Patent Application
20240360626
The present disclosure relates to the field of applying additives to wet paper webs. More particularly, the present disclosure relates to the application of dry strength agents using foamed application techniques to wet newly-formed webs in the production of a paper product.
In paper manufacturing, additives are introduced into the papermaking process to improve paper properties. For example, known additives improve resistance to wetting and penetration by liquid, paper strength, drainage properties, retention properties, and so on.
In a conventional papermaking machine, pulp is prepared for papermaking in a stock preparation system. Chemical additives, dyes, and fillers are sometimes added into the thick stock portion of the stock preparation system, which operates at a consistency of from 2.5 to 5% dry solids; additives may be added into the blend chest, the paper machine chest, a pulp suction associated with either of these chests, or other locations. In the thin stock circuit of the stock preparation system, the pulp is diluted from a consistency of 2.5 to 3.5% to a consistency of from 0.5 to 1.0% dry solids prior to passing through the thin stock cleaners, screens, an optional deaeration system, and approach flow piping. During or after this dilution, additional chemical additives may be added to the pulp, either in a pump suction, or in the headbox approach flow piping. Addition of chemical additives in the thick stock or the thin stock portions of the stock preparation system would be considered “wet-end addition” as used herein.
The fully prepared stock slurry, at from 0.5 to 1.0% dry solids consistency, is typically pumped to the headbox, which discharges the stock slurry onto a moving continuous forming fabric. The forming fabric may have the form of a woven mesh. Water drains through the forming fabric and the fibers are retained on the forming fabric to form an embryonic web while traveling from the headbox to the press section. As water drains away, the water content of the embryonic web may drop from 99 to 99.5% water to 70 to 80% water. Further water may be removed by pressing the wet web with roll presses in a press section, from which the wet web may exit with only from 50 to 60% water content (that is, a consistency of from 40 to 50% dry solids). Further water is typically removed from the web by evaporation in a dryer section, from which the web may exit with a consistency of from 90 to 94% dry solids. The sheet may then be treated in a size press and post dryers. The sheet may then be calendered to improve the surface smoothness of the sheet, and to control the sheet thickness or density to a target value. The sheet is typically then collected on a reel.
As explained above, chemical additives may be introduced into the pulp within the stock preparation section, in what is known as “wet-end addition”. In some cases, additives may also be added via either spraying onto the wet web in the forming section, or by using a size press to apply the additives to the dry sheet. Spray application and size press addition of additives are optional.
In wet-end applications, the chemistry is distributed throughout the web and the retention of the chemical additives varies depending on the papermaking system and the chemistry being applied. There are additional considerations with wet-end application of additives such as deposits on the forming fabric and other surfaces within the forming section, and potential cycle up issues (accumulation of wet-end additives within the recirculated water due to poor fixation of the additives to the fibers). Spray application can be somewhat problematic due to accumulation of overspray on nearby surfaces, uneven distribution due to spray patterns, and the plugging of the spray nozzles.
Further, chemical additives applied via traditional wet-end application typically provide relatively uniform distribution of additives throughout the Z-direction of the web, which may be desirable, or may result in less additive in some Z-direction locations within the sheet than desired. Thus, the wet-end approach is not targeted and can result in some cost inefficiencies in the chemistry application.
Accordingly, it is desirable to provide a method for manufacturing paper with improved application of dry strength agents. In addition, it is desirable to provide a method for manufacturing paper in which a dry strength agent or agents is applied via foam application. Further, it is desirable to provide a foam formulation for application of dry strength agents. Furthermore, other desirable features and characteristics of embodiments will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description section.
In an exemplary embodiment, a method for manufacturing a paper product is provided. The method includes producing a foam of a gas, water, a dry strength agent, and a combination of foaming agents including an anionic sulfated/sulfonated surfactant and a polysorbate-type nonionic surfactant. Further, the method includes applying the foam to a web and processing the web to form the product.
In another exemplary embodiment, a formulation is provided for producing a foam with a gas content upon incorporation of gas into the formulation. The formulation includes water, a dry strength agent having a cationic functional group, an anionic sulfated/sulfonated surfactant, and a polysorbate-type nonionic surfactant.
Other desirable features will become apparent from the following detailed description and the appended claims, taken in conjunction with the accompanying drawing and this background.
A more complete understanding of the subject matter may be derived from the following detailed description taken in conjunction with the accompanying drawing, wherein:
The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the systems and methods defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding Technical Field, Background, Brief Summary or the following Detailed Description. For the sake of brevity, conventional techniques and compositions may not be described in detail herein.
Herein, the term “paper” is used, for convenience, to mean all forms of paper, paperboard and related products including molded three-dimension products such as cups, bowls, containers, packaging, and the like. As used herein, “a,” “an,” or “the” means one or more unless otherwise specified. The term “or” can be conjunctive or disjunctive. Open terms such as “include,” “including,” “contain,” “containing” and the like mean “comprising.” The term “about” as used in connection with a numerical value throughout the specification and the claims denotes an interval of accuracy, familiar and acceptable to a person skilled in the art. In general, such interval of accuracy is ±ten percent. Thus, “about ten” means nine to eleven. All numbers in this description indicating amounts, ratios of materials, physical properties of materials, and/or use are to be understood as modified by the word “about,” except as otherwise explicitly indicated. As used herein, the “%” described in the present disclosure refers to the weight percentage unless otherwise indicated.
Embodiments of the present disclosure relate to introducing dry strength agents to paper substrates via a foam-assisted application technique. The technique distributes the dry strength agents in a foam that is then applied to the formed wet web. In exemplary embodiments, the dry strength agent is applied via foam at a location prior to, or upstream of, a vacuum box. At the vacuum box, the foam is pulled into the wet web prior to pressing and drying. In other embodiments, the foam may be applied at a different location depending on the equipment configuration. Typically, the foam is applied prior to the dryer section to allow penetration of the foam and chemistry into the wet web prior to reactions in the dryer section.
Application of dry strength agent or agents to the wet web via foam application can be advantageous in that the chemistry is applied to the wet-end, as with traditional approaches, but some of the typical disadvantages are avoided. Foam application can be expected to have better dry strength agent retention, thereby avoiding deposits, and the application to the wet web surface allows some benefits of the spray applications while providing a more even distribution of the dry strength agent across the surface of the sheet.
Embodiments using foam application of dry strength agents to paper substrates have advantages over the standard practices in terms of retention, efficiency, cost, and targeted application. For example, foam application processes have shown improved strength performance with a reduction in the dry strength agent dosage required to achieve particular desired properties in the paper product.
As described herein, dry strength agents are applied via foam to the surface of a web. The foam is pulled into the web via a vacuum or negative pressure force, which can provide multiple advantages over traditional approaches. For example, the concentrations in the foam and application to the surface can be optimized to provide better retention in the web as compared to conventional wet-end applications. Further, foam is more easily controlled and managed than a spray application, and foam does not cause accumulation of sprayed component droplets on surfaces as overspray. Also, there is potential to apply higher viscosity chemistries as well as higher concentrations of chemistry in a foam as compared to typical limitations of spray application. Additionally, the application to the web surface allows for tunable penetration into the web and a controlled distribution to and through one surface as opposed to an even distribution throughout the Z-direction of the web.
It is contemplated herein that dry strength agents are applied via foam to the surface of a web when the web has a selected pulp fiber consistency, such as less than 45% dry solids. In certain embodiments, the selected pulp fiber consistency is less than 30% dry solids, such as less than 20% dry solids, less than 15% dry solids or less than 10% dry solids. In certain embodiments, the selected pulp fiber consistency is greater than 1% dry solids, such as greater than 2% dry solids, greater than 5% dry solids or greater than 6% dry solids. In certain embodiments, dry strength agents are applied via foam to the surface of an embryonic web.
An exemplary embryonic web has a pulp fiber consistency of less than 50% dry solids, such as less than 45% dry solids, for example less than 40% dry solids, such as less than 35% dry solids, for example less than 30% dry solids, such as less than 25% dry solids, for example less than 20% dry solids, or less than 15% dry solids. An exemplary embryonic web has a consistency of greater than 5% dry solids, such as greater than 6% dry solids, for example greater than 7% dry solids, such as greater than 8% dry solids, for example greater than 9% dry solids, or greater than 10% dry solids.
Exemplary embodiments herein introduce a natural, bio-based, or synthetic dry strength agent (hereafter, a strength agent or a dry strength agent) into a multi-ply paper product via foaming formulation that includes a unique combination of foaming agents.
A schematic of a device 10 provided for the formation of a three-ply sheet using the “dry on dry” method, and for applying a foamed formulation to a wet embryonic web is shown in
In the middle ply blend chest 22b, the stock component 20b may optionally be blended with middle ply stock component or components 23b from other sources, for example, broke. Additionally, the stock component 20b may be blended with chemical additives 24b in the middle ply blend chest 22b. After exiting from the middle ply blend chest 22b, the middle ply stock components 20b and 23b may be diluted through the addition of water 25b in order to control the consistency of the middle ply stock components 20b and 23b to be within a pre-determined target range and forms blended and consistency adjusted middle ply stock 26b.
The blended and consistency adjusted middle ply stock 26b then enters a middle ply paper machine chest 27b where additional chemical additives 28b may be added. In an embodiment, as the stock exits from the middle ply paper machine chest 27b, the middle ply stock 26b is diluted with a large amount of water 29b to control the consistency of the middle ply stock 26b to be from about 0.5 to 1.0% dry solids as the middle ply stock 26b exits the middle ply thick stock circuit 12b. The middle ply stock 30b, with a consistency of from 0.5 to 1.0% dry solids, enters the middle ply thin stock circuit 13b.
In an exemplary embodiment, within the middle ply thin stock circuit 13b, the middle ply stock 30b may pass through low consistency cleaning, screening, and deacration devices. In exemplary embodiments, additional chemical additives 32b may be added to the stock 30b in any number of locations within the middle ply cleaning, screening, and deacration area 31b, for example at location 32b, and also at location 33b in the approach flow piping 34b, such as 34b, to the middle ply forming section 35b. The middle ply stock 37b enters the mid ply forming section 35b.
In exemplary embodiments, in the middle ply forming section 35b, a middle ply headbox 36b distributes the middle ply stock 37b onto a moving woven fabric (the middle ply “forming fabric”) 40b. In exemplary embodiments, the middle ply forming fabric 40b transports the middle ply stock 37b over one or more boxes of hydrafoils 41, such as 41b, which serve to drain water from the middle ply stock 37b and thereby increase the consistency of the stock 37b to form an embryonic middle ply web 42b. In exemplary embodiments, when the embryonic middle ply web 42b has a consistency of from 2 to 3% dry solids, the web 42b then passes over one or more low vacuum boxes 43, such as 43b, which are configured to apply a “low” vacuum to the embryonic middle ply web 42b in order to remove additional water from the web. The embryonic middle ply web 42b may also be dewatered further by an optional additional dewatering unit 44b mounted above the middle ply forming fabric 40b. The embryonic middle ply web 42b be may subsequently pass over one or more “high” vacuum boxes 45b, where a higher vacuum, i.e., stronger negative pressure, force removes additional water until the web 42b has a consistency of from 6 to 12% dry solids. The wet middle ply web, no longer embryonic, is now referred to as 46b.
In an exemplary embodiment, uncooked starch 50b, one or more dry strength agents 51b, and a foaming agent 52b, collectively called the foaming formulation 53b, is mixed with a gas 54b (usually air) in a middle ply foam generator 55b to create a foam 56b. In an exemplary embodiment, after the incorporation of gas 54b into the foaming formulation 53b, the resultant middle ply foam 56b is conveyed via a pipe or a hose 57b to a middle ply foam distributor 58b where the middle ply foam 56b is applied onto the wet middle ply web 46b. In an exemplary embodiment, the foam 56b is applied between a high vacuum box 45b and a post-application high vacuum box 47b. The vacuum created by the high vacuum box 47b following the foam application draws the foam 56b into the wet middle ply web 46b. The foam coated and vacuum treated middle ply web, now called 48b, is also typically at a somewhat higher consistency, from 8 to 12%, due to the influence of vacuum from the high vacuum boxes 47b.
