Patent Publication Number: US-2003228822-A1

Title: Cleansing tissue

Description:
[0001] The present invention is related to a cleansing tissue, especially a pre-wet cleansing tissue.  
       BACKGROUND OF THE INVENTION  
       [0002] Several fabrics are known in the state of the art to be applied for cleaning purposes, especially for cleaning parts of the human body. Generally, the fabrics used in the manufacture of cleaning products are manufactured by a process that does not involve any weaving operation, so such fabrics are called “non-woven” fabrics.  
       [0003] The non-woven fabrics need to have specific characteristics, mainly concerned with the softness and thickness, to suitably provide an efficient and pleasing cleanness.  
       [0004] To provide such characteristics, several manufacturing processes can be used, amongst which we have card and bind, thermobonding, spunbonding, meltblown, airlaid (air flow), spunlace (water jet) and hydrospun.  
       [0005] For the manufacture of deansing tissues, such as wet cleansing tissues, a basic feature to be considered is the possibility of producing non-woven fabrics that are thick, soft and capable of absorbing liquids. It is noted that cellulose improves the absorption of liquids from fabrics.  
       [0006] Meltblown and spunlace processes provide non-woven structures having a sufficient thickness and softness, the latter (spunlace) also allowing the use of cellulose, which is known to provide higher mechanical strength and higher capacity to absorb liquids from fabrics. The great shortcoming these processes at present, however, is that they are extremely expensive, the consequence of which is that the final cost of the product increases significantly.  
       [0007] The processes known to involve low costs do not completely satisfy the required characteristics for cleansing tissues, since non-woven fabrics so produced have a structure substantially comprised of high density and low thickness regions, making them not desirable. FIG. 1 illustrates a portion of a non-woven fabric  1  produced by a thermobonding process of the prior art, wherein small and low density regions  2  are disposed amongst high density regions  3 . Consequently, the products obtained do not suitably have the combination of softness and liquid absorption.  
       [0008] An objective of the present invention is therefore to provide a cleansing tissue and the process for the manufacture thereof, having a low manufacture cost.  
       [0009] A second objective of the present invention is to provide a thick and soft cleansing tissue having both a high capacity of retaining fluid and a high wettability.  
       SUMMARY OF THE INVENTION  
       [0010] The objectives above are attained by means of a cleansing tissue, comprising a thermobonding non-woven fabric formed from a mixture of fibers containing at least 76% of thermoplastic fibers, the non-woven fabric having a plurality of cells, each cell having a first density and a first volume, the cells being disposed adjacent to one another defining a region between adjacent cells, the region having a second density and a second volume, the second density being higher than the first density, and the second volume being less than the first volume. In the preferred embodiments, said non-woven fabric may comprise thermoplastic fibers or a mixture of thermoplastic fibers and cellulosic fibers.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011] The Figures are briefly described below:  
     [0012]FIG. 1 is a view of the arrangement of known non-woven fabric cells.  
     [0013]FIG. 2 is a view of the arrangement of a non-woven fabric cells of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0014]FIG. 2 illustrates the embodiment of a cleansing tissue, specially a pre-wet cleansing tissue of the present invention. It can be seen that this non-woven fabric  4  comprises a plurality of cells  6  disposed adjacent to one another, uniformly or not, particularly in the form of a honeycomb. Adjacent cells  6  define a wall between them, forming a region  5  between cells, so that a wall is common to at least two adjacent cells  6 . Alternatively, cells  6  can be provided with several forms, provided that defining walls between them. Each cell  6  have a first density and a first volume, and the region  5  between cells has a second density and a second volume. Due to the process of manufacturing this fabric, which will be disclosed below, the second density of the region  5  between cells is higher than the first density of the cells  6  and the second volume of the region  5  between cells is less than the first volume of the cells  6 . In addition, the fact that cells  6  have large sized low density regions makes the fabric thicker, as well as intensifies its softness.  
     [0015] In the process of manufacturing this fabric, preferably polypropylene fibers and rayon fibers are homogeneously mixed in a mixing and blending chamber, and then formed into cards to compose a fibrous web. It should be noticed, however, that other thermoplastic fibers, or even a combination of thermoplastic fiber with cellulose fibers, could be used without departing from the scope of the present invention.  
     [0016] After the preparation of the fibrous screen, it is fed into a calendering station, which comprises at least two calendering rolls: a hot flat roll and a patterned embossing roll having protruding walls in a shape that will define the cells  6  to be formed. This patterned embossing roll deforms the fibrous web, fusing the thermoplastic fibers in the regions determined by the protruding walls (forming the region  5  between cells), reducing the thickness and consequently increasing the density in this region, forming a non-woven fabric composed of a plurality of cells uniformly disposed in the shape of a honeycomb, the cells  6  being determined by the fused region  5  between cells, as illustrated in FIG. 2. It should be noted that (i) the cells  6  have a higher thickness, since they are not formed by fused fibers and (ii) the shape of the cells is determined by the embossing of the roll. In other words, if, instead of having a hexagon-shaped embossing, the roll had a pentagon-shaped embossing, for example, the cells  6  of the non-woven fabric would have such shapes.  
     [0017] The process for manufacturing cleansing tissue described above makes it possible to obtain a product different from the others obtained through thermobonding already known of the state of the art, in view of the fact that a very thick product can be obtained because it is basically composed of a low density cells.  
     [0018] The fact that the rayon textile fiber is present in the fibrous structure together with the thermoplastic fiber makes it possible to obtain an additional wetability due to the chemical absorbency of polar chemical groups of the regenerated cellulose, herein called rayon or viscose.  
     [0019] In an further embodiment of the present invention, the cleansing tissue of the present invention can also include opacifying agents or dyeing agents, such as TiO 2  or the like, providing an easy color pigmentation in the thermoplastic polypropylene fiber and an easy combination of colors during the process for the preparation of the fibrous web.  
     [0020] The process of the present invention also makes it possible to obtain a highly flexible fabric, since several fast adjustments in the control of the polymer mass addition, in the control of the fiber denier within a large range of deniers, and in the control of the fiber cut length within a large range of lengths can be made in the process for the preparation of the fibrous web, as well as the possibility of producing textile fibers having one or several denier with cut dimensions of one or several lengths. In addition, said flexibility, also makes it possible to use a large variety of polypropylene and rayon textile fibers. More specifically, the present invention makes it possible to use several ranges of varying parameters, such as different fiber denier (the thickness unit for silk yams and artificial fibers such as rayon and nylon, equal to the thickness of a yarn that weighs 0.05 g every 450 m of length or 1 g every 9,000 m), addition of fibers, fiber mixture, fiber size and several levels of basis weight of the thermobonded fabric. The web has a basis weight of 20 to 60 grams per square meter.  
     [0021] In the preferred embodiment of the present invention, a mixture containing greater than about 75% of thermoplastic fibers is used, preferably a mixture of polypropylene fiber and rayon fiber at a 95%:5% to substantially 76:24% ratio, and more preferably at 90%:10% and 80%:20% ratios can be considered.  
     [0022] Preferably, the polypropylene fiber has a denier between 0.5 and 5.0 denier, more preferably in the 0.8 to 4.0 range, and still more preferably in the 1.3 to 1.5 range.  
     [0023] The rayon fiber can have the same denier range above, however the preferred value specifically ranges between 0.8 and 3.  
     [0024] Both rayon fibers and polypropylene fibers are processed in a 30 mm to 60 mm cut size range, and even a mixture of one or several sizes can be used in the present invention.  
     [0025] The thickness of the tissue subject of this invention varies preferably between 250 to 800 micrometers, and a comparison between already known thermobonded tissue and the present tissue is in the following table 1:  
                                                   Base weight (g/m 2 )   Thickness (micrometers)                                                Known thermobonded   20   200       tissue   45   350       Tissue of present   20   280       invention   45   600                  
 
     [0026] As can be seen in the table above, the thermobonded formed tissue object of this invention is at least 40% thicker than conventional thermobonded formed tissues. These comparison can be measured by a test procedure TN 253.  
     [0027] With respect to the TiO 2  content, it can be in the 0 to 3% range, and preferably in the 0.5 to 2% range for the polypropylene fiber. In its turn, the rayon fiber has a 0% to 1.5% TiO 2  content as an opacifying agent.  
     [0028] In addition, colored fibers can be produced by using available standard industrial pigments available in polypropylene manufacturing plants.  
     [0029] In accordance with a preferred embodiment of the present invention, the polypropylene fiber is treated with a surface finishing surfactant in order to attain a suitable hydrophilic control of the thermobonded fabric.  
     [0030] The control of the surface energy in the polypropylene fiber range can be attained by applying the surfactant in the polypropylene weaving process (in 30 to 72 dyne/cm 2  range). The surface energy of the rayon fibers is approximately 72 dyne/cm 2 , thus promoting the wettability in both types of related fibers and fabrics.  
     [0031] To better illustrate the advantages of the present invention, let us consider two areas of comparison, such as the areas shown in FIGS. 1 and 2.  
     [0032] The relief configurations of the two areas shown in FIGS. 1 and 2 follow the standard below:  
     [0033] Honeycomb configuration (FIG. 2)—approximately 6.25 cells/area;  
     [0034] Pointed configuration (FIG. 1)—approximately 30 points/area.  
     [0035] In FIG. 1, the areas of the cells shown have the following values:  
     [0036] Area 1—37.6670  
     [0037] Area 2—35.6920  
     [0038] Area 3—37.4697  
     [0039] Area 4—34.5172  
     [0040] Area 5—34.8073  
     [0041] Area 6—34.1308  
     [0042] Area 7—35.7971  
     [0043] Area 8—45.4778  
     [0044] Area 9—31.4983  
     [0045] Area 10—37.2842  
     [0046] Area 11—38.1189  
     [0047] Area 12—38.5612  
     [0048] Area 13—34.5146  
     [0049] Area 14—29.0410  
     [0050] Area 15—31.3793  
     [0051] Area 16—39.4947  
     [0052] Area 17—35.7229  
     [0053] Area 18—42.9106  
     [0054] Area 19—35.3365  
     [0055] Area 20—23.2021  
     [0056] Area 21—37.5624  
     [0057] Area 22—40.9941  
     [0058] Area 23—15.4413  
     [0059] Area 24—31.7039  
     [0060] Area 25—31.9049  
     [0061] Area 26—35.9084  
     [0062] Area 27—35.9239  
     [0063] Area 28—14.9239  
     [0064] Area 29—10.2084  
     [0065] Area 30—8.8107  
     [0066] In FIG. 2, the areas of the pointed relief shown have the following values:  
     [0067] Area 1—126.9520  
     [0068] Area 2—67.5332  
     [0069] Area 3—681.8963  
     [0070] Area 4—4.7257  
     [0071] Area 5—263.2115  
     [0072] Area 6—1121.0791  
     [0073] Area 7—241.0448  
     [0074] Area 8—1396.5022  
     [0075] Area 9—222.6300  
     [0076] Area 10—171.7930  
     [0077] Area 11—896.0243  
     [0078] Area 12—11.8360  
     [0079] It can be seen that the area of each cell in the honeycomb is on the average 53% larger than the area of point relief.  
     [0080] Let us assume that the following comparative data are obtained, in which:  
     [0081] MD corresponds to a cut in the “machine direction” 
     [0082] CD corresponds to a cut in the transversal direction, and  
     [0083] 45° corresponds to a cut in the 45° direction.  
               TABLE 2                          Comparative table between the honeycomb structure and the pointed       structure                             Linking                                         Percentage of linking area   Surface Area                                         Standard   (fused area/total area)   MD   CD   45°                                                     Points   16%   597   410   392           Walls   12%   773   752   598       Difference   Higher    4%    30%    80%    50%                  
 
