JP2010002628A - Transfer member and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure good transfer properties even in a low-temperature and low-humidity environment by confining the voltage dependence of the electric resistance of a transfer member to 0.13-0.42 and the pressing force dependence of the electric resistance of the transfer member on compression to 0.30-1.35 (logΩ/mm), so that a high-quality image can be formed. <P>SOLUTION: There is provided a transfer member for transferring a toner image formed on a surface of an image carrier to a transfer material 21. The transfer member includes a metallic cylinder and elastomeric conductive foamed rubber, the voltage dependence of the electric resistance of the transfer member is 0.13-0.42, and the pressing force dependence of the electric resistance of the transfer member on compression is 0.30-1.35 (logΩ/mm). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a transfer member and an image forming apparatus.

Conventionally, in an image forming apparatus such as a printer, a transfer roller is used to transfer a toner image formed on a photosensitive drum onto a recording sheet. The electrical resistance increases by 1 to 3 digits as the applied voltage increases so that stable transfer characteristics can be obtained without being affected by environmental fluctuations such as temperature and humidity around the image forming apparatus. A transfer roller having a conductive rubber having a decreasing characteristic has been proposed (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 7-248669

  However, if a transfer roller having a large voltage dependency is used like the conventional transfer roller, the leakage current to the outer side of the sheet tends to increase. For this reason, there has been a problem that blurring occurs when printing on a postcard or the like which is a recording paper having a narrow width and high resistance in a low temperature and low humidity environment.

  The present invention solves the above-mentioned conventional problems, sets the voltage dependency of the electrical resistance value of the transfer member to 0.13 to 0.42, and sets the pressure dependency of the electrical resistance value of the transfer member to 0.30. By setting the [log Ω / mm] to 1.35 [log Ω / mm], a transfer member and an image capable of obtaining good transfer characteristics even in a low-temperature and low-humidity environment and forming a high-quality image. An object is to provide a forming apparatus.

  Therefore, the transfer member of the present invention is a transfer member for transferring a toner image formed on the surface of the image carrier onto a transfer material, and the transfer member is a core metal and an elastic conductive material. The voltage dependency of the electrical resistance value of the transfer member is 0.13 to 0.42, and the pressure dependency of the electrical resistance value of the transfer member on the compression is 0.30 [1 Ω / mm]. It is 1.35 [1 Ω / mm] or less.

  According to the present invention, the voltage dependence of the electrical resistance value of the transfer member is 0.13 to 0.42, and the pressure dependence of the electrical resistance value on compression is 0.30 [log Ω / mm] or more and 1.35. [Log Ω / mm] or less. Thereby, good transfer characteristics can be obtained even in a low temperature and low humidity environment, and a high quality image can be formed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram showing a configuration of a main part of the image forming apparatus according to the first embodiment of the present invention.

  In the figure, reference numeral 10 denotes an image drum unit as an image forming unit of the image forming apparatus in the present embodiment. The image forming apparatus is, for example, a printer, a facsimile machine, a copying machine, a multifunction machine having various functions, or the like, but may be of any kind. The image forming apparatus may be a color printer that performs color printing by arranging image drum units 10 that form images of respective colors in a multi-stage manner. Here, for convenience of explanation, a single image is used. A case where the drum unit 10 is a monochrome printer that performs monochrome (for example, black) printing will be described.

  In this case, the image drum unit 10 includes a drum-type photosensitive drum 11 as an image carrier. Around the photosensitive drum 11, a charging roller 13 for charging the surface of the photosensitive drum 11 and an LED (Light) for forming an electrostatic latent image on the surface of the uniformly charged photosensitive drum 11 are provided. Emitting Diode (Light Emitting Diode) Light Source 18, Developing Electrostatic Latent Image Formed on Surface of Photosensitive Drum 11, Developing Roller 14 for Adhering Toner as a Toner as a Toner Image, Toner on Photosensitive Drum 11 A transfer roller 12 as a transfer member for transferring an image onto a transfer material 21 such as a recording paper or a postcard, and a cleaning blade 16 for removing toner remaining on the photosensitive drum 11 are provided. Yes. Reference numeral 17 denotes a toner cartridge for containing toner, and reference numeral 15 denotes a supply roller for supplying toner to the developing roller 14.

  Reference numeral 19 denotes a fixing unit as a fixing device for fixing the toner image transferred onto the transfer material 21 to the transfer material 21 by heat and pressure. The fixing unit 19 includes a fixing roller 19a having a heat source (not shown) therein, and a pressure roller 19b pressed against the fixing roller 19a by a biasing member (not shown). Reference numeral 22 denotes a discharge tray on which the transfer material 21 on which the toner is fixed and discharged outside the apparatus is placed.

  Next, the configuration of the transfer roller 12 will be described in detail.

  FIG. 2 is a schematic view of the transfer roller according to the first embodiment of the present invention.

  As shown in the figure, the transfer roller 12 has a cylindrical cored bar 12a made of a conductive metal, and a rubber layer 12b formed around the cored bar 12a. This is a conductive roller whose electric conductivity is adjusted.

  The rubber layer 12b is made of conductive foam rubber having elasticity. Specifically, silicone rubber was used as the rubber, and as described below, the rubber was mixed with a vulcanizing agent, a foaming agent, a filling agent, a conductivity imparting agent, etc., and vulcanized and foam-molded. Is.

  First, as the rubber, dimethyl silicone raw rubber, methyl vinyl silicone raw rubber, methylphenyl silicone raw rubber and the like can be used as the organopolysiloxane polymer. Also, vinyl group-containing silicone raw rubber may be used.

  Next, as vulcanizing agents, organic peroxide crosslinking agents such as benzoyl peroxide, bis 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-bis ( t-Butylperoxy) hexane or the like can be used. In addition, a hydrodieneorganosiloxane that is an addition-type crosslinking agent can also be used. In this case, a platinum compound catalyst is added to form a combination with a vinyl group-containing silicone raw rubber.

  Next, as the foaming agent, a chemical foaming agent such as azobisisobutyronitrile (AIBN) or azodicarbonamide (ADCA) can be used.

