JPS6228332A - Multilayer gas barrier polyester vessel and manufacture thereof - 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] The present invention relates to a stretched multilayer plastic container and a method for manufacturing the same. The present invention relates to a biaxially oriented plastic container with a laminated structure that has excellent moisture resistance as well as a method for manufacturing the same.

Furthermore, the present invention also relates to the reuse of scrap produced as a by-product during container manufacturing.

Polyester containers produced using conventional and modern stretch blow molding methods have excellent transparency, moderate rigidity, and are suitable for liquid detergents.

In addition to shampoo, cosmetics, soy sauce, sauces, etc.

It has come to be widely used in containers for charcoal drinks such as beer, cola, and cider, as well as soft drinks such as fruit juice and mineral water.

This stretched polyester container is said to have superior gas permeability compared to general-purpose resin containers such as polyethylene and polypropylene [7], although metal bottles and glass bottles have almost zero gas permeability. On the other hand, it has a non-negligible permeability to oxygen and charcoal gases, and the storage period of the contents is limited to a relatively short period.

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, ethylene-
#I adhesion cannot be obtained between a gas barrier resin such as vinyl furfur copolymer and a polyester layer.
There is a tendency for peeling to occur during stretch molding, or even in other cases, peeling to occur due to drop impact, etc., and further troubles such as pinholes, cracks, and breaks in the gas layer.

Another problem is that it is difficult to completely encapsulate a gas-heral resin such as an ethylene-vinyl alcohol copolymer in a continuous manner in a substantial portion of the container without exposing it to the inner and outer surfaces of the container. When the ethylene-vinyl alcohol copolymer is exposed on the surface, the copolymer absorbs moisture and gas barrier performance is significantly reduced.

Furthermore, in the manufacturing of preforms and the stretching process thereof, a proportion of non-defective products are produced, and it is desirable to reuse the scraps of these defective products for containers.

SUMMARY OF THE INVENTION The present invention relates to the production of containers by stretch-blow molding a multilayer preform consisting of inner and outer surface layers of polyester resin and an inner layer made of gas barrier resin such as ethylene-vinyl alcohol copolymer. In this process, scrap resin, which is a mixture of polyester, gas barrier resin, and polyester and gas barrier resin, is used as the inner and outer layers of polyvarnish, the middle layer of gas barrier resin, and the intervening layer of scrap resin between both elbows. When making a multilayer preform by co-injecting the polyester into a multi-layer preform, it not only becomes possible to reuse the scrap as a container, but also improves the delamination properties between the polyester and the gas barrier layer. It was discovered that it acts effectively as a moisture barrier.

Ta.

OBJECTS OF THE INVENTION An object of the present invention is to provide a multilayer stretched plastic container made of a single layer of polyester-gas lining, which solves the above-mentioned problems, and a method for producing the same.

Another object of the present invention is to provide a multilayer stretched plastic container and a method for manufacturing the same, in which scrap (2 ton rig) made of a mixture of polyester and gas-resistance resin can be effectively utilized for manufacturing the container.

Still another object of the present invention is to provide a multilayer stretched plastic that has excellent gas barrier properties, moisture resistance, and delamination properties.

The present invention provides a container and a manufacturing method thereof.

According to the present invention, there is provided a multilayer plastic container formed by stretch blow molding of a multilayer plastic preform by co-injection and having a body portion with a mouth monomolecule oriented and a closed bottom portion, the container being made of ethylene terephthalate. It was provided with inner and outer layers made of polyester mainly composed of units, an intermediate layer of gas barrier resin, and between the inner layer and the middle 11J1 layer and between the middle layer and the outer layer. Provided is a container comprising a blank layer made of a mixture of polyester and a gas barrier resin, wherein the gas barrier resin intermediate layer and the scrap layer are completely enclosed between the inner and outer layers. .

According to the present invention, a multilayer preform is manufactured by co-injecting a polyester mainly containing ethylene terephthalate and a gas barrier resin, and the multilayer preform is stretched in a blow mold. In a method for manufacturing multilayer plastic containers consisting of blow stretch molding at high temperatures, a portion of the required polyester resin is placed in an injection mold with a cavity corresponding to the preform and a gate at the top corresponding to the bottom of the preform. Inject and fill the cavity halfway with the resin; midway through, after the primary injection, or a short time after the primary injection, the gas barrier resin is placed in a multilayer sandwiching the gas barrier resin. A scrap resin consisting of a mixture of the polyester and a gas barrier resin is co-injected to spread the gas barrier resin and the scrap resin toward the tip of the cavity; before the cavity is filled with resin. Stopping the injection of the scrap resin and the gas barrier resin, and performing secondary injection of the polyester to encapsulate the gas barrier intermediate layer and the scrap resin layer in the polyester;
This provides a fully featured method for forming multilayer preforms.

