JPH0788943A - Plastic container and mold for producing it - Google Patents

Abstract

PURPOSE:To prevent a bottom of a plastic container from being cracked by a method wherein depressed parts are formed on a bottom surface on the both sides of a pinch-off part so as to be staggered to each other toward the top and base parts of the pinch-off part. CONSTITUTION:Depressed parts 6, 7 each having a semi-circular cross section are provided on surfaces 4, 5 across a pinch-off part 3 so as to be staggered to each other. The depressed part 6 is provided nearer the top of the pinch-oft part 3 than the depressed part 1. At the molding of the pinch-off part 3, staggered protuberances 12, 22 of both molds 10, 20 compress the pinch-off part 3 on its way to be molded to reduce resin layers 1a, 1b, 1c in wall thickness as well as press up the second resin.layer 1b and the third resin layer 1c as inner layers apart from the top of the pinch-off part 3. As a result, the second resin layer 1b and the third resin 1ayer 1c are prevented from being squeezed out of the top of' the pinch-off part 3. in addition, the second resin layer 1b and the third resin layer 1c reduced in wall thickness are improved in adhesion, and the bottom crack of a plastic container 1 is prevented by the synergistic effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic container having a pinch-off portion protruding from the bottom and a mold for manufacturing the same.

[0002]

2. Description of the Related Art An extrusion blow molding method is one of the methods for manufacturing a bottle bottle made of plastic. Containers manufactured by this molding method are disclosed in Japanese Utility Model Publication No. 3-32013 and Japanese Utility Model Publication No.
As disclosed in Japanese Patent No. 3460, etc., the pinch-off portion projects from the bottom portion.

FIG. 5 is a sectional view of a pinch-off portion 50 of a conventional plastic container. In this case, the plastic container is formed by blow molding a tubular parison formed by laminating three kinds of resins. .

In the conventional plastic container, the resin layers 51, 52 and 53 remain up to the tip of the pinch-off portion 50 without changing the wall thickness.

[0005]

However, as in the conventional case, the resin layer 5 located inside the pinch-off portion 50 as far as the tip end.
If 2,3,53 remain without changing the wall thickness, there is a drawback that bottom cracking easily occurs in the plastic container.

The present invention has been made in view of the above problems of the conventional technique, and an object of the present invention is to provide a plastic container in which bottom cracking is unlikely to occur and a mold for manufacturing the same.

[0007]

The present invention has the following features to attain the object mentioned above. The plastic container of the present invention is formed by extrusion blow molding and has a pinch-off portion protruding from the bottom portion. On both side surfaces of this pinch-off portion, different pressure depressions are formed on the tip side and the base side of the pinch-off portion. The cross-sectional shape of the pressing recess is semicircular, etc.
Various shapes can be adopted.

The mold for producing a plastic container of the present invention is
A die for extrusion blow molding, comprising a pair of left and right dies for manufacturing the plastic container, wherein the left and right dies face each other in different steps on the pinch-off portion molding surface of each of the left and right dies. A ridge is provided.

The pinch-off portion of the plastic container and the molding surface of the pinch-off portion of the mold are preferably tapered so that the pinch-off portion is tapered toward the tip.

[0010]

When the left and right dies are clamped, the parison, which is the material of the plastic container, is pinched by the pinch-off portion molding surface to form the pinch-off portion. At that time, the projecting ridges on the left and right molds having different steps act to compress and push up the pinch-off portion which is being formed. As a result, the thickness of the pinch-off portion can be reduced.

In particular, when the parison is made of a laminated resin, the ridge pushes up the resin in the inner layer and moves it away from the tip of the pinch-off portion, so that the resin in the inner layer does not protrude from the tip surface of the pinch-off portion. become. Further, in the pinch-off portion which has been compressed to have a reduced thickness, the thickness of the resin in the inner layer is also reduced, and the adhesiveness is improved. This prevents bottom cracking of the plastic container.

[0012]

Embodiments of the present invention will be described below with reference to the drawings of FIGS. FIG. 2 is a front view showing the bottom of the plastic container of the present invention in a broken manner. The plastic container 1 is formed by blow molding a laminated resin, and has a pinch-off portion 3 on a bottom portion 2 thereof.

FIG. 1 is an enlarged sectional view showing the pinch-off portion 3. The laminated resin is composed of three layers, the outermost first resin layer 1a is formed of high density polyethylene, the inner second resin layer 1b is formed of modified polyolefin, and the innermost third resin layer 1c is formed. It is formed of an ethylene vinyl acetate copolymer emulsion. As is clear from FIG. 1, the thickness of the second resin layer 1b and the third resin layer 1c is extremely thin in the pinch-off portion 3.

