JPH0346376B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to impact-resistant plastic containers, and more specifically to impact-resistant plastic containers that have excellent gas barrier properties and extremely high resistance to drop impacts, etc. This invention relates to a biaxially stretched plastic container with a laminated structure that also has excellent blister properties.

Prior Art and Technical Problems of the Invention A polyester container made by a stretch blow molding method is
With excellent transparency and moderate rigidity, it can be used not only for liquid detergents, shampoos, cosmetics, soy sauce, sauces, etc., but also for containers for carbonated drinks such as beer, cola, cider, and soft drinks such as fruit juice and mineral water. It has come into widespread use.

Although this stretched polyester container has superior gas barrier properties compared to general-purpose resin containers such as polyethylene and polypropylene, it is ignored, whereas metal cans and glass bottles have almost zero gas permeability. It has an extremely high permeability to oxygen and carbon dioxide, and its contents can only be stored for a relatively short period of time.

In order to improve this drawback, various proposals have been made to improve the gas barrier properties of containers by combining polyester with gas barrier resins such as ethylene-vinyl alcohol copolymers to create 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, there is almost no heat difference between the gas barrier resin such as ethylene-vinyl alcohol copolymer and the orientation and creep resistant resin such as polyester. Since adhesive properties cannot be obtained, it is thought that it is necessary to interpose a special adhesive resin layer between the two resin layers, and many efforts are being made to search for such an adhesive resin.

One of the important problems with such multilayer plastic containers is that in areas where the stretching ratio is high, the thickness of the container wall becomes thinner according to the stretching ratio, and even though there is an improvement in gas barrier properties due to molecular orientation, ,
The problem is that the gas permeability in this part ends up being higher than in other parts.

Another problem is that there is a tendency for delamination to occur between the gas barrier resin intermediate layer and the oriented, creep-resistant resin, especially when the filled container is subjected to a drop impact. The problem is that delamination easily occurs in the gas barrier resin layer, and the gas barrier resin layer tends to break or pinholes occur.
The second important problem is that when filled with a content that has a self-generating pressure, such as a content containing carbon dioxide gas, the carbon dioxide gas that has permeated through the inner surface layer will form blisters at the boundary with the gas barrier resin layer. This causes carbonation loss, deterioration of gas barrier properties, and furthermore, significantly impairs the appearance of the container. This blistering tends to occur more significantly in the shoulder area of the container.

SUMMARY OF THE INVENTION The present inventors have developed a container by stretch blow molding a multilayer preform consisting of inner and outer surface layers of oriented resin such as polyester and an intermediate layer made of gas barrier resin such as ethylene-vinyl alcohol copolymer. During manufacturing, the intermediate layer is completely encapsulated between the inner and outer surface layers, and the intermediate layer has a distribution structure in which the thickness ratio is smallest at the center of the bottom and increases as it moves toward the upper part of the body. By providing this, the molecular orientation of both resins is effectively carried out, the adhesion state of both resin layers is maintained, and sufficient gas barrier properties are imparted even to the thinned part where the stretching ratio is the highest. I discovered that. Furthermore, the inventors of the present invention have provided this intermediate layer with a distribution structure that is biased toward the innermost surface at the center of the bottom and toward the center between the inner and outer surfaces as it moves toward the upper part of the trunk. It has been found that this method effectively prevents delamination and damage to the shoulders due to drop impact, as well as the formation of blisters in the shoulders.

OBJECT OF THE INVENTION That is, the object of the present invention is to provide an inner and outer layer of a directional and creep-resistant resin, in which the above-mentioned drawbacks are effectively eliminated;
The object of the present invention is to provide a multilayer container with biaxial molecular orientation and a gas barrier resin intermediate layer.

Another object of the present invention is to improve the gas barrier properties of the thinnest part, the drop impact resistance of the bottom part, and especially the delamination resistance of the bottom part.
To provide a biaxially oriented multilayer plastic container which is excellent in combination with blister resistance of the shoulder part.

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

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

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 includes a torso, an opening connected to the torso through the shoulder, and an occluded body. In a plastic container having a flat bottom, the oriented, creep-resistant resin inner and outer surface layers are continuous in the surface direction over the entire area of the container, and the gas barrier resin intermediate layer is continuous at least over the bottom and shoulders. It is continuous in the plane direction and is completely enclosed between the inner and outer surface layers, and each resin layer has molecular orientation in the biaxial direction at least in the container body, and the thickness ratio of the intermediate layer to the entire container wall is A multilayer plastic container is provided which is characterized in that it is smallest at the center of the bottom and tends to become larger toward the top of the body.

