DIATOM COMPOSITIONS AND METHOD FOR USING SUCH COMPOSITIONS FOR MAKING PAPER PRODUCTS

CROSS REFERENCE TO RELATED APPLICATION This present disclosure claims the benefit of the earlier filing date of U.S. provisional application No. 60/765,263, filed on February 3, 2006, which is incorporated herein by reference.

FIELD The present disclosure concerns embodiments of a composition comprising at least one diatom, or a mixture of two or more diatoms, such diatom(s) having physical features that facilitate paper processing, particularly recycled paper processing, embodiments of a method for using the diatom composition for processing cellulosic compositions and for making paper products and paper products made according to the process.

BACKGROUND

Recycling post consumer paper products is becoming more important.

Growing concerns about the environment, alternatives to solid waste disposal, increasing consumer demand for quality recycled papers, and various state and federal laws that mandate levels of recycled fibers all have combined to increase the use of recycled paper. See, for example, "Paper Recycling," edited by K. L. Patrick,

Miller Freeman Inc., San Francisco, 1991.

There are several sources of contaminates in recycled paper. One obvious source of contamination is the accidental inclusion of foreign material. Other sources of contaminants include inks and materials, such as binders, adhesives, sealants, glues, etc., generally categorized as "stickies."

Newspapers, magazines and other printed media have been recycled for many years. To reclaim fibers from printed material, a deinking process is required to remove the ink and other contaminants. Deinking waste paper has become increasingly more difficult because of changes in the printing techniques being used and the wide variety of printing inks. As a result, a slurry of recycled waste paper

contains a complex mixture of inks, resin binders, fillers, and the like, which must be removed.

Conventional industry chemical formulations used for floatation deinking typically include a fatty acid or fatty acid soap. See, for example, U.S. Patent Nos. 4,964,949 and 4,483,741. However, there are a number of problems associated with using fatty acids and fatty acid soaps, including high dosage rates (typically about 16 pounds/ton of waste paper but as high as 30 pounds/ton), relatively poor foamability thus causing the high dosage rates, and the general need for high levels of water hardness to achieve acceptable performance. The hard water often leads to handling problems as well as scale and deposit buildup in mill equipment. More recently, non-ionic surfactants have been developed for use in deinking systems.

Since ink by its nature is colored (usually black), the presence or retention of ink in the formed sheet reduces brightness and can cause dark spots. The increasing use of mixed office waste as a source of recycled fiber for printing and writing grades poses a particular problem in recycling waste paper. Mixed office waste . contains a high percentage of nonimpact printed material such as xerographic or laser printed paper that is difficult to deink. The density of the separated ink material tends to be about equal to that of the medium, which makes removal by conventional mechanical means, such as screening, cleaning, flotation and washing, difficult. The best solution to ink contamination is to remove the ink prior to paper formation.

Stickies come from varying sources, including polyvinyl acetate and polyvinyl alcohol resins, hot melt adhesives, wet strength residuals, SBR and vinylacrylic rubber lattices, pressure sensitive adhesives, and so forth. Stickies are so chemically diverse that removal by known chemical means alone is very difficult. Stickies interfere with paper production by fouling equipment and reducing the quality of the finished product. Stickies accumulate in white water recycle systems resulting mostly in deposits on paper forming fabrics, on felt and on wet end equipment. Consequently, quality problems such as pinholes, increased down time due to frequent break down and clean ups, additional costs for cleaning and prevention, inherent damages to felt, fabric, and drying equipment are commonly encountered in the production and use of secondary or recycled fiber furnish. See,

for example, Moreland, Robert D., "Stickies Control by Detackification." 1986 Pulping Conference, Tappi Press, Atlanta, 1986, p. 193. As will be readily understood, these problems cost mills time and money.

Current techniques for controlling stickies can be grossly categorized into mechanical methods and chemical methods. Mechanical methods include combinations of coarse and fine screening, hydrodynamic washing and high intensity dispersion. High intensity dispersion units attempt to break the stickies into small particulates that can be absorbed onto the pulp fiber without adversely impacting the quality of the finished sheet. Traditional chemical additives used to facilitate removing stickies include talc, organic solvents, alum, sequestering agents, dispersants (cationic, anionic, and nonionic), zirconium compounds, and organotitanium compounds. See, for example, Doshi, Mahendra R., "Properties and Control of Stickies," Recycled Paper Technology, Tappi Press, Atlanta, 1994, p. 73. All these chemical additives have exhibited some, albeit limited, success in controlling stickies. The mechanisms associated with chemical additives involve dispersion, electrostatic attraction, agglomeration, surface tension modification, adsorption, detackification and so forth.

A number of issued U.S. patents concern papermaking processes. For example, U.S. Patent No. 4,964,955 to Lamar and other literature teach pitch control processes using cationic polymeric agents and/or chemically modified bentonites and clays in papermaking processes. However, using the Lamar method, the pitch is not removed but instead ends up being dispersed and retained in the paper.

U.S. Patent No. 5,151,155 to Cody teaches a deinking process using a cationic smectite clay. Cody teaches removing the ink waste either by floatation or washing. Smectite is a group of clay minerals with a layer charge between 0.2 and 0.6 charge per formula unit, which swell in the presence of water. Kaolin, in contrast, has approximately a zero layer charge. The Cody process requires about 26% or about 535 pounds of smectite clay on a dry basis per ton dry pulp. By contrast, about 20 pounds of cationic kaolin are used per ton of pulp on a dry basis.

U.S. Patent No. 5,362,362, entitled "Methods of Deinking Cellulosic Materials," concerns a method for deinking cellulosic materials comprising

shredding or chopping the cellulosic materials to create uniform paper shreds, immersing the paper shreds into a nonaqueous organic solvent while agitating the paper shreds, removing the organic solvent, bleaching the paper shreds to form a pulp, diluting the pulp to form a fiber suspension and submitting the suspension to high speed, high shear dispersion to form a pulp ready for papermaking. According to the '362 patent, methods of deinking which involve cooking and the use of chemicals in aqueous media have become increasingly unsatisfactory for a number of reasons. Ink formulations have become more and more complex and involve an increasing use of a wide variety of synthetic resins and plasticizers; with each ink having its own special formulation. Also, increasing amounts of synthetic resins and plasticizers are being used in a wide variety of sizings, coatings, plastic binding adhesives, thermoplastic resins and pressure sensitive label adhesives. Furthermore, the use of multicolored printing and multicolored advertisements have become increasingly popular in recent years and these involve a wide variety of new ink formulations. Many of the new ink formulations incorporate new pigments, dyes and toners which are difficult to remove by conventional aqueous deinking chemicals. The former methods of deinking and reclaiming waste paper by chemical and cooking techniques are not adapted for, nor are they adequate for, removing the new types of inks and coating resins. Pigments such as talc, bentonite, PCC and diatomaceous earth also are being used for their adsorptive properties. U.S. Patent No. 6,977,027, entitled Additive and Process for Sticky Control in Recycled Pulps," teaches away from using diatomaceous earth, which can be used in any pH environment, because such materials are very abrasive and have a tendency to adhere to parts of the paper making equipment. This requires replacing and/or cleaning various pieces of equipment more often than other types of adsorptive materials.

Diatomaceous earth materials have been used in the paper industry for other purposes. For example, U.S. Patent No. 5,290,454, entitled "Process for Removal of Suspended Solids from Pulp and Paper Mill Effluents," describes a process for removing suspended solids containing colloidal particles of resin and fatty acids from a pulp mill effluent. The method comprises forming a mat of non-biological sludge on a porous support. The sludge is selected from the group consisting of pulp

mill primary sludge, woodroom sludge, and a mixture of primary and secondary pulp mill sludges. Aqueous pulp mill effluent comprising suspended solids containing colloidal particles of resin and fatty acids is passed through the mat. The suspended solids containing colloidal particles of resin and fatty acids are retained in the mat. The filtration aid may be selected from diatomaceous earth and lime mud.

SUMMARY

New technologies and compositions are needed for processing paper furnish despite the previous technologies discussed above. The present application describes embodiments of a method for processing cellulosic material, such as recycled or waste paper, that address deficiencies of known prior processes.

One embodiment of the disclosed method comprises providing an aqueous pulp composition. Often at least a portion of the pulp comprises furnish derived from recycled or waste paper. At least one Melosira diatom, at least one Aulacoseira diatom, or combinations thereof, or a composition comprising such diatom or diatoms, is added to the pulp composition to form a process composition. The process composition is then further processed to form a pulp furnish.

Working embodiments have used Melosira or Aulacoseira diatomaceous earth products. However, diatom species other than those used in exemplary embodiments also likely can be used to practice the present invention. For example, the morphology of the diatom may be an important characteristic. Working embodiments of the present invention used substantially tubular diatoms. Another characteristic that can be used to identify suitable diatoms is the available surface area. It currently is believed that diatom(s) suitable for practicing the present invention have available surface areas of from about 40 to about 70 square meters of available surface area, more typically from about 50 to about 65 square meters of available surface area, per gram of material.

A person of ordinary skill in the art will appreciate that the amount of the diatom(s) added to cellulosic material can vary. For example, in working embodiments the diatom(s) have been added to cellulosic compositions in an amount ranging from greater than 0 to at least as high as 100 milligrams per liter of pulp

composition, more typically from greater than about 5 milligrams per liter to at least as high as 100 milligrams per liter of pulp composition.

The diatom(s) can be formulated as a fluid composition or suspension, typically an aqueous composition, prior to addition to aqueous pulp compositions. For example, working embodiments have used an aqueous diatom composition comprising about 1 gram dry diatom material to about 100 milliliters of water.

Another method for determining the amount of diatom, or mixture of diatoms, to use concerns adding an amount of a diatom, or mixture of diatoms, that is effective to achieve a desired result. For example, the diatom(s), or composition comprising the diatom(s), can be added in an amount effective to improve at least one property, such as amount of rejects, free ink in accepts, gain in brightness, effective residual ink concentration (ERIC), reduction in total spots, reduction in spot ppm, gain in _. reduction in TAPPI spots, gain in amount of trash removed, reduction of organics, and/or reduction in stickies. Another embodiment of the disclosed method for processing cellulosic material to provide a pulp furnish first comprises providing an aqueous pulp composition at least a portion of which comprises recycled paper pulp. Greater than 0 to at least as high as about 100 milligrams per liter of at least one tubular Melosira diatom, at least one tubular Aulacoseira diatom, or combination thereof, or composition comprising such diatom or diatoms, is added to the pulp composition. Such diatom(s) typically have available surface areas of from about 40 to about 70 square meters per gram.

Still another embodiment of the disclosed method for processing cellulosic material to provide a pulp furnish comprises providing an aqueous pulp composition at least a portion of which comprises recycled paper pulp. An aqueous diatom composition is formed comprising about 1 gram dry diatom material to about 100 milliliters of water, the diatom comprising at least one tubular Melosira diatom, at least one tubular Aulacoseira diatom, or combination thereof, or composition comprising such diatom or diatoms, the diatom(s) having available surface areas of from about 40 to about 70 square meters per gram. The aqueous diatom composition is then added to the aqueous pulp composition to provide from greater than 0 to at least as high as 100 milligrams of diatom per liter of pulp composition.

Still another embodiment of the disclosed method concerns a method for making a paper product. The method comprises providing an aqueous pulp composition at least a portion of which comprises recycled paper pulp. An aqueous diatom composition is formed comprising at least one tubular Melosira diatom, at least one tubular Aulacoseira diatom, or combination thereof, or composition comprising such diatom or diatoms, the diatom(s) having available surface areas of from about 40 to about 70 square meters per gram. The aqueous diatom composition is added to the aqueous pulp composition to form a processing composition. The aqueous diatom composition provides from greater than 0 to at least as high as 100 milligrams of diatom per liter of pulp composition. The processing composition is processed to form a pulp, and then desired paper products are formed from the pulp.

Paper products also are described. Such paper products comprise some amount of pulp greater than zero that is processed according to embodiments of the disclosed method.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a photomicrograph of a Melosira diatom.

FIG. 2 is a graph illustrating spot reduction obtained by practicing disclosed embodiments of the present invention for market pulp, tissue and paper towel furnish versus a control.

FIG. 3 is a graph of percent improvement in dirt removal for furnish treated with varying amounts of a diatom composition as disclosed herein.

FIG. 4 is a graph of brightness gain (points) for a one week mill trial for furnish treated with a varying amounts of a diatom composition as disclosed herein relative to control furnish produced for a week by the same process but without being treated with disclosed diatom compositions.

FIG. 5 is a graph of brightness gain (percent gain) for a one week mill trial for furnish treated with a varying amounts of a diatom composition as disclosed herein relative to control furnish produced for a week by the same process but without being treated with disclosed diatom compositions.

FIG. 6 is a graph of spot surface reduction for a one week mill trial for furnish treated with a varying amounts of a diatom composition as disclosed herein

relative to control furnish produced for a week without being treated with disclosed diatom compositions.

FIG. 7 is a graph of spot surface for hand sheets made over the course of a one-week continuous mill trial. FIG. 8 is a graph of total number of spots for hand sheets made over the course of a one- week continuous mill trial.

DESCRIPTION

Throughout this disclosure, the singular terms "a," "an," and "the" include plural referents unless the context clearly indicates otherwise. Similarly, the word "or" is intended to include "and" unless the context clearly indicates otherwise.

I. DIATOM

The present invention concerns compositions comprising diatoms having physical properties that facilitate certain processes, such as deinking processes, commonly used to make paper products, particularly paper products made from recycled paper furnish. Diatomaceous Earth (D.E) comprises skeletal remains of diatoms (plankton), which are microscopic aquatic plants belonging to the Bacillariae class of unicellular plants. Their skeletons are almost pure silica (SiO ₂ ). Particular diatom species have been used by applicants in working embodiments to demonstrate the substantially superior results that are obtained relative to a standard process, and relative to other diatoms. For example, both Melosira and Aulacoseira diatoms have been used in working embodiments of the present invention. Diatomaceous earth compositions comprising such diatoms are commercially available, such as the DiaSource® product from DE Industries, LLC.

However, a person of ordinary skill in the art will appreciate that other species of diatoms may be useful for practicing the present invention. Thus, in addition to considering particular species of diatoms, the genus of diatoms useful for the present invention also can be determined by considering physical properties of diatoms that allow further identification of useful species. For example, and without limiting the present invention to a theory of operation, it currently is believed that the surface area provided by diatomaceous earth samples comprising one or more

suitable diatoms is a property by which useful diatom species can be identified. Diatoms used in working embodiments of the present invention typically have a surface area of from about 40 to 70 square meters of available surface area per gram of material, more typically from about 50 to about 65 square meters of available surface area per gram of material. Melosira diatoms used in working embodiments typically were tubular, and had sizes ranging from about 5 by 10 μm up to about 30 by 50 μm. Pore sizes in diatoms used in working embodiments also have varied, but typically were about 1 μm to about 5 μm.

Diatoms used in working embodiments also typically are tubular in shape. See, FIG. 1, which is a photomicrograph of a Melosira diatom used in disclosed embodiments of the present invention.

A capillary reaction appears to occur when diatom(s)/diatom compositions are introduced into aqueous compositions. It does not seem to matter what is in the water as long as it is within a size range that makes it suitable for removal by the diatom(s)/diatom compositions. This size currently is believed to be in the 1 micron size range or smaller. The diatom appears to work like a sponge when it is dry because of the high available surface area.

The chemical composition of a diatomaceous each sample used in working embodiments has been determined to comprise 90%+ SiO ₂ , with the remainder being magnesium silicates and water. The specific gravity of the diatom was 2.2, and it had a melting point of about 1,700 ⁰ C.

When the diatom is introduced to water, some of the diatoms fall out of suspension while others stay suspended. The more colloidal debris present in the solution, the more diatoms fall from suspension. Solely by way of possible explanation, and without limiting the present invention to a theory of operation, diatom(s) used to practice disclosed embodiments of the present invention may be filled with atmospheric gas that is trapped inside the tube of the diatom (see FIG. 1, a Melosira diatom having a tube running the length of the diatom body). Colloidal debris is drawn into the diatom cavity and displaces the atmospheric gas present causing the diatom to loose buoyancy and fall out of suspension.

When properly matched to the colloidal debris present in an aqueous sample, water treated according to disclosed embodiments of the present invention visually

clears in a short period of time. When "over dosed," there are more diatoms present than colloids, and the water remains cloudy.

II. DIATOM AMOUNTS The diatom, mixture of diatoms, or composition comprising a diatom or diatoms, is added to compositions comprising cellulosic materials in amounts effective to accomplish desired results. A person of ordinary skill in the art therefore will appreciate that the amount of the diatom(s) added to cellulosic compositions can vary. For example, in working embodiments the diatom(s) have been added to cellulosic compositions in an amount ranging from greater than 0 to at least as high as 100 milligrams per liter of pulp composition, more typically from greater than about 5 milligrams per liter to at least as high as 100 milligrams per liter of pulp composition.

The diatom(s) can be formulated as a suspension prior to addition to cellulosic compositions. The liquid used to form the suspension can vary, but typically is water. For some working embodiments, suitable diatom compositions were made using mill process water. Working embodiments have used aqueous diatom compositions comprising from greater than 0 pound/gallon to at least about 0.1 pound/gallon , more typically from about 0.05 pound/gallon to at least 0.075 pound/gallon (from about 1 mg/ml to at least about 20 mg/ml, more typically from about 5 to about 10 mg/ml). A person of ordinary skill in the art will appreciate that compositions having diatom amounts other than that expressly disclosed herein for certain working embodiments can be used and still be within the scope of the present invention Another method for determining the amount of diatom, or mixture of diatoms, to use concerns adding an amount of a diatom, or mixture of diatoms, that is effective to achieve a desired result. For example, the diatom(s), or composition comprising the diatom(s), can be added in an amount effective to improve at least one property selected from reduced rejects, reduced free ink in accepts, gain in brightness, reduction in ERIC values, reduction in total spots, reduction in spot ppm, gain in reduction in TAPPI spots, gain in amount of trash removed, reduction of organics, and/or reduction in stickies. More specifically, the diatom(s) can be used

in an amount useful to: (1) reduce the percentage of pulp rejected by at least 4 percent and up to about 40 percent; (2) provide a reduction in ERIC values of at least 2 percent, preferably at least 10 percent; (3) provide a gain in deinking efficiency of at least 1 percent, preferably at least 9 percent; (4) provide a reduction in total spots of up to at least 15 percent; and (5) provide a reduction in spot ppm of up to at least 100 percent, preferably at least 400 percent, and even more preferably at least 900 percent.

III. EXAMPLES The following examples are provided to illustrate certain exemplary embodiments of the present invention. The scope of the present invention is not limited to the particular features of these exemplary working embodiments.

Example 1 An amount of pulp to give a 1% float when diluted was weighed, the appropriate amount of surfactant was added and was stirred for 3 minutes to insure uniform distribution. This composition was then floated in a Wemco floatation device for 5 minutes. Rejects were collected and weighed. Percent solids were determined on the rejects. Three gram handsheets were made from the pulp (feed), the float (accepts), and brightness and ERIC analyses were run on the consistency pad for the rejects.

A 1 % aqueous solution was formed comprising Melosira diatom obtained from DE Industries, LLC using distilled water. 3.5 milliliter aliquots of the 1% solution were added to the Wemco floatation cell comprising 3,500 mis of floatation stock at a 1% solids consistency.

In addition to the floatation handsheets, both "blank" and additive samples were hyperwashed and handsheets were prepared. The results of analyses on the handsheets for the standard feed pulp and test handsheets are provided below. "Blank" entries concern standard formulations, i.e. those that do not use diatom compositions as disclosed herein, and the deinking results associated with such. Data for this Example 1 is provided below in Table 1.

Table 1

Calculated results from the data in Table 1 are provided below in Table 2.

Table 2

Tables 1 and 2 show that using the diatom additive provides improved brightness, reduced ERIC, a large reduction in the amount of free ink in the accepts, higher deinking efficiency and fewer grams of solids were rejected, which increases product yield. There also appears to be a reduction in the length of whiskers when using the additive as determined by measuring reticule in a hand held microscope and looking at random areas of the handsheets.

Example 2

Dump chest stock was used for this example. The stock was evaluated for various parameters and is designated as the "feed" (or stock). Coated sections are being added at a 24:1 ratio (as opposed to a 10:1 ratio in the previous example). The dump chest stock was subjected to a standard floatation process to provide baseline data.

An aqueous composition was formed comprising Melosira diatomaceous earth (a 1% solution in mill water). 3.5 milliliter aliquots of this stock composition were added either (1) directly to the float (pulp compositions being processed in a floatation device), or (2) to pulp compositions prior (e.g., about 10 minutes prior) to being processed in the floatation device, which were designated pre-float. Pre-float samples comprised raw dump chest sample (at 4% solids) processed for laboratory purposes in a Kitchen Aid processor and mixed 5 minutes (setting 2), with dilution and floatation commencing at 9 minutes. All floats were 5 minutes in length. Rejects were collected and weighed. 3-gram handsheets were made, and were evaluated for various properties, including optical properties, spots and used for the extractive samples. Pulmacs were run on the float accepts. As an alternative, organic extractives were run (methylene chloride extractives). Data and analyses thereof are presented below in Tables 3-7.

Table 3

Table 4

Table 6

Conclusions concerning data presented in this example are provided below in Tables 8 and 9.

Table 8

Table 9

Example 3

Dump chest stock was used for this example. The stock was evaluated for various parameters and is designated as the "feed" (or stock). Coated sections are being added at a 24:1 ratio (as opposed to a 10:1 ratio in the previous example). The dump chest stock was subjected to a standard floatation process to remove a certain portion of materials being separated from the pulp to be used to provided baseline data.

An aqueous composition was formed comprising Melosira diatomaceous earth (a 1% solution in mill water). 2.63 milliliter aliquots of this stock composition were added either (1) directly to the float (pulp compositions being processed in a floatation device), or (2) to pulp compositions prior (e.g., about 10 minutes prior) to being processed in the floatation device, which were designated pre-float. Pre-float samples comprising raw dump chest sample (at 4% solids) were diluted to 3,500 milliliters in the mixer (which may account for the sample variation) and processed for laboratory purposes in a Kitchen Aid processor and mixed 5 minutes (setting 2), with dilution and floatation commencing at 9 minutes. All floats were 5 minutes in length. Rejects were collected and weighed. 3-gram handsheets were made, and were evaluated for various properties, including optical properties, spots and used for the extractive samples. Pulmacs were run on the float accepts. As an alternative, organic extractives were run (methylene chloride extractives).

Table 10

Table 11

Table 12

Table 13

Table 14

Table 15

Table 16

Example 4

This example concerns a mill trial for production of market pulp, such as by using tissue and paper towel furnish, by practicing disclosed embodiments of the present invention. The recycled furnish included office pack and coated book. A 1% aqueous pulp composition was formed using the recycled furnish. This pulp was bleached and screened according to the mill's normal procedure.

Melosira diatoms, screened to 325 mesh, were used to make two different aqueous compositions having different diatom amounts. A first "high dose" composition was made by adding 15.5 pounds of diatom to 225 gallons of mill water (about 0.07 pounds/gallon; about 8.26 milligrams/milliliter). A second low dose composition was made by adding 11 pounds of the diatom to 225 gallons of mill water

(about 0.05 pounds/gallon; about 5.86 milligrams per milliliter). The pulp stream for this particular mill trial was 6,300 gallons/minute. The two different diatom compositions were delivered to the pulp stream at an effective rate for the gallons per minute rate of the pulp stream, i.e. these compositions were delivered to the pulp stream at about 6 gallons/minute. These rates were predetermined based on other test results and found to be in a range suitable as base dose rates for this trial. The diatom compositions were introduced in slurry form and injected seconds before the floatation deink cells (DI cell) by a hydraulic pump. This trial continued for an extended period of about 4 months. Spot reduction was the primary interest for the subject mill. FIGS. 2 and 3 illustrate the results obtained for this example. FIG. 2 illustrates the total reduction in spots per unit area for hand sheets made from furnish treated with the diatoms relative to the rate of spot reduction for the control week. Paper product produced by the mill as a control had spots at about 1.5 spots/unit area. By practicing disclosed embodiments of the present invention, the high dose diatom composition produced paper products having just under 0.6 spot/unit area. The low dose diatom composition produced paper products having just over 0.6 spot/unit area. This reflects about a 60% decrease in the number of spots per unit area.

FIG. 3 illustrates the percent dirt removal for different dirt sizes: small dirt refers to dirt particles greater than 0.001 mm ² ; medium dirt refers to dirt particles greater than 0.02 mm ² ; large dirt refers to dirt particles greater than 0.04 mm ² . Percent dirt removal was determined by using initial dirt count minus finish dirt count divided by initial dirt count, e.g. 1000 - 100 / 1000 = 0.90. Both front side (initial) dirt counts and finish dirt counts were taken and compared hourly for a 4 month period. FIG. 3 shows that by using diatom compositions according to the present invention small dirt amounts were reduced by about 10%, medium dirt amounts were reduced by more than 12%, and large dirt amounts were reduced by about 5.5%.

Dirt counting can be accomplished using any suitable method. For example, a sheet of paper may be scanned with a flat bed scanner to produce an image. The smallest elements of the image, pixels, are each assigned a grey scale value, where 0 . is black and 255 is white. The computer then processes the image to determine whether each pixel is dark dirt or bright background. This is done by having the operator input a grey scale threshold, which indicates that any pixel less than the

threshold should be considered dirt. The computer groups adjacent dark pixels into objects, calculates the size of the dirt particle, and then determines the fraction of paper covered by dirt spots.

Example 5

This example illustrates the increase in brightness and spot reduction that can be achieved for bright white paper furnish by practicing disclosed embodiments of the present invention. The disclosed results concern a mill trial that was set up for a 24- hour, around-the-clock cycle for a period of 5 days. Melosira diatoms screened to 325 mesh were used to make two different compositions having different diatom amounts. A first "high dose" composition was made by adding 16 pounds of diatom to 212 gallons of mill water (about 0.075 pounds/gallon; about 9 milligrams/milliliter). A second low dose composition was made by adding 1 1 pounds of the diatom to 212 gallons of mill water (about 0.05 pounds/gallon; about 6.2 milligrams per milliliter).

Recycled paper furnish useful for making white paper was formed into an aqueous composition comprising approximately 1% cellulosic material. The pulp was then processed according to the normal procedure used by the mill. Briefly, recycled paper furnish was shredded and mixed with water. The paper was repulped and detrashed to remove any large contaminates, like plastics and large metals. Small contaminants, such as staples or fine sand, were removed in high-density cleaners and screens. The pulp was de-inked using soap and dissolved air flotation, screened and cleaned. After cleaning, the pulp was washed, pressed, diluted and stored prior to being pumped to the paper machine blend chest. Melosira diatom compositions were injected into the process stream seconds before the floatation system by a hydraulic pump calibrated to the GPM flow of the pulp stream.

The trial was set up for a 24-hour, around the clock cycle for a period of 5 days. The low and high dose diatom compositions were introduced in slurry form and injected seconds before the floatation system by a hydraulic pump calibrated to 4 gallons per minute. These rates were predetermined based on other test results and found to be in a range suitable as base dose rates for this trail. Each diatom composition was given approximately 2 '/_• days for evaluation.

The trial data was then compared to a previous week's data compiled using similar furnish and processing conditions but without using disclosed embodiments of Melosira diatom compositions. Averages were then run on both weeks' data using a 24 and 60 hour collective average. The primary improvement sought in this trial was an overall increase in brightness and an overall decrease in spots. The results of this trial are reflected in FIGS. 4-8.

Reduction in rejected fiber was not looked at in this trial. Reductions in rejected fiber have been noticed during testing done at other locations and those reductions were found to be substantial.

Brightness

Paper samples were made from recycled pulp treated using disclosed embodiments of the present invention. Brightness refers to the percent light reflected back from a paper sheet measured by a light meter. To measure paper brightness, a light source shines a beam of light, typically 457 nanometers, onto the paper, typically at a 45 degree angle. Another device measures the amount of reflection from the paper based on a scale from 1-100. Higher numbers indicate brighter sheets. A brighter sheet has a higher number and tends to reflect more light from the paper surface. Slight increases at the higher end of the scale change the paper's appearance more dramatically than large changes at the lower end.

Brightness was determined for each of the products using a commercially available, online brightness meter that measures brightness in process. All data was then sent to a systems control computer for compilation and comparison. Results were provided in terms of brightness points. For the first half of the trial week, the high dose diatom composition was used, and an overall brightness level for that period was 74. When the low dose was used in the second half of the trial week, the brightness increased dramatically to 84.96. When compared to the same time periods on the previous week's data (average first half, 81.71 and average second half 79.39) the lower dose has the most consistent higher brightness levels.

FIG. 4 illustrates that greater than 3 brightness points were obtained using the high dose, about 5.5 brightness points were gained using the low dose, and the

overall gain in brightness points for the week was about 4,5. FIG. 5 illustrates the percent increase in brightness obtained using disclosed embodiments of the present invention. For the first half of the trial week, the high dose diatom composition produced a 4% increase in brightness. When the low dose was used in the second half of the trial week, the brightness increased about 1%. Thus, for the trial week the percent brightness increase was about 5.8%. A 4% to 6% increase in brightness provides a significantly improved product. For example, a 4% to 6% increase in brightness can increase a paper product having an 88 brightness to a bright white paper product having a 92-94 brightness, which has a considerably higher market value.

The test was divided into two dose levels to show the actual impact of the low dose compositions. The results of this example are the same as results obtained for previous tests, indicating that the amount of diatom used may be further reduced and still provide acceptable results.

Spots

Spot reduction was quite dramatic when using disclosed embodiments of the diatom composition. Spots are determined visually as the number of spots per unit area, such as number of spots per inch. The data reflects an overall reduction in total number of spots in excess of 40% and a reduction in spot surface in excess of 55%. This is consistent with findings in other testing. More specifically, FIG. 6 shows that the number of spots per unit area for the control product was just about 4 spots/unit area. When the high dose diatom composition was used, the number of spots decreased to about 1.5 spots per unit area, which is about a 63% decrease. For the low dose test, the number of spots was reduced to about 1.8 spots per unit area, which is about a 55% decrease.

FIG. 7 illustrates the total spot count for the control (previous week) versus samples obtained from the continuously produced product made according to disclosed embodiments of the present invention. FIG. 7 clearly demonstrates that paper products produced using "high dose" Melosira compositions as disclosed herein consistently had fewer spots than the control. Similarly, FIG. 8 shows that

paper products produced using "low dose" Melosira compositions as disclosed herein consistently had fewer spots than the control.

Rejects, or yield, were not tested for in this trial. The higher dosage may be more effective in improving yields while still attaining improvements, albeit slightly smaller, improvements on brightness.

The present invention has been disclosed with reference to certain embodiments. A person of ordinary skill in the art will appreciate that the scope of the invention is not limited to these particular embodiments.