JPS63216B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a polyethylene terephthalate resin bottle that is mainly used for filling materials such as soy sauce and carbonated beverages by low-temperature to normal temperature filling. This is a manufacturing method.

[Prior Art] A polyethylene terephthalate resin bottle that is biaxially oriented by biaxial stretching has molecular chains aligned and microcrystals formed, resulting in improved mechanical strength and gas permeability. Furthermore, because it has excellent transparency and is non-toxic, it has begun to be widely used in applications such as filling liquid seasonings.

[Problems to be Solved by the Invention] Incidentally, although the polyethylene terephthalate resin bottle obtained by the biaxial stretching process has improved mechanical strength and gas permeability as a result of the biaxial stretching process, Due to biaxial stretching, significant distortion remains inside the bottle wall, and this distortion may be alleviated even over a short period of time, such as after the bottle is formed and before the filling process. This force causes shrinkage, and this shrinkage occurs in addition to the shrinkage of the bottle that occurs during the cooling process during demolding during bottle molding. For this reason, the polyethylene terephthalate resin bottle subjected to the biaxial stretching process has a significant problem in dimensional stability even at room temperature.

In contrast, the present invention has accurate grain (capacity), maintains the mechanical strength imparted by biaxial stretching, has extremely low deformation over time, and has excellent transparency. The purpose of the present invention is to provide a method for efficiently and economically obtaining a polyethylene terephthalate resin bottle having properties.

[Means for Solving the Problems] The method for producing a polyethylene terephthalate resin bottle of the present invention comprises a polyethylene terephthalate resin bottle heated to a stretching temperature above the glass transition temperature and below the melting point of the polyethylene terephthalate resin. When manufacturing a bottle by biaxially stretching and heat-setting a bottom cylindrical intermediate material in a blow-molding mold, the size of the blow-molding mold is set to the size of the bottle after molding. The size of the blow-molding mold is set to include the amount of shrinkage of the bottle that occurs during the cooling process during demolding, and the heating temperature of the blow-molding mold is set to be higher than the glass transition temperature of the polyethylene terephthalate resin. Moreover, the temperature is set so as not to exceed either the stretching temperature or 90° C., and the bottomed cylindrical intermediate material made of polyethylene terephthalate resin heated to the stretching temperature is expanded in biaxial directions. In addition, the method for producing a polyethylene terephthalate resin bottle includes biaxial stretching and heat setting, which comprises bringing the outer wall surface of the intermediate material into close contact with the inner wall surface of the molding die for at least 5 seconds.

The method for manufacturing a polyethylene terephthalate resin bottle of the present invention will be explained below with reference to the drawings.

In the method of the present invention, preferably a polyethylene terephthalate resin having an intrinsic viscosity of at least 0.55 is used, and the resin has a rounded end and is manufactured by any molding method such as an extrusion parison molding method or an injection parison molding method. A cylindrical intermediate material 1 is used. Mouth and neck part 2 of this intermediate material 1
It is convenient that the screw 3 for screwing the cap and the cap are formed in the same shape as the neck and the screw of the intended bottle.

When producing the intermediate material 1, cooling from the molding temperature to room temperature is not recommended, since if the cooling following the molding process is slow cooling, the so-called whitening phenomenon will occur due to the increase in crystals, resulting in a decrease in transparency. This must be done by rapid cooling.

In the method of the present invention, the manufactured intermediate material 1 made of polyethylene terephthalate resin is set in a blow molding mold, and then stretched in biaxial directions, and in the final step of the stretching process, the intermediate material 1 is extruded. Heat fixing is carried out by bringing the wall surface 4 into close contact with the inner wall surface of the mold for at least 5 seconds. In this case, the intermediate material is heated to a stretching temperature that is higher than the glass transition temperature and lower than the melting point of the polyethylene terephthalate resin constituting the intermediate material, and the blow molding mold is heated to a stretching temperature that is lower than the melting point of the polyethylene terephthalate resin. It is necessary to heat the film to a heat-setting temperature that is above the transition temperature and does not exceed either the above-mentioned stretching temperature or 90°C.

Therefore, immediately before setting the aforementioned intermediate material 1 made of polyethylene terephthalate resin into a blow molding mold where it is subjected to biaxial stretching treatment and heat setting treatment, the glass transition temperature of the polyethylene terephthalate resin is heated in a heating chamber. Stretching temperature that allows molecular orientation, which is below the melting point, that is, generally 70 to 220℃
must be heated to.

