Synthetic resin container

Abstract

The present invention suppresses the occurrence of bursting at the thinnest portion of a bottom part that is stretched thinner when blow-molding a synthetic resin container. The following relationships are satisfied between a wall thickness T of the thinnest portion of a bottom part 5 of a container 1 obtained by blow-molding a bottomed cylindrical preform P and a wall thickness T0 at a site corresponding to the thinnest portion of the bottom part 5 in the preform P. (1): T0 / T = K×T-0.94; (2): 3.26 ≤ K ≤ 4.40; and (3): 3.83 × T-0.94 ≤ 30.

Description

Synthetic resin containers

[0001] The present invention relates to a synthetic resin container.

[0002] Conventionally, synthetic resin containers have been used in a wide range of fields as containers for various liquid contents such as beverages, etc., by preparing a preform using a polyester resin such as polyethylene terephthalate and then molding the preform into a bottle by biaxial stretch blow molding or the like. This type of container is generally known as a PET bottle.

[0003] In recent years, a recycling technology called "bottle-to-bottle" has been studied, in which polyester resin molded products such as used PET bottles are collected and reused as recycled materials to manufacture PET bottles. For example, Patent Document 1 proposes a preform manufacturing apparatus including a decontamination machine that removes contaminants from thermoplastic resin flakes, an injection molding machine that injection-moldes the thermoplastic resin supplied from the decontamination machine, a filter disposed between the decontamination machine and the injection molding machine, and a gear pump disposed between the filter and the injection molding machine.

[0004] Patent No. 6895990

[0005] The inventors have found that when recycled materials are used to blow mold synthetic resin containers such as PET bottles, bursting occurs more frequently at the thinnest part of the bottom, which is stretched to be thinner. Based on this finding, the inventors have investigated the cause of the high frequency of bursting and conducted further studies to suppress the occurrence of bursting, which has led to the completion of the present invention.

[0006] That is, an object of the present invention is to suppress the occurrence of bursting at the thinnest part of the bottom, which is stretched to be thinner, when a synthetic resin container is blow-molded.

[0007] The synthetic resin container according to the present invention is a synthetic resin container obtained by blow molding a cylindrical preform with a bottom into a predetermined container shape having a mouth, a shoulder, a body, and a bottom, and the thickness T of the thinnest part of the bottom and the thickness T of the part of the preform corresponding to the thinnest part are ０ Between ０ / T = K × T －０．９４ ...(1) 3.26≦K≦4.40 ...(2) 3.83×T －０．９４ The configuration satisfies the following relationship: ≦30 (3).

[0008] According to the synthetic resin container of the present invention, the occurrence of bursting at the thinnest part of the bottom, which is stretched to be thinner during blow molding, can be suppressed.

[0009] FIG. 1 is a perspective view showing an outline of a synthetic resin container according to an embodiment of the present invention; FIG. 2 is a front view showing an outline of a synthetic resin container according to an embodiment of the present invention; FIG. 3 is a bottom view showing an outline of a synthetic resin container according to an embodiment of the present invention; and FIG. 4 is an explanatory view showing a part of a process for producing a synthetic resin container according to an embodiment of the present invention by blow molding. ０ 1 is a graph showing the correlation between the thickness T of the thinnest part and the dimensionless stretch ratio T ０ 10 is a graph showing the correlation between the α- and β-blocking ratios.

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0011] Fig. 1 is a perspective view showing a schematic diagram of a synthetic resin container according to this embodiment, Fig. 2 is a front view of the same, and Fig. 3 is a bottom view of the same. The container 1 shown in these figures has a mouth 2, a shoulder 3, a body 4, and a bottom 5.

[0012] The mouth 2 is a cylindrical portion that serves as an outlet for pouring the liquid content. A screw thread 21 is provided on the side of the open end of the mouth 2 for attaching a lid (not shown) when sealing the container 1 filled with the liquid content.

[0013] The mouth 2 is provided with a neck ring 22 that extends annularly in the circumferential direction. The mouth 2 includes a cylindrical portion of approximately the same diameter that hangs down from directly below the neck ring 22. The lower end of the mouth 2 is connected to a shoulder 3 that connects the mouth 2 and the body 4. In the illustrated example, the shoulder 3 is formed in a rounded truncated cone shape, but the shape of the shoulder 3 is not limited to this. For example, it may be formed in a so-called hanging neck shape.

[0014] The body 4 occupies most of the height of the container 1, and the upper end of the roughly cylindrical body 4 is connected to the shoulder 3, while the lower end is connected to the bottom 5. Here, the height direction refers to the direction perpendicular to the horizontal plane when the container 1 is stood upright on the horizontal plane with the mouth 2 facing up, and defines the up-down, left-right, length-width directions of the container 1 in this state (the state shown in Figure 2).

[0015] In this embodiment, the container 1 is configured as a pressure-resistant bottle for carbonated beverages, having a petaloid-shaped bottom 5 with multiple (five in the illustrated example) legs 51 arranged rotationally symmetrically and radially at equal intervals around the central axis C of the container 1 so that the container's stability is not compromised even when positive pressure is created inside the container.

