U.S. patent application number 10/505157 was filed with the patent office on 2005-09-15 for biodegradable molding.
Invention is credited to Hashimoto, Akihisa, Ozasa, Akio, Tanaka, Shinji.
Application Number | 20050202229 10/505157 |
Document ID | / |
Family ID | 27750568 |
Filed Date | 2005-09-15 |
United States Patent
Application |
20050202229 |
Kind Code |
A1 |
Ozasa, Akio ; et
al. |
September 15, 2005 |
Biodegradable molding
Abstract
A bowl-shaped container (10a) which is as a biodegradable molded
article adheres a coating film (12) mainly made of biodegradable
plastic and having at least hydrophobicity to the surface of the
main body (11a) of the container mainly made of starch. The main
body (11a) is molded through steam expansion of a slurry or dough
molding material containing high-amylose starch and water, or a
slurry or dough molding material containing starch, polyvinyl
alcohol and water. For these reasons, it is possible to accomplish
sufficient strength and at least sufficient water resistance, to
exert a very excellent biodegradability and further to provide a
biodegradable molded article having excellent moisture absorption
strength mainly made of starch even if the biodegradable molded
article has a complicated shape.
Inventors: |
Ozasa, Akio; (Kaisha,
JP) ; Hashimoto, Akihisa; (Shiga, JP) ;
Tanaka, Shinji; (Shiga, JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 8910
RESTON
VA
20195
US
|
Family ID: |
27750568 |
Appl. No.: |
10/505157 |
Filed: |
April 28, 2005 |
PCT Filed: |
February 20, 2003 |
PCT NO: |
PCT/JP03/01858 |
Current U.S.
Class: |
428/304.4 ;
428/318.4; 428/318.8 |
Current CPC
Class: |
B29K 2995/006 20130101;
B65D 65/466 20130101; B29L 2031/712 20130101; B29K 2003/00
20130101; Y10T 428/249987 20150401; B29C 2043/3615 20130101; Y02W
90/10 20150501; B29C 43/361 20130101; B29L 2031/7132 20130101; B29C
44/12 20130101; Y02W 90/13 20150501; B29C 44/14 20130101; Y10T
428/249953 20150401; B29K 2105/04 20130101; Y02W 90/11 20150501;
B29C 43/003 20130101; B29C 44/3426 20130101; Y10T 428/249989
20150401; B29K 2029/04 20130101; B29C 43/206 20130101; B29C 43/184
20130101 |
Class at
Publication: |
428/304.4 ;
428/318.8; 428/318.4 |
International
Class: |
B32B 009/00; B32B
003/26; B32B 005/20 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2002 |
JP |
2002-45059 |
Claims
1. A biodegradable molded article comprising: a biodegradable
expanded molded article molded in a specified shape; and a coating
film attached to a surface of the biodegradable expanded molded
article, the film being mainly made of a biodegradable plastic and
having at least hydrophobicity, the biodegradable expanded molded
article being molded, through steam expansion, from a slurry or
dough molding material mainly made of a starch and a derivative
thereof and prepared by adding water to the starch or the
derivative thereof, the starch and the derivative thereof
containing high-amylose starch or a derivative thereof.
2. The biodegradable molded article as set forth in claim 1,
wherein the starch and a derivative thereof contains not less than
50 weight % high-amylose starch or a derivative thereof.
3. A biodegradable molded article comprising: a biodegradable
expanded molded article molded in a specified shape; and a coating
film attached to a surface of the biodegradable expanded molded
article, the film being mainly made of a biodegradable plastic and
having at least hydrophobicity, said biodegradable expanded molded
article being molded, through steam expansion, from a slurry or
dough molding material mainly made of a starch and a derivative
thereof and prepared by adding water and polyvinyl alcohol to the
starch or the derivative thereof.
4. The biodegradable molded article as set forth in claim 3,
wherein the polyvinyl alcohol has a polymerization degree of not
less than 1500.
5. The biodegradable molded article as set forth in claim 3,
wherein the polyvinyl alcohol has a saponification degree of not
less than 75%.
6. The biodegradable molded article as set forth in claim 1,
wherein the coating film is mainly made of a modified
polyester.
7. The biodegradable molded article as set forth in claim 1,
wherein the coating film is biaxially stretched.
8. The biodegradable molded article as set forth in claim 1,
wherein the molding material further contains a water-insoluble
fiber.
9. The biodegradable molded article as set forth in claim 1,
wherein the expanded molded article accounts for not less than 60
weight % of total weight of the biodegradable molded article.
10. The biodegradable molded article as set forth in claim 1,
wherein the molding material contains water which accounts for 20
weight % to 70 weight %, assuming that the biodegradable molded
article is 100 weight %.
11. The biodegradable molded article as set forth in claim 1,
wherein the coating film is directly and substantially adhered to
the surface.
12. The biodegradable molded article as set forth in claim 1,
wherein the biodegradable expanded molded article has a final water
content between 3 weight % and 20 weight %.
13. The biodegradable molded article as set forth in claim 4,
wherein the polyvinyl alcohol has a saponification degree of not
less than 75%.
14. The biodegradable molded article as set forth in claim 3,
wherein the coating film is mainly made of a modified
polyester.
15. The biodegradable molded article as set forth in claim 3,
wherein the coating film is biaxially stretched.
16. The biodegradable molded article as set forth in claim 3,
wherein the molding material further contains a water-insoluble
fiber.
17. The biodegradable molded article as set forth in claim 3,
wherein the expanded molded article accounts for not less than 60
weight % of total weight of the biodegradable molded article.
18. The biodegradable molded article as set forth in claim 3,
wherein the molding material contains water which accounts for 20
weight % to 70 weight %, assuming that the biodegradable molded
article is 100 weight %.
19. The biodegradable molded article as set forth in claim 3,
wherein the coating film is directly and substantially adhered to
the surface.
20. The biodegradable molded article as set forth in claim 3,
wherein the biodegradable expanded molded article has a final water
content between 3 weight % and 20 weight %.
Description
TECHNICAL FIELD
[0001] The present invention relates to a biodegradable expanded
molded article mainly derived from starch, and a biodegradable
molded article including a coating film bonded on a surface
thereof, and particularly to a biodegradable molded article that
can suitably be used for disposable expanded molded articles that
are disposed after the use as a food container, a molding buffer
material, GES, a wrapping tray, etc.
BACKGROUND ART
[0002] Conventionally, a plastic molded article and a paper/pulp
molded article are the mainstream of a disposable molded article
that is disposed after the use. This is because in most cases, raw
materials of the disposable molded article should be durable and
strong and at the same time readily formable depending on usage of
the molded article.
[0003] However, the plastic molded article and the paper/pulp
molded article both have difficulties to be used as the disposable
molded article, as shown below.
[0004] First, when incinerated, the plastic molded article damages
an incinerator because of the generation of extremely high heat, or
additionally produces environmental pollutants such as dioxin.
Also, when the plastic molded article is buried for reclamation, it
is impossible to bury the molded article where once the same is
buried, since plastics are rarely decomposed naturally. Moreover,
due to a recent increase of the amount of waste, it has become
difficult to secure new dumping sites year after year. Furthermore,
continuous environmental pollution for a long period of time could
be caused, since the plastic molded article cannot be decomposed
easily.
[0005] Also, reserves of fossil fuels such as oil, which are raw
materials of plastics, are decreasing year after year, so the
plastic molded article could become more expensive in the
future.
[0006] Meanwhile, the paper/pulp molded article is superior to the
plastic molded article in that it can easily be disposed of by
incineration and can be decomposed naturally. However, trees, of
which paper and pulps are made, grow slowly and thus the mass
consumption of paper and pulps substantially reduce forest
resources. The reduction of forest resources brings about not only
heavy destruction of an environment of the area but also a great
impairment of an ability of forests to absorb CO.sub.2, and a spun
for global warming because of the increase of CO.sub.2 from a broad
perspective.
[0007] So, to solve the aforementioned problems, particularly from
an environmental perspective, the disposal method of the molded
article has recently shifted from dumping to recycling.
[0008] However, as for the recycling, for instance, when a food
container, one of the main use of the disposable molded articles,
is recycled, residues in the container such as remaining foods and
seasonings have to be removed. This is required to avoid a
contamination of impurities in the material to be recycled.
[0009] Usually the removal of the residues is washed in water, so
this induces another pollution such as an increase of the amount of
polluted water and subsequent water-pollution in rivers and the
sea. Also, the recycling requires high cost, because the removal of
the residues itself lowers the efficiency of recycling as it needs
a lot of time and efforts, and the system of recycling has not been
really socially established at the moment.
[0010] So, what has become a focus of attention is a
recently-developed biodegradation disposal method for the molded
article by using microbe, as a new disposal method of the molded
article being different from the recycling. This disposal method
can avoid the problems above, since in this case the molded article
is mainly made of various biodegradable plastics or natural high
polymers such as starch.
[0011] Especially, in the biodegradation disposal method above, a
method to utilize the natural high polymers such as starch and
protein particularly draws attentions in terms of its practicality.
This is because the various biodegradable plastics have a problem
that despite having a fine quality almost comparable to
conventional plastics (non-degradable or degradable-retardant),
practically they cannot be decomposed quickly enough.
[0012] For instance, when the thickness of a molded article made of
the biodegradable plastic is heavy, it takes a very long time until
the molded article is completely decomposed, so practically it is
not possible to produce a molded article with enough volume. Also,
when the molded article made of the biodegradable plastic is used
practically as a disposable food container, composting the molded
article together with food residues is the least harmful disposal
method for the environment. However, actually it is difficult to
compost them together since the biodegradable plastic above is only
decomposed much slower than the food residues. Furthermore, it is
also difficult to crash the molded article to hasten the
decomposition of the biodegradable plastic, because normally the
molded article cannot be crushed easily when it has a certain
thickness and strength. Thus it is almost impossible to compost the
molded article made of the biodegradable plastic.
[0013] Whereas starch and protein, etc. are positively evaluated as
the materials because of advantages such as:
[0014] with fine biodegradability, decomposition is quite easy even
if the volume is large;
[0015] the resource can be acquired easily on account of an
availability of a vegetable starch that is mass-produced by
agriculture; and
[0016] a molded article with adequate thickness and thermal
insulation can be acquired, since the molded article is usually an
expanded molded article.
[0017] (1) Japanese Laid-Open Patent Application. No. 5-320401/1993
(Tokukaihei 5-320401; published on Dec. 3, 1993, (2) Japanese
Laid-Open Patent Application No. 7-224173/1995 (Tokukaihei
7-224173; published on Aug. 22, 1995), (3) Japanese Laid-Open
Patent Application No. 7-10148/1995 (Tokukaihei 7-10148; published
on Jan. 13, 1995), (4) Japanese Laid-Open Patent Application No.
2000-142783 (Tokukai 2000-142783; published on May 23, 2000), and
(5) Japanese Laid-Open Patent Application No. 7-97545/1995
(Tokukaihei 7-97545 published on Apr. 11, 1995) disclose
biodegradation disposal technologies using starch, protein,
etc.
[0018] First, a molded article derived from the technology (1) or
(2) have the advantages that it has better decomposability than a
molded article mainly made of the biodegradable plastic and also
superior to those derived from paper/pulps in its diversity of the
molded shape, since natural starch is mainly used as the material.
However, at the same time the molded article derived from the
technology (1) or (2) has the disadvantages that it can be used
only for limited purposes and is required to barrier moisture, due
to its poor water and humidity resistance.
[0019] Second, a molded article derived from the technology (3) or
(4) is mainly made of starch or similar polysaccharide, and to
enhance its water resistance, a natural resin (dammer resin,
shellac resin, etc.) is painted on the surface of the molded
article to form a water-resistant coating.
[0020] However, the surface of the molded article (including
expanded molded article) mainly made of starch cannot be completely
smoothed, and generation of small irregularities cannot be avoided.
Thus small pinholes are likely to be formed on the surface
corresponding to the irregularities of the water-resistant coating
if the resin is simply painted, so it could be possible to render
the molded article water repellent but difficult to make the same
complete water proof. Particularly, if the molded article is
required to be moisture-resistant, moisture is likely to be
absorbed from the pinholes on the water-resistant coating, and the
molded article becomes apt to be disfigured.
[0021] Furthermore, the dammer resin, the shellac resin, etc. must
be dissolved in an organic solvent such as alcohol, etc., when
applied to the surface. So this introduces problems in terms of a
manufacturing facility. For instance, when the organic solvent is
removed after the paint, large-scale equipment is required to
prevent diffusion of the organic solvent in the air that causes air
and environment pollution.
[0022] Now, on a surface of a molded article derived from the
technology (5) that is made of, as in the cases of the molded
articles of the technologies (3) and (4), poorly water-resistant
biodegradable material such as starch, a biodegradable coating
agent composed of aliphatic polyester being dissolved in
halogenated hydrocarbon is painted. In this case, using a dip
method (dip coating method) for actual coating of the surface, an
adequately water-resistant coating can be formed even on a
complicatedly-shaped molded article.
[0023] However, in this method, it is required to remove the
halogenated hydrocarbon used to dissolve the coating agent, and as
in the case of the technologies (3) and (4), problems such as a
requirement of equipment to prevent diffusion of halogenated
hydrocarbon arise. Many halogenated hydrocarbons are often harmful
for a human body and the environment, and moreover the halogenated
hydrocarbon that is concretely mentioned in the technology (5)
contains CFC so that it should be released to the air as little as
possible. On this account, a large-scale hermetic room and a
reclaiming device are required as the equipment above.
[0024] In addition to the technologies introduced above, there is a
technology in which wax or hydrophobic protein, prepared as a
solution to be applied, is painted on the surface of the molded
article. Generally, speaking, it is difficult to paint a
water-resistant coating on the surface of the molded article evenly
and entirely, while the coating on a flat molded article such as a
flat plate is relatively easy. However, small irregularities are
likely to be formed on the surface of the molded article mainly
made of starch as described above and obstruct the formation of an
uniform film, and furthermore, the molded article or a painting
device has to be rotated when the molded article is roughly
circular in cross section, for instance formed like a cup or a
bowl. Therefore the painting becomes more difficult.
[0025] Besides, even if the coating agent can be painted evenly and
entirely by using the dip method, the painted agent runs down
before it solidifies and becomes the coating, and an unevenness is
likely to show up on the coating.
[0026] The wax has a problem of poor heat resistance due to its
relatively low melting point. In the meantime, although the
hydrophobic protein has better heat resistance and does not need
the organic solvent, the molded article absorbs water and is
softened/disshaped in the painting process owing to a frequent use
of aqueous solvents.
[0027] So, a technology that has already been proposed is to
laminate a water-resistant coating instead of painting thereof.
More specifically, such examples include (6) Japanese Laid-Open
Patent Application No. 11-171238/1999 (Tokukaihei 11-171238;
published on Jun. 29, 1999), (7) Japanese Laid-Open Patent
Application No. 5-278738/1993 (Tokukaihei 5-278738; published on
Oct. 26, 1993), (8) Japanese Laid-Open Patent Application No.
5-294332/1993 (Tokukaihei 5-294332; published on Nov. 9, 1993).
[0028] A container of the technology (6), made by a pulp molding
method instead of molding starch, is covered by a water-impermeable
or non-absorbing protective coat. This method has the advantage
that conventional plastic coating method can be applied almost
without any change. However, at the same time the method has
problems such as:
[0029] the biodegradation of the pulp-molding takes place slowly
since it is made of fiber so that the molded article cannot be
disposed together with remaining foods, etc.; and
[0030] only limited types of the molded article can be produced
because it is difficult to make the molded article thicker, and
also the molded article is not suitable for a deep drawing.
[0031] Meanwhile, a thin film made of biodegradable plastic is
formed on a surface of a biodegradable container of the
technologies (7) or (8) made of either one of natural
polysaccharide or protein, or either of the two materials that are
chemically modified but still biodegradable.
[0032] In this technology, while the biodegradable plastic is
provided as the thin water-resistant coating, the container itself
is made of natural polysaccharide, protein, etc. with enough
thickness. On this account, the container is sufficiently
water-resistant as well as biodegradable. Thus it can be said that
this technology is particularly promising among the disposal
technologies by dint of biodegradation using starch, protein,
etc.
[0033] However, the technology (7) is an arrangement that the
biodegradable plastic thin film simply covers the main body of the
biodegradable container, and a concrete arrangement of the
biodegradable container is hardly mentioned.
[0034] For instance, when the main body of the biodegradable
container is mainly made of polysaccharide or protein, the main
body's strength should be cared of, but the technology (7) does not
mention the strength at all. Also, the technology does not explain
how the biodegradable plastic thin film is actually formed, such as
by painting, by attaching preformed film, etc., for instance.
[0035] Moreover, the technology (7) does not stipulate the coating
state of the biodegradable plastic thin film with respect to the
main body of the biodegradable container at all. The biodegradable
plastic thin film covers the main body of the biodegradable
container mainly made of polysaccharide or protein, to improve the
main body's water resistance. But the technology (7) does not
mention anything except that the main is covered, so there is no
statement about how it is covered.
[0036] Even if the biodegradable container is made as disposable
one, still the container should have a stability and durability as
a one-way container. So the biodegradable plastic thin film should
not fall off from the main body of the biodegradable container, and
thus the state of coating on the main body of the container is an
important factor, but no mention with respect to this can be found
in (7).
[0037] Furthermore, as already described, it is difficult to use
biodegradable plastics as a thick molded article due to its slow
biodegradation, so the speed of the biodegradation also greatly
depends on not only the thickness of the molded article but also a
total amount of biodegradable plastics contained in the molded
article. In relation to this, the technology (7) only describes
that an effectiveness of the biodegradation is improved if the main
body of the biodegradable container is expanded, and there are not
comments on a relationship between a degree of the expansion and
the biodegradation, and a balance between the biodegradation of the
biodegradable plastic and that of the main body of the
biodegradable container. As a result, it is not possible to manage
the biodegradation of the whole container favorably.
[0038] In the meantime, the technology (8) can be assumed to
correspond to one of the manufacturing technologies of the
biodegradable container disclosed by (7). In this technology, a
thermoplastic is dissolved in a solvent and painted on the surface
of the main body of the biodegradable container. Then after the
solvent is dried and volatilized, another coating thin film made of
a thermoplastic is laminated and bonded by thermocompression. That
is to say, the technology (8) discloses that thermoplastic is used
as an adhesive to bond the coating thin film (equivalent to the
biodegradable plastic thin film) securely.
[0039] Now, as described in relation to technologies (3) to (5),
when -the thermoplastic dissolved in the solvent is used, problems
such as a requirement of equipment to prevent diffusion of the
solvent arise. Moreover, an embodiment of (8) uses chloroform as
the solvent and this substance should be scattered in the air as
little as possible, thus as in the case of (5), a large-scale
hermetic room and reclaiming device are required as the equipment
above.
[0040] Also, the manufacturing technology of (8) acquires the main
body of the biodegradable container by press-molding a sheet made
of polysaccharide or protein that is formed in advance in a metal
mold. Thus it is impossible to mold molded articles such as a
container with deep drawing shape like a cup, molded articles
having irregular thickness like a food tray with partitions and a
wrapping tray, and molded articles having complex shape like
cushioning material for wrapping.
[0041] Also, in a conventional art relating to a biodegradable
container derived from starch, sufficient strength is acquired.
However, "strength" generally means strength under a dry condition
and normal atmosphere such as "piercing strength". As mentioned
below, according to the present inventors, there is no relation
between strength under a dry condition and normal atmosphere and
strength under moisture absorption (moisture absorption strength).
Therefore, even if the biodegradable container derived from starch
has sufficient "strength" what is generally called, it does not
have sufficient moisture absorption strength and it may soften or
disshaped due to moisture absorption during a long-term storage
under high humidity due to moisture absorption.
[0042] Furthermore, an expanded molded article derived from starch
such as (1) and (2) mentioned above, has a porous matrix structure
of starch formed through steam expansion which is a starch
structure having a very wide surface area thereon. Since an
expanded molded article is expanded and foamed by using evaporative
expansion of water, a surface of the starch structure has strong
hydrophilicity. On this account, the starch structure is an
important factor showing excellent biodegradability. At the same
time, it absorbs water and moisture very easily.
[0043] Even if the water-resistant coating such as (3) and (4) is
formed to protect the molded article which easily absorbs water and
moisture, it is possible to prevent water in liquid form from
penetrating into the starch structure, while it is impossible to
block water vapor in gaseous form.
[0044] Also, even if an expanded molded article derived from starch
is covered with a film or coating made from a biodegradable plastic
available at present, it is difficult to block water vapor as the
above case unless it is more than hundreds of .mu.m thick.
[0045] Therefore, an expanded molded article derived from starch
(starch structure) with high moisture resistance is especially
desired.
DISCLOSURE OF INVENTION
[0046] The inventors of the present invention filed the patent
application for a biodegradable molded article including a
biodegradable expanded molded article molded into a specified
shape, and a coating film attached to a surface of the
biodegradable expanded molded article, wherein the coating film is
mainly made of a biodegradable plastic and has at least
hydrophobicity, said biodegradable expanded molded article being
mainly made of starch or a derivative thereof and molded through
steam expansion of a slurry or dough molding material prepared by
adding water to the starch or the derivative thereof (International
application PCT/JP01/07903, application dated Sep. 12, 2001,
unpublished as of the priority date of the present invention).
[0047] However, a biodegradable expanded molded article of the
above prior invention, starch or a derivative thereof absorbs
moisture during a long-term storage under high humidity, and the
molded article may be softened or disshaped.
[0048] The present invention takes the problem above into account,
and hence the object is to provide a biodegradable molded article
mainly made of starch that has satisfactory strength regardless of
a degree of complexity of the shape, and at least satisfactory
water resistance, and a very good biodegradation, furthermore
excellent moisture absorption strength (moisture resistant
strength).
[0049] To achieve the purpose above, the biodegradable molded
article of the present invention includes a biodegradable expanded
molded article molded in a specified shape, and a coating film
attached on a surface of the biodegradable expanded molded article,
wherein the coating film is mainly made of a biodegradable plastic
and has at least hydrophobicity, said biodegradable molded article
being characterized in that the biodegradable expanded molded
article is mainly made of starch or a derivative thereof and molded
through steam expansion of a slurry or dough molding material
prepared by adding water to the starch or the derivative thereof,
and that the starch or the derivative thereof includes high-amylose
starch or a derivative thereof.
[0050] According to the arrangement above, producing the slurry or
dough molding material mainly made of starch and steam-expanding
this material easily allow manufacture of a highly complicatedly
shaped molded article, and make the molded article have improved
strength compared with conventional molded article made of starch,
since the resultant expanded molded article includes a certain
amount of water. Furthermore, inasmuch as a biodegradable coating
film is attached on the expanded molded article, it becomes
possible to apply the coating film to the molded article in
correspondence with the shape thereof easily and certainly, by, for
instance, thermocompression bonding using a mold identically shaped
as a mold used when the expanded molded article is molded, or
simultaneously attaching the coating film at the moment of
expansion molding.
[0051] The coating film is mainly made of a biodegradable plastic
having similar quality to common plastics and has at least
hydrophobicity. Thus the expanded molded article mainly made of
starch can be water resistant simply by attaching the coating film.
Moreover, extrinsic functions such as gas impermeability can be
added by choosing appropriate types of biodegradable plastics and
so on.
[0052] Moreover, according to the arrangement above, the starch or
the derivative thereof includes high-amylose starch or a derivative
thereof, which can prevent a reduction of strength caused by
moisture absorption under high humidity and improve physical
strength.
[0053] In the description of the present invention, "high-amylose
starch" means starch containing not less than 50% of amylose.
[0054] To solve the problems above, the biodegradable molded
article of the present invention is characterized in that the
biodegradable molded article includes a biodegradable expanded
molded article molded in a specified shape, and a coating film
attached on a surface of the biodegradable expanded molded article,
wherein the coating film is mainly made of a biodegradable plastic
and has at least hydrophobicity, said biodegradable expanded molded
article being mainly made of starch or a derivative thereof and
molded through steam expansion of a slurry or dough molding
material prepared by adding water and polyvinyl alcohol to the
starch or the derivative thereof.
[0055] According to the arrangement above, producing the slurry or
dough molding material mainly made of starch and steam-expanding
this material easily allow manufacture of a highly complicatedly
shaped molded article, and make the molded article have improved
strength compared with a conventional molded article of starch,
since the resultant expanded molded article includes a certain
amount of water. Furthermore, inasmuch as a biodegradable coating
film is attached on the expanded molded article, it becomes
possible to apply the coating film to the molded article in
correspondence with the shape thereof certainly and easily, by, for
instance, thermocompression bonding using a mold identically shaped
as a mold used when the expanded molded article is molded, or
simultaneously attaching the coating film at the moment of
expansion molding.
[0056] The coating film is mainly made of a biodegradable plastic
having similar quality to common plastics and has at least
hydrophobicity. Thus the expanded molded article mainly made of
starch can be water resistant simply by attaching the coating film.
Moreover, extrinsic functions such as gas impermeability can be
added by choosing appropriate types of biodegradable plastics and
so on.
[0057] Furthermore, according to the arrangement above, inasmuch as
the molding material includes polyvinyl alcohol, it is possible to
prevent a reduction of strength caused by moisture absorption of
starch under high humidity and to improve physical strength.
[0058] Therefore, according to the arrangement above, as described
above, it is possible to provide a biodegradable molded article
mainly made of starch which is sufficiently strong and at least
sufficiently water resistant and has a very good biodegradability
and excellent moisture absorption strength regardless of the
complicated shape, to exert a very excellent biodegradability, and
to provide a biodegradable molded article mainly made of starch
having an excellent water absorption strength.
[0059] It is preferable that in the biodegradable molded article in
each arrangement, the molding material further includes water
insoluble fiber.
[0060] According to the arrangement above, strength, especially
pressure capacity can be further improved, thereby preventing any
damage at a fall.
[0061] Other and further objects, features and advantages of the
present invention will appear more fully from the following
description. Also, the merits of the present invention will be
apparent from the following description taken in connection with
the accompanying drawing.
BRIEF DESCRIPTION OF DRAWINGS
[0062] FIG. 1(a) and FIG. 1(b) are schematic cross-sectional views
showing a shape of a bowl-shaped container as an example of a
biodegradable molded article of an embodiment in accordance with
the present invention.
[0063] FIG. 2(a) and FIG. 2(b) are schematic cross-sectional views
showing a shape of a plate-shaped container as another example of a
biodegradable molded article of an embodiment in accordance with
the present invention.
[0064] FIG. 3(a) and FIG. 3(b) are a schematic cross-sectional view
and a schematic plan view showing a shape of a cup-shaped container
as still another example of a biodegradable molded article of an
embodiment in accordance with the present invention.
[0065] FIG. 4 is a graph that shows a composition of a molding
material in the present invention, as measured in relation to the
whole molding materials in a graph (I), and a total amount of main
solid matter in a graph (II), and by means of a relation between a
total amount of the materials and water in a graph (III), and a
relationship between those measurement schematically.
[0066] FIG. 5(a) and FIG. 5(b) are schematic cross-sectional views
showing an arrangement of a mold to mold an expanded molded article
that is a main body of the bowl-shaped container shown in FIG. 1(a)
and FIG. 1(b).
[0067] FIG. 6(a) and FIG. 6(b) are schematic cross-sectional views
showing an arrangement of a mold to mold an expanded molded article
that is a main body of the plate-shaped container shown in FIG.
2(a) and FIG. 2(b).
[0068] FIG. 7(a) and FIG. 7(b) are schematic cross-sectional views
showing an arrangement of a mold to mold an expanded molded article
that is a main body of the cup-shaped container shown in FIG. 3(a)
and FIG. 3(b)
[0069] FIG. 8(a) and FIG. 8(b) are schematic cross-sectional views
showing another arrangement of a mold to mold an expanded molded
article that is a main body of the cup-shaped container shown in
FIG. 3(a) and FIG. 3(b).
[0070] FIG. 9 is a schematic explanatory view showing an example of
an arrangement that the mold shown in FIG. 5(a) and FIG. 5(b)
includes an electrode for internal heating.
[0071] FIG. 10(a) is a schematic cross-sectional view showing a
shape of the expanded molded article molded by the mold shown in
FIG. 5(a) and FIG. 5(b), FIG. 10(b) is a schematic cross-sectional
view showing a shape of the expanded molded article molded by the
mold shown in FIG. 6(a) and FIG. 6(b), and FIG. 10(c) is a
schematic cross-sectional view showing a shape of the expanded
molded article molded by the mold shown in FIG. 7(a) and FIG. 7(b)
or FIG. 8(a) and FIG. 8(b).
[0072] FIG. 11 is a schematic explanatory view describing an
attaching step that a coating film is attached on the surface of
the biodegradable expanded molded article shown in FIG. 10(a) by
using an after attaching method.
[0073] FIG. 12(a) is a schematic explanatory view showing an
attaching state of the coating film on the surface of the
biodegradable molded article on which the coating film is attached
by using the after attaching method, and FIG. 12(b) is a schematic
explanatory view showing an attaching state of the coating film on
the surface of the biodegradable molded article on which the
coating film is attached by using a simultaneous attaching
method.
[0074] FIG. 13 is an explanatory view describing a case that a
manufacturing method 1 is used, in the simultaneous attaching
method for manufacturing the biodegradable molded article shown in
FIG. 2(a).
[0075] FIG. 14 is an explanatory view describing a case that a
manufacturing method 2 is used, in the simultaneous attaching
method for manufacturing the biodegradable molded article shown in
FIG. 1(a).
[0076] FIG. 15 is an explanatory view describing a case that a
manufacturing method 3 is used, in the simultaneous attaching
method for manufacturing the biodegradable molded article shown in
FIG. 2(a).
[0077] FIG. 16 is an explanatory view describing a case that a
manufacturing method 4 is used, in the simultaneous attaching
method for manufacturing the biodegradable molded article shown in
FIG. 1(a).
[0078] FIG. 17(a) is a schematic plan view showing an example that
the coating film is cut off in two pieces of film when the
biodegradable molded article shown in FIG. 3(a) is manufactured by
using a manufacturing method 5, and FIG. 17(b) is a schematic plan
view showing an example that the coating film is cut off in three
pieces of film.
[0079] FIG. 18 is an explanatory view describing a case that a
manufacturing method 5 is used, in the simultaneous attaching
method for manufacturing the biodegradable molded article shown in
FIG. 3(a)
[0080] FIG. 19 is an explanatory view describing a case that a
manufacturing method 6 is used, in the simultaneous attaching
method for manufacturing the biodegradable molded article shown in
FIG. 3(a).
[0081] FIG. 20 is an explanatory view describing a case that a
manufacturing method 7 is used, in the simultaneous attaching
method for manufacturing the biodegradable molded article shown in
FIG. 3(a).
[0082] FIG. 21(a) is a schematic explanatory view showing a state
that an adhesive lid is adhered to an edge of the biodegradable
molded article shown in FIG. 1(b), and FIG. 21(b) is a schematic
explanatory view showing a state that the coating film is not
adhered on the edge shown in FIG. 21(a).
[0083] FIG. 22 is an explanatory view describing a case that a
manufacturing method 1B is used in the simultaneous attaching
method.
[0084] FIG. 23 is a schematic cross-sectional view showing a shape
of a plate-shaped container acquired by the manufacturing method 1B
as still another example of the biodegradable molded article of an
embodiment in accordance with the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0085] An embodiment of the present invention is described below in
accordance with attached figures. By the way, the invention is not
limited to this embodiment.
[0086] A biodegradable molded article in accordance with the
present invention includes a biodegradable expanded molded article
molded in a specified shape and a coating film attached to the
surface thereof, wherein the coating film is mainly made of
biodegradable plastic and has at least hydrophobicity. The
biodegradable expanded molded article is made of (a) starch or a
derivative thereof as the main material including high-amylose
starch or a derivative thereof and molded by conducting steam
expansion to slurry or dough molding material which is made by
adding water to the main material, or is made of (b) starch or a
derivative thereof as the main ingredient and molded by conducting
steam expansion to slurry or dough molding material which is made
by adding water and polyvinyl alcohol.
[0087] Also, in the biodegradable molded article above, a preferred
arrangement is either:
[0088] an amount of biodegradable plastics such as the coating film
is stipulated to be steady with respect to the biodegradable
expanded molded article; or a ratio of the amount of gas phase
included in the biodegradable expanded molded article is stipulated
as a certain amount,
[0089] and moreover, the coating film above preferably coats the
surface of the biodegradable expanded molded article in the state
that the coating film is substantially adhered to the surface. In
this case, an adhesive layer may be inserted between the surface
and the coating film, despite it is preferred if the coating film
is directly adhered.
[0090] By the way, in the description below, the term "the
biodegradable expanded molded article" may be shortened as
"expanded molded article" without notice. Also, the "slurry" state
as above indicates a state that starch has enough fluidness when at
least water is added. Thus the starch only needs to be suspended
and does not have to be dissolved in water. Meanwhile, the "dough"
state as above has lower fluidness compared to the slurry state,
and the material is half solidified.
[0091] The biodegradable molded article in accordance with the
present invention is described. More specifically, if a bowl-shaped
container is taken as an example of the biodegradable molded
article, as FIG. 1(a) shows, the bowl-shaped container 10a includes
a main body 11a of the container which is the biodegradable
expanded molded article and a coating film that is directly adhered
substantially fast to the main body 11a to cover the surface
thereof. Also, as FIG. 1(b) shows, the bowl-shaped container 10a
may include an adhesive layer 13 inserted between the coating film
12 and the main body 11a, to attach the coating film 12 to the
surface of the main body 11a. By the way, as described later, the
surface of the main body 11a is not necessarily to be completely
covered by the coating film 12, so may be partly covered by the
same.
[0092] Correspondingly, if a plate-shaped container is taken as
another example of the biodegradable molded article in accordance
with the present invention, the plate-shaped container 10b is also
arranged either to include the main body 11b and the coating film
12 as FIG. 2(a) shows, or additionally to include the adhesive
layer 13 between the main body 11b and the coating film 12 as FIG.
2(b) shows.
[0093] Moreover, if a cup-shaped container is taken as another
example of the biodegradable molded article in accordance with the
present invention, the cup-shaped container 10c is also arranged
either to include the main body 11c and the coating film 12 as FIG.
3(a) shows, or additionally include the adhesive layer 13 between
the main body 11c and the coating film 12 as FIG. 3(b) shows. By
the way, in FIGS. 3(a) and (b), the upper figure is a vertical
cross-sectional view of the cup-shaped container 10c and the lower
figure is a plan view (a figure looking down at the cup-shaped
container 10c from above) in relation to the upper figure.
[0094] The biodegradable expanded molded article, which constitutes
the main body (the main bodies 11a, 11b, and 11c) of the
biodegradable molded article in accordance with the present
invention, is molded from a slurry or dough molding material mainly
made from starch or a derivative thereof and prepared by adding
water, through steam expansion.
[0095] The molding material above is a molding material wherein at
least part of starch or a derivative thereof is high-amylose starch
(hereinafter referred to as "a first molding material"), or a
molding material further containing polyvinyl alcohol (hereinafter
referred to as "a second molding material"). It is possible to
prevent a reduction of strength caused by moisture absorption of
starch under high humidity and to improve physical strength by
using the first or second molding material.
[0096] High-amylose starch used for the first molding material is
not particularly limited, but starch containing not less than 60%
of amylose is preferable. It is thus possible to further improve
strength when starch absorbs moisture during a long-term storage
under high humidity (hereinafter referred to as moisture absorption
strength without notice).
[0097] Starch and a derivative thereof (including high-amylose
starch) used as the main material of the molding material is not
limited to any particular type. For instance, starch easily
acquired from agricultural products worldwide as major cereals,
such as potato, corn, tapioca, rice, wheat, sweet potato, etc. can
be preferably used. The starch above may be either produced from a
particular agricultural product or a mixture of starch produced
from more than one agricultural product.
[0098] Also, the derivative of high-amylose starch is a derivative
that is chemically modified but still biodegradable, more
specifically, such as c-high-amylose starch, cross linked
high-amylose starch, and denatured high-amylose starch. Moreover, a
mixture of unmodified high-amylose starch and a derivative of
high-amylose starch can be used.
[0099] The percentage-of high-amylose starch or a derivative
thereof in starch or a derivative thereof is preferably not less
than 50 weight %, more preferably not less than 60 weight %, still
more preferably not less than 75 weight %, which can further
improve moisture absorption strength.
[0100] As a graph "(II) Total Amount of Main Solid Matter=100%" in
FIG. 4 shows, the percentage of starch content in the first molding
material is preferably within the range between 50 weight % and 100
weight %, if a total amount of the main solid matter of the molding
material is taken as 100 weight %. Meanwhile, if a total amount of
the molding material including water is taken as 100 weight %, as a
graph "(I) Molding Material=100%" in FIG. 4 indicates, the
percentage of starch content is preferably within the range between
20 weight % and 60 weight %. When the starch content falls in the
ranges above, the main material of the biodegradable molded article
in accordance with the present invention can be regarded as starch,
so good biodegradability can be expected. By the way, the main
solid matter and the total amount thereof are described later.
[0101] Polyvinyl alcohol used for the second molding material is
not limited to a particular type, but polymerization degree is
preferably not less than 1000, especially preferably not less than
1500.
[0102] Saponification degree of polyvinyl alcohol used for the
second molding material is preferably not less than 75%, more
preferably not less than 90%.
[0103] The content of polyvinyl alcohol used in the second molded
material molding is preferably not less than 4.0weight %, more
preferably not less than 5.0 weight %, which can improve moisture
absorption strength.
[0104] Starch used as the main material of the second molding
material is not limited to any particular type. For instance,
starch easily acquired from agricultural products worldwide as
major cereals, such as potato, corn, tapioca, rice, wheat, sweet
potato, etc. can be preferably used. The starch above may be either
produced from a particular agricultural product or a mixture of
starch produced from more than one agricultural product.
[0105] Also, a derivative of the starch used as the main material
of the second molding material is starch that is chemically
modified but still biodegradable, more specifically, such as
.alpha.-starch, cross linked starch, and denatured starch, etc.
Moreover, a mixture of the unmodified starch and the derivative of
starch can be used as well. Thus in a broad sense, the starch in
the present invention includes unmodified starch (starch in a
narrow sense), a derivative thereof, and a mixture of these two.
So, in the description below, "starch" indicates the starch in a
broad sense, unless particularly notices.
[0106] The percentage of starch content in the second molding
material is preferably within the range between 50 weight % and 95
weight %, if a total amount of the main solid matter of the molding
material is taken as 100 weight %. Meanwhile, if a total amount of
the molding material including water is taken as 100 weight %, the
percentage of starch content is preferably within the range between
20 weight % and 75 weight %. When the starch content falls in the
ranges above, the main material of the biodegradable molded article
in accordance with the present invention can be regarded as starch,
so good biodegradability can be expected. By the way, the main
solid matter and the total amount thereof are described later.
[0107] It is preferable that also in the second molding material,
starch or a derivative thereof contains high-amylose starch, which
can further improve moisture absorption strength. Also, the
percentage of high-amylose starch or a derivative thereof in starch
or a derivative thereof is preferably not less than 50 weight %,
more preferably not less than 60 weight %, and still more
preferably not less than 75 weight %, which further improve
moisture absorption strength.
[0108] Apart from the above essential components (high-amylose
starch or a derivative thereof in the first molding material and
starch and polyvinyl alcohol in the second molding material), the
first molding material and the second molding material
(hereinafter, collectively referred to as the "molding material")
may include various additives. More specifically, the additives are
such as an extending agent, strength adjusting agent, plasticizer,
emulsifier, stabilizer, mold releasing agent, homogeneity adjusting
agent, moisture retaining agent, handling adjusting agent,
conductivity adjusting agent, dielectric loss adjusting agent,
swelling agent, coloring agent, etc.
[0109] Some additives are beneficial in the manufacturing process
of the biodegradable molded article, such as improving efficiency
of manufacturing the biodegradable molded article or avoiding
problems happening in the manufacturing process, and others are
advantageous for the biodegradable molded article as a finished
product, such as improving the quality of the acquired
biodegradable molded article and cutting costs thereof. The type of
these additives is not limited, unless significantly lowering the
quality of the expanded molded article or the biodegradable molded
article.
[0110] The extending agent is an additive added to the molding
material to increase the bulk of the molding material and decrease
the amount of starch included in the material as much as possible,
to cut costs. Therefore, a substance used as the extending agent is
not limited to any particular one as long as cheaper than starch,
but by-products of processing and manufacturing of foods, etc. are
preferred, to dispose the wastes simultaneously.
[0111] More specifically, what can be used are:
[0112] (1) a remained juice, residue of squeezing, that are
produced in food (food and drink) processing and manufacturing
using vegetables and fruits such as celery, carrot, tomato, citrus
fruits (mandarin orange, lemon, grapefruit, etc.), apple, grape,
berries, pineapple, sugarcane, sugarpeat, etc., and mixture of
thereof;
[0113] (2) by-products of a manufacture of processed foods using
cereals, such as bean curd lees and tofu;
[0114] (3) sake lees, shouchu lees, beer yeast lees, wine yeast
lees, etc. that are produced in processes of producing liquors such
as sake, shochu, beer, wine, etc., and any mixture thereof;
[0115] (4) residues of used luxury drinks such as coffee, black
tea, barley tea, green tea, oolong tea, etc., tea dregs and any
mixture thereof;
[0116] (5) oil cakes remained after squeezing oil from soybean,
corn, rapeseed, sesame, etc., and any mixture thereof;
[0117] (6) residues produced in a process to polish cereals such as
wheat bran, rice bran, rice husks, etc., and any mixture
thereof;
[0118] (7) by-products produced in a process to produce starch such
as gluten meal, etc.;
[0119] (8) baking residues produced in a process of manufacturing
sweets and bread such as a cone cup, biscuit, wafer, waffle, and
any mixture thereof;
[0120] (9) the aforementioned by-products etc. above being dried or
crushed.
[0121] Furthermore, either one of the substances or any mixture
thereof may be used.
[0122] The strength adjusting agent is an additive to adjust
(especially enhance) the strength of the expanded molded article
and the biodegradable molded article. Although the type of the
agent is not limited to any particular substance, what are taken as
the concrete examples are, for instance:
[0123] the aforementioned by-products (1) to (9) taken as the
extending agents;
[0124] (10) saccharide such as glucose, dextrin, isomerized
saccharide, etc., and any mixture thereof;
[0125] (11) sugar-alcohols such as sorbitol, mannitol, lactitol,
etc., and any mixture thereof;
[0126] (12) fats and oils such as vegetable fat and oil, animal fat
and oil, processed fat and oil made thereof, etc., and any mixture
thereof;
[0127] (13) waxes such as carnauba wax, candelilla wax, bees wax,
paraffin, microcrystalline wax, and any mixture thereof;
[0128] (14) thickener polysaccharide (microbe producing
polysaccharide or vegetable polysaccharide, etc.) such as xanthan
gum gellan gum, guar gum, locust bean gum, pectin, gum Arabic,
karaya gum, tara gum, carrageenan, furcellaran, agar, alginate,
water-soluble carboxymethyl cellulose, etc. and salts thereof, and
any mixture thereof;
[0129] (15) chlorides of metals, such as calcium, sodium,
potassium, aluminum, magnesium, and iron; sulfates, organic acid
salts, carbonates, hydroxides, phosphates, and other salts of these
metals; and any mixture thereof;
[0130] (16) insoluble minerals such as quartz powder, diatomaceous
earth, talc, silicone, etc., and any mixture thereof;
[0131] (17) water-insoluble fibers
[0132] (18) structures of inorganic substances such as glass,
metal, carbon, ceramic and etc.
[0133] (19) natural materials such as a shell, bone powder,
eggshell, leaf, wood powder, etc., and any mixture thereof;
[0134] (20) calcium carbonate, carbon, talc, titanium dioxide,
silica gel, aluminum oxide, non-fiber filler, etc., and any mixture
thereof;
[0135] (21) fatty acid (stearic acid, lactic acid, lauric acid,
etc.), salt such as metal salt of the acid substances, etc., fatty
acid derivatives such as acid amide, ether, etc., and any mixture
thereof;
[0136] (22) other food additives such as glycerin, polyglycerin,
propylene glycol, ethylene glycol, glycerine fatty acid ester,
polyglycerin fatty acid ester, propylene glycol fatty acid ester,
sugar ester, lecithin, sorbitan fatty acid ester, polysorbate,
etc., and any mixture thereof;
[0137] (23) natural resins such as shellac, rosin, sandarac resin,
gutta-percha, dammer resin, etc., and any mixture thereof;
[0138] (24) biodegradable resins such as polylactic acid, etc., and
any mixture thereof;
[0139] (25) acetyltributyl citrate, solution of zirconium salt,
alkali solution of ammonium zirconium carbonate, and any mixture
thereof. Furthermore, either one of the substances above or any
mixture thereof may be used.
[0140] It is preferable that the molding material of the present
invention may contain water-insoluble fibers (fibers that is
insoluble in water) as strength adjusting agent, which can further
improve strength, especially pressure strength, and prevent damages
at a fall.
[0141] The water-insoluble fibers may be inorganic fibers
consisting of inorganic materials such as glass, metal, carbon,
ceramic, synthetic fibers, vegetable fibers, and animal fibers
including silk. Vegetable fibers are preferable since they are
biodegradable.
[0142] The vegetable fibers are not limited to particular type, for
instance; polysaccharide and a derivative thereof such as
cellulose, microcrystalline cellulose, (water-insoluble)
carboxymethyl cellulose, methyl cellulose, acetyl cellulose, etc.;
paper and pulp, natural fibers from cotton, hemp, and other plants
and vegetables; animal fibers such as silk, etc., and any mixture
thereof. Pulp is the most preferable among these insoluble
fibers.
[0143] Pulp means fibers constituting conifers, broad-leaf tree,
kouzo, mitumata and other plants. The fibers are collected from
these raw materials after they are properly processed. Pulp may
include virgin pulp or wastepaper pulp.
[0144] The percentage of the insoluble fibers content in the
molding material is preferably within the range between 2 weight %
and 10 weight %, thereby further improving strength. Especially it
is possible to further improve pressure strength and prevent
damages at a fall more securely.
[0145] The plasticizer is an additive to improve fluidity of the
molding material and gives flexibility to the acquired expanded
molded article and biodegradable molded article. Although the type
of the plasticizer is not limited to any particular substance, what
are taken as the concrete examples are, for instance:
[0146] the aforementioned by-products (1) to (9) taken as the
extending agents;
[0147] the aforementioned compounds (10) to (21), (23) and (24)
that are taken as the strength adjusting agents;
[0148] (26) acetylpolybutyl citrate, or sugar-alcohols such as
glycerin, polyglycerin, propylene glycol, ethylene glycol, etc.,
and any mixture thereof.
[0149] Furthermore, either one of the substances above or any
mixture thereof may be used.
[0150] The emulsifier is an additive to mix an oily additive
adequately and emulsify the additive to be a oil-drop-in-water
shape, provided that the oily additive is added to the molding
material. Although the type of the emulsifier is not limited to any
particular substance, what are taken as the concrete examples are,
for instance:
[0151] (27) surface active agents such as glycerine acid ester,
polyglycerine acid ester, propylene glycol fatty acid ester, sugar
ester, sorbitan acid ester, lecithin, polysorbate, etc., and any
mixture thereof.
[0152] The stabilizer is an additive to stabilize the state of the
processed molding material. Although the type of the stabilizer is
not limited to any particular substance, what are taken as the
concrete examples are, for instance:
[0153] starch (in a narrow sense, not modified) as the main
material and a derivative thereof; and
[0154] the substances taken as the strength adjusting agents such
as (10) saccharide, (11) sugar-alcohols, (14) thickener
polysaccharide, (17) vegetable fibers and a derivative thereof
(except paper), and (21) fatty acid, fatty acid salts, and fatty
acid derivatives etc.
[0155] Either one of the substances above and any mixture thereof
may be used.
[0156] The mold releasing agent is an additive-to easily release
the expanded molded article from the mold and also make the surface
of the expanded molded article as smooth as possible. Although the
mold releasing agent is not limited to any particular type, what
are taken as the concrete examples are, for instance, the
substances taken as the strength adjusting agents, such as (12)
fats and oils, (13) waxes, (14) thickener polysaccharide, (21)
fatty acid, fatty acid salts, and fatty acid derivatives, etc.
[0157] Either one of the substances above or any mixture thereof
may be used.
[0158] The homogeneity adjusting agent is an additive to make
homogeneity in the slurry/dough molding material, that is, "grain"
(in this case, grain, etc. of a solid matter in the slurry/dough
material) of the slurry/dough molding material as fine, smooth and
homogeneous as possible. Although the homogeneity adjusting agent
is not limited to any particular type, what are taken as the
concrete examples are, for instance:
[0159] starch (in a narrow sense, not modified) as the main
material, and the derivative thereof;
[0160] the aforementioned by-products (1) to (9) taken as the
extending agents;
[0161] the aforementioned components (10) to (25) taken as the
strength adjusting agents.
[0162] Furthermore, either one of the substances above and any
mixture thereof may be used.
[0163] The moisture retaining agent makes the expanded molded
article include a certain amount of water, and has the same effect
as the plasticizer. That is to say, if the expanded molded article
mainly made of starch includes a certain amount of water (if
retaining moisture), while the brittleness of .alpha.-starch is
decreased, strength and flexibility thereof are improved. Thus the
moisture retaining agent can be used as a plasticizer and a
strength adjusting agent as well.
[0164] The type of the moisture retaining agent is not limited to
any particular substance either. So, what are taken as the concrete
examples are, for instance:
[0165] the starch (in a narrow sense, not modified) as the main
material and the derivative thereof;
[0166] the aforementioned by-products (1) to (9) taken as the
extending agents; and
[0167] the substances taken as the strength adjusting agents such
as (10) saccharide, (11) sugar-alcohols, (12) fats and oils, (13)
waxes, (14) thickener polysaccharide, (15) metallic salts, (17)
vegetable fibers and their derivatives, (19) natural materials such
as a shell, bone powder, eggshell, leaf, wood powder, etc., and
(22) food additives.
[0168] Furthermore, either one of the substances above or any
mixture thereof may be used.
