JP2631726B2 - Mold for manufacturing polyolefin resin foam molding - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mold for producing a polyolefin-based resin foam molded article, and more specifically, to project a molded article when foaming a polyolefin-based resin foam bead. TECHNICAL FIELD The present invention relates to a mold for producing a polyolefin-based resin foam molded article which has solved the problem of local defective fusion of foam beads in a part.

[Conventional technology]

Polyolefin foams such as polyethylene foams and polypropylene foams are more flexible and have a greater buffering effect than polystyrene foams, so recently, in addition to electronic devices such as computers, word processors and printers, cameras, watches, etc. It has been widely used as a cushioning material for precision equipment.

The polyolefin resin foam molded article is molded by a molding method similar to that of polystyrene, that is, a series of operations such as filling of foam beads in a mold, heating and release. However, in the case of a polyolefin-based resin, the heat-fusibility is lower than that of polystyrene. Therefore, simply by molding with a mold having a uniform steam hole as in the prior art, a foam molded article having a projecting portion 2 such as a partition plate provided on a bottom portion 1 as shown in FIG. In such a case, a defective fusion occurs at the tip portion 2a of the protruding portion, and there is a problem that the strength of the protruding portion 2 is reduced.

To improve this, a tip portion of the protruding portion 2 is used.
A method has been proposed in which a metal mold having a structure as shown in FIG. 6 in which the vapor transmission density of the mold near 2a is larger than the vapor transmission density of the other parts of the mold is used (JP-A-63-1529). No.).

[Problems to be solved by the invention]

However, when molding is performed using the above-described mold, fusion of the tip 2a of the protruding portion 2 of the molded body is somewhat improved,
The strength, water permeability, etc. are clearly inferior to the base of the protrusion,
There is a problem that the fusion improvement is insufficient.

The steam holes are formed by arranging core vents as shown by 12 in FIGS. 6 and 2, but there is a problem that as the number of the steam holes increases, the mold becomes more expensive.

The present invention is capable of producing a polyolefin-based resin foam molded article in which the fusion of the periphery of the tip end of the protruding portion of the molded article has been significantly improved, and the strength and water permeability have been significantly improved. An object of the present invention is to provide a mold that can be manufactured at a low cost by reducing the mold production cost.

[Means for solving the problem]

The inventors of the present invention have intensively studied why the effect of improving the fusion by the mold described in JP-A-63-1529 is insufficient. Therefore, a close observation of the mold disclosed in the official gazette shows that not only the mold portion 4a corresponding to the upper surface portion of the protruding portion is provided with a steam hole as shown in FIG. Steam holes are also provided in the mold portion 4b corresponding to both side surfaces of the protruding portion 2. Therefore, a large amount of water vapor flows into the tip of the protruding portion from the steam hole.On the contrary, the water vapor from both sides of the side portion of the protruding portion interferes with each other, and the streamline of the water vapor is disturbed. It was speculated that the replacement of air and water vapor was not successful. Based on this inference, if a steam hole is provided in the mold portion 4a corresponding to the upper surface portion of the protruding portion, and the steam hole of the mold portion 4b corresponding to one side surface portion on both sides is closed, the foam molded body The present inventors have found that the mechanical strength at the tip of the protruding portion is large and the water permeability is small, and the present invention has been achieved.

That is, according to the present invention, a mold for producing a foam molded article having a protruding portion such as a partition plate is filled with polyolefin resin foam beads in a mold cavity formed by a core mold and a cavity mold. In the mold, a steam hole is provided in a mold portion corresponding to an upper surface portion of the protrusion and a mold portion corresponding to one side surface portion of both side surfaces, and corresponds to another one side surface portion of both side surfaces. There is provided a mold for producing a polyolefin-based resin foam molded article, characterized in that the mold portion has no steam hole.

As the polyolefin resin used in the present invention,
Examples include polyethylene, polypropylene, copolymers thereof, copolymers with other monomers copolymerizable therewith, and mixtures thereof.

〔Example〕

Next, the present invention will be specifically described with reference to the drawings.

FIG. 1 is a sectional view showing an example of the mold of the present invention. FIG. 2 is a sectional perspective view of a portion corresponding to a protruding portion of the foam molded article of the mold shown in FIG.

In FIGS. 1 and 2, a plurality of steam holes 8a are provided in a mold portion 4a corresponding to the upper surface portion of the molded body projecting portion 2. Further, a steam hole is also provided in the mold portion 4b corresponding to one side surface portion of both side surfaces of the molded body projecting portion. But,
The mold portion 4c corresponding to the other side surface portion of both side surfaces has no steam hole.

The diameter and arrangement pitch of the steam holes provided in the mold portion 4a corresponding to the upper surface portion of the above-mentioned molded body projecting portion 2 and one side surface portion 4b of both side surfaces depend on the type of resin, the size of the molded body, and the like. However, although it is not possible to simply define it, it is preferable to arrange the core bends 12 having a diameter of 5 to 12 mm at a pitch of 7.5 to 30 mm. The steam holes are provided so that the opening ratio of the steam holes is 1 to 6%.
The steam hole opening ratio refers to a hole area ratio of the steam holes to an area of the upper surface portion 4a or the side surface portion 4b of the protrusion 2 of the molded body. Specifically, in FIG. 1, the mold is a cavity mold 3
And a core mold 4, and the mold cavity formed by both molds is filled with polyolefin resin foam beads 6 by a filling machine 5.

