JPS58140225A - Molding of plastic bottle - Google Patents

Abstract

PURPOSE:To obtain the titled bottle which prevents the whitening in the stopper section and the bottom by a method wherein a preform is stretched axially only in the stopper section and the bottom and shifted into a die heated to a specific temperature and after stretched under an internal pressure, while thermally treated adhering to the inner wall of the die. CONSTITUTION:A preform 3 is placed into a heating furnace holding the open end 3c thereof with a holder 4 and heated to the stretching temperature. The stopper section 3a and the bottom 3b of the preform 3 is once heated slightly higher than other parts to facilitate the orientation thereat and a rod 5 is inserted thereinto the stretch it only at the stopper section 3a and the bottom 3b. Then, the preform 3 is set into a die 1 heated at a temperature lower by 30 deg.C than the melting temperature above the crystalizing temperature thereof and blow stretched with an internal pressure applied to the inside thereof. Under such a condition, it is thermally treated adhering for a specified time adhering to the inner wall of the die 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plastic bottle molding method, and its purpose is to mold a plastic bottle at a high temperature of 1λ (a temperature higher than the crystallization temperature of the preform and 30C lower than the melting temperature).
To provide a plastic bottle with a good appearance by preventing whitening of the Poldro stopper part and bottom part when a plastic bolt made of polyethylene terephthalate or other material is stretch blow-molded and heat treated in a mold heated to be.

Conventionally, in order to mold a plastic bottle with excellent thermal stability, a mold 1 is heated with a heater 2, as shown in the cutaway front view of FIG. 3-of-3 molding is performed, and during this bottle molding, 8 to 30 Kl /
7) A method of heat-treating in a gaseous state is generally used. .

In this case, there will be no problem if the temperature of the mold is below the crystallization temperature of the plastic (approximately 1000 F for PET), but if it exceeds the crystallization temperature, the stretching of the bottle stopper 3a and bottom 3b will be difficult. If this is not done sufficiently, whitening of the spherulites will occur in the four parts, significantly impairing the appearance and lowering the commercial value.

In order to prevent this kind of whitening, it is possible to make the temperature of the spout and bottom part higher than the body part during the heating stage of the preform before stretching, but this can make the molding unstable. Otherwise, the spout becomes extremely easily deformed.

This instability of forming is due to the ejection speed of the stretch rod,
This is due to the synergistic effect of minute fluctuations in the pressurized fluid (Af, 2°), and their start timings, resulting in variations in the wall thickness near the spout and at the bottom. It is extremely difficult to prevent this using normal methods.Also, the deformation of the spout part (B) is caused by the deformation of the spout, which is heated considerably during the preheating stage before blow molding, and is brought into close contact with the hot mold during the blow molding stage. This is something to be said.

The present invention has been made to solve the above problems, and involves stretching only the spout and bottom part in the axial direction by protruding a stretch rod into a preform heated to a stretching temperature.
Next, this preform is set in a mold heated to a temperature higher than the crystallization temperature of the preform and 30C lower than the melting temperature, and pressurized fluid is blown into the preform to mold the bottle. Furthermore, the plastic bottle has excellent thermal stability and does not cause whitening on the spout and bottom, which is a plastic bottle molding method characterized by applying heat treatment to the inner wall of a mold for a predetermined period of time while applying internal pressure. This provides a molding method.

As described above, the present invention will be explained with reference to FIGS. 1 to 3.
FIG. 1 shows the preform, FIG. 2 shows the preform in a state where the stopper and bottom part are stretched, and FIG. 3 shows the preform in a blow molded state. The molding order is as follows.

First, the preform 3 is attached to the holder 4 at its open end 3C.
The stretching temperature is maintained at (~) and heated to the stretching temperature by inserting it into a heating furnace (not shown). This stretching temperature varies depending on the resin age of the preform, but is 20° below the glass transition temperature (T g ).
~30C higher temperatures are preferred. and the preform 3
The spout part 3a and bottom part 3b are heated to a temperature slightly higher than the body temperature (for example, 2 to 5 degrees Celsius) so that they can be easily stretched, and the stretch rod 5 is inserted into the preform 3 as shown in FIG. Only the protruding spout portion 3a and the bottom portion 3b are stretched. In this case, the stretch rod is used to connect the spout part 3a and the bottom part 3.
Since b is stretched only in the axial direction, both parts 3ay3b and their vicinity can be stably and sufficiently stretched with uniform thickness. In addition, the opening end 3C of the preform is connected to the holder 4.
is cooled by cooling with cooling water 4a, so no deformation occurs, and even if it comes into contact with a heated mold during blow molding in the next mold, deformation occurs at the open end 3ciC of the preform. Not at all. Moreover, the temperature of the spout 3a and the bottom 3b stretched in this preliminary stretching step decreases due to contact with the stretch rod 5 and the cooling effect during stretching, so that when blow-stretched in the subsequent blow-stretching step, It is becoming difficult to grow.

Next, as shown in FIG.
/'cri), the preform is stretched and expanded to completely fill the inner surface of the mold l to mold the desired plastic bottle 30. In this case, since the frame portion 3a and the bottom portion 3b are difficult to stretch as described above, the body portion is mainly stretched, and the degree of stretching of the entire bottle is equalized, and a stable wall thickness without variation can be obtained. Therefore, internal pressure is further applied inside the bottle and held for a predetermined period of time to bring it into close contact with the inner wall surface of the mold l. Since the mold 1 is heated by the heater 2 to a temperature higher than the crystallization temperature of the preform and υ30C lower than the melting temperature, the bottle can be heat-treated by maintaining this close contact.

Since the plastic bottle V manufactured according to the present invention was stretched in advance and the entire bottle was blow-molded as described above, the entire bottle had a substantially uniform wall thickness, and the spout and bottom part were spherical. Not only is crystal whitening prevented and the appearance is good, but the strength decrease due to spherulite whitening as in the past is avoided.
It is resistant to impact and has excellent thermal stability without causing cracks or cracks.

[Brief explanation of the drawing]

Fig. 1 is a front view of the preform, Fig. 2 is a cutaway front view of the preform with the spout and bottom portion extended, and Fig. 3 is a front view of the preform.
The figure is a cutaway IE side view of the pre-stretched preform shown in Figure 2 being blow-molded with a mold, and Figure 4 is a cutaway W showing the mold of the conventional molding method and a fully molded plastic bottle.
In the top view, 7) 1゜l is the mold, 2 is the heater, 3 is the preform, 3a is the bottom of the plug part 3, 3c is the open end,
4 is a holding rod, 4at:i cooling water, and 5.6 is a stretch rod. Patent Applicant Mitsubishi Plastics Co., Ltd. Representative Patent Attorney Denbu Kido

Claims (1)

[Claims] 1. A stretch knot rod is protruded into the preform heated to the stretching temperature, and only the spout and the bottom are stretched in the axial direction, and then this preform is melted at a temperature equal to or higher than the crystallization temperature of the preform. The preform is placed in a mold heated to a temperature 30C lower than the preform, and a pressurized fluid is blown into the preform to form a bottle.The preform is then heat treated by being brought into close contact with the inner wall of the mold for a predetermined period of time while applying internal pressure. A plastic bottle molding method characterized by: