Tissue products containing deliquescent materials and non-ionic surfactants

Abstract

Tissue products, such as facial tissue, bath tissue, paper towels, table napkins and the like can be improved by incorporating a sufficient amount of a deliquescent material and a non-ionic surfactant into the product. The deliquescent material is capable of maintaining a very high equilibrium amount of water in the product which can be advantageous in preventing the products from drying out and improving hand feel. The non-ionic surfactant improves the ability to incorporate the deliquescent materials into the tissue products quickly during manufacture and can help control the equilibrium moisture content of the product.

Description

BACKGROUND OF THE INVENTION

Tissue products, such as facial tissue, toilet paper, table napkins, paper towels and the like, generally have a very low moisture content of about 5 percent or less. While it is known to add humectants to tissue products to absorb moisture and improve the hand feel, humectants do not absorb appreciable quantities of water relative to their weight. Hence, very large amounts of the humectant material are required to absorb moisture in amounts sufficient to be effective. In addition, humectant materials do not form solutions with the water but rather exist as water/humectant complexes. Hence the water is bound to the humectant material and does not impart the same effect as free water in the sheet. Further, if the humectant material is a solid particulate, it will remain as a solid particulate in the sheet and can impart a gritty feel.

In commonly-assigned co-pending patent application Ser. No. 10/808,744, filed Mar. 24, 2004, by Shannon et al., it is disclosed that deliquescent materials can be incorporated into tissue products to provide a high equilibrium moisture content and improved feel. However, it has since been discovered that producing such products can be difficult at the high speeds associated with commercial tissue making equipment because concentrated deliquescent salt solutions are not quickly transferred to the sheet and/or quickly absorbed into the sheet. This reduces the amount of the deliquescent material in the sheet and adversely impacts the properties of the final product.

Therefore, there is a need for a means to produce tissue products containing deliquescent materials and having a high, more easily controlled equilibrium moisture content and for a better means of producing such products at the high speeds associated with commercial tissue manufacturing operations.

SUMMARY OF THE INVENTION

It has now been discovered that aqueous solutions having a sufficiently high concentration of deliquescent salts, in particular deliquescent inorganic salts, can be incorporated into tissue product sheets at high speeds so as to impart a noticeable wet feel to the product. In particular, it has been determined that combining a non-ionic surfactant with the deliquescent salt solution reduces the surface tension of the solution sufficiently to enable the deliquescent salt solution to be quickly absorbed by the tissue sheet. Furthermore, it has been discovered that the non-ionic surfactant can be used to control the equilibrium moisture content of the sheet and thereby optimize the tactile sheet properties insuring that the sheet has sufficient moisture to provide a significant improvement in handfeel, yet does not give the appearance of a wet tissue sheet. In addition, certain non-ionic surfactants are capable of providing improved feel characteristics to the sheet by themselves, thus making the use of such materials particularly advantageous.

Hence, in one aspect the invention resides in a tissue product comprising a tissue sheet containing a deliquescent salt and a non-ionic surfactant, said tissue sheet having an equilibrium moisture content of from about 10 to about 30 percent, more specifically from about 10 to about 25 percent and still more specifically from about 15 to about 25 percent. It has been determined that for equilibrium moisture contents above about 30 percent, the tissue product feels too wet, while for equilibrium moisture contents below about 10 percent, the increased moisture is not appreciably noticeable to the user.

In another aspect, the invention resides in a method for treating a tissue sheet comprising: (a) providing a dry tissue sheet; (b) preparing a surfactant/deliquescent salt solution containing about 0.0001 dry weight percent or greater of a non-ionic surfactant and from about 20 to about 80 dry weight percent of a deliquescent salt; and (c) topically applying the surfactant/deliquescent salt solution to the tissue sheet, wherein the equilibrium moisture content of the tissue sheet is increased.

(As used herein, the weight-percent of the deliquescent salt refers to the weight percent of the non-hydrated salt. For example, when CaCl₂.6H₂0 is used, the concentration refers only to the CaCl₂ portion and not the absorbed water.)

