MXPA06004585A - Process for making abrasion resistant paper and paper and paper products made by the process. - Google Patents

Abstract

In this papermaking process, a first strength agent is added to a stock suspension containing pulp and optionally other additives prior to its being formed into a web at the wet end of a papermaking machine. The web is then formed and processed into paper. A second strength agent is then applied to the surface of the paper. The strength agents may be selected to have opposite charge.

Description

PROCEDURE FOR MANUFACTURING ABRASION-RESISTANT PAPER AND PAPER AND PAPER PRODUCTS MANUFACTURED THROUGH THE PROCESS CROSS REFERENCE TO RELATED REQUEST This application claims the benefit of provisional application Serial No. 60/514279, filed on October 24, 2003, which is incorporated herein by reference.

FIELD OF THE INVENTION The present invention relates to papermaking and, more particularly to papermaking processes having improved properties such as abrasion resistance, decreased coefficient of friction, and increased brightness.

BACKGROUND OF THE INVENTION The surface strength of manufactured paper products is receiving increased attention as the papermaking technology advances and the paper products produced thereby find a field that is always growing in use. Poor surface resistance has numerous repercussions on the papermaking machinery and the products themselves. Paper products that have a low surface resistance can be attached or trapped in the rollers during the manufacturing process causing costly delays and waste in materials. Simi- larly, paper used in a component of a commercial product, such as backing paper for gypsum board, should ideally have a high surface resistance in order to prevent tearing or damage to core components as well as prevent get trapped or join the conveyor belts during several steps of product manufacturing and transportation. Accordingly, it must be highly desirable to be able to manufacture paper having an increased surface strength in order to improve the abrasion resistance, especially when the paper to be used as backing paper in abuse resistant panel products. A variety of different solutions have been proposed to solve or minimize the problem of abrasion resistance on paper surfaces. For example, U.S. Patent No. 6,083,586 describes compositions and methods for making sheets of material having a starch binding matrix, optionally reinforced with fibers and inorganic mineral filler. U.S. Patent No. 6,153,040 discloses a method for reducing coils in gypsum board panels when the panels are laminated. At least one side of the gypsum board paper is treated with a friction reducing agent, such as a wax or wax emulsion, or in order to reduce its coefficient of friction, which results in the reduction of the shear stress develops between the backing paper of a drywall panel and the conveyor belts used to transport such a panel. The addition of cationic moisture-resistant polyamide resins for paper cover sheets, especially polyamide epichlorohydrin resins, is described in U.S. Patent No. 6,489,040. U.S. Patent No. 6,517,674 discloses a process for making tough abrasion resistant paper that incorporates spacer or separator particles to minimize the amount of surface damage on the paper surface. The particles described and incorporated into the paper are microcells, such as glass microspheres, and particles resistant to resistance abrasion such as aluminum oxide or silicon carbide. According to the '674 patent, the particles are added to the paper fiber pulp at the wet end of the paper machine from a primary or secondary main box using a curtain groove coater as the application device. In the procedure taught in the Patent of E. U. A. No. 6,551, 457, the paper is produced from an aqueous suspension containing cellulosic fibers and optional fillers. After draining the suspension, the paper web obtained is passed through the clamp of a papermaking machine. A chemical system comprising a polymer component and a micro or nanoparticle component is added to the paper suspension / network. The addition of such a mixture of components is said to improve the quality and overall strength of the paper product, such as its coefficient of friction. U.S. Patent No. 6,562,444 discloses a fiber-cement composite and plaster laminate construction material containing an adhesive layer interposed between the fiber-cement sheet and the gypsum panel, to improve the abrasion resistance of the laminate. The adhesive layer is a polymeric adhesive, such as modified starches. US Patent No. 6,568,148 discloses a cover element for building surfaces and method for the production of such an element. The cover element is described as having an upper surface with a support layer formed of cellulose in which a material resistant to abrasion, such as corundrum particles, is fixed, thereby providing increased abrasion resistance and a decreased coefficient of friction. . The literature has also reported several methods to the abrasion resistance problem in papers. Zhang, and others, in Wear, Volume 253 (2002), p. 1086-1093 ("Effect of Particle Surface Tratmeat on the Tribological Performance of Epoxy Based Nanocomposites") describes the preparation of covalently bonded nanosilicon bound to polyacrylamide particles, thereby increasing the interfacial interaction between particles and the matrix, and resulting in reductions in surface abrasion. Gurnagul, et al., Described factors that affect the coefficient of friction of paper, and suggested that the coefficient of friction is a function of the number of extracts present on or on a paper surface (Journal of Applied Polymer Science, Volume 46 (1992 ), pp. 805-814; "Factors Affecting the Coefficient of Friction of Paper"). According to the article, the amount of identity of the particles significantly affects the coefficient of friction. Finally, a description describing the effect of fillers on the coefficient of friction of papers was detailed in TAPPI Journal Volume 74 (1991, pp. 341-347 ("Effect of Fillers on Paper Friction Properties"), which describes how the use of various fillers such as kaolin, talc, and synthetic precipitated silica in the papermaking process can affect the coefficient of friction.While it is known that the addition of small particles resistant to hard abrasion (also referred to as "resistant") to the paper , or resin mixtures that can coat the sheet, can increase the abrasion resistance of papers, paper products and high pressure laminates, its use is frequently accompanied by costly side effects.For example, the use of alumina has been reported It provides 400 to 600 cycle wear resistance, however, the use of abrasion resistant particles, including microparticles or nanoparticles, tend to tearing and causing significant damage to highly polished thin membrane plates and rollers used during the paper production process to produce both high pressure and low pressure products. Rollers and thin membrane plates ripped or otherwise damaged through contact with abrasion resistant materials as described above must be coated or replaced at a significant cost. In view of the foregoing, it will be appreciated that there is a need for abrasion-resistant paper, and a process for producing such an abrasion-resistant paper that avoids damage to the papermaking machinery caused by the incorporation of paper strength.