Background In the paper industry there are increasing problems with deposition of organic contaminants. Contaminants may originate from the tree itself as extractives that have not been removed during the preparation of the fiber furnish used in the paper making process. Alternatively, the contaminants enter the process through the use of recycled paper. Such paper may contain substances such as glues, lattices. waxes, adhesives and other depositable material added to the paper to improve its properties or make it suitable for its intended use.

One of the most important reasons for the increased tendency for deposit formation is the increased recycling of whitewater. This is done to reduce the quantity of effluent discharged into the environment. A second reason is that, in order to preserve natural resources, the degree of recycling of paper is increasing. Recycled paper contains a multitude of potentially depositable substances, generally called stickies. For simplicity, the term"stickies"as used in this application is also meant to include natural wood resins A third reason is that higher system temperatures are being used. Higher temperatures tend to reduce the viscosity, hence increase the adhesiveness, of pitch/stickies.

Deposition can take place in many different locations of the paper making process. Practically any surface may accumulate a deposit, but some surfaces are more prone to deposition than others. Examples of common areas of deposition are: screens in the screen room after the pulp digester, oxygen stage in the bleach section of a pulp mill, machine chest, approach pipe leading the head box, head box, forming wire, press rolls, press felts, drying cylinders and dryer fabrics.

Deposition is a complex phenomenon where a multitude of parameters determines the extent of deposition. Attempts have been made to rationalize experience

to a cohesive theory. However, effective organic deposition control is much more based on empirical experience than scientific data.

Because linkages between cause and effect in a paper making system are not well understood, it is particularly difficult to rationalize a change in one part of the paper making process to an effect in a different part of the process. For this reason it is customary to concentrate on one part of the process and attempt to deal with this as a separate problem rather than take an overall system perspective in defining an appropriate treatment program.

Thus, there are methods for prevention of stickies deposits in the wet end of a papermaking machine, but no discussion has been found of the relation between formation of wet end deposits and deposits at subsequent stages of the paper making process. Similarly, methods for treating stickies deposits in the dryer end do not address stickies in the wet end farther up the line.

Numerous approaches have been proposed for paper machine organic deposition control. One method to prevent deposition on the paper machine is based on removal of contaminants in the furnish preparation. Screening methods and washing methods are used for this purpose. Sometimes these are also enhanced by the addition of a chemical additive. Such an additive could improve the extraction by removing entrapped air.

Other methods involve the use of a surfactant to increase the separation of the contaminant from the fiber.

Another method, commonly referred to as de-inking, is based on the principle of contaminant removal in the preparation of the furnish for the paper production.

Yet another method is to use a polymer added to a pulp composition before sheet formation for removal of contaminants with the paper. This is particularly preferred when the machine is operated with a high degree of water reuse. Such methods are not always used for retention of contaminants only, but may well also be used for retention of fines, fillers and paper additives such as sizing agents. Many different polymers are used in this regard. Cationic polymers used include condensation polymers from epichlorohydrin and amines (as taught in, e. g., U. S. Patent No. 5, 626, 720 and Canadian Patent No. 1,150,914, the disclosures of which are incorporated by reference in their entireties); condensation polymers formed by reacting formaldehyde

with a nitrogen-containing compound, such as dicyandiamide or another material that provides cationicity to the final product (as taught in, e. g., U. S. Patent No. 3, the disclosure of which is incorporated by reference in its entirety); cationic starches that are specifically designed to remove contaminants (as taught in, e. g., EP Application No. 0 626 022, the disclosure of which is incorporated by reference in its entirety); cationic starches that are used for overall retention rather than specifically for the retention of contaminants: cationic polyacrylamides; modifie polyethylene imine (as taught in, e. g., U. S. Patent No. 3, 514, 398, the disclosure of which is incorporated by reference in its entirety); water soluble quaternary ammonium polymers (as taught in, e. g., U. S. Patent No. 3, 288,770, the disclosure of which is incorporated by reference in its entirety) ; and polyvinyl amine polymers (as taught in, e. g., U. S. Patents Nos.

5.521 and 4,421, the disclosures of which are incorporated by reference in their entireties).

Nonionic polymers, including, e. g., polyethylene oxide, are also used for paper machine retention of contaminants.

The use of these methods often increases the cleanliness of the wet end of the paper machine. This may not always be the case as for some often unknown reason the use of a specific contaminant retention program may result in an increased tendency for contaminant deposition.

It is believed that retention aids bind the contaminant to the paper at the stage of sheet formation preventing the contaminant from accumulation and subsequent deposition. It may in some rare cases also reduce the deposition at stages after the sheet formation although generally it increases the tendency for deposition subsequent to the stage of sheet formation.

Yet another method, as disclosed in U. S. patent 5, 300, 194, the disclosure of which is incorporated by reference in its entirety, is based on separate application of anionic and cationic polymers onto certain surfaces in the wet end of a paper machine, e. g., during sheet formation or just after sheet formation.

Yet other methods have been suggested. Japanese kokai patent application no.

HEI 3 [1991]-113089 teaches a surface-soiling prevention method for a paper machine dryer. Japanese publication"Merits and achievements of dryer surface modification"

(Tomohiro Maezono : Japanese TAPPI, Vol. 52, No. 2. 1998, pp. 232-238) describes a method to keep the dryer section of a paper machine free from deposits.

Yet another method is based on reduction of the tackiness of the contaminants.

Examples of this method can be found in, e. g., U. S. Patents Nos. 5,866,618,5,723,021 and 4. 886, 575.

Yet another method uses the adsorbing potential of talc and other adsorbents. By this method, the contaminant will not be removed from the system but is instead pacified so that it will not form a deposit.

Most paper machines use at least one of the above methods for wet end deposit control, but none of the methods in use provides a"system solution,"a solution that keeps the entire paper machine free from deposits in a consciously planned manner. A problem associated with each of these methods is that once stickies are incorporated into the paper sheet, the stickies can present deposition problems down the line in the dryer end of the paper machine.

Stickies that become incorporated into a paper sheet also present problems in the drying section of a paper machine. In the hot environment of the drying section, such stickies have a tendency to detach from the surface of the paper sheet, and attach to the drying drum and drying fabric. As the stickies on the drum and fabric repeatedly contact the paper web, the stickies deposits grow in size, collect lint, etc. Eventually, this is observed in the paper product as holes or tears in the paper, which may necessitate halting the production line for a cleaning operation, and discarding batches of paper.

Methods of keeping the dryer clean and free of deposits generally fall into one of two categories: by mechanical means, and by water pressure. In the mechanical methods, the dryer drums are typically equipped with one or more doctor blades which scrape stickies and lint off of the dryer drums. A drawback of the mechanical methods is that the doctor blades roughen the drying drum, thereby shortening its useful life.

Similar mechanical methods are also used to remove deposits from dryer fabric.