[0016] In the bottom 5 having such a shape, bottom grooves 56 that fit into the inside of the container are formed between adjacent leg portions 51 and extend radially from the bottom center 50. Meanwhile, the leg portions 51 have outer peripheral surface portions 52 that hang down (in the illustrated example, hang down at a slight angle toward the inside of the container) from the upper end of the bottom 5 that connects to the body 4 and whose circumferential length (width) narrows toward their lower ends, side surfaces 53 that extend from both circumferential edges of the outer peripheral surface portion 52 toward the bottom grooves 56, and leg bottom surface portions 54 that extend at a downward angle from the bottom center 50 toward the lower end of the outer peripheral surface portion 52. The connecting portions between the outer peripheral surface portions 52 and the leg bottom surface portions 54 and their vicinity are formed to form ground contact portions 55 that come into contact with the ground when the container 1 is upright.

[0017] In addition, the container 1 can be manufactured by using recycled materials prepared by applying recycling techniques known as mechanical recycling, chemical recycling, etc. from polyester resin molded products such as recovered used PET bottles, and then producing a preform P molded into a bottomed cylindrical shape by injection molding, compression molding, etc., and molding this preform P into a predetermined container shape by biaxial stretch blow molding, etc.

[0018] When blow molding the container 1, for example, as shown in Fig. 4, a blow molding mold M can be used, which includes a body mold M1 consisting of an openable and closable split mold designed with mold opening in mind, and a bottom mold M2 that is fitted to the bottom side of the body mold M1. More specifically, after being softened by heating to a state suitable for blow molding, the preform P set in the blow molding mold M is stretched in the axial direction (longitudinal direction) by a stretching rod (not shown), with the stretching starting point being directly below the neck ring 22 supported by the blow molding mold M, while also being stretched in the axial and radial directions (lateral direction) by a high-pressure fluid blow. The cavity shape of the blow molding mold M is then transferred to the stretched portion, thereby forming a shoulder portion 3, a body portion 4, and a bottom portion 5, and molding the container 1 into a predetermined container shape.

[0019] In the example shown in Figure 4, the blow molding mold M is shown as a cross section cut along a plane parallel to the paper surface that includes the central axes of the preform P and the container 1, and Figure 4(a) shows the state in which the preform P is set in the blow molding mold M, and Figure 4(b) shows the state in which the blow molding mold M has been opened to remove the blow-molded container 1.

[0020] The inventors investigated the cause of the increased frequency of bursting at the thinnest part of the bottom 5, which is stretched to be thinner when blow-molding the container 1 using recycled material, and discovered that if fine particles of less than about 50 μm, which are difficult to capture by a filter when preparing the recycled material, are present in the part that will become the thinnest part of the bottom 5, these fine particles will become the starting point for bursting during blow-molding.

[0021] It is believed that bursts originating from such fine particles occur during the process in which the preform P is stretched and the corresponding portion is molded into the thinnest portion of the bottom 5. Therefore, focusing on the amount of stretching in the thinnest portion of the bottom 5, in other words, the local stretch ratio in the thinnest portion of the bottom 5, the following study was conducted to examine the relationship between this and the burst occurrence rate when the container 1 is blow molded using recycled material.

[0022] That is, in the container 1 configured as a pressure-resistant bottle with a capacity of 500 mL and a mass of 17 g excluding the mouth portion 2, the relationship between the burst occurrence rate when blow molding was performed using recycled material and the stretch amount at the thinnest part of the bottom 5 was investigated by changing the ground contact diameter and ground contact width of the bottom 5 formed in a petaloid shape. In this case, the stretch amount at the thinnest part of the bottom 5 was calculated by the ratio of the thickness T of the thinnest part of the bottom 5 to the thickness T of the part of the preform P corresponding to the thinnest part of the bottom 5 before stretching. ０ The ratio of (hereinafter referred to as "dimensionless stretching ratio") T ０ An example of the sample used in the study is shown in Table 1 and FIG.

[0023] In Fig. 3, a circle including the ground contact portion 55 of each leg portion 51 is shown by a chain line, and the radius of the circle is the ground contact diameter, and the length along the circumferential direction of the ground contact portion 55 is the ground contact width. The vicinity of both ends in the circumferential direction of the ground contact portion 55 of each leg 51 becomes the thinnest wall portion that is stretched to be thinner during blow molding. Also, as shown by the chain line arrow in Fig. 4(a), the lower end side of the cylindrical body portion of the preform P becomes the portion that corresponds to the thinnest wall portion of the bottom portion 5. ０ can be measured, for example, by making a plurality of circular notches parallel to the axial direction on the lower end side along the circumferential direction, and identifying in advance the location corresponding to the thinnest part of the bottom 5 from the traces of the notches remaining on the blow-molded container 1.

