CA1167215A - Multi-ply vessel and method for production thereof - Google Patents

Abstract

Abstract:
The invention relates to a multi-ply vessel which comprises an inner layer composed of a thermoplastic polyester resin, a middle layer composed of a metaxyly-lene group-containing polyamide resin and an outer layer composed of a moisture impermeable synthetic resin. The inner layer and middle layer are orientated in at least one direction at the thin parts of the vessel wall. This vessel can be produced by orientating a parison having the above-mentioned multi-ply structure at a draw ratio of 1 to 4 times in the longitudinal direction and of 2 to 7 times in the crosswise direction at a temperature of from Tg + 15°C to 2(Tg) + 15°C (wherein Tg is a glass transi-tion temperature of the thermoplastic polyester resin).
The resulting vessel has high transparency as well as good chemical resistance, impact resistance and the like because a thermoplastic polyester resin is used as the inner layer, and also has good gas barrier properties against oxygen because a metaxylylene group-containing polyamide resin is used as the middle layer.

Description

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Multi-ply vessel and method for production thereof The present invention relates to multi-ply vessels : having good gas barrier properties and high transparency, and a method for the production thereof.
Thermoplastic polyester resins, mainly polyethylene terephthalate, have widely been used for various vessels and packaging materials in the form of films and sheets ~ ; because of their excellent mechanical properties, gas :: ~ barrier properties, chemical resistance, scent mainten-ance and hygienic qualities. In particular, with the 10: progress made in blow-molding techniques, especially biaxial orientation blow-molding techniques, these resins are now frequently employed for the production of hollow vessels~, such as bottles and cans. For ex-ample~, thermoplastic polyester bottles produced by a ~;:: :: 15 biaxial orientation blow-molding technique are disclosed in United States Pa~tent No. 3,733,309.
However, the vessels produced from thermoplastic : polyester resins, mainly polyethylene terephthalate, by : : such biaxial orientation techniques are not satisfactory :

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~'t for all applications. For example, these vessels are not suitable for packaging food whlch require strict iso-lation from the atmosphere because they have poor gas barrier properties against oxygen.
Known thermoplastic resins having high gas barrier properties include saponified e~hylene-vinyl acetate copolymers r styrene-acrylonitrile copolymers and the like but the vessels made from these resins alone are in~erior in impact resistance or are not favorable from the hygienic viewpoint and, hence, can not be used in practice.
In Japanese Patent Laid Open Publication No.
108162/1978, it is disclosed that a vessel having gas barrier properties can be produced by orienta~ing and blow-molding a vessel preform (hereinafter referred to ;, ~ as a parison) having a two-layer structure composed of i a thermoplastic polyester resin and a saponified ethylene-vinyl acetate copolymer. However, when a saponified ethylene-vinyl acetate copolymer is used, the parison becomes opaque during formation thereof because the co-polymer itself lS a crystalline resin. Of course, if he parison is designed and oriented to produce thin walls, the transparency thereof is somewhat improved, but the non-orientated parts, such as the bottom part . ~ : :
25 of a~bottle, are still opaque, which results in an over-all poor appearance.

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When a ~ulti-ply vessel is produced by using a styrene-acrylonitrile copolymer, which is a resin known to have high gas barrier properties, together with a thermoplastic polyester resin, the parison does not lose ~ransparency during formation thereof because the copolymer itself is a non-crystalline resin. However, the copolymer has a high glass transition temperature and7 hencel the parison can not be sufficiently orientated at an orienting tem-perature suitable for the polyester resin. Moreover, because of the non-crystalliæability of the copolymer, no crystalli~ation of the copolymer is induced by orientation and, thereby, the vessel may be unfavorably deformed by ; orientation release stress.
An object of the pres~nt invention is to provide a vessel combining gas barrier properties against oxygen and the desirable properties of a thermoplastic polyester resin, e.g. good mechanical properties, transparency, chemical resistance, hygienic qualities and the like.
According to one aspect of the invention there is provided a multi-ply vessel having a multi-ply structure composed of at least two kinds of synthetic resins which comprises an inner layer composed of a thermoplastic polyester resin having an intrinsic viscosity of 0.55 or more, a middle layer composed of a metaxylylene group-containing polyamide resin and a moisture impermeable ~: , , ' ` ' i'7'~ -outer layer composed of a synthetic resin, said layers of the thermoplastic polyester resin and the metaxylylene group-containing polyamide resin being oriented in at least one direction at thin parts of ~he vessel wall.
According to another aspect of the invention there is provided a process for production of a multi-ply vessel which comprises forming a multi ply parison having a multi ply structure of an inner layer composed of a thermoplastic polyester resin having an intrinsic viscosity of 0.55 or more, a middle layer composed of a metaxylylene group-containing polyamide resin and a moisture impermeable outer layer composed of a thermo-plastic synthetic resin, and then orientating the multi-ply parison thus-formed in a draw ration of 1 to 4 times in the longitudinal direction and of 2 to 7 times in the crosswise direction at a temperature of from Tg + 15C to