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

Container Structure and Effects In FIG. 1 showing the overall arrangement of the stretched multilayer plastic container of the present invention and FIG. 2 showing its partial sectional view structure,
Does this container l have a thick mouth part (nozzle part)? , thin body part 3
and a closed bottom part 4, and a frustum-shaped shoulder part 5 exists between the IH part 3 and the mouth part 2 to connect them.

This container consists of an inner layer 6 and an outer layer 7 made of a polyester resin having orientation and creep resistance, and an intermediate layer 8 of a gas barrier resin such as an ethylene-vinyl alcohol copolymer completely encapsulated therebetween. and scrap resin layers 9a and 9b inserted between the intermediate layer 8 and the outer layer 7. The intermediate layer 8 and the scrap resin layers 9a and 9b are shown in FIG. As is clear from the fact that each part above is uniform, no part of the wall is exposed to the surface, and the bottom, cave,
It is present as an intermediate layer and a scrap layer over all of the 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.

In the present invention, by providing a scrap layer between the inner and outer polyester layers, which have excellent creep resistance and other mechanical properties, and the gas barrier intermediate layer, it is possible to have a negative effect on the above properties of the inner and outer layers and the intermediate layer. This means that scraps can be effectively used as container materials without any negative impact.

Moreover, this scrap layer is made of a composition mainly composed of polyester and containing an ethylene-vinyl alcohol copolymer used as a gas barrier layer.

Therefore, according to the present invention, by interposing this resin composition within or between the polyester layer and the gas barrier intermediate layer, the resin composition can be applied to both the polyester layer and the gas barrier intermediate layer. Name vs. 1. It exhibits strong adhesion and has the effect of significantly improving the delamination resistance between both phase resin layers. Furthermore, it is known that the gas permeability of ethylene-vinyl alcohol copolymers to oxygen, carbon dioxide, etc. increases by one order of magnitude under high moisture absorption conditions. For this reason, in a multilayer container including an ethylene-vinyl alcohol copolymer layer, it is necessary to take measures to prevent the ethylene-vinyl alcohol copolymer layer from absorbing moisture as much as possible. In the present invention, between the ethylene-vinyl alcohol copolymer layer and the polyester layer.

By interposing a scrap layer of a composition containing polyester and an ethylene-vinyl alcohol copolymer, water vapor that permeates through the polyester layer and enters the ethylene-vinyl alcohol copolymer dispersed in the scrap composition. It is effectively captured by the combined components, and the tendency of the gas barrier intermediate layer to deteriorate due to moisture absorption is effectively suppressed.

In addition, in the container of the present invention, the intermediate layer 8 and the scrap layers 9a, 9b are completely enclosed between the inner and outer layers 6, 7. There is a completely unexpected and novel fact that the adhesion between the inner and outer layers 6.7 made of polyester or the like is completely maintained to an extent that is unexpected from normal adhesion. That is,
As long as this container is kept in an integrated state, both resin layers exhibit a completely adhered appearance and behavior, and show no peeling phenomenon even when the container is subjected to a drop impact or is subjected to slight deformation. It was found that complete adhesion was maintained. The reason for this has not yet been elucidated, but the intermediate layer such as ethylene-vinyl alcohol copolymer is completely encapsulated between the inner and outer layers of creep-resistant resin such as polyester, and the airtightness between the two phase resin layers is improved. It is also relevant to ensure that the inner layer and/or the outer layer of polyester are subjected to the clamping force of the inner layer and/or outer layer of polyester, and that the inner and outer layers of polyester and the intermediate layer are This is thought to be due to the fact that the bond between the two resin layers is made by a scrap layer that also serves as an adhesive, and the adhesion effect due to the molecular orientation of both resin layers.

