JP3150293B2 - Rubber roll manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a rubber roll used in an image forming apparatus such as an electrophotographic apparatus.

[0002]

2. Description of the Related Art An image forming apparatus such as an electrophotographic apparatus is equipped with various rubber rolls including a charging roll as a charging member.

When such a rubber roll is manufactured by pressureless foaming and vulcanization in a molding die, bubbles are leaked to the outside during foaming, resulting in insufficient foaming, pinhole defects, uneven foaming cells, skin layers (surfaces). ) Problems such as non-uniform thickness occur. In order to prevent these, a method is known in which a non-foamable rubber layer is provided as a skin layer on the surface of an unvulcanized foamed rubber molded article.

Examples of application of such a method to rubber rolls and charging rolls are disclosed in, for example, JP-A-62-83131 and JP-A-7-295331. However,
Since the non-foamable rubber needs to maintain the internal foaming pressure and air bubbles, if the rubber viscosity is increased, the extrudability deteriorates, and the foamable rubber may not expand due to the internal foaming pressure. Conversely, if the viscosity of the non-foamable rubber is reduced, bubbles from the inside cannot be retained and the skin layer formation becomes incomplete. Further, the adjustment of the viscosity of rubber itself is not easy because there are many restrictions in terms of compounding.

[0005] In recent years, a contact charging system has been used in an image forming apparatus such as an electrophotographic apparatus. The contact charging method charges the surface of a charged body to a predetermined polarity and potential by bringing a charged member (conductive member) to which a voltage is applied into contact with the charged body. It is advantageous in that corona products such as ozone are less generated, the structure is simple and the cost can be reduced.

In the contact charging system, as is well known, a voltage is alternatingly superimposed on a charging roll, which is a kind of charging member, in a state where the charging roll is pressed and contacted with a photoreceptor, which is a kind of a member to be charged. When applied in this manner, the photoreceptor is vibrated by the action force exerted between the charging roll and the photoreceptor by a change in the frequency of the AC electric field. This is particularly noticeable in a high-speed copying machine or a high-speed printer in which the copying or printing speed is increased, and there is a problem that noise (charge noise) is generated with such vibration. The charging noise is generated not only when the contact charging member is a charging roll but also on a charging blade, a charging pad, or the like.

As a measure for reducing charging noise, Japanese Patent Application Laid-Open No. 7-29
A charging roll 5331 is also used, which has a structure in which a foamable rubber layer is laminated on the outer periphery of the shaft body and a non-foamable rubber layer is laminated outside the shaft, as described above. With the charging roll having such a configuration, the vibration absorption characteristics of the roll are improved to some extent.

As another approach for reducing the charging noise, a method has been proposed in which the spring constant of the charging member is reduced, that is, the elastic modulus and hardness are reduced. Incidentally, it is known that the frequency of the roll is represented by the following equation (1).

[0009]

(Equation 1)

Therefore, in order to lower the charging noise (natural frequency), it is necessary to reduce the spring constant, increase the mass m, or use both of them.

Sponge rubber made of foamable rubber can reduce the spring constant and suppress the charging noise to some extent. However, since the specific gravity of the sponge rubber is small and the weight of the entire charging member is also small, the natural frequency is increased, and the effect of suppressing the charging noise may be offset.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a rubber roll having reduced vibration noise and excellent vibration absorption characteristics.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a rubber roll, comprising: providing a foamed rubber layer on the outer peripheral surface of a shaft body; and providing a non-foamed rubber layer on the outer peripheral surface of the foamed rubber layer. A foamed rubber layer-forming composition and a non-foamed rubber layer-forming composition, wherein the scorch time of the non-foamed rubber layer-forming composition is shorter than the scorch time of the foamed rubber layer-forming composition by separate extruders. A mold having a circular cross-section having an inner diameter larger than the outer diameter of the laminated body and substantially equal to the desired outer diameter of the rubber roll; The method for producing a rubber roll is characterized in that foaming and vulcanization of the laminate are simultaneously performed by heating after being placed in the rubber roll.

