JPH058087B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a highly efficient method for obtaining biaxially oriented bolts from ethylene terephthalate-based polyester resin that have low thermal shrinkage and have a shape that is faithful to the shape of a mold. (Prior art) Bottles made of polyester resin, typified by polyethylene terephthalate, are widely used for various purposes due to their excellent transparency, strength, and hygienic properties. However, they have been known to shrink when exposed to high temperatures. There are some difficulties. In order to overcome this drawback, a method is known in which blow-stretched bolts are heat treated at high temperatures, but if the bolts are not heat-treated for a considerable period of time, the bolts will shrink and deform when taken out, resulting in extremely slow bolt manufacturing speed. Put it away. (Problems to be Solved by the Invention) The present invention solves the conventional problem that trying to obtain a bottle with low heat shrinkability reduces the manufacturing speed, and increasing the manufacturing speed only results in a bottle with high heat shrinkability. This solves the problem. (Means for Solving the Problems) That is, the present invention heats a polyester cylindrical parison with a bottom to 110 to 125°C, and places the parison in a mold whose surface is maintained at 80 to 110°C. The bottle is stretched at a stretching speed of 25,000%/min or more, and the resulting bottle is subsequently held in the mold while being pressed, and then released from the mold. The present invention will be specifically explained below. The polyester resin used in the present invention contains 70% or more of ethylene terephthalate units, and a conventional resin having an intrinsic viscosity of 0.6 or more can be used. Methods for obtaining a parison from this polyester resin are also conventionally well known, such as obtaining a parison in the shape of a cylinder with a bottom by injection molding, or by closing one end of a pipe produced by extrusion molding to form a cylinder in the form of a cylinder with a bottom. In stretch-blow molding this parison, the parison temperature is in the range of 110 to 125°C, and the parison is blow-stretched at a stretching speed of 25,000%/min or more in a mold whose surface is maintained at 80 to 110°C. It is important to do this. In general, when the mold temperature is raised, the heat treatment effect when the blow stretch-molded bottle comes into contact with the mold becomes larger, and the heat shrinkability of the bottle becomes smaller.
At high temperatures exceeding 100°C, the bottle shrinks and deforms when it is removed from the mold, making it impossible to obtain a bottle with the desired shape and capacity in a short period of time. As a result of the study, it was found that when the mold temperature is set in the range of 80 to 100℃, it is possible to significantly reduce heat shrinkage by simply bringing the bottle into contact with the mold for a short time, and it is also possible to remove the bottle. However, the shrinkage and deformation of the bottle still remained, which could not be said to be sufficient. As a result of further investigation, we found that if we raise the parison temperature to 110-125℃, which is higher than normal temperature, and blow-stretch it, the bottle can be taken out while maintaining its mold shape even if the mold temperature is raised to about 110℃. They found that the strength of the bottle was slightly reduced, but this could be solved by stretching at a high speed of 25,000% or higher. When the parison temperature is lower than 110℃, 80~110℃
If a mold maintained at a constant temperature is used, the shape of the bottle taken out will not be accurate, and if the temperature is higher than 125°C, crystal whitening will likely occur in the parison during heating. Polyester resin parison on the inside and outside
To heat the parison to 110-125°C, it is preferable to heat the parison from both the inside and outside. If heating is performed only from the outer surface, the inner surface of the parison, where the stretching ratio is greatest, will be at a low temperature, making it difficult to obtain the desired bottle. Methods of heating the parison from the inside include (1) inserting a radiant heater such as an indicative heater inside the parison; (2) inserting a hot air blowing rod inside the parison;
How to heat with hot air. (3) A method in which a black body rod is inserted inside the parison, and among the radiation from an external infrared heater, visible to near-infrared light that is not absorbed by the polyester parison is absorbed by the internal rod to raise the temperature. There is. In addition, if you want to create an axial temperature distribution on the inner surface, you can move a radiation heater, which is much shorter than the length of the parison, in the axial direction of the parison in a predetermined movement-stop pattern, and heat each part of the parison over a heating time. It is also effective to provide a desired temperature profile by changing the temperature. The mold maintains its surface at 80-110℃. 80
If the temperature is lower than ℃, the heat shrinkage of the bottle will increase.
If the temperature exceeds 110℃, the shrinkage deformation when taking out the bottle will increase. The stretching speed is 25000%/min or more, preferably
Set to 35000%/min or higher. If the temperature is lower than that, the parison will be at a high temperature, so the stretching orientation effect will be reduced, and the strength of the bottle will be reduced. The upper limit of the stretching speed is about 50000%/min. The stretching speed can be adjusted by adjusting the amount of blowing air. Note that the stretching speed here is
Stretching magnification in the circumferential direction (displayed in %, for example, 3x magnification is
200%) divided by the time from the start of blow stretching to contact with the mold, which is the average stretching speed in the circumferential direction. The stretching speed in the axial direction is usually lower than this because the axial magnification is usually smaller than the circumferential magnification. The stretching ratio is 2 to 3 times in the axial direction, which is a normal condition, in order to give the bottle sufficient strength.
The magnification should be as high as possible within the range of 3 to 4 times in the circumferential direction. The blow-stretched bottle is brought into contact with the inner surface of the mold for about 2 to 15 seconds while maintaining the internal pressure (blow pressure), and then the internal pressure is released and the bottle can be taken out without any particular cooling process. (Example) By injection molding from polyethylene terephthalate resin with an intrinsic viscosity of 0.85, the body has an outer diameter of 27 mm and a length of
A parison of 125 mm and 3.6 mm thickness was manufactured. This was heated from the inside and outside with an infrared heater, then blow-stretched, and brought into contact with the mold for 4 seconds while maintaining the internal pressure, and then taken out.
mm, and the bottle had a capacity of 1 liter. The stretching ratio is 2.5 times in the axial direction and 3.5 times in the circumferential direction. Here, the following quality items were evaluated for the resulting bottles by changing the parison temperature, mold temperature, and stretching speed. (1) Heat shrinkage rate Fill a bottle with 72°C hot water up to the bottom of the neck, measure the full capacity at room temperature, leave it unstopped at room temperature for 24 hours, then measure the full capacity, and calculate the rate of decrease in capacity. is expressed as a percentage. (2) Tensile yield strength 65mm length taken along the circumferential direction of the bottle,
The yield point strength was determined when a test piece with a width of 3 mm was pulled at a tensile speed of 50 mm/min in accordance with ASTM-D1822. (3) Bottle shape The shrinkage rate of the bottle immediately after being removed from the mold is 5% or less in terms of capacity and 2% in dimensions compared to the shape of the mold.
% or less: ○, larger than that: ×
And so. Blow stretch molding conditions and bottle quality evaluation results are also shown in Table 1.

[Table] From the results, it can be seen that the bottle (No. 7) obtained by the method of the present invention is already excellent in all properties. (Effects of the Invention) According to the present invention, by stretching a parison at high temperature and high speed in a mold maintained at an appropriate temperature, a bottle with a small thermal shrinkage and an accurate shape can be manufactured with high efficiency.

Claims (1)

[Claims] 1 In a method for producing a biaxially oriented bottle by blow-stretching a parison of ethylene terephthalate polyester, a bottomed cylindrical parison is heated to 110 to 125°C, and the parison is heated to a temperature of 80 to 125°C.
The bottle is stretched at a stretching speed of 25,000%/min or more in a mold maintained at 110°C, and the resulting bottle is held while being pressed against the mold, and then released from the mold. A method for manufacturing polyester bottles.