Liquid responsive materials and personal care products made therefrom

BACKGROUND OF THE INVENTION

[0001] The present invention concerns formed materials mainly for personal care products like diapers, training pants, swim wear, absorbent underpants, adult incontinence products and feminine hygiene products. This material may also be useful for other applications such as, for example, in bandages and wound dressings, nursing pads and in veterinary and mortuary applications.

[0002] One of the problems identified in the field of personal care articles has been the issue of body fit. The fit of the product to the body is important for a number of reasons, most importantly being comfort for the wearer and effectiveness of the product. A product which exhibits poor body fit feels uncomfortable for the user and may result in the user restricting his or her activity and movement in order to avoid slippage or other movement of the product. Secondly, a gap caused by poor body fit may allow fluid to avoid contact with the product and so escape absorption, possibly causing staining of clothing or bedding.

[0003] Simply providing a thicker product would do much to resolve the issue of gapping between the product and the wearer's body. This would enhance fluid transfer between the body and the product and improve fluid intake to the product. It is important, however, for personal care products to be thin for ease of packaging and to minimize shipping volume. Thinness also makes the product less noticeable in use. Contrarily, it is also important that the product have sufficient void volume in use to provide space in which to hold body exudates These competing functional desires require careful balancing in order to produce a commercially successful product. There remains a need in the art for a material for use in personal care products which will remain thin before use but will still provide the requisite storage and absorption capacity, and provide enhanced product fit to the body of a wearer.

SUMMARY OF THE INVENTION

[0004] In response to the discussed difficulties and problems encountered in the prior art, a new structural composite including a nonwoven fabric has been developed. The composite has been compressed in the presence of a temporary liquid soluble binder, and will spring back upon insult of bodily fluids to nearly its original thickness in order to decrease the gap between the product and the wearer's body.

[0005] The nonwoven may be a stabilized spunbond, meltblown, bonded-carded, airlaid, vertically oriented or creped web. A suitable web is a vertically oriented or “Z-directionally” oriented web. Such a web may be made from a variety of synthetic polymeric fibers like polyolefins, polyamides, polyesters, polyethers, and combinations thereof, and may be in conjugate or biconstituent forms. The nonwoven can be bonded by any variety of thermal, mechanical or chemical means. It is preferred that the web contain no more than a minor percentage of natural fibers.

[0006] Examples of suitable bodily-fluid soluble binders include but are not limited to polyvinyl alcohol (PVOH), polyvinyl pyrrilidone (PVP), polyethylene oxide (PEO), and blends thereof. The temporary binder may be added to the nonwoven in an aqueous solution by various means such as spraying, dipping, and the like. The binder is present in an amount effective to hold the nonwoven in a compressed state until dissolution.

[0007] After addition of the bodily-fluid soluble binder, the web is subjected to compressive force for a time and at a temperature sufficient to dry the adhesive solution. The time and temperature needed for drying will vary according to the nonwovens and temporary adhesive materials used and the effective drying temperature and time can be developed by those skilled in the art without undue experimentation. In one example, compression took place at about 52° C. for about one hour. The inventive material should have a Percentage of Average Retained Thickness (PART5) of at least 55 and still more preferably, at least 70. It's also preferred that the material have a PART2 of 50 or less and more particularly 35 or less, as defined below.

[0008] These materials are suitable for use in personal care products like diapers, training pants, incontinence products, bandages, and sanitary napkins.

BRIEF DESCRIPTION OF THE FIGURES

[0009]
FIG. 1 is a diagram of a vibrating lapper used to produce webs having perpendicularly laid (Z-directional) fibers.

[0010]
FIG. 2 is a diagram of a rotary lapper used to produce webs having perpendicularly laid (Z-directional) fibers.

[0011]
FIG. 3 is a diagram of the sample drying assembly for compressing and drying the adhesive treated nonwoven.

[0012]
FIG. 4 is a diagram of a rate block used in functional testing the materials of this invention.

[0013]
FIG. 5 is a pressure platform for Triple Gush testing.

DEFINITIONS

[0014] As used herein the term “nonwoven fabric or web” means 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 fabrics or webs 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 fiber diameters useful are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91).

[0015] As used herein the term “meltblown fibers” means 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 molten 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 dispersed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than 10 microns in average diameter, and are generally tacky when deposited onto a collecting surface.

[0016] “Spunbonded fibers” refers to small diameter fibers that are formed by extruding molten thermoplastic material as filaments from a plurality of fine capillaries of a spinneret. Such a process is disclosed in, for example, U.S. Pat. No. 4,340,563 to Appel et al. and U.S. Pat. No. 3,802,817 to Matsuki et al. The fibers may also have shapes such as those described, for example, in U.S. Pat. No. 5,277,976 to Hogle et al. which describes fibers with unconventional shapes.

[0017] As used herein the term “conjugate fibers” refers to fibers which have been formed from at least two polymers extruded from separate 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 in U.S. Pat. No. 5,108,820 to Kaneko et al., U.S. Pat. No. 4,795,668 to Krueger et al., U.S. Pat. No. 5,540,992 to Marcher et al. and U.S. Pat. No. 5,336,552 to Strack et al. Conjugate fibers are also taught in U.S. Pat. No. 5,382,400 to Pike et al. and may be used to produce crimp in the fibers by using the differential rates of expansion and contraction of the two (or more) polymers. 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. Pat. No. 5,277,976 to Hogle et al., U.S. Pat. Nos. 5,466,410 to Hills and 5,069,970 and 5,057,368 to Largman et al., which describe fibers with unconventional shapes.

[0018] 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. The term “blend” is defined below. 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 also referred to as multiconstituent fibers. Fibers of this general type are discussed in, for example, U.S. Pat. Nos. 5,108,827 and 5,294,482 to Gessner. Bicomponent and 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.

