Wet Wiper Natural Acid and Salt Preservative Composition

The present invention relates to wet wiper products and, more particularly, to a wet wiper product having a liquid preservative composition of both a naturally occurring acid and a naturally occurring salt.

Wet wiper products require preservative properties to destroy or inhibit the growth of various microorganisms, bacteria, yeast, and molds. The use of a chemical preservative agent dispersed or dissolved in a liquid phase of a wet wiper has previously met various disadvantages because the nature of the required chemicals and the complexity of the final liquid phase formulations typically result in harsh or irritating residues being left behind on the skin of the user.

The preservative used in a wet wiper should meet two often competing criteria, namely effectiveness as a preservative and non-irritability in contact with human skin. As resistant strains to commonly utilized preservatives appear, the industry has typically increased usage levels and the number of preservative components in the wet wiper. As more potent strains of preservatives are utilized to achieve the desired effect, skin irritations and allergic reactions are often provoked in the user.

In an attempt to solve these problems, U.S. Pat. Nos. 4,615,937 and 4,692,374 to Michael P. Bouchette discloses that a superior wet wiper product can be produced in which the antimicrobial treatment is substantive to the wet wiper fibers. As a result of having the antimicrobial agent substantive to the fibers, no chemicals in the liquid or lotion phase of the wiper are required

As a further improvement, U.S. Pat. No. 4,781,974 to Bouchette et al. discloses a wet wiper that has both a substantive antimicrobial agent on the fibers of the wet wiper product and a second antimicrobial agent, such as an organic acid, in the liquid or lotion phase of the wiper. Moreover, U.S. Pat. Nos. 4,732,797 and 4,772,501 to Johnson et al. discloses a wet wiper product that maintains a fibrous wipe in a liquid preservative composition that consists essentially of a mixture of citric acid and sorbic acid, water, and optional ingredients such as skin moisturizers and fragrance compounds. This wet wiper does not leave a harsh or irritating residue on the user's skin.

The present invention improves upon these previous wet wiper products and achieves various advantages by providing a wet wiper product that comprises a fibrous wipe and a hypotonic liquid preservative composition for the wipe. The liquid preservative composition comprises: (i) water, (ii) a naturally occurring organic acid in an amount effective to be a preservative, and (iii) a naturally occurring salt in an amount effective to increase the efficacy of the naturally occurring organic acid.

The present inventors have discovered that such a liquid preservative composition could improve a wet wiper product that contains a naturally occurring acid, such as sorbic acid and citric acid, in the liquid preservative composition without any salt. It has been found that the addition of a naturally occurring salt, such as sodium chloride, to the liquid preservative composition can increase the efficacy, as well as the antimicrobial spectrum, of the naturally occurring acid.

Thus, the wet wipe product of the present invention has an effective liquid preservative composition that has all naturally occurring components, namely the naturally occurring acid and the naturally occurring salt. The wet wiper product exhibits the requisite preservative functions without the need for any other preservative agents, especially a non-naturally occurring agent, in the preservative composition. Importantly, the present invention provides the advantage of not being irritating or harsh to the skin.

These and other features of the present invention will be made more apparent from the following description of the preferred embodiments.

In accordance with the present invention, the wet wiper product comprises a fibrous wipe and a liquid preservative composition for the wipe. For this discussion of fibrous wipes and liquid preservative compositions, U.S. Pat. Nos. 4,732,797 and 4,772,501 to Johnson et al. are hereby incorporated by reference.

The fibrous wipe can be selected from those conventionally known in the art. Preferably, the fibrous wiper is a non-woven web that comprises bonded fibers and a binder in an amount effective to bind the fibers. The non-woven web can be antimicrobial. Such a web is disclosed in U.S. Pat. No. 4,692,374.

Various synthetic and natural fibers known in the art can be effectively used. Preferred fibers are cellulosic fibers and, more preferably, wood pulp fibers. The cellulosic fibers, such as wood pulp fibers, can be chemically treated prior to the formation of the web or fabric, if desired. Examples of wood pulp fibers include various mechanical and chemical pulp fibers, such as cedar fibers, southern pine fibers, spruce fibers, and hemlock fibers. The particular fibers may be specifically selected to enhance properties such as texture (soft, wooly or fluffy), porosity, caliper, brightness, and strength. Alternatively, the fibers can be a combination of natural and synthetic fibers, or synthetic fibers alone, depending upon the final attributes sought and the method of forming the web.

The weight of the fibers, such as cellulosic fibers, used to form the unbonded fibrous web can vary depending upon the ultimate non-woven web that is produced. Typically, the weight of the fibers forming the web will vary within the range of about 5 lbs. per 3000 ft.sup.2 to about 60 lbs. per 3000 ft.sup.2.

