the present invention comprises disposable , personal care products that , upon use , maintain a better core integrity and absorption than conventional products . such products include , but are not limited to , diapers , training pants , feminine care products , and incontinence products . generally , personal care products of the invention comprise three or more layers of synthetic and natural materials . these layers include a liquid permeable inner liner , an absorbent core , and a liquid impermeable outer cover . the absorbent core is positioned between the inner liner and outer cover . the inner liner can be manufactured from a wide range of materials , such as woven and nonwoven polymeric fibers or a combination of synthetic and natural fibers . typical polymeric fibers include polyethylene , polypropylene and polyester fibers . typical natural fibers include cellulose , wood pulp and cotton . the outer impermeable cover in one instance comprises a multilayered polymer films , nonwovens , laminates of films and nonwovens , laminates of nets and films , laminates of nets and nonwovens of polyethylene , polypropylene , polyesters , polyvinyl alcohols , and polyvinyl acetates . in another instance , the outer cover comprises a composite material , such as a film - coated nonwoven material . the absorbent core comprises natural fibers , such as cellulose , wood pulp , or cotton . the core has a strong affinity for water and other hydrophilic components of bodily secretions . the absorbent core can take any form suitable for use in absorbent composites . for example , the core can be in the form of a natural fiber batt or regenerated cellulose and can contain a dispersion of superabsorbent particles . other forms of superabsorbent materials include , but are not limited to , fibers , flakes , spheres , films , foams , sprays , and printable superabsorbent materials . the inner liner and outer cover can comprise one or more individual layers of materials . for example , the inner liner may comprise a surge layer containing , for example , thermoplastic fibers positioned beneath a thermoplastic mesh . further , additional layers can be interposed between any of the three general layers . for example , an inner tissue material or wrap sheet is optionally positioned between the outer cover and absorbent core , and between the surge layer and the absorbent core . the natural fiber core of the present invention can be heated and compressed between two fusible materials using ultrasonic energy without forming an ultrasonic bond or weld and without significantly deforming the fusible materials . it may also be possible to form compressions using sufficient localized pressure in the absence of ultrasonic energy . ultrasonic compressions are employed to provide improved contact between the layers of the article . this contact occurs without bonding the fusible materials to the natural fiber core , or to one another . the compression sites are used in place of an ultrasonic bond to keep the natural fiber core in place and serve to reduce the break - up of the absorbent core , thus maintaining the absorption capacity of the core . while the use of ultrasonic compressions are preferred , other methods of forming the compressions are contemplated by the invention . such methods include the use of air or hydraulic pressure . in particular , ultrasonic energy can be applied to either the inner liner or outer cover of the article or both . ultrasonic energy involves high frequency mechanical energy in the form of a reciprocating vertical motion . such ultrasonic energy applied to thermoplastic materials results in a softening or melting of the thermoplastic if the heat generated increases the temperature of the thermoplastic above the glass transition temperature or melting temperature . in contrast , the high crystallinity and high melting point of the natural fibers used in the absorbent core of the present invention makes the core infusible at the temperatures needed to soften or melt conventional thermoplastics . the compressions eliminate the need for an adhesive between the material layers of the article . the compressions can be done during assembly of the article , or can be done as a one - step process after complete assembly of all the article layers , eliminating intermittent bonding procedures and saving manufacturing time and expense . the compressions can be applied to either the inner liner or outer cover of the article . the compressions can be formed at discrete locations within the surge area of the diaper and can be prepared manually using a hand - held bonder , or in a continuous fashion on a rotary bonder . the ultrasonic compressions , extending within the unexposed fibrous layer of the absorbent core anchor the core fibers between compression sites . in addition , the compressions act as stress points , absorbing a higher shear force , as opposed to uncompressed core , before breaking apart . thus , these ultrasonic compressions help to reduced breaks in the continuum of the absorbent core , and this , in turn , reduces the