According to the present invention, in the plastic container, the intermediate layer has a distribution structure in which it is biased toward the innermost surface at the center of the bottom, and toward the center between the inner surface and the outer surface as it moves toward the upper part of the body. A container is provided that is characterized by:

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 is used as a typical example of the creep-resistant resin, and ethylene-vinyl alcohol copolymer is used as a typical example of the gas barrier resin, but the invention is not limited to these examples.

Structure and Effects of Container FIG. 1 shows the overall arrangement of the stretched multilayer plastic container of the present invention, and FIG. 2 shows its partial cross-sectional structure.
-A to 2-D, this container 1 has a thick mouth part (nozzle part) 2, a thin body part 3 and a closed bottom part 4, and there is a gap between the body part 3 and the mouth part 2. There is a frustum-shaped shoulder 5 connecting these.

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 intermediate layer 8 of gas barrier resin such as ethylene-vinyl alcohol copolymer completely encapsulated therebetween. That is, this intermediate layer 8 has a cross-sectional view showing the bottom part (Fig. 2-A), a cross-sectional view showing the trunk part (Fig. 2-B), a cross-sectional view showing the shoulder part (Fig. 2-C), and a cross-sectional view showing the bottom part (Fig. 2-C). It is clear from the cross-sectional view (Figure 2-D) showing the base of the tube that no part of the tube wall is exposed to the surface, and the bottom,
It exists as an intermediate layer throughout the torso and shoulders. As shown in FIG. 1, 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, or Alternatively, the intermediate layer 8 may not be present. 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, although the thickness of the stretched plastic container wall varies considerably depending on the location of the container and the degree of stretching, the ratio of the thickness of the gas barrier intermediate layer 8 to the overall thickness is smallest at the center of the bottom 4. In addition, it has a tendency to gradually increase as it moves toward the upper part of the body (2-A to 2-2).
-See figure D). To explain further, 2-A to 2
In Figure 2-D, the scale of the thickness of each part is the same, but the bottom 4 shown in Figure 2-A
In the body part 3 shown in Fig. 2-B, the middle layer thickness ratio is the smallest, and in the shoulder part 5 shown in Fig. 2-C, the middle layer thickness ratio is considerably larger than that of the bottom part 4. is larger than that of the body 3, and furthermore, directly below the mouth 2 shown in FIG. 2-D, it is considerably larger than that of the shoulder.

Now, the thickness ratio (C) of the intermediate layer is calculated by the following formula: C = t _C / t _A + t _B + t _C ... (1) In the formula, t _A represents the thickness of the outer layer of the oriented and creep-resistant resin, and t _B represents the thickness of the orientation and creep-resistant resin inner layer, and t _C represents the thickness of the gas barrier resin intermediate layer. On the other hand, the distribution of the intermediate layer thickness ratio in each part of the container is Let C _B , C _C , and C _S be the intermediate layer thickness ratios at the center of the shoulder and shoulder portions, respectively, then C _C /C _B ,
It can be evaluated by comparing C _S /C _C.

The multilayer plastic container of the present invention has the distribution of intermediate layer thickness ratios shown below.

C _C /C _B =1.1 to 50, especially 1.3 to 30.

C _S /C _B =1.1 to 200, especially 1.5 to 150.

In addition, the thickness ratio of the intermediate layer directly under the neck of the container was
Assuming C _N , it is desirable that C _N /C _B = 1.3 to 500, particularly 1.5 to 200.

According to the present invention, by providing the above-described distribution of interlayer thickness ratios, a very significant improvement is made in reducing gas permeation through the container wall.
That is, it has been found that when a polyester preform is subjected to stretch blow molding, the part that is most strongly stretched, that is, the part that is thinnest most, is the shoulder part. For example, when a polyester preform is stretch-blow molded so that the average area stretch ratio from just below the neck to the bottom is 4 times, the stretch ratio at the shoulders is 6 to 10 times, at the top of the body it is 5 to 9 times, and at the top of the body the stretching ratio is 6 to 10 times. It has been confirmed that the amount increases by 4 to 7 times in the center of the body and 3 to 5 times in the lower part of the body. Thus, although physical properties are improved due to molecular orientation in areas where the stretching ratio is large, the wall of the container becomes significantly thinner due to stretching, and the gas barrier layer also becomes thinner as a result of this, resulting in less gas permeation through the wall. For example, the loss of oxygen permeation from the outside of the vessel to the inside of the vessel and the permeation loss of carbon dioxide from the inside of the vessel to the outside of the vessel cannot be ignored. In the container of the present invention, the stretching ratio is increased by setting the thickness ratio of the intermediate layer to the entire container wall to be smallest at the center of the bottom and gradually increasing toward the trunk and shoulders. A distribution structure in which the thickness of a gas barrier layer such as ethylene-vinyl alcohol copolymer increases is added to the area where the container wall thickness is large and the container wall thickness is reduced to compensate for this reduction in container wall thickness, and as a result, the container wall thickness decreases. The overall gas barrier properties are significantly improved.

