JPH08323851A - Extrusion blow molding method - Google Patents

Abstract

PURPOSE: To prevent the drawdown of an extrusion molded parison, to set that the parison is adjusted to temp. suitable for stretch blow molding to a technical subject and to adapt extrusion blow molding as a molding means of a bottle body made of a saturated polyester resin. CONSTITUTION: A parison 1 of a saturated polyester resin is forcibly cooled from the outer surface 2 thereof while subjected to extrusion molding to be adjusted to viscosity not generating drawdown and cooled to temp. developing stretching effect while the inner surface 3 thereof is held to a molten state and, in this state, cutting and stretch blow molding are achieved by a mold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extrusion blow molding method for molding a synthetic resin bottle made of a saturated polyester resin such as a polyethylene terephthalate resin and forcibly cooled.

[0002]

2. Description of the Related Art Conventionally, for example, when a hollow container such as a bottle is molded from polyethylene terephthalate resin (PET), heat-melted PET is injection-molded into a preform molding die to form a preform, and then natural preform. The cooled preform was heated again to a temperature suitable for blow molding and stretch blow molded, and the physical properties that were satisfactory as a bottle were obtained by going through such a plurality of steps.

In contrast to the ordinary stretch blow molding described above, a parison obtained by extruding heat-melted PET from an extruder is used.
There is an extrusion blow molding method in which stretch blow molding is performed without the steps of molding into a preform and reheating, but this extrusion blow molding method is a general method for stretching blow molding a parison in a molten state. Compared to stretch blow molding, the shape of the bottle can be molded extremely well.

Further, a so-called one material, which is not possible with ordinary stretch blow molding, can mold a bottle body without molding a preform, or can mold a bottle body in which a handle is integrally molded from one parison. It has the great advantage that it can mold bottles with handles.

[0005]

However, the product molded by the above-mentioned conventional extrusion blow molding method has a problem that it is inferior in physical properties to a general blow molded product, such as being weak against a drop impact. .

This is because the parison formed by extruding the PET resin or the like melted in the extruder through a die is stretch-blow-molded, so that the parison naturally has a low resin viscosity at high temperature and causes a so-called drawdown that extends due to its own weight. , The lower part of the bottle is thicker and the upper part is thinner,
One reason is that the thickness cannot be controlled.

Further, since the parison at the time of stretch blow molding has a temperature of at least the melting point or higher, that is, a temperature higher than the temperature suitable for stretching (stretching temperature), oriented crystals of the stretched resin material cannot be achieved well. There is.

Therefore, the present invention was devised to solve the above-mentioned problems in the prior art. In the extrusion blow molding method, the occurrence of drawdown of the extruded parison is prevented and the parison is prevented. It is a technical problem to make the temperature suitable for stretch blow molding, and it is therefore an object of the present invention to enable the extrusion blow molding method to be suitably applied as a molding means for a bottle of a saturated polyester resin.

[0009]

Means for Solving the Problems The means for solving the above technical problem is to cool the outer surface of a parison of a saturated polyester resin material in a molten state, which is being extruded from an extruder. Cooling prevents the parison from drawing down and brings the parison close to the temperature suitable for stretch blow molding (stretching temperature), and prevents this drawdown and cools the parison cooled to a temperature suitable for stretch blow molding. , Stretch blow molding into a bottle.

It is preferable to start cooling before the parison extruded from the extruder reaches a certain length and drawdown starts due to its own weight, and stop the cooling when the parison is extruded to a predetermined length.

It is desirable to minimize the cooling strength immediately after the start of cooling and then increase the cooling strength as the parison is extruded.

It is advantageous to achieve cooling by blowing air.

[0013]

Since the outer surface of the parison that is being extruded from the extruder is cooled, the viscosity of the outer surface portion of the parison becomes high, and drawdown does not occur in the parison due to the increased viscosity of the outer surface portion.

Since no drawdown occurs,
The thickness of the parison will be as set for the entire length,
Since the thickness of the bottle molded by the subsequent stretch blow molding is also as set, the physical properties such as impact resistance are almost the same as those of the bottle which is biaxially stretch blow molded from the usual injection molded preform. .

Further, by cooling the outer surface of the parison, the temperature of the parison in the molten state is brought close to the stretching temperature for stretch blow molding, so that compared to the conventional stretch blow molding at a high melting temperature. The oriented crystals of the saturated polyester resin material are smoothly carried out, and the physical properties of the bottle are improved.

Since only the outer surface of the parison is cooled, the inner surface is indirectly cooled, but the melting temperature is still maintained, and the temperature of the parison (at least the inner surface) at the time of mold clamping during stretch blow molding is melted. The temperature is maintained.

Therefore, the welding of the cut portion by the mold can be achieved well, and the original advantages of the extrusion blow molding (the shape of the bottle can be excellently formed, and the handle and the like can be integrally formed). It still works.

