WO2017116429A1

WO2017116429A1 - Dispersible wet wipes constructed with a plurality of layers having different binders

Info

Publication number: WO2017116429A1
Application number: PCT/US2015/068006
Authority: WO
Inventors: Nathan John Vogel; Wan Duk Lee
Original assignee: Kimberly Clark Worldwide Inc; Kimberly Clark Corp
Current assignee: Kimberly Clark Worldwide Inc; Kimberly Clark Corp
Priority date: 2015-12-30
Filing date: 2015-12-30
Publication date: 2017-07-06
Anticipated expiration: 2018-06-30

Abstract

A dispersible wet wipe includes a wipe substrate having a first layer and a second layer, each comprised of cellulosic fibers. The first layer is held together by a first binder, and the second layer is held together by a second, different binder. The wipe includes a wetting solution having a first insolubilizing agent in which the first binder is stabilized and a second insolubilizing agent in which the second binder is stabilized. In particular embodiments, the first layer is a wet-laid tissue, and the second layer is an airlaid nonwoven.

Description

DISPERSIBLE WET WIPES CONSTRUCTED WITH

A PLURALITY OF LAYERS HAVING DIFFERENT BINDERS

BACKGROUND OF THE DISCLOSURE

Pre-moistened wipes are popular in the marketplace, including baby wipes, toddler wipes, surface cleaning wipes, feminine wipes, hemorrhoid wipes, make-up removal wipes, and child and adult toileting wipes. Consumers flush many of these wipes down the toilet. Some of the wipes are designed to be flushed, and labeled as such. It is important that wipes that are intended to be flushed are compatible with sewer and septic systems, but also important that such wipes do not fall apart when used for their intended purpose. Specifically, when a flushable disposable product is flushed down a toilet into sewer or septic systems, the product, or designated portions of the product, should degrade or break apart as it moves through various steps of wastewater processing.

One common approach to making a flushable wet wipe is using "hydroentangling" technology, in which fibers, primarily or exclusively cellulosic fibers, are "entangled" together using very small high- pressure water jets. However, some wipes made with this technology require a substantial amount of agitation to break apart after flushing, and may not lose significant strength in relatively static environments.

Another conventional approach to making a wet wipe that exhibits satisfactory in-use strength, but that adequately breaks down in sewer or septic systems, is via the use of a binder on a substrate comprising cellulose fibers. The binder attaches to cellulose fibers, and bonds those fibers together in a network to deliver in-use strength. The binder is stable and delivers this strength when soaking in a stabilizing solution, but swells and weakens in the fresh water of the toilet and sewer system, thus allowing the fiber network to break apart. The strength of the wipe can be manipulated by varying the amount of binder used and the process conditions by which the binder is applied, such as how and when it is applied to the wipe substrate, and by varying the time and temperature at which the binder is dried/cured.

One variant of such a binder/stabilizing solution is a salt-sensitive triggerable binder, such as that disclosed in U.S. Patent No. 6,994,865. The binder holds the fibers of the wet wipe together when soaked in a salt solution, which stabilizes the binder. When the salt solution is washed away, the binder swells and fails, and the wipes lose strength. However, such binders can be relatively expensive, and it can be challenging to achieve the right balance of binder in-use strength and post-flush degradation. One example of the use of such binders is described in U.S. Patent No. 8,603,297. Two layers of cellulosic fiber - a tissue layer and an "air-laid" layer - are each formed using the same salt-sensitive binder, and sandwiched together to form the wipe. Although the sheet exhibits excellent dispersion characteristics, the binder functions somewhat differently within the different layers of the sheet.