However, these methods are generally less effective as the fabric is of a softer material. typically plastic, and less pressure can be applied to remove the deposits. Further the deposits have a tendency to be incorporated in the structure of the fabric, and this makes is even more difficult to remove the deposit mechanically.

In methods using water pressure, high pressure jets spray water onto the fabric, generally followed by a vacuum to remove the liquid. Even when used only intermittently, these methods typically use large amounts of water and increase wear of the fabric.

Chemical methods have also been suggested, including a method developed by Maintech Technologies (Tokyo, Japan). This method involves spraying a small amount of solid or liquid lubricant at low pressure onto the dryer drums and/or dryer fabric. The lubricant reduces the adhesiveness of the stickies for the machine components, thereby preventing harmful deposition onto those components. This technology is the subject of Japanese Patent Applications Nos. 10/288934,10/288942 and 10/288945, filed 25 September 1998, all of which are incorporated by reference herein in their entireties.

There is currently a poor understanding of cause and effect relationships between the operations of different parts of a paper machine. One exception to this is the understanding that has developed in the areas of quality control over such characteristics as, for example, basis weight, moisture, ash, caliper, color, and sheet strength. U. S.

Patent No. 3,687,802, for example, discloses a method for controlling mullen, basis weight, and moisture in paper by obtaining signals from different portions of the paper making machine and using the information to adjust fiber flow into the headbox, steam supplied to the dryer, and energy input per fiber.

There is a need in the industry for more effective methods of overall system design and operation which leads to improved deposit control.

There is a need in the industry for a method to improve the cleanliness of the whole paper machine. As a corollary, there is also a need in the industry for a method to increase the cleanliness of the wet end of a paper machine while still maintaining a clean dryer section.

There is also a need in the industry for a method of counteracting the fouling tendency of a treatment method at one stage (e. g., wet end) of a paper making process with a remedy at a subsequent stage (e. g., drying section) of the process.

Disclosure of the Invention The present invention relates to a method for controlling operation parameters in disparate segments of a paper machine for the purpose of overall regulation of machine

operations, including, e. g., runnability and/or cleanliness. The present invention also relates to methods for measuring variables and adjusting parameters which couple operations in disparate segments of a paper machine.

The present invention also relates to a method for maintaining cleanliness in a papermaking machine through control of parameters in the wet and dry ends of the machine. In a particular aspect, the invention relates to elimination or reduction of agglomerates, preferably anionic agglomerates, e. g., pitch and/or stickies, by use of a retention agent in the wet end. coupled with pacifying the retained agglomerates in the dryer to reduce or eliminate runnability problems that agglomerates would otherwise cause in the dryer.

The absence of understanding of cause and effect relationships between different parts of the paper machine has created a compartmentalized thinking regime, which has established state-of-the-art deposit control programs. It would have been considered inadvisable to increase pitch/stickies retention by the increased use of retention agents to effect their removal from the paper machine if this would increase dryer deposition problems down the line. By addressing formerly unconnected concerns in the dryer end and the wet end of a paper machine, however, the present invention, makes it possible, for example, to use higher addition rates of cationic polymer than otherwise would be possible.

The present invention provides a method for improving paper machine operation, the paper machine comprising a wet end and a dryer end, the method comprising: a) determining whether it is desired to improve paper machine operations by determining whether frequency of paper breaks is acceptable and whether paper appearance is acceptable; b) attributing paper machine operating problems primarily to the wet end, primarily to the dryer end, or to both, by analyzing where in the paper machine deposits are occurring and where paper breaks are caused : and c) improving paper machine operation by: cl) if paper machine problems are primarily attributed to the dryer end, then applying a treatment agent to the dryer; c2) if paper machine problems are primarily attributed to the wet end, or are attributed to both the wet and dryer ends, then applying a treatment agent to the dryer, and introducing or increasing amount of retention agent in the wet end.

If paper machine problems are primarily attributed to the wet end, then the method preferably includes: a) first. introducing or increasing amount of retention agent in the wet end; b) second, determming that problems of breaks or paper appearance are attributable to the dryer end; and c) third, applying a treatment agent to the dryer.

In preferred aspects of the method, parameters are adjusted by performing at least two times at least one of a), b) and c) of the previous paragraph. Preferably, the amount of retention agent is increased until problems of paper breaks or appearance attributable to the dryer end become unacceptable ; then applying a treatment agent to the dryer.

The invention also provides a method for determining paper machine operating parameters, the paper machine comprising a wet end and a dryer end, the method comprising: a) determining an acceptable level of depositable substances in the wet end: b) determining a retention agent and retention agent addition rate that obtains about the acceptable level of depositable substances; and c) determining a treatment agent and treatment agent addition rate in the dryer end, which treatment agent addition rate is sufficient to reduce deposition of depositable substance in the dryer end; wherein the treatment agent and treatment agent addition rate are based on the acceptable level of depositable substances, the retention agent, and retention agent addition rate. Also in the scope of the present invention is a method of operating a paper machine comprising employing a) the retention agent: b) approximately the retention agent addition rate; c) the treatment agent ; and d) approximately the treatment agent addition rate; determined by this method.

The invention also provides a method for determining paper machine operating parameters, the method comprising: a) determining an acceptable level of depositable substances in the wet end; b) determining a retention agent and retention agent addition rate that obtains about the acceptable level of depositable substances; and c) determining a treatment agent and treatment agent addition rate in the dryer end, which treatment agent addition rate is sufficient to reduce deposition of depositable substance in the dryer end ; wherein the retention agent and retention agent addition rate are based on the acceptable level of depositable substances, the treatment agent, and treatment agent addition rate. Also in the scope of the present invention is a method of operating a

paper machine comprising employing a) the retention agent ; b) approximately the retention agent addition rate; c) the treatment agent; and d) approximately the treatment agent addition rate ; determined by this method.

The invention also provides a method for determining paper machine operating parameters, the method comprising: a) determining an acceptable level of depositable substances in the wet end : b) determming a retention agent and retention agent addition rate that obtains about the acceptable level of depositable substances; and c) determining a treatment agent and treatment agent addition rate in the dryer end, which treatment agent addition rate is sufficient to reduce deposition of depositable substances in the dryer end; wherein the acceptable level of depositable substances is based on the retention agent, the retention agent addition rate, the treatment agent, and the treatment agent addition rate. Also in the scope of the present invention is a method of operating a paper machine comprising employing a) the retention agent; b) approximately the retention agent addition rate; c) the treatment agent; and d) approximately the treatment agent addition rate; determined by this method.

The present invention also provides a method for operating a paper machine having a wet end and a dryer end, the method comprising: a) preparing a pulp slurry comprising a retention agent; b) separating whitewater from the pulp slurry to form a sheet ; c) drying the sheet in a dryer; and d) applying a treatment agent to the dryer; wherein the paper machine is operated with an average water consumption of less than about 50 l/kg.

