Reclosable zipper with tamper evident feature

A plastic bag having a reclosable plastic zipper is provided with a tamper-evident, non-reclosable peel seal formed by applying an adhesive to a treated strip adjacent to the interlocking zipper. The treatment is preferably by corona discharge, which causes the adhesive used to provide the peel seal to preferentially adhere to the treated strip when the peel seal is broken. A method for manufacturing the reclosable plastic zipper includes the steps of extruding a zipper profile, treating a portion of its surface, preferably by corona discharge, applying an adhesive to the treated portion, slitting the profile lengthwise, and folding over one of the resulting sides of the zipper to interlock them with one another.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This relates in general to the packaging art, and more particularly is 
concerned with a continuous reclosable plastic zipper of a type which is 
used to close the mouth of a bag or package, and which includes, either 
before or after the zipper relative to the mouth of the bag or package, a 
tamper-evident non-reclosable peel-seal feature. 
2. Description of the Prior Art 
In the use of plastic bags and packages, particularly for foodstuffs, it is 
important that the bag be hermetically sealed until the purchaser acquires 
the bag and its contents, takes them home, and opens the bag or package 
for the first time. It is then commercially attractive and useful for the 
consumer that the bag or package be reclosable so that its contents may be 
protected. Flexible plastic zippers have proven to be excellent for 
reclosable bags, because they may be manufactured with high-speed 
equipment and are reliable for repeated reuse. A typical zipper is one 
which has a groove at one side of the bag mouth and a rib at the other 
side, which rib may interlock into the groove when the sides of the mouth 
of the bag are pressed together. Alternatively, a member having a 
plurality of ribs may be on one side of the bag mouth, while a member 
having a plurality of channels may be on the other side, the ribs locking 
into the channels when the sides of the mouth of the bag are pressed 
together. In such a case, there may be no difference in appearance between 
the two members, as the ribs may simply be the intervals between channels 
on a strip which may lock into another of the same kind. In general, and 
in short, some form of male/female interengagement is used to join the two 
sides of the bag mouth together. The so-called members, or strips, are 
bonded in some manner to the material from which the bags themselves are 
manufactured. 
Usually, pull flanges extend above the rib and groove strips, which pull 
flanges may be pulled apart for access to the interior of the bag. 
Although flexible zippers of this variety are quite popular, they do not 
always prevent the inadvertent or unwelcome opening of a bag or package 
within the store, and various additions have been made to provide 
tamper-evident seals which would reveal when it has been opened prior to 
purchase. 
It is clear then that, in spite of the fairly high state of development in 
this art, there are certain objectives which have not been fully met. In 
particular, tamper-evident non-reclosable peel seals in plastic bags of 
the prior art remain characterized by highly inconsistent opening forces. 
That is to say, the development of a tamper-evident non-reclosable peel 
seal requiring a reproducibly consistent opening force, large enough to 
obviate accidental or unintended opening, yet small enough that the bag 
itself may not be damaged during separation of the peel seal, has to date 
eluded those skilled in the art. At the same time, the requirement that 
the adhesive used to form the peel seal remain on only one side of the 
bag, without the formation of adhesive filaments across the bag opening, 
and not readhere when the bag is closed, has not been satisfied in the 
bags of the prior art. 
It is accordingly an object of the present invention to provide an improved 
tamper-evident non-reclosable peel seal suitable for use with reclosable 
plastic zippers in plastic bags and other packages to provide a hermetic 
seal until the peel seal is opened for the first time, and to provide a 
peel seal which is non-reclosable after being opened. 
SUMMARY OF THE INVENTION 
The present invention may be summarized as follows. In a process by which 
reclosable plastic bags and packages are assembled, a strip-like area 
adjacent and parallel to one of the two interlocking rib or groove members 
which reclosably seal the plastic bag or package is continuously given a 
treatment, for example, a corona discharge treatment, to cause an adhesive 
to preferentially adhere to the treated area. The adhesive, which is 
applied to the treated area to form the peel seal, is retained on the 
treated area, rather than on the opposed interlocking rib or groove member 
not so treated, when the peel seal is broken for the first time. 
Thereafter, the peel seal remains broken, as the adhesive does not have an 
affinity for the untreated plastic of the opposite rib or groove member 
once it has been separated therefrom. 
The present invention will now be described in more complete detail with 
reference being made to the figures identified below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a schematic cross-sectional view of a portion of two 
reclosable plastic packages is shown. The packages 10 comprise a common 
lower plastic sheet 12 of lightweight plastic material, such as of 
polyethylene, and a common upper plastic sheet 14, which may be of similar 
material. The lower sheet 12 may be thermoformed to produce compartments 
16 in which a product may be carried. At a suitable point in the package 
manufacturing and filling process, the packages 10 may be separated from 
one another by cutting at the point indicated by dashed line 18. 
When such a cut has been made, the open end, or mouth, of each package 10 
has interlockable rib and groove members, which, in the embodiment shown, 
may be referred to as the long web 20 and the short webs 22. The so-called 
long web 20 has two such interlockable rib and groove members on its 
opposed edges; the short webs 22 have but one. It will be evident, 
however, that, when the packages 10 are separated from one another by 
cutting as indicated by dashed line 18, the long web 20 must be cut as 
well. 
The long web 20 and short webs 22 are, in an actual package 10, bonded to 
the inside of the lower sheet 12 and upper sheet 14, respectively. When 
the packages 10 are separated by cutting as indicated by dashed line 18, 
the long web 20, having been cut in half, and the short webs 22 are 
adjacent to the mouths of the packages 10. In such a case, the lower sheet 
12 and the upper sheet 14 provides means whereby the package 10 may be 
opened by pulling the upper sheet 14 away from the lower sheet 12 to open 
the plastic zipper formed by half of the long web 20 and a short web 22 to 
gain access to the contents of the package 10. 
The present tamper-evident, non-reclosable peel seal is provided by 
treating those portions 24 of the short webs 22 adjacent to the rib and 
groove members to cause the adhesive 26 used to form the peel seal to 
preferentially adhere thereto. The treating may, for example, be carried 
out by corona discharge treatment, which modifies the surface of the short 
web 22 so that the adhesive may preferentially adhere thereto. It should 
be observed, however, that appropriate locations on the long web 20 could 
be so treated instead of the short webs 22. In either case, once the 
chosen locations have been treated, an appropriate amount of the adhesive 
being used is applied thereto. Adhesive 26 may also be applied to the 
untreated web in addition to the treated web, but, when the peel seal is 
broken, all of the adhesive 26 will reside on the treated side by virtue 
of the adhesive-adhesive bond being greater than the bond between the 
adhesive and untreated web. 
The so-called long web 20 and short webs 22 may be extruded from a 
synthetic, polymeric material, such as polyethylene. Any of the adhesives 
used by those skilled in the art for providing peel seals may be used in 
the present case. For example, Pierce and Stevens E4009D adhesive has been 
applied to just corona treated short webs 22 in coating weights of 2.0, 
1.8 and 1.6 lbs/1000 ft, and has provided excellent peel seals at those 
coating weights. 
FIG. 2 is a perspective view of the package 10 partially shown in cross 
section in FIG. 1. The lower plastic sheet 12 thereof is thermoformed to 
produce a compartment 16 for a product. The upper plastic sheet 14 is 
bonded or fused to the lower plastic sheet 12 on three sides of the 
perimeter of the package 10, as indicated by regions 25. On the fourth 
side, which is the farthest from a viewer of FIG. 2, the adhesive 26 
provides a peel seal between the upper plastic sheet 14 and the lower 
plastic sheet 12. Zipper 28, formed by the interlocking rib and groove 
members on the long web 20 and short web 22, is inward of the adhesive 26. 
The peel seal provided by the adhesive 26 must be broken before access to 
the compartment 16 and to its contents may be gained. 
FIG. 3 is a schematic cross-sectional view of a reclosable plastic bag 
having the peel seal of the present invention. The bag 30, shown in a 
sealed condition, comprises a pair of webs 32 affixed to the sheet 34 from 
which the bag 30 is formed. The webs 32 are affixed so as to leave flanges 
36 of sheet 34 thereabove, the flanges 36 being pulled apart to open the 
bag 30. One of the two webs 32 is treated, such as by corona discharge 
treatment, to make that one web 32 more receptive to the adhesive than the 
other web and adhesive 38 is applied to the just treated area to form the 
peel seal 40. When the peel seal 40 has been broken, the adhesive 38 will 
reside entirely upon the treated web, and will not again adhere to the 
untreated web to reclose the peel seal 40. As will be noted in FIG. 3, the 
reclosable zipper 42 formed by the interlocking rib and groove members of 
the webs 32 may be closer to the mouth of the bag than the peel seal 40. 
FIG. 4 is a schematic, cross-sectional view of another reclosable plastic 
bag 50 having the present peel seal. It will be observed that bag 50 is 
identical to bag 30, shown in FIG. 3, except that the peel seal 52 is 
closer to the mouth of the bag 50 than is the reclosable zipper 54 formed 
by the interlocking rib and groove members on webs 56. 
FIG. 5 is a schematic view illustrating the process by which long webs and 
short webs, or profiles, such as long web 20 and short web 22 shown in 
FIG. 1, may be formed with the peel seal of the present invention. The 
process begins with an extruder 60, with which the profile 62 is extruded 
from a synthetic polymeric material, such as polyethylene. 
The profile 62 exits from the extruder 60 into a water tank 64, which 
quenches and cools the newly extruded profile rapidly to a desired 
temperature. The profile 62 then passes through a treater 66, which may be 
a corona discharge treater to modify part of the surface of the profile 62 
so that the adhesive may preferentially adhere thereto. 
Having been so treated, the profile 62 progresses through a coater 68, and 
thence through a cooling tower 70. In slitter 72, the profile 62 is 
continually slit lengthwise into at least two components 74,76 in a manner 
to be illustrated below. Components 74,76 are rejoined to one another by 
joiner 78, and, finally, are wound onto a spool 82 by winder 80 for 
subsequent use in the manufacture of plastic bags or packages. 
