U.S. patent application number 11/351971 was filed with the patent office on 2006-09-07 for heat retentive food server.
Invention is credited to David M. Dean.
Application Number | 20060196497 11/351971 |
Document ID | / |
Family ID | 36498884 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060196497 |
Kind Code |
A1 |
Dean; David M. |
September 7, 2006 |
Heat retentive food server
Abstract
The present invention discloses a heat retentive food server for
maintaining food at an elevated temperature, especially important
in food service operations. The server is a container having an
upper shell and lower shell and cavity defined therebetween
containing a phase change material. The phase change material is
preferably an ethylene acrylate copolymer, which absorbs energy
upon heating, and then keeps freshly prepared hot foods placed in
the server warm as the phase change material slowly cools and
releases heat.
Inventors: |
Dean; David M.; (West
Chester, 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: |
36498884 |
Appl. No.: |
11/351971 |
Filed: |
February 10, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60652130 |
Feb 11, 2005 |
|
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Current U.S.
Class: |
126/246 |
Current CPC
Class: |
A47J 41/0044 20130101;
F28D 20/02 20130101; A47G 19/027 20130101; A47J 36/24 20130101;
A47J 41/0077 20130101 |
Class at
Publication: |
126/246 |
International
Class: |
A47G 23/04 20060101
A47G023/04; F24C 15/18 20060101 F24C015/18 |
Claims
1. A heat-retentive food server comprising: (a) an upper shell; (b)
a lower shell; said upper shell and said lower shell being joined
together and having a cavity defined therebetween, said upper and
lower shells being comprised of a thermoplastic material, and (c) a
heat storage material disposed in said cavity, said heat storage
material comprising a phase change material substantially filling
said cavity and being unrestrained therein, whereby said food
server may be heated and placed adjacent to food for maintaining
food at an elevated temperature, wherein said phase change material
comprises an ethylene acrylate copolymer.
2. The server of claim 1 wherein said phase change material
comprises greater than about 12% by weight ethylene acrylate
copolymer, based on the total weight of the phase change
material.
3. The server of claim 1 wherein said phase change material is a
solid at room temperature, said phase change material being formed
to substantially match the shape of said cavity.
4. The server of claim 1 where said phase change material comprises
an injection molding having a shape substantially matching the
shape of said cavity.
5. The server of claim 1, wherein said phase change material
changes phase from a solid to a viscous, gelatinous state when
heated to an elevated temperature.
6. The server of claim 5, wherein said phase change material
changes phase at a temperature of about 190.degree. F. to about
230.degree. F.
7. The server of claim 1 wherein said ethylene acrylate is selected
from the group consisting of: ethylene methyl acrylate, ethylene
ethyl acrylate and ethylene n-butyl acrylate.
8. The server of claim 1 wherein said heat storage material
additionally comprises a microwave absorbing additive.
9. The server of claim 1 wherein said heat storage material
additionally comprises up to 88% of one or more polymers selected
from the group consisting of ethylene polymers and ethylene
copolymers.
10. The server of claim 1 wherein said phase change material
consists essentially of an ethylene acrylate copolymer.
11. The server of claim 1 wherein said server comprises a food
cover for use with an underlying food holder, wherein said food
cover may be heated and placed over said underlying food holder to
maintain food placed upon said holder at an elevated
temperature.
12. The food server of claim 11 wherein said food cover comprises
said lower shell, and said lower shell comprises (a) a top wall,
and (b) a side wall depending downwardly from said top wall, said
upper shell being spaced apart from and surrounding said lower
shell thereby defining said cavity.
13. The food cover of claim 12 further comprising an insulator
positioned between said heat storage material and said upper shell
so that heat is transferred from said heat storage material through
said lower shell, and so that a minimum amount of heat is lost
through said upper shell, thereby maintaining said food placed
under said lower shell at an elevated temperature for an extended
period of time.
14. The server of claim 1 wherein said upper shell comprises (a) a
substantially flat base portion for placing food thereon; and (b) a
side wall extending upwardly from said base portion thereby forming
a trough for holding food, said lower shell comprising: (i) a
substantially flat support portion spaced downwardly from said
upper shell base portion; (ii) a side wall extending upwardly from
said flat portion, said upper and lower shell side walls being
joined at the upper ends thereof.
15. The server of claim 15 further comprising an insulator
interposed between said phase change material and said lower shell,
so that heat is transferred from said phase change material through
said upper shell, and so that a minimum amount of heat is lost
through said lower shell, thereby maintaining said food placed on
said upper shell at an elevated temperature for an extended period
of time.
16. A method for repeatedly storing and releasing thermal energy
comprising heating a phase change material so that it undergoes a
phase transition and stores thermal energy, and allowing the phase
change material to cool so that it undergoes a second phase change
transition and releases thermal energy, wherein the improvement
comprises the phase change material comprises an ethylene acrylate
copolymer.
17. The method of claim 16 wherein the phase change material
comprises greater than 12% by weight of ethylene acrylate
copolymer.
18. The method of claim 16 wherein the phase change material is
molded and shaped to fit into the space between the walls of a
dual-walled serving container for food or beverages.
19. A method for making a re-heatable food warming device
comprising the steps of: (a) forming a container from a
thermoplastic material wherein said container has an upper shell
and a lower shell; (b) injection molding a phase change material
comprising an ethylene acrylate copolymer into an internal cavity
formed between the upper and lower shells such that the phase
change material substantially fills the cavity; and (c) sealing the
upper and lower shells with a polymeric sealant at their periphery
to contain the phase change material within the internal cavity.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C. .sctn. 120
to U.S. Provisional Application No. 60/652,130, filed on Feb. 11,
2005, which is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention The present invention relates to a
heat retentive food server for maintaining food at an elevated
temperature. The food server uses a phase change material as a heat
storage medium. The invention also relates specifically to a
thermoplastic, moldable, non-exuding phase change material for use
in such food servers.
[0003] 2. Description of Related Art Several patents and
publications are cited in this description in order to more fully
describe the state of the art to which this invention pertains. The
entire disclosure of each of these patents and publications is
incorporated by reference herein.
[0004] Phase change materials may be repeatedly converted between
solid and liquid phases. Their latent heat of fusion can be used to
absorb, store and release heat. These latent heats of fusion are
greater than the sensible heat capacities of the materials. For
example, in phase change materials, the amount of energy absorbed
upon melting or released upon freezing is much greater than the
amount of energy absorbed or released upon increasing or decreasing
the temperature of the material over an increment of 10.degree. C.
for example, in the absence of a phase change.
[0005] Stated alternatively, upon melting and freezing, a phase
change material absorbs and releases substantially more energy per
unit weight than a sensible heat storage material that is heated or
cooled over the same temperature range. The ability of a phase
change material to absorb and release a large quantity of energy in
the vicinity of its melting/freezing point is the key to its
usefulness in heat retention uses, e.g., for food servers.
[0006] Various food service operations encounter the problem of
keeping food warm after preparation and for a period of time until
consumption. These include hospitals, nursing homes, hotels,
airlines, among others. Numerous devices have been developed to
help alleviate the problem of food getting cold. The simplest
approach may be a cover or dome with a layer of insulating material
disposed therein which can be place over a plate containing the
warm food. Insulated bases that can hold a plate or container can
be used in conjunction with such covers or domes. Other devices
include servers which can be heated to an elevated temperature.
[0007] Many servers which can be heated to an elevated temperature
comprise a hollow shell with a cavity disposed therein. A
heat-retentive medium is placed in the cavity so that when the
container is heated, the heat-retentive medium will store heat and
then release heat to maintain food placed adjacent to the server at
an elevated temperature. The heat-retentive medium typically has
been a wax or wax mixture, though this requires an additional
enclosure within the server to seal the wax so that leakage through
the server does not occur. Construction of such servers is
time-consuming and expensive.
[0008] Phase change materials have also been used as heat-retentive
media with varying degrees of success. For example, U.S. Pat. No.
5,565,132 discloses a multi-component composite for use as a phase
change material to alleviate problems with "oozing" or exuding that
are typical of alkyl hydrocarbon phase change materials, and to
lower the overall cost of the phase change material. The composite
comprises a mixture of an alkyl hydrocarbon phase change material,
a polyolefin resin, an ethylene copolymer and silica particles. A
microwave absorbing additive can also be added. The ethylene
copolymer component is disclosed to comprise about 8-12% by weight
of the mixture.
