Methods of forming paper products and paper products formed through the methods

Abstract

Methods of forming paper products are provided herein. A method comprises providing an aqueous suspension of cellulosic fibers; diluting the aqueous suspension with water to form a diluted aqueous suspension having a solids content from about 0.3 wt % to about 1.8 wt %, based on a total weight of the diluted aqueous suspension; subjecting the diluted aqueous suspension to a high shear operation; adding an aqueous composition comprising an adduct formed from the reaction of glyoxal and a polyvinylamide prepolymer to the diluted aqueous suspension; forming the diluted aqueous suspension into a sheet; and drying the sheet. The aqueous composition is added after the diluted aqueous suspension is subjected to the high shear operation and before the diluted aqueous suspension is passed to a headbox. The method is free of any high shear operation after the aqueous composition is added and before the diluted aqueous suspension is passed to the headbox.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional application No. 63 / 691,724, filed Sep. 6, 2024, the entire contents of which are hereby incorporated by reference.TECHNICAL FIELD

[0002] The present disclosure generally relates to methods of forming paper products. The present disclosure more particularly relates to methods of forming paper products using a dry strength additive.BACKGROUND

[0003] The use of synthetic water-soluble polymers as wet end additives for the strengthening of paper products is widely practiced. Addition of polymers during various stages of the papermaking process, including in the stock approach flow, has known benefits. For example, addition of polymers may improve retention and drainage during the papermaking process, and / or may improve wet strength and / or dry strength of the resulting paper product.

[0004] In the stock approach flow of a paper making process, a thick stock (i.e. an aqueous suspension of cellulosic fibers and fines) is diluted and processed to form a thin stock. The thin stock has a lower concentration of cellulose, and a lower solids content, than the thick stock. The thin stock may also contain a higher percentage of cellulosic fines than the thick stock. Fines are much smaller than fibers and have less surface area than fibers. The thin stock is generally subjected to high shear operations, such as by passing through a fan pump and / or a high pressure screen, before the thin stock is sent to the headbox of a papermaking machine to be formed into a sheet or web, which is then dried to form the paper product.

[0005] One example of a type of polymer that may be added during the papermaking process to increase dry strength of the resulting paper product is a polyvinylamide. Specifically, polyvinylamides that are modified with glyoxal (i.e. glyoxalated polyvinylamides) are known to be effective dry strength aids. In existing processes, glyoxalated polyvinylamides are always added prior to the last high shear operation in the stock approach flow prior to the headbox because the high shear operation(s) are thought to provide necessary mixing of the polymer and the cellulosic material. Glyoxalated polyvinylamides are preferentially added to the thick stock in the stock approach flow, before the thick stock stream is diluted and processed to form the thin stock. Addition of the glyoxalated polyvinylamides to the thick stock is believed to provide the highest known levels of dry strength of the resulting paper product because the cellulosic fibers present in the thick stock have maximized surface area to interact with the glyoxalated polyvinylamide. Less commonly, the glyoxalated polyvinylamides may be added to the thin stock prior to the last high shear operation in the stock approach flow prior to the headbox. Addition to the thin stock does not provide as much dry strength as addition to the thick stock, but addition to the thin stock may provide other benefits such as improved drainage and retention during the papermaking process.

[0006] Synthetic water-soluble polymers such as glyoxalated polyvinylamides are expensive to produce and may have a limited shelf life. At the same time, some paper products still do not exhibit maximized dry strength, even when polymers that contribute to dry strength are used during the papermaking process.

[0007] Accordingly, it is desirable to provide a papermaking process that yields paper products having a maximized dry strength while adding a minimized amount of glyoxalated polyvinylamide during the process. Furthermore, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.BRIEF SUMMARY

[0008] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0009] Methods of forming paper products and paper products formed through the methods are provided herein. In an embodiment, a method comprises providing an aqueous suspension of cellulosic fibers, diluting the aqueous suspension with water to form a diluted aqueous suspension, subjecting the diluted aqueous suspension to a high shear operation, adding an aqueous composition to the diluted aqueous suspension, forming the diluted aqueous suspension into a sheet by a headbox, and drying the sheet to form the paper product. The diluted aqueous suspension has a solids content of from about 0.3 wt % to about 1.8 wt %, based on a total weight of the diluted aqueous suspension. The aqueous composition comprises an adduct formed from the reaction of glyoxal and a polyvinylamide prepolymer. The aqueous composition is added to the diluted aqueous suspension after the diluted aqueous suspension is subjected to the high shear operation and before the diluted aqueous suspension is passed to the headbox. The method is free of any high shear operation after the aqueous composition is added and before the diluted aqueous suspension is passed to the headbox.DETAILED DESCRIPTION

[0010] The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

[0011] The methods provided herein enable production of a paper product unexpectedly having the same or improved dry strength as compared to a paper product formed through existing methods, as a result of adding the same amount or a smaller amount of a dry strength additive (e.g. a glyoxalated polyvinylamide) than is added in existing methods, but by adding the dry strength additive at a location after the last high shear operation and before a headbox. The methods thus provide flexibility in addition points for dry strength additives. Particularly, it has unexpectedly been found that adding the glyoxalated polyvinylamide to the thin stock after the last high shear operation prior to the headbox yields comparable or even greater dry strength of the resulting paper product as compared to the conventional step of adding the glyoxalated polyvinylamide to the thick stock before the dilution and high shear operations.

