JPH01310933A - Preparation of container made of synthetic resin - Google Patents

Abstract

PURPOSE:To almost prevent the generation of heat shrinkage even when high temp. filling is performed by applying blow molding to a parison, which is formed from amorphous polyethylene terephthalate by injection molding, in a heated mold and quenching the molded body while holding the same to a pressurized state. CONSTITUTION:An amorphous polyethylene terephthalate resin is used to be molded into a parison having an arbitrary shape by injection molding and the molded parison is preheated before cooled perfectly and subjected to stretching blow molding to form, for example, a bottle-shape container. At this time, the surface temp. of a mold is set to 140 deg.C or higher and the polyethylene terephthalate constituting the container is set to crystallinity of 40% or more. Thereafter, the surface temp. of the mold is allowed to fall to 100 deg.C or lower while blow pressure is kept. Next, the blow pressure is released and the mold is opened to take out the bottle-shape container.

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for manufacturing containers made of synthetic resin, and particularly to a method for manufacturing containers with excellent heat resistance using amorphous polyethylene terephthalate resin (A-PET). KSummary of the Invention The present invention involves preheating a parison injection-molded with amorphous polyethylene terephthalate and blow-molding it in a mold heated to 140°C or higher, simultaneously heat-setting it, and then placing it in a pressurized state. Hold this mold at 100
The present invention relates to a method for manufacturing a container in which the container is rapidly cooled to a temperature below 1000 C, and then the container is removed from the mold, and almost no thermal shrinkage occurs even when high-temperature filling is performed.

[Conventional technology]

In recent years, disposable plastic containers have become widely used as an alternative to glass containers. In particular, recently, polyethylene terephthalate resin has come to be used as containers for carbonated drinks and juices due to its J3 chemical resistance, mechanical strength, transparency, and carbon dioxide permeability that is superior to polyethylene resin. . However, when used as a juice container,
In order to perform high temperature sterilization during filling, the container is required to have heat resistance and heat shrinkage resistance. The f2 bacteria conditions are not necessarily constant depending on the type of juice or manufacturing process, but are generally in the range of 85 to 95°C. If polyethylene terephthalate resin is simply subjected to stretch blow molding, it will thermally shrink at a temperature of about 70°C. Therefore, various techniques are used to improve the heat resistance and heat shrinkage resistance of such containers. The first method is to make a container by once stretch blow molding an injection molded parison with a bottom. This container is then heat-set using a heat-setting mold. The mold for heat setting is heated in advance, and after heat setting is performed for a certain period of time, the mold is cooled and then the container is removed. In this case, since the inside of the container is pressurized, the container is brought into close contact with the wall surface of the mold. In the second method, the mold is heated during stretch blow molding in the first method, and heat setting is performed at the same time. Then, the mold is taken out and heat shrinkage is allowed at this time. Stretch blow molding is then performed again using another mold having a volume comparable to that of the contracted container.

[Problems to be solved by the invention]

