Abstract:
A machine for making bags from sheet material of indeterminate length, especially thermoplastic material, has a pair of spaced folders of special construction for folding the material lengthwise. The entry end of the machine can be adjusted as to height. An applicator for adhesive tape can be positioned between the folders. A special construction thermowelds the folded layers together along transverse lines and severs or perforates them along those lines.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a machine for making bags, more particularly for making bags of thermoplastic material from a sheet of thermoplastic material of indefinite length, by folding the sheet to form a bottom closed edge of the bags, thermowelding the layers of the folded material together along spaced lines transverse to the length of the material and severing or perforating the material along those lines to form closed side edges of the bags, leaving the top of the bags open. Depending on whether a cutting or perforating operation is performed along the thermowelded lines, individual severed bags, or a continuous strip of bags that can easily be torn apart, will be formed. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide a machine for making bags from folded sheet material of indefinite length, in which the tension in the two edges of the folded material can easily be maintained substantially equal. 
     Another object of the present invention is the provision a machine for making bags, in which sheet material of indefinite length can be folded with the edges of the folded material maintained in accurate relationship with each other. 
     Still another object of the invention is the provision of a machine for making bags, in which a tape of pressure-sensitive adhesive can be firmly applied to the open ends of the bags. 
     A still further object of the present invention is the provision of a machine for making bags of thermoplastic sheet material of indefinite length, in which thermowelding along lines transverse to the lengthwise extent of the sheet material and cutting or perforating along those thermowelded lines, can be performed with improved precision. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a top, end and side perspective view of a machine for making bags, according to the present invention. In  FIG. 1 , the movement of the material from which the bags will be made, is from right to left. The material supply, as well an optional device for receiving the completed bags, have been omitted for clarity. 
         FIG. 2  is a view taken in the same general direction as  FIG. 1 , showing the material supply. 
         FIG. 3  is a fragmentary perspective view of the mechanism for adjusting the height of the entry end of the machine. 
         FIG. 4  is an enlarged fragmentary perspective view of the entry end of the machine. 
         FIG. 5  is a fragmentary view similar to a portion of  FIG. 1  and showing in more detail the outlet end of the machine. 
         FIG. 6  is an enlarged fragmentary perspective view of the thermowelding and cutting or perforating assembly. 
         FIGS. 7-9  are enlarged fragmentary side elevational views showing successive stages in the operation of thermowelding and severing or perforating. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1  of the accompanying drawings, there will first be given a broad overview of the machine of the present invention. There is accordingly shown a machine for making bags, according to the present invention, indicated generally at  1 , comprising a base frame  3 , which for convenience may be portable. Frame  3  supports a vertically swinging frame  5  extending lengthwise of the machine and supported at the outlet end of the machine for vertical swinging movement about horizontal pivots  7 . 
     Frame  5  supports a pre-folding device  9 , followed (in the sense of the direction of movement of the sheet material) by an optional tape applicator of conventional nature, followed in turn by a final folding device  13 . 
     A drive roll assembly  15  drives the material to the left as seen in  FIG. 1 , immediately upstream of a welding and perforating or severing assembly  17 . As is well known in the art, assembly  17  can equally well perform either of two alternative functions: either it can sever separate bags, which can then be collected in any desired receptable (not shown), or else it can perforate the strip so that individual bags can be torn off one by one as needed, from an indefinite number of bags in a roll. Such a roll can be formed by the optional rewinder  19  seen in  FIG. 4 . 
       FIG. 2  shows the material supplied to the machine. The material to be made into bags is thermoplastic sheet material of indefinite length shown at  21 . The thermoplastic material can be any used for such purposes, such as polyethylene, copolymers of ethylene and C 3 -C 8  olefins, polypropylene, polyvinylidine choride, ethylene vinyl acetate, polylactic acid, etc. 
