JPH0624431A - Container made by multilayer blow molding, and manufacture thereof - Google Patents

Abstract

PURPOSE:To make various characteristics in a pinch-off bonding part the same as those in other parts of a container made by multilayer blow molding with the pinch-off bonding part of parison provided to its bottom by a method wherein a protuberance in specified projection height is provided to the bonding part. CONSTITUTION:A plastic container that is made of a plastic tubular parison by blow molding and is composed of a wall made of at least three layers including an internal surface layer 3, an intermediate layer 1 and an external surface layer 2 has a bonding part formed by pinching off the parison at least at its bottom. A protuberance 16 that projects outward beyond the container wall in the direction of its thickness is formed to the pinch-off bonding part. The protuberance 16 is equipped with a drawn breadth part D1 on the vicinity of the base part of its projection and is equipped with a thick part D2 in the size the same as or larger than the drawn breadth part on its front end. The protuberance 16 is also formed so that it can satisfy the following relations: 0.25<=H<=2.2t, 0.2<=D1<=1.4t, D1<=D2<=3D1 with the projection height of the protuberance 16 taken as H, and the thickness of the container wall taken as t.

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a multi-layer blow-molded container made of plastic and a method for producing the same, and more particularly to a multi-layer blow-molded container having a joint formed by pinch-off at the bottom thereof, wherein each joint has a multi-layer structure. The same layers are substantially continuous, which is an advantage of the multi-layer structure, for example,
The present invention relates to a container excellent in oxygen permeation resistance, moisture resistance, organic solvent resistance, chemical resistance, mechanical strength and the like even in a pinch-off joint portion, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, it has been known that a multi-layer molded container having a plastic multi-layer structure is excellent as a container having the unique characteristics of each layer, but a multi-layer container having a joint formed by pinch-off at the bottom. In a blow-molded container, the same layer of the multilayer structure is continuous at the joint, and the oxygen permeation resistance, which is an advantage of the multilayer structure at the joint,
Difficulty is involved in a container that maintains moisture resistance, organic solvent resistance, chemical resistance, mechanical strength, and the like and its manufacturing method. Although various proposals have been made so far regarding this type of container and a method for producing the same, the present invention is particularly concerned with Japanese Patent Application Publication No. 53-15432 and Japanese Patent Application Publication No. 59-11.
The technique described in Japanese Patent No. 5234 can be cited as a conventional technique.

The container described in the former publication and the manufacturing method thereof are as follows: the inner and outer surface layers made of a known polyolefin.
Similarly, the bottom pinch-off joint of the tubular parison, which has a container wall having an intermediate layer having a specific oxygen barrier property, which is also known per se, is formed into a ridge having a tapered portion outwardly protruding from the container wall, which is known per se. Is formed to make the same layers substantially continuous with each other at the joint,
It is recognized that the combination is unique and patentable, but in particular, the pinch-off joint part is, for example, V-shaped,
U-shaped, semi-circular, semi-elliptical, Mt. Fuji-shaped, U- and V-shaped, etc. are formed in a taper shape, and the greatest feature is that the same layers are connected to each other. In the shape, it is excluded that the same layers are not continuous, and the reason for this has not been clarified.The reason for this is that if a split mold with a concave groove having a tapered portion is used, the protrusion of the pinch-off portion at the bottom of the container is used. The pressure starts to be applied from the narrowest part of the cross-sectional width of the container, and the thickness of the outer layer of the container that is in contact with the split mold is larger than the width of the tapered part of the split mold. It is explained that the exposure of the intermediate layer to the outside that affects the performance of the container does not occur.

The multi-layer container described in the latter publication has a multi-layer parison in which at least two layers including a main layer such as a polyolefin and a gas permeation resistant layer such as a saponified product of ethylene-vinyl acetate copolymer are laminated. In a multi-layer container in which a rib is formed in a pinch-off portion formed by sandwiching the multi-layer parison in a mold by sandwiching with a mold and performing hollow molding,
Both side surfaces of the rib are formed in an inclined shape so as to expand from the base end toward the tip, and the width of the tip is 1.1 to 5 times the width of the base end,
The height of the rib is characterized by being 0.5 to 5 times the width of the base end, and the description is limited only to the dimensional ratio of the shape of the rib, and refers to the layer structure of the container wall, There is no mention of the rib size relative to the wall thickness of the container.

