TroubleshooTing and Technical arTicles

This e-book contains a compilation of articles written by Mark Miller and additional authors where noted. The articles were originally published by Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

E-Book I, novEmBEr, 2014,

About the Author

Mark Miller, Founder And PrinciPAl, coAting tech Slot dieSWith slot die coating experience since 1996 in a broad range of precision coated products, Mark Miller has vast experience in process troubleshooting and project management services for trial support, equipment analysis, or process development. As a certified Six Sigma Black Belt for 3M, Mark has been integral to new developments and technology that minimize product waste and improve process scalability in web coating applications. Mark holds a Juris Doctor from Hamline University School of Law, a Masters degree in Polymer Science and Engineering from Lehigh University, and a Bachelors degree in Chemical Engineering from the University of Wisconsin. Mark is a principal and founder of Coating Tech Slot Dies.

About the PubliSher

the AuthoritAtive voice oF the converting community Since 1927PFFC is the most authoritative source of information in the converting, package printing, and label printing industry. Every facet of the industry is covered by experts who assist converters around the world to become more efficient, profitable, productive, and knowledgeable in their manufacturing and business practices. PFFC coverage includes technical innovations; marketing; business and management trends; and products and services. PFFC is the top choice to reach the converting industry. Depend on our resources to provide valuable information when making key business decisions.

The articles included in this book are for the private use of our audience. Any re-use of the language or articles is prohibited without written permission from PFFC-online.com and Mark Miller.

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troubleShooting And technicAl ArticleS

tAble oF contentS

About Coating Tech Slot Dies 4About the Author 6Process Troubleshooting 8Defects: Finding the Cause 12Dont Blame Chatter on the Coating Head 144 Steps to Resolving Coating Defects 16Steam: The Cure for Curl 18Open Up the Coating Process Window 20Slot Die Coating Fundamentals 22Coating, Not Printing 24Surface Energy Matchmaking 26What the Coating Bead Can Tell You 28How to Avoid Bubble Defects 30How to Select a Coating Method 32Fluid Coating & Extrusion Coating: What is the Difference? 34

About coAting tech Slot dieS

Coating Tech is a custom manufacturer of slot dies with full on-site manufacturing and r&D capabilities Work with experts in the slot die industry and learn about Coating Techs 3P approach:

Process Knowledge:The team of engineers at Coating Tech Slot Dies are experienced at solving process problems for clients in a wide range of industries. in particular, Coating Tech has extensive experience in adhesives, aerospace, construction, energy, filtration, graphics, medical and optical films industries. From design to installation, Coating Tech shares the clients goal of an efficient and successful coating process.

Precision manufacturing:our facility has full, on-site slot die manufacturing capabilities with machine tool research and development, and analytical tool divisions. our products are manufactured in the United States of America with exacting quality control.

Product Performance:The service you receive after the sale will ensure your coating system maintains peak performance for maximum return on investment. As experts in the science of slot dies, we are on the leading edge of new product development and are uniquely positioned to ensure our coating systems continue to serve you as new technologies and material advances affect your industry.

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Decades of experience in the fluid coating slot die industryWork with the experts in the slot die coating industry.

With years of industry experience working in internationally known firms, the principals of Coating Tech Slot Dies understand your coating process and the results you need to provide.

We apply our extensive process knowledge to your unique situation and promptly provide the most effective and efficient solutions for you.

sloT die coaTing TechnologySlot dies provide more reliable, faster, and more efficient coating operations than any other coating method. See immediate savings when you experience fewer product defects, accelerated production, and less raw material waste.

How does a slot die system provide these results?Slot dies work in a closed system providing a stable environment eliminating the majority of contaminants or other problem-causing variables.

Slot dies are designed specifically to distribute fluids uniformly while maintaining temperature resulting in fewer defects and less raw material waste. A slot die is custom designed to provide optimal conditions for the coating process.

Slot die systems with pre-metered coating, or positive coat weight control, help eliminate wasted coating fluid.

Slot dies provide precision results and are designed to a specific process requirement. The die can be customized to specific coating widths, discreet coating of specialized products, and other fluid or substrate behaviors. reformulation of fluids can be sustained with slot die technology, leading to increased production speeds through solvent reduction.

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coAting mAtterS

Process TroubleshooTingSix Sigma is a quality control system utilized for everything from discrete parts to organizational efficiency. The question is: How do you best utilize Six Sigma to reduce web defects?

Utilization in the converting industry hinges on applying discrete measures to a continuous product. Applications can be as varied as optical film coating to adhesive tape manufacturing. regardless of the product being made, Six Sigma can be applied to web-coated products.

Six SigmaLike the scientific method, Six Sigma follows a road map: Define, Measure, Analyze, improve, and Control the problem. Six Sigma is derived from the standard deviation, a statistical analysis parameter, and is defined as defect levels below 3.4 defects per million opportunities. it is important that the defect and the opportunity are correctly defined or the measurement is useless.

Six Sigma doctrine holds to continuous efforts to achieve stable results that are of vital importance to business success; manufacturing processes have characteristics that can be affected; and achieving sustained quality improvement requires commitment from the entire organization.

