JP2002275276A - Electro conductive molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electro conductive molded article excellent in electroconductivity and manifesting a big impact resistance. SOLUTION: This electro conductive molded article includes a thermoplastic resin and 0.1-5.1 wt.% of carbon fibrils based on the sum of the of thermoplastic resin and the carbon fibrils, having <=100 nm of an average fiber diameter and >=10 of a length/diameter ratio, having <=180 of the number of a part surrounded by the network of the fibrils on a part adjacent to the surface (2-10 μm) of the molded article and >=12 of the standard deviation of the surface area of the surrounded parts. The preferable thermoplastic resin is a polycarbonate resin and the preferable weight average molecular weight (Mw) of polycarbonate resin constituting the molded article is <=45,000.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly conductive molded article, and more particularly to an antistatic part in the electric and electronic fields and in the field of automobiles. Trays, cases, packaging materials such as packages in the manufacturing and transport processes, especially disks for hard disk drives,
The present invention relates to a conductive molded product suitable for an antistatic member for a magnetic head.

[0002]

2. Description of the Related Art In recent years, semiconductor devices have become extremely vulnerable to static electricity as information recording density has increased and processing speed has increased, and measures to prevent static electricity in cases and jigs have become important. .

[0003] Therefore, these antistatic products generally require a surface resistance value (ie, conductivity) of 10 ¹² Ω / □ or less.

Conventionally, in order to prevent static electricity, for example, AB
A method is employed in which a thermoplastic resin such as S, polycarbonate, and modified polyphenylene ether (PPE) is mixed and dispersed with a conductivity imparting component such as an antistatic agent, carbon black, and carbon fiber.

[0005]

However, these methods have the following problems, respectively. That is, in the case of an antistatic agent, the conductive mechanism is affected by environmental humidity due to ionic conduction, and the antistatic agent flows out due to washing or long-time use, and the antistatic property is reduced. If added in large amounts, heat resistance may be impaired.
Although carbon black and carbon fiber are not affected by humidity, washing and the like, carbon particles and carbon fiber are liable to fall off, causing problems such as damage to devices.

[0006] On the other hand, when carbon fibrils having a diameter of 100 nm or less are added as a conductivity-imparting component, it is effective because the falling off of the filler is reduced. However, there are also the following problems. (1) By adding carbon fibrils, mechanical strength, particularly impact strength, is significantly impaired, and cracks tend to occur when dropped. (2) Since carbon fibrils are extremely expensive, this leads to an increase in product cost. On the other hand, when the amount of carbon fibrils is reduced, the conductivity of the molded article is significantly impaired.

[0007] An object of the present invention is to provide a conductive molded article which can obtain high conductivity even when the amount of carbon fibrils is reduced.

[0008]

The conductive molded article of the present invention is a molded article containing a thermoplastic resin and carbon fibrils having an average fiber diameter of 100 nm or less and a length / diameter ratio of 10 or more, 4. The content of the carbon fibrils is 0.1% by weight or more based on the total of the thermoplastic resin and the carbon fibrils.
Less than 1% by weight, near the surface of the molded article (2 to 10 μm).
m), wherein the number of portions surrounded by the carbon fibril network per 25 μm ² is 180 or less, and the standard deviation of the area of the surrounded portions is 12 or more.

In such a conductive molded article, carbon fibrils are not uniformly dispersed, but are dispersed in a thermoplastic resin matrix in a state where they are aggregated or entangled to some extent to form a continuous network. , High conductivity. That is, when the carbon fibrils are uniformly dispersed,
There is no conduction between carbon fibrils and the conductivity is low. On the other hand, the conductivity of the carbon fibrils is increased by agglomeration of the carbon fibrils and contact or proximity to each other to form a network.

[0010] In the present invention, since the sufficient amount of carbon fibrils is reduced to achieve sufficient conductivity, a reduction in impact strength due to the addition of carbon fibrils is suppressed, and a highly conductive molded article having high impact strength is provided. Can be provided. In addition, since the amount of high-priced carbon fibrils is small, the cost is low.

