U.S. patent application number 12/085887 was filed with the patent office on 2010-06-17 for food heating device.
Invention is credited to Hisao Kimura, Yukako Kumagai, Yumiko Mine, Mikio Takaiwa, Yukio Urume.
Application Number | 20100147282 12/085887 |
Document ID | / |
Family ID | 38156665 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100147282 |
Kind Code |
A1 |
Urume; Yukio ; et
al. |
June 17, 2010 |
Food Heating Device
Abstract
The heat source 1 comprises a bag 10 and a heat-generating
composition 20 containing aluminum powder, calcium hydroxide powder
and calcium oxide powder, enclosed in the bag 10. The bag 10 is
formed by a packing material made of a base material of nonwoven
fabric of which one surface is laminated with a watertight layer.
The packing material is punched with a plurality of pinholes and
has a water permeable rate of 13 to 81 milliliter/min/1 cm.sup.2
measured when head of water is 27 cm. The heat source 1 can satisfy
preferable heating conditions including rate of temperature rise of
the food, risen temperature of the food, duration of the risen
temperature of the food under conditions in which a food heating
device is conventionally used. Accordingly, a food heating device
using the heat source capable of causing a rapid and stable
heat-generating reaction can be provided.
Inventors: |
Urume; Yukio; (Tochigi,
JP) ; Kimura; Hisao; (Tochigi, JP) ; Takaiwa;
Mikio; (Tochigi, JP) ; Kumagai; Yukako;
(Tochigi, JP) ; Mine; Yumiko; (Tochigi,
JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
220 Fifth Avenue, 16TH Floor
NEW YORK
NY
10001-7708
US
|
Family ID: |
38156665 |
Appl. No.: |
12/085887 |
Filed: |
March 12, 2007 |
PCT Filed: |
March 12, 2007 |
PCT NO: |
PCT/JP2007/054839 |
371 Date: |
June 2, 2008 |
Current U.S.
Class: |
126/263.05 ;
126/261 |
Current CPC
Class: |
B65D 81/3484 20130101;
C09K 5/18 20130101; A47J 36/28 20130101 |
Class at
Publication: |
126/263.05 ;
126/261 |
International
Class: |
F24J 1/00 20060101
F24J001/00; A47G 23/04 20060101 A47G023/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 21, 2006 |
JP |
2006-117741 |
Claims
1. A food heating device comprising a heat source and a container
having an exhaust vent, in which said heat source is put in said
container together with a food to be heated and water is added to
said container so that said heat source is reacted with said water
to generate heat and to heat the food by the generated heat,
wherein said heat source comprises: a bag formed by a packing
material made of a base material of nonwoven fabric of which one
surface is laminated with a waterproof layer, said packing material
being punched with a plurality of pinholes, and a heat-generating
composition containing aluminum powder in an amount of 40 to 60% by
weight, calcium hydroxide powder in an amount of 10 to 40% by
weight and calcium oxide powder in an amount of 10 to 40% by
weight, enclosed in said bag, said packing material has a water
permeable rate of 13 to 81 milliliter/min/1 cm.sup.2 measured under
the following measurement conditions (1) to (4): (1) ion-exchanged
water of 23.+-.3.degree. C. is used, (2) head of water is
27.+-.0.95 cm, (3) a water permeable area of said packing material
is 2.85 cm.sup.2, and (4) the water permeable amount (milliliter)
is defined in such a manner that after an amount of the permeated
water per unit time gets constant (after a variation in amount of
the permeated water per 10 seconds is within 5% at least
consecutive three times), an amount of the permeated water measured
in any one minute during the measurement for one minute or more is
converted into a water permeable amount (milliliter) using a
specific gravity of the ion-exchange water of 1.000 (g/cm.sup.3).
Description
TECHNICAL FIELD
[0001] The present invention relates to a food heating device to
heat a food (cooked food such as a retort-packed food and canned
drink) using a heat source activated by reaction with water. More
particularly, it relates a food heating device improved in
heat-generating property when temperature of water to be used is
low.
BACKGROUND ART
[0002] As a heat source activated by reaction with water, a mixture
of aluminum powder and calcium oxide powder has been popularly used
for a heat-generating composition (referring to Patent literature
1, for example). And, a food heating device to heat a lunch bag or
Japanese sake, or to re-heat a cooked food such as a retort-packed
food in emergency situations, which uses the heat source, has been
also known.
[0003] In such the heat-generating composition, the calcium oxide
powder is reacted with the water to generate heat and also calcium
hydroxide produced by the reaction is reacted with the aluminum
powder to generate heat. The group of reactions makes it possible
to generate enough amounts of heat to warm the food within a short
period. The above Japanese Patent shows that the disclosed
heat-generating composition generates heat of about 100.degree. C.
after about 30 seconds from the reaction and the temperature is
kept for 20 minutes or longer. And, the heat-generating composition
has advantages in which it reacts without generating odor, and a
small amount of the composition is enough for generating sufficient
amounts of heat.
[0004] Patent literature 1: Japanese Patent number 3467729
DISCLOSURE OF THE INVENTION
Problems to be solved by the Invention
[0005] In the aforesaid food heating device, the heat-generating
composition is enclosed in an inner bag made by nonwoven fabric and
further tightly enclosed in a watertight outer bag. When to be
used, the enclosed heat-generating composition is taken out of the
outer bag and comes in contact with water, resulting in that the
heat-generating composition in the inner bag contacts the water to
be reacted. The water permeates the inner bag made by nonwoven
fabric and reacts with the heat-generating composition in the inner
bag. In this case, it is considered that the faster the water
contacts the heat-generating composition, the faster the
heat-generating reaction proceeds. The generated heat diffuses
through the heated water and water vapor. And, it is also
considered that the higher the water permeability of the inner bag
is, the faster the rate of the heat diffusion is. Accordingly, it
is considered that an efficiency of the water permeation of the
inner bag (water permeability) influences the proceeding of the
heat-generating reaction of the heat-generating composition.
