U.S. patent application number 11/083491 was filed with the patent office on 2005-09-22 for multilayer sheet of liner for packaging hot foods.
Invention is credited to Chambers, Jeffrey Allen, Visioli, Donna Lynn.
Application Number | 20050208243 11/083491 |
Document ID | / |
Family ID | 34962831 |
Filed Date | 2005-09-22 |
United States Patent
Application |
20050208243 |
Kind Code |
A1 |
Chambers, Jeffrey Allen ; et
al. |
September 22, 2005 |
Multilayer sheet of liner for packaging hot foods
Abstract
The present invention discloses a multilayer sheet for packaging
hot foods especially useful in the "take-out" market. The
multilayer sheet has two, and optionally three, layers. The first
inner layer comprises a water-wicking material, preferably a
nonwoven with a moisture-vapor transmission rate (MVTR) of at least
about 20,000 g/m.sup.2-day and a hydrostatic head pressure of less
than about 5 cm H.sub.2O. The second layer comprises a somewhat
absorbent and highly-thermally insulating material. The multilayer
sheet may be used in various packaging embodiments, e.g., as a
wrap, pouch or bag, etc. The multilayer sheet maintains
freshly-cooked food quality by improving heat retention and
moisture control.
Inventors: |
Chambers, Jeffrey Allen;
(Hockessin, DE) ; Visioli, Donna Lynn; (Lower
Gwynedd, PA) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
34962831 |
Appl. No.: |
11/083491 |
Filed: |
March 18, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60554585 |
Mar 19, 2004 |
|
|
|
Current U.S.
Class: |
428/36.1 |
Current CPC
Class: |
B32B 5/022 20130101;
B32B 2307/724 20130101; B32B 2262/067 20130101; Y10T 428/1362
20150115; B32B 5/26 20130101; B32B 27/32 20130101; B32B 2439/70
20130101; B32B 7/02 20130101; B32B 2307/306 20130101; B32B 27/36
20130101; B32B 7/12 20130101; B32B 2262/0276 20130101; B32B
2307/726 20130101; B65D 65/42 20130101; B32B 2262/14 20130101 |
Class at
Publication: |
428/036.1 |
International
Class: |
B65D 001/00 |
Claims
1. A article comprising at least two layers including a first
layer, a second layer, and optionally a third layer wherein the
article is a multilayer sheet or a liner; the first layer comprises
or is produced from a water-wicking material; the second layer
comprises or is produced from an absorbent and insulating material;
the third layer comprises or is produced from a structural
material; and the article optionally comprises an additive
including a desiccant, thermal and ultraviolet (UV) stabilizer, UV
absorber, antistatic agent, processing aid, fluorescent whitening
agent, pigment, lubricant, or combinations of two or more
thereof.
2. The article of claim 1 wherein the first layer has a
moisture-vapor transmission rate of at least about 20,000
g/m.sup.2-day.
3. The article of claim 1 wherein the first layer has a
moisture-vapor transmission rate of at least about 150,000
g/m.sup.2-day.
4. The article of claim 1 wherein the first layer has a hydrostatic
head pressure of less than about 5 cm H.sub.2O.
5. The article of claim 4 wherein the first layer has a
moisture-vapor transmission rate of at least about 20,000
g/m.sup.2-day and a moisture-vapor transmission rate of at least
about 170,000 g/m.sup.2-day.
6. The article of claim 5 wherein the first layer is, or is
produced from, a nonwoven.
7. The article of claim 6 wherein the nonwoven comprises a
spunlaced fabric comprising a mixture of fibers of poly(ethylene
terephthalate) and wood pulp.
8. The article of claim 1 wherein the second layer has a thermal
resistance, as measured in units of insulation, of at least about
0.0077 m.sup.2.K/W (0.05 CLO).
9. The article of claim 7 wherein the second layer has a thermal
resistance, as measured in units of insulation, of at least about
0.0077 m.sup.2.K/W (0.05 CLO).
10. The article of claim 8 wherein the second layer comprises
fiberfill batt, melt-blown fibers, foam, knit material, felt, or
combinations of two or more thereof.
11. The article of claim 9 wherein the second layer comprises
fiberfill batt, melt-blown fibers, foam, knit material, felt, or
combinations of two or more thereof.
12. The article of claim 9 wherein the second layer comprises the
fiberfill batt, which comprises or is produced from poly(ethylene
terephthalate).
13. The article of claim 12 wherein the second layer ranges in
thickness from about 10 mils to about 500 mils.
14. The article of claim 13 comprising the third layer and the
structural material is oriented polypropylene, oriented polyester,
or combinations thereof.
15. The article of claim 14 wherein the first layer is a nonwoven
comprising a spunlaced fabric having a moisture-vapor transmission
rate of at least about 20,000 g/m.sup.2-day and a hydrostatic head
pressure of less than about 5 cm H.sub.2O, and the second layer has
a thermal resistance of at least about 0.0077 m.sup.2.K/W (0.05
CLO).
16. The article of claim 15 wherein the spunlaced fabric comprises
a mixture of fibers of poly(ethylene terephthalate) and wood pulp,
and the second layer is fiberfill batt.
17. A packaging wrap, bag, or pouch comprising or produced from a
multilayer sheet wherein the multilayer sheet is as recited in
claim 1.
18. The packaging wrap, bag, or pouch of claim 17 wherein the
multilayer sheet is as recited in claim 16.
19. A process comprising laminating, by contacting under suitable
pressure and heat, a first layer to a second layer wherein the
first layer and the second layer are each as recited in claim
1.
20. The process of claim 19 wherein the first layer and the second
layer are each as recited in claim 15.
21. The process of claim 19 comprising interposing a layer of a
thermoplastic adhesive scrim between the first layer and the second
layer, and laminating the first layer to the second layer.
22. The process of claim 21 wherein the first layer and the second
layer are each as recited in claim 15.
23. The process of claim 21 further comprising, prior to
laminating, interposing a layer of a thermoplastic adhesive scrim
between the second layer and a third layer, which is as recited in
claim 14.
