Synthetic resin container and preform

Abstract

To provide a synthetic resin container and a preform allowing for the reduction of weight and cost of a container by reducing the amount of resin to be used for its mouth.SOLUTION: Each of a synthetic resin container and a preform includes a mouth in which an annular protrusion that protrudes annularly in a radially outward direction along a peripheral edge at an opening of the mouth and a neck ring that protrudes annularly in a radially outward direction along a circumferential direction are provided axially spaced apart from each other. The mouth has an inner diameter reduced relative to an opening diameter of the mouth closer to the opening, in an intermediate portion between a portion where the annular protrusion is provided and a portion where the neck ring is provided. A maximum thickness T21 in a radial direction of the portion where the annular protrusion is provided closer to the intermediate portion, a maximum thickness T22 in the radial direction of the portion where the inner diameter is reduced in the intermediate portion, and a maximum thickness T23 in the radial direction of the portion where the neck ring is provided satisfy T22 / T21>0.65 and T22 / T23>0.42.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a synthetic resin container and a preform for producing a synthetic resin container by blow molding. [Background technology]

[0002] BACKGROUND ART Conventionally, synthetic resin containers have been used in a wide range of fields as containers for various beverages, seasonings, and the like, which are made by injection molding a bottomed cylindrical preform using a thermoplastic resin such as polyethylene terephthalate and then molding this preform into a bottle shape using biaxially stretched blow molding.

[0003] For this type of container, attempts have been made to mold the container as thin as possible in order to reduce the weight and cost by reducing the amount of resin used. For example, Patent Document 1 discloses that a plastic bottle and preform are provided with a lightweight mouth by providing a narrow thread portion that is thinner than usual at a specific location on the thread of the male screw portion provided at the mouth of the plastic bottle. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-177336 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, the demand for thinner walls has become increasingly stringent, but there are various constraints in reducing the weight and cost of plastic containers. For example, the mouth of a plastic bottle must not only be able to be threaded, engaged, or fitted with a lid or nozzle, but also must have an outer shape that is compatible with the molding line or filling line. Furthermore, by designing the shape to reduce the amount of resin material used, it is necessary to avoid defects in the molding process during injection molding.

[0006] The present invention aims to provide a synthetic resin container and a preform for producing a synthetic resin container by blow molding, which makes it possible to reduce the weight and cost of the container by reducing the amount of resin in the mouth portion. [Means for solving the problem]

[0007] One aspect of the present invention is a synthetic resin container having a mouth, a shoulder, a body, and a bottom, wherein the mouth is provided with an annular protrusion that protrudes radially outward in an annular shape along the periphery of the opening of the mouth, and a neck ring that protrudes radially outward in an annular shape along the circumferential direction, the annular protrusion and the neck ring are spaced apart in the axial direction, the inner diameter of the mouth is reduced in an intermediate portion between a portion where the annular protrusion is provided and a portion where the neck ring is provided, relative to the opening diameter on the opening side of the mouth, and the maximum radial thickness T 21 and the maximum radial thickness T of the portion where the inner diameter is reduced in the intermediate portion. 22 and the maximum radial thickness T of the portion where the neck ring is provided. 23 What is that? T 22 / T 21 >0.65 and T 22 / T 23 >0.42 It is a synthetic resin container that meets the above requirements.

