NANOTECHNOLOGY-DRIVEN, COMPUTER-CONTROLLED, HIGHLY SUSTAINABLE PROCESS FOR MAKING PAPER AND BOARD

Abstract

In simple form the stock comprises water, cellulose fiber, pigment or filler, a cationic, charge-neutralizing chemical, and an anionic nanoparticle. The process introduces stock components in proper order, while homogenizing them towards molecular dimensions with low surface tension catalyst and vigorous mixing. The amount of catalyst is optimized for stock dispersion, and formation of an azeotrope in the dryer section. A classical nanostructure is formed. Solids exiting the press increase by as much as 6-7%; water removal energy in the dryer section is reduced in a 40-60% range. Homogeneity is maximized by controlling the standard deviation of a convenient process parameter. The system is controlled at zero zeta potential, at the specific filtration resistance level required for maximum productivity. Chemical usage is reduced by at least an order of magnitude. The process is highly sustainable.

Description

This application is a submission to take priority on the provisional patent application, number 60/991059 dated Nov. 29, 2007.

FIELD OF THE INVENTION

This invention relates to the paper making process, and more specifically, paper, tissue, towel and board.

BACKGROUND OF THE INVENTION

The paper making process can be divided into four portions, a stock preparation portion, a wet end portion, a press portion, and a dry end portion. The stock preparation portion provides equipment and working space for collecting and preparing the pulp, chemicals and other additives. The wet end portion entails formation of stock from water, pulp and chemical additives such as fillers, sizes, coloring agents, and cationic chemicals and anionic chemicals which adjust the zeta potential of the stock; control retention and drainage; and control formation of a web of stock on a wire mesh, and optimize physical properties of the finished product for its intended use. The press portion entails pressing the web of stock, supported on a continuous strip of felt, in a series of roller pairs to remove water from the web. The dry end portion entails drying the pressed web on steam-heated drier rollers to further remove water and produce a paper product. Water is recovered from the web forming step, the pressing step and the drying step, and is recycled.

A key failure that the inventor has identified in the paper making process is the lack of homogeneity of the stock. Increasing stock homogeneity in the wet end will result in enhanced process cost efficiency, and a significant increase in performance of the finished product.

Additionally, one of the problems faced in the paper making process is the removal of water during the pressing and drying steps. There is a need to increase the efficiency of water removal from the web in the last three steps, wet end, pressing and drying.

Finally, lack of computer control results in what we have termed “gratuitous chemical consumption.” Because on-line measurement is not used to control functional chemical additive usage, and because of the inherent variabilities of the wet end papermaking process, chemical usage has a strong tendency to creep up, to ensure that performance reaches at least the prescribed minimum. Excess consumption can easily reach an order of magnitude. Control of the head box zeta potential at zero millivolts can immediately eliminate this excess consumption, and additionally provide unprecedented uniformity of quality at the highest quality level and lowest raw material usage.

SUMMARY OF THE INVENTION

It has been discovered that the homogeneity of the stock can be improved; cost efficiency of chemicals can be improved; and that the efficiency of water removal from the web can be increased by the addition of a synthetic isoparaffinic petroleum hydrocarbon to the stock.

Additionally, it has been discovered that by measuring the zeta potential of the recirculating stock from the web forming step; and by adding cationic chemicals such as a charge-neutralizing chemical plus cationic functional chemicals to enhance physical properties, followed by mixing to homogeneity; and in a second step, adding a sufficient amount of anionic nanoparticle, plus any anionic functional chemicals that may be needed to improve physical properties, in amount sufficient to obtain a zeta potential of zero in the stock, increases the retention cellulose fines, fillers and of the various chemicals added to the stock; maximizes drainage of the water from the web as well as provides increased formation and strength of the formed paper.

Broadly, the present invention can be defined as a paper making process, comprising:

• • preparing a stock comprising water and pulp;
  • mixing synthetic iso-paraffinic petroleum hydrocarbon with cationic chemicals and adding to the stock, the iso-paraffin having a boiling point of 150° C. or greater,
  • in two stages, the first with cationic chemicals;
  • pre-mixing the cationic chemicals and hydrocarbon;

applying high positive displacement pump pressure, up to 5000 Ibs per square inch or more;

• • circulating the mixture under high pressure through a high shear mixer, preferably of an ultrasonic nature;
  • injecting the ultrasonicated mixture into the stock at a 90 degree angle to the direction of wet end machine flow;
  • further mixing the ultrasonicated mixture with the stock, using in-line static mixers well known to those skilled in the art;
  • measuring the specific conductance of the flowing stock, calculating and outputting the standard deviation as a function of homogeneity;
  • adjusting the upstream parameters such as positive displacement pump pressure, ultrasonication energy and chemical concentration, respectively, so as to maintain homogeneity at an appropriate level;
  • followed by a second stage of iso-paraffin mixed with anionic chemicals which is a mirror image of the first stage, except that after an appropriate level of homogeneity is reached on start-up, the flow rates of cationic and anionic chemicals are balanced to obtain zero zeta potential.

