JP2017218560A - Charging roller and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging roller capable of satisfactorily suppressing occurrence of an image failure by adhesion of an external additive compared to the current situation, and to provide a method for producing the same.SOLUTION: A charging roller 1 has an outer layer 5 formed of a tube 4 with no seam that is formed of THV and to which semiconductivity is imparted provided on the outer periphery of a cylindrical inner layer 2 formed of a porous body of a semiconductive rubber composition, and arithmetic average roughness Ra of an outline curve of an outer peripheral surface 8 of the outer layer is 0.3 μm or more and 1.5 μm or less. A production method includes press fitting an inner layer having an outer diameter Dlarger than an inner diameter Dof a tube into the tube which constitutes the outer layer and has a thickness T of 100 μm or more and 300 μm or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a charging roller used by being incorporated in an image forming apparatus using electrophotography and a method for manufacturing the same.

As a toner used in image forming apparatuses using electrophotography such as laser printers, electrostatic copying machines, plain paper facsimile machines, or multi-function machines, these days, the purpose is to improve the quality of formed images. As a result, a toner by a so-called polymerization method, which has a smaller particle diameter than a conventional pulverization toner and has a substantially spherical shape, is becoming popular.
Further, in order to adjust the fluidity, chargeability, and other characteristics of the toner, it is common to externally add fine particles of submicron order such as silica and titanium oxide as external additives.

However, in particular, an external additive externally added to the toner by a polymerization method, or a fragment of toner particles finely pulverized that is generated when image formation is repeated (hereinafter sometimes referred to as “external additive etc.”). ) May not be completely removed from the surface of the photoreceptor by a cleaning blade or the like.
During repeated image formation, external additives that could not be removed adhere to the outer peripheral surface of the charging roller that is always in contact with the surface of the photoconductor and gradually accumulate, resulting in uneven charging of the photoconductor. Or adhere to the formed image and cause image defects such as density unevenness.

Therefore, in Patent Document 1, the outer peripheral surface of the charging roller has a resin composition containing a solvent-soluble fluororesin, an acrylic resin having a glass transition temperature of 40 to 90 ° C., a fluorine-modified acrylate resin as a surface conditioner, and a conductive agent. It has been proposed to coat with an outer layer of material.
According to such a configuration, as described above, the fluororesin is included in the outer layer, thereby reducing the surface free energy of the outer peripheral surface of the outer layer, that is, the outer peripheral surface of the charging roller, and suppressing the adhesion of external additives and the like to some extent. it can.

JP 2007-72200 A

However, according to the inventor's study, the configuration of Patent Document 1 has a problem that the effect of suppressing adhesion of external additives and the like is not yet sufficient.
That is, in Patent Document 1, the outer layer is mainly formed by applying a coating agent obtained by dissolving and dispersing each of the above-described components in an arbitrary organic solvent directly on the outer peripheral surface of the charging roller and then drying the coating agent. When acrylic resin or fluorine-modified acrylate is not used together with the resin, the surface free energy of the coating agent tends to be too small.

  If the surface free energy of the coating agent becomes too small, the coating agent is uniformly applied to the outer peripheral surface of the charging roller to form an outer layer having a uniform thickness, or particularly an electronic conductive conductive agent such as carbon black (conductive There is a possibility that the conductive filler) cannot be uniformly dispersed in the coating agent, or the outer layer formed by applying and drying the coating agent cannot be satisfactorily adhered to the outer peripheral surface.

However, in order to prevent these problems from occurring, as described in Patent Document 1, when an acrylic resin or a fluorine-modified acrylate is used in combination with a fluororesin, the ratio of the fluororesin contained in the outer layer is Therefore, the surface free energy of the outer peripheral surface of the outer layer cannot be sufficiently reduced, and the effect of suppressing the adhesion of external additives and the like becomes insufficient.
An object of the present invention is to provide a charging roller and a method for manufacturing the same that can more effectively suppress the occurrence of image defects due to adhesion of external additives and the like.

  The present invention relates to a cylindrical inner layer made of a porous body of a semiconductive rubber composition, and a tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer (hereinafter referred to as “THV”) provided on the outer periphery of the inner layer. And an outer layer made of a seamless tube to which semiconductivity is imparted, and the arithmetic mean roughness Ra of the contour curve of the outer peripheral surface of the outer layer is 0.3 μm or more. The charging roller is 5 μm or less.

The present invention is a manufacturing method of the charging roller, the underlying of the outer layer, the thickness T is 100μm or more, in said tube is 300μm or less, the outer diameter D ₁ is than the inner diameter D ₂ of the tube And a step of press-fitting a larger inner layer.

  ADVANTAGE OF THE INVENTION According to this invention, the charging roller which can suppress the image defect by the adhesion | attachment of an external additive etc. generating better than the present condition, and its manufacturing method can be provided.

FIG. 1 (a) is a perspective view showing the overall appearance of an example of the charging roller of the present invention, and FIG. (B) is an end view of the charging roller of the above example. FIG. 1 (a) is a perspective view showing an example of a process for manufacturing the charging roller of FIGS. 1 (a) and 1 (b) by the manufacturing method of the present invention, and FIG. (B) is an end view of an inner layer used in the above process. FIG. 3 (c) is an end view of the tube that forms the outer layer.

<Charging roller>
Referring to FIGS. 1 (a) and 1 (b), a charging roller 1 of this example is made of THV on a peripheral surface 3 of an inner layer 2 formed in a cylindrical shape by a porous body of a semiconductive rubber composition. The outer layer 5 which consists of the seamless tube 4 to which electroconductivity was provided is laminated | stacked. A shaft 7 is inserted into and fixed to the through hole 6 at the center of the inner layer 2.