Another variant of a binder/stabilizer solution approach is a carboxymethyl cellulose (CMC) binder, such as that disclosed in U.S. Patent No. 5,281 ,306 or WO 2013/164913. This type of binder holds the fibers of the wet wipe together when soaked in a wetting solution having divalent cations and organic solvents such as alcohols or glycols, which act as a stabilizing solution. When the divalent cations and organic solvents in the wetting solution are washed away via flushing, the binder fails and the tissue exhibits rapid strength loss. However, this technology can produce a relatively stiff, paper-like sheet, which is undesirable for a wipe to be used on skin. Furthermore, commercial executions of this have required the use of multiple tissue plies, such as four plies, embossed together to provide the requisite product durability and thickness, which creates manufacturing complexity and additional cost. Finally, relatively high amounts of organic solvents such as alcohols or glycols are needed in the wetting solution to stabilize the CMC binder; this is undesirable, because certain alcohols are not suitable for perennial wipes, and glycols can result in an undesirable greasy-like feeling to the user of the wipe.

What is needed is a cellulose-based wipe that combines sufficient in-use strength, sufficient thickness, softness, and adequate strength loss after flushing even in relatively non-turbulent water.

SUMMARY OF THE DISCLOSURE

In a first embodiment, the invention provides a dispersible wet wipe comprises a wipe substrate having a first layer and a second layer, the first layer being adhered to the second layer, each layer comprising cellulosic fibers. The first layer is held together by a first binder, the second layer is held together by a second binder, and the first binder is different than the second binder. The wipe further includes a wetting solution containing a first insolubilizing agent in which the first binder is stabilized and a second insolubilizing agent in which the second binder is stabilized.

In a second embodiment, the invention provides the wet wipe of the first embodiment wherein the first layer comprises a wet-laid tissue.

In a third embodiment, the invention provides the wet wipe of the first or second embodiments wherein the first binder is carboxymethyl cellulose.

In a fourth embodiment, the invention provides the wet wipe of any of the first through third embodiments wherein the first insolubilizing agent is butylene glycol.

In a fifth embodiment, the invention provides the wet wipe of any of the first through fourth embodiments wherein the second layer is a nonwoven web. In a sixth embodiment, the invention provides the wet wipe of any of the first through fifth embodiments wherein the second binder is a salt-sensitive binder.

In a seventh embodiment, the invention provides the wet wipes of any of the first through sixth embodiments wherein the second insolubilizing agent is a chloride salt.

In an eighth embodiment, the invention provides the wet wipes of any of the first through seventh embodiments wherein the wet wipe has a machine direction wet tensile strength of greater than 400 grams per linear inch, and a post-soak machine wet direction tensile strength of less than 60 grams per linear inch.

In a ninth embodiment, the invention provides the wet wipe of any of the first through eighth embodiments wherein the time required to break into pieces all of which are less than approximately 1 square inch in the Slosh Box Test is less than 10 minutes.

BRIEF DESCRIPTION OF DRAWING

Figure 1 is a side view of one embodiment of the dispersible wet wipe of the present invention, with its thickness exaggerated to show detail. DETAILED DESCRIPTION OF THE DISLOSURE

The present disclosure generally relates to dispersible wet wipes. In particular embodiments, a wipe 1 comprises a wipe substrate 2. The substrate has a first layer 3, and a second layer 4. The first layer 3 is superposed over the second layer 4, and the first layer 3 is adhered to the second layer 4. Such adherence can be provided via embossing, via adhesive, via hydrogen bonding, via fiber entangling, via pressure, and/or via the use of one or more binders, as described below. Both the first and second layers comprise cellulosic fibers. Preferably, all of the fibers of both layers are cellulosic fibers. Examples of suitable cellulosic fibers include softwood fibers, hardwood fibers, regenerated cellulosic fibers, and the like.