[0012] Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art measured using standard measurement devices for a given measurement, for example within 2 standard deviations of the mean for a particular measurement device. “About” can be understood as within 10%, 5%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. “About” can alternatively be understood as implying the exact value stated. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”

[0013] As used herein, “solids content” refers to the percent, by weight, of non-volatile components that would remain after any solvents and / or volatile components are removed from a solution or suspension, based on a total weight of the solution or suspension. The term “active solids” used for the glyoxalated polyvinylamide adduct of the aqueous composition used in the present methods represents the weight of the glyoxalated polyvinylamide adduct, excluding water and any other components that may be present. When used in reference to a mass in kilograms, “active solids” refers to the total mass of the glyoxalated polyvinylamide adduct present. When used in reference to a weight percentage, “active solids” refers to the weight of the glyoxalated polyvinylamide adduct present as a percentage of the total weight of the aqueous composition.

[0014] The methods provided herein comprise the steps of providing an aqueous suspension of cellulosic fibers, diluting the aqueous suspension with water to form a diluted aqueous suspension, subjecting the diluted aqueous suspension to a high shear operation, adding an aqueous composition to the diluted aqueous suspension, forming the diluted aqueous suspension into a sheet, and drying the sheet to form the paper product. The details of each method step are discussed in further detail below.

[0015] The cellulosic fibers in the aqueous suspension provide the material needed to form the paper product. The aqueous suspension may be provided to the papermaking process by pumping the aqueous suspension through a pipe. The aqueous suspension may undergo operations such as mixing before it is provided to the papermaking process. For example, in embodiments, the aqueous suspension passes through a mixing chest and / or a machine chest in accordance with standard practice. The aqueous suspension may alternatively be referred to as the “thick stock” (i.e. a mix of cellulosic fibers prior to any dilution steps). In the aqueous suspension, the cellulosic material is present in the form of fibers and fines. As used herein, “fibers” are materials extracted from the cellulose found in the cell wall of plants. In embodiments, the fibers in the thick stock may have a length of from about 0.2 mm to about 100 mm, alternatively from about 0.5 mm to about 50 mm, alternatively from about 0.5 mm to about 10 mm. As used herein, “fines” are cellulosic materials having a length of less than about 200 micrometers (μm). The cellulosic fibers and fines may be derived from, for example, trees, cotton, or flax. In embodiments, the aqueous suspension of cellulosic fibers has a solids content of from about 2.0 wt % to about 5.0 wt %, alternatively from about 3.0 wt % to about 4.5 wt %, alternatively from about 3.5 wt % to about 4.0 wt %, based on a total weight of the aqueous suspension.

[0016] The aqueous suspension is then diluted with water to form a diluted aqueous suspension in accordance with standard practice. In embodiments, the aqueous suspension may be diluted by passing the aqueous suspension through a silo such as a white water silo, by passing the aqueous suspension through a dilution tank, or by adding water to the aqueous suspension in-line. The diluted aqueous suspension may alternatively be referred to as the “thin stock.” The diluted aqueous suspension may contain a combination of cellulosic fibers and cellulosic fines. The diluted aqueous suspension has a solids content of from about 0.3 wt % to about 1.8 wt %, alternatively from about 0.4 wt % to about 1.5 wt %, alternatively from about 0.5 wt % to about 1.0 wt %, based on a total weight of the diluted aqueous suspension.

[0017] The diluted aqueous suspension is subjected to a high shear operation (i.e. subjected to mechanical shear) before passing to a headbox. The high shear operation may provide enhanced bonding properties of fines and fibers in the diluted aqueous suspension, disperse additives throughout the diluted aqueous suspension, break down clumps of fibers, achieve uniform mixing, and / or provide other benefits. After the high shear operation, the cellulosic fibers in the diluted aqueous suspension may have shorter lengths, on average, than before the high shear operation. The diluted aqueous suspension may also contain a higher percentage of fines after the high shear operation than before the high shear operation.

[0018] The diluted aqueous suspension may be subjected to only one high shear operation, or alternatively, the diluted aqueous suspension may be subjected to more than one high shear operation in accordance with standard practice. In embodiments, the diluted aqueous suspension is subjected to at least two high shear operations. The high shear operation may include passing the diluted aqueous suspension through a shear stage selected from pumping or mixing stages. In embodiments, subjecting the diluted aqueous suspension to the high shear operation may comprise subjecting the diluted aqueous suspension to a fan pump, a high pressure screen (i.e. a centri-screen), or a combination thereof.

[0019] The methods provided herein include the step of adding an aqueous composition comprising an adduct formed from the reaction of glyoxal and a polyvinylamide prepolymer (hereinafter “GPAM adduct”) to the diluted aqueous suspension after the high shear operation and before the headbox. Adding the aqueous composition comprising the GPAM adduct may improve the dry strength of the resulting paper product. In embodiments, the aqueous composition comprising the GPAM adduct is added to the diluted aqueous suspension such that the ratio of the flow velocity of the aqueous composition to the flow velocity of the diluted aqueous suspension, as measured in meters per second, is from about 1:1 to about 10:1, alternatively from about 1.5:1 to about 5:1. In embodiments, the aqueous composition comprising the GPAM adduct is added through a nozzle, wherein the flow of the aqueous composition out of the nozzle is turbulent flow. The flow velocity ratios and the turbulent flow of the aqueous composition aid in mixing of the GPAM adduct into the diluted aqueous suspension so that the GPAM adduct comes into contact with a greater surface area of the cellulosic fibers and fines. Maximized contact between the GPAM adduct and the cellulosic fibers and fines may lead to maximized dry strength of the resulting paper product.

[0020] In the methods provided herein, the aqueous composition comprising the GPAM adduct is added to the diluted aqueous suspension after the diluted aqueous suspension is subjected to the high shear operation and before the diluted aqueous suspension is passed to the headbox. The method is free of any high shear operation after the aqueous composition comprising the GPAM adduct is added and before the diluted aqueous suspension is passed to the headbox. Addition of the aqueous composition comprising the GPAM adduct to the diluted aqueous suspension after the last high shear operation and before the headbox has unexpectedly been found to provide a comparable or even greater dry strength in the resulting paper product as compared to addition of the same amount and concentration of the aqueous composition comprising the GPAM adduct to the aqueous suspension before the aqueous suspension is diluted. Addition of the aqueous composition comprising the GPAM adduct to the diluted aqueous suspension after the last high shear operation and before the headbox may also allow for addition of a smaller amount of the aqueous composition (and thus a smaller amount of the GPAM adduct) without compromising dry strength performance of the resulting paper product. Addition of the aqueous composition comprising the GPAM adduct to the diluted aqueous suspension after the last high shear operation and before the headbox has not previously been known for dry strength additives and would have been expected to produce a paper product with an inferior dry strength. Flexibility in addition points for the GPAM adduct may lead to improvements in process efficiency. For example, if other additives such as drainage and retention aids are also added during the process, the adduct comprising the GPAM adduct can be added at the same time as the other additives.

[0021] In embodiments, the aqueous composition comprising the GPAM adduct is prepared by reacting a substantially aqueous reaction mixture of the polyvinylamide prepolymer and the glyoxal, wherein the concentration of the polyvinylamide prepolymer is below, equal to or no more than 1% above a Critical Concentration. As used herein, “Critical Concentration” is defined as the concentration of the polyvinylamide prepolymer above which Critical Concentration the viscosity increases for the reaction mixture resulting from the forward progress of the adduct formation, and below which Critical Concentration the viscosity decreases for the reaction mixture resulting from the forward progress of adduct formation. Running the reaction close to the Critical Concentration may minimize the risk of gelation, maximize the consumption of glyoxal, and enhance the shelf life of the resulting composition. In embodiments, the Critical Concentration is from about 0.1 wt % to about 4.0 wt %, alternatively from about 1.0 wt % to about 3.0 wt %, based on a total weight of the reaction mixture. In embodiments, the polyvinylamide prepolymer is present in the reaction mixture in an amount of less than about 5 wt %, alternatively less than about 4 wt %, alternatively from about 0.1 wt % to about 4 wt %, based on a total weight of the reaction mixture, at the onset of the reaction. In embodiments, at least 40 wt %, alternatively at least 50 wt %, of the total glyoxal is consumed during the reaction. In embodiments, the molar ratio of the amide functionality on the polyvinylamide prepolymer to the glyoxal during the reaction is from about 2:1 to about 12:1, alternatively from about 2.5:1 to 8:1. In embodiments, the solids content of the resulting aqueous composition is no more than about 2.5%.

[0022] The polyvinylamide prepolymer may be a homopolymer, copolymer or terpolymer. The polyvinylamide prepolymer may be cationic, potentially cationic, anionic, potentially anionic, nonionic or amphoteric. The GPAM adduct may be formed from only one polyvinylamide prepolymer, or alternatively, the adduct may be formed from more than one polyvinylamide prepolymer. In embodiments, the adduct may be formed from a blend of a polyvinylamide prepolymer and another miscible non-polyvinylamide polymer. In embodiments, the polyvinylamide prepolymer has a weight average molecular weight of from about 50,000 Daltons to about 5 million Daltons, alternatively from about 80,000 Daltons to about 400,000 Daltons, alternatively from about 100,000 Daltons to about 300,000 Daltons, as measured using gel permeation chromatography (GPC). As used herein, the term “polyvinylamide prepolymer” refers to a polymer formed by vinyl polymerization from any vinyl monomer containing an amide functionality including but not limited to (meth)acrylamide, N-methyl acrylamide or any other substituted acrylamide. As used herein, the term “(meth)acrylamide” includes both acrylamide and methacrylamide. In embodiments, the polyvinylamide prepolymer is a homopolymer or copolymer formed from (meth)acrylamide or a substituted (meth)acrylamide.

[0023] The GPAM adduct may be cationic, potentially cationic, anionic, potentially anionic, nonionic or amphoteric. In embodiments, the GPAM adduct has a weight average molecular weight of from about 70,000 Daltons to about 500 million Daltons, alternatively from about 2 million Daltons to about 100 million Daltons, alternatively from about 4 million Daltons to about 50 million Daltons as measured using GPC. The adduct is a glyoxalated version of the polyvinylamide prepolymer, so the chemistry of the adduct is dependent on the chemistry of the polyvinylamide prepolymer. In embodiments, the adduct is glyoxalated polyacrylamide.

[0024] In embodiments, upon addition of the aqueous composition comprising the GPAM adduct to the diluted aqueous suspension, the GPAM adduct is present in the aqueous composition in an amount of from about 0.02 wt % to about 5.0 wt %, alternatively from about 0.1 wt % to about 5.0 wt %, alternatively from about 0.5 wt % to about 4.0 wt % active solids. In embodiments, upon addition of the aqueous composition to the diluted aqueous suspension, the GPAM adduct is present in the diluted aqueous suspension in an amount such that from about 0.25 kilograms to about 10 kilograms, alternatively from about 0.5 kilograms to about 9 kilograms, alternatively from about 1 kilogram to about 7.5 kilograms of the GPAM adduct, based on active solids, is present for every metric ton of solids present in the diluted aqueous suspension.

[0025] In embodiments, the aqueous composition further comprises an additive different from the GPAM adduct. In embodiments, the additive may be selected from a filler, a sizing agent, a retention aid, a colorant, a defoaming or antifoaming agent, a biocide, a pH control agent, a wet strength agent, a dry strength agent different from the GPAM adduct, or combinations thereof.

