JPH04149239A - Electrically conductive molded article and its production - Google Patents

Abstract

PURPOSE:To obtain an electrically conductive molded article without impairing excellent flow properties and moldability by curing a mixture obtained by dispersing electrically conductive carbon black into an uncured resin liquid of curable liquid resin under a mold rotating at a high speed. CONSTITUTION:Electrically conductive carbon black such as acetylene black is added to an uncured resin liquid of curable liquid resin such as urethane elastomer or epoxy resin and these components are uniformly dispersed to afford a mixture. Then the mixture is poured into a mold and cured by high- speed rotation to provide the objective molded article being a ring-like or circumferential molded article having a relatively high carbon content along the outer circumference face.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a conductive resin molded product and a method for producing the same, and in particular,
The present invention relates to a resin molded product with excellent conductivity that can be effectively used in fields requiring conductivity such as antistatic products and electromagnetic shielding, and an industrially advantageous manufacturing method thereof.

[Prior Art] In general, polymeric substances are non-conductive substances having an electrical resistance of 10"Ωcm or more. In order to impart conductivity to these substances, cationic activators, quaternary ammonium It is known to add and blend antistatic agents such as salts and special amine compounds. However, there is a limit to the conductivity improvement effect of such additives, and the electrical resistance can be reduced to 10".
It is difficult to make it less than Ω·cm.

On the other hand, it is known that a method of dispersing metal powder or carbon black in a polymeric material is an effective method for lowering electrical resistance. In particular, acetylene black and ECF (Extra conductive fur)
Conductive carbon black such as Nace Black is widely used because it is inexpensive and has high conductive efficiency.

By the way, curable liquid resin can be injected into a mold in a liquid state and molded after curing, and does not require a special molding machine such as a press or an injection molding machine. It is a material that has advantages such as a simple mold structure and low cost manufacturing because the resin injection pressure is low. In order to impart electrical conductivity to such a curable liquid resin, an effective means is to add conductive carbon black to the resin and disperse it in the resin, as described above. After uniformly dispersing conductive carbon black into liquid resin before hardening using a dispersion machine such as a paint roll, it is injected into a mold, hardened, and demolded to create a conductive molded product. can be obtained. Therefore, the conductivity of the obtained molded product is proportional to the amount of conductive carbon black added, and the larger the amount added, the more conductive the molded product can be obtained.

[Problem to be solved by the invention] However, on the other hand, as the amount of conductive carbon black added increases, the viscosity of the liquid resin increases, and the fluidity becomes poor, resulting in poor casting, which is a characteristic of liquid resins. A defect occurs, which makes molding difficult.

There are various types of conductive carbon black, and carbon black with good conductivity efficiency can impart high conductivity to molded products by adding a small amount, but in general, carbon black with good conductivity efficiency can be added in small amounts. Conventionally, the trade-off between conductivity and moldability of liquid resins has been a point of contention, as the addition of 100% chloride greatly increases the viscosity of the liquid resin, impairing its fluidity.

The present invention overcomes the drawbacks of the trade-off between the conductivity and the molding processability of the liquid resin caused by the conductivity of the conventional curable liquid resin using four-electrode carbon black, and improves the flow processing of the liquid resin during molding. The purpose of the present invention is to provide a conductive resin molded product having excellent conductivity and conductivity, and a method for producing the same.

[Means for Solving the Problem] The conductive resin molded article of claim (1) is a ring-shaped or cylindrical molded article of conductive carbon-containing resin, and the carbon content of the portion along the outer peripheral surface is relatively low. The method for producing a conductive resin molded product according to claim (2), characterized in that the conductive resin molded product has a high
), the method for producing a conductive resin molded article,
It is characterized in that a mixture of a curable liquid resin and an uncured resin liquid containing a fraction of conductive carbon black is cured in a mold rotating at high speed.

The present invention will be explained in detail below.

First, a method for producing a conductive resin molded article of the present invention will be explained.

In the method of the present invention, first, a mixture is prepared in which conductive carbon black is added and uniformly dispersed in an uncured resin liquid of a curable liquid resin.