Define | it is important that a goal is defined and entitlement is understood. Entitlement is a stretch goal defined by the subject matter experts. This goal should have a continuous process focus but a discrete product plan. The measurement needs to focus on improving the performance of the product within the confines of the process.

it is important that the human side of the operation is understood. Emphasis on support from manage-ment is just as vital as an operators understanding of the project. Team buy-in from the top down and the bottom up is critical. never assume the project will work because people do what they are told.

if we take an existing product and process, individuals who have been involved with this system can be tapped to identify where the weaknesses and strengths of the process are as applied to the product. For a new product on an existing line, the borders of the process and materials need to be the constraints for the product. Ultimately, for a new product with an unidentified process, the world is wide open (which may be a blessing or a curse).

The process map needs to be drawn up regardless of the product constraints. This is a unit operations diagram taking into account human interaction with equipment, raw material variations, and measurement system limitations.

measure | The key consideration in measuring a web process is the final product use. The difficulty in measuring a product in roll form is that it cannot be fully measured. in theory, each discrete widget can be measured for quality if the test is not destructive. not so with a continuous web. improvements can be made at the main variable locations to reduce defects and improve quality.

one simple example is to have idler rolls of different diameters grouped by sections throughout the process. Therefore, if you see a repeating defect, you can isolate it to the section of the correlating diameter. The unit operations include the following:

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Fluid and fluid delivery: in fluid delivery, the equipment variables to be monitored include mixers, pumps, flow meters, and hoses. The material characteristics to be measured include viscosity. The issues (typically downweb in form) include contamination, air entrapment, and temperature control.

Substrate and substrate delivery: in substrate delivery, the equipment variables to be monitored include web cleaners, steering, tension, static control, and temperature control. The material characteristics to be measured include surface energy and substrate manufacturing data. The issues (typically downweb in form) include wrinkles and debris. Communication with the upstream provider of substrate is critical in understanding what is available for use.

Coating head: in the coating head (specifically in a slot die), the equipment variables to be monitored include attack angle (positioning), temperature control, roll total indicated runout (Tir), and chatter. The material characteristics at this point are a function of the roll throughput yield (failures combined up to this point in the process) of the interfaces. The issues (typically crossweb in form) include air entrainment and edge effects.

in the coating head, interfaces are the name of the game. Fluid distribution within the coating station can be simulated prior to manufacturing or operation. in a production setting, the improvement of edge effects needs to be balanced against the overall cost of waste.

Curing: in curing operations, equipment variables to monitor include energy into the web, drying, and stability. issues include temperature control, rate of cure, and effect on substrate. There are various cure methods and each has different effects. A preventive maintenance schedule helps maintain stability of an operation.

measurement systems: it is critical to measure the process at the intersection of the unit operations. This means monitoring the incoming substrate, fluid, coating head, and the outgoing web, in addition to ensuring the measurements capture crossweb, downweb, and machine chatter defects. remember continuous changes and defects occur over time, so steady state operation is important to accurate measurement and reaction.

Analyze | Analysis of the variables (causes) and the effect on the defects is the next step. once the subject matter experts have identified what to mea-sure to improve product performance, it is again time to get management on board. A key issue is the time it will take to measure the process accurately.

An example is when a consumable backing roll was made to order and had a limited lifespan. Although this Six Sigma project took months to analyze, the root cause was identified, and the problem was solved. We

need to narrow the scope so the team can identify the unit operation upon which to work. The team should be focusing on having no wasted effort.

Improve | There are two types of experiments that are important: design of experiments (DoE) and keeping a process journal. DoE allows focus on the identified variables. in a 2 (5-1) factorial design, all five variables can be studied with minimal work. Process journals allow previously unidentified variables to uncover new root causes.

A critical idea is roll Throughput Yield (rTY), which is defined as the combined variability of the process. i worked with a coater that had a product within spec for the discrete sample but in roll form had a hard band that made it unacceptable. This caliper variation did not show until the on-line gauge and process journal pointed the engineer in the right direction.

Control | The goal has been met for product improvement and the changes need to be implemented. Make sure the changes are understood and upheld by having a brief description of the why behind these new control measures.

This stage usually means a redefinition of the product and process. So in the end, control means a new beginning.

remember to utilize the Six Sigma methodology and identify the important differences when you consider webs over widgets.

Excerpted from Mark Millers column Coating Matters, November 2010: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

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DefecTs: finDing The cause

in the world of coating equipment, the coating station is considered the heart of the beast. For better or worse, when the fluid comes in contact with the substrate, the coating station is where the action is. A manufacturing engineer spends a large chunk of time looking at, adjusting, measuring, and hovering around the coating station to determine how to make a coated product as fast as possible with the fewest defects.

As you learn more about coating - the interactions and the limitations of the equipment and materials - the more you will be able to directly influence defect reduction and product yield. Lets take an example:

A flexible web coating company has been slot die coating a polyester substrate with a 50% solids fluid at room temperature. Unfortunately,

a third of the coated web is scrap due to a consistent streak being coated in the machine direction. What can we blame for the defect?

The first step is to make sure the coating head itself is in proper operating condition. This includes making sure that the front edges of the slot die are not damaged.

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This is a great starting point, but where do you go from here? This is where you have to think about all the interactions.

Typically, a down-web streak is contamination of a trapped particle, so you have to go after the contamination and the gap problem. The particle can be dirt from the fluid or substrate or simply a particle that is too large for the gaps provided in the equipment setup.

Analyzing the head of a streak on the coated web may provide you with a particle that, under a microscope, will reveal whether it is dirt or a large fluidized particle. if it is a useful particle, the next step is to understand why the particle is not being filtered properly or why the particle gets trapped. if the particle is dirt, make sure the fluid is filtered and the substrate is cleaned.

once particles have been eliminated as a defect causing agent, you need to review the equipment setup. is the slot opening narrower at the site of the defect? is the web quality or tension poor in that area?

To analyze the interaction with the web, flip the substrate by replacing the existing roll with one from a different lot. if the streak remains in the same location, then the web is not to blame.

Another quick technique is to shim the slot die by running some plastic shim stock into the slot opening to clean out the exit of the coating head. once the coating defect origin is found, you can start working on the solution.

As you can see, adjustments to the coating head itself may not solve the problem. That is why this column is going to focus not just on the coating station itself but everything that influences the coating process.

Because knowing what you have to work with (the equipment, fluid, and substrate limitations) is only half the battle. Knowing how to recognize common defects, understanding the mechanical challenges, and even the manufacturing management philosophy can affect the product success.

My goal is to help manufacturing engineers and operators, the product engineers who provide the new challenge, and the process engineer who is scaling up this new product to production. Coating Matters is dedicated to understanding the coating station, the interactions that occur with upstream and downstream equipment, common defects and cures, and especially how to utilize this information to improve the bottom line of the business.

Excerpted from Mark Millers column Coating Matters, January 2011: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

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DonT blaMe chaTTer on The coaTing heaDLets talk chatter. not just because its cold outside, but because it is a common defect in the coating industry.

What is chatter? For those who have not dealt with this issue, chatter is a variation in coating that looks like a solid crossweb line at regular intervals down the web.

The reason i want to talk chatter is because it is a common defect that people want to blame on the coating head. However, it typically aligns with another piece of equipment.

But if i see the fluid coming out of the coating head, and the defect starts right at the application of the fluid to the web, why cant i blame the coating station? Because the underlying reason for chatter is one of two things, and you cant see either of them.

The first possibility is the pump delivering the fluid to the coating station. if the fluid is not being delivered at a constant rate, the output at the coating head will be apparent.

For the best pulse-free results, a coating station should be equipped with a gear, progressive cavity, or pressure pot pump. These constant feed-style pumps reduce down web variations in the coating fluid. if another style of pump is required, then dampening the pulsation can improve the coating appearance.

Also be aware that compressible tubes from the pump to the coating station can cause pulsations and coating fluctuations. Be aware of the fluid delivery system, and make this a starting point for process troubleshooting.

The second possibility is a mechanical solution. The easiest check on this issue (which requires no downtime!) is to compare the chatter frequency to the mechanical variation. if the chatter matches the regular intervals of an up-stream piece of equipment, the answer may lie in replacing the equipment.

Mechanical variations can occur from rolls that are not in compliance, vibrations in the structure or framework, or drives that run the upstream equipment. The rolls that are not true will match up with the frequency of the defect, so it is good to know the diameters of the rolls in the process.

The vibrations can be monitored with a vibration analyzer, and the drives can be matched for frequency.

how do you Solve the Problem of chatter?Well, the mechanical problems should have mechanical solutions (i.e., replace the bad rollers, drives, etc.). Likewise, the pumps should be replaced with non-pulsating alternatives.

However, if there is still some chatter after these adjustments have been made, you can consider a piece of stabilizing equipment. one option is a vacuum chamber at the site where the fluid interacts with the substrate. A vacuum box can stabilize the substrate/fluid interface and reduce variation.

But be careful, a vacuum box also can cause chatter! You need to make sure the box is sealed and operating properly.

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The reason a vacuum box may help reduce the defect of chatter is simply that the fluid likes itself more than it likes the substrate. This interface problem also may be improved by encouraging the fluid to adhere to the substrate by pre-treating the substrate chemically or with an energy source.

i hope this has provided an example of how coating is an interactive process. For the coating defect of

chatter, even though the fluid meets the substrate at the coating head, the main issue is not the coating station itself but the peripheral equipment.

So remember to keep your thoughts open and look outside of the coating station when analyzing defects. The root cause may not be obvious to the observer.

Excerpted from Mark Millers column Coating Matters, February 2011: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

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4 sTePs To resolving coaTing DefecTs Every coating process engineer and equipment operator wants to know where to start when a coating problem surfaces with their product. So lets start with the surface of the problem.

The main thing to do is properly identify the coating defect you are seeing. This will allow you to concen-trate on the process, equipment, or material issue and not spend time on unnecessary investigation.

So look at the coating defect and identify the issue. noreally look at the coating defect. Analyze it.

How? Besides looking at the defect off-line after it is produced - with the naked eye or under a microscope - you can look at the defect as it occurs on the web with on-line inspection equipment.

1. Visualization and understanding the defect is an important first step in the troubleshooting process. The remaining four areas are based on truly understanding what you are seeing.

A good example of this is when a coating streak occurred in a process with which i was involved. initially, the thought was that the fluid had gels in it.

Without looking at the coating defect under a microscope, the process engineer immediately tore down the pumps, hoses, and filters and re-placed them. guess what? The defect remained.

Upon closer examination (100X magnification), the streak was a film particle that was trapped between the fluid and the substrate. once the substrate was properly cleaned, the defect went away. So, again, look at the defect.

