JP2002285035A - Carbon black and electrically conductive composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon black which can produce an electrically conductive composition with low dependence on temperature of volume resistivity and the electrically conductive composition. SOLUTION: The carbon black whose inclination of the volume resistivity at temperature of 20 to 160 deg.C is 0.03 Ωcm/ deg.C or less when a silicone rubber is filled with the carbon black of 60 mass parts is provided. The carbon black can produce the electrically conductive composition with low dependence on temperature of volume resistivity. The electrically conductive composition which is filled with a rubber and/or a resin and has the volume resistivity of 10<3> to 10<10> Ωcm is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carbon black capable of obtaining a conductive composition having a low temperature dependence of volume resistivity and a conductive composition filled with the same.

[0002]

2. Description of the Related Art In recent years, demand for conductive compositions obtained by imparting conductivity to rubber, resin, and the like has been rapidly expanding due to the refinement of electronic devices, and they are used for various purposes. One of the uses is OA equipment such as an electronic copying machine, a laser beam printer, and a facsimile. As an image forming method in these OA devices, an electrophotographic method is mainly used. In this method, Se or OPC (Organic Photo) is used.
Various types of semiconductive rolls such as a charging roll, a developing roll, and a transfer roll are used around a photoreceptor such as a photoconductor, and when printing conditions, paper type and environment change, a voltage or current applied to each roll. Is changed so that the print quality is kept constant.

[0003] As these semiconductive rolls, those having a volume resistivity of 10 ³ to 10 ¹⁰ Ωcm are used.
Generally, rubber components such as silicone rubber and urethane constituting the conductive composition have a high volume resistivity, and carbon black is used as a conductivity-imparting material in order to impart appropriate conductivity. Then, as the carbon black, generally acetylene black called conductive carbon black, Ketjen black or the like is used.

[0004]

[Problems to be solved by the invention]
When attempting to obtain a conductive composition by filling conventional carbon black into a resin or the like, a small difference in the filling amount of carbon black significantly changes the volume resistivity. Was very difficult. Further, temperature change, change in applied voltage, the environmental changes such as deformation of the roll itself, or variations in volume resistivity, can uneven, poor print quality has been a problem.

In order to solve this problem, for example, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. 1-106657 discloses a conductive rubber composition using thermal black.
No. 5 proposes a conductive rubber composition using carbon black coated with a resin. In each case, carbon black having a high volume resistivity is used, but there is still room for improvement in stability against environmental changes such as a variation in volume resistivity due to a temperature change. Furthermore, in the former, uniform dispersion is difficult because the structure of carbon black is not developed, and in the latter,
Since other substances are added, the process becomes complicated and costs are increased.

The present invention has been made in view of the above, and an object of the present invention is to provide a carbon black and a conductive composition capable of easily and inexpensively obtaining a conductive composition having further excellent environmental stability. It is to be.

[0007]

That is, according to the present invention, the slope of the volume resistivity at a temperature of 20 to 160 ° C. when 100 parts by mass of silicone rubber is filled with 60 parts by mass of carbon black is 0.03 Ωcm / ° C. or less. The carbon black is characterized by being able to obtain a conductive composition having a low temperature dependence of volume resistivity, characterized by comprising carbon black. In particular, Lc is 25 ° or more, DBP absorption is 70 to 95 ml / 100 g, and iodine adsorption is 45
It is preferably from 55 to 55 mg / g. Further, the present invention is a conductive composition characterized by being filled with the above-mentioned carbon black in rubber and / or resin.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

In general, conductive compositions used for rolls and the like often become high in temperature due to continuous operation, friction, and the like, and furthermore, a temperature change occurs due to paper quality, thickness, humidity, and the like. When the resistivity changes, the printing becomes uneven and leads to a decrease in print quality. The carbon black of the present invention has a temperature of 20 to 100 parts by mass when carbon black is filled with 60 parts by mass of silicone rubber in 100 parts by mass.
The inclination of the volume resistivity at 160 ° C. is 0.03Omucm /
℃ or less. The conductive composition using the carbon black sufficiently responds to such a temperature change,
Printing quality can be kept high.