Further, in the container of the present invention, the gas barrier resin layer, such as an ethylene-vinylfluorcopolymer copolymer, is effectively stretched together with the inner and outer polyester layers so that the molecules are oriented in one plane. 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
This is a small value of 1/5 to 1/17T7. It is known that ethylene-vinylfluor resin is one of the resins that is difficult to stretch, and if it is stretched in the form of a single layer, that is, if it is stretched under normal molding conditions, it will break. (Japanese Patent Publication No. 57-42493), tf is a laminate in which an ethylene-vinyl alcohol copolymer is sandwiched between stretchable resin layers, and if the laminate is stretched, it becomes an ethylene-vinyl alcohol copolymer. It is known that molecular orientation of the combined layer can be imparted, but in this case, it is essential to firmly bond the ethylene-vinyl alcohol copolymer and the stretchable resin layer, otherwise Ba,
It is said that rupture of the ethylene alcohol copolymer layer occurs (Japanese Patent Application Laid-open No. 103-481-1981).
Even when only the inner surfaces are bonded between the vinyl alcohol copolymer layer and the polyester layer, molecular orientation is effectively imparted to the ethylene-vinyl alcohol copolymer layer. This 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 (/!+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 with no defects is due to the fact that the bow part of the container III is cut in the thickness direction and the copolymer layer is removed from the polyester outer layer. Confirmed by. Moreover, by this peeling, the distribution or distribution structure of each layer and the presence or absence of a predetermined molecular orientation can be confirmed.

In the specific example shown in FIG. 2, the present invention has a three-type, five-layer structure in which scrap layers 9a and 9b are provided between the inner and outer shuttles 6, the outer layer 7, and the intermediate layer 8.

Polyethylene terephthalate (PET) is used as the inner and outer layers of the material.
is preferably used, but copolyesters mainly composed of ethylene terephthalate units and containing other polyester units may also be used as long as the wood quality of polyethylene terephthalate is not impaired. Copolymerization components for forming such a copolyester include inphthal #, P-β-oxydiethoxybenzoic acid, naphthalene 2,6-dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, and 5-sodium sulfoisophthalene. Acid, adipic acid, dicarboxylic acid components such as sebacic acid or their alkyl ester derivatives, propylene glycol, 1,4-butanediol,
Neopentyl glycol/1,6-hexyl glycol φ cyclohexane dimetatool/bisphenol A
ethylene oxide adduct, diethylene glycol,
Mention may be made of glycol components such as triethylene glycol.

The thermoplastic polyester used has an intrinsic viscosity [η] of 0.5 or more in terms 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.

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 gas barrier resin layer. That is, the ethylene-vinyl alcohol copolymer is one of the resins with the best gas barrier properties, and its gas barrier properties and moldability depend on the vinyl alcohol unit content. When the vinyl alcohol content is less than 40 mol%, the permeability to # and carbon dioxide gas is greater than when it is within the above range, and the objective of the present invention, which is to improve gas barrier properties, is not met. On the other hand, if this content exceeds 85 mol%,
Since the permeability to water vapor increases and the melt formability decreases, it is also not suitable for the purpose of the present invention.

The ethylene-vinyl alcohol copolymer is obtained by saponifying a copolymer of ethylene and a vinyl ester such as vinyl butyrate so that the degree of saponification is 96% or more, particularly 99% or more. In addition to the above-mentioned components, this copolymer may also contain propylene, butylene-1, imbutylene, etc., in an amount of up to 3 mol%, within a range that does not impair the barrier properties to oxygen, carbon dioxide, etc. It may contain three or more olefins as a co-scientific component.

The molecule m 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, 30"O The intrinsic viscosity [
η] is preferably in the range of 0.07 to o, 171ag.

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

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 fEW. For this purpose, it is preferable to use a combination of polyester and ethylene-vinyl alcohol copolymer having a difference in structural viscosity index in the range of 0.01 to 1Ol, especially 0.05 to 5.

In this specification, the structural viscosity index is 10 at a temperature 5° C. higher than the higher melting point of both resins.
It is a value determined from the flow curve of the melt at a shear rate of 0 sec-1 or more, and more specifically.

Plot the values with the log value of shear stress (Kg/cm2) on the vertical axis and the log value of shear rate γ (5ec-1) on the horizontal axis, and from the straight line approximated to this curve, the formula log
τ=−'−−1og? is the value α found as α of .

If the difference in the structural viscosity index is smaller than the above range, the two side resin layers will be mixed during co-injection, which will be described later, and the ethylene-vinyl alcohol copolymer layer will be clearly differentiated in the preform. It becomes difficult to form a continuous and complete layer of coalescence. 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 a melt depends on the molecular weight, molecular weight distribution, and chemical structure of the resin. In the present invention, the structural viscosity index can be adjusted by selecting the molecular weight and molecular weight distribution of the polyester and ethylene-vinyl alcohol copolymer used. The difference can be within the ranges described above.

As scrap resin (regrind), used are defective products, scraps, etc. produced in the manufacturing process of multilayer preforms and the stretch blow molding process of multilayer preforms. This scrap resin has a certain composition ratio depending on the layer structure of polyester and ethylene-vinyl alcohol copolymer. The ratio is in the range from 99:1 to 50:50, in particular from 20:1 to 30:1.

To reuse scrap resin, crush the scrap and dry the resulting chips. That is, under conditions where the ethylene-vinyl alcohol copolymer in the scrap absorbs moisture, significant deterioration of the copolymer occurs during melt injection of the resin. In order to prevent this, the scrap resin is dried so that the moisture content in the scrap resin is 0.5% by weight or less, and 0.05% by weight or less.

This scrap resin is used for co-injection in the form of chips or after being pelletized if necessary.

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 gage 14 is located at a position corresponding to the bottom of the preform of the mold 11, and is connected via a hot runner nozzle 15 and a hot runner block 16 to injection machines 17, 18, 29A, and 29B of the die. The main injection machine F is for polyester injection, and is equipped with a barrel 9 and a screw 20 inside it.The first sub-injection machine 18 is for injection of ethylene-vinyl alcohol copolymer, and has a barrel 21 and its internal screw 20. It is equipped with an internal screw 22. The second sub-injection machine 29A is for injecting scrap resin on the outer layer side, and is equipped with a barrel 30A and a screw 31A inside the barrel 30A. Furthermore, the third sub-injection machine 29B is for injecting the inner layer side scrap resin, and is equipped with a barrel 30B and a screw 31B inside the barrel 30B. The block 16 and the nozzle 15 include a hot runner 23 with an annular cross section for injection of ethylene-vinyl alcohol copolymer, and a hot runner 24 (32B) for injection of polyester (scrap resin) located at the center thereof. A hot runner for scrap resin injection located on the outermost periphery and having a large diameter annular cross section.
'32A, which are coaxial and arranged so as to merge near the tip of the nozzle 15. The main injection machine is
The second sub-injection machine 18 is connected to the hot runner 24 via a sprue bush 26 and a sprue 26A, while the second sub-injection machine 18 is connected to the hot runner 24 via a sprue bush 28 and a sprue 27.
3, the scrap resin injection machines 29A, 29B are connected to sprue bushes 33A, 33B and sprue 34A.

It is connected to hot runners 32A and 32B via 34B. Furthermore, a rotary valve 45 is installed at the confluence of the flow path for polyester injected from the main injection machine 17 and the flow path for scrap resin injected from the third sub-injection fi29B.
is provided so that both resins can be switched as appropriate. The resin to be injected is melted into the barrel 19 (21 or 3OA, 30B).

After the molten resin is stored in the barrel barrel 19 (21 or 30A, 30B) by rotation of the screw 20 (22 or 31A, 31B), the screw 20 (22 or 31A, 31B) is advanced to transfer the molten resin to the sprue 26a (28 or 34A). ,
34B), hot runner-23 (24 or 32A, 32
B) and injection into the cavity 13 through the gate 14. According to the present invention, the injection of polyester, ethylene-vinyl alcohol copolymer and scrap resin is carried out under the following conditions.

In FIG. 4 showing the relationship between injection time and injection pressure for polyester (PET) ethylene-vinyl alcohol copolymer (EV OH) and scrap resin, alphabetical symbols A to G in the figure are as follows.

This corresponds to the explanatory diagrams in FIGS. 5-A to 5-G.

First, advance the polyester injection screw 20,
The primary injection is made into the cavity 13 under constant pressure. 7th
Figure -A shows the state of polyester just before injection, with polyester 35 at the tip of nozzle 15, but ethylene-
Vinyl alcohol copolymer 36 is placed at the tip of hot runner 24, and scrap resin 37A is placed at the tip of hot runner 3.
They each stay at the tip of 2A. As the polyester is injected, the cavity 13 is filled up to the middle with the primary injected polyester 35, as shown in FIG. 5-D.

