U.S. patent application number 12/593849 was filed with the patent office on 2010-04-15 for polylactic acid composition.
This patent application is currently assigned to Teijin Limited. Invention is credited to Kohei Endo, Midori Ikegame, Ryuji Nonokawa, Shin To, Kiyotsuna Toyohara.
Application Number | 20100093889 12/593849 |
Document ID | / |
Family ID | 39808403 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100093889 |
Kind Code |
A1 |
Toyohara; Kiyotsuna ; et
al. |
April 15, 2010 |
POLYLACTIC ACID COMPOSITION
Abstract
An object of the present invention is to provide a composition
containing polylactic acid and having improved blow moldability and
a blow molded product thereof. The polylactic acid composition
meets the following requirements (a) to (g) at the same time: (a)
the weight average molecular weight must be 70,000 to 700,000; (b)
the total content (metal content) of Sn atom, Ti atom, Al atom and
Ca atom must be 3 to 20 ppm; (c) the content of P atom must be 3 to
3,000 ppm; (d) the (total number of gram-atoms of Sn, Ti, Al and
Ca)/(number of gram-atoms of P) value must be 0.01 to 5; (e) the
content of a compound having a molecular weight of 150 or less must
be not more than 0.2 wt %; (f) the COOH terminal group
concentration must be not more than 30 equivalents/ton; and (g) the
following expressions (1) and (2) must be satisfied: 10
Pas<P<100 Pas (1) 10 MPa<S (2) (P is a melt viscosity at
230.degree. C. and S is a stress at 150.degree. C.).
Inventors: |
Toyohara; Kiyotsuna;
(Yamaguchi, JP) ; Nonokawa; Ryuji; (Yamaguchi,
JP) ; Endo; Kohei; (Yamaguchi, JP) ; Ikegame;
Midori; (Yamaguchi, JP) ; To; Shin; (Tokyo,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
Teijin Limited
Osaka-shi
JP
Musashino Chemical Laboratory, Ltd.
Chuo-ku
JP
|
Family ID: |
39808403 |
Appl. No.: |
12/593849 |
Filed: |
March 31, 2008 |
PCT Filed: |
March 31, 2008 |
PCT NO: |
PCT/JP2008/056831 |
371 Date: |
December 24, 2009 |
Current U.S.
Class: |
523/124 |
Current CPC
Class: |
B29B 2911/1404 20130101;
B29B 2911/1402 20130101; B29B 2911/14366 20130101; B29B 2911/1498
20130101; B29B 2911/14026 20130101; B29C 49/0005 20130101; B29B
11/08 20130101; C08L 67/04 20130101; B29L 2031/7158 20130101; B29B
2911/14106 20130101; B29B 2911/14653 20130101; B29B 2911/14713
20130101; C08L 67/04 20130101; B29B 11/14 20130101; B29K 2105/258
20130101; B29B 2911/14033 20130101; B29B 2911/14326 20130101; B29B
2911/14133 20130101; C08L 2666/18 20130101 |
Class at
Publication: |
523/124 |
International
Class: |
D06P 1/52 20060101
D06P001/52 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2007 |
JP |
2007-092122 |
Claims
1. A polylactic acid composition which comprises: (A) 30 to 70
parts by weight of polylactic acid (A) comprising not less than 90
mol % of an L-lactic acid unit and less than 10 mol % of a D-lactic
acid unit and/or a comonomer unit except for lactic acid; and (B)
70 to 30 parts by weight of polylactic acid (B) comprising not less
than 90 mol % of a D-lactic acid unit and less than 10 mol % of an
L-lactic acid unit and/or a comonomer unit except for lactic acid,
and which meets the following requirements (a) to (g) at the same
time: (a) the weight average molecular weight must be 70,000 to
700,000; (b) the total content (metal content) of Sn atom, Ti atom,
Al atom and Ca atom must be 3 to 20 ppm based on the total weight
of the polylactic acid composition; (c) the content of P atom must
be 3 to 3,000 ppm; (d) the (total number of gram-atoms of Sn, Ti,
Al and Ca)/(number of gram-atoms of P) value must be 0.01 to 5; (e)
the content of a compound having a molecular weight of 150 or less
must be not more than 0.2 wt %; (f) the COOH terminal group
concentration must be not more than 30 equivalents/ton; and (g) the
following expressions (1) and (2) must be satisfied: 10
Pas<P<100 Pas (1) 10 MPa<S (2) (P is a melt viscosity at
230.degree. C. and S is a stress at 150.degree. C.).
2. A blow molded product which comprises: (A) 30 to 70 parts by
weight of polylactic acid (A) comprising not less than 90 mol % of
an L-lactic acid unit and less than 10 mol % of a D-lactic acid
unit and/or a comonomer unit except for lactic acid; and (B) 70 to
30 parts by weight of polylactic acid (B) comprising not less than
90 mol % of a D-lactic acid unit and less than 10 mol % of an
L-lactic acid unit and/or a comonomer unit except for lactic acid,
and which meets the following requirements (a) to (g) at the same
time: (a) the weight average molecular weight must be 100,000 to
500,000; (b) the total content (metal content) of Sn atom, Ti atom,
Al atom and Ca atom must be 3 to 20 ppm based on the total weight
of the blow molded product; (c) the content of P atom must be 20 to
5,000 ppm; (d) the (total number of gram-atoms of Sn, Ti, Al and
Ca)/(number of gram-atoms of P) value must be 0.1 to 5; (e) the
content of a compound having a molecular weight of 150 or less must
be not more than 0.1 wt %; (f) the COON terminal group
concentration must be not more than 30 equivalents/ton; and (g) the
following expressions (1) and (2) must be satisfied: 10
Pas<P<100 Pas (1) 10 MPa<S (2) (P is a melt viscosity at
230.degree. C. and S is a stress at 150.degree. C.).
3. The blow molded product according to claim 2, wherein the
polylactic acid (A) and the polylactic acid (B) form a
stereocomplex crystal in the blow molded product.
Description
TECHNICAL FIELD
[0001] The present invention relates to a composition comprising
polylactic acid. More specifically, it relates to a composition
comprising polylactic acid and having improved blow moldability and
a blow molded product thereof.
BACKGROUND ART
[0002] Most plastics derived from petroleum are light in weight,
tough and durable, can be molded easily and arbitrarily and have
been mass-produced to support our lives in many ways. However, when
these plastics are thrown away into the environment, they are not
easily decomposed and are accumulated. When they are burnt, they
release a large amount of carbon dioxide, thereby accelerating
global warming.
[0003] In view of this situation, researches into resins obtained
from non-oil raw materials or biodegradable plastics which are
degraded by microorganisms are now actively under way. Most of the
biodegradable plastics which are now under study have an aliphatic
carboxylic acid ester unit and are easily degraded by
microorganisms. On the other hand, they have low heat stability,
thereby causing a serious problem such as a reduction in their
molecular weights or the deterioration of their colors in the step
where they are exposed to a high temperature, such as melt
spinning, injection molding or melt film formation.
[0004] Although polylactic acid, out of these, is a plastic which
has excellent heat resistance and good balance between color and
mechanical strength, as compared with petrochemical-based
polyesters typified by polyethylene terephthalate and polybutylene
terephthalate, it is inferior in moldability, especially blow
moldability. To overcome this situation, various studies have been
made, such as methods in which a specific additive is added to
improve the moldability of polylactic acid (patent documents 1 and
2). However, they are still unsatisfactory.
(Patent Document 1) JP-A 2006-193540
(Patent Document 2) JP-A 2005-239932
DISCLOSURE OF THE INVENTION
[0005] It is an object of the present invention to provide a
polylactic acid composition having improved blow moldability and a
blow molded product thereof.
[0006] The inventors of the present invention have found that the
blow moldability of a polylactic acid composition is improved by
controlling the amounts of specific metal atoms contained in
polylactic acid and have accomplished the present invention.
[0007] That is, the present invention is a polylactic acid
composition which comprises: [0008] (A) 30 to 70 parts by weight of
polylactic acid (A) comprising not less than 90 mol % of an
L-lactic acid unit and less than 10 mol % of a D-lactic acid unit
and/or a comonomer unit except for lactic acid; and [0009] (B) 70
to 30 parts by weight of polylactic acid (B) comprising not less
than 90 mol % of a D-lactic acid unit and less than 10 mol % of an
L-lactic acid unit and/or a comonomer unit except for lactic acid,
and which meets the following requirements (a) to (g) at the same
time: [0010] (a) the weight average molecular weight must be 70,000
to 700,000; [0011] (b) the total content (metal content) of Sn
atom, Ti atom, Al atom and Ca atom must be 3 to 20 ppm based on the
total weight of the polylactic acid composition; [0012] (c) the
content of P atom must be 3 to 3,000 ppm; [0013] (d) the (total
number of gram-atoms of Sn, Ti, Al and Ca)/(number of gram-atoms of
P) value must be 0.01 to 5; [0014] (e) the content of a compound
having a molecular weight of 150 or less must be not more than 0.2
wt %; [0015] (f) the COOH terminal group concentration must be not
more than 30 equivalents/ton; and [0016] (g) the following
expressions (1) and (2) must be satisfied:
[0016] 10 Pas<P<100 Pas (1)
10 MPa<S (2) [0017] (P is a melt viscosity at 230.degree. C. and
S is a stress at 150.degree. C.) [0018] Further, the present
invention is a blow molded product which comprises: [0019] (A) 30
to 70 parts by weight of polylactic acid (A) comprising not less
than 90 mol % of an L-lactic acid unit and less than 10 mol of a
D-lactic acid unit and/or a comonomer unit except for lactic acid;
and [0020] (B) 70 to 30 parts by weight of polylactic acid (B)
comprising not less than 90 mol % of a D-lactic acid unit and less
than 10 mol % of an L-lactic acid unit and/or a comonomer unit
except for lactic acid, and which meets the following requirements
(a) to (g) at the same time: [0021] (a) the weight average
molecular weight must be 100,000 to 500,000; [0022] (b) the total
content (metal content) of Sn atom, Ti atom, Al atom and Ca atom
must be 3 to 20 ppm based on the total weight of the blow molded
product; [0023] (c) the content of P atom must be 20 to 5,000 ppm;
[0024] (d) the (total number of gram-atoms of Sn, Ti, Al and
Ca)/(number of gram-atoms of P) value must be 0.1 to 5; [0025] (e)
the content of a compound having a molecular weight of 150 or less
must be not more than 0.1 wt %; [0026] (f) the COOH terminal group
concentration must be not more than 30 equivalents/ton; and [0027]
(g) the following expressions (1) and (2) must be satisfied:
[0027] 10 Pas<P<100 Pas (1)
10 MPa<S (2) [0028] (P is a melt viscosity at 230.degree. C. and
S is a stress at 150.degree. C.)
[0029] The present invention also includes a blow molded product in
which the polylactic acid (A) and the polylactic acid (B) form a
stereocomplex crystal in the blow molded product.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a diagram showing the characteristic properties of
a bottle obtained in Example 3; and
[0031] FIG. 2 is a diagram showing the characteristic properties of
a bottle obtained in Example 3.
BEST MODE FOR CARRYING OUT THE INVENTION
Polylactic Acid Composition
[0032] In the present invention, the polylactic acid (A) and the
polylactic acid (B) contain an L-lactic acid unit or a D-lactic
acid unit represented by the following formula.
##STR00001##
[0033] The polylactic acid (A) is a polymer which contains an
L-lactic acid unit as the main component. The polylactic acid (A)
contains preferably 90 to 100 mol %, more preferably 95 to 100 mol
%, much more preferably 98 to 100 mol % of an L-lactic acid unit.
Other units are a D-lactic acid unit and a unit except for lactic
acid. The total amount of the D-lactic acid unit and the unit
except for lactic acid is preferably 0 to 10 mol %, more preferably
0 to 5 mol %, much more preferably 0 to 2 mol %.
[0034] The polylactic acid (B) is a polymer which contains a
D-lactic acid unit as the main component. The polylactic acid (B)
contains preferably 90 to 100 mol %, more preferably 95 to 100 mol
%, much more preferably 98 to 100 mol % of a D-lactic acid unit.
Other units are an L-lactic acid unit and a unit except for lactic
acid. The total amount of the L-lactic acid unit and the unit
except for lactic acid is preferably 0 to 10 mol %, more preferably
0 to 5 mol %, much more preferably 0 to 2 mol %.
[0035] Examples of the unit except for lactic acid include units
derived from dicarboxylic acids, polyhydric alcohols,
hydroxycarboxylic acids and lactones having a functional group
capable of forming at least two ester bonds and units derived from
polyesters, polyethers and polycarbonates comprising these as
constituent components.
[0036] The dicarboxylic acids include succinic acid, adipic acid,
azelaic acid, sebacic acid, terephthalic acid and isophthalic acid.
The polyhydric alcohols include aliphatic polyhydric alcohols such
as ethylene glycol, propylene glycol, butanediol, pentanediol,
hexanediol, octanediol, glycerin, sorbitan, neopentyl glycol,
diethylene glycol, triethylene glycol, polyethylene glycol and
polypropylene glycol, and aromatic polyhydric alcohols such as an
adduct of bisphenol with ethylene oxide. The hydroxycarboxylic
acids include glycolic acid and hydroxybutyric acid. The lactones
include glycolide, .epsilon.-caprolactone glycolide,
.epsilon.-caprolactone, .beta.-propiolactone,
.delta.-butyrolactone, .beta.- or .gamma.-butyrolactone,
pivalolactone and .delta.-valerolactone.
[0037] In the polylactic acid composition of the present invention,
the weight ratio of the above polylactic acid (A) to the above
polylactic acid (B) is 30:70 to 70:30, preferably 45:55 to 55:45
based on the total weight of the polylactic acid (A) and the
polylactic acid (B). Outside this range, heat resistance
degrades.
[0038] The polylactic acid composition of the present invention
meets the following requirements (a) to (g). A description is
subsequently given of each of the requirements.
(Requirement (A))
[0039] The weight average molecular weight of the polylactic acid
composition of the present invention is 70,000 to 700,000,
preferably 100,000 to 500,000, more preferably 150,000 to 350,000.
Within this range, the polylactic acid composition can be molded
properly. The weight average molecular weight is a value in terms
of standard polystyrene measured by gel permeation chromatography
(GPC) using chloroform as an eluant. The polylactic acid
composition having a weight average molecular weight within the
above range is obtained by melt kneading together the polylactic
acid (A) and the polylactic acid (B), both having a weight average
molecular weight of 70,000 to 700,000, preferably 100,000 to
500,000, more preferably 150,000 to 350,000.
(Requirement (B))
[0040] The total content (metal content) of the Sn atom, Ti atom,
Al atom and Ca atom in the polylactic acid composition of the
present invention is 3 to 20 ppm, preferably 1 to 15 ppm, more
preferably 1 to 10 ppm based on the total weight of the polylactic
acid composition. These atoms are derived from a catalyst used to
produce the polylactic acid (A) and the polylactic acid (B).
Outside this range, melt stability is greatly impaired
disadvantageously.
[0041] The polylactic acid composition having a metal content
within the above range is obtained from the polylactic acid (A) and
the polylactic acid (B) produced by using these metals as a
catalyst. That is, the polylactic acid (A) and the polylactic acid
(B) are preferably produced by using 3 to 3,000 mg, preferably 3 to
20 mg, more preferably 3 to 15 mg of these metal atoms as a
catalyst based on 1 kg of lactide.
(Requirement (C))
[0042] The content of the P atom in the polylactic acid composition
of the present invention is 3 to 3,000 ppm, preferably 50 to 2,000
ppm, more preferably 50 to 1,000 ppm based on the total weight of
the polylactic acid composition. The P atom is derived from a
catalyst deactivator or a stabilizer used to produce the polylactic
acid (A) and the polylactic acid (B). Outside this range, melt
stability is impaired and depolymerization proceeds
disadvantageously.
[0043] The polylactic acid composition having a P atom content
within the above range is obtained from the polylactic acid (A) and
the polylactic acid (B) which are produced by using a compound
containing a P atom as a catalyst deactivator or a stabilizer. The
polylactic acid (A) and the polylactic acid (B) are preferably
produced by using a catalyst deactivator or a stabilizer to ensure
that the content of the P atom becomes 3 to 3,000 mg, preferably 50
to 2,000 mg, more preferably 50 to 1,000 mg based on 1 kg of
lactide.
(Requirement (D))
[0044] The polylactic acid composition of the present invention has
a (total number of gram-atoms of Sn, Ti, Al and Ca)/(number of
gram-atoms of P) value of 0.01 to 5, preferably 0.5 to 5. The
number of gram-atoms of each of Sn, Ti, Al, Ca and P means the
number of moles. The polylactic acid composition which meets the
above condition is obtained by adjusting the weight ratio of the
catalyst and the catalyst deactivator or stabilizer at the time of
producing the polylactic acid (A) and the polylactic acid (B).
(Requirement (E))
[0045] The content of the compound having a molecular weight of 150
or less in the polylactic acid composition of the present invention
is not more than 0.2 wt %, preferably not more than 0.04 wt %, more
preferably not more than 0.02 wt % based on the polylactic acid
composition. Outside this range, long-term durability greatly
lowers. Examples of the compound having a molecular weight of 150
or less include lactide and lactic acid. However, the compound is
not limited to these. The polylactic acid composition which meets
the above condition is obtained from the polylactic acid (A) and
the polylactic acid (B) from which the compound having a molecular
weight of 150 or less has been removed by depressurizing the inside
of the reaction system at the time of production. Depressurizing
the inside of the system at the time of melt kneading together the
polylactic acid (A) and the polylactic acid (B) is also
effective.
(Requirement (F))
[0046] The carboxyl terminal group concentration of the polylactic
acid composition of the present invention is not more than 30
equivalents/ton, preferably not more than 10 equivalents/ton, more
preferably not more than 8 equivalents/ton. Outside this range,
hydrolysis resistance degrades. The polylactic acid composition
which meets the above condition is obtained by reducing the amount
of carboxylic acid contained in the raw material polylactic acid to
less than 4 equivalents/ton and the amount of the residual water to
less than 30 ppm.
(Requirement (G))
[0047] The polylactic acid composition of the present invention
satisfies the following expressions (1) and (2).
10 Pas<P<100 Pas (1)
10 MPa<S (2)
[0048] (P is a melt viscosity at 230.degree. C. and S is a stress
at 150.degree. C.)
[0049] In the expression (1), when the melt viscosity falls within
this range, the molding of a preform can be easily carried out. In
the expression (2), when the tensile stress (S) is outside this
range, blow molding cannot be carried out properly. The polylactic
acid composition which meets the above condition is obtained by
adjusting its weight average molecular weight in terms of styrene
measured by gel permeation chromatography to 100,000 or more and
the melting point of the resin to a temperature higher than
200.degree. C.
<Method of Producing Polylactic Acid Composition>
[0050] The composition of the present invention can be produced by
melt kneading together the polylactic acid (A) and the polylactic
acid (B).
[0051] The polylactic acid (A) and the polylactic acid (B) can be
produced by heating L- or D-lactide in the presence of a metal
catalyst to ring-opening polymerize it. They can also be produced
by crystallizing a polylactic acid which has a low molecular weight
and contains a metal catalyst and heating it in reduced pressure or
in an inert gas stream to solid-phase polymerize it. Further, they
can also be produced by a direct polymerization method in which
lactic acid is dehydrated and condensed in the presence or absence
of an organic solvent.
[0052] The polymerization reaction can be carried out in a
conventionally known reactor, for example, vertical reactors
equipped with a high viscosity stirring blade such as helical
ribbon blade, which may be used alone or in combination. An alcohol
may be used as a polymerization initiator. The alcohol preferably
does not impede the polymerization of polylactic acid and is
nonvolatile, as exemplified by decanol, dodecanol, tetradecanol,
hexadecanol, octadecanol, ethylene glycol, triethylene glycol and
benzyl alcohol.
[0053] In the solid-phase polymerization method, a relatively
low-molecular weight lactic acid polyester obtained by the above
ring-opening polymerization or the direct polymerization of lactic
acid is used as a prepolymer. It is preferred from the viewpoint of
preventing fusion that the prepolymer should be crystallized at a
temperature of its glass transition temperature (Tg) or higher and
lower than its melting point (Tm) in advance. The crystallized
prepolymer is charged into a fixed vertical reactor or a rotary
reactor such as tumbler or kiln and heated at the glass transition
temperature (Tg) or higher and lower than the melting point (Tm) of
the prepolymer. There will be no problem if the polymerization
temperature is raised stepwise along with the proceeding of
polymerization. It is also preferred that the inside of the reactor
should be depressurized or the heated inert gas stream should be
circulated in order to remove water generated during solid-phase
polymerization efficiently.
[0054] The metal catalyst used to produce the polylactic acid (A)
and the polylactic acid (B) is a compound which contains at least
one metal selected from the group consisting of alkali earth
metals, rare earth metals, the transition metals in the third low
of the periodic table, aluminum, germanium, tin and antimony. The
alkali earth metals include magnesium, calcium and strontium. The
rare earth metals include scandium, yttrium, lanthanum and cerium.
The transition metals in the third low of the periodic table
include iron, cobalt, nickel and zinc.
[0055] The metal catalyst can be added to the composition as a
carboxylate, alkoxide, aryloxide or enolate of .beta.-diketone of
at least one of these metals. When polymerization activity and
color are taken into consideration, tin octylate, titanium
tetraisopropoxide and aluminum triisopropoxide are particularly
preferred.
[0056] The content of the metal catalyst is not less than 0.001
part by weight and less than 1 part by weight, preferably not less
than 0.005 part by weight and less than 0.1 part by weight based on
100 parts by weight of the polylactic acid. When the content of the
metal catalyst is too low, the polymerization rate greatly drops
disadvantageously. When the content is too high, the coloring of
polylactic acid by reaction heat or the coloring of a
carbodiimide-based compound is promoted, and the color and heat
stability of the obtained composition become worse.
<Blow Molded Product>
[0057] A description is subsequently given of the blow molded
product of the present invention.
[0058] The blow molded product of the present invention comprises
30 to 70 parts by weight of the above-described polylactic acid (A)
and 70 to 30 parts by weight of the above-described polylactic acid
(B) and meets the following requirements (a) to (g) at the same
time. A description is subsequently given of each of the
requirements.
(Requirement (A))
[0059] The weight average molecular weight of the blow molded
product of the present invention is 100,000 to 500,000, preferably
150,000 to 350,000. Within this range, the blow molded product has
excellent physical properties. The weight average molecular weight
is a value in terms of standard polystyrene measured by gel
permeation chromatography (GPC) using chloroform as an eluant. The
blow molded product having a weight average molecular weight within
the above range is obtained by blow molding the polylactic acid
composition of the present invention having a weight average
molecular weight of 70,000 to 700,000.
(Requirement (B))
[0060] The total content (metal content) of the Sn atom, Ti atom,
Al atom and Ca atom in the blow molded product of the present
invention is 3 to 20 ppm, preferably 3 to 15 ppm, more preferably 3
to 10 ppm based on the total weight of the blow molded product.
Outside this range, melt stability is impaired and depolymerization
proceeds disadvantageously. The blow molded product having a metal
content within the above range is obtained by blow molding the
polylactic acid composition of the present invention having a total
content (metal content) of the Sn atom, Ti atom, Al atom and Ca
atom of 3 to 20 ppm.