[0019] As used herein the term “blend” means a mixture of two or more polymers while the term “alloy” means a sub-class of blends wherein the components are immiscible but have been compatibilized. “Miscibility” and “immiscibility” are defined as blends having negative and positive values, respectively, for the free energy of mixing. Further, “compatibilization” is defined as the process of modifying the interfacial properties of an immiscible polymer blend in order to make an alloy.

[0020] “Bonded carded web” refers to webs that are made from staple fibers which are sent through a combing or carding unit, which separates or breaks apart and aligns the staple fibers in the machine direction to form a generally machine direction-oriented fibrous nonwoven web. This material may be bonded together by methods that include point bonding, through air bonding, ultrasonic bonding, adhesive bonding etc.

[0021] “Airlaying” is a well-known process by which a fibrous nonwoven layer can be formed. In the airlaying process, bundles of small fibers having typical lengths ranging from about 3 to about 52 millimeters (mm) are separated and entrained in an air supply and then deposited onto a forming screen, usually with the assistance of a vacuum supply. The randomly deposited fibers then are bonded to one another using, for example, hot air to activate a binder component or a latex adhesive. Airlaying is taught in, for example, U.S. Pat. No. 4,640,810 to Laursen et al., and U.S. Pat. No. 5,885,516 to Christensen.

[0022] “Perpendicularly laid” or “Z-directional fabrics” are fabrics in which the fibers are oriented in a direction perpendicular to the predominant plane (X-Y) of the fabric. This predominant plane is also generally the MD-CD plane. This refers to fabrics wherein the fibers are predominately oriented in the Z-direction during the formation of the fabric, as opposed to during a post-treatment step like creping. Examples of such materials and methods may be found in PCT publication WO 00/66057 and WO 00/66284, corresponding to U.S. patent application Ser. Nos. 09/538,744 and 09/537,564, respectively, and both commonly assigned.

[0023] As used herein “thermal point bonding” involves passing a fabric or web of fibers to be bonded between a heated calender roll and an anvil roll. The calender roll is usually, though not always, patterned in some way so that the entire fabric is not bonded across its entire surface, and the anvil roll is usually flat. As a result, various patterns for calender rolls have been developed for functional as well as aesthetic reasons. One example of a pattern has points and is the Hansen Pennings or “H&P” pattern with about a 30% bond area with about 200 bonds/square inch as taught in U.S. Pat. No. 3,855,046 to Hansen and Pennings. The H&P pattern has square point or pin bonding areas wherein each pin has a side dimension of 0.038 inches (0.965 mm), a spacing of 0.070 inches (1.778 mm) between pins, and a depth of bonding of 0.023 inches (0.584 mm). The resulting pattern has a bonded area of about 29.5%. Another typical point bonding pattern is the expanded Hansen Pennings or “EHP” bond pattern which produces a 15% bond area with a square pin having a side dimension of 0.037 inches (0.94 mm), a pin spacing of 0.097 inches (2.464 mm) and a depth of 0.039 inches (0.991 mm). Another typical point bonding pattern designated “714” has square pin bonding areas wherein each pin has a side dimension of 0.023 inches, a spacing of 0.062 inches (1.575 mm) between pins, and a depth of bonding of 0.033 inches (0.838 mm). The resulting pattern has a bonded area of about 15%. Yet another common pattern is the C-Star pattern which has a bond area of about 16.9%. The C-Star pattern has a cross-directional bar or “corduroy” design interrupted by shooting stars. Other common patterns include a diamond pattern with repeating and slightly offset diamonds with about a 16% bond area and a wire weave pattern looking as the name suggests, e.g. like a window screen, with about a 19% bond area. Typically, the percent bonding area varies from around 10% to around 30% of the area of the fabric laminate web. As in well known in the art, the spot bonding holds the laminate layers together as well as imparts integrity to each individual layer by bonding filaments and/or fibers within each layer.

[0024] As used herein, through-air bonding or “TAB” means a process of bonding a nonwoven bicomponent fiber web in which hot air is forced through the web. The temperature of the air is sufficient to melt one of the polymers of which the fibers are made. The air velocity is usually between 100 and 500 feet per minute and the dwell time may be as long as 6 seconds. The melting and resolidification of the polymer provides bonding. Through-air bonding (TAB) requires the melting of at least one component to accomplish bonding, so it is usually restricted to webs with two components like conjugate fibers or those which include an adhesive. In the through-air bonder, air having a temperature above the melting temperature of one component and below the melting temperature of another component is directed from a surrounding hood, through the web, and into a perforated drum supporting the web. Alternatively, the through-air bonder may be a flat arrangement wherein the air is directed vertically downward onto the web. The operating conditions of the two configurations are similar, the primary difference being the geometry of the web during bonding. The hot air melts the lower melting polymer component and thereby forms bonds between the filaments to integrate the web.

[0025] Bonding can be accomplished in a number of other ways such as hydroentanglement, needling, ultrasonic bonding, adhesive bonding, stitchbonding, through-air bonding and thermal point bonding.

[0026] “Personal care product” means diapers, training pants, swim wear, absorbent underpants, adult incontinence products, bandages and feminine hygiene products. It may further encompass veterinary and mortuary products. “Target area” refers to the area or position on a personal care product where an insult is normally delivered by a wearer.

[0027] Basis Weight: A circular sample of 3 inches (7.6 cm) diameter is cut and weighed using a balance. Weight is recorded in grams. The weight is divided by the sample area. Five samples are measured and averaged.

[0028] Material caliper (thickness): The caliper of a material is a measure of thickness and is measured at 0.05 psi (3.5 g/cm2) with a STARRETT® bulk tester, in units of millimeters. Samples are cut into 4 inch by 4 inch (10.2 cm by 10.2 cm) squares and five samples are tested and the results averaged.

[0029] Density: The density of the materials is calculated by dividing the weight per unit area of a sample in grams per square meter (gsm) by the material caliper in millimeters (mm). The caliper should be measured at 0.05 psi (3.5 g/cm2) as mentioned above. The result is multiplied by 0.001 to convert the value to grams per cubic centimeter (g/cc). A total of five samples should be evaluated and averaged for the density values.

DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention comprises a new structural composite comprising a nonwoven fabric which has been compressed in the presence of a temporary liquid soluble binder and, which will spring back upon insult of bodily fluids to nearly its original thickness. In this fashion the nonwoven fabric can expand during usage to decrease the gap between the product and the wearer's body.

[0031] Effective Nonwoven Webs

[0032] The nonwoven web of this invention may be made from a number of processes, such as airlaying, spunbonding, carding and bonding, and meltblowing and coforming. The nonwoven can be consolidated and bonded by any number of available thermal, chemical or mechanical means known to those knowledgeable in the art of nonwoven materials formation.

[0033] The webs may be made from a variety of fibers and mixtures of fibers including synthetic fibers, natural fibers and binders. The fibers in such a web may be made from the same or varying diameter fibers and may be of different shapes such as pentalobal, trilobal, elliptical, round, etc. The web may also include particles, flakes or spheres to impart additional properties to the absorbent system. Synthetic fibers include those made from polyamides, polyesters, rayon, polyolefins, acrylics, Lyocel regenerated cellulose and any other suitable synthetic fibers known to those skilled in the art. Synthetic fibers may also include kosmotropes for product degradation. The fabric used in the practice of this invention may have natural fibers, but it is preferred that the web contain no more than a minor percentage of natural fibers.

[0034] The web of this invention may include insoluble binders used to give mechanical integrity and stabilization to the original web so that is will remain intact during usage. By “insoluble binder” it is meant that the binder is insoluble by bodily fluids. Insoluble binders include fiber, liquid or other binder means that may be thermally activated to consolidate or bond the web as it is produced. These insoluble binders are different from the soluble binders discussed below since the soluble binders serve to temporarily hold the resilient nonwoven fabric in a form that is more dense than that at which the web was produced and bonded with the insoluble binders, i.e., more dense than the original web.

[0035] Insoluble binder fibers preferred for inclusion are those having a relatively low melting point such as polyolefin fibers. Lower melting point polymers provide the ability to bond the fabric together at fiber cross-over points upon the application of heat. In addition, heterogeneous fibers having a lower melting polymer, like conjugate and biconstituent fibers are suitable for practice of this invention. Fibers having a lower melting polymer are generally referred to as “fusible fibers”. By “lower melting polymers” what is meant are those having a glass transition temperature less than about 175° C. It should be noted that the texture of the absorbent web can be modified from soft to stiff through selection of the fusion and quenching behavior of the polymer. Exemplary insoluble binder fibers include conjugate fibers of polyolefins, polyamides and polyesters. Three suitable insoluble binder fibers are sheath core conjugate fibers available from KoSa Inc. (Charlotte, N.C.) under the designation T-255 and T-256, both with a polyolefin sheath, or T-254, which has a low melt co-polyester sheath. Many suitable insoluble binder fibers are known to those skilled in the art, and are also available from manufacturers such as Chisso of Japan and Fibervisions LLC of Wilmington, Del.

[0036] Many polyolefin polymers with lower melting points are available for fiber production, for example polyethylenes such as Dow Chemical's ASPUN® 6811A linear low density polyethylene, 2553 LLDPE and 25355 and 12350 high density polyethylene are such suitable polymers. The polyethylenes have melt flow rates, respectively, of about 26, 40, 25 and 12. Fiber forming polypropylenes include Exxon Chemical Company's ESCORENE® PD 3445 polypropylene and Montell Chemical Co.'s PF304. Many other polyolefins are also available.

[0037] A suitable insoluble liquid binder is KYMENE® 557LX available from Hercules Inc. of Wilmington, Del. Other suitable insoluble liquid binders include ethylene vinyl acetate emulsion polymers sold by National Starch and Chemical Company (Bridgewater, N.J.) under the tradename DUR-O-SET® ELITE® series (including ELITE® 33 and ELITE® 22). Other suitable insoluble binders are sold by Air Products Polymers and Chemicals under the name AIRFLEX®.

[0038] The nonwoven material may be corrugated after formation, given Z-direction fiber orientation during formation, or may be a relatively flat nonwoven structure. Additional layers may be added to the structure and it may be included in personal care products.

[0039] Recognized in the instant invention has been the unique benefit of perpendicularly laid fibers to fluid intake and compression resilience. The Z-directional orientation of the fibers results in mechanical resilience which enables the fabric, once compressed, to recover to nearly its original uncompressed size and shape upon dissolution of the fluid-soluble binder.

[0040] Corrugated fabrics have been known in the art and a number of examples of methods of making such fabrics may be found in, for example, U.S. Pat. Nos. 4,111,733, 5,167,740, 5,558,924 and 5,620,545, incorporated herein by reference. A particularly suitable method may be found in the October 1997 issue of Nonwovens Industry magazine at page 74 in an article by Krema, Jirsak, Hanus and Saunders entitled “What's New in Highloft Production?” as well as in Czech patents 235494 entitled “Fibre Layer, Method of its Production and Equipment for Application of Fibre Layer Production Method” issued May 15, 1995 and 263075 entitled “Method for Voluminous Bonded Textiles Production” issued April 14, 1989. The vibrating lapper (FIG. 1) and the rotary lapper (FIG. 2) therein described are commercially available from Georgia Textile Machinery of Dalton, Ga., USA.