Moreover, the container of the present invention has a structure as a whole in which the inner and outer surface layers 7 of the two creep-resistant resin layers are thick and the inner surface layer 6 is thin. For this reason,
The outer surface layer 7 that receives external force acts as a stress carrier, and also because it is given molecular orientation by stretching, stable shape retention as a container is obtained, and pressure resistance and deformation resistance are also improved. The effect of doing so can be obtained. In addition, since the inner surface layer 6 has a thin structure, the amount of dissolved and adsorbed carbon dioxide gas on creep-resistant resin such as polyester is reduced, resulting in carbonation loss when filling containers containing carbon dioxide gas. This has the advantage that there are fewer

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, etc., and the inner and outer surfaces are made of polyester, etc. Surface 6,7
There is a completely unexpected and novel fact that the state of close contact between the two is completely maintained even though there is no adhesive force between the two. 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 ( 200
(g/1.5cm width or less), this is confirmed by the occurrence of interlayer peeling. However, when this container is kept in an integrated state without being cut as described above,
Both resin layers exhibit a completely adhering appearance and behavior,
It was found that even when the container was subjected to a drop impact or was subjected to slight deformation, no peeling phenomenon was observed and a complete adhesion state was maintained. The reason for this is
Although it has not yet been elucidated, 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 to maintain airtightness between both resin layers. In relation to the sagging and the distribution structure of the resin layer mentioned above,
The cause seems to be that the hoop-clamping force of the inner and outer polyester layers acts on the intermediate layer of ethylene-vinyl alcohol copolymer or the like, and that there is an adhesion effect due to the molecular orientation of both resin layers.

Furthermore, the gas barrier resin layer such as ethylene-vinyl alcohol copolymer in the container of the present invention is effectively stretched together with the inner and outer polyester layers to have molecular orientation 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 (Po ₂ ) for oxygen is as small as 1/2 to 1/5 of that of an unoriented copolymer. . 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, that is, stretched under normal molding conditions, it will break (especially Publication No. 57-42493). It is also known that molecular orientation of the ethylene-vinyl alcohol copolymer can be imparted by forming an ethylene-vinyl alcohol copolymer into a laminate sandwiched with stretchable resin layers 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 may break. (Japanese Unexamined Patent Publication No. 103481/1983).
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 resin layers. Nevertheless, molecular orientation was effectively imparted to the ethylene-vinyl alcohol copolymer layer, which was a surprising effect of the present invention.

Generally, the ethylene-vinyl alcohol copolymer constituting the trunk intermediate layer is molecularly oriented so that the in-plane orientation coefficient (l+m) determined by fluorescence polarization method is 0.4 or more.

In the present invention, the fact that the ethylene-vinyl alcohol copolymer layer exists as a continuous film layer without defects is confirmed by cutting the container body in the thickness direction and peeling the copolymer layer from the polyester layer. Ru. Furthermore, by 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.

In a preferred container of the present invention, in addition to the above-mentioned features, the gas barrier intermediate layer is biased toward the innermost surface at the center of the bottom, and gradually forms a gap between the inner and outer surfaces as it moves upward to the body and shoulders. It has a distribution structure that is biased toward the center. The extent to which this middle class is biased is
It can be evaluated using the distribution ratio (R) defined by the following formula: R=t _B /t _A +t _B +t _C (2) where t _A , t _B , and t _C have the meanings described above.

As an example, specific values of the intermediate layer distribution ratio (R) in each part of the container are as follows.
Note that R _B , R _C , and R _S represent the intermediate layer distribution ratios at the centers of the bottom, body, and shoulders, respectively.

R _B =0.01 to 0.20, especially 0.02 to 0.15, R _C =0.07 to 0.35, especially 0.10 to 0.30, R _S =0.15 to 0.40, especially 0.20 to 0.35, R _C −R _B ≧0.05, R _S −R _C ≧ 0.01.

