Web Coating Blog

Defect Reduction and Prevention

Defect Reduction and Prevention

Defects are an ongoing source of extra costs and an impediment to the successful operation of an operating coating line. I know of no coater that does not have defect problems with both old and new products. Thus programs to eliminate defects when they occur and preventing their reoccurrence is an essential technical effort for a coating line.

Optimizing a current coating line to reduce defects is essential to insure economic success and remain competitive. It is also an essential process when a new coater is being designed and installed. The new coater should have improvements in design and fabrication so that it performs betters then the old designs. It should not be a duplicate of previous coating lines. If it is the new unit will have all of the deficiencies of the old unit.

Defects are defined as the lack of something necessary or desirable, a deficiency, or an imperfection that impairs worth or utility. Physical defects such as chatter, haze, streaks, repeats, ribbing, spots are typically considered as the largest class of defects in a coating line. However, there are other process and product performance defects that are detrimental, such as
• Coating weight non-uniformity and poor reproducibility
• Inadequate drying which lowers line speed and productivity
• Downtime to eliminate defects
• Drying sensitive product performance properties, adhesion, haze, are not being obtained

In developing technical programs there are several Process Success Factors that need to be considered when formulating the technical program:

• There are ~25 major process elements and each of them have several hardware components. All of them are important and need to be evaluated and deficiencies corrected. A deficiency in one element can limit the performance of the entire unit
• Defects created in any step in the coating line will not be corrected in the subsequent steps,
• The major process elements, web drive components, coating station & applicator, dryer, solution preparation, control systems, safety and Environmental must be robust.
• Online instrumentation to measure coating weight, and defects are necessary for optimum performance.
•Because of the complexity of the process detailed operating procedures are needed along with and on going training of operating personnel.

The program to reduce or to scale-up new product with minimum defects should have a defined protocol that covers all of the steps needed for success. This defines the steps needed to implement the program and insure success

These steps in the Defect Reduction Procedure are as follows:

1.Define all the product and process requirements that are needed for success in the marketplace. This is particularly important because the end product must be competitive and the overall needs should be established at the start of the effort rather then in the middle of the effort.

2.Insure availability of valid analytical techniques to measure and characterize properties and process variables. If you cannot measure an important property with the accuracy needed, then a quality product cannot be produced. Similarity, the process instrumentation needs to be evaluated to determine if it can control process variables with the precision and reproducibility needed. If a coating weight measurement precision of 1% is needed and the current method gives 5 %, the program will not be successful. Instrumentation needed should be ordered at this point in program to insure valid experimental data.

3.Insure that the web coating process can meet the required specifications. Variables such as line speed precision, drying load, drying configuration, tension control, cleanliness, web transport, substrate thickness range need to be analyzed to insure that they are adequate. It is possible that coater may not have the capability to make product at the goal specifications. Once identified, corrective action should be started.

4.Use the appropriate coating method. There are a wide range of available coating methods each of which has an operating window, which gives the best defect free product. For example, The Mayer rod gives a coating weight uniformity of 6-10 % and has a maximum line speed of 300 fpm. If you need a uniformity of 1% and need to coat at 600 fpm, this method will not be adequate. The curtain coater functions at high speed and will not coat at speeds below 400 fpm. A low volume product will not give good results. A previous Blog article, Selecting a Coating Method describes this procedure in more detail

5. Develop and implement operational procedures. The coating line is complex and has many variables that need to be controlled. There should be operating procedures for the coater and all products so that all variables are controlled and reproducible. Operating personnel should be trained to use these procedures and they should be kept current.

6. Quantify and understand defect losses. When defects occur, the type of defect and amount of product lost must be recorded. This should include product defects as well as coater defects such as coater downtime and mechanical problems. This will give an accurate depiction of losses and a method to calculate Economic impact due losses to help justify future efforts. It can help determine if any product has a superior or inferior performance

7. Use a structured troubleshooting protocol when defects occur. There will be defects with products as they are manufactured on an ongoing basis. A structured protocol will help determine the reason for the defects and to rapidly correct them and recommend improvements. Next article will discuss this.

8. Set up a computer database to store and share information. The converting process generated a lot of data, which should be analyzed to help understand the process and identify areas for improvements,

9. Implement process improvement technology. Many new technologies for the converting process are being developed each year. These should be evaluated and implemented so that coater performance is always improving.

10. Use statistical process control. The best method to control the process and insure reproducibility and good performance is to utilize one of the many quality control methods. The process is to complex to control without using one of these methods.

The Importance Of Accurately Quantifying Defect Losses

37. The Importance Of Accurately Quantifying Defect Losses

There are many essential factors in the effective running of a high quality and economically effective web coating process. One of these factors is to maintain a quantitative detailed accurate database of defect losses in the process. This analysis should provide an ongoing:

• Accurate summary of product yield losses
• What caused the specific losses, streaks, bubbles scratches coverage etc?
• Summary of losses by product and defect type type.
• Specific losses for coating line down, product change, start-up losses
• The ability to calculate dollar losses for each defect
• Easy access to the data for all personnel

Utilization of this database will provide:
• Understanding of defect types in process and where they occur
• The ability to compare product performance and identify better performing products
• The ability to dentify process elements that need upgrading
• With accurate yield loss number the economic Justification for programs and new hardware can be calculated
• A priority list to work on
• An aid in understand mechanisms and

A barrier to developing this database is that often, the yield data collected can be rudimentary and does not accurately reflect the total losses and is not very helpful in identifying the potential causes for defects. The losses are characterized by where they are detected, i.e. in slitting or sheeting process and when the customer uses the product and return the product because it is defective. The classification also can be very general categories, which are not very helpful in finding the sources of the defect, and quantifying losses.