amount of void space within the core , and the amount of fluid accumulating in the void spaces and leaking out of the periphery of the article . this is especially beneficial when the article is a diaper . although the scope of the invention encompasses any type of disposable personal care product , the invention will be further illustrated with regard to diapers . it will be understood by one skilled in the art that the following discussion would also apply to other types of personal care products and in no way limits the scope of the invention . the present application teaches that the ultrasonic compression of a natural fiber core between at least one upper and at least one underlying fusible material serves to maintain the core &# 39 ; s integrity and absorption properties when the diaper is in use . the ultrasonic compressions can replace costly adhesives and other costly bonding procedures . moreover , the ultrasonic compressions can be formed after the product is completely assembled . moreover , the surface area of each compression can be small enough so that total surface area of all of the compressions comprises only a small percentage of the total surface area of the absorbent core . for example in this invention , the total area of the compressions comprises about 1 . 5 % of the total area of the absorbent core , spread out , for example , in a pattern of 10 × 10 , 35 × 40 , or 20 × 20 . this small area of compression helps to maintain the absorbent properties of the core by maximizing the amount of core fibers free to absorb and wick fluids . finally , the compressions can be used in place of an adhesive , and thus eliminate the problems associated with the adhesive blocking the passage of fluids into the core . although these compression sites can be formed in one step , that is by one application of ultrasonic energy to the surface of a fusible material , after the product is completely assembled , the compression sites are generally formed during intermediate steps in the diaper assembly process so that the material layers are bonded together as individual components and then introduced to the product line . this invention is further illustrated by the following examples , which are not to be construed in any way as imposing limitations upon the scope thereof . to the contrary , it is to be clearly understood that resort may be had to various other embodiments , modifications , and equivalents thereof which , after reading the description herein , may suggest themselves to those skilled in the art without departing from the spirit of the present invention and / or the scope of the appended claims . ultrasonic compressions were preformed on six , size 3 , test diapers . each diaper consisted of a liqiud impervious backsheet , a cellulose pulp absorbent core , and a nonwoven thermoplastic fibrous inner liner . the cellulose core contained a dispersion of superabsorbent particles . no adhesive was applied between any of the material layers in these diapers . the diapers were processed on a standard diaper machine . all material layers were assembled together and bonded only at the perimeter of each diaper using conventional means . the perimeter bonding did not come in contact with the absorbent core . ultrasonic compressions were then applied to the surge area of the assembled diapers . a hand - held , plunge bonder from sonics & amp ; materials , inc ., model hsm 3 , was used to ultrasonically compress the test diapers . the bonder was powered by a 2000 auto - trac ( 20 khz , 2000 watt ) ultrasonic generator from dukane corporation . the bonder also contained a rectangular slotted horn and a dot - pattern anvil design . the horn , manufactured by branson ultrasonics corporation , had dimensions of 0 . 5 ″ depth × 6 . 0 ″ wide × 5 . 5 ″ high . the bonder was equiped with an oblong tip , 4 ½ mm in length and 1 ½ mm in width . the bonder , operating at a power setting of “ five ,” efficiently locally compressed the inner liner , absorbent core and outer cover together without burning any of the material layers , or poking holes through these layers . during the compression process , each diaper remained stationary by firm , hand - held pressure . the ultrasonic compressions were placed in the surge area of each diaper , where the absorbent core breaks apart more extensively . to identify any performance differences resulting from the direction the ultrasonic energy was applied , compressions were delivered to either the inner liner or the outer cover for each test diaper . compressions were placed at three different spacing within the surge area : 35 mm × 45 mm , 20 mm × 20 mm , and 10 mm × 10 mm . the integrity of the absorbent core in the test diapers was compared against two controls . in one control , an adhesive bonded the outer cover to a wrap sheet , placed between the absorbent core and the outer cover . the adhesive add - on ( loading ) on the coversheet or outer liner was approximately 0 . 3 gram adhesive per diaper spread uniformly using a swirl pattern . in the second control , no adhesive or any other bonding mechanism , was used to hold the material layers together , other than the bonding at the diaper periphery . the core integrity of each diaper was evaluated using a “ high kick ” test described below . the core integrity of each diaper was evaluated using a “ high kicking baby model .” this model simulates the high kick of an active child . each kick is approximately 60 ° to 90 ° from floor level . each diaper , in the dry state , was tested on this high kick model for a total of 120 minutes . the dry diaper , high kick test represents the worst case scenario for absorbent core break - up . the integrity of the diaper core was analyzed at the following time points : 10 , 20 , 30 , 60 , 90 and 120 minutes . the core integrity was analyzed by stretching each diaper along its longitudinal axis in front of a light box , with the inner liner facing the light . each diaper was stretched to its full length and place against the surface of the light box . two clips mounted to the glass surface of the light box held the top end of the diaper , containing the side adhesive tabs , in place . two weights were placed at the opposite end of the diaper to stretch the diaper , and hold it in place . prior to subjecting a diaper to the high kick test , the diaper was stretched out before the light box , and the perimeter of the intack absorbent core was traced with a permanent ink marker . the enclosed area served as a reference from which future measurements were compared . the enclosed core area in an untested diaper averaged around 22 , 500 square millimeter , and encompassed the entire range of the absorbent core , from the front to the back of the diaper . fig1 shows an intack diaper core in front of the light box . at each time interval during the “ high kick ” test , each diaper was examined in front of the light box , and the approximate void space , or total area separation , within the absorbent core , measured . fig2 and 3 show the “ no - adhesive ” control after 120 minutes , and the 10 mm × 10 mm , inner liner test diaper after 120 minutes , respectively . the lighter regions , where the background light transmitted , denoted the voids or separation within the absorbent core . the darker regions , where the background light scattered , represented intack core . the end results of the kick test are shown in table 1 . tables 2 and 3 list the total area of separation at each time point for the ultrasonic energy delivered to the inner liner and outer cover , respectively . the data clearly shows that the break - up the core structure significantly decreased in the test diapers containing the ultrasonic compressions as opposed to the control diapers . the integrity of the core also improves when the ultrasonic compressions are spaced closer together . a slight improvement is observed when the ultrasonic energy is applied to the inner liner as opposed to the outer cover . also , only minimal improvement in core integrity is observed when the constructive adhesive is used as opposed to no adhesive . these results verify the conclusion that the ultrasonic compressions are anchoring the core between compression sites , and also serving as stress points , absorbing a higher shear force , before breaking apart . the improved core continuum maintains the core &# 39 ; s absorbent properties and thus reduces the amount of leakage of fluids out of the periphery of the diaper . in this invention , the area of compression comprised about 1 . 5 % of the total area of the absorbent core . this small area of compression sites helps to maintain the absorbent properties of the core by maximizing the amount of core fibers free to absorb and wick fluids . in addition , the elimination of any adhesive reduces the risk that the adhesive blocks the passage of fluids into the absorbent core . the above description is intended to be illustrated and not restrictive . while particular embodiments of the present invention have been illustrated and described , it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention .
disposable personal care products , such as diapers , feminine care products and adult incontinence products , are provided . more specifically , disposable personal care products having improved absorbent core integrity and core absorbency are provided . these products eliminate the need for costly adhesives . a method for making the products is also provided . the method includes forming a plurality of localized compressions by ultrasonically compressing the natural fiber core between , although not necessarily adjacent to , at least one upper and at least one underlying fusible material . the periphery of the article is then bonded by conventional means , such as adhesives , crimping or fusing . this process reduces costs associated with the manufacturing of such articles by eliminating or reducing the amount of adhesives in the final product , and by eliminating costly and intermittent bonding procedures . the method also improves the continuum of the absorbent core without increasing material and manufacturing costs associated with these products .