U.S. patent application number 11/548503 was filed with the patent office on 2007-04-12 for thermally conductive resin article for food contact and food processing and method for manufacturing same.
This patent application is currently assigned to COOL OPTIONS, INC.. Invention is credited to James D. Miller.
Application Number | 20070080162 11/548503 |
Document ID | / |
Family ID | 37944298 |
Filed Date | 2007-04-12 |
United States Patent
Application |
20070080162 |
Kind Code |
A1 |
Miller; James D. |
April 12, 2007 |
THERMALLY CONDUCTIVE RESIN ARTICLE FOR FOOD CONTACT AND FOOD
PROCESSING AND METHOD FOR MANUFACTURING SAME
Abstract
A method of making a net-shape molded article for use with food
processing and food contact is disclosed. The article is made from
a molten resin including a polypropylene base matrix loaded with a
thermally conductive filler such that the molten resin has a
thermal conductivity between about 1.0 W/mK and about 20 W/mK when
fully set. The molten resin is formed into an article, such as a
food tray, using injection molding techniques. Preferably, the
thermally conductive material includes hexagonal boron nitride and
natural graphite.
Inventors: |
Miller; James D.; (Roswell,
GA) |
Correspondence
Address: |
BARLOW, JOSEPHS & HOLMES, LTD.
101 DYER STREET
5TH FLOOR
PROVIDENCE
RI
02903
US
|
Assignee: |
COOL OPTIONS, INC.
333 Strawberry Field Road
Warwick
RI
|
Family ID: |
37944298 |
Appl. No.: |
11/548503 |
Filed: |
October 11, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60725211 |
Oct 11, 2005 |
|
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|
Current U.S.
Class: |
220/592.2 |
Current CPC
Class: |
B65D 1/34 20130101; B65D
81/3813 20130101 |
Class at
Publication: |
220/592.2 |
International
Class: |
B65D 81/38 20060101
B65D081/38 |
Claims
1. A thermally conductive resin for use with food processing and
food contact, consisting essentially of: a polypropylene base
matrix; a thermally conductive filler loaded into the polypropylene
base matrix; said resin having a thermal conductivity between about
1.0 W/mK and about 20 W/mK.
2. The resin of claim 1, wherein said thermally conductive filler
comprises a mixture of hBN and natural graphite.
3. The resin of claim 1, wherein said resin had a thermal
conductivity between about 2.0 W/mK and about 10 W/mK.
4. The resin of claim 1, wherein said thermally conductive filler
comprises about 5 to about 70 weight percent of said resin.
5. The resin of claim 1, wherein said thermally conductive filler
comprises about 20 to about 50 weight percent of said resin.
6. A thermally conductive food tray, comprising: a tray body having
a bottom wall bounded by at least one side wall defining a food
containing portion therein; said tray body, net-shape molded from a
resin, consisting essentially of: a polypropylene base matrix; a
thermally conductive filler loaded into the polypropylene base
matrix; said resin having a thermal conductivity between about 1.0
W/mK and about 20 W/mK.
7. The tray of claim 6, wherein said thermally conductive filler
comprises a mixture of hBN and natural graphite.
8. The tray of claim 6, wherein said resin had a thermal
conductivity between about 2.0 W/mK and about 10 W/mK.
9. The tray of claim 6, wherein said thermally conductive filler
comprises about 5 to about 70 weight percent of said resin.
10. The tray of claim 6, wherein said thermally conductive filler
comprises about 20 to about 50 weight percent of said resin.
11. The tray of claim 6, further comprising a plurality of surface
area enhancements.
12. The tray of claim 11, where said plurality of surface area
enhancements are a number of spaced-apart parallel grooves.
13. A method of making a net-shape molded article for use with food
processing and food contact, comprising the steps of: providing a
mold press having a mold cavity; providing a molten resin
consisting essentially of a polypropylene base matrix; and a
thermally conductive filler loaded into the polypropylene base
matrix; said molten resin having a thermal conductivity between
about 1.0 W/mK and about 20 W/mK when fully set; and injecting said
molten resin into the mold cavity of the mold press to form said
net-shape molded article.
14. The method of claim 13, wherein said thermally conductive
filler comprises a mixture of hBN and natural graphite.
