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Image Durability Guidelines1 Introduction 1.1 Objective To develop documented, fundamental guidelines and procedures for assessing image durability for imaging technologies including thermal transfer, direct thermal, laser, ink jet, flexography, lithography, photocomposition, gravure, impact printing, et al. 1.2 Methodology The following steps should be employed as tools in creating an evaluation procedure that is appropriate for the application under consideration. This will help to insure that the results can be duplicated consistently. When defining any procedure it is important to understand that many factors can influence the outcome. In our application some of these factors include selection of imaging technology(equipment), receiver selection, ribbon/ink selection, environmental conditions (temperature, humidity), printer settings (speed, printhead energy, printhead pressure), lapsed time between printing and conducting durability testing (curing), and handling. It is important to always compare like materials and to prepare samples under like conditions. Establish a procedure that best emulates your process. Final results should be obtained by selecting the most representative samples obtained from multiple tests. Please note, test results from one piece of test equipment should not be compared with results from any other piece of test equipment. 2 Image Durability Definitions A. Scratch Resistance: the ability of the image to withstand repeated rubbing with a sharp or pointed object or stylus. This test is meant to emulate the physical contact made with a contact wand scanner, paper clip or fingernail. B. Smudge Resistance: the ability of the image to withstand repeated rubbing with a blunt or flat object. This test is meant to emulate the physical contact made by a finger tip, or one corrugated box rubbing against another. C. Crock Resistance: the ability of the image to withstand repeated rubbing with a cloth. This test is meant to emulate the physical contact made by tags and labels when in contact with garments or fabrics. 3 Image Durability Guidelines In all of the tests below it is recommended that we use an instrument
that is widely known and used in the printing industry. Although
other testing devices were considered, the A.A.T.C.C. Crockmeter
was selected. The A.A.T.C.C. Crockmeter is a standard instrument
of the American Association of Textile Chemists and Colorists.
Other test equipment is sometimes specified as the standard in
some industries. The A.A.T.C.C. Crockmeter was specified because
of its availability, ease of use, low cost, consistency of results
and requirement for using specified test cloths (crock test).
This device works by subjecting an image to direct contact with
a rubbing tip or finger mounted on the end of a weighted arm.
The standard finger supplied with the unit is a 15mm diameter
solid acrylic rod. This finger rests on the image sample with
a pressure of 900g. and inscribes a straight path through the
image with each turn of the handle. The stroke length may be adjusted
to 76mm or 50mm when the test image is limited in size. The arm
is then moved repeatedly back and forth across the image in an
attempt to elicit a change in the image quality. 4 Crockmeter Test Methods: Scratch Resistance 1. The acrylic finger supplied with the crockmeter is replaced with another finger that has been retrofitted with a contact wand verifier tip or suitable alternative. This device can be fashioned in any maintenance shop using an old verifier wand tip, or a half inch brass rod formed to the shape shown in Figure number 1. Care should be taken to insure that this tip remains at the same height and angle as the supplied acrylic finger. Figure 1 - Profile of Alternative Tip for Scratch Resistance Test and Acrylic Finger 2. The crockmeter stroke arm provided with the unit is replaced with a light weight aluminum arm, sometimes referred to as a "Chrysler" arm. This lightweight arm reduces the likelihood of damaging the receiver with the sharp wand tip. 3. The test sample (typically a bar code image) is mounted on the flat base of the instrument that is covered with abrasive paper to prevent sliding. The sample is positioned so the image is diagonal to the direction of travel of the stroke arm. 4. The wand tip is cleaned with rubbing alcohol before each test to insure that there is no cross-contamination of samples. 5. The tip rests on the image sample and when the crank is turned,
a straight path is inscribed across the test sample. The number
of strokes the test sample is subjected to changes with the end
use requirements: Image Durability Rating Guidelines Rating Scale: The rating given will be on a scale of 0-5, with 5 representing excellent and 0 being poor scratch resistance. The grade assigned will be based on the difference in image quality, based on ANSI letter grade obtained from a verifier capable of evaluating print quality in compliance with ANSI X3.182- Bar Code Print Quality Guideline, before and after the image is subjected to contact rubbing. See Table 1 for the rating scale. Table 1 - Rating Scale for the Scratch Test
For images other than bar codes, a visual assessment like the
example below may be employed after conducting the contact rubbing:
5 Crockmeter Test Methods: Smudge Resistance 1. A clean, new 50 x 50mm square of standard crocking cloth is mounted to the standard acrylic finger supplied with the crockmeter using the spring clip. The standard crockmeter stroke arm is used. 2. The test sample (typically a bar code image) is mounted on the flat base of the instrument that is covered with abrasive paper to prevent sliding. The sample is positioned so that the arm stroke travels diagonally across the printed image. (Since the equipment is a fixed device, the image will need to be placed at an angle relative to the arm stroke) 3. The covered acrylic finger rests on the sample and when the
crank is turned, a straight path is inscribed across the test
sample. Image Durability Rating Guidelines Rating Scale: The rating given will be on a scale of 0-5, with 5 representing excellent and 0 being the poor smudge resistance. The grade assigned will be based on the difference in image quality, based on the ANSI letter grade obtained using a verifier capable of evaluating print quality in compliance with ANSI X3.182- Bar Code Print Quality Guideline, before and after the image is subjected to contact rubbing. See Table 2 for the rating scale. 6 Crockmeter Test Methods: Crock Resistance 1. A clean, new 50 x 50mm square of standard crocking cloth is mounted to the standard acrylic finger supplied with the crockmeter using a spring clip. The standard crockmeter stroke are is used. 2. The test sample is mounted on the flat base of the instrument that is covered with abrasive paper to prevent sliding. The sample is positioned so the printed image is perpendicular to the direction of travel of the stroke arm. 3. The covered acrylic finger rests on the sample and when the crank is turned, a straight path is inscribed across the test sample. The number of strokes the test sample is subjected to changes with the end use requirements: o Standard Durability (eg. shipping label, one time use) - 10
cycles/20 strokes Image Durability Rating Guidelines Rating Scale: The rating given will be on a scale of 1-5, with 5 representing excellent and 1 being poor crock resistance. The grade assigned will be based on a comparison to a previously established grade scale that you have developed (See Figure 2) of the amount of ink transferred to the crocking cloth after contact rubbing:
* Control samples may be necessary to assure consistency of results. See attached example. (See Figure 2) Figure 2 - Typical Crockometer Limit Samples This document is intended as a guide to aid the manufacturer,
the consumer, and the general public. The use of the document
and material contained therein is entirely voluntary. The material
presented should not be used as a substitute for user's engineering CAUTION: THIS GUIDELINE MAY BE REVISED OR WITHDRAWN AT ANY TIME. Reprinted with permission from AIM, Inc. |
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