The following is an example of a basic yield loss summary, which provides insufficient information:

• Finishing yield loss 9-62 % of square feet processed
o Pattern length loss 2-14%
o Pattern width loss 1.5-35 %
o Quality yield loss 0-22 %
• Customer returns 10-15 %

For example, what is needed is the exact defects, which resulted in the loss. In regard to pattern width loss there are several potential losses and each may require different corrective action:

• Poor coating weight profile in either machine or transverse direction
• A streak or scratches which prevents using optimum slitting pattern
• Substrate defect such as gauge bands
• Poor edge coverage profile
• Quality Defects
• Missing coating

The database must be maintained in a computer system with intranet access for all company personnel. With advent of computer process control systems, on-line thickness gauges and on-line inspection systems; a significant amount of the data required can be added to the database without requiring personnel costs to add data.

The following is some of the typical data that is needed for an effective database:

• Identification information
• Roll number
• Raw material batches
• slit location
• Defect type
• Amount lost in sq.ft. for each defect type
• Segregated according to product
• Type classification
• Downtime losses,
• Time lost
• Causes such as
• Mechanical failure
• Product change
• Start-up times
• Getting on target for coverage and drying conditions
• Best estimate of defect origination, not where detecte
• Bubble detected in sheeting is coating defect
• Data for each product

The sources of data for the database are:
• Coater logs & inspection data
• Losses from slitters and sheeting
• Customer complaints
• Quality control testing
• On-line inspection data
• On-line thickness gauges

Another requirement of the database design is the ability to interact with other quality control and process databases so that losses can be correlated with process variables to determine defect causes.

One of the difficulties with this database is that there are no standard names and occasionally jargon names are used. This can result in different names for the same defect. One way to minimize this effect is to classify defect by attributes as well as the name. Figure 1 is an example of a classification scheme. An advantage of this approach is that the loss from general defect classes can be identifies and the cost of losses identified, such as streaks, chatter, base defects, etc. In addition, coater losses for operational variables can be determined.

Figure 1

DEFECT CLASSIFICATION

1. Linear Continuous
a. Machine direction
i. STREAKS
ii. RIBBING
b. Transverse direction
i. CHATTER
c. Diagonal
i. DIAGONAL CHATTER
2. Linear Intermittent
a. Machine direction
i. SCRATCHES
b. Transverse direction
c. Diagonal
3. Discrete point defect
a. Spot
i. BUBBLE SPOTS
ii. GELS
b. Contamination coating
i. REPELLENT SPOTS
ii. DIRT
c. Contamination substrate
i. REPELLENT SPOTS
d. Other types
i. REPEAT SPOTS

4. Pattern & diffuse defects
a. MOTTLE
b. DRYER BANDS
c. ORANGE PEEL
5. Process specific defects
a. Raw Materials
i. REPELLENTS
ii. BENARD CELLS
b. Coating
i. AIR ENTRAINMENT
c. Drying
i. MOTTLE
ii. DRYER BANDS
d. Web Transport & winding
i. WRINKLES
ii. SCRATCHES
iii. REPEAT SPOTS
e. Metallizing process
i. BLOOMING
6. Substrate defects
a. Plastic
i. GAUGE BANDS
ii. POLYMER SPOTS
iii. COATING NON-UNIFORMITY
b. Paper
i. WRINKLES
c. MEtalized

T

Comment on Question about Chatter

Response to Question on Chatter submitted to web coating blog

Mechanical chatter is the defect that you are describing. This appears as straight transverse direction bars across the web. It usually is caused by vibrations being transmitted to the coating bead, inducing vibrations in the coating bead, which leads to differences in coating weight. The vibration sources can be from pumps, drives, building, unwinding rolls, dryer heating and ventilating systems, coater rolls and bearings, and exterior sources.

The first step is to calculate the chatter frequency. The formula for this is:
chatter frequency in cycles/sec = web speed inches/sec* measured cycles/inch
This frequency should help suggest possible vibration sources, For example 60 cycles sec suggests electrical. Vibration frequencies in coater and or specific components can be measured with appropriate equipment

To control vibrations:
• A rigid coating station, isolated from vibrations of the rest of the building, is needed. It should not vibrate and maintain settings.
• There should be uniform tension in the web and no vibrations or surges
• All rolls should be balanced and should not stick, vibrate, or wobble.
• Other vibration sources should be isolated or removed.

Recession Impact on Converting Technology

There is no doubt that the current economic slowdown, recession, or economic adjustment is presenting a major challenge for all businesses, Volume for most converting products are down significantly and profits are only fond memories. Businesses are responding to the changing scenario by the typical reaction of layoffs, reducing forces, and cost
cutting and a little bit of wishful thinking. The federal and local governments are also responding with a variety of actions. The Arizona legislature has taken several steps including reducing funding for all levels of education. It seems ironic that at time when we need more educated people to solve these problems, they are trying to reduce the supply

My interest is to try and ascertain what the effect is going to be on the industries’ manufacturing facilities and particularly on the personnel from R&D to Manufacturing. I expect that there will be:

• A major focus on short-term earnings, by improving quality and productivity and reducing losses
• Modernizing of existing equipment
• A reduction in long term capital projects for new facilities
• A need for personnel to rapidly acquire additional new skills as people in their companies are reduced
• A focus on energy savings in all aspects of the process.
• A reduction in support activities, instruments, analytical tests, education and travel expenses as management views their people as a cost and liability instead of an asset which can be optimized.

There are several technologies that can rapidly be implemented in the coating lines to improve efficiency and reduce costs. On-line coating weight thickness gauges will improve thickness control and can reduce product variability and save on raw material costs, An out of specification thickness can rapidly be determined and corrective action taken immediately. The devices can be used as part of a closed loop control system. Thus reducing amount of scrap produced.

On line-inspection devices can rapidly detect defects and permit rapid corrective actions. A major attribute is that they can detect small defects which are difficult for the human eye to detect, but will result in scrap product when the customer uses. Also, given an accurate position of defects, the final conversion of roll stock to the sizes required by customers can be optimized.

Both of these technologies if utilized correctly can have rapid payoffs and return of investments. They can also be used to develop a true quantitative estimate of real production losses. I have often found that the loss data is not in sufficient detail to identify the root causes. These technologies will rapidly provide reliable information can then permit technical effort on the real problems. These process detection devices can be integrated with computer technology to process data and reduce the burden on people.

Other technologies that should be investigated and upgraded are the ancillary support equipment, such as surface treatment, improved coater line speed and tension control, statistical process control, solution handling equipment and instrument performance and accurate easy to understand procedures. Improvements in these areas often require small expenditures and can resulting rapid process improvement and coat savings.

The process is very dependent on fossil fuels, as a source of energy. There has been an unlimited of fuels at reasonable prices.
However, in recent years the energy costs have increased dramatically, leading to higher energy costs for the convertor. The operating personnel need to focus on the newly available energy conservation technologies. To reduce costs.

One of the issues in the evaluation, selection and installation of the above technologies is that there will be less people to do these functions. In addition, the remaining people may not have expertise in the needed areas. The reduction in travel will reduce the ability of personnel to travel to technical meetings and continuing education courses to learn these technologies. I believe that this need will be met by more effective utilization of the Internet technology in which no one travels. All will have to get more comfortable with the computer and internet technology so they can institute and attend webinars, on-line courses, the use of sharing software. Technical meetings, which are currently almost exclusively face-to-face events will change to include a virtual meeting component. Some of the face-to-face component will gradually be replaced by remote participation by both attendees and presenter. This will permit rapid and less costly information transfer,

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,

Comment on Dyne SOlution Sources

                                    

A new comment from “David Tanner” was received on the post “Response to Query” of the weblog “Web Coating Blog”.

                         

Comment:
I would like to add to this post by saying that the Dyne Solutions that referred to are availible from selected companies, in the UK and Europe for instance CDE Products have manufactured Dyne solutions for over 20 years.

            

• Commenter name: David Tanner
• Commenter email: info@cdeproducts.co.uk

Response to Query on Curl

                                    Response to Query on Curl
                                        Edward D Cohen

In response to your question about curl when ink is applied to film, the curl is the usually towards the coated side of the film.  It is caused by   residual stresses in the coating applying a force to the substrate, which causes the substrate to bend. The stresses can arise form several causes. Stresses generated, as the coating shrinks during the drying process will cause curl if not relieved. The magnitude of these stresses will depend on the amount of shrinkage, the properties of the binder system, the substrate physical properties transition temperatures and stress relieving in the dryer.  Often a high relative humidity et eh end of the dryer and in ambient air.  A stronger substrate may also be needed.following diagram shows  curl and stresses.

Response to Query on Curl

In response to your question about curl when ink is applied to film, the curl is the usually towards the coated side of the film.  It is caused by   residual stresses in the coating applying a force to the substrate, which causes the substrate to bend. The stresses can arise form several causes. Stresses generated, as the coating shrinks during the drying process will cause curl if not relieved. The magnitude of these stresses will depend on the amount of shrinkage, the properties of the binder system, the substrate physical properties transition temperatures and stress relieving in the dryer.  Often a high relative humidity et eh end of the dryer and in ambient air.  A stronger substrate may also be needed.following diagram shows  curl and stresses.

The following diagram shows  curl and stresses

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.

Response to Query on Drying Stresses

                                                    Drying Stresses

                                            Edgar B. Gutoff, Sc.D., P.E.
                                        Consulting Chemical Engineer
                                                ebgutof@coe.neu.edu