15. The method of claim 13, wherein said resin had a thermal
conductivity between about 2.0 W/mK and about 10 W/mK.
16. The method of claim 13, wherein said thermally conductive
filler comprises about 5 to about 70 weight percent of said
resin.
17. The method of claim 13, wherein said thermally conductive
filler comprises about 20 to about 50 weight percent of said resin.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority to earlier filed
U.S. Provisional Patent Application No. 60/725,211, filed Oct. 11,
2005, the contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is related generally to thermally
conductive resins and in particular to a thermally conductive resin
for use in contact with food and food processing.
[0004] 2. Background of the Related Art
[0005] In the food packaging, preparation and processing industries
it is desirable to prepare or process certain food products by
applying heat to the food product or by chilling or freezing the
food product. For instance, to freeze dry foods the frozen water
contained within the food product must be sublimed in order to
preserve the food product. This process necessarily involves
applying heat to the food product while it is in a partial vacuum.
To mold other food products, such as chocolate, ice cream, candies
and even ice cubes, the food product, while in a liquid or
semi-liquid state, is poured into a mold and chilled or frozen
until it condenses into a solid.
[0006] During these chilling or heating processes, whatever
container the food product is being held within is also necessarily
heated or chilled. If the container has a low thermal conductivity
it resists the change in temperature and thereby requires more
energy and time to prepare the food product. Therefore, it would be
advantageous to have a container made of a material that has a high
thermal conductivity in order to reduce the time and energy
consumption of the chilling or heating processes being applied to
certain food products.
[0007] Because of safety concerns and regulatory restrictions
regarding food products, it is also desirable that thermally
conductive materials that are used in close proximity or contact
with food products are safe and suitable for such use. Thermally
conductive materials that might be candidates for use in food
processing applications, such as aluminum, aluminum oxide, aluminum
nitride, beryllium oxide and copper, suffer from the disadvantage
of being unsuitable for food processing applications because of
their chemical composition, ability to transfer contaminants, or
the product form. Therefore, there is a need for a thermally
conductive material that is suitable for use in close proximity or
contact with food products.
SUMMARY OF THE INVENTION
[0008] The present invention solves the problems of the prior art
by providing a thermally conductive resin that is safe to use with
food processing applications. The thermally conductive resin of the
present invention is composed of polypropylene with a thermoplastic
additive that includes natural graphite and hexagonal boron
nitride. The thermal conductivity of the resin is between about 1.0
W/mK and 20 W/mK when fully set, and more preferably between about
2.0 W/mK and 10 W/mK to have improved mechanical properties. Also,
a method of making a net-shape molded article for use with food
processing and food contact is disclosed.
[0009] Accordingly, among the objects of the present invention is
the provision for a thermally conductive resin that can be used in
food processing and food contact.
[0010] Another object of the present invention is the provision for
a thermally conductive resin that exhibits sufficient mechanical
strength.
[0011] Another object of the present invention is the provision for
a thermally conductive resin that can be formed into an article for
use as a food mold that has good mold-release characteristics.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] These and other features, aspects, and advantages of the
present invention will become better understood with reference to
the following description, appended claims, and accompanying
drawings where:
[0013] FIG. 1 is a perspective view of an exemplary food tray that
can be constructed using the resin of the present invention;
[0014] FIG. 2 is a side view of the food tray shown in FIG. 1;
and
[0015] FIG. 3 is a bottom view of the food tray shown in FIG.
1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0016] Thermally conductive molding compounds based on
polypropylene with specific constituents to impart thermally
conductivity have been found to be sufficiently thermally
conductive and have the appropriate food contact requirements that
allow them to be broadly used in the food processing industries as
food molds, trays and other components that come in direct contact
with foodstuffs and consumable water or water products.
[0017] For example, FIG. 1 shows perspective view of a food tray
that can be constructed using the resin of the present invention
generally at 10. The food tray 10 has a tray body with a food
holding portion formed by a bottom wall 12 and bounded by sidewalls
14. Optional handles 16, 18 can be formed to ease handling of the
tray 10. The try 10 shown is by example only and one skilled in the
art would appreciate the fact that other trays having multiple
wells and other food handling implements could be formed using the
resin of the present invention.
