SIZED FOAM CELLS

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0001991 filed in the Korean Intellectual Property Office on January 07, 2020, the entire contents of which are incorporated herein by reference.

BACKGROUND

[0002] In an electrophotographic image forming apparatus, a toner image formed on a photoconductor drum is electrostatically transferred to an image receiving member by a transfer roller. The transfer roller may have electrical conductivity to charge the photoconductor drum and the image receiving member. A transfer roller may be classified as an ion-conductive-type transfer roller or an electron-conductive-type transfer roller. In the case of an ion-conductive-type transfer roller, disparity of resistance does not easily occur even when an elastic body layer is deformed. However, a high voltage may be applied because there is a large change in resistance according to the environment, and a charge control material (that is, an ion-conducting agent or the like) may leak and contaminate the photoconductor drum. In the case of an electron-conductive-type transfer roller, resistance stability against the environment is good, but it is difficult to control an amount of carbon black that controls the resistance, and uniform foaming is difficult due to non-uniform dispersion of carbon black upon foaming. Thus, electrical resistance becomes uneven, and fatigue increases as electrical voltage is applied, which may degrade the lifetime. Therefore, a hybrid transfer roller using advantages of the two types of transfer roller has been developed. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Various examples will be described below by referring to the following figures.

[0004] FIG. 1 is a perspective view schematically illustrating a transfer roller-type transfer member according to an example.

[0005] FIG. 2 is a cross-sectional view schematically illustrating an electrophotographic image forming apparatus including a transfer-roller-type transfer member according to an example.

DETAILED DESCRIPTION OF EXAMPLES

[0006] Hereinafter, various examples will be described with reference to the drawings. Like reference numerals in the specification and the drawings denote like elements, and thus a redundant description may be omitted.

[0007] In the case of a hybrid transfer roller, in order for a printer to be suitable for a high speed printing and to have a longer lifetime, there is still a need to make carbon black uniformly dispersed when forming an elastic body layer by foaming, thereby increasing resistance uniformity and resistance stability while improving wear resistance so as to withstand friction with the photoconductor drum or the image receiving member.

[0008] Hereinafter, a transfer member for an electrophotographic image forming apparatus according to various examples, and an electrophotographic image forming apparatus including the transfer member will be described. A description will be made based on a transfer roller, but the present disclosure is not limited thereto. For example, the following description may be equally applied to a belt-shaped transfer member.

[0009] FIG. 1 is a perspective view schematically illustrating a transfer roller-type transfer member according to an example.

[0010] Referring to FIG. 1 , a transfer roller 10 includes a support 1 including a conductive material, and an elastic body layer 2 coupled to the support 1. In an example, the support 1 may be a shaft-shaped support and the elastic body layer 2 may be a cylindrical elastic body layer. Examples of the conductive material of the support 1 may include aluminum, an aluminum alloy, and stainless steel. The support 1 and the elastic body layer 2 are electro-conductively coupled to each other by a conductive adhesive, and are mechanically fixed to each other to be rotated integrally at the time of operation of an image forming apparatus. [0011] The elastic body layer 2 may include a foamed layer, and in some cases, may be a non-foamed layer. A diameter of the support 1 and a diameter of the elastic body layer 2 are not particularly limited. In an example, a diameter of the support 1 may be about 5 mm to about 10 mm, and an overall diameter of the support 1 and the elastic body layer 2 may be about 10 mm to about 30 mm. [0012] A coating layer (not shown) may be provided on an outer circumference surface of the elastic body layer 2. However, since electrical conductivity may deteriorate due to the presence of the coating layer, a measure for reducing or minimizing this deterioration is considered. For example, when the coating layer includes a mixture of carboxymethyl cellulose (CMC) and nano fibrillated cellulose (NFC), a surface transition problem of contaminants may be effectively reduced or suppressed and electrical conductivity may be improved. A mixture of cellulose derivatives other than CMC and NFC, and other nano-sized particles such as nano silica particles, nano precipitation calcium carbonate particles may also be used. The coating layer may be applied to have a thickness of about 0.2 pm to about 10 pm.