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a process for making paper as well as paper and paper products manufactured by the process. In this papermaking process, a first strength agent is added to the slurry containing pulp and optionally other additives before it is formed into a web at the wet end of a papermaking machine. The network is then formed and processed on paper. Then a second resistance agent is applied to the surface of the paper. In this procedure, the resistance agents are selected to have opposite charge (or to be amphoteric). Thus, in one embodiment, for example, the first resistance agent is an agent resistant to cationic drying and the second resistance agent is an agent resistant to anionic drying. The process of this invention can be used to make paper that is resistant to abrasion. The modalities of this process produce paper having other desirable physical properties such as high optical brightness and a low friction surface. An optically bright paper can be obtained by applying the second strength agent in a solution that also contains an optical brightener. A paper having a low friction surface can be obtained by including a hydrophobic organosilicon in the solution that is used to apply the second strength agent. The paper manufactured by the process is useful in a variety of paper products. In particular, the process is useful for making abrasion resistant backing paper for the gypsum board.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES When not expressly defined, the terms used in this description are intended to be interpreted as those skilled in the art will understand them. The following express definitions are in accordance with the understanding of those skilled in the art. "Paper", as used herein, refers to a network of pulp fibers that are formed from an aqueous suspension in a cable or screen and held together at least in part through hydrogen bonding, and which can be manufactured by hand or by machine. Included in this definition is a wide variety of networks entangled or covered by plant fiber felt (in most wood) that have formed on a screen of a water suspension, such as "tree paper" made of wood pulp derived of trees, "plant papers" or "plant papers" that include a wide variety of plant fibers (also known as "secondary fibers"), such as straw, flax, and rice fibers, and is widely referred to as "paper based on cellulose ", and Kraft paper (paper manufactured by the Kraft process). Furthermore, the term "paper" as used herein means that it refers to products that contain substantially all virgin pulp fibers, substantially all recycled pulp fibers, or both virgin and recycled pulp fibers. "Papermaking machine", as used herein, refers to any of the papermaking machines known in the art, all of which are suitable for use with the process of the present invention. Such machines include cylinder machines, fourdrinier machines, twin wire forming machines, old FC machines and modifications thereof. "Pulp" refers to fibers that are plant-based, including but not limited to wood and similar "lumpy" plants, soybeans, rice, cotton, straw, flax, abaca, hemp, bagasse, lignin-containing plants, and the like. . Such pulps include, but are not limited to, thermomechanical pulps, bleached thermomechanical pulps, chemithermomechanical pulps (CTMP), bleached chemithermomechanical pulps, and bleached thermo-mechanical pulps bleached. "Sheet", as used herein, is intended to include any substantially flat sheet, corrugated, curved, bent, or textured manufactured using the compositions and methods described herein. The sheets may have a widely varying thickness depending on the particular application for which the sheet is intended. That is, the sheets can be as thin as about 0.01 mm and as thick as 1 cm or more, where strength, durability, and / or volume are important considerations depending on the final use of the sheet of paper. "Concentrated suspension", as used herein, refers to a mixture, or slurry, of pulp, fillers, water and other papermaking materials. As used herein, the term "concentrated suspension" means that it is equivalent to the term "pulp slurry". "Resistance agent" refers to compounds that are incorporated into the paper in order to increase their tear strength. "Moisture-resistant agents" are agents that make paper that is more resistant to tearing when the paper is wet. "Drying resistant agents" are agents that make paper more resistant to tearing when the paper is dry, but less effective on paper that resists moisture than are moisture resistant agents. The drying-resistant agents may be cationic, anionic or amphoteric in nature. "Red", as used herein, refers to continuous entanglement of fibers that are deposited on the wire or felt, drained, pressed and dried to form paper. The present invention provides a method for making paper. The paper and paper products manufactured by the process can exhibit improved surface resistance, abrasion resistance, a low friction surface and / or high optical brilliance depending on the particular mode of the process that was followed. The process of the present invention can be practiced in conventional papermaking equipment. Although the papermaking equipment varies in operation and mechanical design, the procedures by which the paper is manufactured in the different equipment contain common steps. Papermaking includes a pulp stage, concentrated preparation stage, a wet end stage and a dry end stage. In the pulp, the individual cellulose fibers are released from a cellulose source such as wood either by mechanical or chemical action, or both. The released fibers, or pulp, are suspended in water in the concentrated preparation step. Additives such as brightening agents, dyes, pigments, fillers, antimicrobial agents, defoamers, pH control agents and drainage aids can also be added to the existence at this stage. While the term is used in this description, "concentrated preparation" includes such operations as diluting, classifying, and cleaning the concentrated suspension that may occur prior to the formation of the network. In particular, it includes feeding the pulp stream to a machine case fan pump. The wet end stage begins after the preparation of the concentrated suspension. For the purpose of this description, the wet end stage