JPH075748B2 - Conductive molding and molding method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive molded body and a molding method thereof, and more particularly to a conductive molded body in which a conductive compounding material is mixed in a non-conductive resin and a molding method thereof.

[0002]

2. Description of the Related Art With the recent rapid spread of electronic equipment and the use of resin in the housing of electronic equipment, malfunctions of electronic equipment due to electromagnetic waves (noise) generated outside have become frequent. One of the methods for preventing such radio interference is to use a housing made of a conductive resin as a housing for electronic equipment. By the way, since the resin is generally non-conductive, it is conceivable to mix the resin with a conductive substance such as a metal to impart conductivity.
In this case, in order to impart conductivity to the resin, it is important to form a continuous layer made of a conductive substance in the resin. Therefore, in Japanese Patent Publication No. 25772/1990 or Japanese Patent Publication No. 27137/1990, when molten resin is extruded into a sheet shape and taken out to produce a resin sheet, molten solder is fibrous or It has been proposed to obtain a conductive resin sheet in which a fibrous body of solder or a narrow solder sheet-like body is formed in the resin sheet take-out direction by extruding into a narrow sheet shape.

[0003]

In the above-mentioned conductive sheet, a fibrous body of solder or a narrow solder sheet-like body is formed as a continuous conductive layer in the conductive sheet pulling direction in the conductive sheet. Therefore, excellent conductivity can be exhibited in this direction. However, in the direction perpendicular to the conductive sheet pulling direction of the conductive sheet, there is no continuous conductive layer, and the conductivity is significantly reduced. On the other hand, when the width of the solder sheet-shaped body is widened in order to eliminate such a directionality of conductivity, the solder sheet-shaped body and the resin sheet may be separated due to poor affinity between the solder and the resin. Therefore, an object of the present invention is to propose a conductive molded body in which the directionality of the conductivity is eliminated and the conductive substance and the resin are not separated, and a molding method thereof.

[0004]

In order to achieve the above-mentioned object, the present inventors have used a low melting point metal such as solder having a melting point lower than the molding temperature at the time of melt molding a resin to form a molded body. Various studies were conducted on the assumption that a conductive molded body having a network structure formed therein is effective. First, when the resin and the solder were kneaded, it was found that it was difficult to uniformly disperse the solder in the resin if only the resin and the solder were kneaded, because an aggregated layer of the solder was likely to develop in the resin. Therefore, the inventors of the present invention have made extensive studies to disperse the solder in the resin, and knead and knead the solder and the copper powder in advance and mix them into the resin to obtain the solder in the obtained molded body. Was found to be well dispersed and the directionality of the conductivity of the molded body was substantially eliminated, and the present invention was reached.

That is, according to the present invention, in a conductive molded product in which a conductive compounding material is mixed in a non-conductive resin, the conductive compounding material is higher than the molding temperature at the time of molding the non-conductive resin. Also has a high melting point and has a high melting point at least the surface of which is made of a high melting point metal having a melting point higher than that of the resin, and a solid having a melting point lower than the molding temperature of the non-conductive resin and normal temperature. And a low-melting-point metal layer made of a low-melting-point metal that covers the surface of the high-melting point metal, and the low-melting point metal flows and diffuses in the resin flow direction in the molded body. It is in a conductive molded body. Further, the present invention uses the above-mentioned conductive compounding material as the conductive compounding material when molding a conductive molded body in which a conductive compounding material is mixed in a non-conductive resin. Melt the resin containing the compounding material, and then
It is also a method of molding a conductive molded body, which is characterized in that the molten resin is filled into a cavity of a mold while flowing. In the present invention having such a configuration, the high melting point body is a powdery body, the low melting point metal constituting the conductive compounding material is solder, and the high melting point body is copper powder, and / or the conductive compounding material. When 20% by volume or more is mixed in the molded product, a conductive molded product exhibiting excellent conductivity can be obtained.

[0006]

In the conductive molded article of the present invention, the low melting point metal layer formed on the surface of the high melting point body is dispersed in a net shape while spreading in the flow direction of the molten resin. Therefore, the electroconductive molding of the present invention exhibits good electroconductivity and the electroconductivity direction is substantially eliminated. The reason why the low-melting-point metal is dispersed like a net in the formed body is presumed as follows. That is, the affinity between the molten low melting point metal and the metal surface of the high melting point body is generally higher than the affinity with the molten resin. Therefore, at the time of molding, when the high melting point body in the molten resin moves with the flow of the molten resin,
The molten low melting point metal existing around the metal surface of the high melting point body also moves together with the high melting point body. At that time, since a part of the molten low melting point metal is dispersed in the molten resin, it is possible to form a network structure of the low melting point metal in the resin.

[0007]

According to the present invention, the conductive compounding material to be blended with the conductive molded article is composed of a high melting point component having a melting point higher than the molding temperature at which the non-conductive resin to be blended is molded, and at least the surface thereof. Where the surface of the high melting point body formed of a high melting point metal having a higher melting point than the molding temperature has a lower melting point than the molding temperature of the non-conductive resin and is a solid low melting point metal at room temperature. It is essential that it is covered with layers. As the high melting point material constituting such a conductive compound material, a powdery body, particularly a metal powdery body is preferable. This is because the powdery material is likely to move with the flow of the molten resin, and the molten low melting point metal around the surface of the powdery material is likely to be dispersed in the resin.
Examples of such metal powders include copper (Cu), nickel (Ni), iron (Fe), zinc (Zn), lead (Pb),
It may be formed of a single metal such as a nickel (Ni) -chromium (Cr) alloy, tungsten (W), or brass, and different metals are attached to the surface of the metal powder by plating or the like. It may be one. Furthermore, even a powdery material made of non-metal such as carbon, glass, or ceramic may be used as long as a metal layer such as nickel (Ni) is formed on the surface by electroless plating or the like. The particle size and the like of such a powder having a high melting point may be determined in consideration of the molding performance and the like of the resin to be mixed, and is usually 100 mesh or less, preferably 200 mesh or less.
Below the mesh is used.

Further, the low melting point metal forming the low melting point metal layer covering the metal surface of the high melting point body may be a metal having a melting point lower than the molding temperature of the non-conductive resin to be blended and solid at room temperature. Better, zinc (Zn), lead (Pb), tin (S
n), solder and the like. Above all, solder is particularly preferably used. When solder is used as the low melting point metal, it is sufficient to use a composition having a desired melting point in relation to the melting point of the resin to be mixed. In the present invention, the coating weight ratio (low melting point metal / high melting point body) showing the coating amount of the low melting point metal varies depending on the type of the high melting point body. For example, when copper powder is used as the high melting point material, the coating weight ratio is preferably 0.7 or more, and particularly preferably 2 or more. With a conductive compounding material having a coating weight ratio of less than 0.7, it tends to be difficult for the obtained molded product to exhibit sufficient conductivity. On the other hand, if the blending weight ratio of the low melting point metal is too high, the low melting point metals tend to aggregate in the molten resin. When iron powder is used as another refractory material, the coating weight ratio is preferably 0.6 or more. Here, the iron powder that can be used may be one that contains an iron component as a main component, and may be carbon steel as well as pure iron. Furthermore, when lead powder is used, it is preferable to set the coating weight ratio to 0.3 or more, and when using iron powder whose surface is nickel-plated, the coating weight ratio is set to 1 or more. Preferably. still,
The upper limit of the coating weight ratio varies depending on the type of the high melting point material, the size such as the particle size, the surface characteristics, the type of the low melting point metal, and the like, so it is preferable to experimentally determine in advance.