2(Tg) ~ 15C, wherein Tg is a glass transition temperature of the thermoplastic polyester resin.
An advantage of the present invention, at least in the preferred forms, is that it can provide a vessel having good dimensional stability and form retention, and g~od adhesion between the layers of the multi-ply structure thereof.
A conventional fiber-forming polyester resin can be ; 25 used as the thermoplastic polyester resin which composes ; :~
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- 4a -the inner layer of the vessel of the present invention.
Polyesters having repeating units consisting predominantly of ethylene terephthalate are preferable. However, poly-esters such as polycyclohexane dimethylene terephthalate can also be used.

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Suitable thermoplastic polyester resins having repeating units consisting predominantly of ethylene terephthalate include polyesters consisting of acid components comprising 80 mol% or more, preferably 90 mol% or more, of terephthalic acid and glycol compon-ents comprising 80 mol% or more, preferably 90 mol% or more, of ethylene glycol. The acid components other than terephthalic acid may be selected Erom isophthalic acid, diphenyl ether-4,4'-dicarboxylic acid, naphthalene-1,4-or 2,6-dicarboxylic acid, adipic acid, sebacic acid~
decane~l,10-dicarboxylic acid, hexahydroterephthalic acid and the like; and the glycol components other than ethylene glycol may be selected from propylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, cyclohexane dimethanol, 2,2-bis(4-hydroxyphenyl)-propane, ; 2,2-bis(4-hydroxyethoxyphenyl)propane and the like. The ~ thermoplastic polyester resin may also contain an oxy-acid i ; component e.g. p-hydroxybenzoic acid, p-hydroxyethoxy-;~ ~ benzoic acid and the like. The thermoplastic polyester :
resin may be used as a blend of two or more polyester ~ ~ resins, provided the content of ethylene terephthalate ; ~ ~ is in the range mentioned above.
: The thermoplastic polyester resin used in the present invention may optionally contain an appropriate amount of an additive e.g. a colorant, ultraviolet absorber, antistatic agent, agent for pre~enting deterioration of ,~

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properties due to heat and oxidation, anti-microbial agent, lubricant and the like.
The intrinsic viscosity of the thermoplastic polyester resin should preferably be 0.55 or more, more preferably 0.65 to 1.4. When the polyester resin has an intrinsic viscosity of less than 0.55, the vessel preform, i.e.
the parison, is difficult to obtain in the transparent amorphous state and, further, the vessel obtained may have poor mechanical properties.
The metaxylylene group-containing polyamide resin (hereinafter referred to as an SM resin) which composes ; the middle layer of ~he vessel o ~he present invention is a polymer containing, in the molecular chain thereof, at least 70 mol% of a unit which consists of metaxylylene-diamine or a mixed xylylenediamine of metaxylylenediamine ~- and 80 % by wéight or less of paraxylylenediamine based on :
the mixture, and an ~,~-aliphatic dicarboxylic acid having 6 to 12 carbon atoms.
Examples of the metaxylylene group-containing poIyamide resin are a homopolymer e.g. polymetaxylylene-; ~ adipamide, polymetaxylylenesebacamide, polymetaxylylene-suberramide; a copolymer e.g. metaxylylene/paraxylylene-adipamide copolymer, metaxylylene/paraxylylene-impelamide copolymer, metaxylylene/paraxylylene-azeramide copolymer;
; 25 and a copolymer of the monomers composing the above homo-polymer or copolymer and other copolymerizable monomers e.g. aliphatic diamines (e.g. hexamethylenediamine), ~ ::

