Abstract:
Apparatus for continually joining paper webs, comprising a device able to compress the webs ( 5,6 ) onto an impression cylinder or roller ( 4 ) while the webs advance toward an outlet section of the apparatus. The compressive device includes a roller or cylinder ( 2 ) which exhibits a hard outer surface ( 20 ) supported by an underlying elastic surface ( 23 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation under 37 CFR 1.53(b) of prior application Ser. No. 10/527,903 filed Mar. 14, 2005, now abandoned which is a United States National Phase application of International Application PCT/IT2003/000849 filed Dec. 22, 2003 and claims the benefit of priority under 35 U.S.C. §119 of Italian Patent Application FI 2003A000015 filed Jan. 17, 2003, the entire contents of each of the applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention refers to an apparatus and a method for continually joining paper webs. 
     BACKGROUND OF THE INVENTION 
     Apparatus for carrying out a continued union of paper web is known from DE-A-100 43 989 and from U.S. 2001/019757. These documents describe an apparatus for carrying out the union of two paper webs by a mutual compression of the concerned webs, in which the webs are compressed between a pressure roller and an impression roller provided with surface reliefs and/or depressions. 
     An apparatus usually employed for a continuous union of paper webs comprises, with reference to the outline of  FIG. 1 , two pairs of rollers and cylinders (A, B; C, D) for embossing paper webs (E, F), a roller (G) for distributing a given amount of glue onto the paper which transits in correspondence of one of the embossing rollers, and an impression roller with rubber-coated surface (H) positioned diametrically opposite to the gluing roller (G): the paper webs (E, F) result embossed as they transit between the surfaces of the corresponding embossing rollers and cylinders, that is, as they pass through the regions indicated by “X” and “Y” in  FIG. 1 , and become definitively glued by their passing onto the embossing roller (B) and because of the pressure exerted thereon by the rubber-coated roller (H). In  FIG. 1 , the arrows (VE, VF, VA) indicate the directions of advancement of web (E), web (F) and of the exiting coupled webs (AC). 
     One drawback relating to this operating technique lies in the fact that, because of the very compliance of the material that sheathes the output pressure roller (H), and of the pressure that this roller exerts on the first embossing cylinder (B), the material of the pressure roller penetrates the surface cavities of the cylinder. As a consequence, a mutual squashing of the two paper webs occurs throughout the space within which the coating material of the pressure roller fits into the cavities of the embossing cylinder (as shown in  FIG. 2A ) and, accordingly, a kind of re-embossing is produced with a noticeable roughness on one of the two sides of the output material (see  FIG. 2B , wherein “L” indicates the deformations in the coupled webs with respect to the ideal profile). Another drawback related to the use of this type of apparatus lies in the fact that the glue distribution&#39;s system brings about significant expenses due to the cost of the mechanical members and of the adhesive, and to the difficulty in keeping the system clean. 
     Another device commonly used for continually joining paper webs comprises a group—downstream of the embossing rollers and cylinders according to the outline of FIG.  3 A—consisting of a smooth roller having a hard surface (Z) and a set of small rollers with surface reliefs (W) so disposed that the outputting coupled webs will pass, by resting on the smooth roller (Z), under the small rollers (W). In this way, the reliefs of the small rollers will cause the mutual squashing of the two paper webs and, thereby, their union, without using any adhesive whatsoever. 
     One drawback related to such a device lies in that, in correspondence of the regions interested by the action of the small rollers, the embossing previously produced is lost and, on the coupled webs exiting from the device, two or more areas developed there along result markedly visible (as illustrated in  FIG. 4  where “AC” indicates the coupled webs, “AM” indicate the above said areas, and an array of dots indicates the embossing operated upstream of the group and including the small rollers). In conclusion, also this known operating technique implies a partial but anyway evident lost of the effects derived by the embossing of the two webs which make up the coupled webs. A further drawbacks related to the use of this type of device is that the small rollers tend to vibrate when a given operating speed of the system has been exceeded and, thus, they tend to wear out prematurely, so that an upper limit is to be provided on the operable speed which results incompatible with the current production requirements. The said marks (AM) do not result, more often than not, perfectly centered with respect to the rolls formed when cutting the log of the coupled webs, which contributes to make the same marks (AM) still more unappealing. 
     SUMMARY OF THE INVENTION 
     The main object of the present invention is to overcome the above said drawbacks. 
     The present invention makes it possible to carry out a continued union of two paper webs, with or without a previous embossing and with or without the use of glue, without producing undesired surface deformations of the coupled webs which, therefore, result of a better quality. Besides, an apparatus according to the invention is easy to make, cost-effective and reliable even after a prolonged service life. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a simplified functional diagram of a known device; 
         FIGS. 2A and 2B  are two enlarged details of  FIG. 1  relating to means for the stabilization of the coupled webs; 
         FIG. 3A  is a diagram similar to that of  FIG. 1  but relating of another known device; 
         FIGS. 3B and 3C  are two enlarged details of  FIG. 3A ; 
         FIG. 4  is a schematic plan view of the coupled webs on output from the device of  FIG. 3A ; 
         FIG. 5A  is a diagram similar to that of  FIGS. 1 and 3A  but relating to an apparatus according to the present invention; 
         FIGS. 5B and 5C  are two enlarged details of  FIG. 5A ; 
         FIGS. 6A-6D  are front views of different embodiments of a stabilizing cylinder for the apparatus according to the invention; 
         FIG. 7  is a schematic view in diametrical section of the roller ( 2 ); 
         FIG. 8  is a diagram relating to another possible use of an apparatus according to the present invention; 
         FIG. 9  is a diagram relating to a further possible use of an apparatus according to the present invention; 
         FIG. 10A  is a diagram relating to yet another possible use of an apparatus according to the present invention; 
         FIG. 10B  is a schematic, partial plan view of the product on output from the system of  FIG. 10A ; 
         FIG. 11A  is a schematic plan view of an impression roller or cylinder to be used in association with an apparatus according to the invention; 
         FIG. 11B  is a sectional view taken on line M-M in  FIG. 11A ; 
         FIG. 12A  is a schematic plan view of a further impression roller or cylinder to be used in association with an apparatus according to the invention; 
         FIG. 12B  is a section view taken on line N-N in  FIG. 12A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reduced to its basic structure, and reference being made to  FIGS. 5A-7  of the attached drawings, an apparatus according to the invention can be used in association with means for the embossing of the coupled webs ( 1 ) and is made up of a roller ( 2 ) having an outer surface ( 20 ) applied upon an elastic support surface: the roller ( 2 ) being engaged, free of rotating about its longitudinal axis, with a supporting fixed structure (not shown in the figures of the attached drawings for the sake of simplicity). 
     According to the example diagrammatically shown in  FIG. 5A , the embossing means comprise an operating group, of a type known to those skilled in the art, having two pairs of embossing rollers and cylinders ( 3 ,  4 ;  30 ,  40 ) associated with a corresponding motor member (not shown) to drive them into rotation about respective longitudinal axes, as indicated by the arrows (R) in  FIG. 5A . 
     According to the example illustrated in  FIG. 7 , the roller ( 2 ) comprises a rigid cylinder ( 21 ), made of steel for example, with coaxial end hubs ( 22 ) which define a shaft to be idly supported by a fixed structure (not shown). The cylinder ( 21 ) is provided with an elastic coating ( 23 ), for example of “Neoprene” rubber having a hardness ranging from 60 to 90 Shore. Applied on said coating ( 23 ), for example by a “Loctite” adhesive, is a hard surface ( 20 ) made of steel, for example. 
     The hard surface ( 20 ) can be formed, for example, by applying a helicoidal element having preset pitch and direction, as shown in  FIGS. 6A-6D . In case of the example of  FIG. 6D , the screw pitch is preset so that the hard surface ( 20 ) will fully cover the elastic surface ( 23 ). 
     In practice, the surface ( 23 ) acts as an elastic support for the surface ( 20 ) which is laid on it. 
     The roller ( 2 ) is positioned downstream of the embossing means, so that the coupled webs ( 1 ) result, before leaving the system, interposed between the embossing cylinder ( 4 ) and the roller ( 2 ). 
     The roller ( 2 ) is associated with hydraulic means, of a type known to those skilled in the art, which keep the same roller all the time in abutment against the cylinder ( 4 ). 
     The cylinder ( 4 ) and roller ( 2 ) cooperate with each other in compressing the two webs ( 5 ,  6 ) which form the coupled webs ( 1 ). More particularly, the two webs are squashed, while advancing towards the outlet, between the surface of cylinder ( 4 ) and the hard surface ( 20 ) of roll ( 2 ), thereby giving rise to a coupling of the webs which is sufficiently stable for the uses this type of material is intended for, even if no adhesive is employed between the two paper webs. The hardness of the surface ( 20 ) of roller ( 2 ) ensures that, in the above said final coupling of the two webs, the same surface will not deform to such an extent that could make it penetrate the cavities or impressions of cylinder ( 4 ), so that the embossing previously operated will not undergo any undesired alteration. Besides, as the surface ( 20 ) is mounted on an elastic support, any vibration possibly derived by the cooperation between the rotating cylinder ( 4 ) and roller ( 2 ) is substantially suppressed. 
     When it is desired that the above described effect will interest the whole width of the coupling, the length of roller ( 2 ) is made substantially equal to that of cylinder ( 4 ). If such effect has to concern only a portion of the coupling, the roller ( 2 ) can be shorter than the cylinder ( 4 ). 
     It will be appreciated that the webs ( 5 ,  6 ) may be either of individual or multiple type. 
     The above described apparatus ( 2 ) is advantageously utilizable also within a system of a type shown in  FIG. 8 , according to which there is provided the union of an embossed web ( 5 ) with a smooth or non-embossed web ( 6 ) by means of a unique embossing group ( 3 ,  4 ) which operates the embossing of only one of the two webs. The operation of the apparatus ( 2 ) is identical to that previously described with reference to the schematic diagram of  FIG. 5A . 
     The present apparatus is also advantageously utilizable also within a system of a type shown in  FIG. 9 , according to which there is provided the union of two webs ( 5 ,  6 ) which are both embossed by a unique embossing group ( 3 ,  4 ). Also in this case, the operation of the apparatus ( 2 ) is identical to that described with reference to the schematic diagram of  FIG. 5A . Moreover, the present apparatus is also advantageously utilizable also within a system of a type shown in  FIG. 10A , wherein no embossing is provided prior to the union of the paper webs. The cylinder ( 4 ) may be of a type provided either with simple pyramidal surface cuts, as illustrated in  FIG. 10A , or with surface reliefs of a preset shape and design ( 401 ) and distributed over the surface of the same cylinder according to a predetermined order, as illustrated in  FIG. 12A . In the latter case, the roller ( 2 ) may be advantageously of a type like the one represented in  FIG. 6D , with the hard surface ( 20 ) fully covering the elastic surface ( 23 ). Also in this case, the operation of the apparatus ( 2 ) is identical to that described with reference to the schematic diagram of  FIG. 5A . 
     The cylinder ( 4 ) represented in  FIG. 11A  may be advantageously used within the scheme of  FIG. 5A . Such cylinder exhibits pyramidal surface cuts ( 400 )—shown in the drawing with a grid-like filling—and reliefs ( 401 ) of predetermined shape and size. 
     In view of the union of the two paper webs ( 5 ,  6 ) which, as previously set forth, may be multiple webs, an operating method according to the present invention includes compressing the paper webs between a pressure roller or cylinder ( 2 ) and an impression roller or cylinder ( 4 ), the impression cylinder being provided with surface reliefs and/or depressions, and the outer surface of said pressure cylinder being a hard surface. 
     According to the method of the present invention, the cylinder ( 4 ) may also be an embossing cylinder. 
     While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.