Abstract:
A web of material serves for use in a corrugating machine for the manufacture of sheets of corrugated board. The corrugating machine comprises at least two unroll stands for unwinding webs of material. A fluting unit serves for the manufacture of at least one corrugated medium from one of the webs of material. A processing equipment serves for uniting the webs of material to form a web of corrugated board. The sheets of corrugated board are cut from the web of corrugated board by means of a cutting unit. A printing system is provided for printing at least one of the webs. The web of material has a coating for improved printing quality. A method for the manufacture of sheets of corrugated board is specified, using such a web of material. The results are sheets of corrugated board with improved imprint.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a method for the manufacture of sheets of corrugated board on a corrugating machine, comprising at least two unroll stands for unwinding webs of material from reels of material; at least one fluting unit for the manufacture of at least one corrugated medium from one of the webs of material; at least one processing equipment for uniting the corrugated medium and at least another web of material to form a web of corrugated board; a cutting station for cutting the sheets of corrugated board from the web of corrugated board; a printing system for printing at least one of the webs.  
           [0003]    2. Background Art  
           [0004]    Corrugating machines for the manufacture of single-faced corrugated board or multi-layer corrugated board are for example known from U.S. Pat. No. 5,632,850. Simple and flexible methods of printing webs of corrugated board have not been known.  
         SUMMARY OF THE INVENTION  
         [0005]    It is an object of the invention to develop a web of material for the manufacture of corrugated board of the type mentioned at the outset in such a way that the quality of printing this web of material is improved. This object is attained in that a coating for improved printing quality is applied to at least one web which is to be printed and in that the web is printed.  
           [0006]    The invention is based on the idea that the coatings used for improved printing quality in other fields, for instance in printing special paper or special films for office purposes, can also be used when webs of material of corrugating machines are printed. This is surprising, given the different nature of the starting material. The coating—also called primer—which improves the printing quality results in that the printing ink can be applied accurately and, in particular, will not run once it has been applied. This will augment the achievable printing resolution, thus improving the printing quality. The coated web of material is provided in reels as they are customarily used in corrugating machines. By alternative, the coating, which improves the printing quality, can also be applied directly prior to printing. This coating will help augment the printing quality even in otherwise unmodified corrugating machines.  
           [0007]    In the case of digital printing, the print application patterns can be distributed rather flexibly on the web that is to be printed. In particular, it is possible to handle rather small printing jobs, imprinting varying patterns on the webs being feasible without exchange of hardware components of the printing system. The patterns can be printed in various directions, in particular lengthwise and crosswise of the web conveying direction, with varying scaling. It is even possible, in particular when an ink jet printer is used, to print a web of single-faced corrugated board on the side of the corrugated medium, which is not feasible when printing cylinders are used. Any subsequent printing of the sheets of corrugated board or printing of reels of material that are kept in the corrugating machine prior to operation can be dropped.  
           [0008]    Details of the invention will become apparent from the ensuing description of several exemplary embodiments, taken in conjunction with the drawing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0009]    [0009]FIG. 1 is a view of a first part of a corrugating machine according to a first embodiment;  
         [0010]    [0010]FIG. 2 is a view of a detail of FIG. 1, on an enlarged scale, in the vicinity of a first web of material;  
         [0011]    [0011]FIG. 3 is a plan view of a detail of the first web of material in the vicinity upstream of a heater in the first part of the corrugating machine;  
         [0012]    [0012]FIG. 4 is a plan view of a detail of the first web of material downstream of the heater in the first part of the corrugating machine;  
         [0013]    [0013]FIG. 5 is a plan view of details of a printed web of material;  
         [0014]    [0014]FIG. 6 is a view of a second part of the corrugating machine according to the first exemplary embodiment;  
         [0015]    [0015]FIG. 7 is a view of a second part of a corrugating machine according to a second exemplary embodiment;  
         [0016]    [0016]FIG. 8 is a view of a first part of a corrugating machine according to a third exemplary embodiment;  
         [0017]    [0017]FIG. 9 is a view of a second part of a corrugating machine according to the third exemplary embodiment;  
         [0018]    [0018]FIG. 10 is a view of a first part of a corrugating machine according to a fourth embodiment; and  
         [0019]    [0019]FIG. 11 is a view of a second part of the corrugating machine according to the fourth embodiment. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0020]    The following is a description of a first embodiment of the invention, taken in conjunction with FIGS.  1  to  6 . A corrugating machine as diagrammatically plotted in FIGS. 1 and 6 comprises a machine  1  for the manufacture of single-faced corrugated board. From a first unroll stand  2 , a first web of material  3  is fed to the machine  1 . The webs of material are continuous paper webs. The web of material  3  constitutes a backer web for the corrugated board manufactured on the machine  1 . FIG. 2 is a side view, on an enlarged scale, of the first web of material  3  in detail. It comprises a backer  3   a  with a primer  3   b  which improves the printing quality. The backer  3   a  to primer  3   b  thickness ratio is not true to scale in FIG. 2. In practice, the primer  3   b  is substantially thinner as compared to the backer  3   a  than shown in FIG. 2. The primer  3   b  must not necessarily be available in a form applied to the web of material  3  when it is rolled up; it can just as well be applied to the web of material  3  later upon unwinding.  