Description
[0001] This application claims the benefit of U.S. provisional
application Ser. No. 60/554585, filed Mar. 19, 2004, the entire
description of which is incorporated herein by reference.
[0002] The invention relates to a multilayer sheet or liner for use
in wrapping and/or packaging foods such as hot foods.
BACKGROUND OF THE INVENTION
[0003] Composite or multilayer sheets or wraps have long been used
for packaging foods. Such sheets aim to keep freshly-made food hot
from the time it is prepared until it is consumed. Current
commercial sheets or wraps include polyethylene-coated paper or
tissue, hot-melt coated paper, foil/tissue laminations,
tissue/aluminum foil/polyethylene film, dry wax, etc. These wrap
materials are of high moisture resistance to maximize heat
retention. Liquid water from condensation is often still left in
contact with food, which can leave the food undesirably soggy.
[0004] Most of the known sheets or wraps involve an absorbent layer
and an impermeable layer. See, for example, U.S. Pat. No.
5,128,182; U.S. Pat. No. 5,310,587; and Japanese Patent Application
11094260. The resulting food quality of using these wraps and
sheets is less than optimum. Thus, there exists a need to improve
packaging for hot foods to maintain freshly-cooked characteristics,
such as by improving heat retention and moisture control in the
package, specially for packaging freshly-cooked foods for the
"take-out" market.
SUMMARY OF THE INVENTION
[0005] The invention includes an article comprising or produced
from at least two layers including a first layer, a second layer,
and optionally a third layer wherein the article is a multilayer
sheet or a liner; the first layer comprises or is produced from a
water-wicking material; the second layer comprises or is produced
from an absorbent and insulating material; and the third layer
comprises or is produced from a structural material.
[0006] The invention also includes a process for making the
multilayer sheet, which can comprise (1) interposing a layer of
thermoplastic adhesive scrim between the first inner layer and
second layer and laminating the first inner layer to the second
layer under suitable heat and pressure; or (2) coating the first
inner layer with a suitable pattern-applied adhesive on one side to
produce a coated side and contacting the coated side with the
second layer prior to lamination.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional view of a specific embodiment of
the multilayer sheet illustrating a fiberfill batt as the
insulating and absorbent material of the second layer, positioned
between and adhesively bonded to a film, as the structural material
of the outermost layer, and a water-wicking material, as the inner
layer, via two separate adhesive layers.
[0008] FIG. 2 is a cross-sectional view of another embodiment of
the multilayer sheet illustrating a fiberfill batt as the
insulating and absorbent material of the second layer, again
positioned between a film, as the structural material of the
outermost layer, and a water-wicking material, as the inner layer,
employing an adhesive layer between the fiberfill batt and inner
water-wicking material.
DETAILED DESCRIPTION OF THE INVENTION
[0009] A multilayer sheet or liner for packaging hot foods
comprises a first inner layer comprising a water-wicking material
with a second layer comprising an absorbent and highly-thermally
insulating material. The multilayer sheet provides improved
moisture control while maintaining heat retention. Freshly-cooked
food quality can be maintained (e.g., "crispness" especially in
fried or baked foods) for time periods of at least about 30 minutes
under ambient conditions, and the food quality is judged to be
"excellent".
[0010] The first inner layer of the multilayer sheet or linercan
comprise a water-wicking material. This layer is the innermost
layer of the sheet, and is the layer in direct contact with the hot
food or interior of the package containing the hot food. The
water-wicking capability prevents the build-up of moisture in the
package as the hot food cools, thereby avoiding undesirably soggy
food.
[0011] The first layer facilitates the passage of water and
moisture vapor (i.e., wicks) from the interior of the package to
the second layer of the multilayer sheet. To do so, the
water-wicking material can have a non-condensable surface and
preferably demonstrate a moisture-vapor transmission rate of at
least about 20,000 g/m.sup.2/day, at least about 100,000
g/m.sup.2/day at least about 150,000 g/m.sup.2/day, or at least
about 170,000 g/m.sup.2/day, as tested by ASTM D-6701 as well as a
hydrostatic head pressure of less than about 5 cm H.sub.2O or less
than about 2 cm H.sub.2O, as tested under AATCC Method
127-1989.
[0012] The first layer preferably comprises a nonwoven fabric,
preferably a "spunlaced" or "hydroentangled" fabric. The term
"spunlaced fabric" or "hydroentangled fabric" refers to a nonwoven
fabric that is produced by entangling fibers in the web to provide
a strong fabric that is free of binders. Such spunlaced fabrics can
be prepared by supporting a nonwoven web of fibers on a porous
support such as a mesh screen and passing the supported web
underneath water jets, such as in a hydraulic needling process. The
fibers can be entangled in a repeating pattern.
[0013] The nonwoven fabric can be made out of fibers such as
polyester, nylon 6,6, or, preferably, a combination of wood pulp
and staple poly(ethylene terephthalate) fibers. Such fabrics are
available from E. I. du Pont de Nemours and Company, Wilmington,
Del. (DuPont) under the trade name Sontara.RTM.. The thickness of
these fabrics can vary, generally a thickness in the range of about
10-50 mils (0.01 to 0.05 inches).
[0014] In preparing such fabrics, the starting nonwoven layer
comprises a thin, supple web of staple fibers, continuous
filaments, plexifilamentary strands or the like. The fibers may be
natural fibers, e.g., cellulosic, or may be formed from synthetic
organic polymers. Preferably the fibers are not bonded to each
other. Suitable starting nonwoven fibrous layers can be selected
based on the desired end-use for the nonwoven fabric that is to be
produced. For example the starting nonwoven fibrous layer is
preferably substantially not bonded, and composed of fibers that
inherently can absorb or wick liquid, e.g., polyester and wood
pulp, or rayon and wood pulp.
[0015] The first layer may also comprise paper, preferably with
sufficient porosity to function as a water-wicking material as
described herein.
[0016] The second layer comprising an absorbent and insulating
material. This layer may be highly thermally insulating and
somewhat absorbent. The high thermal insulating capability
effectively retains heat, slows condensation and thereby reduces
liquid moisture formation within a given package. At the same time,
any condensate that is produced is wicked through the first layer
and absorbed by the second layer. These combined characteristics of
high thermal insulating capability and some absorbency can be key
to preventing the build-up of condensate in the package and
avoiding undesirably soggy food.
[0017] Though not bound by any particular theory, it appears that
the multilayer sheet or liner may work successfully because the
absorbent and insulating material in the second layer aims to keep
the temperature within a given package above the dew point,
preventing condensation from forming within the package. If the
temperature falls just below the dew point, the water-wicking
material of the first layer wicks the liquid from the package
interior to the second layer. Hence, the interior of the package is
warm but free of liquid moisture that can cause crisp food to turn
soggy.
[0018] The second layer preferably has a thermal resistance, as
measured in units of insulation, or CLO, of at least about 0.05, or
at least about 0.1, or about 0.1 to about 2.5, or 0.1 to 0.5.
[0019] The CLO unit is defined as a unit of thermal resistance of a
garment. The SI unit of thermal resistance is the square-meter
kelvin per watt (m.sup.2.multidot.K/W) (See "Textile Terms and
Definitions", Tenth Edition, The Textile Institute, (1995), pp. 66,
350). Thus, the range of thermal resistance in SI units of the
absorbent and insulating material of the present invention is at
least about 0.0077, preferably at least about 0.0154
m.sup.2.multidot.K/W. Although CLO is defined in terms of a
garment, this measurement can be used to describe the thermal
resistance of any textile system, and is used herein to describe
the thermal resistance of the absorbent and insulating material of
the present invention. CLO values depend on the material used for
the layer and its thickness.
[0020] For the "take-out" food packaging market, the level of
thermal resistance preferably is high enough to maintain the
temperature within the package above the dew point for at least
about 30 minutes when the package is exposed to ambient conditions.
It is expected that the water-wicking material of the first layer
also contributes some thermal resistance.
[0021] The second layer also has some absorbency, though high
levels may not be necessary due to the high efficiency of the
insulating capability, and the resulting minimization of
condensation formation. The absorbency, in terms of water pressure
resistance, can be less than about 50 cm H.sub.2O.
[0022] The second layer may comprise an organic thermoplastic
fiber-based material comprising, e.g., polyester, polyethylene or
polypropylene. In a preferred embodiment, the thermal insulating
layer is a fiberfill batt comprising polyester. A fiberfill batt
sold as Thermolite.RTM. Active Original by DuPont is especially
suitable for use. The fiberfill batt useful for the present
invention generally has an areal weight in the range of 10
gm/m.sup.2 to 200 gm/m.sup.2, and a bulk density of less than 0.3
gm/cm.sup.3. Alternatively, the thermal insulating layer may
comprise melt-blown fibers, such as melt-blown polyolefins, sold as
THINSULATE.RTM., by 3M.
[0023] Many other variations of material for the absorbent and
insulating material can be used. For instance, the absorbent and
insulating material may possibly comprise an inorganic
thermoplastic fiber-based material comprising glass wool,
borosilicate glass or rockwool.
[0024] Alternatively, the absorbent and insulating material may
comprise a knit fabric, made, for example from a tetrachannel or
scalloped oval fiber, sold under the trademark Coolmax.RTM. by
DuPont. Or the absorbent and insulating material may be a woven or
fleece material. The absorbent and insulating material could also
comprise some sort of nonwoven, such as felt, or a highloft
nonwoven or needled nonwoven fabric.
[0025] The thickness of the second layer may vary and depend on the
desired level of insulating capability, i.e., thermal resistance.
As more thermal resistance is required, the thickness of the layer
increases. Generally, the thickness can fall in the range of about
10 to about 500 mils, or about 10 to about 200 mils, or about 10 to
about 50 mils.
[0026] The multilayer sheet or liner may comprise an optional
third, outermost layer comprising a structural material. Use of the
third layer may be helpful for certain considerations in designing
a practical package (e.g., impermeability, strength, flexibility),
but may be entirely unnecessary in other embodiments (e.g., as a
package liner as discussed below). Hence, the optional nature of
the layer.
[0027] Generally, the structural material may comprise film, foil,
paper and/or fabric. A film may be made of a thermoplastic material
comprising, e.g., polyester, polyethylene or polypropylene. For
many uses where impermeability and flexibility are desired, films
of oriented polypropylene or oriented polyester are especially
preferred. Films of oriented polyester are available from DuPont
Teijin Films under the trade names Mylar.RTM. and Melinex.RTM..
[0028] The choice of material for the optional third layer may
depend on how the multilayer sheet or liner is used in the
packaging, e.g., what type of package will be used and what type of
food product will be packaged. For example, if the desired
packaging is a bag or pouch, then paper, foil or a film may be
useful. If the multilayer sheet or liner of the invention herein is
used as a liner in a package, then it may be helpful to have the
structural material contain an adhesive layer to adhere the
multilayer sheet or liner to the inside of the package. A peelable
backing can also be useful.
[0029] One example of a film that is suitable for use as a
structural material is Melinex.RTM.854, commercially available from
DuPont Teijin Films of Wilmington, Del. Melinex.RTM.854 is a
multilayered film, one layer being heat-sealable, allowing for
heat-sealing between the second and third layers. Melinex.RTM.854
is a 120 gauge (0.0012 inch, or 0.0030 cm.) thick co-extruded
biaxially oriented polyester film. The first layer of the film is
made from a standard polyester homopolymer, intrinsic viscosity of
about 0.590, containing 2500 ppm of inorganic slip additive
particles. This layer comprises approximately 65% of the total film
thickness. A co-polyester resin comprised of 18 weight %
isophthalic acid, intrinsic viscosity of about 0.635, containing
2300 ppm inorganic slip additive particles, is co-extruded to form
the heat-sealable layer and comprises 35% of the total film
thickness (15-40% preferred). The surface of the first layer
opposite the heat sealable layer is coated in-line by a gravure
coater (during the film manufacturing process) with a print primer
coating based on an aqueous polyester dispersion at a dry
coat-weight of 0.03 g/m.sup.2.
[0030] The multilayer sheet or liner can further comprise an
additive. The additive can be a desiccant such as silica, thermal
and ultraviolet (UV) stabilizers, UV absorbers, antistatic agents,
processing aids, fluorescent whitening agents, pigments,
lubricants, etc. These additives may be present in the compositions
used in this invention in quantities that are generally from 0.01
to 20, or 0.1 to 15, weight.
[0031] This layer comprises approximately 65% of the total film
thickness. A co-polyester resin comprised of 18 weight %
isophthalic acid, intrinsic viscosity of about 0.635, containing
2300 ppm inorganic slip additive particles, is co-extruded to form
the heat-sealable layer and comprises 35% of the total film
thickness (15-40% preferred).
[0032] The structural material may be modified on the surface
facing away from the second layer to facilitate printing thereon by
a corona discharge treatment. In addition, surface modification
(i.e., coating or corona discharge treatment) may be used to
facilitate bonding to another surface with an adhesive layer, as
mentioned above. In order to bond to another surface, an adhesive
primer layer is applied to the untreated surface of the structural
material or to the corona discharge treated surface. This adhesive
primer layer is pressure sensitive to enable application of the
multilayer sheet or liner to a container to function as a package
liner.
[0033] Generally, the layers of the multilayer sheet or liner of
the invention may be joined by various methods known in the art,
one such method being lamination, i.e., uniting layers of material
by an adhesive or other means. The adhesive can be applied in
various ways, e.g., pattern-application or spray application, or
through the use of an adhesive layer, e.g., a thermoplastic
adhesive scrim, which is a web-like layer of adhesive. The use of
pattern-application adhesive or an adhesive scrim achieves a
similar effect within the multilayer sheet or liner of the
invention herein, i.e., there is no complete barrier to moisture
transport due to the abundance of free space or holes within the
adhesive layer which allows moisture to flow through. This is
especially desirable when laminating the first and second layers of
the invention herein. Other means of joining the layers may include
pinpoint embossing, needling and quilting, among others known to
those of skill in the art. These methods may allow for the free
transport of moisture between layers.
[0034] Or the adhesive may be a heat-sealable coating on one of the
layers to be joined, e.g., on the structural material as discussed
above. The multilayer sheet or liner may optionally be sealed, such
as with a hot knife, at its edges so that fluid cannot penetrate
the edges.
[0035] A flexible, impermeable layer may be used to prevent leakage
of moisture from the food to the consumer. The multilayer sheet or
liner can be used in sheet form to act as liner within a package
(e.g., take-out tray, box, bag, etc.), or even on the exterior of a
package (e.g., covering perforations in a take-out tray lid).
[0036] The multilayer sheet or liner of the invention herein may be
used in various ways to package hot foods. One specific embodiment
is simply to use the multilayer sheet or liner in sheet form as a
packaging wrap to directly wrap hot foods.
[0037] In another embodiment, the multilayer sheet or liner may be
formed into a pouch or bag for wrapping hot foods, e.g., hot
sandwiches. The pouches or bags may be manufactured according to
any well-known method. One skilled in the art can recognize that a
"pouch" means an enclosure sealed on at least two of four sides,
though generally sealed on three of four sides with the fourth side
being an opening. A pouch is typically made from a flat web of film
by forming a tubular film therefrom with a longitudinal seal and
subsequently flattening the tubular film at a first position and
transversely heat-sealing said tubular film at the flattened
position. A "bag" may be a pouch, but can also include a "stand-up
pouch", similar to the commonly-known paper lunch bag, comprising
four sides and a rectangular bottom opposite an opening.
[0038] After inserting the hot food into a pouch or bag of the
invention herein, the pouch or bag can be sealed or closed in
various ways known to those of skill in the art. The closing means
may be mechanical, such as flaps or tabs that can be folded over
and/or tucked in; and/or adhesive, such as pressure sensitive
adhesive, among others.
[0039] In these various packaging embodiments, it may be helpful to
use the optional third layer. For example, a flexible, impermeable
layer may be chosen to prevent leakage of moisture from the food to
the consumer. However, when the multilayer sheet or liner is used
in sheet form to act as liner within a package (e.g., take-out
tray, box, bag, etc.), or even possibly on the exterior of a
package (e.g., covering perforations in a take-out tray lid), then
the third optional layer would not be absolutely necessary. As
demonstrated in the Examples, significant improvement in food
temperature and food quality can be attained by affixing the liner
to the inside, top of a package. It is possible that extending the
duration of desired temperature and moisture levels within the
package could also be attained by affixing the liner to other areas
within a package, such as the inside, bottom, of the package.
[0040] There is provided a method for making a multilayer sheet.
The method involves the step of laminating a first inner layer to a
second inner layer under suitable pressure and heat. The suitable
amount of pressure and heat may depend upon the type of adhesive
method chosen. Suitable adhesives may be activated by chemical
reaction, or be activated by heat, i.e. heat-sealable. Depending on
the materials chosen for the first and second layers, other methods
known in the art for laminating the layers may also be used, e.g.,
pinpoint embossing, as disclosed above.
[0041] Pressure may be useful when laminating two layers to
facilitate even bonding across the layers, at least enough to
ensure contact between the two layers to be joined, e.g., for
adhesives that are activated by chemical reaction. The application
of heat may be necessary for heat-activated adhesives, such as the
thermoplastic adhesive scrim described in Examples 1 and 2.
[0042] In one embodiment of the method of the invention, the first
inner layer may be coated with a suitable pattern-applied adhesive
on one side, which is the side placed in contact with the second
layer prior to lamination. In another embodiment, a thermoplastic
adhesive scrim is interposed between the first inner layer and
second layer prior to lamination. These methods may be used to join
the second layer to an optional third layer, also. As discussed
above, many other lamination methods known in the art could be
suitable for joining the first and second layers, as well as for
joining the second layer to an optional third layer.
[0043] The first inner layer, second layer and optional third layer
are the same as those disclosed above.
[0044] The present invention is illustrated by the following
examples, which are not to limit the scope of the invention.
