U.S. patent application number 11/792455 was filed with the patent office on 2008-06-05 for hinge cap having biodegradability.
Invention is credited to Masami Fujita, Kunio Murakami, Manabu Sakamoto, Akira Yamamoto.
Application Number | 20080128382 11/792455 |
Document ID | / |
Family ID | 36587740 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080128382 |
Kind Code |
A1 |
Yamamoto; Akira ; et
al. |
June 5, 2008 |
Hinge Cap Having Biodegradability
Abstract
A hinge cap is provided which includes: a cap body having a top
wall, a spout provided in the top wall and a side wall extending
downward from a peripheral edge of the top wall; and an upper cap
portion connected to the cap body via a hinge and capable of
capping and uncapping the spout. The hinge cap is composed of a
resin composition comprising polylactic acid and an aliphatic
polyester resin other than the polylactic acid. The polylactic acid
and the aliphatic polyester resin other than the polylactic acid
are present in the resin composition in a mass ratio of (polylactic
acid):(aliphatic polyester other than polylactic acid)=90:10 to
5:95.
Inventors: |
Yamamoto; Akira; (Osaka,
JP) ; Fujita; Masami; (Kyoto, JP) ; Murakami;
Kunio; (Nara, JP) ; Sakamoto; Manabu; (Nara,
JP) |
Correspondence
Address: |
Fildes & Outland P.C.
20916 Mack Avenue, Suite 2
Grosse Pointe Woods
MI
48236
US
|
Family ID: |
36587740 |
Appl. No.: |
11/792455 |
Filed: |
December 5, 2005 |
PCT Filed: |
December 5, 2005 |
PCT NO: |
PCT/JP05/22273 |
371 Date: |
June 6, 2007 |
Current U.S.
Class: |
215/236 |
Current CPC
Class: |
C08L 67/04 20130101;
C08K 5/20 20130101; Y02W 90/12 20150501; B65D 47/0814 20130101;
C08L 67/02 20130101; C08K 5/09 20130101; Y02W 90/10 20150501; Y02W
90/13 20150501; C08L 67/02 20130101; C08L 2666/18 20130101; C08L
67/04 20130101; C08L 2666/18 20130101 |
Class at
Publication: |
215/236 |
International
Class: |
B65D 47/08 20060101
B65D047/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2004 |
JP |
2004-363750 |
Claims
1. A biodegradable hinge cap comprising: a cap body having a top
wall, a spout provided in the top wall and a side wall extending
downward from a peripheral edge of the top wall; and an upper cap
portion connected to the cap body via a hinge and capable of
capping and uncapping the spout; the hinge cap being composed of a
resin composition comprising polylactic acid and an aliphatic
polyester resin other than the polylactic acid; wherein the
polylactic acid and the aliphatic polyester resin other than the
polylactic acid are present in the resin composition in a mass
ratio of (polylactic acid):(aliphatic polyester other than
polylactic acid)=90:10 to 5:95.
2. A biodegradable hinge cap as set forth in claim 1, wherein the
mass ratio between the polylactic acid and the aliphatic polyester
resin other than the polylactic acid in the resin composition is
(polylactic acid):(aliphatic polyester other than polylactic
acid)=60:40 to 10:90.
3. A biodegradable hinge cap as set forth in claim 1, wherein the
mass ratio between the polylactic acid and the aliphatic polyester
resin other than the polylactic acid in the resin composition is
(polylactic acid):(aliphatic polyester other than polylactic
acid)=40:60 to 20:80.
4. A biodegradable hinge cap as set forth in claim 1, wherein the
resin composition has a flexural modulus of 700 to 3000 MPa.
5. A biodegradable hinge cap as set forth in claim 1, wherein the
resin composition has a flexural modulus of 1100 to 1800 MPa.
6. A biodegradable hinge cap as set forth in claim 1, wherein the
aliphatic polyester resin other than the polylactic acid is a
polyalkylene alkanoate.
7. A biodegradable hinge cap as set forth in claim 6, wherein the
polyalkylene alkanoate is one of polybutylene succinate, a
copolymer of polybutylene succinate and a mixture of polybutylene
succinate and the polybutylene succinate copolymer.
8. A biodegradable hinge cap as set forth in claim 7, wherein the
polybutylene succinate copolymer is polybutylene succinate
adipate.
9. A biodegradable hinge cap as set forth in claim 1, wherein the
resin composition further comprises 0.01 to 5 parts by mass of one
of a fatty acid, a fatty amide and a mixture of the fatty acid and
the fatty amide based on a total of 100 parts by mass of the
polylactic acid and the aliphatic polyester resin other than the
polylactic acid.
10. A biodegradable hinge cap as set forth in claim 1, wherein the
resin composition further comprises 1 to 10 parts by mass of an
anti-blocking agent based on a total of 100 parts by mass of the
polylactic acid and the aliphatic polyester resin other than the
polylactic acid.
11. A biodegradable hinge cap as set forth in claim 1, wherein the
resin composition further comprises 0.1 to 10 parts by mass of a
hydrolysis suppressing agent based on a total of 100 parts by mass
of the polylactic acid and the aliphatic polyester resin other than
the polylactic acid.
12. A biodegradable hinge cap as set forth in claim 1, wherein the
hinge has a snap function for opening and closing the upper cap
portion with respect to the cap body.
13. A biodegradable hinge cap as set forth in claim 12, wherein the
hinge includes a thin hinge portion which connects the side wall of
the cap body to a side wall of the upper cap portion, and a pair of
resilient connection plates provided on opposite sides of the thin
hinge portion to connect the side wall of the cap body to the side
wall of the upper cap portion.
14. A biodegradable hinge cap as set forth in claim 1, wherein the
hinge has a tensile break stress retention ratio of not less than
20% after the upper cap portion is subjected to an opening/closing
operation 1,000 times.
15. A biodegradable hinge cap as set forth in claim 1, wherein the
hinge has a tensile break stress retention ratio of not less than
40% after the upper cap portion is subjected to an opening/closing
operation 1,000 times.
Description
TECHNICAL FIELD
[0001] The present invention relates to a biodegradable hinge cap
of a synthetic resin.
BACKGROUND ART
[0002] Known as a hinge cap for use with a bottle or a tubular
container is a cap which includes a cap body and an upper cap
portion connected to each other by a hinge having a thinner portion
(for example, Japanese Unexamined Utility Publication No. 49
(1974)-26863). Another known hinge cap is a snap hinge cap which
includes a cap body and an upper cap portion connected to each
other by a hinge having a thinner portion and a pair of resilient
connection plates provided on opposite sides of the hinge and
thereby has a snap function (for example, JP-A-8-301329).
[0003] These hinge caps can be conveniently opened and closed by a
single hand with no possibility of missing the upper cap portion,
because the upper cap portion is connected to the cap body.
Further, the snap hinge cap can be opened and closed by a snap
action (biasing force) of the resilient connection plates without
the need for applying a force.
[0004] Conventionally, these hinge caps are each composed of a
synthetic olefin resin such as polyethylene or polypropylene.
However, such a polyolefin polymer has almost no biodegradability
in the natural environment. If the polyolefin hinge caps are
discarded and buried in ground, the hinge caps permanently remain
in the ground. This presents environmental problems.
[0005] To cope with this, a cap composed of a biodegradable
polylactic acid is disclosed, for example, in JP-A-6-105887. The
polylactic acid is expected to be used for package material
applications and the like, because L-lactic acid as a material for
the polylactic acid is mass-produced at lower costs and the
polylactic acid has excellent biodegradability. Where the hinge cap
is composed of the polylactic acid, however, the strength of the
hinge is reduced to result in breakage of the hinge during repeated
opening and closing of the upper cap portion.
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0006] It is an object of the present invention to provide a
biodegradable hinge cap which maintains a sufficient hinge strength
and is less liable to suffer from the breakage of a hinge thereof
even if an upper cap portion thereof is repeatedly opened and
closed, like the prior-art hinge cap of polyethylene or
polypropylene.
Means for Solving the Problems
[0007] As a result of intensive studies for solving the
aforementioned problems, the inventors of the present invention
found that a hinge cap formed of a resin composition prepared by
mixing polylactic acid with an aliphatic polyester resin other than
the polylactic acid in a specific mass ratio maintains a sufficient
hinge strength even if an upper cap portion thereof is repeatedly
opened and closed and even if the hinge cap has a snap function,
and the snap function thereof is excellent. Thus, the present
invention has been attained.