Furthermore, the middle layer distribution ratio (R _o ) just below the neck
is in the range of 0.25 to 0.45, and it is desirable that R _o −R _S ≧0.03.

According to this aspect of the invention, such a distribution structure of the intermediate layer achieves the advantage that the impact and blister resistance of the stretched multilayer plastic container is significantly improved. In a multilayer plastic container, the part that is most vulnerable to impact is the bottom, which is subjected to a drop impact as described above, and delamination occurs between the creep-resistant resin layer and the gas barrier resin layer at this bottom. Furthermore, the gas barrier resin layer may be broken, or pinholes, cracks, etc. may occur. In addition, when filling with contents containing carbon dioxide gas, blisters often occur on the shoulders. The occurrence of blisters is caused by gas passing through the creep-resistant resin inner layer causing blisters at the boundary between the inner layer and the gas-barrier intermediate layer, especially at parts of the vessel wall where the thickness is relatively small and the curvature is large, that is, the shoulders. This is due to the fact that it accumulates.

According to this aspect of 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, and gas This prevents delamination between the barrier intermediate layer 8 and the creep-resistant resin layers 6 and 7 due to impact, and also prevents damage to the intermediate layer 8 itself. By biasing the surface and the outer surface toward the center side, the creep-resistant resin inner surface layer 6 is also given sufficient thickness and rigidity, thereby preventing the formation of blisters due to the carbon dioxide content in the shoulder portion. It is something.

Material In the present invention, thermoplastic polyester, particularly polyethylene terephthalate (PET), is suitably used as the orientation and creep-resistant resin. , copolyesters containing other polyester units may also be used. Copolymerization components for forming such a copolyester include isophthalic acid and P-β.
-Oxyethoxybenzoic acid/naphthalene 2,6-
Dicarboxylic acid components such as dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, adipic acid, sebacic acid or their alkyl ester derivatives, propylene glycol, 1,4-butanediol,
Glycol components such as neopentyl glycol, 1,6-hexylene glycol, cyclohexanedimethanol, and ethylene oxide adducts of bisphenol A, diethylene glycol, and triethylene glycol can be mentioned.

The thermoplastic polyester used should have an intrinsic viscosity [n] of 0.5 or more, from the viewpoint of the mechanical properties of the vessel wall.
In particular, it is desirable that it be 0.6 or more. 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:
Polycarbonate, polyarylate, polysulfone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyetheretherketone, poly-4-methylpentene-1, polypropylene, high-impact polystyrene,
Polymethyl methacrylate, acrylonitrile/
Examples include styrene copolymers and polyvinyl chloride.

In the present invention, the gas barrier resin layer has a vinyl alcohol content of 40 to 85 mol%,
In particular, it is particularly preferable to use an ethylene-vinyl alcohol copolymer containing 50 to 80 mol%. That is, the ethylene-vinyl alcohol copolymer is one of the resins with the best gas barrier properties, and its gas barrier properties and thermoformability depend on the vinyl alcohol unit content. When the vinyl alcohol content is less than 40 mol%, 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 gas barrier properties. On the other hand, if the content exceeds 85 mol %, the permeability to water vapor increases and the melt moldability decreases, which is not suitable for the purpose of the present invention.

Ethylene-vinyl alcohol copolymer is obtained by saponifying a copolymer of ethylene and a vinyl ester such as vinyl acetate so that the degree of saponification is 96% or more, especially 99% or more. In addition to the above-mentioned components, this copolymer may contain, for example, 3
Propylene, butylene, up to mol%
1. An olefin having 3 or more carbon atoms such as isobutylene may be contained 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 it is generally used at a temperature of 30°C in a mixed solvent of 85% by weight of phenol and 15% by weight of water. It is preferable that the intrinsic viscosity [n] is in the range of 0.07 to 0.17/g.

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

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 detailed later, polyester and ethylene-
Forming a clearly differentiated laminar flow with the vinyl alcohol copolymer is important from the viewpoint of gas barrier properties of the container. For this purpose, polyester and ethylene-vinyl alcohol copolymers must have a difference in structural viscosity index of 0.01 to 10, especially 0.05.
It is preferable to use combinations within the range of 5 to 5.

In this specification, the structural viscosity index is a value determined from the flow curve of the melt at a temperature 5°C higher than the melting point of the higher one of both resins and at a shear rate of 100 sec ^-1 or more. In detail, the log value of the shear stress τ (Kg/cm ² ) is plotted on the vertical axis, and the shear rate γ
Plot the value using the log value of (sec ^-1 ) as the horizontal axis,
This is the value found as α in the equation logτ=1/α logγ〓 from a straight line approximated to this curve.

