Container

Abstract

To provide a container that is superior in sealability and free of scraped chips of a cap.SOLUTION: A container comprises a main body 10 which has a fitting part 32 where a thread 33 is formed and a lid which is threadedly fitted to the fitting part. The thread is formed spirally and continuously from a starting point to an end point. The main body is formed by injection molding of synthetic resin and has burrs at the thread, the projection length L2 of the part having the burrs is 20 to 70% of a maximum projection length L1 of the thread, and the overrun torque when the lid is threadedly fitted to the main body is 400 N cm or larger.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] FIELD OF THEINVENTION This invention relates to containers, and more particularly to containers having threads for threadably engaging a lid. [Background technology]

[0002] 2. Description of the Related Art Resin containers that are sealed by screwing a cap onto them are widely used. Such containers are sometimes formed by injection molding.

[0003] When manufacturing containers by injection molding, it is inevitable that burrs will occur near the parting line where the mold joins. If burrs occur on the threads, the outer diameter of the threads will increase by the amount of the burrs. As a result, the cap may be scraped by the burrs, resulting in problems such as shavings.

[0004] The plastic bottle described in Patent Document 1 has discontinuous screw threads to allow gas to escape when the bottle is opened. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-177336 A Summary of the Invention [Problem to be solved by the invention]

[0006] If the discontinuous portion of the thread described in Patent Document 1 is located near the parting line, it is possible to prevent the outer diameter of the thread from increasing due to the burrs. However, after investigation, the inventors found that this method may not provide sufficient sealing, as will be described in detail below. The inventors further investigated and completed the present invention.

[0007] An object of the present invention is to provide a container that has excellent sealing properties and does not produce shavings from the cap. [Means for solving the problem]

[0008] The present invention is a container that includes a body having a fitting portion on which a screw thread is formed, and a lid that is screwed onto the fitting portion. The thread is formed in a continuous spiral shape from the starting point to the end point. The main body is made of synthetic resin by injection molding, and has burrs on the threads. The protruding length of the burred part is between 20% and 70% of the maximum protruding length of the thread, and the overrun torque when screwing the lid onto the body is 400 N·cm or more. Effect of the Invention

[0009] The container according to the present invention has excellent sealing properties and does not generate shavings from the cap. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view showing a container according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view showing the main body of the container. [Diagram 3] FIG. 4 is a partially enlarged view showing a fitting portion of the main body. [Figure 4] FIG. 4 is a partially enlarged view showing the main body as viewed from above. [Diagram 5] FIG. 11 is a partially enlarged view showing a main body according to a modified example of the present invention as viewed from above. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present invention will be described with reference to FIGS. 1 is a perspective view showing a container 1 according to this embodiment. The container 1 is substantially cylindrical, and includes a main body 10 and a lid 20 that is attached to the main body 10 to seal the internal space of the main body 10. In this embodiment, the outer shape of the container 1 is substantially cylindrical, but there is no particular limitation to the outer shape. For example, the diameter of the upper part of the body may be smaller, so that the maximum diameter of the lid is smaller than that of the body, or the outer shapes of the body and the lid may be changed so that the outer shape of the container with the lid attached is substantially polygonal prism-like.

[0012] 2 is a diagram showing the main body 10 with the lid 20 removed. The main body 10 has an opening 31 at the top. A certain range from the top end of the main body 10 serves as a fitting portion 32 that is screwed into a lid (not shown). A single screw thread 33 is formed on the outer circumferential surface of the fitting portion 32.

[0013] 3 is an enlarged view of the fitting portion 32. The thread 33 protrudes from the outer circumferential surface of the fitting portion 32 and extends in the vertical direction while spirally going around the periphery of the fitting portion 32. Although the amount of protrusion of the thread 33 from the outer circumferential surface varies depending on the location as described later, the thread 33 is formed continuously and without interruption from the starting point 33a at the bottom to the end point 33b at the top.

[0014] In this embodiment, the length of the thread 33 is set to approximately 1.5 revolutions around the fitting portion 32, but this is just one example and can be set as appropriate. From the viewpoint of ensuring a tight seal when the lid 20 is fitted, it is preferable that the length be set to at least one revolution around the fitting portion 32. 3, the cross-sectional shape of the thread 33 is substantially triangular. As a result, the middle part 33c of the thread 33 in the vertical direction protrudes the most from the outer circumferential surface of the fitting part 32. This cross-sectional shape is also one example, and for example, the cross-sectional shape may be one that has substantially the same protruding length in the vertical direction.

[0015] The main body 10 is made of synthetic resin, and the fitting portion 32 including at least the screw thread 33 is formed by injection molding using two dies. The storage portion 40 below the fitting portion 32 may be formed by injection molding like the fitting portion 32, or may be formed by another method such as blow molding.

[0016] Formed by injection molding using two dies, parting lines, which are the seams between the two dies, are generated in two places on the fitting portion 32. The thread 33 of this embodiment overlaps with the parting line PL in a total of three places: one place on the front side shown in Fig. 3 and two places on the rear side not visible in Fig. 3.

[0017] In injection molding, resin burrs always occur along the parting line. Although it is possible to reduce the burrs by forming the mold precisely or adjusting the resin injection pressure, it is impossible to completely eliminate the occurrence of burrs with current technology.

[0018] Burrs on the thread 23 become protrusions that increase the length of protrusion from the outer circumferential surface of the fitting portion. This protrusion does not pose much of a problem when the resin forming the body 10 is relatively soft. However, when the body 10 is formed of a hard resin such as polyethylene terephthalate (PET) because high rigidity is required for the body 10, the protrusions rub strongly against the inner surface of the lid 20 when the lid 20 is fitted, causing a problem in which the lid 20 is scraped. When the lid 20 is scraped, scrapings adhere to the fitting portion after opening, marring the appearance. If the degree of scraping is large, there is a possibility that the lid will be damaged and unable to be resealed.

[0019] The inventor first tried to solve this problem by dividing the thread into multiple discontinuous regions and positioning the non-threaded areas at the parting line. As a result, although burrs due to the parting line were generated on the outer periphery of the fitting part, they were lower than the threads, so no chipping of the lid occurred. However, on the other hand, by providing discontinuous parts in the threads, the rigidity of the mating part was reduced, making it more susceptible to deformation due to external forces. As a result, despite using hard resins such as PET, the main body could not be given the desired rigidity, which could have been counterproductive.

[0020] After further investigation, the inventors have solved the above problem by changing the shape of the screw thread without making it discontinuous. 4 is a partially enlarged view of the main body 10 as viewed from above. The middle portion 33c of the thread 33 protrudes from the outer circumferential surface 32a of the fitting portion 32 by a protruding length L1, but the protruding length is smaller in a certain region including the parting line. As a result, the thread 33 has small diameter portions 35 with protruding length smaller than L1 in one location each before and after the parting line PL.

[0021] Specifically, the screw thread 33 has a basic arc-like shape, but a portion of it is cut off in a direction perpendicular to the line connecting the parting line and the central axis C of the main body 10 when the main body 10 is viewed from above.

[0022] In this embodiment, the central axis C of the main body 10 coincides with the central axis of the cylindrical shape of the fitting portion 32, so that the outer peripheral surface 32a of the fitting portion 32 and the intermediate portion 33c of the thread 33 are located on a circumference centered approximately on the central axis C when the main body 10 is viewed from above. Therefore, the protrusion length L1 is the difference between the radius of the circle formed by the outer peripheral surface 32a and the radius of the circle formed by the intermediate portion 33c when the main body 10 is viewed from above. The distance between the small diameter portion 35 and the central axis is shortest at the parting line PL, and the protruding length L2 at this portion is approximately the smallest. The protruding length of the small diameter portion 35 from the outer circumferential surface 32a gradually increases with increasing distance from the parting line PL, approaching L1.

[0023] The protruding length L2 changes when the shape of the small diameter portion 35 is changed by changing the design of the mold. In theory, if the protruding length L2 including the burrs formed on the parting line is set to be equal to or less than L1, which is the maximum protruding length of the thread, the lid will not be chipped, but it is not easy to control the amount of protruding burrs. On the other hand, the inventors have found that making the protruding length L2 too small causes another problem.

[0024] If the protruding length L2 is too small, the contact area between the thread 33 and the inner surface of the lid 20 decreases. If this phenomenon occurs excessively, it becomes difficult for the lid 20 to seal the body 10. This phenomenon appears as a decrease in overrun torque when the lid 20 is screwed onto the body 10. Overrun torque means the force required to make the screwed lid overcome the threads and spin freely. If the overrun torque is small, the lid easily spins freely, causing problems in the capping process by the filling machine and insufficient sealing, resulting in reduced quality.

[0025] As a result of the inventor's investigation, it was found that when the protrusion length L2 is 20% to 70% of the protrusion length L1, it is possible to prevent the lid from being chipped and ensure sealing by maintaining an appropriate overrun torque. Therefore, by forming the mold for the main body 10 so that the protrusion length L2, including the estimated maximum protrusion length of the burrs formed on the parting line, falls within the above range, the main body 10 of this embodiment in which the protrusion length L2 satisfies the above numerical range can be manufactured.