At the stage when a predetermined amount of polyester has been injected (during the injection of polyester, immediately after the end of the injection, or after a short period of time after the end of the injection), the screw 32B for injecting the scrap resin is advanced. The screw 22 for ethylene-vinyl alcohol copolymer injection and the screw 32A for scrap resin are also advanced, and the ethylene-vinyl alcohol copolymer 3 is injected into the cavity 13.
6 and scrap resins 37A and 37B are injected. In this case, as shown in Figure 5-0, on the surface of the cavity 13, the primary injection polyester 35 is solidified due to contact with the mold, or even if it is not solidified, the viscosity is extremely high. Therefore, the injected ethylene-vinyl alcohol copolymer 36 and scrap resins 37A, 37B flow toward the tip of the cavity along approximately the center plane of the polyester filled layer, and the intermediate layer of the copolymer flows toward the tip of the cavity. form.

In this case, it is preferable to inject the ethylene-vinyl alcohol copolymer at the same time as the scrap resin, so that the ethylene-vinyl alcohol copolymer can be used as an intermediate layer to form a completely continuous layer.

5-D and 5-E show a state in which the ethylene-vinyl alcohol copolymer 36 and the scrap resins 37A and 37B are continuously injected. As shown in FIG. 5-F, before the cavity 13 is filled with resin, the injection of the scrap resins 37A and 37B is first stopped, and then the ethylene-vinyl alcohol copolymer 36 is injected, and the polyester 38 is injected. Secondary injection is performed. As shown in FIG. 5-G, secondary injection effectively enlarges the ratio of the ethylene-vinyl alcohol copolymer intermediate layer 36 and scrap resin layers 37A and 37B in the vicinity of the preform tip. At the same time, the area near the gate and the tip of the nozzle is
The virgin polyester 38 is filled to provide complete containment of the ethylene-vinyl alcohol copolymer interlayer 36 and scrap layers 3.7A, 37B within the preform, as well as virgin polyester for the next injection cycle. It will be prepared within the nozzle 15.

In addition, scrap resin 37B and secondary injection polyester 3
8 is performed at an arbitrary timing, and if this switching timing is early, the secondary injection polyester also stretches the ethylene-vinyl alcohol copolymer 36 toward the tip.

According to the present invention, scrap resin is injected between the inner and outer layers of the primary injection polyester and the ethylene-vinyl alcohol copolymer layer, and finally the ethylene-vinyl alcohol is injected into the vicinity of the tip of the preform by secondary injection of the polyester. It is possible to extend it until At this time, the intermediate layer of ethylene-vinyl alcohol copolymer has a preferable distribution structure which is sufficiently thin so as to be suitable for the stretching operation and is biased towards the inner surface side of the vessel wall rather than the center plane. Also, ethylene
It becomes possible to completely confine the vinyl alcohol copolymer intermediate layer and the scrap layer between the polyesters.

In the present invention, the primary injection pressure of polyester is PI, the injection pressure of ethylene-vinyl alcohol copolymer is P2,
When the injection pressure of the scrap resin is P3 and the secondary injection pressure of the polyester is P1, these pressure conditions can be varied quite widely.

Generally speaking, it is advantageous for the injection pressure P2 of the ethylene-vinyl alcohol copolymer to be higher than the primary injection capacity I of the polyester in order to form the ethylene-vinyl alcohol copolymer as a completely continuous phase. , while scrap resin injection pressure P3 and polyester secondary injection pressure P
It is clear that 4 is much lower than the primary injection volume of the polyester, which is advantageous in order to form a continuous intermediate layer.

PI, P2. P3. It is desirable that Pl has the following relationship.

P+ = 80 to 80 Kg/cm2 (gauge pressure).

Pn=80 to 110Kg/c+w2 (gauge pressure)
and a pressure of 1.2 to 1.8 times that of Pl.

P3 *Pa = 20 to 50 Kg/cm2 (gauge pressure), a pressure 0.3 to 0.8 times the anal PI.

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

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 scrap resin injection and the amount of secondary injection of polyester are closely related to the degree of deviation of the ethylene-vinyl alcohol copolymer intermediate layer from the center of the thickness of the preform toward the inner surface side. is connected with.

In the present invention, since the ethylene-vinyl alcohol copolymer intermediate layer is quite thin compared to the overall thickness, the cavity volume is V, the primary injection capacity of the polyester is vl, and the secondary injection capacity of the polyester is V2,
The injection capacity of ethylene-vinyl alcohol copolymer is V3
, when the injection capacity of scrap resin is v4, v3
is set to 1 to 20% of V, especially 5 to 10%, and VI is set to 5% of V.
30%, especially 10 to 20%, v3 1 to 5
0%, especially 4 to 8%, V4 10 to 70%, especially 2
It is desirable to set it to 0 to 40%.