[0009] U.S. Pat. No. 5,520,103 discloses a phase change material
that, when used as a heat storage medium, eliminates the problem of
leakage common to servers using wax. The phase change temperature
of the heat storage medium is preferably from 190.degree. F. to
230.degree. F. The only heat storage medium disclosed is ethylene
vinyl acetate (EVA). Various food server configurations using a
phase change material as the heat-retentive medium are also
disclosed.
[0010] One problem with the use of EVA as a heat-retentive medium
in food servers is that over time and with repeated heatings, the
EVA degrades and eventually cannot be re-used. This makes the life
cycle for such food servers relatively short, thereby increasing
the cost of use.
[0011] A need exists to improve the heat storage medium for
heat-retentive food servers, and more specifically to increase the
life cycle of such servers.
BRIEF SUMMARY OF THE INVENTION
[0012] The present invention overcomes the problems associated with
the prior art by improving the durability and usefulness of heat
retentive food servers.
[0013] In accordance with this concept, the invention herein
provides a heat-retentive food server comprising: [0014] (a) an
upper shell; [0015] (b) a lower shell; [0016] said upper shell and
said lower shell being joined together and having a cavity defined
therebetween, said upper and lower shells being comprised of a
thermoplastic material, and [0017] (c) a heat storage material
disposed in said cavity, said heat storage material comprising a
phase change material substantially filling said cavity and being
unrestrained therein, whereby said food server may be heated and
placed adjacent to food for maintaining food at an elevated
temperature, [0018] wherein said phase change material comprises an
ethylene acrylate copolymer.
[0019] The invention also provides a heat-retentive food server
comprising: [0020] (a) an upper shell; [0021] (b) a lower shell;
[0022] said upper shell and said lower shell being joined together
and having a cavity defined therebetween, said upper and lower
shells being comprised of a thermoplastic material, and [0023] (c)
a heat storage material disposed in said cavity, said heat storage
material comprising a phase change material substantially filling
said cavity and being unrestrained therein, whereby said food
server may be heated and placed adjacent to food for maintaining
food at an elevated temperature, [0024] wherein said phase change
material consists essentially of an ethylene acrylate
copolymer.
[0025] Moreover, in another embodiment, the invention provides a
material for thermal energy storage comprising an ethylene acrylate
copolymer.
[0026] Furthermore, the invention provides a method for making a
re-heatable food-warming device comprising the steps of: [0027] (a)
forming a container from a thermoplastic material wherein said
container has an upper shell and a lower shell; [0028] (b)
injection molding a phase change material comprising an ethylene
acrylate copolymer into an internal cavity formed between the upper
and lower shells such that the phase change material substantially
fills the cavity; and [0029] (c) sealing the upper and lower shells
with a polymeric sealant at their periphery to contain the phase
change material within the internal cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 shows a top view of a heat retentive food server of
the present invention.
[0031] FIG. 2 shows a view taken through section 2-2 of FIG. 1.
[0032] FIG. 3 shows a bottom view of the heat retentive food server
of the present invention.
[0033] FIG. 4 shows the heat retentive food server of FIG. 1, in
combination with an underlying food plate.
[0034] FIG. 5 shows a top view of an additional embodiment of a
food server of the present invention.
[0035] FIG. 6 shows a view taken through section 6-6 of FIG. 5.
[0036] FIG. 7 shows a view taken through section 7-7 of FIG. 5.
[0037] FIG. 8 shows a section view of an additional embodiment of
the present invention.
[0038] FIG. 9 is a graph depicting the thermal stability of certain
ethylene copolymers under nitrogen.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
[0039] The following definitions apply to the terms as used
throughout this specification, unless otherwise limited in specific
instances.
[0040] As used herein, the term "about" means that amounts, sizes,
formulations, parameters, and other quantities and characteristics
are not and need not be exact, but may be approximate and/or larger
or smaller, as desired, reflecting tolerances, conversion factors,
rounding off, measurement error and the like, and other factors
known to those of skill in the art. In general, an amount, size,
formulation, parameter or other quantity or characteristic is
"about" or "approximate" whether or not expressly stated to be
such.
[0041] In this disclosure, the term "copolymer" refers to a polymer
polymerized from two or more monomers, and includes terpolymers.
The more specific description `ethylene acrylate copolymer`,
`ethylene-methyl acrylate (EMA) copolymer`, and the like, is meant
to include copolymers which may also have a third monomer
present.
[0042] Copolymers of ethylene and an unsaturated C.sub.1-C.sub.8
alkyl acrylate are well known. "Ethylene acrylate copolymers" may
also be referred to as ethylene-acrylic acid ester copolymers. They
can be manufactured from two high-pressure free radical processes:
tubular processes or autoclave processes. The difference in
ethylene acrylate copolymers made from the two processes is
described in, e.g., "High flexibility EMA made from high pressure
tubular process." Annual Technical Conference--Society of Plastics
Engineers (2002), 60.sup.th (Vol. 2), 1832-1836.
[0043] The term "ethylene copolymer", as used herein, refers to a
polymer copolymerized from ethylene and one or more olefinic
monomers, preferably one or more alpha-olefin monomers or vinyl
acetate monomer. The copolymers of ethylene and alpha olefin can be
made by processes employing Ziegler Natta catalysts or single site
catalysts, for example, metallocene catalysts. Copolymers of
ethylene and vinyl acetate are typically produced using free
radical polymerization.
Description
[0044] In accordance with the present invention and referring now
to the drawings, and more particularly to FIG. 1, there is shown an
embodiment of a heat retentive food server. FIG. 1 shows a food
cover 1 which may be used with an underlying food holder 2, such as
the plate schematically shown in FIG. 4. The food cover 1 includes
an outer shell assembly 10 having an outer surface 11 and inner
surface 12. The outer assembly 10 is comprised of an upper shell 15
and a lower shell 20, and has a cavity 25 defined by the upper and
lower shells. As shown in FIG. 2, the cavity 25 defined by the
upper and lower shells is preferably a single cavity which is
uninterrupted and undivided. In other words, there are no
restrictions, partitions or additional enclosures located within
the cavity.
[0045] Lower shell 20 has an inner surface 30, an outer surface 32,
and a top wall 34. A side wall 38 extends downward from and merges
with top wall 34. Side wall 38 may also include a lip 42 at a
peripheral portion 44, which may also be referred to as the lower
end 44 thereof. Lip 42 is comprised of a substantially horizontal
portion 46 and a downwardly extending portion 48. Lip 42 can engage
the rim of a plate or other food holder placed therebelow as shown
in FIG. 4 to completely cover the plate and any food placed
thereon.
[0046] Upper shell 15 may include a top wall 50 with a side wall or
side leg 52 extending downwardly therefrom. Upper shell 15 has an
inner surface 54, an outer surface 56, and a lower end, or
peripheral portion 62. Thus, outer surface 11 of outer shell 10 is
comprised of outer surfaces 32 and 56 of the lower and upper
shells, 15 and 20 respectively. As shown in FIG. 2, the upper shell
15 surrounds the lower shell 20, thereby defining the cavity
25.
[0047] The upper shell 15 may also include a central recess 58 and
a handle 60. The handle 60 may span the full diameter of the
central recess 58. The upper and lower shells 15 and 20 are joined
at their peripheral portions at a joint 64. FIG. 1 shows a
snap-ring configuration at joint 64. However, numerous other
configurations are acceptable. For instance, the upper and lower
shells 15 and 20 may have flat surfaces at the ends thereof that
can simply abut each other as depicted in FIG. 2A. The joint 64 may
be sealed with a polymeric sealant, for example. Any polymeric
sealant capable of withstanding repeated heating to a temperature
of at least about 230.degree. F. without losing its material
properties may be used. Examples of such sealants include
polycarbonate sealants, e.g., 3M.RTM. No. 1838 which will withstand
temperatures up to 350.degree. F.
[0048] A heat storage material 70 may be disposed in cavity 25. The
heat storage material 70 comprises, and more preferably is, a phase
change material as described herein more fully below. The phase
change material substantially fills the cavity and has a phase
change temperature that is preferably in the range of about
190.degree. F. to about 230.degree. F. Generally, the phase change
material is thermoplastic, moldable and non-exuding. Preferably, it
is a solid at room temperature and changes to a viscous, gelatinous
state when heated.
