Patent Publication Number: US-2021186777-A1

Title: Method and apparatus of manufacturing a multilayer absorbing element for sanitary articles

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention refers to a multilayer absorbent element for sanitary articles, in particular a so-called “topsheet”. 
     The invention also refers to a method and an apparatus for manufacturing such element. 
     BACKGROUND 
     Numerous sanitary articles with absorbent function are present on the market, such as diapers for children, products for senile and light incontinence and feminine sanitary pads. 
     Generally, such articles comprise an absorbent core and a multilayer element, that is absorbent too. The latter, commonly denoted as a “topsheet”, is interposed between the user&#39;s skin and the absorbent core during use. 
     The function of the topsheet is to collect the flow of organic fluid, for example urine or menstrual blood, and transfer it to the underlying absorbent core so as to provide the user with a feeling of comfort and dryness. Therefore, the topsheets must be soft, of nice aspect to the user and have good absorption characteristics. 
     Generally, the structure of a topsheet is formed by two overlapping layers of sheet material. The first layer acts as a receptor and is, in use, in contact with the user&#39;s skin; therefore, such first layer must be soft and with a slight tendency to “lint”, that is the release of fibrous or loamy residues. The second layer, interposed between the upper layer and the absorbent core, must be denser and provided with greater capillary power with respect to the first layer, so as to dry the latter by draining and transferring the organic fluid to the absorbent core. 
     In known topsheets, this structure is obtained by coupling two layers of sheet material of different type of “non-woven fabric” (NWF), in order to guarantee that each of the two layer has the abovementioned respective characteristics. The NWF layers can be pierced, thus facilitating the drainage of the liquid from the first upper layer to the lower second layer. Furthermore, in order to make the topsheet particularly soft, a “concave-convex” structure is conferred to it, characterized by an alternation of protrusions and depressions. 
     The abovementioned shaped structure is commonly obtained by means of a manufacturing process which employs, for the second topsheet layer, NWF formed by heat-retractable fibers (“self-crimping fibers”), i. e. capable of autonomously contracting with heat. The two NWF layers are initially joined, for example by ultrasound, in some contact points. The layers of NWF thus coupled are then subjected to a heat treatment which activates the contraction of the fibers present in the NWF which constitutes the second layer of the topsheet. This contraction induces the formation of protrusions and depressions on both the layers. 
     The process just described, and the resulting product, however, shows some drawbacks. 
     First of all, the shaping of the topsheet makes its adhesion to the absorbent core more difficult and less reliable. 
     Moreover, said shaping does not allow to optimize the storage of the topsheet in coils or in packaging stacks, also because, in these conditions, the integrity of the conferred shaping cannot be guaranteed. 
     A further drawback consists then in the need to use heat-retractable fibers for the second layer of NWF, because this impacts negatively on the production process in terms of costs, complexity and time necessary for the manufacturing operations. 
     SUMMARY OF THE INVENTION 
     The technical problem posed and solved by the present invention is therefore that of providing a multilayer absorbing element and a related manufacturing method and apparatus which allow to overcome the abovementioned drawbacks with reference to the prior art. 
     This problem is solved by a manufacturing method according to claim  1  and a related apparatus according to claim  10 . 
     The invention also provides a multilayer absorbent element according to claim  21 . 
     Preferred features of the present invention are the subject of the dependent claims. 
     The invention provides some relevant advantages. The main advantage lies in the fact that the absorbent element has an improved structure, in which the second layer, being devoid of protrusions or depressions—and in particular flat and/or substantially flat—guarantees a better adherence to the absorbent core, or possibly to other components of the sanitary article. In addition, the structure of the absorbent element allows a better preservation of the characteristics of the material even if the latter is subjected to compression or, in general, stored in the form of stacks or coils. 
     In a preferred embodiment, the absorbent element can be added with pigments suitable for obtaining a “masking” effect. Such characteristic is appreciated especially in the case of coloured organic fluids, such as urine or menstrual blood, and consists in having an area of the stain of reduced surface and in masking from sight the colour of the fluid absorbed by the different elements of the sanitary article. 
     In one embodiment, the absorbent element can also perform the function of Acquisition Distribution Layer (ADL), that is an element which accelerates the absorption and distribution of the organic fluid to the other components, in particular to the absorbent core, of the sanitary article. In this way, it is possible to make the manufacturing process of the entire sanitary article simpler, faster and cheaper. 
     Furthermore, the multilayer element of the invention may have better capacity of absorbency and guarantee the dryness of the sanitary article in which it is incorporated, thus improving the user&#39;s comfort of use. 
     In addition, the manufacturing method according to the present invention allows to reduce the production costs. In fact, this method is simple and quick and moreover requires the use of less expensive raw materials. In fact, the need to use a NWF with heat-retractable fibers for the second layer of the absorbent element is eliminated. 
     Other advantages, features and methods of use of the present invention will be apparent from the following detailed description of some embodiments, presented by way of a non-limiting example. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Reference will be made to the figures of the attached drawings, wherein: 
         FIG. 1  shows an exemplary schematic cross-sectional view of an absorbent element according to a preferred embodiment of the present invention; 
         FIG. 1   bis  shows an exemplary schematic cross-sectional view of an absorbent element according to a preferred embodiment of the present invention; 
         FIG. 2  shows an exemplary schematic top view of an absorbent element according to a preferred embodiment of the present invention; 
         FIG. 3  shows an exemplary schematic representation in a side view of a first preferred embodiment of an apparatus for manufacturing the absorbent element of  FIG. 1 or 2 ; 
         FIG. 4  shows an exemplary schematic representation in lateral view of another preferred embodiment of an apparatus for manufacturing the absorbent element of  FIG. 1 or 2 ; 
         FIG. 5  shows a schematic perspective view of a portion of an embossing roller of the apparatus of  FIG. 3 or 4 , according to a preferred embodiment thereof; 
         FIG. 6  shows an exemplary schematic perspective top view of a portion of a pierced roller of the apparatus of  FIG. 3 or 4 , according to a preferred embodiment thereof. 
     
    
    
     The thicknesses and the profiles shown in the above figures are to be understood as examples, they can be magnified and are not necessarily shown in proportion. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter various embodiments and variants of the invention will be described, with reference to the above figures. 
     Similar components are denoted in different figures with the same numerical reference. 
     In the following detailed description, embodiments and further variants with respect to embodiments and variants already disclosed in the description itself will be illustrated only with regard to the differences with what already stated. 
     Moreover, the various embodiments and variants described below are susceptible of being used in combination, where consistent. 
     With reference initially to  FIG. 1 , an absorbent element, and in particular a so-called “topsheet”, according to a preferred embodiment of the invention is overall denoted by  100 . Such topsheet is suitable to be incorporated in sanitary articles, such as, for example, baby diapers, incontinence products or sanitary pads. 
     In particular, the topsheet  100  comprises a first layer of sheet material  11  and a second layer of sheet material  12 . Such first and/or second layer  11  and  12  can be a laminated material. 
     The first layer  11 , in the present application, during use is in contact with the user&#39;s body. It has a structure based on an alternation of protrusions  13  and contractions, depressions, valleys or recesses, that are intermediate zones  14  without said protrusions  13 . In the present example, the intermediate zones  14  are substantially flat or planar. 
     The second layer of sheet material  12  is substantially free of depressions or protrusions, and in particular substantially flat or planar. 
     In the present embodiment, the protrusions  13  on the first layer  11  can have each a round shape and/or a substantially circular geometry in plan view. In the embodiment shown in  FIG. 1 , said protrusions  13  have a cylindrical geometry. Possible embodiments can provide the presence of protrusions  13  with a hemi-spherical geometry. In an exemplary implementation, the base diameter of the protrusions  13  is about 2 mm. 
     The first and second layers  11  and  12  are superimposed one to the other and are coupled at the intermediate zones  14  of the first layer  11 . At these intermediate zones  14 , there are a plurality of holes  15  passing between the first layer  11  and the second layer  12 , which help to direct the flow of organic fluid to other elements of the sanitary article, in particular towards an absorbent core. In the proximity of each hole  15 , the first layer  11  and the second layer  12  are joined to each other, preferably along the perimeter which defines each hole  15 . 
     The drainage of the biological fluid from the first layer  11  to the second layer  12  is facilitated by the presence of a deposition of a surfactant agent  16 , which has the function of an hydrophilizing agent. Said surfactant agent  16  is shown in black in  FIG. 1 . Advantageously, it is deposited on the first layer  11 , preferably only on it and not on the second layer  12 . In particular, the agent  16  is present in proximity of, or at, walls of the holes  15  or portions of the first layer  11  which are lateral or circumscribed with respect to the same holes, while the remaining areas of the first layer  11  are left substantially hydrophobic or neutral. In this way, a surface tension gradient is realized, both on the first layer  11  and between the latter and the second layer  12 , which helps to draw the biological fluid towards the holes  15 . 
     According to embodiment variants, the surfactant agent  16  is also applied onto the protrusions  13 , as their total or partial coating. 
     In one embodiment, the surfactant agent can be applied as “coating” on one or both sides of the layer  11 . 
     In particular, also in this case said agent can be applied further, or only, on the walls of the holes. 
     A surfactant agent selected from one of those commercially available for hygienic applications can be used. For example, Silastol PST-N® from Schill &amp; Seilacher company in concentrations from 0.3% to 0.6% by weight. 
       FIG. 2  shows an exemplary schematic top view of a preferred embodiment of the topsheet. In that Figure it is visible how the first layer  11  presents an alternation of protrusions  13  and intermediate zones  14 , at which the holes  15  passing through the first layer  11  and second layer  12  are made. 
     Preferably, the first layer of sheet material  11  is made of non-woven fabric (NWF). 
     Preferred characteristics of such NWF are softness and absence of release of fibers. 
     Furthermore, it is preferable that the NWF is composed by fibers which make it easily joinable with the second layer of sheet material  12 . 
     A NWF suitable for the present application is composed by thermoplastic fibers, which are composed by thermoplastic polymers comprising polyolefins such as polyethylene and polypropylene, polyesters, copolyesters, polyvinyl acetate, polyamides, copolyamides, polystyrene, polyurethanes, and vinyl chloride/vinyl acetate copolymers. 
     The thermoplastic fibers may be composed by a single polymer (single-component fibers) or may be composed by more than one polymer (e.g. two-component fibers). 
     The two-component fibers can be composed by a “core” fiber surrounded by a thermoplastic “sheath” composed by a second polymer. The polymer of the “sheath” melts at a lower temperature than the core. As a result, the two-component fibers establish a bond among the fibers due to the melting of the polymer on the sheath, after adequate heat treatment. The resistance characteristics of the core polymer are maintained. 
     Two-component fibers useful in the present development are those constituted by fibers having the following combinations of sheath/core polymers: polyethylene/polypropylene, polyethylvinylacetate/polypropylene, polyethylene/polyester, polypropylene/polyester, copolyester/polyester. 
     The two-component fibers can be either concentric or eccentric. Eccentricity is related to section of the bicomponent fiber and depends on how the sheath is centered or not around the core section. 
     The length of the fibers may vary depending on the properties of the fibers and the manufacturing method of the NWF. Typically, the fibers of the present development have a length of 0.3-7.5 cm, preferably 0.4-3.0 cm. The diameter of the fibers is generally expressed in deniers (grams per 9.000 m of fiber) or in decitex (grams per 10.000 m of fiber). For the present development, the fibers have a decitex in the range of &lt;1 decitex (e.g. 0.4 decitex) up to about 20 decitex. 
     TNT is generally bonded in order to acquire sufficient integrity and resistance. The technologies widely used for this purpose are: chemical bonding and thermal bonding, by merging part of the web. In the latter case, the fibers can be compressed in separate points that can constitute a significant part of the NWF area. In particular, for structures where it is desired to maintain a low density of the material it is useful to apply the “air-through bonding”. In this case, part of the fibers (for example the coat of the two-component fibers) are melted by the use of hot air passing through the web. As the web cools, the partially fused fibers bond with each other at the points where they came into contact. 
     In some embodiments of the present development, the NWF used can be an airthrough bonded, a carded thermobonded, spunbonded, or spunbond-meltblown-spunbond. The weight of the NWF can be varied according to specific needs. In general, TNWF can be used with weights of 6-150 grams/m 2  (gsm) and more preferably 8-20 gsm. The weights are intended to be measured in according to ASTM D3776. 
     In summary, the total thickness of the first layer can vary from 350 to 1.000 microns and more preferably from 500 to 800 microns. The thicknesses are intended to be measured in accordance with EDANA 30.5-99. 
     Some examples of manufacturing technologies to manufacture a NWF having similar characteristics are: carded air-through bonded, spunbonded, spunlaced. Finally, the TNT fibers of the first layer  11  may contain additives, in particular pigments, to make them opaque, white or coloured. 
     The second layer of sheet material  12  preferably is constituted by a plastic film, still more preferably of an olefin or polyolefin film. Said layer could also be elastic. It is also preferable that said second layer of sheet material  12  has a plurality of additional apertures, or holes,  17 , shown in  FIG. 1 , which allow the biological fluid to flow towards the other elements of the absorbent article. To the second layer of sheet material  12  pigments can be added, for example titanium dioxide, to reduce, at the sight, the size of the stain formed by the biological fluid absorbed and to mask its colour. 
     The holes  15  passing between the first layer  11  and the second layer  12  have a preferably tapered shape, in particular conical; alternatively, such holes  15 , as shown in  FIG. 1 , may have cylindrical geometry. Indicatively, said holes  15  have a diameter of the order of 0.5 mm. 
     The openings  17  on the second layer  12  have preferably a conical, or alternatively, a cylindrical geometry. 
     The holes  15  passing between the first  11  and the second layer  12  and/or the openings  17  on the second layer  12  may have different dimensions and/or orientation to each other. 
     The arrangement and shape of the openings (round, rhomboidal, elliptical, or other) can be customized to guarantee the most suitable solution for specific application needs. 
     According to a variant embodiment, the position of the first and second layers can be reversed, for example with the second layer provided for contact with the skin of the subject. 
     Some possible variations of realization provide for the configuration of the topsheet  100  in order to make it also act as “Acquisition Distribution Layer”. This can be done by inverting the layers of sheet material  11  and  12  and properly selecting the NWF, or by dimensioning the plastic film which constitutes the second layer  12  in order to have a thickness and mechanical characteristics suitable to make it work as ADL. 
     According to a different embodiment shown in  FIG. 1   bis,  the holes  15  may be provided only onto the first or second layer. Advantageously, they are provided only on the layer which, during use, is arranged above/in proximity to the subject. In the example of  FIG. 1   bis,  the holes are present only on the first layer  11 . 
     The absorbent element  100  may also constitute a component of a multilayer structure. For example, it may be associated with a third layer of non-woven fabric. 
     With reference to  FIG. 3 , a manufacturing apparatus of the topsheet  100  above described is overall denoted by  300 . 
     The sheet materials which composed the first layer  11  and the second layer  12  mentioned above are fed to the apparatus  300 . For the sake of simplicity, these materials are here denoted with the same numerical reference of the layer that they are going to realize. This feeding occurs by known means, for example return and/or feed rollers, schematically shown in the figure, which will not be further described. 
     The apparatus  300  realizes the topsheet  100  mainly through a sequence of embossing, coupling, joining and piercing phases of the sheet materials. 
     In particular, the apparatus  300  comprises a rotating embossing roller  310  having a plurality of first protruding elements  31  and configured to be engaged, in use, by the first sheet material  11 . 
     The embossing roller  310  cooperates in rotation with a counter-roller, in particular a pierced roller  320  coupled to it according to opposite rotation directions, as shown in the figure. The pierced roller  320  comprises a plurality of cavities  32 , each suitable for receiving a respective protruding element  31  of the embossing roller  310  during a rotation in phase of the rollers themselves. The pierced roller  320  preferably also comprises a second plurality of protruding elements  33 , the latter better visible in  FIG. 6 . 
