JP2966130B2 - Injection molding method and injection mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method using an injection mold having a gate and an injection mold.

[0002]

2. Description of the Related Art In order to manufacture a large-sized molded product or to set a welding position, that is, a weld line, of a flow of a molten resin in a molded product to a desired position, a plurality of cavities are formed in one molded product. There is a molding method of supplying a molten resin from a gate of the apparatus. In a conventional injection mold having a plurality of gates, a sprue, a hot runner and a gate are provided in a hot runner block forming a resin passage, and a valve opening / closing device for opening / closing the gate is provided at a fixed portion of the injection mold. The valve body is mounted so that the valve body is slidably penetrated through the hole of the hot runner block to reach the gate (see Japanese Patent Application Laid-Open No. 59-169827).

[0003]

However, there is a problem that it is difficult to form a hollow molded article having a uniform thickness by the above method. That is, since the molten resin is supplied from a plurality of gates, the molten resin tends to be biased to one side when air is blown, and it has been difficult to produce a hollow molded article having a uniform thickness. As a method for molding a hollow molded article, a method having a hot runner block is not described.
There is one as shown in Japanese Patent Publication No. The molding die has a resin passage and a gas passage that reach the inside of the cavity. The molten resin is injected into the cavity through the resin passage of the mold. Next, gas is blown into the molten resin through the gas passage. Thereby, a hollow molded article can be formed. However, according to this method, the pressure of the blown gas may cause the molten resin in the cavity to be pushed back to the resin passage, so that the weight of the molded product is reduced below a predetermined value or the molded product having a predetermined thickness is formed. There are problems such as not being able to obtain. An object of the present invention is to solve such a problem.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems by providing a gas passage in a valve body for opening and closing each gate so that gas can be supplied into the molten resin of the cavity from the gas passage. That is, in the injection molding method of the present invention, the openable gate is opened, the molten resin is injected into the mold cavity from the hot runner, then the gate is closed, and the cavity is melted from the gas passage of the valve body that opens and closes the gate. A hollow molded article is injection molded by injecting a gas into the resin. The apparatus for performing the above method is a fixed type (30).
And a movable mold (32) and a hot runner block (40) provided on the fixed mold (30) side, for supplying molten resin to a cavity (C) for molding a molded product. A plurality of gates (G) are connected to the hot runner block (4
0), a valve element (26) for opening and closing the gate (G) is provided on the fixed mold (30) side, and the valve element (26) has a gas passage penetrating in the axial direction. (26
c) is formed, and a gas supply device (28) connected to the gas passage (26c) is provided. With the gate (G) closed, the valve ( Gas can be supplied into the molten resin of the cavity (C) through the gas passage (26c) of 26). In addition, the code | symbol in a parenthesis shows the corresponding member of an Example.

[0005]

With the valve body for opening and closing the gate of the hot runner block positioned at the gate open position, the molten resin is injected into the mold cavity through the hot runner. Next, by closing the valve body to the gate closed position, the space between the gate and the cavity is shut off. Next, a gas such as air is blown into the molten resin of the cavity through the gas passage of the valve body. As a result, the molten resin in the cavity does not flow backward to the hot runner side, that is, a hollow molded article having a predetermined thickness with almost no decrease in weight is formed.

[0006]

FIG. 1 shows a first embodiment of the present invention. Fixed type 3
0 and the movable mold 32 are in contact with each other on the mold parting surface. A cavity C is formed by the fixed mold 30 and the movable mold 32. A hot runner block 40 is fitted to the fixed mold 30. In the hot runner block 40, a sprue 40a, a hot runner 40b, and a gate G are formed as resin passages. Gate G
Can be opened and closed by a valve body 26 described later. Cylinder holes 30a are respectively formed at left and right positions in the figure of the fixed mold 30, and holes 40c are respectively formed at right and left positions of the hot runner block 40 in the figure. The valve element 26 is disposed through these holes. ing. That is, the piston 26a, the valve 26b, the gas passage 2
6c and the like are formed, and the piston portion 26a is movably fitted into the cylinder hole 30a of the fixed die 30,
The piston rod on the lower side of the piston portion 26a in the drawing is
The hot runner block 40 is movably fitted to the hole 40c. The gas passage 26 c penetrating in the axial direction of the valve body 26 is connected to an air source 28. The valve element 26 is
In the illustrated closed position, the gate G is closed to shut off the space between the hot runner 40b and the cavity C, and gas can be supplied from the air source 28 into the cavity C through the gas passage 26c. At the open position where the valve body 26 is retracted upward in the drawing, the gate G is opened to communicate between the hot runner 40b and the cavity C. Cylinder hole 30
a can be supplied with forward air pressure from the air pressure passage A, and can be supplied with backward air pressure from the air pressure passage B. Between the upper surface of the portion of the hot runner block 40 where the hot runner 40b is formed and the fixed die 30, and between the lower surface of the portion of the hot runner block 40 where the hot runner 40b is formed and the fixed die 30. , A ring-shaped heat insulating member 42 and a heat insulating member 20 are provided. As a result, the fixed mold 30 reduces heat conduction from the hot runner block 40. Next, the operation of the first embodiment will be described. The molds 30 and 32 are closed and clamped by a mold clamping device (not shown). Air pressure is introduced from the air pressure passage B to move the valve body 26 to an open position above the illustrated closed position. That is, the gate G is opened. Thus, the molten resin is injected into the cavity C through the sprue 40a, the hot runner b, and each gate G. That is, the molten resin is injected into the cavity C from each gate G in a lump. After the completion of the injection of the molten resin, the air pressure in the air pressure passage B is released, and the air pressure is introduced from the air pressure passage A to move the valve body 26 to the illustrated closed position. That is, the gate G is closed. Next, air pressure is supplied from the air source 28 into each molten resin of the cavity C through each gas passage 26c. As a result, each molten resin expands in a hollow shape, and the boundaries come into contact with each other. This allows the ribs 44 to be
Is formed. After cooling both molds 30 and 32, the molds are opened and a hollow molded article having ribs 44 is taken out. By repeating the above operation, there is no variation in weight,
A hollow molded article having a uniform thickness can be repeatedly molded.

FIG. 2 shows a second embodiment of the present invention. The difference of the second embodiment from the first embodiment is that independent cavities C corresponding to the respective gates are formed, thereby making it possible to take a large number of hollow molded products. is there. The hollow molded article obtained by this has a shape without ribs inside. Other operations are the same as those of the first embodiment.

FIG. 3 shows a third embodiment of the present invention. This mold includes a fixed mold 36 and a movable mold 38.
The fixed die 36 is fixed to a fixed mounting plate 34 via a ring member 16 to be described later, and the movable die 38 is fixed to a movable mounting plate (not shown). Fixed mounting plate 3
4 is fitted with a cylindrical portion of the hot runner block 10. In the hot runner block 10, a first hot runner 10b is formed as a resin passage. The first hot runner 10b is connected to the sprue 10a. The first hot runner 10b is formed of a portion arranged parallel to the mold parting surface and an opening orthogonal to the part and opening to the lower surface in the figure. Hot runner block 1
0 is formed with holes 10c, and a valve opening / closing device 12 described later is fitted to these holes with a radial gap H. The ring-shaped ring member 16 is provided between the fixed mold mounting plate 34 and the fixed mold 36, and the hot runner block 10 and the valve opening / closing device 12 are arranged in the cylindrical hole of the ring member 16. Hot runner block 10
A gate bush 14 is provided on the lower surface in the figure at a position facing the opening of the first hot runner 10b. The gate bush 14 has a stepped cylindrical shape and has a fixed mold 3
6 are arranged with a predetermined radial clearance. The gate bush 14 is formed with a resin passage 14a that communicates the resin chamber 14b provided therein with the first hot runner 10b. Resin chamber 14b and resin passage 1
4a forms a second hot runner. A gate G is formed below the gate bush 14 in the drawing. The gate G is open to a cavity C formed between the fixed die 36 and the movable die 38. The hot runner block 10 and the gate bush 14 are merely pressed against each other on a surface parallel to the mold parting surface, and can relatively move on this surface. A ring-shaped heat insulating member 18 is provided between the gate bush 14 and the fixed mold 36. This allows
The gate bush 14 is configured to reduce heat conduction to the fixed mold 36. The valve opening / closing device 12 is fixed to the fixed mounting plate 34. The valve opening / closing device 12 includes a gas passage 12
d forming a valve element 12c, a piston 1 capable of driving the valve element 12c
2b and a cylinder 12a accommodating the piston 12b. The valve body 12c can close the gate G at the illustrated closed position, and can supply air from the air source 28 into the molten resin of the cavity C through the gas passage 12d of the valve body 12c. In the open position where the valve element 12c is retracted upward in the drawing, the gate G is opened and the resin chamber 14 is opened.
b communicates with the cavity C. A heat insulating material (not shown) is provided between the lower surface of the hot runner block 10 in the figure and the upper surface of the fixed mold 36 as in the first embodiment. An air pressure passage A is provided at the upper end side of the cylinder 12a in the drawing.
Forward air pressure can be supplied from the
The backward air pressure can be supplied from the air pressure passage B to the lower end side in FIG. In addition, a ring-shaped heat insulating member 22 is provided on a surface of the cylinder 12a in contact with the hot runner block 10. As a result, the valve opening / closing device 12 reduces heat conduction from the hot runner block 10. A sealing member 24 for sealing the first hot runner 10b and the resin passage 14a is provided on the mating surface of the hot runner block 10 and the gate bush 12. Next, the operation of the third embodiment will be described. The air pressure is introduced from the air pressure passage B and the valve body 12 of the valve
c is moved to an open position above the closed position shown. That is, the gate G is opened. As a result, the molten resin is injected into the cavity C through the sprue 10a, the hot runners 10b, 14a, 14b, and the gate G. After the injection of the molten resin is completed, the air pressure in the air pressure passage B is released, and air pressure is introduced from the air pressure passage A to move the valve body 12c to the illustrated closed position. That is, the gate G is closed. Next, air source 2
From 8, air pressure is supplied into the molten resin of the cavity C through the gas passage 12 d. As a result, the molten resin expands in a hollow shape, and a hollow molded product is formed. After cooling both the molds 36 and 38, the molds are opened and the molded product is taken out. By repeating the above operation, it is possible to repeatedly mold a hollow molded product having a uniform thickness without any variation in weight. In this embodiment, the valve opening / closing device 12
Are arranged so as to be hardly affected by heat, so that the gate G can be stably opened and closed. In the above description, the valve 26 (or the valve 12c) is moved to the closed position after the molten resin has been injected into the cavity C. However, the hot runner 40b (or the hot runner 10b) is The injection pressure may always be applied, and the gate G may be closed when a predetermined amount of molten resin is supplied into the cavity C. In the description of the second embodiment, one gate G is provided for one cavity C.
However, for one cavity C, 2
One or more gates G can be provided.

[0009]

As described above, according to the present invention, it is possible to mold a molded article having a predetermined thickness with a hollow inside. The molded article can be of uniform weight with little weight loss. Also, a large number of molded articles can be molded simultaneously.

[Brief description of the drawings]

FIG. 1 is a sectional view of a molding die according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a molding die according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a molding die according to a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 hot runner block 10b hot runner 12 valve opening / closing device 12a cylinder 12b piston 12c valve body 12d gas passage 14 gate bush 14a resin passage (hot runner) 14b resin chamber (hot runner) 26 valve body 26c gas passage 28 air source (gas supply) Equipment) 30 Fixed type 32 Movable type 36 Fixed type 38 Movable type 40 Hot runner block 40b Hot runner

Claims (6)

(57) [Claims] An openable gate is opened, molten resin is injected from a hot runner into a mold cavity, and then the gate is closed and gas is introduced into the molten resin from the gas passage of a valve body that opens and closes the gate. Injection molding method for molding a hollow molded product by injecting a liquid. 2. The injection molding method according to claim 1, wherein the hot runner is always kept in a pressurized state, and the injection of the molten resin is terminated by closing the gate. 3. A fixed mold (30), a movable mold (32),
A hot runner block (40) provided on the fixed mold (30) side, and a plurality of gates (G) for supplying molten resin to a cavity (C) for molding a molded product are provided. In an injection molding die formed on a block (40) and provided on a fixed die (30) side for opening and closing the gate (G), the valve (26) has a shaft. Gas passage (26)
c) is formed, and a gas supply device (28) connected to the gas passage (26c) is provided. With the gate (G) closed, the valve ( 26) An injection mold capable of supplying gas into the molten resin in the cavity (C) through the gas passage (26c). 4. An injection mold having a plurality of gates (G) for supplying a molten resin to a cavity (C) for molding a molded product, wherein a hot runner block (10) is provided on a fixed mold (36) side. A gate bush (14) and a valve opening / closing device (12) are provided, and the hot runner block (10) is overlapped with the gate bush (14) on a plane parallel to the mold parting surface, and relatively moves on this surface. It is possible to use the sprue (1) of the hot runner block (10).
0a) to the gate (G) of the gate bush (14) includes the first hot runner (10b) on the hot runner block (10) side and the gate bush (1).
The first hot runner (10b) is formed of the second hot runner (14a and 14b) on the 4) side. One opening of the first hot runner (10b) communicates with the sprue (10a), and the other opening is the hot runner block (10). The second hot runner (14a and 14b) has one opening communicating with the opening of the first hot runner (10b).
The other opening communicates with a gate (G) provided on the gate bush (14), and a valve opening / closing device (12) for opening and closing the gate (G) penetrates the hot runner block (10), The valve body (12c) extends to the gate (G) of the gate bush (14), and the fitting of the valve opening / closing device (12) with the hot runner block (10) is performed by the axial center of the valve body (12c). The valve body (12c) is formed with a gas passage (12d) penetrating in the axial direction, and the gas connected to the gas passage (12d) is formed in the valve body (12c). A supply device (28) is provided. When the gate (G) is closed, the gas (28) is melted from the gas supply device (28) through the gas passage (12d) of the valve body (12c). Injection molding that can supply gas into resin . 5. The fixed type (36) is provided with a fixed type mounting plate (3).
The valve opening / closing device (12) fixed to 4) comprises a valve (12c), a piston (12b) capable of driving the valve (12c), and a cylinder (12a) accommodating the piston (12b). 5. The injection mold according to claim 4, wherein the mold is fixed to a fixed mold mounting plate (34). 6. The injection mold according to claim 3, wherein a plurality of cavities (C) are formed, and the number of gates (G) is equal to or greater than the number of cavities (C).