The parison extruded from the extruder reaches a certain length, cooling is started before the drawdown starts due to its own weight, and the cooling is stopped when the parison is extruded to a predetermined length. It is possible to prevent drawdown before the parison is cooled more than necessary, that is, while maintaining the inner surface of the parison in a molten state.

Further, the cooling strength is minimized immediately after the start of cooling, and then the cooling strength is increased as the extrusion of the parison progresses. In addition to being able to properly cool the entire surface of the parison by heating the inner surface of the parison, the temperature distribution pattern on the cylinder wall of the parison can be made uniform at a temperature suitable for stretch molding. .

By performing the cooling by blowing air, it becomes easy to accurately control the degree of cooling of the parison by setting the temperature of the cooling air and controlling the flow rate, and the strength control of the cooling is easy. Therefore, it becomes possible to simplify the configuration of the cooling equipment.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method of the present invention will be described with reference to the drawings. In this embodiment, as shown in FIGS. 1 to 3, the die 5 of the extruder 4 was used to melt (250 ° C. to 30 ° C.).
Polyethylene terephthalate resin (PE at 0 ° C)
While T) is extruded to form the parison 1, the outer surface 2 of the parison 1 is forcedly cooled by blowing air 7 from the cooling device 6 provided on the lower surface of the extruder 4.

Forced cooling of the outer surface 2 of the parison 1 is about 240 ° C. in this embodiment, where the temperature of the outer surface 2 of the parison 1 is lower than the melting point of the PET material used.
However, this cooling is usually the PET used
It is performed in the range of about 90 ° C to 240 ° C according to the melting point of the material.

As shown in FIG. 4, this cooling hardly cools when the parison 1 starts to be extruded from the extruder 4, but the parison 1 is further extruded and lengthened downward,
This parison 1 starts before it draws down due to its own weight, and its cooling strength increases as the extrusion length of the parison 1 increases.

Therefore, the extruded parison 1
Will be cooled as strongly as the outer surface 2 above it, and the cooling will stop just before the parison 1 is extruded to a predetermined length and cut, thus reliably preventing the drawdown of the parison 1. are doing.

The parison 1 shown in FIG. 4 is subjected to forced cooling by the method of the present invention and no drawdown occurs. On the contrary, the parison 1 shown in FIG. 5 is not subjected to forced cooling and drawdown occurs. Shows what is extended.

FIG. 6 shows the difference between the temperature of the inner surface 3 and the outer surface 2 of the parison 1 cooled by this embodiment and the uncooled parison 1 and the temperature gradient distribution in the wall of the parison 1. The temperature difference between the inner surface 3 and the outer surface 2 of the parison 1 cooled according to this example is shown in the graph on the left side, and the inner surface 3 of the uncooled parison 1 is shown.
The temperature difference between the outer surface 2 and the outer surface 2 is shown in the graph on the right.

It can be confirmed that the temperature of the outer surface 2 of the parison 1 cooled by this embodiment is extremely lower than the temperature of the inner surface 3 and that the cooling effect is exhibited, and the inner surface 3 of the uncooled parison 1 is shown. There is almost no difference in temperature between the outer surface 2 and the outer surface 2.

FIG. 7 shows changes in temperature of the inner surface 3 and the outer surface 2 of the lower end of the parison 1 cooled according to this embodiment. The vertical axis represents temperature (degrees) and the horizontal axis represents the extruder 4. It shows the time (second) after being extruded from the graph. From this graph, the outer surface 2 of the parison immediately after being extruded from the extruder 4 is strongly subjected to the cooling power of the cooling device 6 and the temperature thereof is rapidly lowered. However, since the cooling force is weakened as the extrusion progresses and is displaced downward, the temperature of the outer surface 2 of the lower end portion of the parison 1 at the time when the parison 1 reaches a predetermined length has a lower cooling strength. As a result, the temperature of the inner surface 3 rises to the same degree as the temperature of the inner surface 3 due to the influence of heat on the inner surface 3 side of the parison.

Since the inner surface 3 of the parison is not directly cooled by the cooling device 6, it is only indirectly cooled.
Although the temperature gradually decreases with the passage of time, since the temperature is maintained at a value close to the melting temperature, welding of the cut-out portion by mold clamping during stretch blow molding can be achieved well.

In this embodiment, the temperature of the outer surface 2 of the parison whose temperature has decreased due to cooling also rises due to the influence of the inner surface 3, and at the time of mold clamping, the temperature of the outside air is low and the outer surface 2 is cooled. The temperature is almost the same as that of the inner surface 3 which is affected and whose temperature is lowered.