2. The second step is to collect defect samples and non-defect comparative samples, process data from those runs, and product data from the raw materials. Time spent with this information will provide the road map to the defect solution. Make sure the information collected includes discussions with the keeper of the information, so you understand if there are discrepancies in what is provided and what is reality.

This is the point at which the defect-solving team is formed. The stakeholders in the solution should include the keepers of the information.

3. The third step is to utilize the collected information to develop a designed experiment that will push the process and materials to define the defect. Work with the defect-solving team (engineers, operators, and material control) to identify the top five materials and process conditions that are most likely to contribute to the defect in question. This will be the basis of the experimental design.

Utilizing five variables will allow you to statistically analyze all the variables with the fewest number of design points without losing their interactions. in the design of experiment (DoE) lingo, this means that you should run a 25-1 DoE.

once the experimental design is established, run the trial test to see what shakes out as important to controlling the defect. The first trial may be one of three, but within three trials, you can narrow down the focus to what is really behind the defect. The result can be qualified simply as yes or no that the defect

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is present, but having a graduated scale for the defect will help concentrate your efforts.

4. The last step in the process is to utilize the results so the defect does not happen again. You may laugh at this, but if you have taken the time to deal with a defect that required as much thought, energy, and time as you have spent on the recent issue, then dont stop before the

results are communicated. it is critical to make sure everyone in the product chain - from raw material supply to converted product delivery - is aware of the defect and the reasons behind the solution.

The only thing worse than a coating defect is a coating defect that comes back after being cured. Happy troubleshooting!

Excerpted from Mark Millers column Coating Matters, March 2011: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

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susPensions, DisPersions, anD eMulsions What variables need to be considered when coating a fluid that isnt simple?When coating a simple fluid, slot die coating operators have enough to worry about if the fluid is a chemical or polymer diluted by a solvent. Viscosity curves at various shear rates and temperatures, stress relaxation of elastomeric materials, and flow dynamics within the slot die manifold geometry are swimming around in your mind as adjustments are made to the physical coating head to adjust for the many variations. Todays production applications sometimes require solid particles or mixtures to be coated within the confines of the slot die manifold. Lets discuss what variables need to be considered when the fluid is no longer simple.

Suspensions | When particles are being sent through a slot die for a coated product, the most important issue is to keep the particles in suspension. This concern works against the design of the slot die, as the internal manifold is designed to place the fluid on the substrate at a consistent velocity at the exit of the coating head. To obtain a consistent velocity, the slot die manifold is designed with a series of expansions and contractions that can create agglomeration points for the suspended particles. The key to success with a suspension is to know the time the particles take to fall out of suspension. This time needs to be longer than the residence time calculated in the slot die manifold. This manifold residence time can be obtained from the slot die manufacturer.

Dispersions | Suspensions are actually a subset of dispersions, but there are some important differences. in a suspension for fluid coating, the solid particle is floating in the fluid but maintains the solid state that allows for separation, such as clay particles in alcohol. in a dispersion, the solid may be more difficult to separate, such as sugar in water. While the sugar could be chemically extracted from the water, we have less concern about the solids dispersed in the fluid than we do with suspensions. The key with dispersions is to verify that the initial mixing has occurred and is stable.

Emulsions | Yet another subset of dispersions is an emulsion or liquid-liquid mixture. Emulsions mix two fluids that dont like each other, and try to keep the fluids from separating. The classic example is oil and water. if you want oil and water to stabilize long enough to be useful, you need to add an agent to promote the mixture. This is how detergents work: the surfactants in the detergent stabilize the oil and the water to allow you to clean a surface and remove the grease from the proverbial frying pan. With emulsions, the strength of the liquid-liquid bond is strong enough to survive the slot die manifold stresses, but care needs to be taken to understand the stress and strain phenomena related to the fluids that are emulsified.

Whether your head was swimming with data and charts before or not, i hope this breakdown of fluid systems has calmed the waters and provided you with a clear vision for improved coating performance.

Excerpted from Mark Millers column Coating Matters, February 2012: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

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how To choose a coaTing siTe What came first, the chicken or the egg? When determining how to initiate a new product in the marketplace, most converting companies face a similar paradox. Do you build a coating line and invest in the infrastructure designed around a product, or do you contract out the coating until the product has a proven track record? it depends.

Lets face it, if you have a test tube of fluid and a couple hand-spreads of coated product to show customers in a potential market, a lot of process and material variables can change as you scale up to manufacturing levels. So until the product has developed a place in the market, it would make a lot of sense to develop an agreement with a contract coating facility (a toll coater) to take on the process efforts while you go through raw material iterations and respond to customer feedback. Contract coaters provide existing, proven coating capabilities and a trained and knowledgeable staff.

The difficulty in utilizing contract facilities, however, is that what makes your product unique may require an investment from your company. While an investment in another facility may seem like money wasted in a manufacturing site that your company does not own, it is good to view the investment as buying time.

Lets say you have a product that requires ultraviolet (UV) curing to bring out the special product performance you have built into the technology, but the contract coating facility you would like to use does not have UV curing capability. Purchasing a UV cure station (or splitting the cost with the toll coater) provides you with the ability to spend

far less money than you would on upgrading an existing line or taking time out of existing manufacturing capacity to run a new product.