     The configuration is such that the first protruding elements  31  cooperate with the cavities  32  to deform the material  11  by embossing. In particular, during the relative rotation a protruding element  31  engages a cavity  32  with interposition of the material  11 , realizing one of the protrusions  13  on the latter material  11 . 
     The pierced roller  320  is also fed with the second material  12  which is superimposed on the first material  11  downstream of the deformation of the latter. 
     In addition, the apparatus  300  advantageously comprises a joining and piercing unit  330 , arranged downstream of the roller portion on which the overlapping of the two materials occurs. In particular, in the present example the unit  330  is in a diametrically opposite position with respect to the roller portion at which the engagement and piercing of the first material  11  take place. 
     The unit  330 , cooperating with the protruding elements  33  on the pierced roller  320 , realizes a plurality of through holes  15  which pass through the first material  11  and the second material  12  at the intermediate zones  14 , that are substantially free of protrusions  13 . The same unit  300  then joins, in proximity of the holes  15 , the first material  11  and the second material  12 . Preferably, the joining occurs along the perimeter defining the holes  15 . 
     Preferably, the joining and piercing unit  330  uses an ultrasonic technology; alternatively, said unit  330  can join the first material  11  and the second material  12  by thermal or mechanical action, for example by the selective application of pressure and depression. 
     Ultrasounds allow to pierce the material at a higher speed, ensuring a more productive use of production lines. 
     In a variant embodiment, the unit  330  performs just a joining of the two materials  11  and  12 , while the piercing is performed only on the first or second layer, advantageously upstream of said joining. 
     In an alternative embodiment, shown in  FIG. 4 , the manufacturing apparatus  300 ′ comprises one or more kiss rollers  340 , coupled in rotation to the embossing roller  310  and/or to the pierced roller  320 . 
     The kiss rollers  340  draw on the surfactant agent  16 , for example from a tank or tub, and transfer the latter to the surface of the embossing roller  310  and/or of the pierced roller  320  with which they cooperate. Hence, by the physical contact with the embossing roller  310  and the pierced roller  320 , the surfactant agent  16  is transferred to the material  11 . 
     In another variant embodiment, the surfactant agent can be applied by means of kiss roll or equivalent means also to the second material. 
     Moreover, the arrangement of the application means of the surfactant agent can be such that to allow a selective application only at selected areas, for example at or in proximity of the walls of the holes. 
     In possible alternative embodiments of apparatus  300 , no one kiss roller  340  is present. In this case, the surfactant agent  16  may already be present in the first material  11 , for example applied to the fibers that constitute the NWF, and/or the surfactant agent  16  may have been applied to the second material  12 , for example added in a mixture to the resins of the plastic film and being present on the surface of the film after a migration. 
     In general terms, the shape of the cavities obtained in the first material  11  is adjusted by selecting the shape of the first protruding elements  31  on the embossing roller  310  and/or the cavities  32  on the pierced roller  320  and/or by their mutual distance and arrangement. 
     In a preferred embodiment, shown in  FIG. 5 , the first protruding elements  31  of the embossing roller  310  have cylindrical geometry. In possible embodiment variants, the geometry of these protruding elements  31  is hemi-spherical. In an exemplary implementation, the diameter of the first protruding elements is about 2 mm. 
     In a preferred embodiment, shown in  FIG. 6 , the cavities  32  of the pierced roller  320  have a cylindrical geometry. Alternatively, such cavities may have hemi-spherical geometry. Similarly to the first protruding elements  31  with which they cooperate, the cavities  32 , in an implementation example, have a diameter of about 2 mm. 
     Preferably, the second protruding elements  33  on the pierced roller  320 , which give rise to the through holes  15 , have a tapered profile, in particular cylindrical or frusto-conical. Alternatively, these protruding elements  33  may have cylindrical geometry, as shown in  FIG. 6 . In general, the diameter of said second protruding elements is about 0.5 mm. 
     Depending on the specific applications, the described absorbent element can be used by using the first layer of sheet material  11  as top layer and the second layer of sheet material  12  as bottom element, or vice versa. 
     The present invention has been so far described with reference to preferred embodiments. It is to be understood that other embodiments which belong to the same inventive core may exist, as defined by the scope of the protection of the claims set forth below.