         [0021]    Between the first unroll stand  2  and the machine  1 , the first web of material  3  passes through a first digital printing unit  4  with an ink jet head  5  which prints the top side of the first web of material in accordance with a printing job. Via a signal line  6 , the printing unit  4  is in connection with an application control unit  7 .  
         [0022]    In the machine  1 , the printed first web of material  3  is united with a second web of material  8  which is supplied from a second unroll stand  9 . When unrolled, the second web of material  8  passes between two adjacent fluted rollers  10  which are allocated to each other for producing a corrugation. After passing there-through, the second web of material  8  is available in the form of a corrugated medium  8 . Then adhesive is applied to the tips of the medium  8  in an adhesive applicator unit  11 , and the medium  8  and the first web of material  3  are pressed together and united in a nip between a nip roller  12  and one of the fluted rollers  10 . Consequently, the machine  1  is a first production unit of a processing equipment  42  for uniting webs of material to form a web of corrugated board. A single-faced web of corrugated board  13  is discharged upwards from the machine  1  and deflected about a deflection roller  14  into a working direction  15 . The machine  1  for the manufacture of single-faced corrugated board is generally known for example from U.S. Pat. No. 5,632,850, GB 2 305 675 A or DE 43 05 158 A1, to which reference is made for details.  
         [0023]    [0023]FIGS. 3 and 4 illustrate details of the first web of material  3  in a plan view. FIG. 3 shows the web of material  3  prior to it passing, in the working direction  15 , through a pre-heater  16  downstream of the deflection roller  14 . The first web of material  3  marginally comprises first marks  17  which are equidistant division marks that extend crosswise of the working direction  15 . Upstream of the pre-heater  16 , two adjacent first marks  17  have a distance a, from each other. At regular distances in the working direction  15 , the first web of material further comprises stripes of second marks  18  which are equidistant short division marks that are parallel to the working direction  15 . Upstream of the pre-heater  16 , two adjacent marks  18  have a distance b 1  from each other. FIG. 4 shows the web of material  3  in an illustration similar to FIG. 3 downstream of the pre-heater  16 . The distance between two adjacent first marks  17  is a 2  and the distance between two adjacent second marks  18  is b 2 . Owing to shrinkage of the web of corrugated board  13  after being heated in the pre-heater  16  and owing to the modifications, resulting therefrom, in the dimensions of the web of material  3 , the following applies to the distances: a 2 &lt;a 1  and b 2 &lt;b 1 .  
         [0024]    A reader  19 , which is disposed above the web of corrugated board and thus above the top side of the first web of material  3  that carries the marks  17 ,  18  and between the deflection roller  14  and the pre-heater  16 , determines the distances a 1  and b 1  between adjacent marks  17 ,  18 . To this end the reader  19  is similar to a bar code scanner. Via a signal line  20 , the reader  19  is in connection with the application control unit  7 .  