In particular embodiments, the first layer 3 comprises a wet-laid tissue. Examples of suitable wet-laid tissue include those made by uncreped through-air dried, creped through-air dried, and modified wet press processes, all of which are known in the art. Desirably, the first layer 3 of the wipe substrate 2 is a wet-laid tissue, such as an uncreped through-air dried tissue ("UCTAD"). Exemplary processes to prepare uncreped through-air dried tissue suitable for use in conjunction with the present invention are described in U.S. Patent No. 5,607,551 , U .S. Patent No. 5,672,248, U.S. Patent No. 5,593,545, U .S. Patent No. 6,083,346 and U.S. Patent No. 7,056,572, all herein incorporated by reference. In particular embodiments, the second layer 4 is a nonwoven web. The term "nonwoven web" as used herein means a structure of fibers randomly formed in a mat-like fashion without the use of an aqueous slurry, in contrast to a wet-laid tissue. Examples of suitable nonwoven webs include meltblown, spunbond, airlaid, bonded-carded web materials, hydroentangled materials, spunlace materials, and combinations thereof. Such materials can be comprised of synthetic or natural fibers, or a combination thereof. One exemplary process to prepare airlaid materials suitable for use in conjunction with the present invention is described in U. S. Patent No. 8,603,297, herein incorporated by reference to the extent consistent herewith.

The first layer 3 is held together by a first binder, and the second layer 4 is held together by a second binder. One suitable binder is a carboxymethyl cellulose ("CMC") material. CMC materials are available from Ashland, under the trade name Aqualon™. Another suitable binder includes a water- dilution triggerable polymer. Particular embodiments of dilution triggerable polymers include ion- sensitive polymers. If the ion-sensitive polymer is derived from one or more monomers, where at least one monomer contains an anionic functionality, the ion-sensitive polymer is referred to as an anionic ion-sensitive polymer. If the ion-sensitive polymer is derived from one or more monomers, where at least one monomer contains a cationic functionality, the ion-sensitive polymer is referred to as a cationic ion- sensitive polymer. An exemplary anionic ion-sensitive polymer is described in U .S. Patent No. 6,423,804, which is incorporated herein in its entirety by reference. An example of a suitable binder composition is disclosed in U.S. Patent No. 6,994,865, hereby incorporated by reference in its entirety.

The wipe further includes a wetting solution. The wetting solution includes in particular embodiments a first insolubilizing agent, and optionally also includes a second insolubilizing agent. Desirably, the binders are insoluble (stable) in the presence of the wetting solution containing one or more insolubilizing agents. In other words, the one or more insolubilizing agents render stable the first binder, the second binder, or both, prior to the wipe being flushed into a toilet or otherwise contacted by tap water. "Stable" as used herein means continuing to hold the fibers of the wipe together as intended for use of the wipe.

For example, a CMC binder is insoluble (stable) in the presence of multivalent cations, such as Ca²⁺, Cu²⁺, Fe²⁺, Sn²⁺, Fe³⁺ or Al³⁺, and organic solvents, such as water-compatible (or water-soluble) solvents typically including monohydric lower alcohols such as ethanol, methanol, and propanol; glycols such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, butylene glycol and hexylene glycol; mono- or diethers of the aforementioned glycols and lower alcohols such as methanol, ethanol and butanol; esters of the aforementioned glycols and lower fatty acids; and polyhydric alcohols such as glycerine and sorbitol. In other examples, binders employing ion-sensitive polymers are desirably insoluble in a wetting solution that includes at least about 0.3 and more particularly from about 0.5 to about 3.5 weight percent of an insolubilizing agent comprised of one or more inorganic and/or organic salts containing monovalent and/or divalent ions. Suitable monovalent ions include, for example, Na⁺ ions, K⁺ ions, Li⁺ ions, NH ⁺ ions, low molecular weight quaternary ammonium compounds (e.g., those having fewer than 5 carbons on any side group), and a combination thereof. Suitable divalent ions include, for example, Zn²⁺, Ca²⁺ and Mg²⁺. These monovalent and divalent ions may be derived from organic and inorganic salts, such as NaCI, NaBr, KCI, NH CI, Na2S0 , ZnCb, CaCb, MgCb, MgS0 , and combinations thereof. Typically, alkali metal halides are the most desirable monovalent or divalent ions because of cost, purity, low toxicity, and availability. In another preferred embodiment, the ion-sensitive polymer may comprise a cationic sensitive polymer, wherein the cationic sensitive polymer is a cationic polyacrylate that is the polymerization product of 92 mol% methyl acrylate, 4 mol% hydroxypropyl acrylate and 4 mol% [2- (acrylolyoxy)ethyl]trimethyl ammonium chloride. Other insolubilizing agents, such as organic or polymeric compounds, can be used.

