JP2005075422A - Bottomed box-shaped resin-made container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sandwiched, bottomed and box-shaped resin-made container which is manufactured with less deflection of a bottom surface and excellent productivity while suppressing the material cost. <P>SOLUTION: In the container, a gate is provided in a bottom side, a skin material layer is formed of highly rigid polypropylene of the bending modulus of elasticity of ≥2,000 MPa with filler mixed therein, a core material layer is formed of block copolymer polypropylene, and a layer structure consisting of one or two core material layers is provided in the middle of the thickness direction of the bottom over 70% of the bottom area. Lead balls of the diameter of 2 mm and the total weight of 20 kg are laid over the bottom with both ends in the longitudinal direction of the bottom surface supported from each lower side 60 mm in width to apply the uniform load to the bottom so that the deflection of the bottom surface is set to be ≤5 mm when the container is naturally left for 12 hours at 23°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a bottomed box type resin container.

Bottomed box-type resin containers such as logistics containers that require rigidity, dimensional stability, etc. are provided with grid-like reinforcing ribs on the bottom, talc, calcium carbonate, glass fiber, carbon fiber, crystal nucleus It is often molded using a polypropylene resin composition (hereinafter referred to as “high-rigidity polypropylene”) having a flexural modulus increased to 2000 MPa or more in which fillers such as materials and nanocomposites are dispersed and mixed (Patent Document 1). Etc.).
However, in the case of the above-mentioned high-rigidity polypropylene, the fluidity is poor. Therefore, when trying to obtain a molded product by injection molding, the mold filling property is poor, and there is a possibility that problems such as warpage of the molded product may occur. Further, in the case of highly synthetic polypropylene, the material becomes expensive and there is a problem in product cost.

Therefore, the inventors of the present invention thought that the above problem could be solved if sandwich molding (see Patent Document 2 etc.) was used.
However, like conventional sandwich molding, when using high-rigidity polypropylene as the resin constituting the core material layer, and using inexpensive block copolymer polypropylene as the resin constituting the skin material layer, for the following reasons, It was found that the section modulus and elastic modulus did not change greatly in terms of material mechanics.

(1) Since a skin material is used for nozzle cleaning for the next shot, the vicinity of the gate is only the low-stiff block copolymer polypropylene as the skin material, and the vicinity of the gate is easily bent.
(2) When the thickness of the general surface other than the reinforcing ribs on the bottom surface is 1.4 mm or less, the high-rigidity polypropylene serving as the core material enters only partially as the core material. That is, only the block copolymer polypropylene having a low rigidity, which is mostly a skin material, is obtained.
(3) In the reinforcing rib on the bottom surface, the core material enters the central portion of the rib, but the core material does not enter the tip portion of the rib. Therefore, a problem arises in the rigidity of the tip portion of the rib.

JP-A-6-157867 JP-A-6-31437

  In view of the above circumstances, an object of the present invention is to provide a bottomed box-type resin container that can be manufactured with high productivity while reducing the deflection of the bottom surface, suppressing the material cost.

In order to achieve the above object, a bottomed box-type resin container according to the present invention is a bottomed box-type resin container that is sandwich injection molded and has a grid-shaped reinforcing rib on a substantially rectangular bottom surface. The gate is provided on the bottom surface, the skin material layer is formed from a high-rigidity polypropylene having a flexural modulus of 2000 MPa or more mixed with a filler, and the core material layer is formed from a resin other than the resin forming the skin material layer. 70% or more of the bottom area is provided with one or two core material layers in the middle of the thickness direction of the bottom, and the bottom end in the longitudinal direction is supported with a width of 60 mm from below. A total of 20 kg of lead balls having a diameter of 2 mm is spread on the plate, a uniform load is applied, and the bottom deflection when left at 23 ° C. for 12 hours is 5 mm or less.

  In the present invention, the skin material layer refers to a layer formed by the resin injected first and last at the time of sandwich molding, and the core material layer refers to an intermediate between the resin and the resin that forms the skin material layer at the time of sandwich molding. A layer formed of a resin injected at the timing.

  As described above, the bottomed box-type resin container according to the present invention is superior in fluidity and has a material higher than that of high-rigidity polyethylene that forms a skin material layer in the middle of the bottom in the thickness direction of 70% or more of the bottom area. Since it is a sandwich molded product having one or two inexpensive core material layers, the productivity is good and the manufacturing cost can be reduced. And since there is little deflection | deviation of a bottom, it can be used conveniently for the distribution container etc. with much stacking.

Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof.
1 to 3 show a container which is one embodiment of a bottomed box type resin container according to the present invention.

As shown in FIGS. 1 to 3, the container 1a is formed by sandwich molding and includes a substantially rectangular bottom 2a and four side walls 3a rising from the bottom 2a. As shown in FIG. A grid-like reinforcing rib 22 is provided on the surface. A one-point gate 23 is provided at the center of the bottom surface 21.
As shown in FIG. 3, the bottom 2a has a total thickness of a five-layer structure of skin material layer 11-core material layer 12-skin material layer 11-core material layer 12-skin material layer 11 in the thickness direction. 70% or more of the area. That is, the two core material layers 12 are provided in the middle of the thickness direction of the bottom 2a. The skin material layer 11 is made of a high-rigidity polypropylene having a flexural modulus of 2000 MPa or more, and the core material layer 12 is less expensive than a high-rigidity polypropylene such as a block-free copolymer polypropylene or a filler-free polypropylene or recycled polypropylene. It is made of a simple material.

Further, the side wall 3a has a core material layer 12 formed in the middle in the thickness direction over substantially the entire height direction.
And this container 1 floats in the air in the state which the bottom 2a was further received by the supporting member 4 from the downward direction with the width of 60 mm in the both ends 13 of a longitudinal direction, as shown in FIG. When the lead balls 5 having a diameter of 2 mm of 20 kg are uniformly spread on the bottom 2a and left at 23 ° C. for 12 hours, the bottom deflection a is 5 mm or less.

  As shown in FIG. 5, the container 1a is formed by first injecting a part of the resin forming the skin material layer 11 (hereinafter referred to as “skin resin”) into the mold, It can be obtained by injecting all the resin forming the core material layer 12 (hereinafter referred to as “core resin”) in a state where the injection is stopped, and injecting the remaining skin resin after the completion of the injection of the core resin. .

The container 1a is configured as described above, and only the skin material layer 11 is formed of high-rigidity polypropylene, and the core material layer 12 is formed of a material that is less expensive than high-rigidity polypropylene. Cost is cheaper than containers made of high-rigidity polypropylene only. Further, if recycled polypropylene is used as the core resin, it becomes more inexpensive and environmentally friendly products (green products and eco products).
On the other hand, if filler-free polypropylene such as block copolymerized polypropylene is used as the core resin, the resin has good fluidity in the mold, so that it becomes a molded product with no warpage and good dimensional accuracy.

FIG. 6 shows a container which is another embodiment of the bottomed box type resin container according to the present invention.
As shown in FIG. 6, this container 1b has a bottom 2b having a three-layer structure of skin material layer 11-core material layer 12-skin material layer 11 in the thickness direction, and the height direction of the side wall 3b. The container 1a is substantially the same as the container 1a except that the core material layer 12 is formed above the intermediate portion.

  The container 1b can be molded in the same manner as the container 1a except that the injection timing of the core resin is adjusted and the total injection amount of the core resin is increased as compared with the case of the container 1a.

  The container 1b bends slightly larger than the container 1a, although the deflection of the bottom 2b is 5 mm or less. However, since the amount of the inexpensive core resin can be increased, it can be manufactured at a lower cost.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the skin resin injection is temporarily stopped, and after the core resin is injected and filled in this stopped state, the remaining skin resin is injected again. The injection may be performed partially at the same time.
In addition, the injection timing of the skin resin and the core resin is not particularly limited as long as the conditions of the present invention are satisfied. First, the skin resin is injected into a mold of 20% to 80% of the total amount, and the rest is injected into the core resin. It is preferable to inject afterwards. That is, if the skin resin to be injected last is less than 20%, the core resin near the gate may not be covered with the skin resin.

  Size: 550 mm × 400 mm × H 200 mm, basic thickness of bottom surface (thickness of portions other than ribs) 2 mm, bottom rib pitch 14 mm (lattice shape), bottom rib width 2.5 mm, bottom rib height 3 mm, side wall thickness 2 A container as shown in FIG. 1 having a thickness of 5 mm, a side rib width of 3.5 mm, a side rib height of 20 mm, and 16 side ribs was formed as follows.

Skin material resin: High-rigidity polypropylene (Daicel PP talc grade tar manufactured by Daicel Corporation)
(20% PT4N1, bending elastic modulus 2700 MPa)
Core material resin: Block copolymer polypropylene (BC03B manufactured by Nippon Polychem Co., Ltd., flexural elasticity
(Rate 1200MPa)
Gate: One point on the lower surface Skin material injection machine: Injection stroke 120mm, screw diameter 105mm
Core material injection machine: injection stroke 90mm, screw diameter 80mm
Skin material resin and core resin injection pattern: After injecting the skin resin until the injection stroke reaches 50 mm, stop the injection of the skin resin and inject the core resin. Ejected.

Looking at the cross section in the thickness direction of the bottom surface of the container obtained as described above, the skin material layer-core material layer-skin material layer-core material layer-skin material layer 5 in the 95% of the total area of the bottom surface. It has a layer structure, and the average thickness of each layer is 0.5 mm skin material layer from the bottom side-core material layer 0.1 mm-skin material layer 0.6 mm-core material layer 0.2 mm-skin material layer 0.6 mm. Met.
Further, 85% by weight of the resin forming the bottom was a high-rigidity polypropylene, which is a skin material resin, and about 40% by weight of the resin forming the side wall was a high-rigidity polypropylene.

A container was obtained in the same manner as in Example 1 except that the container was molded under the following conditions.
Skin material injection machine: injection stroke 100mm, screw diameter 105mm
Core material injection machine: injection stroke 120mm, screw diameter 80mm
Skin resin and core resin injection pattern: After the skin resin is injected until the injection stroke reaches 40 mm, the skin resin injection is temporarily stopped and then the core resin is injected. After the core material resin injection is completed, the remaining skin resin is injected again. did.

Looking at the cross section in the thickness direction of the bottom surface of the container obtained as described above, the skin material layer-core material layer-skin material layer-core material layer-skin material layer 5 in 70% of the total area of the bottom surface. It has a layer structure, and the average thickness of each layer from the bottom side is 0.5 mm skin material layer-0.3 mm core material layer-0.5 mm skin material layer-0.3 mm core material layer-0.4 mm skin material layer. Met.
Further, 70% by weight of the resin forming the bottom was a high-rigidity polypropylene which is a skin resin, and about 50% by weight of the resin forming the side wall was a high-rigidity polypropylene.

A container was obtained in the same manner as in Example 1 except that the container was molded under the following conditions.
Skin material injection machine: injection stroke 80mm, screw diameter 105mm
Core material injection machine: injection stroke 150mm, screw diameter 80mm
Skin material resin and core resin injection pattern: After injecting the skin resin until the injection stroke reaches 15 mm, the skin resin injection is temporarily stopped, the core resin is injected, and after the core material resin injection is completed, the remaining skin resin is again applied. Ejected.

When the cross section in the thickness direction of the bottom surface of the container obtained as described above is seen, it has a three-layer structure of skin material layer-core material layer-skin material layer in a portion of 75% of the total area of the bottom surface. The average thickness of the skin material layer was 0.5 mm from the bottom side, the core material layer was 0.8 mm, and the skin material layer was 0.7 mm.
Further, 55% by weight of the resin forming the bottom was a high-rigidity polypropylene which is a skin material resin. And the upper end part of the side surface was mostly formed only with core material resin.

  In addition to the containers obtained in Examples 1 to 3 above, containers having the same shape as the examples injection-molded only with the high-rigidity polypropylene used in the Examples (Comparative Example 1), block copolymer used in the Examples A total of 20 kg of lead balls having a diameter of 2 mm are laid on the bottom of each container (Comparative Example 2) having the same shape as the embodiment injection-molded only with polypropylene, and both ends in the longitudinal direction are supported from below with a width of 60 mm. After floating in the air and left at 23 ° C. for 12 hours, the deflection of the bottom surface was measured, and the results are shown in Table 1.

  From Table 1 above, it can be seen that the bottomed box type resin container according to the present invention satisfies the deflection of 5 mm or less and is suitable as a distribution container.

It is a perspective view showing one embodiment of a bottomed box type resin container concerning the present invention. It is a bottom view of the bottomed box type resin container of FIG. It is a figure which shows typically the principal part cross section of the bottomed box type resin container of FIG. It is a figure explaining the test method of a bottom face deflection. It is a time chart explaining the injection timing of the skin material and core material at the time of shaping | molding of the bottomed box type resin container concerning this invention. It is other embodiment of the bottomed box type resin container concerning this invention, Comprising: It is a figure which represents typically the principal part cross section.

Explanation of symbols

1a, 1b container (bottomed box type resin container)
DESCRIPTION OF SYMBOLS 11 Skin material layer 12 Core material layer 13 End 2a, 2b Bottom 21 Bottom 22 Reinforcement rib 23 Gate 3a, 3b Side wall 5 Lead ball

Claims (1)

A bottomed box-shaped resin container that is sandwich injection-molded and has grid-shaped reinforcing ribs on a substantially rectangular bottom surface, a gate is provided on the bottom surface, a skin material layer is mixed with a filler and bent It is formed from a polypropylene resin composition having an elastic modulus of 2000 MPa or more, the core material layer is formed from a resin other than the resin forming the skin material layer, and 70% or more of the bottom area is in the middle of the bottom thickness direction. Equipped with one or two core material layers, both ends in the longitudinal direction of the bottom are 60m
A bottomed base having a bottom deflection of 5 mm or less when left at 23 ° C. for 12 hours, with a total load of 20 kg of 2 mm diameter lead balls laid on the bottom in a state of being supported from below at a width of m. Box-shaped resin container.