The curable liquid resin used in the present invention is one that can be cast into a mold in a liquid state and can be cured in the mold to obtain a molded article. Such curable liquid resins generally consist of a liquid polymer compound called the main material and a curing agent, etc. After uniformly mixing a predetermined amount of the curing agent into the main material, it is poured into a mold and heated. It is cured at low temperature or at room temperature. Typical curable liquid resins include cast urethane elastomer, epoxy resin,
Examples include acrylic resin and latent rubber.

On the other hand, as conductive carbon black, acetylate
Black YaE CfExtra conductive
) grade, which has a particularly large effect of imparting electrical conductivity, -bon black is preferred, but common carbons such as FEF and 15AF grades can also be used.

The amount of conductive carbon black added to the curable liquid resin is not particularly limited, but generally, if the amount of conductive carbon black is less than 0.2% by weight based on the main material of the curable liquid resin, it is insufficient to improve the conductivity. If the content is 10% by weight or more, the fluidity of the liquid resin will be significantly deteriorated, so it is preferably 02% by weight or more and less than 10% by weight.

As a method for uniformly dispersing conductive carbon black in the uncured resin liquid of the curable liquid resin, for example, conductive carbon black is added to a curing agent composition other than the main material of the curable liquid resin using a paint roll or the like. A method may be mentioned in which a uniformly mixed and dispersed curing agent masterbatch is mixed and stirred into the main material, but the method is not limited to this method.

Next, the liquid resin/conductive carbon black mixture thus obtained is cured under the conditions for curing the liquid resin in a mold rotating at high speed. In this case, the liquid resin/conductive carbon black mixture is injected into a stationary mold, and then the mold is rotated.
Molding may be carried out by injecting a liquid resin/conductive carbon black mixture into a rotating mold, but these methods may be selected as appropriate depending on the mold structure, etc., and any method may be used.

Here, although the rotational speed given to the mold varies depending on the diameter of the mold, it is usually good to set it to a rotational speed of 500 rpm or more, preferably a rotational speed of 11,000 rpm or more.

In such a method for manufacturing a conductive resin molded product of the present invention,
By selecting a mold with an appropriate shape, the conductive resin molded product of the present invention can be formed into a ring-shaped or cylindrical shape in which the content of conductive carbon black is higher along the outer circumferential surface than on the inner circumferential surface. A conductive resin molded article can be obtained.

[Function] Generally, the specific gravity of a liquid polymer compound is about 0.9 to 1.2, while the specific gravity of conductive carbon black is 1.8.
It has a specific gravity of ~2.0, which is higher than that of liquid polymer compounds. Therefore, when these mixtures are molded in a mold that rotates at high speed, the conductive carbon black with a high specific gravity moves slightly to the inner and outer walls of the mold due to the action of centrifugal force.
The density of conductive carbon black on the outer wall side increases.

This increases the conductivity of the entire molded product, but the effect of improving conductivity in the present invention far exceeds the effect of improving conductivity commensurate with the increase in the conductive carbon black content on the outer wall side. , and significantly superior significance is achieved according to the present invention.

The details of the mechanism behind this excellent conductivity are not clear at present, but because the anisotropic conductive carbon black is aligned in a certain direction due to the action of centrifugal force, the conductive carbon black inside the molded body is It is estimated that due to the orientation of , it is possible to obtain conductivity that far exceeds the conductivity estimated from the content of conductive carbon black.

The conductive resin molded product provided by the present invention is different from the molded product obtained by normal pressure casting method or vacuum casting method, which is a normal liquid resin molding method, based on the same amount of conductive carbon black added. 10 to 100 times higher conductivity can be obtained. Therefore, by adding a very small amount of conductive carbon black, it is possible to obtain a molded article with excellent conductivity as desired. Therefore, by reducing the amount of conductive carbon black added, the increase in viscosity of the liquid resin due to the addition of conductive carbon black can be suppressed to an extremely small amount, maintaining the flow processability of the liquid resin and improving the conductivity. It is possible to obtain excellent molded products.

[Example] The present invention will be described in more detail with reference to Examples below.

Example 1 A mixture of an uncured curable liquid resin and conductive carbon black having the composition shown in Table 1 was prepared and molded according to the method of the present invention.

First, a curing agent and a catalyst are added to and uniformly dissolved in a plasticizer heated to 120°C, and then the solution is cooled to 50°C.

