JPS5814307B2 - Multilayer molded product with reinforced pinch-off part and method for reinforcing the pinch-off part - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to reinforcement for increasing the strength of joints (pinch-off parts) of multilayer molded products.

For example, in multilayer molded products applied to large containers such as chemical drums and automobile gasoline tanks, the greatest focus is currently on increasing the strength of the pinch-off portion.

Pinch-off always occurs in multi-layer molding (blow molding, clamshell, etc.), but this pinch-off part has lower strength than in the case of a single-layer molded product.

Conventional methods that have been attempted to increase the pinch-off strength in this multilayer molding include: ■ Research on pinch-off shapes, and at this stage, the method is to increase the bonding area by increasing the adhesive force ■ The adhesive force between each layer There is a way to try to increase the pinch-off strength by making it stronger.

However, in this method (■), the pinch-off part becomes large and strength cannot be achieved unless it is made larger than practically allowable, so this solution has the disadvantage that it can only be applied to a very limited number of designs. There is.

Furthermore, according to method (2), the resin for the adhesive layer is expensive, which not only increases the cost of the finished product, but also no resin with very high adhesive strength has been developed.

In addition, due to physical properties, when resins of different types are firmly adhered, problems such as increased distortion and decreased impact strength occur.

The purpose of the present invention is to improve the strength of multilayer molded products by eliminating defects in the concept of increasing the strength of pinch-off parts of multilayer molded products and solving weaknesses in the pinch-off parts. In a multilayer molded product having a multilayer molded product, a resin that is weldable to the outer layer is applied between the outer layers separated by a resin such as an inner layer at the pinch-off part of the multilayer molded product, and the resin is welded to the outer layer to form an integrated product. The present invention relates to a multilayer molded product with a reinforced pinch-off portion, characterized by: and a method for reinforcing the pinch-off portion.

Embodiments of the present invention will be described below with reference to the drawings.

Figures 1 and 2 show the cross-section of the pinch-off part in a normal configuration of a multilayer molded product. The figure shows a cross section of the shape.

In the figure, the inner layer 1 is made of a gas barrier resin such as nylon or saponified EVA and has a thickness of 100 to 200 microns.
The middle layer 2 is made of adhesive resin and has a thickness of 100 to 200 microns, and the outer layer 3 is made of high-density polyethylene, and depending on the purpose, ultra-high molecular weight (polyethylene) is used, and the thickness is determined by the conditions of use. It is something.

Since such a multilayer molded product is molded from a parison, (a
) There is a pinch-off part like this.

In this pinch-off part (a), the resin of the outer layer 3 is separated from the inner layer 1 by the interposition of the resin of the intermediate layer 2, so the strength of the pinch-off part is weak.
It is simply glued and held in place with adhesive resin.

Therefore, it is difficult to obtain the same pinch-off strength as a single-layer molded product.

For this reason, in the case of a normal pinch-off shape as shown in FIG. 1, for example, it may be possible to remove the inner layer 1 and intermediate layer 2 of the pinch-off part (a) during molding, and weld the pinch-off part only as the outer layer 3. However, the shape of the pinch-off portion in the longitudinal direction is complicated and is not practical, and even if the pinch-off shape is a linear shape, the mold is complicated and is not practical.

Further, the structure (FIG. 2) in which the strength is increased by increasing the pinch-off length without welding only the outer layer 3 as described above has the drawbacks described in method (2) above.

FIG. 3 shows a partial cross section of a molded article according to the present invention.
Between the outer layer 3 separated by the presence of the inner layer 1 and the intermediate layer 2 at the pinch-off part (a), a reinforcing resin 4 having weldability with the resin of the outer layer 3 is brought into contact and pressure-welded to form the pinch-off part. One and the other outer layer 3 are integrally connected via the resin 4 so that the resin of the outer layer 3 wraps around the inner layer 1 and the intermediate layer 2.

With this configuration, the same effect as welding of the outer layers 3 of the pinch-off part is produced, the pinch-off part is reinforced, and the pinch-off part (
The strength of a) can be significantly improved.

Next, a method for reinforcing the outer layer 3 by welding the reinforcing resin 4 will be explained. The welding of the resin 4 is carried out immediately after blow molding a multilayer molded product using a normal method and taking the product out of the mold. to be done.

In other words, the molded product is cooled to the limit that it does not deform after being released from the mold, so the outer surface in contact with the mold is cooled to around 20°C and hardened, but the inner surface is at a temperature of 80 to 150°C. ing.

