Patent Application
20180209097
The present invention relates to methods for manufacturing bath tissue paper and, more particularly, to the application of a softening agent to bath tissue paper as part of a through-air dryer (TAD) bath tissue paper manufacturing method.
It has been found that low levels of softening agent applied to tissue paper structures can provide a softened, silky, bulky, flannel-like, non-greasy tactile sense of feel without the aid of additional materials such as oils or lotions.
Conventionally, additives such as softening agents, scents, and ornamental surface features are applied to the bath tissue paper after manufacture.
However, because the application of the softening agent is performed after the paper web has been dried, additional time and energy are required. Post-production application requires performing an unwind/rewind step, which in turn requires an additional drying process.
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 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.
This disclosure describes an apparatus and method for manufacturing bath tissue paper in which a softening agent is applied to the paper web before the paper web is sent through at least one through-air dryer. The application of the softening agent to the paper web prior to at least one through-air dryer has been found to provide softening to the bath tissue paper while avoiding the time and energy consumption of application of a softening agent after paper production.
These benefits can be obtained for the embodiments of the present invention in combination with high wettability within the ranges desirable for bath tissue paper application.
The present invention, in an embodiment, provides for a method for manufacturing bath tissue paper, the method including forming the paper web, dewatering the paper web, and applying a softening agent to the paper web, and drying the paper web. In this disclosure, “dewatering” and “drying” both refer to the removal of water from the fibrous paper web. In this disclosure, “dewatering” generally refers to the removal of water by mechanical means. For example, water can be removed by pressing or by applying a vacuum. In this disclosure, “drying” generally refers to the evaporation of water by heating with air or a hot surface.
In an embodiment, the method includes at least one through-air dryer (TAD). TAD drying can rapidly dry porous products. A TAD removes water and solvents from a paper web by uniformly transporting heated air through the entire thickness of the paper web.
In an embodiment, a forming roll is used to form the paper web, and the paper web is disposed between a pair of forming wires. (As used herein, “forming wire” is the same as “forming fabric.”) A headbox is used to deposit a slurry between the two fabrics so as to form a paper web between the fabrics. In an example, the headbox is pressurized and has an opening for delivering a thin deposit of the slurry between the forming fabrics.
In an embodiment, the two forming wires are guided to travel about a portion of the circumference of the forming roll.
The forming roll and a first web transfer device may be arranged such that the two forming wires, with the paper web sandwiched there between, travel along a substantially straight path between the forming roll and the first web transfer device.
At the first web transfer device, the paper web is separated from the outer forming wire by the application of vacuum through and onto the inner forming wire, such that the paper web is supported by the inner forming wire.
The paper web and inner forming wire travel toward a TAD fabric loop. A second web transfer device is disposed within the TAD fabric loop to pull the paper web onto the TAD fabric and separate the paper web from the inner forming wire.
In an embodiment, following separation of the inner forming wire at the second web transfer device, when the paper web is on the TAD fabric and before the paper web reaches a TAD, a softening agent is sprayed onto one surface of the paper web. Ideally, a softening agent is applied to a single side of the paper web to avoid waste, because the consumer only detects the softness on the side that makes contact with their body.
In an embodiment, the coated paper web is then transported on the TAD fabric through at least one TAD for at least partially drying the paper web, and through a second type of dryer for further drying the paper web. In an embodiment, a yankee dryer is the second type of dryer. In an embodiment, the paper web is dried with dry air that is supplied adjacent to part of the paper web's travel path from a dryer to a reel, via a blow box supplied with dry air by a blower.
An advantage of the method described in this disclosure is that the softening agent is applied to the paper web following the forming process and before drying. No additional drying step is needed, nor is a separate rewinding step needed to apply the softening agent.
The multi-ply bath tissue paper product of this invention can be used in any application where soft, absorbent multi-ply bath tissue paper products are required. Particularly advantageous uses of the multi-ply tissue paper product of this invention are in bath tissue paper and other tissue products.
The detailed description is described with reference to non-limiting and non-exhaustive embodiments shown in the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same reference numbers in different figures indicate similar or identical items.
This disclosure describes methods and apparatuses that, in an embodiment, apply a softening agent at a point in a paper manufacturing process before the paper web is dried in a TAD.
In this disclosure, a “slurry” is semiliquid mixture of paper-making fibers and other particles suspended in water. The slurry is delivered via headbox between forming wires to form a paper web. Once the slurry is deposited by the headbox, the slurry becomes known as a “paper web.”