By forcibly cooling the outer surface 2 of the parison 1, the inner surface 3 of the parison 1 is indirectly cooled and its temperature is lowered, and the temperature of the parison 1 at the time of mold clamping approaches the stretching temperature.
Or, since at least the outer surface 2 is at the drawing temperature, as a result, the PE drawn by the stretch blow molding is drawn.
Oriented crystals of T are achieved, and impact resistance and the like are enhanced by improving the physical properties of the product.

The outer surface 2 of the parison according to the method of the present invention.
Cooling of the parison 1 is long like a large bottle (0.5 liters or more) and drawdown is severe,
It is particularly effective for preventing the drawdown.

Further, since the wall thickness of the puff blow parison 1 in the puff blow for welding the lower part of the parison 1 is thinner than that of the normal straight parison 1, the inner surface 3 of the parison is also cooled when cooled by the method of the present invention. Therefore, there is a concern that the welding of the cut-out portion due to the mold clamping may not be achieved well.

However, since the puff blow parison 1 is extruded with its lower end welded and closed, the inner surface 3 of the puff blow parison 1 is more difficult to cool than the normal straight parison 1, and the temperature maintaining state of the inner surface 3 is maintained. Since it is good, the welding of the cutting parts such as the bottom part, the neck part, and the grip part of the product which is cut off by the mold is well achieved.

Also in this case, the parison 1 can be brought close to the stretching temperature of PET by cooling the outer surface 2 of the parison according to the method of the present invention, the impact strength and the like are improved by the stretching effect, and the conventional extrusion blow method is used. The physical properties are improved as compared with the molded product. That is,
Since the puff parison 1 is forcibly cooled near the exit of the die 5, it is not affected by the puff shape in which the puff parison 1 expands.

[0036]

Since the present invention has the above-described structure, the following effects can be obtained. The outer surface of the parison being extruded from the extruder is forcibly cooled, and the viscosity of the part on the outer surface of the parison is increased according to this cooling degree, so that drawdown of the extruded parison is prevented in advance. Therefore, the parison can be extruded with a wall thickness distribution as set.

Since the forced cooling of the parison is performed on the outer surface of the parison, the temperature of the inner surface portion of the parison can be maintained at the melting temperature when the extrusion molding of the parison is completed, so that the stretching effect is averaged. It is possible to obtain reliable and strong welding of the bite part by the parison mold cooled to the temperature that can be developed.

Since the parison is extruded with a wall thickness distribution as set and is cooled to a temperature at which a stretching effect can be exhibited, it is possible to suitably obtain oriented crystallization by subjecting it to a stretch blow molding treatment. Therefore, a stretch blow-molded article having excellent physical properties such as impact resistance and content resistance can be obtained.

Since the inner surface portion of the parison can be locally brought to the melting temperature in a state where the parison is cooled to a temperature at which the stretching effect can be exhibited evenly, the stretch blow molding can be performed in a state where the stretching effect can be exhibited. In addition, it is possible to achieve reliable and strong welding of the bite part, so that the handle is integrally molded 2
Axial stretch blow molded products can be molded.

[Brief description of drawings]

FIG. 1 is a front view showing an apparatus for carrying out the method of the present invention.

FIG. 2 is an enlarged vertical sectional front view of a main part of FIG.

FIG. 3 is an enlarged cross-sectional view of a main part of FIG.

FIG. 4 is a graph showing an air flow rate (cooling strength) of forced cooling according to the method of the present invention and an explanatory view showing a parison.

FIG. 5 is a front sectional view showing a state of an extruded parison without forced cooling.

FIG. 6 is a graph and an explanatory view showing a temperature difference between an inner surface and an outer surface of a parison which is subjected to forced cooling and a parison which is not subjected to forced cooling according to the method of the present invention.

FIG. 7 is a graph showing the relationship between time and temperature after extrusion of the inner surface and the outer surface of the parison subjected to forced cooling according to the method of the present invention.

[Explanation of symbols]

 1; Parison 2; Outer surface 3; Inner surface 4; Extruder 5; Die 6; Cooling device 7; Air

Claims (4)

[Claims] 1. Extruding from the extruder (4),
Parison of saturated polyester resin material in molten state (1)
The outer surface (2) of the is cooled to prevent drawdown of the parison (1), and the parison (1) is brought to a temperature (stretching temperature) suitable for stretch blow molding, and then stretch blow molded. An extrusion blow molding method comprising: 2. A parison extruded from the extruder (4).
The method according to claim 1, wherein (1) reaches a certain length, cooling is started before drawdown starts due to its own weight, and cooling is stopped when the parison (1) is extruded to a predetermined length. Extrusion blow molding method. 3. The extrusion blow molding method according to claim 1, wherein the cooling strength is minimized immediately after the start of cooling, and then the cooling strength is increased as the extrusion of the parison (1) proceeds. 4. The extrusion blow molding method according to claim 1, 2 or 3, wherein the cooling is achieved by blowing air (7).