JP3994575B2 - Magnet roll and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnet roll used for an electrophotographic developing device such as a copying machine, a facsimile machine, a printer, and the like, a magnet roll used for other purposes, and a manufacturing method thereof.
[0002]
[Prior art]
For example, a magnet roll melts a resin magnet composition in which a thermoplastic resin such as nylon, a magnetic powder such as ferrite, and an additive such as a surface treatment agent are mixed at a high temperature to form a fixed mold and the fixed mold. The molten resin composition is poured into a split mold composed of a movable mold that can be separated and solidified to form a substantially cylindrical shape.
Generally, when producing such a cylindrical molded product, a product with little warpage can be obtained basically by uniformly cooling the main body after molding.
[0003]
[Problems to be solved by the invention]
On the other hand, the magnet roll needs to be provided with a magnetic pole portion extending in the axial direction in a plurality of predetermined parts divided along the circumferential direction for the purpose of use. By applying a magnetic field to the molten resin composition being molded by a permanent magnet or an electromagnet placed in the molding die, and performing magnetic field molding in which the magnetic powder is oriented and magnetized in a certain direction, magnetic pole portions are formed at the respective parts. Forming.
In each part where the magnetic pole part is formed, the density of the magnetic powder increases as the magnetic powder concentrates, so the molding shrinkage rate becomes relatively small. If the cross section of the magnet roll is measured in detail, the true part of FIG. As shown in the circularity measurement shape, a molded product is obtained in which the magnetic pole portion is deformed into a mountain shape and the inter-electrode portion is deformed into a valley shape. This deformation amount is not constant because it depends on the magnetic force, molding conditions, etc., but in the case of a large one, the maximum value of the difference between the crests and troughs, that is, the radial dimension difference between the magnetic pole part and the interpole part is about 0.1 mm. It may become.
[0004]
In particular, when the magnetic poles are not equally spaced in the circumferential direction, the magnetic force of each magnetic pole is significantly different, or the cross-sectional shape is asymmetrical in order to obtain a predetermined strong magnetic force, In spite of cooling almost uniformly, the warpage inevitably occurs, and the amount of warping after hardening depends on the size of the magnet roll, but it is not negligible for a magnet roll having a longitudinal dimension of about 200 mm or more. It becomes. For example, in the case of an A3 size magnet roll having a longitudinal dimension of about 350 mm, a large warp of about 0.3 to 0.5 mm has conventionally occurred.
[0005]
The problem caused by the warp of the magnet roll is manifested as a variation in the separation distance between the magnet roll in the developing device and the developing surface, and the variation in the axial magnetic flux density can cause uneven density in the image. Cause.
[0006]
The present invention has been made in view of the present situation, and even when the radial dimension difference between the magnetic pole part and the interpole part is large, the amount of warpage is small, and good image quality that does not cause density unevenness when used in a developing device. It is intended to provide a magnet roll and a method for producing the same.
[0007]
[Means for Solving the Problems]
That is, the present invention is molded from a resin magnet composition (hereinafter simply referred to as “resin magnet”) containing a thermoplastic or thermosetting resin, ferromagnetic powder, and an additive such as a surface treatment agent, and has a longitudinal dimension of 200 mm. A magnet roll formed by integrally forming a substantially cylindrical magnet roll main body formed with a plurality of magnetic pole parts extending over the entire length along the circumferential direction, and a shaft part supporting the main body at both ends, After the molded magnet roll is taken out of the molding die, a cooling die having a concave portion with a circular arc in cross section formed based on the curvature of the outer circumference of the magnet roll is used while the magnet roll is in an incompletely cured state. Thus, with respect to the outer peripheral portion approximately 180 ° opposite to the warp direction of the magnet roll, the recessed portion is formed from 1/8 of the entire circumference along the circumferential direction on the outer periphery of the magnet roll body. In it to correct the warp of the magnet roll was locally cooled by pressure contact with one of the range of minutes, the maximum value of the radial dimension difference of the magnetic pole portions and interpole portion in the magnet roll body 0.01mm or more The present invention also provides a magnet roll for use in an electrophotographic developing device such as a copying machine, a facsimile machine, or a printer, wherein the amount of warpage of the main body is 0.1 mm or less. In such a magnet roll with a small amount of warping, the magnetic flux density due to each magnetic pole is substantially uniform along the longitudinal direction, and when used in a developing device, a good image with no density unevenness can be obtained.