begins when the pulp first contacts a wire or felt in a papermaking machine. The wet end stage also includes such subsequent operations as forming the network, draining the network and consolidating the network (by pressing). In the dry end stage, the network is dried and can be subjected to the additional process such as size pressure, calendar, aerosol coating of surface modifiers, printing, cutting, corrugation and the like. Of relevance to the present invention, a size pressure is a device for applying a solution to paper, it includes a pair of pressable rolls that are moistened with the solution sought to be applied. The size pressure is typically located between the drying sections to allow removal of excess moisture. Size pressures are typically used to apply the surface adjustment to improve the water resistance of the paper and improve ink absorption. A calendar group is a series of solid rolls, usually made of iron or steel through which the dry paper is passed in a serpentine form. The pressure applied to the paper as it passes between the rolls in the calendar group can improve the smoothness of the surface, increase the brightness, make the caliper of the paper more uniform and decrease the porosity. Relevant to the present invention, a clamp (or multiple clamps) between the calendar rolls may be flooded in a "water box" application. The calendar water box can be used to apply coatings to paper for a variety of purposes, such as increasing water resistance, reducing curling and improving gloss. In addition to a size pressure and calendar water box, the dried paper can be coated by the spray coating using an aerosol pump. Three general types of papermaking machines are routinely used in the papermaking industry that differ in the way they form the network. In a fourdrinier papermaking machine, the network is formed by delivering a concentrated suspension band to a porous belt known to those skilled in the art as "cable" of a main case. The main box is a tank placed on or next to the cable. The cable is drawn between a "chest roll" and a "bed roll" and is typically directed through the bed roll. The main box is typically placed on the cable near chest roll. The network is delivered from the main box to the wire through a narrow opening in the main box which is known to those skilled in the art as the "slice". While the wire travels, the net is carried to the bed roll. As it travels, the water drains from the pulp through the porous wire under the effect of gravity and typically with the help of tube rolls, hydrofoil and / or suction boxes. From the wire, the network is passed to the pressure section of the paper machine. The network typically has a consistency of about 12% to about 25% before being pressed. In the pressure section, the network is tightened between pressure rolls to remove more water. From the pressure section, the partially dried network is passed to the drying section. There, the network is dried, typically at a moisture content of about 4% to about 12% when passing over heated dryer containers, although many paper machines in the plaster industry dry at 0% to about 1% moisture content for greater dimensional stability. Another common papermaking machine is the cylinder machine. The concentrated suspension is fed into one more tanks. In each tank, there is a horizontally arranged cylinder that has a wire around its circumference. The cylinder is partially immersed in the concentrated suspension. The cylinder is rotated. While doing this, the wire picks up fibers, takes them out of the concentrated suspension and delivers them to a "felt picker". The felt catcher is a porous belt that travels asynchronously with the cylinder. In a multi-cylinder machine, multiple-sided paper can be manufactured by providing a different concentrated suspension to each tank. The net of the felt collector is then transferred to the pressure section and then to the drying section. In another common design, the concentrated suspension is sprayed between two converging wires. Such twin wire formers accelerate the removal of water making it suitable for high speed machines. It has been found that adding a cationic drying resistance agent prior to the moisture step of the papermaking process and an anionic drying resistance agent during the drying step of the papermaking process generates paper having a strength of increased surface. Accordingly, the present invention provides a process for making paper and paper products comprising the steps of (1) preparing a concentrated suspension of cellulosic fibers, (2) adding a first strength agent to the concentrated suspension, (3) forming the cellulosic fibers in a substantially uniform network, and (4) drying the network in paper and applying a second resistance agent to the paper surface. The first resistance agent is either an agent resistant to cationic drying, an agent resistant to amphoteric drying, or an agent resistant to cationic moisture, with agents resistant to cationic drying being preferred. The second resistance agent is either an anionic drying resistant agent or an amphoteric drying resistant agent, with anionic drying resistant agents being preferred. Cationic drying resistant agents useful in the practice of the present invention include, but are not limited to, cationic polyacrylamides, natural polymers, modified natural polymers, synthetic polymers, modified starches to have quaternary ammonium functional groups, celluloses, natural gums, polyvinyl alcohols and any number of commercially available compounds having bipolar functional groups that allow the formation of hydrogen bonds. The cationic drying resistant agents are cationic polyacryiamides and cationic synthetic polymers. As those skilled in the art will appreciate, a cationic polyacrylamide can be made with the polymerization of acrylamide with another acrylic monomer having a quaternary ammonium substitute therein, such as (CH3, 3N1-CH2CH20C (O) CHCH2. A commercially available cationic polyacrylamide is Nalco 997, available from Nalco Chemical Company (Naperville, Ill.) Anionic drying resistant agents useful in the practice of the present invention include, but are not limited to, anionic polyacryiamides, natural starches, and carboxymethylcellulose. (CMC) The most preferred anionic drying agents are anionic polyacryiamides, As those skilled in the art will appreciate, an anionic polyacrylamide can be manufactured by the copolymerization of acrylamine with an anionic acrylic monomer such as sodium acrylate. an anionic polyacrylamide commercially available is Nalco 1044, available from Nalco Chemical Company (Naperville, IL). In an alternative embodiment, either the cationic drying resistant agent or the anionic drying resistant agent, or both, are replaced by an agent resistant to amphoteric drying, such as amphoimeric starches. Amphoteric compounds useful in the practice of the present invention have a ratio of anionic groups to cationic groups of from about 0.1: 1.0 to about 1.0: 1.0. Preferably, the amphoteric compounds have a ratio of anionic groups to cationic groups of about 1.0: 1.0. For example, the ratios of anionic groups to cationic groups in amphoteric compounds suitable for use with the present disclosure include ratios of about 0.1: 1.0, about 0.2: 1.0, about 0.3: 1.0, about 0.4: 1.0, about 0.5: 1.0, about 0.5: 1.0, approximately 0.6: 1.0, approximately 0.7: 1.0, approximately 0.8: 1.0, approximately 0.9: 1.0, approximately 1.0: 1.0, and proportions that fall within either of two of these proportions. Even in another alternative embodiment, the agent resistant to cationic drying is replaced by a cationic moisture resistant agent. The moisture resistant agents are typically thermosetted resins that are added to the concentrated suspension, network or paper in order to impart moisture resistance to the paper product. They also frequently contribute to the drying resistance of the paper. Moisture resistant agents are often cationically thermosetted resins, and are typically added to the stock before being shipped to the paper machine. Through thermoconfiguration, this means that with drying and / or heating, the moisture-resistant resins of a substantially insoluble and water-resistant network that can withstand the moisture of the paper, thereby, contribute to the moisture resistance of the paper. Generally speaking, the moisture resistant agents are polymeric, polar enough to be soluble or substantially water dispersible, cationic to be substantive to the pulp, and reactive / thermoconfigurable. The types of water resistant agents useful in the practice of the present invention include acid-restoring resins, neutral to acid-restoring resins, and neutral to alkaline restorative resins. Useful acid-base or formaldehyde-based resins that include urea-formaldehyde (UF) resins, melamine-formaldehyde (MF) resins, and other resins that can be used at a system pH between about pH 4 and pH 5 Neutral to the acid restoration resins which are useful as moisture resistant agents in the practice of the present invention include dialdehyde starch (DAS), polyacrylamide glyoxal resins (PAMG), and modified aldehyde starches. Neutral / alkaline restoration resins which are useful as polyamide-epichlorohydrin resins of moisture resistant agents (PAE), resins containing at least one epoxide functional group, and derivatives of the reaction of epichlorohydrin with a polyamine resin. Agents resistant to cationic, anionic and amphoteric drying, as well as moisture resistant agents, preferably have a specific gravity of about 1.00 to about 1.20, and more preferably a specific gravity of about 1.01 to about 1.10. More preferably, the specific gravity is from about 1.02 to about 1.08. The drying resistant agents preferably have a viscosity of about 1,000 cps (1 Pa-s) to about 15,000 cps (15 Pa-s), and more preferably from about 2,000 cps (2 Pa-s) to about 14,000 cps ( 14 Pa) Cationic drying agents added before the wet end (eg, fed in the presence of coarse liner) can be added in an amount of about 0.5 kg / t (total paper) to about 9.1 kg / t, and more preferably from approximately 2.3 kg / t to approximately 6.8 kg / t. For example, the cationic drying resistant agents added before the wet end of the manufacturing process can be added in an amount of about 0.5 kg / t, about 0.9 kg / t, about 1.4 kg / t, about 1.8 kg / t, about 2.3 kg / t, approximately 2.7 kg / t, approximately 3.2 kg / t, approximately 3.6 kg / t, approximately 4.1 kg / t, approximately 4.5 kg / t, approximately 6.8 kg / t and approximately 9.1 kg / t, as well as scales between any of two of these values. When the cationic drying resistant agent is Nalco 997, it is preferably added at a rate of about 4.5 kg / t dry. Agents resistant to anionic drying are added to the dry end (e.g., in the calendar water box) in an amount of about 2.3 kg / t (from liner folds) to about 1.3 kg / t, and more preferably from approximately 2.7 kg / t to approximately 9.1 kg / t. The drying-resistant agents added to the dry end of the manufacturing process can be added at an amount of about 2.3 kg / t, about 2.7 kg / t, about 3.2 kg / t, about 3.6 kg / t, about 4.1 kg / t, about 4.5 kg / t, about 6.8 kg / t, about 9.1 kg / t, and about 11.3 kg / t, as well as at scales between any of these two values. When the anionic drying resistant agent is Nalco 044, it is preferably added at a rate of about 0.9 kg / t dry. Drying resistant agents can be added in one portion, or in increments in a predetermined period of time. For example, the cationic drying resistant agent may be added to the wet end of the papermaking machine in substantially a portion, or charge. Preferably, the agent resistant to cationic drying is added to the wet end in increments in predetermined amounts over a period of time. A typical method of making a paper product having increased surface strength according to the present invention is as follows. A suspension of pulp and fiber is prepared and additives are added, as necessary. An agent resistant to cationic drying or agents can be added at this point. The pulp "formed", or applied to the wire in a suitable consistency to provide good formation. That means, that the existence is applied so that a fixed distribution of fibers results, following the generation of a paper product of uniform thickness. This is done by circulating the concentrated suspension in a main box so that the existence is delivered as a substantially uniform network of pulp in the wire through the slice at a rate substantially equivalent to that of the wire. An optional secondary main box can be provided to deliver a high quality fiber top coat on the primary paper product sheet as it moves down the production line. Following the placement of the concentrated suspension of the main box in the mobile wire, the network is transported on rolls (such as chest rolls, board rolls, and bed rolls) and suction boxes, and off the table. While the paper web is transported in the wire, the sheet loses the water by drainage and through the suction boxes, and optionally through sheets, lovacs, vacuum units, and the like. The extra water is removed from the net when pressing and drying. Drying can be done through the use of drying devices such as drying tanks (hollows, revolvers, filled steam drums), felts driers, steam control systems, pocket ventilation systems, dryer covers, Yankees drying drums , pulse drying, combinations thereof, and the like. The choice of type of drying medium will generally depend on the machine and / or the type of paper product being manufactured. Adjustments, defoamers, and the like can be added using one or more size pressures located between the dryer sections.

