JPH0659681B2 - Method for producing multi-layer stretch-molded container in which intermediate layer is arranged with its inner surface biased - Google Patents

Description

The present invention relates to a method for producing a multilayer stretch-molded container,
More specifically, a blow-molded intermediate layer is blow-molded using a multi-layered preform comprising an inner and outer layer made of a thermoplastic polyester resin and an intermediate layer of a gas barrier thermoplastic resin layer located in the middle of the layer. Was biased toward the inner surface side. The present invention relates to a method for manufacturing a multilayer stretch-molded container.

[Prior Art] A polyester container produced by a stretch blow molding method has excellent transparency and appropriate rigidity. In addition to liquid detergent, shampoo, cosmetics, soy sauce, sauce, etc., carbonated beverages such as beer, cola, cider, etc. It has come to be widely used for containers.

Compared to general-purpose resin containers such as polyethylene and polypropylene, this stretched polyester container has excellent gas barrier properties, but the gas permeability of cans and glass bottles is almost zero. It is permeable to carbon dioxide and carbon dioxide, and the storage period of its contents is limited to a relatively short period compared to cans and glass bottles.

In order to improve this drawback, various proposals have been made to improve the gas barrier property of a container by combining a polyester with a gas barrier resin such as an ethylene-vinyl alcohol copolymer to form a multilayer structure. There is.

In order to manufacture a stretched multi-layer plastic container, it is first necessary to manufacture a preform having a multi-layer structure, and in order to manufacture this multi-layer preform, various co-extrusion molding methods, multi-stage injection molding methods, co-injection molding methods and the like are used. The method described in (1) is used, and the multilayer preform obtained is stretch-blown to produce a multilayer stretch-molded container.

However, the multi-layer stretch-molded container thus obtained has poor gas barrier properties and impact delamination resistance, and is not practical, so that improvement thereof has been strongly demanded.

[Problems to be Solved by the Invention] It is an object of the present invention to provide a method for producing a multi-layer stretch-molded container which has both excellent gas barrier properties and impact delamination resistance and is useful as a pressure resistant container having good appearance characteristics.

[Means for Solving the Problems] That is, the present invention provides "1. Co-injection molding of a thermoplastic polyester resin of an inner layer, a thermoplastic polyester resin of an outer layer, and a gas barrier thermoplastic resin of an intermediate layer of both layers. At the beginning of injection, the injection of the gas barrier thermoplastic resin is delayed a little,
A blow mold is used to produce a multi-layered preform in which a gas barrier thermoplastic resin layer is hermetically disposed at a position equidistant from the inner surface and the outer surface in the middle of both layers by finishing a little earlier at the end of injection. By stretching blow molding in the inside, the gas barrier thermoplastic resin layer is moved to the inner surface side, and the gas barrier thermoplastic resin is placed on the inner surface side from the center position between the inner layer and the outer layer of the thermoplastic polyester resin. A method for producing a multi-layer stretch-molded container in which an intermediate layer is arranged so as to be biased toward the inner surface side, which comprises forming a layer. It is.

The inventors of the present invention are a preform having a multilayer structure composed of an inner and outer layer of a thermoplastic polyester resin molded by a co-injection method and an intermediate layer of a gas barrier thermoplastic resin, the intermediate layer being located in the middle of the inner and outer layers. By using a multi-layer preform that is positioned and sealed in the inner and outer layers, stretch blow molding moves the intermediate layer to the inner surface side and biases it, not only the polyester resin inner and outer layers but also the gas. Effective molecular orientation is also imparted to the barrier thermoplastic resin intermediate layer to significantly improve the gas barrier property, and the outer layer is formed to be thicker than the inner layer, so that the impact in a container state is prevented. It was found that even when given or filled with high-pressure contents, the adhesive state of both resin layers is maintained, and the surprising effect that peeling does not occur at all is achieved, and the present invention has been completed. It is.

[Operation] In the present invention, one of the essential requirements is to use a preform in which the intermediate layer of the gas barrier resin is provided in the center of the inner layer of the polyester resin.

