Abstract:
Pulp fibers can be treated with adsorbable chemicals with a minimal amount of unadsorbed chemical additives present later in the papermaking process water. A method for adding an adsorbable chemical to pulp includes mixing pulp fibers that have never been dried with water to form a fiber slurry. An adsorbable chemical additive is added to the fiber slurry. The fiber slurry having the adsorbable chemical additive is transported to a web-forming apparatus where a wet fibrous web is formed. The wet fibrous web may be dried to a predetermined consistency thereby forming a dried fibrous web having from between about 10 to about 100 percent retention of the adsorbable chemical additive. The dried fibrous web is transported to a paper machine where the dried fibrous web is mixed with water to form a wet slurry. In other embodiments, the fiber slurry can be processed to provide crumb fibers or wet lap fibers. The wet slurry containing the fibers having the adsorbable chemical additive adhered thereto is transported through the paper machine to form a finished paper or tissue product having enhanced quality due to the retention of the adsorbable chemical additive on the pulp fibers.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to paper or tissue products. More particularly, the invention concerns methods for applying adsorbable chemical additives to the fibers of pulps during the pulp processing and the paper products that can be obtained by the methods. 
     In the manufacture of paper products, it is often desirable to enhance physical and/or optical properties by the addition of chemical additives. Typically, chemicals such as softeners, colorants, brighteners, strength agents, etc. are added to the fiber slurry upstream of the headbox in a paper making machine during the manufacturing or converting stages of production to impart certain attributes to the finished product. These chemicals are usually mixed in a stock chest or stock line where the fiber slurry has a fiber consistency of from between about 0.15 to about 5 percent or spraying the wet or dry paper or tissue during production. 
     One disadvantage of adding a chemical at each paper machine is that the manufacturer has to install equipment on each paper machine to accomplish the chemical addition. This, in many cases, is a costly proposition. In addition, the uniformity of the finished product coming off of each paper machine may vary depending upon how the chemical was added, variations in chemical uniformity and concentrations, the exact point of chemical introduction, water chemistry differences among the paper machines as well as personnel and operational differences of each paper machine. 
     Another difficulty associated with wet end chemical addition is that the water soluble or water dispersible chemical additives are suspended in water and are not completely adsorbed onto the fibers prior to formation of the wet mat. To improve adsorption of wet end additives, chemical additives are often modified with functional groups to impart an electrical charge when in water. The electrokinetic attraction between charged additives and the anionically charged fiber surfaces aids in the deposition and retention of chemical additives onto the fibers. Nevertheless, the amount of chemical additive that can be retained in the paper machine wet end generally follows an adsorption curve exhibiting diminishing incremental adsorption with increasing concentration, similar to that described by Langmuir. As a result, the adsorption of water soluble or water dispersible chemical additives may be significantly less than 100 percent, particularly when trying to achieve high chemical additive loading levels. 
     Consequently, at any chemical addition level, and particularly at high addition levels, a fraction of the chemical additive is retained on the fiber surface. The remaining fraction of the chemical additive remains dissolved or dispersed in the suspending water phase. These unadsorbed chemical additives can cause a number of problems in the papermaking process. The exact nature of the chemical additive will determine the specific problems that may arise, but a partial list of problems that may result from unadsorbed chemical additives includes: foam, deposits, contamination of other fiber streams, poor fiber retention on the machine, compromised chemical layer purity in multi-layer products, dissolved solids build-up in the water system, interactions with other process chemicals, felt or fabric plugging, excessive adhesion or release on dryer surfaces, physical property variability in the finished product. 
     Therefore, what is lacking and needed in the art is a method for applying adsorbable chemical additives onto pulp fiber surfaces in the initial or primary pulp processing, providing more uniform chemical additions to the pulp fiber and a reduction or elimination of unadsorbed chemical additives in the process water on a paper machine. The method minimizes the associated manufacturing and finished product quality problems that would otherwise occur with conventional wet end chemical addition at the paper machine. 
     SUMMARY OF THE INVENTION 
     It has now been discovered that adsorbable chemical additives can be adsorbed onto pulp fibers that have never been dried at high and/or uniform levels with at most a minimal amount of unadsorbed chemical additives present in the papermaking process water after the treated pulp fiber has been redispersed in water. This is accomplished by treating a fiber slurry comprising pulp fiber and water with an excess of the adsorbable chemical additive, allowing sufficient residence time for adsorption to occur, and filtering or otherwise dewatering the fiber slurry to remove water and unadsorbed chemical additives. 
     Hence in one aspect, the invention resides in a method for applying adsorbable chemical additives to the pulp fibers. The method comprises creating a fiber slurry comprising water, pulp fibers that have never been dried, and an adsorbable chemical additive. The fiber slurry having the chemical additive may be formed into a wet fibrous web using a web forming apparatus. The wet fibrous web is dried to a predetermined consistency. In other embodiments of the present invention, the process may include further dewatering thereby forming a crumb-form. The dried fibrous web may have retained from between about 10 to about 100 percent of the adsorbable chemical additive. 
     According to another embodiment of the present invention is a method for adding an adsorbable chemical to the pulp fiber during the pulp processing prior to the drying stage. During the pulp processing, upstream of a paper machine, one can obtain chemically treated pulp fiber that is essentially homogeneous in chemical adsorption. Furthermore, the chemically treated pulp fiber can be transported to several different paper machines that may be located at various sites, and the quality of the finished product from each paper machine will be more consistent. Also, by chemically treating the pulp fiber before the pulp fiber is available for use on multiple paper machines or multiple runs on a paper machine, the need to install equipment at each paper machine for the adsorbable chemical addition can be eliminated. 
     This method for processing pulp fibers also enables higher and more uniform concentrations of adsorbable chemical additives to be adsorbed by the pulp fibers while at the same time maintaining significantly lower levels of unadsorbed chemical additive in the water phase of a papermaking machine compared to paper machine wet end chemical additions. 
     The term “adsorbable” is used herein to refer to a chemical additive that can be assimilated by the surface of a pulp fiber, in the absence of any chemical reaction involving the chemical additive and the fiber. Once the chemical additive is adsorbed, it may or may not be absorbed into the pulp fiber. The term “unadsorbed” refers to any portion of the adsorbable chemical additive that is not adsorbed by the pulp fiber and thus remains suspended in the process water. The term “web-forming apparatus” includes fourdrinier former, twin wire former, cylinder machine, press former, crescent former, and the like known to those skilled in the art. 
     The consistency of the fiber slurry is from about 0.5 to about 15 percent. In other embodiments, the consistency of the fiber slurry is from about 2 to about 10 percent or from about 3 to about 5 percent. The consistency of the dried fibrous web is from about 45 to about 100 percent. In other embodiments, the consistency of the dried fibrous web is from about 60 to about 100 percent or from about 85 to about 95 percent. The consistency of the wet fibrous web is from about 30 to about 45 percent. In other embodiments, the consistency of the wet fibrous web is from about 35 to about 45 percent or from about 40 to about 45 percent. The consistency of the crumb form is from about 50 to about 85 percent. In other embodiments, the consistency of the crumb form is from about 60 to about 85 percent or from about 80 to about 85 percent. 
     The present method allows for the production of pulp fibers that are useful for making paper products. This results in a pulp fiber, which after drying, has different mechanical properties than if the chemical treatment is carried out on pulp fiber in the once dried state. One aspect of the present invention is a more uniformly chemically treated pulp fiber, replacing the need for costly and variable chemical treatments at one or more paper machines. Another aspect of the invention resides in a pulp fiber that has a higher chemical additive loading than could otherwise be achieved in combination with no or a relatively low level of unadsorbed chemical additive in the process water on a paper machine. This is because chemical additive loading via wet end addition is often limited by the level of unadsorbed chemical and/or contact time, as well as its associated processing difficulties such as foam, deposits, chemical interactions, felt plugging, excessive dryer adhesion or release or a variety of paper physical property control issues caused by the presence of unadsorbed chemical in the process water on the paper machines. 
     In another embodiment, a fiber slurry of the present invention comprises water, pulp fibers having an adsorbable chemical additive adsorbed onto the fiber surface. The amount of chemical additive adsorbed onto the pulp fibers is about 0.1 kilogram per metric ton or greater, and the amount of unadsorbed chemical additive in the water is between 0 and about 90 percent of the amount of adsorbable chemical additive added to the pulp fibers. In particularly desirable embodiments, the amount of adsorbed chemical additive is about 0.5 kg/metric ton or greater, particularly about 1 kg/metric ton or greater, and more particularly about 2 kg/metric ton or greater. Once the wet or dried fibrous wet is redispersed at the paper machine, the amount of unadsorbed chemical additive in the water phase is between 0 and about 15 percent, particularly between 0 and about 10 percent, and more particularly between 0 and about 7 percent, of the amount of adsorbed chemical additive. 
     According to one embodiment of the present invention, the method for adding an adsorbable chemical additive to pulp fiber comprises creating a fiber slurry. The fiber slurry comprises water, pulp fibers that have never been dried, and an adsorbable chemical additive The fiber slurry having the adsorbable chemical additive is passed to a web-forming apparatus where a wet fibrous web is formed from the fiber slurry. The wet fibrous web is dried to a predetermined consistency. The resulting dried fibrous web may have from between about 10 to about 100 percent retention of the adsorbable chemical additive on the fibers. The dried fibrous web may be transported to a paper machine. The dried fibrous web is mixed with water to form a wet slurry. The wet slurry contains the fibers having the adsorbable chemical additive secured thereto. A finished product having enhanced quality due to the retention of the adsorbable chemical additive on the fibers may be produced from the wet slurry. 
