Disclosed is a multi-layer gas-barrier drawn polyester vessel, which comprises an open end portion, a barrel portion which is molecularly oriented in at least one axial direction and a closed bottom portion, said vessel having inner and outer layers composed of a thermoplastic polyester or copolyester and a gas-barrier intermediate layer composed of an ethylene/vinyl alcohol copolymer having an ethylene content lower than 50 mole %, wherein a copolymer nylon resin or a blend of a plurality of nylon resins is interposed as an adhesive between two adjacent layers.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a multi-layer drawn polyester vessel. More 
particularly, the present invention relates to a gas-barrier vessel 
comprising a gas-barrier layer composed of an ethylene/vinyl alcohol 
copolymer and a substrate layer composed of a polyester, in which the 
vessel wall is molecularly oriented in at least one axial direction by 
drawing and the interlaminar adhesion is improved. 
(2) Description of the Prior Art 
Formation of vessels such as drawn polyester bottles is popular at the 
present. These formed vessels have excellent transparency and appropriate 
gas-barrier property, and they have been broadly used as vessels for 
liquid detergents, shampoos, cosmetics, soys and sauces and recently also 
for carbonated drinks such as beer, cola and soda pop and refreshing 
drinks such as fruit juices and mineral water. 
However, since even drawn polyester bottles are plastic vessels, they have 
a permeability to oxygen, carbon dioxide gas and the like though the 
permeability is very small, while the gas permeability of completely 
sealed vessels such as glass bottles and metal cans is substantially zero. 
Accordingly, drawn polyester bottles are inferior to cans and glass 
bottles in the food filling and storing properties, and in case of 
carbonated drinks, loss of carbon dioxide gas is caused and in case of 
beer, cola and soda pop, there is a difinite limit of the storage period. 
As means for improving the gas barrier property in drawn polyester vessels, 
there has been practically adopted a method in which a drawn polyester 
bottle is coated with a polyvinylidene chloride resin. Lamination or 
coating of a polyester with a resin having a poorer gas-barrier property 
than that of the polyester is insignificant for improving a drawn 
polyester resin which has inherently an appropriate gas-barrier property. 
Namely, a resin which is excellent over a polyester in the gas-barrier 
property should be used for lamination or coating. As such resin, there 
can be mentioned thermoplastic resins selected from vinyldiene chloride 
resins, acrylonitrile type resins and vinyl alcohol type resins. At any 
rate, an appropriate resin should be selected while the properties and 
processability of the resin are taken into consideration. 
We previously found that in the production of a multi-layer drawn polyester 
vessel comprising a polyester substrate and a gas-barrier layer of an 
ethylene/vinyl alcohol copolymer, if the steps of forming a pipe by 
co-extrusion, cutting the pipe, heat-forming the bottom and biaxially 
draw-blowing the bottomed tube are combined in this order, a multi-layer 
drawn polyester vessel having an excellent gas-barrier property and a high 
molecular orientation can be obtained (see Japanese Patent Application No. 
73893/83). 
However, since there is no substantial heat bondability between the 
polyester layer and the ethylene/vinyl alcohol copolymer layer, it is 
eagerly desired to develop an adhesive resin which can provide such a 
strong interlaminar bonding between both the layers that the bonded 
structure can resist falling shocks. 
SUMMARY OF THE INVENTION 
As the result of our research, it was found that the above problem involved 
in the production of a multi-layer drawn polyester vessel can be solved by 
using an ethylene/vinyl alcohol copolymer having an ethylene content lower 
than 50 mole% for a gas-barrier resin layer, a polyester resin for an 
inner layer, an outer layer or inner and outer layers as the substrate and 
a copolymer nylon resin or a blend of a plurality of nylon resins for an 
adhesive resin layer. 
It is therefore a primary object of the present invention to provide a 
multi-layer vessel in which a gas-barrier layer of an ethylene/vinyl 
alcohol copolymer and a molecularly oriented polyester copolyester are 
strongly bonded and this bonding is not influenced by a falling shock, 
deformation or inner carbon dioxide gas pressure. 
Another object of the present invention is to provide a multilayer 
gas-barrier drawn polyester vessel which is excellent in the interlaminar 
peeling resistance, gas barrier property and transparency. 
More specifically, in accordance with the present invention, there is 
provided a multi-layer gas-barrier drawn polyester vessel, which comprises 
an open end portion, a barrier portion which is molecularly oriented in at 
least one axial direction and a closed bottom portion, said vessel having 
inner and outer layers composed of a thermoplastic polyester or 
copolyester and a gas-barrier intermediate layer composed of an 
ethylene/vinyl alcohol copolymer having an ethylene content lower than 50 
mole%, wherein a copolymer nylon resin or a blend of a plurality of nylon 
resins is interposed as an adhesive between two adjacent layers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A bottle-shaped or cup-shaped vessel comprising a molecularly oriented 
polyester substrate layer and a gas-barrier layer of an ethylene/vinyl 
alcohol copolymer is known. A bottle or cup of this structure having an 
adhesive layer between both the resin layers can be practically used under 
certain use conditions. However, it is generally impossible to provide a 
strong interlaminar heat-bonding strength between the polyester layer and 
ethylene/vinyl alcohol copolymer layer. Accordingly, in the case where no 
adhesive layer is interposed between both the resin layers, if water or 
the like is filled and sealed in a bottle or cup and a falling shock or 
large deformation is given to the vessel or if a carbonated drink is 
filled and sealed in such a vessel, interlaminar peeling is readily caused 
between the polyester layer and ethylene/vinyl alcohol copolymer layer. 
The critical feature of the present invention resides in the finding that 
if a copolymer nylon resin or a blend of a plurality of nylon resins is 
interposed between the above-mentioned two resin layers to provide a 
bonding force between both the resin layers, when various deformations are 
given or when a carbonated drink is filled and sealed, interlaminar 
peeling is not caused and the multi-layer vessel shows a complete 
gas-barrier property, and even if this adhesive is interposed between the 
two resin layers, the transparency is not degraded but maintained at a 
high level. 
Although an amide group-containing thermoplastic resin such as a polyamide 
is known as a resin material constituting a multi-layer vessel, it is not 
known that a copolymer nylon resin or nylon resin blend as used in the 
present invention can be interposed between a polyester layer and an 
ethylene/vinyl alcohol copolymer layer or that this copolymer nylon resin 
or nylon resin blend has an excellent bondability to the two layers and 
exerts the above-mentioned functional effects. 
The present invention will now be described in detail with reference to the 
accompanying drawings. 
Structure of Vessel 
Referring to FIG. 1 illustrating an embodiment (bottle) of the multi-layer 
polyester vessel according to the present invention, this bottle 1 
comprises a neck portion 5 having an opening 2 on the top end and 
lid-engaging, screw and anchoring parts, such as a screw 3 and a support 
4, on the periphery, a barrel portion 7 connected to the neck portion 5 
through a shoulder portion 6 and a closed bottom portion 8. The barrel 
portion 7 of this bottle 1 is molecularly oriented biaxially, that is, in 
the axial and circumferential directions of the bottle, by draw-blow 
forming. As is seen from the enlarged section in FIG. 1, this bottle 1 has 
a multi-layer structure comprising an outer layer 9 composed of 
polyethylene terephthalate or a copolyester thereof, an inner layer 10 
composed of polyethylene terephthalate or a copolyester thereof, and an 
intermediate layer 11 interposed between the two layers 9 and 10 and 
composed of an ethylene/vinyl alcohol copolymer having an ethylene content 
lower than 50 mole%. Adhesive layers 12a and 12b composed of a copolymer 
nylon resin or nylon resin blend, described in detail hereinafter, are 
interposed between the outer layer 9 and intermediate layer 11 and between 
the intermediate layer 11 and inner layer 10, respectively. 
Adhesive 
In the present invention, a copolymer nylon resin or a blend of a plurality 
of nylon resins is used as the above-mentioned adhesive. As the adhesive, 
there can be mentioned, for example, a 6/6,6 copolymer nylon 
(copolyamide), various copolyamides, and blends of a plurality of nylon 
resins. 
More specifically, there can be mentioned copolyamides comprising plural 
kinds of amide recurring units, for example, those represented by the 
following formula: 
##STR1## 
wherein R, R.sup.1 and R.sup.2 stand for a linear alkylene group, and 
blends comprising a plurality of nylon resins having the above amide 
recurring units. In view of the gas-barrier property to oxygen, carbon 
dioxide gas or the like, it is preferred that a copolyamide having 3 to 30 
amide groups, especially 4 to 25 amide groups, per 100 carbon atoms of the 
copolyamide or a blend of such polyamides be used as the adhesive. As 
preferred examples of polyamide units, there can be mentioned units of 
polycapramide (nylon 6), poly-.omega.-aminoheptanoic acid (nylon 7), 
poly-.omega.-aminononanoic acid (nylon 9), polyundecanamide (nylon 11), 
polylauryl lactam (nylon 12), polyethylenediamineadipamide (nylon 2,6), 
polytetramethyleneadipamide (nylon 4,6), 
polyhexamethyleneadipamide (nylon 6,6), 
polyhexamethylenesebacamide (nylon 6,10), 
polyhexamethylenedodecamide (nylon 6,12), 
polyoctamethyleneadipamide (nylon 8,6), 
polydecamethyleneadipamide (nylon 10,6) and 
polydodecamethylenesebacamide (nylon 10,8). 
As specific examples of preferred copolyamides, there can be mentioned a 
caprolactam/lauryl lactam copolymer, a caprolactam/hexamethylene 
diammonium adipate copolymer, a lauryl lactam/hexamethylene diammonium 
adipate copolymer, a hexamethylene diammonium adipate/hexamethylene 
diammonium sebacate copolymer, an ethylene diammonium 
adipate/hexamethylene diammonium adipate copolymer and a 
caprolactam/hexamethylene diammonium adipate/hexamethylene diammonium 
sebacate copolymer. 
So-called blends of homopolyamides or copolyamides having amide recurring 
units as described above may be used. For example, a blend of 
polycaprolactam and polyhexamethyleneadipamide and a blend of 
polycarolactam and a caprolactam/hexamethylene diammonium adipate 
copolymer can be used for attaining the objects of the present invention. 
Furthermore, aromatic polyamides containing in the molecule chain at least 
70 mole% of structural units formed from m-xylylene diamine or a mixed 
xylylene diamine comprising m-xylylene diamine and up to 30%, based on the 
total mixed xylylene diamine, of p-xylylene diamine and an 
.alpha.,.omega.-aliphatic dicarboxylic acid having 6 to 10 carbon atoms, 
as disclosed in Japanese Patent Publication No. 1156/75, No. 5751/75, No. 
5753/75 or No. 10196/75 or Japanese Patent Application No. 29697/75, can 
be used as an adhesive for bonding a polyester layer and an ethylene-vinyl 
alcohol copolymer, though aromatic polyamides of this type are slightly 
inferior to the above-mentioned aliphatic polyamides in the moldability. 
The molecular weight of the copolyamide or the blend-constituting polyamide 
is not particularly critical, so far as it is in the film-forming range. 
However, it is generally preferred that the relative viscosity (.eta. rel) 
of the polymer be 1.8 to 3.5 as measured at 20.degree. C. with respect to 
a solution of 1 g of the polymer in 10.0 cc of 98% sulfuric acid. When a 
polyamide having this relative viscosity lower than 1.8 is used, it is 
often difficult to provide a laminate structural excellent in the 
mechanical strength of the adhesive layer. A polyamide having this 
relative viscosity higher than 3.5 is ordinarily inferior in the 
melt-moldability. 
It has been found that a copolymer nylon of nylon 6 and nylon 6,6 is 
especially suitable for attaining the objects of the present invention. 
