JPH085117B2 - Pressure-resistant thin synthetic resin container and method of molding the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pressure-resistant thin-walled synthetic resin container suitable for packaging beverages such as carbonated beverages and beer that generate pressure in the container, and a method for molding the same.

[Prior Art] A bottom structure has a thin outer peripheral wall portion connected to a container body, an inner peripheral wall portion formed by folding back from the lower end of the outer peripheral wall portion, and an annular grounding surface formed at the folded portion of the inner and outer peripheral walls. And a pressure-resistant synthetic resin container composed of a dome-shaped bottom wall central part formed continuously on the upper part of the inner peripheral wall part is disclosed in Japanese Patent Application Laid-Open No. 55-1631.
It is publicly known from Japanese Patent No. 37, Japanese Utility Model Publication No. 58-183308, and the like.

[Problems to be Solved by the Invention] In the container having the above-mentioned bottom structure, pressure resistance is provided by the inner peripheral wall portion and the central portion of the dome-shaped bottom wall continuously formed thereabove, but the pressure resistance is mainly If the wall thickness is formed differently from the design depending on the molding state of the annular grounding surface and the inner peripheral wall portion, there is a problem that the pressure resistance and the impact strength are likely to decrease.

Therefore, if many products are molded at the same time using the same mold, there will be no problem in appearance due to slight differences in molding conditions depending on cavities, but the strength of the bottom of the container may be inferior, resulting in molding loss. Many.

This invention was conceived in order to solve the difficulty of molding in the above conventional pressure-resistant container, and its purpose is to form the main part of the container bottom by forming it to be thicker than the container body, To provide a pressure-resistant thin-walled synthetic resin container having a new structure and a molding method capable of improving the pressure resistance and molding a uniform wall thickness distribution even if some molding condition difference occurs. is there.

[Means for Solving the Problems] According to one aspect of the present invention according to the above object, a bottomed preform made of a thermoplastic synthetic resin is stretched in an axial direction, and
A container is thinned by air pressure and a container bottom is formed into an arc-shaped container, and the arcuate bottom is pushed back inward, and the container bottom is connected to the container body by a thin outer peripheral wall and a lower end of the outer peripheral wall. A thin-walled synthetic resin container composed of an inner peripheral wall formed by folding back from the inner side, an annular grounding surface formed in the folded back portion of the inner and outer peripheral wall, and a bottom wall center formed continuously on the upper part of the inner peripheral wall. In the pressure-resistant thin synthetic resin container, the entire bottom surface extending from the outside of the annular grounding surface to the central portion of the bottom wall is formed to have a substantially equal thickness by providing a step at the boundary with the outer peripheral wall.

According to another aspect of the present invention, a bottomed preform container bottom molding portion made of a thermoplastic synthetic resin is formed with a step inside so as to be thicker than other portions, and the preform can be raised and lowered freely. Inside the blow mold having a mold, while extending axially above the step, the main part of the container bottom is thicker than the container body by air pressure, and an arc-shaped container is primarily formed. The bottom part is pushed back inward except the thin outer peripheral wall part integrally with the body part by the above-mentioned bottom die, and the inner peripheral wall part is formed by being folded back inward from the lower end of the outer peripheral wall part, and the folded part of the inner and outer peripheral wall parts. It consists of the resulting annular grounding surface and the center of the bottom wall continuously formed on the top of the inner peripheral wall, and the entire bottom surface from the outside of the annular grounding surface to the center of the bottom wall is the boundary with the outer peripheral wall. Pressure-resistant thin-walled synthetic resin container formed at the bottom of a thick container having a step In the molding process.

[Operation] In the container with the above configuration, since the entire bottom surface is stretch-molded from the outside of the ring-shaped grounding surface, the bending strength of the ring-shaped grounding surface is stronger than when it is thin, and the load due to the internal pressure of the contents Withstands the load even when concentrated on. Further, since the thickness distribution of the inner peripheral wall portion and the center portion of the bottom portion is uniform and the occurrence of internal strain is small, an eccentric load is not applied to the inner bottom surface and the impact strength is increased.

Example FIG. 1 to FIG. 3 show a cross section of a main part of a pressure-resistant container formed in a bottle shape. The container 1 is made of stretch blow-molded thermoplastic resin such as polyethylene terephthalate.

The container body 2 of the container 1 is stretch-blow molded to a thin wall up to the outer peripheral wall 31 of the bottom 3. Further, the container bottom portion 3 is gradually reduced in diameter to form a curved surface, and from the lower end of the outer peripheral wall portion 31, an inner peripheral wall portion 32 formed by folding back inward, an inner peripheral wall portion 31, and an inner peripheral wall portion.
An arcuate annular grounding surface 33 formed at the folded portion of 32 and a central portion of the bottom wall continuously and horizontally formed on the upper portion of the inner peripheral wall portion 32.
And 34.

The inner peripheral wall portion 32 is formed in a state of being obliquely bent from the upper end of the annular grounding surface 33, and the bottom surface extending from the outside of the annular grounding surface 33 to the bottom wall central portion 34 is a boundary with the outer peripheral wall portion 31. On the step
35 is provided and is generally equal in thickness, and is formed to have a thickness that is approximately four times the thickness of the outer peripheral wall portion.

In the container 1 having such a structure, the drop strength in the state of being filled with the contents is increased due to the formation of the thick bottom surface, and the container 1 can sufficiently withstand a large internal pressure. Specifically, the following specifications may be adopted. preferable.

Wall thickness of container body 2 and outer peripheral wall 31 a 0.4 to 0.5 mm Bottom wall thickness b 1.6 to 2.0 mm Curvature R 1.5 of annular grounding surface 33
1.8 mm Height of step 35 from the ground plane H 2.0 to 6.0 mm FIGS. 4 to 10 are explanatory views of the molding process, and the container 1 is molded from the bottomed preform 4 shown in FIG. .

The preform 4 is injection-molded such that the thickness of the preform bottom portion 41, which is the bottom molding portion of the container 1, is thicker than the thickness of the preform side portion 42, which is the body molding portion, and the preform bottom portion 41 and the side portions 42. The inner side of the boundary with is formed in a stepped portion 43. The width c of the step 4 may be about 0.5 to 1.0 mm, and the height h from the bottom end to the step 43 is the same as the container 1 described above.
It is arbitrarily set according to the bottom area of the.

Although this preform 4 is omitted in the drawing, as shown in FIG.
Adjust to a temperature suitable for stretching. Immediately after the preform 4 is injection-molded, the holding temperature differs depending on the wall thickness distribution, and the thicker wall has a higher temperature. Therefore, the temperature adjustment is performed separately for the preform bottom portion 41 and the side portion 42. In addition, a temperature control core 51 is inserted into the preform and brought into contact therewith, and a lower preform bottom portion 41 from the step portion 43 is brought into contact with the pot bottom plate 52 so that the temperature of the side portion 42 is controlled by radiant heat from the heating ring 53. At a different temperature than.

Specifically, this temperature control may be a core temperature of 30 ° C, a heating ring temperature of 205 ° C, and a bottom plate temperature of about 15 ° C. The preform temperature is 110 to 120 ° C at the preform bottom portion 41, and the side portion 42.
The temperature is adjusted to 90-100 ℃.

After the temperature control, the preform 4 is transferred to the blow mold 6.
As shown in FIG. 8, a bottom die 61 for molding the inner side of the annular grounding surface of the container bottom is provided at the bottom of this die so that it can be raised and lowered. A stretch rod 62 is inserted into the preform 4 located at the center of the cavity when the mold is closed. The distal end portion 63 of the extension rod 62 is formed of a material having heat insulating property or low thermal conductivity into a shape that matches the inner shape of the preform distal end portion 41, and the engaging edge 64 is formed on the bottom of the preform. Are formed to project. The engaging edge 64 engages the step 43 in the preform and the tip 63 fits within the preform bottom 6.

When the extension rod 62 is extended in such a state,
As shown in the figure, the preform 4 is stretched only at the side portion 42 between the held neck portion and the step portion 43, and the preform bottom portion 41 is cooled to about 15 ° C while maintaining the same thickness. Move up to 61 with the tip 63 of the draw rod. Further, since the side portion 42 is reduced in diameter and comes into contact with the rod along with the stretching, 8 to 10 kg / cm ² of air is blown as the primary air during stretching. This blowing pressure is switched to a pressure of 25 Kg / cm ² immediately after stretching, the preform 4 is expanded as a secondary air to the full extent of the cavity, and the main portion of the bottom portion 71 is thicker than the body portion 72 and the arc-shaped container 7 is formed. Primary molding is performed (see FIG. 9).

After forming the container, as shown in FIG. 10, the bottom die 61 is raised to push the thick arc-shaped bottom portion 71 inward with the body portion 72 except the thin outer peripheral wall portion, and the arc-shaped bottom portion 71. The thick-walled part is not stretched in the axial direction, and unlike the thin-walled body 72 that has been stretched in the biaxial direction, it must have a heat amount that can be molded even if it is stretched to some extent by air pressure. From the above, while being uniformly stretched in the radial direction by the pressing force of the bottom die 61, it is folded back at the boundary between the cavity surface and the bottom die to present a concave shape,
The folded back portion serves as an annular contact surface 73.

By the secondary molding by the bottom mold 61, the container 7 primary molded is formed into a bottle-shaped container having a bottom structure shown in FIG. 3, that is, the thin outer peripheral wall portion 31 is folded inward from the lower end thereof. The inner peripheral wall portion 32, an annular grounding surface 33 formed at the folded portion of the inner and outer peripheral wall portions, and a bottom wall central portion 34 formed continuously on the upper portion of the inner peripheral wall portion 32, and of the annular grounding surface 33 The entire bottom surface extending from the outer side to the central portion 34 of the bottom wall is completed as the packaging container 1 having a thick container bottom having a step 33 at the boundary with the outer peripheral wall 31.

