U.S. patent application number 14/284697 was filed with the patent office on 2014-11-13 for flat container comprising thermoplastic resin and method for molding the same.
This patent application is currently assigned to TOYO SEIKAN GROUP HOLDINGS, LTD.. The applicant listed for this patent is Toyo Seikan Group Holdings, Ltd.. Invention is credited to Takuya Fujikawa, Hiroyuki Honda, Atsushi Komiya, Akihiko Morofuji.
Application Number | 20140332490 14/284697 |
Document ID | / |
Family ID | 36060207 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140332490 |
Kind Code |
A1 |
Komiya; Atsushi ; et
al. |
November 13, 2014 |
FLAT CONTAINER COMPRISING THERMOPLASTIC RESIN AND METHOD FOR
MOLDING THE SAME
Abstract
The invention realizes easy manufacturing of a flat container
molded by blow molding, in which the wall thickness of a container
wall is made uniform, and which provides improved mechanical
strength, heat resistance, etc. and has a good appearance. The flat
container obtained by the blow molding of a polyester resin is
characterized in that the container has a flatness ratio of not
less than 1.3, and in that its body has a wall thickness ratio of a
maximum wall thickness to a minimum wall thickness of not more than
1.6, a difference in elongation between a maximally stretched
portion and a minimally stretched portion of not more than 150% in
a tensile test at 95.degree. C., a crystallinity of not less than
30%, and a difference in TMA non-load change between a maximally
stretched portion and a minimally stretched portion of not more
than 500 .mu.m at 75.degree. C. and 100.degree. C.
Inventors: |
Komiya; Atsushi;
(Yokohama-shi, JP) ; Honda; Hiroyuki; (Tokyo,
JP) ; Fujikawa; Takuya; (Yokohama-shi, JP) ;
Morofuji; Akihiko; (Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Toyo Seikan Group Holdings, Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
TOYO SEIKAN GROUP HOLDINGS,
LTD.
Tokyo
JP
|
Family ID: |
36060207 |
Appl. No.: |
14/284697 |
Filed: |
May 22, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11575435 |
Jul 16, 2008 |
8784957 |
|
|
PCT/JP2005/017442 |
Sep 15, 2005 |
|
|
|
14284697 |
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Current U.S.
Class: |
215/12.1 ;
215/371; 215/382 |
Current CPC
Class: |
Y10T 428/1352 20150115;
B29B 2911/14466 20130101; B29C 49/22 20130101; B29B 2911/14066
20130101; B29B 2911/14053 20130101; B29B 2911/1444 20130101; B29C
37/0067 20130101; B29B 2911/1408 20130101; Y10T 428/1359 20150115;
B29B 2911/14113 20130101; B29L 2031/7158 20130101; B29K 2995/0043
20130101; B29B 2911/14173 20130101; B29K 2995/0097 20130101; B29C
49/04 20130101; B65D 1/0215 20130101; B65D 1/0223 20130101; Y10T
428/139 20150115; B29B 2911/14653 20130101; B29C 49/06 20130101;
B29B 2911/14146 20130101; B29K 2067/00 20130101; Y10T 428/13
20150115; Y10T 428/1303 20150115; B29B 2911/1414 20130101; B29C
49/4242 20130101; B29B 2911/14713 20130101; B29K 2995/0077
20130101; B29B 2911/1412 20130101; B65D 2501/0036 20130101; B65D
2501/0081 20130101; B29B 2911/14926 20130101; B29B 2911/14593
20130101; B29C 49/0073 20130101; B29K 2995/0041 20130101; B65D
2501/0018 20130101; B29B 2911/14166 20130101; B29C 49/18 20130101;
B29K 2067/003 20130101; B29B 2911/14093 20130101 |
Class at
Publication: |
215/12.1 ;
215/371; 215/382 |
International
Class: |
B65D 1/02 20060101
B65D001/02; B29C 49/18 20060101 B29C049/18; B29C 49/22 20060101
B29C049/22 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 17, 2004 |
JP |
2004-272637 |
Jul 19, 2005 |
JP |
2005-209281 |
Claims
1. A flat polyester resin container, comprising a polyester resin,
the container being obtained by blow molding the polyester resin,
wherein the flatness ratio, which is the ratio of a major axis to a
minor axis of a cross section parallel to the bottom of the
container, is not less than 1.3 to 2.5, the flat polyester resin
container is a heat resistant container, the wall thickness ratio
of a maximum wall thickness to a minimum wall thickness of a body
of the container is not more than 1.6, a difference in elongation
between a maximally stretched portion and a minimally stretched
portion of the body of the container in a tensile test at
95.degree. C. is not more than 150%, the crystallinity of the body
of the container is not less than 30%, and a difference in TMA
non-load change between a maximally stretched portion and a
minimally stretched portion of the body of the container at
75.degree. C. and 100.degree. C. is not more than 500 .mu.m.
2. The flat polyester resin container according to claim 1, wherein
the sectional shape of the body of the flat container is a
rectangle or an ellipse.
3. The flat polyester resin container according to claim 1, wherein
the polyester resin is polyethylene terephthalate.
4. The flat polyester resin container according to claim 1, wherein
the flat container is of a multilayer structure comprising a
polyester resin layer and a functional thermoplastic resin
layer.
5. The flat polyester resin container according to claim 1, wherein
one or more transverse ribs are provided in a horizontal concavity
on a long-side side surface.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation application of U.S. patent
application Ser. No. 11/575,435, filed on Jul. 16, 2008, which is a
371 of International Application No. PCT/JP2005/017442, filed on
Sep. 15, 2005, which claims the benefit of priority from the prior
Japanese Patent Application Nos. 2004-272637, filed on Sep. 17,
2004 and 2005-209281 filed on Jul. 19, 2005, the entire contents of
which are incorporated herein by references.
TECHNICAL FIELD
[0002] The present invention relates to a flat container made of a
thermoplastic resin and, more particularly, to a flat container
whose section is an ellipse or a rectangle or has other shapes, the
body of which has a uniformly formed wall thickness, and which has
high thermal resistance and is not deformed at high temperatures
and a method for molding the flat container.
BACKGROUND ART
[0003] Thanks to their excellent mechanical strength, moldability,
transparency, recyclability of resources, etc. polyester resin
containers, such as PET bottles, have been recognized as containers
for food and drink and they have been in great demand. In
particular, recently polyester resin containers have been
habitually used by consumers as portable small containers for
beverage use. The heat resistance and pressure resistance of such
small containers for beverage use have been remarkably improved by
the development of the two-stage blow molding process (refer to
Japanese Patent Publication No. 4-56734 (claim 1 and the upper
section of the left column on page 2)) and small containers have
become capable of being used for high-temperature beverages and
beverages requiring high-temperature pasteurization. Thus, they
have become able to meet consumers' strong requests for portable
high-temperature beverages for the winter season in daily life.
[0004] Furthermore, reuse systems of PET bottles have been
established to meet the social requests for resource savings and
environmental protection, and the cleanliness due to the
transparency of containers and the sense of safety by seeing the
beverages inside through containers meet consumers'
cleanliness-oriented trends, with the result that the demand for
polyester resin containers represented by PET bottles has been
increasing further.
[0005] Recent consumers prefer beverage bottles of flat shape
having a rectangular section etc. because these bottles are easy to
hold and beautiful thanks to their complex shapes, whereas bottles
having a circular section tend to be avoided because they are
difficult to grip due to slipperiness when their surfaces become
wet and because they lack aesthetic impressions due to the simple
shape of a circle.
[0006] Flat containers having flat shapes with rectangular,
elliptical or other sections that tend to be liked by consumers and
have a very strong demand are manufactured by blow molding (molding
by blowing the air), with a preformed, bottomed parison (a preform)
inserted into the interior of a mold having a flat section and
attached thereto. On the occasion of molding into a flat shape, the
wall thickness of a container wall tends to become nonuniform due
to a difference in the amount of elongation in the major axis
direction and minor axis direction of the section of the container
and for other reasons.
[0007] As a measure to prevent this, there is known, for example a
method for obtaining a flat container that involves inflating a
bottomed parison having a circular section in a first blow mold
into an intermediate molded article, inserting this intermediate
molded article into a second blow mold, flattening the intermediate
molded article into an elliptical shape by mold closing, and
performing thereafter blow molding (refer to Japanese Patent
Publication No. 59-53861 (Claims for the Patent and FIG. 1)). In
this method, however, the shapability by blow molding is
insufficient and wrinkles due to the waviness of concavities
occurring partially on the surface of an intermediate molded
article are apt to remain on the surface of a product, posing the
problems of a poor appearance and insufficient strength.
[0008] In addition, some methods and apparatus for aiming at a
uniform wall thickness in the manufacture of a flat container by
blow molding have been disclosed. They are, for example, a bottomed
cold parison blow molding process, which involves heating a
bottomed cold parison before blow molding so that a portion
stretched in the minor axis direction of a flat shape obtains a
higher temperature than a portion stretched in a major axis
direction or using a bottomed parison that is formed with thickness
uniformity so that the wall thickness of a portion stretched in the
major axis direction becomes large and the wall thickness of a
portion stretched in the minor axis direction becomes small, and
radiant heating the bottomed parison in its periphery while
rotating the bottomed parison in the axial direction (refer to
Japanese Patent Laid-Open No. 2000-127230 (Claims for the Patent
and paragraphs 0005 to 0008)), and a molding mold that performs
blow molding by housing a parison within a cavity of a split mold,
advancing moving mold member to the parison surface and flattening
the parison, and molds a container having high flatness which is
such that the size ratio of a flat surface to side surfaces is not
more than 1/2 with a uniform wall thickness (refer to Japanese
Patent Laid-Open No. 8-294958 (Claims for the Patent and paragraphs
0003 and 0004)). In general, however, it is difficult to obtain the
uniformity of the wall thickness of container walls because the
elongation and expansion of a parison within a cavity do not become
uniform due to the flat section and material accumulation occurs
due to insufficient elongation on the minor axis side, with the
result that it is difficult to manufacture a flat container with a
uniform wall thickness of the container body.
[0009] When the wall thickness becomes nonuniform, the mechanical
strength and heat resistance of a container decrease due to
thin-walled portions. When such containers are used as
high-temperature beverage containers, there is a fear that the
deformation of the containers may occur because they cannot
withstand inner pressure loads due to the expansion of beverages in
the containers at high temperatures and external pressure loads due
to the shrinkage of the interior during temperature drops.
[0010] On the other hand, in a flat container obtained by blow
molding, from viewpoints different from the intension to improve
the blow molding process, there has scarcely been made any proposal
as yet to make improvements on mechanical strength, heat
resistance, etc. specific to flat containers by specifying flat
containers by physical properties and imparting characteristics to
flat containers and to prevent the fear that the deformation of the
containers may occur because they cannot withstand inner pressure
loads due to the expansion of beverages in the containers at high
temperatures and external pressure loads due to the shrinkage of
the interior during temperature drops, and under the present
circumstance, there is only a proposal which is such that a
polyolefin-based flat container obtained by injection blow molding
in which only the flatness ratio (the maximum major axis of the
body/the minimum minor axis of the body) and wall thickness are
specified is shown (refer to Japanese Patent Laid-Open No.
11-170344 (claims 1 to 3 of Claims for the Patent)).
[0011] In view of the condition of such conventional techniques in
flat thermoplastic resin containers such as polyester resin
containers obtained by blow molding, which are liked by consumers
as beverage plastic containers and their demand is especially
increasing because they are easy to carry and beautiful thanks to
complex shapes, the present inventors consider that the first
problem to be solved by the invention is to realize a flat
container excellent in mechanical properties and heat resistance by
specifying flat containers by physical properties and imparting
characteristics to flat containers and improving mechanical
strength, heat resistance, etc. specific to flat containers. At the
same time, in the manufacture of a plastic flat container for
beverage having a flat sectional shape, such as a rectangle by blow
molding, from the standpoint of a molding method of such a flat
container, the present inventors consider that the second problem
to be solved by the invention is to realize a molding method for
easily manufacturing a flat container with an improved uniformity
of wall thickness, with improved mechanical strength, heat
resistance, etc. and with a good appearance without a wrinkle.
DISCLOSURE OF THE INVENTION
[0012] Aiming at solving the above-described first problem in flat
containers made of a thermoplastic resin in order to clearly
materialize a flat container excellent in mechanical strength, heat
resistance, etc. by a uniform wall thickness of the container wall
and the like, the present inventors investigated the specification
and impartment of characteristics in flat containers in which blow
molding is used, considered techniques for giving a concrete form
to them from various view points of physical properties and a
structure of a container, and made trials. Through these processes,
the present inventors could discover that the ratio of the major
axis to the minor axis (flatness ratio) of a body section of a
container, which expresses flatness, the wall thickness ratio of a
container body, which is an index indicative of the uniformity of
the whole container body, etc. relate to the extensibility in the
container body at high temperatures, thermal no-load changes of the
container body at high temperatures, the crystallinity of the
container body, etc., and are deeply related to the mechanical
strength, heat resistance, etc. of flat containers while having
correlations to each other. And as a result of this, the present
inventors finally reached the creation of a novel flat container as
the first basic invention in the present application by specifying
these correlations as numerical values.
[0013] Concretely, the above-described flatness ratio and wall
thickness ratio are specified by experimentally selecting the
flatness ratio and wall thickness ratio, a difference in elongation
between a maximally stretched portion and a minimally stretched
portion of the container body in a tensile test at 95.degree. C. is
adopted as the specification of extensibility in the container body
at high temperatures, a difference in TMA non-load change between a
maximally stretched portion and a minimally stretched portion in
the range of 75.degree. C. to 100.degree. C. is selected as the
specification of a thermal no-load change of the container body at
high temperatures, and these relationships are correlated with each
other, whereby it has become possible to clearly give a concrete
form to a flat polyester resin container excellent in mechanical
properties, heat resistance, etc. and to materialize the flat
polyester resin container.
[0014] On the other hand, in order to easily manufacture flat
containers with improved mechanical properties and heat resistance
and with a good appearance without a wrinkle by performing blow
molding with a uniform wall thickness of a flat container wall, the
present inventors considered the construction of molding machines
and molds in blow molding, molding techniques, materials for
parisons, etc. from various perspectives, and accumulated
experimental investigations. And as a result of this, the present
inventors recognized that in order to perform blow molding with a
uniform wall thickness of the container wall of a flat container by
use of a simple apparatus or means and economically, contrivances
in the preliminary wall thickness of a parison have an effect,
discovered new means during this process, and created inventions,
for which applications were filed as prior inventions (Japanese
Patent Application No. 2003-314851, Japanese Patent Laid-Open No.
2005-81641).
[0015] When a parison is stretched and inflated in a mold cavity of
blow molding in order to mold a flat container, the difference in
the magnification of elongation between the major axis side and the
minor axis side is large, and the parison is stretched greatly to
the major axis (long side) side of the flat shape, with the result
that the wall thickness of the parison on the major axis (long
side) side is smaller than on the minor axis (short side) side.
Furthermore, during the insertion of the parison into the mold,
only on the minor axis side of the cavity, the parison comes into
contact with the mold surface having a temperature lower than the
parison and becomes cooled, resulting in a reduced degree of
elongation, and a thick-walled resin accumulation is formed mainly
in the pertinent contact point on the minor axis side. This causes
the phenomenon that a desired amount of resin is not supplied for
the stretch molding on the major axis side requiring a large
magnification of elongation, thereby exerting an adverse effect on
stretch molding. Furthermore, when the time required by the stretch
molding on the major axis side (the time for which the parison
reaches the cavity) becomes long, the pertinent resin accumulation
on the minor axis side is cooled further and the degree of
elongation decreases. These were recognized as the causes of the
nonuniform wall thickness, and if a parison is housed in the cavity
in a flat shape beforehand, as a result of molding, the difference
in the magnification of elongation between the minor axis side and
major axis side decreases, the adverse effect of a thick-walled
resin accumulation on stretch molding is reduced, a decrease in the
degree of elongation is suppressed, and wall thickness balance is
obtained between the minor axis side and the major axis side, with
the result that the uniformity of wall thickness of the container
wall is realized in a molded article of a flat container. This
knowledge constituted basic elements in the prior inventions.
[0016] In order to give a concrete form to these basic invention
elements, in the prior applications, a preformed parison having a
uniform wall thickness in transverse section and a roughly circular
section is subjected to primary blow molding and molded into a
bottomed cylindrical body having a diameter larger than the minor
axis of a mold for secondary blow molding, and this bottomed
cylindrical body is caused to shrink in a heated condition. On the
other hand, a mold having a cavity of the sectional shape of a flat
container, which is a molded article, is prepared, the bottomed
cylindrical body which has been caused to shrink is housed in a
cavity for secondary blow molding, and mold clamping is performed,
with the bottomed cylindrical body depressed (crushed) in the minor
axis direction of the cavity. As a result, the bottomed cylindrical
body is housed in such a manner that the section of the bottomed
cylindrical body becomes longer on the major axis side of the
cavity (the side corresponding to the major axis or long-side
length of the body of the flat container) than on the minor axis
side of the cavity (the side corresponding to the minor axis or
short-side length of the body of the flat container), and the
bottomed cylindrical body is depressed and deformed in a flat
condition. This condition is schematically shown as a sectional
view in (d) of FIG. 2. And when secondary blow molding is
performed, the wall thickness on the minor axis side and major axis
side of the formed flat container becomes sufficiently uniform.
