JP4059008B2 - Press molding method and press molding apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a press molding method and a press molding apparatus, and more particularly, to a press molding method and a press molding apparatus suitable for manufacturing a glass substrate or the like applied to a magnetic disk or the like.
[0002]
[Prior art]
Conventionally, magnetic disks including substrates made of raw materials such as glass and plastic have been widely used. Since such a magnetic disk substrate is required to have a very smooth surface, it is initially manufactured by cutting a glass material or the like into a predetermined size and polishing the surface smoothly. It was. However, the method of manufacturing the substrate for the disk one by one in this way requires a large number of steps and labor, and has a big problem in reducing the manufacturing cost of the substrate. For this reason, in recent years, when a substrate is manufactured, a press molding method is employed in which a raw material such as glass is heated and pressurized in a mold to transfer a desired shape to the raw material with high accuracy. It has become to.
[0003]
Such a press molding method is generally performed according to the following procedure. First, a glass material or the like as a raw material is disposed between the upper and lower molds (between the fixed mold and the movable mold). Then, in order to prevent so-called air stagnation in which the surrounding gas is trapped on the surface of the molded product and oxidation of the mold, the periphery of the mold or the like is decompressed to be in a vacuum state. Further, the mold and the raw material are heated by a predetermined heat source, and when the mold and the raw material reach a predetermined temperature, the raw material is pressurized between the molds. And after pressurization completion, a molded article is cooled and taken out from a metal mold | die. According to such a press molding method, post-processing for the molded product is not required, and a high-quality substrate can be produced at low cost.
[0004]
By the way, in the case of press molding a substrate for a disk whose ratio between the outer diameter and the plate thickness is finally increased, the flatness is improved by suppressing the undulation of the substrate surface, and the undulation on the same radius is suppressed. In order to improve the dimensional accuracy of the inner and outer diameters of the substrate, it is extremely important to sufficiently control the temperature of the raw material during the pressing process. However, it is practically difficult to actually measure the temperature of the raw material during press molding. For this reason, in press molding, the temperature of the mold is generally measured and used as a reference for determining various parameters.
[0005]
[Problems to be solved by the invention]
Here, as described above, in order to prevent the so-called air accumulation or the oxidation of the mold, in which the surrounding gas is trapped on the surface of the molded product, the periphery of the mold or the like is depressurized to be in a vacuum state. It is effective to do. However, when the raw material is heated under reduced pressure, the temperature of only the raw material rises rapidly due to the difference in heat capacity between the raw material and the mold, the magnitude of the thermal resistance between the two, and the like between the raw material and the mold. It is considered that a temperature difference often occurs.
[0006]
In addition, when the raw material is heated under reduced pressure, it may take a long time to raise the temperature of the raw material to the softening temperature due to the small amount of gas components that serve as a heat conducting medium. The pressurization process may be started before it is sufficiently heated. These phenomena are caused by the point contact between the mold and the raw material microscopically during the pressurizing process, and become more noticeable as the atmospheric pressure is smaller. This often occurs when spherical or marble shaped raw materials are used.
[0007]
As described above, conventional press molding still has problems in terms of temperature management of raw materials and molds, such as causing a temperature difference between the raw material and the mold. It was difficult to execute at low cost.
[0008]
Accordingly, an object of the present invention is to realize press forming that enables temperature control during molding to be performed easily and accurately, and a highly accurate molded product can be obtained at low cost.
[0009]
[Means for Solving the Problems]
One aspect of the present invention is a press molding method for producing a desired molded product by heating and pressurizing raw materials between molds. This method includes (a) radiant heating of a mold and raw materials in a vacuum state. And a step of pressurizing the raw material with a preliminary load lower than a predetermined original press load, and a step of pressurizing the raw material with a press load after step (a).