[0041] In FIG. 1, the vibrating lapper has a reciprocating comb 103 which pulls a carded web 101 along a guide board 106 towards the conveyor belt 107. A fold is formed in the carded web 101 and pulled off the comb 103 by a system of needles placed on a reciprocating compressing bar 104. The folded carded web 101 is pushed by the reciprocating compressing bar 104 to form a perpendicularly laid fiber batt 102, which is then moved forward between a conveyor belt 107 and a wire guide 105. The conveyor belt 107 brings the fiber batt 102 into a bonding device 108, which typically functions either thermally or mechanically.

[0042] The rotary lapper shown in FIG. 2 feeds the carded web 101 between a feeding disc 110 and a feeding pan 111 and into the working disc teeth 109. The folds are created in the carded web 101 as it passes between the teeth 109 producing a perpendicularly laid fiber batt 102, which is transported between a conveyor belt 107 and a wire guide 105 towards a bonding device 108.

[0043] The rotating lapper process and variants are further described in European patent application EP 0516964 B1 which teaches that fabrics so produced are useful primarily in the clothing industry as heat insulating lining materials, in the furniture industry as elastic fillers, in the automotive and construction industries as thermal and noise insulation, etc.

[0044] The use of perpendicularly laid fabrics, according to the definition above, has been known for production of carpet under pads, sleeping bag insulation and sound insulation where basis weights were considerably higher than that permissible for personal care products which must be lightweight and comfortable. Z-directional fabrics have been investigated previously for personal care products wherein the fibers provide superior fluid movement. U.S. Pat. Nos. 4,578,070 and 4,681,577 for example, teach aligning the corrugations parallel to the longitudinal axis of a personal care product. U.S. Pat. No. 4,886,511 teaches the use of elasticized strands across the crotch of a diaper so as to corrugate the product. EP 0767649 A1 describes a pleated front covering layer for a sanitary napkin with longitudinal channels on the surface. U.S. Pat. No. 5,695,487 teaches the use of meltblown webs for such fabrics wherein the fibers were aligned in the longitudinal direction.

[0045] The Soluble Binders

[0046] After the formation of the web to be used in the practice of this invention, the nonwoven is treated with a bodily-fluid soluble binder and the web is subjected to a compressive force and dried. It is important that the web not be subjected to excessively high temperatures during compression and drying because such temperatures will tend to soften or melt the fusible fibers, causing the fibers of the web to adhere to one another. The curing and drying temperature must be below that at which the fibers of the web begin to melt or soften.

[0047] As noted previously, these soluble binders are different from the insoluble binders discussed above since the soluble binders serve to only temporarily hold the resilient nonwoven fabric in a form that is more dense than that at which the web was produced and bonded with the insoluble binders.

[0048] The soluble binder should meet a number of criteria for usage in the web; it must easily penetrate the web, it should contain a low amount of water for ease of drying, it should contain a high amount of solids to hold the fabric compressed, it should not leave a residual sticky or tacky feel on the nonwoven, and it should provide a hydrophilic surface on the nonwoven to maintain good fluid intake properties.

[0049] A number of suitable soluble binders have been identified. These include, but are not limited to, polyvinyl alcohol (PVOH), polyvinyl pyrrolidone (PVP) and polyethylene oxide (PEO) and blends thereof. Suitable PVOH soluble binders include those identified as Airvol® 502, 205,523 and 540 from Celanese Chemicals Company, a division of Celanese AG, Kronberg, Germany (formerly by Air Products and Chemicals Co.). Suitable PVP soluble binders include those identified as K-15, K-30, K-90 and K-120 from International Specialty Products of Bound Brook N.J. Suitable PEO soluble binders include WSRN-10, WSRN-3000, WSRN-12K and WSR 301 from Union Carbide. Many other suppliers of these chemicals may be found and equivalent commercially available materials may be used.

[0050] Sample Preparation

[0051] Adhesive solutions were prepared by slowly adding the requisite amount of soluble binder to water and using a commercially available stirrer (Caframo Stirrer model RZR50 from Caframo, Ltd., of Wiarton, Ontario, Canada) to prepare a uniformly dispersed adhesive solution. In the case of polyvinyl alcohol, a mixer-emulsifier (Model HSM100L from Charles Ross & Sons, Co. Hauppauge, N.Y.) and moderate heat on the solution (92° C. for 20 minutes) was used to disperse the adhesive adequately. There were two main trends observed in the treating process: the ease of handling an adhesive solution increases with less viscous and less elastic solutions; and solids addition levels onto the nonwoven increase with an increase in molecular weight and concentration of adhesive solution.

[0052] Fabric samples measuring about 10″×10″ (25.4 cm by 25.4 cm) were saturated with the adhesive solution. Excess solution was then removed by compressing the samples with an Atlas Laboratory Wringer model LW-1, from Atlas Electric Devices Co. of Chicago, Ill., loaded to 130 pounds (59 kg). Pre- and post-saturation weights were used to determine solids addition levels.

[0053] Wet, adhesive-treated samples were sandwiched between two pieces of flexible TEFLON® chemical coated window screening (16 by 18 strands per inch screen mesh, 121 gsm, 0.014 inches (0.036 mm) thick) and this sandwich was placed between two plates of perforated sheet metal. The perforated metal sheets were made of 20 gauge type 304 stainless steel with 0.156 inch (0.396 cm) diameter holes, {fraction (3/16)} inches (0.472 cm) on center, yielding 63 percent open area. The perforated metal sheets were supplied by McMaster Carr Supply Company, Chicago, Ill., as item number 9358T291. The two plates were 11 by 11 inches (27.9 by 27.9 cm) and were hinged together along one edge to close like a book as depicted in FIG. 3. The corners opposite the hinge were held together with nuts and bolts to compress and densify the inserted sample and screening. The plates, screening and wet nonwoven assembly were then ready for drying.

