U.S. patent application number 10/250308 was filed with the patent office on 2004-03-11 for molded pulp product, and method and apparatus for production thereof.
Invention is credited to Eto, Keiji, Ishikawa, Masataka, Kumamoto, Yoshiaki, Nonomura, Akira.
Application Number | 20040045690 10/250308 |
Document ID | / |
Family ID | 31986135 |
Filed Date | 2004-03-11 |
United States Patent
Application |
20040045690 |
Kind Code |
A1 |
Eto, Keiji ; et al. |
March 11, 2004 |
Molded pulp product, and method and apparatus for production
thereof
Abstract
A pulp molded article having a pulp fiber layer (2) of single
layer structure which is formed by papermaking from a single raw
material composition and has a density distribution in the
thickness direction thereof. The pulp fiber layer (2) has such a
density distribution that the density increases or decreases in the
thickness direction thereof.
Inventors: |
Eto, Keiji; (Tochigi,
JP) ; Kumamoto, Yoshiaki; (Tochigi, JP) ;
Ishikawa, Masataka; (Tochigi, JP) ; Nonomura,
Akira; (Tochigi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
31986135 |
Appl. No.: |
10/250308 |
Filed: |
June 30, 2003 |
PCT Filed: |
July 30, 2002 |
PCT NO: |
PCT/JP02/07757 |
Current U.S.
Class: |
162/225 ;
162/218; 162/224; 162/226; 162/231; 162/382; 162/383 |
Current CPC
Class: |
D21J 7/00 20130101; D21J
3/10 20130101 |
Class at
Publication: |
162/225 ;
162/231; 162/218; 162/226; 162/382; 162/383; 162/224 |
International
Class: |
D21J 003/00; D21J
003/12; D21J 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 3, 2001 |
JP |
2001-235858 |
Claims
1. A pulp molded article having a pulp fiber layer of single layer
structure which is formed by papermaking from a single raw material
composition and has a density distribution in the thickness
direction thereof.
2. The pulp molded article according to claim 1, wherein said pulp
fiber layer has a density distribution such that the density
increases or decreases in the thickness direction thereof.
3. The pulp molded article according to claim 1, wherein at least
one of the inner surface and the outer surface of said pulp fiber
layer is coated with a coating layer.
4. The pulp molded article according to claim 1, wherein the outer
surface of said pulp fiber layer is coated with another pulp fiber
layer.
5. The pulp molded article according to claim 4, wherein said
another pulp fiber layer has a density higher than the highest
density of said pulp fiber layer.
6. The pulp molded article according to claim 1, wherein said pulp
fiber layer and said coating layer are each made from a
biodegradable material.
7. The pulp molded article according to claim 1, wherein said pulp
fiber layer is the main body of a cup-shaped container and has a
flange around the brim of the main body.
8. The pulp molded article according to claim 7, wherein the body
portion of said main body is provided with said density
distribution.
9. The pulp molded article according to claim 7, wherein said
flange and the bottom portion of said main body has a higher
density than the body portion of said main body.
10. A method of producing a pulp molded article comprising a
papermaking and dewatering step in which a pulp fiber layer is made
from a single raw material composition by papermaking and dewatered
and a drying step in which the dewatered pulp fiber layer is fitted
into a drying mold and dried while creating a density distribution
in the thickness direction thereof, wherein: said drying mold has
evacuation holes connecting to the outside on the inner wall
thereof in the portion corresponding to the portion of said pulp
fiber layer where a density distribution is not to be created, said
pulp fiber layer fitted in said drying mold is pressed onto the
inner wall of said drying mold by an elastically deformable
pressing member, while the drying mold is forcibly evacuated
through said evacuation holes, the pressing force by said pressing
member is reduced and, the evacuation through said evacuation holes
is stopped to separate said pressing member from said pulp fiber
layer to obtain said pulp fiber layer provided with a density
distribution in the thickness direction thereof.
11. The method of producing a pulp molded article according to
claim 10, wherein the step of pressing said pulp fiber layer by
said pressing member and the step of reducing the pressing force of
said pressing member and stopping the evacuation are repeated to
dry said pulp fiber layer.
12. The method of producing a pulp molded article according to
claim 10, which further comprises a step of coating at least one of
the inner surface and the outer surface of said pulp fiber layer
with a coating layer.
13. An apparatus for carrying out the method of producing a pulp
molded article according to claim 10, which comprises a drying mold
into which a pulp fiber layer is fitted and an elastically
deformable pressing member which presses the pulp fiber layer
fitted into said drying mold from the inside of the pulp fiber
layer toward the inner wall of said drying mold, said drying mold
having evacuation holes connecting to the outside on the inner wall
thereof in the portion corresponding to the part of the pulp fiber
layer where a density distribution is not to be created.
Description
TECHNICAL FIELD
[0001] The present invention relates to a pulp molded article and a
method and an apparatus for producing the same. More particularly,
it relates to a thin-walled, lightweight, and yet highly
heat-insulating pulp molded article and a method and an apparatus
for producing the same.