As used herein, a “deliquescent salt” is any salt that exists as a solid at a temperature of 30° C. or less when said material is dried to around five percent or less moisture, said dry solid being capable of absorbing a sufficient amount of moisture from the air to form a solution. Specifically, such conditions for water absorption and solution formation are met when the deliquescent material is exposed to conditioning at 50% relative humidity and a temperature of 23° C.±1° C. While any deliquescent salt can be used for purposes of this invention, particularly suitable deliquescent salts certain inorganic salts and their hydrates such as, but not limited to, calcium chloride, calcium chloride dihydrate, calcium chloride hexahydrate, magnesium chloride, magnesium chloride dihydrate, magnesium chloride hexahydrate, lithium chloride, sodium acetate, potassium acetate and ammonium acetate. A particularly suitable organic salt is trimethylamine n-oxide.

As used herein, the “equilibrium moisture content” is the moisture content of a tissue sheet at 50% relative humidity and 23° C.±1° C. (standard TAPPI conditions). At equilibrium, the amount of moisture within the sheet will not change with time at the same humidity condition. The equilibrium moisture content is expressed as a weight percent of the dry sheet including the deliquescent salt and any additional non-volatile components. More specifically, the dry tissue sheet should be conditioned at least 4 hours at the TAPPI standard conditions prior to determining the equilibrium moisture content of the sheet. The equilibrium moisture content in the sheet can be controlled by the absorbent capacity of the sheet, the amount of water on a percent basis that the deliquescent salt absorbs and the amount of the deliquescent salt in the sheet.

The effectiveness of the surfactant/deliquescent salt solution added to the tissue sheet can be characterized by providing a Single Water Drop Test value (hereinafter described) of about 12 seconds or less, more specifically about 8 seconds or less, more specifically about 6 seconds or less, more specifically about 4 seconds or less, and still more specifically about 1 second or less. Consequently, the surfactant/deliquescent salt solution can be advantageously applied to tissue sheets traveling at machine speeds of about 100 feet or greater per minute, more specifically from about 200 to about 8000 feet per minute, more specifically from about 200 to about 5000 feet per minute.

The surfactant/deliquescent salt solution can be incorporated into the tissue sheet by any suitable means known in the art, such as spraying or printing. The add-on amount of the surfactant/deliquescent salt solution that is applied to the tissue sheet can be any amount sufficient to increase the equilibrium moisture content of the tissue sheet to which it is applied and will depend on the concentration of the deliquescent salt, the concentration of the non-ionic surfactant, the desired equilibrium moisture content, the particular deliquescent salt or salts in the solution, etc.

It is found that in the absence of the non-ionic surfactant, the concentration of the salt solution does have an impact on the ability of the sheet to rapidly absorb the salt solution. In particular, concentrated salt solutions are found to be much more slowly absorbed than dilute solutions. On the other hand, it will be readily apparent to those skilled in the tissue making art that being able to apply solutions having a high solids concentration to the web can be advantageous in that the need to transfer less material can allow higher machine speeds to be achieved, there are fewer issues with web handling and there is less of a need to dry/condition the product in order to obtain the desired moisture level in the final product. Accordingly, for purposes herein, the amount of the deliquescent salt in the surfactant/deliquescent salt solution can be from about 20 to about 80 dry weight percent, more specifically from about 25 to about 70 dry weight percent, and still more specifically from about 30 to about 70 dry weight percent.