[0169] The handling adjusting agent works as a slurry adjusting
agent and is an additive to improve the handling of the
slurry/dough molding material. Although the handling adjusting
agent is not limited to any particular substance, it is noted that
all materials and compounds taken as the plasticizer, the
emulsifier, and stabilizer can be used. Either one of the
substances above or any mixture thereof may be used.
[0170] The conductivity adjusting agent is an additive to adjust a
conductivity of the molding material, which is one of the factors
to control the state of heating in the case of internal heating as
described later, especially in the case of heat molding using the
internal heat generated by electric heating, when the expanded
molded article is molded. Although the conductivity adjusting agent
is not limited to any particular type, what are taken as the
concrete examples are, for instance:
[0171] (12) fats and oils, (13) waxes, (14) thickener
polysaccharide, and (15) metallic salts that are taken as the
strength adjusting agents, and (28) water soluble electrolytes such
as salts, acid, alkali, alcohol, etc.
[0172] Either one of the substances above or any mixture thereof
may be used.
[0173] The dielectric loss adjusting agent is an additive to adjust
a dielectric loss of the molding material, which is one of the
factors to control the state of heating especially in the case of
heat molding using the internal heat generated by high frequency
dielectric heating, when the expanded molded article is molded.
Although the dielectric loss adjusting agent is not limited to any
particular, what are taken as the concrete examples are, for
instance:
[0174] the substances that are taken as the strength adjusting
agents such as (12) fats and oils, (13) waxes, (15) metallic salts,
(16) insoluble minerals, and (17) vegetable fibers and their
derivatives;
[0175] the substance taken as the conductivity adjusting agent such
as (28) water soluble electrolytes; and (29) compounds including
zirconium salt such as zirconium salt, solution of ammonium
zirconium carbonate, etc., and any mixture thereof.
[0176] Either one of the substances above or any mixture thereof
may be used.
[0177] The swelling agent is an additive to adjust the degree of
expansion of the molding material and further the swelling to form
the expanded molded article having an appropriate shape for the
use. Although the swelling agent is not limited any particular
type, what are taken as the concrete examples are, for
instance:
[0178] (30) formulations including organic swelling agents such as
benzenesulfonyl hydrazine compounds, azonitryl compounds, nitroso
compounds, diazo acetamide compounds, azocarboxylic acid compounds,
etc.;
[0179] (31) formulations including ammoniacal swelling agents such
as espata, etc.;
[0180] (32) formulations including inorganic swelling agents such
as sodium bicarbonate, ammonium alum hydrogen tartaric acid,
magnesium carbonate, etc.
[0181] Either one of the substances above and any mixture thereof
may be used.
[0182] The coloring agent is an additive to color the whole
expanded molded article. Although the coloring agent is not limited
to any particular type, what are taken as the concrete examples
are, for instance:
[0183] (33) inorganic pigments such as titanium dioxide and carbon
black, etc.;
[0184] (34) natural or synthetic organic dyes such as colorants
specified by a color index;
[0185] (35) colorants made of natural materials such as a caramel,
cacao powder, etc.
[0186] Either one of the substances above or any mixture thereof
may be used.
[0187] Among the additives included in the molding material, a
content of the extending agent (may be alternatively termed as an
extending additive) is preferably not more than a content of the
starch contained in the total amount of the main solid matter in
the molding material.
[0188] That is to say, although the extending additive (extending
agent) may not be necessarily contained, it is preferable if the
extending additive is contained not exceeding the content of the
starch at the maximum, from the viewpoint to cut the cost of raw
materials of the biodegradable molded article in accordance with
the present invention and to utilize the wastes as described above
efficiently. So the starch that is the main material, and the
extending agent that is the extending additive among the additives,
are termed together as the main solid matter.
[0189] By the way, in the main solid matter, if the extending
additive is contained more than the content of the starch, the
starch is not virtually the main ingredient of the acquired
biodegradable molded article. This should be avoided since the
quality of the biodegradable molded article is degraded. Also, the
starch and the extending agent are integrally termed as "main solid
matter", because "solid matter" included in the biodegradable
molded article includes solid matter of functional additives (see a
graph "(I) Molding Material=100%" in FIG. 4).
[0190] That is, in the present invention, as the graph "(II) Total
Amount of Main Solid Matter=100%" in FIG. 4 indicates, assuming
that the total amount of the main solid matter (starch and
extending agent) is taken as 100 weight %, the content of starch
(including the derivatives) is within the range between 50 weight %
and 100 weight %, while the content of extending agent is within
the range between 0 weight % and 50 weight % (0--less than 50
weight % in the figure).
[0191] Moreover, as described beside the graph "(I) Molding
Material=100%" in FIG. 4, the total amount of the main solid matter
in the first molding material in accordance with the present
invention is preferably not more than 70 weight %, assuming that
the whole molding material including water is taken as 100 weight
%.
[0192] Furthermore, among the additives included in the molding
material, as the graph "(I)Molding Material=100%" in FIG. 4 shows,
a content of each additive (termed as functional additives) except
that the extending agent (extending additive) in the first molding
material in accordance with the present invention is preferably
within the range between 0 weight % and 25 weight %, and more
preferably between 0 weight % and 20 weight %, assuming that the
whole molding material including water is taken as 100 weight %.
Also, an amount of the functional additives when the total amount
of the main solid matter is taken as 100 weight %, i.e. an amount
of the functional additives with respect to the total amount of the
main solid matter is not particularly limited, as long as the
amount thereof in the molding material falls in the range as
above.
[0193] In other words, as is the case with the extending agent, the
functional additives are not necessarily contained in the molding
material. However, it is preferable if the content of additives is
not more than 25 weight % out of 100 weight % of the molding
material, to improve performance of the biodegradable molded
article. By the way, it is not desirable that the content of the
functional additives is not less than 25 weight %, because the
additives cannot deliver the expected performance in accordance
with the content thereof, and moreover, the performance of the
biodegradable molded article may be degraded in some cases.
[0194] Provided that the main solid matter (the starch as the main
material+the extending agent) and the functional additives are
collectively termed material ingredients, the molding material used
in the present invention further includes water. In this case, the
type of water is not particularly limited as long as industrial
water is used.
[0195] As shown in the graph "(I) Molding Material=100%" in FIG. 4,
when water is added to the-molding material, a content of water in
the molding material should be within the range between 20 weight %
and 70 weight %, more preferably within the range between 25 weight
% and 55 weight %, assuming that the molding material is taken as
100 weight %.
[0196] In other words, as a graph "(III) Ratio of Material
Ingredients to Water" in FIG. 4 shows, provided that the total
amount of the material ingredients (main solid matter+functional
additives) of the molding material is taken as 100 weight %, the
amount of water added is within the range between 25 weight % and
230 weight %, more preferably within the range between 33 weight %
and 120 weight %. When the content of the water is within the above
range, the molding material is in slurry/dough state.
[0197] On the one hand, if the content of the water in the molding
material is less than 20 weight %, the molding material is scarcely
fluid because of too small water content, so this is not preferable
in terms of molding. On the other hand, if the content of the water
is more than 70 weight %, the content of the solid matter in the
molding material becomes too low because of too large water
content, so this is not preferable in terms of molding.
[0198] When the molding material is in slurry/dough state,
moldability is improved since it becomes easy to make the molding
material fill a cavity of the mold, as described later. It also
becomes possible to make the expanded molded article after molding
contain a certain amount of water, and flexibility of the expanded
molded article can be improved, as described later.
[0199] By the way, along with the main material, additives, and
water that are described above, the molding material may include
other additives. The ingredients are determined in accordance with
functions to be added to the biodegradable molded article, and
hence not particularly limited to any additive.
[0200] Furthermore, slurry/dough state in this embodiment is
categorized in accordance with fluidity of the molding material for
the sake of convenience. Thus the categorization is nothing to do
with the content of the water. For instance, assuming that a
molding material containing a certain amount of water is in slurry
state, the molding material may be transformed to dough form if a
content of a stabilizer, a water-absorbing extending agent such as
bean curd lees, or pulp, etc. are increased. Similarly, when a
binding agent such as protein is added to the molding material, the
material sometimes loses a certain degree of fluidity and may be
transformed to dough state.
[0201] The expanded molded article is molded by using the molding
material, as described above. As for the molding-method, there is a
method to use a mold including a cavity matched with a shape of a
desired molded article and consisting at least two parts. The
expanded molded article is molded by heating and pressurizing the
molding material charged into the cavity of the mold.
[0202] One of the arrangements of the mold is that at least two
metal parts capable of being detached for removing the expanded
molded article after molding article are included.
[0203] More specifically, examples of the mold are molds shown in
FIGS. 5(a), 6(a) and 7(a) such as a metal mold 20a including upper
and lower metal parts 21a and 22a, a metal mold 20b including parts
21b and 22b, and a metal mold 20c including parts 21c and 22c, and
a metal mold 20d shown in FIG. 8(a) including an upper part 21d
having the same shape as the part 21c and lower parts 23d and 24d
having the same shape as the lower part 22c being split in two.
[0204] That is to say, the mold of the present invention has to
include dividable multiple molds but the style of splitting (i.e.
the number of parts) is not particularly limited, since the style
depends on the shape of the expanded molded article.
[0205] For instance, for the bowl-shaped container 10a and the
plate-shaped container 10b, as the metal molds 20a and 20b, the
molds split in two, i.e. the upper and lower parts, are preferably
used, since these two containers are large in horizontal
dimensions. In the meantime, the metal mold 20c, which is split in
two (the upper and lower parts) as the metal molds 20a and 20b, is
possibly used for the cup-shaped container 10c. However, a
three-way split mold such as the metal mold 20d is more suitable
than the two-way types such as the metal mold 20c, since the
cup-shaped container 10c is taller than the bowl-shaped container
10a and the plate-shaped container 10b.
[0206] As shown in FIGS. 5(b), 6(b), and 7(b), cavities 25a, 25b,
and 25c matched with the shapes of desired expanded molded articles
(see FIG. 1 and FIG. 3) are formed in the metal molds 20a, 20b and
20c, when the upper parts 21a, 21b, and 21c are joined with the
lower parts 22a, 22b, and 22c. Similarly, as FIG. 8(b) shows, a
cavity 25d is formed in the metal mold 20d, when the parts 21d,
23d, and 24d are joined.
[0207] Moreover, although not illustrated, the metal molds 20a,
20b, 20c, and 20d may include a knockout pin for removing the
expanded molded article and a hinge, guide, bar, etc., for movably
connecting the parts 21a to 21d, 22a to 22c, 23d, and 24d.
[0208] Furthermore, in this embodiment, although the metal molds
20a, 20b, 20c and 20d are taken as examples of the mold, various
conventional molds can be used and an appropriately shaped mold can
be selected in accordance with a shape of the expanded molded
article.
[0209] However, as described later, the mold used in the present
invention requires heat resistance for the steam expansion molding,
and strength and abrasion resistance are also necessary.
Furthermore, microwave permeability is required if internal heating
is conducted by using microwave. Therefore, molds made of resin or
ceramic having microwave permeability, heat resistance, strength,
and abrasion resistance are preferably used when the internal heat
is generated by using microwave, but otherwise a metal mold is more
suitable because the mold itself performs as a part of an electrode
in the case of internal heating by using electric conduction or
high frequency dielectric heating that are described later.
[0210] As for the heating method for the above molding, what can be
used are:
[0211] external heating by direct heating means that the mold is
directly heated, such as direct heat, far-infrared radiation,
electric heater, IH device, etc.; or internal heating by internal
heating means that the internal molding material itself is heated,
such as electric conductive heating, high frequency dielectric
heating, microwave heating, etc.
[0212] In the case of the external heating, the mold (metal mold
20a etc.) is directly heated by the direct heating means above. On
this account, external heating is performed on the molding material
in the cavity (cavity 25a etc.) by the mold, and the expanded
molded article is molded through the steam expansion of the molding
material.
[0213] In the meantime, a mold having the same shape as that for
the external heating can be used for the internal heating. So if
the metal mold 20a is taken as the example, as FIG. 9 schematically
shows, when the parts 21a and 22a are paired, the mold is possibly
arranged so that:
[0214] each of the parts 21a and 22a is connected to an individual
electrode 26 and 26, respectively;
[0215] an insulator 27 is provided at contacts between the parts
21a and 22a; and
[0216] the electrodes 26 and 26 are connected to a power supply
28.
[0217] On this account, it becomes possible to internally heat the
molding material charged in the cavity 25a. By the way, apart from
the power supply 28, the electrode 26 is connected to unillustrated
switch, control circuit, etc.
[0218] It is also possible to apply the arrangement in which the
electrode 26 is connected either to the part 21a or the part 22a,
for the external heating. That is to say, the arrangement including
the direct heating means and the electrode 26 is possibly used to
heat the molding material directly, in the case of external heating
too. Thus the arrangement shown in FIG. 9, in which the electrode
26 is provided, is possibly used for both internal and external
heating.
[0219] Although a heating temperature of the heat molding is not
particularly limited, it is preferred that the mold is heated
within the range between 140.degree. C. and 240.degree. C., in the
case of external heating. When the heating temperature of the mold
falls within the range above, the slurry/dough molding material in
the cavity (cavity 25a etc.) is properly heated and the molded
article as solid matter can be acquired. Also, the water contained
in the molding material surely be vaporized and bubbles are formed
because the range of the temperature is more than 100.degree. C.
i.e. the boiling point of water. Thus the expanded molded article
can easily be acquired, since the acquired molded article surely
achieves the steam expansion.
[0220] In the meantime, a heating temperature in the case of
internal heating is not particularly limited as long as the heating
temperature is in a range at which the steam expansion happens to
the molding material, since the molding material itself in the
cavity (cavity 25a etc.) is internally heated by applying low
frequency alternating voltage or high frequency electric field to
the electrode 26, and the heating temperature depends on conditions
related to the internal heating.
[0221] More specifically, characteristics of the electrode 26, a
level of the low frequency alternating voltage, and strength of the
high frequency electric field are deeply related to the
determination of the conditions. Simultaneously, other major
conditions include the conductivity and the dielectric loss of the
molding material that are described above, since the heating
condition depends on the conductivity of the molding material when
the molding material is heated and molded through electric heating,
and the heat condition depends on the dielectric loss of the
molding material, when the molding material is molded through high
frequency dielectric heating.
[0222] Practically, the range of the conditions above are not
specifically limited, as long as the temperature in the cavity is
within the range of the temperature in the case of external
heating.
[0223] The heating time should be appropriately set depending on
the heating temperature and the shape, thickness, etc. of the
expanded molded article. It is however preferable if the water
content of the expanded molded article after molding falls at least
within a specified range. In other words, it is favorable to set
the heating time so that the water in the molding material is not
almost completely evaporated during the heating time.
[0224] When the amount of water in the molding material is less
than the specified range of water content (described later) due to
long heating time, undesirably the quality of the expanded molded
article is reduced, since the expanded molded article is expanded
too much as well as cannot contain the specified amount of water,
and as a result the expanded molded article becomes hard and
brittle.
[0225] The heating time is not specifically limited. For instance,
while it i-s possible to mold the expanded molded article in a much
shorter time through the high frequency dielectric heating
comparing to a conventional external heating, the heating time
tends to be longer when a thick expanded molded article is molded.
Thus basically the heating time is appropriately determined in
accordance with which heating method is used and how the expanded
molded article is shaped, although generally it is preferably if
the heating time falls within the range of 10 second to 5
minutes.
[0226] Pressure applied in the process of heat molding is not
particularly limited as well. However, generally, it is preferred
if pressure is within the range between 5 kg/cm.sup.2 and 50
kg/m.sup.2. Of course, this molding pressure is variable with
reference to the conditions.
[0227] By heating and pressurizing the molding material in the
cavities 25a, 25b, 25c and 25d with the metal molds 20a, 20b, 20c,
and 20d, respectively, as FIGS. 10(a), (b), and (c) indicates, main
body 11a of the bowl-shaped container, the main body 11b of the
plate-shaped container, and the main body 11c of the cup-shaped
container are acquired as the expanded molded articles. A final
content of water in the expanded molded articles after molding
falls within the range between 3 weight % and 20 weight %, more
preferably within the range between 3 weight % and 15 weight %.
[0228] On the one hand, it is undesirable that the final content of
water is less than 3 weight %, because excessively low water
content renders the expanded molded article hard and brittle so
that the flexibility thereof is reduced. On the other hand, it is
also undesirable that the water content is more than 20 weight %,
because excessively high water content renders the expanded molded
article unnecessarily moist so that the weight thereof is gained
and attaching and adhering the coating film 12 become
difficult.
[0229] As described in the description of the moisture retaining
agent, the use of the molded article is seriously limited due to
the hardness and brittleness of the same, when starch is simply
transformed to .alpha.-starch. Thus, in the present invention, it
is possible to set water content of the expanded molded article
within the range as above by simply molding the same, since enough
water is contained in the molding material in slurry/dough state.
By the way, sometimes the water content goes a little out of bounds
depending on molding conditions and other environmental conditions.
In this case, the water content is adjustable by leaving the
expanded molded article in a warehouse under a fixed level of
humidity for a certain period of time, spraying water to the same,
and inversely leaving the same in a dry warehouse for a fixed
period of time.
[0230] In the biodegradable molded article in accordance with the
present invention, the coating film 12 made of biodegradable
plastics is attached on the surface of the expanded molded article
(the main body 11a, etc.). Attaching the coating film 12 having at
least hydrophobicity can impart the expanded molded article at
least water resistance. Also, it is preferable if the coating film
12 further imparts gas impermeability, heat insulation, abrasion
resistance, improved strength, and flexibility to the expanded
molded article.
[0231] More specifically, when the biodegradable molded article in
accordance with the present invention is used for a highly hermetic
preserving container, a gas impermeable coating film 12 is highly
preferable, since oxidation of, and moisture absorption by, an
article in the container must be avoided.
[0232] Moreover, when the biodegradable molded article of the
present invention is used for a container of noodles, a coating
film 12 with high heat resistance is preferably arranged, since
deformation and melting of the biodegradable molded article because
of the heat of an article inside the container must be avoided.
More specifically, the softening point of the coating film 12 is
preferably not less than 130.degree. C., and more preferably not
less than 150.degree. C. Also, the melting point of the coating
film 12 is preferably not less than 170.degree. C., and more
preferably not less than 200.degree. C. Furthermore, it is
especially preferable the softening point thereof is not less than
130.degree. C. and at the same time the melting point is not less
than 170.degree. C. It is the most preferable that the softening
point thereof is not less than 150.degree. C. and at the same time
the melting point is not less than 200.degree. C. On this account,
deformation and melting of the biodegradable molded article caused
by the heat of an article inside the container can be avoided.
[0233] The material of the coating film 12 is not specifically
limited as long as materials that are able to impart water
resistance and preferably gas impermeability to the expanded molded
article after the film 12 is attached on the surface thereof.
[0234] More specifically, what are used as the materials are those
conventionally known as biodegradable plastics such as
3-hydroxybutyric acid-3-hydroxyvaleric acid copolymer,
poly-p-hydroxybenzaldehyde (PHB), polybutylene succinate (PBS),
polycaprolactone (PLC), acetylcellulose (PH) polymer, polyethylene
succinate (PESu), polyester amide, modified polyester, polylactic
acid (PLA), Mater-Bi (trademark of Novamont, Italy: having starch
as the major ingredient and polyvinyl alcohol resin and aliphatic
polyester resin having biodegradability as the minor ingredients),
cellulose, and chitosan composite, etc. Either one of the materials
above or any mixture of more than one material may be used. Also,
accessory materials such as a biodegradable plasticizer, filler,
etc. may be added to the biodegradable plastics.
[0235] It is preferable that the material of the coating film 12 is
modified polyester because of its excellent gas impermeability,
moisture permeability resistance, and heat resistance. Also, it is
preferable the coating film 12 is biaxially stretched biodegradable
film because of its excellent strength, heat resistance, and gas
impermeability. Therefore, biaxially stretched modified polyester
is the most preferable for the coating film 12.
[0236] Furthermore, the coating film 12 may be produced by adding
starch to the materials (biodegradable plastics) above. In this
case, although a mixing ratio between the biodegradable plastic and
starch is not particularly limited as long as qualities of the
coating film 12 such as hydrophobicity are not impaired; for
instance, what is preferable is more or less 1:1 mixing ratio by
weight.
[0237] In addition, additives may be added to the coating film 12.
More specifically, although the additives are not particularly
limited to specific types, what are able to be added are coloring
agents, additives capable of improving water resistance, gas
impermeability, etc., an additive improving qualities in relation
to the softening when the coating film 12 is attached, etc.
[0238] Although the thickness of the coating film 12 (thickness of
the film) is not particularly limited, it is preferred if the
thickness of the film or sheet before attached on the expanded
molded article falls within the range between 0.01 mm and a few
millimeters.
[0239] As described later, the thickness of the coating film 12
becomes below the range above after attached on the surface of the
expanded molded article, since the coating film 12 is heated and
softened when attached. The thickness of the coating film 12 after
attached is set at an appropriate thickness capable of having water
resistance, gas impermeability, etc. in accordance with the type of
biodegradable plastics used as the materials, hence not
particularly limited. However, preferably the thickness is not more
than 80 .mu.m, and more preferably not more than 50 .mu.m. Although
the lower limit is also not particularly limited as long as water
resistance and gas impermeability, etc. are acquired, preferably
the thickness is not less than 5 .mu.m in general.
[0240] The expanded molded article preferably accounts for not less
than 60 weight % of the total weight of the biodegradable molded
article in accordance with the present invention. In other words,
the biodegradable plastics preferably account for at least less
than 40 weight % of the total weight of the biodegradable molded
article in accordance with the present invention.
[0241] As described above, the speed of biodegradation of
biodegradable plastics is slower than that of starch. More
specifically, although the speed of biodegradation of the
biodegradable plastics having the same weight greatly varies
depending on the type and shape of the biodegradable plastics,
generally, the speed of biodegradation of the biodegradable
plastics can be considered within the range of some tenths to
around a fourteenth, if that of the expanded molded article mainly
made of starch is set as one.
[0242] Therefore, if the amount of biodegradable plastics included
in the biodegradable molded article is too much, biodegradability
of the biodegradable molded article on the whole becomes poor, even
if the biodegradable plastics have biodegradability. Thus it is
highly preferable to stipulate the maximum amount of the
biodegradable plastics accounting for in the total weight.
[0243] So, in the biodegradable molded article in accordance with
the present invention, biodegradable plastics are always used for
the coating film 12 and may be used as an adhesive (adhesive layer
13) that is described later. Thus to stipulate the maximum amount
of the biodegradable plastics is equivalent to stipulate the
maximum amount of the coating film 12 and adhesive layer 13.
[0244] However, the adhesive 13 does not always have to be used
(for instance, the bowl-shaped container 10a shown in FIG. 1(a)),
and moreover, as described later, non-plastic natural materials
such as starch are possibly used as the adhesive layer 13. So in
the biodegradable molded article in accordance with the present
invention, the amount of the biodegradable plastics is stipulated
by stipulating the amount of the expanded molded article mainly
made of starch.
[0245] Since the coating film 12 and the adhesive layer 13 are
shaped as film, the biodegradable plastics are easily biodegraded
in the biodegradable molded article in accordance with the present
invention. Taking this into account, as described above, the
maximum weight of the biodegradable plastic (coating film 12 and
adhesive layer 13) in the biodegradable molded article of the
present invention is stipulated as less than 40 weight %, when the
weight of the expanded molded article is set as not less than 60
weight %. As a result, biodegradability of the biodegradable
plastics and that of the expanded molded article are well-balanced,
so biodegradability of the biodegradable molded article is further
improved.
[0246] Very good biodegradability can be acquired on the whole,
especially since the expanded molded article, having good
biodegradability for its expanded structure, lessen the content of
the coating film 12 and the adhesive layer 13. Thus when, for
instance, the biodegradable molded article of the present invention
is used as a food tray, the food tray can be composted together
with residues of food without causing any problem.
[0247] The weight of the expanded molded article preferably
accounts for not less than 60 weight % of the total weight of the
biodegradable molded article of the present invention. That is to
say, the biodegradable plastics preferably account for at least
less than 40 weight % of the total weight of the biodegradable
molded article in accordance with the present invention.
[0248] In the present invention, there are two arrangements in
which the coating film 12 is attached in accordance with a
difference of the manufacturing method of the biodegradable molded
article. In the first arrangement, the coating film 12 is directly
attached on the expanded molded article (for instance, see FIG.
1(a)), and in the second arrangement the film is attached with the
adhesive layer 13 in between (for instance, see FIG. 1(b)). In the
latter arrangement, an adhesive is required for attaching the
coating film 12.
[0249] Although the adhesive is not particularly limited as long as
having biodegradability and also capable of attaching the coating
film 12 to the expanded molded article, specific examples of the
adhesive are such as natural glues and binding agents mainly made
of starch, protein, or these natural substances mixed with PVA
(polyvinyl alcohol), aqueous adhesives, protein
refractory/insoluble in water and congealed due to thermal
metamorphism, biodegradable plastics (generally synthetic product)
having a low melting point and being able to be melted below the
melting point of the coating film 12, adhesives having a low
melting point such as a mixture of any aforementioned substances,
and thermosetting adhesives having fluidity at room
temperature.
[0250] The aqueous adhesives have the advantage of very high level
of biodegradability and safety, since they are mainly naturally
occurring substances and basically made of starch, etc. as in the
case of the expanded molded article. The use of the aqueous
adhesives is not particularly limited. However, generally the
coating film 12 is attached after the adhesive is put on the
surface of the expanded molded article with a brush or inversely
the adhesive is put on the surface of the coating film 12 before
the film 12 is attached on the surface of the expanded molded
article.
[0251] The biodegradable plastics (generally synthetic product)
having a low melting point and being able to be melted below the
melting point of the coating film 12, and a mixture thereof can
also be used as the adhesive with low melting point. In other
words, among the biodegradable plastics taken as the concrete
examples of the coating film 12, a plastic having a lower melting
point than that of the biodegradable plastic used for the outermost
layer of the coating film 12, more specifically, melted either at
temperature lower than the softening point of the coating film 12
or within the range between the softening point of the coating film
12 and the melting point of the coating film 12, can be selected
accordingly.
[0252] For instance, when a film mainly made of polylactic acid,
modified polyester and the like are used as the coating film 12,
since the melting points of these substances are within the range
between 80.degree. C. and 100.degree. C., polycaprolactone whose
melting point is within the range between 60.degree. C. and
70.degree. C. is preferably used as the adhesive with a low melting
point.
[0253] The biodegradable plastics having a low melting point is
generally used in film-shape. That is, the biodegradable plastics
having a low melting point is highly suitable for use as an
adhesive film. As described later, the coating film 12 is heated
pressure-pressed and attached on the expanded molded article by
using the attaching mold. So if the adhesive film made of the
biodegradable plastics having a low melting point is arranged
between the coating film 12 and the expanded molded article in the
step above, the adhesive works well, since the biodegradable
plastics having a low melting point is melted by the heat and
pressure pressing.
[0254] As the adhesive used in the present invention including the
aqueous adhesive and the biodegradable plastics having a low
melting point, adhesives not including a volatile organic solvent
are suitable. The organic solvent is unfavorable because, if the
same is used, a device to prevent volatilization and diffusion,
etc. of the organic solvent has to be provided and thus the
manufacturing facilities have to be upsized.
[0255] Now, a manufacturing method of the biodegradable molded
article in accordance with the present invention is described.
[0256] There are two methods of manufacturing the biodegradable
molded article in accordance with the present invention. The first
one is a method that after a molding material is molded to be a
specifically shaped expanded molded article through a steam
expansion, a coating film is attached (termed as after attaching
method). The second one is a method that molding a molding material
through steam expansion and attaching a coating film are done at
the same time (termed as simultaneous attaching method).
[0257] First, the after attaching method is described. This method
at least includes two steps of:
[0258] molding a specifically shaped expanded molded article (such
as the main bodies 11a, 11b, 11c, etc.) from the molding material
through the steam expansion; and
[0259] attaching to compress-bond the coating film 12 on the
surface of the expanded molded article after the coating film 12 is
heated and softened.
[0260] The biodegradable molded articles acquired by using this
method are arranged to have the adhesive layer 13 between the
coating film 12 and the expanded molded article (the main bodies
11a, 11b, and 11c), as shown in FIGS. 1(b), 2(b), 3(b), etc.
[0261] On this account, the biodegradable molded article with a
water content that gives enough strength to the same and arranged
so that the coating film 12 is steadily attached on the main body
(expanded molded article) containing a stable water content can be
acquired.
[0262] So, when the coating film 12 is attached, an attaching mold,
having substantially identical shape as that of a mold (metal mold
20a, etc.) for molding the expanded molded article is used. For
instance, as shown in FIG. 11, a mold 30 having substantially
identical shape as that of the metal mold 20a is used, when the
coating film 12 is attached on the main body 11a to produce the
bowl-shaped container 10a.
[0263] The shape of the attaching mold does not have to be
completely matched with the outside shape of the expanded molded
article, as long as being capable of guiding the coating film 12 to
be attached on the surface of the expanded molded article
adequately. So, generally a copy of the mold of the expanded molded
article is used. On this account, it becomes possible to produce
the attaching mold at low cost and to attach the coating film 12
certainly and easily, even on a complicatedly shaped expanded
molded article. As a result, this allows to manufacture the
biodegradable molded article in simpler procedure.
[0264] The shape of the attaching mold is not particularly limited
as long as the attaching mold has substantially identically shaped
cavity as that of the mold. However, if two layers of films, that
is, the coating film 12 and the adhesive film, are attached, the
heating means is provided as in the case of the mold, to melt the
adhesive film with certainty. Thus, for instance, it is possible to
use the metal mold 20a without any modification as the attaching
mold, shown in FIGS. 5(a), 5(b), or 9, to attaching the film 12,
when the bowl-shaped container 10a is manufactured.
[0265] Provided that a concrete example of the attaching method is
described, first of all, as shown in FIG. 11, the main body 11a of
the bowl-shaped container, which is an expanded molded article, is
arranged with respect to the mold 30, and also the coating film 12
is arranged on a part of the mold 30 corresponding to the surface
of the main body 11a where the coating film 12 is to be
attached.
[0266] FIG. 11 shows an example to attach the coating film 12 to
the whole expanded molded article. Above a part 32, which is a
below part of the mold 30, the coating film 12 is arranged. The
main body 11a is provided above the film 12, then above the main
body 11a the coating film 12 is arranged again, and further above,
a part 31, which is an upper part of the mold 30, is arranged. In
other words, the main body 11a is sandwiched between two coating
films 12.
[0267] Furthermore, when the-biodegradable plastics having a low
melting point is adopted as the adhesive, as FIG. 11 shows, the
adhesive film 13a made thereof is provided between the coating film
12 and the main body 11a. That is to say, above the lower part 32,
the coating film 12, the adhesive film 13a, the main body 11a
(expanded molded article), the adhesive film 13a, and the coating
film 12, are arranged in that order. By the way, in FIG. 11, spaces
are left between the films and between the molded article and the
film, for convenience of description.
[0268] After the step above, temperatures of the parts 31 and 32
are preset between not less than the softening point of the coating
film 12 and less than the melting point thereof in advance, and
then the coating film 12 is attached on the surface of the main
body 11a by pressing the upper part 31 and the lower part 32 from
both above and below and exerting appropriate pressure on the parts
31 and 32. At this moment, since the adhesive film 13a is melted at
a temperature not higher than the softening point of the coating
film 12, the melted adhesive film 13a is fused and adhered to the
surface of the main body 11a and becomes the adhesive layer 13,
then on the same, the coating film 12 is attached.
[0269] By the way, if a biodegradable plastic, melted at a
temperature between the softening point of the coating film 12 and
less than the melting point thereof, is adopted as the adhesive
film 13a, heating temperature of the parts 31 and 32 also have to
be set between the softening point of the coating film 12 and the
melting point thereof.
[0270] The exerted pressure when the coating film 12 is attached is
not specifically limited if it is set depending on type of adhesive
used, but what is preferable is such relatively high pressure that
the thickness of the expanded molded article is reduced. On this
account, it becomes possible to make adhesion of the coating film
12 better thanks to the adhesive layer 13 and also to make the
thickness of the biodegradable molded article (bowl-shaped
container 10a in FIG. 1(b)), which is the final molded article,
thinner. Therefore, it is possible to improve stackability
(easiness to stack cups and the number of cups when stacked to a
specified height) of the biodegradable molded article.
[0271] When the after attaching method is adopted in the
manufacturing method of the present invention, as described above,
it is especially preferable that the adhesive film 13a is used for
the adhesive to attach the coating film 12. When this method is
used, it becomes possible to omit the step to apply the adhesive on
the surface of the expanded molded article and the manufacturing
method of the biodegradable molded article is further simplified,
since providing the adhesive film 13a before attaching the coating
film 12 is all that is needed in this method.
[0272] That is to say, the expanded molded article (main body 11a,
etc.), which is the main body of the biodegradable molded article
of the present invention, is clearly hydrophilic, because the
molded article is mainly made of starch and contains a certain
amount of water. Meanwhile, as already described, the coating film
12 is hydrophobic. Thus it is highly likely that the coating film
12 is not sufficiently attached to the expanded molded article,
when the film 12 is simply attached by using the after attaching
method.
[0273] On the contrary, if the coating film 12 is attached by using
the adhesive film 13a, as FIG. 12(a) shows, the coating film 12 is
certainly attached to the hydrophilic expanded molded article 11
with the adhesive layer 13 in between. As a result, it becomes
possible to stabilize the attaching condition of the coating film
12 in the biodegradable molded article in accordance with the
present invention, and also to further improve water resistance and
gas impermeability of the same.
[0274] By the way, in the after attaching method, it is possible to
use as the coating film 12, what are preshaped substantially
identical with outside shape of the resulting biodegradable molded
article such as a molding film, a film part, an outside shape film,
etc. that are used in the simultaneous attaching method descried
later.
[0275] In this manner, the coating film is not ripped in the step
of attaching, if the coating film is molded in a shape
substantially identical with the outside shape of the biodegradable
molded article in advance, hence this enables manufacture of the
biodegradable molded article with deep draw depth properly. The
molding film, the film part, and the outside shape film are
described in detail in the description of the simultaneous
attaching method.
[0276] Now, the simultaneous attaching method is described. As
described above, this method includes at least a simultaneous
molding and attaching step in which the molding material is molded
through the steam expansion and at the same time the coating film
12 is attached. The biodegradable molded article acquired by using
this method is arranged so that the coating film 12 is formed
directly on the surface of the expanded molded article (main bodies
11a, 11b, and 11c), as shown in FIGS. 1(a), 2(a), 3(a), etc.
Comparing to the aforementioned after attaching method, this
simultaneous attaching method has advantages as follows.
[0277] Firstly, the number of the steps can be reduced. That is, it
is possible to reduce the steps in comparison to the after
attaching method requiring at least two steps to attach the coating
film 12, since the simultaneous attaching method is capable of
attaching the coating film 12 virtually in one step. Moreover, it
is possible to reduce the manufacturing time thanks to the
capability of attaching in one step. As a result, it becomes
possible to manufacture the biodegradable molded article of the
present invention more efficiently.
[0278] Secondly, the attaching mold becomes unnecessary. That is to
say, in the simultaneous attaching method, attaching the coating
film 12 is done concurrently with molding the expanded molded
article (main body 11a, etc.) by using the mold (metal mold 20a,
etc.). Thus the attaching mold (mold 30 shown in FIG. 11, etc.) for
attaching the coating film 12 in the after attaching method is
unnecessary. On this account, it becomes possible to cut costs for
the manufacturing facilities and also to downsize the facilities,
since the attaching facilities including the attaching mold becomes
unnecessary.
[0279] Thirdly, it becomes unnecessary to use adhesives. That is,
in the simultaneous attaching method, since the coating film 12 is
attached concurrently with molding the expanded molded article, the
coating film 12 is substantially bonded to the surface of the
expanded molded article (main body 11a, etc.) Thus it becomes
possible to cut costs of the material of the adhesive and also to
further improve biodegradability of the biodegradable molded
article, since the omission of the adhesive induces a higher
content of starch in the biodegradable molded article.
[0280] Fourthly, the attaching condition of the coating film 12 is
as stable as that of the coating film 12 using the adhesive film
13a in the after attaching method, since the coating film 12 is
substantially bonded to the expanded molded article.
[0281] As already described, while the expanded molded article such
as main body 11a is hydrophilic, the coating film 12 is
hydrophobic. Thus it is highly likely that the coating film 12 is
not sufficiently attached to the expanded molded article, when the
film 12 is simply attached on the expanded molded article.
[0282] However, in the simultaneous attaching method, the coating
film 12 is attached concurrently with the steam expansion molding
of the molding material, at a temperature at least between not less
than the softening point of the biodegradable plastic that is the
main ingredient of the coating film 12 and less than the melting
point of the biodegradable plastic. Hence the heated and
pressurized coating film 12 faces the expanded molded article in
the step of expansion. So the softened coating film 12 receives
pressure of the mold from outside and that of the expanded molded
article in the step of expansion from inside so as to closely
contact with the expanded molded article. As a result, the coating
film 12 is fused and attached on the surface of the expanded molded
article.
[0283] On this account, as shown in FIG. 12(b), the boundary
surface 15 of a layer of the coating film 12 and the surface of the
expanded molded article 11 in a cross section of the acquired
biodegradable molded article does not become a smooth surface
created by the simple attaching (see the condition in the after
attaching method in FIG. 12(a)) but becomes, for instance, an
irregular surface with bumps and dips, so the coating film 12 is
adequately adhered to the expanded molded article 11. Consequently,
the attaching condition of the coating film 12 becomes highly
strong and as stable as the condition of the attaching by the
adhesive layer 13. Thus it is possible to further improve the water
resistance and the gas impermeability of the acquired biodegradable
molded article.
[0284] By the way, although the boundary surface 15 of the layer of
the coating film 12 and the surface of the expanded molded article
11 is schematically described as, for instance, an irregular
surface with bumps and dips in FIG. 12(b), of course the state of
the surface 15 is not limited to this, and the surface 15 possibly
takes various forms depending on the ingredients of the coating
film 12 and the expanded molded article 11, or conditions of the
simultaneous attaching method, etc. Therefore, in the present
invention, the attaching condition of the layer of the coating film
12 and the expanded molded article 11 of the biodegradable molded
article acquired by the simultaneous attaching method is not
particularly limited as long as these two are almost completely
adhered.
[0285] Taking these four advantages into account, adopting the
simultaneous attaching method makes it possible to provide the
biodegradable molded article at lower cost, since the biodegradable
molded article of the present invention, having the same quality as
the one manufactured by the after attaching method, can be
manufactured more efficiently and at lower cost than using the
after attaching method. Hence this makes it easier to utilize the
biodegradable molded article of the present invention for the
disposal use.
[0286] However, it is sometimes difficult to apply the simultaneous
attaching method, depending on the type of the coating film 12, the
composition of the molding material, etc. In this case, the after
attaching method is very preferably used. In other words, each of
the after attaching method and the simultaneous attaching method
has advantages thereof, thus the methods are appropriately selected
in accordance with the situation. So both of the methods have
benefits and advantages as the manufacturing methods of the
biodegradable molded article in accordance with the present
invention.
[0287] Now, the simultaneous attaching method is a method that the
coating film 12 is softened at the temperature within the range
between less than the melting point and not less than the softening
point at the same time with the steam expansion molding of the
molding material, and then the coating film 12 is attached
concurrently with molding the expanded molded article. Thus it is
required to set the conditions of the heating method with respect
to the coating film 12 to be attached appropriately.
[0288] That is to say, since heating at a temperature not less than
100.degree. C. is simply required to mold the molding material
through the steam expansion, a biodegradable plastic whose melting
point is not less 100.degree. C. should be selected as the main
ingredient of the coating film 12, if the external heating is
adopted as the heating method. If the coating film 12 is mainly
made of the biodegradable plastic whose melting point is not more
than 100.degree. C., the coating film 12 is completely melted at a
temperature for sufficient steam expansion molding of the molding
material. Hence it becomes impossible for the coating film 12 to be
film-shaped or sheet-shaped, so a uniform layer of the coating film
12 without any gaps and holes cannot be formed on the surface of
the expanded molded article.
[0289] In the meantime, it is preferable to use the coating film 12
mainly made of the biodegradable plastic whose melting point is not
less than 100.degree. C., even in the case of using the internal
heating as the heating method. However, it is possible to use the
one having relatively low melting point, compared to the external
heating.
[0290] The molding material itself is heated in the case of the
internal heating. Thus the coating film 12 is heated by the molding
material that is in the step of the expansion molding and under
high temperature conditions, and then attached on the surface of
the expanded molded article. Hence using the internal heating
permits the use of the coating film 12 mainly made of a
biodegradable plastic having relatively low melting point, since
the coating film 12 is not directly heated by the mold.
[0291] Dielectric heating is particularly suitable for the internal
heating. By the dielectric heating, the molding material is rapidly
heated in an early stage of the expansion molding and the whole of
the molding material is expanded altogether. Because of this,
pressure to press the coating film 12 against the mold is generated
strongly as well as evenly. Also, controlling the temperature of
the mold and the heat generation of the mold allows to raise the
temperature of an adhesive surface (surface to be bonded with the
coating film) of the expanded molded article to near the melting
point, while keeping the temperature of a mold contact surface
(surface to contact with the mold) below the melting point. As a
result of these features, it becomes possible to acquire a
biodegradable molded article in which the expanded molded article
and the coating film 12 are intensely adhered.
[0292] The dielectric heating is a method to heat an object by
means of dielectric loss of the object. There are different types
of dielectric heating, such as:
[0293] high frequency dielectric heating in which high frequency
wave (HF; 3 to 30 MHz) is fed to an object (dielectric) to
dielectrically heat the same; and microwave heating in which
microwave (HF; 1 to 100 GHz) is fed to an object (dielectric) to
dielectrically heat the same.
[0294] Of the methods above, the high frequency dielectric heating
is more suitable because the dielectric heating can be done by
using a metal mold as an electrode and heating of the molding
material can be easily controlled under precise control by an
output device (high frequency generator).
[0295] Meanwhile, in the case of the external heating, the coating
film 12 is heated to very high temperature to conduct the expansion
molding of the molding material sufficiently, because, in this
method, after the coating film 12 is directly heated by the mold,
the molding material located further inside is heated. Hence it is
preferred if the coating film 12 has a higher melting point, and
the heating temperature of the mold should be adjusted more
precisely, in consideration of the melting point and softening
point of the coating film 12.
[0296] Therefore, in the case of the simultaneous attaching method,
the internal heating has higher versatility as the heating method
of the simultaneous attaching method, in terms of easier attaching
and wider choice of the coating film 12, etc.
[0297] However, the external heating has advantages in that the
softening of the coating film 12 and the adhesion thereof to the
surface of the expanded molded article are easily controllable,
since the coating film 12 is directly heated by the mold. Also, in
case of the coating film 12 having a high softening point, when the
molding material is heated enough to melt the coating film 12 by
using internal heating, the expanded molded article might be
degraded due to over expansion molding and so on, depending on the
kind of molding materials. Hence external heating may be preferred
in the case. In this manner, in the case of the simultaneous
attaching method, the external heating and the internal heating
have each own advantage as the heating method, thus the heating
method is not particularly limited but appropriately chosen to use
either of the external heating, the internal heating, or both.
[0298] It is possible to classify the simultaneous attaching
method, for instance, under seven types (eight types if a variation
is included) as below, depending on the use of the coating film 12
when attached.
[0299] [Method 1]
[0300] As in the case of the attaching step of the coating film 12
in the after attaching method above, the method 1 is a method that
the molding material is inserted between the coating films 12 which
are not formed and are still sheet-shaped, then the coating film 12
is attached to the expanded molded article which is simultaneously
molded though the steam expansion molding. This method is
particularly preferred for molding a horizontally long and wide
biodegradable molded article such as the plate-shaped container 10b
shown in FIG. 2(a), in correspondence with a sheet-shaped coating
film 12.
[0301] To describe the method 1 concretely, as FIG. 13 shows, the
metal mold 20b shown in FIGS. 6(a), and 6(b) is arranged so that
two sheet-shaped coating films 12 are provided between the upper
and lower parts 21b and 22b, and further the slurry/dough molding
material 14 is provided between the coating films 12 and 12. At
this moment, the metal mold 20b is heated to less than the melting
point of the biodegradable plastic that is the main ingredient of
the coating film 12. Then the upper and lower parts 21b and 22b are
paired up and heated and pressurized to be molded, by the external
heating and/or the internal heating. It is possible to acquire the
plate-shaped container 10b (see FIG. 2(a)) as the biodegradable
molded article of the present invention only by this step.
[0302] [Method 2]
[0303] Method 2 is similar to the method 1, except that the coating
film 12 is preformed to be substantially matched with an outside
shape of the biodegradable molded article in advance. This method
can be preferably used for a biodegradable molded article with a
relatively deep draw depth, i.e. vertically tall shape, such as the
bowl-shaped container 10a shown in FIG. 1(a).
[0304] Some types of the coating films 12 cannot be stretched
extensively, depending on the type of the main ingredient thereof,
i.e. the biodegradable plastic. Hence if method 1 is employed to
mold the biodegradable molded article with the deep draw depth such
as the bowl-shaped container 10a shown in FIG. 1(a), the coating
film 12 might be ripped and not be able to cover the expanded
molded article sufficiently. So a molding film, which is the
coating film 12 being preformed similar to the desired shape in
advance, is prepared. On this account, the coating film 12 can
cover expanded molded articles having more complicated shape and
the deep draw depth certainly and efficiently.
[0305] Although the forming method of the coating film 12 is not
particularly limited and conventional methods to form sheet films
are used, various forming methods, for instance, vacuum forming,
injection molding, blow molding, etc. are preferably used. By the
way, it is not necessary to shape the coating film 12 precisely
identical to the molded biodegradable molded article, as long as
the shape of these two are substantially similar to each other. It
is sufficient that the coating film 12 is roughly identical with
the shape of the biodegradable molded article after molding, i.e.
the shape of the mold, inasmuch as the coating film 12 has some
flexibility.
[0306] To describe the method 2 more specifically, as shown in FIG.
14, the metal mold 20a shown in FIGS. 5(a) and 5(b) is arranged so
that two molding films 12a shaped substantially similar to the
bowl-shaped container 10a are provided between the upper and lower
parts 21a and 22a, and further the slurry/dough molding material 14
is provided between the molding films 12a and 12a. At this moment,
the metal mold 20a is heated at less than the melting point of the
biodegradable plastic that is the main ingredient of the forming
film 12a (coating film 12). Then the upper and lower parts 21a and
22a are paired up and heated and pressurized to be molded, by the
external heating or the internal heating. It is possible to acquire
the bowl-shaped container 10a (see FIG. 1(a)) as the biodegradable
molded article of the present invention by this single step.
[0307] [Method 3]
[0308] Method 3 is identical with method 1, except that the coating
film 12 is preformed like a bag, wherein the molding material is to
be placed. This method is also particularly preferred for molding a
horizontally long and wide biodegradable molded article such as the
plate-shaped container 10b shown in FIG. 2(a), in correspondence
with the sheet-shaped coating film 12.
[0309] In the case of this method, as a bag film, the coating film
12 is formed into a bag to accommodate the molding material inside.
If the molding material is placed inside this bag film, the molding
material can be regarded as substantially wrapped by the bag film.
So it becomes possible to store large amounts of the molding
material prepared and pre-portioned in each bag film for a certain
period of time. Furthermore, preparation of the molding is
completed only by putting the wrapped material in the mold, at the
time of manufacturing the biodegradable molded article. This makes
it possible to further simplify the manufacturing process.
[0310] The method to form the coating film 12 into the bag film is
not particularly limited to any method, so conventional methods to
form sheet or film-shaped plastics into bag-shaped ones can be
preferably used. Such example includes pillow type packaging. The
storing method of wrapped material wherein the molding material is
portioned in the bag film is not particularly limited to any method
as well, if conventional storing methods to prevent starch from
going rotten are used.
[0311] By the way, in the present invention, the bag film 12b
storing the molding material inside is termed "composition for
expansion molding". As described above, the compositions for
expansion molding (abbreviated as molding composition) are capable
of being prepared as large in numbers in advance and being stored
for a certain period of time, and at the same time the
biodegradable molded article on which the coating film is attached
can be easily manufactured by simply putting the molding
compositions in the molds. So the molding composition is suitable
for manufacturing the biodegradable molded article in an easy and
simple step.
[0312] To describe the method 3 more specifically, as shown in FIG.
15, the coating film 12 is preformed into a bag shape to make the
bag film 12b, and then molding compositions 40b is prepared in
advance by portioning a certain amount of the molding material 14
in each of the bag films 12b. These molding compositions 40b are
stored in a specified storage etc. Following the steps above, in
the metal mold 20b shown in FIGS. 6(a) and 6(b), the molding
compositions 40b taken out from the storage is placed on the lower
part 22b, and the molding preparation is now done.
[0313] At this moment, the metal mold 20b is heated up to a
temperature of less than melting point of the biodegradable plastic
that is the main ingredient of the coating film 12 (bag film 12b).
Then the upper and lower parts 21b and 22b are paired up and heated
and pressurized to be molded, by the external heating or the
internal heating. It is possible to acquire the plate-shaped
container 10b (see FIG. 2(a)) as the biodegradable molded article
of the present invention by this single step.
[0314] [Method 4]
[0315] Method 4 is a method that integrates methods 1, 2, and 3,
wherein the coating film 12 is preformed substantially similar to a
bag shape as well as an outside shape of the biodegradable molded
article. In other words, the bag film 12d of the method 3 is
further modified to a molding bag film with substantially identical
shape as that of the biodegradable molded article. This method is
also preferably used for a biodegradable molded article with
relatively deep draw depth, i.e. vertically tall shape, such as the
bowl-shaped container 10a shown in FIG. 1(a).
[0316] The molding bag film may be formed so that the coating film
12 is modified to be a bag-shaped film in advance and then formed
to be substantially identical with the outside shape of the
biodegradable molded article, or modified to the molding bag film
after being substantially molded to the outside shape of the molded
article. The forming method and the method to make the bag film are
not particularly limited and conventional methods can suitably be
used, as stated above.
[0317] To describe method 4 more specifically, as shown in FIG. 16,
the coating film 12 is preformed to the molding bag film 12c, and
then the molding compositions 40c are prepared by portioning a
certain amount of the molding material into each of the molding bag
films 12c. It is possible to store these molding compositions 40c
in a specified storage etc. Following the steps above, in the metal
mold 20a shown in FIGS. 5(a) and 5(b), the molding compositions 40c
taken out from the storage is placed on the lower part 22a, and the
molding preparation is now done.
[0318] At this moment, the metal mold 20a is heated up to a
temperature of less than the melting point of the biodegradable
plastic that is the main ingredient of the coating film 12 (molding
bag film 12c). Then the upper and lower parts 21a and 22a are
paired up and heated and pressurized to be molded, by the external
heating or the internal heating. It is possible to acquire the
bowl-shaped container 10a (see FIG. 1(a)) as the biodegradable
molded article of the present invention by this single step.
[0319] [Method 5]
[0320] Method 5 is identical with method 1, except that the coating
film 12 is used as a film part cut out to be preformed
substantially identical to the outside shape of the biodegradable
molded article. This method is preferably used for a biodegradable
molded article with a deeper draw depth of more complicated shape,
such as the cup-shaped container 10c shown in FIG. 3(a).
[0321] Although the concrete form of the film part is not
particularly limited, usually, as FIGS. 17(a) and 17(b) show, it is
preferable to make film parts 12d by cutting into individual face
of rough development elevator of the biodegradable molded article
after molding (for instance the cup-shaped container 10c).
[0322] The film part 12d further has an overlap section 12e
equivalent to an overlap width, as FIGS. 17(a) and 17(b) show. This
overlap section 12e is provided around a bottom film part 12d, and
along an edge of a side film part 12d where the film part 12d is
overlapped with itself to be adhered when the film part 12d is
cylindrically wound, etc.
[0323] These overlap sections 12e are overlapped with each other at
a designated section of each film part 12d, when the film part 12d
is arranged in the cavity of the mold in the step of molding. On
this account, the overlap section 12e and a part of the overlapping
film part 12d are both softened and adhered (fused) to each other.
Consequently, the film parts 12d is assembled as one substantially
cup-shaped coating film 12, and after this coating film 12 is
further adhered to the surface of the expanded molded article, the
cup-shaped container 10c of the present invention is acquired.
[0324] The shape of the unfolded film part 12d is not particularly
limited. So taking the cup-shaped container 10c as the example, the
film part 12d may be cut out in two as the side and the bottom,
i.e. the side and the bottom are each film part 12d as indicated in
FIG. 17(a), or in three as two sides and the bottom as indicated in
FIG. 17(b). In this matter, it is sufficient that an assembly of
all film parts 12d overlapped at the overlap sections 12e takes a
shape matched with the biodegradable molded article such as the
cup-shaped one.
[0325] The coating film 12 before attaching is more similar to the
shape after the molding in this method, than the methods 2 and 4.
This method is adequately used when the coating film 12 mainly made
of a biodegradable molded article with low drawability, especially
when the biodegradable molded article with the deep draw depth such
as the cup-shaped container 10c is molded using the coating film 12
with low drawability, and further when the thickness of the coating
film 12 after attaching is desired to be freely adjusted, etc.
[0326] To describe the method 5 more specifically, in the metal
mold 20d shown in FIGS. 8(a) and 8(b), the film part 12d matched
with the bottom of the cup-shaped container 10c and the film part
12d matched with the side are arranged along the shapes of the
cavity of the lower parts 23d and 24d, as shown in FIG. 18. At this
time, the overlap sections 12e have to be surely overlapped with
each other.
[0327] Then the molding material 14 is provided for the
substantially cup-shaped film part 12d. At the same time, the film
part 12d matched with the bottom of the cup-shaped container 10c
and the film part 12d matched with the side thereof are arranged in
accordance with the shape of the upper part 21, then the upper part
21d is paired with the lower parts 23d and 24d with the arranged
film parts 12d. Of course the parts 21d, 23d, and 24d are heated up
to a temperature of less than the melting point of the
biodegradable molded article, of which the coating film 12 is
mainly made.
[0328] After the steps above, heat and pressure molding is done by
the external or internal heating. By this step of heat and pressure
molding, the overlap sections 12e of the film parts 12d are fused
as above and a layer of the coating film 12 is formed on the
surface of the expanded molded article (main body 11c) without a
gap between them. As a result, it is possible to acquire the
cup-shaped container 10c (see FIG. 3(a)) as the biodegradable
molded article of the present invention, by the single step
above.
[0329] [Method 6]
[0330] Method 6 is identical with method 5, except that the film
parts 12c are adhered at the overlap sections 12e for the purpose
to make the film parts 12c almost match with the outside shape of
the biodegradable molded article before molding the same. As in the
case of the method 5, this method is preferably used for a
biodegradable molded article with a deeper draw depth or more
complicated shape, such as the cup-shaped container 10c shown in
FIG. 3(a).
[0331] Being almost identical to the method 5, this method is
arranged so that an outside shape film is preformed by securely
adhering the overlap sections 12e and 12e by way of fusing etc.
This method is preferable when the coating film 12, in which the
overlap sections 12e and 12e are not easily fused, is used in the
method 5.
[0332] To describe the method 6 more specifically, as shown in FIG.
19, in the metal mold 20d indicated in FIGS. 8(a) and 8(b), two
outside shape films 12f, which are adhered to be substantially
similar to a cup-shape in advance, are overlaid and arranged
between the upper and lower parts 21d, 23d, and 24d, and then the
molding material is provided between the outside shape films 12f.
At this moment, the metal mold 20b is heated up to a temperature of
not more than the melting point of the biodegradable plastic that
is the main ingredient of the outside shape film 12f (coating film
12). Then the upper and lower parts 21c, 23d, and 24d are paired up
and the heat and pressure molding is conducted using the external
or internal heating. As a result, it is possible to acquire the
cup-shaped container 10c (see FIG. 3(a)) as the biodegradable
molded article of the present invention, by the single step
above.
[0333] [Method 7]
[0334] In method 7, the method 6 is further combined with method 3.
That is to say, after the film parts 12c are adhered at the overlap
sections 12e and formed to be almost identical with the outside
shape of the biodegradable molded article before the molding
process, the shaped film parts 12c are overlaid to be a
substantially bag shape and the molding material is portioned into
the same. As in the cases of the methods 5 and 6, this method is
preferably used for a biodegradable molded article with a deeper
draw depth or more complicated shape, such as the cup-shaped
container 10c shown in FIG. 3(a).
[0335] As in the cases of the methods 3 and 4, the molding
compositions are prepared by converting the coating film 12 to the
bag film and putting the molding material therein. Thus the molding
composition can be stored for a certain period of time and also the
preparation of molding can be completed only by putting the molding
compositions into the mold at a time, so it becomes possible to
further simplify the manufacturing process.
[0336] To describe method 7 more specifically, as shown in FIG. 20,
after the coating film 12 is connected to be the film parts matched
with the outside shape of the cup-shaped container 10c, the film
parts are adhered to make the outside shape film, and two of the
same are adhered to make a bag-shaped outline bag film 12g before
the procedures below. Then a certain amount of the molding material
14 is portioned into each of the-outline bag films 12g and the
molding compositions 40g are stored in a designated storage etc.
Following the steps above, in the metal mold 20d shown in FIGS.
8(a) and 8(b), preparation for molding is completed easily by
simply taking out the molding composition 40g substantially formed
into a cup shape from the storage and placing the same on the lower
parts 23d and 24d.
[0337] At this moment, the metal mold 20d is heated up to a
temperature of less than the melting point of the biodegradable
plastic that is the main ingredient of the coating film 12 (outline
bag film 12g). Then the upper and lower parts 21d, 23d, and 24d are
paired up and the heat and pressure molding is conducted using the
external or internal heating. As a result, it is possible to
acquire the cup-shaped container 10c (see FIG. 3(a)) as the
biodegradable molded article of the present invention, by the
single step above.
[0338] In all attaching methods described above, i.e. both after
attaching method and simultaneous attaching method, the coating
film 12 is not necessarily attached to the whole expanded molded
article, so it is sufficient that the coating film 12 is attached
only on a part of the expanded molded article desired to be coated
for instance, a plate used only for placing food on the face such
as:
[0339] a one-way plate on which light meals such as takoyaki, Fried
noodles, Japanese-style pancake, hot dogs, and fried potato are
temporarily placed when eaten and thrown away after the
consumption; and
[0340] a plate used as a base for wrapping a cake etc. does not
have to be coated except that the top face of the plate. So it is
sufficient that the coating film 12 is only attached on the top
face.
[0341] For instance, in the simultaneous attaching methods 1 to 7,
the molding material is sandwiched by two coating films 12 and the
whole surface of the expanded molded article is coated by the
coating film 12 at the time of the steam expansion molding using
the mold. However, it is possible to coat only the top face of the
expanded molded article by the coating film 12 in the simultaneous
attaching methods 1 to 7.
[0342] Moreover, when the biodegradable molded article in
accordance with the present invention is used as a cushioning
material for wrapping electrical appliances etc., it is sufficient
that the coating film is attached only on areas directly touching
the appliances. Especially, the cushioning as well as the attaching
mold to attach the coating film become large when the appliances to
be wrapped is large in size, so it is sufficient to attach the
coating film on a requisite minimum space when the biodegradable
molded article becomes large.
[0343] In the meantime, if the whole parts of the container
requires gas impermeability in the case such as a container of
noodles (such as the bowl-shaped container 10a shown in FIGS. 1(a)
and 1(b)) in which not only boiling water is poured but also dried
noodles that have to avoid oxidation or moisture absorption are
placed in the container, it is preferable if the coating film 12
coats every part of the container.
[0344] Next, what is described is an example of a simultaneous
attaching method in which only a part of the surface of the
expanded molded article is coated by the coating film 12.
[0345] [Method 1A]
[0346] Method 1A is a modification of the method 1, and a method
that only one coating film 12 is provided on the top side of the
molding material, instead of two coating films 12 sandwiching the
molding material in the case of the method 1, thus the coating film
12 is attached only on the top face of the expanded molded
article.
[0347] To describe the method 1A more specifically, as FIG. 22
shows, only one coating film 12, which is still shaped like a
sheet, is provided between the upper and lower parts 21b and 22b of
the metal mold 20b shown in FIGS. 6(a) and 6(b), and subsequently
the slurry/dough molding material 14 is provided between the
coating film 12 and the lower part 22b. At this moment, the metal
mold 20b is heated up to a temperature of less than the melting
point of the biodegradable plastic that is the main ingredient of
the coating film 12. Then the upper and lower parts 21b and 22b are
paired up and heated and pressurized to be molded, by the external
heating or the internal heating. It is possible to acquire a
plate-shaped container 10d (see FIG. 23) as the biodegradable
molded article of the present invention by the single step
above.
[0348] As FIG. 23 shows, in the plate-shaped container 10d only top
side of the main body 11b to place food is coated by the coating
film 12. The top side of the plate-shaped container 10d has good
water resistance. Thus the container 10d is preferably used for the
plates described above, such as the one-way plate thrown away after
food is placed thereon and the plate used as a base for wrapping a
cake etc.
[0349] In the present invention, in addition to the mold for
molding the expanded molded article, the attaching mold having a
cavity that is substantially identical to that of the mold is
required, when the after attaching method is adopted for attaching
the coating film 12. Meanwhile, when the simultaneous-attaching
method is adopted, the attaching mold is unnecessary and the
coating film 12 can be attached simultaneously with molding the
expanded molded article.
[0350] Therefore, it is possible to make the coating film 12
substantially adhere to the surface of the expanded molded article
with precision and certainty. Especially, even when a complicatedly
shaped molded article is manufactured by using the after attaching
method, simply copying the shape of the mold allows to manufacture
the molded article without creating the attaching mold 30 matched
with the expanded molded article or adjusting the shape delicately,
because the shape of the molded article depends on a shape of the
cavity of the mold.
[0351] Moreover, the present invention is arranged so that the
coating film 12 is attached either after the expanded molded
article is preformed to a designated shape from starch (natural
material) as main ingredient through the steam expansion or
simultaneously with the steam expansion of the expanded molded
article above. Thus molded articles having any kind of shapes can
be molded as long as capable of being released from the mold. For
instance, it is possible to steadily mold the molded articles such
as those which have a deep draw depth like a cup, those which have
uneven thickness like a food tray with partitions and a wrapping
tray, a really complicatedly shaped cushioning material, etc.
[0352] Furthermore, when the coating film 12 is attached using the
after attaching method, as described above, it is possible to
acquire variously shaped molded articles with biodegradability and
good water/moisture resistance, since the attaching mold that has
the shape substantially identical to that of the mold for molding,
is used.
[0353] Also, if the coating film 12 which is not only water
resistant but also gas impermeable etc. is used, when the molded
article is used for a container etc., it becomes possible to
prevent the contents thereof from being oxidized or getting moist
etc. and a molded container suitable for preserving can be
acquired, since it becomes possible to add various characteristics
such as gas impermeability to the biodegradable molded article of
the present invention.
[0354] In addition, when words and pictures are printed on the
surface of the coating film 12 in advance by using biodegradable
ink, simply attaching the coating film 12 allows to print beautiful
and detailed design on the surface of the expanded molded article
much easily, compared to printing directly on the surface
thereof.
[0355] In other words, in the present invention, it is possible to
add various characteristics to the biodegradable molded article of
the present invention easily and certainly, if the coating film 12
is attached on the expanded molded article after functions are
imparted to the coating film 12 in advance.
[0356] When the biodegradable molded article of the present
invention is used as a sealable container for holding things inside
thereof, the container is often shaped as having an opening. So to
seal the container, there is a method to seal the opening by an
adhesive lid, for instance. In this case, as FIG. 21(a) shows, it
is preferable that at least the coating film 12 is attached on an
edge 16 of the opening.
[0357] The expanded molded article is mainly made of natural starch
on which steam expansion is conducted. Thus microscopic bumps and
dips are formed on the surface of the expanded molded article 11 as
a result, as schematically shown in FIGS. 21(a) and 21(b). These
bumps and dips are predominantly caused by the steam expansion
molding, and as FIG. 21(b) shows, they make the contact between the
adhesive lid 17 and the edge 16 worse and the sealability becomes
insufficient.
[0358] There is a conventional technology to apply water resistant
resin on the surface. However, because of the microscopic bumps and
dips, no matter how the resin is applied evenly, gaps and pinholes
are likely to be created on a coating of the applied resin to be
matched with the bumps and dips, and it is impossible to form a
smooth coating. Thus adequate water/moisture resistance cannot be
acquired. Furthermore, gas impermeability is required when
oxidation etc. of the contents needs to be prevented. However, the
microscopic bumps and gaps lower the gas impermeability too.
[0359] To take measures against this, in the present invention, the
coating film 12 which is naturally formed as a complete film is
attached, for instance, via the adhesive layer 13 or by being
softened concurrently with the expansion molding and then directly
adhered. Thus, as FIG. 21(a) shows, in the edge 16, adhesion
between the adhesive lid 17 and the edge 16 on which the coating
film 12 is attached is improved. On this account, the sealability
of the opening, such as water resistance, moisture resistance, gas
impermeability, etc., is improved, and the contents are better
preserved.
[0360] As described above, when the coating film 12 is partly
attached, after the attaching mold (mold 30 shown in FIG. 11, for
instance) for attaching is prepared, an appropriately sized coating
film 12 and the adhesive film 13a are arranged to be sandwiched by
the attaching mold and the expanded molded article, and then the
coating film 12 is pressed and attached to the expanded molded
article.
[0361] In this manner, the biodegradable molded article in
accordance with the present invention is arranged so that the
coating film made of biodegradable plastics is attached on the
surface of the expanded molded article mainly made of starch. As a
result, high water resistance can be added to the surface of the
expanded molded article, while keeping stability of the shape
(property of keeping an appropriate thickness) and heat insulation.
In addition, it becomes possible to improve strength and
flexibility of the expanded molded article.
[0362] Moreover, both the expanded molded article and the film have
biodegradability and are adequately biodegraded, and especially an
expanded molded article with a large thickness has very good
biodegradability since the same is mainly made of starch. In the
meantime, the film is thin enough despite the same is made of
biodegradable plastic which is biodegraded slowly. On this account,
the biodegradable molded article in accordance with the present
invention is biodegraded well when disposed.
[0363] Furthermore, since the complete coating film is attached on
the surface of the expanded molded article, when the expanded
molded article is used as a container with an opening, it becomes
possible to completely seal the adhesive lid on the edge of the
opening by heating.
