Note: Descriptions are shown in the official language in which they were submitted.
2 0 Q ~ 2 9 6
The present invention relates generally to the
structure of a film for a high temperature cooking apparatus
and, more particularly, to the structure of the film with
improved heat resistivity and non-tackiness. The invention
further relates to a method of forming such a film structure.
In the development of a high-temperature high-speed
cooking apparatus, it is desirable to reduce the cooking time
while making cooked food more tasty and effectively using the
cooking time. Accordingly, it is necessary to process food
at a high temperature and to make the cooking surface of a hot
plate and the inner surfaces of a microwave oven resistive to
high temperatures. However, conventional microwave ovens and
electric hot plates have insufficient heat resistance
properties.
Typically, the inner surfaces of a microwave oven
and the cooking surface of an electric hot plate can be formed
of a heat-resistive stainless steel sheet, an enamelled steel
sheet or a steel sheet coated with a heat-resistive ceramic
coating comprising a binder of a boro-siloxane resin, a
silicone resin, a siloxane resin and the like, an inorganic
pigment, a filling material and the like. However, there are
disadvantages with the enamelled steel sheet. In particular,
the enamelled steel sheet needs to be heated to a high
temperature in the range of from 400 to 700~C, so that it is
difficult to achieve accurate dimensions. Further, the
thickness of the steel sheet cannot be substantially reduced
so that the microwave oven is very heavy. Moreover, the
enamelled steel sheet presents design problems in that a
reinforcing rib or a diaphragm is required to prevent thermal
deformation. Also, the enamel coated on the steel sheet is
liable to crack, resulting in a poor production yield. This
enamelled steel sheet is also ~p~n~ive.
With respect to a steel sheet coated with the
heat-resistive ceramic coating, only a stainless sheet can be
used as the steel sheet. Thus, the use of an aluminum-plated~
a zinc-plated, or other inexpensive steel sheet, cannot be
used since properties including resistance to corrosion and
contamination, and adhesion of the coated film at high
temperatures cannot be achieved. Therefore, the stainless
,...
, . .
2 0 ~ 2 2 ~ 6
steel must be used thereby increasing the cost of the
microwave oven.
It is an object of the present invention to provide
a film for the surfaces of a high temperature cooking
apparatus which demonstrates improved properties including
heat resistance, corrosion resistance, resistance to
contamination and scorching by food, adhesion between layers,
resistance to the formation of micro-cracks to which ceramics
are typically prone, and which has low manufacturing costs.
It is another object of the present invention to
provide a method of forming such a film for surfaces of a
high temperature cooking apparatus.
In order to achieve the above objects, a film for a
high temperature cooking apparatus provided on a substrate
forming a surface of said high temperature cooking apparatus,
according to a first aspect of the present invention,
comprises:
a ceramic layer including ceramic poly-titano-
carbosilane and a non-tacky resin, provided over said
substrate; and
a non-tacky resin layer including a non-tacky resin,
provided on said ceramic layer;
wherein the concentration of said non-tacky resin
included in said ceramic layer progressively increases
towards the upper surface of the ceramic layer.
In the first aspect of the present invention, the film
preferably comprises a heat-resistive pigment including a
heat-resistive metal oxide or composite oxide.
The film exhibits corrosion resistance and non-
tackiness up to a temperature of 300~C, becomes totallyceramic at a temperature above 400~C to be durable up to
1000~C and forms a fine hard film which is corrosion
resistant. Thus, this film can be utilized for the inner
surface of the heating chamber of a microwave oven. Further,
the film can be coated onto an inexpensive steel sheet,
thereby decreasing the cost of the microwave oven.
~ .
2 0 ~ 2 2 9 6
-- 3
A film, provided on a substrate forming a surface of
a high temperature cooking apparatus, according to a second
aspect of the present invention, comprises a ceramic layer
including poly-titano-carbosilane and a fluororesin, provided
on the substrate, and a fluororesin layer provided on the
ceramic layer wherein the concentration of the fluororesin
increases toward the upper surface of the ceramic layer, and
becomes 100~ at the uppermost layer portion thereof.
The ceramic layer preferably comprises a heat-
resistive pigment including a heat-resistive metal oxide or
composite oxide.
In both the first and second aspects of the present
invention, since the non-tacky resin or fluororesin layer
formed of a non-tacky resin or fluororesin is formed in the
uppermost layer portion of the ceramic layer, even oil drops
adhered to the film can easily be removed. Moreover, a body
portion of the film is highly resistive to heat at a high
temperature because it is formed of a ceramic layer including
poly-titano-carbosilane which is made ceramic. Since the
proportion of the non-tacky resin or fluororesin to poly-
titano-carbosilane changes successively in a vertical
direction at the interface between the ceramic layer and the
non-tacky resin or fluororesin layer, the ceramic layer and
the non-tacky resin or fluororesin layer have a good
adhesiveness.
In the film according to the second aspect of the
present invention, since the fluororesin is included in the
ceramic layer, the fluororesin layer provided on the ceramic
layer and the ceramic layer are compatible with each other
and thus are strongly bonded together. Further, since the
fluororesin layer is reliably formed on the ceramic layer,
the film has excellent non-tackiness properties.
A method of forming a film on a substrate forming a
surface for a high temperature cooking apparatus, according
to a third aspect of the present invention, comprises the
steps of:
2 0 ~ 2 2 9 6
blending a non-tacky resin into an organic solvent
varnish including poly-titano-carbosilane, so as to form a
coating material having a specific gravity of from
approximately 1.1 to approximately 1.8 and a non-volatile
component of from approximately 50~ to approximately 70~;
coating said coating material over said substrate;
pre-drying the resultant coating; and
sintering the coating at a temperature above 300~C so
as to form a ceramic layer, including ceramic poly-titano-
carbosilane, having a concentration of the non-tacky resin
which progressively increases towards the upper surface
thereof, such that the uppermost portion of the ceramic layer
substantially comprises non-tacky resin. A fluororesin is
preferably employed as the non-tacky resin.
In the method according to the third aspect, poly-
titano-carbosilane, which serves as a binder, becomes ceramic
during sintering to form an aggregate of minute particles.
At the same time, powders of the fluororesin melt and rise to
the surface due to a difference in specific gravities, so
that the fluororesin is distributed among the ceramic
particles. This leads to the formation of a film with a high
concentration of fluororesin in the upper most layer portion
of the film structure.
A method of forming a film on a substrate forming a
surface of a high temperature cooking apparatus, according to
a fourth aspect of the present invention, comprises the steps
of:
blending a non-tacky resin into an organic solvent
varnish including poly-titano-carbosilane, thereby forming a
coating; and
applying the coating on the substrate and sintering
the applied coating, wherein the concentration of said non-
tacky resin included in said coating progressively increases
toward outer surface of said coating.
A method of forming a film on a substrate forming a
cooking surface of a high temperature cooking apparatus,
according to a fifth aspect of the present invention
,,.~
~ ~ ~ 2 2 9 6
- 4a -
comprises the steps of:blending a fluororesin into an organic
solvent varnish including poly-titano-carbosilane, thereby
forming an undercoating. The undercoating is then applied on
the substrate, and thereafter evaporation of the organic
solvent causes formation of an undercoated film on the
substrate. Subsequently, a liquid coating of a dispersion-
type fluororesin is applied on the undercoated film and is
then sintered. The concentration of said fluororesin
included in said undercoated film progressively increases
toward the interface of the undercoated film and the liquid
coating.
In the method according to the fifth aspect of the
present invention, the fluororesin is reliably formed on the
uppermost layer portion of the ceramic layer, resulting in a
highly non-tacky film structure.
The invention will be more readily understood from the
following description of a preferred embodiment thereof
given, by way of example, with reference to the accompanying
drawings, in which:
Figure 1 is a perspective view of a microwave oven;
r
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2~2~6
-- 5 --
Figure 2 is a perspective view of an inner
compartment of a microwave oven;
Figure 3 is a cross-sectional view of an electric
hot plate;
s Figure 4A is a cross-sectional view of a film
structure prior to sintering, according to one embodiment of
the present invention;
Figure 4B is a cross-sectional view of the film
structure of Figure 4A after sintering;
Figure 5A is a cross-sectional view of a film
structure prior to sintering, according to another embodiment
of the present invention;
Figures 5B and 5C are cross-sectional views of the
film structure of Figure 5A after sintering;
Figure 6 is a cross-sectional view of a film
structure according to still another embodiment of the present
invention;
Figures 7A and 7B are cross-sectional views
illustrating a method of manufacturing a film structure of the
2 0 present invention;
Figures 8A and 8B are cross-sectional views
illustrating another example of the method of manufacturing
the film structure of the present invention;
Figures 9A and 9B are cross-sectional views
25 illustrating still another example of the method of
manufacturing the film structure of the present invention;
Figures lOA and lOB are cross-sectional views
illustrating a still further embodiment of the method of
manufacturing the film structure of the present invention;
Figures llA and llB are cross-sectional views
illustrating still another example of the method of
manufacturing the film structure of the present invention;
Figures 12A and 12B are cross-sectional views
illustrating a still further example of the method of
35 manufacturing the film structure of the present invention; and
B
. . -- , . ~,
~ ~ ~ 2 ~ ~ fi
Figures 13A and 13B are cross-sectional views
illustrating still another example of the method of
manufacturing the film structure of the present invention.
Referring now to Figures 1 and 2, a microwave oven
2 comprises a main body 4 and a door 6. An inner compartment
8 is inserted in the main body 4 and comprises sidewalls 10,
a top panel 12, a bottom panel 14, a rear panel 16 and a front
panel 18. The top panel 12 comprises a high temperature heat
irradiated portion 20 formed of a plurality of holes, for
introducing heat from a heater (not shown) provided in the top
panel 12 into the inner compartment 8.
As shown in Figure 3, an electric hot plate 24
comprises a plate 26 and a lid 28. Sheath heaters 30 are
inserted in the plate 26. The plate 26 is formed of an
aluminum alloy die casting material.
The inner surface of the inner compartment 8 of the
microwave oven 4 and the cooking surface 25 of the plate 26
of the electric hot plate 24, are typically formed of a
heat-resistive stainless steel sheet, an enamelled steel
sheet, or a steel sheet coated with a heat-resistive ceramic
coating comprising a binder of a boro-siloxane resin, a
silicone resin, a siloxane resin and the like, an inorganic
pigment, a filling material and the like.