For this reason, first, cut off the edge from the pinch-off part of the finished product taken out from the mold, and make it into a state as shown in Figures 1 and 2.
Next, a reinforcing resin 4 that is weldable to the resin of the outer layer 3 is applied.
After being heated to 150 to 300° C. to make it plastic, the plasticized resin 4 is applied across the outer layer 3 of the pinch-off portion, pressure welded, and cooled.

This pressing operation of the resin 4 is carried out by pressing the resin 4 in a plastic state against the pinch-off portion from the outside using, for example, a roller, cooling it to approximately room temperature by air cooling, and releasing it.

At this time, the thickness of the resin 4 is determined depending on the required strength of the product.

In addition, as described above, the present invention realizes strong welding by using the heat capacity of the resin 4 and the amount of heat inside the molded product immediately after molding the product, but the temperature drops to room temperature as time passes after molding. When the finished product is pressed, heat is taken away from the resin 4 and the resin does not weld.
It is necessary to preheat the product.

In this case, pressure welding of the resin 4 is preferably performed by heating the pinch-off part to the required preheating temperature, that is, to a temperature (approximately 60 to 150°C) that is close to the melting point of the product and does not soften the pinch-off part.

Further, any method such as ultrasonic welding or hot plate heating welding can be used for welding, and rapid cooling by forced air can be used as needed for air cooling.

Next, the present inventors measured the strength of the pinch-off portion of the tank reinforced according to the present invention and the tank that was not reinforced in the following manner, and the results are shown below.

The object of the experiment was a multilayer molded product with an inner layer of nylon, an intermediate layer of high-density polyethylene, and an outer layer of ultra-high molecular weight polyethylene, and a tank with a capacity of 55 liters and a weight of 5 Kp.
The shape of the pinch-off part on the top and bottom of the tank is the same, and the length is 600mm.
mm, resin 4 is 15mm wide and 1
A tank whose pinch-off portion was reinforced according to the present invention using a resin having an adhesive force of ~3 kg and a tank whose pinch-off portion was not reinforced with resin 4 were used.

Both tanks were filled with 50 liters of water and sealed, and the effect was measured at the critical height at which the pinch-off part would break, using a fall method in which the pinch-off part hit the concrete surface.

First, a tank reinforced according to the present invention was dropped from a height of 7 m twice, but the pinch-off part did not break, but in the case of an unreinforced tank as shown in Figure 2,
The pinch-off part was destroyed by dropping it from a height of m.

From this result, it was confirmed that the tank according to the present invention has several times the strength of the tank without reinforcing the pinch-off portion.

Note that the present invention is not limited to the example shown in FIG. 3, but can also be applied as shown in FIGS. 4 to 6.

Fig. 4 shows an example in which the outer layer 3 of the pinch-off part is wrapped with a resin 4 having a U-shaped cross section, Fig. 5 shows an example in which the outer layer 3 of the pinch-off part is reinforced with a resin 4 having a This is an example in which the resin 4 is reinforced with a mold cross section.

As described above, according to the present invention, the strength of the pinch-off part of a multilayer molded product can be significantly improved, which facilitates its practical application to large containers such as automobile gasoline tanks and chemical drums. By welding, it becomes integrated with the outer layer and can enhance the reinforcing effect.

, and other excellent effects can be achieved.

[Brief explanation of the drawing]

1 and 2 are both partial sectional views of a multilayer molded product showing the shape of a conventional pinch-off part, FIG. 3 is a partial sectional view of a molded product of the present invention, and FIGS. 4 to 6 are FIG. 3 is a partial cross-sectional view showing an application example of the present invention. 1...Inner layer, 2...Middle layer, 3...
...outer layer, 4...resin.

Claims (1)

[Scope of Claims] 1. In a multilayer molded product having a pinch-off portion, a resin having weldability to the outer layer is applied between the outer layers separated by a resin such as an inner layer at the pinch-off portion of the multilayer molded product, A multi-layer molded product with a reinforced pinch-off part that is welded to the outer layer to form an integral piece. 2. In a multilayer molded product having a pinch-off part, the pinch-off part is heated to 60 to 150°C, a resin that is weldable to the outer layer of the pinch-off part is heated to 150 to 300°C to make it plastic, and then, A method for reinforcing a pinch-off part of a multilayer molded product, characterized in that the resin in a plastic state is passed between the outer layers separated by the inner layer at the pinch-off part, pressure welded, and then cooled.