The amount of the non-ionic surfactant(s) in the surfactant/deliquescent salt solution for the purpose of providing the desired rapid absorption into the tissue sheet will depend upon factors such as the HLB value of the non-ionic surfactant, the structure of the surfactant, its critical micelle concentration and the concentration of the salt solution. Typically, the amount of the non-ionic surfactant(s) in the surfactant/deliquescent salt solution will be about 0.0001 dry weight percent of the total solution weight or greater, more specifically from about 0.0001 to about 1 dry weight percent of the total solution weight, more specifically from about 0.001 to about 0.5 dry weight percent of the total solution weight, and still more specifically from about 0.005 to about 0.1 dry weight percent of the total solution weight. It is often desirable to keep the surfactant concentration below the critical micelle concentration so as to reduce the level of foaming associated with the application of the solution. At times, however, it may be beneficial to use substantially higher amounts of the non-ionic surfactant, such as from about 0.5 to about 30 dry weight percent. This will be the case when the surfactant is also capable of imparting additional improvement to the handfeel of the product. For example, high molecular weight polyether polysiloxanes, amino-functional polyether polysiloxanes and alkyl ethoxylates are found to improve the handfeel of tissue products. The amounts of these materials added to the surfactant/deliquescent salt solution can be controlled in order to optimize both the equilibrium moisture content and the surface feel of the tissue sheet.

The amount of deliquescent material residing in the tissue sheets of the products of this invention can be any amount that provides the desired equilibrium moisture content. More specifically, the amount can be from about 2 to about 40 percent by weight of dry fiber or greater, more specifically from about 3 to about 30 dry weight percent, more specifically from about 4 to about 25 dry weight percent, and still more specifically from about 5 to about 20 dry weight percent. The specific amount of the deliquescent material in the tissue sheet will depend upon the desired equilibrium moisture content in the sheet, the specific deliquescent material selected, the temperature of application of the surfactant/deliquescent salt solution to the tissue sheet and the solubility of the particular deliquescent salt at the application temperature. Solutions having a high deliquescent salt concentration are preferred because such solutions, when applied to the tissue sheet, will not require additional drying of the tissue after they are applied. In a preferred embodiment, the surfactant/deliquescent salt solution is a saturated salt solution or one very near the saturation concentration.

The amount of the non-ionic surfactant residing in the tissue sheets of the products of this invention can be from about 0.00002 to about 3 weight percent based on dry fiber in the sheet, more specifically from about 0.00005 to about 3 weight percent, more specifically from about 0.00005 to about 2 weight percent, more specifically from about 0.0001 to about 1 weight percent, and still more specifically from about 0.0001 to about 3 weight percent.

Any non-ionic surfactant can be used provided it gives the desired effect. The lack of charge is an important feature of these surfactants because ionic surfactants will undergo ion exchange reactions with the deliquescent salts and typically will form insoluble precipitates such that the surfactants are rendered useless. On other occasions, the ion exchange reaction causes the deliquescent material to lose its deliquescent properties. Particularly preferred non-ionic surfactants are water-soluble surfactants having a solubility greater than 0.02 percent in the surfactant/deliquescent salt solution at a temperature of 25° C. Other preferred water-soluble surfactants are those having, in particular, a Hydrophilic-Lipophilic Balance (HLB) number of 4 or greater, more specifically from about 4 to about 24, more specifically from about 4 to about 20, and still more specifically from about 4 to about 16. The HLB index is well known in the chemical arts and is a scale which measures the balance between the hydrophilic and lipophilic solution tendencies of a compound. The HLB scale ranges from 1 to approximately 50, with the lower numbers representing highly lipophilic tendencies and the higher numbers representing highly hydrophilic tendencies.

Suitable non-ionic surfactant families include acetylenic diols such as those sold under the trade name Surfynol® manufactured and sold by Air Products, Inc. Additional examples of acetylenic diols include: 2,4,7,9-tetramethyl-5-decyne-4,7-diol; 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate (1.75 EO/OH); 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate (5 EO/OH); 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate (15 EO/OH); and mixtures of the acetylenic diols thereof. Such acetylenic diols are available from Aldrich Chemical Co., Milwaukee, Wis.

Another family of acceptable non-ionic surfactants includes the ethoxylate fatty alcohols, which can generally be represented by the formula R¹—(CH₂CH₂O)_n—R²; wherein R¹ is a C₆ or higher linear, branched or substituted alkyl group, “n” is an integer from 1 to 40 and R² is H or a C₁-C₄ alkyl group. Examples of suitable surfactants in this category include those manufactured and sold by Dow Chemical, Midland, Mich. under the trade name Tergitol® such as Tergitol TMN-6; Tergitol TMN-3 and Tergitol TMN-10.

Water-soluble silicone glycols may also be used as a non-ionic surfactant for purposes of this invention. Such materials are widely known in the art for use as surfactants and wetting agents. The silicone glycols or silicone polyethers will have a general formula of:
wherein “x” and “y” are integers≧0 and “z” is an integer>0. The mole ratio of “x” to (x+y+z) can be from about 0 percent to about 95 percent. The ratio of “y” to (x+y+z) can be from about 0 percent to about 25%. The R⁰-R⁹ moieties can be independently any organofunctional group including C₁ or higher alkyl groups, ethers, polyethers, polyesters, amines, imines, amides, or other functional groups including the alkyl and alkenyl analogues of such groups or hydrogen or hydroxyl. The R¹⁰ moiety is an amino functional moiety including but not limited to primary amine, secondary amine, tertiary amines, quaternary amines, unsubstituted amides and mixtures thereof. An exemplary R¹⁰ moiety contains one amine group per constituent or two or more amine groups per substituent, separated by a linear or branched alkyl chain of C₁ or greater. R¹¹ is a polyether functional group having the generic formula: —R¹²—(R¹³—O)_a—(R¹⁴O)_b—R¹⁵, wherein R¹², R¹³, and R¹⁴ are independently C_1-4alkyl groups, linear or branched; R¹⁵ can be H or a C_1-30 alkyl group; and “a” and “b” are integers of from 1 to about 100, more specifically from about 5 to about 30. R¹¹ groups may also contain amine, amide, carboxyl or other functionality within or attached to the polyether substituent. Exemplary silicone polyethers include DC-2501 and Q2-5211 manufactured and sold by Dow Corning, Midland, Mich., Rhodasil® SP3300 PEX and Rhodasil Surfactant 5193 Manufactured and sold by Rhodia, Inc., and SF-1488 manufactured and sold by GE Silicones.

An especially interesting class of polyether polysiloxanes are the amino-funcitonal polyether polysiloxanes. Exemplary aminofunctional polyether polysiloxanes are the Wetsoft CTW family manufactured and sold by Wacker, Inc. Other exemplary polysiloxanes can be found in U.S. Pat. No. 6,432,270 by Liu, et.al. These amino-functional polyethers are found to be capable of substantially increasing the surface feel of the product. Hence, use of such materials can simultaneously increase the transfer efficiency of the surfactant/deliquescent salt solution to the tissue sheet while further increasing the surface softness of the product.

Combinations of silicone surfactants with non-ionic, non-silicone surfactants can also be used.

Additional chemical additives, such as permanent wet strength agents, may be applied to the sheets provided their use is not antagonistic to the desired results. It is necessary to avoid a reaction that would cause precipitation of one or more components of the deliquescent material that would render the material no longer being deliquescent. For example, with calcium chloride, the interaction with sodium carbonate would cause precipitation of calcium carbonate with formation of the non-deliquescent compound sodium chloride. Hence, the resulting sheet would no longer be capable of a high equilibrium moisture content.

The tissue products of this invention can have one, two, three or more tissue sheets or plies containing non-ionic surfactants and deliquescent salts. The tissue sheets can be positioned in different ways to deliver the desired benefits. For example, for a three-ply product, the two outer plies can contain a non-ionic surfactant and a deliquescent salt while the inner ply does not. For a two-ply product, it is advantageous that both plies contain a non-ionic surfactant and a deliquescent salt. For a single-ply product, the non-ionic surfactant and the deliquescent salt can be applied to one or both outer surfaces of the ply.

As used herein, a “tissue” sheet is any low density cellulosic sheet useful for tissue products and having a dry sheet bulk of 2 cubic centimeters or greater per gram, more specifically about 3 cubic centimeters or greater per gram, more specifically about 5 cubic centimeters or greater per gram, more specifically about 10 cubic centimeters or greater per gram, more specifically from about 5 to about 25 cubic centimeters per gram, and still more specifically from about 10 to about 20 cubic centimeters per gram. Excluded are relatively high density sheets commonly used as writing papers and the like. Particularly suitable tissue sheets include cellulosic sheets useful for facial tissues, bath tissues, paper towels, table napkins and the like. The “dry sheet bulk” is calculated as the quotient of the “dry sheet caliper” (hereinafter defined) of a sheet, expressed in microns, divided by the dry basis weight, expressed in grams per square meter. The resulting dry sheet bulk is expressed in cubic centimeters per gram. More specifically, the dry sheet caliper is the representative thickness of a single sheet measured in accordance with TAPPI test methods T402 “Standard Conditioning and Testing Atmosphere For Paper, Board, Pulp Handsheets and Related Products” and T411 om-89 “Thickness (caliper) of Paper, Paperboard, and Combined Board” with Note 3 for stacked sheets. The micrometer used for carrying out T411 om-89 is an Emveco 200-A Tissue Caliper Tester available from Emveco, Inc., Newberg, Oreg. The micrometer has a load of 2 kilo-Pascals, a pressure foot area of 2500 square millimeters, a pressure foot diameter of 56.42 millimeters, a dwell time of 3 seconds and a lowering rate of 0.8 millimeters per second.

As used herein, the “equilibrium moisture content” represents the moisture content of the tissue sheet at 50% relative humidity and 25° C. (standard TAPPI conditions). At equilibrium, the amount of moisture within the sheet will not change with time at the same humidity condition. The equilibrium moisture content is expressed as a weight percent of the dry sheet including the deliquescent material and any additional non-volatile components. More specifically, the dry sample sheets should be conditioned at least 4 hours at the TAPPI standard conditions prior to determining the equilibrium moisture content of the sheet. The equilibrium moisture content in the sheet can be controlled by the absorbent capacity of the sheet, the amount of water on a percent basis that the deliquescent material absorbs, the amount of deliquescent material in the sheet and the amount of non-ionic surfactant added.

As used herein, the “Single Water Drop Test” is used to determine the hydrophilicity of a tissue sheet and characterize the effectiveness of the surfactant/deliquescent salt solution. The “Single Water Drop Test” is performed on the equilibrated substrate to which the surfactant/deliquescent salt solution is to be applied. The substrate is conditioned for a minimum of 4 hours at 23.0° C.±2.0° C. and a relative humidity of 50%±5%. The conditioned test sample is then placed on a dry glass plate. A single drop (100 microliters, 0.1±0.01 ml.) of the aqueous surfactant/deliquescent salt solution (23.0° C.±2.0° C.) is dispensed from an Eppendorf style pipet positioned slightly above the surface of the test specimen. The drop should be positioned close to the center of the test specimen. The aqueous surfactant/deliquescent salt solution drop is viewed by the naked eye on a plane horizontal to the surface of the test specimen. A stopwatch is started immediately after the water drop is dispensed onto the test specimen. The elapsed time for the water drop to be completely absorbed by the sample, measured in seconds, is the Single Water Drop Test value (wet out time) for that test specimen. The water drop is completely absorbed when it completely disappears, that is, there is no visible vertical element of the water drop remaining. To determine the Single Water Drop Test value for any given material, the foregoing procedure is carried out on three representative equilibrated substrate sample sheets and the average value from the three tests is the Single Water Drop Test value for the material. If, after 3 minutes, the water drop is not completely absorbed, the test is stopped and the Single Water Drop Test value is assigned a value of 180 seconds.

In the interests of brevity and conciseness, any ranges of values set forth in this specification contemplate all values within the range and are to be construed as written description support for claims reciting any sub-ranges having endpoints which are whole number values within the specified range in question. By way of a hypothetical illustrative example, a disclosure in this specification of a range of from 1 to 5 shall be considered to support claims to any of the following ranges: 1-5; 1-4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5. In addition, any of the foregoing aspects of this invention can be further defined by any combination of one or more of the specified values and ranges recited for any properties described herein.

EXAMPLES

For the applicable examples below, the equilibrium moisture content was determined for tissue samples as follows:

Treated samples were placed in a 100° C. oven and air-dried for 1 hour. Sample sizes of 1-2 grams were selected, although larger or smaller sizes can be used depending upon the degree of accuracy desired. A dry 400 cc wide mouth jar with a screw cap was weighed and the weight (W₂) recorded to the nearest 0.001 gram. After drying, the tissue sample was placed immediately into the weighed-400 cc wide mouth jar and capped. Samples were allowed to cool to ambient temperature and the weight of the dry tissue sample and bottle (W₁) determined to the nearest 0.001 gram. The bone dry weight of the tissue sample, (W_d), was then calculated from the equation (W₁−W₂). The jars with sample were then uncapped and placed in standard TAPPI conditions to equilibrate for 16 hours. After equilibration time was complete, the jars were capped and the weight of the conditioned tissue, jar and lid (W₃) recorded. In cases where air circulation into the container is an issue, it is preferred to remove the dried samples from the sample jar and allow the samples to equilibrate on a raised rack instead of within the container. After conditioning the sample is then returned to the jar, capped and weighed. The equilibrium moisture content (W_e) is then calculated from the equation (W₃−W₁). The percent equilibrium moisture was then calculated from the equation [(W_e/W_d)*100].

Example 1

This example demonstrates the reduction in the Single Water Drop Test values by incorporating small amounts of a non-ionic surfactant into the surfactant/deliquescent salt solution. Specifically, an aqueous solution of magnesium chloride (MgCl₂) was prepared by dissolving 2.95 parts of MgCl₂.6H₂0 in 1 part of distilled water at room temperature. This ratio gave a deliquescent salt solution having 35 percent by weight MgCl₂. The solution had a Single Water Drop Test value of 41 seconds when placed on a 3-ply creped, untreated, facial tissue basesheet.

For comparison, 20×10⁻³ ml of an non-ionic surfactant was added to 100 parts of the concentrated magnesium chloride solution. The non-ionic surfactant was, 2,4,7,9-tetramethyl-5-decene-4,7-diol ethoxylate (1.75 EO/OH) obtained from Aldrich Chemical Co., Milwaukee, Wis. After mixing, when placed on the same 3-ply creped, untreated facial tissue basesheet, the resulting surfactant/deliquescent salt solution was found to have a Single Water Drop Test value of about 4 seconds.

Examples 2 and 3

These comparative examples demonstrate the impact that the addition of a small amount of non-ionic surfactant can have on speed and absorption of the deliquescent salt solution into a tissue product run on commercial manufacturing equipment. For both Examples 2 and 3, a two-ply creped tissue sheet having a finished basis weight of 15.0 pounds per 2880 square feet and a furnish consisting of 65 percent hardwood and 35 percent softwood fibers was used. Each ply was made from a stratified fiber furnish including two outer layers and a middle layer. The deliquescent salt solution was printed on both outer sides of the 2-ply tissue product via a simultaneous offset rotogravure printing process. The salt solutions were delivered as aqueous solutions having approximately 42 percent solids. The gravure rolls were electronically engraved, chrome-over-copper rolls supplied by Southern Graphics Systems, located at Louisville, Ky. The rolls had a line screen of 360 cells per lineal inch and, a volume of 8 Billion Cubic Microns (BCM) per square inch of roll surface. The rubber backing offset applicator rolls had a 75 Shore A durometer cast polyurethane surface and were supplied by American Roller Company, located at Union Grove, Wis. The process was set up to a condition having 0.375 inch interference between the gravure rolls and the rubber backing rolls and 0.003 inch clearance between the facing rubber backing rolls. The simultaneous offset/offset gravure printer was run at the speeds given in the examples.

For Example 2, a deliquescent salt solution of calcium chloride (CaCl₂) was prepared by mixing 100 parts of CaCl₂.6H₂0 with 20 parts of water to give a solution containing 42 percent by weight calcium chloride. The deliquescent salt solution was printed onto the two-ply tissue product described above by passing it through the printer twice at a slow speed of 50 feet per minute. The resulting product contained 4.9 dry weight percent calcium chloride and had an equilibrium moisture content of 8.1%.

For Example 3, 500 ppm of Surfynol® 420 non-ionic surfactant from Air Products, Inc. was added to the CaCl₂ solution used in Example 2. The resulting surfactant/deliquescent salt solution was mixed for 5 minutes at room temperature using a standard mechanical mixer run a speed of 300 rpm. The solution was found to have a Single Water Drop Test value of less than 5 seconds. The same untreated two-ply tissue product described above was run through the printer twice, but at a much higher speed of 200 feet per minute. The resulting tissue product contained 13.9 percent calcium chloride and an equilibrium moisture content of 22.5%.

A comparison of Examples 2 and 3 illustrates the advantage of using a non-ionic surfactant to increase the amount of deliquescent salt retained by tissue product, even at higher speeds. Because of the greater hydrophilicity of the non-ionic surfactant-containing solution, more solution is transferred from the printing cells to the tissue sheet, resulting in greater deliquescent salt add-on.

It will be appreciated that the foregoing description and examples, given for purposes of illustration, are not to be construed as limiting the scope of this invention, which is defined by the following claims and all equivalents thereto.

Claims

1. A tissue product comprising a tissue sheet containing a deliquescent salt and a water-soluble non-ionic surfactant, said tissue sheet having an equilibrium moisture content of from about 10 to about 30 dry weight percent.

2. The product of claim 1 wherein the deliquescent salt is selected from the group consisting of aluminates, calcium chloride, magnesium chloride, lithium chloride, sodium acetate, potassium acetate, ammonium acetate and trimethylamine n-oxide.

3. The product of claim 1 wherein the deliquescent material is lithium chloride.

4. The product of claim 1 wherein the deliquescent material is calcium chloride.

5. The product of claim 1 wherein the deliquescent material is magnesium chloride.

6. The product of claim 1 wherein the non-ionic surfactant is an acetylenic diol.

7. The product of claim 1 wherein the non-ionic surfactant is an ethoxylated fatty alcohol.

8. The product of claim 1 wherein the non-ionic surfactant is a water-soluble silicone glycol.

9. The product of claim 1 wherein the non-ionic surfactant is a silicone polyether.

10. The product of claim 1 wherein the non-ionic surfactant is an amino-functional polyether polysiloxane.

11. A method for treating a tissue sheet comprising:

(a) providing a dry tissue sheet;

(b) preparing a surfactant/deliquescent salt solution containing about 0.0001 dry weight percent or greater of a non-ionic surfactant and from about 20 to about 80 dry weight percent of a deliquescent salt; and

c) topically applying the surfactant/deliquescent salt solution to the tissue sheet, wherein the equilibrium moisture content of the tissue sheet is increased.

12. The method of claim 11 wherein the equilibrium moisture content of the tissue sheet is from about 10% to about 30% by weight of dry fibers.

13. The method of claim 11 wherein the non-ionic surfactant has an HLB value of about 4 or greater.

14. The method of claim 11 wherein the surfactant/deliquescent salt solution is sprayed onto the surface of the sheet.

15. The method of claim 11 wherein the surfactant/deliquescent salt solution is printed onto the surface of the sheet.

16. The method of claim 11 wherein the Water Drop Test value of the tissue sheet is about 12 seconds or less.

17. The method of claim 11 wherein the Water Drop Test value of the tissue sheet is about 8 seconds or less.

18. The method of claim 11 wherein the Water Drop Test value of the tissue sheet is about 6 seconds or less.

19. The method of claim 11 wherein the Water Drop Test value of the tissue sheet is about 4 seconds or less.

20. The method of claim 11 wherein the Water Drop Test value of the tissue sheet is about 1 second or less.

21. The method of claim 11 wherein the tissue sheet is traveling at a speed of about 100 feet or greater per minute.