JPH04105908A - Graphite die for plastic molding - Google Patents

Abstract

PURPOSE:To improve workability and handling convenience and ensure a sufficient strength of a die by a method wherein a part or whole of the graphite material constituting a base material is divided with the projecting parts of a molding cavity independent of one another and the faces of the projecting parts are supported by a reinforcing member in such a manner that the projection faces combine to constitute a molding cavity completely. CONSTITUTION:A base material 21 for a die for use in the formation of plastic is formed of graphite material and a part or whole of the die surface other than a molding cavity surface 22 is supported by metal reinforcing member 23 to protect the base material 21. The graphite material constituting the base material 21 is divided by the surface coplanar with the faces of projecting parts 27 with the projecting parts 27 of the molding cavity 22 independent of one another. Since the graphite material having the projecting parts 27 is made free from the corner parts by this graphite dividing method, there is no localized concentration of stress due to resin pressure and solidification pressure and no cracking or breaking is caused to the divided graphite material.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a mold used for molding plastic molded articles, and particularly to a graphite mold for plastic molding whose base material is made of graphite material.

(Prior Art) So-called plastics are generally materials with key properties such as light weight, economy, workability, and corrosion resistance, and are used in an extremely wide range of applications, from all kinds of industrial applications such as electrical, mechanical, and automobiles to daily necessities. ing.

To mold these various plastic products, molds made of metal materials such as iron and its alloys are generally used.

For molds made of this type of metal material (hereinafter referred to as molds), when a large number of molds are to be made, it is necessary that the mold material be metal from the viewpoint of mold life. However, with the recent trend toward high-mix, low-volume production, the need for prototype mold production is increasing.

■Mold costs account for a larger proportion of molded products, increasing product costs.

■Producing molds requires a great deal of time and money.

The molds commonly used in the past had these drawbacks.

Therefore, the present inventors have developed a special mold using a high-strength and high-density graphite material that can sufficiently withstand the pressure during plastic injection molding and has a good mold-polished surface as a mold material to replace metal. Various proposals have been made in JP-A-63162205 and others. In making the invention proposed in this publication, the inventors focused their attention on the following points.

(1) Since the cutting resistance of graphite during machining is 115 to 1/10 that of metal, high-speed machining is possible.

(2) Since graphite is a material that can be more easily finished by hand than metal, parts or processes that previously relied on electrical discharge machining can be easily finished by hand.

(3) Since graphite is a material with an extremely small coefficient of thermal expansion, it is easy to obtain precision when molding plastics.

(4) The specific gravity of the graphite mold is less than 1/4 of that of the mold, making it relatively lightweight, making it easy to handle plastic molding molds even in complex or high-speed operations.
Easy to operate.

(5) Since graphite has good thermal conductivity, the time required for heating and cooling recycling is short, making it possible to mold plastics in a high-speed cycle.

The above effects make it possible to mold plastic products in extremely small lots and prototypes.

(6) Graphite has excellent thermal stability, with a heat resistance temperature of 3000°C compared to the several hundred degrees Celsius for metals, and its coefficient of thermal expansion is extremely small. It is something that

By the way, subsequent research by the present inventors has revealed that the following points must be taken into consideration in this type of graphite mold for plastic molding.

That is, first of all, when forming plastic products, for example, if we consider injection molding using thermoplastic plastic as a material, the molding pressure for vinyl chloride resin is about 141 kg/cm2. With acrylic resin, a molding pressure of approximately 700 kg/cm2 must be applied, and the mold must naturally be able to withstand such molding pressure. Moreover, in addition to simply applying molding pressure to the mold, for example, in a mold in which a movable mold is moved relative to a fixed mold to form a sealed molding cavity,
In order to form the sealed cavity, the movable mold must be pressed against the fixed mold with a pressure (pressing force) higher than the molding pressure. The mold must be able to withstand this pressing force. When the mold is made of graphite material, it has the above-mentioned advantages (1) to (6) over the so-called mold, but the reality is that the strength against applied pressure is not as strong as the mold. It is.

Second, when the mold is made of graphite material, if there is a gap between the graphite material and the member that supports it,
Pressure changes during the molding cycle using this graphite mold cause the graphite material to crack, resulting in damage to the mold itself. In order to avoid this problem, it is necessary to support the mold made of graphite material so that there are no gaps.