In methods of the present invention, the acceptable level of depositable substances in the wet end is preferably determined based on experience of mill management to levels below which they expect to experience an acceptable level of difficulties. This determination preferably includes at least one of several factors, including fiber raw material, paper grade, age of machinery, and an opinion of management based on experience.

The retention agent preferably comprises at least one of cationic polymer, preferably a synthetic cationic polymer, and cationic starch.

Preferably, the pulp slurry has a solids content and comprises greater than about 0.2 kg cationic starch per ton of paper on a dry basis, or greater than about 0.01 kg synthetic cationic polymer per ton of paper on a dry basis.

Preferably, the dryer comprises a dryer fabric and a drum. and the treatment agent is applied to at least one of the dryer fabric and drum. The treatment agent preferably comprises at least one of an oil and a synthetic resin powder. Where a treatment agent comprises an oil, the oil preferably comprises a mineral oil, a paraffin wax. a natural or derivatized vegetable oil, a natural or derivatized animal oil, or a silicone oil. Where a treatment agent comprises a natural or derivatized vegetable oil, the natural or derivatized vegetable oil preferably comprises a partially hydrogenated animal or vegetable oil. a completely hydrogenated animal or vegetable oil, an animal or vegetable oil transesterified with a polyol, or an acetylated animal or vegetable oil.

The rate at which a treatment agent is applied preferably depends on the treatment agent and the dryer surface to which it is applied. A treatment agent comprising an oil applied to a fabric is preferably applied at a rate of about 0.1 to 100 mg oil per m'ouf fabric surface per minute, more preferably about 0.2 to 40 mg oil per m2 of fabric surface per minute, more preferably about 0.4 to about 20 mg oil per m2 of fabric surface per minute, more preferably about 0.5 to 10 mg oil per m'ouf fabric surface per minute.

A treatment agent applied to a dryer drum is preferably applied at an average rate of about 0.1 to 5000 mg oil per m-ouf drum surface per minute, more preferably about 5 to 1000 mg oil per m'ouf drum surface per minute, more preferably about 30 to 800 mg oil per m2 of drum surface per minute.

Where the treatment agent comprises an oil, the oil is preferably in the form of an oil-in-water emulsion. Where the treatment agent comprises a synthetic resin powder, the synthetic resin powder is preferably in the form of a dispersion in water or other aqueous phase. Preferably, a treatment agent comprises a surfactant. Where the treatment agent comprises a surfactant, the surfactant preferably comprises at least one of a nonionic ethoxylated surfactant, an anionic alkyl sulfonate, and a soap.

A treatment agent applied to a dryer drum can comprise a synthetic resin powder, preferably in the form of an aqueous dispersion. Aqueous dispersions of

synthetic resin powder preferably comprise a surfactant, the surfactant preferably comprising at least one of a nonionic ethoxylated surfactant, an anionic alkyl sulfonate, and a soap.

Where a treatment agent applied to a dryer drum comprises a synthetic resin powder, the synthetic resin powder is preferably applied at a rate of about 10 llg to 50 mg synthetic resin powder per m of drum surface per minute. In a treatment agent comprising a synthetic resin powder, the synthetic resin powder preferably comprises at least one of melamine cyanurate (preferably comprising melamine cyanurate prepared from about equal weights of melamine and isocyanuric acid) and polytetrafluoroethylene. Application of the synthetic resin powder can be continuous or intermittent. Preferably, the synthetic resin powder comprises particles having sizes in the range of about 0.1 to 10 um, more preferably about 1 to 5 nm.

In methods of the present invention, retention agent is preferably added in sufficient quantity to decrease the turbidity of the whitewater by at least about 20% compared to operating the paper machine without retention agent, more preferably by at least about 30%, more preferably by at least about 40%.

Methods of the present invention are preferably employed in paper machines operated with an average water consumption of less than about 40 I/kg, more preferably less than about 25 I/kg, more preferably less than about 10 l/kg.

Brief Description of Drawings The present invention is further described in the detailed description which follows, in reference to the noted plurality of non-limiting drawings, and wherein: Figure 1 is a schematic diagram of a method for detemuning paper machine operating parameters according to the present invention.

Detailed Description of Invention The particulars shown herein are by way of example and for purposes of illustrative discussion of the various embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with

the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

AU percent measurements in this application, unless otherwise stated, are measured by weight based upon 100% of a given sample weight. Thus, for example, 30% represents 30 weight parts out of every 100 weight parts of the sample. As noted below, some percentages are given in terms of active ingredients, or"actives."Such percentages are calculated only in terms of the total amount of active ingredients, disregarding water that might be present.

Unless otherwise stated, weights of paper or other cellulosic product are based on dry weight of the paper or other cellulosic product.

Unless otherwise stated, a reference to a compound or component, includes the compound or component by itself, as well as in combination with other compounds or components, such as mixtures of compounds.

Further, when an amount, concentration, or other value or parameter, is given as a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of an upper preferred value and a lower preferred value, regardless whether ranges are separately disclosed.

Before further discussion, a definition of the following terms will aid in the understanding of the present invention.

Paper machine deposits are generally attributed to either natural or synthetic sources. Natural sources of deposits comprise, or arise from, components naturally present in wood, and can include resins and other compounds. Synthetic sources comprise, or arise from, components intentionally or unintentionally added during production of the paper; during converting paper to an end product; or, in the case of recycled furnish, as a result of use of product later recycled. Synthetic deposits can include insoluble inks, adhesives, etc. Natural sources of deposits are generally referred to as'pitch,"and synthetic sources are generally referred to as"stickies."As used herein, the two terms are interchangeable, and use of either term, unless otherwise stated, should be considered as including the other term as well.

Both pitch and stickies comprise insoluble, hydrophobic compounds, and tend to agglomerate into particles in aqueous media, such as pulp slurries. The particles may

also deposit in machine surfaces, which those of ordinary skill in the art recognize can cause a variety of problems. Particles comprising materials attributable to pitch and/or stickies, therefore, are referred to herein as"depositable substances." The present invention is directed toward a method for controlling disparate segments of a paper machine in order to improve operational characteristics including, for example, paper machine wet end cleanliness, and deposits on dryer drums and fabrics.

The invention includes methods for removal of pitch and/or stickies from a paper machine by use of a retention agent in the wet end of a paper machine in order to bind the pitch/stickies to the paper fibers, and implementation of a dryer deposit control program in the dryer section in order to reduce or eliminate deposition and/or runnability problems which would otherwise be caused by the pitch/stickies in the paper. The invention includes use of a retention agent capable of reducing water turbidity in the wet end of a paper making machine, combined with use of a deposits inhibitor in the dryer end of a paper machine.

