JP2024009985A - Synthetic resin case - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soft synthetic resin case made of an injection molded body of a synthetic resin, in which occurence of torsion is suppressed.

SOLUTION: A soft synthetic resin case 400 made of an injection molded body of polyethylene comprises a rectangular bottom surface 100, and a side wall 200 provided to rise from each side of the bottom surface. Only one gate arrangement portion 140 in which a gate for flowing polyethylene during injection molding is arranged, is provided on the bottom surface. A height of the side wall from the bottom surface to an opening portion is formed larger than a distance from the gate arrangement portion to the side wall located farthest from the gate arrangement portion. An MFR of polyethylene measured by a test method in accordance with JIS K 7210-1 is 10 to 60 (g/10 min), and flexural modulus is 50 to 900 MPa. A height of the side wall is less than 4 times of the shortest distance from the gate arrangement portion to the side wall. An edge portion of the opening portion is linear.

SELECTED DRAWING: Figure 2

COPYRIGHT: (C)2024,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to a synthetic resin case for housing objects, and particularly to a soft synthetic resin case made of an injection molded body.

Conventionally, various types of synthetic resin cases have been known. For example, the synthetic resin case disclosed in Patent Document 1 has a rectangular bottom surface and a side wall that rises from the bottom surface. It is equipped with an opening at the upper end and allows objects to be stored therein. Such synthetic resin cases are injection molded using soft synthetic resin to make the entire synthetic resin case soft and flexible, for example, to prevent damage or injury when dropped. ing.

However, due to the characteristics of soft synthetic resin, thermal contraction during injection molding tends to be uneven, and residual stress tends to remain near the gate on the bottom of the synthetic resin case, resulting in differences in distance from the gate on the bottom. There was a problem in that the synthetic resin case would become twisted due to the large difference in thermal contraction caused by the heat shrinkage.

Japanese Patent Application Publication No. 9-301395

Therefore, in view of the above problems, the present invention provides a soft synthetic resin case made of an injection molded synthetic resin that suppresses the occurrence of twisting.

In order to solve the above problems, a synthetic resin case according to claim 1 of the present invention is provided with a rectangular bottom surface and side walls provided to rise from each side of the bottom surface, and a polyethylene injection molded case. A soft synthetic resin case consisting of
Only one gate arrangement part is provided on the bottom surface for arranging a gate for pouring the polyethylene during injection molding,
The height of the side wall from the bottom surface to the opening is greater than the distance from the gate placement portion to the side wall at the farthest position,
The polyethylene has an MFR of 10 to 60 (g/10 min) and a flexural modulus of 50 to 900 MPa, as measured by a test method according to JIS K 7210-1,
The height of the side wall is smaller than four times the shortest distance from the gate arrangement part to the side wall,
The edge of the opening is preferably linear.

Furthermore, the synthetic resin case according to claim 2 of the present invention is characterized in that the side wall is formed thicker than the bottom surface.

Furthermore, the synthetic resin case according to claim 3 of the present invention is characterized in that a reinforcing portion that is thicker than the side wall is formed at the edge of the opening.

Furthermore, the synthetic resin case according to claim 4 of the present invention is characterized in that the edge of the opening is covered with a synthetic resin lid.

Furthermore, the synthetic resin case according to claim 5 of the present invention is characterized in that talc is blended into the polyethylene.

Furthermore, the synthetic resin case according to claim 6 of the present invention is characterized in that the polyethylene is low density polyethylene or high density polyethylene.

Furthermore, in the synthetic resin case according to claim 7 of the present invention, a handle hole is provided on the upper end side of the side wall, and the wall thickness of the side wall around the handle hole is greater than the wall thickness of the other side walls. It is also characterized by being thick.

Furthermore, the synthetic resin case according to claim 8 of the present invention is characterized in that the side wall is provided with a handle hole, and the side wall is formed with a solid surface except for the handle hole.

Furthermore, in the synthetic resin case according to claim 9 of the present invention, the side wall is provided with a handle hole, and the handle hole is formed below the edge of the opening of the side wall. Features.

According to the present invention, it is possible to provide a soft synthetic resin case made of an injection molded synthetic resin body that suppresses twisting.

(a) is an overall perspective view of a synthetic resin case according to Embodiment 1 of the present invention, (b) is an AA end view, and (c) is a BB end view. (a) is a plan view of a synthetic resin case according to Embodiment 1 of the present invention, and (b) is a side view of the synthetic resin case. 1 is a schematic cross-sectional view of injection molding a synthetic resin case according to Embodiment 1 of the present invention. (a) is a bottom view of a lid that can be attached to a synthetic resin case according to Embodiment 1 of the present invention, (b) is a side view of the lid, and (c) is a CC end view. (a) is a plan view of a synthetic resin case according to Embodiment 2 of the present invention, and (b) is a side view of the synthetic resin case.

100 Bottom surface 140 Gate arrangement section 200 Side wall 300 Opening section 400 Synthetic resin case 530 Gate

Each embodiment of the present invention will be described below with reference to the drawings. In this specification, "upward" refers to the upward direction in the vertical direction when the synthetic resin case is placed on a horizontal surface with the opening facing upward, and "downward" refers to the upward direction in the vertical direction. This refers to the downward direction in the direction.

<Embodiment 1>
First, FIGS. 1 and 2 show a synthetic resin case 400 according to Embodiment 1 of the present invention. Note that FIG. 1(a) is an overall perspective view of the synthetic resin case 400, FIG. 1(b) is an AA end view, and FIG. 1(c) is a BB end view. Further, FIG. 2(a) is a plan view of the synthetic resin case 400, and FIG. 2(b) is a side view of the synthetic resin case 400.

This synthetic resin case 400 includes a rectangular bottom surface 100 and side walls 200 that rise upward from each side of the bottom surface 100. Further, the synthetic resin case 400 can store items therein through the opening 300 on the upper end side.

Further, the side wall 200 includes a first side wall 210 provided to rise upward from the short side 110 of the bottom surface 100 and a second side wall 220 provided to rise upward from the long side 120 of the bottom surface 100. The lower surfaces of the short sides 110 and long sides 120 of the bottom surface 100 are portions that come into contact with a flat surface when the bottom surface 100 is placed on the flat surface. Further, the length of the bottom surface 100 on the long side 120 side is L7. Furthermore, as shown in FIG. 2(a), the first side wall 210 extends over a range P1 between the vertices P of adjacent corner parts. Similarly, the second side wall 220 extends over a range P2 between the vertices P of adjacent corner parts. The first side wall 210 and the second side wall 220 are provided so as to surround the bottom surface 100. The thickness T1 of the first side wall 210 is thicker than the thickness T0 of the bottom surface 100. Further, the lower end of the first side wall 210 bulges downward from the bottom surface 100 and forms a leg portion 211 that curves outward. Further, the upper end of the first side wall 210 is a reinforcing portion 212 into which a lid, which will be described later, can be fitted. The thickness T2 of the reinforcing portion 212 is formed to be thicker than the thickness T1 of the first side wall 210. Note that a handle hole V is provided on the upper end side of the first side wall 210 so that a person can easily hold it by hand. Note that although the handle hole V is formed, no weld line occurs because talc is not blended. Further, the first side wall 210 has a solid surface except for the handle hole V, and the second side wall 220 is also formed entirely in a solid surface. Furthermore, the first side wall 210 may be formed entirely on a solid surface without providing the handle hole V, and in that case, the second side wall 220 is entirely formed on a solid surface.

Similarly, the thickness T3 of the second side wall 220 is thicker than the thickness T0 of the bottom surface 100. Further, the lower end of the second side wall 220 bulges downward from the bottom surface 100 and forms a leg portion 221 that curves outward. Further, the upper end of the second side wall 220 is a reinforcing portion 222 into which a lid, which will be described later, can be fitted. The thickness T4 of the reinforcing portion 222 is thicker than the thickness T3 of the second side wall 220.

