U.S. patent application number 14/650739 was filed with the patent office on 2015-11-26 for microwaveable sheet, and production method of microwaveable sheet.
The applicant listed for this patent is KEIWA INC.. Invention is credited to Tadashi AKAMATSU, KOICHI SAWADA.
Application Number | 20150337497 14/650739 |
Document ID | / |
Family ID | 50934318 |
Filed Date | 2015-11-26 |
United States Patent
Application |
20150337497 |
Kind Code |
A1 |
SAWADA; KOICHI ; et
al. |
November 26, 2015 |
MICROWAVEABLE SHEET, AND PRODUCTION METHOD OF MICROWAVEABLE
SHEET
Abstract
A microwaveable sheet (1) that prevents permeation of the oil
and is superior in moisture permeability, and a production method
thereof. The microwaveable sheet (1) has a paper substrate (2), a
resin layer (3) laminated through applying a coating liquid of a
resin composition on one face of the paper substrate (2), in which
the resin layer (3) has a plurality of air holes (3a). The
microwaveable sheet (1) preferably has a water vapor transmission
rate of from 200 g/m.sup.2/24 hrs to 15,000 g/m.sup.2/24 hrs. The
microwaveable sheet (1) may have air holes (3a) formed by applying
a coating liquid on one face of the paper substrate (2) using a
roll having an intaglio on the surface thereof, or may have air
holes (3a) formed by applying a coating liquid on one face of the
paper substrate (1) having a shape with fine irregularity.
Inventors: |
SAWADA; KOICHI; (Osaka,
JP) ; AKAMATSU; Tadashi; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KEIWA INC. |
Osaka |
|
JP |
|
|
Family ID: |
50934318 |
Appl. No.: |
14/650739 |
Filed: |
December 6, 2013 |
PCT Filed: |
December 6, 2013 |
PCT NO: |
PCT/JP2013/082885 |
371 Date: |
June 9, 2015 |
Current U.S.
Class: |
428/137 ;
427/288 |
Current CPC
Class: |
D21H 23/58 20130101;
Y10T 428/24322 20150115; D21H 19/84 20130101; D21H 27/10 20130101;
D21H 19/14 20130101; B65D 81/3453 20130101; B65D 65/40
20130101 |
International
Class: |
D21H 27/10 20060101
D21H027/10; D21H 19/14 20060101 D21H019/14 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 11, 2012 |
JP |
2012-270833 |
Claims
1. A microwaveable sheet comprising: a paper substrate; and a resin
layer laminated through applying a coating liquid of a resin
composition on one face of the paper substrate, wherein the resin
layer comprises a plurality of air holes.
2. The microwaveable sheet according to claim 1, having a water
vapor transmission rate of no less than 200 g/m.sup.2/24 hrs and no
greater than 15,000 g/m.sup.2/24 hrs.
3. The microwaveable sheet according to claim 1, wherein the air
holes are formed through applying the coating liquid on the one
face of the paper substrate with a roll having an intaglio on a
surface thereof.
4. The microwaveable sheet according to claim 1, wherein the air
holes are formed through applying the coating liquid on the one
face of the paper substrate having a shape with fine
irregularity.
5. The microwaveable sheet according to claim 1, wherein an
application amount of the resin composition is no less than 0.01
g/m.sup.2 and no greater than 20 g/m.sup.2 on a basis of a solid
content.
6. The microwaveable sheet according to claim 1, wherein the resin
layer is laminated on both two faces of the paper substrate.
7. The microwaveable sheet according to claim 1, wherein a
principal component of the resin layer is an acrylic resin, an
olefin-derived resin or a carbonyl group-containing resin.
8. The microwaveable sheet according to claim 1, wherein the paper
substrate is an oil-resistant paper.
9. The microwaveable sheet according to claim 1, further comprising
a printing portion provided on one face of the paper substrate.
10. The microwaveable sheet according to claim 1 having an oil
shieldability from one side to another of no less than 1 hour.
11. A method for producing a microwaveable sheet comprising:
applying a coating liquid of a resin composition on one face of a
paper substrate to form a resin layer, wherein the resin layer is
formed such that a plurality of air holes are provided on/through
the resin layer.
Description
TECHNICAL FIELD
[0001] The present invention relates to a microwaveable sheet, and
a production method of a microwaveable sheet.
BACKGROUND ART
[0002] Conventionally, exemplary sheets for use in wrapping a
variety of foods include oil resistant sheets that are capable of
suitably wrapping oily foods such as deep fried foods. As such
sheets, oil-resistant papers for wrapping foods containing a large
amount of oil ingredients have been publicly known (Japanese
Unexamined Patent Application, Publication No. 2006-183221).
[0003] The oil-resistant paper has: a paper support; and a resin
layer containing a hydrogen-bondable resin and oil absorptive
particles provided on at least one face of the paper support,
whereby superior oil resistance is attained.
[0004] However, a resin layer is included for ensuring oil
resistance in such an oil-resistant paper, and therefore moisture
permeability is likely to be diminished due to the resin layer.
Thus, when foods such as deep fried foods are wrapped, qualities of
the wrapped foods may not be maintained after a lapse of a certain
period of time following the wrapping of the foods as a result of
dew condensation on the surface of the wrapped foods since water
vapor within the space surrounded by the sheet is not released
outside. Additionally, also in the case in which the foods are
heated in a microwave oven while the state of being wrapped is
maintained, water vapor within the space surrounded by the sheet
fails to be released outside, and thus the moisture is attached to
the surface of the foods, whereby the qualities of the foods may be
deteriorated.
PRIOR ART DOCUMENTS
[0005] Patent Document 1: Japanese Unexamined Patent Application,
Publication No. 2006-183221
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0006] The present invention was made in view of such
circumstances, and it is an object of the invention to provide a
microwaveable sheet that prevents permeation of the oil to the
external face and that is superior in moisture permeability, and to
provide a method for producing a microwaveable sheet.
Means for Solving the Problems
[0007] The microwaveable sheet according to the present invention
made for solving the foregoing problems includes:
[0008] a paper substrate; and
[0009] a resin layer laminated through applying a coating liquid of
a resin composition on one face of the paper substrate,
[0010] in which the resin layer has a plurality of air holes.
[0011] Since the microwaveable sheet has a resin layer on one face
of a paper substrate, permeation of oil is less likely to occur. In
addition, the resin layer includes a plurality of air holes
properly formed by applying a coating liquid of a resin composition
on one face of the paper substrate; therefore, water vapor can be
suitably permeabilized by way of the air holes while the permeation
of oil as described above is prevented. Since such a microwaveable
sheet has superior moisture permeability while securing the oil
resistance as described above, even in the case in which foods such
as deep fried foods and hamburgers wrapped by the microwaveable
sheet are subjected to a heat treatment in a microwave oven in the
wrapped state, water vapor is released outside while the permeation
of oil is prevented, and therefore, deterioration of the texture is
less likely to be accompanied through inhibition of the attachment
of the water droplets onto the surface of the foods.
[0012] In addition, the microwaveable sheet preferably has a water
vapor transmission rate of no less than 200 g/m.sup.2/24 hrs and no
greater than 15,000 g/m.sup.2/24 hrs. According to such a
constitution, when foods wrapped by the microwaveable sheet are
heated in a microwave oven or the like in the wrapped state, water
vapor generated from the foods can be suitably released outside.
Thus, deterioration of the texture is less likely to be accompanied
even if the foods are cooked by heating in a microwave oven or the
like.
[0013] Furthermore, according to the microwaveable sheet, it is
preferred that air holes are formed on the one face of the paper
substrate through applying the coating liquid with a roll having an
intaglio on the surface thereof. By thus forming the air holes
through applying the coating liquid with a roll having an intaglio,
the air holes as desired can be easily and certainly formed
on/through the resin layer. Thus, the microwaveable sheet can
achieve superior moisture permeability, while the oil resistance is
maintained.
[0014] According to the microwaveable sheet, the aforementioned air
holes may be formed through applying the coating liquid on the one
face of the paper substrate having a shape with fine irregularity.
By thus applying the coating liquid on one face of the paper
substrate having a shape with fine irregularity, the air holes as
desired can be easily and certainly formed on/through the resin
layer. Accordingly, the microwaveable sheet can achieve superior
moisture permeability while the oil resistance is maintained.
[0015] Moreover, in the microwaveable sheet, an application amount
of the resin composition is preferably no less than 0.01 g/m.sup.2
and no greater than 20 g/m.sup.2 on the basis of the solid content.
Thus, the microwaveable sheet can achieve further superior moisture
permeability while the oil resistance is sufficiently
maintained.
[0016] The microwaveable sheet preferably has the resin layer
laminated on both two faces of the paper substrate. Accordingly,
the microwaveable sheet can have preferred oil resistance and
moisture permeability by way of the resin layers of both two faces
of the paper substrate.
[0017] Additionally, a principal component of the resin layer is
preferably an acrylic resin, an olefin-derived resin, or a carbonyl
group-containing resin. According to such a constitution, the oil
resistance of the microwaveable sheet can be improved.
[0018] Moreover, the paper substrate is preferably an oil-resistant
paper. When the paper substrate is an oil-resistant paper, the oil
resistance of the microwaveable sheet can be improved.
[0019] It is preferred that the microwaveable sheet further has a
printing portion provided on the one face of the paper substrate.
When such a constitution is adopted, for example, varying printing
for each type of the food wrapped is made, whereby the type of the
food can be distinguished through viewing the external face of the
microwaveable sheet.
[0020] Additionally, the microwaveable sheet preferably has oil
shieldability from one side to another of no less than 1 hour. When
such a constitution is adopted, permeation of the oil can be more
effectively prevented.
[0021] In addition, the method for producing a microwaveable sheet
according to the present invention includes the step of:
[0022] applying a coating liquid of a resin composition on one face
of a paper substrate to form a resin layer,
[0023] wherein the resin layer is formed such that a plurality of
air holes are provided on/through the resin layer.
[0024] According to such a production method, the microwaveable
sheet aforementioned can be produced, and thus the advantages as
aforementioned can be achieved. More specifically, the
microwaveable sheet produced according to the production method,
oily matter and/or moisture are/is less likely to be permeated from
one side to another of the microwaveable sheet, and the water vapor
is likely to be released outside from one side to another of the
microwaveable sheet.
[0025] It is to be noted that the term "air hole" as referred to
means fine pores formed on/through the resin layer. The term "water
vapor transmission rate" as referred to means a value determined in
accordance with an upright cup test (JIS Z0208). The term "oil
shieldability" means a determined value of a time period required
for passage of 3 g of salad oil through a resin layer after
dropwise addition, under a condition of a temperature of 40.degree.
C.
Effects of the Invention
[0026] As explained in the foregoing, the microwaveable sheet
according to the present invention prevents permeation of the oil
to the external face, and is superior in moisture permeability. In
addition, the method for producing the microwaveable sheet
according to the present invention enables a microwaveable sheet
that prevents permeation of the oil to the external face and that
is superior in moisture permeability to be produced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 shows a schematic cross sectional view illustrating a
microwaveable sheet according to a first embodiment of the present
invention;
[0028] FIG. 2 shows a schematic explanatory view illustrating a
method for producing the microwaveable sheet shown in FIG. 1;
[0029] FIG. 3 shows a schematic cross sectional view illustrating a
microwaveable sheet according to a second embodiment of the present
invention; and
[0030] FIG. 4 shows a schematic explanatory view illustrating a
method for producing the microwaveable sheet shown in FIG. 3.
DESCRIPTION OF EMBODIMENTS
[0031] Hereinafter, modes for carrying out the invention will be
explained with appropriate references to the drawings.
First Embodiment
Microwaveable Sheet 1
[0032] As shown in FIG. 1, a microwaveable sheet 1 has a paper
substrate 2, a resin layer 3 laminated on one face of the paper
substrate 2, and a printing portion 4 formed on another face of the
paper substrate 2.
[0033] Although the paper substrate 2 is not particularly limited,
a paper substrate produced by paper making from a pulp slurry
containing pulp fibers as a principal component is suitably used.
Examples of such a paper substrate 2 include virgin white roll
papers, glassine papers, paraffin papers, kraft papers, simili
papers, thin papers, general quality papers, Japanese papers, and
the like. Of these, virgin white roll papers are preferred.
[0034] The grammage of the paper substrate 2 is preferably no less
than 15 g/m.sup.2 and no greater than 60 g/m.sup.2, more preferably
no less than 20 g/m.sup.2 and no greater than 50 g/m.sup.2, and
still more preferably no less than 25 g/m.sup.2 and no greater than
30 g/m.sup.2. When the grammage of the paper substrate 2 is greater
than the above upper limit, the stiffness of the paper substrate 2
increases, whereby the paper substrate 2 is less likely to be
deformed so as to meet the shape of the food to be wrapped, and
thus direct wrapping of the food with the microwaveable sheet 1 may
be difficult. On the other hand, when the grammage of the paper
substrate 2 is less than the above lower limit, the strength is
reduced, whereby the paper substrate 2 may be likely to be
broken.
[0035] The paper substrate 2 may contain a fluorochemical additive
in order to impart or improve the oil resistance. The
fluorochemical additive is exemplified by a composition containing
a compound that includes a perfluoroalkyl group having a carbon
chain of 6 or less carbon atoms, and the like. In the compounds
that include a perfluoroalkyl group having a carbon chain of 6 or
less carbon atoms, a longer carbon chain is preferred in light of
superior oil resistance, and compounds that include a
perfluoroalkyl group having a carbon chain of 5 or 6 carbon atoms
are more preferred. It is to be noted that the carbon chain of the
perfluoroalkyl group having 7 or more carbon atoms is not preferred
since environmental burden may be increased. The fluorochemical
additive used may be a commercially available product, and examples
of the commercially available product include trade name "AG-E060"
manufactured by Asahi Glass Co., Ltd., and the like.
[0036] The content of the fluorochemical additive in the paper
substrate 2 on the basis of the solid content is preferably no less
than 0.001 g/m.sup.2 and no greater than 1.0 g/m.sup.2, and more
preferably no less than 0.3 g/m.sup.2 and no greater than 0.7
g/m.sup.2. When the content of the fluorochemical additive in the
paper substrate 2 is greater than the above upper limit, the
stiffness of the paper substrate 2 increases, whereby wrapping to
meet the shape of the food may be difficult. On the other hand,
when the content of the fluorochemical additive in the paper
substrate 2 is less than the above lower limit, sufficient oil
resistance may not be attained.
[0037] As the method for allowing the fluorochemical additive to be
contained in the paper substrate 2, for example, a method in which
the paper substrate 2 is impregnated with a solution containing the
fluorochemical additive, a method in which a coating liquid
containing the fluorochemical additive is applied on at least one
face of the paper substrate 2, and the like may be exemplified. In
the case in which a coating liquid containing the fluorochemical
additive is applied on the surface of the paper substrate 2, the
application may be executed either by on-machine coating with a
coater attached to a paper-making machine, or by off-machine
coating with a coater provided separately from the paper-making
machine.
[0038] Although the thickness of the paper substrate 2 is not
particularly limited, the thickness is preferably no less than 0.03
mm and no greater than 0.1 mm, and more preferably no less than
0.04 mm and no greater than 0.08 mm. When the thickness of the
paper substrate 2 is greater than the above upper limit, the
stiffness of the microwaveable sheet 1 increases, whereby the
microwaveable sheet 1 is less likely to be deformed so as to meet
the shape of the food to be wrapped, and thus direct wrapping of
the food may be difficult. On the other hand, when the thickness of
the paper substrate 2 is less than the above lower limit, the
strength of the microwaveable sheet is reduced, whereby the paper
substrate 2 may be likely to be broken.
[0039] The resin layer 3 is formed by applying a coating liquid of
a resin composition on one face of the paper substrate 2. As a
principal component of the resin composition, an acrylic resin, an
olefin-derived resin or a carbonyl group-containing resin may be
employed.
[0040] Examples of the acrylic resin include acryl polymers,
copolymers such as acryl-styrene copolymers, and the like.
Specifically, acrylic copolymers prepared by copolymerizing
styrene, a styrene derivative, acrylic acid (methacrylic acid), an
acrylic acid alkyl ester such as methyl acrylate, ethyl acrylate or
butyl acrylate, as well as a methacrylic acid alkyl ester such as
methyl methacrylate, and the like; ethylene-acrylic acid copolymer
water soluble salts such as an ethylene-acrylic acid copolymer
sodium salt and an ethylene-acrylic acid copolymer ammonium salt;
copolymers of acrylamide with acrylic acid (methacrylic acid);
copolymers of acrylonitrile with acrylic acid (methacrylic acid),
and the like may be exemplified.
[0041] Examples of the olefin-derived resin include low-density
polyethylene, high-density polyethylene, polypropylene,
ethylene-based copolymers, and the like.
[0042] Examples of the carbonyl group-containing resin include
styrene-acrylic acid ester copolymers, epoxy ester resins, urethane
resins, oil-modified phenol resins, and the like.
[0043] The styrene-acrylic acid ester copolymer is not particularly
limited, and may be produced by a well-known emulsion
polymerization method. In this regard, when an emulsion
polymerization method is employed, a surfactant is preferably used
in order to attain a certain hydrophilicity. Examples of the
surfactant include anionic surfactants such as fatty acid soap,
alkylsulfonic acid salts, alkylbenzenesulfonic acid salts,
alkylsulfosuccinic acid salts and polyoxyethylene alkylsulfuric
acid salts. The surfactant is preferably used in an amount of no
less than 1 part by weight and no greater than 10 parts by weight
with respect to 100 parts by weight of the monomer mixture.
[0044] As the epoxy ester resin, a variety of epoxy ester resins
may be adopted, which may be obtained by a reaction of an epoxy
resin with a compound that includes a carboxyl group to cause
esterification accompanied by opening of the oxirane ring.
[0045] The urethane resin is not particularly limited, and, for
example, a product of polymerization of polyisocyanate with polyol
may be employed. Examples of the polyol include polyether polyols,
polyester polyols, polylactone polyols, polycarbonate polyols, and
the like.
[0046] The isocyanate is not particularly limited, and examples
thereof which may be employed include: aliphatic diisocyanate
compounds such as hexamethylene diisocyanate and
2,2,4-trimethylhexamethylene diisocyanate; alicyclic diisocyanate
compounds such as isophorone diisocyanate, hydrogenerated xylylene
diisocyanate, 1,4-cyclohexane diisocyanate and
4,4'-dicyclohexylmethane diisocyanate; aromatic aliphatic
diisocyanate compounds such as xylylene diisocyanate and
tetramethylxylene diisocyanate; aromatic diisocyanate compounds
such as toluylene diisocyanate and phenylmethane diisocyanate;
modification products of the diisocyanates described above
(carbodiimide-, uretdione- or uretonimine-containing modification
products, etc.), and the like.
[0047] The polyether polyol is not particularly limited, and
examples thereof which may be employed include polyethylene glycol,
polypropylene glycol, polytetramethylene ether glycol,
polyhexamethylene ether glycol, and the like.
[0048] The polyester polyol is not particularly limited, and
examples thereof which may be employed include polyethylene
adipate, polybutylene adipate, polyneopentylene adipate,
poly-3-methylpentylene adipate, polyethylene/butylene adipate,
polyneopentylene/hexylene adipate, and the like.
[0049] The polylactone polyol is not particularly limited, and
examples thereof which may be employed include polycaprolactone
diol, poly-.omega.-hydroxycaproic acid polyol, and the like.
[0050] The polycarbonate polyol is not particularly limited, and
examples thereof which may be employed include products obtained by
a reaction of: a diol such as propanediol-(1,3), butanediol-(1,4),
hexanediol-(1,6), diethylene glycol, triethylene glycol or
tetraethylene glycol; phosgene; and a diaryl carbonate such as
diphenyl carbonate, or a cyclic carbonate such as ethylene
carbonate or propylene carbonate, and the like. In addition, the
polycarbonate polyol is exemplified by polyester carbonates
obtained by a reaction of: a polyester or polylactone; phosgene;
and a diaryl carbonate or a cyclic carbonate.
[0051] The oil-modified phenol resin is not particularly limited,
and examples thereof which may be employed include resins obtained
by allowing a phenol, an aldehyde and an oil to be reacted in the
presence of an acidic catalyst.
[0052] The oil for use in the modification is not particularly
limited, and examples thereof which may be employed include at
least one selected from plant oils, particularly, cashew nut oil,
linseed oil, wood oil, castor oil and tall oil. Of these, cashew
nut oil is preferred in light of the storage stability. Moreover,
as the oil-modified phenol resin, a cashew nut oil-modified
novolak-type phenol resin is preferably employed.
[0053] The resin layer 3 may contain a filler such that the resin
layer 3 has flat and smooth feature with respect to foods (i.e., an
effect of preventing the resin layer 3 from attaching to the
foods). The filler which may be contained in the resin layer 3 is
not particularly limited, and exemplified by inorganic fine
particles and organic fine particles. As the filler contained in
the resin layer 3, aluminum silicate is suitably used,
alternatively, silica, barium sulfate, titanium oxide and the like
may be also used. The filler may be used either alone of one type,
or two or more types may be used as a mixture.