The remainder of the process comprises:

• • forming a web of stock on a wire mesh;
  • pressing the web of stock to remove water;
  • and drying the pressed web of stock to form paper.

A unique advantage of this aspect of the invention is that productivity can be maximized by increasing the flow rates of both the cationic and anionic components in tandem, while maintaining zero zeta potential. Maximum productivity may thereby be achieved, subject only to mechanical limitations such as machine speed.

Preferably, the synthetic petroleum iso-paraffinic hydrocarbon is one or more iso-paraffins selected from the group consisting of ISOPAR G, ISOPAR H, ISOPAR K, ISOPAR L, ISOPAR M, and ISOPAR V. Each iso-paraffin is a fluid at room temperature and pressure.

The addition of iso-paraffin to the stock is accomplished by adding the isoparaffin to the stock on the wet end, prior to web formation. It is preferred that the iso-paraffin is added to the stock prior to formation of the web and more preferably the iso-paraffin is added to the stock as a mixture with the conventional chemical additives and homogenized down to molecular dimensions with high shear mixing such as ultrasonic energy; in the first instance combined with cationic chemicals, and in the second instance, after homogeneity is achieved, with anionic chemicals, followed again by homogenizing with ultrasonic energy.

It is preferred that high shear mixing, such as that available from an ultrasonic generator, is used to disperse the mixture of iso-paraffinic hydrocarbon and chemicals. Alternatively, the dispersion of iso-paraffin is sprayed onto the web as it moves to the presses; and the energy of pressing is used to generate the necessary shear force to obtain molecular dispersion and homogeneity. This option, however, decisively the maintenance of zeta potential at zero millivolts, and is otherwise uncontrollable.

Preferably, the addition of the iso-paraffin comprises:

• • mixing iso-paraffin and one or more additives selected from the group consisting of cationic process additives, such as charge-neutralizing chemicals; and cationic-compatible functional additives such as fillers, sizes, and coloring agents, using a high shear mixer such as an ultrasonic generator to form a homogeneous mixture; and in a succeeding step
  • mixing iso-paraffin and one or more additives selected from the group consisting of anionic process additives, such as the nanoparticles smectite (termed “bentonite” by the paper industry) or such as colloidal silica;
  • followed by anionic-compatible functional additives such as optical brightening agents;
  • followed by homogenization of the anionic components; and finally adding the mixture to the stock prior to formation of a homogeneous web of stock on the wire mesh.

The low surface tension iso-paraffin serves two purposes. On the wet end, in low concentration levels, from about 0.1 to 2% of stock, it efficiently facilitates the dispersion of chemical aggregates into molecular dimensions. The precise amount of iso-paraffin that is used for chemical dispersion purposes depends upon the continuous reading of a surface tension sensor of the currently prevailing conditions, and is the minimum amount required to provide the lowest surface tension This greatly enhances the cost-efficiency of the chemicals, reducing chemical usage by one or 2 orders of magnitude. It also reduces water re-wetting in the press section, increasing press section water removal efficiency significantly.

The iso-paraffin azeotropes efficiently with water. When added at levels on the wet end, up to about 10% of stock, it greatly reduces the energy required for drying. The total energy cost reduction can exceed 50%.

The process of the present invention is more preferably implemented using the following steps:

• • determining the zeta potential of recirculated stock from the downstream leg of the headbox; and adding both cationic chemicals and anionic chemicals to the stock in separate increments, each also comprising the addition of iso-paraffin, and mixing each to homogeneity using ultrasonic energy, prior to injection into the stock stream under high pressure at a 90 degree angle to stock flow, followed by static in-line mixing; and followed in turn by sensing the specific conductance, or any other appropriate physical property parameter, calculating and outputting the standard deviation as a function of homogeneity; and automatically by computer, adjusting upstream conditions such as injection pressure and ultrasonication energy or high shear energy and chemical concentration, to maintain the most appropriate level of homogeneity; and finally making a closed loop computer controlled adjustment to obtain a zeta potential of zero.

The addition of the cationic and anionic chemicals must be done at separate times and at two separate addition points to allow them to act on the stock independently of one another, and not to prematurely react with each other. They are thereby enabled to form a co-valent lattice-like nanoflocculation structure which maximizes filler and fiber retention while permitting maximum water removal, optimum formation, maximum strength and physical properties.

Preferably, the cationic chemicals are added simultaneously with the isoparaffin to the stock as the first addition; and after attaining homogeneity the anionic chemicals are also simultaneously added to the stock with the second addition of iso-paraffin.

The present invention further entails a novel stock composition comprising: water, pulp, and an iso-paraffin having a boiling point of 150° C. or greater, and a surface tension below 30 dynes/cm².

The stock can further include process chemicals that comprise the process termed microparticulate by the industry. It typically includes a charge-neutralizing cationic component plus a nanoparticle; and whatever functional chemical additives are conventionally used to realize necessary product performance objectives, including one or more conventional additives selected from the group consisting of fillers, sizes, coloring agents, strength additives, optical brightening agents, cationic chemicals and anionic chemicals.

Nanotechnology

What magic is bringing forth these miracles? A nanometer, one billionth of a meter, is the size measure of nanotechnology. It is the most precise (and perhaps the least useful) characterization; not dissimilar from using billions and trillions of dollars to discuss economics with those whose purchases are principally at the food market and gas station.

The reason is that, as particles get smaller, their properties change. Nanoparticles are typically not described by size, but by surface area. For example, the colloidal silica used at the wet end has a surface area of about 600 m2/gram. Additionally, the smaller they are, the more negative, and (for quite different reasons) the more attracted to each other.

Please refer to FIG. 1, the graph entitled “Computer Control of Papermaking Nanotechnology”

BRIEF DESCRIPTION OF THE DRAWING

The stock is a bleached hardwood Kraft (BHK) with precipitated calcium carbonate (PCC) as filler. The cationic chemical component is added first, mixed to homogeneity, and followed by the negative nanoparticle which is also mixed to homogeneity.

The nanotechnology papermaking example depicted is represented by the line furthest to the right: cationic starch and colloidal silica. The two chemicals interact electrostatically to form a lattice work which functions to simultaneously increase both retention and water removal, or “drainage”.

It is important to know that this particular nanoflocculation lattice work represents the most efficient papermaking means so far discovered to simultaneously maximize retention and water removal on the one hand, and formation on the other. This is of great significance because retention and water removal are paramount process objectives, and good formation is indispensable to surface smoothness and strength.

To illustrate the significance of zero zeta potential, two additional lines are plotted. The orange line is polyethylenimine (PEI). It shows a sharp charge reversal at zero zeta potential, towards re-dispersion, which results from its highly cationic nature, and demonstrates the importance of maintaining zero zeta potential in order to maximize retention, water removal and strength.

The blue line is a monomeric cationic starch which, because of its greatly reduced cationicity, manifests a more gentle inclination change at charge reversal.

The red line represents an optimum nanotechnology papermaking system, exhibiting the best retention and water removal. The line extends to zero zeta potential.

Maximum retention and drainage are simultaneously achieved by increasing both feed rates in balance, for example, that is both the cationic starch and the colloidal silica, to maintain zero zeta potential, until the SFR is maximized. This action also maximizes productivity.

Among the many benefits realizable by closed loop computer control is a calculation and output of real-time cost of each real to the penny, and the continuous attainment of minimum cost.

• • forming a web of stock on a wire mesh;
  • pressing the web of stock to remove water;
  • and drying the pressed web of stock to form paper.

DEFINITIONS

Papermaking carries its own vernacular, and it is appropriate to offer a few definitions for some of the more esoteric expressions:

“Process Chemical Additives” are chemicals employed to manifest or improve the papermaking process. Examples are retention of fines and/or fillers, drainage on the wire, water removal in the press section and/or dryer section, runnability, productivity, up-time, etc.

“Functional Chemical Additives” are chemicals employed to manifest or improve physical properties of the finished product. Examples include strength, sizing, printability, brightness, opacity, color, etc.

“Zeta Potential” refers to the on-line measurement of electrostatic charge on the stock particulates, as assessed by the streaming potential process, expressed in millivolts. Operating the headbox at zero zeta potential with the nanoparticulate process, for example cationic starch and colloidal silica, maximizes retention of fines and fillers; creates a nanoflocculation which enables a stronger, thinner product; and an exceptionally smooth, uniform printing surface.

The alternative to zeta potential control, and the current industry practice, is to use a high molecular weight “retention and drainage aid” which creates macroflocculation, poor formation, and degraded strength properties.

“Homogeneity” is assessed by measuring the standard deviation of an easily measured parameter such as conductance; or otherwise easily available parameter such as zeta potential. The lower the standard deviation, the greater is the homogeneity. Inspiration for this approach came to the inventor from the well-known 6 sigma technology for quality control.

These and other aspects of the present invention may be more fully understood by reference to the following description:

Introduction

ISOPAR is a brand name for different grades of isoparaffin, a high purity isoparaffinic solvent which has a narrow boiling range. ISOPAR solvents are available from ExxonMobil and are generally sold under various letter designations. In the present invention, the boiling of the iso-paraffin should be 150° C. or greater. This means, that ISOPAR G, H, K, L, M, and V are suitable in the present invention. Such iso-paraffins are also available under the name ISOZOR provided by NIHON Petrochemical and under the trade name IP SOLVENT from Idemitsu Petrochemical. These hydrocarbon chemicals comprise mainly aliphatic hydrocarbons, virtually no aromatics, and have surface tensions in the range of 24 to 27 dynes/cm² when measured at 25° C. Such hydrocarbons are considered water insoluble.

Sizes typically include hydrophobic organic molecules such as rosin, alkenylsuccinic-anhydride (ASA), and alkyl-ketene-dimer (AKD). Typically, the amount of size added to the stock is in the range of 0.03 to 3 weight % based on the weight of the fiber.

Coloring agents include various dyes or pigments used to either improve the color of the finished paper or to change the color of the finished paper, to increase apparent whiteness or to raise the level of brightness.

Cationic chemicals added to affect the zeta potential of the stock, include conventional cationic chemicals used in the paper industry such as cationic starches, cationic functional chemicals such as alkyl-ketene dimer (AKD) and cationic scavengers such as poly-diallyl-dimethyl-ammonium-chloride (polydadmac) and polyamines.

Anionic chemicals added to the stock include conventional anionic nanoparticles used in the paper industry such as colloidal silica and bentonite. The amount of anionic chemicals added to the stock is sufficient to bring the zeta potential to zero.

The use of cationic and anionic chemicals to change the zeta potential is disclosed in U.S. Pat. No. 5,373,229, the contents of which are incorporated herein by reference. The '229 patent discloses an apparatus for measuring the zeta potential and is used in the present invention to measure the zeta potential of the recirculating stock from the head box.

Suitably, the zeta potential sensor measures the zeta potential and transfers the information to a computer which then controls the addition of cationic and anionic chemicals. Zeta potential is controlled at zero millivolts in order to maximize quality, process efficiency and cost-efficiency of chemical usage.

Retention and Water Removal

The process of the present invention creates a lattice-like nano structure that enables simultaneous maximizing of retention and formation, while simultaneously facilitating water removal.

Maximum process and physical property parameters are achieved by precisely neutralizing the repulsive negative surface charge, a key factor in maximizing productivity.

Papermaking Nanotechnology

The energy of conventional mixing is not sufficient to accomplish stock homogeneity on a modern high speed paper making machine. The present invention provides for homogeneity, and in turn, allows for reduction of chemical usage on a magnitude of 1 to 2 orders. The benefit is very large. For example, on a large modern high-speed machine that consume $3 per ton of a particular chemical or $600K per year, the chemical cost can be reduced to between $60K and $6K per year; the saving is more than $500K.

It has been found that iso-paraffin is removed from the web in the drying section. The iso-paraffin evaporated from the web in the dryer is collected in a conventional manner using technology well known to those skilled in the art.

It has been found that an increased water removal of 6 to 7% was achieved in the pressing section when iso-paraffin was added to the stock. This in turn reduces the energy needed in the drying section by 24 to 28%.

Furthermore, it has been found that water removal in the drying section is improved by as much as 20% because of the presence of iso-paraffin. In fact, a total energy savings of 50% can be obtained with the use of iso-paraffin in the stock.

Iso-paraffin is also present in the water recovered from press section. This is likewise recovered and recycled. Conventional equipment operating in the conventional manner is used to recover the iso-paraffin from the water obtained from the press section.

It has been found that the amount of iso-paraffin that is in the paper is so low as to be analytically undetectable, or less than 5 ppm.

The nanotechnology-driven process accomplishes stock homogeneity by use of a water insoluble, low surface tension, iso-paraffin hydrocarbon catalyst, preferably with a boiling range well above 150° C., and a surface tension below 30 dynes/cm². There are major collateral benefits. See U.S. Pat. No. 4,684,440, issued to the present inventor.

The process creates a nano-structure on the wire that enables simultaneous maximizing of retention and formation, while facilitating water removal. Maximum process and physical property parameters are achieved by precisely neutralizing the repulsive negative surface charge, a key factor in maximizing productivity.

The energy of conventional mixing is not sufficient to accomplish stock homogeneity on a modern, high-speed machine, nor does the industry practice control of the electrostatic surface charge, or zeta potential.

Two conditions must simultaneously apply:

• 1. The spreading coefficient must be increased by reducing the surface tension from 72 dynes/cm² down below 30 dynes/cm².
• 2. The addition of ionically polar molecules must be accompanied by computer control of the ultimate zeta potential at zero mV.

Chemical usage, both of process and functional chemical additives, is typically reduced by 1 or 2 orders of magnitude. The benefit is very large: on a large, modern, high speed machine that consumes, for example, 3$/ton of a particular chemical, or $600K/year, the chemical cost can be reduced to between $60K and $6K/year, saving more than $500K.

The first step in the process is to add the catalyst, premixed with chemicals, at the wet end, preferably with a positive displacement pump, an ultrasonic generator and an in-line static mixer, to homogenize the stock. The catalyst rapidly diffuses and circulates throughout the entire white water system.

Food-Related Applications

The iso-paraffin catalyst is permitted for certain direct food applications under FDA Regulation CFR 21 172.882 and 172.884, and for certain indirect food applications under FDA Regulations 21 CFR 178.3530 and 178.3650. It is also permitted for use under FDA Regulations 40 CFR 180.1001 (d) and (e).

Functional and Process Chemicals “Cationic”, or positively charged, process improvement and functional chemicals are added to the stock via a positive displacement pump and a high shear mixer until the entire system becomes positively charged, typically in a zeta potential range of +5 to +10 mV zeta potential. See U.S. Pat. No. 5,373,229, issued to the present inventor.

A negatively charged or “anionic” nanoparticle is introduced downstream, via a second positive displacement pump and high shear mixer; in amount sufficient to reach a final charge of precisely zero zeta potential. This enables maximum retention, drainage, formation and strength to be simultaneously attained.

