JP5611082B2 - Crosshead die and method of manufacturing conductive rubber roller - Google Patents

Description

  The present invention relates to a crosshead die for forming a conductive rubber roller that is mainly used when forming an electrophotography and whose core metal is covered with a rubber composition, and a method for manufacturing the conductive rubber roller.

  2. Description of the Related Art Conventionally, there is a crosshead die as a die for extruding a thermosetting unvulcanized rubber composition such as rubber into a roller shape by an extruder. The crosshead die is installed with a certain angle between the screw shaft and the die. Therefore, it becomes possible to let the cored bar pass through the rubber composition in the form of a roller. Thereby, since the core metal coating process can be incorporated into the rubber layer extrusion process, there is an advantage that the process can be simplified (see Patent Document 1).

  In a general crosshead die, a mandrel having a mandrel guide hole is inserted into an outer die having an outer die hole having a substantially circular cross section and a supply port for supplying the rubber composition to the outer die hole. . In the gap between the outer die and the mandrel, a flow path for the rubber composition that connects the supply port and the extrusion port is formed. The extrusion port is formed at a position away from the tip of the mandrel in a direction in which the mandrel is extruded, and has a circular cross section.

  Below, the flow of the rubber composition in the inside of the general crosshead die described above will be described. The rubber composition supplied to the supply port from the extruder passes through a development portion flow passage surrounded by the inner peripheral surface of the outer die hole and the outer peripheral surface of the mandrel. In the development portion flow path, the flow of the rubber composition is converted from a circular shape into an annular shape in which the inner side and the outer side are substantially circular by bending the flow path from the screw shaft direction of the extruder. In addition, the expansion part flow path is generally a flow path in which a manifold and a preland formed on the outer peripheral surface of the mandrel are combined. Subsequently, the flow of the rubber composition passes through an annular flow path formed in a gap between the inner peripheral surface of the outer die hole and the outer peripheral surface of the mandrel. Thereafter, the rubber composition comes into contact with the cored bar extruded from the tip of the mandrel, and passes through the extrusion port together with the cored bar. In this way, a conductive roller whose core metal is covered with the rubber composition is molded.

  In the above-described crosshead die, when the circular flow path is converted to the annular flow path, the flow of the two rubber compositions merges (impacts), and a weld line that is a joining mark is generated along with the merge. It has been known. When the weld line is generated, the uneven electrical resistance in the circumferential direction of the roller is increased. In particular, it appears remarkably in the electronic conductive rubber used as the rubber composition of the conductive rubber roller.

  Therefore, Patent Document 2 discloses a manufacturing method of a rubber roller for suppressing unevenness of electrical resistance in the circumferential direction of the roller due to a weld line. In this rubber roller manufacturing method, the circular rubber composition supplied from the extruder branches into two along a pair of manifolds formed on the outer peripheral surface of the mandrel, and then merges at the end of the manifold. The rubber composition is converted from a circular shape into an annular shape by the merge. Thereafter, the rubber composition flows along the spiral groove formed on the outer peripheral surface of the mandrel. According to the manufacturing method disclosed in Patent Document 2, since the flow of the rubber composition is agitated by flowing along the spiral groove, variation in the electrical resistance in the circumferential direction of the roller due to the influence of the weld line. It can be reduced.

JP 2005-329639 A JP 2008-94050 A

  As described above, the weld line uses the joining point of two flows of the rubber composition as the generation point. However, the manufacturing method disclosed in Patent Document 2 does not take measures to suppress the occurrence of the weld line itself at the joining point (terminal end of the manifold) of the two flows of the rubber composition. Therefore, it is conceivable that a sufficient effect cannot be obtained with respect to reducing the unevenness of the electrical resistance in the circumferential direction of the conductive rubber roller.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a crosshead die and a method for manufacturing a conductive rubber roller that can enhance the effect of reducing the unevenness of electrical resistance in the circumferential direction of the conductive rubber roller.

