JPH0451333B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing a multilayer stretch-molded container, and more specifically, it relates to a method for manufacturing a multilayer stretch-molded container, and more specifically, a method for manufacturing a multilayer stretch-molded container, which is made of a multilayer stretch-molded container made of inner and outer surface layers made of thermoplastic polyester and an intermediate layer made of gas barrier resin. The present invention relates to an improvement in a method for manufacturing containers comprising stretch-blow molding a multilayer plastic preform.

(Conventional technology) Polyester containers made by stretch blow molding are
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 negligible compared to cans and bottles whose gas permeability is almost zero. It has no oxygen or carbon dioxide permeability,
The shelf life of the contents is limited to a relatively short period.

In order to improve this drawback, it is possible to improve the gas barrier properties of containers by combining polyester with gas barrier resins such as ethylene-vinyl alcohol copolymers and xylylene group-containing polyamides to create a multilayer structure. Various proposals have been made.

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. It has been known.

(Problems to be Solved by the Invention) When forming a multilayer preform by co-injection molding, a layer structure is generally adopted in which the inner and outer surface layers are thermoplastic polyester and the intermediate layer is a gas barrier resin. Injection molding method (Japanese Patent Application Laid-Open No. 1983-
2773), it is recognized that certain drawbacks arise regarding the thickness distribution of each layer within the multilayer preform.

That is, the position of the gas barrier layer (intermediate layer) in the thickness direction at the bottom of the preform is biased inward,
The thickness of the inner surface layer polyester is significantly reduced at the bottom. For example, the ratio of the thickness of the outer surface layer (A) to the thickness of the inner surface layer (B) is A:B = 2:1 at the body, but it becomes A:B = 5:1 at the bottom. In addition, the thickness of the bottom inner surface layer is significantly reduced.

The reason for this is that in the injection mold cavity,
This is thought to be because the gate through which the molten resin flows is provided at the bottom, and therefore the bottom is at a high temperature in other parts, and the resin on the inner surface of the bottom is also subjected to pressure that causes it to flow to other parts. .

When the bottom inner surface layer becomes thinner in this way, the inner surface layer becomes even thinner during stretch blow molding, and in severe cases, there is a tendency for the gas barrier layer to be exposed to the inside, causing moisture absorption of the gas barrier layer from the contents. This may increase the gas permeability of the intermediate layer or cause delamination between the intermediate layer and the polyester layer.

In order to avoid the above-mentioned drawbacks in stretch blow molding of a multilayer preform, a multilayer preform in which a gas barrier intermediate layer is located between the inner and outer surface layers of uniform thickness over all parts of the body and the bottom has been developed. However, due to the problems mentioned above, the production of such multilayer preforms is difficult in the case of co-injection methods.

Therefore, an object of the present invention is to manufacture a multilayer preform used for manufacturing a multilayer stretch blow-molded container by co-injection molding, so that the thickness ratio between the polyester inner surface layer and the polyester outer surface layer is maintained at any part of the preform. The object of the present invention is to provide a method for forming a multilayer preform having a structure in which a gas barrier resin layer is encapsulated between the inner and outer surface layers of polyester.

(Means for Solving the Problems) According to the present invention, the inner and outer surface layers of thermoplastic polyester mainly composed of ethylene terephthalate units, and the intermediate layer of gas barrier thermoplastic resin located between the inner and outer surface layers. A method for producing a multilayer stretch molded container comprising stretch blow molding a multilayer plastic preform comprising: a thermoplastic polyester for the inner surface layer in a solid stream; a thermoplastic polyester for the inner surface layer; Outer annular flow, corresponding to thermoplastic polyester
The gas barrier resin corresponding to the intermediate layer is co-injected translationally into the injection mold via a hot runner and gate as an inner annular flow located between the solid flow and the outer annular flow, and this co-injection At this time, the injection timing of the gas barrier resin corresponding to the intermediate layer is
Compared to the injection timing of thermoplastic polyester, the injection timing is controlled to be slightly slower at the beginning of injection and slightly earlier at the end of injection, so that the ratio of the thickness of the outer surface layer and the inner surface layer of the formed preform is A method is provided which is characterized in that any portion of the preform present is substantially equal and the preform is molded such that the uppermost mouth and the gate-receiving bottom portion of the preform consist essentially only of polyester.