The above description of the middle ply production capabilities of device 10 (middle ply stock preparation system 11b, middle ply paper forming system 35b, and middle ply foam addition system 53b-58b). It acts in conjunction with a top ply former 35a and bottom ply former 35c (comparable to middle ply former 35b). The top ply forming section 35a and the back ply forming section are supported by corresponding top and back ply stock preparation systems (not shown in
The wet top ply 48a and the wet middle ply 48b, called 61 when combined, is transferred to the wet back ply web 48c by combining roll 60a, which presses the combined wet top ply and middle ply web 61 to the wet back ply web 48c immediately following the back ply high vacuum box 45c and before back ply subsequent high vacuum boxes 47C on back ply former 35c. The web 71 is comprised of the combined wet top ply web 48a, the wet middle ply web 48b, and the wet back ply web 48c. The combined wet web 71 may be further dewatered by additional high vacuum boxes 47c on back ply former 35c to about 20 to 25% solids, and is now called 72.
Combined web 72 enters the pressing section 80, where press rolls press additional water from the wet web 72. The wet web 72 exits the pressing section with a consistency of about 40 to 55% dry solids and is then called web 73. Wet web 73 enters a drying section 81, where heated dryer cylinders heat the web 73 and evaporate additional water from the web 73. The heat from the dryers and the remaining moisture within the wet sheet swell the uncooked starch particles (if used), which form a gel and adhere the top ply 48a to the middle ply 48b as the wet plies continue to dry. The wet web 73 is dried to from 6 to 10% moisture content (90 to 94% dry) within the drying section and is now called dry sheet 74. After the drying section 81 the dry web 74 may go directly to the calendar 84 and reel 85, or it may be treated with a surface size in the optional size press 82; if so treated, it is then dried again with additional dryers 83. Following the drying section 81 or optionally size press 82 and additional drying 83, the sheet 74 may be treated with a calender 84 to improve surface smoothness and control sheet thickness, then the sheet may be reeled by a reel device 85.
It should be understood that the description of the middle ply stock preparation system 11b and middle ply former 35b which produces the wet middle ply web 48b, is also a good general description of the top ply and back ply stock preparation systems. Further, the description of the middle ply forming section 35b is also a good general description of the top ply forming section 35a and the back ply forming section 35c, respectively. Each numbered item in each web forming system are correspondingly numbered, with the suffix “b” applied to the components of the middle ply forming system 35b, the suffix “a” applied to the correspondingly numbered components of the top ply system, and the suffix “c” applied to the correspondingly numbered components of the back ply forming system 35c. For example, top ply headbox 36a corresponds to middle ply headbox 36b and back ply headbox 36c, and so on.
It is also clearly understood by those skilled in the art that a number of variations in the details may differ from one manufacturing plant location to another, yet the same purpose is accomplished and hence such variations are contemplated as part of the system described and claimed herein. For example, middle ply stock preparation thick stock system 12b shows refiners acting on stock component 20b, but not on additional stock component or components 23b. In some cases, other stock components may be blended with stock component 20b before refiners 21b and co-refined with stock component 20b. There may be fewer or more foil boxes 41b, low vacuum boxes 43b, or high vacuum boxes 45b prior to the addition of foamed paper additives 56b. Additional dewatering step 44b for example is identified as optional. The foam distributor 58b may advantageously apply foam 56b at any accessible location after the first low vacuum box 43b and before the last high vacuum box 45b. In some embodiments, there may be only two plies and in other embodiments there may be three or more plies. Foam may be advantageously applied between any two adjacent plies to enhance ply bonding and other Z-direction strength properties. Size press 82 combined with additional drying 83 are likewise shown as optional-they may be present in some cases and absent in other cases, within the scope of the system described herein. Many other similar variations may be within the scope of the system described herein.
It has been surprisingly observed that the application of uncooked starch and dry strength agents through a foam-assisted addition technique results in an improvement (or, in some scenarios, at least equivalent performance) in bonding-related strength properties of multi-ply paper products as compared to multi-ply paper products where dry strength agents are added through wet-end addition, and uncooked starch is added via a spray shower. Previously, foaming agents were known to reduce paper strength properties due to the foaming agents disrupting bonding between pulp fibers. However, when dry strength agents are added with the foam, the negative impact of the foaming agents may be reduced, or the bonding strength may be improved significantly.
Further, adjustment of the process variables (amount of wet foam coating per unit of sheet area, time and strength of vacuum application before and after the addition of foamed additives, ply thickness, ply % dry solids at the time of foamed additives application, and many other variables) can allow the distribution of the dry strength agent to be altered. This allows a more even distribution of dry strength agent within the sheet, or a higher concentration of dry strength agent closer to the surface where the foam was applied, to be chosen. Without being bound by theory, the dry strength agent is believed to strengthen the ply overall, and in particular, the bonding strength in the portion of the web closest to the foamed additives application surface, while the uncooked starch (if applied), upon gelatinization in the dryer section, improves the ply bonding (the bonding between two adjacent plies). The bonding strength within the top ply may be less important as it is typically produced from well refined kraft fibers, which usually bond relatively well. The bonding within the middle ply is often lower, due to the use of lower bonding potential and high bulk fibers like bleached chemithermomechanical pulp (BCTMP) in the middle ply. The bonding within the back ply and the ply bond between the middle ply and the back ply are often less of an issue since the top ply is usually the printed surface. Exceptions may occur, especially if both sides are to be printed.
By strengthening the bonding within the middle ply with dry strength agents and by strengthening the ply bond between the top ply and the middle ply with uncooked starch, a considerably stronger internal bonding strength can be obtained for the overall multi-ply sheet. The process described herein allows this to be accomplished with relatively good chemical efficiency by improving the strength selectively where it most needs to be improved.
It has been discovered herein that a combination or blend of selected foaming agents used with a dry strength agent and, optionally starch provides a formulation exhibiting surprising and unexpected superior results in improved foaming properties while requiring less foaming agent content.
