JPH0144576B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a multilayer parison laminated with at least two layers, including a main layer such as polyolefin and a gas permeation resistant layer such as saponified ethylene-vinyl acetate copolymer, in a split mold. The present invention relates to a multilayer container formed by sandwiching and hollow molding, and more specifically to a multilayer container with excellent peel resistance and gas permeation resistance without humidity dependence.

Many conventionally used blow-molded containers are made of polyolefin, but polyolefin blow-molded containers have low moisture permeation due to the characteristics of polyolefin, and have low moisture permeability but high gas permeability. However, it did not meet the conditions for sufficient use.

For example, ethylene-
Saponified vinyl acetate copolymers (hereinafter referred to as saponified products) also include polyamides, polyvinyl chloride, polyvinyl alcohol, and the like.

Therefore, for example, if both materials are used to form a multilayer container in which a polyolefin layer and a saponified material layer are laminated, the excellent properties of both materials can be utilized to compensate for each other's shortcomings, resulting in a practically useful container. be able to.

However, a multilayer container made by extruding a multilayer parison consisting of a polyolefin layer and a saponified material layer and integrally molding it with a blow molding die has a part where the multilayer parison is sandwiched between split molds and welded together during blow molding. That is, the wall thickness of the pinch-off portion became thinner, and the saponified layer was exposed to the surface at the end of the pinch-off portion, resulting in a disadvantage of poor peel resistance.

One of the reasons why adjacent layers tend to peel off is that the inner surface of the pinch-off part has a V-shaped cross section, making this part thinner.As a means to solve the above problem, It is conventionally known to form outwardly projecting ribs 18 on the pinch-off portion 17 as shown in FIG. 7 to increase the contact area between adjacent layers.

However, by forming ribs as shown in FIG. 7, the contact area between adjacent inner layers 19 increases; however, for example, in the case of a multilayer container composed of an inner layer 19 made of saponified material and an outer layer 20 made of polyolefin. Since the inner layer 19 is exposed at the tip surface of the rib and is thickly interposed near the center of the rib 18 in a relatively unstretched state due to hollow molding, it is difficult to fully utilize the advantages of the inner layer 19, that is, the saponified material. Moreover, the peeling resistance could hardly be improved.

The present invention was created in view of the above-mentioned drawbacks, and the saponified layer is not thickly exposed on the tip surface of the rib, and the saponified layer interposed near the center of the rib is stretched, thereby reducing the effect on peel resistance strength. is extremely thin and even erased to the extent that it can be virtually ignored,
The present invention provides a multilayer container with excellent peel resistance and gas permeation resistance.

That is, by sandwiching and hollow-molding a multilayer parison in which at least two layers, including a main layer of polyolefin or the like and a gas permeation resistant layer of saponified material or the like, are stacked in a split mold, the multilayer parison is molded into the mold. In a multilayer container in which ribs are formed on pinch-off portions that are pinched, both side surfaces of the ribs are configured to be inclined so as to widen from the base end toward the distal end,
The width of the tip is 1.1 to 5 times the width of the base, preferably
1.25~3 times, and the height of the rib is 0.5~3 times the width of the proximal end.
By configuring 5 times, preferably 0.5 to 3 times, the contact area of adjacent layers is increased, and
Immediately before completely closing the mold, after filling the rib recesses above the cutout with resin, the resin near the outer layer that contacts the mold is kept within the ribs, and the resin near the inner layer that does not contact the mold is filled. By stretching the resin toward the base of the rib, the gas permeation resistant layer is not thickly exposed on the tip surface of the rib, and the effect of the gas permeation resistant layer interposed near the center of the rib on peel resistance is virtually ignored. extremely thin and even erased to the extent possible,
A multilayer container with excellent peel resistance and gas permeation resistance can be obtained. In addition, in the hollow-molded container body, the thickness of the gas permeation resistant layer is Tb=(x-0.5D ₁ /D ₂ )Ta 0.25≦x≦0.7 (where Tb is the thickness of the gas permeation resistant layer, Ta is the thickness of the main layer, D ₁ is the width of the rib base, D ₂ is the width of the rib tip)
Furthermore, in the rib formed at the pinch-off part, both sides of the rib are expanded from the proximal end to the distal end in the range of 3° to 40°, preferably 5° to 25°. By doing so, the resin near the inner layer can be pushed up toward the proximal end of the rib in a desirable state. In the above equation, if x is set in the range of 0.3≦x≦0.5, the resin near the inner layer can be pushed up toward the rib base end in the most desirable state.