[0013] The elastic body layer may include i) a binder such as ethylene- propylene-diene monomer rubber (EPDM), acrylonitrile-butadiene rubber (NBR), epichlorohydrin-ethylene oxide rubber (ECO), chloroprene rubber (CR), styrene- butadiene rubber (SBR), isoprene rubber (IR), acrylic rubber (ACM), urethane rubber (UR), butadiene rubber (BR), and silicone rubber (SiR), ii) an electron conducting agent, iii) an ion-conducting agent, and iv) a cyan pigment containing metal phthalocyanine. In an example of the contents of the components i) to iv), based on 100 parts by weight of the binder resin, the content of the electron conducting agent may be about 5 parts by weight to about 15 parts by weight, the content of the ion-conducting agent may be about 0.1 parts by weight to about 1 part by weight, and the content of the cyan pigment containing metal phthalocyanine may be about 1 part by weight to about 5 parts by weight. For example, the binder resin may be a mixture of NBR and ECO. In this case, the mixing ratio by weight of NBR to ECO may be 65:35 to 90:10, for example, 80:20 or 70:30. When the mixing ratio by weight of NBR to ECO is more than 90:10, the efficiency of the conductive transfer member may be reduced, and when the mixing ratio thereof is less than 65:35, the resistance stability and elastic modulus of the conductive transfer member may be reduced.

[0014] In various examples, the electron-conducting agent is not particularly limited as long as it may conduct electrons. Examples thereof may include conductive carbon black particles such as acetylene black and ketjen black, oxidized carbon particles for ink, pyrolytic carbon particles, natural graphite particles, and artificial graphite particles, conductive metal oxide particles such as tin oxide, titanium oxide, and zinc oxide, and metal particles such as silver, nickel, copper, and germanium. In an example, the electron-conducting agent may be carbon black particles, and may be carbon black powder particles having a small average particle diameter and a large surface area. The content of the electron conducting agent may be about 5 parts by weight to about 15 parts by weight based on 100 parts by weight of the binder resin. When the content of the electron-conducting agent is less than 5 parts by weight, the resistance efficiency of the transfer member may be reduced, and when the content thereof is more than 15 parts by weight, image defects may occur.

[0015] The ion-conducting agent is not particularly limited as long as it may conduct ions. Examples of the ion-conducting agent include an ammonium salt, a perchlorate, a chlorate, a hydrochloride, a bromate, an oxy salt, a fluoroboric acid salt, a sulfate, an ethyl sulfate salt, a carbonate, and a sulfonate. As the salt selected therefrom, salt further including an alkali metal or alkali earth metal such as lithium, sodium, potassium, calcium, and magnesium may be used. Examples of the ammonium salt include a tetraethyl ammonium salt, a tetrabutyl ammonium salt, a lauryltrimethyl ammonium salt, a decyltrimethyl ammonium salt, an octadecyltrimethyl ammonium salt, a stearyltrimethyl ammonium salt, a benzyltrimethyl ammonium salt, and a dimethylethyl ammonium salt. Examples of content of the ion-conducting agent may be about 0.1 parts by weight to about 1 part by weight based on 100 parts by weight of the binder resin. When the content of the ion-conducting agent is less than 0.1 parts by weight, the resistance stability against the environment of the transfer member may be reduced, and when the content thereof is more than 1 part by weight, image contamination and/or image defects may occur. As described above, the transfer member may be a hybrid-type transfer member including both an ion-conducting agent and an electron-conducting agent.

[0016] In an example, the cyan pigment containing a metal phthalocyanine may be a cyan pigment containing copper phthalocyanine. The elastic body layer may be a foamed layer or a non-foamed layer. In various examples, the cyan pigment allows the electron-conducting agent, such as carbon black particles, to be uniformly dispersed when foaming a rubber formulation for forming an elastic body layer and to assist the elastic body layer to have uniformly-sized foam cells. Thus, the resistance uniformity and resistance stability of a transfer member are increased, and the wear resistance of the transfer member may be improved to withstand the friction with the photoconductor drum or the image receiving member. Accordingly, the cyan pigment assists the foamed elastic body layer to have uniformly-sized foam cells through the uniform dispersion of carbon black. The content of the cyan pigment may be about 1 part by weight to about 5 parts by weight, for example, about 1 part by weight to about 4.5 parts by weight, about 1 part by weight to about 4 parts by weight, about 1 .5 parts by weight to about 5 parts by weight, about 1 .5 parts by weight to about 4.5 parts by weight, about 2 parts by weight to about 5 parts by weight, or about 1 .5 parts by weight to about 4 parts by weight. For example, when the content of the cyan pigment containing a metal phthalocyanine, for example, cyan pigment containing copper phthalocyanine is less than 1 part by weight, carbon black may not be well dispersed, and thus it may be difficult to obtain a uniform foam. When the content of the cyan pigment is more than 5 parts by weight, aggregation of the cyan pigment particles may occur, and thus it may be difficult to obtain an elastic body layer having a uniform cell size.