In the present invention, the area and the number of the portion surrounded by the carbon fibril network are defined as values measured by the following method.

[0012] From the surface of the molded body, an ultrathin section is cut out in a range of 2 to 10 µm with a thickness of 70 to 100 nm.

The following analysis is performed on the dispersion image of carbon fibrils obtained by photographing the ultrathin section of the sample with a transmission microscope (× 40,000). First, an image in the range of 5 μm × 5 μm is
The image is converted into a digital image by 512 × 512 pixels having a pixel size of 9.77 nm × 9.77 nm. As a result, the pixels in which carbon fibrils exist are turned on, and the pixels in which carbon fibrils do not exist are turned off, and binarization processing is performed. At this time, an image obtained by tracing the original image on another paper or the like in advance may be digitized in order to perform the binarization processing with higher accuracy and easier. FIG. 6 shows an example of this trace diagram. In FIG. 6 (1), carbon fibrils are relatively uniformly dispersed, and in FIG. 6 (2), they are aggregated to some extent.

[0014] Three consecutively adjacent three vertically, horizontally, and vertically
If at least one of the 3 × 9 pixels is on,
Image processing (expansion processing) for assuming that all nine pixels are on is performed over the entire image. FIG. 1 (a) to (d)
Shows the first expansion processing (image processing) when only one pixel is ON. Specifically, as shown in FIG.
When one ON point exists in a certain range, all 3 × 3 pixels are scanned, and when ON pixels are included in the area, all nine pixels are turned ON {FIG. 1 (b),
(C), (d)｝. As a result, 5 × 5 pixels around one pixel that was on are turned on {FIG. 1D}. FIG.
As shown in (e) and (f), the carbon fibrils separated by the expansion treatment are bonded. By one expansion process, the carbon fibrils expand four pixels in the vertical and horizontal directions. By performing the image processing five times, the carbon fibril images that are close to each other or separated from each other in the initial imaging are connected to become thick.

Therefore, only the pixel at the center in the width direction (thickness direction) of the fibril image after the fifth processing is turned on, and the other pixels are turned off. That is, the center line of the image is replaced with a continuum of one pixel. FIG. 2 (a),
(B) is a schematic diagram showing this example.

The same dilation processing as described above is repeated twice for the center line image obtained as described above. The continuous line in the obtained image is defined as “carbon fibril network”. FIG. 3 is a schematic diagram showing an example of an image having a carbon fibril network obtained in this manner.

The number of closed regions surrounded by the carbon fibril network is defined as a “portion surrounded by the carbon fibril network”. Note that a region intersecting the edge of the visual field (image) is excluded from the analysis. The number and area of the “portion surrounded by the carbon fibril network” are measured.

This is similarly performed for five visual fields, and the average value is obtained. The average thus obtained is defined as the “number of portions surrounded by the carbon fibril network” and “the area of the portion surrounded by the carbon fibril network” of the present invention.

In the present invention, the number of portions surrounded by the carbon fibril network is 180 or less. This numerically represents the degree to which the carbon fibrils are aggregated to some extent and are gathered together to form a network.
The fact that the standard deviation of the area of the portion surrounded by the carbon fibril network is 12 or more indicates that the area has a large variation, in other words, the density of the network is large. Furthermore, a large network density indicates that carbon fibrils are not uniformly dispersed.

The number and standard deviation of the above-mentioned “region surrounded by the carbon fibril network” both indicate the heterogeneity of dispersion of carbon fibrils, that is, the degree of carbon fibril aggregation, but the number is microscopic. And the standard deviation indicates a macroscopic aggregation degree.

The number range is preferably 170 or less, 2
0 or more, and the standard deviation is desirably 15 or more and 200 or less.

If the number is larger or the standard deviation is smaller, the conductivity will not be exhibited within the range of the added amount of the carbon fibrils of the present invention.

On the other hand, when the number is smaller or the deviation is larger, the dispersion becomes too uneven.
The conductivity decreases.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the highly conductive molded article of the present invention will be described below in detail.