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alicyclic diamines (e.g~ piperazine), aromatic diamines (e.g. para-bis(2 aminoethyl)benzene), aromatic dicar-boxylic acids (e.g. terephthalic acid), lactams (e~g.
~-caprolactam), ~-aminocarboxylic acids (e.g. y-amino-heptanoic acid), aromatic aminocarboxylic acids (e.g.p-aminomethylbenzoic acid) and the like. To improve the impact resistance at low temperature and adhesion, it is preferable ~o copolymerize, during the polymer-ization of the polyamide resin, 0.2 to 10 % by weight based on the polyamide resin of a polyalkylene ether compound having at least one amino group or carboxyl group and having a molecular weight of 2,000 to 20,000, preferably 3,000 to 8,000, Eor example, bis(aminopropyl)~
poly(ethylene oxide), bis(aminopropyl)-poly(butylene oxide) or the like. In ~he above copolymer, the content of paraxylylenediamine in the total xylylenediamines is 80% by weight or less and the content of the unit consisting of the xylylenediamines and the aliphatic dicarboxylic acid in the molecular chain of the copolymer is at least 70 mol%. ~he polymers may optionally inlcude a small amount of other polymers e.g. nylon-6, nylon-6,6, nylon-6,10, nylon-ll, nylon-12 and the like and other additives e.g~ antistatic agents, lubricants, an~i-blocking agents, stabilizers, dyestuffs, pigments and the like.
SM resin is intrinsically brittle in the amorphous , ;7 state, and, hence, it should have preferably a relative viscosity of 1.5 or more, more preferably 2.0 or more.
Generally, a vessel is produced by forming a vessel preform, i.e. a mul~i-ply parisonl and then orientating and blow-molding the parison. In order to obtain a vessel having good gas barrier properties and high transparency, the multi ply parison should also have good transparency and further the resin components at the thin parts of the vessel wall (mainly the body thereof) should be at least uniaxially orientated. Hence, the parison should be also at least uniaxially orientated to produce such a vessel.
The outer layer of moisture-impermeable synthetic resin can be formed as an outer layer of a multi-ply parison or can be formed on the S~ resin layer after orientation and blow-molding of the parison, e.g., as -- a surface finishing of the SM resin layer, by coating the SM resin layer with a film, by topcoating which is employed in certain kinds of glass and bottles, by spray coating and the like. Preferably, the outer layer is formed as that of a multi-ply parison and then the parison orientated and blow-molded to produce the vessel.
~ xamples of the compounds or the synthetic resins used for the above finishing, topcoating or spray coating methods are an unsaturated monomer consisting predominant-,:
; 25 ly of an unsaturated silane, a polymer of an unsaturated monomer consisting predominantly of an unsaturated silane, . .

' ' _ 9 _ an epoxy silane compound, an alkoxy silane compound, anorganic titanium compound, a silicone resin, a fluoro-plastic, polyvinyl chloride, polyvinylidene chloride and the like. The formation of the outer layer employing these resins improves impermeability to moisture and prevents changes of the gas barrier properties with time.
Of course, when the orientation and blow-molding are dif-ficult to carry out because of the formation of the outer layer, the layer should be formed after the orientation and the blow-molding.
The synthetic resin used for the outer layer formed on the multi-ply parison is a thermoplastic resin which does not prevent the orientation and blow-molding of the thermo-plastic polyester resin of the inner layer. Examples of the resin are the same kind of the thermoplastic polyester resin used for the inner layer9 polyvinyl chloride, poly-propylene, and a copolymer consisting predominantly of an acrylonitrile component containing 80 mol% or less of acrylonitrile and an unsaturated monomer e.g. styrene, ethyl acrylate and methyl acrylate.
Thermoplastic polyester resins, particularly those having repeating units consisting predominantly of ethylene terephthalate and having an intrinsic viscosity of 0.55 or more, are preferred in view o the transparency and other desirable properties of the resulting vessel as well as possible recovery and reuse of the ve~sel. The .

