Abstract:
A fibrous nonwoven sheet is electrophotographically printed with a given pattern and formed with a fibrous nonwoven fabric wherein toner has an outer layer slightly permeating the nonwoven fabric through its surface and deposited around fibers lying in the vicinity of the surface of the nonwoven fabric and an inner layer deposited around fibers immediately underlying the surface and wherein respective pairs of adjacent portions of the toner are not mingled together and present on the nonwoven fabric in the form of a plurality of independent dots.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a fibrous nonwoven sheet printed with a given pattern using an electrophotographic process.  
           [0002]    Japanese Patent Application Publication No. 2000-266A describes a body fluid absorbent wearing article including a sheet member printed with a pattern being visible from the outside using an inkjet process. The articled is closed in this Publication requires no stereotyped roll as gravure or flexography requires and allows the sheet member to be quickly printed with various patterns by a printer or a plotter using a so-called ink jet process.  
           [0003]    The ink jet process has conventionally used a super-penetrant liquid ink in order to avoid undesirable color bleeding with respect to the sheet member. The Publication describes an example of the sheet member used as the component of the wearing article, which is formed with a plurality of thermoplastic synthetic resin fibers and printed with a pattern using the ink jet process. However, if the super-penetrant ink is used, the ink may permeate the nonwoven fabric through its surface and spread therein until the pattern is made indistinct due to bleeding of the ink and the color tone of the pattern is varied due to mingling of the ink.  
         SUMMARY OF THE INVENTION  
         [0004]    It is an object of this invention to provide a fibrous nonwoven sheet printed with a pattern adapted to maintain its distinctness substantially without variation in its color tone.  
           [0005]    According to this invention, there is provided a fibrous nonwoven sheet printed with a given pattern using an electrophotographic process comprising the steps of photoconductively forming an electrostatic latent image on a photosensitive body, electrostatically depositing colored toner (charged fine grains) on the electrostatic latent image to convert the electrostatic latent image to the corresponding visible image and transferring the visible image onto a surface of the fibrous nonwoven sheet.  
           [0006]    The improvement according to this invention is in that the fibrous nonwoven sheet is a plurality of thermoplastic synthetic resin fibers and having a given thickness, the toner has having an outer layer slightly permeating the fibrous nonwoven sheet through its surface and deposited around fibers lying in a vicinity of the surface of the fibrous nonwoven sheet and an inner layer deposited around fibers immediately underlying the surface and respective pairs of adjacent portions of the toner being not mingled together and present on the fibrous nonwoven sheet in the form of a plurality of independent dots.  
           [0007]    According to one preferred embodiment of this invention, the outer layer has a thickness dimension in a range of 1˜100 μm.  
           [0008]    The outer layer exposed on the surface of the fibrous nonwoven sheet has a surface area in a range of 10˜100 μm.  
           [0009]    According to still another preferred embodiment of this invention, a thickness dimension of the toner inclusive of the outer layer and the inner layer is 10 μm or larger and less than a thickness of the fibrous nonwoven sheet itself.  
           [0010]    According to further another preferred embodiment of this invention, the sheet member is used as at least a liquid-impervious backsheet in disposable body fluid absorbent wearing article comprising a liquid-pervious topsheet, said liquid-impervious backsheet and a liquid-absorbent core disposed between the top- and backsheets. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a perspective view of a fibrous nonwoven sheet according to this invention;  
         [0012]    [0012]FIG. 2 is a fragmentary perspective view showing a part of the fibrous nonwoven sheet of FIG. 1 in an enlarged scale;  
         [0013]    [0013]FIG. 3 is a sectional view taken along a line A-A in FIG. 2;  
         [0014]    [0014]FIG. 4 is a diagram illustrating an example of electrophotographic printing process;  
         [0015]    [0015]FIG. 5 is a perspective view of a disposable diaper using a fibrous nonwoven sheet printed with a pattern; and  
         [0016]    [0016]FIG. 6 is a perspective view of a package using a fibrous nonwoven sheet printed with the pattern. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    Details of a fibrous nonwoven sheet according to this invention will be more fully understood from the description given hereunder with reference to the accompanying drawings.  
         [0018]    [0018]FIG. 1 is a perspective view of a sheet member  1 , FIG. 2 is a fragmentary perspective view showing a part of a fibrous nonwoven sheet (fabric)  1  of FIG. 1 in an enlarged scale and FIG. 3 is a sectional view taken along a line A-A in FIG. 2. The fibrous nonwoven sheet  1  is printed with a pattern  3  (a plurality of individually paper-wrapped candy balls) using the so-called electrophotographic printing process as will be described more in details. The pattern  3  is defined by toner  4  deposited on the fibrous nonwoven sheet.  
         [0019]    The fibrous nonwoven sheet  1  comprises a fibrous nonwoven fabric  2  formed with a plurality of thermoplastic synthetic resin fibers and having a predetermined thickness. The nonwoven fabric  2  may be selected from those made by spun lace- and needle punch-processes in which the component fibers are mechanically entangled and those made by melt blown-, thermal bond-, spun bond-, chemical bond- and air through-processes in which the component fibers are hot welded or bonded by means of adhesive together at points of entanglement.  
         [0020]    It is also possible to use composite a nonwoven fabric consisting of a melt blown nonwoven fabric having a high water-resistance and two layers of a spun bond nonwoven fabric having high strength and flexibility sandwiching the melt blown nonwoven fabric.  
         [0021]    Component fiber of the nonwoven fabric may be selected from a group including polyolefine-, polyester- and polyamide-based fibers and polyethylene/polypropylene or polyethylene/polyester core-sheath type conjugated fiber and side-by-side-type conjugated fiber.  
         [0022]    The nonwoven fabric  2  is preferably surface treated with corona discharge or plasma discharge to improve a wettability of the nonwoven fabric′ surface to 40 dyn/cm or higher and thereby to improve a printability, or the surface of the nonwoven fabric  2  is preferably coated with resin primer in order to achieve such an improvement.  
         [0023]    The toner  4  slightly permeates also into the nonwoven fabric  2  in a direction of its thickness through the surface thereof so that the toner  4  is partially deposited to fibers  2   a  lying on the surface of the nonwoven fabric  2  to define an outer layer  4   a  exposed on the surface of the nonwoven fabric  2  and partially deposited to fibers  2   b  lying in the interior of the nonwoven fabric  2  to define an inner layer  4   b  being contiguous to the outer layer  4   a.  Each pair of the individual fine toner portions  4  lying adjacent are not mixed together and these individual toner portions  4  are present in the nonwoven fabric  2  in the form of a plurality of dots.  
         [0024]    While the toner  4  may slightly permeate the nonwoven fabric  2  through its surface, it never occurs that the toner  4  might permeate and spread throughout the nonwoven fabric  2 . Thus, there occurs neither indistinctness of the pattern due to the toner  4  spreading nor unintentional variation in the color tone due to the toner portions  4  mixed together.  
         [0025]    The outer layer  4   a  of the toner  4  has a thickness dimension in a range of 1˜100 μm. Strictly to describe, the outer layer  4   a  has its thickness dimension L 1  in a range of 1˜10 μ. In the case of the outer layer  4   a  having its thickness dimension L 1  less than 1 μm, a desired diffused reflection of light on this outer layer  4 a would become difficult and the color tone of the outer layer  4   a  would largely depend on the angle of sight. Variation of the color tone in the outer layer  4   a  may blur the surface color based on the diffused reflection of the light on the surface of the nonwoven fabric  2  and may lead to a corresponding indistinctness of the pattern  3 . In the case of the outer layer  4   a  having its thickness dimension L 1  exceeding 100 μm, the outer layer  4   a  of the toner  4  would be readily collapsed depending on a fastness of the toner  4  and, if collapsed, the diffused reflection of the light in the outer layer  4   a  would become difficult. Like the case in which the outer layer  4   a  has its thickness dimension L 1  less than 1 μm.  
         [0026]    A surface area of the outer layer  4   a  of the toner  4  exposed on the surface of the nonwoven fabric  2  is in a range of 10˜100 μm 2 . With the surface area of the outer layer  4   a  being less than 10 μm 2 , the desired diffused reflection of the light on the outer layer  4   a  would become difficult and the surface color would be blurred to make the pattern  3  indistinct like the case in which the outer layer  4   a  has its thickness dimension L 1  less than 1 μm. With the surface area of the outer layer  4   a  exceeding 100 μm 2 , the surface of the nonwoven fabric  2  would be able to a resolution sufficient to represent details of the pattern  3  distinctly. It should be understood that the resolution on the surface of the nonwoven fabric  2  can be adjusted within a range of 400×400 dpi˜2,400×1,200 dpi.  
         [0027]    A total thickness dimension L 2  of the toner  4  inclusive of the outer layer  4   a  and the inner layer  4   b  is 10 μm or larger and less than the thickness of the nonwoven fabric  2  itself. With the thickness L 2  less than 10 μm, the desired diffused reflection of the light in the inner layer  4   b  would become difficult and, in consequence, the color tone of the inner layer  4   b  would be largely depend on the angle of sight. Variation of the color tone in the inner layer  4   b  would blur a transmitted color based on light absorption in the nonwoven fabric  2  and would make the pattern  3  indistinct.  
         [0028]    The toner  4  may be liquid toner or powder toner. The liquid toner may be an appropriate mixture of binder resin, colorant to color the toner, insulating liquid comprising isoparaffin-based organic solvent, charge regulating agent serving to provide the toner with a polarity. The colorant may be selected from a group of various pigments such as carbon black, C.I. pigment Yellow 12, C.I. Pigment Red 48, C.I. Pigment Blue 15. For full color printing, color toners of yellow, magenta and cyan may be placed one upon another to express colorful effect.  
         [0029]    [0029]FIG. 4 is a diagram illustrating an example of electrophotographic printing process, in which a rotating direction of a photosensitive drum  11  is indicated by an arrow X and a travelling direction is indicated by an arrow Y. The electrophotographic process comprises the steps of charging, exposure, development, transfer and cleaning. Specifically, an electrostatic latent image is photoconductively formed on a peripheral surface of the photosensitive drum  11 , the colored toner  4  (charged fine grains) is electrostatically deposited on the electrostatic latent image to convert the latent image to a visible image and the visible image formed by the toner  4  is transferred to the surface of the sheet member  1 .  
         [0030]    The step of charging comprises a step of uniformly charging the peripheral surface of the photosensitive drum  11  with positive ions using the corona discharge from an electrifying device  10 . The step of exposure comprises a step of irradiating with the peripheral surface of the photosensitive drum  11  with the light rays emitted from an exposure device  12  and reflected on the original so that the charge on a region other than image region may be erased and the image region may remain charged (in the case of copying machine) or irradiating the image region with laser beam or LED beam from the exposure device  12  so that the charge on the image region may be erased (in the case of printer). The step of exposure forms on the peripheral surface of the photosensitive drum with the electrostatic latent image.  
         [0031]    The step of development comprises a step of using a development device  13  to deposit the negatively charged toner  4  on the electrostatic latent image formed on the peripheral surface of the photosensitive drum  11  under the electrostatic effect to convert this electrostatic latent image to the visible image. Below the development device  13 , there is provided a drum-like developer  14  in contact with the photosensitive drum  11 .  
         [0032]    The step of transfer comprises a step of transferring the visible image formed by the toner  4  to the fibrous nonwoven sheet  1  using a transfer roll  15  normally in contact with the peripheral surface of the photosensitive drum  11 . Am example of this step is a so-called electrostatic transfer process, in which the fibrous nonwoven sheet  1  is electrified with the positive charge opposite to that of the toner  4  and the toner  4  is transferred from the peripheral surface of the transfer roll  15  to the fibrous nonwoven sheet  1 . An impression drum  16  underlies the transfer roll  15  so that the impression drum  16  may press the fibrous nonwoven sheet  1  against the peripheral surface of the transfer roll  14 .  
         [0033]    The step of cleaning comprises a step of removing the residual toner  4  from the peripheral surface of the photosensitive drum  11 . An example of this step is a so-called blade cleaning step comprising steps of erasing the charge on the peripheral surface of the photosensitive drum I 1  by a charge eraser  17  and bringing a cleaner  18  having an urethane rubber blade in contact with the peripheral surface of the photosensitive drum  11 .  
         [0034]    [0034]FIG. 5 is a perspective view of a disposable diaper  20  using the nonwoven fabric  2  printed with the pattern  3 . The diaper  20  basically comprises a liquid-pervious topsheet  21 , a liquid-impervious backsheet  22  and a liquid-absorbent core  23  disposed between the top- and backsheets  21 ,  22  and having its entire surface covered with and bonded to water-pervious tissue paper. The core  23  is bonded to at least one of the top- and backsheets  21 ,  22  with the tissue paper therebetween. This diaper  20  uses the nonwoven fabric  2  printed with the pattern  3  by the electrophotographic process as the backsheet  22 .  