         [0025]    A second unroll stand  21  for a third web of material  22  as another liner of the single-faced web of corrugated board  13  is disposed downstream of the machine  1  in the working direction  15 . The corrugated medium  8 , the first web of material  3  which is the backer web, and the third web of material  22  which is the liner web are suitably selected paper webs. In part, it is also usual to call the third web of material  22  the liner web, with the first web of material  3  in this case being called primer web. The webs of material  3 ,  8  and  22  are unrolled at a speed of up to 400 m/min.  
         [0026]    Downstream of the second unroll stand  21 , the third web of material  22  is first deviated about a deflection roller  23  so that it runs in the working direction  15 . Then the third web of material  22  is deviated by 180° by another two deflection rollers  24 ,  25  so that the side that faces downwards between the deflection rollers  23  and  24  is now turned upwards, the third web of material  22 , downstream of the deflection roller  25 , running counter to the working direction  15 . Downstream of the deflection roller  25 , the third web of material  22  passes through a second printing unit  26  which cooperates with the first printing unit  4 , forming a digital printing system  27 . The side of the third web of material  22  that is turned upwards downstream of the deflection roller  25  is printed by an ink jet head  28  in the printing unit  26 , in accordance with a printing job. The third web of material  22  is also of two-layer design, having a backer and a primer such that the ink jet head  28  of the second printing unit  26  imprints the primer of the third web of material  22 . The primer of the third web of material can also be applied after being unrolled and upstream of the second printing unit  26 .  
         [0027]    For print application control, the second printing unit  26  is in connection with the application control unit  7  via a signal line  29 . After passing the second printing unit  26 , the third web of material  22 , by the aid of another two deflection rollers  30 ,  31 , is again deflected substantially by 180° so that downstream of the deflection roller  31 , the third web of material  22  again runs substantially in the working direction  15 .  
         [0028]    Downstream of the deflection roller  31 , the third web of material is fed to the pre-heater  16 . The pre-heater  16  comprises two heating rollers  32  that can be heated and are disposed one on top of the other. The single-faced web of corrugated board  13  and the third web of material  22  run one on top of the other, partially being in contact with the respective heating rollers  32 . An adhesive applicator unit  33  is disposed downstream of the pre-heater  16 , having an adhesive roller  33  which partially dips into an adhesive pan  35 . The medium  8  of the web of single-faced corrugated board  13  is in contact with the adhesive roller  34 .  
         [0029]    Downstream of the adhesive applicator unit  33 , provision is made for a heating contact pressure device  36  which comprises a horizontal hot plate table  37  that extends in the working direction  15 . A continuously driven contact pressure belt  39  is provided above the table  37 ; it is deflected by way of three rollers  38 . A nip  40  is formed between the contact pressure belt  39  and the table, with the web of single-faced corrugated board  13  and the third web of material  22  passing through the nip  40  where they are pressed one upon the other. A corresponding heating device  36  is known from DE 199 54 754 A1. A three-layer web of corrugated board  41  is being formed in the heating device  36 . The heating device  36  and the table  37  constitute a second production unit of the processing equipment  42  for uniting webs of material to form a web of corrugated board  41 .  
         [0030]    [0030]FIG. 5 shows two sections of the printed first web of material  3  as part of the web of corrugated board  41  after discharge from the heating device  36 . Various printing patterns  43  are illustrated, which are necessary for printing certain sizes and types of boxes or cartons. As seen in FIG. 5 by way of example, the printing patterns  43  may differ in dimensions lengthwise or crosswise of the working direction  15 .  
         [0031]    The printing patterns  43  are for example advertising imprints, or instructions in the form of folding or cutting stencils, or printed numbers or dates, or imprints dealing with a certain batch of goods that must be wrapped by the aid of the sheets of corrugated board  62 ,  67 . They may be clearly worded, readable information or bar codes. Owing to the possibilities of the digital printing system  27 , printing-pattern- 43  variations are virtually unlimited. It is for instance conceivable to design the patterns  43  so that they represent individual parts of an entire picture which originates when sheets  62 ,  67  with these individual parts of printing patterns are joined or when wrappings are produced from these sheets.  
         [0032]    [0032]FIG. 6 illustrates a second part of the corrugating machine, following the discharge of the web of corrugated board  41  from the heating device  36 . At the upstream end of FIG. 6, a second reader  44  is disposed above the web of corrugated board  41 . The reader  44  is in connection with the application control unit  7  via a signal line  45  illustrated by dashes in FIG. 6. The second reader  44  registers the top side of the web-of-material- 3  section seen in FIG. 4. The second reader  44  measures the distances a 2 , b 2  between adjacent first marks  17  and adjacent second marks  18 .  
         [0033]    Downstream of the reader  44 —seen in the working direction  15 —a lengthwise cutting/grooving unit  46  is disposed, consisting of two successive grooving stations  47  and two successive lengthwise cutting stations  48 . The grooving stations  47  have grooving tools  49  which are arranged in pairs one on top of the other, with the web of corrugated board  41  passing there-between. The lengthwise cutting stations  48  have rotatably drivable cutters  50  which are movable into engagement with the web of corrugated board  41  for it to be cut lengthwise. The detailed design of the lengthwise cutting/grooving unit  46  is known from U.S. Pat. No. 6,071,222 and DE 101 31 833 A which reference is made to for further details of design.  
         [0034]    Downstream of the lengthwise cutting/grooving unit  46 —seen in the working direction  15 —provision is made for a shunt  51  where lengthwise cut sections  52 ,  53  of the web of corrugated board  41  are separated. The web sections  52 ,  53  are then fed to a cross-cutting unit  54 . It comprises a pair of top crosscutting rollers  55  for the top web section  52  and a pair of bottom crosscutting rollers  56  for the bottom web section  53 . The rollers of the pairs of rollers  55 ,  56  each have a cutter bar  57  which is perpendicular to the working direction  15 , extending radially outwards. The cutter bars  57  of a pair of crosscutting rollers  55 ,  56  cooperate for crosscutting the web sections  52 ,  53 . A top conveyor belt  58  is disposed downstream of the top pair of crosscutting rollers  55 ; it is deviated by rotatably drivable rollers  59 . Downstream of the top conveyor belt  58 , provision is made for a place of deposit  60  with a vertical stop  61  where sheets of corrugated board  62 , which have been cut from the web section  52  by means of the crosscutting unit  54 , are piled up, forming a stack  63 . As roughly outlined by an arrow  64  in FIG. 6, the place of deposit  60  is adjustable in height. For further dis-patch of the stack  63 , the place of deposit  60  can in particular be lowered as far as to a bottom  65  that supports the corrugating machine.  
         [0035]    Another bottom conveyor belt  66  is disposed downstream of the pair of crosscutting rollers  56 , stacking sheets of corrugated board  67  on another place of deposit  68 ; the sheets are cut from the web section  53  by means of the crosscutting unit  54 . For adaptation to the height of the stack  63 , the bottom conveyor belt  66  can be lifted as roughly outlined by the arrow  68 a.  
         [0036]    Printing the web of corrugated board  41  with patterns  43  takes place as follows: First the webs of material are provided with primers and supplied to the unroll stands  2  and  21 . The primers may also be dropped, in which case a non-coated web of material is made available at the unroll stand  9 . By alternative, the primer can also be applied directly upstream of the printing units  4 ,  26  after the webs of material have been unrolled. The marks  17 ,  18  are applied by the printing unit  4 . Then the corrugating machine starts running, producing a non-printed web of corrugated board  41 . This continues until the web of corrugated board that is produced has reached the area where it is registered by the second reader  44 . The two readers  19 ,  44  then register the distances a 1 , b 1  and a 2 , b 2  of the marks  17  and  18 . The readers  19 ,  44  then pass this information to the application control unit  7 . Based on the ratio a 2 /a 1  of the distances of the marks  17  upstream and downstream of the heating devices  16 ,  36 , a computer of the application control unit  7  determines a degree of longitudinal shrinkage of the webs of material  3 ,  8 ,  22  in the working direction  15 , i.e. a modification of the web dimensions in the longitudinal direction between the web in the vicinity of the first printing unit  4  of the printing system  27  on the one hand (reader  19 ) and the web prior to the sheets  62 ,  67  being cut on the other hand (reader  44 ). Correspondingly, cross-shrinkage of the webs of material  3 ,  8 ,  22  is determined by the aid of the ratio of the distances b 1 , b 2  of adjacent marks  18  in the vicinity of the reader  19  on the one hand and in the vicinity of the reader  44  on the other. Determining the cross shrinkage can be dropped as well as the associated marks. The distance parameters a 1 , a 2 , b 1 , b 2  are transmitted by the readers  19 ,  44  to the application control unit  7 .  