However, according to the first method, two types of molds of approximately the same size are required. In addition, stretch blow molding must be performed once, and the container may have a complex shape with irregularities that are approximately the same as the final product. Therefore, it becomes extremely troublesome to align such a container with a second mold having a corresponding shape. Furthermore, since the container placed in the mold is left to cool after being stretched and blown, it has to be heated again by the heat of the mold, which is a wasteful method in terms of energy. The second method also requires a mold for stretch blowing and heat setting, and a final blow mold. Moreover, the sizes of the two molds differ due to shrinkage after heat setting. Therefore, two types of molds of different sizes are required, which not only increases costs but also increases the size of the apparatus. In addition, the relationship between the sizes of the two molds must be balanced, as shrinkage M is affected by the resin grade and molding conditions in order to allow one degree of shrinkage after heat setting. It lacks applicability in some respects. Furthermore, since stretch blowing is performed again after heat setting, residual stress due to this stretch blowing will be present in the container, which poses a problem of adversely affecting heat shrinkage resistance during high temperature filling. The present invention was made in view of these problems, and aims to reduce the number of types of molds, reduce the size of the device, and suppress the shrinkage rate during high-temperature charging to a range that does not cause any practical problems. It is an object of the present invention to provide a method for manufacturing a heat-resistant synthetic resin container that allows for the following. Means for Solving Problem K] The present invention involves preheating a bottomed parison injection-molded from an amorphous polyethylene terephthalate resin to a necessary stretching temperature before it is completely cooled, and then applying the preheated gold to the required stretching temperature. The product is heat-set in the mold under biaxial stretch blow molding conditions, the temperature of the mold is rapidly cooled, and the molded product is held under pressure until it reaches a certain temperature or below, and then removed from the mold. be. Amorphous polyethylene terephthalate, which is a raw material for forming parisons by injection molding, has an intrinsic viscosity (IV) of 0.7 to 1.2 and a glass transition temperature of 65 to 80°C. A parison of any shape is molded by injection molding using amorphous polyethylene terephthalate resin in the range of . This molded body is unoriented and amorphous. Preheating is performed before the parison formed in this way is completely cooled down. This preheating method is performed by conventionally known methods such as oven heating, far infrared heating, and high frequency dielectric heating. The preheating temperature is preferably in the range of 80 to 130°C, preferably in the range of 90 to 100°C. The preheated bottomed parison is stretch blow molded to form a container having a predetermined shape, for example a bottle shape. A mold is used to mold the container. The mold has passages for passing heating and cooling fluids, which are connected to a source of heating and cooling fluids via switching valves. and preferably a valve and a check valve are connected to the heated fluid supply vibrator,
A pressure gauge is also connected. On the other hand, it is preferable that a valve and a check valve are connected to the cooling fluid supply vibe. Further, the outlet side of the passage of the mold is connected to a discharge vibrator, and a valve may be connected to this vibrator. When performing stretch blow molding using such a mold, the switching valve is switched to supply heating fluid from the heating fluid supply source to the passage in the mold, and the temperature of the mold is maintained at a predetermined temperature, preferably 140°C. Set the temperature to ℃ or higher. The heating fluid in this case may be heated oil or heated steam. Then, the preheated bottomed parison is attached to the mouth of the mold, and a stretching rod is inserted into the bottomed parison to stretch it in the axial direction. Next, blowing pressure is applied using compressed air supplied through the stretching rod to stretch it in the radial direction. The air pressure at this time is 15 to 25
It is preferably within the range of kg/c. The stretched container is heat-set by holding it at the above temperature and pressure for a predetermined period of time, for example, 6 to 10 seconds. The temperature of the mold surface is 140°C or higher, preferably 140 to 160°C. The polyethylene terephthalate constituting the container has a crystallinity of 40% or more by undergoing stretch blow heat setting. After this, cold W is performed without opening the mold and taking out the container, while maintaining the blowing pressure. That is, the switching valve is switched to circulate the cooling fluid into the mold passage through the cooling fluid supply vibrator. Then, the surface temperature of the mold is lowered to 100° C. or less. As the cooling fluid, for example, cooling water at about 10° C., liquid nitrogen gas, liquefied carbon dioxide gas, etc. may be used. The time required for descent is approximately 10 seconds. By cooling the mold while applying blow pressure, the container is solidified in its original shape. Next, the blow pressure is released, the mold is opened, and the bottle-shaped container is removed. In addition, since the surface temperature of the blow molding mold mentioned above, especially the temperature during blow molding and heat setting, and the cooling temperature have a large effect on the heat resistance of the container, experiments were conducted to investigate the relationship between these temperatures and shrinkage rate. Upon further investigation, the following facts were discovered. In other words, in order to manufacture containers with heat resistance that can withstand practical use, the surface temperature of the mold during blow molding must be approximately 140°C or higher, and the temperature of the mold during cooling must be lower than 100°C. It turned out to be favorable. Functions and Effects of the Invention According to the present invention, the injection-molded bottomed parison is preheated to the stretching temperature without being cooled. Therefore, the heat during injection molding can be used efficiently. In addition, after the temperature of the parison reaches the stretching temperature, blow molding is performed by biaxial stretching in a mold whose surface temperature is 140°C or higher, further heat setting is performed, and then the mold temperature is rapidly cooled and taken out. I have to. Therefore, only one blow molding process is required. Furthermore, the container can be molded using one mold without using separate heat-setting molds and cooling molds. Furthermore, there is no need to re-blow, and residual stress caused by stretch-blowing is completely removed at the time of heat-setting, so the container will not shrink during use, especially during high-temperature filling. Furthermore, since there is no need to transfer the container to another mold during manufacturing, there is no need to consider shrinkage during heat setting, and it is possible to obtain a container molded with high precision. According to the invention, therefore:
It becomes possible to obtain a container with excellent heat resistance under stretch blow molding conditions with efficient use of a heat source and high production efficiency. The equipment will also be downsized. K Example Example 1 A bottomed parison 10 as shown in FIG. 1 was molded from amorphous polyethylene terephthalate resin (IV=0.9) by injection molding. This parison 10 was blow-molded using a mold 18 as shown in FIG. 4 to form a bottle-shaped container 13 as shown in FIGS. 2 and 3. The bottomed parison 10 is provided with seven flange 11 on the upper end side, and the upper part of the seven flange 11 is a mouth part 12 to which a cap can be attached. Further, as shown in FIGS. 2 and 3, the bottle-shaped container 13 made from this parison 10 has a protrusion 14 formed in the longitudinal direction on the outer peripheral surface of the body part, and a protrusion 14 The gap is a recess 15 as shown in FIG. Next, the mold for molding the container 13 from the parison 10 will be explained. As shown in FIG. 4, the blow molding mold 18 has a hollow interior, and the mouthpiece 19 is attached to and detached from the opening at the upper end. In addition, the blow vibe 2 is inserted into the mold 18 through the base 19.
0 is inserted. Further, the opening on the lower end side of the mold 18 is closed by a bottom plate 21. Furthermore, a plurality of passages 22 are formed vertically penetrating inside the mold 18, and these passages 2
2 is connected to a steam pipe 23 and a cooling water pipe 24 shown in FIG. Manually operated valves 27 and 28 and a relief valve 29 are connected to the steam pipe 23, and further downstream there is a manually operated valve 3.
0, one-way valve 31, and solenoid valve 32 are connected in that order. Also, a manually operated valve 3 is connected in parallel to the relief valve 29.
3 is connected, and a pressure gauge 34 is connected to the tip side thereof. On the other hand, manually operated valves 35, 36 and a one-way valve 37 are connected to the cooling water pipe 24. Furthermore, a solenoid valve 38 is connected to the tip side of the one-way valve 37. Further, another electromagnetic valve 39 is connected to the cooling water pipe 24, and the cooling water flows into the tank through this electromagnetic valve 39. Further, the outlet side of the passage 22 of the mold 18 is connected to a manifold 40, and the downstream side of the manifold 40 is connected to a discharge port. The parison 10 shown in FIG. 1 was preheated to 100°C before being completely cooled after injection molding, and the surface temperature reached 1.
It was inserted into a mold 18 shown in FIG. 4 which was heated to 60°C. The parison 10 was placed in the recess of the mold 18 while being held by the blow vibe 20, and was stretched in the axial direction by moving the blow vibe 20 downward. Then, by supplying compressed air through the blow vibrator 20, the parison 10 expanded in the radial direction and was brought into close contact with the surface of the recessed portion of the mold 18, thereby performing blow molding. Mold 1 pressurized to a surface temperature of 160°C in this way
After the parison 10 is biaxially stretch-blow molded in the mold 8 and heat-set for another 7 seconds, the solenoid valve 32 is closed and the solenoid valve 38 is opened to coat the surface of the mold 18 with high-pressure water (9 kg/c/). for 10 seconds, then the container 13
I took it out. Note that the surface temperature of the mold 18 when taken out was 100° C. as shown in Table 1. Further, the crystallinity of the body portion of the container 13 was 50%. Further, the molding cycle time at this time was 36 seconds. The heat resistance of such a bottle-shaped container 13 was measured by the following method. That is, the internal volume of the preformed container 13 was measured by filling it with 20° C. water. Next, the container 13 was filled with water at 95°C or 85°C, allowed to cool to room temperature, and then discharged. Then, water at 20° C. was filled again, and the internal volume of the container 13 was measured. Then, the heat shrinkage rate was calculated from the measured values. That is, assuming that the initial volume of the container 13 is A and the volume after filling is B, the heat shrinkage rate is calculated by the following equation. Heat shrinkage rate - (A-8)/A It was found that the material had sufficient heat resistance. Example 2 The surface temperature of the blow molding mold was set at 140° C., and the other conditions were the same as in the first example above.
3 was manufactured. The crystallinity of the body portion of the obtained container 13 was 40%. When the heat shrinkage rate of such containers was measured in the same manner as above, when filled with hot water at 85°C, the shrinkage rate of the containers in Table 1 Example and Comparative Example was 0.9%. was. Comparative Example 1 A container was manufactured under the same conditions as in Example 1 except that the surface temperature of the blow molding die was set at 120°C. As shown in Table 1, the thermal shrinkage rate of this container is 2.5% when the temperature of the hot water to be filled is 85°C, and 8.5% when the temperature of the hot water to be filled is 95°C.
1%, and shrinkage was obvious from the appearance, making it impractical. Comparative Example 2 A container was manufactured under the same conditions as in Example 1 except that the surface temperature of the blow molding die was set to room temperature. At this time, the crystallinity of the body of the container was 28%. The heat shrinkage rate of such a container is 15.0% when filled with water at 85°C and 28.5% when filled with water at 95°C.
It contracted and deformed to the extent that it could no longer retain its original shape.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a parison used in a manufacturing method according to an embodiment of the present invention, FIG. 2 is a front view of a bottle-shaped container obtained by blow-molding this parison, and FIG. 4 is a longitudinal sectional view of the blow molding die, and FIG. 5 is a piping diagram thereof. The names of the main parts in the drawings are as follows. 10... Bottomed parison 13... Bottle-shaped container 18... Mold 20... Blow vibe 22... Passage 23... Steam piping 24... Cooling water piping

Claims (1)

[Claims] 1. A method for producing a parison by injection molding using amorphous polyethylene terephthalate, and then manufacturing a container from the parison by blow molding, which comprises preheating the parison to a temperature at which it can be stretched; , the parison is placed in a heated mold, blow molding is performed, and heat setting is performed at the same time, and then the mold is rapidly cooled down to a predetermined temperature or less while being kept under pressure; A method for manufacturing a synthetic resin container, characterized in that the container is removed from a mold. 2. The method for manufacturing a synthetic resin container according to claim 1, wherein the surface temperature of the mold is 140° C. or higher during the blow molding and heat fixing. 3. The method for manufacturing a synthetic resin container according to claim 1 or 2, characterized in that the surface temperature of the mold is lowered to 100° C. or less during the rapid cooling of the mold. 4. The manufacturing method according to claim 1, 2, or 3, wherein the crystallinity of the manufactured container is 40% or more in the body.