U.S. patent number 3,923,198 [Application Number 05/499,279] was granted by the patent office on 1975-12-02 for stress-opacifiable tamper indicator.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to Wilfred R. Brochman.
United States Patent |
3,923,198 |
Brochman |
December 2, 1975 |
Stress-opacifiable tamper indicator
Abstract
A container is hermetically sealed with an easy opening tape
closure, at least a portion of which opacifies when stressed,
providing a visual indication that the closure has been tampered
with.
Inventors: |
Brochman; Wilfred R. (Oakdale,
MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
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Family
ID: |
27016034 |
Appl.
No.: |
05/499,279 |
Filed: |
August 21, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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397876 |
Sep 17, 1973 |
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Current U.S.
Class: |
220/359.2;
220/214; 283/81; 283/95; 215/203; 283/94; 283/114 |
Current CPC
Class: |
B65D
55/0818 (20130101); B65D 55/0854 (20130101); B65D
17/502 (20130101); B65D 2517/0013 (20130101); B65D
2517/5035 (20130101); B65D 2517/5083 (20130101); B65D
2401/55 (20200501) |
Current International
Class: |
B65D
55/08 (20060101); B65D 55/02 (20060101); B65D
17/00 (20060101); B65D 17/50 (20060101); B65D
041/00 () |
Field of
Search: |
;220/359,214,260 ;215/7
;229/7R,51AS |
References Cited
[Referenced By]
U.S. Patent Documents
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3312368 |
April 1967 |
Reynolds et al. |
3516852 |
October 1967 |
Janssen et al. |
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Primary Examiner: Hall; George T.
Attorney, Agent or Firm: Alexander, Sell, Steldt &
DeLaHunt
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of my copending
application Ser. No. 397,896 filed Sept. 17, 1973, now abandoned.
Claims
What we claim is:
1. In a container sealed by means of a tape closure, the
improvement which comprises:
at least a portion of the closure surfaced with an indicator strip
comprising a stress-opacifying colored backing;
whereby when said indicator layer is flexed to open said closure,
said backing will become opaque and display a color difference
between the flexed and unflexed portions indicating said flexing
even if said covering is returned to its previous sealing
position.
2. The sealed container of claim 1 where said indicator strip
comprises a heat-shrinkable tape which has been exposed to heat
whereby the tape forms a tight seal.
3. The sealed container of claim 1 wherein said indicator strip
bears on its exposed surface printed indicia of the same color as
the colored backing, whereby when the indicator is unflexed, the
indicia are invisible and when the indicator is flexed, the indicia
will be visible against an opaque background.
4. The sealed container of claim 1 further characterized by said
container having a rigid wall with formed aperture therein, the
cover over said aperture being a tape closure having a free end,
said closure comprising a sheet material removably adhered directly
to a portion of said wall which surrounds said aperture, said
closure capable of being grasped by said free end and pulled back
upon itself without rupture to expose the underlying material and
said indicator layer being adhered to said closure by an
adhesive.
5. The sealed container of claim 4 wherein the adhesive which bonds
the strip to the closure has a peel force of at least 50 ounces per
inch of width.
6. The sealed container of claim 1 where said stress opacifying
material is an oriented polyvinyl chloride polymeric film.
7. The sealed container of claim 1 where said container is a slip
cover can sealed by a length of tape having a free end suitable for
gripping having said indicator layer adhered to said closure so
that at least a portion of the indicator layer is flexed before any
portion of said closure is removed from said can.
8. A container sealed with a tape closure, said closure comprising
a sheet material coated over one face with an adhesive which was at
least originally tacky and pressure-sensitive, at least a portion
of the opposite face of said tape being surfaced with an indicator
comprising a stress-opacifying backing, whereby when said closure
is flexed, the backing will opacify and display a color difference
between the flexed and unflexed portions, even if the tape is
thereafter returned to its previous sealing position.
Description
BACKGROUND OF THE INVENTION
This invention relates to an improved container closure.
In recent years, many containers have been hermetically sealed with
easy opening tape closures which are affixed over a hole in the top
of the container by a heat-sealing or pressure-sensitive adhesive;
see Abere and Brochman, U.S. Pat. No. 3,389,827. A typical closure
has a free end which is easily gripped by the fingers to facilitate
removal, after which the contents, e.g., fruit juice, oil, salt,
etc., can be removed via the exposed hole.
Although tape closures of the Abere et al type provide an effective
and easily opened seal, they are subject to tampering. It is
possible to carefully break the seal, remove or adulterate the
contents of the container and then replace the tape without leaving
any visible traces.
A tape closure which changes color when an attempt has been made to
remove it with the aid of an organic solvent is disclosed in U.S.
Pat. No. 3,680,236. This closure incorporates a dye-containing
layer which dissolves and stains the tape when contacted with an
organic solvent, e.g., kerosene or toluene. Unfortunately, however,
most tampering is purely mechanical in nature.
A further type of tape closure is the heat shrunk sleeve found
around the neck of many bottles containing barbecue sauce, wine and
other comestibles. This type of closure is generally not resealable
once it has been opened, but each type of bottle requires a custom
sized sleeve which is useful only for a particular size and
configuration. In the past, such sleeves have been mechanically
held in position before and during heat shrinking.
The present invention provides a simple way of detecting whether
any of several types of tape closure seal has been broken. In each
case, the closure visually indicates when it has been mechanically
tampered with, thereby providing increased safety and product
confidence to the ultimate consumer. In making heat shrunk
closures, the sleeve is held in place by adhesive until shrinkage
has occurred, eliminating the need for a separate holding
means.
This invention comprises, in one aspect, an improved form of
previously known tape closures. The invention provides a closure
having, at an exposed surface, a layer of material which is
originally transparent or translucent but which opacifies when
stressed (as occurs when the closure is removed to open the
container). Before the stress-opacifying material is stressed, any
underlying substrate is visible; after stressing; however, the
material becomes opaque white or pastel. Any underlying surface or
material which was previously visible is thereby obscured,
resulting in a change of appearance which indicates that the tape
closure has been tampered with. The evidence of tampering remains
even if the closure is thereafter resealed. The entire closure can
be formed from a stress-opacifying material; alternatively, the
stress-opacifying material can be part of a separate indicator
layer disposed on top of an otherwise conventional tape
closure.
The tape closure chosen can be of the type described in the
aforementioned U.S. Pat. No. 3,389,827, the disclosure of which is
incorporated herein by reference. The closure of this invention can
also be used in the form of an elongated pressure-sensitive
adhesive coated strip to seal the joint between a can and lid in
slip-cover or collar cans of the type commonly used to package
coffee, canned ham, etc.; see U.S. Pat. No. 3,516,852. The strip is
also useful in holding conventional fitted caps or tops on plastic
or cardboard food containers (e.g., of yogurt or cottage cheese).
In such cases, the closure of this invention can be formed by
wrapping a strip of heat-shrinkable tape around the container
overlying the joint between the body and the tape and extending
below, and optionally above the rim. The application of heat
shrinks the tape around the rim, thereby forming a tight tape seal.
The heat shrunk tape collar may thus be utilized either primarily
as a seal (as in the slip-cover cans) or primarily as a tamper
indicator (as in bottles, etc.) providing an air tight secondary
seal in the latter case. Thus, if the primary seal should fail as
may occur if the sealing lip of a bottle is chipped, the tape will
protect the container's contents.
Where the indicator layer is a separate layer attached to the
closure used, at least a portion of the indicator layer is
partially disposed on the free end of the tape closure so that it
is flexed and begins opacifying before any substantial portion of
the closure is removed, thus insuring that the contents of the
sealed container cannot be altered without detection.
The stress-opacifying indicator layer is advantageously formed from
a 1-10 mil (25-250 micron) film of normally transparent
stress-opacifying unplasticized polyvinyl chloride, other suitable
stress-opacifying materials including films of
polybutadiene/polystyrene, polyvinyl chloride/polyvinyl acetate and
isotactic polypropylene/butyl rubber blends.
Where the stress-opacifying film constitutes the entire tape
closure, it will generally be thicker than where it appears only in
a layer on top of a supporting tape closure. The thickness of the
films used will necessarily depend on the internal pressure of the
container being sealed. Cans containing carbonated beverages, for
example, will naturally require a thicker, stronger, closure than
packages of unpressurized dry materials, such as breakfast
cereals.
When a separate indicator layer is used, it is advantageously
secured to the tape closure by pressure-sensitive adhesive,
although other thermosetting and thermoplastic adhesives may be
used. The adhesive should, of course, bond the indicator to the
tape closure so firmly and adherently that the indicator strip will
be stressed beyond its opacification point when the tape closure is
flexed. Adhesives which do not sufficiently firmly bond the
indicator layer to the tape closure will allow the indicator to
buckle or separate from the tape closure; therefore, the indicator
will not be flexed and no visual change will occur to indicate
tampering. Functionally stated, the adhesive should be so firmly
bonded to both the indicator layer and the tape closure that the
force required to peel the indicator layer from the closure exceeds
the force required to stress-opacify the indicator layer.
The peel adhesion of the adhesive can be measured using a modified
version of the Pressure-Sensitive Tape Council's 180.degree. peel
adhesion test PSTC-1. In this modification, a strip is formed by
coating the adhesive to be measured on a 1-3 mil (25-75 micron)
biaxially oriented polyethylene terephthalate film at a dry coating
weight of 10-12 grains per 24 square inches (about 40-50
grams/m.sup.2). A strip 10 inches (about 25 cm) long and 1 inch
(2.5 cm) wide is cut from the tape and applied to a clean 2-inch
.times. 5-inch (about 5 .times. 12.5 cm) steel plate so that 5
inches (about 12.5 cm) extends beyond one end and rolled to insure
that no air bubbles are entrapped. The test piece is allowed to age
for 24 hours at room temperature, after which the free end of the
tape strip is doubled back over the adhered portion, pulled beyond
the end of the panel and clamped in one pair of jaws of an Instron
tensile testing machine. The exposed end of the steel panel,
adjacent the doubled-back end of the tape, is then clamped in the
second pair of jaws of the tensile tester, so that when the two
pairs of jaws are separated, the tape is stripped free from the
steel panel. The jaws are separated at the rate of 12 inches (about
30.5 cm) per minute, the force required giving a measure of peel
adhesion. Adhesives which have a peel adhesion of at least about 50
ounces per inch of width (about 560 grams per centimeter of width)
have been found generally suitable for securing an indicator layer
to a tape closure to insure sufficient stress to opacify the
indicator. Beneath the stress-opacifying layer is a colored
material. When the stress-opacifying layer is unflexed and
therefore transparent, the colored layer is visible along the
entire closure. When the stress-opacifying layer is flexed, it
becomes translucent or opaque, blocks out the underlying color and
thus creates a different visual impact, indicating tampering with
the closure in which the stress-opacified layer is
incorporated.
It is also possible to print indicia, such as the words "open" or
"opened" on the upper surface of the stress-opacifying layer, the
indicia being the same color as the underlying colored layer. Such
indicia are invisible before the closure has been flexed but show
up as colored words or patterns on the opaque white or pastel
background after the closure has been flexed.
It is also within the purview of this invention to prepare closures
which incorporate colored layers both above and below the
stress-opacifiable layer, the exposed colored layer being
transparent so that the indicator initially has an appearance which
is the sum of the two separate colors. Upon opacification, only the
top color will be visible. Further information on such colored
systems and materials for forming them can be found in U.S. Pat.
No. 3,468,744, the disclosure of which is incorporated herein by
reference.