First, the forming raw material used in the present invention will be described. <Carbon fibrils> The carbon fibrils used in the present invention are carbon fibrils having an average fiber diameter of 100 nm or less, and for example, those described in JP-T-8-508534 can be used.

The carbon fibrils have an outer graphite layer deposited substantially concentrically with the cylindrical axis of the fibrils, the fiber central axis being non-linear and having a undulating and winding tubular configuration. Have. The fiber diameter of the carbon fibrils depends on the production method and is almost uniform. However, if the average fiber diameter of the carbon fibrils is larger than 100 nm, the contact between the fibrils in the resin becomes insufficient, and the conductivity becomes sufficient. And it is difficult to obtain stable conductivity. Therefore, as carbon fibrils, the average fiber diameter is 100 nm or less, preferably 2 nm or less.
The thing of 0 nm or less is used.

On the other hand, the average fiber diameter of carbon fibrils is
It is preferably at least 0.1 nm, particularly preferably at least 0.5 nm. When the fiber diameter is smaller than the above range, the production is extremely difficult, and the cost of the product is increased.

Carbon fibrils having a length / diameter ratio (length / diameter ratio, ie, aspect ratio) of 10 or more;
Preferably, 20 or more, particularly preferably 100 or more are used. With such a length / diameter ratio,
A conductive network can be easily formed, and excellent conductivity can be exhibited by adding a small amount.

The fiber diameter and length (length / diameter ratio) of the carbon fibrils are determined, for example, by removing the resin component of the obtained molded article by a solvent or ion sputtering, exposing the carbon fibrils, It can be measured by observing with a microscope or by observing an ultra-thin section cut out from a molded product with an electron microscope, and in such an electron microscope observation, an average value of ten actually measured values can be obtained.

The wall thickness (wall thickness of the tubular body) of the carbon fibrils having a fine tubular shape is usually 3.5 to 75.
nm. This usually corresponds to about 0.1 to 0.4 times the outer diameter of carbon fibrils.

When at least a portion of the carbon fibrils is in the form of aggregates, the fibril aggregates having a diameter greater than about 50 μm, preferably greater than 10 μm, as measured on an area basis, in the matrix resin as the raw material. It is desirable not to contain a fibril aggregate having the following in order to reduce the amount of addition for expressing desired conductivity and not to deteriorate mechanical properties.

The carbon fibrils used in the present invention preferably have a degree of bending of at least 10 °, preferably at least 20 °, more preferably at least 40 °. The degree of bending is a value that is a measure of the ease of entanglement between carbon fibrils, and a conductive network is formed by forming an entangled network of carbon fibrils, whereby conductivity can be exhibited.

The degree of bending is measured by removing the resin component of the molded product by a solvent, ion sputtering or the like to expose carbon fibrils, or by observing an ultra-thin section cut out from the molded product with an electron microscope. The degree of bending was observed with a microscope as shown in FIG.
2 times by using a method such as measuring the fiber diameter (d in FIG. 7) and measuring it five times along the fiber with a divider or the like.
Select B, the tangent _L A to each point, pulling the _{L B,} (indicated by α in Fig. 7) tangent _L A, the exterior angle of the crossing points Q of _{L B}
Is measured. The average value of 10 points is taken and defined as the degree of bending. That is, if the fiber is straight, the degree of bending is 0 °, 180 ° in a semicircle, and 360 ° in a circle.

For example, a conventional carbon fiber (pitch type, PA
N-type) is a rigid and straight fiber having a fiber diameter of about 7 to 13 μm, and a degree of bending of less than 10 °. Such straight fibers do not entangle with each other, and it is difficult to control the network structure within the scope of the present invention.

As such carbon fibrils, commercially available products can be used. For example, “BN” manufactured by Hyperion Catalysis International Co., Ltd. can be used. In particular, since the degree of bending changes depending on the kneading conditions, it is important to obtain the conditions empirically.

<Thermoplastic resin> The thermoplastic resin used in the present invention includes, for example, polycarbonate, polybutylene terephthalate, polyamide, ABS resin, AS resin, polyethylene, polypropylene, polyacetal, polyamideimide, polyether sulfone, polyethylene terephthalate, and polyimide. , Polyphenylene oxide, polyphenylene sulfide, polyphenylsulfone, polystyrene, thermoplastic polyurethane, polyvinyl chloride, fluororesin, liquid crystalline polyester, thermoplastic resin such as polyetheretherketone, or a mixture thereof. Mechanical strength, depending on the purpose of use
It can be appropriately selected from characteristics such as moldability.

Among the above-mentioned thermoplastic resins, polycarbonate resins are desirable because of good balance among dimensional accuracy, heat resistance, mechanical properties and the like.

As the polycarbonate resin, a general resin produced by reacting phosgene with a dihydric phenolic compound as a main component by a solution method such as an interfacial polymerization method, a pyridine method, a chloroformate method, or the like is used. Can be used.

The weight average molecular weight of the polycarbonate in the final molded article is 45,000 or less, preferably 30,000 to 45,000, more preferably 35,000 to 43,000 in terms of polystyrene. It is desirable to select the molecular weight of the raw material polycarbonate and the production conditions in advance. When the molecular weight is within this range, the portion of the conductive molded body surrounded by the carbon fibril network is likely to be within the range of the present invention, and as a result, the conductivity is excellent. And it does not lower the mechanical strength.

The polycarbonate composition constituting the molded article of the present invention has a melt flow rate (MFR) of 280
2C / 10 minutes or more and 30 g / 10 minutes or less, especially 4 g / 10 minutes or more and 15 g /
10 minutes or less is desirable.

As a method for obtaining a polycarbonate resin molded article having a weight average molecular weight in the range of the present invention, for example, molding is performed beforehand using a polycarbonate resin having a molecular weight within the range of the present invention or a higher value. A method of appropriately reducing the molecular weight of the polycarbonate by adjusting the processing temperature conditions and the like or repeating molding can be adopted.

<Proportion of Carbon Fibrils> The mixing ratio of carbon fibrils is 0.1% by weight or more and less than 5.1% by weight based on the total of the thermoplastic resin and carbon fibrils.
Preferably from 0.1 to 4% by weight, more preferably from 0.5 to 4% by weight.
3.5% by weight. If the amount of the carbon fibrils is less than the above range, sufficient conductivity cannot be obtained, and if the amount is too large, the resulting molded article may have a reduced impact strength or an increased cost, which is not preferable.

<Additives> In the present invention, if necessary, optional additives other than the thermoplastic resin and carbon fibrils can be blended within a range not to impair the object of the present invention. For example, glass fiber, silica fiber, silica
Inorganic fibrous reinforcement such as alumina fiber, potassium titanate fiber, aluminum borate fiber, etc., organic fibrous reinforcement such as aramid fiber, polyimide fiber, fluororesin fiber, talc, calcium carbonate, mica, glass beads, glass powder, glass Inorganic fillers such as balloons, various carbon blacks, fluoroplastic powders, solid lubricants such as molybdenum disulfide, plasticizers such as paraffin oil, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, and neutralizers And various additives such as a lubricant, a compatibilizer, an anti-fogging agent, an anti-blocking agent, a slip agent, a dispersant, a colorant, a bactericide, and a fluorescent brightener.

<Production Method> The production method of the conductive molded article of the present invention can be produced by a usual thermoplastic resin processing method. For example, a polycarbonate resin composition can be produced by previously mixing a conductive filler and then melt-kneading the mixture with a Banbury mixer, a roll, a Brabender, a single-screw kneading extruder, a twin-screw kneading extruder, a kneader, or the like. Thereafter, the conductor can be obtained by molding using various melt molding methods. Specific examples include press molding, extrusion molding, vacuum molding, blow molding, and injection molding. Of the molding methods, injection molding is particularly desirable in terms of high productivity.

As the injection molding method, in addition to a general injection molding method, integral molding with metal parts or other parts by insert injection molding, two-color injection molding, core back injection molding, sandwich injection molding, etc. And various molding methods such as an injection press molding method.

