Web Coating Blog

AIMCAL Fall Technical Conference October 2008

AIMCAL Fall Technical Conference
October 2008
Edward Cohen
The AIMCAL Fall Technical Meeting was help in October in Myrtle Beach,
NC. It provided a forum for the exchange of Information between
technical personnel in the web coating Industry. Technical papers were
presented in four sessions as follows:
• Environmental Responsiveness
• Web Coating & Laminating
• Vacuum Web Coating
• EmergingT echnologies
• Advances in Web Coating Technology
In addition there were table to exhibits, which also provide an
opportunity for additional technical discussions.

I found all of the presentations were useful and relevant to the technology of importance
to the Converting Industry. While the Coating process is sold, there is
still a a lrge amont of new technology that is being developed.

Wide ranges of topics were discussed, energy concerns, coating methods, slitting,
barrier layers, Coating hardware etc.

The following are the titles and a summary of some of the key
presentation. Details of the papers and contact information can be
found in the Conference Proceedings available from AIMCAL.

A Paradigm Shift In Knife Holder Slitting Technology
David Rumson
Sigmala, USA

Conventional slitting systems, consisting of mechanically
mounted and pneumatically activated knife holders (Mech/Pneu) have been
in existence for approximately 60 years. Although shear knife holder
and positioning systems have advanced during this time, there are some
basic operating requirements that remain limited in efficiency and
usefulness relative to today’s computer controlling capabilities. This
paper will present a basic overview of the physical operating
differences of Mech/Pneu holders and Servo Motor-Computer Controlled
holders (Serv/Com).

Application Of Surface Analysis For Root Cause Failure Analysis
David Cole
Evans Analytical Group

X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary
Ion Mass Spectrometry (TOF-SIMS) are valuable analytical techniques in
determining the rooot cause of failure in multilayer films.

Breaking Thru A Paradigm:New Technology For Coating And Laminating
Mike Budai
TW Dynatec

The purpose of this presentation is to break thru a paradigm in
laminating nonwovens, textiles, and composites. This paper will present is to
introduce the latest technologies in coating and laminating utilizing
hot melt polymers.

Reducing Changeover Time on a Coating Line,
Larry Gogolin
Gogolin & Associates

This paper will cover the steps to consider in establishing a reduction in the changeover time. It will look at planning, data collection, analysis and what to do with this
information.

Optimizing Mix Performance”
Ken McCarthy

This paper presents a discussion of mixing time and its importance to
coating operations.

Stay Ahead of Static Problems in Film Conveyance
Kelly Robinson,
Electrostatic Answers LLC

Demands for static control in film conveyance are increasing because
products are more complex and sensitive to static discharges. Four keys
to staying ahead of static problems in web conveyance are presented T
he implementation of these four recommendations for a typical coating
operation is presented.

Primerless Heat Seal Coatings for Film Substrates
Virginia Cushing &Robin Cooper
Michelman

This paper presents a single pass, aqueous heat seal coating which
exhibits excellent hot tack and a wider operating window as compared to
conventional heat seal coatings and common extruded sealants.

Increasing Energy Efficiency in the Web Coating Process
Edward Cohen, Dan Bemi Megtec

This paper focuses on reducing energy consumption, by modifying the
overall coating process and to utilizie renewable resources in their
production in order to remain competitive in this climate of rising
energy costs.

Intelligent Process Cooling: Saving Money, Protecting the
Environment
& Curing Process Headaches
Steven Petrakis
Frigel

Process cooling with ambient air, closed loop cooling systems can save
up to 25% on energy and water consumption in addition to eliminating chemical
evaporation and the disposal of contaminated waste water.

Nanoparticulate Barrier Films and Gas Permeation Measurement Techniques
for Thin Film Solar and Display Applications
Senthil Ramadas*, Shwe Zin Ma, Mark Auch, Chua Soo Jin
Institute of Materials Research and Engineering.

This paper presents innovative approach to resolving the ‘pore effect’
by literally plugging the defects in the barrier oxide films using
nanoparticles. The nanoparticles used in the barrier stack have a dual
function – not only sealing the defects but also reacts with moisture
and oxygen. The result is an achievement of moisture barrier
performance of better than 10-6g/m2/day that surpasses the ideal
requirements needed for flexible applications,

Effective Networking, A Path Through The Information Overload

                        Effective Networking, A Path Through The Information Overload
                                            Edward Cohen

Even though we live on large planet, with large physical dimension (a Volume of 1.0832073_1012 km_ and a  Mass of 5.9736_1024 kg); technologies such as the Internet, Information Sciences, World Wide Web, rapid digital communications ,easily accessible databases and search engines have made it a very small world. It now possible to instantly communicate with persons all over the world and to obtain technical information from most countries, businesses and Universities.

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:

CEMA Coating & Laminating Fundamentals

AIMCAl & CEMA will be sponsoring a Seminar on Coating & Laminating. The schedule is below. For more information and to register go to
        www.AIMCAL.ORG

Continuing Education Courses.

The Association of Industrial Metallizers, Coaters and Laminators (AIMCAL) is sponsoring several continuing education courses in Converting Process Technology in 2008.

Importance of Solution Properties in Web Coating Process Quality

Link: . Importance of Solution Properties in Web Coating Process Quality Edward Cohen 
Importance of Solution Properties in Web Coating Process Quality
Edward Cohen

The properties of the coating solution(s) are critical factors for the reproducible ongoing production of a high quality low cost web coated product. The ability of the coating applicator to uniformly and reproducibly apply coating, final coating quality, physical defects, coater operability and many surface features of the coated product critically; all depend upon the rheological properties, stability and purity of the coating solution.  In addition, if the solution does not meet all the requirements of the coating application and drying process and is defective in any way, none of the subsequent process steps can correct these deficiencies and a defective product will result.