Various web or fabric forming techniques known in the art can be effectively used to form the unbonded fibers. The web can be formed by nonwoven techniques, such as air-laying or wet-laying the web. One type of apparatus for air forming fibers is shown in U.S. Pat. No. 4,292,271 to Buob et al. Other nonwoven manufacturing techniques, such as melt blown, spun-bonded, needle punched, and spun laced, may also be used.

Various binders known in the art can be used to bind the fibers together. A preferred binder is a polymeric binder, such as a latex binder. Acceptable latex binders include acrylate emulsions, butadiene-styrene emulsions, ethylene vinyl acetate emulsions and acrylonitrile-butadiene emulsions. An especially effective latex binder is ethylene vinyl acetate, which is sold under the trademark AIRFLEX A-410 by Air Products, Inc. of Allentown, Pa. The binder can also include a mixture of anionic and nonionic binders, such as an ethylene vinyl acetate binder sold under the trademark AIRFLEX A-106 by Air Products, Inc. and an ethylene acetate binder sold under the trademark HA-8 by Rohm & Haas of Philadelphia, Pa.

The amount of the binder that is to be applied to the fibers depends, in part, upon the type of fibers, such as cellulosic. Typically, the amount of the binder applied to the fibers varies within the range of about 5% to about 30% of the total web weight. Similarly, the amount of solids in the binder, as applied to the web, especially in a latex binder, depends, among other things, on the weight of the fibers in the nonwoven web. Generally, latex binders having from about 5% to about 25% application solids content are used. Of course, one of ordinary skill in the art can select the particular binder, the amount of the binder used, and the amount of solids present in the binder, depending upon, in part, the type of fibers that are to be bound. The binder is applied to the fibers by various techniques known in the art, such as spraying, foaming, or padding.

In accordance with the present invention, the wet wiper product has a hyptonic liquid preservative composition comprising: (i) water, (ii) a naturally occurring acid in an amount effective to be a preservative, and (iii) a naturally occurring salt in an amount effective to increase the efficacy of the naturally occurring organic acid. The liquid preservative composition acts as an antimicrobial to preserve and prevent microbial contamination of the fibrous wipe until it can be used. In addition to increasing the efficacy of the organic acid, the salt can also increase the antimicrobial spectrum of the acid so that the acid is effective against a wider range of microorganisms.

The present invention achieves the desired properties in a wet wiper with only a naturally occurring acid as the preservative component without the need for any other preservative component, such as an antimicrobial agent, in the wet wiper. This can be achieved since the naturally occurring salt enhances this antimicrobial effect of the naturally occurring acid.

The naturally occurring acid is preferably selected from the group consisting of citric acid, sorbic acid, malic acid, tartaric acid, benzoic acid, and mixtures thereof. Of course, other naturally occurring acids may be used so long as they provide the requisite preservative effect without being harsh or irritating to the skin of the user. The naturally occurring acid is preferably present in a concentration within the range of about 0.1 w/v % to about 0.7 w/v % based upon the liquid preservative composition.

Preferably, the naturally occurring acid comprises a mixture of sorbic acid and citric acid and, most preferably, a mixture in an amount of about 0.01 w/v % to about 0.2 w/v % sorbic acid and about 0.1 w/v % to about 0.5 w/v % citric acid based upon the liquid preservative composition. An especially effective naturally occurring acid is a mixture of 0.05 w/v % to about 0.10 w/v % sorbic acid and 0.3 w/v % to about 0.5 w/v % citric acid. The weight ratio of citric acid to sorbic acid in the liquid preservative composition is preferably in the range of about 20 to 1 to about 1 to 1, and, most preferably, in the range of about 10 to 1 to about 3 to 1.

Citric acid (2-hydroxy-1,2,3-propanetricarboxylic acid) and sorbic acid (2,4-hexadienoic acid) are mild, naturally occurring organic acids that are relatively safe for skin contact and are edible. Consequently, users of the wet wiper typically do not exhibit adverse reactions to the wet wiper, even under repeated occlusive applications to human skin under conditions in which conventionally preserved products exhibit some irritation.

The pH of the liquid preservative composition is preferably below about 3.5. More preferably, the liquid preservative composition has a pH in the range of about 2.0 to about 3.2. Such a pH range for a wet wiper does not necessarily result in extensive skin or eye irritation when a naturally occurring acid, such as sorbic acid and citric acid, are the only preservative components. Any such skin and eye irritation that may occur is especially minimized in the present invention because the acid, such as citric acid and sorbic acid, are relatively nonirritating substances.

The combination of citric acid and sorbic acid in the liquid preservation composition provides excellent preservative activity against various microorganisms, particularly the five pathogenic microorganisms identified in the U.S.P. XXI Antimicrobial Preservatives-Effectiveness twenty-eight day challenge test: Aspergilua niger, Candida albicans, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. Neither component alone demonstrates the breadth of kill spectrum or speed as the combination of the citric and sorbic acids.

The naturally occurring salt in the preservative composition is present in a concentration effective to increase the efficacy of the naturally occurring organic acid. Preferably, the salt also incrases the antimicrobial spectrum of the acid. Preferably, the naturally occurring salt is selected from the group consisting of monobasic or dibasic sodium phosphate, potassium chloride, sodium chloride, and mixtures thereof. The naturally occurring salt is preferably present in a concentration of about 0.1 w/v % to about 0.9 w/v % based upon the liquid preservative composition. Sodium chloride is the preferred natural salt and is preferably prsent in an amount of 0.1 w/v % to 0.5 w/v %.

The liquid preservative composition is hypotonic, which property is believed to increase the efficacy and antimicrobial spectrum of the natural acid preservative composition. To determine whther the liquid preservative composition is hypotonic, its osmotic pressure after the addition of the naturally occurring salt is to be compared to a 0.9% w/v physiological saline having an osmotic pressure of 286 milli-osmole/kg. If after the addition of the salt the osmotic pressure of the composition is lower, than that of the saline solution, it is hypotonic. The osmotic pressure of the preservative composition is preferably within the range of about 110 milli-osmole/kg to about 280 milli-osmole/kg to render the composition hypotonic.

Solutions with high osmotic pressure (hypertonic) have historically been used for food preservation (pickling in brine), since most microorganisms are killed by high salt concentrations. The present invention, however, is the first use of a hypotonic salt solution to improve the efficacy and antimicrobial spectrum of a wet wiper natural acid preservative system. A hypotonic solution, as demonstrated in the medical literature, is non-irritating to the skin and eyes when compared to hypertonic solutions. Without being bound by theory, it is believed that the sorbic acid and citric acid as the natural acid preservative inhibits and/or kills microorganisms by (i) causing leakage of hydrogen ions across the cell membrane, (ii) acidifying the cell interior, and (iii) inhibiting nutrient transport. The salt may aid in this action and therefore increase the efficacy of the preservative system; and/or the effect of the acid combination may allow salt ions to enter the cell and interfer with cellular functions; and/or it is simply the osmotic effect of the salt.

The osmotic pressure of the natural acid preservative composition can be adjusted by the addition of the naturally occurring salt in an amount sufficient to cause the osmotic pressure to be within the desired range.

The liquid preservative composition in the present invention also includes water and can include optional ingredients selected from the group consisting of skin moisturizers and fragrance compounds. Pure water that is safe for skin contact is preferred. The liquid preservative composition need not include any skin moisturizers or fragrance compounds since these are optional ingredients. The wt. % total of the preservative component, water and the optional ingredients is 100 wt. %.

The skin moisturizers can be selected from various moisturizers well known in the art, such as glycerine, aloe vera, lecithin, lanolin and lanolin derivatives Other skin moisturizers known in the art can also be readily used in amounts known in the art to achieve the intended purpose of moisturizing the skin upon use. In one embodiment, an effective amount of aloe vera could be used as a skin moisturizer.

Similarly, fragrance compounds, such as water soluble fragrance compounds, can be used. Such fragrance compounds are well known and conventionally used in the art. For example, fragrance compounds can be readily obtained from International Food and Flavor, Inc. (I.F.F.). The proper fragrance compound can be selected by one skilled in the art without undue experimentation.

A means can be used to enclose the fibrous wipe in the liquid preservative composition. In one embodiment of the present invention, the enclosure means for the fibrous wipe is a sealed package or sealed envelope, of the type conventionally used in the art, to enclose the fibrous wipe in the liquid preservative composition until the time of use. The fibrous wipe and the preservative composition can be sealed within the enclosure by various techniques well known in the art. Other enclosure means well known in the art can also be used.

In one embodiment of the present invention, the wet wiper product comprises: (1) a latex bonded, cellulosic fiber wipe, (2) a liquid preservative composition consisting essentially of (i) 0.4 w/v % citric acid and 0.05 w/v % sorbic acid, (ii) 0.5 w/v % sodium chloride, and (iii) water to 100 wt. %; and (3) an outer sealed package enclosing the wet wipe to maintain the wet wipe in the liquid preservative composition until use. The wet wipe also can include, as noted, an effective amount of a moisturizer, such as aloe vera, and an effective amount of a fragrance compound.

The following are examples of the present invention and are intended to be merely exemplary.

A wet wiper product was prepared. The product comprised: (1) a latex bonded cellulosic fiber wipe and (2) a liquid preservative composition consisting essentially of 0.105 w/v % sorbic acid, 0.375 w/v % citric acid, 0.005 v/v % of a moisturizer, and 0.22 v/v % of a fragrance, and water to 100 wt. %. This wet wiper without a naturally occurring salt in the preservative composition was compared to wet wipers that were the same but for the inclusion of also a naturally occurring salt in the preservative composition.

The primary microorganism used to test for antimicrobial efficacy was an Acetobacter aceti bacterium isolated from the environment and identified by the American Type Culture Collection (ATCC). The antimicrobial effect was tested using a modified minimum lethal concentration (MLC) protocal as described in the Manual of Clinical Microbiolgy (3d ED), published by the American Society for Microbiology. The total test period was 6 hours. Incubation was performed at room temperature.

The test results presented in Tables IA, IB, and IC show the increased efficacy of a preservative composition having a naturally occurring acid and a naturally occurring salt in comparison to a preservative composition having a naturally occurring acid, but no naturally occurring salt.

The test results shown in Table IIA and IIB demonstrate the increased efficacy of the present preservative composition having both a naturally occurring acid and salt compared to a preservative composition having only the salt when the preservative composition is used with an antimicrobiallly active, nonwoven web as described in U.S. Pat. Nos. 4,692,374 and 4,772,501.

A preservative composition containing a naturally occurring acid was compared to the same preservative compositions that also contained 0.5 w/v sodium chloride, 0.5 w/v sodium phosphate (monobasic), or 0.5 w/v potassium sorbate. Each sample was diluted to a 75%, a 50%, and a 25% concentration. These sample concentrations were then inoculated with Acetobacter aceti at a concentration of 7.55.times.10.sup.5 and incubated at 70.degree. F. for various time periods. The bacterial colony forming units (CFU) were enumerated at 0 time, 1 hour, 2 hours, 4 hours, and 6 hours and the percent reductions were then calculated. The osmolarity of each sample and 0.9% saline at the 75% concentration was also determined. The results are shown in Table III.

The results for the four test samples demonstrate that the preservative composition containing 0.5 w/v sodium chloride exhibited the best preservative properties and the preservative composition having 0.5 w/v potassium sorbate exhibited the second best preservative properties. Without being bound by theory, it is believed that the potassium sorbate acts as a biocide as well as serving to raise the osmotic pressure of the preservative compositions.

A liquid preservative composition not containing a naturally occurring organic salt (Sample No 1 at 75% concentration and 30 mOs/kg) was compared with sample Nos 2-6 of the same preservative composition plus the designated naturally occurring organic salt Example No. 7 was plain water.

Each sample was inoculated with Acetobacter aceti and incubated for 8 hours at 72.degree. F. Aliquotes of the test samples were analyzed for CFU recoveries at 0 minutes, 1 hour, 2 hours, 4 hours, 6 hours and 8 hours. The bacterial CFUs were enumerated using standard microbiological technologies. The test results are shown in Table IV.

As shown in the table, at the end of the 8 hour test period, Sample No. 1 had reduced the CFU by 99.7%. Sample No. 2 had a 99.999% reduction in CFU recoveries within 2 hours after the initial innoculation.

A 28 day fabric challenge test was performed with the following samples:

Pres. comp. denotes a liquid preservative composition. Results of the test are shown in Table V.

The results of the 28 day fabric challenge tests can be summarized as follows:

Thus, the use of 0.75% saline in Sample Nos. 1 and 2 increased the efficacy of the laboratory prepared bioweb and preservative composition.

A 56 day tub challenge test was performed on the following test samples against Acetobacter aceti and Aspergillus niger.

Each sample tub was inoculated with the appropriate test organism near the top of the tub and near the bottom of the tub. The inoculated wipes were then segregated from the uninnoculated wipes with a layer of Saran Wrap.RTM. located one towel below the inoculated towel and one towelette above the inoculated towel. The results of the test can be summarized as follows.

Therefore, the addition of 0.50% sodium chloride to the preservation composition on either the bioweb (Sample No. 1) or non-bioweb (Sample No. 2) samples showed improved effectiveness then the control (Sample No 3) against Acetobacter aceti. The effects of the biocide system against A. niger were essentially the same for all the samples tested. It is not believed that because A. niger was absent from the samples at 4 days, 7 days, etc., in some of the tests and was present in these same samples at later periods is indicative of A. niger regrowth. Rather, the reappearance of A. niger is believed to have been due to experimental variability of a slightly longer kill time in some of the individual samples used for testing.

Other embodiments of the invention will be apparent to one skilled in the art from a consideration of the specification or with the practice of the disclosed invention. It is intended that the specification and examples be considered as exemplary only with the true scope and spirit of the invention being indicated by the claims.