As is known, the successful application of chemistry via foam typically requires the use of a foaming agent. The foaming agent may impact, positively or negatively, the properties of the final paper product and also can represent a significant cost. In order to minimize these negative impacts, there is a goal to reduce or minimize the dosage of the foaming agent while providing a high quality foam with acceptable air content and stability.
Sodium lauryl sulfate or sodium dodecyl sulfate (SDS) is a foaming agent that can produce high quality foams. SDS alone can produce foams that meet target properties at about one-fifth of the dosage of certain commercial foaming agents, representing a significant cost reduction. However, during testing, the combination of SDS with dry strength agents has resulted in zero foam generation.
It has been discovered that a combination of first foaming agent consisting of an anionic sulfated/sulfonated surfactant, such as SDS, with a second foaming agent consisting of polysorbate-type nonionic surfactant, for example, polysorbate 20 (polyoxyethylene (20) sorbitan monolaurate) also known under the tradename Tween® 20, performs significantly better with a dry strength agent and, optionally, starch. Specifically, the unique combination of foaming agents provides a quality foam in the presence of the dry strength agent.
As described herein, a formulation for producing a foam with a gas content upon incorporation of gas into the formulation is provided. In exemplary embodiments, the formulation comprises water; a dry strength agent having a cationic functional group; an anionic sulfated/sulfonated surfactant; and a polysorbate-type nonionic surfactant.
In certain embodiments, the dry strength agent comprises a graft copolymer of a vinyl monomer and functionalized vinyl amine, wherein the anionic sulfated/sulfonated surfactant comprises sodium dodecyl sulfate (SDS), and wherein the polysorbate-type nonionic surfactant comprises polysorbate 20.
In certain embodiments, the formulation has a sodium dodecyl sulfate to polysorbate 20 ratio of from 3:7 to 9:1. Further, in certain embodiments, the formulation has a sodium dodecyl sulfate to polysorbate 20 ratio of from 5:5 to 7:3.
In certain embodiments, the formulation is substantially free of surfactants other than the sodium dodecyl sulfate (SDS) and the polysorbate 20.
In certain embodiments, the formulation consists essentially of water; the dry strength agent having a cationic functional group; the anionic sulfated/sulfonated surfactant; and the polysorbate-type nonionic surfactant.
In certain embodiments, the formulation is free of starch. In other embodiments, the formulation further includes uncooked starch.
In certain embodiments, the formulation consists essentially of uncooked starch; water; dry strength agent having a cationic functional group; anionic sulfated/sulfonated surfactant; and polysorbate-type nonionic surfactant.
As indicated above, the foaming formulation used to form the foam for application to the web includes a foaming agent blend separate from and in addition to the dry strength agent. As used herein, the term “foaming agent” defines a substance which lowers the surface tension of the liquid medium into which it is dissolved, and/or the interfacial tension with other phases, to thereby be absorbed at the liquid/vapor interface (or other such interfaces). Foaming agents are generally used to generate or stabilize foams.
In exemplary embodiments, the foaming formulation includes at least two foaming agents. In certain embodiments, the foaming formulation consists essentially of two foaming agents. In certain embodiments, the foaming formulation consists of two foaming agents.
Foaming agents generally reduce bonding-related paper strength parameters by disrupting bonding between pulp fibers. Certain foaming agents can also have a negative impact on the strength performance of the sheet. It was observed that the use of a foaming formulation having about the minimum amount of foaming agent sufficient to produce a foam minimizes the reduction of paper strength parameters and other negative impacts to the paper properties. In particular, it was observed that the dosage of foaming agent required to effectively disperse a certain amount of dry strength agents and, optionally, dry strength agent in a foam having gas bubbles with a mean maximum dimension or diameter of from 50 to 150 micrometers and a gas content of from 70% to 80% may vary in relation to the type and dosage of the dry strength agents and optional dry strength agent, and the foaming formulation temperature and pH. This amount of foaming agent is defined herein as the “minimally sufficient” foaming agent dose, and is desirable to reduce the negative effects many foaming agents have on fiber bonding, and also to reduce cost and reduce potential subsequent foaming problems elsewhere in the paper machine white water circuit.
An investigation was performed into which foaming agents produced foams with the desired qualities of gas content and bubble size range for the foam-assisted application of certain strength agents. It was observed that improved physical parameters in the investigative paper sheet samples were obtained when the foam applied to the samples had a gas content of from 40% to 95%, for example from 70% to 90%. In an exemplary embodiment, the gas is air. In various exemplary embodiments, the foams are formed by shearing a foaming formulation in the presence of sufficient gas, or by injecting gas into the foaming solution, or by injecting the foaming solution into a gas flow.
It was also observed that improved physical properties of the paper sheet samples were obtained when the foaming formulation included one or more foaming agents in an amount of from 0.001% to 10% by weight, based on a total weight of the foaming formulation, for example from 0.01% to 1% by weight, based on a total weight of the foaming formulation. Still further, it was observed that improved physical properties of the paper sheet samples resulted when the amount of foaming agent was minimized to only about that sufficient to produce a foam with a target gas content and bubble size.
Generally, the desired total foaming agent blend concentration results in a foam with about all of the gas bubbles within the preferred diameter range of from 50 to 150 micrometers. Adding a foaming agent blend in excess of about the minimally sufficient dose of foaming agent required to produce a foam with the targeted gas content increases the likelihood of loss of bonding-related strength properties and therefore the increase in the magnitude of the strength parameter loss. Use of excessive foaming agent blend beyond that required to produce a foam, for example using an excessive amount of foaming agent blend of more than 10% by weight of the foaming solution, also increases the total cost of the treatment.
It was known that some foaming agents, such as the anionic foaming agent sodium lauryl sulfate or sodium dodecyl sulfate (SDS), tend to result in a decrease in bonding-related strength parameters of final paper products. SDS is conventionally known as a preferred foaming agent because of its low cost and the small dose normally required to achieve a target gas content in the foam. However, it has been discovered that the anionic charge of SDS may interfere with certain synthetic dry strength agents that have a cationic functional group and result in the formation of a gel-like association (i.e., coacervate). This association may create foam handling problems and inhibit the migration of the foamed strength agent into the web. Even under ideal circumstances (with no charge interference occurring between SDS and a cationic-group-containing dry strength agent) SDS still acts to reduce strength due to bonding interference. Certain other types of foaming agents were also unable to produce a foam of the targeted gas content range, unless cost-prohibitive concentrations of the foaming agent were used.
