Synthetic resin container

Abstract

A synthetic resin container has improved formability while preventing deformation of corner walls. The synthetic resin container includes a mouth that serves as a dispensing opening for contents, a body that is continuous with the mouth via a shoulder, and a bottom that closes a lower end of the body. The body includes a pair of main walls arranged so as to face each other with a gap therebetween, a pair of side walls arranged so as to face each other with a gap therebetween, and corner walls that couple respective ends in a circumferential direction of the main walls and the side walls. Each corner wall is provided with U-shaped ribs that are formed in a substantially U-shape within a surface of the corner wall and that are concave toward an inner side in a thickness direction of the corner wall.

Description

CROSS-RENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2021-109541 filed on Jun. 30, 2021, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a bottle-shaped synthetic resin container including a mouth that serves as a dispensing opening for contents, a body that is continuous with the mouth via a shoulder, and a bottom that closes a lower end of the body.

BACKGROUND

Synthetic resin containers, typical examples of which include oriented polypropylene (OPP) bottles and polyethylene terephthalate (PET) bottles, are used for various applications, such as beverages, foods, or cosmetics, because they are lightweight and easy to handle, have excellent preservation stability of contents, and are low in cost.

For example, in Patent Literature 1, a square-shaped synthetic resin container is described in which vertically long recesses are provided on corner walls of the body, so as to prevent loss of rigidity of the container. By preventing deformation of the corner walls, occurrence of wrinkles on a label, such as a shrink label or a roll label, can be prevented when it is attached to the container.

CITATION LIST

Patent Literature

• • PTL 1: JP 2004-149126 A

SUMMARY

The present inventor has conducted earnest studies and found that it is more effective to provide annular grooves (ribs) formed in annular shapes within the surfaces of the corner walls, in order to increase rigidity of the corner walls. Generally, however, reduced pressure absorption panels are provided in such a square-shaped synthetic resin container, so as to deal with a reduced pressure that occurs when the container is cooled after it is filled with high-temperature contents. In a case in which annular grooves are provided adjacent to reduced pressure absorption panels, the width of protrusions formed in areas located between the reduced pressure absorption panels and the annular grooves narrows. As a result, during molding, resin is less likely to reach parts of a mold surface that correspond to the protrusions, thus sometimes resulting in poor formability (that causes sink marks or the like). Improvement can be made in this respect.

It would be helpful to provide a synthetic resin container with improved formability while preventing deformation of corner walls.

A synthetic resin container according to the present disclosure includes a mouth that serves as a dispensing opening for contents, a body that is continuous with the mouth via a shoulder, and a bottom that closes a lower end of the body, wherein

the body includes a pair of main walls arranged so as to face each other with a gap therebetween, a pair of side walls arranged so as to face each other with a gap therebetween, and corner walls that couple respective ends in a circumferential direction of the main walls and the side walls, and

each of the corner walls is provided with U-shaped ribs that are formed in a substantially U-shape within a surface of the corner wall and that are concave toward an inner side in a thickness direction of the corner wall.

In a preferred embodiment of the present synthetic resin container configured as above, each of the U-shaped ribs includes a longitudinal groove extending substantially in a vertical direction, and horizontal grooves extending substantially in a horizontal direction from both ends in the vertical direction of the longitudinal groove.

In another preferred embodiment of the present synthetic resin container configured as above, the side walls have a narrower width in the circumferential direction than the main walls, and the U-shaped ribs are formed so as to open toward the side walls.

According to the present disclosure, a synthetic resin container with improved formability can be provided while preventing deformation of corner walls.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a front view of a synthetic resin container according to an embodiment of the present disclosure;

FIG. 2 is a side view of the synthetic resin container according to the embodiment of the present disclosure;

FIG. 3 is a plan view of the synthetic resin container according to the embodiment of the present disclosure; and

FIG. 4 is a bottom view of the synthetic resin container according to the embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, the present disclosure will be described in more detail by way of example with reference to the drawings.

A synthetic resin container 1 of FIG. 1 according to an embodiment of the present disclosure stores, for example, beverages, such as fruit juice or tea, and seasonings, such as soy sauce, vinegar, or other sauces, as contents, and it is adapted for hot filling in which the contents are heated to a predetermined temperature before being filled into the container in a high-temperature state. In the present specification, claims, abstract, and drawings, a vertical direction is defined with reference to a state in which the synthetic resin container 1 is upright on a horizontal plane, and the term upward means upward in FIG. 1 and the term downward means downward in FIG. 1.