The paper then passes through a calendar group equipped with a water box, where an agent or agents resistant to anionic drying are added. Optionally, a hydrophobic organosilicon compound in combination with the anion drying agent and an optical brightener are fed into the water box, and consequently applied to the paper as it passes through the water box of the calendar group. As further illustrated in Example 1, which follows, the paper and paper products manufactured by the process of this invention exhibit strength and improved surface. Normal plaster face paper will lose approximately 0.023 cm in 100 to 200 abrasion cycles while paper manufactured according to our procedure only loses 0.000 to 0.013 cm after 1000 cycles. The surface resistance was measured using a modification of the procedure specified in ASTM D 4977-98 b. A particular embodiment of the inventive method generates a paper with a surface having a low coefficient of friction. This embodiment includes the steps of: (1) preparing a concentrated suspension of cellulosic fibers, (2) adding a first strength agent to the concentrated suspension, (3) forming the cellulosic fibers in a substantially uniform network, and (4) drying the paper net and apply a solution containing a second resistance agent and a hydrophobic organosilicon compound to the surface of the paper.

Preferred hydrophobic organosilicones are described in U.S. Patent No. 3,389,042, the disclosure which is incorporated herein by reference in its entirety. Commercially available silicones that are specifically preferred for use in the present invention are RE-29, GE-OSI and SM-8715 available from Dow Corning Corp. (Midland, MI). The hydrophobic organosilicon is preferably added in a solution with the anionic drying resistant agent that is fed into a water box. Previously, due to the high cost of silicone, surface adjustment is made before a silicone coating, and its use as an adjustment agent is deteriorated by its cost (Duraiswamy, C, et al., "Effect of Starch Type on the Silicon Hi-Out of Relay Papers, 2000 Coating Conference Proceedings, "TAPPIJ Hournal, 2001, Volume 84 (3)). However, it has been found that the addition of silicone in combination with an agent resistant to anionic drying in the water box creates a synergistic effect, where the silicone imparts some adjustment while the drying resistant agent increases the surface strength of the paper product. Of course, silicone adjusting agents can also be added in any conventional manner during the papermaking process. The hydrophobic organosilicon is preferably added in an amount of about 0.5 kg / t to about 4.5 kg / t, and more preferably from about 0.5 kg / t to about 2.3 kg / t, and more preferably 0.5 kg / t to about 0.5-1.5 kg / t. Another particular embodiment of the inventive method generates a paper with a glossy surface. Surfaces with an L * value of 89 or greater can be obtained, this modality includes the steps of: (1) preparing a concentrated suspension of cellulosic fibers, (2) adding a first agent of resistance to the concentrated suspension, (3) forming the cellulosic fibers in a substantially uniform network; and (4) drying the network in paper and applying a solution containing a second strength agent and a polish to the surface of the paper. Compounds useful as brightening agents in the practice of the present invention include but are not limited to azoles; bifenllos; chelating agents such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA, hydroxyethylethylenediaminetriacetic acid (HEDTA) and nitrilotriacetic acid (NTA) and other compounds that are capable of chelating heavy metals that catalyze color-forming reactions.The useful optical brighteners also include coumarinos; furans; ionic brighteners, including anionic, cationic, and anionic (neutral) compounds, such as, Eccobrite and Eccowhite @ compounds available from Eastern Color & Chemical Co. (Providence, Rl); naphthalimides; pirazenas; stilbenes, such as the Leucophor scale of optical brighteners available from the Clariant Corporation (Muttenz, Switzerland), and Tinopal from Ciba Specialty Chemicals (Basel, Switzerland); salts of such compounds including, but not limited to, alkali metal salts, ferrous alkali metal salts, transition metal salts, organic salts (e.g., cyclohexyl salts and citric acid); and ammonium salts of such brightening agents, and combinations of one or more of the above agents. Preferably, the brightening agent is added to the paper in an amount of about 0.01% by weight to about 90% by weight. More preferably, the paper contains from about 0.1 wt% to about 50 wt% of the brightening agent. For example, the optical brightener may be added in an amount of about 0.045 kg / 92.903 cm2 of paper to about 0.227 kg / 92.903 cm2 of paper. In accordance with this particular embodiment of the inventive process, the brightener is added to the solution of the second strength agent and applied simultaneously to the paper during the drying stage of the papermaking process. Of course, brightening agents can also be added in any conventional manner during the papermaking process. The paper and paper products manufactured according to the inventive process may also optionally contain other useful additives by improving one or more properties of the finished paper product, assisting the process of making the same paper, or both. These additives are generally characterized as either functional additives or control additives. Functional additives are typically those additives which are used to improve or impart certain properties specifically desired to the final paper product and include but not be limited to brighteners, dyes, fillers, setting agents, starches, and adhesives. The control additives, on the other hand, are additives incorporated during the papermaking process to improve the total process without significantly affecting the physical properties of the paper. Control additives include biocides, retention aids, defoamers, pH control agents, level control agents, and drainage aids. Paper and paper products made using the process of the present invention may contain one or more functional additives and / or control additive. The pigments and dyes impart color to the paper. The dyes include organic compounds that have double conjugated link systems; azo compounds; azo metal compounds; anthraquinones; triaryl compounds, such as triarylmethane; quinoline and related compounds; acid dyes (anionic organic dyes containing sulfonate groups, used with organic / cations such as alum); basic dyes (cationic organic dyes containing amine functional groups); direct dyes (acid type dyes having high molecular weights and a direct specific affinity for cellulose); as well as combinations of the suitable dye compounds listed above. The pigments are finely divided minerals that can be white or colored. The pigments that are most commonly used in the papermaking industry are clay, calcium carbonate and titanium dioxide. Fillers are added to the paper to increase the opacity and brilliance. Fillers include but are not limited to calcium carbonate (calcite); precipitated calcium carbonate (PCC); calcium sulfate (including several hydrated forms); calcium aluminate; zinc oxides; magnesium silicates, such as talc; titanium dioxide (Ti02), such as anatase or rutila; clay, or kaolin, consisting of hydrated Si02 and AI2O3; synthetic clay; mica; verniculite; inorganic aggregates; perlite; sand, gravel; sandstone; pearls of vidirio; aerogels; xerogels; safe emulsion agar gel; volatile ash; alumina; microspheres; hollow glass spheres; porous ceramic spheres; cork; seeds; lightweight polymers; zonotlite (a crystalline calcium silicate gel); pumice; exfoliated rock; waste concrete products; partially hydrated or unhydrated hydraulic cement particles; and diatomaceous earth, as well as combinations of such compounds. The average diameter of the filler particles is typically less than about 5 microns, although sizes up to 200 microns can be used depending on the thickness of the finished paper sheet. Generally, however, the average particle size diameter of the filler particles typically ranges from about 0.001 microns to about 100 microns, and more typically from about 0.01 to about 50 microns in diameter. The fillers are typically added to the pulp suspension in amounts of about 1% by weight to about 70% by weight, and more typically from about 5% by weight to about 40% by weight, and more typically about 10% by weight to about 30% by weight, based on the total dry weight of the existence of start pulp. Fillers typically have a refractive index of about 1.50 to about 3.00, and more typically from about 1.53 to about 2.80. The refractive indices of fillers include about 1.50, about 1.51, about 1.52, about 1.53, about 1.54, about 1.55, about 1.56, about 1.57, about 1.58, about 1.59, about 1.60, about 1.61, about 1.62, about 1.63, about 1.64, approximately 1.65, approximately 1.70, approximately 1.75, approximately 1.80, approximately 1.90, approximately 2.00, approximately 2.10, approximately 2.20, approximately 2.30, approximately 2.40, approximately 2.50, approximately 2.60, approximately 2.70, approximately 2.80, approximately 2.90, approximately 3.00, and scales between any two of these values. The fillers typically have a specific gravity of from about 1.50 to about 4.5, and more typically from about 1.50 to about 4.2, and more typically from about 2.50 to about 2.70. Adjusting agents are added to the paper during the manufacturing process to help! development of a resistance for the penetration of liquids through paper. The adjusting agents can be internal adjustment agents or external adjustment agents (surface), and can be used for tension adjustment and low voltage adjustment, or both adjustment methods. More specifically, the adjusting agents include rosin, rosin precipitated with alum (Al2 (So4) 3); abietic acid and abietic acid homologs such as neoabietic acid and levopimaric acid; stearic acid and stearic acid derivatives; ammonium zirconium carbonate; silicone and silicone-containing compounds, such as RE-29 available from GE-OSI and SM-8715, available from Dw Corning Corporation (Midland, MI); fluorochemicals of the general structure CF3 (CF2) n, wherein R is an anionic, cationic or other functional group, such as Gortex ™; alkylquitine dimer (AKD), such as Aquapel 364, Aquapel 752, Hercon 70, Hercon 79m Precise 787, Precise 2000, and Precise 3000, all are commercially available from Hercules, Incorporated (Willmington, DE); and alkyl succinic anhydride (ASA); emulsions of ASA or AKD with cationic starch; Alum incorporating (ASA, starch, hydroxymethyl starch, carboxymethylcellulose (CMC), polyvinyl alcohol, methylcellulose, alginates, waxes, wax emulsions, and combinations such as adjusting agents.Starch has many uses in papermaking. example, it functions as a retention agent, drying-resistant agent, surface-adjusting agent, etc. Starches include but are not limited to amylase, amylopectin, starches containing various amounts of amuase and amyiopectin, such as 25% amylase and 75% amyiopectin (corn starch) and 20% amylase and 80% amylopectin (potato starch); enzymatically treated starches; hydrolyzed starches; heated starches, also known in the art as "sticky starches"; cationic starches, such as those resulting from the reaction of a starch with a tertiary amine to form a quaternary ammonium salt, anionic starches, ampholytic starches (containing cationic as well as anionic functionalities); cellulose and cellulose derivatives; and combinations of these compounds. Microorganisms such as bacteria, algae, yeast, and fungi are a common problem associated with the papermaking process, which frequently occur around papermaking machines and produce sludge that can result in chopped paper products, damage of corrosion to machines, or even breaks in the paper web. The growth of the microorganism can be inhibited with biocides.

