PAPER CHEMISTRY LABORATORY, INC.
May Newsletter 2003
THE ‘SIX SIGMA’ QUALITY DOCTRINE
ENHANCES PAPERMAKING CHEMISTRY NANOTECHNOLOGY
Introduction to Nanotechnology
“Nanotechnology” sounds pretty high-faluting, and the author will concede that serendipity played a major role. However, 6 years of work and the execution of 5000 experiments provided major new understandings and powerful insights.
In the 5th year we learned that using a microparticle process on the Lab Zeta Data with a magnetic stirrer maximized drainage, retention, sizing and Scott Bond of a coated free sheet (CFS) process at a zeta potential in the range +2 to +4mV. It was a magic moment when we discovered the process could one day be beautifully harmonized.
Much later, on the CFS machine in question, a change of -10mV zeta potential was observed in a headbox stock sample, measured first on-line, then quickly removed to the lab and re-measured on a Lab Zeta Data. We learned two things: that cationic decay made a huge difference, and that machine quality of mixing and residence time was woefully inadequate.
We had wondered why the optimum zeta potential in our lab work was slightly positive instead of zero. Now we realized that the magnetic stirrer was not mixing thoroughly and cationic decay was occurring in the time between measurement on the Lab Zeta Data and the making of handsheets.
Thereafter, all of our Lab Zeta Data evaluation work was done as close to zero zeta potential as we were able to get. In one series, working with large amounts of precipitated calcium carbonate (PCC) as filler, we observed that under these optimum conditions we could obtain a 5% increase in ash level and greater strength, in comparison with an uncontrolled process.
How to explain such a counter-intuitive result? The gecko lizard helped. It runs upside down on ceilings because each foot has thousands of spatulae that make intermolecular contact with the ceiling surface, activating van der Waals powerful intermolecular attractive Force. Thoroughness of mixing to the point of homogeneity was emerging as essential to best results.
Enter serendipity. In the mid to late 80’s the undersigned added size to a low surface tension hydrocarbon and sprayed it on the wet web. Two orders of magnitude less size was required than when the size was simply mixed in with conventional technology. It certainly looked like conventional mixing was not close to creating stock homogeneity.
Parenthetically, we also learned that 1% of the innocuous hydrocarbon sprayed on the web could reduce press section re-wetting sufficiently that productivity could be increased up to 12-15% on a high speed machine. It becomes very tempting to consider use of TrumpJet technology to introduce the hydrocarbon, as well as certain chemical additives, to the process.
Preface
It has recently become clear that papermaking chemistry is a nanotechnology. Successful execution depends on maximizing intermolecular contact, which requires thoroughness of mixing of chemicals and stock. In fact, complete stock homogeneity is necessary.
Accordingly, we describe the first paper manufacturing technology that embodies the ‘Six Sigma’ quality doctrine. Three successive hardware components are used. The first is a new instrument that measures specific conductance, calculates its standard deviation, and quickly quantifies the current level of stock homogeneity at the headbox: the Six Sigma Homogeneity Index instrument.
After this is accomplished, a second new instrument, Trial Zeta Data is available that measures zeta potential, specific conductance and Homogeneity Index. It is used to demonstrate the great importance of precise charge neutralization of a homogeneous stock. Trial Zeta Data is available in an on-line architecture that can monitor the headbox, and is also convertible to laboratory bench use for process chemistry development work.
The third instrument is the tried and true on-line Zeta Data System, first fielded in 1989 and now in its 6th generation. It measures specific conductance, zeta potential and drainage (specific filtration resistance) together with Homogeneity Index.
The on-line on-line Zeta Data System enables operation at the zeta potential that maximizes drainage, retention and physical properties. The Zeta Data System has been proven to operate in the mill environment without human intervention during the 5-6 week normal operating period between routine shut-downs for maintenance.
Effective application of these technologies can result in greatly improved physical properties, increased productivity and quality uniformity, and reduced cost of production, in the range $2-5,000,000/year on a modern machine. For example, because we are taking advantage of intermolecular forces for the first time, in a process where filler is used, ash can increase by 5% with greater sheet strength.
Introduction to 'Six Sigma'
The balance of this document will describe in more detail the performance properties of new instrumentation that introduces the 'Six Sigma' quality doctrine to paper manufacture, and can greatly enhance the execution of papermaking chemistry by treating it as nanotechnology. This is partly accomplished by creating stock homogeneity through reducing the standard deviation of a key parameter to a six sigma level. This is otherwise equivalent to reducing the error rate to only 3.4 per million.