Following each of the two chemical addition points, a specific conductance sensor is installed. The computer calculates standard deviation of the two conductance sensor outputs as a function of thoroughness of mixing, or homogeneity. Chemical addition, booster pump and high shear mixing system parameters are then automatically adjusted by the computer to maximize homogeneity.

The inventor did research on many machines, measuring zeta potential standard deviation as a function of thoroughness of mixing, or homogeneity. Machines with poor runnability, characterized by many breaks and poor runnability, had zeta potential standard deviations in the very high range of 4 to 5 mV. They were often plagued by a common white water system shared with other machines, multiple head boxes, or producing coated board made with recycle fiber.

On the other hand, a slow 1920′s machine had a standard deviation in the range 0.5 to 1 mV, accompanied by excellent runnability.

Conventional practice has six decisive flaws:

• • It fails the task of mixing to homogeneity
  • It does not offer a means of measuring homogeneity.
  • It typically uses a “retention aid”, intended to create macroflocculation.
  • In contrast to the present invention, this usage sharply degrades formation and strength properties, at a significantly higher cost.
  • It lacks the capability of appropriately measuring and controlling electrostatic surface charge, or zeta potential.
  • It fails to control the process by computer, a task essential to both process efficiency and quality uniformity.
  • Finally, it fails to reduce the surface tension of the water, thereby greatly increasing the amount of energy required for its removal to specified finished product solids content.

Zeta Potential

In the new method, an on-line zeta potential sensor is installed on the downstream re-circulation leg of the head box. Zeta potential, specific filtration resistance (SFR) or drainage, specific conductance and temperature are measured and out-put to the computer for process control purposes.

Chemical addition rates are computer controlled. The process is optimized and at maximum efficiency when the total amount of process chemicals is controlled at the optimum level of specific filtration resistance (SFR). See U.S. Pat. No. 5,365,775, issued to the present inventor. FIGS. 7 and 9 show the typically sharp, optimum peak in SFR on addition of a cationic, charge-neutralizing chemical, followed (after thorough mixing) by an anionic nanoparticle.

Early laboratory investigations with a zeta potential sensor indicated that the conventional process was optimized at a low, positive zeta potential, typically in the range of +2 to +6 mV, raising the question as to why it is not zero millivolts. The reason is that, in the conventional practice, the charge-neutralizing chemicals are initially dispersed as aggregates and it takes time for them to unbundle. The phenomenon is familiar to the industry as “cationic decay”.

The reason why there is such a broad zeta potential range is that, at the early date our lab experiments were executed, the time between zeta potential measurement and making of hand sheets varied substantially, because we had no idea that it was a major influential factor.

The new method disperses the chemicals towards monomolecular scale, with three benefits: cationic decay and its time dependence are completely eliminated; chemicals become far more effective, as reflected in the fact that the amount required can be reduced by one or two orders of magnitude; product quality and cost-efficiency are maximized.

Inefficiency of the conventional process was illustrated on a coated free sheet (CFS) machine. The zeta potential was monitored continuously for a period of months, while the level of alkyl-ketene-dimer (AKD) sizing was measured on a sample removed from the end of each reel. The Correlation Coefficient of zeta potential with the AKD sizing level was high, at 0.71. However, the absolute level of sizing was about 10× greater than necessary. The data clearly indicates that lack of a means of appropriate control of AKD feed rate invites use of a costly excess of AKD, to ensure that a satisfactory minimum level of sizing is achieved.

Consider that the amount of AKD sizing approximates $3/ton of product, or $600K/year on the CFS machine on which we did the experiment. Computer control of zeta potential would decrease AKD purchase cost to about $60K/year. Increasing mixing efficiency to obtain homogeneity would further reduce AKD cost to at least $6K/year, and perhaps ultimately reach as low as $600 annually.

The annual cost difference between $600K and $6000 (or perhaps $600) speaks volumes about the poor efficiency of the conventional process. Internal size is the chemical chose for the illustration of increased cost efficiency because the sizing measurement is easily quantifiable in the laboratory. The principle, however, applies equally to all process and functional chemical additives.

The current, widely used, conventional means of charge measurement is the off-line assessment of cationic demand, using a special instrument. The cationic demand of white water is measured, with the objective of reaching and maintaining a small negative charge so as to avoid over-cationization. Its exceptionally poor effectiveness was revealed in the following described experiment.

An on-line zeta potential sensor was installed at the head box of a large specialty groundwood machine, and the zeta potential was continuously monitored for a period of one year. On each working day, a cationic demand measurement was made in the lab by the chemical supplier, and a notation simultaneously made of the current on-line zeta potential measurement. At the end of the year, a Correlation Coefficient calculation of zeta potential vs. cationic demand produced the exceptionally low value of 0.17.

This experiment, and others with similar results, provides compelling evidence that the cationic demand measurement, in global use by the industry, is not repeatable. Even if it were repeatable, the objective of leaving a residual negative charge is totally incompatible with the tenets of nanoscience.

Use of cationic demand for process control has the benefit of giving mill personnel a warm, fuzzy feeling that something useful is going on. By any other criterion, it is counter-productive.

The efficiency of the conventional process, on a modern machine, is poor.

Special Properties

We have described a nanotechnology-driven, computer controlled process that maximizes productivity, quality and cost-efficiency. It can serve as the ideal platform for realizing any reasonably specified special properties, for example, stiffness.

The nano sheet is inherently thinner and stronger. It can be increased in bulk to increase stiffness. For example, feed rates of both the cationic charge-neutralizing chemical and the anionic nanoparticle can be increased in tandem, under computer control, while holding the net charge at zero zeta potential.

The result will be a bulkier, stiffer sheet.

Strength can be increased by adding a small amount of natural gum, plus whatever amount of cationic starch is appropriate to the task.

Water Removal

Research utilizing the variable speed pilot plant of a felt manufacturer, Albany International of Albany, N.Y., revealed that hydrodynamics play an important role in operation of the press section. At slow speed, the inventor's catalyst had little effect. However, as the speed increased, water re-wetting was reduced. The result, as machine speed increased, was a progressive consistency increase up to 6 or 7% out of the press section.

The amount of catalyst that exits the machine with the product is so low as to be undetectable, less than Sppm. Surface tension is monitored on-line, and catalyst addition is adjusted by software under computer control, to maintain a minimum surface tension value, ensuring cost effectiveness. Use of the isoparafine hydrocarbon will require effective recovery systems to eliminate environmental concerns. Addition upstream of, or in the press section will result in the hydrocarbon coming out in press whitewater, vacuum pump discharges, and dryer hood exhaust. Proven technology for removing hydrocarbon is available for all three areas.

Iso-paraffin hydrocarbon can be removed from vacuum pump and hood exhaust air flows with an activated carbon system. Hydrocarbon laden air flows through a filter/cooler before entering a blower, which forces the hydrocarbon laden air stream through an adsorber vessel containing activated carbon. Hydrocarbon contained in the processed air is adsorbed by the activated carbon and clean air released to atmosphere. When an adsorber vessel becomes saturated with hydrocarbon, the air stream is transferred to a previously regenerated adsorber. Regeneration of the saturated adsorber than proceeds by using steam in a direct contact thermal desorption process or by replacing the activated carbon.

A minimum of two adsorbers is required to provide continuous operation. Desorbed hydrocarbon can be condensed and decanted for return to the process and reused. Recovery efficiencies of 99% are common. The hydrocarbon not recovered in the charcoal is replaced.

Water and iso-paraffin hydrocarbon are immiscible liquids, and form a constant boiling azeotrope, with a lower boiling point than either pure component. The iso-paraffine is separated in the dryer by employing the most cost-effective of several engineering solutions, depending on the operational scale: distillation, fractional distillation or use of a rotary evaporator.

The two components volatilize sequentially, hydrocarbon first, and create two liquid layers on condensation. The azeotrope is easily broken by using a liquid-liquid separator (a decanter) to separate the two liquid layers.

Increased water removal occurs in three different ways:

• 1. At the wet end, it is enhanced by formation of an open nanoparticulate structure which facilitates water removal on the wire.
• 2. In the press section, it decreases water re-wetting on high speed machines. Press section water removal efficiency is increased by 6-7%. Since each 1% increase in consistency translates to 4% in the dryer, the total press contribution can be as much as 24-28% on the dry end.
• 3. In the dryer section, the attractive influence of hydrogen bonding is greatly decreased, so that much less energy is required to volatilize water. First section dryer efficiency is increased by as much as 20%, according to differential scanning calorimetry and thermogravimetric studies.

Sum total of energy saving from the three sources approaches 50% at low hydrocarbon levels. It can be increased by mixing up to 10% or more hydrocarbon, so as to increase the amount available to azeotrope.

Fire Safety

When asked about fire safety, the supplier of iso-paraffin hydrocarbon requested extensive data on the machine in question, and its operation. The analysis that followed required a total of 7 pages, too extensive to fully report here. Bottom line is that the exposure did not exceed 5% of the LEL, lower explosive limit.

The iso-paraffinic hydrocarbon used in our research was Isopar G and the upper homologues produced by ExxonMobil. The lower homologues are less desirable because of increased volatility and therefore flammability.

The particular hydrocarbon is extensively consumed in the copy process: millions of copy machines, barge loads of product, and no reported incidents.

Sustainability

A leading retailer has embarked on a sustainability program, initiated on Feb. 1, 2008. Instead of purchasing packaging materials at the lowest cost, Wal-Mart is applying quite a different set of sustainability metrics, weighted as follows:

• 1. 15% is based on GHG/CO2 per ton of Production
• 2. 15% is based on Material Value
• 3. 15% is based on Product/Package Ratio
• 4. 15% is based on Cube Utilization
• 5. 10% is based on Transportation
• 6. 10% is based on Recycled Content
• 7. 10% is based on Recovery Value
• 8. 5% is based on Renewable Energy
• 9. 5% is based on Innovation

The new process goes much further than the conventional process in meeting these criteria. The author anticipates that the Wal-Mart initiative will lead to a sea change in the manufacture of paper and board. This is the first time that a complex, definitive set of specifications has been imposed on the industry.

