Abstract:
Corrugated boards are creased in three stages: the first being controlled crushing of the board to force air out of the flutes; the second is applying heated moisture or mist to the board to increase pliability; and the third is creasing the board by passing it between endless conveyor belts one of which has an elongated scoring bead projecting from its inner surface.

Description:
FIELD OF INVENTION 
       [0001]    The present inventions are methods and apparatus for creasing boards or boxes typically made from material commonly referred to as “corrugated board”. 
       BACKGROUND OF INVENTIONS 
       [0002]    Typically a Flexo-Folder-Gluer is used to produce corrugated boxes also known in the art as RSC&#39;s (Regular Slotted Cartons). 
         [0003]    A Flexo-Folder-Gluer performs its basic functions as follows: 
         [0004]    Flat corrugated blank sheets (also termed “boards”) are fed one at a time from a stack into the machine by a feeding mechanism. 
         [0005]    One side of the sheet can be printed typically using printing plates mounted on to a rotating cylinder. 
         [0006]    Slots are cut into the front and rear edges of the corrugated sheets while longitudinal crease lines connecting the slots are impressed into the sheet to produce four side-by-side panels. 
         [0007]    A glue tab is cut on one side of the corrugated sheet and glue is applied to a tab. 
         [0008]    A folding mechanism folds the two outside panels of the corrugated sheet 180° and creates a folded box (knocked down or flat state) as the glue tab panel meets the opposite side panel. 
         [0009]    A counter ejector mechanism accepts the folded boxes and discharges them in stacks. 
         [0010]    The dimensional accuracy of a folded box is primarily determined by the above-described creasing process used to produce the creases in the sheet that will define the box panel sizes. A common method used to crease sheets employs multiple sets of upper and lower rotating scoring heads or rolls. Referring to  FIG. 1  of the drawings, male scoring bead (A) compresses the corrugated board into the female ring (B). This nip forms a longitudinal crease line (C) in the sheet ( FIG. 1 a   ). There is a critical value of nip pressure that must be maintained in order to produce a useful crease line. Too little pressure results in undefined scores, whereas extreme pressure will cut or crack the liner paper of the board (E) and (F). After the creasing process, the two outside panels in the sheet are urged either up or down 180° by some folding method, generally stationary bars ( FIG. 1 a   ) or moving belts. Due to the many variables encountered in the manufacture of corrugated board, such as liner and medium paper weights, moisture content and recycled grade of paper, and flutes (G) adjacent to the crease line that may be weaker than the crease line itself, panels might fold about a “false” score line (D). This will produce a folded box whose panels are dimensionally inaccurate and not within specifications. These so called “rolling scores” can occur at any time during a production run and are very difficult to eliminate using this type of scoring method. By nature, folding a corrugated sheet requires the outer liner paper (F) to stretch, the inner paper liner (E) to contract, and the corrugated medium paper (H) to compress. 
       SUMMARY OF PRESENT INVENTIONS 
       [0011]    In order to better control the dimensional accuracy of folded panels, a novel and improved creasing method and apparatus are provided by the present inventions that will condition and prepare a sheet in a non-destructive manner and produce well-defined creases. The benefits of this proposed creasing method will be to eliminate crease-line cracking of the inner liner due to the creasing process, eliminate cracking of the outer liner due to the folding process, and produce well defined creases in the sheet that will allow accurate folding about the true crease line as shown in ( FIG. 1 b   ). 
         [0012]    The method of the present invention includes the steps of compressing the boards to a controlled amount to force the air out of the flutes in the area which will include the score line to be formed. A steam shower mist is applied to the board to prevent cracking in the area where the crease will be formed. A crease line is then pressed or “ironed” into the above pre-conditioned areas by an elongated scoring bead for an extended period of time. In one preferred method the boards are fed in the nip between endless bands one of which contains an elongated and scoring endless bead and forms the crease as the board proceeds through the bands. 
     