[0017] Incidentally, Japanese Patent Publication No. 59-53861
described above discloses a method for obtaining a flat container
that involves inflating a bottomed parison having a circular
section in a first blow mold into an intermediate molded article,
inserting this intermediate molded article into a second blow mold,
flattening the intermediate molded article into an elliptical shape
by mold closing, and then performing blow molding. Under this
method, as can be seen in Figure (C) of this document, an
intermediate molded article 7 is depressed by mold closing, whereby
also the major axis portion of the intermediate molded article 7 is
brought into close contact with the mold. On the other hand, in the
above-described prior inventions, a parison is subjected to primary
blow molding and molded into a bottomed cylindrical body having a
diameter larger than the minor axis of a mold for secondary blow
molding, the bottomed cylindrical body is then caused to shrink in
a heated condition, whereby the bottomed cylindrical body is caused
to maintain a diameter which is larger than the minor axis of a
cavity within the mold for secondary blow molding, the bottomed
cylindrical molded article is then attached to the interior of the
mold for secondary blow molding. And as shown in (d) of FIG. 2,
mold clamping is performed, with the bottomed cylindrical molded
article depressed in a flat condition in the minor axis direction
of the cavity within the mold for secondary blow molding, so that
the major axis portion of the bottomed cylindrical body does not
come into contact with mold surfaces. The prior inventions differ
from the invention of this document in the two points of shrinkage
under heat and mold clamping performed so that the major axis
portion does not come into contact with mold surfaces. Thanks to
these differences, in the prior inventions, the wall thickness is
sufficiently made uniform and mechanical strength and heat
resistance are improved.
[0018] In the method of the above-described document, the
shapability by blow molding is insufficient and wrinkles due to the
waviness of concavities occurring partially on the surface of an
intermediate molded article during secondary blow molding are apt
to remain on the surface of a product, posing the problems of a
poor appearance and insufficient strength of the product. When an
intermediate molded article 7 shown in FIG. 1(C) of the
above-described document is depressed by a molding tool 3b and
deformed into a shape 7' to perform blow molding, concavities 11
like waviness occur in the upper and lower parts of the
intermediate molded article 7 on the long-side side due to
insufficient shapability, as shown in of FIG. 1(a) of the present
application. Even if blow molding as shown in FIG. 1(D) of the
above-described document is performed in this condition, the
shapability is poor and the waviness of the concavities 11 is not
eliminated. Therefore, in a product container after blow molding,
the concavities 11 are apt to remain as the wrinkles 12 shown in
FIG. 1(b) in the present application, posing the problems of a poor
appearance, insufficient strength and the like of the product
7.
[0019] On the basis of such circumstances, the present application
is filed as the second basic invention in order to make more
uniform the wall thickness of a container in the inventions related
to the prior applications and to further improve mechanical
strength, heat resistance, etc., and to aim at solving the problems
of a poor appearance and insufficient strength in conventional
techniques described in the above-described document, which are
posed by the fact that the shapability by blow molding is
insufficient and wrinkles due to the waviness of concavities
occurring partially on the surface of an intermediate molded
article on the major axis side are apt to remain on the surface of
a product. The present inventors sought after new means by
continuing considerations and trials mainly concerning blow molding
conditions, mold constructions, etc. as factors for the uniformity
of the wall thickness of the container in the prior inventions and
the conventional techniques of the above-described document, and
discovered that the surface structure of a blow mold is deeply
associated with the uniformity of the wall thickness of a
container. The present inventors came to recognize that the
slipperiness of resin materials for blow molding on the mold
surface is associated with the uniformity of wall thickness and the
occurrence of concavities, that in the method of the
above-described document concavities and wrinkles occur remarkably
when the slipperiness between the intermediate molded articles 7
and 7' and the mold tool 3b of FIG. 1 of this document is poor, and
that wrinkles of a product container occur remarkably when an
intermediate molded article is caused to shrink by high heat of not
less than 150.degree. C. and residual stresses are relieved in
order to impart heat resistance to a flat container as in the
above-described prior inventions, because a resin material softened
in secondary blow molding becomes apt to stick to the blow
mold.
[0020] On the basis of these recognitions, the inventors of the
present application arrived at the constituent features: (1) by
subjecting an upper portion and/or a lower portion of a body
molding surface of the mold for blow molding at least on the
long-side side of a container to mold surface treatment, the
slipperiness of a resin material on a partial surface of the mold
for blow molding is improved, and as a result of this, further
uniformity of the wall thickness of the container is achieved; and
(2) by forming one or more convexities, which are horizontal as
viewed from the height of a container, in an upper portion and/or a
lower portion of a body molding surface in the mold for blow
molding at least on the long-side side of the container, the
waviness of concavities which partially occurs on the major axis
side surface of an intermediate molded article is caused to be
absorbed in the convexities and removed, and in a case where minor
wrinkles incapable of being completely removed tend to remain, by
stretching the wrinkles during secondary blow molding, the
prevention of the occurrence of wrinkles on the surface is
realized. Thus the present inventors found out the constituent
features as the second basic invention of the present application.
Furthermore, by combining the features (1) and (2), the occurrence
of concavities and wrinkles can be suppressed more as the feature
(3).
[0021] Incidentally, as the feature (4), in the body of the product
container on the major axis side, transverse (horizontal) concave
ribs (cross beams of grooves) are formed by convexities on the blow
mold surface as shown in FIG. 7, and it has become possible to form
a flat container with transverse ribs that has remarkable
uniformity of wall thickness and is excellent in mechanical
strength and heat resistance.
[0022] Although the second basic invention of the present
application is constituted by the features (1) to (3) described
above as basic elements of the invention, the features (1) and (2)
may also be combined. Furthermore, mold surface treatment,
thermoplastic resins that are molding materials, the size of
concavities on the mold surface, etc. are also specified.
[0023] An overview of the background of the creation of the present
invention and basic elements of the present invention was given
above. The whole present invention viewed and summarized for
clearness is constituted by the following invention unit groups,
with [1] and [2] as well as [9] and [10] being basic inventions.
The inventions [1] and [2] are the first basic inventions and [9]
and [10] are the second basic inventions. These basic inventions
are given a concrete form in other inventions, applied to them or
embodied in them. Incidentally, all of the invention groups are
collectively called "the present invention."
[0024] [1] A flat polyester resin container obtained by the blow
molding of a polyester resin, which is characterized in that the
flatness ratio, which is the ratio of a major axis to a minor axis,
is not less than 1.3, that the wall thickness ratio of a maximum
wall thickness to a minimum wall thickness of a body of the
container is not more than 1.6, and that a difference in elongation
between a maximally stretched portion and a minimally stretched
portion of the body of the container in a tensile test at
95.degree. C. is not more than 150%.
[0025] [2] A flat polyester resin container obtained by the blow
molding of a polyester resin, which is characterized in that the
flatness ratio, which is the ratio of a major axis to a minor axis,
is not less than 1.3, that the wall thickness ratio of a maximum
wall thickness to a minimum wall thickness of a body of the
container is not more than 1.6, that the crystallinity of the body
of the container is not less than 30%, and that a difference in TMA
non-load change between a maximally stretched portion and a
minimally stretched portion of the body of the container at
75.degree. C. and 100.degree. C. is not more than 500 .mu.m.
[0026] [3] A flat polyester resin container obtained by the blow
molding of a polyester resin, which is characterized in that the
flatness ratio, which is the ratio of a major axis to a minor axis,
is not less than 1.3, that the wall thickness ratio of a maximum
wall thickness to a minimum wall thickness of a body of the
container is not more than 1.6, that a difference in elongation
between a maximally stretched portion and a minimally stretched
portion of the body of the container in a tensile test at
95.degree. C. is not more than 150%, that the crystallinity of the
body of the container is not less than 30%, and that a difference
in TMA non-load change between a maximally stretched portion and a
minimally stretched portion of the body of the container at
75.degree. C. and 100.degree. C. is not more than 500 .mu.m.
[0027] [4] The flat polyester resin container according to any one
of [1] to [3], which is characterized in that the sectional shape
of the body of the flat container is a rectangle or an ellipse.
[0028] [5] The flat polyester resin container according to any one
of [1] to [4], which is characterized in that the polyester resin
is polyethylene terephthalate.
[0029] [6] The flat polyester resin container according to any one
of [1] to [5], which is characterized in that the flat container is
of a multilayer structure comprising a polyester resin layer and a
functional thermoplastic resin layer.
[0030] [7] The flat polyester resin container according to any one
of [1] to [6], which is characterized in that one or more
transverse ribs are provided in a horizontal concavity on a
long-side side surface.
[0031] [8] The flat polyester resin container according to any one
of [1] to [6], which is characterized in that the flat polyester
resin container is obtained by subjecting a bottomed parison
preformed from a polyester resin to primary blow molding, thereby
molding the bottomed parison into a bottomed cylindrical body
having a diameter larger than the minor axis of a cavity within a
mold for secondary blow molding, thereafter causing the bottomed
cylindrical body to shrink in a heated condition, thereby to cause
the bottomed cylindrical body to maintain a diameter which is
smaller than the major axis of the cavity within the mold for
secondary blow molding and larger than the minor axis thereof,
attaching the bottomed cylindrical molded article to the interior
of the mold for secondary blow molding, performing mold clamping,
with the bottomed cylindrical molded article depressed in the minor
axis direction of the cavity within the mold, feeding thereafter a
pressure fluid into the bottomed cylindrical molded article, and
causing the bottomed cylindrical molded article to flow in a heated
condition along the shape of the cavity on an inner surface of the
mold, thereby to mold the flat polyester resin container.