'5 ~e~in may optionally contain additivest e.g. lubricants, anti-blocking agents, stabilizers, colorants, agents Eor providing metallic sheen and the like.
A typical method for the production of the multi-ply vessel of the present invention is given below.
The vessel can be produced by forming a multi-ply parison and orientating and blow-molding the parison according to a conventional method. Particularly, the vessel can be conveniently produced by a biaxial orien-10 tation blow-molding technique at a specific temperature.
When the vessel is produced by a biaxial orientation blow-molding technique, a multi ply parison is heated to an orientation temperature and then expanded and orien-tated by a rod which moves axially in a metal mold and lS compressed air is blown into the mold to form the vessel.
The multi-ply parison can be produced by successively forming the multi-ply structure from the inner layer with a conventional injection molding machine or a molding machine having equipment for melting and injecting several 20 materials, or by providing a bottom in a pipe having a multi~ply structure formed by a multi-ply extrusion molding machine.
The shape of the multi-ply parison is not critical 25 provided it is in a geometric form which can be expanded.
When the~multi-ply parison is injection molded, the mold t~mperature should be kept low. In particulrr, when the , ~`7'~

middle and outer layers are formed, it is preferable to keep the temperature lower than that employed in the formation of the inner layer. When the middle and outer layers are formed, the mold temperature is usually below 30C, preferably 5 to 20C.
In order to maintain the mold temperature in the above range, it is preferable to pass a fluid, e.g. tap water or chilled water, through the inside of the mold.
When the a~ove molding technique i5 carried out, a multi~ply parison having good transparency can be obtained.
Moreover, one of the characteristics of the present inven-tion is that the adhesion between the layers of the vessel produced by expanding and orientating the multi-ply parison is superior to that of a vessel produced by orientating a partially opaque multi-ply parison.
Each resin layer of the parison is generally 0.1 to 5 mm, preferably 1 to 3 mm, in thickness and the total thickness of the inner, middle and outer layers is generally 1 to 8 mmr preferably 2 to 6 mm. If each layer of the parison is less than 0.1 mm in thickness, the resin to be used for the layer hardly flows in the mold. If the total thickness of the layers is more than 8 mm, the multi-ply parison becomes opaque during the formation of ; the middle and outer layers thereof, or an extremely high blowing pressure is necessitated. In comparison with injection molding, when the multi-ply parison is produced ' ;:

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7~5 by multi-ply extruslon molding, each resin layer can be formed as thin as several tens of microns, if desired.
However, in order to retain the shape of the vessel after biaxial orientation blow-molding, each resin layer should generally be about 0.1 to 4 mm in thickness. Of course, when a parison consisting only of the inner and middle layer is prepared by extrusion molding and then the outer layer is formed on the parison by surface treatment or surface coating, the thickness of the outer layer may be 10 much thinner.
The multi-ply parison thus obtained is heated to a orientating temperature and then expanded and orientated -~ in a blow-mold to produce a hiaxially orientated vessel.
The orientation temperature is from (Tg ~ 15)C to 15 ~2Tg + 15~C, preferably 90 to 150C, wherein Tg means the glass transition temperature of the polyester resin.
This is based on the fact that the glass transition temperatures of the metaxylylene group-containing poly-~;~ amide resin are close to those of the polyester resins.
20 When the parison is heated to the above temperature range,expansion and orientation can be carried out without any problem.
It is not desirable that the preheating temperature be lower than (Tg ~ 15)C since microvoids are formed in the 25 vessel due to cold orien~a~ion and the resulting vessel has a pearly appearance which makes it opaque. Likewise, ~' ' ~ ' , `
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it is not desirable that the preheating temperature be higher than (2Tg + 15)C, since the polyester resin of the outer layer then becomes opaque due to crystallization thereof and adhesion between the resin layers is Leduced.
A draw ratio of 1 to 4 times in the longitudinal direction and of 2 to 7 times in the crosswise direction is neces-sary for expanding and orientating the multi-ply parison.
In view of the adhesion between the layers, e.g. between the outer layer and the middle layer or between the middle 1~ layer and the inner layer, as well as the transparency of the vessel, an area draw ratio (draw ratio in longitudinal - direction x draw ratio in crosswise direction) of 5 to 18 times is preferable.
Although SM resin itself is intrinsically a crystal-15 line resin, the glass transition temperature thereo is relatively high and it readily takes on an amorphous form when the molten resin is quenched, to give a parison having good transparency. Additionally, since the glass transision temperature of the SM resin is almost equal to 20 that of the polyester resin, it is sufficiently orientated :
and crystallized under orientation conditions for the polyester resin. Thus, in contrast to other known resins ;~ having high gas barrier properties, a vessel having high transparency as well as good gas barrier properties and 25 heat stability and, therefore, having high commercial value, can be obtained.

