JPH11105039A - Mold for injection molding and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve corrosion resistance while abrasion resistance is secured, by forming an additional surface layer consisting of the nitride of titanium or chromium which forms a molding face by coating a nickel layer. SOLUTION: In a core 13 and a molding piece 15, the whole backing is constituted of a copper alloy having a proper rigidity such as berylium-copper and phosphorus-bronze. In other words, the surface of the backing 19 is coated with an electroless plating nickel layer 20. The layer 20 is coated with a chromium nitride layer 21 as a surface layer, and the surface of the layer 21 forms a molding surface 22 to be a cavity. With the use of the core 13 and the molding piece 15, even when an ABS resin of a flame retardant grade is injection- molded, a molding having good durability and abrasion resistance is obtained. Even when a resin generating a corrosive gas is molded, the corrosion of a mold backing can be prevented surely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection mold having a mold base mainly composed of copper having a high thermal conductivity and a nickel layer covering the surface of the mold base, and a method of manufacturing the mold. About the method.

[0002]

2. Description of the Related Art In order to shorten the injection molding cycle of a resin, it is necessary to rapidly cool and solidify a molten resin injected into a cavity to a temperature at which the molten resin can be taken out of a mold.

For this reason, a molding piece or a molding core of a mold for forming a cavity of a molded article is mainly made of copper having high thermal conductivity, and a refrigerant passage is formed in the molding piece or the molding core. By flowing a coolant such as water and quickly transmitting the heat of the molten resin injected into the cavity to the coolant,
Promoting cooling of molded articles has been performed.

[0004] However, a mold material mainly composed of copper has good thermal conductivity, but has problems of low hardness and low corrosion resistance. For example, copper alloys such as beryllium copper and phosphor bronze, which are typical mold materials having good thermal conductivity, are about two to four times as large as pre-hardened steel, which is a typical mold material, that is, 0.20 to 0.20. Although it has a thermal conductivity of 45 (cal / cm · sec · ° C), its hardness is only about half that of pre-hardened steel. Moreover, it is a well-known fact that, in addition to hydrogen halide generated when a molding resin containing a halogen-based flame retardant undergoes thermal decomposition, that is, it easily corrodes under a strong acid and also easily under a weak acid. It is.

For this reason, as shown in FIG. 6, which shows an example of a cross-sectional structure of a conventional mold, a hard corrosion-resistant layer 3, for example, about 5 to 10 μm, is formed on a molding surface 2 of a mold base 1 mainly made of copper. A hard chrome plating layer having a thickness of about 3 to 5 μm and a nitride layer of titanium or chromium having a thickness of about 3 to 5 μm are formed to prevent the molding surface 2 from being damaged by friction and to improve the corrosion resistance of the molding surface 2. Was.

[0006] On the other hand, those requiring high processing accuracy,
2. Description of the Related Art In injection molding for a complicated processing shape, a mold is manufactured by an electroforming method. In this electroforming method, a metal serving as a mold is electroformed on the surface of a matrix having the same shape as a molded product, and the electroformed ingot obtained after peeling the matrix is used as a mold. As the metal used in this electroforming method, nickel or the like is generally used in terms of hardness and durability required for a mold, and is usually used so as to withstand molding pressure during molding. Precipitated to a thickness of 5 mm or more.

[0007]

In the conventional mold shown in FIG. 6, the hard chromium plating layer and the titanium or chromium nitride layer constituting the hard corrosion-resistant layer 3 are microscopically porous and gaseous. When a resin that generates a highly corrosive gas is injection-molded, the gas generated from the resin reaches the mold substrate 1 through microcracks existing in the hard corrosion-resistant layer 3 and is injected into the mold substrate. There was a possibility that the base material 1 would be corroded.

On the other hand, in the case of a mold made by electroforming,
Particularly, the internal stress of the nickel electroformed ingot is very large, and the internal stress tends to increase in proportion to the deposited thickness. For this reason, when the nickel electroformed ingot is separated from the matrix, the nickel electroformed ingot is distorted by its internal stress, and the shape of the surface of the matrix is not accurately transferred to the nickel electroformed ingot. As a method of reducing the internal stress of the nickel electroformed ingot, it is effective to reduce the current density at the time of electroforming, but this method requires a very long time to precipitate nickel to a required thickness. I need it.