[0054] The assembly was placed in a forced air oven (Thermolyne Oven Series 9000, model OU47335 from Barnstead/Thermolyne of Dubuque, Iowa) for drying excess water from the sheet at a temperature of about 52° C. (125.6° F.) for about one hour. It is important to dry the excess water from the sheet without elevating the sheet temperature so high as to soften/weaken some of the bonds of the lower melting point fibers. Early drying experiments at significantly hotter temperatures resulted in re-fusing any lower melting point fibers into a much denser sheet that was unable to ever recover to its original thickness. The time and temperature for compression will vary according to the materials used. The effective temperature and time can be developed by those skilled in the art without undue experimentation.

[0055] After one hour in the forced air oven the assembly was removed and allowed to cool for 20 to 30 minutes. Once the plates were cool enough to handle, the bolts were removed and the fabric removed from the assembly. Fabric thickness after adhesive addition and compression was measured and recorded.

[0056] Thickness Recovery Testing

[0057] The compressed and dried fabric was cut into four equally sized squares measuring about 5 inches by 5 inches (12.7 by 12.7 cm). Each square of fabric was placed in a container having inside length, width and depth dimensions respectively of 6.5 by 6.5 by 2.75 inches (16.5 by 16.5 by 7 cm). The fabric was laid flat in the container and not allowed to touch the sides. A 60 ml insult of room temperature tap water was poured into the center of the fabric as rapidly as possible, the container was tilted a few degrees to fully wet the sample, and the container with fabric was placed on a flat surface for 15 minutes. The sample was then removed from the container by lifting it by one corner, allowed to drip for 1 minute and then measured for thickness.

[0058] The sample was then placed in a second container with dimensions of length, width and depth respectively of 11.125 by 13.125 by at least 3 inches (28.3 by 33.3 by at least 7.6 cm) that had been filled with a large reservoir of room temperature tap water (about 5000 mls) and was allowed to remain for 15 minutes. The sample was then removed from the container by lifting it by one corner, allowed to drip for 1 minute and then measured for thickness.

[0059] Finally the nonwoven sample was allowed to dry at room temperature for about 12 hours (overnight) under no load and measured for thickness a final time.

[0060] Calculations

[0061] The following terms can be calculated for the inventive nonwoven composite of this invention.

[0062] TK1=Original nonwoven fabric dry thickness.

[0063] TK2=Thickness after adhesive addition and compression drying.

[0064] TK3=Thickness after 60 ml water insult and 15 minutes wait time.

[0065] TK4=Thickness after 60 ml water insult+15 minute wait time and 15 minutes in a large reservoir of water.

[0066] TK5=Thickness after the water insult and water reservoir steps and overnight air drying.

[0067] The Percentage of Average Retained Thickness (PART) after each step in the sample preparation was calculated as follows.

PART = 1 - \frac{(original  dry  thickness - thickness  after  modification)}{(original  dry  thickness)}

[0068] and PARTx=1−(TK1−TKx)/TK1

[0069] where x represents the modification that the nonwoven has experienced.

[0070] PART2=1−(TK1−TK2)/TK1 or Percent Average Retained Thickness after adhesive addition and compression drying.

[0071] PART3=1−(TK1−TK3)/TK1 or Percent Average Retained Thickness after 60 ml water insult and 15 minutes wait time.

[0072] PART4=1−(TK1−TK4)/TK1 or Percent Average Retained Thickness after 60 ml water insult+15 minutes wait time, and 15 minutes in a large reservoir of water.

[0073] PART5=(TK1−TK5)/TK1 or Percent Average Retained Thickness after 60 ml water insult, water washing in a large reservoir and overnight air drying.

[0074] Example Materials

[0075] Two classes of nonwoven webs were adhesive treated and compressed in order to compare solids addition levels and compression efficiency of each of the solutions.

[0076] One type of web so treated was a Z-directionally oriented bonded-carded web. This web was made from 6 denier polyethylene/polypropylene bicomponent fiber having an HR6 finish from the Chisso Corporation of Japan and known as Chisso ESC Type 236 HR6, 6 denier. The web was produced using a vibrating lapper as described in Nonwovens Industry magazine, October 1997 as noted above. The final web had a basis weight of 143.1 gsm and a density under 0.05 psi (3.5 g/cm2) load of 0.0097 g/cc. This web also had a thickness of approximately 0.582 inches (14.8 mm), referred to below as the original dry thickness or TK1.

[0077] The second type of web was a through-air bonded carded web made of 60 weight percent Chisso ESC Type 233 HR6 3 denier and 40 weight percent KoSa polyester 6 denier fiber. The web had a basis weight of 86.3 gsm and a bulk density of 0.0296 g/cc. This web also had an approximate thickness of 0.115 inches (2.9 mm), referred to below as the original dry thickness or TK1.

[0078] Thickness Recovery Results

[0079] Recovery of the fabric thickness is impacted by the starting web, the adhesive selection and amount, and the amount of body fluid dispensed onto this inventive material. The optimal material should have enough adhesive so that it keeps the web in a compressed state, even when exposed to atmospheric humidity and moisture, but not so much that it does not release the web quickly upon being wetted by bodily fluid. Thickness recovery after the addition of 60 mls of water may be, for example, relatively minimal. Some absorbent products like diapers, however, may experience as much as 400 mls of urine entering the product across this novel intake fabric. As a result of exposure to such relatively large volumes of fluid, a large portion of the soluble adhesives should dissolve and loosen the constraint on the nonwoven web, thus allowing the web to return to almost its original thickness.

[0080] Tables 1 and 2 show the thickness recovery results for each of the two types of webs at the different stages of the testing.

[0081] The Percentage of Average Retained Thickness (PART) term is a quantifiable demonstration of the thickness change which occurs with each step of materials modification. The PART2 value reflects the magnitude of thickness change which has occurred due to adhesive treatment and drying under compression. A small PART2 value indicates a large thickness reduction has occurred compared to the original dry thickness of the nonwoven. It's clear that the thicker the starting web, the greater the thickness reduction can be, and thus the smaller the PART2 value when subjected to this treatment. Fabrics with a starting thickness of about 0.600 inches (15 mm) like the Z-directionally oriented webs can achieve a lower PART2 than the thinner, through-air bonded webs with a beginning thickness of 0.115 inches (3 mm). This increased thickness reduction provides the potential for greater thickness recovery during consumer use as compared to the thinner webs.

[0082] In addition, higher levels of adhesive add-on and higher molecular weights of adhesive each result in smaller PART2 results. Smaller PART2 values also indicate a thin material which can be placed in an absorbent product. Such thinness enhances packaging efficiency as well as consumer perception of comfort due to a thinness. It is preferred that the PART2 values be equal to about 50 or less. It is more preferable that PART2 values be 35 or less.

[0083] By contrast, PART3, PART4 and PART5 values indicate the magnitude of thickness recovery which occurs after greater exposure time and greater quantities of fluid which remove the temporary soluble binder. PART5 reflects the thickness recovery occurring after a limited (60 mls) water insult, a large reservoir water washing and final air drying. Higher thickness recoveries are indicated by higher PART5 values. Greater thickness recoveries, therefore, yield smaller gaps between body and product, greater potential for bodily fluid transfer from body to product and potentially reduced leakage.

[0084] It is preferred that the PART5 values be equal to about 55 or above. It is more preferable that PART5 values be 70 or above. The relatively flat starting nonwovens shown in Table 2 had PART5 values greater than 70, and indeed, many exceeded 90, although the absolute thickness gain (in inches or cm) of these materials was not as great as that of the thicker Z-directionally oriented webs.

1TABLE 1Thickness Recovery for Z-Directionall Oriented WebsThicknessAfterThickness60AfterThicknessmlLarge%OriginalAfterWaterResevoirThickness AfterAdhesiveSolutionSolidsThickness,Adhesive,Insult,Washing,Overnight Drying,ChoiceConcentrationAdd-OnmmmmPART 2mmPART 3mmPART 4mmPART 5K-15 PVP12%33.415.0611.0573.410.6870.910.8070.911.2874.9K-15 PVP12%35.015.2410.8671.311.1172.911.1172.911.1373.0K-90 PVP7%20.815.285.7737.77.0045.87.6550.19.4361.7K-90 PVP7%16.715.136.1640.87.9452.58.2554.510.0566.4K-90 PVP7%25.015.095.5531.66.5743.57.1847.68.5756.8K-90 PVP7%18.614.385.3834.86.4644.96.8247.49.2264.1Airvol 2053%55.1814.97.137.77.650.810.671.2PVOHAirvol 2055%4.7015.25.633.66.140.49.0059.2PVOHAirvol 2055%4.0714.66.238.16.846.89.3063.5PVOHAirvol 20510%55.9713.95.236.25.640.37.856.19.0064.3PVOHAirvol 20510%54.4814.84.128.4534.010.3069.3PVOHAirvol 20515%46.9214.94.227.1533.46.543.69.1060.9PVOHAirvol 20515%43.7113.94.833.85.237.57.453.28.9064.2PVOH

[0085]

2

TABLE 2

Thickness Recovery for Through Air Bonded Carded Webs

Thickness

Large

After

Resevoir

60

Thickness

Original

ml

After

Adhesive

Thickness,
Thickness After

Water

Washing

Thickness After Final

Choice
Solids Add-On
mm
Adhesive, mm
PART 2
insult
PART 3
mm
PART 4
Drying, mm
PART 5

None
0.0%
2.92
3.01
103.0
2.85
97.6
2.88
98.7
3.04
103.9

K-15 PVP
43.8%
2.92
2.99
102.4
2.77
94.8
2.77
94.8
2.90
99.3

K-15 PVP
45.8%
2.92
2.74
93.9
2.57
87.8
2.51
86.1
2.83
96.7

K-90 PVP
22.6%
2.92
2.34
80.2
2.33
79.8
2.32
79.6
2.65
90.9

K-120 PVP
18.1%
2.92
1.75
60.0
1.77
60.4
1.80
61.7
2.13
72.8

K-120 PVP
24.4%
2.92
1.81
62.0
1.76
60.2
1.80
61.5
2.15
73.7

[0086] It is known that disposable absorbent products will perform most effectively with minimal product-to-body gap, since this reduces the opportunity for leakage and speeds the absorption of liquid by the product. Greater thickness recoveries, therefore, provide smaller gaps between body and product and greater potential for fluid transfer from body to product. Higher thickness recoveries are indicated by higher PART5 values.

[0087] Consumers have grown accustomed to products that are thin when taken from the packaging. This thin state also allows the product to be more easily donned. The utilization of the material of this invention will allow products to be thin when taken from the package, yet expandable to provide little gap between wearer and product once wetted. The material of this invention may be placed in a personal care product as a liner or in a position below a liner and above an absorbent core. The material may be in a shape so that it covers only the target area or, if manufacturing or other constraints require, may be shaped to cover the entire area of the personal care product, or an intermediate area.

[0088] Functional Testing with Body Fluid Simulants

[0089] Another series of nonwoven samples was subjected to adhesive treatment, compression drying and functional testing. The Triple Gush and Rewet Test is used to examine the fluid handling properties of a fabric by insulting the fabric with a series of 2 ml doses of menses simulant, followed each time by a waiting period. The test concludes with a blotter rewet step. The testing of these inventive intake materials with menses simulant was intended to 1) Quantify fluid intake and rewet as a result of adhesive treatment and densification, and 2) Differentiate fluid handling as a result of adhesive chemistry choice and addition level.

[0090] The ingredients and equipment used in the preparation of artificial menses are readily available as is the equipment needed to conduct the test procedure. Below is a listing of items used and their sources, though of course other sources may be used providing they are approximately equivalent.