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s The degree of orientation can be determined by meas-uring the difference between the refractive index in the cross sectional direction and that in the plan direction of a thin part of the vessel wall. In order to obtain good gas barrier properties and high transparency, the difference between the refractive i~dexes is desirably 0.02 or more, preferably, 0.03 or more, more preferably~
0.05 or more. When the difference between the refractive indexes is less than 0.02, the mechanical properties and lO gas barrier properties may be insufficiently improved and, further, the adhesion between the layers is reduced.
When the measure~.ent of a refractive index is diffi-cult, the degree of orientation can also be determined based on anisotropy of mechanical properties and the like.
In the multi-ply vessel of the present invention, the ;~ middle layer of SM resin is generally 5~ to l mm, prefer-ably, lO~ to 500~ in thickness. The inner resin layer and the outer resin layer are generally 50~ to 1 mm, preferably 100~ to 500~ in thickness, respectively. In practice, the 20 total thickness of the inner, middle and outer layers is 100~ to 2 mm, preferably, 200~ to l mm. Further, the ratio of the thickness of the polyester resin inner layer to that of SM resin middle layer is l or less. Even i~ this ratio becomes more than l, no Eurther improvement in the gas 25 barrier properties can be expected, but rather, defects are produced such as an increase in the orientating stress ~'~

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2~5 during blow-molding and the like.
The description hereinbefore refers to a process for the production of a multi-ply vessel having inner and outer layers both made of polyester resin and having a middle layer of SM resinO Optionally, the vessel of the present invention can also be produced by forming adhe-sive layers between the middle and the outer layers and/or between the middle and the inner layers. When the area draw ratio is 5 times or less, the adhesion between the 10 polyes~er resin and SM resin is insufficient and hence, it is preferable to provide an adhesive layer. Further, when polyvinyl chloride or the like is substituted for the polyester resin of the outer layer, a vessel of the present invention can be produced under the above con-15 ditions. However~ when the outer layer is formed by ~- finishing of the surface oE SM resin layer or topcoating, the thickness of the outer layer may be much thinner.

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~; ExampIes o~ an adhesive for improving the ply separa-tion resistance are a copolyester resin, a copolyamide 20 resin, an ~-olefin vinyl ester copolymer, a modified olefin resin containing carbonyl groupr a urethane modified copolyester resin or the like, the melting or softening temperature of which is about 200C or less, ; preferably, 70 to 200C. Optionally, these resins may 25 be further copolymerized with an ingredient containing a small amount of an acid metallic salt group.

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If the moisture permeation resistance of the synthetic resin outer layer is insufficient, a treatment for improv-ing the moisture permeation resistance can be effected on the surface of the outer layer or an additional layer can be provided on the outer layer.
Although the description so far has referred to a multi-ply vessel (bottle) produced by orientating and blow-molding a multi-ply parison and the method there-for, the present invention is not limited thereto. For 10 examplef the multi-ply vessel of the present invention includes a can produced by orientating and blow-molding a multi-ply cylinder to expand the cylinder, optionally thermosetting the cylinder, cutting the cylinder in an appropriate length and then sealing at least one end 15 thereof with a sealing plate of a metal or a plastic, ,~ or a vessel produced by deep-drawing a laminate sheet.
The following examples further illustrate the present invention.
The methods of measurement of main characteristics 20 determined in the present invention are as follows:
(1) Intrinsic viscosity [~] of the polyester resin: It was measured at 30C by using the mixed solvent of phenol-tetrachloroethane (6 : 4, w/w).
(2) Relative viscosity [nrel] of the polyamide resin: It 25 was measured at 25C by dissolving the resin (1 g) in 96 ~sulfuric acid l100 ml).