[0026] In embodiments, the method further comprises the step of adding to the diluted aqueous suspension a second composition different from the aqueous composition comprising the GPAM adduct. When added to the diluted aqueous suspension, the second composition is added separately from the aqueous composition comprising the GPAM adduct. The second composition may be added at the same point in the process as the aqueous composition, or alternatively, the second composition may be added to the diluted aqueous suspension at a different point in the process than the aqueous composition comprising the GPAM adduct. In embodiments, the second composition may comprise an additive selected from a filler, a sizing agent, a retention aid, a colorant, a defoaming or antifoaming agent, a biocide, a pH control agent, a wet strength agent, a dry strength agent different from the GPAM adduct, or combinations thereof.

[0027] The methods provided herein include the step of forming the diluted aqueous suspension into a sheet. More specifically, in embodiments, the diluted aqueous suspension is passed to the headbox. The diluted aqueous suspension is concentrated in the headbox by removing water. The diluted aqueous suspension is distributed across the length of a moving forming fabric to form a uniform paper sheet. The forming fabric is a porous fabric, a wire, or a plastic screen. The flow velocity of the diluted aqueous suspension may be adjusted by the headbox.

[0028] The methods provided herein include the step of drying the sheet to form the paper product. Drying the sheet removes any residual moisture to create the paper product in its final form. The sheet may be dried by, for example, applying vacuum under the forming fabric, pressing the sheet with rolls and / or felt blankets, heating the sheet, air drying the sheet, infrared drying, or calendaring.

[0029] The paper products provided herein are formed through the methods provided herein. In embodiments, the paper product may be printer paper, notebook paper, photographic paper, security paper, cardboard, paperboard, containerboard, toilet paper, paper towels, facial tissue, tissue paper, filter paper, envelopes, newspaper, gift wrap, or another kind of paper. In embodiments, the paper product has a dry edgewise compressive strength, as measured by the Ring Crush Test (RCT) in accordance with the Technical Association of the Pulp and Paper Industry (TAPPI) standard method TAPPI / ANSI T 822 om-22, that is equal to or greater than a comparative paper product formed by a process comprising adding the aqueous composition to the aqueous suspension before diluting the aqueous suspension and before subjecting the aqueous suspension to the high shear operation. In embodiments, the paper product has a dry short span compressive strength, as measured by the Short Span Compression Test (SCT) in accordance with the standard method TAPPI / ANSI T 826 om-21, that is equal to or greater than a comparative paper product formed by a process comprising adding the aqueous composition to the aqueous suspension before diluting the aqueous suspension and before subjecting the aqueous suspension to the high shear operation. In embodiments, the paper product has a dry burst strength, as measured by the Mullen Burst Test in accordance with the standard method TAPPI / ANSI T 403 om-22, that is equal to or greater than a comparative paper product formed by a process comprising adding the aqueous composition to the aqueous suspension before diluting the aqueous suspension and before subjecting the aqueous suspension to the high shear operation. In embodiments, the paper product has a dry internal bond strength, as measured by the Scott Bond method in accordance with the standard method TAPPI / ANSI T 569 om-22, that is equal to or greater than a comparative paper product formed by a process comprising adding the aqueous composition to the aqueous suspension before diluting the aqueous suspension and before subjecting the aqueous suspension to the high shear operation.

[0030] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the present disclosure. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the present disclosure as set forth in the appended claims.

Examples

Embodiment Construction

[0010]The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

[0011]The methods provided herein enable production of a paper product unexpectedly having the same or improved dry strength as compared to a paper product formed through existing methods, as a result of adding the same amount or a smaller amount of a dry strength additive (e.g. a glyoxalated polyvinylamide) than is added in existing methods, but by adding the dry strength additive at a location after the last high shear operation and before a headbox. The methods thus provide flexibility in addition points for dry strength additives. Particularly, it has unexpectedly been found that adding the glyoxalated polyvinylamide to the thin stock after the last high shear operation prior to the head...

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional application No. 63 / 691,724, filed Sep. 6, 2024, the entire contents of which are hereby incorporated by reference.TECHNICAL FIELD

[0002] The present disclosure generally relates to methods of forming paper products. The present disclosure more particularly relates to methods of forming paper products using a dry strength additive.BACKGROUND

[0003] The use of synthetic water-soluble polymers as wet end additives for the strengthening of paper products is widely practiced. Addition of polymers during various stages of the papermaking process, including in the stock approach flow, has known benefits. For example, addition of polymers may improve retention and drainage during the papermaking process, and / or may improve wet strength and / or dry strength of the resulting paper product.

[0004] In the stock approach flow of a paper making process, a thick stock (i.e. an aqueous suspension of cellulosic fibers and fines) is diluted and processed to form a thin stock. The thin stock has a lower concentration of cellulose, and a lower solids content, than the thick stock. The thin stock may also contain a higher percentage of cellulosic fines than the thick stock. Fines are much smaller than fibers and have less surface area than fibers. The thin stock is generally subjected to high shear operations, such as by passing through a fan pump and / or a high pressure screen, before the thin stock is sent to the headbox of a papermaking machine to be formed into a sheet or web, which is then dried to form the paper product.

[0005] One example of a type of polymer that may be added during the papermaking process to increase dry strength of the resulting paper product is a polyvinylamide. Specifically, polyvinylamides that are modified with glyoxal (i.e. glyoxalated polyvinylamides) are known to be effective dry strength aids. In existing processes, glyoxalated polyvinylamides are always added prior to the last high shear operation in the stock approach flow prior to the headbox because the high shear operation(s) are thought to provide necessary mixing of the polymer and the cellulosic material. Glyoxalated polyvinylamides are preferentially added to the thick stock in the stock approach flow, before the thick stock stream is diluted and processed to form the thin stock. Addition of the glyoxalated polyvinylamides to the thick stock is believed to provide the highest known levels of dry strength of the resulting paper product because the cellulosic fibers present in the thick stock have maximized surface area to interact with the glyoxalated polyvinylamide. Less commonly, the glyoxalated polyvinylamides may be added to the thin stock prior to the last high shear operation in the stock approach flow prior to the headbox. Addition to the thin stock does not provide as much dry strength as addition to the thick stock, but addition to the thin stock may provide other benefits such as improved drainage and retention during the papermaking process.