Conductive carbon black was added to this solution, and the carbon black was uniformly dispersed in the solution using a paint roll to prepare a curing agent masterbatch. Next, the liquid urethane main material was heated to 70°C in a flask, stirred and degassed under reduced pressure, then the curing agent masterbatch was added, and after stirring vigorously for about 30 seconds under reduced pressure, the temperature was reduced to normal pressure. Reconstituted, uncured liquid urethane and conductive carbon black mixture No.
, 1 to 5 were prepared.

Among the obtained mixtures N011-5, No.

Mixtures Nos. 1 to 4 were liquid and could be molded by casting, but mixtures No. 5 and 5 were grease-like and could not be molded by casting.

Table 1 Urethane main material: Polytetramethylene ether glycol-toluene diisocyanate prepolymer (Coronate 4090J manufactured by Nippon Polyurethane Co., Ltd.) Curing agent: 4,4'-methylenebis(2-chloroaniline) (manufactured by Ihara Chemical Co., Ltd. [ Curemin MTJ) Plasticizer Nidioctyl phthalate Catalyst: Azelaic acid Conductive carbon black: Acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.: granular product) Next, the obtained mixture was molded using the mold shown in FIG. The mold 1 shown in FIG. 1 is a flat belt mold, and consists of an outer mold 2 and a core 3.
A cylindrical cavity 4 is formed between the core 3 and the core 3. The entire mold 1 has a structure that allows it to rotate at high speed with the central axis of the cylinder as the rotation axis. In addition, the entire mold is 100
It is heated to ℃.

Inside the cavity 4 of this mold 1, the N
Inject each of the mixtures of 001 to 4 at 200 rpm.
After curing while rotating for 20 minutes at a rotation speed of
The molded product was taken out from the mold to obtain four types of cylindrical molded products having different contents of conductive carbon black. This cylindrical molded product was slit into a ring shape with a width of 15 mm to obtain a flat belt with an inner diameter of 80 m and a thickness of 2 m.

Cut a part of this flat belt to make a strip-shaped sample, wrap aluminum foil with a width of 1 cm on both ends at intervals of 10 cm, and measure the electrical resistance between the aluminum foils at a measurement voltage of 500 V to determine the conductivity of the sample. I made it a gender major. Also,
In order to measure the content of conductive carbon black on the outer peripheral surface of the flat belt, a small piece with a thickness of about 0.2 mm was scraped off from the outer peripheral surface, and the content of carbon black was determined by thermal analysis.

The results are shown in Table 2 and Figure 4.

Comparative Example 1 For comparison, the electrical resistance of a belt obtained by molding without rotating the mold and the content of conductive carbon black on the outer peripheral surface were measured in the same manner as in Example 1.

That is, the mixtures No. 1 to 4 obtained in Example 1 were molded in a static mold shown in FIG. 1, and the electrical resistance of the resulting molded product was measured, and the conductive carbon black content was measured. was measured.

On the other hand, the mixture No. 5 obtained in Example 1 is not liquid and cannot be molded by the molding method of Example 1.
This was placed in a 2 mm slab mold, compression molded using a press, and cured at 100°C for 20 minutes to give a thickness of 2 mm.
A sheet of mm was prepared. This was cut into strip-shaped samples with a width of 15 mm, and the electrical resistance and conductive carbon black content were measured in the same manner as in Example 1.

The results are shown in Table 2 and Figure 4.

The conductive carbon black content of the mixtures N011-5 was calculated from the blending ratio, and the results are also listed in Table-2.

The following is clear from Table-2.

The carbon black content measured in Comparative Example 1 is in good agreement with the conductive carbon black content calculated from the blending ratio, but the The actual value of the carbon content is slightly higher than the conductive carbon black content calculated from the blending ratio.

This indicates that the conductive carbon black content on the outer peripheral surface side is increasing because the conductive carbon black moves toward the outer peripheral surface side due to centrifugal force.

As is clear from FIG. 4, which shows the relationship between the electrical resistance and the conductive carbon black content (actually measured value) obtained in Example 1 and Comparative Example 1, Example 1 was obtained in a mold rotating at high speed. It can be seen that the molded product has significantly lower electrical resistance and excellent conductivity than the molded product of Comparative Example 1 obtained in a stationary mold, which is a normal molding method.