Thirdly, when forming a mold made of graphite material, an integral piece of graphite material of a predetermined size is cut out to form the cavity surface, which is the necessary mold surface. subject to restrictions. In other words, graphite material is more brittle than metal, so for example, the protrusion shown in Figure 9 (2)
7) In areas where the strength is weak, such as the lower end, the curved surface must be as large as possible, and the height of this protrusion (27) must be made as low as possible and its width must be made as large as possible. In particular, the first
As shown in Figure 0, when the plastic material is forcibly injected into the molding cavity with the above-mentioned pressure, the protrusion (27) is pressed by the plastic material, causing a crack in a part of the corner of the mold. Furthermore, as shown in Fig. 11, when the plastic material solidifies after injection, force is applied to this protrusion (27) due to shrinkage of the plastic material, which tends to cause cracks in some corners of the mold. It is.

Therefore, when using a mold made of graphite material, the shape of the molded product is also restricted by the restrictions of the mold itself.

Therefore, the present inventors have conducted various studies on how to give sufficient strength to graphite molds while making full use of the characteristics of the graphite material used as molds, and as a result, they have developed the present invention. It was completed.

(Problems to be Solved by the Invention) The present invention has been made based on the above circumstances, and the problem to be solved is to ensure the strength of graphite molds while making full use of the characteristics of graphite.

It is an object of the present invention to provide a graphite mold for plastic molding that has good workability, is easy to handle, can sufficiently guarantee strength, and is free from restrictions on the formation of a cavity surface. be.

(Means and operations for solving the problem) In order to solve the above problem, the means taken by the invention according to the first claim will be explained with reference numerals used in the examples. [Plastic molding] The base material (21) of the mold used for this is formed from a graphite material, and part or all of the mold surface other than the molding cavity surface (22) of this graphite material is supported by a metal reinforcing member (23). In a graphite mold (20) for plastic molding designed to protect a base material (21) made of graphite material, part or all of the graphite material constituting the base material (21) is placed in the molding cavity (2
2) is characterized in that when the projections (27) are separated into independent parts and supported on the reinforcing member (23), each surface completely constitutes the molding cavity (22). This is a graphite mold (20) J for plastic molding.

That is, in this graphite mold for plastic molding (2o), the graphite material constituting the base material (21) is
As shown in FIGS. 3 and 4, the molding cavity (22
It is necessary that the protrusions (27) of ) are divided into independent parts. The reason for this is that when the plastic material is injected or solidified, stress is concentrated at the corners due to the force generated by this, and it is necessary to completely eliminate such stress concentration points from each graphite material. It is. For this purpose, as shown in FIG. 4, each graphite material is preferably divided by a plane that is continuous in plan with the plane of the protrusion (27) constituting the molding cavity (22).

Here, the reinforcing member (23) needs to be formed on at least a part or all of the mold surface other than the molding cavity (22) surface. The reason for this is that if it is on the molding cavity (22) side, the mold surface will be formed by the reinforcing member (23), and there will be no point in constructing the graphite mold (2o) for plastic molding with graphite material. Naturally, in a type of mold in which a movable mold is pressed against a fixed mold, this is to reinforce the outside of the molding cavity (22) in the direction in which the pressing force is applied.

For this purpose, as shown in FIG. 5 or 6, for example, it is preferable to interpose a pusher (26) made of a metal material in contact with both, and this pusher (26)
It is preferable to fix it to the reinforcing member (23) with a bolt (25) that is tightened on the J' (23) side. In addition, the pusher (26
), it is preferable to use a pair of pushers having a size such that they come into contact with the entire two adjacent sides of the substantially square base material (21), and these pushers (26) push the base material (21) It is preferable to press the other two sides of the reinforcing member (23). Or, as shown in Figure 7,
The bottom surface (21a) of the base material (21) is brought into contact with the reinforcing member (23), and the supporting parts (24) integrally provided on both sides of this base material (21) are screwed onto the reinforcing member (23) side. It is preferable to support the reinforcing member (23) in pressure contact with the reinforcing member (23) by the pole (25) to be attached. That is, the bottom surface (21a) of the base material (21)
) and the reinforcing member (23) are in perfect contact with each other, so that no problematic gap is always formed between the base material (21) and the reinforcing member (23), and therefore, the base material ( The support part (24) formed integrally with the reinforcing member (23) may be supported in pressure contact with the reinforcing member (23) by means of a bolt (25) that is screwed and fixed to the reinforcing member (23).

In the graphite mold (20) for plastic molding according to the invention of the first claim configured as described above, first, the base material (21) is formed from a graphite material divided into a plurality of pieces, so that it is different from that in the case of metal. The cutting resistance is as low as 115 to 1/10, making it very easy to process, and the coefficient of thermal expansion is small, resulting in very high molding accuracy.

As described above, it is necessary to divide the graphite material in a state in which the projections (27) of the molding cavity (22) are made independent, but the state in which the projections (27) are made independent means that the projections In addition to dividing the graphite material on a plane that is continuous with the plane of the part (27), it also includes all cases where the side surface shown in Figure 4 of the graphite material that has a part that becomes the protrusion part (27) is flat. For this reason, graphite materials that do not have protrusions (27) may have irregular shapes such as triangles or trapezoids.

As a result of dividing the graphite material in this way, the protrusions (27
), some of the corners do not exist at all, so the stress due to the force shown in Figure 10 or 11 is not concentrated and applied to each divided graphite material. Cracks and damage will no longer occur.

Of course, since the base material (21) in this graphite mold (20) for plastic molding is composed of the graphite material divided as described above, its manufacture is even easier. In addition, since the base material (21) is composed of divided graphite materials, even if a damaged part occurs, only the damaged graphite material can be replaced and the graphite mold (21) for plastic molding can be reused. ) can be configured. In addition,
It goes without saying that the entire base material (21) may be divided or a necessary portion thereof may be divided.

In addition, in this graphite mold for plastic molding (20), the bottom surface (21a) of the graphite base material (21) located on the opposite side of the molding cavity (22) is supported by the reinforcing member (23) as shown in FIGS. Although it is protected as shown in the figure, when force is applied from the outside to this graphite mold for plastic molding (20), the force is transferred to the graphite mold for plastic molding (20) through this reinforcing member (23). In other words, this reinforcing member (23) ensures the strength of the graphite base material that makes up the graphite mold (20) for plastic molding, while also dispersing the applied force well. It is.

Therefore, in this graphite mold for plastic molding (20), each divided graphite material is in close contact with each side thereof, and moreover, the reinforcing member (23)
) is supported on the entire bottom surface (21a), and
Each supporting portion (24) integrally oriented with the base material (21) has a reinforcing portion H (
Since the reinforcing member (23) is pressed against the reinforcing member (23) by each bolt (25) screwed onto the reinforcing member (23), there is no gap between the base material (21) and the reinforcing member (23). The graphite base material (21) will not be damaged by external forces, the pressure of the injected plastic material, or the forces generated during its curing.

In addition, since molding pressure from the injected plastic material is applied inside the molding cavity (22), even if this pressure is applied directly to each graphite material constituting the graphite base material (21), the graphite base material Since (21) is backed up by the reinforcing member (23), each graphite material will not crack or be damaged by this molding pressure.

The means taken by the invention according to the second claim is the base material (21) of the graphite mold for plastic molding (2o) according to the first claim.
), each of the graphite materials separated with their protrusions (27) separated from each other was integrated with an adhesive. In this case, any adhesive may be used as long as it can bond the graphite materials together and can sufficiently withstand the temperature during plastic molding. For example, epoxy resin or Copna resin may be used. If the graphite material bonded with Copna resin is fired at an appropriate temperature, this Copna resin can be carbonized or graphitized, which is very advantageous.

The graphite mold (20) for plastic molding integrated using an adhesive as described above has the same effect as that of the first claim above, and also has the same effect as that of the base material (21). This allows for easy handling or storage of the base material (21) within the reinforcing member (23).

(Example) Next, graphite molds for plastic molding (20) according to each invention
will be explained according to examples. In Figure 1, a graphite mold (20) for plastic molding according to each invention is inserted into an injection molding machine (
10) is shown, and this injection molding machine (
In step 10), the plastic material introduced from the hopper is pressurized and kneaded by the screw (11) in the cylinder (12) while simultaneously sending it to the molding cavity (22) on the graphite mold (20) side for plastic molding. , the plastic material is heated to its plasticizing temperature. The plasticized plastic material is then forcibly fed into the cavity of the graphite mold (20) for plastic molding according to the present invention.

The graphite mold (20) for plastic molding is made of a base material (21).
) is made of graphite material, and a fixed mold and a movable mold for constructing the mold were formed using isotropic graphite material, and a mold for injection molding was produced. The processing time required for this molding is approximately 1/8 compared to metal molding.
It was possible to shorten it to

In this graphite mold for plastic molding (2o), as shown in FIG. 1 or 2, a graphite base material (
A reinforcing member (23) made of metal is integrally formed on at least the surface of the mold other than the surface of the molding cavity (22) of 21). In particular, in the embodiment shown in Fig. 1, the graphite mold (2o) for plastic molding is of a two-piece type with a fixed mold and a movable mold, and the reinforcing member (
The surface 23) is formed to match the parting surfaces of the fixed mold and the movable mold. Thereby, when the fixed mold and the movable mold are pressed against each other by a strong pressing force, the fixed mold and the movable mold made of graphite material are reliably protected.