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(3) Glass transition temperature (Tg): It was measured at a heat-up rate of ~0C/min by using Differential Scanning Colorimeter manufactured by Perkin Elmer (DSC - lB~.

(4) Melting point (Tm): It was measured by the same manner as in Tg.

(5) Refractive index: It was measured at 25C by using Abbe refractometer equipped with a polarising plate and using ~he D-line of a sodium lamp. A specimen (1.5 cm square) was cut off from a thin part of the body of the 10 multi-ply vessel obtained and the refractive indexes thereof in ax;al and peripheral directions were measured.
The degree of orientation was determined by calculating the birefringence of the specimen as follows:

Birefringence ~n) = -~ 2 ny -nz 15 in which nx and ny are refractive indexes in the axial 'L,. and peripheral directions (plane direction), respectively, and nz i5 refractive index of the specimen in the cross-sectional direction.
(6~ Transparency and haze: I~aze meter-S manufactured by 20 Toyo Seiki was used and according to JIS - K6714, these were calculated as follows:
Transparency = (T2/Tl) x 100 (%~

T4 - T3-(T2/Tl) Haze = - - x 100 (%) ~: in which Tl is an amount of incident light, T2 is a 25 total amount of transmitted light, T3 is an amount of .

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light scattered by the device and T4 is an arnount oflight scattered by the device and the specimen.
(7) Amount of oxygen permeation: It was determined according to ASTM-D-1434-58 by measuring pressure the change at 30C with a twin gas transmission measuring instrumen~ manufactured by Rika Seiki Kogyo (cc/m2.24 hr. atm).
(8) ~mount of moisture permeation: It was determined according to JIS-Z~0208 by measuring the weight gain at 10 40C under 90 % RH by cup method ~g/m2.24 hr).
(9) Tensile characteristics: Yield strength, tensile elongation at break and tensile ~trength at break oE a specimen strip of 10 mm in width were measured at 23C, 50 mm/min of strain rate by using a Tensilon (Trade Mark) 15 manufactured by Toyo Bowldwin having 50 mm of distance - between the chucks.
Examples 1 and 2 and Reference Example 1 A multi-ply parison having an outer diameter of 35 mm, a length of 140 mm and a thickness of 5 mm was formed by 20 using a polyethylene terephthalate (hereinafter referred to as PET) of [n] = 0.72, Tm = 257C and Tg = 70C as the polyester resin of the inner and outer layers thereof and a polymetaxylylene-adipamide (metaxylylenediamine : para-xylylerlediamlne = 99 : 1, w/w) of nrel = 2.2, Tm = 37C
25 and Tg = 75C (hereinaEter referred to as S~-l) in Example 1 or SM-l compolymerized with 2.5 % by weight of : ~, ~7~ ~
,9 polyethylene glycol diamine having a molecular weight of 4000 of nrel = 2.35, Tm = 235C and Tg = 73C (hereinafter referred to as SM-2) in Example 2 as the metaxylylene group-containing polyamide resin of the middle layer S thereof. In Reference Example 1, a parison of the same shape as in Examples 1 and 2 was formed by using a poly-ethylene terephthalate of [~] = 0~72.
The formation of the multi-ply parison was carried out by forming the inner parison of the polyester resin of 2 mm 10 in thickness and laminating the SM resin middle layer, and then the polyester resin outer layer on the inner parison while successively changing the metal molds ~o obtain the ` multi-ply parison. Thickness of each layer of the parison was inner layer : middle layer : outer layer = 2 mm : 1.5 15 mm : 1~5 mm.
~The molding was carried out by using an N-95 (Trade ; ~Mark) injection machine manufactured by Nippon Seikosho under the conditions shown in Table 1.