BACKGROUND ART
[0002] Known techniques pertinent to pulp molded heat-insulating
containers include the technique disclosed in JP-A-11-301753. This
technique relates to a heat-insulating double container comprising
a main container and an outer container which is provided on the
outside of the main container with a prescribed gap
therebetween.
[0003] Such a heat-insulating container must have an outer
container provided on the outside of the main container to achieve
heat insulation. Accordingly, the container has an increased
thickness as a whole. Further, there is a limit in achieving weight
reduction of the container because of its double layer
structure.
[0004] The present invention provides a novel pulp molded article
which is thin, lightweight, and excellent in heat-insulating
performance and a method and an apparatus for producing the pulp
molded article efficiently.
DISCLOSURE OF THE INVENTION
[0005] The pulp molded article according to the present invention
has a pulp fiber layer having a single layer structure which is
formed by papermaking from a single raw material composition
(stock) and has a density distribution in its thickness
direction.
[0006] The present invention relates to a method of producing a
pulp molded article comprising a papermaking and dewatering step in
which a pulp fiber layer is made from a single stock by papermaking
and dewatered and a drying step in which the dewatered pulp fiber
layer is fitted into a drying mold and dried while creating a
density distribution in the thickness direction thereof. More
concretely, the drying mold has evacuation holes connecting to the
outside on the inner wall thereof in the portion corresponding to
the portion of the pulp fiber layer where a density distribution is
not to be created. The pulp fiber layer placed in the drying mold
is pressed from its inside onto the inner wall of the drying mold
by an elastically deformable pressing member, while the drying mold
is forcibly evacuated through the evacuation holes. Then the
pressing force by the pressing member is reduced and, at the same
time, the evacuation is stopped, whereby the pressing member is
separated from the pulp fiber layer to obtain the pulp fiber layer
provided with the density distribution.
[0007] The present invention also relates to an apparatus for
producing a pulp molded article of the present invention. More
concretely, it provides an apparatus for producing a pulp molded
article which comprises a drying mold in which a pulp fiber layer
is fitted and an elastically deformable pressing member which
presses the pulp fiber layer fitted into the drying mold from the
inside of the pulp fiber layer toward the inner wall of the drying
mold, the drying mold having evacuation holes connecting to the
outside on the inner wall thereof in the portion facing the part of
the pulp fiber layer where a density distribution is not to be
created.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a vertical half cross-section of a heat-insulating
container as an embodiment of the pulp molded article according to
the present invention.
[0009] FIG. 2 schematically illustrates an embodiment of the
apparatus for producing a pulp molded article according to the
present invention.
[0010] FIG. 3(a), FIG. 3(b), FIG. 3(c) and FIG. 3(d) schematically
illustrates the step of drying a pulp fiber layer which forms the
main body of the heat-insulating container, wherein FIG. 3(a) shows
a pulp fiber layer formed by papermaking and fitted into a drying
mold; FIG. 3(b) shows the pulp fiber layer being pressed in the
cavity of the drying mold by a pressing member; FIG. 3(c) shows the
pressing member being shrinking; and FIG. 3(d) shows the main body
of the container removed from the mold.
[0011] FIG. 4(a) and FIG. 4(b) schematically illustrate the step of
forming a coating layer of the heat-insulating container, in which
FIG. 4(a) shows a resin film which is being superposed on the inner
side of the main body of the container by vacuum forming; and FIG.
4(b) is an enlarged view of an essential part of the main body of
the container laminated with the resin film.
BEST MODE FOR CARRYING OUT THE INVENTION
[0012] The present invention will be described based on its
preferred embodiments by referring to the accompanying
drawings.
[0013] FIG. 1 shows an embodiment of the pulp molded article
according to the present invention, which is a heat-insulating
container used to hold a food such as an instant noodle. In FIG. 1,
numerical reference 1 indicates the heat-insulating container; 23,
a line indicative of the level to which hot water is to be poured;
and 24, a stacking shoulder.
[0014] As shown in FIG. 1, the heat-insulating container 1
comprises a cup-shaped main body 20 of the container (hereinafter
referred to as a container main body) formed of a pulp fiber layer
2. The container has a flange 21 of prescribed thickness formed
around its brim. The inner side of the container main body 20 (pulp
fiber layer 2) and the flange 21 are coated with the coating layer
3.
[0015] The pulp fiber layer 2 has a single layer structure formed
by papermaking from a single slurry (stock) described later. The
body 22 of the container main body 20 is provided with a density
distribution such that the density of the pulp fiber layer 2
increases from its inside toward the outside.
[0016] The language "the pulp fiber layer has a density
distribution" as used throughout the description means that the
size of the interstitial voids (void or void volume) between pulp
fibers bound in the pulp fiber layer has a distribution in the
thickness direction. The larger the voids, the smaller the density
of the pulp fiber layer. The smaller the voids, the larger the
density. Accordingly, if the interfiber voids are equal in size in
the thickness direction, the pulp fiber layer has no density
distribution.
[0017] It is preferred that the density change in the pulp fiber
layer 2 be continuous for obtaining high strength or be
discontinuous (stepwise) for securing high heat insulation.