[0010]
In this method, in order to obtain a desired molded product by press molding, the mold and the raw material are radiantly heated under a vacuum state. As described above, when the mold and the raw material disposed between the molds are radiantly heated, the heat capacity of the raw material such as glass or plastic is basically smaller than the heat capacity of the mold. The temperature rises quickly and reaches the glass transition point in a relatively short time. Here, if radiation heating is continued in a vacuum state without taking any countermeasures as it is, due to the fact that there are few gases serving as a heat conduction medium around the mold and the raw material, the raw material and the mold It takes a long time until the temperature becomes approximately isothermal.
[0011]
In view of this point, in this method, when the mold and the raw material are heated, the raw material is pressed through the mold with a relatively small preload lower than the original press load. Thereby, when the raw material pressed with the preload reaches the glass transition point, the raw material is smoothly adhered to the mold surface. As the adhesion between the mold and the raw material progresses, the thermal conductivity between the two increases. Therefore, the temperature of the raw material and the mold temperature are determined by pressing with a preload after starting heating by the radiant heater. Compared with the case where no heat treatment is performed, the temperature becomes approximately isothermal in a short time.
[0012]
Thus, in the present invention, since the mold and the raw material become substantially isothermal in a short time during the step (a), the temperature control in the step (b) is based on only the mold temperature. Is easily and accurately executed. As a result, according to the present invention, the temperature of the raw material at the time of molding can be easily and accurately controlled, and a molded product having high dimensional accuracy, flatness, smoothness, etc., with suppressed distortion and warpage can be produced. it can. Further, in the present invention, no special and expensive temperature measuring means or the like is required for temperature control of the mold and the raw material, so that a highly accurate molded product can be obtained at low cost. Furthermore, since the step (a) is completed in a relatively short time, according to the present invention, the press molding cycle itself can be shortened.
[0013]
In this case, preload is a load range of a fractured such have 1 0～1000MPa raw materials before reaching the glass transition point, and to improve the adhesion to the mold raw material after reaching the glass transition temperature It is preferable that the load range is selected.
[0014]
This method is particularly suitable for forming a substrate or the like of a storage medium disk in which the ratio of the outer diameter to the plate thickness is finally increased.
[0015]
Another embodiment of the present invention is a press molding apparatus for producing a desired molded product by heating and pressurizing the raw material between the molds, and this apparatus includes a vacuum means for making the mold periphery a vacuum state, A radiation heater capable of heating the mold and the raw material, a predetermined original press load, and a press unit capable of pressurizing the raw material with a preliminary load lower than the press load, the radiation heater comprising: Before the press unit pressurizes the raw material with the press load, the mold is brought to a temperature required for pressure molding exceeding the glass transition point of the raw material in a vacuum state by the vacuum means. And the raw material is heated, and the press unit is configured such that the radiant heater is heated to a temperature required for pressure molding that exceeds the glass transition point of the raw material. When heating the raw material, the raw material is pressurized with the preliminary load through the mold so as to enhance the thermal conductivity between the mold and the raw material, and the preliminary load is applied to the raw material before reaching the glass transition point. It is a load of 10 to 1000 MPa that does not break the glass, and a load that can improve the adhesion of the raw material to the mold after reaching the glass transition point .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a press molding method and a press molding apparatus according to the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 1 is a schematic configuration diagram showing an embodiment of a press molding apparatus according to the present invention. The press molding apparatus 1 shown in the figure is particularly suitable for molding a substrate of a storage medium disk, etc., in which the ratio of the outer diameter to the plate thickness is finally increased from a raw material G such as glass or plastic. As a method for heating the mold and the raw material G, a radiation heating method is adopted. The press molding apparatus 1 has a frame 2 including a base 3, an upper stage 4, a lower fixed stage 5a, and a lower movable stage 5b. The upper stage 4 is fixed on the base 3 by a plurality of columns 6.
[0018]
The lower fixed stage 5 a has an opening at the center thereof, and is fixed to the plurality of columns 6 between the base 3 and the upper stage 4. The lower movable stage 5b is connected to the lower fixed stage 5a via a bellows 5c so as to cover the opening, and is connected to the rod 7a of the press unit 7 installed on the base 3. By operating the press unit 7, the lower movable stage 5 can be moved between the base 3 and the upper stage 4 in the vertical direction in the figure. The press unit 7 can freely set the press load to a desired value.