     Another aspect of the present invention resides in a method for making chemically treated paper products. The method comprising mixing pulp fibers that have never been dried with water to form a fiber slurry. An adsorbable chemical additive is added to the fiber slurry. The fiber slurry, containing the adsorbable chemical additive is formed into a wet fibrous web. This may be accomplished in a web-forming apparatus. The wet fibrous web may be dried to a predetermined consistency. The resulting dried fibrous web may have from about 10 to about 100 percent retention of the chemical additive. The pulp fibers, as a dried fibrous web, may be transported or otherwise delivered to one or more paper machines. The pulp fiber, as a dried fibrous web, is mixed with water to form a wet slurry. The wet slurry contains the pulp fibers having the adsorbable chemical additive secured thereto. A finished product having enhanced qualities due to the retention of the adsorbable chemical additive on the fibers may be produced. 
     Another aspect of the present invention resides in a method for making chemically treated finished paper or tissue products. The method comprising mixing pulp fibers that have never been dried with water to form a fiber slurry. An adsorbable chemical additive is added to the fiber slurry. The fiber slurry, containing the adsorbable chemical additive is formed into a wet fibrous web. This may be accomplished in a web-forming apparatus. The wet fibrous web may be dewatered to a predetermined consistency. In other embodiments, the pulp fiber may be processed to a wet lap or processed to a crumb form. The resulting pulp fiber may have from about 10 to about 100 percent retention of the adsorbable chemical additive. The pulp fibers, once treated with the adsorbable chemical additive, may be transported or otherwise delivered to one or more paper machines in the form of a wet fibrous web, a dried fibrous web, a wet lap, or a crumb form. The pulp fiber, as a wet fibrous web, a wet lap, or a crumb form, is mixed with water to form a wet slurry. The wet slurry contains the pulp fibers having the adsorbable chemical additive secured thereto. A finished product having enhanced qualities due to the retention of the adsorbable chemical additive on the fibers is produced. 
     Another aspect of the present invention resides in a method for making chemically treated paper products. The method comprises creating a fiber slurry comprising water, pulp fibers that have never been dried, and a first adsorbable chemical additive. At least a second adsorbable chemical additive may be added to the fiber slurry, thereby forming a multi-treated fiber slurry. The additional adsorbable chemical additives may be added simultaneously with the first adsorbable chemical additives or at different times or points of the pulp processing. The additional adsorbable chemical additives may be added simultaneously or at different times or points of the pulp processing. The multi-treated fiber slurry, containing the adsorbable chemical additives, is formed into a wet fibrous web. This may be accomplished in a web-forming apparatus. The wet fibrous web may be dried to a predetermined consistency. The resulting dried fibrous web may have from about 10 to about 100 percent retention of the adsorbable chemical additives. The pulp fibers, as a multi-treated dried fibrous web, is transported or otherwise delivered to one or more paper machines. The pulp fiber, as a multi-treated dried fibrous web, is mixed with water to form a wet slurry. The wet slurry contains the pulp fibers having the adsorbable chemical additives secured thereto. A finished product having enhanced qualities due to the retention of the adsorbable chemical additives on the fibers may be produced. 
     In other aspects of the present invention reside a method for making chemically treated paper products. The method comprises creating a fiber slurry comprising water, pulp fibers that have never been dried, and a first adsorbable chemical additive. At least a second adsorbable chemical additive may be added to the fiber slurry, thereby forming a multi-treated fiber slurry. The second or additional adsorbable chemical additives may be added simultaneously with the first adsorbable chemical additive or at different times or points of the pulp processing. The additional adsorbable chemical additives may be added simultaneously or at different times or points of the pulp processing. The multi-treated fiber slurry, containing the adsorbable chemical additives, is formed into a wet fibrous web. This may be accomplished in a web-forming apparatus. The wet fibrous web may be dried to a predetermined consistency. In other embodiments, the pulp fiber may be processed to a wet lap or processed to a crumb form. The resulting pulp fiber may have from about 10 to about 100 percent retention of the adsorbable chemical additives. The pulp fibers, once treated with the adsorbable chemical additives, may be transported or otherwise delivered to one or more paper machines in the form of a wet fibrous web, a wet lap, or a crumb form. The pulp fiber, as a multi-treated wet fibrous web, a wet lap, or a crumb form, is mixed with water to form a wet slurry. The wet slurry contains the pulp fibers having the adsorbable chemical additives secured thereto. A finished product having enhanced qualities due to the retention of the adsorbable chemical additives on the fibers may be produced. 
     The present invention is particularly useful for adding adsorbable chemical additives such as softening agents to the pulp fibers, allowing for the less problematic and lower cost production of finished products having enhanced qualities provided by the retained adsorbable chemical additives. 
     Hence, another aspect of the present invention resides in paper products formed from pulp fibers that have been chemically treated prior to a drying phase to minimize the amount of residual, unadsorbed chemical additives in the process water on a paper machine. The term “paper” is used herein to broadly include writing, printing, wrapping, sanitary, and industrial papers, newsprint, linerboard, tissue, bath tissue, facial tissue, napkins, wipers, wet wipes, towels, absorbent pads, intake webs in absorbent articles such as diapers, bed pads, meat and poultry pads, feminine care pads, and the like made in accordance with any conventional process for the production of such products. With regard to the use of the term “paper” as used herein includes any web containing cellulosic fibers alone or in combination with other fibers, natural or synthetic. It can be layered or unlayered, creped or uncreped, and can consist of a single ply or multiple plies. In addition, the paper or tissue web can contain reinforcing fibers for integrity and strength. 
     The adsorbable chemical additives that can be used in conjunction with the present invention include: dry strength aids, wet strength aids, softening agents, adsorbency aids, sizing agents, dyes, optical brighteners, chemical tracers, opacifiers, dryer adhesive chemicals, and the like. Additional forms of adsorbable chemical additives may include: pigments, emollients, humectants, viricides, bactericides, buffers, waxes, fluoropolymers, odor control materials and deodorants, zeolites, perfumes, vegetable and mineral oils, humectants, sizing agents, surfactants, moisturizers, UV blockers, antibiotic agents, lotions, fungicides, preservatives, aloe-vera extract, vitamin E, or the like. Suitable adsorbable chemical additives are adsorbable by the papermaking fibers and are water soluble or water dispersible. 
     The term “softening agent” refers to any adsorbable chemical additive that can be incorporated into paper products such as tissue to provide improved tactile feel and reduce paper stiffness. A softening agent may be selected from the group consisting of quaternary ammonium compounds, quaternized protein compounds, phospholipids, silicone quaternaries, quaternized, hydrolyzed wheat protein/dimethicone phosphocopolyol copolymer, organoreactive polysiloxanes, and silicone glycols. These adsorbable chemical additives can also act to reduce paper stiffness or can act solely to improve the surface characteristics of tissue, such as by reducing the coefficient of friction between the tissue surface and the hand. 
     The term “dye” refers to any adsorbable chemical that can be incorporated into paper products, such as bathroom tissue, facial tissue, paper towels, and napkins, to impart a color. Depending on the nature of the adsorbable chemical, dyes may be classified as acid dyes, basic dyes, direct dyes, cellulose reactive dyes, or pigments. All classifications are suitable for use in conjunction with the present invention. 
     The term “water soluble” refers to solids or liquids that will form a solution in water, and the term “water dispersible” refers to solids or liquids of colloidal size or larger that can be dispersed into an aqueous medium. 
     The method for applying adsorbable chemical additives to the pulp fibers may be used in a wide variety of pulp finishing processing, including dry lap pulp, wet lap pulp, crumb pulp, and flash dried pulp operations. By way of illustration, various pulp finishing processes (also referred to as pulp processing) are disclosed in  Pulp and Paper Manufacture: The Pulping of Wood , 2nd Ed., Volume 1, Chapter 12. Ronald G. MacDonald, editor, which is incorporated by reference. 
     In addition, in situations where more than one adsorbable chemical additive is to be employed, the adsorbable chemical additives may be added to the fiber slurry in sequence to reduce interactions between the adsorbable chemical additives. In other situations, the adsorbable chemical additives may be removed from the fiber slurry after another adsorbable chemical additive has been added to facilitate the removal process. 
     Many fiber types may be used for the present invention including hardwood or softwoods, straw, flax, milkweed seed floss fibers, abaca, hemp, kenaf, bagasse, cotton, reed, and the like. All known papermaking fibers may be used, including bleached and unbleached fibers, fibers of natural origin (including wood fiber and other cellulose fibers, cellulose derivatives, and chemically stiffened or crosslinked fibers), some component portion of synthetic fiber (synthetic papermaking fibers include certain forms of fibers made from polypropylene, acrylic, aramids, acetates, and the like), virgin and recovered or recycled fibers, hardwood and softwood, and fibers that have been mechanically pulped (e.g., groundwood), chemically pulped (including but not limited to the kraft and sulfite pulp processings), thermomechanically pulped, chemithermomechanically pulped, and the like. Mixtures of any subset of the above mentioned or related fiber classes may be used. The pulp fibers can be prepared in a multiplicity of ways known to be advantageous in the art. Useful methods of preparing fibers include dispersion to impart curl and improved drying properties, such as disclosed in U.S. Pat. No. 5,348,620 issued Sep. 20, 1994 and U.S Pat. No. 5,501,768 issued Mar. 26, 1996, both to M. A. Hermans et al. and U.S. Pat. No. 5,656,132 issued Aug. 12, 1997 to Farrington, Jr. et al. 
     According to the present invention, the adsorbable chemical treatment of the pulp fibers occurs prior to the drying phase of the pulp processing. The two generally accepted methods of drying include flash drying and can drying. Flash drying is most common with bleached, chemi-thermo-mechanical pulp (BCTMP). The present invention may also be applied to wet lap pulp processes without the use of can or flash dryers. 
     Numerous features and advantages of the present invention will appear from the following description. In the description, reference is made to the accompanying drawings which illustrate preferred embodiments of the invention. Such embodiments do not represent the full scope of the invention. Reference should therefore be made to the claims herein for interpreting the full scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a schematic process flow diagram of a method according to the present invention for treating pulp fibers with adsorbable chemical additives. 
     FIG. 2 depicts a schematic process flow diagram of a method according to the present invention for treating pulp fibers with multiple adsorbable chemical additives. 
     FIG. 3 depicts a schematic process flow diagram of a method of making a creped tissue sheet. 
    
    
     DETAILED DESCRIPTION 
     The invention will now be described in greater detail with reference to the Figures. A variety of conventional pulping apparatuses and operations can be used with respect to the pulping phase, pulp processing, and drying of pulp. Nevertheless, particular conventional components are illustrated for purposes of providing the context in which the various embodiments of the invention can be used. 
     FIG. 1 depicts pulp processing preparation equipment used to apply adsorbable chemical additives to pulp fibers according to one embodiment of the present invention. The pulp processing equipment comprises a (high density) storage tank  12  where the bleached and never dried pulp fiber is held in the form of a fiber slurry  10  comprised of the pulp fiber and water. The consistency of the fiber slurry  10  when contained in the storage tank  12  may range from about 10 to about 12 percent fiber. In other embodiments, the consistency of the fiber slurry  10  in the storage tank  12  may range from about 8 to about 15 percent fiber. 
     The fiber slurry  10  is diluted and transferred from the storage tank  12  through suitable conduits  13  to the blend chest  14  where the fiber slurry  10  is subjected to agitation using a mixing blade, rotor, recirculation pump, or other suitable device  16 , thereby reducing variations in the fiber slurry  10 . The consistency of the fiber slurry  10  in the blend chest  14  may be from about 0.5 to about 15 percent fiber. In other embodiments, the consistency of the fiber slurry  10  in the blend chest  14  may be from about 2 to about 10 percent fiber or from about 3 to about 5 percent fiber. 
     The fiber slurry  10  is transferred from the blend chest  14  through suitable conduits  15  to a machine chest  18 . The consistency of the fiber slurry  10  in the machine chest  18  may be from about 0.5 to about 15 percent fiber. In other embodiments, the consistency of the fiber slurry  10  in the machine chest  18  may be from about 2 to about 10 percent fiber or from about 3 to about 5 percent fiber. 
     One or more adsorbable chemical additives  24  are supplied from a reservoir  22  and added to the fiber slurry  10  in the conduit  16  prior to the machine chest  18 . The amount of adsorbable chemical additive  24  is suitably about 0.1 kg./metric ton of pulp fiber or greater. In particular embodiments, the adsorbable chemical additive  24  comprises a softening agent and is added in an amount from about 0.1 kg./metric ton of pulp fiber or greater. The fiber slurry  10  and the adsorbable chemical additive  24  are desirably allowed to remain together in the machine chest  18  under agitation for a residence time sufficient to allow the pulp fibers to adsorb a substantial portion of the adsorbable chemical additive  24 . A residence time of at least about 10 minutes, for instance may be sufficient. In other embodiments, the residence time may range from about 10 seconds to about 30 minutes or from about 2 minutes to about 15 minutes. 
     The fiber slurry  10  is thereafter transferred from the machine chest  18  through suitable conduits  19  and a fan pump  20  to the screen device  26  where contaminates are removed based on size. The consistency of the fiber slurry  10  is typically decreased at some point during the transfer from the machine chest  18  to the fan pump  20 . One example of the screen device  26  is a slotted screen or a pressure screen. The fiber slurry  10  may also be subjected to a series of centricleaners (not shown) to remove heavy particles from the fiber slurry  10  and an atenuator (not shown) to reduce the variability of the pressure going into the headbox  28 . 
     The fiber slurry  10  is thereafter transferred through suitable conduits  27  to the headbox  28  where the fiber slurry  10  is injected or deposited into a fourdrinier section  30  thereby forming a wet fibrous web  32 . The wet fibrous web  32  may be subjected to mechanical pressure to remove water and unadsorbed chemical additive  24 . In the illustrated embodiment, the fourdrinier section  30  precedes a press section  44 , although alternative dewatering devices such as a nip thickening device, or the like may be used. The fiber slurry  10  is deposited onto a foraminous fabric  46  such that the fourdrinier section filtrate  48  is removed from the wet fibrous web  32 . The fourdrinier section filtrate  48  comprises a portion of the process water in addition to the unabsorbed chemical additive  24  in the water. The press section  44  or other dewatering device suitably increases the fiber consistency of the wet fibrous web  32  to about 30 percent or greater, and particularly about 40 percent or greater. The water and unadsorbed chemical. additive  24  removed as fourdrinier section filtrate  48  during the web forming step may be used as dilution water for dilution stages in the pulp processing, as the dilution water base for the adsorbable chemical additive  24 , or discarded. But, importantly, the fourdrinier section filtrate  48  containing the unadsorbed chemical additive  24  is not sent forward with the pulp fiber into the papermaking process. 
     The wet fibrous web  32  may be transferred to a dryer section  34  where evaporative drying is carried out on the wet fibrous web  32  to an airdry consistency, thereby forming a dried fibrous web  36 . The dried fibrous web  36  is thereafter slit, cut into sheets, and baled for delivery to paper machines  38 . At the paper machines  38 , the dried fibrous web  36  is mixed with water to form a wet slurry  40 . The wet slurry  40  contains the pulp fiber having the adsorbable chemical additive  24  adhered to the individual fibers. The wet slurry  40  is passed through the papermaking machine and processed to form a finished product  42 . By way of illustration, various paper or tissue making processes are disclosed in U.S. Pat. No. 5,667,636 issued Sep. 16, 1997 to Engel et al.; U.S. Pat. No. 5,607,551 issued Mar. 4, 1997 to Farrington, Jr. et al.; U.S. Pat. No. 5,672,248 issued Sep. 30, 1997 to Wendt et al.; and, U.S. Pat. No. 5,494,554 issued Feb. 27, 1996 to Edwards et al., which are incorporated herein by reference. The finished product  42  has enhanced qualities due to the retention of the adsorbable chemical additive  24  onto the pulp fibers during the pulp processing. 
     In other embodiments of the present invention, the adsorbable chemical additives  24  may be added to the fiber slurry  10  at a variety of positions in the pulp processing apparatus. In the alternative, the adsorbable chemical additives  24  may be added to the fiber slurry  10  at the storage tank  12 , the blend chest  14 , the machine chest  18 , the fan pump  20 , the screen device  26 , or any of the conduits  13 ,  15 , and  19  through which the fiber slurry  10  is transferred. To enhance the absorption of the adsorbable chemical additives  24  onto the pulp fibers of the fiber slurry  10 , agitation devices  16  may be utilized. In the conduits  13 ,  15 , and  19 , the agitation devices  16  may include static mixers such as baffles, or kinetic mixers such as pumps. 
     In another embodiment, a second machine chest  21  may be included in the pulp processing apparatus. (See FIG. 2.) The second machine chest  21  may be disposed between the first machine chest  18  and the fan pump  20 . 
     FIG. 2 depicts an alternative embodiment of the present invention in which sequential addition of adsorbable chemical additives  24  and  26  are added to the fiber slurry  10 . The pulp processing equipment comprises a (high density) storage tank  12  where the bleached and never dried pulp fiber is held in the form of a fiber slurry  10  comprised of the pulp fiber and water. The consistency of the fiber slurry  10  when contained in the storage tank  12  may range from about 10 to about 12 percent fiber. In other embodiments, the consistency of the fiber slurry  10  in the storage tank  12  may range from about 8 to about 15 percent fiber. 
     The fiber slurry  10  is diluted and transferred from the storage tank  12  through suitable conduits  13  to the blend chest  14  where the fiber slurry  10  is subjected to agitation using a mixing blade, rotor, recirculation pump, or other suitable device  16 , thereby reducing variations in the fiber slurry  10 . The consistency of the fiber slurry  10  in the blend chest  14  may be from about 0.5 to about 15 percent fiber. In other embodiments, the consistency of the fiber slurry in the blend chest  14  may be from about 2 to about 10 percent fiber or from about 3 to about 5 percent fiber. 
     The fiber slurry  10  is transferred from the blend chest  14  through suitable conduits  15  to the machine chest  18 . The consistency of the fiber slurry  10  in the machine chest  18  may be from about 0.5 to about 15 percent fiber. In other embodiments, the consistency of the fiber slurry  10  in the machine chest  18  may be from about 2 to about 10 percent fiber or from about 3 to about 5 percent fiber. 
     A first adsorbable chemical additive  24 , comprising one or more adsorbable chemical components, is supplied from a reservoir  22  and added to the fiber slurry  10  in a suitable conduit  15  prior to the machine chest  18 . The amount of first adsorbable chemical additive  24  is suitably about 0.1 kg./metric ton of pulp fiber or greater. In particular embodiments, wherein the first adsorbable chemical additive  24  is a softening agent and is added in an amount from about 0.1 kg./metric ton of pulp fiber or greater. The fiber slurry  10  and the first adsorbable chemical additive  24  are desirably allowed to remain together in the machine chest  18  under agitation for a residence time sufficient to allow the pulp fibers to adsorb a substantial portion of the first adsorbable chemical additive  24 . A residence time of at least about 10 minutes, for instance may be sufficient. In other embodiments, the residence time may range from about 10 seconds to about 30 minutes or from about 2 minutes to about 15 minutes. 