BRIEF DESCRIPTION OF THE DRAWINGS
A further understanding of the invention may be had by referring to
the accompanying drawing in which like numbers refer to like parts
in the several views and in which:
FIG. 1 is a top plan view of a can lid having an aperture covered
by the tape closure of this invention;
FIG. 2 is a cross-sectional view of the can lid of FIG. 1 taken
along section line 2--2 and looking in the direction of the
arrows;
FIG. 3 is a perspective view of a roll of tape suitable for making
can closures of this invention;
FIG. 4 is a perspective view of a slip cover can sealed by a
closure of this invention;
FIG. 5 is a partial elevation of a food container in partial
section with its fitted cover in place showing a heat shrinkable
tape in position for shrinking; and
FIG. 6 depicts the container of FIG. 5 after the tape has been heat
shrunk.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 depicts a can lid 10 having aperture 12 covered and sealed
by tape closure 14, transparent stress-opacifiable indicator layer
16 being firmly adhered to the upper surface thereof.
Indicator strip 16 comprises stress-opacifying layer 20 overlying
and bonded to colored layer 22, the latter being firmly attached to
tape closure 14 by means of adhesive layer 24. Tape closure 14
comprises a layer of strong film 26 attached to can top 10 in the
area surrounding aperture 12 by adhesive 28.
In an alternative embodiment, film 26 of closure 14 is itself a
strong stress-opacifying material, thereby eliminating the need for
a separate indicator layer. In this embodiment, colored layer 22 is
disposed between adhesive 28 and film 26, and closure 14 itself
opacifies when flexed giving a visual change which shows the
closure has been tampered with.
As shown in FIG. 3, tape closure 14 of FIGS. 1 and 2, with its
indicator strip 16, is conveniently died from an elongated strip
unwound from a convolutely wound roll 30 of material. Film 32,
suitable for forming a tape closure, has a continuous indicator
layer 16 of stress-opacifying material adhesively bonded to its
exposed surface. A layer of adhesive 33, suitable for attaching the
closure to a can top, is firmly adherently bonded to the surface of
film 32 opposite indicator strip 16. Tape closures are conveniently
die-cut from the strip of roll 30 to the desired shape, such as
that shown in FIG. 3. (It will be understood, of course, that roll
30 will conventionally be wound upon itself about a core, adhesive
side in, and is shown otherwise in FIG. 3 for convenience in
understanding.)
In FIG. 4, slip cover can 35, comprising cover 36 and body 38, is
sealed with strip closure 34, which covers the line (not shown)
along which the lower edge of cover 36 overlaps the upper edge of
body 38. Closure 34 has pull tab 40 with indicator 41 disposed
between tab 40 and the point 42 where the closure 34 overlaps and
is adhered to itself slightly to insure a hermetic seal. A portion
of cover 36 and container 38 is recessed slightly so that strip
closure 34 does not protrude beyond the major circumferential
surface of the can, thereby protecting strip 34 from accidental
damage during shipping and handling. Further details of this type
of sealing construction can be found in aforementioned U.S. Pat.
No. 3,516,852, the disclosure of which is incorporated herein by
reference.
In FIGS. 5 and 6, food container 44 is sealed with easily removable
depressed center cover 46. A strip of heat-shrink tape 47, having
pressure-sensitive adhesive 48 disposed on one side, wound around
and adhered to rim 49 formed by the cover and container overlying
the line of abutment between the two. As shown in FIG. 5, tape 47
is applied along rim 49 of the container and its ends overlapped so
that the film will form a complete sleeve when heat shrunk. After
being attached to rim 49, tape 47 is heated, e.g., by means of a
jet of air at a temperature of about 100.degree.-200.degree.C.,
causing the film to shrink and enclose the rim as shown in FIG.
6.
The invention is further described with reference to the following
nonlimiting examples. Parts and percentages are by weight unless
otherwise noted.
EXAMPLE 1
A 7.5 mil (about 190-micron) film of oriented rigid unplasticized
polyvinyl chloride (commercially available from B.A.S.F. under the
trade designation "Luvitherm") was reverse roll coated on one side
with a black vinyl ink comprising carbon black pigment in a
phthalate-plasticized polyvinyl chloride:polyvinyl acetate binder
resin solution. The coated film was then placed in a 65.degree.C.
warm air oven for 15 minutes to drive off the solvent and leave a
dry coating weight of 0.25 to 0.30 gram ink per 24 square inches
(about 50 mg/cm.sup.2). A suitable ink can be made by diluting
MRX-9243 black vinyl ink, sold by Crescent Ink and Color Company,
from its normal 39% solids content to 24% solids content, using a
blend of equal volumes of toluene and methyl ethyl ketone.