[0049] The phase change material comprises an ethylene acrylate
copolymer, and, preferably, consists essentially of an ethylene
acrylate copolymer. The ethylene acrylate copolymer is preferably
ethylene methyl acrylate, ethylene ethyl acrylate, ethylene n-butyl
acrylate or a combination of one or more of ethylene methyl
acrylate, ethylene ethyl acrylate, and ethylene n-butyl acrylate.
More preferably, the ethylene acrylate copolymer comprises or
consists essentially of ethylene methyl acrylate.
[0050] The heat storage material 70 may contain additional
components to enhance or improve certain attributes, or to reduce
cost. For example, a microwave absorbing additive could be included
to facilitate heating the phase change material using a microwave
oven. Possible additional components include other polymers, e.g.,
polyethylene and/or higher melting polyethylenes such as high
density polyethylene or low density polyethylene, as well as other
ethylene copolymers. Generally, the heat storage material 70, and
preferably the phase change material, should contain at least about
12% by weight of an ethylene acrylate copolymer.
[0051] Referring again to FIGS. 1 and 2, the upper and lower shells
15 and 20 are preferably made from a thermoplastic material capable
of withstanding repeated prolonged temperature increases to at
least about 230.degree. F. without a loss of material properties.
Any type of thermoplastic material capable of withstanding great
temperatures can certainly be used. The heat storage material 70 is
used to fill the cavity 25.
[0052] The fact that the phase change material is a solid at room
temperature facilitates construction of the food cover 1 containing
the phase change material in cavity 25. The phase change material
may be formed as a block in substantially the same shape as the
cavity 25. The block can be formed by injection molding or other
suitable means to the desired configuration. The upper and lower
shells 15 and 20 can then simply be joined together around the
phase change material and sealed with sealant (such as a
polycarbonate sealant discussed above) at joint 64.
[0053] Alternatively, the upper and lower shells 15 and 20 may be
partially sealed together. The phase change material may be
injection molded into the cavity 25, and then the seal between the
upper and lower shells 15 and 20 may be completed to contain the
phase change material.
[0054] An advantage of the phase change material disclosed herein
is that leakage problems are eliminated without the need for other
artificial seals, enclosures or restraints in the cavity as
required with many prior art servers. The food server may be made
of a simple two-piece construction.
[0055] When the food server is heated so that the phase change
material in cavity 25 reaches its phase change temperature (i.e.,
it changes from a solid to a gelatinous state), heat is stored
therein. The phase change material will typically change phase when
heated above its melting temperature for a sufficient time to
ensure the phase change is complete. The exact time will depend on
the particular material and the design of the server.
[0056] The heat stored in the material 70 is released at a
relatively slow rate as the material changes from a gelatinous
state back to a solid. Also, the temperature of the material 70
remains relatively constant during the phase change. Thus, when the
food server 1 is placed over a plate containing food, heat is
directed through the outer shell 10 and will maintain food placed
thereunder at an elevated temperature for an extended period of
time.
[0057] The underlying food holder may be of virtually any material,
e.g., ceramic or thermoplastic. Typically, food will be placed
under the cover shortly after it is removed from a cooking
apparatus, for example an oven or a steamer, and will be at a
temperature in the range of about 170.degree. to 200.degree. F. and
more preferably from about 185.degree. to 195.degree. F. The food
cover 1 will generally maintain such food at a temperature of at
least about 145.degree. F. for at least 60 minutes. Thus, when it
reaches its ultimate destination, the food is still at an
acceptable and desirable serving temperature.
[0058] The food server 1 may also include an insulator 80. In the
embodiment shown in FIG. 2, the insulator 80 is interposed between
the phase change material and the upper shell 15. The insulator 80
will prevent heat stored in the phase change material from
dissipating rapidly through the upper shell 15. In this way, the
heat stored is transferred more efficiently to the food to maintain
the food at an elevated temperature rather than dissipating through
the upper shell 15 and into the environment. The insulator 80 can
be any type of insulating material capable of withstanding the
temperatures described herein. One acceptable insulating material
80 is a high strength composite paper made from a combination of
ceramic fiber, inert fillers and reinforcing fiberglass One such
paper is commercially available from the Unifrax Corporation of
Niagara Falls, N.Y. (formerly the Carborundum Company) and is known
as Fiber Frax.RTM. grade 440 ceramic fiber paper.