[0032] [9] A two-stage blow molding process of a flat container,
which is characterized in that the flat container two-stage blow
molding process comprises subjecting a bottomed parison, which is a
first intermediate molded article formed from a thermoplastic
resin, to primary blow molding to form the first intermediate
molded article into a second intermediate molded article having a
diameter larger than the minor axis of a cavity within a mold for
secondary blow molding, causing the second intermediate molded
article to undergo thermal shrinkage, thereby to form the second
intermediate molded article into a third intermediate molded
article having a body diameter smaller than the major axis of the
cavity within the mold for secondary blow molding and larger than
the minor axis thereof, attaching the third intermediate molded
article to the interior of the mold for secondary blow molding
subjected to mold surface treatment in an upper portion and/or a
lower portion of a body molding surface thereof at least on the
long-side side of a container in order to ensure that the third
intermediate molded article is slippery when the third intermediate
molded article comes into contact, performing mold clamping, with
the third intermediate molded article depressed in the minor axis
direction of a mold cavity, and then performing secondary blow
molding.
[0033] [10] A two-stage blow molding process of a flat container,
which is characterized in that the flat container two-stage blow
molding process comprises subjecting a bottomed parison, which is a
first intermediate molded article formed from a thermoplastic
resin, to primary blow molding to form the first intermediate
molded article into a second intermediate molded article having a
diameter larger than the minor axis of a cavity within a mold for
secondary blow molding, causing the second intermediate molded
article to undergo thermal shrinkage, thereby to form the second
intermediate molded article into a third intermediate molded
article having a body diameter smaller than the major axis of the
cavity within the mold for secondary blow molding and larger than
the minor axis thereof, attaching the third intermediate molded
article to the interior of the mold for secondary blow molding,
which has convexities formed in an upper portion and/or a lower
portion of a body molding surface thereof at least on the long-side
side of a container, performing mold clamping, with the third
intermediate molded article depressed in the minor axis direction
of a mold cavity, and then performing secondary blow molding.
[0034] [11] A two-stage blow molding process of a flat container,
which is characterized in that the flat container two-stage blow
molding process comprises subjecting a bottomed parison, which is a
first intermediate molded article formed from a thermoplastic
resin, to primary blow molding to form the first intermediate
molded article into a second intermediate molded article having a
diameter larger than the minor axis of a cavity within a mold for
secondary blow molding, causing the second intermediate molded
article to undergo thermal shrinkage, thereby to form the second
intermediate molded article into a third intermediate molded
article having a body diameter smaller than the major axis of the
cavity within the mold for secondary blow molding and larger than
the minor axis thereof, attaching the third intermediate molded
article to the interior of the mold for secondary blow molding
subjected to mold surface treatment in an upper portion and/or a
lower portion of a body molding surface thereof at least on the
long-side side of a container in order to ensure that the third
intermediate molded article is slippery when the third intermediate
molded article comes into contact, and which mold has convexities
formed in at least an upper portion and/or a lower portion of a
body molding surface thereof at least on the long-side side of a
container, performing mold clamping, with the third intermediate
molded article depressed in the minor axis direction of a mold
cavity, and then performing secondary blow molding.
[0035] [12] The flat container two-stage blow molding process
according to [9] or [11], which is characterized in that the mold
surface treatment is coating with a fluororesin.
[0036] [13] The flat container two-stage blow molding process
according to [12], characterized in that the fluororesin is a
tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) or
polytetrafluoroethylene (PTFE).
[0037] [14] The flat container two-stage blow molding process
according to [10] or [11], which is characterized in that the size
of convexities formed on a mold surface is such that the lateral
width thereof is 30 to 90% of the major axis of a mold cavity
surface, the longitudinal width thereof is 1 to 30% of the formed
height of a flat product on the mold cavity surface, and the height
thereof is 2 to 40% of the minor axis of the mold cavity
surface.
[0038] [15] The flat container two-stage blow molding process
according to any one of [9] to [14], which is characterized in that
the thermoplastic resin is a polyester resin or polyethylene
terephthalate.
[0039] [16] The flat polyester resin container according to any one
of [1] to [7], which is characterized in that the flat polyester
resin container is molded by the flat container two-stage blow
molding process according to any of [9] to [14].
[0040] [17] A method for manufacturing a flat container by the
two-stage blow molding process, which is characterized in that the
method comprises subjecting a bottomed parison preformed from a
polyester resin to primary blow molding, thereby molding the
bottomed parison into a bottomed cylindrical body having a diameter
larger than the minor axis of a cavity within a mold for secondary
blow molding, thereafter causing the bottomed cylindrical body to
shrink in a heated condition, thereby to cause the bottomed
cylindrical body to maintain a diameter which is smaller than the
major axis of the cavity within the mold for secondary blow molding
and larger than the minor axis thereof, attaching the bottomed
cylindrical molded article to the interior of the mold for
secondary blow molding, performing mold clamping, with the bottomed
cylindrical molded article depressed in the minor axis direction of
the cavity within the mold, then feeding a pressure fluid into the
bottomed cylindrical molded article, and causing the bottomed
cylindrical molded article to flow in a heated condition along the
shape of the cavity on an inner surface of the mold, thereby to
mold the flat container.
BRIEF DESCRIPTION OF DRAWINGS
[0041] FIG. 1(a) and FIG. 1(b) are respectively a drawing showing
the condition of concavity occurrence and a container drawing of a
product in which wrinkles are formed when a third intermediate
molded article is subjected to blow molding by use of a
conventional blow mold for flattening molding;
[0042] FIG. 2 is a schematic diagram that shows each step in the
blow molding of the present invention;
[0043] FIG. 3(a) are a front view and a side view of a rectangular
flat container of the present invention, the front view including
places where measurement samples are taken;
[0044] FIG. 3(b) is a diagram that shows a section taken along line
A-A in the front view of FIG. 3(a);
[0045] FIG. 3(c) is a diagram that shows a section taken along line
B-B in the front view of FIG. 3(a);
[0046] FIGS. 4(a), 4(b) and 4(c) are a front view, a plan view and
a sectional view, respectively, of a ellipsoidal flat container of
the present invention;
[0047] FIG. 5 is a graph that shows measurement results of a
difference in elongation in a high-temperature tensile test at
95.degree. C.;
[0048] FIG. 6 is a graph that shows measurement results of a
difference in TMA non-load change; and
[0049] FIG. 7 shows a front view, a side view and a sectional view
of a flat container having transverse ribs of the present
invention.
BEST MODE OF CARRYING OUT THE INVENTION
[0050] Embodiments of the above-described invention of the present
invention groups will be concretely described in detail with
reference to the drawings.
[0051] 1. Basic Constitution
[0052] (1) Flat Container
[0053] The flat container of the present invention is a container
which is specified by various kinds of physical properties and to
which characteristics are imparted, as will be described in detail
below. As shown in FIGS. 3(a) to 3(c) and FIGS. 4(a) to 4(c), the
flat container of the present invention is a container whose
section has preferably a flat shape, such as a rectangle and an
ellipse, with the exception of the mouth opening. Appearance views
and sectional views, such as front views, side views and views with
arrows, in flat containers are shown in FIGS. 3(a) to 3(c) and
FIGS. 4(a) to 4(c).
[0054] Because of the flat shapes, beverage bottles formed from the
flat container of the present invention can be easily held by
consumers with hand and fingers, are not slippery even when the
container surfaces are wet while in use, and are beautiful thanks
to complex shapes.
[0055] (2) Flat Container Formed from Polyester Resin by Blow
Molding
[0056] The specified flat container of the present invention is
manufactured by blow molding a bottomed parison preformed from a
polyester resin.
[0057] Incidentally, as described above, prior to the creation of
the present invention, the inventors of the present application
devised the inventions relating to a blow molding method of a flat
container in order to manufacture a flat container which has a
uniformly formed wall thickness and is excellent in mechanical
strength and thermal resistance and which shape is stable even at
high temperatures, and they filed applications for these
inventions. Therefore, in the molding of the flat container of the
present invention, in particular in the above-described inventions
[1] and [2], it is possible to use the blow molding method relating
to the prior inventions in manufacturing a desired flat container,
in which molding is performed with a uniform wall thickness of the
container wall, as the above-described invention [8].
[0058] Concretely, as shown in FIGS. 2(a) to 2(d) as step drawings,
a preformed bottomed parison having a uniform wall thickness in
transverse section and a roughly circular section is subjected to
primary blow molding and stretched into a bottomed parison having a
diameter larger than the minor axis of a mold for secondary blow
molding (corresponding to the minor axis of a flat container), and
this bottomed parison is caused to shrink in a heated condition to
cause the bottomed parison to maintain a diameter which is smaller
than the major axis of the cavity within the mold for secondary
blow molding. On the other hand, a mold having a cavity of the
sectional shape of the flat container, which is a molded article,
is prepared, this bottomed, stretched parison is housed in a cavity
for secondary blow molding, and mold clamping is performed, with
the bottomed, stretched parison depressed into flat condition in
the minor axis direction of the cavity to perform the secondary
blow molding. As a result, the bottomed, stretched parison is
housed in such a manner that the section of the bottomed, stretched
parison becomes longer on the major axis side of the cavity than on
the minor axis side of the cavity, and the bottomed, stretched
parison is depressed and deformed in a flat condition. And when
secondary blow molding is performed, the wall thickness on the
minor axis side and major axis side of the formed flat container
becomes uniform or sufficiently uniform. As a result of this,
two-stage blowing of biaxial stretching is performed and this
enables the stretching and crystallization of the bottomed parison
to be sufficiently carried out and yields the subsidiary action
that the heat resistance and pressure resistance of a flat
container are remarkably improved.