Furthermore, this improvement in conductivity far exceeds the effect of improving conductivity commensurate with the increase in the content of conductive carbon black, which is caused by the movement of conductive carbon black toward the outer peripheral surface due to centrifugal force. I understand something.

That is, according to the present invention, an excellent conductivity improvement effect can be obtained with the addition of a small amount of conductive carbon black, so it is possible to impart conductivity without impairing the excellent flow processability that is a characteristic of liquid resin. It is clear that

Example 2, Comparative Example 2 Using the mold shown in FIG.
A mixture of o and 2 was molded.

The mold 5 shown in FIG. 2 is a mold for a 120MXL toothed power transmission belt, and is composed of an outer mold 6 and a core 7, with a cylindrical cavity between the outer mold 6 and the core 7. 8
is formed. A large number of tooth-shaped grooves 9 are cut into the outer peripheral surface of the core 7, and a tensile member 10 is further wound in a spiral shape. The entire mold 5 has a structure that allows it to rotate at high speed with the central axis of the cylinder as the rotation axis. Note that the entire mold was heated to 100°C.

The mixtures No. and 2 obtained in Example 1 were injected into the cavity of this mold 5, and after the mixture was cured while rotating at a rotational speed of 200 rpm for 20 minutes, the molded product was polished from the mold. It was slit into a ring shape with a width of 15 mm to obtain a toothed power transmission belt equivalent to 120MXL15.0. A part of this belt was cut to make a strip sample, and the electrical resistance was measured in the same manner as in Example 1.2. It was IMΩ.

For comparison, the electrical resistance of a belt obtained by molding in the same manner except that the mold was not rotated was 180 MΩ (Comparative Example 2).

From these results, it was confirmed that the Hada belt obtained in a mold rotating at high speed had a remarkable effect of improving conductivity.

Example 3, Comparative Example 3 Using the mold shown in FIG.
A mixture of O12 was molded.

The mold 11 shown in FIG. 3 has a volume of 190J.
This mold is composed of an outer mold 12 and a core 13, and a cylindrical cavity 14 is formed between the outer mold 12 and the core 13.

A large number of grooves 15 are cut into the inner peripheral surface of the outer mold 12.

Further, a tensile member 16 is spirally wound around the outer peripheral surface of the core 13. The entire mold 11 has a structure capable of rotating at high speed with the central axis of the cylinder as the rotation axis. In addition,
The entire mold is heated to 100°C.

The mixtures No. and 2 obtained in Example 1 were injected into the cavity 14 of this mold 11, and after the mixture was cured while rotating at a rotational speed of 200 Orpm for 20 minutes, the molded product was removed from the mold. Every 6 mountains (approximately 14
A poly V-belt equivalent to 190J6 was obtained by slitting it into a ring shape (mm width). A portion of this belt was cut to obtain a strip-shaped sample, and the electrical resistance was measured in the same manner as in Example 1 and found to be 0.75 MΩ. For comparison,
As a result of measuring the electrical resistance of a belt obtained by molding in the same manner except that the mold was not rotated, it was found to be 70M.
Ω (Comparative Example 3).

From these results, it was concluded that the belt obtained in a mold rotating at high speed had a remarkable effect of improving conductivity.

[Effects of the Invention] As detailed above, according to the present invention, by blending a small amount of conductive carbon black, a conductive material having excellent conductivity can be produced without impairing the excellent flowability that is a characteristic of liquid resin. It is said that it is possible to obtain a plastic molded product.

[Brief explanation of drawings]

Figure 1 is a sectional view showing the mold used in Example 2.
3 is a sectional view showing the mold used in Example 2, FIG. 3 is a sectional view showing the mold used in Example 3, and FIG. 4 is a graph showing the results of Example 1 and Comparative Example 1. 1.5.11...mold, 2.6.12...outer mold, 3,7.13...core,
4.8.14... Cavity agent Patent attorney Tsuyoshi Shigeno Diagram 3 Inkono

Claims (2)

[Claims] (1) A conductive resin molded product, which is a ring-shaped or cylindrical molded product made of a conductive carbon-containing resin, and is characterized by having a relatively high carbon content in a portion along the outer peripheral surface. (2) Conductive resin molding according to claim (1), characterized in that a mixture of conductive carbon black dispersed in an uncured resin liquid of a curable liquid resin is cured in a mold rotating at high speed. How things are made.