[0006] Synthetic water-soluble polymers such as glyoxalated polyvinylamides are expensive to produce and may have a limited shelf life. At the same time, some paper products still do not exhibit maximized dry strength, even when polymers that contribute to dry strength are used during the papermaking process.

[0007] Accordingly, it is desirable to provide a papermaking process that yields paper products having a maximized dry strength while adding a minimized amount of glyoxalated polyvinylamide during the process. Furthermore, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.BRIEF SUMMARY

[0008] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0009] Methods of forming paper products and paper products formed through the methods are provided herein. In an embodiment, a method comprises providing an aqueous suspension of cellulosic fibers, diluting the aqueous suspension with water to form a diluted aqueous suspension, subjecting the diluted aqueous suspension to a high shear operation, adding an aqueous composition to the diluted aqueous suspension, forming the diluted aqueous suspension into a sheet by a headbox, and drying the sheet to form the paper product. The diluted aqueous suspension has a solids content of from about 0.3 wt % to about 1.8 wt %, based on a total weight of the diluted aqueous suspension. The aqueous composition comprises an adduct formed from the reaction of glyoxal and a polyvinylamide prepolymer. The aqueous composition is added to the diluted aqueous suspension after the diluted aqueous suspension is subjected to the high shear operation and before the diluted aqueous suspension is passed to the headbox. The method is free of any high shear operation after the aqueous composition is added and before the diluted aqueous suspension is passed to the headbox.DETAILED DESCRIPTION

[0010] The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

[0011] The methods provided herein enable production of a paper product unexpectedly having the same or improved dry strength as compared to a paper product formed through existing methods, as a result of adding the same amount or a smaller amount of a dry strength additive (e.g. a glyoxalated polyvinylamide) than is added in existing methods, but by adding the dry strength additive at a location after the last high shear operation and before a headbox. The methods thus provide flexibility in addition points for dry strength additives. Particularly, it has unexpectedly been found that adding the glyoxalated polyvinylamide to the thin stock after the last high shear operation prior to the headbox yields comparable or even greater dry strength of the resulting paper product as compared to the conventional step of adding the glyoxalated polyvinylamide to the thick stock before the dilution and high shear operations.

[0012] Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art measured using standard measurement devices for a given measurement, for example within 2 standard deviations of the mean for a particular measurement device. “About” can be understood as within 10%, 5%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. “About” can alternatively be understood as implying the exact value stated. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”

[0013] As used herein, “solids content” refers to the percent, by weight, of non-volatile components that would remain after any solvents and / or volatile components are removed from a solution or suspension, based on a total weight of the solution or suspension. The term “active solids” used for the glyoxalated polyvinylamide adduct of the aqueous composition used in the present methods represents the weight of the glyoxalated polyvinylamide adduct, excluding water and any other components that may be present. When used in reference to a mass in kilograms, “active solids” refers to the total mass of the glyoxalated polyvinylamide adduct present. When used in reference to a weight percentage, “active solids” refers to the weight of the glyoxalated polyvinylamide adduct present as a percentage of the total weight of the aqueous composition.

[0014] The methods provided herein comprise the steps of providing an aqueous suspension of cellulosic fibers, diluting the aqueous suspension with water to form a diluted aqueous suspension, subjecting the diluted aqueous suspension to a high shear operation, adding an aqueous composition to the diluted aqueous suspension, forming the diluted aqueous suspension into a sheet, and drying the sheet to form the paper product. The details of each method step are discussed in further detail below.

[0015] The cellulosic fibers in the aqueous suspension provide the material needed to form the paper product. The aqueous suspension may be provided to the papermaking process by pumping the aqueous suspension through a pipe. The aqueous suspension may undergo operations such as mixing before it is provided to the papermaking process. For example, in embodiments, the aqueous suspension passes through a mixing chest and / or a machine chest in accordance with standard practice. The aqueous suspension may alternatively be referred to as the “thick stock” (i.e. a mix of cellulosic fibers prior to any dilution steps). In the aqueous suspension, the cellulosic material is present in the form of fibers and fines. As used herein, “fibers” are materials extracted from the cellulose found in the cell wall of plants. In embodiments, the fibers in the thick stock may have a length of from about 0.2 mm to about 100 mm, alternatively from about 0.5 mm to about 50 mm, alternatively from about 0.5 mm to about 10 mm. As used herein, “fines” are cellulosic materials having a length of less than about 200 micrometers (μm). The cellulosic fibers and fines may be derived from, for example, trees, cotton, or flax. In embodiments, the aqueous suspension of cellulosic fibers has a solids content of from about 2.0 wt % to about 5.0 wt %, alternatively from about 3.0 wt % to about 4.5 wt %, alternatively from about 3.5 wt % to about 4.0 wt %, based on a total weight of the aqueous suspension.

[0016] The aqueous suspension is then diluted with water to form a diluted aqueous suspension in accordance with standard practice. In embodiments, the aqueous suspension may be diluted by passing the aqueous suspension through a silo such as a white water silo, by passing the aqueous suspension through a dilution tank, or by adding water to the aqueous suspension in-line. The diluted aqueous suspension may alternatively be referred to as the “thin stock.” The diluted aqueous suspension may contain a combination of cellulosic fibers and cellulosic fines. The diluted aqueous suspension has a solids content of from about 0.3 wt % to about 1.8 wt %, alternatively from about 0.4 wt % to about 1.5 wt %, alternatively from about 0.5 wt % to about 1.0 wt %, based on a total weight of the diluted aqueous suspension.

[0017] The diluted aqueous suspension is subjected to a high shear operation (i.e. subjected to mechanical shear) before passing to a headbox. The high shear operation may provide enhanced bonding properties of fines and fibers in the diluted aqueous suspension, disperse additives throughout the diluted aqueous suspension, break down clumps of fibers, achieve uniform mixing, and / or provide other benefits. After the high shear operation, the cellulosic fibers in the diluted aqueous suspension may have shorter lengths, on average, than before the high shear operation. The diluted aqueous suspension may also contain a higher percentage of fines after the high shear operation than before the high shear operation.

[0018] The diluted aqueous suspension may be subjected to only one high shear operation, or alternatively, the diluted aqueous suspension may be subjected to more than one high shear operation in accordance with standard practice. In embodiments, the diluted aqueous suspension is subjected to at least two high shear operations. The high shear operation may include passing the diluted aqueous suspension through a shear stage selected from pumping or mixing stages. In embodiments, subjecting the diluted aqueous suspension to the high shear operation may comprise subjecting the diluted aqueous suspension to a fan pump, a high pressure screen (i.e. a centri-screen), or a combination thereof.

[0019] The methods provided herein include the step of adding an aqueous composition comprising an adduct formed from the reaction of glyoxal and a polyvinylamide prepolymer (hereinafter “GPAM adduct”) to the diluted aqueous suspension after the high shear operation and before the headbox. Adding the aqueous composition comprising the GPAM adduct may improve the dry strength of the resulting paper product. In embodiments, the aqueous composition comprising the GPAM adduct is added to the diluted aqueous suspension such that the ratio of the flow velocity of the aqueous composition to the flow velocity of the diluted aqueous suspension, as measured in meters per second, is from about 1:1 to about 10:1, alternatively from about 1.5:1 to about 5:1. In embodiments, the aqueous composition comprising the GPAM adduct is added through a nozzle, wherein the flow of the aqueous composition out of the nozzle is turbulent flow. The flow velocity ratios and the turbulent flow of the aqueous composition aid in mixing of the GPAM adduct into the diluted aqueous suspension so that the GPAM adduct comes into contact with a greater surface area of the cellulosic fibers and fines. Maximized contact between the GPAM adduct and the cellulosic fibers and fines may lead to maximized dry strength of the resulting paper product.

[0020] In the methods provided herein, the aqueous composition comprising the GPAM adduct is added to the diluted aqueous suspension after the diluted aqueous suspension is subjected to the high shear operation and before the diluted aqueous suspension is passed to the headbox. The method is free of any high shear operation after the aqueous composition comprising the GPAM adduct is added and before the diluted aqueous suspension is passed to the headbox. Addition of the aqueous composition comprising the GPAM adduct to the diluted aqueous suspension after the last high shear operation and before the headbox has unexpectedly been found to provide a comparable or even greater dry strength in the resulting paper product as compared to addition of the same amount and concentration of the aqueous composition comprising the GPAM adduct to the aqueous suspension before the aqueous suspension is diluted. Addition of the aqueous composition comprising the GPAM adduct to the diluted aqueous suspension after the last high shear operation and before the headbox may also allow for addition of a smaller amount of the aqueous composition (and thus a smaller amount of the GPAM adduct) without compromising dry strength performance of the resulting paper product. Addition of the aqueous composition comprising the GPAM adduct to the diluted aqueous suspension after the last high shear operation and before the headbox has not previously been known for dry strength additives and would have been expected to produce a paper product with an inferior dry strength. Flexibility in addition points for the GPAM adduct may lead to improvements in process efficiency. For example, if other additives such as drainage and retention aids are also added during the process, the adduct comprising the GPAM adduct can be added at the same time as the other additives.

[0021] In embodiments, the aqueous composition comprising the GPAM adduct is prepared by reacting a substantially aqueous reaction mixture of the polyvinylamide prepolymer and the glyoxal, wherein the concentration of the polyvinylamide prepolymer is below, equal to or no more than 1% above a Critical Concentration. As used herein, “Critical Concentration” is defined as the concentration of the polyvinylamide prepolymer above which Critical Concentration the viscosity increases for the reaction mixture resulting from the forward progress of the adduct formation, and below which Critical Concentration the viscosity decreases for the reaction mixture resulting from the forward progress of adduct formation. Running the reaction close to the Critical Concentration may minimize the risk of gelation, maximize the consumption of glyoxal, and enhance the shelf life of the resulting composition. In embodiments, the Critical Concentration is from about 0.1 wt % to about 4.0 wt %, alternatively from about 1.0 wt % to about 3.0 wt %, based on a total weight of the reaction mixture. In embodiments, the polyvinylamide prepolymer is present in the reaction mixture in an amount of less than about 5 wt %, alternatively less than about 4 wt %, alternatively from about 0.1 wt % to about 4 wt %, based on a total weight of the reaction mixture, at the onset of the reaction. In embodiments, at least 40 wt %, alternatively at least 50 wt %, of the total glyoxal is consumed during the reaction. In embodiments, the molar ratio of the amide functionality on the polyvinylamide prepolymer to the glyoxal during the reaction is from about 2:1 to about 12:1, alternatively from about 2.5:1 to 8:1. In embodiments, the solids content of the resulting aqueous composition is no more than about 2.5%.

