JPH0457175B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a molding die used for manufacturing precision molded products such as magnetic disk substrates.

(Prior Art) Generally, extremely high precision display smoothness is required for substrates for magnetic disks and optical disks. Therefore, when manufacturing these substrates by injection molding, when injecting the resin into the cavity, the fixed mold and the movable mold are heated to heat the molding surface above the resin solidification temperature to prevent the resin from entering the cavity. After the resin is sufficiently distributed, each mold is cooled to solidify the resin and then released from the mold.

One of the above-mentioned heating methods uses induction heating as disclosed in Japanese Unexamined Patent Publication No. 57-4748. The above publication discloses two types of methods. That is, in the first method, before injecting the resin, a metal body (hereinafter referred to as an inductor) having a coil connected to a high-frequency oscillator is sandwiched between a movable mold and a fixed mold, and a high-frequency current is applied to the coil. After heating the molding part by high-frequency induction heating,
The method is to open the mold, remove the inductor, close the mold again, and inject the resin into the cavity.The second method is to embed the inductor in the back of the molding part of the movable mold and the fixed mold, respectively. In this method, each molding surface is heated by high-frequency induction heating while the mold is closed, and resin is injected into the cavity.

(Problems to be Solved by the Invention) However, each of the above induction heating methods has the following problems.

In the first method, the work of attaching and removing the inductor is necessary before injecting the resin, which is complicated, and the heated molding part is heated while injecting the resin after removing the inductor. The disadvantage was that it was cooled.

In the second method, since the inductor is in direct contact with the molded part, induction heating is applied not only to the molded part of each mold but also to the inductor.
The heat capacity was large, and heating and cooling took a long time, resulting in poor productivity.

(Means for Solving the Problems) This invention has been made to solve the above problems, and its gist is to have a molded part made of metal constituting the cavity, and a non-metallic molded part on the back of the molded part. The molding die is characterized in that a heat insulating part made of aluminum is formed, a cooling passage is provided on the molding part side of the heat insulating part, and an induction heating coil is arranged at the back of the heat insulating part.

(Function) When a high frequency current is passed through the induction heating coil, an induced current is generated in the molded part, and the molded part is heated by induction. Since the heat insulating part interposed between the coil and the molded part is made of nonmetallic material, no induced current is generated and the heat insulating part is not heated. This heat insulating part blocks heat transfer to the back part more than the heat insulating part. Therefore, only the molded part is efficiently heated in a short time.

Further, after the resin is injected into the cavity in the heated state, the induction heating is stopped, and the molded part is cooled by circulating a refrigerant in the cooling passage, thereby cooling the resin in the cavity. At this time, since the refrigerant almost directly contacts the molded part, the molded part and the resin are quickly cooled.

Therefore, the time required for heating and cooling cycles of the molding section can be shortened, and productivity is improved.

(Embodiment) Hereinafter, an embodiment of the present invention will be described based on the drawings from FIG. 1 to FIG. 3.

In FIG. 1, reference numeral 20 denotes a molding unit of a molding die, and the molding unit 20 has a cylindrical ring core 1 made of metal. ring core 1
A step portion 1a is formed at the outer peripheral end of the step portion 1a, and a protrusion portion 1b protrudes toward the center on the same side as the step portion 1a.
is formed.

A heating plate 2 is fitted onto the center side of the projection 1b of the ring core 1. The heating plate 2 is made of metal, has a disk shape, is thicker than the projection 1b, and has a hole 2a formed in the center.

The ring core 1 and the heating plate 2 have their right surfaces flush with each other in FIG. 1, and each right surface has a mirror finish and has extremely high precision smoothness.

The ring core 1 and the heating plate 2 constitute a molding section, and the right surfaces of the ring core 1 and the heating plate 2 serve as the molding surface 3.

Furthermore, inside the ring core 1, on the back of the heating plate 2 (on the left side of the heating plate 2 in FIG. Heating plate 2 by bolt 5
is fixed.