     The fiber slurry  10  containing the first adsorbable chemical additive  24  is transferred from the machine chest  18  through suitable conduits  17  to the second machine chest  21 . A second adsorbable chemical additive  25 , comprising one or adsorbable chemical additives, is supplied from a second reservoir  23  and added to the fiber slurry  10  in a suitable conduit  17  prior to the second machine chest  21 . The amount of the second adsorbable chemical additive  25  is suitably about 0.1 kg./metric ton of pulp fiber or greater. In particular embodiments, wherein the second adsorbable chemical additive  25  is a softening agent and is added in an amount from about 0.1 kg./metric ton of pulp fiber or greater. The fiber slurry  10  and the second adsorbable chemical additive  25  are desirably allowed to remain together in the second machine chest  21  under agitation for a residence time sufficient to allow the pulp fibers to adsorb a substantial portion of the second adsorbable chemical additive  25 . A residence time of at least about 10 minutes, for instance may be sufficient. In other embodiments, the residence time may range from about 10 seconds to about 30 minutes or from about 2 minutes 10 to about 15 minutes. 
     The fiber slurry  10  containing the first and second adsorbable chemical additives  24  and  25  is thereafter transferred from the second machine chest  21  through suitable conduits  19  and a fan pump  20  to the screen device  26  where contaminates are removed based on size. One example of the screen device  26  is a slotted screen or pressure screen. The fiber slurry  10  may also be subjected to a series of centricleaners (not shown) to remove heavy particles from the fiber slurry  10  and an atenuator (not shown). 
     The fiber slurry  10  is thereafter transferred through suitable conduits  27  to the headbox  28  where the fiber slurry  10  is injected or deposited into a fourdrinier section  30  thereby forming a wet fibrous web  32 . The wet fibrous web  32  may be subjected to mechanical pressure to remove water and unadsorbed chemical additive  24 . 
     The wet fibrous web  32  may be transferred to a dryer section  34  where evaporative drying is carried out on the wet fibrous web  32 , thereby forming a dried fibrous web  36 . The dried fibrous web  36  is thereafter slit, cut into sheets, and baled for delivery to paper machines  38 . At the paper machines  38 , the dried fibrous web  36  is mixed with water to form a wet slurry  40 . The wet slurry  40  contains the pulp fiber having the first and second adsorbable chemical additives  24  and  25  adhered to the individual fibers. The wet slurry  40  is passed through the paper machine and processed to form a finished product  42 . The finished product  42  has enhanced qualities due to the retention of the first and second adsorbable chemical additives  24  and  25  onto the pulp fibers during the pulp processing. 
     In other embodiments of the present invention, each of the first and second adsorbable chemical additives  24  and  25  may be added to the fiber slurry  10  at a variety of positions in the pulp processing apparatus. In alternative embodiments, the first and second adsorbable chemical additives  24  and  25  may be added to the fiber slurry  10  at the storage tank  12 , the blend chest  14 , the first or second machine chests  18  and  21 , the fan pump  20 , the screen device  26 , or any of the conduits  13 ,  15 ,  17 , and  19  through which the fiber slurry  10  is transferred. In addition, the first and second adsorbable chemical additives  24  and  25  may be added to the same piece of pulp processing equipment at different times, such as the addition of the second adsorbable chemical additive  25  to the blend chest  14  after a sufficient residence time has elapsed after the addition of the first adsorbable chemical additive  24  to the blend chest  14 . To enhance the uniformity of the absorption of the first and second adsorbable chemical additives  24  and  25  onto the pulp fibers of the fiber slurry  10 , agitation devices  16  may be utilized. In the conduits  13 ,  15 , and  19 , the agitation devices  16  may include static mixers such as baffles, or kinetic mixers such as pumps. 
     In other embodiments of the present invention, one batch of pulp fibers may be treated with a first chemical additive according to the method of the present invention as discussed above while a second batch of pulp fibers may be treated with a second chemical additive according to the present invention. During the papermaking process, different pulp fibers or pulp fibers having different treatments may be processed into a layered paper or tissue product as disclosed in the U.S. Pat. No. 5,730,839 issued Mar. 24, 1998 to Wendt et al., which is incorporated herein by reference. 
     Referring to the FIG. 3, a tissue web  64  is formed using a 2-layer headbox  50  between a forming fabric  52  and a conventional wet press papermaking (or carrier) felt  56  which wraps at least partially about a forming roll  54  and a press roll  58 . The tissue web  64  is then transferred from the papermaking felt  56  to the Yankee dryer  60  applying the vacuum press roll  58 . An adhesive mixture is typically sprayed using a spray boom  59  onto the surface of the Yankee dryer  60  just before the application of the tissue web to the Yankee dryer  60  by the press roll  58 . A natural gas heated hood (not shown) may partially surround the Yankee dryer  60 , assisting in drying the tissue web  64 . Two tissue webs  64  may be plied together and calendered. The resulting 2-ply tissue product can be wound onto a hard roll. 
     EXAMPLES 
     Example 1 
     This example will describe how to produce chemically modified pulp as described according to the present invention. Referencing FIG. 1, the fully bleached eucalyptus pulp fiber slurry having about 10% solids was diluted to about 2.5% solids in the conduit as the fiber slurry was pumped out of the high density storage tank. The fiber slurry was then pumped to the blend chest. As the fiber slurry was transferred from the blend chest to the machine chest through a conduit, a 1 percent dispersion of an imidazoline softening agent (methyl-1-oleyl amidoethyl-2-oleyl imidazolinium methylsulfate identified as Mackernium DC-183, commercially available from McIntyre Ltd., located in University Park, Ill.), was mixed into the fiber slurry. 
