JPH0525286A - Method for evaluating state of conductive coating layer and preparation of conductive resin material - Google Patents

Abstract

PURPOSE:To provide a method for evaluating easily and objectively the state of a conductive coating layer formed on the surface of a resin particle and to prepare a conductive resin material by this method. CONSTITUTION:A great number of resin particles S each having a surface coated with a conductive layer are compressed to give a molded specimen, of which the volume resistivity or dielectric dissipation factor is measured.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is used as a molding material for molding an electromagnetic shield material, an antistatic material, and the like.
In the conductive resin material coated with a conductive coating on the surface of the resin particles, a method of evaluating the coating state of the conductive coating,
The present invention relates to a method for producing a conductive resin material, to which this is applied.

[0002]

2. Description of the Related Art Conventionally, a molding material obtained by mixing a thermoplastic resin and a conductive powder (fine metal particles, carbon, etc.) with a mixer, a ball mill, etc. and melt-kneading them with a heating roll, an extruder, etc. Even if the mixing and kneading takes a long time, it is difficult to uniformly disperse the conductive powder in the thermoplastic resin, so that a molded product having sufficiently high conductivity cannot be obtained.

Therefore, the present inventors previously conducted a single step of mixing the resin particles and the conductive fine particles sufficiently smaller than the resin particles with a high shearing force and a high compressing force, so that the particulate conductive particles are electrically conductive. It has been proposed to produce a resin material and use it as a molding material for a conductive molded article such as the electromagnetic shield material (see Japanese Patent Laid-Open No. 3-84038). According to this method, the conductive fine particles are crushed into primary particles by high shearing force and uniformly dispersed on the surface of the resin particles, and the high compression force mechanically strongly presses them on the surface of the resin particles. And it is fixed. Then, a conductive resin material in which the surface of the resin particles is coated with a conductive coating composed of a large number of conductive fine particles is obtained.

When metal particles having malleability or ductility are used as the above-mentioned conductive particles, the metal particles are integrated when they are mixed with high shearing force and high compressive force to form resin particles. A conductive resin material having the surface thereof coated with a conductive coating made of a thin film of the above metal is obtained.

[0005]

However, in the production of the conductive resin material by the above method, since there is no means for objectively measuring the coating state of the conductive coating on the resin particle surface, the surface of the resin particle is not measured. Was directly observed by an electron microscope to evaluate the coating state. Therefore, it takes time and effort to prepare the sample, and the evaluation is easily influenced by the subjective judgment of the observer, which makes it difficult to stably manufacture a product of the same quality. Further, there has been a demand for a method for easily evaluating the quality of products even after manufacturing.

A main object of the present invention is to provide a method for evaluating the coating state of a conductive coating, which can objectively and easily evaluate the coating state of the conductive coating on the surface of resin particles. Another object of the present invention is to provide a method for producing a conductive resin material, which can stably produce a conductive resin material of the same quality by using the coating state evaluation method for the conductive coating. is there.

[0007]

In order to solve the above problems, the present inventors have made various studies on a method for evaluating the coating state of the conductive coating on the resin particle surface from the electrical characteristics of the conductive resin material. I went. As a result, they have found that the coating state of the conductive coating on the surface of the resin particles can be evaluated by measuring the volume resistivity or dielectric loss tangent of the compressed body obtained by compressing the powdery conductive resin material.

Therefore, the method for evaluating the coating state of the conductive coating of the present invention compresses a large number of resin particles whose surfaces are coated with the conductive coating, and calculates the volume specific resistance value and dielectric loss tangent of the compressed body. At least one of them is measured to evaluate the coating state of the conductive coating on the surface of the resin particles. Further, the method for producing a conductive resin material of the present invention,
By mixing the resin particles and the conductive fine particles with a high shearing force and a high compressive force, in the method for producing a conductive resin material for coating the conductive coating on the surface of the resin particles, during or after mixing of both components A part is sampled and compressed, and at least one of the volume resistivity value and the dielectric loss tangent of the compressed body is measured to evaluate the coating state of the conductive coating on the resin particle surface.

As shown in FIG. 2, when the resin particles are in contact with each other by being compressed, the resistance value R of the entire compression body is R.
Is the surface resistance R _L of each resin particle and the internal resistance R
_It can be obtained from _S and the contact resistance R _C between the resin particles by the equivalent circuit of FIG. Since the resin particles are an insulator, the infinite internal resistance R _S and the contact resistance R _C can be ignored in the above equivalent circuit, and as a result, the resistance value R of the compression body can be approximated to It can be represented by the surface resistance R _L of each resin particle.

The same applies to the conductive resin material in which the conductive fine particles are fixed on the surface of the resin particles, and the resistance value R of the compressed body is approximately the surface resistance R of each conductive resin material.
It can be represented by _T. This is because the internal resistance R _S of the resin particles themselves and the contact resistance R _C between the resin particles can be ignored as described above, and even if the conductive fine particles are present between the conductive resin materials, Because its total resistance R _M is extremely small, it can be ignored as well.

The surface resistance R _T of the conductive resin material changes according to the state of adhesion of the conductive fine particles to the surface of the resin particles, that is, the change of the covering state of the conductive coating. For example, as shown in FIG. 4, when the conductive fine particles M are in contact with the surfaces of the resin particles P at one point, the surface resistance R _T of each conductive resin material is the surface resistance R _L ( = R _L1 +
_RL2 ) and the total resistance R _M of the conductive fine particles, it is obtained by the equivalent circuit of FIG. As is clear from the figure, since the total resistance R _M of the conductive fine particles does not contribute to the surface resistance R _T , R _T = R _L1 + R _L2 = R _L , and the resistance value R of the compressed body is approximately , The surface resistance R _L of each resin particle.

On the other hand, as shown in FIG.
However, in the state where the resin particles P are fixed and integrated on the surface,
The surface resistance R _T of each conductive resin material is obtained from the surface resistance R _L (= R _L1 + R _L2 ) peculiar to the resin particles and the total resistance R _M of the conductive particles by the equivalent circuit of FIG. 7. Then, the total resistance R _M of the conductive fine particles are the R _M «R _L2, the surface resistance R _T ≒ R _L1 becomes conductive resin material, the resistance value R of the compression body, in recent, the individual It is represented by R _L1 , which is a part of the surface resistance R _L of the resin particles, and is lower than in the previous case.

As is clear from the above, the resistance value R of the compressed body changes depending on the adhered state of the conductive fine particles on the surface of the resin particles, that is, the covered state of the conductive coating. By measuring the resistance value R of the compressed body, it can be understood that the coating state of the conductive coating on the resin particle surface can be evaluated. Therefore, it is possible to objectively evaluate the coating state of the conductive coating by obtaining the volume resistivity ρ by correcting the variation of the resistance value R due to the size difference of the compression body by the following formula (I). .

Ρ = R (S / d) (I) (where S is the cross-sectional area of the compression body and d is the thickness of the compression body.) Further, the volume resistivity value ρ and Similarly, the coating state of the conductive coating can be evaluated by measuring the dielectric loss tangent tan δ having the relationship of the formula (II). tan δ = X / ρ (II) X in the above formula (II) is the reactance when an AC voltage is applied to the compressed body, but in a normal conductive resin material, the conductivity that affects this reactance X is Since the addition rate of the conductive fine particles is as small as 10 to 25% by weight and the volume fraction thereof is also as small as 1 to 5% by volume, the reactance X shows a substantially constant value regardless of the coating state of the conductive coating. Therefore, if the dielectric loss tangent tan δ of the compressed body is measured, the volume resistivity ρ
Similarly, the coating state of the conductive coating can be objectively evaluated.

Since the reactance X is a value obtained by generalizing the variation of the measured reactance value X'in the compressed body due to the difference in the size of the compressed body by the following equation (III), the above equation (3) is obtained. As is clear from II), when this dielectric loss tangent tan δ is used to evaluate the coating state of the conductive coating, there is an advantage that it is not necessary to make a correction due to the difference in the dimensions of the compressed body.

X = X '(S / d) (III) (where S and d in the above formula are the same as those in the above formula (I).) The conductive coating of the present invention based on the above theory. The covering state evaluation method can be carried out by the measuring device shown in FIG. 1, for example. The measuring device shown in FIG. 1 includes a cylindrical shield case 11, a cylindrical electrode 12 with a flange,
13 and the ring body 14, respectively, the insulating ring 15
The cylinder-shaped electrodes 12 and 13 are connected to an electric characteristic measuring device 16 and the ring body 14 is grounded.

