Patent Publication Number: US-2005116976-A1

Title: Method of inkjet printing in high efficiency production of hygienic articles

Description:
FIELD OF INVENTION  
      This invention relates to a method of inkjet printing in high-efficiency production of hygienic articles having print images.  
     BACKGROUND OF THE INVENTION  
      Hygienic articles, such as disposable absorbent articles, including feminine hygiene articles, baby diapers, baby pull-on articles, adult incontinence articles, and the like, including images printed on inner and/or outer surfaces thereof have been disclosed in a copending, commonly assigned U.S. application Ser. No. 10/025,059, filed on Dec. 19, 2001, which is hereby incorporated herein by reference.  
      The print images can be single-tone, multi-tone, single-color, or multi-color. These images should be visible to the consumer in order to provide the consumer with a variety of desired benefits including improved aesthetics, product functional benefits, or consumer awareness of how good the product is. For example, a two-tone image, shown in  FIGS. 1-3 , emits a perception of depth, which can be important for the consumer expecting satisfactory liquid absorption and retention capabilities from the product. The perception of depth indicates that although the product is thin, the performance of the product will not be compromised by the thinness.  
      The print images are generally provided by printing ink on substrate materials by various printing methods, such as flexographic printing, rotogravure printing, screen-printing, ink-jet printing, and the like. Typically, the printing operations are accomplished on high-speed printing lines, separately from the converting lines that are dedicated to manufacturing disposable absorbent articles. After printing on the printing lines, the printed substrates are delivered to the converting lines, typically in a form of continuous webs comprising printed images thereon. However, the above practice of separately printing the substrates off the converting lines typically requires additional cost associated with handling, winding and unwinding, storing and shipping of the substrates. In addition, the above steps can negatively affect the quality of the printed substrate, resulting in uneven and often excessive deformations of the wound layers of the substrate inside the roll due to uneven distribution of the compression forces inside the roll. Furthermore, the separately printed substrates often require special registration control methods to ensure proper phasing of the printed images with the converting operations to effect a desired and consistent positioning of the printed image in the produced article.  
      However, combining the printing operations with converting operations on the converting lines producing disposable absorbent articles at a high-speeds and a high production efficiency can result in substantial production losses, as overall efficiency of the converting line is often compromised. This is due generally to the multiplicity and complexity of the converting operations, wherein any malfunction of any of the converting operations can affect the performance of the printing operation, and vice versa, any malfunction of the printing operation can affect the converting operations. In addition, the printing operations often require periodic maintenance procedures that can also affect the production efficiency of the converting lines. Because converting lines can be high-speed operations, producing hundreds or thousands of hygienic articles per minute, any interruption of the production process can result in substantial production losses.  
      Therefore, it would be beneficial to provide a reliable method of combining printing operations with converting operations on a converting line for high-efficiency production of hygienic articles having print images.  
     SUMMARY OF THE INVENTION  
      The present invention can provide a method of inkjet printing in a high efficiency production of hygienic articles, having print images, on a converting line including at least two inkjet print stations, wherein each of the inkjet print stations comprises at least two inkjet print heads. The method includes the steps: 
          (a) providing a substrate moving in the web direction at a first velocity;     (b) printing on the substrate a first plurality of images by a first inkjet print head of the first print station and a first inkjet print head of the second print station, both print stations being disposed in proximity to the substrate, the images are separated from each other in the web direction at a pitch interval;     (c) switching from the first inkjet print head of the first print station to a second inkjet print head of the first print station while the substrate continues its movement; and     (d) printing on the substrate a second plurality of images by the second ink-jet print head of the first print station and the first inkjet print head of the second print station, both print stations being disposed in proximity to the substrate, the images are separated from each other at the pitch interval,     wherein the first plurality of images is separated from the second plurality of images by an unprinted region in the web direction, wherein the unprinted region is no greater than 50 times the pitch interval.        

      In another aspect of the invention, the unprinted region is no greater than 10 times of the pitch interval. In yet another aspect of the invention, the unprinted region is no greater that 1 time of the pitch interval.  
      In one aspect of the invention, the step of switching between inkjet heads can include the following steps: 
          (a) initiating a second start signal by an operator to a converter controller for starting the second inkjet print head of the first print station;     (b) ceasing sending a first output signal from the converter controller to the inkjet controller; and     (c) sending a second output signal from the converter controller to the ink-jet controller.        

      In another aspect of the invention, the step of switching between inkjet heads can include the following steps: 
          (a) ceasing sending a first OK signal from the inkjet controller responding to a fail mode of the first inkjet print head of the first print station     (b) ceasing sending a first output signal from the converter controller to the inkjet controller; and     (c) starting sending a second output signal from the converter controller to the inkjet controller.        

