JPS61203332A - Shock-resistant plastic vessel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to impact-resistant plastic containers.
More specifically, the present invention relates to a biaxially stretched plastic container having a laminated structure that has extremely high resistance to drop impacts and the like and also has excellent blister resistance.

PRIOR ART AND TECHNICAL PROBLEMS OF THE INVENTION Polyester containers made using the stretch blow molding method have excellent transparency and appropriate rigidity, and can be used not only for liquid detergents, shampoos, cosmetics, soy sauce, sauces, etc., but also for beer, cola, and cider. It has come to be widely used in containers for soft drinks such as carbonated drinks, fruit juices, and mineral water.

This stretched polyester container is made of polyethylene or IJ
Compared to general-purpose resin containers such as propylene, the gas barrier
However, while metal cans and glass bottles have almost zero gas permeability, they have a non-negligible permeability to oxygen and carbon dioxide, making it difficult to preserve their contents. The period is limited to a relatively short period.

In order to improve this drawback, various proposals have been made to improve the spalling properties of containers by combining polyester with a gas sparing resin such as an ethylene-vinyl alcohol copolymer to form a multilayer structure.

To manufacture a stretched multilayer plastic container, it is first necessary to manufacture a multilayer preform, and various methods such as coextrusion, multistage injection molding, and coinjection molding are used to manufacture this multilayer preform. However, when using any of these methods, ethylene-
Since there is almost no thermal adhesion between a gas barrier resin such as a vinyl alcohol copolymer and an oriented and creep-resistant resin such as polyester, a special adhesive resin is used between the two resin layers. Since it is believed that intervening layers are necessary, much effort has been put into searching for adhesive resins.

One of the important problems in such multilayer plastic containers is the tendency for delamination between the gas barrier resin intermediate layer and the oriented, creep-resistant resin, especially in filled containers. When subjected to drop impact,
Gas barrier that easily peeled off between the eyebrows at the bottom.
The problem is that the resin layer is likely to break or form holes. Another important problem is that when filled with a content that has an autogenous pressure, such as a content containing carbon dioxide gas, the carbon dioxide gas that has permeated through the inner surface layer forms blisters (blisters) at the boundary with the gas barrier resin layer. ) in the form of tamashi, car? This results in a loss of nation, a decrease in gas barrier properties, and a significant loss of appearance characteristics as a container. This blistering tends to occur more significantly in the shoulder area of the container.

SUMMARY OF THE INVENTION The present inventors developed a container by stretch blow molding a multilayer preform consisting of inner and outer surface layers made of oriented resin such as polyester and an intermediate layer made of gas barrier resin such as ethylene-vinyl alcohol copolymer. When manufacturing the intermediate layer, the intermediate layer is completely enclosed between the inner and outer surface layers, and the intermediate layer is biased toward the innermost surface at the center of the bottom, and then toward the center between the inner and outer surfaces as it moves toward the upper part of the body. By providing a biased distribution structure, the molecular orientation of both resins is effectively carried out, and the adhesion between both resin layers is always maintained, and more importantly, the bottom part is prevented from peeling off or being damaged due to drop impact, etc. It has also been found that the occurrence of blisters in the shoulders can be very effectively eliminated.

An object of the present invention is to provide a biaxially oriented multilayer container comprising an inner and outer layer of an oriented and creep-resistant resin and an intermediate layer of a gas barrier resin, in which the above-mentioned drawbacks are effectively eliminated.

Another object of the present invention is to provide a biaxially oriented multilayer plastic container that has an excellent combination of drop impact resistance at the bottom, especially resistance to glabella peeling, and blister resistance at the shoulder.

Still another object of the present invention is to provide a resin film composed of inner and outer surface layers of polyester and an intermediate layer of ethylene-vinyl alcohol copolymer, in which both of these resin layers are imparted with biaxial molecular orientation; To provide a stretched multilayer plastic container in which the adhesive state of a resin layer is maintained in the shape of the container, and which has excellent appearance characteristics, impact resistance, and internal pressure resistance.

Still another object of the present invention is to achieve extremely low loss of carbon dioxide gas (cardenesi, loss) and excellent blister resistance even when filled with contents having autogenous pressure, especially contents containing carbon dioxide gas. To provide pressure resistant plastic containers.

Structure of the Invention According to the present invention, the laminate is composed of an inner and outer surface layer of an oriented, creep-resistant resin and an intermediate layer of a gas barrier resin, and has a thick mouth part, a shoulder part, and a thin body part. In a plastic container having a bottom part and a bottom part, the inner and outer surface layers of the oriented, creep-resistant resin are continuous in the surface direction over the entire area of the container, and the gas barrier resin intermediate layer covers at least the bottom part, the body part and the shoulder part. The resin layers are continuous in the plane direction throughout the container and are completely enclosed between the inner and outer surface layers. Each resin layer has molecular orientation in biaxial directions at least in the container body, and the intermediate layer is the innermost layer in the center of the bottom. An impact-resistant plastic container is provided, characterized in that it has a distribution structure in which K is biased toward the surface side, and K is biased toward the center between the inner surface and the outer surface as K moves toward the upper part of the body.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on specific examples shown in the accompanying drawings.

In the following description, polyester will be used as a typical example of the creep-resistant resin, and ethylene-vinyl alcohol copolymer will be used as a typical example of the svalier resin, but the invention is not limited to these examples.

Structure and Effects of Container FIG. 1 shows the overall arrangement of the stretched multilayered ZOLASTI container of the present invention, and FIGS. 2-2 to 2-D show its partial cross-sectional structure.
In the figure, this container 1 has a thick mouth part (nozzle part) 2,
It has a thin body 3 and a closed bottom 4, and a frustum-shaped shoulder 5 exists between the body 3 and the mouth 2 to connect them.

This container has an inner surface layer 6 and an outer surface layer 7 made of an oriented, creep-resistant resin such as polyester, and an ethylene-vinyl alcohol copolymer completely encapsulated between them. It consists of an intermediate layer 8 of resin. That is, this intermediate layer 8 is shown in a cross-sectional view (second
-A), a sectional view showing the torso (Fig. 2-B), a sectional view showing the shoulder (Fig. 2-0), and a sectional view showing the base of the mouth (Fig. 2-B).
It is clear from Fig. 2-D that no part of the vessel wall is exposed to the surface, and moreover, the bottom part.

It exists as an intermediate layer throughout the torso and shoulders. As shown in FIG. 2-D, the intermediate layer 8 does not exist at the tip of the mouth portion 2, but the intermediate layer 8 may be present up to the vicinity of the tip of the mouth portion (nozzle portion) 2. 2 has a middle layer 8
may not be involved. Such changes can be easily made by changing the injection amount and melt viscosity of the ethylene-vinyl alcohol copolymer, as described below.

The multilayer stretched plastic container according to the invention has significant features not found in conventional containers of this type. That is, the thickness of the stretched plastic container wall varies depending on the position of the container and the degree of stretching, but
The intermediate layer 8 has a distribution structure that is biased toward the innermost surface at the center of the bottom portion 4 and toward the center between the inner surface and the outer surface as it moves toward the upper part of the torso. To explain further, the sparring intermediate layer 8 extends over the entire cross section of the container wall, from the center plane of the cross section of the container wall (indicated by the dashed line 9 in FIGS. 2-A to 2-D) and to the inner surface. The cross-sectional distribution structure is biased to the side, but the degree of this bias is
It is largest at the bottom t shown in Figure 2-A, and
In the body part 3 shown in the figure, the degree of unevenness is smaller, and the degree of unevenness is smaller in the shoulder part 5 shown in Fig. 2-0 and the mouth part 2 shown in Fig. 2-D. The degree of force is the smallest.

The degree of this deviation is determined by the following formula, where tA represents the thickness of the outer layer of the resin with orientation and creep resistance, tA represents the thickness of the inner layer of the resin with orientation and creep resistance, and to represents the thickness of the inner layer of the resin with gas barrier properties. The smaller the value of the intermediate layer distribution ratio (R), the more the intermediate layer is biased toward the inner surface.

As an example, the specific values of the intermediate layer distribution ratio (R) in each part of the container are as follows. Furthermore, R,,Rc,
RIl indicates the intermediate layer distribution ratio at the center of the bottom, torso, and shoulder, respectively.

R,=0.01 to 0.20°, especially 0.02 to 0.15, Rc=0.07 to 0.35, especially 0.10 to 0.30°R,=0.15 to 0.40, In particular, 0.20 to 0.35, Rc-R, ≧0.05, R, -R, ≧0.01°, and the intermediate layer distribution ratio (Rn) directly below the neck is 0.2.
Toshi in the range of 5 to 0.45, Rn-R, ≧0.03
It is desirable that

According to the invention, with such a distribution structure of the intermediate layer,
The effect is achieved that the impact resistance and blister resistance of the stretched multilayer plastic container are significantly improved. In a multilayer plastic container, the most vulnerable part to impact is the bottom part, which is subjected to drop impact as mentioned above, and apart from this bottom part, peeling occurs between the creep resistant resin layer and the gas barrier resin layer. This also causes breakage, pinholes, cracks, cracks, etc. in the gas barrier resin layer. Furthermore, when filling a container with carbon dioxide gas, blisters (7 creases) often occur on the shoulders. This blistering occurs because gas that has permeated through the creep-resistant resin inner layer causes blisters at the boundary between the inner layer and the gas barrier intermediate layer, at areas where the wall thickness is relatively small and the curvature is large, that is, at the shoulders. Due to the fact that it comes off and accumulates.

