TECHNICAL FIELD

The present disclosure relates to an image forming apparatus and an image forming method.

BACKGROUND ART

Recently, an intermediate transfer belt system has been used in full-color electrophotographic devices, where the intermediate transfer belt system is a system configured to superimpose four color developed images of yellow, magenta, cyan, and black on an intermediate transfer member temporarily, and then to transfer the images onto a transfer medium, such as paper, at once.

In order to impart flexibility and toner releasing ability to the intermediate transfer belt and realize a high transfer rate regardless of a transfer medium for use, proposed are various transfer belts each having a structure where a flexible rubber elastic layer is laminated on a base layer and a layer formed of particles is formed on a surface of the belt.

For example, PTL 1 discloses to over a surface of an intermediate transfer belt with beads having diameters of 3 micrometers or less. PTL 2 and PTL 3 each disclose to form a surface of an intermediate transfer belt with a layer formed of a material having affinity with hydrophobic-treated particles. PTL 4 and PTL 5 each disclose a structure where relatively large particles are embedded in a resin of a surface layer of an intermediate transfer belt. PTL 6 discloses to arrange particles obtained by treating inorganic particles, such as alumina, boron nitride, and glass, with a silane coupling agent on a surface of an intermediate transfer belt. PTL 7 and PTL 8 each discloses to arrange spherical particles including a resin, such as a silicone resin and a fluororesin, as a main component, on a surface of an intermediate transfer belt. PTL 9 discloses that particles having relatively low volume resistivity are arranged on a surface of an intermediate transfer belt.

Moreover, it is important for toners used in recent ultra high-speed printing systems to have stable transfer properties and cleaning properties in order to continuously output images of a constant image quality in severe conditions for use, such as fluctuations of the temperature and humidity at which an image forming apparatus is used and continuous output of images on the large number of sheets. To this end, numerous inventions associated with types of external additives, various physical properties, and numerical values in parts of formulation ingredients are disclosed.

For example, PTL 10 discloses a technique where separation of external additives from toner base particles or embodiment of the external additives in the toner base particles can be suppressed and a long-term stability of the toner is obtained by using the external additives produced by a sol-gel method, and specifying particle diameters of the external additives, a ratio between the minimum particle diameter and the number average primary particle diameter, and a ratio between the maximum particle diameter and the number average primary particle diameter.

CITATION LIST

Patent Literature

[PTL 1] Japanese Unexamined Patent Application Publication No. 09-230717

[PTL 2] Japanese Unexamined Patent Application Publication No. 2002-162767

[PTL 3] Japanese Unexamined Patent Application Publication No. 2004-354716

[PTL 4] Japanese Unexamined Patent Application Publication No. 2007-328165

[PTL 5] Japanese Unexamined Patent Application Publication No. 2009-75154

[PTL 6] Japanese Unexamined Patent Application Publication No. 2015-148660

[PTL 7] Japanese Patent No. 5786181

[PTL 8] Japanese Unexamined Patent Application Publication No. 2012-194223

[PTL 9] Japanese Unexamined Patent Application Publication No. 2004-053918

[PTL 10] Japanese Unexamined Patent Application Publication No. 2011-043759

SUMMARY OF INVENTION

Technical Problem

The present disclosure has an object to provide an image forming apparatus having stably excellent transfer properties over a long period on a special transfer member, such as paper having surface irregularities, having excellent half-tone transfer properties with a full-color mode, and having excellent cleaning properties.

Solution to Problem

According to one aspect of the present disclosure, an image forming apparatus includes an image bearer where a latent image is to be formed on the image bearer and the image bearer can bear a toner image, a developing unit configured to develop a latent image formed on the image bearer with a toner to form the toner image, an intermediate transfer member, on which the toner image formed through the development performed by the developing unit is primary transferred, and a transferring unit configured to secondary transfer the toner image born on the intermediate transfer member to a recording medium. The intermediate transfer member includes a laminate including a base layer and an elastic layer. The elastic layer includes particles at a surface of the elastic layer to form convex-concave shapes at the surface. The particles have volume resistivity of from 1×100ohm*cm through 1×109ohm*cm. The toner includes an additive. An amount of the additive separated from the toner is from 20 percent by mass through 35 percent by mass relative to a total amount of the additive in the toner, when a toner dispersion liquid in which the toner is dispersed in a dispersant is irradiated with ultrasonic wave vibration with an irradiation energy dose of 4 kJ. The toner has a dielectric constant of 2.6 or greater but 3.9 or less.

Advantageous Effects of Invention

The present disclosure can provide an image forming apparatus having stably excellent transfer properties over a long period on a special transfer member, such as paper having surface irregularities, having excellent half-tone transfer properties with a full-color mode, and having excellent cleaning properties.