[0054] The mean particle size of the filler is not particularly
limited, and is preferably no less than 50 nm and no greater than
500 nm. The upper limit of the mean particle size of the filler is
more preferably 350 nm, and still more preferably 300 nm. The lower
limit of the mean particle size of the filler is more preferably 60
nm, and still more preferably 80 nm. When the mean particle size of
the filler is greater than the above upper limit, the flat and
smooth feature of the resin layer 3 with respect to foods may not
be satisfactorily improved. To the contrary, when the mean particle
size of the filler is less than the above lower limit, the filler
is aggregated within the coating liquid, and thus the flat and
smooth feature of the resin layer 3 with respect to foods may not
be sufficiently exhibited.
[0055] The content of the filler in the resin layer 3 is not
particularly limited, and is preferably no less than 1 part by
weight and no greater than 20 parts by weight with respect to 100
parts by weight of the resin contained as a principal component of
the resin composition. The upper limit of the content of the filler
is more preferably 15 parts by weight, and still more preferably 10
parts by weight. Further, the lower limit of the content of the
filler is more preferably 3 parts by weight, and still more
preferably 5 parts by weight. When the content of the filler is
greater than the above upper limit, the flat and smooth feature of
the resin layer 3 with respect to foods may not be satisfactorily
improved. To the contrary, when the content of the filler is less
than the above lower limit, the condensity of the filler decreases,
and thus the flat and smooth feature of the resin layer 3 with
respect to foods may not be sufficiently exhibited.
[0056] The average thickness of the resin layer 3 is not
particularly limited, and is preferably no less than 0.01 mm and no
greater than 0.08 mm, and more preferably no less than 0.03 mm and
no greater than 0.05 mm. When the thickness of the resin layer 3 is
less than the above lower limit, the oil resistance of the
microwaveable sheet 1 may not be sufficiently ensured. Whereas,
when the thickness of the resin layer 3 is greater than the above
upper limit, the stiffness of the microwaveable sheet 1 increases,
whereby the microwaveable sheet 1 is less likely to be deformed so
as to meet the shape of the food to be wrapped, and thus direct
wrapping of the food may be difficult.
[0057] Additionally, the resin layer 3 has a plurality of air holes
3a formed. It is to be noted that the confirmation of the air holes
3a is not particularly limited, and a well-known method may be
adopted for the confirmation. Also, the air holes 3a may be
confirmed through applying a pigment on the resin layer 3.
[0058] The printing portion 4 is not particularly limited, and a
portion including a pigment fixed on the paper substrate 2 by a
binder may be employed. The pigment is not particularly limited,
and a black pigment, a white pigment, a red pigment, a blue
pigment, a yellow pigment, a green pigment, an orange pigment, a
purple pigment or the like may be appropriately used. Further, the
binder is not particularly limited, and one type, or a mixture, a
copolymer or the like of two or more types of a variety of
synthetic resins such as an acrylic resin, a styrene-based resin, a
polyester-based resin, a urethane-based resin, a polyvinyl-based
resin, an alkyd-based resin, a petroleum-based resin, a ketone
resin, an epoxy-based resin, a melamine-based resin, a
fluorine-containing resin, a silicone-based resin, a cellulose
derivative and a rubber-based resin may be employed.
[0059] The water vapor transmission rate of the microwaveable sheet
1 is not particularly limited, and is preferably no less than 200
g/m.sup.2/24 hrs and no greater than 15,000 g/m.sup.2/24 hrs. The
upper limit of the water vapor transmission rate of the
microwaveable sheet 1 is more preferably 13,000 g/m.sup.2, and
still more preferably 11,000 g/m.sup.2. Moreover, the lower limit
of the water vapor transmission rate of the microwaveable sheet 1
is more preferably 1,000 g/m.sup.2, and still more preferably 4,000
g/m.sup.2. When the water vapor transmission rate falls within the
above range, in heating the food wrapped by the microwaveable sheet
1, in the wrapped state, in a microwave oven or the like, the water
vapor generated from the food can be suitably released outside, and
thus deterioration of the texture is less likely to be accompanied
even if a heat treatment is carried out in a microwave oven or the
like.
[0060] The oil shieldability of the microwaveable sheet 1
therethrough (from one side to another) is not particularly
limited, and is preferably no less than 1 hour, more preferably no
less than 1.5 hours, and still more preferably no less than 2
hours. Accordingly, permeation of the oil can be effectively
prevented.
Production Method of Microwaveable Sheet 1
[0061] The production method of the microwaveable sheet 1 includes
a resin layer-forming step, and a printing step.
[0062] According to the resin layer-forming step, the resin layer 3
is formed on one face of the paper substrate 2. In the resin
layer-forming step, a coating liquid of a resin composition is
applied on one face of the paper substrate 2, and the applied
coating liquid is hardened with drying to form the resin layer
3.
[0063] The coating liquid is prepared by mixing the resin
composition and a solvent. For example, the coating liquid is
prepared by mixing the resin composition of a carbonyl
group-containing resin or the like, with a water-based solvent.
Although the water-based solvent is not particularly limited, it
may be, for example, water alone, or a mixture of an alcohol such
as ethanol or propanol with water, and the like.
[0064] The application method onto the paper substrate 2 may be
carried out with a roll having an intaglio on the surface thereof.
Thus, desired air holes 3a can be formed easily and certainly
on/through the resin layer 3. As a specific application method, a
gravure coating method by a gravure printer may be exemplified. As
shown in FIG. 2, the surface of a gravure roll 14 is has a
plurality of recessed cells 14a for the purpose of retaining a
large amount of a coating liquid 13 of the material for forming the
resin layer 3. Thus, by rotating the gravure roll 14 in a vessel 15
containing the coating liquid 13 so as to bring the gravure roll 14
into contact with the surface of the paper substrate 2, a large
amount of the coating liquid 13 is held onto sites corresponding to
the cell 14a portions on the gravure roll 14, whereas a small
amount of the coating liquid 13 is applied onto sites other than
those corresponding to the cell 14a portions. Accordingly, suitable
air holes 3a are likely to be formed at the sites other than those
corresponding to the cell 14a portions (i.e., sites where a small
amount of the coating liquid 13 was applied). It is to be noted
that before the gravure roll 14 is brought into contact with the
surface of the paper substrate 2, a desired amount of the coating
liquid 13 attached can be appropriately adjusted by dabbing a
doctor blade (not shown in the Figure) on the surface of the
gravure roll 14. Alternatively, a desired amount of the coating
liquid 13 attached can be also adjusted by regulating the speed of
rotation of the gravure roll 14.
[0065] The average depth of the recessed part of the cell 14a of
the gravure roll 14 is not particularly limited, and is preferably
no less than 10 .mu.m and no greater than 70 .mu.m and more
preferably no less than 30 .mu.m and no greater than 50 .mu.m. When
the average depth of the recessed part of the cell 14a is less than
the above lower limit, a large number of the air holes 3a of the
resin layer 3 may be formed, whereby the oil resistance of the
microwaveable sheet 1 is likely to be deteriorated. Whereas, when
the average depth is greater than the above upper limit, the
thickness of the resin layer 3 may be so great that the stiffness
of the microwaveable sheet 1 increases, whereby direct wrapping of
the food with the microwaveable sheet 1 may be difficult.
[0066] The application amount on the basis of the solid content is
preferably no less than 0.01 g/m.sup.2 and no greater than 20
g/m.sup.2, and more preferably no less than 3 g/m.sup.2 and no
greater than 8 g/m.sup.2. When the application amount falls within
the above range, the microwaveable sheet 1 can achieve further
superior moisture permeability while the oil resistance is
sufficiently maintained.
[0067] The hardening with drying of the coating liquid is not
particularly limited, and the coating liquid may be hardened with
drying using a drying apparatus (not shown in the Figure).
[0068] According to the printing step, characters, pattern designs
and the like for decoration are printed on one face of the paper
substrate 2. In the printing step, printing portions 4 are provided
on the face on the other side of the face of the paper substrate 2
on which the resin layer 3 was laminated in the resin layer-forming
step. In this step, a variety of well-known methods may be employed
as for the printing method. The printing method may be exemplified
by a gravure printing method, an offset lithography method, a
flexography method, a screen printing method, and the like.
Advantages
[0069] Since the microwaveable sheet 1 has the resin layer 3 on one
face of the paper substrate 2, when foods are wrapped such that the
resin layer 3 is brought to be the inner side (side facing to the
food), permeation of oil exuded from the foods to the external side
of the microwaveable sheet 1 can be certainly prevented by the
resin layer 3. In addition, since the resin layer 3 includes a
plurality of air holes 3a, water vapor is suitably released outside
through the air holes 3a. Thus, even if foods such as deep fried
foods and hamburgers are subjected to a heat treatment in a
microwave oven in the wrapped state, the water vapor is suitably
released outside from the air holes 3a while the permeation of oil
is prevented; therefore, deterioration of the texture is less
likely to be accompanied through inhibition of the attachment of
the water droplets onto the surface of the foods.
[0070] In addition, since the principal component of the resin
layer 3 is an acrylic resin, an olefin-derived resin, or a carbonyl
group-containing resin, the oil resistance of the microwaveable
sheet 1 can be improved.
[0071] Still further, according to the microwaveable sheet 1, the
air holes 3a that suitably release water vapor outside the
microwaveable sheet 1 can be easily and certainly formed by
applying the coating liquid 13 with a roll having an intaglio on
the surface thereof. Thus, the microwaveable sheet 1 can achieve
superior moisture permeability while the oil resistance is
maintained.
[0072] Additionally, since the microwaveable sheet 1 has the
printing portion 4 on another face of the paper substrate 2, for
example, when varying printing for each type of the food wrapped is
made, the type of the food can be distinguished through merely
viewing the external side of the microwaveable sheet 1.
Second Embodiment
[0073] Next, a microwaveable sheet 21 according to the second
embodiment of the present invention is explained. It is to be noted
that in the explanation of the second embodiment, regarding any
member, etc., having an identical constitution or identical
function to that in the first embodiment, detailed explanation
thereof may be omitted through referring to the identical reference
symbol.
[0074] The microwaveable sheet 21 according to the second
embodiment is, as shown in FIG. 3, has a paper substrate 22, a
resin layer 23 laminated on one face of the paper substrate 22, and
a printing portion 4 formed on another face of the paper substrate
22.
[0075] One face of the paper substrate 22 employed has a shape with
fine irregularity. The surface roughness resulting from the shape
with fine irregularity of the paper substrate 22 (average roughness
of the measurements at ten points) is not particularly limited, and
is preferably no less than 0.01 mm and no greater than 0.05 mm and
more preferably no less than 0.02 mm and no greater than 0.03 mm.
When the surface roughness of the paper substrate 22 does not fall
within the above range, the air holes 23a as desired may not be
properly formed on/through the resin layer 23 of the microwaveable
sheet 21.
[0076] It is to be noted that as the paper substrate 22, similar
ones to those for use in the first embodiment such as virgin white
roll papers, glassine papers, paraffin papers, kraft papers, simili
papers, thin papers, general quality papers, Japanese papers and
the like may be used, which may also have similar grammage and
thickness.
[0077] The resin layer 23 is formed on the face having a shape with
fine irregularity of the paper substrate 22. In addition, the resin
layer 23 has a plurality of air holes 23a formed thereon.
[0078] Furthermore, the average depth in the irregularity having
the air holes 23a of the resin layer 23 is preferably similar to
the average depth of the air holes 3a of the resin layer 3 in the
first embodiment.
[0079] As the material for forming the resin layer 23, similar
materials for use in forming the resin layer 3 employed in the
first embodiment may be used.
[0080] Next, a production method of the microwaveable sheet 21
according to the second embodiment of the present invention is
explained with references to FIG. 4.
[0081] The production method of the microwaveable sheet 21
includes, similarly to the first embodiment, a resin layer-forming
step and a printing step.
[0082] In the resin layer-forming step, a coating liquid 13 is
applied on one face of the paper substrate 22 to form the resin
layer 23.
[0083] The application method which may be employed includes a roll
coating method carried out using a roll having a smooth surface, as
well as a bar application method, and the like. Specifically, as
shown in FIG. 4, by rotating a solid roll 34 in the vessel 15
containing the coating liquid 13, the coating liquid 13 is held
onto the solid roll 34. Then, pressing the solid roll 34 against
the face having irregularity of the paper substrate 22 enables the
coating liquid 13 to be applied onto the paper substrate 22.
[0084] Also, when the solid roll 34 is pressed against the face
having irregularity of the paper substrate 22, the pressure is
adjusted in bringing the solid roll 34 into contact while the solid
roll 34 is pressed against the resin layer 23, such that a thin
resin layer is formed on the protruding parts of the face having
irregularity of the resin layer 23. Thus, the resin layer is formed
on the surface of the paper substrate 22 such that the resin layer
23 is formed to have a constant thickness with the smooth solid
roll; therefore, appropriate air holes 23a are likely to be formed
at the parts on which the thin resin layer 23 was formed (top parts
of the protruding parts of the paper substrate).
[0085] Furthermore, in the printing step, the printing portion 4 is
formed on one face of the paper substrate 22, similarly to the step
in the first embodiment.
[0086] In the microwaveable sheet 21 according to the second
embodiment, the resin layer 23 is formed on one face of the paper
substrate 22 having a shape with fine irregularity, and the air
holes 23a are likely to be appropriately formed at sites on which a
thin resin layer 23 was formed (top portions of the protruding
parts of the paper substrate 22 having a shape with fine
irregularity. Therefore, water vapor is suitably released outside
by way of the air holes 23a. Therefore, since the microwaveable
sheet 21 has superior moisture permeability while the oil
resistance is secured, even in the case of heating in a microwave
oven, the water vapor is suitably released outside by way of the
air holes 23a, and thus deterioration of the texture is less likely
to be accompanied.
Other Embodiment
[0087] The present invention may be appropriately altered without
departing from the scope intended by the present invention, without
any limitation to the foregoing embodiments.
[0088] In the above embodiments, the explanations have been made on
modes in which the resin layer is laminated on one face of the
paper substrate; however, in the present invention, the resin layer
may be laminated on both two faces of the paper substrate.
Accordingly, the water vapor transmission rate as well as the oil
resistance and the moisture permeability can be easily
controlled.
[0089] Also, the application method on the paper substrate is not
limited to the method aforementioned, but well-known methods such
as a knife coating method, a blade coating method, a die coating
method, a flexo coating method and a dipping method may be
employed. When these methods are employed, the resin layer having
desired air holes can be formed by, for example, adjusting the
application amount of the coating liquid of the material for
forming the resin layer.
[0090] Alternatively, the resin layer having desired air holes may
be formed by applying on the paper substrate, the coating liquid of
the material for forming the resin layer, in which the coating
liquid contains a filler. The filler which may be contained in the
coating liquid is not particularly limited, and inorganic fine
particles and organic fine particles may be exemplified. As the
filler which may be contained in the resin layer 3, aluminum
silicate is suitably used, or silica, barium sulfate, titanium
oxide, etc., can be also used. The filler may be used either one
type alone, or two or more types may be used as a mixture.
[0091] The mean particle size of the filler is not particularly
limited, and is preferably no less than 50 nm and no greater than
500 nm. The upper limit of the mean particle size of the filler is
more preferably 350 nm, and still more preferably 300 nm. The lower
limit of the mean particle size of the filler is more preferably 60
nm, and still more preferably 80 nm. When the mean particle size of
the filler does not fall within the above range, desired air holes
may not be suitably formed.
[0092] The content of the filler in the resin layer 3 is not
particularly limited, and the content is preferably no less than 1
part by weight and no greater than 20 parts by weight with respect
to 100 parts by weight of the resin as the principal component of
the resin layer 3. The upper limit of the content of the filler is
more preferably 15 parts by weight, and still more preferably 10
parts by weight. Whereas, the lower limit of the content of the
filler is more preferably 3 parts by weight, and still more
preferably 5 parts by weight. When the content of the filler does
not fall within the above range, the desired air holes may not be
suitably formed.
[0093] In the embodiments described above, the explanation has been
made on the resin layer having air holes formed thereon; however,
in the present invention, the resin layer may have valves of the
air holes described above.
[0094] The valves of the air holes are formed so as to cover the
air holes respectively, and are formed by adjusting the application
amount when the coating liquid of the resin layer is applied. For
example, when the resin layer is formed through applying the
coating liquid with a roll having an intaglio on the surface
thereof, the application amount is adjusted for the application
such that a small amount of the coating liquid is applied at sites
where cells of the gravure roll fail to abut, and that the air
holes are formed at the sites on which a small amount of the
coating liquid is applied and resin films that cover the air holes,
respectively, are formed. An appropriate application amount allows
the air holes to be formed on/through the resin layer, and the
coating liquid surrounding the air holes joins above the air holes
thus formed, whereby thin film valves are formed above the air
holes. Accordingly, the valves also enable the permeation of oil to
be prevented, whereas in regard to the release of the water vapor,
the thin film valves are pressed by the pressure from the water
vapor to generate gaps between the air holes and the valves,
respectively; therefore, the water vapor is suitably released
outside from the gaps.
[0095] It is to be noted that in order to form the valves of the
air holes, the resin layer may be laminated such that the valves of
the air holes are formed not only through adjusting the application
amount, but also through adjusting the speed of rotation of the
gravure roll, the components of the coating liquid, and the
temperature and time period in drying the coating liquid, and the
like.
[0096] Also, as the paper substrate, an oil-resistant paper may be
used. The oil-resistant paper which may be used is any of
well-known oil-resistant papers. Accordingly, the oil resistance of
the microwaveable sheet can be improved.
[0097] Moreover, the material for forming the resin layer is not
limited to those exemplified in the above embodiments, and any oil
resistant resin is acceptable.
[0098] Although providing a printing portion is described in the
above embodiments, the printing portion is not essential
constituent feature according to the present invention. Also, in
providing the printing portion, the modes are not limited to those
in the above embodiments, and for example, a microwaveable sheet in
which the printing portion is provided on one face of the paper
substrate and the resin layer is laminated on the printing portion
is also involved in the scope intended by the present
invention.
[0099] Still further, the method for producing the microwaveable
sheet in which the printing step is carried out after the resin
layer-forming step is explained in the above embodiments, but the
present invention is not limited thereto, and the printing step may
be carried out before the resin layer-forming step S1. In addition,
it would be possible to skip the printing step by providing a
previously printed paper substrate beforehand.
EXAMPLES
[0100] Next, two Examples of the microwaveable sheet are explained,
but the present invention is not limited thereto.
Example 1
[0101] As the paper substrate, an oil-resistant paper (trade name
"EC grease-proof paper 25": manufactured by Tenma Special Paper
Manufacturing Co., Ltd.) having a grammage of 25 g/m.sup.2 was
used. A coating agent (trade name "Harvill B-7": manufactured by
Daiichi Toryo MFG., Ltd.) was diluted in water to prepare a coating
liquid, and gravure coating of the coating liquid was carried out
on one face of the paper substrate to form a resin layer. Thus, a
microwaveable sheet of Example 1 was obtained having a plurality of
air holes on/through a resin layer.
Example 2
[0102] The coating liquid was similarly applied also on another
face of the microwaveable sheet in Example 1, and the coating
liquid was hardened with drying to obtain a microwaveable sheet of
Example 2.
Comparative Example
[0103] In Comparative Example, a thin Paper (trade name "HS21
paper": manufactured by Oji Paper Co., Ltd.) on which polyethylene
having a thickness of 8 .mu.m was laminated was used.
[0104] Oil Resistance
[0105] An oil shieldability test was performed on Example 1 and
Example 2, and Comparative Example. The shieldability test was
conducted through determining a time period required for passage of
3 g of salad oil through the resin layer after dropwise addition,
under a condition of a temperature of 40.degree. C.
[0106] In Example 1, the oil did not pass through even after lapse
of at least 3 hours. In Example 2, the oil did not pass through
even after lapse of at least 5 hours. On the other hand, in
Comparative Example, the passage of the oil occurred within 30
min.
[0107] Water Vapor Transmission Rate
[0108] Next, a water vapor transmission rate test was performed on
Example 1 and Example 2, and Comparative Example. The water vapor
transmission rate test was conducted in accordance with an upright
cup test (JIS Z0208).
[0109] In Example 1, the water vapor transmission rate was 12,400
g/m.sup.2/24 hrs. In Example 2, the water vapor transmission rate
was 8,500 g/m.sup.2/24 hrs. On the other hand, in Comparative
Example, the water vapor transmission rate was 96 g/m.sup.2/24
hrs.
[0110] Results
[0111] Example 1 and Example 2 revealed results indicating a high
water vapor transmission rate, accompanied by the oil resistance
falling within a suitable range as described above. It is to be
noted that in Comparative Example, the water vapor transmission
rate was low, and thus an attachment of water droplets onto the
inner face of the sheet was caused as a result of the heating in a
microwave oven.
INDUSTRIAL APPLICABILITY
[0112] As described in the foregoing, the microwaveable sheet of
the present invention, and the microwaveable sheet produced by the
method for producing the microwaveable sheet of the present
invention have oil resistance, and also have moisture permeability;
therefore, the microwaveable sheets can be suitably used as a sheet
for wrapping when foods are subjected to a heat treatment in a
microwave oven or the like.
EXPLANATION OF THE REFERENCE SYMBOLS
[0113] 1 microwaveable sheet [0114] 2 paper substrate [0115] 3
resin layer [0116] 3a air hole [0117] 4 printing portion [0118] 13
coating liquid [0119] 14 gravure roll [0120] 14a cell [0121] 15
vessel [0122] 21 microwaveable sheet [0123] 22 paper substrate
[0124] 23 resin layer [0125] 23a air hole [0126] 34 solid roll
* * * * *