One Thing to Optimize Process

A question that is often asked about the Web Coating Process is “ What are the one or two most critical areas of the process that I should concentrate on to obtain a coated product with high quality and low cost?”. A possible basis for this question can be found in an interchange in the 1991 movie “City Slickers”, between Billy Crystal and Jack Palance

The Importance of Viscosity in the Web Coating Process

 

The viscosity of the coating fluid is an important rheological property, which needs to be accurately measured, and controlled during the development of the product and in manufacturing.  This will insure optimum quality and a reproducible cost effective manufacturing process

A fluid is defined as a substance that undergoes irreversible deformation when subject to a steady state shear or tensile stress.  The viscosity is a key parameter to characterize this deformation and is a measure of the resistance of the solution to flow under mechanical stress.  High viscosity solutions require a high level of stress to flow rapidly, while a low viscosity solution will deform and flow rapidly with a minimum of force.  For example, water has a low viscosity and will flow readily out of a glass under normal gravity forces, whereas molasses, a high viscosity material, will take a long time to flow from a glass. The definitions of the viscosity and its components are as follows:

There are two unit to characterize the viscosity value. The original cgs units and the relatively new SI units. The usual units of viscosity used in the U.S. are centipoise, cP.  One cP is equal to one millipascal second, mPa◊s. 

The standard measurement approach is to obtain the  shear stress versus shear rate curves over arrange of shear rates at a constant temperature. In addition data at different temperatures can be obtained., A variety of viscometers with a wide range of variable shear rates are available for this measurement, Haake, Anton Paar, Malvern or Rheometrics. The slope of the curve is the viscosity.  When the curve is a straight line, the slope is constant and the viscosity is independent of the shear rate. If a variable shear rate viscometer is not available then a constant rate should be used.  A measurement of viscosity versus time is also important to determine if the fluid is stable over extended time periods. This can be critical in coating methods with recirculating fluids.
The viscosity behavior for coating fluids is complex and as a result there a are a variety of responses that can be obtained. In general, the viscosity of fluids depends on the shear rate at which it is measured.

•A Newtonian fluid has a constant viscosity independent of shear rate.  The shear stress is a linear function of shear rate and the stress is zero at zero shear rate.  Common, low molecular weight fluids are Newtonian.

•A pseudo-plastic or shear-thinning behavior occurs when the viscosity decreases with increasing shear rate.  This is typical of polymer solutions.  The curve of shear stress versus shear rate bends toward the shear rate axis.

•A dilatant or shear-thickening behavior occurs when the viscosity increases with increasing shear rate.  In the shear stress - shear rate plot, the curve bends toward the shear stress axis.

•A Bingham solid with yield-stress behavior occurs when the stress has to exceed some finite value before the fluid flows.

Figure 1 gives example of these different flow behaviors.

In some liquids the viscosity can also depend on how long the liquid has been flowing, giving rise to:
•Thixotropic liquids, in which the viscosity decreases with time while undergoing shear.  This behavior is common in latex paints, where the thick paint flows easily while being brushed.

•Rheopectic liquids, in which the viscosity increases with time while undergoing shear.

The importance of characterizing the viscosity behavior over a wider range of shear rates is that there are a wide variety of shear rates in the coating  and ancillary processes process, Table 2. Therefore , the behavior needs to be determined to insure compatibility.

The fluid viscosity is a key variable in the following properties:

    • Determing the best coating method to be used

    • Coating weight control in roll coating methods

    • Coating quality level and reproducibility from applicator

    • Coating quality in dryer

    • Levelling of coating after application

Routine measurements of viscosity prior to coating should be part of the normal quality control system for the coater.  Often a problem is detected after the solutions are all consumed in the production process.  If rheological data are not available, then it may be very difficult to determine the source of the problem. 

Figure 1
Viscosity Shear Rate Behavior

Reducing Contamination Caused Defects ?

One of the major sources of coating defects is the introduction of foreign material (contamination) into the coating.  This results in a non-uniform coating that is not functional. That has to  be removed before sending to the customer.  These contamination defects can have several different appearances:

    • spots with a clear center with no coating. These are caused by low surface tension contaminant which repels coating

    • spots with a foreign particle in the center, which reduces coverage by repelling t he coating solution

    • a continuous coating in which the parts of the web have a visible contaminant, such as a fiber, lint dirt, which are coated over.   

    • a spot which has different coverage and no contaminants in the defect area. These are caused by contaminants on the coating roll that lead to a deformation in the coating bead and a resulting change in coverage.

    • a streak caused by contaminants in the  coating bead which disturb the coating flow.

The Role of Contract Coaters

Contract Coater, also called Toll Coaters, are a very important part of the converting industry.  They specialize in manufacturing web coated products for other companies and have a wide range of coating, drying process and slitting equipment and significant expertise in these areas. Their technical capabilities include:
    • mixing and filtration equipment and technologies 
    • availability  and expertise in a wide range of coating techniques,
    • drying technology
    • optimizing process for quality, high yield and low cost
    • specialized web coating testing capability and testing capability.

In terms of facilities they have process capability from pilot plant coaters to full-scale manufacturing.

There are several technical and economic reasons for companies and laboratories who are using or will need to produce web coated products to consider the use of contract coaters.