JPH037740A - Electroconductive thermoplastic resin composition and production thereof - Google Patents

Abstract

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

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a conductive thermoplastic resin composition and a method for producing the same, and particularly to a molded article suitable for fields where antistatic properties and electromagnetic wave shielding properties are required. The present invention relates to a conductive thermoplastic resin composition useful as a molding material and a method for producing the same.

[Conventional technology] In addition to broadcasting radio waves from televisions and radios, daily living spaces contain various frequencies such as high-frequency noises such as ignition noise from cars and barbers, and leakage electromagnetic waves from heating devices such as microwave ovens. The world is full of electromagnetic waves, and problems have arisen in that these electromagnetic waves affect televisions, radios, computer terminals, medical equipment, process control equipment, etc.

In addition, plastics, which have been frequently used in electronic equipment and other equipment in recent years, are not only prone to generating static electricity and being charged due to contact friction, etc., but also are transparent to electromagnetic waves, making them difficult to protect internal electronic devices. Therefore, countermeasures against electrostatic interference and electromagnetic interference are becoming a socially important issue.

Various attempts and research have been made to deal with these disturbances caused by static electricity and electromagnetic waves in a wide range of industrial fields.

Generally, by increasing the conductivity of a charged object, the charge will be reduced, and as a result, it will become less likely to be charged and cause electrostatic disturbances.On the other hand, with regard to the shielding effect of electromagnetic waves, objects with high conductivity The attenuation of both radio waves is large, indicating a greater electromagnetic wave shielding effect. In addition, in general, countermeasures against electromagnetic interference often require higher conductivity than countermeasures against static electricity, and if the conductivity is in the low resistance range required for recent electromagnetic shielding materials, it will also prevent static electricity. In many cases, it satisfies the prevention requirements of

In recent years, particularly advanced electromagnetic shielding materials have been required for housings for electronic devices such as computers, and highly conductive metals such as gold, silver, copper, nickel, aluminum, iron, carbon black, graphite, etc. Attempts have been made to utilize fibers or fine particles of carbon compounds such as carbon fibers.

Among these, metal powders such as silver, copper, and nickel, or graphite powders are mainly used as conductive fillers in conductive paints used for electromagnetic shielding of computer housings. , a binder, a solvent, additives, etc., and it is thought that conductivity is developed through chain-like connections of conductive fillers during coating film formation.

[Problem to be solved by the invention] By the way, thermoplastic resins, especially thermoplastic resins synthesized using petroleum as a raw material, have become popular in the household due to their stable product characteristics and moldability that is easily accepted industrially. There is an increasing tendency for thermoplastic resins to be used in commercial and industrial electrical appliances, automobile electronic devices, and parts of the housings of electronic devices, and technology that provides antistatic or electromagnetic wave shielding functions to these thermoplastic resins. Demand for this is increasing year by year.

The present invention has been made in view of the above circumstances, and is a conductive thermoplastic that can be molded into a product having excellent antistatic performance and electromagnetic shielding performance by imparting high conductivity to a thermoplastic resin. An object of the present invention is to provide a resin composition and a method for producing the same.

[Means for Solving the Problems] The conductive thermoplastic resin composition of claim (1) has a molecular weight of 8 to 50
The conductive thermoplastic resin composition according to claim (2), characterized in that it contains % by weight of expanded graphite powder.
), the expanded graphite powder has an expansion degree of 1 compared to acid-treated graphite.
The method for producing a conductive thermoplastic resin composition according to claim (3), wherein the conductive thermoplastic resin composition is obtained by expanding acid-treated graphite to an expansion degree of 100 to 300 mf/g.
By compressing the expanded graphite powder obtained by expanding it to mIt/g to form compressed graphite with a density of 0.05 to 0.8 g/crrI'', and then mixing and kneading it with a thermoplastic resin. , characterized in that the conductive thermoplastic resin composition of claim (2) is produced.

That is, as a result of intensive studies to achieve the above object of the present invention, the present inventors have found that extremely high conductivity can be imparted by incorporating a predetermined amount of a specific graphite powder into a thermoplastic resin composition. They discovered that it is possible to do this and completed the present invention.

The present invention will be explained in detail below.

First, the expanded graphite used in the present invention will be explained.

In the present invention, "expanded graphite" refers to graphite that has been expanded by rapid heating as described below, and includes a wide variety of compositions prepared by various methods. Expansion degree of treated graphite is 100-300m
j2. It is preferable to use one obtained by expanding the amount to 1/g. In addition, "acid-treated graphite" in the present invention is obtained by treating graphite such as natural graphite, pyrolytic graphite, quiche graphite, etc. with a mixture of concentrated sulfuric acid and a strong oxidizing agent, washing with water, and drying. Industrial thermally expandable graphite used in the manufacture of graphite sheets and the like usually corresponds to this type of graphite.

In this acid-treated graphite, sulfuric acid remains and is fixed between the layers of the graphite's layered structure, and when it is rapidly heated to about 500°C or higher, the sulfuric acid present between the eyebrows expands, resulting in a change in the C-axis direction. The graphite layer has the property of expanding several tens to hundreds of times over time, and the graphite layers after thermal expansion have a structure in which they are in loose contact with each other.

The acid-treated graphite used in the present invention is not particularly limited in its raw material graphite or manufacturing method, but its characteristics are as follows:
The degree of expansion when heated rapidly for 10 seconds at 0℃ is 100.
~300 mIt/g is desirable, and such acid-treated graphite is prepared, for example, by 98% by weight concentrated sulfuric acid and 6%
It can be produced by contacting graphite pulverized into about 20 to 150 meshes in a mixture of 0% by weight hydrogen peroxide at a temperature below 45° C. for 10 to 30 minutes, followed by washing with water and drying.

In the present invention, the development of conductivity occurs during the process in which graphite pieces are mixed with thermoplastic resin, heated, and kneaded in a fluid state, in which the graphite pieces that are loosely in contact with each other deform while peeling off, and partially form each other. The main reason is thought to be that an electrical connection circuit is formed by having connection points or being dispersed at extremely small distances. Therefore, the particle diameter of the acid-treated graphite used in the present invention is preferably larger than 150 mesh, particularly preferably larger than 100 mesh, from the viewpoint of imparting electrical conductivity. On the other hand, when the particle size is large, for example larger than 20 meshes, the expanded graphite pieces are of sufficient size, but no particular improvement in conductivity is observed. Therefore, the particle size of the acid-treated graphite used in the present invention is preferably classified in the range of 20 to 150 meshes for practical purposes.

In general, the particle size of acid-treated graphite usually depends on the particle size of the raw material graphite used to manufacture it, and therefore has a particle size distribution within a certain range depending on the particle size of the raw material, and can be used depending on the purpose. There is. Therefore, the particle size of acid-treated graphite can be easily adjusted by pulverizing raw graphite or acid-treated graphite.

In the case of the acid-treated graphite used in the present invention, there is a general relationship between the particle size and expansion degree of the acid-treated graphite and the bulk density of the expanded graphite powder, and usually for acid-treated graphite with a particle size of 150 to 100 mesh. The degree of expansion is 100-160mJZ
/g and the bulk density is 0.01-0.0063g/mIt, 1
For particles with a mesh size of 00 to 40, the expansion degree is 13.
Bulk density 0.0077~ at 0~250 m42/g
For particles with a particle size of 0.004 g/mJ2.40 to 20 mesh, the swelling degree is 200 to 300 mIt/g and the bulk density is 0. OO5~O, OO3g/mlt. For this reason, the degree of expansion of the acid-treated graphite used in the present invention is preferably 100 to 300 mA/g.

The expanded graphite powder used in the present invention is prepared by heating acid-treated graphite having the above-mentioned particle size distribution at 500°C or higher, preferably at 700 to 1500°C for several seconds, and more preferably at 80°C.
It is obtained by thermal expansion by heating at 0 to 1100°C for 2 to 5 seconds.

In this case, thermal expansion can be carried out on an industrial scale, for example, by continuously feeding the acid-treated graphite into an electric furnace or gas burner furnace controlled at a predetermined temperature.

In addition, the "degree of expansion" here refers to 150℃ heated by holding it in an electric furnace maintained at 1000℃ for 10 minutes or more.
Take out the quartz bead of c to the outside of the furnace and immediately add acid-treated graphite o.
, 5g was put into the furnace which was also maintained at 1000°C, held for 10 seconds, taken out of the furnace, and allowed to cool naturally. This is the value (unit: +nQ/g) calculated by reading the upper position and measuring the volume.

In addition, "bulk density" is the reciprocal of the degree of expansion (unit: g/
mJ2), and can be calculated immediately by measuring the degree of expansion, but it can also be measured by the following method.