A small investment can go a long way. You are not only buying time, but you are also buying expertise. You are the expert of your product, but the contract coater is the expert of their process. The learning curve for a new coating facility (usually with new coating operators) is steep, and you may not have the time available to allow for this education.

Toll coating is not always the best option. if you have run trials and scaled up the product to production levels, it may make more sense to purchase a new coating line. Just remember, it does take time to manufacture the coating equipment and install the process at your location. Utilizing a toll coater for the time you are waiting for your own equipment is useful. But dont forget your customer. Unless you are purchasing a duplicate machine, the product may run differently on your production line than it did at the toll coater.

There are many variables to consider when you are developing a new product for the coating marketplace, and the decision depends on the complication inherent in your technology and the dollars you would need to invest to bring the product to market.

Whether you decide to invest in new equipment or utilize a contract coating location, keep your future in mind. What you introduce to the marketplace will be the basis of customer expectations going forward.

Excerpted from Mark Millers column Coating Matters, January 2012: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

coAting mAtterS

oPen uP The coaTing Process winDowif you have worked around a coating process facility, you have undoubtedly heard someone refer to the coating process window. This statistical assessment of the capabilities of the equipment as it interacts with the materials is the key to optimizing the money you can make.

Whoa! Did i get your attention? Yes, the money you make with the equipment and materials at your disposal is based on the yield of the final converted product you are selling in roll form. More yield equals more money. To maximize yield, you need to know where the coated product is good and where it fails.

Pushing the process to its limits and mapping the extent of these variables on a graph will provide you with an understanding of a process in which the coating can survive. This map of the process is the coating window (see Figure 1 and Figure 2).

To develop the coating window, you need to understand the critical processes that control your system. in slot die coating, the variables that can pry open the window (or slam it shut) are the slot die

attack angle, the slot die-to-substrate proximity, the slot die lip (offset/geometry/gap), along with the line speed, raw material variation, and equipment precision. Because you typically are stuck with the raw materials developed for the product and the line speed requirements for the market pricing, the variables to be considered in the coating process window are centered at the coating station.

Making sure the backing roll, the positioning stand, and the coating head are manufactured to exacting tolerances is the first step to opening the window of coatability. After this equipment precision is verified, it is time to get to work.

The slot die can be varied physically at high and low line speeds to determine if the final coated product is acceptable. in the example presented in Figure 1, a good coating (one that is acceptable to the end-user) can be achieved up to 400 mpm. However, as the speed is increased, the coating head needs to be moved farther away from the substrate. This picture of coating quality gives the operator a good idea of where to go based on empirical data.

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in the example presented in Figure 2, a good coating falls within 1-3 deg of the attack angle of the die to the substrate. The attack angle is the radial variation from tangent that the slot die lips are from the centerline of the backing roll.

You will notice, however, that above 350 mpm, the coating seems to fall off a cliff. This would warn the coating operators that as speed increases, they would be well positioned if they adjusted the coating head closer to 1 deg.

To achieve the coating process windows presented here, a design of experiments (DoE) should be conducted to develop the limits of the operating

system. The key to success, however, is to push the process beyond the acceptable limits.

A good rule of thumb is to go 20% more than the limit tested. For example, if the plan is to run the coating line at 300 mpm, it needs to be tested at least to 360 mpm.

now, if the coating is still good at 360 mpm, dont stop! Push the system so the next time you are asked to make a process improvement, the DoE does not have to be redone. This preliminary experimental work will turn the current process window into a chasm of opportunity. open it up, and let the profits come in!

Excerpted from Mark Millers column Coating Matters, May 2011: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

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coaTing, noT PrinTingWhether you work in the battery industry, the packaging industry, or the publishing industry, you have come across these two words: coating and printing. For as different as they are, it is easy to confuse the technologies and the capabilities.

Both processes provide an operator the ability to coat a thin film of fluid onto a substrate, but there are some fundamental differences in capability. namely, the shapes that are possible.

Printing technology provides the operator with the ability to produce any shape a computer can form on a screen and translate through a print head. The images/pictures on a printed page are a good example. They can vary in size and shape and are printed dot by dot.

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Coating, on the other hand, allows you to place a fluid in any shape you want - as long as it is rectangular! A good way to distinguish coating and printing is to imagine that printing is discrete and coating is continuous (mostly).

of course, this rule of thumb has many exceptions, but discrete versus continuous is a good baseline to develop an understanding of the two technologies. The disadvantage of the shape limitation with coating for a coated/printed product is overcome with speed and continuous operation.

Coating technology includes fluid deposition through roller (gravure), slot die, and other continuous full-web applications. More broadly, other fluid coating techniques could be considered, but the confusion seems to lie in coating head technology and print head technology.

Examples of printing technology include inkjet and roller technology. The fine line occurs at the roller technology of printing and coating.

While i have already stated that coating is full web and continuous, techniques developed by operators and equipment suppliers alike have broadened the ability of coating heads to allow for intermittent coating and lanes of coating. This improvement on the capabilities of coating technology still is limited to the shape that can be properly displaced by a roll head or released from a slot die - a rectangle.

Why is this difference important to the world of printed and coated products? Lets take the rFiD market. in developing a circuit that has a fluid to be placed on a substrate, an rFiD system can require the fluid to move and snake around, see photo. This would be relatively easy with a print head but unusual for a coating head.