The slope of the volume resistivity can be measured, for example, by the following method.

[0011] end is closed with a trimethylsilyl group, (about 6000 degree of polymerization) 100 parts by weight of polydimethylsiloxane containing 0.15 mole% of methylvinylsiloxane units and (and a carbon black 60 parts by mass, the internal volume 60
ml of kneading tester ("Laboplastograph R-60" manufactured by Toyo Seiki Seisaku-sho, Ltd.) and the blade rotation speed is 30 rpm.
and kneading at 180 ° C. for 30 minutes. Next, 2 parts by mass of 2,5-dimethyl-2,5-di-t-butylperoxyhexane was mixed as a crosslinking agent to prepare an uncured silicone rubber composition, and the mixture was heated to a temperature of 1 at a heating press.
After pressing at 80 ° C. and a pressure of 9.8 × 10 ⁶ Pa for 10 minutes, a further vulcanization is performed at 200 ° C. for 4 hours to produce a silicone rubber sheet. The obtained silicone rubber sheet is placed in a temperature-variable oven, and the temperature is set to 20 to 200.
° C and the volume resistivity at an arbitrary temperature is measured using a digital multimeter (for example, “Digital Multimeter 7562” manufactured by Yokogawa Electric Corporation).
The gradient of volume resistivity is obtained by measuring according to 1 and determining the ratio of volume resistivity to temperature.

[0012] Carbon blacks of the present invention, in addition to the above characteristics, Lc is at least 25 Å, DBP absorption amount 70-9
5ml / 100g, iodine adsorption amount is 45-55mg / g
It is preferred that The reason is as follows.

Lc is the average thickness of the graphite crystal structure in which the network lattice planes of the polycyclic aromatic compound are layered, and the larger Lc is, the more the crystal structure is developed.
In the carbon black of the present invention, when Lc is less than 25 °, the crystal structure is not developed, so that the conductivity is poor, and further, the thermal conductivity is lowered, and the heat resistance is deteriorated.

The DBP absorption indicates the degree of development of the structure. If the DBP absorption is less than 70 ml / 100 g, the formation of conductive paths is insufficient due to the short structure, and the conductivity deteriorates. Further, the DBP absorption amount is 95 ml / 10
If it exceeds 0 g, the conductivity is good because the structure is developed, but large voids are formed between the structures due to the structure. It is considered that generally used rubber easily expands thermally, and the conductive path due to the structure of carbon black is interrupted in some places by a rise in temperature, so that the volume resistivity shows a positive temperature dependency (PTC characteristic). That is, in order to suppress the temperature dependence, it is important to highly fill the carbon black, and in consideration of the formation of the conductive path, the carbon black of the present invention has a DBP absorption of 70 to 95 ml / 100 g. It is desirable that

[0015] While iodine adsorption shows a specific surface area, the carbon black of the present invention, 45 mg /
When the particle size is less than 5 g, the particle diameter increases, so that the gap between the carbon blacks also increases, which is not appropriate.
If it exceeds 5 mg / g, it becomes bulky and hinders handling.

The carbon black of the present invention can be produced by grinding commonly available carbon black. As a crusher, a ball mill type such as a pot mill, a conical mill, and a vibration mill, a medium stirring mill type such as an attritor mill and a sand grinder mill,
An airflow pulverization type such as a jet mill is used. Lc, DB of carbon black to be pulverized during pulverization
By selecting the amount of P absorption and the amount of iodine adsorption, the above-described preferable carbon black of the present invention can be easily produced. Incidentally, carbon black to be ground is,
It can be produced by well-known techniques by pyrolysis and / or combustion of hydrocarbons.

Examples of the type of carbon black of the present invention include furnace black, thermal black, acetylene black, contact black and the like.