[0045] Thermal Resistance--CLO Measurement
[0046] For measurement of insulating capability, CLO was measured
on a "Thermolabo II", which is an instrument with a refrigerated
bath, commercially available from Kato Tekko Co. L.T.D., of Kato
Japan, and the bath is available from Allied Fisher Scientific of
Pittsburgh, Penn. Lab conditions were 21.degree. C. and 65%
relative humidity. Each sample was a one-piece sample measuring
10.5 cm.times.10.5 cm.
[0047] The thickness of the sample (in inches) at 6 gm/cm.sup.2 was
determined using a Frazier Compressometer, commercially available
from Frazier Precision Instrument Company, Inc., of Gaithersburg,
Md. To measure thickness at 6 g/cm.sup.2, the following formula was
used to set PSI (pounds per square inch) (kilograms per square
centimeter) on the dial: (6.4516 cm.sup.2/in.sup.2) (6 g/cm.sup.2)
/453.6 g=0.8532 lb/in.sup.2.
[0048] A reading of 0.8532 on the Frazier Compressometer
Calibration Chart (1 in., or 2.54 cm. diameter presser foot) showed
that by setting the top dial to 3.5 psi (0.2 kilograms per square
centimeter), thickness at 6 g/cm.sup.2 was measured.
[0049] The Thermolabo II instrument was then calibrated. The
temperature sensor box (BT box) was then set to 10.degree. C. above
room temperature. The BT box measured 3.3 inch .times.3.3 inch (8.4
cm.times.8.4 cm). A heat plate measuring 2".times.2" was in the
center of the box, and was surrounded by styrofoam. Room
temperature water was circulated through a metal water box to
maintain a constant temperature. A sample was placed on the water
box, and the BT box was placed on the sample. The amount of energy
(in watts) required for the BT box to maintain its temperature for
one minute was recorded. The sample was tested three times, and the
following calculations were performed: 1 Heat Conductivity ( W /
cm.degree. C . ) = ( W ) ( D .times. 2.54 ) ( A ) ( T )
[0050] where W=Watts and D=Thickness of sample measured in inches
at 6 g/cm.sup.2. (6 g/cm.sup.2 was used because the weight of the
BT box is 150 g, the area of the heat plate on the BT box was 25
cm.sup.2). Multiplying the thickness by 2.54 converted it to
centimeters.
[0051] A=Area of BT Plate (25 cm)
[0052] .DELTA.T=10.degree. C.
[0053] CLO=Thickness.times.0.00164/Heat Conductivity
[0054] The value of 0.00164 was a combined factor including the
correction of 2.54 (correcting thickness from inches to
centimeters) times the correction factor of 0.0006461 to convert
thermal resistance in cm.sup.2.times..degree. C./Watts. To convert
heat conductivity to resistance, conductivity was put in the
denominator of the equation.
EXAMPLE 1
Preparation of Multilayer Sheet
[0055] A multilayer sheet or liner for hot food packaging was made
according to the process described above and as illustrated in FIG.
1 wherein the first layer, 1, is a water-wicking material, second
layer, 2, is an absorbent and insulating material, and a third
layer, 3, is a structural layer. In this example, interposed
between these layers are porous, thermoplastic adhesive scrims, 4.
These adhesive scrims, 4, are constructed of polyester materials
that are spunlaced. They provide a web-like layer, with an
abundance of holes, through which water vapor or condensed water
can easily pass through. These layers were bonded together by
thermal lamination means on a tunnel laminator with a calendar
roll, such as the one provided by Inta-Roto Machine Company of
Richmond, Va. The adhesive layers, 4, were activated at
temperatures 240-350.degree. F. (116-177 C).
[0056] In this example the structural layer, 1, was a film of the
type sold by DuPont-Teijin under the tradename Mylar.RTM.. The film
was 1.2 mils (0.0012 inch or 0.0030 cm) thick. The absorbent and
insulating material, 2, was a fiberfill batt of the type sold by
DuPont under the trademark Thermolite.RTM. Active Original. The
fiberfill batt, 2, had an areal weight of 80 g/m.sup.2 at a
specified thickness of 0.25 inch (0.63 cm) or a bulk density of
0.013 g/cm.sup.3. The water-wicking material, 3, was a nonwoven
fabric available from DuPont under the trademark Sontara.RTM.. The
Sontara.RTM. comprised hydroentangled, white fibers (45%
polyester/55% wood pulp), having an areal weight of 68
grams/m.sup.2 and thickness of 13 mils (0.013 in or 0.033 cm). The
adhesive webs were of the type sold by Bostik Findley, Inc., and
were about 8-10 mils (0.008 to 0.01 inches) thick. (The thickness
varied depending on how much pressure was applied to the web during
measuring.)
EXAMPLE 2
Preparation of Multilayer Sheet:Bicomponent Third Layer
[0057] A multilayer sheet or liner for hot food packaging was made
according to the process described above and as illustrated in FIG.
2 wherein the first layer, 1, was a water-wicking material, second
layer, 2, was an absorbent and insulating material, and a third
layer, 3, was a structural layer. In this example, the structural
layer, 1, was a bicomponent film of polyester and a heat-sealable
layer. The heat-sealable layer acts as the adhesive required to
laminate the structural layer to the absorbing and insulating
layer. An adhesive scrim, 4, as described in Example 1 (above) was
used to adhere the absorbent and insulation layer, 1, to the
water-wicking nonwoven layer, 2. These layers were bonded together
by thermal lamination means on a tunnel laminator with a calendar
roll, such as the one provided by Inta-Roto Machine Company of
Richmond, Va. The adhesive layers were activated at temperatures
between 240 and 350.degree. F. (116-177 C).