Here, being provided in the middle means providing the gas barrier resin intermediate layer at a position equidistant from the inner surface and the outer surface of the polyester resin layer.

By placing the intermediate layer in the center of the polyester resin inner and outer layers in this way, the intermediate layer can be moved and biased toward the inner surface side by the subsequent stretching blow process, and as a result, the outer layer is thicker than the inner layer. It is formed, imparts excellent impact resistance, and does not impair the gas barrier property.

If the intermediate layer is not in the center but in an appropriate position, the inner layer or the outer layer is crushed and exposed during stretching, and the gas barrier property and impact delamination resistance are extremely deteriorated.

Further, it is one of many requirements that the intermediate layer is completely sealed by the polyester resin inner and outer layers.

In particular, when the intermediate layer is exposed from the top surface of the mouth of the preform, the gas barrier property and the impact delamination resistance are extremely deteriorated.

for that reason. At the time of injection molding of the preform, a method is effective in which the polyester resin first flows into the cavity, the gas barrier resin flows in after a slight delay, and the gas barrier resin is stopped a little earlier at the end of injection.

In the present invention, polyethylene terephthalate (hereinafter abbreviated as PET) is preferably used as the thermoplastic polyester resin for the inner and outer layers, but as long as it does not impair the essence of PET, the main component is ethylene terephthalate unit, and other Copolyesters containing polyester units may also be used.

As a copolymerization component for forming such a copolyester, isophthalic acid: p-β-oxyethoxybenzoic acid;
Naphthalene 2,6-dicarboxylic acid; diphenoxyethane-4,
4'-dicarboxylic acid; 5-sodium sulfoisophthalic acid; adipic acid; dicarboxylic acid components such as sebacic acid or alkyl ester derivatives thereof, propylene glycol; 1,4-butanediol; neopentyl glycol; 1,6-hexylene Glycol; cyclohexane dimethanol; ethylene oxide adducts of bisphenol A; glycol components such as diethylene glycol and triethylene glycol.

The thermoplastic polyester resin used has an intrinsic viscosity (IV) of 0.5 / from the viewpoint of the mechanical properties of the container.
It is preferably at least g, particularly at least 0.6 / g.
Further, this polyester resin may contain a colorant such as a pigment or a dye, an ultraviolet absorber, an additive such as an antistatic agent.

As the gas barrier resin for the intermediate layer which can be used in the present invention, an ethylene-vinyl alcohol copolymer having a vinyl alcohol content of 40 to 85 mol%, particularly 50 to 80 mol%, is very suitable.

That is, the ethylene-vinyl alcohol copolymer is one of the resins having the best gas barrier properties, and the gas barrier properties and thermoformability thereof depend on the vinyl alcohol unit content. When the vinyl alcohol unit content is less than 40 mol%, the permeability to oxygen and carbon dioxide gas is large and the gas barrier property is improved as compared with the case where the content is within the above range. Not suitable. On the other hand, if this content exceeds 65 mol%, the permeability to water vapor increases and the melt moldability decreases, which is also unsuitable 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 acetate so that the saponification degree is 96 mol% or more, particularly 99 mol% or more. In addition to the above components, the copolymer has a carbon number of 3 such as propylene, butylene-1, and isobutylene within a range that does not impair the barrier property against oxygen, carbon dioxide, etc., for example, within a range up to 3 mol%.
You may contain the said olefin as a copolymerization component.

The molecular weight of the ethylene-vinyl alcohol copolymer is not particularly limited as long as it is a molecular weight sufficient to form a film, but generally, in a mixed solvent of 85% by weight of phenol and 15% by weight of water, a temperature of 30 ° C is used. Intrinsic viscosity (I
V) is preferably in the range of 0.07 to 0.17 / g. In addition, a xylylene group-containing polyamide can be used as the gas barrier resin for the intermediate layer.

The xylylene group-containing polyamide is a polyamide containing m-xylylenediamine and / or p-xylylenediamine as a diamine component, and more specifically, 35 mol% or more, particularly 50 mol% or more of the diamine component is m.
-Xylylenediamine and / or p-xylylenediamine, the dibasic acid component is a fatty acid dicarboxylic acid and / or an aromatic dicarboxylic acid, and, if desired, not more than 25 mol%, in particular 20 mol%, per total amide repeating unit.
The following ω-aminocarboxylic acid units are included.

Examples of diamine components other than xylylenediamine include aliphatic diamines such as hexamethylenediamine and alicyclic diamines such as piperazine, and aliphatic dicarboxylic acids include adipic acid, sebacic acid,
Suberic acid and the like, and examples of the aromatic dicarboxylic acid include terephthalic acid and isophthalic acid.

Examples of the ω-aminocarboxylic acid component include ε-caprolactam, aminoheptanoic acid, aminooctanoic acid and the like.

Examples of xylylene group-containing polyamides include, but are not limited to, polymetaxylylene adipamide, polymetaxylene sepacamide, polymetaxylylene sveramide, m-
Xylylene- / p-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 exemplified above may be used alone or in the form of a mixture of two or more kinds.

The preform in which the intermediate layer of the gas barrier thermoplastic resin is provided in the middle of the inner and outer layers of the thermoplastic polyester resin can be manufactured by the co-injection molding method.

[Embodiment] Next, an embodiment of the present invention will be described with reference to the drawings.

That is, each resin is co-injected into the cavity in the mold by using a multi-layer die as shown in FIG. The multi-layer die 1 includes a central flow passage 2 for polyester resin corresponding to the inner layer of the multi-layer preform, an outer annular flow passage 3 for polyester resin corresponding to the outer layer of the multi-layer preform, and a multi-layer between them. Inner annular flow paths 4 for the gas barrier thermoplastic resin corresponding to the intermediate layer (gas barrier thermoplastic resin) of the preform are respectively provided, and each of these flow paths is provided.
2,3 and 4 open to a single hot runner nozzle 5 which is connected to an injection mold gate (not shown).

In the present invention, as shown in FIG. 2, a polyester resin for the inner layer, a polyester resin for the outer layer, and a thermoplastic resin for the gas barrier layer for the intermediate layer are injected through each flow path and gate of the hot runner to obtain an injection mold. It injects translationally inward.

"Translationally inject" means that the resins are simultaneously injected in an aligned state through the respective flow paths, and therefore the flow rate ratio between the resins is constant.

Further, in the present invention, the injection timing of the gas barrier thermoplastic resin for the intermediate layer is started a little later than the injection timing of the polyester resin for the inner and outer layers, and is ended a little earlier at the end of injection. To control.

Thus, according to the present invention, the injection flow rate of the polyester resin for the inner layer and the injection flow rate of the polyester resin for the outer layer are maintained constant over substantially the entire process of injection, so that the outside of the formed preform is The layer to inner layer thickness ratio will remain substantially the same in any part of the preform where the intermediate layer is present.

Of course, since the injection speed of the gas barrier thermoplastic resin is constant, the thickness of the intermediate layer is also constant in any part of the preform.

Also, by slightly delaying the start of injection of the gas barrier resin for the intermediate layer, it is possible to prevent the gas barrier resin from being exposed at the uppermost opening of the preform, and to make the injection end point of the gas barrier resin slightly By shifting early, the bottom portion of the preform corresponding to the gate can be formed of only the polyester resin to prevent the gas barrier resin from being exposed, and thus the gas barrier resin layer is completely sealed. The injection of the polyester resin prior to the injection of the gas barrier resin and the injection of the polyester resin after the injection of the gas barrier resin may be performed with either the inner layer polyester resin or the outer layer polyester resin. Alternatively, both may be performed.
As a suitable example, pre-injection is performed with the polyester resin for the inner layer, and post-injection is performed with the polyester resin for the outer layer. In this way, the multi-layer preform manufactured by the co-injection molding method is molded into a container by stretch blow.

Prior to this stretch blow molding, the multilayer preform is first subjected to a stretchable temperature of the main resin, that is, a stretchable temperature of the polyester resin, generally 80 to 135 ° C, especially 90 to 125.
Maintain a temperature of ° C.