Embodiment 1
In accordance with an embodiment of the present
invention, a coating is comprised of a mixture of an organic
solvent varnish including poly-titano-carbosilane (for
example, Tilanocoat* supplied by Ubekosan Co., Ltd.) serving
as a binder, and a mixture of a heat-resistive pigment
comprising a metal oxide or a composite oxide including Fe,
Co, Mn or Cr, a thickener such as aluminum silicate, a
silicone oil, and an organic solvent such as toluene or
xylene.
The general proportions of the mixture are shown in
Table I below.
* - Trade-mark
~0~22~6
,
-- 7 --
Table I
Component Proportion
Organic solvent varnish including 20 - 60 parts
poly-titano-carbosilane
Heat-resistive pigment 20 - 30 parts
Thickener 0.1 - 1.0% by weight
Silicone oil 0.5 - 8% by weight
organic solvent 20 - 40 parts
The components of the coating are preferably mixed
such that a specific gravity of the coating is in the range
from about 1.3 to 2.8, and a nonvolatile component of the
coating is in the range from about 50 to 70%.
The coating turns black due to the presence of the
heat-resistive pigment. The black coating mixture is then
mixed with about 30 parts of a pigment, comprising an Fe-Zn
oxide and an Fe-Co-Mn oxide in the ratio of 1:8, resulting in
a brown coating. Further mixing a pigment comprising a Ti-Zr
oxide into the brown coating results in a white coating.
The above coating is sprayed to form a coating of
a thickness in the range of from about 10 to 100~m on a
zinc-plated steel sheet, an aluminum-plated steel sheet, and
a low-quality 13 or 18 Cr stainless steel sheet, pretreated
by degreasing, rust removing, and/or sandblasting. The
applied coating is then baked at a temperature in the range
of from about 280 to 300~C for 20 minutes to form a coated
film (here in a one-coating one-baking finish).
Referring again to Figure 2, the coated zinc-plated
steel sheet is employed for the sidewalls 10 and the bottom
panel 14 where the temperature reaches from 250 to 300~C. The
coated low-quality stainless steel sheet is employed for the
top panel 12 where, due to the provision of heaters therein,
the temperature can reach 800~C. The coated aluminum-plated
steel sheet is employed for the rear panel 16 because an
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~ Q ~ 2 ~ 9 6
-- 8
outlet for a hot air for convection is provided thereon and
the temperature can reach 500~C. The zinc-plated steel sheet
or the aluminum-plated steel sheet is employed for the front
panel 18 of the oven portion 8 and for a contact face 22 (as
shown more clearly in Figure 1) of the door portion contacting
the front panel 18 where the temperature reaches approximately
300~C.
In the microwave oven structured as described above,
the front panel 18 of the inner compartment 8 and the contact
face 22 of the door 6 are superior in resistivity to
abrasiveness, contamination by food, tackiness and the like,
and are more rigid than conventional enamelled steel sheet or
stainless steel coated with a heat-resistant ceramic coating.
Thus, the door 6 is more durable because the coated film does
not tend to peel due to the opening/closing of the door 6.
Further, since the above coating is resistant to
corrosiveness, contamination by food, heat and the like, an
acid component, an alkali component and the like discharged
from the food being cooked does not cause softening or peeling
of the coated film.
When holes are formed in the steel sheet on the
inner surface of the inner compartment 8, by a punching
process, a coating containing a scaly mineral is preferably
coated in a thickness of from about 150-250~m on an external
exposed surface of an edge portion from which the punched
holes project. If a self-cleaning function is re~uired for
the inner surface of the oven, it is also possible to mix a
known catalyst such as MnO2, platinum or palladium in the
coating shown in Table I to form a coated film.
According to this embodiment, inexpensive steel
sheets can be employed for panels of the oven and the door,
thereby decreasing the cost of the microwave oven. Moreover,
since the above coating satisfies all the desired properties
of a microwave oven, such as anti-corrosiveness, adhesiveness
of the coated film at a high temperature and resistivity to
contamination by food, the coating onto the steel sheet can
be achieved by a single coating, as compared to the
. ~ . . _ . = _
~ Q
conventional three coatings, resulting in a reduction in cost
and enhancements in productivity, durability or reliability.
Further, a coated film in which ceramics and a metal oxide are
mixed is formed, so that a superior microwave oven exhibiting
a shielding effect of a microwave can be obtained.
Embodiment 2
Figures 4A and 4B schematically illustrate the steps
of forming a film structure according to the second embodiment
of the present invention. Figure 4A is a cross-sectional view
of the film structure prior to sintering, and Figure 4B is a
cross-sectional view of the film structure after sintering.
Referring to Figure 4A, a coating 42 is first coated
on a substrate 32 by spraying to achieve a thickness of from
about 10 to 40~m. The coating 42 is made by mixing a
heat-resistive pigment 46 comprised of a metal oxide or a
composite oxide including Fe, Co, Mn, or Cr, fluororesin
powders 48 (for example, Phostaflon* #9205 supplied by Hoechst
Japan Ltd.), a thickener such as aluminum silicate, a silicone
oil, and an organic solvent varnish comprising poly-titano-
carbosilane as a binder.
A general proportion of the coating mixture ispresented in Table II.
* - Trade-mark
B
~Q~96
-- 10 --
Table II
Component Proportion
Organic solvent varnish including 20 - 40 parts
poly-titano-carbosilane
Heat-resistive pigment 20 - 40 parts
Phostaflon #9205 3 - 30% by weight
Thickener 0.1 - 1.0% by weight
Silicone oil 0.1 - 1.0% by weight
Organic solvent 20 - 40 parts
The above materials are preferably mixed such that
the specific gravity of the coating is from about 1.1 to 1.8
and the nonvolatile component thereof is from about 50 to 70%.
Further, the color of the coating can be black,
brown or white due to components of the heat-resistive
pigment, as described above.
An aluminum-plated steel sheet, which is previously
subject to pretreatments, such as degreasing, rust removing,
and sandblasting, is employed for the substrate 32.
Next, after a pre-drying step at 160~C for 20
minutes, the resultant coating is baked at a temperature of
from about 300 to 400~C for 20 minutes and then sintered,
thereby forming a coated film, as shown in Figure 4B.
The baking step at a temperature of from about 300
to 400~C (detailed conditions will be described later) causes
poly-titano-carbosilane to become ceramic forming an aggregate
of minute sintered ceramic particles (a ceramic layer 34).
At the same time, the fluororesin powders 48 melt and rise due
to a difference in specific gravity. Consequently, the film
structure is such that the fluororesin 40 fills the voids
between the ceramic particles, so that the uppermost layer
portion of the film structure has a high concentration of the
fluororesin (a non-tacky resin layer 38). The film has the
same structure as a coating of tetrafluoroethylene; however,
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~ ..., ,, .... ,.,,~ ,..
~ ~ ~ 2 2 9 6
-
11 --
it differs from tetrafluoroethylene in that the concentration
of the non-tacky resin 40 becomes successively higher toward
the upper layer portion of the ceramic layer 34, at an
interface between the ceramic layer 34 and the non-tacky resin
layer 38. Accordingly, the ceramic layer 34 becomes more
adhesive to the non-tacky resin layer 38. Moreover, since a
binded layer of the ceramic particles and the fluororesin is
formed also in the inner portion of the ceramic layer 34, the
film has a good resistance to corrosion and the occurrence of
micro-cracks, and serves to protect against scorching by food
at a high temperature (300 - 400~C).
The amount of the fluororesin to be added and
burning conditions are discussed in embodiments 2A and 2B with
reference to the microwave oven shown in Figures 1 and 2. The
aluminum-plated steel sheet or a stainless steel sheet (SS430,
SS410 or SS304) is employed for the sidewalls 10, the bottom
panel 14, the rear panel 16, the front panel 18 and the
contact face 22 of the door 6 so as to be resistive to a
temperature in the range of from about 250 to 450~C. Since
the top panel 12 comprises heaters (not shown) and the
temperature thereof reaches about 800~C, a stainless steel
sheet, such as SS440, resistant to heat is employed for the
top panel 12.
Embodiment 2A
A coating is formed according to Table II with the
fluororesin powders (Phostaflon #9205 supplied by Hoechst
Japan Ltd.) varied in weight percent such as 3, 6, 8, 15, 20%
by weight. Another coating is also prepared without
fluororesin. Referring to Figures 1 and 2, the coating
including the fluororesin powders are coated on the substrate
forming the sidewalls 10, the bottom panel 14, the rear panel
16, the front panel 18 and the contact face 22 of the door 6
in a thickness of from about 10 to 40~m. The method of
coating is as shown in Figure 7A, wherein a coating 50 is
applied on the substrate 32. The coating including no
fluororesin powders is coated on the top panel 12 to achieve
a thickness of from about 10 to 40~m. Next, after a pre-
1~ .
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2 ~ 6
- 12 -
drying step at 150~C for 20 minutes, the coating is baked at
a temperature of about 300 to 400~C for 20 minutes.
Embodiment 2B
A coating is prepared in accordance with Table II
without fluororesin and is sprayed onto the sidewalls 10, the
bottom panel 14, the rear panel 16, the front panel 18, and
the contact face 22 of the door 6 in a thickness of about 10
to l5~m. The coating is applied to the top panel 12 to
achieve a thickness of from about 10 to 40~m. The method of
coating is as shown in Figure 8A, wherein a coating 52
including no fluororesin is sprayed on the substrate 32.
Thereafter, the coating is left at room temperature to
evaporate the organic solvent. When the surface is no longer
glossy, the coating 50 including fluororesin powders in the
range of from about 3 to 20% by weight (for example 3, 6, 8,
15, 20% by weight) is coated on the sidewalls 10, the bottom
panel 14, the rear panel 16, the front panel 18 and the
contact face 22 of the door 6 so that the thickness thereof
is from about 10 to 20~m after dry baking. Thereafter, the
resultant coating is subject to a pre-drying step at 150~C for
20 minutes, and then baked at a temperature of from about 300
to 400~C for 20 minutes for hardening.
Analysis of Embodiments 2A and 2B
(1) A method of coating
In Embodiment 2A (Figure 7A), wherein the coating
50 including fluororesin is coated on the substrate 32, the
coating drips from the surface when applied in a thick layer.