However, to produce a Li-ion battery, the fluid needs to be placed in rectangular patterns to match the final construction of the battery. Utilizing a coating tech-nique for the battery industry allows for increased production speeds and improved accuracy over a continuous web. in addition, utilizing a curtain coat-ing technique via a slot die, coating more than one fluid at a time is possible with one coating head.

Both techniques have limitations based on the rheology of the fluid being dispersed. in many cases, the rheology dictates the method and not the other way around. This chemical dependence forces an engineer to be aware of a wide variety of techniques and capabilities to solve the process problem.

As you can see, printing and coating both have advantages and disadvantages. The key is matching the application correctly with the system best suited for the fluid placement. For some applications, a coating technique will provide the necessary tools to optimize a product, while other applications may require a printing technique to meet the functionality. remember: Coating and Printing Matter!

Excerpted from Mark Millers column Coating Matters, June 2011: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

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sloT Die coaTing funDaMenTalsrecently, a lot has been asked of coating technology. Products in the printed electronic fields, such as solar panels and battery technology, have pushed the limits of traditional roll-to-roll processes.

For a production facility to have a technical edge, a coating solution must be robust enough to coat thin, precise, and clean. Slot die coating technology provides this accurate and metered technology in a closed process for better control.

Here is a summary of the extent of capability of a slot die (for typical coating fluids):

Line speeds | 1-600 mpm

Wet thickness coated | 1-2,000 microns

viscosity of fluid | 1-100,000 cP

Accuracy | 1%

Process uses | Dual-sided coating, multiple layer coating, intermittent coating, lane coating

if slot die technology is so great, what is it? Slot dies are defined as premetered coating equipment, because all the fluid you send to the slot die gets coated on the web. But lets start at the beginning.

Lets say you have a special sauce that you want coated on a substrate, but the special sauce is really special. Thousands of dollars special! You cant afford to make enough of your sauce to fill a coating pan (open to the atmosphere) and have a traditional roll coating method slather the sauce onto the web for a trial and then throw away the rest.

What you would prefer - and the slot die technology provides - is a closed system that moves your special sauce from an enclosed tank through a pump to the slot die. The speed of delivery of the pump matches the web speed of the substrate, which allows whatever is sent to the slot die to be deposited on the web to form your product.

When you need to stop making your product, the pump is shut off and the wasted fluid is what remains in the pump, hose, and slot die.

So how much volume is in the slot die? That depends on the internal design or the manifold.

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T

The manifold of the slot die is designed for the rheological family of fluids you will be running through the coating head. in other words, dont expect an adhesive slot die to run anode battery slurry. That would be like asking a smart car to haul cargo like a truck - different design and different results.

The manifold of the slot die is the internal distribution chamber that the fluid uses as a roadmap to distribute correctly onto the web to make your product. This manifold design is one of the five main characteristics that are important in slot die coating. The other four include lip geometry, lip offset, lip adjustability, and manufacturing tolerance.

As you can see, of the five main variables associated with slot die coating, three concern the lip or exit of the slot die. This exit is critical for many reasons but most importantly because the lips of the slot die are the last surface the fluid touches before wetting out onto the web. if the lip surface is not manufactured to an exacting tolerance, the fluid will remember the imperfections as defects in coating.

So if your new product development requires coating thin, precise, and clean fluids for value-added product design, i suggest investigating slot die coating. Precision-manufactured equipment provides you with the technology and adaptive coating techniques required for novel product development.

Excerpted from Mark Millers column Coating Matters, July 2011: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

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surface energy MaTchMakingTypically, when you coat a fluid onto a substrate, the fluid flows to the limits of the coating head and provides a solid layer of fluid over the substrate. Sometimes, however, the fluid resists this reformation and coating defects occur.

Pinholes, ribs, and beading-up of the fluid are common when the fluid resists flow. These coating defects are an example of the fluid liking itself more than it likes the substrate.

Because of the fluids fondness of itself (chemically speaking, of course), the fluid contracts or beads up. We have all seen this - water droplets form on a window and dont want to wet out, so they form individual beads, see photo below.

in the coating world, though, we need the fluid to like the substrate more than itself. We actually need the fluid to really like the substrate, or we risk adhesion failure after coating.

in more technical terms, the fluid and substrate both have an inherent amount of energy exhibited at the surface where they come into contact. if the energy

within the fluid is high relative to the substrate, the fluid will attract itself more and form droplets (i.e., coating defects).

if the energy of the substrate is high relative to the fluid, the fluid will be unable to resist the attractive force of the substrate and be willing to wet out the surface (i.e., good coated product). The key is to encourage the fluid to like this new, dissimilar material it is contacting and spread evenly over a large surface area.

if you are unlucky enough to have mismatched materials, what can you do? Lets investigate what is going on.

in a coating operation, the fluid meets the substrate at the location of the coating head. if the fluid and substrate surface energies are near equilibrium, defects will occur at the interface. if we can increase the energy of the substrate, reduce the energy of the fluid, or otherwise promote the marriage of the dissimilar materials, we win.

To develop this harmonious matrimony of fluid and substrate, we can do the following:

Increase the surface energy of the substrate | Prior to the coating head, energy can be added to the substrate surface via corona, flame, or plasma treatment. These treatments activate the end groups that attract the fluid, also called oxidizing.

Decrease the surface energy of the fluid | Primer coating can act as a chemical binder for the fluid of interest and the substrate,

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creating a bridge for secure coating, or a surfactant can reduce the surface energy of the fluid, allowing it to wet out over the substrate.