[0022] The polyvinylamide prepolymer may be a homopolymer, copolymer or terpolymer. The polyvinylamide prepolymer may be cationic, potentially cationic, anionic, potentially anionic, nonionic or amphoteric. The GPAM adduct may be formed from only one polyvinylamide prepolymer, or alternatively, the adduct may be formed from more than one polyvinylamide prepolymer. In embodiments, the adduct may be formed from a blend of a polyvinylamide prepolymer and another miscible non-polyvinylamide polymer. In embodiments, the polyvinylamide prepolymer has a weight average molecular weight of from about 50,000 Daltons to about 5 million Daltons, alternatively from about 80,000 Daltons to about 400,000 Daltons, alternatively from about 100,000 Daltons to about 300,000 Daltons, as measured using gel permeation chromatography (GPC). As used herein, the term “polyvinylamide prepolymer” refers to a polymer formed by vinyl polymerization from any vinyl monomer containing an amide functionality including but not limited to (meth)acrylamide, N-methyl acrylamide or any other substituted acrylamide. As used herein, the term “(meth)acrylamide” includes both acrylamide and methacrylamide. In embodiments, the polyvinylamide prepolymer is a homopolymer or copolymer formed from (meth)acrylamide or a substituted (meth)acrylamide.

[0023] The GPAM adduct may be cationic, potentially cationic, anionic, potentially anionic, nonionic or amphoteric. In embodiments, the GPAM adduct has a weight average molecular weight of from about 70,000 Daltons to about 500 million Daltons, alternatively from about 2 million Daltons to about 100 million Daltons, alternatively from about 4 million Daltons to about 50 million Daltons as measured using GPC. The adduct is a glyoxalated version of the polyvinylamide prepolymer, so the chemistry of the adduct is dependent on the chemistry of the polyvinylamide prepolymer. In embodiments, the adduct is glyoxalated polyacrylamide.

[0024] In embodiments, upon addition of the aqueous composition comprising the GPAM adduct to the diluted aqueous suspension, the GPAM adduct is present in the aqueous composition in an amount of from about 0.02 wt % to about 5.0 wt %, alternatively from about 0.1 wt % to about 5.0 wt %, alternatively from about 0.5 wt % to about 4.0 wt % active solids. In embodiments, upon addition of the aqueous composition to the diluted aqueous suspension, the GPAM adduct is present in the diluted aqueous suspension in an amount such that from about 0.25 kilograms to about 10 kilograms, alternatively from about 0.5 kilograms to about 9 kilograms, alternatively from about 1 kilogram to about 7.5 kilograms of the GPAM adduct, based on active solids, is present for every metric ton of solids present in the diluted aqueous suspension.

[0025] In embodiments, the aqueous composition further comprises an additive different from the GPAM adduct. In embodiments, the additive may be selected from a filler, a sizing agent, a retention aid, a colorant, a defoaming or antifoaming agent, a biocide, a pH control agent, a wet strength agent, a dry strength agent different from the GPAM adduct, or combinations thereof.

[0026] In embodiments, the method further comprises the step of adding to the diluted aqueous suspension a second composition different from the aqueous composition comprising the GPAM adduct. When added to the diluted aqueous suspension, the second composition is added separately from the aqueous composition comprising the GPAM adduct. The second composition may be added at the same point in the process as the aqueous composition, or alternatively, the second composition may be added to the diluted aqueous suspension at a different point in the process than the aqueous composition comprising the GPAM adduct. In embodiments, the second composition may comprise an additive selected from a filler, a sizing agent, a retention aid, a colorant, a defoaming or antifoaming agent, a biocide, a pH control agent, a wet strength agent, a dry strength agent different from the GPAM adduct, or combinations thereof.

[0027] The methods provided herein include the step of forming the diluted aqueous suspension into a sheet. More specifically, in embodiments, the diluted aqueous suspension is passed to the headbox. The diluted aqueous suspension is concentrated in the headbox by removing water. The diluted aqueous suspension is distributed across the length of a moving forming fabric to form a uniform paper sheet. The forming fabric is a porous fabric, a wire, or a plastic screen. The flow velocity of the diluted aqueous suspension may be adjusted by the headbox.

[0028] The methods provided herein include the step of drying the sheet to form the paper product. Drying the sheet removes any residual moisture to create the paper product in its final form. The sheet may be dried by, for example, applying vacuum under the forming fabric, pressing the sheet with rolls and / or felt blankets, heating the sheet, air drying the sheet, infrared drying, or calendaring.

[0029] The paper products provided herein are formed through the methods provided herein. In embodiments, the paper product may be printer paper, notebook paper, photographic paper, security paper, cardboard, paperboard, containerboard, toilet paper, paper towels, facial tissue, tissue paper, filter paper, envelopes, newspaper, gift wrap, or another kind of paper. In embodiments, the paper product has a dry edgewise compressive strength, as measured by the Ring Crush Test (RCT) in accordance with the Technical Association of the Pulp and Paper Industry (TAPPI) standard method TAPPI / ANSI T 822 om-22, that is equal to or greater than a comparative paper product formed by a process comprising adding the aqueous composition to the aqueous suspension before diluting the aqueous suspension and before subjecting the aqueous suspension to the high shear operation. In embodiments, the paper product has a dry short span compressive strength, as measured by the Short Span Compression Test (SCT) in accordance with the standard method TAPPI / ANSI T 826 om-21, that is equal to or greater than a comparative paper product formed by a process comprising adding the aqueous composition to the aqueous suspension before diluting the aqueous suspension and before subjecting the aqueous suspension to the high shear operation. In embodiments, the paper product has a dry burst strength, as measured by the Mullen Burst Test in accordance with the standard method TAPPI / ANSI T 403 om-22, that is equal to or greater than a comparative paper product formed by a process comprising adding the aqueous composition to the aqueous suspension before diluting the aqueous suspension and before subjecting the aqueous suspension to the high shear operation. In embodiments, the paper product has a dry internal bond strength, as measured by the Scott Bond method in accordance with the standard method TAPPI / ANSI T 569 om-22, that is equal to or greater than a comparative paper product formed by a process comprising adding the aqueous composition to the aqueous suspension before diluting the aqueous suspension and before subjecting the aqueous suspension to the high shear operation.