In order to achieve the above object, a crosshead according to the present invention intersects a circular outer die hole penetrating the inside in an axial direction from an upper end portion to a lower end portion and a wall portion surrounding the outer die hole in the axial direction. An outer die formed with a supply port that penetrates in the direction and supplies the rubber composition to the outer die hole, and a cored bar guide hole that penetrates the inside in the axial direction and through which the cored bar flows is the outer die hole A mandrel that is formed substantially coaxially with the central axis of the outer die and is installed in the outer die hole, and the core metal that has flowed out from the core metal guide hole toward the lower end of the outer die is the rubber. In the crosshead die for molding the conductive rubber roller coated with the composition, the mandrel includes a manifold part and a tip part extending downward from the lower surface of the manifold part in the axial direction, and the manifold Part is the outer peripheral surface A pair of grooves formed symmetrically with respect to a plane including the central axis of the cored bar guide hole and the central axis of the supply port, facing the supply port, and the rubber composition is the supply An inlet that flows in from the mouth, and is spaced apart from the inlet in the circumferential direction of the outer peripheral surface and is opposed to each other across the central axis of the cored bar guide hole at a position below the inlet in the axial direction, from the inlet A pair of grooves having two outlets through which the inflowed rubber composition flows out downward in the axial direction, and the lower surface is formed symmetrically with respect to the central axis of the cored bar guide hole, and communicating with each of the exit, in a section including the center axis of the central shaft and the supply opening of the metal core guide holes has a semicircular groove convex in a direction toward the upper portion, the distal portion Formed in a gap between the outer peripheral surface of the outer die and the inner peripheral surface of the outer die hole, A first annular channel that communicates with the outlet and the semicircular groove and flows out of the two outlets in the circumferential direction; and the first annular channel between the gaps And a second annular flow path formed on the lower side in the axial direction and having a cross-sectional area smaller than that of the first annular flow path.

In addition, the manufacturing method of the conductive rubber roller according to the present invention for achieving the above object includes: a circular outer die hole penetrating the inside in an axial direction from an upper end portion to a lower end portion; and a wall portion surrounding the outer die hole. An outer die formed with a supply port penetrating in a direction intersecting the axial direction, and a cored bar guide hole penetrating the inside in the axial direction and formed substantially coaxially with the central axis of the outer die hole A pair of grooves formed in a symmetrical shape with respect to a plane including the central axis of the cored bar guide hole and the central axis of the supply port are formed on the outer peripheral surface, and with respect to the central axis of the cored bar guide hole A manifold portion formed in a symmetric shape and having a semicircular groove convex on the lower surface in a direction toward the upper end portion in a cross section including the central axis of the cored bar guide hole and the central axis of the supply port ; , Extending downward from the lower surface of the manifold portion in the axial direction. In a method of manufacturing a conductive rubber roller in which a metal core is covered with a rubber composition using a mandrel having a tip portion, the rubber composition is supplied from the supply port to the outer die hole and supplied. The rubber composition is separated from the inlet facing the supply port in the circumferential direction of the outer peripheral surface from the inlet, and the central axis of the cored bar guide hole is positioned at a position below the inlet in the axial direction. The first annular flow formed in the gap between the outer peripheral surface of the tip and the inner peripheral surface of the outer die hole is allowed to flow to two outlets facing each other with the rubber composition flowing out from the two outlets. The composition that has flowed in the circumferential direction along the path and passed through the first annular flow path is formed in the gap below the first annular flow path in the axial direction, The second cross-sectional area is smaller than that of the first annular channel A first step of flowing along the channel, a second step of flowing the cored bar into the cored bar guide hole in parallel with the first step, and the core flowing out of the cored bar guide hole And a third step of coating gold with the rubber composition.

  According to the present invention, when the rubber composition flowing out from the two outlets of the pair of grooves joins (impacts) the first annular flow passage in the circumferential direction, the turbulent flow is generated in the semicircular groove. Can be generated. Because of this turbulent flow, the weld line is reduced, so that the effect of reducing unevenness in electrical resistance in the circumferential direction of the conductive rubber roller is enhanced.

It is sectional drawing which shows one Embodiment of the crosshead die | dye of this invention. It is an external view of the mandrel of the crosshead die shown in FIG. It is an enlarged view of the area | region S shown in FIG. FIG. 3 is a perspective view of the mandrel shown in FIG. 2. It is sectional drawing of the annular flow path of the crosshead die shown in FIG. It is sectional drawing which shows the other form of the annular flow path shown in FIG.5 (b). It is sectional drawing of the conventional crosshead die.

