JP2002254477A - Injection mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection mold capable of inexpensively molding a molded product without lowering a yield while shortening a time from injection of a resin to completion of the molded product. SOLUTION: The injection mold consists of a fixed mold 2 having a sprue part 3 for injecting a resin provided to the central part thereof and a movable mold 4 provided so as to form a cavity 6 in opposed relation to the fixed mold 2 and having a projected part 5 at the central part thereof. The sprue part 3 has a sprue bush 31, which has a through-hole 34 for injecting the resin and also has a cooling groove 31a formed to the outer periphery thereof, and the die mold core 32 provided to the outer periphery of the sprue bush 31 to close the cooling groove 31a. The sprue bush 31 comprises a material having large heat conductivity like a beryllium-copper (Be-Cu) alloy and the die mold core 32 or the like comprises a material having high hardness such as stainless steel or the like as is conventional.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk such as a compact disk (CD), a digital versatile disk (DVD) and a mini disk (MD), and fine irregularities such as a light guide plate of a liquid crystal display. The present invention relates to an injection mold capable of shortening the time from resin injection to removal of a molded product when a thin plate is formed by injection molding. More specifically, the present invention relates to an injection mold that cures a resin almost at the same time as resin injection and allows the injected resin to be molded and taken out without drawing a thread.

[0002]

2. Description of the Related Art For example, a compact disk (hereinafter referred to as C)
D) is formed in a structure as shown in FIG. That is, the fixed mold 2 and the movable mold 4 are formed, and a cavity (cavity) 6 for forming a compact such as a CD is formed between the fixed mold 2 and the movable mold 4.

The fixed mold 2 includes a mounting plate 21, a mold plate 22,
Mirror plate 23 and mirror plate mounting plate 2 for fixing mirror plate 23
4, and the sprue portion 3 penetrates a central portion thereof. The sprue portion 3 is provided so as to form a water channel by covering a sprue bush 31 having a through hole 34 formed therein so that molten resin flows into the cavity 6 in the center portion, and a cooling groove 31a formed therearound. The heat retention efficiency of the die core 32 and the sprue portion 3 is increased, and the sprue portion 3
And an insulation bush 33 holding the same. This sprue portion 3 is formed in a circular cross section. A spiral groove 23a, such as a mosquito coil, is formed on the back surface of the mirror plate 23 so as to allow cooling water (warming water) to flow in the same manner, and the cooling water (or water) is passed from the water channel 25 to the water channel 26 via the groove 23a. Hot water) is allowed to flow to maintain the mirror plate 23 at a constant temperature.

[0004] Similarly, the movable mold 4 also includes a mounting plate 41, a mold plate 42, a mirror surface plate 43, and a mirror surface mounting plate 44, and a protruding portion 5 is formed penetrating through the central portion thereof. . The protruding portion 5 is provided at the center with the through hole 3 of the sprue portion 3.
4, a protruding pin 51 that protrudes the resin (sprue) portion that has hardened, a protruding pin holding core 52 that slidably holds the outer circumference of the protruding pin 51, and a protruding pin that holds the outer circumference of the protruding pin holding core 52. A punch-type core 53 that covers a cooling groove 52a formed on the outer periphery of the pin holding core 52 to form a cooling channel, and also punches out a central portion of a CD or the like formed in the cavity 6 with a sprue; A projecting bush 54 for holding a molded body 53 such as a CD punched out from the cavity 6 at the center and holding the molded body 53. The protruding portion 5 is also formed in a circular cross section. Similar to the fixed side mirror plate 23, the mirror plate 43 is formed with a spiral groove 43 a, and has a structure in which cooling water (hot water) flows through the water channels 45 and 46.

Using such an injection molding die, a polycarbonate resin melted at about 300 to 360 ° C. from the center of the sprue portion 3 is poured into the cavity 6, cooled, and almost starts to be hardened. 5, a punched core 53 is used to punch out the central portion, and furthermore, the protruding pin 51 is used to separate the punched-out central portion.
By taking D out of the cavity 6, a molded body is obtained. From the injection of the resin to the removal of the molded body, 1
It takes about 6 to 7 seconds per unit.

As described above, this type of injection mold requires a gate cutting step such as punching of a central portion thereof together with resin molding, so that its mechanical strength is particularly required. Is formed of stainless steel having a Rockwell hardness of about 50 HRC or more.

[0007]

As described above, in a mold that is formed by injection-molding a thin plate-like molded body such as a CD and performing mechanical processing such as punching out the center thereof, the mechanical strength of the mold is low. Required. On the other hand, from recent demands for cost reduction of electronic devices, it is desired to further shorten the time from the injection of the resin to the removal of the molded product, thereby achieving cost reduction. However, if the resin does not cure to a certain extent after the resin is injected, it cannot be processed cleanly in the in-mold gate cutting process, the nozzle touch part pulls a thread, or after the center part is cut, the protruding pin separates the center part. When the central part is pushed up, the protruding pin sinks into the resin and cannot be separated. Therefore, as described above, it is limited to about 6 to 7 seconds to form one CD.

On the other hand, if the temperature of the cooling water flowing on the outer periphery of the sprue bush or the back surface of the mirror surface plate is set low to lower the temperature of the sprue bush or the mirror surface plate in order to speed up the curing, the curing will occur in the middle of the resin flow. In addition, there is a problem that the resin does not sufficiently flow to the outer periphery of a molded product such as a CD and molding defects easily occur.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it is possible to reduce the time from the injection of resin to the completion of a molded product, to reduce the yield without lowering the quality and to reduce the yield. An object of the present invention is to provide an injection mold that can be molded.

[0010]

The inventor of the present invention has conducted intensive studies to produce a thin plate-like molded product such as a CD in a short time. As a result, the temperature of the cooling water in the sprue portion was not reduced so much. Even at a similar temperature of about 20 to 90 ° C., the thin plate portion on the mirror plate is immediately cured with a thickness of about 1.2 mm (about 0.6 mm for DVD), while the inside of the sprue bush is thick. Is about 3 to 4 mmφ, and it takes a long time to cure. This improves the heat conduction of the sprue bush, and cools the resin in the sprue bush in a short time without excessive cooling. By doing
It has been found that the time from resin injection to removal of a molded article can be reduced to about 3 seconds.

An injection molding die according to the present invention is provided so as to have a fixed side die having a sprue portion for injecting a resin in a central portion, a cavity opposed to the fixed side die, and a cavity formed in the central portion. It consists of a movable mold having a protruding part,
The sprue portion has a through hole for injecting the resin, a sprue bush having a cooling groove formed on the outer periphery, and a die core provided on the outer periphery of the sprue bush and covering the cooling groove. The projecting portion slidably holds a projecting pin at a central portion, a projecting pin holding core having a cooling groove formed on the outer periphery thereof, and a projecting pin provided on the outer periphery of the projecting pin holding core, A cover having a punch-type core and a projecting bush provided on the outer periphery of the punch-type core, wherein the sprue bush is made of a material having a higher thermal conductivity than the die-type core; It is made of a material with high hardness.

With this structure, the temperature of the cooling water (hot water) flowing through the water channel provided on the outer periphery of the sprue bush can be quickly transmitted to the molten resin flowing through the central portion thereof. As a result, the temperature of the molten resin flowing through the central portion can be brought close to the temperature of the cooling water (warm water) in a very short time, and the resin can be cured. On the other hand, the die core, which is the receiving side when punching a part such as the center of a molded article such as a CD, is made of a material having the same hardness as the conventional one, so that sufficient mechanical strength can be obtained, No damage. On the other hand, in the first time of the resin injection, the speed in the sprue bush is also high, flows sufficiently into the interior of the cavity without being cooled so much, and is quickly cured by cooling water (warm water) of the mirror surface plate since the cavity is thin. As a result, even if the center part is punched immediately after the resin is injected, the thread on the sprue nozzle contact side is pulled to the molded product and the sprue part, the burr on the cut surface, the buckling on the sprue protrusion pin side, etc. Molding can be performed without the problem described above.

The projecting pin holding core is made of a material having a higher thermal conductivity than the punch type core, and the punch type core is made of a material having a higher hardness than the projecting pin holding core. In addition to cooling, the central part of a CD or the like can be rapidly cooled by a protruding pin and protruded by a pin-holding core. In addition, it is more preferable that the protrusion pins do not sink when pushing out the portion punched by the protrusion pins. Also in this case, since a punched core made of a material having high hardness is used for the punched portion, punching can be performed without damage.

The sprue bush or the material having high thermal conductivity of the protruding pin holding core has a thermal conductivity of 70.
W / (m · K) or more and hardness is 30 in Rockwell hardness
A material of HRC or higher is preferable because it has a certain degree of mechanical strength as a mold while having excellent heat conduction. Specifically, the sprue bush or the protruding pin holding core is made of a beryllium copper alloy, and the die core and the punch core are formed of stainless steel.

[0015]

Next, an injection mold according to the present invention will be described with reference to the drawings. As shown in FIG. 2, the injection mold according to the present invention has a fixed mold 2 having a sprue portion 3 for injecting a resin in a central portion thereof, and a fixed mold 2 having the sprue portion 3. And a movable mold 4 having a protruding portion 5 at the center.

The sprue 3 is shown in FIG.
As shown in the enlarged explanatory view of the protruding portion 5, it has a through hole 34 for injecting resin, and has a cooling groove 3
The sprue bush 31 includes the sprue bush 31 on which the lamination 1a is formed, and a die core 32 provided on the outer periphery of the sprue bush 31 to cover the cooling groove 31a. An insulation bush 33 for holding the sprue portion 3 is provided around the periphery. The sprue bush 31, the die core 32, and the insulation bush 33 are joined by fitting or brazing, respectively. In the present invention, the sprue bush 31 is made of a material having high thermal conductivity such as a beryllium copper (Be-Cu) alloy, and the die core 32 and the insulation bush 33 are made of a hard material such as stainless steel as in the prior art. It is characterized by being made of a material with a large size.

In general, Be-Cu alloys (Be content 1.6 to 1.6)
2 at%) has a thermal conductivity of about 100 W / (m · K), which is greater in each stage than a thermal conductivity of about 30 W / (m · K) of stainless steel (for example, JIS symbol SUS420). The temperature of the cooling water (warm water) flowing through the central portion can be quickly transmitted to the molten resin flowing through the central portion. On the other hand, the hardness is 30-40 in Rockwell hardness.
It is weaker than HRC and about 50 HRC of stainless steel. However, the sprue bush 31 is hardly consumed even if the sprue bush 31 is not as hard as the stainless steel, and is not a portion directly hit by the punch-type core 53 of the protrusion 5 when punching out the center of the CD which is a molded product. The present inventor has found. By using a material having a higher thermal conductivity than the hardness for the sprue bush 31, the temperature of the cooling water can be quickly transmitted to the molten resin in the central portion of the sprue, and can be cooled instantaneously. Can be performed quickly and reliably.

Also, as shown in FIG. 5 which is a cross-sectional explanatory view of the joint between the nozzle 13 and the sprue bush 31 when the resin is injected from the nozzle, the nozzle 13 of the molding machine and the sprue bush 13 are The molten resin is injected into the through-hole 34 of the sprue bush by making contact with the sprue touch portion 31b having the same shape as the outer shape of the thirteen. Since a conventional Be-Cu alloy was used for the nozzle 13 and the sprue bush was made of stainless steel having a high hardness, the nozzle tip portion was severely worn and had to be replaced frequently. However, by using a material having a high thermal conductivity such as a Be-Cu alloy for the sprue bush 31, the hardness becomes almost the same as that of the nozzle, so that mutual abrasion can be reduced and the frequency of replacement can be reduced. There is also an effect of being able to do so. That is, in general, when materials having different hardnesses collide with each other, the material having low hardness is extremely worn, and the tip of the nozzle 13 is worn. However, by using materials having the same hardness, wear is reduced in both cases.

On the other hand, as for the metal material, for example, in the material shown in FIG. 6, the thermal conductivity and the hardness thereof are in a reciprocal relationship, and
Materials with high thermal conductivity have low hardness, and materials with high hardness have low thermal conductivity. As the material used for the sprue bush 31 or the protruding pin holding core 52 to be described later, even though the thermal conductivity is important, the sprue bush 31 holds a die or a punch that punches out the center of a molded product,
In addition, since it has a function of sliding a protruding pin that protrudes a molded product, hardness (abrasion resistance) is required to some extent, and the present inventor has made various materials as shown in FIG. As a result of actually forming the sprue bush and the protruding pin holding core 52 described later, and examining the molding speed and the degree of wear of the mold, the hardness was 30 HRC or more and the thermal conductivity was 7 or more.
With a material of 0 W / (m · K) or more, in the molding of CD, a cycle from injection of resin to removal of the resin could be performed in about 3 seconds, and the molding die could be hardly damaged. In FIG. 6, A is Al, B is Hitachi HIT75, C is Kobe Steel Corporation HR75, D is NGK Corporation BEA50, E is MOLDMAX LH, Wooddeholm, Sweden. (Be-Cu alloy with a Be content of 1.6 to 2 at%), F is the company's trade name M
OLDMAX HH (B with a Be content of 1.6 to 2 at%)
e-Cu alloy), G is equivalent to AISI standard P20 prehardened steel, H is JIS standard SKD61 alloy tool steel equivalent, and I is JIS standard SUS420 stainless steel equivalent.

Into the cooling groove 31a formed on the outer periphery of the above-mentioned sprue bush 31, warm water of, for example, about 20 to 90 ° C. is poured from one of the water passages 35, and is discharged to the other side of the water passage 35. The temperature of the cooling water is set according to the size of the molded article, and for example, cold water close to 0 ° C. or hot water close to 100 ° C. may be used.

The protruding portion 5 is a sprue of a molded product which is formed by filling the cavity 6 with a molten resin and hardened (resin portion solidified in a resin passage leading to the cavity 6 in the sprue bush 31; FIG. Parts (7a, 7 in FIG. 4)
b, 7c), and a molded product is separated from the cavity. The projected pin 51 at the center is slidably held, and a projected pin holding core 52 having a cooling groove 52a formed on the outer periphery thereof. Projection pin holding core 52
A punch-type core 53 for punching a sprue portion of a molded product while covering a cooling groove 52a provided on the outer periphery of the molded product, and a projecting bush 54 provided on the outer periphery of the punch-shaped core and projecting a molded product such as a CD from a cavity. Have. A water channel 55 is connected to the cooling groove 52a, and cooling water or hot water is supplied from an external supply device (not shown) to one of the water channels 5a.
5, the cooling groove 52 a, the projecting portion, the folded portion formed on the tip end side of the pin holding core 52, and the flow again to another water channel 55 through a different portion of the cooling groove.

In the conventional injection mold, each of the protruding pin 51, the protruding pin holding core 52, the punch core 53, and the protruding bush 54 is formed of a stainless steel material, and the protruding pin 51 and the protruding pin holding core 52 are both formed. Although the quenching has been used to slightly increase the quenching hardness of the protrusion pin 51, in the present invention, the protrusion pin holding core 52 is made of a Be-Cu alloy (Be content 1: 1) of the same material as the sprue bush 31 described above. (0.6 to 2 at%).

For this reason, since the projecting pin 51 is formed of stainless steel and the projecting pin holding core 52 is formed of a Be-Cu alloy, the hardness of the projecting pin holding core 52 becomes smaller than the hardness of the projecting pin 51, and By providing a difference in hardness between the pin 51 and the protruding pin holding core 52, the conventional relationship of reducing wear of both can be maintained. Further, by using a material having a high thermal conductivity for the protruding pin holding core 52, the temperature of the cooling water (warm water) is immediately transmitted, and the top (7b in FIG. 4 described later) with which the tip of the protruding pin 51 abuts. Since it can be cooled and hardened, the tip of the protruding pin 51 can be separated without sinking into the sprue portion. However, the top of the sprue (7b in FIG. 4) to which the projecting pin 51 contacts is small and its periphery is surrounded by the projecting pin holding core 52 and the projecting pin 51, so that the thermal conductivity of the projecting pin is so remarkable. Has no effect,
Conventional stainless steel can also be used.

A flange 51a is provided at the bottom of the protruding pin 51.
Are formed through a spring 56, and flange portions 57 are formed at the bottoms of the protruding pin holding core 52 and the punch type core 53, respectively, so that they can be simultaneously pushed up via the spring 58. The projecting bush 54 is formed so as to be pushed up via a spring 59. In addition, 5
7a is a protruding plate that protrudes the flange portion 57.

The fixed mold 2 is, as shown in FIG.
The sprue unit 3 includes a mounting plate 21, a template plate 22, and a mirror plate 23, and a central portion thereof is penetrated by the sprue unit 3. The mounting plate 21 side is for fixing to the clamping plate 11 of the molding machine. As shown in the plan view of the injection molding machine in FIG. 3, the clamping plate 1 of the injection molding machine 1 is used.
A fixed mold 2 and a movable mold 4 are fixed to 1 and 12, respectively. The clamping plate 11 to which the fixed mold 2 is fixed is connected to a heating and injection device 14 via a nozzle 13, and the molten resin heated by the heating and injection device 14 and melted into a mushroom is passed through the nozzle 13 as described above. The sprue bush 31 is fed to the through hole 34.