[Advantages of the Invention] As described above, the present invention includes a thin outer peripheral wall portion that connects the container bottom portion to the container body portion, an inner peripheral wall portion that is formed by folding back from the lower end of the outer peripheral wall portion to the inside, and an inner peripheral wall portion. It consists of an annular grounding surface that occurs at the folded portion and a bottom wall central part that is formed continuously on the top of the inner peripheral wall, and the entire bottom surface from the outside of the annular grounding surface to the bottom central part Since a step is provided on the boundary with the wall to form a substantially equally thick wall,
It is possible to prevent the drop strength from decreasing due to the non-uniformity of the wall thickness distribution.Because the main part of the bottom surface is biaxially oriented and the ring-shaped ground surface is also formed to be thick, not to mention the internal load. It withstands a large internal pressure, and it is extremely rare that the ground contact surface will be deformed or the bottom of the container will be damaged even if it falls while being filled with a carbonated beverage or the like.

When molding, the container bottom part of the bottomed preform is thickly molded in advance, and that part is stretched by the bottom mold after stretching the body part. It is possible to form a thick bottom surface without failing to prevent the resin amount from being taken up by the portion of the container and to ensure that the wall thickness distribution is approximately equal at all times. Molding is easier than conventional pressure-resistant containers that do not produce sufficient effect, and even when molding a large number of products at the same time, it is possible to form a homogeneous product with less molding loss. Have the advantage of.

[Brief description of drawings]

The drawings show a pressure-resistant thin synthetic resin container according to the present invention and a molding method thereof. Fig. 1 is a partially longitudinal front view of the container, Fig. 2 is a cross-sectional plan view of the container bottom, and Fig. 3 is the container. Fig. 4 is a vertical cross-sectional view of the bottom, Fig. 4 is a vertical cross-sectional view of the bottom preform, and Fig. 5 is a partial cross-sectional view of the bottom of the preform.
The drawings are vertical cross-sectional views for sequentially explaining the molding process. 1 ... Pressure-resistant container, 2 ... Container body 3 ... Container bottom, 31 ... Outer wall 32 ... Inner wall 33 ... Annular ground plane, 34 ... Bottom center 35 ... Step 4 ... Bottom preform 41 ...... Preform bottom, 42 ... Side, 43 ... Step 5 ... Temperature control pot, 6 ... Blowing die 61 ... Bottom 62 ... Stretching rod 63 ... Tip, 64 …… Engagement rim 7 …… Primary molding container 71 …… Arc bottom

Claims (5)

[Claims] 1. A bottomed preform made of a thermoplastic synthetic resin is axially stretched, and a container body is thinned by air pressure to form a container having an arc-shaped bottom, and the arc-shaped bottom is pushed back inward. A thin outer peripheral wall portion connecting the bottom of the container to the body of the container, an inner peripheral wall portion formed by folding back from the lower end of the outer peripheral wall portion, an annular grounding surface formed at the folded portion of the inner and outer peripheral wall portions, and an inner peripheral wall In a thin-walled synthetic resin container composed of a central portion of the bottom wall formed continuously on the upper part of the portion, the entire bottom surface extending from the outside of the annular grounding surface to the central portion of the bottom wall is stepped at the boundary with the outer peripheral wall portion. A pressure-resistant thin-wall synthetic resin container characterized in that it is formed to have a substantially uniform thickness. 2. The pressure-resistant thin-walled synthetic resin container according to claim 1, wherein the thickness of the entire bottom surface extending from the outside of the annular grounding portion to the center of the bottom wall is approximately four times the thickness of the outer peripheral wall portion. 3. A blow-in mold having a bottom mold for forming a bottomed preform container bottom portion made of a thermoplastic synthetic resin so as to be thicker than other portions by providing a step portion inside and forming the preform. In the mold, while extending axially above the step, the main part of the bottom part is primarily formed by air pressure to form an arc-shaped container whose wall thickness is thicker than the body part, and the arc-shaped bottom part is formed by the bottom mold. The inner peripheral wall part that is formed by folding back inward except the thin outer peripheral wall part that is integral with the inner part, and the inner peripheral wall part that is formed by being folded back inward from the lower end of the outer peripheral wall part; It is composed of a bottom wall center portion formed continuously on the upper portion of the peripheral wall portion, and from the outside of the annular grounding surface to the bottom wall center portion and the entire bottom surface, a thick wall having a step portion at the boundary with the outer peripheral wall portion. A pressure resistant thin synthetic resin container characterized by being formed on the bottom of the container. Form method. 4. The axial extension of the bottomed preform above the step portion has a shape such that the tip portion conforms to the molding portion of the container bottom portion below the step portion, and the step portion is formed on the tip portion. The method for molding a pressure-resistant thin-walled synthetic resin container according to claim 3, which is performed by using a stretch rod having an engaging edge. 5. The molding of a pressure-resistant thin synthetic resin container according to claim 3, wherein the axial extension above the stepped portion of the bottomed preform is carried out under the blowing of an air pressure lower than the air pressure at the time of blowing the container. Method.