JPS5829215B2 - Multilayer hollow molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for blow molding multilayer resin bolts and the like formed by bonding multiple resin layers.

A number of multilayer blow molding methods have been devised in the past for producing multilayer resin bolts. Or, if the material is a resin that fully bonds to each other in a semi-molten state, there are no particular disadvantages, but this is difficult because the extrusion temperature of nylon and polyethylene is very different, for example. When applied to the production of multilayer resin bolts in which materials that are difficult to bond are bonded together to form each layer, there is a problem in that the respective materials are not fully bonded and easily peel off.

That is, the molding temperature range of the image materials is different, for example, low @concubine polyethylene is 140 to 180 °C, high density melon polyethylene is 160 to 200 °C, while 6-nylon is 235 to 250 °C. In the multilayer forming stage of coextrusion, the extrusion die temperature will naturally be set in accordance with the forming temperature of 6-nylon.

In this case, one material, polyethylene, will be extruded at a parison temperature that exceeds its reasonable forming temperature.

For this reason, (1) excessive fluidity appears due to the decrease in viscosity of the resin melted at high temperature, resulting in a decrease in resin pressure in the extrusion head, and a good multilayer tubular resin flow is not necessarily formed. It does not result in the extrusion of the desired multilayer parison.

Furthermore, the resin pressure within the extrusion die is reduced, and the adhesion between each layer is also likely to be reduced.

(2) The parison after extrusion naturally has increased drawdown, which becomes an obstacle to adjusting the thickness of each part of the product.

(3) The difference between the amount of heat retained by the parison and the amount of heat of the product at the time of completion of molding is the amount of cooling heat, and as the parison temperature i increases, the flow rate of the cooling medium in the mold and the cooling time also increase.

(4) Polyethylene is susceptible to thermal deterioration and requires the addition of an antioxidant, but it is not preferable to add this additive to containers for foods, medicines, etc.

(5) The 6-nylon layer, together with the polyethylene layer, transitions from a high-temperature molten parison to rapid cooling by extension in the mold, resulting in uneven film thickness distribution and deterioration of properties such as gas permeability. Cheap.

In this way, the multilayer hollow molded product obtained by the conventional molding method has a high molding temperature of the constituent resins, for example, when two or more resins differ by 35°C or more, the adhesiveness of each layer and the In addition, conventional molding methods tend to cause resin deterioration, the thickness of each layer becomes uneven, and the molding time becomes longer. Ta.

The present invention has been made to solve many of the problems mentioned above, and its purpose is to form a multilayer hollow molded body made of two or more types of resins with greatly different molding temperatures, by bonding the layers between each layer. In addition, the properties of the resins that make up each layer can be fully utilized, and there is no deterioration of the resin at lower molding temperatures, the thickness of each layer is uniform, and the molding cycle is shortened. It is an object of the present invention to provide a multilayer hollow molding method that allows the shaft to be formed.

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

In the figure, 1 is a three-layer parison extrusion die used for molding a three-layer container, and is composed of a die body part 2 and a die nozzle part 3.

Three molten resin supply ports 4, 5.6 are provided in the die main body 2 at positions shifted in the axial direction, and these are successively connected to the tubular resin channel 7 via annular grooves 4a, 5a, 6a, respectively. It is configured such that five tubular tubes join together.

This tubular resin flow path 7 is provided with an annular constriction portion 7b.

The tubular resin flow path 7 passes through the tubular resin cooling flow path 7a inside the die nozzle part 3 and is connected to a parison extrusion port 8 that opens to the die face.
is connected to.

A cooling chamber 9 is provided on the outer periphery of the die nozzle part 3, and 10 is a cooling medium inlet port, which is a cooling medium source (
(not shown).

Reference numeral 11 denotes an annular jet nozzle for cooling medium, which is connected to the die nozzle portion 3.
The die face is the tip of the die.

The spacing between the openings of this spout 11 is determined by the screw-on cylinder lid 12 having a cylindrical shape.
It can be adjusted or closed by adjusting the tension.

13 is a discharge port which can be opened and closed freely. Reference numeral 14 denotes a blockage ring for making the cooling medium flow evenly throughout the cooling chamber.

A hole 15 is bored through the axial center of the extrusion die 1.
The upper part of this hole 15 has a larger diameter than the lower part where the cooling chamber 9 is located.

A tube 16 that fits tightly in the small diameter part and has a gap with the inner surface of the hole in the large diameter part is penetrated through this hole 15, and a pipe 16 with a diameter smaller than that of this tube 16 is inserted through the hole 15. A thin tube 17 is installed through the gap in the radial direction.

The lower ends of the tube 16 and capillary tube 17 are both open below the die face, the upper end of tube 16 is open to the atmosphere, and the upper end of capillary tube 17 is in communication with a suitable source of pressurized air.

The compressed air from the upper end of this thin tube 17 is
It is ejected from the tip of 7 to the bottom of the die face, but when the parison is being extruded from the die face, this
It flows backward through the gap between the die nozzle part 3 and the pipe 16, and is discharged upward while cooling the center of the die nozzle part 3.

At this time, since there is a gap between the tube 16 and the die body 2, the die body 2 is not cooled.

The process of blow-molding a three-layer container having the inner and outer layers made of polyethylene and the middle layer made of 6-nylon using the extrusion die 1 having the above configuration will be described.

The polyethylene resin and the 6-nylon resin are each melted and pressurized by an extruder (not shown), and the polyethylene is divided into two parts and flows through the supply ports 4 and 6 to the annular grooves 4a and 6a, and the 6-nylon resin is flowed through the supply port 5. are respectively supplied to the annular groove 5a through
These are successively merged in the tubular resin channel 7, and the intermediate layer 6 is formed.
- A three-layer tubular flow with nylon and inner and outer polyethylene layers.

At this time, the die main body 2 is heated to an appropriate temperature for extruding 6-nylon.

The resin of each layer that has merged in the tubular resin flow path 7 flows directly down to the cooling flow path 7a of the die nozzle part 3, but before that, it passes through the throttle 7b, so that the Calorie pressure is applied in the thickness direction in this part. be done.

Then, the three-layer tubular flow flows into the cooling channel 7a of the die nozzle section 3.
At this point, the polyethylene of the inner and outer layers are cooled from the inside and the outside, and at the same time, the 6-nylon of the middle layer is also indirectly cooled.

Therefore, the viscosity of each resin increases in the die nozzle section 3, and the temperature of the 6-nylon layer is lowered to near the hardening temperature.

Further, at this time, each resin is cooled while passing through the die nozzle portion 3 and its viscosity increases, so that the extrusion pressure increases, and the resin passing through this portion is pressurized at this portion.

The three-layer annular flow whose temperature has been lowered in this manner is extruded as a multilayer parison from the parison extrusion port 8 opened in the die face.

This multilayer parison is then closed with a split-type mold (not shown), and a pressurized flow such as compressed air is introduced into the parison for blow molding, so that the middle layer is 6-nylon and the middle and outer layers are polyethylene. A multilayer resin bottle with a layered structure is obtained.

The structure of the extrusion die main body 2 described above, together with the die nozzle 3, has a variety of designs, and is not limited to the structure shown in FIG. 1. As shown in FIG. In order to blow cooling air from the parison, a tubular tube 22 provided with a slit 21 for air blowing may be provided independently so as to look over the outer periphery of the parison.

Note that this example shows a two-layer extrusion die 1a.

The multilayer blow molding method according to the present invention is as described in detail above, and in the multilayer blow molding method for molding a multilayer blow molded body formed by laminating two or more resins having significantly different molding temperatures, the molding force Loe temperature The respective resins are merged into a multilayered tube shape at the confluence section of the die body, which is set to the molding temperature of the resin with a higher temperature, and then pressurized in the thickness direction at the constriction section 7b, and further lowered to a temperature lower than that of the confluence section. Since the resin is pressurized in the cooled tubular resin cooling channel 7a by increasing viscosity due to cooling, it is extruded from the die face as a multilayer parison, and then blow molded, so the molding temperatures for forming each layer differ greatly. When two or more resins are combined in the die body, the molding temperature is set to the molding temperature of the higher resin, so each resin is uniformly merged and laminated.

Also, the multilayer tubular resin that has merged in this die body is in the constricted part 7b.
The multilayer tubular resin is pressurized in the thickness direction in the die nozzle, and is then cooled and pressurized in the die nozzle, so that the multilayer tubular resin after merging is pressurized in the thickness direction in two stages while flowing down the passage in the die. The resins in the layers, which have significantly different molding temperatures, are well bonded between each layer and do not peel off after molding, making it possible to obtain a multilayer hollow body with good adhesion.

Furthermore, since the two-stage pressurization is performed uniformly from both the inside and outside sides after the merging, each layer of the multilayered tubular resin can be squeezed at the same ratio to easily obtain a desired wall thickness ratio.

Furthermore, since the parison extruded from the extrusion die according to the present invention is cooled to a predetermined temperature +i, the amount of cooling heat during blow molding is reduced, and the molding cycle can be significantly shortened.

Furthermore, since the polyethylene whose temperature has been raised more than necessary during the formation of the tubular flow is immediately cooled down, there is no risk of thermal deterioration, thus eliminating the need for an antioxidant addition port.

Furthermore, since the parison is considerably cooled when it is extruded from the die face, drawdown does not occur, and the film thickness distribution is averaged during blow molding, and the air permeation resistance of nylon etc. can fully demonstrate its characteristics.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, with FIG. 1 being a longitudinal sectional view and FIG. 2 being a longitudinal sectional view showing another embodiment. 2 is a die main body part, 3 is a die nozzle part, 4,5° 6 is a molten resin supply port, 7 is an annular resin flow path, 7a is a constriction part, 9 is a cooling chamber, and 11 is a jet port.

Claims (1)

[Claims] 1 In a multilayer blow molding method in which two or more resins having significantly different molding temperatures are laminated and molded, each resin is mixed at the confluence part of the die body, which is set to the molding temperature of the resin with a higher molding temperature. are merged into a multi-layered tubular shape, and then pressurized in the thickness direction at the constriction section 7b, and further pressurized by increasing viscosity due to cooling in the tubular resin cooling channel 7a, which is cooled to a lower temperature than the merged section. A multilayer hollow molding method characterized by pressing a multilayer parison from the die face and then blow molding.