Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02389078 2002-04-25
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POLYMER COMPOSITIONS SUITABLE FOR
MICROWAVE COOKING APPLICATIONS
This application claims the benefit of U.S. Provisional Application No.
60/162,461, filed October 29, 1999.
This invention relates to cookware, and more particularly to cookware useful
in
microwave ovens. Still more particularly, the invention relates to cookware
for use in
microwave processing of foodstuffs, particularly pizzas and the like, and to
filled
compositions therefor containing high temperature resin and a radiation
absorbent
filler, preferably carbon fiber.
Filled compositions according to the invention absorb microwave energy and
are thereby heated. Such compositions may be particularly useful in the
fabrication
of oven cookware adapted for cooking food in a microwave oven, for example
cooking trays, sheets, pans, dishes, casseroles, and the like.
Background of the Invention
~5 Conventional methods of heating and cooking food, whether by grilling,
boiling, baking or frying, supply heat to the food externally. The surface of
the food
becomes heated, establishing a temperature gradient from the surface to the
interior.
Heat is transferred from the surface to the interior by thermal diffusion, so
that the
coldest point approaches the warmest temperature of the system with time. When
2o the internal temperature reaches the desired final temperature, the cooking
or
heating process is complete. The maximum temperature of the food is limited by
the
temperature of the heating medium. For example, food immersed in water at
ambient pressures may reach the boiling point of water, 100 °C, and no
more.
The surface of food cooked by conventional heating methods will be
25 maintained at the highest temperature and thus heated for the greatest
length of
time. Generally food surfaces will take on an appearance and texture
characteristic
of the cooking method. For example, meats that are grilled will have seared
surfaces, baked breads will have crusts, and fried foods may be crisp. While
the
particulars will vary from culture to culture, the acceptability of foods
turns on having
3o a proper surface appearance, based on preferences that develop or are
acquired
over many generations.
More recently, microwave heating has become used for cooking and reheating
foods and is widely accepted for its rapid heating of foods and ease of use.
In
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microwave heating, food is exposed to high frequency electromagnetic
radiation.
Water molecules contained within the food, due to their dipolar nature, try to
follow
the very high frequency oscillations of the electric field associated with the
electromagnetic radiation, and thus are heated. When there is little or no
water
present in the foodstuff, or the water becomes substantially lost by
evaporation, no
further heating can occur.
Although food cannot be heated above about 100 °C in home and food
service microwave ovens, the temperatures are sufficiently high for reheating
cooked
food, and the ovens will cook most foods adequately. However, microwave
heating
~o tends to cause foods to soften, producing undesirable changes in texture.
Browning
and other surface effects attained with conventional cookery, which are
essential to
acceptability are not directly reproduced by microwave heating. The food
surfaces
do not reach the high temperatures encountered during conventional cookery;
indeed, the surface of food heated in a microwave oven often is at a lower
temperature than the interior due to external cooling. Foods cooked in
microwave
ovens thus do not resemble the products of conventional cookery and, even
though
fully cooked and safety edible, may be thought unappetizing and unpalatable.
One of the most popular frozen entrees is pizza, constructed of a lower crust
layer of dough and an upper topping layer including a mixture of various
substances,
2o generally cheese, tomato sauce and meat. The topping materials are selected
to
provide a variety of products for the consuming public. Commonly the crust is
baked,
and the topping is added in an uncooked, usually frozen condition, intended to
extend their shelf life. For the best consumer acceptance from a taste and
texture
sense, such layered food products or articles should be thawed and then baked
by
25 some heating appliance that will restore the desired reconstituted texture
and
condition. Due to the characteristics of the crust, high quality
reconstitution is
accomplished only by heating in a convection oven. The standard convection
oven
produces a crunchy, high quality crust that is crisp with a topping cooked to
duplicate
fresh, hand made pizza.
3o Attempts to reconstitute pizza by microwave heating have been less
satisfactory, producing pizza having a compromised ultimate quality when
compared
with pizza reconstituted only in a convection oven. Using a microwave oven to
bake
or cook frozen pizza definitely shortens the cooking time; however, the
texture is
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deteriorated and the crust has almost no crispness or crunchiness. Generally,
providing sufficient heat to make the crust crisp tends to overcook the
topping
material. Delay in eating the pizza may cause the crust to become hard and
brittle
and the product generally loses its resiliency, turning leathery and causing
the hot
sauces forming part of the topping to migrate into the cells of the prebaked
crust.
Loss of crispness and texture in reheating foods, including pizza, has been
addressed by packaging design. Such packaging may include ribs or protrusions
to
support the food within and allow air circulation to remove vapors from the
surface.
Materials employed for such packaging frequently are thermoplastic sheet
materials
~o containing radiation absorbent filler, for example, carbon black, graphitic
particles,
comminuted carbon fiber particles or the like. The filler absorbs microwave
energy,
undergoing dielectric heating and thereby raising the temperature of the
container or
packaging. Such packaging continues to transmit heat to the food after the
microwave irradiation cycle has been completed, reducing the occurrence of
cold
~5 spots in the food and enhancing drying and crisping.
Packaging designs particularly suited for use in reheating pizza may include a
microwave susceptor sheet on or spaced from the lower wall of the microwave
oven
to serve as a plate or platform. Susceptors generally comprise a layered sheet
stock
with layers having a metallized surface or formed of other conductive material
to
2o absorb microwave energy. Placed in the energy field of a microwave oven,
susceptors undergo inductive heating, reaching temperatures above 100
°C, and
thus may be designed to remove moisture and enhance drying and crisping during
heating.
The materials disclosed in the art for the construction of such improved
25 packaging have generally included cellulosic sheet stock and filled
thermoplastics
including polyethylene, polypropylene and polyesters such as polyethylene
terephthalate and the like. Although the improved packaging may have some
capability for producing higher temperatures needed for browning and similar
processing of foods, generally, the packaging has been intended for use in
reheating
3o pre-cooked foods requiring crisping and for cooking foods that can be
successfully
processed at moderate temperatures, i.e. temperatures that do not much exceed
about 100°C.
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Filled ceramic composite materials capable of attaining high temperatures
when irradiated with microwave energy are also known. For example, self-
heating
structures comprising silicon carbide filled with a microwave susceptible
filler such as
carbon fiber, alumina fiber or the like have been disclosed for use in
microwave
s cooking. When irradiated in a microwave oven, these self-heating structures
may
attain temperatures as great as 500°C. Surfaces of food in contact with
such a
vessel will thus be rapidly heated, much as in a conventional oven, while the
internal
temperature becomes rapidly increased through microwave heating, cooking the
food. The resulting food product may thus be appropriately cooked throughout
and
~o simultaneously provided the desired browned or seared surface. Similar
structures
have been used in processing pizza. In this, use the self-heating vitroceramic
disc or
plate is irradiated with microwaves and preheated to a temperature near 300
°C.
Raw pizza base or crust is placed on the plate and allowed to precook, thereby
pasteurizing the crust and providing a crisped or browned lower surface. The
base is
~5 then removed from the plate, provided with the topping and stored for
subsequent
final cooking in a conventional convection oven.
Vitroceramic plates are generally somewhat brittle, thus subject to damage
and breakage, and are heavy and are thus more difficult to use and
inconvenient to
store. Moreover, filled ceramic materials and particularly fiber filled
silicon carbide
2o structures require complex operations to produce and may not be readily
formed into
attractive utensils.
The convenience of a microwave oven has thus allowed the consumer to
rapidly and easily reheat prepared foods, for example, by simply removing a
frozen
food item from the consumer's freezer and heating the item in the microwave
oven.
25 Heating and cooking with microwave ovens has been more limited to
processing soft
foods and foods with gravies, sauces and the like that do not require browning
or
crisping. There remains a great need in the art for improved materials that
permit
using microwave heating to heat or cook foods needing browning and crisping
such
as, for example, pizza, hashbrown potatoes, fish sticks and the like, and for
cooking
3o utensils and containers comprising such improved materials.
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Summary of the Invention
This invention is directed to improved polymer compositions suitable for use
in
food cooking applications, said compositions comprising at least one high
temperature polymeric material and a heating effective amount of at least one
s microwave susceptible filler material suitable for use as microwave
temperature
enhancing material. The invented compositions are useful in providing cookware
suitable for microwave use; hence, the invention is further directed to
microwave
cookware and to a method for making such cookware. The invention may also be
viewed as directed to a method for preparing food wherein the food is placed
in or on
~o cookware comprising at least one high temperature polymeric material and a
heating
effective amount of at least one microwave susceptible filler.
As used herein, the term "heating effective amount" means an amount of
microwave susceptible filler that, when subjected to microwave radiation, will
cause
the temperature of the cookware comprising the filler to increase to a
temperature
~ s such that the cookware will heat, cook or preferably brown food placed in
or on the
cookware but not result in the melting or excessive softening of the polymeric
material during such heating, cooking or browning.
Detailed Description of the Invention
The improved polymer compositions according to this invention are filled
2o polymers comprising a high temperature polymer and microwave susceptible
filler.
High temperature polymers or resins useful in forming the compositions and
cookware of this invention are polymers that have high temperature properties
sufficient to withstand temperatures typically necessary to heat food to a
temperature
suitable for cooking and particularly for browning the surfaces thereof.
Crystalline or
2s partially crystalline thermoplastic polymers having a melting point (Tm) of
at least
about 140°C, preferably at least about 200°C, and most
preferably at least about
250°C, and amorphous thermoplastic polymers having a glass transition
temperature
(Tg) of at least about 140°C, preferably of at least about 200°C
and more preferably
of at least about 250°C will generally be suitable for the purposes of
this invention.
so Generally, where rapid browning of meats and the like with brief exposure
to heat is
desired, temperatures well in excess of 250°C to as great as
350°C or greater may
be encountered, necessitating the use of crosslinked and thermoset resins and
the
like. Such resins thus may also be found useful, provided the thermal
decomposition
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temperature of the resin is greater than use temperature envisioned, i.e.
greater than
about 250 to 350°C.
Tg and Tm are conventionally determined in the art, as are polymer thermal
decomposition temperatures, using standardized thermogravimetric analysis
methods. For the purposes of describing and characterizing compositions
according
to this invention, differential scanning calorimetry (DSC) procedures
conducted at a
heating rate of 20°C per minute are conveniently employed.
Polymers having high temperature properties suitable for use in the practice
of
this invention may include poly(arylether sulfones), polysulfones, aromatic
polyesters,
~o polycarbonates, poly(arylether ketones), polyetherimides, aliphatic,
partially aromatic
and aromatic polyamides, polyimides, particularly aromatic polyimides, and the
like.
Particularly preferred are the aromatic polyesters and the poly(arylether
sulfones).
Poly(arylether sulfones) are well known in the art. Suitable commercial
examples of such polymers include Udel and Radel thermoplastics available from
BP
Amoco Polymers, Inc. Poly(arylether sulfones) that may be found useful in the
practice of this invention are further described in the art, for example, in
U.S. Patent
4,293,670 and in Canadian Patent 847,963. Aromatic polyesters, particularly
liquid
crystalline aromatic polyesters, that may be useful in the practice of this
invention are
also well known in the art, and include for example, Xydar liquid crystal
polymers
2o commercially available from BP Amoco Polymers, Inc. Particularly useful and
suitable are Xydar SRT-400 and Xydar SRT-900 liquid crystal polymers. These
Xydar thermoplastic polymers are wholly aromatic polyesters made by
polymerizing a
mixture of terephthalic, isophthalic and p-hydroxybenzoic acid with biphenol.
Aromatic polyesters suitable for use in this invention and methods for their
manufacture are disclosed in U.S. Patents 3,637,595; 4,503,168; 4,563,508; and
4,626,557.
Polyetherimides are also well known high temperature polymeric materials,
and polyetherimides suitable for use and available from the trade include
Ultem
thermoplastics, manufactured by the General Electric Company. Additional
so polyetherimides and methods for their manufacture are disclosed in U.S.
Patent
4,293,670 and in U.S. Patent 4,503,168.
Poly(arylether ketones) useful in the practice of this invention are available
commercially from BP Amoco Polymers, Inc. and from Victrex. Examples of useful
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poly(arylether ketones) and methods for their manufacture are disclosed, for
example, in U.S. Patent 4,713,426.
Aromatic and partially aromatic polyamides may also be found useful in the
practice of this invention. Such polyamides are commercially available from BP
s Amoco Polymers, Inc. under the name Amodel, and methods for making aromatic
and partially aromatic polyamides, as well as examples of suitable aromatic
and
partially aromatic polyamides, are disclosed and described in U.S. Patent
Reissue
34,447. Aromatic polycarbonates may also be found useful in some applications
according to this invention, and are commercially available from the General
Electric
~o Company under the name Lexan and from the Bayer Corporation. Polycarbonates
and method for their manufacture are disclosed and described in U.S. Patents
4,018,750: 4,123,436, and 3,153,008. The U.S. Patents and Canadian Patent
recited above are hereby incorporated by reference in their entirety.
It will be understood that when in use, the compositions according to this
~s invention will directly contact the food being heated. Foods, and
particularly foods
that are wet or produce juices and other fluids on heating, tend to extract
and
dissolve lower molecular weight components including plasticizer, residual
monomer,
stabilizing additives and the like from resin formulations. In addition, some
resins
may be subject to hydrolytic attack by moisture and by food components that
are
2o acidic or strongly alkaline, and may even chemically react with the food
components
at elevated temperatures. Thus, it will be necessary that the resin
formulations be
selected to be resistant to such interaction with foods, and contain only
grades of
resins and fillers, and additive components, if any are included, that are
deemed
acceptable for such use. Generally, plastic materials intended for use in food
contact
2s applications are provided by resin manufacturers in particular grades
formulated to
be suitable for food use. Approved, food-grade versions of lower temperature
thermoplastics including polyethylene and polypropylene, as well as
polyethylene
terephthalate, are widely available. Grades of Xydar liquid crystal
thermoplastics
deemed suitable for food contact are also available, and suitable grades of
other high
so temperature thermoplastics, including poly(arylether sulfones),
polycarbonates and
polyether imides, may also be available.
Generally described, microwave susceptible fillers are electrically conductive
particulates that absorb microwave energy and thereby become heated. Fillers
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suitable for use in the practice of this invention include metals in finely
divided form
such as, for example, powered elemental iron, tin, copper, aluminum, silver or
the
like, either as elemental metals or in the form of oxides. Metal salts such
as, for
example, hydroxides, halides such as chlorides or bromides, sulfates and the
like
may also be found useful; preferably such compounds will be insoluble and not
subject to being leached by foods or when immersed in water such as during
cleaning operations.
Particulate carbon, and particularly carbon fibers are particularly suitable
for
use as microwave susceptible fillers. Carbon in the form of carbon black or
similarly
~o finely divided particles may be used. More preferred will be carbon that is
at least
partially, for example at least about 50 weight percent, more preferably at
least about
75 weight percent, graphitic, and still more preferably substantially entirely
graphitic,
and most preferably will be particulate in form.
Carbon fiber manufactured from pitch or from a synthetic source such as
polyacrylonitrile (PAN) fibers is particularly useful. Graphitized pitch-based
carbon
fiber containing at least about 50 weight percent graphitic carbon, more
preferably
greater than about 75 weight percent graphitic carbon and up to substantially
100%
graphitic carbon is readily available from commercial sources. Highly
graphitic
carbon fiber particularly suitable for use in the practice of this invention
may be
2o further characterized as highly conductive, and such fiber is generally
supplied
having a modulus of about 80 to about 120, more preferably about 100 to about
115
million pounds per square inch, i.e., million Ibs/inz (MSI).
Carbon fiber may be employed as chopped carbon fiber, or in other particulate
form such as may be obtained by milling or comminuting the fiber.
2s The amount of microwave susceptible filler employed for the compositions
according to the invention will depend in part upon the nature of the filler
selected.
More highly conductive fillers such as highly graphitized carbon fiber and
metals will
be employed at lower levels than less susceptible fillers including carbon
black, metal
oxides and the like. Generally, the amount employed will be selected to raise
the
so temperature of cookware surfaces in contact with the pizza or other
foodstuff, or in
close proximity thereto, to a level sufficient to produce browning or
scorching, without
causing undesirable burning or damage to the cookware. Surface temperatures
suitable for these purposes lie in the range of from about 180°C to the
upper use
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temperature of the resin component, and preferably from about 200°C to
about
260°C. While it is believed to be essential that the browning or
cooking temperature
be reached quickly, compositions with an excessive amount of susceptible
filler may
continue to rapidly increase in temperature and reach temperatures above a
level
s considered safe for such ovens. In addition, compositions containing high
levels of
conductive filler tend to reflect microwave radiation and may thereby cause
damage
to the oven. Hence the level of filler will also be selected with a
consideration of the
envisioned enduse. Preferably articles comprising the filled composition will
withstand normal heating cycles of from about 1 to about 20 minutes without
~o exceeding a safe upper temperature or causing damage to the oven.
For compositions comprised of a resin selected from the higher temperature
resins suitable for food contact use and resistant to hydrolytic or other
attack by food
components, the amount of microwave susceptable filler employed will
preferably lie
in the range of from about 0.1 to about 10.0 wt%, more preferably from about
0.2 to
~s about 5 wt%, and still more preferably from about 0.5 to about 5 wt%, based
on
combined weight of filler and polymer. As noted, more conductive fillers
including
graphitic carbon fibers will be employed at levels at the lower end of these
preferred
ranges, preferably in amounts of from about 0.5 to about 4 wt%. Fillers may be
employed singly or in combination; for example, comminuted carbon fiber may be
2o combined with pigment grade carbon black to provide a suitably pigmented
composition having the desired thermal properties together with an attractive
color
and appearance.
In addition to high temperature resin and microwave susceptible filler,
compositions according to the invention may include other additives and
components
25 that are not considered microwave susceptible fillers such as talc or other
mineral
fillers and reinforcing fillers, non-conductive fibers or the like at levels
sufficient to
improve mechanical properties including high temperature strength and rigidity
according to common practice in the resin compounding molding arts. Thermal
stabilizers, plasticizers, ultraviolet light stabilizers, lubricants, mold
release agents,
so colorants, and other additives and components commonly used in the polymer
molding arts may also be included as desired. As noted, it will be understood
that
only grades of additive components, if any are included, that are deemed
acceptable
for such use will be employed.
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The high temperature resin and microwave susceptible filler, together with
such other additive components as may be used, may be blended and extruded
according to well known and widely practiced methods and procedures, using
standard equipment commonly employed in the polymer blending arts. The polymer
s compositions of this invention will be further fabricated to form cookware
and similar
articles using methods and practices commonly used in the plastics fabricating
art,
including injection molding, blow molding, thermoforming, melt extrusion and
the like.
Cookware according to the invention may take any convenient form, for example,
a
pan, a tray, a sheet, a dish, bowl, casserole dish, a pizza stone or any other
type of
~o cookware. Trays, sheets and the like are readily produced from the
compositions of
this invention and may be found suitable for a wide variety of cooking and
baking
uses; hence such articles will be the most preferred form of cookware.
Examples
Components used in preparing the formulations of the following examples
~s include:
LCP: liquid crystal polymer, an aromatic polyester having a melting
point of 350°C, obtained as Xydar SRT 900 resin from BP Amoco Polymers,
Inc.
Talc: obtained as Vertal 1000 from Luzenac America, Inc.
Carbon fiber: comminuted graphitized carbon fiber, obtained as
2o ThermalGraph DKXD from BP Amoco Polymers, Inc.
Examples 1-4 and Comparison Example: Formulations according to the
invention, together with control formulations, were prepared and molded to
provide 3
in. by 2 in. by 1/8 in. thick plates for thermal testing. The compositions are
summarized in Table I, below. The formulations further included as colorants
25 pigment grades of 0.25 pph titanium dioxide, 0.32 pph Channel black, 0.55
pph Kelly
Green and 2.0 pph Lightfast Yellow, based on 100 parts combined weight of LCP,
Talc and Carbon Fiber.
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TABLE/
Ex. No.: C-1 1 2 3 4
LC wt% 55 55 55 55 55
P
CarbonFiber - 2 4 6 8
wt%
Talc wt% 45 43 41 39 37
The plates were placed in a microwave oven rated at 1000 watts and exposed
to microwave radiation for 10 minutes. The plates of Examples 1-4 reached a
high
temperature, as determined by touch; the plate of the Comparative Example did
not
significantly increase in temperature.
Additional plates were molded from a composition substantially as shown in
Examples 1 and 2. The molded plates were used to cook commercial pizza
comprising a dough crust and a topping, the topping comprising cheese and a
o tomato-based sauce. After approximately 5 min. of heating, the pizza was
found to
have an acceptably browned surface, together with an adequately cooked
topping.
Examples 5 - 11 Additional formulations according to the invention were
prepared and molded to provide 3 in. by 2 in. by 1/8 in. thick plates for
thermal
testing. The molded plates were placed in a microwave oven rated at 1000 watts
~5 and the surface temperature of each was measured with thermocouples as each
was
exposed to microwave radiation. Total time required to reach 200 °C and
then
exceed 260° C was recorded.
The compositions and test results are summarized in Table II, below.
TABLE II
Ex. No.: C-2 5 6 7 8 9 10 11 12
LCP wt% 55 55 55 55 55 55 55 55 55
Talc wt% 45 44.5 44 43.5 43 42.8 42.5 42 41.5
Carbon Fiber wt% - 0.5 1.0 1.5 2.0 2.2 2.5 3.0 3.5
Carbon Black pph 0.32 0.32 0.32 0.32 0.32 0.32 0.32 0.32 0.32
Time min. > 10 > 10 > 10 > 10 9* > 10 6 4.5 3.8
2o Notes: * An additional sample tested at > 10 min.
It will be seen that maintaining the test plate for more than 10 minutes
without
exceeding the limit temperature of 260 °C requires the level of
susceptible filler be
less than about 2.5 wt% of the combned weight of resin, fiber and talc, or 4.4
wt%
based on combined weight of resin and carbon fiber. Inasmuch as carbon black
is
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somewhat conductive and thus also susceptible to microwave heating,
compositions
with increased levels of carbon black were evaluated.
Examples 12 - 21 Additional formulations according to the invention were
prepared and molded to provide 3 in. by 2 in. by 1/8 in. thick plates for
thermal
s testing. The molded plates were placed in a microwave oven rated at 1000
watts
and the surface temperature of each was measured with thermocouples as each
was
exposed to microwave radiation. Total time required to reach 200 °C and
then
exceed 260° C was recorded.