      In yet another aspect of the invention, the first print station and the second print stations can print different inks, including different color inks. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as forming the present invention, it is believed that the invention will be better understood from the following descriptions which are taken in conjunction with the accompanying drawings in which like designations are used to designate substantially identical elements, and in which:  
       FIG. 1  is a perspective view of an exemplary hygienic article having a print image;  
       FIG. 2  is a plan view of the hygienic article of  FIG. 1 ;  
       FIG. 3  is a plan view of an alternative embodiment of a hygienic article;  
       FIG. 4  is an exemplary two-tone image shown as a gray scale image;  
       FIG. 5  is the two-tone image of  FIG. 4  shown as a pcx image;  
       FIG. 6  is a magnification of a portion of the pcx image of  FIG. 5 ;  
       FIG. 7  illustrates a side-by-side comparison of various gray scale and pcx scale images;  
       FIG. 8  is a simplified elevation view of one embodiment of the method of the present invention designed to manufacture the hygienic articles of  FIGS. 1, 2  and  3 , as well as any other hygienic article defined herein;  
       FIG. 8A  is a simplified elevation view of another embodiment of the method of the present invention designed to manufacture the hygienic articles of  FIGS. 1, 2  and  3 , as well as any other hygienic article defined herein.  
       FIG. 9  is a block diagram of one embodiment of the control system of the method of present invention;  
       FIG. 10  is a block diagram of a switching logic between the operating modes of the ink-jet print heads according to the method of the present invention;  
       FIG. 11  is a top view of a portion of a substrate having a first plurality of images and a second plurality of images separated by an unprinted region B from the first plurality of images;  
       FIG. 12  illustrates a print image having a gray level A at a resolution X;  
       FIG. 13  illustrates a print image having a gray level A at a resolution X-30%; and  
       FIG. 14  illustrates a print image having gray level A+30 at a resolution X-30%. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention will be described with respect to a disposable absorbent article, having a multi-tone signal of at least one color printed on a topsheet surface of the absorbent article, disclosed in a copending and commonly assigned U.S. patent application Ser. No. 10/025,059, filed Dec. 19, 2001. Specifically, the present invention will be described with respect to a feminine hygiene article disclosed in the above patent application. However, the present invention can be applicable to any disposable absorbent article having single-color and/or multi-color and/or single-tone and/or multi-tone images printed on the outer and/or inner surfaces to provide a variety of desired benefits including improved product performance, product aesthetics, consumer awareness, consumer perception, and the like.  
     Definitions  
      The term “hygienic article,” “disposable absorbent article,” or “absorbent article” refers herein to a device that normally absorbs and retains fluids. In certain instances, the phrase refers to devices that are placed against or in proximity to the body of the wearer to absorb and contain the excreta and/or exudates discharged from the body, and includes such personal care articles as feminine hygiene articles, baby diapers, baby pull-on articles, baby swim articles, adult incontinence articles, and the like. In other instances, the phrase refers to protective articles, such as, for example, dining bibs that have the ability to absorb food items to prevent staining of the wearer&#39;s clothing. In still other instances, the phrase refers to devices providing some therapeutic benefit, such as, for example, pain relief, wound coverage or to hold another device or article near the body.  
      The term “disposable” is used herein to describe products which generally are not intended to be laundered or otherwise restored or extensively reused in their original function, i.e., preferably they are intended to be discarded after several uses or after a single use.  
      The term “substrate” is meant herein any material, preferably in a form of a continuous web, suitable for printing an image on at least one of the opposite surfaces thereof. The term “substrate” can include a film (breathable or non-breathable), a non-woven material, a woven material, a foam material, or any combination thereof. The substrate can be a single layer or multiple layers, comprising synthetic and/or natural materials. The substrate can also include a dry lap material including wood pulp, and the like, having a single layer or multiple layers. Furthermore, the substrate can be part of any component of a hygienic article, such as, for example, a topsheet, a secondary topsheet, an insert, a backsheet, an absorbent core, or any combination thereof.  
      The term “color” as referred to herein includes any primary color, i.e., white, black, red, blue, violet, orange, yellow, green, and indigo as well as any declination thereof or mixture thereof. The term ‘non-color’ or ‘non-colored’ refers to the color white which is further defined as those colors having an L* value of at least 90, an a* value equal to 0±2, and a b* value equal to 0±2. The color scale values utilized herein can be made with a Hunter Color reflectance meter, a description of which can be found in an article by R. S. Hunter, ‘Photoelectric color difference Meter’, Journal of the Optical Society of America, Vol. 48, pp. 985-95, 1958. Devices specially designed for the measurement of color on the Hunter scales are described in U.S. Pat. No. 3,003,388 to Hunter et al., issued Oct. 10, 1961.  