[0018] Referring now to FIGS. 2 and 3, the food tray 10 has an
underside 20 with a number of surface area enhancements 22 to
improve the thermal conductivity of the food tray 10. Although the
surface area enhancements 22 shown are a number of space-apart
parallel grooves, one skilled in the art could appreciate that
other configurations are possible.
[0019] Polypropylene has been found to be the most suitable
thermoplastic base resin in these uses because it provides:
[0020] 1 ) a composition that can be food approved;
[0021] 2) a tensile and flex modulus that is appropriate so that in
combination with thermally conductive additives provides a final
part that has sufficient mechanical properties including impact
strength; and
[0022] 3) forms a resin rich layer at the molded surface that
contributes to good release and other properties.
[0023] Although polypropylene is preferred, other polymers may be
used such as polyethylene, polyethylene terephthalate, and liquid
crystal polymers to name a few. Polypropelene is more advantageous,
however, because it retains flexibility where other polymers are
too rigid. For example, fins could be used as well. To maximize the
thermal conductivity of the food tray 10, it is desirable that the
surface area enhancements are pronounced to maximize the surface
area of the underside 20 of the food tray 10.
[0024] Additives that have been found to be suitable for providing
the thermal conductivity enhancement to the thermoplastic
composition of the invention include: 1) natural graphite and 2)
hexagonal boron nitride. These materials add suitable thermally
conductivity enhancement and are capable of passing food contact
regulations when compounded with specific polypropylene materials.
Natural graphite is preferred to synthetic graphites since
synthetic graphites start as lower molecular weight organics that
may include restricted compounds that form during their high
temperature processing (e.g. PNAs). Natural graphites do not
contain these compounds. Hexagonal boron nitride is a synthetic
material but the boron nitride itself and impurities resulting from
the synthetic process do not contain regulated ingredients. The
majority of materials that might be considered for enhancing the
thermal conductivity of a resin to the level required for suitable
heat transfer in food applications are not suitable for food
contact due to their chemical composition, contaminants, or product
form (e.g. aluminum, aluminum oxide, beryllium oxide, aluminum
nitride, and copper).
[0025] The suitable conductivity range of the invention for the
intended use is approximately 1.0 W/mK to 20 W/mK, and most
optimally in the range of approximately 2.0 W/mK to 10 W/mK. The
suitable level of additive in the polypropylene compositions is
10-70 weight % and more preferably 20-50 weight %. Loading as low
as between 5 and 10 weight % of the additive can be use if
conductivity of 1.0 W/mK threshold is desired.
[0026] Low loading levels may be desirably where self-heating
properties induced by microwave ovens is desired. In this case,
graphite is preferably used as the thermally conductive
additive.
[0027] The compositions and preferred compositions have also been
discovered to have other properties required in food processing
including but not limited to 1) release characteristics; 2)
sufficient mechanical properties throughout a temperature range
from -40.degree. C. to near 100.degree. C.; 3) resistance to
detergents and other cleaning agents; 4) resistance to
cooling/heating fluids.
[0028] Therefore, it can be seen that the present invention
provides a unique solution to the problem of providing a thermally
conductive molding compound that can be used safely in the food
preparation industries.
[0029] It would be appreciated by those skilled in the art that
various changes and modifications can be made to the illustrated
embodiments without departing from the spirit of the present
invention. All such modifications and changes are intended to be
within the scope of the present invention except insofar as limited
by the appended claims.
[0030] Examples using natural graphite additive and a polypropylene
base: TABLE-US-00001 % nat. graphite/remainder polypropylene W/mK
70 18 50 10 30 3 30 5 25 5 15 2 Note: depending on the type of
natural graphite, different thermal conductivities may be
obtained.
[0031] Examples using Boron Nitride as an additive and
polypropylene as a base: TABLE-US-00002 % BN/remainder
polypropylene W/mK 75 5.8 60 4.5 25 1.3 15 1.4
[0032] Comparative examples using Alumina as an additive and
polypropylene as a base: TABLE-US-00003 % Alumina (Al2O3)/remainder
polypropylene W/mK 65 1.2 65 1.2 60 NA 25 NA
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