Patent Publication Number: US-2003236158-A1

Title: Method of and apparatus for producing a reclosable pouch

Description:
TECHNICAL FIELD  
       [0001] The present invention relates generally to reclosable pouches, and more particularly, to a method of and apparatus for manufacturing a thermoplastic bag.  
       BACKGROUND ART  
       [0002] The use of reclosable thermoplastic bags for the storage of household items, such as food or other articles, is well known. An example of a reclosable thermoplastic bag is disclosed in Ausnit U.S. Pat. No. 5,259,904. The plastic bag includes thermoplastic bag walls of consistent thickness throughout. A closure profile comprised of male and female closure profile portions are disposed on internal portions of the bag walls. Two opposing lips with grip strips are disposed directly above the closure profiles. A user may place an item in the bag, interlock the closure profiles to close the bag, and re-open the bag using the grip strips to disengage the closure profiles.  
       [0003] There are several methods for manufacturing such reclosable thermoplastic bags. Known processes include the blown method, the cast integral method, and the cast post applied method. Bags manufactured by one of these methods may have characteristics that are different than bags made by another of these methods. Also, the production speeds are different and the costs associated with the methods vary widely.  
       [0004] The blown method is a two-up process that extrudes a cylindrical bag web of a single thickness simultaneously and integrally with two male and two female closure profiles. The two male profiles are disposed adjacent one another on an inside surface of the cylindrical bag web and the two female profiles are disposed adjacent one another on the inside surface of the web diametrically opposite the male profiles. As the bag web is extruded, air is blown into the interior thereof so that the thermoplastic is cooled. Thereafter, the bag web is slit between adjacent male and female closure profiles to form two web portions. The profiles of each web portion are then interlocked and the web portions are simultaneously severed and sealed at spaced locations by a hot wire resulting in individual reclosable thermoplastic bags. The production speed of the blown method is relatively slow as compared to other bag-making processes owing to the fact that the blown method utilizes convective cooling as opposed to conductive cooling. A bag manufactured by this method includes a bag web with a relatively uniform thickness throughout and, typically, lips of equal lengths. Any variation in the lip length or lip offset can be difficult to control using this manufacturing method.  
       [0005] The cast integral method includes the step of using a flat extrusion die to extrude the bag web and male and female closure profiles together in an integral fashion directly onto a temperature-controlled driven casting roll. The production speed of the cast integral process is approximately twice the speed of the blown method and the bag web extruded by the cast integral method is typically of a uniform thickness. However, because the profiles are extruded at the same time as the bag web and the profiles are located at the edges of the bag web, neck-in of the extrudate complicates the correct formation of the profiles.  
       [0006] The cast post applied method includes the steps of using a first extrusion die to extrude the bag web onto a casting roll and using one or more additional extrusion dies or other apparatus to extrude or adhere the closure profiles onto the bag web when the bag web is disposed at a location substantially downstream of the casting roll. An example of this method is disclosed in Geiger et al., U.S. Pat. No. 4,755,248. This method has the advantage of being operable at a production speed that is higher than the other two methods. In addition, the method can be used to produce bags having readily controllable portion dimensions and thicknesses.  
       [0007] It has been found that consumers prefer a bag having relatively thick top portions, even where a relatively high force is required to close the closure profiles of the bag, as compared with a bag having uniform wall thickness and a relatively lower required closing force. Also, it has been found that the lengths of the bag lips, as measured from the top of the bag to the closure profiles, as well as the difference between the lengths of the lips (i.e., the lip offset) and other dimensions have a significant impact on bag quality as perceived by consumers. These dimensions are most readily controlled in the cast post applied method, but some variability in these dimensions is encountered even in this process. Further, it has been found that the cost required to change over a cast integral production line to a cast post applied production line (which is the typical manner in which a cast post applied line is implemented) is extremely high due to the implementation cost of the required additional hardware components.  
       SUMMARY OF THE INVENTION  
       [0008] According to one aspect of the present invention, a method of producing a reclosable pouch includes the steps of extruding a bag web onto a casting roll and separately forming a closure profile on the bag web while the bag web is in contact with the casting roll.  
       [0009] According to another aspect of the present invention, a method of producing thermoplastic bags includes the steps of extruding a web onto a casting roll wherein the bag web includes a top portion and a body portion and wherein the top portion has a thickness at least twice a thickness of the body portion and forming a closure profile on the top portion of the bag web while the bag web is in contact with the casting roll.  
       [0010] According to yet another aspect of the present invention, a storage bag is produced by a method comprising the step of extruding a bag web onto a casting roll wherein the bag web includes spaced top portions each of a first thickness and a body portion of a second thickness and wherein the first thickness is at least about 6 to 10 mils and the second thickness is in a range between about 1.5 mils and about 3.0 mils. The method further includes the steps of forming first and second closure profiles on the spaced top portions while the bag web is in contact with the casting roll and converting the bag web into individual storage bags.  
       [0011] In accordance with a still further aspect of the present invention, an apparatus for producing thermoplastic storage bags includes a casting roll and extrusion apparatus for extruding a bag web onto the casting roll, wherein the extrusion apparatus further forms a closure profile on the bag web after the bag web is formed while the bag web is in contact with the casting roll.  
       [0012] Still further in accordance with another aspect of the present invention, an apparatus for producing thermoplastic storage bags includes a casting roll and a first extrusion die for extruding a bag web onto the casting roll. An air knife is provided for pinning the bag web as a whole to the casting roll and second and third extrusion dies are provided for forming male and female closure profiles on the bag web while the bag web is in contact with the casting roll.  
       [0013] Other aspects and advantages of the present invention will become apparent upon consideration of the following detailed description. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014]FIG. 1 comprises an elevational view of a thermoplastic storage bag produced according to the present invention;  
     [0015]FIG. 2 comprises a sectional view of the thermoplastic storage bag taken generally along the lines  2 - 2  of FIG. 1;  
     [0016]FIG. 3 comprises an isometric view of apparatus according to the present invention;  
     [0017]FIG. 4 comprises an enlarged isometric view of the apparatus of FIG. 3;  
     [0018]FIG. 5 comprises an enlarged end elevational view of the apparatus of FIGS. 3 and 4;  
     [0019]FIG. 6 comprises an isometric view of a bag web produced by the apparatus of FIGS.  3 - 5  before folding thereof;  
     [0020]FIG. 7 comprises an isometric view of the bag web of FIG. 6 during folding thereof; and  
     [0021]FIG. 8 comprises a combined diagrammatic and block diagram of apparatus for forming individual bags from an elongate folded web of thermoplastic material. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0022] Referring now to FIGS. 1 and 2, a reclosable pouch in the form of a thermoplastic bag  18  comprises a top portion  20  integral with a body portion  22 . The top portion  20  includes closure profiles  24  and first and second lips  28 ,  30 . The bag  18  further includes a first sealed side  32 , a second sealed side  34 , and a bottom edge  36 . The top portion  20  and the body portion  22  are formed from a thermoplastic bag web  38  produced in accordance with the method described hereinafter.  
     [0023] A plurality of grip strips  40  is disposed on the inner surfaces  28   a ,  30   a  of the first and second lips  28 ,  30 , respectively. As seen in FIG. 2, the first and second lips  28 ,  30  form an opening  44  for placement of items therein. Disposed on the inner surface  28   a  of the first lip  28  is a male closure profile  46  while a female closure profile  48  is disposed on the inner surface  30   a  of the second lip  30 . The male and female closure profiles  46 ,  48  extend from the first sealed side  32  to the second sealed side  34  parallel to the grip strips  40 . A user may close the bag  18  by contacting outer surfaces  28   b ,  30   b  of the first and second lips  28 ,  30  over the profiles  46 ,  48  at an end  50  (FIG. 1) of the bag  18  using the thumb and a finger, pinching the lips  28 ,  30  such that the male closure profile  46  is inserted into the female closure profile  48  at the end  50  and sliding the thumb and finger across the bag  18  to an end  52  (FIG. 1), thereby interlocking the male and female closure profiles  46 ,  48  across the full width of the bag  18 .  
     [0024] The method of the present invention is capable of producing bags of differing designs. For example, the method may be used to produce bags having a first thickness at the body portion  22  and a second thickness greater than the first thickness at the top portion  20 . The thickness of each wall of the top portions  20   a ,  20   b  of the bag web  38  is preferably at least twice, and, more preferably, approximately 3-5 times the thickness of each wall of body portion  22   a ,  22   b  forming the body portion  22 . According to a first design suitable for freezer bags, the thicknesses of the walls  22   a ,  22   b  are preferably (although not necessarily) equal to one another and each wall  22   a ,  22   b  preferably has a thickness in a range between approximately 1.5 and approximately 3.0 mils, with a thickness between approximately 2.55 mils and 2.90 mils being more preferred and a thickness of approximately 2.70 mils being most preferred. Still further, the thicknesses of the walls  20   a ,  20   b  are preferably (although not necessarily) equal to one another and each wall  20   a ,  20   b  is of a thickness between approximately 5 and approximately 15 mils, with a thickness of approximately 10 to approximately 13 mils being more preferred and a thickness of approximately 12 mils being most preferred. In a second design suitable for storage bags, the thicknesses of the walls  22   a ,  22   b  are preferably (although not necessarily) equal to one another and each wall  22   a ,  22   b  preferably has a thickness in a range between approximately 1.0 and approximately 3.0 mils with a thickness of 1.75 mils being most preferred. Also in this design, the thicknesses of the walls  20   a ,  20   b  are preferably (although not necessarily) equal to one another and each wall  20   a ,  20   b  is of a thickness between approximately 5 and approximately 15 mils with a thickness of 10 mils being most preferred. In a third design suitable for sandwich bags, the thicknesses of the walls  22   a ,  22   b  are preferably (although not necessarily) equal to one another and each wall  22   a ,  22   b  preferably has a thickness in a range between approximately 0.5 and approximately 1.5 mils with a thickness of 1.00 mil being most preferred. In addition, the thicknesses of the walls  20   a ,  20   b  are preferably (although not necessarily) equal to one another and each wall  20   a ,  20   b  is of a thickness between approximately 2 and approximately 5 mils with a thickness of 3-4 mils being most preferred. It should be evident to one of ordinary skill in the art that the foregoing ranges and preferred values may be varied, as desired.  
     [0025] Each wall  20   a ,  20   b  is joined to an associated wall  22   a ,  22   b , respectively, at a transition portion  54   a ,  54   b . Preferably, although not necessarily, the transition portions  54   a ,  54   b  are of equal lengths (i.e., they extend equal distances from the top to the bottom of the bag  18  as seen in FIG. 2) and the thicknesses thereof preferably taper uniformly and continuously from the wall  20   a ,  20   b  to the associated wall  22   a ,  22   b . Also preferably, the transition portions  54   a ,  54   b  are relatively short and are disposed at substantially equal heights (as seen in FIG. 2) above the bottom edge  36  of the bag  18 , although the transition portions  54   a ,  54   b  may be disposed at unequal heights above the bottom edge  36  of the bag  18 , if desired.  
     [0026] As seen in FIG. 2, the first and second lips  28 ,  30  are preferably of differing lengths to create an offset wherein the magnitude of the offset is the difference between the length of the first lip  28 , as measured from a top  55  of the female profile  48  to an upper edge  56  of the first lip  28 , and the length of the second lip  30 , as measured from the top  55  of the female profile  48  to an upper edge  58  of the second lip  30 , while the profiles  24  are closed. Preferably, the lip  30  has a length of approximately 0.50-0.80 inch, and more preferably has a length of 0.65-0.75 inch, and most preferably has a length of 0.70 inch. Further, the lip  28  preferably has a length of approximately 0.825 inch, thereby establishing a preferred offset of approximately 0.125 inch, although the offset can be established at a different value by adjusting the positions of a male profile  46  and the female profile  48  below the upper edges  56 ,  58 . Also, preferably, the transition portions  54   a ,  54   b  are centered at a distance between 0.75 inch and 2.00 inches below the upper edge  58  of the lip  30 , with a distance of about 1.00 and 1.50 inch being more preferred, and a distance of about 1.25 inch being most preferred.  
     [0027] The grip strips  40  preferably extend parallel to the bottom edge  36  of the bag  18  from the first sealed side  32  to the second sealed side  34 . Preferably, the grip strips are manufactured in accordance with the teachings of McCree U.S. Pat. No. 5,009,828, owned by the assignee of the present application and the disclosure of which is incorporated by reference herein. A user grasps the lips  28  and  30  during opening of the bag  18  and the grip strips  40  help prevent the fingers and/or thumbs of the user from sliding off the lips  28  and  30 .  
     [0028] In the illustrated embodiment, the interlocked male and female closure profiles  46 ,  48  and the first and second lips  28 ,  30  have a combined thickness of approximately 65 to approximately 125 mils, with approximately 90 to approximately 105 mils being more preferred and approximately 94 mils being most preferred.  
     [0029] Still further in accordance with the illustrated embodiment, the male and female closure profiles  46 ,  48  may have the configuration disclosed in Fisher, et al. U.S. Pat. No. 4,736,496 or Porchia, et al. U.S. Pat. No. 5,012,561, both owned by the assignee of the present application and the disclosures of which are incorporated by reference herein.  
     [0030] Referring next to FIGS. 3 and 4, bags such as the bag  18  are produced according to a production method according to the present invention that utilizes extrusion apparatus including a first extrusion slot die  60 , a temperature-controlled driven casting roll  62 , edge pinning devices or apparatus  64   a ,  64   b , an air knife  65 , second and third extrusion dies  66   a ,  66   b  (which, together with the die  60 , form the extrusion apparatus) and cooling apparatus  68   a ,  68   b . The extrusion die  60  receives molten thermoplastic from an extruder (not shown) and deposits the thermoplastic in sheet form as a web  70  onto the casting roll  62 . The extrusion die  60  includes a slot opening (not shown) that forms thickened areas  72 ,  74  at outside edge portions  75   a ,  75   b  of the resulting web  70  and a relatively thinner portion  76  intermediate the thickened areas  72 ,  74 . The edge portions  75   a ,  75   b  are pinned to the casting roll  62  by the edge pinning devices  64   a    64   b , respectively. The web  70  is then pinned across the entire width thereof (i.e., as a whole) to the casting roll  62  by the air knife  65 .  
     [0031] After the web  70  is pinned to the casting roll  62 , the male and female closure profiles  46 ,  48  are formed on the web  70 . Preferably, the extrusion dies  66   a ,  66   b  receive molten thermoplastic from separate extruders and extrude the male and female closure profiles  46 ,  48 , respectively, onto the thickened areas  72 ,  74 . Alternatively, the separate extrusion dies  66   a ,  66   b  may be replaced by a single extrusion die having two outlets at which the male and female closure profiles  46 ,  48  are simultaneously extruded onto the thickened areas  72 ,  74 . In any event, as seen in FIG. 5, the angle of a face  90  of each die  66  is at least initially disposed substantially parallel to a horizontal (as seen in FIG. 5) radial line  92  extending from the center of the casting roll  62 . The position of the die  66  (or each die  66   a ,  66   b  individually if separate dies are used) may then be adjusted by moving the die left, right, up, or down (all as seen in FIG. 5) or the die may be tipped (i.e., angularly displaced) to adjust the angle of the die face  90  to obtain desirable results. The closure profiles  24  formed by the die(s)  66  may exit the die(s)  66  at a point coincident with a vertical tangent line  93  (FIG. 5) intersecting the surface of the casting roll  62  on the side of the casting roll  62  where the web  70  is first deposited thereon. Alternatively, the closure profiles  24  formed by the die(s)  66  may exit the die(s)  66  at a point displaced to the right or left (as seen in FIG. 5) of the tangent line  93 . If the extrudate exits the die(s)  66  at a point displaced to the right of the line  93 , some provision must be made at the initiation of production to attach the extrudate stream to the casting roll  62 . Thereafter, production may commence, (provided that the exit of the die(s)  66  is not disposed too far to the right of the tangent line  93 ) whereupon the melt strength of the extrude stream carries the stream into contact with the roll  62 .  