(Function) In FIG. 1, which conceptually shows a simplified cross-sectional structure of a multilayer die used in the present invention, this multilayer die 1
The solid flow channel 2 for polyester corresponds to the inner surface layer of the multilayer preform, the outer annular flow channel 3 for polyester corresponds to the outer surface layer of the multilayer preform,
and an inner annular flow path 4 for gas barrier resin corresponding to the intermediate layer (gas barrier resin layer) of the multilayer preform is provided between these, and each of these flow paths 2, 3, and 4 is connected to an injection mold gate. (not shown)
It opens into a single hot runner nozzle 5 connected to the hot runner nozzle 5.

In the present invention, polyester for the inner surface layer,
The polyester for the outer surface layer and the gas barrier resin for the intermediate layer are injected translationally into the injection mold through the channels and gates of the hot runner. In this specification, "translationally injecting" means that each resin is injected simultaneously through each channel in a uniform state, and therefore means that the flow rate ratio between each resin is constant. .

Furthermore, in the present invention, the injection timing of the gas barrier resin for the intermediate layer is controlled so that it starts a little later at the beginning of the injection and ends a little earlier at the end of the injection compared to the injection timing of the polyester for the inner and outer surface layers. do.

Therefore, according to the present invention, since the injection flow rate of the polyester for the inner surface layer and the injection flow rate of the polyester for the outer surface layer are maintained constant over substantially the entire injection process, the preform to be formed is The thickness ratio of the outer surface layer to the inner surface layer of the preform will remain substantially the same wherever the intermediate layer is present. For example, the thickness of the outer surface layer at the center of the body is A, and the thickness of the outer surface layer at the bottom is A.
A', the thickness of the inner surface layer at the center of the body is B, and the thickness of the inner surface layer at the bottom is B', then the relationship of the formula A/B≒A'/B' holds true, especially A=B, A It is also possible to set ′=B′. Of course, since the injection flow rate of the gas barrier resin is constant, the thickness (C) of the intermediate layer is also constant at any part of the preform.

In addition, by shifting the injection start point of the gas barrier resin for the intermediate layer slightly later, it is possible to prevent the gas barrier resin from being exposed at the uppermost opening of the preform, and furthermore, the injection end point of the gas barrier resin can be slightly delayed. By shifting the preform quickly, the bottom part of the preform corresponding to the gate can be formed only of polyester, thereby preventing exposure of the gas barrier resin.

The injection of polyester prior to the injection of the gas barrier resin and the injection of polyester after the injection of the gas barrier resin may be performed with either the polyester for the inner surface layer or the polyester for the outer surface layer, or both may be You can turn around and go. As a preferred example, the pre-injection is carried out with the polyester for the inner surface layer and the post-injection is carried out with the polyester for the outer surface layer.

(Description of Structure) In FIG. 2 showing the schematic arrangement of the apparatus used to carry out the method of the present invention, an injection machine 6 for inner layer polyester, an injection machine 7 for outer layer polyester, and an injection machine 8 for intermediate layer gas barrier resin are shown. Each will be provided.
Each of these injection machines is connected to a corresponding runner 6b, 7b and 8b of the hot runner block 9 via their respective tip nozzle 6a, 7a, 8a, respectively. The hot runner nozzle 5 has a solid flow path 2 for the inner layer polyester at the center, an annular inner annular flow path 4 for the intermediate layer gas barrier resin around the solid flow path 2, and an outer annular flow path 3 for the outer layer polyester around the outer periphery. are located, and these channels are arranged to merge near the hot runner nozzle tip 10. In the multilayer die shown in FIG. 2, the first solid channel 2 corresponds to the injection of the inner layer of the preform, the inner annular channel 4 corresponds to the injection of the intermediate layer of the preform, and the outer annular channel 3 corresponds to the injection of the outer layer of the preform. be.
Although only one hot runner nozzle is shown in the hot runner block 9, it should be understood that a plurality of hot runner nozzles may be provided. A cavity mold 11 is provided above the block 9 and is integrally fastened thereto. The cavity mold 11 is provided with a cavity 12 whose axis extends in the vertical direction, and this cavity 12 is connected to the block 9 through a gate 13.
The hot runner nozzle 5 is connected to the hot runner nozzle 5. Naturally, the number of cavities 12 corresponding to the number of hot runner nozzles 5 are provided in parallel.

