cross-Web Variation 5

Web Dimensional Analysis 9

Industry Units of Measure 9

Web Length Estimation 11

Roll Rewind Designation 12

Essentially all flexible packaging converting processes involve rolls of web materials (thin materials, manufactured and processed in the form of a continuous, flexible strip). The full length of the strip represents the “machine direction” and its width, the “cross direction”. Equipment pulls material from the roll and then modifies it in some way that increases its suitability for use as a package. If the eventual fit-for-use packaging material requires several converting processes, the equipment will rewind the modified material into roll form again. The basic flexible packaging converting processes are printing, laminating, and slitting. The modifications at each stage are generically called “value-adding” processes and they form the basis for converters’ selling margins over their costs of purchased raw material.

Web handling in general reflects a dynamic, but otherwise simple, model of Newton’s laws of motion:

1. Any object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

2. Force applied to a material accelerates it in direct proportion to its mass; the direction of acceleration is the same as that of the applied force.

3. For every action there is an equal and opposite reaction.

These and related “laws” of classical mechanics make web handling a model system for mechanical engineering science to understand and control web processes. The physical and mathematical relationships developed by this science to describe and design web processes involve several sophisticated concepts. This chapter can only highlight some of the powerful insights of the science when designing and operating web handling equipment, but the interested reader can find more detailed sources in the further reading chapter.¹

Web Tension

“Pulling” a web off an unwinding roll and rolling it onto a rewinding one presents major mechanical issues. A force must be applied to the unwinding web. The general term for this force is called “tension.” Tension in web converting is often expressed in terms of “pounds per linear inch (PLI).” The units reflect the actual force pulling the web divided by its width (without regard to the thickness of the web material). Web process conditions typically report only this value. To better understand the physical effects of tension on a material, its “tensile stress” must be recognized. Instead of force per unit width, this measure addresses force per unit area, “pounds per inch².” This value relates directly to laboratory measures of tensile properties, an “Intrinsic Property” of the web material (Chapter 31).²

Tension applied to a web may not only pull it off the unwind roll, but also stretch it, or even break it (depending on the web’s tensile properties). Flexible plastic films in particular have tensile and elongation properties that can result in diversion of some of the applied unwind force to stretching the film (Figure 1.1). When cross-web length variation (called “bagginess”) is present, the stretching force can sometimes “pull out” the bagginess, so that the web appears to lie in a flat plane to observers as well as to the mechanics of the value-adding processes.

Figure 1.1 Distortion of plastic film in response to applied force. Force is applied to web at an unwind, the web resists, the roll turns, releasing web, at the same time the web itself deforms and reshapes.

In addition to moving the web through the equipment to the unwind, tension on the web helps to resist side to side movement, to reduce drooping (“catenary” effect) in horizontal spans between supports, and to establish friction against rollers along the web path and in the rewinding roll itself.

Web Winding

The rewind roll of a web process represents a protective means of storing the web for subsequent use in converting or at an end user. Consideration of the winding step itself reveals many of the additional mechanical considerations critical to successful web processes. Consistent winding of an excellent roll involves three critical factors at the rewind: Tension of the web as it wraps onto the roll; Nip pressure of drum or roller that presses down on the winding web; Torque of the rotating roll as it winds more web material onto itself. Controlling various combinations of “T N T” factors at different points along the whole web process provides the essence of its design and operation. Tension was described above. Torque is simply a “turning” force, which is the one acting in a clockwise or counterclockwise, rather than a linear direction. Nip represents a point along the process at which two rollers contact t...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Introduction
• 1. Basics of Web Processes
• 2. Rotogravure Printing
• 3. Flexographic Printing
• 4. Adhesive Lamination
• 5. Extrusion Lamination and Coating
• 6. Finishing and Slitting
• 7. In-Line Processes
• 8. OEE Effectiveness
• 9. Efficiency and Cost Accounting
• 10. Basics of Control Systems
• 11. Rotogravure Presses
• 12. Flexographic Presses
• 13. Adhesive Laminators
• 14. Flexible Packaging Extrusion Coating/Laminating Line
• 15. Slitters
• 16. Preventative Maintenance versus Available Production Time
• 17. Setup/Cleanup versus Scheduled Production Time
• 18. Saleable Product versus Product Produced
• 19. Paper
• 20. Foil
• 21. Unoriented Plastic Films
• 22. Oriented Plastic Films
• 23. Bulk Polyolefin Resins
• 24. Specialty Sealant and Adhesive Resins and Additives
• 25. Barrier Resins
• 26. Inks
• 27. Overprint Varnishes and Coatings
• 28. Adhesives
• 29. Primers
• 30. Conditioning
• 31. Intrinsic Material Properties
• 32. Secondary Quality Characteristics
• Index