[0017] As described above, when uniform foaming is performed by using a suitable amount of the cyan pigment, foam cells may be tightly connected to increase resistance to electrical fatigue, and resistance to friction with a photoconductor drum or a printing medium such as paper is increased to increase the lifetime of the transfer member. In addition, contamination due to, for example, paper powders, toner, etc., is reduced, and thus the transfer member assists the photoconductor drum to stably form a high-quality image for a long period of time. In the rubber formulation not including the cyan pigment, carbon black may not be uniformly dispersed before foaming, so that uneven distribution of carbon black during foaming inhibits uniform foaming, which may cause a foamed elastic body layer having non-uniform foam cells. In this case, uneven distribution of carbon black in the foam may occur. This uneven distribution of carbon black deteriorates the resistance stability and lifetime of the transfer member. Examples of the cyan pigment containing copper phthalocyanine include C.l Pigment Blue 1 , C.l Pigment Blue 1 :2, C.l Pigment Blue 9, C.l Pigment Blue 15:1 , C.l Pigment Blue 15:2, C.l Pigment Blue 15:3, C.l Pigment Blue 15:4, C.l Pigment Blue 15:6, C.l Pigment Blue 16, C.l Pigment Blue 24, C.l Pigment Blue 25, C.l Pigment Blue 63, C.l Pigment Blue 66, C.l Pigment Blue 68, C.l Pigment Blue 75, and C.l Pigment Blue 79.

[0018] An example transfer member may be integrated into an electrophotographic image forming apparatus such as a printer, a copier, a scanner, a fax machine, or a multi-function peripheral incorporating two or more of these.

[0019] FIG. 2 is a cross-sectional view schematically illustrating an electrophotographic image forming apparatus including a transfer roller type transfer member according to an example.

[0020] Referring to FIG. 2, an electrophotographic photoconductor drum 11 is charged by a charging roller 13, which is a charging means disposed in contact with the electrophotographic photoconductor drum 11. An image portion is exposed by laser light to form an electrostatic latent image on the electrophotographic photoconductor drum 11. The electrostatic latent image is converted into a visible image, for example, a toner image by a developing device 15, and the toner image is transferred to an image receiving member 19 by a transfer member, for example, a transfer roller 17, to which a voltage is applied. In an example, the transfer roller 17 may be implemented by the transfer roller 10, an example of which is shown in FIG. 1. Toner remaining on a surface of the electrophotographic photoconductor drum 11 after the image transfer is cleaned by a cleaning device, for example, a cleaning blade 21. The electrophotographic photoconductor drum 11 may be used again for image formation. The developing device 15 may include a regulating blade 23, a developing roller 25, and a supply roller 27.

[0021] Hereinafter, an example method of manufacturing the above- described transfer member will be described.

[0022] A transfer member according to an example, such as a conductive transfer roller, may be manufactured by blending i) a binder such as ethylene- propylene-diene rubber (EPDM), acrylonitrile-butadiene rubber (NBR), epichlorohydrin-ethylene oxide rubber (ECO), chloroprene rubber (CR), styrene- butadiene rubber (SBR), isoprene rubber (IR), acrylic rubber (ACM), urethane rubber (UR), butadiene rubber (BR), and silicone rubber (SiR), ii) an electron conducting agent, iii) an ion-conducting agent, iv) a cyan pigment containing a metal phthalocyanine, v) a crosslinking agent, and vi) a foaming agent to obtain a rubber formulation, extruding the rubber formulation, foaming the extrudate while passing the extrudate through a continuous moving foaming apparatus, pressing the foam into a shaft and subjecting the foam to secondary vulcanization, and polishing the foam.

[0023] In the contents of the component i) to the component iv) in the obtaining of the rubber formulation, based on 100 parts by weight of the binder resin, the content of the electron-conducting agent may be about 5 parts by weight to about 15 parts by weight, the content of the ion-conducting agent may be about 0.1 parts by weight to about 1 part by weight, and the content of the cyan pigment containing a metal phthalocyanine may be about 1 part by weight to about 5 parts by weight.

[0024] Examples of a crosslinking agent are not particularly limited and may include, for example, selenium, tellurium, sulfur or sulfur compounds such as sulfur chloride. The blending amount of the crosslinking agent may be about 1 part by weight to about 4 parts by weight based on 100 parts by weight of the binder resin. When the blending amount of the crosslinking agent is less than 1 part by weight, rubber may not be completely crosslinked, and when the blending amount thereof is more than 4 parts by weight, the hardness of the elastic body layer may be too high.

[0025] The foaming agent is not particularly limited and may include, for example, an inorganic foaming agent, an azo compound, a hydrazide compounds, and a nitroso compound, which are mainly used in a chemical foaming method. Various examples of the foaming agent may include azodicarbonamide (ADDA), 4,4'-oxybis (benzenesulfonyl hydrazide), N, N'- dinitorosopentamethylenetetraamine, and the like. The blending amount of the foaming agent may be about 1 part by weight to 5 parts by weight, about 2 parts by weight to about 5 parts by weight, or about 3 parts by weight to about 5 parts by weight, based on 100 parts by weight of the binder resin. When the blending amount of the foaming agent is less than 1 part by weight, due to a small amount of gas generated, foaming is insufficiently performed to increase the hardness of the elastic body layer. When the blending amount thereof is more than 5 parts by weight, due to a large amount of gas generated, the hardness of the elastic body layer is decreased, and thus the elastic body layer is vulnerable to compression set, which may cause image defects.

[0026] In addition, considering properties and uses for a final product, a crosslinking accelerator, a filler such as calcium carbonate, clay, silica, or talc, a plasticizer, an anti-aging agent, a crosslinking aid, or a foaming aid may be further added to the rubber formulation.

[0027] An example rubber formulation obtained as described above may be mixed using a kneader and formed into a sheet or a pellet. The sheet or pellet may be aged at room temperature for about 24 hours and introduced into an extruder. The extrusion conditions in the extruder may be appropriately set in consideration of the composition of the rubber formulation, and a barrel temperature range of about 20°C to about 70°C, and a screw rotation speed of about 100 rpm to about 300 rpm may be selected. The rubber formulation may pass through the extruder in a hot molten state to be extruded into an elongate, continuous and annular extrudate through a die mounted at the tip of the extruder. The annular extrudate discharged from the extruder may be transferred to a continuous moving foaming apparatus connected to the extruder, and a foaming process may be performed while moving the annular extrudate through the foaming apparatus to obtain a foam (continuous foaming method). In this case, the internal temperature of the continuous moving foaming apparatus may be appropriately selected in consideration of properties of the final transfer member, such as the decomposition temperature of the foaming agent and the composition of the rubber formulation. The internal temperature may be in a range of about 200°C to about 250°C. When the internal temperature thereof is lower than 200°C, foaming may be insufficiently performed and a foam structure may not be stable, so that resistance uniformity may be poor and sufficient cells may not be formed in the foam. When the internal temperature thereof is higher than 250°C, the electrical resistance of the transfer roller may increase, which may cause image defects.

[0028] A length of the continuous moving foaming apparatus may be about 10 m to about 30 m. When the length thereof is shorter than 10 m, the cell structure of the obtained foam may be unstable, and the resistance stability thereof may decrease. When the length thereof is longer than 30 m, over-foaming may occur, and thus the hardness of the foam may be unstable. The time taken for the extrudate to pass through the continuous moving foaming apparatus may be appropriately selected in consideration of the composition of the rubber formulation and the properties of the final transfer member, and may be about 5 minutes to about 60 minutes.