Methods according to the present invention are especially suited for use in paper machines having high degrees of system closure, which translates to low rates of water consumption. Preferably, water consumption in methods according to the present invention will be less than about 50 liters of water per kilogram of paper produced (50 1/kg), more preferably less than about 40 l/kg, more preferably less than about 25 1/kg, even more preferably less than about 10 I/kg. Because of water losses due to evaporation in dryer sections, it is impractical to approach 0 I/kg water consumption, and water consumption is generally greater than about 2 or 4 I/kg.

Any method for determining residual quantities of contaminants in paper making process waters can be used. Such methods include, for example, turbidimetric methods ; TOC (total organic carbon); COD (chemical oxygen demand); and microscopic methods, such as hemocytometric methods; for counting colloidal particles.

Turbidimetric methods are preferred, but the methods tend to correlate for a given paper machine with a given furnish composition. For the best results, the white water is preferably filtered through coarse filter paper to remove large particles such as fibers.

When a turbidimetric method is used for determining quantities of contaminants in paper making process waters, e. g., pitch and/or stickies, any reduction in turbidity is beneficial. Reduction in turbidity can be gauged by measuring turbidity of whitewater when retention agent is used, and comparing that turbidity to the turbidity of whitewater obtained in substantially the same way, but without the addition of any retention agent.

It is preferred that use of a retention aid will lower the turbidity of whitewater by at least about 20% compared to when no retention agent is used, preferably by at least about 30%, more preferably by at least about 40%. Ideally, one would like to reduce the turbidity by about 100%. but in practice it will seldom be economically feasible to do so.

It is preferable, therefore, that turbidity be reduced by less than about 100%, more preferably less than about 95%, more preferably less than about 90%, more preferably less than about 85%.

Any substance that is capable of reducing turbidity in paper machine whitewater can be used in the present invention. Such substances preferably comprise a polymer, more preferably a cationic polymer. Mixtures of such substances may also be used.

Preferred cationic polymers include those disclosed in U. S. Patent No.

5,300,194, the disclosure of which is incorporated herein in its entirety. Such cationic polymers include, e. g., polyethyleneimines; protonated or quaternary ammonium polymers ; dicyandiamide-formaldehyde condensates; polymers of diallyldimethylammonium chloride; copolymers of diallyldimethylammonium chloride, with, e. g., an acrylic acid derivative such as an acrylamide; polybutadienes reacted with lower alkyl amines and partially quaternized, cationic starch, lignin, and tannin derivatives, Manniched tannins, cross-linked polyamines : and mixtures thereof. Also nonionic retention systems can be used if these reduce turbidity. Example of such systems include polyethylene oxide, and the combination of polyethylene oxide with phenolic resin marketed by the company Kemira under the trade name Netbond. Finally also anionic polymers such as anionic polyacrylamide can be used.

The reduction in turbidity should be as high as possible, because this will reduce the quantity of residual contaminants in the process water. Application of polymer that does not reduce turbidity is not useful. The amount of synthetic polymer used can be determined by a person of ordinary skill in the art for each particular application.

Typically, synthetic polymers will be added at an addition rate below about 1 kg polymer per ton paper (dry basis), more preferably less than about 400g per ton, more preferably less than about 250g per ton. If too little polymer is used, however, then there will be insufficient reduction in turbidity. Generally, the polymer addition rate will be greater than about 10 g per ton, more preferably greater than 100g per ton.

Naturally derived polymers. such as cationic starches and guar gum, generally require a higher addition rate. The amount of naturally derived polymer used can be determined by a person of ordinary skill in the art for each particular application.

Typically, naturally derived polymers are added at a rate greater than about 1 kg/ton, preferably greater than about 5kg/ton. The addition rates will generally be less than about 20 kg/ton, more preferably less than about 10 kg/ton.

Methods according to the present invention employ dryer pacification of depositable substances. While any method of dryer pacification can be used, it is preferred to use the methods disclosed in Japanese Patent Applications Nos. 10/288934, 10/288942 and 10/288945, and methods disclosed in U. S. Patent No. 5,246,548, the disclosures of which are incorporated by reference in their entireties. These methods are directed toward spraying of a treatment agent on the dryer of a paper machine. In order to prevent deposition on a dryer fabric, a dryer fabric is preferably sprayed with a treatment agent comprising an oil. In order to prevent deposition on a dryer drum, a dryer drum is preferably sprayed with a treatment agent comprising an oil, a synthetic resin powder, or a combination thereof. In preferred embodiments, a treatment agent is sprayed onto a dryer fabric and a second treatment agent, optionally the same as the first treatment agent, is sprayed onto a dryer drum.

When treatment agent is applied to the dryer, the heat of the dryer generally evaporates most or all of water or other volatiles that may be present, and the remainder of the treatment agent forms a film on a dryer surface, preferably a dryer fabric and/or dryer drum. As paper goes through the dryer, that is, as paper is dried, some of the treatment agent is removed with the paper, which eventually depletes the amount of treatment agent on a dryer surface. Treatment agent should be replenished, therefore, preferably at a rate approximately equal to the rate of treatment agent depletion. Thus, treatment agent is preferably applied to the dryer, preferably by spraying, either

continuously or intermittently. Intermittent application can be at regular or irregular intervals. By"intermittent"is meant, e. g., applying for 15 minutes every 30 or 60 minutes, spraying for 10 minutes every hour, or spraying for several minutes whenever it is determined that treatment levels have sufficiently declined. An appropriate treatment agent and an appropriate treatment agent addition rate can be determined by one of ordinary skill in the art based on the present disclosure.

In conventional dryer treatment methods, in which fabrics and/or drums are treated with a treatment agent during a machine downtime, there is a gradual depletion of treatment agent, which leads to gradual increase in deposition of depositable substances on dryer surfaces. By continuous or intermittent application of treatment agent. however, prevention of deposition of depositable substances can be maintained over extended periods of paper machine operations. Accordingly, the surface of the dryer fabric is always in a condition where a suitable amount of the actives contained in the surface treatment agent is present, enabling the fabric to withstand continuous operation satisfactorily.

Different chemical treatments can be used to reduce deposition in a dryer section. Such chemical treatments can be applied in the form of a solution, in a solvent, as a dispersion, or as neat material, and can be classifie as oils, synthetic resin powders, and mixtures thereof.

Several factors should be considered when selecting which treatment agent to use. One factor is the release performance of the treatment agent, i. e., how well the treatment agent prevents deposition on the dryer surface. Another factor is film stability, i. e., how well the treatment agent maintains as a film under the dryer conditions, especially dryer temperature. Another factor is chemical stability, i. e., how chemically stable the treatment agent is, especially with regard to pH and furnish additives. Another factor is chemical interaction with contaminants, i. e., how stable the treatment agent is with regard to pitch and/or stickies. Yet another factor is adhesiveness, i. e., the treatment agent should not be adhesive enough to pick up fibers from the wet sheet at dryer surface temperatures. The final factor is impact on the sheet. i. e., the treatment agent should not have an adverse effect on sheet properties at the application rate, especially on sizing and color. The person of ordinary skill in the

art is able to balance these factors using ordinary experimentation to determine a suitable treatment agent for the particular paper grade being produced.

