JP3549171B2 - Extrusion blow molding method - Google Patents

Description

[0001]
[Industrial applications]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extrusion blow molding method with forced cooling for molding a synthetic resin bottle made of a saturated polyester resin such as a polyethylene terephthalate resin.
[0002]
[Prior art]
Conventionally, for example, when a hollow container such as a bottle is formed from polyethylene terephthalate resin (PET), a preform is formed by injection-molding the heated and melted PET into a preform mold, and then the naturally cooled preform is formed. Stretch blow molding is performed by heating again to a temperature suitable for blow molding, and through these multiple steps, satisfactory physical properties as a bottle have been obtained.
[0003]
In contrast to the above-mentioned ordinary stretch blow molding, there is a method called an extrusion blow molding method in which a parison obtained by extruding a heated and melted PET from an extruder is stretch blow-molded without forming and reheating a preform. According to this extrusion blow molding method, since the parison in a molten state is stretch blow-molded, the shape of the bottle can be extremely well formed as compared with ordinary stretch blow molding.
[0004]
In addition, with a so-called one-material handle, it is possible to form a bottle without forming a preform, or to form a bottle body with a handle integrally formed from one parison, which was impossible with ordinary stretch blow molding. It has the great advantage that bottles can be molded.
[0005]
[Problems to be solved by the invention]
However, products molded by the above-mentioned conventional extrusion blow molding method have a problem that they are inferior in physical properties as compared with ordinary blow molded products, such as being vulnerable to drop impact.
[0006]
This is because a parison extruded from a PET resin or the like melted by an extruder through a die is stretch-blow-molded, and the parison naturally has a low viscosity at high temperatures, causing a so-called drawdown that extends by its own weight. This is partly due to the inability to control the wall thickness, with the lower part being thicker and the upper part being thinner.
[0007]
In addition, since the parison at the time of stretch blow molding is at least a temperature equal to or higher than the melting point, that is, a temperature higher than a temperature suitable for stretching (stretching temperature), oriented crystals of the stretched resin material are not successfully achieved.
[0008]
In view of the above, the present invention has been made in order to solve the above-mentioned problems in the prior art. In the extrusion blow molding method, the drawdown of the extruded parison is prevented, and the parison is stretch blown. It is an object of the present invention to make a temperature suitable for molding a technical subject, and to thereby allow the extrusion blow molding method to be suitably applied as a means for molding a saturated polyester resin bottle.
[0009]
[Means for Solving the Problems]
Means of the present invention for solving the above technical problems include:
Cooling the outer surface of the parison of the saturated polyester resin material in the molten state being extruded from the extruder,
This cooling prevents the parison from drawing down and brings the parison close to a temperature suitable for stretch blow molding (stretching temperature).
This drawdown is prevented, and the parison cooled to a temperature suitable for stretch blow molding is stretch blow molded to a bottle,
It is in.
[0010]
Another object of the present invention is to start cooling before the parison extruded from the extruder reaches a certain length and drawdown starts due to its own weight, and stops cooling when the parison is extruded to a predetermined length.
[0011]
Another object of the present invention is to minimize the cooling strength immediately after the start of cooling, and then increase the cooling strength as the parison is extruded.
[0012]
Cooling is advantageously achieved by blowing air.
[0013]
[Action]
Since the outer surface of the parison being extruded from the extruder is cooled, the viscosity of the outer surface portion of the parison increases, and the parison does not draw down due to the increased viscosity of the outer surface portion.
[0014]
Since the drawdown does not occur, the thickness of the parison becomes as set over its entire length, and the thickness of the bottle formed by subsequent stretch blow molding also becomes as set. Is substantially equivalent to a bottle obtained by biaxially stretch blow molding from the injection molded preform.
[0015]
In addition, since the outer surface of the parison is cooled and the temperature of the parison in the molten state is approached to the stretching temperature and stretch blow-molded, compared with the conventional case of stretch blow-molding at a high melting temperature, saturated polyester is used. The oriented crystal of the resin material is smoothly performed, thereby improving the physical properties of the bottle.
[0016]
Since only the outer surface of the parison is cooled, its inner surface is indirectly cooled but still maintains the melting temperature, and the temperature of the parison (at least the inner surface) at the time of mold clamping during stretch blow molding maintains the melting temperature are doing.
