U.S. patent application number 10/689146 was filed with the patent office on 2004-05-06 for oxygen detection system for a solid article.
Invention is credited to Barmore, Charles R., Espinel, R. Karina, Havens, Marvin R., Kennedy, Thomas D., Speer, Drew V., Thomas, Jeffrey A..
Application Number | 20040086749 10/689146 |
Document ID | / |
Family ID | 25365942 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040086749 |
Kind Code |
A1 |
Kennedy, Thomas D. ; et
al. |
May 6, 2004 |
Oxygen detection system for a solid article
Abstract
The present invention relates to the non-invasive use of a
luminescent compound to detect and measure concentrations of oxygen
dissolved in solids, particularly polymeric materials present in
multi-layered packaging materials. The measurement is made
independent of the oxygen concentration of the surrounding
atmosphere. The invention is especially useful as a quality
assurance check to verify oxygen scavenger activation during the
assembly of modified atmosphere and vacuum packages. The method
according to the invention is faster and less wasteful than
previous methods that rely on measuring oxygen concentration within
the headspace of an assembled package. Novel articles, methods, and
packages are also disclosed.
Inventors: |
Kennedy, Thomas D.;
(Simpsonville, SC) ; Havens, Marvin R.; (Greer,
SC) ; Speer, Drew V.; (Simpsonville, SC) ;
Barmore, Charles R.; (Moore, SC) ; Espinel, R.
Karina; (Cortlandt Manor, NY) ; Thomas, Jeffrey
A.; (Cortlandt Manor, NY) |
Correspondence
Address: |
CRYOVAC, INC.
SEALED AIR CORP
P.O. BOX 464
DUNCAN
SC
29334
US
|
Family ID: |
25365942 |
Appl. No.: |
10/689146 |
Filed: |
October 20, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10689146 |
Oct 20, 2003 |
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09875515 |
Jun 6, 2001 |
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6689438 |
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Current U.S.
Class: |
428/690 |
Current CPC
Class: |
G01N 31/225 20130101;
Y10T 428/13 20150115; Y10T 428/1341 20150115; Y10T 428/1324
20150115; Y10T 428/1383 20150115; Y10T 428/24851 20150115; Y10T
428/1359 20150115; Y10T 428/1334 20150115; Y10T 428/1379 20150115;
G01N 33/02 20130101; Y10T 428/1352 20150115 |
Class at
Publication: |
428/690 |
International
Class: |
B32B 009/00 |
Claims
What is claimed is:
1. An article comprising: a) an oxygen scavenger; and b) an oxygen
indicator comprising a luminescent compound; wherein the oxygen
scavenger and the oxygen indicator are substantially shielded from
sources of oxygen exterior to the article.
2. The article of claim 1 wherein the oxygen scavenger comprises a
material selected from the group consisting of: i) oxidizable
organic compound and a transition metal catalyst, ii) ethylenically
unsaturated hydrocarbon and a transition metal catalyst, iii) a
reduced form of a quinone, a photoreducible dye, or a carbonyl
compound which has absorbence in the UV spectrum, iv) a polymer
having a polymeric backbone, cyclic olefinic pendent group, and
linking group linking the olefinic pendent group to the polymeric
backbone, v) a copolymer of ethylene and a strained, cyclic
alkylene, vi) ethylene/vinyl aralkyl copolymer, vii) ascorbate,
viii) isoascorbate, ix) sulfite, x) ascorbate and a transition
metal catalyst, the catalyst comprising a simple metal or salt, or
a compound, complex or chelate of the transition metal, xi) a
transition metal complex or chelate of a polycarboxylic acid,
salicylic acid, or polyamine, xii) a tannin, and xiii) reduced
metal.
3. The article of claim 1 wherein the luminescent compound
comprises at least one material selected from the group consisting
of metallo derivatives of octaethylporphyrin, tetraphenylporphyrin,
tetrabenzoporphyrin, or the chlorins, bacteriochlorins, or
isobacteriochlorins thereof.
4. The article of claim 1 wherein the article is in the form of a
film.
5. The article of claim 1 wherein the article comprises: a) a film
comprising: i) a first layer comprising an oxygen barrier having an
oxygen transmission rate of no more than 100 cc/m.sup.2/24 hr at
25.degree. C., 0% RH, 1 atm (ASTM D 3985); ii) a second layer
comprising a blend of the oxygen indicator comprising a luminescent
compound, and the oxygen scavenger; and b) a patch comprising an
oxygen barrier having an oxygen transmission rate of no more than
100 cc/m.sup.2/24 hr at 25.degree. C., 0% RH, 1 atm (ASTM D 3985),
the patch adhered to the film.
6. The article of claim 1 wherein the article is in the form of a
film comprising: i) a first layer comprising an oxygen barrier
having an oxygen transmission rate of no more than 100
cc/m.sup.2/24 hr at 25.degree. C., 0% RH, 1 atm (ASTM D 3985); ii)
a second layer comprising the oxygen indicator comprising a
luminescent compound; and iii) a third layer comprising the oxygen
scavenger.
7. The article of claim 6 wherein the film comprises a fourth layer
comprising a sealant.
8. The article of claim 6 wherein the oxygen indicator comprises a
printed image.
9. The article of claim 1 wherein the article comprises: a) a film
comprising: i) a first layer comprising an oxygen barrier having an
oxygen transmission rate of no more than 100 cc/m.sup.2/24 hr at
25.degree. C., 0% RH, 1 atm (ASTM D 3985); ii) a second layer
comprising the oxygen scavenger; and iii) a third layer comprising
the oxygen indicator comprising a luminescent compound; and b) a
patch comprising an oxygen barrier having an oxygen transmission
rate of no more than 100 cc/m.sup.2/24 hr at 25.degree. C., 0% RH,
1 atm (ASTM D 3985), the patch adhered to the film.
10. The article of claim 9 wherein the film comprises a fourth
layer comprising a sealant.
11. The article of claim 1 wherein the article comprises: a) a film
comprising the oxygen scavenger; and b) a patch comprising i) an
oxygen barrier having an oxygen transmission rate of no more than
100 cc/m.sup.2/24 hr at 25.degree. C., 0% RH, 1 atm (ASTM D 3985),
and ii) the oxygen indicator comprising a luminescent compound.
12. The article of claim 11 wherein the film comprises i) a first
layer comprising an oxygen barrier having an oxygen transmission
rate of no more than 100 cc/m.sup.2/24 hr at 25.degree. C., 0% RH,
1 atm (ASTM D 3985); and ii) a second layer comprising the oxygen
scavenger.
13. The article of claim 11 wherein the patch comprises i) a first
layer comprising the oxygen barrier having an oxygen transmission
rate of no more than 100 cc/m.sup.2/24 hr at 25.degree. C., 0% RH,
1 atm (ASTM D 3985); ii) a second layer comprising an adhesive; and
iii) a third layer comprising the oxygen indicator comprising a
luminescent compound; wherein the oxygen indicator is encapsulated
by the adhesive.
14. The article of claim 1 wherein the article comprises: a) a
bottle wall comprising: i) a first layer comprising a polymer
comprising polyethylene terephthalate; ii) a second layer
comprising the oxygen scavenger; and iii) a third layer comprising
a polymer comprising polyethylene terephthalate; and b) a patch
comprising i) an oxygen barrier having an oxygen transmission rate
of no more than 100 cc/m.sup.2/24 hr at 25.degree. C., 0% RH, 1 atm
(ASTM D 3985), and ii) an oxygen indicator comprising a luminescent
compound.
15. A package comprising: a) a tray comprising a barrier liner, and
a tray flange; b) an oxygen sensitive product disposed on the tray;
and c) a film, disposed over the oxygen sensitive product and
adhered to the tray flange, comprising: i) a first layer comprising
an oxygen barrier having an oxygen transmission rate of no more
than 100 cc/m.sup.2/24 hr at 25.degree. C., 0% RH, 1 atm (ASTM D
3985); ii) a second layer comprising an oxygen scavenger; and iii)
a third layer comprising an oxygen indicator comprising a
luminescent compound.
16. The package of claim 15 wherein the oxygen barrier comprises a
material selected from the group consisting of polyester,
polyamide, ethylene vinyl alcohol copolymer, polyvinyl alcohol
homopolymer, polyvinyl chloride, homopolymer and copolymer of
polyvinylidene chloride, polyethylene naphthalate,
polyacrylonitrile homopolymer and copolymer, liquid crystal
polymer, SiO.sub.x, carbon, metal, and metal oxide.
17. The package of claim 15 wherein the oxygen scavenger comprises
a material selected from the group consisting of: i) oxidizable
organic compound and a transition metal catalyst, ii) ethylenically
unsaturated hydrocarbon and a transition metal catalyst, iii) a
reduced form of a quinone, a photoreducible dye, or a carbonyl
compound which has absorbence in the UV spectrum, iv) a polymer
having a polymeric backbone, cyclic olefinic pendent group, and
linking group linking the olefinic pendent group to the polymeric
backbone, v) a copolymer of ethylene and a strained, cyclic
alkylene, and vi) ethylene/vinyl aralkyl copolymer, vii) ascorbate,
viii) isoascorbate, ix) sulfite, x) ascorbate and a transition
metal catalyst, the catalyst comprising a simple metal or salt, or
a compound, complex or chelate of the transition metal, xi) a
transition metal complex or chelate of a polycarboxylic acid,
salicylic acid, or polyamine, xii) a tannin, and xiii) reduced
metal.
18. The package of claim 15 wherein the luminescent compound
comprises at least one material selected from the group consisting
of metallo derivatives of octaethylporphyrin, tetraphenylporphyrin,
tetrabenzoporphyrin, or the chlorins, bacteriochlorins, or
isobacteriochlorins thereof.
19. The package of claim 15 wherein the third layer comprising the
oxygen indicator comprising a luminescent compound is disposed in
the film in the form of a stripe or spot.
20. The package of claim 15 wherein the third layer comprising the
oxygen indicator comprising a luminescent compound comprises a
printed image.
21. An article comprising: a) a first layer comprising an adhesive;
b) an oxygen indicator comprising a luminescent compound, the
oxygen indicator encapsulated by the adhesive; and c) a second
layer comprising an oxygen barrier having an oxygen transmission
rate of no more than 100 cc/m.sup.2/24 hr at 25.degree. C., 0% RH,
1 atm (ASTM D 3985).
22. The package of claim 21 wherein the luminescent compound
comprises at least one material selected from the group consisting
of metallo derivatives of octaethylporphyrin, tetraphenylporphyrin,
tetrabenzoporphyrin, or the chlorins, bacteriochlorins, or
isobacteriochlorins thereof.
