JP2015102622A - Conductive belt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive belt in which the reduction rate of surface resistivity is low even when high voltage is applied.SOLUTION: The conductive belt is made of conductive resin produced by mixing 15-30 pts.wt. carbon black into 100 pts.wt. synthetic resin. The common logarithm value of surface resistivity (Ω/sq.) when voltage is applied to the surface at a gradient of 100 V/2.55 mm is in a range of 7-12. The difference between the common logarithm value of the surface resistivity when voltage is applied to the surface at a gradient of 100 V/2.55 mm and the common logarithm value of the surface resistivity when voltage is applied to the surface at a gradient of 500 V/2.55 mm is lower than 0.5.

Description

  The present invention relates to a conductive belt used as a transfer belt, a conveyance belt or the like of an electrophotographic copying machine or a laser printer.

In an electrophotographic copying machine or the like, many endless conductive belts are used for image fixing, intermediate transfer, conveyance, development, and the like. Many of them are formed using a conductive resin in which carbon black is blended as a conductive filler in a synthetic resin. The resistivity varies depending on the application, and those having a surface resistivity of 10 ⁰ to 10 ¹³ Ω / □ are used.

  Carbon black forms primary aggregates (aggregates) having a complicated structure in which spherical basic particles are fused to branch into irregular chains. This degree of structure development is called a structure, and the fact that the number of basic particles contained in one aggregate is large means that the structure is developed or has a high structure. The carbon black in the resin imparts conductivity to the resin by the aggregate forming a network. It is believed that electrons travel through the aggregate and move from one aggregate to another by tunnel effects.

  At this time, if the blending amount of carbon black is the same, the smaller the particle diameter, the higher the dispersion density in the resin, and the shorter the distance between aggregates. Thereby, since it becomes easy to form a conductive circuit, high electroconductivity is provided by conductive resin. Since the specific surface area is larger as the particle diameter is smaller, the resistivity of the conductive resin is smaller at the same blending amount as carbon black having a larger specific surface area is used.

  In addition, the resistance when electrons move in a single aggregate is much smaller than the resistance when moving between aggregates. The resistivity of the conductive resin becomes smaller. Oil absorption (also referred to as oil absorption) is used as an index for quantitatively evaluating the degree of structure development. The greater the oil absorption, the more developed the structure.

JP-A-6-228335 JP 2003-177612 A

  Since most of the conductive belts used in copying machines and the like are used in a state where a voltage is applied, voltage durability, that is, a change in resistivity with use over a long period of time becomes a problem. It is thought that the reason why the resistivity changes is that the resin at the connection point between the aggregates in the conductive circuit is “broken” by spark or the like, and the electrical resistance between the aggregates becomes small.

  As an index of such a change in resistivity over time, the surface resistivity is measured while applying a high voltage to a new conductive belt. When the rate of decrease in surface resistivity is small when a high voltage is applied, it is estimated that the voltage durability of the conductive belt is high.

  The present invention has been made in view of the above, and an object of the present invention is to provide a conductive belt having a small rate of decrease in surface resistivity even when a high voltage is applied.

  As a result of diligent research, the inventors of the present invention have found that a conductive belt having a relatively high resistivity used for intermediate transfer and the like has a high resistivity when a high voltage is applied by blending a large amount of carbon black having a low conductivity. It has been found that the reduction rate can be reduced, and the present invention has been achieved.

  The conductive belt of the present invention comprises a conductive resin in which 15 to 30 parts by weight of carbon black is blended with 100 parts by weight of a synthetic resin, and the surface when a voltage is applied to the surface with a gradient of 100 V / 2.55 mm. The common logarithm of the resistivity (Ω / □) is in the range of 7 to 12, and the common logarithm of the surface resistivity when a voltage is applied to the surface with a gradient of 100 V / 2.55 mm, and the surface is 500 V / The difference from the common logarithm of the surface resistivity when a voltage is applied with a gradient of 2.55 mm is less than 0.5.

  Here, the surface resistivity at the time of voltage application is determined by pressing a probe having a double ring electrode structure in which the outer diameter of the inner circle electrode is 5.9 mm and the inner diameter of the annular electrode is 11 mm against the surface of the conductive resin. Measurement can be performed by applying a predetermined DC voltage between the electrodes, with the electrode being positive and the annular electrode being negative. Moreover, you may convert a result using the probe from which a dimension differs.

As the carbon black, a DBP oil absorption 30~140cm ³ / 100g, specific surface area can be used for 20 to 200 m ² / g.

  Here, the DBP oil absorption is the absorption of dibutyl phthalate (DBP) measured according to ASTM D2414. Here, the specific surface area of carbon black is a value measured by adsorption of iodine according to ASTM D1510.