As a result, the fluororesin powders cannot float to an upper
layer portion, as shown in Figure 4B, resulting in
insufficient non-tackiness. Further, due to the small
thickness, the coating peels and cracks and demonstrates poor
corrosion resistance and durability. On the other hand, such
disadvantages do not occur in a dual-layer structure of
Embodiment 2B (Figure 8A). That is, as shown in Figure 4B,
the fluororesin melts and rises to form a fluororesin layer
38 at the uppermost layer portion of the coated surface. This
results from the following reasons. That is, referring to
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.. ~ ... ..
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Figure 8A, when the coating 50 including the fluororesin is
coated over the undercoating 52, the organic solvent within
the overcoating 50 permeates into the undercoating 52, thereby
increasing the tackiness and causing no drippings, thereby
resulting in a thick coating. Further, by this method, it is
possible to dilute the coating 50 by a thinner and spray it
so that the fluororesin powders can sufficiently rise to the
surface. Consequently, it is possible to efficiently float
the fluororesin as shown in Figure 4B. This is also proven
by the following facts. That is, if the undercoating 52 is
forced to be dried at a temperature in the range of from about
80 to 150~C and then is coated with the overcoating 50, no
fluororesin floats. Moreover, if the overcoating 50 is coated
after baking the undercoating 52 at a high temperature of from
about 300 to 320~C, peeling between layers occurs.
(2) Amount of Fluororesin Powders and Baking Conditions
A test panel is made in accordance with Embodiment
2B with the amount of the fluororesin powders varied in weight
percent, namely 3, 6, 8, 15, 20% by weight, and three burning
conditions are selected, namely temperature ranges of from 300
to 320~C, from 330 to 360~C and from 370 to 400~C for testing.
At a baking temperature in the range of from 300 to
320~C, oil drops scattered from fish or meat scorch on the
coated film in cooking by a convection-type grill oven. The
degree of scorching is the same at all concentrations of the
fluororesin powders and no significant difference in cleaning
property is demonstrated. However, there is a general
increase in the cleaning property as the concentration of
fluororesin powder is increased.
A similar result is also obtained at temperatures
in the range of from 330 to 360~C.
At temperatures in the range of from 370 to 400~C,
the coatings with 6, 8 and 15% by weight of fluororesin
exhibit the best performance in long-lasting heat resistance,
corrosion resistance and durability. Although it is found
that the coating with 20% by weight of fluororesin also has
2 ~ 6
- 14 -
a tendency to be powdered at the uppermost layer portion, the
one with no obstacle for practical use is obtained.
A thermoplastic fluororesin (tetrafluoroethylene)
is illustrated as a non-tacky resin in the above embodiment;
however, the present invention is not limited to this, as the
same effect can be achieved with thermoplastic engineering
plastic powders such as PPS and PES.
In Embodiments 3 through 7 shown in Figures 9A, lOA,
llA, 12A and 13A, the present invention is applied to the
cooking surface of the electric hot plate shown in Figure 3.
The cooking surface of the electric hot plate to which the
present invention is applied exhibits a good non-tackiness and
cleanability in cooking at high temperatures in the range of
from about 250 to 450~C. A method of manufacturing the coated
film on the cooking surface will now be described.
Embodiment 3
Referring to Figure 9A, the cooking surface of the
substrate 32 is baked with oil at 400~C and then is subjected
to a shot blast to form an unevenness on the surface thereof.
After a resultant rough surface 54 is cleaned, a coating 52
for undercoating including no fluororesin is coated on the
rough surface 54 to achieve a thickness in the range of from
about 10 - 20~m. The film is then left at room temperature
to evaporate the organic solvent, and then a coating 50
including from about 8 to 15% by weight of fluororesin is
coated to achieve a thickness in the range of from about 10
to 30~m. The coating used here is identical to those shown
in Table II and in Embodiments 4, 5, 6 and 7 which will be
described later. Thereafter, the film is dried at 150~C for
20 minutes and then baked at a temperature from about 370 to
400~C for 20 minutes for hardening. The resultant cooking
surface shows a good non-tackiness and cleanability.
Embodiment 4
Referring to Figure lOA, after the cooking surface
of the substrate 32 is baked with oil at 400~C, it is subject
to a shot blast to form an unevenness on the surface thereof.
After the resulting rough surface 54 is cleaned, alumina-
.
r~
~ .... . ..
~ ~ ~ 2 2 9 6
- 15 -
titania 56 of a ceramic quality is melted and injected onto
the rough surface 54. After that, the coating 52 including
no fluororesin is coated to achieve a thickness of from about
10 to 20~m. Next, the film is left at room temperature to
evaporate the organic solvent, and then the coating 50
including from 8 to 15% by weight of the fluororesin is coated
to achieve a thickness of from about 20 to 30~m. In this
embodiment, since the alumina-titania 56 of the ceramic
quality is melted and injected on the rough surface 54, a good
adhesiveness can be obtained between the substrate 32 and the
coated film.
Embodiment 5
Referring to Figure llA, after the cooking surface
of the substrate 32 is baked with oil at 400~C, it is subject
to a shot blast to form an unevenness on its surface. After
the resultant rough surface 54 is cleaned, alumina-titania 56
of ceramic quality is melted and injected onto the rough
surface 54. Thereafter, the coating 50 including from about
8 to 15% by weight of fluororesin powders is coated to achieve
a thickness of from about 20 to 40~m. The film exhibits a
superior performance in non-tackiness and cleanability even
in this embodiment. In this case, employing no undercoating
results in a decrease in the manufacturing cost.