     The dosage of the chemical softener was 3 kilograms per tonne of eucalyptus pulp fiber in the fiber slurry. The chemical softener was mixed with the fiber slurry in the machine chest for about 10 minutes. The fiber slurry was then diluted to about 0.6% solids and used to form a wet fibrous web on the wet end of a dry lap machine. 
     During the formation of the wet fibrous web, a substantial portion of the chemical softener remained attached to the pulp fiber in the fiber slurry. The unadsorbed chemical softener remained in the water phase, which was drained as filtrate from the pulp fiber. The wet fibrous web was pressed in a press section and dried in a dryer section, thereby forming a dried fibrous web having 90% solids. As treated, the pulp fiber was now in the form to be used as a raw material in the tissue papermaking process. 
     The filtrate removed during the drainage step was recycled back in the process and used for the dilution of the fiber slurry in the conduits. Recycling of the filtrate containing the unadsorbed Mackernium DC-183 chemical softener provided additional opportunities for adsorption of the chemical softener by the pulp fiber of the fiber slurry. 
     Example 2 
     A layered soft tissue product was made using the pulp fiber produced according to the process disclosed in Example 1. The tissue product was made using the overall process shown in FIG.  3 . The first stock layer contained the chemically treated Eucalyptus hardwood pulp fiber produced as described in Example 1, which made up about 65 percent of thee tissue web by weight. This first stock layer was the first layer to come into contact with the forming fabric and was also the layer that came into contact with the drying surface of the Yankee dryer. The second stock layer contained northern softwood kraft pulp fiber. The second stock layer made up about 35 percent of the tissue web by weight. A modified polyacrylamide dry strength agent, Hercobond 1366 commercially available from Hercules Inc. located in Wilmington, Del., was added to the pulp fiber of the softwood layer. The Hercobond 1366 was added to the thick stock, that was at about 1.9% solids, at an addition level of about 0.3% of the pulp As fiber in the entire tissue web. A polyamide epichlorohydrin wet strength agent, Kymene 557LX commercially available from the Hercules, lnc., was added to both the Eucalyptus and northern softwood kraft furnishes at an addition level of about 0.2% based on the pulp fiber in the entire tissue web. 
     Referring to the FIG. 3, the tissue web was formed using a 2-layer headbox between an Albany P-621 forming fabric commercially available from Albany International Corp., located in Menasha, Wis., and a conventional wet press papermaking (or carrier) felt (Weavex M1C commercially available from Weavex located in Wake Forest, N.C.) which wraps at least partially about a forming roll and a press roll. The basis weight of the tissue web was about 7.3 pounds per 2880 square feet of air dried tissue web. 
     The tissue web was then transferred from the papermaking felt to the Yankee dryer by the vacuum press roll. The water content of the tissue web on the papermaking felt just prior to transfer of the tissue web to the Yankee dryer was about 87 percent. The moisture content of the tissue web after the application of the press roll was about 55 percent. An adhesive mixture was sprayed using a spray boom onto the surface of the Yankee dryer just before the application of the tissue web by the press roll. The adhesive mixture consisted of about 40% polyvinyl alcohol, about 40% polyamide resin and about 20% quaternized polyamido amine as disclosed in U.S. Pat. No. 5,730,839 issued to Wendt et al. which is herein incorporated by reference. The application rate of the adhesive mixture was about 5.5 pounds of dry adhesive per tonne of dry pulp fiber in the tissue web. A natural gas heated hood (not shown) partially surrounding the Yankee dryer had a supply air temperature of about 680° to assist in drying the tissue web. The temperature of the tissue web after the application of the creping doctor was about 240° as measured with a handheld infrared temperature gun. The machine speed of the 24 inch wide tissue web was about 3000 feet per minute. The crepe ratio was about 1.30 or about 30%. 
     Two tissue webs were unwound from two soft rolls (or parent rolls) and plied together and calendered with two steel rolls at 90 pounds per lineal inch. The 2-ply tissue product was constructed such that the first stock layer containing the chemically treated Eucalyptus pulp fiber disclosed in Example 1 was plied to the outside of the 2-ply tissue product which was wound onto a hard roll. The hard roll is converted into finished product, such as facial tissue and the like. The finished basis weight of the 2-ply tissue product at standard TAPPI standard temperature and humidity was about 17.1 pounds per 2880 square feet. The MD tensile was about 951 grams per 3 inches and the CD tensile was about 449 grams per 3 inches. The thickness of one 2-ply tissue product was about 0.0097 inches. The MD stretch in the finished tissue product was about 23.3 percent. All tensile tests were conducted at standard TAPPI conditions. 
     While the invention has been described in conjunction with a specific embodiment, it is to be understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the aforegoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.