JPS6040966B2 - Method for manufacturing multilayer containers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a multilayer container with excellent gas barrier properties, which is formed by coextrusion blow molding and has a storage space formed inside by a garden wall.

Saponified ethylene-vinyl acetate copolymer has extremely low permeability to gases such as oxygen gas, but has high green permeability, and gas permeability is highly dependent on humidity, and gas permeability increases in high humidity areas. There are drawbacks.

To compensate for this drawback, when trying to make a container with low gas permeability using saponified ethylene-vinyl acetate copolymer (hereinafter referred to as saponified material), a resin with low moisture permeability is layered on the surface of the saponified material. Until now, coextrusion blow molding has been used to laminate a saponified material in the middle layer and different low-transparency synthetic resins in both outer layers.
Layered containers have been proposed.

By the way, in the above-mentioned subordinate three-layer container, the intermediate saponified layer has sufficient gas barrier performance when its wall thickness is 1 micron or more, and as the wall thickness becomes thinner, the degree of interlayer interaction with both outer layers increases. Since saponified materials are very expensive, it is advantageous in all respects to make the wall thickness of the intermediate saponified material layer as thin as possible.

However, if the wall thickness of the saponified material in the intermediate layer is made extremely thin, film breakage (pinholes) due to welds in the coextrusion die will easily occur, and if pinholes occur in the saponified material layer, the container will be damaged. As a result, in conventional three-layer containers, the intermediate saponified material layer had to be made relatively thick in consideration of the risk of pinhole formation.

The present invention was conceived in view of the above, and includes an ethylene-
A plurality of intermediate layers made of saponified vinyl acetate copolymer are independently spaced apart in the thickness direction, and the low-permeable synthetic resin is interposed between each intermediate layer, and they are joined together in a multilayered manner so as to be interposed over the entire garden wall. By supplying the resin of the intermediate layer from a position shifted in the circumferential direction of the mandrel and merging it into the multilayered form, the plurality of saponified material layers constituting the intermediate layer are coextruded through a coextrusion die. To provide a method for manufacturing a multilayer container that can be made extremely thin without worrying about internal welds, has strong interlayer adhesive strength, is inexpensive, and has an extremely high safety factor in terms of gas barrier properties. It is something.

Embodiments of the present invention will be described below based on the drawings.

In the figure, reference numeral 1 indicates a multilayer container manufactured by the manufacturing method according to the present invention, which is formed by coextrusion blow molding with a housing space defined inside by a surrounding wall.

The main wall 2 of this multilayer container 1 is made of a synthetic resin with low moisture permeability such as low density, medium density, and high density polyethylene or polypropylene, and the main wall 2 has an ethylene content of 25 to 60 mol%. , saponification degree 90
% or more of ethylene-pinyl acetate copolymer are independently spaced apart in the thickness direction of the main body 2 of the box wall, and are interposed over the entire surrounding wall. FIG. 2 shows a method for manufacturing a multilayer container according to the present invention, in which the surrounding wall is divided into layers, a parison 6 is extruded from a coextrusion die 5, and this multilayer parison 6 is covered with a mold 7. Blow molding is performed by holding the mold and blowing fluid under positive pressure.

The resin of each layer constituting the multilayer parison 6 is supplied to a coextrusion die 5 from two or more extruders, and inlets 5a are provided at positions shifted in the circumferential direction and axial direction of the mandrel 8. It is supplied from 5b, 5c, 5d, and 5e.

At this time, especially when both the intermediate layers 3 and 4 are made extremely thin, the resin for the intermediate layer that flows in from the inlets 5b and 5d is divided in the circumferential direction of the mandrel 8 and then merges at the weld portion on the opposite side of the inlet. Pinholes may occur due to film breakage. For this reason, the positions of the resin inlets 5b and 5d for both intermediate layers 3 and 4 are shifted in the circumferential direction of the mandrel 8. As a result, even if pinholes are formed in the weld portions of both intermediate layers 3 and 4, the positions of these pinholes will not shift in the circumferential direction and the gas barrier properties will not deteriorate. The configurations of multilayer containers according to an embodiment of the present invention and a conventional example will be shown below and compared.

Example: A multilayer container with an internal capacity of 300 cc and a weight of 12 mm, the main wall 2 being made of low density polyethylene, and the two intermediate layers 3 and 4 being made of saponified material (ethylene content 35 mol%, degree of saponification 99%), The average wall thickness of each torso is 0.8 thick on the outside of each middle layer 3 and 4 of the surrounding wall main body, 0.7 thick on the inside, and 0.5 thick between middle layers 3 and 4, and Each of the intermediate layers 3 and 4 was made by coextrusion blow molding so that the outer intermediate layer 3 had a thickness of 0.002 mm, and the inner intermediate layer 4 had a thickness of 0.003 mm.

Comparative Example A multilayer container having the same shape as the above embodiment was constructed by interposing an intermediate layer of the same saponified material as that used in the above embodiment within the surrounding wall main body made of low density polyethylene, The average wall thickness of each chest is 0.008 ribs in the middle layer, and 1.08 ribs outside of this middle layer in the surrounding wall main body. Vengeance, inside 1. It was made using co-extrusion blow molding to make it more durable.

Comparison Results The multilayer container made according to the example of the present invention was superior to the multilayer container made according to the conventional comparative example in terms of oxygen gas barrier, moisture permeation resistance, and interlayer peel strength.

Note that the multilayer container in the present invention is a general term for hollow bodies obtained by coextrusion blow molding, and also includes containers for foods, seasonings, cosmetics, industrial chemicals, etc., and industrial parts such as gasoline tanks.

In addition, appropriate thermoplastics, additives, colorants, and antistatic materials are added to the saponified materials and low-transparency resins that make up each layer in order to improve interlayer adhesion and moldability without impairing their properties. A UV protection agent, ultraviolet ray inhibitor, etc. may be added. Further, in the embodiment of the present invention, a five-layer container having two intermediate layers has been described, but the intermediate layer may be three or more layers, making the total seven or more layers. Since the present invention is as described above, the plurality of saponified layers constituting the intermediate layer can be made extremely thin without worrying about welding in the coextrusion die, thereby increasing the adhesive strength between each layer. Moreover, since the saponified material layer is extremely thin, it is possible to obtain a multilayer container that is inexpensive and has an extremely high safety factor in terms of gas barrier properties.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway front view of a multilayer container manufactured by the manufacturing method according to the present invention, and FIG. 2 is an explanatory view showing the method for manufacturing a container according to the present invention. 1 is the container, 2 is the main garden wall, and 3 and 4 are the middle layers. Figure 1 Figure 2

Claims (1)

[Claims] 1. A synthetic resin with low moisture permeability such as polyethylene and a saponified ethylene-vinyl acetate copolymer are each melt-kneaded using two or more extruders, and then each resin is supplied to a coextrusion die 5. In this coextrusion die 5, a plurality of intermediate layers 3 and 4 made of saponified ethylene-vinyl acetate copolymer are added in the thickness direction within the surrounding wall main layer made of the above-mentioned low moisture permeability synthetic resin. The synthetic resin with low moisture permeability is interposed between each of the intermediate layers, which are separated independently, and are merged in a multilayered manner so as to be interposed over the entire surrounding wall. By shifting the position of the inlet in the circumferential direction of the mandrel 8, the intermediate layer resin is supplied from a position shifted in the circumferential direction of the mandrel 8 and merged, and then the multilayer parison 6 is extruded from the coextrusion die 5, A method for manufacturing a multilayer container, characterized in that the container is formed by blow molding.