PFFC - August 2008 - (Page 14)

PROCESS MANAGEMENT COF Testing: Why Does it Matter? oefficient of friction (COF) is a property critical to the optimum processing and handling of packaging from filling operations through to the consumer. COF is defined as the force required to move one surface over another, divided by the total force applied normal to those surfaces. The values are between zero and one and are dimensionless. There are two common basic COF testers—sliding plane and incline plane. By David Argent Contributing Editor �� Sliding Plane | Testing is performed by sliding a metal plane at constant speed beneath a block. The print specimen is attached to the base of the block. The block is connected to a stationary gauge that measures the frictional force between the plane and the block. To simulate a particular use condition, a piece of print or other packaging material may be attached to the block. Static COF is the number generated �� the instant motion starts between the surfaces. Kinetic COF is the value indicated after motion is established between the surfaces. �� C Why does it matter? If the static COF is too high, problems with stacking and unstacking of cartons, boxes, and sacks will occur. Flexible films may bind when sliding onto filling collars. If the static COF is too low, problems in maintaining stability in stacks could result, as well as difficulty pulling materials through automatic processing machinery. If kinetic COF is too high, this can cause hangups along packaging lines, undue folds, erratic web tension, and a buildup of static electricity. If the kinetic COF is too low, guide rolls may not rotate, tracking along the production line becomes irregular, web tensions again may be erratic, and the material will run eccentrically. COF is defined as the force required to move one surface over another, divided by the total force applied normal to those surfaces. Getting the COF right is mostly a process of qualifying a packaging product and then supplying this product at a consistent COF specification based on a given instrument and testing procedure. Be aware that different instruments and procedures have poor correlation. In packaging films, the traditional technology to lower COF is to incorporate a fatty amide, which over time migrates to the film’s surface. Newer technology uses more stable proprietary non�� migratory slip packages. Inks and coatings employ waxes, fatty amides, and Incline Plane | This COF tester is a simple silicones to lower COF and silica particles to and robust device. It is used for routine increase COF. Many converting variables measurement and control of static cause COF to vary. This property is COF. A sample is clamped to the insensitive to application viscosity, coatclined plane; another is clamped to ing weight, drying conditions, and the sliding block. The tester graduenvironmental humidity. In energyally inclines the samples until the cure systems, COF is affected by LIGHTFASTNESS block starts to slide and automatithe degree of cure. So, once again, IN PACKAGING cally locks and captures the angle of running to proven standards ensures slide. The tangent of this angle is the low waste and fewer field problems static coefficient of friction. and returns. COMING NEXT MONTH Process improvement expert David Argent has 30+ years of experience in process analysis with particular emphasis on ink and coating design and performance. Contact him at 314-409-4304; djvargent@sbcglobal.net. 14 | AUGUST 2008 WWW.PFFC-ONLINE.COM http://WWW.PFFC-ONLINE.COM

Table of Contents Feed for the Digital Edition of PFFC - August 2008

PFFC - August 2008 Table of Contents First Glance Calendar of Events From the Editor Web Lines Process Management News Clips Carton & Box Reporter Carton & Box What’s New Products Narrow Web & Label Reporter Narrow Web & Label What’s New Products Cover - Show Preview - Labelexpo Labelexpo Floor Plan Conference Program Digital Printing Gravure Printing Bagmaking What’s New Products Services Directory Classified Marketplace Equipment Buyers & Sellers Advertisers Index Experience Speaks

PFFC - August 2008

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