Ceramics (SiC), which is the material of the heat insulating member 4, has excellent mechanical strength, impact resistance, and thermal shock resistance, low high frequency absorption, and furthermore, has low heat conductivity, high insulation properties, and free machinability. .

The heat insulating member 4 has a disk shape, and a hole 4a having the same diameter as the hole 2a of the heating plate 2 is formed in the center. In the heat insulating member 4, an inner groove 6a and an outer groove 6b having a U-shaped cross section are formed concentrically on the side in contact with the heating plate 2. As shown in FIG. 2, the outer groove 6b is separated into left and right parts at the upper and lower parts of the figure, and the inner groove 6a is separated into left and right parts at the lower part of the figure. The outer groove 6b and the inner groove 6a are connected to each other at the left and right lower portions.

The inner groove 6a and the outer groove 6b are made into a closed cross section by the heating plate 2, and the inside thereof becomes a cooling passage 7.

Furthermore, as shown in FIG. 2, the ring core 1 and the heat insulating member 4 have a refrigerant inlet passage 8a and a refrigerant outlet passage extending from the upper outer circumferential surface of the ring core 1 toward the center and reaching the left and right upper ends of the outer groove 6b. 8b is formed. The refrigerant inlet passage 8a and the refrigerant outlet passage 8b are connected to a refrigerant supply device (not shown), and the refrigerant flowing through the cooling path 7 is controlled to a desired temperature by a temperature control device (not shown). .

The heat insulating member 4 has O-ring grooves 4b, 4 in a portion facing the inner end of the heating plate 2 and a portion facing the outer end.
O-rings 9a and 9b are attached to the respective O-ring grooves 4b and 4c to seal the refrigerant flowing through the cooling passage 7.

Furthermore, inside the ring core 1, on the back of the heat insulating member 4 (on the left side of the heat insulating member 4 in FIG. 1), a copper pipe 10 serving as an induction heating coil is arranged in a spiral shape. One end 10a on the outermost side and one end 10b on the innermost side of 10 are connected to a high frequency oscillator (not shown). copper pipe 10
An insulating member 11 is fixed to the back (the left side of the copper pipe 10 in FIG. 1) and the upper and lower parts of the insulating member 11, and the center of the insulating member 11 also has a hole 11 having the same diameter as the hole 2a of the heating plate 2.
a is formed.

A pair of molding unit units 20 are prepared and fixed to fixed and movable bases (none of which are shown) with their molding surfaces 3 facing each other.

Note that the heating plate 2, the heat insulating member 4, and the holes 2a, 4 in the insulating member 11 of the fixed molding unit 20 are
A sprue bush (not shown) is inserted and fixed in a and 11a, and each hole 2 of the heating plate 2, the heat insulating member 4, and the insulating member 11 of the movable molding unit 20
a, 4a, 11a have center cores (not shown)
The insertion has been fixed.

When the fixed mold and the movable mold are closed, a cavity (not shown) is formed between the molding surfaces 3 of both molding unit units 20.

A case will be described in which a magnetic disk substrate is molded in the above configuration.

Close the fixed mold and movable mold to form a cavity.
Oil as a refrigerant is passed through the cooling passage 7, and the molding surface 3 of each molding unit 20 is heated to 130°C. At this time, since the oil is in direct contact with the heating plate 2, heat transfer between the refrigerant and the heating plate 2 occurs extremely quickly. Heat is also transferred to the ring core 1 via the contact surface between the heating plate 2 and the ring core 1. On the other hand, since the heat insulating member 4 is made of ceramics having a low heat transfer coefficient, heat does not diffuse further to the back than the heat insulating member 4.

Next, the flow of oil is stopped, and a high-frequency current with an output of 15 Kw and 400 kHz is passed through the copper pipe 10 using a high-frequency oscillator to generate an induced current in the ring core 1 and the heating plate 2, so that each molding surface 3 reaches 200°C. Induction heating is performed to achieve this. At this time, no induced current is generated in the heat insulating member 4 made of nonmetallic ceramics and the oil in the cooling passage 7, and the insulating member 4 and the oil are not heated by induction. That is, since only a limited portion of the ring core 1 and the heating plate 2 are heated by induction, heating can be performed quickly. Furthermore, the presence of the heat insulating member 4 prevents heat from diffusing toward the back side of the ring core 1 and the heating plate 2.

In this example, the temperature of the molding surface 3 is
The time required to raise the temperature from 130°C to 200°C was 5 seconds.

Then, resin is injected into the cavity while the molding surface 3 is maintained at 200° C. by induction heating. At this time, since the molding surface 3 is at an extremely high temperature higher than the resin solidification temperature, the resin maintains high fluidity and flows to every corner of the cavity, coming into close contact with the molding surface 3.

Thereafter, the flow of high frequency current to the copper pipe 10 is stopped, and oil is made to flow in the cooling passage 7 to cool each molding surface 3 to 130° C. again. This cooling solidifies the resin.

Then, the fixed mold and the movable mold are opened and the solidified product inside the cavity is taken out.

In this example, the time required from the start of induction heating to the time of product removal was approximately 60 seconds.

The magnetic disk substrate formed in this manner had an extremely smooth surface and had extremely little distortion such as warping or deformation.

The graph in FIG. 3 shows the temperature change over time of the molding surface 3 in the above example, and the vertical axis represents the temperature of the molding surface 3, and the horizontal axis represents time. In the figure, point A is the starting point of induction heating, point B is the starting point of resin injection, and point C is the point of product removal.

This invention is not limited to the above-mentioned embodiments, and various embodiments are possible.

For example, the heat insulating part may be made of ceramics such as Al ₂ O ₃ , SiN, C, etc., it may also be made of plastics instead of ceramics, or it may be made of a layered structure of ceramics and plastics. It may also be a composite material.

In addition, on the surface of the heat insulating part, a layer of 5 μm or more is applied by vapor deposition, sputtering, ion plating, etc.
A thin metal film having a thickness of 20 mm may be formed and this thin metal film may be used as the molded part. In this case, the cooling passage may be provided in the form of a tunnel as close as possible to the metal thin film inside the heat insulating section.

Furthermore, the refrigerant flowing through the cooling passage may be water or steam.

(Effects of the Invention) As explained above, according to the present invention, since the non-metallic heat insulating part is formed between the metal molded part and the induction heating coil, the molded part to be subjected to induction heating is can be made extremely small, and as a result, the heat capacity can be made small. Furthermore, the heat insulating portion can prevent heat from dispersing to the back. Therefore, the molding part can be heated extremely efficiently and in a short time.

Further, since the cooling passage is provided on the molding part side of the heat insulating part and the refrigerant comes into almost direct contact with the molding part, the molding part can be cooled extremely efficiently and in a short time.

As a result, the time required for heating and cooling cycles of the molding section can be shortened, and productivity can be improved.

Further, when injecting the resin into the cavity, the temperature of the molding part can be maintained at a temperature higher than the resin solidification temperature, so that extremely high quality products can be molded.

[Brief explanation of the drawing]

The drawings from FIG. 1 to FIG. 3 show one embodiment of the present invention, and FIG. 1 is a cross-sectional view of FIG. 2, FIG. 2 is a front view of the main part of the mold, and FIG. is a graph showing the temperature transition of the molded part. DESCRIPTION OF SYMBOLS 1...Ring core (molded part), 2...Heating plate (molded part), 4...Cross section, 7...Cooling passage, 10
...Induction heating coil.

Claims (1)

[Scope of Claims] 1 It has a metal molded part constituting the cavity, a non-metallic heat insulating part is formed on the back of the molded part, a cooling passage is provided on the molded part side of the heat insulating part, and the heat insulating part A molding die characterized in that an induction heating coil is placed on the back of the mold. 2. The molding die according to claim 1, wherein the heat insulating part is made of ceramics. 3. The molding die according to claim 1, wherein the heat insulating part is made of plastic. 4. The molding die according to claim 1, wherein the heat insulating portion is made of a layered composite material of ceramics and plastics.