[0019]
The upper stage 4 is provided with a relatively small-capacity flat plate-shaped upper heater (flat heater) 9 via a support member 8a, and the upper heater 9 has an upper mold (fixed) made of WC material or the like. A mold 11 is attached. Similarly, a relatively small capacity flat plate lower heater (flat heater) 10 is mounted on the lower movable stage 5b via a support member 8b. A lower die (movable type) 12 made of a WC material or the like is attached to the lower heater 10, and a regulating ring 14 is further attached to the lower die 12. As shown in FIG. 1, the lower mold 12 protrudes toward the upper stage 4 through the opening of the lower fixed stage 5 a and faces the upper mold 11.
[0020]
Further, in this press molding apparatus 1, the temperature of the upper mold 11 is detected by an upper mold temperature sensor (not shown), and the temperature of the lower mold 12 is detected by a lower mold temperature sensor (not shown). Then, the detection signals of the upper mold temperature sensor and the lower mold temperature sensor are sent to a temperature controller that controls the upper heater 9 and the lower heater 10. This temperature controller controls the outputs of the upper heater 9 and the lower heater 10 so that the temperature difference between the upper mold 11 and the lower mold 12 becomes zero based on the detection values of the upper mold temperature sensor and the lower mold temperature sensor. To do.
[0021]
On the other hand, cooling jackets (cooling means) 17 and 18 are arranged between the upper stage 4 and the upper heater 9 and between the lower movable stage 5 b and the lower heater 10. A cooling medium can be circulated in each of the cooling jackets 17 and 18 as indicated by white arrows in FIG. The cooling jackets 17 and 18 are moved close to and away from the back surface of the upper heater 9 (the surface opposite to the upper die 11) or the back surface of the lower heater 10 (the surface opposite to the lower die 12) by a moving mechanism (not shown). Can be done. The upper heater 9 and the lower heater 10 are turned off, and the cooling jackets 17 and 18 in which the cooling medium is circulated are pressed against the upper heater 9 and the lower heater 10, so that the molded product is obtained via the upper mold 11 and the lower mold 12. Can be cooled.
[0022]
Now, in this press molding apparatus 1, since the radiation heating system which heats the upper mold | type 11 and the lower mold | type 12 and the raw material G from the side is employ | adopted, it is cylindrical around the upper mold | type 11 and the lower mold | type 12. The radiant heater 20 is arranged. As the radiant heater 20, a ceramic heater using a substrate of alumina, zirconia, aluminum nitride, boron nitride or the like, a graphite heater, a nichrome heater, an infrared lamp heater, or the like can be used. The radiant heater 20 is capable of heating the upper mold 11, the lower mold 12, and the raw material G to a molding temperature of about 200 ° C. or more by receiving power supply from the power source 21. A reflector 22 is disposed around the radiant heater 20 in order to improve heating efficiency and protect outer parts.
[0023]
Furthermore, in the press molding apparatus 1, as shown in FIG. 1, the upper mold 11, the lower mold 12, the radiant heater 20, the reflector 22, and the like are housed in a chamber 16 defined by the housing member 15. A vacuum pump VP is connected to the chamber 16 via a vacuum suction line L1. By operating the vacuum pump VP, the chamber 16 can be evacuated to about 1 Pa, for example. In addition to the vacuum pump VP, a vacuum gauge VG, a vent line L2, and the like are connected to the vacuum suction line L1. Further, an inert gas supply device (not shown) is connected to the chamber 16 via an inert gas supply line L3. Thereby, the inside of the chamber 16 can be in an inert gas atmosphere such as N ₂ gas.
[0024]
Next, operation | movement of the above-mentioned press molding apparatus 1 is demonstrated. First, in a state where the upper mold 11 and the lower mold 12 are completely opened, the raw material G is arranged at the approximate center of the lower mold 12 in the chamber 16 by a transfer unit (not shown). When the raw material G is disposed on the lower mold 12, the press unit 7 is operated, and the lower mold 12 is brought close to the upper mold 11 until the upper part of the raw material G contacts the molding surface of the upper mold 11. Then, the vacuum pump VP is operated, and the inside of the chamber 16 is vacuumed. Thereby, the surroundings of the upper mold 11 and the lower mold 12 are in a vacuum state, and various members in the chamber 16 including the upper mold 11 and the lower mold 12 can be prevented from being deteriorated by oxidation at a high temperature. .
[0025]
When the periphery of the upper die 11 and the lower die 12 is in a vacuum state, as shown in FIG. 2, heating of the upper die 11, the lower die 12 and the raw material G by the radiant heater 20 is started under the vacuum state. Is done. As described above, when the raw materials G between the molds 11 and 12 and both molds are radiantly heated, the heat capacity of the raw materials G such as glass and plastic is basically smaller than the heat capacities of the upper mold 11 and the lower mold 12. G rises faster than the molds 11 and 12 (see the broken line in the time vs. temperature graph of FIG. 2), and reaches the glass transition point in a relatively short time. Here, when radiant heating is continued in a vacuum state without taking any countermeasures as it is, due to the fact that there are few gases serving as a heat conducting medium around the upper mold 11, the lower mold 12 and the raw material G. Therefore, it takes a long time until the raw material G and the upper mold 11 and the lower mold 12 become substantially isothermal.
[0026]
In view of this point, in the press molding apparatus 1, when the upper mold 11, the lower mold 12 and the raw material G are radiantly heated, the original press load P <b> 2 set for obtaining a desired molded product such as a disk substrate is obtained. The raw material G is pressed through the upper die 11 and the lower die 12 by the press unit 7 under a relatively small preload P1 that is lower.
[0027]
When the raw material G heated by the radiant heater 20 and pressurized with the preliminary load P1 reaches the glass transition point, the raw material G adheres extremely smoothly to the surfaces of the upper mold 11 and the lower mold 12. Then, as the adhesion between the upper mold 11 and the lower mold 12 and the raw material G progresses, the thermal conductivity between them increases. Therefore, as shown in FIG. 2, the temperature of the raw material G and the upper mold temperature and lower The mold temperature becomes approximately isothermal in a very short time as compared with the case where no pressure is applied by the preload after the raw material G reaches the glass transition point after heating by the radiation heater 20 is started. That is, in the press molding apparatus 1, the process of heating the upper mold 11, the lower mold 12 and the raw material G is completed within a relatively short time, and the press molding cycle itself can be shortened.
[0028]
In this case, the preload P1 applied to the raw material G during radiant heating is such that the raw material G is not destroyed before reaching the glass transition point, and after reaching the glass transition point, the upper mold 11 of the raw material G and It is preferable to select from a load range that can improve the adhesion to the lower mold 12. The upper limit of the preliminary load P1 is preferably about 50 to 100 kg in the case of, for example, a spherical or marble material. Thereby, time until the raw material G and the upper mold | type 11 and the lower mold | type 12 become isothermal can be shortened very favorably.
[0029]
When the above heating and preliminary press are performed for a predetermined time, the heating by the radiation heater 20 is stopped. As shown in FIG. 2, the press load by the press unit 7 is raised from the preliminary load P <b> 1 to the original press load P <b> 2 within an extremely short time, and the lower die 12 is moved to the upper die 11 by the press unit 7. And get closer. Thereby, the raw material G between the upper mold | type 11 and the lower mold | type 12 will be pressurized with the original press load P2 (this press process). The ascending operation of the lower mold 12 is stopped when the upper end of the regulating ring comes into contact with the upper mold 11, thereby making it possible to obtain a molded product having a uniform thickness.
[0030]
In this main press, the upper mold 11 and the lower mold 12 and the raw material G are almost isothermal in a short time due to the previous heating and preliminary press. The raw material G is required for pressure molding simply by controlling the temperature of the upper heater 9 and the lower heater 10 so that the temperature difference between the upper mold 11 and the lower mold 12 becomes almost zero based on the temperature of Can be kept at a temperature. That is, the press molding apparatus 1 does not require any special and expensive temperature measuring means or the like for the temperature management of the upper mold 11 and the lower mold 12 and the raw material G, and the temperature management of the raw material G during molding is easy and easy. It will be executed with high accuracy. As a result, according to the press molding apparatus 1, it is possible to manufacture a molded product having high dimensional accuracy, flatness, smoothness, etc. at low cost, with distortion and warpage suppressed.
[0031]
When this press is performed for a predetermined time, the upper heater 9 and the lower heater 10 are turned off, and the inert gas is supplied into the chamber 16 via the inert gas supply line L3. The cooling jacket 17 is pressed against the back surface of the upper heater 9 and the cooling jacket 18 is pressed against the back surface of the lower heater 10 (cooling step), thereby cooling the molded product in the mold. Then, after the cooling is completed, the lower mold 12 is lowered, the mold is opened, and the molded product is taken out.
[0032]
In the present embodiment, the heating by the radiant heater 20 and the pressing of the raw material G by the preliminary load P1 are performed at the same timing for the same time. However, the present embodiment is not limited to this. That is, depending on various conditions such as the type of the molded product, the heating by the radiant heater 20 may be continued during the press.
[0033]
【The invention's effect】
As described above, according to the present invention, temperature control during molding can be performed easily and accurately, and a molded product having high dimensional accuracy, flatness, smoothness, etc. with reduced distortion and warpage can be reduced. Can be manufactured at cost.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of a press molding apparatus according to the present invention.
FIG. 2 is a timing chart for explaining the operation of the press molding apparatus shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Press molding apparatus 4 Upper stage 5a Lower fixed stage 5b Lower movable stage 7 Press unit 9 Upper heater 10 Lower heater 11 Upper mold 12 Lower mold 14 Control ring 16 Chamber 20 Radiation heater 22 Reflector G Raw material L1 Vacuum suction line L3 Not Active gas supply line VP Vacuum pump

Claims (4)

In the press molding method to produce the desired molded product by heating and pressurizing the raw material between molds,
(A) To increase the thermal conductivity between the mold and the raw material while radiatively heating the mold and the raw material in a vacuum state to a temperature required for pressure molding exceeding the glass transition point of the raw material. Pressurizing the raw material through the mold with a preload lower than a predetermined original press load; and
(B) after the step (a), pressurizing the raw material with the press load,
The preload is a load range of a fractured such have 1 0～1000MPa the raw material before reaching the glass transition temperature, and improved adhesion to the mold of the raw material after reaching the glass transition temperature A press molding method characterized by being selected from a load range that can be made.   2. The press molding method according to claim 1, wherein radiant heating is continued when the raw material is pressurized with the press load in the step (b).   The press molding method according to claim 1, wherein the molded product is a substrate of a disk for a storage medium. In press molding equipment that produces desired molded products by heating and pressurizing raw materials between molds,
Vacuum means for creating a vacuum around the mold,
A radiant heater capable of heating the mold and the raw material;
A press unit capable of pressurizing the raw material with both a predetermined original press load and a preliminary load lower than the press load;
Before the press unit pressurizes the raw material with the press load, the radiant heater is in a vacuum state by the vacuum means up to a temperature required for pressure forming exceeding the glass transition point of the raw material. , before Kikin type and heating said raw material,
The press unit enhances thermal conductivity between the mold and the raw material when the radiant heater heats the mold and the raw material to a temperature required for pressure molding exceeding the glass transition point of the raw material. through the mold to pressurize the raw material in the preload as,
The preload is a load weight of a fractured such have 1 0～1000MPa the raw material before reaching the glass transition temperature, and improved adhesion to the mold of the raw material after reaching the glass transition temperature press forming apparatus which is a load weight which can be.

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