The biocides used in papermaking include tlazoles and thiazolidinones such as isothiozoline, 3-chloroisothiazolidinone, 2-methyl-4-isothiazolin-3-one, 5-chloro-4-isothiazolin-3-one, and 1,2-benzothiazolin -3-one; quaternary ammonium salts containing alkyl, aryl, or heterocyclic substitutes; aldehydes capable of acting as entanglement agents, such as glutaraldehyde, formaldehyde, and acetaldehyde; alcohols and diols such as 2-bromo-2-nitropropan-1,3-diol (NBG 88, available from Nova BioGenetics, Inc., Atlanta, GA); amides, and especially halogenated propionamides such as dibromopropionamide (NBG 20, available from Nova BioGenetics, Inc. (carbamates such as monoalkyl carbamates; chlorine compounds, including both inorganic and organic chemicals that contain chlorine or can split chlorine and are commonly used in the paper industry, including but not limited to alkali hypochloride, alkaline earth metal hypochloride, chlorine, and chlorine dioxides; cyanates such as methylene bis-thiocyanate and disodium carbodiomide carbonate; gases such as ozone or chlorine are capable of bubbling in a slurry of pulp, peroxides such as acid peroxide (eg, 35% solution), sulfides such as tetramethylthiuram disulfide, salts such as sodium chloride, sodium peroxide, and sodium acid sulfite; sulfones such as phenyl- (2) -chloro-2-cyanovinyl) -sulfone and phenyl- (1,2-dichloro-2-cyanovinyl) -sulfone, organic acids such as benzoic acid, ascorbic acid, formic acid, sorbic acid, p-hydroxybenzoic acid, and mixtures thereof; and silicates such as sodium hexafluorosilicate, and mixture and combinations of the foregoing. The biocides are typically added to the concentrated suspension in an amount ranging from about 0.05 to about 0.9 kg / ton of paper. The optimal use will depend on the procedure variables of a given paper machine (mainly the degree of closure and incoming raw materials). The retention and drainage aids affect the amount of pulp that is retained in the wire and then incorporated into the paper. The retention and drainage aids include polyamines, polyethylene imine (PEI) and polydiallyldimethylammonium chloride (DADMAC); polyacrylamides of high molecular weight (for example, those with a molecular weight greater than 500,000); polyethylene oxide (PEO); starch; gums; alum; polymers containing aluminum; wood fibers; and double component systems containing both cationic and anionic agents, such as polyethyleneimine (PEI) and anionic polyacrylamide, or cationic starch or PAM with colloidal silica, as well as combinations of such compounds. Defoamers, compounds used to destabilize and remove existing foams can also be added to the concentrated suspension, network or paper. Defoamers are typically used to control the foam that results when air or other suspended gases are mixed with the concentrated suspension, especially one of the ingredients of the suspension is a surfactant. The defoamers are usually added later in the papermaking process, close to the origin of the foam. Defoamers include but are not limited to aliphatic chemicals such as kerosene; fuel oils; hydrophobic oils, such as vegetable oils; hydrophobic particles such as hydrocarbon or polyethylene waxes; fatty alcohols; fatty acids; fatty esters; hydrophobic silica; ethylenedisteramide (EBS) suspended in oil, hydrocarbons, or a water emulsion; alkylpolyethers; silicon oils such as polydimethylsiloxanes; oligomers of ethylene oxide or polypropylene oxide bound to an alcohol, amine, or organic acid, the oligomer having a degree of polymerization of about 3 to about 8; as well as combinations of these compounds. Typically such defoamers are added in an amount of about 0.01% by weight to about 1.0% by weight, and more typically from about 0.01% by weight to about 0.5% by weight, based on the total weight of the pulp mixture. Additives for pH control can also be optionally added to the pulp suspension to regulate the total pH and thereby reduce machine corrosion and minimize the growth of fungi and bacteria. Typical pH control agents include sulfuric acid, carbon dioxide gas bubbled in the slurry, organic pH regulated agents, and combinations thereof. The training aids promote the dispersion of fibers through the slurry. The addition of such compounds can lead to improvements in product formation, as well as improved core box consistencies. Formation aids include linear, water soluble polyelectrolytes of high molecular weight, such as anionic polyacrylamides, and natural gums such as lous seed gum, cocoa gum, and guar gum, as well as mixtures and combinations thereof. These forming aids are typically used in a volume of about 0.5 kg / t of concentrated suspension solution at about 4.5 kg / t, and more preferably from about 0.9 kg / t to about 2.7 kg / t. Having described the present invention with reference to certain preferred embodiments, it is further illustrated by the following examples. These examples are provided for illustrative purposes only and are not intended to limit in any way the invention that is defined by the claims that follow the examples.