The synthetic resin container 1 is formed in a bottle shape including a mouth 2 that serves as a dispensing opening for contents, a shoulder 3 that is continuous with a lower end of the mouth 2 and that expands in diameter downward, a body 4 that is continuous with the mouth 2 via the shoulder 3 and that has a rectangular shape in the plan view (refer to FIG. 3), and a bottom 5 that closes a lower end of the body 4. An area below a stepped portion 5a located below the body 4 is referred to as a heel portion 5h. Reference sign O in FIG. 1 represents a central axis common to the mouth 2, the shoulder 3, the body 4, and the bottom 5. In the present specification and claims, a radial direction is a direction that passes the central axis O and that is also perpendicular to the central axis O. A direction toward an inner side in the radial direction is a direction toward the central axis O along the radial direction, and a direction toward an outer side in the radial direction is a direction away from the central axis O along the radial direction.

The synthetic resin container 1 can be configured as a so-called PET bottle, by biaxially stretch blow molding a preform made of polyethylene terephthalate (PET), for example. The synthetic resin container 1 is not limited to polyethylene terephthalate, and it can also be formed by biaxially stretch blow molding a preform made of other thermoplastic resins, such as oriented polypropylene (OPP). In addition to biaxial stretch blow molding of a preform, various manufacturing methods can be adopted to manufacture the synthetic resin container 1, such as extrusion blow molding of a resin material.

As illustrated in FIG. 1, a male thread 2a is formed on an outer peripheral surface of the mouth 2. After the contents are hot-filled, a cap that is not illustrated can be screw-engaged with the mouth 2 so as to close the mouth 2. Instead of the male thread 2a provided on the outer peripheral surface of the mouth 2, a projection may be provided, and a cap as a plug may be engaged with the projection, so as to close the mouth 2. A neck ring 2c may be provided below the male thread 2a of the mouth 2, so as to support the synthetic resin container 1 when the contents are filled into the synthetic resin container 1, for example. The neck ring 2c projects in an annular shape toward the outer side in the radial direction from the outer peripheral surface of the mouth 2.

As illustrated in FIG. 3 or the like, the body 4 has a rectangular tube structure having a chamfered rectangular shape in the plan view. The body 4 includes a pair of main walls 4a and a pair of side walls 4b. The pair of main walls 4a are arranged so as to face each other with a gap therebetween. The pair of side walls 4b are substantially orthogonal to the main walls 4a, arranged so as to face each other with a gap therebetween, and coupled to respective ends in the circumferential direction of the main walls 4a via corner walls 4c.

The main walls 4a and the side walls 4b are formed substantially in flat plate shapes, and both have vertically long shapes, as illustrated in FIG. 1 and FIG. 2. The main walls 4a each include a reduced pressure absorption panel 11a located at a substantially central position within the surface, and the side walls 4b each include a reduced pressure absorption panel 11b located at a substantially central position within the surface. The reduced pressure absorption panels 11a, 11b have vertically long shapes similarly with the main walls 4a and the side walls 4b. In the present embodiment, the pair of main walls 4a facing each other have the same shape as each other, and the pair of side walls 4b facing each other also have the same shape as each other. Similarly, the pair of reduced pressure absorption panels 11a facing each other have the same shape as each other, and the pair of reduced pressure absorption panels 11b facing each other also have the same shape as each other.

The reduced pressure absorption panels 11a, 11b are arranged on the main walls 4a and the side walls 4b at substantially central positions in the horizontal and vertical directions, as illustrated in FIG. 1 and FIG. 2. The reduced pressure absorption panels 11a, 11b are formed so as to cave in toward the inner side in the radial direction from the main walls 4a and the side walls 4b. This configuration of the reduced pressure absorption panels 11a, 11b that is three-dimensional in the radial direction can prevent unfavorable deformation that occurs in unexpected parts of the body 4 after the contents being hot-filled into the synthetic resin container 1. That is, in a case in which the contents are hot-filled into the synthetic resin container 1 and the mouth 2 is subsequently closed with a cap, the contents cool, and accordingly, a reduced pressure is created inside the container. In response to the reduced pressure inside the container, the reduced pressure absorption panels 11a, 11b with the three-dimensional shape in the radial direction can easily undergo elastic deformation toward the inner side of the container and absorb the reduced pressure, thereby preventing unfavorable deformation that occurs in unexpected parts of the body 4.