[0008] Another aspect of the present invention is a preform for manufacturing a synthetic resin container by blow molding, the preform being molded into a bottomed tubular shape with one open end serving as a mouth portion, the mouth portion being provided with an annular protrusion that protrudes radially outward in an annular shape along the periphery of the opening of the mouth portion, and a neck ring that protrudes radially outward in an annular shape along the circumferential direction, the annular protrusion being axially spaced apart from the periphery of the opening of the mouth portion, the inner diameter of the mouth portion being reduced in diameter relative to the opening diameter at the opening side of the mouth portion at an intermediate portion between a portion where the annular protrusion is provided and a portion where the neck ring is provided, and the maximum radial thickness T 21 and the maximum radial thickness T of the portion where the inner diameter is reduced in the intermediate portion. 22 and the maximum radial thickness T of the portion where the neck ring is provided. 23 What is that? T 22 / T 21 >0.65 and T 22 / T 23 >0.42 It is a preform that satisfies the above. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a synthetic resin container and a preform for manufacturing a synthetic resin container by blow molding, which can reduce the weight and cost of the container by reducing the amount of resin in the mouth portion. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an explanatory diagram showing an outline of a synthetic resin container according to an example of this embodiment. [Figure 2] 1 is an explanatory diagram showing a state in which a preform for producing a synthetic resin container by blow molding according to an example of this embodiment is set in a blow molding mold. FIG. [Figure 3] 3 is an enlarged front view of a main part showing an enlarged mouth portion of the preform shown in FIG. 2. FIG. [Figure 4] FIG. 3 is an enlarged plan view of the preform shown in FIG. 2. [Figure 5] FIG. 5 is an enlarged cross-sectional view taken along the line AA in FIG. 4. [Figure 6] 6 is an enlarged cross-sectional view of a main part showing an area surrounded by a two-dot chain line in FIG. 5 in an enlarged scale. [Figure 7] 1 is a table showing the results of examples. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0012] FIG. 1 is an explanatory diagram showing an outline of a synthetic resin container 1 according to this embodiment. The container 1 can be formed into a predetermined container shape including a mouth portion 2, a shoulder portion 3, a body portion 4, and a bottom portion 5. In the illustrated example, the container 1 is formed to have a cylindrical container shape, but the shape of the container 1 is not limited to this.

[0013] The mouth 2 is a cylindrical portion that serves as an outlet for pouring the contents. The lower end of the mouth 2 is connected to a shoulder 3 that widens in diameter toward the body 4 and connects the mouth 2 and body 4. The body 4 occupies most of the height of the container 1, with its upper end connected to the shoulder 3 and its lower end connected to the bottom 5.

[0014] Here, the height direction refers to the direction perpendicular to the horizontal plane when the container 1 is placed upright on the horizontal plane with the mouth 2 side facing up, and the up / down, left / right and length / width directions of the container 1 are defined as shown in Figure 1 when the container is placed upright with the mouth 2 side facing up.

[0015] Such a container 1 can be manufactured by molding a preform 10 by injection molding using a thermoplastic resin, and then molding this preform 10 into a predetermined container shape by biaxial stretch blow molding or the like. FIG. 2 is an explanatory diagram that schematically shows the state in which the preform 10 is set in the blow molding mold BM indicated by the dotted line in the figure, and also shows the relationship of this preform 10 to the container 1 that is molded into a predetermined container shape in the blow molding mold BM by biaxial stretch blow molding or the like.

[0016] A preform 10 suitable for producing a container 1 by blow molding can be molded into a bottomed cylindrical shape with one open end serving as a mouth portion 2, and the other end of the preform 10 is closed by a bottom portion 30 molded into a hemispherical shape. In the following description, the up-down, left-right and length-width directions of the preform 10 are defined in the state shown in FIG. 2 with the mouth portion 2 side facing up.

[0017] The thermoplastic resin used can be any resin that can be blow molded. More specifically, thermoplastic polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, amorphous polyarylate, polylactic acid, polyethylene furanoate, or copolymers thereof can be used, and ethylene terephthalate-based thermoplastic polyesters such as polyethylene terephthalate are particularly suitable. Two or more of these resins can be mixed, or blended with other resins. Polycarbonate, acrylonitrile resin, polypropylene, propylene-ethylene copolymer, polyethylene, etc. can also be used. Furthermore, the preform 10 formed using such a thermoplastic resin is not limited to being formed as a single layer, but can also be formed as multiple layers including a gas barrier layer or the like depending on the properties required of the container 1. Various environmentally friendly materials have been developed for the above-mentioned materials, and for example, mechanically recycled materials, chemically recycled materials, flake materials obtained by crushing used products, plant-derived bioplastic materials, etc. may be used alone or blended with other materials.