A thin primer layer of 7.5% solids dimer based polyamide
(obtainable from General Mills under the trade designation
"Versalon" 1140) in 2:1 isopropanol:toluene solvent was coated over
the ink. A pressure-sensitive adhesive was made by dissolving (1)
100 parts of an ABA block copolymer where A is 15,000 molecular
weight polystyrene and B is 30,000 molecular weight polybutadiene
(available from Shell Chemical Company under the trade designation
"Kraton" 1101) and (2) 95 parts of .alpha.-terpene in toluene. The
blend was diluted with toluene to 40% solids and knife coated on
the primed, inked surface. The film was dried at 65.degree.C. for
20 minutes to evaporate the toluene, leaving 12 grains of adhesive
per 24 square inches (about 50 grams/m.sup.2). The resulting strip
was laminated to the upper surface of a container sealing closure
similar to those described in U.S. Pat. No. 3,389,827, Example II,
the closure being formed of an aluminum vaporcoated biaxially
oriented polyethylene terephthalate film to form a laminated
structure similar to FIG. 2.
When viewed from its exposed side, after being applied to the
sealing closure, the indicator strip originally appeared black,
since the black ink printed on the nonexposed side of the
transparent "Luvitherm" polyvinyl chloride film was visible. When
the closure was flexed during removal, however, the polyvinyl
chloride film attained an opaque white appearance blocking the
black color from view and thereby indicating that the closure had
been partially removed.
Example 2 ______________________________________ A polyvinyl
chloride based film was made by mixing: Parts polyvinyl chloride
resin available from Union Carbide Co. 100 acrylate-butadiene
styrene copolymer available from Rohm and Hass as "Acryloid" KM 228
9 Montan wax acid derivative available as "E" wax from B.A.S.F.
Wyandotte Corp. 5 Barium/cadmium stabilizer available as "Mark 99"
from Argus Chemical Co. 3 Acrylic ester polymer available as
"Acryloid" K-120N from Rohm and Hass 2 Epoxy stabilizer available
as "Drapex" 3-2 from Argus Chemical Co. 2 Phosphite chelate
available as "Mark C" from Argus Chemical Co. 1
______________________________________
The mixture was calendered to form a 7-mil (190-micron) thick
polymeric film. The calendered film was stretched in the
longitudinal direction at a 2.5 to 1 stretch ratio, reducing the
film's thickness to about 2.75 mils and making it heat
shrinkable.
The stretched film was reverse roll coated with a black vinyl ink
as in Example 1. A thin primer layer was coated over the ink. A
pressure-sensitive adhesive was made by dissolving 100 parts of the
ABA block copolymer of Example 1 and 95 parts of alpha-pinene resin
in toluene (commercially available from Pennsylvania Industrial
Chemical Co. under the trade designation "Piccolyte".alpha.135. The
blend was diluted with toluene to 40% solids, knife coated on the
primed inked surface, and dried at 65.degree.C. for about 20
minutes to evaporate the toluene, leaving 8 grains of adhesive per
24 square inches (about 27.5 grams/m.sup.2).
A 2-inch (about 5 cm) strip of the tape was formed into a band with
its ends overlapping about 5/8 inch (about 9 cm) and placed around
the neck of a ketchup bottle with about 1/16 inch (about 0.16 cm)
extending beyond the cap. The bottle with the tape held in position
was rotated in a stream of hot air at about 300.degree.F. (about
160.degree.C.) for about 3 seconds. The tape shrunk conforming to
the bottle and cap providing an air tight seal.
When the end of the tape is pulled away from the bottle, the film
stress opacifies changing the appearance of the film surface from
black to white.
* * * * *