The rubber of the conductive composition used in the present invention
As resin components, in addition to silicone rubber, urethane rubber, ethylene propylene rubber, isoprene rubber, butadiene rubber, chloroprene rubber, butyl rubber, styrene butadiene rubber, acrylonitrile rubber, chlorosulfonated polyethylene, epichlorohydrin rubber, acrylic rubber, polysulfide rubber, fluorine rubber, synthetic rubber such as norbornene rubber, and natural rubber, and further can be exemplified a thermoplastic elastomer polyester, nylon and olefin. These rubber and resin components are selected depending on the application, and may be used alone,
Two or more kinds can be used in combination.

When the rubber / resin component is silicone rubber, the compounding amount of carbon black is 20 to 100 parts by mass of the polyorganosiloxane base polymer (a).
Preferably it is 100 parts by mass. The uncured silicone rubber composition, the (a) a polyorganosiloxane base polymer, are used those with various additives are mixed optionally (b) a curing agent and (c).

As the polyorganosiloxane base polymer of the component (a), the organic group is a monovalent substituent or an unsubstituted hydrocarbon group, and specifically, a methyl group, an ethyl group, a propyl group, a butyl group Group, hexyl group, alkyl group such as dodecyl group, aryl group such as phenyl group, unsubstituted hydrocarbon group such as aralkyl group such as β-phenylethyl group, β-phenylpropyl group, chloromethyl group, 3,
Examples thereof include a substituted hydrocarbon group such as a 3,3-trifluoropropyl group. In general, a methyl group is frequently used because of ease of synthesis.

The types and amounts of the components (a) and (b) are determined according to the properties such as hardness of the target rubber composition.
The reaction mechanism is appropriately selected together with the reaction mechanism. As the reaction mechanism, (1) a crosslinking method using an organic peroxide vulcanizing agent, (2) a method using a condensation reaction, (3) a method using an addition reaction, and the like are employed. Is done.

For example, when the crosslinking method (1) is applied, the base polymer of the component (a) is usually
Polydiorganosiloxane in which at least two of the organic groups bonded to silicon atoms in one molecule are vinyl groups is used. As the curing agent of the component (b), benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxy Various organic peroxide vulcanizing agents such as hexane and di-t-butyl peroxide are used, and in particular, dicumyl peroxide, cumyl-t-butyl peroxide,
2,5-Dimethyl-2,5-di-t-butylperoxyhexane, di-t-butyl peroxide and the like are preferable because they give low compression set.

One or more of these organic peroxide vulcanizing agents are used, and the compounding amount thereof is preferably 0.05 to 15 parts by mass with respect to 100 parts by mass of the component (a). If the amount is less than 0.05 parts by mass, vulcanization is not sufficiently performed, and 1
If the amount is more than 5 parts by mass, no further effect can be expected, and the physical properties of the obtained cured silicone rubber may be adversely affected.

When the condensation reaction of the above (2) is applied, a polydiorganosiloxane having hydroxyl groups at both ends is used as the base polymer of the component (a).
When the curing agent (b) is a cross-linking agent, ethyl silicate, propyl silicate, methyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, methyltris (methoxyethoxy) silane, vinyltris Alkoxy type such as (methoxyethoxy) silane and methyltripropenoxysilane: acetoxy type such as methyltriacetoxysilane and vinyltriacetoxysilane: methyltri (acetone oxime) silane, vinyltri (acetone oxime) silane, methyltri (methylethylketoshikim) silane, vinyltri (methyl ethyl ketoxime) silane, and partial hydrolysates thereof are used. Furthermore, hexanomethyl-bis (diethylaminoxy) cyclotetrasiloxane, tetramethyldibutyl-bis (diethylaminoxy) cyclotetrasiloxane, heptamethyl (diethylaminoxy) cyclotetrasiloxane, pentamethyl-tris (diethylaminoxy) cyclotetrasiloxane, hexamethyl-bis Cyclic siloxanes such as (methylethylaminoxy) cyclotetrasiloxane and tetramethyl-bis (diethylaminoxy) -mono (methylethylamoxy) cyclotetrasiloxane can also be used. One or more crosslinking agents are used, and the amount of the crosslinking agent is based on 100 parts by mass of the component (a).
0.1-20 mass parts is preferable. If the amount is less than 0.1 part by mass, the strength of the rubber cured product is not sufficiently increased, and if it exceeds 20 parts by mass, the rubber composition becomes brittle.