Embodiment 6
Referring to Figure 12A, after the cooking surface
of the substrate 32 is baked with oil at 400~C, it is subject
to a shot blast to form an unevenness on its surface. After
the resulting rough surface 54 is cleaned, alumina-titania 56
of ceramic quality is melted and injected onto the rough
surface 54. Thereafter, a silver-colored heat-resistive
primer coating 58, which is mixed with aluminum, including
poly-titano-carbosilane as a binder, is coated to achieve a
thickness of from about 3 to 5~m. The film is then dried at
room temperature to evaporate the solvent, and thereafter the
coating 50 including from about 8 to 15% by weight of
fluororesin is coated to achieve a thickness of from about 20
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~Q 02~ ~ 6
- 16 -
to 40~m. Since the primer coating 58 is employed in this
embodiment, corrosion resistance increases.
Embodiment 7
Referring to Figure 13A, after the cooking surface
of the substrate 32 is baked with oil at 400~C, it is
subjected to a shot blast to form an unevenness on its
surface. The resulting rough surface 54 is cleaned, and then
alumina-titania 56 of ceramic quality is melted and injected
on the rough surface 54. Thereafter, silver-colored
heat-resistive primer coating 58, which is mixed with aluminum
powders, including poly-titano-carbosilane as a binder, is
coated to achieve a thickness of from about 3 to 5~m. After
the film is dried at room temperature to evaporate the
solvent, the coating 52 including no fluororesin is coated to
achieve a thickness of from about 10 to 15~m. After that, the
film is dried at room temperature, and coated with the coating
50 including from about 8 to 15~ by weight of the fluororesin
to achieve a thickness of from about 10 to 30~m. The
resultant film is then dried at 150~C for 20 minutes, and
sintered at a temperature of from about 370 to 400~C for 20
minutes. Corrosion resistance and adhesiveness are further
enhanced in this embodiment.
Embodiment 8
In the above described embodiment shown in Figure
4B, in order to float the non-tacky resin 40 on the surface,
the greatest care should be taken for viscosity of the
coating, a thickness of the coated film and the like, and thus
it is difficult to determine the optimum conditions thereof.
The following embodiments are presented to serve as solutions
for such disadvantages.
Figures 5A, 5B and 5C schematically illustrate the
steps of forming the film structure according to this
embodiment.
Figure 5A is a cross-sectional view of the film
prior to sintering, and Figures 5B and 5C are cross-sectional
views of the film after sintering.
'~
2 ~ 6
- 17 -
First, referring to Figure 5A, the coating 42 mixed
in the proportion shown in Table II is coated on the substrate
32 by spraying to achieve a thickness of from about 10 - 40~m.
Next, after pre-drying (150~C, 20 minutes) or drying
at a room temperature, a dispersion-type tetrafluoroethylene
resin (for example, "Silkware* (EK-4609BK)" of black supplied
by Daikin Kogyo Co., Ltd.), which is a liquid coating of the
fluororesin, is coated thinly, in a mottled and streaked
manner or in a continuous thin film. Subsequently, after
drying at room temperature or pre-drying at 150~C for 20
minutes and then sintering at a temperature of from about 380
to 420~C for 20 to 30 minutes, a coated film shown in Figure
5B or 5C is formed.
Figure 5B is a cross-sectional view of the film
after sintering when the dispersion-type tetrafluoroethylene
resin coating is coated in the continuous pattern of a thin
film. Figure 5C is a cross-sectional view of the film
finished by thinly coating the dispersion-type
tetrafluoroethylene resin coating in the mottled and streaked
manner.
Referring to Figures 5B and 5C, a ceramic layer 34
including poly-titano-carbosilane, which is a principal
component being made ceramic, is formed on the substrate 32.
The ceramic layer 34 includes a non-tacky resin 40 therein.
The concentration of the non-tacky resin 40 increases through
the layer and is 100% at the uppermost layer portion. On the
ceramic layer 34, there is reliably formed a fluororesin layer
60 resulting from the dispersion-type fluororesin coating with
the tetrafluoroethylene resin as a principal component.
In this embodiment, as the amount of the non-tacky
resin powders 40 to be added in the ceramic layer 34 is
greater than or equal to 20%, the strength of the surface
layer sharply decreases, resulting in a fragile film. As a
result, the film is liable to be cracked by nails and to be
peeled off and thus lose non-tackiness gradually. Therefore,
* - Trade-mark
f ~ ~
2 Q o 2 ~ ~ 6
- 18 -
the amount of the non-tacky resin powders 40 to be added is
preferably less than or equal to 20%.
The film structure formed as described above is hard
and hence is not cracked by contacting a metal pallet,
enamelled utensils, or stainless steel cooking utensils.
Further, even if oil drops of food are adhered to and scorched
firmly to the film, they can be easily removed, and thus there
are few remarkable stains left after removal of the scorches.
Further, the film is durable up to a high temperature of about
450~C and demonstrates good adhesiveness.
Referring to Figure 5A, a mechanism of the sintering
which can be considered will now be described. First, an
overcoating which is a dispersion-type fluororesin coating is
coated on a half-burned undercoating whose principal
components are an organic solvent varnish including
Tilanocoat*, and a heat-resistive pigment. As a result, a
solvent, such as toluene, interacts and dissolves between a
coated film layer of the undercoating and that of the
overcoating, forming a mixed interlayer between those film
layers. When the resultant film layer is then sintered at a
temperature in the range of from about 380 to 420~C,
fluororesin powders of the undercoating and dispersion-type
fluororesin particles of the overcoating are mixed and melted
by heat, and further bonded firmly together to be integrated.
At this time, if the film is sintered longer, the fluororesin
of the undercoating and that of the overcoating are highly
melted, so that no peeling occurs between the layers even when
the layer of the overcoating is thick. In this case,
referring to Figure 6, mixing several percent of potassium
titanate fibers 70 into an undercoating 34 causes a further
enhanced adhesiveness, thereby preventing micro-cracks, a
specific defect of ceramics.
Referring now to Figure 6, the ceramic layer 34 is
formed on the substrate 32. The potassium titanate fibers 70
are mixed in the ceramic layer 34. The fluororesin layer 60
is formed on the ceramic layer 34. A composite layer 80 that
* - Trade-mark
B
-- 19 --
the potassium titanate fibers 70 are mixed into the
fluororesin layer, is formed at the boundary portion of the
ceramic layer 34 and the fluororesin layer 60. An enhancement
in adhesiveness of the film results from the presence of this
composite layer 80. To simplify Figure 6, no pigment
particles are illustrated in the figure.
Embodiment 8A
A coating including fluororesin powders is formed
in the proportion shown in Table II. Meanwhile, another
coating with no fluororesin is also prepared. Referring to
Figures 1 and 2, the coating including the fluororesin powders
is coated on the sidewalls 10, the bottom panel 14, the rear
panel 16, the front panel 18 and the contact face 22 of the
door 6 to achieve a thickness of from about 10 to 40~m. A
method of coating is as shown in Figure 7B. That is, the
coating 50 including the fluororesin is sprayed on the
substrate 32. After the solvent is evaporated by drying at
room temperature or by pre-drying at 150~C for 20 minutes, a
dispersion-type liquid coating 43 of tetrafluoroethylene resin
is coated thinly, in a mottled and streaked manner or in a
continuous pattern of a thin film. The above coating
including no fluororesin powders is coated on the top panel
12 to achieve a thickness of from about 10 to 40~m. After a
pre-drying step at 150~C for 20 minutes, the film is baked to
harden the film at a temperature of from about 380 to 420~C
for 20 minutes. The resultant film has a good non-tackiness.
Embodiment 8B
A coating including no fluororesin is prepared in
the proportion shown in Table II. This coating is sprayed on
the sidewalls 10, the bottom panel 14, the rear panel 16, the
front panel 18, and the contact face 22 of the door 6 to
achieve a thickness of from about 10 to 15~m. The coating
including no fluororesin is coated on the top panel 12 to
achieve a thickness of from about 10 to 40~m. The method of
coating is as shown in Figure 8B. That is, the coating 52
including no fluororesin is coated on the substrate 32 by
spraying. Thereafter, the coated film is left at room
,~v ,5.". . .,~ .,
~2~96
- 20 -
temperature to evaporate the organic solvent. When the
surface is no longer glossy, a coating 50 including 3 - 20%
by weight of the fluororesin powders is coated on the front
panel 18 and the contact face 22 of the door 6 such that a
thickness thereof is from about 10 to 20~m after dry-baking.
After the film is left and dried at room temperature or
pre-dried at 150~C for 20 minutes, the dispersion-type liquid
coating 43 of a tetrafluoroethylene resin is coated thinly,
in a mottled and streaked manner or in the continuous pattern
of a thin film. Then, after pre-drying at 150~C for 20
minutes, the film is baked to harden the film at a temperature
of from about 380 to 420~C for 20 to 30 minutes. The
resultant coated film has a good non-tackiness.
In Embodiments 9 through 13 shown in Figures 9B,
lOB, llB, 12B and 13B, the method shown in Figure SA is
applied to the cooking surface of the electric hot plate. The
cooking surface of the electric hot plate to which the present
invention is applied exhibits a good non-tackiness and
cleanness in cooking at a high temperature in the range of
from about 250 to 450~C. A detailed description will be given
as follows.
Embodiment g
Referring to Figure 9B, after the cooking surface
of the substrate 32 is baked with oil at 400~C, it is subject
to a shot blast to form an unevenness on its surface. After
the resultant rough surface 54 is cleaned, the coating 52 for
undercoating including no fluororesin is coated to achieve a
thickness of from about 10 to 20~m. Thereafter, the resulting
film is left at room temperature to evaporate the organic
solvent, and then the coating 50 including from about 8 to 15~
by weight of the fluororesin is coated to achieve a thickness
of from about 10 to 30~m. The coating is the same as the
coating of the Embodiment 8. The same coating will be
employed in the following embodiments. After the film is left
at room temperature or dried at 150~C for 20 minutes, it is
coated with the dispersion-type liquid coating 43 of a
tetrafluoroethylene resin and then pre-dried at 150~C for 20
b~
. . .