According to the present invention, by biasing the intermediate layer 8 toward the inner surface side in the bottom portion 4 and making the thickness of the creep-resistant resin outer layer 7 sufficiently large, the impact on the intermediate layer 8 is alleviated.
Gas barrier intermediate layer 8 and creep-resistant resin layers 6 and 7
Peeling between the eyebrows due to impact with the container is prevented, and damage to the intermediate layer 8 itself is also prevented.
By biasing the intermediate layer 8 toward the center between the inner surface and the outer surface, the creep-resistant resin inner surface layer 6 is also given sufficient thickness and rigidity. This prevents the occurrence of blisters due to

Moreover, in the container of the present invention, the outer surface layer 7 of the two creep-resistant resin layers is thick and the inner surface layer 6 is thin as a whole. For this reason, the outer surface layer 7 that receives external force does not act as a stress carrier, and in conjunction with the fact that the molecular orientation is given by the stretching pressure, stable shape retention as a container can be obtained, and furthermore, it can withstand pressure. , the effect that deformation resistance is also improved can be obtained.

In addition, since the inner surface layer 6 has a thin structure, the amount of carbon dioxide dissolved and adsorbed on the creep-resistant resin such as polyester is reduced, resulting in less carkenation loss when filling the container with carbon dioxide gas. This has the advantage that it is less.

Furthermore, in the container of the present invention, in connection with the fact that the intermediate layer 8 is completely enclosed between the inner and outer surface layers 6 and 7, the intermediate layer 8 is made of ethylene-vinyl alcohol copolymer or the like, and the intermediate layer 8 is made of polyester or the like. There is a completely unexpected and novel fact that the state of close contact with the inner and outer surface layers 6, 7 is completely maintained even though there is no adhesion between them. The fact that these resin layers have no or almost no adhesive strength means that when the body of this container is cut in the thickness direction, there is no immediate or slight peeling force ( 200g/l,
This is confirmed by the occurrence of delamination at a width of 51 mm or less.

However, when the container is not cut as described above and is kept in an integrated state, both resin layers appear and behave in complete contact, and if the container is subjected to a drop impact or is slightly deformed, It was also found that no peeling phenomenon was observed, and a state of complete adhesion was maintained. The reason for this has not yet been elucidated, but an intermediate layer such as an ethylene-vinyl alcohol copolymer is completely encapsulated between the inner and outer surface layers of creep-resistant resin such as polyester, resulting in an airtight seal between the two phase resin layers. In relation to the distribution structure of the resin layer mentioned above, the hoop tightening force of the inner and outer layers of preester acts on the intermediate layer such as ethylene-vinyl alcohol copolymer, and This is thought to be caused by the adhesion effect caused by the molecular orientation of both resin layers.

Furthermore, the gas barrier resin layer of ethylene-vinyl alcohol copolymer or the like in the container of the present invention is effectively stretched together with the inner and outer layers of the 4-reproduced ester, so that the molecules are oriented in the plane direction. Due to this molecular orientation, the gas barrier of the ethylene-vinyl alcohol copolymer is significantly improved; for example, the gas permeability coefficient (Po2) for oxygen is 2
It is a small value of 1/5 to 1/5. Ethylene-
Vinyl alcohol copolymer is one of the resins that is difficult to stretch, and it is known that if it is stretched in the form of a single layer, it will break if stretched under normal molding conditions (Japanese Patent Publication No. 5
7-42493). It is also known that molecular orientation can be imparted to the ethylene-vinyl alcohol copolymer layer by forming an ethylene-vinyl alcohol copolymer into a laminate with a stretchable resin layer and stretching the laminate. However, in this case, it is essential to firmly bond the ethylene-vinyl alcohol copolymer and the stretchable resin layer, otherwise the ethylene-vinyl alcohol copolymer layer It is said that rupture occurs (
JP-A No. 52-103481). In contrast, in the present invention, no adhesive layer is interposed between the ethylene-vinyl alcohol copolymer layer and the polyester layer, and there is virtually no adhesion between these two phase resin layers. Despite this, molecular orientation was effectively imparted to the ethylene-vinyl alcohol copolymer layer, which was a surprising effect of the present invention.

In general, the ethylene-vinyl alcohol copolymer constituting the middle layer of the body is determined by the in-plane orientation coefficient (t
+m ) is 0.4 or more.

In the present invention, the fact that the ethylene-vinyl alcohol copolymer layer exists as a continuous film layer with no defects is achieved by cutting the container body in the thickness direction and peeling the copolymer layer from the preester layer. Confirmed by Further, through this peeling, the presence or absence of the distribution or distribution structure of each layer and the predetermined molecular orientation described above can be confirmed.

