JPH09123260A - Plastic container and bottom die for molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a plastic container to be easily centered and shaped to have a bottom shape with a uniform wall thickness by forming in an arc face broadening downward with an inclined part continuous from the peripheral edge of a top part and facing outward, and forming a second inclined part broadening downward continuous to the outer peripheral edge of the inclined part. SOLUTION: A first inclined part 3 is continuous downward from the peripheral edge of a top part 2 formed in a slightly recessed shape, and further, is formed into a parabolic or an arc sector shape spread outward. A second inclined part 4 is tapered to be broadened downward in a fan shape in such a way that it is continuous to the outer peripheral edge of the first inclined part 3. Therefore, in a first molding step, a bottom die 12 with a middle-part- protruding tapered plane is used, so that the center of the bottom part 72 of an intermediate container 7 is molded into a concave profile. In addition, in a second molding step, a bottom die 1 with the first inclined plane part 3 of a parabolic sector shape facing outward from the peripheral edge of a slightly recessed top part 2, is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic container and a bottom mold for molding the same, and belongs to the field of technology for manufacturing heat-resistant bottles made of PET (polyethylene terephthalate resin), for example.

[0002]

2. Description of the Related Art Bottles made of PET resin are almost satisfactory in transparency and strength, but have insufficient heat resistance. Therefore, when filled with a high temperature content liquid or heat-sterilized after filling the content liquid, The temperature of the bottle was about 75 ° C., but at that time, there was a problem that it was easily deformed. In order to solve such a problem, for example, JP-A-51-53566.
In the publication, while the mouth and or bottom is heated and crystallized,
A method has been proposed in which the body is stretched and heat set.

Further, recently, in Japanese Examined Patent Publication No. 4-39416, a heat-resistant bottle with less deformation is obtained by heating and crystallizing the mouth portion and blow-molding the body portion in two steps. Is disclosed. This is because in the first blow molding, an intermediate product having a height and a cylinder diameter larger than that of the final product is formed, and then heat treatment is performed to remove residual stress and shrink (about 70%) and crystallize. In the next blow molding, a product having the same dimensions as the final product is formed.

[0004]

However, the former method described above is not suitable for molding large bottles and prismatic bottles because it is not easy to obtain a high draw ratio, and the latter method is not suitable. Although it is suitable for the production of large bottles and prismatic bottles, when the intermediate product is heated and shrunk to relax the stress, the intermediate product, especially the bottom mold, is greatly contracted and deformed. It was difficult to accurately align (center) with each other, and it was not easy to obtain a bottom having a uniform wall thickness.

In order to perform accurate centering in the final molding stage, usually, a method of forming the bottom of the intermediate product into a concave shape by using a bottom die having a tapered surface and having a convex shape is adopted. However, if such a bottom mold with a tapered surface is used during blow molding in the final stage, deformation bottles may occur due to incorrect centering, the bottom wall thickness may become uneven, and the bottom of the intermediate product may not be localized. However, there is a problem in that the temperature of the contact portion is extremely lowered by contact with the tapered surface and the wall thickness becomes thicker, and the thickness of the bottom portion becomes uneven.

The present invention has been made in view of such circumstances,
It is an object of the present invention to provide a plastic container and a bottom mold for molding the plastic container, which can be easily centered and can obtain a bottom shape having a uniform thickness by performing various tests and studies on various shapes of the bottom.

[0007]

According to the present invention, means for solving the above-mentioned problems are constituted as follows. That is, in the bottom mold according to the first aspect of the present invention, the first sloped surface that extends downward from the peripheral edge of the top formed in a flat shape or a concave shape is a parabolic surface that spreads toward the outside or It is characterized in that a linear or curved downward second sloping second slope portion is formed continuously on the outer peripheral edge of the first slope portion formed in an arc surface.

In the bottom mold according to the invention as defined in claim 2,
In the invention according to claim 1, a linear portion is formed in a part of the first slope portion.

A plastic container according to a third aspect of the present invention has a truncated cone-shaped bottom shape having a recess formed by the bottom mold according to the first or second aspect of the invention. It has a feature.

Since the shape of the above-mentioned first inclined surface portion becomes steeper as the angle with respect to the axis becomes smaller, it is possible to enlarge the bottom portion which is originally difficult to be stretched. This angle is preferably 0 to 40 °, more preferably 0 to 20.
° is good.

For example, if the parabola of the first slope is expressed by the formula y = x ^a , it is preferable that a is 4 or more,
More preferably, a is 7-10. Further, in this parabola, the top side or a part of the second slope portion may be a straight portion, and thus, the outer peripheral edge of the first slope portion may be a straight or curved downward downward divergent second slope. The parts are continuously formed.

As described above, since the plastic container has the shape of a truncated cone having a concave portion, the concave portion is formed at the bottom of the intermediate container, and the residual stress is applied by heat treatment. In the final molding stage after the removal and shrinkage, the blow-molded body and the bottom die are in good alignment, and the first sloped surface of the parabolic surface or arc has a divergent flare. By forming it on the surface, the bottom that is difficult to stretch when the intermediate container expands is greatly stretched and easily follows the slope, and except for the top of the bottom, local contact with the bottom mold is avoided and partial thickness It is possible to avoid fleshing, and it is possible to obtain a bottom-shaped plastic container having a uniform thickness and a large stretch. Further, it is possible to reduce the weight by reducing the thickness.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the plastic container and the bottom mold for molding the same according to the present invention will be described below with reference to the drawings. 1 (A) and 1 (B) are cross-sectional views of a bottom mold used at the final stage of blow molding, and FIG. 2 is a plan view thereof. In these drawings, reference numeral 1 is a bottom die, 2 is a top portion formed in a slightly concave shape, 3 is a first sloped surface that extends downward from the peripheral edge of the top portion 2, and has a flared outward shape. It is formed on the object surface (or arc surface). Reference numeral 4 denotes a second inclined surface portion which is continuously provided on the outer peripheral edge of the inclined surface portion 3 and which is formed as a downwardly-diverging tapered surface. The angle formed by the tangent and the axis at the intersection of the first slope and the top is 10
°.

A preferred example of the blow molding method for PET bottles using the bottom mold 1 will be described with reference to the explanatory view of FIG. 3. First, in the first molding step, the body 51 of the parison 5 is A mandrel is inserted to extend axially to the bottom of the mold cavity and blown with compressed air of 3 bar or more, and then with 20 bar to expand the barrel 51 to the inner wall of the mold.

This first molding step requires approximately 3 to 10 seconds. During this molding operation, the inner wall of the mold is air and / or water and the temperature is between about 5-40 ° C, preferably about 10-15 ° C.
Cooled to be maintained between.

In the first molding step, the body (mouth 6
The intermediate container 7 having a size of about 71 to 70 times larger than the final container (plastic container) 9 is formed. At this time, the bottom mold 12 having a tapered surface with a middle protrusion
Is used, and the central portion of the bottom portion 72 of the intermediate container 7 is formed in a concave shape.

Next, the intermediate container 7 is moved to the heating station, where the body portion 71 of the intermediate container 7 is 180-220.
Heat at a temperature of C for approximately 1 to 15 minutes, preferably 210 C for 1 minute and 30 seconds. In this heating step, the mouth portion 6 must be protected from heat (usually protected at a temperature not exceeding 80 ° C, preferably about 70 ° C or less).

The intermediate container 8 obtained in this heating step is shrunk to a size of about 0.9 times that of the final container 9. The contraction deformation also extends to the bottom portion 82.

Next, the intermediate container 8 is transferred to the second molding step for final molding. In this second molding step, the cavity is introduced into a mold having the same size and shape as the body 91 of the final container 9. As the bottom mold 1, those shown in FIGS. 1 (A), 1 (B) and 2 are used.

The second molding step is performed in the same procedure as the first molding step. That is, the body 81 of the intermediate container 8
A mandrel is inserted inside the barrel to axially extend the barrel 81 until it reaches the bottom mold 1, and compressed air of 40 bar is blown until it matches the shape of the cavity having the inner wall at a temperature of 80 ° C. This second molding step requires approximately 2 to 6 seconds. When the barrel portion 91 is completed in this second molding step, the final container 9 having a truncated cone-shaped bottom portion is obtained.