(Requirement (C))
[0061] The content of the P atom in the blow molded product of the
present invention is 20 to 5,000 ppm, preferably 50 to 2,000 ppm,
more preferably 50 to 1,000 ppm based on the total weight of the
blow molded product. Outside this range, long-term durability
greatly lowers. The P atom is preferably added as a phosphoric
acid, phosphorous acid, hypophosphorous acid, phosphorous acid
ester, phosphoric acid ester, polyphosphoric acid or metaphosphoric
acid. The blow molded product having a P atom content within the
above range is obtained by blow molding the polylactic acid
composition of the present invention.
(Requirement (D))
[0062] The (total number of gram-atoms of Sn, Ti, Al and
Ca)/(number of gram-atoms of P) value of the blow molded product of
the present invention is 0.1 to 5, preferably 0.1 to 4. The number
of gram-atoms of each of Sn, Ti, Al and Ca means the number of
moles contained in the blow molded product. The blow molded product
which meets the above condition is obtained by blow molding the
polylactic acid composition of the present invention.
(Requirement (E))
[0063] The content of a compound having a molecular weight of 150
or less in the blow molded product of the present invention is not
more than 0.1 wt %, preferably not more than 0.05 wt %, more
preferably not more than 0.02 wt % based on the polylactic acid
composition. Outside this range, long-term durability greatly
lowers. Examples of the compound having a molecular weight of 150
or less include lactide and lactic acid. The compound is not
limited to these. The blow molded product which meets the above
condition is obtained by blow molding the polylactic acid
composition of the present invention.
(Requirement (F))
[0064] The COOH terminal group concentration of the blow molded
product of the present invention is not more than 30
equivalents/ton, preferably not more than 15 equivalents/ton.
Outside this range, hydrolysis resistance degrades. The blow molded
product which meets the above condition is obtained by blow molding
the polylactic acid composition of the present invention.
(Requirement (G))
[0065] The blow molded product of the present invention satisfies
the following expressions (1) and (2).
10 Pas<P<100 Pas (1)
10 MPa<S (2)
[0066] (P is a melt viscosity at 230.degree. C. and S is a stress
at 150.degree. C.)
[0067] The blow molded product which meets the above condition is
obtained by blow molding the polylactic acid composition of the
present invention.
[0068] In the expression (1), when the melt viscosity falls within
this range, the molding of the preform can be easily carried out.
In the expression (2), when the tensile stress (S) is outside this
range, blow molding cannot be carried out properly.
[0069] In the present invention, preferably, the polylactic acid
(A) and the polylactic acid (B) form a stereocomplex crystal in the
blow molded product. The content of the stereocomplex crystal is
preferably 80 to 100%, more preferably 95 to 100%.
[0070] The term "stereocomplex crystal" as used herein means that
the proportion of melting peaks at 195.degree. C. or higher out of
the melting peaks in the temperature elevation step in the
differential scanning calorimeter (DSC) measurement of a sample is
preferably not less than 80%, more preferably not less than 90%,
much more preferably not less than 95%. The melting point is in the
range of preferably 195 to 250.degree. C., more preferably 200 to
220.degree. C. The melting enthalpy is not less than 20 J/g,
preferably not less than 30 J/g. Stated more specifically, it is
preferred that the proportion of the melting peaks at 195.degree.
C. or higher out of the melting peaks in the temperature elevation
step in the differential scanning calorimeter (DSC) measurement
should be not less than 90%, the melting point should be 195 to
250.degree. C., and the melting enthalpy should be not less than 20
J/g. The stereocomplex crystal can be formed by heat setting after
the blow molded product is obtained.
[0071] In the present invention, to obtain the blow molded product,
any known blow molding technique may be employed. For example, a
stretch blow molding technique in which a preform is molded by
extrusion molding and re-heated directly or after its stopper
portion and bottom portion are processed may be employed.
[0072] The molding temperature in this case (specifically, the
temperature of the cylinders and the nozzle of a molding machine)
is 60.degree. C. or lower, preferably 45 to 20.degree. C. The
stretch temperature is generally 80 to 120.degree. C. The draw
ratio is generally 1 to 4 times in the longitudinal direction and 1
to 5 times in the circumferential direction.
[0073] Although the obtained bottle may be used as it is, in the
case of a liquid to be contained in the bottle which must be heat
charged, such as fruit juice or oolong tea, the bottle is heat
fixed in a heated blow metal mold and further provided with heat
resistance before use. Heat fixing is generally carried out at a
metal mold temperature of 100 to 160.degree. C. under pneumatic
tension or the like for 20 seconds to 2 minutes. Alternatively, a
bottle larger than the final size is molded, its barrel portion is
crystallized by thermal shrinking, and then the bottle is blow
molded in a metal mold having the final shape to obtain a bottle
product.
EXAMPLES
[0074] The following examples are provided for the purpose of
further illustrating the present invention but are in no way to be
taken as limiting. In the examples, the physical properties of the
composition were measured by the following methods.
(1) Measurement of Weight Average Molecular Weight (Mw)
[0075] The weight average molecular weight (Mw) was measured with
the GPC-11 of Showdex Co., Ltd. by dissolving 50 mg of the
composition in 5 ml of chloroform at 40.degree. C. The weight
average molecular weight (Mc) was calculated as a value in terms of
polystyrene.
(2) Measurement of Amounts of Sn Atom, Ti Atom, Al Atom, Ca Atom
and P Atom
[0076] These were obtained by IPC.
(3) Measurement of Numbers of Gram-Atoms of Sn, Ti, Al, Ca and
P
[0077] These were obtained from raw materials charged into a
resin.
(4) Measurement of Content of Compound Having a Molecular Weight of
150 or Less
[0078] This was obtained by GPC.
(5) Measurement of COOH Terminal Group Concentration
[0079] This was obtained by neutralization titration.
(6) Measurement of Melt Viscosity
[0080] This was obtained with a flow tester.
(7) Measurement of Tensile Stress
[0081] The obtained resin composition was molded into a
dumbbell-like form by an injection molding machine to obtain a
molded piece. A tensile test was made on this by using a heating
type Tensilon measuring instrument (of A&D Co., Ltd.) at a
pulling rate of 20 mm/min at 150.degree. C.
Example 1
Polylactic Acid (A)
[0082] 100 parts by weight of L-lactide and 0.15 part by weight of
stearyl alcohol were fed from the material feed port of a
polymerization reactor equipped with a cooling distillation tube in
a nitrogen stream. Subsequently, the inside of the reactor was
substituted by nitrogen 5 times, and L-lactide was molten at
190.degree. C. When L-lactide was completely molten, 0.005 part by
weight of tin 2-ethylhexanoate was added from the material feed
port together with 500 .mu.l of toluene to carry out polymerization
at 190.degree. C. for 1 hour.
[0083] After the end of polymerization, surplus L-lactide was
volatilized, 0.25 part by weight of dihexyl phosphonoacetate was
added, and strand-like polylactic acid (A) was obtained from the
discharge port of the reactor and cut into a pellet while it was
cooled.
Polylactic Acid (B)
[0084] Then, the polylactic acid (B) was prepared by the same
operation as above. That is, 100 parts by weight of D-lactide and
0.15 part by weight of stearyl alcohol were fed, the inside of the
reactor was substituted by nitrogen 5 times, and D-lactide was
molten at 190.degree. C. When D-lactide was completely molten,
0.005 part by weight of tin 2-ethylhexanoate was added from the
material feed port together with 500 .mu.l of toluene to carry out
polymerization at 190.degree. C. for 1 hour.
[0085] After the end of polymerization, surplus D-lactide was
volatilized in the end, 0.1 part by weight of dihexyl
phosphonoacetate was added, and strand-like polylactic acid (B) was
discharged from the discharge port of the reactor and cut into a
pellet while it was cooled.
(Melt Kneading)
[0086] 50 parts by weight of the polylactic acid (A) pellet and 50
parts by weight of the polylactic acid (B) pellet obtained by the
above operations were mixed together well and kneaded together at
230.degree. C. in a nitrogen gas stream for 10 minutes by using the
50C150 Labo Plastomill kneader of Toyo Seiki Co., Ltd. The
characteristic properties of the obtained composition are shown in
Table 1.
Example 2
Polylactic Acid (A)
[0087] 100 parts by weight of L-lactide and 0.15 part by weight of
stearyl alcohol were fed from the material feed port of a
polymerization reactor equipped with a cooling distillation tube in
a nitrogen stream. Subsequently, the inside of the reactor was
substituted by nitrogen 5 times, and L-lactide was molten at
190.degree. C. When L-lactide was completely molten, 0.005 part by
weight of tin 2-ethylhexanoate was added from the material feed
port together with 500 .mu.l of toluene to carry out polymerization
at 190.degree. C. for 1 hour.
[0088] After the end of polymerization, surplus L-lactide was
volatilized, 0.1 part by weight of dihexyl phosphonoacetate was
added, and strand-like polylactic acid (A) was obtained from the
discharge port of the reactor and cut into a pellet while it was
cooled.
Polylactic Acid (B)
[0089] Then, the polylactic acid (B) was prepared by the same
operation as above. That is, 100 parts by weight of D-lactide and
0.15 part by weight of stearyl alcohol were fed, the inside of the
reactor was substituted by nitrogen 5 times, and D-lactide was
molten at 190.degree. C. When D-lactide was completely molten,
0.005 part by weight of tin 2-ethylhexanoate was added from the
material feed port together with 500 .mu.l of toluene to carry out
polymerization at 190.degree. C. for 1 hour.
[0090] After the end of polymerization, surplus D-lactide was
volatilized in the end, 0.01 part by weight of sodium metaphosphate
was added, and strand-like polylactic acid (B) was discharged from
the discharge port of the reactor and cut into a pellet while it
was cooled.
(Melt Kneading)
[0091] 50 parts by weight of the polylactic acid (A) pellet and 50
parts by weight of the polylactic acid (B) pellet obtained by the
above operations were mixed together well and kneaded together at
230.degree. C. in a nitrogen gas stream for 10 minutes by using the
50C150 Labo Plastomill kneader of Toyo Seiki Co., Ltd. The
characteristic properties of the obtained composition are shown in
Table 1.
Example 3
[0092] After the composition obtained in Example 1 was pelletized
and dried with a drier at 120.degree. C. for 4 hours, it was
injection molded into a conical preform having an outer diameter of
about 61 mm, an inner diameter of about 55 mm, a length of 5 mm and
a weight of about 27 g by a bottle molding machine (12N/10T of
Nissei ASB Co., Ltd.) under the following conditions: a cylinder
temperature of 240.degree. C., a screw revolution of 80 rpm, a
metal mold temperature of 20.degree. C. and a cycle of 16
seconds.
[0093] The obtained preform was subsequently preheated at a preform
surface temperature of about 90.degree. C. with an infrared heater
and stretch blow molded by a blow molding machine in which a blow
pressure was set to 1 to 1.8 MPa and a metal mold temperature of
50.degree. C. to obtain a bottle having a barrel average thickness
of 0.9 mm and an inner capacity of about 180 ml. Its oxygen
permeability was 0.072 g/day/package (in the case of a polyethylene
terephthalate bottle, it is generally 0.142 g/day/package). The
characteristic properties of the obtained bottle are shown in Table
2 and FIGS. 1 and 2. Table 2 shows the actual measurement values of
its thickness. The measurement was made 4 times.
TABLE-US-00001 TABLE 1 Example 3 Example 1 Example 2 (blow molded
(composition) (composition) product) Weight average molecular
weight 130000 125000 120000 Total content of Sn atom, Ti atom, Al
atom and 12 11 12 Ca atom Content of P atom 100 30 100 (total
number of gram-atoms of Sn, Ti, Al and <0.04 <0.13 <0.04
Ca)/(number of gram-atoms of P) content of compound having a
molecular weight 0.04 0.04 0.04 of 150 or less (%) COOH terminal
group concentration is not more .largecircle. .largecircle.
.largecircle. than 30 equivalents/ton Melt viscosity 70 70 --
(230.degree. C./1000 S-1) (Pa/s) Tensile stress 30 40 --
TABLE-US-00002 TABLE 2 0.degree. 45.degree. 90.degree. 135.degree.
180.degree. 225.degree. 270.degree. 315.degree. Avg. 1 40 mm 1.17
1.17 1.13 1.15 1.15 1.11 1.26 1.24 1.17 30 mm 0.95 0.93 0.92 0.90
0.95 0.92 0.83 0.85 0.91 17 mm 0.60 0.59 0.60 0.58 0.60 0.55 0.52
0.53 0.57 Avg. 0.91 0.90 0.88 0.88 0.90 0.86 0.87 0.87 0.88 2 40 mm
1.19 1.17 1.21 1.19 1.15 1.15 1.14 1.18 1.17 30 mm 0.95 0.94 0.96
0.95 0.94 0.92 0.90 0.90 0.93 17 mm 0.65 0.59 0.58 0.54 0.56 0.56
0.59 0.62 0.59 Avg. 0.93 0.90 0.92 0.89 0.88 0.88 0.88 0.90 0.90 3
40 mm 1.20 1.18 1.16 1.14 1.20 1.17 1.18 1.27 1.19 30 mm 0.91 0.91
0.90 0.92 0.96 0.94 0.89 0.85 0.91 17 mm 0.55 0.56 0.57 0.61 0.63
0.62 0.57 0.54 0.58 Avg. 0.89 0.88 0.88 0.89 0.93 0.91 0.88 0.89
0.89 4 40 mm 1.18 1.18 1.16 1.14 1.10 1.12 1.14 1.30 1.17 30 mm
0.93 0.93 0.92 0.93 0.92 0.92 0.94 0.82 0.91 17 mm 0.54 0.56 0.55
0.58 0.60 0.60 0.66 0.50 0.57 Avg. 0.88 0.89 0.88 0.88 0.87 0.88
0.91 0.87 0.88
EFFECT OF THE INVENTION
[0094] According to the present invention, a polylactic acid
composition having improved blow moldability can be provided.
* * * * *