In particular embodiments, the first binder is different than the second binder. In other words, the first layer employs one type of binder technology, and the second layer employs a different type of binder technology. In one example, the first layer includes a CMC binder. Preferably, the first layer is constructed of a wet-laid UCTAD tissue and a CMC binder. In another example, the second layer includes a salt-sensitive binder. Preferably, the second layer is constructed of an airlaid cellulosic nonwoven and a salt-sensitive binder.

As described earlier, the dispersible wet wipe includes a wetting solution. The liquid wetting solution can be any liquid that can be absorbed into the wipe substrate and may include any suitable components that provide the desired wiping properties. For example, the solution may include water, emollients, surfactants, fragrances, preservatives, organic or inorganic acids, chelating agents, pH buffers, or combinations thereof, as are well known to those skilled in the art. Further, the wetting solution may also contain lotions, medicaments, and/or antimicrobials. The wetting solution may contain additional agents that impart a beneficial effect on skin or hair and/or further act to improve the aesthetic feel of the compositions and wipes described herein. Examples of suitable skin benefit agents include emollients, sterols or sterol derivatives, natural and synthetic fats or oils, viscosity enhancers, rheology modifiers, polyols, surfactants, alcohols, esters, silicones, clays, starch, cellulose, particulates, moisturizers, film formers, slip modifiers, surface modifiers, skin protectants, humectants, sunscreens, and the like. The wetting solution may be incorporated into the wipe in an add-on amount of from about 10 to about 600 percent, more desirably from about 100 to about 500 percent, and even more desirably from about 200 to about 300 percent of the dry weight of the substrate. In one example, the wetting solution contains water. The wetting solution can in particular embodiments contain water in an amount of from about 40 to about 99 percent of the total weight of the solution.

In particular embodiments, the wetting solution contains a first insolubilizing agent in which the first binder is stabilized, and also contains a second insolubilizing agent in which the second binder is stabilized. In one such example, the first layer is constructed of a wet-laid UCTAD tissue and a CMC binder, and the first insolubilizing agent is butylene glycol. In another example, the second layer is constructed of an airlaid cellulosic nonwoven and a salt-sensitive binder, and the second insolubilizing agent is a calcium chloride salt.

The dispersible wet wipe of particular embodiments of the present invention has a machine direction wet tensile strength ("MDWT") of greater than 350 grams, and more particularly great than 400 grams per linear inch. Having a MDWT strength in this range helps prevent the wipe from tearing or puncturing during personal hygiene use. In particular embodiments, the wipe has a machine direction wet tensile strength after soaking for 15 minutes in room temperature tap water ("Post-Soak MDWT") of less than 60 grams per linear inch. For example, the wipe preferably has a Post-Soak MDWT of less than 80, more preferably less than 50, and still more preferably less than 30 grams per linear inch. Having a Post-Soak MDWT in this range bears on the wipe's ability to lose strength and break down in wastewater conveyance infrastructure after flushing, as the minimum time that a wipe would reside in a home drain line after being flushed is 15 minutes (although typically wipes reside in the home drain line longer than 15 minutes).

In particular embodiments, the dispersible wet wipe of particular embodiments of the present invention has a Slosh-Box Break-Up Time of less than 15, more particularly less than 10, and more particularly less than 6 minutes, in accordance with the test procedure set forth below. Prior to the present invention, it has not been possible to achieve Slosh-Box Break-Up Times in this range in the construction of the wet wipe having highly desirable consumer use properties.