In this example, the reinforcing member (23) is configured to extend to the side of the molding cavity (22), but this is due to the molding pressure being extremely high. This is to deal with cases where the lateral area of the product is very large. Therefore, when molding a flat plate-like plastic product or something similar to this, the reinforcing member (23) is used in the molding cavity (23).
2) There is no need for the structure to extend to the side portions of 2).

Various materials can be considered for constructing the reinforcing member (23), but metal is the most suitable, and in this example, metals used as so-called mold materials such as 350C steel and SCM steel are used. material used.

In each graphite mold (20) for plastic molding, the graphite material constituting the base material (21) is divided into parts as shown in FIGS. 3 and 4, for example. In this case, what is important is that the surface of the molding cavity (22) formed by the base material (21) has a complicated shape depending on the plastic molded product, but the surface of the molding cavity (22) that protrudes In other words, the projections (27) are divided into independent parts.

An example of how to divide the graphite material is shown in Figure 4.As shown in Figure 4, each divided graphite material has a corner part where stress tends to concentrate as shown in Figure 9. does not exist at all. Therefore, when dividing the graphite material, it is preferable to use a cutting surface that lowers the side surface of the protrusion (27). Note that it is advantageous that the divided graphite materials are formed so as to be in surface contact with each other.

The above are examples common to each invention. Next, examples showing the characteristic parts of each invention will be explained in separate sections.

・About the graphite mold for plastic molding (20) of the first claim Figures 2 to 8 show the graphite mold for plastic molding (20) according to the first claim. The base material (21) constituting the reinforcing member (20) is stored in a storage section formed in the center of the reinforcing member (23), and its bottom surface (21a)
) comes into contact with the inner surface of the storage section.

Note that supporting parts (24) as shown in FIG. 8 may be formed integrally on both sides of this base material (21), and each of these supporting parts (24) is connected to a reinforcing member using bolts (25). It may be fixed by pressing on the (23) side. In this case, the base material (21) has a reinforcing member (23) l on its bottom surface (21a).
It is supported by pressure. Of course, each support part (2
4) is formed in a place that does not interfere with the molding cavity (22), and the bolt (2) inserted through this support part (24)
5) is pressed and fastened within the support portion (24) so as not to come into contact with other base material (21), etc. (not shown).

Further, in this graphite mold for plastic molding (20), support for the reinforcing member (23) of the base material (21) is provided by the fifth
As shown in the figure or FIG. 6, this is done through a pusher (26) placed between the base material (21) and the reinforcing member (23). In this case, basically the base material (21)
is stored in a storage portion formed in the center of the reinforcing member (23), and the reinforcing member (23) of this base material (21)
) is not supported by pressing the bottom surface (21a) of the base material (21) against the reinforcing member (23), but by pressing the side surface of the base material (21) against the side surface inside the storage part formed on the reinforcing member (23). This is what I am trying to do.

In particular, in this example, the substantially rectangular base material (21)
A part of the corner is reinforced with reinforcing members (23) on two sides sandwiching it.
It is supported by pressing it to the side.

That is, in this graphite mold for plastic molding (20), as shown in FIG. The pushers (26) are stored in the base material (21), as shown in FIG.
) located in the same direction as the bottom surface (21a) of ) (2
5) is pressed and supported on the opposite side.

Therefore, each bolt (25) is formed in the reinforcing member (23) and is screwed into a screw hole parallel to the bottom surface (21a) of the base material (21), and the amount of screwing is the same as that of the base material (21). ) is set in consideration of the pressure applied to the reinforcing member (23).

In particular, the pressing surface of each pusher (26) in this graphite mold (20) for plastic molding is the bottom surface (21) of the base material (21).
a), and in order to completely contact the pressing surface of this pusher (26), the contact surface on the base material (21) side is also perpendicular to the bottom surface (21a). It is formed. In this case, as shown in FIG. 7, support parts (24) are formed at the ends of each graphite material constituting the base material (21), and each of these support parts ( 2
4) and insert the bolt (25) into the reinforcing member (23).
) may be fixed by screwing on the side.

FIG. 6 shows another embodiment of this graphite mold (20) for plastic molding. In this graphite mold for plastic molding (20), the pusher (26) constituting it
An inclined surface (26a) is formed on the side opposite to the surface that contacts the base material (21) of the pusher (26), and the thickness of the pusher (26) is gradually reduced. An inclined surface (23a) corresponding to the inclined surface (26a) of this pusher (26)
) is formed. In this embodiment, bolts (
25), the axial direction of which is the bottom surface (21a) of the base material (21).
), and by tightening the pusher (26) to the reinforcing member (23) side with this bolt (25), the inclined surface (26a) on the pusher (26) side and the reinforcing member (23 ) by guiding the inclined surface (23a) on the sixth side.
A pressing force to the left in the figure acts on the pusher (26). In order to ensure this effect, the insertion hole for the bolt (25) formed in the pusher (26) is designed to allow movement in the lateral direction with respect to the bolt (25). ) is formed to be sufficiently larger than the diameter of the

・Graphite mold for plastic molding (20) according to the second claim
Regarding this graphite mold for plastic molding (20), the graphite material that is the base material (21) is divided into parts in the same way as that according to the first claim described above, but each of these divided parts is divided into two parts. The only difference from the first claim is that graphite materials are bonded together with an adhesive on their mutually contacting surfaces.

The adhesive used in this graphite mold for plastic molding (20) is epoxy resin or so-called Copna resin. If the adhesive itself can sufficiently withstand the temperature of the plastic molding material or the temperature during molding, it is sufficient to bond each divided graphite material with this adhesive.

(Effect of the invention) By configuring as described above, according to each invention,
It has good workability, is easy to handle, and has sufficient strength, and has about 4 to 6 times the strength and durability of conventional products. Moreover, to provide a graphite mold for plastic molding that can sufficiently withstand even if force is applied to the protrusion (27) projecting into the molding cavity (22) during injection or solidification of the material. It is something that can be done. In addition to this effect, each invention also has the following effects.

In the invention according to the first claim, since the graphite material constituting the base material (21) is formed by dividing it according to the projections (27) protruding into the molding cavity (22), The formation of each graphite material itself becomes easy, and the structure of the base material (21) as a whole becomes simple.However, if there is a damaged graphite material, just replace it and replace it with the other one. Although the part can be used as is, this graphite mold for plastic molding (2o
) can be repaired at low cost. Moreover, with such a so-called simplest configuration, the base material (21) can be supported on the reinforcing member (23) = 25 side without any gap, so that the base material (21) is supported against the reinforcing member (23). This makes it possible to reliably perform pressure contact support.

The graphite mold for plastic molding (20) according to the second claim has exactly the same effect as the graphite mold for plastic molding (20) according to the first claim, except that its parts can be easily replaced. In addition, when the divided graphite materials are integrated to form a base material (21), this base material (21) can be easily handled, and leakage of resin to the dividing interface can be prevented. This has the effect of being able to prevent this.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a main part of a graphite mold for plastic molding according to the present invention and an injection molding machine configured using the same, Fig. 2 is a plan view of the graphite mold for plastic molding according to the present invention, and Fig. 3 is a partial plan view showing the schematic structure of this graphite mold for plastic molding, FIG. 4 is a sectional view of FIG. 3, FIG. 5 is a partial sectional view taken along the line V-V of FIG. 2, and FIG. is a partial sectional view corresponding to FIG. 5 showing another embodiment, FIG. 7 is a plan view showing another embodiment of the graphite mold for plastic molding, and FIG. 8 is a partial sectional view corresponding to FIG. 5 showing another embodiment. FIG. 9 to 11 show a conventional technique, in which FIG. 9 is a partial sectional view of a graphite mold for plastic molding, FIG. 10 is a partial sectional view showing the state when plastic material is injected, FIG. 11 is a partial sectional view showing the state of the graphite mold for plastic molding when the injected material solidifies. Explanation of symbols 10... Injection molding machine, 20... Graphite mold for plastic molding, 21... Base material, 21a... Bottom surface, 22...
- Molding cavity, 23... Reinforcement member, 24... Support part, 24a... Inclined surface, 25... Bolt, 26...
- Pusher, 27... protrusion. That's all / Akira γ21 Figure 7 Figure 6a Figure 9 11■

Claims (1)

[Claims] 1) The base material of a mold used for plastic molding is formed from a graphite material, and part or all of the mold surface other than the molding cavity surface of this graphite material is supported by a metal reinforcing member. In the graphite mold for plastic molding, which protects the base material made of the graphite material, part or all of the graphite material constituting the base material is separated from the protrusion of the molding cavity. 1. A graphite mold for plastic molding, characterized in that when the graphite mold is divided and supported by the reinforcing member, each surface completely constitutes the molding cavity surface. 2) The graphite mold for plastic molding according to claim 1, wherein the divided graphite materials are integrated with each other using an adhesive.