  Next, as filler, silica, calcium carbonate, quartz powder, zirconium silicate, clay (aluminum silicate), talc (hydrous magnesium silicate), titanium oxide, zinc oxide, magnesium oxide, alumina (aluminum oxide), Chromium oxide, iron oxide, aluminum sulfate, barium sulfate, mica (mica powder), graphite and the like can be used.

Next, as the conductivity imparting agent, carbon black, graphite, silver, copper, nickel and other metal powders, conductive zinc white, conductive calcium carbonate, carbon fiber and other electronic conductivity imparting agents and ion conductivity imparting agents Can be used. The ion conductivity-imparting agent may be a cationic substance, and may be an electrolyte such as H ⁺ , Li ⁺ , Na ⁺ , K ⁺ , Ag ⁺ , Zn ₂ ⁺ . Examples of the inorganic electrolyte include LiBF ₄ , LiAlCl ₄ , NaBr, NaI, KI, and AgNO _3. Examples of the organic electrolyte include primary, secondary, tertiary amine salts, quaternary ammonium salts, and quaternary ammonium salts. Quaternary phosphonium salts and the like can be mentioned. Examples of the solvent for dissolving them include polyethers, polyesters, and polyimines.

  The transfer roller 12 can flexibly abut against the photosensitive drum 11 and the toner, which is a contact object, by foaming the rubber layer 12b, and can obtain a large contact width. Thus, it is possible to widen a region having a good transfer electric field. Further, it is possible to obtain a mechanical toner transfer effect with an appropriate pressing force.

  Next, an equivalent circuit model of the photosensitive drum 11, the transfer roller 12, and the transfer material 21 included in the image forming apparatus will be described.

  3 is a diagram showing an equivalent circuit model in the comparative example, FIG. 4 is a diagram showing the relationship between the current and voltage of the transfer roller in the comparative example, and FIG. 5 is a diagram showing the equivalent circuit model in the first embodiment of the present invention. It is.

  Here, an equivalent circuit model of the photosensitive drum 11, the transfer roller 12, and the transfer material 21 included in the image forming apparatus according to the present embodiment will be described using the image forming apparatus described in Patent Document 1 as a comparative example. In the comparative example, it is assumed that the photosensitive drum is 111, the transfer roller is 112, its core metal and rubber layers are 112a and 112b, and the transfer material is 121.

  The transfer roller 112 in the comparative example uses conductive rubber having a characteristic that the electrical resistance decreases by 1 to 3 digits as the applied voltage increases. In this case, since the electric conductivity greatly varies with respect to the applied voltage, the voltage dependency of the electric resistance is large.

  The voltage dependency can be increased when carbon black is used as the conductive carrier. As shown in FIG. 4, in the case of the transfer roller 112 having a large voltage dependency, a current tends to flow more with respect to a high voltage. Therefore, even if the conductivity of rubber decreases due to durable use, the transfer roller 112 It is an advantage that a desired transfer current can be generated without increasing the burden of the above. On the other hand, the drawback is that a fading or dusting occurs on a transfer material 121 having a narrow width such as a postcard.

  Here, an equivalent circuit model as shown in FIG. 3 is assumed.

  Since the resistance value in the sheet passing portion is larger by the resistance value Rs of the transfer material 121 than in the sheet passing outer portion, the current density in the sheet passing outer portion is large. Further, in the paper passing portion, the power supply voltage Vall is distributed to the voltage Vp consumed by the transfer material 121 and the voltage Vt1 consumed by the transfer roller 112. The relationship of Vt1 <Vt2 (= Vb) is established with respect to Vt2. From the voltage dependency shown in FIG. 4, since Rt (Vt1)> Rt (Vt2), the resistance value {Rs + Rt1 (Vt1)} of the sheet passing portion is larger than Rt2 (Vt2).

  That is, because the voltage dependency of the transfer roller 112 is large, a leakage current to the outer side of the sheet passing is promoted, and the electric field for moving the toner is weakened. This is because, when the voltage dependency is large, if the transfer material 121 exists between the transfer roller 112 and the photosensitive drum 111, the difference in current flowing between the region where the transfer material 121 exists and the region where the transfer material 121 does not exist is large. It is to become. That is, a large amount of current flows in a region where the transfer material 121 does not exist, and no current flows in a region where the transfer material 121 having a high resistance exists. This is because the current escapes to the place where the current easily flows. That is, the transfer material 121 does not exist, the current escapes to the area where the transfer roller 112 and the photosensitive drum 111 are in direct contact, and the current does not flow in the area where the transfer material 121 exists. Therefore, the electric field becomes weak in the region where the transfer material 121 exists. In particular, when a postcard or the like, which is a narrow high-resistance transfer material 121, is printed in a low-temperature and low-humidity environment where the electrical resistance of the transfer material 121 increases, the transfer blur becomes worse.

  As a countermeasure against this, there is a method of adding an ion conductivity imparting agent having almost no voltage dependency to the rubber. However, as shown in FIG. 4, since the resistance value fluctuations in the environment are severe and the resistance is increased in a low temperature and low humidity environment, a large capacity power source is required to generate an optimum transfer current, which is a problem.

  As another countermeasure, there is a method in which the elastic portion of the transfer roller 112 is divided into two layers and a high resistance material is used for the surface layer. If the resistivity of the surface layer is set to the same level as that of the transfer material 121, the region where the resistance becomes high while suppressing the leakage current is partial, so that the load on the power source can be slightly suppressed. However, the configuration of the transfer roller 112 is complicated, which makes it difficult to manufacture.

  On the other hand, the transfer roller 12 according to the present embodiment has a simple configuration and uniform electrical resistance (ion conduction), and at the same time, an appropriate pressure dependency in the resistance increasing direction against the compression of the electrical resistance ( This is a transfer roller 12 having a hybrid characteristic having an electron conduction) and an appropriate voltage dependency (electron conduction).

  In the present embodiment, as shown in FIG. 5, the electrical resistance value in the vicinity of the surface of the rubber layer 12 b is approximately equal to the electrical resistance of the transfer material 21 by effectively utilizing the pressure dependency of the carbon black electron conduction. Until the desired characteristics were obtained. Since the transfer material 21 is thin, there is no problem regarding an increase in resistance due to compression. In addition, the optimum range for voltage dependence was examined.

  Next, an experimental example of the actually produced transfer roller 12 will be described.