TEST METHODS

Tensile Strength

For purposes herein, tensile strength may be measured using a Constant Rate of Elongation

(CRE) tensile tester using a 1-inch jaw width (sample width), a test span of 3 inches (gauge length), and a rate of jaw separation of 25.4 centimeters per minute after maintaining the sample at the ambient conditions of 23 ± 2°C and 50 ± 5% relative humidity for four hours before testing the sample at the same ambient conditions. The wet wipes are cut into 1-inch wide by 5.5 inches long strips cut from the center of the wipes in the machine direction (MD) orientation. The "machine direction wet tensile strength" ("MDWT") is the peak load in grams-force per inch of sample width when a specimen is pulled to rupture in the machine direction.

The instrument used for measuring tensile strength was an MTS Systems Sinergie 200 model. The data acquisition software was MTS TestWorks® for Windows Ver. 4.0 commercially available from MTS Systems Corp., Eden Prairie, MN . The load cell was an MTS 50 Newton maximum load cell. The gauge length between jaws is 3 inches. The top and bottom jaws are operated using pneumatic-action with maximum 80 P.S.I. The break sensitivity is set at 40 percent. The data acquisition rate is set at 100 Hz (i.e., 100 samples per second). The sample is placed in the jaws of the instrument, centered both vertically and horizontally. The test is then started and ended when the force drops by 40 percent of peak. The peak load expressed in grams-force is recorded as the "MDWT" of the specimen. Eight representative specimens were tested for each product and the average peak load determined.

To simulate post-flush tensile strength measurements, eight specimens are submerged in 4 liters of tap water at room temperature for 15 minutes and then measured for MDWT as described above. This measurement is the "Post-Soak MDWT."

Basis Weight

The dry basis weight of the basesheet material forming the wet wipes can be obtained using the ASTM active standard D646-96(2001), Standard Test Method for Grammage of Paper and Paperboard (Mass per Unit Area), or an equivalent method.

Dispersibility

This test method evaluates the dispersibility of flushable consumer products, simulating travel through a wastewater conveyance system ("Slosh Box Test"). In this test method, a plastic tank is loaded with a product and 2 liters of tap water at room temperature. The container is then tipped back and forth at a specified oscillation speed to simulate the movement of wastewater in the collection system. The time required for the wipe specimen to break up entirely into pieces measuring at most approximately 1 in x 1 in (25 mm x 25 mm) is recorded. The construction and motion of the apparatus is conducted as set forth in the "Guidelines for Assessing the Flushability of Disposable Nonwoven Products, Third Edition, FG502 - Slosh Box Disintegration Test," available from the "Association of the Nonwovens Fabrics Industry," 1 100 Crescent Green, Suite 115 Cary, NC, 27518, wwwJnGa.orG. Room temperature tap water (2 liters) is placed in the plastic tank. The cycle speed is set for 26 oscillations (revolutions) per minute. One wipe is placed in the tank and observed as the tank tips back and forth. The test is terminated when the wipe has broken up into pieces and fibers none of which is larger than approximately 1 square inch (6.5 square centimeters) in area. The amount of time to reach this point is measured ("Slosh-Box Break-Up Time").

Caliper

"Caliper" as used herein means the thickness of a single sheet. A caliper tester having an anvil diameter of 3 inches and an anvil pressure of 0.345 kilopascals was used. Specimens 3.5 inches by 4 inches were measured. EXAMPLES

Examples 1 -20 in the Table are dispersible wet wipes incorporating principles of the present invention. Each Example employs a wipe substrate having two layers of cellulosic fiber.