  Preferably, the synthetic resin is a thermoplastic resin and has a melting point of 200 ° C. or higher. Alternatively, the synthetic resin is an amorphous thermoplastic resin and has a glass transition point of 85 ° C. or higher.

  According to the conductive belt of the present invention, the effect that the change in resistivity is small and the voltage durability is excellent even when used for a long time in a state where a voltage is applied.

  First, an outline of one embodiment of the conductive belt of the present invention will be described.

The conductive belt of the present embodiment belongs to a relatively high resistance class among those used for electronic copying machines, laser printers, and the like, and is used for an intermediate transfer belt and the like. In this conductive belt, 15 to 30 parts by weight of carbon black is blended with 100 parts by weight of a synthetic resin, whereby a surface resistivity (hereinafter referred to as 100 V) when a voltage is applied to the surface with a gradient of 100 V / 2.55 mm. 10 ⁷ to 10 ¹² Ω / □ as surface resistivity at the time of application (abbreviated as R _S1 ). The common logarithmic value of R _S1 and the surface resistivity when a voltage is applied to the surface with a gradient of 500 V / 2.55 mm (hereinafter also referred to as the surface resistivity when 500 V is applied, abbreviated as R _S5 ). The difference from the logarithmic value is less than 0.5.

The type of carbon black is not particularly limited, but it needs to have relatively low electrical conductivity. Therefore, if the blending amount of carbon black is too small, a predetermined resistivity cannot be obtained. On the other hand, if the blending amount of carbon black is too large, the adhesion and surface smoothness of the conductive belt are impaired. Therefore, specifically, by blending 15 to 30 parts by weight of carbon black with respect to 100 parts by weight of the synthetic resin, the conductive belt R _S1 is in the range of 10 ⁷ to 10 ¹² Ω / □. It is necessary to have sex. Preferably, by adding 18 to 25 parts by weight of carbon black to 100 parts by weight of the synthetic resin, the conductive belt has conductivity such that R _S1 is in the range of 10 ⁹ to 10 ¹¹ Ω / □.

Here, the surface resistivity during voltage application is measured by pressing a probe having a double ring electrode structure against the surface of the conductive belt and applying a predetermined voltage between the electrodes. Specifically, the surface resistivity during voltage application was determined by pressing a probe having a double ring electrode structure in which the outer diameter of the inner circular electrode was 5.9 mm and the inner diameter of the annular electrode was 11 mm against the surface of the conductive resin, Measurement can be performed by applying a predetermined DC voltage between the electrodes, with the inner circular electrode being positive and the annular electrode being negative. Further, measurement may be performed using probes having different dimensions, for example, a probe having a double ring electrode structure used in JIS K6911: 1995, and R _S1 and R _S5 may be obtained by converting the results.

Further, the smaller the difference between the common logarithm values of R _S1 and R _S5 (hereinafter sometimes referred to as voltage dependency), the higher the voltage durability of the conductive belt, and it can be used for a wider range of applications. The voltage dependency value of the conductive belt is preferably less than 0.5.

Carbon black is preferably DBP oil absorption amount is 30~140cm ³ / 100g, further preferably 50~130cm ³ / 100g. As described above, the DBP oil absorption is an indicator of the degree of carbon black structure development, and is an indicator of conductivity. If the DBP oil absorption is too large, the conductivity of the carbon black is too high, and it becomes difficult to obtain a conductive belt having a predetermined resistivity with the above blending amount. On the other hand, if the DBP oil absorption is too small, the amount of blending for obtaining a conductive belt having a predetermined resistivity increases, and the adhesion and surface smoothness of the conductive belt tend to be impaired. The DBP oil absorption can be measured according to ASTM D2414.

Carbon black is preferably a specific surface area of 20 to 200 m ² / g, more preferably from 80~180m ² / g. When the specific surface area is too small, it means that the basic particles are too large, which is not preferable because the adhesion and surface smoothness of the conductive belt are impaired. On the other hand, when the specific surface area is too large, gas molecules adsorbed on the surface of the carbon black are easily released during the kneading and molding of the resin, so that a large amount of gas is likely to be generated and the surface smoothness of the conductive belt is likely to be impaired. The specific surface area of carbon black can be measured according to ASTM D1510 using iodine.

More preferably, the carbon black has a DBP oil absorption in the above preferred range and a specific surface area in the preferred range at the same time. That is, a DBP oil absorption 30~140cm ³ / 100g or 50~130cm ³ / 100g, and it is more preferably a specific surface area of 20 to 200 m ² / g or 80~180m ² / g.