In order to push the resin near the inner layer toward the proximal end of the rib as described above, during blow molding, the resin near the outer layer is held in the rib recess located above the mold cutout, and the resin flows from within the rib recess. It is necessary to prevent this from happening. Therefore, it is preferable to form fine irregularities on both inclined surfaces of the rib recess to increase the amount of heat exchange of the resin in contact with the inclined surfaces, so that the resin near the outer layer rapidly cools down. That is, in the rib formed in the pinch-off part, by forming fine irregularities on both sides of the rib, the resin near the outer layer is held in the rib recess located above the mold cutting part during blow molding, It can be suppressed from flowing from within the rib recess.

In the present invention, the main layer is a layer made of thermoplastic resin that protects the gas permeation resistant layer and is relatively thick among the container wall layers. Polyolefins with excellent blow moldability such as polyethylene, polypropylene, ethylene-propylene copolymer, polybutene-1, polypentene-1, etc., or modified polyolefins containing polar groups to improve interlayer adhesion, and other ethylene - It may be a vinyl acetate copolymer, an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, or a mixture of these and the above polyolefin.

In the present invention, the gas permeation resistant layer is a thermoplastic material with excellent gas permeability and an oxygen permeability coefficient of 200 c.c./atm・m ²・24 hr (20°C, 65% RH, thickness 0.025 mm) or less. The layer is made of resin, and the resin is, for example, saponified material, polyamide, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, or a mixture thereof. The saponified product (saponified ethylene-vinyl acetate copolymer) used in the present invention has an ethylene content of 25 to 75 mol% and a saponification degree of 80% or more, and when the ethylene content is lower than 25%, it is gas resistant. As the humidity dependence of permeability increases, the processability by extrusion molding decreases, and when the ethylene content exceeds 75%, the permeability to gases such as oxygen gas is lost. On the other hand, when the degree of saponification is lower than 80%, the permeability to gases such as oxygen gas is lost.
In addition, other resins such as polyethylene, polypropylene, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, and modified polyolefins containing polar groups to improve interlayer adhesion are also used in addition to resins with excellent gas permeation resistance. A mixture of 40% by weight or less may also be used.

Furthermore, the multilayer containers referred to in the present invention include bottles, tubes, containers, tank-shaped food containers, industrial chemical containers, etc., which are obtained by hollow-molding multilayer parisons between split molds.
There are also automobile parts such as gasoline tanks, and multilayer means at least two layers, a main layer and a gas permeation resistant layer, and further improves the interlayer adhesion between the main layer and the gas permeation resistant layer. Therefore, it is also possible to form an adhesive layer mainly made of a modified polyolefin containing a polar group or a mixture of a resin used for the main layer and the gas permeation resistant layer.

The specific layer structure is 2 layers...A/B 3 layers...A/B/A, A/C/B 4 layers...A/B/A/B, A/C/B/A 5 Layer...A/B/A/B/A, A/C/B/C/
It is used in the form of A (where A is the main layer, B is the gas permeation resistant layer, and C is the adhesive layer).

The following is an example of the present invention in which a polyolefin is used as the main layer and a saponified material is used as the gas permeation-resistant layer.
A multilayer container having a five-layer structure of saponified material layer/polyolefin layer will be explained based on the drawings.

In FIG. 1, 1 is a multilayer container showing an embodiment of the present invention, in which an inner layer 2, an outer layer 6, and an intermediate layer 4 are made of polyolefin, and an inner layer 3 and an outer layer 6 located between the inner layer 2 and the intermediate layer 4 The outer layer 5 located between the inner layer and the intermediate layer 4 is composed of a saponified material. Additionally, a rib 8 is formed at the pinch-off portion 7 of the container 1 to project outward. As shown in FIG. 2, both side surfaces 8a and 8b of the rib 8 are configured to be inclined so as to widen from the base end 9 toward the distal end 10.
The width D ₂ of the rib 8 is 1.1 to 5 times the width D ₁ of the base end 9, and the height H of the rib 8 is 0.5 to 5 times the width D ₁ of the base end.
If the width D ₂ of the distal end 10 is lower than 1.1 times the width D ₁ of the proximal end 9, and if the height H of the rib 8 is lower than 0.5 times the width D ₁ of the proximal end, the blow molding die is completely closed. Immediately before this, when the excessively filled resin in the rib recess is pushed up toward the proximal end 9, the layer state is likely to be disturbed and the peel strength is poor. The width D ₂ of the other tip 10 is the proximal end 9
If the width _D exceeds 5 times the height H of the rib 8, and if the height H of the rib 8 exceeds 5 times, the effect of pushing up the resin in the rib recess toward the proximal end 9 will not work, and the saponified material will reach the tip 10. It is exposed thickly and is relatively thickly interposed near the center of the rib 8 in a state that is not stretched due to hollow molding.

In addition, in the hollow-molded container body 1a,
The thickness Tb, which is the sum of the inner layer 3 and the outer layer 5 made of saponified material, is preferably 0.005 to 0.5 times the thickness Ta, which is the sum of the inner layer 2, the outer layer 6, and the intermediate layer 5 made of polyolefin. Wall thickness Tb is 0.005 of wall thickness Ta
If it is less than twice that, the thickness of the saponified material layer in the entire container will be extremely thin, and there is a risk that pinholes will occur when extruding the multilayer parison. On the other hand, if the wall thickness Tb exceeds 0.5 times the wall thickness Ta, there is a drawback that when pushing up the resin filled in the rib recess, the resin will be thick at the center of the rib 8 even if it is stretched.

Further, it is preferable that the thickness Tb is configured within the following range.

Tb=(x-0.5D ₁ /D ₂ )Ta 0.25≦x≦0.7 In other words, if the thickness Tb of the layer made of saponified material is thicker than the thickness Ta of the layer made of polyolefin, the space between the rib recesses The effect of pushing up the filled resin needs to be improved accordingly, and therefore the wall thickness ratio Tb/Ta is proportional to the rib width ratio D ₁ /D ₂ with a specific coefficient.

In addition, in order to push up the resin after filling the rib recess with the resin, the inner surface of the rib 8
It is effective for both a and 8b to widen from the proximal end 9 toward the distal end 10 within a range of 3° to 40°.

In addition, as shown in FIG. 2, the pinch-off portion 7
In the rib 8 formed on the rib 8, fine irregularities are formed on both end surfaces 8a and 8b, and the depth of the fine irregularity is 30μ to 1000μ (for example, 30μ to 600μ in the case of a small food bottle, and 30μ to 600μ in the case of a large gasoline tank). 400μ to 1000μ). That is, fine irregularities are formed on both slopes of the rib recess to bring the resin into contact with it during hollow molding, so that both sides 8 of the rib 8 to be molded are
In order to form fine irregularities that are almost faithful to a and 8b, the depth of the fine irregularities must be 30μ or more, and if the depth exceeds 1000μ, the shape of the rib 8 itself will be damaged, and the resin near the inner layer will not be cannot push up.

The fine irregularities mentioned above include striped patterns, sanded patterns,
It can be carried out with any fine irregularities such as embossed patterns.

Hereinafter, the process of manufacturing the multilayer container 1 will be explained based on FIGS. 3 to 6.

11 is multilayer parison 1 (hereinafter referred to as parison)
The extrusion head 12 is a split type mold, and the inner surface of the mold 12 is formed with a cavity 13 corresponding to the shape of the container to be molded, and a parison 1' is formed on the bottom parting line. A sandwiching cutout portion 14 is formed. Reference numeral 15 indicates a rib recess formed above the cutout 14, and 16 indicates an inclined surface formed on both sides of the rib recess 15, which is configured to expand in the direction of the cutout 14. 16 has fine irregularities formed thereon. Third
In the figure, polyolefin and saponified material melt-kneaded and plasticized in respective extruders (not shown) are joined in an extrusion head 11, and inner layer 2, outer layer 6, and intermediate layer 4 are made of polyolefin, and inner layer 3 is and outer layer 5 are extruded from extrusion head 11 as a five-layer parison 1' of saponified material.
The extruded parison 1' is placed in a split mold 12.
As shown in FIG. 4, as shown in FIG. The surface of the outer layer 2 in contact with the surface 16 rapidly hardens due to heat exchange caused by the contact. In this state, the inner layer 6 is still kept at a relatively high temperature and the fluidity of the resin is maintained. As the mold 12 further closes and the cut-out portion 14 approaches, the outer layer 6 is maintained in contact with the entire inclined surface 16 having fine asperities, as shown in FIG. is filled with resin. On the other hand, since the inner layer 2 and the intermediate layer 4 have fluidity, as they are compressed, they are separated inwardly and outwardly using the cutout 14 as a boundary, and the inner layer 3 and the outer layer 5 are bonded to each other. It constitutes an integrated layer within the rib recess 15. Furthermore, mold 12
As the closing progresses and the cut-out portion 14 approaches, as shown in FIG. A force is applied to the integrated layer of saponified material located near the center of the rib recess 15 in the direction of the cavity 13, and the layer is rapidly stretched and separated at the cut-out portion 14 as a boundary. Then, the pushed up resin is pushed up in the direction of the cavity 13, pushing up the fusion surface of the inner layer and completely closing the mold 12, so that the inner layer 2 is bonded to each other at the pinch-off part, and the outer layer 6 is also bonded to each other depending on the molding conditions. Although they are different, they are joined at least to the extent that the strength is not affected.
Moreover, the inner layer 3 and the outer layer 5 are bonded to each other to be integrated, and the thickness of the inner layer 3 and the outer layer 5 are gradually reduced. Furthermore, middle layer 4
The saponide is separated by the integrated layer of saponide.

Incidentally, the step of inflating the parison 1' by blowing a pressure fluid such as compressed air into the parison 1' is optionally performed in the process shown in FIGS. 4 to 6.

As described above, the present invention comprises a multilayer parison laminated with at least two layers, a main layer such as a polyolefin and a gas permeation resistant layer such as a saponified material, by sandwiching the multilayer parison in a split mold and hollow-molding the main layer. This multi-layer container has ribs formed on the pinch-off part formed by sandwiching the multi-layer parison between molds.The ribs have a special structure as explained in the example, so they have excellent peel resistance and are resistant to humidity. A multilayer container with excellent gas permeability resistance and no dependence can be provided.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway front view of a multilayer container according to the present invention, FIG. 2 is an enlarged sectional view of a pinch-off portion of FIG. 1, and FIGS. 3, 4, 5, and 6 are according to the present invention. FIG. 7, which is a schematic diagram of the manufacturing process of such a multilayer container, is an enlarged sectional view of a pinch-off portion of a conventional container. 1...Multilayer container, 2...Inner layer, 3...Inner layer,
4... middle layer, 5... outer layer, 6... outer layer, 7...
...Pinch-off part, 8...Rib, 9...Proximal end, 1
0...Tip.

Claims (1)

[Scope of Claims] 1. A multilayer parison laminated with at least two layers of a main layer such as a polyolefin and a gas permeation resistant layer such as a saponified ethylene-vinyl acetate copolymer is sandwiched between split-type molds and hollowed. In a multilayer container formed by molding, a rib is formed at a pinch-off portion formed by sandwiching the multilayer parison between molds,
Both sides of the rib are configured in an inclined manner so as to widen from the base to the tip, and the width of the tip is equal to the width of the base.
A multilayer container characterized in that the height of the rib is 1.1 to 5 times the width of the base end and the height of the rib is 0.5 to 5 times the width of the base end. 2 In the hollow-molded container body, the thickness of the gas permeation-resistant layer is 0.005 to 0.5 times the thickness of the main layer, and the following formula Tb = (x-0.5D ₁ /D ₂ )Ta 0.25≦x≦ 0.7 (Tb is the thickness of the gas permeation resistant layer, Ta is the thickness of the main layer, D ₁ is the width of the base of the rib, and D ₂ is the width of the tip of the rib)
The multilayer container according to claim 1, characterized in that the multilayer container is configured within the following range. 3 In the rib formed at the pinch-off part,
2. The multilayer container according to claim 1, wherein both sides of the rib widen from the proximal end to the distal end within a range of 3° to 40°. 4 In the rib formed at the pinch-off part,
2. The multilayer container according to claim 1, wherein fine irregularities are formed on both sides of the rib, and the depth of the fine irregularities is 30 μ to 1000 μ.