Strip material used in forming air inflated cushioning material
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to strip materials of the type having inflatable chambers formed between two heat sealable films which chambers are subsequently filled with gas and sealed to form cushioning material. 
     2. Description of the Prior Art 
     U.S. Pat. Nos. 3,660,189 and 3,868,285 describe an elongate strip material which is formed by fusing together two flexible heat sealable films in discrete areas to define a plurality of chambers between the films with each chamber having an inlet opening. The strip material is shipped to the site of its intended use, and is then inflated and sealed to form air cushioning material. The use of this strip material and method reduces bulk handling problems and the costs of shipping air which would otherwise result if the strip material were inflated and sealed at a central production facility and was then shipped in an inflated condition to the site of its intended use. The chambers formed prior to inflation in the strip material of U.S. Pat. Nos. 3,660,189 and 3,868,285, however, extend transversely nearly across the strip material. Each chamber has at least one end which is open across the entire width of the chamber to provide the inlet opening and is positioned adjacent a longitudinal edge of the strip material. The strip material is moved to sequentially position the open ends of the chambers adjacent to a nozzle through which air flows to inflate the chambers, and the strip material must then be extensively sealed both to seal across the open ends of the chambers, and to divide the chambers longitudinally of the strip material into smaller chambers of a more suitable size. Because of the large number of seals that must be made, the strip material requires a filling and sealing device that is more complex and expensive than might be desired for use by a small manufacturing facility. Also, sealing across the full width of the inflated chambers may cause wrinkles which tend to leak air through the sealed areas. This occurs because opposed arcuate lengths of each film are gathered and sealed together in about the length of their common chord. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved strip material of the aforementioned type which affords more complete preparation of chambers in the strip material at a central location and the use of a simple device for filling and sealing the chambers. 
     The strip material according to the present invention comprises two films fused together to define between the films two rows of inflatable chambers and a passageway extending the length of the strip material between the passageways with each chamber having an inlet opening communicating with the passageway. When it is to be filled and sealed, the strip material is propelled along a strip path from an inlet to an outlet end and gas or air under pressure is passed into the passageway at a predetermined position along the strip path. The passageway is blocked within a predetermined distance toward the inlet end of the strip path from the predetermined position to direct gas in the passageway into the chambers. Heat is then applied to sequentially seal the inlet openings of the inflated chambers along sealing paths longitudinal of the strip material on both sides of the passageway after which the sealed areas are cooled. 
     The inflatable chambers preferably have inlet openings with dimensions longitudinally of the strip material which are quite narrow compared to the width of the chambers in the corresponding direction. Preferably the dimension of the inlet opening longitudinally of the strip material is less than 1/2 the width of the chambers longitudinally of the strip material. Under these conditions, the sealed together portions of the films aligned with the inlet openings to the chambers add rigidity which helps reduce lengthwise shrinking of the film across the inlet openings under the influence of air pressure in the chambers and which allows the films at the inlet openings to be more easily tensioned to a flat, wrinkle free condition. Additionally, the use of inlet openings having a reduced dimension longitudinally of the strip material as compared with the corresponding dimension of the chamber affords the use of generally arcuate sealing lines around the junction between the inlet opening and the chamber, thereby eliminating stress concentration points and maximizing the bursting strength of the chamber. 
     Preferably the inflatable chambers are elongate and are initially formed with constrictions along their lengths. These constrictions both (1) might preclude the need to seal the chambers into smaller chambers after inflation, thereby simplifying the device for sealing the chambers, and (2) define chamber portions interconnected by the constrictions which restrict air transfer between the portions of the inflated cushion to provide damping for the inflated chamber portions during use of the cushioning material. 
     Also preferably the fused areas of the films defining the walls of the chamber portions flanking the constrictions are generally aligned, and the constrictions have a width transverse of the chamber which is much narrower than (e.g. less than approximately one fifth) the transverse dimension of the chamber portion. This relationship of the constriction and chamber portion widths, compared to constrictions which are wider relative to the width of the chamber portions, reduces the stress concentration at the constriction and increases the damping between the chamber portions. This apparently happens both because of the reduced air capacity of the constriction and because stresses in the aligned walls of the chamber portions flanking the constriction when the chamber portion is inflated, tend to tension the films across the constriction in general alignment with corners of the sealed areas defining the constriction. Such tensioning reduces the effect of the corners as stress concentration points while the tensioned film tends to close and partially block the constriction which increases damping. 
     The elongate chambers can extend with their center lines at a right or an acute angle to the center line of the passageway. Acute angles in the range of about 30° to 75° afford close proximity of circular chamber portions of adjacent chambers to minimize the uninflated areas of the cushioning material. Also chambers so disposed can provide an advantage when the cushioning material is wrapped around an object and one chamber of the cushioning material ruptures, since the cushioning material will not have an uninflated area in a path normal to one of its edges which path often is aligned with an edge of a protected object. 
     Since the two rows of chambers in the strip material can be inflated from a central passageway, the inflating and sealing means need only engage the strip material around the passageway. Thus shrinking of the strip material width, which may occur during inflation of the chambers, will not adversely affect the operation of the inflating device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The present invention will be more fully understood after reading the following detailed description which refers to the accompanying drawing wherein: 
     FIG. 1 is a plan view of an uninflated strip material according to the present invention; 
     FIG. 2 is a schematic view of a device for forming the strip material of FIG. 1; 
     FIG. 3 is a vertical end view of an inflating device for inflating the strip material of FIG. 1; 
     FIG. 4 is a sectional view taken approximately along line 4--4 of FIG. 3; 
     FIG. 5 is a sectional view taken approximately along line 5--5 of FIG. 3; 
     FIG. 6 is a sectional view taken approximately along line 6--6 of FIG. 3; 
     FIG. 7 is an enlarged fragmentary sectional view taken approximately along line 7--7 of FIG. 3; 
     FIG. 8 is a sectional view taken approximately along line 8--8 of FIG. 7; 
     FIG. 9 is a sectional view taken approximately along line 9--9 of FIG. 7; and 
     FIG. 10 is a plan view of an alternate embodiment of an uninflated strip material according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1 there is illustrated a preformed elongate layered strip material 12 according to the present invention which may be inflated and sealed on a device 10 illustrated in FIGS. 3 through 9. 
     The strip material 12 comprises two thin flexible heat fusible films 14, each of which film 14 comprise a heat sealable thermoplastic material forming at least one surface of the film 14. The films 14 are positioned with their thermoplastic surfaces adjacent, and with adjacent portions of their thermoplastic surfaces in contact, and are fused together in discrete areas 16 to define a plurality of unfused adjacent surface areas in a pattern providing between the films 14 two rows of inflatable chambers 19, a longitudinal passageway 18 extending the length of the strip material 12 between the rows of inflatable chambers 19, and an inlet tube or opening 20 communicating between each of the chambers 19 and the passageway 18, with the inlet openings 20 for each row of chambers 19 being aligned longitudinally of the strip material 12. Each chamber 19 also has two constricted chamber areas 21 dividing the chamber 19 into three generally circular portions with the fused areas 16a of the films 14 defining the perimeter of the chamber portions flanking the constricted area 21 being generally aligned. The constricted areas 21 afford transfer of air between the chamber portions when the chamber 19 is inflated and subsequently afford restricted movement of air between the chamber portions to provide a damping effect for the chamber portions during use of the inflated cushioning material. Each chamber 19 is generally elongate and oriented with its center line extending generally at a right angle with the center line of the passageway 18. Also the strip material 12 has spaced transverse perforations 17 between adjacent chambers 19 to afford separating portions of the inflated cushioning material. 
     The films 14 referred to herein may consist of a polyolefin such as polyethylene or polypropylene, or be a layered film (e.g. coated, laminated or co-extruded film) such as a polyester backed ethylene vinyl acetate copolymer, a polyvinylidene chloride coated polyethylene, a thermoplastic coated paper or a polyolefin coated polyester. The main requirement for the film is that a heat sealable material forming at least one of its surfaces will fuse to a mating surface to form an air tight seal under the influence of moderate pressure and heat, and that it has desired strength and gas barrier properties. A polyester film coated with an ethylene vinyl acetate copolymer (e.g. the film sold under the trademark &#34;Scotchpak 113&#34; by Minnesota Mining and Manufacturing Company) has been found to produce air cushions having a very high bursting strength, which may be particularly desirable for some applications; whereas a co-extruded film having polyethylene layers on both sides of a layer of vinylchloridevinylidene chloride copolymer (e.g. the film sold under the trade name &#34;Saranex 11&#34; by Dow Chemical Company) is less expensive and has an adequate bursting strength and gas barrier for most air cushion applications. 
     As is schematically illustrated in FIG. 2, the layered strip material 12 is prepared by feeding the films 14 along separate paths to a forming station 22. At the forming station 22 the films 14 may be supported on a planar surface 23 in face-to-face contact with their edges aligned, and the face of an electrically heated die 24 having raised ridges in the configuration of the discrete areas 16 to be fused between the films 14 may be pressed against the adjacent films 14 to fuse the films 14 together between stepwise advancements of the films 14. Alternatively the discrete areas 16 between the films 14 could be fused together between heated rotating members to afford continuous movement of the films 14, or by ultrasonic or induction means, or by the known process of infra-red black line sealing. After the forming station the strip material 12 passes through a perforating die 26 which forms the perforations 17 across the strip material 12 at spaced intervals along its length, and then is helically wound on a spool 25 for shipment to the site where the inflatable chambers 19 formed therein will be inflated and the inlet openings 20 sealed by the device 10. Alternately the die 24 can be adapted to permanently stretch the portions of the films 14 defining the chambers 19 so that shrinking of the strip material 12 will be reduced upon subsequent inflation of the chambers 19. 
     The device 10 for inflating and sealing the chambers 19 is illustrated in FIGS. 3 through 9. Briefly the device 10 includes means for defining a path for the strip material 12 through the device 10, means for propelling a portion of the strip material 12 along the path through the device 10; means along the path defining an inflation station for inflating the chambers 19 of the strip material 12; means along the path subsequent to the inflation station defining a heat sealing station for applying heat and pressure to seal the inlet openings 20 of the chambers 19 along a predetermined sealing path longitudinally of the strip material for each row of chambers 19; means for tensioning the strip material along the path through the inflation and heat sealing station to remove wrinkles from the films 14 across the inlet openings 20; and means for pressing the films 14 together along the predetermined sealing path and in an area on the side of the sealing path adjacent the chambers 19 both during the sealing of the inlet openings 20 at the inflation station and subsequent thereto while the sealed films 14 at the inlet openings 20 are cooled to prevent air pressure in the chambers 19 from rupturing the film along the sealed inlet openings 20 while the sealed inlet openings 20 are hot. 
     The means for defining the path for the strip material through the device comprise opposed slots 29 on a frame 30 for the device 10 in which a shaft 32 on the spool 25 supporting the wound strip material 12 is rotatably and removably supported to define an inlet end of the path. Means (not shown) are provided on the device 10 for frictionally retarding rotation of the shaft 32 in the slots 29 to restrict overrunning of the spool 25. From the spool 25 the strip material 12 extends first between a pair of nip rollers 34 fixed to shafts 35 rotatably mounted on the frame 30. From the nip rollers 34 the strip material 12 extends between an endless belt 44 and a wheel 40 fixed to a shaft 41 rotatably mounted on the frame 30 from a first end 37 to a second end 38 of a common path for a peripheral support surface 39 of the wheel 40 and a contact surface 43 on the belt 44, and then leaves the device at an outlet end of the path along a guide plate 45 positioned to separate the strip material from the wheel 40. The belt 44 is supported on a flanged guide roller 46, a guide roller 47, and a cylindrical tensioning roller 48. The guide rollers 46 and 47 are respectively fixed to shafts 49 and 50 rotatably mounted on the frame 30, whereas the tensioning roller 48 is rotatably mounted on a shaft 52 fixed at the ends of a pair of parallel bars 53. The ends of the bars 53 opposite the shaft 52 are pivotably mounted about the shaft 50 to afford pivotal movement of the tensioning roller 48 about the shaft 50. The tensioning roller 48 is biased to a position tensioning the belt 44 between the rollers 46, 47, and 48 and along the periphery of the wheel 40 by means comprising a pair of springs 55 coupled between the frame 30 and the bars 53. 