Despite the tendency of sodium dodecyl sulfate (SDS) or other anionic sulfated/sulfonated surfactants, to result in a decrease in bonding-related strength parameters of the final paper product, it has been found herein that, when a surfactant like SDS is used as a first foaming agent in combination with a second foaming agent, the blend of foaming agents provides for surprising and unexpected superior results in improved foaming properties while requiring less foaming agent content. Specifically, a blend of an anionic sulfated/sulfonated surfactant foaming agent, such as SDS, with a polysorbate-type nonionic surfactant foaming agent has been found to provide improved foam performance. In exemplary embodiments, the polysorbate-type nonionic surfactant foaming agent may include polysorbate 20, polysorbate 40, polysorbate 60 or polysorbate 80. In certain embodiments, the second foaming agent is polysorbate 20. Polysorbate 20 or Tween 20 is an ethoxylated (20) sorbitan ester based on a natural fatty acid (lauric acid).
In certain embodiments, the blend of the anionic sulfated/sulfonated surfactant foaming agent and polysorbate-type nonionic surfactant foaming agent is provided in the foaming formulation in an anionic surfactant:ionic surfactant ratio of 90:10 to 10:90, such as from 80:20 to 40:60, or from 70:30 to 50:50. In exemplary embodiments, the blend of the anionic sulfated/sulfonated surfactant foaming agent and polysorbate-type nonionic surfactant foaming agent is provided in the foaming formulation in an anionic surfactant:ionic surfactant ratio of at least 30:70, at least 40:60, at least 45:55, at least 50:50, at least 55:45, at least 60:40, at least 65:35, at least 70:30, at least 75:25, at least 80:20, at least 85:15, at least 90:10, or at least 95:5. In exemplary embodiments, the blend of the anionic sulfated/sulfonated surfactant foaming agent and polysorbate-type nonionic surfactant foaming agent is provided in the foaming formulation in an anionic surfactant:ionic surfactant ratio of at most 95:5, at most 90:10, at most 85:15, at most 80:20, at most 75:25, at most 70:30, at most 65:35, at most 60:40, at most 55:45, at most 50:50, at most 45:55, at most 40:60, at most 35:65, at most 30:70, at most 20:80, or at most 10:90.
In exemplary embodiments, the foaming formulation includes a total amount of the blend of the anionic sulfated/sulfonated surfactant foaming agent and polysorbate-type nonionic surfactant foaming agent, with a basis of actives on a total foam formulation, of at most 0.1 wt. %, such as at most 0.09 wt. %, at most 0.085 wt. %, at most 0.08 wt. %, at most 0.075 wt. %, at most 0.0725 wt. %, at most 0.07 wt. %, at most 0.0675 wt. %, at most 0.065 wt. %, at most 0.0625 wt. %, at most 0.06 wt. %, at most 0.0575 wt. %, at most 0.055 wt. %, at most 0.0525 wt. %, at most 0.05 wt. %, at most 0.0475 wt. %, at most 0.045 wt. %, at most 0.0425 wt. %, at most 0.04 wt. %, at most 0.0375 wt. %, at most 0.035 wt. %, at most 0.0325 wt. %, at most 0.03 wt. %, at most 0.0275 wt. %, at most 0.025 wt. %, at most 0.0225 wt. %, at most 0.02 wt. %, at most 0.0175 wt. %, at most 0.015 wt. %, at most 0.0125 wt. %, at most 0.01 wt. %, at most 0.0075 wt. %, at most 0.005 wt. %, or at most 0.0025 wt. %.
In exemplary embodiments, the foaming formulation includes a total amount of the blend of the anionic sulfated/sulfonated surfactant foaming agent and polysorbate-type nonionic surfactant foaming agent, with a basis of actives on a total foam formulation, of at least 0.0025 wt. %, at least 0.005 wt. %, at least 0.0075 wt. %, at least 0.01 wt. %, at least 0.0125 wt. %, at least 0.015 wt. %, at least 0.0175 wt. %, at least 0.02 wt. %, at least 0.0225 wt. %, at least 0.025 wt. %, at least 0.0275 wt. %, at least 0.03 wt. %, at least 0.0325 wt. %, at least 0.035 wt. %, at least 0.0375 wt. %, at least 0.04 wt. %, at least 0.0425 wt. %, at least 0.045 wt. %, at least 0.0475 wt. %, at least 0.05 wt. %, at least 0.0525 wt. %, at least 0.055 wt. %, at least 0.0575 wt. %, at least 0.06 wt. %, at least 0.0625 wt. %, at least 0.065 wt. %, at least 0.0675 wt. %, at least 0.07 wt. %, at least 0.0725 wt. %, at least 0.075 wt. %, at least 0.08 wt. %, at least 0.085 wt. %, as at least 0.09 wt. %, or at least 0.1 wt. %.
In exemplary embodiments, the blend of foaming agents consists essentially of the anionic sulfated/sulfonated surfactant foaming agent and polysorbate-type nonionic surfactant foaming agent. In exemplary embodiments, the blend of foaming agents consists of the anionic sulfated/sulfonated surfactant foaming agent and polysorbate-type nonionic surfactant foaming agent.
In exemplary embodiments, the blend of foaming agents consists essentially of SDS and polysorbate-type nonionic surfactant foaming agent. In exemplary embodiments, the blend of foaming agents consists of SDS and polysorbate-type nonionic surfactant foaming agent.
In exemplary embodiments, the blend of foaming agents consists essentially of SDS and polysorbate-20. In exemplary embodiments, the blend of foaming agents consists of SDS and polysorbate-20.