In this temperature adjustment step, the polyester resin layer of the multi-layer preform is supercooled so as to be maintained substantially in an amorphous state (amorphous state), and then hot air, an infrared heater,
It can also be carried out by heating the multilayer preform to the above temperature by a known heating means such as high frequency induction heating, or the temperature of the multilayer preform in the injection mold or the mold is It can also be carried out by cooling or cooling until the temperature is reached.

By this stretching and blowing step, the intermediate layer located in the middle of the inner and outer layers of the preform is moved and biased toward the inner surface side. By placing the middle layer in the middle of the inner layer of the preform, the stretch blow process allows
It is possible to obtain a multilayer stretch-molded container in which the intermediate layer can be moved to the inner surface side, and which has both excellent gas barrier properties and impact delamination resistance.

3 and 4 for explaining the stretch blow molding operation
In the figure, the mandrel 21 is inserted into the mouth of the bottomed multi-layer preform 20, and the mouth of the mandrel 21 is inserted into a pair of split molds 22a, 22.
Hold with b. A mandrel 21 is provided with a stretching rod 23 that is vertically movable coaxially with the mandrel 21.
Between and is an annular passage 24 for fluid intake.

By applying the tip 25 of the stretching rod 23 to the inside of the bottom portion 26 of the preform 20 and moving the stretching rod 23 downward,
Along with performing axial stretching, a fluid is blown into the preform 20 through the passage 24, and the fluid pressure causes the preform to expand and stretch in the mold to form the container 27.

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

The present invention will be described with reference to production examples as more specific examples.

Manufacturing example In the central channel 2 and outer annular channel 3, an intrinsic viscosity of 0.9 /
g polyethylene terephthalate (PET),
Polymetaxylene adipamide (PMA) is supplied to the inner annular flow path 4 as a gas barrier resin.

At the beginning of injection, a part of the molten PET is injected into the cavity from the central flow path through the hot runner nozzle 5, and subsequently, the molten PET is injected from the central flow path and the outer annular flow path, and the molten PMA is simultaneously injected from the inner annular flow path. Then, at the end of injection, molten PET was injected from the outer annular flow path, and the intermediate layer was provided in the middle.
A multi-layer preform having a two-kind three-layer wall thickness of 5 mm was formed.

This multi-layer preform is heated to about 100 ° C and doubled vertically,
Biaxially stretch blow molding was performed three times horizontally to obtain a container having an internal volume of 1000 ml.

The thickness ratio of inner layer: middle layer: outer layer of this container is 3.5: 0.9: 5.6 in the shoulder portion and 3.5: 1: 5.5 in the body portion.
It is 3.4: 0.8: 5.8 at the bottom, the position and thickness ratio of the intermediate layer in each part of the container are almost uniform, and the position of the intermediate layer is 37 to 39% of the thickness from the inner surface. It was evenly distributed in the position.

Comparative Example 1 According to a conventional molding method, a part of molten PET was injected from the annular flow channel at the initial stage of injection, and then melted from the central flow channel.
MA, the molten PET is injected in parallel from the annular flow path, the molten PET is injected from the annular flow path at the final stage of injection, and the intermediate layer is arranged so as to be biased toward the inner surface side, and the thickness is 5 mm. A multi-layer preform was molded.

Further, using this preform, a container having an internal volume of 1000 ml was molded in the same manner as in the example.

The thickness ratio of inner layer: middle layer: outer layer of this container was 3.4: 0.9: 5.7 in the shoulder portion and 2.7: 2.3: 5 in the body portion.
0, 1.6: 0.1: 8.3 at the bottom, and the position and thickness of the intermediate layer were uneven in each part of the container.

Comparative Example 2 According to the conventional molding method, a part of the molten PET was injected from the central flow path at the initial stage of injection, and then the molten P was melted from the annular flow path.
MA, molten PET is injected in parallel from the central flow path, and molten PET is injected from the central flow path at the final stage of injection to dispose the intermediate layer on the outer surface side with a 5 mm inner thickness of 2 types and 3 layers. , A multi-layer preform was molded.

Further, using this preform, a container having an internal volume of 1000 ml was molded in the same manner as in the example.