      The term “feminine hygiene article” refers herein to sanitary napkins, panty liners, tampons, and incontinence articles worn by women to absorb and contain menses as well as other vaginal and incontinent exudates. Non-limiting examples of feminine hygiene articles that can be provided with a multi-tone signal that operates to create depth perception include those manufactured by The Procter &amp; Gamble Company of Cincinnati, Ohio as: ALWAYS® Pantiliners with DriWeave® manufactured according to U.S. Pat. Nos. 4,324,246; 4,463,045; and 6,004,893; ALWAYS® Ultrathin Slender Maxi with Wings manufactured according to U.S. Pat. Nos. 4,342,314, 4,463,045, 4,556,146, B1 4,589,876, 4,687,478, 4,950,264, 5,009,653, 5,267,992, and Re. 32,649; ALWAYS® Regular Maxi; ALWAYS® Ultra Maxi with Wings; ALWAYS® Maxi with Wings; ALWAYS® Ultra Long Maxi with Wings; ALWAYS® Long Super Maxi with Wings; and ALWAYS® Overnight Maxi with Wings, each aforesaid publication being incorporated by reference herein.  
      The term “pitched unit operation” refers herein to any device on a converting line, having a pitch-related function for working one or more webs in the manufacture of disposable absorbent articles. For example, the unit operation can include, but is not limited to such pitched-related web-working devices as a cutting device (e.g., a final knife), a discrete patch placing device (e.g., a cut-and-slip unit, a cut and placement unit), an embossing device having a pitched embossing pattern, a web activator device (e.g., incremental-stretch activation devices disclosed in U.S. Pat. No. 5,151,092 to Buell et al.; U.S. Pat. No. 5,156,793 to Buell et al., and U.S. Pat. No. 5,518,801 to Chappell et al.), a rotary printing device, and the like, all of which have in common that they include a manufacturing cycle corresponding to a product pitch length, which is the length of the product in a web form on a converting line before the web is cut into individual products.  
      The term “efficiency” or “reliability” of a production operation refers herein to a ratio, expressed in percents, of a production output produced during a period of seven (7) consecutive working days, 24 hours per day, to a theoretical production output that could have been produced if there were no production outages of any of the unit operations of the converting line due to malfunctions, maintenance, and the like.  
      The term “high efficiency production” referrers herein to the efficiency or reliability of a converting line producing hygienic articles, wherein the efficiency of the converting line is at least 60%, at least 70%, or at least 85%. The efficiency of the converting line depends on the efficiency of each unit operation of the converting line. For example, the efficiency of the printing operation of the present invention is about 99.7%.  
     Description  
       FIG. 1  provides a perspective view of an absorbent article  10 , which is presented herein in a form of a feminine hygiene article.  FIG. 2  provides a plan view of the absorbent article  10  of  FIG. 1 . The absorbent article  10  herein has an upper surface or user facing surface  13 , a lower surface or garment facing surface  14 , and a periphery  12 . The absorbent article  10  comprises a topsheet  25  having a viewing surface  28  facing upwardly towards the upper surface  13 . The absorbent article  10  further comprises a backsheet  15  positioned oppositely to the topsheet  25 . The backsheet  15  is joined to the topsheet  25  preferably at least partially at the periphery  12 . The absorbent article  10  also comprises an absorbent core  20  positioned between the topsheet  25  and the backsheet  15 . In a preferred embodiment of the present invention, the absorbent article  10  also includes a secondary topsheet or an insert  26  positioned beneath the topsheet  25 , i.e., at least partially, between the topsheet  25  and the absorbent core  20 .  
      In the embodiment shown in  FIG. 1  and in  FIG. 2 , the absorbent article  10  has at least two portions, i.e., a colored portion  40  and a non-colored portion  50 . The colored portion  40  and the non-colored portion  50  are viewable from the viewing surface  28  of the topsheet  25 . The colored portion  40 , which in a preferred embodiment of the present invention is a print image  40 , has at least two shades: a first shade  42  and a second shade  44 . Preferably, but not necessarily, and as is shown in  FIGS. 1 and 2 , the first shade  42  is positioned substantially within the second shade  44 . The second shade  44  is different, either in lightness, darkness, and/or color, from the first shade  42 . The multi-shades operate to create a perception of depth within the absorbent article by a user looking upon the viewing surface  28  of the topsheet  25 . In the embodiment shown in  FIGS. 1 and 2 , the first shade  42  of the print image  40  is darker than the second shade  44  of the print image  40 .  
      Alternatively, in another embodiment of the absorbent article  10 A, a print image or a colored portion  40 A can comprise a first shade  42 A that is lighter than a second shade  44 A, as shown in  FIG. 3 . The lightness and darkness of the shades, whether two or greater than two shades, are configured to create a perception of depth by a user looking upon the viewing surface  28  of the absorbent article  10 A.  
      As described above, in one embodiment of the present invention, the print image  40  can be the secondary topsheet or an insert  26  positioned between the topsheet  25  and the absorbent core  20 . In another embodiment, the colored portion  40  can form a part of the topsheet  25 . In yet another embodiment, the print image  40  can form a part of the absorbent core  20  whereby the print image  40  is viewable from the viewing surface  28  of the topsheet  25 . Alternatively, the print image  40  can be a multi-layer insert positioned beneath the topsheet  28 .  
      Any topsheet material that allows the print image  40  to be readily seen from the viewing surface  28  of the topsheet  25  is suitable. For example, formed film materials, nonwoven materials, or combinations thereof are suitable.  
      Alternatively to the color scale values described above, the two-tone portions  40  and  40 A can be shown as gray scale images. For example,  FIG. 4  illustrates a two-tone image  60  having a darker portion  60 A and a lighter portion  60 B. The two-tone gray scale images of the present invention were measured using Adobe Illustrator® available from Adobe Systems Incorporated, the headquarters of which is located in San Jose, Calif. In one embodiment, the darker portion  60 A was measured  45  on a gray scale and a lighter portion  60 B was measured  20  on a gray scale.  
      A gray scale image can be converted into a pcx image by using Adobe Photoshop® also available from Adobe Systems Incorporated.  FIG. 5  shows an image  70  as a pcx image converted from the gray scale image  60  of  FIG. 4 . Because a pcx image is comprised of individual pixels and dots, the pcx image can be useful in creating inkjet images, wherein each dot of a pcx image represents an ink dot formed by an inkjet of a print head.  FIG. 6  shows a magnified view of the image  70 , wherein the darker portion  70 A is composed of a greater number of dots than the lighter portion  70 B. For the reference purposes,  FIG. 7  illustrates a side-by-side comparison of several gray scale images having gray scale values of 10, 25, 40, 55, 70, 85, and 100 to the corresponding pcx images, where the gray scale value of a 100 represents a completely black image.  
       FIG. 8  is a simplified elevation view of one embodiment of a method  100  of the present invention designed to manufacture the absorbent articles of  FIGS. 1, 2  and  3 , as well as any other absorbent articles defined above and having any desired print image, including multi-colored, multi-tone, or multi-gray images.  
      The method  100  includes an inkjet printing station  101  capable of printing a desired image on a substrate  102 . The substrate  102  can be any substrate according to the definition of a substrate provided above. Also, as described above, the substrate  102  can form any component or part of a disposable absorbent article  10 . However, in the preferred embodiment of the present invention, the substrate  102  is a nonwoven web for use as the secondary topsheet or the insert  26 , as shown in  FIGS. 1 and 2 .  
      The substrate  102  can be provided to the printing station  102  by any suitable means, such as, for example a metering device  104  (e.g., an omega roll or an s-wrap device), a series of idle rollers  106  and  108 , and a metering device  110  (e.g., a vacuum conveyor). Both the metering devices  104  and  110  create a desired tension in the substrate  102  and move the substrate  102  in a web or machine direction  111  at a desired linear velocity V, which in the high-speed production method of the present invention can be as high as about 6 meters/second or even greater. However, the present invention is applicable at any other linear velocity V of the substrate, such as, for example, at least 5 meters/second, at least 4 meters/second, at least 3 meters/second, at least 2 meters/second, and lower (which occurs during a startup of the converting line when the converting line speed, including the linear velocity V of the substrate  102 , is gradually increasing from a zero to a desired production speed).  
      As shown in  FIG. 8 , the printing station  101  preferably includes a dual-head arrangement comprising a first inkjet print head  112  and a second inkjet print head  114 , disposed at a spatial distance  116  extending in the web direction  111 . However, it should be noted that the first and the second print heads  112  and  114  could be disposed from each other at any desired spatial distance.  
      The first and the second print heads  112  and  114  can be any type that is suitable to print a desired image, and are preferably non-contact inkjet print heads disposed at a certain suitable distance from the substrate  102 , i.e., from the first surface  118  of the substrate  102 , facing the print heads  112  and  114 .  
      The print heads  112  and  114  can be preferably supplied by ink provided by a common ink source; although, if desired, separate ink sources can be also utilized.  
      Each of the print heads  112  and  114  includes a multiplicity of jets dispensing a multiplicity of substantially uniform ink dots. In one embodiment of the present invention, each of the print heads  112  and  114  includes 256 jets, forming a linear configuration of about 2 inches long (about 50.8 mm). Therefore, each of the print heads  112  and  114  can print an ink image containing 256 ink dots extending linearly about 50.8 mm across the substrate  102 . This arrangement is sufficient for printing any image of up to about 50.8 mm wide, as measured across the substrate  102  and shown as a width W of the printed images  40  and  40 A in  FIGS. 1-2  and  3 , respectively. However, any number of jets per a print head can be provided, if desired, to print a desired width W of a desired image, which, for example, for feminine hygienic articles of the present invention can vary from 5 mm to 85 mm. For other types of hygienic articles listed above, the width W of the print image can vary even greater.  
      With respect to the print heads having 256 jets, such print heads are available from Videojet Technologies, Inc., which offices are located in Wood Dale, Ill. The printing station  101  can be a part of an inkjet printing system that is also available from Videojet Technologies, Inc., as the PrintPro™ inkjet print system including an ink source and a controller for providing ink and controlling jets forming individual ink droplets.  
      In the PrintPro™ inkjet print system, the ink droplets are dispensed from all of the jets of the print heads  112  and  114  continuously, but only certain ink droplets are allowed to reach the substrate  102  at desired locations to form a printed image. The other ink droplets can be prevented from reaching the substrate  102  by deflecting the ink droplets into a recycling flow for a continuous re-use. The operation of the individual ink jets of each print head can be controlled by a controller included in the PrintPro™ system.  
      Alternatively to the continuous type of the inkjet printing system of one embodiment of the present invention, the inkjet printing system can be an on-demand type inkjet printing system, wherein ink typically is not recycled, and wherein ink droplets are not formed continuously, but on the demand basis, in a desired order, to print a desired image.  
      Referring again to  FIG. 8 , in the method of the present invention, each of the first and the second print heads  112  and  114  is capable of printing the images  40  and  40 A of  FIGS. 1-2 , and  3 , or any other desired image, separately from each other. For example, when the first print head  112  is in a print mode (i.e., is printing the image  40  on the substrate  102  at a desired location on the substrate  102 ), the second print head  114  can be in a standby or idle mode (i.e., is not printing the image  40  on the substrate  102 ). Conversely, when the first print head  112  is in a standby mode, the second print head  114  is in a print mode, printing the image  40 . As described above, in both modes of operation, the print mode and the standby mode, the droplet formation by each of the 256 jets of each of the print heads  112  and  114  occurs continuously; however, in the standby mode, all of the dispensed droplets are deflected and recycled into a recycled ink flow, but in the print mode the un-deflected droplets are deposited on the substrate  102  and the deflected droplets are recycled into the recycle ink flow.  
      In the method of the present invention, by switching from the print mode of the first print head  112  to the print mode of the second print head  114 , and vice versa, a desired continuity of the production process can be provided. The switching between the print heads  112  and  114  enables continuous, uninterrupted production of hygienic articles on a converting line when a print head needs to be taken out of the print mode for any reason, including any type of malfunction or scheduled maintenance, for cleaning and the like. The second print head provides a desired back up by automatically switching from a standby mode to a production mode.  
      This continuity is important to maintain a high production efficiency of a converting line producing hygienic articles at high production speeds, which, as described above, can be as high as 6 meters/second and greater, and at high production rates, which can be at least 600 products/minute, in order to avoid production losses, which, at such high speeds and production rates, can be substantial. (It should be noted that the method of the present invention is also applicable to any production rate, lower or greater of at least 600 products/minute, as high as 3,000 products per minute.)  
      It is important for the disposable absorbent articles of the present invention, to have a print image disposed at a desired, predetermined, and consistent location of hygienic articles. Therefore, in the method of the present invention, when the first print head  112  stops printing and the second print  114  starts printing, the second print head  114  can print in the identical location as did the first print head  112 . Further, in one embodiment of the present invention, the switching between the print heads occurs simultaneously, with preferably a minimum loss of production of hygienic articles during the switching. This operation will be described in more detail below.  
      Referring again to  FIG. 8 , after the inkjet printing, the substrate  102  travels to a cut and placement device  120 , capable of severing the substrate  102  into individual sheets comprising the secondary topsheet  26  and then placing the secondary topsheets  26  at a desired pitch interval P onto a topsheet web  122  moving in a web direction  124  at a desired velocity. The topsheet web  122  can be provided and metered at a desired velocity by any suitable means known to one skilled in the art. Then, an absorbent core web  126  (which can be also provided and metered by any suitable means) is cut into individual absorbent cores  20 , which are then placed onto the secondary topsheet  26 , previously disposed on the topsheet web  122 . The cutting and placing operations of the absorbent core  20  can be provided by a cut-and-slip device  128  or any suitable web cutting and placing device known in the art. Further, a backsheet web  130  (which can be also provided and metered by any suitable means) is deposited onto the cores  20  to provide a sandwiched-type web  132 , which is subsequently bonded together and cut into individual hygienic articles  10  of the present invention. The bonding, cutting, and placing operations of the sandwiched-type web  132  can also be provided by any suitable means known in the art, for example, by a final knife  134 . The individual articles  10  then can be transported by any suitable means, such as a conveyor  136 , to other downstream operations, such as folding, wrapping, and packing.  
       FIG. 9  illustrates a block diagram  200  of one embodiment of the control system of the present invention. The diagram  200  includes the printing station  101  having the first inkjet print head  112  and the second inkjet print head  114 . The block diagram  200  also includes an ink-jet controller  211  for calculating the deflection of each ink droplet of each of the 256 nozzles of each of the print beads  112  and  114 . The calculated information is then transferred from the ink-jet controller  211  to the inkjet print heads  112  and  114 , using a first communication link  230  and a second communication link  231 , respectively. The inkjet controller  211  also receives information from a first encoder  202  with respect to a converter speed reference (e.g., a linear velocity of the moving substrate  102 ), which can be provided from any suitable speed reference representing the speed of the substrate  102 . In one embodiment of the present invention, the speed reference  212  is provided from the cut and placement device  120  via the first encoder  202  connected to the cut and placement device  120 . The inkjet controller  211  further receives triggering information with respect to the print heads  112  and  114 , wherein each print head  112  and  114  has its own triggering signal, i.e., a first triggering signal  215  and a second triggering signal  216 , respectively.  
      With respect to controlling the first print head  112 , as shown in  FIG. 9 , the first triggering signal  215  is a result of information calculated by a first calculation unit  222  receiving a first start cycle signal  217  and a first output signal  219 . The first calculation unit  222  can be any suitable electronic device capable of calculating a binary AND logic function, for example, an opto-couple device and the like. The first start cycle signal  217  is provided by a second encoder  203 , which in the preferred embodiment of the present invention, is connected to the final knife  134 . However, the second encoder  203  can be connected to any pitched unit operation defined above, including the cut and placement device  120  that can be attached to both the first encoder  202  and the second encoder  203 . The first output signal  219  is provided from a converter logic controller  210  (referred hereinafter as a converter controller  210 ). In order to provide the first output signal  219 , the converter controller  210  receives both a first OK signal  225  and a second OK signal  226  from the inkjet controller  211 .  
      Similarly, with respect to controlling the second print head  112 , as shown in  FIG. 9 , the second triggering signal  216  is a result of information calculated by a second calculation unit  223  receiving a second start signal  218  and a second output signal  220 . The second calculation unit  223 , similarly to the first calculation unit  222 , can be any suitable electronic device capable of calculating a binary AND logic function. The second start cycle signal  218  is provided by the second encoder  203 . The second output signal  220  is provided from the converter controller  210 . In order to provide the second output signal  220 , the converter controller  210  receives both the first OK signal  225  and the second OK signal  226  from the inkjet controller  211 .  
      The first start cycle signal  217  and the second start cycle signal  218  are related to each other, representing the spatial distance  116  between the respective nozzles of the first and the second print heads  112  and  114 . The spatial distance  240  presents a portion of a single product cycle corresponding to a cycle distance between the first and the second print heads  112  and  114 .  
       FIG. 10  shows a block diagram  300  illustrating logic for switching between three operating modes of the first and the second inkjet print heads  112  and  114 , within the converter controller  210 . The three operating modes of each of the print heads  112  and  114  are illustrated by three circles representing a standby or idle mode  301 , a run mode  302 , and a fault mode  303 .  
      In the standby mode  301 , the first print head  112  or the second print head  114  (or both print heads  112  and  114 ) are ready for printing at any moment, while continuously forming and re-circulating ink droplets into a recycled ink flow.  
      In the run mode  302 , the first print head  112  or the second print head  114  prints an image on the substrate  102 . (As noted above, in a preferred embodiment of the present invention, only one of the print heads  112  or  114  can operate in the run mode  302  at the time.) In both the standby mode  301  and the run mode  302 , the converter controller  210  receives the OK signal  215  or  216  and sends the output signal  219  or  220  (see  FIG. 9 ).  
      In the fault mode  303 , the converter controller  210  does not receive the OK signal  215  or  216  and does not send the output signal  219  or  220  (see  FIG. 9 ).  
      Referring to  FIG. 10 , from the standby mode  301 , a print head can switch to the run mode  302  by a transition  311  or to the fault mode  303  by a transition  314 . The transition  311  can happen as a consequence of two different situations: (1) an operator switching between print heads by initiating start signals  228  or  229  (see  FIG. 9 ) for the first print head  112  or the second print head  114 , respectively, to the converter controller  210 ; or (2) the transition  311  is an automated sequence happening immediately after a transition  313  on the other print head, which switched from the run mode  302  to the fault mode  303 . With respect to the transition  314 , it can also happen as a consequence of two different situations: (1) an operator switching an idling print head to the fault mode  303  when the idling print head needs maintenance, such as cleaning and the like; or (2) an idling print head failing for any reason, and, accordingly, not sending the OK signal  225  or  226  to the converter controller  210 .  
      Referring to  FIG. 10 , from the run mode  302 , a print head can switch to the standby mode  301  by a transition  312 , or to the fault mode by a transition  313 . The transitions  312  and  313  are equal in priority, and, therefore, each one becomes executed depending upon which of the transitions  312  or  313  occurs first. The transition  312  can happen when an operator switches between the print heads, and the transition  313  can happen when a print head fails in the run mode  302  (i.e., does not send the OK signal  225  or  226  to the converter controller  210 ) and needs operator service. When a print head fails in the run mode  302 , the other, idling print head, switches to the run mode  302  by the transition  311 .  
      Referring to  FIG. 10 , from the fault mode  303 , a print head can switch only to the standby mode  301  by the transition  315 . This happens after a faulted print head has been serviced and is ready for operation.  
     Operating Procedures  
      Referring again to  FIGS. 9 and 10 , below are described various procedures for continuous operation of the first and the second print heads  112  and  114 .  
      At the start, the first and the second print heads  112  and  114  are preferably in the standby mode  301  controlled by the converter PLC  210 . When both print heads  112  and  114  are in the standby mode  301 , the inkjet controller  211  sends both OK signals  225  and  226  to the converter controller  210 . Now the operator has an option to select either one of the print heads  112  or  114  to start printing by initiating the first start signal  228  for starting the first print head  112  or the second start signal  229  for starting the second print head  114 . If the operator selects to start the first print head  112  by initiating the first start signal  228 , the converter controller  210  sends the first output signal  219 , which is combined with the first cycle start signal  217  in the first calculation unit  222  sending the first triggering signal  215  to the inkjet controller  211  for starting the first print head  112 . During the printing by the first print head  112  in the run mode  302 , the second print head  114  remains in the standby mode  301 , ready to be switched to the run mode  302  when needed. When the first print head  112  is printing in the run mode  302  and the second head  114  is in the standby mode  301 , the inkjet controller  211  is sending both the first and the second OK signal to the converter controller  210 .  
      When the first print head  112 , becomes faulted, the inkjet controller  211  switches the first print head  112  to the fault mode  303  and stops sending the first OK signal  225  to the converter controller  211 , which in response, stops sending the first output signal  219  and starts sending the second output signal  220 . The second output signal  220  is then combined with the second start cycle signal  219  in the second calculation unit  223  sending the second triggering signal  216  to the inkjet controller  211  switching the second print head  114  to the run mode  302 .  
      Similarly, when the second print head  114 , becomes faulted, the inkjet controller  211  switches the second print head  114  to the fault mode  303  and stops sending the first OK signal  225  to the converter controller  211 , which in response, stops sending the first output signal  220  and starts sending the first output signal  219 . The first output signal  219  is then combined with the first start cycle signal  218  in the first calculation unit  222  sending the first triggering signal  215  to the inkjet controller  211  switching the first print head  112  to the run mode  302 .  
      Alternatively to the automatic switching between the print heads described above when one of the print heads becomes faulted, the operator can switch between the print heads any time when the converter PLC is receiving both OK signals  225  and  226 . For example, when the first print head  112  is working in the run mode  302  and the second print head  114  is in the standby mode  301  (in such condition, the converter PLC is receiving both OK signals  225  and  226  from the inkjet controller  210 ), and the operator can switch the printing from the first head  112  to the second print head  114  at any time by initiating the second start signal  229 . In this case, the converter PLC stops sending the first output signal  219  and starts sending the second output signal  220 , which is then combined with the second start cycle signal  219  in the second calculation unit  223  sending the second triggering signal  216  to the inkjet controller  211  switching the second print head  114  to the run mode  302 . When the converter PLC  210  stops sending the first output signal  219  above, in response, the inkjet controller  210  stops receiving the first triggering signal  215  and stops sending the first OK signal  225  to the converter PLC  210 . This manual switching between the print heads by the operator may be needed when the operator needs to do any service procedure (e.g., cleaning and the like) to a print head working in the run mode  302 . Also, the operator may need to switch print head when there is a need to change the printing image by loading a new data. Such capability enables the operator to change a printing image “on the fly” without interrupting the production process on the converter.  
       FIG. 11  shows a top view of a portion of the substrate  102  having a first plurality  351  of images  40  and a second plurality  352  of images  40 . In the first plurality  351  of images  40  and in the second plurality  352  of images  40 , the images  40  are separated from each other at a pitch interval P, which is the length of a hygienic article. The pitch interval P can very depending on a particular hygienic article, for example, generally from about 100 mm to about 400 mm. Specifically, with respect to feminine hygienic articles, the pitch interval P can vary from about 220 mm to about 320 mm. (As noted before, in the embodiments of the present invention, the length and the width of the print image  40  can vary. Specifically, with respect to feminine hygiene articles of the present invention, the length L of the print image  40  can vary from about 10 mm to about 300 mm and the width of the print image  40  can vary from about 5 mm to about 85 mm. However, any desired length and width of the print image  40  can be used in the present invention.)  
      Referring again to  FIG. 11 , the first plurality  351  of images  40  is separated from the second plurality  352  of images  40  by an unprinted region B. The unprinted region B represents a portion of the substrate  102  having no print images  40  by the method disclosed herein. (It should be noted that the unprinted region B can include print images, however, the quality of the print image(s) may not be sufficient.) The unprinted region B also represents a portion of the substrate  102  that moved in relation to the printing station  101  (see  FIGS. 8 and 9 ) during the switching between the first and the second print heads  112  and  114 , or vice versa. In one embodiment of the present invention, the unprinted region B is no greater than 50 times the pitch interval P, or no greater than 10 times the pitch interval P, or no greater than 1 time the pitch interval P.  
      It should be noted that the first plurality  351  of images and/or the second plurality  352  of images could include the same image  40  or different images, wherein the different images, which have been stored in the inkjet controller  211 , can be printed on demand at any desired sequence.  
     Another Embodiment  
       FIG. 8A  is a simplified elevation view of another embodiment of a method  700  of the present invention designed to manufacture the hygienic articles of  FIGS. 1, 2  and  3 , as well as any other hygienic article defined above and having any desired print image, including multi-color, multi-tone, or multi-gray images.  
       FIG. 8A  (illustrating the method  700 ) is similar to  FIG. 8  (illustrating the method  100 ), except that  FIG. 8A  shows more than one inkjet print station  101 . As an example,  FIG. 8A  shows two print stations: a first print station  101  (previously shown in  FIG. 8 ) and a second print station  701 . However, it should be noted that the number of print stations of the method  700  can include any suitable number: 2, 3, 4, and the like.  
      The print stations  101  and  701  can be identical in any respect and can be controlled separately, in a manner as was described above and illustrated in  FIGS. 9 and 10  with respect to controlling the print station  101 . Each print station  101  and  701  can include preferably two ink-jet print heads, which can be similar to the print heads  112  and  114  described in detail above with respect to the print station  101 .  
      As shown in  FIG. 8A , the first print station  101  includes the first inkjet print head  112  and the second inkjet print head  114 , disposed at the spatial distance  116  extending in the web direction  111 . Similarly, the second print station  701  includes a first inkjet print head  712  and a second inkjet print head  714 , disposed at a spatial distance  716 . The spatial difference  716  of the second print station  701  can be the same as or different from the spatial difference  116  of the print station  101 .  
      The method  700  of the present invention can be particularly suitable for printing multiple inks to form the image  40  ( FIG. 11 ), including multiple color inks. However, as noted above, the method  700 , as well as the method  100 , is also suitable for inkjet printing of multi-tone or multi-gray images.  
      With respect to printing color images, the method  700  can include any suitable number of print stations, each one printing a specific color ink. For simplicity, the method  700  is described as having two print stations  101  and  701 , each one printing a specific color ink. For example, the print station  101  can print yellow ink, and the print station  701  can print blue ink. In this case, the resulted image  40  ( FIG. 11 ) includes two color inks.  
      When, for example, a first print head  112  of the first print station  101  printing yellow ink becomes defaulted, the control system switches from the first print head  112  to the second print head  114 , also printing yellow ink. Similarly, when, for example, the first head  712  of the second print station  701  printing a blue ink becomes defaulted, the control system switches from the first print head  712  to the second head  714 , also printing a blue ink. The switching between the first inkjet print head to the second inkjet print head (and vice versa) of the multiple print stations of the method  700 , enables continuous, uninterrupted production of hygienic articles including, for example, color images  40 .  
     Overcoming Limitations of Printing Equipment  
      In addition to providing an efficient, uninterrupted operation of two inkjet print heads on a converting line producing hygienic articles, the method of present invention provides an efficient connection between a product designing stage and a product production stage, especially, for the instances having to do with certain limitations of a particular printing equipment utilized for printing inkjet images on the converting line. For example, at high substrate speeds, and, especially, when not one but several ink drops per a dot (i.e., several ink drops, composing a dot, are deposited into a single pixel on the substrate surface) are needed, certain printing equipment may not be capable of printing ink drops at a required rate, resulting in a decreased resolution of the printed image, and, thus, in a decreased visual impression by a consumer viewing the image. The method of the present invention provides compensation for such a decrease of the visual impression by the consumer by adjusting the visual level of the lower resolution image, as shown in  FIGS. 12, 13 , and  14 .  
       FIG. 12  shows an inkjet print image  400  having gray level A at resolution X, which, assumingly, for the purpose of explanation, cannot be provided by a given printing equipment at a certain high speed of a substrate. To overcome this speed limitation, the resolution X of the image  400  of  FIG. 12  can be stretched, for example, 30% or any other suitable number.  FIG. 13  illustrates a print image  500  having the same gray level A as the original image  400  at a lower resolution, X-30%. It can be clearly seen by comparing grids of  FIGS. 12 and 13 , that the grid of  FIG. 13  is longer in one direction in comparison to the grid size in  FIG. 12  (in this case about 30%), and, thus, the density of inkjet drops in  FIG. 13  is less than the density of drops in  FIG. 12 , resulting in a less intense visual impression for the consumer. To compensate for the loss of the visual impression, more drops can be deposited in vacant pixels of the stretched grid of  FIG. 13 , as shown, for example, in  FIG. 14 , illustrating a print image  600  having a gray level A+30 (which is greater than the original gray level A of the original image  400  of  FIG. 12 ) at a resolution X-30% (which is less than the original resolution X of the original image  400  of  FIG. 12 ). The modified image  600  of  FIG. 14  provides a similar visual impression on the consumer as compared to the originally designed image  400  of  FIG. 12 , thus, overcoming the above described speed limitation of the printing equipment.  
      All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention.  
      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. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.