In this disclosure, a “through-air dryer” or “TAD” is a dryer that removes water and/or solvents from air-permeable products, such as a paper web, by uniformly transporting heated air through the entire thickness of the product, without making contact with the product.
In an embodiment, the paper-making fibers used in the slurry may be made from cellulosic and/or lignocellulosic fibers, which can be virgin fibers from softwood and/or hardwood species, recycled bleached or unbleached paper, or a combination thereof, recycled fibers obtained from recycled paper and paper machine and converting tailings, or combinations thereof. In at least one example, wood pulp in all its varieties comprise the paper-making fibers. Other examples of cellulose fibrous pulps include but are not limited to, as cotton liners, bagasse, rayon, etc., may be used. Pulps derived from both deciduous and coniferous trees can be used.
In an embodiment, the paper web is sprayed with a softening agent before the paper web is routed through a TAD. The softening agent may be applied to one layer of the paper web (that is, what will become the outer layer of the bath tissue paper products). In at least one example, the pressure from the spray applicator of the softening agent is at a pressure of about 20 to about 120 psi, between about 40 to about 100 psi, and between about 60 to about 80 psi.
In addition to papermaking fibers, the slurry used to make bath tissue paper structures may have other components or materials added thereto: for example, wet-strength and temporary wet-strength resins. The slurry may also contain an effective amount of a wet strength binder (permanent and/or temporary), and a dry strength binder to control linting and/or to offset any loss in tensile strength resulting from the use of the softening agent. The use of both wet strength binders and dry strength binders also improves the retention of the softening agent in the sheet.
The paper web, before entering the TAD, has a solids content of about 20% to about 90%, from about 25% to about 75%, and from about 30% to about 40%.
In addition to spraying the softening agent onto the paper web, the softening agent can be also applied by creating a drop pattern (e.g. inkjet) or by printing (e.g. rotogravure or flexography) extrusion or by a flooded NIP press.
In an embodiment, when the softening agent is applied to the paper web, the paper web is past the second web transfer device but not yet at a TAD, and the paper web is in contact with a moving TAD fabric sheet.
In an embodiment, the softening agent may be selected from the group of amine salts and, more particularly, quaternary ammoniums (including first and higher generations of quaternary ammonium compounds). In an embodiment, the amine salts and the quaternary ammoniums may be cationic. In an embodiment, the amine salts and the quaternary ammoniums may have antimicrobial properties. In some examples, the amine salts can be poly(hexamethylene biguanide) hydrochloride (PHMB), and chlorhexidine salts such as 1,6-Di-(4-chlorophenyldiguanide)-hexan digluconate (chlorhexidine digluconate).
In an embodiment, the softening agent comprises a quaternary ammonium salt present in aqueous solution, the amount of water in the aqueous solution being 70% or less by weight.
In an embodiment, the softening agent contains from about 0.1% to about 60% of a quaternary ammonium compound by weight, or from about 5% to about 30% of a quaternary ammonium compound by weight.
The quaternary ammonium compound may be biodegradable. In an embodiment, the chemical formula for the quaternary ammonium compounds used is:
R12R22N+Cl−
wherein R1=alkyl group C10-C22
and wherein R2═CH3
As described above, in an embodiment, the softening agent is added during the manufacturing process of the bath tissue paper prior to the paper web entering at least one TAD. For example, the softening agent is added while the paper web has a solids content from about 10% to about 40% if applied before the first TAD, from about 30% to about 60% if applied after the first TAD, or from about 50% to about 90% if applied after the second TAD.
The softening agent may be added to the paper web in a concentration from about 0.5 lb/ton of paper web to about 5.0 lb/ton of paper web.
The softening agent concentrations can be selected in accordance with the desired ultimate bath tissue paper properties and in accordance with whether the end product will be formed as part of a single-ply tissue paper or a multi-ply tissue paper.
Bath tissue paper includes one ply or more than one superposed plies. As used herein the term “multi-ply tissue paper product” refers to a bath tissue paper consisting of at least two plies. Each individual ply in turn can consist of single-layered or multi-layered tissue paper webs. The bath tissue paper can include from one ply to about ten superposed plies. The multi-ply structures may be formed by bonding together two or more paper webs such as by gluing or embossing.
For example, multi-ply bath tissue paper products are formed by placing at least two multi-layered bath tissue paper webs in juxtaposed relation. For example, a two-layered, two-ply tissue paper product can be made by joining a first two-layered tissue paper web and a second two-layered tissue paper web in juxtaposed relation. In this example, each ply is a two-layer tissue sheet comprising an inner layer and an outer layer.