As used herein, a “dry strength agent” or “DSA” provides for increased strength properties of the final paper product, measured when the paper is conditioned to equilibrium at 23° C.+/−1° C. and 50%+/−2% relative humidity. Typically, dry strength agents function by increasing the total bonded area of fiber-fiber bonds. In certain cases, the improvement in fiber bonding-related paper strength properties achieved through the foam-assisted application of dry strength agents was shown to be larger than the wet-end addition of the same strength agents. In particular, one advantage associated with the foam-assisted application of dry strength agents is that a higher concentration of dry strength agent can be introduced into the wet formed sheet, whereas the practical dosage range of dry strength agent limits the concentration of wet-end additives in the very low consistency environment of traditional wet-end addition. In traditional wet-end addition, the limitation of dosage of dry strength agent led to bonding-related sheet strength property “plateauing” of the dose-response curve at relatively low dosages, whereas the foam-assisted addition of dry strength agent led to a continued dosage response, where an increase in the concentration of dry strength agent applied to the wet sheet resulted in an increase in the strength properties of the resultant paper product, even at much higher than normal dose applications.
In an exemplary embodiment, the dry strength agent is a dry strength agent comprising a cationic functional group, for example a cationic strength agent or an amphoteric strength agent. It is noted that synthetic strength agents having a cationic functional group improve the bonding related strength properties of the final paper sheet. In certain embodiments, the dry strength agent is a synthetic dry strength agent. In certain embodiments, the dry strength agent is a bio-based or natural dry strength agent.
In an exemplary embodiment, the dry strength agent is a synthetic dry strength agent that comprises a graft copolymer of a vinyl monomer and functionalized vinyl amine, a vinyl amine containing polymer, or an acrylamide containing polymer. It is noted that, as used herein, the term “synthetic” strength agent excludes natural strength agents, such as starch strength agents. In certain embodiments starch or other natural dry strength agents are used.
In an exemplary embodiment, a synthetic dry strength agent having a cationic functional group is selected from the group of: acrylamide-diallyldimethylammonium chloride copolymers; glyoxylated acrylamide-diallyldimethylammonium chloride copolymers; vinylamine containing polymers and copolymers; polyamidoamine-epichlorohydrin polymers; glyoxylated acrylamide polymers; polyethylencimine; acryloyloxyethyltrimethyl ammonium chloride. An exemplary synthetic dry strength agent including a graft copolymer of a vinyl monomer and a functionalized vinyl amine.
Additionally or alternatively, in an exemplary embodiment, a synthetic dry strength agent having a cationic functional group is selected from the group of DADMAC-acrylamide copolymers, with or without subsequent glyoxylation; Polymers and copolymers of acrylamide with cationic groups comprising AETAC, AETAS, METAC, METAS, APTAC, MAPTAC, DMAEMA, or combinations thereof, with or without subsequent glyoxylation; Vinylamine containing polymers and copolymers; PAE polymers; Polyethyleneimines; Poly-DADMACs; Polyamines; and Polymers based upon dimethylaminomethyl-substituted acrylamide, wherein: DADMAC is diallyldimethylammonium chloride; DMAEMA is dimethylaminoethylmethacrylate; AETAC is acryloyloxyethyltrimethyl chloride; AETAS is acryloyloxyethyltrimethyl sulfate; METAC is methacryloyloxyethyltrimethyl chloride; METAS is methacryloyloxyethyltrimethyl sulfate; APTAC is acryloylamidopropyltrimethylammonium chloride; MAPTAC is acryloylamidopropyltrimethylammonium chloride; and PAE is polyamidoamine-cpichlorohydrin polymers.
In certain embodiments, synthetic dry strength agents having a cationic functional group and also containing primary amine functional units, in the form of polyvinylamine polymer units, were effective in improving strength parameters as compared to synthetic dry strength agents which did not contain primary amine functional units. In an exemplary embodiment, the synthetic dry strength agent having a cationic functional group included in the foaming formulation has a primary amine functionality of from 1 to 100%.
In another embodiment, dry strength agents based on natural materials are used as the dry strength agent in the foaming formulation. Dry strength agents based on natural materials include cooked starch, guar, chitosan, microfibrillated cellulose (MFC), and many other materials known to those skilled in the arts. Foam application offers unique opportunities for application of MFC, which is difficult to apply via spraying due to the potential to clog the nozzles, and often must be diluted to very low solids content for conventional handling and application.
In yet another embodiment, bio-based strength agents composed of polymers synthesized from bio-based versions of fossil-based materials, to produce more sustainable versions of known synthetic strength agents.
In exemplary embodiments the dry strength agent is selected from a graft copolymer of a vinyl monomer and functionalized vinyl amine commercially available from Solenis LLC of Wilmington, Del., under the trade name Hercobond™ 7700-EU dry strength aid; a cationic polymer obtained by partial hydrolysis of poly (vinylformamide) with a hydrolysis rate of 30 mol %, molecular weight 350,000 daltons and active material 16.4% commercially available from BASF under the trade name Xelorex® RS 1100; and a terpolymer of vinylamine, vinylformamide and sodium acrylate (35:35:30 molar), amphoteric, having a high molecular weight, and a solids content of 10-12 wt % commercially available from BASF under the trade name Xelorex® F3000.
In an exemplary embodiment, the foaming formulation includes a dry strength agent or agents in a total amount of from 0.01% to 50% by weight solids, based on a total weight of the foaming formulation, for example at least 0.1%, at least 1%, at least 2% at least 5%, or at least 10%, by weight solids, based on a total weight of the foaming formulation, and at most 40%, at most 30% at most 25%, at most 20%, at most 15%, or at most 10%, by weight solids, based on a total weight of the foaming formulation. It is anticipated that commercial scale equipment would allow for more concentrated foam formulations than those used in a laboratory setting.
In an exemplary embodiment, the foaming formulation includes a dry strength agent or agents in a total amount, with a basis of actives on a total foam formulation, of at least 0.25 wt. %, at least 0.5 wt. %, at least 1 wt. %, at least 1.25 wt. %, at least 1.5 wt. %, at least 1.75 wt. %, at least 2 wt. %, at least 2.25 wt. %, at least 2.5 wt. %, at least 2.75 wt. %, at least 3 wt. %, at least 3.25 wt. %, at least 3.5 wt. %, at least 3.75 wt. %, at least 4 wt. %, at least 4.25 wt. %, at least 4.5 wt. %, at least 4.75 wt. %, at least 5 wt. %, at least 5.25 wt. %, at least 5.5 wt. %, at least 5.75 wt. %, or at least 6 wt. %.
In an exemplary embodiment, the foaming formulation includes a dry strength agent or agents in a total amount, with a basis of actives on a total foam formulation, of at most at most 8 wt. %, at most 7.75 wt. %, at most 7.5 wt. %, at most 7.25 wt. %, at most 7 wt. %, at most 6.75 wt. %, at most 6.5 wt. %, at most 6.25 wt. %, at most 6 wt. %, at most 5.75 wt. %, at most 5.5 wt. %, at most 5.25 wt. %, at most 5 wt. %, at most 4.75 wt. %, at most 4.5 wt. %, at most 4.25 wt. %, at most 4 wt. %, at most 3.75 wt. %, at most 3.5 wt. %, at most 3.25 wt. %, at most 3 wt. %, at most 2.75 wt. %, at most 2.5 wt. %, at most 2.25 wt. %, or at most 2 wt. %.
In certain embodiments, uncooked starch is used to provide the manufactured paper product with improved ply-bonding. Uncooked starch is introduced to the surface of a wet web before the wet web is contacted with another wet web to form an interface between the plies. The purpose of the uncooked starch is to help with ply to ply adhesion, also called ply-bonding. The uncooked starch will gelatinize under heat in the dryer section in the presence of water. This aids in adhesion between the different plies. The purpose of the uncooked starch is not to necessarily improve the strength of either ply on its own, but rather to improve the bond between plies.
In exemplary embodiments, the uncooked starch is provided in the form of particles, and the particles have a mean maximum dimension of from 5 to 50 microns.
In an exemplary embodiment, the foam-assisted application of uncooked starch and dry strength agent occurs with the foam having an air content of from 40% to 95%, for example from 70% to 90%, based on a total volume of the foam. The foam may be formed by injecting gas into a foaming formulation, by shearing a foaming formulation in the presence of sufficient gas, by injecting a foaming formulation into a gas flow, or by other suitable means.
In an exemplary embodiment, the foam is produced with a foam density of from 50 to 300 g/L, for example, from 100 to 300 g/L, such as from 150 to 300 g/L.
In an exemplary embodiment, when applying the foam to a wet ply web, the foam is applied at a foam coverage level of from 30 to 300 wet g/m2, such as less than 200 wet g/m2, for example, from 60 to 150 wet g/m2.
In an exemplary embodiment, when applying the foam to the ply web, the foam is applied such that a dosage of the dry mass of uncooked starch to the wet ply web area is from 0.1 to 4 g/m2, for example, at least 0.75 g/m2, or at least 1 g/m2, and no more than about 3 g/m2, or no more than about 2.5 g/m2.
In an exemplary embodiment, when applying the foam to the ply web, the foam is applied such that a dosage of the dry strength agent or agents to the wet ply web is at least 0.075% actives, such as at least 0.2% actives, and no more than 1.2% actives, such as no more than 0.8 actives, all based on the ply dry weight.
In an exemplary embodiment, when applying the foam to the ply web, the ply web is from 5 to 20% solids, for example, 5 to 15% solids or 8 to 15% solids.
Without being bound by theory, it may be that the improvement in paper bonding related strength properties achieved through the foam-assisted application of certain strength agents as compared to wet-end addition of the same agents is that there is a better retention of the agents with foam-assisted application. In particular, since the foamed application of agents is performed when the sheet has a higher concentration of fibers to water (with the water content typically being from 70 to 90%) as compared to the wet-end addition of strength agents to the pulp in the stock preparation sections (where the water content is typically from 95 to 99% or more), less strength agent loss occurs when the pulp is passed through subsequent water removal sections. In exemplary embodiments, the step of applying foam to the wet formed embryonic web is performed when the wet formed embryonic web has a pulp fiber consistency of from 5% to 45%, for example from 5% to 30%.
Without being bound by theory, it is believed that the improvement in paper strength parameters resulting from the foam-assisted application of certain strength agents as compared to the wet-end addition of the same agents is because contaminating substances, i.e., contaminants, that interfere with the additive adsorption of the strength agents onto the fibers may be present in greater quantities in the stock preparation section, particularly in the thin stock section.
Without being bound by theory, it is believed that the improvement in paper parameters resulting from the foam-assisted application of certain strength agents as compared to the wet-end addition of the same agents is that, because the strength agents are incorporated into the sheet at least in part by a physical means instead of only by a surface charge means, a lack of remaining available charged sites in the forming web does not limit the amount of strength agent that can be incorporated into the sheet. A lack of remaining available charged bonding sites in the forming web, such as a lack of remaining available anionic charged sites, may occur when additives are introduced by wet-end addition, especially when large amounts of additives are introduced in this manner. Alternatively or additionally, and without being bound by theory, the improved strength could be due to the unique DSA distribution in the sheet provided by embodiments herein. Rather than uniform distribution throughout, it is believed that the foam application concentrates the DSA distribution in the sheet in targeted areas.
Without being limited by theory, it is noted that when a small batch of foaming formulation is foamed by incorporating air into the liquid by means of a high speed homogenizer in an open top container, the amount of gas that is dispersed into fine bubbles having a maximum dimension, such as diameter, of from 10 to 300 micrometers (μm) is limited by the characteristics and concentration of the foaming agent and its interaction with the uncooked starch particles and dry strength agent molecules. As the air content increases, the foam becomes more viscous, and at some air content, it cannot effectively fall back into the vortex created by the homogenizer. For a given type and concentration of the foaming agent, a maximum gas content is typically achieved within less than a minute. Further homogenizing cannot entrain more gas as 10 to 300 micrometer diameter bubbles, as any additional gas drawn into the vortex is dispersed as much larger bubbles having a maximum dimension of from 2 to 20 millimeter (mm) diameter. Bubbles of this size quickly coalesce and float to the top of the foam, where they typically burst, and the gas exits the foam. The actual air content achieved at equilibrium (after from 30 to 60 seconds of homogenization) varies with the amount and type of dry strength additives and/or starch incorporated in the foaming formulation.
