JPS62208916A - Method and apparatus for molding precision form - Google Patents

Abstract

PURPOSE:To decrease the consumption of energy under shortening a molding cycle, by executing injection under a state where the temperature of a primary mold is high and by cooling under compression with a secondary mold. CONSTITUTION:A molten resin is injected into a cavity 13 from the nozzle of an injection machine through the sprue 14a of a primary mold 10. The temper ature of a cooling medium for the primary mold 10 is preset by 10-40 deg.C lower than the glass transition point to a resin material. The fluidity of the molten resin is not damaged, and thereby good transfer can be performed. The sectional thickness of a disc part 41 of the primary form 40 is t1 and slightly thicker than a final form 45. Then a die plate 32 at moving side is released from a die plate 31 at a fixed side, and the disc part 41 is transmitted to a secondary mold 20. It is compressed to a thickness t2 at the secondary mold 20 and cooled to a temperature less than about 100 deg.C, thereby a base plate for magnetic disc is obtained.

Description

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

(Prior Art) Aluminum or glass is generally used for the substrate of a magnetic disk. Since the recording surface of a magnetic disk requires highly precise smoothness, aluminum or glass substrates require a process of grinding and polishing to a mirror finish, resulting in poor productivity.

It also had the disadvantage of being heavy.

Therefore, Japanese Patent Application Publication No. 53-224730 and Japanese Patent Application Publication No. 60
As seen in Japanese Patent No. 19518, a technique for injection molding magnetic disk substrates using engineering plastics has been developed.

Engineered plastics are lightweight and can achieve high productivity without the need for grinding and polishing. In the case of magnetic disk substrates, the magnetic layer is formed by coating, plating, sputtering, etc. while applying high heat to the recording surface, so high heat resistance is required, and the substrate is rotated at 3600 rpm during recording and reproduction. Therefore, high strength is required, and engineered plastics can meet these requirements.

However, engineering plastics have a melting temperature of 4
Since the temperature is extremely high, around 00°C, there are various problems that must be solved in order to perform high-precision molding.

In the general injection molding method, the mold is cooled at room temperature, so the extremely high temperature molten resin comes into contact with the molding surface of the mold during the process of being injected from the center of the mold cavity to the periphery. The molten resin is rapidly cooled and its fluidity deteriorates, and as a result, the injection pressure is not sufficiently applied to the molten resin, resulting in poor transferability and failure to achieve highly accurate smoothness. In addition, the solidification of the resin begins at the periphery, and since there is a difference in solidification rate, the pressure required to maintain the pressure in the shotgun is higher at the center than at the periphery, and as a result,
The center part becomes thicker than the peripheral part.

Furthermore, the pressure distribution becomes uneven due to the difference in solidification rate, and the resin density also becomes uneven, resulting in residual strain and deformation over time. Further, deformation occurs due to contraction during cooling.

Injection compression molding is a well-known method for injection molding precision products. Specifically, injection is performed with the cavity of the mold made wider than the wall thickness of the molded product, and the resin is compressed by narrowing the cavity during the process of cooling and solidifying the resin. With this method, injection can be performed at low pressure and high speed, and unevenness in solidification rate can be alleviated, thereby eliminating residual strain that causes deformation over time.
After injection, compression is started while the resin is in a molten state, so it is possible to make the wall thickness uniform and prevent deformation due to shrinkage during cooling.

However, with the injection compression method described above, it is unavoidable that the extremely high temperature molten resin is rapidly cooled on the molding surface, resulting in a decrease in fluidity, and it is still difficult to achieve the strict smoothness standards required for magnetic disk substrates. It is insufficient.

Therefore, in this injection compression method, the mold temperature is raised at the start of injection to improve transferability, and then the mold is cooled to a lower temperature (a temperature that does not cause deformation due to cooling shrinkage) and compressed. It is possible that

(Problems to be Solved by the Invention) However, when the mold temperature control cycle as described above is executed, the temperature difference between the upper and lower limits is large, especially when using O (fat), which has a high melting temperature. This temperature control lengthens the molding cycle, drastically reducing productivity, and consumes a large amount of energy, making it uneconomical.Furthermore, molds require rigidity to improve precision, and The above disadvantages are due to the thick thickness and large heat capacity.

(Means for Solving the Problems) This invention was made to solve the above problems, and the key point is that the final mold width of the cavity is slightly wider than the thickness of the molded product. , prepare a secondary mold in which the final width of the cavity is approximately equal to the thickness of the molded product, heat the primary mold at a relatively high temperature, set the secondary mold at a relatively low temperature, and set the primary mold to a relatively high temperature. Precision molding characterized by injecting and filling a molten resin into a mold cavity, cooling and shaping, and then transferring the shaped primary molded product to a secondary mold and compressing and cooling it to obtain a final molded product. The problem lies in the method of molding the product.

Another key feature of the invention is that it includes a primary mold and a secondary mold, the fixed mold of each mold is installed on a common fixed die plate, and the movable mold of each mold is installed on a common fixed die plate. Move! The primary mold has a sprue that serves as a passage for the injected resin, and a cavity that communicates with this sprue and has a final width slightly wider than the thickness of the molded product. The mold has a cavity whose final width is approximately equal to the thickness of the molded part, the primary mold has temperature control means to maintain this mold at a relatively high temperature, and the secondary mold has a The apparatus for molding precision molded products is characterized by having a temperature control means for maintaining the mold at a relatively low temperature.

(Function) In the method of this invention, injection is performed while the temperature of the primary mold is relatively high, so good transfer can be achieved and highly accurate smoothness can be obtained, as well as smoothness inside the cavity. It is possible to alleviate unevenness in the solidification rate of the resin and prevent residual distortion, thereby preventing deformation over time.When molding precision molded products in the form of a flat plate, such as a magnetic disk substrate, it is possible to make the wall thickness uniform. It can be done.

By performing compression cooling using the main and secondary molds, deformation during cooling can be eliminated.

Moreover, because the primary mold performs injection and cooling shaping, and the secondary mold performs compression cooling, these molds do not require temperature control cycles with large temperature differences, and the molding cycle can be shortened. It is possible to shorten the time and reduce energy consumption.

In this invented device, the primary mold and secondary mold are installed on a common die plate, so the equipment cost is low, and each mold can perform injection, cooling shaping, and compression cooling at the same time. Because of this, productivity is high. The primary molded product obtained in the first mold can be reliably transferred to the second mold in a short time, and deformation of the primary molded product during transfer can be prevented.

(Example) Hereinafter, the method and apparatus of the present invention will be explained based on the drawings, taking as an example the case of molding a substrate (precision molded product) for a magnetic disk.

In the figure, 10 is a primary mold, and 20 is a secondary mold. Each mold 10.20 has a fixed mold 11.21 and a movable mold 12.22.

The fixed die 11.21 is fixed to a common fixed die plate 31, and the parting surfaces 1ib and 21b are arranged on the same surface. Further, the movable die 12.22 is fixed to a common movable die plate 32, and the parting surfaces 12b and 22b are arranged on the same plane. An air gap 33 is interposed between the fixed type 11.21 and the movable type 12.22, which functions as a thermal insulation. The mechanism for moving the movable die plate 32 relative to the fixed die plate 31 is the same as that of a normal injection molding apparatus.

The fixed mold 11 and the movable mold 12 of the primary mold 10 are formed with molding surfaces 11a and 12a that are mirror-finished with high precision. During mold clamping, these molding surfaces 11a, 12a
A cavity 13 is formed therebetween.

In this cavity 13, the width (final width 1.) when the parting surfaces 11b and 12b of the fixed mold 11 and the movable mold 12 are in contact is approximately 2 mm, which is the thickness of the final molded product 45 described later.
It is set to be about 20 to 200 μ wider.

There are holes 11C and 112c in the center of the fixed mold 11 and the movable mold 12.
are formed, and slide cut cores 14 and 15 are slidably housed in these holes 11c and 12c.

The slide cut core 14 of the fixed mold 11 has a resprue 14a that also serves as a sprue bush. Also,
An ejector pin 16 passes through the slide cut core 15 of the movable die 12.

An air passage 17 is formed in the fixed mold 11 and the movable mold 12, and the air passage 17 has molding surfaces 11a and 12a.
A cylindrical slot 7) 17a extending from the main part is in communication.

The fixed mold 11 and the movable mold 12 have a spiral medium passage 1.
8 is formed, and a relatively high temperature cooling medium flows through this medium passage 18. Although the temperature is relatively high, it is called a cooling medium because the temperature is lower than the melting temperature of the resin (molten resin can be cooled down).These medium passages 18 and the cooling medium constitute a temperature control means.

The fixed mold 21 and the movable mold 22 of the secondary mold 20 are formed with highly precisely mirror-finished molding surfaces 21a and 22a. During mold clamping, these molding surfaces 21a, 22a
A cavity 23 is formed in between.

In this cavity 23, the width (final width L2) when the parting surfaces 21b and 22b of the stationary mold 21 and the movable mold 22 are in contact with each other is set to be approximately equal to the thickness of the final molded product 45. Note that the most p-molded product 45, which will be described later, is further cooled to room temperature after being taken out from the second mold 20, and shrinks by a minute amount. Also, when compressed with huge pressure, there is elastic return. Therefore, the final width 2 of the cavity 23 is set in consideration of minute cooling shrinkage and elastic return of the final molded product 45, and this
This is why the final width L2 of the cavity 23 is expressed as "approximately equal" to the thickness of the final molded product 45.

A hole 21c is provided in the center of the fixed mold 21 and the movable mold 22.

22c is formed, and fixed cores 24 and 25 are housed in these holes 21c and 22c. The fixed core 25 of the movable mold 22 protrudes from the molding surface 22a by two times the final width of the cavity 23, and a protruding sleeve 26 is disposed between the fixed core 25 and the inner peripheral surface of the hole 22c. .

An air passage 27 is formed in the fixed mold 21 and the movable mold 22, and the air passage 27 includes molding surfaces 21a, 22.
A cylindrical groove 27a extending to a point 27a is connected.

The fixed mold 21 and the movable mold 22 have a spiral medium passage 2.
8 is formed, and a cooling medium at a relatively low temperature, for example, room temperature, flows through this medium passage 28.

These medium passages 28 and the cooling medium constitute a temperature control means.

In the above configuration, in the mold clamping state shown in FIG. 1, the sprue 1 of the primary mold 10 is
The molten resin is injected into the cavity 13 via 4a. The resin is, for example, PEI (polyetherimide) or PE5 (polyether sal 7one), which has a melting temperature of about 400°C. The temperature of the cooling medium in the primary mold 10 is set to about 10 to 40'C lower than the glass transition point of the resin material.

In the case of the above resin, the glass transition point is around 200°C, so the temperature of the cooling medium is set to 160 to 190°C, more preferably 170 to 180°C. 16
If the temperature is below 0°C, the transferability described below will not be sufficient, mainly due to
If the temperature is 190° C. or higher, it will cause problems in the excipient process described below.

During the above injection, the molding surface 11a of the primary mold 10.

Since the temperature of 12a is relatively high at 170 to 180'C as described above, the fluidity of the molten resin is not impaired, and the molding surface 11a forms a mirror surface when the molten resin receives injection pressure.
, 12aL: Very good transfer is possible due to close contact,
Highly accurate smoothness can be obtained. Moreover, the molding surface 1
1a and 12a are at high temperatures, there is little difference in the solidification rate from the periphery to the center of the cavity 14, and the injection pressure is not extremely high, so the generation of residual strain can be prevented. It is possible to prevent deformation caused by aging over time.

Furthermore, since there is no difference in solidification rate, it is possible to prevent the wall from becoming thick only in the central part due to injection pressure.

The molten resin is cooled and shaped in the primary mold 10 until the surface temperature becomes below the glass transition point.

The shaped primary shaped product 40 has a disk portion 41 and a sprue portion 42. The thickness of the disk portion 41 is that of the cavity 1
Final width of 3 1. , and is slightly thicker than the final molded product 45 described later.

After shaping, slide cut core 14. The primary molded product 40 is cut as shown by the broken line A by moving the IS slightly to the right in FIG. Separate from the pond part. At this time, the nozzle of the injection machine also slide cut core 1
4. Retreat following 15.

Next, move the moving die plate 32 to the fixed die plate 3.
Move it in the direction away from 1 and open the mold as shown in Figure @2. At this time, compressed air is supplied from the air passage 17 and blown out toward the primary molded product 40 through the cylindrical sleeve 17a.

Thereby, the primary molded product 40 in close contact is separated from the mirror-finished molded products 11a and 12a.

Next, 12 movable molds are taken out of the disk part 41 with the central part hollowed out by a means such as vacuum suction using a take-out machine 50, and the sprue part 42 etc. are pushed out and the pin 16 is removed.
to push it out and drop it from the movable mold 12.

In the tapping rock 50, the disc part 41 is moved by the secondary mold 20, and the central hole 41a of the disc part 41 is inserted into the fixed core 25 of the movable mold 22. At this time, since the movable mold 12 and the movable mold 22 are located close to each other, the disc part 41 can be quickly moved and deformation of the disc part 41 can be prevented. Note that the protruding rib 26 protrudes from the molding surface 22a by a slight force of a spring (not shown), and the disc portion 41
is positioned at the tip of this sleeve 26, and the molding surface 2
It is far from 2a. Therefore, only one surface of the disk portion 41 is not cooled first.

Next, the movable die plate 32 is brought close to the stationary die plate 31 again and the molds are clamped. At this time, the disc part 4
1 hits the molding surface 21a of the fixed mold 21 and is pressed, the ejecting sleeve 26 retreats, and immediately after this, the Ike side surface of the disc part 41 hits the molding surface 22a of the movable mold 22. In this way, since both surfaces of the disk g41 come into contact with the molding surfaces 21a and 22a almost simultaneously, distortion caused by the difference in cooling rate can be prevented.

In the secondary mold 20, by plastically deforming the inner center of the disc part 41 with the mold clamping force, the disc part 4 with a thickness Ll is
1 is compressed to a thickness equal to the width of the cavity 23, and cooled at a temperature below approximately IoO'c (a temperature at which deformation due to cooling shrinkage does not occur) to form the final magnetic disk substrate. A molded product 45 is obtained. By the compression cooling described above, the final molded product 45 can reliably prevent deformation such as warpage caused by shrinkage due to cooling. Furthermore, even if there are still minute non-uniformities in the wall thickness, this can be corrected and made uniform.

In the above molding process, the primary mold 10 and the secondary mold 2
The temperature at 0 only needs to be maintained constant, and a temperature control cycle that includes transitions from high to low temperatures and from low to high temperatures is not executed, so the molding cycle can be shortened and energy can be saved. .

In the second mold 20, the mold is opened after the compression cooling described above.

At this time, the compressed air supplied from the air passage 27 is
) 27a onto the final molded product 45 to separate it from the mirror-like molding surfaces 21a and 22a, and at the same time eject it with the ejecting sleeve 26 and take it out at a takeout rock in the pond.

As mentioned above, when the mold is closed, the primary mold 10 performs injection and cooling shaping, and the secondary mold 20 performs compression cooling, and when the mold is opened, the primary molded product is molded in the primary mold 10. 40 and the final molded product 45 from the secondary mold 20. Since two steps are performed at the same time, productivity is high.