     The means for tensioning the strip material along the path through the heat sealing station is incorporated in the means for propelling a portion of the strip material 12 along the path. A gear reduced motor 56 coupled to a shaft 57 (FIG. 3) is rotatably mounted on the frame 30. A sprocket 58 (FIG. 5) is fixed to the shaft 57 and via a chain 59 drives a sprocket 60 fixed to the shaft 49 on which the flanged guide roller 46 is fixed and a sprocket 61 driving a shaft 62 which is rotatably mounted on and extends transverse of the frame 30. A sprocket 63 (FIG. 5) is fixed to the end of the shaft 62 opposite the sprocket 61 and drives a chain 64. The chain 64 extends around an idler sprocket 65 a sprocket 66 fixed to the shaft 41 to which the wheel 40 is fixed, and a sprocket 67 fixed to the shaft 35 of one of the nip rollers 34. Thus activation of the motor 56 drives the wheel 40, the belt 44 and one of the nip rollers 34. The drive components are selected so that for a given motor speed the contact surface 43 of the belt 44 is driven slightly faster than the peripheral surface of the driven nip roller 34 to tension the length of strip material 12 therebetween and along the belt 44 at the heat sealing station and the peripheral surface 39 of the wheel 40 drives at a rate slightly faster than the contact surface 43 of the belt 44 so that the peripheral surface 39 of the wheel 40 also tends to tension and smooth the portion of the strip material 12 positioned along the belt 44 at the heat sealing station. 
     The means for defining the inflation station comprise a nozzle 69 at the end of a generally S-shaped tube 70 which extends through a circumferential groove 71 around the wheel 40. The tube 70 is coupled to a regulated source of air under pressure (not shown) via an air line 73 and a bore through a heat sink block 90 (the purpose of which block 90 will be explained later). Semi-circular gussets 74 are welded to the concave side surfaces of the tube 70 to provide support for the nozzle 69. The nozzle 69 is a generally straight hollow cylindrical end portion of the tube 70 positioned to extend centrally along the passageway 18 of the length of the strip material 12 positioned between the nip rollers 34 and the wheel 40. The nozzle 69 has an outside diameter just slightly smaller than the inside diameter of the passageway 18, an open terminal end 75 through which air passes into the strip material 12, and may have a plurality of side openings 76. The nip rollers 34 press the films 14 of the strip material 12 together across the passageway 18 and provide means for blocking the flow of air from the nozzle 69 through the passageway 18 within a predetermined distance from the end 75 of the nozzle 69 so that the air will enter the inlet openings 20 of the chambers 19 between the nozzle 69 and the nip rollers 34 and inflate the chambers 19. A knife blade 78 with a sharpened edge 79 positioned between the end 75 of the nozzle 69 and the outlet end of the path provides means for opening or severing one of the films 14 to afford movement of the strip material 12 over the nozzle 69. Severing could alternatively be provided by a score wheel positioned to rotate against the surface of the nozzle 69. 
     The means defining the heat sealing station for applying heat and pressure to seal off the inlet openings 20 of the chambers 19 comprise the surfaces 39 and 43 of the wheel 40 and belt 44 adjacent the first end 37 of their common path and the spring 55 which biases the contact surface 43 toward the peripheral surface 39 to press together the films portions defining the inlet openings 20 on the portion of the strip material 12 therebetween. A heated shoe 81 having parallel rails 82 with curved surfaces is positioned to engage the belt 44 on its surface opposite the contact surface 43 over the inlet openings 20 to the chambers 19 inflated by the nozzle 69 and apply heat to fuse the strip material 12 through the belt 44. The belt 44 is of stainless steel and has a coating, as of Teflon, defining its contact surface 43 so that the contact surface 43 does not adhere to the strip material 12 when it has again cooled after the sealing of the films 14. A thermostatically regulated electrical heating element 83 (FIG. 9) is mounted in and heats the shoe 81 to a desired temperature (e.g. 150° C). Sufficient heat to fuse the films 14 together will only be transferred to the strip material 12 in the areas over which the contact surfaces of the rails 82 pass, and each of the rails 82 is positioned to define the predetermined sealing path along which the inlet openings 20 of one of the two aligned rows of chambers 19 will be sealed as the strip material 12 is driven through the device 10. 
     The heated shoe 81 is pivotably mounted between the ends of a pair of parallel arms 84. The arms 84 are centrally pivoted at pins 85 on the frame 30 and are biased to move the rails 82 into firm engagement with the belt 44 by a spring 86 coupled between a bar 87 joining the ends of the arms 84 opposite the shoe 81 and the frame 30. One of the arms 84 pivotably supports a hook 88 adapted to engage a plate-like portion 89 of the frame 30 and retain the arms 84 in a position with the heated shoe 81 spaced from the belt 44 when the arms 84 are moved to that position against the bias of the spring 86, as is desirable to prevent over heating of the films 14 when the drive means for the strip material 12 is not operating. 
     The means for pressing the films 14 together along the predetermined sealing path and on the side of the sealing path adjacent the chambers 19 both during the sealing of the inlet openings 20 and subsequently while the sealed films 14 at the inlet openings 20 are cooled, comprise the surfaces 39 and 43 of the wheel 40 and belt 44 and the spring 55 which biases the contact surface 43 of the belt 44 toward the peripheral surface 39 of the wheel 40. As is best seen in FIGS. 8 and 9, the belt 44 and wheel 40 have sufficient width that they extend beyond both side edges of the rails 82 (e.g. by about 0.4 centimeter), so that the extending portions of the tensioned belt 44 and wheel 40 press together portions of the films 14 defining the inflated chambers 19 or the portions of the inlet openings 20 adjacent the inflated chambers 19 and restrict air pressure in the inflated chambers 19 from rupturing the softened films 14 during the application of heat thereto through the belt 44. After the moving wheel 40 and belt 44 move the fused strip material 12 from beneath the heated shoe 81, they maintain the films 14 together while their newly fused areas are cooled. Such cooling is facilitated by the finned heat sink block 90 mounted on the frame 30 which draws heat from the fused films 14 through the belt 44 adjacent the second end 38 of the common path for the belt 44 and the peripheral surface 39 of the wheel 40. The heat sink block 90 is of black anodized aluminum for efficient heat disposition, is pivotably mounted on the frame 30 so that the weight of the block 90 will bias it into engagement with the belt 44, and has a brass facing sheet contacting the belt to provide the needed lubricity therebetween. The air line 73 connected to the regulated source of air under pressure is coupled to the tube 70 through the bore in the block 90 so that the expanded air passing through the line 73 and tube 70 will help cool the block 90. 