In 1983 a Motorola reliability engineer concluded that if a product was defective and corrected during production, then other defects were probably being missed and later found by customers. The point is that if products were assembled completely free of defects they probably wouldn't fail customers later.
Six Sigma statistically measures and reflects true process capability, correlating to such characteristics as defects per unit and probabilities of success or failure. Most companies function at four sigma---tolerating 6,210 defects per one million opportunities.
Operating at six sigma creates an almost defect-free environment, allowing only 3.4 defects per one million opportunities. Products and services are 99.997% perfect.
It is an incredible error of omission for the paper industry to continue ignoring the ‘Six Sigma’ doctrine.
Six Sigma Stock Homogeneity
Unfortunately, we have a long ways to go. Chemists generally recognize that the chemicals are rarely mixed thoroughly with the stock. On the other hand, we increasingly hold the contradictory perception that papermaking chemistry is a nanotechnology.
Two examples are offered of six sigma chemistry significance. Most chemists have some conception of charge neutralization. In reality, the naturally occurring, repulsive negative surface charge must be precisely neutralized. This action permits van der Waals Force to play its important role of maximizing inter-molecular attraction.
"Thoroughness of mixing" understates the real need. In fact, the stock must be homogeneous in order to function efficiently on an intermolecular scale. A fair measure of stock homogeneity is obtained by evaluating specific conductance standard deviation on the six sigma scale.
We are now offering such an instrumental capability, named "Six Sigma Homogeneity Index". One immerses the working end of the hardened specific conductance sensor in the flowing stock for a few minutes, during which it logs 100 data points. Next, one dumps the data through an rs232 port to the provided handheld computer, equipped with special, analytical software. The handheld outputs a single number, the Homogeneity Index, providing a quantitative assessment of thoroughness of stock mixing.
For the past 10 years we have been measuring on-line zeta potential standard deviation as a measure of process chemistry efficiency, as reported in the January 2003 Web site Newsletter, "THOROUGHNESS OF MIXING QUANTIFIED". Two interesting and unexpected conclusions have been reached:
1. As the zeta potential standard deviation increases, so does the number of breaks.
2. Multiple headbox board machines seem to have in common generally poor runnability, resulting from poor mixing.
TRIAL ZETA DATA
After thoroughness of mixing has been improved so that it attains the six sigma standard, measuring and controlling zeta potential can do more than merely stabilize the process. It can optimize the process, maximizing the effect of functional chemical additives, increasing quality and productivity and minimizing cost.
To get some sense of what is possible, the next step is to install Trial Zeta Data at the headbox. It differs from the long established on-line Zeta Data System in that it is does not have a recirculation manifold, is not self-cleaning, does not measure drainage, outputs to a Control Room PC instead of the Distributed Control Computer itself, is lighter and more transportable, designed for temporary installation.
The Trial Zeta Data is intended to be installed for about a six-month period of time in order to put dimensions on the value of optimizing wet end chemistry. If the stock is homogeneous and the negative surface charge has been accurately neutralized, the results should be highly beneficial.
On-Line ZETA DATA SYSTEM
The most important competitive features of the on-line System are that:
1. It is self-cleaning and does not require human intervention during the 5-6 week customary period between shut-downs for maintenance.
2. It measures both zeta potential and drainage, enabling process chemistry optimization by operating the headbox at the zeta potential that maximizes drainage.
3. Finally, well over a decade of field experience, and progression through 6 generations of improving technology, enable remarkable Robustness. We have even eliminated the spare parts kit.)
Inputs to the Zeta Data System are electricity, headbox stock, compressed air, rinse water. Outputs are Homogeneity Index, zeta potential, drainage and specific conductance. The headbox stock sample used for measurement is discharged to the wire pit. The System is otherwise described on the Web site.
An important potential source of cost reduction is to use less costly fiber or filler, or another stock component that normally has an adverse effect on drainage. Increasing flow rate of the cationic chemical and the microparticle in tandem can cause a drainage increase of as much as 70%, while keeping chemistry in perfect balance. Operation at minimum stock materials cost and maximum productivity becomes a fait accompli.
John G. Penniman
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