However, in such food heating devices, development and proposal
concerning to the water permeability of the inner bag have not been
done.
[0006] Such a food heating device is sometimes used under a
condition in which temperature of the water to be reacted is low.
Therefore, such a food heating device is required which has
excellent heat-generating abilities (rate of temperature rise, heat
retaining period and the like) even under a condition in which
temperature of the water to be reacted is low.
[0007] In view of this regard, the present invention focuses
attention on the permeability of the inner bag and the object of
the present invention is to provide a food heating device utilizing
a heat source capable of a rapid and stable heat-generating
reaction. Another object of the present invention is to provide a
food heating device having a heat source providing excellent
heat-generating abilities even when it reacts with low-temperature
water.
Means of Solving the Problems
[0008] A food heating device according to the present invention
comprises a heat source and a container having an exhaust vent, in
which said heat source is put in said container together with a
food to be heated and water is added to said container so that said
heat source is reacted with said water to generate heat and to heat
the food by the generated heat. And, said heat source comprises: a
bag formed by a packing material made of a base material of
nonwoven fabric of which one surface is laminated with a waterproof
layer, said packing material being punched with a plurality of
pinholes, and a heat-generating composition containing aluminum
powder in an amount of 40 to 60% by weight, calcium hydroxide
powder in an amount of 10 to 40% by weight and calcium oxide powder
in an amount of 10 to 40% by weight, enclosed in said bag, said
packing material has a water permeable rate of 13 to
milliliter/min/1 cm.sup.2 measured under the following measurement
conditions (1) to (4): [0009] (1) ion-exchanged water of
23.+-.3.degree. C. is used, [0010] (2) head of water is 27.+-.0.95
cm, [0011] (3) a water permeable area of said packing material is
2.85 cm.sup.2, and [0012] (4) the water permeable amount
(milliliter) is defined in such a manner that after an amount of
the permeated water per unit time gets constant (after a variation
in amount of the permeated water per 10 seconds is within 5% at
least consecutive three times), an amount of the permeated water
measured in any one minute during the measurement for one minute or
more is converted into a water permeable amount (milliliter) using
a specific gravity of the ion-exchange water of 1.000
(g/cm.sup.3).
[0013] On reacting with water, calcium hydroxide (Ca(OH).sub.2) is
hydrolyzed to exhibit strong alkaline. It is known that
water-solubility of calcium hydroxide becomes high as the
temperature of the water is low (for example, 0.189 wt % at
0.degree. C. and 0.106 wt % at 80.degree. C.). On the other hand,
while aluminum does not react with water at room temperatures, it
reacts with water under alkaline environment to cause the following
decomposition reaction of water:
2Al+2OH.sup.-+6H.sub.2O.fwdarw.2Al(OH).sub.4.sup.-+3H.sub.2.
[0014] When calcium hydroxide (Ca(OH).sub.2) is used as an alkaline
material, the above reaction formula is as follows:
2Al+Ca(OH).sub.2+6H.sub.2O.fwdarw.Ca.sup.2++2Al(OH).sub.4.sup.-+3H.sub.2-
.
[0015] Since Ca.sup.2+ and 2Al(OH).sub.4.sup.-, shown in the
right-side hand in this formula, does not exhibit alkaline as
strong as NaOH and KOH and an amount of dissociated Ca.sup.2+ and
2Al(OH).sub.4.sup.- is significantly small, both ions are combined
into CaO.Al.sub.2O.sub.3.4H.sub.2O. However, since the reaction
proceeds in alkaline aqueous solution, the following reaction
occurs:
2Al+Ca(OH).sub.2+2H.sub.2O.fwdarw.-CaO.Al.sub.2O.sub.3+3H.sub.2+183.7
Kcal
[0016] Therefore, in order to sift the chemical equilibrium toward
the right-side hand, that is, to produce a heat-generating
reaction, it is necessary that the dissolved Ca(OH).sub.2 be
hydrolyzed to shift the pH toward alkaline and to increase the
dissolution rate of the aluminum.
[0017] Accordingly, by adding calcium hydroxide powder, which has a
higher water-solubility under low-temperature environments, to the
mixed powder previously, an excellent heat-generating ability can
be provided even if temperature of the water to be reacted is
low.
[0018] For heating a food, NaOH and KOH can not be used as an
alkaline material because of the poisonous property. Or, substances
which are easily dissociated by hydrolysis are also not suitable
for heating a retort-packed rice and the like because the reaction
terminates quickly. It means that an amount of heat which is
discharged out of the food heating device is so large that the
reaction can not proceed continuously.
[0019] Accordingly, it is preferable to use calcium hydroxide as an
alkaline material in view of cost and manufacturing method.
[0020] According to the present invention, by controlling water
permeable rate of the bag, the proceeding of the heat-generating
reaction can be controlled. That is, when a water permeable rate of
the inner bag is set to 13 to 81 milliliter/min/1 cm.sup.2,
preferably 13 to 65 milliliter/min/1 cm.sup.2, and more preferably
22 to 44 milliliter/min/1 cm.sup.2 measured when head of water is
27 cm, preferable heating conditions including rate of temperature
rise of a food, risen temperature and duration of the risen
temperature under conditions in which a food heating device is
typically used can be obtained. And, leakage of the heat-generating
composition from the bag can be prevented.
[0021] In the present invention, the heat-generating composition
contains calcium oxide powder in an amount of 10 to 40% by
weight.
[0022] In this case, the calciumoxide (CaO) causes the following
hydration reaction;
CaO+H.sub.2O.fwdarw.Ca(OH).sub.2+15.6 Kcal.
[0023] The hydration reaction also generates heat and the produced
Ca(OH).sub.2 reacts with aluminum to generate heat because it is an
alkaline material. Accordingly, rate of temperature rise becomes
fast.
[0024] In the present invention, the heat-generating composition
contains aluminum powder in an amount of 40 to 60% by weight and
calcium oxide powder in an amount of 10 to 40% by weight.
[0025] A heating device in which a heat-generating composition
containing aluminum powder and calcium oxide (CaO) powder is
reacted with water to generate heat has been widely known. The
present inventors have found that an addition of calcium hydroxide
(Ca(OH).sub.2) to the above heat-generating composition allows an
excellent heat-generating abilities even if temperature of water to
be reacted is low. By using such a heat-generating composition, it
becomes possible to accomplish a request for-heating a food
(retort-packed cooked curry or rice, 350-milliliter plastic bottled
tea and the like) to 40.degree. C. or higher after 5 minutes from
the heat-generating reaction, to 60.degree. C. or higher after 10
minutes and to keep the temperature after 20 minutes when
temperature of water to be reacted is low as 5 to 30.degree. C. (an
environmental temperature is -10 to 40.degree. C.), for
example.
[0026] Examples of the heat-generating composition and nonwoven
fabric for use in the prevent invention are described below.
[0027] Examples of the nonwoven fabric include natural fabric such
as cotton and wool; regenerated fiber such as viscose (rayon) and
cupra; polyamide such as nylon 6, nylon6,6; straight-chain or
branched polyesters having 20 or less carbon atoms such as
polyethylene terephthalate, polytrimethylen terephthalate,
polybutylene terephalate, polylactic acid and polyglycolic acid;
polyolefins such as polyethylene and polypropylene; and synthetic
fiber such as acrylic. Two or more kinds of those materials may be
used together. The nonwoven fabric may be made by a spunlaced
method, spunbond method and the like.
[0028] Exemplary properties of the nonwoven fabric are followed:
basis weight (g/m.sup.2);40.about.70,thickness
(.mu.m);170.about.460, longitudinal tensile strength (N/5 cm);
35.about.380, transverse tensile strength(N/5 cm);13.about.165,
longitudinal extensibility (%); 80 and below and transverse
extensibility (%); 120 and below.
[0029] The watertight layer may be formed by laminating a
synthetic-resin film on the nonwoven fabric. Exemplary
synthetic-resin films include polyolefin resin such as polyethylene
and polypropylene; polyamide resin; polyester resin; polyvinyl
chloride resin; polystyrene resin; copolymer polyamide resin;
copolymer polyester resin; ethylene-vinyl acetate resin; elastmer;
and mixed resin of two or more of those resins. The synthetic-resin
film may be a single layer or laminated layer. The synthetic-resin
film has a thickness of 0.01 to 0.3 mm, preferably 0.02 to 0.1
mm
[0030] In order to heat a retort-packed cooked rice or curry and
plastic bottled tea, the heat-generating composition preferably has
a weight of 30 g or more. A weight ratio of the aluminum powder,
the calcium hydroxide powder and the calcium oxide powder of the
heat-generating composition is set to
40.about.60:10.about.40:10.about.40. Especially, in view of rate of
temperature rise and duration of the risen temperature, a weight
ratio of the aluminum powder, the calcium hydroxide powder and the
calcium oxide powder is preferably set to
40.about.50:15.about.40:20.about.40.
[0031] The aluminum powder preferably has following grain size
distribution: .about.45 .mu.m; 70.about.95%, 45.about.63 .mu.m;
5.about.20%, 63.about.75 .mu.m; 0.about.5% and +75 .mu.m;
0.about.5%.
[0032] The calcium hydroxide powder preferably has following grain
size distribution: .about.45 .mu.m; 0.about.10%, 45.about.75 .mu.m;
0.about.30%, 75.about.150 .mu.m; 20.about.45% and +150 .mu.m;
30.about.78%
[0033] The calcium oxide powder preferably has following grain size
distribution: .about.75 .mu.m; 5.about.25%, 75.about.150 .mu.m;
20.about.40% and +150 .mu.m; 45.about.65% or .about.75 .mu.m;
25.about.90%, 75.about.150 .mu.m; 5 .about.70% and +150 .mu.m;
0.about.15%.
[0034] Examples of the food to be heated include a food such as a
retort-packed food, canned drink, boiled egg and lunch bag.
[0035] The container may have any forms including a bag, box
andpan. The exhaust vent is for discharging H.sub.2 and H.sub.2O
produced by the aforesaid heat-generating reaction. A size and
number of the vent is selected such that expansion and breakage of
the container can be prevented while keeping heat-retaining
property.
Advantageous Effect of the Invention
[0036] As described above, according to the present invention, a
food heating device utilizing a heat source, having preferable
heating conditions including rate of temperature rise of the food,
risen temperature of the food and duration of the risen temperature
under conditions in which a food heating device is typically used,
can be provided. Especially, a food heating device can be provided
which has excellent heat-generating abilities even if temperature
of the water to be reacted is low. And, the present invention shows
that heat-generating ability of the heat source can be controlled
by water permeability of the inner bag as well as the property of
the heat-generating composition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] Hereinafter, preferred embodiments of the present invention
will be precisely described, referring to the drawings.