The conductive compounding material used in the present invention is composed of a component having a melting point higher than the molding temperature at the time of molding the non-conductive resin to be compounded, and at least the surface is formed of a metal having a melting point higher than the molding temperature. And a low melting point metal having a melting point lower than the molding temperature point and solid at room temperature in the presence of a flux that prevents the formation of an oxide film on the metal surface of the high melting point material. It can be produced by kneading while heating to a temperature not lower than the melting point of the metal and lower than the melting point of the high melting point metal to form a low melting point metal layer on the surface of the high melting point body. Here, even if the high melting point metal having an oxide film formed on the metal surface and the low melting point metal are kneaded, the wettability between the low melting point metal and the metal surface of the high melting point body is insufficient. The metal layer cannot sufficiently cover the surface of the high melting point body. In order to prevent the formation of such an oxide film, a flux is present in the present invention.
As the flux used at this time, a zinc chloride-based flux can be used.

As a method for producing a conductive compound material using such a flux, a high melting point material and a flux are kneaded in advance, and then a low melting point metal is added and heated to knead while melting the low melting point metal, It is possible to employ a method in which a flux is added to a low-melting-point metal that has been melted in advance, and then a high-melting-point body is added and kneading, or a method in which the high-melting-point body, the low-melting-point metal and the flux are simultaneously kneaded and heated. At this time, the heating temperature needs to be equal to or higher than the melting point of the low melting point metal and lower than the melting point of the high melting point metal. In such a manufacturing method, when the metal surface of the high melting point material becomes invisible,
It can be judged that the metal surface of the high melting point body is covered with the melted low melting point metal. After the metal surface of the high melting point metal is covered with the low melting point metal, the low melting point metal is cooled and solidified, and then the lumps that have been solidified into lumps are re-particled, and then the flux remaining in the low melting point metal layer is washed To do. The kneading of the high melting point metal and the low melting point metal in the presence of such a flux can be performed in the atmosphere, but a flux cleaning step is required.

In this respect, if the kneading is carried out under a substantially non-oxygen condition, it is not necessary to allow the flux to be present and the flux cleaning step can be omitted. Furthermore, the heating temperature can be lower than that in the case of kneading in the presence of a flux, and may be lower than or equal to the melting point of the low melting point metal (preferably (melting point of low melting point metal-10 ° C) or higher). Here, "substantially in a non-oxygen state" means that kneading is performed under a high vacuum of 5 mmHg or less, or under a nitrogen or hydrogen atmosphere. In order to mix the conductive compound thus obtained with a resin that imparts conductivity, the resin to be mixed and the conductive compound may be directly added to an injection molding machine or the like and molded, You may shape | mold by what is called a master-chip method which supplies the chip | tip which mix | blended the electroconductive compounding material in resin with high concentration with the resin which gives electroconductivity to an injection molding machine etc. Incidentally, as the resin to be mixed with the conductive compounding material of the present invention, conventionally used resins such as polypropylene, nylon, polyester, ABS resin,
Polycarbonate, polyacetal, etc. can be used. However, when adding a conductive compounding material prepared by adding flux to polyacetal or polycarbonate, the flux should be thoroughly washed and removed to prevent the resin from being decomposed by the added flux. It is preferable.

Here, the distribution state of the low melting point metal in the molded body shown in FIG. 1 will be described. The molded body shown in FIG. 1 is formed by injection molding a resin mixed with a conductive compounding material, and a sprue portion 2 is formed on the upper surface of a disc portion 1.
When molding this molded body, the molten resin flows downward from above the sprue portion 2 in the cavity of the mold, and further radially flows from the lower end of the sprue portion 2 toward the peripheral edge of the disc portion 1. FIG. 2 shows a cross section of the disk portion 1 of the molded body in a direction parallel to the flowing direction of the molten resin, and FIG. 3 shows a cross section perpendicular to the flowing direction of the molten resin. Figure 2
3 to 3 are photomicrographs showing a cross section magnified about 150 times. As is apparent from FIGS. 2 to 3, particularly FIG. 3, the low melting point metal M is diffused in the resin P while flowing in the flow direction of the resin P, and the low melting point metal M is dispersed to form a network structure. Can be inferred. In such a molded product, there is substantially no variation in conductivity within the molded product, and uniform conductivity can be exhibited. The molded product thus obtained can exhibit excellent conductivity, and thus can be suitably used for electromagnetic wave shielding. Further, when lead or the like having an X-ray shielding ability is used as the high melting point body or the low melting point metal constituting the conductive compounding material, this molded product has
Since it has the ability to shield rays, it can also be used for X-ray shielding.

Further, when a case of an electric product such as an electric washing machine is formed from the molded product of the present invention, the case can be directly grounded. At that time, since the surface of the molded article of the present invention can be directly soldered, the ground terminal can be directly soldered to the case. Moreover, when soldering to the surface of the molded body, the effect of the solder heat is practically limited to the soldered portion, so a means for protecting the components and the like arranged in other portions from the solder heat. Can be eliminated. In addition, a composite molded body composed of a core component having a conductive resin in which the conductive compounding material of the present invention is blended in the central portion, and a sheath component having a non-conductive resin disposed around the conductive resin. May be
The molded product containing the electrically conductive compounding material of the present invention exhibits excellent electroconductivity as well as good vibration damping properties, thermal conductivity and sound insulation properties, and therefore can be used as a building material and the like.

[0014]

EXAMPLES The present invention will be described in more detail with reference to Examples. Example 1 After mixing copper powder passing through a 200-mesh net and zinc chloride-based flux (0.2 g / Cu1 g), a coating weight ratio (solder / copper powder) of copper powder was 3/1. Solder having a melting point of 183 ° C. (Sn—Pb type) was melted and added. Then
Temperature at which the previously added flux melts (approximately 2
Knead while heating to 00 ℃) until the copper color completely disappears,
The flux was washed after the solder was solidified by cooling and then granulated. The obtained particles were such that the surface of the copper powder was completely covered with the solder layer. Using pure iron powder, nickel powder, and carbon steel powder instead of copper powder, the particles obtained by kneading at the same temperature as in the case of copper powder are those in which the surface of the metal powder is covered with a solder layer. there were. Among the metal particles thus obtained, copper / solder particles composed of copper powder and solder were mixed in ABS resin to injection-mold the molded body shown in FIG. In such injection molding, copper / solder particles are previously
The master chip and the ABS resin, which were blended at a high concentration in the S resin and made into chips, were prepared using an injection molding machine. At this time, the master chip was mixed in the ABS resin so that the copper / solder particles would be 40 vol% in the molded body. The volume resistivity of the obtained molded body was 3 × 10 ⁻⁴ Ω · cm both in the direction parallel to the flow direction of the resin and in the direction perpendicular ^thereto .

Example 2 Copper powder passing through a 200-mesh net and solder having a melting point of 183 ° C. (Sn-Pb system) with a coating weight ratio (solder / copper powder) of 3/1 were 5 mmHg high. The mixture was kneaded for about 3 hours while heating to about 200 ° C. under vacuum. Then, the flux which had been added in advance was kneaded while being heated to a temperature at which the flux was melted (approximately 200 ° C.) until the copper color completely disappeared, and then the solder was cooled and solidified and then granulated. In this example, as in Example 1, since the flux was not added, the obtained particles which were not washed with the flux were
Similar to the particles obtained in Example 1, the surface of the copper powder was covered with the solder layer. A master chip obtained by previously kneading the metal particles and polypropylene was mixed with polypropylene resin so that the amount of the conductive compounding agent was as shown in Table 1, and the molded body shown in FIG. 1 was molded by injection molding. . The conductivity of the obtained molded body is also shown in Table 1 below.

[0016]

[Table 1]

As is clear from the above table, the molded product obtained in this example had good conductivity, and there was substantially no directionality of conductivity. In addition, when the cross section of the No. 3 molded body with the parallel plane parallel to the resin flow and the plane perpendicular to the resin flow was observed under a microscope, the parallel plane was in the state shown in FIG. It was in the state shown in FIG. Therefore, it can be presumed that the low melting point metal, solder, forms a network structure in the molded body obtained in this example.

Comparative Example The copper powder and the solder forming the electrically conductive compound added to the resin in No. 3 of Example 2 were directly kneaded into the resin without being kneaded in advance to form a master chip. Others were the same as those in No. 3 of Example 2. In the obtained molded body, the solder was partially aggregated, and the volume resistivity was partially different.

Example 3 An injection-molded article of FIG. 1 made of an ABS resin mixed with various metal powders and a conductive compounding material having a coating weight ratio shown below was molded by injection molding. Table 2 shows the mixing ratio of the conductive compounding material and the volume resistance value of the obtained injection-molded product. Types of conductive compound materials A: Solder / copper powder = 0.7 / 1 B: Solder / pure iron powder = 1/1 C: Solder / pure iron powder = 0.6 / 1 D: Solder / plated metal powder = 1/1 (plated metal powder: pure iron powder with nickel plating on the surface) E: solder / lead powder = 0.3 / 1

[0020]

[Table 2]

As is apparent from Table 2, in this example using various metal powders, the obtained molded body had good conductivity, and there was substantially no directionality of conductivity. It was In Table 2, there are injection molded products having a volume specific resistance value of 5.23 × 10 ² Ω · cm or 1.11 × 10 ² Ω · cm. When used as a body, it is possible to prevent malfunction of the electronic device due to electromagnetic waves (noise).

[0022]

EFFECTS OF THE INVENTION Since the electroconductive molding of the present invention exhibits good electroconductivity, a electroconductive resin molding for electromagnetic wave shielding or X-ray shielding can be molded. Furthermore, it is also possible to mold a resin case or the like of an electric product that can be directly grounded.

[Brief description of drawings]

FIG. 1 is a perspective view of a molded body showing an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a state of a cross section parallel to the resin flow in the molded body shown in FIG.

FIG. 3 is an enlarged cross-sectional view showing a state of a cross section perpendicular to the resin flow in the molded body shown in FIG.

[Explanation of symbols]

 1 Disc part 2 Sprue part P Resin M Low melting point metal

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C08K 3/08 KAB 9/02 KCN C08L 101/00 H01B 1/22 Z 7244-5G // B29K 105 : 06 B29L 31:34 C08L 23:00 33:18

Claims (7)

[Claims] 1. A conductive molded body, wherein a conductive compounding material is mixed in a non-conductive resin, wherein the conductive compounding material has a melting point higher than the molding temperature at the time of molding the non-conductive resin. A high-melting-point body composed of components and at least the surface of which is formed of a high-melting-point metal having a higher melting point than the molding temperature; and a low-melting point metal having a lower melting point than the molding temperature of the non-conductive resin and solid at room temperature. And a low-melting-point metal layer covering the surface of the high-melting-point body, wherein the low-melting-point metal flows and diffuses in the resin flow direction in the molded body. . 2. The electrically conductive molded body according to claim 1, wherein the high melting point body is a powdery body. 3. The low melting point metal constituting the conductive compounding material is solder, and the high melting point material is copper powder.
The electrically conductive molded article described. 4. The electroconductive molded product according to claim 1, wherein the electroconductive compounding material is compounded in the molded product in an amount of 20 vol% or more. 5. A conductive compound material according to claim 1 is used as the conductive compound material when molding a conductive molded product in which a conductive compound material is blended in a non-conductive resin. A method for molding a conductive molded body, which comprises melting a resin mixed with the conductive compounding material, and then filling the melted resin into a cavity of a mold while flowing the resin. 6. The method for molding a conductive molded body according to claim 5, wherein the low melting point metal constituting the conductive compound material is solder and the high melting point body is copper powder. 7. The method for molding a conductive molded article according to claim 5, wherein the conductive compounding agent is compounded in the resin in an amount of 20 vol% or more.