That is, when the value of V3 is smaller than the above range, it tends to be difficult to significantly improve the gas barrier properties of the container, and when the value of V3 is larger than the above range,
If the eVl ratio is smaller than the above range, the ethylene-vinyl alcohol copolymer will be exposed on the surface of the preform, which will lead to the disadvantages of reduced stretch-blowing properties of the preform and increased cost of the container. On the other hand, if the ratio of Vl is larger than the above range, it is difficult to spread the ethylene-vinyl alcohol copolymer as an intermediate layer over the area of the substantial portion of the preform. becomes. When the value of v2 is smaller than the above range, it tends to be difficult to contain the ethylene-vinyl alcohol copolymer layer and the scrap resin layer.

According to the method of the present invention, the thus obtained multilayer preform having the structure shown in FIG. 5-G is subjected to stretch blow molding.

Prior to this stretch blow molding, the multilayer preform is first heated to a temperature at which the polyester can be stretched, generally from 80 to 135°C.
The temperature is maintained at 0.degree. C., especially between 90 and 125.degree. This temperature control process involves supercooling the polyester layer of the multilayer preform so that it is maintained in a substantially non-solidified state ff1f (amorphous state), and then using a heating method known per se such as hot air, an infrared heater, or a high-frequency dielectric heating. By mechanism.

This can be done by heating the multilayer preform to the above temperature, or it can be cooled or allowed to cool in the injection mold or within the mold until the temperature of the multilayer preform reaches the above temperature. It can also be done by

In FIGS. 6 and 7 for explaining the stretch blow molding operation, a mandrel 41 is inserted into the mouth of the bottomed multilayer preform 40, and the mouth is inserted into the pair of ratio molds 4.
It is held between 2a and 42b. A vertically movable stretching rod 43 is provided coaxially with the mandrel 41, and this stretching rod 4
3 and the mandrel 41 there is an annular passage 44 for fluid injection.

The tip 39 of the stretching rod 43 is applied to the inside of the bottom of the preform 45 and the stretching rod 43 is moved downward to perform axial stretching, and at the same time, fluid is introduced into the preform 40 through the passage 44. 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 described in detail later, but for this purpose, the stretching ratio in the container axial direction must be 1.2 to 10 times, particularly 1.5 to 5.
It is desirable to double the amount.

The molecular orientation of the polyester layer can be easily confirmed by a fluorescence polarization method, a birefringence method, a density method, etc., but can be easily evaluated by a density method. Generally speaking, the density of polyester at 20°C in the thinnest interior of the body is 1.34 to 1.39.
g/c+m3. Especially 1.35 to 1.38g/c+m3
If it is within the range of , it can be said that the molecular orientation has been carried out effectively.

Because the container of the present invention has the above-mentioned outstanding characteristics, it is useful as a container for various contents, especially as a lightweight container that blocks the permeation of oxygen, carbon dioxide gas, or aroma components. , cola, cider, carbonated fruit juice drinks, carbonated alcoholic beverages, etc., and has the advantage of significantly less carponation loss compared to known containers.

衷-Ren-3 The invention is illustrated by the following example.

Example 1 Using the injection molding machine shown in Fig. 3,
Co-injection molding of the multilayer preform was performed at the injection timing shown in Figures 5-5 to 5-G.

First, dried virgin polyethylene terephthalate (PET) with an intrinsic viscosity of 1.0 is supplied to the main injection fi 17, and dried ethylene with an ethylene content of 70 mol% is supplied to the first sub-injection machine 18. - A pellet of co-vinyl alcohol (EVOH) was supplied.

On average 97% by weight polyethylene terephthalate and 3f
Scraps from multi-layer preforms and stretched bottles containing ethylene-vinyl alcohol copolymer with an average chip size of 2 cm were chipped with a moisture content of 0.5%. After drying to 0.01% or less.

It was supplied to the second and third sub-injection molding machines.

The injection pressure and injection time were as follows, and the wall thickness was 3.5 m.
A bottomed preform having a multilayer structure of 3 types and 5 layers of m was manufactured.

Time 7 seconds Scrap resin injection pressure LOOKg/cm2 hours 6.5 seconds PET secondary injection pressure 60 Kg/cm2 hours 0.5 seconds.

The obtained multilayer preform was preheated to a temperature of about 110° C. and biaxially stretched blow molded to double the length and quadruple the circumferential direction to produce a multilayer bottle with an internal volume of 1500 cm.

The resulting multilayer bottle has a body, bottom and shoulders made of PET.
It has a layer structure of outer layer/scrap resin layer/EVOH intermediate layer/scrap resin/PET inner layer, and the results of an iodine adsorption test on the inner and outer surfaces of the bottle show that the EVOH layer and scrap resin layer are not exposed at all on the inner and outer surfaces of the bottle. It was confirmed that the sample was completely encapsulated.

Furthermore, the volume fraction of the scrap resin layer in this multilayer preform, and hence the multilayer bottle, was 40%, indicating that the scrap resin can be effectively used for manufacturing the multilayer bottle.

The results of filling this bottle with tap water and subjecting it to a drop impact test from a height of 1.5 mm, and the results of filling it with carbonated water at a pressure of 4 kg/am2 and storing it for 14 days, showed no tendency to peel off at all. There wasn't.

Comparative Example 1 For comparison, Example 1 was repeated except that PET was secondarily injected without injecting scrap resin in Example 1 above.
A three-layer multilayer bottle was manufactured in the same manner as above.

For each multilayer bottle of Example 1 and Comparative Example 1 obtained, 3
Oxygen permeability at 7°C, RHO%, 37°C, ioo
The oxygen permeability was measured under conditions of %RH and the obtained results are shown in Table 1. Also, the height of the tap water filling container was 1.5 m.
The number of pieces that were damaged or delaminated in the drop impact test was compared.

Furthermore, 20 panelists were used to judge the appearance characteristics, and the number of people who judged the appearance to be good was expressed.

The results are shown in Table 1 below.

Table 1

[Brief explanation of drawings]

FIG. 1 is a side sectional view of a plastic container according to the present invention. FIG. 2 is an enlarged sectional view of the container shown in FIG. 1, FIG. 3 is a sectional view of essential parts of a co-injection machine used in the manufacturing method of the present invention, and FIG. 4 is a time chart of co-injection. 5-A,
Figure 5-B, Figure 5-0, Figure 5-D, Figure 5-E, Figure 5-F and Figure 5-G, injection of each resin into the gearbity in relation to Figure 4. FIG. 7 is an explanatory diagram illustrating the state, and FIG. ■ is a plastic container, 2 is the neck, 3 is the body, 4 is the bottom,
5 layer parts, 6 is a polyester inner layer, 7 is a polyester outer layer, 8 is an ethylene-vinyl alcohol copolymer intermediate layer, 9
A, 9B are scrap resin layers, 11 is an injection mold, 12 is a core mold, 17.18.29 is an injection machine, 23, 24.3
2 is true runner, 35.38 is polyester, 36
is ethylene-vinyl alcohol copolymer, 37A, 37
B is scrap resin, 40 is preform, 42a, 4
2b is a blow mold.

Claims (2)

[Claims] (1) A multilayer plastic container formed by stretch blow molding of a multilayer plastic preform by co-injection and having a mouth, a molecularly oriented body, and a closed bottom, the container being made of polyester mainly containing ethylene terephthalate units. , a gas barrier resin intermediate layer, and a scrap layer made of a mixture of polyester and gas barrier resin provided between the inner layer and the intermediate layer and between the intermediate layer and the outer layer. A container characterized in that the intermediate resin layer and the scrap layer are completely enclosed between the inner and outer layers. (2) A multilayer preform is produced by co-injecting polyester mainly composed of ethylene terephthalate units and a gas barrier resin, and this multilayer preform is blow stretch-molded in a blow mold at a temperature that allows stretching. In the method for manufacturing a multilayer plastic container, a part of the required polyester resin is injected into an injection mold having a cavity corresponding to the preform and a gate at a position corresponding to the bottom of the preform, and part of the polyester resin is injected halfway into the cavity. Fill with the resin; during, after, or a short time after the primary injection, the gas barrier resin, and the polyester and gas barrier resin arranged in a multilayer sandwiching the gas barrier resin. The gas barrier resin and the scrap resin are spread toward the tip of the cavity by co-injection with a scrap resin consisting of a mixture of A method comprising: stopping and secondary injection of the polyester to encapsulate the gas barrier intermediate layer and the scrap resin layer in the polyester, thereby forming a multilayer preform.