     [0084] From the data above, we can conclude as follows:  
     [0085] A—With respect to a low density cells (3—FIG. 1; 6—FIG. 2): The honeycomb structure has 30/6.25 more a low density regions than the structure of the state of the art.  
     [0086] B—With respect to the area of a low density cells:  
     [0087] (1) The honeycomb structure has average that is 4% higher.  
     [0088] (2) The honeycomb structure is 4 to 5 times higher than the pointed pattern with respect to the amount of free fibers, due to the formation of cells in the fabric web.  
     [0089] By considering the fact that the same basis weight of the honeycomb and pointed structures has been maintained for the data above, as well as the same fiber compositions of the analyzed structures, we can get a estimate of the thickness increment by using a ratio between the following parameters:  
                                                       Symbol   Property   Unit                          Df   Cell fiber diameter   μm           D   Cell fiber denier   g/9,000 m           ρfiber   Cell fiber specific mass   g/cm 3             W   Fabric base weight   g/cm 2             θ   Fabric thickness   Mm           ρfabric   Fabric specific mass   g/cm 3             Vf   Void fraction   air/fiber                      
 
     [0090] For similar fabric structures, the increment in the volume is related with the increment of the screen void fraction.  
     [0091] The void fraction of a fabric can be calculated by using the following equation:  
       Vf= 1−1.335( W /θρfiber)  
     [0092] By calculating Vf for the honeycomb and pointed structures in described, we have the following results:  
     [0093] Honeycomb—Vf=13.3/1  
     [0094] Pointed—Vf=7.6/1  
     [0095] The result of this relationship for the increment in the thickness is 13.3/7.6, that is, approximately 76% of the apparent additional volume of the fabric (in the honeycomb structure), when compared with the pointed structure fabric.  
     [0096] Considering the results of items A and B above and considering the calculation the void fraction, the honeycomb structure presents a larger area of free surface fibers, as well as a higher volume of the screen due to the relief of the cells when compared with the standard pointed structure.  
     [0097] Also considering that the surface area and the apparent volume of the non-woven structure is a function of the a low density cells, we can express the following relationship, which is related with the comparison of the pointed and honeycomb structures.  
                                                   Cell surface area   Cell volume                                                        Pointed structure   1   1           Honeycomb structure   1.53   1.75                      
 
     [0098] Thus, it can be seen that the honeycomb pattern of the present invention results in a free fiber cell with 53% more area and 75% more volume.  
     [0099] After having been described the examples of preferred embodiments, it should be understood that the scope of the present invention covers other possible variations, being limited only by the appended claims, wherein the possible equivalents are included