  First, Experimental Example 1 will be described.

In Experimental Example 1, TSE260-5U (trade name, manufactured by Toshiba Silicone Co., Ltd.) 100 [wt%] as a silicone raw rubber, and 10 [wt] of LiClO ₄ (lithium perchlorate) in polyalkylene glycol as an ionic conductivity imparting agent. %] 5 [wt%] of the dissolved ion conductive composition, MT99 (Medium Thermal Carbon Black, medium-sized pyrolytic carbon black), N991 (product name, manufactured by Cancarb Inc.), 55 [wt%], C-25A / C-25B (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) 0.2 [wt%] / 3 [wt%] as an additional crosslinking agent, and ADCA-P (Shin-Etsu Chemical Co., Ltd.) as a foaming agent 2.3 [wt%] (manufactured by the company, product name) was added, and kneading was performed until it was uniformly dispersed with an open roll.

  The obtained silicone rubber semiconductive composition was injected by transfer molding into a pipe-shaped mold in which a core metal 12a coated with a primer was set. Then, using a hot air oven, vulcanization was performed at 150 [° C.] for 30 minutes, and after cooling, the pipe mold was removed to obtain a primary forming roller.

  Then, using a hot air oven, vulcanization was performed at 200 [° C.] for 2 hours and 230 [° C.] for 4 hours to obtain a secondary forming roller. After 24 hours from cooling, the transfer roller 12 was produced by grinding with a cylindrical grinder.

The MT carbon is carbon black having a low structure, a large particle size and a small specific surface area. The manufacturer's published value of N911 is DBP oil absorption 44 [cm ³ ] / 100 [g], average particle diameter 270 [nm]. The nitrogen adsorption specific surface area is 7 to 12 [m ² / g]. In addition, the electrical conductivity is small because of the low structure and large particle size.

  Next, Experimental Example 2 will be described.

  In Experimental Example 2, 60 wt% MT carbon was added. Otherwise, a transfer roller 12 was prepared in the same manner as in Experimental Example 1.

  Next, Experimental Example 3 will be described.

  In Experimental Example 3, 65 wt% MT carbon was added. Otherwise, a transfer roller 12 was prepared in the same manner as in Experimental Example 1.

  Next, Experimental Example 4 will be described.

  In Experimental Example 4, 70 wt% MT carbon was added. Otherwise, a transfer roller 12 was prepared in the same manner as in Experimental Example 1.

  Next, Experimental Example 5 will be described.

  In Experimental Example 5, 75 [wt%] MT carbon was added. Otherwise, a transfer roller 12 was prepared in the same manner as in Experimental Example 1.

  For comparison with Experimental Examples 1 to 5, a transfer roller 12 having typical electronic conductivity was produced. First, Comparative Example 1 will be described.

  In Comparative Example 1, MT carbon in Experimental Example 1 was changed to Asahi Thermal # 80 (trade name, manufactured by Asahi Carbon Co., Ltd.), and 20 wt% was added.

Otherwise, the transfer roller 12 was produced in the same manner as in Experimental Example 1. Asahi Thermal # 80 has a DBP oil absorption of 113 [cm ³ ] / 100 [g], an average particle diameter of 22 [nm], and a nitrogen adsorption specific surface area of 115 [m ² / g] as disclosed by the manufacturer.

  Next, Comparative Examples 2 and 3 will be described.

  In Comparative Examples 2 and 3, for comparison with Experimental Examples 1 to 5, a transfer roller 12 was prepared by vulcanizing and foaming a rubber obtained by mixing acrylonitrile butadiene rubber having typical ionic conductivity and epichlorohydrin rubber.

  In a rubber composition comprising 70% by weight of acrylonitrile butadiene rubber and 30% by weight of epichlorohydrin rubber, 3% by weight of hydrotalcite compound as an acid acceptor and 3% by weight of azodicarbonamide as a foaming agent. %] And 3 [wt%] of benzenesulfonylhydrazite, 1 [wt%] of powdered sulfur as a vulcanizing agent, 1 [wt%] of trimethylthiourea as a vulcanizing accelerator, and 1 [wt] of enylene thiourea wt%] was added, and the mixture was kneaded at 100 [° C.] for 10 minutes by a closed kneader.

  The rubber mixture obtained by removing the ribbon from the closed kneader was put into a single-screw extruder whose temperature was adjusted to 40 [° C.] and extruded into a hollow tube shape. The hollow tube-shaped rubber was cut into an appropriate length to form a preformed tube. The preformed tube was put into a pressurized steam vulcanization can and subjected to primary vulcanization at 160 [° C.] for 60 minutes.

  At this time, the chemical foaming agent gasified and foamed, and the rubber component was also crosslinked. A cored bar (outer diameter 6 [mm]) made of a metal shaft coated with a hot melt adhesive was press-inserted into the hollow portion of the cylindrical vulcanized foam tube to obtain a primary forming roller.

  The primary molding roller is placed in a hot air oven, subjected to secondary vulcanization at 160 [° C.] for 1 hour, the cored bar and the conductive foam rubber are bonded and integrated, and then cooled and 24 hours have passed. Then, the transfer roller 12 was manufactured by grinding with a cylindrical grinder.

  Next, measurement of characteristic values of the experimental examples and comparative examples and image evaluation of the image forming apparatus using the experimental examples and comparative examples will be described.

  FIG. 6 is a diagram showing a method for measuring the resistance value of the transfer roller in the first embodiment of the present invention, FIG. 7 is a diagram showing the definition of the surface foam cell diameter in the first embodiment of the present invention, and FIG. FIG. 9 is a diagram showing a case where foam cells in the first embodiment of the present invention are connected on the surface, and FIG. 9 fixes the distance between the axes of the photosensitive drum and the transfer roller in the first embodiment of the present invention. It is a figure which shows the state which carried out.

  First, an electrical resistance value as a characteristic value was measured in a low temperature and low humidity environment (L / L environment) having a temperature of 10 ° C. and a humidity of 20%. The electric resistance value was measured by a method as shown in FIG. That is, it is an average value of current values when a DC voltage is applied while rotating the metal 35 and the transfer roller 12 in a stable environment with the transfer roller 12 pressed against the drum-shaped metal 35. By adjusting the inter-axis distance between the rotating shaft of the drum-shaped metal 35 and the rotating shaft of the transfer roller 12, the pressure dependency can be obtained by the change in the electrical resistance to the pressing at that time. In addition, 32 is a constant pressure power supply and 33 is an ammeter. Further, the pressing amount of the transfer roller 12 is appropriately adjusted.

  Next, electrical resistance circumferential unevenness was measured in an L / L environment at a temperature of 10 ° C. and a humidity of 20%. The electrical resistance circumferential unevenness is a ratio between the maximum value and the minimum value of the electrical resistance within one circumference of the transfer roller 12.

  Next, the product hardness was measured. The measured value of the product hardness is a value obtained by pressing the pressure surface of the asker C hardness meter against the side surface of the transfer roller 12 with a load of 1000 [gf]. The pressure surface is stopped by a roller so as not to be bitten.

  Next, the average surface foam cell diameter was measured. The measured value of the average surface foam cell diameter is obtained by averaging the foam cell diameter on the surface of the rubber layer 12b made of elastic foam rubber, that is, on the side surface of the cylindrical rubber layer 12b.

In this case, the foam cell diameter means the diameter of the foam cell 31 on the curved surface where the surface of the transfer roller 12 and the contour of the metal 35 intersect as shown in FIG. 7, and is defined by the following equation (1). The
Foamed cell diameter = √ (A × B) / 2 Formula (1)
A is the short diameter [μm] of the foam cell 31, and B is the long diameter [μm] of the foam cell 31.

  Further, as shown in FIG. 8 (a), when a plurality of foam cells 31 are connected like open cells, the contour of each foam cell 31 is assumed as shown in FIG. 8 (b). And each foam cell 31 is grasped | ascertained as an independent cell, and the diameter of the foam cell 31 is calculated | required.

  Next, the voltage dependence of electrical resistance was measured. The measured value of the voltage dependence of the electrical resistance is obtained by subtracting from 1 the ratio of the electrical resistance values R (Vu) and R (Vl) at a voltage of ± 500 [V] from the voltage Vtr when the specified current value is generated. Is. The case of generating a specified current value is a case of generating a current of 15 [μA] in an L / L environment at a temperature of 10 [° C.] and a humidity of 20 [%].

Here, R (Vu) is a current resistance value when Vu = Vt + 500 [V], and R (Vl) is a current resistance value when Vl = Vt−500 [V]. And
Voltage dependence of electrical resistance = 1- {R (Vu) / R (Vl)}
It is.

In addition, in order to obtain the pressure dependency, first, the resistance values Ra and Rb are obtained at predetermined push amounts a [mm] and b [mm]. And the logarithm of resistance value Ra and Rb is taken, and it is set as La and Lb, respectively. Then
Press dependency = (Lb−La) / (b−a)
It is. In the present embodiment, the pressure dependency was obtained under the conditions of the pushing amount a = 0.20 [mm] and b = 0.30 [mm].

  Next, image evaluation was performed. The image evaluation was performed using an optical LED type electrophotographic printer having a resolution of 600 [DPI]. In this case, as shown in FIG. 9, the distance between the axes of the photosensitive drum 11 and the transfer roller 12 was fixed, and the overlap amount, that is, the push-in amount was fixed at 0.25 [mm]. Then, in an L / L environment with a temperature of 10 ° C. and a humidity of 20%, a postcard was used as the transfer material 21, and 100% density, gray scale, and character pattern printing were performed to evaluate the image quality. .

  The 100% density pattern has a printing density of 100%, the gray scale pattern has a printing density of 25%, and the character pattern has a printing density of 5%. That is, the 100% density pattern is a solid pattern in which an image is formed over the entire image formable area. The gray scale pattern is a 2-by-2 image with a resolution of 600 [DPI], that is, when forming dots, out of 16 dots for 4 dots vertically and 4 dots horizontally, 2 dots vertically and 2 dots horizontally It forms a dot of 4 minutes. Furthermore, the character pattern is a character pattern and is a pattern corresponding to a density of 5% in the image formable area.

  The reason why the postcard is used as the transfer material 21 is that the size of the transfer material 21 having the strictest condition is the postcard size with respect to the problem of leakage current. Leakage current is more likely to occur as the area of the transfer material 21 is narrower, that is, the area where the photosensitive drum 11 and the transfer roller 12 are in direct contact with each other is larger. Therefore, if a good result can be obtained with the postcard-size transfer material 21, the problem of leakage current does not occur even in the case of the transfer material 21 with a wider width.

  Next, the measurement result of the characteristic value and the result of image evaluation will be described.

  FIG. 10 is a diagram showing the relationship between the amount of carbon black blended and the voltage-current curve in the first embodiment of the present invention, and FIG. 11 is a characteristic value measurement result and image in the first embodiment of the present invention. It is a figure which shows the result of evaluation.

  FIG. 10 shows a voltage-current curve of the electric resistance value in the L / L environment. Further, FIG. 11 shows the voltage dependence of the electric resistance value in the L / L environment, the electric resistance unevenness in the medium temperature / humidity environment (N / N environment) of the temperature 20 [° C.] and the humidity 50 [%]. And the pressure dependency of the electrical resistance value in the L / L environment are shown.

  In addition, the definition of good (◯) or not (×) in the evaluation of the image quality in the experimental example and the comparative example is “◯: no blurring or dusting” and “×: blurring or dusting”. . Here, “fading” is a state in which the toner image is not transferred to the portion that should be printed and the surface of the transfer material 21 is exposed (peeled). “Dust” is a state in which the toner scattered by the transfer adheres to the background portion of the transfer material 21 that should not be printed.

  First, Experimental Example 1 will be described.

  In Experimental Example 1, in the L / L environment, good image quality could be obtained with respect to the postcard 100% density, gray scale, and character pattern printing. Since the average value of the pressure dependency is as large as 1.35, the vicinity of the surface of the transfer roller 12 is close to the resistivity of the postcard, and the voltage dependency is slightly large as 0.42.

  Next, Experimental Example 2 will be described.

  In Experimental Example 2, in the L / L environment, good image quality could be obtained for the 100% density of the postcard, the gray scale, and the character pattern printing. The voltage dependency was 0.33, and the average value of the pressure dependency was 1.01.

  Next, Experimental Example 3 will be described.

  In Experimental Example 3, in the L / L environment, good image quality could be obtained with respect to the postcard 100% density, gray scale, and character pattern printing. The voltage dependency was 0.22, and the average value of the pressure dependency was 0.97.

  Next, Experimental Example 4 will be described.

  In Experimental Example 4, in the L / L environment, good image quality could be obtained for the 100% density of the postcard, the gray scale, and the character pattern printing. The voltage dependency was 0.13, and the average value of the pressure dependency was 0.30.

  Next, Experimental Example 5 will be described.

  In Experimental Example 5, in the L / L environment, good image quality could be obtained with respect to the postcard 100% density, gray scale, and character pattern printing. The voltage dependency was 0.16, and the average value of the pressure dependency was 0.73.

  Next, Comparative Example 1 will be described.

  In Comparative Example 1, since the voltage dependency was as large as 0.76, the leakage current to the outside of the sheet was increased, and a good image quality could not be obtained for the postcard.

  Next, Comparative Example 2 will be described.

  In Comparative Example 2, in the L / L environment, good image quality could be obtained for the 100% density of the postcard, the gray scale, and the character pattern printing. However, the necessary voltage for transfer is 3750 [V], and the burden on the transfer power source capacity is large.

  Next, Comparative Example 3 will be described.

  In Comparative Example 3, good image quality could not be obtained for the 100% density of the postcard, the gray scale, and the character pattern printing in the L / L environment. That is, since the voltage dependency and the pressure dependency were high, the leakage voltage to the outer side of the paper passage increased, and a good image quality could not be obtained for the postcard.

  Thus, in the present embodiment, the voltage dependency of the electrical resistance value in the L / L environment is 0.13 to 0.42 when the blending amount of carbon black is 55 wt% to 75 wt%. In addition, the transfer roller 12 having a pressure dependency of 0.30 to 1.35 [log Ω / mm] could be obtained. Due to this characteristic, the postcard in the L / L environment could obtain a good image quality.

  More desirably, the voltage dependency of the electrical resistance value in the L / L environment is 0.13 to 0.33, and the pressure dependency is 0.30 to 1.01 [log Ω / mm]. High quality printing can be obtained.

  In the present embodiment, the transfer roller 12 in which the blending amount of carbon black is more than 75 [wt%] was not evaluated. This is because, when the blending amount of carbon black is more than 75 [wt%], the variation in hardness occurs. For this reason, the electric resistance circumferential unevenness increases, and the shading derived from the pitch of the transfer roller 12 during printing. This is because unevenness occurs.

  Next, a second embodiment of the present invention will be described. In addition, about the thing which has the same structure as 1st Embodiment, the description is abbreviate | omitted by providing the same code | symbol. The description of the same operation and the same effect as those of the first embodiment is also omitted.

  FIG. 12 is a diagram showing changes in voltage-current characteristics due to endurance in the second embodiment of the present invention, and FIG. 13 is a diagram showing changes in voltage-current characteristics after endurance in the second embodiment of the present invention. It is.

  The transfer control of the printer used for image evaluation in the first embodiment includes processes such as detection of a roller resistance value, determination of a transfer voltage, and application of a print voltage. In the process of detecting the roller resistance value, the endurance change and environmental fluctuation of the electric resistance value of the transfer roller 12 are monitored. Then, based on a printing voltage table stored in advance with respect to the detected roller resistance value, a printing voltage for supplying an optimum transfer current is determined. Further, a printing voltage is applied in accordance with the transfer of the transfer material 21.

  The detection voltage is a constant voltage and is always 1500 [V]. The reason is that, in a high temperature and high humidity environment (H / H environment) with a temperature of 28 ° C. and a humidity of 80%, even if the roller resistance value is small and the voltage consumed by the transfer roller 12 is small, the photosensitive drum. This is because an excessive voltage is supplied to 11 and no transfer shock occurs. The transfer voltage in printing is adjusted so that the transfer current is 15 [μA].

  Using a printer similar to the first embodiment on which the transfer roller 12 of Experimental Example 3 is mounted, 100% density pattern printing of a postcard is performed in an L / L environment. However, when 1000 sheets were printed, a detection failure of the resistance value of the transfer roller 12 occurred. And when the voltage-current characteristic was confirmed about the transfer roller 12 of Experimental example 3, it came to be shown by FIG. The endurance roller as the transfer roller 12 that printed 1000 sheets has a small rise in current at a low voltage, and the generated current with respect to an applied voltage of 1500 [V] is weak, so that the detection sensitivity of the apparatus is insufficient. .

  In the transfer mechanism, the transfer current flows through the voids of the foam cells on the surface of the transfer roller 12 according to Paschen's law. The ozone generated by the discharge deteriorates the surface of the transfer roller 12. The transfer roller 12 of Experimental Example 3 had an average surface foam cell diameter as large as 400 [μm], and a high voltage was required to generate discharge in the surface cell, and the degree of progress of deterioration became faster.

  Further, as shown in FIG. 13, the durability roller is expressed by separate voltage-current curves with a boundary of about 1800 [V] / 3 [μA]. If the detection process can be performed on the higher voltage side than the boundary, transfer control can be performed.

  Therefore, in this embodiment, the transfer control is performed as follows as Experimental Example 6.

  In Experimental Example 6, constant current control was performed in the detection process, and the constant current was always controlled to 6 [μA]. Since constant current control is performed, fluctuations in the detection applied voltage due to environmental fluctuations and endurance changes are mostly due to changes in the electrical resistance value of the transfer roller 12, and an excessive voltage is applied to the photosensitive drum 11 to cause a transfer shock. There is no worry of it occurring.

  The transfer voltage was determined according to a transfer control table based on a voltage-current curve stored on the high voltage side based on the detected current 6 [μA] and the voltage value at that time. In this case, an optimum transfer control table value was applied in accordance with the transfer of the transfer material 21.

  Thus, in the present embodiment, a voltage of 2300 [V] is applied at a detection current of 6 [μA]. Then, according to the transfer control table on the high voltage side of the endurance roller, 3200 [V] was applied as a transfer voltage to generate an optimal transfer current of 15 [μA].

  Thereby, when the transfer roller 12 of Experimental Examples 1 to 4 was used, good image quality could be obtained even in durability.

  Next, a third embodiment of the present invention will be described. In addition, about the thing which has the same structure as 1st and 2nd embodiment, the description is abbreviate | omitted by providing the same code | symbol. Also, the description of the same operations and effects as those of the first and second embodiments is omitted.

  FIG. 14 is a diagram showing the measurement result of the characteristic value and the result of image evaluation in the third embodiment of the present invention.

  As described in the second embodiment, the average surface foam cell diameter of the transfer roller 12 of Experimental Example 3 was 400 [μm]. Then, using the printer on which the transfer roller 12 of Experimental Example 3 is mounted, transfer control is performed as in Experimental Example 6, and after a durability test for printing 5000 sheets, in the L / L environment, 100% of the postcard When density pattern printing was performed, transfer omission occurred.

  In the transfer mechanism, ozone generated by discharge according to Paschen's law deteriorates the surface of the transfer roller 12, and the durability of the transfer roller 12 increases. A desired current can be obtained by applying a high voltage, but the discharge becomes more intense.

  Therefore, in the present embodiment, the following transfer roller 12 was manufactured as Experimental Examples 7 and 8.

  First, Experimental Example 7 will be described.

  In Experimental Example 7, C-23N / C-3 (manufactured by Shin-Etsu Chemical Co., Ltd., trade name) as an organic peroxide cross-linking agent was 1 wt% / 3 wt%, and KE-P- was used as a foaming agent. 13 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) was added in an amount of 2 wt%. Otherwise, a transfer roller 12 was produced in the same manner as in Experimental Example 3.

  Next, Experimental Example 8 will be described.

  In Experimental Example 8, C-25A / C-25B (manufactured by Shin-Etsu Chemical Co., Ltd., trade name) as an addition crosslinking agent is 0.5 wt% / 2 wt%, and KE-P-26 is used as a foaming agent. 3 [wt%] (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) was added. Otherwise, a transfer roller 12 was produced in the same manner as in Experimental Example 3.

  Then, using the printer equipped with the transfer roller 12 of Experimental Examples 7 and 8, printing was performed as follows.

  First, in Experimental Example 7, as shown in FIG. 14, the average surface foamed cell diameter of the transfer roller 12 was 360 [μm]. After an endurance test for printing 5000 sheets, it was possible to obtain a good image quality by printing a 100% density of a postcard and printing a gray scale pattern in an L / L environment.

  Next, in Experimental Example 8, as shown in FIG. 14, the average surface foamed cell diameter of the transfer roller 12 was 130 [μm]. After an endurance test for printing 5000 sheets, it was possible to obtain a good image quality by printing a 100% density of a postcard and printing a gray scale pattern in an L / L environment.

  Theoretically, a smaller cell diameter is advantageous, but Experimental Example 8 became a limit in molding.

  As described above, in the present embodiment, when the cell diameter is 130 [μm] to 360 [μm], good image quality can be obtained.

  Next, a fourth embodiment of the present invention will be described. In addition, about the thing which has the same structure as the 1st-3rd embodiment, the description is abbreviate | omitted by providing the same code | symbol. Explanation of the same operations and effects as those of the first to third embodiments is also omitted.

  FIG. 15 is a diagram showing the measurement results of characteristic values and the results of image evaluation in the fourth embodiment of the present invention.

  As described in the second embodiment, the average surface foam cell diameter of the transfer roller 12 of Experimental Example 3 was 400 [μm]. Then, using the printer on which the transfer roller 12 of Experimental Example 3 is mounted, transfer control is performed as in Experimental Example 6, and after a durability test for printing 5000 sheets, in the L / L environment, 100% of the postcard When density pattern printing was performed, transfer omission occurred. This is because the cell diameter is large and the discharge start voltage according to Paschen's law is high, so that the ozone deterioration proceeds rapidly.

  Therefore, in this embodiment, the following transfer roller 12 was manufactured as Experimental Examples 9 and 10.

  First, Experimental Example 9 will be described.

  In Experimental Example 9, C-23N / C-3 (manufactured by Shin-Etsu Chemical Co., Ltd., trade name) as an organic peroxide crosslinking agent was 1 [wt%] / 3 [wt%], and KE- as a foaming agent 3 [wt%] of P-13 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) was added. Otherwise, the transfer roller 12 was produced in the same manner as in Experimental Example 3.

  Next, Experimental Example 10 will be described.

  In Experimental Example 10, C-24 / C-3 (manufactured by Shin-Etsu Chemical Co., Ltd., trade name) as an organic peroxide crosslinking agent was 1 [wt%] / 3 [wt%], and KE- as a foaming agent 3 [wt%] of P-13 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) was added. Otherwise, the transfer roller 12 was produced in the same manner as in Experimental Example 3.

  Then, using the printer equipped with the transfer roller 12 of Experimental Examples 9 and 10, printing was performed as follows.

  First, in Experimental Example 9, as shown in FIG. 15, the product hardness of the transfer roller 12 was Asker C24 degrees, and the average surface foam cell diameter was 370 μm. After an endurance test for printing 5000 sheets, good image quality could be obtained with 100% density of postcards, gray scale and character pattern printing in an L / L environment. This is because the cell diameter is the same as in Experimental Example 3, but because the rubber has a low hardness, the amount of crushing of the cell becomes large and deterioration can be suppressed.

  Next, in Experimental Example 10, as shown in FIG. 15, the product hardness of the transfer roller 12 was Asker C 19 degrees, and the average surface foam cell diameter was 390 [μm]. Since the rubber has a low hardness, if the indentation amount (indentation amount by the printer: 0.25 [mm]) is set to a fixed value, the cell easily collapses, but the repulsion of the rubber is small, so the pressure on the transfer material 21 is weak. Therefore, the transfer efficiency is not good. In addition, if the indentation load is set to a constant load, the amount of crushing of the cells will be violent and the resistance value will appear very high, so setting the transfer nip sufficiently weak to avoid this phenomenon will reduce the hardness of the rubber. It contradicts and contradicts.

  Further, when the product hardness exceeds asker C 40 degrees as compared with the first embodiment, the variation in electric resistance becomes large, and a good image quality cannot be obtained.

  As described above, in the present embodiment, when the product hardness is 24-40 degrees, good image quality can be obtained.

  Next, a fifth embodiment of the present invention will be described. In addition, about the thing which has the same structure as 1st-4th embodiment, the description is abbreviate | omitted by providing the same code | symbol. Explanation of the same operations and effects as those of the first to fourth embodiments is also omitted.

  FIG. 16 is a first diagram showing a characteristic value measurement result and image evaluation result in the fifth embodiment of the present invention, and FIG. 17 is a characteristic value measurement result and image in the fifth embodiment of the present invention. FIG. 18 is a second diagram showing the results of the evaluation, FIG. 18 is a first diagram showing a voltage-current curve in the fifth embodiment of the present invention, and FIG. 19 is a voltage-current in the fifth embodiment of the present invention. It is a 2nd figure which shows a curve.

  In the printer used for image evaluation, as described in the first embodiment, the pressing amount of the photosensitive drum 11 and the transfer roller 12 is fixed to 0.25 [mm]. However, since the transfer rollers 12 of Experimental Examples 1 to 4 are low-hardness foamed rubber, it was difficult to accurately polish to a predetermined outer diameter.

  Therefore, in the present embodiment, even when the pressing amount of the photosensitive drum 11 and the transfer roller 12 changes due to the variation in the outer diameter of the transfer roller 12, it is possible to print with good image quality. We examined possible conditions. In addition, since the outer diameter dimension of the transfer roller 12 of Experimental Examples 1 to 4 was φ16.4 [mm], in this embodiment, as Experimental Examples 11 and 12, the outer diameter dimension of each prescription is The following different transfer rollers 12 were produced.

  First, Experimental Example 11 will be described.

  In Experimental Example 11, as shown in FIG. 16, the transfer roller 12 having the outer diameter size of φ16.2 [mm] in the prescriptions of Experimental Examples 1 to 4 is set to Experimental Example 1a, Experimental Example 2a, and Experimental Example, respectively. 3a and Experimental Example 4a. Then, using a printer equipped with each transfer roller 12, 100% density of the postcard, gray scale, and character pattern printing were performed in an L / L environment. In the case of Experimental Example 11, the pushing amount was 0.15 [mm].

  Next, Experimental example 12 will be described.

  In Experimental Example 12, as shown in FIG. 17, the transfer roller 12 having the outer diameter dimension φ of 16.7 [mm] in the prescriptions of Experimental Examples 1 to 4 is set to Experimental Example 1b, Experimental Example 2b, and Experimental, respectively. It was set as Example 3b and Experimental example 4b. Then, using a printer equipped with each transfer roller 12, 100% density of the postcard, gray scale, and character pattern printing were performed in an L / L environment. In the case of Experimental Example 12, the pushing amount was 0.4 [mm].

  And it printed using the printer which mounted the transfer roller 12 of Experimental example 1a demonstrated in Experimental example 11, Experimental example 2a, Experimental example 3a, and Experimental example 4a. Thereby, a voltage-current curve as shown in FIG. 18 could be obtained.

  First, in Experimental Example 1a, good image quality could be obtained only by printing a postcard character pattern in an L / L environment. Although good image quality could not be obtained by printing with 100% density and gray scale pattern, it is at a level where there is no problem in practical use. This is because the voltage dependency has become as large as 0.46 although the pressure dependency is large.

  Further, in Experimental Example 2a, good image quality could be obtained by printing the postcard gray scale and character pattern in the L / L environment. This is because the voltage dependency is as large as 0.37. However, there is no problem in practical use.

  Furthermore, in Experimental Example 3a, in the L / L environment, it was possible to obtain a good image quality by printing the postcard with 100% density, gray scale, and character pattern printing.

  Furthermore, in Experimental Example 4a, good image quality could be obtained with 100% density of the postcard, gray scale, and character pattern printing in the L / L environment.

  Similarly, printing was performed using the printer on which the transfer roller 12 of Experimental Example 1b, Experimental Example 2b, Experimental Example 3b, and Experimental Example 4b described in Experimental Example 12 was mounted. As a result, a voltage-current curve as shown in FIG. 19 was obtained.

  In any of Experiment Example 1b, Experiment Example 2b, Experiment Example 3b, and Experiment Example 4b, good image quality can be obtained with 100% density of the postcard, gray scale, and character pattern printing in the L / L environment. It was.

  However, in Experimental Example 4b, when the transfer current is 15 [μA], the resistance value is high until the same applied voltage as that of the ion-conducting transfer roller in Experimental Example 2b is required, and the outer diameter is large. If this is done, the toner cannot be transferred unless a voltage higher than that of the ion conducting roller is applied, and this is the limit at which the object of the present invention can be achieved.

  As described above, in the present embodiment, by setting the transfer roller 12 of Experimental Examples 1 to 4 so that the pressing amount in the printer is 0.15 to 0.4 [mm], good image quality is obtained. I was able to.

  Next, a sixth embodiment of the present invention will be described. In addition, about the thing which has the same structure as 1st-5th embodiment, the description is abbreviate | omitted by providing the same code | symbol. Explanation of the same operations and effects as those of the first to fifth embodiments is also omitted.

  FIG. 20 is a diagram showing a change in the outer diameter of the transfer roller in the sixth embodiment of the present invention, and FIG. 21 is a diagram showing a state in which the transfer roller in the sixth embodiment of the present invention is pressed against the photosensitive drum. It is.

  Since the transfer rollers 12 of Experimental Examples 1 to 4 described in the first embodiment are low-hardness foamed rubber, it is difficult to accurately polish to a predetermined outer diameter, and in view of molding ability. Therefore, the standard tolerance needs to be ± 0.1 [mm]. However, the abrasion resistance of silicone rubber is not sufficient, and as shown in FIG. 20, the outer diameter decreases due to the durability test. For this reason, when the outer diameter of the transfer roller 12 is initially close to the lower limit of the standard tolerance, the amount of pressing with the photosensitive drum 11 decreases as the number of printed sheets increases, and 100% density and gray scale pattern printing is performed. However, there is a problem that good image quality cannot be obtained.

  This is because the amount of pushing into the photosensitive drum 11 is reduced, and the voltage dependency is increased as in the case of the experimental example 11 described in the fifth embodiment.