As used herein, the term “multi-layered tissue paper web,” “multi-layered paper web,” “multi-layered web,” “multi-layered paper sheet,” and “multi-layered paper product” all refer to sheets of paper prepared from two or more layers of slurry.
Other chemicals commonly used in paper making can be added to the biodegradable softening agent or to the slurry described herein, so long as they do not significantly and adversely affect the softening or the absorbency of the bath tissue paper.
For example, surfactants may be used to treat the multi-layered tissue paper webs of the present invention. The amount of surfactant, if used, is in at least one example from about 0.01% to about 2.0% by weight, and in some examples from about 0.001% to about 10% by weight, based on the dry fiber weight of the multi-layered tissue paper.
Different softening agents or combinations of several softening agents can be applied to the paper web.
The bath tissue paper that is the product of the method of manufacture described herein is a lightweight paper, which can be a creped paper. In at least one example, a single ply of the bath tissue paper has a basis weight from about 5 lb/3000 ft2 to about 20 lb/3000 ft2. In some examples, the single ply of bath tissue paper has a basis weight ranging from about 9 lb/3000 ft2 to about 15 lb/3000 ft2 and, in some examples, the single ply of bath tissue paper has a basis weight ranging from about 10 lb/3000 ft2 to about 12 lb/3000 ft2.
In an embodiment, the bath tissue paper that is the product of the method of manufacture has a thickness ranging between about 125 micrometers to about 1000 micrometers. For example, the bath tissue paper has a thickness of about 122 micrometers to about 600 micrometers and, in an alternative embodiment, it has a thickness ranging from about 200 micrometers to about 300 micrometers.
For example, bath tissue paper treated with the softening agent in accordance with the present invention may comprise up to from about 0.05% to about 4% of the softening agent by weight.
As low as 0.05% of softening agent retained by the bath tissue paper by weight is at least an effective level for imparting a tactile difference in softness, silkiness, or flannel-like quality to the paper. The minimum effective level may vary depending upon the particular type of sheet, the method of application, the particular type of fiber, and whether the tissue sheet is supplemented by starch, surfactant, or other additives or treatments.
An example of the method of manufacture of bath tissue paper discussed in this disclosure is now described.
The method of manufacture of bath tissue paper described in this disclosure includes the forming of a slurry. In an example, the slurry comprises at least paper-making fibers (hereinafter sometimes referred to as wood pulp), and a combination of wet strength binder (permanent and temporary), and a dry strength binder.
A forming roll 108, a pair of forming wires (an inner forming wire 110 and an outer forming wire 102), and a headbox 106 are used to form the paper web 112. Each of the forming wires—the inner wire 110 and the outer wire 102—forms a continuous loop about a number of guide rolls 104 and each is disposed relative to each other such that both inner forming wire 110 and outer forming wire 102 converge as they are guided to travel about a portion of the circumference of the forming roll 108. The headbox 106 is disposed adjacent the forming roll 108 where inner forming wire 110 and outer forming wire 102 converge. The headbox 106 is operable to deposit a slurry (not shown) between inner forming wire 110 and outer forming wire 102 at the forming roll 108 so as to form a paper web 112 between inner forming wire 110 and outer forming wire 102.
Following formation of the paper web 112 about a portion of the forming roll 108, the paper web 112 remains sandwiched between inner forming wire 110 and outer forming wire 102. The paper web 112 is then directed downstream in this manner to a first web transfer device 114, at which point the paper web 112 is separated from the outer forming wire 102 and is retained on the inner forming wire 110. The first web transfer device 114 may comprise, for example, a suction transfer box or the like.
In an embodiment, the slurry can be spread substantially uniformly on other forming apparatuses or with other methods such as and without being limited to a C-former, a twin wire former, a crescent former, an uncreped through air dried (UCTAD) technology, Structured Tissue Technology (STT), Atmos, any equivalent TAD paper (ETAD) products, suction breast roll formers, inclined suction breast roll formers, and the like.
In an embodiment of the present invention, a vacuum dewatering device 116 is disposed after the first web transfer device 114. In this configuration, the vacuum dewatering device 116 partially dewaters the paper web 112 through the inner forming wire 110.
The paper web 112 and inner forming wire 110 travel toward the TAD fabric 118 loop. A second web transfer device 120 is disposed within the TAD fabric 118 loop to pull the paper web 112 onto the TAD fabric 118 as it separates from the inner forming wire 110.
The paper web 112 is then transported, on the TAD fabric 118, to an applicator of the softening agent. In an embodiment, the softening agent may be added by a spray applicator 122 located between the second web transfer device 120 and a TAD 124.