The first layer of each Example was an uncreped through-air dried ("UCTAD") tissue made of bleached Northern softwood kraft (NSWK) fibers and having a basis weight of 45 grams per square meter. To form the tissue, an aqueous solution of softwood fibers was pumped in a single layer through a headbox. The fiber was diluted to between 0.19 and 0.29 percent consistency in the headbox to ensure uniform formation. The resulting single-layered sheet structure was formed on a twin-wire, suction form roll. The speed of the forming fabric was 900 feet per minute (fpm). The newly-formed web was then dewatered to a consistency of about 20 to 27 percent using vacuum suction from below the forming fabric before being transferred to the transfer fabric, which was traveling at 738 fpm (18 percent rush transfer). A vacuum shoe pulling about 10 to 14 inches of mercury vacuum was used to transfer the web to the transfer fabric. A second vacuum shoe pulling about 4 to 10 inches of mercury vacuum was used to transfer the web to a t1205-2 through-air drying fabric manufactured by Voith Fabrics Inc. The web was carried over a pair of honeycomb through-air dryers operating at temperatures of about 375 to 410 degrees Fahrenheit and dried to a final dryness of about 96 to 99 percent consistency. The dried cellulosic web was rolled onto a core to form a roll of tissue. The UCTAD tissue was unrolled, and a carboxymethyl cellulose ("CMC") binder in a one percent solution was sprayed onto the UCTAD tissue using a hand-held spray bottle such that the weight-percent of CMC binder relative to the basis weight of the UCTAD tissue was 4.5, 5.5, or 6.5 percent. After being sprayed with the CMC binder solution, the UCTAD tissue was dried in a Mathis through air dryer at 120 degrees Celsius for between 2.5 and 3.5 minutes, depending on the add-on of the CMC binder solution. The second layer of each Example was an airlaid nonwoven web made of bleached southern softwood kraft (SSWK) fibers and having a basis weight of 30 grams per square meter. UCTAD tissue sheets were cut into handsheets approximately 10 inches by 13 inches in dimension. The airlaid nonwoven layer was formed directly onto the dried UCTAD tissue sheet in an airlaid hand-sheet former. The airlaid layer and the UCTAD tissue layer were pressed together using bench top hydraulic laboratory press (Carver, Inc., Wabash, IN, USA), employing 3,000 pounds per square inch (psi) at 1 10 degrees Celsius for 5 seconds, and then embossed together using Beloit Wheeler heating compaction rolls, employing a 400 pounds per square inch (psi) nip pressure at 110 degrees Celsius. The two-layer composite was sprayed with a salt-sensitive binder composition of a cationic polyacrylate that is the polymerization product of 92 mol% methyl acrylate, 4 mol% hydroxypropyl acrylate, and 4 mol% [2- (acrylolyoxy)ethyl]trimethyl ammonium chloride, and VINNAPAS® EZ123 in a 70:30 ratio was used to bond the substrate binder composition. A single Unijet® spray nozzle, Nozzle type 800017, manufactured by Spraying Systems Co., Wheaton, IL, operating at 80 psi were used to spray the binder composition onto the two-layer composite web within a spray unit. In most examples, the salt-sensitive binder composition was sprayed only onto the airlaid layer of the two-layer composite (at 3, 4, or 5 grams per square meter); in Examples 4 and 5, the salt-sensitive binder composition was sprayed both onto the airlaid layer (at 3 or 5 grams per square meter) and onto the UCTAD tissue layer (at 2 grams per square meter). In all Examples, the salt-sensitive binder composition was sprayed in a 15 percent solution. After being sprayed with the salt-sensitive binder solution, the two-layer composite tissue was dried in a Mathis through air dryer at drying times ranging from 6 seconds to 30 seconds, and at a drying temperature of either 160 or 180 degrees Celsius.