Preferred oils include silicones and triglycerides. Preferred silicone oils include dialkylsilicones, alkylaryl silicones, and amino silicones. Examples of these include, but are not limited to, methylphenyl silicone oil, dimethyl silicone oil, amino silicone oil, epoxy silicone oil, denatured higher fatty acid silicone oil. Triglycerides or other oily materials, e. g., natural or hydrogenated vegetable or ammal oil, e. g., castor oil, can also be used. Also preferred are mineral oils and paraffin waxes.

As used in regard to a treatment agent, the term"oil"should be understood to mean that the active ingredient is a liquid at temperatures of use, e. g., at the temperature of the surface in the dryer section to which treatment agent is applied. Similarly, the term"synthetic resin powder"should be understood to refer to a material which is solid at those temperatures. Thus, for example, because dryers are typically operated at temperatures greater than 100 °C, a paraffm wax having a melting temperature of about 60 °C would be considered an oil rather than a solid.

Examples of commercial treatment agents include a variety of treatment agents from Maintech, Co. Ltd., (Tokyo, Japan) for example, Dusclean liner board Nos. 1 and 2, Dusclean white board Nos. 1, 2 and 4, Dusclean corrugating medium Nos. 1, 2, and 3, Dusclean calendar Nos. 1 and 2, Dusclean fine paper No. 1, Duslean news print Nos.

1, and 3, Cleankeeper C, Cleankeeper E, Cleankeeper S, and Cleankeeper LF treatment agents. Hercules Incorporated (Wilmington. Delaware, USA) has Zenix DS 7148, Zenix DS 7141, Zenix DS 7149 and Zenix DS 7151 treatment agents.

The treatment agent can be applied in any manner determined by one of ordinary skill in the art, and is preferably applied by spraying the treatment agent on to the dryer surface to be treated. An oil, e. g., a silicone oil, can be sprayed as a solution, or in the form of an emulsion. A treatment agent comprising an oil is preferably applied with the oil in the form of an emulsion as this lowers viscosity of the treatment agent, and improves dispersion characteristics during spraying. When a treatment agent comprises an oil in the form of an emulsion, the oil is preferably emulsified with surfactant, by methods determined by those of ordinary skill in the art. Where the oil has surfactant properties, an additional surfactant can be used.

Any amount of surfactant, or mixture of surfactants, that permits formation of an emulsion by a method determined by one of ordinary skill in the art may be used.

Preferred surfactants include anionic and nonionic surfactants. Preferably, a nonionic surfactant comprises ethoxylated surfactants, preferably including at least one of ethoxylated glycerides, ethoxylated fatty acids, or other ethoxylated polyols, such as polysorbate 80. When a surfactant comprises an anionic surfactant, the anionicity preferably arises from either a carboxylic acid functionality or a sulfonate functionality.

Preferred anionic surfactants include soaps, e. g., sodium or potassium salts of Cl0-C22 fatty acids, and alkyl sulfonates, e. g., Cl0-C22 alkyl sulfonates.

The surfactant used for emulsification of oil is preferably present at about 15 to 70 wt% of the oil, e. g., silicone oil. Emulsions of oil in water can be prepared in any concentration determined useful by one of ordinary skill in the art. Emulsions preferably have weight ratios of water to oil in the range of about 4 to 15.

It should be noted that an excessive supply rate of oil in a treatment agent can result in clogging of the eyes of dryer fabric, thereby deteriorating drying efficiency; can result in dripping or pooling on drums, leading to waste of material; and can possibly result in excessive pick-up of treatment agent on paper, causing change or variation in paper quality. On the other hand, with an insufficient supply rate of oil, a depleted amount of oil on the fabric and/or drum cannot be replenished quickly enough. An oil treatment rate can vary depending on, e. g., the type of the dryer fabric and/or dryer drum, and quality of the paper strip, and can be determined by one of ordinary skill in the art. Whenever a treatment rate is for non-constant or non-continuous treatment, then the treatment rate should be understood as referring to average treatment rate.

The treatment rate for a dryer fabric can be determined by one of ordinary skill in the art, and can depend on the surface area of the fabric, the material from which the fabric is made, and other factors. As a general rule, the oil in a treatment agent applied to a dryer fabric is preferably applied at a rate greater than about 0. more preferably greater than about 0.2 mg/m2/min, more preferably greater than about 0.4 mg/m2/min, more preferably greater than about 0.5 mg/m2/min, and more preferably greater than about 1 mg/m2/min, where"m2"refers to the area of fabric, i. e., for a simple closed loop of fabric, the area is simply length times width. Generally, the oil in a

treatment agent is applied to a dryer fabric at a rate less than about 100 mg/m2/min, preferably less than about 50 mg/m2/mm, more preferably less than about 40 mg/m2/min, more preferably less than about 25 mg/m2/min, more preferably less than about 20 mg/m2/min, and more preferably less than about 10 mg/m2/min.

As a general rule, the oil in a treatment agent applied to a dryer drum is preferably applied at a rate greater than about 0.1 mg/m2/min, preferably greater than about 0.5 min, more preferably greater than about 1 mg/m/niin, more preferably greater than about 2 mg/m2/mm. more preferably greater than about 5 mg/m2/min, more preferably greater than about 10 mg/m2/min, more preferably greater than about 30 mg/m2/min, where"m2"refers to the surface area, square meters, of dryer drum, i. e., ji (drum length) (drum diameter). Generally, the oil in a treatment agent is applied to a dryer fabric at a rate less than about 5000 mg/m2/min, preferably less than about 1000 mg/m2/min, preferably less than about 800 mg/m2/min, more preferably less than about 500 mg/m2/min, more preferably less than about 300 mg/m2/min, more preferably less than about 200 mg/m2/min.

The treatment agent can be diluted with water to any concentration of actives (non-aqueous components) determined by a person of ordinary skill in the art to be used in a particular paper machine, and can depend on the nature of the pulp, other additives used, etc. Preferably, however, the treatment agent sprayed onto the dryer has greater than about 0.033 wt% actives, more preferably greater than about 1 wt% actives, and more preferably greater than about 5 wt% actives. Preferably, the treatment agent sprayed onto the dryer has less than about 60 wt% active, more preferably less than about 40 wt% actives, more preferably less than about 30 wt% actives.

A treatment agent applied to a dryer drum may contain a synthetic resin powder in addition to, or in place of, an oil. Any synthetic resin powder of appropriate size and type to reduce the effects of asperities in a dryer drum can be used. Since the surface of a drum dryer can be heated up to a high temperature (typically in the range of about 50 to 135 °C), however, use of synthetic resin powders stable at dryer temperatures, e. g., not susceptible to denaturation at dryer temperatures, is preferable.