  Although the kind of resin is not specifically limited, In order to extend the service life of an electroconductive belt, it is preferable to use what is excellent in thermal stability. When the resin is thermoplastic, it is preferable to use a resin having a melting point of 200 ° C. or higher, and more preferably 250 ° C. or higher. Examples of the resin having a melting point of 200 ° C. or higher include nylon 6 (PA6), nylon 66 (PA66), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polybutylene terephthalate (PBT), and polyethylene terephthalate (PET). And thermoplastic polyimide. Examples of the resin having a melting point of 250 ° C. or higher include PA66, PPS, PEEK, and PET among the above. Among them, it is particularly preferable to use PPS because it has excellent heat resistance and chemical resistance and has self-extinguishing properties. Further, when the melting point is not clear because the thermoplastic resin is amorphous, it is preferable to use a glass transition point of 85 ° C. or higher. For example, it is preferable to use polycarbonate (PC).

  When a resin having a high melting point or a high glass transition point is used, the temperature of the kneading and molding process becomes high, and gas molecules adsorbed on the surface of the carbon black are desorbed and gas is easily generated. It is particularly important that the specific surface area of the carbon black is not too large.

  In addition to the resin and carbon black, various additives may be added to the conductive belt to the extent that conductivity and mechanical properties are not impaired. For example, an antioxidant, a pigment, a dispersant, a plasticizer, and the like can be added.

  As a method for manufacturing the conductive belt of the present embodiment, a general method can be used. For example, a method in which a resin, carbon black, and other raw materials are mixed and kneaded and extruded into a tube shape and then cut into round pieces can be used.

  The reason why high voltage durability is obtained by the conductive belt of the present embodiment can be explained as follows. In order to achieve the same conductivity, when a small amount of highly conductive carbon black having a well-structured structure is blended, the number of aggregate connection points is reduced. Therefore, when a voltage is applied, the resin at the connection point is easily broken by spark, and the resistance is likely to decrease. On the other hand, when a lot of carbon black with low conductivity and less developed structure is blended, the aggregates and their connection points exist densely, and the resin does not easily break even when voltage is applied. , Resistance is difficult to decrease.

  Next, the results of experiments conducted to confirm the effects of this embodiment will be described. In the experiment, a film-like test piece was prepared using several conductive resins, and the surface resistivity and the surface state during voltage application were evaluated.

  The main resin is polyphenylene sulfide (PPS) having a glass transition point (Tg) of 93 ° C., a melting point (Tm) of 278 ° C., a melt flow rate (MFR) of 70 g / 10 min, and a linear type. used.

  Carbon black includes A (Cabot Specialty Chemicals, Furnace Black, V9A32), B (Cabot Specialty Chemicals, Furnace Black, M880), C (Electrochemical Co., Ltd., Acetylene Black, Denka Black), D (Lion Stock) 4 types of company, Ketjen Black, EC-600JD) were used.

  The test piece was produced as follows. A predetermined amount of carbon black was blended in PPS and pre-blended, and pellets were produced using a biaxial kneader (Kobe Steel Works, KTX-37). Next, an extruded film (test piece) was produced with a sheet die using the produced pellets. The film was extruded with a thickness of 80 μm and a width of 100 mm, and this was cut into 50 mm × 50 mm to obtain test pieces.

The surface resistivity R _S1 when 100 V was applied and the surface resistivity R _S5 when 500 V was applied were measured using a resistivity meter (Mitsubishi Chemical Analytech Co., Ltd., Hiresta IP), and the test piece was coated with polyfluoroethylene resin. Mounted on a table (Mitsubishi Chemical Analytech Co., Ltd., register table FL), and a probe with a double ring electrode structure (Mitsubishi Chemical Analytech Co., Ltd., HRS probe, inner circle electrode outer diameter 5.9 mm, annular electrode inner diameter Is measured by applying a predetermined voltage to 11 mm).

In addition, the resistivity of the conductive resin molded product depends on the molding process, and differs depending on whether it is extruded into a tube shape or a film shape in this experiment when the conductive belt is manufactured. In this experiment, a film-like test piece was simply evaluated. Therefore, a preliminary experiment was conducted, and it was confirmed that the surface resistivity of the test piece was about 10 ^8.5 Ω / □ when the carbon black content was about 10 ¹⁰ Ω / □ as a conductive belt. It was done. In this experiment, since the evaluation is performed with a carbon black blending amount that provides a surface resistivity of 10 ^9.5 to 10 ^10.5 Ω / □ when a conductive belt is manufactured, the surface resistivity of this test piece is 10 ^The amount of carbon black was adjusted with the goal of ⁸ to 10 ⁹ Ω / □.

The experimental results are shown in Table 1. In Table 1, the blending amount indicates the weight part of carbon black with respect to 100 weight parts of PPS resin. Those having a surface resistivity of “> 12.0” or “<7.0” are outside the measuring range of the apparatus. The voltage dependency is a value obtained by subtracting the common logarithmic value of R _S5 from the common logarithmic value of R _S1 . The surface foaming and blistering columns indicate the presence or absence of bubbles and carbon black aggregates on the surface of the test piece, respectively, “○” indicates that the presence was not observed by visual observation, and “ × ”.

