Abstract:
An apparatus for obtaining watermarks or patterns in paper or cardboard while being formed on a formation tape or table in a paper or cardboard manufacturing plant, comprising: 
     a primary fibrous mix source for storing a primary fibrous mix; 
     at least one manifold, which can be arranged proximate to the formation table; 
     at least one jet nozzle which can be fed by the at least one manifold and is arranged above the formation table so that it can be angularly adjusted with respect thereto; 
     a feeding duct for a secondary fibrous mix and a return duct from the at least one manifold; and 
     a secondary fibrous mix source arranged to supply the feeding duct and to receive material discharged from the feeding duct for return from the at least one manifold.

Description:
This is a divisional application of patent application Ser. No. 08/854,729 filed May 12, 1997, now U.S. Pat. No. 5,916,416. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method and an apparatus for manufacturing paper and cardboard having watermarks or patterns and to the paper and cardboard thus obtained. 
     SUMMARY OF THE INVENTION 
     A first object of the present invention is to provide a method for manufacturing papers and cardboards which makes it possible to produce a plurality of patterns or watermarks during paper manufacture without the need of interrupting the manufacturing process, thus avoiding downtimes caused by machine stops. 
     An object of the present invention is to provide an apparatus for producing watermarks or patterns in the paper being manufactured which can be applied on the conventional formation table or tape of a paper manufacturing plant of any suitable type. 
     Another object of the present invention is to provide papers and cardboards with watermarks or patterns obtained without using a conventional dandy roll. 
     A further object of the present invention is to make it possible to obtain papers or cardboards provided with security watermarks, i.e., watermarks which can be made visible only by adding chemicals which react with adapted markers. 
     According to the present invention, there is provided an apparatus for obtaining watermarks or patterns in paper or cardboard while being formed on a formation tape or table in a paper or cardboard manufacturing plant, comprising: 
     a primary fibrous mix source for storing a primary fibrous mix; 
     at least one manifold, which can be arranged proximate to the formation table; 
     at least one jet nozzle which can be fed by said at least one manifold and is arranged above said formation table so that it can be angularly adjusted with respect thereto; 
     a feeding duct for a secondary fibrous mix and a return duct from said at least one manifold; and 
     a secondary fibrous mix source arranged to supply the feeding duct and to receive material discharged from the feeding duct for return from said at least one manifold. 
     Advantageously, said source of cellulose mix comprises a feeder reservoir provided with an agitator, a delivery pump, and a filtration system, for feeding dyed and/or pigmented mix to the or each feed duct, a reservoir for storing the cellulose mix provided with a pump delivering to the feeder reservoir and with a level measuring device, and a dye or pigment reservoir arranged to feed the storage reservoir in a controlled manner. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further aspects and advantages of the method according to the present invention will become apparent from the following detailed description of some embodiments thereof, given only by way of non-limitative examples. 
     EXAMPLE 1 
     A primary fibrous mix was prepared which had softness and good rigidity characteristics and had the following composition: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 cotton cellulose designed to give softness 
                  8.5% 
               
               
                   
                 to the final product 
               
               
                   
                 mechanical wood pulp, adapted to give a 
                  27.0% 
               
               
                   
                 fluffy effect to the final product 
               
               
                   
                 sulfate cellulose, adapted to give 
                  64.5% 
               
               
                   
                 mechanical strength to the final product 
               
               
                   
                 Total 
                 100.0% 
               
               
                   
                   
               
             
          
         
       
     
     Note: Throughout the present specification, the percentages are to be understood by weight unless otherwise specified. 
     This mix was spread on a formation table or tape of a conventional paper-manufacturing plant and was treated with an apparatus (described in detail hereinafter) with a plurality of jets of a mix having the same composition as that specified above, but pigmented with light dye. 
     The result was a dark gray paper affected by parallel lines approximately 1.2-1.3 mm wide which were significantly lighter in colour and integral with the paper body and suitable for giving a “pinstripe” appearance to the paper. The impact force of the jets in fact produced a continuous groove-shaped recess or hollow between the surface fibers of the body or base paper layer being formed, and a simultaneous application of secondary fibrous mix (as also specified hereinafter), i.e. dyed pulp-like material having the same composition as the base paper layer, which results in the filling of the grooved recess. 
     Since the base paper layer which advances on the tape is still relatively fluid, the formation of a groove simply causes fibers to move apart and to amalgamate and level out in the pulp-like layer immediately thereafter, thereby also acting as confinement sides or barriers for the applied material supplied by the jet. 
     EXAMPLE 2 
     The same procedure as in Example 1 was followed, but with a primary fibrous mix having the following composition: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 cotton cellulose 
                  15% 
               
               
                   
                 mechanical wood pulp 
                  16% 
               
               
                   
                 sulfate cellulose 
                  69% 
               
               
                   
                 Total 
                 100% 
               
               
                   
                   
               
             
          
         
       
     
     The result was a rather resistant pinstripe paper with deep blue linear dashes. The linear dashes were obtained by rhythmically interrupting the jets of blue-dyed cellulose mix at a preset rate. 
     EXAMPLE 3 
     The same procedure as in Example 1 was followed, but using a primary fibrous mix having the following composition: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 cotton cellulose 
                  20% 
               
               
                   
                 mechanical wood pulp 
                  34% 
               
               
                   
                 sulfate cellulose 
                  46% 
               
               
                   
                 Total 
                 100% 
               
               
                   
                   
               
             
          
         
       
     
     A relatively rigid pinstripe white paper with pale blue lines was obtained. 
     EXAMPLE 4 
     The same procedure as in Example 1 was followed, but using a primary fibrous mix having the following composition: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 cotton cellulose 
                  6% 
               
               
                   
                 mechanical wood pulp 
                  16% 
               
               
                   
                 sulfate cellulose 
                  78% 
               
               
                   
                 Total 
                 100% 
               
               
                   
                   
               
             
          
         
       
     
     The result was a red paper affected by wave-shaped white lines obtained by causing the jets of fibrous mix to wave. 
     An average of the physical and mechanical characteristics of papers obtained according to the above Examples 1 to 4 is given in the following Table 1, which also indicates maximum and minimum tolerances. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Unit of 
                 Nominal 
                 Tolerances 
                 Type of 
               
             
          
           
               
                   
                 measure 
                 value 
                 min. 
                 max. 
                 analysis 
               
               
                   
                   
               
             
          
           
               
                 Grammage 
                 g/sq.m 
                 100 
                 98 
                 102 
                 primary 
               
               
                 Thickness 
                 micron 
                 160 
                 150 
                 170 
                 secondary 
               
               
                 Absolute humidity 
                 % 
                 50 
                 45 
                 55 
                 primary 
               
               
                 Gurley air res. 
                 sec. 
                 30 
                 15 
                 50 
                 secondary 
               
               
                 Cobb index (felt) 
                 g/sq.m 
                 25 
                 20 
                 30 
                 primary 
               
               
                 Bursting strength 
                 KPa 
                 200 
                 180 
                 &gt; 
                 secondary 
               
               
                 Tearing strength 
               
               
                 longitudinal 
                 mN 
                 700 
                 500 
                 900 
                 secondary 
               
               
                 transverse 
                 mN 
                 700 
                 500 
                 900 
                 secondary 
               
               
                 Dry pulling strength 
               
               
                 longitudinal 
                 N/15 mm 
                 60 
                 50 
                 &gt; 
                 secondary 
               
               
                 transverse 
                 N/15 mm 
                 32 
                 28 
                 &gt; 
                 secondary 
               
               
                 Dry pulling strength 
               
               
                 longitudinal 
                 % 
                 2.0 
                 1.8 
                 &gt; 
                 secondary 
               
               
                 transverse 
                 % 
                 4.0 
                 3.0 
                 &gt; 
                 secondary 
               