The thickness ratio of the inner layer: middle layer: outer layer of this container is 5.7: 1.0: 3.3 in the shoulder portion and 5.1: 1.9: 3 in the body portion.
0, 7.2: 0.2: 2.6 at the bottom, and the position and thickness of the intermediate layer were uneven in each part of the container.

Comparative Test The containers obtained in the production examples and comparative examples of the present invention were tested for impact resistance and delamination property. The results are shown in Table 1.

(Test method) 1. Impact resistance A blown bottle is filled with water at 5 ° C. and sealed, and repeatedly dropped onto a concrete floor surface from a height of 1 m to measure damage due to impact and delamination.

2. Interlaminar peelability (1) Interlaminar adhesive strength: The bottle wall surface is cut into a width of 15 mm, and the interlaminar adhesive strength is measured using a tensile tester (Toyo Ballwin UTM-III-500) to measure T peel strength.

(2) Storage test: Bottles are filled with 4 gas volumes of carbonated water and sealed, and then 3
It is stored in a thermostatic chamber at 7 ° C and the presence or absence of delamination is measured over time.

[Effects of the Invention] As is clear from the above description, in the container produced according to the present invention, in each part of the container, the gas barrier resin layer of the intermediate layer is uniformly present, and the inner layer, the intermediate layer,
The thickness ratio of the outer layer and the outer layer is almost constant in any part of the container, and the position of the intermediate layer is about 37 to 3 of the thickness from the inner surface.
It was evenly present at a distance of 9%. Moreover, since the middle layer of the gas barrier resin layer is completely enclosed by the polyethylene terephthalate resin of the inner and outer layers and the end portions are not exposed, peeling between the layers is unlikely to occur, and the humidity of the gas barrier resin layer causes The decrease in gas barrier property is controlled to be small.

Since the container of the present invention has the above-mentioned excellent properties, it is useful as a container for containing various contents, particularly as a lightweight container for blocking the permeation of oxygen, carbon dioxide or scent components, such as beer, cola and cider. As a container for carbonated fruit juice beverages, carbonated alcoholic beverages, etc., it has the advantage of significantly less carbonation loss than conventional containers.

[Brief description of drawings]

FIG. 1 is a sectional view of a multilayer die used in the present invention, FIG. 2 is a sectional view showing molding of a co-injection preform used in the present invention, and FIGS. 3 and 4 are sectional views of the present invention. It is a sectional view showing an operation of stretch blow molding which is an example. 1 ......, multi-layer die, 2 ...... central flow passage, 2a ...... polyester resin central flow, 3. ...... outer annular flow passage, 3a ...... outer peripheral polyester resin annular flow, 4. ...... inner annular flow passage, 4a …… Middle gas barrier resin annular flow, 5 …… Hot runner nozzle, 12 …… Preform mold cavity, 16 …… Preform inner surface layer, 17 …… Preform outer surface layer, 18 …… Preform Middle layer, 20 …… preform, 21 …… mandrel, 22a, 22b …… pair of split molds, 23 …… stretch rod, 24
...... Annular passage for sucking fluid, 25 …… Extension rod tip, 26
…… Bottom of preform, 27 …… Multilayer stretch-molded container.

Claims (1)

[Claims] 1. A gas barrier thermoplastic resin at the initial stage of injection when co-injecting a thermoplastic polyester resin of an inner layer, a thermoplastic polyester resin of an outer layer and a gas barrier thermoplastic resin of an intermediate layer of both layers. By slightly delaying the injection and terminating it slightly early at the end of injection, a gas barrier thermoplastic resin layer is hermetically disposed at a position equidistant from the inner surface and the outer surface in the middle of both layers. Reform, by stretch blow molding in a blow mold, to move the gas barrier thermoplastic resin layer to the inner surface side, the inner surface side from the center position of the inner layer and the outer layer of the thermoplastic polyester resin, A method for producing a multi-layer stretch-molded container in which an intermediate layer is arranged so as to be biased toward the inner surface side, which comprises forming a gas barrier thermoplastic resin layer.