Then the paper web 112 is dried by at least one TAD 124. A TAD 124 generally comprises a rotatable porous cylinder 128 and a dryer hood 126. In an embodiment of a paper-making apparatus, a second TAD is located before the second type of dryer (not shown). In this embodiment of a paper-making apparatus, the spray applicator 122 can be located between a first TAD and a second TAD, and the softening agent is therefore sprayed on the paper web after the paper web exits a first TAD or is sprayed on the paper web before the paper web enters a first TAD.
In an embodiment, the paper-making apparatus 100 includes at least one TAD 124 and a second type of dryer, which in some examples is a yankee dryer 130. In this disclosure, a “yankee dryer” is a large diameter drum that is internally heated with steam to provide a hot surface for completely drying a paper web 112. The yankee dryer 130 is also typically employed to shorten the paper web 112 in the machine direction so as to make it thicker, bulkier, and extensible in the machine direction in a process known as creping, which is accomplished by a blade 132. In an example, the blade 132 is a doctor blade. Upon removal of the paper web 112 from the yankee dryer 130, the blade creates a plurality of microfolds in the paper web 112, the microfolds extending in the cross-machine direction.
In a TAD 124, typically, the TAD fabric 118 and the paper web 112 wrap about a portion of the rotatable porous cylinder 128 and air is blown through the rotatable porous cylinder 128, paper web 112, and TAD fabric 118 to at least partially dry the paper web 112 having the applied softening agent. The TAD fabric 118 and the paper web 112 are guided about the rotatable porous cylinder 128 by at least one guide roll 104. The dryer hood 126 is generally disposed to cover the portion of the surface of the rotatable porous cylinder 128 about which the TAD fabric 118 and the paper web 112 are wrapped. In an embodiment, the TAD 124 is configured in an inward flow arrangement, wherein the drying air is flowed from the dryer hood 126 through the paper web 112 and the TAD fabric 118, and into the interior of the rotatable porous cylinder 128. In some examples, the TAD 124 is configured in an outward flow arrangement.
In an embodiment in which the paper-making apparatus 100 has more than one TAD, there may be a separate hood for each TAD or a common hood for all of the TADs.
At the end of the paper-making apparatus 100, the bath tissue paper is winded by a reel 134 into parent rolls (not shown) for further processing in converting steps such as embossing, rewinding, and cutting into small roll products for paper dispensers or folded products.
At 206, the paper web 112 is directed to a first web transfer device 114, the paper web 112 sandwiched between inner forming wire 110 and outer forming wire 102. The outer forming wire 102 is separated from the paper web 112, with the paper web 112 being retained on the inner forming wire 110.
At 208, the paper web is partially dewatered with a vacuum dewatering device 116 through the inner forming wire 110.
At 210, the paper web 112 is transferred off the inner forming wire 110 and onto the TAD fabric 118 at the second web transfer device 120.
Then at 212, the softening agent is applied to the paper web 112, the paper web 112 still affixed to the TAD fabric 118.
Next, at 214, the TAD fabric 118 with paper web 112 affixed is directed through one or more TADs 124 to partially dry the paper web 112.
At 216, the TAD fabric 118 with paper web 112 affixed is directed to a second type of dryer, for example, a yankee dryer 130. There, the paper web 112 is pulled onto the yankee dryer 130 and separated from the TAD fabric 118. The yankee dryer 130 completes the drying of the paper web 112.
At 218, the paper web 112 is wound into a parent roll 124.
Softness is a fundamental quality parameter of bath tissue paper. It may be characterized by smoothness, compressibility, stiffness, and “crumple-ability.”
Softness testing was performed on the bath tissue paper produced via the methods described herein. Each of these softness testing methods are known to those of ordinary skill in the art. For that reason, this disclosure only briefly summarizes the particular softness testing methods used.
One type of testing was performed on the bath tissue paper using an Emtec Tissue Softness Analyzer (“TSA”). The TSA is a multifunctional measuring instrument that measures “handfeel” of bath tissue paper.
The “handfeel” is a fundamental quality parameter of bath tissue paper. It may be characterized by, e.g., real softness (determined by fiber stiffness, refining, and softener chemicals), smoothness (creping/embossing), stiffness (e.g. fiber behavior, structure), compressibility, and “crumpleability.” The higher the handfeel measurement, the softer the bath tissue paper.