     FIG. 10 illustrates an alternate embodiment of a strip material according to the present invention generally designated by the numeral 91 which may also be inflated by the device 10. Like the strip material 12, the strip material 91 comprises two thin flexible heat fusible films 92 each of which films 92 comprise a heat sealable thermoplastic material forming at least one of its surfaces and may be of any one of the materials listed for the films 14. The films 92 are positioned with their thermoplastic surfaces adjacent, and with adjacent portions of their thermoplastic surfaces in contact, and are fused together in discrete areas 93 by means such as are illustrated in FIG. 2 to define a plurality of adjacent unfused adjacent surface areas in a pattern providing two rows of inflatable chambers 95, and a passageway 94 extending the length of the strip material 91 between the rows of chambers 95, with each of the chambers 95 having an inlet opening 96 communicating with the passageway 94. Like the chambers 19, each chamber 95 is generally elongate and has two constricted chamber areas 97 which divide the chamber 95 into three portions with the fused areas 93a of the films 92 defining the peripheries of the chambers 95 on both sides of the constricted chamber areas 95 being generally aligned. Unlike the strip material 12, however, the center lines of the chambers 95 extend at an acute angle of about 60° with the center line of the passageway 94. This configuration allows the chambers 95 to be closely spaced and insures that rupturing a single chamber 95 will not cause an uninflated portion of cushioning material that extends at a right angle to its edge which is helpful in providing maximum protection for items around which the cushioning material is wrapped. Also the strip material 91 has spaced transverse perforations 99 which afford separating portions of the inflated cushioning material. 
     Also, as illustrated in FIG. 10, the strip material 91 may include means for blocking flow of air at predetermined positions along the passageway 94, which, when the strip material 91 is positioned along the path through the device 10, blocks the flow of air from the nozzle through the passageway within a predetermined distance from the nozzle independent of the nip rollers 34. The portions of the films 92 defining the passageway 94 are sealed together transverse of the passageway in areas 100 at spaced intervals along the passageway 94. The areas 100 are not sealed with the amount of heat and/or pressure used to seal the areas 93, but are sealed to provide sufficient adhesion between the films 92 so that the films 92 will remain adhered to effectively block air passing through the passageway 94. Upon movement of the passageway 94 over the nozzle 69, however, the areas 100 will peel apart under the separating force of the terminal end 75 of the nozzle 69. If desired, similar spaced peelably sealed areas could also be provided in the strip material 12 illustrated in FIG. 1. 
     For operation the motor 56 is actuated to drive the belt 44, the wheel 40 and one of the nip rollers 34 to withdraw the strip material 12 from the spool 25 and propel it through the device 10 over the nozzle 69 while tensioning it at the inflation and heat sealing stations between the nip rollers 34, belt 44 and wheel 40 by differential speeds of the driven members as has previously been explained. The source of air under pressure is coupled to the air line 73, and air flows into the chambers 19 of the tensioned length of strip material 12 through the nozzle 69, central passageway 18 and inlet openings 20 therein, with the nip rollers 34 pinching the strip material 12 to block movement of the air in the passageway 18 causing the air from the nozzle 69 to enter the inlet openings 20 and inflate the chambers 19 between the nozzle 69 and nip rollers 34. The edges of the strip material 12 are not constrained so that any transverse shrinkage that occurs in the strip material 12 during inflation of the chambers 19 does not affect the operation of the device 10. From the inflation station 27 the inflated chambers 19 move between the belt 44 and wheel 40 so that their surfaces 43 and 39 press together the films 14 at and adjacent the inlet openings 20 of the inflated chambers 19. Subsequently each inlet opening 20 moves under one rail of the heated shoe 81, which supplies heat to fuse the inlet opening 20 through the belt 44. The rail 82 is more narrow than the contact surface 43 of the belt 44 and support surface 39 of the wheel 40 and the portions of those surfaces 43 and 39 adjacent the rails 82 press the films 14 together under the influence of the spring 86 and prevent air pressure in the chambers 19 from rupturing the heated and softened films 14 as the inlet openings 20 are fused shut and while the films 14 cool after they move out from under the heated shoe 81 and pass under the heat sink block 90 which draws heat from the belt 44 and films 14. The strip material 12 then passes from between the belt 44 and wheel 40 as inflated cushioning material ready for use.