Material In the present invention, as an oriented and creep-resistant resin,
Thermoplastic polyesters, particularly polyethylene terephthalate (PET'), are preferably used, but copolyesters containing ethylene terephthalate units as the main unit and other polyester units may also be used as long as the essence of polyethylene terephthalate is not impaired. It is possible. Copolymerization components for forming this stiff copolyester include isophthalic acid and P-
β-oxyethoxybenzoic acid, naphthalene 2,6-dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, adipic acid,
Dicarboxylic acid components such as sepacic acid or their alkyl ester derivatives, globylene glycol, 1.4-
Glycol components such as butanediol, neopentyl glycol, 1,6-hexylene glycol, cyclohexane dimetatool, ethylene oxide adduct of bisphenol A, diethylene glycol, and triethylene glycol can be mentioned.

The thermoplastic polyester to be used should have an intrinsic viscosity [η] of 0.5 or more and a special IC of 0.6 from the viewpoint of the mechanical properties of the vessel wall.
The above is desirable. Furthermore, this polyester can also contain additives such as coloring agents such as pigments and dyes, ultraviolet absorbers, and antistatic agents.

Other examples of orientation and creep-resistant resins include dilicarbonate, polyarylate, polysulfone, polyethersulfone, polyphenylene oxide, polyphenylene sulfite P5, polyetheretherketone, poly-4-methylpentene-1, and polyglycerol. (To name a few, polyethylene, high-impact polystyrene, polymethyl methacrylate, acrylonitrile/styrene copolymer, polyvinyl chloride, etc.)

In the present invention, it is particularly preferable to use an ethylene-vinyl alcohol copolymer having a vinyl alcohol content of 40 to 85 mol, particularly 50 to 80 mol, as the sparring resin layer. That is, ethylene-vinyl alcohol copolymer is one of the resins with the best sparring properties, and its sparring properties and thermoformability depend on the vinyl alcohol unit content. When the vinyl alcohol content is less than 40 molt, the permeability to oxygen and carbon dioxide gas is greater than when it is within the above range, and it is not suitable for the purpose of the present invention, which is to improve the sparring properties. , on the other hand, if this content exceeds 85 molt,
This is no longer suitable for the purpose of the present invention because the permeability to water vapor increases and the melt formability decreases.

Ethylene-vinyl alcohol copolymer layer, which can be obtained by saponifying a copolymer with a vinyl ester such as ethylene vinyl acetate, to a degree of saponification of 96% or higher, particularly 99% or higher. In addition to the above-mentioned components, this copolymer may contain propylene, butylene-1, imbutylene, etc. within a range of up to 3 molt, for example, within a range that impairs the barrier properties to oxygen and carbonic acid. It may contain an olefin having 3 or more carbon atoms as a comonomer component.

The molecular weight of the ethylene-vinyl alcohol copolymer is not particularly limited as long as it has a molecular weight sufficient to form a film, but in general, it is mixed at 30°C in a mixed solvent of 85% by weight of phenol and 15% by weight of water. Measured at temperature, the intrinsic viscosity [η
] is preferably in the range of 0.07 to 0.17, Q.

Other examples of gas barrier resins include aliphatic polyamides, aromatic polyamides, unsaturated nitrile resins, polyvinylidene chloride, and gas barrier polyesters.

In the following examples, polyester will be used as a representative resin having orientation resistance and creep resistance, and ethylene-vinyl alcohol copolymer will be used as a representative resin for gas barrier properties.

In the present invention, as will be described in detail later, the gas barrier property of the container is improved by forming a clearly differentiated layered flow of polyester and ethylene-vinyl alcohol copolymer in the cavity of the injection mold. becomes important. For this purpose, polyester and ethylene-vinyl alcohol copolymers must have a difference in structural viscosity index of 0.01 to 1.
It is best to use a combination within the range of 0, special KO905 to 5.

In this specification, the structural viscosity index is 1005 at a temperature 5°C higher than the higher melting point of both resins.
This is the value obtained from the flow curve of the melt at a shear rate of ec-' or more.More specifically, the shear stress τ (kg/an
The Log value of 2) is plotted on the vertical axis, and the shear speed r (5ee-'
Plot the values using the Log value of ) as the horizontal axis.

Then, from a straight line approximated to this curve, the formula logτ=i!
This is the value found as α of Agr.

If the difference in the structural viscosity index is smaller than the above range, it may be necessary to mix the two phase resin layers during the co-injection described below, so that clearly differentiated ethylene-vinyl resin is formed in the preform. It becomes difficult to form a continuous and complete layer of alcohol copolymer. Furthermore, if the difference in the structural viscosity index is larger than the above range, co-injection itself tends to become difficult.