The TSA test compared “base paper” from the same process of manufacture—such that all components of the manufacture were the same except for the spraying on of the softener. Two samples of the bath tissue paper manufactured using the method of this disclosure (that is, the softener sprayed before the tissue reaches the TAD) were tested on the TSA, and the average handfeel measurement of the two samples was 95.8. Two samples of bath tissue paper manufactured without the innovation described herein were also tested, and the average handfeel measurement of these two samples was 87.8. Thus, the Emtec TSA test shows an objective improvement in softness when the method described in this disclosure was used.
Another assessment of the softness of the bath tissue by the method described herein was a “hand panel” test performed by a human panel. This hand panel test gauges panel members' subjective perception of the softness of tissue. The hand panel test was performed on finished tissue paper manufactured with the instant method and a finished tissue paper that was manufactured using a method in which a softener was sprayed after the bath tissue paper was dried. Approximately 80 persons were on the panel and rated various samples of both types of bath tissue paper for softness.
The bath tissue treated according to the method of this disclosure was rated as the same softness as bath tissue treated “offline,” which means the softener is applied after the tissue has been dried. Doing offline softener application adds cost to the bath tissue paper manufacturing process. The present method increases efficiency by applying the softening agent in the course of the customary bath tissue manufacturing process; no post-manufacturing steps are needed. That is, without the instant method, the softening agent is applied after the bath tissue paper is dried and rolled, thus requiring an un-winding in order to apply the softening agent. The hand panel test showed that for less cost (using the method described herein), the same softness can be achieved as the conventional post-dry softening application.
Also, bath tissue produced according to the method described herein was tested by Underwriters Laboratories (“UL”). The UL test, like the hand panel test, compares the finished tissue product of this method with that of the conventional manufacturing method. The sample of bath tissue paper submitted to UL (“the sample”) was tested against Charmin Ultra Soft® bath tissue (“the national brand”).
Various qualities of the bath tissue paper (both the sample and the national brand) were measured, including average sheet weight, thickness, whiteness, machine direction, absorbency rate, and softness.
The UL “Overall Quality Rating” for the sample was 9.5, which falls into the 9.0 to 10.0 range of “comparable to the national brand; meets Technically Advanced Quality Assurance (“TAQA”®) quality criteria.” The UL softness rating for the sample was the same as that for the national brand: UL softness was rated at 8 for the national brand and 8 for the sample. Therefore, as with the hand panel test described above, the UL test softness rating demonstrates the increased efficiency/lower cost of the method described herein because the sample was rated as highly as the national brand even with the in-line softener application described herein rather than offline application used by the national brand method.
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as illustrative forms of implementing the claims.
One skilled in the art will realize that a virtually unlimited number of variations to the above descriptions are possible, and that the examples and the accompanying figures are merely to illustrate one or more examples of implementations.
It will be understood by those skilled in the art that various other modifications can be made, and equivalents can be substituted, without departing from claimed subject matter. Additionally, many modifications can be made to adapt a particular situation to the teachings of claimed subject matter without departing from the central concept described herein. Therefore, it is intended that claimed subject matter not be limited to the particular embodiments disclosed, but that such claimed subject matter can also include all embodiments falling within the scope of the appended claims, and equivalents thereof.
In the detailed description above, numerous specific details are set forth to provide a thorough understanding of claimed subject matter. However, it will be understood by those skilled in the art that claimed subject matter can be practiced without these specific details. In other instances, methods, apparatuses, or systems that would be known by one of ordinary skill have not been described in detail so as not to obscure claimed subject matter.
Reference throughout this specification to “one embodiment” or “an embodiment” can mean that a particular feature, structure, or characteristic described in connection with a particular embodiment can be included in at least one embodiment of claimed subject matter. Thus, appearances of the phrase “in one embodiment” or “an embodiment” in various places throughout this specification are not necessarily intended to refer to the same embodiment or to any one particular embodiment described. Furthermore, it is to be understood that particular features, structures, or characteristics described can be combined in various ways in one or more embodiments. In general, of course, these and other issues can vary with the particular context of usage. Therefore, the particular context of the description or the usage of these terms can provide helpful guidance regarding inferences to be drawn for that context.
Conditional language such as, among others, “can,” “could,” “might” or “may,” unless specifically stated otherwise, are understood within the context to present that certain examples include, while other examples do not include, certain features, elements and/or steps. Thus, such conditional language is not generally intended to imply that certain features, elements and/or steps are in any way required for one or more examples or that one or more examples necessarily include logic for deciding, with or without user input or prompting, whether certain features, elements and/or steps are included or are to be performed in any particular example. Conjunctive language such as the phrase “at least one of X, Y or Z,” unless specifically stated otherwise, is to be understood to present that an item, term, etc., can be either X, Y, or Z, or a combination thereof.