[0030] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the present disclosure. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the present disclosure as set forth in the appended claims.

Examples

Embodiment Construction

[0010]The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

[0011]The methods provided herein enable production of a paper product unexpectedly having the same or improved dry strength as compared to a paper product formed through existing methods, as a result of adding the same amount or a smaller amount of a dry strength additive (e.g. a glyoxalated polyvinylamide) than is added in existing methods, but by adding the dry strength additive at a location after the last high shear operation and before a headbox. The methods thus provide flexibility in addition points for dry strength additives. Particularly, it has unexpectedly been found that adding the glyoxalated polyvinylamide to the thin stock after the last high shear operation prior to the head...

Claims

1. A method of forming a paper product, the method comprising the steps of:providing an aqueous suspension of cellulosic fibers;diluting the aqueous suspension with water to form a diluted aqueous suspension having a solids content of from about 0.3 wt % to about 1.8 wt %, based on a total weight of the diluted aqueous suspension;subjecting the diluted aqueous suspension to a high shear operation;adding an aqueous composition to the diluted aqueous suspension, wherein the aqueous composition comprises an adduct formed from the reaction of glyoxal and a polyvinylamide prepolymer;forming the diluted aqueous suspension into a sheet by a headbox; anddrying the sheet to form the paper product;wherein the aqueous composition is added to the diluted aqueous suspension after the diluted aqueous suspension is subjected to the high shear operation and before the diluted aqueous suspension is passed to the headbox; andwherein the method is free of any high shear operation after the aqueous composition is added and before the diluted aqueous suspension is passed to the headbox.

2. The method of claim 1, wherein the adduct has a weight average molecular weight of from about 70,000 Daltons to about 500 million Daltons, as measured using gel permeation chromatography.

3. The method of claim 1, wherein the prepolymer has a weight average molecular weight of from about 50,000 Daltons to about 5 million Daltons, as measured using gel permeation chromatography.

4. The method of claim 1, wherein subjecting the diluted aqueous suspension to a high shear operation comprises subjecting the diluted aqueous suspension to a fan pump, a high pressure screen, or a combination thereof.

5. The method of claim 1, wherein subjecting the diluted aqueous suspension to a high shear operation comprises subjecting the diluted aqueous suspension to at least two high shear operations.

6. The method of claim 1, wherein the aqueous composition is added to the diluted aqueous suspension such that the ratio of the flow velocity of the aqueous composition to the flow velocity of the diluted aqueous suspension is from about 1:1 to about 10:1.

7. The method of claim 1, wherein, upon addition of the aqueous composition to the diluted aqueous suspension, the adduct is present in the aqueous composition in an amount of from about 0.02 wt % to about 5.0 wt % active solids.

8. The method of claim 1, wherein the adduct is present in the diluted aqueous suspension in an amount such that from about 0.25 kilograms to about 10 kilograms of adduct, based on active solids, is present for every metric ton of solids present in the diluted aqueous suspension.

9. The method of claim 1, wherein the aqueous composition is added through a nozzle, wherein the flow of the aqueous composition out of the nozzle is turbulent flow.

10. The method of claim 1, wherein the aqueous composition further comprises an additive different from the adduct.

11. The method of claim 1, further comprising adding to the diluted aqueous suspension a second composition different from the aqueous composition comprising the adduct.

12. The method of claim 11, wherein the second composition comprises an additive different from the adduct.

13. The method of claim 1, further comprising preparing the aqueous composition comprising the adduct by reacting a substantially aqueous reaction mixture of the polyvinylamide prepolymer and the glyoxal, wherein the concentration of the polyvinylamide prepolymer is below, equal to or no more than 1% above a Critical Concentration, and the Critical Concentration is defined as the concentration of the polyvinylamide prepolymer above which Critical Concentration the viscosity increases for the reaction mixture resulting from the forward progress of the adduct formation, and below which Critical Concentration, the viscosity decreases for the reaction mixture resulting from the forward progress of adduct formation.

14. The method of claim 13, wherein the Critical Concentration is from about 1.0 wt % to about 3.0 wt % of the polyvinylamide prepolymer, based on a total weight of the reaction mixture.

15. The method of claim 13, wherein the polyvinylamide prepolymer is present in the reaction mixture in an amount of less than about 4 wt %, based on a total weight of the reaction mixture, at the onset of the reaction.

16. The method of claim 13, wherein the solids content of the aqueous composition is no more than about 2.5%.

17. The method of claim 1, wherein the polyvinylamide prepolymer is a homopolymer or copolymer formed from (meth)acrylamide or a substituted (meth)acrylamide.

18. The paper product formed through the method of claim 1.

19. The paper product of claim 18, having a dry strength, as measured by the Ring Crush Test in accordance the standard method TAPPI / ANSI T 822 om-22, that is equal to or greater than a comparative paper product formed by a process comprising adding the aqueous composition to the aqueous suspension before diluting the aqueous suspension and before subjecting the aqueous suspension to the high shear operation.

20. The paper product of claim 18, having a dry strength, as measured by the Mullen Burst Test in accordance with the standard method TAPPI / ANSI T 403 om-22, that is equal to or greater than a comparative paper product formed by a process comprising adding the aqueous composition to the aqueous suspension before diluting the aqueous suspension and before subjecting the aqueous suspension to the high shear operation.