[0024]

[0025] In the graph shown in FIG. 5, the regression line obtained as a result of the regression analysis is shown by a dotted line, and the dimensionless stretching ratio T ０A strong positive linear relationship is observed between / T and the burst occurrence rate. Therefore, from these results, it is possible to determine whether the dimensionless stretching ratio T of the thinnest part of the bottom 5 is adjusted so that the stretching amount at the thinnest part of the bottom 5 is reduced. ０ It can be confirmed that by reducing / T, the occurrence of bursting during blow molding using recycled materials can be suppressed.

[0026] To adjust the amount of stretch at the thinnest part of the bottom 5, in addition to changing the contact diameter and contact width of the bottom 5, the depth of the bottom groove 56 formed between adjacent legs 51 may also be changed. Furthermore, the amount of stretch at the thinnest part of the bottom 5 can also be adjusted by changing the blow molding conditions (including the use of a device for reducing the amount of local stretch) and the preform shape (including setting the stretch ratio and setting the local thickness of the preform).

[0027] Furthermore, as shown in Table 2 and FIG. 6, even if the volume of the container 1 and the mass of the preform P used in the blow molding (particularly the mass of the portion to be stretched excluding the mouth portion) are different, the thickness T of the thinnest portion of the bottom portion 5 and the dimensionless stretch ratio T ０ It can be seen that there is a strong correlation between the volume, mass, and the shape of the bottom 5. In other words, Table 2 and FIG. 6 show examples of samples used in the study, which differ not only in volume and mass but also in the shape of the bottom 5. In the graph shown in FIG. 6, the regression curve obtained as a result of the regression analysis is shown by a dotted line, and this regression curve is ０ / T = K × T －０．９４ It can be seen that the distribution is within the range of ±15% (3.26≦K≦4.40) with K=3.83 as the central value.

[0028] Furthermore, the occurrence of bursting was evaluated based on the following criteria and the results are also shown in Table 2. Even if the capacity of the container 1 is different, the dimensionless stretching ratio T ０ It can be confirmed that by reducing / T, the occurrence of bursting during blow molding using recycled materials can be suppressed.

[0029] [Burst evaluation] ⊚: No bursts were observed. ◯: Sporadic bursts were occasionally observed. ×: Many bursts occurred.

[0030]

[0031] From the above, the thickness T of the thinnest part of the bottom part 5 and the thickness T of the part of the preform P corresponding to the thinnest part are ０ Between ０ / T = K × T －０．９４ ...(1) 3.26≦K≦4.40 ...(2) 3.83×T －０．９４ It has been discovered that the relationship (3) can be used as an index when designing a container 1 so as to suppress the occurrence of bursting when blow-molded using recycled materials. Therefore, a container 1 designed based on such an index will suppress the occurrence of bursting at the thinnest part of the bottom 5, which is stretched to be thinner.

[0032] In this way, when designing the container 1 so as to suppress the occurrence of bursting when blow molding is performed using recycled materials, the following formula is used instead of the formula (3): 3.83×T －０．９４ It is preferable that the following relationship holds: ≦26 (4).

[0033] Dimensionless stretching ratio T of the thinnest part of the bottom 5 ０ It is preferable to set the lower limit of / T appropriately within a range (for example, preferably not less than 6, more preferably not less than 7) that allows the amount of stretching to be reduced at the thinnest part of the bottom 5, while not causing the amount of stretching in other parts to be insufficient, thereby contradicting the requirement for thinning and lightening of the container 1.

[0034] Furthermore, as mentioned above, considering that the lower end portion of the cylindrical body portion of the preform P corresponds to the thinnest portion of the bottom portion 5, the wall thickness of the lower end portion of the cylindrical body portion of the preform P is preferably 2.3 to 4.4 mm. Furthermore, it is preferable that the wall thickness of the body portion 4 be as thin as possible within the range of 0.09 to 0.60 mm, so as to ensure the wall thickness of the bottom portion 5. These aspects are advantageous in reducing the dimensionless draw ratio of the thinnest portion of the bottom portion 5 so that the amount of draw at the thinnest portion of the bottom portion 5 is alleviated.

[0035] 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.

[0036] 1 Container 2 Mouth 3 Shoulder 4 Body 5 Bottom 51 Leg P Preform

Claims

1. A synthetic resin container formed by blow molding a bottomed cylindrical preform into a predetermined container shape having a mouth, a shoulder, a body, and a bottom, the thickness T of the thinnest part of the bottom and the thickness T of a part of the preform corresponding to the thinnest part ０ Between ０ / T = K × T －０．９４ ...(1) 3.26 ≤ K ≤ 4.40 ...(2) 3.83 × T －０．９４ A synthetic resin container, characterized in that the following relationship holds: ≦30 (3).

2. Replace the above formula (3) with 3.83 x T －０．９４ 2. The synthetic resin container according to claim 1, wherein the following relationship holds: ≦26 (4).

3. A synthetic resin container as claimed in claim 1 or 2, in which a plurality of legs are provided with a bottom portion which are rotationally symmetrical about a central axis and radially arranged at equal intervals.

Images