Recognition that the manufacture of paper and board is a scientific task, instead of an art form, is long over-due.

Re-cycling of the nanotechnology paper is easily accomplished by adding an increment of the cationic charge-neutralizing component used to create the nanostructure. This breaks the lattice-work down into pieces as small as molecules, which can be added as broke to fresh stock and easily reincorporated as nano paper.

SUMMARY

Implementation of the new method entails first achieving stock homogeneity by dispersing chemicals to the molecular level. Chemical usage can then be reduced by 1 or 2 orders of magnitude. Precise neutralization of the repulsive negative charge is a key step in activating and maximizing powerful intermolecular attractive forces; it can enable an increased fine paper loading at a (counter-intuitive) higher strength than the lower loading level.

It will produce the highest possible quality product from the available stock, at the highest level of productivity and lowest feasible cost; with exceptional uniformity under computer control.

The greatly reduced need for both chemicals and water removal energy, and appropriate control of the production process, leads to a thinner, stronger product, accompanied by decreased need for landfill, resulting in higher sustainability Since the fibers can be unlocked by adding a cationic charge-neutralizing component that re-disperses them, re-cycling of fibers can be accomplished many more times than with the conventional process, another major sustainability factor.

The novel nanotechnology-driven process first homogenizes the stock towards molecular dimensions with a small amount of low surface tension, water insoluble, catalyst. The catalyst remains, circulating in the white water system. It is introduced, together with process and functional chemicals by a total of two booster pumps, the first for cationic chemicals and the catalyst, and the second for anionic chemicals, including an anionic nanoparticle. A classical microparticle nanostructure is formed with commonly available, cost-effective chemicals such as cationic starch and colloidal silica. Zeta potential and specific filtration resistance (SFR) are also sensed, and the zeta potential is controlled at zero, at the total nanostructure level, (or SFR level) required for maximum productivity. The amount of catalyst is optimized by computer, with guidance from an on-line surface tension sensor, at the lowest achievable surface tension. It increases water removal on the wire; reduces press section water re-wetting on a modern, high speed machine, increasing consistency exiting the press section by as much as 6-7%; and reduces water removal energy in the dryer section in the 20% range. Total energy saving from the three sources, at a hydrocarbon level up to 2%, amounts to about a 50% reduction in energy usage. Energy saving increases at higher hydrocarbon levels because of thee mass action azeotropic efficiency increase.

Homogeneity is maximized, first by measuring it as a function of the standard deviation of data produced by two specific conductance sensors, one installed immediately downstream of each positive displacement pump, high shear mixer and in-line static mixer; and secondly by making computerized adjustments to improve it. The finished product is thinner and stronger. Because the chemicals are reduced toward molecular dimensions by a low surface tension catalyst, chemical usage is reduced by one to two orders of magnitude. Actual product and process costs are calculated on a running basis, so that the cost of each reel is available as it is produced. The nanotechnology-driven process is highly sustainable.

The invention can be defined in the following items:

• Item 1. A microparticulate process in which a low functionality cationic chemical such as cationic starch is added to the negatively charged cellulose fibers in excess amount, typically to a zeta potential of +5 or +10 mV. This is followed by addition of a nanoparticle such as colloidal silica until the final zeta potential is precisely zero.
• Item 2. A process for manufacturing paper and board that catalytically disperses the chemicals, fibers and fillers to obtain a homogeneous stock, down to individual molecules of chemicals and particles of fiber and filler. Chemical addition points are supported by a positive displacement pump followed by a high shear mixer, preferably a source of ultrasonic energy; inline static mixers; and homogeneity sensors, under computer control. The first chemical addition point injects a dilute solution or dispersion of cationic functional and charge-neutralizing chemicals, plus catalyst. The second injects a dilute solution or dispersion of an anionic nanoparticle plus anionic functional chemical additives if needed. Injection is at high speed, vertical to the flow of stock through the main stock pipe. A nano-structure is formed, maintained at a zeta potential of zero millivolts electrostatic charge, in order to enable maximizing both process and physical property parameters, while minimizing cost. The quality of homogeneity, or thoroughness of mixing, is determined by use of a sensor to measure the specific conductance, followed by calculation of its standard deviation. A high level of sustainability results from a significant reduction in chemical usage, reduced energy usage in the press and dryer sections, increased strength at a decreased basis weight which translates to greater recyclability of fibers, ease of re-processing broke, and decreased landfill. Cost savings on a high speed machine can range well into 7 dollar figures annually.
• Item 3. The method of item 1 in which homogeneity of stock is obtained by effective dispersion use of a small amount of iso-paraffin, low surface tension hydrocarbon which acts as a catalyst to achieve chemical and particulate homogeneity down to a molecular scale and greatly facilitate water removal in the press and dryer sections. A larger amount of catalyst is required, and its function in the dryer section is to azeotrope with the water, reducing the heat of evaporation; and displacing water as the adsorbed liquid, thereby reducing the hydrogen bonding which normally requires an enormous amount of energy to overcome.
• Item 4. The method of item 1 in which an on-line surface tension sensor is used to enable process adjustments in order to hold surface tension at the minimum and most efficient value.
• Item 5. The method of item 1 in which standard deviation of an easily measured process parameter, such as specific conductance, is used to assess thoroughness of mixing, or stock homogeneity, so that adjustments to the positive displacement pump pressure and/or high shear mixer energy input and/or chemical additive concentration, can be made to improve it.
• Item 6. The method of item 1 in which the iso-paraffin hydrocarbon is collected for re-use.

