JP3924082B2 - Method for producing flat bottle by cold parison blow molding method, and parison for cold parison blow molding - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a flat bottle by a cold parison blow molding method using uneven thickness parison, and a parison for cold parison blow molding.
[0002]
[Prior art]
The blow molding method is systematically divided into a hot parison method and a cold parison method. In the cold parison method, only parison formation is performed independently by extrusion molding or injection molding, and once cooled and solidified, the parison is heated and temperature-controlled immediately before blow molding to perform blow molding.
[0003]
According to such cold parison blow molding, once the cooled parison is radiantly heated, the temperature of the entire parison becomes uniform, so that the stretchability of blow molding becomes uniform and stable blow moldability can be obtained. In addition to this, when the parison heating is performed from the outer peripheral direction, the temperature of the parison surface becomes high, the transferability of the mold surface during blow molding is good, and the surface gloss of the product is good.
[0004]
This cold parison molding achieves good blow moldability by making the parison temperature uniform at the time of blow molding. For this reason, the circumferential thickness of the parison is uniform, and further, during the heating process By rotating the parison, uniform heating is ensured even in heating from one direction, and good blow moldability is ensured.
[0005]
[Problems to be solved by the invention]
When the cross-sectional shape of the final molded product is a perfect circle, the wall thickness of the molded product becomes almost uniform over the entire circumference if blow molding is performed by the conventional molding method.
[0006]
However, if the bottle of the final molded product has a flat shape, the wall thickness of the short diameter part of the formed bottle is the result of an increase in the length of the long diameter direction compared to the amount of stretch in the short diameter direction. It is relatively thick and the wall thickness of the long diameter portion becomes thin.
[0007]
The thickness distribution of the final molded product blow-molded in this way becomes a thickness distribution inversely proportional to the stretch amount during blow molding. Then, if the wall thickness in the minor axis direction is set to an appropriate value, the wall thickness in the major axis direction becomes too thin and the necessary strength cannot be obtained, while the wall thickness in the major axis direction becomes an appropriate value. If so, the wall thickness in the minor axis direction becomes too thick.
[0008]
Accordingly, an object of the present invention is to make the wall thickness of the final molded product uniform by changing the parison temperature during blow molding.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention takes the following technical means.
[0010]
That is, in the method for producing a flat bottle by the cold parison blow molding method of the present invention, the portion of the cold parison that is stretched in the minor axis direction is more elongated than the portion of the flat shape that is elongated in the major axis direction before blow molding. After heating to a high temperature, blow molding is performed in a blow molding die that defines the outer shape of the flat bottle.
[0011]
According to this manufacturing method, since the high temperature portion (ie, the short-axis direction stretched portion) of the parison is more plastic than the low-temperature portion (ie, the long-axis direction stretch portion), the gas pressure in the parison increases. In the process, the hot part begins to swell faster than the cold part. Such a high temperature portion has a small blow ratio but starts to swell first, so that it is stretched more than in the conventional case, and is pressed and fixed to the inner surface of the blow mold.
[0012]
Thereafter, the low temperature portion is stretched, and at this time, the pressing portion gradually spreads from the high temperature portion already pressed against the inner surface of the mold and is stretched so as to be extended from the outer periphery of the low temperature portion of the parison wall. Since this low temperature part has a large blow ratio, the stretch ratio becomes equal to that of the high temperature part as a result, and the wall thickness of the formed flat bottle becomes uniform. Further, according to the present invention, it is possible to make the minor axis direction of the final product shape thinner than the major axis direction by increasing the temperature difference of the parison temperature.
[0013]
In the above manufacturing method, as a cold parison, when using an uneven thickness formed so that the elongated portion in the major axis direction is thick and the elongated portion in the minor axis direction is thin, heating the parison before blow molding is performed. The parison can be rotated by rotating it around the axis and radiatively heating it from the periphery with far infrared rays or the like. According to such a heating method, the temperature of the thin-walled stretched portion in the short axis direction rises in a relatively short time and is heated to a higher temperature than the stretched portion of the thick-walled long axis direction.
[0014]
In the case of a parison that is not rotated during heating, heating of the parison before blow molding can be performed by radiative heating with far infrared rays or the like only from the outside of the elongated portion in the short direction. According to this method, a bottle having a uniform wall thickness can be blow-molded without using an uneven parison.
[0015]
Furthermore, after heating the whole parison once, heating with a temperature difference can also be performed by locally adjusting the temperature by applying a cooling plate to the elongated portion in the major axis direction.
[0016]
This molding method is not limited to blow molding or stretch blow molding with a bottomed cylindrical parison, and may be performed by a molding method in which the extruded cylindrical parison is cooled and then heated and blow molded.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0018]
1 and 2 show an uneven thickness parison 1 according to an embodiment of the present invention, and a cold parison blow molding process using the uneven thickness parison 1, and by this process, as a final molded product, The flat bottle 2 having a flat surface shape is formed.