A wetting solution was added to the wipes at an add-on rate of 210 percent of the weight of the dry wipe. For Examples 2-20, the wetting solution comprised 3 weight-percent calcium chloride (CaC ), which acted as an insolubilizing agent for the salt-sensitive binder and also contributed a degree of insolubilizing effect on the CMC binder. For Examples 2-20, the wetting solution also comprised 12, 15, or 18 weight-percent of butylene glycol, which acted as the primary insolubilizing agent for the CMC binder. The wetting solution for Example 1 , which was the control sample and which resembled COTTONELLE Flushable Cleansing Cloths available at the time of filing this application, comprised 2 weight-percent of sodium chloride. A stack of several wipes for each Example was stored in a plastic bag to prevent evaporation of the wetting solution, placed under a 1 kilogram weight (to mimic the pressure exerted on the wipe during the converting process and in a retail package), and stored for 24 hours before testing as set forth below. For each Example listed in the Table, eight specimens, roughly 2.5 centimeters by

14 centimeters in dimension, were tested for Machine Direction Wet Tensile strength ("MDWT"), in units of grams per linear inch, and another eight specimens were tested for MDWT after being soaked for fifteen (15) minutes in tap water at room temperature ("Post-Soak MDWT"), and results averaged. The machine-direction tensile strength was measured because tissue products are typically stronger in the machine-direction than in the cross-machine direction. The 15 minute soak was intended to simulate the minimum time that a wipe typically resides in a home drain line after being flushed (although typically wipes reside in the home drain line longer than 15 minutes). Specimens weaker than about 25 grams per linear inch had insufficient integrity to be tested in the tensile tester; such "mush" samples were thus recorded as having a Post-Soak MDWT strength of "< 25 gli." Finally, the dispersibility of 3 wet wipe specimens (entire wipes) was examined using the Slosh Box Test described above, and results averaged. The time required for each wipe to break apart into pieces none of which were larger than approximately one square inch (6.5 square centimeters) was measured ("Slosh-Box Break-Up Time").

The presence of the airlaid layer provides desirable bulk due to its low density. For example, the wipes of Examples 2-20 (all UCTAD/airlaid two-layer composites) had a total fiber basis weight of 75 grams per square meter (gsm), and a caliper of 0.68 millimeter. By comparison, a wipe made of 70 gsm UCTAD tissue and no airlaid nonwoven layer (not listed in the table above) had a caliper of 0.48 millimeter. Thus, the two-layer wipes of Examples 2-20, which include an airlaid layer, were over 40 percent thicker than a wipe made only of UCTAD tissue having a similar basis weight. This is desirable from a product performance and consumer experience standpoint.

To the inventors' surprise, it was possible to reduce the concentration of the butylene glycol insolubilizing agent in the wetting solution from 18 to 15 percent and even 12 percent (Examples 19 and 20), and still achieve sufficient wipe MDWT (that is, preferably greater than 350 grams per linear inch MDWT). It is desirable to minimize the use of butylene glycol in wet wipe solution because research has shown that consumers dislike the "greasy residue" sensation that relatively high amounts of butylene glycol can create. It was unexpected that butylene glycol levels below 18 percent could provide adequate stabilizing effect to the CMC binder present in the tissue layer.

Finally, it was learned that the application of the salt-sensitive binder composition to the UCTAD tissue-plus-CMC layer (in addition to the airlaid layer), as in Examples 4 and 5, provided only a marginal increase in wipe strength, but substantially negatively affected (increased) the Post-Soak MDWT and the Slosh-Box Break-Up Time. This effect can be seen by comparing Examples 2 and 3 to Examples 4 and 5.

To the inventors' surprise, the dryer conditions had a significant effect on the dispersibility of the wipes. By drying at a relatively lower temperature for a relatively shorter period of time, dispersion rates could be improved (made lower). Without wishing to limit the scope of the invention, the inventors believe that presence of the tissue with the CMC binder provided sufficient temporary strength to the two-layer composite. This allowed both the cure temperature and the cure time for the salt-sensitive binder in the airlaid layer to be reduced, which resulted in faster dispersibility, as shown in Examples 8, 12-13, and 17-20.

Other modifications and variations to the appended claims may be practiced by those of ordinary skill in the art, without departing from the spirit and scope as set forth in the appended claims. It is understood that features of the various examples may be interchanged in whole or part. The preceding description, given by way of example in order to enable one of ordinary skill in the art to practice the claimed invention, is not to be construed as limiting the scope of the invention, which is defined by the claims and all equivalents thereto.

Claims

WHAT IS CLAIMED IS:

1. A dispersible wet wipe comprising:

a wipe substrate having a first layer and a second layer, the first layer being adhered to the second layer, each layer comprising cellulosic fibers,

wherein the first layer is held together by a first binder, and the second layer is held together by a second binder, wherein the first binder is different than the second binder; and

a wetting solution containing a first insolubilizing agent in which the first binder is stabilized and a second insolubilizing agent in which the second binder is stabilized.

2. The dispersible wet wipe of claim 1 wherein the first layer comprises a wet-laid tissue.

3. The dispersible wet wipe of claim 2 wherein the first binder is carboxymethyl cellulose.

4. The dispersible wet wipe of claim 3 wherein the first insolubilizing agent is butylene glycol.

5. The dispersible wet wipe of claim 1 wherein the second layer is a nonwoven web.

6. The dispersible wet wipe of claim 5 wherein the second binder is a salt-sensitive binder.

7. The dispersible wet wipe of claim 6 wherein the second insolubilizing agent is calcium chloride.

8. The dispersible wet wipe of claim 1 wherein the first layer is wet-laid tissue and the second layer is nonwoven airlaid web.

9. The dispersible wet wipe of claim 8 wherein the first binder is carboxymethyl cellulose and the second binder is a salt-sensitive binder, and wherein the first insolubilizing agent is butylene glycol and the second insolubilizing agent is calcium chloride.

10. The dispersible wet wipe of claim 1 wherein the wet wipe has a machine direction wet tensile strength of greater than 400 grams per linear inch and a post-soak machine wet direction tensile strength of less than 60 grams per linear inch.

11 . The dispersible wet wipe of claim 1 wherein the time required to break into pieces all of which are less than approximately 1 square inch in the Slosh Box Test is less than 10 minutes.

12. A dispersible wet wipe comprising:

a wipe substrate having a first layer comprising a wet-laid tissue web and a second layer comprising a nonwoven web, the first layer being adhered to the second layer, each layer comprising cellulosic fibers,

13. The dispersible wet wipe of claim 12 wherein the first binder is carboxymethyl cellulose, and wherein the first insolubilizing agent is butylene glycol.

14. The dispersible wet wipe of claim 12 wherein the second binder is a salt-sensitive binder, and wherein the second insolubilizing agent is a chloride salt.

15. The dispersible wet wipe of claim 12 wherein the first binder is carboxymethyl cellulose and the second binder is a salt-sensitive binder, and wherein the first insolubilizing agent is butylene glycol and the second insolubilizing agent is calcium chloride.

16. The dispersible wet wipe of claim 12 wherein the wet wipe has a machine direction wet tensile strength of greater than 400 grams per linear inch and a post-soak machine direction wet tensile strength of less than 60 grams per linear inch.

17. The dispersible wet wipe of claim 12 wherein the time required to break into pieces all of which are less than approximately 1 square inch in the Slosh Box Test is less than 10 minutes.

18. A dispersible wet wipe comprising:

a wetting solution containing a first insolubilizing agent in which the first binder is stabilized and a second insolubilizing agent in which the second binder is stabilized,

wherein the first binder is carboxymethyl cellulose and the second binder is a salt-sensitive binder, and wherein the first insolubilizing agent is butylene glycol and the second insolubilizing agent is calcium chloride,

wherein the wet wipe has a machine direction wet tensile strength of greater than 400 grams per linear inch and a post-soak machine direction wet tensile strength of less than 60 grams per linear inch,

wherein the time required to break into pieces all of which are less than approximately 1 square inch in the Slosh Box Test is less than 10 minutes.