The structural viscosity index of the melt depends on the molecular weight distribution and chemical structure of the resin. In the present invention, by selecting the molecular weight and molecular weight distribution of the polyester and ethylene-vinyl alcohol copolymer used, the difference in structural viscosity index can be set within the range described above.

Production method The third diagram shows the co-injection device used for manufacturing the multilayer preform.
In the figure, a cavity 13 corresponding to a preform is formed between an injection mold 11 and a core mold 12. A gate 14 is located at a position corresponding to the bottom of the preform of the mold 11 and is connected to two injection machines 17 and 18 via a runner nozzle 15 and a hot runner nozzle 16. The main injection machine 17 is for polyester injection, and is equipped with a barrel 19 and a screw 20 inside it.The sub-injection machine 18 is for injection of ethylene-vinyl alcohol copolymer, and has a Nororel 21 and its It is equipped with an internal screw 22.

The block 16 and the nozzle 15 have a hot runner 23 with an annular cross section for injection of polyester, and a hot runner 24 for injection of ethylene vinyl alcohol copolymer located at the center of the hot runner 23, which are coaxial. Nozzle 15
Nine pipes are arranged so that they meet near the tip of the pipe. The sprue 26 for polyester injection is connected to the hot runner 23 via the sprue bush 25, while the sprue 27 for ethylene-vinyl alcohol copolymer injection is connected to the sprue bush 25.
8 to the hot runner 24. After the resin to be injected is melted in the barrel 19 (21) and stored in the barrel 19 (21) by rotation of the screw 20 (22), the screw 20 (22) is advanced □.
The molten resin is passed through the sprue 26 (27) and the hot runner 23 (
24) and is injected into the cavity 13 through the gate 14, but according to the present invention, polyester and ethylene-
Injection of the vinyl alcohol copolymer is carried out under the following conditions.

In FIG. 4, which shows the relationship between injection time and injection pressure of polyester, polyester, and ethylene-vinyl alcohol copolymers, the alphabetical symbols A to A in the figure are 5-A to 5-5.
- This corresponds to the explanatory diagram of diagram H.

First, advance the polyester injection screw 20,
The primary injection is made into the cavity 13 under constant pressure. Fifth
- In figure A, polyester is in a state just before injection, and polyester 30 is under pressure at the tip of nozzle 15, but ethylene-
The vinyl alcohol copolymer 31 remains at the tip of the hot runner 24. With the injection of polyester,
As shown in FIG. 5-B, the cavity 13 is partially filled with the primary injection polyester 30.

At the stage where a predetermined amount of polyester has been injected, that is, after the injection time t1 has elapsed, the screw 22 for injecting the ethylene-vinyl alcohol copolymer is advanced, and the cavity 1
An ethylene-vinyl alcohol copolymer 31 is injected into the container. In this case, as shown in Figure 5-0, at the surface of the cavity 13, -th injection? The polyester 30 is solidified upon contact with the mold, or even if it is not solidified, it is in a state of extremely high viscosity, and therefore the injected ethylene-vinyl alcohol copolymer 3
1 flows toward the tip of the cavity along approximately the central plane of the polyester-filled layer, forming an intermediate layer of the copolymer.

At the time point 1 when the injection of the ethylene-vinyl alcohol copolymer is completed, secondary injection of the remaining polyester is performed. Figure 5-D shows the state of the ethylene-vinyl alcohol copolymer at the end of injection, and Figure 5-E shows the state of the ethylene-vinyl alcohol copolymer at the end of injection.
This shows the initial state when the next injection is performed in the cavity.

The secondary injection polyester 32 is shown in Figures 5-E and 5-G.
As shown in the figure, the polyester layer 30 m on the outer surface of the cavity side and the ethylene-vinyl alcohol copolymer layer 3
1 and presses the ethylene-vinyl alcohol copolymer layer 31 toward the inner surface of the cavity, and this secondary injection polyester 32 stretches the ethylene-vinyl alcohol copolymer layer toward the tip of the cavity. At the same time, it also moves forward toward the tip of the cavity between the ethylene-vinyl alcohol copolymer layer 31 and the primary injection polyester outer layer 30m4.

The advancement of the secondary injection polyester 32 and the accompanying stretching of the ethylene-vinyl alcohol copolymer layer 31 occur near the tip of the cavity 13 as shown in Figure 5-H. At the stage, i.e. time t3, the fifth
The injection cycle is completed when the secondary injection polyester 32 reaches the cavity tip 34 as shown in FIG.