Some preferred synthetic resins for use in treatment agents include, for example, melamine cyanurate (MCA); polytetrafluoroethyelene; and combinations thereof. A

treatment agent comprising a synthetic resin preferably comprises a melamine cyanurate (MCA), which preferably comprises MCA prepared by reacting about equal weights of melamine and isocyanuric acid.

As it is believed that particles of synthetic resin act to fill up asperities in the dryer drum, particle size is an important consideration in selecting a synthetic resin powder. Any particle size distribution that is capable of efficiently filling up asperities in a dryer roll may be used in methods of the present invention, and can be determined by one of ordinary skill in the art for the particular equipment used. If the particle size is too small, the fill-up condition becomes unstable, and if the particle size is too large, it becomes difficult to fill up the recesses in the microscopic asperities on the surface of the drum dryer.

From the viewpoint of achieving high efficiency in filling up recesses in microscopic asperities on the surface of the drum dryer, synthetic resin powders will generally have average particle sizes greater than about 0.1 um, more preferably greater than about 1 pm. Generally, the synthetic resin powders will have average particle sizes less than about 10 zm, more preferably less than about 5 um.

An application rate of synthetic resin powder may be determined by a person of ordinary skill in the art to deliver a sufficient amount of powder to the drum surface, and may depend on a number of factors, including, for example, on the average particle size in the resin powder, on the material and condition of the drum to which the treatment is applied, and the method of application. It is preferable to spray a treatment agent comprising a synthetic resin powder on the surface of the dryer, preferably at a low rate of application. Preferably, the rate of application is greater than about 2 Pg/M2/min, more preferably greater than about 10 llg/m2/min, more preferably greater than about 30 Mg/m2/min based on the weight of the resin powder and the drum surface area. The rate of application is preferably less than about 50 mg/m2/min, more preferably less than about 10 mg/m2/min.

It is preferable that the treatment agent comprising a synthetic resin powder also comprise a surfactant to improve the quality of the dispersion, so that spraying as described hereinafter can be facilitated. Any surfactant that improves the dispersion can be used. Preferable surfactants include anionic and nonionic surfactants. Preferably, a

nonionic surfactant comprises ethoxylated surfactants. preferably including at least one of ethoxylated glycerides, ethoxylated fatty acids, or other ethoxylated polyols, such as polvsorbate 80. When a surfactant comprises an anionic surfactant, the anionicity preferably arises from either a carboxylic acid functionality or a sulfonate functionality.

Preferred anionic surfactants include soaps, e. g., sodium or potassium salts of fatty acids, and alkyl sulfonates, e. g., Clo-C22 alkyl sulfonates.

When present, surfactant preferably represents about 15 to 60 wt% based on the total of surfactant and synthetic resin powder. A treatment agent comprising a dispersion of synthetic resin powder generally contains about 5 to 100 times as much water (by weight) as much as the synthetic resin powder or sum of synthetic resin powder and surfactant.

Whether a treatment agent comprises an oil, a synthetic resin powder, or both. water used for dilution and/or application can be heated, e. g., to a temperature in the range of 50 to 80 °C, to reduce the risk of the nozzles getting clogged, e. g., with scum and slime. In this case, the surface treatment agent is preferably also heated to a substantially equivalent temperature.

Further, in actually supplying the surface forming agent onto the surface of the dryer, a spray nozzle or spray nozzles are preferably employed. In order to prevent spray nozzles from getting clogged, the treatment agent may be further diluted with water (on the order of 10-to 100-fold) before the treatment agent is applied to a dryer surface.

Treatment agents for use in the present invention may also contain other additives as deemed necessary by one of ordinary skill in the art to control or modify the treatment agent. These may include, for example, preservatives, antistatic agents, viscosity modifiers, and mixtures thereof.

Further, a treatment agent can comprise ingredients to alter the characteristics of the paper product produced. Depending on the type of paper product being manufactured, such ingredients include, for example, lipid (including oil or solid wax) based dusting inhibitor.

A treatment agent can be applied to a dryer by any means. The method of application is not important as long as the treatment is evenly applied to the surface

which is to be treated, e. g., a dryer drum or dryer fabric. A preferred method of application is with spray nozzles.

Several different methods of spraying a treatment onto a dryer are available, and can vary, for example in the number of spray nozzles and whether the nozzles are stationary or traversing nozzles. Stationary nozzles are generally employed in one of two ways. First, there can be two jets, one situated on each outer edge of the width of the drum or fabric to be treated. Second, there can be a multiplicity of nozzles arranged across a width of drum or fabric to be treated. When treatment agent is pumped through the jets, or through the nozzles, the treatment agent is sprayed approximately uniformly across surface to be sprayed, e. g., the width of drum or fabric.

In contrast to stationary nozzles, with traversing nozzles, one or more nozzles are mounted on tracks which permit the nozzles to traverse the width of the surface to be sprayed, thereby covering the entire width of the surface to be sprayed.

Any spraying apparatus, whether commercially available or custom made, can be used. Preferred spraying apparatuses are manufactured by Maintech Co. Ltd, Tokyo, Japan under the trade names MISTRUNNER, CLEAN HIT and SPRAY BAR.

MISTRUNNER comprises a single traversing spray nozzle. CLEAN HIT comprises two types of stationary nozzles: a needle nozzle to spray the center part of the fabric or drum, and fan nozzles to spray from each end. SPRAY BAR comprises a plurality of stationary nozzles. Each of these apparatuses can be obtained with heating and mixing units for the treatment agent.

When a treatment agent is applied to a dryer fabric, it is applied either directly, e. g., by spraying the fabric, or indirectly, e. g., by applying the treatment agent to a roll that contacts the fabric. It is preferred to apply treatment agent to a fabric either by a single traversing nozzle, or with two jet nozzles.

In order to permit water a chance to substantially or completely evaporate, treatment agent applied to a fabric is preferably applied to the fabric at a location distant from where the fabric contacts the paper, such as at the stretch roll. It is also preferable to apply a treatment agent to the side of the fabric that comes in contact with the paper, or to a roll that contacts the side of the fabric that contacts the paper.

When a treatment agent is to be applied to a dryer drum, the treatment agent is preferably applied directly to the drum with a single traversing nozzle. Evaporation is less of a consideration when spraying a drying drum than when treating a fabric because the high heat of the drying drum results in rapid evaporation of water that may be present in the treatment agent.

In one aspect of the present invention, strategies and parameters for operation of a paper machine can be determined by following the methodology that is schematically represented in Figure 1. When two or more paper mills have similar equipment and/or produce similar papers, it is also possible to follow the methodology in one mill, and apply the results in other nulles.

The first step is an analysis relating to paper appearance and break frequency.