If the difference in structural viscosity index is smaller than the above range, the two resin layers will mix during co-injection, which will be described later, and the clearly differentiated ethylene-vinyl alcohol copolymer will be mixed in the preform. It becomes difficult to form continuous and complete layers. Furthermore, if the difference in 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, 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.

Manufacturing method In FIG. 3 showing a co-injection device used for manufacturing a multilayer preform, an injection mold 11 and a core mold 1 are shown.
2, a cavity 13 corresponding to the preform is formed. 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 hot runner nozzle 15 and a hot runner block 16. The main injection machine 17 is for polyester injection, and includes a barrel 19 and a screw 2 inside it.
0, the sub-injection machine 18 is for injection of ethylene-vinyl alcohol copolymer, and the barrel 2
1 and a screw 22 therein.
The block 16 and the nozzle 15 have a hot runner 24 with an annular cross section for polyester injection, and a hot runner 24 for ethylene vinyl alcohol copolymer injection located at the center of the hot runner 24. They are provided so that they merge near the tip. The polyester injection sprue 25 is connected to the hot runner 23 via a sprue bush 26, while the ethylene vinyl alcohol copolymer injection sprue 27 is connected to the hot runner 24 via a sprue bush 28. The resin to be injected is melted into the barrels 12 and 21, and the barrel 1 is heated by the rotation of the screws 20 and 22.
After storing in screws 9 and 21, screws 20 and 22
is advanced to inject the molten resin into the cavity 13 through the sprues 25, 27, hot runners 23, 24 and gate 14. According to the present invention, the injection of polyester and ethylene vinyl alcohol copolymer is carried out as follows. It will be carried out under the following conditions.

In Figure 4, which shows the relationship between injection time and injection pressure for polyester and ethylene-vinyl alcohol copolymers, the alphanumeric symbols A to I in the figure are
corresponds to the explanatory diagrams in FIGS. 5-A to 5-I.

First, the polyester injection screw 20 is advanced to perform primary injection into the cavity 13 under constant pressure. FIG. 5-A shows the polyester immediately before injection, with the polyester 30 at the tip of the nozzle 15, but the ethylene-vinyl alcohol copolymer 31 remaining at the tip of the hot runner 24. With the injection of polyester, the fifth
As shown in Figure B, the cavity 13 is filled up to the middle 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 ethylene-vinyl alcohol copolymer 31 is injected into the cavity 13. let In this case, as shown in Figure 5-C, the primary injection polyester 30 is solidified by contact with the mold on the surface of the cavity 13, or even if it is not solidified, it is in an extremely high viscosity state. It's getting old,
Therefore, the injected ethylene-vinyl alcohol copolymer 31 flows toward the cavity tip along approximately the center plane of the polyester-filled layer, forming an intermediate layer of the copolymer.

At time _t2 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;
Figure E shows the initial state where the secondary injection of polyester is performed within the cavity.

As shown in Figures 5-F and 5-I, the secondary injection polyester 32 flows between the polyester layer 30a on the outer surface of the cavity side and the ethylene-vinyl alcohol copolymer layer 31, and the ethylene-
While pressing the vinyl alcohol copolymer layer 31 toward the inner surface of the cavity, the secondary injection polyester 32 stretches the ethylene-vinyl alcohol copolymer layer toward the tip of the cavity, and also forms an ethylene-vinyl alcohol copolymer layer. layer 31
and the primary injection polyester outer layer 30a,
Move forward toward the tip of the cavity.

The advancement of the secondary injection polyester 32 and the accompanying stretching of the ethylene-vinyl alcohol copolymer layer 41 are performed up to the vicinity of the tip of the cavity 13, as shown in Figure 5-H. At the stage, i.e., time _t3 , as shown in Figure 5-I, 2
The next injected polyester 32 reaches the cavity tip 34 and the injection cycle ends.