Claims

1. A method for papermaking, comprising:

preparing a stock of water and pulp;

adding iso-paraffin to the stock, the iso-paraffin having a boiling point of 150° C. or greater, and a surface tension below 30 dynes/cm2.

forming a web of stock on a wire mesh;

pressing the web of stock including the iso-paraffin to remove water; and

drying the pressed web of stock to form paper.

2. The method of claim 1, wherein

the iso-paraffin is one or more iso-paraffins selected from the group consisting of ISOPAR G, ISOPAR H, ISOPAR L. ISOPAR M and ISOPAR V; produced by Exxon-Mobil.

3. The method of claim 1, wherein

the addition of iso-paraffin to the stock is performed before the formation of the web.

4. The method of claim 1, wherein

the addition of iso-paraffin to the stock is performed on the web of the stock before the pressing of the web.

5. The method of claim 3, wherein the addition of iso-paraffin further comprises:

forming a mixture of iso-paraffin and one or more additives selected from the group consisting of fillers, sizes, coloring agents, cationic chemicals, and anionic chemicals.

6. The method of claim 5, wherein

the formation of the mixture is performed by a high shear mixer, preferably utilizing ultrasonic energy.

7. The method of claim 5, wherein

an in-line static mixer is employed to mix the chemicals homogeneously with the stock.

8. The method of claim 7, wherein

a function of homogeneity is measured by first, for example, measuring the specific conductance, then calculating and outputting its standard deviation, and using this value to adjust the upstream parameters such as mixing energy input and chemical concentration, to maximize homogeneity by minimizing the amount of standard deviation.

9. The method of claim 4, wherein the addition of iso-paraffin is performed by spraying iso-paraffin on the web.

10. The method of claim 7, wherein the dispersion of iso-paraffin is created by mixing chemicals and iso-paraffin in a high shear mixer, preferably with ultrasonic energy.

11. The method of claim 1, wherein the iso-paraffin is present in the stock in an amount of about 0.05 to 10% by weight stock.

12. The method of claim 1, wherein the amount of iso-paraffin is about 0.5 to 2% by weight stock.

13. The method of claim 1 further comprising:

adding cationic chemicals and anionic chemicals to the stock prior to forming a web of the stock, wherein the anionic chemical addition point is sufficiently downstream of the cationic chemicals that stock homogeneity is attained prior to reaching the anionic chemical addition point; determining the zeta potential of recirculating stock from a headbox of a paper making apparatus.

14. The method of claim 13 wherein the cationic chemicals are added simultaneously with adding the iso-paraffin to the stock with appropriate cationic functional chemical additives mixed thoroughly; and the anionic chemicals are likewise added simultaneously, preferably with an additional increment of iso-paraffin in the stock, with appropriate anionic chemical additives and mixed thoroughly; and

the result is an increase in the functional chemical additive performance of at least one order of magnitude.

15. The method of claim 14 comprising controlling the zeta potential of stock recirculating from a headbox at zero millivolts by use of a computer programmed to balance the feed rates of cationic and anionic process chemicals to attain and maintain a continuous headbox stock value of zero millivolts.

16. The method of claim 15 in which the computer is programmed to maximize flow rates of both cationic and anionic process chemicals while maintaining zero zeta potential in the head box, thereby maximizing productivity.

17. A stock used for making paper comprising:

water, pulp and iso-paraffin preferably having a boiling point of 150° C. or greater and a surface tension below 30 dynes/cm2.

18. The stock of claim 14 further comprising:

one or more additives selected from the group consisting of fillers, sizes, coloring agents, cationic and anionic chemicals, including functional chemical additives and process chemical additives.

19. The stock of claim 16 wherein

the iso-paraffin is one or more iso-paraffins selected from the group consisting of ISOPAR G, ISOPAR H, ISOPAR L. ISOPAR M and ISOPAR V.

20. The stock of claim 16 wherein the iso-paraffin is present in an amount of about 0.05 to 2% by weight stock, and serves to improve water removal on the wet end and in the press section, thereby increasing energy efficiency.

21. The stock of claim 16 wherein the iso-paraffin is present in an amount of about 2.0 to 20% by weight of stock, and serves additionally to greatly improve dryer energy efficiency, reducing it by upwards of 50%.

22. The finished product of claim 16 which is re-processed as “broke”, wherein the addition of a cationic charge neutralizing chemical, such as a polydadmac, disperses the product particles to the original primary composition, such as fibers, fillers and fines, making the broke easy to re-process and the product highly sustainable.