A core 14 that defines the inner surface of the preform during molding and a neck grip split mold (not shown) that defines the outer periphery of the preform mouth during molding are provided to be combined with this cavity mold 11 during injection molding.

In the present invention, polyethylene terephthalate is preferably used as the thermoplastic polyester (hereinafter sometimes simply referred to as PET) for the inner and outer layers, but ethylene terephthalate units may be used as long as the essence of polyethylene terephthalate is not impaired. Copolyesters based on and 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/diphenoxyethane-4,
Dicarboxylic acid components such as 4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, adipic acid, sebacic acid or their alkyl ester derivatives, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexylene Glycol, cyclohexanedimethanol,
ethylene oxide adduct of bisphenol A,
Glycol components such as diethylene glycol and triethylene glycol can be mentioned.

In terms of the mechanical properties of the vessel wall, the thermoplastic polyester used has an intrinsic viscosity () described below.
It is desirable that it be 0.5 or more, especially 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 one embodiment of the present invention, the gas barrier resin layer for the intermediate layer has a vinyl alcohol content.
It is important to use 40 to 85 mol %, especially 50 to 80 mol % of ethylene-vinyl alcohol copolymer. 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. The intrinsic viscosity () is 0.07 to 0.17/g as measured by
It is good that it is within the range of .

In another embodiment of the invention, a xylylene group-containing polyamide is used as the gas barrier resin for the intermediate layer. What is xylylene group-containing polyamide?
A polyamide containing m-xylylene diamine and/or p-xylylene diamine as a diamine component, more specifically 35 mol% of the diamine component.
Above, especially 50 mol% or more is m-xylylene and/or
or p-xylylene diamine, in which the dibasic acid component is an aliphatic dicarboxylic acid and/or an aromatic dicarboxylic acid, optionally containing up to 25 mol%, especially up to 20 mol% of ω-amino acid per total amide repeating unit. Contains carboxylic acid units.

Examples of diamine components other than xylylene diamine include aliphatic diamines such as hexamethylene diamine and alicyclic diamines such as piperazine, and examples of aliphatic dicarboxylic acids include adipic acid, sebacic acid, and suberin. Acid etc.
Further, examples of aromatic dicarboxylic acids include terephthalic acid and isophthalic acid. Further, examples of the ω-aminocarboxylic acid component include ε-caprolactam, aminoheptanoic acid, aminooctanoic acid, and the like. Examples of xylylene group-containing polyamides are:
Examples include, but are not limited to, polymethaxylylene adipamide, polymethaxylylene sebacamide, polymethaxylylene veramide, m-xylylene/p-
These include xylylene adipamide copolymer, m-xylylene adipamide/isophthalamide copolymer, m-xylylene adipamide/isophthalamide/ε-aminocaproic acid copolymer, and the like.

The xylylene group-containing polyamide used preferably has a relative viscosity (ηrel) of 0.4 to 4.5, measured using 96% by weight sulfuric acid at a concentration of 1 g/100 ml and a temperature of 25°C.

The gas barrier resin for the intermediate layer illustrated above is
It can be used alone or in the form of a mixture of two or more. Furthermore, in order to improve the adhesiveness with the inner and outer polyester layers, the intermediate layer can be injected by supplying a dry blend or melt blend with the adhesive resin to an injection machine for the intermediate layer.
Suitable examples of adhesive resins are aliphatic polyamide resins, especially copolymeric polyamides such as nylon 6/nylon 6,6 copolymer. The adhesive resin can be used in an amount of 1 to 100 parts by weight, particularly 5 to 50 parts by weight, per 100 parts by weight of the gas barrier resin.

First, during injection molding, each injection machine, hot runner block, and injection mold are in the state shown in FIG.

At this position, the screw of the inner layer injection machine 6 moves forward, and a small amount of polyester resin is injected into the cavity 12 through the nozzle 6a, the inner layer resin runner 6b, the solid channel 2 in the hot runner nozzle, and the gate 13. With a slight delay in timing, the screws of the outer layer injection machine 7 and the screws of the middle layer injection machine 8 are advanced. As a result, the outer layer resin is transferred to the nozzle 7a, the runner 7
b. The middle layer resin is supplied to the hot runner nozzle tip 10 through the outer annular flow path 3, and the intermediate layer resin is supplied to the nozzle 8.
a, runner 8b, and is supplied to the hot runner nozzle tip 10 through the inner annular flow path 4.

In FIG. 3, which shows the initial stage of injection, only the leading edge 15 of the resin flow is made of polyester, which includes a solid polyester flow 2a, an annular flow 4a of gas barrier resin around it, and a polyester annular flow 3a around it. A smooth multilayer resin flow is formed at the nozzle tip. Next, in FIG. 4 showing the progress of injection, this multilayer resin flow flows into the orifice in the injection mold, the polyester solid flow 2a forms the preform inner surface layer 16, and the polyester outer annular flow 3a forms the outer surface layer. It can be seen that the annular flow 17 and the gas barrier resin inner annular flow 4a form the preform intermediate layer 18. Further, by finishing the injection of the gas barrier resin immediately before the cavity 12 of the injection mold is filled with resin, it is possible to prevent the gas barrier resin from being exposed at the bottom corresponding to the gate.

The multilayer preform obtained by the co-injection molding method of the present invention is used for stretch blow molding into multilayer containers.

Prior to this stretch-blow molding, the multilayer preform is first heated at the stretchable temperature of the main resin layer, that is, the stretching temperature of polyester, generally 80 to 135°C, particularly 90°C.
Maintain temperature between 125°C and 125°C. This temperature adjustment process is
After supercooling so that the polyester resin layer of the multilayer preform is maintained in a substantially non-crystalline state (amorphous state), using a heating mechanism known per se such as hot air, infrared heater, high frequency dielectric heating, etc.
This can be done by heating the multilayer preform to the above temperature, or by cooling or leaving it to cool in the injection mold or the mold until the temperature of the multilayer preform reaches the above temperature. You can do it even if you have to.

In FIGS. 5 and 6 for explaining the stretch blow molding operation, a mandrel 21 is inserted into the mouth of a bottomed multilayer preform 20, and the mouth is held between a pair of split molds 22a and 22b. A vertically movable stretching rod 23 is provided coaxially with the mandrel 21, and the stretching rod 23 and the mandrel 2
1, there is an annular passage 24 for fluid suction.

The tip 25 of the stretching rod 23 is applied to the inside of the bottom 26 of the preform 20 and the stretching rod 23 is moved downward to perform tension stretching in the axial direction, and at the same time blow fluid into the preform 20 through the passage 24. The container 27 is formed by expanding and stretching the preform within the mold by this fluid pressure.

The degree of stretching of the preform is sufficient to impart molecular orientation to at least the main resin layer,
For this purpose, it is desirable that the stretching ratio in the axial direction of the container be 1.2 to 10 times, particularly 1.5 to 5 times.

The invention is illustrated in the following examples.

Example Intrinsic viscosity 0.9 for inner layer injection machine and outer layer injection machine
Polyethylene terephthalate (PET) will be supplied, and polymethaxylylene adipamide (PMR) will be supplied as a gas barrier resin to the injection machine for the intermediate layer.

At the beginning of injection, a part of molten PET is injected into the cavity from the inner layer injection machine, then molten PET is simultaneously injected from the inner layer injection machine and outer layer injection machine, and molten PMA is simultaneously injected from the middle layer injection machine, and at the end of injection. Molten PET is injected from the outer layer injection machine to create a wall thickness of 5.
A multilayer preform of 2 types and 3 layers of 3 mm was molded.

The thickness ratio of the inner layer: middle layer: outer layer of this preform is 4.5:0.9:4.6 in the upper part and 4.5: in the middle part.
1:4.5, 4.4:0.8:4.8 at the lower part (bottom),
The position and thickness ratio of the intermediate layer were almost uniform in each part of the preform.

This multilayer preform is heated to approximately 100°C and biaxially stretched blow molded to double the length and triple the width to create an inner volume.
I got a bottle of 1000c.c.

The middle layer was uniform in each part of the bottle.

Comparative Example According to the conventional molding method disclosed in JP-A No. 51-2773, a part of molten PET is injected from the injection machine for the inner and outer layers at the initial stage of injection, and then while the molten PET is injected from the injection machine for the inner and outer layers. Molten PMA was simultaneously injected from an injection machine for the intermediate layer, and molten PET was injected from the injection machine for the inner and outer layers at the end of the injection to mold a multilayer preform of two types and three layers with a wall thickness of 5 mm.

The thickness ratio of the inner layer: middle layer: outer layer of this preform is 3.4:0.9:5.7 in the upper part and 2.7: in the middle part.
2.3:5, 1.6:0.1:8.3 at the lower part (bottom),
The position and thickness ratio of the intermediate layer were non-uniform in each part of the preform.

Furthermore, using this preform, a bottle with an internal volume of 1000 c.c. was molded in the same manner as in the example.

The middle layer was non-uniform in each part of the bottle.

(Effects of the Invention) As is clear from the above description, in the container manufactured according to the present invention, the gas barrier resin of the intermediate layer is uniformly present in each part of the container, and
The thickness ratio of the inner surface layer, intermediate layer, and outer surface layer is almost constant in any part of the container, and the intermediate layer of gas barrier resin is completely encapsulated by the polyethylene terephthalate of both the inner and outer surface layers, and the edges are Since it is not exposed, peeling between the layers is less likely to occur, and deterioration of the gas barrier due to humidity of the gas barrier resin is suppressed to a small extent.

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.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the multilayer die, Fig. 2 is a sectional view of main parts of the co-injection device, Figs. 3 and 4 are explanatory diagrams showing the initial stage and middle of injection, and Figs. 5 and 6 are It is an explanatory view showing operation of stretch blow molding. 1... Multilayer die, 2... Solid channel, 3... Outer annular channel, 4... Inner annular channel, 5... Hot runner nozzle, 6... Injection machine for inner layer, 7... For outer layer Injection machine, 8... Injection machine for intermediate layer, 11... Cavity type, 13... Gate, 14... Core, 20...
Preform, 27...container.

Claims (1)

[Scope of Claims] 1. A multilayer plastic preform consisting of inner and outer surface layers of thermoplastic polyester mainly composed of ethylene terephthalate units, and an intermediate layer of gas barrier thermoplastic resin located between the inner and outer surface layers, is prepared by blow molding. A method for producing a multilayer stretch molded container comprising stretch blow molding in a mold at a temperature that allows stretching, wherein a thermoplastic polyester corresponding to the inner surface layer is formed in a solid flow, and a thermoplastic polyester corresponding to the outer surface layer is formed in a solid flow. The gas barrier resin corresponding to the outer annular flow and the intermediate layer is co-injected in parallel into the injection mold through a hot runner and gate as an inner annular flow located between the solid flow and the outer annular flow. During this co-injection, the injection timing of the gas barrier resin corresponding to the intermediate layer is controlled so that it is slightly slower at the beginning of the injection and slightly earlier at the end of the injection compared to the injection timing of the thermoplastic polyester. The ratio of the thicknesses of the outer surface layer and the inner surface layer of the preform is substantially equal in any part of the preform where the intermediate layer is present, and the uppermost opening and the gate-receiving bottom of the preform are made of substantially only polyester. A method characterized by performing molding as follows.