The intermediate material 1 heated to a predetermined temperature is set in a blow molding mold as shown by the reference numeral 5 in FIG. 2, and then compressed air is blown into the intermediate material 1.
At the same time as expanding the intermediate material 1, using the push-down rod 6,
The bottom part 4 of the intermediate material 1 is pushed down, and as shown in FIG. The outer wall surface 1a of the intermediate material 1 is brought into close contact with the inner wall surface 5a of the molding die 5 heated to a predetermined temperature for at least 5 seconds to perform a heat setting process, thereby producing a molded product having a predetermined bottle shape. It is intended to produce.

The stretching process shown in the drawings is performed by drilling a compressed air hole 8 on the axis of the push-down rod 6 and providing blow-off ports 9 ₁ , 9 ₂ , 9 ₃ on the lower end and side surface of the push-down rod 6 . This shows a case where the lowering rod 6 is used as a compressed air inlet for expansion, but the biaxial stretching process is performed by simultaneously biaxially stretching the intermediate material 1 set in the molding die 5, as described above. Alternatively, before expanding the intermediate material 1 by blowing compressed air, only the push-down rod 6 is actuated to stretch the intermediate material 1 uniaxially only in the axial direction, and then A sequential biaxial stretching method may also be used, in which the intermediate material 1, which has been stretched in the axial direction, is further stretched in the radial direction by blowing compressed air.

In the heat setting process after the biaxial stretching process in the method of the present invention, the outer wall surface 1a of the intermediate material 1, which has expanded due to the stretching process performed prior to the heat setting process, is fixed to the inner wall surface 5a of the molding die 5. However, if the temperature of the mold during this heat setting treatment is heated to a high temperature that exceeds the stretching temperature, a so-called whitening phenomenon will occur and cause devitrification. In such a case, not only is the heating control for this heat treatment process complicated, but the cost for heat treatment rises and becomes uneconomical. must be below the stretching temperature and below 90°C. On the other hand, if the temperature of the mold during the heat setting process is low enough to not reach the glass transition temperature of the polyethylene terephthalate resin constituting the intermediate material 1, the purpose of the heat setting process is to remove distortion. Since this cannot be achieved satisfactorily, the mold used for heat setting must have a temperature higher than the glass transition temperature of the polyethylene terephthalate resin.

Furthermore, in order to obtain the desired dimensional stability through the heat setting treatment at the above temperature, the outer wall surface 1a of the expanding intermediate material 1 is brought into close contact with the inner wall surface 5a of the molding die 5 for at least 5 seconds. If the contact time is less than 5 seconds, sufficient distortion cannot be removed.

Immediately after the heat setting process is completed, it is preferable to lower the temperature of the bottle 7 by an appropriate method to prevent the bottle 7 from being deformed during removal, and then take the bottle 7 out of the molding die 5.

The blow molding mold 5 can be heated and cooled by, for example, simultaneously providing a heat source and a through hole through which a cooling liquid or the like passes through the molding mold 5, and heating to a predetermined heat fixing temperature. By stopping the flow of the cooling liquid and setting the heat source, cooling after the heat setting process can be performed by turning off the heat source and allowing the cooling liquid to flow, so that the heat setting process The bottle 7 can be cooled by cooling the mold 5 or by directly blowing cooling air into the bottle 7 set in the mold 5.

Furthermore, during the cooling process when removing the bottle from the blow-molding mold after completing the stretching and heat-setting treatments as described above, a considerable amount of shrinkage occurs depending on the heat-setting temperature and time. ) will be different from that calculated from the mold, so in the method of the present invention it is necessary to use a blow molding mold of a size that takes into account such shrinkage. In general, the higher the heat-setting temperature and the shorter the heat-setting time, the smaller the amount of shrinkage of the molded bottle during cooling when it is removed from the blow-molding mold after stretching and heat-setting. By the way, when the heat setting time is 8 seconds, the shrinkage will be about 4.3% at 70℃, about 4.6% at 80℃, and about 5.3% at 90℃. As has been established, it is necessary to use blow molds that are sized to compensate for the amount of shrinkage that varies with heat setting time and heat setting temperature.