In the example shown in FIG. 2, a cooling tank 29 is formed by arranging nozzle mounting plates 27 at regular intervals on the opposite side of the mirror surface plate 23 from the cavity 6, and a cooling tank 29 is formed. The nozzles 28 are concentrically fixed at predetermined intervals. Then, from the cooling nozzle 28 through the cooling water channel 25, for example, hot water (or cold water) of about 100 ° C.
Is sprayed, the hot water stored in the cooling tank 29 is stirred and exchanged, and is discharged from the water channel 26, so that the mirror plate 23 is always kept at a uniform temperature of about 100 ° C.
Is held. That is, in the example shown in FIG.
Rather than flowing hot water into a spiral groove provided on the back surface of the mirror plate as shown in FIG. 9, a cooling tank 29 is formed, and the mirror plate 23 is efficiently stirred by the nozzle 28 or the like. Are made uniform.

Similarly, the movable mold 4 also includes a mounting plate 41, a mold plate 42, a mirror surface plate 43, and a mirror surface mounting plate 44, and the above-mentioned protruding portion 5 is formed through a central portion thereof. ing. The mounting plate 41 is fixed to the clamping plate 12 of the injection molding machine 1 as shown in FIG. 3 described above, and the movable mold 4 is moved back and forth by the mold clamping device 15 so that the fixed mold 2 is moved. The cavity 6 formed therebetween is filled with a molten resin in a state where the movable side mold 4 is punched out of a sprue portion, which will be described later, and the movable side mold 4 is separated from the fixed side mold 2 to take out a molded product. By repeating the process of pressing the mold 2 and injecting the resin, resin molded products are manufactured one after another.

Next, a method of molding a CD using this injection molding machine will be described with reference to the process sectional view of FIG.

First, the fixed mold 2 and the movable mold 4 described above are used.
And 300 to 360 made of polycarbonate.
When the resin melted to about ° C is injected, the resin is filled into the cavity through the through hole in the sprue bushing 31 as shown in FIG. A contact portion (top portion) 7b of the pin 51 protrudes from the back side of the CD 7, the sprue (resin in the through hole) 7a, and the CD 7 facing the sprue 7a. From the initial stage of injecting the resin, 20 to 90
Cooling water of about ° C is flowing. In addition, mirror plates 23, 4
As described above, warm water of about 100 ° C. is also supplied to 3 to maintain the temperature at a constant temperature. The thickness of the CD 7 is about 1.2 mm, and the sprue 7a is about 3 to 4 mmφ. However, as described above, since the thermal conductivity of the sprue bush 31 is large, it starts to harden almost at the same time as the resin is filled. Although not shown, a stamper having fine irregularities corresponding to the pits formed on the CD 7 is attached to one of the mirror plates 23 and 43 of the fixed mold 2 or the movable mold 4, and a CD. A row of fine pits (irregularities) is formed on one surface along the circumferential direction.

Next, as shown in FIG. 4 (b), the projecting pin 51, the projecting pin holding core 52, and the punching core 53 are moved toward the fixed mold 2 in conjunction with each other, so that the center of the CD is reached. The portion (gate portion) 7c is punched. Thereafter, as shown in FIG. 4C, the movable mold is separated from the fixed mold so that the cured resin portion 7,
7a, 7b and 7c are separated from the fixed mold together with the movable mold.

Thereafter, as shown in FIG. 4D, by further projecting the projecting pin 51, the sprue portions 7a to 7c are completely separated from the CD.
As shown in (e), by pushing up the protruding bush 54, the CD 7 is separated and taken out from the movable mold. Thereafter, by repeatedly pressing the movable mold against the fixed mold and filling the cavity with the molten resin, CDs 7 can be similarly produced one after another. By using the injection molding machine of the present invention, a series of steps from the filling of the molten resin to the removal of the CD 7 could be repeated in 2.8 to 3 seconds per piece. The CD is formed into a product by forming a reflective film such as a metal on a surface on which fine irregularities are formed, and further forming a protective film on the surface.

According to the injection molding die of the present invention, when a thin plate-shaped resin molded product such as a CD is molded, the temperature of the cooling water is increased by a material having a high thermal conductivity at a slightly thick portion of the sprue portion. , The thin plate portion and the sprue portion can be cured at the same time, almost simultaneously with the filling of the molten resin, and the cutting step of the sprue portion can be performed almost simultaneously with the filling of the molten resin. As a result, while a series of processes are performed in a short time of about 3 seconds, the thread is not pulled due to the insufficient hardening of the cut portion, and when the projecting pin is pushed out by the projecting pin, the sprue portion is pulled out. A high-quality CD can be manufactured in a very short time without being immersed.

Although the above-described example is an example of manufacturing a CD, not only CDs but also optical disks such as DVDs and MDs can be manufactured in a very short time. In addition, the sprue portion is not limited to a circular shape such as an optical disk, but may be a rectangular shape such as a light guide plate used for a backlight of a liquid crystal display device, or a thin plate shape through a sprue portion. By using a material having high thermal conductivity for the nearby sprue bush, the tact time can be similarly reduced.

FIG. 8 is a perspective explanatory view similar to FIG. 7A when a light guide plate for a liquid crystal display device is formed. In FIG. 8, reference numeral 8 denotes a light guide plate, 8a denotes a sprue, 8c denotes a gate portion, and is cut by a punch core along a line CC in FIG. That is, in this example, two light guide plates are manufactured by one molding.
This is an example in which two straight cutters are formed on both sides instead of a circular cross section. However, it is also possible to use a mold in which four or more molds are formed at a time, and in this case, the cutter can also be formed in another shape such as a square cross section.

[0035]

According to the present invention, an injection molding die for forming a thin plate-shaped resin molded product and punching a part thereof can be used as a material for a sprue bush for cooling a slightly thick portion of a sprue portion. Since a material having high thermal conductivity is used, the whole can be cured in a very short time together with a thin thin plate-like portion. For example, it takes about 6 to 7 seconds to produce a CD, for example. Can be repeatedly manufactured in about 3 seconds. As a result, a thin plate-shaped resin molded product such as a CD can be formed at very low cost, which can further contribute to the spread of optical disks and liquid crystal display devices.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of a main part of a mold according to an embodiment of the present invention.

FIG. 2 is an explanatory sectional view of a part of a fixed side mold and a movable side mold of the mold of FIG. 1;

FIG. 3 is an explanatory plan view showing the entirety of an injection molding machine incorporating the mold of FIG. 2;

FIG. 4 is a process explanatory view of an example of molding a CD using the mold of FIG. 1;

FIG. 5 is an explanatory cross-sectional view showing a joint between a nozzle and a sprue bush when a resin is injected into a mold from an injection machine.

FIG. 6 is a diagram showing a relationship among hardness, abrasion degree, thermal conductivity, and molding time of a material usable for a mold.

FIG. 7 is an explanatory view of a resin molded product obtained in steps (a) and (d) of FIG.

FIG. 8 is a perspective explanatory view showing an example of a resin molded product when a light guide plate of a liquid crystal display device is manufactured by the injection molding machine of the present invention.

FIG. 9 is an explanatory sectional view showing a main part of a conventional injection molding machine for forming a CD.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injection molding machine 2 Fixed mold 3 Sprue part 4 Movable mold 5 Projecting part 6 Cavity 7 CD 31 Sprue bush 32 Die core 51 Projecting pin 52 Projecting pin holding core 53 Punch type core 54 Projecting bush

Claims (4)

[Claims] 1. A fixed mold having a sprue portion for injecting a resin in a central portion, and a movable mold provided to form a cavity in opposition to the fixed mold and having a projecting portion in the central portion. A sprue bush having a through hole for injecting the resin and having a cooling groove formed on the outer periphery thereof; and a die mold provided on the outer periphery of the sprue bush to cover the cooling groove. A core, wherein the projecting portion slidably holds a projecting pin at a central portion, and a projecting pin holding core having a cooling groove formed on an outer periphery thereof; and a projecting portion provided on an outer periphery of the projecting pin holding core. A punch-type core covering the cooling groove, and a projecting bush provided on the outer periphery of the punch-type core, wherein the sprue bush is made of a material having a higher thermal conductivity than the die-type core; An injection mold in which a core is made of a material having a higher hardness than the sprue bush. 2. The injection molding according to claim 1, wherein the protruding pin holding core is made of a material having higher thermal conductivity than the punch type core, and the punch type core is made of a material having higher hardness than the protruding pin holding core. Mold. 3. The sprue bush or the protruding pin holding core having a high thermal conductivity has a thermal conductivity of 7 or less.
0W / (m ・ K) or more, hardness is 3 in Rockwell hardness
The injection mold according to claim 1 or 2, wherein the injection mold is a material of 0HRC or more. 4. The injection mold according to claim 1, wherein the sprue bush or the protruding pin holding core is made of a beryllium copper alloy, and the die core and the punch core are made of stainless steel.