[0059] In the primary blowing of the bottomed parison, the mold is
used to stabilize the shape after blowing. However, from an
economical aspect, free blowing in which a mold is not used may
also be performed.
[0060] It is possible to raise the magnification of transverse
elongation up to 3 to 5 times and the magnification of longitudinal
elongation up to 2 to 4 times in the primary blowing and this
brings about the high orientation of crystals and the
homogenization of elongation. It is also possible to suppress the
magnification of elongation on the minor axis side (the minor axis
of the container/the center diameter of the preform) to the order
of 2.5 times. In PET, the mold temperature in primary blowing is on
the order of 150.degree. C. and cooling is performed by air cooling
in free blowing. As the blow molding, the two-stage blowing process
of biaxial stretching is desirable in order to improve the physical
properties of molded articles.
[0061] Incidentally, in general, the mouth opening of a container
is not stretched and, therefore, strength and heat resistance are
improved by separately performing crystallization under heat.
[0062] 2. Specification of Flat Container
[0063] The specified flat container of the present invention is
advantageously manufactured by the blow molding of a bottomed
parison preformed from a polyester resin by methods as described
above. Properties such as the flatness ratio and wall thickness
ratio described below are imparted to the flat container by setting
molding conditions and the like and by appropriate designing as in
each embodiment, which will be described later.
[0064] (1) Flatness Ratio
[0065] The flatness ratio is the ratio of the major axis to the
minor axis (both being an outside diameter) of the body section of
a container, which shows flatness, and provides an index of the
flatness of the body section of a container. Concretely, in the
containers having a flat shape shown in FIGS. 3(a) to 3(c) and
FIGS. 4(a) to 4(c), the flatness ratio is expressed by the ratio of
the major axis (6, 106) to the minor axis (7, 107) in the
horizontal section (B-B, D-D) of the body (2, 102) of a container
(1, 101). Incidentally, in FIGS. 3(a) to 3(c) and FIGS. 4(a) to
4(c), the reference numerals 1 and 101 denote a flat polyester
resin container, the reference numerals 2 and 102 denote a
container body, the reference numerals 3 and 103 denote a container
bottom, the reference numerals 4 and 104 denote a container neck,
the reference numerals 5 and 105 denote a container shoulder, the
reference numerals 6 and 106 denote the major axis of the container
body, the reference numerals 7 and 107 denote the minor axis of the
container body, the reference numerals 8 and 108 denote a container
mouth opening, the reference numeral 9 denotes a sampling position
for the measurement of a maximally stretched portion (a column
part), and the reference numeral 10 denotes a sampling position for
the measurement of a minimally stretched portion (the middle part
of a panel).
[0066] In the present invention, the flatness ratio along with the
wall thickness ratio etc. of the container body is deeply
associated with the mechanical strength, heat resistance, etc. of a
flat container in association with the extensibility in the
container body at high temperatures, the thermal no-load change of
the container body at high temperatures, the crystallinity of the
container body, etc. Therefore, from the experiment data (shown in
Table 1, which will be described later) it is necessary that the
flatness ratio be not less than 1.3, and this specification of the
numerical value ensures that beverage bottles are easily held by
consumers with hand and fingers and are beautiful because of their
complex shapes.
[0067] (2) Wall Thickness Ratio of Container Body
[0068] The wall thickness ratio of the container body is an index
indicative of the uniformity of the wall thickness of the whole
container body. The closer to the numerical value of 1, the more
the wall thickness will be uniform as a whole, and this is
desirable. The wall thickness ratio is expressed as the ratio of a
maximum wall thickness to a minimum wall thickness of the section
of the container body except the container neck and the part in
contact with the ground.
[0069] As with the flatness ratio, the wall thickness ratio is
deeply associated with the mechanical strength, heat resistance,
etc. of a flat container, in association with the extensibility in
the container body at high temperatures, the thermal no-load change
of the container body at high temperatures, the crystallinity of
the container body, etc. Therefore, from the experiment data (shown
in Table 1, which will be described later) it is necessary that the
wall thickness ratio be not more than 1.6.
[0070] (3) Difference in Elongation at High Temperatures
[0071] The difference in elongation at high temperatures is deeply
associated with the mechanical strength, heat resistance, etc. of a
flat container. Therefore, concretely, a difference in elongation
between a maximally stretched portion (a column part) and a
minimally stretched portion (the middle part of a panel) of the
container body in a tensile test at 95.degree. C. is adopted as the
difference in elongation at high temperatures. The difference in
elongation at high temperatures is illustrated as a graph in FIG.
5, and calculated by an experiment method, which will be described
later. From the experiment data (shown in Table 1, which will be
described later) it is necessary that the difference in elongation
at high temperatures be not more than 150%.
[0072] When the difference in elongation between a maximally
stretched portion and a minimally stretched portion at high
temperatures is not more than 150%, the shape of a container is
stable even when the contents of the container are filled at
temperatures of the order of 95.degree. C., and the shape is not
distorted by deformation unlike conventional flat containers.
[0073] (4) Crystallinity
[0074] Crystallinity is an index (unit: %) indicative of the
crystallizability of the body of a flat container. Crystallinity
along with the flatness ratio etc. is deeply associated with the
mechanical strength, heat resistance, etc. of a flat container.
Therefore, from the experiment data (shown in Table 1, which will
be described later) it is necessary that crystallinity be not less
than 30%.
[0075] Crystallinity is a numerical value particularly
indispensable for the improvement of the heat resistance of a
container and calculated by an experiment calculating formula,
which will be described later.
[0076] (5) Difference in No-Load Change
[0077] The difference in no-load change of a flat container along
with the difference in elongation at high temperatures is deeply
associated with the mechanical strength, heat resistance, etc. of a
flat container. Therefore, concretely, a difference in TMA
(thermomechanical analysis) no-load change between a maximally
stretched portion and a minimally stretched portion of the
container body in the range from 75.degree. C. to 100.degree. C. is
adopted as the difference in no-load change. The difference in
no-load change is illustrated as a graph in FIG. 6, and calculated
by an experiment method, which will be described later. From the
experiment data (shown in Table 1, which will be described later)
it is necessary that the difference in no-load change be not more
than 500 .mu.m.
[0078] The difference in TMA no-load change indicates the
evaluation of heat resistance, in particular. When the difference
in TMA no-load change is not more than 500 .mu.m, the shape of a
container is stable even when the contents of the container are
filled at temperatures of the order of 95.degree. C., and the shape
is not distorted by deformation unlike conventional flat
containers.
[0079] In a flat container, a maximally stretched portion and a
minimally stretched portion of the container body exhibit different
magnifications of elongation and amounts of secondary working and
hence the column part and panel part have different heat resistance
values. Therefore, when the contents are filled at high
temperatures, the panel part bulges and heat resistance tends to
become poor. The flat container of the present invention that meets
this requirement has a small difference in orientation condition
between a maximally stretched portion and a minimally stretched
portion compared to conventional flat containers and is excellent
in heat resistance and hence the panel part does not bulge even
when the contents are filled at high temperatures.
[0080] (6) Thermoplastic Resin Materials
[0081] Molding resin materials for flatness containers are
polyester resins. Although polylactate resin and the like can be
mentioned as examples, usual polyethylene terephthalate (PET) is
mainly used in consideration of mechanical strength and heat
resistance.
[0082] In polyethylene terephthalate, the main repetition unit is
ethylene terephthalate and it is desirable to use a crystalline
resin in which not less than 90 mol % of the acid constituents is
terephthalic acid and not less than 90 mol % of the glycol
constituents is ethylene glycol. Isophthalic acid, naphthalene
dicarboxylic acid, etc. can be mentioned as examples of other acid
constituents of this PET, and diethylene glycol, 1,4-butanediol,
cyclohexane dimethanol, propylene glycol, etc. can be mentioned as
examples of other glycol constituents.
[0083] It is also possible to blend an oxygen-absorbing or
oxygen-blocking functional resin with the resin constituting a
container. Furthermore, according to the use, in order to impart
other performance, it is possible to appropriately blend various
kinds of additives, such as a usual coloring agent, ultraviolet
absorbing agent, antioxidant, antibacterial agent and oxygen
absorbing agent.
[0084] (7) Multilayer Materials
[0085] The present invention also covers a flat thermoplastic resin
container characterized by comprising a multilayer structure of a
polyester resin layer and a functional thermoplastic resin layer.
For this reason, in the present invention, a laminated, bottomed
parison, which is a multilayer material, can be appropriately used,
and the oxygen blocking properties are improved by the laminating
with, for example, polyamide and EVAL. The oxygen absorbing
properties may also be improved by providing an oxygen absorbing
layer in the intermediate layer. A polymer induced from polyene is
desirable as an oxidizable material used in the oxygen absorbing
layer. Resins containing units induced from polyenes containing 4
to 20 carbon atoms or open-chain or cyclic conjugated or
nonconjugated polyenes are advantageously used as such polyene.
[0086] (8) Formation of Transverse Ribs
[0087] As one of the ways of specifying the present invention, as
illustrated in FIG. 7, it is also possible to provide one or more
transverse ribs of concavities on the long-side side surface of a
flat container, and particularly one or more transverse ribs of
concavities that are horizontal as viewed from the height of the
container. The mechanical strength, heat resistance, etc. are
improved more by the ribs. The ribs can be formed by a molding
process which will be described later in 3.(2).
[0088] 3. Method for Molding Flat Containers
[0089] The flat container of the present invention can be
manufactured by the following basic molding method and improved
molding method as two-stage biaxial stretching blow molding.
[0090] (1) Basic Molding Method
[0091] As already described, the basic steps of the two-stage blow
molding process are shown as schematic diagrams in FIGS. 2(a) to
2(d). This is a manufacturing method of a flat container by the
two-stage blow molding process comprising the steps (a) to (d): (a)
subjecting a bottomed parison (a first intermediate molded article)
22 preformed from a polyester resin to primary blow molding,
thereby molding the bottomed parison into a bottomed cylindrical
body (a second intermediate molded article) having a diameter
larger than the minor axis of a cavity within a mold for secondary
blow molding, (b) causing thereafter the bottomed cylindrical body
to shrink in a heated condition, thereby to cause the bottomed
cylindrical body to maintain a diameter which is smaller than the
major axis of the cavity within the mold for secondary blow molding
and larger than the minor axis thereof, (c) attaching the bottomed
cylindrical molded article (a third intermediate molded article) to
the interior of the mold for secondary blow molding 20, and
performing mold clamping, with the bottomed cylindrical molded
article 23 depressed (crushed) in the minor axis direction of the
cavity 21 within the mold, (d) feeding thereafter a pressure fluid
into the bottomed cylindrical molded article, and causing the
bottomed cylindrical molded article to flow in a heated condition
along the shape of the cavity on an inner surface of the mold,
thereby to mold the flat container.
[0092] The step (a) involves subjecting a bottomed parison having a
section of a roughly circular shape preformed from a thermoplastic
resin to primary blow molding, thereby molding the bottomed parison
into a bottomed cylindrical body having a section of a roughly
circular shape and a diameter larger than the minor axis of a
cavity within a mold for secondary blow molding.
[0093] The parison is formed by usual means, such as an injection
molding machine and an extrusion molding machine, and thermoplastic
polyethylene terephthalate (PET) is used as the material. However,
in addition, any resin such as polyethylene, polypropylene and
polycarbonate may also be used. As the parison to be used, a
bottomed parison having a section of a roughly circular shape is
desirable from the standpoints of production efficiency and blow
efficiency, and the size of the parison is appropriately set
according to the size of a desired flat container, secondary blow
efficiency, etc.
[0094] In the primary blowing of a parison, a mold is used to
stabilize the shape after blowing. However, from an economical
aspect, the primary blowing may be performed by free blowing in
which a mold is not used.
[0095] It is possible to raise the magnification of transverse
elongation up to 3 to 5 times and the magnification of longitudinal
elongation up to 2 to 4 times in the primary blowing and this
brings about high orientation of crystals and the homogenization of
elongation. In PET, the mold temperature in primary blowing is on
the order of 150.degree. C. and cooling is performed by air cooling
in free blowing.
[0096] The step (b) involves causing the bottomed cylindrical body
to shrink in a heated condition. After the bottomed parison is
molded into a bottomed cylindrical body (an intermediate molded
article) having a section of a roughly circular shape and a
diameter which is larger than the minor axis of the cavity within
the mold for secondary blow molding, the bottomed cylindrical body
is caused to shrink under heat in an oven, whereby residual strains
generated in the resin by the primary blow molding are relieved and
the bottomed cylindrical body is caused to maintain a diameter
which is smaller than the major axis of the cavity within the mold
for secondary blow molding and larger than the minor axis
thereof.
[0097] In PET, heating conditions which are such that the bottle
temperature behind the oven is not less than 150.degree. C. are
adopted. Crystallization and thermal fixing are homogeneously and
sufficiently performed by this step and the parison that has been
stretched and inflated by primary blowing is caused to shrink and
is reduced in diameter.
[0098] The size of the section diameter of the intermediate molded
article after thermal shrinkage is an important requirement to be
considered when the intermediate molded article is housed
(attached) in the mold for secondary blowing by being depressed in
a flat shape. In order to ensure that the stretching on the major
axis side is sufficiently performed and that the wall thickness
becomes uniform, this size is set in such a manner that a gap for
the stretching of the intermediate molded article is maintained
between the intermediate molded article which has been stretched by
the deformation due to depression on the major axis side and the
inner surface of the mold. Incidentally, in order to ensure a
uniform wall thickness of a molded article, it is preferred that
the size of the section diameter of the intermediate molded article
be on the order of 1.1 to twice the minor axis of the cavity of the
secondary blow mold.
[0099] The step (c) involves attaching the intermediate molded
article to the interior of the mold for secondary blow molding, and
performing mold clamping, with the intermediate molded article
depressed in the minor axis direction of the cavity within the
mold. By ensuring that the intermediate molded article is attached
to the interior of the mold for secondary blow molding, that mold
clamping is performed, with the intermediate molded article
depressed in the minor axis direction of the cavity within the mold
as viewed from the section thereof, and that the intermediate
molded article is housed in the cavity beforehand in a flat
condition, the intermediate molded article is housed in such a
manner that the section of the intermediate molded article becomes
longer on the major axis side of the cavity than on the minor axis
side thereof and the intermediate molded article is deformed by
depression into a flat shape so that a gap for the stretching of
the intermediate molded article is maintained between the
intermediate molded article which has been stretched by the
deformation due to depression on the major axis side and the inner
surface of the mold.
[0100] The step (d) involves feeding a pressure fluid into the
bottomed cylindrical molded article, and causing the intermediate
molded article to flow in a heated condition along the shape of the
cavity on an inner surface of the mold, thereby to mold the flat
container. The step corresponds to secondary blowing in the
two-stage blow molding to mold by blowing the intermediate molded
article to a final shape of the flat container.
[0101] It is preferred that a split mold be used as the mold for
secondary blow molding, and for the sake of convenience, it is
preferred that heated air be used as the pressure liquid. The
blowing air pressure is on the order of 2 to 4 MPa, which are usual
values.
[0102] As a result of such secondary blowing, the balance of wall
thickness between the minor axis side and the major axis side is
obtained and the uniformity of the wall thickness of container wall
is realized in a molded article of a flat container. And by
performing secondary blow molding, the difference in the
magnification of elongation on the minor axis side and the major
axis side is reduced and the wall thickness of a formed flat
container on the minor axis side and the major axis side becomes
sufficiently uniform.
[0103] (2) Improved Molding Method
[0104] As illustrated in FIGS. 1(a) and 1(b), in the
above-described method of conventional technique of Japanese Patent
Publication No. 59-53861, the shapability of blow molding is
insufficient and wrinkles due to the waviness of concavities
occurring partially on the surface of an intermediate molded
article during the second blow molding are apt to remain on the
surface of a product, posing the problems of a poor appearance and
insufficient strength. Therefore, in this application, which might
be called the second basic invention, by solving such problems, an
improved molding method which will be described below was created
in order to make the wall thickness uniform to a greater extent and
to improve mechanical strength, heat resistance, etc. This improved
molding method basically involves performing surface treatment to a
mold or forming convexities in a mold.
[0105] a. Surface Treatment of Mold
[0106] In the basic step of the feature (1) described above, by
subjecting an upper portion and/or a lower portion of a body
molding surface of the mold for blow molding at least on the
long-side side of a container (corresponding to the major axis side
in the case of a elliptical section) to mold surface treatment, the
slipperiness of a resin material on a partial surface of the mold
for blow molding is improved, and as a result of this, further
uniformity of the wall thickness of the container is achieved. And
at the same time, by thoroughly performing the shaping by blow
molding, wrinkles due to the waviness of concavities occurring
partially on the surface of an intermediate molded article are
prevented from being formed and the problems of poor appearance and
insufficient strength are solved.
[0107] Examples of the mold surface treatment include surface
roughening treatment and coating treatment. In surface roughening
treatment, for example, the mold surface may be roughened by being
rubbed with sandpaper, water-resistant paper and the like, or the
mold surface may be roughened by sandblasting treatment and iepco
treatment (a surface treatment method which involves performing
peening with ultrafine hard balls after the removal of burrs from
the surface to be treated and cleaning thereof.
