Toilet paper
BACKGROUND OF THE INVENTION 
     The invention concerns toilet paper. Toilet paper is usually manufactured as rolls; for some uses it may be precut into sheets of suitable sizes. 
     Standard types of toilet paper are made of crepe paper or tissue paper arranged in one or more plies. An essential criterion for the quality of the paper is its resistance to tearing when wet, its so-called &#34;wet strength&#34;. The toilet paper ordinarily available has inadequate wet strength. The consequences thereof are immediately obvious and require no elaboration. 
     In order to compensate for this shortcoming, the user must fold several sheets over one another. A means of avoiding this need would be increasing the number of plies in the paper during manufacture. Both of these practices are undesirable due to their inefficient use of paper. 
     It is known from German utility model No. 19 39 788 to add an additional paper ply onto a paper strip along the longitudinal axis of said paper strip, or to insert an additional narrow paper strip between two plies having normal width. Unfortunately the manufacture of this kind of toilet paper has shown to be rather difficult. 
     SUMMARY OF THE INVENTION 
     It is a general object of this invention to specify toilet papers which demand reduced usage of paper while providing the required strength. 
     This is achieved by a toilet paper having a greater thickness in its central area than that at its edges. This offers the advantage of providing both central and edge areas with thicknesses sufficient to meet the demands placed upon them in use while significantly reducing the weight and amounts of paper required compared to standard toilet papers having uniform thicknesses over their full widths. 
     Since toilet paper is manufactured and used in large quantities, the approximate 30% savings in the amounts of wood required for manufacture will be a matter of economic importance. 
     Useful is to reinforce the central area of the paper with a Z-fold along its longitudinal axis. The invention concerns methods for the manufacture of Z-folded toilet paper, as well as equipment for the performance of these methods. 
     Extensions and additional forms of the invention are designated in the rights claimed and are described in the--at times schematically simplified--figures displaying examples of the different forms of the invention. In these figures, parts which are related to one another are given the same reference symbols, and all details which are not required for the explanation of the invention have been omitted. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-section through a toilet paper manufactured according to the invention. 
     FIG. 2 is a further version, with a reinforced central section created by Z-folding a strip of paper, seen in cross-section, 
     FIG. 3 is a simpler version, generated by Z-folding a paper strip, seen in cross-section, 
     FIG. 4 is another two-ply version, in which one ply is Z-folded, seen in cross-section, 
     FIG. 5 is a two-ply version, in which both plies are Z-folded, seen in cross-section, 
     FIG. 6 is a three-ply version, in which the inner ply is Z-folded, seen in cross-section, 
     FIG. 7 is a greatly simplified drawing of equipment for the manufacture of toilet paper, shown in an isometric view, 
     FIG. 8 is a section through the paper guides in the C--C plane, perpendicular to the transport direction of the paper strip, presented as a structural detail, 
     FIG. 9 is a section through the paper guides in the D--D plane, perpendicular to the transport direction of the paper strip, presented as a structural detail, 
     FIG. 10 is a simplified drawing of another equipment for the manufacture of toilet paper, shown in plan view, 
     FIGS. 10A, 10B and 10C are sections perpendicular through the paper guides of the equipment of FIG. 10 in the AA&#39; plane, in the BB&#39; plane and in the CC&#39; plane respectively, perpendicular to the transport direction of the paper strip, presented as structural detail. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates the principle of the invention. If the paper has been reinforced in the central area 2, for example, by suitably controlling the manufacturing process, then an increased resistance to tearing will be obtained in the more heavily stressed central area, while the edge areas 3 maintain strength adequate for the stresses which they will encounter in use. A significant savings, which can be more than 30%, in the amounts of paper used is achieved in comparison to standard types of toilet paper which have uniform thicknesses over their full areas. This will substantially reduce the amounts of wood required for the large quantities of toilet paper which are manufactured. 
     In the version shown in FIG. 2 the reinforcement of the central area is achieved by folding a strip of paper. The paper ply 4B is folded upon itself twice before it is bonded to the paper ply 4A, so that the central area contains four plies, the right-hand edge has a single ply, and the left-hand edge has two plies. 
     A reinforcement of the central area to thrice that of the edge areas may be achieved by Z-folding a strip 4, as shown in FIG. 3. If a two-ply strip is to be used, when the strip 4A can remain unaltered, while the strip 4B is Z-folded so that the central area 2 has a thickness twice that of the edge zones, as shown in FIG. 4. 
     FIG. 5 shows a particularly simply-manufactured version in which the central area 2 has thrice the thickness of the edge zones, achieved by Z-folding the strips 4A and 4B. 
     If a three-ply strip is to be used for the manufacture of the toilet paper, then the two outer plies, 4A and 4B, can be left unaltered and only the inner ply Z-folded to strengthen the central area 2, as indicated in FIG. 6. 
     Each folded strip has folded edges which are bonded to the plies so as to form a single piece therewith. 
     The system shown in FIG. 7 for the accomplishment of the folding along the longitudinal axis of the paper strip has two pairs of rollers, 11--11&#39; and 12--12&#39;, arranged perpendicularly to one another and to the longitudinal axis of the paper, AB. The paper strip 13 enters the system unfolded at roller pair 11--11&#39; and leaves it folded parallel to its longitudinal axis after passing through the roller pair 12--12&#39;. In order to better show this folding operation, the surface of the paper 13, has been drawn in FIG. 7 provided with a hatch-pattern. The space between the two roller pairs, 11--11&#39; and 12--12&#39;, contains two paper guides formed from sheet material. These guides are not shown in FIG. 7 in order to simplify the drawing. Sections through the guides perpendicular to the longitudinal axis of the paper AB are shown in FIGS. 8 and 9. Both of the paper guides 15 and 15&#39;, have the same form and are mounted separated slightly from one another. These guides define a narrow included gap 16, through which the paper 13 is fed. The form of these paper guides changes continuously along the paper transport direction. At the roller pair 11--11&#39;, the paper guides are nearly planar and equidistant from one another (17 and 17&#39; in FIG. 8); they continuously evolve into increasingly curved and folded surfaces, with cross-sections like those shown in FIG. 9 at the roller-pair 12--12&#39;. The roller pair 11--11&#39; controls primarily the paper transport, while the roller-pair 12--12&#39; performs the folding operation in conjunction with the paper guides 15 and 15&#39;. 
     The paper guides 15 and 15&#39; simplify the startup of the system. Once the system is in operation, they can be at least partially withdrawn. 
     In an actual operational version of the system, the rollers 12 and 12&#39; should ideally each be made up of three rollers 12A, 12B, 12C, and 12A&#39;, 12B&#39;, and 12C&#39;. The roller-pairs at the two edges of the paper strip are to be dimensioned in width such that they grip only the single-ply areas 19 and 19&#39; of the paper; the roller-pair 12B and 12B&#39;, which lies between these two roller-pairs is to be dimensioned such that its rollers contact only the central area of the paper 13. This center roller-pair performs the longitudinal folding while the two roller-pairs at the outer edges 18 and 18&#39; of the paper perform control functions. In conjunction with the sensors 21 and 21&#39;, indicated in FIG. 7, which scan the edges 18 and 18&#39; of the paper, the width of the single-ply sections of the paper 19 and 19&#39; may be adjusted and regulated as required by a slight tilting of the control rollers 12A-12C and/or 12A&#39;-12C&#39;, off their axes in the horizontal plane. 
     For the manufacture of various specific types of toilet papers, foldings, such as double Z-folding, or the creation of parallel longitudinal pleats across the paper width, may be obtained by an appropriate shape of the paper guides as shown in FIG. 10. 
     In the apparatus illustrated in FIG. 10 a tissue web 13 having a large width enters the device from the left side and leaves it on the right side with several Z-foldings in longitudinal direction, after having passed the guide plates 15, 15&#39;. To produce toilet paper this paper web is cut in single strips with one Z-folding each in longitudinal direction. 
     Cross sections of the guide plates along the sections AA&#39;, BB&#39;, CC&#39; are shown in FIGS. 10A, 10B, 10C.