'Break frequency"refers to how often there is a break in the paper, which entails machine downtime and lost productivity."Paper appearance"refers to spots, discolorations, holes, or other imperfections that can arise in paper. The first step, determming whether break frequency and paper appearance are acceptable, is highly subjective, and depends on a multitude of factors, including paper grade produced, machine speed, and even subjective opinions of decision makers. For example, in some rmils, experiencing three or four breaks per month might be considered excessive, whereas in another mill, possibly using different equipment and/or producing different paper grades, breaks even more often than three per day might be considered acceptable.

If, in the first step, it is determined that breaks and appearance are acceptable, or that there is no interest in improving either of these, then there is no need to implement changes in operating parameters. If, instead, the result of this analysis is that either the break frequency or the paper appearance is unacceptable, or that there is an interest in improving either of these, then the second step is taken.

In the second step, the cause of paper breaks and the locations of paper machine deposits is analyzed.

It is easy for one of ordinary skill in the art to determine the location of the break. Once the location of the break is determined, it must then be determined whether the break is related to a sheet imperfection, such as pitch or stickies incorporated in the sheet; is due to deposits, such as pitch or stickies on a fabric or other machine surface;

or to. e. g., a mechanical reason, such as improperly calibrated rolls exceeding the stretch limit of the paper at that location. As those of ordinary skill in the art are aware, there is interplay between the mechanical and non-mechanical reasons for paper breaks. For example, mechanical stress can exacerbate sheet imperfections, and vice versa.

If it is determined that the break is at least partly attributable to non-mechanical causes, then the analysis according to the present invention continues with an analysis of machine deposits.

Deposits can be formed in the wet end of the paper machine as well as in the dry end. and their locations can be determined visually, such as by inspecting the machine parts. as well as indirectly, such as by analyzing consequences of the deposits. A person of ordinary skill in the art is able to undertake the necessary analysis to determine the location of deposits in a paper machine.

Deposits formed on dryer fabric generally can have two relevant consequences.

First. the deposits may leave marks as imprints on the paper. Second, deposits on the dryer fabric may also impair moisture removal leading to wet streaks in the final paper.

When either of these two consequences of deposits has developed to an unacceptable level. the machine will have to be closed down and the fabric will have to be cleaned or replaced.

Deposits on dryer drums can result in fiber removal from the sheet as a result of adhesion to the roll caused by adhesive contaminant substances. These fibers can accumulate in the dryer section and may form bundles of fibers that may cause a break on the machine. Deposits on the dryer drum are typically removed with a doctor blade, which can damage a dryer drum, reducing its useful lifetime.

Deposits may form in the wet end of a paper machine with a high degree of water closure due to accumulation of contaminants caused by reusing the water enclosed in paper making applications. These deposits may be located on a variety of different surfaces. Common areas of deposition are usually areas of high shear. These include the approach pipe to the headbox, the headbox, the forming wire, and foils.

These deposits may break loose to be incorporated in the paper, creating a spot or a hole, potentially causing a break on the paper machine. Wet end deposits, in addition to visual examination, can also be determined indirectly. For example, deposits on the

forming fabric can alter the flow of water through the fabric, leading to a non-uniform fiber distribution in that area. This non-uniformity leads to an imperfection in the sheet, which may cause a break in paper production.

Someone of ordinary skill in the art is expected to be able to relate a sheet imperfection in a paper to locations of deposits. It is in most cases also possible to determine the location of each break in paper production. The analysis of the location of the breaks and the relative distribution of deposits between the wet end and the dry end of the paper machine will determine, in accordance with this invention, the preferred course of action.

If the primary problem is attributable to deposits in the dry end, the desired course of action, in accordance with this invention, is the application of a deposit control program in the dryer end of the paper machine. Problems in the dryer end might be attributed to deposits on the fabric or on a dryer drum. As is known to those of ordinary skill in the art, deposits can form on the dryer fabric and not on a drying drum, on a drying drum and not on a drying fabric, or on both a drying drum and a drying fabric. Further, on a dryer comprising more than one dryer drum, dryer drum deposits can occur on a dryer drum contacting only one side of the paper sheet, or on dryer drums contacting both sides of the paper sheet. Further, where deposits form on dryer drums contacting both sides of the paper sheet, the deposits need not be equally distributed among drums. Thus, when implementing a dryer deposits control program, only those dryer surfaces in need of deposition control need to be treated.

When there is a plurality of dryer drums facing the same side of the paper, the deposition problem is generally more severe in the first drum, and lessens in severity with each succeeding drum. In such a situation, the first drum should be treated with a dryer deposits control treatment, and the treatment is carried to later drums. As necessary, a deposits control program can be implemented down the line to treat additional drums if deposits problems continue.

If, on the other hand, it is determined that the primary problem is attributable to deposition in the wet end, the desired course of action is the introduction of a retention agent to retain the contaminants with the sheet. If a retention agent is already used, then the retention agent can be increased, or an additional retention agent employed. The

retention agent should be added or supplemented to the point where the imperfections caused by deposits in the wet end are acceptable, and the break frequency caused by these deposits is also acceptable. This increased removal may lead to increased deposition in the dryer section. In the event that this deposition and its consequences are considered unacceptable, in accordance with this invention, then a deposit control agent in the dryer section is introduced.

It may be, however, that runnability problems and paper imperfection are caused by deposits that originate in both the wet end, as well as in the dryer section. In such case. in accordance with this invention, the use of a retention agent in the wet end is introduced or increased to further enhance the removal of these contaminants from this part of the paper machine system, combined with the introduction of a deposit control method in the dry end of the paper machine.

The inventive methodologies can be applied either retrospectively or prospectively. By retrospective application is meant that parameters are analyzed retrospectively, e. g., based on past paper machine performance, such as based on paper breaks and/or deposits locations, such as described above. By prospective application is meant that the parameters are based on operating changes that a paper machine operator would like to implement, such as, for example, increasing machine speed, increasing water closure, or using cheaper fiber furnish. For instance, suppose a production manager was required to increase water closure by lowering consumption from 50 Ukg to 30 I/kg. In the first step of the inventive method, the manager would recognize that breaks might increase in frequency, or that paper appearance would suffer. Thus, based on the equipment used and paper produced, the manager would determine likely areas of deposits problems and paper breaks. Based on the results of the analysis, the manager could decrease water consumption, and simultaneously implement retention agents and a dryer deposition control program according to the present invention.

In viewing the present from a different approach, methods of the present invention are directed toward determining paper machine operating parameters, of which three sets of parameters are involved. Each set of parameters can be determined by one of ordinary skill in the art using the methods disclosed herein.

The first set of parameters is an acceptable level of visible imperfections caused by depositable substances. This parameter relates to the final paper product produced in the machine, and does not specifically relate to a particular segment of the paper machine. This set of parameters can be determined, for example, based on the type of paper product being produced. A paper product destined to be used as corrugated medium in cardboard boxes, for example, can have a higher level of depositable substances than a paper product destined to be used in fine stationery.

