Abstract:
A method and apparatus for forming a rib on a section of plastic film utilizes a roll having a groove, extrudes molten polymer into the groove, and places the section of plastic film in contact with the molten polymer in the groove. The molten polymer in the groove is allowed to cool below the melting point thereof while the section of plastic film is in contact with the polymer to cause bonding therebetween and thereby form the rib.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to thermoplastic storage bags, and more particularly to a method and apparatus for producing guide ribs for reclosable thermoplastic storage bags.  
         BACKGROUND ART  
         [0002]    Thermoplastic storage bags having reclosable fasteners have been in wide use to store various items. One type of bag includes interengagable male and female closure elements or profiles that may be closed by pinching the elements together at one end thereof between a user&#39;s finger and thumb and sliding the user&#39;s opposed finger and thumb along the elements toward another end of the bag. One difficulty faced by a user of such a bag results from misalignment of the male and female closure elements of the bag as the user is attempting to seal the bag. Often, such misalignment prevents full closure of the bag and typically results in wasted effort and frustration by the user.  
           [0003]    Attempts have been made over the years to provide a structure that facilitates closing of a bag by a user. An example of such a structure comprises a guide rib disposed on each side of the closure elements and extending parallel thereto. The guide rib(s) guide the user&#39;s finger and thumb as the user is attempting to close the bag so that the incidence of closure element misalignment is minimized.  
           [0004]    Kamp U.S. Pat. No. 4,306,924 discloses an apparatus for producing a plastic container having occludable closure strips. The closure strips are supplied from a supply source and fed to a control roll, wherein the control roll in turn feeds the closure strips to an optional heating means that preheats a base portion of the closure strips. The closure strips are then transferred to a rotating casting cylinder having a pair of spaced apart circumferential grooves. The closure profiles are disposed in the grooves of the casting cylinder as the casting cylinder rotates and plastic film is extruded onto the casting cylinder to produce a plastic film with integral closure profiles.  
           [0005]    Zieke et al. U.S. Pat. No. 4,741,789 discloses a method and apparatus for applying a profile and adjacent ribs to a traveling film web. The method comprises the steps of drawing a web of bag film over idler rolls into a forming and joining station. The forming and joining station includes a hopper for receiving plastic material, a body with heating means for heating and melting the plastic material and a screw auger for advancing the molten plastic material to a die block. The method further comprises the steps of applying a base member to the film by means of a polytetrafluorethylene-coated lay-on roller and extruding a male profile member, a first rib member and a second rib member as separate extrudates on a bag film web.  
           [0006]    Geiger et al. U.S. Pat. No. 4,755,248 discloses a method and apparatus for producing a reclosable bag film. The method comprises the steps of drawing a film web from a die block around a driven rotatable casting roll and passing the film web over idler rolls to a closure member extrusion and joining station. A female profile is extruded from a first extruder and a male profile is extruded from a second extruder onto the film web as the film web passes around an idler roll at the station. The method further comprises the step of passing the film web and profiles around a chilled casting roll to cool the film web and profile.  
         SUMMARY OF THE INVENTION  
         [0007]    According to one aspect of the present invention, a method of forming a rib on a section of plastic film includes the steps of providing a roll having a groove, extruding molten polymer into the groove, and placing the section of plastic film in contact with the molten polymer in the groove. The molten polymer in the groove is allowed to cool below the melting point thereof while the section of plastic film is in contact with the polymer to cause bonding therebetween and thereby form the rib.  
           [0008]    In accordance with a further aspect of the present invention, a method of forming a pair of ribs on either side of a closure element carried by a section of plastic film includes the steps of providing a roll having a pair of grooves, extruding molten polymer into the grooves, and placing the section of plastic film in contact with the molten polymer in the grooves such that the closure element is disposed between the grooves. The molten polymer in the grooves is allowed to cool below the melting point thereof while the section of plastic film is in contact with the polymer to cause bonding therebetween and thereby form the ribs.  