In this manner, by forming the side wall 200 thicker than the bottom surface 100, it is possible to effectively prevent the side wall 200 from expanding outward or inward. Furthermore, since the reinforcing parts (212, 222) provided at the edge of the opening 300 are formed thicker than the wall thickness of the side wall 200, it is easy to fit a lid to be described later. Note that the curvature of the curved surface at the connection point between the first side wall 210 and the second side wall 220 is made larger than the curved surface at the connection point between the bottom surface 100 and the side wall 200.

Further, the synthetic resin case 400 is injection molded using polyethylene in order to make the entire synthetic resin case 400 soft and flexible in order to prevent damage or injury when dropped. Here, this injection molding will be briefly explained with reference to FIG. 3. Note that FIG. 3 is a schematic cross-sectional view of injection molding of the synthetic resin case 400.

As shown in FIG. 3(a), molten polyethylene , through the gate 530 under pressure. Then, as shown in FIG. 3(b), a synthetic resin case 400 made of an injection molded polyethylene X is manufactured, and after cooling and solidifying, it is taken out from the fixed side mold 510 and the movable side mold 520. As shown in FIG. 3(b), a gate 530 into which polyethylene X is poured is arranged on the bottom surface 100 of the synthetic resin case 400, and this arrangement part is called a gate arrangement part 140.

As shown in FIG. 2, one gate arrangement section 140 is provided at the center of the bottom surface 100 of the synthetic resin case 400. The polyethylene X poured from the gate 530 arranged in the gate arrangement part 140 is poured so as to spread radially around the gate arrangement part 140. However, in the rectangular bottom surface 100, there are parts whose distances from the gate arrangement part 140 are different (for example, the distances from the gate arrangement part 140 are different around the short side 110 and around the long side 120). Since the difference in shrinkage increases, there is a possibility that twisting may occur in the cooled and solidified bottom surface 100. In particular, in the peripheral portion of the side wall 200 that is farthest from the gate arrangement portion 140 (near the corner portion of the side wall 200, as shown in FIG. 2), the difference in thermal contraction is greatest, and there is a possibility that large twisting may occur. .

Therefore, in the synthetic resin case 400 of the present invention, as shown in FIGS. 1 and 2, the height H1 of the side wall 200 from the bottom surface 100 to the opening 300 is the side wall at the farthest position from the gate placement section 140. It is set larger than the distance L1 up to 200. At the bottom surface 100 around the side wall 200 located at the farthest position from the gate arrangement part 140, the distance L1 from the gate arrangement part 140 is the largest, and the amount of twist is also large. Therefore, by making the height H1 of the side wall 200 surrounding the bottom surface 100 longer than at least the distance L1 from the gate arrangement part 140 to the farthest side wall, the side wall 200 can be This strongly reinforces the bottom surface 100. Furthermore, the side wall 200 is located away from the gate arrangement portion 140 on the bottom surface 100 and has less heat shrinkage than the vicinity of the gate arrangement portion 140 on the bottom surface 100 and is less likely to be twisted. It can be effectively prevented.

Note that when the height H1 of the side wall 200 is four times or more the shortest distance L0 from the gate arrangement part 140 to the side wall 200 (that is, when the synthetic resin case 400 is tall and has a large capacity), the height H1 of the side wall 200 is Since the strength is relatively strong, twisting of the bottom surface 100 is difficult to occur in the first place. However, in the present invention, even if the height H1 of the side wall 200 is smaller than four times the shortest distance L0 from the gate placement part 140 to the side wall 200 (in other words, the height of the synthetic resin case 400 is low). , in the case of small/medium capacity), the twisting of the bottom surface 100 can be suppressed by devising the height H1 of the side wall 200 as described above, or by devising the MFR and bending elastic modulus of polyethylene as described later. It is characterized by the fact that Therefore, in the synthetic resin case 400 of the present invention, the height H1 of the side wall 200 is made smaller than four times the shortest distance L0 from the gate placement part 140 to the side wall 200.

By the way, in the present invention, by using polyethylene, the entire synthetic resin case 400 can be made soft and flexible, but if the MFR or flexural modulus of the polyethylene is too high or low, twisting tends to occur. . Therefore, it is necessary to derive optimal conditions under which twisting is less likely to occur and the entire synthetic resin case 400 can be made soft and flexible.

Therefore, through repeated experiments, the inventors of the present invention have found the optimal conditions for making the entire synthetic resin case 400 soft and flexible without causing twisting, that is, the optimal MFR and flexural modulus. Specifically, when polyethylene has an MFR of 1 to 60 (g/10 min) and a bending modulus of 50 to 900 MPa, a synthetic resin case 400 with appropriate flexibility is manufactured by injection molding. be able to. Furthermore, the polyethylene has an MFR of 1 to 60 (g/10 min), preferably 8 to 20 (g/10 min), more preferably 10 to 15 (g/10 min), and a flexural modulus of 50 to 900 MPa. , preferably 120 to 900 MPa, more preferably 650 to 800 MPa, it is possible to manufacture the synthetic resin case 400 with more appropriate flexibility.

In addition, if the MFR of polyethylene is less than 1 (g/10 min), the fluidity of polyethylene will be too low, and the molten polyethylene will not flow uniformly to the edge of the mold during injection molding, resulting in the density of polyethylene being unstable. A uniform synthetic resin case 400 is molded, and twisting is likely to occur. Conversely, when the MFR of polyethylene exceeds 60 (g/10 min), the effect of twisting becomes greater and burrs are more likely to occur than when the MFR is low.

Furthermore, the polyethylene used during injection molding may be low density polyethylene, high density polyethylene, or a mixture of low density polyethylene and high density polyethylene. Since the minimum value of the bending elastic modulus of low density polyethylene is 50 MPa, the lower limit of the bending elastic modulus of the synthetic resin case 400 of the present invention was set to 50 MPa. On the other hand, if the bending modulus exceeds 900 MPa, the synthetic resin case 400 becomes too hard and loses its flexibility. In addition, in the synthetic resin case 400 shown in FIG. 2, low-density polyethylene with an MFR of 20 (g/10 min) and high-density polyethylene with an MFR of 8 (g/10 min) are mixed, and the MFR of the mixed polyethylene is is set to 13 (g/10min). Alternatively, talc may be blended with polyethylene to increase the strength of the synthetic resin case 400 to the extent that flexibility is not lost.

Furthermore, in FIG. 2 , the gate placement portion 140 is provided at the center of the bottom surface 100 , but the present invention is not limited to this, and the gate placement portion 140 may be provided at any position on the bottom surface 100 . For example, as shown in FIG. 2, when the gate placement portion 140' is offset from the center of the bottom surface 100, the distance from the gate placement portion 140' to the farthest side wall 200 is L1'.

The MFR (melt mass flow rate) of the polyethylene constituting the synthetic resin case 400 of the present invention was measured by a test method based on JIS K 7210-1. Further, the flexural modulus of polyethylene was measured by a test method based on JIS K 6924-2.

Next, FIG. 4 shows a lid 600 that can be attached to the synthetic resin case 400 of the present invention. 4(a) is a bottom view of the lid 600, FIG. 4(b) is a side view of the lid 600, and FIG. 4(c) is a CC end view. Note that the lid 600 is optionally attached to the synthetic resin case 400 and is not an essential component of the synthetic resin case 400.

As shown in FIG. 4, the lid 600 is a plate-like member made of synthetic resin, and has a size that can cover the opening 300 of the synthetic resin case 400. The lid 600 also includes a rectangular top plate 610 and an outer wall 620 extending downward from each side of the top plate 610. A wall 630 is provided. A fitting groove 640 is formed between the outer wall 620 and the inner wall 630, and the reinforcing portions 212 and 222 of the side wall 200 of the synthetic resin case 400 are fitted into the fitting groove 640. It will be done. Therefore, when the lid 600 is placed over the opening 300 of the synthetic resin case 400, the fitting groove 640 of the lid 600 is fitted into the reinforcing portions 212 and 222 of the side wall 200, and the lid 600 is firmly attached. .

<Embodiment 2>
Next, FIG. 5 shows a synthetic resin case 400A according to a second embodiment of the present invention. Note that FIG. 5(a) is a plan view of the synthetic resin case 400A, and FIG. 5(b) is a side view of the synthetic resin case 400A. Furthermore, the synthetic resin case 400A according to the second embodiment differs from the synthetic resin case 400 according to the first embodiment shown in FIGS. 1 to 4 only in the position of the gate arrangement part 140A and the height of the side wall 200A. Since the other configurations are the same as the synthetic resin case 400 according to the first embodiment, detailed explanation will be omitted.

As shown in FIG. 5, two gate placement portions 140A are provided on the bottom surface 100A. The shortest distance L2 from each gate placement portion 140A to the first side wall 210A closest to the gate placement portion 140A, and the shortest distance L2 from each gate placement portion 140A to the second side wall 220A closest to the gate placement portion 140A. The shortest distance L3 is approximately equal. Furthermore, the distance L4 between the two gate arrangement parts 140A is approximately twice the shortest distance L2 or the shortest distance L3.

Therefore, on the bottom surface 100A, there are many parts having equal distances from each gate arrangement part 140A, so that the polyethylene poured from the gate arrangement part 140A spreads uniformly, and furthermore, the difference in thermal shrinkage can be reduced. As a result, twisting of the synthetic resin case 400A can be suppressed.

Note that since the bottom surface 100A has a rectangular parallelepiped shape, the shortest distance L2 is the distance between the gate placement portion 140A and the first side wall 210A in a straight line that passes through the gate placement portion 140A and intersects the first side wall 210A at right angles. It means. Similarly, the shortest distance L3 means the distance between the gate placement portion 140A and the second side wall 220A in a straight line passing through the gate placement portion 140A and intersecting the second side wall 220A at right angles.

Furthermore, the fact that the shortest distance L2 and the shortest distance L3 are approximately equal means that both shortest distances are equal, and that humans cannot recognize the twisting due to the difference in thermal contraction of polyethylene that exists on each shortest distance. This includes that both shortest distances are close to each other. Furthermore, the fact that the distance L4 between the two gate arrangement parts 140A is approximately twice the shortest distance L2 or the shortest distance L3 means that the distance L4 is twice the shortest distance L2 or the shortest distance L3. This also includes that the distance L4 is set to a distance between twice the shortest distance L2 and twice the shortest distance L3. Note that the distance L4 between the two gate placement portions 140A is approximately twice the shortest distance L2 or the shortest distance L3, but is not limited to this, and the two gate placement portions 140A may be placed further inside, The distance L4 between the two gate placement parts 140A may be approximately 1.5 times the shortest distance L2 or the shortest distance L3. However, it is preferable to arrange the two gate arrangement parts 140A on the outside than the arrangement in which the two gate arrangement parts 140A are arranged on the inside. It may be approximately 2.5 to 3 times L2 or the shortest distance L3.

Furthermore, as shown in FIG. 5, in the first side wall 210A closest to the left gate arrangement section 140A, the distance from the gate arrangement section 140A to the part (corner section in FIG. 5) located farthest from the gate arrangement section 140A is , becomes L5. Similarly, in the first side wall 210A closest to the right gate arrangement section 140A, the distance from the gate arrangement section 140A to the part (corner section in FIG. 5) located farthest from the gate arrangement section 140A is L6. In the synthetic resin case 400A, the height H2 of the side wall 200A from the bottom surface 100A to the opening 300A is larger than the distance L5 and the distance L6. In other words, in the case 400A made of synthetic resin, the height H2 of the side wall 200A is determined from the distance from the first side wall 210A closest to each gate arrangement part 140A to the side wall part at the farthest position from each gate arrangement part 140A. It has also been forming for a long time. Therefore, the side wall 200A surrounding the bottom surface 100A strongly reinforces the bottom surface 100A so that the bottom surface 100A is not twisted.

In addition, when the height H2 of the side wall 200A is four times or more the shortest distance from each gate placement part 140A to the side wall 200A, the strength of the side wall 200A becomes relatively strong, so twisting of the bottom surface 100A is difficult to occur in the first place. . However, in the present invention, even if the height H2 of the side wall 200A is smaller than four times the shortest distance from each gate arrangement part 140A to the side wall 200A, the positional relationship of the gate arrangement part 140A on the bottom surface 100A, The unique feature is that the MFR and bending elastic modulus of polyethylene have been improved to suppress twisting of the bottom surface of 100A. Therefore, in the synthetic resin case 400A of the present invention, the height H2 of the side wall 200A is smaller than four times the shortest distance (L2 and L3) from each gate placement part 140A to the side wall 200A.

Note that, like the synthetic resin case 400 according to the first embodiment, the synthetic resin case 400A according to the second embodiment has a polyethylene MFR of 1 to 60 (g/10 min) and a flexural modulus of 50 to 60 (g/10 min). 900 MPa, and is constructed by injection molding to have appropriate flexibility. Furthermore, the polyethylene has an MFR of 1 to 60 (g/10 min), preferably 8 to 20 (g/10 min), more preferably 10 to 15 (g/10 min), and a flexural modulus of 50 to 900 MPa. , preferably from 120 to 900 MPa, more preferably from 650 to 800 MPa, to provide more appropriate flexibility.

In addition, if the side wall 200A is high and the two gate placement parts 140A are provided on the bottom surface 100A, there is a possibility that the molten resin (polyethylene) will be drawn in during injection molding and an air pocket will be formed. The side length L7 is made longer than the height H2 of the side wall 200A.

In addition, in the synthetic resin case 400A shown in FIG. 5, two gate arrangement parts 140A are provided on the bottom surface 100A, but the present invention is not limited to this, and three or more gate arrangement parts 140A may be provided. However, it is necessary to arrange at least two gate arrangement parts 140A at the positions shown in FIG. 5.

Furthermore, the synthetic resin case of the present invention is not limited to the above-mentioned embodiments, and can be modified in various ways and combinations within the scope of the claims and embodiments. Examples and combinations are also included within the scope of the right.

Claims (9)

A soft synthetic resin case made of a polyethylene injection molded body, comprising a rectangular bottom surface and side walls rising from each side of the bottom surface,
Only one gate arrangement part is provided on the bottom surface for arranging a gate for pouring the polyethylene during injection molding,
The height of the side wall from the bottom surface to the opening is greater than the distance from the gate placement portion to the side wall located at the farthest position,
The polyethylene has an MFR of 10 to 60 (g/10 min) and a flexural modulus of 50 to 900 MPa, as measured by a test method according to JIS K 7210-1,
The height of the side wall is smaller than four times the shortest distance from the gate arrangement part to the side wall,
A synthetic resin case characterized in that the edge of the opening is linear. 2. The synthetic resin case according to claim 1, wherein the side wall is thicker than the bottom surface. 3. The synthetic resin case according to claim 1, further comprising a reinforcing portion thicker than the side wall formed at the edge of the opening. 4. The synthetic resin case according to claim 3, wherein an edge of the opening is covered with a synthetic resin lid. 5. The synthetic resin case according to claim 1, wherein the polyethylene contains talc. 6. The synthetic resin case according to claim 1, wherein the polyethylene is low density polyethylene or high density polyethylene. Claims 1 to 6, wherein a handle hole is provided at an upper end side of the side wall, and a wall thickness of the side wall around the handle hole is formed to be thicker than a wall thickness of the other side walls. Synthetic resin case described in any of the above. 8. The synthetic resin case according to claim 1, wherein the side wall is provided with a handle hole, and the side wall is formed with a solid surface except for the handle hole. The synthetic resin according to any one of claims 1 to 8, wherein the side wall is provided with a handle hole, and the handle hole is formed below the edge of the opening of the side wall. case made of

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