The second set of parameters is the retention agent and retention agent addition rate in the wet end of the paper machine. The parameters can be based, for example, on the degree of turbidity reduction desired in the whitewater, the degree of cleanliness required in a paper machine.

The third set of parameters is the treatment agent or agents, and addition level or levels thereof, in the dryer section of the paper machine. This set of parameters can be determined by the level of depositable substances expected or found to be present in the dryer section.

The present invention ties together the above three sets of parameters. Any two sets of the three sets of parameters can be independently determined by a person of ordinary skill in the art, and used as the basis for determining the unknown set of parameters.

It is also possible to combine the treatment program of this invention with other programs to reduce deposit formation. By way of example, it would still be advisable to use deairator in the washing of the pulp to reduce the level of contaminants. It would also be possible to use talk as adsorbent in the preparation of the pulp. To complement the program on the paper machine it may be desirable to use products that prevent deposition on specific surfaces such as press roll by application of a treatment program directly onto this surface.

Employing methods of the present invention requires measuring or estimating a number of variables and parameters, and requires that decisions be made. It will be understood by one of ordinary skill in the art that each measurement, estimation, and decision can be made by a person through mental processes, can be made by a

computer, or can be made by a combination of mental processes and computer calculations.

Examples The present invention is further illustrated by way of the following contemplative examples, which, for one of ordinary skill in the art, suffice to illustrate adjustment processes and paper making machine operations according to the present invention.

These examples are non-limiting and do not restrict the scope of the invention.

Unless stated otherwise, all percentages, parts, etc. presented in the examples are by weight.

Example 1 A closed (water consumption 10 Ukg) paper machine using recycled fiber experiences deposition in the head box of contaminants from the recycled fiber. The m first evaluates a cationic polymer derived from dimethyl amine and epichlorohydrin added to the furnish at an addition rate of 1 lb. per ton paper to eliminate this problem.

This method indeed reduces the concentration of contaminants in the wet end and prevents deposition in the head box, but causes increased deposits on the drying cylinders and on the dryer fabric. The application is for this reason terminated, as the deposits in the drying section are considered a more serious problem than the deposits formed in the head box.

The mill then proceeds to use the combined method of application according to this invention of the same cationic polymer added to the furnish at the addition rate of 1 lb. per ton paper combined with the application of treatment agent applied to the drying cylinders. The treatment agent used is a silicone oil administered as an oil-in-water emulsion directly onto the first and second dryer rolls by a single traversing nozzle at an addition rate of active ingredients of l mUm2/min. This combined process eliminates not only the deposits in the head box but also the deposits on the drying cylinders. The overall machine cleanliness is improved.

Example 2 A mill producing newsprint paper from a mixture of thermomechanical pulp and deinked newsprint has a problem with deposits in the forming section, press section and drying section. It is using a modifie polyethylene imine cationic polymer (1.5 lb/ton of

the trade product Polymin SK from BASF) in the forming section for the retention of fines and colloidal contaminant material. Applying this program the mill experiences increased deposition in the press section and in the drying section resulting in breaks in the paper production. A program applied in the drying section to eliminate deposits on the press felts and press rolls prevents deposition onto these two surfaces, but the increased deposition in the drying section still prevails.

The mill then implements a treatment agent application program in the dryer section, applying a silicone oil in the form of an emulsion at a rate of active ingredients of 1 ml/m2/min to the dryer fabric, and a silicone oil in the form of an emulsion at a rate of active ingredients of 1 ml/m2/min to the first and seventh dryer drum. With the treatment application in the dryer section, the dryer fabrics, felts, and drum (s) are kept free of deposits.

As a consequence of the elimination of the dryer section deposits, the mill is able to increase the use of the cationic polymer in the forming section to 2 lb/ton for an overall improved machine cleanness.

Example 3 A producer of corrugated medium using 80% old corrugated containers (OCC) and 20% mixed office waste as furnish is forced to reduce water consumption from 14 1/ton to 8 1/ton. In consequence of this closure, the concentration of colloidal contaminants in the white water increases 100%. To cope with the much increased concentration of colloidal material in the back water the mill increases the addition rate of cationic polyacrylamide retention agent from 200 g/ton to 300 g/ton. This results in heavy deposition on the dryer fabrics of pitch and stickies from the recycled paper. The mill then begins applying a dryer deposition program to the fabric comprising essentially the method used in Example 1 of U. S. patent 5,246,548, by which aqueous solutions of a cationic polymer and an anionic polymer are sprayed separately onto the fabric using atomizing nozzles. The cationic polymer is a polyquarternary compound as taught in U. S. patent 5,626, and the anionic polymer is a lignosulphonate. The application of this program eliminates the formation of deposits on the dryer fabric.

Example 4 A paper mill is operating at a water consumption level of 40 I/kg to produce paper of acceptable quality for its clients. The mill experiences about 1 paper break per week, which the process manager considers acceptable.

The mill is then required to reduce its water consumption to 30 Ukg. Upon imposing water closure to meet the new requirement, the mill experiences an increase in paper breaks to about three paper breaks per week. The clients also begin to complain about spots in the paper received.

It is determined that most page breaks are occurring in the second dryer drum of the paper dryer section, which has twenty-two dryer drums. A closer analysis of the entire paper machine reveals many deposits on the second drum. and somewhat fewer deposits on the fourth dryer drum, but few deposits on the dryer fabric, on the other dryer drums, and in the wet end.

The mill applies a treatment agent comprising an emulsion of mineral oil to the second dryer drum using a single traversing nozzle spraying at a rate of 2 mUm2/min, and applies the spray continuously. As a result, paper quality returns to an acceptable level, and the frequency of paper breaks decreases to about one every two weeks, which the process manager considers acceptable.

Example 5 A new process manager in the mill of Example 4 decides to increase the cleanliness of the paper machine. Without examming the equipment, the manager decides to increase the level of retention agent used in the fiber furnish. The mill had been using 250 g/ton of cationic polyacrylamide with molecular weight about 1.2 x106 g/mol. The process manager decides to supplement this with 200 g/ton of poly (diallyl dimethyl ammonium chloride), made according to U. S. Patent No. 3,288,770. Based on the manager's experience in other milles, however, the manager concludes that such an addition rate would lead to an unacceptable level of paper breaks in the dryer section.

In addition to the dryer treatment agent already being applied to the second dryer roll (Example 4). the manager decides to apply dryer treatment to the dryer fabric and first dryer drum before increasing the retention agent, in order to prevent dryer section problems.

The dryer treatment program is implemented, the retention agent is increased, and it is observed that the wet end is now cleaner, with fewer deposits forming in the headbox and foils. Additionally, paper breaks are reduced to about one every five weeks.

While the invention has been described in connection with certain preferred embodiments so that aspects thereof may be more fully understood and appreciated, it is not intended to limit the invention to these particular embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the scope of the invention as defined by the appended claims.