  Therefore, in the present embodiment, as Experimental Examples 13 and 14, in order to always press the transfer roller 12 against the photosensitive drum 11 with a constant load, as shown in FIG. A cored bar 12a which is the central axis of the roller 12 is pushed by a spring. As a result, the transfer roller 12 is always pressed with a constant load, and the amount of overlap between the photosensitive drum 11 and the transfer roller 12 is always constant.

  First, Experimental Example 13 will be described.

  In Experimental Example 13, the photosensitive drum 11 and the transfer roller 12 were always brought into contact with each other with a linear pressure of 37 [gf / cm] (equivalent to the spring 400 [gf]). Then, after the initial stage of the transfer roller 12 and an endurance test for printing 200K sheets, the 100% density of the postcard, the gray scale, and the character pattern were printed in the L / L environment.

  Next, Experimental example 14 will be described.

  In Experimental Example 14, the photosensitive drum 11 and the transfer roller 12 were always brought into contact with each other with a linear pressure of 84 [gf / cm] (equivalent to the spring 900 [gf]). After the initial stage of the transfer roller 12 and an endurance test for printing 200K sheets, 100 [%] density of the postcard, gray scale and character pattern printing were performed in the L / L environment.

  In Experimental Example 13, good image quality could be obtained by printing a postcard character pattern both in the initial stage and after the endurance test. Note that the voltage dependency of the transfer roller 12 in Experimental Example 13 is the same as that shown in FIG. 12, and the pressing condition corresponds to Experimental Example 11.

  In Experimental Example 14, good image quality could be obtained with the postcard 100% density, gray scale, and character pattern printing both in the initial stage and after the endurance test. Note that the voltage dependency of the transfer roller 12 in Experimental Example 14 is the same as that shown in FIG. 12, and the pressing condition corresponds to Experimental Example 12.

  As described above, in this embodiment, by designing the pressing amount of the photosensitive drum 11 and the transfer roller 12 in the printer so that the linear pressure is always 37 to 84 [gf / cm], the durability test can be performed. Regardless of the nip change of the transfer roller 12, it was possible to always ensure the optimum pressing condition. In the L / L environment, the voltage dependency could be set to 0.11 to 0.34, and good image quality could be obtained.

  In addition, this invention is not limited to the said embodiment, It can change variously based on the meaning of this invention, and does not exclude them from the scope of the present invention.

1 is a schematic diagram illustrating a configuration of a main part of an image forming apparatus according to a first embodiment of the present invention. It is the schematic of the transfer roller in the 1st Embodiment of this invention. It is a figure which shows the equivalent circuit model in a comparative example. It is a figure which shows the relationship between the electric current and voltage of a transfer roller in a comparative example. It is a figure which shows the equivalent circuit model in the 1st Embodiment of this invention. It is a figure which shows the measuring method of the resistance value of the transfer roller in the 1st Embodiment of this invention. It is a figure which shows the definition of the surface foam cell diameter in the 1st Embodiment of this invention. It is a figure which shows the case where the foam cell in the 1st Embodiment of this invention is connected on the surface. FIG. 3 is a diagram illustrating a state in which an interaxial distance between the photosensitive drum and the transfer roller is fixed in the first exemplary embodiment of the present invention. It is a figure which shows the relationship between the compounding quantity of the carbon black in the 1st Embodiment of this invention, and a voltage-current curve. It is a figure which shows the measurement result of the characteristic value in the 1st Embodiment of this invention, and the result of image evaluation. It is a figure which shows the change of the voltage-current characteristic by durability in the 2nd Embodiment of this invention. It is a figure which shows the change of the voltage-current characteristic after the endurance in the 2nd Embodiment of this invention. It is a figure which shows the measurement result of the characteristic value in the 3rd Embodiment of this invention, and the result of image evaluation. It is a figure which shows the measurement result of the characteristic value in the 4th Embodiment of this invention, and the result of image evaluation. It is a 1st figure which shows the measurement result of the characteristic value in the 5th Embodiment of this invention, and the result of image evaluation. It is a 2nd figure which shows the measurement result of the characteristic value in the 5th Embodiment of this invention, and the result of image evaluation. It is a 1st figure which shows the voltage-current curve in the 5th Embodiment of this invention. It is a 2nd figure which shows the voltage-current curve in the 5th Embodiment of this invention. It is a figure which shows the change of the outer diameter of the transfer roller in the 6th Embodiment of this invention. It is a figure which shows the state which pressed the transfer roller in the 6th Embodiment of this invention against the photosensitive drum.

Explanation of symbols

11 Photosensitive drum 12 Transfer roller 12a Core metal 21 Transfer material

Claims (7)

(A) a transfer member for transferring a toner image formed on the surface of the image carrier to a transfer material,
(B) The transfer member includes a cored bar and an elastic conductive foam rubber,
(C) The voltage dependency of the electrical resistance value of the transfer member is 0.13 to 0.42.
(D) A transfer member having a pressure dependency on compression of the electrical resistance value of the transfer member is 0.30 [1 Ω / mm] or more and 1.35 [1 Ω / mm] or less. 2. The transfer member according to claim 1, wherein the conductive foamed rubber is vulcanized and foamed by adding an ionic conductive composition and carbon black, and the amount of the carbon black added to the weight of the rubber is 75 wt% or less. . 2. The transfer member according to claim 1, wherein the conductive foam rubber has an average foam cell diameter of 90 μm to 360 μm on the surface. The transfer member according to claim 3, wherein the product hardness is 24 to 40 degrees. An image forming apparatus having the transfer member according to claim 4,
The transfer member is in contact with the image carrier, the distance from the axis of the transfer member to the axis of the image carrier is constant, and the overlap amount is 0.15 mm to 0.4 mm. The image forming apparatus is pressed so as to satisfy the following conditions. An image forming apparatus having the transfer member according to claim 4,
The image forming apparatus, wherein the transfer member is pressed against the image carrier at a linear pressure of 37 to 84 [g / cm]. The image forming apparatus according to claim 5, wherein a constant current power source is provided as a power source of a transfer current control circuit for the transfer member, and a constant current is applied to measure an electric resistance value of the transfer member.

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