In the above measuring apparatus, the powdery sample S is filled in the void formed by the cylindrical electrodes 12 and 13 and the ring body 14, and the upper cylindrical electrode 1
2 is pressed downward as indicated by an arrow in the figure to compress the sample S, and an AC voltage of a predetermined frequency is applied from the electrical characteristic measuring device 16 between the cylindrical electrodes 12 and 13 to compress the sample S. Characteristics of the sample S in the state (resistance value R, dielectric loss tangent tanδ
Etc.) is measured.

The electrical characteristic measuring device 16 is as follows.
An impedance analyzer manufactured by Yokogawa Hewlett-Packard Company is preferably used. According to the above measuring apparatus, since it is not necessary to perform compression molding of the sample S in advance, the coating of the conductive coating can be performed more easily than the case where the electrical characteristics of the molded product is measured after compression molding the sample. The condition can be evaluated.

The method for evaluating the coating state of the conductive coating of the present invention can be used, for example, for evaluating the quality of the conductive resin material supplied as a product, and can also be applied to the manufacturing process of the conductive resin material. It enables stable production of conductive resin materials of the same quality. That is, applying the coating state evaluation method of the conductive coating, in the method for producing a conductive resin material of the present invention, during the step of mixing the resin particles and the conductive fine particles at high shear and high compression force or At the end of the process, a part of the mixture is sampled, the coating state of the conductive coating formed on the surface of the resin particles is evaluated, and by feeding back the result to the mixing process, the conductive coating having the same coating state is obtained. It is possible to stably mass-produce the conductive resin material that it has.

In the method for producing a conductive resin material of the present invention, a method of mixing resin particles and conductive fine particles with high shearing force and high compressing force is known as a surface modification method of powder particles, so-called. The mechanochemical method is exemplified. For carrying out the mechanochemical method, for example, a mixing device “Angmill” manufactured by Hosokawa Micron Co., Ltd. is preferably adopted. The outline of this mixing apparatus is shown in FIG. A ball mill has been widely used as a mixing device, but it is not preferable because a compression force is hardly recognized in the ball mill and it is difficult to firmly adhere the conductive fine particles to the surface of the resin particles.

The mixing device shown in FIG.
And a rotary shaft 2 provided at the center of rotation in the rotary casing 1 so as to be rotatable in the same direction as the rotary casing 1, an inner piece 3 attached to the rotary shaft 2 and a scraper 4 for scraping. Has been done. In the mixing operation, powder particles 5 that are not premixed as the objects to be mixed (in the case of the present invention, resin particles and conductive fine particles)
After being charged into the rotary casing 1, the rotary casing 1 is rotated at a high speed (the rotation speed is v ₁ ). As a result, the powder particles 5 receive a centrifugal force and are strongly pressed against the inner wall surface 1 a of the rotary casing 1. On the other hand, the rotating shaft 2 rotates at a speed v ₂ slower than that of the rotating casing 1
Is rotated in the same direction as.

Due to the difference in speed between the rotating casing 1 and the rotating shaft 2, the powder particles 5 generate strong mechanical energy (shearing force and shearing force) between the rotating casing 1 and the inner piece 3 attached to the rotating shaft 2. Receive compressive force). That is, as shown in FIG. 8, the powder particles 5 receive a strong compressive force in the arrow x direction and a strong shearing force in the arrow y direction.

The inner piece 3 and the scraper 4 may be fixed so as not to rotate (that is, the rotation speed v ₂ of the rotary shaft ₂ is 0, and hereinafter referred to as "fixed type"). On the other hand, as described above, a type in which the rotating shaft 2 also rotates in the same direction is referred to as a "co-rotating type". In carrying out the method for producing a conductive resin material of the present invention using such a mixing device, first, the resin particles and the conductive fine particles are put into the rotating casing 1 and the mixing operation is performed as described above. To do.

Next, a part of the mixture in the rotary casing 1 is sampled, the coating state of the conductive coating is evaluated using the measuring device shown in FIG. 1, and the mixing operation is continued based on the result. It is determined whether or not the rotation speed of the mixing device is changed, and the like is fed back to the operation of the mixing device. By repeating the above operation until the conductive coating reaches a predetermined coating state, a conductive resin material of the same quality can be stably manufactured.

As the resin particles, for example, acrylic resin,
Polystyrene resin, polyacetal, polyamide, polybutylene terephthalate, polycarbonate, polyphenylene sulfide, polysulfone, polyvinyl chloride,
In addition to thermoplastic resins such as olefin resins such as polyamide-imide, polyethylene and polypropylene, thermosetting resins such as epoxy resins, phenolic resins, polyesters and polyurethanes are also included.

These resin particles may be spherical or amorphous, and have a particle size of several μm or more, specifically about 3 to 100 μm.
m is preferred, and more preferably about 8-50 μm. When the particle size is smaller than the above range, the compressive force and shearing force applied to the particles are too small, and when the particle size is larger than the range, the conductivity is low and the compression molding becomes difficult.

Examples of the conductive fine particles include Ag, Al, F
In addition to malleable or ductile metal particles such as e, Au, Cu, Sn, Ni, etc., for example, carbon, conductive metal oxide fine powder, titanium oxide whose surface is coated with metal (silver etc.), etc. It is also possible to use conductive fine particles having no malleability and ductility. When metal particles having malleability or ductility are used as the conductive particles, they are deformed and integrated by mixing with high shearing force and high compressive force and partially melted to form a conductive coating on the surface of the resin particles. As a result, a continuous metal film is formed.

When conductive fine particles having no malleability and ductility are used as the conductive fine particles, the conductive fine particles are mixed by a high shearing force and a high compressive force.
The resin particles are uniformly dispersed and fixed on the surface of the resin particles to form a conductive coating composed of a large number of conductive fine particles. Furthermore, when the metal fine particles having malleability or ductility and the conductive fine particles not having malleability and ductility are used in combination, a composite film of both is formed as a conductive coating on the surface of the resin particles. .

The amount of the conductive fine particles charged into the rotary casing 1 is preferably in the range of 5 to 66% by weight in terms of the ratio (% by weight) of the conductive fine particles to the amount of the resin particles charged. When the ratio of the conductive fine particles is larger than this range, the obtained conductive resin material is inferior in mechanical strength, and when it is smaller than this range, the obtained conductive resin material is obtained. Has poor electrical conductivity, which is not preferable.

The rotation speed v ₁ of the rotary casing 1 is of a fixed type and is preferably about 1100 to 3000 rpm. In the co-rotating type, the speed difference between the rotating casing 1 and the inner piece 3 is 1100 to 30 which is the same as the above range.
It is preferably about 00 rpm. When the rotation speed v ₁ of the rotary casing 1 in the case of the fixed type or the speed difference in the case of the co-rotation type is larger than the above range, the frictional heat during mixing becomes excessive, and conversely, when it is smaller than the above range, the friction heat is compressed. Both the force and the shearing force are insufficient, which is not preferable.

Further, in mixing, it is necessary to take care so that the temperature does not rise excessively due to friction during mixing. When frictional heat is generated above the melting point of the resin particles or the glass transition point due to friction during mixing, the resin particles are melted and deformed, and the conductive fine particles are embedded in the resin particles. Also, care must be taken not to generate frictional heat above the glass transition point. Therefore, in addition to adjusting the rotation speed, a cooling device (not shown) such as air cooling or water cooling may be attached to the mixing device so as to reduce the frictional heat while mixing.

When metal fine particles are used as the conductive fine particles, if the temperature is excessively increased, the metal may be oxidized and the resistance value may be increased to lower the conductivity. In order to prevent metal oxidation, they may be mixed under a nitrogen atmosphere or under reduced pressure.

[0033]

EXAMPLES The conductive resin material of the present invention will be described in detail below with reference to examples. Example 1 100 parts by weight of spherical resin particles made of polymethylmethacrylate (average particle diameter 50 μm, glass transition temperature 130 ° C., “MB-50” made by Sekisui Plastics Co., Ltd.), and copper as conductive fine particles. Fine particles (amorphous, average particle size 2.5μ
m) and 10 parts by weight were added to "Ongmill AM-15F" manufactured by Hosokawa Micron Co., Ltd. without premixing. This device is a mixing device as shown in FIG.
It is a fixed type. The mixing condition is that the rotation speed of the rotating casing 1 is 1500 rpm and the inner wall surface 1 of the rotating casing 1 is 1.
The gap between a and the inner piece 3 was set to 3.4 mm, and the mixing process was performed at room temperature.

Then, every 900 seconds from the start of mixing, the mixture being mixed is taken out from the rotary casing 1, and the volume resistivity ρ (Ω is measured by using the measuring device shown in FIG.
m) and dielectric loss tangent tan δ were measured, and the coating state of the conductive coating was observed with a scanning electron microscope (magnification: 2000 times). The measurement results of the volume resistivity ρ (Ωm) and the dielectric loss tangent tan δ are shown in Table 1, and the observation results by the scanning electron microscope are shown in FIGS. 9 to 11.

The volume resistivity ρ and the dielectric loss tangent t
FIG. 12 shows the relationship between an δ and the mixing time. Note that FIG.
In 2, the symbol ● ─ ● indicates the volume resistivity ρ, ○ ─ ○
Indicates the dielectric loss tangent tan δ.

[0036]

[Table 1]

From the results of FIGS. 9 to 11 in which the coating state of the conductive coating was observed, 900 seconds after the start of mixing (FIG. 9), 270
It was confirmed that the copper thin film on the surface of the resin particles grew in the order of 0 second (FIG. 10) and 3600 seconds (FIG. 11).
By comparing this result with changes in the volume resistivity ρ and the dielectric loss tangent tanδ, it was found that the volume resistivity ρ decreases and the dielectric loss tangent tanδ increases as the copper thin film grows.

Example 2 Spherical resin particles made of polymethylmethacrylate (average particle size 50 μm, glass transition temperature 130 ° C., “MB-50” manufactured by Sekisui Plastics Co., Ltd.) and nickel fine particles (spherical, average particles) Diameter 0.02 μm) and 100 parts by weight of composite particles obtained by previously mixing with high shearing force and high compressing force,
15 parts by weight of titanium dioxide fine particles whose surface is coated with silver (indeterminate shape, average particle size 0.5 μm) as conductive fine particles are pre-mixed and the product is manufactured by Hosokawa Micron Co., Ltd. “Angmill AM-15F”. , The rotational speed of the rotary casing 1 is 1200 rpm, and the gap between the inner wall surface 1a of the rotary casing 1 and the inner piece 3 is 3.4 mm.
The mixing treatment was performed at room temperature under the conditions of.

Then, every 900 seconds from the start of mixing, the mixture being mixed is taken out from the rotary casing 1, and the volume resistivity ρ (Ω is measured by using the measuring apparatus shown in FIG.
m) and dielectric loss tangent tan δ were measured. The results are shown in Table 2.

[0040]

[Table 2]

From the results in Table 2 above, the volume resistivity ρ decreases as the mixing time increases, and the dielectric loss tangent tanδ
Was found to rise. After 3600 seconds from the start of mixing, the volume resistivity ρ and the dielectric loss tangent tan δ did not change. Then, 900 seconds after the start of mixing and 3
When the coating state of the conductive coating was observed with a scanning electron microscope (magnification: 2000 times) for the sample after 600 seconds, at the stage 900 seconds after the start of mixing, as shown in FIG. The titanium dioxide fine particles were partially adhered to the surface, but at the stage 3600 seconds after the start of mixing, the titanium dioxide fine particles were uniformly adhered to the entire surface of the composite particles as shown in FIG. Was confirmed.

Example 3 Spherical resin particles made of polymethylmethacrylate (average particle size 50 μm, glass transition temperature 130 ° C., “MB-50” manufactured by Sekisui Plastics Co., Ltd.) and copper fine particles (amorphous, average) 100 parts by weight of composite particles obtained by previously mixing with 100 μm of a particle size of 2.5 μm) with a high shearing force and a high compressing force, and nickel fine particles (spherical shape, average particle size 0.02) as conductive fine particles.
μm) 15 parts by weight without pre-mixing, “Ongmill AM-15F” manufactured by Hosokawa Micron Co., Ltd.
, The rotation speed of the rotating casing 1 is 750 rpm.
The mixing process was performed at room temperature under the condition that the gap between the inner wall surface 1a of the rotating casing 1 and the inner piece 3 was 3.4 mm.

Then, every 900 seconds from the start of mixing, the mixture being mixed is taken out from the rotary casing 1, and the volume resistivity ρ (Ω is measured by using the measuring apparatus shown in FIG.
m) and dielectric loss tangent tan δ were measured. The results are shown in Table 3.

[0044]

[Table 3]

From the results shown in Table 3 above, the volume resistivity ρ decreases as the mixing time increases, and the dielectric loss tangent tanδ
Was found to rise. After 2700 seconds from the start of mixing, neither the volume resistivity value ρ nor the dielectric loss tangent tan δ stopped changing. Therefore, the scanning electron microscope (magnification: 2000 times) was applied to the sample 2700 seconds after the start of mixing.
When the coating state of the conductive coating was observed at
As shown in, it was confirmed that the nickel thin film was uniformly adhered to the entire surface of the composite particle.

[0046]

According to the method for evaluating the coating state of the conductive coating of the present invention, a large number of resin particles having the surface coated with the conductive coating are compressed to measure the volume resistivity or dielectric loss tangent of the compressed body. By doing so, the coating state of the conductive coating on the resin particle surface can be objectively and easily evaluated.

Further, according to the method for producing a conductive resin material of the present invention, it is possible to stably produce a conductive resin material of the same quality by using the above evaluation method.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a measuring device for carrying out the method for evaluating the coating state of a conductive coating of the present invention.

FIG. 2 is an explanatory diagram showing a relationship among surface resistance, internal resistance, and contact resistance of individual resin particles in a compressed body of resin particles.

FIG. 3 is a circuit diagram equivalently representing the resistance value of a compressed body of resin particles by the surface resistance, the internal resistance, and the contact resistance of the individual resin particles.

FIG. 4 shows a contact state of conductive fine particles on the surface of resin particles,
It is explanatory drawing which shows the relationship between the surface resistance of resin particles, and the total resistance of electroconductive fine particles.

FIG. 5 is a circuit diagram in which the surface resistance of the conductive resin material in the above state is equivalently expressed by the surface resistance of the resin particles and the total resistance of the conductive fine particles.

FIG. 6 shows a contact state of conductive fine particles on the surface of resin particles,
It is explanatory drawing which shows the relationship between the surface resistance of resin particles, and the total resistance of electroconductive fine particles.

FIG. 7 is a circuit diagram in which the surface resistance of the conductive resin material in the above state is equivalently expressed by the surface resistance of the resin particles and the total resistance of the conductive fine particles.

FIG. 8 is a schematic cross-sectional view showing an example of a mixing device used for manufacturing a conductive resin material.

9 is a scanning electron micrograph showing the particle structure of the conductive resin material 900 seconds after the start of mixing in Example 1. FIG.

10 is a scanning electron micrograph showing a particle structure of a conductive resin material 2700 seconds after the start of mixing in Example 1. FIG.

FIG. 11 is a scanning electron micrograph showing the particle structure of the conductive resin material in Example 1 3600 seconds after the start of mixing.

12 is a graph showing the relationship between the mixing time and the measured values of volume resistivity ρ and dielectric loss tangent tan δ in Example 1. FIG.

FIG. 13 is a graph showing the result obtained in Example 2 900 seconds after the start of mixing
It is a scanning electron micrograph which shows the particle structure of electroconductive resin material.

FIG. 14 is a scanning electron micrograph showing a particle structure of a conductive resin material 3600 seconds after the start of mixing in Example 2.

FIG. 15 is a scanning electron micrograph showing a particle structure of a conductive resin material 2700 seconds after the start of mixing in Example 3.

Claims (2)

[Claims] 1. A large number of resin particles coated with a conductive coating on the surface are compressed, and at least one of a volume resistivity value and a dielectric loss tangent of the compressed body is measured to obtain conductivity on the surface of the resin particles. A coating state evaluation method for a conductive coating for evaluating the coating state of a coating. 2. A method for producing a conductive resin material, wherein resin particles and conductive fine particles are mixed with a high shearing force and a high compressive force to coat the surface of the resin particles with a conductive coating. Or, after mixing, a part of the mixture is sampled and compressed, and at least one of the volume resistivity value of the compressed body and the dielectric loss tangent is measured to evaluate the coating state of the conductive coating on the resin particle surface. A method for producing a conductive resin material, comprising: