ANTISTATIC COMPOSITION

Abstract: An antistatic composition that contains an antistatic agent and a humectant is provided. The antistatic agent, for example, can be an organic phosphate salt or an inorganic salt. Moreover, examples of suitable humectants are glycerin, propylene glycol, and the like. The humectant is present in an amount such that its resulting add-on level is less than about 0.05 wt.% when applied to a fabric. By utilizing such levels of the humectant, the resulting fabric can possess improved conductive properties, while also retaining water repellancy properties.

Description: ANTISTATIC COMPOSITION Background of the Invention Nonwoven fabrics are commonly used for a variety of applications, such as in medical products, e.g., lab coats, head wear, gowns, drapes, towels, sterilization wraps, and the like. Typically, it is desired that such items have good electrical conductivity, as measured by static decay or surface resistivity, to prevent the buildup of static electricity. For example, conductive fabrics that reduce the build-up of static electricity may be particularly useful in surgical environments because sparking can pose a danger of explosion when pure oxygen is utilized in the operating room. In the past, various antistatic compositions that contain an antistatic agent have been topically applied to nonwoven fabrics to reduce static build-up. Moreover, some antistatic compositions also contain a humectant. For example, U.S. Patent No. 3,898,166 to Coonev describes an antistatic composition containing a textile antistatic agent and 10 to 50 parts by weight of humectant. In Coonev, a preferred dry coating weight for textiles was stated to be from 0.8% to about 3.0% based on fabric weight. However, such antistatic compositions can often adversely affect certain properties of a substrate to which they are applied. For example, due to the high levels of humectant utilized, the water repellancy of the resulting textile may be reduced. Accordingly, a need currently exists for an antistatic composition that can further reduce static build-up without substantially adversely affecting certain properties of the substrate, such as a nonwoven web, to which it is applied. Summary of the Invention In response to the discussed difficulties and problems encountered in the prior art, an antistatic composition has been discovered. The present invention is generally directed to an antistatic composition that can be applied to a nonwoven fabric. In particular, the antistatic composition contains an antistatic agent and a humectant. The humectant of the present invention can "boost" the ability of the antistatic agent to absorb water from the surrounding environment, thereby further reducing static build-up without substantially adversely affecting certain properties (e.g., water repellancy) of the nonwoven fabric to which it is applied. For example, in one embodiment, the antistatic composition contains a humectant, such as glycerin, in an amount such that the resulting add-on level of the humectant is less than about 0.05 wt.% of the fabric when applied thereto. As used herein, the term "add-on level" refers to the weight of a fabric treated with an antistatic composition subtracted by the weight of the fabric prior to treatment, wherein this calculated weight is divided by the weight of the treated fabric and then multiplied by 100. Any compound that aids in reducing the electrostatic charges of a surface when applied thereto can be utilized as an antistatic agent in the composition of the present invention. For example, suitable antistatic agents can include, but are not limited to, organic phosphate esters, inorganic salts (e.g., lithium nitrate), etc. In one embodiment, for example, the antistatic agent is an organic phosphate salt, such as mono- or disubstituted potassium n-butyl phosphate. When applied to a nonwoven fabric, the add-on level of the antistatic agent is typically less than about 1 wt.%. For instance, in one embodiment, the add-on level of the antistatic agent is between about 0.005 wt.% to about 0.03 wt.%, and particularly between about 0.015 wt.% to about 0.03 wt.%. Moreover, in another embodiment, the add-on level of the antistatic agent is between about 0.4 wt.% to about 1 wt.%, and particularly between about 0.5 wt.% to about 0.6 wt.%. In addition, an antistatic composition of the present invention also contains a humectant. Examples of suitable humectants include, but are not limited to, glycerin, propylene glycol, alkyl phosphate esters, quaternary amines, inorganic salts (e.g., potassium polymetaphosphate, sodium chloride, etc.), polyethylene glycols, and the like. In one embodiment, for instance, glycerin is used as the humectant. The add-on level of the humectant is generally low enough so that the water repellancy properties of the nonwoven web applied therewith are not substantially adversely affected. In particular, when applied to a nonwoven fabric, the humectant used in the antistatic composition typically has an add-on level of less than about 0.05 wt.%. For instance, in one embodiment, the add-on level of the humectant is between about 0.02 wt.% to about 0.05 wt.%. Moreover, in another embodiment, the add-on level of the humectant is between about 0.02 wt.% to about 0.03 wt.%. In general, the antistatic composition of the present invention can be applied to any of a variety of substrates, such as textiles, nonwoven webs, etc. In one embodiment, for example, the antistatic composition is applied to a multilayer nonwoven laminate, such as an (spunbond/meltblown/spunbond (SMS) or spunbond/meltblown (SM) material. Generally, an SMS material contains a meltblown web sandwiched between two exterior spunbond webs. Similar to an SMS laminate, an SM laminate is essentially a spunbond layer laminated to a meltblown layer. A variety of methods can also be employed to apply the antistatic composition of the present invention to a nonwoven fabric. For example, the antistatic composition may be printed, sprayed, coated, saturated, foamed, etc., onto the nonwoven fabric. In one embodiment, for example, the composition may be applied by a "dip and squeeze" process, i.e., running a web into a bath of the composition and removing any excess solution by applying pressure and squeeze rolls. In another embodiment, the antistatic composition may be atomized and sprayed onto the fabric. Other features and aspects of the present invention are discussed in greater detail below. Detailed Description of Representative Embodiments Definitions As used herein, the term "antistatic" generally refers to the reduction or minimization of electrostatic charges. As used herein, the term "biconstituent fibers" refers to fibers which have been formed from at least two polymers extruded from the same extruder as a blend. Biconstituent fibers do not have the various polymer components arranged in relatively constantly positioned distinct zones across the cross-sectional area of the fiber and the various polymers are usually not continuous along the entire length of the fiber, instead usually forming fibrils or protofibrils which start and end at random. Biconstituent fibers are sometimes referred to as multiconstituent fibers. Fibers of this general type are discussed in, for example, U.S. Patent Nos. 5,108,827 and 5,294,482 to Gessner. Biconstituent fibers are also discussed in the textbook Polymer Blends and Composites by John A. Manson and Leslie H. Sperling, copyright 1976 by Plenum Press, a division of Plenum Publishing Corporation of New York, IBSN 0-306-30831-2, at pages 273 through 277. As used herein, the term "conjugate fibers" refers to fibers which have been formed from at least two polymers extruded from separated extruders but spun together to form one fiber. Conjugate fibers are also sometimes referred to as multicomponent or bicomponent fibers. The polymers are usually different from each other though conjugate fibers may be monocomponent fibers. The polymers are arranged in substantially constantly positioned distinct zones across the cross-section of the conjugate fibers and extend continuously along the length of the conjugate fibers. The configuration of such a conjugate fiber may be, for example, a sheath/core arrangement, wherein one polymer is surrounded by another or may be a side-by-side arrangement, a pie arrangement or an "islands-in-the-sea" arrangement. Conjugate fibers are taught by U.S. Patent Nos. 5,108,820 to Kaneko et a and 4,795,668 to Krueαer et al.. 5,336,552 to Strac et aL Conjugate fibers are also taught in U.S. Patent No. 5,382,400 to Pike et al. and may be used to produced crimp in the fibers by using the differential rates of expansion and contraction of the two (or more) polymers. Crimped fibers may also be produced by mechanical means and by the process of German Patent DT 25 13 251 A1. For two component fibers, the polymers may be present in ratios of 75/25, 50/50, 25/75, or any other desired ratios. The fibers may also have shapes such as those described in U.S. Patent Nos. 5,277,976 to Hoαle et al.. 5,466,410 to Hill, 5,069,970 to Larαman et al.. and 5,057,368 to Largman et al.. which describe fibers with unconventional shapes. As used herein, a "humectant" generally refers to compounds that have an affinity for water. As used herein, "meltblown fibers" refers to fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity, usually hot gas (e.g. air) streams which attenuate the filaments of thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly disbursed meltblown fibers. Such a process is disclosed, for example, in U.S. Patent No. 3,849,241 to Butin et a Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than about 10 microns. As used herein, the term "microfibers" means small diameter fibers having a diameter not greater than about 75 micrometers, for example, having a diameter of about 0.5 micrometers to about 50 micrometers. More particularly, microfibers may have a diameter from about 2 micrometers to about 40 micrometers. Another frequently used expression of fiber diameter is denier, which is defined as grams per 9000 meters of a fiber and may be calculated as fiber diameter in micrometers squared, multiplied by the density in grams/cc, multiplied by 0.00707. A lower denier indicates a finer fiber and a higher denier indicates a thicker or heavier fiber. For example, the diameter of a polypropylene fiber given as 15 micrometers may be converted to denier by squaring and then multiplying the result by 0.00707. Thus, a 15 micrometer polypropylene fiber has a denier of about 1.42. Outside the United States, the unit of measurement for average fiber diameter is more expressed as the "tex", which is defined as the grams per kilometer of fiber. "Tex" may be calculated as denier/9. As used herein, the term "monocomponent" fiber refers to a fiber formed from one or more extruders using only one polymer. This is not meant to exclude fibers formed from one polymer to which small amounts of additives have been added for coloration, anti-static properties, lubrication, hydrophilicity, etc. These additives, e.g., titanium oxide for coloration, are generally present in an amount less than about 5 weight percent and more typically less than about 2 weight percent. As used herein, the term "nonwoven web" or "nonwoven" refers to a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted fabric. Nonwoven webs or fabrics have been formed from many processes, such as, for example, meltblowing processes, spunbonding processes, and bonded carded web processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fibers diameters are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91). As used herein, "spunbond fibers" refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine, usually circular capillaries of a spinneret with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Patent Nos. 4,340,563 to Appel et a 3,692,618 to Dorschner et al.. 3,802,817 to Matsuki et a , 3,338,992 to Kinney. 3,341 ,394 to Kinney, 3,502,763 to Hartman. and 3,542,615 to Dobo et al.. Spunbond fibers are generally not tacky when they are deposited on a collecting surface. Spunbond fibers are generally continuous and have diameters larger than about 7 microns, and more particularly, between about 10 and 40 microns. It should be noted that any given range presented herein is intended to include any and all lesser included ranges. For example, a range of from 45-90 would also include 50-90; 45-80; 46-89 and the like. Thus, the range of 95% to 99.999% also includes, for example, the ranges of 96% to 99.1%, 96.3% to 99.7%, and 99.91 to 99.999%. Detailed Description Reference now will be made in detail to various embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. In general, the present invention is directed to an antistatic composition containing an antistatic agent and a humectant. By utilizing a humectant and an antistatic agent, it has been discovered that the resulting antistatic composition can better inhibit the build-up of static electricity on a nonwoven web applied therewith. In particular, a humectant of the present invention can "boost" the ability of the antistatic agent to absorb water from the surrounding environment, thereby further reducing static build-up. Moreover, by utilizing an antistatic composition containing an antistatic agent with a relatively small amount of a humectant, it has been discovered that such a reduction in static build-up can be achieved without substantially adversely affecting certain properties (e.g., water repellancy) of the nonwoven fabric to which it is applied. For example, such a reduction in static build-up can be achieved without increasing the hydrohead value of the web greater than about 25% above the hydrohead value of the web without a humectant. As stated, the antistatic composition of the present invention generally contains an antistatic agent. Any compound that aids in reducing the electrostatic charges of a surface when applied thereto can be utilized as an antistatic agent in the composition of the present invention. In particular, antistatic agents that reduce static-build up by absorbing water from the surrounding environment may be utilized. For example, antistatic agents commonly applied to textiles, tissues, and/or other materials can be used in the present invention. Some conventional antistatic agents are described in U.S. Patent Nos. 3.898.166 to Coonev: 4.115,605 to Hultman. et al.: and 5,001 ,015 to Havens, which are incorporated herein in their entirety by reference thereto. In particular, suitable antistatic agents can include, but are not limited to, organic phosphate esters, inorganic salts (e.g., lithium nitrate), etc. In one embodiment, for example, the antistatic agent is an alkyl phosphate ester. Commercially available examples of suitable alkyl phosphate esters include "ZELEC KC" from Stepan Chemical (mono- and disubstituted potassium n-butyl phosphate); "ALKANOL MP" from Stepan Chemical (mono- and disubstituted potassium n-propyl phosphate); "POLYFIX N" from Schill & Seilacher (mono- and disubstituted potassium i-butyl phosphate); "QUADRASTAT PBK" from Manufacturers Chemical (mono- and disubstituted potassium n-butyl phosphate); and "QUADRASTAT 1662" from Manufacturers Chemical (mono- and disubstituted potassium l-butyl phosphate). Other suitable antistatic agents can include, but are not limited to, quaternary amines, inorganic salts (e.g., potassium polymetaphosphate, sodium chloride, etc.), polyethylene glycols, and the like. In addition to an antistatic agent, the antistatic composition of the present invention also contains a humectant. In general, a humectant of the present invention can act as a "booster" for the antistatic agent in absorbing water from the surrounding environment, thereby further enhancing the reduction of static build-up. Some examples of suitable humectants include, but are not limited to, glycerin, propylene glycol, capric acid; caproic acid; caprylic acid; caprylic/capric mixed acids; cholesterol; lauric acid; magnesium stearate; myristic acid; oleic acid; palmitic acid; pentaerythritol; sorbitol; stearic acid; sterols (vegetable); various humectants available from Lipo Chemicals (e.g., acetamide MEA, ethoxylated glycerin, lactamide MEA, etc.); and the like. In one embodiment, for instance, glycerin, which was obtained from Fisher Scientific, was utilized as a humectant in the antistatic composition. In another embodiment, propylene glycol, which was obtained from Fisher Scientific, was utilized as the humectant. Besides the above-mentioned components, other components can also be included within the antistatic composition of the present invention. For instance, in some embodiments, a solvent, such as water or alcohol-based solvents, can be included within the antistatic composition. Moreover, in some embodiments, wetting agents, such as low-molecular weight alcohols, can be utilized. A wetting agent can generally be any compound that aids in initially wetting the nonwoven fabric without affecting the ability of the antistatic composition to effectively reduce static build-up. In one embodiment, for example, hexanol is used as a wetting agent in the antistatic composition. In general, the desired add-on level of various components of the antistatic composition can be varied to achieve fabrics having different antistatic properties. For example, the antistatic agent used in the antistatic composition can, in some embodiments, be provided to have a resulting add-on level of less than about 1.0 wt.%. It should be understood, however, that the desired add-on level of the antistatic agent may vary depending on the particular antistatic agent and/or the particular nonwoven fabric. For instance, in one embodiment, a sterile wrap can be applied with the antistatic composition such that the resulting add-on level of the antistatic agent is between about 0.005 wt.% to about 0.03 wt.%, and particularly between about 0.01 wt.% to about 0.015 wt.%. Moreover, in another embodiment, a surgical fabric containing fluorocarbon treatment, such as a surgeon's gown, can be applied with the antistatic composition such that the resulting add-on level of the antistatic agent is between about 0.4 wt.% to about 1.0 wt.%, and particularly between about 0.5 wt.% to about 0.6 wt.%. In addition to varying the add-on level of the antistatic agent, the add-on level of the humectant may also be varied as desired. For example, the humectant used in the composition can, in some embodiments, have an add-on level of less than about 0.05 wt.%. For instance, in one embodiment, the humectant is incorporated into the antistatic composition such that the resulting add-on level of the humectant is between about 0.02 wt.% to about 0.05 wt.%, and particularly between about 0.02 wt.% to about 0.03 wt.%. It should be understood, however, that the desired add-on level of the humectant may vary depending on the particular humectant. By utilizing such levels of the humectant, the water repellancy of the resulting nonwoven fabric is typically not substantially adversely affected. For example, a reduction in static build-up can be achieved without increasing the hydrohead value of the web greater than about 25% above the hydrohead value of the web without a humectant. In general, an antistatic composition of the present invention can be applied to any of a variety of substrates, such as textiles, woven fabrics, nonwoven webs, etc. In one embodiment, for example, the antistatic composition can be applied to a nonwoven fabric. Fibers commonly used in the art to manufacture nonwoven webs, such as pulp fibers, synthetic fibers, thermomechanical pulp fibers, or mixtures thereof, can be utilized. In addition, the fibers used in making the nonwoven web may have any suitable morphology and may include hollow or solid, straight or crimped, single component, conjugate or biconstituent fibers or filaments, and blends or mixtures of such fibers, as are well known in the art. In one embodiment, the nonwoven fabric applied with an antistatic composition of the present invention is a multilayer laminate. For instance, the multilayer laminate may be a spunbond/meltblown/spunbond (SMS) or a spunbond/meltblown (SM) material. An SMS laminate may be made by sequentially depositing onto a moving forming belt first a spunbond fabric layer, then a meltblown fabric layer and last another spunbond layer and then bonding the laminate in a manner described below. Alternatively, the fabric layers may be made individually, collected in rolls, and combined in a separate bonding step. Such fabrics usually have a basis weight of from about 0.1 to 12 ounces per square yard (osy), or more particularly from about 0.75 to about 3 osy. Such SMS laminates are available from Kimberly-Clark Corporation under marks such as Spunguard® and Evolution®. Moreover, SMS materials are described in U.S. Patent No. 4,041 ,203 to Brock et al.; 5,464,688 to Timmons. et al.; 4,374,888 to Bornslaeαer: 5,169,706 to Collier, et al.: and 4,766,029 to Brock et al., all of which are also incorporated herein in their entireties by reference thereto. The spunbonded layers on the SMS laminates provide durability and the internal meltblown barrier layer provides porosity. Similar to an SMS laminate, an SM laminate is essentially a spunbond layer laminated to a meltblown layer. Besides multilayer laminates, other nonwoven fabrics may also be used. For example, a fabric containing a single layer of spunbond fibers can be applied with an antistatic composition of the present invention. In general, any of a variety of methods can be employed to apply the antistatic composition of the present invention to a substrate, such as a nonwoven web. For example, the antistatic composition may be printed, sprayed, coated, saturated, foamed, etc., onto a nonwoven fabric. In one embodiment, for example, the composition may be applied by running a web into a bath of the composition and removing any excess solution by applying pressure and squeeze rolls. This process, also known as a "dip and squeeze" process, is described in more detail in U.S. Patent No. 5,151 ,321 to Reeves, et al.. which is incorporated herein in its entirety by reference thereto. For example, the "dip and squeeze" may be particularly desired when applying the composition to certain types of fabrics, such as surgical fabrics. However, in another embodiment, it may be more desirable to atomize the antistatic composition and apply it onto a fabric by spraying. Various atomizers may be used, such as those described in U.S. Pat. No. 4,270,913, which is incorporated herein in its entirety by reference thereto. Further, in another embodiment, a WEKO sprayer can be utilized to spray the composition onto the fabric. Spraying may be particularly desired when applying the composition to certain types of fabrics, such as sterilization wraps. Moreover, the antistatic composition may be applied, either uniformly or non-uniformly, to one or both sides of a substrate. Further, when utilizing a multilayer laminate, the antistatic composition may also be applied to any number of the laminate layers. For instance, in one embodiment, the antistatic composition can be applied only to an internal meltblown layer of an SMS laminate. In other embodiments, the antistatic composition can be applied to the internal meltblown layer, as well as to one or more of the outer spunbond layers, such as, for example, by saturating the entire fabric with the composition. When applied to one or more multiple layers, the add-on level of the antistatic composition is typically less than about 0.05 wt.% of the total weight of the fabric. In order to apply the antistatic composition to a nonwoven fabric utilizing an application method, such as described above, the composition is typically formed as an aqueous solution. In particular, the above-mentioned components are combined with water to form a solution that can applied to the fabric. The amount of each component added to the solution can generally vary depending on the desired add-on level, the wet pick-up of the application method utilized, and/or the amount of other components utilized. For example, in one embodiment, the aqueous solution can contain 0.0133 wt.% "ZELEC KC", 0.007 wt.% glycerin, 0.50 wt.% hexanol, and 99.4797% water to obtain a target add-on level of 0.02 wt.% "ZELEC KC" and 0.02 wt.% glycerin when applied to a 1.8 osy substrate by a "dip and squeeze" process. The present invention may be better understood with reference to the following examples. EXAMPLE 1 The ability of a nonwoven fabric to be treated with an antistatic composition of the present invention was demonstrated. SMS nonwoven laminates having a basis weight of 1.8 ounces per square yard and formed from polypropylene (available from Kimberly-Clark under the tradename WORKWEAR® ), were treated with various solutions of antistatic compositions. Four sets of samples were developed from the solutions. Each set included one sample containing only water, an antistatic agent, and hexanol (Samples 1 , 4, 7, and 10). The remaining samples within each set contained water, an antistatic agent, glycerin (humectant), and hexanol (Samples 2-3, 5-6, 8-9, and 11-12). The antistatic composition solutions were applied to the substrates utilizing a "dip and squeeze" process, such as described above. The liquid pick-up (i.e., the ratio of liquid weight on a sheet to the weight of the dry sheet, multiplied by 100) for each sample was target at approximately 300%. The characteristics of the solutions utilized to form the samples are given below in Table 1. Table 1 : Antistatic Solution Characteristics *For each sample, hexanol was present in an amount of 0.50 wt.% and water constituted the balance of the solution. After applying the solutions, the fabrics were then dried using a dryer at 230°C for approximately 5 minutes, or until dry. The characteristics of the resulting nonwoven fabric samples are given below in Table 2. Table 2: Target Add-On Levels Once dried, the ability of each sample to minimize static buildup was determined. In particular, the hydrohead, surface resistivity, and static decay were determined. Two tests were conducted for each sample. The results are given below in Table 3. Hydrohead: Hydrohead is generally a measure of the liquid barrier properties of a fabric. The hydrohead test determines the height of water (in centimeters) that the fabric will support before a predetermined amount of liquid passes through. A fabric with a higher hydrohead reading indicates it has a greater repellancy to liquid penetration than a fabric with a lower hydrohead. The hydrohead test is performed in accordance with Federal Test Standard No. 191 A, Method 5514. Surface Resistivity: The surface resistivity of the fabric was determined in accordance with National Fire Protection Association (NFPA) 99A. For example, a 4" x 1" sample of the fabric was placed between two 1" metal poles. A weight was then put on top of the fabric. Thereafter, the resistance was measured using a resistivity meter. Static Decay: Static decay generally refers to the amount of time it takes to dissipate a given electrical charge. "90% Decay" represents the time (seconds) it takes for a sample to decay from +5000 volts to +500 volts. The 90% static decay values were determined in accordance with National Fire Protection Association (NFPA) 99A. In particular, a 6" x 3" section of each sample was placed into a Faraday cage. Thereafter, a 5000 volt positive charge was imposed on each sample and the decay time measured for that sample when the its charge reached 500 positive volts. A 5000 volt negative charge was then imposed on that sample and the decay time measured for that sample when its charge reached 500 negative volts. "50% Decay" represents the time (seconds) it takes a sample to decay from +5000 volts to +2500 volts. The 50% static decay values were also determined using National Fire Protection Association (NFPA) 99A, except that the samples were allowed to decay from +5000 volts to +2500 volts before recording the decay time. Table 3: Conductivity Results The surface resistivity of the samples containing a humectant varied from 4.7 x 10 10 to > 3.4 x 10 13 ohms/square. The 90% static decay times for the samples containing a humectant ranged from 0.02 to 1.42 seconds. According to the National Fire Protection Association (NFPA) 99A, in order to be considered conductive, a fabric must generally have a 90% static decay time less than 0.50 seconds or a surface resistivity less than 1 x 10 11 ohms/square. As indicated above, such as in the results obtained from samples 10-12, the use of a humectant can decrease the surface resistivity and static decay of a fabric sample. Moreover, such a decrease can be accomplished without substantially adversely affecting the liquid repellancy of the fabric, e.g., a hydrohead increase of greater than about 20%. In fact, as indicated, the liquid repellancy is actually improved in some instances. EXAMPLE 2 The ability of a nonwoven fabric to be treated with an antistatic composition of the present invention was demonstrated. Various SMS laminate fabrics having a basis weight of 2.2 ounce per square yard (osy) and made from polypropylene (available from Kimberly- Clark under the tradename KIMGUARD ®), were treated with various solutions of antistatic compositions. Four sets of samples were developed from the solutions. Each set included one sample containing only water, an antistatic agent, and hexanol (Samples 13, 16, 19, and 22). The remaining samples within each set contained water, an antistatic agent, glycerin (humectant), and hexanol (Samples 14-15, 17-18, 20-21 , and 23-24). The antistatic composition solutions were applied to the substrates utilizing a "dip and squeeze" process, such as described above. The liquid pick-up (i.e., the ratio of liquid weight on a sheet to the weight of the dry sheet, multiplied by 100) for each sample was target at approximately 360%. The characteristics of the solutions utilized to form the samples are given below in Table 4. Table 4: Antistatic Solution Characteristics *For each sample, hexanol was present in an amount of 0.50 wt.% and water constituted the balance of the solution. After applying the solutions, the fabrics were then heated using a dryer at 115°C until dry. The characteristics of the resulting nonwoven fabric samples are given below in Table 5. Table 5: Target Add-On Levels Once dried, the ability of each sample to minimize static buildup was determined. In particular, the hydrohead, surface resistivity, and static decay were determined as in Example 1. The results are given below in Table 6. Table 6: Conductivity Results Only one data point is represented for these samples. The surface resistivity of the samples containing a humectant varied from 6.7 x 10 11 to > 1 x 10 14 ohms/square. The 90% static decay times for the samples containing a humectant ranged from 0.01 to 5.52 seconds. As demonstrated in the results obtained from samples 19-21 , for example, the use of a humectant can decrease the surface resistivity and static decay of a fabric sample, without substantially adversely affecting the liquid repellancy of the fabric. In fact, as indicated, the liquid repellancy is actually improved in some instances. Some of the samples tested did not indicate a significant improvement in static decay and/or surface resistivity upon the addition of a humectant. It is believed that, under some conditions, the humectant may somewhat decrease conductivity by inhibiting the ability of the antistatic particles from residing close to each other for conductive purpose. Thus, in some instances, certain methods of application that can apply the antistatic composition in smaller particle sizes may be more desirable. For example, atomized spraying and the "dip-and-squeeze" methods may sometimes provide better conductivity results than WEKO spraying. However, the data referred to above may also have been the result of testing error. While the invention has been described in detail with respect to the specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. Accordingly, the scope of the present invention should be assessed as that of the appended claims and any equivalents thereto.

Claims: WHAT IS CLAIMED IS: 1. A fabric to which has been applied an antistatic composition, said antistatic composition comprising: an antistatic agent; and a humectant, said humectant being incorporated into said antistatic composition in an amount such that the add-on level of said humectant is less than about 0.05 wt.% of said fabric when applied thereto. 2. A fabric as defined in claim 1 , wherein said antistatic agent is incorporated into said antistatic composition in an amount such that the add-on level of said antistatic agent is less than about 1 wt.% of said fabric when applied thereto. 3. A fabric as defined in claim 1 , wherein said antistatic agent is incorporated into said antistatic composition in an amount such that the add-on level of said antistatic agent is between about 0.005 wt.% to about 0.03 wt.% of said fabric when applied thereto. 4. A fabric as defined in claim 1 , wherein said antistatic agent is incorporated into said antistatic composition in an amount such that the add-on level of said antistatic agent is between about 0.4 wt.% to about 1 wt.% of said fabric when applied thereto. 5. A fabric as defined in claim 1 , wherein said humectant is incorporated into said antistatic composition in an amount such that the add-on level of said humectant is between about 0.02 wt.% to about 0.05 wt.% of said fabric when applied thereto. 6. A fabric as defined in claim 1 , wherein said humectant is incorporated into said antistatic composition in an amount such that the add-on level of said humectant is between about 0.02 wt.% to about 0.03 wt.% of said fabric when applied thereto. 7. A fabric as defined in claim 1 , wherein said humectant is glycerin. 8. A fabric as defined in claim 1 , wherein said humectant is propylene glycol. 9. A fabric as defined in claim 1 , wherein said antistatic agent is an alkyl phosphate ester. 10. A fabric as defined in claim 1 , wherein said fabric contains multiple layers. 11. A fabric as defined in claim 10, wherein said antistatic composition is applied to one layer of said fabric. 12. A fabric as defined in claim 10, wherein said antistatic composition is applied to more than layer of said fabric. 13. A fabric as defined in claim 10, wherein said fabric contains a meltblown layer positioned between first and second spunbond layers. 14. A fabric as defined in claim 1 , further comprising a wetting agent. 15. A fabric as defined in claim 1 , further comprising a solvent. 16. A nonwoven fabric to which has been applied an antistatic composition, said antistatic composition comprising: an antistatic agent, said antistatic agent being incorporated into said antistatic composition in an amount such that the add-on level of said antistatic agent is less than about 1 wt.% of said nonwoven fabric when applied thereto; and a humectant, said humectant being incorporated into said antistatic composition in an amount such that the add-on level of said humectant is between about 0.02 wt.% to about 0.05 wt.% of said nonwoven fabric when applied thereto. 17. A nonwoven fabric as defined in claim 16, wherein said antistatic agent is incorporated into said antistatic composition in an amount such that the add-on level of said antistatic agent is between about 0.01 wt.% to about 0.015 wt.% of said nonwoven fabric when applied thereto. 18. A nonwoven fabric as defined in claim 16, wherein said antistatic agent is incorporated into said antistatic composition in an amount such that the add-on level of said antistatic agent is between about 0.5 wt.% to about 0.6 wt.% of said nonwoven fabric when applied thereto. 19. A nonwoven fabric as defined in claim 16, wherein said humectant is glycerin. 20. A nonwoven fabric as defined in claim 16, wherein said humectant is propylene glycol. 21. A nonwoven fabric as defined in claim 16, wherein said antistatic agent is an alkyl phosphate ester. 22. A nonwoven fabric as defined in claim 16, wherein said nonwoven fabric contains multiple layers. 23. A nonwoven fabric as defined in claim 22, wherein said nonwoven fabric contains a meltblown layer positioned between first and second spunbond layers. 24. A nonwoven fabric to which has been applied an antistatic composition, said antistatic composition comprising: an antistatic agent comprising an alkyl phosphate ester, said antistatic agent being incorporated into said antistatic composition in an amount such that the add-on level of said antistatic agent is less than about 1 wt.% of said nonwoven fabric when applied thereto; and a humectant comprising glycerin, said humectant being incorporated into said antistatic composition in an amount such that the add-on level of said humectant is between about 0.02 wt.% to about 0.03 wt.% of said nonwoven fabric when applied thereto. 25. A process for forming a fabric, said process comprising the steps of: providing a nonwoven fibrous web; and applying an antistatic composition containing an antistatic agent and a humectant to said nonwoven fibrous web such that the add-on level of said antistatic agent is less than about 1 wt.% of said nonwoven fabric and the add-on level of said humectant is less than about 0.05 wt.% of said nonwoven fabric. 26. A process as defined in claim 25, wherein the add-on level of said antistatic agent is between about 0.01 wt.% to about 0.015 wt.% of said nonwoven fabric. 27. A process as defined in claim 25, wherein the add-on level of said antistatic agent is between about 0.5 wt.% to about 0.6 wt.% of said nonwoven fabric. 28. A process as defined in claim 25, wherein the add-on level of said humectant is between about 0.02 wt.% to about 0.05 wt.% of said nonwoven fabric. 29. A process as defined in claim 25, wherein said humectant is glycerin. 30. A process as defined in claim 25, wherein said humectant is propylene glycol. 31. A process as defined in claim 25, further comprising the step of providing at least one other nonwoven web to form a multi- layered fabric. 32. A process as defined in claim 31 , further comprising the step of applying said antistatic composition to said other nonwoven web. 33. A process as defined in claim 31 , further comprising the step of providing a second and third nonwoven web formed from spunbonded fibers to form said multi-layered fabric. 34. A process as defined in claim 33, further comprising the step of positioning said nonwoven web between said second and third nonwoven webs, said nonwoven web being formed from meltblown fibers.

Inventors: POWERS MICHAEL D, POWERS, MICHAEL, D.
Applicants: KIMBERLY CLARK CO, KIMBERLY-CLARK WORLDWIDE, INC.
Application year: 2001
Main classification: D06M13
IPC codes: C09K3, D04H1, D04H3, D06M13, D06M23