23. The article of claim 21 wherein the oxygen barrier comprises a
material selected from the group consisting of polyester,
polyamide, ethylene vinyl alcohol copolymer, polyvinyl alcohol
homopolymer, polyvinyl chloride, homopolymer and copolymer of
polyvinylidene chloride, polyethylene naphthalate,
polyacrylonitrile homopolymer and copolymer, liquid crystal
polymer, SiO.sub.x, carbon, metal, and metal oxide.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a solid article that
includes an oxygen scavenger, and includes or is proximate to a
luminescent compound that indicates the absence of oxygen dissolved
in the solid article, particularly a polymeric solid such as a film
that can be used to package an oxygen sensitive product, such as a
food product. The article and associated method is useful as a real
time or very rapid quality assurance check to verify oxygen
scavenger activity during package assembly.
BACKGROUND OF THE INVENTION
[0002] Oxygen spoils many products. Foods, beverages,
pharmaceuticals, medical devices, corrodible metals, analytical
chemicals, electronic devices, and many other products may perish
or experience diminished shelf life when stored too long in the
presence of oxygen. To combat this problem, manufacturers of
packaging materials have developed packaging materials and systems
to protect these products by providing a package environment, or
"headspace", with reduced oxygen levels.
[0003] In many cases, the low oxygen level that can be obtained
with these packaging systems is still insufficient to provide the
desired shelf life. In these cases, packagers find it advantageous
to include an oxygen scavenger within a low oxygen modified
atmosphere package (MAP) or a vacuum package (VP). Packaging
materials that include oxygen scavengers have grown increasingly
sophisticated in recent years. For example, Speer et al. have
developed clear, multi-layered packaging films that incorporate an
oxygen scavenging composition within its layers. See U.S. Pat. Nos.
5,529,833, 5,350,622, and 5,310,497, the contents of which are
incorporated herein by reference in their entirety. In this regard,
see also Babrowicz et al. U.S. Pat. No. 5,993,922, also
incorporated herein by reference.
[0004] For oxygen scavengers made from ethylenically unsaturated
hydrocarbons and their functional equivalents, oxygen scavenging
activity is triggered with actinic radiation, typically in the form
of ultra violet (UV-C) light. For details on preferred methods for
activating such oxygen scavenging compositions at point of use, see
Speer et al., U.S. Pat. No. 5,211,875, Becraft et al., U.S. Pat.
No. 5,911,910, and 5,904,960, and co-pending applications U.S. Ser.
No. 09/230,594 filed Aug. 1, 1997, and Ser. No. 09/230,776 filed
Jul. 29, 1997, and U.S. Pat. No. 6,233,907 (Cook et al.), all of
which are incorporated herein by reference in their entirety.
[0005] Unfortunately, oxygen scavengers do not always activate on
command. This may result from a number of factors, including
defective scavenger compositions, inadequate triggering conditions,
operator error, or a combination of these or other factors.
Conventional scavengers do not themselves visually indicate whether
or not they are active. In response to this uncertainty, operators
of packaging assembly plants prefer to verify scavenger activity as
soon as possible after triggering. The longer a failed triggering
attempt remains undiscovered, the more waste and expense is
incurred, especially where packaging equipment operates at high
speeds.
[0006] Prior art methods for verifying oxygen scavenger activity in
a low oxygen package involve detecting oxygen concentrations in the
package headspace. The measurement cannot take place until after
the package has been assembled and equilibrium of oxygen levels
established among the headspace, package layers, and package
contents. Detection of sufficiently reduced oxygen levels within
the headspace allows one to infer successful scavenger
activation.
[0007] Under this approach, one typically has two options, neither
of which is particularly satisfactory. One option is to leave an
oxygen indicator in the package headspace after it has been
assembled and sealed. For example, Mitsubishi teaches an indicator
comprising glucose and methylene blue, encased within a sachet. The
sachet is left inside the package after it is sealed. A color
change within the sachet indicates the presence of unwanted
oxygen.
[0008] This approach has several disadvantages, however. Sachets
must be attached to the package to avoid their being accidentally
ingested by the consumer. Some package contents require a
moisture-free storage environment. Yet, in the case of the
Mitsubishi glucose/methylene blue indicator, moisture may be
required to produce a color change. Also, sachets potentially
introduce contaminants or other substances into the package that
may be incompatible with its contents or accidentally ingested. For
some applications, manufacturers may not want to leave indicators
in packages where consumers may misinterpret the information the
indicator provides.
[0009] Another option is to use probes to measure the gas content
within the headspace. One commonly used headspace gas analyzer is
available from Mocon Inc. Unfortunately, probes that rely on gas
chromatography and other such analytical techniques cannot measure
oxygen concentration in vacuum packages, where there is
substantially no atmosphere to measure. In all cases, probes
require sacrificing the sampled package. They invariably require
some sort of device that will penetrate the package and remove a
portion of the gas within the headspace. The device inevitably
leaves a hole in the package, destroying the integrity of the
package.
[0010] Measuring headspace oxygen, whether by indicator or invasive
probe, has an important additional disadvantage as well. It
requires time, often hours, for scavengers seated deep within the
walls of MAP materials to consume enough oxygen to affect
measurably the oxygen levels in the headspace. This is often
further delayed and complicated by out-gassing by package contents
(as occurs with foods) or by poor circulation of gasses within the
package. Clearly, there remains a need in the art for a
significantly faster, less wasteful article and method for
verifying oxygen scavenger activity in a package, than the old
method that relies on measuring oxygen concentration within the
headspace of an already assembled package. The present invention
provides such an article and method.
SUMMARY OF THE INVENTION
[0011] In a first aspect, an article comprises an oxygen scavenger;
and an oxygen indicator comprising a luminescent compound; wherein
the oxygen scavenger and the oxygen indicator are substantially
shielded from sources of oxygen exterior to the article.
[0012] In a second aspect, a package comprises a tray comprising a
barrier liner, and a tray flange; an oxygen sensitive product
disposed on the tray; and a film, disposed over the oxygen
sensitive product and adhered to the tray flange, comprising a
first layer comprising an oxygen barrier; a second layer comprising
an oxygen scavenger; and a third layer comprising an oxygen
indicator.
[0013] In a third aspect, an article comprises a first layer
comprising an adhesive; an oxygen indicator comprising a
luminescent compound, the oxygen indicator encapsulated by the
adhesive; and a second layer comprising an oxygen barrier.
[0014] In a fourth aspect, a method of verifying oxygen scavenging
activity by an oxygen scavenger comprises providing a solid article
comprising an oxygen scavenger and an oxygen indicator, the oxygen
indicator comprising a luminescent compound shielded from oxygen
outside the article; triggering the oxygen scavenging activity of
the oxygen scavenger; exposing the oxygen indicator to the
excitation frequency of the luminescent compound; and detecting
luminescence by the oxygen indicator as an indication of oxygen
scavenging activity by the oxygen scavenger.
[0015] In a fifth aspect, a method of verifying oxygen scavenging
activity by an oxygen scavenger comprises providing a solid article
comprising an oxygen scavenger and having dissolved oxygen; placing
a patch comprising an oxygen indicator, comprising a luminescent
compound shielded from oxygen outside the article, proximate to the
solid article; exposing the oxygen indicator to the excitation
frequency of the luminescent compound; and detecting luminescence
by the oxygen indicator as an indication of oxygen scavenging
activity by the oxygen scavenger.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings illustrate several embodiments of
the invention:
[0017] FIG. 1 is a fragmentary, cross-sectional view of a packaging
material enclosing an oxygen sensitive product;
[0018] FIG. 2 is a fragmentary, cross-sectional view of a packaging
material enclosing an oxygen sensitive product;
[0019] FIG. 3 is a view like FIG. 2, but wherein the packaging
material has no sealant layer separate from the oxygen barrier
layer;
[0020] FIG. 4 is a fragmentary, cross-sectional view of a packaging
material enclosing an oxygen sensitive product;
[0021] FIG. 5 is a view like FIG. 4, but wherein the packaging
material has no sealant layer separate from the oxygen barrier
layer;
[0022] FIG. 6 is a fragmentary, cross-sectional view of a packaging
material enclosing an oxygen sensitive product;
[0023] FIG. 7 is a fragmentary, cross-sectional view of a packaging
material enclosing an oxygen sensitive product;
[0024] FIG. 8 is a view like FIG. 6, but wherein the packaging
material has no separate sealant or oxygen barrier layers;
[0025] FIG. 9 a fragmentary, cross-sectional view of a bottle wall,
with an indicator patch adhered to an interior surface of the
bottle wall;
[0026] FIG. 10 is a perspective view of a patch comprising an
indicator;
[0027] FIG. 11 is a cross-sectional view of a fully assembled
package;
[0028] FIG. 12 is an enlarged cross section of the encircled area
of FIG. 11;
[0029] FIG. 13a is an enlarged cross section of the encircled tray
flange area of FIG. 12;
[0030] FIG. 13b is an enlarged cross section of another embodiment
of the encircled tray flange area of FIG. 12;
[0031] FIG. 14 is a top view of a fully assembled package enclosing
an oxygen sensitive product;
[0032] FIG. 15 is a schematic view of the relative placement of a
triggering unit and an oxygen scavenger detector unit;
[0033] FIG. 16 is a graph showing the decay rate of a platinum dye
as the percent of residual oxygen decreases with time;
[0034] FIG. 17 is a graph showing the decay rate of a palladium dye
as the percent of residual oxygen decreases with time; and
[0035] FIG. 18 is a top view of a film section that includes
registered labels and indicator spots.
DETAILED DESCRIPTION OF THE INVENTION
[0036] The present invention relates to the use of luminescent
compounds to measure concentrations of oxygen dissolved in solids,
particularly polymeric materials present in multi-layered packaging
materials. The measurement is made independent of the oxygen
concentration of the surrounding atmosphere, because the indicator
is disposed in the solid, and is substantially shielded from
atmospheric effects (the external atmosphere of the outside
environment, as well as the internal atmosphere of any head space
oxygen if present), by oxygen barrier layers. The phrase
"substantially shielded" herein means that the oxygen scavenger
within the solid article is removing oxygen faster than the oxygen
can enter from the environment surrounding the article, and the
oxygen indicator is thus not quenched by environmental oxygen
during the time that the indicator is to be monitored. Thus,
although some small amount of environmental oxygen may enter the
solid article (dependent on factors such as choice of oxygen
barrier material, thickness of the article, etc.) during the time
the indicator is being monitored for an indication of scavenging
activity, this amount is not so large as to affect the luminescent
activity of the indicator. These oxygen barrier layers can be
discrete layers with a relatively low oxygen transmission rate
(OTR), or can be an adhesive or other layer which allows limited
ingress of oxygen, but at a rate that allows the indicator to be
monitored for an indication of the presence or absence of oxygen
dissolved in the solid material carrying the oxygen scavenger,
without significant influence from atmospheric effects.
[0037] The invention is especially useful as a quality assurance
check to verify oxygen scavenger activation during the assembly of
packages, including but not limited to modified atmosphere and
vacuum packages. The method according to the invention is faster
and less wasteful than previous methods that rely on measuring
oxygen concentration within the headspace of an assembled package.
Novel compositions, articles of manufacture, and improved packaging
materials for use with these methods are also disclosed.
[0038] Luminescent compounds are compounds that strongly absorb
electromagnetic radiation (EMR) at one frequency (the excitation
frequency), and emit EMR at the same or another frequency (the
emitting frequency). Luminescent compounds appropriate as
indicators in the present invention will luminesce only in the
absence of oxygen. More precisely, the indicators will luminesce
upon exposure to their excitation frequency only when oxygen
concentrations fall below a threshold level. As long as the
concentration of oxygen to which the indicators are exposed exceeds
threshold levels, the oxygen will prevent, or "quench"
luminescence.
[0039] The inventors have found that placing a luminescent compound
proximate to an oxygen scavenger, and sandwiching the luminescent
compound and oxygen scavenger between two appropriate oxygen
barrier layers within the packaging material, provides a
non-invasive, real-time indication of scavenger activity. Before
triggering the oxygen scavenging reaction, the concentration of
oxygen dissolved within the packaging materials will be at ambient
levels. Such levels will be in excess of threshold levels, and
sufficient to quench luminescence. After triggering, if scavenging
occurs, oxygen levels near the scavenger will fall rapidly, since
the barrier layers will significantly limit further ingress of
environmental oxygen into the solid. As the oxygen concentration
passes below threshold levels, an indicator proximate to the
scavenger will luminesce when exposed to EMR at the luminescent
compound's excitation frequency. The presence, or onset, of
luminescence within the package material permits the inference that
the scavenger has been triggered successfully.
[0040] Active oxygen scavengers consume available oxygen nearest
themselves first. Therefore, the concentration of oxygen dissolved
in the material immediately surrounding the active scavenger will
reach threshold levels before such levels are reached in more
distant regions. "Proximate" herein means the placement of the
indicator close enough to the scavenger that the length of time for
reduction in oxygen concentration, by the scavenger, in the region
occupied by the indicator, is sufficiently small that those skilled
in the art will find the information provided by the indicator to
be timely and useful. "Proximate" is thus a relative term that
depends on factors readily ascertainable by those of ordinary skill
in the art. Such factors include, inter alia, the rate at which the
scavenger consumes oxygen, the nature of the indicator, and the
permeability of any materials between the scavenger and the
indicator.
[0041] The Indicator can be placed proximate to the oxygen
scavenger in a number of ways.
[0042] In one embodiment, the indicator can be extruded with the
scavenger, using known techniques, such that the indicator and
scavenger are in the same layer.
[0043] In another embodiment, the indicator may be coated,
laminated, or extruded onto another layer, or portion of another
layer, within the package material. Such a layer may be adjacent to
the scavenging layer or separated from the scavenging layer by one
or more other oxygen permeable layers.
[0044] In yet another embodiment, the indicator can comprise all or
part of a printed image.
[0045] In still another embodiment, the indicator composition may
be coated, laminated, or extruded onto a separate substrate. The
substrate/indicator combination could be die cut to form a patch.
The patch could then be affixed to the package material, optionally
with an adhesive or heat seal or the like, such that the indicator
faces the permeable, scavenger-occupied side of the package
material. The inventors found that, ceteris paribus, the closer the
indicator is to the scavenger, the quicker the luminescent compound
will indicate oxygen scavenger activity.
[0046] As the scavenger consumes oxygen, migration of new oxygen
toward the scavenger from external sources can delay the onset of
luminescence by the indicator. The oxygen scavenger is shielded
from substantial introduction of oxygen from external sources in
the vicinity of the indicator. Shielding allows the scavenger to
achieve threshold oxygen concentrations sooner by slowing or
preventing the influx of new oxygen to replace the oxygen consumed
by the scavenger. Verification of scavenger activity can be made
soon after triggering, or at any convenient time thereafter, in
ambient atmospheric conditions.
[0047] In contrast, conventional methods require the packager or
food processor to wait until an unproven section of packaging
material has been assembled into a package, a headspace created,
and equilibrium among the package layers, package contents, and
headspace reached, before evidence of the oxygen scavenging
reaction can be confirmed.
[0048] Effective shielding is a matter of relative rates. The rate
of oxygen influx from external sources (such as from other regions
of the package material, the headspace, the product, or the
external environment) must be sufficiently less than the rate of
oxygen consumption by the scavenger. This will allow the scavenger
to reduce the oxygen concentration around the indicator to
threshold levels fast enough for the indicator to fulfill its
function at a timely (e.g., commercially useful) rate.
[0049] Effective shielding of the oxygen scavenger in the vicinity
of the indicator can be accomplished by surrounding the
scavenger/indicator combination with materials that serve an oxygen
barrier function. Such materials include, but are not limited to,
the oxygen barrier layer typically present in packaging materials;
a barrier patch, i.e., a patch comprising a substrate having oxygen
barrier properties; the substrate upon which the indicator
composition is placed when the indicator forms part of a patch; the
scavenger layer itself, serving a dual function as scavenger and
active oxygen barrier, or any combination thereof. Additionally,
oxygen permeable materials may, alone or together with other
materials, serve as effective barriers if their permeability,
inherently or by adjustment, is low enough to achieve the rate
balance just described. Even the external, lateral, or outer
portions of the indicator composition itself may serve the oxygen
barrier function with respect to the interior portions of the
indicator composition.
[0050] Oxygen barrier properties of the barrier layer of the
packaging materials and patches just described would permit a
maximum oxygen transmission rate (OTR) of 100 cc/m.sup.2/24 hr at
25.degree. C., 0% RH, 1 atm oxygen (ASTM D 3985). Preferably, the
oxygen barrier properties of the barrier layers would permit a
maximum OTR of 50 cc/m.sup.2/24 hr at 25.degree. C., 0% RH, 1 atm
oxygen. More preferably, the oxygen barrier property of the oxygen
barrier layer would permit a maximum OTR of 25 cc/m.sup.2/24 hr at
25.degree. C., 0% RH, 1 atm oxygen. Most preferably, the oxygen
barrier property of the oxygen barrier layer would permit a maximum
OTR of 1 cc/m.sup.2/24 hr at 25.degree. C., 0% RH, 1 atm
oxygen.
[0051] All polymeric materials are capable of providing these
oxygen permeation rates, provided their cross-sectional thickness
is sufficient. A polyethylene, with an oxygen permeability of 2000
cc at a thickness of 1 mil/m.sup.2/24 hr at 25.degree. C., 0% RH, 1
atm oxygen, will meet the 100 cc/m.sup.2/24 hr at 25.degree. C., 0%
RH, 1 atm oxygen barrier requirement described above if the
cross-sectional thickness exceeds 20 mils. Materials that are
capable of providing the oxygen barrier requirements at very thin
cross-sectional thickness include, but are not limited to,
polyester, polyamide, ethylene vinyl alcohol copolymer, polyvinyl
alcohol homopolymer, polyvinyl chloride, homopolymer and copolymer
of polyvinylidene chloride, polyethylene naphthalate,
polyacrylonitrile homopolymer and copolymer, and liquid crystal
polymer. Additionally, the oxygen barrier properties of polymeric
materials can be enhanced by depositing a thin coating of carbon,
metal, metal oxide, silica and/or silicon oxide, and SiOX. It is
also known that barrier properties of polymeric materials can also
be enhanced through melt blending a polymer with glass, clay,
and/or a polymer having a relatively low oxygen transmission rate
(i.e. a relatively high oxygen barrier). It can also be enhanced
through blending polymers, metals, metal halides, etc., with oxygen
scavenging materials.
[0052] From the foregoing discussion, one of ordinary skill in the
art will appreciate that the minimum amount of time needed for a
luminescent composition to indicate scavenger activity depends on
the interplay of several factors. Such factors include, inter alia,
the rate at which the scavenger consumes oxygen, the proximity of
the indicator to the scavenger, the permeability of any materials
between the scavenger and the indicator, the threshold at which the
luminescent compounds respond to changes in oxygen concentrations,
the amount of oxygen that must be removed in order to reach
threshold levels, the species of luminescent compound(s) used, the
ambient temperature, and the effectiveness of any shielding
present.
[0053] The minimum amount of time between triggering and detection
may also be influenced by the factors listed above, and by
engineering considerations or quality assurance criteria as well.
Thus, in contrast to previous methods which typically take in
excess of 18 hours, the present invention allows one to verify
oxygen scavenging activity within 1 hour of triggering, optionally
within 30 minutes of triggering, optionally within 10 minutes of
triggering, optionally within 5 minutes of triggering, optionally
immediately after triggering, or any time period intermediate
thereto. Put another way, it will be preferable in some instances
to detect the presence or absence of luminescence immediately after
the portion of the film to be tested leaves the triggering
apparatus, within minutes thereafter, at any suitable place along
the assembly line, or after the assembled package leaves the
assembly line.
[0054] Those interested in tracking the continued progress of the
oxygen scavenger activity may test, or re-test, the indicator for
scavenging activity any suitable number of times thereafter. Such
intervals include, for example, at 30 minutes, 1 hour, 4 hours, 24
hours, 1 month, and so on.
[0055] The figures present non-limiting, exemplary arrangements of
scavengers, indicators and barriers according to the invention. For
simplicity, additional layers that may be present (or absent) in a
packaging material are not shown. One of ordinary skill in the art
will appreciate, however, that (1) such additional layers,
including sealant layers and the like, may be added or subtracted
without departing from the spirit or scope of the invention, and
that (2) the packaging material, such as a film, although
illustrated in most of the drawings as a film section disposed
above an oxygen sensitive product, will preferably entirely
surround the oxygen sensitive product, or else form a lidstock
and/or tray to be used in conjunction with other appropriate
packaging components to package an oxygen sensitive product.
[0056] FIGS. 1, 2, 3, 4, and 5 depict multi-layer packaging
materials where the indicator forms an integral component of the
primary packaging material.
[0057] In FIG. 1, a film 10 includes a layer 12 comprising an
oxygen barrier. Layer 12 will normally be positioned on the outside
of a final package made from the film, and enclosing an oxygen
sensitive product 11. Suitable oxygen barriers are disclosed
herein. The oxygen sensitive product 11 can be a foodstuff such as
a red meat, poultry, cheese, pumpable food, refrigerated prepared
food, snack food, bakery product, beverage, candy or confectionery
product, dried fruit, vegetable, nut, coffee, tea,
parenteral/enteral nutrition, adult/baby formula, frozen food,
cereal, grain, grain product, dehydrated juice mix, fresh produce,
or spice product, or a non-food item such as a medical or
pharmaceutical, electronic, recorded programming, personal care or
cosmetic, fertilizer, pesticide, herbicide, tobacco, metal, or
chemical product.
[0058] Layer 14 comprises a blend, in any suitable relative
amounts, of an oxygen indicator and an oxygen scavenger. Suitable
oxygen indicators are disclosed herein, and will exhibit oxygen
quenched luminescence, i.e. will luminesce in the absence of
oxygen.
[0059] Suitable oxygen scavengers are e.g. oxidizable organic
compound and a transition metal catalyst; ethylenically unsaturated
hydrocarbon and a transition metal catalyst; a reduced form of a
quinone, a photoreducible dye, or a carbonyl compound which has
absorbence in the UV spectrum; a polymer having a polymeric
backbone, cyclic olefinic pendent group, and linking group linking
the olefinic pendent group to the polymeric backbone; a copolymer
of ethylene and a strained, cyclic alkylene; ethylene/vinyl aralkyl
copolymer; ascorbate; isoascorbate; sulfite; ascorbate and a
transition metal catalyst, the catalyst comprising a simple metal
or salt, or a compound, complex or chelate of the transition metal;
a transition metal complex or chelate of a polycarboxylic acid,
salicylic acid, or polyamine; tannin; or reduced metal such as
iron.
[0060] The indicator can be present in layer 14 in an amount of
between 1% and 99%, by weight of the layer 14. The scavenger can be
present in layer 14 in an amount of between 99% and 1%, by weight
of the layer 14.
[0061] In the embodiment illustrated in FIG. 1, the oxygen
indicator is disposed in the same layer (or a portion of the same
layer) occupied by the oxygen scavenger.
[0062] A barrier patch 19 is adhered to layer 14 of film 10. Patch
14 comprises any of the oxygen barrier materials disclosed herein.
Patch 14 can itself be a monolayer film, or can be a multilayer
film having at least one layer or coating comprising an oxygen
barrier, preferably a polymeric oxygen barrier such as those
disclosed herein. The patch 19 can be adhered to film 10 by any
suitable means, such as heat or RF sealing, pressure sensitive
adhesive, or the like. Corresponding barrier patches disclosed
herein likewise can be adhered to the primary packaging article,
such as a film, by any suitable sealing or adhesive means.
[0063] In FIGS. 2, 3, 4, and 5, the indicator and the scavenger
occupy different layers. Although the scavenger and indicator
layers are shown in adjacent layers, they may also be separated by
one or more sufficiently oxygen permeable layers as well. In each
instance, the oxygen barrier layer and other nearby materials
provide shielding of the indicator from environmental oxygen. In
FIGS. 1, 4, and 5, a barrier patch assists in providing shielding.
In FIGS. 2 and 3, the oxygen scavenger layer itself helps provide
shielding.
[0064] A general feature of the present invention is that the
oxygen indicator is shielded from environmental oxygen, including
oxygen present outside the finished package, as well as any head
space oxygen if present, or oxygen dissolved in the oxygen
sensitive product if present, during the time that the indicator is
to be monitored for an indication of the presence or absence of
oxygen dissolved in the solid material carrying the oxygen
scavenger.
[0065] In FIG. 2, the film 20 that encloses oxygen sensitive
product 21 includes an oxygen barrier layer 22, an oxygen indicator
layer 24, and an oxygen scavenger layer 26. The indicator of layer
24 is therefore disposed in a layer between the external oxygen
barrier layer 22 and the layer 26 containing the scavenger. The
scavenging layer thus functions herein both as a scavenger and as
an active oxygen barrier. Layer 26, together with the oxygen
barrier layer 22 and other components, shields the indicator from
substantial influx of oxygen from the headspace of a finished
package made from the film, from an oxygen sensitive product
disposed in the finished package, and from the exterior
environment. Of course, before the film is used to make a package,
the layers 22 and 26 protect the indicator from environmental
oxygen surrounding the film on either exposed side of the film.
[0066] The indicator of layer 24 can comprise any of the indicators
disclosed herein, and for layer 14 of FIG. 1. The oxygen barrier
material of layer 22 can comprise any of the oxygen barrier
materials disclosed herein, and for layer 12 of FIG. 1. The oxygen
scavenger of layer 26 can comprise any of the oxygen barrier
materials disclosed herein, and for layer 14 of FIG. 1.
[0067] Layer 28 comprises a sealant material, preferably a heat
sealable material. Suitable examples of sealant materials include
an olefinic polymer such as ethylene/alpha olefin copolymer,
homogeneous ethylene/alpha olefin copolymer, ethylene/vinyl acetate
copolymer, ethylene/alkyl acrylate copolymer, ethylene/acrylic acid
copolymer, ionomer, propylene homopolymer and copolymer, butylene
polymer and copolymer, multi-component ethylene/alpha-olefin
interpenetrating network resin, a blend of a propylene homopolymer
and a propylene/ethylene copolymer, high density polyethylene, a
blend of high density polyethylene and ethylene/vinyl acetate
copolymer, a blend of high density polyethylene and low density
polyethylene; or a blend of any of these materials; polyamide or
copolyamide; or other appropriate polymeric materials. The sealant
layer 28, and corresponding sealant layers in other embodiments
shown herein, are preferably positioned as an exterior (surface)
layer. This layer will typically be closest to the oxygen sensitive
product and serve to provide a means to seal the film to itself or
a barrier liner or the like (in the case of a trayed product)
during a packaging operation.
[0068] FIG. 3 shows a film 30 having the same configuration and
composition as in FIG. 2, but without the sealant layer.
[0069] FIG. 4 shows a film 40 that encloses an oxygen sensitive
product 41. The film comprises an oxygen barrier layer 42, an
oxygen indicator layer 44, an oxygen scavenger layer 46, and a
sealant layer 48. A barrier patch 49 is adhered to the sealant
layer 48 of film 40.
[0070] FIG. 5 depicts the same configuration and compositions as in
FIG. 4, but without the sealant layer.
[0071] Thus, layers 32, 42, and 52 correspond to layer 22 of FIG.
2; layers 34, 44, and 54 correspond to layer 24 of FIG. 2; layers
36, 46, and 56 correspond to layer 26 of FIG. 2; layer 48
corresponds to layer 28 of FIG. 2; patches 49 and 59 correspond to
patch 19 of FIG. 1; and oxygen sensitive products 21, 31, 41, and
51 correspond to oxygen sensitive product 11 of FIG. 1.
[0072] FIGS. 6, 7, 8, and 9 depict packaging materials where the
indicator is placed proximate to the scavenger layer using a patch.
The patch, as noted above, comprises an oxygen barrier
material.
[0073] In FIG. 6 an adhesive 63 is deposited on the substrate
oxygen barrier layer 65 of patch 69, and the indicator 64 deposited
on the adhesive. The adhesive of this and other embodiments
disclosed herein can be of any suitable type, including pressure
sensitive adhesive, glue, or the like. Examples include
thermoplastic hot melt adhesives, silicone adhesives, acrylic
pressure sensitive adhesives, solvent cast adhesives, UV
(ultraviolet) or EB (electron beam) cured acrylic adhesives, or the
like. The combination is affixed to the oxygen permeable (product)
side of the packaging material, more specifically to sealant layer
68 of film 60, by the adhesive, in such a manner that the indicator
is encapsulated by the adhesive, and the indicator is thus shielded
from environmental oxygen, including oxygen from outside the
finished package, as well as any head space oxygen if present, and
dissolved oxygen from the oxygen sensitive product 61 if present,
during the time that the indicator is to be monitored for an
indication of the presence or absence of oxygen dissolved in the
solid material carrying the oxygen scavenger. The adhesive layer
63, though permeable, should preferably have sufficient lateral
width to prevent substantial influx of oxygen into the indicator
from the lateral edges of the adhesive during the time the
indicator is to be used. In the example of FIG. 6, the patch 69 is
attached to the film 60 by the adhesive layer 63. Other methods of
adhesion could also be used, such as heat sealing. Film 60 also
includes an oxygen barrier layer 62, scavenger layer 66, and
sealant layer 68.
[0074] FIG. 7 depicts a cross-sectional view of a patch 79 affixed
to the sealant layer 78 of a film 70, similar to that shown in FIG.
6. As in FIG. 6, the adhesive encapsulates the indicator 74. FIGS.
6 and 7 differ in the configuration of the adhesive layer. The
relative positions of the indicator and adhesive are reversed to
enlarge the area of the adhesive that is exposed to the packaging
material surface. In the embodiment of FIG. 7, the adhesive layer
73 between the indicator 74 and the packaging film 70 should be
sufficiently thin to provide the required oxygen permeability. The
adhesive layer 73 may be thicker on the sides in order to provide
an oxygen barrier against lateral oxygen influx.
[0075] The oxygen barrier layers 62 and 72 thus correspond to
oxygen barrier layer 12 of FIG. 1; oxygen scavenger layers 66 and
76 correspond to oxygen scavenger layer 26 of FIG. 2; sealant
layers 68 and 78 correspond to sealant layer 28 of FIG. 2;
indicators 64 and 74 can be of the type disclosed for indicator 24
of FIG. 2; and oxygen sensitive products 61 and 71 correspond to
oxygen sensitive product 11 of FIG. 1.
[0076] FIG. 8 shows a film 80 with a patch 89 adhered to an oxygen
scavenger layer 86 of the film 80, wherein the film 80 has no
separate sealant or barrier layers. The oxygen scavenger forms an
active barrier layer that, together with the barrier
characteristics of the adhesive 83 and oxygen barrier layer 85 of
the patch 89, shield the indicator 84 from substantial introduction
of oxygen from external sources. Oxygen scavenger layer 86
corresponds to oxygen scavenger layer 66; patch 89 and the
components thereof correspond to patch 69 and the components
thereof; oxygen sensitive product 81 corresponds to oxygen
sensitive product 61.
[0077] FIG. 9 depicts a cross-sectional view of an oxygen scavenger
layer 96 laminated between two layers 91 and 93 respectively, each
comprising polyethylene terephthalate (PET). PET is a material
typically used in rigid or semi-rigid beverage containers such as
beer bottles. Other functionally equivalent materials may also be
used. The oxygen sensitive product 91 shown could be a carbonated
beverage or the like. The indicator 94 is placed proximate to the
scavenger layer 96 by use of a barrier patch 99. The patch 99 forms
an oxygen barrier shield on one side of indicator 94. The thickness
and/or composition of the PET layers 91 and 93 are adjusted such
that it is substantially oxygen permeable on the indicator side of
the bottle wall, and forms a substantial oxygen barrier on the
product side of the bottle wall. The oxygen scavenger provides an
active barrier that, together with the patch, provide sufficient
shielding of the indicator/scavenger pair.
[0078] Although the patch is shown in FIG. 9 as attached to the
interior (product) side of a bottle wall, the patch can in fact be
disposed on either the interior or exterior side of the bottle
wall, or both. If the oxygen scavenger is displaced more toward one
side of the bottle wall than the other, then the patch is
preferably disposed on that side of the bottle that will bring the
indicator into closer proximity to the oxygen scavenger.
[0079] More generally, a patch carrying the indicator can be
disposed on either a product side or exterior side of a packaging
material, such as a film, web, laminate, tray, lidstock, or the
like, with similar considerations as above.
[0080] The oxygen indicator patch 99 of FIG. 9 is shown with the
oxygen indicator layer 94 laterally coextensive with the oxygen
barrier layer 99 of the patch. FIG. 9 additionally shows the patch
as having a finite lateral extent compared with the overall length
of the bottle wall. In this embodiment, it will sometimes be
preferable to encapsulate the indicator within the oxygen barrier
of the patch, analogous to the way the adhesive encapsulates the
indicator in FIGS. 6 and 7. However, if the indicator layer is
sufficiently wide, for example by creating a wide patch, or even a
patch substantially coextensive with the length of the bottle, then
the lateral end regions of the indicator can act to help shield a
central portion of the indicator layer from environmental oxygen.
Thus, the central part of the indicator, furthest removed from the
lateral extremities of the patch, can be the target area that is
monitored for luminescence.
[0081] Oxygen scavenger layer 86 corresponds to oxygen scavenger
layer 66; patch 89 and the components thereof correspond to patch
69 and the components thereof; oxygen sensitive product 81
corresponds to oxygen sensitive product 61.
[0082] Oxygen scavenger layer 96 corresponds to oxygen scavenger
layer 66; patch 99 and the components thereof correspond to patch
69 and the components thereof; oxygen sensitive product 91
corresponds to oxygen sensitive product 61.
[0083] FIG. 10 shows a patch 109 unattached to any packaging
material. The patch 109 as shown comprises an oxygen indicator 104,
an adhesive layer 103 which encapsulates the indicator 104, and an
oxygen barrier layer 105 having a printable surface layer 107 (the
printable surface layer will in practice have no appreciable
thickness, but is shown with a substantial thickness for the sake
of clarity). The patch 109 thus comprises an oxygen indicator 104
on an oxygen barrier substrate. The printable surface layer is
optional. The patch is capable of being affixed to the permeable
(product side) surface of a packaging material such as a film,
placing at least a portion of the oxygen indicator proximate to the
packaging material's scavenger component using an adhesive. The
adhesive may be present or absent. If present, it may be made of
any suitable adhesive substance, including, but not limited to,
pressure sensitive or heat sensitive substances.
[0084] FIGS. 11, 12, 13a and 13b each depict cross sectional views
of assembled trays comprising oxygen barrier packaging
materials.
[0085] FIG. 11 shows a package 117 including a tray 118; an oxygen
sensitive product 111, such as ground beef, disposed in the tray;
and a lidstock 110 sealed to the tray flange 113. The encircled
section of FIG. 11 is enlarged in FIG. 12. In the package shown in
FIG. 11, a barrier patch 119 is adhered to the interior (product)
side of lidstock 110. This patch is optional; corresponds in
construction to other patches shown herein, e.g. patch 19 or 69;
and enables the indication of scavenging activity in lidstock 110,
independent of environmental oxygen present in the outer
atmosphere, or in the headspace 135 of the package.
[0086] FIG. 12 shows the tray 118 comprising a polymer layer 115
comprising e.g. polystyrene or polypropylene, foamed or unfoamed,
and also comprising a layer 116 adhered to the polymer layer, and
comprising an oxygen barrier material of the type disclosed herein.
This liner provides oxygen barrier properties to the tray portion
of the package. The lidstock 110 preferably comprises multiple
layers. In FIG. 11, lidstock 110 is simply shown as two layers for
sake of clarity; FIGS. 13a and 13b show in more detail two
embodiments of lidstock 110. The encircled section is enlarged in
FIGS. 13a and 13b.
[0087] FIG. 13a shows the lidstock 110 sealed to the tray flange
113 of tray 118 by heat sealing according to methods well known in
the art. More specifically, the sealant layer 138 of lidstock 110
is sealed to the barrier liner 116 of tray 118 in the tray flange
113 portion of tray 118. Oxygen barrier layer 132, oxygen scavenger
layer 136, oxygen indicator 134, and sealant layer 138 correspond
respectively in function and composition to those shown elsewhere
herein, including layers 42, 46, 44, and 48 respectively of FIG. 4.
The barrier liner can be monolayer or multilayer in composition,
and includes an oxygen barrier layer of the type disclosed herein.
Suitable olefinic sealants, comprising olefinic materials of the
type disclosed herein, can form separate layers in the barrier
liner. A typical five-layer construction for barrier liner 116
is:
[0088] olefin polymer or copolymer/tie/EVOH/tie/olefin polymer or
copolymer
[0089] FIG. 13b is like FIG. 13 a in all particulars, except that
the position of the oxygen scavenger and oxygen indicator layers is
reversed.
[0090] In each of these embodiments, it is not necessary to place
indicator compositions everywhere the scavenger composition
resides. It may be sufficient (and less expensive) to place
indicators only in portions of the packaging material instead. For
example, one may affix indicator patches to the packaging materials
at set time or distance intervals, to provide sufficiently frequent
scavenger verification for quality assurance purposes. The
substrates of the patches may optionally contain metal or other
machine-detectable backing. Metal or other detectors may be set up
along the assembly line to ensure that patches are not
inadvertently left with the assembled package where the consumer
may misinterpret the information the indicator provides. An example
of spaced apart patches is shown in FIG. 18. A packaging film 180
includes a web 182 of a suitable polymeric monolayer or multilayer
film. A plurality of patches 189 are installed at regular spaced
apart intervals along the length of the web. These patches
correspond to e.g. patch 19 or 69. Eye spots 186 or other suitable
indexing means can be used to register the web in a packaging
process. The indicator 189 can be applied by printing in
registration with other graphics comprising a product label. Where
the scavengers comprise a component of one or more layers of a
multi-layer film, one could include the indicators in the form of a
pattern, such as a strip, spot, coupon, or grid. These strips,
spots, coupons, or grids could be placed periodically along a
portion, such as along an edge or in a row, of the material
containing the oxygen scavenger. Such portions may or may not be
placed such that they ultimately become part of the assembled
package. A suitable barrier patch or layer or coating is used in
conjunction with such strips, spots, coupons, or grids, to ensure
that the oxygen indicator is shielded from environmental oxygen
during the time that the indicator is to be monitored for an
indication of the presence or absence of oxygen dissolved in the
solid material carrying the oxygen scavenger.
[0091] Alternatively, the eye spot 186 can itself carry an oxygen
indicator. The eye spot will typically become part of the sealed
edge or flange of a barrier package, thus effectively shielding it
from environmental oxygen.
[0092] For example, FIG. 14 depicts a top view of an assembled
package 147 made from a tray e.g. of polystyrene or polypropylene,
preferably with a barrier liner as disclosed in FIGS. 13a and 13b,
including a tray flange 143 to which lidstock 140 is sealed. The
longitudinal stripes 144 indicate areas where an oxygen indicator
may be placed. The scavengers may be incorporated into one or more
layers throughout the entire area of the preferably clear film 140.
The indicator may be incorporated in the areas represented by the
vertical stripes. The stripes could be longitudinal or transverse,
or any other orientation. The number, width, and shape of the
stripes may be varied according to preference. A single stripe can
be beneficially used.
[0093] The stripes that comprise the indicator composition(s) may
be incorporated into the packaging material layer(s) by well known
techniques easily adapted to the introduction of compositions
comprising indicator compounds. Such techniques are described by
Havens in U.S. Pat. Nos. 5,110,530 and 5,298,310. The disclosures
of these two patents are incorporated herein by reference in their
entirety. These patents disclose two or more preferably polymeric
layers, of which at least one continuous or discontinuous layer
includes a pigmented resin. The width, number, and distribution of
the stripes can be varied by altering the arrangement, number, and
configuration of the thin grooves or other means for controlling
the flow of pigmented or dyed resin in any particular die
configuration. The intensity of the striped or banded effect can
also be affected by the choice of pigments, concentration of the
pigment within the base or carrying resin, and thickness of the
pigmented layer. The pigment can be a material invisible in
ordinary light but visible in e.g. ultraviolet light. The striped
film is produced by modifying conventional coextrusion dies to
restrict the flow of a pigmented melt stream. In the case of
multiple concentric cylinder dies, one or more of the exit annular
openings is eliminated by making the two cylinders come together in
a slight interference fit, in essence, sealing the channel exit.
Pigmented or dyed resin is allowed to exit the channel only through
very narrow grooves machined radially across the interference fit
zone. In this way the exiting pigmented resin forms lanes of
pigment, or stripes, between adjacent layers of resin or on the
inner or outer surface of the coextruded film. By varying the
relative width of the machined exit grooves and their relative
spacing, different patterns of stripes may be achieved. In
feed-block technology, two resin directing guides are machined to
form a tight fit. Across this tight fitting lip, small grooves are
machined for the exit of the pigmented resin which will form
stripes. The use of a constricted exit into which thin grooves are
cut for the pigmented resin to exit may be similarly applied to
other die systems to achieve the same effect of stripes.
[0094] The information provided by the indicator dye, whether in
the form of patches, stripes or other configuration, may be read by
machine or human eye, depending upon the emitting frequency of the
luminescent compound(s) used and other factors such as engineering
preference.
[0095] FIG. 15 depicts a system 157 in which a film 150 containing
an oxygen scavenger tracks past a detector unit 154 positioned
downstream of a triggering unit 152 as part of a package assembly
line. Both units can thus comprise part of a package assembly
process. The space between the triggering unit and detector may
vary according to engineering expediency or other
considerations.
[0096] The term "luminescent" as used herein, encompasses
phosphorescence, fluorescence, or any electromagnetic emission that
can serve the indicator function. When the emission frequency is in
the visible spectrum, the indicator may be read by either machine
or the human eye. When the emission frequency is not visible,
luminescence may be detected by machine.
[0097] Luminescent compounds suitable for use in this invention
include any known or after-discovered compounds having the
functionality just described. Additionally, suitable luminescent
compounds and compositions comprising them preferably have one or
more of the following characteristics as well:
[0098] a) Their response to changes in oxygen concentration are
predictable, linear, and fully reversible. Linearity is desirable
for calibration and quantitative monitoring purposes. Reversibility
allows the oxygen concentration to be monitored at any stage of the
packaging and storage process;
[0099] b) They are sensitive to oxygen concentrations within target
ranges. Ranges can include between 0% and 5% oxygen, such as
between 0% and 1%, or between 0 to 1000 ppm. Combinations of
indicators having different ranges and sensitivities may be used to
extend such ranges if desirable;
[0100] c) They respond quickly to changes in oxygen concentration
in the conditions in which they will be used. A typical response
time of a luminescent compound to a change in oxygen concentration
is within 1 minute or less of the atmosphere change over a
temperature range of between 0.degree. C. and 25.degree. C.;
[0101] d) They exhibit luminescence over a range of frequencies
easily monitored. For use with an inexpensive interrogative device,
the indicator(s) should have suitable excitation and emission
frequencies, preferably visible;
[0102] e) They are selectively responsive to oxygen concentration
changes and insensitive to other gases that may permeate the dye
containing packaging material, such as carbon dioxide;
[0103] f) They are stable under conditions of use and storage.
Photostability is desirable but not required temperature stability,
and stability to changes in humidity, are desirable and
preferred;
[0104] g) They are clear or color-compatible with the packaging in
which they are used. Color-compatibility is important for example
where the indicator may form all or part of a printed image. In
embodiments where a discrete patch is used, clarity or color
compatibility is usually not as important;
[0105] h) They exhibit good coating and/or printability properties,
and/or are amenable to extrusion; and
[0106] i) The indicator is useful in relatively low concentrations
in order to minimize the cost of the overall packaging
material.
[0107] Preferred luminescent compounds for use in this invention
include fluorescent or phosphorescent dyes that exhibit oxygen
quenched luminescence. Phosphorescent dyes are preferable to
fluorescent dyes for oxygen sensing as the former are characterized
by well separated excitation and emission frequencies. These
frequencies are commonly in the visible region of the spectrum and
have long excited-state lifetimes. Phosphorescent dyes also have
improved sensitivity to low levels of oxygen to facilitate
monitoring.
[0108] Compounds suitable as indicators in the context of this
invention are known in the art. For example, Khalil et al., U.S.
Pat. Nos. 4,810,655 and 5,043,286, both incorporated by reference,
disclose suitable compounds and methods for their manufacture. Such
compounds include metallo derivatives of octaethylporphyrin,
tetraphenylporphyrin, tetrabenzoporphyrin, or the chlorins,
bacteriochlorins, or isobacteriochlorins and their partially or
fully fluorinated analogs. Other suitable compounds include
palladium coproporphyrin (PdCPP), platinum and palladium
octaethylporphyrin (PtOEP, PdOEP), platinum and palladium
tetraphenylporphyrin (PtTPP, PdTPP), camphorquinone (CQ), and
xanthene type dyes such as erythrosin B (EB). Other suitable
compounds include ruthenium, osmium and iridium complexes with
ligands such as 2,2'-bipyridine, 1,10-phenanthroline,
4,7-diphenyl-1,10-phenanthroline and the like. Suitable examples of
these include, tris(4,7,-diphenyl-1,10-
-phenanthroline)ruthenium(II) perchlorate,
tris(2,2'-bipyridine)ruthenium(- II) perchlorate, and
tris(1,10-phenanthroline)ruthenium(II) perchlorate. While the
perchlorate salts are particularly useful, other counterions that
do not interfere with the luminescence may be used.
[0109] Compositions comprising one or more indicator compounds will
preferably be dissolved in a polymeric carrier or solvent matrix
(system). There are two reasons for this. One reason is that
solution achieves the maximum dispersion and therefore utilization
of the indicator compound for maximum efficiency. The other is that
agglomeration of the indicator compounds must be avoided because of
an adverse interaction between two indicator molecules that results
in self quenching and reduced efficiency. It is well known that the
polymer matrix can influence the luminescence decay of the
indicator (see J. Phys. Chem., 1995, 99, 3162-3167).
[0110] The indicator composition can be chosen for maximum
solubility in the polymer or solvent system. One can change the
solubility of a ligand indicator in a polymer or solvent matrix by
varying the substituent group(s) on the ligand. For example, one
can substitute non-fluorinated porphyrins for partially or fully
fluorinated porphyrins, or tetraphenyl porphyrins for octaethyl
porphyrins, or the like, to select the porphyrin having the
solubility in a polymer or solvent matrix desired. Where the
complexes involve counterions, the selection of the counterion can
influence the solubility of the compound in the polymer matrix.
[0111] Those skilled in the art will understand that only a very
minor amount of indicator is needed to achieve luminescence
sufficient for good detection. Indicator compounds are preferably
used in relatively low concentrations in order to minimize cost of
the overall packaging material. Suitable concentrations of
indicator compounds can be from a few micrograms per square inch
(area) to a few milligrams per square inch (area).
[0112] The various embodiments of the present invention are based
in part on the choices of polymer or solvent system and necessary
concentrations for the indicator compound. If an indicator is
sufficiently heat stable, it can be effectively dissolved in a
polymer and extruded. One can achieve a suitable area concentration
to observe luminescence by adjusting the indicator concentration
and the polymer thickness. Furthermore, this indicator and polymer
system can be extruded in several ways to be incorporated into a
suitable solid. For example, the indicator can be dispersed in a
monolayer film or in one or more layers of a multilayer film that
also includes a barrier layer or coating. The monolayer or
multilayer film can be cut to form an applique and attached to a
suitable backing material.
[0113] If the indicator compound is more compatible with specific
solvents, it can be incorporated into a solvent and/or ink system
and effectively printed onto a suitable film or substrate. As part
of a suitable ink system, the indicator compound could be trap
printed along with the graphics that comprise the oxygen scavenging
film. This arrangement of layers would be like that shown in FIG.
2. The printed indicator would be arranged such that it became part
of the seal area of a package as in FIGS. 12 and 13a and 13b. This
can be useful if the indicator compound is heat sensitive or of
limited solubility in a resin system. A more compatible or stronger
solvent, such as tetrahydrofuran (THF) or xylene, may better
dissolve the indicator compound to maximize its efficient
utilization. One skilled in the art can see how to do this
including the use of multiple indicator compounds and/or multiple
strikes (layers) of an ink system indicator compositions comprising
the above described luminescent compounds may be used as a quick
way to determine whether oxygen concentrations are at or below
threshold levels, or to measure precisely the oxygen concentration
surrounding the indicator. The former can be used, for instance, as
a pass-fail test to verify scavenger activation, as detection of
luminescence verifies that the scavenger has consumed enough oxygen
to cause oxygen concentration surrounding the indicator to fall
below threshold levels. Knowing the threshold for the luminescent
compound used allows one to infer the maximum oxygen concentration
proximate to the scavenger when luminescence is observed. For more
precise measurements, one may use combinations of different
luminescent compounds simultaneously. Threshold oxygen
concentrations often vary from one luminescent species to another.
Selecting two or more luminescent species, each having different
thresholds, allows one to track scavenging progress as the oxygen
concentration passes through different levels. For easier tracking,
the different species of luminescent compounds may be used within
the same or different patches. Or they may occupy the same or
different areas within a predetermined portion of the packaging
material, such as a grid or stripe or other pattern of indicator
material. Detecting luminescence in one luminescent species, but
not another, would allow one to conclude that the oxygen
concentration is somewhere between each indicator's threshold
levels. For even more precise measurements, the inventors
contemplate straight-forward adaptation of the well known
Stern-Volmer methods to the present context.
[0114] In 1919, Stern and Volmer reported that oxygen quenches the
luminescence of certain compounds. Since luminescence is one mode
of decay from the excited state, the oxygen quenching competes with
other decay modes. From their experiments, they determined what has
become known as the Stern-Volmer relationship between the half-life
of the excited luminescent state and the oxygen partial pressure: 1
I @ O2 = 0 I = 1 + P 02 P 1 / 2
[0115] where: I.sub.@O2=0=intensity at zero oxygen
concentration
[0116] I=measured intensity
[0117] P.sub.O2=measured oxygen partial pressure
[0118] P.sub.1/2=oxygen partial pressure for a half-life of the
intensity
[0119] This equation can be inverted and the fractions cleared to
express the intensity ratio or brightness (B): 2 B = I I @ O2 = 0 =
P 1 / 2 P 1 / 2 + P O2
[0120] As brightness is a ratio of two related intensive variables,
it is extensive. Brightness is easily measured. From this, it is a
straightforward calculation to obtain the oxygen partial
pressure.
[0121] It is also possible to express the relationship on a time
basis by simple substitution of the mean luminescent lifetimes,
with and without oxygen present: 3 T T @ O2 = 0 = P 1 / 2 P 1 / 2 +
P O2
[0122] where T and T.sub.@O2=0 are the lifetimes with and without
oxygen present respectively.
[0123] In both cases, the inverse relationship between the
brightness or persistence of the luminescence and the oxygen
pressure can readily be seen.
[0124] For a given luminescent species, the values of I.sub.@O2=0,
T.sub.@O2=0 and P.sub.1/2 are often known and published. In 1987,
Bacon and Demas used both intensity and lifetime measurements to
demonstrate the measurement of oxygen concentration in fluid or gas
using ruthenium complexes (see Anal. Chem. 1987, 59, 2780-2785).
One must chose the lifetimes and intensities to suit the range of
oxygen concentration to be studied.
[0125] From these equations, one can quickly see three mathematical
ways to calculate the oxygen pressure from the luminescence
measurement:
[0126] Method 1. Measure the luminescence intensity with oxygen
present and ratios it to the luminescence without oxygen present.
Equipment for this measurement technique is commonly available from
several sources of optical equipment, such as Ocean Optics,
Dunedin, Fla.
[0127] Method 2. Measure the luminescence lifetime with oxygen
present and ratio it to the luminescence lifetime without oxygen
present. There is a variation on this lifetime calculation (Abbott
Laboratories) that assumes that the luminescence intensity
immediately after excitation ceases is proportional to the net
amount of active species where there has been no time for oxygen
quenching. After a second time delay, the remaining luminescence
intensity is measured again. Since the luminescence is time
dependent as an exponential decay, the intensity at the second time
can be related to the exponential decay curve. From this, the
oxygen pressure can be calculated. Resolution of decay time curves
is common in a number of technical fields. In 1991, Demas et al.
published a method for utilizing a non-linear Stern-Volmer
quenching response that involves fitting multiple quenching rate
constants to the data (see Anal. Chem., 1991, 63, 337-342).
[0128] Method 3. Since luminescence lags the excitation, it is
possible to pulse the excitation and monitor the resulting
luminescence intensity and its time lag (or phase shift) to resolve
the oxygen concentration. This phase shift calculation has been
detailed by Colvin, et. al., Johns Hopkins APL Technical Digest,
V17, N4 (1996), pgs 377-385. In this approach, the excitation
source is pulsed at a fixed frequency whose period is comparable to
the lifetime of the emission. The modulated emission is detected
with a photodiode or photomultiplier and analyzed with a
phase-sensitive lock-in amplifier. The phase angle .theta. is
related to the lifetime by:
Tan .theta.=2.pi.f.tau.
[0129] where .tau. is the lifetime of the emission and f is the
frequency of the modulation. Maximum phase difference occurs at
f=(1/2.pi.)(.tau..sub.1.tau..sub.2).sup.-1/2, where .tau..sub.1 and
.tau..sub.2 are the lifetimes of the quenched and unquenched
species. This data is used in an alternate form of the Stern-Volmer
equation where:
.tau..sub.0/.tau.=1+k.sub.svp.sub.o2
[0130] where .tau..sub.0 is the luminescence lifetime in the
absence of oxygen, k.sub.sv is the Stern-Volmer quenching constant,
and p.sub.o2 is the partial pressure of oxygen. The following
describes non-limiting examples of the invention.
EXAMPLES
[0131] Determining the Suitability of Various Indicators
[0132] In general, three polymer matrices were used for standard
screening; these were cellulose acetate butyrate (CAB), polystyrene
(PS) and polymethylmethacrylate (PMMA). These polymers exhibit very
good, good and poor oxygen sensitivity, respectively, and were
chosen to demonstrate the ability to tune the response via the
polymer matrix.
[0133] Film solutions were prepared by adding the indicator,
dissolved in an appropriate solvent to a solution of the polymer
and mixing thoroughly. The final solvent-free films were prepared
by casting the film solutions onto a glass plate support
(0.85.times.3.times.0.1 cm) through a 100 .mu.m thick brass
template with a rectangular hole (0.8.times.1.5 cm) and drying
overnight at ambient temperatures. Calculations based on the known
area and weight of the films and the density of the polymer
matrices gave film thickness estimates of 15-20 .mu.m.
[0134] Spectral Profiles
[0135] Phosphorescence spectra were obtained using a Perkin Elmer
LS50B scanning luminescence spectrometer. The glass plates bearing
the plastic films were mounted into the center of a plastic or
quartz luminescence cell using PTFE supports to ensure correct
positioning of the film in the incident light beam. The cell was
equipped with an airtight stopper, which had inlet and outlet lines
to allow gas flow. The cell was controlled at 23.degree. C. and all
excitation and emission wavelengths were determined in an
atmosphere of 100% nitrogen.
[0136] In order to record phosphorescence spectra two values,
t.sub.d, the delay time and t.sub.g, the gating time need to be
selected. These correspond to the time after the initial flash that
measurement of the signal begins and the length of time over which
data is subsequently collected. The values of these parameters is
particularly important when taking measurements of sensitivity at
different oxygen levels as gross distortions in the resultant
Stern-Volmer plot can result from an inappropriate choice. In
general, short delay times (e.g. 0.02 ms) and long gating times
(e.g. 5 ms) were chosen to overcome or minimize these problems.
[0137] Sensitivity
[0138] The sensitivity of the films to oxygen was determined by
both intensity decay measurements and lifetime decay measurements.
The former was performed on the Perkin Elmer LS50B scanning
luminescence spectrometer and the latter were recorded using a
Nd/YAG Spectron Laser with an Applied Photophysics Laser Kinetic
spectrometer. Traces from laser excitation were recorded on a Gould
OS4072 digital storage oscilloscope and transferred to a computer
for kinetic analysis. Nitrogen/oxygen gas mixtures were generated
using a Signal Instruments gas blender.
[0139] The data were treated according to the following form of the
Stern-Volmer equation which, in general, was well obeyed.
I.sub.0/I=1+K.sub.sv%O.sub.2
[0140] where I.sub.0 and I are the emission Intensities in the
absence and presence of oxygen, K.sub.sv is the Stern-Volmer
constant and % O.sub.2 is the percentage oxygen present. Plots of
I.sub.0/I VS. % O.sub.2 yield the Stern-Volmer constant, K.sub.sv.
Another useful measure of the sensitivity of an oxygen sensor is
given by 1/K.sub.sv. This represents the % O.sub.2, required to
decrease the phosphorescence intensity, I, to a value of
I.sub.0/2.
[0141] Plasticizers
[0142] In many thin film sensors plasticizers are used to increase
the gas permeability of the polymer matrix. While most of the
measurements reported here were made on unplasticized films some
work with plasticized films is also reported. 1
[0143] The film formulation for the porphyrin/polystyrene film was
as follows:
[0144] 1 mg PdCPP in 2 ml THF
[0145] or 1 mg PtOEP in 200:I THF
[0146] or 1 mg PdOEP in 200:I THF
[0147] 5 cm.sup.3 20% wt/vol polystyrene (MW=180,000) in
dichloromethane
[0148] The indicator solution was added to the polymer solution and
stirred thoroughly. In the other polymer films the same procedure
was followed using cellulose acetate butyrate (CAB) (20% wt/vol in
acetone) and polymethylmethacrylate (PMMA) (30% wt/vol in
dichloromethane).
1TABLE 1 Spectral Data and Sensitivity of Porphyrin Containing
Films Intensity and time data K.sub.SV .tau. Indi- .lambda..sub.ex
.lambda..sub.em % 1/K.sub.SV (ms) .tau. (ms) cator Matrix (nm) (nm)
O.sub.2.sup.-1 R.sup.2 % O.sub.2 N.sub.2 5% O.sub.2 PdCPP CAB 392
663 I data 509 3.23 0.995 0.30 .tau. data 545 3.64 0.988 0.27 1.50
0.07 I data PS 392 663 1.91 0.999 0.52 .tau. data 509 2.11 0.981
0.47 0.7 0.06 545 I data PMMA 392 663 0.39 0.997 2.56 .tau. data
509 1.16 0.999 0.86 1.47 0.23 545 PtOEP CAB 535 644 I data 0.50
0.998 2.0 .tau. data 0.44 0.992 2.3 0.10 0.031 I data PS 535 644
0.40 0.999 2.5 .tau. data 0.32 0.999 3.1 0.09 0.04 I data PMMA 535
644 0.05 0.997 20 .tau. data 0.04 0.983 25 0.10 0.09 PdOEP CAB 546
670 I data 4.70 0.995 0.21 .tau. data 4.31 0.994 0.23 1.48 0.08 I
data PS 546 670 4.77 0.995 0.21 .tau. data 4.27 0.994 0.23 1.49
0.09 I data PMMA 546 670 0.41 0.989 2.44 .tau. data 0.44 0.992 2.30
1.51 --
[0149] The data in Table 1 show that there is good agreement
between the intensity and lifetime measurements made on the same
film. The data also shows that the palladium materials are
typically more sensitive to oxygen than the corresponding platinum
indicators. The data also demonstrate that the sensitivity can to
some extent be modulated by the permeability of the matrix.
[0150] Intensity based measurements were also made on a PtOEP/CAB
film at two different temperatures, 5.degree. C. and 23.degree. C.
These results are shown in Table 2.
2TABLE 2 Sensitivity of PtOEP/CAB Film at Different Temperatures
Temp. K.sub.SV 1/K.sub.SV (.degree. C.) % O.sub.2.sup.-1 R.sup.2 %
O.sub.2 23 0.52 0.998 1.92 5 0.46 0.997 2.17
[0151] These data show that there is very little effect on the
sensitivity between room temperature and refrigerated
conditions.
[0152] The effect of adding a plasticizer, tributyl phosphate to a
PtOEP/PMMA film was investigated. The effect of the level of
plasticizer on the film sensitivity is shown below in Table 3.
3TABLE 3 Effect of Plasticizer on the Sensitivity of PtOEP/PMMA
Films Plasticizer K.sub.SV 1/K.sub.SV (phr) % O.sub.2.sup.-1
R.sup.2 % O.sub.2 0 0.065 0.966 15.0 10 0.114 0.986 8.8 25 0.354
0.991 2.8 50 0.776 0.993 1.3 75 3.274 0.985 0.3
[0153] It is apparent from these results that substantial
alterations can be made to the sensitivity of a film by the
addition of a plasticizer. No substantial deviation from linear was
found in the Stern-Volmer plots due to the plasticizer
concentration.
[0154] Camphorquinone
[0155] Camphorquinone (CQ) is an .alpha.-diketone which exists in
two optically isomeric forms. The structure of the R-form is shown
below, though the sample used here is a mixture of the two
isomers.
[0156] Structure of Camphorquinone 2
[0157] The film formulation for the CQ/polystyrene film was as
follows:
[0158] 0.4 Camphorquinone
[0159] 10 cm.sup.3 20% wt/vol polystyrene (mwt. 180,000) in
dichloromethane.
[0160] The indicator was added directly as a solid to the polymer
solution and stirred thoroughly. In the other polymers the same
procedure was followed using cellulose acetate butyrate (CAB) (20%
wt/vol in acetone) and polymethylmethacrylate (PMMA) (30% wt/vol in
dichloromethane). The spectral and sensitivity data is summarized
for camphorquinone below in Table 4.
4TABLE 4 Spectral and Sensitivity Data of CQ Films Intensity Data
unless Otherwise Noted .tau. Matrix .lambda..sub.ex .lambda..sub.em
K.sub.SV R.sup.2 1/K.sub.SV .tau. (ms) (ms) CQ CAB 470 560 0.524
0.995 1.90 .tau. data 0.547 0.994 1.83 0.29 0.11 CQ PS 470 560
0.536 0.996 1.87 CQ PMMA 470 560 0.03 0.996 33.4
[0161] These data show that camphorquinone films have good oxygen
sensitivity.
[0162] Eryhrosin B
[0163] Erythrosin B is tetraiodo-substituted xanthene dye which is
available in two forms whose structures are shown below. Although
one is specifically designated "spirit-soluble" neither is
particularly soluble in water.
Structure of Erythrosine B
[0164] 3
[0165] Film Formulation
[0166] Two formulations were used in the present study. In its
capacity as an oxygen sensor erythrosin B has previously been
immobilized on resin beads which have then been packed into columns
or dispersed in silicone films. These beads are reported to be
sensitive to extremely low oxygen concentrations (0.0005%). In the
present study an attempt was made to reproduce this work and also
to disperse the dye directly into plastic films in order to try to
adjust the sensitivity to levels more suitable for our purposes.
The two formulations were as follows:
[0167] 1. Beads
[0168] 0.1 g Amberlite XAD-2 nonionic polymeric adsorbent
[0169] 4 cm.sup.3 1.times.10.sup.-5M erythrosin B in 90%
ethanol/10% 0.1M acetic acid/sodium acetate pH 6 buffer.
[0170] The resin was prepared by washing first with ethanol then
with water and then dried in an oven at 80 EC. 0.1 g of the resin
was immersed in 4 cm.sup.3 of the dye solution and left for 24
hours, stirring occasionally. The resultant bright pink beads were
filtered, washed thoroughly with double distilled water, dried at
40 EC for 12 hours and stored dry until use. These beads were
sprinkled onto a tacky polymer film (e.g. polystyrene) cast on a
glass slide.
[0171] 2. Films
[0172] 0.6 mg erythrosin B in 150 .mu.L acetone
[0173] 5 cm.sup.3 20% wt/vol polystyrene in dichloromethane
[0174] The indicator solution was added to the polymer solution and
stirred thoroughly. Films were then cast in the normal way.
Erythrosin B has an excitation wavelength at about 550 nm and an
emission wavelength at about 625 to 700 nm. The film showed a
luminescence spectrum in 100% nitrogen that was completely quenched
by 5% oxygen.
Example 1-2
[0175] Two oxygen scavenging films containing oxygen sensing
luminescent dyes were prepared by coextrusion and adhesive
lamination. The generalized structure was as follows:
5 PVDC coated 90% EVA PE PET Adhesive EVA 10% PtTPP MB EVA OSL heat
seal Film 1 0.56 mil -- 0.80 1.00 0.20 0.50 0.30 Film 2 0.56 mil --
0.80 1.00 0.20 0.50 0.30 Where: PVDC = polyvinylidene dichloride
EVA = ethylene/vinyl acetate copolymer PET = polyethylene
terephthalate MB = masterbatch PE = polyethylene
[0176] The Oxygen Scavenging Layer (OSL) comprised an ethylenically
unsaturated hydrocarbon resin with a cobalt salt catalyst and
photoinitiator. The PtTPP and PdTPP masterbatches contained 750 ppm
of each of the respective platinum or palladium
tetraphenylporphyrin indicators. Empty packages were formed on a
Multivac R230 equipped with a Cryovac Model 4104 (SIS) using either
Film 1 or Film 2 as top web and T6070B (from Cryovac Inc.) as the
bottom web. Samples were produced that were exposed to either 1 or
3 banks of UV lamps. Package speed was 8.4 cycles/min.,
corresponding to UV doses of approximately 400 or 1200 mJ/cm.sup.2.
Packages were flushed with 1.15-1.20% oxygen (balance nitrogen).
Total package volume was 838 cc.
[0177] Total headspace oxygen concentration was analyzed on a Mocon
PacCheck O.sub.2 analyzer. Residual oxygen levels of the four test
samples were measured at 0 h, 24 h, 72 h, and 96 h. Ratio of decay
of luminescence in the two indicators was measured at 0 h, 1 h, 24
h, and 72 h with an O.sub.2 analyzer that utilizes method 2
described earlier. Packages were first checked approximately 5 min
after exiting the machine (.about.7-8 min after triggering). If the
film was not activated and exposed to 20.6% O.sub.2 (atmospheric)
then the optical O.sub.2 analyzer would indicate a decay rate of 0.
If the film was exposed to 1% O.sub.2 the decay rate would be
between 400 and 500 for palladium and slightly higher for platinum.
The lower the oxygen concentration within the film, the higher the
decay rate will be. From experience, it is known that about 18
hours are required to reliably detect oxygen scavenging from the
headspace of this type of test package using a Mocon headspace
analyzer. The optical data is shown below in Table 5.
6TABLE 5 Average of Phosphorescent Decay Rate Ratios and Standard
Deviation for Samples 1 and 2. Film # of Banks Time RATE RATIOS
Sample On (hour) Avg. Std. Dev. 1 3 0 2752 56 1 3 1 3111 37 1 3 24
3207 18 1 3 72 3302 26 1 1 0 2702 34 1 1 1 2803 42 1 1 24 3213 5 1
1 72 3312 7 2 3 0 1509 45 2 3 1 1876 218 2 3 24 2246 90 2 3 72 2775
19 1 0 1455 48 2 1 1 1468 30 2 1 24 2284 26 2 1 72 2469 11
[0178] These data indicate that the oxygen sensing luminescent
compounds in the oxygen scavenging film are capable of detecting
the initiation of the scavenging reaction within 1 hour. In fact,
based on the expected ratio values for 1% oxygen, all samples
showed oxygen reduction at the indicator layer by the time the
first measurement was taken (.about.7-8 min. after triggering).
Furthermore, the indicators show different rates of increase for
the 1 bank versus the 3 bank treatment as expected. Higher UV doses
typically produce faster initial scavenging reactions.
Example 3
[0179] This example illustrates the use of a luminescent oxygen
sensing indicator (PdTPP) in a patch format. Patches were
constructed from an extruded multilayer film, which contained 2000
ppm of PdTPP in a 0.36 mil PE surface layer, and a metallized PET
label stock with a pressure sensitive adhesive. The dimensions of
the oxygen-sensing portion of the patch was 0.5.times.0.5 inches,
the dimensions of the entire patch was 1.5.times.1.5 inches. The
patch was applied to commercially available oxygen scavenging film
(OS 1000.TM., Cryovac Inc.) that had been triggered as described
above (see FIG. 15). Various UV doses were accomplished by varying
the machine speed and the number of light banks as shown in Table
6. Control packages were also prepared using a standard
non-scavenging, oxygen barrier commercial top web, T6230B available
from Cryovac Inc.
7TABLE 6 Treatments Tested Machine Gas # Light Speed Approximate
Cumulative Flush Top Web Banks (cpm) Dose (mJ/cm.sup.2) (% O.sub.2)
OS 1000 1 9 400 0.5% OS 1000 1 7 600 0.5% OS 1000 2 9 800 0.5% OS
1000 4 10 1200 0.5% OS 1000 4 7 1600 0.5% T6230B 4 7 1600 2.0%
[0180] The decay ratio of the palladium TPP luminescence was
measured at 0 min (immediately after packaging--several minutes
after triggering), 1 h, 1 h 40 min, 4 h, and 6 h min with an
optical analyzer that utilizes method 2 described earlier. The
average luminescence decay ratios
(Luminescence.sub.T1/Luminescence.sub.T2) are shown in Table 7 for
the various doses.
8TABLE 7 Average Luminescence Decay Rate Ratios for OS1000 Dosed
with Various UV Intensities. UV Dose (mJ/cm.sup.2) Time 400 600 800
1200 1600 0 min 0 0 2011 1451 1888 40 min 0 0 1651 1324 1905 60 min
0 0 1518 1422 1973 100 min 0 0 1447 1651 1848 240 min 0 0 1976 1605
1977 375 min 0 0 2172 1809 2104
[0181] Residual headspace oxygen was analyzed using a Mocon
PacCheck O.sub.2 analyzer on day 0, 2, 5, and 7. From this data,
average scavenging rates were calculated at 0,1, 2, 5 and 7 days
after triggering and are tabulated in Table 8. The rates are
calculated with the following formula: total cc O.sub.2 scavenged
at n days)/(scavenging film area.multidot.n days), where n is the
number of days since triggering the sample.
9TABLE 8 Average Scavenging Rate of OS 1000 Packages Dosed with
Various UV Intensities UV Dose Average Scavenging Rate (cc
O.sub.2/(m.sup.2 .multidot. day)) (mJ/cm.sup.2) Day 0 Day 1 Day 2
Day 5 Day 7 400 0 0 0 0 0 600 0 0 0 0 0 800 0 50.1 36.4 18.4 13.4
1200 0 61.2 38.9 18.5 13.5 1600 0 65.2 39.9 18.5 13.3
[0182] As can be seen from the data, packages given a UV dose of
400 or 600 mJ/cm.sup.2 did not scavenge oxygen from the package
headspace up to 1 week after treatment. Packages given a UV dose of
800 mJ/cm.sup.2 or higher did begin to scavenge oxygen from the
headspace at 24 hours. The data provided by the oxygen sensing
labels clearly indicates that as well; however, the label provides
this information essentially immediately after the packaging
(within several minutes of the triggering step). This example
clearly demonstrates the utility of an oxygen-sensing label in
making a rapid determination of the state of activation of an
oxygen-scavenging package.
[0183] The T6230B standard laminate film (control), dosed at 1600
mJ/cm.sup.2 and flushed with 2.0% oxygen yielded scavenging rates
of zero, and likewise no decay rate ratios were observed. The
sealant layer of T6230B is similar to that of OS films. This
illustrates that a false positive reading due to the UV treatment
alone is unlikely.
[0184] The oxygen indicator can comprise two or more luminescent
compounds, each having different threshold levels of luminescence.
The exposure of the excitation frequency can administered in the
form of a pulse.
[0185] The foregoing specification and examples are intended as
exemplary only. Other embodiments of the invention will be apparent
to those skilled in the art from consideration of the specification
and practice of the invention disclosed herein. For example,
although the drawings feature an oxygen barrier layer as a surface
layer of a packaging film, many films can be made in which the
oxygen barrier layer will be an internal layer flanked on both
major surfaces by other layers. Thus, the invention can be
beneficially used in connection with an article such as a
multilayer film, e.g. FS.TM. film made by Cryovac, Inc. for the
packaging of fluid or pumpable foods in pouches made on vertical
form/fill/seal apparatus. A film of this type has the general
structure:
[0186] sealant/tie/nylon/EVOH/nylon/tie/sealant
[0187] where the sealant comprise any of those disclosed herein;
the tie layers are anhydride-modified polymeric olefinic or amidic
adhesives; the nylon layers comprise any polyamide or copolyamide;
and the EVOH (ethylene/vinyl alcohol copolymer) layer functions as
the oxygen barrier layer. An oxygen scavenger can be suitably
included as a layer within the above film structure, and an oxygen
indicator layer can likewise be included within the structure
itself, or in an adjacent patch as disclosed herein, preferably
accompanied by a discrete oxygen barrier layer in the patch.
[0188] Regardless of the film structure, the oxygen scavenger and
oxygen indicator should be positioned such that they are shielded
from environmental oxygen by discrete oxygen barrier layers or
coatings, bearing in mind that in some cases the oxygen scavenger
itself, or even lateral edges of the oxygen indicator, can function
as one or both of these oxygen barrier layers.
* * * * *