Promote adhesion at the coating interface | Sometimes the surface energy is only part of the reason for poor adhesion, and a vacuum at the coating head is enough to reduce the air barrier and allow for proper adhesion of the fluid to the substrate.

To know if you may have a problem before you have a problem, it is good to obtain the surface energy information for both the fluid and the substrate. The manufacturer typically provides this in the product literature, or a test facility can determine the fluid surface tension.

For the substrate, dyne pens can be purchased to provide an estimation of the surface energy, showing fluids of specific surface energy levels, and you can observe the wettability under static conditions.

The fluid and substrate marriage is tricky enough to encourage without the right energy present. Make these partners like each other more than they like themselves, and you have a coated product that will have fewer defects to overcome and a high likelihood of a persistent product. Happy matchmaking!

Excerpted from Mark Millers column Coating Matters, August 2011: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

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whaT The coaTing beaD can Tell youWhen a fluid is being coated out of a slot die, it can be positioned in a variety of ways. This ability to position the coating head is an inherent capability of the slot die because of the closed system mode of operation.

in a typical arrangement, with the slot die coating a fluid in close proximity of a precision backing roll, we observe the fluid coming out onto the substrate and moving away from the coating head. The coating either looks clean, clear, and precise, or simply terrible.

When the coating comes out poorly, we tend to scramble for a solution; looking high and low for an answer. But have you ever looked behind the slot die? one critical location for understanding what is going on with your coating is the coating bead or the meniscus of fluid on the underside of the slot die.

As the web passes in between the coating head and the backing roll, the substrate carries the fluid away. However, the fluid does not always exit the coating head the same way every time.

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The fluid is squeezed between the substrate and the coating head, pushing out behind the die to create a coating bead and being stretched out on the substrate as it moves away from the slot die. The coating bead can tell you a lot of what is going on in the fluid as it moves away from the coating head.

if the coating bead is too large, you will observe the fluid dripping back into an overflow pan. This phenomenon tells you that you are simply providing too much fluid to the coating head.

The opposite problem occurs when the slot die is running dry and the coating bead is not even present. This will show up as a skip coating without full coverage. What happens in between an over-full and an under-developed coating bead is very interesting!

Assuming the surface energy of the fluid and the surface energy of the substrate are compatible for a happy adhesion, the lack of a substantial coating bead can lead to air entrapment. The fluid/fluid interface between the liquid being coated and the air above the substrate can develop coating defects and reduce what would be a good adhesive effect. What you need to do is get up under the slot die and observe what is going on.

With a good set of eyes, a flashlight, and some patience, you will visualize some coating bead (also called a rolling bank) phenomenon that you will also recognize in long form on the coated substrate

on the other side of the slot die. Stagnant areas in the coating bead may coat fine for a while, but then the liquid can degrade because of lack of movement and develop coating defects.

What do you do if the coating bead looks horrible, but you need to be at the specific set points within the coating window. Peripheral energy and equipment can help.

Similar to the ability to effect surface energy, supporting and promoting the coating bead is a balancing act between substrate, fluid, and coating head. Surface energy treatment options can help, including corona, flame, or controlling electrostatic forces.

The most common piece of equipment utilized to improve coating bead behavior is a vacuum box. This box seals against the slot die and the precision backing roll. A displacement of air and pressure differentiation cause the liquid to pin against the substrate better, and therefore reduce the effect of the air interface between the fluid and the substrate. This will improve the coating bead and reduce defects. in the opposite direction, if the coating bead is too large, then the line speed or pump needs to be altered to accommodate.

So when you setup the coating head and you are recording process conditions, make sure to take a look under the hood to verify that the coating bead looks solid and stable. it will be well worth your time.

Excerpted from Mark Millers column Coating Matters, September 2011: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

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how To avoiD bubble DefecTsone of the most common issues in coating is bubbles. not solids. not liquids. Bubbles.

Where do bubbles come from, and how can we avoid the defects they create? Well, first of all, the bubbles are air. Air can be introduced in a variety of points in the coating process, but there are two main types of air: air entrainment and air entrapment. These very similar words have very different causes.

Air entrainmentAir that is introduced into the fluid prior to the coating head is entrained. i remember the term by thinking about the fact that the bubble is already on the train track before it enters the coating head. You are probably already thinking this, but it is easier to keep air out than to remove it once it is in the system.

So how does air enter the system prior to the coating head? one way is through excessive agitation of the liquids in the mixing tank. This can be reduced through proper mixing techniques and preparing batches ahead of time to allow settling prior to the coating run.

it is also possible to place a nitrogen blanket over the fluid to remove air. if the liquid moves from one vessel into another, before the coating head, both vessels need to have air reduction measures.

The fluid moves, right? So when the fluid passes a seal, make sure the seal does not leak and cause air entrainment. Lastly, make sure the fluid moves uphill

as much as possible. Any bends in the pipe/tubing will allow air to settle. This curved settlement area for the air will slowly leak into the coating head, showing up as a random and difficult to diagnose bubble problem. if a curve in the tube or pipe is necessary, a relief valve will help.

Temperature and pressure also can be your friend. if the process and materials allow, you can heat the fluid up and pull a vacuum. These process conditions will help reduce bubble formation prior to the fluid traveling to the coating head. Ultrasonic measures also have been utilized to reduce bubbles, but these have had mixed results.