[0005]

According to the description of the above-mentioned Japanese Patent Application Publication No. 53-15432, pinch-off joints are formed in, for example, V-shape, U-shape, semicircle, semi-ellipse,
It is possible to form the taper into an arbitrary tapered shape such as a Mt. Fuji type or a combination of U and V shapes so that the same layers can be continuous with each other. In the planar shape or the rectangular shape, the same layers are not continuous with each other.
According to an experiment conducted by the inventor under the necessity, unlike the description in the publication, it is difficult to completely connect the same layers to each other by forming the pinch-off junction in a tapered shape. Although it is a specific dimension for the wall thickness of the container wall, if the pinch-off joint is formed in a rectangular shape having a narrowed width portion at the base of the protruding portion, it is possible to obtain the knowledge that the same layers are surely continuous. I arrived. That is, even if the pinch-off joint is formed in a taper shape and the same layers are made continuous, the fact that the joint can be made continuous can be obtained by looking at the joint in the longitudinal direction, that is, near the center (that is, the center of the bottom). Near both ends of the joint (that is, near both sides of the bottom)
Then, there was a problem that the intermediate layer was exposed to the outer surface layer.

Further, the above-mentioned patent application publication Sho 59-1152
The multilayer container described in JP-A-34-34 is a multilayer container in which a rib is formed in a pinch-off portion, and both side surfaces of the rib are formed in an inclined shape so as to expand from the base end toward the tip, and the width of the tip is The feature is that the width of the base end is 1.1 to 5 times and the height of the rib is 0.5 to 5 times the width of the base end, but the size of the rib is simply restricted to such a range. However, there is a problem that the same layers cannot be surely continuous with each other. That is, the shape A of the split mold of the pinch-off joint portion of the multilayer blow molding container having a specific dimension with respect to the wall thickness of the container wall, and the vicinity B and the center C of the layer cross-section of the pinch-off joint portion molded by this. 5 to FIG.
As shown in FIG. 5, in the case of the planar shape shown in FIG. 5, the intermediate layer 1 is exposed to the outer surface layer 2 over the entire longitudinal direction of the joint portion of the center C and both ends B as described in the above publication. However, in the case of forming the taper shape of the V-shape of FIG. 6, the inverted trapezoidal shape of FIG. 7, and the semicircular shape of FIG. However, the intermediate layer 1 is exposed to the outer surface layer 2 in the vicinity of both ends B, and conversely, the rectangular shape of FIG.
When it is formed in a trapezoidal shape of 0, both ends B and middle C
It was also found that the same layers of each layer were continuous over the entire joint. The reason for this has not been fully clarified yet, but the inventor has found that the reason for this is that when the pinch-off joint is sandwiched between split molds and the parison is expanded in the split molds, the vicinity of the center of the joint (that is, the bottom of the container). In the vicinity of the center), the expansion force mainly acts in the direction orthogonal to the longitudinal direction of the joint, so that the clamping force can be appropriately and uniformly applied to the joint.
In the vicinity of both ends of the joint (that is, in the vicinity of both ends of the container bottom), the expansion force acts strongly even along the longitudinal direction of the joint, and the clamping force cannot be maintained appropriately compared with the vicinity of the center and becomes uneven. Therefore, in the conventional tapered split mold, the outer surface layer in contact with the split mold is pulled quickly or strongly and the vicinity of the tapered top becomes thin, and the intermediate layer may be exposed from the thin outer surface layer, On the other hand, when sandwiching with a split mold with a wide bottom such as a rectangular shape or a trapezoidal shape, even if both ends of the joint are subjected to expansive force in the same way, when sandwiched, there is sufficient space in the split mold. Since the outer surface layer is confined, it is thought that it may maintain its thickness and prevent the intermediate layer from being exposed from the outer surface layer. From the knowledge based on this additional experiment, in the conventional technique described in the above publication, for example, a multilayer structure of polyolefin / barrier resin / polyolefin,
Even in the case of a container having a preferable combination of oxygen barrier property and moisture resistance, since the same layers in these laminates cannot be completely continuous at the pinch-off joint at the bottom of the container, this discontinuous portion It is unavoidable that the oxygen barrier property and the moisture resistance are lost and that the joint part is peeled off by a drop impact or the like.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a multi-layer molded container wall comprising at least three layers, an inner surface layer, an intermediate layer and an outer surface layer formed by blow molding a plastic tubular parison. And a plastic container having a joint formed by pinch-off of the parison at least on the bottom, the joint forms a protrusion protruding outward in the thickness direction of the container wall, and the protrusion is A thick portion approximately equal to or thicker than the narrow portion near the projecting base is provided in the projecting tip portion direction, and the projecting height H of the projecting portion, the width D1 of the narrow width portion, and the thick portion. Width D
2 is the thickness t of the container wall after molding,

