JPS6246336B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention aims to produce a multilayer stretched hollow container that has excellent gas and water vapor barrier properties, has good appearance such as transparency and surface gloss, and also has excellent physical properties such as drop strength, rigidity, and heat resistance. It is about the method. Specifically, when manufacturing a hollow container, a preform before being molded into a predetermined shape is formed into a multilayer bottomed cold parison by a multilayer blow molding method, and after being reheated to a predetermined temperature, it is molded into a mold. The present invention relates to a method for manufacturing a multilayer stretched hollow container in which the longitudinal direction is stretched with a stretching rod and the transverse direction is stretched with pressurized air. Conventionally, single-layer hollow containers made of polyethylene, polypropylene, and polyvinyl chloride have been on the market. Recently, multilayer containers made of a combination of resins with excellent gas barrier properties, such as nylon and ethylene-vinyl alcohol copolymers, and polyolefins have been attracting attention. This multilayer container has attracted attention and has been put into practical use, particularly in the food field. In addition, biaxially stretched polypropylene hollow containers have 5 to 6
Biaxially stretched hollow containers made of polyethylene terephthalate and acrylonitrile resin have recently been put into practical use as containers for carbonated beverages, and they have been used for cosmetics and pharmaceutical containers for many years. These hollow plastic containers have come into the spotlight as an alternative to glass bottles. In order to obtain a container with excellent content preservation properties, it is sufficient to use a resin with low gas permeability and water vapor permeability, but in such a single-layer resin container,
In addition to being expensive, it had the drawbacks of poor moldability. For this reason, the above-mentioned multilayer hollow container, which is a combination of resin with excellent gas barrier properties and polyolefin, has been attracting attention because of its low cost and stable moldability. However, since the container is mainly made of polyolefin such as polyethylene or polypropylene as its base material, it has the disadvantage that the contents cannot be seen through sufficiently. In addition, when used in a ring fluid container, certain conditions must be met in order to inspect for foreign substances in the contents, that is, it must have a transmittance of 60% or more at a wavelength of 450 mμ.
It was necessary to perform sufficient sterilization. Methods for this sterilization treatment include high temperature and high pressure sterilization (retort method), gas sterilization using ethylene oxide gas, and radiation sterilization. Among these sterilization methods, the gas sterilization method has the problem that the gas used is adsorbed into the plastic container. Furthermore, the radiation sterilization method was difficult to handle. Therefore, the retort method is used as the simplest and most stable sterilization method. However, this retort method required a container that could withstand high pressure. There has been a need for a molded container that satisfies the above conditions of gas barrier properties, excellent transparency, and heat resistance, and is also cost-effective. Therefore, it was found that a biaxially oriented multilayer container that takes advantage of the characteristics of each material satisfies the above conditions. This biaxial stretch blow molding is often used with polypropylene or polyethylene phthalate. Regarding the former, for example, as shown in Japanese Patent Publication No. 38-16245, a method for obtaining a hollow container with excellent mechanical strength is to heat the container to a crystalline melting point or below and expand it under internal pressure. Kaisho
No. 47-13670 describes a stretch blow molding process by reheating a continuous tube of mono-α-olefin polypropylene. Furthermore, Japanese Patent Publication No. 49-32962 describes a molding method in which a cut polypropylene tubular body is heated to a temperature above the crystalline melting point and below the melting point and then stretch-hollow-formed to produce a polypropylene hollow container. There is. As described above, it has been recognized that by biaxially stretching a crystalline polymer, the transparency, rigidity, and impact resistance are significantly improved compared to a hollow container formed by a conventional uniaxial stretching method. However, for biaxially stretched polypropylene hollow containers made from a single layer, most polypropylene is extruded into a tubular shape, then cut continuously or into a certain length, and then reheated to achieve sufficient stretching orientation. A biaxially oriented polypropylene container was obtained by stretching and blow-molding within a temperature range. At this time, the stretching in the longitudinal direction is carried out by pinching both sides of the tubular body with a pulling machine when the tubular body is taken up. In such a molding method, since molding is performed at a temperature below the melting point, there are restrictions on the thread diameter and shape of the container. Furthermore, since the tubular body is stretch-molded, it is suitable for cylindrical containers, but in the case of square or flat containers, the wall thickness distribution becomes uneven and it is difficult to synchronize with a wall thickness control device. Furthermore, there still remained problems in the molding process, such as a decrease in fusion strength at the pinch-off portion and a tail remaining at the bottom of the container because the bottom is grabbed and stretched. As a method for molding polyester or acrylonitrile resin, for example, as disclosed in Japanese Patent Publication No. 49-3073, polyethylene phthalate is first injection molded to form an amorphous tubular body with a bottom of a certain length.
There is a method in which this tubular body is mechanically stretched in the longitudinal direction using a stretching rod, and then stretched in the transverse direction using pressurized air to perform blow molding. Further, in Japanese Patent Application Laid-Open No. 51-101516, a control device for a biaxially oriented plastic container is described, in which an injection molded plastic preform of acrylic resin is molded, and the tip of the blow pin moves in the vertical direction, and the tip of the blow pin moves in the horizontal direction. A method of orientation with pressurized fluid is described. In most of these molding methods, a preform of a tubular body called a cold parison is reheated within a certain temperature and then stretch-hollow molded by injection molding. These materials are limited to polyethylene terephthalate and acrylic resins because they are materials that exhibit sufficient stretching effects and gas barrier properties necessary to retain the contents. In order to obtain a preform using these resins by injection molding, a single material must be used, which is expensive and economically inferior. Furthermore, since the preform is obtained by injection molding, a taper at a certain angle is required so that it can be easily removed from the cavity, which is a significant limitation.
Furthermore, since polyethylene phthalate has a more rigid molecule than polypropylene, its crystallization rate is slow and it is easily stretched, resulting in an amorphous transparent container. However, since the glass transition point is 70°C, when it is sterilized by the above-mentioned retort method at 100 to 130°C for 5 to 20 minutes, it becomes the original crystalline polyethylene terephthalate, whitening and devitrification. This biaxially oriented terephthalate container was prone to devitrification even when filled with hot water of about 70° C. or higher, and also suffered from significant deformation, resulting in poor heat resistance. The purpose of the present invention is to study these biaxially stretched blow molding methods, and to achieve a multilayer structure that not only provides an appearance such as transparency and surface gloss, but also has excellent physical properties such as drop strength, rigidity, and heat resistance. An object of the present invention is to obtain a method for manufacturing an axially stretched blow-molded container. Another object of the present invention is to provide a method for producing a biaxially stretched blow-molded container that eliminates molding restrictions as much as possible, allows hollow containers of many shapes to be obtained, and is easy to mold. The present invention is a method for manufacturing a multilayer stretched hollow container, in which a uniaxially stretched preform is molded by a multilayer blow molding method, and then reheated and stretched within a certain temperature range. The present invention will be explained in detail below. First, a uniaxially stretched preform is molded using a multilayer blow molding machine shown in FIG. For example, when molding a four-layer parison, the sub-extruders 1 and 3 and the main extruder 2 are connected to a multilayer die head 5 of three types and four layers. The main extruder 2 is supplied with polypropylene forming the inner layer. The sub-extruder 3 is supplied with a resin having excellent gas barrier properties such as intermediate layer (second layer from the outer layer) nylon or saponified ethylene-vinyl acetate copolymer. The other sub-extruder 1 includes
The outer layer and the middle layer (third layer from the outer layer) are supplied by a branch adapter. For this layer, a resin having good adhesiveness to the resin extruded from the sub-extruder 3 and the main extruder 2 is used. This resin is a modified polyolefin modified with an unsaturated carboxylic acid or its derivative. The amount of unsaturated carboxylic acid or its derivative grafted onto the modified polyolefin is 0.01 parts by weight per 100 parts by weight of the polyolefin.
~20 parts by weight. Furthermore, in order to improve adhesiveness, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylic acid copolymer, or hydrocarbon-based synthetic rubber and a tackifier such as rosin are added to the modified polyolefin. Sometimes. The amount added is 1 part by weight per 100 parts by weight of modified polyolefin.
~30 parts by weight. The resin extruded from each of these extruders is transferred to the inner layer, the third layer, and the second layer in the multilayer die head 5.
The layers and outer layers are sequentially laminated through concentric channels, and the four-layer parison is apparently extruded as one parison. The mold of the blow molding machine is a reduced shape of the container shape of the final product except for the mouth, and its size is 1/4 to 1/1.5 in the vertical direction and 1/5 to 1/1.5 in the horizontal direction. is within the range of This mold is used to mold a preform before being biaxially stretched. Unlike the conventional method described above, this preform is not limited in shape and can be formed into a shape close to that of the final product. Therefore, the bottom portion, which requires impact strength, can be made thicker, and an appropriate thickness distribution can be easily obtained even if the bottom portion is flat or square. Furthermore, since the mouth and bottom parts can be molded at a temperature higher than the melting temperature, it is possible to obtain an acute-angled shape, and furthermore, a product with strong fusion strength at the pinch-off part can be obtained. In addition, since a bottomed parison can be obtained in advance, no tail can be seen in the bottom gripping portion, resulting in an excellent appearance. Then, as shown in FIG. 2, the preform 6 is aligned with the mandrel 7 attached to the rotating shaft. Next, as shown in FIG. 3, the preform 6 is inserted and fixed onto the mandrel 7. This insertion is performed by automatic equipment. The preform is fixed by the regulation between the inner diameter of the mouth and the outer diameter of the mandrel. This fixed preform 6 is heated by a heating device 8, as shown in FIG. This heating device 8 is equipped with an infrared heater. At this time, the time and temperature settings are controlled so that the preform 6 has a temperature of 140 to 180°C. This heated preform is introduced into a final mold 9 as shown in FIG. When introduced into the mold 9, the stretching rod 10 is elongated as shown in FIG. 6, and is forcibly stretched in the longitudinal direction. This stretching rod 10 stops near the mold 9 at the bottom of the container and has a length that does not touch the mold 9. At the same time, compressed air is blown from the tip of the mandrel 7, and the container is sufficiently pressed against the mold wall. The mold is cooled with cooling water at a temperature of 5 to 10°C, and is sufficiently cooled at the same time as compressed air is blown into the mold. The temperature of the resin in the container during this stretch blow molding must be at a temperature that allows for sufficient stretching. This stretch-molded container 11 is taken out by opening the mold 9, as shown in FIG. The mandrel 7 then returns to the state shown in FIG. 2, and the aforementioned steps are repeated. As described above, in the manufacturing method of the present invention, after the preform of the container is molded, it is stretch-hollow molded. The container obtained by this method has excellent gas and water vapor barrier properties, and also has excellent physical properties such as heat resistance, transparency, and drop strength. In the detailed description above, modified polyolefin/
A four-layer structure of A/modified polyolefin/unmodified polypropylene was explained. (A is nylon with excellent gas barrier properties or saponified ethylene-vinyl acetate copolymer) Other containers having the following configurations can also be molded. There are also three-layer structures such as modified polyolefin/A/modified polyolefin and A/modified polyolefin/unmodified polypropylene. Next, examples of the present invention will be described. Example In a multilayer blow molding machine equipped with a four-layer die head, the outer layer was made of maleic anhydride-modified polypropylene (MI=1.0), and the middle layer (second layer from the outer layer) was made of saponified ethylene-vinyl acetate copolymer (MI= 1.5, mp=180℃), middle layer (third layer from outer layer)
The preforms were extruded so that the same resin as the outer layer and the inner layer was made of polypropylene (MI=1.0) to form preforms of 3 types and 4 layers. This preform was reheated to about 140° C., introduced into a mold, and stretched 1.5 times in the longitudinal direction and 3 times in the transverse direction to obtain a biaxially stretched four-layer hollow container. Table 1 shows the physical properties of this container. Comparative Example 1 A parison with the same four-layer structure as in Example 1 was molded,
This parison was molded by a conventional blow molding method to obtain a hollow container. The physical properties of this container are shown in Table 1. Comparative Example 2 A bottomed parison made of polyethylene terephthalate was molded by injection molding, and this parison was
After reheating to 100°C, it was stretched 1.5 times in the longitudinal direction and 3 times in the transverse direction to obtain a hollow container. The physical properties of this container are shown in Table 1. Comparative Example 3 A parison with a bottom made of polypropylene was molded by injection molding, and after reheating the parison to 140° C., it was stretched 1.5 times in the longitudinal direction and 3 times in the transverse direction to obtain a hollow container. The physical properties of this container are shown in Table 1.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a multilayer extrusion molding machine, and FIGS. 2 to 7 are explanatory diagrams showing the steps of the manufacturing method of the present invention.

Claims (1)

[Scope of Claims] 1. A uniaxially stretched preform with a multilayer structure including a resin layer with excellent gas barrier properties and a reduced size of the final container except for the opening is directly molded by blow molding, and this preform is rotated. It is inserted into a mandrel attached to a shaft and heated to 140°C using a heating device.
After reheating to ~180℃, it is heated vertically in the mold by 1.5~4
1. A method for manufacturing a multilayer stretched hollow container, characterized by stretching the container by 1.5 to 5 times in the transverse direction. 2. The method for producing a multilayer stretched hollow container according to claim 1, wherein the resin layer having excellent gas barrier properties is made of nylon or a saponified ethylene-vinyl acetate copolymer.