JPS62135564A - Improvement of conductivity of plastic material containing metal filler - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

BACKGROUND OF THE INVENTION This invention relates to electrically conductive plastic composite materials and, more particularly, to methods of making such composite materials. More particularly, the present invention relates to a method of increasing the electrical conductivity of such composite materials and to products obtained by the method. Although the present invention is primarily concerned with solid or foamed resin composite materials, the principles of the present invention apply to various other high resistivity composite materials other than resin materials,
For example, it can also be applied to materials such as ceramics, wood composites, and concrete.

It has been a long-standing goal to provide plastic materials with superior electrical conductivity for a variety of purposes.

Techniques for increasing the electrical conductivity of thermoplastic molded articles to a level that makes them useful as metal replacements for a variety of purposes are well known. Two different approaches have been taken to achieve this objective. The first approach is to compound the plastic material with some type of conductive layer. A second approach is by filling the material with conductive fillers such as carbon black, aluminum flakes and stainless steel fibers. In one of the latter techniques, conductive or metallized filaments, such as metallized glass fibers, are introduced into the plastic material primarily to dissipate electrostatic charges and to shield against electromagnetic radiation, among other benefits. It is carried out. The high electrical conductivity of these materials is due to the fact that relatively short metal fibers or filaments, each of which are in direct contact with each other or in close proximity to each other at numerous points throughout the volume of the plastic material, This is because excellent conductivity can be obtained despite being isolated from the surrounding area.

In manufacturing such thermoplastics, short lengths of metallized fibers or conductive filaments are mixed with a fluid polymerizable material. In such a manufacturing technique, a thin film of insulating plastic is formed on each of a large number of conductive filaments.

This thin insulating film can increase the distance between adjacent conductive fibers in the finished material to an extent that desirable conductivity is not achieved. Because the metal or conductive fibers are scattered in a three-dimensional random network throughout the entire volume of the plastic, the conductivity of the entire plastic material is a function of the conductivity of the many different individual current paths that can occur between adjacent metal elements. is a cumulative effect. One quick way to increase the electrical conductivity of such composite materials is to increase the proportion of metallized particles or fibers in the material.

However, as a practical matter, there are limits to how much conductive material can be added without adversely affecting the desirable properties of the plastic material. Furthermore, it is preferable to decrease, rather than increase, the proportion of conductive material required to provide a given level of conductivity to a plastic material. The use of conductive fillers not only adversely affects the physical properties of the plastic, but also typically significantly increases the cost of the final product.

OBJECT AND SUMMARY OF THE INVENTION Therefore, the main object of the present invention is to provide a conductive composite material,
In particular, the object is to provide a method for increasing the electrical conductivity of electrically conductive plastic composite materials.

Another object of the invention is to increase the electrical conductivity of plastic materials filled with electrically conductive fillers of the type mentioned above, without appreciably increasing the content of electrically conductive material included in order to achieve a given electrical conductivity. The goal is to provide a way to increase weight.

Another object of the present invention is to produce a conductive plastic composite material having a predetermined conductivity even if the content (weight %) of conductive material is low.

Yet another object of the invention is the production of plastic composite materials of the above-mentioned type by reducing the amount of relatively expensive metal conductive fillers introduced into the composite material in order to achieve a given electrical conductivity. The goal is to lower costs.

These and other objects of the present invention are achieved by including a material of low ionization potential in a conductive plastic composite. This low ionization potential material acts to enhance electrical conductivity between adjacent but separate metal or conductive filler elements in the composite material.

The products of the methods described above are extremely useful in a variety of applications, including enclosures for electronic equipment where electrical conductivity, shielding and grounding are important, such as cabinets for electronic equipment such as communications equipment, meters, computers, etc. . The electrostatic shielding capacity of the plastic composite material is improved significantly enough that the composite material can be used as a low cost alternative to metal enclosures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention relates primarily to conductive plastic composite materials, including a wide variety of conductive resin composite materials, including both thermoplastic and thermoset plastic materials. Examples of suitable thermoplastic materials include, but are not limited to, polycarbonates, polyesters, oxide polymers, polyurethanes, polyamides, acrylics, polyvinyl chloride, and hydrocarbon polymers. Examples of suitable thermosetting plastic materials include polyester,
These include, but are not limited to, epoxies, ureas, and silicones.

Conductive materials useful for incorporation into plastic composites include metal fibers and ribbons of various types, metal particles of various shapes, metallized glass, metallized graphite or other conductive or non-conductive fibers, and various There are carbon fibers and carbon particles with various shapes. Although there is a wide range of metal choices for certain desirable overall conductive properties, in practice the choice is usually limited to inexpensive metals that are highly conductive and easy to form. Aluminum is most preferred as it meets the above criteria. However, the method of the invention is equally applicable to composite materials incorporating other metals, such as stainless steel, silver, copper, zinc, iron, nickel, carbon steel, etc., and mixtures thereof. Similarly, coating metallized glass fibers with aluminum is also desirable due to the criteria mentioned above, low melting point, and therefore ease of manufacture.

For more information on the formation and molding of metal fibers, how they are incorporated into plastic materials, and the range of inclusions (% by weight or % by volume) that should be incorporated into plastic materials to achieve the desired conductive properties, please refer to those skilled in the art. Reference is made to the numerous prior patents and publications well known in the art.

Examples are shown below to specifically explain the present invention. These Examples are given to specifically illustrate the present invention, and are not intended to limit the invention. In each of the Examples below, test samples were cut from the selected base material or mature cedar board. Samples are typically 5 cm long, 0.5 cm wide, and 0.33 cm thick.
Met. Small side of each sample (0,5XO,33
) DuPont conductive paint 4817 on both sides.
and the resistance between both sides before and after treatment,
Beckman RM S 3030
Measured with an altimeter. Resistivity was calculated from the measured resistance and is shown in the table.

The variation in resistivity values for the untreated samples in each table is primarily due to differences in the density and orientation of the conductive filler in a particular molded plate. Further, RB and RA in the table below represent the resistivity (Ω-cm) before and after treatment.

Example 1 5E9 sold under the trade name NOIiYL
A number of samples cut from molded plates containing 6% by weight stainless steel fibers made of a polymer designated as 0-960 were exposed to N,N in a bell jar at atmospheric pressure.
'-dimethylaniline (DMA) vapor. The amount of pMA absorbed into the sample was determined from its weight gain. Measurement of resistivity was carried out by DMA according to the method described above.
before and after exposure to.

The following table shows the resistivity (R) of each sample before DMA g exposure.
a) and the resistivity (RA) after absorption of DMA in the indicated weight % are listed together.

Table I Noryl resin sE90-960/6% stainless steel fiber Rs DMA (wt%) RA28
0.38 1421
0.17 6284 0.3
1 4798 0.18
8744 0.34 2
3 Example 2 A sample containing 6% by weight of stainless steel fibers made of Noryl resin, designated as SE90-CI (100) was
It was treated and tested in the same manner as in Example 1.

The test results are shown in Table ■.

Table ■ Noryl resin SE90-GHI 00/6% stainless steel fiber RB DMA (wt%) RAll
0.40 025
0.25 515 0
．． 28 52 0.32
16 0.40 2
4 0.27 21
0.35 11 0
．． 58, 1 Example 3 Experiments similar to Examples 1 and 2 were carried out using LEXA
N) Performed using test samples cut from polycarbonate flat plates. DMA in weight percent with resistivity
This was done before and after absorption. Sample processing was carried out in a bell jar in air at room temperature. The results of this experiment are shown in Table ①.

Table ■ Lexan polycarbonate 141R/6% stainless steel fiber Re DMA (weight %) RA>7.2
Xl051.74 14380
1.27 12285 0.72
15>7.2 xlO51,424g 1.7 Xl041.25 1ft1.9
X104 0.83 If>4.9
x1062.53 193151
3.98 24221 4.1
0 285'l 3.94
31238 1.50
31151 1.25' 25
23 1.25 1215
3.21 23222 3
．． 03 4230 2.9g
719 0.27
1126 0.29
132B 0.30
24184 4.49
1420 4.25
9214 3.80
2811 O,219 220,0719 440,2015 1290,9871 1G5 1.0B 4
459 1.11 42
51 1.24 317
8J,, 10 42 78 1.27 9G
ll 1.20 14
4g5 1.09 50
142 1.45 45
98 1.10 318
2 1.55 2815
5 1.02
67233 1.91
2940 1.91
1774 1.22
2238 1
．． 10 3692
1.99 4461
2.39 4453
1.40 46471
1.6 [i 911
45 2.72 1
13294 2.48
95 Example 4 Same as Example 3. However, in this example, the test sample was exposed to tetrathiafulvalene (TTF) vapor at 130° C. under reduced pressure. ” Measurements were carried out in the same manner as in Example 2. The measurement results are shown in Table ①.

Table ■ Lexan polycarbonate 141R/6% stainless steel fiber RB TTF (weight %) RA38
' 0.14 2136
0.16 1434
0.13 2826
0.13 1436 0.1
1 20 Examples 5 Same as Example 4. However, in this example, the test sample was
Exposure to N,N,N',N'-tetramethyl p-phenylenediamine (TMPD) vapor at 0'C. Measurements were performed in the same manner as in the above examples. The results are shown in Table 7.

Table 7 Lexan polycarbonate 141R/6? o Stainless steel fiber RB TMPD (weight%) RA16
2.20 4B128
2.10 33108
1.87 3394 2.1
9 2781 1.98
35104 2.11
57 Example 6 The same procedure as in Example 5 was repeated. However, in this example, the lexan polycarbonate sample was placed in air at an atmospheric pressure of 5
Exposure to 2-methylnaphthalene (2MN) vapor at 0°C. Table 3 shows the resistivity values measured before and after adding 2MN at the indicated concentration to the test sample.

Table ■Lexan polycarbonate) 141R/6% stainless steel fiber Rs 2MN (wt%) RA172
0.82 22898
1.04 2579
0.90 8154
1.27 1364 0.
89 10222 0.91
1231 0.95
1234 0.68
832 0.49 727
0.94 830
0, Gl g63
1.3[) 10 Example 7 The same procedure as in Example 5 was repeated. However, in this example, 26
A sample of Lexan polycarbonate containing % aluminum flakes by weight was exposed to DMA vapor in air at atmospheric pressure in a bell jar.

Measured values of resistivity before and after treatment are shown in Table ①.

Table ■Lexan polycarbonate ML4545-11 /
2696 aluminum RB DMA (weight%) RA78
0.15 7810 0.
08 463 0.09 1
11 0.10 430
0.15 3>8. [i Xl060.13
>G, OXIO'5(i 0
．． L4 50313 0.12
2258 0.31 31 As is clear from the examples described above, the addition of substances of low ionization potential to a composite plastic material of the type described above significantly reduces the resistivity of the composite material.

The low ionization potential materials used in the above examples are only some of the materials that can be used to achieve similar results. The ionization potential of a substance used here is the energy required to extract one electron (the weakest bonded electron) from the outermost filled orbit of a neutral molecule of the substance in the ground state. Therefore, substances with low ionization potential, when added to the base plastic/metal composite, generally act to donate electrons with the application of a relatively small potential, thereby increasing the overall electrical conductivity of the material. It has the following characteristics. Of course, these substances
One criterion must be selected based on compatibility (compatibility) with the base material or base plastic material used.

The gas phase ionization potentials of the substances used in the above examples are N,N'-DMA7.14eV, 2MN7.96
eL TMPD 6.33eV and TTF7, OeV
It is. The substrate or parent polymeric material has a gas phase ionization potential in the range of 8.3eV-9.3eV. Thus, it has been demonstrated that materials with ionization potentials in the range of about 15%-30% lower than the base plastic material result in significant reductions in resistivity. It is thought that similar effects can be obtained using a wider range of base materials and materials with lower ionization potentials. Substances that may be suitable candidates are discussed in Brownstein and Christofoulou, On the Parameters of Physically, Chemically and Biologically Important Molecules, Three Radiation Research, pp. 69-118, 1971. Blaunstc
in and Chistophorou, On Ho
Tecular Parameters of Phys
sical, chemical and biology
cal Interest, 3Radlatlon
Res., 69-118 (1971)). The final determination of a particular low ionization potential material is based on its compatibility with the substrate or matrix material.

No experiments were performed to determine the minimum effective proportion (wt %) of low ionization potential material necessary to achieve the measured resistivity reduction. In practice, this amount varies widely depending on the specific composition of the composite material. However, in general, according to the examples above, a minimum value of about 0.1% by weight appears reasonable. The maximum amount of low ionization potential material appears to be largely governed by the effect such multiple low ionization potential materials have on the overall chemical and physical properties of the composite material. in general,
An upper limit of about 10% by weight is expected.

Some materials with low ionization potential are unstable when combined with certain base plastics;
A suitable stable composition may be selected or well known stabilization techniques may be used to improve the properties of the final composite material.

In the embodiments described above, the pre-fabricated base plastic/
Although low ionization potential materials have been added to the metal filler composite, it is equally possible and preferred to produce the final composite using conventional compounding equipment and methods.

Specifically, the thermoplastic resin composition is heated in an extruder to a sufficiently high temperature to achieve a viscosity that allows the thermoplastic polymer to flow and mix with other components. The appropriate heating temperature will, of course, depend on the thermoplastic polymer selected. A low ionization potential conductivity enhancer and metal filler are placed in the extruder where the thermoplastic composition is molten. During this processing, conventional techniques are used to uniformly disperse the components within the composite material.

After this, the resulting blended composition is passed through a die at the end of the extruder and pelletized. This pellet can then be extruded or injection molded to obtain a final product suitable for certain high conductivity applications.

The principles, preferred embodiments, and modes of operation of the invention have been described above. However, the specific embodiments disclosed herein should be considered illustrative rather than limiting, and the invention sought to be protected by this application should not be considered limited to these specific embodiments. do not have. Various changes and modifications can be made without departing from the gist of the invention.

Claims (1)

[Claims] 1. In order to increase the electrical conductivity of a composite material in which a metal component is dispersed in an electrically insulating material, an increasing agent having a lower ionization potential than the insulating material is contained in the composite material. A method for producing a composite material with increased electrical conductivity, comprising the step of introducing a sufficient amount of the above-mentioned composite material to increase its electrical conductivity compared to the electrical conductivity before introducing the increasing agent. 2. A method according to claim 1, wherein the amount of said increasing agent is 0.1-10% by weight of said insulating material. 3. The above metal components are aluminum, stainless steel, silver,
2. The method of claim 1, wherein the material is selected from the group consisting of copper, zinc, iron, nickel, carbon steel and mixtures thereof. 4. The method of claim 1, wherein the insulating material is selected from thermoplastic materials and thermosetting materials. 5. The method according to claim 4, wherein the insulating material is a thermoplastic material. 6. The method of claim 5, wherein said thermoplastic material is selected from the group consisting of polycarbonate, polyamide, polyester, oxide polymer, polyurethane, acrylic resin, polyvinyl chloride, and hydrocarbon polymer. 7. The method according to claim 1, wherein the insulating material is a resin material. 8. The method of claim 1, wherein said metal component is selected from the group consisting of metal coated glass fibers, metal coated graphite fibers and aluminum strips. 9. The above-mentioned low ionization potential increaser is N, N'-
2. The method of claim 1, wherein the compound is selected from the group consisting of dimethylaniline, N, N, N', N'-tetramethyl p-phenylenediamine, 2-methylnaphthalene, and tetrathiafulvalene. 10. A metal component is dispersed as a filler in an electrically insulating material, and an increasing agent having a lower ionization potential than the above-mentioned insulating material increases the conductivity of the composite material compared to the conductivity before introducing the increasing agent. A conductive composite material characterized in that it is introduced in a sufficient amount to 11. The amount of the increaser is 0.1-10 of the insulating material.
11. A composite material according to claim 10, which is % by weight. 12. The composite material according to claim 10, wherein the metal component is selected from the group consisting of aluminum, stainless steel, silver, copper, zinc, iron, nickel, carbon steel, and mixtures thereof. 13. The composite material according to claim 10, wherein the insulating material is selected from thermoplastic materials and thermosetting materials. 14. The composite material according to claim 13, wherein the insulating material is a thermoplastic material. 15. The composite material of claim 14, wherein the thermoplastic material is selected from the group consisting of polycarbonate, polyamide, polyester, oxide polymer, polyurethane, acrylic resin, polyvinyl chloride, and hydrocarbon polymer. 16. The composite material according to claim 10, wherein the insulating material is a resin material. 17. The composite material of claim 10, wherein said metal component is selected from the group consisting of metal coated glass fibers, metal coated graphite fibers and aluminum strips. 18. The low ionization potential increaser is N, N'
11. The composite material of claim 10, wherein the composite material is selected from the group consisting of -dimethylaniline, N, N, N', N'-tetramethyl p-phenylenediamine, 2-methylnaphthalene and tetrathiafulvalene.