[0029] The foam prepared as described above is pressed into a mold. The mold may be a rubber tube. The annular foam obtained in this way is coercively pressed into the support 1 , an outer circumference surface of which is coated with a conductive adhesive or not coated with the conductive adhesive. Secondary vulcanization is carried out for the support 1 and the elastic body layer 2 to be attached electro-conductively to each other and to mechanically fix the elastic body layer 2 to the support 1 . Polishing may be performed to achieve a desired outer diameter of the final transfer roller 10 in transfer roller-type. In an example, an outer circumference surface of the elastic body layer 2 may be further polished to a predetermined surface roughness. Further, the elastic body layer 2 may include a coating layer. Thus, the transfer roller 10 shown in FIG. 1 may be obtained.

[0030] The transfer roller 10 obtained in this way may include a single layered elastic body layer 2. The hardness of the elastic body layer 2 may be about 30 degree to about 50 degree as measured by an ASKER-C hardness tester using a load of 1 kg, and the electrical resistance thereof may be adjusted in a range of about 106 W to about 1010 W.

[0031] In the above-described example transfer member, an electron conducting agent, such as carbon black particles, is uniformly distributed in the elastic body layer and uniformly-sized foam cells are provided in the elastic body layer. In that case, resistance uniformity and resistance stability are high, and wear resistance is excellent. Accordingly, since the transfer member has excellent electrical properties and also may withstand friction with the photoconductor drum or the image receiving member, the transfer member may stably provide a high- quality image at high speed over a long period of time.

[0032] hereinafter, various examples will be described. However, the scope of the disclosure is not limited thereto.

Examples 1 to 9 and Comparative Examples 1 to 13: Manufacture of Transfer Roller

[0033] Based on 100 parts by weight of a mixture (weight mixing ratio = 80:20) of NBR rubber (product name: KNB 0230L, manufactured by Kumho Petrochemical Co., Ltd.) and ECO rubber (product name: T3106, manufactured by Zeon Co., Ltd.), 0.2 parts by weight of tetraethyl ammonium as an ion conducting agent and 2 parts by weight of sulfur powder (product name: Sulfax PN, manufactured by Tsurumi Chemical Industry Co., Ltd.) as a crosslinking agent were fixed and mixed, and C. I Pigment Blue 15:2 as a cyan pigment containing copper phthalocyanine, azodicarbonamide (ADCA) as a foaming agent, and conductive carbon black (Product name: MA100, manufactured by Mitsubishi Chemical Co., Ltd.) were added thereto according to the contents given in Table 1 below, so as to form rubber formulations.

[0034] A transfer roller was manufactured using these rubber formulations through the above-described continuous foaming method. The rubber formulations obtained as above were mixed using a kneader and were formed into a sheet. The sheet was aged at room temperature for about 24 hours, and was put into a twin-screw extruder provided with a die having an annular cross- section at the tip thereof and melt-extruded. An elongate, continuous, and annular extrudate was obtained by the die.

[0035] The annular extrudate was transferred to a continuous moving foaming apparatus having a length of about 20 m and connected to the extruder, and a foaming process and a vulcanization process were performed while moving the annular extrudate through the foaming apparatus to obtain an annular foam having an outer diameter of about 16.2 mm and an inner diameter of about 5 mm. The internal temperature of the foaming apparatus was set to about 200°C to about 220°C.

[0036] The obtained continuous elastic body was cut to a length of about 250 mm, a stainless steel shaft having an outer diameter of about 5 mm was inserted and fixed into the elastic body, and secondary vulcanization was performed to manufacture a transfer roller 10 in which the elastic body layer 2 is attached to the support 1 electro-conductively and is mechanically fixed to the support 1. The outer circumference surface of the elastic body layer 2 was polished to adjust to the outer diameter thereof to about 16 mm. Various characteristics of this transfer roller 10 were evaluated. Evaluation results of various physical properties of the transfer roller in Examples and Comparative Examples are summarized in Tables 1 and 2.

Table 1

* CE: Comparative Example, E: Example

Evaluation Method

[0037] Foaming uniformity, resistance increase ratio, surface defect, and transferability of the transfer rollers, given in Tables 1 and 2, were evaluated as described below.