[0091] Equipment Used

[0092] 1. Fabric sample, usually 5 inches×5 inches (12.5 cm×12.5 cm).

[0093] 2. Desorbing fiberized fluff pad, 600 gsm with a sine wave embossing pattern, available from Kimberly-Clark Corporation, Neenah, Wis., composed of Georgia Pacific 4825 Golden Isles southern softwood kraft debonded pulp, cut to a size equal to or larger than the sample specimen in both dimensions.

[0094] 3. Plexiglass rateblock shown in FIG. 4 and described in detail below.

[0095] 4. Menses Simulant prepared by the procedure described below.

[0096] 5. Gilson Pipetman® P5000 pipet with RC-5000 pipette tips from Rainin Instruments LLC, Woburn, Mass.

[0097] 6. Stopwatch, capable of measuring 0.01 second increments.

[0098] 7. Blotter paper—James River Verigood 100 lb Paper, available from the Georgia Pacific Corporation, 3″×5″ (7.5 cm×12.5 cm) pieces, each piece weighing about 0.28 grams and measuring about 0.024 inches (0.61 mm) thick.

[0099] 8. Blotter rewet pressure platform (500) with water bottle (501) and timer (502) (Omega Engineering pressure gauge with timer, Model HHP-701-20), depicted in FIG. 5.

[0100] Plexiglass rateblock (see FIG. 4): The rate block 10 is 3 inches (76.2 mm) wide and 2.87 inches (72.9 mm) deep (into the page) and has an overall height of 1.125 inches (28.6 mm) which includes a center area 19 on the bottom of the rate block 10 that projects farther from the main body of the rate block 10 and has a height of 0.125 inches (3.2 mm) is and a width of 0.886 inches (22.5 mm). The rate block 10 has a capillary 12 with an inside diameter of 0.186 inches (4.7 mm) that extends diagonally downward from one side to the center line 16 at an angle of 21.8 degrees from the horizontal. The capillary 12 may be made by drilling the appropriately sized hole from the side 15 of the rate block 10 at the proper angle beginning at a point 0.726 inches (18.4 mm) above the bottom of the rate block 10; provided, however, that the starting point of the drill hole in the side 15 must be subsequently plugged so that test fluid will not escape there. The top hole 17 has a diameter of 0.312 inches (7.9 mm), and a depth of 0.625 inches (15.9 mm) so that it intersects the capillary 12. The top hole 17 is perpendicular to the top of the rate block 10 and is centered 0.28 inches (7.1 mm) from the side 15. The top hole 17 is the aperture into which the funnel 11 is placed. The center hole 18 is for the purpose of viewing the progression of the test fluid and is actually of an oval shape into the plane of FIG. 4. The center hole 18 is centered width-wise on the rate block 10 and has a bottom hole width of 0.315 inches (8 mm) and length of 1.50 inches (38.1 mm) from center to center of 0.315 inch (8 mm) diameter semi-circles making up the ends of the oval. The oval enlarges in size above 0.44 inches (11.2 mm) from the bottom of the rate block 10, for ease of viewing, to a width of 0.395 inches (10 mm) and a length of 1.930 inches (49 mm). The top hole 17 and center hole 18 may also be made by drilling.

[0101] Menses simulant: The artificial menses fluid used in the testing was made according to U.S. Pat. No. 5,883,231 from blood and egg white by separating the blood into plasma and red cells and separating the white into thick and thin portions, where “thick” means it has a viscosity after homogenization above about 20 centipoise at 150 sec−1, combining the thick egg white with the plasma and thoroughly mixing, and finally adding the red cells and again thoroughly mixing. A more detailed procedure follows:

[0102] Blood, in this example defibrinated swine blood, is obtained from Cocalico Biologicals, Inc. (449 Stevens Road, Reamstown, Pa. 17567, 717-336-1990). The swine blood is separated by centrifuging at 3000 rpm for 30 minutes, though other methods or speeds and times may be used if effective. The plasma is separated and stored separately, the buffy coat removed and discarded and the packed red blood cells stored separately as well. It should be noted that the blood must be treated in some manner so that it may be processed without coagulating. Various methods are known to those skilled in the art, such as defibrinating the blood to remove the clotting fibrous materials, the addition or anti-coagulant chemicals and others. The blood must be non-coagulating in order to be useful and any method which accomplishes this without damaging the plasma and red cells is acceptable.

[0103] Jumbo chicken eggs are separated, the yolk and chalazae discarded and the egg white retained. The egg white is separated into thick and thin portions by straining the white through a 1000 micron nylon mesh screen (1000 micron mesh, item number CMN-1000-B from Small Parts, Inc., P.O. Box 4650, Miami Lakes, Fla. 330144-0650, 1-800-220-4242) for about 3 minutes, and the thinner portion discarded. The thick portion of egg white, which is retained on the mesh, is collected and drawn into a 60 cc syringe, which is then placed on a programmable syringe pump (Harvard Apparatus Programmable Syringe Pump Model No. 55-4143 from Harvard Apparatus, South Natick, Mass. 01760) and homogenized by expelling and refilling the contents five times. The amount of homogenization is controlled by the syringe pump rate of about 100 ml/min, and the tubing inside diameter of about 0.12 inches. After homogenizing the thick egg white has a viscosity of about 20 centipoise at 150 sec−1 and is then placed in the centrifuge and spun to remove debris and air bubbles at about 3000 rpm for about 10 minutes