In order to perform foam molding using the mold of the present invention, at least one of the following one-side heating and one-side heating is required, followed by heating on both sides. In order to ensure heating, double-sided heating may be performed after reverse one-side heating and normal one-side heating.

In the case of reverse one-side heating, in FIG.
It is supplied to the core mold 4 from 10 and further discharged from the cavity side drain valve 11 through the steam holes 8, 8a and 8b. Here, as shown in FIG. 4, the steam at the time of the reverse one-side heating is formed such that the steam flowing from the steam hole 8a and the steam flowing from the steam hole 8b merge well without forming a vortex and form a stagnation portion. To flow, the air that was present between the beads before passing the water vapor is easily replaced by the water vapor. Therefore, the heating of the beads is performed uniformly.

In the one-side heating, steam is supplied from the cavity-side steam valve 7, and the cavity mold 3 is supplied through the steam hole 8.
From the core-side drain valve 9 through the core mold 4.

As shown in FIG. 5, the water vapor at the time of heating on the one side flows out from the vapor holes 8a and 8b, but also in this case, the water vapor does not form a vortex and flows well without forming a stagnation portion. As in the case of heating, heating of the beads is performed uniformly.

In the double-sided heating, both the cavity mold 3 and the core mold 4 are heated simultaneously with the cavity-side drain valve 11 and the core-side drain valve 9 closed.

In the double-sided heating, steam does not flow in the mold cavity, and the resin is heated by the heat of the mold, which can be said to be the finishing heating of the molding.

In the present invention, the molded article having a protruding portion is not limited to a partition plate, but includes a molded article having a surface having irregularities widely. Also, the present invention can be applied to the case of manufacturing a hollow molded body commonly called a core punch.

Hereinafter, advantages of the mold of the present invention will be clarified with reference to examples and comparative examples.

Example 1 Using a mold as shown in FIGS. 1 and 2, a partition box having a magnification of 20 times was molded under the following conditions. Table 1 shows the fusion rate, tensile strength, and water permeability of the periphery of the end of the obtained middle partition.

Raw material: Polyethylene foam beads (14x magnification) Molding impregnation internal pressure: 1.3Kg / cm ² G Molded form: 400mm long × 300mm wide × 100mm high × 20mm thick 20mm Middle partition plate shape: 260mm wide × 80mm high × meat Thickness 15mm Steam hole: Core vent 10mmφ, slit 0.3mm width (5 rows of slits) Steam hole arrangement pitch: 20mm Steam hole opening rate: Top 4.5%, side 3.4% Steam heating condition: positive one-way heating 0.3Kg / cm ² G3 sec. Reverse heating 0.5 kg / cm ² G5 sec. Double-sided heating 1.3 kg / cm ² 3 sec. Comparative Example 1 A molded body was obtained in the same manner as in Example 1 except that a mold as shown in FIG. 6 was used. Was. Table 1 shows the fusion ratio, tensile strength, and water permeability of the peripheral edge of the middle partition of the obtained molded article.

[Effects of the Invention] As is apparent from the above description, according to the present invention, the fusion of the peripheral portion of the tip of the projecting portion of the molded article is significantly improved, the strength is large, and the polyolefin resin foam molded article having a small water permeability is obtained. Can be manufactured, and the number of steam holes can be reduced as a whole to provide a mold having a low mold manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a mold for producing a polyolefin resin foam molded article of the present invention, FIG. 2 is a cross-sectional perspective view of a portion corresponding to a protruding portion of the mold in FIG. 1, and FIG. FIG. 4 and FIG. 5 are cross-sectional views showing an example of a molded article having a protruding portion, and FIG. 4 is a cross-sectional view of a portion corresponding to the protruding portion of the mold. FIG. FIG. 5 shows streamlines of water vapor at the time of heating on one side. FIG. 6 is a sectional perspective view showing a portion corresponding to a protruding portion of the mold used in Comparative Example 1. DESCRIPTION OF SYMBOLS 1 ... bottom part of molded object, 2 ... protrusion part of molded object, 3 ... cavity mold, 4 ... core mold, 5 ... foamed bead filling machine, 6 ... foamed bead, 7 ... cavity Side steam valve, 8: Steam hole, 9: Core side drain valve, 10: Core side steam valve, 11: Cavity side drain valve, 12: Core vent, 13: Drill hole

Claims (1)

(57) [Claims] 1. A mold for producing a foam molded article having a projection such as a partition plate by filling polyolefin resin foam beads in a mold cavity formed by a core mold and a cavity mold. A steam hole is provided in a mold portion corresponding to the upper surface portion of the protrusion and a mold portion corresponding to one side surface portion of both side surfaces, and a mold portion corresponding to another one side surface portion of both side surfaces. A mold for producing a polyolefin resin foam molded article, characterized in that the mold has no vapor holes.