[0038] The transfer roller to be measured was mounted on an electrical resistance measuring jig, and 500 g of a weight was placed on the transfer roller. Transfer roller samples corresponding to states of one sheet printed, 50,000 sheets printed, 100,000 sheets printed, and 200,000 sheets printed were made in a method in which DC voltages of -2000 V are repeatedly applied to the shaft of the transfer roller while rotating a photoconductor drum at a constant rotation speed of 30 rpm in the electrical resistance measuring jig. The transfer roller in contact with the photoconductor drum rotates in the opposite direction at the same speed during the measurement. Evaluations of the foam uniformity, resistance increase ratio, surface defects, and transferability of these transfer roller samples were performed based on the following criteria.

Evaluation of foam uniformity

[0039] The uniformity and continuity of a foam cell shape were evaluated with the naked eyes. In order to secure evaluation reliability, the foaming uniformity was evaluated by field effect scanning electron microscopy (FE SEM). After measuring the size of the cells on a 2000x magnification photograph of the foam obtained by scanning electron microscopy, the foam uniformity was evaluated by the ratio of maximum cell diameter (Dmax) / minimum cell diameter (Dmin). When the ratio is 1 .5 or less, it may be evaluated that the foam uniformity is excellent.

Evaluation of resistance increase ratio

[0040] The transfer roller to be measured was mounted on an electrical resistance measuring jig, and 500 g of a weight was placed on the transfer roller. A DC voltage of -2000 V is applied to the shaft of the transfer roller while rotating the photoconductor drum at a constant rotation speed of 30 rpm in the electrical resistance measuring jig, and electric current is measured by an ammeter connected to the shaft of the transfer roller. The transfer roller in contact with the photoconductor drum rotates in the opposite direction at the same speed during the measurement. For the transfer roller samples corresponding to states of one sheet printed and 200,000 sheets printed, the resistance increase ratio according to the increase in the number of prints was measured from the measured electric current by converting a resistance value using Ohm's law. When this resistance increase ratio is 2.5 or less, it may be evaluated that resistance stability is good. The resistance increase ratio was determined using Equation 1. Resistance increase ratio resistance value of transfer roller corresponding to 200,000 prints resistance value of transfer roller corresponding to one print

...Equation 1

Evaluation of surface defects

[0041] For the transfer roller samples corresponding to states of one sheet printed, 50,000 sheets printed, 100,000 sheets printed, and 200,000 sheets printed, the surface defects of the foam were observed with the naked eyes. The occurrence of cracks was confirmed by fatigue due to repeated electrical application, and surface defects were evaluated based on the following criteria: [0042] OK: cracks are not observed with the naked eye; and

[0043] NG: cracks of 0.1 mm or more are observed with the naked eyes.

Evaluation of transferability

[0044] A transfer roller was removed from a laser printer (product name: Laser printer model SL-M4580, manufactured by Samsung Electronics Co., Ltd.), and, instead of the transfer roller, transfer roller samples corresponding to states of one sheet printed, 50,000 sheets printed, 100,000 sheets printed, and 200,000 sheets printed was mounted on the laser printer. A 1 % black solid pattern was printed using this laser printer under a printing operation condition of 45 ppm. For the transfer roller samples of Examples 1 , 2, 4, and 5, and Comparative Examples 5 and 6, the presence or absence of transfer omission in the solid pattern was checked, and transferability was evaluated based on the following criteria:

[0045] E (excellent transferability): transferability is 90% or more when printing was performed after mounting the transfer roller sample corresponding to a state of 200,000 sheets printed;

[0046] G (good transferability): transferability is 90% or more when printing was performed after mounting the transfer roller sample corresponding to a state of 100,00 sheets printed; and

[0047] B (bad transferability): transferability is 90% or more when printing was performed after mounting the transfer roller sample corresponding to a state of 5,000 sheets printed.

Table 2

[0048] Referring to Table 1 , the changes in foaming uniformity and resistance increase ratio according to the content of a foaming agent, the content of carbon black, the addition of the cyan pigment containing copper phthalocyanine, and the content of the cyan pigment may be observed. Regardless of the content of a foaming agent and the content of carbon black, in the case of Examples 1 to 9 where the content of the cyan pigment was 1 part by weight to 5 parts by weight, both a foaming uniformity and a resistance increase rate were excellent, as compared with the cases where the cyan pigment was not added or the case of Comparative Examples 1 to 13 where the content of the cyan pigment was less than 1 part by weight or more than 5 parts by weight. In the cases (Comparative Examples 1 and 2) where the content of the cyan pigment was less than 1 part by weight, the cyan pigment lacked the ability to uniformly disperse the carbon black, so that the carbon black dispersion was not sufficient, and thus a uniform foam was not obtained. In the cases (Comparative Examples 3 and 4) where the content of the cyan pigment was more than 5 parts by weight, aggregation of the cyan pigment particles occurs, so that it was difficult to obtain the elastic body layer having a uniform cell size.

[0049] Referring to Table 2, the change in a resistance increase ratio according to the content of a foaming agent, the content of carbon black, the addition of the cyan pigment containing copper phthalocyanine, and the content of the cyan pigment, the change in surface defect, which is a durability index according to application of electric current, and the change in transferability may be observed. Regardless of the content of a foaming agent and the content of carbon black, in the cases of the transfer rollers of Examples 1 , 2, 4, and 5 where the content of the cyan pigment was 1 part by weight to 5 parts by weight, the resistance increase ratio is 1.9 to 2.3, that is, less than 2.5, which is good. In contrast, in the cases of the transfer rollers of Comparative Examples 5 and 6 where the cyan pigment is not included, the resistance increase ratios are 2.9 and 3.0, respectively. Thus, it may be ascertained that the resistance increase ratios were greatly increased. That is, it may be found that, in the cases where the cyan pigment is not included, the change of the resistance value of the transfer roller over time is large due to application of electric current.

[0050] In the transfer rollers of Examples 1 , 2, 4, and 5, even in the case of the transfer roller sample corresponding to a state of 200,000 sheets printed, cracks due to application of electric current did not occur. However, in the transfer roller of Comparative Example 5, even in the case of the transfer roller sample corresponding to a state of 100,000 sheets printed, cracks occurred. Thus, in the case where the cyan pigment is not included, cracks occurred by application of electric current to cause the deterioration phenomenon of the elastic body layer 2.

[0051] When deterioration phenomenon and/or resistance increase phenomenon occur by application of electric current, there is a tendency that the transferability of the transfer roller becomes poor. Therefore, when the transfer roller sample corresponding to a state of 200,000 sheets printed was mounted on the laser printer and printing was performed, transferability was evaluated. Referring to Table 2 again, in Comparative Examples 5 and 6 where the cyan pigment is not included, when the transfer roller samples corresponding to states of 50,000 sheets printed and 100,000 sheets printed, respectively, were mounted on the laser printer and printing was performed, transferability became poor. This is a result of the deterioration phenomenon and the resistance increase phenomenon due to application of electric current in the cases of the transfer rollers of Comparative Examples 5 and 6. However, in the cases of all of the transfer rollers of Examples 1 , 2, 4, and 5 where the content of the cyan pigment is 1 part by weight to 5 parts by weight, transferability was excellent. The reason for this may be presumed because the cyan pigment containing copper phthalocyanine uniformly disperses carbon black, and the uniformly dispersed carbon black suppresses the deterioration and resistance increase of the elastic body layer due to application of electric current. When directly comparing the evaluation results of Examples 4 and 5 and Comparative Examples 5 and 6 in which the contents of the elastic body layer are almost similar to each other except for the presence or absence of the cyan pigment, it may be found that the transfer rollers of Examples 4 and 5 are significantly improved in all terms of foaming uniformity, resistance increase ratio, surface defect, and transferability, as compared with the transfer rollers of Comparative Examples 5 and 6.

[0052] From the above results, it may be found that the transfer roller is provided with the elastic body layer including the cyan pigment containing a metal phthalocyanine, and thus carbon black is uniformly dispersed in the elastic body layer to form uniformly-sized foam cells. An example transfer roller was excellent in resistance uniformity and resistance stability while having high wear resistance. Accordingly, since the transfer member has excellent electrical properties and also may withstand friction with the photoconductor drum or the image receiving member, the transfer member may stably provide a high-quality image at high speed over a long period of time. Therefore, the transfer member is suitable for high speed printing and extending lifetime of the printer.

[0053] While the present disclosure has been described with reference to examples thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therefrom. Therefore, the scope of the present disclosure will be defined by the claims below.