[0104] After centrifuging, the thick, homogenized egg white, which contains ovamucin, it is added to a 300 cc FENWAL® Transfer pack container using a syringe (300 mls transfer pack with coupler, code 4R2014 from Baxter HealthCare Corporation, Fenwal Division, Deerfield, Ill. 60015). Then 60 cc of the swine plasma is added to the FENWAL® Transfer pack container. The FENWAL® Transfer pack container is clamped, all air bubbles removed, and placed in a Stomacher lab blender where it is blended at normal (or medium) speed for about 2 minutes. (The Stomacher 400 Laboratory Blender Model No. BA 7021, serial number 31968 was obtained from Seward Medical, London, England, United Kingdom.) The FENWAL® transfer pack container is then removed from the blender, 60 cc of swine red blood cells are added, and the contents mixed by hand kneading for about 2 minutes or until the contents appear homogenous. A hematocrit of the final mixture should show a red blood cell content of about 30 weight percent and generally should be at least within a range of 28-32 weight percent for artificial menses made according to this example. (Hematocrit was measured using a Hemata-Stat II device, serial number 1194Z03127 from Separation Technology Inc., 1096 Rainer Drive, Altamount Springs, Fla. 32714). The amount of egg white is about 40 weight percent.

[0105] Triple Gush Test Procedure Used

[0106] 1. Record the dry weights, dimensions and thickness of one piece of the sample and one piece of embossed fluff pulp. Place sample on top of fluff pad to make a test stack. No cover material was used.

[0107] 2. Center the rate block on top of the test stack.

[0108] 3. Place a funnel in the top hole in the rate block. Attach a disposable pipette tip to the Gilson Pipetman. Set Gilson Pipetman to deliver 2.00 mL of fluid into the funnel on the rate block.

[0109] 4. Dispense 2.00 mL of menses simulant to test stack through the rate block using the Pipetman. Use the stopwatch to measure the length of time from delivery of fluid to materials until all fluid is fully absorbed. Record this time.

[0110] 5. Wait 9 minutes.

[0111] 6. Insult the test stack again with 2.00 mL of menses simulant fluid. Measure and record this second intake time.

[0112] 7. Wait 9 minutes.

[0113] 8. Insult the test stack again with 2.00 mL of menses simulant fluid. Measure and record this third intake time.

[0114] 9. Wait 9 minutes. Remove the rate block from the test stack.

[0115] 10. Place test stack on the hot water bottle of the pressure platform. Place two pieces of pre-weighed blotter on top of the test stack. The test button on the pressure gauge is then depressed, starting a program that applies 1.00 psi (51.7 mmHg) of pressure to the system for 3 minutes. At the end of 3 minutes, the pressure stand lowers, releasing the pressure from the absorbent materials.

[0116] 11. Reweigh the wet blotter papers. Record the weights. The moisture pick-up in the blotter reflects the fluid the paper absorbs from the system.

[0117] 12. Weigh and check thicknesses (bulks) of the embossed fluff and sample. Record the results.

[0118] Table 3 displays the results of the triple gush and rewet tests conducted on Z-directionally oriented nonwovens which had been treated with temporary and soluble adhesives and dried under compression.

3TABLE 3Triple Gush and Rewet ResultsAdhesive% SolidsBasis Wt-Density,Intake Times, secondsChoiceSoln. Conc.Additiongsmg/ccInsult 1Insult 2Insult 3Rewet, gPolyethylene Oxide (PEO)WSRN-1024.2119.90.0133.963.205.830.30WSRN-1046.8123.00.0155.974.274.900.31WSRN-300026.8123.00.02416.105.917.630.33WSRN-3000413.7134.40.03237.2410.5012.450.31WSRN-12K26.8118.10.02819.516.988.850.26WSRN-12K412.1131.00.04232.188.179.310.35Polyvinyl Alcohol (PVOH)Airvol 50277.1135.40.0334.703.934.190.20Airvol 5021013.2141.20.0304.384.144.210.21Airvol 205710.6133.20.0316.113.714.090.26Airvol 2051022.0150.80.0325.194.793.500.25Airvol 523725.0133.70.0435.734.935.300.30Airvol 5231041.6188.90.0405.474.774.230.32Airvol 540729.6138.30.0446.645.195.730.28Airvol 5401048.6191.50.0497.205.475.880.41Polyvinyl Pyrrolidone (PVP)K-15715.1153.50.0133.322.943.160.22K-30714.1119.90.0153.182.963.200.24K-90727.3143.20.03410.845.825.840.28K-120725.9154.10.03319.665.537.540.26

[0119] The low-density structure with Z-dimensionally oriented fibers appeared to allow menses simulant to flow directly into the absorbent core. The nonwoven web was expected to experience significant density increases as a result of the adhesive addition and drying under constraint. All soluble adhesive treated fabric densities were less than 0.060 g/cc which should allow the treated materials to provide good intake performance.

[0120] Results indicate that increased solids levels on the nonwoven resulted in increased intake times. As solids addition levels increase, there is more polymer on each sheet and therefore more time is required for the fluid to dissolve it. The fluid does not penetrate as far into the system when there is more polymer in its path. In addition, as adhesive solution concentration increases, it becomes more difficult to make a solution of uniform concentration. Correspondingly, it becomes more difficult to produce these small sample sheets with uniform addition levels, so there is greater variability of fluid handling data because the fluid can encounter varying polymer amounts throughout the sheet.

[0121] It is apparent that inventive nonwovens must have a balance between good compression efficiency (staying shut due to adhesive chemistry choice and addition level) and thickness recovery (minimal adhesive for easy removal with minimal fluid).

[0122] As will be appreciated by those skilled in the art, changes and variations to the invention are considered to be within the ability of those skilled in the art. Examples of such changes and variations are contained in the patents identified above, each of which is incorporated herein by reference in its entirety to the extent consistent with this specification. Such changes and variations are intended by the inventors to be within the scope of the invention.

Liquid responsive materials and personal care products made therefrom

Information

Publication Number

Date Filed

Date Published

Inventors

CPC

US Classifications

International Classifications

Abstract

Description

Claims

Provisional Applications (1)