Although in the present embodiment the reduced pressure absorption panels 11a, 11b have a relatively simple configuration by which they are depressed toward the inner side in the radial direction at the outer edges, the present disclosure is not limited to this. For example, recesses and protrusions may be alternately arranged adjacent to each other so that the reduced pressure absorption panels 11a, 11b can be even more easily deformed toward the inner side in the radial direction, whereby the reduced pressure absorption effect can be enhanced. Additionally, the reduced pressure absorption panels 11a, 11b may be provided on only either the main walls 4a or the side walls 4b, and the reduced pressure absorption panels 11a, 11b may also be omitted.

A stepped portion 3a is formed in boundary areas of the main walls 4a and the side walls 4b with respect to the shoulder 3, as illustrated in FIG. 1 and FIG. 2. The stepped portion 3a is slightly reduced in diameter toward the inner side in the radial direction from the main walls 4a and the side walls 4b to the shoulder 3. As illustrated in FIG. 1, the stepped portion 3a includes a substantially arc-shaped protrusion 3b that bulges (to be convex) toward the outer side (upward in the step portion 3a of FIG. 1) in the vertical direction at the substantially central position in the circumferential direction of each main wall 4a. As illustrated in FIG. 2, the stepped portion 3a also includes a substantially arc-shaped protrusion 3c that is convex upward at the substantially central position in the circumferential direction of each side wall 4b. By thus providing the stepped portion 3a at a lower end of the shoulder 3, the container can be prevented from undergoing plastic deformation (distortion and deformation) in a direction that causes creases to form in the vertical direction at this area. In particular, providing the stepped portion 3a with the protrusions 3b, 3c exerts a preventive effect against not only distortion in the direction that causes creases to form in the vertical direction but also distortion in a direction that causes creases to form in the horizontal direction. Additionally, the protrusions 3b, 3c of the stepped portion 3a do not necessarily need to be formed in substantially arc shapes, and they may have other shapes, such as triangular or trapezoidal shapes. Further, the stepped portion 3a may include only the protrusions 3b on the main walls 4a or the protrusions 3c on the side walls 4b. The protrusions 3b, 3c may also be omitted, and the stepped portion 3a may extend linearly in the circumferential direction.

A stepped portion 5a is formed in boundary areas of the main walls 4a and the side walls 4b with respect to the heel portion 5h, as illustrated in FIG. 1 and FIG. 2. The stepped portion 5a is slightly reduced in diameter toward the inner side in the radial direction from the main walls 4a and the side walls 4b to the heel portion 5h. As illustrated in FIG. 1, the stepped portion 5a includes a substantially arc-shaped protrusion 5b that bulges (to be convex) toward the outer side (downward in the stepped portion 5a of FIG. 1) in the vertical direction at the substantially central position in the circumferential direction of each main wall 4a. As illustrated in FIG. 2, the stepped portion 5a also includes a substantially arc-shaped protrusion 5c that is convex downward at the substantially central position in the circumferential direction of each side wall 4b. By thus providing the stepped portion 5a at lower portions of the main walls 4a and the side walls 4b, the container can be prevented from undergoing plastic deformation (distortion and deformation) in a direction that causes creases to form in the vertical direction at these areas. In particular, providing the stepped portion 5a with the protrusions 5b, 5c exerts a preventive effect against not only distortion in the direction that causes creases to form in the vertical direction but also distortion in a direction that causes creases to form in the horizontal direction. Additionally, the protrusions 5b, 5c of the stepped portion 5a do not necessarily need to be formed in substantially arc shapes, and they may have other shapes, such as triangular or trapezoidal shapes. Further, the stepped portion 5a may include only the protrusions 5b on the main walls 4a or the protrusions 5c on the side walls 4b. The protrusions 5b, 5c may also be omitted, and the stepped portion 5a may extend linearly in the circumferential direction.

A T-shaped rib 20 is provided in an area located at the central position in the circumferential direction of an upper end of each main wall 4a between the reduced pressure absorption panel 11a and the stepped portion 3a, as illustrated in FIG. 1. The T-shaped rib 20 includes a transverse groove 20a and a longitudinal groove 20b. The transverse groove 20a extends substantially in the horizontal direction and is concave toward an inner side in a thickness direction of the body 4. The longitudinal groove 20b is continuous with the transverse groove 20a, extends in an upward direction substantially orthogonal to the transverse groove 20a, and is concave toward the inner side in the thickness direction of the body 4. In the present embodiment, the longitudinal groove 20b is configured so that its upper end overlaps the stepped portion 3a. This configuration can enhance both the rigidity in a direction concerning formation of creases in the vertical direction and the rigidity in a direction concerning formation of creases in the horizontal direction within the main wall 4a, thereby improving restoring force. Distortion and deformation within the main wall 4a can therefore be more effectively prevented.

Although the upper end (tip) of the longitudinal groove 20b extends to the stepped portion 3a, the present disclosure is not limited to this. The longitudinal groove 20b may extend beyond the stepped portion 3a to the shoulder 3. By the longitudinal groove 20b extending to the stepped portion 3a, rigidity can be enhanced within and across an area surrounded by ridges that define the main wall 4a, and distortion and deformation of the main wall 4a can therefore be more effectively prevented. The longitudinal groove 20b may also extend in the vicinity of the stepped portion 3a, while terminating before reaching the stepped portion 3a.

In the present embodiment, the transverse groove 20a is formed deeper toward the inner side in the thickness direction of the body 4 than the longitudinal groove 20b. This configuration further enhances rigidity against distortion in a direction that causes creases to form in the vertical direction, thereby more effectively preventing distortion and deformation.

Although in the present embodiment the T-shaped rib 20 is arranged at the upper end of the main wall 4a, the present disclosure is not limited to this. For example, a T-shaped rib 20 may be provided in an area located at the central position in the circumferential direction of a lower end of the main wall 4a between the reduced pressure absorption panel 11a and the stepped portion 5a. In this case, the T-shaped rib 20 includes a transverse groove 20a that extends substantially in the horizontal direction, and a longitudinal groove 20b that is continuous with the transverse groove 20a and that extends in a downward direction substantially orthogonal to the transverse groove 20a. In this case also, a lower end of the longitudinal groove 20b may extend to the stepped portion 5a, or the longitudinal groove 20b may extend beyond the stepped portion 5a to the heel portion 5h. The longitudinal groove 20b may also extend in the vicinity of the stepped portion 5a, while terminating before reaching the stepped portion 5a.

Further, the body 4 may be divided in the vertical direction into an upper body and a lower body by a peripheral groove that is not illustrated, and a longitudinal groove 20b of a T-shaped rib 20 provided at a lower end of the upper body may extend to the peripheral groove or extend beyond the peripheral groove to the lower body. In this case also, the longitudinal groove 20b may extend in the vicinity of the peripheral groove, while terminating before reaching peripheral groove.

Moreover, the body 4 may be divided in the vertical direction into an upper body and a lower body by a peripheral groove that is not illustrated, and a longitudinal groove 20b of a T-shaped rib 20 provided at an upper end of the lower body may extend to the peripheral groove or extend beyond the peripheral groove to the upper body. In this case also, the longitudinal groove 20b may extend in the vicinity of the peripheral groove, while terminating before reaching the peripheral groove.

Although in the present embodiment the T-shaped ribs 20 are provided only on the main walls 4a, the present disclosure is not limited to this. T-shaped ribs 20 may be provided on the side walls 4b, in addition to the main walls 4a, or only on the side walls 4b.

As illustrated in FIG. 3 and FIG. 4, the corner walls 4c are provided at four locations along the circumferential direction of the body 4. The corner walls 4c couple respective ends in the circumferential direction of the main walls 4a and the side walls 4b. Each corner wall 4c is formed as a chamfered edge of the body 4 with a substantially rectangular shape in the plan view. In the present embodiment, the corner wall 4c includes a central corner wall 4c1 and side corner walls 4c2, as illustrated in FIG. 1 and FIG. 2. The central corner wall 4c1 is provided in the middle in the circumferential direction and made of a curved surface. The side corner walls 4c2 are made of curved surfaces adjacent to, and located on either side in the circumferential direction of, the central corner wall 4c1. The corner walls 4c may be made of only one or more flat surfaces, or they may be made of one curved surface or a combination of curved and flat surfaces.

In order to increase rigidity of each corner wall 4c, U-shaped ribs 30 are provided on the corner wall 4c, as illustrated in FIG. 1 and FIG. 2. Each U-shaped rib 30 is formed in a substantially U-shape within a surface of the corner wall 4c and is recessed toward the inner side in the thickness direction of the corner wall 4c. In the present embodiment, the U-shaped rib 30 includes a longitudinal groove 30b and a transverse groove 30a. The longitudinal groove 30b extends in the vertical direction while drawing substantially an arc that is convex toward an adjacent main wall 4a, and the transverse groove 30a extends substantially in the horizontal direction from both ends in the vertical direction of the longitudinal groove 30b. As illustrated in FIG. 2, the U-shaped rib 30 is formed so that its opening 30c is open toward an adjacent side wall 4b, and the periphery of the U-shaped rib 30 and a central protrusion 30d surrounded by the U-shaped rib 30 are coupled via the opening 30c. In the present embodiment, four U-shaped ribs 30 are arranged with a substantially regular gap in the vertical direction on each corner wall 4c. Both ends in the circumferential direction of the U-shaped ribs 30 may extend to the adjacent main wall 4a and/or the adjacent side wall 4b.

In order to increase rigidity of the corner walls 4c, it is effective to provide annular ribs obtained by closing the openings 30c of the U-shaped ribs 30 of FIG. 2. However, in a case in which annular ribs are provided on the corner walls 4c, longitudinal grooves are also formed at the positions of the openings 30c of FIG. 2. As a result, during molding, resin is less likely to reach protrusions located between the longitudinal grooves (recesses) and the reduced pressure absorption panels 11b (concave part) of the side walls 4b that have a narrow width in the circumferential direction, thus resulting in poor formability and causing sink marks. In the present embodiment, as illustrated in FIG. 2, the U-shaped ribs 30 include the openings 30c provided near the side walls 4b with a narrow width. Accordingly, there is no protruding portion with a narrow width, and the peripheries of the U-shaped ribs 30 and the central protrusions 30d surrounded by the U-shaped ribs 30 are coupled via the openings 30c. Poor formability is therefore prevented.

Although in the present embodiment the U-shaped ribs 30 each have an ideal U-shape as illustrated in FIG. 2, the present disclosure is not limited to this. Each longitudinal grooves 30b may linearly extend in the vertical direction or may have an R-shape with an even smaller radius of curvature. Further, by bringing parts of each transverse groove 30a that are located near the opening 30c closer to each other in the vertical direction, the U-shaped rib 30 may have a substantially C-shape. Moreover, the openings 30c do not necessarily need to be provided to be oriented toward the side walls 4b, and they may be provided to be oriented toward the main walls 4a or in the vertical direction.

Additionally, in the present embodiment, the body 4 has a chamfered rectangular shape in the plan view, and it includes two main walls 4a and two side walls 4b that constitute the rectangular portion, and four corner walls 4c that constitute the chamfered portion. The present disclosure is, however, not limited to this. For example, the body 4 may be configured so that the main walls 4a and the side walls 4b have substantially the same width in the circumferential direction, or the body 4 may have substantially an octagonal shape in the plan view, wherein four main walls 4a and four side walls 4b are alternately arranged via corner walls 4c. Other configurations may also be adopted.

As described above, the synthetic resin container 1 according to the present embodiment is a synthetic resin container 1 including a mouth 2 that serves as a dispensing opening for contents, a body 4 that is continuous with the mouth 2 via a shoulder 3, and a bottom 5 that closes a lower end of the body 4, wherein the body 4 includes a pair of main walls 4a arranged so as to face each other with a gap therebetween, a pair of side walls 4b arranged so as to face each other with a gap therebetween, and corner walls 4c that couple respective ends in a circumferential direction of the main walls 4a and the side walls 4b, and each of the corner walls 4c is provided with U-shaped ribs 30 that are formed in a substantially U-shape within a surface of the corner wall 4c and that are concave toward an inner side in a thickness direction of the corner wall 4c. By adopting such a configuration, rigidity is increased in the corner walls 4c. Besides, by providing the openings 30c to be oriented toward where protrusions with a narrow width are formed, filling of resin to the protrusions can be facilitated. Thus, the synthetic resin container 1 with improved formability can be provided while preventing deformation of the corner walls 4c.

Further, in the present embodiment, each U-shaped rib 30 is configured to include a longitudinal groove 30b that extends substantially in the vertical direction, and a transverse groove 30a that extends substantially in the horizontal direction from both ends in the vertical direction of the longitudinal groove 30b. By adopting such a configuration, rigidity of the corner walls 4c against pressing force in the radial direction can be enhanced by the transverse grooves 30a, and rigidity of the corner walls 4c against pressing force in the vertical direction can be increased by the longitudinal grooves 30b. Thus, the synthetic resin container 1 with improved formability can be provided while more effectively preventing deformation of the corner walls 4c.

Moreover, in the present embodiment, the side walls 4b have a narrower width in the circumferential direction than the main walls 4a, and the U-shaped ribs 30 are configured to open toward the side walls 4b. By adopting such a configuration, since the openings 30c of the U-shaped ribs 30 are provided near the side walls 4b with a narrow width in the circumferential direction, there is no protruding portion with a narrow width between the reduced pressure absorption panels 11b and the U-shaped ribs 30, and the peripheries of the U-shaped ribs 30 and the central protrusions 30d surrounded by the U-shaped ribs 30 are coupled via the openings 30c. Poor formability and occurrence of sink marks can therefore be more effectively prevented.

While the present disclosure has been described based on the drawings and examples, it is to be noted that various changes and modifications may be implemented by those skilled in the art based on the present disclosure. Accordingly, such changes and modifications are included within the scope of the present disclosure. For example, functions or the like included in each component can be rearranged without logical inconsistency, and a plurality of components can be combined together or divided. These are to be understood as included in the scope of the present disclosure.

For example, the pair of main walls 4a do not need to have the same shape as each other, and the pair of side walls 4b do not need to have the same shape as each other. The main walls 4a may have different shapes from each other, and the side walls 4b may have different shapes from each other. Further, the shapes of the reduced pressure absorption panels 11a, 11b are not limited to the above embodiment, and various configurations can be adopted. Each of the reduced pressure absorption panels 11a, 11b may have a different shape from each other.

Further, the number of reduced pressure absorption panels 11a, 11b, T-shaped ribs 20, and U-shaped ribs 30 are not limited to the above embodiment. For example, two or more reduced pressure absorption panels 11a may be provided on one main wall 4a, or reduced pressure absorption panels 11a may be provided only on some of main walls 4a. Two or more T-shaped ribs 20 may be provided on one main wall 4a. Any number of U-shaped ribs 30 may be provided on one corner wall 4c.

Moreover, although in the present embodiment the side walls 4b have a narrower width in the circumferential direction than the main walls 4a, and the U-shaped ribs 30 are configured to open toward the side walls 4b, the present disclosure is not limited to this. In a case in which protrusions with a narrow width are formed between the U-shaped ribs 30 and recessed portions other than the reduced pressure absorption panels 11a, 11b, the openings 30c may be provided to be oriented toward the protrusions.

The contents to be filled into the synthetic resin container 1 are not limited to beverages, such as fruit juice or tea, and seasonings, such as soy sauce, vinegar, or other sauces, and they may also include other foods and cosmetics.

Claims

1. A synthetic resin container comprising a mouth that serves as a dispensing opening for contents, a body that is continuous with the mouth via a shoulder, and a bottom that closes a lower end of the body, wherein the body includes a pair of main walls arranged so as to face each other with a gap therebetween, a pair of side walls arranged so as to face each other with a gap therebetween, and corner walls that couple respective ends of the main walls that extend along a central axis of the synthetic resin container to respective ends of the side walls that extend along the central axis of the synthetic resin container, andall of the corner walls are provided with U-shaped ribs that are formed in a substantially U-shape, that are formed only within a surface of the corner wall, and that are concave toward an inner side in a thickness direction of the corner wall,wherein each of the U shaped ribs includes a longitudinal groove extending substantially in a vertical direction, horizontal grooves extending substantially in a horizontal direction from both ends of the longitudinal groove in the vertical direction, an opening at an end opposite from the longitudinal groove between the horizontal grooves, and a central protrusion surrounded by the longitudinal groove and the horizontal grooves, and the central protrusion is at least partially present between:(i) the horizontal grooves in the vertical direction and(ii) the longitudinal groove and the opening in the horizontal direction.

2. The synthetic resin container according to claim 1, wherein the side walls have a narrower width in a direction transverse to the central axis of the synthetic resin container than a width of the main walls in another direction transverse to the central axis of the synthetic resin container, and the U-shaped ribs are formed so as to open toward the side walls.