Learning the Lingo

The lack of a standard naming convention for web coating defects complicates communications between people working to eliminate the problem. AIMCAL's Coating Defects Lexicon aims to end the confusion.

Currently, there is no source of standard names or naming conventions for web coating defects. The naming process is a function of the observer's impression of the defect, past history, and the industry in which it is seen. This results in the widespread use of jargon to describe the defect. Consequently, the same defect can have many different names, and conversely, many different defects can have the same name. This lack of standard naming convention leads to an inefficient troubleshooting process and can result in wasted effort. It also makes it harder to find literature references and technology on the defect.

Another consequence is that the names given to the defect often imply both the cause of the defect and the corrective action to be taken. This name can be incorrect but still is communicated to all involved in the troubleshooting process. Then corrective action is started, often on the wrong problem. It is a particular problem in efforts that involve different sites, companies, and countries.

The Association of Industrial Metallizers, Coaters and Laminators (AIMCAL) has developed a Coating Defects Lexicon that is intended to solve these problems by providing standard defect naming conventions and a common language for all to use when referring to the web coating process. The lexicon is a computer-based, user-friendly reference that provides a variety of information on the web coating process. It assists in identifying and eliminating web coating defects by providing representative images of the defects, their causes and cures, and standardized definitions of these defects. It also contains standardized definitions of web coating process terms and unit operations and is a good reference for training new personnel.

The lexicon is available as a compact disk. This format was chosen because it offers the ability to provide high quality images at a reasonable cost, can be upgraded readily, and user search capability is easy and powerful. The lexicon consists of four main sections. The various sections and functions are accessed by the home page (see Figure 1).

In order to simplify the locating and presenting of the appropriate information, each of the defects in the Troubleshooting Guide and Defect Image Section is classified according to the basic characteristics of the defect. The classification scheme is shown in Figure 2. Typical defects in each category are in bold type.

Figure 2
Defect Classification


Continuous defect,
includes continuous
and intermittent
a. Machine Direction

  • Streaks
  • Ribbing
  • Scratches

Traverse direction

  • Chatter

Point defects
a. Spots

  • Bubbles
  • Gels


  • Repellent spots

Other types

  • Repeat spots


  • Air entrainment


  • Mottle
  • Dryer Bands
  • Orange peel

a. Polymer

  • Gauge bands
  • Carbon spots


  • Wrinkles


The glossary section contains definitions of coating defects, web coating process terms, and images where appropriate. Definitions included are coating and substrate defects, coating applicators, process hardware, and rheological and performance properties. Substrate definitions also are included along with metallizing process terms. More than 1,000 entries are contained. A standard defect name has been selected where there are multiple defect names. The alternate names also are included and referred to in the standard definitions.

The images contained in the definitions are thumbnails, which can be expanded to full screen for detailed viewing. There is also a link to the troubleshooting guide, which has more detailed information about the defect.

Figures 3-6 are examples of specific glossary entries.

Troubleshooting Guide
The troubleshooting guide provides detailed information on coating process defects. This section is designed to permit users to identify correctly a defect they are working with and to obtain information to help eliminate the defect. In those cases where defects have multiple names, the author selected the name with the most common usage as the standard name. Alternate names also are listed.

Each defect has a separate record, which contains the following defect information:

  • standard name

  • alternate names

  • description

  • cause

  • actions to eliminate

  • representative pictures of the defect.

Each defect is classified by scheme in Figure 2 to assist in searching this section.

Figure 7 is an example of a defect record.

Defect Image Section
This section contains only the defect images for many defects and permits the user to identify a defect and determine the standard name by comparing it with the images in this section. Another advantage is that more defect images are displayed in this section, whereas the previous sections had only selected images. The images are classified according to the classification scheme discussed in Figure 2 to assist in naming and locating the defect. A typical record is shown in Figure 8. It shows the various shapes that streaks can have.

Search Capability
There are several different methods that can be used to retrieve information from the lexicon. The glossary section is alphabetized and can be browsed. It also can be searched using key words. The troubleshooting guide is indexed for ease in searching, and it also can be searched by either key words or for specific classes of defects. The image section is arranged by the classification system shown in Figure 7 and also can be searched by using key words.

In addition to the individual compact disk, a networking version is available, which can be customized to meet the specific needs of the users. The lexicon will be updated periodically. Information on obtaining the lexicon is on the AIMCAL Web site at aimcal.org.

Edward D. Cohen is a technical consultant in all aspects of the web coating process. His expertise is in the coating and drying of thin films, coating process development and scale-up, polyester base development, film defect mechanisms, and defect characterization techniques. He has more than 40 years of experience in coating research and manufacturing technology and has many publications in the field, including two books. Currently he is technical consultant for AIMCAL. He can be reached at 480/836-9452; This email address is being protected from spambots. You need JavaScript enabled to view it.

This article, along with future articles by other authors, is provided as a cooperative effort between PFFC and AIMCAL. Authors contribute to AIMCAL's technical and education offerings, which include the association's Fall Technical Conference, Summer School, and Ask AIMCAL.

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