When the component (b) is a curing catalyst, iron octoate, cobalt octoate, manganese octoate, tin naphthenate, tin caprylate,
Carboxylic acid metal salts such as tin oleate, dimethyltin dioleate, dimethyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, dibutyltin dilaurate, dibutyltin dioleate, diphenyltin diacetate, dibutyltin oxide, dibutyltin dimethoxide, dibutyltin dimethoxide, dibutylbis (tributyl Organotin compounds such as ethoxysiloxy) tin and dioctyltin dilaurate are used. One or more curing catalysts are used, and the amount thereof is preferably 0.01 to 5 parts by mass based on 100 parts by mass of the component (a). If the amount is smaller than this, it takes a long time for curing, and further, the effect in the interior far from the contact surface with air becomes poor. Also, if there is more than this,
Storage stability will be reduced. A more desirable ratio is
0.1 to 3 parts by mass.

When the addition reaction of the above (3) is applied, the same base polymer as the above (1) is used as the base polymer of the component (a). Also,
When the curing agent of the component (b) is a curing catalyst,
Platinum catalysts such as chloroplatinic acid, platinum olefin complex, platinum vinyl siloxane complex, platinum black, and platinum triphenylphosphine complex are used. The amount of the component (b)
The amount of the platinum element is preferably in the range of 1 to 1000 ppm based on the component (a). If it is less than 1 ppm, curing will not proceed sufficiently, and if it exceeds 1000 ppm, there will be no remarkable improvement in curing speed. When the curing agent is a crosslinking agent, hydrogen atoms bonded to silicon atoms have an average of at least 2 in one molecule.
A polydiorganosiloxane having a number exceeding the number is used. The amount of the polydiorganosiloxane is 0.5 to 4.0 with respect to one alkenyl group in the component (a) and hydrogen atoms bonded to silicon atoms in the crosslinking agent. The number is preferably such that the number is 1.0, more preferably 1.0 to 3.0. If the amount of hydrogen atoms is less than 0.5, curing does not proceed sufficiently,
3. The hardness of the rubber composition is reduced, and the amount of hydrogen atoms is 4.
If it exceeds 0, the physical properties and heat resistance of the composition after curing are reduced.

To produce the conductive composition of the present invention, the addition reaction of (3) or the vulcanization method using an organic peroxide of (1) is preferred from the viewpoint of imparting high conductivity. In this case, the component (a) is most preferably a millable silicone having a degree of polymerization of 1000 or more. The reason is that the shear stress at the time of mixing is likely to be moderate, the carbon black is uniformly dispersed, and the conductivity is more stable.

Furthermore, if necessary, a filler, a pigment,
Component (c) such as a heat resistance improver and a flame retardant can also be used. In addition, a polyorganosiloxane other than the above can be used in combination as long as the effects of the present invention are not impaired. For example, fumed silica, precipitated silica, diatomaceous earth, titanium oxide, aluminum oxide, zinc oxide, iron oxide, cerium oxide, mica, clay, zinc carbonate, manganese carbonate, cerium hydroxide, Examples include glass beads, polydimethylsiloxane, and an alkyl group-containing polysiloxane.

When the rubber / resin component is a rubber / resin other than silicone rubber, a conductive composition can be produced by a commonly used method.

[0030]

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

Example 1 Comparative Examples 1 and 2 A polydimethylsiloxane having a terminal closed with a trimethylsilyl group and containing 0.15 mol% of a methylvinylsiloxane unit (degree of polymerization: about 6000), and carbon black shown in Table 1 Was charged into a kneading tester ("Laboplastograph R-60" manufactured by Toyo Seiki Seisaku-sho, Ltd.) having an inner volume of 60 ml, and the blade rotation speed was 30 rpm, the temperature was 180 ° C and the temperature was 30 ° C.
Kneaded for minutes. In Example 1, "H" manufactured by Denki Kagaku Kogyo
S-100 "was produced by grinding with a vibration mill. Comparative Example 1
Used "HS-100" itself, and Comparative Example 2 used "Asahi # 60" manufactured by Asahi Carbon Co., Ltd.).

Next, 2,5-dimethyl-2,5-di-tert-butylperoxyhexane 2 was used as a crosslinking agent.
Part uncured silicone rubber composition was prepared by mixing, temperature 180 ° C. by hot press, pressure 9.8 × 10 ⁶ P
After pressing for 10 minutes at a, a further vulcanization was performed at 200 ° C. for 4 hours to produce a silicone rubber sheet. By the following methods for the obtained sheet was evaluated volume resistivity, hardness and PTC characteristics. Table 1 shows the results.

(A) Volume resistivity: measured using a digital multimeter (“Digital Multimeter 7562” manufactured by Yokogawa Electric Corporation) in accordance with SRIS2301.

(Ii) Hardness: Hardness (JIS-A) was measured according to JIS K 6301 (physical test method for vulcanized rubber).

(C) PTC characteristics: The rubber sheet is placed in an oven, the temperature is raised from 20 ° C. to 160 ° C., and the volume resistivity is measured using a digital multimeter (“Digital Multimeter 7562” manufactured by Yokogawa Electric Corporation). SRIS23
01 and the inclination was determined.

The physical properties of the carbon black used in this test were measured as follows. (D) the amount of iodine adsorption and DBP absorption: iodine adsorption amount, JIS K 1474, also DBP absorption JIS
It was measured according to K 6217.

[0037] (e) Lc: by Cu-K [alpha ray X-ray diffractometry using from (002) diffraction line was calculated according to the formula of the sealer shown below. Lc = (180 · K · λ) / (π · β · cos θ) K = shape factor (using 0.9) λ = wavelength of X-ray (1.54 °) θ = (002) maximum value in diffraction line Β = (002) half-width at diffraction line indicated by angle

[0038]

[Table 1]

From Table 1, it can be seen that the conductive composition filled with carbon black of the present invention has lower temperature dependency of volume resistivity and lower hardness than those using commercially available carbon black. Has features.

[0040]

The carbon black of the present invention is capable of obtaining a conductive composition having a low temperature dependence of volume resistivity.

Since the semiconductive composition of the present invention has a very low temperature dependency of the volume resistivity, for example, when used in a roll or the like, the printing quality is stable without causing printing unevenness. In addition, paper feed rolls and transfer rolls in electronic copiers, laser beam printers, facsimile machines, etc. can prevent paper jams due to electrification, improve image quality, and improve heat resistance, flexibility, weather resistance, etc. the thing that was.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G03G 15/08 501 G03G 15/08 501D 15/16 103 15/16 103 H01B 1/24 H01B 1/24 Z F term ( Reference) 2H077 AD06 AD14 FA22 FA27 2H200 FA01 HA02 HA28 HB12 HB45 JA02 JA25 MA03 MA14 MB04 4J002 AC011 AC031 AC061 AC081 AC091 BB001 BB151 BB181 BB271 BD121 BG041 BG101 BK001 CE001 CH041 CK021 CL001 CN037G02 FA001 DA18 DA42 DD10

Claims (3)

[Claims] A temperature of 20 to 160 when 100 parts by mass of silicone rubber is filled with 60 parts by mass of carbon black.
A carbon black capable of obtaining a conductive composition having a low temperature dependence of volume resistivity, characterized by being composed of carbon black having a volume resistivity gradient of 0.03 Ωcm / ° C or less at ° C. Wherein Lc is more than 25 Å, DBP absorption amount 70
~ 95ml / 100g, iodine adsorption amount is 45 ~ 55mg
/G./g. 3. A conductive composition comprising the carbon black according to claim 1 or 2 filled in a rubber and / or a resin.