The inventor of the present invention, based on the above configuration, forms a foamed rubber layer having a longer scorch time on the outer periphery of the shaft body and a non-foamed rubber layer having a shorter scorch time on the outer side thereof. It was found that a rubber roll having a foamed rubber layer having a good foaming state and a non-foamed rubber layer having excellent surface properties was obtained, while the foaming internal pressure and bubbles were properly maintained, vulcanization proceeded quickly, and Completed the invention.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the drawings.

FIG. 1 is a longitudinal sectional view showing an example of a rubber roll according to the present invention. In the figure, 1 is a shaft, 2 is an inner foamed rubber layer, and 3 is an outer non-foamed rubber layer (skin layer).
And 4 represents a rubber roll.

The shaft 1 is made of, for example, a metal such as iron, aluminum, or various stainless steels, or a synthetic resin having conductivity.

A foamed rubber layer 2 provided on the outer periphery of the shaft 1
Can be preferably formed from a foamed rubber composition containing a conductive agent. Specific examples of the rubber component of the foamed rubber composition include chloroprene rubber, styrene-butadiene rubber, ethylene propylene rubber, butyl rubber, acrylonitrile-butadiene rubber, isoprene rubber, silicon rubber, and the like, and monomers of these rubbers. And rubbers obtained by polymerization. A simple substance consisting of any one of these synthetic rubbers and natural rubbers, or a mixture of two or more kinds is used.

Examples of the conductive agent that can be compounded in the rubber composition include:
Examples include particles of carbon black, graphite, metal, and conductive metal oxides (for example, tin oxide and titanium oxide).

Further, as a foaming agent to be added to the foamed rubber composition, dinitrosopentamethylenetetramine (DP
T), azodicarbonamide (ADCA), organic blowing agents such as paratoluenesulfonylhydrazine, azobisisobutyronitrile, 4,4'-oxybisbenzenesulfonylhydrazine, and inorganic blowing agents such as sodium bicarbonate.

The non-foamed rubber layer 3 provided on the outer peripheral surface of the foamed rubber layer 2 can be preferably formed from a non-foamed rubber composition containing a conductive agent. The rubber component used in the non-foamed rubber composition is selected from the various rubbers described above, and may be the same as or different from the rubber component used in the foamed rubber layer 2.

To the rubber composition, besides rubber, conductive agent and foaming agent, various compounding agents and additives such as known vulcanizing agents, vulcanization accelerators, softeners, fillers, processing aids and the like are added. , Can be mixed and used.

In the present invention, the scorch time of the outer non-foamed rubber layer 3 is set shorter than the scorch time of the foamed rubber layer 2. For this reason, it is necessary to prepare a foamed rubber composition and a non-foamed rubber composition in advance, and to examine the behavior in a vulcanization system. As the scorch time, the Mooney scorch time (ML) typically obtained from the Mooney scorch test is used.
(125 ° C.) t5 is used as an index. For the method of measuring Mooney scorch time, see Unvulcanized Rubber Physical Test Method JIS
K 6300 (1974).
A description of this measurement is considered to be part of the present description.

The above ML 125 ° C. represents the Mooney viscosity measured at a test temperature of 125 ° C. using an L-shaped rotor,
On the other hand, t5 is obtained by actually measuring the time (minutes) elapsed from the lowest Mooney viscosity value Vm until the viscosity reading increases by 5M. This value of t5 is set to t1 for the foamed rubber layer 2 and t2 for the non-foamed rubber layer.

Particularly preferable effects are t1, t5 on the basis of t5.
2 is obtained when the relationship of 0.5 ≦ t1−t2 is satisfied. If the difference between t1 and t2 is less than 0.5 minutes, the scorch time of the foamed rubber layer 2 and the non-foamed rubber layer 3 becomes too close,
The expected effect is halved.

Further, the scorch time of the foamed rubber layer 2 is as follows:
When measured as Mooney scorch time (ML180 ° C.) t5, and expressed as t3 (min), it is preferable that t3 ≦ 60. If t3 exceeds 60 minutes, the time required for vulcanization and curing of the foamed rubber layer 2 becomes too long, which is impractical for rubber roll production. Here, ML180 ° C is JIS
Expresses the Mooney viscosity measured at a test temperature of 180 ° C. according to K 6300. It is possible to appropriately adjust the amounts of the vulcanizing agent and the vulcanization accelerator blended in each composition such that t1, t2, and t3 of the foamed rubber composition and the non-foamed rubber composition fall within the above ranges, respectively. Those skilled in the art can easily accomplish this.

The hardness of the foamed rubber layer 2 and the non-foamed rubber layer 3 is as follows:
20 ° to 70 ° for Asker C. Further, regarding the thickness of the foamed rubber layer 2 and the non-foamed rubber layer 3, the inner foamed rubber layer 2 has a thickness of 1 to 50 mm, preferably 2 to 10 mm, and the outer non-foamed rubber layer 3 has a thickness of 0.1 to 3 mm. 0.5
２2 mm.

When the rubber roll 4 of the present invention is used as a charging roll, the amount of the conductive agent to be added to the foamed rubber composition or the non-foamed rubber composition is determined according to the electrical properties required for the roll. However, as a desirable charging roll, the resistance value of the roll is 10 ³ to 10 ⁷ Ω, and the volume resistivity of the rubber layer is 10 ¹ to 10 ¹³ Ωcm.

In such a charging roll, a surface coating layer may be provided on the outer peripheral surface of the outer non-foamed rubber layer by coating. The surface coating layer is formed of a semiconductive thermoplastic resin or the like (for example, urethane) in which a conductive agent is dispersed.

Using the above-mentioned foamed and non-foamed rubber compositions, the rubber roll 4 is produced by various extrusion molding methods, for example, as disclosed in JP-A-7-295331. Among these, a particularly preferable extrusion molding method uses a crosshead extruder 20 capable of co-extrusion to form a foamed rubber composition for forming an inner foamed rubber layer 2 and an outer non-foamed rubber layer 3. This is a method of simultaneously extruding a non-foamed rubber composition and obtaining a continuous cylindrical laminate represented by 21 as shown in FIG.

In FIG. 2, reference numeral 22 denotes a shaft cut to a predetermined length, which is conveyed in the extrusion direction together with the co-extrusion of the rubber composition. After obtaining the laminated body 21 in which the two rubber layers are formed on the outer periphery of the shaft body 22, the gripping shaft grasps the cut boundary of the shaft body 22 and cuts the rubber layer according to the length of the shaft body 22. As a result, a molded body having a desired length including the shaft body is obtained. Such a molded body is loaded into a mold having a cylindrical capacity having an appropriate size (considering expansion due to foaming).
FIG. 3 shows an example of such a mold. In the figure, 1 is a shaft, 5 is a mold, 6 is the molded body, and 7 is a flange.
The molded body 6 placed in the mold 5 is vulcanized and foamed by heating to integrate the inner foamed rubber layer 2, the outer non-foamed rubber layer 3, and the shaft 1 into the mold 5. The target rubber roll 4 has a shape along the peripheral surface.

According to the present invention, since the scorch time of the non-foamed rubber layer 3 is set shorter than the scorch time of the foamed rubber layer 2, the non-foamed rubber layer 3 is quickly cured during vulcanization and foaming. Internal pressure generated by foaming of the foamed rubber layer 2,
Can hold air bubbles.

Further, when the non-foamed rubber layer 3 comes into contact with the inner surface of the mold 5, the hardening of the surface proceeds rapidly, and a smooth surface (skin layer) free from surface defects is formed. Therefore,
A rubber roll 4 having a good foaming state and an excellent surface state as a whole can be manufactured.

When the rubber roll 4 is used as a charging roll, the surface of the roll (that is, the outer peripheral surface of the outer non-foamed rubber layer 3) is preferably further coated with a surface coating layer by a conventional method.

The rubber roll of the present invention is optimally applied to a charging member, for example, a charging roll, but can also be used for a transfer roll, a developing roll, and the like used in OA-related equipment.

FIG. 4 is a sectional view of a charging roll as an example of the present invention. In the drawing, 1 denotes a shaft, 10 denotes a foamed rubber layer, 11 denotes a surface coating layer, and 14 denotes a charging roll. .

The foamed rubber layer 10 provided on the outer periphery of the shaft 1
Can be preferably formed from a foamed rubber composition containing a conductive agent. As the rubber component of this foamed rubber composition, various rubber materials already listed for the rubber roll of the present invention can be used. Similarly, as the conductive agent, the foaming agent, other compounding agents and additives, conventionally known ones or specifically described ones can be mentioned.

The expansion ratio of the foamed rubber layer 10 is set to 2.0 or more. This can be achieved by appropriately adjusting the amount of the foaming agent to be blended in the foamed rubber composition. If the expansion ratio is less than 2.0, the charge sound absorption of the foamed rubber layer 10 deteriorates, which is not preferable.

Adjustment is made so that the specific gravity of the foamed rubber layer after foaming becomes 0.5 or more. For this purpose, the foamed rubber composition is made to contain fine particles having a true specific gravity of 4 or more and foamed. Examples of such fine particles include barium sulfate powder and zinc powder.

Fine particles having a particle size of 0.1 to 100 μm, preferably 2.0 to 50 μm are used.
If the particle size exceeds 100 μm, the dispersion in the foamed rubber composition is poor, and after foaming, the dispersion is not uniform, and a sufficient noise reduction effect cannot be obtained. Even if the particle size is less than 0.1 μm, a sufficient sound-absorbing effect cannot be obtained in the same manner, but it is considered that the fine particles are adsorbed by additives other than the rubber material in the foamed rubber composition.

The amount of the fine particles in the foamed rubber composition is 2 to 20 parts by weight (preferably 10 parts by weight) based on 100 parts by weight of the rubber base material. Rolls, etc.) and other compounding agents and additives in the foamed rubber composition are not limited to this range.

The characteristic of the charging roll is that, since the foamed rubber layer of the charging portion contains fine particles having a true specific gravity of 4.0 or more, the weight of the charging member (while maintaining the advantage of using sponge rubber (lowering the spring constant)) is maintained. Mass) can be increased. Thus, as described above, in accordance with equation (1), the natural frequency of the charging member is reduced, and thus the charging noise is reduced.

The charging roll 14, which is an embodiment of the charging member of the present invention, is manufactured, for example, as follows.
That is, the foamed rubber composition is extruded into a tube shape on the outer peripheral surface of the shaft body 1 and then the shaft body 1 is inserted. Next, the charging roll 14 as shown in FIG. 4 can be manufactured by installing the mold in a mold having a cylindrical cavity (for example, FIG. 3), heating, foaming, and vulcanizing.

A surface coating layer 11 may be provided by coating on the outermost layer of the charging roll 14 (that is, on the outer periphery of the foamed rubber layer 10 and the contact surface with the member to be charged). The surface coating layer is formed of a semiconductive thermoplastic resin or the like (for example, urethane) in which a conductive agent is dispersed. Charging roll 14
Is adjusted to be in the semiconductor region (10 ³ to 10 ¹⁰ Ωcm).

Embodiments of the present invention will be further described with reference to Examples and Comparative Examples, but these do not limit the scope of the present invention. All parts are by weight unless otherwise indicated.

(Production Example) Ethylene-propylene-diene terpolymer (EPD)
M: 40 parts of carbon black (SRF class carbon), 80 parts of paraffin oil, 3 parts of zinc oxide, 2 parts of vulcanizing agent (sulfur) per 100 parts of EP65 manufactured by JSR Corporation,
One part of stearic acid was blended and kneaded with an open roll to prepare a master batch (MB). Using this master batch, 278 parts of MB, 3.0 parts of dinitrosopentamethylenetetramine (DPT) as a foaming agent, 3.0 parts of Celton N (manufactured by Sankyo Kasei) as a foaming aid, and a vulcanizing agent (sulfur ) 1.5 parts and 1.5 parts of zinc dimethyldithiocarbamate as a vulcanization accelerator were mixed and kneaded with an open roll to prepare a composition for a foamed rubber layer.

Similarly, master batch (278 parts of MB)
, Various additives were added at the following compounding ratios (Table 1) and kneaded with an open roll to prepare a composition for a non-foamed rubber layer.

[0048]

[Table 1]

The scorch time t5 of each of the composition for a foamed rubber layer (foamed rubber) and the composition for a non-foamed rubber (formulations 1 to 5) was measured in accordance with JIS K 6300 (1974). Table 2 shows the measured values.

[0050]

[Table 2]

Example 1 Extrusion molding was carried out integrally using a two-color extruder with foamed rubber for the inner layer and Formulation 1 for the outer layer. A body (stainless steel round bar with a diameter of 6 mm and a length of 250 mm) is sent out to obtain a molded body composed of an inner layer and an outer layer and a shaft, which is formed into a predetermined length according to the length of the shaft. Cut.

The obtained molded body was loaded into a cylindrical mold, and the mold was heated in an oven at 180 ° C. for 30 minutes to perform foam vulcanization. The expansion ratio was about 3 times.

After vulcanization, the molded product is taken out of the mold,
The rubber roll of the present invention was obtained by leaving it to reach room temperature.

With respect to the rubber roll of this embodiment, the difference between the Mooney scorch time (ML125 ° C.) t5 (ie, t1) of the foamed rubber layer and the Mooney scorch time (ML125 ° C.) t5 (ie, t2) of the non-foamed rubber layer is 3.21.
Minutes.

Example 2 A rubber roll of the present invention was produced in exactly the same manner as in Example 1 except that foam rubber was extruded for the inner layer and Formulation 2 was extruded for the outer layer.

Regarding the rubber roll of the present embodiment, the Mooney scorch time (ML125 ° C.) t5 of the foamed rubber layer and the Mooney scorch time (ML125 ° C.) of the non-foamed rubber layer
The difference in t5 was 1.5 minutes.

Example 3 A rubber roll of the present invention was produced in exactly the same manner as in Example 1, except that foamed rubber was extruded for the inner layer and Formulation 3 was extruded for the outer layer.

Regarding the rubber roll of this example, Mooney Scorch Time (ML125 ° C.) t5 of the foamed rubber layer and Mooney Scorch Time (ML125 ° C.) of the non-foamed rubber layer
The difference in t5 was 0.72 minutes.

Comparative Example 1 A rubber roll was produced in exactly the same manner as in Example 1, except that foam rubber was extruded for the inner layer and Formulation 4 was extruded for the outer layer.

Regarding the rubber roll of the present example, the Mooney scorch time (ML125 ° C.) t5 of the foamed rubber layer is equal to the Mooney scorch time (ML125 ° C.) t5 of the non-foamed rubber layer.
It was shorter.

Comparative Example 2 A rubber roll was produced in exactly the same manner as in Example 1, except that foam rubber was extruded for the inner layer and Formulation 5 was extruded for the outer layer.

Regarding the rubber roll of this example, the Mooney scorch time of the foamed rubber layer is (ML125 ° C.) t5 and the Mooney scorch time of the non-foamed rubber layer is (ML125 ° C) t.
It was shorter than 5.

Evaluation of Roll The surface condition of each of the rubber rolls obtained from the above Examples and Comparative Examples was visually evaluated. Table 3 shows the results.

[0064]

[Table 3]

As is clear from Table 1, the rubber roll of the example had a smooth surface and no defects, while the rubber roll of the comparative example had wrinkles and pinholes on the surface.

Example 4 For 100 parts of EPDM (EP65 manufactured by JSR),
50 parts of carbon black (SRF class carbon), 80 parts of softener (for example, paraffin oil), 5 parts of zinc oxide
Parts, 1.5 parts of a vulcanizing agent (sulfur), 1 part of stearic acid, 3 parts of azodicarbonamide (ADCA) as a foaming agent, 3 parts of Celton NP (manufactured by Sankyo Chemical) as a foaming aid, a vulcanization accelerator 2.5 parts of zinc dimethyldithiocarbamate as
5 parts of calcium oxide was blended as a moisture absorbent and kneaded with an open roll to prepare a composition for a foamed rubber layer. To 100 parts of this preparation, barium sulfate, which is fine particles having a true specific gravity of 4.0 or more, was further added, kneaded, and uniformly dispersed.

This composition was extruded using a die to prepare a cylindrical roll material. This is passed through a shaft (stainless steel round bar of 6 mm in diameter and 250 mm in length), heat-treated (200 ° C., 20 minutes) in a cylindrical mold, foamed and vulcanized, and a conductive foam rubber is applied to the outer periphery of the shaft. A layer was formed to obtain a roll.
The expansion ratio was about 3 times, and the specific gravity of the foamed rubber layer was 0.7.

Thereafter, the mold was cooled to room temperature, the molded roll was taken out, and the roll surface was washed with a solvent. This was further added to a urethane coating solution (Resamine ME-3119 10
0 parts; carbon black ATL8794 40 parts; methyl ethyl ketone 91 parts; dimethylformamide
49 parts) and dried at room temperature after immersion to form a surface coating layer which is a semiconductive thermoplastic resin having a thickness of about 100 μm on the outer peripheral surface of the foamed rubber layer. Obtained.

Comparative Example 3 A charging roll was manufactured in exactly the same manner as in Example 4 without adding barium sulfate to the foamed rubber layer composition obtained in Example 4.

Evaluation of Rolls Each of the charged rolls obtained from the above Examples and Comparative Examples was measured for physical properties and variously evaluated.

In the charging test, the contact charging device on which the charging roll was mounted was set in an anechoic chamber, and the generated charging noise was measured. The measurement conforms to ISO 7779-6, and AC voltage 2.0k
V, frequency 500Hz, DC voltage (-700V)
Was applied to the charging roll.

The evaluation of the image quality was made based on the image quality of the copy obtained after copying 4000 sheets by attaching the charging roll to the actual machine. Table 4 shows the results.

[0073]

[Table 4]

As is clear from Table 4, the charging rolls of the examples maintain low hardness and suppress generation of noise during charging.

[0075]

As described above, the rubber roll of the present invention comprises a foamed rubber layer provided on the outer peripheral surface of a shaft, and a non-foamed rubber layer provided on the outer peripheral surface of the foamed rubber layer. Since the scorch time of the layer is set shorter than the scorch time of the foamed rubber layer, the non-foamed rubber layer forms a skin layer with a constant thickness, maintains the internal pressure during foaming of the foamed rubber layer, and prevents gas escape from the surface. . Thus, wrinkles due to surface shrinkage,
A rubber roll having a smooth surface without surface defects such as pinholes was obtained. Further, when a rubber roll is used as a charging roll, the low hardness of the roll is maintained and the surface characteristics are good, so that image unevenness does not occur during image formation.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a rubber roll of the present invention.

FIG. 2 is a cross-sectional view illustrating a step of manufacturing a rubber roll according to the present invention and illustrating the formation of a laminate by co-extrusion.

FIG. 3 is a view showing another step of manufacturing a rubber roll according to the present invention, and is a cross-sectional view for explaining a case where a laminate is foamed and vulcanized in a cylindrical mold.

FIG. 4 is a sectional view of a charging roll as an example of the present invention.

[Explanation of symbols]

 1, 22 shaft body 2, 10 foamed rubber layer 3 non-foamed rubber layer 4 rubber roll 11 surface coating layer 14 charging roll 20 extruder 21 laminate

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-29521 (JP, A) JP-A-3-203613 (JP, A) JP-A-5-24134 (JP, A) JP-A-6-205 58324 (JP, A) JP-A-6-175470 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 35/00-35/18 B29C 47/00-47/96

Claims (1)

(57) [Claims] 1. A method for producing a rubber roll, comprising: providing a foamed rubber layer on the outer peripheral surface of a shaft body; and further providing a non-foamed rubber layer on the outer peripheral surface of the foamed rubber layer. A composition for forming a non-foamed rubber layer, wherein the scorch time of the composition for forming a non-foamed rubber layer is shorter than the scorch time of the composition for forming a foamed rubber layer, by a separate extruder, on the outer peripheral surface of the shaft. Simultaneously and integrally extruded to form a laminate, the laminate is placed in a mold having a circular cross section having an inner diameter larger than the outer diameter and substantially equal to the desired outer diameter of the rubber roll, and then heated. A method for producing a rubber roll, wherein foaming and vulcanization of a laminate are simultaneously performed.