Air entrapmentAir that is trapped between a fluid and a solid (substrate) is entrapped. This can occur for many reasons, but if you read my article on What the Coating Bead Can Tell You, you would understand that the surface energy of the fluid and the substrate play a major role in the reduction of air entrapment.

Vacuum again can be used to reduce bubble formation. At the point of interaction of the fluid and substrate, the vacuum can remove air from the interface, allowing the fluid to adhere more substantially to the substrate.

in an extreme case of air interfering with coating, a coating defect appears that is referred to as herringbone (where there is a periodic cross-web defect that resembles the angled look of the v-shaped weaving pattern). This coating

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defect usually means that the coating head and substrate are not in proper position to seal the fluid to the substrate.

As the coating head is positioned for a better seal, the air introduced becomes more of a minor defect that may be noticeable only on the final coated product. Even with full coating, however, the improper seal of the fluid to the substrate may lead to fluid flow changes in the coating bead or build-up and streaking of the coating fluid on the substrate.

The interaction of fluid, substrate, and vacuum all are affected by the speed of the line. The faster you go, the more difficult it is to avoid air.

Youll never look at a bubble the same way again!

Excerpted from Mark Millers column Coating Matters, October 2011: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

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how To selecT a coaTing MeThoDWhy would you coat with a roller instead of a knife; a rod instead of a slot die? There are many methods for fluid coating and just as many techniques for utilizing the equipment. outside of space constraints, original equipment manufacturers (oEMs) have made it possible to slide in almost any fluid coating equipment as a replacement for existing equipment. So what do you have to choose from? Check out the table to the right.

roll ApplicationPre-metered Application

Direct gravure Slot dieoffset gravure Curtainreverse gravure rotary rodMayer rod SlideKnife Multilayer slotComma Multilayer slideDip Direct roll reverse roll Flexo

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Coating methods fall into two major areas: roll application and pre-metered application. Pre-metered application typically requires a slot die where a pump and line speed of a substrate determine the fluid coat weight. roll application requires that the fluid flow between two rotating rolls that dictate the fluid coat weight and the uniformity of the coated fluid across the substrate. The table presented above does not cover every possible coating method or variation of those presented. Many coating facilities have developed methods and techniques that are unique to an individual product.

With so many options available, a good place to start is with product specification. Lets take, for example, an optically clear coating that needs to have reduced debris from handling and coating. This low level of contamination leans the decision toward pre-metered coating contained within a slot die. if the coating does not require contamination control, but instead requires quick change-over from one product to another, a self-metered arrangement with a comma coater may be sufficient.

Another consideration should be the scale of the fluid coating. There is a distinction between lab, pilot, and production scale that plays into the choice of methods. Many times a Mayer rod may be used in the lab to allow for multiple handspreads to be completed in a short time. This

is great if you are scaling to a production Mayer rod manufacturing facility, but there are many process factors that will not scale properly if the production facility runs a gravure roll instead. if possible, the method should be based on the physical parameters of the product (required cross-web uniformity, volume of fluid to be coated, solution characteristics, number of coating layers, and substrate type).

Dont forget to keep in mind expertise! Even if the product requires a specific type of coating method, the fluid coating operators have developed an understanding and skill with the current coating method used in your facility. Training on a new coating method will require some downtime, and this needs to be factored into the return on investment in the newly installed equipment.

The bottom line, however, is always the bottom line. The cost of one fluid coating method can vary substantially with the cost of another fluid coating method. Do not look simply at the sticker price however! Make sure to keep in mind the requirements of changeover, replacement parts, precision rolls, and process limitations (line speed and rheological design of the fluid). The decision of which fluid coating method to utilize is multifaceted and requires some thought. good luck and happy coating!

Excerpted from Mark Millers column Coating Matters, December 2011: Paper, Film & foil Converter (PFFC-online.com), a property of YTC Media Inc.

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coaTing Tech serviceWith experience in a broad product range since 1996, Coating Tech Service provides in-depth knowledge for slot die coating across all fluid coated products.Coating Tech Service is a project management and slot die coating service consulting company providing exceptional process engineering and on-site services to domestic and international clients in coating and converting companies.

Support services include:TrialsupportProjectManagementReturnoninvestmentorefficiencyconsultingProcesstroubleshootingEngineeringanddesignservicesOn-sitetechnicalserviceAnalysisofexistingprocessforcoatingimprovementplanEquipmentevaluationInstallationTrainingRepairandre-workingManifoldsimulationsFiniteelementanalysisProcessvariablesimulations

Coating Tech Service provides a flexible project manager to develop specifications, implement process upgrades, or improve process efficiencies for value added projects.

www.coatingtechservice.com

Further Slot die coAting technology reSourceS

coaTing Tech insTiTuTeCoating Tech Slot Dies hosts an annual user conference which includes an intensive training session featuring a day and a half of classroom instruction and a day of hands-on training with slot die coating technology.

The conference focuses on:IntroductiontoslotdiecoatingtechnologyRheologyProcessSystemTechniqueCoatingDefectsandResolutionsSlotdiefeaturesandsetupSlotdieoperation

www.coatingtechinstitute.com

The science of slot diesHeadquarters 2322 Alpine road Suite 4 Eau Claire, Wi 54703 office 715.544.7568

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