[0008] According to the present invention, a biodegradable hinge
cap is provided which comprises: a cap body having a top wall, a
spout provided in the top wall and a side wall extending downward
from a peripheral edge of the top wall; and an upper cap portion
connected to the cap body via a hinge and capable of capping and
uncapping the spout; the hinge cap being composed of a resin
composition comprising polylactic acid and an aliphatic polyester
resin other than the polylactic acid; wherein the polylactic acid
and the aliphatic polyester resin other than the polylactic acid
are present in the resin composition in a mass ratio of (polylactic
acid):(aliphatic polyester other than polylactic acid)=90:10 to
5:95.
[0009] The inventive hinge cap is preferably composed of a resin
composition comprising the polylactic acid and the aliphatic
polyester resin other than the polylactic acid in a mass ratio of
(polylactic acid):(aliphatic polyester other than polylactic
acid)=60:40 to 10:90, so that the hinge cap can maintain a
sufficient hinge strength even after the upper cap portion is
opened and closed. It is particularly preferred that the inventive
hinge cap is composed of a resin composition comprising the
polylactic acid and the aliphatic polyester resin other than the
polylactic acid in a mass ratio of (polylactic acid):(aliphatic
polyester other than polylactic acid)=40:60 to 20:80.
[0010] According to the present invention, the resin composition to
be used for the hinge cap preferably has a flexural modulus of 700
to 3000 MPa to impart the hinge cap with a snap function, and
particularly preferably has a flexural modulus of 1100 to 1800
MPa.
[0011] According to the present invention, the aliphatic polyester
resin other than the polylactic acid is preferably a polyalkylene
alkanoate. For example, the polyalkylene alkanoate may be
polybutylene succinate, a copolymer of polybutylene succinate or a
mixture of polybutylene succinate and the polybutylene succinate
copolymer. An example of the polybutylene succinate copolymer is
polybutylene succinate adipate.
[0012] The resin composition to be used for the inventive hinge cap
may further comprise 0.01 to 5 parts by mass of a fatty acid, a
fatty amide or a mixture of the fatty acid and the fatty amide
based on a total of 100 parts by mass of the polylactic acid and
the aliphatic polyester resin other than the polylactic acid.
[0013] The resin composition to be used for the inventive hinge cap
may further comprise 1 to 10 parts by mass of an anti-blocking
agent based on a total of 100 parts by mass of the polylactic acid
and the aliphatic polyester resin other than the polylactic
acid.
[0014] The resin composition to be used for the inventive hinge cap
preferably further comprises 0.1 to 10 parts by mass of a
hydrolysis suppressing agent based on a total of 100 parts by mass
of the polylactic acid and the aliphatic polyester resin other than
the polylactic acid.
[0015] In the inventive hinge cap, the hinge may have a snap
function for opening and closing the upper cap portion with respect
to the cap body. In the inventive hinge cap, the hinge may include
a thin hinge portion which connects the side wall of the cap body
to a side wall of the upper cap portion, and a pair of resilient
connection plates provided on opposite sides of the thin hinge
portion to connect the side wall of the cap body to the side wall
of the upper cap portion, wherein the resilient connection plates
have a snap function for opening and closing the upper cap portion
with respect to the cap body.
[0016] In the inventive hinge cap, the hinge preferably has a
tensile break stress retention ratio of not less than 20%,
particularly preferably a tensile break stress retention ratio of
not less than 40%, after the upper cap portion is subjected to an
opening/closing operation 1,000 times.
EFFECTS OF THE INVENTION
[0017] The inventive biodegradable hinge cap is composed of the
resin composition comprising the polylactic acid and the aliphatic
polyester resin other than the polylactic acid, and the mass ratio
between the polylactic acid and the aliphatic polyester resin other
than the polylactic acid in the resin composition is set at a value
within the specific range. Thus, even if the upper cap portion is
repeatedly opened and closed, the hinge maintains a given hinge
strength. Further, the hinge cap has excellent biodegradability in
the natural environment and under composting conditions and,
therefore, is an environmentally friendly package material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a plan view of a hinge cap according to an
embodiment of the present invention.
[0019] FIG. 2 is a sectional view of the hinge cap of FIG. 1.
[0020] FIG. 3 is a plan view of a hinge cap according to another
embodiment of the present invention.
[0021] FIG. 4 is a sectional view of the hinge cap of FIG. 3.
BEST MODE FOR CARRYING OUT THE INVENTION
[0022] The present invention will hereinafter be described in
detail.
Polylactic Acid
[0023] Examples of the polylactic acid to be contained in the resin
composition for the inventive hinge cap include poly(L-lactic acid)
having a structural unit of L-lactic acid, poly(D-lactic acid)
having a structural unit of D-lactic acid, poly(DL-lactic acid)
having structural units of L-lactic acid and D-lactic acid, and a
mixture of any of these polylactic acids. Particularly, a molar
ratio between L-lactic acid and D-lactic acid in the polylactic
acid is preferably (L-lactic acid):(D-lactic acid)=100:0 to 90:10
or (L-lactic acid):(D-lactic acid)=0:100 to 10:90, more preferably
(L-lactic acid):(D-lactic acid)=100:0 to 94:6 or (L-lactic
acid):(D-lactic acid)=0:100 to 6:94. If the ratio between L-lactic
acid and D-lactic acid falls outside the aforesaid range, it is
difficult to impart the hinge cap with heat resistance, thereby
limiting the application of the hinge cap.
[0024] In the present invention, polylactic acids containing
L-lactic acid and D-lactic acid in different copolymerization
ratios may be blended. In this case, the average of the
copolymerization ratios between L-lactic acid and D-lactic acid of
the polylactic acids preferably falls within the aforesaid
range.
[0025] A known method such as a condensation polymerization method
or a ring-opening polymerization method may be employed for
polymerization for preparation of the polylactic acid. In the
condensation polymerization method, for example, L-lactic acid,
D-lactic acid or a mixture of L-lactic acid and D-lactic acid is
directly subjected to dehydration/condensation polymerization to
provide a polylactic acid having a desired composition. In the
ring-opening polymerization method (lactide method), lactide which
is a cyclic dimer of lactic acid is employed together with a proper
catalyst and optionally a polymerization modifier to provide a
polylactic acid having a desired composition and a desired
crystallinity. Examples of the lactide include L-lactide which is a
dimer of L-lactic acid, D-lactide which is a dimer of D-lactic acid
and DL-lactide which contains L-lactic acid and D-lactic acid.
These lactides are mixed as required and subjected to the
polymerization to provide a polylactic acid having a desired
composition and a desired crystallinity.
[0026] The polylactic acid to be used in the present invention
preferably has a weight-average molecular weight of 50,000 to
400,000, more preferably 100,000 to 250,000. If the weight-average
molecular weight of the polylactic acid is lower than 50,000, it is
impossible to impart the hinge cap with practical properties such
as mechanical properties and heat resistance. If the weight-average
molecular weight is higher than 400,000, the polylactic acid has an
excessively high melt viscosity and hence an inferior
moldability.
[0027] Aliphatic Polyester Resin Other than Polylactic Acid
[0028] A polyalkylene alkanoate, for example, is employed as the
aliphatic polyester resin other than the polylactic acid to be
contained in the resin composition for the inventive hinge cap in
order to allow the hinge cap to maintain a given hinge strength
even if the upper cap portion is repeatedly opened and closed.
[0029] A polyalkylene alkanoate prepared by condensing one or more
of the following aliphatic polyalcohols and one or more of the
following aliphatic polybasic acids (or derivatives thereof) may be
used.
[0030] Examples of the aliphatic polyalcohols as one of the
ingredients of the polyalkylene alkanoate include ethylene glycol,
1,4-butanediol, 1,6-hexanediol, 1,8-octylene glycol,
1,10-decamethylene glycol, 1,4-cyclohexanedimethanol, among which
ethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol are
preferred in consideration of the physical properties of the
resulting polyalkylene alkanoate.
[0031] Examples of the aliphatic polybasic acids (or the
derivatives thereof) as the other ingredient of the polyalkylene
alkanoate include succinic acid, succinic acid anhydride, adipic
acid, sebacic acid, dodecane dicarboxylic acid and 1,4-cyclohexane
dicarboxylic acid, among which succinic acid and adipic acid are
preferred in consideration of the physical properties of the
resulting polyalkylene alkanoate. An aromatic polybasic acid such
as terephthalic acid may be used as a comonomer in combination with
the aliphatic polybasic acid.