[0364] The biodegradable molded article in accordance with the
present invention is preferably used as a molded article for
wrapping such as cushioning material, GES, and a wrapping tray, a
container of ready-to-eat food such as noodles (Chinese noodles,
Japanese wheat noodles, buckwheat noodles, fried Chinese noodles
and etc.), one-way plate or tray used in the catering industry, and
a container of food such as soup and juice.
[0365] Especially the water resistance enables the biodegradable
molded article of the present invention to be preferably used for a
container of food having a high water content, and the same is also
preferably used as a container of ready-to-eat food such as noodles
to be stored for a certain period of time, because of the gas
impermeability thereof.
[0366] Now, the present invention is described further in detail,
on the basis of examples and comparative examples. However, the
present invention is not limited to these examples.
[0367] [Moisture Absorption Strength (Moisture Resistance
Strength)]
[0368] For moisture absorption strength (moisture resistance
strength) of the biodegradable molded article in examples and
comparative examples, the assessment was made by the following
method.
[0369] After the resultant biodegradable molded article was left
for 30 days under high humidity kept at a temperature of 40.degree.
C. and at a 90% relative humidity, the assessment was made in terms
of softening or deformation of the biodegradable molded article due
to moisture absorption. The double circle indicates that there is
no change (deformation or softening) and no reduction of strength
due to moisture absorption. The single circle indicates that there
is no deformation (change of outside shape) but slight softening
due to moisture absorption. The triangle indicates that there is
softening and deformation due to moisture absorption but the shape
and strength is maintained at practical level. The cross mark
indicates that there is softening and deformation at a non-usable
level.
EXAMPLE 1
[0370] First of all, 30.0 grams of starch as the main ingredient,
7.0 grams of coniferous virgin pulp as water-insoluble fiber
(strength adjusting agent), 7.0 grams of calcium carbonate as
strength adjusting agent, 0.2 gram of guar gum as stabilizer and
strength adjusting agent, 55.8 grams of water were mixed to prepare
100 grams of dough molding material. In this example, only
high-amylose starch (corn starch containing 60% of amylose) was
used as starch.
[0371] Next, in the aforementioned method 1 of the simultaneous
attaching method the above molding material as the molding material
14, the biaxially stretched modified polyester film (50 .mu.m
thick) as the coating film 12, and the metal mold 20a shown in
FIGS. 5(a) and 5(b), were used to manufacture the bowl-shaped
container 10a. As for the heating method, both external heating to
heat the metal mold 20a by an electric heater and internal heating
by high-frequency dielectric heating were used. Also, in the
external heating and internal heating, a temperature of the metal
mold 20a was adjusted to 130 to 150.degree. C.
[0372] Water absorption strength of the resultant bowl-shaped
container 10a was assessed by the aforementioned method. The result
is shown in table 1.
EXAMPLE 2
[0373] The bowl-shaped container 10a was manufactured in the same
way as example 1 except that a mixture of 25 weight % of potato
starch and 75 weight % of high-amylose starch (corn starch
containing 60% of amylose) is used as starch instead of
high-amylose starch.
[0374] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 1.
EXAMPLE 3
[0375] The bowl-shaped container 10a was manufactured in the same
way as example 1 except that a mixture of 40 weight % of potato
starch and 60 weight % of high-amylose starch (corn starch
containing 60% of amylose) is used as starch instead of
high-amylose starch.
[0376] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 1.
EXAMPLE 4
[0377] The bowl-shaped container 10a was manufactured in the same
way as example 1 except that a mixture of 50 weight % of potato
starch and 50 weight % of high-amylose starch (corn starch
containing 60% of amylose) is used as starch instead of
high-amylose starch.
[0378] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 1.
COMPARATIVE EXAMPLE 1
[0379] The bowl-shaped container 10a was manufactured in the same
way as example 1 except that only potato starch is used as starch
instead of high-amylose starch.
[0380] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 1.
1 TABLE 1 Example Example Example Example Comparative 1 2 3 4
example 1 Potato 0% 25% 40% 50% 100% starch High- 100% 75% 60% 50%
0% amylose starch Moisture .circleincircle. .circleincircle.
.largecircle. .DELTA. X absorption strength % shows weight % in the
above table.
[0381] Comparing the result of the comparative example 1 in table 1
with the results of the examples 1 to 4, it is found that moisture
absorption is improved in case of using starch containing
high-amylose starch, as compared with the case of using starch
containing potato starch only. Moreover from the results of
examples 1 to 4, to improve moisture absorption strength, among
starch containing high-amylose starch, starch containing not less
than 50 weight % of starch high-amylose starch is preferable, more
preferably starch containing not less than 60 weight % of starch
high-amylose starch, and still more preferably starch containing
not less than 75 weight % of starch high-amylose starch.
EXAMPLE 5
[0382] First of all, 30.0 grams of potato starch and 15.0 grams of
polyvinyl alcohol having less than 1000 polymerization degree and
less than 70% saponification degree as the main ingredient, 4.0
grams of coniferous virgin pulp as water-insoluble fiber (strength
adjusting agent), 10.0 grams of calcium carbonate as strength
adjusting agent, 0.2 gram of guar gum as stabilizer and strength
adjusting agent, and water were mixed to prepare dough molding
material. Water was adjusted to make solid content 54.2 weight %
(percentage of solids to total weight of molding material). In this
case, water was 58.5 grams and total weight of molding materials
was 127.7 grams. Also, weight of solids (components except water in
the molding material) was 69.2 grams.
[0383] Next, in the aforementioned method 1 of the simultaneous
attaching method, the above molding material as the molding
material 14, the biaxially stretched modified polyester film (35
.mu.m thick) as the coating film 12, and the metal mold 20a shown
in FIG. 5(a) and FIG. 5(b), were used to manufacture the
bowl-shaped container 10a.
[0384] As for the heating method, both external heating to heat the
metal mold 20a by an electric heater and internal heating by
high-frequency dielectric heating were used. Also, in the external
heating and internal heating, a temperature of the metal mold 20a
was adjusted to 130 to 150.degree. C.
[0385] Water absorption strength of the resultant bowl-shaped
container 10a was assessed by the aforementioned method. The result
is shown in table 2.
EXAMPLE 6
[0386] The bowl-shaped container 10a was manufactured in the same
way as example 6 except that the volume of polyvinyl alcohol was
changed to 12.0 grams and the volume of water was changed to adjust
solid content to 54.2 weight %. In this case, water was 55.9 grams
and total weight of the molding material was 122.1 grams. Also,
weight of solids (components except for water in the molding
material) was 66.2 grams.
[0387] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 2.
EXAMPLE 7
[0388] The bowl-shaped container 10a was manufactured in the same
way as example 6 except that the volume of polyvinyl alcohol was
changed to 8.0 grams and the volume of water was changed to adjust
solid content to 54.2 weight %. In this case, water was 52.6 grams
and total weight of the molding material was 114.8 grams. Also,
weight of solids (components except for water in the molding
material) was 62.2 grams.
[0389] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 2.
COMPARATIVE EXAMPLE 2
[0390] The bowl-shaped container 10a was manufactured in the same
way as example 6 except that the volume of polyvinyl alcohol was
not used and the volume of water was changed to adjust solid
content to 54.2 weight %. In this case, water was 45.8 grams and
total weight of the molding material was 100.0 grams. Also, weight
of solids (components except for water in the molding material) was
54.2 grams.
[0391] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 2.
2 TABLE 2 Example Example Example Comparative 5 6 7 example 2
Potato starch (g) 40.0 40.0 40.0 40.0 Polyvinyl alcohol (g) 15.0
12.0 8.0 0 Pulp (g) 4.0 4.0 4.0 4.0 Calcium carbonate (g) 10.0 10.0
10.0 10.0 Guar gum (g) 0.2 0.2 0.2 0.2 Water (g) 58.5 55.9 52.6
45.8 Total weight (g) 127.7 122.1 114.8 100.0 Solids (g) 69.2 66.2
62.2 54.2 Percentage of solids 54.2 54.2 54.2 54.2 (weight %)
Content of polyvinyl 11.7 9.8 7.0 0 alcohol (weight %) Moisture
absorption .circleincircle. .largecircle. .DELTA. X strength
[0392] Comparing the result of the comparative example 2 in table 2
with the results of the examples 5 to 7, it is found that moisture
absorption is improved in case of using polyvinyl alcohol, as
compared with the case that polyvinyl alcohol is not used.
EXAMPLE 8
[0393] First of all, 37.0 grams of starch and 7.0 grams of
polyvinyl alcohol (PVA) having less than 1000 polymerization degree
and less than 70% saponification degree as the main ingredient, 7.0
grams of coniferous virgin pulp as water-insoluble fiber (strength
adjusting agent), and 49.0 grams of water were mixed to prepare
dough molding material. In this case, total weight of the molding
material was 100.0 grams. Also, content of polyvinyl alcohol in the
molding material is 7.0 weight %. Also, in this case, weight of
solids (components except for water in the molding material) is
51.0 grams and percentage of solids in the molding material is 51.0
weight %.
[0394] Next, in the aforementioned method 1 of the simultaneous
attaching method, the above molding material as the molding
material 14, the biaxially stretched modified polyester film (50
.mu.m thick) as the coating film 12, and the metal mold 20a shown
in FIG. 5(a) and FIG. 5(b), were used to manufacture the
bowl-shaped container 10a.
[0395] As for the heating method, both external heating to heat the
metal mold 20a by an electric heater and internal heating by
high-frequency dielectric heating were used. Also, in the external
heating and internal heating, a temperature of the metal mold 20a
was adjusted to 140 to 160.degree. C.
[0396] Water absorption strength of the resultant bowl-shaped
container 10a was assessed by the aforementioned method. The result
is shown in table 3.
EXAMPLE 9
[0397] The bowl-shaped container 10a was manufactured in the same
way as example 8 except that polyvinyl alcohol having
polymerization degree between 1000 and less than 1500 and less than
70% saponification degree was used instead of polyvinyl alcohol
used in example 8.
[0398] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 3.
EXAMPLE 10
[0399] The bowl-shaped container 10a was manufactured in the same
way as example 8 except that polyvinyl alcohol having not less than
1500 polymerization degree and less than 70% saponification degree
was used instead of polyvinyl alcohol used in example 8.
[0400] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 3.
EXAMPLE 11
[0401] The bowl-shaped container 10a was manufactured in the same
way as example 8 except that polyvinyl alcohol having less than
1000 polymerization degree and saponification degree between 70%
and less than 90% was used instead of polyvinyl alcohol used in
example 8.
[0402] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 3.
EXAMPLE 12
[0403] The bowl-shaped container 10a was manufactured in the same
way as example 8 except that polyvinyl alcohol having
polymerization degree between 1000 and less than 1500 and
saponification degree between 70% and less than 90% was used
instead of polyvinyl alcohol used in example 8.
[0404] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 3.
EXAMPLE 13
[0405] The bowl-shaped container 10a was manufactured in the same
way as example 8 except that polyvinyl alcohol having not less than
1500 polymerization degree and saponification degree between 70%
and less than 90% was used instead of polyvinyl alcohol used in
example 8.
[0406] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 3.
EXAMPLE 14
[0407] The bowl-shaped container 10a was manufactured in the same
way as example 8 except that polyvinyl alcohol having less than
1000 polymerization degree and not less than 90% saponification
degree was used instead of polyvinyl alcohol used in example 8.
[0408] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 3.
EXAMPLE 15
[0409] The bowl-shaped container 10a was manufactured in the same
way as example 8 except that polyvinyl alcohol having
polymerization degree between 1000 and less than 1500 and not less
than 90% saponification degree was used instead of polyvinyl
alcohol used in example 8.
[0410] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 3.
EXAMPLE 16
[0411] The bowl-shaped container 10a was manufactured in the same
way as example 8 except that polyvinyl alcohol having not less than
1500 and not less than 90% of saponification degree.
[0412] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 3.
3 TABLE 3 Moisture Polymerization Saponification absorption degree
of PVA degree of PVA strength Example 8 Less than 1000 Less than
70% .DELTA..about.X Example 9 Between 1000 and Less than 70%
.DELTA. less than 1500 Example 10 Not less than 1500 Less than 70%
.largecircle. Example 11 Less than 1000 Between 70% and .DELTA.
less than 90% Example 12 Between 1000 and Between 70% and
.largecircle. less than 1500 less than 90% Example 13 Not less than
1500 Between 70% and .circleincircle. less than 90% Example 14 Less
than 1000 Not less than 90% .largecircle. Example 15 Between 1000
and Not less than 90% .circleincircle. less than 1500 Example 16
Not less than 1500 Not less than 90% .circleincircle.
[0413] From the comparison of the results in the examples 8 to 16
in table 3, it is found that the higher polymerization degree of
polyvinyl alcohol used and the higher saponification degree is, the
further moisture absorption strength is improved. Moreover, it is
found that saponification degree especially effects improvement of
moisture absorption strength. From the above, to improve moisture
absorption strength, polymerization degree of polyvinyl alcohol in
the molding material is preferably not less than 1000, more
preferably not less than 1500. Also, to improve moisture
absorption, saponification degree of polyvinyl alcohol in the
molding material is preferably not less than 70%, and more
preferably not less than 90%.
[0414] In the meantime, as for the bowl-shaped container 10a
acquired in the examples 1 to 16 and comparative examples 1 and 2,
to assess the piercing strength, maximum stress and entering
distance were measured when a bar-shaped plunger of 2 mm in
diameter and 1R of a curved surface rate at the end is pierced in
the container at a rate of 6 cm/min. using a Rheometer produced by
Rheotech under a condition before moisture absorption strength is
measured. In the result, there is no meaningful difference among
all the samples for both maximum stress and entering distance.
Accordingly, there is no relation between piercing strength and
moisture absorption strength.
[0415] It is proven that an excellent nature of the biodegradable
container in the present invention is quite different nature from
"strength" generally referred to for a conventional biodegradable
container made from starch, that is, strength when handled under
dry condition or a normal atmosphere such as the above piercing
strength.
EXAMPLE 17
[0416] The bowl-shaped container 10a was manufactured in the same
way as example 16 except that the volume of polyvinyl alcohol was
changed to 4.8 grams and the volume of water was changed to adjust
solid content to 54.2 weight %. In this case, the content of
polyvinyl alcohol in the molding material is 5.0 weight %.
[0417] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown together with the result of example 16 in table 4.
EXAMPLE 18
[0418] The bowl-shaped container 10a was manufactured in the same
way as example 16 except that the volume of polyvinyl alcohol was
changed to 3.7 grams and the volume of water was changed to adjust
solid content to 54.2 weight %. In this case, the content of
polyvinyl alcohol in the molding material is 4.0 weight %.
[0419] Moisture absorption strength of the resultant bowl-shaped
container 10a was assessed in the aforementioned method. The result
is shown in table 4.
EXAMPLE 19
[0420] The bowl-shaped container 10a was manufactured in the same
way as example 16 except that the volume of polyvinyl alcohol was
changed to 2.75 grams and the volume of water was changed to adjust
solid content to 54.2 weight %. In this case, the content of
polyvinyl alcohol in the molding material is 3.0 weight %.
[0421] Moisture absorption of the resultant bowl-shaped container
10a was assessed in the aforementioned method. The result is shown
in table 4.
4 TABLE 4 Content of PVA in the Moisture absorption molding
material strength Example 16 7.0 weight % .circleincircle. Example
17 5.0 weight % .circleincircle. Example 18 4.0 weight %
.largecircle. Example 19 3.5 weight % .DELTA.
[0422] From the results of examples 8 to 17, it is proven that
sufficient moisture absorption strength is improved by controlling
polymerization degree and saponification degree of polyvinyl
alcohol even if a content of polyvinyl alcohol is limited to 5 to 7
weight %.
[0423] Also, from the results of examples 16 to 19, it is proven
that moisture absorption strength is improved if the content of
polyvinyl alcohol in the molding material is not less than 4.0
weight %, and moisture absorption strength is further improved if
the content of polyvinyl alcohol is not less than 5.0 weight %.
[0424] The embodiments or examples shown in "BEST MODE FOR CARRYING
OUT THE INVENTION" are intended to disclose technical information
on the present invention, and it should not be interpreted that the
present invention is limited to these examples or embodiments in
narrow sense. The present invention can be executed by making
various changes within the range of the claims described below
under the sprit of the present invention.
INDUSTRIAL APPLICABILITY
[0425] According to the present invention, as mentioned above, it
is possible to accomplish sufficient strength and at least
sufficient water resistance, to exert a very excellent
biodegradability and further to provide a biodegradable molded
article having excellent moisture absorption strength mainly made
from starch even if the biodegradable molded article has a
complicated shape.
[0426] Accordingly, the biodegradable molded article in accordance
with the present invention is preferably used as a molded article
for wrapping such as GES and a tray for wrapping, a container of
ready-to-eat food such as noodles (Chinese noodles, Japanese wheat
noodles, buckwheat noodles, fried Chinese noodles and etc.),
one-way plate or tray used in the catering industry, and a
container of food such as soup and juice.
* * * * *