EXAMPLES The abrasion resistance, indentation resistance, and impact resistance of the paper product produced by the methods of the present invention can be determined by methods and modifications of methods used in such standard industry tests as ASTM D 4977-98b ( Standard Test Method for Granule Adhesion to Mineral Surfaced Roofing by Abrasion), ASTM D 5420 (Impact Resistance of Fiat, Rigid Plastic Specimen by Jeans of a Striker by a Falling Weight (Gardner Impact), or other suitable abrasion or impact tests.

EXAMPLE 1 A concentrated suspension for the outer linear folds of the paper was prepared from the recycled waste paper. The grades of wasted paper were blank sheets, sections, and envelope cutouts. This concentrated suspension is pumped from the machine chest to the fan pump.

A measuring pump was precisely fed to the cationic drying resistance agent in a water dilution flow which was then fed in the existence of the thick liner before the fan pump. The dilution water was used to help mix the drying resistance with the existence of thickness. The dry strength agent is fed before the addition of the retention aid, ASA, and the defoamer. The anionic drying resistant agent was mixed in a tank with other ingredients (silicone, optical brightener, water). The solution was mixed until all the ingredients were completely dispersed. The solution is pumped into an operating tank, which feeds the water box of the calendar with the overflow of the water box returning to the operating tank to keep a clamp submerged in water.

TABLE 1 Abrasion Test Results4 Corrida Resistant Agent Resistant Agent Number of Drying Reduction Aggregate to Drying Cycles Calibrator Before to Aggregate End in (cm) Humid2 Drying End (kg / ton) (kg / ton) control '0 2 200 0.023 1 4.5 2.7 1000 0.003 2 4.5 2.7 1000 0.003 3 4.5 2.7 1000 0.003 4 4.5 2.7 1000 0.005 1 Cover sheet of ordinary gypsum board. 2 The amount of agent resistant to cationic drying added to the earlier existence to the wet end of the process. 3 The amount of agent resistant to anionic drying added to the existence at the dry end of the process. The abrasion test was performed following generally the procedure of ASTM D4977-98b. As can be seen in Table 1, the front paper of the gypsum board manufactured according to the method of the invention loses only 0.003 to 0.005 cm of surface material after 1000 abrasion cycles. In contrast, normal plaster front paper will lose approximately 0.023 cm of surface material after only 200 cycles. Thus, this example illustrates the improvement in surface resistance that can be accomplished with the process.

EXAMPLE 2 The paper was produced according to the procedure described in Example 1, with the addition of an optical brightener, Leucophor® BCW Liquid, T-26 Liquid, or T-4 Liquid (Clariant Corporation, Muttenz, Switzerland) to the solution that circulates between the operating tank and the water box in the quantities shown in Table 2. The optical brightness was determined using the CIE Lab values, as measured in a profilometer where L * refers to the value that is related to the brightness / darkness of the color; a * refers to the chromaticity on the red / green axis; and b * refers to the chromaticity in the blue / yellow axis.

TABLE 2 As can be seen in Table 2, the addition of an optical brightener in the water box, together with the anionic drying resistant agent, generated a paper product having a marked improvement in optical brilliance. While the control paper product did not contain optical brightener it has a brightness (L *) of 87.55, the addition of an optical brightener such as Leucofor in the water box (e.g., operation 6) results in a markedly brighter paper product (L * = 89.64, a * approximately 0 and b * is approximately 0). That means, L * is approximately 100 (ideal), while a * and b * are both approaches to zero, the ideal optical brightness point (pure white). While the compositions and methods of the invention have been described in terms of preferred embodiments, it will be apparent to those skilled in the art that variations can be applied to the compositions and / or methods and / or methods and in the steps or sequence of steps of the methods described herein without departing from the spirit and scope of the invention. More specifically it will be apparent that certain agents that are chemically related can be substituted for the agents described herein while achieving the same or similar results. All of such similar substitutes and obvious modifications for those skilled in the art are claimed to be within the spirit and scope of the invention.

Claims (1)

1. NOVELTY OF THE INVENTION CLAIMS 1. - A process for manufacturing paper and paper products comprising: a) a concentrated preparation step wherein a concentrated suspension of cellulosic fibers is prepared, b) adding a first resistance agent selected from the group consisting of agents resistant to cationic drying , agents resistant to amphoteric drying and agents resistant to cationic moisture for the concentrated suspension, c) a wet end stage wherein the cellulosic fibers are formed in a substantially uniform network, and d) a dry end stage wherein the network is dry on a paper and a second strength agent selected from the group consisting of anionic drying resistance agents and amphoteric resistance agents are applied to the surface of the paper. 2. The process according to claim 1, further characterized in that the first resistance agent is an agent resistant to cationic drying. 3. The process according to claim 2, further characterized in that the agent resistant to cationic drying is selected from the group consisting of cationic polyacrylamides, cationic natural polymers, cationic modified natural polymers, cationic synthetic polymers, modified starches to have functional groups of quaternary ammonium, cationic celluloses, cationic natural gums, cationic polyvinyl alcohol adducts, and combinations thereof. 4. The process according to claim 3, further characterized in that the agent resistant to cationic drying is a cationic polyacrylamide. 5. The process according to claim 2, further characterized in that the agent resistant to cationic drying is added in an amount of about 0.5 kg / t to about 9.1 kg / t. 6. The process according to claim 2, further characterized in that the agent resistant to cationic drying has a viscosity of about 1 000 cps (1 Pa-s) to about 15,000 cps (15 Pa-s). 7. - The method according to claim 2, further characterized in that the agent resistant to cationic drying has a specific gravity of about 1.00 to about 1.20. 8. The process according to claim 1, further characterized in that the first resistance agent is a cationic moisture resistant agent. 9. The process according to claim 8, further characterized in that the cationic moisture resistant agent is selected from the group consisting of cationic acid, cationic neutral resins for acid restoration resins, and cationic neutral for resins. alkaline restoration resins. 10. The process according to claim 8, further characterized in that the cationic moisture resistant agent is added in an amount of about 0.5 kg / t to about 9.1 kg / t. 11. The process according to claim 1, further characterized in that the second resistance agent is an agent resistant to anionic drying. 12. The process according to claim 1, further characterized in that the agent resistant to anionic drying is selected from the group consisting of anionic polyacrylamides, natural anionic starches, and anionic carboxymethylcellulose. 13. The process according to claim 12, further characterized in that the agent resistant to anionic drying is an anionic polyacrylamide. 14 - The method according to claim 1, further characterized in that the agent resistant to anionic drying is added in an amount of about 2.3 kg / t to about 11.3 kg / t. 15. The process according to claim 1, further characterized in that the agent resistant to anionic drying has a specific gravity of about 1.00 to about 1.20. 16. The process according to claim 11, further characterized in that the agent resistant to anionic drying has a viscosity of about 1,000 cps (1 Pa-s) to about 15,000 cps (15 Pa-s). 17. The process according to claim 1, further characterized in that the second strength agent is applied to the surface of the paper through a technique selected from the group consisting of: a) immersing the paper in a solution of the second agent of resistance in a calendar water box, b) applying a solution of the second strength agent to the paper with a size pressure, and c) spraying a solution of the second strength agent into the paper using an aerosol pump. 18. The process according to claim 17, further characterized in that the solution of the second drying-resistant agent is applied to the paper in a calendar water box. 19. - The method according to claim 17, further characterized in that the solution also contains at least one optical brightener. 20. The method according to claim 19, further characterized in that at least one optical brightener is selected from the group consisting of azoles, biphenyls, chelating agents, coumarins, furans, ionic brighteners, naphthalimides, pyranes, stilbenes, tetrasulfonated stilbenes, hexasulfonated stilbenes, salts thereof, and combinations thereof. 21. - The method according to claim 19, further characterized in that at least one optical brightener is added in an amount of approximately 0.5 kg / 92.93 cm2 approximately 0.227 kg / 92,903 cm2. 22. The method according to claim 19, further characterized in that the paper product has an optical brightness with a brightness value, L *, greater than about 0.89 after application of the solution. 23. The process according to claim 1, further characterized in that it additionally comprises adding at least one biocide to the concentrated suspension. 24. - The method according to claim 17, further characterized in that the solution also contains at least one hydrophobic organosilicon. 25. - Paper made by the process described in claim 1. 26. - The method according to claim 1, further characterized in that it comprises incorporating the paper in a paper product. 27. - A paper product manufactured by the method according to claim 26. 28. - The paper product according to claim 27, further characterized in that it is dry wall front paper (panel) applied to the dry wall through a conventional gypsum panel industry manufacturing process or by the dry wall lamination after its manufacture.