           [0009]    In accordance with yet another aspect of the present invention, an apparatus for forming a rib on a section of plastic film includes a roll having a groove and an extrusion die for extruding molten polymer into the groove. A positioning system places the section of plastic film in contact with the molten polymer in the groove such that the molten polymer in the groove is allowed to cool below the melting point thereof while the section of plastic film is in contact with the polymer to cause bonding therebetween and thereby form the rib.  
           [0010]    Other aspects and advantages of the present invention will become apparent upon consideration of the following detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is an elevational view of a reclosable thermoplastic storage bag according to the present invention;  
         [0012]    [0012]FIG. 2 is an enlarged, fragmentary, sectional view taken generally along the lines  2 - 2  of FIG. 1;  
         [0013]    FIGS.  3 - 8  are sectional views similar to FIG. 2 illustrating alternative bags produced in accordance with the present invention;  
         [0014]    [0014]FIG. 9 is an isometric view of a bag according to the present invention having intermittent ribs;  
         [0015]    [0015]FIG. 10 is a fragmentary and enlarged elevational view of a portion of zipper tape according to the present invention;  
         [0016]    [0016]FIG. 11 is an isometric view of an apparatus for producing bags according to the present invention;  
         [0017]    [0017]FIG. 12 is a bottom elevational view of an extrusion die profile plate used in the apparatus of FIG. 11;  
         [0018]    [0018]FIG. 13 is a cross-sectional view taken generally along the lines  13 - 13  of FIG. 11;  
         [0019]    FIGS.  14 - 16  are isometric views similar to FIG. 11 of an alternate apparatus for producing bags according to the present invention;  
         [0020]    [0020]FIG. 17 is a cross sectional view taken generally along the lines  17 - 17  of FIG. 16;  
         [0021]    [0021]FIG. 18 is an isometric view similar to FIGS. 11 and 14- 16  of an alternate apparatus for producing bags; and  
         [0022]    [0022]FIG. 19 is an isometric view similar to FIGS. 11 and 14- 16  of a still further alternate apparatus for producing bags. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Referring to FIG. 1, a reclosable pouch in the form of a thermoplastic storage bag  20  comprises first and second body portions  22 ,  24  joined to one another to form first and second bag walls  26 ,  28 . The first and second bag walls  26 ,  28  are joined at first and second side portions  30 ,  32 , respectively, and at a bottom portion  34 . An opening  35  is disposed at a top portion  36  of the bag  20 . A closure mechanism  38  and two lips  40  are also disposed at the top portion  36  of the bag  20 .  
         [0024]    Referring to FIG. 2, female and male closure elements  44   a ,  44   b  of the closure mechanism  38  are disposed on opposing inside surfaces  46 ,  48  of the first and second body portions  22 ,  24 , respectively. According to a first embodiment, guide ribs  50   a ,  50   b  are disposed on the inside surface  46  of the first body portion  22  on either side of (i.e., flanking) the female closure element  44   a . The guide ribs  50   a ,  50   b  extend in a direction generally parallel to the closure elements  44   a ,  44   b  and are spaced sufficiently therefrom to guide a user&#39;s finger(s) and facilitate alignment of the closure elements  44   a  and  44   b  into interlocking engagement when sealing the closure mechanism  38 .  
         [0025]    The male closure element  44   b  comprises a base  58  integral with flanking side members  54  and  56  and an arrow-shaped engagement member  60  that extends from the base  58 . The female element  44   a  comprises a base  62  with a C-shaped profile member  64  extending therefrom, wherein the female element  44   a  is adapted to receive the male element  44   b  when pressure is exerted on the closure elements by a user&#39;s finger(s) during closing of the bag. The side members  54  and  56  are of a sufficient size and proximity to the engagement member  60  such that the side members  54  and  56  move together with the member  60  when the members  60  and  64  are engaged and disengaged. The side members  54  and  56  also have a height which is less than the height of the engagement member  60 , and the members  54  and  56  extend beyond tips  68  of the female profile member  64  when the engagement member  60  is engaged with the female profile member  64 . Thus, at such time, the tips  68  of the female profile member  64  reside between the side members  54  and  56  and the male engagement member  60 .  
         [0026]    In a preferred embodiment, the guide ribs  50   a ,  50   b  are of the same height and such height is greater than the height of the female profile member  64 . The guide ribs  50   a ,  50   b  can have any suitable cross-sectional configuration, such an inverted T-shape, as seen in FIGS.  2 - 4  and  7 - 8 , an inverted Y-shape as seen in FIG. 6, a semi-circular cross-sectional shape as seen in FIG. 5, a triangular cross-sectional shape as seen in FIG. 5, etc . . . Preferably, the guide ribs  50   a ,  50   b  are spaced apart approximately 0.4 inches on center, are approximately 0.09 inches in height and have an approximate width of 0.067 inches at the widest point thereof.  
         [0027]    If desired, a number of guide rib(s)  50  other than two may be provided. In the event that two or more guide ribs are provided, the guide ribs  50  may all have the same cross-sectional shapes and dimensions, or the cross-sectional shapes and/or dimensions may be different. The guide rib(s)  50  may be present in various different arrangements. Thus, for example, as seen in FIGS. 3 and 4, a single rib  50   c  may be provided on either inside surface  46  or  48 , wherein the rib  50   c  is positioned and configured identically to either of the ribs  50   a ,  50   b  described above. In this case, the single rib  50   c  can be disposed on a side of the member  60  or  64  toward the top portion  36  or toward the bottom portion  34  of the bag.  
         [0028]    Other various configurations of guide ribs can be seen in FIGS. 5 and 6. In FIG. 5, two guide ribs  50   d  and  50   e  may be provided on the inside surface  46 . The ribs  50   d  and  50   e  are positioned identically to the ribs  50   a ,  50   b  described above, but are configured such that the guide rib  50   d  has a triangular cross-sectional configuration and the guide rib  50   e  has a semi-circular cross-sectional configuration. The ribs  50   f  and  50   g  of FIG. 6 are configured identically to the ribs  50   a ,  50   b  described above, but are disposed on the inside surface  48 .  
         [0029]    Still more configurations of guide ribs are shown in FIGS. 7 and 8. FIG. 7 illustrates a first guide rib  50   h  positioned on the inside surface  46  and a second guide rib  50   i  positioned on the opposite inside surface  48 , wherein the guide ribs are configured similarly to the ribs  50   a ,  50   b  as described above. In FIG. 8, a first set of guide ribs  50   j  and  50   k  is positioned on the inside surface  46  and a second set of guide ribs  50   m  and  50   n  is positioned on the inside surface  48 . The ribs  50   j ,  50   k  are disposed within the ribs  50   m ,  50   n  and the ribs  50   j ,  50   k ,  50   m  and  50   n  are otherwise configured similarly to the ribs  50   a ,  50   b  as described above and shown in FIG. 2.  
         [0030]    Preferably, although not necessarily, if two guide ribs  50  are positioned adjacent a closure element  44   a  or  44   b , the guide ribs  50  may be spaced equidistant from and on opposite sides of the closure element. Also, if a single rib  50  is positioned on the inside surface  48  adjacent the male closure element  44   b  and a second single rib  50  is positioned on the opposite inside surface  46  adjacent the female closure element  44   a , the guide ribs  50  are preferably (although not necessarily) disposed on opposite sides of the closure elements  44   a ,  44   b  and equidistant therefrom.  
         [0031]    No matter what configuration is chosen, the guide rib(s)  50  provide raised portions that can be felt by a user&#39;s fingers when the user&#39;s fingers are brought into contact with one or both external surfaces  70 ,  72  of the bag walls  26 ,  28 . The raised portion(s) act as a guide for a user&#39;s fingers to facilitate the engagement of the male and female closure elements  44   a  and  44   b , and thus sealing of the bag  20 .  
         [0032]    If desired, one or more gripping ribs  74  may be disposed on the internal surfaces  46 ,  48  of the bag  20  between the closure elements  44   a  and  44   b  and the top portion  36  of the bag  20 , wherein the gripping ribs  74  are integrally extruded with the walls of the bag. Any number of gripping ribs  74  can be used, although space is necessary between adjacent ribs in order to facilitate a gripping action with a user&#39;s fingers. In a preferred embodiment, about six or seven gripping ribs  74  are disposed on each lip  40  of the bag.  
         [0033]    According to an alternate embodiment, one or more intermittent ribs may be provided, as opposed to the continuous ribs  50   a - 50   n  described above. FIG. 9 illustrates the second bag wall  28  of the bag  20 , wherein two guide ribs  50   p  and  50   q  are disposed on the inner surface  48  parallel to and spaced apart from the male closure element  44   b  and wherein the two ribs  50   p ,  50   q  extend intermittently from the first side portion  30  to the second side portion  32  of the bag  20 .  
         [0034]    Yet another embodiment as shown in FIG. 10 comprises a zipper tape  140 . The zipper tape  140  includes first and second thermoplastic strips  142 ,  144 , wherein female and male closure elements  44   a ,  44   b  are attached to or otherwise formed on the first and second thermoplastic strips  142 ,  144 , respectively. Continuous or intermittent guide ribs  50   r ,  50   s  may be disposed on the first or second thermoplastic strips  142 ,  144 , parallel to and spaced apart from the female or male closure elements  44   a ,  44   b  in any configuration as described above. Alternatively, a single guide rib or three or more guide ribs may be disposed on the strips  142 ,  144  as noted above. The zipper tape  140  may be attached to a folded thermoplastic sheet by any suitable conventional process and apparatus and the resulting structure may be severed and sealed at spaced locations to form individual bags.  
         [0035]    Reclosable thermoplastic storage bags as described herein can be produced by any conventional bag-making process, such as a cast post applied process, a cast integral process, a blown process or any other process known in the art. Alternatively, any one of the processes implemented by the apparatus shown in FIGS.  11 - 19  could be used to produce the bag described herein.  
         [0036]    If the female and male closure elements  44   a ,  44   b  are to be added to a section of film subsequent to the formation of one or more guide ribs  50  thereon, an apparatus as seen in FIGS.  11 - 13  can be employed. FIG. 11 depicts an apparatus for forming one or more ribs at high speeds that includes a rotatable first roll  160 , a rotatable second roll  162 , an extrusion profile die  166 , and an air nozzle  168  disposed below the extrusion profile die  166 . The extrusion profile die  166  includes a profile plate  167  having at least one, and preferably two outlet orifices  169 ,  171  through which molten polymeric material is extruded into a like number of associated grooves  173 ,  174 , respectively, formed in the first roll  160  at a first axial end  160   a  thereof. The grooves  173 ,  174  in the first roll  160  have the same cross-sectional shapes as the desired end shapes of the ribs  50 . Preferably, although not necessarily, the grooves  173 ,  174  have cross-sectional shapes that are substantially identical to one another and the outlet orifices  169 , 171  have shapes that are substantially identical to one another. Also preferably, (although not necessarily, as noted below) each of the outlet orifices  169 , 171  has a shape similar or substantially identical to the cross-sectional shape of the associated groove  173 ,  174  of the first roll  160 , whether that shape is an inverted T-shape, an inverted Y-shape, triangular, semi-circular, or another geometric shape. As seen in FIGS. 11, 15,  16  and  18 , a positioning system  150  includes the second roll  162  and the film  172  and, in other embodiments such as FIG. 14, may include another rotatable roll  164 .  
         [0037]    In an alternative embodiment, the outlet orifices  169 , 171  have cross-sectional shapes that are substantially different than the cross-sectional shapes of the grooves  173 ,  174 . For example, the outlet orifices  169 , 171  may have a circular shape while the grooves  173 ,  174  may be triangular in cross-section.  
         [0038]    The method includes the steps of feeding molten polymer to extrusion profile die  166  by way of an extruder or melt pump and extruding molten polymer into the grooves  173 ,  174  of the rotating first roll  160  at an extrusion rate that ensures that the grooves  173 ,  174  are filled with molten polymer. Thereafter, the air nozzle  168  directs an air flow onto the molten polymer before it is deposited in the grooves  173 ,  174 .  
         [0039]    If desired, a different fluid may be directed against the molten polymer in the grooves  173 ,  174 . Also, the single air nozzle  168  may be replaced by two air nozzles wherein each air nozzle directs air against molten polymer in an associated groove  173 ,  174 . Still further, it is possible to eliminate the air nozzle  168  from this process; however, this may require greater positioning accuracy so that the extrudate falls exactly into the grooves  173 ,  174 .  
         [0040]    The method further includes the step of moving a section of plastic film  172  over the rotating second roll  162  toward the first roll  160  and into contact with the molten polymer in the grooves  173 ,  174 . Thereafter, the section of plastic film  172  is drawn around a predetermined angular extent of the first roll  160 , for example, one half to three quarters of the entire angular extent of the first roll  160 . It is also preferred that the first roll  160  be chilled, preferably by passing water therethrough to facilitate bonding of the ribs to the film  172 . As should be evident, the larger the diameter of the roll  160 , the more cooling can be imparted to the ribs. If desired, water, air or another coolant can be directed against the outer surface of the film section  172  as the film  172  and ribs  50  are moving about the first roll  160  to aid further in cooling of the ribs.  
         [0041]    Again, if the female and male closure elements  44   a ,  44   b  are added to the film in a step subsequent to the step of adding or forming guide ribs  50 , another method implemented by the apparatus shown in FIG. 14 can be employed. The apparatus of FIG. 14 is similar to that of FIG. 11, except that it further includes a third rotatable roll  164  positioned below the second roll  162 . During movement of the section of plastic film  172 , the third roll  164  further presses the section of plastic film  172  overlying the grooves  173 ,  174  into intimate contact with the molten polymer in the grooves  173 ,  174  to facilitate bonding and proper formation of the ribs. The third roll  164  is controlled by a hydraulic actuator  175  that controls the amount of pressure exerted on the plastic film  172  by the third roll  164 .  
         [0042]    If the female and male closure elements  44   a ,  44   b  have already been applied to the film section  172 , the embodiment of FIG. 15 can be employed to add or form the guide ribs  50 . In FIG. 15, a rotatable roll  176  is situated adjacent the first roll  160 . The method includes the same steps as described above in connection with FIGS.  11 - 13 , except that pressure may be applied by the roll  176  against the roll  160  so that the film is brought into intimate contact with the molten polymer in the grooves  173 ,  174  without deforming the female and male closure elements  44   a ,  44   b . Thereafter, the section of plastic film  172  is drawn around substantially the entire perimeter of the first roll  160 . The position of the second roll  176  is controlled by hydraulic actuators  178  that control the amount of pressure exerted by the roll  176  on the roll  160 .  
         [0043]    If the female and male closure elements  44   a ,  44   b  have already been applied to the film section  172 , the first roll  160  can include first and second additional grooves  182   a ,  182   b , as seen in FIG. 16. The groove  182   a  is disposed between the grooves  173 ,  174  at a first end  184  of the roll  160 , while the second groove  182   b  is disposed at a second end  186  of the roll  160 . The grooves  182   a ,  182   b  accommodate the female and male closure elements  44   a ,  44   b , respectively, in the event that the ribs are to be applied to the same side of the film section  172  as the closure elements  44   a ,  44   b . FIG. 17 shows a cross-sectional view of the three grooves  173 ,  174  and  182   a  of FIG. 16. The groove  182   a  has dimensions that are just slightly larger than the cross-sectional dimensions of the female closure element  44   a  so that the fit of the closure element  44   a  in the groove  182   a  is tight so that positioning accuracy is established and maintained. If desired, the male closure element  44   b  may also have a tight fit within the groove  182   b  to obtain further positioning accuracy.  
         [0044]    As a still further alternative, where the ribs are to be applied to a side of the plastic film  172  opposite to the side that carries the female and male closure elements  44   a ,  44   b , grooves may be provided in the first roll  160  and the second roll  162  (or the rolls  164  and/or  176 , if used), as shown in FIG. 18. The groove  188   a  is disposed at a first end  190  of the second roll  162 , while the second groove  188   b  is disposed at a second end  192  of the second roll  162 . The grooves  188   a ,  188   b  accommodate the female and male closure elements  44   a ,  44   b , respectively. The grooves  188   a ,  188   b  have dimensions similar to the grooves  182   a ,  182   b  of FIG. 16.  
         [0045]    If desired, any or all of the rolls  162 ,  164  and  176  may be made of rubber or another deformable material that assists in applying pressure to the film while minimizing permanent deformation of the rib(s) and/or closure elements  44   a ,  44   b.    
         [0046]    [0046]FIG. 19 illustrates yet another alternative apparatus wherein a further pair of grooves  200 ,  202  substantially identical to the grooves  173 ,  174  are provided at a second axial end  160   b  of the roll  160 . An extrusion profile die  206  identical or similar to the extrusion profile die  166  is provided having outlet orifices aligned with the grooves  200 ,  202 . The extrusion profile die  206  deposits extrudate into the grooves  200 ,  202  and the roll  162  presses the film  172  into intimate contact with the extrudate in the grooves  200 ,  202  to form ribs adjacent an edge  208  of the film  172  opposite an edge  210  at which the ribs  50  are formed in accordance with the apparatus of FIGS.  11 - 13 . An air nozzle  212  directs air against the extrudate before deposit thereof into the grooves  200 ,  202 . As in all of the preceding embodiments, once the ribs are formed by the apparatus of FIG. 19, the film  172  is folded lengthwise and severed and sealed at spaced locations to form individual bags, for example, as seen in FIG. 8.  
         [0047]    If desired, the apparatus of FIG. 19 can be modified in accordance with the teachings of any of FIGS.  14 - 16  and  18 .  
         [0048]    As should be evident from the foregoing, the bag of FIG. 3 can be produced by any of the apparatus of FIGS.  11 - 17 , so long as a single orifice is provided in the profile plate  167  and a single groove is provided in the roll  160 . The same is true of the bag of FIG. 5, so long as grooves  173 ,  174  of different cross-sectional shape are provided in the roll  162 . The bags of FIGS. 4 and 6 can be produced by the apparatus of FIG. 19, so long as the extrusion profile die  166  and the grooves  173 ,  174  are omitted and the desired number of orifices are provided for the die  206  and a like number of grooves are provided in the roll  160  at the second axial end  160   b . The bag illustrated in FIG. 7 can be produced by the apparatus of FIG. 19, modified as noted above to provide a single groove at each axial end  160   a ,  160   b  and a single outlet orifice for each die  166  and  206 .  
       INDUSTRIAL APPLICABILITY  
       [0049]    The bag described herein advantageously includes at least on guide surface that guides a user&#39;s fingers during closure of the bag. Thus, closing efficiency is increased and the expenditure of wasted effort by the user is minimized.  
         [0050]    Further, the apparatus and method described herein extrude polymer from a profile die into grooves on a first grooved and cooled roller to create ribs. The still molten ribs are combined with a film and cooled as it rotates around the grooved roller. The use of grooves in the first roller to create the ribs allows the ribs to have a uniform size and shape, whereas, when molten polymer is extruded directly onto a film to create ribs, the ribs may deform or spread out.  
         [0051]    The method described herein also has the advantage of being a continuous process that has relatively high production rates of up to or greater than 300 feet per minute. Other similar processes cannot reach such production levels because the time necessary to cool the ribs and film is longer.  
         [0052]    Numerous modifications will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is presented for the purpose of enabling those skilled in the art to make and use the invention and to teach the best mode of carrying out same. The exclusive rights to all modifications which come within the scope of the appended claims are reserved.