The Importance of Coating Process Support Systems

                             The Importance of Coating Process Support Systems
                                            Edward Cohen

Ongoing technical projects are needed to improve the quality, cost & productivity of a coating line in order to remain competitive and rapidly develop new products. There are several important considerations when developing and identifying coater needs and deciding on the most effective programs too work on. These are:

    • The process limitations, defects losses and product deficiencies must be identified.

    • The economic benefit of solving these problems must be established.

    •  Technology and hardware to improve these limitations need to be identified and the technical feasibility and cost of development and hardware estimated.

    • Typically, in the analysis procedure many needs and potential solutions are identified. Therefore, these must be prioritized based on cost, return on investment, technical feasibility and the time required to implement.

    • When priorities are established the best projects are selected and, then resources, people. Money facilities etc. committed to implement the project.

    • Once priorities are established resources, people, money facilities etc must be allocated.

A major requirement for this process to succeed is an understanding of all of the elements in a coating line and how they interact with each other.  For most improvement or defect reduction projects, there are several possible solutions to obtain the desired results and criteria should be established to select he best results.  It is often more effective to select smaller projects. Which can be implemented rapidly with a high probability of success; then it is to select large project, which may require longer time and more resources.

In analyzing process for improvement opportunities there are two general hardware categories which should be investigated, The first is the major process equipment, i.e., coating solution applicators, applicator support stand, dryers, unwinder, rewinder, and web transport system.

The second category is the ancillary equipment that supports the major process equipment such as, filters, pumps, surface treaters, mixers, process control instrumentation, etc. This category also includes items that are not process equipment but are essential for the coating line to function, such as quality control procedures, training, and defect measurement systems.  This category is often minimized in importance. However, it can often lead to significant improvements with minimal expenditures. In addition an improvement in one category can lead to improvements in several products and defect types. The system can also introduce defects if not operated properly. In addition some of these elements can be rate limiting and correcting them will have major impact on performance

The following section discusses the basic categories and the hardware that is included in the category.

    1. Surface treatment
  Surface treatments are applied to the web either before coating applicator or in areas from the end of the dryer to the winder. Flame, electrical discharge or Plasma are used to wetabbility & adhesion. Several types of web cleaners are available to remove contamination on substrate. Several techniques are available to remove substrate static.

2. Solution Mixing Process
    The coating solution properties affect the performance of the coating line and if it is not at standards, it cannot be corrected for in any of the subsequent process elements. Both high and low shear rate mixers should be available. Filtrations should be used and all parts of the mixers should be cleaned frequently

    3. Solution delivery System   
The solution delivery system, which moves the coating fluid from the holding tank to the coating applicator, has several elements that are several elements that are critical in obtaining good quality and can be source of defects if not used or run properly. Filtration removes contaminants from the solution. Deaeration removes entrapped air from the solution. The pumps used an introduce defects such as chatter and bubbles and non-uniform flow will adversely effect coating weight uniformity. Temperature control is needed for uniform viscosity

    4. On-line quality control instruments
There are commercially available instruments which can evaluate film for defects, This can lead to rapid problem solving and more effective use of coated product when it is converted, The coating weight average and uniformity Td and Md can be measured on-line. This will improve product uniformity and yields.

5. Process Instrumentation
The process control system must accurately measure and reproducibly control process variables. The line speed control capability must be precise and provide the control needed to maintain coating weight uniformity. Precise control of the dryer conditions is need for product quality and to maximize productivity.

6. Contamination control
There are many contaminants that can be introduced into the coated product and cause defects. The dryer can be a major source of contaminants unless filters are used in the air streams and their efficiency maintained. Similarly all of the room air should be filtered and temperature and humidity controlled.

    7. Coater support station.
The coater support station must maintain the desired conditions throughout a coating campaign. It should also have instrumentation to continually measure gaps and roll speeds.

    8. Coater Rolls and bearings
The rolls in the coater provide a variety of functions will wear as the coater is used, which will lead to problems. They should be monitored and removed when either the roll or bearings are defective or do not meet specifications.

9. Quality Control Systems
Quality control systems such as Statistical Process Control and 6-sigma will help to insure uniform process operations, provide early indication of defects and help identify problems sources.

    10. Procedures and Training.
    A coating line is complex and can manufacture a variety of products.  Detailed procedures for all products should be available. In addition coating line personnel should be trained in implementing procedures and operation of coater elements.

       

Comments

[Raymond Ashley]

Dear Mr. Cohen,
I have some request from a Chinese firm to build a melamine evaporator for web coaters. Was just wondering if you have any idea, about the direct adhesion on OPP or PET? Thanks,
Ashley