Without being limited by theory, it is noted that a commercially available foam generator can be used to produce suitable foam for foam assisted additive addition at pilot scale or commercial scale. Suitable commercially available foam generators sometimes produce foam by high shear caused by close clearance in a rotary device, by an oscillating device, by air induction, or by other suitable means. Most are pressurized, which is convenient for feeding the foam to a foam distributor over the ply forming device. When excess gas is added into a pressurized foam generator, beyond what the foam generator can disperse as acceptable quality foam (10 to 300 μm bubbles), the excess gas is discharged (with the foam) as very large 2 to 20 mm diameter bubbles, dispersed within the foam. Bubbles of 2 to 20 mm diameter are much larger in diameter than the typical thickness of the wet ply web or the foam layer. Since uncooked starch particles and dry strength agent are only found in the liquid film and interstice area of the bubbles in the foam, very large diameter bubbles cannot deliver the uncooked starch particles and dry strength agent to the fiber crossing area if a large area of the sheet has only the film over a single bubble applied to the sheet. Bubbles smaller than the foam layer thickness or the wet web thickness are preferred for a more even distribution of uncooked starch and dry strength agent. Bubbles of from 20 to 300 μm diameter are preferred, especially bubbles of from 50 to 150 μm diameter, for this application, because bubbles of this size can carry the uncooked starch onto the wet ply web and dry strength agent into the wet ply web without disruption of the web and can therefore more efficiently distribute the uncooked starch and strength agent. A foam containing bubbles of from 50 to 150 um diameter and from 70 to 80% air is convenient because it can be poured readily from an open top container. A foam containing up to from 90 to 95% air can be conveyed by pressure through a hose to and out of a foam distributor can be used to apply the foam to the ply web. Most foam generators cannot reliably produce acceptable quality foam for the described purpose with more than about 90% air.
Various examples were prepared and tested to illustrate the effectiveness of the foaming blends described herein. In the blended foaming agent cases the reported ratio is on an actives basis.
Example 1 is a foaming formulation with various foaming agents or foaming agent blends. Specifically, Examples (a1)-(a8) in Table 1 include (a) a single foaming agent in the form of an anionic sulfated/sulfonated surfactant, e.g., sodium dodecyl sulfate (SDS); Examples (b1)-(b3) in Table 1 include (b) a foaming agent blend of about 70% anionic sulfated/sulfonated surfactant, e.g., sodium dodecyl sulfate (SDS) and about 30% polysorbate-type nonionic surfactant, e.g., polysorbate-20 (Tween 20); Examples (c1)-(c3) in Table 1 include (c) a foaming agent blend of about 50% anionic sulfated/sulfonated surfactant, e.g., sodium dodecyl sulfate (SDS) and about 50% polysorbate-type nonionic surfactant, e.g., polysorbate-20 (Tween 20); and Examples (d1)-(d5) include (d) a single foaming agent in the form of a polysorbate-type nonionic surfactant, e.g., polysorbate-20 (Tween 20).
Further, Examples 2-3 provide foaming formulation with various combinations of foaming agent or blend, DSA, and uncooked starch. Specifically, Example 2 is a foaming formulation with Hercobond™ 7700-EU as the dry strength agent with no uncooked starch; Example 3 is a foaming formulation with Hercobond™ 7700-EU as the dry strength agent with uncooked starch (Raisamyl® 30067 Chemigate, Lapua, Finland). Examples 2-3 were tested for use with (a) a single foaming agent in the form of an anionic sulfated/sulfonated surfactant, e.g., sodium dodecyl sulfate (SDS); (b) a foaming agent blend of about 70% anionic sulfated/sulfonated surfactant, e.g., sodium dodecyl sulfate (SDS) and about 30% polysorbate-type nonionic surfactant, e.g., polysorbate-20 (Tween 20); (c) a foaming agent blend of about 50% anionic sulfated/sulfonated surfactant, e.g., sodium dodecyl sulfate (SDS) and about 50% polysorbate-type nonionic surfactant, e.g., polysorbate-20 (Tween 20); and (d) a single foaming agent in the form of a polysorbate-type nonionic surfactant, e.g., polysorbate-20 (Tween 20).
In the Examples, the “foamability” of various foam formulations was analyzed using a dynamic foam analyzer instrument (DFA 100, Kruss USA, Matthews, North Carolina USA). Each foam formulation was prepared in the measuring cell of the device by adding water, foaming agent, dry strength agent (if applicable), and uncooked starch (if applicable). The total formulation was designed to be about 100 grams of material. Each total formulation was placed on the dynamic foam analyzer instrument for foam generation. Agitation was run for three minutes to generate foam. Then the agitation was stopped, and the foam was allowed to sit stationary for at least 20 minutes. In the Examples, the dynamic foam analyzer instrument was used to measure two properties for analysis: the “maximum foam volume” (in mL) and the “foam half-life time”, a measure of the amount of time in which the foam volume stability is reduced to half of the initial value. The maximum foam volume is representative of the “foamability” of the system whereas the half-life is a measure of the stability of that generated foam. Both properties are important for successful foam application processes.
In summary, each Example using only Tween 20 as the foaming agent, i.e., Examples (d1), (d2), (d3), (d4), (d5), (2D), and (3D), made poor quality foams with low volumes and unacceptable half-lives.
As shown in Examples (a1)-(a8), formulations using only SDS as the foaming agent performed well at high concentrations and when lowered to a concentration of 0.0003 g/g, i.e., 0.03%, began to produce poorer foams with a much shorter half life. In Examples (2A) and (3A), the formulation using only SDS as the foaming agent in concentrations of 0.076% and 0.048% (actives basis to total foam formulation), respectively, produced no foam. Surprisingly, the introduction of a small quantity of Tween in Examples (2B), (2C), (3B) and (3C) improved foaming performance and made high quality foams in the presence of Dry Strength Agent with and without uncooked starch. This is surprising because the combinations of Dry Strength Agent and Tween 20 (2D) and (3D) as the only foaming agent were poor quality.
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 disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof.
This application claims the benefit of U.S. Provisional Application No. 63/498,292, filed Apr. 26, 2023, which is hereby incorporated in its entirety by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63498292 | Apr 2023 | US |
