JP3106917B2 - Method for measuring resistance of unvulcanized semiconductive silicone rubber composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the resistance of an unvulcanized semiconductive silicone rubber composition useful for obtaining a semiconductive silicone rubber having a small variation in resistance.

[0002]

2. Description of the Related Art Silicone rubber is used as a material for various rolls of copiers, printers, facsimiles, etc. because of its excellent environmental stability and compression set resistance. .

In particular, recently, as a part of measures against ozone, a charging roller, a developing roller, a cleaning roller, and a transport roller used in a contact-type developing device have a resistance between the roll surface and the core metal of 1 × 10 ^{4 or} less. Use of a silicone rubber molded product in a conductive region of about 1 × 10 ¹⁰ Ω is being studied.

However, in this silicone rubber molded product, the resistance between the roll surface and the core metal is 1 × 10 ⁴ to 1
Within a range of about × 10 ¹⁰ Ω, there is little variation, and it is necessary to limit the resistance to a predetermined narrow range. In this case, generally, a silicone rubber having a resistance of 1 × 10 ⁴ to 1 × 10 ¹⁰ Ω can be obtained by adding a predetermined amount of conductive carbon black or the like to the silicone rubber composition. Stabilization in the conductive region
It is difficult to simply control the amount of the conductive material such as conductive carbon black in the silicone rubber composition. In practice, the resistance of the silicone rubber cannot be determined without curing the silicone rubber composition.

In view of the above, the present inventor has found that by controlling the resistance value of an unvulcanized semiconductive silicone rubber composition, the variation in resistance between lots of silicone rubber can be reduced and a predetermined narrow value can be obtained. We have considered limiting the resistance value of silicone rubber to the range, but as a method of measuring the electric resistance, conventionally, the Japan Rubber Association Standard SR
IS 2301 (10 ⁵ Ω-cm or less) or ASTM D
-991, JIS C-2123, etc. are known as "Test Methods for Silicone Rubber Compounds for Electricity", but these are all standards for measuring the electrical properties of vulcanized silicone rubber, and are unvulcanized. There is no known method for measuring the resistance of the semiconductive silicone rubber composition.

The present invention has been made in view of the above circumstances,
An object of the present invention is to provide a method for reliably measuring the resistance value of an unvulcanized semiconductive silicone rubber composition.

[0007]

Means for Solving the Problems and Embodiments of the Invention The present inventor has achieved the above object and has achieved an unvulcanized semiconductive silicone rubber composition, particularly 1 × 10 ² to 1 × 10 ⁸ Ω. As a result of intensive studies on the method of measuring the electric resistance of the unvulcanized semiconductive silicone rubber composition within the range, a current of 5 mA or less was passed through this semiconductive silicone rubber composition, and the current value at that time was measured. And measuring the voltage value, in particular by first flowing a current under a constant voltage, and then measuring the current and the voltage while controlling to a constant current, so that the unvulcanized silicone rubber composition can be measured favorably. I found that.

That is, in order to measure the resistance, the voltage and the current may be measured as apparent from Ohm's law. However, when a voltage is applied to the silicone rubber composition in the semiconductive region, no current flows between the measurement electrodes due to a charging current and an absorption current appropriate for the system, and a high resistance is exhibited.
Thereafter, when the system becomes stable, the current gradually starts to flow, and eventually approaches a constant value. Therefore, the resistance of these materials is very high at the beginning, and a voltage corresponding to this is required at first. For example, a voltage of 1000 V needs to be applied in order to measure a resistance by flowing a current of 1 mA through a material of 1 × 10 ⁶ Ω. When the absorption of the current reaches saturation, the current starts to flow rapidly. Therefore, if a voltage of 1000 V is continuously applied, the temperature of the material rises, and eventually discharge occurs. The inventor initially flows a current at a constant voltage to prevent such a phenomenon,
When the current value exceeds a certain value, the control is shifted to the constant current control, whereby the resistance can be measured without damaging the semiconductive silicone rubber composition.

Accordingly, the present invention provides an unvulcanized semiconductive silicone rubber composition sandwiched between two parallel metal electrodes, and a constant voltage applied to the unvulcanized semiconductive silicone rubber composition. A current of 5 mA or less flows under the
When the current reaches A, the constant voltage state is released and the current is reduced to 5 mA.
Provided is a method for measuring the resistance of an unvulcanized semiconductive silicone rubber composition, wherein the resistance is determined from the equilibrium voltage at the following constant current.

The method of measuring the resistance of the unvulcanized semiconductive silicone rubber composition of the present invention will be described in more detail below. A current is applied across the composition, and the resistance is determined from the current and the voltage.

Here, the composition of the semiconductive silicone rubber composition whose resistance is to be measured is not particularly limited, can be a known composition, and its curing method is not limited. Any curing method such as a mold and an addition reaction vulcanization type may be used. Further, there is no limitation on the type of conductive material to be added to make the silicone rubber composition semiconductive, and conductive carbon black or the like can be used, and the amount thereof can be appropriately selected. The method is 1 × 10 ²
This is effective when measuring the resistance of a semiconductive silicone rubber composition having a resistance of about 1 × 10 ⁸ Ω. When preparing a silicone rubber composition, a method of first preparing a silicone rubber compound not containing a curing agent and then adding a curing agent thereto is often adopted,
The resistance measuring method of the present invention can be applied to a composition before adding a curing agent or to a composition after adding a curing agent.

When measuring the resistance according to the present invention, for example, an apparatus as shown in FIG. 1 can be used. That is, in FIG. 1, 1 is an anode, 2 is a cathode,
Are fixed by non-conductive plates 3 and 4 of acrylic resin or the like, respectively. Reference numeral 5 denotes a voltage / current control power supply. The positive terminal is connected to the anode 1 via a lead wire 6, and the negative terminal is connected to the cathode 2 via a lead wire 7.

In the present invention, first, a sheet-like specimen S of an unvulcanized semiconductive silicone rubber composition whose resistance is to be measured is sandwiched between the two metal electrodes (anode 1 and cathode 2). In this case, the thickness t of the specimen S is 0.1 to 10 m
m, particularly preferably 0.5 to 3 mm. 0.1
If it is thinner than 10 mm or thicker than 10 mm, the fluctuation of the obtained resistance measurement is large.

Next, in the above state, 5 mA or less,
Preferably, a current of 2 mA or less is passed, and the resistance is determined from the current value and the balanced voltage value at that time. When the flowing current exceeds 5 mA, the temperature of the material rises due to power consumption,
It is not preferable because an accurate resistance cannot be obtained. In this case, as described above, since the current is difficult to flow in the initial stage, first, a constant voltage control is performed to supply a current at a constant voltage in the range of, for example, 100 to 700 V, and the silicone rubber composition reaches a maximum of 5 mA. Switching from constant voltage control to constant current control, flowing a constant current of 5 mA or less, particularly 2 mA or less, until the voltage is balanced, and measuring the current and the equilibrium voltage at that time to determine the resistance, and obtaining a silicone rubber composition. This is preferable because the resistance can be reliably measured without damaging the device. Note that the time until the voltage reaches equilibrium under a constant current varies depending on the material, but after the measurement is started or after switching to the constant current control, the current and the voltage for a fixed time in the range of 0.5 to 5 minutes are calculated. A method of comparing and evaluating the resistance value between test pieces with the obtained resistance value is adopted.

According to the method for measuring the electric resistance of the unvulcanized silicone rubber composition of the present invention, the resistance value of the material before vulcanization can be easily grasped and adjusted, whereby the vulcanized silicone rubber can be adjusted. It is possible to control the resistance value to a stable area with little variation, and it is effectively used especially when molding semiconductive roll materials with small variation in volume resistance value, and roll material with a desired narrow resistance value range This is suitable as control means for obtaining

[0016]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. In the following examples, parts are parts by weight.

As a dispersant, 100 parts of methylvinylpolysiloxane having an average degree of polymerization of about 8000, comprising 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units and 0.025 mol% of dimethylvinylsiloxane units, was used. Of diphenylsilanediol, 4 parts of dimethylpolysiloxane having a terminal silanol group (polymerization degree: 10), and 30 parts of silica (manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g, and the mixture was mixed at 150 ° C. with a kneader mixer. Heat treatment was performed for 2 hours to prepare a base compound A.

Next, 100 parts of Denka acetylene black (manufactured by Denki Kagaku) was added to 100 parts of the base compound A.
Part, spherical silicone elastomer (average particle size 13μ)
m, 50 parts of Shin-Etsu Chemical Co., Ltd., trade name X-52-874) was added to prepare a semiconductive silicone rubber composition. After 0.5 part of dicumyl peroxide was further added as a curing agent, the mixture was press-cured at 170 ° C. for 10 minutes under a pressure of 25 kgf / cm ² to obtain a 1 mm sheet. The volume resistivity of this sheet is 1 × according to JIS-C-2123.
Was 10 ⁵ Ω-cm.

On the other hand, the above-mentioned unvulcanized silicone rubber composition was applied to an electrode having an electrode area of 1 cm ² and a distance of 1 mm as shown in FIG.
Between the parallel electrodes fixed with an acrylic resin as shown in the above, a voltage of 500 V is first applied, and a constant current control is performed when a current of 1 mA flows, and a change in resistance is observed. Resistance value. Resistance value is 1.1 × 10 ⁵
Ω. The measurement voltage at this time was 110V. FIG. 2 shows the behavior of the measured resistance Ω and the applied voltage V.
Under these conditions, the power consumption of the sample was 0.11 W, and the sample did not deteriorate.

As a comparative example, 5
An experiment was performed in which the application of 00 V was continued, but after about 40 seconds, discharge occurred between the samples, and the resistance could not be measured.

[0021]

According to the method for measuring the resistance of an unvulcanized semiconductive silicone rubber composition of the present invention, the resistance of a semiconductive silicone rubber composition before vulcanization can be measured reliably and easily. The material can be adjusted by predicting the resistance value of the vulcanized silicone rubber from this, so that a silicone rubber exhibiting a target conductive region can be suitably obtained.

[Brief description of the drawings]

FIG. 1 is a side view showing an apparatus used for a method for measuring the resistance of a semiconductive silicone rubber composition of the present invention.

FIG. 2 is a graph showing the time-dependent behavior of resistance and voltage in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anode 2 Cathode 5 Voltage / current control power supply S Unvulcanized semiconductive silicone rubber composition

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01R 27/02 G01N 27/04

Claims (1)

(57) [Claims] An unvulcanized semiconductive silicone rubber composition is sandwiched between two parallel metal electrodes, and is not more than 5 mA at a constant voltage with respect to the unvulcanized semiconductive silicone rubber composition. When the current reaches a maximum of 5 mA, the constant voltage state is released and the current is reduced to a constant current of 5 mA or less.
A method for measuring the resistance of an unvulcanized semiconductive silicone rubber composition, wherein the resistance is determined from an equilibrium voltage at that time.