[0018] From the standpoint of strength, heat insulation, and
lightness of the container, the thickness of the body 22 having the
density distribution is preferably 0.5 to 3.0 mm, more preferably
0.5 to 2.0 mm. Strength and heat-insulation required of a noodle
container are not secured with a body thickness smaller than 0.5
mm. Containers with a body thickness exceeding 3.0 mm would be too
heavy as a noodle container.
[0019] The bulk density (bulk density after drying) of the body 22
having the density distribution preferably ranges from 0.1 to 0.6
g/cm.sup.3, particularly 0.2 to 0.5 g/cm.sup.3. A bulk density less
than 0.1 g/cm.sup.3 results in a failure to secure strength
necessary for use as a noodle container. A bulk density more than
0.6 g/cm.sup.3 results in insufficient heat-insulating properties
so that a user can hardly hold the container by the hand. Where the
bottom portion is provided with a density distribution, the bulk
density of the bottom portion is preferably in the same range as
that of the body.
[0020] The bulk density (bulk density after drying) of the portions
other than the body 22 is preferably 0.2 to 0.9 g/cm.sup.3. The
density of a portion which needs strength, in particular, is
preferably 0.3 to 0.9 g/cm.sup.3.
[0021] The pulp fiber layer 2 is preferably made solely of pulp
fiber. The pulp fiber includes wood pulp, such as virgin pulp and
recycled pulp; nonwood pulp, such as cotton pulp, linter pulp,
bamboo and straw; and hydrophobilized pulp fiber obtained by
mercerizing or crosslinking these pulps. In particular, the
hydrophobilized pulp fiber preferably includes HBA-LA, HBA-S, and
HBA-FF, all available from Weyerhauser, U.S.A. Two or more of these
pulp fibers can be used as a mixture in an appropriate ratio.
[0022] The pulp fiber layer 2 preferably contains a bulking agent
in addition to the pulp fiber in order to improve heat insulating
properties and surface properties. Useful bulking agents include
anionic surface active agents, cationic surface active agents,
nonionic surface active agents, and amphoteric surface active
agents. These bulking agents can be used either individually or as
a mixture thereof. In particular, KB-115 or KB-08W available from
Kao Corp. is preferably used as a bulking agent bringing about
improved heat insulating properties.
[0023] The pulp fiber layer 2 can contain, in addition to the
bulking agent, other additives such as pigments, fixing agents,
antifungal agents, and sizes.
[0024] The coating layer 3 imparts such functions as
waterproofness, oil resistance, and gas barrier properties, to the
heat-insulating container 1. The thickness of the coating layer 3
is decided according to the desired function. The coating layer 3
is formed by laminating with a resin film.
[0025] The resin film which can be used as the coating layer 3
includes a film of thermoplastic resins, such as polyolefin resins,
e.g., polyethylene and polypropylene, polyester resins, e.g.,
polyethylene terephthalate, polyamide resins, e.g., nylon,
polyvinyl resins, e.g., polyvinyl chloride, and styrene resins,
e.g., polystyrene; and a film of biodegradable resins, such as
modified polyethylene terephthalate and aliphatic polyesters.
Polyolefin resins are preferred for the cost of production and
formability, and biodegradable resin films are preferred in view of
disposability from the consideration for the environment. The
coating layer may be formed by laminating with two or more of these
resin films.
[0026] A preferred apparatus for producing the pulp molded article
of the present invention will then be described with particular
reference to an apparatus for producing the container main body 20
of the heat-insulating container 1 by referring to FIG. 2.
[0027] FIG. 2 shows an embodiment of the apparatus for producing a
pulp molded article according to the present invention, applied to
the production of a heat-insulating container for holding a food,
such as an instant noodle. In FIG. 2, numerical reference 10
indicates the apparatus.
[0028] The apparatus 10 has a drying mold 11 in which a pulp fiber
layer 2 is fitted and an elastically deformable pressing member 16
which presses the pulp fiber layer 2 from the inside toward the
cavity-forming wall of the drying mold 11.
[0029] The drying mold 11 has a pair of splits 12 and 12. The
splits 12 and 12 are joined together to form a cavity 110
corresponding to the contour of the container main body 20.
[0030] Evacuation holes 13 connecting to the outside are made on
the inner wall of the drying mold 11 in the portion facing the part
of the pulp fiber layer 2 where a density distribution is not to be
created.
[0031] In this particular embodiment, the cavity-forming wall of
the drying mold 11 has no evacuation holes for steam escape in its
portion facing the body 22 of the container main body 20.
Evacuation holes 13 for steam escape are made on the cavity-forming
wall in the portions facing the flange 21 and the bottom portion
(including the base and the rising part of the wall).
[0032] Each evacuation hole preferably has a slit form from the
viewpoint of the surface smoothness of the resulting molded
article, evacuation efficiency, and prevention of clogging of the
evacuation holes. The width of each evacuation hole (slit width) is
preferably 0.1 to 0.5 mm, more preferably 0.1 to 0.3 mm. In the
present embodiment the total open area of the evacuation holes is
preferably 100 to 1500 mm.sup.2, more preferably 200 to 1000
mm.sup.2, for obtaining container strength and preventing stains.
Where it is desired to form a molded article with a clear corner or
edge, it is preferred to make the evacuation hole 13 open at the
part facing to the corner or edge to be formed.