               
                 Folding strength 
               
               
                 longitudinal 
                 no. 
                 40 
                 30 
                 60 
                 secondary 
               
               
                 transverse 
                 no. 
                 30 
                 20 
                 50 
                 secondary 
               
               
                 Taber rigidity 
               
               
                 longitudinal 
                 U.T. 
                 2.3 
                 2.0 
                 &gt; 
                 secondary 
               
               
                 transverse 
                 U.T. 
                 2.0 
                 1.5 
                 &gt; 
                 secondary 
               
               
                   
               
             
          
         
       
     
     The cotton cellulose used in the above Examples has a high content of alpha-cellulose designed to give the paper a soft touch which can be similar to the touch of fabric, whilst the mechanical wood pulp helps to give “fluffy” visual characteristics to the final paper. 
     Examples of composition of the secondary fibrous mix to be added by jet to a sheet of paper being formed in order to produce immediate monolithic composition are given hereafter. 
     Example A 
     To obtain a pinstripe effect of the final paper, with bluish lines at average viscosity for a finished paper grammage between 80 and 120 g/sq m, with a white color, the following composition was used for the secondary fibrous mix: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 % 
                 weight in grams 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Cellulose fiber, in the same 
                 2.2 
                 22 
               
               
                 proportion and with the same 
               
               
                 composition as in the primary mix 
               
               
                 Inorganic pigment 
                 1.6 
                 16 
               
               
                 Surfactants 
                 0.000016 
                 0.00016 
               
               
                 Direct blue dye 
                 0.006 
                 0.06 
               
               
                 Antifoaming agent 
                 0.0001 
                 0.001 
               
               
                 Water 
                 96.193884 
                 961.93884 
               
               
                 Total 
                 100 
                 1000 
               
               
                   
               
             
          
         
       
     
     Example B 
     The same procedure as in Example A was followed to obtain a pinstripe effect with bright red lines with high viscosity for a finished paper grammage between 130 and 250 g/sq.m in a plurality of colors (green, yellow, blue) by using the following composition for the secondary mix: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 % 
                 weight in grams 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Cellulose fiber, in the same 
                 3.7 
                 37 
               
               
                 proportion and with the same 
               
               
                 composition as in the primary mix 
               
               
                 Inorganic pigment 
                 2.2 
                 22 
               
               
                 Surfactants 
                 0.000018 
                 0.00018 
               
               
                 Dye 
                 0.12 
                 1.2 
               
               
                 Antifoaming agent 
                 0.00014 
                 0.0014 
               
               
                 Water 
                 93.979842 
                 939.79842 
               
               
                 Total 
                 100 
                 1000 
               
               
                   
               
             
          
         
       
     
     Example C 
     The same procedure as in Example A was followed in order to obtain a pinstripe effect with lemon yellow lines with very high viscosity for a finished paper grammage between 260 and 700 g/sq.m in a plurality of colors (black, blue, green, brown, red) by using the following composition for the secondary mix: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 % 
                 weight in grams 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Cellulose fiber, in the same 
                 5.5 
                 55 
               
               
                 proportion and with the same 
               
               
                 composition as in the primary mix 
               
               
                 Inorganic pigment 
                 4.2 
                 42 
               
               
                 Surfactants 
                 0.000011 
                 0.00011 
               
               
                 Dye 
                 0.023 
                 0.23 
               
               
                 Antifoaming agent 
                 0 
                 0 
               
               
                 Water 
                 93.276989 
                 902.76989 
               
               
                 Total 
                 100 
                 1000 
               
               
                   
               
             
          
         
       
     
     All the dyes used in Examples A to C for colorimetric differentiation of the watermark lines are inclined in the light solidity scale which equals the oxidation rate of the cellulose fiber forming the sheet of paper. 
     Viscosity at 20° C. ranges between 30 and 100 mPa.s by the Brookfield SP no. 3 test and can be chemically anionic and cationic in nature with a pH ranging between 5 and 9. 
     If desired, it is possible to use a fluorescent dye or a dye which can be detected with a UV system at wavelengths between 50 and 400 nm in the visible part of the spectrum. 
     A detailed description is given hereafter, with reference to the drawings, of an embodiment of a multiple-jet apparatus used to obtain a paper featuring watermarks, security watermarks or patterns without using the conventional dandy roll. 
    
    
     In the drawings: 
     FIG. 1 is a schematic perspective view of a formation table, provided with a tape of a paper-manufacturing plant provided with a multiple-jet apparatus according to the present invention; 
     FIG. 2 is a schematic lateral elevation view, with parts shown in cross-section, illustrating the operation of an apparatus according to the present invention; 
     FIG. 3 is a partial perspective view of a nozzle-supporting manifold mounted so that it can be orientated astride the formation table or tape of FIG. 1; 
     FIG. 4 is an enlarged-scale transverse sectional view of the nozzle-supporting manifold of FIG. 3; 
     FIGS. 5 and 6 are views of two nozzle-supporting spacers of different lengths for the manifold of FIGS. 3 and 4; 
     FIG. 7 is a partial axial longitudinal sectional view of a nozzle fitted in a respective spacer; 
     FIG. 8 is a schematic perspective view of a groove formed by a jet of applied secondary mix material which binds and amalgamates, so as to become fully included in an underlying ribbon of paper lying on the formation table or tape; and 
     FIGS. 9 to  12  are views of patterns obtained on paper produced according to the method of the present invention. 
    
    
     In the accompanying drawings, identical or similar parts or components have been designated by the same reference numerals. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the Figures in the drawings, it will. be seen that an apparatus for manufacturing watermarks or patterns in paper or cardboard while being manufactured is constituted by one or more manifolds  1  which can be arranged transversely above a formation table or tape  2  of a paper or cardboard-manufacturing apparatus, generally designated by the reference numeral  3  (FIG.  1 ). Preferably, the manifold  1  is arranged downstream of a conventional dandy roll  4  with respect to the advancement direction of the formation tape  2 , indicated by the arrow A, but it might also be placed upstream of the dandy roll  4 , or it is possible to provide one manifold upstream and one downstream of said dandy roll, according to requirements. 
     The at least one manifold  1 , as better shown in FIG. 3, is supported so as to straddle two lateral longitudinal members  5  extending along the sides of the formation table or tape  2  so that the manifold can rotate about its own longitudinal axis. More particularly, the manifold  1  has two end flanges  6 , to each of which a flange  8  is fixed, e.g. by means of bolts  7 , to the end of a respective portion of rigid pipe  9 , whose other end is provided with a coupling or nipple  10 . Each portion of the pipe  9  is in turn inserted and fixed, by means of locking grub screws or headed screws  11 , in a sleeve  12  having two wings  13  and  14  opposite to each other. The wing  14  is linked to an articulation pivot  15  supported by a fixing block  16  integral with the longitudinal members  5 , whilst the wing  13  is formed with a threaded through hole into which an adjustment screw  17  can be screwed to make it possible to adjust the distance at which it must stop with respect to the longitudinal members  5  when the entire rotating assembly formed by the sleeve  12  and by the portion of pipe and thus by the flanges  6  and  7  and the manifold  1  is rotated about the pair of aligned pivots  15 . 
     If desired, the support  16  or some other fixed part can support a pointer  18  pointed towards the flange  8 , on which a dividing scale in angular degrees  19  is suitably provided or otherwise applied for reading the values of the angular displacements of the moving assembly from a reference position. 
     The couplings  10  of the portions of pipe  9  can be connected to a respective flexible hose  20  and  21 ; the hose  20  acts as feeding hose for the manifold, whilst the hose  21  acts as discharge hose. If the hose  21  is made of a flexible plastic material, in use, it can advantageously also act as a damping element for pulsations occurring inside the manifold  1  above the level of the liquid mix contained therein. 
     The manifold  1  is constituted by a tubular body having an internal opening having a four-sided cross-section. One of its side walls supports a plurality of jet nozzles  23 , which are arranged for example in a staggered configuration along two parallel longitudinal rows or lines. Each nozzle  23  is constituted by a supporting ring  24 , a threaded connector  25 , an internal filter  26 , and a nozzle tip  27  supported by the threaded connector. 
     The internal opening of the manifold  1  having a four-sided cross-section is more advantageous than a round cross-section for fluid-dynamics reasons, since it ensures a more uniform size and distribution of the threads of the fluid mix directed towards the respective nozzles  23  distributed along said manifold. 
     The supporting ring  24  is longer for the nozzles of the upper row and shorter for those of the lower row, so that, in use, the tips of the nozzles of both rows are substantially at the same level, albeit staggered, above the underlying paper or cardboard web being formed on the formation tape  2  (FIG.  4 ). Moreover, each ring  24  has an externally threaded end designed to be screwed into a corresponding threaded through hole in the wall of the manifold and to at least partially accommodate a filter  28 ; the other end of each ring  24  is internally threaded for receiving therein a threaded connector  25  to fix a respective nozzle tip  27 . Said nozzle tip can be internally provided, at its end, with a gauged nozzle  29  made of tough material, typically a ceramic material (FIG.  7 ). 
     Once the nozzles  23  have been placed above the formation tape  2 , by turning the sleeves  12  about the pivots  15 , by screwing the adjustment screw  17  in one direction or the other, it is possible to vary the angle of incidence of the nozzles  23  with respect to the plane in which the formation tape  2  is arranged. 
     Said tape is provided underneath, as is conventional in the art, with suction boxes (not shown in the drawings) and is stretched by a rear free guiding roller  30  and suction driving roller  31 , whilst its return portion follows a zigzag washing path guided by guiding rollers  32 . A conventional head box  33  is located above the rear guiding roller  30  and spreads on the formation tape a substantially uniform web of primary paper mix which, as it is moved towards the driving roller  31 , loses water mainly owing to the action of the suction boxes and gradually becomes a paper or cardboard web. 
     When passing under the manifold  1 , the web is affected by jets of a secondary mix which is substantially of the same type as that of the mix of the paper being formed, but differently pigmented. 
     To this end, the supply duct  20  of the manifold  1  is connected to a filtering system  34  by means of a pressure sensor and a cutoff valve  36 . The filtering system  34  is in turn connected via a duct  38  to the delivery of an electric pump  37 , whose suction inlet is connected to the interior of a feeder reservoir  39  just above the bottom thereof. 
     Preferably, between the cutoff valve  36  and the filtering system  34  a shunt duct  40  is provided which starting from the duct  20  discharges into the feeder reservoir through a cutoff valve  41  and a pressure adjustment valve  42 . 
     The filtering system  34  preferably comprises two filtering units  34   a  and  34   b , which are connected in parallel and have interposed therebetween cutoff valves  34   c . Uninterrupted filtration is thus ensured even when it is necessary to clean one filtering assembly, since the other filtering unit can be held in operation. 
     The discharge or return duct  21  instead discharges directly into the feeder reservoir  39 . 
     Said feeder reservoir is provided with sensors  43  for detecting the level of the dyed and/or pigmented liquid mix contained in the tank and is also equipped with a motorized agitator  44  and optionally with a discharge cock  45 . 
     A pipe  46  also discharges into the feeder reservoir  39  and is provided with an adjustment valve  47 , driven by the level sensors  43 , and with a cutoff valve  48 , and is connected, across a viscosity meter  49 , to the delivery of an electric pump  50  arranged on the bottom of a storage reservoir  51  for primary cellulose mix. Downstream of the viscosity meter  49 , the pipe  46  is connected to a discharge pipe  52  inside the storage reservoir, with interposition of a cutoff valve  53 . The storage reservoir  51  also has level detecting probes  54  and a discharge cock  55  on the bottom. 
     A water duct  56  and a duct  61  discharge into the storage reservoir  51 ; said duct  56  is provided with an electric valve  57 , driven by the probes  54 , for maintaining a preset level within the storage reservoir, with a filter  58 , with a liter counter  59  and with a cutoff valve  60 , and the duct  61  is provided with a filter  62  and a liter counter  63  and is connected to the delivery of an electric pump  64 . The intake port of said pump is connected to the inside of a reservoir  65  for the dye or pigment designed to be fed in a controlled manner to the storage reservoir  51 . The dye or pigment reservoir  65  is provided with an agitator  66 . 
     The entire feeder system of the manifold  1  is controlled by a control unit, shown schematically and generally designated by the reference numeral  67  in FIG. 2, which has an electrical control panel provided with a pressure regulator  69 , a viscosity control regulator, a general control PLC, and a luminous revolving alarm  71 . 
     A load of cellulose mix having the same composition as that fed to the head box  33  at the leading edge of the formation tape  2  is maintained in the storage reservoir  51  (for example by means of an adapted feeder duct, not. illustrated in the drawings). The dispersion of the components and additives must reach a level which ensures; that no clots are formed. For this purpose, agitation and mix transfer from one reservoir to the other must be performed gently, so as to avoid formation of foam. 
     The temperature of the mix must be kept strictly within a range between 15 and 85° C. and preferably between 5 and 10° C. above or below the paper-like medium temperature in order to constantly maintain the correct viscosity for impact with the paper medium on the formation tape  2 , so as to ensure that the material added by jet-spraying through the nozzles  23  binds almost immediately to it, so as to become amalgamated therewith. 
     In order to do this, the material leaving the nozzles  23  must have a correct jet pressure, between 10 and 1000 cm of water head, preferably between 25 and 35 cm of water head, a specific vacuum interval in the suction box or boxes directly below the manifold  1 , preferably in the range between 100 and 400 millibars, and a preset angle of incidence between the jets from the nozzles  23  and the web of paper lying on the formation tape  2 . It has been found that in practise such an angle can be between 0 and 90° and preferably between 25° and 35°. 
     With the above-described apparatus it is thus possible to obtain watermarks or patterns, for example as shown in FIGS. 9 to  12 , which illustrate merely by way of example papers with a so-called “pinstripe” effect obtained with the method and apparatus according to the present invention. 
     By arranging the manifold downstream of the dandy roll  4 , as shown in FIG. 1, one obtains sharply outlined patterns or watermarks DVn within the margins of the deformation or hollow Ic (FIG. 8) formed in the layer of primary mix paper Cp by the jet or jets  23   a  from the nozzles  23 , whilst by arranging the manifold upstream, where the layer or web of primary mix paper is more liquid, one obtains patterns or watermarks which are less sharply outlined and have less defined outlines. 
     It will be noted that in any case the patterns and the watermarks are obtained online, i.e., during manufacture of the paper, without having to interrupt the manufacturing process, to the full benefit of the productivity per unit time of the apparatus. 
     The above-described apparatus is susceptible to numerous modifications and variations within the scope of its protection defined by the claims. 
     Thus, for example, the at least one manifold  1  can feed a plurality of nozzles  23 , which are mounted on a supporting structure separate from the manifold and arranged so as to straddle the formation tape  2  and are connected to the manifold by means of a respective duct which is for example flexible to allow various angular configurations of the structure and therefore of the nozzles with respect to the plane containing the formation tape. In this case, the manifold or manifolds  1  can also be fitted to the side of the formation tape. 
     The manifold  1 , or in any case the nozzle supporting structure, can be mounted so that it can move along a transverse axis with respect to the direction of advancement of the formation tape and can be driven so as to perform a back-and-forth motion, for example to obtain particular wavy patterns or laid lines on the paper or cardboard being formed. 
     Moreover, instead of a single manifold  1  it is possible to use two or more manifolds I arranged in sequence above the formation tape  2 , each manifold being optionally provided with one or two rows of nozzles  23  and contributing to the formation of specific patterns or laid lines on or in the underlying layer of primary mix paper, as will be apparent to an expert in the field.