[0038] First, water permeability of an inner bag will be
described.
<Water Permeability>
[0039] Sample bags made by various base materials which were
punched with pinholes in various densities were prepared. And,
water permeability (water permeable rate) of each sample was
measured.
(1) Base Material
[0040] As the base material, a non water-repellent nonwoven fabric
(made by 100% rayon, MR-50/PP40, manufactured by Kokko Paper Mfg.
Co., Ltd.) was used. The nonwoven fabric has the following
properties: basis weight (g/m.sup.2) ; 50, thickness (.mu.m) ; 400,
longitudinal tensile strength (N/25 cm) ; 41, transverse tensile
strength (N/25 cm); 9.5, longitudinal extensibility (%) ; 27 and
below and transverse extensibility (%); 120 and below. The nonwoven
fabric is made by a spunlaced method in which columnar water flow
injects toward fibers at high pressure to entwine the fibers and
thus to produce a nonwoven fabric. The spunlaced method allows a
production of a highly flexible napless nonwoven fabric having high
drape property. A nonwoven fabric produced by the method is used
for livelihood materials such as diaper, medical supplies, food
supplies and cleaning supplies. On one surface of the nonwoven
fabric, a water-resistant layer (made by polypropylene) was
laminated. Or, the water-resistant layer may be made by a heating
bonding and the like in exchange for the laminating. The
water-resistant layer had a thickness of 40 .mu.m.
(2) Pinholes
[0041] Each of the prepared base materials was punched with
pinholes in various densities using a pinhole opening machine,
which comprised a roller on which needles were arranged at
intervals of 3. 0mm in the transverse direction and at intervals of
about 2.9 mm in the longitudinal direction and a base material
supporting roller confronting to the former roller. Or, another
type of the pinhole opening machine may be used, which is provided
with needles capable of being heated and the heated needles are
made to contact the laminated film to fuse the film, resulting in
opening pinholes. After the base material was supported to the base
material supporting roller, each of the rollers rotated in opposite
directions. As the result, pinholes were formed on the base
material in substantially the uniform density over the almost full
area. By changing a contact depth of the rollers, six base
materials having various pinhole diameters were prepared. The
pinhole diameters varied over a range of 0.05 to 0.4 mm. The
pinhole density was 1150/100 cm.sup.2. If the diameter of the
pinhole is larger, the small particulate heat-generating
composition may be leaked through the pinhole from the bag, causing
unfavorable situation. Accordingly, the pinhole diameter should be
small (0.05 to 0.4 mm) within the scope showing excellent
heat-generating property.
[0042] Each of the base materials was cut into a piece having a
size of 50 mm by 50 mm to prepare a sample for measuring water
permeability.
(3) Water Permeability
[0043] There is no official standard showing water permeability of
fabric and the like. According to a method for measuring water
permeable rate of perforated film, water permeability of each
sample was examined by a water permeable rate measuring method,
described later.
[0044] FIG. 3 is a drawing showing the water permeable rate
measuring method in the present invention.
[0045] A stainless-steel measuring tank 51 (inside dimension of
335.times.535.times.178 mm) was prepared and filled with
ion-exchange water of 23.+-.3.degree. C. An in flow pipe 53 from
which the ion-exchange water flowed in the tank 51 was formed at
the under portion of the side wall of the tank 51 and an overflow
pipe 55 was formed at the upper portion of the side wall of the
tank 51. The pipes 53 and 55 were openable and closable by cocks 54
and 56, respectively. The ion-exchange water was poured into the
tank 51 from the inflow pipe 53 and overflowed through the overflow
pipe 55.
[0046] An outflow pipe 57 (diameter of 19.05 mm) extending downward
was formed on the bottom of the tank 51. The outflow pipe 57 was
openable and closable by a cock 58. The sample base materials S was
temporarily attached to the opening of the outflow pipe 57 by a
rubber band 59 with the watertight surface of the sample S being
upside. Then, the periphery of the sample was closely attached to
the pipe by a sealing tape to block the opening with the sample S
and then further tightly attached by a water impermeable adhesive
tape made by polypropylene. A distance H between the opening of the
outflow pipe 57 and the overflow port of the overflow pipe 55 was
270.+-.9.5 mm (head of water). Under the opening of the outflow
pipe 57, a collection vessel 61 was disposed. The collection vessel
61 was set on a measurement apparatus (not shown, GF-3000,
manufactured by A&D Co., Ltd.).
[0047] The tank 51 was kept the overflow state with the both cocks
54 and 56 opened. When the cock 58 of the outflow pipe 57 was
opened, the water was collected by the vessel 61. And, the amount
(milliliter) of the collected water was weighed. In this case,
after an amount of the permeated water per unit time had got
constant (after a variation in amount of the permeated water per 10
seconds was within 5% at least consecutive three times), an amount
of the permeated water measured in any one minute during the
measurement for one minute or more was defined as a water permeable
amount (milliliter). And, a water permeable amount per one minuet
per 1 cm.sup.2 of the sample was converted to water permeable rate
(milliliter/min/cm.sup.2). A specific gravity of the ion-exchange
water is set to 1.000 (g/cm.sup.3).
[0048] Then, a relation between the measured water permeable rate
and publicly known air permeability was examined. Because, the
measurement of the water permeable rate needs troublesome handling,
and, therefore if the water permeable rate is correlated with the
air permeability, the measurement of the air permeability can be
employed in exchange for the measurement of the water permeable
rate.
[0049] The air permeability was measured using a gurley type
densometer (range; 300 ml, timer;s, t<1, a diameter of measuring
section; 30 mm, manufactured by Toyo Seiki Seisaku-Sho, Ltd., based
on JIS P8117). The measured value (sec/300 ml) was converted to an
air permeable rate (milliliter/min/cm.sup.2).
[0050] The prepared six samples having various pinhole diameters
were examined for water permeability using the aforesaid measuring
apparatus and also for air permeability using the gurley type
densometer.
[0051] Table 1 shows the measured air permeability, air permeable
rate converted from the measured air permeability, the measured
water permeability and water permeable rate converted from the
measured water permeability.
TABLE-US-00001 TABLE 1 air permeability water permeability measured
air permeable measured water permeable Sample value rate value rate
No. (sec/300 ml) (ml/min./cm.sup.2) (ml/min.) (ml/min./cm.sup.2) 1
31.4 81.1 37.05 13 2 18.3 139.15 67.6 23.72 3 11.4 223.38 114.34
40.12 4 9.3 273.81 126 44.21 5 6.3 404.2 185.35 65.03 6 5 509.3
233.01 81.75
[0052] FIG. 4 is a graph showing a relation between the air
permeable rate and the water permeable rate. The vertical axis
indicates the water permeable rate converted from the measured
water permeability, and the horizontal axis indicates the air
permeable rate converted from the air permeability measured by the
gurley type densometer.
[0053] As shown in the graph, the water permeable rate can be
expressed by a direct function of the air permeable rate. From the
direct function, a ratio of the water permeable rate to the air
permeable rate is substantially equal to 1/5.5 in a case of the
packing material of the present invention.
[0054] The following examinations were carried out using the air
permeable rate capable of converting to the water permeable rate
because the measurement of the water permeable rate is a
time-consuming process as described above. So, the water permeable
rate was expressed as the air permeable rate divided by 5.5.
<Relation between the Water Permeability of the Bag and the
Temperature of Heat Source>
[0055] A heat source was produced using each of the prepared bags.
And, a relation between the temperature of the heat source and the
air permeability of the bags was examined.
(1) Heat-Generating Composition
[0056] As the heat-generating composition, a mixed powder of
aluminum powder (#280A, manufactured by MINALCO Co., Ltd.) of 20 g,
calcium hydroxide powder (tokusen, manufactured by Tagen lime
industry) of 10 g and calcium oxide powder (manufactured by Tagen
lime industry) of 20 g and was used.
[0057] The aluminum powder has the following grain size
distribution: -45 .mu.m; 90.80%, 45.about.63 .mu.m; 8.30%,
63.about.75 .mu.m; 0.64% and +75 .mu.m; 0.25%. The calcium
hydroxide powder has the following grain size distribution:
.about.45 .mu.m; 4.60%, 45.about.75 .mu.m; 21.90%; 75.about.150
.mu.m; 35.92% and +150 .mu.m; 37.58%. The calcium oxide powder has
the following grain size distribution: .about.75 .mu.m; 15.68%,
75.about.150 .mu.m; 34.24% and +150 .mu.m; 50.07%.
[0058] The calcium oxide powder includes the following elements:
calcium oxide (measured by an EDTA titration method (NN
indicator)); 93% or more, carbon dioxide (measured by a Storelain
method); 2.0% and below and impurities (measured by an EDTA
titration method, perchloric acid method, absorption spectroscopy);
3.2% or less. The impurities include silicon dioxide, aluminum
oxide, ferric oxide and magnesium oxide.
(2) Samples of the Bag
[0059] The same nonwoven fabric as that used for the measurement of
the water permeability was used. By varying a contact depth of the
rollers and thus varying the pinhole diameter, the samples of
nonwoven fabrics in various air permeable rates, described below,
were prepared.
[0060] Sample 1; 60.about.110 (milliliter/min/cm.sup.2),
[0061] Sample 2; 110.about.180 (milliliter/min/cm.sup.2),
[0062] Sample 3; 180.about.250 (milliliter/min/cm.sup.2),
[0063] Sample 4; 250.about.340 (milliliter/min/cm.sup.2),
[0064] Sample 5; 340.about.450 (milliliter/min/cm.sup.2) and
[0065] Sample 6; 450.about.550 (milliliter/min/cm.sup.2).
[0066] By using the samples, the bag having a receptacle for
containing the heat-generating composition was produced. The
receptacle had a size of 70 mm.times.170 mm.
(3) Method for Measuring Temperature
[0067] FIG. 5 is a drawing showing the method for measuring the
temperature.
[0068] The heat source 1, a food F (a retort-packed cooked rice and
a 350 millilitter-plastic bottled tea, or a retort-packed cooked
rice and a retort-packed curry) and water of 130 g were put in a
heating bag 31 having exhaust vents 32. In this example, the
heating bag 31 was openable and closable and had two exhaust vents
32 having a diameter of 5 mm. In a temperature-controlled room of
which room temperature was kept at 20.degree. C. (in a case of
measurement under a low-temperature environment, the temperature
was kept at -10.about.10.degree. C.), the heating bag 31 was
supported in a stainless-steel container 73 set on a heat
insulating material 71. And, for 20 minutes after the
heat-generating reaction, a temperature T1 in the heating bag 31
(steam temperature), a temperature T2 of the heated water, an
environmental temperature T3 and a temperature T4 of the food were
measured by the measuring apparatus D.
[0069] Next, whether the food temperature T4 of each sample
satisfied the following heating conditions under the
temperature-controlled room was considered.
Condition A
[0070] 1) 40.degree. C. or higher after 5 minutes.
[0071] 2) 60.degree. C. or higher after 10 minutes.
[0072] 3) 60.degree. C. or higher after 20 minutes.
Condition B
[0073] 1) 50.degree. C. or higher after 5 minutes.
[0074] 2) 60.degree. C. or higher after 10 minutes.
[0075] 3) 65.degree. C. or higher after 20 minutes.
Condition C
[0076] 1) 60.degree. C. or higher after 5 minutes.
[0077] 2) 65.degree. C. or higher after 10 minutes.
[0078] 3) 65.degree. C. or higher after 20 minutes.
[0079] Table 2 shows a result whether the samples satisfied the
heating conditions.
TABLE-US-00002 TABLE 2 condition A condition B condition C
40.degree. C. or higher 50.degree. C. or higher 60.degree. C. or
higher after 5 min. after 5 min. after 5 min. 60.degree. C. or
higher 60.degree. C. or higher 65.degree. C. or higher after 10
min. and after 10 min. and after 10 min. and Sample 60.degree. C.
or higher 65.degree. C. or higher 65.degree. C. or higher No. after
20 min. after 20 min. after 15 min. 1 .smallcircle. x x 2
.smallcircle. .smallcircle. .smallcircle. 3 .smallcircle.
.smallcircle. .smallcircle. 4 .smallcircle. .smallcircle.
.smallcircle. 5 .smallcircle. x x 6 x x x
[0080] From these results, the following were obtained:
[0081] (1) Temperature of the heat source can be controlled by the
air permeable rate of the bag.
[0082] (2) The air permeable rate of the bag required for heating a
food is 110 to 340 milliliter/min/cm.sup.2 (water permeable rate is
about 24 to 44 milliliter/min/cm.sup.2).
[0083] However, even when the air permeable rate is 60 to 450
milliliter/min/cm.sup.2 (water permeable rate is about 13 to 65
milliliter/min/cm.sup.2), it is possible to heat the food.
[0084] Moreover, even when the air permeable rate is 60 to 550
milliliter/min/cm.sup.2 (water permeable rate is about 13 to 81
milliliter/min/cm.sup.2), if the food is small (for example, a
retort-packed rice), it is possible to heat such a food.
[0085] Accordingly, a preferable water permeable rate of the bag
for heating a food is 13 to 81 milliliter/min/cm.sup.2.
[0086] It is considered that the heat-generation of the
heat-generating composition is caused by a heat-generating reaction
of the aluminum after a formation of alkaline environment resulting
from hydrolysis of the calcium hydroxide, as described above, and
also by a heat-generating reaction of the aluminum activated by a
heat-generating resulting from a hydration reaction of the calcium
oxide. Under a low-temperature (low-water temperature) condition,
either one of the heat-generating reactions alone will not generate
sufficient amount of heat. However, when a part of the calcium
hydride is replaced by the calcium hydroxide, rate of temperature
rise becomes better. The reason is because when the aluminum powder
and calcium hydroxide powder exist, while Ca(OH.sub.2 has a high
water-solubility, since the dissolved Ca(OH).sub.2 hydrolyzes
slowly under low-temperature conditions, a dissolution rate of
aluminum may be also slow and therefore the reaction of the
aluminum powder may be initiated slowly.
[0087] On the other hand, when the aluminum powder and calcium
oxide (CaO) powder exist, Ca(OH).sub.2 produced by a hydration
reaction of CaO does not have so high water-solubility because the
water temperature rises rapidly to 70 to 80.degree. C. due to heat
generated by the aforesaid hydration reaction. Accordingly,
although hydrolysis rate is rapid, it requires a longer time until
the pH sifts toward alkalis.
[0088] When the aluminum powder, calcium hydroxide powder and
calcium oxide powder exist, Ca(OH).sub.2 dissolves just after the
hydrolysis. And, the hydrolysis rate becomes higher due to heat
produced by the hydration of CaO and therefore a period until the
starting of dissolution of the aluminum becomes shorter.
Accordingly, the heat-generating reaction begins rapidly even under
low-temperature environments and thus rate of temperature rise can
be improved. Therefore, when the water permeable rate of the bag is
set smaller than that in a case in which the aluminum powder and
calcium oxide powder exist, the temperature lasting ability can be
improved.
[0089] Next, an effect of a construction and amount ratio of the
heat-generating composition on the temperature of the heat source
under a low-temperature condition (a temperature of water to be
reacted is 5.degree. C.) will be described.
(1) An Amount Ratio of the Heat-Generating Composition
[0090] By using the aluminum powder, calcium oxide powder and
calcium hydroxide powder used for the aforesaid measurement of
water permeability, the following samples were prepared (a total
weight of 50 g). [0091] (1) Sample 1; aluminum powder:calcium
hydroxide powder:calcium oxide powder=50:15:35, [0092] (2) Sample
2; aluminum powder:calcium hydroxide powder:calcium oxide
powder=60:10:30, [0093] (3) Sample 3; aluminum powder:calcium
hydroxide powder:calcium oxide powder=60:20:20, [0094] (4) Sample
4; aluminum powder:calcium hydroxide powder:calcium oxide
powder=40:40:20, [0095] (5) Sample 5; aluminum powder:calcium
hydroxide powder:calcium oxide powder=40:20:40, [0096] (6) Sample
6; aluminum powder:calcium hydroxide powder:calcium oxide
powder=50:30:20, [0097] (7) Sample 7; aluminum powder:calcium
hydroxide powder:calcium oxide powder=60:30:10, [0098] (8) Sample
8; aluminum powder:calcium hydroxide powder:calcium oxide
powder=30:30:40, [0099] (9) Sample 9; aluminum powder:calcium
hydroxide powder:calcium oxide powder=30:20:50, [0100] (10) Sample
10; aluminum powder:calcium hydroxide powder:calcium oxide
powder=35:30:35, [0101] (11) Sample 11; aluminum powder:calcium
hydroxide powder:calcium oxide powder=35:20:45, [0102] (12) Sample
12; aluminum powder:calcium hydroxide powder:calcium oxide
powder=40:50:10, [0103] (13) Sample 13; aluminum powder:calcium
hydroxide powder:calcium oxide powder=45:10:45, [0104] (14) Sample
14; aluminum powder:calcium hydroxide powder:calcium oxide
powder=45:5:50 and [0105] (15) Sample 15; aluminum powder:calcium
hydroxide powder:calcium oxide powder=60:5:35. (2) Heat-generating
ability
[0106] Each of the sample heat-generating compositions was enclosed
with the bag made of base material (a non water-repellent nonwoven
fabric (made by 100% rayon, MR-50/PP40,manufactured by Kokko Paper
Mfg. Co., Ltd.) having a water permeable rate of about 40 to 44
milliliter/min/cm.sup.2) used for measurement of the water
permeability. According to the temperature measurement method of
FIG. 5, a temperature of the food was measured. In this embodiment,
after 25 minutes, in which the reaction continues for 20 minutes
and further the heating was kept for 5 minutes, from the
heat-generating reaction, a retort-packed rice was measured in
temperature in such a manner that a stick type temperature sensor
was inserted into the center of the retort-packed rice. Then,
whether the samples satisfied the heating condition D (to heat the
retort-packed rice to 60.degree. C. or higher after 25 minutes) and
condition E (to heat the retort-packed rice to 65.degree. C. after
25 minutes) was discussed.
[0107] Table 3 shows results whether the samples satisfied the
heating conditions.
TABLE-US-00003 TABLE 3 condition D condition E amount ratio
temperature 60.degree. C. or 65.degree. C. or Sample calcium
calcium (.degree. C.) after 25 higher after higher after No.
aluminum hydroxide oxide min. 25 min. 25 min. 1 50 15 35 67.3
.smallcircle. .smallcircle. 2 60 10 30 72.7 .smallcircle.
.smallcircle. 3 60 20 20 66.5 .smallcircle. .smallcircle. 4 40 40
20 64.3 .smallcircle. x 5 40 20 40 60.2 .smallcircle. x 6 50 30 20
62.4 .smallcircle. x 7 60 30 10 60.7 .smallcircle. x 8 30 30 40
51.3 x x 9 30 20 50 51.2 x x 10 35 30 35 53.5 x x 11 35 20 45 55.3
x x 12 40 50 10 56.6 x x 13 45 10 45 57.7 x x 14 45 5 50 59.0 x x
15 60 5 35 58.7 x x
[0108] Under a low-temperature environment (water temperature is
about 5.degree. C.), the following is found.
(1) The food heating condition D (to heat the retort-packed rice to
60.degree. C. or higher after 25 minutes) is satisfied when the
aluminum powder, calcium hydroxide powder and calcium oxide powder
has an amount ratio of 40.about.60:10.about.40:10.about.40. (2) The
food heating condition E (to heat the retort-packed rice to
65.degree. C. or higher after 25 minutes) is satisfied when the
aluminum powder, calcium hydroxide powder and calcium oxide powder
has an amount ratio of 50.about.60:10.about.20:20.about.35.
[0109] Concerning a weight of the heat-generating composition, the
following measurement was carried out. The heat-generating
composition containing the aluminum powder, calcium hydroxide
powder and calcium oxide powder with an amount ratio of the
aluminum powder, calcium hydroxide powder and calcium oxide powder
being 50:15:35 was enclosed in the bag to prepare the heat sources
each having a weight of 30 g, 40 g, 50 g and 60 g. Each of the heat
sources was examined in temperature measurement. As a result, all
of the heat sources showed substantially the same heat-generating
ability. Therefore, a weight of the heat-generating composition is
preferably 30 g or larger.
EXAMPLE 1
[0110] FIG. 1 is a drawing showing a structure of a heat source
according to the present invention; FIG. 1A is a plane drawing and
FIG. 1B is a cross-section drawing.
[0111] The heat source 1 comprises a bag 10 and a heat-generating
composition 20 enclosed in the bag 10.
[0112] The bag 10 is made of a non water-repellent nonwoven fabric
11 (100% rayon, MR-50/PP40, manufacturedbyKokko Paper Mfg. Co.,
Ltd.). Almost full area of the bag 10 is punched with pinholes 15
in substantially the uniform density. The pinhole 15 has a diameter
of 0.1 to 0.3 mm. The bag 10 has a water permeable rate, measured
by the aforesaid method (as shown in FIG. 3), of about 40
milliliter/min/cm.sup.2. The water permeable rate can be converted
from the air permeable rate measured by the gurley type densometer.
The bag 10 has a size of 70 mm.times.170 mm.
[0113] The heat-generating composition 30 is a mixed powder of
aluminum powder (#280A, manufactured by MINALCO Co., Ltd.) of 25 g,
calcium hydroxide powder (tokusen, manufactured by Tagen lime
industry) of 7.5 g and calcium oxide powder (manufactured by Tagen
lime industry) of 17.5 g (an amount ratio of
aluminum:calciumhydroxide:calciumoxide is 50:15:35. A total weight
is 50 g). The heat-generating composition 20 is enclosed in the bag
10 to produce the heat source 1.
EXAMPLE 2
[0114] The same heat-generating composition as that of Example (an
amount ratio of aluminum:calcium hydroxide:calcium oxide is
50:15:35. A total weight is 50 g) was enclosed in the bag 10 having
a water permeable rate of about 81 milliliter/min/cm.sup.2 to
produce another heat source 3.
EXAMPLE 3
[0115] FIG. 2 is a drawing showing a heating device according to
the present invention. In this embodiment, the heating device is
used for heating a retort-packed cooked rice and a retort-packed
cooked curry.
[0116] The food heating device 30 comprises a heating bag
(container) 31 having exhaust vents 32; the heat source 1 shown in
FIG. 1 and water W for activating a heat-generating reaction. In
this embodiment, two circular exhaust vents 32 having a diameter of
5 mm are formed. Or, two to four exhaust vents 32 having a diameter
of 3 to 7 mm may be formed. Depending on the container, one to two
exhaust vents having a diameter of 10 to 15 mm, or eight to ten
exhaust vents having a diameter of 1 to 2 mm may be formed. The
shape of the exhaust vent is not limited to a circular shape; may
be any shape capable of venting water vapor and hydrogen gas. When
the bag is a three sided seal pack, the exhaust vent may have a
shape formed by turning the opening of the back.
[0117] The heat source 1 is enclosed in an air-tight outer bag
during storing in order to prevent the heat-generating composition
from contacting moisture in air.
[0118] The heat source 1, taken out of the outer bag, the
retort-packed cooked rice and the retort-packed cooked curry D were
put in the heating bag (container) 31, water of about 5.degree. C.
in an amount of 130 g was added and then the container 31 was
sealed. The heat source 1 caused a heat-generating reaction to heat
the retort-packed cooked rice and retort-packed cooked curry Din
the container 31. Water vapor and hydrogen gas produced by the
heat-generating reaction were vent through the exhaust vents 32.
And, after 25 minutes from the activation of the heat-generating
reaction, the retort-packed cocked rice was heated to 67.3.degree.
C. And, leakage of the heat-generating composition did not
occur.
EXAMPLE 4
[0119] In the same food heating device as that of Example 3, the
heat source 3 was used in exchange for the heat source 1. As with
Example 3, the heat source 3, taken out of the outer bag, and 350
milliliter-plastic bottled tea D were put in the heating bag
(container) 31, water of about 20.degree. C. in an amount of 130 g
was added and then the container 31 was sealed. In the same way,
the heat source 3, taken out of the outer bag, and a retort-packed
cooked rice D were put in the heating bag (container) 31, water of
about 5.degree. C. in an amount of 130 g was added and then the
container 31 was sealed.
[0120] FIG. 6 is a graph showing a relation between the measurement
time and temperatures.
[0121] When an initial temperature of the water to be reacted is
20.degree. C., the water temperature rises to 60.degree. C. or
higher after 5 minutes from the heat-generating reaction and the
risen temperature higher than 80.degree. C. is kept after 10
minutes from the reaction. When an initial temperature of the water
to be reacted is 5.degree. C., the water temperature rises to
90.degree. C. after 2 minutes from the heat-generating reaction and
the risen temperature higher than 90.degree. C. is kept for about
10 minutes after the reaction. However, the temperature falls down
rapidly after 10 minutes and decreases to 50.degree. C. or less
after 20 minutes. But, the temperature of the retort-packed rice,
which was measured by inserting the stick type temperature sensor
into the center of the retort-packed rice after 25 minutes, was
60.4.degree. C. This shows that the retort-packed rice was
sufficiently heated.
[0122] In exchange for the aforesaid non water-repellant nonwoven
fabric, another type of non water repellent nonwoven fabric maybe
used, for example, CO40s (manufactured by Unitika Co., Ltd.), which
has the following properties: basis weight (g/m.sup.2); 40,
thickness (.mu.m); 330, longitudinal tensile strength (N/5 mm); 35,
transverse tensile strength (N/5 mm); 15, longitudinal
extensibility (%); 25 and transverse extensibility (%); 75. The
nonwoven fabric was made by a spunlaced method.
[0123] A weight ratio of the aluminum power, calcium hydroxide
powder and calcium oxide powder, weight of the heat-generating
composition and properties are not limited to the aforesaid
values.
BRIEF DESCRIPTION OF THE DRAWINGS
[0124] FIG. 1 is a drawing showing a structure of a heat source
according to the present invention; FIG. 1A is a plane drawing and
FIG. 1B is a cross-section drawing.
[0125] FIG. 2 is a drawing showing a heating device according to
the present invention.
[0126] FIG. 3 is a drawing showing the water permeable rate
measuring method in the present invention.
[0127] FIG. 4 is a graph showing a relation between the air
permeable rate and the water permeable rate.
[0128] FIG. 5 is a drawing showing the method for measuring the
temperature.
[0129] FIG. 6 is a graph showing a relation between the measurement
time and temperatures.
EXPLANATION OF ITEM NUMBERS
[0130] 1,2,3 heat source [0131] 10 bag [0132] 11 nonwoven fabric
[0133] 13 water resistant layer [0134] 15 pinholes [0135] 20
heat-generating composition [0136] 30 hood heating device [0137] 31
heating bag [0138] 32 exhaust vent
* * * * *