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Table 1 Inner Middle ¦ Outer layer layer I l~yer (PET) (SM) , (~ET) Cylinder temperature (C, from hopper270x290x290260x280x280 i 270x290x290 side) g . . ..
Inject~on pressure i 40 .
10 (kg/cm gauge) ~ 50 60 i Mold temperature (C)~, 20 ¦ 15 1 12 In ection pressure ! 15 15 ¦ 15 ! i : Cooling tlme (sec) ¦ 25 25 ¦ 25 ~::
The open end of the parison thus obtained was fitted into a parison fitting part having a rotary drive and ~he parison was heated and rotated in an oven having a far infrared heater until the surface temperature of the parison rose to 110C. After heating, the parison was transferred into a blow~mold and blow-molded at a travel ~:~ : rate of an orientating rod of 22 cm/sec under a compressed gas pressure of 20 kg/cm2 to obtain a hollow vessel in :
a beer bottle shape of 265 mm in length, 80 mm in outer : diameter of the body and 1000 ml in internal space. The : 25 properties of the vessel thus ob~ained are shown in Table 2.

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,1 ~ 21 -Table 2 jExample 1 ~Example 2 iReference~
¦ j IExample 1 Transparency (%) I 87 ¦ 86 ~ 89 IHaze (%) '2.0 ; 6.5 j 1.3 ' ¦Amoun~ of oxygen permeation ~ '. .
. ~ (cc/m .24 hr~atm) !1.5 1.7 14 Amou~t of moisture permeation . i ~(g/m .24 hr) 0.6 . 0.6 , 0.5 !Birefringence (~) O.058 'O.053 ,O.068 _ _ ~
Yield strength (kg/cm2) , 972 ~ 824 1 1068 i ¦Tensil~ strength at break ' .
''(kg/cm ) 1417 `, 1212 1 1542 :, '. . i I
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'Tensil elongation at break i(%) 180 86 76 I Note: Ail the specimens used were cut off from the main body portions.
As is clear from the results of Table 2, the vessels , of Examples 1 and 2 have remarkably improved oxygen barrier properties without any deterioration of transparency and mechanical properties in comparison with the vessel of the polyethylene terephthalate alone.

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~ 22 -Examples 3 to 6 and Reference Examples 2 to 4 Various parisons were formed by using the PET in Example l as the polyester resin oE the inner and outer layers thereof and the SM-l as the metaxylylene group-containing polyamide resin of the middle layer thereof.In each case, the thickness of each layer of the parison was inner layer : middle layer : outer layer = 2 mm :
1.5 mm : 1.5 mm. The molding of the parison was carried out by using an N-95 (Trade Mark) injection machine manu-10 factured by Nippon Seikosho and biaxial orientation blowmolding was effected by using a molding machine in Katata Laboratories of Toyo Boseki manufactured by way of experi-ment~ Each hollow vessel thus obtained had a beer bottle shape of 265 mm in length, 80 mm in outer diameter of the 15 body and 1000 ml in internal space (Examples 3 to 6 and Reference ~xamples 2 and 3) or of 200 mm in leng-th, 80 mm in outer diameter of the body and 700 ml in internal space (Reference Example 4). The molding conditions in each Example are shown in Table 3 and properties of the vessel ~ 20 thus obtained are shown in Table 4.

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~ 7 As is clear from the results of Tables 3 and 4, all the vessels of the present invention obtained in Examples 3 to 6 have high transparency as well as excellent gas barrier properties and mechanical properties.
In contrast, in ~eference Example 2, the orientation temperature is too low and hence, an extremely high-stress is needed in orientation. As a result, the parison may be broken in the orientating and blowing step or can not be shaped to the desired form, or, even if the parison can 10 be shaped, the bottle is unsuitable in practice since the appearance thereof becomes extremely pearly. In Reference Example 3, the orientation temperature is too high and the parison becomes opaque due to crystalli2ation of the sur-face layer thereof in the heating step. Moreover, there ;~ 15 are some defects, Eor example, insufficient mechanical properties such as drop impact strength and the llke due to an insufficient orientation e~fect.
Further, in Reference Example 4, the area draw ratio is 5 times or less and hence, adhesion between the resin 20 layers is insufficient which resulks in ply separation by drop impact. If the area draw ratio is small, the problem of ply separation can be solved by providing an adhesive layer between the polyester layer and SM resin layer. An improvement of the mechanical properties due to improved ~5 adhcsion is also expected by providing the adhesive layer.