         [0035]    The diaper  20  is composed, in the longitudinal direction, of a front waist region  24 , a rear waist region  26  and a crotch region  25  extending between the front and rear waist regions  24 ,  26 . The top- and backsheets  24 ,  26  have their transversely opposite side edge portions put flat and bonded to each other to define a waist-opening  27  and a pair of leg-openings  28 .  
         [0036]    An elastic member  29  comprising a plurality of elastic elements extending in a waist-surrounding direction are secured under tension to a peripheral edge portion of the waist-opening  27  so that this elastic member  29  is associated with the waist-opening  27 . Similarly, elastic members  30  each comprising a plurality of elastic elements extending in a leg-surrounding direction are secured under tension to peripheral edges portions of the respective leg-openings  28  so that these elastic members  30  are associated with the leg-openings  28 .  
         [0037]    In this diaper  20 , even when the backsheet  22  is curved as a wearer&#39;s body moves and, in consequence, an angle of sight with respect to the pattern  3  correspondingly varies, no change of color tone occurs in both the outer layer  4   a  and the inner layer  4   b  of the tone grains  4  so significant to make the pattern  3  indistinct. This is because a diffused reflection occurs in both the outer layer  4   a  and the inner layer  4   b  of the toner  4 .  
         [0038]    The topsheet  21  may be formed with the liquid-pervious sheet such as a hydrophilic nonwoven fabric or porous plastic film. The backsheet  22  may be formed with a hydrophobic nonwoven fabric or a laminated sheet consisting of the liquid-impervious plastic film placed upon the hydrophobic nonwoven fabric.  
         [0039]    The core  23  is a mixture of fluff pulp, high absorption polymer particles and thermoplastic synthetic resin fiber compressed to a desired thickness. The high absorption polymer may be selected from a group including starch-, cellulose-based polymer and synthetic polymer.  
         [0040]    Bonding of the top- and backsheets  21 ,  22  together, bonding of the core  23  and bonding of the elastic members  29 ,  30  may be carried out using a suitable adhesive agent such as a hot melt adhesive agent or a technique of welding such as a heat- or sonic-sealing.  
         [0041]    [0041]FIG. 6 is a perspective view of a package  30  using the nonwoven fabric  2  printed with the pattern  3  by the electrophotographic process. The package  30  has its side faces printed with the same patterns  3  as in the diaper  20  of FIG. 5. A plurality of the folded diapers  20  are packed within the package  30 .  
         [0042]    The fibrous nonwoven sheet  1  according to this invention is applicable not only to the disposable diaper but also to a other body fluid absorbent wearing article such as a diaper cover, a training pant, a pant for incontinent patient or a sanitary napkin.  
         [0043]    The fibrous nonwoven sheet according to this invention is formed with a nonwoven fabric electrophotographically printed with a given pattern. While the toner may slightly permeate the nonwoven fabric, there is less likely that the toner might permeate the nonwoven fabric to its interior and spread therein. Therefore, it is not concerned that the toner might run so as to make the pattern indistinct and/or mingled together to cause unintentional variation of the color tone.  
         [0044]    In the sheet member according to this invention, the outer layer of the toner  4  has its thickness dimension in a range of 1˜100 μm and has its surface area exposed on the surface of the nonwoven fabric in a range of 10˜100 μm 2 . With such dimensioning, the desired diffused reflection of the light is ensured in the outer layer and the color tone in this outer layer is substantially free from any remarkable affection of a variation in the angle of sight. Additionally, the total thickness dimension of the toner inclusive of the outer and inner layers is 10 μm or larger and less than the thickness of the nonwoven fabric itself. With such dimensioning, the desired diffused reflection of the light is ensured in the inner layer and the color tone is substantially not affected by a variation in the angle of sight. In this manner, the sheet member according to this invention allows the patter to maintain its distinctness independently of a variation in the angle of sight.  
         [0045]    With the disposable body fluid absorbent wearing article using the fibrous nonwoven sheet according to this invention as the backsheet, the desired diffused reflection of light occurs in both the outer layer and the inner layer of the toner even when the angle of sight with respect to the pattern varies as the backsheet is curved. Therefore, a difference in the color tone between the outer and inner layers is minimized. In other words, the pattern printed on the backsheet are distinctly seen independently of a variation in the angle of sight.