     [0032] Once the molten thermoplastic from the die(s)  66  has been deposited onto the web  70 , coolant is applied to the profiles  46 ,  48  by the coolant apparatus  68   a ,  68 b to bring the temperature thereof below the melting point of the thermoplastic material forming the profiles  46 ,  48  as quickly as possible. Preferably, the coolant comprises water or any other suitable cooling fluid and the coolant is applied to the material of the profiles  46 ,  48  only after such material contacts the material of the web  70  so that adhesion thereto is optimized. The web  70  and the closure profiles  46 ,  48  are maintained in contact with the temperature-controlled casting roll  62  for a period of time as the roll  62  is rotated so that the web  70  and profiles  46 ,  48  are further cooled. The casting roll  62  should be maintained at a temperature below the melting point of the thermoplastic material(s) forming the web  70  and the closure profiles  46 ,  48 , typically about 20-80 degrees C.  
     [0033] Thereafter, the coolant that was applied to the closure profiles  46 ,  48  is removed by any conventional method, such as by any known dewatering process. The method results in the production of an elongate web  70  with closure profiles  46 ,  48  applied thereto, a section of which is seen in FIG. 6. Subsequently, as seen in FIG. 7, the elongate web  70  is folded longitudinally by any suitable apparatus and the elongate folded web  70  is sealed and cut at spaced points thereof by a hot wire, a hot knife or any other conventional apparatus  100  (FIG. 8) to form individual bags. Alternatively, the elongate web  70  could be wound on one or more rolls and processed at a later point (i.e., off-line) to create individual bags.  
     INDUSTRIAL APPLICABILITY  
     [0034] The method and apparatus of the present invention are useful to extrude the web  70  and apply the male and female profiles  46 ,  48  in a single unit operation. This eliminates a unit operation, as compared with the cast post applied process described above, where the closure profiles  24  are applied separate from the point at which the web  70  is extruded. Because a unit operation is eliminated a significant savings is realized in terms of the conversion costs from a cast integral line.  
     [0035] The method and apparatus of the present invention also have the advantage of relatively fast production rates (approximately 10% faster than the cast integral method) and avoid the controllability issues encountered by the cast integral method. The method of the present invention also avoids the variability in lip length encountered by the cast post applied method. In addition, the method disclosed herein can be used to produce bags having the dimensions noted above. It has been found that such bags are preferred by most consumers, presumably due to the relatively thicker bag tops, which create the perception that the closure profiles  46 ,  48  are substantially self aligning, thereby facilitating closure of the bag  18 , when desired, without substantial wasted effort on the part of the consumer.  
     [0036] In addition to the foregoing, the relatively thick walls  20   a ,  20   b  of the top portion  20  cause such walls to have a haze at the top portion  20 . It has been found that consumers find such hazy appearance to be a desirable attribute, apparently for the reason that the hazy appearance connotes strength and durability. Still further, the relatively thick portions at the bag tops apparently create the perception that the entire bag is of durable and sturdy construction perhaps because the bag walls are thickest where the bag is most often handled by the consumer.  
     [0037] The method and apparatus of the present invention as described herein may be modified as desired. For example, the profiles  46 ,  48  may be extruded at a location above the air knife  65  and may be attached onto the web  70  either at or below the point at which the web  70  is pinned by the air knife  65 . Also, the first though third extrusion dies  60 ,  66   a  and  66   b  may be replaced by a single extrusion die or multiple extrusion dies.  
     [0038] Numerous modifications to the present invention 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 the same. The exclusive rights to all modifications that come within the scope of the appended claims are reserved.