.,~ . ' Examples 7 to 10 and Reference Examples 5 to 7 -Hollow vessels were obtained by the same procedure as in Examples 3 to 6 and Reference Examples 2 to 4 except that SM-2 was used as the metaxylylene group-containing 5 polyamide resin of the middle layer. Further, the molding conditions employed in Examples 7 to 10 and Reference Examples S to 7 corresponded to those in Examples 3 to

6 and reference Examples 2 to 4 as shown in Table 3.
The properties of the vessels thus obtained are shown lOin Table 5.

.

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As is clear from the results of Table 5, Examples 7 to 10 and Reference Examples 5 to 7 showed the same results as those in Examples 3 to 6 and Reference Examples 2 to 4, respectively. That is, vessels having high transparency 5 as well as excellent gas barrier properties and mechanical properties were obtained in Examples 7 to 10. However, in Reference Examples 5 to 7, a vessel having sufficient commercial value as in the present invention could not be obtained. Further, the vessel obtained according to the 10 present invention had excellent dimensional stability and form retention.
Example 11 By using PET and SM-1 as in Example 1, a two-layer parison without an outer layer (PET layer = 3.5 mm in ; ~ 15 thickness, SM-1 layer - 1.5 mm in thickness) was formed under the same conditions as in Example 3. After applying a coat of a polyvinyl chloride resin on the outer surface of the parison, a vessel was produced by orientating and ; blow-molding the parison under the same conditions as in Example 3. As a result, a vessel having 85 % of trans-parency, 2.2 % of haze, 1.3 cc/m~.24 hr atm of oxygen :::
~; permeation and 0.6 g/m2.24 hr of moisture permeation, ;;~ that isr having excellent transparency and gas barrier properties was obtained, The vessel had a yield strength of 1195 kg/cm2 and a tensile strength of 1820 kg/cm2.

~ ~ .

Claims (10)

Claims:

1. A multi-ply vessel having a multi-ply structure composed of at least two kinds of synthetic resins which comprises an inner layer composed of a thermoplastic polyester resin having an intrinsic viscosity of 0.55 or more, a middle layer composed of a metaxylylene group-containing polyamide resin and a moisture impermeable outer layer composed of a synthetic resin, said layers of the thermoplastic polyester resin and the metaxylylene group-containing polyamide resin being oriented in at least one direction at thin parts of the vessel wall.

2. A multi-ply vessel according to claim 1 wherein the thermoplastic polyester resin is that having repeating units consisting predominantly of ethylene terephthalate.

3. A multi-ply vessel according to claim 1 wherein the synthetic resin having impermeability to moisture is a thermoplastic polyester resin having an intrinsic vis-cosity of 0.55 or more.

4. A multi-ply vessel according to claim 3 wherein the thermoplastic polyester resin is that having repeating units consisting predominantly of ethylene terephthlate.

5. A process for production of a multi-ply vessel which comprises forming a multi-ply parison having a multi-ply structure of an inner layer composed of a thermoplastic polyester resin having an intrinsic viscosity of 0.55 or more, a middle layer composed of a metaxylylene group-containing polyamide resin and a moisture impermeable outer layer composed of a thermoplastic synthetic resin, and then orientating the multi-ply parison thus-formed in a draw ration of 1 to 4 times in the longitudinal direc-tion and of 2 to 7 times in the crosswise direction at a temperature of from Tg + 15°C to 2(Tg) + 15°C, wherein Tg is a glass transition temperature of the thermoplastic polyester resin.

6. A process according to claim 5 wherein the thermo-plastic polyester resin is that having repeating units consisting predominantly of ethylene terephthalate.

7. A process according to claim 5 wherein the thermo-plastic synthetic resin having impermeability to moisture is a thermoplastic polyester resin having an intrinsic viscosity of 0.55 or more.

8. A process according to claim 7 wherein the thermo-plastic polyester resin is that having repeating units consisting predominantly of ethylene terephthalate.

9. A process according to claim 5 wherein orientation is carried out by biaxial orientation blow-molding.

10. A process according to claim 5 wherein the parison is orientated at an area draw ratio (draw ratio in longitudinal direction x draw ratio in crosswise direction) of 5 times or more.