According to the present invention, polyester is secondarily injected between the outer surface layer of the firstly injected polyester and the ethylene-vinyl alcohol copolymer layer, and this second injection spreads the ethylene-vinyl alcohol to the vicinity of the tip of the preform. Furthermore, it is possible to make the intermediate layer of ethylene vinyl alcohol copolymer sufficiently thinner than the outer surface layer of polyester, and to have a distribution structure that is biased toward the inner surface of the vessel wall than the center surface of the vessel wall. Furthermore, it becomes 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 or speed of each resin are more preferably adjusted so that the ratio of the intermediate layer thickness to the total thickness has the above-mentioned distribution. is performed so that the distribution ratio (R) of the intermediate layer falls within the range described above. To illustrate this point, the intermediate layer resin 31 is then injected into the secondary injection polyester 32 under its own injection pressure.
The injection pressure advances between the inner and outer surfaces of the primary injection polyester 30 toward the cavity tip. Under conditions where the temperature of the intermediate layer resin 31 is high and therefore its melt viscosity is low, the intermediate layer resin will be spread thinly, while under the opposite conditions, the intermediate layer resin will remain thick. To provide this distribution structure, for example, the intermediate layer resin is maintained at a relatively high temperature near the nozzle 15, that is, at the bottom of the parison, and at a relatively low temperature as it approaches the cavity tip, that is, the upper end of the parison. Adjust the injection mold temperature accordingly. For this purpose, the temperature is adjusted so that the nozzle side of the mold cavity is relatively high temperature and the cavity side opposite to the nozzle is relatively low temperature. Further, when the injection of the intermediate layer resin and the secondary injection of the polyester resin are performed slowly, the gradient of the thickness distribution of the cooling effect on the intermediate layer resin tends to become large.

In the present invention, the primary injection pressure of polyester is
It has been found that these pressure conditions can be varied fairly widely, where P ₁ is the injection pressure of the ethylene vinyl alcohol copolymer, P ₂ is the secondary injection pressure of the polyester, and P ₃ is the secondary injection pressure of the polyester.

Generally speaking, it is advantageous for the injection pressure P ₂ of the ethylene vinyl alcohol copolymer to be higher than the primary injection pressure P ₁ of the polyester in order to form the ethylene vinyl alcohol copolymer as a completely continuous phase. Yes, while the secondary injection pressure of polyester
It is advantageous to set P ₃ to be considerably lower than the primary injection pressure P ₁ of the polyester in order to produce the above-mentioned cooling effect.

It is desirable that P ₁ , P ₂ , and P ₃ have the following relationship.

P ₁ =60 to 80Kg/cm ² (gauge pressure).

P ₂ = 80 to 110Kg/cm ² (gauge pressure) and P ₁
1.2 to 1.8 times the pressure.

P ₃ = 20 to 50Kg/cm ² (gauge pressure) and P ₁
0.3 to 0.8 times the pressure.

Furthermore, under the above-mentioned injection conditions of P ₂ > P ₁ , it was observed that the polyester injection screw substantially stopped during injection of the ethylene-vinyl alcohol copolymer, so the ethylene-vinyl alcohol copolymer was It is confirmed that injection is taking place after passing through the gate, but it is of course possible to continue primary injection of polyester when injecting ethylene-vinyl alcohol copolymer, and in this case, 5-C and 5-D, it can be considered that the injection of two layers of ethylene-vinyl alcohol copolymer and polyester is proceeding.

In the present invention, it was a particularly surprising new finding that the secondary injection of polyester proceeded smoothly with a lower 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 molten ethylene-vinyl alcohol copolymer that comes into contact with the secondary injection polyester It is conceivable that it acts as a lubricant to facilitate flow.

In the co-injection molding method used in 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 It is related to the thickness of the inner surface layer, and the amount of secondary injection of polyester is ethylene-
It is closely related to the degree of deviation of the inner surface from the center in the thickness direction of the preform of the intermediate layer of vinyl alcohol copolymer.

In the present invention, since the ethylene-vinyl alcohol copolymer intermediate layer is considerably thinner than the polyester outer surface layer, the cavity volume is V, the primary injection capacity of the polyester is V ₁ , and the secondary injection capacity of the polyester is V ₂ , the injection capacity of the ethylene-vinyl alcohol copolymer is V ₃ , it is generally desirable that V ₃ be 1 to 20% of V, especially 5 to 10%, and the primary injection capacity and secondary injection capacity The ratio V ₁ :V ₂ is preferably in a volume ratio of 30:70 to 80:20, particularly 50:50 to 70:30.

That is, when the value of V ₃ becomes 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 V ₃ is larger than the above range, the stretch-blowing properties of the preform will deteriorate, and the cost of the container will increase. will occur. If the ratio of V ₁ is smaller than the above range, a fatal drawback may arise in that the ethylene-vinyl alcohol copolymer is exposed on the preform surface, while if the ratio of V ₁ is larger than the above range In some cases, it becomes difficult to spread the ethylene-vinyl alcohol copolymer as an intermediate layer over substantially the majority of the area of the preform, or it becomes difficult to spread the ethylene-vinyl alcohol copolymer intermediate layer on the inner surface side. The significant advantages (discussed below) of biasing to

In order to obtain a distribution structure in which the intermediate layer thickness ratio has a gradient as specified in the present invention, the temperature on the nozzle side (t ₁ ) of the injection mold cavity should be 100℃≧t with respect to the temperature on the opposite side of the nozzle (t ₂ ). ₁ -t ₂ ≧1°C, especially 60°C≧t ₁ -t ₂ ≧3°C, and t ₁ is desirably in the range of 30 to 100°C, especially 40 to 70°C.

Furthermore, in order to obtain the distribution structure of the intermediate layer specified in the preferred embodiment of the present invention, the core temperature (t ₃ ) of the injection mold must be
Regarding the temperature of the cavity mold ( _t4 ), 20℃≧ _t4 − _t3 ≧3℃, especially 15℃≧ _t4 − _t3 ≧5℃, and _t3 is 30 to 100℃, especially 40 to 70℃. It is desirable to set it in the range of ℃.

According to the method of the present invention, the fifth-
A multilayer preform having the structure shown in Figure I is subjected to stretch blow molding. Prior to this stretch blow molding,
The multilayer preform is first maintained at the temperature at which the polyester can be stretched, generally from 80 to 135°C, particularly from 90 to 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
It can also be carried out by heating the multilayer preform to the above temperature using a heating mechanism known per se, such as hot air, an infrared heater, or a high-frequency dielectric heating, or in the injection mold or in the mold.
This can also be done by cooling or allowing the multilayer preform to cool until the temperature reaches the above temperature.

In FIGS. 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 held between a pair of split molds 37a and 37b. A stretching rod 38 that is vertically movable coaxially with the mandrel 36
is provided, and between the stretching rod 38 and the mandrel 36 there is an annular passage 39 for fluid injection.

The tip 30 of the stretching rod 38 is applied to the inside of the bottom of the preform 35, and the stretching rod 38 is moved downward to perform stretching in the axial direction, and at the same time, fluid is blown into the preform 35 through the passage 39. This fluid pressure causes the preform to expand and stretch within the mold.

The degree of stretching of the preform is sufficient to impart molecular orientation, which will be detailed later.
In particular, it is desirable to increase the amount by 1.5 to 5 times.

The thickness of each layer is preferably within the following ranges: t _A =0.1 to 1.0 mm, t _B =0.02 to 0.7 mm, and t _C =0.005 to 0.2 mm.

The molecular orientation of the polyester layer can be easily confirmed by a fluorescence polarization method, a birefringence method, a density method, etc., and can be easily evaluated by a density method. Generally speaking, the density of polyester at 20°C in the thinnest part of the body is 1.34 to 1.39 g/cm ³ , particularly 1.35 to 1.38 g/cm 3 .
If it is within the range of cm ³ , it can be said that the molecular orientation has been carried out effectively.

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

Example The invention is illustrated by the following example.

Example 1 Polyethylene terephthalate (PET) having an intrinsic viscosity of 0.75 is supplied to the main injection machine, and ethylene-vinyl alcohol copolymer (EVOH) having a vinyl alcohol content of 70 mol% is supplied to the sub-extruder.

First, about 60% of the melted PET is sent from the main injection machine.
Perform the primary injection at a pressure of Kg/ ^cm2 , then after a delay of about 1 second, at an injection pressure higher than the primary injection pressure at 80 ~
A predetermined amount of molten EVOH is injected from the sub-injection machine into an injection mold whose temperature is controlled so that the cavity temperature is approximately 10℃ lower than the core temperature for approximately 0.9 seconds by controlling the pressure to 120Kg/ ^cm2 . Finally, the molten PET was secondly injected from the main injection machine at an injection pressure of about 30 kg/cm ² lower than the primary injection pressure to form a multilayer preform of two types and three layers with a thickness of 4 mm.

This multilayer preform is heated to about 98℃ and then
A bottle with an internal volume of 1000 c.c. was molded by biaxially stretching and blowing to double the width and triple the width. The middle layer EVOH of this bottle
The ratio of the thickness of the body and shoulders to the thickness of the bottom of
C _C /C _B = 5.5 and C _S /C _B = 17.5, and the middle layer
The EVOH was thinnest at the bottom and located on the inner layer side, and gradually became thicker as it moved to the torso and shoulders, and was located on the outer layer side. This bottle is a mid-tier
EVOH is also highly stretch oriented and has an in-plane orientation coefficient of l = 2.5 and m = 2.9 as determined by polarized fluorescence, and the density of the PET layer in the body is 1.36 g/cm ³ , resulting in extremely low delamination strength. (approximately 30g/1.5cm width), the middle layer is biased toward the outside in the shoulder area where blisters are likely to form, so fill it with 4 gas volume carbonated drink and store it at 38℃ for 6 weeks to form a blister. In addition to exhibiting a good appearance with no occurrence of scratches, the EVOH in the middle layer is completely encapsulated in the PET inner and outer layers, and the middle layer is biased inward at the bottom, so it can withstand the impact of dropping from a height of 1 m to the floor. On the other hand, there was no delamination between the layers and no damage to the bottom. Also, the oxygen permeability of this bottle is 100% inside the bottle at 37℃.
RH, 2.4cc/m ² 24H・atm under external 20%RH condition
In a single polyethylene terephthalate bottle of the same weight and shape, the oxygen permeability is 9.8cc/
m ² ·24H ·1 atm, and the oxygen permeability of the bottle of the present invention was about 1/4 that of a bottle made of PET alone.

Comparative example Extruder for outer layer and extruder for inner layer with built-in full-flight screw with diameter of 65 mm and effective length of 1430 mm, extruder for middle layer with built-in full-flight screw with diameter of 5.0 mm and effective length of 1100 mm machine,
Using a three-layer ring die, the inner and outer layers are made of polyethylene terephthalate with an intrinsic viscosity of 0.75, the middle layer is an ethylene-vinyl alcohol copolymer with a vinyl alcohol content of 60 mol%, and the thickness ratio of each layer is determined: outer layer: middle layer : Outer diameter with inner layer as 100:20:50
A pipe with a diameter of 30.3 mm and a thickness of 3.8 mm was coextruded 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. The thickness ratio of the intermediate layer of this pipe was approximately the same over the entire length.
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 molded into a blow molding mold. Biaxial stretch blow molding was performed in a mold to obtain a multilayer stretched bottle with an internal volume of 1000 c.c.

The ratio of the thickness of the body and shoulder to the thickness of the bottom of the middle layer EVOH of this bottle C _C /C _B = 0.3 and
C _S /C _B =0.2.

When this bottle was subjected to the same test as in Example 1, the delamination strength was as low as about 20 g/1.5 cm width, and blisters were generated on the shoulders, reducing the product value. The pinch-off part was damaged.

[Brief explanation of drawings]

FIG. 1 shows a plastic container according to the invention;
Figure -A, Figure 2-B, Figure 2-C, and Figure 2-D are cross-sectional views of the bottom, body, shoulder, and base of the neck of the container in Figure 1, and Figure 3 is co-injection molding. 4 is a chart showing the relationship between injection time and injection pressure, 5-A to 5-I are explanatory diagrams showing the injection process, and 6 and 7 are sectional views of the main parts of the machine. FIG. 2 is a sectional view of main parts of a stretch blow molding machine. 1...Plastic container, 2...Neck, 3...
Body, 4... Bottom, 5... Shoulder, 11... Injection mold, 12... Core mold, 17, 18... Injection machine,
23, 24... Hot runner, 30... Polyester, 31... Ethylene-vinyl alcohol copolymer, 35... Preform, 37a, 37b
...Blow mold.

Claims (1)

[Scope of Claims] 1. Comprised of a laminate consisting of inner and outer surface layers of oriented, creep-resistant resin and an intermediate layer of gas barrier resin, and includes a torso, an opening connected to the torso through the shoulders, and a closed bottom. In the plastic container, the oriented, creep-resistant resin inner and outer surface layers are continuous in the planar direction over the entire area of the container, and the gas barrier resin intermediate layer is continuous in the planar direction from at least the bottom to the shoulder. The resin layer is continuous with the inner and outer surface layers and is completely enclosed between the inner and outer surface layers, and each resin layer has molecular orientation in biaxial directions at least in the container body, and the thickness ratio of the intermediate layer to the entire container wall is A multilayer plastic container characterized by having a tendency to be smallest at the center and gradually become larger toward the upper part of the body. 2. Claim 1, characterized in that the intermediate layer has a distribution structure that is biased toward the innermost surface at the center of the bottom and toward the center between the inner surface and the outer surface as it moves toward the upper part of the trunk. Plastic containers as described in section. 3. The plastic container according to claim 1 or 2, wherein the oriented creep-resistant resin is a thermoplastic polyester and the gas barrier resin is an ethylene-vinyl alcohol copolymer.