  FIG. 1 is a cross-sectional view showing an embodiment of the crosshead die of the present invention. More specifically, FIG. 1 shows that the rubber composition 11 supplied from the extruder 1 and the core metal 13 sent from the core metal supply device 6 are crossed in a crosshead die 20 and extruded together. It is sectional drawing of a process. FIG. 1 is a cross-sectional view including the central axis of the outer die hole and the central axis of the supply port.

  In the present embodiment, first, the rubber composition 11 is fed into a strip shape or a ribbon shape from a rubber inlet (not shown) of the extruder 1. By rotating the screw 3 inside the cylinder 2 of the extruder 1, the rubber composition 11 is gradually pushed out toward the crosshead die 20 connected to the tip of the cylinder 2. Hot water is circulated in the cylinder 2 and the screw 3 in order to keep the temperature constant. The temperature of the hot water depends on the type of rubber composition to be extruded. In this embodiment, it is in the range of 30 ° C. to 100 ° C. The flow of the rubber composition 11 extruded by the screw 3 is rectified by passing through the breaker plate 4 installed at the tip of the screw 3. Thereafter, the rubber composition 11 flows into the outer die hole 57 of the crosshead die 20 through the supply port 50. In addition, when a mesh (not shown) is attached to the breaker plate 4, it becomes possible to remove foreign matters and the like in the rubber composition 11. The crosshead die 20 is also temperature controlled by circulating hot water.

  Next, the configuration of the crosshead die 20 of this embodiment will be described.

  The crosshead die 20 has an outer die 22 and a mandrel 21. The outer die 22 has an outer die hole 57 that penetrates the inside from the upper end portion to the lower end portion in the axial direction, a supply port 50 that penetrates a wall portion surrounding the outer die hole 57, and an extrusion port 59. .

  The outer die hole 57 is a hole having a substantially straight central axis and continuously having a substantially circular cross section perpendicular to the central axis. Specifically, the outer die hole 57 is a hole having a cylindrical shape, a conical shape, or a combination thereof. Hereinafter, the upper direction of the outer die hole 57 in the axial direction is referred to as the upstream direction 71, and the lower direction of the axial direction (direction opposite to the upstream direction 71) is referred to as the downstream direction 72. The extrusion port 59 is a substantially circular port for extruding the rubber composition 11 supplied to the crosshead die 20 to the outside.

  The supply port 50 is a substantially circular port for supplying the rubber composition 11 extruded from the extruder 1 to the outer die hole 57. In the present embodiment, the central axis of the supply port 50 is orthogonal to the central axis of the outer die hole 57. However, in the present invention, it is only necessary to secure a dimension for feeding the cored bar 13, so that the central axis of the supply port 50 and the central axis of the outer die hole 57 do not necessarily need to be orthogonal to each other, but may intersect.

  The mandrel 21 is installed in the outer die hole 57. By installing the mandrel 21 in the outer die hole 57, a flow path surrounded by the outer die hole 57 and the mandrel 21 is formed from the supply port 50 to the extrusion port 59. In FIG. 1, this flow path is connected in order of a manifold flow path, a first annular flow path 60, a second annular flow path 62, and a third annular flow path 63 described later from the supply port 50. It is a flow path. In the present embodiment, the above-described flow channel shape is formed by processing the outer periphery of the mandrel 21 by grooving or the like. Can be formed.

  The mandrel 21 includes a mandrel guide hole 31 that penetrates the inside in the axial direction. The mandrel 21 is installed on the outer die 57 so that the central axis of the cored bar guide hole 31 is coaxial with the central axis of the outer die hole 57. Since the mandrel 21 has the cored bar guide hole 31, the cored bar 13 and the rubber composition 11 can be extruded together.

  The extrusion port 59 of the outer die 22 is an outlet of the rubber composition 11 extruded from the crosshead die 20. Depending on the shape of the extrusion port 59, a roller having a desired shape can be extruded. In the present embodiment, as shown in FIG. 1, the extrusion 59 is formed on the die 23, but the extrusion port 59 may be integrated with the outer die hole 57. The die 23 is connected to the outer die 22 by the thickness adjusting portion 24 so that the coaxiality between the central axis of the cored bar guide hole 31 and the central axis of the extrusion port 59 can be adjusted. In many cases, the central axis of the nozzle and the central axis of the extrusion port 59 are adjusted so as to be substantially coaxial. By changing the die 23, various shapes of the rubber composition 11 can be extruded. By using such a crosshead die 20, the rubber composition 11 supplied from the extruder 1 passes through a flow path formed between the outer die 22 and the mandrel 21 and is supplied to the extrusion port 59. The The supplied rubber composition 11 is integrated with the core metal 13 that has flowed out of the core metal guide hole 31 and is extruded from the extrusion port 59, thereby forming a rubber roller in which the core metal 13 and the rubber composition 11 are integrated. Extruded.

  Next, the core metal supply device 6 will be described. The core metal supply device 6 includes a core metal feed roller 7. The cored bar feed roller 7 feeds the cored bar 13 into the cored bar guide hole 31. In the present embodiment, an adhesive 32 for adhering to the rubber composition 11 is applied to the core bar 13 except for both ends of the core bar 13. The inner diameter of the cored bar guide hole 31 is 0.01 to 0.02 mm larger than the outer diameter of the cored bar 13. The core bar 13 is continuously fed from the core bar guide hole 31 to the extrusion port 59. In the present embodiment, the cored bar guide hole 31 is the same member as the mandrel 21, but may be a separate member. For example, a structure in which another cylindrical member is inserted into the mandrel 21 may be used. Further, in order to prevent the core bar 13 from being scratched, the mandrel 21 may be made of resin. The core metal 13 fed into the extrusion port 59 from the core metal guide hole 31 is covered with the rubber composition 11 fed into the extrusion port 59 from the outer die hole 57 at the extrusion port 59. At this time, the cored bar 13 and the rubber composition 11 are both formed into a rubber roller shape while the outer diameter is controlled by the shape of the extrusion port 59. The outer diameter of the conductive rubber roller 12 extruded from the extrusion port 59 is determined by the diameter of the extrusion port 59 and the supply speed of the core metal 13 when the extrusion amount of the rubber composition 11 is constant. In the present embodiment, the cored bar 13 has a cylindrical shape, and the material may be conductive, but is preferably made of metal.

  Next, the shape of the mandrel 21 and the shape of the flow path of the rubber composition 11 will be described in detail with reference to FIGS. FIG. 2 is an external view of the mandrel 21. 2A is a left side view, FIG. 2B is a front view, and FIG. 2C is a right side view. In addition, the front view of FIG.2 (b) makes the direction when the mandrel of FIG. 1 is seen from the position with a supply port the front.

  The mandrel 21 has a manifold portion 21a and a tip portion 21b. A pair of grooves 61 having a symmetrical shape with respect to a plane including the central axis of the outer die hole 57 and the central axis of the supply port 50 are formed on the outer peripheral surface of the manifold portion 21a. Constitutes the road.

The pair of grooves 61 has an inlet 61 a into which the rubber composition 11 flows from the supply port 50 at a position facing the supply port 50. The pair of grooves 61 branches from the inlet 61a in the circumferential direction of the outer peripheral surface of the manifold portion 21a, and terminates at two outlets 61b that are opened downstream. The pair of grooves 61 extend from the inlet 61a to a position 90 ° apart in the circumferential direction, and then the two outlets 61b are positioned at 180 ° apart from each other in the circumferential direction so that the central axis of the cored bar guide hole 31 is It is desirable that they are opposed to each other. In the present embodiment, the pair of grooves 61 has a substantially semicircular shape with a radius of 8 mm, a cross-sectional area of about 86 mm ² , and a flow path length along the flow direction of about 35 mm.

  A semicircular groove 65 having a symmetrical shape with respect to the central axis of the core metal guide hole 31 is formed on the lower surface of the manifold portion 21 a that communicates with the two outlets 61 b and is perpendicular to the central axis of the core metal guide hole 31. (See FIG. 4). FIG. 3 is an enlarged view of the region S shown in FIG. FIG. 4 is a perspective view of the mandrel 21.

  A tip 21b extends in the downstream direction 72 from the lower surface of the manifold portion 21a. A first annular channel 60, a second annular channel 62, and a third annular channel 63 are formed in the gap between the outer peripheral surface of the tip 21b and the inner peripheral surface of the outer die hole 57. Has been. The first annular channel 60 communicates with the outlet 61 b and the groove 65 of the pair of grooves 61. The second annular channel 62 is formed on the downstream side of the first annular channel 60. FIG. 5 is a cross-sectional view showing the shapes of the first annular channel and the second annular channel. FIG. 5A is a cross-sectional view taken along the cutting line AA shown in FIG. 1, and is a cross-sectional view of the first annular channel 60. FIG. 5B is a cross-sectional view taken along the cutting line BB shown in FIG. 1, and is a cross-sectional view of the second annular flow path 62. In addition, description of the core metal guide hole 31 is abbreviate | omitted in FIG. 5 (a), (b).

  As shown in FIG. 5, the first annular channel 60 and the second annular channel 62 have a cross-sectional shape perpendicular to the central axis of the outer die hole 57, and both the outer side and the inner side are substantially circular. It has become. The outer circle is the inner peripheral surface of the outer die hole 57, and the inner circle is constituted by the outer peripheral surface of the mandrel 21. As shown in FIG. 5, the cross-sectional area of the second annular flow path 62 is smaller than the cross-sectional area of the first annular flow path 60.

  The rubber composition 11 that has flowed out from the two outlets 61 b of the pair of grooves 61 flows along the first annular flow path 60 and also in the downstream direction 72. The rubber composition 11 flowing along the first annular flow path 60 merges (collises). At this time, since the semicircular groove 65 is formed on the lower surface of the manifold portion 21a, turbulent flow is generated in the internal space of the groove 65 after the two flows of the rubber composition 11 merge. This turbulent flow suppresses the generation of weld lines. The width t1 (see FIG. 3) of each groove 65 is the difference t (see FIG. 3) between the radius of the outer circle and the radius of the inner circle forming the first annular channel 60 shown in FIG. ) Is better, and should be about 80% or more. In other words, the width t1 is preferably 80% or more of the difference t.

  In the present embodiment, the first annular channel 60 has an annular cross-sectional shape in which the diameter of the inner circle is 16.8 mm and the diameter of the outer circle is 30 mm, and the length of the channel is 10 .5 mm. The radius r (see FIG. 3) of the groove 65 is 5.3 mm. In the second annular channel 62, the flow 161 in the downstream direction 72 of the rubber composition 11 is inhibited by making the cross-sectional area smaller than that of the first annular channel 60. Thereby, the flow of the two rubber compositions 11 flowing out from the two outlets 61 b of the pair of grooves 61 is rectified into the circumferential flow 162.

  In the present invention, the shape of the second annular channel 62 is not limited to an annular cross-sectional shape in which the outer circle and the inner circle are substantially circular. For example, as shown in FIG. 6A, in order to make the flow of the rubber composition 11 having an annular cross section uniform, the outer side (the inner peripheral surface of the outer die hole 57) is a perfect circle, and the inner side (the tip portion 21b) The outer peripheral surface may be substantially elliptical. The ellipse should have a major axis in the direction connecting the two outlets of the pair of grooves 61. Thereby, the cross-sectional area of the channel near the outlet 61b of the pair of grooves 61 is reduced, and the cross-sectional area of the channel at a position away from the outlet 61b is increased. Therefore, the effect of making the flow of the rubber composition 11 immediately after flowing out of the pair of grooves 61 can be enhanced. Moreover, the following effects are obtained by using the annular flow path 63 having a substantially elliptical shape inside. As shown in FIG. 5B, when the annular flow path 63 is a perfect circle both on the outside and on the inside, the flow of the rubber composition 11 flowing out from the outlet 61b of the pair of grooves 61 is the flow 161 in the downstream direction. strong. On the other hand, as shown in FIG. 6A, when the annular channel 63 has a perfect circle on the outside and a substantially elliptical shape on the inside, the flow 161 is obstructed, so the circumferential flow 162 is strong. Become. Therefore, since the circumferential flow 162 collides and disturbs the flow, it is possible to efficiently generate a weld line.

  Here, the oval shape means not only the oval shape shown in FIG. 6 (a) but also two semicircles having the same radius as shown in FIG. It includes a shape in which both ends of a circular arc are connected by two straight lines having the same length and parallel to each other.

  In the second annular channel 62 shown in FIG. 6B, the inner side has a major axis length of 26.8 mm, the minor axis length of 25.8 mm, and a radius of 12.8 mm, and an outer circle Is 30 mm in diameter, and the length of the flow path is about 4.1 mm. In addition, the dimension of each flow path mentioned above is a typical value.

  In the present embodiment, since the two grooves 61 are used, the inner side of the second annular flow path 62 has a substantially elliptical shape. However, in the present invention, a different shape according to the number of grooves is used. It can also be taken. For example, when four grooves are formed, the second annular flow path 62 has a substantially circular shape on the outside and a substantially square shape on the inside. In the second annular flow path 62, it is preferable that the apexes of the inner substantially quadrilateral are arranged in the vicinity of the outlet of the groove.

  The third annular channel 63 has a substantially perfect circle both inside and outside. In the third annular channel 63, the rubber composition 11 that has passed through the second annular channel 62 flows toward the extrusion port 59.

By using the crosshead die 20 configured as described above, it is possible to convert the rubber composition 11 supplied from the supply port 50 into a stable annular cross-sectional flow that is less affected by the weld line. Therefore, unevenness in the electrical resistance in the circumferential direction of the conductive rubber roller 12 due to the influence of the weld line can be reduced. As a result, it is possible to reduce variation in electrical resistance in the circumferential direction of the conductive rubber roller 12. Further, when the overall volume of the flow path formed in the crosshead die 20 is reduced, the time during which the rubber composition 11 is in contact with the flow path is shortened, and the change in electrical resistance is also reduced. Therefore, it is desirable that the volume of the flow path in the crosshead die 20 is about 32 cm ³ or less. The volume of the channel here is the total of the volume of the pair of grooves 61 and the volume of the first annular channel 60 to the third annular channel 63. The volume of the third annular channel 63 includes the volume up to the extrusion port 59. In other words, as shown in FIG. 1, the volume of the inner space surrounded by the extrusion port 59, the cored bar 13, the mandrel 21, and the outer die hole 57.

  Examples of the present invention will be described below.

Example 1
In this example, the conductive rubber roller 12 was manufactured by extrusion molding using the crosshead die 20 described above.

  First, the rubber composition 11 used in this example will be described. As elastic material, 100 parts of EPT-4045 (Mitsui Petrochemical Co., Ltd.), 5 parts of zinc oxide (Hakusitek Co., Ltd.), 1 part of stearic acid (Nippon Oil Co., Ltd.), PEG # 400 1 part (manufactured by Nippon Oil Co., Ltd.) was used. As the conductive material, 8 parts of Ketjen Black EC-600JD (manufactured by Ketjen Blab International Co., Ltd.) and 30 parts of Seast SO (manufactured by Tokai Carbon Co., Ltd.) were used. As a plasticizer, 60 parts of Diana Process Oil PW-380 (manufactured by Idemitsu Co., Ltd.) was used. As a dehydrating agent, 4 parts of VESTA BS (manufactured by Inoue Lime Industry Co., Ltd.) was used. As other additives, 1 part of Noxeller M (manufactured by Ouchi Shinsei Chemical Co., Ltd.), 1 part of Noxeller TET (manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.), Noxeller TRA (manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) And 1 part of Sunfax 200S (manufactured by Tsurumi Chemical Co., Ltd.) were used.

Next, the detailed shape of the mandrel 21 used in the present embodiment will be described. In this embodiment, the second annular channel 62 has an elliptical shape as shown in FIG. Further, in the pair of grooves 61, the cross-sectional area is about 86 mm ² , the radius is 8 mm, and the flow path length along the flow direction is about 35 mm. The third annular channel 63 has an inner circle diameter of about 16.8 mm, an outer circle diameter of 30 mm, and a channel length of about 10.5 mm. The radius of the groove 65 is 5.3 mm. The second annular channel 62 is a circle whose inside has a major axis length of 26.8 mm, minor axis length of 25.6 mm, a radius of 12.8 mm, and an outer side of a diameter of 30 mm. The length of the flow path is about 4.1 mm. The third annular channel 63 is substantially circular on the inside and outside, has a maximum cross-sectional area of about 505 mm ² and a volume of about 18600 mm ³ . And the total of the volume of each flow path mentioned above is about 32 cm < ³ >.
The molding conditions were set as follows.

Number of extrusions: 2000 conductive rubber rollers are continuously extruded Core metal: Total length 252 mm, outer diameter φ 6.0 mm
Conductive rubber roller: Extrusion outer diameter average φ8.7 aim Extruder: φ70mm, L / D20, manufactured by Mitsuba Corporation
Screw rotation speed: 8.0rpm
Die diameter: φ8.8mm
Extrusion speed (time required for one extrusion): 5 seconds In this example, the above-mentioned unvulcanized rubber composition 11 is extruded by the extruder 1 (in parallel) and continuously in a cored bar. The rubber composition 11 is coated on the outer periphery of the core bar 13 by passing the core 13 through the core bar guide hole 31 of the mandrel 21 of the crosshead die 20. Then, one conductive rubber roller 12 is formed by cutting between the rear end portion of the preceding core metal 13 and the front end portion of the subsequent core metal 13 with the cutting blade 8. Thereafter, the conductive rubber roller 12 is placed in a hot air oven at 170 ° C. for 30 minutes for vulcanization. Cut off both ends 10 mm of the vulcanized conductive rubber roller to expose the cored bar 13 and polish the rubber part to a diameter of 8.5 mm to prepare a conductive rubber roller.

(Example 2)
In the conductive rubber roller according to the present embodiment, the second annular channel 62 is an annular channel whose outer side and inner side are substantially circular as shown in FIG. In the second annular channel 62, the diameter of the inner circle is 26.8 mm, the diameter of the outer circle is 30 mm, and the length of the channel is about 4.1 mm. Other than that is manufactured like Example 1. FIG.

(Comparative Example 1)
In this comparative example, a conductive rubber roller was extruded from the same rubber composition 11 as in Example 1 using a conventional crosshead die 120 shown in FIG. In FIG. 7, the same components as those in the crosshead die 20 shown in FIG.

In the crosshead die 120 shown in FIG. 7, a pair of manifolds 161 with a preland 162 is formed on the outer peripheral surface of the mandrel 121. The manifold 161 constitutes a development part flow path 151. The width of the pre-land 162 is about 3 mm. The area of the cross section perpendicular to the flow path of the development part flow path 151 is about 710 mm ² . Further, in the crosshead die 120, an annular flow channel 152 is formed following the development portion flow channel 151. The annular channel 152 has a taper shape with a length of 90 mm and a maximum cross-sectional area of 1725 mm ² . A spiral groove 153 is formed on the outer periphery of the mandrel 121 constituting the annular flow path 152. The molding conditions for the conductive rubber roller are the same as those in the first embodiment. In addition, the volume of the flow path in the crosshead die 120 of this comparative example is about 330 cm ³ .

(Evaluation)
About the conductive rubber roller manufactured in each Example and Comparative Example 1, the current value in the circumferential direction was measured at intervals of 400 extrusions, and the unevenness of electric resistance was calculated as follows. Specifically, a conductive rubber roller is brought into contact with a cylindrical metal drum with a load of 500 g at both ends, and a voltage of 200 V is applied between the conductive rubber roller and the metal drum while the metal drum is rotated, and measurement is performed. Current is measured at a period of 50 msec. Then, the unevenness of electric resistance is evaluated by a value obtained by dividing the maximum value of the current value by the minimum value.

  The measurement results in the above Examples and Comparative Examples are shown in Table 1 below.

┌────┬─┬──┬──┬──┬──┬──┐
Number of extrusions│50│400│800│1200│1600│2000│
├────┼─┼──┼──┼──┼──┼──┤
Example 1 1.42│1.42│1.43│1.43│1.47│1.46│
├────┼─┼──┼──┼──┼──┼──┤
Example 2 1.46│1.45│1.46│1.49│1.51│1.50│
├────┼─┼──┼──┼──┼──┼──┤
Comparative Example 1 1.48│1.58│1.66│1.68│1.72│1.77│
└────┴─┴──┴──┴──┴──┴──┘
From Table 1, regarding the non-uniformity of electrical resistance in the circumferential direction of the conductive rubber roller, the conductive rubber roller manufactured in each example could be a stable value even when the number of extrusions increased. Therefore, it is considered that when the conductive rubber roller is molded with the crosshead die of each example, the unevenness of electric resistance in the circumferential direction can be reduced.

  On the other hand, in the conductive rubber roller manufactured in the comparative example, it can be seen that the electrical resistance unevenness in the circumferential direction increases as the number of extrusions increases. This is because the crosshead die 120 of Comparative Example 1 is like a groove 65 provided in the crosshead die 20 of Examples 1 and 2 at the end of the manifold 161 where two flows of the rubber composition 11 merge. This is probably because there is no structure that generates turbulent flow.

  From the above results, it is possible to form a conductive rubber roller with less uneven electrical resistance in the circumferential direction by the cross head die 20 of the present invention.

  In consideration of the pressure loss of the flow path, the diameter range of the cored bar 13 is desirably 4 to 10 mm, and the outer diameter range of the conductive rubber roller 12 is desirably 7 mm to 16 mm.

21 Mandrel 22 Outer die 50 Supply port 57 Outer die hole 60 First annular channel 62 Second annular channel 65 Groove

Claims (3)

A circular outer die hole penetrating the inside in the axial direction from the upper end to the lower end,
A supply port that passes through a wall portion surrounding the outer die hole in a direction intersecting the axial direction, and supplies a rubber composition to the outer die hole;
An outer die formed with,
A mandrel that penetrates the inside in the axial direction and a cored bar guide hole through which a cored bar flows is formed substantially coaxially with the central axis of the outer die hole, and is installed in the outer die hole;
Have
In the crosshead die for molding the conductive rubber roller coated with the rubber composition, the core metal that has flowed out from the core metal guide hole toward the lower end portion of the outer die.
The mandrel is
Manifold section,
A tip portion extending downward from the lower surface of the manifold portion in the axial direction;
Have
The manifold portion is
A pair of grooves formed on the outer peripheral surface in a symmetrical shape with respect to a plane including the central axis of the cored bar guide hole and the central axis of the supply port,
Opposite to the supply port, an inlet through which the rubber composition flows from the supply port,
The rubber composition that is separated from the inlet in the circumferential direction of the outer peripheral surface and is opposed to each other across the central axis of the cored bar guide hole at a position lower in the axial direction than the inlet, Two outlets flowing downward in the axial direction;
A pair of grooves having
Is formed symmetrically with respect to the center axis of the metal core guide holes in the lower surface, said communicated to each of the two outlets, in a cross section including the central axis of the central shaft and the supply opening of the metal core guide holes, wherein A semicircular groove convex in the direction toward the upper end ,
Have
Formed in a gap between the outer peripheral surface of the tip and the inner peripheral surface of the outer die hole, communicated with the two outlets and the semicircular groove, the rubber composition flowing out from the two outlets, A first annular channel that flows in the circumferential direction;
A second annular channel formed in a lower side of the gap in the axial direction than the first annular channel, and having a smaller cross-sectional area than the first annular channel;
The crosshead die further comprising:   The crosshead die according to claim 1, wherein an outer side of the second annular channel is circular, and an inner side of the second annular channel is elliptical. A circular outer die hole penetrating the inside in the axial direction from the upper end to the lower end,
A supply port penetrating a wall portion surrounding the outer die hole in a direction intersecting the axial direction;
An outer die formed with,
A cored bar guide hole penetrating through the inside in the axial direction and formed substantially coaxially with the central axis of the outer die hole;
A pair of grooves formed in a symmetric shape with respect to a plane including the central axis of the cored bar guide hole and the central axis of the supply port are formed on the outer peripheral surface, and are symmetric with respect to the central axis of the cored bar guide hole In a cross section including a central axis of the cored bar guide hole and a central axis of the supply port, a manifold portion having a semicircular groove formed on the lower surface in a direction toward the upper end portion ;
A mandrel having a tip extending from the lower surface of the manifold portion to the lower side in the axial direction;
In a method for producing a conductive rubber roller in which a core metal is coated with a rubber composition,
Supplying the rubber composition from the supply port to the outer die hole;
The supplied rubber composition is separated from the inlet facing the supply port in the circumferential direction of the outer peripheral surface from the inlet and at the center of the cored bar guide hole at a position below the inlet in the axial direction. Flow to two outlets facing each other across the shaft,
Flowing the rubber composition flowing out from the two outlets in the circumferential direction along a first annular flow path formed in a gap between the outer peripheral surface of the tip and the inner peripheral surface of the outer die hole;
The composition that has passed through the first annular channel is formed below the first annular channel in the gap in the axial direction, and has a cross-sectional area that is larger than that of the first annular channel. A first step for flowing along a small second annular channel;
In parallel with the first step, a second step of flowing the cored bar through the cored bar guide hole;
A third step of coating the core metal that has flowed out of the core metal guide hole with the rubber composition;
A method for producing a conductive rubber roller, comprising:

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