In the experiment using carbon black A, a predetermined R _S1 was obtained when the blending amount was 20 parts by weight (experiment A1) and 20.5 parts by weight (experiment A2) with respect to 100 parts by weight of the resin. The voltage dependence was 0.4 and 0.3, respectively, and even when 500 V was applied, the rate of decrease in surface resistivity was small. Furthermore, the surface condition of the test piece was also good.

In Experiment A2 and Experiment A3, test pieces were prepared using the same pellet, but _RS1 was different due to the difference in cylinder temperature during molding. In experiment A2 where the cylinder temperature was as high as 340 ° C., R _S1 was 10 ^8.8 , but in experiment A3 where the cylinder temperature was as low as 310 ° C., R _S1 was 10 ^11.4, which was higher than the target range. . This is presumably because when the cylinder temperature is low, the shear stress applied to the screw is high, so that the carbon structure is destroyed and the resistance increases.

In the experiment using carbon black B, the target R _S1 was not obtained when the cylinder temperature was 340 ° C. and the blending amount was in the range of 10 to 15 parts by weight (experiments B1 to B3). Therefore, a test piece was produced at a cylinder temperature of 310 ° C. using the same pellet as in Experiment B2 with a carbon blending amount of 12 parts by weight (Experiment B4). Since R _S1 of Experiment B2 and Experiment B4 is 10 ^8.0 and 10 ^9.8 , respectively, the target R _S1 can be obtained by setting the cylinder temperature between 310 ° C. and 340 ° C. it is conceivable that. The value of voltage dependence at that time is considered to be about 0.5, which is considered to be larger than when carbon black A is used. In addition, foaming and blisters were observed on the sample surface in Experiment B2, and foaming was observed in Experiment B4.

In the experiment using carbon black C, the target R _S1 was not obtained when the cylinder temperature was 340 ° C. and the blending amounts were 16 and 25 parts by weight (experiments C1 and C2). Therefore, a test piece was produced at a cylinder temperature of 310 ° C. using the same pellet as in Experiment C1 with a carbon blending amount of 16 parts by weight (Experiment C3). Since R _S1 of Experiment C1 and Experiment C3 is 10 ^7.9 and 10 ^10.1 , respectively, the target R _S1 can be obtained by setting the cylinder temperature between 310 ° C. and 340 ° C. it is conceivable that. The voltage dependency value at that time is considered to be about 0.7, which is considered to be larger than when carbon black A or B is used. The sample surface was good in both Experiment C1 and Experiment C3.

In the experiment using carbon black D, the cylinder temperature was 310 ° C., the blending amount was 3 parts by weight, and R _S1 in the target range was obtained. However, the voltage dependency was 2 or more.

The above results are summarized as follows. In the case of carbon black A having a relatively small specific surface area and a relatively small DBP absorption amount, the target R _S1 was obtained when the blending amount was about 20 parts by weight, and the voltage dependency was as small as 0.4 or less. With carbon black B having a relatively large specific surface area and a relatively small DBP absorption amount, it is considered that the target R _S1 can be obtained with a blending amount of about 12 parts by weight, but the voltage dependence at that time is about 0.00. It is estimated to be 5 and is larger than that of carbon black A. Moreover, the surface state of the test piece was not good. With carbon black C having a small specific surface area and a relatively large DBP absorption amount, it is considered that the target R _S1 can be obtained when the blending amount is about 16 parts by weight, but the voltage dependency at that time is about 0.7. Estimated and larger than carbon black A. Moreover, the surface state of the test piece was not good. In the case of carbon black D having a large specific surface area and a large DBP absorption amount, the target R _S1 was obtained when the blending amount was 3 parts by weight, and the voltage dependency at that time was about 2 or more.

  The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the idea.

Claims (4)

The conductive resin is composed of 15 to 30 parts by weight of carbon black with respect to 100 parts by weight of the synthetic resin.
The common logarithm of the surface resistivity (Ω / □) when a voltage is applied to the surface with a gradient of 100 V / 2.55 mm is in the range of 7 to 12,
The common logarithm of the surface resistivity when a voltage is applied to the surface with a gradient of 100 V / 2.55 mm, and the common logarithm of the surface resistivity when a voltage is applied to the surface with a gradient of 500 V / 2.55 mm; The difference is less than 0.5,
Conductive belt. The carbon black is
DBP oil absorption amount is 30~140cm ³ / 100g,
The specific surface area is 20 to ²⁰⁰ m ² / g,
The conductive belt according to claim 1. The synthetic resin is a thermoplastic resin and has a melting point of 200 ° C. or higher.
The conductive belt according to claim 1 or 2. The synthetic resin is an amorphous thermoplastic resin having a glass transition point of 85 ° C. or higher;
The conductive belt according to claim 1 or 2.