Furthermore, in order to use the nickel electroformed ingot obtained after the mother die has been peeled off as a mold, it is necessary to perform secondary processing such as end face processing and drilling for mounting on the template. Nickel has the disadvantage that its processing efficiency is not so good, and its thermal conductivity is smaller than that of a mold mainly composed of copper, so that the injection molding cycle of resin cannot be shortened.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide an injection molding die and a method for producing the same, which can improve the corrosion resistance as compared with the conventional one while ensuring the wear resistance.

A second object of the present invention is to provide a high-precision injection molding die by an electroforming method capable of shortening a resin injection molding cycle and a method of manufacturing the same.

[0012]

According to a first aspect of the present invention, there is provided an injection mold having at least a copper-based mold base and a nickel layer covering the surface of the mold base. And a surface layer made of a nitride of titanium or chromium which forms a molding surface by covering the nickel layer.

According to the present invention, the mold base mainly made of copper ensures the ease of temperature control of the injection mold itself. The nickel layer suppresses separation between the mold base material and the surface layer. In addition, the surface layer made of nitride of titanium or chromium which forms the molding surface has a sufficient Hv against wear.
It has a hardness of around 2000.

According to a second aspect of the present invention, there is provided a step of forming an electroless plating layer on at least a surface of a mold base mainly composed of copper, and forming titanium or titanium forming a molding surface on the surface of the electroless plating layer. Forming a surface layer made of chromium nitride by a PVD method.

According to a third aspect of the present invention, there is provided an injection mold comprising at least a mold base mainly composed of copper, and a nickel layer covering the surface of the mold base, wherein The mold base is formed by electroforming copper, and the nickel layer forming the molding surface is formed by electroforming.

According to the present invention, the temperature of the injection molding die itself can be improved by forming most of the injection molding die, that is, the die base material by copper electroforming having low internal stress and good workability. Easy adjustment is ensured. Further, since the molding surface requiring high hardness is formed by nickel electroforming, the generated stress is reduced.

According to a fourth aspect of the present invention, there is provided a step of electroforming a nickel layer on a surface of a matrix having a surface shape corresponding to a molding surface, and electroforming copper on the surface of the nickel layer to form a mold base. A method of manufacturing a metal mold for injection molding, comprising a step of forming a material and a step of peeling the master from the nickel layer.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the injection molding die according to the first embodiment of the present invention, the die base may be beryllium copper or phosphor bronze. Further, the nickel layer may be formed by electroless plating, whereby a dense and uniform film thickness is obtained. In this case, it is desirable that the hardness of the nickel layer formed by electroless plating be kept in the range of Hv750 to Hv850 by heat treatment in order to cover the low hardness of the mold base material. The thickness of the nickel layer formed by the electroless plating may be a thickness that can withstand gas corrosion generated during molding, and is preferably in the range of 5 to 10 μm. If it is less than 5 μm, when the surface roughness of the mold substrate is rough, pinholes are generated in the nickel layer and the mold substrate is easily corroded.

Further, the surface layer may be formed by a PVD method, whereby the surface layer is formed at a temperature lower than the softening temperature of the mold base, and the softening and deformation of the mold base are prevented. The thickness of the surface layer by the PVD method is preferably in the range of 3 to 5 μm. If the thickness of the surface layer is less than 3 μm, it will be difficult to obtain sufficient wear resistance. Conversely, if it exceeds 5 μm, it will be easy to peel off the nickel layer with the generation of stress.

In the method of manufacturing a mold for injection molding according to the second embodiment of the present invention, the mold base may be beryllium copper or phosphor bronze. It is also effective to add a step of keeping the electroless nickel layer to a hardness of Hv750 to Hv850 by heat treatment, thereby covering the low hardness of the mold base material.

In the injection molding die according to the third embodiment of the present invention, it is effective that the thickness of the die substrate is 5 mm or more and the thickness of the nickel layer is within the range of 0.5 to 2 mm.

In the method for manufacturing an injection mold according to a fourth embodiment of the present invention, the thickness of the mold base is set to 5 mm or more,
It is effective to keep the thickness of the nickel layer in the range of 0.5 to 2 mm.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an injection mold according to the present invention will be described in detail with reference to FIGS. 1 to 5. However, the present invention is not limited to such an embodiment, but includes similar problems. It can be applied to technologies in other fields.

FIG. 1 shows a schematic structure of this embodiment. That is, a core 13 on which a runner 12 of molten resin is formed is integrally attached to a stationary mold 11 to which a nozzle at the tip of an injection device (not shown) is connected. A molding piece 15 which forms a cavity 14 of a molded article with the core 13 is integrally attached to a movable mold 16 movable in a direction facing the fixed mold 11 by a mold clamping device (not shown). ing. Cooling water passages 17 and 18 are formed in the core 13 and the molding piece 15 to connect to a cooling water supply source (not shown) and allow the cooling water to flow therethrough. The cooling water passages 17 and 18 are injected into the cavity 14 by an injection device. The molten resin is rapidly cooled and solidified by the cooling water flowing through the cooling water passages 17 and 18.

The core 13 and the molding piece 1 in this embodiment
Numeral 5 is composed of a copper alloy such as beryllium copper or phosphor bronze having relatively high thermal conductivity and appropriate rigidity, and the entire base material is shown. FIG.
That is, the surface of the base material 19 is
The electroless nickel plating layer 20 is further covered with a chromium nitride layer 21 as a surface layer of the present invention, and the surface of the chromium nitride layer 21 is
4 is formed.

The electroless nickel plating layer 20 in this embodiment has a pH of 5.6 containing sodium hypophosphite as a main component.
Is deposited on the surface of the substrate 19 to a thickness of 7 .mu.m in the aqueous solution of the above, and then heated at 270.degree. C. for 70 minutes to increase the hardness to Hv800.
The chromium nitride layer 21 is made of PVD (physical vapor d).
3μ on the surface of the chromium nitride layer 21 by the eposition method.
m.

Injection molding of the flame-retardant grade ABS resin using the core 13 and the molding piece 15 obtained as described above resulted in more than three times the abrasion and corrosion resistance of the conventional mold shown in FIG. It was found to be durable.

The core 13 and the molding piece 15 described above can be manufactured by an electroforming method. FIG. 3 shows the appearance of a base material according to another embodiment of the present invention. That is, the base material 23 in this embodiment is
16 (see FIG. 1) for mounting a plurality of female screw holes 2
4 and the like are formed as secondary processing. This base material 23
Is made of copper electroformed in a copper sulfate bath and has a thickness of 5 mm or more. The surface of the base material 23 is covered with a nickel layer 25 electroformed in a nickel sulfamate bath, and the surface of the nickel layer 25 becomes a resin molding surface. It is effective that the thickness of the nickel layer 25 be within the range of 0.5 to 2 mm.

Here, the physical properties of copper electroforming with a copper sulfate bath and nickel electroforming with a nickel sulfamate bath are shown in Table 1.

[0030]

[Table 1]

As is apparent from Table 1, by forming the base material 23 by copper electroforming with small internal stress and good workability, the temperature control of the core 13 and the forming piece 15 itself can be easily controlled. can do. Further, since the molding surface requiring high hardness is formed by the electroformed nickel layer 25, the internal stress can be reduced.

In the above-described nickel electroforming, a nickel sulfamate bath is used. However, a nickel bath can be used with a Watt bath or a Hoofka salt bath. Copper electroforming can also be performed in a Hoofka copper bath or a copper cyanide bath. In any case, there is no particular limitation on the additives added to the bath.

The core 13 and the molding piece 1 described above by electroforming.
5 is manufactured as follows. That is, a mother die 26 made of glass or copper alloy having the same shape as the molded product as shown in FIG. 4 is prepared, and aluminum or gold is formed on the surface of the mother die 26 having a shape corresponding to the molding surface of the metal mold by vacuum evaporation. A conductive film 27 such as is formed.

Next, the nickel layer 25 is electroformed to a thickness of about 0.5 to 2 mm in a nickel sulfamate bath so as to cover the surface of the matrix 26, that is, the conductive film 27. The resulting copper is electroformed in a copper sulfate bath to a thickness of about 5 mm.

The electroformed ingot 28 thus obtained is subjected to secondary processing into a predetermined shape, and the mother die 26 is peeled from the electroformed ingot 28 and used as the core 13 and the forming piece 15 as shown in FIG. . Since the matrix 26 and the conductive film 27 are joined by the vacuum evaporation method at the time of the separation of the matrix 26, the joining force is weak, and the joining force between the conductive film 27 and the nickel layer 25 by electroforming is smaller. Therefore, the surface of the core 13 and the molding piece 15, that is, the molding surface is in a state formed by the conductive film 27.

[0036]

According to the present invention, at least the surface of a mold base mainly composed of copper is covered with a nickel layer, and this nickel layer is further covered with a surface layer made of titanium or chromium nitride forming a molding surface. As a result, compared to the conventional mold base material mainly composed of copper, it is possible to provide better corrosion resistance and wear resistance, and it is a molding of a resin that generates corrosive gas. In addition, the corrosion of the mold base can be reliably prevented.

Further, since the mold base is formed by electroforming copper, and a nickel layer covering the surface of the mold base and forming a molding surface is formed by electroforming.
The internal stress generated in the electroformed ingot can be reduced as compared with the case where the entire mold is formed by nickel electroforming, and the shape of the master mold can be transferred more faithfully. In addition, since the deposition rate of copper, which is the main component of the mold base material, is faster than that of nickel, the electroforming operation can be completed in a short time. In addition, since most of the mold base is made of copper, the working efficiency in the secondary working can be improved, and the cooling effect on the molded product can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of an injection mold used as an object of the present invention.

FIG. 2 is an enlarged sectional view of a main part of one embodiment of an injection mold according to the present invention.

FIG. 3 is a perspective view showing the appearance of another embodiment of the injection mold according to the present invention.

FIG. 4 is a conceptual working diagram showing a manufacturing procedure of the embodiment shown in FIG. 3 together with FIG.

FIG. 5 is a conceptual working diagram showing a manufacturing procedure of the embodiment shown in FIG. 3 together with FIG. 4;

FIG. 6 is a cross-sectional view in which main parts of an example of a conventional injection mold are extracted and enlarged.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 Fixed side mold 12 Runner 13 Core 14 Cavity 15 Molding piece 16 Movable mold 17, 18 Cooling water passage 19 Base material 20 Electroless nickel plating layer 21 Chromium nitride layer 22 Molding surface 23 Base material 24 Female screw hole 25 Nickel layer 26 matrix 27 conductive film 28 electroformed ingot

Claims (12)

[Claims] 1. A mold base mainly composed of at least copper,
An injection mold having a nickel layer covering the surface of the mold substrate, further comprising a surface layer made of a nitride of titanium or chromium that forms a molding surface by covering the nickel layer. A mold for injection molding. 2. The injection mold according to claim 1, wherein the mold base is beryllium copper or phosphor bronze. 3. The injection mold according to claim 1, wherein the nickel layer is formed by electroless plating. 4. The injection mold according to claim 3, wherein the hardness of the electroless nickel layer is kept in a range of Hv750 to Hv850 by heat treatment. 5. The injection molding die according to claim 1, wherein the surface layer is formed by a PVD method. 6. A step of forming an electroless plating layer on at least a surface of a mold base mainly composed of copper, and a surface made of titanium or chromium nitride constituting a molding surface on the surface of the electroless plating layer. Forming the layer by a PVD method. 7. The method according to claim 6, wherein the mold base is beryllium copper or phosphor bronze. 8. The method according to claim 6, further comprising the step of heat-treating the electroless nickel layer to a hardness of Hv750 to Hv850 by heat treatment. 9. A mold base mainly composed of at least copper,
An injection mold comprising a nickel layer covering the surface of the mold substrate, wherein the mold substrate is formed by electroforming copper,
The injection molding die, wherein the nickel layer forming the molding surface is formed by electroforming. 10. The injection mold according to claim 9, wherein said mold base material has a thickness of 5 mm or more, and said nickel layer has a thickness of 0.5 to 2 mm. 11. A step of electroforming a nickel layer on a surface of a matrix having a surface shape corresponding to a molding surface; a step of electroforming copper on a surface of the nickel layer to form a mold base; Peeling the master from the nickel layer. 12. The injection molding die according to claim 11, wherein the thickness of the mold base is 5 mm or more, and the thickness of the nickel layer is in the range of 0.5 to 2 mm. Production method.