[Example] A bottle with a total height of 255 mm and a capacity of 1 is produced by producing an intermediate material made of polyethylene terephthalate resin by the injection parison method, heating it to the stretching temperature of 95 °C, and then heating it to the heat setting temperature of 86 °C. It is set in a blow molding mold, and then compressed air is blown into the transparent polyethylene terephthalate resin that has been biaxially stretched and heat-set in three different ways with blowing times of 6 seconds, 8 seconds, and 10 seconds. Made an excellent bottle.

In addition, in this method, the heat setting time for bringing the outer wall of the intermediate material into close contact with the inner wall of the mold is almost
This can be considered to be the same as the blowing time.

Figure 3 shows the total height and opening of the three types of bottles obtained after 30 minutes of molding.

The resulting three types of bottles were heated to 70°C after 30 minutes of molding.
Fig. 4 shows the changes in the total height and opening of the bottle measured after filling with warm water and leaving it at room temperature for 2 hours, and the difference from the total height and opening of the bottle before filling with hot water.

The three types of bottles obtained in the same manner after 30 minutes of molding were further left in an oven at 40℃ and RH75% for 1 to 5 days, and the changes in the total height and mesh of the bottles over time were measured. Figure 5 shows the total height of the bottle before filling and the difference between the opening and opening.

From Figure 4, the biaxially stretched and heat-set polyethylene terephthalate resin bottle obtained by the method of the present invention has excellent high-temperature dimensional stability that can withstand filling with high-temperature liquid at 70°C. Furthermore, from FIG. 5, it is clear that the material has excellent dimensional stability with a small amount of change over time.

[Operations and Effects of the Invention] The method for producing a polyethylene terephthalate resin bottle of the present invention comprises stretching a bottomed cylindrical intermediate material at a stretching temperature of at least the glass transition temperature and below the melting point of the polyethylene terephthalate resin constituting the intermediate material. Immediately following the biaxial stretching process, the outer wall of the intermediate material in the expanded state is heated to a temperature higher than the glass transition temperature of the polyethylene terephthalate resin, and the inner wall of the bottle is subjected to the axial stretching process. It is removed by heat-setting the inner wall of a blow-molding mold, which has been heated in advance to a temperature below the stretching temperature and below 90°C, for at least 5 seconds. A bottle made of polyethylene terephthalate resin that retains the same mechanical strength as it is, has extremely low deformation over time, and has excellent transparency. It is.

In addition, in the method of the present invention, the size of the blow molding mold that brings the outer wall of the expanded intermediate material into close contact with each other is adjusted to the amount of shrinkage of the bottle that occurs during the cooling process during demolding during bottle molding. Since the sizes are set to offset each other, it has the effect of making it possible to obtain a bottle with an accurate grain size.

Furthermore, in the method of the present invention, the stretching step and heat setting step of bottle forming are completed simultaneously, that is,
Since the production of stretched and heat-set polyethylene terephthalate resin bottles is completed in a series of steps, heat utilization efficiency is high, and the heating temperature of the blow molding mold is 90℃ or less. This provides functions and effects such as easy heating control of the mold and less expense for heating.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an example of the intermediate material used in the present invention, Fig. 2 is a sectional view showing the intermediate material set in a mold and formed into a bottle, and Fig. 3 is a sectional view showing an example of the intermediate material used in the present invention. FIG. 4 is a graph showing the total height and filling (capacity) of a bottle molded according to one example after 30 minutes of molding, along with changes in heat setting time. This is a graph showing the amount of change in the size (capacity) along with the change in heat setting time. It is a graph shown along with changes in fixation time. 1: Intermediate material, 5: Blow mold, 7:
Bottle, 5a: Inner wall surface of molding die 5.

Claims (1)

[Claims] 1 A bottomed cylindrical intermediate material made of polyethylene terephthalate resin heated to a stretching temperature above the glass transition temperature and below the melting point of the polyethylene terephthalate resin is biaxially stretched and heat-set in a blow molding mold. In the method of manufacturing bottles by processing, the size of the blow molding mold is determined by adding the amount of shrinkage of the bottle that occurs during the cooling process when demolding the bottle after molding. In a blow mold, the stretching temperature is set at a temperature that is higher than the glass transition temperature of the polyethylene terephthalate resin and does not exceed either the stretching temperature or 90°C. By biaxially expanding a bottomed cylindrical intermediate material made of polyethylene terephthalate resin heated to , and bringing the outer wall surface of the intermediate material into close contact with the inner wall surface of the molding die for at least 5 seconds, A method for producing a polyethylene terephthalate resin bottle, which comprises performing biaxial stretching and heat setting.