    
     
       DRAWINGS 
         [0013]    Other objects and advantages of the present invention will become more apparent from the following description taken in conjunction with the attached drawing in which: 
           [0014]      FIG. 1  is a fragmental cross-sectional view of apparatus used for creasing corrugated boards in accordance with the prior art; 
           [0015]      FIG. 1 a    is a fragmental cross-sectional view of a corrugated board that has been folded but not at the intended crease line representing the problem caused by methods and apparatus of the prior art; 
           [0016]      FIG. 1 b    is a view similar to  FIG. 1 a    but showing a properly formed crease produced by the method and apparatus of the present invention; 
           [0017]      FIG. 2  is a side elevational view of preferred apparatus for performing the creasing method of the present invention; 
           [0018]      FIG. 2 a    is a cross-sectional view taken along lines A-A of  FIG. 2 ; 
           [0019]      FIG. 3  is a schematic top view of the apparatus of  FIG. 2 ; 
           [0020]      FIG. 4  is a plan view of a board showing the crease lines in dotted lines; and 
           [0021]      FIGS. 5A , B, C and D are side elevational views of another preferred apparatus of the present invention showing both vertical and angular adjustment of platens which engage creasing bands for creasing the boards. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0022]    Referring to the drawings in detail there is shown for illustrative purposes only, preferred methods and apparatus embodying the present inventions. 
         [0023]    According to the present invention, the creasing method shown in  FIG. 2  employs three distinct stages, each providing a specific operation needed to produce a well-defined score line in the corrugated board  10  in  FIGS. 3 and 4  where in this particular box to be formed requires four creases or scores shown by dotted lines  14  in  FIG. 4 . As shown in  FIG. 3  four creasing systems are used to produce the required four creases respectively. Each system includes compression or forming beads  1 , a steam shower or mist chamber  2  and what will be termed here as a “creasing conveyor” comprised of overlying and underlying endless belts  3  and  4  as shown in  FIG. 2 . 
         [0024]    Referring to  FIG. 2 , Stage  1  performs a mechanical operation by passing the corrugated board through a nip of rotating forming heads or pinch rolls ( 1 ) to compress and impart a controlled crush into the sheet while forcing air out of the flutes in the area which will contain the score line. Rolls  1  further serve to convey the board  10  along the horizontal processing path to the next operating station where it enters a chamber  2  for Stage  2 . 
         [0025]    Stage  2  supplies moisture and heat, preferably a steam shower mist, in chamber  2  to the side of the board in the area where the crease will be formed. The heat and moisture supplied at this point will aid in conditioning the fibers of the inside liner paper to help make the board more pliable and prevent cracking when the crease is introduced into this surface. It should be noted that crease line cracking will weaken the structure and lead to failure. Additionally, crease line cracking is visible to the customer and reveals itself as a quality issue. The amount of moisture and subsequent time to condition the paperboard is dependent on the thickness of the paperboard and ambient conditions. 
         [0026]    After the board emerges from the chamber  2 , it is conveyed along a horizontal path to the creasing conveyor at Stage  3  that “irons in” a score profile into the pre-conditioned area of the board by means of upper and lower continuous nip “bands” or belts  3 ,  4 . The latter are of a predetermined length in order to provide extended contact time between the board and a raised scoring bead ( 6 ). The “bands”  3 ,  4  can be made from but not limited to an elastomeric material such as rubber or urethane, or a plastic or metal continuous or segmented in which one band has a projecting scoring bead  6  as a part of its surface as shown in  FIG. 2 a   . Each “band” is driven over a platen  7  such as a flat plate shown in  FIGS. 2 and 2   a  or a series of rollers shown in the embodiment of  FIGS. 5 a   - 5   d.  The upper and lower platens form a compressive nip on the sheet and as shown in  FIG. 5 a    and b are adjustable in a vertical direction to accommodate different board calipers, and are also adjustable angularly by pivoting about a horizontal axis extending transversely to the conveyor path of the lower rollers  5   c  or upper rollers  5   d,  or both sets of rollers to provide progressive contact creating a gradual crease. This adjustability allows for extended, gradual creasing to accommodate varying flute profiles; varying base weight (thickness) liners and medium paper; varying quality liners and medium; varying creasing profiles; environmental conditions, e.g. temperature, relative humidity, etc. In the embodiment of  FIGS. 5 a - d   , the platen rollers  20  are rotatably mounted in any suitable frame  30  which is mounted for vertical movement and for pivotal movement about a horizontal axis extending transverse to the conveyor path to provide the above indicated adjustability of the platens. 
         [0027]    As shown in  FIG. 3 , each of the four creasing systems including apparatus of the three stages are preferably mounted on frames  8  which may also be mounted to a common yoke bar  18  to be able to travel across the board to adjust for different panel sizes of the boards. 
         [0028]    Although preferred embodiments of the present inventions have been shown and described above, variations of these embodiments will become apparent to those of ordinary skill in the art but without departing from the scope of the present inventions defined in the attached claims.