         [0037]    The degrees of shrinkage of the web of corrugated board  41  in the longitudinal and cross direction, which are determined by the application control device  7 , serve for the application control device  7  to determine scaling factors for the printing pattern  43  that will be applied by the printing units  4  and  26 . The printing units  4  and  26  apply the printing patterns  43  by dimensional reservation so that the desired size of the printing patterns  43  will appear on the web sections  52 ,  53  owing to the pre-determined shrinkage of the web. Simultaneously, the application control unit  7 , via signal lines (not shown), controls the lengthwise cutting stations  48  on the one hand and the crosscutting unit  54  on the other in accordance with the printing jobs transmitted by the application control unit  7  to the printing system  27 . The sheets of corrugated board  62 ,  67  are cut in such a way that the printing patterns  43  are located at pre-determined places on the sheets  62 ,  67 . The printing jobs transmitted from the application control unit  7  to the printing system  27  may involve small or minimal serial manufacture of only few sheets of corrugated board  62 ,  67 . Upon modification of the printing job, the lengthwise cutting stating  48  is triggered by the application control unit  7  so that the width of the web sections  52 ,  53  is cut correspondingly. Instead of the illustrated cross-cutting unit  54  with pairs of rollers  55 ,  56 , use can be made of a cross-cutting unit which is equally triggered by the application control unit  7 , enabling sheets of corrugated board of varying lengths to be cut in the working direction  15 . The sheets of corrugated board  62 ,  67  can then be adapted in size perfectly flexibly to the shape and size of the printing patterns  43  of the respective printing jobs.  
         [0038]    If necessary, prior to being printed, the sides of the webs of material  3 ,  22  that are to be printed can be cleaned by a corresponding equipment, for instance a compressed air sprayer. Sucking off is conceivable alternatively of blowing off the sides, to be printed, of the webs of material  3  and  22 . Finally, it is also possible to prepare the webs of material  3 ,  22  in such a way that they are antistatic, dust being prevented from depositing on the sides that are to be printed. Preferably, printing the webs of material  3 ,  22  takes place in an air-conditioned environment. The temperature is kept at less than 40° C. Once the webs of material  3 ,  22  have been printed, the printed sides can be sealed by a corresponding protective layer being applied. This type of sealing can take place prior to or after the sheets of corrugated board  62 ,  67  are cut.  
         [0039]    [0039]FIG. 7 illustrates a second part of a corrugating machine according to a second embodiment. FIGS.  8  to  11  illustrate further embodiments of corrugating machines. Components that correspond to those described with reference to FIGS.  1  to  6  have the same reference numerals and are not going to be explained in detail again.  
         [0040]    In the corrugating machine according to the second embodiment, a digital printing system  69  is disposed downstream of the heater (not shown). With no relevant shrinkage of the web taking place between the jobs of printing the web of corrugated board  41  and depositing the cut sheets of corrugated board  62 ,  67 , the readers  19 ,  44  of the first embodiment can be dropped.  
         [0041]    In the second exemplary embodiment, a reader  70  is disposed upstream of the lengthwise cutting/grooving unit  46 , crosswise scanning the web of corrugated board  41  and recognizing the distribution of printing patterns  43  on the web of corrugated board  41 . Signal lines  71 ,  72  provide for signalling connection of the reader  70  with the lengthwise cutting stations  48 . Depending on recognition of the printing patterns  43  by the reader  70 , the lengthwise cutting stations  48  are triggered for web sections  52 ,  53  to be cut, having a width that corresponds to the arrangement of the printing patterns.  
         [0042]    Another reader  73  is disposed between the lengthwise cutting/grooving unit  46  and the cross-cutting unit  54 , within its range scanning the web sections  52 ,  53  of the web of corrugated board in the working direction  15  i.e., lengthwise, and registering the distribution of printing patterns  43  on the web of corrugated board  41  in the working direction  15 . A signal line  74  connects the reader  73  with the cross-cutting unit  54 . Corresponding to what has been said about lengthwise cutting of the web of corrugated board  41 , the reader  73  triggers the cross-cutting unit  54  in such a way that this unit  54  cuts the sheets of corrugated board  62 ,  67  in accordance with the distribution of printing patterns in the working direction  15 . By the aid of the readers  70 .  73 , a plane shape of the sheets of corrugated board can be determined, the longitudinal and transverse dimensions of which are adjustable; this plane shape can be cut to size by the lengthwise cutting stations  48  and the cross-cutting unit  54  being correspondingly triggered.  
         [0043]    In variation of the second embodiment, printing units may be provided in addition to the printing system  69 , corresponding to the printing units  4  and  26  of the first embodiment for printing individual webs of material upstream of the machine  1  or the heating device  36 .  
         [0044]    In further variation of the second embodiment, the printing system  69  can be provided with two ink jet heads in such a way that the web of corrugated board  41  is bilaterally printed, i.e. simultaneously on the top and bottom side.  
         [0045]    [0045]FIGS. 8 and 9 show the two parts of a corrugating machine according to a third embodiment. As compared to the first embodiment, the second printing unit  26  misses in the first part, seen in FIG. 8, of the corrugating machine. Also the deviation of the third web of material by the deflection rollers  23 ,  24 ,  25 ,  30 ,  31  has been dropped, which is no longer needed. Further, the first reader  19  misses in the third embodiment. The application control unit exists also in this embodiment, however it is not shown. In the corrugating machine of the third embodiment, a first web of material  3  is being printed, having marks  17 ,  18  at an initial distance that is given and has been fed into the application control unit of the third embodiment prior to the start of production of the corrugating machine. Therefore the application control unit of the third embodiment knows the distances a 1 , b 1  although they have not been measured by a reader.  
         [0046]    The second part of the third embodiment of the corrugating machine seen in FIGS.  9  corresponds to the second part of the corrugating machine of the first embodiment seen in FIG. 6, a difference residing in that the reader  44  of the first embodiment, which evaluates the distance from each other of the marks  17  and the marks  18 , is functionally split into a first reader  75  for determination of the distance of the marks  17  and a second reader  76  for determination of the distance of the marks  18 . Signal lines (not shown) connect the readers  75 ,  76  to the application control unit of the corrugating machine of the third embodiment.  
         [0047]    [0047]FIGS. 10 and 11 illustrate the two parts of a corrugating machine of a fourth embodiment. These parts correspond to those of the third embodiment with the difference that the web of corrugated board, in the fourth embodiment, is printed from below instead of from above. Therefore, the printing unit  4  misses in the first part of the corrugating machine of the fourth embodiment. It is replaced by the printing unit  26  which corresponds to the first embodiment, serving for printing the bottom side of the third web of material  22 . Correspondingly, in the second part of the corrugating machine of the fourth embodiment, the readers  75 ,  76  are located underneath the web of corrugated board  41 , there registering the printing patterns imprinted by the printing unit  26 . Otherwise, the fourth embodiment corresponds to the third embodiment.  
         [0048]    The readers  19 ,  44 ,  70 ,  73 ,  75 ,  76  may be embodied as a camera, in particular a CCD camera. In addition to the function described above, the reader  19  still has the function of synchronizing the two printing units  4 ,  26  when bilaterally accurately aligned printing is to take place on the web of corrugated board  41 . To this end, the reader  19  registers the time when a certain printing pattern  43  finds itself within in the range of the reader  19 .  
         [0049]    Depending on the difference of the conveying paths of the web of single-faced corrugated board  13  from the reader  19  as far as to the nip  40  on the one hand and of the third web of material  22  from the ink jet head  28  as far as to the nip  40  on the other hand, the application control unit  7  computes the instant at which the printing unit  26  must print the third web of material  22  for this third web  22  to be printed true to the position of the print on the opposite side of the web of corrugated board, which is the top side of the web of corrugated board  13  that is printed by the printing unit  4 .