[0026] The reduction in overrun torque and the sealing failure are also caused by deformation due to insufficient rigidity of the fitting portion. In the container of this embodiment, although the thread 33 has a small diameter portion 35, the thread itself is continuous from the start point to the end point without any breaks, so that the rigidity of the entire fitting portion can be kept higher than that of the configuration with the discontinuous portion described above. As a result, the overrun torque can be appropriately maintained, and the inside of the main body 10 can be reliably sealed by the screw fitting of the lid 20.

[0027] An experimental example regarding the thread of this embodiment is given below. The main body was made by injection molding using PET, and the lid was made by injection molding using polypropylene (PP). Experimental Examples 1 to 4 were made by varying only the shape of the small diameter part of the thread as follows. Experimental Examples 1 and 2 satisfy the above-mentioned numerical range. Experimental example 1: Protrusion length L2 is 60% of protrusion length L1 Experimental example 2: Protrusion length L2 is 30% of protrusion length L1 Experimental Example 3: Protrusion length L2 is 80% of protrusion length L1 Experimental Example 4: Protrusion length L2 is 10% of protrusion length L1

[0028] Each container was placed in the capping machine, and the tightening torque was set to 490 N·cm, and capping was performed while measuring the torque value with a torque meter. If the cap idly spun, the torque value at that point was recorded as the overrun torque, and if capping was performed without any problems, the overrun torque value was recorded as "490 N·cm or more." Furthermore, the lid was removed from the capped container, and the presence or absence of shavings of the lid at the fitting portion was visually evaluated. The results are shown in Table 1.

[0029] [Table 1]

[0030] In Experimental Examples 1 and 2, no chipping of the lid occurred and an overrun torque value of 450 N·cm or more was ensured. An overrun torque value of 400 N·cm or more is a good result because it ensures reliable sealing in most applications.

[0031] In the experimental example 3 in which the protrusion length L2 exceeded 70% of the protrusion length L1, the overrun torque value was good, but chipping of the lid, which was probably due to burrs, was observed. In Experimental Example 4, in which the protrusion length L2 was less than 20% of the protrusion length L1, no chipping of the lid was observed, but the overrun torque value was less than 300, and sufficient sealing was not achieved.

[0032] Although one embodiment of the present invention has been described above, the specific configuration is not limited to this embodiment, and configuration changes and combinations within the scope of the gist of the present invention are also included. Some modifications are exemplified below, but these are not all inclusive, and other modifications are also possible. Two or more of these modifications may be appropriately combined.

[0033] The shape of the small diameter portion is not limited to the above. The small diameter portion 35A of the modified example shown in Fig. 5 has two slopes that are not perpendicular to the line connecting the center axis C and the parting line PL and extend from the thread 33 toward the parting line PL. Even with such a small diameter portion, the same effect can be achieved as long as the protruding length L2 satisfies the above-mentioned numerical range.

[0034] Instead of changing the shape of the mold, the small diameter portion may be formed by cutting a part of the thread after molding. However, the method of changing the shape of the mold is preferable because it allows the main body of the present invention to be produced by injection molding alone.

[0035] The technical concept of the present invention is particularly effective when the main body is made of a relatively hard resin. For example, other than the above-mentioned PET, it is also suitable for the main body to be made of polypropylene, polyethersulfone (PES), polyphenylsulfone (PPSU), polycarbonate, etc.

[0036] The fitting structure according to the present invention can also be applied to preforms, which are intermediate products used in the manufacture of PET bottles. [Explanation of symbols]

[0037] 1 container 10 Main unit 20 Lid 32 Fitting part 33 Thread 33a Start 33b End point 35, 35A small diameter section L1 Maximum thread protrusion length L2 Protruding length of burred part

Claims

1. a body having a mating portion on which a screw thread is formed; A lid that is screwed into the fitting portion; Equipped with The thread is formed in a spiral shape without interruption from the starting point to the end point, The body is formed by injection molding of a synthetic resin and has burrs on the threads, The protruding length of the burred portion is 20% or more and 70% or less of the maximum protruding length of the thread, The overrun torque when the lid is screwed onto the main body is 400 N cm or more. container.

2. The thread has a small diameter portion having a relatively small protruding length from the fitting portion, The small diameter portion has the burr.

2. The container of claim 1.

3. The burrs are formed along the seams of a mold used in the injection molding.

2. The container of claim 1.

4. The synthetic resin includes any one of polyethylene terephthalate, polyethersulfone, polyphenylsulfone, and polycarbonate.

4. The container of claim 3.

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