[0018] The preform 10 is softened by heating to a state where it can be blow-molded, and then set in the blow mold BM, and the mouth portion 2 supported by the blow mold BM is stretched in the axial direction (longitudinal direction) using a stretching rod as needed, with the starting point of stretching being directly below a neck ring 23 (described later), while the preform is stretched in the axial and circumferential directions (lateral directions) by blow air blown into the preform 10. The cavity shape of the blow mold is then transferred to the stretched portion, thereby forming the shoulder portion 3, body portion 4, and bottom portion 5, and the container 1 is molded into a predetermined container shape.

[0019] 2, the mouth portion 2 of the preform 10 becomes the mouth portion 2 of the container 1 in its original shape, and is indicated by the same reference numeral in the drawing. In the following description, unless otherwise specified, the mouth portion 2 of the preform 10 and the mouth portion 2 of the container 1 will not be distinguished from each other, and will be described as a common portion.

[0020] The structure of the mouth portion 2 of this embodiment will be described in detail with reference to the drawings. 3 is an enlarged front view of the main part showing an enlarged mouth portion of the preform shown in FIG. 2, FIG. 4 is an enlarged plan view of the preform shown in FIG. 2, FIG. 5 is an enlarged cross-sectional view along line AA in FIG. 4, and FIG. 6 is an enlarged cross-sectional view of the main part showing an enlarged area surrounded by a two-dot chain line in FIG. 5. The mouth portion 2 is provided with an annular protrusion 21 that protrudes radially outward in a ring shape along the periphery of the opening of the mouth portion 2, and a neck ring 23 that protrudes radially outward in a ring shape along the circumferential direction, spaced apart in the axial direction with an intermediate portion 22 in between.

[0021] Annular protrusion 21 rises in a direction perpendicular to the axial direction and includes a surface 21c facing neck ring 23 so as to engage or fit with a lid, nozzle, etc. (not shown in FIG. 1) in an undercut shape. Annular protrusion 21 also includes a surface 21b parallel to the axial direction on the outer circumferential surface on the side of intermediate portion 22 where annular protrusion 21 is provided. Annular protrusion 21 also includes an inclined portion 21a on the opening side that guides a lid, nozzle, etc. (not shown) when plugging them into opening 2. Furthermore, a plurality of protruding pawls (ratchets) 21d are provided at regular intervals in the circumferential direction on surface 21b parallel to the axial direction of annular protrusion 21 to prevent rotation of the lid, nozzle, etc.

[0022] The middle portion 22 has an upper end connected to the annular protrusion 21 and a lower end connected to the neck ring 23, and includes a surface 22a on its outer circumferential surface that is parallel to the axial direction. In addition, in the longitudinal cross section of the mouth 2 (a cross section cut by a plane including the central axis C, the same applies below), the intermediate portion 22 is connected to the annular protrusion 21 via a curved portion, and the intersection of an extension line of the lower surface of the annular protrusion 21 (the surface 21c facing the neck ring in the illustrated example) connected to the intermediate portion 22 and an extension line of the intermediate portion 22 is defined as the boundary between the intermediate portion 22 and the annular protrusion 21, and the upper side of the intersection is defined as the annular protrusion 21, and the lower side of the intersection is defined as the intermediate portion 22. Similarly, in the longitudinal cross section of the mouth 2, the intermediate portion 22 is connected to the neck ring 23 via a curved portion, and the intersection of an extension line of the upper surface of the neck ring 23 connected to the intermediate portion 22 and an extension line of the intermediate portion 22 is defined as the boundary between the intermediate portion 22 and the neck ring 23, and the upper side of the intersection is defined as the intermediate portion 22, and the lower side of the intersection is defined as the neck ring 23. 22 refers to the distance on a vertical line parallel to the central axis C between the intersection of the extension line of the lower surface of the annular protrusion 21 connected to the intermediate portion 22 and the extension line of the intermediate portion 22, and the intersection of the extension line of the upper surface of the neck ring 23 connected to the intermediate portion 22 and the extension line of the intermediate portion 22, in the longitudinal cross section of the mouth portion 2 (see Figure 6).

[0023] A cylindrical neck portion 24 of roughly the same diameter is provided at the lower end of the neck ring 23 and hangs down from directly below the neck ring 23. Here, the annular protrusion 21, the middle portion 22, the neck ring 23, and the neck portion 24 are collectively referred to as the mouth portion 2. That is, in the container 1, the neck portion 24 of the mouth portion 2 is connected to the shoulder portion 3. The neck ring 23 is connected to the neck portion 24 via a curved portion in the vertical cross section of the mouth portion 2, and the intersection of the extension line of the neck portion 24 connected to the neck ring 23 and the extension line of the underside of the neck ring 23 is defined as the boundary between the neck ring 23 and the neck portion 24, and the area above the intersection is defined as the neck ring 23, and the area below the intersection is defined as the neck portion 24. The height direction thickness HT of the neck ring 23, which will be described later, 23 refers to the distance on a vertical line parallel to the central axis C between the intersection of the extension line of the middle part 22 connected to the neck ring 23 and the extension line of the top surface of the neck ring 23, and the intersection point of the extension line of the neck part 24 connected to the neck ring 23 and the extension line of the bottom surface of the neck ring 23 in the longitudinal cross section of the mouth part 2 (see Figure 6).

[0024] Since such a mouth 2 serves as an outlet for pouring the contents and has a lid and a nozzle (not shown) attached to its outer periphery, the dimensions and shape of the mouth 2, including the annular protrusion 21, must be designed according to the lid and the nozzle. Furthermore, the neck ring 23 is a necessary part for gripping and transporting the container 1 in the molding line or filling line, and there are limitations to the degree of freedom in its design.

[0025] On the other hand, when molding the preform 10 by injection molding, the resin material used is melted and injected into a mold through a gate provided at a position corresponding to the bottom 30 of the preform 10, filling the mold. In this case, designing the thickness of the mouth portion 2 to be thin in order to reduce the amount of resin used increases the possibility of causing molding defects such as short shots, depending on the shape of the mouth portion 2. Specifically, for example, reducing the height or radial thickness of the neck ring 23, reducing the radial thickness of the middle portion 22, or increasing the radial thickness of the annular protrusion 21 may cause molding defects, particularly in the annular protrusion 21 located closer to the tip of the mouth portion 2 than the neck ring 23. This is thought to be due to the fact that when the resin material injected from a position corresponding to the bottom 30 of the preform 10 of the mold flows and fills up to a position corresponding to the opening tip side of the mouth portion 2, the molten resin material is more likely to solidify in the thin-walled parts, further reducing the flow cross-sectional area, and as the flow cross-sectional area further reduces, the momentum with which the resin material with a predetermined viscosity flows up to the position corresponding to the tip of the mouth portion 2 of the mold is weakened. Therefore, in this embodiment, the mouth portion 2 is designed as follows, thereby preventing poor shaping while achieving the intended purpose of reducing the weight and cost of the container by reducing the amount of resin used.

[0026] In this embodiment, the inner diameter of the mouth portion 2 is smaller than the opening diameter on the opening side of the mouth portion 2 in the intermediate portion 22 between the portion where the annular protrusion 21 is provided and the portion where the neck ring 23 is provided. More specifically, the inner peripheral surface of the intermediate portion 22 includes a tapered portion 25 disposed adjacent to the portion where the annular protrusion 21 is provided, and the inner diameter of the mouth portion 2 is designed to be reduced via the tapered portion 25. The inner diameter ID of the portion where the annular protrusion 21 is provided is 21 is constant along the axial direction except for the edge of the opening of the mouth portion 2. The reduced inner diameter ID of the portion where the intermediate portion 22 and the neck ring 23 are provided is 23is constant along the axial direction except for the tapered portion 25. In the example shown, the tapered portion 25 is formed as an inclined portion whose longitudinal cross section is linear so that the inner diameter of the mouth portion 2 decreases, but the tapered portion 25 may also be formed so that its longitudinal cross section is curved.

[0027] In the illustrated example, the tapered portion 25 has a height H 22 The tapered portion 25 is located in the vicinity of 5 / 7 to 6 / 7 of the center of the mold. However, the position where the tapered portion 25 is located in the height direction is not limited to that shown in the drawing. From the viewpoint of reducing the amount of resin used, it is preferable to locate the tapered portion 25 as close to the neck ring as possible in the middle portion 22, but the position where the tapered portion is located can be appropriately designed to prevent molding defects, taking into consideration the size and shape of the preform, the surface condition of the mold, the viscosity of the resin, and the injection conditions.

[0028] By providing the tapered portion 25 in this manner, it is possible to help ensure a sufficient flow cross-sectional area for the resin material when injection molding the preform 10, and to prevent poor molding.

[0029] Furthermore, the shape of the inner and outer peripheral surfaces of the mouth portion 2, specifically, the outer diameter (excluding the claws 21d) D of the intermediate portion 22 at the portion where the annular protrusion 21 is provided, is determined so as not to hinder the movement of the resin material during injection molding while thinning the mouth portion 2. 21 , the outer diameter D of the part where the intermediate portion 22 is provided 22 , the outer diameter D of the part where the neck ring 23 is provided 23 , the maximum radial thickness (excluding the claws 21d) T of the intermediate portion 22 side of the portion where the annular protrusion 21 is provided 21 , the maximum radial thickness T of the part where the inner diameter of the intermediate portion 22 is reduced 22 , the maximum radial thickness T of the portion where the neck ring 23 is provided 23 , Height direction thickness HT of neck ring 23 23 , the inner diameter ID of the portion where the annular protrusion 21 is provided 21 , the reduced inner diameter ID of the portion where the intermediate portion 22 and the neck ring 23 are provided 23 It is preferable to design the above.

[0030] In this embodiment, the maximum radial thickness T 21 , the maximum radial thickness T of the part where the inner diameter of the intermediate portion 22 is reduced 22 , the maximum radial thickness T of the portion where the neck ring 23 is provided 23 is designed as follows: This helps to ensure a sufficient flow cross-sectional area for the resin material when the preform 10 is injection molded.

[0031] The mouth portion 2 of this embodiment is The maximum radial thickness T of the part of the intermediate portion 22 where the inner diameter is reduced 22 / Maximum radial thickness T of the intermediate portion of the portion where the annular protrusion 21 is provided 21 >0.65 and The maximum radial thickness T of the part of the intermediate portion 22 where the inner diameter is reduced 22 / Maximum radial thickness T of the part where the neck ring 23 is provided 23 >0.42 and preferably, The maximum radial thickness T of the part of the intermediate portion 22 where the inner diameter is reduced 22 / Maximum radial thickness T of the intermediate portion of the portion where the annular protrusion 21 is provided 21 ≧0.71 and The maximum radial thickness T of the part of the intermediate portion 22 where the inner diameter is reduced 22 / Maximum radial thickness T of the part where the neck ring 23 is provided 23 ≧0.50 Meet the following.

[0032] The maximum radial thickness T of the part where the neck ring 23 is provided 23 The maximum radial thickness T of the neck portion 24 can be appropriately set so that the container 1 can be gripped and transported in a molding line or a filling line. For example, the maximum radial thickness T of the portion where the neck ring 23 is provided is 23 The thickness can be set to 3.0 to 4.5 mm, and preferably 3.0 to 3.7 mm. The maximum radial thickness T of the intermediate portion of the portion where the annular protrusion 21 is provided 21 , the maximum radial thickness T of the part where the inner diameter of the intermediate portion 22 is reduced 22 , the maximum radial thickness T of the portion where the neck ring 23 is provided 23 By designing the thickness T of the neck ring 23 to be within the above-mentioned range, 23 Even if the molded body is designed to be thin, it is possible to effectively prevent defective molding when the preform 10 is injection molded.

[0033] In this embodiment, the thickness HT of the neck ring 23 in the height direction 23 The maximum thickness T in the radial direction on the intermediate portion 22 side of the portion where the annular protrusion 21 is provided can be set to, for example, 2.0 to 3.0 mm, and preferably 2.0 to 2.5 mm. By designing in this way, it is possible to reduce the amount of resin used while maintaining the predetermined strength required for the neck ring 23. In addition, the maximum thickness T in the radial direction on the intermediate portion 22 side of the portion where the annular protrusion 21 is provided can be set to, for example, 2.0 to 3.0 mm, and preferably 2.0 to 2.5 mm. 21 , the maximum radial thickness T of the part where the inner diameter of the intermediate portion 22 is reduced 22 , the maximum radial thickness T of the portion where the neck ring 23 is provided 23 By designing the thickness of the neck ring 23 in the height direction HT 23 Even if the molded body is designed to be thin, it is possible to effectively prevent defective molding when the preform 10 is injection molded.

[0034] In this embodiment, the maximum radial thickness T 21 , the maximum radial thickness T of the part where the inner diameter of the intermediate portion 22 is reduced 22 , the maximum radial thickness T of the portion where the neck ring 23 is provided 23 is designed to be within the above range, and the inner diameter ID of the part where the annular protrusion is provided is 21 , the reduced inner diameter ID of the portion where the intermediate portion 22 and the neck ring 23 are provided 23 But, 0.97≦reduced inner diameter ID of the portion where the intermediate portion 22 and the neck ring 23 are provided 23 / Inner diameter ID of the part where the annular protrusion is provided 21 ≦0.99 The relationship between the axial direction and the axial direction can be designed as follows. By designing in this way, it becomes possible to reduce the weight of the mouth portion and effectively prevent defective shaping when injection molding the preform 10.

[0035] In this embodiment, the angle of elevation (the upward angle relative to the horizontal plane) θ 23 The neck ring can be designed so that the angle is 0 to 8°, preferably 0.5 to 1.0°. Designing the neck ring 23 in this way is preferable because it allows the amount of resin in the mouth portion 2 to be further reduced. [Example]

[0036] The present invention will be described in more detail below with reference to specific examples.

[0037] [Examples 1-2, Comparative Examples 1-4, Reference Examples 1-2] The preform 10 shown in Fig. 5 was injection molded using polyethylene terephthalate. The outer diameter D of the portion of the opening where the annular protrusion 21 was provided was 21 is 32.81 mm, and the outer diameter D of the part where the intermediate part 22 is provided is 22 The outer diameter D of the part where the neck ring 23 is provided is 30.65 mm. 23 , the inner diameter ID of the portion where the annular protrusion 21 is provided 21 , the reduced inner diameter ID of the portion where the intermediate portion 22 and the neck ring 23 are provided 23 , the maximum radial thickness (excluding the claws 21d) T of the intermediate portion of the portion where the annular protrusion 21 is provided 21 , the maximum radial thickness T of the part where the inner diameter of the intermediate portion 22 is reduced 22 , the maximum radial thickness T of the portion where the neck ring 23 is provided 23 , Height direction thickness HT of neck ring 23 237. The protrusion height H of the claws 21d provided on the outer peripheral surface of the annular protrusion 21 is 21c is 0.545mm, protruding width W of claw 21d 21c was 1.3 to 1.6 mm.

[0038] For the preforms in each Example, Comparative Example, and Reference Example, moldability was evaluated as follows: those that were molded without any molding defects during injection molding were marked "Good", those that were molded into the desired shape due to molding defects were marked "Poor", and those that were molded into the roughly desired shape despite slight molding defects were marked "Good". The evaluation results are shown in Figure 7. Figure 7 also shows the "mouth mass", which is the mass of the area including the annular protrusion 21, the middle portion 22, and the neck ring 23, i.e., the area excluding the neck portion 24, as the mouth mass.

[0039] In Examples 1 and 2, it was confirmed that molding was possible without forming defects when injection molding the preform. It was also confirmed that the mass of the mouth portion could be effectively reduced, making it possible to reduce the amount of resin used. In Reference Examples 1 and 2, molding was possible without forming defects when injection molding the preform, but the objective of reducing the amount of resin used could not be achieved. In Comparative Example 1, forming defects were observed in the area on the middle portion 22 side of the annular protrusion 21. In Comparative Example 2, forming defects were observed in the area on the middle portion 22 side of the annular protrusion 21. In Comparative Example 3, slight forming defects were observed in the neck ring 23. In Comparative Example 4, slight forming defects were observed in the claws 21d of the annular protrusion 21.

[0040] The present invention has been described above by showing preferred embodiments, but it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention. [Explanation of symbols]

[0041] 1 container 10 Preform 2 Mouth 21 Annular protrusion 22 Middle section 23 Neck Ring 24 Neck 25 Tapered section

Claims

1. A synthetic resin container having a mouth, a shoulder, a body, and a bottom, The mouth portion is provided with an annular protrusion that protrudes annularly radially outward along a circumferential edge of an opening of the mouth portion, and a neck ring that protrudes annularly radially outward along the circumferential direction, the annular protrusion and the neck ring are spaced apart in the axial direction, an inner diameter of the mouth portion is reduced in an intermediate portion between a portion where the annular protrusion is provided and a portion where the neck ring is provided, compared to an opening diameter on the opening side of the mouth portion; The maximum radial thickness T of the intermediate portion of the portion where the annular protrusion is provided ２１ and the maximum radial thickness T of the portion where the inner diameter is reduced in the intermediate portion. ２２ and the maximum radial thickness T of the portion where the neck ring is provided. ２３ What is that? T ２２ / T ２１ >0.65 and T ２２ / T ２３ >0.42 A synthetic resin container characterized by satisfying the above.

2. 2. The synthetic resin container according to claim 1, wherein the inner peripheral surface of the intermediate portion includes a tapered portion disposed adjacent to the portion where the annular protrusion is provided, and the inner diameter of the mouth portion is reduced via the tapered portion.

3. 3. The synthetic resin container according to claim 2, wherein the inner diameter of the portion where the annular protrusion is provided is constant along the axial direction except for the edge of the opening of the mouth portion, and the reduced inner diameter of the portion where the intermediate portion and the neck ring are provided is constant along the axial direction except for the tapered portion.

4. 3. The synthetic resin container according to claim 1, wherein the annular protrusion extends in a direction perpendicular to the axial direction and includes a surface facing the neck ring.

5. 5. The synthetic resin container according to claim 4, wherein the outer peripheral surface of the intermediate portion of the portion where the annular protrusion is provided includes a surface parallel to the axial direction.

6. 6. The synthetic resin container according to claim 5, wherein the outer peripheral surface of the intermediate portion includes a surface parallel to the axial direction.

7. A preform for manufacturing a synthetic resin container by blow molding, The opening end is formed into a cylindrical shape with a bottom and a mouth portion. The mouth portion is provided with an annular protrusion that protrudes annularly radially outward along a circumferential edge of an opening of the mouth portion, and a neck ring that protrudes annularly radially outward along the circumferential direction, the annular protrusion and the neck ring are spaced apart in the axial direction, an inner diameter of the mouth portion is reduced in an intermediate portion between a portion where the annular protrusion is provided and a portion where the neck ring is provided, compared to an opening diameter on the opening side of the mouth portion; The maximum radial thickness T of the intermediate portion of the portion where the annular protrusion is provided ２１ and the maximum radial thickness T of the portion where the inner diameter is reduced in the intermediate portion. ２２ and the maximum radial thickness T of the portion where the neck ring is provided. ２３ What is that? T ２２ / T ２１ >0.65 and T ２２ / T ２３ >0.42 A preform characterized by satisfying the above.

8. 8. The preform according to claim 7, wherein the inner peripheral surface of the intermediate portion includes a tapered portion disposed adjacent to a portion where the annular protrusion is provided, and the inner diameter of the mouth portion is reduced via the tapered portion.

9. 9. The preform according to claim 8, wherein the inner diameter of the portion where the annular protrusion is provided is constant along the axial direction except for the edge of the opening of the mouth portion, and the reduced inner diameters of the portion where the intermediate portion and the neck ring are provided are constant along the axial direction except for the tapered portion.

10. 9. The preform according to claim 7, wherein the annular protrusion rises in a direction perpendicular to the axial direction and includes a surface facing the neck ring.

11. The preform according to claim 10 , wherein the outer peripheral surface of the intermediate portion side of the portion where the annular protrusion is provided includes a surface parallel to the axial direction.

12. The preform according to claim 11 , wherein the outer peripheral surface of the intermediate portion includes a surface parallel to the axial direction.

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