According to the charging roller 1, the outer layer 5 is pressurized in, for example, the extrusion molding method or in a molten state of the resin composition that forms the outer layer 5, poured into the cavity of the cylindrical mold, cooled, and then removed. The tube 4 can be formed independently of the inner layer 2 by a so-called transfer molding method.
Therefore, the outer layer 5 having a uniform thickness can be formed without using an acrylic resin, a fluorine-modified acrylate, or the like together with a conventional outer layer formed by directly applying a coating agent to the outer peripheral surface.

Further, by forming the outer layer 5 by extrapolating the tube 4 to the inner layer 2, the outer layer 5 can be satisfactorily adhered to the outer peripheral surface 3 of the inner layer 2.
Moreover, since THV has a lower melting point than ordinary fluororesins and is excellent in kneadability with an electronic conductive conductive agent (conductive filler) such as carbon black, the THV and the electronic conductive conductive agent are softened, for example, by THV. After kneading in a state heated above the temperature, the tube 4 is manufactured by the above-described various molding methods, etc., so that it is not necessary to use an acrylic resin or a fluorine-modified acrylate or the like together with an outer layer made of a conventional coating agent. The outer layer 5 in which the electronic conductive agent is uniformly dispersed can be formed.

Therefore, the outer layer 5 is formed by a seamless tube 4 made of THV and provided with semiconductivity without using acrylic resin, fluorine-modified acrylate, etc., so that the surface free energy of the outer peripheral surface 8 of the outer layer 5 can be reduced. The adhesion of external additives and the like can be suppressed even better.
In addition, since THV is more flexible than ordinary fluororesin, the rubber hardness of the entire charging roller 1 can be made smaller than the current state.

Therefore, when the charging roller 1 is brought into contact with the photosensitive member, a suitable discharge area having an appropriate nip width can be secured to uniformly charge the surface of the photosensitive member, and adhesion and accumulation of external additives and the like can be achieved. In combination with this, it is possible to suppress the occurrence of image defects such as density unevenness and to stabilize the image quality of the formed image.
In addition to further improving the above effect, and taking into consideration, as much as possible, contamination of the photosensitive member and other members by bleeding as much as possible, the tube 4 that is the basis of the outer layer 5 is composed of only THV and an electronic conductive agent. (Including the case where two or more types of THV and / or two or more types of electronic conductive agents are used in combination), for example, a plasticizer, a processing aid, an ionic conductive conductive agent, or the like bleeds to cause contamination. It is preferable not to contain the component which becomes.

The surface roughness of the outer peripheral surface 8 is the arithmetic mean of the contour curve defined in Japanese Industrial Standards JIS B0601: 2013 “Product Geometrical Specification (GPS) —Surface Properties: Contour Curve Method—Terminology, Definitions, and Surface Property Parameters”. Expressed by roughness Ra, it is limited to 0.3 μm or more and 1.5 μm or less.
That is, the charging roller 1 is required to have an appropriate number and size of protrusions on the outer peripheral surface 8 as a starting point of discharge for charging the surface of the photoreceptor. The outer peripheral surface 8 having a roughness Ra less than the above range is too smooth and cannot have appropriate protrusions. Therefore, the surface of the photosensitive member is uniformly charged by functioning as the charging roller 1 to improve the image quality of the formed image. It cannot be stabilized.

On the other hand, the outer peripheral surface 8 in which the arithmetic mean roughness Ra of the contour curve exceeds the above range is too uneven, and the outer layer 5 constituting the outer peripheral surface 8 is formed by the tube 4 made of THV. Further, adhesion and accumulation of external additives and the like, and image defects associated therewith are likely to occur.
On the other hand, by setting the arithmetic mean roughness Ra of the contour curve of the outer peripheral surface 8 in the above range, appropriate protrusions are provided on the outer peripheral surface 8 to suppress adhesion and accumulation of external additives as much as possible. The surface of the photoreceptor can be uniformly charged, and image quality such as density unevenness can be suppressed to stabilize the image quality of the formed image.

In consideration of further improving such an effect, the arithmetic mean roughness Ra of the contour curve of the outer peripheral surface 8 is preferably 0.8 μm or more even in the above range, and is 1.2 μm or less. Is preferred.
The method for adjusting the arithmetic average roughness Ra of the contour curve to the above range is not particularly limited. For example, it is possible to employ at least one kind of conventional polishing such as wet polishing, laser processing, and thermal transfer processing that thermally transfers a mold surface shape having a predetermined arithmetic average roughness Ra.

The charging roller 1 preferably has a total Asker C hardness of 20 ° or more, and preferably 40 ° or less.
When the Asker C-type hardness is less than this range, for example, when the image forming apparatus is stopped for a certain period of time in a state where the charging roller 1 is pressed against the surface of the photoreceptor and deformed, There is a risk that the charging roller 1 may become so-called sag that does not return to its original position while being deformed at the portion that is in pressure contact with the photosensitive member.

On the other hand, if the Asker C-type hardness exceeds the above range, the charging roller 1 is not flexible enough and has a suitable nip width when brought into contact with the photoreceptor as described above. There is a possibility that the area cannot be secured and the effect of stabilizing the image quality of the formed image by uniformly charging the surface of the photoconductor may not be obtained.
On the other hand, by setting the Asker C-type hardness of the entire charging roller 1 within the above range, the charging roller 1 is imparted with appropriate flexibility while suppressing the occurrence of the settling as much as possible. A suitable discharge region having an appropriate nip width can be ensured when brought into contact with the body, and image quality such as density unevenness can be suppressed and the image quality of the formed image can be stabilized.

In consideration of further improving this effect, the Asker C-type hardness of the entire charging roller 1 is preferably 25 ° or more even in the above range.
Incidentally the Asker-C hardness of the whole of the charging roller 1, in the present invention, Japanese Industrial Standard JIS K7312 _{-1 996} incorporated in Annex 2 of "Physical testing method for thermosetting polyurethane elastomer molded article" The Japan Value measured by the following method using a Type C hardness tester (for example, Asker Rubber Hardness Tester Type C manufactured by Kobunshi Keiki Co., Ltd.) in accordance with Rubber Association Standard SRIS0101 “Physical Test Method for Expanded Rubber” I will represent it.

That is, with both ends of the shaft 7 integrated with the charging roller 1 fixed to the support base, the pressing needle of the type C hardness tester is pressed against the central portion of the charging roller 1 and further 10 N (≈1 kgf). The Asker C-type hardness is measured with a load of.
<Method for manufacturing charging roller>
Referring to FIGS. 2 (a) to 2 (c), in the manufacturing method of this example, a seamless tube 4 made of THV and provided with semiconductivity, which is the base of the outer layer 5, and a central passage in advance. An inner layer 2 having an outer diameter D ₁ larger than an inner diameter D _{2 of the} tube 4, in which the shaft 7 is inserted and fixed in the hole 6, is prepared, and the inner layer 2 is press-fitted into the tube 4.

Then, the inner layer 2 and the tube 4 are electrically joined and mechanically fixed, and the outer layer 5 made of the tube 4 is formed, whereby the charging roller 1 is manufactured.
The thickness T of the tube 4 is limited to 100 μm or more and 300 μm or less.
The thickness T of the tube 4 is less than the above range, although it varies depending on the interference of the outer layer 5 with respect to the inner layer 2 represented by the difference D ₁ -D ₂ between the outer diameter D ₁ of the inner layer 2 and the inner diameter D ₂ of the tube 4. Then, the Asker C-type hardness of the entire charging roller 1 becomes less than 20 ° as described above, and it becomes easy to cause settling. Further, the outer layer 5 is likely to be worn and lost in a relatively short period of time.

On the other hand, when the thickness T of the tube 4 exceeds the above range, the overall Asker C-type hardness exceeds 40 °, and the charging roller 1 is not flexible enough to be brought into contact with the photoreceptor. In this case, a suitable discharge area having an appropriate nip width cannot be secured, and the surface of the photoreceptor cannot be charged uniformly to stabilize the image quality of the formed image.
On the other hand, when the thickness T of the tube 4 is set in the above range, the charging roller 1 is imparted with appropriate flexibility while being prevented from causing the settling as much as possible, and is brought into contact with the photoreceptor. A suitable discharge area having a moderate nip width can be secured, the surface of the photoreceptor can be uniformly charged, and image defects such as density unevenness can be suppressed to stabilize the image quality of the formed image. .

Also represented by D ₁ -D _2, interference of the outer layer 5 with respect to the inner layer 2 is preferably but not limited to at 100μm or more to, it is preferably at 300μm or less.
If the tightening allowance is less than this range, sufficient tightening force of the inner layer 2 by the outer layer 5 cannot be obtained, so that the outer layer 5 is likely to be displaced with respect to the inner layer 2.

On the other hand, when the tightening allowance exceeds the above range, the inner layer 2 is too tightly tightened by the outer layer 5, the overall Asker C-type hardness exceeds 40 °, and the flexibility of the charging roller 1 is insufficient. As a result, a suitable discharge region having an appropriate nip width cannot be secured when brought into contact with the photosensitive member, and the surface of the photosensitive member may not be uniformly charged to stabilize the image quality of the formed image.
On the other hand, by setting the tightening margin within the above range, the charging roller 1 is imparted with an appropriate flexibility while preventing the outer layer 5 from being displaced as much as possible during image formation, and is brought into contact with the photoreceptor. Ensures a suitable discharge area with an appropriate nip width, and uniformly charges the surface of the photoconductor to suppress image defects such as density unevenness and stabilize the image quality of the formed image. Can do.

<Inner layer 2>
The inner layer 2 can be formed of various rubber compositions having semiconductivity. However, the inner layer 2 is preferably formed of a semiconductive rubber composition containing ethylene propylene rubber and paraffin oil.
By using both of the above-mentioned components having excellent affinity and compatibility with each other, the melt viscosity of the semiconductive rubber composition can be lowered and foamed and cross-linked with improved foaming properties. The flexibility of the inner layer 2 can be improved as compared with the current situation.

Moreover, the THV forming the outer layer 5 has particularly low affinity and compatibility with paraffinic oil and functions as a barrier layer against the paraffinic oil, so that the paraffinic oil blended in the inner layer 2 bleeds to the outer peripheral surface 8. Thus, contamination of the photoconductor and other members can be suppressed.
Therefore, by combining the inner layer 2 with the outer layer 5, a flexible charging roller 1 having a total Asker C-type hardness of 40 ° or less can be obtained without causing contamination of the photoreceptor and other members. Can be formed.

(Ethylene propylene rubber)
Examples of the ethylene propylene rubber used as the inner layer 2 include ethylene propylene rubber (EPM) which is a copolymer of ethylene and propylene, and ethylene propylene diene rubber (EPDM) which is a copolymer of ethylene, propylene and diene. Either can be used, and EPDM is particularly preferable.

As EPDM, any of various copolymers obtained by copolymerizing ethylene, propylene, and diene can be used. Examples of the diene include ethylidene norbornene (ENB) and dicyclopentadiene (DCPD).
Among these, as EPDM whose diene is ENB, for example, Esplen (registered trademark) EPDM 501A manufactured by Sumitomo Chemical Co., Ltd. [Mooney viscosity ML _{1 + 4} (100 ° C.): 44, ethylene content: 52%, diene content: 4.0] %], 505A [Mooney viscosity ML _{1 + 4} (100 ° C.): 47, ethylene content: 50%, diene content: 9.5%] and the like. Moreover, as EPDM whose diene is DCDP, for example, Esprene EPDM 301A manufactured by Sumitomo Chemical Co., Ltd. [Mooney viscosity ML _{1 + 4} (100 ° C.): 44, ethylene content: 50%, diene content: 5.0%], 301 [ Mooney viscosity ML _{1 + 4} (100 ° C.): 55, ethylene content: 62%, diene content: 3.0%], 305 [Mooney viscosity ML _{1 + 4} (100 ° C.): 60, ethylene content: 60%, diene content: 7. 5%] or the like.

In addition to the non-oil-extended EPDMs exemplified above, there are also known oil-extended EPDMs that have been extended with an extension oil. In the present invention, among these oil-extended EPDMs, the extension oil is a paraffinic oil. Can also be used as a substitute for EPDM + paraffinic oil.
As the EPDM, one or more of the above examples may be mentioned.
(Other rubber)
In consideration of further improving the above-described effects by combining ethylene propylene rubber, paraffin oil, and THV, as the rubber forming the inner layer 2, only ethylene propylene rubber is used alone (two or more kinds). It is preferable to use the ethylene propylene rubber in combination.

However, other rubbers may be used in combination as long as the above effects are not impaired.
Examples of such other rubbers include one or more of natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, acrylonitrile butadiene rubber, chloroprene rubber, and the like.
The blending ratio of the other rubber is preferably 20 parts by mass or less, particularly 10 parts by mass or less, in 100 parts by mass of the total amount of rubber.

(Paraffinic oil)
As the paraffin oil, various paraffin oils having good compatibility with ethylene propylene rubber can be used.
Examples of the paraffinic oil include one or more of various paraffinic oils of Diana (registered trademark) process oil PW series manufactured by Idemitsu Kosan Co., Ltd.

The blending ratio of the paraffinic oil is preferably 20 parts by mass or more and preferably 100 parts by mass or less per 100 parts by mass of the total amount of rubber including at least ethylene propylene rubber.
When the blending ratio of the paraffinic oil is less than this range, the foaming property of the foamed body is improved by reducing the melt viscosity of the semiconductive rubber composition as described above by blending the paraffinic oil. There is a possibility that the effect of increasing the magnification to improve the flexibility of the inner layer 2 and thus the charging roller 1 may not be sufficiently obtained. That is, there is a possibility that the charging roller 1 cannot be provided with a high flexibility that satisfies the entire Asker C-type hardness of 40 ° or less.

On the other hand, when the blending ratio of the paraffinic oil exceeds the above range, excess paraffinic oil oozes out to the interface with the outer layer 5 and inhibits electric conduction between the outer layer 5 and the inner layer 2, There is a risk of lowering the semiconductivity of the charging roller 1. Further, the outer layer 5 may be easily displaced with respect to the inner layer 2.
On the other hand, by setting the blending ratio of the paraphytic oil in the above range, the semiconductive rubber composition can be foamed while suppressing the semiconductive deterioration of the charging roller 1 and the displacement of the outer layer 5. The flexibility of the inner layer 2 is improved by improving the foaming ratio and the flexibility of the inner layer 2 can be improved, and the charging roller 1 can be provided with the flexibility that satisfies the overall Asker C-type hardness of 40 ° or less.

In consideration of further improving this effect, the blending ratio of the paraffinic oil is preferably 50 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the total amount of rubber even in the above range. Is preferred.
Further, as described above, when using an oil-extended EPDM whose extending oil is a paraffinic oil, an oil-extended EPDM having an oil-extended amount per 100 parts by mass of EPDM within the above range may be selected and used.

However, oil-extended EPDM whose oil expansion amount is outside the above range can also be used. For example, when the oil expansion amount of the oil-extended EPDM is insufficient, it is sufficient to add paraffinic oil, and the oil expansion amount is excessive. In this case, it is sufficient to add a non-oil-extended EPDM.
The semiconductive rubber composition that forms the inner layer 2 includes a rubber containing at least the ethylene-propylene rubber and a cross-linking component for cross-linking the rubber with paraffin oil, and the inner layer 2 should have a porous structure. A foaming component for foaming and a conductive agent for imparting semiconductivity to the inner layer 2 can be blended at a predetermined ratio.

(Crosslinking component)
Examples of the crosslinking component include a crosslinking agent and an accelerator.
Among these, examples of the crosslinking agent include one or more of sulfur-based crosslinking agents, thiourea-based crosslinking agents, triazine derivative-based crosslinking agents, peroxide-based crosslinking agents, various monomers, and the like.
Examples of sulfur-based crosslinking agents include sulfur such as powdered sulfur, oil-treated powdered sulfur, precipitated sulfur, colloidal sulfur, and dispersible sulfur, and organic sulfur-containing compounds such as tetramethylthiuram disulfide and N, N-dithiobismorpholine. Is mentioned.

The thiourea-based cross-linking agent, such as tetramethyl thiourea, trimethyl thiourea, ethylene thiourea, in _{(C n H 2n + 1 NH} ) 2 C = S [wherein, n is a number from 1 to 10. ] 1 type (s) or 2 or more types, such as thiourea represented by these.
Further, examples of the peroxide crosslinking agent include benzoyl peroxide.
When the ethylene propylene rubber is EPDM, sulfur is preferable as the crosslinking agent.

The blending ratio of sulfur is preferably 0.5 parts by mass or more and preferably 3 parts by mass or less per 100 parts by mass of the total amount of rubber including at least the ethylene propylene rubber.
For example, when oil-treated powder sulfur, dispersible sulfur, or the like is used as sulfur, the above-mentioned blending ratio is the ratio of sulfur itself as an active ingredient contained therein.
Examples of the accelerator include one or more inorganic accelerators such as slaked lime, magnesia (MgO), and resurge (PbO), and organic accelerators.

  Examples of the organic accelerator include guanidine accelerators such as 1,3-di-o-tolylguanidine, 1,3-diphenylguanidine, 1-o-tolylbiguanide, dicatechol borate di-o-tolylguanidine salt, and the like. A thiazole accelerator such as 2-mercaptobenzothiazole and di-2-benzothiazolyl disulfide; a sulfenamide accelerator such as N-cyclohexyl-2-benzothiazylsulfenamide; tetramethylthiuram mono One type or two or more types of thiuram accelerators such as sulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, dipentamethylenethiuram tetrasulfide; and thiourea accelerators may be mentioned.

Since the function of the accelerator varies depending on the type, it is preferable to use two or more kinds of accelerators in combination.
The blending ratio of the individual accelerators can be arbitrarily set depending on the type, but usually it is preferably 0.5 parts by mass or more and preferably 3 parts by mass or less individually per 100 parts by mass of the total amount of rubber.
(Foaming component)
As the foaming component, various foaming agents that decompose by heating to generate gas can be used.

Examples of the foaming agent include one or more of azodicarbonamide (ADCA), 4,4′-oxybis (benzenesulfonylhydrazide) (OBSH), N, N-dinitrosopentamethylenetetramine (DPT), and the like. Can be mentioned.
The blending ratio of the foaming agent is preferably 3 parts by mass or more and preferably 8 parts by mass or less per 100 parts by mass of the total amount of rubber.

If the blending ratio of the foaming agent is less than this range, the foaming ratio of the inner layer 2 may be insufficient, and the effect of improving the flexibility of the inner layer 2 and thus the charging roller 1 may not be sufficiently obtained. That is, there is a possibility that the charging roller 1 cannot be provided with a high flexibility that satisfies the entire Asker C-type hardness of 40 ° or less.
On the other hand, when the blending ratio of the foaming agent exceeds the above range, the foaming ratio of the inner layer 2 becomes too high, and the Asker C-type hardness of the entire charging roller 1 is less than 20 °, which tends to cause settling. There is a risk.

When the foaming agent is ADCA, it may be used in combination with, for example, a urea-based foaming aid that acts to promote decomposition by lowering the decomposition temperature of the ADCA.
The blending ratio of the foaming aid can be arbitrarily set according to the type of foaming agent to be combined, but is preferably 1 part by mass or more and preferably 3 parts by mass or less per 100 parts by mass of the total amount of rubber.

(Conductive agent)
Examples of the conductive agent include an electronic conductive conductive agent and / or an ionic conductive conductive agent, and an electronic conductive conductive agent is particularly preferable.
Examples of the electronic conductive agent include one or more of various types of carbon black, graphite, metal powder, metal fiber, and conductive metal oxide having electronic conductivity. Carbon black is particularly preferable.

The blending ratio of the electron conductive conductive agent is preferably 30 parts by mass or more and preferably 60 parts by mass or less per 100 parts by mass of the total amount of rubber.
If the blending ratio of the electronic conductive agent is less than this range, the resistance value of the inner layer 2 becomes too high, and sufficient semiconductivity cannot be imparted to the entire charging roller 1.
On the other hand, if the blending ratio of the electronic conductive agent exceeds the above range, even if paraffinic oil is blended, the inner layer 2 and thus the charging roller 1 become hard, and the charging roller 1 has the entire Asker. There is a possibility that high flexibility that satisfies the C-type hardness of 40 ° or less cannot be provided.

(Other additives)
You may mix | blend various additives with a semiconductive rubber composition as needed further. Examples of the additive include a crosslinking aid, a deterioration preventing agent, a filler, a scorch preventing agent, a lubricant, a pigment, an antistatic agent, a flame retardant, a neutralizing agent, a nucleating agent, and a co-crosslinking agent.
Among these, examples of the crosslinking assistant include metal compounds such as zinc oxide; fatty acids such as stearic acid, oleic acid, and cottonseed fatty acid, and one or more conventionally known crosslinking assistants. In particular, it is preferable to use zinc oxide and stearic acid in combination.

The blending ratio of the crosslinking aid is preferably individually 0.5 parts by mass or more and preferably 6 parts by mass or less per 100 parts by mass of the total amount of rubber.
Examples of the filler include one or more of zinc oxide, silica, reinforcing carbon black, clay, talc, calcium carbonate, magnesium carbonate, aluminum hydroxide, and the like.

By blending the filler, the mechanical strength and the like of the inner layer 2 can be improved.
The blending ratio of the filler is preferably 20 parts by mass or more, and preferably 40 parts by mass or less, per 100 parts by mass of the total amount of rubber.
(Semiconductive rubber composition)
The semiconductive rubber composition containing each component described above can be prepared in the same manner as before.

First, knead the rubber, then add and knead the paraffinic oil, conductive agent, and various additives other than the crosslinking component and foaming component, and finally add the crosslinking component and foaming component and knead. A conductive rubber composition is obtained.
For kneading, for example, a closed kneader such as an intermix, a Banbury mixer, a kneader, an extruder, or an open roll can be used.

(Preparation of inner layer 2)
In order to produce the inner layer 2, the semiconductive rubber composition is first extruded into a cylindrical shape using an extruder, then cut into a predetermined length, pressurized and heated in a vulcanizing can. Foam and crosslink.
Then foaming, the tubular body was crosslinked, by heating using an oven or the like to secondary crosslinking, polished to a predetermined outer diameter D ₁ After cooling.

<Shaft 7>
The shaft 7 is integrally formed of a metal such as iron, aluminum, an aluminum alloy, or stainless steel.
The shaft 7 can be inserted through the through-hole 6 and fixed at an arbitrary time after the tubular body is cut and after the inner layer 2 is pressed into the tube 4.

However, after the cut, it is preferable to first perform secondary cross-linking, polishing, and press-fitting into the tube 4 as shown in FIG.
Thereby, the curvature and deformation | transformation of the inner layer 2 by the expansion-contraction at the time of secondary bridge | crosslinking can be prevented. Further, by polishing while rotating around the shaft 7, the workability of the polishing can be improved, and the flare of the outer peripheral surface 3 can be suppressed. Furthermore, workability at the time of press-fitting the inner layer 2 into the tube 4 can be improved.

The shaft 7 is electrically joined to the inner layer 2 via, for example, a conductive adhesive and is mechanically fixed, or the shaft 7 has a larger outer diameter than the inner diameter of the through hole 6. By being press-fitted, it is electrically joined to the inner layer 2 and is mechanically fixed to be integrated with the inner layer 2.
In the former case, the thermosetting adhesive is cured simultaneously with the secondary cross-linking of the cylindrical body by heating in the oven, and the shaft 7 is electrically joined to the inner layer 2 and mechanically. Fixed.

In the latter case, electrical joining and mechanical fixing are completed simultaneously with press-fitting.
<Outer layer 5>
As described above, the outer layer 5 is composed of a seamless tube 4 made of THV and provided with semiconductivity.
As described above, the tube 4 is obtained by mixing a resin composition in which an electronic conductive agent or the like is mixed with the above THV at a predetermined ratio by various molding methods such as an extrusion molding method, a transfer molding method, or an injection molding method. It is manufactured by molding into a cylindrical shape with a thickness T, and the inner diameter D _2.

(THV)
As THV, any of various terpolymers obtained by copolymerizing three kinds of monomers of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride at an arbitrary ratio can be used.
Examples of such THV include at least one kind of thermoplastic fluororesin THV of various grades of DYNEON (registered trademark) series manufactured by 3M Japan.

(Conductive agent)
As the conductive agent for imparting semiconductivity to the tube 4, an electronic conductive conductive agent is preferable in consideration of preventing contamination of the photosensitive member and other members as much as possible as described above.
Examples of the electronic conductive agent include carbon fibrils such as carbon nanotubes in addition to the above-described various carbon blacks and graphites having electronic conductivity. One or more of these electronically conductive agents can be used.

In particular, considering the cost, the characteristics of the charging roller 1 and the like, carbon black having a large DBP oil absorption capable of forming a conductive circuit with a small amount of addition and capable of adjusting the resistance is preferable.
The blending ratio of the electron conductive conductive agent is preferably 1 part by mass or more per 100 parts by mass of THV, and preferably 15 parts by mass or less.
If the blending ratio of the electron conductive conductive agent is less than this range, there is a possibility that moderate semiconductivity cannot be imparted to the tube 4.

On the other hand, when the blending ratio of the electronic conductive agent exceeds the above range, the outer layer 5 and thus the charging roller 1 become hard, and the entire Asker C-type hardness is 40 ° or less in the charging roller 1. There is a possibility that high flexibility that satisfies the above cannot be imparted. There is also a risk of increasing costs.
(Other ingredients)
As described above, the tube 4 is formed only from the above THV and the electronic conductive conductive agent in consideration of preventing contamination of the photosensitive member and other members by bleed as much as possible, for example, a plasticizer, a processing aid, It is preferable not to include a component that bleeds and becomes a contamination source, such as an ion conductive conductive agent.

Even in this case, THV has a melting point lower than that of a normal fluororesin and is excellent in kneadability, so that the outer layer 5 in which the electronic conductive agent is uniformly dispersed can be formed. Further, since THV is more flexible than ordinary fluororesin, the rubber hardness of the entire charging roller 1 can be made smaller than the current state.
The charging roller 1 having the above-described parts can be used by being incorporated into various image forming apparatuses using electrophotography, such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine, or a complex machine thereof.

<Example 1>
(Inner layer 2)
Among the ethylene propylene rubbers, EPDM [Esprene EPDM 505A manufactured by Sumitomo Chemical Co., Ltd., non-oil extended, Mooney viscosity ML _{1 + 4} (100 ° C.): 47, ethylene content: 50%, diene content: 9.5 %] Was used.

As the paraffinic oil, Diana Process Oil PW-380 manufactured by Idemitsu Kosan Co., Ltd. was used.
While kneading 100 parts by mass of the above EPDM with a Banbury mixer, 70 parts by mass of paraffinic oil, and kneading by adding other than the crosslinking component and the foaming component among the components shown in Table 1 below, adding the crosslinking component and the foaming component. Further, kneading was performed to prepare a semiconductive rubber composition which is the basis of the inner layer 2.

Each component in Table 1 is as follows. In addition, the mass part in a table | surface is a mass part per 100 mass parts of EPDM.
Filler: Heavy calcium carbonate, BF-300 manufactured by Shiraishi Calcium Co., Ltd.
Crosslinking aid I: 2 types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Crosslinking aid II: Bead stearic acid, product name Tsubaki manufactured by NOF Corporation Electronic conductive agent: Carbon Black ISAF, Tokai Carbon Co., Ltd. 6) Seast 6
Foaming agent: ADCA, Eibin Kasei Kogyo Co., Ltd. binihole AC # 3
Foaming aid: Urea-based cell paste 101 manufactured by Eiwa Kasei Kogyo Co., Ltd.
Cross-linking agent: sulfur containing 5% oil, manufactured by Tsurumi Chemical Co., Ltd. (mass part of sulfur itself as an active ingredient is 1.5 parts by mass per 100 parts by mass of EPDM)
Accelerator TS: Tetramethylthiuram monosulfide, thiuram accelerator, Sunseller (registered trademark) TS manufactured by Sanshin Chemical Industry Co., Ltd.
Accelerator MBTS: Di-2-benzothiazolyl disulfide, thiazole accelerator, Shandong Sunsine Chemical Co. Ltd .. SUNSINE MBTS made by
The semiconductive rubber composition is supplied to an extruder and extruded into a cylindrical shape having an outer diameter of φ15 mm and an inner diameter of φ6.5 mm, mounted on a temporary shaft for crosslinking, and 160 ° C. × 1 in a vulcanizing can. Time cross-linked and foamed.

Next, the cross-linked and foamed cylindrical body is remounted on a shaft 7 having an outer diameter of φ 7.0 mm and coated with a conductive thermosetting adhesive on the outer peripheral surface, and is heated to 160 ° C. in an oven. Then, the outer peripheral surface 3 was polished and finished to have an outer diameter D ₁ = 16.1 mm using a cylindrical polishing machine, and further washed with water to produce the inner layer 2 integrated with the shaft 7.
(Outer layer 5)
As THV, DYNEON THV221GZ manufactured by 3M Japan Co., Ltd. was used, and Denka Black (registered trademark) manufactured by Denka Co., Ltd. was used as the electronic conductive agent.

A resin composition is prepared by adding 10 parts by weight of Denka Black to 100 parts by weight of the THV, and preparing the resin composition by molding the prepared resin composition by the transfer molding method described above to obtain an inner diameter D ₂ = 15.9 mm and a thickness T. = A tube 4 of 100 μm was produced. The interference represented by the difference D ₁ -D ₂ between the outer diameter D ₁ and the inner diameter D ₂ was 200 μm.
Then, after the inner layer 2 is press-fitted into the tube 4, both ends are cut to form the outer layer 5 made of the tube 4 on the outer periphery of the inner layer 2, and the outer peripheral surface 8 is formed with a # 2000 wrapping film [Sankyo Rika The charging roller 1 was manufactured by roughening by mirror polishing using a mirror film (registered trademark) manufactured by Co., Ltd.

The overall Asker C-type hardness of the charging roller 1 was measured according to the measurement method described above and found to be 25 °.
Further, the arithmetic mean roughness Ra of the contour curve of the outer peripheral surface 8 was measured using a laser microscope [VX-100 manufactured by Keyence Co., Ltd.] and found to be 1 μm in accordance with the above-mentioned rules. .

<Example 2>
The charging roller 1 was manufactured in the same manner as in Example 1 except that the thickness T of the tube 4 was 195 μm.
The tightening allowance represented by the difference D ₁ -D ₂ between the outer diameter D ₁ and the inner diameter D ₂ is 200 μm, the entire Asker C-type hardness of the charging roller 1 is 31 °, and the arithmetic average of the contour curve of the outer peripheral surface 8 The roughness Ra was 1 μm.

<Example 3>
A charging roller 1 was manufactured in the same manner as in Example 1 except that the thickness T of the tube 4 was 290 μm.
The tightening allowance expressed by the difference D ₁ -D ₂ between the outer diameter D ₁ and the inner diameter D ₂ is 200 μm, the overall Asker C-type hardness of the charging roller 1 is 38 °, and the arithmetic average of the contour curve of the outer peripheral surface 8 The roughness Ra was 1 μm.

<Comparative example 1>
A charging roller 1 was manufactured in the same manner as in Example 1 except that the thickness T of the tube 4 was 420 μm.
The tightening allowance represented by the difference D ₁ -D ₂ between the outer diameter D ₁ and the inner diameter D ₂ is 200 μm, the overall Asker C-type hardness of the charging roller 1 is 48 °, and the arithmetic average of the contour curve of the outer peripheral surface 8 The roughness Ra was 1 μm.

<Example 4>
A charging roller 1 was produced in the same manner as in Example 1 except that the outer peripheral surface 8 was roughened by mirror polishing using a # 1500 wrapping film (mirror film manufactured by Sankyo Rikagaku Co., Ltd.).
The interference represented by the difference D ₁ -D ₂ between the outer diameter D ₁ and the inner diameter D ₂ is 200 μm, the entire Asker C-type hardness of the charging roller 1 is 25 °, and the arithmetic average of the contour curve of the outer peripheral surface 8 The roughness Ra was 1.4 μm.

<Example 5>
A charging roller 1 was manufactured in the same manner as in Example 1 except that the outer peripheral surface 8 was roughened by mirror polishing using a # 3000 wrapping film (mirror film manufactured by Sankyo Rikagaku Co., Ltd.).
The interference represented by the difference D ₁ -D ₂ between the outer diameter D ₁ and the inner diameter D ₂ is 200 μm, the entire Asker C-type hardness of the charging roller 1 is 25 °, and the arithmetic average of the contour curve of the outer peripheral surface 8 The roughness Ra was 0.32 μm.

<Comparative example 2>
Except that the thickness T of the tube 4 was 195 μm and the outer peripheral surface 8 was roughened by mirror polishing using a # 4000 lapping film (mirror film manufactured by Sankyo Rikagaku Co., Ltd.), the same as in Example 1. A charging roller 1 was manufactured.
The tightening allowance represented by the difference D ₁ -D ₂ between the outer diameter D ₁ and the inner diameter D ₂ is 200 μm, the entire Asker C-type hardness of the charging roller 1 is 31 °, and the arithmetic average of the contour curve of the outer peripheral surface 8 The roughness Ra was 0.1 μm.

<Comparative Example 3>
In place of THV, polyester elastomer (Hytrel (registered trademark) 5557 manufactured by Toray DuPont Co., Ltd.) was used, and after adding 10 parts by mass of Denka Black to 100 parts by mass of the polyester elastomer, the same as in Example 1 Thus, a tube 4 having an inner diameter D ₂ = 15.9 mm and a thickness T = 105 μm was produced.

A charging roller 1 was manufactured in the same manner as in Example 1 except that the tube 4 was used.
The tightening allowance represented by the difference D ₁ -D ₂ between the outer diameter D ₁ and the inner diameter D ₂ is 200 μm, the overall Asker C-type hardness of the charging roller 1 is 26 °, and the arithmetic average of the contour curve of the outer peripheral surface 8 The roughness Ra was 1 μm.

<Comparative example 4>
A charging roller 1 was manufactured in the same manner as in Example 1 except that the outer peripheral surface 8 was roughened by mirror polishing using a # 1000 wrapping film (mirror film manufactured by Sankyo Rikagaku Co., Ltd.).
The interference represented by the difference D ₁ -D ₂ between the outer diameter D ₁ and the inner diameter D ₂ is 200 μm, the entire Asker C-type hardness of the charging roller 1 is 25 °, and the arithmetic average of the contour curve of the outer peripheral surface 8 The roughness Ra was 1.7 μm.

<Real machine test>
In place of a genuine charging roller of a toner cartridge of a commercially available laser printer that includes a photoconductor and a charging roller that is always in contact with the surface of the photoconductor and is detachable from the laser printer body, The charging roller 1 manufactured in Examples and Comparative Examples was incorporated.
The assembled toner cartridge is loaded into the laser printer, and 30000 images of 5% density are continuously formed in an environment of a temperature of 23 ± 1 ° C. and a relative humidity of 55 ± 1%. The following criteria were used to evaluate whether or not white density irregularities or white spot density irregularities were observed.

○: No density unevenness was observed.
Δ: Slight density unevenness that could hardly be observed visually was observed, but it was at a practical level.
X: Density unevenness was observed.
Further, the charging roller 1 used for the image formation was taken out, and the presence or absence of adhesion or accumulation of an external additive or the like on the outer peripheral surface 8 was evaluated according to the following criteria.

○: No adhesion or accumulation of external additives or the like was observed.
Δ: Although slight adhesion was observed, there was no problem in image evaluation.
X: Adhesion and accumulation of external additives and the like were observed.
The above results are shown in Tables 2 and 3.

From the results of Examples 1 to 5 and Comparative Example 3 in Tables 2 and 3, the outer layer 5 is formed by a seamless tube 4 made of THV and provided with semiconductivity, so that adhesion of external additives and the like is achieved. As a result, it was found that the occurrence of image defects such as density unevenness associated therewith can be suppressed better than the current situation.
Further, from the results of Examples 1 to 3 and Comparative Example 1, the charging roller 1 provided with the outer layer 5 has an Asker C-type hardness of 40 ° or less and has an appropriate nip width when brought into contact with the photoreceptor. In order to stabilize the image quality of the formed image by suppressing the occurrence of image defects such as density unevenness by securing a suitable discharge area and uniformly charging the surface of the photoconductor, It was found that the thickness T of the tube 4 required to be less than 300 μm.

  Further, from the results of Examples 1, 4, 5 and Comparative Examples 2 and 4, an appropriate protrusion is provided on the outer peripheral surface 8 to suppress the adhesion and accumulation of external additives as much as possible and to make the surface of the photoreceptor uniform. In order to suppress the occurrence of image defects such as density unevenness by charging and stabilize the image quality of the formed image, the arithmetic mean roughness Ra of the contour curve of the outer peripheral surface 8 is 0.3 μm or more, 1 It has been found that it is necessary to set the thickness to 0.5 μm or less, and it is preferable to set the thickness to 0.8 μm or more and 1.2 μm or less.

1 Charging roller ₂ Inner layer 3 Outer surface 4 Tube 5 Outer layer 6 Through hole 7 Shaft 8 Outer surface D ₁ Outer diameter D ₂ Inner diameter T Thickness

Claims (4)

  A cylindrical inner layer made of a porous body of a semiconductive rubber composition, and a semiconductive property made of a tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer provided on the outer periphery of the inner layer. A charging roller comprising an outer layer made of a seamless tube, and having an arithmetic mean roughness Ra of a contour curve on the outer peripheral surface of the outer layer of 0.3 μm or more and 1.5 μm or less.   2. The charging roller according to claim 1, wherein the tube includes only the tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer and an electronic conductive agent.   The charging roller according to claim 1 or 2, wherein the overall Asker C-type hardness is 40 ° or less. The method for manufacturing a charging roller according to any one of claims 1 to 3, wherein an outer diameter D ₁ is provided in the tube having a thickness T of 100 µm or more and 300 µm or less, which is the basis of the outer layer. method for producing a charging roller but including the step of press-fitting the inner layer larger than the inner diameter D ₂ of the tube.

Images