In the second molding step, the bottom mold 1 having the first sloped surface portion 3 formed on the parabolic surface which is flared outward from the peripheral edge of the top portion 2 which is slightly concave is used. By this, the bottom of the intermediate container and the bottom mold can be stably aligned with each other, the bottom of the intermediate container 8 is easily aligned with the first sloped part 3, and it is greatly stretched. Since local contact is avoided, partial thickening can be avoided, and a bottom portion 92 having a uniform thickness can be obtained. When the top of the bottom is made flat instead of being concave, the stability of centering is somewhat deteriorated, but the draw ratio of the top is increased, so that the heat resistance is improved. In consideration of the above, the shape of the top can be changed appropriately.

Further, in combination with the bottom mold 1 for final molding having such a middle protrusion, the bottom mold 82 having the middle protrusion is also used in the first molding step to make the bottom portion 82 of the intermediate container 8 concave. By doing so, centering of the contracted container bottom and the final molding bottom die in the second molding step is ensured, and the container bottom can be stretch-molded with a uniform wall thickness. By setting the outer diameter of the bottom mold top to be smaller than the maximum recessed inner diameter of the container bottom after contraction, the second
The centering in the molding process can be made more reliable, the guiding and maintaining of the intermediate container 8 can be further improved, and a container with good shape quality can be obtained.
By making the outer diameter of the top of the bottom mold smaller than the maximum recessed inner diameter of the bottom of the container after contraction, centering can be reliably performed.

4 (A), (B) and FIG. 5 show different embodiments of the bottom mold 1, wherein the angle between the tangent and the axis at the intersection of the first slope and the top is 15 ° and the second. Slope 4
Since the flange portion 41 is provided so as to project from the outside to the outside, and it is possible to form substantially three-step recessed portions, it is possible to obtain a higher draw ratio and obtain a larger container. it can.

[0024]

As described above, according to the first and third aspects of the invention, the first slope portion extending downward from the peripheral edge of the flat or concave top is directed outward. Since it is formed into a parabolic or arcuate surface that spreads toward the end, when the intermediate container expands in the final molding process, its bottom part easily follows the first slope part of the molding bottom die, avoiding local contact. Therefore, it is possible to avoid partial thickening, and to obtain a bottom shape with a uniform thickness.

Further, the bottom mold for final molding can be stably and accurately fitted to the bottom of the intermediate container, which enables more accurate centering, and the bottom which is difficult to be stretched has a uniform thickness and heat resistance. It is possible to improve molding quality such as imparting.

According to the first and second aspects of the present invention, since the second slope portion is formed continuously with the first slope portion, not only round bottles but also polygonal square bottles and the like can be formed. it can.

[Brief description of the drawings]

1A and 1B are sectional views showing an embodiment of a bottom mold for molding a plastic container of the present invention, FIG. 1A is a sectional view taken along the line AA of FIG. 2, and FIG. FIG. 3 is a sectional view taken along the line BB of FIG.

FIG. 2 is a plan view of the same bottom type.

FIG. 3 is an explanatory view of the molding process.

4A and 4B are cross-sectional views showing different embodiments of the bottom mold of the present invention, FIG. FIG.

FIG. 5 is a plan view of the same bottom type.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Bottom type, 2 ... Top part, 3 ... 1st slope part, 4 ... 2nd slope part, 9 ... Plastic container.

Claims (3)

[Claims] 1. A first sloped surface that extends downward from the peripheral edge of a flat or concave top is formed in an outwardly flared parabolic surface or arcuate surface. A bottom die for molding a plastic container, comprising a linear or curved downward downward diverging second slope portion continuously formed on the outer peripheral edge of the slope portion. 2. The bottom die for molding a plastic container according to claim 1, wherein a linear portion is formed at a part of the first slope portion. 3. A plastic container having a frustoconical bottom shape having a recess formed by the bottom mold for molding a plastic container according to claim 1. Description: