JP2013190796A - Semiconductive rubber belt, and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductive rubber belt capable of reducing a variation in resistance in a circumferential direction and forming images with high image quality, and a manufacturing method of a semiconductive rubber belt.SOLUTION: Provided is a semiconductive rubber belt having the volume specific resistance of 10to 10Ω cm, and made of an unvulcanized rubber composition having a scorch time tof 10 to 18 minutes. On the single straight line in the circumferential direction of the belt, when a is the maximum value of the molecular orientation degree of the belt MOR-C represented by the following formula (1), where tis a correction thickness (mm), and tis a belt thickness (mm); b is the minimum value; and c is the average value, the following formulas (2) and (3) are satisfied.

Description

  The present invention relates to a semiconductive rubber belt used for a transfer portion or the like in an image forming apparatus using an electrophotographic process such as a copying machine, a printer, and a facsimile, and a method for manufacturing the same.

A semiconductive rubber belt used for a transfer portion or the like in an image forming apparatus is generally adjusted to have a volume resistivity of 10 ⁴ to 10 ¹² Ω · cm by adding a conductive filler such as graphite or carbon black. Is used. Here, the range of the volume resistivity is generally referred to as a semiconductive region, and in this region, the electric resistance of the semiconductive rubber belt tends to vary due to a slight difference in the amount of filler added. If the electric resistance of the rubber belt varies, unevenness occurs in the formed image. Therefore, it is very important to make the electric resistance of the semiconductive rubber belt uniform. As a method for producing this semiconductive rubber belt, a tube-shaped unvulcanized rubber belt molded body is prepared by tube extrusion molding of an unvulcanized rubber composition containing a filler, and this is coated on a mold. A “tube extrusion method” in which a belt is manufactured by heat vulcanization is known.

  In the above tube extrusion method, the flow rate (extrusion speed) of the unvulcanized rubber composition containing the filler can be set low, so that the unvulcanized rubber composition passes through the extrusion die. The shearing force that is received during the process can be made relatively small. However, when the electrical resistance is made uniform in the semiconductive region, the electrical resistance of the semiconductive rubber belt may vary locally even by a slight shear history during extrusion molding. In particular, the weld line of the unvulcanized rubber itself is in the belt width direction (belt extrusion direction) at the bridge portion that is usually provided with three or more dies (die) required when extruding the unvulcanized rubber composition into a tube shape. ), The thickness of the belt is reduced at this portion, and variations in electrical resistance may occur. Therefore, in a normal tube extrusion molding method, a weld line is formed at an interval in the “belt circumferential direction” orthogonal to the belt width direction, so that the electrical resistance of the semiconductive rubber belt varies in the belt circumferential direction. There was a problem.

  In Patent Document 1 below, even if the electric resistance in the belt circumferential direction of the semiconductive rubber belt changes by controlling the strength of the transfer bias (that is, the electric resistance of the semiconductive rubber belt varies in the belt circumferential direction). Even in this case, an image forming apparatus capable of keeping the charge amount of the semiconductive rubber belt constant is disclosed. However, the apparatus described in this document requires additional equipment for controlling the intensity of the transfer bias. Further, when the rotational speed of the semiconductive belt is increased in order to increase the image forming processing speed of the image forming apparatus, it is difficult to control the strength of the transfer bias. Therefore, there is a great demand in the market that the electrical resistance of the semiconductive rubber belt should be made uniform at a high level.

  In the following Patent Document 2, on the same line along the belt width direction, the average value of the molecular orientation angle θ with respect to the belt width direction is in the range of −15 ° to + 15 °, and the molecular orientation degree MOR-C of the conductive layer is By setting the relationship between the average value, the maximum value and the minimum value to be (maximum value−minimum value) / average value <0.4, variation in electric resistance in the belt width direction is reduced, and unevenness occurs in the formed image. A semiconductive belt that can prevent this is described. However, since the semiconductive belt is manufactured by a normal tube extrusion method, the above-described problem that the electric resistance in the belt circumferential direction varies cannot be solved.

  On the other hand, in Patent Document 3 below, the production of a semiconductive rubber belt using an extruder equipped with a crosshead having an inner cylinder part formed with a spiral flow type groove reduces the occurrence of variations in electrical resistance. It is disclosed that a semiconductive rubber belt can be manufactured. However, as a result of intensive studies by the present inventors, it has been found that there is room for further improvement in the semiconductive rubber belt manufactured by such a manufacturing method, particularly in terms of variation in electric resistance in the belt circumferential direction.

Japanese Patent No. 3414514 Japanese Patent No. 3056413 Japanese Patent No. 3998344

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductive rubber belt capable of forming a high-quality image with reduced variation in electrical resistance, particularly in the belt circumferential direction, and a method for manufacturing the same. It is to provide.

  In order to solve the above-mentioned problems, the present inventors diligently studied the relationship between the molecular orientation degree MOR-C of the semiconductive rubber belt in the belt circumferential direction and the image quality at the time of image formation. As a result, the above problem can be solved by making the maximum value, the minimum value, and the average value of the molecular orientation degree MOR-C of the semiconductive rubber belt have a specific relationship on the same straight line extending in the belt circumferential direction. I found.

（式中、ｔ_ｃは補正厚み（ｍｍ）、ｔ_ｓはベルト厚み（ｍｍ）を示す。）で表される、前記半導電性ゴムベルトの分子配向度ＭＯＲ−Ｃの最大値をａ、最小値をｂ、および平均値をｃとしたとき、次式（２）および（３）：

を満たすことを特徴とする。 That is, the semiconductive rubber belt according to the present invention is a seamless semiconductive rubber belt having a volume specific resistance of 10 ⁴ to 10 ¹² Ω · cm, and is the same straight line extending in the belt circumferential direction perpendicular to the belt width direction. On the line, the following formula (1):

(Wherein, _{t c} is corrected Thickness (mm), _{t s} indicates a belt thickness (mm).) Represented by the maximum value of the orientation ratio MOR-C of semiconductive rubber belt a, the minimum value Where b is the average value and c is the average value, the following formulas (2) and (3):

It is characterized by satisfying.

  In the semiconductive rubber belt, since the unevenness of the degree of molecular orientation in the belt circumferential direction is reduced, variation in electrical resistance particularly in the belt circumferential direction is reduced. For this reason, the image quality at the time of image formation can be improved, and the semiconductive rubber belt has a uniform electrical resistance at a high level. The rotational speed of the conductive belt can be increased. As a result, high-speed copying machines and printers equipped with the above-described semiconductive rubber belt can ensure high image quality and conveyance stability without newly installing special equipment.

The method for producing a semiconductive rubber belt according to the present invention is a method for producing a seamless semiconductive rubber belt having a volume resistivity of 10 ⁴ to 10 ¹² Ω · cm, wherein a spiral flow type groove is formed. using an extruder equipped with a crosshead having a cylindrical portion in the, and plasticize the unvulcanized rubber composition scorch time t ₅ is 10 to 18 minutes, step extrusion extruding from the extruder, the extruder The unvulcanized rubber composition is layered on the outer surface of the cylindrical mold while moving the cylindrical mold inside the inner cylindrical portion in a direction substantially orthogonal to the extrusion direction of the unvulcanized rubber composition in And an unvulcanized rubber belt molding step for forming an unvulcanized rubber belt molded body, and a vulcanization step for vulcanizing the unvulcanized rubber belt molded body to obtain a semiconductive rubber belt.

Using an extruder equipped with a crosshead having a cylindrical portion in which the groove of the spiral flow type is formed, the unvulcanized rubber composition scorch time t ₅ is 10 to 18 minutes, extruded in a specific molding method Thus, it is possible to manufacture a semiconductive rubber belt in which unevenness in the degree of molecular orientation in the belt circumferential direction is reduced. More specifically, according to the method for producing a semiconductive rubber belt, a semiconductive rubber belt satisfying the above formulas (2) and (3) can be produced.