The method of this invention is not limited to the above embodiments, and various embodiments are possible.

For example, in the primary mold 10.7), two types of cooling media with different temperatures are alternately flowed into the medium passage 18, and the mold temperature is made to be above the glass transition point at the start of injection, and then reduced to below the glass transition point after injection. It's okay. In this case, since the mold temperature cycle is executed, energy consumption is higher than in the above embodiment, but smoothness etc. can be further improved. Even in this case,
Since the range between the upper and lower limits of the temperature cycle is relatively narrow, it does not consume much energy.

In addition, the primary molded product is obtained by performing injection and cooling shaping using a normal injection molding device, and the primary molded product is compressed using a press device equipped with a cooling means that is separate from the injection molding device. Cooling may also be performed.

In the apparatus of this invention, a molding recess is formed in a fixed mold of a secondary mold, a molding projection is formed in a movable mold, and the projection is inserted into the recess, thereby forming a cavity whose volume can be changed. may be formed.

By dividing the fixed mold of the main primary mold into two parts and moving the part on the cavity side when the movable mold opens slightly, a part of the sprue of the primary molded product supported by the slide cut core is cut. It may be configured to do so.

(Effects of the Invention) As explained above, in the method of the present invention, since transfer can be performed well, highly accurate smoothness can be achieved, high dimensional accuracy can be obtained, and deformation can mainly be prevented reliably. Moreover, it is not necessary to perform a mold temperature control cycle with a large temperature difference, so the molding cycle can be shortened and energy consumption can be reduced.

Furthermore, in the device of this invention, the primary mold and the secondary mold are installed on a common die plate, so the equipment cost is low and productivity is high. Since the primary molded product obtained in the first mold can be reliably transferred to the second mold in a short time, deformation of the primary molded product during transfer can be prevented.

[Brief explanation of drawings]

The drawings show one embodiment of the invention, and include FIG.
FIG. 2 is a cross-sectional view of the molding apparatus showing the mold-clamping and mold-opening states, respectively. 10... Primary mold, 20... Secondary mold, 11.
21...solid type, 12.22...mobile type, lla,
12a. 21a, 22a... Molding surface, 13.23... Cavity, 14a... Sprue, 18.28... Medium passage (temperature control means), 31... Solid side die plate,
32... Moving side die plate, 40...-Next molded product, 45... Final molded product.

Claims (3)

[Claims] (1) Prepare a primary mold in which the final width of the cavity is slightly wider than the thickness of the molded product, and a secondary mold in which the final width of the cavity is approximately equal to the thickness of the molded product. The mold is kept at a relatively high temperature, the secondary mold is kept at a relatively low temperature, the molten resin is injected into the cavity of the primary mold, cooled and shaped, and the shaped primary molded product is transferred to the secondary mold. A method for forming precision molded products, characterized by obtaining a final molded product by transferring the product to a mold and compressing and cooling it. (2) Perform injection with the molding surface temperature of the primary mold set at a temperature 10 to 40°C lower than the glass transition point of the injected resin, and cool until the surface temperature of the resin falls below the glass transition point. A molded product is obtained, and the surface temperature of the resin in the second mold is 10
The method for molding a precision molded product according to claim 1, wherein the final molded product is obtained by cooling to 0° C. or lower. (3) Equipped with a primary mold and a secondary mold, the fixed mold of each mold is installed on a common fixed die plate, and the movable mold of each mold is installed on a common movable die plate The primary mold has a sprue that serves as a passage for the injected resin, and
The secondary mold has a cavity that communicates with this sprue and whose final width is set to be slightly wider than the thickness of the molded product, and the secondary mold has a cavity whose final width is set approximately equal to the thickness of the molded product. Precision molding characterized in that the mold has temperature control means for maintaining the mold at a relatively high temperature, and the secondary mold has temperature control means for maintaining the mold at a relatively low temperature. Molding equipment for molded products.