Injection stretch blow container

An injection stretch blow container consisting of a combination of 97 to 70 parts by weight of saturated polyester and 3 to 30 parts by weight of a saponification product of an ethylene-vinyl acetate copolymer, said container having many areas, particularly at the body wall portion of said container in each of which areas substantially two-dimensional thin layers of said saponification product of said ethylene-vinyl acetate copolymer are laminated in parallel to the wall surface of said container in a matrix of saturated polyester, said saponification product of said ethylene-vinyl acetate copolymer in said area (20.times.20.mu.; vertical section or longitudinal section of the body wall of said container) is 0.001 to 1 .mu.m in average thickness and at least 5 in average aspect ratio and the laminated structural index represented by the following formula is at least 5: PA0 Laminated structural index ##EQU1## wherein L.sub.i represents a length of the overlapped portion of adjacent layers of the saponification product of the ethylene-vinyl acetate copolymer, and PA0 h.sub.i represents a distance between adjacent layers of saponification product of ethylene-vinyl acetate copolymer. This container has a high gas-barrier quality and is useful as a bottle for carbonated beverages or the like.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an injection stretch blow container having 
a high gas-barrier quality due to the laminar structure of the blend of a 
saturated polyester and a saponification product of an ethylene-vinyl 
acetate copolymer (hereinafter referred to as "EVOH"). 
2. Description of the Prior Art 
With respect to a composition of saturated polyester and EVOH, Japanese 
Laid-Open Pat. No. 20073/1981 discloses one of such composition, Japanese 
Laid-Open Pat. No. 76325/1985 discloses a biaxially stretched molded 
product, and Japanese Laid-Open Pat. No. 148442/1985 discloses a blown 
bottle. 
When containers are produced by the methods disclosed in the above 
referenced Japanese patents, the gas barrier quality is improved if the 
amount of EVOH is less than about 30 wt %, but the degree of improvement 
is too low to be satisfactory in terms of enhancement of the 
preservability of foodstuffs. On the other hand, if the amount of EVOH is 
increased in order to improve the preservability, the moldability in 
during stretch blowing is reduced. Thus, it is difficult to produce the 
intended gas-barrier container. For these reasons, a container made of a 
composition of saturated polyester and an EVOH has not yet been put to 
practical use. It is known that a container having a high gas-barrier 
quality is obtained by laminating saturated polyester and an EVOH 
employing a co-extrusion technique, but this method has not been put to 
practical use either because of the high molding cost. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to eliminate the 
above-described problems in the prior art and to provide an injection 
stretch blow container having a high gas-barrier quality due to the 
laminar structure of the blend of saturated polyester and an EVOH. 
To achieve this aim, the present injection stretch blow container 
comprising a combination of 97 to 70 parts by weight of a saturated 
polyester and 3 to 30 parts by weight of a saponification product of an 
ethylene-vinyl acetate copolymer, having many areas, particularly at the 
body wall portion of said container, in which substantially 
two-dimensional thin layers of said saponification product of said 
ethylene-vinyl acetate copolymer are laminated in parallel to the wall 
surface of said container in a matrix of saturated polyester, said 
saponification product of said ethylene-vinyl acetate copolymer in said 
area (20.times.20 .mu.m; vertical section or longitudinal section of the 
body wall of said container) is 0.001 to 1 .mu.m in average thickness and 
at least 5 in average aspect ratio, and the laminated structural index 
represented by the following formula is at least 5: 
Laminated structural index 
##EQU2## 
wherein L.sub.i represents a length of the overlapped portion of adjacent 
layers of the saponification product of the ethylene-vinyl acetate 
copolymer, and 
h.sub.i represents a distance between adjacent layers of the saponification 
product of the ethylene-vinyl acetate copolymer. 
A container having the above-described structure has not been obtained by 
the methods disclosed in the prior-art literature. A container of the 
present invention is very useful for packaging a wide range of foods 
including carbonated beverages, because it has a high gas barrier quality 
which is equivalent to that of a laminate obtained by the co-extrusion of 
saturated polyester and the EVOH. 
The above and other objects, features and advantages of the present 
invention will become clear from the following description of the 
preferred embodiments thereof, taken in connection with the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Examples of saturated polyester resins which are used in the present 
invention, are as follows: poly(ethylene terephthalate) (PET), 
poly(butylene terephthalate), poly(ethylene terephthalate/isophthalate), 
and poly(ethylene glycol/cyclohexanedimethanol/terephthalate). In 
addition, the above described polymers which contain the following 
copolymerization components are also usable: diols such as ethylene 
glycol, cyclohexane dimethanol, neopentyl glycol and pentanediol; 
dicarboxylic acids such as isophthalic acid, benzophenonedicarboxylic 
acid, diphenylsulfone dicarboxylic acid, diphenylmethane dicarboxylic 
acid, propylene bis(phenylcarboxylic acid), diphenyloxide dicarboxylic 
acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic 
acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and diethyl 
succinic acid. Among these, poly(ethylene terephthalate) is usually 
preferable for achieving the aim of the present invention, and 
poly(ethylene terephthalate/isophthalate) containing 2 to 12 mol% of 
isophthalate in a monomer of the acid component is also preferable due to 
the ease of molding and the excellent gas-barrier property of the 
container obtained therewith. The intrinsic viscosity of saturated 
polyester is not specified, but is preferably 0.5 to 1.4 dl/g, more 
preferably 0.6 to 0.9 dl/g. 
The saponification product of ethylene-vinyl acetate copolymer (EVOH) in 
the present invention may be any product that is obtained by hydrolyzing 
the vinyl acetate unit of a copolymer of ethylene and vinyl acetate. In 
particular, a product which contains 25 to 60 mol% of the ethylene unit, 
the degree of saponification of which is at least 96% and the melt index 
(at 190.degree. C., 2160 g) of which is in the range of 0.2 to 60 g/10 
min. is preferable. Unexpectedly it has been found that a blend 
composition produced using an EVOH containing 37 to 50 mol % of ethylene 
units exhibits a propensity of forming a laminar structure in the wall 
material of the container, thereby displaying a high gas-barrier quality 
and excellent injection stretch blow moldability. Since an EVOH which has 
an especially high gas-barrier quality contains 28 to 36 mol% of ethylene, 
the above finding was not anticipated. The EVOH in the present invention 
may be modified by a comonomer of less than 5 mol%. Such a modifying 
monomer will be exemplified by propylene, 1-butene, 1-hexene, 
4-methyl-1-pentene, acrylic ester, methacrylate ester, maleic acid, 
fumaric acid, itaconic acid, higher fatty acid vinyl ester, alkyl vinyl 
ester, N-(2-dimethylaminoethyl)methacrylamides or their quaternary 
monomers, N-vinyl imidazole or its quaternary monomer, N-vinyl 
pyrrolidone, N-n-butoxymethylacrylamide, vinyl trimethoxysilane, vinyl 
methyl dimethoxysilane, and vinyl dimethyl methoxysilane. 
If the amount of EVOH in a composition of the present invention is less 
than 3 parts by weight, sufficient gas barrier quality is not obtained 
even if the EVOH is molded into a laminar structure. If the amount of EVOH 
exceeds 30 parts by weight, it is difficult to obtain a good laminar 
molded product. According to the method of the present invention, it is 
not necessary to use such a great amount of EVOH. 
In producing a container in accordance with the present invention, a 
predetermined amount of saturated polyester and EVOH are first blended, 
preferably by a dry blend method. Pelleting by pre-blending, which is 
employed in an ordinary polymer blend and which is disclosed in Japanese 
Laid-Open Pat. No. 76325/1985, is not preferred. However, if pelleting by 
pre-blending is desired, then by controlling the mixture to an extremely 
low level, it is possible to obtain a container having a structure as 
specified in the present invention. In particular, melting and kneading in 
a multi-axial extruder, kneader, Banbury mixer, etc. will not produce the 
excellent molding quality of the present invention, thereby being 
unfavorable for accomplishing the aim of the present invention. The size 
of the resin being used has a potent influence of the result. A particle 
size of less than 0.5 mm is not preferable and it is preferable that the 
shortest side is between 1 mm and 7 mm in order to obtain a good result. 
The thus-dry-blended is charged into an extruder, usually, an injection 
molder provided with a uniaxial extruder, while avoiding additional 
excessive mixture. It is preferable that this uniaxial extruder has no 
portion which accelerates mixing such as a mixing screw, DIS screw, and 
static mixer as a dulmadge, barrier type and pin type screws, 
respectively, which are generally used in molding polymer blends. The most 
preferable uniaxial extruder in accordance with the present invention is 
an extruder which has a simple full-flight type screw having, for example, 
an L/D of 10 to 30 and a compression ratio of 1.2 to 4. The temperature of 
injection molding is usually 220.degree. to 330.degree. C., preferably 
240.degree. to 280.degree. C. In order to form the excellent laminar 
structure disclosed in the present invention, specific injection 
conditions are required. That is, the rotational speed of the screw must 
be low, 20 to 160, preferably 20 to 100 rpm. It is necessary not to retain 
the blended resin more than 30 minutes at a temperature above 260.degree. 
C. If it is retained for more than 30 minutes, it is difficult to form the 
laminar structure which is characteristic of the present invention, and 
the stretch blow moldability is reduced. It is necessary that the 
injection pressure is high (more than 80 kg/cm.sup.2, preferably 95 
kg/cm.sup.2) and the injection time is short (within 3 seconds, preferably 
1.5 seconds). It has been found that the laminar structure is rapidly 
developed by suddenly cooling the injected resin by lowering the 
temperature of the mold in advance. A suitable temperature to which the 
mold is cooled is 5.degree. to 18.degree. C. In the present invention it 
is essential to use an injection molder, and even if a molding method 
which can avoid additional mixture is used, neither compression molding 
nor extrusion molding (disclosed in Japanese Laid-Open Pat. No. 
121017/1980) can produce a container having a high gas barrier quality 
such as those disclosed in the present invention. The parison thus 
obtained by injection molding is stretch-blown, thereby obtaining a 
container of the present invention. The parison is enlarged 5 to 20 times, 
preferably 7 to 15 times by stretch blowing at a temperature of 80.degree. 
to 120.degree. C., preferably 90.degree. to 110.degree. C. The 
thus-obtained container (bottle or the like) is excellent in resistance to 
shock and resistance to creep as well as gas-barrier quality, and acquires 
importance as a container for carbonated beverages such as beer and soda. 
In order to bottle carbonated beverages, it is necessary not only to 
prevent the carbon dioxide gas from escaping through the walls of the 
container but also to prevent the foodstuff within the container from 
being oxidized by oxygen which may permeate the container. The container 
of the present invention has an extremely high gas barrier quality. The 
main characteristic of the present invention is that the EVOH among the 
wall materials of the container has the above-described laminar structure, 
which particular structure is considered to be responsible for producing a 
container having such a high gas-barrier quality. Accordingly, the 
container of the present invention is easily distinguished from a 
container in the prior art in that it has the aforementioned laminar 
structure. This laminar structure is obtained by the above-described 
specific injection stretch blowing method. The formation of the laminar 
structure is easily confirmed by observing a section of the container 
using a transmission electron microscope. The container obtained according 
to the present invention is characterized in that said container has many 
areas, particularly at the body wall portion of said container in which 
substantially two-dimensional thin layers of said saponification product 
of said ethylene-vinyl acetate copolymer are laminated in parallel to the 
wall surface of said container in a matrix of saturated polyester, said 
saponification product of said ethylene-vinyl acetate copolymer in said 
area (20.times.20 .mu.m; vertical section or longitudinal section of the 
body wall of said container) is 0.001 to 1 .mu.m in average thickness, 
preferably 0.001 to 0.2 .mu.m and is at least 5 in average aspect ratio, 
preferably at least 15, and the laminated structural index represented by 
the following formula is at least 5, preferably at least 15. 
Laminated structural index 
##EQU3## 
wherein L.sub.i represents a length of the overlapped portion of adjacent 
layers of the saponification product of the ethylene-vinyl acetate 
copolymer, and 
h.sub.i represents a distance between adjacent layers of the saponification 
product of the ethylene-vinyl acetate copolymer. 
At least the body portion of the container must have many of such areas. 
The shoulder portion, neck portion, and bottom of the container need not 
necessarily have that structure. 
Although an injection-molded container which is formed solely of a 
composition of saturated polyester and an EVOH has been explained in the 
above, a multi-layered injection-molded container which contains a 
saturated polyester layer (P) in addition to the blend layer (B) is 
included in the scope of the present invention. The structure of the layer 
in this case is preferably P/B (outer layer), B/P (outer layer), or P/B/P, 
and it is usually unnecessary to use a bonding resin. 
It is possible to add another thermoplastic resin, antioxidant, pigment, 
filler, nucleating agent, etc., to the composition of the present 
invention in a range which does not impair the object of the present 
invention. 
The present invention will be explained in more detail with reference to 
the following examples. 
EXAMPLE 1 
90 parts of pellets (size: 2.times.2.times.4 mm) of polyethylene 
terephthalate (hereinafter referred to as "PET") having an intrinsic 
viscosity of 0.80 dl/g were dried under reduced pressure so as to have a 
water content of not greater than 50 ppm. 10 parts of pellets (size: 
2.times.3.times.4 mm) of an EVOH in which the ethylene units were 44 mol 
%, the degree of saponification was 99% and the melt index (at 190.degree. 
C., 2160 g) was 5 g/10 min. were dried under a reduced pressure so as to 
have a water content of not greater than 200 ppm. A stretch bottle blower 
having an extruder with a built-in full-flight screw (L/D: 20, diameter: 
36 mm, effective length: 720 mm, compression ratio: 2.5) was prepared. 
After dry blending both pellets, they were injected into a mold which was 
provided with an injection gate having a diameter of 2.1 mm and which had 
been cooled to 9.degree. C. at an injection pressure of 100 kg/cm.sup.2. 
The temperature of the cylinders C.sub.1, C.sub.2 and C.sub.3 were 
268.degree. C., 273.degree. C. and 273.degree. C., respectively, and the 
rotational speed of the screw was 80 rpm. The pellets were retained in the 
extruder for 2.5 minutes. The injection time was 1.5 seconds, and the 
injection holding time was 9 seconds. Thus, a closed-end parison (total 
length: 165 mm, outer diameter: 24 mm, inner diameter: 16 mm) was molded. 
Immediately thereafter the parison was held at 100.degree. C. for 15 
seconds. Stretch blow molding (draw ratio by stretching: about 10) was 
then carried out, whereby a bottle-shaped container having the body 
portion of 380.mu. thick and a capacity of 1 l was obtained. 
Comparative Example 1 
Dry-blended materials having the same composition as those of Example 1 
were blend-pelleted at 280.degree. C. using a biaxial extruder (40.phi.). 
This blended pellet was used and a stretch blow bottle was obtained under 
the same molding conditions as in Example 1. 
Comparative Example 2 
Dry-blended materials having the same composition as those of Example 1 
were extruded using the same uniaxial extruder in the same way as in 
Example 1 except that the residence was 40 minutes, thereby stretch 
blowing the molded parison, but it was impossible to obtain a uniformly 
blown product. 
Comparative Example 3 
Dry-blended materials having the same composition as those of Example 1 
were extruded using uniaxial extruder (40.phi.) with a circular hollow 
pipe die at 280.degree. C. (the residence time in the extruder and die: 
4.5 minutes), thereby obtaining a pipe having an outer diameter of 24 mm 
and an inner diameter of 16 mm. This pipe was cut to form a mouth portion 
and a bottom using a LM-01 and 02, produced by Corpoplast Ltd, so that a 
parison of 165 mm in total length was obtained. The parison was then 
preheated at 100.degree. to 110.degree. C. for 30 minutes by an infrared 
heater and thereafter it was stretch blown by an LD-01 type stretch blow 
extruder produced by Corpoplast Ltd, whereby a bottle havin abody portion 
of 380.mu. in average thickness and a capacity of 1 l was obtained. 
The three kinds of bottles obtained in Example 1, and Comparative Examples 
1 and 3 were filled with saturated CO.sub.2 water (O.sub.2 concentration: 
0 ppm) so as to be 2 atm at 20.degree. C. and were kept at 20.degree. C. 
in an atmosphere of 65% RH. The concentrations of CO.sub.2 and O.sub.2 
were measured by a gas chromatograph and the changes thereof were 
recorded. The time at which the CO.sub.2 concentration was reduced by 15% 
of that present at the initial time (hereinafter referred to as "CO.sub.2 
15% loss") and the time at which the O.sub.2 concentration became 3 ppm 
(hereinafter referred to as "O.sub.2 concentration 3 ppm") were made the 
criteria for the foodstuff preservability. The results are shown in Table 
1. Table 1 also shows the results of observation of the wall structures of 
the containers using a light microscope and an electron microscope. As 
will be clear from Table 1, the preservation time of the container in 
accordance with the present invention in terms of CO.sub.2 15% and O.sub.2 
concentration 3 ppm is 2.7 to 3 times those of the containers of blend 
compositions of Comparative Examples 1 and 3. Further, the bottle obtained 
according to Example 1 had a favorable external appearance and had an 
excellent strength in drop and pressure resistance. 
It is to be noted that the preservation time of the container of the 
present invention is much longer than those of the containers of 
Comparative Examples 1 and 3. FIGS. 1 and 2 are photomicrographs 
(20,000.times.magnification) taken with a transmission electron microscope 
of a vertical section and a longitudinal section, respectively of the body 
portion of a bottle. It is understood from these photomicrographs that the 
EVOH exhibits a laminar structure consisting of a multiplicity of distinct 
substantially two-dimensional layers in the matrix of saturated polyester. 
Many areas (each area is 20.times.20 .mu.m) were observed. The average 
thickness of the layers was 0.001 to 0.03 .mu.m, the average aspect ratio 
was more than 100, and the laminated structural index was more than 30. 
According to the photomicrographs by an electron microscope (FIG. 3 shows a 
vertical section, and FIG. 4 shows a longitudinal section), the EVOHs 
dispersed in the wall of the container of Comparative Example 1 were flat 
and particulate, or displayed a lamellar structure 3 to 7 in average 
aspect ratio and 0.8 to 2.6 in laminated structural index, which was very 
different from the laminar structure of the container of the present 
invention. According to the photomicrographs taken using an electron 
microscope, the EVOHs dispersed in the wall of the container of 
Comparative Example 3 had configurations similar to those of the EVOHs in 
Comparative Example 1, and displayed a lamellar structure 2 to 6 in 
average aspect ratio and 0.8 to 4.4 in laminated structural index, which 
was very different from the laminar structure of the container of the 
present invention. 
TABLE 1 
__________________________________________________________________________ 
Preservability (week) 
Composition of EVOH of Body of Container 
Blend O.sub.2 Average Aspect Ratio 
Laminated Structure Index 
Structure 
CO.sub.2 
Concentration 
Average 
Vertical 
Longitudinal 
Vertical 
Longitudinal 
PET/EVOH 
15% loss 
3 ppm Thickness .mu.m 
Section 
Section 
Section 
Section 
__________________________________________________________________________ 
Example 1 
90/10 40 35 0.003.about.0.03 
more than 
more than 
more than 
more than 
100 100 30 30 
Comparative 
90/10 15 13 0.03.about.0.07 
3.about.6 
4.about.7 
0.8.about.2.5 
0.7.about.2.6 
Example 1 
Comparative 
90/10 13 11 0.1.about.0.3 
2.about.5 
3.about.6 
0.8.about.3.8 
0.9.about.4.4 
Example 3 
__________________________________________________________________________ 
Average Thickness . . . the average thickness of the EVOH layers on the 
vertical section and the longitudinal section (section in the diametrical 
direction) of the body wall of the container in each area (20 .times. 20 
.mu.m). (Minimum average thickness to maximum average thickness). 
Average Aspect Ratio . . . the average ratio of the length to the 
thickness of the EVOH layers on the vertical section and the longitudinal 
section of the body wall of the container represented 
by 
##STR1## 
(Minimum average ratio to maximum average ratio). 
Laminated Structural Index . . . the average ratio of the distance (hi) 
between adjacent EVOH layers to the length (Li) of the overlapped portion 
on the vertical section and the longitudinal section of the body wall of 
the container represented by 
##STR2## 
EXAMPLES 2 TO 6 
Injection stretch blow containers were obtained in the same way as in 
Example 1 except for changing the kinds and the amount of EVOH to be 
blended. Table 2 shows the results of measurement of the preservabilities 
and observation of the wall structures. Each of these bottles had a 
favorable external appearance and had approximately the same strength in 
drop and pressure resistance as that of the container consisting solely of 
PET. In addition, each of these bottles displayed high preservability, as 
shown in Table 2, and is therefore suitable as a container for carbonated 
beverages. 
TABLE 2 
__________________________________________________________________________ 
Preservability 
Blend 
(week) Composition of EVOH of Body of Container 
Structure 
CO.sub.2 
O.sub.2 
Average 
Average Aspect Ratio 
Laminated 
Structure Index 
EVOH PET/ 15% 
Concentra- 
Thickness 
Vertical 
Longitudinal 
Vertical 
Longitudinal 
Et*.sup.1 
MI*.sup.2 
EVOH loss 
tion 3 ppm 
.mu.m Section Section Section 
Section 
__________________________________________________________________________ 
Example 2 
44 5 95/5 25 22 0.002.about.0.2 
more than 100 
more than 100 
more than 
more than 30 
Example 3 
44 8 80/20 
67 58 0.002.about.0.2 
more than 100 
more than 100 
more than 
more than 30 
Example 4 
48 8 75/25 
69 61 0.001.about.0.1 
more than 100 
more than 100 
more than 
more than 30 
Example 5 
37 3 90/10 
39 34 0.001.about.0.1 
50.about.120 
more than 100 
10.about.30 
more than 30 
Example 6 
33 1 90/10 
25 21 0.005.about.0.5 
5.about.80 
10.about.100 
5.about.20 
5.about.25 
__________________________________________________________________________ 
*.sup.1 Et: content (mol %) of ethylene unit 
*.sup.2 MI: melt index (at 190.degree. C., 2160 g) (g/10 min.) 
EXAMPLE 7 
90 parts of dried pellets (size: 2.times.2.times.4 mm) of poly(ethylene 
terephthalate/isophthalate) having 6 mol % of isophthalate in monomers of 
the acid component, and an intrinsic viscosity of 0.82 dl/g and 10 parts 
of the same pellets of the EVOH as used in Example 1 were dry blended. 
Thereafter the blend was injected into a mold by the same stretch bottle 
blower as used in Example 1 under the same conditions as those of Example 
1 except that the temperatures of the cylinders C.sub.1, C.sub.2 and 
C.sub.3 were 247.degree. C., 256.degree. C. and 256.degree. C., 
respectively. Thus a bottle-shaped container having a capacity of 1 l was 
obtained. When this bottle was filled with saturated calcareous water 
(O.sub.2 concentration: 0 ppm) so as to be 2 atm at 20 C. and the 
preservation term was measured in the above-described way, it showed 
excellent preservability; the CO.sub.2 15% loss was 44 weeks and the 
O.sub.2 concentration 3 ppm was 37 weeks. Further this bottle had a 
favorable external appearance and an excellent strength in drop and 
pressure resistance. The EVOH at the body portion of the bottle exhibited 
a distinct laminar structure consisting of a multiplicity of substantially 
two-dimensional layers in the matrix of saturated polyester. The average 
thickness of the layers was 0.001 to 0.1 .mu.m, the average aspect ratio 
was more than 100, and the laminated structural index was more than 30.