     This sheet material can be in a variety of forms, such as clear plastic sheet or film, or foamed plastic sheet, or else it can be the padded sheet material formed with air bubbles between two adhered sheets of plastic, e.g. BubbleWrap® (registered trademark of Sealed Air Corporation). 
     Such material is supplied from a roll  23  that rotates about a vertical axis on a vertical spindle  25  supported rotatably on a base  27 . 
     Upon leaving roll  23 , the material is folded in two, the folded material being shown in  FIG. 2  at  29 . Thereafter, the material remains folded throughout the entire operation. 
     Upon folding the material, at least one edge of the material becomes tensioned, because it is deflected from the vertical plane in which it leaves roll  23 . It is desirable to keep the tension in both edges substantially equal; and to this end, the deflection is shared equally between the two edges of the material. To do this, the material is made to enter the machine at a level which is about mid-height of the roll  23 . 
     But the roll  23  will vary in height according to the width of the material in question. This means that an adjustment must be made in order to accommodate rolls of different height. In the past, this adjustment has been made by making the assembly of the spindle  25  and base  27  adjustable in height, thereby to bring the midpoint of the roll into horizontal alignment with the entry end of the machine. This arrangement is shown in U.S. Pat. Nos. 236,633 and 3,269,722. 
     But according to the present invention, this adjustment to mid-height is made in a simpler manner, by making the frame  5  vertically swingable about the pivots  7 . The structure for doing this is shown in  FIGS. 1 and 3 , from which it will be seen that a rack  31  is provided that supports the entry end of the frame  5  on the base frame  3 . This rack  31  is provided with teeth  33  and is mounted for vertical swinging movement about a horizontal axis at its upper end, for which purpose bolt holes  35  are provided through frame  5  and rack  31  for the reception of a bolt (not shown). 
     Similarly, at the lower end of rack  31 , bolt holes  37  are provided through frame  3  and rack  31 , the holes  37  removably receiving a bolt (not shown) that selectively engages with one of the teeth  33  to adjust the effective height of rack  31  as desired. Once this adjustment has been made and the bolt received in holes  37  is positioned between the desired pair of teeth  33 , a further bolt (not shown) is inserted through bolt holes  39  through frame  3  such that the rack cannot escape from its adjusted position. 
     Positioning the pivot  7  for the swinging frame  5  at the outlet end of the machine has two advantages: in the first place, it avoids any deflection of the path of the material  21  through the machine; and in the second place, by making use of the full length of the frame  5 , it reduces to a minimum the angle through which the frame  5  must be swung vertically in order to come into coincidence with the middle of roll  23 . The smaller this angle is, the easier it is to equalize the tension in the two edges of the strip. 
     Turning now to  FIG. 4 , we are looking in the direction of the material encountering the entry end of the machine. The first device encountered by the material on the machine is the prefolding device  9 . The prefolding device  9  and the final folding device  13  are identical in structure, and so a description of one serves for the other. 
     Device  9  (or  13 ) comprises an upper plate  41  and a lower plate  43 , parallel to each other and spaced apart at their ends adjacent the fold in the material, by a spacer  45 . At their other ends, plates  41  and  43  are spaced apart by spacers  47  which grip between them an elongated horizontal tongue  49  spaced equally distant between and parallel to plates  41  and  43 . Tongue  49  terminates at the right of  FIG. 4  in a free end  51  about which the fold of the material  21  is formed. 
     At their open ends, the bags to be formed can have open end edges which coincide with each other, or one edge can protrude beyond the other. The protuberant edge can be tucked inside the other edge to close the bag, or it can be folded over the other edge to seal the bag. In this latter case, a strip of pressure-sensitive adhesive is conventionally applied to one of the open end edges, which is of course covered by a protective strip that can be peeled off immediately prior to use. Such closures are quite conventional and find a multiplicity of applications to boxes, bags and envelopes. 
     An important feature of the present invention, is the provision that is made for accurately locating the edges of the bags to be formed. This is done in the folding devices  9  and  13  themselves. To this end, the plates  41  and  43  of each folding device are provided with spaced parallel slots  53  extending lengthwise of the plates  41  and  43 , which is to say transversely of the length of the material  21 . Slidably disposed between the plates  41  and  43  and the tongue  49  are guides  55  for the edges of the material  21 . Each guide  55  can be tightened against its respective plate  41  or  43  by manually rotating a handle  57  that tightens a screw attached to guide  55  and passing through slot  53 . The guides  55  associated with the plate  41  will ordinarily be in alignment with each other lengthwise of the machine, as will also be guides  55  associated with the plate  43 ; but the position of the guides  55  associated with plate  41  can bear only the same relation to the position of the guides  55  associated with the plate  43 , as the desired positions of the respective edges of the material  21  will bear to each in the finished bag. It is thus possible both very accurately to fold the sheet and very accurately to position its edges relative to each other, thanks to the novel construction of the folding devices  9  and  13 . 
     Notice also that, as the guides  55  are in sliding contact with both the tongue  49  and their respective plates  41  or  43 , the guides  55  perform a bracing and stiffening function, thereby to reduce the bending of the folding devices that would otherwise result from the folding operation. 
     Now with respect to  FIG. 5 , it will be seen that the tape applicator  11  is positioned intermediate the folding devices  9  and  13  with respect to the path of movement of the material  21 . As previously indicated, the tape applicator is optional in the sense that it will be used only when a pressure sensitive adhesive strip, with its protective tape, is to be applied. 
     Thus, the tape applicator  11  is mounted for sliding movement transversely of the length of the machine, on a bridge  59  that straddles material  21 . A set screw arrangement  61  selectively fixes the position of tape applicator  11  along bridge  59 , depending of course on the location at which it is desired to apply tape to the bags. The tape applicator comprises a supply reel  63  from which tape (not shown) is withdrawn, the tape passing under an applicator roller  65  which presses it onto what will ultimately be the appropriate part of the bags. 
     The tape applicator itself is of course conventional and need not be described in greater detail. But in the environment of the present invention, it imparts to final folder  13  a unique dual function for the first time in this art. 
     Specifically, it has been found that the particular combination of prefolding device  9 , tape applicator  11 , and final folding device  13 , in that order, results in a more reliably applied tape. Thus, the prefolding device  9  precisely positions the edges of the bags to receive the tape. The tape is then applied by the applicator  11 , after which the final folding device  13  performs the unique dual function both of perfecting the fold and of improving the adhesion of the tape to the material  21 . 
     But regardless of whether the tape applicator  11  is or is not present, there will be two folding devices  9  and  13 . This is because it has been found that the precision of folding is improved by providing two such spaced folding devices. 
     Turning now to  FIG. 6 , the drive roller assembly generally indicated at  15  is seen, comprising an upper pinch roller  67  and a lower pinch roller  69  between which the material is pulled from the supply roll  23  and drawn through the folding devices  9  and  13 . In a conventional manner, the pinch roller  69  is driven by a variable speed DC motor  71  (see  FIG. 1 ) via a drive belt (not shown). Air cylinders  73  can raise or lower the upper pinch roller  67  for threading the material. All of this is of course quite conventional. 
     From the drive roller assembly  15 , the material  21  proceeds to the welding and perforating or severing assembly  17 , broadly seen in  FIG. 6  but shown in greater detail in  FIGS. 7-9 . 
     As is seen in these latter figures, the assembly  17  comprises an upstanding knife  75  with a horizontal cutting or perforating edge which extends transversely of the machine, which is to say transversely of the direction of movement of the material  21 . In  FIG. 6 , this knife is seen to be a perforating knife, whose cutting edge comprises spaced-apart segments that will perforate the material without severing it. This is useful for the production of a roll of finished bags that can be torn apart one by one for use as needed. Alternatively, however, the cutting edge of knife  75  can be continuous for the purpose of severing individual bags. Both arrangements are quite conventional in this art. 
     Blade  75  is held in the upright position on a mounting block  77  secured to frame  5 . Knife  75  is disposed between and spaced from two halves of a bottom die  79 , which halves are mounted on springs  81  so that bottom die  79  is vertically movable between the positions shown in  FIGS. 7 and 8 , on the one hand, and  FIG. 9  on the other hand. 
     A top die  83  is provided, with a slot  85  extending therethrough transversely of the path of material  21  and in vertical registry with knife  75 . Top die  83  is heated by a heating rod  87 . 
     Hold-down bars  89  ensure that the material  21  will not follow die  83  to its upper position. A guide strip  91  is also found to be useful to keep the material down. 
     An air cylinder  93  raises and lowers top die  83 . 
     A feed-out plate  95  is adapted to receive and slidably support individually cut-off bags if knife  75  performs a severing function. 
     But if knife  75  performs a perforating function, then the material  21 , still in the form of a continuous strip, can be wound on the optional rewinder  19  shown in  FIG. 5 . This rewinder comprises a bracket  97  by which the rewinder is detachably secured to frame  3 , the bracket  97  supporting a rewind spindle  99  and a variable torque compressed air motor  101  by which spindle  99  is rotated to wind up the continuous strip of formed bags. 
     Rewind spindle  99 , when present, should always be horizontal, as the rolls of formed bags can be quite heavy, and it is difficult to wind up such a roll about any axis other than horizontal. This in turn means that, following the material backward through the machine, the material should be horizontal full length of the machine, which in turn means that the supply roll  23  has to be vertical so as to permit achieving equal tension in both edges of the strip. 
     If the rewinder were never used, then the machine could be oriented 90° from its present position and the supply roll  23  could be horizontal. But to adapt the machine both to the production of separate bags and to the production of a continuous roll of bags, it is convenient that the machine have its illustrated orientation. 
     Thus, the invention is in no way limited as to the orientation of the machine about an axis extending lengthwise of the machine. 
     Operation 
     To begin the bag making operation, a roll  23  of thermoplastic sheet material of indefinite length is placed on spindle  25  and comes to rest on base  27 . The leading end of the material is then folded manually to approximately the desired condition and threaded through the prefolding device  9 , below the tape applicator  11  if used, through the final folding device  13 , and thence to the drive roller assembly  15 . The air cylinders  73  are actuated to raise upper pinch roller  67  so that the folded leading end of the material  21  can be introduced past the rollers  67  and  69 , after which the air cylinders  73  are again actuated to pinch the material  21  between rollers  67  and  69 . 
     Before the motor  71  is actuated to move the material through the machine, the controls of motor  71  and of air cylinders  73  that actuate the top die  83  are set as desired, so that the pinch rollers  67  and  69  will deliver a predetermined length of material  21  corresponding to the desired width of the bag to be formed intermittently and in alternation with the actuation of the air cylinder  93  of top die  83 . 
     These motor and air cylinder controls are computer coordinated so that motor  71 , driving roller  69 , will act intermittently and alternately with air cylinder  93 , such that the rollers  65  and  67  will advance the length of material  21  equal to the desired width of the bags to be formed, and then stop for a period of time sufficient for the top die  83  to be depressed, perform its thermowelding and perforating or severing function, and then rise again. 
     If separate bags are to be produced, that is, if knife  75  is to perform a severing function, then nothing need be done downstream of the thermowelding and severing station other than to collect the individual formed bags. But if instead a continuous strip of bags separated by perforations is to be formed, then the thermowelding and perforating station is operated a sufficient amount of time to provide a length of a series of bags sufficient to wind about the spindle  99 , after which the air motor  101  can be continuously operated. Of course the operation of the heater  87  is continuous. 
     The computer controls for the intermittent and alternate operation of the feed rolls and the die  83  are well known to persons having ordinary skill in this art and so need not be described in greater detail. 
     Referring now to  FIGS. 7-9 , the thermowelding and severing or perforating operation will now be described. At the outset of this operation, the motor  71  is stopped so that the feed of material  21  is discontinued, whereupon the material  21  is stationary for a time sufficient to complete thermowelding and severing or perforation. If perforation is performed and all of the completed bags are to be wound on spindle  99 , the air motor  101  can continue to operate and need not be stopped, because its torque is limited and so the tension in the strip being wound on spindle  99  cannot exceed a predetermined limit, that is, it cannot tear the bags apart. 
     At the beginning of the thermowelding and severing or perforating operation, the parts are in the position shown in  FIG. 7 , with the top die  83  continuously heated and raised and the material  21  stopped. The two-piece bottom die  79  is unheated and is in its raised position, the springs  81  being extended. These springs can conventionally be coil compression springs surrounding mounting bolts and are not shown in detail for simplicity of illustration. 
     The heated top die  83  then descends until it contacts material  21 , as seen in  FIG. 8 . The heat of the top die  83  causes a thermowelding operation, by which folded-over layers of material  21  are thermally bonded together along lines that extend transversely of the width of the material  21 . 
     Continuing its downward stroke, the heated top die  83  presses with sufficient force against the thermowelded material  21  to depress the two-piece bottom die  79  against the action of the springs  81 , so that the assembly moves from the  FIG. 8  position to the  FIG. 9  position (in  FIG. 9  the material  21  is not shown, for simplicity of illustration). This causes the stationary knife blade  75  to perforate or sever the material  21 , after which the air cylinder  93  raises the heated top die  83 , whereupon the blade  75  retreats from slot  85  and the two-piece bottom die  79  follows upwardly because it is no longer urged downwardly, the springs  81  causing the bottom die  79  to rise. 
     The rising of the bottom die  79  strips the material  21  from the blade  75 . Notice that the blade  75  is out of contact with bottom die  79 . As a result, any heat from heated top die  83  that passes through the material  21  to the bottom die  79  is not transmitted to the blade  75 . The blade  75  thus remains relatively cool, which facilitates stripping the material  21  therefrom. 
     Notice also that the raised bottom die  79  shields material  21  from knife  75  when material  21  is moving, as can be seen from  FIG. 7 . 
     Similarly, blade  75  never touches the sidewalls of slot  85  in heated top die  83 . 
     The hold-down bars  89  prevent the material  21  from following the heated top die  83  upwardly, so that a clean separation of the thermowelded material  21  from the dies  79  and  83  and the knife  75 , is completed. 
     It is known in the art of thermowelding bags in this manner, to provide a heated top die and an unheated bottom die, as shown for example in U.S. Pat. Nos. 3,555,974 and 4,630,429. It is also known, in the art of severing paper products without thermal welding, to provide a spring-urged bottom die that retreats downwardly under the pressure of a top die thereby to expose a knife which severs the paper, as in U.S. Pat. Nos. 833,470 and 3,227,024. But the present invention differs significantly from either of these techniques, and goes beyond the teaching of these references in that the heating of the top die and the thermowelding of the folded-over layers, prevents the slippage relative to the dies and the knife, that is encountered in the latter case of unheated dies severing paper material, and the slippage that occurs in the former instance of heated dies that cause severance or perforation prior to pressing against the lower die. In other words, the present invention, by combining the two techniques, solves the problem of slippage that plagued both techniques individually. 
     Notice also the position of pinch rollers  67  and  69  immediately adjacent assembly  17 . This arrangement also contributes to avoiding slippage in assembly  17 . 
     From a consideration of the foregoing disclosure, therefore, it will be evident that all of the initially-recited objects of the invention have been achieved. 
     Although the present invention has been described and illustrated in connection with a preferred embodiment, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention. Such modifications and variations are considered to be within the purview and scope of the present invention as defined by the appended claims.