[0108] Examples of the coating treatment include coating with
silicon, tungsten disulfide, fluororesin, etc. In particular,
however, coating with fluororesin is desirable from the standpoints
of the slipperiness between a third intermediate molded article and
the mold in the blow molding of the third intermediate molded
article and of the durability of a coating agent.
[0109] As the fluororesin, a tetrafluoroethylene perfluoroalkyl
vinyl ether copolymer (PFA) and polytetrafluoroethylene (PTFE) are
preferably be used.
[0110] b. Formation of Convexities on Mold Surface
[0111] In the basic step of the feature (1) described above, by
forming one or more convexities, which are preferably horizontal as
viewed from the height of a container, in an upper portion and/or a
lower portion of a body molding surface in the mold for blow
molding at least on the long-side side of the container, the
waviness of concavities which partially occurs on the major axis
side surface of an intermediate molded article is caused to be
absorbed in the convexities, and in a case where minor wrinkles
incapable of being completely removed tend to remain, by stretching
the wrinkles during secondary blow molding, further uniformity of
the wall thickness of the container is achieved. And at the same
time, by thoroughly performing the shaping by blow molding,
wrinkles due to the waviness of concavities occurring partially on
the surface of an intermediate molded article are prevented from
being formed in a product container and the problems of poor
appearance and insufficient strength are solved.
[0112] For the size of convexities formed on a mold surface, it is
preferred from experimental verifications that the lateral width
thereof be 30 to 90% of the major axis of a mold cavity surface,
that the longitudinal width thereof (the width equivalent to the
vertical height of a container) is 1 to 30% of the formed height of
a flat product on the mold cavity surface, and that the height
thereof is 2 to 40% of the minor axis of the mold cavity surface.
It is because the waviness of concavities which partially occurs on
the major axis side surface of an intermediate molded article is
absorbed in the convexities.
[0113] Incidentally, by providing a large number of convexities
parallel to the body diameter direction on the side surface on the
major axis side of a container as shown in FIG. 7, the surface area
of the convexities increases and it becomes easier to absorb the
waviness of the concavities in an intermediate molded article. The
concavities on the container surface may be made deep stepwise and
may also be provided in a pressure-reducing absorption panel. In
FIG. 7, the formation of convexities on the mold surface is also
illustrated as indicated by the hatched area.
[0114] c. Combination of Surface Treatment of Mold Surface and
Formation of Convexities
[0115] The problem in the conventional techniques as illustrated in
FIGS. 1(a) and 1(b) can be solved more sufficiently and efficiently
by adopting the combination of the above-described surface
treatment of the mold surface and formation of convexities on the
mold surface.
Embodiments
[0116] The present invention will be concretely described below in
further detail by comparing embodiments with reference examples
(comparative examples) with reference to the drawings. The
following embodiments and comparative examples are to illustrate
the preferred embodiment of the present invention and to describe
the present invention more clearly. Furthermore, these embodiments
and comparative examples are to demonstrate the rationality and
significance of the constituent features of the present
invention.
[Measuring Methods]
[0117] 1) Measurement of Crystallinity
[0118] Test pieces are cut out of the body of a flat container and
the density of the test pieces .rho. (g/cm.sup.3) is found by the
density-gradient tube method. The crystallinity is calculated by
the following equation.
Crystallinity
(%)={.rho.c(.rho.-.rho.a)/.rho.(.rho.c-.rho.a)}.times.100
[0119] .rho.c: Crystal density (1.455 g/cm.sup.3)
[0120] .rho.a: Noncrystal density (1.335 g/cm.sup.3)
[0121] 2) Measurement of Difference in Elongation in 95.degree. C.
Tensile Test
[0122] As shown in FIG. 3(a), a strip-like test piece having a size
5.times.40 mm is cut out in the longitudinal (height) direction
each in the maximally stretched portion (a column part) 9 and a
minimally stretched portion (the middle part of a panel) 10 at the
same level of the body of a flat container, and the test pieces are
subjected to a tensile test in a thermoregulator at 95.degree. C. A
difference in a maximum elongation between the two places is
regarded as the difference in elongation by stretching at
95.degree. C.
[0123] Incidentally, the measurement was made, with the chuck
distance set at 10 mm and the crosshead speed set at 10 mm/minute,
and measurement results were indicated by elongation
(%)=(.DELTA.L/L.sub.0).times.100, where the chuck distance is
denoted by L.sub.0 and the distance over which the sample is
stretched is denoted by .DELTA.L.
[0124] TENSILON universal testing machine UCT-500 made by ORIENTEC
Co., Ltd. was used as the test apparatus.
[0125] FIG. 5 illustrates a graph that shows measurement results of
a difference in elongation in the tensile test at 95.degree. C. In
FIG. 5, the difference in the maximum elongation between a
maximally stretched portion and a minimally stretched portion is
389-333=56%.
[0126] 3) Measurement of Difference in TMA No-Load Change
[0127] As shown in FIG. 3(a), a strip-like test piece having a size
5.times.40 mm is cut out in the longitudinal (height) direction
each in the maximally stretched portion (a column part) 9 and a
minimally stretched portion (the middle part of a panel) 10 at the
same level of the body of a flat container, and the test pieces are
measured by TMA (a thermomechanical analysis) method. A difference
in change between the two places is regarded as the difference in
TMA no-load change.
[0128] As the measurement method of the difference in TMA no-load
change, measurements are made, with the stress applied to the test
piece set at zero, the chuck distance set at 20 mm, and the
temperature rise rate from room temperature to 100.degree. C. at
5.degree. C./minute. In the digitalization of changes, calculations
are made on the basis of changes from 75.degree. C. near the glass
transition temperature, which is the starting point, to 100.degree.
C. DMS-6100 made by Seiko Instruments Inc. was used as the test
apparatus.
[0129] FIG. 6 illustrates a graph that shows measurement results of
a difference in TMA non-load change. From FIG. 6, the difference in
a change between a maximally stretched portion and a minimally
stretched portion observed when the temperature rose from
75.degree. C., which is the starting point, to 100.degree. C. is
42-(-68)=110 .mu.m.
Equivalent to Embodiment 1
[0130] 4) Method of Heat Resistance Evaluation
[0131] Hot water at 87.degree. C. was filled in a flat container,
the flat container was showered with warm water at 75.degree. C.
for five minutes after hermetical sealing, and the container was
visually checked for deformation. (.largecircle.: without
deformation, x: with deformation)
Embodiment 1
[0132] A bottomed parison, which was a first intermediate molded
article having an outside diameter of 22 mm, a thickness of 3.4 mm
and a height of 80 mm, was preformed from commercially available
polyethylene terephthalate (PET), heated air was blown in by free
blowing and the first intermediate molded article was subjected to
primary blow molding to form a second intermediate molded article
having an outside diameter of 90 mm.
[0133] The second intermediate molded article subjected to the
primary blow molding was caused to shrink and be fixed for 8
seconds in an oven at 600.degree. C. and a shrunk, molded article
having an outside diameter of 60 mm, which was a third intermediate
molded article, was obtained.
[0134] A mold for second blow molding (set at 140.degree. C.) had a
cavity (section: minor axis 50 m, major axis 66 mm) with the
rectangular section shown in (d) of FIG. 2, and an upper portion of
a body molding surface of the blow mold on the long-side side of a
container was coated with a fluororesin. The third intermediate
molded article was housed in the cavity by being depressed into the
cavity in the minor axis direction.
[0135] Air at 20.degree. C. and 3 MPa was fed into the third
intermediate molded article deformed by depression and secondary
blow molding was performed, whereby a flat container having a
rectangular section and a flatness ratio of 1.3 was molded. No
wrinkle remained in the body of this flat container.
[0136] Table 1 shows measurement results of the crystallinity of
the body of this flat container, the wall thickness ratio of a
maximum wall thickness to a minimum wall thickness of the section
of the container, the difference in elongation between a maximally
stretched portion and a minimally stretched portion of the
container body in a tensile test at 95.degree. C., and the
difference in TMA no-load change in a maximally stretched portion
and a minimally stretched portion of the container body in the
range from 75.degree. C. to 100.degree. C.
Embodiment 2
[0137] A flat container having an elliptical section and a flatness
ratio of 1.5 was molded in the same way as in Embodiment 1, with
the exception that primary blow molding was performed by using a
mold for primary blow molding instead of performing free blow
molding and that a mold which upper portion of a body molding
surface thereof on the long-side side (major axis side) of a
container was coated with a fluororesin and which had a cavity
(section: minor axis 47 mm, major axis 70 mm) with an elliptical
section was used as a second blow mold.
Embodiment 3
[0138] A flat container having a rectangular section and a flatness
ratio of 2.0 was molded in the same way as in Embodiment 1, with
the exception that primary blow molding was performed by using a
mold for primary blow molding instead of performing free blow
molding and that a mold which upper portion of a body molding
surface thereof on the long-side side of a container was coated
with a fluororesin and which had a cavity (section: minor axis 40
mm, major axis 80 mm) with a rectangular section was used as a
second blow mold.
Embodiment 4
[0139] A flat container having a rectangular section and a flatness
ratio of 2.5 was molded in the same way as in Embodiment 1, with
the exception that primary blow molding was performed by using a
mold for primary blow molding instead of performing free blow
molding and that a mold which upper portion of a body molding
surface thereof on the long-side side of a container was coated
with a fluororesin and which had a cavity (section: minor axis 36
mm, major axis 90 mm) with a rectangular section was used as a
second blow mold.
Embodiment 5
[0140] A flat container having a rectangular section and a flatness
ratio of 2.0 was molded in the same way as in Embodiment 3, with
the exception that a mold which lower portion of a body molding
surface thereof on the long-side side of a container was coated
with a fluororesin and which had a cavity (section: minor axis 40
mm, major axis 80 mm) with a rectangular section was used as a
second blow mold.
Embodiment 6
[0141] A flat container having a rectangular section and a flatness
ratio of 2.0 was molded in the same way as in Embodiment 3, with
the exception that a mold which had convexities in an upper portion
of a body molding surface thereof on the long-side side of a
container and had a cavity (section: minor axis 40 mm, major axis
80 mm) with a rectangular section was used as a second blow
mold.
Embodiment 7
[0142] A flat container having a rectangular section and a flatness
ratio of 2.0 was molded in the same way as in Embodiment 3, with
the exception that a mold which had convexities in a lower portion
of a body molding surface thereof on the long-side side of a
container and had a cavity (section: minor axis 40 mm, major axis
80 mm) with a rectangular section was used as a second blow
mold.
Embodiment 8
[0143] A flat container having a rectangular section and a flatness
ratio of 2.0 was molded in the same way as in Embodiment 3, with
the exception that a mold which had convexities in an upper portion
and a lower portion of a body molding surface thereof on the
long-side side of a container and in which the whole area of a
container molding surface was coated with a fluororesin, and which
had a cavity (section: minor axis 40 mm, major axis 80 mm) with a
rectangular section was used as a second blow mold.
[0144] Also the flat containers molded in Embodiments 2 to 8 were
product containers having no wrinkle in the body and a good
appearance. Table 1 shows measurement results of the crystallinity
of the bodies of these flat containers, the wall thickness ratio of
a maximum wall thickness to a minimum wall thickness of the
sections of the containers, the difference in elongation between a
maximally stretched portion and a minimally stretched portion of
the container bodies in a tensile test at 95.degree. C., and the
difference in TMA no-load change in a maximally stretched portion
and a minimally stretched portion of the container bodies in the
range from 75.degree. C. to 100.degree. C.
Comparative Example 1
[0145] A flat container having a rectangular section and a flatness
ratio of 1.3 was molded by using the same preformed parison as used
in Embodiment 1, stretching the preformed parison by use of a mold
for primary blow molding, housing a shrunk, intermediate molded
article in the mold with a size not depressed in the minor axis
direction, using the same mold for secondary blowing molding as
used in Embodiment 1, and performing blow molding under the same
blowing conditions.
Comparative Example 2
[0146] A flat container having a rectangular section and a flatness
ratio of 2.0 was molded by using the same preformed parison as used
in Embodiment 1, stretching the preformed parison by use of a mold
for primary blow molding, housing a shrunk, intermediate molded
article in the mold with a size not depressed in the minor axis
direction, using the same mold for secondary blowing molding as
used in Embodiment 3, and performing blow molding under the same
blowing conditions.
Comparative Example 3
[0147] A flat container having a rectangular section and a flatness
ratio of 2.0 was molded in the same way as in Embodiment 3, with
the exception that a mold in which the whole area of a container
molding surface was subjected to mirror finish treatment and which
had a cavity (section: minor axis 40 mm, major axis 80 mm) with a
rectangular section was used as a mold for secondary blowing. In
the flat container formed in Comparative Example 3, wrinkles
remained in an upper portion and a lower portion of the body on the
long-side side and the shape was poor.
[0148] Table 1 shows measurement results of the crystallinity of
the bodies of the flat containers molded in Comparative Examples 1
to 3, the wall thickness ratio of a maximum wall thickness to a
minimum wall thickness of the sections of the containers, the
difference in elongation between a maximally stretched portion and
a minimally stretched portion of the container bodies in a tensile
test at 95.degree. C., and the difference in TMA no-load change in
a maximally stretched portion and a minimally stretched portion of
the container bodies in the range from 75.degree. C. to 100.degree.
C.
TABLE-US-00001 TABLE 1 Difference in Wall elongation in TMA
Flatness Crystallinity thickness 95.degree. C. tensile test
difference Heat ratio (%) ratio (%) (.mu.m) resistance Embodiment 1
1.3 38 1.24 49 110 .smallcircle. Embodiment 2 1.5 40 1.30 71 209
.smallcircle. Embodiment 3 2.0 42 1.35 106 313 .smallcircle.
Embodiment 4 2.5 41 1.41 138 404 .smallcircle. Embodiment 5 2.0 42
1.36 107 320 .smallcircle. Embodiment 6 2.0 41 1.35 109 331
.smallcircle. Embodiment 7 2.0 40 1.36 110 328 .smallcircle.
Embodiment 8 2.0 41 1.35 115 320 .smallcircle. Comparative 1.3 40
1.65 177 701 x Example 1 Comparative 2.0 39 1.72 195 900 x Example
2 Comparative 2.0 42 1.35 106 313 Unevaluated Example 3 because of
poor shape
Consideration of Results of Each Embodiment and Each Comparative
Example
[0149] By comparing each of the embodiments with each of the
comparative examples, it is made obvious that a flat container in
the present invention is excellent in heat resistance and
mechanical strength if it meets the requirements for the flatness
ratio, the wall thickness ratio, crystallinity, the difference in
elongation in a tensile test at 95.degree. C., and the TMA
difference. Furthermore, it has become obvious that a poor
appearance, such as wrinkles, does not occur any more by performing
two-stage blow molding that involves secondary blow molding after a
third intermediate molded article is depressed by use of a
secondary blowing mold which is subjected to coating with a
fluororesin or in which convexities are formed.
[0150] In Embodiments 1 to 8, as is apparent from the numerical
figures shown in Table 1, the circumferential wall thickness ratio
of the body of each container was small with high uniformity of the
wall thickness and the difference in physical properties in a
maximally stretched portion and a minimally stretched portion of
the container body was small. Therefore, the mechanical strength
was sufficient and the heat resistance was also good. In each of
the embodiments, the difference in elongation between a maximally
stretched portion and a minimally stretched portion at high
temperatures was small compared to the comparative examples and
also the difference in TMA no-load change was also small compared
to the comparative examples. Therefore, even when the contents are
filled at high temperatures, the shape is stable and the shape is
not distorted by deformation unlike conventional flat
containers.
[0151] In Comparative Examples 1 and 2, a shrunk, intermediate
molded article is housed in the mold with a size not depressed in
the minor axis direction. Therefore, as is apparent from the
numerical values shown in Table 1, the circumferential wall
thickness ratio of the container body was large compared to each of
the embodiments. Thus Comparative Examples 1 and 2 were inferior to
each of the embodiments in the uniformity of the wall thickness.
Also the difference in elongation between a maximally stretched
portion and a minimally stretched portion at high temperatures and
the difference in TMA no-load change were large compared to each of
the embodiments. Thus Comparative Examples 1 and 2 were inferior to
each of the embodiments in heat resistance and mechanical
strength.
[0152] In Comparative Example 3, a shrunk, intermediate molded
article is housed in the mold by being depressed in the minor axis
direction. However, because a mold for blow molding subjected to
mirror finish treatment is used, as is apparent from the numerical
values shown in Table 1, Comparative Example 3 is excellent in the
circumferential wall thickness ratio of the container body, the
difference in elongation in a maximally stretched portion and a
minimally stretched portion at high temperatures, and the
difference in TMA no-load change to the same extent as each of the
embodiments. However, since the shapability (moldability) of
secondary blow molding was poor, the heat resistance could not be
evaluated.
[0153] It can be said from the foregoing that it is obvious that
the rationality and significance in the constituent features of the
present invention and the advantage of the present invention over
conventional techniques have been demonstrated.
INDUSTRIAL APPLICABILITY
[0154] The flat container in the present invention is excellent in
mechanical strength and heat resistance, the shape of the container
is stable even at high temperatures, and there is no fear that the
container might be deformed because of insufficient resistance
against inner pressure loads due to the expansion of beverages in
the container at high temperatures and against external pressure
loads due to the shrinkage of the interior during temperature
drops.
[0155] Therefore, this flat container is particularly excellent as
containers for high-temperature beverages and containers for
high-temperature pasteurized beverages, and is also advantageously
used for food in general, medical products, etc.
[0156] The flat container two-stage blow molding process in the
present invention can easily manufacture a flat container whose
wall thickness is made uniform remarkably and which is particularly
excellent in mechanical strength, heat resistance and pressure
resistance, without the occurrence of wrinkles due to defective
molding on the container surface.
[0157] As described above, the present invention enables excellent
containers used in various technical fields and their molding
methods to be developed, is useful in the industries of plastic
molding and plastic containers, and has high industrial
applicability.
* * * * *