Referring now to FIG. 6, the profile 62, which comprises both the long web 
20 and the short webs 22 shown in FIG. 1, passes through treater 66, which 
may be a corona discharge treater, as shown in FIG. 5. It will be observed 
that, in the cross section shown in FIG. 6, the profile 62 comprises plane 
areas 90 along its lateral edges, groove and rib members 92 and a central 
plane region 94. The lateral plane areas 90 are preferably treated by 
treating elements 96 to enable the adhesive used to form the peel seal to 
preferentially adhere thereto. Alternatively, the central plane region 94 
may be so treated instead of the lateral plane areas 90. 
The treater 66 is a surface modification instrument. Its purpose is to 
modify the surface of the lateral plane areas 90, so that the peel seal 
material may be retained on the treated surface when the resealable 
plastic zipper is first opened. 
The treater 66 may apply a flame treatment to the surface of the lateral 
plane areas 90. The flame treatment will modify the surface so that the 
peel seal material, the adhesive, will adhere more firmly to the treated 
surface than it will to the untreated surface. As a consequence, when the 
resealable plastic zipper is first opened, the peel seal material will 
remain preferentially on the treated surface as opposed to the untreated 
surface. 
Flame treating renders inert thermoplastics, such as polyolefins, receptive 
to other materials by bathing the surface in a highly oxidizing flame. 
This treatment oxidizes or modifies the surface layer making it 
particularly receptive to the peel seal material. 
The treater 66, as noted above, may also be a corona discharge device. 
Corona discharge treatment is another method of rendering plastics, such 
as polyolefins, receptive to material such as peel seal material. A 
typical method is to pass the surface over a grounded metal cylinder above 
which is located a sharp-edged high voltage electrode spaced as to leave a 
small air gap between the plastic and electrode. The corona discharge 
oxidizes the sheet by means of the formation of polar groups on reactive 
sites making the surface receptive to the peel seal material. 
Referring now to FIG. 7, the profile 62 next passes through a coater 68, as 
shown in FIG. 5. In the cross section provided in FIG. 7, the profile 62 
passes under a coating head 98, which may apply a coating of adhesive onto 
any preselected portion or portions of the width thereof. In the present 
case, it would do so onto those portions which have previously been 
treated, such as by corona discharge, in treater 66. The adhesive 100, 
accordingly, is shown on the two lateral plane areas 90 of the profile 62. 
FIG. 8 depicts what is done to the profile 62 as it passes through the 
slitter 72. At least one slitting blade 102 cuts the profile 62 
longitudinally through the rib and groove members 92. It will be noted, by 
comparison with FIG. 1, that the profile 62 is thereby divided into a long 
web 20 and two short webs 22. In the preceding discussion of FIG. 5, these 
were referred to as components 74,76. 
FIG. 9 shows the appearance of profile 62 upon its exit from the joiner 78. 
In the joiner 78, shown previously in FIG. 5, the two short webs 22, 
produced from the profile 62 by slitting blades 102, are folded over or 
inverted, and joined to the long web 20 by rib and groove members 92. The 
adhesive 100, as a consequence of this inversion, is disposed on those 
faces of the short webs 22 facing the long web 20. 
FIG. 10 illustrates components of the joiner 78 which leave the profile 62 
in the condition shown in FIG. 9. The long web 20 and short webs 22 are 
separated from one another as shown in FIG. 8, and the short webs 22 
folded over as noted in the preceding paragraph. Separated from one 
another, they proceed, within the joiner, toward a merging wedge 102, 
which aligns rib and groove members 92 for subsequent engagement. Thus 
merged, the long web 20 and short webs 22 proceed through the nip 104 
formed by a pair of pinch rolls 106, which force the rib and groove 
members 92 to interlock with one another as shown in FIG. 9. In such 
condition, the profile 62 may be wound onto spools 82 by winder 80 in FIG. 
5 for subsequent use in the manufacture of plastic bags or packages. 
When the peel seal is actually formed, the profile 62 as shown in FIG. 9 
passes over or against heated sealing bars. The short webs 22 pass in 
contact with a first sealing bar, while the long web 20 passes in contact 
with a second sealing bar. The first and second sealing bars may force or 
squeeze the short webs 22 against the long web 20. Alternatively, rollers, 
downstream from the sealing bars, may be used for this purpose. 
Short webs 22 may be heated to a higher temperature than long web 20 such 
as by setting the temperature of the first sealing bar to be higher than 
that of the second sealing bar. For example, the first sealing bar may be 
at a temperature of 360.degree. F., while the second sealing bar may be at 
a temperature of 302.degree. F. The application of a higher temperature to 
the side bearing the adhesive, in this case, the short webs 22, is 
important for achieving the consistency of the peel seal. As the hot peel 
seal material, or adhesive, cools, a hermetic seal bond is formed 
essentially bonding the short webs 22 to the long web 20. When the peel 
seal is first opened, this bond is broken and does not reseal. 
Modifications to the above would be obvious to those skilled in the art, 
but would not bring the invention so modified beyond the scope of the 
appended claims.