According to the present invention, a polyester is secondarily injected between the outer surface layer of the injected polyester and the ethylene-vinyl alcohol copolymer layer, and diethylene-vinyl alcohol is added by this second injection. In addition, the intermediate layer of ethylene-vinyl alcohol copolymer is sufficiently thinner than the polyester outer surface layer, and the center surface of the vessel wall is also on the inner surface side. It is possible to obtain a distribution structure with a biased distribution, and it is also possible to completely confine the ethylene-vinyl alcohol copolymer intermediate layer between the polyesters.

At this time, according to the present invention, the cooling rate of the injection mold 11 and the injection timing of each resin are adjusted so that the distribution ratio (R) of the intermediate layer falls within the above-mentioned range. To explain this point, in general, under conditions where the cooling rate of the resin from the injection molding 11 is slow or under conditions where secondary injection of polyester is performed rapidly, the intermediate layer resin 31 is uniformly pressed against the inner surface of the preform. Molding is performed in the state, and the intermediate layer distribution ratio (R)
tends to take a relatively uniformly low value from the bottom of the container and preform to just below the neck. On the other hand, under conditions in which the resin from the injection mold 11 is cooled relatively quickly and/or the secondary injection of the polyester 32 is relatively slow, the intermediate layer resin 31 at the bottom of the preform
While the resin 30b is pressed toward the inner surface side, the cooling effect on the inner surface layer resin 30b becomes effective as it goes from the bottom to the upper end, and its thickness gradually increases, so that the intermediate layer distribution effect specified in the present invention is achieved. It is something that can be achieved.

In the present invention, when the primary injection pressure of polyester is Pl, the injection pressure of ethylene-vinyl alcohol copolymer is Pl, and the secondary injection pressure of polyester is P3, these pressure conditions can be varied widely. It was found that it can be obtained.

Generally speaking, the injection pressure P of the ethylene-vinyl alcohol copolymer is less than the primary injection pressure Ptj of the polyester.
As mentioned above, it is advantageous for the ethylene-vinyl alcohol copolymer to be formed as a completely continuous phase, while the secondary injection pressure P3 of the polyester is much lower than the primary injection capacity l of the polyester. This is advantageous in producing a cooling effect.

It is desirable that P1# Pl r P3 have the following relationship.

pt = 60 to 80 kg/am2 (1'-dipressure)
.

p! = s o to 110 kll/an2 (gauge pressure) and a pressure of 1.2 to -168 times Pi.

Ps = 20 to 50 kg7cm2 (gauge pressure) and a pressure of 0.3 to 0.8 times Pl.

It should be noted that under the above-mentioned injection conditions of p, >p, it was observed that the polyester injection screw substantially stopped during injection of the ethylene-vinyl alcohol copolymer, so the ethylene-vinyl alcohol copolymer It is confirmed that injection is carried out by passing through the y-t alone, but it is of course possible to continue the primary injection of polyester when injecting the ethylene-vinyl alcohol copolymer, and in this case In Figures 5-C and 5-D, ethylene-
It may be considered that injection of two layers of vinyl alcohol copolymer and polyester proceeds.

In the present invention, it is a particularly surprising new finding that the secondary injection of polyester proceeds smoothly with less pressure than the primary injection. The exact reason for this is unknown, but the secondary injection polyester passes through the molten resin with low resistance, and the melt of the ethylene-vinyl alcohol copolymer that comes into contact with the secondary injection polyester passes through the secondary injection polyester. It is thought that it acts as a lubricant to facilitate the flow of the liquid.

In the co-injection molding method of the present invention, it is natural that the injection amount of the ethylene-vinyl alcohol copolymer is related to the thickness of the intermediate layer of the ethylene-vinyl alcohol copolymer, but the primary injection amount of the polyester is It is related to the thickness of the surface layer, and the amount of secondary injection of polyester is closely related to the degree of deviation of the intermediate layer of ethylene-vinyl alcohol copolymer from the center in the thickness direction of the preform toward the inner surface side.

In the present invention, since the ethylene-vinyl alcohol copolymer intermediate layer is stronger and thinner than the polyester outer surface layer, the capacity volume is V, the primary injection capacity of the polyester is vl, and the secondary injection capacity of the polyester is V
', When the injection capacity of the ethylene-vinyl alcohol copolymer is v3, it is generally desirable to set v3 to 1 to 20 of V, especially 5 to 101, and the ratio of the -second injection capacity to the secondary injection capacity. v1: v, is 30 near 0 to 8
A volume ratio of 0:20, particularly 50:50 to 70:30 is desirable.

That is, if the value of v3 is 4 or so smaller than the above range, it tends to be difficult to significantly improve the gas barrier properties of the container, and if the value of v3 is larger than the above range, the preform's The drawbacks are that the stretch-blowing properties are reduced and the cost of the container is increased. If the ratio of vl is smaller than the above range, a fatal drawback may occur in that the ethylene-vinyl alcohol copolymer is exposed on the surface of the preform, whereas the ratio of v1 is larger than the above range. In some cases, it may be difficult to spread the ethylene-vinyl alcohol copolymer as an intermediate layer over substantially the majority of the area of the preform. The significant advantages of biasing to the side (discussed below) will be lost.