In the injection molding, the carbon fibril network in the product changes depending on the resin temperature, the mold temperature, the molding pressure, and the injection speed. As a result, the conductivity changes, so that appropriate conditions must be set. Must.

When molding conditions are set such that a decrease in molecular weight by injection molding is 2% or more (preferably 2 to 5%) when polycarbonate is used, the conductivity of the molded product is good. This is desirable.

After the melt molding, the dispersion of the carbon fibrils may be adjusted by performing a heat treatment with hot air or infrared rays.

[0049]

The present invention will be described more specifically below with reference to examples and comparative examples.

The raw material components used in the following Examples and Comparative Examples are as follows.

Polycarbonate (PC) (Tg; 145)
° C): "Iupilon" manufactured by Mitsubishi Engineering-Plastics Corporation Carbon fibrils: "Hyperion BN" manufactured by Hyperion Catalysis International

Examples 1 to 5, Comparative Examples 1 and 2 (1) Kneading and blending Polycarbonate and carbon fibril masterbatch were
The mixture was mixed according to the formulation shown in Table 1, and a twin-screw extruder (“PCM45” manufactured by Ikegai Iron & Steel Co., Ltd., L / D = 32 (L; screw length,
D; screw diameter)) and melt-kneaded at a barrel temperature of 300 ° C. and a screw rotation speed of 160 rpm to obtain pellets of a resin composition having a carbon fibril content shown in Table 1. In addition, when compounding carbon fibrils, mixing and kneading the carbon fibrils in a matrix resin in advance
A masterbatch to which 5% by weight was added was manufactured, and this was diluted to a predetermined carbon fibril addition amount.

(2) Measurement of Molecular Weight of Polycarbonate in Pellets The molecular weight of the polycarbonate in each composition obtained in (1) was measured in the following manner. A chloroform solution (2 mg / ml) of the composition was prepared, which was filtered through a 0.2 μm filter, and carbon fibrils were separated to obtain a polycarbonate solution. Using this polycarbonate solution,
The weight average molecular weight (Mw) was measured by GPC. Detailed conditions are described below. Detector: Waters UV490 (254 nm) Column: Shodex GPC AD-806MS Column temperature: 30 ° C Flow rate: 1 ml / min
Internal standard: toluene Injection amount: 0.05 ml Table 1 shows the measurement results of the weight average molecular weight of each composition. The weight average molecular weight is a value in terms of polystyrene.

[0054]

[Table 1]

(3) Sample formation for resistance measurement A sheet for resistance measurement of 100 × 100 × 2 mm (thickness) was molded using a 75TON injection molding machine using each of the obtained compositions. The molding temperature is shown in Table 2. Mold temperature is 90
° C. The injection rate is 18 to 20 cc / sec.
The molding was performed by adjusting the injection pressure and the injection speed so that only 9 cc / sec.

(4) Polycarbonate molecular weight in molded article A sample for molecular weight measurement was sampled from the obtained sheet, and the weight average molecular weight (Mw) of the polycarbonate was measured in the same manner as in (2). The results are shown in Table 2. Was.

(5) Measurement of Surface Resistance The surface resistance of the central portion of the sheet sample was measured with a UA probe using Hiresta UP manufactured by Dia Instruments Co., Ltd., and the results are shown in Table 2. The applied voltage is 1
It was measured at 0V.

(6) Izod impact strength According to ASTM D256. The results are shown in Table 2.

(7) Diameter and length of carbon fibril fiber /
Ultra-thin section was cut out along the flow direction from the surface of the central part (resistance measuring part) of the sample obtained by the diameter ratio and the degree of bending (3) in the range of 2 to 10 μm. A section cut out under the same conditions was embedded in an epoxy resin, and then the section was cut out and the thickness of the section was measured. As a result, it was 85 nm. This ultra-thin section was measured at 10 points with a transmission electron microscope to find a fiber diameter of 10.5 n.
m, it was confirmed that the average length / diameter ratio was 35 or more. As described above, Table 2 shows the results of measuring the tangent angles of two points 52.5 nm (diameter 10.5 nm × 5) apart on the carbon fibrils (10 points) and measuring the degree of bending.

(8) The number of portions surrounded by the carbon fibril network and the dispersion analysis of carbon fibrils photographed at a magnification of 40,000 with a transmission microscope at an ultra-thin section of standard deviation (7) were analyzed as follows. . For the analysis, an image analysis device (type; Spica 2) manufactured by Avionics was used. First, an image in the range of 5 μm × 5 μm is
Using a CCD camera, integration input (16 times) was taken into the computer, and 9.77 nm x 9.77 nm (512
× 512) pixels were used as a digital image (hereinafter, pixels in which carbon fibrils exist are turned on and pixels not present are turned off in accordance with the procedure as defined above). The number of parts surrounded by the carbon fibril network,
And the standard deviation of the area of the enclosed portion was calculated. Table 2 shows the measurement results. 4 and 5 show the relationship between the number of portions surrounded by the carbon fibril network and the surface resistance value, and the relationship between the standard deviation of the area of the portion surrounded by the carbon fibril network and the surface resistance value, respectively.

[0061]

[Table 2]

From the results, the following items are recognized.

Comparative Example 1 has poor conductivity (high resistance value) because the dispersion parameter is out of the range.

As in Comparative Example 2, if the amount of carbon fibrils added is increased, conductivity can be obtained even when the parameters are out of the range. However, this method leads to an increase in cost and a decrease in physical properties.

By optimizing the molecular weight and molding conditions as in Examples 1 to 5, conductivity can be obtained without increasing the cost or reducing the physical properties.

Among them, as in Examples 1 to 4, when the molecular weight is 4
When it is 5000 or less, excellent conductivity can be obtained without significantly increasing the molding temperature.

When the molding temperature is increased to 340 ° C. in the fifth embodiment, resin deterioration in the cylinder during continuous production is likely to occur.

Although not shown in this example, the dispersion behavior of carbon fibrils in the resin and the mechanism of developing conductivity are as follows:
Since it is the same, it is easily expected that the same result will be obtained even with a thermoplastic resin other than the polycarbonate resin.

[0069]

As described above, according to the present invention, a conductive molded product having excellent conductivity and high impact strength is provided. This conductive molded article is inexpensive because it has a low content of carbon fibrils.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an image processing method for obtaining the number and area of a portion surrounded by a carbon fibril network.

FIG. 2 is a schematic diagram showing an image processing method for obtaining the number and area of a portion surrounded by a carbon fibril network.

FIG. 3 is a schematic diagram showing an image processing method for obtaining the number and area of a portion surrounded by a carbon fibril network.

FIG. 4 is a graph showing the relationship between the number of portions surrounded by the carbon fibril network and the surface resistance value in Examples 1 to 5 and Comparative Examples 1 and 2.

FIG. 5 is a graph showing the relationship between the standard deviation of the area surrounded by the carbon fibril network of Examples 1 to 5 and Comparative Examples 1 and 2 and the surface resistance.

FIG. 6 is a trace diagram of carbon fibril imaging.

FIG. 7 is a diagram showing a method of measuring a degree of bending.

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Claims (2)

[Claims] 1. A thermoplastic resin having an average fiber diameter of 100 n
m and a length / diameter ratio of 10 or more carbon fibrils, wherein the content of the carbon fibrils is 0.1% by weight or more with respect to the total of the thermoplastic resin and the carbon fibrils. .1% by weight
Less than 180, and the number of portions surrounded by the carbon fibril network per 25 μm ² near the surface ( ² to 10 μm) of the molded article is 180 or less, and the standard deviation of the area of the surrounded portions is 12 or more. A conductive molded article characterized by the above-mentioned. 2. The conductive molded article according to claim 1, wherein the thermoplastic resin is polycarbonate, and the polycarbonate resin constituting the molded article has a weight average molecular weight (Mw) of 45,000 or less.