[Equation 1]

[Equation 2]

There is provided a multi-layer blow molding container characterized in that the same layers constituting the container wall are continuous in the surface at the joint portion, as well as the inner surface layer and the intermediate layer. Layers and an outer surface layer of a multi-layered plastic parison including at least three layers are formed by simultaneous melt extrusion, and the melt extruded parison is outwardly squeezed to the fusing part when the molds are fitted, and the narrowed width part near the base part. And the narrowed width portion is sandwiched by a pair of split dies having a groove having the same or greater wall thickness portion in the front end direction, and the depth H of the concave groove, the width D1 of the narrowed width portion, and The width D2 of the thick portion is relative to the wall thickness t of the container wall after molding,

[Equation 1]

[Equation 2]

Then, the parison is expanded in the split mold, thereby forming a protrusion on the parison joint outwardly corresponding to the concave groove, thereby forming an inner surface layer in the parison,
The present invention provides a method for producing a multi-layer blow-molded container made of plastic, characterized in that the same layer of the intermediate layer and the outer surface layer are continuous in the joint at the surface.

Here, in the present invention, the narrowed width portion in the vicinity of the projecting base portion of the projecting portion projecting outward in the thickness direction of the container wall means the pinch-off joint portion of the tubular parison at the bottom portion of the container.
Because the width of the container wall is a squeezed part that overlaps,
If the wall thickness of the container wall is t, theoretically, the wall thickness of the portion where the container walls overlap is 2t. Therefore, this wall thickness 2t
The width of the diaphragm obtained by adding a diaphragm is 2t or less.
However, the diaphragm effect is surely recognized at an interval of about 1.4t or less, and the optimum condition is that the interval of the diaphragm width portion is about 0.3t to 1.2t, which will be described later.
If it is less than about 5t, the aperture will be too narrow. It is considered that the reason is that the container wall is in a molten state at the time of joining, so that a sufficient throttling effect cannot be achieved unless a certain degree of throttling is applied. It is considered that the conditions for the projection height H and the spread width D2 with respect to the wall thickness t of the container similarly affect the drawing effect. Further, when there is no adhesiveness between the polymer layers of the inner surface layer, the intermediate layer and the outer surface layer in the parison, a blend containing the two types of polymers between two layers adjacent to each other. The layers can be provided as an adhesive to improve the peel strength between the layers.

[0009]

According to the present invention, a multilayer blow molded container having a multilayer structure including at least three layers of an inner surface layer, an intermediate layer and an outer surface layer is provided at a pinch-off joint at the bottom thereof outward in the thickness direction of the container wall. A projecting protruding portion is formed, and in a specific range with respect to the wall thickness of the container wall, the projecting protruding portion has a thick portion that is approximately equal to or thicker than the narrowed width portion near the projecting base portion. Since it is provided in the part direction, each of the same layers constituting the container wall is substantially completely continuous in the entire joint portion, the inner and outer surface layers are provided with moisture resistance and water impermeability, and If the intermediate layer is made of polyethylene or the like having excellent toughness and the intermediate layer is made of a gas barrier resin which is weak in high humidity conditions but normally has excellent oxygen barrier property, the other blow molding container of the present invention has the pinch-off joint portion. Of the surrounding area Walls in substantially the same manner as the same layer with each other continuously in the plane, synergistically exert layers specific characteristics, oxygen, water vapor, and various gases such as carbon dioxide, water, organic liquids,
It has excellent barrier properties against various liquids such as ammonia water and hydrochloric acid, and since the joint is formed thicker than the entire wall of the container, it is stable in strength and fills the contents. It has excellent strength and peeling resistance enough to withstand the impact of a drop even in the above state. In the present invention, in the joint portion of the multilayer blow-molded container, in order to form a protrusion having a wall thickness portion approximately equal to or greater than the drawing width portion in the vicinity of the protrusion base in the protrusion tip end direction, The melt-extruded parison is used as a fusing part when the molds are matched,
The parison is sandwiched between a pair of split molds with a groove formed in the direction of the projecting tip, which is thicker than or equal to the width of the narrowed portion near the projection base, and then expanded in the split mold. By doing so, it can be easily molded.

[0010]

EXAMPLES In the present invention, the inner and outer surface layers are made of polyethylene, isotactic polypropylene, ethylene-propylene copolymer, polypten-1, polypentene-1, etc., which are excellent in moisture resistance, water impermeability and toughness. Saponified ethylene-vinyl acetate copolymer having an ethylene content of 25 to 75 mol% and a saponification degree of at least 93%, which can be composed of polyolefin and has excellent oxygen barrier properties, and acrylonitrile-acryl. The multi-layer blow molding container of the present invention, which can be composed of an acid copolymer, polyamide, or the like, as a result, can completely protect the contents from intrusion and leakage of moisture and oxygen, and further has a joint part. Since it is formed to be thick over the entire wall of the container, the container is stable in strength. As the oxygen barrier resin for the intermediate layer, in addition to the saponified ethylene-vinyl acetate copolymer and acrylonitrile-acrylic acid copolymer, nylon 6, nylon 6 and
Various polyamides such as 6 and nylon 12 can also be used. When there is no adhesiveness between these respective polymer layers, at least one of the adjacent polymer layers is blended with a carbonyl group-containing polymer in an amount of 0.5 to 15% by weight, or As described above, a blend layer containing the two kinds of polymers is provided as an adhesive between two layers adjacent to each other, and the peel strength between the layers can be improved.

The blow molding process of the present invention will be described with reference to FIGS. 3 and 4.
Explaining in the figure, a multi-layered molten resin flow composed of a plurality of types of polymers heated and melted by a plurality of extruders passes through an annular resin passage 5 of a die 4 to form a multi-layered parison 6. It is melt extruded. Around the extruded parison 6, a pair of split dies 7 and 8 are reciprocally provided. The pair of split molds 7 and 8 are provided with spaces 9 and 10 that match the outer shape of the container when the molds are matched, and the parison at the bottom of the molds is sandwiched when the molds are matched.
In addition, the fusing parts 11 and 12 for fusing are formed with a concave groove 13 having a wall thickness portion approximately equal to or larger than the minimum width portion near the protruding base portion in the protruding tip end direction. The shape and size of the concave groove 13 are set so as to match the protruding portion in the joint portion of the blow molding container. In FIG. 3, when the multi-layered parison 6 is extruded to a predetermined size, the pair of split molds 7 and 8 move in the die-matching direction of the arrow mark direction, as shown in FIG.
The parison 6 is sandwiched between the fusing parts 11 and 12 and melted, and together with this, the compressed air blowing port 14 is placed inside the parison.
Compressed air is blown through to form the blow-molded container 15. At this time, corresponding to the concave groove 13 formed in the fusing part of the split molds 7 and 8, the joint of the blow-molded container 15 has a thickness approximately equal to or larger than that of the drawing width part near the protruding base part. The protruding portion 16 having the thick portion in the protruding tip portion direction is formed.

[0012]

[Molding Example] Density (JIS-K-676) for inner and outer surface layers
0) is 0.949 g / cm ³ , and the melt flow index (JIS-K-6760) is 0.30 g / 10 min, to 99% by weight of high-density polyethylene, and 1% by weight of titanium oxide (IV) as a coloring agent (anatase type). And a mixture of rutile type in a weight ratio of 1: 1), for the intermediate layer, density (ASTM-D-1505)
Of 1.188 g / cm ³ , melt flow index (A
STM-D-1238) is 1.30 g / 10 min, ethylene content is 32 mol%, and saponification degree is 95% or more.
After being dried for a minute, for the adhesive layer between the inner and outer surface layers and the intermediate layer, the density (A
STM-D-1505) is 0.901 g / cm ³ , melt flow index (ASTM-D-1238) is 1.10 g / 10 min, and 97% by weight of adhesive modified polyethylene having 5 mol% of a carboxyl group introduced. 3% by weight of di-tert. A mixture of butyl-p-cresol, with a screw diameter of 35 m for each of the inner and outer surface layers
m, screw length 800 mm, screw diameter 30 mm for intermediate layer, screw length 650 mm, screw diameter 30 mm for adhesive layer, screw length 650 mm, inner and outer surface layer extruder, intermediate layer extruder and bonding A layer extruder and an intermediate layer extruder are coextruders connected to a five-layer die for three-kind five layers, coextrusion is performed under the temperature conditions described below, whereby the outermost layer and the innermost layer are the high-density polyethylene, A parison having a symmetrical five-layer type laminated structure in which the intermediate layer was a saponified product of ethylene vinyl acetate copolymer and these two layers were adhered by the above-mentioned adhesive modified polyethylene layer was produced and subjected to bottle molding. The temperature conditions of the extruder are as follows:
0 ° C., cylinder front temperature 180 ° C., middle layer extruder has cylinder rear temperature 185 ° C., cylinder front temperature 200 ° C., adhesive layer extruder has cylinder rear temperature 1
The temperature of the front part of the cylinder was 65 ° C., the temperature of the front part of the cylinder was 185 ° C., and the temperature of the five-layer die for three kinds of five layers was 190 ° C. The mold used for molding has a diameter of 40 mm, a height of 100 mm, and an internal capacity of 100.
It was a cylinder with a raised bottom of cc, and the mold temperature was 15 ° C.

In the embodiment shown in FIG. 1, the wall thickness t of the container is t =
With respect to 3.5 mm, the narrowing width D1 of the narrowing portion near the projecting base portion by the groove 13 is D1 = 2 mm, the projecting tip portion (that is, the spreading width) D2 = 3 mm, the projecting height H = 2 mm, and the rising angle of the projecting portion. θ = 68 ° 50 'and container wall thickness t
= 3.0 mm, the narrowing width D1 of the narrowing width portion near the protruding base portion by the groove 13 is D1 = 1 mm, the protruding tip portion (that is, the spread width) D2 = 3 mm, the protruding height H = 2.0 mm, and the protruding portion. Of which the rising angle θ = 60 ° was molded, and the intermediate layer 1, the outer surface layer 2 and the inner surface layer 3 including the adhesive layer were formed over the entire longitudinal direction of the pinch-off joint in any container. A container having one continuous layer was obtained. In the embodiment of FIG. 2, for the wall thickness t = 1.5 mm of the container wall, the narrowing width portion D1 near the protruding base portion and the protruding tip portion (that is, the spread width)
D2 is equal, D1 = D2 = 1.5 mm, and protrusion height H = 1.
A container having a diameter of 0 mm and a rising angle θ of the protrusion of 90 ° was molded, and similarly, a container in which the same ones were continuous over the entire pinch-off joint was obtained. The continuous state at these joints is a plane that is orthogonal to the longitudinal direction of the joints, cut at multiple points throughout the joint, and the inner and outer surface layers are colored by the colorant mixed in the material, and the intermediate layer is polarized. The continuous state of each layer was confirmed by a microscope and a phase contrast microscope. In addition, these containers are sliced into 10 equal parts in the lateral direction, the colored inner and outer surface layers, the intermediate layer measured using the same microscope as described above, and the thicknesses of the adhesive layers appearing between the layers. As a result of the measurement, the average ratio of the wall thickness of each layer is: outer surface layer: adhesive layer: middle layer: adhesive layer: inner surface layer = 4
It was 0: 5: 10: 5: 40. The average weight of the container was 14 g. In addition, from the results of molding under various conditions,

[Equation 1]

[Equation 2]

In (3), a continuous state of the joint is obtained, and in particular,

[Equation 4]

[Equation 5]

It was possible to obtain the knowledge that the optimum continuous state of the joint was obtained under the condition of [Equation 1]. It should be understood that, in a multilayer structure in which the outer surface layer is extremely thin and the intermediate layer is located near the outer surface, it is obvious that the intermediate layer tends to be exposed to the outer surface at the joint.

[0014]

[Effect] In the multilayer blow-molded container of the present invention, since the same layers are continuous in the same plane as the surrounding container wall in the entire area of the pinch-off joint portion, the characteristics peculiar to each layer are synergistically exhibited. However, it has excellent barrier properties against various gases such as oxygen, water vapor, carbon gas, and various liquids such as water, organic liquids, ammonia water, hydrochloric acid, etc., and even when it is filled with contents, it can be impacted by falling. It has excellent strength and peel resistance that it can withstand sufficiently. Due to this property, the multi-layer blow-molded container of the present invention has various contents, particularly liquids, creams, pasty foods, cosmetics, pharmaceuticals, inks, developers, various organic solvents, inorganic and organic chemicals. , It is excellent and effective for storing liquid fuel and the like for a relatively long period of time.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a cross section of a main part of an embodiment of a container of the present invention.

FIG. 2 is a vertical cross-sectional view showing a cross section of a main part of another embodiment.

FIG. 3 is a schematic explanatory view illustrating a state in which a split mold is open, which illustrates the multilayer blow molding method of the present invention.

FIG. 4 is a schematic explanatory view illustrating a state in which a split mold is closed for explaining the multilayer blow molding method of the present invention. , Fig. 3 shows the split mold open, and Fig. 4 shows the split mold closed.

FIG. 5 is a cross-sectional view schematically showing a cross section of a pinch-off joint portion of a conventional container together with a split mold shape of a fusing portion.

FIG. 6 is a cross-sectional view schematically showing a cross section of a pinch-off joint part of a conventional container together with a split mold shape of a fusing part.

FIG. 7 is a cross-sectional view showing a typical cross section of a pinch-off joint portion of a conventional container together with a split mold shape of a fusing portion.

FIG. 8 is a cross-sectional view schematically showing a cross section of a pinch-off joint portion of a conventional container together with a split mold shape of a fusing portion.

FIG. 9 is a cross-sectional view showing a typical cross-section of the pinch-off joint of the container of the present invention together with the split mold shape of the fusing part.

FIG. 10 is a cross-sectional view showing a typical cross-section of the pinch-off joint of the container of the present invention together with the split mold shape of the fusing part.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Intermediate layer 2 ... Outer surface layer 3 ... Inner surface layer 4 ... Die 6 ... Parison 7, 8 ... Split mold 11, 12 ... Fusing part 13 ... Groove 16 ... Projection

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location B32B 1/02 7016-4F 27/28 101 6122-4F 102 6122-4F 27/30 A 8115-4F 27/32 8115-4F // B29K 23:00 B29L 22:00 4F

Claims (4)

[Claims] 1. A multi-layered container wall comprising at least three layers of an inner surface layer, an intermediate layer and an outer surface layer formed by blow molding of a plastic tubular parison and formed by pinch off of the parison at least at the bottom. In a plastic container having a joined portion formed therein, the joined portion forms a protrusion protruding outward in the thickness direction of the container wall, and the protrusion is substantially with respect to the narrowed width portion near the protruding base. The same or more thick-walled portions are provided in the direction of the protruding tip portion, and the protruding height H of the protruding portion and the width D1 of the aperture width portion are provided.
And the width D2 of the thick portion with respect to the wall thickness t of the container wall after molding, [Equation 2] [Equation 3] The multi-layer blow-molded container is characterized in that the same layers constituting the container wall are substantially continuous in the joint portion in the plane. 2. The container wall of the tubular parison according to claim 1, wherein an inner surface layer made of polyolefin, an outer surface layer made of polyolefin, and an ethylene content of 25 to 75 mol% and a saponification degree. Is at least 93
% Ethylene-vinyl acetate copolymer saponified product, acrylonitrile-acrylic acid copolymer, or multilayer blow molded container comprising a multilayer molded product including an intermediate layer composed of polyamide 3. A plastic parison having a multilayer structure including at least three layers of an inner surface layer, an intermediate layer and an outer surface layer is formed by simultaneous melt extrusion, and the melt extruded parison is melted when a mold is fitted. To the outside is sandwiched by a pair of split molds in which a narrow groove near the base portion and a groove having the same or more wall thickness portion as the narrow width in the projecting direction are formed,
In addition, the depth H of the groove, the width D1 of the narrowed width portion, and the width D2 of the thick wall portion are as follows with respect to the thick wall portion t of the molded container wall. Then, the parison is expanded in the split mold, whereby a protrusion corresponding to the concave groove is formed outward at the parison joint, and an inner surface layer in the parison is formed.
A method for producing a multi-layer blow-molded container made of plastic, characterized in that the same layers of the intermediate layer and the outer surface layer are substantially continuous in the joint at the surface. 4. The plastic parison according to claim 3, wherein the plastic parison has an inner surface layer made of polyolefin, an outer surface layer made of polyolefin, and an ethylene content of 25 to 75 mol% and a saponification degree of at least 93.
% Ethylene-vinyl acetate copolymer saponification product, acrylonitrile-acrylic acid copolymer, or a multilayer blow molding container characterized by being formed by simultaneous melt extrusion of a multilayer structure containing an intermediate layer consisting of polyamide.