[0059] An additional embodiment of the present invention is shown
in FIGS. 5 through 7. Referring now to FIG. 5, a food server 100,
which comprises a food holder, or food pan, is shown therein. As
shown in FIG. 6, the pan includes an outer shell assembly 102
having an inner surface 104 and outer surface 106. The outer shell
assembly 102 is comprised of a lower shell 108 and an upper shell
110. The lower shell 108 can be described as surrounding the upper
shell 110. The upper shell 110 has an inner surface 112 and an
outer surface 114. The lower shell 108 has an inner surface 116 and
an outer surface 118. Thus, inner surface 104 is comprised of inner
surface 112 and inner surface 116 of the upper and lower shells,
110 and 108 respectively. A cavity 120 is defined by the outer
shell assembly 102. The cavity is defined by the upper and lower
shells 110 and 108 and is preferably a single, undivided and
uninterrupted cavity as previously described with respect to the
embodiment shown in FIGS. 1 and 2. While the particular embodiment
shown in FIG. 5 is rectangular in shape, the server can be of any
shape that is desired, including, but not limited to, shapes such
as circular, oval and square.
[0060] The upper shell 110 has a substantially flat base portion
for placing food thereon, i.e., a bottom wall or base 122 and
upwardly extending side wall 124. The bottom wall 122 and upwardly
extending side wall 124 thereby form a trough or open space for
holding food. The upper shell 110 may further include an outwardly
extending lip 126 at the upper end or peripheral portion 128 of the
upper shell. The lip 126 circumscribes the entire periphery 128 of
the upper shell 110.
[0061] The lower shell 108 includes a substantially flat support
portion, i.e., a bottom wall or support portion 130, and upwardly
extending side walls 132. The lower shell 108 surrounds the upper
shell 110 as previously described, and may include an outwardly
extending lip 135 at the upper end, or peripheral portion 134
thereof. The upper and lower shells 110 and 108 are joined together
at their peripheral portions 134 at a joint 138, thereby defining
cavity 120. The joint 138 is sealed with a sealant such as a
polycarbonate sealant, discussed above.
[0062] A phase change material 136 is disposed in cavity 120. The
phase change material 136 substantially fills the cavity 120 and is
unrestrained therein as described with respect to the food cover
embodiment. The phase change material 136 is as described above,
comprising an ethylene acrylate copolymer. Outer shell 102 may
likewise be made of the materials described with respect to the
embodiment shown in FIGS. 1 and 2.
[0063] When the server 100 is heated so that the phase change
material 136 changes phase to a gelatinous state, food which is
typically at a temperature in the range of about 170.degree. F. to
200.degree. F. or more preferably, from about 185.degree. to
195.degree. F. is placed on the food holder 100 after being removed
from an oven or other heating device, such as boiling water or a
steamer. The phase change material 136 will transfer heat through
the upper shell 110 to the food so that it is maintained at a
temperature of at least about 145.degree. F. for at least about 60
minutes. Because the food is in direct contact with the shell 110,
the temperature of the food will most likely stay above about
145.degree. F. for a period generally longer than an hour. An
insulator 140 may be disposed between the phase change material 136
and lower shell 108 so that less or no heat is lost to the
environment and is instead directed through upper shell 110 to the
food placed-thereon. The insulator 140 may be made from any
suitable material, including any material that is described above
with respect to the insulator 80.
[0064] An additional embodiment of an upwardly opening food holder
is shown in FIG. 8. The configuration shown there, designated by
the numeral 200, is similar to a commonly-known dinner plate and is
comprised of an outer shell assembly 202 having a cavity 204
disposed therein. Outer shell assembly 202 is comprised of a lower
shell 206 and an upper shell 208. The two shells are joined at
joint 210 and sealed with a sealant such as a polycarbonate
sealant. As described elsewhere herein, the cavity 204 will be
substantially filled with a phase change material 211 and can be
heated so that it will maintain food at an elevated temperature. An
insulator 212 may be disposed between the lower shell 206 and the
phase change material 211.