More specifically, various copolyamide adhesives are almost satisfactory 
for bonding a thermoplastic polyester and an ethylene/vinyl alcohol 
copolymer, but they are still insufficient in that when contents are 
filled in formed multi-layer vessels and they undergo falling shocks, many 
mesh-like clefts or openings are formed in the adhesive layers and the 
appearance characteristics of the vessels are drastically degraded and the 
vessels become insufficient in the strength. The reason has not been 
completely elucidated, but it is considered that since most of copolyamide 
type adhesives are low in the cohesive force and the copolyamide type 
adhesives cannot follow up with the difference of the elastic deformation 
(elongation and contraction) between the polyester layer and the 
ethylene/vinyl alcohol copolymer layer under shocks or impacts, mesh-like 
clefts will be readily formed. In contrast, the above-mentioned nylon 
6/nylon 6,6 copolymer preferably used in the present invention has an 
exceptionally large cohesive force as the copolyamide, and this 
copolyamide has such characteristic physical properties as shown below. 
The corresponding physical properties of nylon 6 and nylon 6,6 are also 
shown below. 
______________________________________ 
Nylon 6/ 
Nylon 6 Nylon 6,6 Nylon 6,6* 
______________________________________ 
Tensile strength 
645 765 575 
(kg/cm.sup.2, ASTM D-638) 
Tensile elongation 
70 50 850 
(%, ASTM D-638) 
Elastic modulus 
18750 28100 14200 
(kg/cm.sup.2, ASTM D-638) 
Impact strength 
1.3 1.5 11.0 
(ft .multidot. lb/m.sup.2, ASTM D-256) 
Melting point 215 260 167 
(.degree.C., DSC method) 
______________________________________ 
Note 
*copolymer nylon comprising 78 mole % of nylon 6 component and 22 mole % 
of nylon 6,6 component 
In connection with the ratio between nylon 6 and nylon 6,6 in the 
copolyamide, it is preferred that the content of the nylon 6 component be 
50 to 93 mole%, especially 70 to 90 mole%, and the content of the nylon 
6,6 component be 7 to 50 mole%, especially 10 to 30 mole%. 
The bonding strength of the adhesive between the polyester layer and the 
ethylene/vinyl alcohol copolymer layer includes not only a strong bonding 
force but also a broad width for the necessary bonding force. 
Generally, it is required that the peel strength should be 20 to 800 g/20 
mm of the width. 
In case of ordinary polyamide adhesives, the bonding force to the 
ethylene/vinyl alcohol copolymer layer is stronger and the bonding force 
to the polyester layer is relatively weak. However, in case of a nylon 
6/nylon 6,6 copolymer, even the bonding force to the polyester layer is 
strong. 
When the polyamide type adhesive of the present invention is used, the 
transparency of the polyethylene terephthalate substrate layer is not 
degraded if the thickness of the adhesive layer is about 5.mu. to about 
50.mu.. On the other hand, when maleic acid-modified polyolefins such as 
maleic acid-modified polypropylene and acid-modified polyethylene are used 
as the adhesive for bonding polyester and ethylene/vinyl alcohol copolymer 
layers, the transparency is considerably degraded. 
Other Constituent Materials 
Known polyethylene terephthalate is optionally used as the polyester (PET), 
and it is sufficient if polyethylene terephthalate has a film-forming 
molecular weight. A polyester having an intrinsic viscosity of at least 
0.8, especially at least 1.0, is preferably used. As the copolyester, 
there is used a copolyester composed mainly of ethylene terephthalate 
units, which contains minor amounts of ester units in which at least one 
of the acid and alcohol components is an acid component other than 
terephthalic acid or an alcohol component other than ethylene glycol. 
Since this copolyester is composed mainly of ethylene terephthalate units, 
the copolyester can be subjected to draw-blow forming and molecularly 
oriented under the same conditions as those adopted for polyethylene 
terephthalate. Moreover, since the copolyester contains ester units other 
than ethylene terephthalte units, the crystallization speed of the 
copolyester is lower than that of polyethylene terephthalate. 
As the acid component other than terephthalic acid in the copolyester, 
there can be mentioned isophthalic acid, naphthalene-dicarboxylic acid, 
diphenyldicarboxylic acid, 2,2-bis(4-carboxyphenyl)propane, 
bis(4-carboxyphenyl)methane, cyclohexane-dicarboxylic acid 
(hexahydroterephthalic acid or hexahydroisophthalic acid), adipic acid, 
sebacic acid, succinic acid and dodecane-dicarboxylic acid. As the alcohol 
component other than ethylene glycol, there can be mentioned propylene 
glycol, butane-diol, neopentyl glycol, hexane-diol, glycerol, diethylene 
glycol, triethylene glycol, tetraethylene glycol, dibutylene glycol and 
tributylene glycol. These acid components and/or alcohol components may be 
used singly or in the form of mixtures of two or more of them. 
In the present invention, also improvement of the gas-barrier property of a 
polyester vessel is intended, and among vinyl alcohol type resins, as 
ethylene/vinyl alcohol copolymer (EVOH) having an ethylene content lower 
than 50 mole% is especially selected and used. As is well-known, polyvinyl 
alcohol is not heat-moldable unless it is subjected to a special 
treatment, and in ethylene/vinyl alcohol copolymers, increase of the 
ethylene content results in reduction of the melting property and increase 
of the thermoplastic property. Therefore, use of an ethylene/vinyl alcohol 
copolymer having a lower melting point and a lower drawing-possible 
temperature will be ordinarily considered to be preferable. However, in 
the present invention, an ethylene/vinyl alcohol copolymer having a high 
melting point and a high drawing-possible temperature is selected. The 
first reason is that in case of an ethylene/vinyl alcohol copolymer having 
an ethylene content higher than 50 mole%, although co-drawing of this 
copolymer with a polyester resin layer is advantageous because the melting 
point is low and the drawing-possible temperature is low, the gas-barrier 
property is abruptly decreased with increase of the ethylene content and 
lamination of the polyester resin with the ethylene/vinyl alcohol 
copolymer becomes insignificant. The second reason is that according to 
the present invention, it has been found that, as described in detail 
hereinafter, even an ethylene/vinyl alcohol copolymer having a high vinyl 
alcohol content can be drawn in the form of a multi-layer structure with a 
polyester resin at a drawing temperature suitable for drawing of the 
polyester resin. Therefore, an ethylene/vinyl alcohol copolymer having an 
ethylene content lower than 50 mole%, that is, a higher vinyl alcohol 
content, is selected and used as the ethylene/vinyl alcohol copolymer to 
be laminated with a polyester resin. 
In the present invention, an ethylene/vinyl alcohol copolymer obtained by 
saponifying a copolymer of ethylene with a vinyl ester such as vinyl 
acetate is used. In view of the moldability and gas-barrier property, an 
ethylene/vinyl alcohol copolymer having an ethylene content of 15 to 50 
mole%, especially 25 to 45 mole%, and a saponification degree of at least 
96% is advantageously used. The molecular weight of the copolymer is not 
particularly critical, so far as the copolymer has a film-forming 
property. 
It is preferred that the thickness ratio of the polyester layer to the 
ethylene/vinyl alcohol copolymer layer be in the range of from 2/1 to 
30/1, especially from 4/1 to 15/1. Furthermore, it is preferred that the 
thickness ratio of the outer polyester layer to the inner polyester layer 
be in the range of from 1/1 to 5/1, especially from 2/1 to 3/1. It must be 
noted that the present invention includes an embodiment in which the 
thickness of the outer polyester layer is increased and the thickness of 
the inner polyester layer is decreased so that cooling of the inner layer 
is promoted and accelerated. Moreover, it is preferred that the thickness 
ratio of the polyester layer to the adhesive layer be in the range of from 
5/1 to 100/1, especially from 10/1 to 50/1. 
Forming Method 
In the present invention, there is advantageously adopted a method in which 
a pipe having the above-mentioned multi-layer structure is formed by 
co-extrusion, the pipe is formed into a bottomed preform and the bottomed 
preform is subjected to draw-blowing, or a method in which the 
above-mentioned resins are formed into a cylindrical or pot-shaped 
multi-layer preform by co-injection and the preform is subjected to 
draw-blowing. 