The compositions and test results are summarized in Table III, below.
o TABLE III
Ex. No.: 13 14 15 16 17 18 19 20 21
LCP wt% 55 55 55 55 55 55 55 55 55
Talc wt% 44.1 44.1 44.1 44 44 44 43.9 43.9 43.9
Carbon Fiber 0.9 0.9 0.9 1.0 1.0 1.0 1.1 1.1 1.1
wt%
Carbon Black 1.4 1.5 1.6 1.4 1.5 1.6 1.4 1.5 1.6
pph
Time min. 4 4.75 3.5 5 5 6.25 7.75 6 5
An additional sample, comprising 1.2 wt% carbon fiber and 1.4 pph carbon
black was molded and tested, producing a heating time of 3.25 min.
Compare the heating behavior of the specimens of Examples 13-21 with the
~s specimen of Example 6 comprising 1 wt% carbon fiber and 0.32 pph carbon
black,
having a heating time of over 10 min. The increased level of carbon black will
be
recognized to have significantly increased the rate of heating. However, it
will be
apparent that small changes in the levels of carbon fiber and in the levels of
carbon
black produced rather erratic differences in heating time. Generally, these
2o differences appear to fall within error limits of the measurement
techniques
employed, and likely arise at least in part from non-uniform dispersion of the
carbon
black and fiber within the test specimens.
Compositions comprising only carbon fiber as the susceptible filler, i.e. with
no
carbon black, were also prepared and evaluated.
2s Examples 22 - 28 Additional formulations according to the invention were
prepared and molded as in Examples 5-11 to provide 3 in. by 2 in. by 1/8 in.
thick
plates for thermal testing. The molded plates were placed in a microwave oven
rated
at 1000 watts and the surface temperature of each was measured with
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thermocouples as each was exposed to microwave radiation. Total times required
to
reach 200 °C and then to exceed 260° C were determined.
The compositions are summarized in Table IV, below.
TABLE IV
Ex. No.: I 22 23 24 25 26 27 28
LCP wt% 55 54.1 54 53.9 53.8 53.7 53.6
Talc wt% 45 45 45 45 45 45 45
Carbon Fiber 0 0.9 1.0 1.1 ~ 1.2 1.3 1.4
wt%
wt% on resin 0 1.6 1.8 2.0 2.2 2.4 2.5
and fiber
For compositions comprising a liquid crystal polymer or polyester resin and
graphitic carbon fiber, a level of carbon fiber of about 2 wt%, based on
combined
weight of resin and fiber, will be suitable for cooking pizza and the like.
The invention will thus be seen to be directed to cookware for use in
~o microwave processing of foodstuffs, particularly pizzas and the like, and
to filled
compositions therefor containing high temperature resin and a radiation
absorbent
filler, preferably carbon fiber. Generally the invented composition will
comprise a
high temperature polymer, preferably a crystalline or semicrystalline polymer
having a
crystal melting temperature Tm of at least 180°C, together with a
microwave
~s susceptable filler. Particularly suitable are compositions comprising a
liquid crystal
polymer having a Tm of from about 200 °C to about 350 °C and a
heating effective
amount, preferably from about 0.2 to about 5 wt%, of a carbon fiber,
preferably a
graphitized carbon fiber, in particulate form. The invented composition may
further
comprise additional fillers including talc and the like as necessary to
provide
2o improved mechanical properties, as well as pigments, colorants, thermal
stabilizers,
antioxidants and the like according to practices and methods commonly employed
in
the resin compounding arts.
The invented compositions are useful in the fabrication of cookware, and in
molded goods for use in the preparation of foods, and may be particularly
useful in
25 microwave cookery. Such cookware, as well as methods of processing food
employing such cookware, are also contemplated as falling within the scope of
the
invention as disclosed and described herein. Although embodiments of the
invention
have been set forth in the form of specific examples, these embodiments are
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provided by way of illustration of the invention and not in limitation
thereof. Further
modifications and adaptations of the teachings will be readily apparent to
those
skilled in the art and are contemplated as within the scope of the invention,
which is
defined by the following claims.
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