[0065] As is clear from the foregoing, the phase change material
can be formed, by injection molding or otherwise, to match the
configuration of virtually any cavity shape. A two-piece
construction can then be placed around the formed phase change
material and sealed to construct the server. Alternatively, the
phase change material may be injected directly into the two-piece
construction.
[0066] Thus, regardless of the exact configuration of the food
server, the servers of the present invention are of simple
construction, eliminate problems of leakage associated with prior
art servers, and effectively transfer the heat required to maintain
food at a desirable temperature for an extended period of time. The
inner chambers and other restraints required in previously known
servers to eliminate leakage are eliminated.
[0067] The invention herein also provides a method for making a
re-heatable food warming device. The first step comprises forming a
container by thermoforming or preferably, injection molding, a
shell from a thermoplastic material. The container preferably has
an upper shell and a lower shell and is similar to the food servers
described for FIGS. 1-7 herein. The upper and lower shells each
have an inner surface. When sealed together, the upper and lower
shells define a specifically configured cavity. Alternatively, the
shell may be molded in one piece.
[0068] In the second step, a phase change material comprising an
ethylene acrylate copolymer is formed to match the size, shape and
configuration of the cavity formed between the upper and lower
shells. Thus, the phase change material will substantially fill the
cavity formed when the upper and lower shells are sealed together.
The phase change material is preferably injection molded into the
cavity. The upper and lower shells are sealed together, or the seal
of a one-piece shell may be completed, in any suitable manner. The
seal may be formed or completed at any suitable time before,
during, or after the injection of the phase change material. One
particularly suitable sealing method is to use a polymeric sealant
such as a polycarbonate sealant.
[0069] Alternatively, the phase change material may be formed
separately, for example when the shell has been molded in two
pieces that allow a molded solid phase change material to be placed
between them. The upper and lower shells are then sealed together
in any suitable manner. One particularly suitable method is to use
a polymeric sealant such as a polycarbonate sealant.
[0070] The resulting food warming device may be heated and reheated
and is useful for holding, or placing adjacent to, freshly prepared
hot foods to maintain the food at an elevated temperature for an
extended period of time.
[0071] The present invention can be illustrated by the following
examples, which are intended to be exemplary only and are not meant
to limit the scope of the invention.
EXAMPLES
Examples 1-3, Comparative Example 1
[0072] The TGA (Thermogravimetric Analysis) test was run by
starting samples at 40.degree. C. and raising temperatures at
10.degree. C. per minute and measuring the weight loss of the
polymers as they degraded. In this way, ageing of the materials was
accelerated and their relative thermal stability determined.
[0073] After 30 minutes the samples were at 340.degree. C. and
after 37 minutes the samples were at 410.degree. C.
[0074] The data demonstrate the fact that EVA (ethylene/18 wt %
vinyl acetate, line 1 of FIG. 9) begins to degrade before the more
stable E/nBA (ethylene/27 wt % n-butyl acrylate, line 2 of FIG. 9),
E/EA (ethylene/18 wt % ethyl acrylate, line 3 of FIG. 9), or even
better E/MA (ethylene/24 wt % methyl acrylate, line 4 of FIG. 9)
copolymers. Without wishing to be held to any theory, it is
believed that the greater thermal stability of the ethylene
acrylate copolymers provides improved durability and usefulness as
a heat storage material in a food server, as described herein.
[0075] The data are tabulated in Table I below. TABLE-US-00001
TABLE I Thermal Stability of Ethylene Copolymers under Nitrogen
Time of Ramp@10.degree. C./m in Example 1 Example 2 Example 3
Comparative (start at E/24 wt % E/18 wt % E/27 wt % Example 1
40.degree. C.) MA EA nBA E/18 wt % VA 0 minutes 100% 100% 100% 100%
(40.degree. C.) remaining remaining remaining remaining 30 minutes
99.8% 99.7% 99.5% 96.5% (340.degree. C.) remaining remaining
remaining remaining 37 minutes 96.6% 93.2% 91.2% 86.4% (410.degree.
C.) remaining remaining remaining remaining
[0076] Although preferred embodiments of the invention have been
illustrated in the accompanying drawings and described in the
foregoing detailed description, it will be understood that the
invention is not limited to the embodiments disclosed, but is
capable of numerous modifications without departing from the scope
and spirit of the invention as defined by the appended claims.
* * * * *