Moreover, there may be adopted a method in which a sheet having the 
above-mentioned multi-layer structure is formed by co-extrusion, the sheet 
is punched into a disc and the disc is formed into a drawn cup by plug 
assist forming, air-pressure forming, overhang forming or forging. 
In short, it is sufficient in the present invention if the inner and outer 
polyester layers 9 and 10 constituting the barrel portion 7 are 
molecularly oriented in at least one axial direction. According to the 
above-mentioned draw-blowing forming method, these layers are molecularly 
oriented biaxially in the axial direction and hoop direction, and 
according to the drawn cup-forming method, these layers are molecularly 
oriented in the radial direction or the direction of the axis of the 
vessel. 
The polyamide type adhesive used in the present invention is advantageous 
in that the polyamide type adhesive can be drawn or stretched at a 
polyester-drawing temperature and shows a strong interlaminar adhesion. 
The present invention will now be described in detail with reference to the 
following examples that by no means limit the scope of the invention. 
EXAMPLE 1 
A multi-layer pipe was formed by co-extrusion by using a homopolymer of 
ethylene terephthalate (PET), an ethylene/vinyl alcohol copolymer (EVOH) 
having an ethylene content of 30 mole% and a vinyl alcohol content of 70 
mole% and a copolymer of nylon 6 and nylon 6,6 (copolymer having a nylon 
6,6 content of 22 mole% and a nylon 6 content of 78 mole%) as an adhesive 
(AD), and after formation of a bottom neck, the pipe was preliminarily 
heated at 100.degree. C. and draw-blown to obtain a bottle having an inner 
volume of 1500 ml and a weight of 59 g. 
The PET (outer layer)/AD/EVOH/AD/PET (inner layer) thickness ratio in the 
formed pipe was 10/0.2/1/0.2/5 (AD indicates the adhesive layer). 
The properties of the so-obtained bottle were as follows. 
The transparency characteristics of the barrel portion of the bottle were 
as shown below. 
______________________________________ 
Present 
Comparison (single 
Invention 
layer of PET) 
______________________________________ 
Total ray 88.7 88.8 
transmission (%) 
Diffusion trans- 
1.2 0.9 
mission (%) 
Haze 1.4 1.1 
Sample thickness 
0.33 0.32 
(mm) 
______________________________________ 
The falling test was carried out in the following manner. 
Water was filled in the sample bottle so that the level of water was 
slightly lower than the eye level, and sodium bicarbonate and citric acid 
were added to water so that the gas volume was 4.0. The bottle was allowed 
to stand still at room temperature for 24 hours and was dropped on a 
concrete floor from a height of 2 m vertically or horizontally. Cracking 
and interlaminar peeling were checked. The obtained results are shown 
below. 
______________________________________ 
Present Comparison (single 
Invention 
PET layer) 
______________________________________ 
2 m Vertical Falling 
cracking not observed 
not observed 
delamination not observed 
-- 
2 m Horizontal Falling 
cracking not observed 
not observed 
delamination not observed 
-- 
______________________________________ 
The oxygen permeability QO.sub.2 of the bottle of the present invention was 
found to be 1.2 cc/m.sup.2.day.atm as measured at 37.degree. C., while the 
oxygen permeability QO.sub.2 of the comparative bottle (single PET layer) 
was found to be 5.9 cc/m.sup.2.day.atm as measured at 37.degree. C. 
COMATIVE EXAMPLE 1 
A bottle was prepared in the same manner as described in Example 1 except 
that the copolyamide adhesive was not used. Namely, the bottle had a 
PET/EVOH/PET layer structure in which the PET/EVOH/PET thickness ratio was 
10/1/5. The shape, inner volume and weight of the bottle were the same as 
those of the bottle prepared in Example 1. 
The falling test of this comparative bottle was carried out in the same 
manner as described in Example 1. It was found that in either vertical 
falling or horizontal falling, delamination was caused along the entire 
surface of the bottle. 
The oxygen permeability QO.sub.2 of this comparative bottle was found to be 
4.8 cc/m.sup.2.day.atm as measured at 37.degree. C.