  In the method of manufacturing a semiconductive rubber belt, a ratio (die drawing ratio) between the maximum outer diameter d of the inner cylinder portion and the outer diameter e of the discharge port is 0.2 ≦ e / d ≦ 0.8, and It is preferable that the moving speed of the cylindrical mold in the unvulcanized rubber belt molding step is 1 m / min or less. According to such a manufacturing method, it is possible to manufacture a semiconductive rubber belt in which unevenness in the degree of molecular orientation in the belt circumferential direction is more reliably reduced and the electric resistance is made uniform at a high level.

Diagram showing an example of the crosshead structure Diagram showing an example of semi-conductive rubber belt manufacturing equipment

  As the extruder used in the present invention, a known rubber extruder can be used. However, in order to remove bubbles in the belt generated in the vulcanization process or the like, it is possible to use an extruder equipped with a vacuum device. Is preferred.

  As the rubber material constituting the rubber base layer of the semiconductive rubber belt of the present invention, a known rubber material can be used without particular limitation, and in addition to natural rubber (NR), styrene butadiene rubber (SBR) Diene rubbers such as isoprene rubber (IR), butadiene rubber (BR), chloroprene rubber (CR), nitrile rubber (acrylonitrile-butadiene rubber; NBR), ethylene-propylene rubber (EPM, EPDM), butyl rubber (IIR), Non-diene synthetic rubber such as acrylic rubber (ACM, ANM), epichlorohydrin rubber (CO, ECO), other urethane rubber (U), fluorine rubber (FKM), silicone rubber (Q), polysulfide rubber (T), etc. It is exemplified and can be used alone or in combination of two or more. Among the rubber materials, it is preferable to use a rubber material containing at least one of CR, EPDM, NBR, and CO (ECO).

  As the filler used for imparting semiconductivity in the present invention, it is preferable to use carbon black. Specifically, EC (Extra Conductive) carbon, ECF (Extra Conductive France) carbon, SCF (Super Conductive France) carbon, CF (Conductive Furnace), AF F, S, F, S Carbon blacks such as FT and MT are exemplified. These may be used alone or in combination of two or more.

  In addition to carbon black, other conductivity imparting materials as required, for example, metal materials such as silver powder, copper powder and nickel powder, metal oxides such as tin oxide and indium oxide, inorganic materials such as mica coated with metal, It is also a preferred embodiment to use a carbon compound such as graphite or carbon fiber in combination.

  In addition to fillers for imparting electrical conductivity, the above rubber materials are kneaded by adding known rubber additives such as process oils or plasticizers, stabilizers, dispersion modifiers, etc. An unvulcanized rubber composition is prepared by adding additives such as a vulcanization accelerator and a crosslinking density adjusting agent, and supplied to an extruder. The crosslinking may be peroxide crosslinking or sulfur vulcanization, and well-known vulcanization methods can be used.

In the method for producing a semiconductive rubber belt according to the present invention, and the rubber material, and a filler, obtained by blending with various additives, unvulcanized rubber scorch time t ₅ is 10 to 18 minutes It is essential to use the composition. By using an extruder equipped with a crosshead having an inner cylinder part in which spiral flow type grooves are formed and extruding this unvulcanized rubber composition by a specific molding method, the degree of molecular orientation in the belt circumferential direction can be improved. Unevenness can be reduced. Unvulcanized rubber composition scorch time t ₅ is 10 to 18 minutes, among the above additives, and be especially properly adjusting the blending ratio of the vulcanizing agent and the vulcanization accelerator for rubber materials, during rubber compounding It can be obtained by appropriately adjusting the discharge temperature and the storage temperature of the unvulcanized rubber composition.

  Hereinafter, the manufacturing method of the semiconductive rubber belt which concerns on this invention is demonstrated. An example of an apparatus used in the practice of the present invention is shown in FIG. An apparatus for producing an unvulcanized rubber belt molded body used in a method for producing a semiconductive rubber belt according to the present invention includes an extruder 1, a crosshead 3 attached to an extruded tip, a cylindrical mold 5, The unvulcanized rubber composition supplied from a hopper (not shown) is heated and plasticized by the screw 17 and sent to the crosshead 3 attached to the tip. The cylindrical mold 5 is fed from one end of the crosshead 3 at a constant speed by the driving means 13 in the rubber pushing direction and the substantially perpendicular direction. The moving speed of the cylindrical mold 5 in the unvulcanized rubber belt molding step is preferably 1 m / min or less. By setting the moving speed of the cylindrical mold 5 within such a range, the unevenness of the molecular orientation degree in the belt circumferential direction is more reliably reduced, and a semiconductive rubber belt that is made uniform at a high electric resistance level is manufactured. be able to.

  The unvulcanized rubber composition extruded from the extruder 1 flows in a cylindrical shape so that the flow direction is changed in the moving direction of the cylindrical mold 5 inside the crosshead 3 and the cylindrical mold 5 is covered. The outer surface of the cylindrical mold 5 is covered with a predetermined thickness by the thickness adjusting means 11.

  As shown in FIG. 1, the cylindrical mold 5 is preferably moved continuously, and the coated layer of the unvulcanized rubber composition is continuous. The joint of the continuous cylindrical mold 5 is detected by an appropriate means, the unvulcanized rubber composition layer is cut by the cutter 9, the mold is separated with the unvulcanized rubber molded body layer, Supply to the sulfur process.

  The drive means 13 for moving the cylindrical mold 5 is an example in which two rollers are used in the example shown in FIG. 1, but is not limited thereto.

  As the vulcanization method used in the vulcanization step, a known vulcanization method can be used without limitation. Specifically, a method using a vulcanization can, a method of heating a mold with steam or an electric heater, etc. , An oven vulcanization method in which heating is performed in a heating oven under normal pressure, and a method in which a heat medium such as superheated steam is fed to expand a rubber film (bladder) to pressurize and vulcanize an unvulcanized rubber belt molded body ( (Bladder vulcanization method), vulcanization methods using high energy radiation such as electron beams, etc. are exemplified, and a vulcanization method using two or more of these may be used.

  Next, a specific example of the structure of the crosshead 3 is shown in FIG. The crosshead 3 has an outer cylinder portion 21 and an inner cylinder portion 23 with a direction substantially orthogonal to the direction in which the unvulcanized rubber composition 6 is extruded from the extruder 1 as an axis, and a front end of the extruder by a flange 29. It is attached to the part. A cylindrical space is formed between the outer cylindrical portion 21 and the inner cylindrical portion 23, and the unvulcanized rubber composition 6 extruded from the extruder 1 is molded into a cylindrical shape in this space, and is formed at the tip portion. Extruded. The outer cylinder part 21 is provided with a flow adjusting ring 17 near the center and a thickness adjusting means 11 at the tip part, and the inner cylinder part 23 is capable of moving the cylindrical mold 5 within the inner cylinder part 23 to adjust the flow. , An edge ring 19 for uniforming and a spiral flow type groove 25 are provided. The cylindrical mold 5 is inserted into the inner cylindrical portion 23 from one end of the crosshead and moves at a constant speed. At the other end of the inner cylindrical portion 23, the cylindrical unvulcanized rubber composition is predetermined by the thickness adjusting means 11. The outer surface of the cylindrical mold 5 is coated with a thickness of 5 to form an unvulcanized rubber belt molded body 7. The thickness adjusting means 11 is preferably configured to be detachable so that it can be exchanged to produce belts of different thicknesses.

  The inner cylinder portion 23 of the crosshead 3 of the present embodiment has the largest outer diameter on the upstream side (extruder side) of the spiral flow type groove 25 and the smallest outer diameter on the most distal portion (discharge port 23E side). It becomes. In the present embodiment, the ratio (die drawing ratio) between the maximum outer diameter d of the inner cylinder portion 23 and the discharge port outer diameter is set to 0.2 ≦ e / d ≦ 0.8. When this die drawing ratio is set within the above range, the unevenness of the degree of molecular orientation in the belt circumferential direction can be more reliably reduced, and a semiconductive rubber belt having a uniform electrical resistance can be produced.

  The method for producing a semiconductive rubber belt according to the present invention may include a polishing step of polishing the rubber base layer of the semiconductive rubber belt obtained in the vulcanization step to a predetermined thickness. As a polishing apparatus that can be used in the polishing process, known belt polishing means can be used without limitation, and polishing is performed with a grinding means such as a rotating grindstone while rotating the belt in a stretched state using a mandrel or a plurality of rollers. The method of doing is illustrated. The thickness of the rubber base material layer after polishing is not particularly limited, and examples thereof include 400 to 700 μm.

（式中、ｔ_ｃは補正厚み（ｍｍ）、ｔ_ｓはベルト厚み（ｍｍ）を示す。）で表される、半導電性ゴムベルトの分子配向度ＭＯＲ−Ｃの最大値をａ、最小値をｂ、および平均値をｃとしたとき、次式（２）および（３）：

を満たすことが肝要である。上述した本発明に係る半導電性ゴムベルトの製造方法によれば、上記式（２）および（３）を満たす半導電性ゴムベルトを製造することができる。 The semiconductive rubber belt according to the present invention can be a rubber belt having a volume resistivity of 10 ⁴ to 10 ¹² Ω · cm, particularly by appropriately adjusting the blending ratio of the rubber material and the filler. Furthermore, in order to reduce the unevenness of the degree of molecular orientation in the belt circumferential direction and reduce the variation in electrical resistance in the belt circumferential direction, the following equation (on the same straight line extending in the belt circumferential direction orthogonal to the belt width direction: 1):

(Wherein, _{t c} is corrected Thickness (mm), _{t s} is the belt thickness (mm) are shown.) Represented by the maximum value of the orientation ratio MOR-C of semiconductive rubber belt a, the minimum value When b and the average value are c, the following formulas (2) and (3):

It is important to satisfy. According to the above-described method for producing a semiconductive rubber belt according to the present invention, a semiconductive rubber belt satisfying the above formulas (2) and (3) can be produced.

In the semiconductive rubber belt according to the present invention, in order to further reduce unevenness in the degree of molecular orientation in the belt circumferential direction and particularly reduce variation in electrical resistance in the belt circumferential direction, the belt circumferential direction orthogonal to the belt width direction It is preferable to satisfy the following expressions (2) ′ and (3) ′ on the same straight line extending to

  In the semiconductive rubber belt of the present invention, a release layer may be appropriately formed on the belt surface made of the rubber base layer as desired. This release layer may be formed on one side of the belt surface or on both sides. The thickness of the release layer is not particularly limited, and examples thereof include 3 to 20 μm.

  As a material for forming the release layer, a material from which toner can be easily peeled is preferable, and a coating layer obtained by painting is preferable. The paint to be used can be selected in consideration of the adhesion to the belt base material layer, the toner peeling property, the electrical characteristics, etc., but the abrasion resistance of the coating layer and the adhesion to the rubber base material layer In view of flexibility, use of a polyurethane-based paint is preferable, and use of a paint added with a fine powder of polytetrafluoroethylene is particularly preferable.

Hereinafter, examples and the like specifically showing the configuration and effects of the present invention will be described. The molecular orientation degree MOR-C of the semiconductive rubber belt was measured using a molecular orientation meter (model number: MOA-6015) manufactured by Oji Scientific Instruments, and the measured orientation degree measurement value MOR was expressed by the above formula (1 ) And calculated. When correcting the thickness of the molecular orientation degree MOR-C, the corrected thickness of the above formula (1) was t _c = 1.08 mm. When measuring the degree of molecular orientation MOR-C, three to six points were measured from the first column to the nth column (n = 2 to 5) on the same straight line extending in the belt circumferential direction of the semiconductive rubber belt. The average value was calculated.

  Table 1 shows the materials, brand names, and suppliers used in this example.

(Preparation of rubber composition)
In 100 parts by weight of the rubber component, the components other than sulfur and the vulcanization accelerator are kneaded in the kneader in the blended formulation of Table 1, and after cooling, the sulfur and the vulcanization accelerator are kneaded again in the kneader. Then, a ribbon-like unvulcanized rubber composition was used for the extruder. Table 1 shows the scorch time t ₅ minutes of the unvulcanized rubber composition used.

  The extruder used was a vent type extruder having a screw diameter of 50 mm, and a cross head capable of continuously feeding a cylindrical mold having an outer diameter of 30 to 150 mm and a length of 400 mm was attached thereto (the used cross Table 1 shows the maximum outer diameter d of the inner cylinder portion of the head, the outer diameter e of the discharge port, and the ratio e / d (die drawing ratio). The extruder adjusts the screw and cylinder temperature to 50 to 60 ° C. and the crosshead temperature to 70 to 90 ° C., and supplies the cylindrical mold in the direction perpendicular to the screw at the moving speed shown in Table 1. An unvulcanized rubber belt molding having a thickness of 0.9 mm was coated around the mold. The cylindrical mold coated with the unvulcanized rubber belt layer was automatically discharged from the crosshead by the rubber extrusion / flow pressure.

  The cylindrical mold coated with the unvulcanized rubber belt molded body obtained in the above extrusion process was accommodated in a vulcanized steam can set at 175 ° C., and vulcanized by heating for 15 minutes. After vulcanization, the front and back surfaces of the belt removed from the cylindrical mold are each polished by 0.2 mm, for a total of 0.4 mm, to obtain a rubber belt (rubber base material layer) with a thickness of 0.5 mm, and both ends are cut. Thus, a belt having a width of 350 mm was obtained. [(Ab) / c], [a / b] when the molecular orientation degree MOR-C of the obtained semiconductive rubber belt, the maximum value is a, the minimum value is b, and the average value is c The values are shown in Table 2. Moreover, the volume specific resistance value of the obtained semiconductive rubber belt was measured at 3 to 6 locations in the belt circumferential direction at an applied voltage of 500 V, and the average value was calculated. The results are shown in Table 2.

Examples 1-4, Comparative Example 1
A semiconductive rubber belt manufactured with the composition and conditions shown in Table 1 was mounted on an image forming apparatus, and an actual machine evaluation was performed. The image quality of the formed image was visually observed and evaluated. In Table 2, ◯ indicates a high image quality level at which there is no problem, Δ indicates a level where there is some transfer unevenness but no problem, and x indicates a level where transfer unevenness is considerable and impractical.

  From the results in Table 2, it can be seen that high-quality image formation is possible in the actual machine evaluation of the semiconductive rubber belts according to Examples 1 to 4. On the other hand, in the actual machine evaluation of the semiconductive rubber belt according to Comparative Example 1, it can be seen that there is much transfer unevenness and impractical.

1: Extruder 3: Crosshead 5: Cylindrical mold 6: Unvulcanized rubber composition 7: Unvulcanized rubber belt molding 21: Outer cylinder part 23: Inner cylinder part 25: Spiral flow type groove

Claims (1)

A seamless semiconductive rubber belt having a volume resistivity of 10 ⁴ to 10 ¹² Ω · cm,
Obtained unvulcanized rubber composition scorch time t ₅ is 10 to 18 minutes as a raw material,
On the same straight line extending in the belt circumferential direction orthogonal to the belt width direction, the following formula (1):

(Wherein, _{t c} is corrected Thickness (mm), _{t s} indicates a belt thickness (mm).) Represented by the maximum value of the orientation ratio MOR-C of semiconductive rubber belt a, the minimum value Where b is the average value and c is the average value, the following equations (2) and (3):

A semiconductive rubber belt characterized by satisfying

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