The pinch-off portion 3 has a substantially trapezoidal shape that is tapered toward the front end, and pressing recesses 6 and 7 having a semicircular cross section are formed on both side surfaces 4 and 5, respectively. The pressing recesses 6 and 7 are arranged in different steps, and the pressing recess 6 is located closer to the tip side than the pressing recess 7. The radius of curvature of the pressing recess 6 is slightly smaller than the radius of curvature of the pressing recess 7.

Next, a mold used for manufacturing the plastic container 1 will be described with reference to FIGS. 3 and 4.
FIG. 3 is a schematic configuration diagram of the blow molding device with the mold opened. The mold is composed of a pair of left and right molds 10 and 20, and when the mold is closed, a cavity having the same shape as the outer shape of the plastic container 1 is formed therein.

FIG. 4 shows the molds 10 and 20 in the mold closed state.
FIG. 3 is an enlarged cross-sectional view showing the bottom part of the mold 10, wherein pinch-off part molding surfaces are formed on the bottom parts of the molds 10 and 20, respectively. The molding surface of the pinch-off portion of the die 10 is a taper surface 11 that approaches the die 20 as it goes downward, and a ridge formed in the middle of the taper surface 11 so as to have a semicircular cross section and extending perpendicularly to the paper surface of FIG. 12 and. The pinch-off portion molding surface of the die 20 also has a tapered surface 21 that approaches the die 10 as it goes downward, and a ridge 22 that is formed so as to project from the tapered surface 21. The ridges 12 and 22 are arranged in different steps, and the radius of curvature of the ridge 12 is slightly smaller than the radius of curvature of the ridge 22. The tips of the tapered surfaces 11 and 21 are connected to the pinch-off blades 13 and 23, respectively.

While the molds 10 and 20 are open, a high density polyethylene, modified polyolefin,
A tubular parison 40 formed by laminating three kinds of ethylene-vinyl acetate copolymer emulsions is extruded.

Thereafter, when the molds 10 and 20 are closed and clamped, the molding surfaces of the pinch-off portions of both molds 10 and 20 press the middle of the parison 40 to mold the pinch-off portion 3 of the plastic container 1. The pinch-off blades 13 and 23 cut off the tip of the pinch-off portion 3.

At the time of molding the pinch-off portion 3, both molds 1
The ridges 12 and 22 having different levels of 0 and 20 compress the pinch-off portion 3 that is being formed to reduce the thickness of the resin layers 1a, 1b, and 1c, and the inner second resin layer 1b and the third resin layer 1b.
The resin layer 1c is pushed up and moved away from the tip of the pinch-off portion 3.

As a result, the second resin layer 1b and the third resin layer 1c do not protrude from the tip of the pinch-off portion 3.
Further, when the thickness of the second resin layer 1b or the third resin layer 1c is thin, the adhesiveness is improved. This synergistic effect prevents bottom cracking in the plastic container 1.

When the ridges 12 and 22 are opposed to each other at the same height, the pressing force of the ridges 12 and 22 hinders the pushing up of the second resin layer 1b and the third resin layer 1c, and
Although there is a possibility that the molds 10 and 20 may be spread, if the protrusions 12 and 22 are arranged in different steps as in the molds 10 and 20 of the present invention, the pushing up of the second resin layer 1b and the third resin layer 1c is smooth. Moreover, the molds 10 and 20 are not expanded.

The process after the molds 10 and 20 are clamped is no different from the general blow molding, and the parison 40 is used.
A pressurized fluid is injected into the inside of the parison 40 to expand it until it contacts the cavity surface, and then it is cooled and solidified to mold the outer surface of the plastic container 1.

[0023]

As described above, according to the present invention,
By forming the pressure depressions having different steps in the pinch-off portion, an excellent effect that the bottom crack of the plastic container does not occur is exhibited.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of a pinch-off portion of a plastic container of the present invention.

FIG. 2 is a partially cutaway front view of the plastic container of the present invention.

FIG. 3 is an overall sectional view of a manufacturing die of the present invention.

FIG. 4 is a partially enlarged cross-sectional view of the manufacturing die of the present invention.

FIG. 5 is an enlarged cross-sectional view of a pinch-off portion of a conventional plastic container.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plastic container 2 Bottom part 3 Pinch-off part 6,7 Press recess 10 Mold 11 Tapered surface (pinch-off molding surface) 12 Projection 20 Mold 21 Tapered surface (pinch-off molding surface) 22 Projection

Claims (2)

[Claims] 1. A plastic container molded by extrusion blow molding and having a pinch-off portion protruding from the bottom, wherein stepped pressing recesses are formed on both ends of the pinch-off portion on the tip side and the base side. Characteristic plastic container. 2. An extrusion blow molding die comprising a pair of left and right dies for producing a plastic container having a pinch-off portion protruding from the bottom, wherein the pinch-off portion molding surface of each of the left and right dies is A mold for manufacturing a plastic container, wherein right and left molds are provided with ridges that face each other in different steps.