JP2001145939A - Method for producing hollow resin molding having good appearance and mold device for the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a hollow resin molding having a good appearance without a weld mark on the surface of the molding which is applicable to bathtub products such as a grip and a bar for a bathtub and a mold device used in the method. SOLUTION: The mold device 1 used when the hollow resin molding having a recession part which is an insert nut embedding port is produced by injection molding is composed of a fixed mold 5 having a resin passage arranged from a sprue 7 to a cavity 12 by way of a runner gate 10, a core mold 11 having a gas injection means 13 for injecting gas into the cavity 12, and a movable mold 24 connected to the core mold 11. A slide pin 18 having a movement means 17 which can protrude/retreat into/from the cavity 12 is fitted to the core mold 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hollow resin molded article having good appearance and a mold apparatus used for the method.
More specifically, the present invention relates to a method for producing a hollow resin molded article having a good appearance without a weld mark on the surface and a mold apparatus used for the same, which is a hollow resin molded article applicable to bathtub products such as a bathtub grip and a bar. .

[0002]

2. Description of the Related Art As a conventional grip for a bath tub, a cast stainless steel product which does not easily generate rust has been used. In addition, recently, in order to reduce the weight, a resin in which a white filler or another pigment is added to a synthetic resin such as a polyamide resin or a modified PPE resin has been proposed. Particularly, in order to reduce the weight, a method is known in which a molten resin is poured into a mold cavity by a gas injection molding method, and a gas is injected before the resin is cured to make the inside of the molded body hollow. Have been. And
Since the product had to be attached to the bathtub body, an insert nut was previously attached to the molded body.
The place where this insert nut is installed is a concave portion.

[0003]

However, since the projections for forming the recesses are fixed to the mold, the projections hinder the flow of the molten resin at the time of casting, which is a major cause of weld marks. Had become. FIG. 3 shows a bottom view of the bathtub grip. The bathtub grip 30 is composed of an arch-shaped grip portion main body 31 and a pair of mounting surfaces 32.
Each has a recessed insertion hole 34 for the insert nut and one gas injection port 35, and a weld mark is generated from the vicinity of the insertion hole 34 of the insert nut in the flow direction of the resin. This weld mark is likely to be generated at a location where the molten resin is divided into two at the projection and merges again, and looks streaky in appearance.

The present invention has been made in view of the above points, and a method of manufacturing a molded article having good appearance without a weld mark on the surface of a hollow resin molded article applicable to bathtub products such as bathtub grips and bars. An object is to provide a mold device to be used.

[0005]

That is, the invention according to claim 1 of the present application is directed to a method for producing a hollow resin molded article having a concave portion, which is an embedding opening of an insert nut, by injection molding. After injecting into the cavity inside, project the slide pin at least close to the runner gate side to form the above concave part in the cavity, then inject gas and mold, then retreat the slide pin, hollow There is a method for producing a hollow resin molded article having a good appearance in which the resin molded article is released from the mold, and a slide pin at least near the runner gate side for forming the concave portion is projected to prevent the flow of the molten resin and the coalescence. To form a concave part by moving the slide pin back and then the slide pin to retreat. .

The invention according to claim 2 of the present application is a mold apparatus used for manufacturing a hollow resin molded article having a concave portion which is an embedding opening of an insert nut by injection molding, wherein a runner and a runner gate are formed from a spool. A fixed mold having a resin passage leading to the cavity via the core mold, a core mold having gas injection means for injecting gas into the cavity, and a movable mold connected to the core mold. In a mold apparatus equipped with a slide pin provided with a moving means capable of projecting and retracting.

[0007]

FIG. 1 is a sectional view of a mold apparatus according to the present invention. In the mold apparatus 1 of the present invention, the tip of the screw 4 installed in the cylinder 3 of the injection molding machine 2 is connected to the spool bush 6 provided on the fixed mold 5 and connected to the sprue 7 and the runner 8. This runner 8 is a fixed type 5
Provided in the core mold 1 via the runner gate 10.
1 to the cavity 12 formed between the two.

On the other hand, a gas injection means 13 for injecting a gas into the cavity 12 is provided in the core mold 11.
0, and immediately after the molten resin 9 of the cylinder 3 is injected into the cavity 12 via the sprue 7, the runner 8, and the runner gate 10, an inert gas such as nitrogen gas is introduced into the cavity 12. Send to In the gas injection means 13, the rear end of the gas nozzle 15 is connected to the gas supply path 16, and the front end is fixed to the core mold 11.

The core mold 11 is provided with a slide pin 18 provided with a moving means 17 which can protrude and retreat into the cavity 12. The slide pins 18 are provided for forming the recessed opening 34 for the tonut, and a pair of slide pins 18 including the runner gate 10 are provided. The slide pin 18 includes a moving means 17 for projecting and retracting into the cavity 12. The moving means 17 includes a pair of guide rods 20 connected to a slide plate 19 for moving the pair of slide pins 18 at the same time. 20, the piston 22 moves the slide plate 19 by the operation of the cylinder 21, and the slide pin 18 projects or retracts into the cavity 12. The movable mold 24 is connected to the core mold 11 and has the moving means 17 mounted thereon.

However, in the manufacturing method of the present invention, first, as shown in FIG.
The core mold 11 equipped with the gas injection means 13 and the slide pin 18 and the movable mold 24 equipped with the moving means 17 are clamped. The mold temperature at this time is adjusted to 20 to 80 ° C.
Thereafter, the synthetic resin is charged into the cylinder 3 of the injection molding machine 2 and melted, and the molten resin 9 is injected. Molten resin 9
Is sprue 7 to runner 8 and runner gate 1
0 and is fed into the cavity 12. The amount of the molten resin to be injected is set in consideration of the volume of the hollow portion of the molded body, but in the case of the present invention, 40 to 95% of the cavity volume
Is appropriate.

At this time, as shown in FIG. 1, the slide pin 18 is retracted so that nothing disturbs the flow of the molten resin 9 in the cavity 12 so that the molten resin 9 flows uniformly, thereby preventing the generation of a weld mark. .

Thereafter, as shown in FIG. 2, while the molten resin is not solidified, the moving means 17 moves to slide the slide pin 18 to form a concave embedding opening. Further, the gas injection means 13 is operated while the molten resin is not solidified, and an inert gas such as nitrogen gas is sent from the gas nozzle 15 into the molten resin. To form a hollow resin molded article having good appearance without weld marks. According to the present invention, even if the slide pin 18 is inserted to form a recess which occupies a relatively large volume, which is an embedding opening of the insert nut, the gas is injected thereafter, so that there is no problem such as sink marks.

The transparent synthetic resin used here includes:
Polypropylene resin, acrylic resin, polyamide resin,
ABS resin, polyethylene terephthalate resin, polycarbonate resin and the like can be mentioned.

Further, a flat glittering material can also be added. The glitter material has a particle size of 20 to 300 μm, and is added in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the transparent synthetic resin. Further, as the glitter material, aluminum flake having a particle size of 20 to 100 μm or a particle size of 50 to 100 μm can be used.
A glass flake coated with a metal having a thickness of 300 μm. The aluminum flake has a rounded shape made of weld-improved aluminum. For example, there is a METAX G type (particle size: 60 μm) manufactured by Toyo Aluminum.
On the other hand, the metal-coated glass flakes are obtained by sputtering an alloy of silver and tin on the surface. If the added amount of the flat glittering material is less than 0.1 part by weight, no glitter and heavy feeling will appear, while if it exceeds 5 parts by weight, the fluidity of the molten resin is impaired, and the glittering material becomes uniform. Plane orientation is lost. In the present invention, a pigment or the like can be added in addition.

[0015]

The present invention will be described in more detail with reference to the following examples. Example 1 To 100 parts by weight of a polypropylene resin, 0.5 parts by weight of aluminum flake METAX G type (particle size: 60 μm) (manufactured by Toyo Aluminum Co., Ltd.), 0.4 parts by weight of a stabilizer, 0.04 parts by weight of a pigment, and 0.1 part by weight of a dispersant. 5 parts by weight were added, mixed well, and melt-kneaded with a twin-screw extruder to prepare pellets. The mold apparatus shown in FIG. 1 was mounted on an injection molding machine, and the pellets were charged into a screw and melted, and the molten resin was injected into the cavity. Injected resin amount is 55% of cavity volume
Was adjusted to. At this time, the slide pin was retracted from the inside of the cavity. Immediately after the injection molding, the slide pin was protruded, and before the molten resin in the cavity was solidified, nitrogen gas was fed into the molten resin from a gas nozzle to complete the molding. The obtained molded body was a hollow body having a gas passage formed substantially in the central region, a concave portion serving as an insertion hole for an insert nut was formed on the bottom surface, and no weld mark was observed.

Comparative Example 1 As Comparative Example 1, the same molding method as in Example 1 above was used, except that a mold apparatus and pellets were used, and injection molding was performed with the slide pins protruding into the cavity, and nitrogen gas was not injected. A resin molded body was formed. On the surface of the obtained molded body,
A clear weld mark was observed in the vicinity of the recess, which is the embedding opening of the insert nut.

[0017]

As described above, according to the invention as claimed in the present application, after injecting the resin composition into the cavity in the mold, at least the slide pin near the runner gate side for molding the concave portion in the cavity is formed. After projecting and subsequently injecting gas for molding, the slide pin is retracted and the hollow resin molded article is released from the mold. It is a mold device, projecting a slide pin near at least the runner gate side for forming the recess, shunting the molten resin, preventing coalescence, making it flow evenly, further forming the recess by retracting the slide pin, There is an effect that a hollow resin molded article having no weld mark and having a good appearance can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a mold apparatus according to the present invention, showing a state immediately after a slide pin is retracted and molten resin is injected into a cavity.

FIG. 2 is a cross-sectional view of the mold apparatus according to the present invention, showing a state in which a slide pin is protruded immediately after a molten resin is injected into a cavity.

FIG. 3 is a bottom view of a conventional bathtub grip.

[Explanation of symbols]

 Reference Signs List 1 mold apparatus 2 injection molding machine 5 fixed mold 7 sprue 8 runner 10 runner gate 11 core mold 12 cavity 13 gas injection means 15 gas nozzle 17 moving means 18 slide pin 24 movable mold

Claims (2)

[Claims] 1. A method of manufacturing a hollow resin molded body having a concave portion which is an embedding opening of an insert nut by injection molding, after injecting a resin composition into a cavity in a mold, the concave portion is formed in the cavity. The method is characterized in that at least a slide pin near the runner gate side for projecting is protruded, and then the gas is injected and molded, the slide pin is retracted, and the hollow resin molded body is released from the mold. A method for producing a hollow resin molded article having a good appearance. 2. A mold device used for manufacturing a hollow resin molded body having a concave portion, which is an embedding opening of an insert nut, by injection molding. The resin device extends from a spool to a cavity via a runner and a runner gate. A fixed mold having a passage, a core mold having gas injection means for injecting gas into the cavity, and a movable mold connected to the core mold, wherein the core mold projects into the cavity,
A mold device comprising a slide pin provided with a moving means capable of retreating.