[0032] In the present invention, preferred examples of the
polyalkylene alkanoate include polybutylene succinate which is a
dehydration condensation product of 1,4-butanediol and succinic
acid, and polybutylene succinate adipate which is a dehydration
condensation product of 1,4-butanediol, succinic acid and adipic
acid. These polyalkylene alkanoates preferably each have a
molecular weight increased by employing a chain extending agent
such as polylactic acid, a polyisocyanate or an acid anhydride in
order to impart a molded product with a sufficient strength.
[0033] Resin Composition
[0034] In the present invention, the mass ratio between the
polylactic acid and the aliphatic polyester resin other than the
polylactic acid in the resin composition for the hinge cap should
be (polylactic acid):(aliphatic polyester resin other than
polylactic acid)=90:10 to 5:95. If the ratio of the aliphatic
polyester resin other than the polylactic acid is less than 10 mass
%, the hinge is liable to be broken. If the ratio of the aliphatic
polyester resin other than the polylactic acid is greater than 95
mass %, the snap function of the hinge is deteriorated. A resin
composition containing the polylactic acid and the aliphatic
polyester resin other than the polylactic acid in a mass ratio of
60:40 to 10:90 is preferably used, and a resin composition
containing the polylactic acid and the aliphatic polyester resin
other than the polylactic acid in a mass ratio of 40:60 to 20:80 is
more preferably used.
[0035] The resin composition to be used in the present invention
preferably has a flexural modulus of 700 to 3000 MPa as determined
in conformity with JIS K1717. If the flexural modulus is less than
700 MPa, the snap function tends to be deteriorated. If the
flexural modulus is more than 3000 MPa, the hinge is liable to be
broken when the upper cap portion is repeatedly opened and closed.
Therefore, it is particularly preferred that the flexural modulus
is in a range of 1100 to 1800 MPa.
[0036] The resin composition to be used in the present invention
preferably further contains 0.01 to 5 parts by mass of a lubricant
based on a total of 100 parts by mass of the polylactic acid and
the aliphatic polyester resin other than the polylactic acid for
improvement of the releasability of the resin in a process for
molding the hinge cap. In detail, where the hinge cap is
injection-molded, the releasability of a molded product from a mold
should be taken into consideration. By adding a specific amount of
the lubricant to the resin composition for the inventive cap as
described above, the releasability and the moldability are improved
in the molding process.
[0037] In the molding process, the addition of the lubricant
improves the screw-biting kneadability of the resin composition. If
the lubricant is contained in an amount within the aforesaid
specific range, the resin smoothly flows along a screw of a molding
machine when being charged into the molding machine. Conversely, if
the lubricant is charged in an amount greater than the aforesaid
specific range, the biting kneadability of the resin composition is
reduced, resulting in molding failures.
[0038] The lubricant may be a so-called internal lubricant for
internal lubrication or an external lubricant for external
lubrication, and these lubricants may be used in combination. Any
of lubricants typically used for resin molding may be used in the
present invention. Where the resin composition according to the
invention is used for food containers, however, a lubricant
admitted as a food additive is desirably used.
[0039] More specific examples of the lubricant include fatty acids
such as stearic acid, fatty amides such as erucamide,
methylene-bis-stearamide, ethylene-bis-stearamide,
ethylene-bis-palmitamide and ethylene-bis-oleamide, and mixtures of
any of the fatty acids and any of the fatty amides as proposed in
JP-A-8-27363.
[0040] The releasability can be improved not only by adding the
lubricant as described above but also by forming pits in a surface
of the molded cap to increase the surface roughness of the cap. In
order to improve the moldability by controlling the biting
kneadability of the resin, the resin composition for the inventive
hinge cap preferably contains 1 to 10 parts by mass of an
anti-blocking agent based on a total of 100 parts by mass of the
polylactic acid and the aliphatic polyester resin other than the
polylactic acid. Any of conventionally known anti-blocking agents
may be used. For example, talc particles are preferably used as the
anti-blocking agent.
[0041] The addition of the lubricant and the anti-blocking agent
may be achieved by an internally adding method in which a master
batch containing the lubricant and the anti-blocking agent in
relatively high concentrations is first prepared and then blended
or by an externally adding method in which the lubricant and the
anti-blocking agent are added directly to pellets.
[0042] The resin composition to be used for the inventive hinge cap
preferably further contains 0.1 to 10 parts by mass of a hydrolysis
suppressing agent based on a total of 100 parts by mass of the
polylactic acid and the aliphatic polyester resin other than the
polylactic acid for suppressing the hydrolysis. The type of the
hydrolysis suppressing agent is not particularly limited, as long
as it suppresses the hydrolysis of the resin composition.
[0043] Examples of the hydrolysis suppressing agent include
carbodiimide compounds, isocyanate compounds and oxazoline
compounds as proposed in JP-B-3514736 and JP-A-2003-165917.
[0044] Hinge Cap
[0045] The hinge cap is produced by mixing the polylactic acid
directly with the aliphatic polyester resin other than the
polylactic acid and, optionally, the lubricant, the anti-blocking
agent, the hydrolysis suppressing agent and other additives, and
injection-molding the resulting resin composition. Alternatively,
the production of the hinge cap may be achieved by extruding a
mixture of dry-blended ingredients into strands by means of a twin
screw extruder, pelletizing the strands and charging the resulting
pellets into an injection molding machine. The latter method is
preferably selected for more homogeneously mixing the
ingredients.
[0046] A hinge cap according to an embodiment of the present
invention will hereinafter be described in detail with reference to
the attached drawings. The hinge cap according to the embodiment of
the present invention shown in FIGS. 1 and 2 includes a cap body 1
to be attached to a mouth of a container such as a bottle or a
tubular container, and an upper cap portion 2 which caps and uncaps
a spout 5 provided on the cap body 1. The cap body 1 has a top wall
3, and the spout 5 is provided in the top wall 3. A reference
numeral 4 denotes a cylindrical side wall extending downward from a
peripheral edge of the top wall 3, and the cylindrical side wall 4
has an inner thread 10 provided on an inner peripheral surface
thereof for attaching the cap body 1 onto the container. The upper
cap portion 2 has a cylindrical side wall 11 having the same
diameter as the side wall 4 of the cap body 1. The side walls 4 and
11 of the cap body 1 and the upper cap portion 2 are integrally
connected to each other by a thin hinge portion 6 and a pair of
resilient connection plates 8 provided on opposite sides of the
thin hinge portion 6.
[0047] The thin hinge portion 6 connects the cap body 1 and the
upper cap portion 2 diametrically to each other between the
cylindrical side wall 4 of the cap body 1 and the side wall 11 of
the upper cap portion 2. The resilient connection plates 8 are
provided in pair on the opposite sides of the thin hinge portion
6.
[0048] With the upper cap portion 2 being opened, the thin hinge
portion 6 is formed so as to make the upper cap portion 2
substantially horizontal. The thin hinge portion 6 has a thinner
portion 7 provided on an upper surface thereof as extending through
a middle position between the cap body 1 and the upper cap portion
2. The thinner portion 7 is bent when the upper cap portion 2 is
opened and closed.
[0049] The pair of resilient connection plates 8 are disposed on
the opposite sides of the thin hinge portion 6 in neighboring
relation, and connected to the side wall 4 of the cap body 1 and
the side wall 11 of the upper cap portion 2 via flexural portions
9. The resilient connection plates 8 are resilient thin plates each
having a generally uniform thickness, and perform a snap action
when the upper cap portion is opened and closed.
[0050] The structure of the hinge is not limited to the
aforementioned one. For example, as shown in FIGS. 3 and 4, the
hinge may have a structure such that a resilient connection plate
18 is provided between a pair of thin hinge portions 16, 16
provided side by side. In FIGS. 1 and 2, the thin hinge portion 6
and the resilient connection plates 8 may be integral. Further, any
other known hinge structure may be employed. A hinge cap including
only the thin hinge portion as the hinge and having no snap
function is also embraced in the present invention.
[0051] The attachment of the hinge cap to the container is
achieved, for example, by threading engagement between an outer
thread provided on an outer peripheral surface of a cylindrical
mouth portion of the container not shown and the inner thread 10
provided on the inner peripheral surface of the side wall 4 of the
cap body 1 shown in FIG. 1. The attachment of the hinge cap to the
container is not limited to the aforementioned attaching method.
The cap body may have engagement projections provided on the inner
surface of the side wall thereof to be engaged with a ring
projection provided on the outer peripheral surface of the
cylindrical mouth portion of the container, and the attachment of
the hinge cap to the container may be achieved by a so-called
squeeze capping method by squeezing the cylindrical mouth portion
into the cap body.
[0052] The inventive hinge cap preferably has a hinge strength
retention ratio of not less than 20% which is determined by
measurement of a hinge strength (tensile break stress) to be
described later after 1000-time opening and closing of the upper
cap portion. A hinge strength retention ratio of less than 20% is
not preferred because the thin hinge portion 6 and the flexural
portions 9 are liable to be broken when the upper cap portion 2 of
FIGS. 1 and 2, for example, is repeatedly opened and closed. More
preferably, the hinge strength retention ratio is not less than
40%.
EXAMPLES
[0053] The present invention will be described more specifically by
way of examples and comparative examples. However, the invention is
not limited to these examples. The flexural modulus of a resin
composition containing the polylactic acid and the aliphatic
polyester resin other than the polylactic acid in each of the
following examples and comparative examples was determined in
conformity with JIS K7171 with the use of a test strip prepared by
injection molding.
[0054] Cap
[0055] Hinge caps shown in FIGS. 1 and 2 or FIGS. 3 and 4 were
molded by an injection molding machine (FE120 available from Nissei
Plastic Industrial Co., Ltd.) under the following conditions: a
cylinder temperature of 170.degree. C.; an injection pressure of
105 MPa; and a molding cycle of 17 seconds.
[0056] Measurement of Hinge Strength
[0057] An upper cap portion 2 of each of the hinge caps produced by
the injection molding as having a structure shown in FIGS. 1 and 2
or FIGS. 3 and 4 was repeatedly subjected to an opening/closing
operation 1000 times by opening the upper cap portion to an angle
of 180 degrees. Thereafter, the hinge strength was measured by
fixing the cap body to a base of a tensile tester with the upper
cap portion 2 being opened to an angle of 180 degrees with respect
to the cap body 1, and pulling the upper cap portion vertically
upward at a pulling rate of 300 mm/min. The hinge strength
retention ratio was determined by comparing the hinge strength thus
measured with the hinge strength of a hinge cap not subjected to
the upper cap portion opening/closing operation.
[0058] Evaluation of Snap Function
[0059] The snap action (biasing force) was observed after the
1000-time opening and closing of the upper cap portion 2. A hinge
cap having a proper snap function was rated good, and a hinge cap
with its snap function lost was rated unacceptable.
Example 1
[0060] A resin composition was prepared by dry-blending a
poly(DL-lactic acid) resin (hereinafter referred to simply as
"polylactic acid") containing D-lactic acid and L-lactic acid in a
molar ratio of (L-lactic acid):(D-lactic acid)-99:1 and
polybutylene succinate as an aliphatic polyester resin other than
the polylactic acid in a mass ratio of (polylactic
acid):(polybutylene succinate)=70:30, and then blending 0.5 parts
by mass of erucamide (lubricant) and 1.5 parts by mass of
bis(dipropylphenyl)carbodiimide (hydrolysis suppressing agent) with
100 parts by mass of the resulting mixture. A hinge cap as shown in
FIGS. 1 and 2 was injection-molded from this resin composition. The
hinge cap thus obtained was stored at an ordinary temperature for
three days after the molding thereof, followed by the measurement
of the hinge strength and the evaluation of the snap function. The
results are shown in Table 1.
Example 2
[0061] A hinge cap as shown in FIGS. 3 and 4 was injection-molded
from a resin composition prepared by dry-blending the polylactic
acid of the same type as used in Example 1 and polybutylene
succinate in a mass ratio of 50:50, and blending 0.5 parts by mass
of erucamide and 1.5 parts by mass of bis(dipropylphenyl)
carbodiimide with 100 parts by mass of the resulting mixture. The
hinge cap thus obtained was stored at an ordinary temperature for
three days after the molding thereof, followed by the measurement
of the hinge strength and the evaluation of the snap function. The
results are shown in Table 1.
Example 3
[0062] A hinge cap as shown in FIGS. 1 and 2 was injection-molded
in substantially the same manner as in Example 1, except that the
resin composition was prepared by dry-blending the polylactic acid
of the same type as used in Example 1 and polybutylene succinate in
a mass ratio of (polylactic acid):(polybutylene succinate)=30:70,
and blending 0.5 parts by mass of erucamide and 1.5 parts by mass
of bis(dipropylphenyl)carbodiimide with 100 parts by mass of the
resulting mixture. The hinge cap thus obtained was stored at an
ordinary temperature for three days after the molding thereof, and
then immersed in hot water at 45.degree. C. for two months,
followed by the measurement of the hinge strength and the
evaluation of the snap function. The results are shown in Table
1.
Example 4
[0063] A hinge cap as shown in FIGS. 1 and 2 was injection-molded
in substantially the same manner as in Example 1, except that the
resin composition was prepared by dry-blending the polylactic acid
of the same type as used in Example 1 and polybutylene succinate
adipate in a mass ratio of 50:50, and blending 0.5 parts by mass of
erucamide (lubricant), 3 parts by mass of talc (anti-blocking
agent) and 1.5 parts by mass of bis(dipropylphenyl)carbodiimide
with 100 parts by mass of the resulting mixture. The hinge cap thus
obtained was stored at an ordinary temperature for three days after
the molding thereof, followed by the measurement of the hinge
strength and the evaluation of the snap function. The results are
shown in Table 1.
Comparative Example 1
[0064] A hinge cap as shown in FIGS. 1 and 2 was injection-molded
from a resin composition prepared by blending 0.5 parts by mass of
erucamide (lubricant) and 1.5 parts by mass of
bis(dipropylphenyl)carbodiimide (hydrolysis suppressing agent) with
100 parts by mass of the polylactic acid of the same type as used
in Example 1. That is, an aliphatic polyester resin other than the
polylactic acid was not used. As in Example 1, the hinge cap thus
obtained was stored at an ordinary temperature for three days, and
then an upper cap portion thereof was opened and closed for
determination of the hinge strength thereof. However, a hinge of
the hinge cap was broken when the opening/closing operation was
repeated 30 times and, therefore, the measurement of the hinge
strength and the evaluation of the snap function were given up. The
results are shown in Table 1.
Comparative Example 2
[0065] A hinge cap as shown in FIGS. 1 and 2 was injection-molded
from a resin composition prepared by dry-blending the polylactic
acid of the same type as used in Example 1 and polybutylene
succinate in a mass ratio of (polylactic acid):(polybutylene
succinate)=95:5, and blending 0.5 parts by mass of erucamide and
1.5 parts by mass of bis(dipropylphenyl)carbodiimide with 100 parts
by mass of the resulting mixture. That is, the blend ratio between
the polylactic acid resin and polybutylene succinate fell outside
the range specified by the present invention. The hinge cap thus
obtained was stored at an ordinary temperature for three days after
the molding thereof, and then an upper cap portion thereof was
opened and closed for determination of the hinge strength thereof.
However, a hinge of the hinge cap was broken when the
opening/closing operation was repeated 80 times and, therefore, the
measurement of the hinge strength and the evaluation of the snap
function were given up. The results are shown in Table 1.
TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 3 4 1 2
Composition Polylactic acid (mass %) 70 50 30 50 100 95
Polybutylene succinate (mass %) 30 50 70 -- 0 5 Polybutylene
succinate adipate (mass %) -- -- -- 50 -- -- Erucamide (parts by
mass) 0.5 0.5 0.5 0.5 0.5 0.5 Talc (parts by mass) -- -- -- 3 -- --
Bis(dipropylphenyl)carbodiimide 1.5 1.5 1.5 1.5 1.5 1.5 (parts by
mass) Properties Flexural modulus (MPa) 2600 2000 1400 1600 4300
3900 Hinge strength retention ratio 32.4 46.3 50.1 49.7 -- -- (%)
Evaluation of snap function Good Good Good Good Unacceptable
Unacceptable
[0066] As can be understood from the results of Examples 1 to 4 in
Table 1, the hinge caps produced by using the resin compositions
based on the present invention each maintained a practically
satisfactory hinge strength even after 1000-time opening and
closing of the upper cap portion thereof, and had a proper snap
function. Particularly, the hinge cap of Example 3, in which the
blend ratio of the polylactic acid was relatively low and
bis(dipropylphenyl) carbodiimide was blended as the hydrolysis
suppressing agent, had a satisfactory hinge strength retention
ratio even through it was stored at the ordinary temperature for
three days after the molding thereof and then immersed in the hot
water at 45.degree. C. for two months.
[0067] In contrast, the hinge caps of Comparative Examples 1 and 2
each employing a resin composition falling outside the scope of the
present invention suffered from breakage of a hinge thereof at an
early stage of the opening/closing operation, and had an
unsatisfactory snap function, thereby failing to satisfy functional
requirements as a hinge cap.
* * * * *