~2296
minutes to be baked to harden the film at a temperature of
from about 380 to 420~C for 20 to 30 minutes. The resultant
coated film has a good non-tackiness.
Embodiment 10
Referring to Figure lOB, after the cooking surface
of the substrate 32 is baked with oil at 400~C, it is subject
to a shot blast to form an unevenness on its surface. After
the resulting rough surface 54 is then cleaned, alumina-
titania 56 of ceramic quality is melted and injected onto the
rough surface 54. After that, the coating 52 for undercoating
including no fluororesin is coated to achieve a thickness of
from about 10 to 20~m. After the film is left at room
temperature to evaporate the organic solvent, it is coated
with the coating 50 including from about 8 to 15% by weight
of the fluororesin to achieve a thickness of from about 20 to
30~m. After the film is then left at room temperature or
dried at 150~C for 20 minutes, it is coated with the
dispersion-type liquid coating 43 of the tetrafluoroethylene
resin and then pre-dried at 150~C for 20 minutes to be baked
to harden the film at a temperature of from about 380 to 420~C
for 20 to 30 minutes. The resulting coated film has a good
non-tackiness.
Embodiment 11
Referring to Figure llB, after the cooking surface
of the substrate 32 is baked with oil at 400~C, it is subject
to a shot blast to form an unevenness on its surface. After
the resultant rough surface 54 is then cleaned, the alumina-
titania 56 of ceramic quality is melted and injected onto the
rough surface 54. After that, the coating 50 including from
about 8 to 15% by weight of fluororesin powders is coated to
achieve a thickness of from about 20 to 40~m. After the film
is then left at room temperature or dried at 150~C for 20
minutes, it is coated with the dispersion-type liquid coating
43 of the tetrafluoroethylene resin and then pre-dried at
150~C for 20 minutes to be baked to harden the film at a
temperature of from about 380 to 420~C for 20 to 30 minutes.
The resulting coated film has a good non-tackiness.
B
20 Q22 9 6
- 22 -
Embodiment 12
Referring to Figure 12B, after the cooking surface
of the substrate 32 is baked with oil at 400~C, it is subject
to a shot blast to form an unevenness on its surface. After
S the resultant rough surface 54 is then cleaned, alumina-
titania 56 is melted and injected onto the rough surface 54.
After that, a silver-colored heat-resistive primer coating 58,
which is mixed with aluminum powders, including poly-titano-
carbosilane as a binder, is coated to achieve a thickness of
from about 3 to 5~m. After the film is then dried at room
temperature to evaporate the solvent, it is coated with the
coating 50 including from about 8 to 15% by weight of the
fluororesin to achieve a thickness of from about 20 to 40~m.
After the film is left at room temperature or dried at 150~C
for 20 minutes, it is coated with the dispersion-type liquid
coating 43 of the tetrafluoroethylene resin and then pre-dried
at 150~C for 20 minutes to be baked to harden the film at a
temperature of from about 380 to 420~C for 20 to 30 minutes.
The resulting coated film has a good non-tackiness.
Embodiment 13
Referring to Figure 13B, after the cooking surface
of the substrate 32 is baked with oil at 400~C, it is subject
to a shot blast to form an unevenness on its surface. After
the resultant rough surface 54 is then cleaned, alumina-
titania 56 is melted and injected onto the rough surface 54.Thereafter, a silver-colored heat-resistive primer coating 58
which is mixed with aluminum powders, including poly-titano-
carbosilane as a binder, is coated to achieve a thickness of
from about 3 to 5~m. After the film is dried at room
temperature to evaporate the solvent, it is coated with the
coating 52 including no fluororesin to achieve a thickness of
from about 10 to 15~m. Then, the film is dried at room
temperature and coated with the coating 50 including from
about 8 to 15% by weight of the fluororesin to achieve a
thickness of from about 10 to 30~m. Thereafter, the film is
dried at 150~C for 20 minutes to evaporate the organic solvent
component. Then, the dispersion type liquid coating 43 of the
2 9 6
- 23 -
tetrafluoroethylene resin is coated thinly, in a mottled or
streaked manner, or in the continuous pattern of a thin film,
and thus after pre-drying at 150~C for 20 minutes, the film
is baked to harden the film at a temperature of from about 380
to 420~C for 20 to 30 minutes. The resulting coated film has
a good non-tackiness.
Although the microwave oven and the electric hot
plate are presented as examples in the above embodiments, the
present invention is also applicable to other high temperature
cooking apparatuses.
As has been described heretofore, in the structure
of the film for a high temperature cooking apparatus according
to the present invention, the film is formed of ceramics,
including poly-titano-carbosilane as its principal component,
resulting in a film that satisfies resisting properties to
corrosiveness and contamination by food, and an adhesiveness
of the coated film at a high temperature. Further, in case
that the fluororesin layer is further formed on the ceramic
layer, the film structure with a further enhanced
non-tackiness can be obtained. If such a film structure is
formed on the inner surface of the microwave oven, i.e., the
high temperature cooking apparatus, the cooking surface of the
electric hot plate and so on, the high temperature cooking
apparatus exhibits a superior performance in heat-resistivity
and non-tackiness.
_. ,,.~ , . ,~"
