U.S. patent application number 09/771878 was filed with the patent office on 2001-08-09 for packaged food and container for packaging food.
Invention is credited to Hiyoshi, Sachiko.
Application Number | 20010012530 09/771878 |
Document ID | / |
Family ID | 18549929 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012530 |
Kind Code |
A1 |
Hiyoshi, Sachiko |
August 9, 2001 |
Packaged food and container for packaging food
Abstract
The present invention provides packaged food and a container for
packaging food, in which a hole-sealing sheet which seals a vent
hole formed at a portion of the container cannot so easily be
peeled off but, when the food is heated by an microwave oven, the
hole-sealing sheet automatically comes off at the time when the
food contained in the container has reached the adequately cooked
state. Specifically, the packaged food of the present invention is
produced by enclosing food, which contains water or an aqueous
solution by an amount suitable for heating by an microwave oven, in
the container for packaging food, the container for packaging food
having, on one side thereof, a surface portion made of plastic
sheet, at least one vent hole being formed in the vicinity of the
center of the surface portion, the vent hole being sealed by an
adhesive hole-sealing sheet whose vertical peeling strength is no
less than 1 N/cm in the temperature range of 40.degree. C. or lower
and is no higher than 0.1 N/cm at the temperature range of
80.degree. C. or higher.
Inventors: |
Hiyoshi, Sachiko; (Tokyo,
JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN, HATTORI,
MCLELAND & NAUGHTON, LLP
1725 K STREET, NW, SUITE 1000
WASHINGTON
DC
20006
US
|
Family ID: |
18549929 |
Appl. No.: |
09/771878 |
Filed: |
January 30, 2001 |
Current U.S.
Class: |
426/118 ;
220/203.11 |
Current CPC
Class: |
B65D 81/3453 20130101;
B65D 77/225 20130101; B65D 2205/02 20130101 |
Class at
Publication: |
426/118 ;
220/203.11 |
International
Class: |
B65D 081/34; B65D
051/16 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 1, 2000 |
JP |
P2000-023830 |
Claims
What is claimed is:
1. A packaged food characterized in that food containing water or
an aqueous solution is enclosed in a container, the container
having a surface portion made of plastic sheet, at least one vent
hole being formed in the surface portion, the vent hole being
sealed by an adhesive hole-sealing sheet whose vertical peeling
strength is no less than 1 N/cm in the temperature range of
40.degree. C. or lower and is no higher than 0.1 N/cm at the
temperature range of 80.degree. C. or higher.
2. A container for packaging food characterized in that the
container has a surface portion made of plastic sheet, at least one
vent hole being formed in the surface portion, the vent hole being
sealed by an adhesive hole-sealing sheet whose vertical peeling
strength is no less than 1 N/cm in the temperature range of
40.degree. C. or lower and is no higher than 0.1 N/cm at the
temperature range of 80.degree. C. or higher.
3. A container for packaging food of claim 2, at least one vent
hole is formed in the vicinity of the center of a surface portion
provided on one side of the container.
4. A container for packaging food of claim 2 or 3, wherein the
hole-sealing sheet seals the vent hole such that the adhesive layer
having uneven width provided in the hole-sealing sheet covers the
periphery of the vent hole.
5. A container for packaging food of any of claims 2 to 4, wherein
the hole-sealing sheet is made of white chemical paper used as a
base material.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a packaged food which is
produced by enclosing unfrozen or frozen food in an airtight
container such that the packaged food can be directly cooked by
heating in a microwave oven. The present invention also relates to
a container for packaging food in which the aforementioned food can
be enclosed for storage.
[0003] 2. Prior Art
[0004] Packaged food produced by enclosing unfrozen food (i.e.,
food at the room temperature) or frozen food in a container for
storage is conventionally known. It is also known that, when such
packaged food is heated in a microwave oven, the pressure inside
the package significantly rises up, to increase the possibility of
the package exploding. Therefore, it has been proposed a technique
for preventing explosion, in which holes are formed in the
container for packaging food such that each hole is covered by a
circular-shaped sealing piece coated with an adhesive (Japanese
Utility Model 62-69466). Similarly, a technique has been proposed
in which holes are formed in the container which packages food, and
a valve sheet is attached, so as to close each hole, by applying a
first adhesive having a low melting point which corresponds to the
heating temperature of the food in the range between the periphery
of the hole and the valve sheet end periphery, and by applying a
second adhesive which does not melt at the heating temperature of
the food at two sides of the low-melting point adhesive-applied
portion (Japanese Utility Model 63-156978).
[0005] These known techniques are useful for prevention of
explosion during heating by an microwave oven. However, in these
conventional techniques, there arises a problem that the holes are
opened before the food is sufficiently heated and thus uneven
heating is caused or a problem that the holes are opened so late to
cause drying or burning of food. These problems have not been
solved. Therefore, in the packaged food to be cooked by heating by
a microwave oven, there has been a demand for a sealing structure
of the holes, in which steam generated by heating the food is
preserved for an appropriate period without allowing the steam to
escape outside too early and the sealing is released only when the
food is sufficiently heated. However, it is not so easy to
determine the most preferable sealing condition of holes with
respect to each (type of) food. In addition, such a
supposed-to-be-preferable sealing structure tends to have a
complicated structure. In short, no prior art has successfully
developed a technique which satisfies the aforementioned demand in
an economical and practical manner.
SUMMARY OF THE INVENTION
[0006] In order to satisfy the aforementioned demand, the present
invention intends to provide, in an economical manner, a sealing
structure in which a hole-sealing sheet for sealing a vent hole
formed in a container for packaging food automatically comes off,
at the most preferable timing, when the food is cooked by heating
by an microwave oven.
[0007] A first object of the present invention is to provide a
packaged food, in which a hole-sealing sheet covering a vent hole
formed at a portion of a container is not so easily peeled off when
the container is preserved at the room temperature or the freezing
condition but the hole-sealing sheet automatically comes off, when
the food is heated by an microwave oven, substantially at the time
when the food contained in the container has reached an adequately
cooked state.
[0008] A second object of the present invention is to provide a
container for packaging food, which container is provided with at
least one vent hole and used for producing packaged food by
enclosing food therein, and in which container a hole-sealing sheet
covering the vent hole is not so easily peeled off when the
container is preserved at the room temperature or the freezing
condition but the hole-sealing sheet automatically comes off, when
the food is heated by an microwave oven, substantially at the time
when the food contained in the container has reached an adequately
cooked state. That is, the second object of the present invention
is to provide a container for packaging food which enables carrying
out the most preferable heating of the food by flexibly adapting,
in function thereof, to the various heating conditions by a
microwave oven which is selected according to the contained
food.
[0009] The packaged food of the present invention, which can
achieve the aforementioned first object, is characterized in that
food containing water or an aqueous solution is enclosed in a
container, the container having, on one side thereof, a surface
portion made of plastic sheet, at least one vent hole being formed
in the vicinity of the center of the surface portion, the vent hole
being sealed by an adhesive hole-sealing sheet whose vertical
peeling strength is no less than 1 N/cm in the temperature range of
40.degree. C. or lower and is no higher than 0.1 N/cm at the
temperature range of 80.degree. C. or higher.
[0010] In addition, the container for packaging food of the present
invention, which can achieve the aforementioned second object, is
characterized in that the container has, on one side thereof, a
surface portion made of plastic sheet, at least one vent hole being
formed in the vicinity of the center of the surface portion, the
vent hole being sealed by an adhesive hole-sealing sheet whose
vertical peeling strength is no less than 1 N/cm in the temperature
range of 40.degree. C. or lower and is no higher than 0.1 N/cm at
the temperature range of 80.degree. C. or higher.
[0011] Further, the hole-sealing sheet of the container for
packaging food of the present invention is preferably made of white
chemical paper used as a base material. It is preferable that the
vent hole formed in the container is sealed by the hole-sealing
sheet such that the adhesive layer having uneven width provided in
the hole-sealing sheet covers the periphery of the vent hole.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a sectional view of a vent hole portion formed in
a lid of a container for packaging food of the present invention;
and
[0013] FIG. 2 is a perspective view which shows a structure of a
container for packaging food of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] Packaged food of the present invention is intended to
represent packaged food which can be cooked by heating by a
microwave oven. At least one vent hole is provided in a container
for packaging food so that, when the pressure inside the container
is increased in heating the food due to volume increase in the air
in the container and generation of steam, the increased pressure is
reduced by releasing the steam and occurrence of explosion is
prevented. In the present invention, the vent hole is sealed by a
hole-sealing sheet having adhesives thereon. That is, the present
invention has been achieved by utilizing and improving the
conventional technique.
[0015] Food in the container must be sufficiently heated in
cooking. Therefore, it is unavoidable that the pressure inside the
container rises up to the value of the vapor pressure which
corresponds to the temperature of the food, because the pressure
inside the container increases as the temperature in the container
is increased. Considering this situation, the known conventional
techniques make the adhesive strength of the hole-sealing sheet
relatively weak or provide, the periphery portion of the vent hole
or the like, with portions where the adhesive strength is
relatively weak, so that the hole-sealing sheet easily comes off
when the pressure inside the container has become high. In other
words, such conventional techniques expect the hole-sealing sheet
to operate as a safe valve for pressure.
[0016] The inventors of the present invention have assiduously
studied a problem that it is not easy to make the preferable
finished state of cooking by heating correspond with the pressure
resistance properties of the hole-sealing sheet. As a result of the
study, the inventors have discovered that the pressure resistance
properties of the hole-sealing sheet can be changed by adjusting
the temperature properties of adhesive strength of the adhesive
agent (the adhesive agent is used for attaching the hole-sealing
sheet). The present invention has been achieved on the basis of
this discovery.
[0017] The container for packaging food of the present invention
may have a box-like shape or a bag-like shape. That is, the shape
of the container is not limited to any particular form and any
structure is acceptable as long as the container is formed by using
a material which is excellent in airtight, watertight, oil
resistant and heat resistant properties, is electromagnetic
wave-transmittable, and has mechanical strength of appropriate
level. However, at least one side surface of the container must be
formed by a plastic sheet. The surface formed by a plastic sheet is
preferably transparent so that the content therein can be seen.
[0018] Examples of the plastic material to be used for forming the
container as described above include: a single material sheet or a
composite material sheet containing, as main components,
polypropylene, polyester, polysulfone, polyamide (nylon),
polycarbonate and the like; and a laminated layer-composite sheet
in which the aforementioned single material or composite material
sheet is combined with polyacrylate, polyvinylidene chloride,
polyvinyl alcohol and the like.
[0019] A vent hole is formed in the plastic sheet surface made of
the aforementioned materials. The vent hole is preferably formed in
the vicinity of the center of the container for packaging food (in
the vicinity of the center of the upper surface, in a case of a
flat-type container in which the height is relatively small as
compared with the longitudinal/lateral dimensions thereof) in terms
of evenly heating the content in the container. The vent hole may
have any shape such as circular, ellipsoidal, oval or polygonal
shape, as long as the shape is suitable for the purpose. The size
of the diameter of the vent hole is preferably 5 mm or so, but is
not particularly limited.
[0020] Similar to the plastic sheet described above, the
hole-sealing sheet for sealing the vent hole is preferably made of
a base material having excellent airtight, watertight, oil
resistance and heat resistance properties. Examples of such a base
material include a sheet made of polyester, polypropylene or the
like, a synthetic paper and a chemical paper made of plastic
materials. It is preferable that the hole-sealing sheet itself
hardly generates heat when it is hit by electromicrowaves nor
increases its temperature when it absorbs infrared light. The
hole-sealing sheet having aluminum deposited thereon so as to
reflect microwaves and the hole-sealing sheet which is colorless
or, in particular, white is especially preferable. The hole-sealing
sheet may have any suitable shape such as circular or ellipsoidal
shape. The size of the diameter of the hole-sealing sheet is
preferably 10 mm or so, but it not limited to this size.
[0021] The adhesive agent for attaching the hole-sealing sheet to
the vent hole formed in the plastic sheet must be an adhesive agent
having stickiness with respect to the plastic sheet, i.e., a
pressure sensitive adhesive. Examples of such a pressure sensitive
adhesive agent include natural rubber, synthetic rubber. A pressure
sensitive adhesive, which is produced by blending styrene
butadiene-based rubber and acryl-based rubber with a rosin-based or
petroleum resin-based stickiness-providing material so as to have
both excellent pressure sensitive properties and excellent
thermosensitive properties, is particularly preferable for use.
[0022] The pressure sensitive adhesive as described above is
required to have thermosensitive properties in which the vertical
peeling strength is no less than 1 N/cm or preferably no less than
2 N/cm in the temperature range of 40.degree. C. or lower and is no
higher than 0.1 N/cm in the temperature range of 80.degree. C. or
higher. By employing the hole-sealing sheet having a back surface
coated with a pressure sensitive adhesive which satisfies the
aforementioned conditions or properties, for sealing the vent hole
formed in the plastic sheet, the hole-sealing sheet now functions
so as to open the vent hole after the food contained in the
container has been sufficiently cooked by heating.
[0023] It should be noted that the numerical values in the
aforementioned conditions are not such numerical values which are
inherent to the adhesive itself as is obtained by measurement in
accordance with the standard adhesive strength testing method and
the like practiced in the industry (described in JIS Z 0237, for
example), but the numerical values which indicate the
thermosensitive properties of adhesive strength of the hole-sealing
sheet, with respect to the plastic sheet of a container for
packaging food having a vent hole formed therein. Accordingly,
attention should be paid because it is generally not known whether
or not a pressure sensitive adhesive, which satisfies the
aforementioned conditions of adhesive strength properties with
respect to a specific polyester sheet, also satisfies the
conditions of adhesive strength properties with respect to a
specific nylon 6 sheet.
[0024] Further, the aforementioned conditions of adhesive
properties are to be applied to a container for packaging food
which is designed for accommodating the most common food, i.e., the
food which contains water or aqueous solutions at appropriate
ratios and is suitable for heating by an microwave oven. Examples
of such "the most common food" include cooked food such as main
meal, snack, half-cooked food and the like. Therefore, with respect
to the food which needs to be heated to a relatively high
temperature of no lower than 100.degree. C. or the food which needs
to be heated only to 40-60.degree. C., it is necessary that a
pressure sensitive adhesive having more preferable adhesive
strength properties within the aforementioned range of the
conditions, is selected. Yet further, needless to say, food which
is not suitable for being heated by an microwave oven such as dry
foods or the like is beyond the scope of the present invention.
[0025] The present invention will be described hereinafter
according to a preferred embodiment.
[0026] In FIG. 1, the reference number 1 represents a food
container which is produced by molding a polycarbonate sheet. A
laminate layer or the like formed by an appropriate material may be
provided inside the food cotainer 1. The reference number 2
represents a flexible lid made of nylon 6 sheet. The periphery
portion of the lid 2 is designed so that the periphery portion can
be fixed to the edge portion 1' of the food container 1 by
melt-attaching or adhesive-attaching. A vent hole 3 having circular
shape is formed in the vicinity of the center position of the lid
2. The vent hole 3 has been airtightly sealed by the hole-sealing
sheet 4 having circular shape.
[0027] A pressure sensitive adhesive layer 5 which sticks to the
nylon 6 sheet is provided on the back surface of the hole-sealing
sheet 4, such that a non-adhesive portion 5' having ellipsoidal
shape is formed substantially in the center portion of the pressure
sensitive adhesive layer 5. In the pressure sensitive adhesive
layer 5, the width of the portion coated with the pressure
sensitive adhesive is made uneven. Further, the center position of
the vent hole 3 does not need to coincide with that of the
hole-sealing sheet 4. A slight misalignment of 1-2 mm or so between
the center position of the vent hole 3 and that of the center
position of the hole-sealing sheet 4 is rather preferable because
such a slight misalignment facilitates, in a reliable manner,
peeling of the hole-sealing sheet 4.
[0028] The hole-sealing sheet 4 used here is produced by:
preparing, as a base material, synthetic paper made of polyester
which has thickness of 60 .mu.m and white surface coating applied
thereon; and coating the base material with an acryl-based pressure
sensitive adhesive a so that the thickness of the adhesive a is 25
.mu.m, thereby forming the pressure sensitive adhesive layer 5. For
comparison, a hole-sealing sheet 4b and a hole-sealing sheet 4c
were produced by coating the base material with another acryl-based
pressure sensitive adhesive b or a styrene butadiene-based pressure
sensitive adhesive c, respectively, so that the thickness of the
adhesives b, c is each 25 .mu.m and the pressure sensitive adhesive
layer is formed in each of a hole-sealing sheet 4b and a
hole-sealing sheet 4c in a manner similar to the hole-sealing sheet
4a.
[0029] The adhesive strength properties of the aforementioned
pressure sensitive adhesives a, b, c with respect to the nylon 6
sheet were measured separately. The results are as follows.
1TABLE 1 Adhesive Strength with respect to Nylon 6 Sheet
(10.sup.-2N/cm) Temperature (.degree. C.) 30 40 50 60 70 80 90
Pressure Sensitive Adhesive a 300 190 110 38 13 8 5 Pressure
Sensitive Adhesive b 220 85 43 18 9 2 -- Pressure Sensitive
Adhesive c 350 240 175 130 92 63 42
[0030] The hole-sealing sheet 4a, the hole-sealing sheet 4b and the
hole-sealing sheet 4c produced by coating the base material with
the pressure sensitive adhesives a, the pressure sensitive
adhesives b, the pressure sensitive adhesives c, respectively, were
each pressingly attached to the vent hole 3 of the lid 2 made of
nylon 6 sheet of a food container so as to seal the vent hole 3
(the three food containers for the three adhesives used here had
substantially the same structure except for the hole-sealing
sheet), thereby producing a container for packaging food A of the
present invention and containers for packaging food B, C as
comparative examples. Five samples were prepared for each of the
container for packaging food A, B and C. 210 g of frozen Shao-mai
was airtightly enclosed in each container and the heat-cooking
tests were carried out by using a microwave oven which satisfied
the standard of output measurement of a microwave oven described in
JIS Z 9212. The results shown in Table 2 were obtained.
2TABLE 2 Heat-Cooking Test of Packaged Food Food Time required the
Hole-Sealing The heat-cooked State Container Sheet to come off
(minute) of Food A 4.5-5.0 Evenly heated allover Core Portion has
not B 3.5-4.0 been sufficiently heated C 7.0-7.5 Surface has been
dried
[0031] From the results described above, it is understood that the
packaged food of the present invention prepared by using the
container for packaging food of the present invention reliably
prevents, when the packaged food is heated by a microwave oven, the
hole-sealing sheet thereof from peeling off at the time when the
food has not sufficiently been heated. In the present invention,
the hole-sealing sheet peels off only when the food has reached an
adequately cooked state, an enough amount of steam is generated
and, due to the steam, the temperature at the vent hole portion has
reached the temperature at which the pressure sensitive adhesive
peels off. Therefore, by stopping the operation of the microwave
oven when the steam has burst, there is no possibility of
overheating the food.
[0032] As described above, the packaged food of the present
invention is produced by enclosing food containing water or an
aqueous solution in the container for packaging food of the present
invention, the container for packaging food having, on one side
thereof, a surface portion made of plastic sheet, at least one vent
hole being formed in the vicinity of the center of the surface
portion, the vent hole being sealed by an adhesive hole-sealing
sheet whose vertical peeling strength is no less than 1 N/cm in the
temperature range of 40.degree. C. or lower and is no higher than
0.1 N/cm at the temperature range of 80.degree. C. or higher. When
the packaged food of the present invention is heated by using a
microwave oven, the hole-sealing sheet thereof automatically peels
off after the food has been sufficiently heated. Therefore, the
hole-sealing sheet peeling off before the cooking by heat has been
completed or the overcooking of the food due to too late peeling of
the hole-sealing sheet will less likely to occur. In other words,
the present invention achieves an excellent effect that adequately
cooked food can be easily obtained.
* * * * *