In order to obtain the distribution structure of the intermediate layer specified in the present invention, the temperature of the core of the injection mold (tl) must be adjusted to the temperature of the cavity mold (tl).
Regarding t2), it is preferable that 20℃≧t, -tl≧3℃, especially 15℃≧t, -tl≧5℃, and that tl is in the range of 30 to 100℃, especially [40 to 70℃]. stomach.

According to the present invention, the thus obtained multilayer preform having the structure shown in FIG. 5-I is subjected to stretch blow molding. Prior to this stretch blow molding, the multilayer preform is first heated at a temperature at which polyester can be stretched, generally 80 to 135°C.
In particular, the temperature is maintained between 90 and 125°C. This temperature control process involves supercooling the polyester layer of the multilayer preform so that it is maintained in a substantially non-crystalline state (amorphous state), and then using a heating method known per se, such as a thermal oven, an infrared heater, or a high-frequency crocodile electric heating. Depending on the mechanism, this can be carried out by heating the multilayer preform to the above temperature, or cooling the multilayer preform within the injection mold or within the mold until the multilayer preform reaches the above temperature. Alternatively, this can also be done by cooling.

6 and 7 for explaining the stretch blow molding operation, a mandrel 36 is inserted into the mouth of a bottomed multilayer preform 35, and the mouth is inserted into a pair of split molds 37.
m, clamp with 37b. A vertically movable stretching rod 3,8 is provided coaxially with the mandrel 36, and between this stretching rod 38 and the mandrel 36 there is an annular passage 39 for the injection of fluid.

By applying the tip 40 of the stretching rod 38 to the inside of the bottom of the preform 35 and moving the stretching rod 38 downward, stretching is performed in the axial direction, and the inside of the preform 35 is drawn through the passage 39. A fluid is blown into the mold, and the fluid pressure causes the preform to expand and stretch within the mold.

The degree of stretching of Bryphonium is sufficient to impart molecular orientation, which will be described in detail later, but for this purpose, the stretching ratio in the axial direction of the container must be 1.2 to 10 times, particularly 1.5 to 5.
It is desirable to double the amount.

The thickness of each layer is tA=o at the thinnest part of the body.
It is preferable that it is in the range of i to 1,0■ t, = 0.02 to 0.7 sw tc = o, oos to 0.2-.

It can be easily confirmed by the molecular orientation of the polyester layer, fluorescence polarization method, birefringence method, density method, etc., but it can be easily evaluated by the density method. Generally speaking, the density of polyester at 20°C in the thinnest interior of the body is 1.34 to 1.39.
11/an', especially 1.35 to 1,38177 cm'
If it is within the range, it can be said that the molecular orientation is effectively performed.

Applications of the Invention Since the container of the present invention has the above-mentioned excellent properties, it is useful as a container for food contents, especially as a lightweight container that blocks the permeation of oxygen, carbon dioxide gas, or aroma components. As a container for beer, cola, cider, carbonated fruit juice drinks, carbonated alcoholic beverages, etc., it has the advantage of significantly less carnese and loss than known containers.

Example The invention is illustrated by the following example.

Example 1 Polyethylene terephthalate (PET) having an intrinsic viscosity of 0.8 is supplied to the main injection machine, and ethylene-vinyl alcohol copolymer (KVOH) having a vinyl alcohol content of 70 mol is supplied to the sub-injection machine.

First, the main injection machine) injects the melted PET into approximately 60) CP/
The primary injection was performed at a pressure of cIn2, and after about 1.4 seconds delay from the injection of the PET, the secondary injection machine was melted at a pressure (about 100 kli/ex2) higher than the primary injection pressure of the PET. : A predetermined amount of vOH is injected in 1.1 seconds into a mold in which the temperature of the core and cavity is adjusted to be about 10 degrees lower, and then the main extruder is heated to a lower injection pressure (approximately 25 degrees Celsius). A multilayer preform of 2 types and 3 layers with a wall thickness of 4 snow was molded by secondary injection of PET with kll/an2'). The distribution ratio of the middle layer of this multilayer preform is R, = 0.0 at the bottom.
5. Rc = 0.18 at the center of the torso and R, = 0.2 at the shoulder.
6, and the EVOH of the middle layer was located on the innermost layer side at the bottom, and shifted toward the outer layer side in the torso and shoulders.

This multilayer preform is heated to about 100℃ and doubled in length.
The product was biaxially stretched and blown three times in width to form a multi-layered mold with an internal volume of 1000 cc.

This multilayer? Toru has a glabellar peel strength of 30 in the torso.
fi/1.5 cmφ, the in-plane orientation coefficient by polarized fluorescence method is 1 = 2.5, m = 2.9, and the body P
The density of the ET layer is 1.3697cm3, and despite the trap having a very low glabellar peeling strength, the middle layer is biased outward at the shoulder area where blisters are likely to occur, so 4f
Filled with IJ Neem's carbonated beverage and stored at 38℃ for 6 weeks, it exhibits a smooth appearance with no blisters, and the middle layer WOH is completely encapsulated in the inner and outer PET layers, and the middle layer at the bottom is completely encapsulated in the inner and outer PET layers. Because the layers were biased inward, there was no peeling between the eyebrows and no damage to the bottom part when the product was dropped from a height of 1 m to the floor. Also, what is the oxygen permeability of &tor at 37℃? Tor internal 1oo% RH1 external 20% R
Under the conditions of H, the oxygen permeability is 2,4 c+/rn224 H・atm, and the oxygen permeability is 9.8 Ce/m2・2 for polyethylene tere-7 tallate alone with the same weight and shape.
At 4 H.1 atm, the oxygen permeability of the &)l of the present invention was about V4 compared to the &)l of PET alone.

Comparative Example An extruder for the outer layer and an extruder for the inner layer, which had a built-in full-flight type IJ with a diameter of 65 m and an effective length of 1,430 m, and an extruder for the inner layer with a diameter of 50 mm and an effective length of 1. Using Loom's extruder for the intermediate layer with a built-in full-flight screw and a ring-shaped die for the 3 layers, the inner and outer layers were made of polyethylene with an intrinsic viscosity of 0.9 (Tele7 turret), medium 1'L [containing cavinyl alcohol]. T6O Molch's ethylene-vinyl alcohol copolymer Tease, thickness ratio of each layer: outer layer: middle layer: inner layer is 100:20:50, outer diameter 30.0 m, thickness 3.8
M) and Eve were co-extruded using two extruders and extruded from a multilayer die into a water-cooled cooling tank to obtain a multilayer pipe with two types and three layers.

Using the obtained pipe, the lower end is fused and closed to form a semicircular sphere, and the upper end is formed into a mouth and neck part with a threaded part.The preform is preheated to 98°C and blow molded. Biaxial stretch blow molding in the mold to create an internal volume of 1.0OOcc
A multilayer stretched polyester S tor was obtained.

this? Fill the bottle with 4 volume carbonated drink and make 38
After storage for 6 weeks at ℃, blisters appeared on the shoulders and under the body, resulting in poor appearance, and when dropped from a height of 1 m to the floor, the bottom of the straw was damaged, and delamination occurred on the shoulders and bottom. did.

[Brief explanation of the drawing]

FIG. 1 shows a plastic container according to the present invention, FIG. 2-A,
Figures 2-D, 2-0, and 2-D are sectional views of the bottom, body, shoulder, and base of the neck of the container in Figure 1, and Figure 3 is the main parts of the co-injection molding machine. Cross-sectional view, Figure 4 is a chart showing the relationship between injection time and injection pressure, Figures 5-A to 5-I are explanatory diagrams showing the injection process, and Figures 6 and 7 are stretch blow molding. It is a sectional view of the main part of the machine. DESCRIPTION OF SYMBOLS 1... Plastic container, 2... Neck, 3... Body, 4... Bottom, 5... Shoulder, 11... Injection mold, 12... Core mold, 17 .18... Injection machine, 23
．． 24... Hot run t-130... Polyester, 31... Ethylene-vinyl alcohol copolymer, 3
5... Preform, 37m, 37b - Blow mold 〇 Figure 3 Figure 4 Figure 5-G II Figure 5-HvlJ Figure 5-I Figure 6 Figure 7

Claims (2)

[Claims] (1) In a plastic container that is composed of a laminate consisting of inner and outer surface layers of oriented creep-resistant resin and an intermediate layer of gas barrier resin, and has a thick mouth, a shoulder, and a thin body and bottom, The oriented creep-resistant resin inner and outer surface layers are continuous in the plane direction over the entire area of the container, and the gas barrier resin intermediate layer is continuous in the plane direction at least over the bottom, body and shoulders, and the inner and outer surface layers are continuous in the plane direction over the entire area of the container. The resin layers are completely encapsulated between the layers, and the molecules of each resin layer are biaxially oriented at least in the body of the container. An impact-resistant plastic container characterized by having a distribution structure that is biased toward the center between an inner surface and an outer surface. (2) The plastic container according to claim 1, wherein the oriented creep-resistant resin is a thermoplastic polyester and the gas barrier resin is an ethylene-vinyl alcohol copolymer.