That is, an appropriate amount of expanded graphite powder discharged from the expansion furnace is gently transferred to a 1000 mft graduated cylinder, the top of the graduated cylinder is immediately covered with a cling film, and the cylinder is left to stand overnight at room temperature. The volume after being allowed to stand is read, and the weight of the expanded graphite powder is separately measured to determine the bulk density.

If the degree of expansion of the acid-treated graphite is less than 100m/75, the expansion of the graphite in the C-axis direction is insufficient, and as a result, the delamination of the acid-treated graphite is not sufficiently performed, and such expanded graphite is Even if it is added to the resin, there will be particles with a large thickness in the C-axis direction, that is, particles that do not peel off and remain in a multilayered state, in the resin. For this reason, the number of graphite powder particles dispersed in the resin decreases, the formation of chain connections by the graphite powder becomes insufficient, and the formation of electrical connection circuits is also insufficient.
No improvement in conductivity can be expected.

On the other hand, even if the degree of expansion of acid-treated graphite exceeds 300 m i/g, no corresponding effect can be expected in terms of imparting conductivity, and it is extremely difficult to industrially produce such expanded graphite powder. difficult and impractical from an economic standpoint.

On the other hand, the thermoplastic resin constituting the thermoplastic resin composition of the present invention is not particularly limited, and includes, for example, polyolefin resins such as polyethylene, polypropylene, polybutylene, and copolymers of these monomers with vinyl acetate, acrylic ester, etc. Polyvinyl chloride resins, polystyrene, polystyrene resins such as acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, polyester resins such as polyethylene terephthalate, polyamide resins such as nylon, polyoxymethylene In addition to ether resins such as ether resins, elastomers such as chlorinated polyethylene, polybutadiene, and polyisoprene can be cited as representative examples.

In the present invention, the addition ratio of expanded graphite powder to the thermoplastic resin is 8 as the content in the thermoplastic resin composition.
The content is set to 50% by weight, more preferably 10 to 40% by weight. If the content of expanded graphite is less than 8% by weight, the graphite pieces will not be sufficiently connected to each other, and the desired conductivity will not be achieved, and if the content is more than 50% by weight, the conductivity will not improve commensurately. Not only is this not acceptable, but it also causes problems such as deteriorating the properties of the resulting molded product.

1 In addition, in the conductive thermoplastic resin composition of the present invention,
Common additives used in ordinary plastic products,
That is, it goes without saying that antioxidants, antistatic agents, lubricants, crosslinking agents, flame retardants, dyes and pigments, conductive fillers, fillers, etc. may be added or blended.

Next, a method for manufacturing the conductive thermoplastic resin composition of the present invention will be explained.

As a method for manufacturing the conductive thermoplastic resin composition of the present invention, a thermoplastic resin raw material, a predetermined amount of expanded graphite powder, and, if necessary, each M additive are mixed using a Henschel mixer, ribbon blender, etc. The mixture is stirred and mixed using a mixing device, and then kneaded using a commonly used kneading machine such as a single or twin screw extruder, kneader, or Banbury mixer, or kneaded using a heated Miki roll or the like. can be mentioned.

Temperature conditions during kneading include temperatures above the melting point of the thermoplastic resin raw material used and below the melting point +100°C, but in general, the fluidity of the mixture decreases due to the addition of expandable graphite powder. Therefore, it is more advantageous to knead at a temperature above the melting point +30°C, and the upper limit temperature is usually determined by the thermal stability of the thermoplastic resin.

Furthermore, an advantageous method for adding expanded graphite powder is the method of claim (3), that is, adding acid-treated graphite to an expansion degree of 10.
The expanded graphite powder obtained by expanding it to 0 to 300 mJL/g is pressurized and compressed to give a powder of 0.05 to 0.8 g/c, preferably 0.1 to 0.4 g/crr. After forming compressed graphite, it is mixed with a thermoplastic resin raw material and then kneaded. That is, the expanded graphite used in the present invention has extremely high lubricity and is slippery, so it does not penetrate into the molten resin easily, and it is too bulky compared to the resin raw material, so it is difficult to add it to the resin. Otherwise, the workability during kneading is not good, and the dispersibility in the resin may be impaired. For this reason, it is preferable to add it in the form of compressed graphite. At this time, the density of compressed graphite is 0.05 g/ct
If it is less than rl'', the workability will not be improved sufficiently and the density will be 0.8.
If it exceeds g/cm3, the dissociation of the graphite particles will be delayed and the dispersibility in the resin will be reduced, which is not desirable. Graphite compressed in this way can be easily crushed into a size of 0.5 to 5 mm square, and not only can it be easily fed to a kneader, but it can also be sufficiently dispersed in the resin in a short kneading time. can.

The conductive thermoplastic resin composition of the present invention can be made into molded products such as directly extruded sheets and injection molded products, and can also be used as foam molded products by adding a foaming agent. Furthermore, it can be diluted with other thermoplastic resins as a masterbatch or compound, or mixed with other thermoplastic resins to form molded products. In either case, it goes without saying that the amount of expanded graphite powder to be added can be freely set within the scope of the present invention depending on the desired conductivity.

The conductive thermoplastic resin composition of the present invention or a molded article obtained by molding the same may be further used as a composite material by combining different materials for the purpose of aestheticizing the surface, making it water resistant, making it flame retardant, etc. It is also possible to do so.

[Function] Expanded graphite is highly expanded in the C-axis direction due to thermal expansion and has a structure in which the graphite layers are loosely in contact with each other.The graphite pieces are mixed with a thermoplastic resin, heated, and kneaded in a fluid state. In the process of being separated, they deform while exfoliating, and either have partial bonding points with each other, or become dispersed with extremely small distances between them. Therefore, an electrical connection circuit is formed in the expanded graphite portion within the resin composition, and good electrical conductivity is exhibited.

In addition, since expanded graphite powder is extremely lightweight, it is also effective in reducing the weight of products.

In particular, according to claim (2), a conductive thermoplastic resin composition having extremely excellent conductivity is provided.

Therefore, such a conductive thermoplastic resin composition can be advantageously produced industrially by the method of claim (3).

[Example] 5 The present invention will be explained in more detail with reference to production examples, working examples, and comparative examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. .

In addition, in production examples, working examples, and comparative examples, "part" is 1
"1 part" indicates "% by weight" and "1%" indicates "% by weight".

Production Example 1: Production of Expanded Graphite Powder 40 parts of natural flaky graphite produced in Canada (particle size: 36 mesh to 80 mesh) with fixed carbon content of 90% and ash content of 8% were mixed with 150 parts of 98% sulfuric acid and 60% peroxide. It was added to a mixture of 2 parts of hydrogen water and reacted at 30 to 35°C for 15 minutes. Next, the reaction product was diluted by adding 150 parts of 30% sulfuric acid, and then suction filtered using a Nutsche filter using glass fiber filter paper (GAloo) to remove the residue. This filtered residue was poured into 500 parts of water, stirred and washed for 30 seconds, and then the residue was separated by suction filtration again. The residue was poured into 500 parts of water again, stirred and washed for 30 seconds, and then filtered with suction in the same manner to separate the residue.

Next, this filtered residue was dried for about 90 minutes in a hot air circulating dryer at 105° C. to obtain acid-treated graphite A.

The expansion degree of this acid-treated graphite A at 1000°C for 10 seconds was 190 mJ2/g.

In order to add and knead the thermoplastic resin, this acid-treated graphite A was separately dropped into a vertical electric furnace set at 1100°C for a residence time of about 2 seconds to obtain expanded graphite powder A. This material was gently transferred to a 1000 mλ graduated cylinder, and the bulk density determined from the volume and weight was 0.0055 g/m°C.

Production Example 2: 'Production of Tensioned Graphite Powder The same procedure as Production Example 1 was used except that natural flaky graphite produced in Canada (particle size: 60 mesh to 100 mesh) with fixed carbon content of 92% and ash content of 6% was used. and acid-treated graphite B
I got it. The expansion degree of this acid-treated graphite B at 1000° C. for 10 seconds was measured to be 1.7 g in 140 ml.

In order to add and knead the thermoplastic resin, this acid-treated graphite B was separately dropped into a vertical electric furnace set at 800° C. with a residence time of about 2 seconds to obtain expanded graphite powder B. This material was gently transferred to a graduated cylinder at 10100O, and the bulk density determined from the volume and weight was 0.010 g/mJ2.

Production Example 3: I-Ku U and 11 Expanded graphite powders A and B obtained in Production Example 1.2 were compressed using a press at room temperature to a thickness of approximately 3 mm.
of compressed graphite is obtained, and then this compressed graphite is approximately 2 to 5 m long.
It was crushed into aggregates of m square size. Note that the density of this compressed graphite is as shown in Table 1.

Examples 1 to 8, Comparative Example 1 The compressed graphite obtained in Production Example 3 and the thermoplastic resin shown in Table 1 were mixed in the formulation shown in Table 1, and the thermoplastic resin composition was prepared by the kneading method described in (1) below. manufactured something. Using the obtained thermoplastic resin composition, a sheet was manufactured by the sheet-forming method described in (1) below, and the volume resistivity of the sheet was measured by the method (2) below. The results are shown in Table 1.

■ Kneading method: Use the mixing chamber of Brabender's "Brabender Plasticorder" at a temperature of 180°C and a rotation speed of 3 Orp.
m, put the thermoplastic resin in the amount shown in Table 1 into this chamber, and after the resin begins to be kneaded in a fluid state, continue to expand the amount shown in Table 1. Compressed graphite obtained by compressing graphite was added over a period of 10 seconds.

After starting the addition of expanded graphite, the kneading operation was continued for 10 minutes while maintaining the same conditions. Three minutes after the start of time measurement, the temperature of the mixture in the chamber was measured and found to be 182° C., which was close to the set value during the kneading operation. After kneading for 10 minutes, the mixture was taken out from the chamber.

■ Sheeting method: A metal spacer of 120 mm x 120 mm x 1 mm is installed in a heat press device preset at the temperature set during kneading in ■ + 20°C, and mixture 1 after the kneading operation in ■ is installed.
Four parts were heated and pressed at 100 kg/cm' for 3 minutes, and then the pressure was released to obtain a sheet. After visual observation, this sheet was used for volume resistivity measurement.
It was cut into a size of 100 mm x 100 mm.

(2) Measurement of volume resistivity It was measured according to JIS-6911.5.13 "Resistivity".

Comparative Examples 2 to 4 The thermoplastic resin shown in Table 1 was used, and the sheeting and volume resistivity were measured in the same manner as in Example 1, except that compressed graphite was not blended, and the results are shown in Table 1. Indicated.

Comparative Example 5.6 Kneading, forming into a sheet, and measuring volume resistivity were carried out in the same manner as in Example 2, except that graphite powder shown in Table 1 was used instead of compressed graphite, and the results are shown in Table 1. Indicated.

Comparative Example 7 A sheet was formed and the volume resistivity was measured in the same manner as in Example 3 except that the expanded graphite obtained in Production Example 1 was used without being compressed. The results are shown in Table 1. In this example, it took 7 minutes to add graphite powder to the resin.

From the results in Table 1, it can be seen that those containing less compressed graphite than the range of the present invention (Comparative Example 1), those containing no compressed graphite at all (Comparative Examples 2 to 4), or those containing expanded graphite that is not compressed. (Comparative Example 7) shows a high volume resistivity, whereas the sheet obtained from the conductive thermoplastic resin composition of the present invention has extremely high conductivity. . On the other hand, in the case of blending natural graphite powder used as a raw material for producing expanded graphite (Comparative Example 56), hardly any effect of improving conductivity can be obtained.

[Effects of the Invention] As detailed above, the conductive thermoplastic resin composition of the present invention provides a thermoplastic resin composition having extremely high conductivity. Therefore, according to the conductive thermoplastic resin composition of the present invention, a thermoplastic resin molded article having excellent antistatic effect and electromagnetic wave shielding effect, which is useful as cabinets for electrical products and electronic products, is provided. Moreover,
Since the expanded graphite powder used in the present invention is extremely lightweight, it is possible to reduce the weight of the product.

In particular, according to the conductive thermoplastic resin composition of claim (2), a thermoplastic resin composition with more excellent conductivity is provided.

Therefore, such a conductive thermoplastic resin composition can be easily produced by the method of claim (3).

Claims (3)

[Claims] (1) A conductive thermoplastic resin composition characterized by containing 8 to 50% by weight of expanded graphite powder in the thermoplastic resin composition. (2) Expanded graphite powder expands acid-treated graphite to an expansion degree of 100.
The conductive thermoplastic resin composition according to claim 1, which is obtained by expanding the composition to 300 ml/g. (3) Expanded graphite powder obtained by expanding acid-treated graphite to an expansion degree of 100 to 300 ml/g is compressed to obtain a powder with a density of 0.
．． 05 to 0.8 g/cm^3 of compressed graphite, and then mixed and kneaded with a thermoplastic resin. Method.