[0058] In this example the structural film layer, 1, was of the
type sold by DuPont Teijin Films of Wilmington, Del, under the
tradename Mylar.RTM. OL and was a biaxially oriented PET film
having a heat-sealable layer. In this embodiment, the film was 1.5
mils (0.0015 inch or 0.00375 cm) thick. The composition of the
heat-sealable layer was an isophthalic acid-base copolyester and
comprised 10-50% of the thickness of the total film thickness;
15-30% was preferred. The absorbing and insulating material, 2, was
a fiberfill batt of the type sold by E. I. du Pont de Nemours and
Company under the trademark Thermolite.RTM. Active Original. The
fiberfill batt had an areal weight of 80 gm/m.sup.2 at a specified
thickness of 0.25 inch (0.63 cm) or a bulk density of 0.013
gm/cm.sup.3. The water-wicking layer, 3, was a nonwoven fabric
available from E. I. du Pont de Nemours and Company under the
trademark Sontara.RTM.. The Sontara.RTM. used in this example
comprised hydroentangled, white fibers (45% polyester/55% wood
pulp), having an areal weight of 68 grams/m.sup.2 and thickness of
13 mils (0.013 in or 0.033 cm). The adhesive webs were of the type
sold by Bostik Findley, Inc., and were about 8-10 mils (0.008 to
0.01 inches) thick. (The thickness varied depending on how much
pressure was applied to the web during measuring.)
EXAMPLE 3
Chicken Nuggets--Insulated v. Un-insulated trays
[0059] Using a small-scale deep fryer, two portions of chicken
nuggets were produced to test the effectiveness of the multilayer
sheet or liner in packaging for heat retention with moisture
control. The deep fryer was filled with vegetable oil and set to
340.degree. F. A batch consisting of 18 frozen "Banquet" brand
chicken nuggets was placed into the hot oil for 4 minutes. After
cooking, the hot nuggets were allowed to drain for 15 seconds.
After draining, the nuggets were quickly placed into a "take
out"-style, polyester (PET) tray, typically available in
supermarkets or restaurants for packaging fresh, hot foods.
[0060] The PET tray comprised a bottom tray reservoir portion and a
top tray or lid, similar in size and shape to the bottom tray. The
lid fitted over the bottom portion to generally seal along the
perimeter (where the lid and bottom portion meet) and lock in
place, typically through the use of small protruding notches on the
perimeter of the lid which fit into matching cavities in the bottom
portion, or vice versa, thus locking and sealing the tray
container. The trays used for this test were Ivex Model #5720-9MO,
Microwave Supreme, medium entre style trays. One tray was insulated
using a multilayer sheet or liner as described in the invention
herein. The multilayer sheet or liner was placed on the interior on
the inside lid. (Ex. 3) The multilayer sheet comprised a first
layer of Sontara.RTM., a second layer of fiberfill batt, and an
outer layer of Mylar.RTM., as constructed and described in Example
2. The other tray was not insulated. (Comparative Ex. I)
[0061] After loading the tray with the hot food product, chicken
nuggets, the lid was snapped into place and two separate digital
temperature probes were inserted into the interior of the tray. One
probe was used to measure the temperature of the air space in the
top of the container, while the second probe was placed in the
bottom of the tray among the food. The container was placed on a
countertop at ambient conditions and readings taken from one to
twenty minutes at various intervals as shown in Table 1.
1TABLE 1 Chicken Nugget Deep fry Test Un-insulated - Comp. Ex. I
Insulated Ex. 3 top .degree. F. Bottom .degree. F. top .degree. F.
bottom .degree. F. time (min) 157 154 164 157 1 154 168 169 1.5 153
157 169 178 2 151 166 169 184 2.5 152 165 169 188 3 169 189 3.5 155
163 168 190 4 156 161 167 190 4.5 156 160 166 189 5 154 155 163 186
7 149 149 161 181 9 147 146 160 180 10 136 135 155 171 15 149 162
20
[0062] After preparation and measuring of the chicken nugget
samples, it was determined that the tray containing the multilayer
sheet of the invention herein on the inside lid, Ex. 3, offered a
definite advantage when compared to the un-insulated one. The
nuggets from the insulated tray were both hotter and crisper.
EXAMPLE 4
Chicken Breast Strips--Tray Liner and Pouch
[0063] An experiment was conducted as described in Example 3,
except that the food product used was frozen chicken breast strips,
rather than chicken nuggets. Four chicken strips were placed in
each package. Temperature, humidity, and dew point were recorded
using a digital hygrometer. Three different packaging methods were
tested; two being modifications to the PET "take-out" tray. The
package for Example 4A had the multilayer sheet of the invention
herein (similar to that described in Example 2) attached to the lid
on the exterior of the PET tray covering holes that were punched in
the lid to allow moisture to escape from inside the container. Each
hole was 1/2 inch in diameter, and there were 36 holes in the lid,
for a total area of 7 square inches. The package used in Example 4B
was a pouch formed from the multilayer sheet of the invention
herein (similar to that described in Example 2). The pouch was
formed as described in Example 6. The package used in Example 4C
was a PET "take-out" tray with a liner comprising the multilayer
sheet of the invention herein attached to the inside lid. The
results are shown in Table 2.
2TABLE 2 Example 4A Example 4B Example 4C Top .degree. F. Bottom
.degree. F. Top .degree. F. Top .degree. F. Bottom .degree. F. Time
(min) 117 114 106 140 151 1 121 118 108 148 151 1.5 151 150 2 128.5
122 112.5 153 149 2.5 130.2 123 115 155 147.5 3 131.5 123.1 116 156
146.5 3.5 132.3 123.2 115.7 156 145 4 132.8 123.2 115.6 156.5 144
4.5 133 123 115.2 156.3 142 5 132 121 113.5 154 137 7 129 119 111
151 132.9 9 128 117 110 148.6 130 10 123 113 105 141 123 15 RH %
Dew point .degree. F. RH % Dew point .degree. F. RH % Dew point
.degree. F. 100 100 103.7 100 118 1 100 100 108.9 100 1.5 100 99
110 100 123.3 2 100 112 93 110 88 122.5 2.5 100 113.2 88 110 83.5
121.6 3 100 113.4 86.5 110.4 80 122 3.5 100 114 86 110.1 78 122 4
100 115.1 82.3 109.5 77 121.2 4.5 100 116.1 76.8 106.6 75.4 121 5
91.6 114 75.7 103.8 74 118.5 7 87.7 112 78.5 102.8 67 113.5 9 87.1
110.8 78.9 101.7 67 112 10 87.5 107 86.9 100.2 72.3 108.6 15
EXAMPLE 5
Chicken Breast Strips--Tray Liner
[0064] Testing was performed using chicken breast strips as the
food product using the procedure described in Examples 3 and 4. In
this example, the trays used for Examples 5A, 5B and 5C were
similar to that example 4C, that is, a PET "take-out" tray with a
liner comprising the multilayer sheet of the invention herein
attached to the inside lid. In Examples 5D and 5E the multilayer
sheet of the invention herein was attached to the exterior lid of
the PET tray covering holes in the lid as described in Example 4.
Comparative Example II used an uninsulated tray. Results are shown
in Tables 3 and 4.
3 TABLE 3 Example 5A, Internally Example 5B, Internally Example 5C,
Internally insulated insulated insulated Time (min) Top .degree. F.
RH (%) DP (.degree. F) Top .degree. F. RH (%) DP (.degree. F.) Top
.degree. F. RH (%) DP (.degree. F.) 1 125.2 100 123.7 135 100 110.5
120 100 119 1.5 130.1 100 127.9 128.4 100 113 123.5 98.6 121.4 2
135.7 100 129.7 125.9 100 114 124.7 92 121.2 2.5 138.6 100 129.6
123.8 100 114.3 127.7 89 121.1 3 139.5 100 131.2 122.9 100 114.8
128.4 84 121.5 3.5 140.2 100 131.5 122.2 100 115.5 128.5 83 122.1 4
141.1 100 132 121.4 99 115.5 128.5 81 122.3 4.5 141.4 100 132.4
120.7 97.7 115.2 128.3 80.3 121.7 5 141 100 133.8 120 98 115 127.5
79 121.1 7 138.2 96.8 133.5 118 95.7 113 124 71 115.7 9 135.7 86.3
125.9 116.6 96.4 110 121.2 71 115 10 134.2 85.3 125.4 115.9 96.6
110.9 120.2 70.2 113.5 15 129 86.7 120.1 113.2 94.4 107.1 116.1
72.1 109.5 20 123.9 92.3 116.3 112 94.4 105.7 112.1 79.5 107.1 25
120.9 96.5 114.2 110.5 100 104.4 108.2 88 106 30 117.2 98.5 111.1
107.5 100 101 103.7 93.15 103.6
[0065]
4 TABLE 4 Example 5D, Externally Example 5E, Externally Comp. Ex.
insulated insulated Uninsulated Time (min) Top .degree. F. RH (%)
DP (.degree. F.) Top (.degree. F.) RH (%) DP (.degree. F.) Top
(.degree. F.) RH (%) DP (.degree. F.) 1 117 100 112 121 100 113
110.3 100 109 1.5 120.2 100 116 123.9 100 116.2 2 120.8 100 118
127.7 100 117.6 117.9 100 115.9 2.5 121.4 100 120.2 130.4 100 117.8
3 121.5 100 120.6 131.2 100 117.9 122.7 100 117.1 3.5 121.8 100 121
131.4 100 117.8 4 122.4 100 121.4 131.1 100 117.6 125.4 100 117 4.5
122.7 100 121.5 130.7 100 117 5 122.9 100 121.4 130.1 100 116.7
126.4 100 117.3 7 121 100 121.7 126.4 100 115.3 126 100 119.9 9
119.4 100 121.7 124 100 113.5 124.3 97.6 117.8 10 118.8 100 121.6
123 100 112.8 123 96.7 116.8 15 114.9 100 115.7 118.1 100 108.6
117.5 90.8 109.2 20 110.7 100 113 113.2 100 106 112.6 94.1 105.2 25
105.3 100 108 108.8 100 103.5 107 97.1 102.2 30 101.3 100 103.8
103.4 100 100 101.8 99.1 98.2
[0066] For Example 5A, after 30 minutes the internal chicken
temperature was 140.degree. F., and the external air temperature
was 117.degree. F. Subjective testing by a food taster rated the
product as "excellent". The food quality rating was focused on the
crispness of the food and the scale ran from "excellent", "very
good", "satisfactory", to "poor".
[0067] In Example 5B, the internal chicken temperature was
137.degree. F. after 30 minutes, and the external temperature was
129.degree. F. The product was again rated as "excellent". Also, by
way of comparison, one freshly-cooked chicken finger was left
outside of the container for 30 minutes to observe how the
temperature changed during cooling without any packaging to retain
heat. The external temperature was 86.degree. F. while the internal
temperature was 93.5.degree. F. after 30 minutes.
[0068] In Example 5C, the internal chicken temperature was
137.degree. F. and the external chicken temperature was 133.degree.
F. after 30 minutes. Product was rated as "excellent". Again, by
way of comparison, a freshly-cooked chicken finger was left outside
the test package for 30 minutes. After 30 minutes, the internal
temperature was 103.degree. F. while the external temperature was
94.degree. F.
[0069] In Example 5D, after 30 minutes the internal chicken
temperature was 138.degree. F. and the external temperature was
133.degree. F. The food product was rated as "very good".
[0070] In Example 5E, the internal chicken temperature was
126.degree. F., and the external temperature was 122.degree. F.
after 30 minutes. The food product was rated as "very good".
[0071] In Comparative Example II, the internal chicken temperature
was 127.degree. F., and the external temperature was 119.degree. F.
after 30 minutes. The food product was rated as "poor to
satisfactory".
[0072] In these examples, the hot, freshly-cooked chicken strips
that were packaged in take-out trays, with a multilayer sheet of
the invention herein attached to the inside lid, better retained
heat and food quality (i.e., were judged to taste better, generally
hotter and crisper, more like freshly-cooked) as compared to
chicken packaged in take-out trays with the multilayer sheet on the
exterior of the tray.
EXAMPLE 6
Chicken Tenders and Steak Fries--Pouches
[0073] An experiment was conducted as described in Example 3,
except the food product used was chicken tenders (Barber brand
"Italian style") and the packaging tested was a pouch made from a
multilayer sheet as constructed and described in Example 1 (Ex.
6A). Two pieces of the multilayer sheet, each the same size
(approximately 12 in..times.12 in.) were used to form a pouch by
aligning the two sheets and sealing on three sides with masking
tape.
5TABLE 5 Ex. 6A - Chicken Tenders in Pouch Time (min) Temp
(.degree. F.) RH DP (.degree. F.) 1 106 100 103.7 1.5 108 99 108.9
2 110 2.5 112.5 93 110 3 115 88 110 3.5 116 86.5 110.4 4 115.7 86
110.1 4.5 115.6 82.3 109.5 5 115.2 76.8 106.6 7 113.5 75.7 103.8 9
111 78.5 102.8 10 110 78.9 101.7 15 105 86.9 100.2
[0074] After 15 minutes, the internal temperature of the chicken
tenders was 150.degree. F. and the food was rated as
"satisfactory".
[0075] Steak fries were tested in a similar manner. (Ex. 6B) A
sample of approximately 370 grams of frozen steak-style french
fries (Ore-Ida brand) d at 375.degree. F. for four minutes, drained
of cooking oil for 15 seconds, and then added to the pouch.
Temperature, relative humidity and dew point were recorded for 15
minutes. Results are shown in Table 6.
6TABLE 6 Ex. 6B - Steak Fries in Pouch Time (min) temp (.degree.
F.) RH DP (.degree. F.) 1 107 100 104.6 1.5 113.9 100 112.7 2 116.6
100 117.5 2.5 118.8 100 117.5 3 120.7 100 120 3.5 122.5 100 123.2 4
124 100 124.4 4.5 125 100 125.3 5 125.6 100 125.8 7 126.5 100 126.5
9 125.5 100 125.7 10 124.7 100 124.6 15 118 100 117.8
[0076] The internal temperature of the fries was 153.degree. F.
after 15 minutes.
[0077] By way of comparison, freshly-cooked chicken tenders (Barber
brand "Itialian style" chicken tenders) and steak fries (Ore-Ida
brand) were also placed in un-insulated pouches made from
Mylar.RTM. film. The pouches were formed as discussed above. This
constituted Comparative Examples III and IV. Temperature, relative
humidity and dew point were recorded for 15 minutes. Results are
shown in Tables 7 and 8.
7TABLE 7 Comp. Ex. III - Chicken tenders, un-insulated pouch Time
(min) Temp (.degree. F.) RH DP (.degree. F.) 1 87.8 100 89.7 2 97.8
100 95 3 98.5 100 98.3 5 96.5 100 98.7 7 95.2 100 98.9 9 91.9 100
94.9 10 91.3 100 89.8 15 92.1 100 86
[0078] Condensation was observed in the pouch after 2 minutes.
Crispness was rated as "poor to satisfactory". Internal temperature
of product was 144.degree. F. after 15 minutes.
8TABLE 8 Comp. Ex. IV - Steak fries, un-insulated pouch Time (min)
Temp (.degree. F.) RH DP (.degree. F.) 1 87.7 100 109.9 2 102.8 100
112.6 3 107.5 100 112.8 5 108.7 100 110.9 7 103.9 100 106 9 101.3
100 101.6 10 100.5 100 99.9 15 99.7 100 100
[0079] There was a large amount of condensation evident in the
pouch after 4 minutes. The internal temperature of the food was
138.degree. F. after 15 minutes. Steak fries were rated as
"poor".
COMPARATIVE EXAMPLE V
Pouch with Melt-Blown Polvolefin Nonwoven First Layer
[0080] This example was conducted in a manner similar to that in
Example 6. The pouches were made from a multilayer sheet similar to
that described in Example 1 with the exception that the first inner
layer was a polyolefin nonwoven, available under the trade name
Tyvek.RTM. from DuPont. The pouch was formed from two pieces of the
multilayer sheet, each the same size, here approximately 10
in..times.10 in., sealed on three sides with masking tape.
[0081] Four pieces of chicken tenders (approximately 240 g) were
cooked at 340.degree. F. for four minutes, drained of cooking oil
for 15 seconds, and then placed in the pouch. Temperature, relative
humidity and dew point were recorded for 15 minutes. The results
are shown in Table 9.
9 TABLE 9 Time Temp (.degree. F.) RH dew point (.degree. F.) 1 75.6
65.5 60.1 2 80.1 100 74.2 3 82.8 96.3 73.4 5 79.7 94 72.3 7 81.7
100 74 9 83.9 100 81.5 10 84 100 81.8 15 83.9 100 81.5 20 81.7 100
79.5 25 80.3 100 78.4 30 78.4 100 76.8
[0082] The results show >20 degree drop in temperature
(83.9.degree. F. v. 105.degree. F.) within the pouch after 15
minutes when compared to the chicken tenders in Example 6 (see
Table 5), while the relative humidity remained very high (100% v.
86.9%). With a resulting lower temperature and higher humidity
within the pouch, one would expect the food quality and crispness
to be less desirable as compared to Example 6A.
[0083] Physical Property Data on Sontara.RTM.
[0084] The following tables provide various physical parameters on
spunlaced, nonwoven fabrics suitable for use in the invention
herein as the water-wicking material and sold under the trade name
Sontara.RTM. (available from E. I. du Pont de Nemours and Company,
Wilmington, Del.). The various grades listed in Tables 10 and 11
below comprise hydroentangled, white, staple polyester fibers, as
well as varying percentages of wood pulp. Moisture-vapor
transmission rate (MVTR) was tested using ASTM D-6701. Hydrostatic
head was tested using MTCC Method 127-1989.
10 TABLE 10 Bulk % Wood Thickness A.sub.e A.sub.l R.sub.e R.sub.l
MVTR Wt. (g/m.sup.2) Pulp (mils) (mL/m.sup.2) (mL/g) (mL/m.sup.2/s)
(mL/g/s) (g/m.sup.2-day) A 54 0 14 200,000 B 136 0 40 .about.25,000
C 68 55 13 290 4.25 1864 27.4 200,000 D 51 54 12 258 4.99 2043 39.9
E 63 25 16 286 4.63 2154 34.9 170,000
[0085]
11TABLE 11 Hydrostatic head (cm H.sub.20) A 1.5 +/- 0.4 B Wets out
(.about.0)
* * * * *