[0008]
Further, the present invention supports a substantially cylindrical magnet roll body using a resin magnet containing a thermoplastic or thermosetting resin, ferromagnetic powder, and an additive such as a surface treatment agent, and the magnet roll body supported at both ends. In the manufacturing method of the magnet roll in which the shaft portion is integrally formed by injection molding, after the molded magnet roll is taken out from the molding die, the curvature of the outer circumference of the magnet roll is increased while the magnet roll is in an incompletely cured state. Using the cooling mold having a concave portion with a circular arc shape in cross section formed based on the outer peripheral portion on the opposite side of the magnet roll approximately 180 ° with respect to the warp direction of the magnet roll, JP that from 1 all around the eighth along locally cooled by pressure contact with one of the range of 2 minutes, to correct the warp of the magnet roll To, a copier, a facsimile, provides a method for producing a magnet roller for use in the developing apparatus of an electrophotographic system such as a printer.
[0009]
By locally cooling the predetermined part in this way, a thick hardened layer is formed at the predetermined part of the magnet roll that is in an incompletely cured state, and the other semi-cured parts that are not cooled are relatively located on the cooling side. It is brought to the other side. In this manner, by locally cooling a predetermined portion and intentionally changing the distribution of the contraction rate of the entire magnet roll, it becomes possible to prevent the warp from expanding or to correct the warp. Then, by locally cooling the outer peripheral part, a hardened layer is formed in the part, and when the whole is cooled, the semi-hardened part in the convex direction mainly contracts, and the entire warpage is offset. As a result, a magnet roll with less warpage can be obtained.
[0010]
Here, it is preferable that the magnet roll outer peripheral part press-contacted to the recessed part of a cooling metal mold | die is the range of 1/4 or more of full length centering on the center part along a magnet roll longitudinal direction.
[0011]
Moreover , the time when the magnet roll is pressed against the recessed portion of the cooling mold and cooling is started is within 120 seconds after the magnet roll is taken out of the molding mold, and the pressure contact time is 2 seconds or more and 120 seconds or less. it is preferred arbitrariness.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 1 to 6 show typical embodiments of the present invention, in which M denotes a magnet roll, A1 and A2 denote molding dies, and B denotes a cooling die.
[0013]
As shown in FIG. 1, a magnet roll M according to the present invention comprises a substantially cylindrical magnet roll body 1 having a longitudinal dimension of 200 mm or more and shaft portions 2 and 3 that support the body 1 at both ends, and are thermoplastic. Alternatively, a resin magnet containing a thermosetting resin binder resin, ferromagnetic powder, a surface treatment agent and other additives is used as a molding material. The magnet roll body 1 has a plurality of magnetic pole portions 4a,... Extending along the circumferential direction, as shown by the roundness measurement shape in FIG. In the inter-electrode portion 4b,..., A magnet roll is formed despite the deformation of a maximum of 0.01 mm or more due to the difference in each radial dimension based on the difference in molding shrinkage due to the variation in magnetic powder density distribution. The amount of warping of the main body is suppressed to 0.1 mm or less.
[0014]
The magnet roll body 1 and the shaft portions 2 and 3 are integrally formed of the same resin magnet material using a molding die A1 or A2 shown in FIGS. 3 to 5 described later, and one shaft portion 2 has positioning or driving force. A notch 2a for transmission is formed. Then, the warpage is corrected by forcibly cooling a predetermined portion within the time of being in an incompletely cured state after being taken out from the molding die A1 or A2.
As the ferromagnetic powder to be blended in the resin magnet, one or more types can be selected from ferrites containing manganese, strontium, rare earths (SmCo, NdFeB), MnAlC, alnico, SmFeN, etc. Resin binders include polyamide resins such as 66 nylon and 12 nylon, polyphthalamide resins, polyamideimide resins, polyolefin resins, polyethylene terephthalate resins, polybutylene terephthalate resins, polyphenylene sulfide resins, polysulfone resins, ethylene-ethyl acrylate resins, ethylene -It can select suitably from vinyl acetate copolymer resin, an epoxy resin, ethylene-vinyl alcohol copolymer resin, etc. The resin binder can be blended with a flame retardant, a reinforcing agent, or the like as necessary.
[0015]
As shown in FIGS. 3 and 4, the molding die A <b> 1 is provided with a cylindrical main molding die 5 that forms a magnet roll body, and a shaft portion 2 of the magnet roll that is disposed at one end of the main molding die 5. An end mold 6 to be moved and a shaft part 3 of the magnet roll, which is disposed in the main mold 5 so as to be movable back and forth. It comprises a slide mold 7 that forms a molding space 8 in the mold 5.
A permanent magnet 9 is disposed in the main mold 5 so as to surround the molding space 8 as a magnetic field orientation means, and the magnetic particles are in a period from the start of injection of the molten resin magnet until the molten resin magnet is solidified or semi-solidified. A plurality of magnetic pole portions are formed in the magnet roll main body by performing the orientation and magnetization. Similarly, the main mold 5 is provided with a flow passage 10 through which a medium such as warm water flows as a cooling means so as to surround the molding space 8, and the entire main mold 5 is maintained at an appropriate temperature. The injected molten resin magnet is cooled and solidified. The end molding die 6 is provided with a molding space 6a that forms the shaft portion 2 and an introduction path 6b that communicates with the molding space 6a, and is a molten resin magnet material that is heated and melted by a plasticizer of an injection molding machine (not shown). Is injected into the molding space 6a at a high pressure through the introduction path 6b connected to the plasticizing apparatus. A molding space 7a for forming the shaft portion 3 of the magnet roll is provided at one end facing the molding space of the slide mold 7, and an actuator 11 is connected to the other end. The actuator 11 is formed by injection of molten resin magnet material. A constant braking force is applied to the backward movement of the slide mold 7. The magnetic field orientation means provided in the main mold 5 may use an electromagnet instead of a permanent magnet.
[0016]
Further, the magnet roll M according to the present invention may be molded using, for example, a split mold A2 as shown in FIG. The illustrated divided molding die A2 is composed of a movable mold 21 having a molding space 21a and a fixed mold 22 having a molding space 22a. The movable mold 21 has a magnet roll taken out after molding. The protruding pin 23 to be performed is provided with a magnetic mold orientation means 24 and a molten resin magnet material introduction path 22b that opens into the molding space 22a.
[0017]
As a method of locally cooling a predetermined portion of the magnet roll, as shown in FIGS. 6A and 6B, a longitudinal section in an arc shape formed in accordance with the outer periphery curvature of the magnet roll M is used. A cooling die B having a substantially straight concave portion 12a is provided, and the magnet roll M is pressed downward as indicated by an arrow in the figure, whereby the magnet roll outer peripheral predetermined portion 1a is pressed against the concave portion 12a. The method is preferably employed.
The cooling mold B is made of a material having good thermal conductivity such as stainless steel or aluminum, and has a single or plural flow passages 12b for circulating a medium such as hot water as a cooling means. Further, the size of the concave portion 12a having an arc shape in cross section is within a range of 1/8 to 1/2 of the entire circumference along the circumferential direction in the outer circumference of the magnet roll body 1 and the center thereof along the longitudinal direction. It is appropriately set so as to be pressed against the predetermined portion 1a in the range of ¼ or more of the entire length centering on the portion.
[0018]
The predetermined portion 1a of the magnet roll main body 1 is an outer peripheral portion on the opposite side of the magnet roll M, which is substantially 180 ° opposite to the direction of warpage of the magnet roll M, that is, the direction projecting in a convex shape. Create one or more prototypes with the same conditions such as shape, magnetic force, etc. with the same molding equipment, and measure in advance the warping direction and the amount of warping when they are completely cooled to room temperature by natural standing. In addition, the measurement data is regarded as a predicted warpage, and an outer peripheral portion approximately 180 ° opposite to the warping direction is specified as a portion to be cooled.
[0019]
The timing of starting the cooling by the cooling mold B is such that after the magnet roll M is taken out from the molding mold A1 or A2, the surface temperature of the magnet roll M is 80 to 180 ° C., preferably around 130 ° C., and the core portion is still The temperature of the hot water to be circulated through the flow passage 12b in the cooling mold B, that is, the temperature of the cooling mold B, is within a half-hardened state within 120 seconds, and the time required for correcting the warp of the magnet roll M is appropriate and It is desirable to select appropriately in the range of 30 to 60 ° C. where control is easy. The cooling time of the magnet roll M by the cooling mold B is set to 2 to 120 seconds, preferably 10 to 30 seconds.
[0020]
【Example】
Next, with respect to a plurality of magnet rolls (Examples 1 to 4) molded under the same conditions using the same molding die, the warpage amount when cooling using the same cooling die set to different temperatures. The change of was measured.
[0021]
The resin magnet as the material is composed of 88 parts by weight of strontium ferrite as a ferromagnetic powder and surface-treated with a silane coupling agent that strengthens the bond with the resin binder, and 12 parts by weight of 6 nylon resin as the binder resin. In addition, a mixture of a very small amount of lubricant and stabilizer is used, and the recessed portion of the cooling mold is slightly shorter than the overall length of the magnet roll body in the range of one third of the outer circumference of the magnet roll. The dimensions were pressed against the range.
And after each magnet roll of Examples 1-4 is taken out from a molding die, respectively, while the surface temperature is in the incomplete hardening state of around 130 ° C, it is in the predicted direction of warpage measured with a sample beforehand. On the other hand, the outer peripheral portion of the main body on the opposite side of 180 ° was pressed against the recessed portion of the cooling mold for 2 to 60 seconds.
The temperature of the cooling mold is controlled by the temperature of hot water flowing through the mold. The magnet roll of Example 1 is 30 ° C., Example 2 is 40 ° C., Example 3 is 50 ° C., and Example 4 is 60 ° C. It cooled and measured the amount of curvature, respectively. The measurement results are shown in FIG.
[0022]
According to FIG. 7, all the magnet rolls of Examples 1 to 4 gradually decrease in warpage amount as the cooling time pressed against the cooling mold elapses, but when the cooling time becomes too long, the warpage amount is reversed. It can be seen that, as a result, the amount of warpage is minimized at a cooling time of 10 to 30 seconds. This is because the magnet roll of each example was cooled 180 ° opposite to the warp direction predicted based on the sample, and at the beginning of cooling, the warp was corrected on the cooling side, and the cooling time was too long. It is caused by overcorrecting and overhanging the cooling side.
Based on the above results, the cooling location of the magnet roll is determined according to the predicted warping direction and warping amount, and the cooling temperature and cooling time are set appropriately so that the cross-sectional shape is deformed or necessary when the magnetic pole part is formed. It can be seen that even a magnet roll which causes a large warp when it is formed by normal injection molding, such as an asymmetric one for obtaining a magnetic distribution, can be obtained with a small warp. In addition, the direction of warpage and the amount of warpage can be predicted by, for example, the composition of the resin magnet, the basic cross-sectional shape of the main body, the magnetization position, and the magnitude of the magnetized magnetic force, in addition to the method in which the sample is molded and measured in advance as described above. It is also preferable to calculate the thermal contraction rate of each part by the above, and theoretically predict the warpage direction and the warpage amount in the cooling process based on the thermal contraction rate.
[0023]
【The invention's effect】
According to the magnet roll and the manufacturing method thereof according to the present invention as described above, the longitudinal dimension is 200 mm or more, the radial dimension difference between the magnetic pole part and the interpole part in the main body is 0.01 mm or more at the maximum, and the amount of warpage. Is 0.1 mm or less, even if the cross-sectional shape is not a perfect circle or the cross-sectional shape is asymmetrical in order to obtain a special magnetic distribution, the warp is small and the magnetic distribution of the developing part becomes uniform, Good images without uneven density can be obtained in copying machines and printers.
[0024]
In particular , after removing the molded magnet roll from the molding die, while the magnet roll is in an incompletely cured state, the predetermined part is locally cooled to reduce the shrinkage rate of the part. The shrinkage distribution of the entire magnet roll can be intentionally changed so as to prevent the warp from expanding or to correct the warp.
[0025]
Furthermore , a cooling mold having a concave portion with an arc shape in cross section formed based on the curvature of the outer circumference of the magnet roll is provided, and a predetermined portion of the outer circumference of the magnet roll is pressed against the concave portion so that the magnet roll is locally Therefore, the predetermined portion to be cooled can be easily positioned and the portion can be efficiently cooled. In addition, the concave portion functions as a receiving mold for a magnet roll to which a pressing force acts, and a warp correcting action by the pressing force can be performed at the same time.
[0027]
In addition , by locally cooling the outer peripheral portion on the opposite side of approximately 180 ° with respect to the warp direction of the magnet roll, the semi-cured portion in the warp direction is mainly contracted when the whole is cooled, and the warp is offset. As a result, a magnet roll with a small amount of warpage can be obtained, and in particular, the range of one-eighth to one-half of the entire circumference along the circumferential direction on the outer circumference of the magnet roll body is uniform, so that one side of the magnet roll is uniformly cooled. As a result, the warped magnet roll can be straightened as a whole.
[0028]
Further, by setting one or more range-quarter of the total length of the magnet roll outer predetermined portions to be pressed against the concave portion of the cooling die about its central portion along the magnet B Lumpur longitudinally of the magnet roll One side is uniformly cooled, and the warped magnet roll can be straightened as a whole.
[0029]
Further , the time when the magnet roll is brought into pressure contact with the recessed portion of the cooling mold and the cooling is started is within 120 seconds after taking out from the molding die, and the pressure contact time is within 2 seconds to within 120 seconds, so that the core portion is the warping of the magnet roll in the semi-cured state kills in a quickly and reliably corrected.
[Brief description of the drawings]
FIG. 1 is an explanatory perspective view showing a magnet roll according to a representative embodiment of the present invention.
FIG. 2 is an explanatory view showing the roundness measurement shape of the magnet roll.
FIG. 3 is a simplified cross-sectional view showing a molding die for molding a magnet roll.
FIG. 4 is a simplified cross-sectional view showing a state in which a molten resin magnet is injected into the molding space of the molding die.
FIG. 5 is a simplified cross-sectional view showing another molding die for molding a magnet roll.
FIG. 6A is an explanatory view showing a cooling mold for cooling the magnet roll and a magnet roll pressed against the cooling mold.
(B) is explanatory drawing similarly seen from the axial direction.
FIG. 7 is a graph showing measurement results of cooling time and warpage in each of Examples 1 to 4.
[Explanation of symbols]
M Magnet roll A1, A2 Molding die B Cooling die 1 Main body 1a Predetermined part 2 End 2a Notch 3 End 4a Magnetic pole 4b Inter-polar part 5 Main molding 6 End molding 6a Molding space 6b Inlet path 7 Slide mold 7a Molding space 8 Molding space 9 Permanent magnet 10 Flow path 11 Actuator 12a Recessed part 12b Flow path 21 Movable mold 21a Molding space 22 Fixed mold 22a Molding space 23 Extrusion pin 24 Magnetic field orientation means

Claims (4)

A substantially cylindrical magnet roll formed of a resin magnet composition containing a thermoplastic or thermosetting resin, a ferromagnetic powder, and an additive, and having a plurality of magnetic pole portions extending over the entire length of 200 mm or more in the circumferential direction. A magnet roll in which a main body and a shaft portion that supports the magnet roll main body at both ends are integrally formed by injection molding , and after the molded magnet roll is taken out from a molding die, the magnet roll is incompletely cured. While in the state, using a cooling mold having a recessed portion in the shape of a circular arc in cross section formed based on the curvature of the outer circumference of the magnet roll, with respect to the outer peripheral portion on the opposite side of the magnet roll approximately 180 °, The recessed portion is locally cooled by being pressed in a range of 1/8 to 1/2 of the entire circumference along the circumferential direction on the outer periphery of the magnet roll body. It was correct warping of the magnet roll, characterized in that and warpage of the body in the maximum value of 0.01mm or more radial dimensional difference between the magnetic pole portion and the interpole portion in the magnet roll body is 0.1mm or less Magnet rolls used in electrophotographic developing devices such as copying machines, facsimiles, and printers . A substantially cylindrical magnet roll body using a resin magnet composition containing a thermoplastic or thermosetting resin, a ferromagnetic powder, and an additive, and a shaft portion that supports the magnet roll body at both ends are integrated by injection molding. In the manufacturing method of the magnet roll to be molded, after the molded magnet roll is taken out of the molding die , the arc shape of the sectional view formed based on the curvature of the outer periphery of the magnet roll while the magnet roll is in an incompletely cured state Using the cooling mold having the concave portion, the concave portion is approximately 8 minutes of the entire circumference along the circumferential direction on the outer circumference of the magnet roll main body with respect to the outer peripheral portion on the opposite side of the magnet roll main body by approximately 180 °. locally cooled by pressure contact with one of the range of one half, characterized in that to correct the warp of the magnet roll, copiers and files Shimiri method of the magnet roller for use in the developing apparatus of an electrophotographic system such as a printer. The magnet roll manufacturing method according to claim 2 , wherein the outer peripheral portion of the magnet roll that is pressed against the recessed portion of the cooling mold is a quarter or more of the entire length centering on the central portion along the longitudinal direction of the magnet roll. When the magnet roll is pressed against the concave portion of the cooling mold starts cooling, to a maximum of 120 seconds after removal of the magnet roll from the molding die, and you the pressed time is within 120 seconds 2 seconds according Item 4. A method for producing a magnet roll according to Item 2 or 3 .

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