Crush resistant zipper

Abstract: A zipper strip (10) for a reclosable package having a transverse zipper is provided. The zipper strip (10) comprises a male profile (12) and a female profile (14). Each profile (12,14) includes at least one interlocking member (18,20,24,26) extending from a base (16,22) towards the opposite profile interlockable with an interlocking member on the opposite profile. One or both of the profiles is provided with at least one high compression member (28,30,32) which allows the interlocking profiles to be sealed to thermoplastic film across the widths of their respective bases (16,22) without the interlocking members (18,20,24,26) being crushed or distorted.

Description: The present invention relates to reclosable plastic bags and packages of the type in which food products, such as crisps, subsequently referred to as chips, other snack foods, cereal, and other goods are packaged for sale to consumers. More particularly, the present invention relates to a reclosable zipper strip for use in transverse-zippered reclosable plastic bags made on form-fill-seal (FFS) machines. The present invention relates to improvements in the package-making art and may be practised in the manufacture of thermoplastic bags and packages of the kind that may be used for various consumer products, but which are particularly useful for food products which must be kept in moisture and air-tight packages, free from leakage until initially opened for access to the product contents, which packages are then reclosable by zipper means to protect any remainder of the product therein. The prior art is fairly well-developed, but nevertheless remains susceptible to improvement contributing to increased efficiency and cost effectiveness. In particular the present invention relates to the area of reclosable packaging known as the transverse zipper. When making a bag having a transverse zipper, the zipper is attached transverse to the longitudinal axis of the material used to make the bag, as opposed to being attached to the material parallel to the longitudinal axis. A method and apparatus for making reclosable plastic bags with a transverse zipper on an FFS machine is disclosed in US-A-4, 909,017. Prior to the introduction of the transverse zipper to the reclosable packaging field, reclosable plastic bags made on FFS machines were typically made with a continuous longitudinal zipper, i.e. a zipper parallel to the longitudinal axis of the thermoplastic film used to make the bags. However, there are two primary problems with the longitudinal zipper technique. First, there is a problem in attaining satisfactory sealing of the bags against leakage since the transverse, or side, sealing bars of the FFS machine must flatten and seal the zipper at the same time they are sealing the thermoplastic film from which the packages are being made. The difficulty with which this sealing is consistently and successfully achieved is reflected by the high occurrence of leaking packages. Second, the length of reclosable bags made on FFS machines when the zipper is attached parallel to the longitudinal axis of the thermoplastic film is limited to the diameter of the filling tube of the FFS machine. Thus, generally bags of this type are wider than they are long. While such bags are suitable for certain products where shorter bags are desirable, such as cheese and chicken parts, these bags are not suitable for applications in which longer bags are desirable, for example, chips and other snack foods. Among the approaches taken to solve these problems has been the substitution of a transverse zipper for the longitudinal zipper. When a transverse zipper is provided, the transverse sealing bars associated with the FFS machine do not flatten the zipper during formation of the top and bottom seals of the package since the transverse sealing bars may seal the zipper to the thermoplastic film transversely thereacross without having to flatten the zipper ends. In addition, when a transverse zipper is used the length of the packages made on the FFS machine can be varied while the width of the zipper remains the same. One example of the use of a transverse zipper is disclosed in our earlier EP-A-0985605. In typical previous transverse zipper package making applications, flanged zipper strips were utilized. The zipper strips were sealed to the thermoplastic film via the flanges, thereby preventing damage to the interlocking closure elements which would otherwise occur during sealing. However, the use of flanged zipper has proven problematic in that the flanges tend to peel or delaminate from the thermoplastic film due to peel forces transmitted to the flanges during opening of the bag by the bag user. Although flangeless zipper is well known in the art, such zippers are unsuitable for use in transverse zipper applications because they are too narrow to ensure proper sealing by inaccurate seal bars and because the sealing of those zippers to thermoplastic film will cause damage and distortion to the interlocking closure elements. US-A-5577305 and US-A-5573614 both describe zipper strips which comprise: a male profile and a female profile; said male profile including a base and an interlocking member extending from said base, toward said female profile; said female profile including a base and an interlocking member extending from said base toward said male profile, said male interlocking member being engageable within said female interlocking member to join said male and female profiles together; said profiles further including two members each extending from the base of one profile toward the other profile, said members being contactable with a portion of the other profile when said profiles are interlocked and pressed together so as to prevent the extremities of said interlocking members from contacting the opposite profile. According to this invention, such a zipper strip is characterised in that said male profile includes two male interlocking members; in that said female profile includes two female interlocking members; and, in that a third high compression member is positioned between said two male interlocking members; whereby said profiles can be sealed to thermoplastic film across the widths of their respective bases through the application of heat and pressure without damaging or distorting the said two male and female interlocking members. Particular embodiments in accordance with this invention will now be described with reference to the accompanying drawings; in which:- Figure 1 is a cross-sectional view of a zipper strip in accordance with a first embodiment of the present invention; Figures 2 (a) - (g) are cross-sectional views of zipper strips in accordance with- alternate embodiments of the present invention; Figure 3 is a perspective view of the zipper strip of Figure 1 being attached to thermoplastic film in accordance with the present invention; Figure 4 is a perspective view of an FFS machine making reclosable bags from thermoplastic film in accordance with the present invention; and Figure 5 is a cross-sectional view of a completed bag in accordance with the present invention. Referring specifically to the Figures identified above, Figure 1 is a cross-sectional view of a zipper strip 10 in accordance with the first aspect of the present invention. The zipper strip 10 comprises a male profile 12 and a female profile 14. The male profile 12 includes a base 16 and first and second male interlocking members 18, 20 extending from the base 16 towards the female profile 14. The first and second male interlocking members 18, 20 each have an asymmetrical arrow shape so that the zipper strip 10 is easier to open from one side than the other. In the case of potato chip bags and the like, the male interlocking members will be adapted so that the bag is easier to open from the contents side of the zipper, since such bags are typically opened from the contents side. The female profile 14 includes a base 22 and first and second female interlocking members 24, 26 extending from the base 22 towards the male profile 12. The first and second female interlocking members 24, 26 are each comprised of two inwardly curving members forming a receptacle or channel into which the first and second male interlocking members 18, 20 may respectively be engaged. It should be noted that while the foregoing configurations for the male and female interlocking members are preferred, any configuration which provides for interlocking may be used. Moreover, any number of male and female interlocking members may be used. The male and female profiles 12, 14 are extruded from a plastic material commonly used in the packaging industry, such as polyethylene. In addition, the profiles may be provided with a sealant on their bases to aid in the sealing of the profiles to the thermoplastic film used to make the bags. The male profile 12 further includes wedge-shaped high compression members 28 at either end of its base 16 and a central high compression member 30 between the first and second male interlocking members 18, 20, all of which extend from the male profile base 16 toward the female profile 14. The high compression members 28, 30 are longer than both of the first and second male interlocking members 18, 20. The female profile 14 includes wedge-shaped high compression members 32 at either end of its base 22 which contact their opposite wedge-shaped high compression members 28 on the male profile 12 when the profiles are interlocked and pushed together. The high compression members function in the following manner. As one or both of the interlocked male and female profiles 12, 14 are sealed to thermoplastic film, such as by seal bars, the profiles are compressed together. This compression causes the opposing wedge-shaped high compression members 28, 32 on the male and female profiles 12, 14 to contact each other and the central high compression member 30 of the male profile to contact an inner surface 34 of the female profile base 22. The lengths of the high compression members are such that said contacts occur before the extremities 36, 37 of the male interlocking members 18, 20 contact the female profile 14, or the extremities 38, 39 of the female interlocking members 24, 26 contact the male profile 12, and thereby damage or distort the interlocking members. In addition, the high compression members are much thicker than the male and female interlocking members, thereby ensuring that the high compression members themselves do not distort during sealing or become sealed to the opposing profile. In this manner the high compression members prevent distortion and crushing of the interlocking members and enable the profiles to be sealed to thermoplastic film across the widths of their bases. In the absence of the high compression members the interlocking members would be distorted and/or crushed by the heater bars, rendering the zipper strip unusable. Because the zipper 10 is not provided with flanges, in order to ensure that the seal bars seal the profiles to the thermoplastic film, the profiles must be wider than is customary. This extra width ensures that the sealing bars, which are not very accurate, do not miss the narrow zipper during the sealing operation. This extra width also provides the added benefit of making the zipper strip easier for the bag user to close because of the wide feel of the zipper strip. It should be noted that the present invention is not limited to the number and configuration of high compression members shown in Figure 1. Any number and any configuration of high compression members may be used to practice the present invention. Examples of other profiles in accordance with the present invention are shown in Figure 2. In Figure 2 (a), the male profile 40 is provided with three rectangular high compression members 42 longer than either of the male interlocking members 43. In Figure 2(b), both profiles 44, 46 are provided with three rectangular high compression members 48 which contact an opposite high compression member on the other profile during sealing. In Figure 2(c), the male and female profiles 50, 52 are each provided with two rectangular high compression members, one of which 54 contacts the base of the opposite profile and the other of which 56 contacts an opposite high compression member on the other profile during sealing. The embodiment of Figure 2(d) is similar to that of Figure 2 (a) , except that the center high compression member of the male profile 58 is replaced with a triangular shaped high compression member 60 which mates with a complementary shaped high compression member 62 on the female profile 64 during sealing. The embodiment of Figure 2(e) is also similar to that of Figure 2(a), except that the high compression members 66 on the male profile 68 are triangular. The embodiment of Figure 2(f) also makes use of triangular high compression members 70, 72, but the compression members are inverted such that the bases of the triangles, rather than the apexes as in Figure 2(e), contact the base of the opposite profile. Additionally, the male profile 74 is provided with a single central high compression member 70 while the female profile 76 is provided with a high compression member 72 at each end. In the embodiment of Figure 2 (g), the male profile 78 is provided with a central rectangular high compression member 80 longer than the male interlocking members 82 and the female profile 84 is provided with a channel 86 for receiving the high compression member 80. Additionally, the members 88 which form the channel 86, also act as high compression members. Although profiles having posts and wedges are well known in the prior art, such as disclosed, for example, in US-A-4,736,451, US-A-3,565,147, US-A-5,509,734 and US-A-5,558,614, the posts and wedges in those references do not act as high compression members, but act to stabilize the zipper and/or enhance locking characteristics. Figure 3 depicts the zipper strip 10 of Figure 1 being attached to thermoplastic film 90 in accordance with the second aspect of the present invention. The zipper strip is supplied from a continuous roll 92 and is pulled across the film 90 and disposed thereon by a positioning device 116 (not shown in Figure 3 for clarity). The positioning device 116 can take any of a variety of forms well known to those skilled in the reclosable packaging art, such as a vacuum conveyor for pulling the zipper strip 10 across the film 90 and a knife for cutting the zipper strip 10 from the continuous roll thereof 92. The thermoplastic film 90 is paid off from a continuous roll 94, as shown in Figure 3, in increments equal to the length of the bags which will ultimately be formed from the film 90 on an FFS machine. The film 90 has a longitudinal axis X which is parallel to the direction of travel of the film 90. The zipper strip 10 is disposed on the film 90 transverse to the longitudinal axis X with the male profile 12 on top of the female profile 14, or vice versa. As disclosed in US-A- 4,909,017, the zipper strip 10 has a length approximately equal to half the width of the film 90 and is disposed centrally thereon. Seal bars 96 are positioned to attach the female profile 14 to the film 90 by initially sealing or tacking the female profile thereto. The high compression members, as discussed above, prevent the seal bars 96 from damaging or distorting the interlocking members. The transverse zipper-equipped film is fed into an FFS machine, as shown in Figure 4. The thermoplastic film 90 is fed downwardly over a collar 98 and folded around a filling tube 100. The edges of the film are brought together and pressed together by a pair of rollers 102. The edges are then welded together by seal bars 104 to form a longitudinal back seam 106. Contents may then be dropped through the tube 100 into the bag 108 which has a lower seam 110. As discussed below, the lower seam 110 was made when the preceding bag was completed. After introduction of the contents, the top of the bag is completed by the action of cross seal jaws 112, which perform four simultaneous functions. First, the cross seal jaws 112 finally seal the male and female profiles 12, 14 to opposing bag walls across the widths of their respective bases. A commercially well known sealant on the profile bases may be used to facilitate the completion of these seals without sealing the profiles 12, 14 to each other. The high compression members, as discussed above, prevent the interlocking members from being crushed and distorted during sealing. Second, the cross seal jaws 112 seal the top of the bag to form a pilfer evident seal 114. Third, the cross seal 112 jaws make the lower seam 110 for the next succeeding bag. And fourth, the cross seal jaws 112 cut the completed bag 108 from the film 90. The completed bag 108 has a pilfer evident seal 114, a transverse zipper 10, a lower seam 110 and a back seam 106. In order to ensure that the high compression members do not seal to the opposite profile during the sealing process, the ends of the high compression members may be treated, such as with a small ink layer. While the thickness of the high compression members would usually prevent sealing from occurring, as discussed above, this treatment would provide additional insurance or cover a situation where smaller profiles are used. A cross section of the completed bag 108 is shown in Figure 5. Because the profiles 12, 14 are sealed to the bag completely across the widths of their bases, there is no danger of peeling of either profile from the bag when the bag is opened by the user, as shown by opening forces F (snack food bags, unlike other bags, are typically opened from the contents side).

Claims: A zipper strip (10) for a reclosable package, said zipper strip comprising: a male profile (12) and a female profile (14); said male profile (12) including a base (16) and an interlocking member (18,20) extending from said base (16), toward said female profile (14); said female profile (14) including a base (22) and an interlocking member (24,26) extending from said base (22) toward said male profile (12), said male interlocking member (18,20) being engageable within said female interlocking member (22,24) to join said male and female profiles (12,14) together; said profiles (12,14) further including two high compression members (28,42,48,54,66,72,88) positioned on opposite ends of said profile bases and each extending from the base of one profile toward the other profile, said high compression members (28,42,48,54,66,72,88) being contactable with a portion of the other profile when said profiles are interlocked and pressed together so as to prevent the extremities of said interlocking members (18,20,24,26) from contacting the opposite profile; characterised in that said male profile (12) includes two male interlocking members (18,20); in that said female profile (14) includes two female interlocking members (24,26); and, in that a third high compression member (30,42,48,56,60,62,66,70,80) is positioned between said two male interlocking members (18,20); whereby said profiles can be sealed to thermoplastic film across the widths of their respective bases (16,22) through the application of heat and pressure without damaging or distorting the said two male and female interlocking members (18,20,24,26). A zipper strip according to claim 1, wherein both of said profiles (12,14) include at least one high compression member (54) contactable with a portion of the other profile. A zipper strip according to claim 1, wherein said male profile (12) includes a pair of wedge shaped high compression members (28) positioned on opposite ends of said male profile base (16), each of said wedge shaped high compression members (28) being contactable with an opposite wedge shaped high compression member (32) on said female profile (14). A zipper strip according to claim 1 or 2, wherein at least one of said high compression members is contactable with the base of the opposite profile. A zipper strip according to any one of the preceding claims, wherein said male profile (12) includes a high compression member (28,30,42,54,66,70,80) longer than said two male interlocking members (18,20). A zipper stip according to any one of the preceding claims, wherein said female profile (14) includes a high compression member (54,72,88) longer than said two female interlocking members (24,26). A zipper strip according to any one of the preceding claims, wherein the end of the high compression members is treated to prevent said high compression members from being sealable to said other profile.

Inventors: MALIN ART, MALIN, ART
Applicants: ILLINOIS TOOL WORKS, ILLINOIS TOOL WORKS INC.
Application year: 2000
Main classification: B65D33
IPC codes: A44B18, B65D33, B65B61, A44B19, A44B99