[0019]
The parison 1 is made of a thermoplastic resin and is formed into a bottomed cylindrical shape by an injection molding machine, and the meat of a portion 3 extending in the major axis direction of a flat bottle 2 that is a blow-molded product on the peripheral side wall thereof. The thickness of the portion 4 extending in the minor axis direction is increased in thickness so that the thickness of the portion 4 is reduced. Further, the thickness is formed so as to gradually change from the thick portion 3 to the thin portion 4.
[0020]
The parison 1 may be manufactured intensively in an injection molding factory, and then transported to a blow molding factory close to the content filling factory for blow molding, or injection molding and blow molding are performed continuously. You can also
[0021]
In any case, after the parison 1 is once cooled, it is blow molded by a cold parison blow molding method.
[0022]
The manufacturing method of the flat bottle 2 by such cold parison blow molding will be described. First, in the pre-process of blow molding, the parison 1 is heated and plasticized. Such heating can be performed by exposing the parison 1 to a high temperature atmosphere. Further, the parison 1 can be brought into contact with a heating mold, or radiant heating with heat rays or dielectric heating with high frequency can be performed.
[0023]
However, since the heating side temperature cannot be increased by contact heating, and the parison is deformed by hot air heating, the parison 1 is preferably used by an appropriate rotation support means (not shown) as shown in FIG. It is preferable to perform radiant heating with far-infrared rays by a heater 10 arranged outside the diameter of the parison 1 while rotating at a constant speed around its axis. Moreover, as shown in FIG. 4, the part 4 extended in the short axis direction of the flat shape of the parison 1 by radiatively heating only from the outer side of the short axis direction of the flat shape of the bottle without rotating the parison 1. Can be at a relatively high temperature, and the portion 3 extending in the major axis direction can be at a relatively low temperature. Further, by applying a cooling plate 9 (cooling member) to the outer side surface of the uniformly elongated major portion 3 of the parison 1, the flat portion 4 of the parison 1 that is elongated in the minor axis direction is heated to a relatively high temperature. And the portion 3 extending in the major axis direction can be at a relatively low temperature.
[0024]
Whatever heating means is used, heating is performed so that the thin-walled portion 4 stretched in the minor axis direction becomes higher in temperature than the thick-walled portion 3 stretched in the major axis direction. The plasticity of the thin portion 4 is made larger than the plasticity.
[0025]
The parison 1 is attached to the lip mold 7, and the lip mold 7 is mounted on the blow molding mold 6 to load the parison 1 into the blow molding mold 6. Next, high-pressure gas is blown into the parison 1 through the blow pipe 8. Then, the thin plastic part 4 having a large plasticity starts to swell at a relatively low pressure, and is pressed against the inner surface of the mold 6 as shown in FIG. 1B, and is fixed by frictional resistance with the inner surface of the mold 6.
[0026]
Thereafter, when the atmospheric pressure in the parison 1 increases, the thick wall portion 3 is also stretched, and the whole is expanded so that the pressing and fixing portion to the inner surface of the mold 6 gradually spreads from the already pressed short diameter portion. Finally, blow molding is completed as shown in FIG.
[0027]
As a result, the flat bottle 2 which is the final molded product has a substantially uniform wall thickness over the entire circumference, ensuring strength in the major axis direction and squeezing property in the minor axis direction (in the minor axis direction of the trunk of the flat bottle). Ensuring the pushability) can be achieved at once, and since the thin wall portion of the bottle wall thickness is eliminated, the barrier function as a container can be improved.
[0028]
【The invention's effect】
According to the present invention, by the heating process of the cold parison before blow molding, the portion of the flat shape extending in the major axis direction is set to a relatively low temperature, and the portion extending in the minor axis direction is set to a relatively high temperature. In addition, since the portion extending in the minor axis direction is stretched faster, as a result, the wall thickness of the blow-shaped flat bottle can be made uniform.
[Brief description of the drawings]
1A and 1B show a blow molding process by a cold parison method according to an embodiment of the present invention, wherein FIG. 1A is a cross-sectional view when the parison is set in a blow mold, and FIG. (C) is a cross-sectional view at the time when blow molding is completed.
FIG. 2 is a longitudinal sectional view corresponding to FIG.
FIG. 3 is a plan view showing an embodiment of a parison heating method.
FIG. 4 is a plan view showing an embodiment of a parison heating method.
FIG. 5 is a plan view showing an embodiment of a parison heating method.
[Explanation of symbols]
1 Parison 2 Flat Bottle (Blow Molded Product)
3 Thick part 4 Thin part 6 Blow mold 9 Cooling member

Claims (1)

After the cold parison (1) is heated so that the portion (4) extending in the minor axis direction becomes higher than the portion (3) extending in the major axis direction of the flat shape before blow molding, In the manufacturing method of the flat bottle by the cold parison blow molding method which blow-molds in the blow mold (6) which defines the outer surface shape of the shaped bottle (2) , as the cold parison (1), the longitudinally elongated portion (3) In addition to using a material that is thickly formed so that the thickness of the elongated portion (4) in the minor axis direction is thin, and is stretched in the major axis direction of the flat shape by the heating process of the cold parison before blow molding. The portion (3) to be stretched at a relatively low temperature and the portion (4) to be stretched in the minor axis direction to be at a relatively high temperature so that the minor axis direction stretched portion (4) is stretched earlier during blow molding. the way Method of manufacturing a flat-shaped bottle by cold parison blow molding method according to claim and.

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