[0033] The evacuation holes 13 are connected to an evacuation line
130 equipped with an on-off valve 131. The end of the evacuation
line 130 is connected to an evacuation source (not shown).
[0034] The drying mold 11 has a lid 15 which shuts the upper
opening 111. The lid 15 has an opening 14 which connects to the
opening 111 and through which a pressing member 16 is let in and
out. Each split 12 constituting the drying mold 11 has a heating
unit 120 attached thereto.
[0035] The pressing member 16 is a bag which is elastic and
therefore expandable and shrinkable. Materials of the pressing
member 16 include urethane, fluororubber, silicone rubber,
elastomers and etc., which are excellent in tensile strength,
impact resilience, and stretchability. The pressing member 16 is
connected to a pipe line 17 for feeding a pressurizing fluid into
the pressing member 16. The pipe line 17 has an on-off valve 18.
The end of the pipe line 17 is connected alternately to an
evacuation source (not shown) and a pressurizing source (not
shown).
[0036] A preferred method of producing the pulp molded article of
the present invention will be described with reference to the
production of the heat-insulating container 1.
[0037] The method of producing the heat-insulating container 1
includes the step of papermaking and dewatering the pulp fiber
layer 2 forming the container main body 20, the step of drying the
dewatered pulp fiber layer 2, and the step of forming the coating
layer 3.
[0038] In the step of papermaking and dewatering the pulp fiber
layer 2, the pulp fiber 2 having a single layer structure is formed
by papermaking from a single slurry (a single stock). In this
papermaking step, a papermaking mold composed of a pair of splits
is used, the splits being joined together to form a cavity of
prescribed shape corresponding to the container main body 2. The
cavity has an opening at the top.
[0039] Each split constituting the papermaking mold has a plurality
of interconnecting passageways which connect the cavity and the
outside. Each interconnecting passageway is led to a sucking unit,
such as a suction pump (not shown).
[0040] The total open area ratio of the interconnecting passageways
on the inner wall of the splits (the cavity-forming side) is
preferably 4 to 20%, more preferably 3 to 50%, in view of reduction
of drain time and moldability.
[0041] The cavity-forming wall preferably has drainage channels
leading to each interconnecting passageway. The total open area
ratio of the drainage channels on the cavity-forming wall is
preferably 50 to 90%, more preferably 60 to 80%, from the
standpoint of prevention of deformation of a papermaking screen,
molding capabilities, drainage, and prevention of clogging of the
papermaking screen. The width of the drainage channel is preferably
1 to 10 mm, more preferably 2 to 5 mm, from the standpoint of
prevention of deformation of a papermaking screen, molding
capabilities, drainage, and prevention of clogging of the
papermaking screen. The drainage channels are preferably formed in
a checkered pattern so as to connect the interconnecting
passageways to each other.
[0042] The inner wall of each split is covered with a prescribed
papermaking screen. The papermaking screen includes a single net
fabricated of natural fiber, synthetic fiber or metal fiber or a
combination of a plurality of these nets. Synthetic fiber is
preferred of these materials for ease of fabricating into a net and
durability. The natural fiber includes vegetable fiber and animal
fiber. The synthetic fiber includes synthetic resin fibers made of
thermoplastic resins, thermosetting resins or semi-synthetic
resins. The metal fiber includes stainless steel fiber and copper
fiber. The fibers of the papermaking screen are preferably
surface-modified to improve slip and durability.
[0043] Taking into consideration papermaking properties,
durability, easy pass of solid matter of the slurry, and prevention
of clogging, the wire diameter of the papermaking screen is
preferably 0.05 to 1.0 mm, more preferably 0.05 to 0.5 mm, and the
distance between wires is preferably 0.15 to 2.0 mm, more
preferably 0.15 to 1.5 mm.
[0044] A predetermined amount of the slurry is injected into the
cavity, and the cavity is sucked by means of a suction pump through
the drainage channels and the interconnecting passageways. Thus,
the water content of the slurry is removed by suction, and a pulp
fiber layer is deposited on the papermaking screen covering the
cavity-forming wall.
[0045] The injection pressure of the slurry into the cavity is
preferably 0.05 to 1.0 MPa, more preferably 0.05 to 0.5 MPa, for
shortening the slurry injection time and securing moldability.
[0046] The inner pressure of the cavity evacuated through the
interconnecting passageways is preferably 10 to 90 kPa, more
preferably 20 to 70 kPa, for shortening the dewatering time and
securing moldability.
[0047] The single slurry used to form the pulp fiber layer 2 by
papermaking preferably consists of pulp fiber and water.
[0048] The pulp fiber includes wood pulp, such as virgin pulp and
recycled pulp; nonwood pulp, such as cotton pulp, linter pulp,
bamboo and straw; and hydrophobilized pulp fiber obtained by
mercerizing or crosslinking these pulps. The hydrophobilized pulp
fiber is particularly preferred. Examples of preferred
hydrophobilized pulp fiber are HBA-LA, HBA-S, and HBA-FF, all
available from Weyerhauser, U.S.A. Two or more of these pulp fibers
can be used as a mixture in an appropriate ratio.
[0049] The pulp fiber content in the slurry is preferably 0.05 to
10 wt %, more preferably 0.05 to 4 wt %.
[0050] Additives, such as the above-recited bulking agents, sizes,
pigments, fixing agents, and antifungal agents, can be added to the
single slurry used to form the pulp fiber layer 2 by papermaking in
appropriate ratios.
[0051] After a predetermined amount of the slurry has been injected
into the cavity, a pressurizing fluid is fed into the cavity while
continuing evacuating the cavity through the interconnecting
passageways, whereby the pulp fiber layer 2 is dewatered.
[0052] The pressurizing fluid used for dewatering includes air,
steam, and superheated steam.
[0053] The pressure of the pressurizing fluid for dewatering is
preferably 0.05 to 1.0 MPa, more preferably 0.05 to 0.5 MPa, from
the standpoint of dewatering efficiency.
[0054] The water content of the pulp fiber layer 2 after dewatering
is preferably 50 to 85%, more preferably 60 to 80%, from the
viewpoint of drying efficiency, surface smoothness and heat
insulating properties of the container after drying, and for
preventing the container from suffering surface scorching on
drying.
[0055] After the pulp fiber layer 2 is dewatered to a desired water
content, the pulp fiber layer 2 is separated from the
cavity-forming wall, and the undried pulp fiber layer 2 is
transferred into the drying mold 11.
[0056] In making the container main body 20 with the flange 21 as
in the present embodiment, the cavity-forming wall of the drying
mold 11 has no evacuation holes for steam escape in its portion
facing the body 22 of the container main body 20, while evacuation
holes 13 for steam escape, which are led to the outside, are
provided on the cavity-forming wall in the portions facing the
flange 21 and the bottom portion (including the base and the rising
part of the wall). As shown in FIG. 3(b), the pulp fiber layer 2 is
set in the drying mold 11, and the upper opening 111 of the drying
mold 11 is shut by the lid 15 having the insertion opening 14. The
drying mold 11 is then heated to a prescribed temperature by the
heating unit 120.
[0057] The temperature of the drying mold 11 (mold temperature) is
preferably 150 to 300.degree. C., more preferably 170 to
250.degree. C., for preventing the pulp fiber layer 2 from
scorching and for improving drying efficiency.
[0058] While the pulp fiber layer is dried in the drying mold as
shown in FIG. 3(b), the pressing member 16 is inserted into the
cavity 110 of the drying mold 11 through the insertion opening 14
of the lid 15 to close the cavity 110. A pressurizing fluid is
supplied into the pressing member 16 to inflate the pressing member
16 within the cavity 110, whereby the pulp fiber layer 2 is heat
dried while being pressed to the cavity-forming wall.
[0059] The pressing force of the pressing member 16 during heat
drying is preferably 0.05 to 1.0 MPa, more preferably 0.1 to 0.3
MPa, from the standpoint of heat insulating properties, drying
efficiency, and surface smoothness.
[0060] Steam generated from the pulp fiber layer 2 during the heat
drying is expelled by forcible evacuation through the evacuation
holes 13. In the portions of the pulp fiber layer 2 facing the
cavity-forming wall with no evacuation holes, water remaining among
fibers partially vaporizes before reaching the evacuation holes and
expands the interfiber voids. It follows that the density of the
pulp fiber layer in the inner side of these portions is lowered. On
the other hand, in the opening portion and the bottom portion of
the container main body 20, where the evacuation holes 13 are
formed, since the vaporized water is allowed to immediately escape
through the evacuation holes, the pulp layer 2 increases its
density while being compressed by the pressing force of the
pressing member.
[0061] The pressure for the forcible evacuation is preferably 4 to
60 kPa, more preferably 4 to 10 kPa, for securing drying efficiency
and making the container bulky.
[0062] On sufficiently drying the pulp fiber layer 2, the
pressurizing fluid is withdrawn from the pressing member 16. And
the forcible evacuation through the evacuation holes 13 is stopped
while the pressing member 16 shrinks to reduce the inner pressure
of the cavity 110 as shown in FIG. 3(c).
[0063] The step of pressing the pulp fiber layer 2 by the pressing
member 16 with forcible evacuation and the step of stopping the
forcible evacuation and shrinking the pressing member 16 can be
conducted repeatedly if needed.
[0064] After a sufficient density distribution is created in the
body 22 of the container main body 20, the splits 12 and 12 are
separated apart to take out the container main body 20 as shown in
FIG. 3(d). If necessary, the container main body is finished by
trimming and the like.
[0065] In the step of forming the coating layer 3, the inner
surface and the flange 21 of the container main body 20 (i.e., the
pulp fiber layer 2) is coated with the coating layer 3.
[0066] The above-described resin film can be formed into the
coating layer 3 by known techniques, such as pressure forming and
vacuum forming.
[0067] Where vacuum forming is adopted, the coating layer can be
formed by use of a vacuum forming mold 5 and a plug 6 having a
heater 60 as shown in FIGS. 4(a) and (b). The vacuum forming mold 5
is substantially the same size as the drying mold 10 used in the
pulp fiber layer 2 drying step. It has air flow channels 51
arranged in a checkered pattern on the cavity-forming wall 50 and
an evacuation path 52 connecting the air flow channels and the
outside. The container main body 20 is fitted into the vacuum
forming mold 5, and a preheated and softened resin film 30 is set
on the opening of the container main body 20 to cover the opening.
A plug 6 is brought down to press the resin film 30 into the
container main body 20. At the same time, the container main body
20, being air permeable, is evacuated through the air flow channels
51 and the evacuation path 52 to thereby bring the resin film 30
into intimate contact with the inner surface and the flange 21 of
the container main body 20. The unnecessary part of the resin film
30 is cut off to complete the production of the heat-insulating
container 1.
[0068] Since the container main body 20 is formed of a
single-layered pulp fiber layer 2 having, in its body 22,
distribution of density increasing from the inner side toward the
outer side in the thickness direction, it is thin, lightweight, and
excellent in heat insulating properties and exhibits desired
strength on its outer side. The heat-insulating container, which
contains no blowing agent for lowering the density, can be made
environmentally friendly by using a biodegradable material to form
the pulp fiber layer and the coating layer. Further, because the
flange 21, the body 22, and the bottom are integrally molded with
no joint seams in the body 22 and the bottom, the container is
excellent in mechanical strength (compressive strength and
durability). Additionally, the outer surface of the pulp fiber
layer 2 has a high density and smoothness and is therefore
excellent in printability.
[0069] Since the container main body 20 is made of the pulp fiber
layer 2 formed by a single papermaking operation using a single
slurry, the production of the heat-insulating container 1 enjoys
simplification and time reduction compared with conventional
methods. Accordingly, the production efficiency of the
heat-insulating container 1 is greatly improved over the
conventional methods.
[0070] The present invention is not limited to the heat-insulating
container 1 according to the above-described embodiment, and
appropriate changes and modifications can be made therein without
departing from the spirit thereof.
[0071] In cases where the pulp molded article of the present
invention is the heat-insulating container 1 as in the
above-described embodiment, while it is preferred that the density
distribution in the pulp fiber layer be provided in the body of the
container main body, the portion where the density distribution is
to be provided can be decided according to the use, the shape, etc.
of the pulp molded article.
[0072] Where the pulp molded article is a container which requires
heat insulation as a whole, such as a bowl or a tray, the pulp
fiber layer can be designed to have the density distribution over
the entire pulp fiber layer.
[0073] The density distribution of a single-layered pulp fiber
layer of the pulp molded article of the present invention is
preferably such that the density increases in the thickness
direction from the inner side to the outer side as in the
heat-insulating container 1 of the above-described embodiment. In
contrast, containers which are primarily intended to protect the
contents, industrial parts having a sound absorbing function, and
like articles may have a single-layered pulp fiber layer with such
a density distribution that the density decreases in the thickness
direction from the inner side toward the outer side.
[0074] It is preferred that the flange 21 of the pulp molded
article of the invention be formed while the pulp fiber layer 2 is
being deposited by papermaking as in the aforementioned embodiment,
while the flange may be formed by bending the pulp fiber layer. The
shape of the flange is not limited to the outward curl at a
prescribed curvature, and other shapes can be formed.
[0075] While the coating layer 3 of the pulp molded article of the
invention is preferably formed of a resin film as in the
aforementioned embodiment, it may be formed by applying a coating
composition. Coating methods include spreading a coating
composition and dipping the container main body 2 in a coating
composition, and like techniques.
[0076] The outer surface of the pulp molded article of the present
invention may be coated with another pulp fiber layer having a
higher density than the fiber layer 2 thereby to improve
printability, strength, water resistance, and like properties.
[0077] The pulp fiber layer of the pulp molded article of the
present invention is preferably formed by papermaking by use of a
papermaking mold composed of a set of splits which are joined to
form a cavity of prescribed shape as in the above-mentioned
embodiment, but use of such a split mold is not always necessary
for producing some shapes of pulp molded articles. Further, other
papermaking methods are employable. For example, papermaking can be
carried out by using a male mold. The male mold comprises a
projected papermaking part corresponding to the contour of a
container main body and having a large number of liquid flow holes
open to the outer surface thereof and a prescribed papermaking
screen covering the papermaking part. The male mold is immersed in
the slurry, and the slurry is sucked up through the liquid flow
holes to deposit the pulp fiber on the surface of the papermaking
screen to form the pulp fiber layer. The male mold may be made of a
rigid material or an elastic material.
[0078] In producing the pulp molded article of the present
invention, while it is preferred to use a hollow pressing member to
heat dry the pulp fiber layer 2 because of the capability of
applying uniform pressure to the pulp fiber layer 2 however
complicated the pulp fiber layer may be shaped, it is possible to
use a solid pressing member to heat dry the pulp fiber layer 2.
[0079] The pulp molded article of the present invention can also be
produced by placing the pulp fiber layer formed by papermaking into
a female mold configured to the contour of the pulp fiber layer and
fitting a heated male mold having a given clearance with the female
mold into the female mold to effect drying the pulp fiber
layer.
[0080] The pulp molded article of the present invention can also be
produced by setting a dried high-density pulp molded article
(another pulp fiber layer) in a female mold, uniting a wet pulp
fiber layer formed by papermaking with the another pulp fiber
layer, fitting a heated male mold having a given clearance with the
female mold into the female mold to dry the united two pulp fiber
layers. According to this drying method, the wet pulp fiber layer
is dried while being expanded by steam generated from the wet pulp
fiber layer. As a result, there is obtained a pulp molded article
having its outer side covered with a high-density pulp fiber layer
and having its density increased from the outer side toward the
inner side. The resulting pulp molded article is very excellent in
printability, strength, and water resistance and also excellent in
inner surface properties. The "another pulp fiber layer" as
referred to above is formed by an ordinary papermaking method using
the fiber employable to form the pulp fiber layer 2.
[0081] While the pulp molded article of the present invention is
especially suitable as a flanged heat-insulating container as in
the above-described embodiment, the application of the present
invention is not limited thereto. For example, the present
invention is applicable to containers of various shapes, such as
bowls, bottles, and trays; hollow articles, such as cylindrical
shapes; and plate-shaped articles.
[0082] The present invention will now be illustrated in greater
detail with reference to Examples.
[0083] Heat-insulating containers were made according to Example 1
and Comparative Example 1 and evaluated for performance. The
results of evaluation are shown in Table 1.
EXAMPLE 1
[0084] Geometry of container main body:
[0085] Height H: 106 mm
[0086] Inner diameter of opening (.phi.1): 90 mm
[0087] Outer diameter of bottom (.phi.2): 68.5 mm
[0088] Maximum outer diameter of flange (.phi.3): 96 mm
[0089] Flange thickness T: 3 mm
[0090] Body thickness T22: 1.4 mm
[0091] Bottom thickness T25: 1.2 mm
[0092] A pulp fiber layer was formed by papermaking under the
following conditions using a papermaking mold having the following
specification. The papermaking mold was composed of a pair of
splits which were joined to form a cavity corresponding to the
container main body having the above-described geometry.
[0093] Papermaking mold:
[0094] Material: aluminum
[0095] Total open area of interconnecting passageways: 1287
mm.sup.2 (54 holes.times..phi.3 (=382 mm.sup.2) in the portions
corresponding to the body and the bottom and 3 mm wide slits (905
mm.sup.2) in the portion corresponding to the whole peripheral
surface of the flange)
[0096] Total open area of drainage channels (in checkered pattern):
25071 mm.sup.2
[0097] Drainage channel width: 3 mm
[0098] Total open area ratio of drainage channels on cavity-forming
wall: 75%
[0099] Papermaking screen: double screen composed of a 20 mesh PET
net and a 80 mesh PET net
[0100] Slurry composition:
[0101] Pulp slurry concentration: 0.1 wt %
[0102] Pulp fiber: crosslinked pulp (50 wt % HBA-LF supplied by
Weyerhauser, U.S.A.+50 wt % bleached kraft pulp (BKP))
[0103] Bulking agent: KB115 available from Kao Corp. (5% based on
the pulp fiber weight)
[0104] Size: AS262 available from Japan PMC Corp. (2% based on the
pulp fiber weight)
[0105] Papermaking conditions:
[0106] Slurry feed: 15 liters (once)
[0107] Slurry feed pressure: 0.2 MPa
[0108] Cavity suction pressure: 0.06 MPa
[0109] A pressurizing fluid was fed into the cavity under the
following conditions to dewater the pulp fiber layer to a water
content of 75%.
[0110] Dewatering conditions:
[0111] Pressurizing fluid: compressed air
[0112] Pressing force: 0.2 MPa.times.15 seconds
[0113] Cavity suction pressure: 0.06 MPa
[0114] A drying mold having evacuation holes specified below was
prepared. The evacuation holes were provided in the portions
corresponding to the periphery of the flange and the bottom
(including the base and the rising part of the wall) of the
container main body to be produced. The pulp fiber layer was fitted
into the drying mold and pressed by a pressing member having the
following specification simultaneously with forcible evacuation
through the evacuation holes. The forcible evacuation was stopped,
and the pressing member was shrunken to produce the container main
body.
[0115] Drying mold:
[0116] Material: aluminum
[0117] Slit width of each evacuation hole: 0.15 mm
[0118] Portion corresponding to flange: 4 slits arranged in the
vertical direction at a 3 mm pitch around the peripheral surface of
the flange, one of which was open to the part corresponding to the
edge between the peripheral surface and the lower side of the
flange.
[0119] Portion corresponding to bottom: 4 slits at a 5 mm pitch on
the base (per split); 5 slits arranged in the vertical direction at
a 3 mm pitch over the whole peripheral surface of the part rising
from the base.
[0120] Total open area of evacuation holes on cavity-forming wall:
396 mm.sup.2
[0121] Total open area ratio of evacuation holes on cavity-forming
wall: 1.2%
[0122] Pressing member:
[0123] Material: silicone rubber
[0124] Pressurizing fluid: compressed air
[0125] Drying conditions:
[0126] Mold temperature: 200.degree. C.
[0127] Pressing force of pressing member: 0.2 MPa.times.15
seconds
[0128] Forcible evacuation pressure: 5 kPa
[0129] Formation of coating layer:
[0130] A coating layer was formed on the resulting container main
body under the following conditions to produce a heat-insulating
container.
[0131] Resin film: polyethylene (LDPE/HDPE double layer
structure)
[0132] Resin film thickness: 150 .mu.m
[0133] Vacuum forming apparatus: PLAVAC-FE36PHS supplied by
Sanwa-Kogyo Co., Ltd.
[0134] Film heating system: infrared heater (heater-to-resin film
distance: 110 mm)
[0135] Film heating temperature: 255.degree. C. (temperature
displayed on forming machine)
[0136] Film heating time: 35 seconds
[0137] Plug dimension: 60 mm in diameter.times.127 mm in length
[0138] Plug material: aluminum, surface-coated with Teflon
(registered trade name)
[0139] Plug temperature: 110.degree. C. (measured surface
temperature)
[0140] Vacuum forming mold: opening diameter .phi., 89.8 mm; bottom
diameter .phi., 68.5 mm; height, 93.5 mm
[0141] Vacuum forming mold temperature: 100.degree. C. (measured
temperature of the inner surface)
[0142] Forming time: 8 seconds
COMPARATIVE EXAMPLE 1
[0143] A heat-insulating container was produced in the same manner
as in Example 1, except for using a drying mold additionally having
evacuation holes on the portion corresponding to the body of the
container main body (0.15 mm wide slits over the whole
circumference arranged in the vertical direction at a 10 mm
interval).
[0144] 1) Evaluation on Density
[0145] Pieces cut out of different portions of the resulting
container main body were measured for apparent volume and weight,
from which a bulk density was calculated.
[0146] 2) Evaluation on Density Distribution
[0147] Different portions of the resulting container were observed
under a field emission scanning electron microscope (Model S-4000,
supplied by Hitachi, Ltd.) at a magnification of 50 times to
examine density distribution.
[0148] 3) Evaluation on Weight
[0149] The resulting container was dried at 100.degree. C. for 1
hour in a low-humidity chamber and then weighed.
[0150] 4) Evaluation on Heat Insulating Properties
[0151] A thermocouple was attached to the outer side of the body of
the resulting container. Hot water at 80.degree. C. was poured into
the container. After 3 minutes from the pouring, the temperature of
the outer side of the body was measured, and whether the container
containing the hot water could be held by the hand (graspability)
was examined.
[0152] Temperature measurement with thermocouple:
[0153] .smallcircle. . . . Lower than 60.degree. C.
[0154] .DELTA. . . . 60 to 65.degree. C.
[0155] X . . . . Higher than 65.degree. C.
[0156] Graspability test:
[0157] .smallcircle. . . . The container felt warm.
[0158] .DELTA. . . . The container felt slightly hot and yet was
graspable.
[0159] X . . . The container felt hot and was not graspable.
[0160] 5) Evaluation on Strength
[0161] The resulting container was measured for vertical
compressive strength and transverse compressive strength with a
compression tester (Tensilon RTA-500, supplied by Orientec) in
accordance with the following methods.
[0162] 5-1) Vertical Compressive Strength
[0163] The resulting container was placed upside down on a stage.
An indenter was pressed down from the bottom of the container at a
crosshead speed of 20 mm/min to obtain the compressive strength of
the container body.
[0164] .smallcircle. . . . 25 kgf or higher (the strength required
in packaging, transportation, and use)
[0165] X . . . Lower than 25 kgf
[0166] 5-2) Transverse Compressive Strength
[0167] The resulting container was placed on its side on a stage
having a groove, into which the flange was fitted. A rounded rod
indenter having a diameter of 10 mm was pressed down from the
container body at a crosshead speed of 20 mm/min to obtain the
compressive strength of the body. The measured strength was rated
as follows in comparison with the value of a commercially available
foamed polystyrene container.
[0168] .smallcircle. . . . Equal to or higher than the strength of
a foamed polystyrene container (the strength necessary for
withstanding packaging, transportation, and use).
[0169] X . . . Lower than the strength of a foamed polystyrene
container.
1 TABLE 1 Example 1 Compara. Example 1 Layer structure*.sup.1
double layer double layer Density distribution*.sup.2 yes no Each
layer thickness*.sup.3 (mm) 1.4/0.03 0.6/0.03 Bulk density*.sup.4
(g/cm.sup.3) 0.4/0.25/0.35 -- Heat insulating properties
.largecircle. X Strength .largecircle. .largecircle. Absolute dry
weight*.sup.5 (g) 13 13 *.sup.1Container main body + coating layer
*.sup.2Density distribution in the container main body (body)
*.sup.3Container main body (body)/coating layer
*.sup.4Flange/body/bottom *.sup.5Dried at 105.degree. C. for 1
hour
[0170] As is shown in Table 1, the heat-insulating container of
Example 1 was confirmed to be thinner, lighter, and more
heat-insulating than that of Comparative Example 1 and sufficiently
usable as a container for instant noodles.
INDUSTRIAL APPLICABILITY
[0171] The present invention provides a novel pulp molded article
which is thin, lightweight, and excellent in heat-insulating
performance and a method and an apparatus for producing the pulp
molded article efficiently.
* * * * *