[0017]
Therefore, the welding of the cut-off portion by the mold can be satisfactorily achieved, and the original advantages of the extrusion blow molding (the shape of the bottle can be formed well, and the handle and the like can be integrally formed) are still exhibited. .
[0018]
In addition, the parison extruded from the extruder reaches a certain length, starts cooling before the drawdown starts to occur due to its own weight, and stops the parison when the parison is extruded to a predetermined length, thereby reducing the parison. Drawdown can be prevented without cooling unnecessarily, that is, while maintaining the parison inner surface in a molten state.
[0019]
In addition, the cooling strength is minimized immediately after the start of cooling, and then, as the extrusion of the parison progresses, the cooling strength is increased, so that the parison can be properly stretched over its entire length without causing drawdown in the parison. In addition to being able to cool and heating the outer surface portion of the parison by the heat storage of the inner surface portion of the parison, the temperature distribution in the parison tube wall can be made uniform at a temperature suitable for stretch forming.
[0020]
By performing cooling by blowing air, it is easy to accurately control the degree of cooling of the parison by controlling the temperature of the cooling air and controlling the flow rate. The configuration of the equipment can be simplified.
[0021]
【Example】
One embodiment of the method of the present invention will be described with reference to the drawings.
In the present embodiment, as shown in FIGS. 1 to 3, polyethylene terephthalate resin (PET) in a molten state (250 ° C. to 300 ° C.) is extruded from a die 5 of an extruder 4 while forming a parison 1. The outer surface 2 of the parison 1 is forcibly cooled by blowing air 7 from a cooling device 6 provided on the lower surface of the extruder 4.
[0022]
In the present embodiment, the forced cooling of the outer surface 2 of the parison 1 is such that the temperature of the outer surface 2 of the parison 1 is about 240 ° C., which is lower than the melting point of the PET material used. Usually, it is carried out in the range of about 90 ° C. to 240 ° C. depending on the melting point of the PET material used.
[0023]
In this cooling, as shown in FIG. 4, the parison 1 hardly cools when it is first extruded from the extruder 4, but the parison 1 is further extruded and lengthens downward, and the parison 1 draws down by its own weight. Starting before, its cooling strength is increased as the extrusion length of parison 1 increases.
[0024]
Therefore, the extruded parison 1 is cooled more strongly as the outer surface 2 at the upper part thereof, and the cooling is stopped immediately before the parison 1 is extruded to a predetermined length and cut, and by doing so, The drawdown of Parison 1 is reliably prevented.
[0025]
The parison 1 shown in FIG. 4 is subjected to forced cooling by the method of the present invention and does not generate a drawdown. Conversely, the parison 1 shown in FIG. Show what you have.
[0026]
FIG. 6 shows the difference between the temperature of the inner surface 3 and the outer surface 2 of the parison 1 cooled by the present embodiment and that of the uncooled parison 1 and the temperature gradient distribution in the wall of the parison 1. The left graph shows the temperature difference between the inner surface 3 and the outer surface 2 of the parison 1 cooled by the embodiment, and the right graph shows the temperature difference between the inner surface 3 and the outer surface 2 of the uncooled parison 1. .
[0027]
The temperature of the outer surface 2 of the parison 1 cooled according to the present embodiment is extremely lower than the temperature of the inner surface 3, and it can be confirmed that the cooling effect is exerted, and the inner surface 3 and the outer surface of the uncooled parison 1 are confirmed. The temperature difference of 2 is hardly observed.
[0028]
FIG. 7 shows a change in temperature of the inner surface 3 and the outer surface 2 of the lower end portion of the parison 1 cooled according to the present embodiment. The vertical axis represents temperature (degrees), and the horizontal axis is extruded from the extruder 4. From this graph, the parison outer surface 2 immediately after being extruded from the extruder 4 is strongly subjected to the cooling force of the cooling device 6 and the temperature 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 is that the cooling strength is weakened. And the temperature of the inner surface 3 rises to the same degree as the temperature of the inner surface 3 due to the heat on the inner surface 3 of the parison.
[0029]
Since the parison inner surface 3 is not directly cooled by the cooling device 6 but is only indirectly cooled, its temperature gradually decreases over time, but the temperature maintains a value close to the melting temperature. As a result, welding of the cut-off portion by mold clamping during stretch blow molding is favorably achieved.
[0030]
In the present embodiment, the temperature of the parison outer surface 2 whose temperature has been lowered by cooling also rises due to the influence of the inner surface 3, and is affected by the low temperature of the outside air and the cooling of the outer surface 2 at the time of mold clamping. The temperature is substantially the same as that of the inner surface 3 whose temperature has been lowered.
[0031]
By forcibly cooling the outer surface 2 of the parison 1, its inner surface 3 is also indirectly cooled and its temperature decreases, and the temperature of the parison 1 at the time of mold clamping approaches the stretching temperature, or at least a portion of the outer surface 2 is Since it is at the stretching temperature, as a result, oriented crystals of PET stretched by stretch blow molding are achieved, and the impact resistance and the like are enhanced by the improvement of the physical properties of the product.
[0032]
The cooling of the parison outer surface 2 by the method of the present invention is particularly effective for preventing the drawdown of a parison 1 having a long and sharp drawdown such as a large bottle (0.5 liter or more). is there.
[0033]
Further, the thickness of the puff blow parison 1 in the puff blow for welding the lower part of the parison 1 is thinner than the thickness of the ordinary straight parison 1, so when cooled by the method of the present invention, the inner surface 3 of the parison is also cooled and the mold is cooled. There is a concern that welding of the cut-away portion due to tightening will not be achieved properly.
[0034]
However, since the puff blow parison 1 is extruded with its lower end welded and closed, the inner surface 3 is harder to cool than a normal straight parison 1 and the temperature of the inner surface 3 is better maintained. Welding of the cut portions such as the bottom, neck, and handle of the product cut by the mold can be achieved well.
[0035]
Also in this case, the parison 1 can be brought close to the PET stretching temperature by cooling the parison outer surface 2 according to the method of the present invention, and the stretching effect improves the impact strength and the like, and the product molded by the conventional extrusion blow method. The physical properties are improved as compared with. 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]
【The invention's effect】
The present invention has the above-described configuration, and has the following effects.
The outer surface of the parison, which is being extruded from the extruder, is forcibly cooled to increase the viscosity of the parison outer surface side according to this degree of cooling, so that the drawdown of the extruded parison is prevented beforehand and reliably. Accordingly, the parison can be extruded with the thickness distribution as set.
[0037]
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 of the parison is completed, so that the stretching effect can be exhibited on average. It is possible to obtain a reliable and strong welding of the cut-off portion by the parison mold cooled to the temperature.
[0038]
The parison is extruded with the thickness distribution as set and is cooled to a temperature at which the stretching effect can be exhibited, so that it is possible to obtain oriented crystallization suitably by undergoing the stretch blow molding process. Thus, a stretch blow-molded article having excellent physical properties such as impact resistance and content physical properties can be obtained.
[0039]
In a state where the parison is cooled to a temperature at which the stretching effect can be exhibited on average, the inner surface portion of the parison can be locally set to the melting temperature. It is possible to achieve reliable and strong welding of the cut-away portion, and thus it is possible to form a biaxially stretched blow-molded article integrally formed with the handle.
[Brief description of the 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 sectional view of a main part of FIG. 2;
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 diagram showing a parison.
FIG. 5 is a front sectional view showing a state of an extruded parison when forced cooling is not performed.
FIG. 6 is a graph and an explanatory diagram showing a temperature difference between an inner surface and an outer surface of a parison subjected to forced cooling according to the method of the present invention and a parison not subjected to forced cooling.
FIG. 7 is a graph showing the relationship between time and temperature after extrusion of the inner surface and outer surface of a 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;

Claims (2)

Cooling the outer surface (2) of the parison (1) of the saturated polyester resin material in the molten state being extruded from the extruder (4), preventing drawdown of the parison (1), After bringing (1) close to the temperature suitable for stretch blow molding (stretching temperature), when performing stretch blow molding , the parison (1) extruded from the extruder (4) reaches a certain length and draws by its own weight. Cooling is started before down begins to occur, and when the parison (1) is extruded to a predetermined length, cooling is stopped, and the cooling intensity is minimized immediately after the start of cooling, and thereafter, the parison (1) Extrusion blow molding method in which the cooling strength is increased as the extrusion proceeds . The extrusion blow molding method according to claim 1, wherein the cooling is achieved by blowing air (7) .

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